Are infant mortality rate declines exponential? The general pattern of 20th century infant mortality rate decline

PubMed Central

Bishai, David; Opuni, Marjorie

2009-01-01

Background Time trends in infant mortality for the 20th century show a curvilinear pattern that most demographers have assumed to be approximately exponential. Virtually all cross-country comparisons and time series analyses of infant mortality have studied the logarithm of infant mortality to account for the curvilinear time trend. However, there is no evidence that the log transform is the best fit for infant mortality time trends. Methods We use maximum likelihood methods to determine the best transformation to fit time trends in infant mortality reduction in the 20th century and to assess the importance of the proper transformation in identifying the relationship between infant mortality and gross domestic product (GDP) per capita. We apply the Box Cox transform to infant mortality rate (IMR) time series from 18 countries to identify the best fitting value of lambda for each country and for the pooled sample. For each country, we test the value of λ against the null that λ = 0 (logarithmic model) and against the null that λ = 1 (linear model). We then demonstrate the importance of selecting the proper transformation by comparing regressions of ln(IMR) on same year GDP per capita against Box Cox transformed models. Results Based on chi-squared test statistics, infant mortality decline is best described as an exponential decline only for the United States. For the remaining 17 countries we study, IMR decline is neither best modelled as logarithmic nor as a linear process. Imposing a logarithmic transform on IMR can lead to bias in fitting the relationship between IMR and GDP per capita. Conclusion The assumption that IMR declines are exponential is enshrined in the Preston curve and in nearly all cross-country as well as time series analyses of IMR data since Preston's 1975 paper, but this assumption is seldom correct. Statistical analyses of IMR trends should assess the robustness of findings to transformations other than the log transform. PMID:19698144

Galaxy Zoo: the interplay of quenching mechanisms in the group environment★

NASA Astrophysics Data System (ADS)

Smethurst, R. J.; Lintott, C. J.; Bamford, S. P.; Hart, R. E.; Kruk, S. J.; Masters, K. L.; Nichol, R. C.; Simmons, B. D.

2017-08-01

Does the environment of a galaxy directly influence the quenching history of a galaxy? Here, we investigate the detailed morphological structures and star formation histories of a sample of SDSS group galaxies with both classifications from Galaxy Zoo 2 and near ultra-violet (NUV) detections in GALEX. We use the optical and NUV colours to infer the quenching time and rate describing a simple exponentially declining star formation history for each galaxy, along with a control sample of field galaxies. We find that the time since quenching and the rate of quenching do not correlate with the relative velocity of a satellite but are correlated with the group potential. This quenching occurs within an average quenching time-scale of ˜ 2.5 Gyr from star forming to complete quiescence, during an average infall time (from ˜10R200 to 0.01R200) of ˜ 2.6 Gyr. Our results suggest that the environment does play a direct role in galaxy quenching through quenching mechanisms that are correlated with the group potential, such as harassment, interactions or starvation. Environmental quenching mechanisms that are correlated with satellite velocity, such as ram-pressure stripping, are not the main cause of quenching in the group environment. We find that no single mechanism dominates over another, except in the most extreme environments or masses. Instead, an interplay of mergers, mass and morphological quenching and environment-driven quenching mechanisms dependent on the group potential drive galaxy evolution in groups.

Calculating Formulae of Proportion Factor and Mean Neutron Exposure in the Exponential Expression of Neutron Exposure Distribution

NASA Astrophysics Data System (ADS)

Feng-Hua, Zhang; Gui-De, Zhou; Kun, Ma; Wen-Juan, Ma; Wen-Yuan, Cui; Bo, Zhang

2016-07-01

Previous studies have shown that, for the three main stages of the development and evolution of asymptotic giant branch (AGB) star s-process models, the neutron exposure distribution (DNE) in the nucleosynthesis region can always be considered as an exponential function, i.e., ρAGB(τ) = C/τ0 exp(-τ/τ0) in an effective range of the neutron exposure values. However, the specific expressions of the proportion factor C and the mean neutron exposure τ0 in the exponential distribution function for different models are not completely determined in the related literature. Through dissecting the basic method to obtain the exponential DNE, and systematically analyzing the solution procedures of neutron exposure distribution functions in different stellar models, the general formulae, as well as their auxiliary equations, for calculating C and τ0 are derived. Given the discrete neutron exposure distribution Pk, the relationships of C and τ0 with the model parameters can be determined. The result of this study has effectively solved the problem to analytically calculate the DNE in the current low-mass AGB star s-process nucleosynthesis model of 13C-pocket radiative burning.

Estimating Distances from Parallaxes. III. Distances of Two Million Stars in the Gaia DR1 Catalogue

NASA Astrophysics Data System (ADS)

Astraatmadja, Tri L.; Bailer-Jones, Coryn A. L.

2016-12-01

We infer distances and their asymmetric uncertainties for two million stars using the parallaxes published in the Gaia DR1 (GDR1) catalogue. We do this with two distance priors: A minimalist, isotropic prior assuming an exponentially decreasing space density with increasing distance, and an anisotropic prior derived from the observability of stars in a Milky Way model. We validate our results by comparing our distance estimates for 105 Cepheids which have more precise, independently estimated distances. For this sample we find that the Milky Way prior performs better (the rms of the scaled residuals is 0.40) than the exponentially decreasing space density prior (rms is 0.57), although for distances beyond 2 kpc the Milky Way prior performs worse, with a bias in the scaled residuals of -0.36 (versus -0.07 for the exponentially decreasing space density prior). We do not attempt to include the photometric data in GDR1 due to the lack of reliable color information. Our distance catalog is available at http://www.mpia.de/homes/calj/tgas_distances/main.html as well as at CDS. This should only be used to give individual distances. Combining data or testing models should be done with the original parallaxes, and attention paid to correlated and systematic uncertainties.

The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. VII. Properties of the Host Galaxy and Constraints on the Merger Timescale

NASA Astrophysics Data System (ADS)

Blanchard, P. K.; Berger, E.; Fong, W.; Nicholl, M.; Leja, J.; Conroy, C.; Alexander, K. D.; Margutti, R.; Williams, P. K. G.; Doctor, Z.; Chornock, R.; Villar, V. A.; Cowperthwaite, P. S.; Annis, J.; Brout, D.; Brown, D. A.; Chen, H.-Y.; Eftekhari, T.; Frieman, J. A.; Holz, D. E.; Metzger, B. D.; Rest, A.; Sako, M.; Soares-Santos, M.

2017-10-01

We present the properties of NGC 4993, the host galaxy of GW170817, the first gravitational-wave (GW) event from the merger of a binary neutron star (BNS) system and the first with an electromagnetic (EM) counterpart. We use both archival photometry and new optical/near-IR imaging and spectroscopy, together with stellar population synthesis models to infer the global properties of the host galaxy. We infer a star formation history peaked at ≳ 10 {Gyr} ago, with subsequent exponential decline leading to a low current star formation rate of 0.01 {M}⊙ yr-1, which we convert into a binary merger timescale probability distribution. We find a median merger timescale of {11.2}-1.4+0.7 Gyr, with a 90% confidence range of 6.8{--}13.6 {Gyr}. This in turn indicates an initial binary separation of ≈ 4.5 {R}⊙ , comparable to the inferred values for Galactic BNS systems. We also use new and archival Hubble Space Telescope images to measure a projected offset of the optical counterpart of 2.1 kpc (0.64r e ) from the center of NGC 4993 and to place a limit of {M}r≳ -7.2 mag on any pre-existing emission, which rules out the brighter half of the globular cluster luminosity function. Finally, the age and offset of the system indicates it experienced a modest natal kick with an upper limit of ˜200 km s-1. Future GW-EM observations of BNS mergers will enable measurement of their population delay time distribution, which will directly inform their viability as the dominant source of r-process enrichment in the universe.

The Diversity of Diffuse Ly α Nebulae around Star-forming Galaxies at High Redshift

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xue, Rui; Lee, Kyoung-Soo; Dey, Arjun

2017-03-10

We report the detection of diffuse Ly α emission, or Ly α halos (LAHs), around star-forming galaxies at z ≈ 3.78 and 2.66 in the NOAO Deep Wide-Field Survey Boötes field. Our samples consist of a total of ∼1400 galaxies, within two separate regions containing spectroscopically confirmed galaxy overdensities. They provide a unique opportunity to investigate how the LAH characteristics vary with host galaxy large-scale environment and physical properties. We stack Ly α images of different samples defined by these properties and measure their median LAH sizes by decomposing the stacked Ly α radial profile into a compact galaxy-like andmore » an extended halo-like component. We find that the exponential scale-length of LAHs depends on UV continuum and Ly α luminosities, but not on Ly α equivalent widths or galaxy overdensity parameters. The full samples, which are dominated by low UV-continuum luminosity Ly α emitters ( M {sub UV} ≳ −21), exhibit LAH sizes of 5–6 kpc. However, the most UV- or Ly α- luminous galaxies have more extended halos with scale-lengths of 7–9 kpc. The stacked Ly α radial profiles decline more steeply than recent theoretical predictions that include the contributions from gravitational cooling of infalling gas and from low-level star formation in satellites. However, the LAH extent matches what one would expect for photons produced in the galaxy and then resonantly scattered by gas in an outflowing envelope. The observed trends of LAH sizes with host galaxy properties suggest that the physical conditions of the circumgalactic medium (covering fraction, H i column density, and outflow velocity) change with halo mass and/or star formation rates.« less

The Diversity of Diffuse Lyα Nebulae around Star-forming Galaxies at High Redshift

NASA Astrophysics Data System (ADS)

Xue, Rui; Lee, Kyoung-Soo; Dey, Arjun; Reddy, Naveen; Hong, Sungryong; Prescott, Moire K. M.; Inami, Hanae; Jannuzi, Buell T.; Gonzalez, Anthony H.

2017-03-01

We report the detection of diffuse Lyα emission, or Lyα halos (LAHs), around star-forming galaxies at z ≈ 3.78 and 2.66 in the NOAO Deep Wide-Field Survey Boötes field. Our samples consist of a total of ˜1400 galaxies, within two separate regions containing spectroscopically confirmed galaxy overdensities. They provide a unique opportunity to investigate how the LAH characteristics vary with host galaxy large-scale environment and physical properties. We stack Lyα images of different samples defined by these properties and measure their median LAH sizes by decomposing the stacked Lyα radial profile into a compact galaxy-like and an extended halo-like component. We find that the exponential scale-length of LAHs depends on UV continuum and Lyα luminosities, but not on Lyα equivalent widths or galaxy overdensity parameters. The full samples, which are dominated by low UV-continuum luminosity Lyα emitters (M UV ≳ -21), exhibit LAH sizes of 5-6 kpc. However, the most UV- or Lyα-luminous galaxies have more extended halos with scale-lengths of 7-9 kpc. The stacked Lyα radial profiles decline more steeply than recent theoretical predictions that include the contributions from gravitational cooling of infalling gas and from low-level star formation in satellites. However, the LAH extent matches what one would expect for photons produced in the galaxy and then resonantly scattered by gas in an outflowing envelope. The observed trends of LAH sizes with host galaxy properties suggest that the physical conditions of the circumgalactic medium (covering fraction, H I column density, and outflow velocity) change with halo mass and/or star formation rates.

The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. VII. Properties of the Host Galaxy and Constraints on the Merger Timescale

DOE Office of Scientific and Technical Information (OSTI.GOV)

Blanchard, P. K.; Berger, E.; Fong, W.

We present the properties of NGC 4993, the host galaxy of GW170817, the first gravitational wave (GW) event from the merger of a binary neutron star (BNS) system and the first with an electromagnetic (EM) counterpart. We use both archival photometry and new optical/near-IR imaging and spectroscopy, together with stellar population synthesis models to infer the global properties of the host galaxy. We infer a star formation history peaked atmore » $$\\gtrsim 10$$ Gyr ago, with subsequent exponential decline leading to a low current star formation rate of 0.01 M$$_{\\odot}$$ yr$$^{-1}$$, which we convert into a binary merger timescale probability distribution. We find a median merger timescale of $$11.2^{+0.7}_{-1.4}$$ Gyr, with a 90% confidence range of $6.8-13.6$ Gyr. This in turn indicates an initial binary separation of $$\\approx 4.5$$ R$$_{\\odot}$$, comparable to the inferred values for Galactic BNS systems. We also use new and archival $Hubble$ $Space$ $Telescope$ images to measure a projected offset of the optical counterpart of $2.1$ kpc (0.64$$r_{e}$$) from the center of NGC 4993 and to place a limit of $$M_{r} \\gtrsim -7.2$$ mag on any pre-existing emission, which rules out the brighter half of the globular cluster luminosity function. Finally, the age and offset of the system indicates it experienced a modest natal kick with an upper limit of $$\\sim 200$$ km s$$^{-1}$$. Future GW$-$EM observations of BNS mergers will enable measurement of their population delay time distribution, which will directly inform their viability as the dominant source of $r$-process enrichment in the Universe.« less

The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. VII. Properties of the Host Galaxy and Constraints on the Merger Timescale

DOE PAGES

Blanchard, P. K.; Berger, E.; Fong, W.; ...

2017-10-16

We present the properties of NGC 4993, the host galaxy of GW170817, the first gravitational wave (GW) event from the merger of a binary neutron star (BNS) system and the first with an electromagnetic (EM) counterpart. We use both archival photometry and new optical/near-IR imaging and spectroscopy, together with stellar population synthesis models to infer the global properties of the host galaxy. We infer a star formation history peaked atmore » $$\\gtrsim 10$$ Gyr ago, with subsequent exponential decline leading to a low current star formation rate of 0.01 M$$_{\\odot}$$ yr$$^{-1}$$, which we convert into a binary merger timescale probability distribution. We find a median merger timescale of $$11.2^{+0.7}_{-1.4}$$ Gyr, with a 90% confidence range of $6.8-13.6$ Gyr. This in turn indicates an initial binary separation of $$\\approx 4.5$$ R$$_{\\odot}$$, comparable to the inferred values for Galactic BNS systems. We also use new and archival $Hubble$ $Space$ $Telescope$ images to measure a projected offset of the optical counterpart of $2.1$ kpc (0.64$$r_{e}$$) from the center of NGC 4993 and to place a limit of $$M_{r} \\gtrsim -7.2$$ mag on any pre-existing emission, which rules out the brighter half of the globular cluster luminosity function. Finally, the age and offset of the system indicates it experienced a modest natal kick with an upper limit of $$\\sim 200$$ km s$$^{-1}$$. Future GW$-$EM observations of BNS mergers will enable measurement of their population delay time distribution, which will directly inform their viability as the dominant source of $r$-process enrichment in the Universe.« less

The decline and fall of Type II error rates

Treesearch

Steve Verrill; Mark Durst

2005-01-01

For general linear models with normally distributed random errors, the probability of a Type II error decreases exponentially as a function of sample size. This potentially rapid decline reemphasizes the importance of performing power calculations.

Documentation for the machine-readable version of the University of Michigan Catalogue of two-dimensional spectral types for the HD stars. Volume 2: Declinations minus 53 deg to minus 40 deg

NASA Technical Reports Server (NTRS)

Warren, W. H., Jr.

1981-01-01

The magnetic tape version of Volume 2 of the University of Michigan systematic reclassification program for the Henry Draper Catalogue (HD) stars is described. Volume 2 contains all HD stars in the declination range -53 degrees to 40 degrees and also exists in printed form.

Disk irradiation and light curves of x ray novae

NASA Technical Reports Server (NTRS)

Kim, S.-W.; Wheeler, J. C.; Mineshige, S.

1994-01-01

We study the disk instability and the effect of irradiation on outbursts in the black hole X-ray nova system. In both the optical and soft X-rays, the light curves of several X-ray novae, A0620-00, GH 2000+25, Nova Muscae 1991 (GS 1124-68), and GRO J0422+32, show a main peak, a phase of exponential decline, a secondary maximum or reflare, and a final bump in the late decay followed by a rapid decline. Basic disk thermal limit cycle instabilities can account for the rapid rise and overall decline, but not the reflare and final bump. The rise time of the reflare, about 10 days, is too short to represent a viscous time, so this event is unlikely to be due to increased mass flow from the companion star. We explore the possibility that irradiation by X-rays produced in the inner disk can produce these secondary effects by enhancing the mass flow rate within the disk. Two plausible mechanisms of irradiation of the disk are considered: direct irradiation from the inner hot disk and reflected radiation from a corona or other structure above the disk. Both of these processes will be time dependent in the context of the disk instability model and result in more complex time-dependent behavior of the disk structure. We test both disk instability and mass transfer burst models for the secondary flares in the presence of irradiation.

A Photometric Survey of the Open Clusters NGC 7789 and M67

NASA Astrophysics Data System (ADS)

Janes, Kenneth

2010-01-01

Although there is strong evidence that stellar activity declines as a star ages, beyond about the age of the Hyades (600 Myr) there is little direct confirmation of this decline in stars of known age. This report is an update of an earlier report (Hayes-Gehrke, et al., 2004, AJ, 128, 2862) of a long-term project to explore stellar activity in old open clusters. I have now accumulated 12 years of photometry of the old clusters NGC 7789 (about 1.8 Gyr) and M 67 (about 4 Gyr). An analysis of these data has revealed a substantial number of low-amplitude variable stars in both clusters, including a number of previously-discovered eclipsing binary stars, and several stars near the main sequence turnoff of both clusters that exhibit apparently erratic variations. Some of the M 67 erratics are known X-ray sources. On the main sequence, the large majority of stars show little or no evidence for variability at the 0.1% - 0.2% level, consistent with a regular systematic decline in activity level with age.

Hydrostatic equilibrium of stars without electroneutrality constraint

NASA Astrophysics Data System (ADS)

Krivoruchenko, M. I.; Nadyozhin, D. K.; Yudin, A. V.

2018-04-01

The general solution of hydrostatic equilibrium equations for a two-component fluid of ions and electrons without a local electroneutrality constraint is found in the framework of Newtonian gravity theory. In agreement with the Poincaré theorem on analyticity and in the context of Dyson's argument, the general solution is demonstrated to possess a fixed (essential) singularity in the gravitational constant G at G =0 . The regular component of the general solution can be determined by perturbation theory in G starting from a locally neutral solution. The nonperturbative component obtained using the method of Wentzel, Kramers and Brillouin is exponentially small in the inner layers of the star and grows rapidly in the outward direction. Near the surface of the star, both components are comparable in magnitude, and their nonlinear interplay determines the properties of an electro- or ionosphere. The stellar charge varies within the limits of -0.1 to 150 C per solar mass. The properties of electro- and ionospheres are exponentially sensitive to variations of the fluid densities in the central regions of the star. The general solutions of two exactly solvable stellar models without a local electroneutrality constraint are also presented.

Student Perspectives on International Education: An Examination into the Decline of Japanese Studying Abroad

ERIC Educational Resources Information Center

Lassegard, James P.

2013-01-01

The number of students going abroad for study purposes continues to grow exponentially, even despite the global economic downturns of recent years. One exception is Japan, where the number of students going overseas has continued to decline since the mid-2000s. This paper first explores various explanations for the persistent decline in Japanese…

Optimal estimation for the satellite attitude using star tracker measurements

NASA Technical Reports Server (NTRS)

Lo, J. T.-H.

1986-01-01

An optimal estimation scheme is presented, which determines the satellite attitude using the gyro readings and the star tracker measurements of a commonly used satellite attitude measuring unit. The scheme is mainly based on the exponential Fourier densities that have the desirable closure property under conditioning. By updating a finite and fixed number of parameters, the conditional probability density, which is an exponential Fourier density, is recursively determined. Simulation results indicate that the scheme is more accurate and robust than extended Kalman filtering. It is believed that this approach is applicable to many other attitude measuring units. As no linearization and approximation are necessary in the approach, it is ideal for systems involving high levels of randomness and/or low levels of observability and systems for which accuracy is of overriding importance.

Estimating Distances from Parallaxes. II. Performance of Bayesian Distance Estimators on a Gaia-like Catalogue

NASA Astrophysics Data System (ADS)

Astraatmadja, Tri L.; Bailer-Jones, Coryn A. L.

2016-12-01

Estimating a distance by inverting a parallax is only valid in the absence of noise. As most stars in the Gaia catalog will have non-negligible fractional parallax errors, we must treat distance estimation as a constrained inference problem. Here we investigate the performance of various priors for estimating distances, using a simulated Gaia catalog of one billion stars. We use three minimalist, isotropic priors, as well an anisotropic prior derived from the observability of stars in a Milky Way model. The two priors that assume a uniform distribution of stars—either in distance or in space density—give poor results: The root mean square fractional distance error, {f}{rms}, grows far in excess of 100% once the fractional parallax error, {f}{true}, is larger than 0.1. A prior assuming an exponentially decreasing space density with increasing distance performs well once its single parameter—the scale length— has been set to an appropriate value: {f}{rms} is roughly equal to {f}{true} for {f}{true}\\lt 0.4, yet does not increase further as {f}{true} increases up to to 1.0. The Milky Way prior performs well except toward the Galactic center, due to a mismatch with the (simulated) data. Such mismatches will be inevitable (and remain unknown) in real applications, and can produce large errors. We therefore suggest adopting the simpler exponentially decreasing space density prior, which is also less time-consuming to compute. Including Gaia photometry improves the distance estimation significantly for both the Milky Way and exponentially decreasing space density prior, yet doing so requires additional assumptions about the physical nature of stars.

Time-resolved photoluminescence investigation of (Mg, Zn) O alloy growth on a non-polar plane

NASA Astrophysics Data System (ADS)

Mohammed Ali, Mohammed Jassim; Chauveau, J. M.; Bretagnon, T.

2018-04-01

Excitons recombination dynamics in ZnMgO alloy have been studied by time-resolved photoluminescence according to temperature. At low temperature, localisation effects of the exciton are found to play a significant role. The photoluminescence (PL) decays are bi-exponential. The short lifetime has a constant value, whereas the long lifetime shows a dependency with temperature. For temperature higher than 100 K the declines show a mono-exponential decay. The PL declines are dominated by non-radiative process at temperatures above 150 K. The PL lifetime dependancy with temperature is analysed using a model including localisation effects and non-radiative recombinations.

The Secular Evolution Of Disc Galaxies And The Origin Of Exponential And Double Exponential Surface Density Profiles

NASA Astrophysics Data System (ADS)

Elmegreen, Bruce G.

2016-10-01

Exponential radial profiles are ubiquitous in spiral and dwarf Irregular galaxies, but the origin of this structural form is not understood. This talk will review the observations of exponential and double exponential disks, considering both the light and the mass profiles, and the contributions from stars and gas. Several theories for this structure will also be reviewed, including primordial collapse, bar and spiral torques, clump torques, galaxy interactions, disk viscosity and other internal processes of angular momentum exchange, and stellar scattering off of clumpy structure. The only process currently known that can account for this structure in the most theoretically difficult case is stellar scattering off disks clumps. Stellar orbit models suggest that such scattering can produce exponentials even in isolated dwarf irregulars that have no bars or spirals, little shear or viscosity, and profiles that go out too far for the classical Mestel case of primordial collapse with specific angular momentum conservation.

Entanglement distribution in star network based on spin chain in diamond

NASA Astrophysics Data System (ADS)

Zhu, Yuan-Ming; Ma, Lei

2018-06-01

After star network of spins was proposed, generating entanglement directly through spin interactions between distant parties became possible. We propose an architecture which involves coupled spin chains based on nitrogen-vacancy centers and nitrogen defect spins to expand star network. The numerical analysis shows that the maximally achievable entanglement Em exponentially decays with the length of spin chains M and spin noise. The entanglement capability of this configuration under the effect of disorder and spin loss is also studied. Moreover, it is shown that with this kind of architecture, star network of spins is feasible in measurement of magnetic-field gradient.

Peculiar spectral statistics of ensembles of trees and star-like graphs

NASA Astrophysics Data System (ADS)

Kovaleva, V.; Maximov, Yu; Nechaev, S.; Valba, O.

2017-07-01

In this paper we investigate the eigenvalue statistics of exponentially weighted ensembles of full binary trees and p-branching star graphs. We show that spectral densities of corresponding adjacency matrices demonstrate peculiar ultrametric structure inherent to sparse systems. In particular, the tails of the distribution for binary trees share the ‘Lifshitz singularity’ emerging in the one-dimensional localization, while the spectral statistics of p-branching star-like graphs is less universal, being strongly dependent on p. The hierarchical structure of spectra of adjacency matrices is interpreted as sets of resonance frequencies, that emerge in ensembles of fully branched tree-like systems, known as dendrimers. However, the relaxational spectrum is not determined by the cluster topology, but has rather the number-theoretic origin, reflecting the peculiarities of the rare-event statistics typical for one-dimensional systems with a quenched structural disorder. The similarity of spectral densities of an individual dendrimer and of an ensemble of linear chains with exponential distribution in lengths, demonstrates that dendrimers could be served as simple disorder-less toy models of one-dimensional systems with quenched disorder.

Peculiar spectral statistics of ensembles of trees and star-like graphs

DOE PAGES

Kovaleva, V.; Maximov, Yu; Nechaev, S.; ...

2017-07-11

In this paper we investigate the eigenvalue statistics of exponentially weighted ensembles of full binary trees and p-branching star graphs. We show that spectral densities of corresponding adjacency matrices demonstrate peculiar ultrametric structure inherent to sparse systems. In particular, the tails of the distribution for binary trees share the \\Lifshitz singularity" emerging in the onedimensional localization, while the spectral statistics of p-branching star-like graphs is less universal, being strongly dependent on p. The hierarchical structure of spectra of adjacency matrices is interpreted as sets of resonance frequencies, that emerge in ensembles of fully branched tree-like systems, known as dendrimers. However,more » the relaxational spectrum is not determined by the cluster topology, but has rather the number-theoretic origin, re ecting the peculiarities of the rare-event statistics typical for one-dimensional systems with a quenched structural disorder. The similarity of spectral densities of an individual dendrimer and of ensemble of linear chains with exponential distribution in lengths, demonstrates that dendrimers could be served as simple disorder-less toy models of one-dimensional systems with quenched disorder.« less

Peculiar spectral statistics of ensembles of trees and star-like graphs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kovaleva, V.; Maximov, Yu; Nechaev, S.

In this paper we investigate the eigenvalue statistics of exponentially weighted ensembles of full binary trees and p-branching star graphs. We show that spectral densities of corresponding adjacency matrices demonstrate peculiar ultrametric structure inherent to sparse systems. In particular, the tails of the distribution for binary trees share the \\Lifshitz singularity" emerging in the onedimensional localization, while the spectral statistics of p-branching star-like graphs is less universal, being strongly dependent on p. The hierarchical structure of spectra of adjacency matrices is interpreted as sets of resonance frequencies, that emerge in ensembles of fully branched tree-like systems, known as dendrimers. However,more » the relaxational spectrum is not determined by the cluster topology, but has rather the number-theoretic origin, re ecting the peculiarities of the rare-event statistics typical for one-dimensional systems with a quenched structural disorder. The similarity of spectral densities of an individual dendrimer and of ensemble of linear chains with exponential distribution in lengths, demonstrates that dendrimers could be served as simple disorder-less toy models of one-dimensional systems with quenched disorder.« less

A Future-Based Risk Assessment for the Survivability of Long Range Strike Systems

DTIC Science & Technology

2007-03-01

Aeronautics and Space Administration ( NASA ) investigated alternative futures to help generate a viable science strategy to address the future aerospace...World American World View ΔTeK World Power Grid Name 1 Global Exponential Dispersed DIGITAL CACOPHONY 2 Global Exponential Concentrated STAR TREK ...The United States has become the “United Kingdom of the Twenty-first Century.” 2.2.3. NASA Study (1997) In the NASA study, the National Research

Modeling steady-state dynamics of macromolecules in exponential-stretching flow using multiscale molecular-dynamics-multiparticle-collision simulations.

PubMed

Ghatage, Dhairyasheel; Chatterji, Apratim

2013-10-01

We introduce a method to obtain steady-state uniaxial exponential-stretching flow of a fluid (akin to extensional flow) in the incompressible limit, which enables us to study the response of suspended macromolecules to the flow by computer simulations. The flow field in this flow is defined by v(x) = εx, where v(x) is the velocity of the fluid and ε is the stretch flow gradient. To eliminate the effect of confining boundaries, we produce the flow in a channel of uniform square cross section with periodic boundary conditions in directions perpendicular to the flow, but simultaneously maintain uniform density of fluid along the length of the tube. In experiments a perfect elongational flow is obtained only along the axis of symmetry in a four-roll geometry or a filament-stretching rheometer. We can reproduce flow conditions very similar to extensional flow near the axis of symmetry by exponential-stretching flow; we do this by adding the right amounts of fluid along the length of the flow in our simulations. The fluid particles added along the length of the tube are the same fluid particles which exit the channel due to the flow; thus mass conservation is maintained in our model by default. We also suggest a scheme for possible realization of exponential-stretching flow in experiments. To establish our method as a useful tool to study various soft matter systems in extensional flow, we embed (i) spherical colloids with excluded volume interactions (modeled by the Weeks-Chandler potential) as well as (ii) a bead-spring model of star polymers in the fluid to study their responses to the exponential-stretched flow and show that the responses of macromolecules in the two flows are very similar. We demonstrate that the variation of number density of the suspended colloids along the direction of flow is in tune with our expectations. We also conclude from our study of the deformation of star polymers with different numbers of arms f that the critical flow gradient ε(c) at which the star undergoes the coil-to-stretch transition is independent of f for f = 2,5,10, and 20.

Bonner Durchmusterung (Southern Durchmusterung)

NASA Technical Reports Server (NTRS)

1993-01-01

The Southern Durchmusterung (SD, Schoenfeld 1886, Becker 1949, Schmidt 1967) is a visual survey of stars in the declination zones -02 to -23 deg, completed as an extension to Argelander's (1859-62) monumental Bonner Durchmusterung (BD). Schoenfeld's survey was carried out using the same methods as had been used for the BD. The procedure consisted of allowing the telescope to drift along the mean declination of each zone and recording the positions and magnitudes of stars crossing the transit line of each field. The goal of the survey was to extend the BD to declination -23 deg (a plan originally adopted by Argelander) with approximately the same magnitude limits, although the primary instrument was of larger aperture (159 mm) than the 78-mm telescope used for the BD. Thus, whereas the BD magnitude estimates extend to 9.4 mag with all fainter stars assigned a magnitude of 9.5, the SD magnitude estimates extend to 9.9 mag with all fainter stars assigned a magnitude of 10. The SD contains a number of stars fainter than 10.0 mag and even some as faint as 11 mag. Lists of all corrections made to the original data as a result of published corrigenda, stars deleted according to overstriking in the printed catalogs or their inclusion in lists of 'missing' stars, and stars inserted in later editions are given. No other corrections or changes have been incorporated into the original data, e.g., from more modern positions and magnitudes or from comparison with other catalogs.

A survey of chromospheric Ca II H and K emission in field stars of the solar neighborhood

NASA Technical Reports Server (NTRS)

Vaughan, A. H.; Preston, G. W.

1980-01-01

Fluxes in 1 A bands at the centers of the H and K lines are being measured in main-sequence F-G-K-M stars in the northern half of the Woolley et al. (1970) 'Catalog of stars within twenty-five parsecs of the sun', in a survey not yet completed. Results for 486 stars are presented in the form of flux-color diagrams and discussed in light of evidence that chromospheric activity declines with age in main-sequence stars. Support is noted for the reality of the Sirius moving group. The relative numbers of more-active (Hyades-like) and less-active (solar-like) F-G stars are tolerably in agreement with a nearly constant rate of formation, but there exists an apparent deficiency in the number of F-G stars exhibiting intermediate activity. The possibility that the gap is an accidental characteristic of the sample will be investigated by extending the survey to southern declinations and greater distances.

C-Peptide Decline in Type 1 Diabetes Has Two Phases: An Initial Exponential Fall and a Subsequent Stable Phase.

PubMed

Shields, Beverley M; McDonald, Timothy J; Oram, Richard; Hill, Anita; Hudson, Michelle; Leete, Pia; Pearson, Ewan R; Richardson, Sarah J; Morgan, Noel G; Hattersley, Andrew T

2018-06-07

The decline in C-peptide in the 5 years after diagnosis of type 1 diabetes has been well studied, but little is known about the longer-term trajectory. We aimed to examine the association between log-transformed C-peptide levels and the duration of diabetes up to 40 years after diagnosis. We assessed the pattern of association between urinary C-peptide/creatinine ratio (UCPCR) and duration of diabetes in cross-sectional data from 1,549 individuals with type 1 diabetes using nonlinear regression approaches. Findings were replicated in longitudinal follow-up data for both UCPCR ( n = 161 individuals, 326 observations) and plasma C-peptide ( n = 93 individuals, 473 observations). We identified two clear phases of C-peptide decline: an initial exponential fall over 7 years (47% decrease/year [95% CI -51%, -43%]) followed by a stable period thereafter (+0.07%/year [-1.3, +1.5]). The two phases had similar durations and slopes in patients above and below the median age at diagnosis (10.8 years), although levels were lower in the younger patients irrespective of duration. Patterns were consistent in both longitudinal UCPCR ( n = 162; ≤7 years duration: -48%/year [-55%, -38%]; >7 years duration -0.1% [-4.1%, +3.9%]) and plasma C-peptide ( n = 93; >7 years duration only: -2.6% [-6.7%, +1.5%]). These data support two clear phases of C-peptide decline: an initial exponential fall over a 7-year period, followed by a prolonged stabilization where C-peptide levels no longer decline. Understanding the pathophysiological and immunological differences between these two phases will give crucial insights into understanding β-cell survival. © 2018 by the American Diabetes Association.

The resolved star formation history of M51a through successive Bayesian marginalization

NASA Astrophysics Data System (ADS)

Martínez-García, Eric E.; Bruzual, Gustavo; Magris C., Gladis; González-Lópezlira, Rosa A.

2018-02-01

We have obtained the time and space-resolved star formation history (SFH) of M51a (NGC 5194) by fitting Galaxy Evolution Explorer (GALEX), Sloan Digital Sky Survey and near-infrared pixel-by-pixel photometry to a comprehensive library of stellar population synthesis models drawn from the Synthetic Spectral Atlas of Galaxies (SSAG). We fit for each space-resolved element (pixel) an independent model where the SFH is averaged in 137 age bins, each one 100 Myr wide. We used the Bayesian Successive Priors (BSP) algorithm to mitigate the bias in the present-day spatial mass distribution. We test BSP with different prior probability distribution functions (PDFs); this exercise suggests that the best prior PDF is the one concordant with the spatial distribution of the stellar mass as inferred from the near-infrared images. We also demonstrate that varying the implicit prior PDF of the SFH in SSAG does not affect the results. By summing the contributions to the global star formation rate of each pixel, at each age bin, we have assembled the resolved SFH of the whole galaxy. According to these results, the star formation rate of M51a was exponentially increasing for the first 10 Gyr after the big bang, and then turned into an exponentially decreasing function until the present day. Superimposed, we find a main burst of star formation at t ≈ 11.9 Gyr after the big bang.

The Arizona Radio Observatory CO Mapping Survey of Galactic Molecular Clouds. V. The Sh2-235 Cloud in CO J=2-1, 13CO J=2-1, and CO J=3-2

NASA Astrophysics Data System (ADS)

Bieging, John H.; Patel, Saahil; Peters, William L.; Toth, L. Viktor; Marton, Gábor; Zahorecz, Sarolta

2016-09-01

We present the results of a program to map the Sh2-235 molecular cloud complex in the CO and 13CO J = 2 - 1 transitions using the Heinrich Hertz Submillimeter Telescope. The map resolution is 38″ (FWHM), with an rms noise of 0.12 K brightness temperature, for a velocity resolution of 0.34 km s-1. With the same telescope, we also mapped the CO J = 3 - 2 line at a frequency of 345 GHz, using a 64 beam focal plane array of heterodyne mixers, achieving a typical rms noise of 0.5 K brightness temperature with a velocity resolution of 0.23 km s-1. The three spectral line data cubes are available for download. Much of the cloud appears to be slightly sub-thermally excited in the J = 3 level, except for in the vicinity of the warmest and highest column density areas, which are currently forming stars. Using the CO and 13CO J = 2 - 1 lines, we employ an LTE model to derive the gas column density over the entire mapped region. Examining a 125 pc2 region centered on the most active star formation in the vicinity of Sh2-235, we find that the young stellar object surface density scales as approximately the 1.6-power of the gas column density. The area distribution function of the gas is a steeply declining exponential function of gas column density. Comparison of the morphology of ionized and molecular gas suggests that the cloud is being substantially disrupted by expansion of the H II regions, which may be triggering current star formation.

Exponential decline of aftershocks of the M7.9 1868 great Kau earthquake, Hawaii, through the 20th century

USGS Publications Warehouse

Klein, F.W.; Wright, Tim

2008-01-01

The remarkable catalog of Hawaiian earthquakes going back to the 1820s is based on missionary diaries, newspaper accounts, and instrumental records and spans the great M7.9 Kau earthquake of April 1868 and its aftershock sequence. The earthquake record since 1868 defines a smooth curve complete to M5.2 of the declining rate into the 21st century, after five short volcanic swarms are removed. A single aftershock curve fits the earthquake record, even with numerous M6 and 7 main shocks and eruptions. The timing of some moderate earthquakes may be controlled by magmatic stresses, but their overall long-term rate reflects one of aftershocks of the Kau earthquake. The 1868 earthquake is, therefore, the largest and most controlling stress event in the 19th and 20th centuries. We fit both the modified Omori (power law) and stretched exponential (SE) functions to the earthquakes. We found that the modified Omori law is a good fit to the M ??? 5.2 earthquake rate for the first 10 years or so and the more rapidly declining SE function fits better thereafter, as supported by three statistical tests. The switch to exponential decay suggests that a possible change in aftershock physics may occur from rate and state fault friction, with no change in the stress rate, to viscoelastic stress relaxation. The 61-year exponential decay constant is at the upper end of the range of geodetic relaxation times seen after other global earthquakes. Modeling deformation in Hawaii is beyond the scope of this paper, but a simple interpretation of the decay suggests an effective viscosity of 1019 to 1020 Pa s pertains in the volcanic spreading of Hawaii's flanks. The rapid decline in earthquake rate poses questions for seismic hazard estimates in an area that is cited as one of the most hazardous in the United States.

Cordoba Durchmusterung, volume 4

NASA Technical Reports Server (NTRS)

1993-01-01

The 'Cordoba Durchmusterung' (CD) is a visual survey of southern stars in the declination zones -22 to -89 deg, carried out as an extension to the 'Bonner Durchmusterung' (BD) catalogs of Argelander and Schoenfeld. This volume covers the declination range -40 deg through -49 deg. The survey was performed using techniques similar to those used for the BD; i.e., the stars were cataloged by allowing the telescope to drift along the mean declination of each zone and recording the positions and magnitudes of stars crossing the transit line of the field. The goal of the survey was to obtain a position and estimated visual magnitude for every star down to 10.0 magnitude inclusive, but the faint limit was confirmed from comparisons with other catalogs, to be somewhat below 10. The positions are given to 0.1 s in right ascension and 0.1 min in declination for the equinox 1875. The positional uncertainties quoted in the original publications are plus or minus 0.42 sec and plus or minus 0.23 min for zones -22 deg to -32 deg. A list of all corrections made to the original data as a result of published corrigenda is presented. No other corrections or changes were incorporated into the original data, e.g., from more modern positions and magnitudes or comparison with the 'Cape Photographic Durchmusterung'.

Cordoba Durchmusterung, volume 1

NASA Technical Reports Server (NTRS)

1993-01-01

The 'Cordoba Durchmusterung' (CD) is a visual survey of southern stars in the declination zones -22 to -89 deg, carried out as an extension to the 'Bonner Durchmusterung' (BD) catalogs of Argelander and Schoenfeld. This volume covers the declination range -22 deg through -30 deg. The survey was performed using techniques similar to those used for the BD; i.e., the stars were cataloged by allowing the telescope to drift along the mean declination of each zone and recording the positions and magnitudes of stars crossing the transit line of the field. The goal of the survey was to obtain a position and estimated visual magnitude for every star down to 10.0 magnitude inclusive, but the faint limit was confirmed from comparisons with other catalogs, to be somewhat below 10. The positions are given to 0.1 s in right ascension and 0.1 min in declination for the equinox 1875. The positional uncertainties quoted in the original publications are plus or minus 0.42 s and plus or minus 0.23 min for zones -22 deg to -32 deg. A list of all corrections made to the original data as a result of published corrigenda is presented. No other corrections or changes were incorporated into the original data, e.g., from more modern positions and magnitudes or comparison with the 'Cape Photographic Durchmusterung'.

Star Formation at z = 2.481 in the Lensed Galaxy SDSS J1110+6459. II. What is Missed at the Normal Resolution of the Hubble Space Telescope?

NASA Astrophysics Data System (ADS)

Rigby, J. R.; Johnson, T. L.; Sharon, K.; Whitaker, K.; Gladders, M. D.; Florian, M.; Lotz, J.; Bayliss, M.; Wuyts, E.

2017-07-01

For lensed galaxy SGAS J111020.0+645950.8 at redshift z = 2.481, which is magnified by a factor of 28 ± 8, we analyze the morphology of star formation, as traced by rest-frame ultraviolet emission, in both the highly magnified source plane and simulations of how this galaxy would appear without lensing magnification. Were this galaxy not lensed, but rather drawn from a Hubble Space Telescope deep field, we would conclude that almost all its star formation arises from an exponential disk (Sérsic index of 1.0 ± 0.4) with an effective radius of {r}e=2.7+/- 0.3 {kpc} measured from two-dimensional fitting to F606W using Galfit, and {r}e=1.9+/- 0.1 {kpc} measured by fitting a radial profile to F606W elliptical isophotes. At the normal spatial resolution of the deep fields, there is no sign of clumpy star formation within SGAS J111020.0+645950.8. However, the enhanced spatial resolution enabled by gravitational lensing tells a very different story; much of the star formation arises in two dozen clumps with sizes of r = 30-50 pc spread across the 7 kpc length of the galaxy. The color and spatial distribution of the diffuse component suggests that still-smaller clumps are unresolved. Despite this clumpy, messy morphology, the radial profile is still well-characterized by an exponential profile. In this lensed galaxy, stars are forming in complexes with sizes well below 100 pc such sizes are wholly unexplored by surveys of galaxy evolution at 1< z< 3.

The SFR-M∗ main sequence archetypal star-formation history and analytical models

NASA Astrophysics Data System (ADS)

Ciesla, L.; Elbaz, D.; Fensch, J.

2017-12-01

The star-formation history (SFH) of galaxies is a key assumption to derive their physical properties and can lead to strong biases. In this work, we derive the SFH of main sequence (MS) galaxies and show how the peak SFH of a galaxy depends on its seed mass at, for example, z = 5. This seed mass reflects the galaxy's underlying dark matter (DM) halo environment. We show that, following the MS, galaxies undergo a drastic slow down of their stellar mass growth after reaching the peak of their SFH. According to abundance matching, these masses correspond to hot and massive DM halos which state could result in less efficient gas inflows on the galaxies and thus could be the origin of limited stellar mass growth. As a result, we show that galaxies, still on the MS, can enter the passive region of the UVJ diagram while still forming stars. The best fit to the MS SFH is provided by a right skew peak function for which we provide parameters depending on the seed mass of the galaxy. The ability of the classical analytical SFHs to retrieve the star-formation rate (SFR) of galaxies from spectral energy distribution (SED) fitting is studied. Due to mathematical limitations, the exponentially declining and delayed SFH struggle to model high SFR, which starts to be problematic at z > 2. The exponentially rising and log-normal SFHs exhibit the opposite behavior with the ability to reach very high SFR, and thus model starburst galaxies, but they are not able to model low values such as those expected at low redshift for massive galaxies. By simulating galaxies SED from the MS SFH, we show that these four analytical forms recover the SFR of MS galaxies with an error dependent on the model and the redshift. They are, however, sensitive enough to probe small variations of SFR within the MS, with an error ranging from 5 to 40% depending on the SFH assumption and redshift; but all the four fail to recover the SFR of rapidly quenched galaxies. However, these SFHs lead to an artificial gradient of age, parallel to the MS, which is not exhibited by the simulated sample. This gradient is also produced on real data as we show using a sample of real galaxies with redshifts between 1.5 and 2.5. Here, we propose an SFH composed of a delayed form to model the bulk of stellar population with the addition of a flexibility in the recent SFH. This SFH provides very good estimates of the SFR of MS, starbursts, and rapidly quenched galaxies at all redshift. Furthermore, when used on the real sample, the age gradient disappears which show its dependency on the SFH assumption made to perform the SED fitting.

Astronomical Data Center Bulletin, volume 1, number 3

NASA Technical Reports Server (NTRS)

Mead, J. M.; Warren, W. H., Jr.; Nagy, T. A.

1983-01-01

A catalog of galactic O-type stars, a machine-readable version of the bright star catalog, a two-micron sky survey, sky survey sources with problematical Durchmusterung identifications, data retrieval for visual binary stars, faint blue objects, the sixth catalog of galactic Wolf-Rayet stars, declination versus magnitude distribution, the SAO-HD-GC-DM cross index catalog, star cross-identification tables, astronomical sources, bibliographical star index search updates, DO-HD and HD-DO cross indices, and catalogs, are reviewed.

Gas production in the Barnett Shale obeys a simple scaling theory

PubMed Central

Patzek, Tad W.; Male, Frank; Marder, Michael

2013-01-01

Natural gas from tight shale formations will provide the United States with a major source of energy over the next several decades. Estimates of gas production from these formations have mainly relied on formulas designed for wells with a different geometry. We consider the simplest model of gas production consistent with the basic physics and geometry of the extraction process. In principle, solutions of the model depend upon many parameters, but in practice and within a given gas field, all but two can be fixed at typical values, leading to a nonlinear diffusion problem we solve exactly with a scaling curve. The scaling curve production rate declines as 1 over the square root of time early on, and it later declines exponentially. This simple model provides a surprisingly accurate description of gas extraction from 8,294 wells in the United States’ oldest shale play, the Barnett Shale. There is good agreement with the scaling theory for 2,057 horizontal wells in which production started to decline exponentially in less than 10 y. The remaining 6,237 horizontal wells in our analysis are too young for us to predict when exponential decline will set in, but the model can nevertheless be used to establish lower and upper bounds on well lifetime. Finally, we obtain upper and lower bounds on the gas that will be produced by the wells in our sample, individually and in total. The estimated ultimate recovery from our sample of 8,294 wells is between 10 and 20 trillion standard cubic feet. PMID:24248376

Gas production in the Barnett Shale obeys a simple scaling theory.

PubMed

Patzek, Tad W; Male, Frank; Marder, Michael

2013-12-03

Natural gas from tight shale formations will provide the United States with a major source of energy over the next several decades. Estimates of gas production from these formations have mainly relied on formulas designed for wells with a different geometry. We consider the simplest model of gas production consistent with the basic physics and geometry of the extraction process. In principle, solutions of the model depend upon many parameters, but in practice and within a given gas field, all but two can be fixed at typical values, leading to a nonlinear diffusion problem we solve exactly with a scaling curve. The scaling curve production rate declines as 1 over the square root of time early on, and it later declines exponentially. This simple model provides a surprisingly accurate description of gas extraction from 8,294 wells in the United States' oldest shale play, the Barnett Shale. There is good agreement with the scaling theory for 2,057 horizontal wells in which production started to decline exponentially in less than 10 y. The remaining 6,237 horizontal wells in our analysis are too young for us to predict when exponential decline will set in, but the model can nevertheless be used to establish lower and upper bounds on well lifetime. Finally, we obtain upper and lower bounds on the gas that will be produced by the wells in our sample, individually and in total. The estimated ultimate recovery from our sample of 8,294 wells is between 10 and 20 trillion standard cubic feet.

Rapid growth of seed black holes in the early universe by supra-exponential accretion.

PubMed

Alexander, Tal; Natarajan, Priyamvada

2014-09-12

Mass accretion by black holes (BHs) is typically capped at the Eddington rate, when radiation's push balances gravity's pull. However, even exponential growth at the Eddington-limited e-folding time t(E) ~ few × 0.01 billion years is too slow to grow stellar-mass BH seeds into the supermassive luminous quasars that are observed when the universe is 1 billion years old. We propose a dynamical mechanism that can trigger supra-exponential accretion in the early universe, when a BH seed is bound in a star cluster fed by the ubiquitous dense cold gas flows. The high gas opacity traps the accretion radiation, while the low-mass BH's random motions suppress the formation of a slowly draining accretion disk. Supra-exponential growth can thus explain the puzzling emergence of supermassive BHs that power luminous quasars so soon after the Big Bang. Copyright © 2014, American Association for the Advancement of Science.

ASCA Observations of the T Tauri Star SU Aurigae and the Surrounding L1517 Dark Cloud

NASA Technical Reports Server (NTRS)

Skinner, Stephen L.; Walter, Frederick M.

1998-01-01

We present the results of a approximately equals 40 ks pointed Advanced Satellite for Cosmology and Astrophysics (ASCA) observation of the L1517 star-forming region, centered on the X-ray-bright T Tauri star SU Aurigae. This star has the highest X-ray luminosity of any classical T Tauri star in the Taurus-Auriga region, and its optical spectra show evidence for both mass inflow and outflow. Strong X-ray emission was detected from SU Aur (L(sub x) = 10(exp 30.9) ergs s(exp -1)) as well as weaker emission from five other pre-main-sequence stars. Although no large-amplitude flares were detected, the X-ray emission of SU Aur showed clear variability in the form of a slow decline in count rate during the 1.3 day observation. We provide the first direct comparison of the coronal differential emission measure (DEM) distribution of a classical T Tauri star with that of a young main-sequence star of similar spectral type. The DEM distributions of SU Aur (G2; age 3 Myr) and the young solar-like star EK Draconis (GO V; age 70 Myr) are qualitatively similar, with both showing a bimodal temperature distribution characterized by a cool plasma component peaking at approximately 8-9 MK and a hot component peaking at approximately 20-21 MK. However, there is a striking difference in the relative proportion of plasma at high temperatures in the two stars, with hot plasma (>20 MK) accounting for approximately equals 80% of the volume emission measure of SU Aur, compared to only approximately equals 40% in EK Dra. These results provide new insight into the changes that will occur in the corona of a T Tauri star as it descends onto the main sequence. A sharp decline in the fraction of coronal plasma at flarelike temperatures will occur during the late-T Tauri and post-T Tauri phases, and other recent X-ray studies have shown that this decline will continue after the young solar-like star reaches the main sequence.

How to form a millisecond magnetar? Magnetic field amplification in protoneutron stars

NASA Astrophysics Data System (ADS)

Guilet, Jérôme; Müller, Ewald; Janka, Hans-Thomas; Rembiasz, Tomasz; Obergaulinger, Martin; Cerdá-Durán, Pablo; Aloy, Miguel-Angel

2017-02-01

Extremely strong magnetic fields of the order of 1015G are required to explain the properties of magnetars, the most magnetic neutron stars. Such a strong magnetic field is expected to play an important role for the dynamics of core-collapse supernovae, and in the presence of rapid rotation may power superluminous supernovae and hypernovae associated to long gamma-ray bursts. The origin of these strong magnetic fields remains, however, obscure and most likely requires an amplification over many orders of magnitude in the protoneutron star. One of the most promising agents is the magnetorotational instability (MRI), which can in principle amplify exponentially fast a weak initial magnetic field to a dynamically relevant strength. We describe our current understanding of the MRI in protoneutron stars and show recent results on its dependence on physical conditions specific to protoneutron stars such as neutrino radiation, strong buoyancy effects and large magnetic Prandtl number.

Residual fields from extinct dynamos

NASA Astrophysics Data System (ADS)

Parker, E. N.

The generation of magnetic fields in convective zones of declining vigor and/or thickness is considered, the goal being to explain the magnetic fields observed in A-stars. The investigation is restricted to kinematical dynamos in order to show some of the many possibilities, which depend on the assumed conditions of decline of the convection. The examples illustrate the quantitative detail required to describe the convection in order to extract any firm conclusions concerning specific stars. The first example treats the basic problem of diffusion from a layer of declining thickness. The second has a buoyant rise added to the field in the layer. The third deals with plane dynamo waves in a region with declining eddy diffusivity, dynamo coefficient, and large-scale shear. It is noted that the dynamo number may increase or decrease with declining convection, with an increase expected if the large-scale shear does not decline as rapidly as the eddy diffusivity. It is shown that one of the components of the field may increase without bound even when the dynamo number declines to zero.

IUE observations of rapidly rotating low-mass stars in young clusters - The relation between chromospheric activity and rotation

NASA Technical Reports Server (NTRS)

Simon, Theodore

1990-01-01

If the rapid spindown of low-mass stars immediately following their arrival on the ZAMS results from magnetic braking by coronal winds, an equally sharp decline in their chromospheric emission may be expected. To search for evidence of this effect, the IUE spacecraft was used to observe the chromospheric Mg II emission lines of G-M dwarfs in the nearby IC 2391, Alpha Persei, Pleiades, and Hyades clusters. Similar observations were made of a group of X-ray-selected 'naked' T Tauri stars in Taurus-Auriga. The existence of a decline in activity cannot be confirmed from the resulting data. However, the strength of the chromospheric emission in the Mg II lines of the cluster stars is found to be correlated with rotation rate, being strongest for the stars with the shortest rotation periods and weakest for those with the longest periods. This provides indirect support for such an evolutionary change in activity. Chromospheric activity may thus be only an implicit function of age.

Lack of synchronization between iron uptake and cell growth leads to iron overload in Saccharomyces cerevisiae during post-exponential growth modes

PubMed Central

Park, Jinkyu; McCormick, Sean P.; Chakrabarti, Mrinmoy; Lindahl, Paul A.

2014-01-01

Fermenting cells growing exponentially on rich (YPAD) medium transitioned to a slow-growing state as glucose levels declined and their metabolism shifted to respiration. During exponential growth, Fe import and cell growth rates were matched, affording an approximately invariant cellular Fe concentration. During the transitionary period, the high-affinity Fe import rate declined slower than the cell growth rate declined, causing Fe to accumulate, initially as FeIII oxyhydroxide nanoparticles but eventually as mitochondrial and vacuolar Fe. Once in slow-growth mode, Fe import and cell growth rates were again matched, and the cellular Fe concentration was again approximately invariant. Fermenting cells grown on minimal medium (MM) grew more slowly during exponential phase and transitioned to a true stationary state as glucose levels declined. The Fe concentration of MM cells that just entered stationary state was similar to that of YPAD cells, but MM cells continued to accumulate Fe in stationary state. Fe initially accumulated as nanoparticles and high-spin FeII species, but vacuolar FeIII also eventually accumulated. Surprisingly, Fe-packed 5-day-old MM cells suffered no more ROS damage than younger cells, suggesting that Fe concentration alone does not accurately predict the extent of ROS damage. The mode and rate of growth at the time of harvesting dramatically affected cellular Fe content. A mathematical model of Fe metabolism in a growing cell was developed. The model included Fe import via a regulated high-affinity pathway and an unregulated low-affinity pathway. Fe import from the cytosol into vacuoles and mitochondria, and nanoparticle formation were also included. The model captured essential trafficking behavior, demonstrating that cells regulate Fe import in accordance with their overall growth rate and that they misregulate Fe import when nanoparticles accumulate. The lack of regulation of Fe in yeast is perhaps unique compared to the tight regulation of other cellular metabolites. This phenomenon likely derives from the unique chemistry associated with Fe nanoparticle formation. PMID:24344915

Stationary orbits of satellites of disk galaxies

NASA Technical Reports Server (NTRS)

Polyachenko, Valerij L.

1990-01-01

The satellite of an S-galaxy will experience opposing dynamical-friction forces from the stars of the disk and the halo. If these forces are in balance, the satellite may travel in a stable, near-circular orbit whose radius, for a wide range of physical parameters, should be limited to a zone 1.2 to 1.4 times the disk radius, much as is observed. The idea is very simple. The dynamical friction acting on a small satellite, moving through a stellar galactic halo, makes this satellite slow down. On the other hand, a stellar disk, rotating faster than a satellite, makes it speed up. But the density distributions in radius for disk's and halo's stars in real flat galaxies are quite different (respectively, exponential and power-law). Moreover, the observational data show that the exponential profile for disk's surface density drops abruptly at some radius (r sub d). So it is natural to expect that a stationary orbit could be near the edge of a disk (where two effects are mutually compensated).

Cosmic Web of Galaxies in the COMOS Field

NASA Astrophysics Data System (ADS)

Darvish, Behnam; Martin, Christopher D.; Mobasher, Bahram; Scoville, Nicholas; Sobral, David; COSMOS science Team

2017-01-01

We use a mass complete sample of galaxies with accurate photometric redshifts in the COSMOS field to estimate the density field and to extract the components of the cosmic web. The comic web extraction algorithm relies on the signs and the ratio of eigenvalues of the Hessian matrix and is enable to integrate the density field into clusters, filaments and the field. We show that at z < 0.8, the median star-formation rate in the cosmic web gradually declines from the field to clusters and this decline is especially sharp for satellite galaxies (~1 dex vs. ~0.4 dex for centrals). However, at z > 0.8, the trend flattens out. For star-forming galaxies only, the median star-formation rate declines by ~ 0.3-0.4 dex from the field to clusters for both satellites and centrals, only at z < 0.5. We argue that for satellite galaxies, the main role of the cosmic web environment is to control their star-forming/quiescent fraction, whereas for centrals, it is mainly to control their overall star-formation rate. Given these, we suggest that most satellite galaxies experience a rapid quenching mechanism as they fall from the field into clusters through the channel of filaments, whereas for central galaxies, it is mostly due to a slow quenching process. Our preliminary results highlight the importance of the large-scale cosmic web on the evolution of galaxies.

How exponential are FREDs?

NASA Astrophysics Data System (ADS)

Schaefer, Bradley E.; Dyson, Samuel E.

1996-08-01

A common Gamma-Ray Burst-light curve shape is the ``FRED'' or ``fast-rise exponential-decay.'' But how exponential is the tail? Are they merely decaying with some smoothly decreasing decline rate, or is the functional form an exponential to within the uncertainties? If the shape really is an exponential, then it would be reasonable to assign some physically significant time scale to the burst. That is, there would have to be some specific mechanism that produces the characteristic decay profile. So if an exponential is found, then we will know that the decay light curve profile is governed by one mechanism (at least for simple FREDs) instead of by complex/multiple mechanisms. As such, a specific number amenable to theory can be derived for each FRED. We report on the fitting of exponentials (and two other shapes) to the tails of ten bright BATSE bursts. The BATSE trigger numbers are 105, 257, 451, 907, 1406, 1578, 1883, 1885, 1989, and 2193. Our technique was to perform a least square fit to the tail from some time after peak until the light curve approaches background. We find that most FREDs are not exponentials, although a few come close. But since the other candidate shapes come close just as often, we conclude that the FREDs are misnamed.

Exponential expansion: galactic destiny or technological hubris?

NASA Astrophysics Data System (ADS)

Finney, B. R.

Is it our destiny to expand exponentially to populate the galaxy, or is such a vision but an extreme example of technological hubris? The overall record of human evolution and dispersion over the Earth can be cited to support the view that we are a uniquely expansionary and technological animal bound for the stars, yet an examination of the fate of individual migrations and exploratory initiatives raises doubts. Although it may be in keeping with our hubristic nature to predict ultimate galactic expansion, there is no way to specify how far expansionary urges may drive our spacefaring descendants.

SUBARU/HDS STUDY OF HE 1015-2050: SPECTRAL EVIDENCE OF R CORONAE BOREALIS LIGHT DECLINE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goswami, Aruna; Aoki, Wako, E-mail: aruna@iiap.res.in

2013-02-01

Hydrogen deficiency and a sudden optical light decline of about 6-8 mag are two principal characteristics of R Coronae Borealis (RCB) stars. The high latitude carbon star HE 1015-2050 was identified as a hydrogen-deficient carbon star from low-resolution spectroscopy. Photometric data of the Catalina Real-Time Transient Survey gathered between 2006 February and 2012 May indicate that the object exhibits no variability. However, a high-resolution (R {approx} 50, 000) optical spectrum of this object obtained with the 8.2 m Subaru telescope using High Dispersion Spectrograph on the 2012 January 13 offers sufficient spectral evidence that the object is a cool HdCmore » star of RCB type undergoing light decline. In contrast to the Na I D broad absorption features seen in the low-resolution spectra on several occasions, the high-resolution spectrum exhibits Na I D{sub 2} and D{sub 1} features in emission. A few emission lines due to Mg I, Sc II, Ti I, Ti II, Fe II, and Ba I are also observed in the spectrum of this object for the first time. Such emission features combined with neutral and singly ionized lines of Ca, Ti, Fe, etc., in absorption are reportedly seen in RCBs spectra in the early stage of decline or during the recovery to maximum. Further, the light decline of RCBs is ascribed to the formation of a cloud of soot that obscures the visible photosphere. The presence of such circumstellar material is evident from the polarimetric observations with an estimated V-band percentage polarization of {approx}1.7% for this object.« less

LBGs properties from z˜3 to z˜6

NASA Astrophysics Data System (ADS)

de Barros, S.; Schaerer, D.; Stark, D. P.

2011-12-01

We analyse the spectral energy distribution (SED) of U, B, V and i-dropout samples from GOODS-MUSIC and we determine their physical properties, such as stellar age and mass, dust attenuation and star formation rate (SFR). Furthermore, we examine how the strength of Lyα emission can be constrained from broad-band SED fits instead of relying in spectroscopy. We use our SED fitting tool including the effects of nebular emission and we explore different star formation histories (SFHs). We find that SEDs are statistically better fitted with nebular emission and exponentially decreasing star formation. Considering this result, stellar mass and star formation rate (SFR) estimations modify the specific SFR (SFR/M_{⋆}) - redshift relation, in compared to previous studies. Finally, our inferred Lyα properties are in good agreement with the available spectroscopic observations.

The role of stellar radial motions in shaping galaxy surface brightness profiles

NASA Astrophysics Data System (ADS)

Ruiz-Lara, T.; Few, C. G.; Florido, E.; Gibson, B. K.; Pérez, I.; Sánchez-Blázquez, P.

2017-12-01

Aims: The physics driving features such as breaks observed in galaxy surface brightness (SB) profiles remains contentious. Here, we assess the importance of stellar radial motions in shaping their characteristics. Methods: We use the simulated Milky Way-mass cosmological discs from the Ramses Disc Environment Study (RaDES) to characterise the radial redistribution of stars in galaxies displaying type-I (pure exponentials), II (downbending), and III (upbending) SB profiles. We compare radial profiles of the mass fractions and the velocity dispersions of different sub-populations of stars according to their birth and current location. Results: Radial redistribution of stars is important in all galaxies regardless of their light profiles. Type-II breaks seem to be a consequence of the combined effects of outward-moving and accreted stars. The former produce shallower inner profiles (lack of stars in the inner disc) and accumulate material around the break radius and beyond, strengthening the break; the latter can weaken or even convert the break into a pure exponential. Further accretion from satellites can concentrate material in the outermost parts, leading to type-III breaks that can coexist with type-II breaks, but situated further out. Type-III galaxies would be the result of an important radial redistribution of material throughout the entire disc, as well as a concentration of accreted material in the outskirts. In addition, type-III galaxies display the most efficient radial redistribution and the largest number of accreted stars, followed by type-I and II systems, suggesting that type-I galaxies may be an intermediate case between types II and III. In general, the velocity dispersion profiles of all galaxies tend to flatten or even increase around the locations where the breaks are found. The age and metallicity profiles are also affected, exhibiting different inner gradients depending on their SB profile, being steeper in the case of type-II systems (as found observationally). The steep type-II profiles might be inherent to their formation rather than acquired via radial redistribution.

Using binary statistics in Taurus-Auriga to distinguish between brown dwarf formation processes

NASA Astrophysics Data System (ADS)

Marks, M.; Martín, E. L.; Béjar, V. J. S.; Lodieu, N.; Kroupa, P.; Manjavacas, E.; Thies, I.; Rebolo López, R.; Velasco, S.

2017-08-01

Context. One of the key questions of the star formation problem is whether brown dwarfs (BDs) form in the manner of stars directly from the gravitational collapse of a molecular cloud core (star-like) or whether BDs and some very low-mass stars (VLMSs) constitute a separate population that forms alongside stars comparable to the population of planets, for example through circumstellar disk (peripheral) fragmentation. Aims: For young stars in Taurus-Auriga the binary fraction has been shown to be large with little dependence on primary mass above ≈ 0.2 M⊙, while for BDs the binary fraction is < 10%. Here we investigate a case in which BDs in Taurus formed dominantly, but not exclusively, through peripheral fragmentation, which naturally results in small binary fractions. The decline of the binary frequency in the transition region between star-like formation and peripheral formation is modelled. Methods: We employed a dynamical population synthesis model in which stellar binary formation is universal with a large binary fraction close to unity. Peripheral objects form separately in circumstellar disks with a distinctive initial mass function (IMF), their own orbital parameter distributions for binaries, and small binary fractions, according to observations and expectations from smoothed particle hydrodynamics (SPH) and grid-based computations. A small amount of dynamical processing of the stellar component was accounted for as appropriate for the low-density Taurus-Auriga embedded clusters. Results: The binary fraction declines strongly in the transition region between star-like and peripheral formation, exhibiting characteristic features. The location of these features and the steepness of this trend depend on the mass limits for star-like and peripheral formation. Such a trend might be unique to low density regions, such as Taurus, which host binary populations that are largely unprocessed dynamically in which the binary fraction is large for stars down to M-dwarfs and small for BDs. Conclusions: The existence of a strong decline in the binary fraction - primary mass diagram will become verifiable in future surveys on BD and VLMS binarity in the Taurus-Auriga star-forming region. The binary fraction - primary mass diagram is a diagnostic of the (non-)continuity of star formation along the mass scale, the separateness of the stellar and BD populations, and the dominant formation channel for BDs and BD binaries in regions of low stellar density hosting dynamically unprocessed populations.

A decades-long fast-rise-exponential-decay flare in low-luminosity AGN NGC 7213

NASA Astrophysics Data System (ADS)

Yan, Zhen; Xie, Fu-Guo

2018-03-01

We analysed the four-decades-long X-ray light curve of the low-luminosity active galactic nucleus (LLAGN) NGC 7213 and discovered a fast-rise-exponential-decay (FRED) pattern, i.e. the X-ray luminosity increased by a factor of ≈4 within 200 d, and then decreased exponentially with an e-folding time ≈8116 d (≈22.2 yr). For the theoretical understanding of the observations, we examined three variability models proposed in the literature: the thermal-viscous disc instability model, the radiation pressure instability model, and the TDE model. We find that a delayed tidal disruption of a main-sequence star is most favourable; either the thermal-viscous disc instability model or radiation pressure instability model fails to explain some key properties observed, thus we argue them unlikely.

CANDELS+3D-HST: Compact SFGs at z ∼ 2-3, the progenitors of the first quiescent galaxies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barro, G.; Faber, S. M.; Koo, D. C.

We analyze the star-forming and structural properties of 45 massive (log(M/M{sub ☉}) >10) compact star-forming galaxies (SFGs) at 2 < z < 3 to explore whether they are progenitors of compact quiescent galaxies at z ∼ 2. The optical/NIR and far-IR Spitzer/Herschel colors indicate that most compact SFGs are heavily obscured. Nearly half (47%) host an X-ray-bright active galactic nucleus (AGN). In contrast, only about 10% of other massive galaxies at that time host AGNs. Compact SFGs have centrally concentrated light profiles and spheroidal morphologies similar to quiescent galaxies and are thus strikingly different from other SFGs, which typically aremore » disk-like and sometimes clumpy or irregular. Most compact SFGs lie either within the star formation rate (SFR)-mass main sequence (65%) or below it (30%), on the expected evolutionary path toward quiescent galaxies. These results show conclusively that galaxies become more compact before they lose their gas and dust, quenching star formation. Using extensive HST photometry from CANDELS and grism spectroscopy from the 3D-HST survey, we model their stellar populations with either exponentially declining (τ) star formation histories (SFHs) or physically motivated SFHs drawn from semianalytic models (SAMs). SAMs predict longer formation timescales and older ages ∼2 Gyr, which are nearly twice as old as the estimates of the τ models. Both models yield good spectral energy distribution fits, indicating that the systematic uncertainty in the age due to degeneracies in the SFH is of that order of magnitude. However, SAM SFHs better match the observed slope and zero point of the SFR-mass main sequence. Contrary to expectations, some low-mass compact SFGs (log(M/M{sub ☉}) =10-10.6) have younger ages but lower specific SFRs than that of more massive galaxies, suggesting that the low-mass galaxies reach the red sequence faster. If the progenitors of compact SFGs are extended SFGs, state-of-the-art SAMs show that mergers and disk instabilities (DIs) are both able to shrink galaxies, but DIs are more frequent (60% versus 40%) and form more concentrated galaxies. We confirm this result via high-resolution hydrodynamic simulations.« less

On the use of star-shaped genealogies in inference of coalescence times.

PubMed Central

Rosenberg, Noah A; Hirsh, Aaron E

2003-01-01

Genealogies from rapidly growing populations have approximate "star" shapes. We study the degree to which this approximation holds in the context of estimating the time to the most recent common ancestor (T(MRCA)) of a set of lineages. In an exponential growth scenario, we find that unless the product of population size (N) and growth rate (r) is at least approximately 10(5), the "pairwise comparison estimator" of T(MRCA) that derives from the star genealogy assumption has bias of 10-50%. Thus, the estimator is appropriate only for large populations that have grown very rapidly. The "tree-length estimator" of T(MRCA) is more biased than the pairwise comparison estimator, having low bias only for extremely large values of Nr. PMID:12930771

Big Data in the SHELA Field: Investigating Galaxy Quenching at High Redshifts

NASA Astrophysics Data System (ADS)

Stevans, Matthew L.; Finkelstein, Steven L.; Wold, Isak; Kawinwanichakij, Lalitwadee; Sherman, Sydney; Gebhardt, Karl; Jogee, Shardha; Papovich, Casey J.; Ciardullo, Robin; Gronwall, Caryl; Gawiser, Eric J.; Acquaviva, Viviana; Casey, Caitlin; Florez, Jonathan; HETDEX Team

2017-06-01

We present a measurement of the z ~ 4 Lyman break galaxy (LBG) rest-frame UV luminosity function to investigate the onset of quenching in the early universe. The bright-end of the galaxy luminosity function typically shows an exponential decline far steeper than that of the underlying halo mass function. This is typically attributed to negative feedback from past active galactic nuclei (AGN) activity as well as dust attenuation. Constraining the abundance of bright galaxies at early times (z > 3) can provide a key insight into the mechanisms regulating star formation in galaxies. However, existing studies suffer from low number statistics and/or the inability to robustly remove stellar and AGN contaminants. In this study we take advantage of the unprecedentedly large (24 deg^2) Spitzer/HETDEX Exploratory Large Area (SHELA) field and its deep multi-wavelength photometry, which includes DECam ugriz, NEWFIRM K-band, Spitzer/IRAC, Herschel/SPIRE, and X-ray from XMM-Newton and Chandra. With SHELA’s deep imaging over a large area we are uniquely positioned to study statistically significant samples of massive galaxies at high redshifts (z > 3) when the first massive galaxies began quenching. We select our sample using photometric redshifts from the EAZY software package (Brammer et al. 2008) based on the optical and far-infrared imaging. We directly identify and remove stellar contaminants and AGN with IRAC colors and X-ray detections, respectively. By pinning down the exact shape of the bright-end of the z ~ 4 LBG luminosity function, we provide the deepest probe yet into the baryonic physics dominating star formation and quenching in the early universe.

SDSS-IV MaNGA: the different quenching histories of fast and slow rotators

NASA Astrophysics Data System (ADS)

Smethurst, R. J.; Masters, K. L.; Lintott, C. J.; Weijmans, A.; Merrifield, M.; Penny, S. J.; Aragón-Salamanca, A.; Brownstein, J.; Bundy, K.; Drory, N.; Law, D. R.; Nichol, R. C.

2018-01-01

Do the theorized different formation mechanisms of fast and slow rotators produce an observable difference in their star formation histories? To study this, we identify quenching slow rotators in the MaNGA sample by selecting those that lie below the star-forming sequence and identify a sample of quenching fast rotators that were matched in stellar mass. This results in a total sample of 194 kinematically classified galaxies, which is agnostic to visual morphology. We use u - r and NUV - u colours from the Sloan Digital Sky Survey and GALEX and an existing inference package, STARPY, to conduct a first look at the onset time and exponentially declining rate of quenching of these galaxies. An Anderson-Darling test on the distribution of the inferred quenching rates across the two kinematic populations reveals they are statistically distinguishable (3.2σ). We find that fast rotators quench at a much wider range of rates than slow rotators, consistent with a wide variety of physical processes such as secular evolution, minor mergers, gas accretion and environmentally driven mechanisms. Quenching is more likely to occur at rapid rates (τ ≲ 1 Gyr) for slow rotators, in agreement with theories suggesting slow rotators are formed in dynamically fast processes, such as major mergers. Interestingly, we also find that a subset of the fast rotators quench at these same rapid rates as the bulk of the slow rotator sample. We therefore discuss how the total gas mass of a merger, rather than the merger mass ratio, may decide a galaxy's ultimate kinematic fate.

Radio synchrotron spectra of star-forming galaxies

NASA Astrophysics Data System (ADS)

Klein, U.; Lisenfeld, U.; Verley, S.

2018-03-01

We investigated the radio continuum spectra of 14 star-forming galaxies by fitting nonthermal (synchrotron) and thermal (free-free) radiation laws. The underlying radio continuum measurements cover a frequency range of 325 MHz to 24.5 GHz (32 GHz in case of M 82). It turns out that most of these synchrotron spectra are not simple power-laws, but are best represented by a low-frequency spectrum with a mean slope αnth = 0.59 ± 0.20 (Sν ∝ ν-α), and by a break or an exponential decline in the frequency range of 1-12 GHz. Simple power-laws or mildly curved synchrotron spectra lead to unrealistically low thermal flux densities, and/or to strong deviations from the expected optically thin free-free spectra with slope αth = 0.10 in the fits. The break or cutoff energies are in the range of 1.5-7 GeV. We briefly discuss the possible origin of such a cutoff or break. If the low-frequency spectra obtained here reflect the injection spectrum of cosmic-ray electrons, they comply with the mean spectral index of Galactic supernova remnants. A comparison of the fitted thermal flux densities with the (foreground-corrected) Hα fluxes yields the extinction, which increases with metallicity. The fraction of thermal emission is higher than believed hitherto, especially at high frequencies, and is highest in the dwarf galaxies of our sample, which we interpret in terms of a lack of containment in these low-mass systems, or a time effect caused by a very young starburst.

Experimental tests of truncated diffusion in fault damage zones

NASA Astrophysics Data System (ADS)

Suzuki, Anna; Hashida, Toshiyuki; Li, Kewen; Horne, Roland N.

2016-11-01

Fault zones affect the flow paths of fluids in groundwater aquifers and geological reservoirs. Fault-related fracture damage decreases to background levels with increasing distance from the fault core according to a power law. This study investigated mass transport in such a fault-related structure using nonlocal models. A column flow experiment is conducted to create a permeability distribution that varies with distance from a main conduit. The experimental tracer response curve is preasymptotic and implies subdiffusive transport, which is slower than the normal Fickian diffusion. If the surrounding area is a finite domain, an upper truncated behavior in tracer response (i.e., exponential decline at late times) is observed. The tempered anomalous diffusion (TAD) model captures the transition from subdiffusive to Fickian transport, which is characterized by a smooth transition from power-law to an exponential decline in the late-time breakthrough curves.

System for star catalog equalization to enhance attitude determination

NASA Technical Reports Server (NTRS)

Liu, Yong (Inventor); Wu, Yeong-Wei Andy (Inventor); Li, Rongsheng (Inventor)

2001-01-01

An apparatus for star catalog equalization to enhance attitude determination includes a star tracker, a star catalog and a controller. The star tracker is used to sense the positions of stars and generate signals corresponding to the positions of the stars as seen in its field of view. The star catalog contains star location data that is stored using a primary and multiple secondary arrays sorted by both declination (DEC) and right ascension (RA), respectively. The star location data stored in the star catalog is predetermined by calculating a plurality of desired star locations, associating one of a plurality of stars with each of the plurality of desired star locations based upon a neighborhood association angle to generate an associated plurality of star locations: If an artificial star gap occurs during association, then the neighborhood association angle for reassociation is increased. The controller uses the star catalog to determine which stars to select to provide star measurement residuals for correcting gyroscope bias and spacecraft attitude.

Turbulent particle transport in streams: can exponential settling be reconciled with fluid mechanics?

PubMed

McNair, James N; Newbold, J Denis

2012-05-07

Most ecological studies of particle transport in streams that focus on fine particulate organic matter or benthic invertebrates use the Exponential Settling Model (ESM) to characterize the longitudinal pattern of particle settling on the bed. The ESM predicts that if particles are released into a stream, the proportion that have not yet settled will decline exponentially with transport time or distance and will be independent of the release elevation above the bed. To date, no credible basis in fluid mechanics has been established for this model, nor has it been rigorously tested against more-mechanistic alternative models. One alternative is the Local Exchange Model (LEM), which is a stochastic advection-diffusion model that includes both longitudinal and vertical spatial dimensions and is based on classical fluid mechanics. The LEM predicts that particle settling will be non-exponential in the near field but will become exponential in the far field, providing a new theoretical justification for far-field exponential settling that is based on plausible fluid mechanics. We review properties of the ESM and LEM and compare these with available empirical evidence. Most evidence supports the prediction of both models that settling will be exponential in the far field but contradicts the ESM's prediction that a single exponential distribution will hold for all transport times and distances. Copyright © 2012 Elsevier Ltd. All rights reserved.

Long-period oxygen-rich optical Miras in the solar neighborhood

NASA Technical Reports Server (NTRS)

Jura, M.; Yamamoto, A.; Kleinmann, S. G.

1993-01-01

The spatial distribution of the oxygen-rich Miras with periods longer than 400 days in the neighborhood of the sun were determined using available survey and the K-band period luminosity relationship. It is found that the exponential scale height of these stars is near 240 pc. There is a marked contrast between the Mira population at about 1 kpc from the Galactic center where there are nearly as many long-period oxygen-rich Miras as intermediate-period oxygen-rich Miras. It is hypothesized that, at about 1 kpc from the Galactic center, the main sequence stars with masses larger than 1 solar mass have higher metallicities than main-sequence stars with the same masses in the solar neighborhood. In the solar neighborhood such main sequence stars become carbon-rich on the AGB and in the region near the Galactic center they become long-period oxygen-rich Miras.

Blue lobes in the Hydra A cluster central galaxy

NASA Technical Reports Server (NTRS)

Mcnamara, Brian R.

1995-01-01

We present new U- and I-band images of the centrally dominant galaxy in the Hydra A cluster, obtained with the 2.5 m Isaac Newton Telescope at La Palma. The galaxy is centered in a poor, X-ray-luminous cluster whose gaseous intracluster medium is apparently cooling at a rate of m-dot(sub CF) approximately 3000 solar masses/yr. The galaxy's structure is that of a normal giant elliptical galaxy, apart from the central approximately 8 x 6 arcsec (approximately 12 x 9 kpc) region which contains an unusually blue, lobelike structure that is spatially coincident with a luminous emission-line nebula in rotation about the nucleus. Based on near spatial coincidence of the central continuum structure and the emission-line nebula, we suggest that the blue continuum is due to a warm stellar population in a central disk. In order to isolate and study the structure of the disk, we have subtracted a smooth galactic background model from the U-band image. The disk's surface brightness profiles along its major and minor axes decline roughly exponentially with radius. The disk's axial ratio is consistent with a nearly edge-on thick disk or a thin disk that is inclined with respect to the line of sight. The bluest regions, located a few arcsec on either side of the nucleus (giving the lobelike appearance), may be due to locally enhanced star formation or a seeing-blurred ring of young stars embedded in the disk observed nearly edge-on. If star-formation is occurring with the local initial mass function, the central color, surface brightness, and dynamical mass would be consistent with models for star formation at a rate of less than and approximately 1 solar masses/yr which has persisted for the past approximately 10(exp 9) yr, a short burst (10(exp 7) yr) of star formation at a rate of approximately 30 solar masses/yr which occurred less than and approximately 10(exp 8) yr ago, or an instantaneous burst of star formation which occurred approximately 5 x 10(exp 7) yr ago. While the young population contributes approximately 30%-40% of the central U-band luminosity, its mass would be less than and approximately 1% to less than and approximately 10% (10(exp 8) solar masses - 2 x 10(exp 9) solar masses of the galaxy's central dynamical mass. We consider a number of possible origins for the disk material.

Tachyon search speeds up retrieval of similar sequences by several orders of magnitude

PubMed Central

Tan, Joshua; Kuchibhatla, Durga; Sirota, Fernanda L.; Sherman, Westley A.; Gattermayer, Tobias; Kwoh, Chia Yee; Eisenhaber, Frank; Schneider, Georg; Maurer-Stroh, Sebastian

2012-01-01

Summary: The usage of current sequence search tools becomes increasingly slower as databases of protein sequences continue to grow exponentially. Tachyon, a new algorithm that identifies closely related protein sequences ~200 times faster than standard BLAST, circumvents this limitation with a reduced database and oligopeptide matching heuristic. Availability and implementation: The tool is publicly accessible as a webserver at http://tachyon.bii.a-star.edu.sg and can also be accessed programmatically through SOAP. Contact: sebastianms@bii.a-star.edu.sg Supplementary information: Supplementary data are available at the Bioinformatics online. PMID:22531216

The hard X-ray spectrum of NGC 5506 as seen by NuSTAR

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matt, G.; Balokovi , M.; Marinucci, A.

2015-01-14

NuSTAR observed the bright Compton-thin, narrow-line Seyfert 1 galaxy, NGC 5506, for about 56 ks. In agreement with past observations, the spectrum is well fitted by a power law with Γ ~ 1.9, a distant reflection component and narrow ionized iron lines. A relativistically blurred reflection component is not required by the data. When an exponential high-energy cutoff is added to the power law, a value of 720more » $$+130\\atop{-190}$$ keV (90 percent confidence level) is found. Even allowing for systematic uncertainties, we find a 3σ lower limit to the high-energy cutoff of 350 keV, the highest lower limit to the cutoff energy found so far in an AGN by NuSTAR.« less

Determining Hβ Color Indices for 23 δ Scuti Variable Stars

NASA Astrophysics Data System (ADS)

Bush, Tabitha C.; Hintz, E. G.; Shreeve, D. K.; Jorgenson, K.

2010-01-01

Color index is a fundamental characteristic in the study of δ Scuti variable stars. The then comprehensive catalog of δ Scutis compiled by Rodriguez et al. (Rodriguez, E. Lopez Gonzalez, M. J., & Lopez de Coca, P. 2000, A&AS, 144, 469) contains 636 δ Scuti stars and several characteristics of these stars, including Hβ color index. Of the 417 stars in this catalog brighter than 13th magnitude, about 20% of them are missing Hβ color index values. We present 23 of these previously unpublished values, calculated from a calibration relation using spectroscopic observations obtained at the Dominion Astrophysical Observatory of 167 δ Scuti stars north of -01 degrees declination and brighter than 13th magnitude.

The LMC geometry and outer stellar populations from early DES data

DOE PAGES

Balbinot, Eduardo; Plazas, A.; Santiago, B. X.; ...

2015-03-20

The Dark Energy Camera has captured a large set of images as part of Science Verification (SV) for the Dark Energy Survey. The SV footprint covers a large portion of the outer Large Magellanic Cloud (LMC), providing photometry 1.5 magnitudes fainter than the main sequence turn-off of the oldest LMC stellar population. We derive geometrical and structural parameters for various stellar populations in the LMC disc. For the distribution of all LMC stars, we find an inclination of i = –38.14°±0.08° (near side in the North) and a position angle for the line of nodes of θ₀ = 129.51°±0.17°. Wemore » find that stars younger than ~4 Gyr are more centrally concentrated than older stars. Fitting a projected exponential disc shows that the scale radius of the old populations is R >4Gyr = 1.41 ± 0.01 kpc, while the younger population has R <4Gyr = 0.72 ± 0.01 kpc. However, the spatial distribution of the younger population deviates significantly from the projected exponential disc model. The distribution of old stars suggests a large truncation radius of R t = 13.5 ± 0.8 kpc. If this truncation is dominated by the tidal field of the Galaxy, we find that the LMC is ≃24 +9 –6 times less massive than the encircled Galactic mass. By measuring the Red Clump peak magnitude and comparing with the best-fit LMC disc model, we find that the LMC disc is warped and thicker in the outer regions north of the LMC centre. As a result, our findings may either be interpreted as a warped and flared disc in the LMC outskirts, or as evidence of a spheroidal halo component.« less

Cold Dust and its Heating Sources in M 33

NASA Astrophysics Data System (ADS)

Komugi, Shinya; Tosaki, Tomoka; Kohno, Kotaro; Tsukagoshi, Takashi; Tamura, Yoichi; Miura, Rie; Onodera, Sachiko; Kuno, Nario; Kawabe, Ryohei; Nakanishi, Koichiro; Sawada, Tsuyoshi; Ezawa, Hajime; Wilson, Grant W.; Yun, Min S.; Scott, Kimberly S.; Hughes, David H.; Aretxaga, Itziar; Perera, Thushara A.; Austermann, Jason E.; Tanaka, Kunihiko; Muraoka, Kazuyuki; Egusa, Fumi

2011-12-01

We have mapped the nearby face-on spiral galaxy M 33 in the 1.1 mm dust continuum using AzTEC on Atacama Submillimeter Telescope Experiment (ASTE). The preliminary results are presented here. The observed dust has a characteristic temperature of ~ 21 K in the central kpc, radially declining down to ~ 13 K at the edge of the star forming disk. We compare the dust temperatures with KS band flux and star formation tracers. Our results imply that cold dust heating may be driven by long-lived stars even nearby star forming regions.

Long-term decline of the mid-infrared emission of normal galaxies: dust echo of tidal disruption flare?

NASA Astrophysics Data System (ADS)

Wang, Tinggui; Yan, Lin; Dou, Liming; Jiang, Ning; Sheng, Zhenfeng; Yang, Chenwei

2018-07-01

We report the discovery of a sample of 19 low-redshift (z < 0.22) spectroscopically non-Seyfert galaxies that show slow declining mid-infrared (MIR) light curves (LCs), similar to those of tidal disruption event (TDE) candidates with extreme coronal lines. Two sources also showed relatively fast-rising MIR LCs. They consist of a 61 per cent sample of Wide-field Infrared Survey Explorer (WISE) MIR variable non-Seyfert galaxies with Sloan Digital Sky Survey (SDSS) spectra. In a comparison sample of optically selected Seyfert galaxies, the fraction of sources with such a LC is only 15 per cent. After rejecting five plausible obscured Seyfert galaxies with red MIR colours, the remaining 14 objects are studied in detail in this article. We fit the declining part of the LC with an exponential law and the decay time is typically one year. The observed peak MIR luminosities (νLν) after subtracting host galaxies are in the range of a few 1042-1044 erg s-1, with a median of 5 × 1043 erg s-1 in the W2 band. The black hole masses are distributed over a wide range, with more than half between 107 and 108 M⊙, but are significantly different from those of optical/UV selected TDEs. Furthermore, MIR luminosities are correlated with the black hole mass, stellar mass or luminosity of their host bulges. Most galaxies in the sample are red and luminous, with an absolute r magnitude between -20 and -23. We estimate the rate of event as about 10-4 galaxy-1 yr-1 among luminous red galaxies. We discuss several possibilities for variable infrared sources and conclude that most likely they are caused by short sporadic fuelling of supermassive black holes via either the instability of accretion flows or tidal disruption of stars.

Observations of southern emission-line stars

NASA Technical Reports Server (NTRS)

Henize, K. G.

1976-01-01

A catalog of 1929 stars showing H-alpha emission on photographic plates is presented which covers the entire southern sky south of declination -25 deg to a red limiting magnitude of about 11.0. The catalog provides previous designations of known emission-line stars equatorial (1900) and galactic coordinates, visual and photographic magnitudes, H-alpha emission parameters, spectral types, and notes on unusual spectral features. The objects listed include 16 M stars, 25 S stars, 37 carbon stars, 20 symbiotic stars, 40 confirmed or suspected T Tauri stars, 16 novae, 14 planetary nebulae, 11 P Cygni stars, 9 Bep stars, 87 confirmed or suspected Wolf-Rayet stars, and 26 'peculiar' stars. Two new T associations are discovered, one in Lupus and one in Chamaeleon. Objects with variations in continuum or H-alpha intensity are noted, and the distribution by spectral type is analyzed. It is found that the sky distribution of these emission-line stars shows significant concentrations in the region of the small Sagittarius cloud and in the Carina region.

False star detection and isolation during star tracking based on improved chi-square tests.

PubMed

Zhang, Hao; Niu, Yanxiong; Lu, Jiazhen; Yang, Yanqiang; Su, Guohua

2017-08-01

The star sensor is a precise attitude measurement device for a spacecraft. Star tracking is the main and key working mode for a star sensor. However, during star tracking, false stars become an inevitable interference for star sensor applications, which may result in declined measurement accuracy. A false star detection and isolation algorithm in star tracking based on improved chi-square tests is proposed in this paper. Two estimations are established based on a Kalman filter and a priori information, respectively. The false star detection is operated through adopting the global state chi-square test in a Kalman filter. The false star isolation is achieved using a local state chi-square test. Semi-physical experiments under different trajectories with various false stars are designed for verification. Experiment results show that various false stars can be detected and isolated from navigation stars during star tracking, and the attitude measurement accuracy is hardly influenced by false stars. The proposed algorithm is proved to have an excellent performance in terms of speed, stability, and robustness.

Regulation of Hemopoietic Stem Cell Turnover and Population Size in Neonatal Mice

DTIC Science & Technology

1975-04-01

Following birth the hematopoietic stem cell population of the liver as measured by the in vivo spleen nodule assay (CFU) declines with a halving time...of about 48 hours. The stem cell population of the spleen grows exponentially with a doubling time of about 17 hours. In vitro incubation with high...single spleen colonies derived from neonatal liver and spleen CFU that both stem cell populations have a high self-renewal capacity. Thus, the decline in

Concurrent change in dehydroepiandrosterone sulfate and functional performance in the oldest old: results from the Cardiovascular Health Study All Stars study.

PubMed

Sanders, J L; Cappola, A R; Arnold, A M; Boudreau, R M; Chaves, P H; Robbins, J; Cushman, M; Newman, A B

2010-09-01

The correlation between dehydroepiandrosterone sulfate (DHEAS) decline and age led to the hypothesis that DHEAS might be a marker of primary aging, though conflicting data from observational studies of mortality do not support this. We evaluated concurrent DHEAS and functional decline in a very old cohort to test if DHEAS change tracks with functional change during aging. DHEAS and functional performance (gait speed, grip strength, Modified Mini-Mental State Examination [3MSE] score, and digit symbol substitution test [DSST] score) were measured in 1996-1997 and 2005-2006 in 989 participants in the Cardiovascular Health Study All Stars study (mean age 85.2 years in 2005-2006, 63.5% women and 16.5% African American). We used multivariable linear regression to test the association of DHEAS decline with functional decline. After adjustment, each standard deviation decrease in DHEAS was associated with greater declines in gait speed (0.12 m/s, p = .01), grip strength (0.09 kg, p = .03), 3MSE score (0.13 points, p < .001), and DSST score (0.14 points, p = .001) in women only. Additional adjustment for baseline DHEAS attenuated the association with grip strength but did not alter other estimates appreciably, and baseline DHEAS was unassociated with functional decline. In this cohort of very old individuals, DHEAS decline tracked with declines in gait speed, 3MSE score, and DSST score, but not grip strength, in women independent of baseline DHEAS level. DHEAS decline might be a marker for age-associated performance decline, but its relevance is specific to women.

Unveiling the Role of Galactic Rotation on Star Formation

NASA Astrophysics Data System (ADS)

Utreras, José; Becerra, Fernando; Escala, Andrés

2016-12-01

We study the star formation process at galactic scales and the role of rotation through numerical simulations of spiral and starburst galaxies using the adaptive mesh refinement code Enzo. We focus on the study of three integrated star formation laws found in the literature: the Kennicutt-Schmidt (KS) and Silk-Elmegreen (SE) laws, and the dimensionally homogeneous equation proposed by Escala {{{Σ }}}{SFR}\\propto \\sqrt{G/L}{{{Σ }}}{gas}1.5. We show that using the last we take into account the effects of the integration along the line of sight and find a unique regime of star formation for both types of galaxies, suppressing the observed bi-modality of the KS law. We find that the efficiencies displayed by our simulations are anti-correlated with the angular velocity of the disk Ω for the three laws studied in this work. Finally, we show that the dimensionless efficiency of star formation is well represented by an exponentially decreasing function of -1.9{{Ω }}{t}{ff}{ini}, where {t}{ff}{ini} is the initial free-fall time. This leads to a unique galactic star formation relation which reduces the scatter of the bi-modal KS, SE, and Escala relations by 43%, 43%, and 35%, respectively.

UCAC3 Proper Motion Survey. I. Discovery of New Proper Motion Stars in UCAC3 With 0.40/yr mu 0.18/yr Between Declinations -90 deg and -47 deg

DTIC Science & Technology

2010-09-01

overlooked during previous SCR and other searches. The Two-Micron All Sky Survey ( 2MASS ) was used to probe for and reduce systematic errors in UCAC CCD...of 50–200 mas, when compared to 2MASS data. For a detailed description of the derived UCAC3 proper motions see Zacharias et al. (2010). An effort was...meeting the declination and proper motion survey limits, all stars (1) must be in the 2MASS catalog with an e2mpho ( 2MASS photometry error) less than

Critical Mutation Rate Has an Exponential Dependence on Population Size in Haploid and Diploid Populations

PubMed Central

Aston, Elizabeth; Channon, Alastair; Day, Charles; Knight, Christopher G.

2013-01-01

Understanding the effect of population size on the key parameters of evolution is particularly important for populations nearing extinction. There are evolutionary pressures to evolve sequences that are both fit and robust. At high mutation rates, individuals with greater mutational robustness can outcompete those with higher fitness. This is survival-of-the-flattest, and has been observed in digital organisms, theoretically, in simulated RNA evolution, and in RNA viruses. We introduce an algorithmic method capable of determining the relationship between population size, the critical mutation rate at which individuals with greater robustness to mutation are favoured over individuals with greater fitness, and the error threshold. Verification for this method is provided against analytical models for the error threshold. We show that the critical mutation rate for increasing haploid population sizes can be approximated by an exponential function, with much lower mutation rates tolerated by small populations. This is in contrast to previous studies which identified that critical mutation rate was independent of population size. The algorithm is extended to diploid populations in a system modelled on the biological process of meiosis. The results confirm that the relationship remains exponential, but show that both the critical mutation rate and error threshold are lower for diploids, rather than higher as might have been expected. Analyzing the transition from critical mutation rate to error threshold provides an improved definition of critical mutation rate. Natural populations with their numbers in decline can be expected to lose genetic material in line with the exponential model, accelerating and potentially irreversibly advancing their decline, and this could potentially affect extinction, recovery and population management strategy. The effect of population size is particularly strong in small populations with 100 individuals or less; the exponential model has significant potential in aiding population management to prevent local (and global) extinction events. PMID:24386200

Coherent e+e- production at very low transverse momentum at STAR

NASA Astrophysics Data System (ADS)

Yang, Chi

2018-02-01

We report the measurements of e+e- pair production at very low e+e- pair transverse momentum (pT < 0.15 GeV/c) in Au+Au collisions at = 200 GeV and U+U collisions at = 193 GeV using the STAR detector at the Relativistic Heavy Ion Collider. In 60-80% centrality, significant excesses are observed with respect to hadronic cocktails in both Au+Au and U+U collisions. These excess yields can not be explained by a theoretical model calculation incorporating in-medium broadened ρ spectral function. Additionally, the distribution for excess yield is shown and found to be exponential at very low pT.

Pulsar recoil by large-scale anisotropies in supernova explosions.

PubMed

Scheck, L; Plewa, T; Janka, H-Th; Kifonidis, K; Müller, E

2004-01-09

Assuming that the neutrino luminosity from the neutron star core is sufficiently high to drive supernova explosions by the neutrino-heating mechanism, we show that low-mode (l=1,2) convection can develop from random seed perturbations behind the shock. A slow onset of the explosion is crucial, requiring the core luminosity to vary slowly with time, in contrast to the burstlike exponential decay assumed in previous work. Gravitational and hydrodynamic forces by the globally asymmetric supernova ejecta were found to accelerate the remnant neutron star on a time scale of more than a second to velocities above 500 km s(-1), in agreement with observed pulsar proper motions.

Unveiling the nature of bright z ≃ 7 galaxies with the Hubble Space Telescope

NASA Astrophysics Data System (ADS)

Bowler, R. A. A.; Dunlop, J. S.; McLure, R. J.; McLeod, D. J.

2017-04-01

We present new Hubble Space Telescope/Wide Field Camera 3 (HST/WFC3) imaging of 25 extremely luminous (-23.2 ≤ MUV ≲ -21.2) Lyman-break galaxies (LBGs) at z ≃ 7. The sample was initially selected from 1.65 deg2 of ground-based imaging in the UltraVISTA/COSMOS and UDS/SXDS fields, and includes the extreme Lyman α emitters, 'Himiko' and 'CR7'. A deconfusion analysis of the deep Spitzer photometry available suggests that these galaxies exhibit strong rest-frame optical nebular emission lines (EW0(Hβ + [O III]) > 600 Å). We find that irregular, multiple-component morphologies suggestive of clumpy or merging systems are common (fmulti > 0.4) in bright z ≃ 7 galaxies, and ubiquitous at the very bright end (MUV < -22.5). The galaxies have half-light radii in the range r1/2 ˜ 0.5-3 kpc. The size measurements provide the first determination of the size-luminosity relation at z ≃ 7 that extends to MUV ˜ -23. We find the relation to be steep with r1/2 ∝ L1/2. Excluding clumpy, multicomponent galaxies however, we find a shallower relation that implies an increased star formation rate surface density in bright LBGs. Using the new, independent, HST/WFC3 data we confirm that the rest-frame UV luminosity function at z ≃ 7 favours a power-law decline at the bright end, compared to an exponential Schechter function drop-off. Finally, these results have important implications for the Euclid mission, which we predict will detect >1000 similarly bright galaxies at z ≃ 7. Our new HST imaging suggests that the vast majority of these galaxies will be spatially resolved by Euclid, mitigating concerns over dwarf star contamination.

RCSED—A Value-added Reference Catalog of Spectral Energy Distributions of 800,299 Galaxies in 11 Ultraviolet, Optical, and Near-infrared Bands: Morphologies, Colors, Ionized Gas, and Stellar Population Properties

NASA Astrophysics Data System (ADS)

Chilingarian, Igor V.; Zolotukhin, Ivan Yu.; Katkov, Ivan Yu.; Melchior, Anne-Laure; Rubtsov, Evgeniy V.; Grishin, Kirill A.

2017-02-01

We present RCSED, the value-added Reference Catalog of Spectral Energy Distributions of galaxies, which contains homogenized spectrophotometric data for 800,299 low- and intermediate-redshift galaxies (0.007< z< 0.6) selected from the Sloan Digital Sky Survey spectroscopic sample. Accessible from the Virtual Observatory (VO) and complemented with detailed information on galaxy properties obtained with state-of-the-art data analysis, RCSED enables direct studies of galaxy formation and evolution over the last 5 Gyr. We provide tabulated color transformations for galaxies of different morphologies and luminosities, and analytic expressions for the red sequence shape in different colors. RCSED comprises integrated k-corrected photometry in up to 11 ultraviolet, optical, and near-infrared bands published by the GALEX, SDSS, and UKIDSS wide-field imaging surveys; results of the stellar population fitting of SDSS spectra including best-fitting templates, velocity dispersions, parameterized star formation histories, and stellar metallicities computed for instantaneous starburst and exponentially declining star formation models; parametric and non-parametric emission line fluxes and profiles; and gas phase metallicities. We link RCSED to the Galaxy Zoo morphological classification and galaxy bulge+disk decomposition results of Simard et al. We construct the color-magnitude, Faber-Jackson, and mass-metallicity relations; compare them with the literature; and discuss systematic errors of the galaxy properties presented in our catalog. RCSED is accessible from the project web site and via VO simple spectrum access and table access services using VO-compliant applications. We describe several examples of SQL queries to the database. Finally, we briefly discuss existing and future scientific applications of RCSED and prospective catalog extensions to higher redshifts and different wavelengths. .

Tracking Planets around the Sun

ERIC Educational Resources Information Center

Riddle, Bob

2008-01-01

In earlier columns, the celestial coordinate system of hour circles of right ascension and degrees of declination was introduced along with the use of an equatorial star chart (see SFA Star Charts in Resources). This system shows the planets' motion relative to the ecliptic, the apparent path the Sun follows during the year. An alternate system,…

All-sky monitor observations of the decay of A0620-00 (Nova monocerotis 1975)

NASA Technical Reports Server (NTRS)

Kaluzienski, L. J.; Holt, S. S.; Boldt, E. A.; Serlemitsos, P. J.

1976-01-01

The All-Sky X-ray Monitor onboard Ariel 5 has observed the 3-6 keV decline of the bright transient X-ray source A0620-00 on a virtually continuous basis during the period September 1975 - March 1976. The source behavior on timescales 100 minutes is characterized by smooth, exponential decays interrupted by substantial increases in October and February. The latter increase was an order-of-magnitude rise above the extrapolated exponential fall-off, and was followed by a final rapid decline. Upper limits of 2.5% and 10% were found for any periodicities in the range 0d.2 - 10d during the early and later decay phases, respectively. A probable correlation between the optical and 3-6 keV emission from A0620-00 was noted, effectively ruling out models involving traditional optical novae in favor of Roche-lobe overflow in a binary system. The existing data on the transient X-ray sources is consistent with two distinct luminosity-lifetime classes of these objects.

Resistive tearing instability in electron MHD: application to neutron star crusts

NASA Astrophysics Data System (ADS)

Gourgouliatos, Konstantinos N.; Hollerbach, Rainer

2016-12-01

We study a resistive tearing instability developing in a system evolving through the combined effect of Hall drift in the electron magnetohydrodynamic limit and Ohmic dissipation. We explore first the exponential growth of the instability in the linear case and we find the fastest growing mode, the corresponding eigenvalues and dispersion relation. The instability growth rate scales as γ ∝ B2/3σ-1/3, where B is the magnetic field and σ the electrical conductivity. We confirm the development of the tearing resistive instability in the fully non-linear case, in a plane-parallel configuration where the magnetic field polarity reverses, through simulations of systems initiating in Hall equilibrium with some superimposed perturbation. Following a transient phase, during which there is some minor rearrangement of the magnetic field, the perturbation grows exponentially. Once the instability is fully developed, the magnetic field forms the characteristic islands and X-type reconnection points, where Ohmic decay is enhanced. We discuss the implications of this instability for the local magnetic field evolution in neutron stars' crusts, proposing that it can contribute to heating near the surface of the star, as suggested by models of magnetar post-burst cooling. In particular, we find that a current sheet a few metres thick, covering as little as 1 per cent of the total surface, can provide 1042 erg in thermal energy within a few days. We briefly discuss applications of this instability in other systems where the Hall effect operates such as protoplanetary discs and space plasmas.

Introducing galactic structure finder: the multiple stellar kinematic structures of a simulated Milky Way mass galaxy

NASA Astrophysics Data System (ADS)

Obreja, Aura; Macciò, Andrea V.; Moster, Benjamin; Dutton, Aaron A.; Buck, Tobias; Wang, Gregory S. Stinson Liang

2018-04-01

We present the first results of applying Gaussian Mixture Models in the stellar kinematic space of normalized angular momentum and binding energy on NIHAO high resolution galaxies to separate the stars into multiple components. We exemplify this method using a simulated Milky Way analogue, whose stellar component hosts: thin and thick discs, classical and pseudo bulges, and a stellar halo. The properties of these stellar structures are in good agreement with observational expectations in terms of sizes, shapes and rotational support. Interestingly, the two kinematic discs show surface mass density profiles more centrally concentrated than exponentials, while the bulges and the stellar halo are purely exponential. We trace back in time the Lagrangian mass of each component separately to study their formation history. Between z ˜ 3 and the end of halo virialization, z ˜ 1.3, all components lose a fraction of their angular momentum. The classical bulge loses the most (˜95%) and the thin disc the least (˜60%). Both bulges formed their stars in-situ at high redshift, while the thin disc formed ˜98% in-situ, but with a constant SFR ˜ 1.5M⊙yr-1 over the last ˜ 11 Gyr. Accreted stars (6% of total stellar mass) are mainly incorporated to the thick disc or the stellar halo, which formed ex-situ 8% and 45% of their respective masses. Our analysis pipeline is freely available at https://github.com/aobr/gsf.

Construction of Database for Pulsating Variable Stars

NASA Astrophysics Data System (ADS)

Chen, B. Q.; Yang, M.; Jiang, B. W.

2011-07-01

A database for the pulsating variable stars is constructed for Chinese astronomers to study the variable stars conveniently. The database includes about 230000 variable stars in the Galactic bulge, LMC and SMC observed by the MACHO (MAssive Compact Halo Objects) and OGLE (Optical Gravitational Lensing Experiment) projects at present. The software used for the construction is LAMP, i.e., Linux+Apache+MySQL+PHP. A web page is provided to search the photometric data and the light curve in the database through the right ascension and declination of the object. More data will be incorporated into the database.

How rapidly does the excess risk of lung cancer decline following quitting smoking? A quantitative review using the negative exponential model.

PubMed

Fry, John S; Lee, Peter N; Forey, Barbara A; Coombs, Katharine J

2013-10-01

The excess lung cancer risk from smoking declines with time quit, but the shape of the decline has never been precisely modelled, or meta-analyzed. From a database of studies of at least 100 cases, we extracted 106 blocks of RRs (from 85 studies) comparing current smokers, former smokers (by time quit) and never smokers. Corresponding pseudo-numbers of cases and controls (or at-risk) formed the data for fitting the negative exponential model. We estimated the half-life (H, time in years when the excess risk becomes half that for a continuing smoker) for each block, investigated model fit, and studied heterogeneity in H. We also conducted sensitivity analyses allowing for reverse causation, either ignoring short-term quitters (S1) or considering them smokers (S2). Model fit was poor ignoring reverse causation, but much improved for both sensitivity analyses. Estimates of H were similar for all three analyses. For the best-fitting analysis (S1), H was 9.93 (95% CI 9.31-10.60), but varied by sex (females 7.92, males 10.71), and age (<50years 6.98, 70+years 12.99). Given that reverse causation is taken account of, the model adequately describes the decline in excess risk. However, estimates of H may be biased by factors including misclassification of smoking status. Copyright © 2013 The Authors. Published by Elsevier Inc. All rights reserved.

Exponential fading to white of black holes in quantum gravity

NASA Astrophysics Data System (ADS)

Barceló, Carlos; Carballo-Rubio, Raúl; Garay, Luis J.

2017-05-01

Quantization of the gravitational field may allow the existence of a decay channel of black holes into white holes with an explicit time-reversal symmetry. The definition of a meaningful decay probability for this channel is studied in spherically symmetric situations. As a first nontrivial calculation, we present the functional integration over a set of geometries using a single-variable function to interpolate between black-hole and white-hole geometries in a bounded region of spacetime. This computation gives a finite result which depends only on the Schwarzschild mass and a parameter measuring the width of the interpolating region. The associated probability distribution displays an exponential decay law on the latter parameter, with a mean lifetime inversely proportional to the Schwarzschild mass. In physical terms this would imply that matter collapsing to a black hole from a finite radius bounces back elastically and instantaneously, with negligible time delay as measured by external observers. These results invite to reconsider the ultimate nature of astrophysical black holes, providing a possible mechanism for the formation of black stars instead of proper general relativistic black holes. The existence of both this decay channel and black stars can be tested in future observations of gravitational waves.

The National Network of Fusion Centers: Perception and Reality

DTIC Science & Technology

2014-12-01

growing exponentially to the post-recession era of austerity. As this pendulum moved from one side to the other, perceptions and attitudes about the...decline. The article provides insight into the advantages and drawbacks of the development of a national marketing strategy and highlights factors

Ingestion of Brachionus plicatilis under different microalgae conditions

NASA Astrophysics Data System (ADS)

Zhou, Wenli; Tang, Xuexi; Qiao, Xiuting; Wang, You; Wang, Renjun; Feng, Lei

2009-09-01

The effects of four microalgae, Chlorella vulgaris, Platymonas helgolandicavar, Isochrysis galbana, and Nitzschia closterium on the grazing and filtering rates of the marine rotifer, Brachionus plicatilis, were evaluated under laboratory conditions. The grazing rates in separate cultures of the four microalga were as follows: C. vulgaris > P. helgolandicavar > I. galbana > N. closterium. However, the filtering rates occurred in the following order: P. helgolandicavar > N. closterium > C. vulgaris > I. galbana. A mixed diets experiment revealed that P. helgolandicavar was the preferred diet of B. plicatilis. In addition, the grazing rate of B. plicatilis increased gradually as the density of the microalgae increased, until concentrations of 2.5×106 cells mL-1 for C. vulgaris and 1.5×106 cells mL-1 for I. galbana were obtained. Furthermore, the filtering rate increased slightly when the density of the microalgae was low, after which it declined as the microalgal density increased. The grazing rates of B. plicatilis were as follows during the different growth phases: stationary phase > exponential phase > lag phase > decline phase. Additionally, the filtering rates during the growth phases were: exponential phase > lag phase > stationary phase > decline phase. The results of this study provide foundational information that can be used to explore the optimal culture conditions for rotifers and to promote the development of aquaculture.

Large decline in injecting drug use in Amsterdam, 1986-1998: explanatory mechanisms and determinants of injecting transitions.

PubMed

van Ameijden, E J; Coutinho, R A

2001-05-01

To study community wide trends in injecting prevalence and trends in injecting transitions, and determinants. Open cohort study with follow up every four months (Amsterdam Cohort Study). Generalised estimating equations were used for statistical analysis. Amsterdam has adopted a harm reduction approach as drug policy. 996 drug users who were recruited from 1986 to 1998, mainly at methadone programmes, who paid 13620 cohort visits. The prevalence of injecting decreased exponentially (66% to 36% in four to six monthly periods). Selective mortality and migration could maximally explain 33% of this decline. Instead, injecting initiation linearly decreased (4.1% to 0.7% per visit), cessation exponentially increased (10.0% to 17.1%), and relapse linearly decreased (21.3% to 11.8%). Non-injecting cocaine use (mainly pre-cooked, comparable to crack) and heroin use strongly increased. Trends were not attributable to changes in the study sample. Harm reduction, including large scale needle exchange programmes, does not lead to an increase in injecting drug use. The injecting decline seems mainly attributable to ecological factors (for example, drug culture and market). Prevention of injecting is possible and peer-based interventions may be effective. The consequences of the recent upsurge in crack use requires further study.

Construction of the Database for Pulsating Variable Stars

NASA Astrophysics Data System (ADS)

Chen, Bing-Qiu; Yang, Ming; Jiang, Bi-Wei

2012-01-01

A database for pulsating variable stars is constructed to favor the study of variable stars in China. The database includes about 230,000 variable stars in the Galactic bulge, LMC and SMC observed in an about 10 yr period by the MACHO(MAssive Compact Halo Objects) and OGLE(Optical Gravitational Lensing Experiment) projects. The software used for the construction is LAMP, i.e., Linux+Apache+MySQL+PHP. A web page is provided for searching the photometric data and light curves in the database through the right ascension and declination of an object. Because of the flexibility of this database, more up-to-date data of variable stars can be incorporated into the database conveniently.

Angular momentum transfer in primordial discs and the rotation of the first stars

NASA Astrophysics Data System (ADS)

Hirano, Shingo; Bromm, Volker

2018-05-01

We investigate the rotation velocity of the first stars by modelling the angular momentum transfer in the primordial accretion disc. Assessing the impact of magnetic braking, we consider the transition in angular momentum transport mode at the Alfvén radius, from the dynamically dominated free-fall accretion to the magnetically dominated solid-body one. The accreting protostar at the centre of the primordial star-forming cloud rotates with close to breakup speed in the case without magnetic fields. Considering a physically motivated model for small-scale turbulent dynamo amplification, we find that stellar rotation speed quickly declines if a large fraction of the initial turbulent energy is converted to magnetic energy (≳ 0.14). Alternatively, if the dynamo process were inefficient, for amplification due to flux freezing, stars would become slow rotators if the pre-galactic magnetic field strength is above a critical value, ≃10-8.2 G, evaluated at a scale of nH = 1 cm-3, which is significantly higher than plausible cosmological seed values (˜10-15 G). Because of the rapid decline of the stellar rotational speed over a narrow range in model parameters, the first stars encounter a bimodal fate: rapid rotation at almost the breakup level, or the near absence of any rotation.

An excess of massive stars in the local 30 Doradus starburst

NASA Astrophysics Data System (ADS)

Schneider, F. R. N.; Sana, H.; Evans, C. J.; Bestenlehner, J. M.; Castro, N.; Fossati, L.; Gräfener, G.; Langer, N.; Ramírez-Agudelo, O. H.; Sabín-Sanjulián, C.; Simón-Díaz, S.; Tramper, F.; Crowther, P. A.; de Koter, A.; de Mink, S. E.; Dufton, P. L.; Garcia, M.; Gieles, M.; Hénault-Brunet, V.; Herrero, A.; Izzard, R. G.; Kalari, V.; Lennon, D. J.; Maíz Apellániz, J.; Markova, N.; Najarro, F.; Podsiadlowski, Ph.; Puls, J.; Taylor, W. D.; van Loon, J. Th.; Vink, J. S.; Norman, C.

2018-01-01

The 30 Doradus star-forming region in the Large Magellanic Cloud is a nearby analog of large star-formation events in the distant universe. We determined the recent formation history and the initial mass function (IMF) of massive stars in 30 Doradus on the basis of spectroscopic observations of 247 stars more massive than 15 solar masses (M☉). The main episode of massive star formation began about 8 million years (My) ago, and the star-formation rate seems to have declined in the last 1 My. The IMF is densely sampled up to 200 M☉ and contains 32 ± 12% more stars above 30 M☉ than predicted by a standard Salpeter IMF. In the mass range of 15 to 200 M☉, the IMF power-law exponent is 1.90‑0.26+0.37, shallower than the Salpeter value of 2.35.

An excess of massive stars in the local 30 Doradus starburst.

PubMed

Schneider, F R N; Sana, H; Evans, C J; Bestenlehner, J M; Castro, N; Fossati, L; Gräfener, G; Langer, N; Ramírez-Agudelo, O H; Sabín-Sanjulián, C; Simón-Díaz, S; Tramper, F; Crowther, P A; de Koter, A; de Mink, S E; Dufton, P L; Garcia, M; Gieles, M; Hénault-Brunet, V; Herrero, A; Izzard, R G; Kalari, V; Lennon, D J; Maíz Apellániz, J; Markova, N; Najarro, F; Podsiadlowski, Ph; Puls, J; Taylor, W D; van Loon, J Th; Vink, J S; Norman, C

2018-01-05

The 30 Doradus star-forming region in the Large Magellanic Cloud is a nearby analog of large star-formation events in the distant universe. We determined the recent formation history and the initial mass function (IMF) of massive stars in 30 Doradus on the basis of spectroscopic observations of 247 stars more massive than 15 solar masses ([Formula: see text]). The main episode of massive star formation began about 8 million years (My) ago, and the star-formation rate seems to have declined in the last 1 My. The IMF is densely sampled up to 200 [Formula: see text] and contains 32 ± 12% more stars above 30 [Formula: see text] than predicted by a standard Salpeter IMF. In the mass range of 15 to 200 [Formula: see text], the IMF power-law exponent is [Formula: see text], shallower than the Salpeter value of 2.35. Copyright © 2018, American Association for the Advancement of Science.

What are the Progenitors of Compace, Massive, Quiescent Galaxies at z (equals) 2.3? The Population of Massive Galaxies at z (greater than) 3 From NMBS AND CANDELS

NASA Technical Reports Server (NTRS)

Stefanon, Mauro; Marchesini, Danilo; Rudnick, Gregory H.; Brammer, Gabriel B.; Tease, Katherine Whitaker

2013-01-01

Using public data from the NEWFIRM Medium-Band Survey (NMBS) and the Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey (CANDELS), we investigate the population of massive galaxies at z > 3. The main aim of this work is to identify the potential progenitors of z 2 compact, massive, quiescent galaxies (CMQGs), furthering our understanding of the onset and evolution of massive galaxies. Our work is enabled by high-resolution images from CANDELS data and accurate photometric redshifts, stellar masses, and star formation rates (SFRs) from 37-band NMBS photometry. The total number of massive galaxies at z > 3 is consistent with the number of massive, quiescent galaxies (MQGs) at z 2, implying that the SFRs for all of these galaxies must be much lower by z 2. We discover four CMQGs at z > 3, pushing back the time for which such galaxies have been observed. However, the volume density for these galaxies is significantly less than that of galaxies at z < 2 with similar masses, SFRs, and sizes, implying that additional CMQGs must be created in the intervening 1 Gyr between z = 3 and z = 2. We find five star-forming galaxies at z 3 that are compact (Re < 1.4 kpc) and have stellar mass M* > 1010.6M; these galaxies are likely to become members of the massive, quiescent, compact galaxy population at z 2. We evolve the stellar masses and SFRs of each individual z > 3 galaxy adopting five different star formation histories (SFHs) and studying the resulting population of massive galaxies at z = 2.3. We find that declining or truncated SFHs are necessary to match the observed number density of MQGs at z 2, whereas a constant delayed-exponential SFH would result in a number density significantly smaller than observed. All of our assumed SFHs imply number densities of CMQGs at z 2 that are consistent with the observed number density. Better agreement with the observed number density of CMQGs at z 2 is obtained if merging is included in the analysis and better still if star formation quenching is assumed to shortly follow the merging event, as implied by recent models of the formation of MQGs.

Demonstrating Diversity in Star-formation Histories with the CSI Survey

NASA Astrophysics Data System (ADS)

Dressler, Alan; Kelson, Daniel D.; Abramson, Louis E.; Gladders, Michael D.; Oemler, Augustus, Jr.; Poggianti, Bianca M.; Mulchaey, John S.; Vulcani, Benedetta; Shectman, Stephen A.; Williams, Rik J.; McCarthy, Patrick J.

2016-12-01

We present coarse but robust star-formation histories (SFHs) derived from spectrophotometric data of the Carnegie-Spitzer-IMACS Survey, for 22,494 galaxies at 0.3\\lt z\\lt 0.9 with stellar masses of 109 M ⊙ to 1012 M ⊙. Our study moves beyond “average” SFHs and distribution functions of specific star-formation rates (sSFRs) to individually measured SFHs for tens of thousands of galaxies. By comparing star-formation rates (SFRs) with timescales of {10}10,{10}9, and 108 years, we find a wide diversity of SFHs: “old galaxies” that formed most or all of their stars early, galaxies that formed stars with declining or constant SFRs over a Hubble time, and genuinely “young galaxies” that formed most of their stars since z = 1. This sequence is one of decreasing stellar mass, but remarkably, each type is found over a mass range of a factor of 10. Conversely, galaxies at any given mass follow a wide range of SFHs, leading us to conclude that (1) halo mass does not uniquely determine SFHs, (2) there is no “typical” evolutionary track, and (3) “abundance matching” has limitations as a tool for inferring physics. Our observations imply that SFHs are set at an early epoch, and that—for most galaxies—the decline and cessation of star formation occurs over a Hubble time, without distinct “quenching” events. SFH diversity is inconsistent with models where galaxy mass, at any given epoch, grows simply along relations between SFR and stellar mass, but is consistent with a two-parameter lognormal form, lending credence to this model from a new and independent perspective. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

Teaching with Laptops

ERIC Educational Resources Information Center

Zucker, Andrew A.; King, Karen E.

2009-01-01

The declining cost of computers and wireless networks has made laptop programs more affordable than ever. At the same time, the internet resources available to teachers and students have grown exponentially in the 15 years since web browsers first became practical. As a result of these trends, growing numbers of students nationwide are provided…

Building a Champagne Network on a Beer Budget

ERIC Educational Resources Information Center

Dolan, Jon; Pederson, Curt

2004-01-01

Oregon State University's demand for bandwidth to support scientific collaboration and research continues to grow exponentially, while state funding declines due to hard economic times. The challenge faced by these authors was to find creative yet fiscally responsible ways to meet OSU's bandwidth demands. Looking at their options for high-capacity…

Global diversity and geography of soil fungi

Treesearch

Leho Tedersoo; Mohammad Bahram; Sergei Põlme; Urmas Kõljalg; Nourou S. Yorou; Ravi Wijesundera; Luis Villarreal Ruiz; Aida M. Vasco-Palacios; Pham Quang Thu; Ave Suija; Matthew E. Smith; Cathy Sharp; Erki Saluveer; Alessandro Saitta; Miguel Rosas; Taavi Riit; David Ratkowsky; Karin Pritsch; Kadri Põldmaa; Meike Piepenbring; Cherdchai Phosri; Marko Peterson; Kaarin Parts; Kadri Pärtel; Eveli Otsing; Eduardo Nouhra; André L. Njouonkou; R. Henrik Nilsson; Luis N. Morgado; Jordan Mayor; Tom W. May; Luiza Majukim; D. Jean Lodge; Su See Lee; Karl-Henrik Larsson; Petr Kohout; Kentaro Hosaka; Indrek Hiiesalu; Terry W. Henkel; Helery Harend; Liang-dong Guo; Alina Greslebin; Gwen Gretlet; Jozsef Geml; Genevieve Gates; William Dunstan; Chris Dunk; Rein Drenkhan; John Dearnaley; André De Kesel; Tan Dang; Xin Chen; Franz Buegger; Francis Q. Brearley; Gregory Bonito; Sten Anslan; Sandra Abell; Kessy Abarenkov

2014-01-01

Fungi play major roles in ecosystem processes, but the determinants of fungal diversity and biogeographic patterns remain poorly understood. Using DNA metabarcoding data from hundreds of globally distributed soil samples,we demonstrate that fungal richness is decoupled from plant diversity.The plant-to-fungus richness ratio declines exponentially toward the poles....

LFsGRB: Binary neutron star merger rate via the luminosity function of short gamma-ray bursts

NASA Astrophysics Data System (ADS)

Paul, Debdutta

2018-04-01

LFsGRB models the luminosity function (LF) of short Gamma Ray Bursts (sGRBs) by using the available catalog data of all short GRBs (sGRBs) detected till 2017 October, estimating the luminosities via pseudo-redshifts obtained from the Yonetoku correlation, and then assuming a standard delay distribution between the cosmic star formation rate and the production rate of their progenitors. The data are fit well both by exponential cutoff powerlaw and broken powerlaw models. Using the derived parameters of these models along with conservative values in the jet opening angles seen from afterglow observations, the true rate of short GRBs is derived. Assuming a short GRB is produced from each binary neutron star merger (BNSM), the rate of gravitational wave (GW) detections from these mergers are derived for the past, present and future configurations of the GW detector networks.

The realistic models of relativistic stars in f (R) = R + αR 2 gravity

NASA Astrophysics Data System (ADS)

Astashenok, Artyom V.; Odintsov, Sergei D.; de la Cruz-Dombriz, Álvaro

2017-10-01

In the context of f(R)=R+α R2 gravity, we study the existence of neutron and quark stars for various α with no intermediate approximation in the system of equations. Analysis shows that for positive α the scalar curvature does not drop to zero at the star surface (as in general relativity) but exponentially decreases with distance. Also the stellar mass bounded by star surface decreases when the value α increases. Nonetheless distant observers would observe a gravitational mass due to appearance of a so-called gravitational sphere around the star. The non-zero curvature contribution to the gravitational mass eventually is shown to compensate the stellar mass decrease for growing α’s. We perform our analysis for several equations of state including purely hadronic configurations as well as hyperons and quark stars. In all cases, we assess that the relation between the parameter α and the gravitational mass weakly depends upon the chosen equation of state. Another interesting feature is the increase of the star radius in comparison with general relativity for stars with masses close to maximal, whereas for intermediate masses 1.4 -1.6 M_⊙ the radius of star depends upon α very weakly. Also the decrease in the mass bounded by star surface may cause the surface redshift to decrease in R 2-gravity when compared to Einsteinian predictions. This effect is shown to hardly depend upon the observed gravitational mass. Finally, for negative values of α our analysis shows that outside the star the scalar curvature has damped oscillations but the contribution of the gravitational sphere into the gravitational mass increases indefinitely with radial distance putting into question the very existence of such relativistic stars.

Flow of 3D Eyring-Powell fluid by utilizing Cattaneo-Christov heat flux model and chemical processes over an exponentially stretching surface

NASA Astrophysics Data System (ADS)

Hayat, Tanzila; Nadeem, S.

2018-03-01

This paper examines the three dimensional Eyring-Powell fluid flow over an exponentially stretching surface with heterogeneous-homogeneous chemical reactions. A new model of heat flux suggested by Cattaneo and Christov is employed to study the properties of relaxation time. From the present analysis we observe that there is an inverse relationship between temperature and thermal relaxation time. The temperature in Cattaneo-Christov heat flux model is lesser than the classical Fourier's model. In this paper the three dimensional Cattaneo-Christov heat flux model over an exponentially stretching surface is calculated first time in the literature. For negative values of temperature exponent, temperature profile firstly intensifies to its most extreme esteem and after that gradually declines to zero, which shows the occurrence of phenomenon (SGH) "Sparrow-Gregg hill". Also, for higher values of strength of reaction parameters, the concentration profile decreases.

Rossby wave instability in astrophysical discs

NASA Astrophysics Data System (ADS)

Lovelace, R. V. E.; Romanova, M. M.

2014-08-01

A brief review is given of the Rossby wave instability in astrophysical discs. In non-self-gravitating discs, around for example a newly forming stars, the instability can be triggered by an axisymmetric bump at some radius r0 in the disc surface mass-density. It gives rise to exponentially growing non-axisymmetric perturbation (\\propto \\exp \\,({ { i}}m\\phi ) , m = 1,2,…) in the vicinity of r0 consisting of anticyclonic vortices. These vortices are regions of high pressure and consequently act to trap dust particles which in turn can facilitate planetesimal growth in proto-planetary discs. The Rossby vortices in the discs around stars and black holes may cause the observed quasi-periodic modulations of the disc's thermal emission.

A MOLECULAR STAR FORMATION LAW IN THE ATOMIC-GAS-DOMINATED REGIME IN NEARBY GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schruba, Andreas; Walter, Fabian; Dumas, Gaelle

2011-08-15

We use the IRAM HERACLES survey to study CO emission from 33 nearby spiral galaxies down to very low intensities. Using 21 cm line atomic hydrogen (H I) data, mostly from THINGS, we predict the local mean CO velocity based on the mean H I velocity. By re-normalizing the CO velocity axis so that zero corresponds to the local mean H I velocity we are able to stack spectra coherently over large regions. This enables us to measure CO intensities with high significance as low as I{sub CO} {approx} 0.3 K km s{sup -1} ({Sigma}{sub H{sub 2}}{approx}1 M{sub sun} pc{supmore » -2}), an improvement of about one order of magnitude over previous studies. We detect CO out to galactocentric radii r{sub gal} {approx} r{sub 25} and find the CO radial profile to follow a remarkably uniform exponential decline with a scale length of {approx}0.2 r{sub 25}. Here we focus on stacking as a function of radius, comparing our sensitive CO profiles to matched profiles of H I, H{alpha}, far-UV (FUV), and Infrared (IR) emission at 24 {mu}m and 70 {mu}m. We observe a tight, roughly linear relationship between CO and IR intensity that does not show any notable break between regions that are dominated by molecular gas ({Sigma}{sub H{sub 2}}>{Sigma}{sub H{sub i}}) and those dominated by atomic gas ({Sigma}{sub H{sub 2}}<{Sigma}{sub H{sub i}}). We use combinations of FUV+24 {mu}m and H{alpha}+24 {mu}m to estimate the recent star formation rate (SFR) surface density, {Sigma}{sub SFR}, and find approximately linear relations between {Sigma}{sub SFR} and {Sigma}{sub H{sub 2}}. We interpret this as evidence of stars forming in molecular gas with little dependence on the local total gas surface density. While galaxies display small internal variations in the SFR-to-H{sub 2} ratio, we do observe systematic galaxy-to-galaxy variations. These galaxy-to-galaxy variations dominate the scatter in relationships between CO and SFR tracers measured at large scales. The variations have the sense that less massive galaxies exhibit larger ratios of SFR-to-CO than massive galaxies. Unlike the SFR-to-CO ratio, the balance between atomic and molecular gas depends strongly on the total gas surface density and galactocentric radius. It must also depend on additional parameters. Our results reinforce and extend to lower surface densities, a picture in which star formation in galaxies can be separated into two processes: the assembly of star-forming molecular clouds and the formation of stars from H{sub 2}. The interplay between these processes yields a total gas-SFR relation with a changing slope, which has previously been observed and identified as a star formation threshold.« less

An Accretion Model for Anomalous X-Ray Pulsars

NASA Astrophysics Data System (ADS)

Chatterjee, Pinaki; Hernquist, Lars; Narayan, Ramesh

2000-05-01

We present a model for the anomalous X-ray pulsars (AXPs) in which the emission is powered by accretion from a fossil disk, established from matter falling back onto the neutron star following its birth. The time-dependent accretion drives the neutron star toward a ``tracking'' solution in which the rotation period of the star increases slowly, in tandem with the declining accretion rate. For appropriate choices of disk mass, neutron star magnetic field strength, and initial spin period, we demonstrate that a rapidly rotating neutron star can be spun down to periods characteristic of AXPs on timescales comparable to the estimated ages of these sources. In other cases, accretion onto the neutron star switches off after a short time and the star becomes an ordinary radio pulsar. Thus, in our picture, radio pulsars and AXPs are drawn from the same underlying population, in contrast to the situation in models involving neutron stars with ultrastrong magnetic fields, which require a new population of stars with very different properties.

The Radial Distribution of Star Formation in Galaxies at z1 From The 3D-HST Survey

NASA Technical Reports Server (NTRS)

Nelson, Erica June; Dokkum, Pieter G. Van; Momcheva, Ivelina; Brammer, Gabriel; Lundgren, Britt; Skelton, Rosalind E.; Tease, Katherine Whitaker; Cunha, Elisabete Da; Schreiber, Natascha Forster; Franx, Marijn;

Our Sun V: A Bright Young Sun Consistent with Helioseismology and Warm Temperatures on Ancient Earth and Mars

NASA Technical Reports Server (NTRS)

Sackmann, I.-Juliana; Boothroyd, Arnold I.

2001-01-01

The relatively warm temperatures required on early Earth and Mars have been difficult to account for with warming from greenhouse gases. A slightly more massive young Sun would be brighter than predicted by the standard solar model, simultaneously resolving this problem for both Earth and Mars. We computed high-precision solar models with seven initial masses, from Mi = 1.01 to 1.07 solar mass - the latter being the maximum permitted if the early Earth is not to lose its water via a moist greenhouse effect. The relatively modest early mass loss that is required remains consistent with observational limits on mass loss from young stars and with estimates of the past solar wind obtained from lunar rocks. We considered three types of mass loss rates: (1) a reasonable choice of a simple exponential decline, (2) an extreme step-function case that gives the maximum effect consistent with observations, and (3) the radical case of a linear decline which is inconsistent with the solar wind mass loss estimates from lunar rocks. Our computations demonstrated that mass loss leaves a fingerprint oil the Sun's internal structure large enough to be detectable with helioseismic observations. All of our mass-losing solar models were consistent with the helioseismic observations; in fact, our preferred mass-losing cases were in marginally better agreement with the helioseismology than the standard solar model was, although this difference was smaller than the effects of other uncertainties in the input physics and in the solar composition. Mass loss has only a relatively minor effect on the predicted lithium depletion; the major portion of the solar lithium depletion must still be due to rotational mixing. Thus the modest mass loss cases considered here cannot be ruled out by observed lithium depletions. For the three mass loss types considered, the preferred initial masses were 1.07 solar mass for the exponential case and 1.04 solar mass for the step-function and linear cases; all of these provided high enough solar fluxes at Mars 3.8 Gyr ago to be consistent with the existence of liquid water. For a more massive early Sun, the planets would have had to be closer to the young Sun in order to end up in their present orbits; the orbital radii of the planets would vary inversely with the solar mass. Both of these effects contribute to the fact that the early solar flux at the planets would have been considerably higher than that of the standard solar model at that time. In fact, the 1.07 solar mass exponential case has a flux at birth 5% higher than the present solar flux, while the radical 1.04 solar mass linear case has a nearly constant flux over the first 3 Gyr only about 10% lower than at present. The early solar evolution would be in the opposite direction in the H-R diagram to that of the standard Sun.

The Radial Distribution of Star Formation in Galaxies at z ~ 1 from the 3D-HST Survey

NASA Astrophysics Data System (ADS)

Nelson, Erica June; van Dokkum, Pieter G.; Momcheva, Ivelina; Brammer, Gabriel; Lundgren, Britt; Skelton, Rosalind E.; Whitaker, Katherine E.; Da Cunha, Elisabete; Förster Schreiber, Natascha; Franx, Marijn; Fumagalli, Mattia; Kriek, Mariska; Labbe, Ivo; Leja, Joel; Patel, Shannon; Rix, Hans-Walter; Schmidt, Kasper B.; van der Wel, Arjen; Wuyts, Stijn

2013-01-01

The assembly of galaxies can be described by the distribution of their star formation as a function of cosmic time. Thanks to the WFC3 grism on the Hubble Space Telescope (HST) it is now possible to measure this beyond the local Universe. Here we present the spatial distribution of Hα emission for a sample of 54 strongly star-forming galaxies at z ~ 1 in the 3D-HST Treasury survey. By stacking the Hα emission, we find that star formation occurred in approximately exponential distributions at z ~ 1, with a median Sérsic index of n = 1.0 ± 0.2. The stacks are elongated with median axis ratios of b/a = 0.58 ± 0.09 in Hα consistent with (possibly thick) disks at random orientation angles. Keck spectra obtained for a subset of eight of the galaxies show clear evidence for rotation, with inclination corrected velocities of 90-330 km s-1. The most straightforward interpretation of our results is that star formation in strongly star-forming galaxies at z ~ 1 generally occurred in disks. The disks appear to be "scaled-up" versions of nearby spiral galaxies: they have EW(Hα) ~ 100 Å out to the solar orbit and they have star formation surface densities above the threshold for driving galactic scale winds.

The Radial Distribution of Star Formation in Galaxies at Z approximately 1 from the 3D-HST Survey

NASA Technical Reports Server (NTRS)

Nelson, Erica June; vanDokkum, Pieter G.; Momcheva, Ivelina; Brammer, Gabriel; Lundgren, Britt; Skelton, Rosalind E.; Whitaker, Katherine E.; DaCunha, Elisabete; Schreiber, Natascha Foerster; Franx, Marijn;

THE ARIZONA RADIO OBSERVATORY CO MAPPING SURVEY OF GALACTIC MOLECULAR CLOUDS. V. THE SH2-235 CLOUD IN CO J  = 2 − 1, {sup 13}CO J  = 2 − 1, AND CO J  = 3 − 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bieging, John H.; Peters, William L.; Patel, Saahil

We present the results of a program to map the Sh2-235 molecular cloud complex in the CO and {sup 13}CO  J  = 2 − 1 transitions using the Heinrich Hertz Submillimeter Telescope. The map resolution is 38″ (FWHM), with an rms noise of 0.12 K brightness temperature, for a velocity resolution of 0.34 km s{sup −1}. With the same telescope, we also mapped the CO J  = 3 − 2 line at a frequency of 345 GHz, using a 64 beam focal plane array of heterodyne mixers, achieving a typical rms noise of 0.5 K brightness temperature with a velocity resolution of 0.23 km s{sup −1}.more » The three spectral line data cubes are available for download. Much of the cloud appears to be slightly sub-thermally excited in the J  = 3 level, except for in the vicinity of the warmest and highest column density areas, which are currently forming stars. Using the CO and {sup 13}CO  J  = 2 − 1 lines, we employ an LTE model to derive the gas column density over the entire mapped region. Examining a 125 pc{sup 2} region centered on the most active star formation in the vicinity of Sh2-235, we find that the young stellar object surface density scales as approximately the 1.6-power of the gas column density. The area distribution function of the gas is a steeply declining exponential function of gas column density. Comparison of the morphology of ionized and molecular gas suggests that the cloud is being substantially disrupted by expansion of the H ii regions, which may be triggering current star formation.« less

Introducing galactic structure finder: the multiple stellar kinematic structures of a simulated Milky Way mass galaxy

NASA Astrophysics Data System (ADS)

Obreja, Aura; Macciò, Andrea V.; Moster, Benjamin; Dutton, Aaron A.; Buck, Tobias; Stinson, Gregory S.; Wang, Liang

2018-07-01

We present the first results of applying Gaussian Mixture Models in the stellar kinematic space of normalized angular momentum and binding energy on NIHAO high-resolution galaxies to separate the stars into multiple components. We exemplify this method, using a simulated Milky Way analogue, whose stellar component hosts thin and thick discs, classical and pseudo bulges, and a stellar halo. The properties of these stellar structures are in good agreement with observational expectations in terms of sizes, shapes, and rotational support. Interestingly, the two kinematic discs show surface mass density profiles more centrally concentrated than exponentials, while the bulges and the stellar halo are purely exponential. We trace back in time the Lagrangian mass of each component separately to study their formation history. Between z ˜ 3 and the end of halo virialization, z ˜ 1.3, all components lose a fraction of their angular momentum. The classical bulge loses the most (˜ 95 per cent) and the thin disc the least (˜ 60 per cent). Both bulges formed their stars in situ at high redshift, while the thin disc formed ˜ 98 per cent in situ, but with a constant SFR ˜ 1.5 M⊙ yr-1 over the last ˜11 Gyr. Accreted stars (6 per cent of total stellar mass) are mainly incorporated to the thick disc or the stellar halo, which formed ex situ 8 per cent and 45 per cent of their respective masses. Our analysis pipeline is freely available at https://github.com/aobr/gsf.

VizieR Online Data Catalog: Uranometria Argentina catalog of bright southern stars (Gould, 1879)

NASA Astrophysics Data System (ADS)

Gould, B. G.

2010-07-01

In 1879 Benjamin Apthorp Gould published in Buenos Aires, Argentina, the Uranometria Argentina catalog of 7756 stars south of declination +10 degrees. This included all those stars he considered magnitude 7 or brighter and some fainter stars which are close companions to brighter stars or to each other and have combined magnitude 7 or brighter. Star positions are in 1875 coordinates, and constellation boundaries also in 1875 coordinates were defined within the aforementioned declination range. With only a few small changes these were incorporated into the boundaries adopted by the IAU in 1930 and subsequently universally accepted. In terms of accurate photoelectric magnitude measurements the Uranometria Argentina is nearly complete to magnitude 6.5 in its declination range. In each constellation the individual stars considered to be magnitude 7 and brighter were numbered in sequence of increasing right ascension in 1875 coordinates, except that in a few cases this sequence was somewhat adjusted so that stars close together could be listed on adjacent lines of text. The numbering system is analogous to that in the Flamsteed Catalogus Brittanicus and now widely used. Star numbers from the Uranometria Argentina rarely appear in the 21st century despite the potential utility of their use. They were included in the American Ephemeris and Nautical Almanac until 1978, and in the FK5 catalog until 1999, always with the letter G following the number in the Uranometria Argentina catalog. This serves to distinguish Flamsteed numbers with no following letters from Gould numbers, and is utilized in this presentation and recommended for general use. The file catalog.dat includes every star in the original Uranometria Argentina. In the original the constellations were presented in sequence of increasing distance from the south pole and numbered accordingly. For the convenience of 21st century astronomers the constellations are presented here by alphabetical sequence in constellation name and the stars in each constellation in the same sequence as in the original. A separate file notes.txt includes a large number of notes for individual stars and for groups of stars recognized in the original catalog as belonging together. Each note is referenced by an asterisk * in the file catalog.dat. Columns 43-63 provide J2000 coordinates and cross identifications from the Flamsteed, HD, and SAO catalogs for the stars and have been added by the author of this data set. Columns 82-154 have been copied verbatim from the Uranometria Argentina catalogue, except that where asterisks are shown errors in the original printed catalogue have been corrected and the originally published values are stated in the notes. Two publications state corrections to the printed Uranometria Argentina. These are by B.A. Gould, Astronomische Nachrichten 116, 379-382 (1887AN....116..379G), and by T. W. Backhouse, Astronomical Journal 12, 112 (1892AJ.....12Q.112B). All of these, and a few others, mostly typographical misprints found by the present author, are presented in this digital version. (5 data files).

Vortex creep and the internal temperature of neutron stars - Linear and nonlinear response to a glitch

NASA Technical Reports Server (NTRS)

Alpar, M. A.; Cheng, K. S.; Pines, D.

1989-01-01

The dynamics of pinned superfluid in neutron stars is determined by the thermal 'creep' of vortices. Vortex creep can respond to changes in the rotation rate of the neutron star crust and provide the observed types of dynamical relaxation following pulsar glitches. It also gives rise to energy dissipation, which determines the thermal evolution of pulsars once the initial heat content has been radiated away. The different possible regimes of vortex creep are explored, and it is shown that the nature of the dynamical response of the pinned superfluid evolves with a pulsar's age. Younger pulsars display a linear regime, where the response is linear in the initial perturbation and is a simple exponential relaxation as a function of time. A nonliner response, with a characteristic nonlinear dependence on the initial perturbation, is responsible for energy dissipation and becomes the predominant mode of response as the pulsar ages. The transition from the linear to the nonlinear regime depends sensitively on the temperature of the neutron star interior. A preliminary review of existing postglitch observations is given within this general evolutionary framework.

Radial distribution of dust, stars, gas, and star-formation rate in DustPedia⋆ face-on galaxies

NASA Astrophysics Data System (ADS)

Casasola, V.; Cassarà, L. P.; Bianchi, S.; Verstocken, S.; Xilouris, E.; Magrini, L.; Smith, M. W. L.; De Looze, I.; Galametz, M.; Madden, S. C.; Baes, M.; Clark, C.; Davies, J.; De Vis, P.; Evans, R.; Fritz, J.; Galliano, F.; Jones, A. P.; Mosenkov, A. V.; Viaene, S.; Ysard, N.

2017-09-01

Aims: The purpose of this work is the characterization of the radial distribution of dust, stars, gas, and star-formation rate (SFR) in a sub-sample of 18 face-on spiral galaxies extracted from the DustPedia sample. Methods: This study is performed by exploiting the multi-wavelength DustPedia database, from ultraviolet (UV) to sub-millimeter bands, in addition to molecular (12CO) and atomic (Hi) gas maps and metallicity abundance information available in the literature. We fitted the surface-brightness profiles of the tracers of dust and stars, the mass surface-density profiles of dust, stars, molecular gas, and total gas, and the SFR surface-density profiles with an exponential curve and derived their scale-lengths. We also developed a method to solve for the CO-to-H2 conversion factor (αCO) per galaxy by using dust- and gas-mass profiles. Results: Although each galaxy has its own peculiar behavior, we identified a common trend of the exponential scale-lengths versus wavelength. On average, the scale-lengths normalized to the B-band 25 mag/arcsec2 radius decrease from UV to 70 μm, from 0.4 to 0.2, and then increase back up to 0.3 at 500 microns. The main result is that, on average, the dust-mass surface-density scale-length is about 1.8 times the stellar one derived from IRAC data and the 3.6 μm surface brightness, and close to that in the UV. We found a mild dependence of the scale-lengths on the Hubble stage T: the scale-lengths of the Herschel bands and the 3.6 μm scale-length tend to increase from earlier to later types, the scale-length at 70 μm tends to be smaller than that at longer sub-mm wavelength with ratios between longer sub-mm wavelengths and 70 μm that decrease with increasing T. The scale-length ratio of SFR and stars shows a weak increasing trend towards later types. Our αCO determinations are in the range (0.3-9) M⊙ pc-2 (K km s-1)-1, almost invariant by using a fixed dust-to-gas ratio mass (DGR) or a DGR depending on metallicity gradient. DustPedia is a project funded by the EU under the heading "Exploitation of space science and exploration data". It has the primary goal of exploiting existing data in the Herschel Space Observatory and Planck Telescope databases.

Evidence for a trophic cascade on rocky reefs following sea star mass mortality in British Columbia

PubMed Central

Cloutier, Ryan N.; Côté, Isabelle M.

2016-01-01

Echinoderm population collapses, driven by disease outbreaks and climatic events, may be important drivers of population dynamics, ecological shifts and biodiversity. The northeast Pacific recently experienced a mass mortality of sea stars. In Howe Sound, British Columbia, the sunflower star Pycnopodia helianthoides—a previously abundant predator of bottom-dwelling invertebrates—began to show signs of a wasting syndrome in early September 2013, and dense aggregations disappeared from many sites in a matter of weeks. Here, we assess changes in subtidal community composition by comparing the abundance of fish, invertebrates and macroalgae at 20 sites in Howe Sound before and after the 2013 sea star mortality to evaluate evidence for a trophic cascade. We observed changes in the abundance of several species after the sea star mortality, most notably a four-fold increase in the number of green sea urchins, Strongylocentrotus droebachiensis, and a significant decline in kelp cover, which are together consistent with a trophic cascade. Qualitative data on the abundance of sunflower stars and green urchins from a citizen science database show that the patterns of echinoderm abundance detected at our study sites reflected wider local trends. The trophic cascade evident at the scale of Howe Sound was observed at half of the study sites. It remains unclear whether the urchin response was triggered directly, via a reduction in urchin mortality, or indirectly, via a shift in urchin distribution into areas previously occupied by the predatory sea stars. Understanding the ecological implications of sudden and extreme population declines may further elucidate the role of echinoderms in temperate seas, and provide insight into the resilience of marine ecosystems to biological disturbances. PMID:27168988

PHOTOMETRY OF THE STINGRAY NEBULA (V839 ARA) FROM 1889 TO 2015 ACROSS THE IONIZATION OF ITS PLANETARY NEBULA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schaefer, Bradley E.; Edwards, Zachary I.

Up until around 1980, the Stingray was an ordinary B1 post-AGB star, but then it suddenly sprouted bright emission lines like in a planetary nebula (PN), and soon after this the Hubble Space Telescope (HST) discovered a small PN around the star, so apparently we have caught a star in the act of ionizing a PN. We report here on a well-sampled light curve from 1889 to 2015, with unique coverage of the prior century plus the entire duration of the PN formation plus three decades of its aftermath. Surprisingly, the star anticipated the 1980s ionization event by declining frommore » B = 10.30 in 1889 to B = 10.76 in 1980. Starting in 1980, the central star faded fast, at a rate of 0.20 mag year{sup −1}, reaching B = 14.64 in 1996. This fast fading is apparently caused by the central star shrinking in size. From 1994 to 2015, the V-band light curve is almost entirely from the flux of two bright [O iii] emission lines from the unresolved nebula, and it shows a consistent decline at a rate of 0.090 mag year{sup −1}. This steady fading (also seen in the radio and infrared) has a timescale equal to that expected for ordinary recombination within the nebula, immediately after a short-duration ionizing event in the 1980s. We are providing the first direct measure of the rapidly changing luminosity of the central star on both sides of a presumed thermal pulse in 1980, with this providing a strong and critical set of constraints, and these are found to sharply disagree with theoretical models of PN evolution.« less

Using the negative exponential distribution to quantitatively review the evidence on how rapidly the excess risk of ischaemic heart disease declines following quitting smoking.

PubMed

Lee, Peter N; Fry, John S; Hamling, Jan S

2012-10-01

No previous review has formally modelled the decline in IHD risk following quitting smoking. From PubMed searches and other sources we identified 15 prospective and eight case-control studies that compared IHD risk in current smokers, never smokers, and quitters by time period of quit, some studies providing separate blocks of results by sex, age or amount smoked. For each of 41 independent blocks, we estimated, using the negative exponential model, the time, H, when the excess risk reduced to half that caused by smoking. Goodness-of-fit to the model was adequate for 35 blocks, others showing a non-monotonic pattern of decline following quitting, with a variable pattern of misfit. After omitting one block with a current smoker RR 1.0, the combined H estimate was 4.40 (95% CI 3.26-5.95) years. There was considerable heterogeneity, H being <2years for 10 blocks and >10years for 12. H increased (p<0.001) with mean age at study start, but not clearly with other factors. Sensitivity analyses allowing for reverse causation, or varying assumed midpoint times for the final open-ended quitting period little affected goodness-of-fit of the combined estimate. The US Surgeon-General's view that excess risk approximately halves after a year's abstinence seems over-optimistic. Copyright © 2012 Elsevier Inc. All rights reserved.

Chemical element concentrations in four lichens on a transect entering Voyageurs National Park

USGS Publications Warehouse

Bennett, J.; Wetmore, C.M.

1997-01-01

A three factor transect study was conducted to test the hypothesis that chemical elements from air emissions in the vicinity of International Falls, Minnesota could not be detected in lichens along a 24 km transect reaching into Voyageurs National Park. It was hypothesized that element concentrations in lichens would decline exponentially downwind and would reach background values at a distance before the park boundary. Four species (Cladina rangiferina, Evernia mesomorpha, Hypogymnia physodes, and Parmelia sulcata) were sampled at ten sites for 3 years and 17 chemical elements were measured. The most notable result was a curvilinear geographic trend for many elements, which decreased from International Falls and then increased towards the park. This trend was significant for many anthropogenic elements, including S, Hg, Cd, and Cr, and for all four species. This type of distribution pattern has been observed in Hypogymnia physodes in other studies downwind of a steel mill and an oil refinery. Cladina, a ground-dwelling lichen, generally had lower tissue concentrations of the elements than the three epiphytic species. Tissue concentrations over the 3 years of sampling declined an average of 12%. Sufficient evidence exists to conclude that lichen tissue element concentrations in the vicinity of International Falls may be related to local air emissions, and that an exponential decline of element concentrations downwind of the sources does not apply to this situation.

Effects of stepwise nitrogen depletion on carotenoid content, fluorescence parameters and the cellular stoichiometry of Chlorella vulgaris

NASA Astrophysics Data System (ADS)

Zhang, Ping; Li, Zhe; Lu, Lunhui; Xiao, Yan; Liu, Jing; Guo, Jinsong; Fang, Fang

2017-06-01

Stressful conditions can stimulate the accumulation of carotenoids in some microalgae. To obtain more knowledge of the stress response, we studied the effects of different N concentrations on unicellular content of carotenoids using Raman spectroscopic technique; cellular stoichiometric changes and the fluorescence parameters of Chlorella vulgaris were concomitantly studied. Initially, we optimized the Raman scattering conditions and demonstrated the feasibility of unicellular carotenoid analysis by Raman spectroscopic technique. The results showed that an integration time of 10 s, laser power at 0.1 mW and an accumulation time of 1 were the optimum conditions, and the peak height at 1523 cm- 1 scaled linearly with the carotenoid content in the range of 0.625-1440 mg/L with a recovery rate of 97% 103%. In the experiment, seven different nitrogen levels ranging from 0 to 2.48 × 105 μg/L were imposed. Samples were taken at the start, exponential phase and end of the experiment. The results showed that nitrogen stress can facilitate the synthesis of carotenoids, while at the same time, excessive nitrogen stress led to lower proliferative and photosynthetic activity. Compared with carotenoids, chlorophylls were more sensitive to nitrogen stress; it declined dramatically as stress processed. There existed no significant differences for Fv/Fm among different nitrogen levels during the exponential phase, while in the end, it declined and a significant difference appeared between cells in 2.48 × 105 μg/L N and other experimental levels. Photosynthetic efficiency, namely the C/N mole ratio in algal cells, didnot significantly change during the exponential phase; however, apparent increases ultimately occurred, except for the stable C/N in BG11 medium. This increase matched well with the carotenoid decline, indicating that an increasing cellular C/N mole ratio can be used as an indicator of excessive stress in carotenoid production. Besides, there also existed an inverse correlation with ETRmax.

Large-scale impacts of sea star wasting disease (SSWD) on intertidal sea stars and implications for recovery

PubMed Central

Burnaford, Jennifer L.; Ambrose, Richard F.; Antrim, Liam; Bohlmann, Heath; Blanchette, Carol A.; Engle, John M.; Fradkin, Steven C.; Gaddam, Rani; Harley, Christopher D. G.; Miner, Benjamin G.; Murray, Steven N.; Smith, Jayson R.; Whitaker, Stephen G.; Raimondi, Peter T.

2018-01-01

Disease outbreaks can have substantial impacts on wild populations, but the often patchy or anecdotal evidence of these impacts impedes our ability to understand outbreak dynamics. Recently however, a severe disease outbreak occurred in a group of very well-studied organisms–sea stars along the west coast of North America. We analyzed nearly two decades of data from a coordinated monitoring effort at 88 sites ranging from southern British Columbia to San Diego, California along with 2 sites near Sitka, Alaska to better understand the effects of sea star wasting disease (SSWD) on the keystone intertidal predator, Pisaster ochraceus. Quantitative surveys revealed unprecedented declines of P. ochraceus in 2014 and 2015 across nearly the entire geographic range of the species. The intensity of the impact of SSWD was not uniform across the affected area, with proportionally greater population declines in the southern regions relative to the north. The degree of population decline was unrelated to pre-outbreak P. ochraceus density, although these factors have been linked in other well-documented disease events. While elevated seawater temperatures were not broadly linked to the initial emergence of SSWD, anomalously high seawater temperatures in 2014 and 2015 might have exacerbated the disease’s impact. Both before and after the onset of the SSWD outbreak, we documented higher recruitment of P. ochraceus in the north than in the south, and while some juveniles are surviving (as evidenced by transition of recruitment pulses to larger size classes), post-SSWD survivorship is lower than during pre-SSWD periods. In hindsight, our data suggest that the SSWD event defied prediction based on two factors found to be important in other marine disease events, sea water temperature and population density, and illustrate the importance of surveillance of natural populations as one element of an integrated approach to marine disease ecology. Low levels of SSWD-symptomatic sea stars are still present throughout the impacted range, thus the outlook for population recovery is uncertain. PMID:29558484

VizieR Online Data Catalog: Catalog of Kepler flare stars (Van Doorsselaere+, 2017)

NASA Astrophysics Data System (ADS)

van Doorsselaere, T.; Shariati, H.; Debosscher, J.

2017-11-01

With an automated detection method, we have identified stellar flares in the long cadence observations of Kepler during quarter 15. We list each flare time for the respective Kepler objects. Furthermore, we list the flare amplitude and decay time after fitting the flare light curve with an exponential decay. Flare start times in long cadence data of Kepler during quarter 15. (1 data file).

VizieR Online Data Catalog: Calibrator stars catalog for interferometers (Swihart+, 2017)

NASA Astrophysics Data System (ADS)

Swihart, S. J.; Garcia, E. V.; Stassun, K. G.; van Belle, G.; Mutterspaugh, M. W.; Elias, N.

2017-04-01

In order to obtain accurate stellar angular sizes, each star was fit with a model SED using the fitting routine sedFit, written by A. Boden (van Belle & von Braun, 2009, Cat. J/ApJ/694/1085; van Belle et al. 2016, Cat. J/AJ/152/16). We compiled a list of positions, spectral types and visual magnitudes for ~3000 bright (Vmag<6) stars in the northern hemisphere with declinations -15°<δ<82° using the SIMBAD database (Wenger et al., 2000A&AS..143....9W). We chose a brightness limit (Vmag<6) given that most visible light interferometers can obtain scientifically useful data on bright stars. We also removed any stars which appear in the JMMC bad calibrator list. (4 data files).

Magnetic confinement, Alfven wave reflection, and the origins of X-ray and mass-loss 'dividing lines' for late-type giants and supergiants

NASA Technical Reports Server (NTRS)

Rosner, R.; An, C.-H.; Musielak, Z. E.; Moore, R. L.; Suess, S. T.

1991-01-01

A simple qualitative model for the origin of the coronal and mass-loss dividing lines separating late-type giants and supergiants with and without hot, X-ray-emitting corona, and with and without significant mass loss is discussed. The basic physical effects considered are the necessity of magnetic confinement for hot coronal material on the surface of such stars and the large reflection efficiency for Alfven waves in cool exponential atmospheres. The model assumes that the magnetic field geometry of these stars changes across the observed 'dividing lines' from being mostly closed on the high effective temperature side to being mostly open on the low effective temperature side.

Exploring the Surface Brightness Breaks and Star Formation in Disk Galaxies

NASA Astrophysics Data System (ADS)

Malko, Bradley Ann; Hunter, Deidre Ann

2018-06-01

Stellar surface brightness profiles of both spirals and dwarf irregular galaxies often show breaks in which the exponential fall-off abruptly changes slope. Most often the profile is down-bending (Type II) in the outer disk, but sometimes it is up-bending (Type III). Stellar disks extend a long ways beyond the profile breaks, but we do not understand what happens physically at the breaks. To explore this we are examining the star formation activity, as traced with FUV emission, interior to the break compared to that exterior to the break in both dwarf irregulars and spiral galaxies. We present the results for the spiral galaxy NGC 2500 and compare it to the LITTLE THINGS dwarf irregular galaxies.

The onset of chromospheric activity among the A and F stars

NASA Technical Reports Server (NTRS)

Simon, Theodore; Landsman, Wayne

1991-01-01

Results are reported from a search for an upper boundary for the onset of main-sequence star activity based on a quest for high-temperature UV line emission in a large collection of IUE spectra. It is shown that strong chromospheric emission is common among early F dwarf and subgiant stars. At its brightest, the emission is equal to that of the most active solar-type stars and is exceeded only by that of the spotted RS CVn and BY Dra variables. It is suggested that the emission from the main-sequence stars reaches a peak near B-V = 0.28, in the vicinity of spectral type F0 V, before it declines to lower flux levels among the late A stars. Emission is seen in some dwarf stars as early as B-V = 0.25. It is demonstrated that the C II emission of stars earlier than the spectral type F5 is uncorrelated with rotation. Previous findings that the coronal X-ray:chromospheric UV flux ratio is lower for stars earlier than spectral type F5 than for those later than F5 are confirmed.

VizieR Online Data Catalog: Spectral Classes in Kapteyn areas 44-67 (Bartaya+, 1992)

NASA Astrophysics Data System (ADS)

Bartaya, R. A.; Kharadze, E. K.

2013-11-01

The present catalogue is the second one of the four catalogues published according to programme of Abastumani Astrophysical Observatory of a massive two-dimensional MK classification of stars in 115 kapteyn Select Areas (KA) of Northen Sky. The catalogue lists the spectral types and luminosity classes for 5888 stars in 24 Kapteyn areas 44-67 through the declination circle of 30°. The catalogue is compiled on the basis of the spectral data obtained with the 70-cm meniscus telescope of Abastumani Astrophysical Observatory using the 8° objective prism (dispersion 166Å/mm near Hγ; in the short-wave region, the spectrum extends up to 3500Å). The field of the meniscus telescope is 4.5°x4.5°. The photo material is taken on Kodak IIa-O, hyper-sensitized Kodak IIIa-J and in order to detect also Hα emission stars and M, S, C type stars in the surveyed Kapteyn areas (KA), hyper-sensitized Kodak IIIa-F plates were also taken. A limiting apparent magnitude in V for stars in question is 12.5 photographic mag. and for M ones - 15.0mag. The catalogue contains 94 stars with peculiarities in the spectrum, in particular Ap, Am, BaII and composite spectrum stars, as well as 9 emission objects, 381 M-type, 16 C and a few S and WC stars. The data for all KA's are uniform not only in the sense of classification accuracy (the whole classification is done by one person - the author of the present catalogue), but also in the sense of penetration. The errors of our determinations are: +/-0.6 for spectral subtype and+/-0.5 for luminosity class. The stars in the KA's are arranged in the Catalogue by increasing right ascension. The stars are numbered according to zones of 1° in declination. The printed catalogue is provided with suitable stellar charts for separate KA's reproduced from the Lick Catalogue. The reference system on the charts refers to 1950 epoch and it is plotted according to the Smithsonian Astrophysical Observatory (SAO) catalogue. (1 data file).

Winds in collision. II - An analysis of the X-ray emission from the eruptive symbiotic HM Sge

NASA Technical Reports Server (NTRS)

Willson, L. A.; Wallerstein, G.; Brugel, E. W.; Stencel, R. E.

1984-01-01

X-ray emissions from HM Sge obtained in 1981 from the HEAO-2 satellite are analyzed and compared quantitatively with observations of HM Sge made in 1980 and of HM Sge, V 1016 Cyg, and RR Tel made in 1979. The change in the X-ray emission from HM Sge between 1979 and 1981 is found to be consistent with the X-ray luminosity and/or temperature of the emitting region declining with an e-folding timescale of the order of one to several decades. Comparison with X-ray data from V 1016 Cyg and RR Tel gives a composite X-ray light curve that is also consistent with such a decline. A comparison of the X-ray observation with spectroscopic information makes it possible to constrain the properties of the X-ray emitting region: the result is consistent with emission from an optically thin region between the two stars in the system where their winds collide head on. It is also shown that the observations are inconsistent with a stellar (blackbody) source, with emission from an accretion disk around a white dwarf or a neutron star, and with emission from a single star wind from either a white dwarf or a neutron star.

The star-forming history of the young cluster NGC 2264

NASA Technical Reports Server (NTRS)

Adams, M. T.; Strom, K. M.; Strom, S. E.

1983-01-01

UBVRI H-alpha photographic photometry was obtained for a sample of low-mass stars in the young open cluster NGC 2264 in order to investigate the star-forming history of this region. A theoretical H-R diagram was constructed for the sample of probable cluster members. Isochrones and evolutionary tracks were adopted from Cohen and Kuhi (1979). Evidence for a significant age spread in the cluster was found amounting to over ten million yr. In addition, the derived star formation rate as a function of stellar mass suggests that the principal star-forming mass range in NGC 2264 has proceeded sequentially in time from the lowest to the highest masses. The low-mass cluster stars were the first cluster members to form in significant numbers, although their present birth rate is much lower now than it was about ten million yr ago. The star-formation rate has risen to a peak at successively higher masses and then declined.

The role of black holes in galaxy formation and evolution.

PubMed

Cattaneo, A; Faber, S M; Binney, J; Dekel, A; Kormendy, J; Mushotzky, R; Babul, A; Best, P N; Brüggen, M; Fabian, A C; Frenk, C S; Khalatyan, A; Netzer, H; Mahdavi, A; Silk, J; Steinmetz, M; Wisotzki, L

2009-07-09

Virtually all massive galaxies, including our own, host central black holes ranging in mass from millions to billions of solar masses. The growth of these black holes releases vast amounts of energy that powers quasars and other weaker active galactic nuclei. A tiny fraction of this energy, if absorbed by the host galaxy, could halt star formation by heating and ejecting ambient gas. A central question in galaxy evolution is the degree to which this process has caused the decline of star formation in large elliptical galaxies, which typically have little cold gas and few young stars, unlike spiral galaxies.

Exponential decline of deep-sea ecosystem functioning linked to benthic biodiversity loss.

PubMed

Danovaro, Roberto; Gambi, Cristina; Dell'Anno, Antonio; Corinaldesi, Cinzia; Fraschetti, Simonetta; Vanreusel, Ann; Vincx, Magda; Gooday, Andrew J

2008-01-08

Recent investigations suggest that biodiversity loss might impair the functioning and sustainability of ecosystems. Although deep-sea ecosystems are the most extensive on Earth, represent the largest reservoir of biomass, and host a large proportion of undiscovered biodiversity, the data needed to evaluate the consequences of biodiversity loss on the ocean floor are completely lacking. Here, we present a global-scale study based on 116 deep-sea sites that relates benthic biodiversity to several independent indicators of ecosystem functioning and efficiency. We show that deep-sea ecosystem functioning is exponentially related to deep-sea biodiversity and that ecosystem efficiency is also exponentially linked to functional biodiversity. These results suggest that a higher biodiversity supports higher rates of ecosystem processes and an increased efficiency with which these processes are performed. The exponential relationships presented here, being consistent across a wide range of deep-sea ecosystems, suggest that mutually positive functional interactions (ecological facilitation) can be common in the largest biome of our biosphere. Our results suggest that a biodiversity loss in deep-sea ecosystems might be associated with exponential reductions of their functions. Because the deep sea plays a key role in ecological and biogeochemical processes at a global scale, this study provides scientific evidence that the conservation of deep-sea biodiversity is a priority for a sustainable functioning of the worlds' oceans.

Stellar and gaseous disc structures in cosmological galaxy equilibrium models

NASA Astrophysics Data System (ADS)

Rathaus, Ben; Sternberg, Amiel

2016-05-01

We present `radially resolved equilibrium models' for the growth of stellar and gaseous discs in cosmologically accreting massive haloes. Our focus is on objects that evolve to redshifts z ˜ 2. We solve the time-dependent equations that govern the radially dependent star formation rates, inflows and outflows from and to the inter- and circumgalactic medium, and inward radial gas flows within the discs. The stellar and gaseous discs reach equilibrium configurations on dynamical time-scales much shorter than variations in the cosmological dark matter halo growth and baryonic accretions rates. We show analytically that mass and global angular momentum conservation naturally give rise to exponential gas and stellar discs over many radial length-scales. As expected, the gaseous discs are more extended as set by the condition Toomre Q < 1 for star formation. The discs rapidly become baryon dominated. For massive, 5 × 1012 M⊙ haloes at redshift z = 2, we reproduced the typical observed star formation rates of ˜100 M⊙ yr-1, stellar masses ˜9 × 1010 M⊙, gas contents ˜1011 M⊙, half-mass sizes of 4.5 and 5.8 kpc for the stars and gas, and characteristic surface densities of 500 and 400 M⊙ pc-2 for the stars and gas.

The evolving price of household LED lamps: Recent trends and historical comparisons for the US market

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gerke, Brian F.; Ngo, Allison T.; Alstone, Andrea L.

2014-10-14

In recent years, household LED light bulbs (LED A lamps) have undergone a dramatic price decline. Since late 2011, we have been collecting data, on a weekly basis, for retail offerings of LED A lamps on the Internet. The resulting data set allows us to track the recent price decline in detail. LED A lamp prices declined roughly exponentially with time in 2011-2014, with decline rates of 28percent to 44percent per year depending on lumen output, and with higher-lumen lamps exhibiting more rapid price declines. By combining the Internet price data with publicly available lamp shipments indices for the USmore » market, it is also possible to correlate LED A lamp prices against cumulative production, yielding an experience curve for LED A lamps. In 2012-2013, LED A lamp prices declined by 20-25percent for each doubling in cumulative shipments. Similar analysis of historical data for other lighting technologies reveals that LED prices have fallen significantly more rapidly with cumulative production than did their technological predecessors, which exhibited a historical decline of 14-15percent per doubling of production.« less

Tachyon search speeds up retrieval of similar sequences by several orders of magnitude.

PubMed

Tan, Joshua; Kuchibhatla, Durga; Sirota, Fernanda L; Sherman, Westley A; Gattermayer, Tobias; Kwoh, Chia Yee; Eisenhaber, Frank; Schneider, Georg; Maurer-Stroh, Sebastian

2012-06-15

The usage of current sequence search tools becomes increasingly slower as databases of protein sequences continue to grow exponentially. Tachyon, a new algorithm that identifies closely related protein sequences ~200 times faster than standard BLAST, circumvents this limitation with a reduced database and oligopeptide matching heuristic. The tool is publicly accessible as a webserver at http://tachyon.bii.a-star.edu.sg and can also be accessed programmatically through SOAP.

VizieR Online Data Catalog: Lower main-sequence stars fundamental param. (Casagrande+, 2006)

NASA Astrophysics Data System (ADS)

Casagrande, L.; Portinari, L.; Flynn, C.

2007-06-01

To recover accurate bolometric fluxes and temperatures for the stars, we have obtained accurate and homogeneous Johnson-Cousins BV(RI)C and JHKs photometry for all the 186 stars in our initial sample. For most of the stars in our sample with declination north of DE=-25°, we have made our own photometric observations from April to December 2004. Observations were done from Finland in full remote mode, using the 35-cm telescope piggybacked on the Swedish 60-cm telescope located at La Palma in the Canary Islands. A SBIG charge-coupled device was used through all the observations. Johnson-Cousins BV(RI)C colours were obtained for all stars. Infrared JHKs photometry for the sample has been taken from the Two-Micron All-Sky Survey (2MASS) catalogue. (1 data file).

VizieR Online Data Catalog: Lower main-sequence stars fundamental param. (Casagrande+, 2006)

NASA Astrophysics Data System (ADS)

Casagrande, L.; Portinari, L.; Flynn, C.

2007-06-01

To recover accurate bolometric fluxes and temperatures for the stars, we have obtained accurate and homogeneous Johnson-Cousins BV(RI)C and JHKs photometry for all the 186 stars in our initial sample. For most of the stars in our sample with declination north of DE=-25{deg}, we have made our own photometric observations from April to December 2004. Observations were done from Finland in full remote mode, using the 35-cm telescope piggybacked on the Swedish 60-cm telescope located at La Palma in the Canary Islands. A SBIG charge-coupled device was used through all the observations. Johnson-Cousins BV(RI)C colours were obtained for all stars. Infrared JHKs photometry for the sample has been taken from the Two-Micron All-Sky Survey (2MASS) catalogue. (1 data file).

Star formation quenching in green valley galaxies at 0.5 ≲ z ≲ 1.0 and constraints with galaxy morphologies

NASA Astrophysics Data System (ADS)

Nogueira-Cavalcante, J. P.; Gonçalves, T. S.; Menéndez-Delmestre, K.; Sheth, K.

2018-01-01

We calculate the star formation quenching time-scales in green valley galaxies at intermediate redshifts (z ∼ 0.5-1) using stacked zCOSMOS spectra of different galaxy morphological types: spheroidal, disc-like, irregular and merger, dividing disc-like galaxies further into unbarred, weakly barred and strongly barred, assuming a simple exponentially decaying star formation history model and based on the H δ absorption feature and the 4000 Å break. We find that different morphological types present different star formation quenching time-scales, reinforcing the idea that the galaxy morphology is strongly correlated with the physical processes responsible for quenching star formation. Our quantification of the star formation quenching time-scale indicates that discs have typical time-scales 60 per cent to five times longer than that of galaxies presenting spheroidal, irregular or merger morphologies. Barred galaxies, in particular, present the slowest transition time-scales through the green valley. This suggests that although secular evolution may ultimately lead to gas exhaustion in the host galaxy via bar-induced gas inflows that trigger star formation activity, secular agents are not major contributors in the rapid quenching of galaxies at these redshifts. Galaxy interaction, associated with the elliptical, irregular and merger morphologies, contributes, to a more significant degree, to the fast transition through the green valley at these redshifts. In light of previous works suggesting that both secular and merger processes are responsible for the star formation quenching at low redshifts, our results provide an explanation to the recent findings that star formation quenching happened at a faster pace at z ∼ 0.8.

Gaia DR1 completeness within 250 pc and star formation history of the Solar neighbourhood

NASA Astrophysics Data System (ADS)

Bernard, E. J.

2017-12-01

Taking advantage of the Gaia DR1, we combined TGAS parallaxes with the Tycho-2 and APASS photometry to calculate the star formation history (SFH) of the solar neighbourhood within 250 pc using the colour-magnitude diagram fitting technique. Our dynamically-evolved SFH is in excellent agreement with that calculated from the Hipparcos catalogue within 80 pc of the Sun, showing an enhanced star formation rate (SFR) in the past ˜4 Gyr. We then correct the SFR for the disc thickening with age to obtain a SFR that is representative of the whole solar cylinder, and show that even with an extreme correction our results are not consistent with an exponentially decreasing SFR as found by recent studies. Finally, we discuss how this technique can be applied out to ˜5 kpc thanks to the next Gaia data releases, which will allow us to quantify the SFH of the thin disc, thick disc and halo in situ.

Galaxy and Mass Assembly (GAMA): Impact of the Group Environment on Galaxy Star Formation

NASA Astrophysics Data System (ADS)

Barsanti, S.; Owers, M. S.; Brough, S.; Davies, L. J. M.; Driver, S. P.; Gunawardhana, M. L. P.; Holwerda, B. W.; Liske, J.; Loveday, J.; Pimbblet, K. A.; Robotham, A. S. G.; Taylor, E. N.

2018-04-01

We explore how the group environment may affect the evolution of star-forming galaxies. We select 1197 Galaxy And Mass Assembly groups at 0.05 ≤ z ≤ 0.2 and analyze the projected phase space (PPS) diagram, i.e., the galaxy velocity as a function of projected group-centric radius, as a local environmental metric in the low-mass halo regime 1012 ≤ (M 200/M ⊙) < 1014. We study the properties of star-forming group galaxies, exploring the correlation of star formation rate (SFR) with radial distance and stellar mass. We find that the fraction of star-forming group members is higher in the PPS regions dominated by recently accreted galaxies, whereas passive galaxies dominate the virialized regions. We observe a small decline in specific SFR of star-forming galaxies toward the group center by a factor ∼1.2 with respect to field galaxies. Similar to cluster studies, we conclude for low-mass halos that star-forming group galaxies represent an infalling population from the field to the halo and show suppressed star formation.

LONG-TERM OPTICAL STUDIES OF THE BE/X-RAY BINARY RX J0440.9+4431/LS V+44 17

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yan, Jingzhi; Zhang, Peng; Liu, Wei

2016-04-15

We present the spectroscopic and photometric observations on the Be/X-ray binary RX J0440.9+4431 from 2001 to 2014. The short-term and long-term variability of the Hα line profile indicates that one-armed global oscillations existed in the circumstellar disk. Several positive and negative correlations between the V-band brightness and the Hα intensity were found from the long-term photometric and spectroscopic observations. We suggest that the monotonic increase of the V-band brightness and the Hα brightness between our 2005 and 2007 observations might be the result of a continuous mass ejection from the central Be star, while the negative correlation in 2007–2010 should bemore » caused by the cessation of mass loss from the Be star just before the decline in V-band brightness began (around our 2007 observations). With the extension of the ejection material, the largest circumstellar disk during the last two decades has been observed in our 2010 observations with an equivalent width of approximately −12.88 Å, which corresponds to a circumstellar disk with a size of 12.9 times the radius of the central Be star. Three consecutive X-ray outbursts peaking around MJD 55293, 55444, and 55591 might be connected with the largest circumstellar disk around the Be star. We also use the orbital motion of the neutron star as a probe to constrain the structure of the circumstellar disk and estimate the eccentricity of the binary system to be ≥0.4. After three years of the Hα intensity decline after the X-ray outbursts, a new circumstellar disk was being formed around the Be star after our 2013 observations.« less

SDSS-IV MaNGA-resolved Star Formation and Molecular Gas Properties of Green Valley Galaxies: A First Look with ALMA and MaNGA

NASA Astrophysics Data System (ADS)

Lin, Lihwai; Belfiore, Francesco; Pan, Hsi-An; Bothwell, M. S.; Hsieh, Pei-Ying; Huang, Shan; Xiao, Ting; Sánchez, Sebastián F.; Hsieh, Bau-Ching; Masters, Karen; Ramya, S.; Lin, Jing-Hua; Hsu, Chin-Hao; Li, Cheng; Maiolino, Roberto; Bundy, Kevin; Bizyaev, Dmitry; Drory, Niv; Ibarra-Medel, Héctor; Lacerna, Ivan; Haines, Tim; Smethurst, Rebecca; Stark, David V.; Thomas, Daniel

2017-12-01

We study the role of cold gas in quenching star formation in the green valley by analyzing ALMA 12CO (1-0) observations of three galaxies with resolved optical spectroscopy from the MaNGA survey. We present resolution-matched maps of the star formation rate and molecular gas mass. These data are used to calculate the star formation efficiency (SFE) and gas fraction ({f}{gas}) for these galaxies separately in the central “bulge” regions and outer disks. We find that, for the two galaxies whose global specific star formation rate (sSFR) deviates most from the star formation main sequence, the gas fraction in the bulges is significantly lower than that in their disks, supporting an “inside-out” model of galaxy quenching. For the two galaxies where SFE can be reliably determined in the central regions, the bulges and disks share similar SFEs. This suggests that a decline in {f}{gas} is the main driver of lowered sSFR in bulges compared to disks in green valley galaxies. Within the disks, there exist common correlations between the sSFR and SFE and between sSFR and {f}{gas} on kiloparsec scales—the local SFE or {f}{gas} in the disks declines with local sSFR. Our results support a picture in which the sSFR in bulges is primarily controlled by {f}{gas}, whereas both SFE and {f}{gas} play a role in lowering the sSFR in disks. A larger sample is required to confirm if the trend established in this work is representative of the green valley as a whole.

Estimating the decline in excess risk of chronic obstructive pulmonary disease following quitting smoking - a systematic review based on the negative exponential model.

PubMed

Lee, Peter N; Fry, John S; Forey, Barbara A

2014-03-01

We quantified the decline in COPD risk following quitting using the negative exponential model, as previously carried out for other smoking-related diseases. We identified 14 blocks of RRs (from 11 studies) comparing current smokers, former smokers (by time quit) and never smokers, some studies providing sex-specific blocks. Corresponding pseudo-numbers of cases and controls/at risk formed the data for model-fitting. We estimated the half-life (H, time since quit when the excess risk becomes half that for a continuing smoker) for each block, except for one where no decline with quitting was evident, and H was not estimable. For the remaining 13 blocks, goodness-of-fit to the model was generally adequate, the combined estimate of H being 13.32 (95% CI 11.86-14.96) years. There was no heterogeneity in H, overall or by various studied sources. Sensitivity analyses allowing for reverse causation or different assumed times for the final quitting period little affected the results. The model summarizes quitting data well. The estimate of 13.32years is substantially larger than recent estimates of 4.40years for ischaemic heart disease and 4.78years for stroke, and also larger than the 9.93years for lung cancer. Heterogeneity was unimportant for COPD, unlike for the other three diseases. Copyright © 2013 The Authors. Published by Elsevier Inc. All rights reserved.

Is the shape of the decline in risk following quitting smoking similar for squamous cell carcinoma and adenocarcinoma of the lung? A quantitative review using the negative exponential model.

PubMed

Fry, John S; Lee, Peter N; Forey, Barbara A; Coombs, Katharine J

2015-06-01

One possible contributor to the reported rise in the ratio of adenocarcinoma to squamous cell carcinoma of the lung may be differences in the pattern of decline in risk following quitting for the two lung cancer types. Earlier, using data from 85 studies comparing overall lung cancer risks in current smokers, quitters (by time quit) and never smokers, we fitted the negative exponential model, deriving an estimate of 9.93years for the half-life - the time when the excess risk for quitters compared to never smokers becomes half that for continuing smokers. Here we applied the same techniques to data from 16 studies providing RRs specific for lung cancer type. From the 13 studies where the half-life was estimable for each type, we derived estimates of 11.68 (95% CI 10.22-13.34) for squamous cell carcinoma and 14.45 (11.92-17.52) for adenocarcinoma. The ratio of the half-lives was estimated as 1.32 (95% CI 1.20-1.46, p<0.001). The slower decline in quitters for adenocarcinoma, evident in subgroups by sex, age and other factors, may be one of the factors contributing to the reported rise in the ratio of adenocarcinoma to squamous cell carcinoma. Others include changes in the diagnosis and classification of lung cancer. Copyright © 2015 The Authors. Published by Elsevier Inc. All rights reserved.

Fate of Escherichia coli O157:H7 on Fresh-Cut Apple Tissue and Its Potential for Transmission by Fruit Flies

PubMed Central

Janisiewicz, W. J.; Conway, W. S.; Brown, M. W.; Sapers, G. M.; Fratamico, P.; Buchanan, R. L.

1999-01-01

Pathogenic Escherichia coli O157:H7, as well as nonpathogenic strains ATCC 11775 and ATCC 23716, grew exponentially in wounds on Golden Delicious apple fruit. The exponential growth occurred over a longer time period on fruit inoculated with a lower concentration of the bacterium than on fruit inoculated with a higher concentration. The bacterium reached the maximum population supported in the wounds regardless of the initial inoculum concentrations. Populations of E. coli O157:H7 in various concentrations of sterilized apple juice and unsterilized cider declined over time and declined more quickly in diluted juice and cider. The decline was greater in the unsterilized cider than in juice, which may have resulted from the interaction of E. coli O157:H7 with natural populations of yeasts that increased with time. Experiments on the transmission of E. coli by fruit flies, collected from a compost pile of decaying apples and peaches, were conducted with strain F-11775, a fluorescent transformant of nonpathogenic E. coli ATCC 11775. Fruit flies were easily contaminated externally and internally with E. coli F-11775 after contact with the bacterium source. The flies transmitted this bacterium to uncontaminated apple wounds, resulting in a high incidence of contaminated wounds. Populations of the bacterium in apple wounds increased significantly during the first 48 h after transmission. Further studies under commercial conditions are necessary to confirm these findings. PMID:9872751

Concave utility, transaction costs, and risk in measuring discounting of delayed rewards.

PubMed

Kirby, Kris N; Santiesteban, Mariana

2003-01-01

Research has consistently found that the decline in the present values of delayed rewards as delay increases is better fit by hyperbolic than by exponential delay-discounting functions. However, concave utility, transaction costs, and risk each could produce hyperbolic-looking data, even when the underlying discounting function is exponential. In Experiments 1 (N = 45) and 2 (N = 103), participants placed bids indicating their present values of real future monetary rewards in computer-based 2nd-price auctions. Both experiments suggest that utility is not sufficiently concave to account for the superior fit of hyperbolic functions. Experiment 2 provided no evidence that the effects of transaction costs and risk are large enough to account for the superior fit of hyperbolic functions.

Order parameters for the high-energy spectra of pulsars

NASA Astrophysics Data System (ADS)

Torres, Diego F.

2018-03-01

Neutron stars are a common compact endpoint of the life of stars. Magnetized and rotating neutron stars emit beams of radiation, which can only be seen when the observer and the beam stand aligned. Periodic recurrence of such alignment gives rise to pulsations and to the name `pulsar' for the star itself. We present a physical model for the non-thermal emission of pulsars. With just four physical parameters, we fit the spectra of the γ- and X-ray pulsars across seven orders of magnitude in energy. We find that all detections can be encompassed in a continuous variation of the model parameters. The model explains the appearance of sub-exponential cutoffs at high energies as a natural consequence of synchro-curvature-dominated losses, unveiling that curvature-only emission plays a less significant role—if any—in the spectrum of most pulsars. The model also explains the flattening of the X-ray spectra at soft energies as a result of propagating particles being subject to synchrotron losses all along their trajectories. Using this model, we analyse how observations in γ-rays can predict the detectability of the pulsar in X-rays, and vice versa.

Exploring Properties of HI Clouds in Dwarf Irregular Galaxies

NASA Astrophysics Data System (ADS)

Berger, Clara; Hunter, Deidre Ann

2018-01-01

Dwarf Irregular galaxies form stars and maintain exponential stellar disks at extremely low gas densities. One proposed method of maintaining such regular outer disks is scattering stars off of HI clouds. In order to understand the processes present in dwarf irregular stellar disks, we present a survey of atomic hydrogen clouds in and around a subset of representative galaxies from the LITTLE THINGS survey. We apply a cloud identification program to the 21 cm HI line emission cubes and extract masses, radii, surface densities, and distances from the center of the galaxy in the plane of the galaxy of each cloud. Our data show a wide range of clouds characterized by low surface densities but varied in mass and size. The number of clouds found and the mass of the most massive cloud show no correlation to integrated star forming rates or luminosity in these galaxies. However, they will be used as input for models of stars scattering off of HI clouds to better understand the regular stellar disks in dwarf Irregular galaxies.We acknowledge support from the National Science Foundation grant AST-1461200 to Northern Arizona University for Research Experiences for Undergraduates summer internships.

An Alternative Lattice Field Theory Formulation Inspired by Lattice Supersymmetry-Summary of the Formulation-

NASA Astrophysics Data System (ADS)

D'Adda, Alessandro; Kawamoto, Noboru; Saito, Jun

2018-03-01

We propose a lattice field theory formulation which overcomes some fundamental diffculties in realizing exact supersymmetry on the lattice. The Leibniz rule for the difference operator can be recovered by defining a new product on the lattice, the star product, and the chiral fermion species doublers degrees of freedom can be avoided consistently. This framework is general enough to formulate non-supersymmetric lattice field theory without chiral fermion problem. This lattice formulation has a nonlocal nature and is essentially equivalent to the corresponding continuum theory. We can show that the locality of the star product is recovered exponentially in the continuum limit. Possible regularization procedures are proposed.The associativity of the product and the lattice translational invariance of the formulation will be discussed.

Yellow evolved stars in open clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sowell, J.R.

1987-05-01

This paper describes a program in which Galactic cluster post-AGB candidates were first identified and then analyzed for cluster membership via radial velocities, monitored for possible photometric variations, examined for evidence of mass loss, and classified as completely as possible in terms of their basic stellar parameters. The intrinsically brightest supergiants are found in the youngest clusters. With increasing cluster age, the absolute luminosities attained by the supergiants decline. It appears that the evolutionary tracks of luminosity class II stars are more similar to those of class I than of class III. Only two superluminous giant star candidates are foundmore » in open clusters. 154 references.« less

Lick Saturn-Voyager reference star catalogue (Klemola, Taraji, and Ocampo 1979): Documentation for the machine-readable version

NASA Technical Reports Server (NTRS)

Warren, Wayne H., Jr.

1990-01-01

The machine readable version of the catalog, as it is currently being distributed from the Astronomical Data Center, is described. The catalog contains accurate equatorial coordinates for 4551 stars in a band of sky against which cameras of the Voyager spacecraft were pointed for observations in the region of Saturn during the flyby. All of the reference stars are in the range 12(exp h) 40(exp m) to 14(exp h) 12(exp m) in right ascension (1950) and +02 to -09 degs in declination. Mean errors of the positions are about 0.25 sec.

VizieR Online Data Catalog: Spectral Classes in Kapteyn areas 68-91 (Chargeishvili+, 2000)

NASA Astrophysics Data System (ADS)

Chargeishvili, K. B.; Bartaya, R. A.; Kharadze, E. K.

2013-11-01

The present catalogue is the third one of the four catalogues published according to programme of Abastumani Astrophysical Observatory of a massive two-dimensional MK classification of stars in 115 kapteyn Select Areas (KA) of Northen Sky (Bartaya, 1983, Cat. III/112; Bartaya, Kharadze, 1992, Cat. III/270). The catalogue lists the spectral types and luminosity classes for 3914 stars in 24 Kapteyn areas 68-91 through the declination circle of 0°. The catalogue is compiled on the basis of the spectral data obtained with the 70-cm meniscus telescope of Abastumani Astrophysical Observatory using the 8° objective prism (dispersion 166Å/mm near Hγ; in the short-wave region, the spectrum extends up to 3500Å). The field of the meniscus telescope is 4.5°x 4.5°. The photo material is taken on Kodak IIa-O, hyper-sensitized Kodak IIIa-J and in order to detect also Hα emission stars and M, S, C type stars in the surveyed KA's, hyper-sensitized Kodak IIIa-F plates were also taken. A limiting apparent magnitude in V for stars in question is 12.5 photographic mag. and for M ones - 15.0 mag. The data for all KA's are uniform not only in the sense of classification accuracy (the whole classification is done by one person - the author of the present catalogue), but also in the sense of penetration. The errors of our determinations are: +/-0.6 for spectral subtype and +/-0.5 for luminosity class. The stars in the KA's are arranged in the Catalogue by increasing right ascension. The stars are numbered according to zones of 1° in declination. The printed catalogue is provided with suitable stellar charts for separate KA's reproduced from the Lick Catalogue. The reference system on the charts refers to 1950 epoch and it is plotted according to the Smithsonian Astrophysical Observatory (SAO) catalogue. (1 data file).

VizieR Online Data Catalog: Spectral Classes in Kapteyn areas 92-115 (Kharadze+, 2003)

NASA Astrophysics Data System (ADS)

Kharadze, E. K.; Bartaya, R. A.; Chargeishvili, K. B.

2014-07-01

The present catalogue is the last one of the four catalogues published according to programme of Abastumani Astrophysical Observatory of a massive two-dimensional MK classification of stars in 115 kapteyn Select Areas (KA) of Northen Sky. The catalogue lists the spectral types and luminosity classes for 3880 stars in 23 Kapteyn areas 92-115 through the declination circle of 0°. KA 95 was skipped because of poor quality of observational data. The catalogue is compiled on the basis of the spectral data obtained with the 70-cm meniscus telescope of Abastumani Astrophysical Observatory using the 8° objective prism (dispersion 166Å/mm near Hγ; in the short-wave region, the spectrum extends up to 3500Å). The field of the meniscus telescope is 4.5°x4.5°. The photo material is taken on Kodak IIa-O, hyper-sensitized Kodak IIIa-J and in order to detect also Hα emission stars and M, S, C type stars in the surveyed KA's, hyper-sensitized Kodak IIIa-F plates were also taken. A limiting apparent magnitude in V for stars in question is 12.5 photographic mag. and for M ones - 15.0mag. The data for all KA's are uniform not only in the sense of classification accuracy (the whole classification is done by one person - the author of the present catalogue), but also in the sense of penetration. The errors of our determinations are: ±0.6 for spectral subtype and ±0.5 for luminosity class. The stars in the KA's are arranged in the Catalogue by increasing right ascension. The stars are numbered according to zones of 1° in declination. The printed catalogue is provided with suitable stellar charts for separate KA's reproduced from the Lick Catalogue. The reference system on the charts refers to 1950 epoch and it is plotted according to the Smithsonian Astrophysical Observatory (SAO) catalogue. (1 data file).

Confronting Models of Massive Star Evolution and Explosions with Remnant Mass Measurements

NASA Astrophysics Data System (ADS)

Raithel, Carolyn A.; Sukhbold, Tuguldur; Özel, Feryal

2018-03-01

The mass distribution of compact objects provides a fossil record that can be studied to uncover information on the late stages of massive star evolution, the supernova explosion mechanism, and the dense matter equation of state. Observations of neutron star masses indicate a bimodal Gaussian distribution, while the observed black hole mass distribution decays exponentially for stellar-mass black holes. We use these observed distributions to directly confront the predictions of stellar evolution models and the neutrino-driven supernova simulations of Sukhbold et al. We find strong agreement between the black hole and low-mass neutron star distributions created by these simulations and the observations. We show that a large fraction of the stellar envelope must be ejected, either during the formation of stellar-mass black holes or prior to the implosion through tidal stripping due to a binary companion, in order to reproduce the observed black hole mass distribution. We also determine the origins of the bimodal peaks of the neutron star mass distribution, finding that the low-mass peak (centered at ∼1.4 M ⊙) originates from progenitors with M ZAMS ≈ 9–18 M ⊙. The simulations fail to reproduce the observed peak of high-mass neutron stars (centered at ∼1.8 M ⊙) and we explore several possible explanations. We argue that the close agreement between the observed and predicted black hole and low-mass neutron star mass distributions provides new, promising evidence that these stellar evolution and explosion models capture the majority of relevant stellar, nuclear, and explosion physics involved in the formation of compact objects.

Decline of Monarch Butterflies Overwintering in Mexico- Is the Migratory Phenomenon at Risk?

NASA Technical Reports Server (NTRS)

Brower, Lincoln; Taylor, Orley R.; Williams, Ernest H.; Slayback, Daniel; Zubieta, Raul R.; Ramirez, M. Isabel

2012-01-01

1.During the 2009-2010 overwintering season and following a 15-year downward trend, the total area in Mexico occupied by the eastern North American population of overwintering monarch butterflies reached an all-time low. Despite an increase, it remained low in 2010-2011. 2. Although the data set is small, the decline in abundance is statistically significant using both linear and exponential regression models. 3. Three factors appear to have contributed to reduce monarch abundance: degradation of the forest in the overwintering areas; the loss of breeding habitat in the United States due to the expansion ofGM herbicide-resistant crops, with consequent loss of milkweed host plants, as well as continued land development; and severe weather. 4. This decline calls into question the long-term survival of the monarchs' migratory phenomenon

Requirements for Radial Migration: How does the migrating fraction depend on stellar velocity dispersion?

NASA Astrophysics Data System (ADS)

Tolfree, Kathryne; Wyse, R. F.

2014-01-01

Radial migration is a way to rearrange the orbital angular momentum of stars in an spiral disk without inducing kinematic heating. When radial migration is very efficient, a large fraction of disk stars experience significant changes in their orbital angular momenta in a short period of time. Such scenarios have strong implications for the chemical and kinematic evolution of disk galaxies. We have undertaken an investigation of the physical dependencies of the efficiency of radial migration on stellar kinematics and spiral structure by deriving the fraction of stars that can migrate radially given certain conditions. In order for a star in a spiral disk to migrate radially, it must first be “captured" in a family of resonant orbits near the radius of corotation with a spiral pattern. Thus far, the only analytic criterion for capture has been for stars in circular orbits. We present the capture criterion for stars on non-circular orbits in a disk galaxy. We then use our analytically derived capture criteria to model the radial distribution of the captured fraction in an exponential disk with a flat rotation curve as well as the dependence of the total captured fraction in the disk on the radial component of the stellar velocity dispersion (σR) and the amplitude of the spiral perturbation to the underlying potential at corotation (|Φs|CR). We find that the captured fraction goes as Exp[-σR2/|Φs|CR].

Requirements for Radial Migration: How Does the Migrating Fraction Depend on Stellar Velocity Dispersion?

NASA Astrophysics Data System (ADS)

Tolfree, K. J. D.; Wyse, R. F. G.

2014-03-01

Radial migration is a mechanism that can rearrange the orbital angular momentum of stars in a spiral disk without inducing kinematic heating. When radial migration is very efficient, a large fraction of disk stars experience significant changes in their orbital angular momenta over a short period of time. Such scenarios have strong implications for the chemical and kinematic evolution of disk galaxies. We have undertaken an investigation of the physical dependencies of the efficiency of radial migration on stellar kinematics and spiral structure by deriving the fraction of stars that can migrate radially. In order for a star in a spiral disk to migrate radially, it must first be “captured” in a family of resonant orbits near the radius of corotation with a transient spiral pattern. To date, the only analytic criterion for capture has been for stars in circular orbits. We present the capture criterion for disk stars on non-circular orbits. We then use our analytically derived capture criterion to model the radial distribution of the captured fraction in an exponential disk with a flat rotation curve. Further, we derive the dependence of the total captured fraction in the disk on the radial component of the stellar velocity dispersion (σR) and the amplitude of the spiral perturbation to the underlying potential evaluated at corotation (|Φs|CR). We find that within an annulus centered around corotation where σR is constant, the captured fraction goes as e-σR2/|Φs|CR.

Star Formation Rate Distribution in the Galaxy NGC 1232

NASA Astrophysics Data System (ADS)

Araújo de Souza, Alexandre; Martins, Lucimara P.; Rodríguez-Ardila, Alberto; Fraga, Luciano

2018-06-01

NGC 1232 is a face-on spiral galaxy and a great laboratory for the study of star formation due to its proximity. We obtained high spatial resolution Hα images of this galaxy, with adaptive optics, using the SAM instrument at the SOAR telescope, and used these images to study its H II regions. These observations allowed us to produce the most complete H II region catalog for it to date, with a total of 976 sources. This doubles the number of H II regions previously found for this object. We used these data to construct the H II luminosity function, and obtained a power-law index lower than the typical values found for Sc galaxies. This shallower slope is related to the presence of a significant number of high-luminosity H II regions (log L > 39 dex). We also constructed the size distribution function, verifying that, as for most galaxies, NGC 1232 follows an exponential law. We also used the Hα luminosity to calculate the star formation rate. An extremely interesting fact about this galaxy is that X-ray diffuse observations suggest that NGC 1232 recently suffered a collision with a dwarf galaxy. We found an absence of star formation around the region where the X-ray emission is more intense, which we interpret as a star formation quenching due to the collision. Along with that, we found an excess of star-forming regions in the northeast part of the galaxy, where the X-ray emission is less intense.

Rotational Velocity Determinations for 118 δ Scuti Variables

NASA Astrophysics Data System (ADS)

Bush, Tabitha C.; Hintz, Eric G.

2008-09-01

A calibration method is presented for the determination of projected rotational velocities of 118 δ Scuti variables from FWHM measurements of metal lines near 4500 Å. The calibration relation used was derived from measurements of 29 stars. Of the 44 stars brighter than 8th magnitude and north of -1° declination which did not have values in the Rodríguez catalog (Rodríguez, E., López González, M. J., & López de Coca, P. 2000, A&AS, 144, 469) we present values for 38. In addition, we present new projected rotational velocity, vsin i, values for 10 stars south of -1° or fainter than 8th magnitude for a total of 48 vsin i values for stars with no previously published values.

VizieR Online Data Catalog: Outer satellites occultation predictions (Gomes-Junior+, 2016)

NASA Astrophysics Data System (ADS)

Gomes-Junior, A. R.; Assafin, M.; Beauvalet, L.; Desmars, J.; Vieira-Martins, R.; Camargo, J. I. B.; Morgado, B. E.; Braga-Ribas, F.

2016-07-01

Tables contain the day of the year and UTC central instant of the prediction; right ascension and declination of the occulted star - at the central instant of the occultation (corrected by proper motions); C/A: apparent geocentric distance between the satellite and the star (a.k.a. the distance between the shadow and the center of the Earth) at the moment of the geocentric closest approach, in arcseconds; P/A: the satellite position angle with respect to the occulted star at C/A, in degrees (zero at north of the star, increasing clockwise); v: relative velocity of event in km/s: positive = prograde, negative = retrograde; D: Geocentric distance to the occulting object in AU; R*: normalized UCAC4 magnitude in the R-band to a common shadow of 20km/s by the relationship R*=RUCAC4+2.5xlog(velocity/(20km/s)), the value 20km/s is typical of events around the opposition; long: east longitude of subplanet point in degrees, positive towards east, at the instant of the geocentric closest approach; LST: UT + long: local solar time at subplanet point, hh:mm; pmra and pmdec: proper motions in right ascension and declination, respectively (mas/year). For more detailed information about the definition and use of these stellar occultation geometric elements see Assafin et al. (2010, Cat. J/A+A/515/A32). (2 data files).

Sea Star Wasting Disease in the Keystone Predator Pisaster ochraceus in Oregon: Insights into Differential Population Impacts, Recovery, Predation Rate, and Temperature Effects from Long-Term Research.

PubMed

Menge, Bruce A; Cerny-Chipman, Elizabeth B; Johnson, Angela; Sullivan, Jenna; Gravem, Sarah; Chan, Francis

2016-01-01

Sea star wasting disease (SSWD) first appeared in Oregon in April 2014, and by June had spread to most of the coast. Although delayed compared to areas to the north and south, SSWD was initially most intense in north and central Oregon and spread southward. Up to 90% of individuals showed signs of disease from June-August 2014. In rocky intertidal habitats, populations of the dominant sea star Pisaster ochraceus were rapidly depleted, with magnitudes of decline in density among sites ranging from -2x to -9x (59 to 84%) and of biomass from -2.6x to -15.8x (60 to 90%) by September 2014. The frequency of symptomatic individuals declined over winter and persisted at a low rate through the spring and summer 2015 (~5-15%, at most sites) and into fall 2015. Disease expression included six symptoms: initially with twisting arms, then deflation and/or lesions, lost arms, losing grip on substrate, and final disintegration. SSWD was disproportionally higher in orange individuals, and higher in tidepools. Although historically P. ochraceus recruitment has been low, from fall 2014 to spring 2015 an unprecedented surge of sea star recruitment occurred at all sites, ranging from ~7x to 300x greater than in 2014. The loss of adult and juvenile individuals in 2014 led to a dramatic decline in predation rate on mussels compared to the previous two decades. A proximate cause of wasting was likely the "Sea Star associated Densovirus" (SSaDV), but the ultimate factors triggering the epidemic, if any, remain unclear. Although warm temperature has been proposed as a possible trigger, SSWD in Oregon populations increased with cool temperatures. Since P. ochraceus is a keystone predator that can strongly influence the biodiversity and community structure of the intertidal community, major community-level responses to the disease are expected. However, predicting the specific impacts and time course of change across west coast meta-communities is difficult, suggesting the need for detailed coast-wide investigation of the effects of this outbreak.

Sea Star Wasting Disease in the Keystone Predator Pisaster ochraceus in Oregon: Insights into Differential Population Impacts, Recovery, Predation Rate, and Temperature Effects from Long-Term Research

PubMed Central

Menge, Bruce A.; Cerny-Chipman, Elizabeth B.; Johnson, Angela; Sullivan, Jenna; Gravem, Sarah; Chan, Francis

2016-01-01

Sea star wasting disease (SSWD) first appeared in Oregon in April 2014, and by June had spread to most of the coast. Although delayed compared to areas to the north and south, SSWD was initially most intense in north and central Oregon and spread southward. Up to 90% of individuals showed signs of disease from June-August 2014. In rocky intertidal habitats, populations of the dominant sea star Pisaster ochraceus were rapidly depleted, with magnitudes of decline in density among sites ranging from -2x to -9x (59 to 84%) and of biomass from -2.6x to -15.8x (60 to 90%) by September 2014. The frequency of symptomatic individuals declined over winter and persisted at a low rate through the spring and summer 2015 (~5–15%, at most sites) and into fall 2015. Disease expression included six symptoms: initially with twisting arms, then deflation and/or lesions, lost arms, losing grip on substrate, and final disintegration. SSWD was disproportionally higher in orange individuals, and higher in tidepools. Although historically P. ochraceus recruitment has been low, from fall 2014 to spring 2015 an unprecedented surge of sea star recruitment occurred at all sites, ranging from ~7x to 300x greater than in 2014. The loss of adult and juvenile individuals in 2014 led to a dramatic decline in predation rate on mussels compared to the previous two decades. A proximate cause of wasting was likely the “Sea Star associated Densovirus” (SSaDV), but the ultimate factors triggering the epidemic, if any, remain unclear. Although warm temperature has been proposed as a possible trigger, SSWD in Oregon populations increased with cool temperatures. Since P. ochraceus is a keystone predator that can strongly influence the biodiversity and community structure of the intertidal community, major community-level responses to the disease are expected. However, predicting the specific impacts and time course of change across west coast meta-communities is difficult, suggesting the need for detailed coast-wide investigation of the effects of this outbreak. PMID:27144391

Socio-Economic Instability and the Scaling of Energy Use with Population Size

PubMed Central

DeLong, John P.; Burger, Oskar

2015-01-01

The size of the human population is relevant to the development of a sustainable world, yet the forces setting growth or declines in the human population are poorly understood. Generally, population growth rates depend on whether new individuals compete for the same energy (leading to Malthusian or density-dependent growth) or help to generate new energy (leading to exponential and super-exponential growth). It has been hypothesized that exponential and super-exponential growth in humans has resulted from carrying capacity, which is in part determined by energy availability, keeping pace with or exceeding the rate of population growth. We evaluated the relationship between energy use and population size for countries with long records of both and the world as a whole to assess whether energy yields are consistent with the idea of an increasing carrying capacity. We find that on average energy use has indeed kept pace with population size over long time periods. We also show, however, that the energy-population scaling exponent plummets during, and its temporal variability increases preceding, periods of social, political, technological, and environmental change. We suggest that efforts to increase the reliability of future energy yields may be essential for stabilizing both population growth and the global socio-economic system. PMID:26091499

Socio-Economic Instability and the Scaling of Energy Use with Population Size.

PubMed

DeLong, John P; Burger, Oskar

2015-01-01

The size of the human population is relevant to the development of a sustainable world, yet the forces setting growth or declines in the human population are poorly understood. Generally, population growth rates depend on whether new individuals compete for the same energy (leading to Malthusian or density-dependent growth) or help to generate new energy (leading to exponential and super-exponential growth). It has been hypothesized that exponential and super-exponential growth in humans has resulted from carrying capacity, which is in part determined by energy availability, keeping pace with or exceeding the rate of population growth. We evaluated the relationship between energy use and population size for countries with long records of both and the world as a whole to assess whether energy yields are consistent with the idea of an increasing carrying capacity. We find that on average energy use has indeed kept pace with population size over long time periods. We also show, however, that the energy-population scaling exponent plummets during, and its temporal variability increases preceding, periods of social, political, technological, and environmental change. We suggest that efforts to increase the reliability of future energy yields may be essential for stabilizing both population growth and the global socio-economic system.

Angular Momentum Evolution in Young Low Mass Stars

NASA Astrophysics Data System (ADS)

Pinzón, G.; de La Reza, R.

2006-06-01

During the last decades, the study of rotation in young low mass stars has been one of the more active areas in the field of stellar evolution. Many theoretical efforts have been made to understand the angular momentum evolution and our picture now, reveals the main role of the stellar magnetic field in all pre-main sequence stage (Ghosh & Lamb 1979, ApJ, 234, 296; Cameron & Campbell 1993, A&A, 274, 309; Cameron & Campbell 1995, A&A, 298, 133; Kúker, Henning, & Rúdiger 2003, ApJ, 589, 397; Matt & Pudritz 2005, MNRAS, 356, 167). The mean rotation of most of the cool low mass stars remains roughly constant during the T Tauri stage. This can be explained by the disc locking scenario. This paradigm suggest that star start out as CTTS with periods of 4-14 days, perhaps locked to their disc, and that this disc is eventually lost mainly by accretion. At the current time, it is not clear that this is true for all low mass stars. Some authors have questioned its validity for stars less massive than 0.5 solar masses. Although the reality may eventually turn out to be considerably more complex, a simple consideration of the effects of and limits on disc locking of young low mass stars seems necessary.We have investigated the exchange of angular momentum between a low mass star and an accretion disc during the Hayashi Track (Pinzón, Kúker, & de la Reza 2005, in preparation) and also along the first 100Myr of stellar evolution. The model incorporates changes in the star's moment of inertia, magnetic field strength (Elstner & Rúdiger 2000, A&A, 358, 612), angular momentum loss by a magnetic wind and an exponential decrease of the accretion rate. The lifetime of the accretion disc is a free parameter in our model. The resulting rotation rates are in agreement with observed vsin and photometric periods for young stars belonging to co-moving groups and open young clusters.

The Gas in Virgo’s “Red and Dead” Dwarf Elliptical Galaxies

NASA Astrophysics Data System (ADS)

Hallenbeck, Gregory L.; Koopmann, Rebecca A.

2017-01-01

As star-forming dwarf irregulars and faint spirals fall onto a cluster, their gas content is easily and quickly removed by ram-pressure stripping or other cluster forces. Residual signs of star formation cease within 100 Myr, and only after approximately 1 Gyr do their optical features transition to elliptical.Despite this, ALFALFA has uncovered a population of three “red and dead” dwarf ellipticals in the Virgo Cluster which still have detectable reservoirs of HI. These dwarf ellipticals are extremely gas-rich—as gas-rich as the cluster’s star-forming dwarf irregulars (Hallenbeck et al. 2012). Where does this gas come from? We consider two possibilities. First, that the gas is recently acquired, and has not yet had time to form stars. Second, that the gas is primordial, and has been disrupted from being able to form stars during the current epoch.We present deep optical (using CFHT and KPNO) and HI (Arecibo and VLA) observations of this sample to demonstrate that this gas is primordial. These observations show that all three galaxies have exponentially decreasing profiles characteristic of dwarf ellipticals and that their rotation velocities are extremely low. However, like more massive elliptical galaxies with HI, these dwarf galaxies show irregular optical morphology. For one target, VCC 190, we additionally observe an HI tail consistent with a recent interaction with the massive spiral galaxy NGC 4224.

Neutron stars and white dwarfs in galactic halos

NASA Technical Reports Server (NTRS)

Ryu, Dongsu; Olive, Keith A.; Silk, Joseph

1989-01-01

The possibility that galactic halos are composed of stellar remnants such as neutron stars and white dwarfs is discussed. On the basis of a simple model for the evolution of galactic halos, researchers follow the history of halo matter, luminosity, and metal and helium abundances. They assume conventional yields for helium and the heavier elements. By comparing with the observational constraints, which may be considered as fairly conservative, it is found that, for an exponentially decreasing star formation rate (SFR) with e-folding time tau, only values between 6 x 10(8) less than similar to tau less than similar to 2 x 10(9) years are allowed together with a very limited range of masses for the initial mass function (IMF). Star formation is allowed for 2 solar mass less than similar to m less than similar to 8 solar mass if tau = 2 x 10(9) years, and for 4 solar mass less than similar to m less than similar to 6 solar mass if tau = 10(9) years. For tau = 6 x 10(8) years, the lower and upper mass limits merge to similar to 5 solar mass. Researchers conclude that, even though the possibility of neutron stars as halo matter may be ruled out, that of white dwarfs may still be a viable hypothesis, though with very stringent constraints on allowed parameters, that merits further consideration.

The EDGE-CALIFA Survey: Interferometric Observations of 126 Galaxies with CARMA

NASA Astrophysics Data System (ADS)

Bolatto, Alberto D.; Wong, Tony; Utomo, Dyas; Blitz, Leo; Vogel, Stuart N.; Sánchez, Sebastián F.; Barrera-Ballesteros, Jorge; Cao, Yixian; Colombo, Dario; Dannerbauer, Helmut; García-Benito, Rubén; Herrera-Camus, Rodrigo; Husemann, Bernd; Kalinova, Veselina; Leroy, Adam K.; Leung, Gigi; Levy, Rebecca C.; Mast, Damián; Ostriker, Eve; Rosolowsky, Erik; Sandstrom, Karin M.; Teuben, Peter; van de Ven, Glenn; Walter, Fabian

2017-09-01

We present interferometric CO observations, made with the Combined Array for Millimeter-wave Astronomy (CARMA) interferometer, of galaxies from the Extragalactic Database for Galaxy Evolution survey (EDGE). These galaxies are selected from the Calar Alto Legacy Integral Field Area (CALIFA) sample, mapped with optical integral field spectroscopy. EDGE provides good-quality CO data (3σ sensitivity {{{Σ }}}{mol}˜ 11 {M}⊙ {{pc}}-2 before inclination correction, resolution ˜1.4 kpc) for 126 galaxies, constituting the largest interferometric CO survey of galaxies in the nearby universe. We describe the survey and data characteristics and products, then present initial science results. We find that the exponential scale lengths of the molecular, stellar, and star-forming disks are approximately equal, and galaxies that are more compact in molecular gas than in stars tend to show signs of interaction. We characterize the molecular-to-stellar ratio as a function of Hubble type and stellar mass and present preliminary results on the resolved relations between the molecular gas, stars, and star-formation rate. We then discuss the dependence of the resolved molecular depletion time on stellar surface density, nebular extinction, and gas metallicity. EDGE provides a key data set to address outstanding topics regarding gas and its role in star formation and galaxy evolution, which will be publicly available on completion of the quality assessment.

Removing the tree-ring width biological trend using expected basal area increment

Treesearch

Franco Biondi; Fares Qeadan

2008-01-01

One of the main elements of dendrochronological standardization is the removal of the biological trend, i.e., the progressive decline of ring width along a cross-sectional radius that is mostly caused by the corresponding increase in stem diameter over time. A very common option for removing this biological trend is to fit a modified negative exponential curve to the...

Some dynamics of spread and infection by aeciospores of Puccinia punctiformis, a biological control pathogen of Cirsium arvense

USDA-ARS?s Scientific Manuscript database

In this study, effective spread of aeciospores from an area source in a field was fit to an exponential decline model with a predicted maximum distance of spread of 30 m from the area source to observed uredinia on one leaf of one C. arvense shoot. However, the greatest number of shoots bearing leav...

Infrared Detection of Very Low Mass Stars.

NASA Astrophysics Data System (ADS)

Probst, Ronald George

We present in this thesis a review of very-low -mass ((TURN)0.1 M(,0)) star research, and results of two observational programs directed at the photometric detection of low mass binary companions in the infrared. Present theoretical desiderata are model atmospheres for very cool dwarf stars and determination of the minimum protostellar mass with all relevant physics included. Luminosities for these stars are well determined, but the effective temperature scale is uncertain and abundance analyses are lacking. Masses are known for very few, and with large relative errors. The luminosity function for M(,v) > 13 is very uncertain. Astrometric methods provide at present the only means of detecting very low mass objects in significant numbers. Completion of the near-star parallax catalogue and measurement of additional low-mass binaries are important observational programs. The potential of photometric selection of red dwarf binaries is explored in Chapter II. Separation of binaries from single stars by color anomalies alone is found impractical. Detection by overluminosity in the HR diagram is hampered by the intrinsic spread of the field star population. However, we find that application of both kinematic and photometric criteria allows binaries to be detected with only moderate contamination by single stars; we discuss several binary suspects selected in this way. Our approach uses an infrared bandpass to provide temperature resolution in the color baseline, and we present JHK photometry for 60 stars, including recent parallax stars with M(,v)>14. We examine the status of the least luminous stars; there is no conclusive evidence that they are not hydrogen-burning objects. Chapter III presents a survey of (TURN)100 white dwarfs at 2 (mu) for infrared excess indicative of low -luminosity cool companions. White dwarf-red dwarf composites are detectable by infared color anomalies down to M(,v)(TURN)21 for the red dwarf component, and our survey is complete to absolute magnitudes on this level. Candidates for astrometric mass determination are suggested. Several stars are found to be composites containing an accretion disk or a hot subdwarf + dK secondary. We find very few new low-luminosity companions to normal white dwarfs. This does not appear to be a selection effect, nor is there reason to believe that all parent systems have been altered or destroyed in the mass loss phase. Our strongly negative result constrains the luminosity function for red dwarf companions to decline steeply past M(,v) (DBLTURN) 13. This may reflect a general decline in the initial mass function for star formation, or a failure of systems with large mass ratios to form or remain bound in the parent star-forming regions.

Condition index monitoring supports conservation priorities for the protection of threatened grass-finch populations

PubMed Central

French, Kristine; Legge, Sarah; Astheimer, Lee; Garnett, Stephen

2015-01-01

Abstract Conservation agencies are often faced with the difficult task of prioritizing what recovery actions receive support. With the number of species under threat of decline growing globally, research that informs conservation priorities is greatly needed. The relative vulnerability of cryptic or nomadic species is often uncertain, because populations are difficult to monitor and local populations often seem stable in the short term. This uncertainty can lead to inaction when populations are in need of protection. We tested the feasibility of using differences in condition indices as an indication of population vulnerability to decline for related threatened Australian finch sub-species. The Gouldian finch represents a relatively well-studied endangered species, which has a seasonal and site-specific pattern of condition index variation that differs from the closely related non-declining long-tailed finch. We used Gouldian and long-tailed finch condition variation as a model to compare with lesser studied, threatened star and black-throated finches. We compared body condition (fat and muscle scores), haematocrit and stress levels (corticosterone) among populations, seasons and years to determine whether lesser studied finch populations matched the model of an endangered species or a non-declining species. While vulnerable finch populations often had lower muscle and higher fat and corticosterone concentrations during moult (seasonal pattern similar to Gouldian finches), haematocrit values did not differ among populations in a predictable way. Star and black-throated finch populations, which were predicted to be vulnerable to decline, showed evidence of poor condition during moult, supporting their status as vulnerable. Our findings highlight how measures of condition can provide insight into the relative vulnerability of animal and plant populations to decline and will allow the prioritization of efforts towards the populations most likely to be in jeopardy of extinction. PMID:27293710

Condition index monitoring supports conservation priorities for the protection of threatened grass-finch populations.

PubMed

Maute, Kimberly; French, Kristine; Legge, Sarah; Astheimer, Lee; Garnett, Stephen

2015-01-01

Conservation agencies are often faced with the difficult task of prioritizing what recovery actions receive support. With the number of species under threat of decline growing globally, research that informs conservation priorities is greatly needed. The relative vulnerability of cryptic or nomadic species is often uncertain, because populations are difficult to monitor and local populations often seem stable in the short term. This uncertainty can lead to inaction when populations are in need of protection. We tested the feasibility of using differences in condition indices as an indication of population vulnerability to decline for related threatened Australian finch sub-species. The Gouldian finch represents a relatively well-studied endangered species, which has a seasonal and site-specific pattern of condition index variation that differs from the closely related non-declining long-tailed finch. We used Gouldian and long-tailed finch condition variation as a model to compare with lesser studied, threatened star and black-throated finches. We compared body condition (fat and muscle scores), haematocrit and stress levels (corticosterone) among populations, seasons and years to determine whether lesser studied finch populations matched the model of an endangered species or a non-declining species. While vulnerable finch populations often had lower muscle and higher fat and corticosterone concentrations during moult (seasonal pattern similar to Gouldian finches), haematocrit values did not differ among populations in a predictable way. Star and black-throated finch populations, which were predicted to be vulnerable to decline, showed evidence of poor condition during moult, supporting their status as vulnerable. Our findings highlight how measures of condition can provide insight into the relative vulnerability of animal and plant populations to decline and will allow the prioritization of efforts towards the populations most likely to be in jeopardy of extinction.

Calculating Formulas of Coefficient and Mean Neutron Exposure in the Exponential Expression of Neutron Exposure Distribution

NASA Astrophysics Data System (ADS)

Zhang, F. H.; Zhou, G. D.; Ma, K.; Ma, W. J.; Cui, W. Y.; Zhang, B.

2015-11-01

Present studies have shown that, in the main stages of the development and evolution of asymptotic giant branch (AGB) star s-process models, the distributions of neutron exposures in the nucleosynthesis regions can all be expressed by an exponential function ({ρ_{AGB}}(τ) = C/{τ_0}exp ( - τ/{τ_0})) in the effective range of values. However, the specific expressions of the proportional coefficient C and the mean neutron exposure ({τ_0}) in the formula for different models are not completely determined in the related literatures. Through dissecting the basic solving method of the exponential distribution of neutron exposures, and systematically combing the solution procedure of exposure distribution for different stellar models, the general calculating formulas as well as their auxiliary equations for calculating C and ({τ_0}) are reduced. Given the discrete distribution of neutron exposures ({P_k}), i.e. the mass ratio of the materials which have exposed to neutrons for (k) ((k = 0, 1, 2 \\cdots )) times when reaching the final distribution with respect to the materials of the He intershell, (C = - {P_1}/ln R), and ({τ_0} = - Δ τ /ln R) can be obtained. Here, (R) expresses the probability that the materials can successively experience neutron irradiation for two times in the He intershell. For the convective nucleosynthesis model (including the Ulrich model and the ({}^{13}{C})-pocket convective burning model), (R) is just the overlap factor r, namely the mass ratio of the materials which can undergo two successive thermal pulses in the He intershell. And for the (^{13}{C})-pocket radiative burning model, (R = sumlimits_{k = 1}^∞ {{P_k}} ). This set of formulas practically give the corresponding relationship between C or ({τ_0}) and the model parameters. The results of this study effectively solve the problem of analytically calculating the distribution of neutron exposures in the low-mass AGB star s-process nucleosynthesis model of (^{13}{C})-pocket radiative burning.

Identification of stars in a J1744.0 star catalogue Yixiangkaocheng

NASA Astrophysics Data System (ADS)

Ahn, S.-H.

2012-05-01

The stars in the Chinese star catalogue, Yixiangkaocheng, which were edited by the Jesuit astronomer Kögler in AD 1744 and published in AD 1756, are identified with their counterparts in the Hipparcos catalogue. The equinox of the catalogue is confirmed to be J1744.0. By considering the precession of equinox, proper motions and nutation, the star closest to the location of each star in Yixiangkaocheng, having a proper magnitude, is selected as the corresponding identified star. I identified 2848 stars and 13 nebulosities out of 3083 objects in Yixiangkaocheng, and so the identification rate reached 92.80 per cent. I find that the magnitude classification system in Yixiangkaocheng agrees with the modern magnitude system. The catalogue includes dim stars, whose visual magnitudes are larger than 7, but most of these stars have Flamsteed designations. I find that the stars whose declination is lower than -30° have relatively larger offsets and different systematic behaviour from other stars. This indicates that there might be two different sources of stars in Yixiangkaocheng. In particular, I find that μ1 Sco and γ1 Sgr approximately mark the boundary between two different source catalogues. The observer's location, as estimated from these facts, agrees with the latitude of Greenwich where Flamsteed made his observations. The positional offsets between the Yixiangkaocheng stars and the Hipparcos stars are 0.6 arcmin, which implies that the source catalogue of stars with δ > -30° must have come from telescopic observations. Nebulosities in Yixiangkaocheng are identified with a few double stars, o Cet (the variable star, Mira), the Andromeda galaxy, ω Cen and NGC6231. These entities are associated with listings in Halley's Catalogue of the Southern Stars of AD 1679 as well as Flamsteed's catalogue of AD 1690.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Forbes, G.B.; Drenick, E.J.

An analysis of the change in total body nitrogen during fasting shows that it declines exponentially, a small fraction being lost rapidly (t/sub 1/2/ of a few days), and the remainder being lost slowly (t/sub 1/2/ of many months). The obese faster loses N, and weight, at a slower relative rate than the nonobese; and the ratio of N loss to weight loss during an extended fast is inversely related to body fat content, being about 20 g/kg in the nonobese and about 10 g/kg in those with body fat burdens of 50 kg or more. The loss of bodymore » N on a low protein-calorie adequate diet can also be described in exponential terms, and this function allows an estimate to be made of the N requirement.« less

Ultraviolet spectrophotometry and optical and infrared photometry of the old nova GK Persei

NASA Technical Reports Server (NTRS)

Wu, Chi-Chao; Holm, Albert V.; Panek, Robert J.; Raymond, John C.; Hartmann, Lee W.; Swank, Jean H.

1989-01-01

IUE observations in the 1150-3250-A region were obtained of GK Per during the rise, at the maximum, and during the decline of the 2.5-mag optical outburst in 1981. The results support previous predictions for the interaction of an accretion disk with the magnetic field of an accretion star. The luminosity at minimum is found to be 2.3 solar luminosities, with 1/3 of this being attributed to the cool secondary star.

Documentation for the machine readable version of the Yale Catalogue of the Positions and Proper Motions of Stars between Declinations -60 deg and -70 deg (Fallon 1983)

NASA Technical Reports Server (NTRS)

Roman, N. G.; Warren, W. H., Jr.

1984-01-01

The machine-readable, character-coded version of the catalog, as it is currently being distributed from the Astronomical Data Center(ADC), is described. The format and data provided in the magnetic tape version differ somewhat from those of the published catalog, which was also produced from a tape prepared at the ADC. The primary catalog data are positions and proper motions (equinox 1950.0) for 14597 stars.

Cape Photographic Durchmusterung, volume 1

NASA Technical Reports Server (NTRS)

1993-01-01

The Cape Photographic Durchmusterung (CPD Gill and Kapteyn 1895-1900) is a photographic survey of southern stars in the declination range -18 to -90 degrees. This volume covers the declination range -18 through -37 degrees. Positions are given for the 1875 equinox. The summary of the positional uncertainties quoted in the third volume of the published catalog gives +/- 0.28 sec (R.A.) +/- 0.044 arcmin (Dec.) for zones -18 to -57 degrees. The probable error of a photographic magnitude as determined by combining results for different magnitudes and weighting proportionately according to the numbers of stars in each class of magnitude is given as +/- 0.055 mag. From an analysis of the taint magnitude limits on the plates discussed in the third volume introduction, the catalog as a whole can be considered complete to photographic magnitude 9.2 but it is stated that it will be found practically complete in or near the Milky Way, to magnitude 9.5.

Methodological Considerations When Quantifying High-Intensity Efforts in Team Sport Using Global Positioning System Technology.

PubMed

Varley, Matthew C; Jaspers, Arne; Helsen, Werner F; Malone, James J

2017-09-01

Sprints and accelerations are popular performance indicators in applied sport. The methods used to define these efforts using athlete-tracking technology could affect the number of efforts reported. This study aimed to determine the influence of different techniques and settings for detecting high-intensity efforts using global positioning system (GPS) data. Velocity and acceleration data from a professional soccer match were recorded via 10-Hz GPS. Velocity data were filtered using either a median or an exponential filter. Acceleration data were derived from velocity data over a 0.2-s time interval (with and without an exponential filter applied) and a 0.3-second time interval. High-speed-running (≥4.17 m/s 2 ), sprint (≥7.00 m/s 2 ), and acceleration (≥2.78 m/s 2 ) efforts were then identified using minimum-effort durations (0.1-0.9 s) to assess differences in the total number of efforts reported. Different velocity-filtering methods resulted in small to moderate differences (effect size [ES] 0.28-1.09) in the number of high-speed-running and sprint efforts detected when minimum duration was <0.5 s and small to very large differences (ES -5.69 to 0.26) in the number of accelerations when minimum duration was <0.7 s. There was an exponential decline in the number of all efforts as minimum duration increased, regardless of filtering method, with the largest declines in acceleration efforts. Filtering techniques and minimum durations substantially affect the number of high-speed-running, sprint, and acceleration efforts detected with GPS. Changes to how high-intensity efforts are defined affect reported data. Therefore, consistency in data processing is advised.

Rossby Wave Instability in Astrophysical Disks

NASA Astrophysics Data System (ADS)

Lovelace, Richard; Li, Hui

2014-10-01

A brief review is given of the Rossby wave instability in astrophysical disks. In non-self-gravitating discs, around for example a newly forming stars, the instability can be triggered by an axisymmetric bump at some radius r0 in the disk surface mass-density. It gives rise to exponentially growing non-axisymmetric perturbation (proportional to Exp[im ϕ], m = 1,2,...) in the vicinity of r0 consisting of anticyclonic vortices. These vortices are regions of high pressure and consequently act to trap dust particles which in turn can facilitate planetesimal growth in protoplanetary disks. The Rossby vortices in the disks around stars and black holes may cause the observed quasi-periodic modulations of the disk's thermal emission. Stirling Colgate's long standing interest in all types of vortices - particularly tornados - had an important part in stimulating the research on the Rossby wave instability.

Yellow supergiants in open clusters

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sowell, J.R.

1986-01-01

Superluminous giant stars (SLGs) have been reported in young globular clusters in the Large Magellanic Cloud (LMC). These stars appear to be in the post-asymptotic-giant-branch phase of evolution. This program was an investigation of galactic SLG candidates in open clusters, which are more like the LMC young globular clusters. These were chosen because luminosity, mass, and age determinations can be made for members since cluster distances and interstellar reddenings are known. Color magnitude diagrams were searched for candidates, using the same selection criteria as for SLGs in the LMC. Classification spectra were obtained of 115 program stars from McGraw-Hill Observatorymore » and of 68 stars from Cerro Tololo Inter-American Observatory Chile. These stars were visually classified on the MK system using spectral scans of standard stars taken at the respective observations. Published information was combined with this program's data for 83 stars in 30 clusters. Membership probabilities were assigned to these stars, and the clusters were analyzed according to age. It was seen that the intrinsically brightest supergiants are found in the youngest clusters. With increasing cluster age, the absolute luminosities attained by the supergiants decline. Also, it appears that the evolutionary tracks of luminosity class II stars are more similar to those of class I than of class III.« less

Star formation across cosmic time and its influence on galactic dynamics

NASA Astrophysics Data System (ADS)

Freundlich, Jonathan

2015-12-01

Observations show that ten billion years ago, galaxies formed their stars at rates up to twenty times higher than now. As stars are formed from cold molecular gas, a high star formation rate means a significant gas supply, and galaxies near the peak epoch of star formation are indeed much more gas-rich than nearby galaxies. Is the decline of the star formation rate mostly driven by the diminishing cold gas reservoir, or are the star formation processes also qualitatively different earlier in the history of the Universe? Ten billion years ago, young galaxies were clumpy and prone to violent gravitational instabilities, which may have contributed to their high star formation rate. Stars indeed form within giant, gravitationally-bound molecular clouds. But the earliest phases of star formation are still poorly understood. Some scenarii suggest the importance of interstellar filamentary structures as a first step towards core and star formation. How would their filamentary geometry affect pre-stellar cores? Feedback mechanisms related to stellar evolution also play an important role in regulating star formation, for example through powerful stellar winds and supernovae explosions which expel some of the gas and can even disturb the dark matter distribution in which each galaxy is assumed to be embedded. This PhD work focuses on three perspectives: (i) star formation near the peak epoch of star formation as seen from observations at sub-galactic scales; (ii) the formation of pre-stellar cores within the filamentary structures of the interstellar medium; and (iii) the effect of feedback processes resulting from star formation and evolution on the dark matter distribution.

Detection of the spatiotemporal trends of mercury in Lake Erie fish communities: a Bayesian approach.

PubMed

Azim, M Ekram; Kumarappah, Ananthavalli; Bhavsar, Satyendra P; Backus, Sean M; Arhonditsis, George

2011-03-15

The temporal trends of total mercury (THg) in four fish species in Lake Erie were evaluated based on 35 years of fish contaminant data. Our Bayesian statistical approach consists of three steps aiming to address different questions. First, we used the exponential and mixed-order decay models to assess the declining rates in four intensively sampled fish species, i.e., walleye (Stizostedion vitreum), yellow perch (Perca flavescens), smallmouth bass (Micropterus dolomieui), and white bass (Morone chrysops). Because the two models postulate monotonic decrease of the THg levels, we included first- and second-order random walk terms in our statistical formulations to accommodate nonmonotonic patterns in the data time series. Our analysis identified a recent increase in the THg concentrations, particularly after the mid-1990s. In the second step, we used double exponential models to quantify the relative magnitude of the THg trends depending on the type of data used (skinless-boneless fillet versus whole fish data) and the fish species examined. The observed THg concentrations were significantly higher in skinless boneless fillet than in whole fish portions, while the whole fish portions of walleye exhibited faster decline rates and slower rates of increase relative to the skinless boneless fillet data. Our analysis also shows lower decline rates and higher rates of increase in walleye relative to the other three fish species examined. The food web structural shifts induced by the invasive species (dreissenid mussels and round goby) may be associated with the recent THg trends in Lake Erie fish.

VizieR Online Data Catalog: G0-G3 main-sequence stars with V<15 (Lopez-Valdivia+, 2014)

NASA Astrophysics Data System (ADS)

Lopez-Valdivia, R.; Bertone, E.; Chavez, M.; Tapia-Schiavon, C.; Hernandez-Aguila, J. B.; Valdes, J. R.; Chavushyan, V.

2015-04-01

We selected in late 2008 a sample of stars from the Set of Identifications, Measurements, and Bibliography for Astronomical Data (SIMBAD) data base using the following criteria: (i) spectral type between G0 and G3; (ii) luminosity class V; (iii) visible magnitude V<15mag; (iv) declination δ>-10°. The selection resulted in about 1200 objects. We report here the results for 233 stars. We carried out the spectroscopic observations at the 2.12-m telescope of the Observatorio Astrofisico Guillermo Haro (Sonora, Mexico) between 2008 and 2013, with a Boller & Chivens spectrograph, equipped with a Versarray 1300x1340 CCD. (3 data files).

Lick Jupiter-Voyager reference star catalogue (Klemola, Morabito, and Taraji 1978): Documentation for the machine-readable version

NASA Technical Reports Server (NTRS)

Warren, Wayne H., Jr.

1990-01-01

The machine-readable version of the catalog, as it is currently being distributed from the Astronomical Data Center, is described. The catalog contains accurate equatorial coordinates for 4983 stars in a band of sky against which cameras of the Voyager spacecraft were pointed for observations in the region of Jupiter during the flyby. All of the reference stars are in the range 6 hr 00 min to 8 hr 04 min in right ascension (1950), declination zones +16 to +23 degrees, and 8 hr to 31 min to 8 hr 57 min, zones +08 to +14 degrees. Mean errors of the positions are about 0.4 sec.

On the theory of group generation of stars

NASA Technical Reports Server (NTRS)

Zhilyayev, B. Y.; Porfiryev, V. V.; Shulman, L. M.

1973-01-01

The hypothesis proposed is that topology of a rotating gaseous cloud can be variable in the contraction process. Due to rotation an originally spherical cloud is transformed into a toroidal body. The contraction of a thin torus is considered with different suppositions on cooling the gas. In the determined time the torus will become gravitationally unstable. The excitation of Jeans' waves is shown to result in the disintegration of the torus into fragments. The number of the fragments and their mass distributions are calculated. The proposed hypothesis on toroidal stages in stellar evolution can remove some difficulties in the theory of structure and evolution of stars, such as absence of limitary stars, distribution of rotation velocities of early-type stars, origin of poloidal magnetic fields and decline rotators with the magnetic axis orthogonal to the axis of rotation.

Balloon-borne observations of the development and vertical structure of the Antarctic ozone hole in 1986

NASA Technical Reports Server (NTRS)

Hofmann, D. J.; Harder, J. W.; Rolf, S. R.; Rosen, J. M.

1987-01-01

The vertical distribution of ozone measured at McMurdo Station, Antarctica using balloon-borne sensors on 33 occasions during November 6, 1986 - August 25, 1986 is described. These observations suggest a highly structured cavity confined to the 12-20 km altitude region. In the 17-19 km altitude range, the ozone volume mixing ratio declined from about 2 ppm at the end of August to about 0.5 ppm by mid-October. The average decay in this region can be described as exponential with a half life of about 25 days. While total ozone, as obtained from profile integration, declined only about 35 percent, the integrated ozone between 14 and 18 km declined more than 70 percent. Vertical ozone profiles in the vortex revealed unusual structure with major features from 1 to 5 km thick which had suffered ozone depletions as great as 90 percent.

The Tully-Fisher relation of the IRAS minisurvey galaxies

NASA Technical Reports Server (NTRS)

Van Driel, W.; Van Den Broek, A. C.; Baan, W. A.

1995-01-01

We investigated the possible influence on the Tully-Fisher relation of active massive star formation in IRAS galaxies, in order to estimate the contribution of star formation to their near-infrared luminosity. We observed 60 galaxies from the infrared complete so-called IRAS Minisurvey sample in the 21 cm H1 line at Arecibo, determined the near-infrared (H-band) Tully-Fisher relation for the 36 objects in the sample we judged to be usable for this purpose, and compared this relation with that of optically selected normal galaxies. The results show no significant enhancement of the near-infrared luminosities of the IRAS Minisurvey galaxies compared to those of the optically selected normal glaxies. From these results we inferred that in the minisurvey galaxies the average contribution of the active massive star formation to the total near-infrared luminosity is less and that exponential decay times for the starbursts occurring in the Minisurvey galaxies are of the order of 10 Myr. The Tully-Fisher relation shows one exceptional galaxy (IRAS 03565+2139) with an about 25 times higher luminosity than average for its rotational velocity.

The white dwarf luminosity function - A possible probe of the galactic halo

NASA Technical Reports Server (NTRS)

Tamanaha, Christopher M.; Silk, Joseph; Wood, M. A.; Winget, D. E.

1990-01-01

The dynamically inferred dark halo mass density, amounting to above 0.01 solar masses/cu pc at the sun's Galactocentric radius, can be composed of faint white dwarfs provided that the halo formed in a sufficiently early burst of star formation. The model is constrained by the observed disk white dwarf luminosity function which falls off below log (L/solar L) = -4.4, due to the onset of star formation in the disk. By using a narrow range for the initial mass function and an exponentially decaying halo star formation rate with an e-folding time equal to the free-fall time, all the halo dark matter is allowed to be in cool white dwarfs which lie beyond the falloff in the disk luminosity function. Although it is unlikely that all the dark matter is in these dim white dwarfs, a definite signature in the low-luminosity end of the white dwarf luminosity function is predicted even if they comprise only 1 percent of the dark matter. Current CCD surveys should answer the question of the existence of this population within the next few years.

The Fate of Gas-rich Satellites in Clusters

NASA Astrophysics Data System (ADS)

Safarzadeh, Mohammadtaher; Scannapieco, Evan

2017-11-01

We investigate the stellar mass-loss of gas-rich galaxies falling into clusters due to the change in the gravitational potential caused by the ram-pressure-stripping of their gas. We model the satellites with exponential stellar and gas disk profiles, assume rapid ram-pressure-stripping, and follow the stellar orbits in the shocked potential. Due to the change of the potential, the stars move from circular orbits to elliptical orbits with apocenters that are often outside the tidal radius, causing those stars to be stripped. We explore the impact of the redshift of infall, gas fraction, satellite halo mass, and cluster mass on this process. The puffing of the satellites makes them appear as ultra-diffuse galaxies, and the stripped stars contribute to the intracluster light. Our results show that these effects are most significant for less massive satellites, which have larger gas fractions when they are accreted into clusters. The preferential destruction of low-mass systems causes the red fraction of cluster galaxies to be smaller at lower masses, an observation that is otherwise difficult to explain.

Progress and Challenges in SPH Simulations of Disk Galaxy Formation: The Combined Role of Resolution and the Star Formation Density Threshold

NASA Astrophysics Data System (ADS)

Mayer, L.

2012-07-01

We review progress in cosmological SPH simulations of disk galaxy formation. We discuss the role of numerical resolution and sub-grid recipes of star formation and feedback from supernovae, higlighting the important role of a high star formation density threshold comparable to that of star forming molecular gas phase. Two recent succesfull examples, in simulations of the formation of gas-rich bulgeless dwarf galaxies and in simulations of late-type spirals (the ERIS simulations), are presented and discussed. In the ERIS simulations, already in the progenitors at z = 3 the resolution is above the threshold indicated by previous idealized numerical experiments as necessary to minimize numerical angular momentum loss (Kaufmann et al. 2007). A high star formation density threshold maintains an inhomogeneous interstellar medium, where star formation is clustered, and thus the local effect of supernovae feedback is enhanced. As a result, outflows are naturally generated removing 2/3 of the baryons in galaxies with Vvir˜50 km/s and ˜ 30% of the baryons in galaxies with (Vvir ˜ 150 km/s). Low angular momentum baryons are preferentially removed since the strongest bursts of star formation occur predominantly near the center, especially after a merger event. This produces pure exponential disks or small bulges depending on galaxy mass, and, correspondingly, slowly rising or nearly flat rotation curves that match those of observed disk galaxies. In dwarfs the rapid mass removal by outflows generates a core-like distribution in the dark matter. Furthermore, contrary to the common picture, in the ERIS spiral galaxies a bar/pseudobulge forms rapidly, and not secularly, as a result of mergers and interactions at high-z.

IN-SYNC. VII. Evidence for a Decreasing Spectroscopic Binary Fraction (from 1 to 100 Myr) within the IN-SYNC Sample

NASA Astrophysics Data System (ADS)

Jaehnig, Karl; Bird, Jonathan C.; Stassun, Keivan G.; Da Rio, Nicola; Tan, Jonathan C.; Cotaar, Michiel; Somers, Garrett

2017-12-01

We study the occurrence of spectroscopic binaries in young star-forming regions using the INfrared Spectroscopy of Young Nebulous Clusters (IN-SYNC) survey, carried out in SDSS-III with the APOGEE spectrograph. Multi-epoch observations of thousands of low-mass stars in Orion A, NGC 2264, NGC 1333, IC 348, and the Pleiades have been carried out, yielding H-band spectra with a nominal resolution of R = 22,500 for sources with H < 12 mag. Radial velocity precisions of ˜0.3 {km} {{{s}}}-1 were achieved, which we use to identify radial velocity variations indicative of undetected companions. We use Monte Carlo simulations to assess the types of spectroscopic binaries to which we are sensitive, finding sensitivity to binaries with orbital periods ≲ {10}3.5 days, for stars with 2500 {{K}}≤slant {T}{eff}≤slant 6000 {{K}} and v \\sin i < 100 {km} {{{s}}}-1. Using Bayesian inference, we find evidence for a decline in the spectroscopic binary fraction, by a factor of 3-4, from the age of our pre-main-sequence (PMS) sample to the Pleiades age . The significance of this decline is weakened if spot-induced radial-velocity jitter is strong in the sample, and is only marginally significant when comparing any one of the PMS clusters against the Pleiades. However, the same decline in both sense and magnitude is found for each of the five PMS clusters, and the decline reaches a statistical significance of greater than 95% confidence when considering the PMS clusters jointly. Our results suggest that dynamical processes disrupt the widest spectroscopic binaries ({P}{orb}≈ {10}3{--}{10}4 days) as clusters age, indicating that this occurs early in the stars’ evolution, while they still reside within their nascent clusters.

High Contrast X-ray Flares In The Anchors Database

NASA Astrophysics Data System (ADS)

McCleary, Jacqueline; Wolk, S.

2010-01-01

The X-ray light curves of pre-main sequence stars can show variability in the form of flares altering a baseline characteristic activity level; the largest X-ray flares are characterized by a rapid rise to 10 or more times the characteristic count rate, followed by a slower quasi-exponential decay. Analysis of these high-contrast X-ray flares enables the study of the innermost magnetic fields of pre-main sequence stars. We have scanned the ANCHORS database of Chandra observations of star-forming regions to extend the study of flare events on pre-main sequence stars both in sky coverage and in volume. We developed a sample of 30 high-contrast flares out of the 14,000 stars available in ANCHORS at the time of our study. By not biasing our sample by cluster, age, or spectral type, we increased the number of X-ray flare events studied and subsequently the strength of any statements about their properties. Applying the generally accepted methods of time-resolved spectral analysis developed by Reale et al. (1997), we measured the temperatures, confining magnetic field strengths, and loop lengths of these large flares. The results of the flare analysis were compared to the 2MASS and Spitzer data available for the stars in our sample. We found that the longest flare loop lengths (of order several stellar radii) are only seen on stars whose IR data indicates the presence of disks, which suggests that the longest flares may stretch all the way to the disk. Such long flares tend to be more tenuous (rarified) than the other large flares studied. A wide range of loop lengths were observed, indicating that two types of flares may occur on disked young stellar objects: either compact and analogous to flares on evolved stars, or long and the result of star-disk magnetic connections.

Reconstructing The Star Formation Histories Of Galaxies Through Sed Fitting Using The Dense Basis Method

NASA Astrophysics Data System (ADS)

Iyer, Kartheik; Gawiser, Eric

2017-06-01

The Dense Basis SED fitting method reveals previously inaccessible information about the number and duration of star formation episodes and the timing of stellar mass assembly as well as uncertainties in these quantities, in addition to accurately recovering traditional SED parameters including M*, SFR and dust attenuation. This is done using basis Star Formation Histories (SFHs) chosen by comparing the goodness-of-fit of mock galaxy SEDs to the goodness-of-reconstruction of their SFHs, trained and validated using three independent datasets of mock galaxies at z=1 from SAMs, Hydrodynamic simulations and stochastic realizations. Of the six parametrizations of SFHs considered, we reject the traditional parametrizations of constant and exponential SFHs and suggest four novel improvements, quantifying the bias and scatter of each parametrization. We then apply the method to a sample of 1100 CANDELS GOODS-S galaxies at 110^9 M_sun, in contrast to current simulations. About 40% of the CANDEL galaxies have SFHs whose maximum occurs at or near the epoch of observation. These results are presented in Iyer and Gawiser (2017, ApJ 838 127), available at https://arxiv.org/abs/1702.04371

Turbulent Mixing in Exponential Transverse Jets

DTIC Science & Technology

1990-09-30

parameter. The flame length of the jets is a direct measurement of the molecular scale mixing rate. ACCOMPLISHMENTS From observations of the trajectory...and cross-sectional size of the vortices, as well as the flame length , our measurements reveal the following: i) Under acceleration, the roll up and... flame lengths are a weak maximum when the acceleration parameter (x is about unity. For large cc, flame lengths slowly decline with increasing a, in

Emerging Science and Technology Trends: 2017-2047

DTIC Science & Technology

2017-11-21

genomics, coupled with the exponentially declining cost of gene editing techniques such as CRISPR , has created fertile ground for rapid technological...sequences from scratch. Falling costs and new gene editing tools like CRISPR are accelerating progress, and the global market is expected to reach...by the Bill & Melinda Gates foundation, is reengineering the bacteria found in the human gut to fight disease.121 eGensis is using CRISPR gene

THE ERUPTION OF THE CANDIDATE YOUNG STAR ASASSN-15QI

DOE Office of Scientific and Technical Information (OSTI.GOV)

Herczeg, Gregory J.; Dong, Subo; Chen, Ping

Outbursts on young stars are usually interpreted as accretion bursts caused by instabilities in the disk or the star–disk connection. However, some protostellar outbursts may not fit into this framework. In this paper, we analyze optical and near-infrared spectra and photometry to characterize the 2015 outburst of the probable young star ASASSN-15qi. The ∼3.5 mag brightening in the V band was sudden, with an unresolved rise time of less than one day. The outburst decayed exponentially by 1 mag for 6 days and then gradually back to the pre-outburst level after 200 days. The outburst is dominated by emission frommore » ∼10,000 K gas. An explosive release of energy accelerated matter from the star in all directions, seen in a spectacular cool, spherical wind with a maximum velocity of 1000 km s{sup −1}. The wind and hot gas both disappeared as the outburst faded and the source returned to its quiescent F-star spectrum. Nebulosity near the star brightened with a delay of 10–20 days. Fluorescent excitation of H{sub 2} is detected in emission from vibrational levels as high as v = 11, also with a possible time delay in flux increase. The mid-infrared spectral energy distribution does not indicate the presence of warm dust emission, though the optical photospheric absorption and CO overtone emission could be related to a gaseous disk. Archival photometry reveals a prior outburst in 1976. Although we speculate about possible causes for this outburst, none of the explanations are compelling.« less

Application of the Calculating Formula for the Mean Neutron Exposure in CEPM-s and CEPM-r/s Stars %Kstars: AGB and post-AGB, nuclear reactions, nucleosynthesis, abundances, methods: analytical

NASA Astrophysics Data System (ADS)

Zhang, F. H.; Zhang, L.; Cui, W. Y.; Zhang, B.

2017-09-01

Recent studies have shown that, for the current s-process nucleosynthesis model for the low-mass asymptotic giant branch (AGB) stars with (13C) pocket radiative burning during the interpulse period, the neutron exposure distribution in the nucleosynthesis region can be regarded as an exponential function, and the relation between the mean neutron exposure (τ0) and the model parameters is τ0 = - Δ τ/ln [q/(1 - r + q)]), in which (Δ τ) is the exposure value of each neutron irradiation, (r) is the overlap factor, and (q) is the mass ratio of the (13C) shell to the He intershell. Using the published data resulted from fitting the observed abundances of neutron-capture elements in 20 CEMP (Carbon-Enhanced Metal-Poor)-s and CEMP-s/r stars with the parametric AGB stellar s-process model, the reliability of the derived formula is tested, and further more the application of the formula in the s-process nucleosynthesis study is explored preliminarily. Our results show that, under the radiative s-process nucleosynthesis mechanism, the formula is suitable for CEMP stars experiencing recurrent neutron exposures. Combined with the parametric AGB nucleosynthesis model, the formula could be regarded as an effective tool to screen the CEMP stars with a single neutron exposure or a special type. Considering the uncertainty of the (13C) pocket, the role of this formula in understanding the physical conditions necessary to reproduce the observed s-process abundances in CEMP stars needs further study.

Diffusive Imaging of Hydraulically Induced and Natural Fracture Systems

NASA Astrophysics Data System (ADS)

Eftekhari, B.; Marder, M. P.; Patzek, T. W.

2017-12-01

Hydraulic fracturing of tight shales continues to provide the US with a major source of energy. Efficiency of gas recovery in shales depends upon the geometry of the resulting network of fractures, the details of which are not yet fully understood. The present research explores how much of the underlying geometry can be deduced from the time dependence of the flow of gas out of the reservoir. We consider both ideal and real gas. In the case of real gas, we calculate production rate for parallel planar hydrofractures embedded in an infinite reservoir. Transport is governed by a nonlinear diffusion equation, which we solve exactly with a scaling curve. The scaling curve production rate declines initially as 1 over square root time, then as an exponential, and finally as 1 over square root of time again at late time. We show that for a given hydraulically fractured well, the onsets of transition between different decline regimes provides a direct estimate of a characteristic spacing of the underlying fracture network. We show that the scaling solution accurately fits the production history of more than 15,000 wells in the Barnett Shale. Almost all of the wells either have not yet transitioned into the late time decline or have been refractured while in exponential decline. However, there are 36 wells which show the late time transition. These allow us to calculate the characteristic spacing, which turns out to have a mode at about 10 m, a minimum at 1.6 m and a maximum at 13.3 m. We estimate that over 30 years these wells will produce on average about 45% more gas because of diffusion from the infinite external reservoir than they would if this contribution is neglected. Finally, we compute the rate at which ideal gas diffuses within an infinite region of rock into a specific absorbing fractal fracture network, which we model using geological constraints and percolation theory. Our solution employs a Brownian walk and the first passage kinetic Monte Carlo algorithm that is robust and efficient. A striking feature of this solution is the presence of a power law decline.

A Bright, Spatially Extended Lensed Galaxy at z = 1.7 Behind the Cluster RCS2 032727-132623

NASA Astrophysics Data System (ADS)

Wuyts, Eva; Barrientos, L. Felipe; Gladders, Michael D.; Sharon, Keren; Bayliss, Matthew B.; Carrasco, Mauricio; Gilbank, David; Yee, H. K. C.; Koester, Benjamin P.; Muñoz, Roberto

2010-12-01

We present the discovery of an extremely bright and extended lensed source from the second Red Sequence Cluster Survey (RCS2). RCSGA 032727-132609 is spectroscopically confirmed as a giant arc and counterimage of a background galaxy at z = 1.701, strongly lensed by the foreground galaxy cluster RCS2 032727-132623 at z = 0.564. The giant arc extends over ~38'' and has an integrated r-band magnitude of 19.1, making it ~20 times larger and ~3.5 times brighter than the prototypical lensed galaxy MS1512-cB58. This is the brightest distant lensed galaxy in the universe known to date. We have collected photometry in nine bands, ranging from u to Ks , which densely sample the rest-frame UV and optical light, including the age-sensitive 4000 Å break. A lens model is constructed for the system and results in a robust total magnification of 2.04 ± 0.16 for the counterimage; we estimate an average magnification of 17.2 ± 1.4 for the giant arc based on the relative physical scales of the arc and counterimage on the sky. Fits of single-component spectral energy distribution models to the photometry result in a moderately young age, t = 80 ± 40 Myr, small amounts of dust, E(B - V) <= 0.11, and an exponentially declining star formation history with e-folding time τ = 10 - 50 Myr. After correcting for the lensing magnification, we find a stellar mass of M * ~ 1010 M sun and a current star formation rate (SFR) <=77 M sun yr-1. Allowing for episodic star formation, an underlying old burst could contain up to twice the mass inferred from single-component modeling. RCSGA 032727-132609 is typical of the known population of star-forming galaxies near this redshift in terms of its age and stellar mass. Its large magnification and spatial extent provide a unique opportunity to study the physical properties of an individual high-redshift star-forming galaxy in great detail, opening up a new window to the process of galaxy evolution between z = 1.7 and our local universe. Based in part on observations collected at the European Southern Observatory, Chile; the 6.5 m Magellan telescopes located at Las Campanas Observatory, Chile; the Southern Astrophysical Research 4.1 m telescope, a collaboration between CNPq-Brazil, NOAO, UNC and MSU; the 3.5 m Apache Point Observatory telescope in New Mexico, which is owned and operated by the Astrophysical Research Consortium; and the Canada-France-Hawaii Telescope (CFHT) on Mauna Kea, which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii.

Devastating Transboundary Impacts of Sea Star Wasting Disease on Subtidal Asteroids.

PubMed

Montecino-Latorre, Diego; Eisenlord, Morgan E; Turner, Margaret; Yoshioka, Reyn; Harvell, C Drew; Pattengill-Semmens, Christy V; Nichols, Janna D; Gaydos, Joseph K

2016-01-01

Sea star wasting disease devastated intertidal sea star populations from Mexico to Alaska between 2013-15, but little detail is known about its impacts to subtidal species. We assessed the impacts of sea star wasting disease in the Salish Sea, a Canadian / United States transboundary marine ecosystem, and world-wide hotspot for temperate asteroid species diversity with a high degree of endemism. We analyzed roving diver survey data for the three most common subtidal sea star species collected by trained volunteer scuba divers between 2006-15 in 5 basins and on the outer coast of Washington, as well as scientific strip transect data for 11 common subtidal asteroid taxa collected by scientific divers in the San Juan Islands during the spring/summer of 2014 and 2015. Our findings highlight differential susceptibility and impact of sea star wasting disease among asteroid species populations and lack of differences between basins or on Washington's outer coast. Specifically, severe depletion of sunflower sea stars (Pycnopodia helianthoides) in the Salish Sea support reports of major declines in this species from California to Alaska, raising concern for the conservation of this ecologically important subtidal predator.

Devastating Transboundary Impacts of Sea Star Wasting Disease on Subtidal Asteroids

PubMed Central

Montecino-Latorre, Diego; Eisenlord, Morgan E.; Turner, Margaret; Yoshioka, Reyn; Harvell, C. Drew; Pattengill-Semmens, Christy V.; Nichols, Janna D.

2016-01-01

Sea star wasting disease devastated intertidal sea star populations from Mexico to Alaska between 2013–15, but little detail is known about its impacts to subtidal species. We assessed the impacts of sea star wasting disease in the Salish Sea, a Canadian / United States transboundary marine ecosystem, and world-wide hotspot for temperate asteroid species diversity with a high degree of endemism. We analyzed roving diver survey data for the three most common subtidal sea star species collected by trained volunteer scuba divers between 2006–15 in 5 basins and on the outer coast of Washington, as well as scientific strip transect data for 11 common subtidal asteroid taxa collected by scientific divers in the San Juan Islands during the spring/summer of 2014 and 2015. Our findings highlight differential susceptibility and impact of sea star wasting disease among asteroid species populations and lack of differences between basins or on Washington’s outer coast. Specifically, severe depletion of sunflower sea stars (Pycnopodia helianthoides) in the Salish Sea support reports of major declines in this species from California to Alaska, raising concern for the conservation of this ecologically important subtidal predator. PMID:27783620

Evidence for Two Neutrino Bursts from SN1987A

NASA Astrophysics Data System (ADS)

Valentim, Rodolfo; Horvath, Jorge E.; Rangel, Eraldo M.

The SN1987A in the Giant Magellanic Cloud was an amazing and extraordinary event because it was detected in real time for different neutrinos experiments (νs) around the world. Approximate ˜ 25 events were observed in three different experiments: Kamiokande II (KII) ˜ 12, Irvine-Michigan-Brookhaven (IMB) ˜ 8 e Baksan ˜ 5, plus a contrived burst at Mont Blanc (Liquid Scintillator Detector - LSD) later dismissed because of energetic requirements (Aglietta et al. 1988). The neutrinos have an important play role into the neutron star newborn: at the moment when the supernova explodes the compact object remnant is freezing by neutrinos ( ˜ 99% energy is lost in the few seconds of the explosion). The work is motivated by neutrinos’ event in relation arrival times where there is a temporal gap between set of events ( ˜ 6s). The first part of dataset came from the ordinary mechanism of freezing and the second part suggests different mechanism of neutrinos production. We tested two models of cooling for neutrinos from SN1987A: 1st an exponential cooling is an ordinary model of cooling and 2nd a two-step temperature model that it considers two bursts separated with temporal gap. Our analysis was done with Bayesian tools (Bayesian Information Criterion - BIC) The result showed strong evidence in favor of a two-step model against one single exponential cooling (ln Bij > 5.0), and suggests the existence of two neutrino bursts at the moment the neutron star was born.

New analytical solutions for chemical evolution models: characterizing the population of star-forming and passive galaxies

NASA Astrophysics Data System (ADS)

Spitoni, E.; Vincenzo, F.; Matteucci, F.

2017-03-01

Context. Analytical models of chemical evolution, including inflow and outflow of gas, are important tools for studying how the metal content in galaxies evolves as a function of time. Aims: We present new analytical solutions for the evolution of the gas mass, total mass, and metallicity of a galactic system when a decaying exponential infall rate of gas and galactic winds are assumed. We apply our model to characterize a sample of local star-forming and passive galaxies from the Sloan Digital Sky Survey data, with the aim of reproducing their observed mass-metallicity relation. Methods: We derived how the two populations of star-forming and passive galaxies differ in their particular distribution of ages, formation timescales, infall masses, and mass loading factors. Results: We find that the local passive galaxies are, on average, older and assembled on shorter typical timescales than the local star-forming galaxies; on the other hand, the star-forming galaxies with higher masses generally show older ages and longer typical formation timescales compared than star-forming galaxies with lower masses. The local star-forming galaxies experience stronger galactic winds than the passive galaxy population. Exploring the effect of assuming different initial mass functions in our model, we show that to reproduce the observed mass-metallicity relation, stronger winds are requested if the initial mass function is top-heavy. Finally, our analytical models predict the assumed sample of local galaxies to lie on a tight surface in the 3D space defined by stellar metallicity, star formation rate, and stellar mass, in agreement with the well-known fundamental relation from adopting gas-phase metallicity. Conclusions: By using a new analytical model of chemical evolution, we characterize an ensemble of SDSS galaxies in terms of their infall timescales, infall masses, and mass loading factors. Local passive galaxies are, on average, older and assembled on shorter typical timescales than the local star-forming galaxies. Moreover, the local star-forming galaxies show stronger galactic winds than the passive galaxy population. Finally, we find that the fundamental relation between metallicity, mass, and star formation rate for these local galaxies is still valid when adopting the average galaxy stellar metallicity.

Paradoxical physiological transitions from aging to late life in Drosophila.

PubMed

Shahrestani, Parvin; Quach, Julie; Mueller, Laurence D; Rose, Michael R

2012-02-01

In a variety of organisms, adulthood is divided into aging and late life, where aging is a period of exponentially increasing mortality rates and late life is a period of roughly plateaued mortality rates. In this study we used ∼57,600 Drosophila melanogaster from six replicate populations to examine the physiological transitions from aging to late life in four functional characters that decline during aging: desiccation resistance, starvation resistance, time spent in motion, and negative geotaxis. Time spent in motion and desiccation resistance declined less quickly in late life compared to their patterns of decline during aging. Negative geotaxis declined at a faster rate in late life compared to its rate of decline during aging. These results yield two key findings: (1) Late-life physiology is distinct from the physiology of aging, in that there is not simply a continuation of the physiological trends which characterize aging; and (2) late life physiology is complex, in that physiological characters vary with respect to their stabilization, deceleration, or acceleration in the transition from aging to late life. These findings imply that a correct understanding of adulthood requires identifying and appropriately characterizing physiology during properly delimited late-life periods as well as aging periods.

Paradoxical Physiological Transitions from Aging to Late Life in Drosophila

PubMed Central

Quach, Julie; Mueller, Laurence D.; Rose, Michael R.

2012-01-01

Abstract In a variety of organisms, adulthood is divided into aging and late life, where aging is a period of exponentially increasing mortality rates and late life is a period of roughly plateaued mortality rates. In this study we used ∼57,600 Drosophila melanogaster from six replicate populations to examine the physiological transitions from aging to late life in four functional characters that decline during aging: desiccation resistance, starvation resistance, time spent in motion, and negative geotaxis. Time spent in motion and desiccation resistance declined less quickly in late life compared to their patterns of decline during aging. Negative geotaxis declined at a faster rate in late life compared to its rate of decline during aging. These results yield two key findings: (1) Late-life physiology is distinct from the physiology of aging, in that there is not simply a continuation of the physiological trends which characterize aging; and (2) late life physiology is complex, in that physiological characters vary with respect to their stabilization, deceleration, or acceleration in the transition from aging to late life. These findings imply that a correct understanding of adulthood requires identifying and appropriately characterizing physiology during properly delimited late-life periods as well as aging periods. PMID:22233126

Simultaneous NuSTAR/Chandra Observations of the Bursting Pulsar GRO J1744-28 During its Third Reactivation

NASA Technical Reports Server (NTRS)

Younes, G.; Kouveliotou, C.; Grefenstette, B. W.; Tomsick, J. A.; Tennant, A.; Finger, M. H.; Furst, F.; Pottschmidt, K.; Bhalerao, V.; Boggs, S. E.;

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schmidt, Edward G., E-mail: eschmidt1@unl.edu

We have obtained VR photometry of 447 Cepheid variable star candidates with declinations north of -14 Degree-Sign 30', most of which were identified using the Northern Sky Variability Survey (NSVS) data archive. Periods and other photometric properties were derived from the combination of our data with the NSVS data. Atmospheric parameters were determined for 81 of these stars from low-resolution spectra. The identification of type II Cepheids based on the data presented in all four papers in this series is discussed. On the basis of spectra, 30 type II Cepheids were identified while 53 variables were identified as cool, mainmore » sequence stars and 283 as red giants following the definitions in Paper III. An additional 30 type II Cepheids were identified on the basis of light curves. The present classifications are compared with those from the Machine-learned All Sky Automated Survey Classification Catalog for 174 stars in common.« less

Rotational Velocity Determinations for 118 δ Scuti Variables

NASA Astrophysics Data System (ADS)

Bush, Tabitha C.; Hintz, E. G.

2009-01-01

We present a calibration method used for the determination of projected rotational velocities (vsin i) of 118 δ Scuti variables from FWHM measurements of metal lines near 4500 Å. The calibration relation used was derived from measurements of 29 stars. Of the 44 stars brighter than 8th magnitude and north of -1° declination which did not have values in the Rodríguez catalog (Rodríguez, E., López González, M. J., & López de Coca, P. 2000, A&AS, 144, 469), we present values for 38. In addition, we present new vsin i values for 10 stars south of -1° or fainter than 8th magnitude for a total of 48 vsin i values for stars with no previously published values. We acknowledge the Dominion Astrophysical Observatory for making available the 1.2-m and 1.8-m telescopes to aid in this research.

Endogenous technological and demographic change under increasing water scarcity

NASA Astrophysics Data System (ADS)

Pande, Saket; Ertsen, Maurits; Sivapalan, Murugesu

2014-05-01

The ancient civilization in the Indus Valley civilization dispersed under extreme dry conditions; there are indications that the same holds for many other ancient societies. Even contemporary societies, such as the one in Murrumbidgee river basin in Australia, have started to witness a decline in overall population under increasing water scarcity. Hydroclimatic change may not be the sole predictor of the fate of contemporary societies in water scarce regions and many critics of such (perceived) hydroclimatic determinism have suggested that technological change may ameliorate the effects of increasing water scarcity and as such counter the effects of hydroclimatic changes. To study the role of technological change on the dynamics of coupled human-water systems, we develop a simple overlapping-generations model of endogenous technological and demographic change. We model technological change as an endogenous process that depends on factors such as the investments that are (endogenously) made in a society, the (endogenous) diversification of a society into skilled and unskilled workers, a society's patience in terms of its present consumption vs. future consumption, production technology and the (endogenous) interaction of all of these factors. In the model the population growth rate is programmed to decline once consumption per capita crosses a "survival" threshold. This means we do not treat technology as an exogenous random sequence of events, but instead assume that it results (endogenously) from societal actions. The model demonstrates that technological change may indeed ameliorate the effects of increasing water scarcity but typically it does so only to a certain extent. It is possible that technological change may allow a society to escape the effect of increasing water scarcity, leading to a (super)-exponential rise in technology and population. However, such cases require the rate of success of investment in technological advancement to be high. In other more realistic cases of technological success, we find that endogenous technology change only helps to delay the peak of population size before it inevitably starts to decline. While the model is a rather simple model of societal development, it is shown to be capable of replicating patterns of technological and population changes. It is capable of replicating the pattern of declining consumption per capita in presence of growth in aggregate production. It is also capable of replicating an exponential population rise, even under increasing water scarcity. The results of the model suggest that societies that declined or are declining in the face of extreme water scarcity may have done so due to slower rate of success of investment in technological advancement. The model suggests that the population decline occurs after a prolonged decline in consumption per capita, which in turn is due to the joint effect of initially increasing population and increasing water scarcity. This is despite technological advancement and increase in aggregate production. We suggest that declining consumption per capita despite technological advancement and increase in aggregate production may serve as a useful predictor of upcoming decline in contemporary societies in water scarce basins.

Endogenous technological and population change under increasing water scarcity

NASA Astrophysics Data System (ADS)

Pande, S.; Ertsen, M.; Sivapalan, M.

2013-11-01

The ancient civilization in the Indus Valley civilization dispersed under extreme dry conditions; there are indications that the same holds for many other ancient societies. Even contemporary societies, such as the one in Murrumbidgee river basin in Australia, have started to witness a decline in overall population under increasing water scarcity. Hydroclimatic change may not be the sole predictor of the fate of contemporary societies in water scarce regions and many critics of such (perceived) hydroclimatic determinism have suggested that technological change may ameliorate the effects of increasing water scarcity and as such counter the effects of hydroclimatic changes. To study the role of technological change on the dynamics of coupled human-water systems, we develop a simple overlapping-generations model of endogenous technological and demographic change. We model technological change as an endogenous process that depends on factors such as the investments that are (endogenously) made in a society, the (endogenous) diversification of a society into skilled and unskilled workers, a society's patience in terms of its present consumption vs. future consumption, production technology and the (endogenous) interaction of all of these factors. In the model the population growth rate is programmed to decline once consumption per capita crosses a "survival" threshold. This means we do not treat technology as an exogenous random sequence of events, but instead assume that it results (endogenously) from societal actions. The model demonstrates that technological change may indeed ameliorate the effects of increasing water scarcity but typically it does so only to a certain extent. It is possible that technological change may allow a society to escape the effect of increasing water scarcity, leading to a (super)-exponential rise in technology and population. However, such cases require the rate of success of investment in technological advancement to be high. In other more realistic cases of technological success, we find that endogenous technology change only helps to delay the peak of population size before it inevitably starts to decline. While the model is a rather simple model of societal development, it is shown to be capable of replicating patterns of technological and population changes. It is capable of replicating the pattern of declining consumption per capita in presence of growth in aggregate production. It is also capable of replicating an exponential population rise, even under increasing water scarcity. The results of the model suggest that societies that declined or are declining in the face of extreme water scarcity may have done so due to slower rate of success of investment in technological advancement. The model suggests that the population decline occurs after a prolonged decline in consumption per capita, which in turn is due to the joint effect of initially increasing population and increasing water scarcity. This is despite technological advancement and increase in aggregate production. We suggest that declining consumption per capita despite technological advancement and increase in aggregate production may serve as a useful predictor of upcoming decline in contemporary societies in water scarce basins.

Documentation for the machine-readable version of the Survey of the Astrographic Catalogue From 1 to 31 Degrees of Northern Declination (Fresneau 1983)

NASA Technical Reports Server (NTRS)

Warren, W. H., Jr.

1983-01-01

A description of the machine readable catalog, including detailed format and tape file characteristics, is given. The machine file is a computation of mean values for position and magnitude at a mean epoch of observation for each unique star in the Oxford, Paris, Bordeaux, Toulouse and Northern Hemisphere Algiers zone. The format was changed to effect more efficient data searching by position and additional duplicate entries were removed. The final catalog contains data for 997311 stars.

Resonance Production at Star

NASA Astrophysics Data System (ADS)

Yamamoto, Eugene T.

2002-03-01

We present the first measurement of mid-rapidity ϕ vector meson production in Au + Au collisions at RHIC (√ {sNN}= 130\\ GeV) from the STAR detector. For the 11% most central collisions, the slope parameter from an exponential fit to the transverse mass distribution is T= 379 ± 51(stat) ± 45(syst) MeV, the yield dN/dy = 5.73 ± 0.37(stat) ± 0.57(syst) per event and the ratio Nϕ/Nh- is found to be 0.021 ± 0.001(stat) ± 0.004(syst). We currently place the value of the Nϕ/NK- ratio between 0.10 and 0.16. The measured ratios Nϕ/Nh- and Nϕ/NK-, as well as T for the ϕ meson at mid-rapidity do not change for the selected centrality bins.

Galacti chemical evolution: Hygrogen through zinc

NASA Technical Reports Server (NTRS)

Timmes, F. X.; Woosley, S. E.; Weaver, Thomas A.

1995-01-01

Using the output from a grid of 60 Type II supernova models (Woosley & Weaver 1995) of varying mass (11 approx. less than (M/solar mass) approx. less than 40) and metallicity (0, 10(exp -4), 0.01, and 1 solar metallicity), the chemical evolution of 76 stable isotopes, from hydrogen to zinc, is calculated. The chemical evolution calculation employs a simple dynamical model for the Galaxy (infall with a 4 Gyr e-folding timescale onto a exponential dsk and 1/r(exp 2) bulge), and standard evolution parameters, such as a Salpeter initial mass function and a quadratic Schmidt star formation rate. The theoretical results are compared in detail with observed stellar abundances in stars with metallicities in the range -3.0 approx. less than (Fe/H) approx. less than 0.0 dex. While our discussion focuses on the solar neighborhood where there are the most observations, the supernova rates, an intrinsically Galactic quality, are also discussed.

A Photometric Variability Survey of Field K and M Dwarf Stars with HATNet

NASA Astrophysics Data System (ADS)

Hartman, J. D.; Bakos, G. Á.; Noyes, R. W.; Sipőcz, B.; Kovács, G.; Mazeh, T.; Shporer, A.; Pál, A.

2011-05-01

Using light curves from the HATNet survey for transiting extrasolar planets we investigate the optical broadband photometric variability of a sample of 27, 560 field K and M dwarfs selected by color and proper motion (V - K >~ 3.0, μ > 30 mas yr-1, plus additional cuts in J - H versus H - KS and on the reduced proper motion). We search the light curves for periodic variations and for large-amplitude, long-duration flare events. A total of 2120 stars exhibit potential variability, including 95 stars with eclipses and 60 stars with flares. Based on a visual inspection of these light curves and an automated blending classification, we select 1568 stars, including 78 eclipsing binaries (EBs), as secure variable star detections that are not obvious blends. We estimate that a further ~26% of these stars may be blends with fainter variables, though most of these blends are likely to be among the hotter stars in our sample. We find that only 38 of the 1568 stars, including five of the EBs, have previously been identified as variables or are blended with previously identified variables. One of the newly identified EBs is 1RXS J154727.5+450803, a known P = 3.55 day, late M-dwarf SB2 system, for which we derive preliminary estimates for the component masses and radii of M 1 = M 2 = 0.258 ± 0.008 M sun and R 1 = R 2 = 0.289 ± 0.007 R sun. The radii of the component stars are larger than theoretical expectations if the system is older than ~200 Myr. The majority of the variables are heavily spotted BY Dra-type stars for which we determine rotation periods. Using this sample, we investigate the relations between period, color, age, and activity measures, including optical flaring, for K and M dwarfs, finding that many of the well-established relations for F, G, and K dwarfs continue into the M dwarf regime. We find that the fraction of stars that is variable with peak-to-peak amplitudes greater than 0.01 mag increases exponentially with the V - KS color such that approximately half of field dwarfs in the solar neighborhood with M <~ 0.2 M sun are variable at this level. Our data hint at a change in the rotation-activity-age connection for stars with M <~ 0.25 M sun.

Decline in Soluble Phosphorus Mobility from Land-Applied Dairy Manure - Modeling and Practical Applications

NASA Astrophysics Data System (ADS)

Archibald, J. A.; Walter, M. T.; Peterson, M.; Richards, B. K.; Giri, S. K.

2014-12-01

Non-point source transport of soluble-reactive phosphorus (SRP) from agricultural systems to freshwater ecosystems is a significant water quality concern. Although farmers are encouraged to avoid manure or fertilizer application before runoff events, the implications of these management choices remain largely unquantified. We conducted soil box experiments to test how manure application timing and temperature or moisture conditions impact SRP concentration in runoff. We found that SRP concentrations dropped off exponentially over time, and that higher temperatures accelerated the decline in SRP in overland runoff over time. During the first runoff events after manure application, infiltration depth prior to runoff was not a primary driver of SRP concentrations. This research has implications for incorporating manure spreading timing into watershed models.

Be Stars in M31

NASA Astrophysics Data System (ADS)

Peters, Matthew L.; Wisniewski, John; Choi, Yumi; Williams, Ben; Lomax, Jamie; Bjorkman, Karen; Durbin, Meredith; Johnson, Lent Cliff; Lewis, Alexia; Lutz, Julie; Sigut, Aaron; Wallach, Aislynn; Dalcanton, Julianne

2018-01-01

We identify Be candidate stars in M31 using two-epoch F625W + F658N photometry from HST/ACS+WFC3 combined with the Panchromatic Hubble Andromeda Treasury (PHAT) Catalog. Using the PHAT catalog allows us to extract stellar parameters such as surface temperature and gravity, thereby allowing us to identify the main sequence B type stars in the field of view. Be candidate stars are identified by comparing their HST narrow-band Hα excess magnitudes with that predicted by Kurucz spectra. We find 314 Be candidate stars out of 5699 B + Be candidate stars (5.51%) in our first epoch and 301 Be candidate stars out of 5769 B + Be candidate stars (5.22%) in our second epoch. Our Be fraction, while lower than that of the SMC, LMC, and MW, is possibly consistent with the fact the M31 has a higher metallicity than the other galaxies because Be fraction varies inversely with metallicity. We note that earlier spectral types have the largest Be fraction, and that the Be fraction strictly declines as the spectral type increases to later types. We then match our Be candidate stars with clusters, establishing that 39 of 314 are cluster stars in epoch one and 36 of 301 stars are cluster stars in epoch two. We assign ages, using the cluster age to characterize cluster Be candidate stars and star formation histories to characterize field Be candidate stars. Finally, we determine which Be candidate stars exhibited disk loss or disk growth between epochs, finding that, of the Be stars that did not show source confusion or low SNR in one of the epochs, 65 / 265 (24.5%) showed disk loss or renewal, while 200 / 265 (75.5%) showed only small changes in Hα excess. Our research provides context for the parameters of candidate Be stars in M31, which will be useful in further determining the nature of Be stars. This paper was supported by a grant from STScI via GO-13857.

The decay of 'mesotrons' (1939-1943), experimental particle physics in the age of innocence

NASA Astrophysics Data System (ADS)

Rossi, B.

An account is given of the experimental work carried out by the author and his associates during the years 1939 through 1943, which produced the first unambiguous evidence of the spontaneous decay of 'mesotrons', showed that this decay occurred according to an exponential law, as expected, and measured the mean life with a 3 percent accuracy. A byproduct of this work was a verification of the relativistic equation for the dilation of time intervals. Previously announced in STAR as N81-76151

Adiabatic invariants in stellar dynamics. 2: Gravitational shocking

NASA Technical Reports Server (NTRS)

Weinberg, Martin D.

1994-01-01

A new theory of gravitational shocking based on time-dependent perturbation theory shows that the changes in energy and angular momentum due to a slowly varying disturbance are not exponentially small for stellar dynamical systems in general. It predicts significant shock heating by slowly varying perturbations previously thought to be negligible according to the adiabatic criterion. The theory extends the scenarios traditionally computed only with the impulse approximation and is applicable to a wide class of disturbances. The approach is applied specifically to the problem of disk shocking of star clusters.

Monitoring survival rates of Swainson's Thrush Catharus ustulatus at multiple spatial scales

USGS Publications Warehouse

Rosenberg, D.K.; DeSante, D.F.; McKelvey, K.S.; Hines, J.E.

1999-01-01

We estimated survival rates of Swainson's Thrush, a common, neotropical, migratory landbird, at multiple spatial scales, using data collected in the western USA from the Monitoring Avian Productivity and Survivorship Programme. We evaluated statistical power to detect spatially heterogeneous survival rates and exponentially declining survival rates among spatial scales with simulated populations parameterized from results of the Swainson's Thrush analyses. Models describing survival rates as constant across large spatial scales did not fit the data. The model we chose as most appropriate to describe survival rates of Swainson's Thrush allowed survival rates to vary among Physiographic Provinces, included a separate parameter for the probability that a newly captured bird is a resident individual in the study population, and constrained capture probability to be constant across all stations. Estimated annual survival rates under this model varied from 0.42 to 0.75 among Provinces. The coefficient of variation of survival estimates ranged from 5.8 to 20% among Physiographic Provinces. Statistical power to detect exponentially declining trends was fairly low for small spatial scales, although large annual declines (3% of previous year's rate) were likely to be detected when monitoring was conducted for long periods of time (e.g. 20 years). Although our simulations and field results are based on only four years of data from a limited number and distribution of stations, it is likely that they illustrate genuine difficulties inherent to broadscale efforts to monitor survival rates of territorial landbirds. In particular, our results suggest that more attention needs to be paid to sampling schemes of monitoring programmes, particularly regarding the trade-off between precision and potential bias of parameter estimates at varying spatial scales.

Monitoring survival rates of Swainson's Thrush Catharus ustulatus at multiple spatial scales

USGS Publications Warehouse

Rosenberg, D.K.; DeSante, D.F.; McKelvey, K.S.; Hines, J.E.

1999-01-01

We estimated survival rates of Swainson's Thrush, a common, neotropical, migratory landbird, at multiple spatial scales, using data collected in the western USA from the Monitoring Avian Productivity and Survivorship Programme. We evaluated statistical power to detect spatially heterogeneous survival rates and exponentially declining survival rates among spatial scales with simulated populations parameterized from results of the Swainson's Thrush analyses. Models describing survival rates as constant across large spatial scales did not fit the data. The model we chose as most appropriate to describe survival rates of Swainson's Thrush allowed survival rates to vary among Physiographic Provinces, included a separate parameter for the probability that a newly captured bird is a resident individual in the study population, and constrained capture probability to be constant across all stations. Estimated annual survival rates under this model varied from 0.42 to 0.75 among Provinces. The coefficient of variation of survival estimates ranged from 5.8 to 20% among Physiographic Provinces. Statistical power to detect exponentially declining trends was fairly low for small spatial scales, although large annual declines (3% of previous year's rate) were likely to be detected when monitoring was conducted for long periods of time (e.g. 20 years). Although our simulations and field results are based on only four years of date from a limited number and distribution of stations, it is likely that they illustrate genuine difficulties inherent to broadscale efforts to monitor survival rates of territorial landbirds. In particular, our results suggest that more attention needs to be paid to sampling schemes of monitoring programmes particularly regarding the trade-off between precison and potential bias o parameter estimates at varying spatial scales.

Characterization of Visual Function, Interocular Variability and Progression Using Static Perimetry-Derived Metrics in RPGR-Associated Retinopathy.

PubMed

Tee, James J L; Yang, Yesa; Kalitzeos, Angelos; Webster, Andrew; Bainbridge, James; Weleber, Richard G; Michaelides, Michel

2018-05-01

To characterize bilateral visual function, interocular variability and progression by using static perimetry-derived volumetric and pointwise metrics in subjects with retinitis pigmentosa associated with mutations in the retinitis pigmentosa GTPase regulator (RPGR) gene. This was a prospective longitudinal observational study of 47 genetically confirmed subjects. Visual function was assessed with ETDRS and Pelli-Robson charts; and Octopus 900 static perimetry using a customized, radially oriented 185-point grid. Three-dimensional hill-of-vision topographic models were produced and interrogated with the Visual Field Modeling and Analysis software to obtain three volumetric metrics: VTotal, V30, and V5. These were analyzed together with Octopus mean sensitivity values. Interocular differences were assessed with the Bland-Altman method. Metric-specific exponential decline rates were calculated. Baseline symmetry was demonstrated by relative interocular difference values of 1% for VTotal and 8% with V30. Degree of symmetry varied between subjects and was quantified with the subject percentage interocular difference (SPID). SPID was 16% for VTotal and 17% for V30. Interocular symmetry in progression was greatest when quantified by VTotal and V30, with 73% and 64% of subjects possessing interocular rate differences smaller in magnitude than respective annual progression rates. Functional decline was evident with increasing age. An overall annual exponential decline of 6% was evident with both VTotal and V30. In general, good interocular symmetry exists; however, there was both variation between subjects and with the use of various metrics. Our findings will guide patient selection and design of RPGR treatment trials, and provide clinicians with specific prognostic information to offer patients affected by this condition.

{phi} meson production in Au + Au and p + p collisions at {radical}s{sub NN}=200 GeV

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adams, J.; Adler, C.; Aggarwal, M.M.

2004-06-01

We report the STAR measurement of {psi} meson production in Au + Au and p + p collisions at {radical}s{sub NN} = 200 GeV. Using the event mixing technique, the {psi} spectra and yields are obtained at midrapidity for five centrality bins in Au+Au collisions and for non-singly-diffractive p+p collisions. It is found that the {psi} transverse momentum distributions from Au+Au collisions are better fitted with a single-exponential while the p+p spectrum is better described by a double-exponential distribution. The measured nuclear modification factors indicate that {psi} production in central Au+Au collisions is suppressed relative to peripheral collisions when scaledmore » by the number of binary collisions (). The systematics of versus centrality and the constant {psi}/K{sup -} ratio versus beam species, centrality, and collision energy rule out kaon coalescence as the dominant mechanism for {psi} production.« less

Planetary cores, their energy flux relationship, and its implications

NASA Astrophysics Data System (ADS)

Johnson, Fred M.

2018-02-01

Integrated surface heat flux data from each planet in our solar system plus over 50 stars, including our Sun, was plotted against each object's known mass to generate a continuous exponential curve at an R-squared value of 0.99. The unexpected yet undeniable implication of this study is that all planets and celestial objects have a similar mode of energy production. It is widely accepted that proton-proton reactions require hydrogen gas at temperatures of about 15 million degrees, neither of which can plausibly exist inside a terrestrial planet. Hence, this paper proposes a nuclear fission mechanism for all luminous celestial objects, and uses this mechanism to further suggest a developmental narrative for all celestial bodies, including our Sun. This narrative was deduced from an exponential curve drawn adjacent to the first and passing through the Earth's solid core (as a known prototype). This trend line was used to predict the core masses for each planet as a function of its luminosity.

ARE THE ULTRA-FAINT DWARF GALAXIES JUST CUSPS?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zolotov, Adi; Hogg, David W.; Willman, Beth, E-mail: az481@nyu.edu

2011-01-20

We develop a technique to investigate the possibility that some of the recently discovered ultra-faint dwarf satellites of the Milky Way might be cusp caustics rather than gravitationally self-bound systems. Such cusps can form when a stream of stars folds, creating a region where the projected two-dimensional surface density is enhanced. In this work, we construct a Poisson maximum likelihood test to compare the cusp and exponential models of any substructure on an equal footing. We apply the test to the Hercules dwarf (d {approx} 113 kpc, M{sub V} {approx} -6.2, e {approx} 0.67). The flattened exponential model is stronglymore » favored over the cusp model in the case of Hercules, ruling out at high confidence that Hercules is a cusp catastrophe. This test can be applied to any of the Milky Way dwarfs, and more generally to the entire stellar halo population, to search for the cusp catastrophes that might be expected in an accreted stellar halo.« less

Proportional Feedback Control of Energy Intake During Obesity Pharmacotherapy.

PubMed

Hall, Kevin D; Sanghvi, Arjun; Göbel, Britta

2017-12-01

Obesity pharmacotherapies result in an exponential time course for energy intake whereby large early decreases dissipate over time. This pattern of declining drug efficacy to decrease energy intake results in a weight loss plateau within approximately 1 year. This study aimed to elucidate the physiology underlying the exponential decay of drug effects on energy intake. Placebo-subtracted energy intake time courses were examined during long-term obesity pharmacotherapy trials for 14 different drugs or drug combinations within the theoretical framework of a proportional feedback control system regulating human body weight. Assuming each obesity drug had a relatively constant effect on average energy intake and did not affect other model parameters, our model correctly predicted that long-term placebo-subtracted energy intake was linearly related to early reductions in energy intake according to a prespecified equation with no free parameters. The simple model explained about 70% of the variance between drug studies with respect to the long-term effects on energy intake, although a significant proportional bias was evident. The exponential decay over time of obesity pharmacotherapies to suppress energy intake can be interpreted as a relatively constant effect of each drug superimposed on a physiological feedback control system regulating body weight. © 2017 The Obesity Society.

A new approach to detailed structural decomposition from the splash and phat surveys: Kicked-up disk stars in the Andromeda galaxy?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dorman, Claire E.; Guhathakurta, Puragra; Widrow, Lawrence M., E-mail: cdorman@ucolick.org, E-mail: raja@ucolick.org, E-mail: widrow@astro.queensu.ca

We characterize the bulge, disk, and halo subcomponents in the Andromeda galaxy (M31) over the radial range 4 kpc < R {sub proj} < 225 kpc. The cospatial nature of these subcomponents renders them difficult to disentangle using surface brightness (SB) information alone, especially interior to ∼20 kpc. Our new decomposition technique combines information from the luminosity function (LF) of over 1.5 million bright (20 < m {sub 814W} < 22) stars from the Panchromatic Hubble Andromeda Treasury survey, radial velocities of over 5000 red giant branch stars in the same magnitude range from the Spectroscopic and Photometric Landscape ofmore » Andromeda's Stellar Halo survey, and integrated I-band SB profiles from various sources. We use an affine-invariant Markov chain Monte Carlo algorithm to fit an appropriate toy model to these three data sets. The bulge, disk, and halo SB profiles are modeled as a Sérsic, exponential, and cored power law, respectively, and the LFs are modeled as broken power laws. We present probability distributions for each of 32 parameters describing the SB profiles and LFs of the three subcomponents. We find that the number of stars with a disk-like LF is 5.2% ± 2.1% larger than the number with disk-like (dynamically cold) kinematics, suggesting that some stars born in the disk have been dynamically heated to the point that they are kinematically indistinguishable from halo members. This is the first kinematical evidence for a 'kicked-up disk' halo population in M31. The fraction of kicked-up disk stars is consistent with that found in simulations. We also find evidence for a radially varying disk LF, consistent with a negative metallicity gradient in the stellar disk.« less

CASBaH: the Multiphase Circumgalactic Medium During the Decline of Cosmic Star Formation

NASA Astrophysics Data System (ADS)

Burchett, Joseph N.; Tripp, Todd; Prochaska, Jason; Werk, Jessica; Willmer, Christopher; Ford, Amanda Brady; Howk, Chris

2018-01-01

The COS Absorption Survey of Baryon Harbors (CASBaH) comprises high-S/N spectra of nine z > 0.9 QSOs with coverage from the far-ultraviolet to the optical. These sightlines access the rich suite of rest-frame extreme-ultraviolet (600 - 1000 Angstroms) spectral transitions, such as Ne VIII, Mg X, and O II/III/IV, in addition to those more well studied at longer wavelengths (O VI, C III, Mg II). We have undertaken a large ground-based spectroscopic follow-up campaign to identify galaxies projected near the QSO sightlines and leverage the myriad diagnostics within the QSO spectra to study the circumgalactic medium (CGM) at 0.2 < z < 1 over the crucial epoch when star formation activity in the Universe was in sharp decline. We will present results from this multiwavelength study characterizing the CGM across multiple ionization states, focusing on the O VI and Ne VIII-probed warm-hot (105-106 K) gas within the halos of our galaxy sample.

Sodium 22+ washout from cultured rat cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kino, M.; Nakamura, A.; Hopp, L.

1986-10-01

The washout of Na/sup +/ isotopes from tissues and cells is quite complex and not well defined. To further gain insight into this process, we have studied /sup 22/Na/sup +/ washout from cultured Wistar rat skin fibroblasts and vascular smooth muscle cells (VSMCs). In these preparations, /sup 22/Na/sup +/ washout is described by a general three-exponential function. The exponential factor of the fastest component (k1) and the initial exchange rate constant (kie) of cultured fibroblasts decrease in magnitude in response to incubation in K+-deficient medium or in the presence of ouabain and increase in magnitude when the cells are incubatedmore » in a Ca++-deficient medium. As the magnitude of the kie declines (in the presence of ouabain) to the level of the exponential factor of the middle component (k2), /sup 22/Na/sup +/ washout is adequately described by a two-exponential function. When the kie is further diminished (in the presence of both ouabain and phloretin) to the range of the exponential factor of the slowest component (k3), the washout of /sup 22/Na/sup +/ is apparently monoexponential. Calculations of the cellular Na/sup +/ concentrations, based on the /sup 22/Na/sup +/ activity in the cells at the initiation of the washout experiments, and the medium specific activity agree with atomic absorption spectrometry measurements of the cellular concentration of this ion. Thus, all three components of /sup 22/Na/sup +/ washout from cultured rat cells are of cellular origin. Using the exponential parameters, compartmental analyses of two models (in parallel and in series) with three cellular Na/sup +/ pools were performed. The results indicate that, independent of the model chosen, the relative size of the largest Na+ pool is 92-93% in fibroblasts and approximately 96% in VSMCs. This pool is most likely to represent the cytosol.« less

Where Is the Flux Going? The Long-term Photometric Variability of Boyajian’s Star

NASA Astrophysics Data System (ADS)

Simon, Joshua D.; Shappee, Benjamin J.; Pojmański, G.; Montet, Benjamin T.; Kochanek, C. S.; van Saders, Jennifer; Holoien, T. W.-S.; Henden, Arne A.

2018-01-01

We present ∼800 days of photometric monitoring of Boyajian’s Star (KIC 8462852) from the All-Sky Automated Survey for Supernovae (ASAS-SN) and ∼4000 days of monitoring from the All Sky Automated Survey (ASAS). We show that from 2015 to the present the brightness of Boyajian’s Star has steadily decreased at a rate of 6.3 ± 1.4 mmag yr‑1, such that the star is now 1.5% fainter than it was in 2015 February. Moreover, the longer time baseline afforded by ASAS suggests that Boyajian’s Star has also undergone two brightening episodes in the past 11 years, rather than only exhibiting a monotonic decline. We analyze a sample of ∼1000 comparison stars of similar brightness located in the same ASAS-SN field and demonstrate that the recent fading is significant at ≳99.4% confidence. The 2015–2017 dimming rate is consistent with that measured with Kepler data for the time period from 2009 to 2013. This long-term variability is difficult to explain with any of the physical models for the star’s behavior proposed to date.

Effects of octylphenol on the expression of StAR, CYP17 and CYP19 in testis of Rana chensinensis.

PubMed

Bai, Yao; Li, Xin-Yi; Liu, Zhi-Jun; Zhang, Yu-Hui

2017-04-01

It has been proposed that a decline in sperm quality is associated with exposure to environmental chemicals with estrogenic activity. Seeking possible explanations for this effect, this study investigated the effects of octylphenol (OP) on the synthesis of steroid hormones in amphibian. Rana chensinensis were exposed to 10 -8 , 10 -7 and 10 -6 mol/L OP after 10, 20, 30 and 40 days. The cDNA fragments of StAR (274bp), CYP17 (303bp) and CYP19 (322bp) were cloned. In situ hybridization and immunohistochemistry revealed that positive signals of StAR, CYP17, CYP19 mRNA and proteins mainly in the Leydig cells of testes. Real-time PCR showed that up-regulation of StAR and CYP19, and down-regulation of CYP17 after exposure to 10 -8 , 10 -7 and 10 -6 mol/L OP. The results suggest that OP can alter transcriptions of StAR, CYP17 and CYP19, thus disturb the expressions of StAR, P450c17 and P450arom, thereby adversely affect steroid synthesis. Copyright © 2017 Elsevier B.V. All rights reserved.

X-ray selected stars in HRC and BHRC catalogues

NASA Astrophysics Data System (ADS)

Mickaelian, A. M.; Paronyan, G. M.

2014-12-01

A joint HRC/BHRC Catalogue has been created based on merging of Hamburg ROSAT Catalogue (HRC) and Byurakan Hamburg ROSAT Catalogue (BHRC). Both have been made by optical identifications of X-ray sources based on low-dispersion spectra of the Hamburg Quasar Survey (HQS) using ROSAT Catalogues. As a result, the largest sample of 8132 (5341+2791) optically identified X-ray sources was created having count rate (CR) of photons ≤ 0.04 ct/s in the area with galactic latitudes |b|≤ 20° and declinations d≤ 0°.There are 4253 AGN, 492 galaxies, 1800 stars and 1587 unknown objects in the sample. All stars have been found in GSC 2.3.2, as well as most of them are in GALEX, USNO-B1.0, 2MASS and WISE catalogues. In addition, 1429 are in SDSS DR9 and 204 have SDSS spectra. For these stars we have carried out spectral classification and along with the bright stars, many new cataclysmic variables (CV), white dwarfs (WD) and late-type stars (K-M and C) have been revealed. For all stars, statistical studies of their multiwavelength properties have been made. An attempt to find a connection between the radiation fluxes in different bands for different types of sources, and identify their characteristics was made as well.

X-ray emission on hybird stars: ROSAT observations of alpha Trianguli Australis and iota Aurigae

NASA Technical Reports Server (NTRS)

Kashyap, V.; Rosner, R.; Harnden, F. R., Jr.; Maggio, A.; Micela, G.; Sciortino, S.

1994-01-01

We report on deep ROSAT observations of two Hybrid atmosphere stars, alpha TrA and iota Aur, and our analysis of these observations. We detect high-energy transient phenomena on alpha TrA and consider the implications of this discovery to the atmospheres of Hybrid stars. We detect iota Aur in the high-energy passband of ROSAT, implying the existence of multimillion degree plasma on the star. Our major results include the following: discovery of two large flare events, detected during pointed observations of alpha TrA; the demonstration that the flare emission most likely comes from the giant itself, rather than from a previously unseen low-mass companion star; the demonstration that the plasma characteristics associated with the flares and with the 'quiescent' component are essentially indistinguishable; and that the geometric dimensions of the emitting plasma are considerably smaller than the critical dimension characterizing stable 'hot' coronal loop structures. Our results suggest that alpha TrA does not have any steady X-ray emission consistent with theoretical expectations, and support the argument that Hybrid stars constitute a transitional type of object in which large-scale magnetic dynamo activity ceases, and the dominant spatial scales characterizing coronal structure rapidly decline as such stars evolve across the X-ray 'Dividing Line' in the H-R diagram.

Calcium and magnesium fluxes across the plasma membrane of the toad rod outer segment.

PubMed Central

Nakatani, K; Yau, K W

1988-01-01

1. Membrane current was recorded from an isolated, dark-adapted toad rod by sucking either its inner segment or outer segment into a tight-fitting glass pipette containing Ringer solution. The remainder of the cell was exposed to bath solution which could be changed rapidly. 2. In normal Ringer solution the current response of a cell to a saturating flash or step of light showed a small secondary rise at its initial peak. The profile of this secondary rise (i.e. amplitude and time course) was independent of both the intensity and the duration of illumination once the light response had reached a plateau level. 3. This secondary rise disappeared when external Na+ around the outer segment was replaced by Li+ or guanidinium, suggesting that it represented an electrogenic Na+-dependent Ca2+ efflux which was declining after the onset of light. 4. This Na+-Ca2+ exchange activity showed a roughly exponential decline, with a time constant of about 0.5 s. Exponential extrapolation of the exchange current to the time at half-height of the light response gave an initial amplitude of about 2 pA. Using La3+ as a blocker, we did not detect any steady exchange current after the initial exponential decline. 5. An intense flash superposed on a just-saturating steady background light failed to produce any incremental exchange current transient. 6. Our interpretation of the above results is that in darkness there are counterbalancing levels of Ca2+ influx (through the light-sensitive conductance) and efflux (through the Na+-Ca2+ exchange) across the plasma membrane of the rod outer segment. The exchange current transient at the onset of light merely represents the unidirectional Ca2+ efflux which becomes revealed as a result of the stoppage of the Ca2+ influx, rather than a de novo Ca2+ efflux triggered by light. 7. Consistent with this interpretation, a test light delivered soon after a saturating, conditioning light elicited little exchange current, which then gradually recovered to control value with a time course parallel to the restoration of the dark current. Conversely, when the dark current was increased above its physiological level by IBMX (isobutylmethylxanthine) the exchange current transient became larger than control.(ABSTRACT TRUNCATED AT 400 WORDS) Images Fig. 8 PMID:2457685

Up in Arms: Immune and Nervous System Response to Sea Star Wasting Disease.

PubMed

Fuess, Lauren E; Eisenlord, Morgan E; Closek, Collin J; Tracy, Allison M; Mauntz, Ruth; Gignoux-Wolfsohn, Sarah; Moritsch, Monica M; Yoshioka, Reyn; Burge, Colleen A; Harvell, C Drew; Friedman, Carolyn S; Hewson, Ian; Hershberger, Paul K; Roberts, Steven B

2015-01-01

Echinoderms, positioned taxonomically at the base of deuterostomes, provide an important system for the study of the evolution of the immune system. However, there is little known about the cellular components and genes associated with echinoderm immunity. The 2013-2014 sea star wasting disease outbreak is an emergent, rapidly spreading disease, which has led to large population declines of asteroids in the North American Pacific. While evidence suggests that the signs of this disease, twisting arms and lesions, may be attributed to a viral infection, the host response to infection is still poorly understood. In order to examine transcriptional responses of the sea star Pycnopodia helianthoides to sea star wasting disease, we injected a viral sized fraction (0.2 μm) homogenate prepared from symptomatic P. helianthoides into apparently healthy stars. Nine days following injection, when all stars were displaying signs of the disease, specimens were sacrificed and coelomocytes were extracted for RNA-seq analyses. A number of immune genes, including those involved in Toll signaling pathways, complement cascade, melanization response, and arachidonic acid metabolism, were differentially expressed. Furthermore, genes involved in nervous system processes and tissue remodeling were also differentially expressed, pointing to transcriptional changes underlying the signs of sea star wasting disease. The genomic resources presented here not only increase understanding of host response to sea star wasting disease, but also provide greater insight into the mechanisms underlying immune function in echinoderms.

Shrinking galaxy disks with fountain-driven accretion from the halo

DOE Office of Scientific and Technical Information (OSTI.GOV)

Elmegreen, Bruce G.; Struck, Curtis; Hunter, Deidre A., E-mail: bge@watson.ibm.com, E-mail: curt@iastate.edu, E-mail: dah@lowell.edu

2014-12-01

Star formation in most galaxies requires cosmic gas accretion because the gas consumption time is short compared to the Hubble time. This accretion presumably comes from a combination of infalling satellite debris, cold flows, and condensation of hot halo gas at the cool disk interface, perhaps aided by a galactic fountain. In general, the accretion will have a different specific angular momentum than the part of the disk that receives it, even if the gas comes from the nearby halo. The gas disk then expands or shrinks over time. Here we show that condensation of halo gas at a ratemore » proportional to the star formation rate in the fountain model will preserve an initial shape, such as an exponential, with a shrinking scale length, leaving behind a stellar disk with a slightly steeper profile of younger stars near the center. This process is slow for most galaxies, producing imperceptible radial speeds, and it may be dominated by other torques, but it could be important for blue compact dwarfs, which tend to have large, irregular gas reservoirs and steep blue profiles in their inner stellar disks.« less

Test of the Hill Stability Criterion against Chaos Indicators

NASA Astrophysics Data System (ADS)

Satyal, Suman; Quarles, Billy; Hinse, Tobias

2012-10-01

The efficacy of Hill Stability (HS) criterion is tested against other known chaos indicators such as Maximum Lyapunov Exponents (MLE) and Mean Exponential Growth of Nearby Orbits (MEGNO) maps. First, orbits of four observationally verified binary star systems: γ Cephei, Gliese-86, HD41004, and HD196885 are integrated using standard integration packages (MERCURY, SWIFTER, NBI, C/C++). The HS which measures orbital perturbation of a planet around the primary star due to the secondary star is calculated for each system. The LEs spectra are generated to measure the divergence/convergence rate of stable manifolds and the MEGNO maps are generated by using the variational equations of the system during the integration process. These maps allow to accurately differentiate between stable and unstable dynamical systems. Then the results obtained from the analysis of HS, MLE, and MEGNO maps are checked for their dynamical variations and resemblance. The HS of most of the planets seems to be stable, quasi-periodic for at least ten million years. The MLE and the MEGNO maps also indicate the local quasi-periodicity and global stability in relatively short integration period. The HS criterion is found to be a comparably efficient tool to measure the stability of planetary orbits.

Gamma-ray emission from globular clusters. Shock high energy emission from the Be-Star/Pulsar System PSR 1259-63. Echoes in x-ray novae

NASA Technical Reports Server (NTRS)

Kaaret, Philip

1995-01-01

This grant covers work on the Compton phase 3 investigation, 'Shock High Energy Emission from the Be- Star/Pulsar System PSR 1259-63' and cycle 4 investigations 'Diffuse Gamma-Ray Emission at High Latitudes' and 'Echoes in X-Ray Novae'. Work under the investigation 'Diffuse Gamma-Ray Emission at High Latitudes' has lead to the publication of a paper (attached), describing gamma-ray emissivity variations in the northern galactic hemisphere. Using archival EGRET data, we have found a large irregular region of enhanced gamma-ray emissivity at energies greater 100 MeV. This is the first observation of local structure in the gamma-ray emissivity. Work under the investigation 'Echoes in X-Ray Novae' is proceeding with analysis of data from OSSE from the transient source GRO J1655-40. The outburst of this source last fall triggered this Target of Opportunity investigation. Preliminary spectral analysis shows emission out to 600 keV and a pure power low spectrum with no evidence of an exponential cutoff. Work is complete on the analysis of BATSE data from the Be-Star/Pulsar Sustem PSR 1259-63.

Hypoxia reduces testosterone synthesis in mouse Leydig cells by inhibiting NRF1-activated StAR expression

PubMed Central

Zou, Zhiran; Wang, Dan; Lu, Yapeng; Dong, Zhangji; Zhu, Li

2017-01-01

Male fertility disorders play a key role in half of all infertility cases. Reduction in testosterone induced by hypoxia might cause diseases in reproductive system and other organs. Hypoxic exposure caused a significant decrease of NRF1. Software analysis reported that the promoter region of steroidogenic acute regulatory protein (StAR) contained NRF1 binding sites, indicating NRF1 promoted testicular steroidogenesis. The purpose of this study is to determine NRF1 is involved in testosterone synthesis; and under hypoxia, the decrease of testosterone synthesis is caused by lower expression of NRF1. We designed both in vivo and in vitro experiments. Under hypoxia, the expressions of NRF1 in Leydig cells and testosterone level were significantly decreased both in vivo and in vitro. Overexpression and interference NRF1 could induced StAR and testosterone increased and decreased respectively. ChIP results confirmed the binding of NRF1 to StAR promoter region. In conclusion, decline of NRF1 expression downregulated the level of StAR, which ultimately resulted in a reduction in testosterone synthesis. PMID:28146428

REVIEWS OF TOPICAL PROBLEMS: The differential rotation of stars

NASA Astrophysics Data System (ADS)

Kitchatinov, Leonid L.

2005-05-01

Astronomical observations of recent years have substantially extended our knowledge of the rotation of stars. Helioseismology has found out that the equator-to-pole decline in the angular velocity observed on the solar surface traces down to the deep interior of the Sun. New information has been gained regarding the dependence of the rotational nonuniformities on the angular velocity and mass of the star. These achievements have prompted the development of the theory of differential rotation, which is the focal point of this review. Nonuniform rotation results from the interaction of turbulent convection with rotation. The investigation into the turbulent mechanisms of angular-momentum transport has reached a level at which the obtained results can serve as the basis for developing quantitative models of stellar rotation. Such models contain virtually no free parameters but closely reproduce the helioseismological data on the internal rotation of the Sun. The theoretical predictions on the differential rotation of the stars agree with observations. A brief discussion is held here on the relation between the magnetic activity of stars and the nonuniformity of their rotation and on prospects for further development of the theory.

Endogenous technological and demographic change under increasing water scarcity

NASA Astrophysics Data System (ADS)

Pande, S.; Ertsen, M.; Sivapalan, M.

2013-12-01

Many ancient civilizations such as the Indus Valley civilization dispersed under extreme dry conditions. Even contemporary societies such as the one in Murrumbidgee river basin, Australia, have started to witness a decline in overall population under increasing water scarcity. Skeptics of hydroclimatic determinism have often cautioned against the use of hydroclimatic change as the sole predictor of the fate of contemporary societies in water scarce regions by suggesting that technological change may ameliorate the effects of increasing water scarcity. We here develop a simple overlapping generations model of endogenous technological and demographic change. It models technological change not as an exogenous random sequence of events but as an endogenous process (as is widely accepted in contemporary literature) that depends on factors such as the investments that are (endogenously) made in a society, the endogenous diversification of a society into skilled and unskilled workers, individuals' patience in terms of its present consumption versus future consumption, the production technology and the (endogenous) interaction of these factors. The population growth rate is modeled to decline once consumption per capita crosses a ';survival' threshold. The model demonstrates that technological change may ameliorate the effects of increasing water scarcity but only to a certain extent in many cases. It is possible that technological change may allow a society to escape the effect of increasing water society, leading to an exponential rise in technology and population. However, such cases require that the rate of success of investment in technological advancement is high. In other more realistic cases of technological success, we find that endogenous technology change has an effect delaying the peak of population before it starts to decline. While the model is a rather simple model of societal growth, it is capable of replicating (not to scale) patterns of technological change (proxies of which in ancient technology include irrigation canals, metal tools, and the use of horses for labor while in contemporary societies its proxies may be the advent of drip irrigation, increasing reservoir storage capacity etc) and population change. It is capable of replicating the pattern of declining consumption per capita in presence of growth in aggregate production. It is also capable of modeling the exponential population rise even under increasing water scarcity. The results of the model suggest, as one of the many other possible explanations, that ancient societies that declined in the face of extreme water scarcity may have done so due to slower rate of success of investment in technological advancement. The model suggests that the population decline occurs after a prolonged decline in consumption per capita, which in turn is due to the joint effect of initially increasing population and increasing water scarcity. This is despite technological advancement and increase in aggregate production. Thus declining consumption per capita despite technological advancement and increase in aggregate production may serve as a useful predictor of upcoming decline in contemporary societies in water scarce basins.

Prediction of solar energetic particle event histories using real-time particle and solar wind measurements

NASA Technical Reports Server (NTRS)

Roelof, E. C.; Gold, R. E.

1978-01-01

The comparatively well-ordered magnetic structure in the solar corona during the decline of Solar Cycle 20 revealed a characteristic dependence of solar energetic particle injection upon heliographic longitude. When analyzed using solar wind mapping of the large scale interplanetary magnetic field line connection from the corona to the Earth, particle fluxes display an approximately exponential dependence on heliographic longitude. Since variations in the solar wind velocity (and hence the coronal connection longitude) can severely distort the simple coronal injection profile, the use of real-time solar wind velocity measurements can be of great aid in predicting the decay of solar particle events. Although such exponential injection profiles are commonplace during 1973-1975, they have also been identified earlier in Solar Cycle 20, and hence this structure may be present during the rise and maximum of the cycle, but somewhat obscured by greater temporal variations in particle injection.

Vacuum statistics and stability in axionic landscapes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Masoumi, Ali; Vilenkin, Alexander, E-mail: ali@cosmos.phy.tufts.edu, E-mail: vilenkin@cosmos.phy.tufts.edu

2016-03-01

We investigate vacuum statistics and stability in random axionic landscapes. For this purpose we developed an algorithm for a quick evaluation of the tunneling action, which in most cases is accurate within 10%. We find that stability of a vacuum is strongly correlated with its energy density, with lifetime rapidly growing as the energy density is decreased. On the other hand, the probability P(B) for a vacuum to have a tunneling action B greater than a given value declines as a slow power law in B. This is in sharp contrast with the studies of random quartic potentials, which foundmore » a fast exponential decline of P(B). Our results suggest that the total number of relatively stable vacua (say, with B>100) grows exponentially with the number of fields N and can get extremely large for N∼> 100. The problem with this kind of model is that the stable vacua are concentrated near the absolute minimum of the potential, so the observed value of the cosmological constant cannot be explained without fine-tuning. To address this difficulty, we consider a modification of the model, where the axions acquire a quadratic mass term, due to their mixing with 4-form fields. This results in a larger landscape with a much broader distribution of vacuum energies. The number of relatively stable vacua in such models can still be extremely large.« less

Density-Dependent Growth in Invasive Lionfish (Pterois volitans)

PubMed Central

Benkwitt, Cassandra E.

2013-01-01

Direct demographic density dependence is necessary for population regulation and is a central concept in ecology, yet has not been studied in many invasive species, including any invasive marine fish. The red lionfish (Pterois volitans) is an invasive predatory marine fish that is undergoing exponential population growth throughout the tropical western Atlantic. Invasive lionfish threaten coral-reef ecosystems, but there is currently no evidence of any natural population control. Therefore, a manipulative field experiment was conducted to test for density dependence in lionfish. Juvenile lionfish densities were adjusted on small reefs and several demographic rates (growth, recruitment, immigration, and loss) were measured throughout an 8-week period. Invasive lionfish exhibited direct density dependence in individual growth rates, as lionfish grew slower at higher densities throughout the study. Individual growth in length declined linearly with increasing lionfish density, while growth in mass declined exponentially with increasing density. There was no evidence, however, for density dependence in recruitment, immigration, or loss (mortality plus emigration) of invasive lionfish. The observed density-dependent growth rates may have implications for which native species are susceptible to lionfish predation, as the size and type of prey that lionfish consume is directly related to their body size. The absence of density-dependent loss, however, contrasts with many native coral-reef fish species and suggests that for the foreseeable future manual removals may be the only effective local control of this invasion. PMID:23825604

Density-dependent growth in invasive Lionfish (Pterois volitans).

PubMed

Benkwitt, Cassandra E

2013-01-01

Direct demographic density dependence is necessary for population regulation and is a central concept in ecology, yet has not been studied in many invasive species, including any invasive marine fish. The red lionfish (Pterois volitans) is an invasive predatory marine fish that is undergoing exponential population growth throughout the tropical western Atlantic. Invasive lionfish threaten coral-reef ecosystems, but there is currently no evidence of any natural population control. Therefore, a manipulative field experiment was conducted to test for density dependence in lionfish. Juvenile lionfish densities were adjusted on small reefs and several demographic rates (growth, recruitment, immigration, and loss) were measured throughout an 8-week period. Invasive lionfish exhibited direct density dependence in individual growth rates, as lionfish grew slower at higher densities throughout the study. Individual growth in length declined linearly with increasing lionfish density, while growth in mass declined exponentially with increasing density. There was no evidence, however, for density dependence in recruitment, immigration, or loss (mortality plus emigration) of invasive lionfish. The observed density-dependent growth rates may have implications for which native species are susceptible to lionfish predation, as the size and type of prey that lionfish consume is directly related to their body size. The absence of density-dependent loss, however, contrasts with many native coral-reef fish species and suggests that for the foreseeable future manual removals may be the only effective local control of this invasion.

Direct Measurements of Dust Attenuation in z ~ 1.5 Star-forming Galaxies from 3D-HST: Implications for Dust Geometry and Star Formation Rates

NASA Astrophysics Data System (ADS)

Price, Sedona H.; Kriek, Mariska; Brammer, Gabriel B.; Conroy, Charlie; Förster Schreiber, Natascha M.; Franx, Marijn; Fumagalli, Mattia; Lundgren, Britt; Momcheva, Ivelina; Nelson, Erica J.; Skelton, Rosalind E.; van Dokkum, Pieter G.; Whitaker, Katherine E.; Wuyts, Stijn

2014-06-01

The nature of dust in distant galaxies is not well understood, and until recently few direct dust measurements have been possible. We investigate dust in distant star-forming galaxies using near-infrared grism spectra of the 3D-HST survey combined with archival multi-wavelength photometry. These data allow us to make a direct comparison between dust around star-forming regions (A V, H II ) and the integrated dust content (A V, star). We select a sample of 163 galaxies between 1.36 <= z <= 1.5 with Hα signal-to-noise ratio >=5 and measure Balmer decrements from stacked spectra to calculate A V, H II . First, we stack spectra in bins of A V, star, and find that A V, H II = 1.86 A V, star, with a significance of σ = 1.7. Our result is consistent with the two-component dust model, in which galaxies contain both diffuse and stellar birth cloud dust. Next, we stack spectra in bins of specific star formation rate (log SSFR), star formation rate (log SFR), and stellar mass (log M *). We find that on average A V, H II increases with SFR and mass, but decreases with increasing SSFR. Interestingly, the data hint that the amount of extra attenuation decreases with increasing SSFR. This trend is expected from the two-component model, as the extra attenuation will increase once older stars outside the star-forming regions become more dominant in the galaxy spectrum. Finally, using Balmer decrements we derive dust-corrected Hα SFRs, and find that stellar population modeling produces incorrect SFRs if rapidly declining star formation histories are included in the explored parameter space.

The primordial and evolutionary abundance variations in globular-cluster stars: a problem with two unknowns

NASA Astrophysics Data System (ADS)

Denissenkov, P. A.; VandenBerg, D. A.; Hartwick, F. D. A.; Herwig, F.; Weiss, A.; Paxton, B.

2015-04-01

We demonstrate that among the potential sources of the primordial abundance variations of the proton-capture elements in globular-cluster stars proposed so far, such as the hot-bottom burning in massive asymptotic giant branch stars and H burning in the convective cores of supermassive and fast-rotating massive main-sequence (MS) stars, only the supermassive MS stars with M > 104 M⊙ can explain all the observed abundance correlations without any fine-tuning of model parameters. We use our assumed chemical composition for the pristine gas in M13 (NGC 6205) and its mixtures with 50 and 90 per cent of the material partially processed in H burning in the 6 × 104 M⊙ MS model star as the initial compositions for the normal, intermediate, and extreme populations of low-mass stars in this globular cluster, as suggested by its O-Na anticorrelation. We evolve these stars from the zero-age MS to the red giant branch (RGB) tip with the thermohaline and parametric prescriptions for the RGB extra mixing. We find that the 3He-driven thermohaline convection cannot explain the evolutionary decline of [C/Fe] in M13 RGB stars, which, on the other hand, is well reproduced with the universal values for the mixing depth and rate calibrated using the observed decrease of [C/Fe] with MV in the globular cluster NGC5466 that does not have the primordial abundance variations.

Constraints on the Efficiency of Radial Migration in Spiral Galaxies

NASA Astrophysics Data System (ADS)

Daniel, Kathryne J.; Wyse, Rosemary F. G.

2015-01-01

A transient spiral arm can permanently rearrange the orbital angular momentum of the stellar disk without inducing kinematic heating. This phenomenon is called radial migration because a star's orbital angular momentum determines its mean orbital radius. Should radial migration be an efficient process it could cause a large fraction of disk stars to experience significant changes in their individual orbital angular momenta on dynamically short timescales. Such scenarios have strong implications for the chemical, structural and kinematic evolution of disk galaxies. We have undertaken an investigation into the physical dependencies of the efficiency of radial migration on stellar kinematics and spiral structure. In order for a disk star to migrate radially, it must first be 'trapped' in a particular family of orbits, called horseshoe orbits, that occur near the radius of corotation with a spiral pattern. Thus far, the only analytic criterion for horseshoe orbits has been for stars with zero random orbital energy. We present our analytically derived 'capture criterion' for stars with some finite random orbital energy in a disk with a given rotation curve. Our capture criterion predict that trapping in a horseshoe orbit is primarily determined by whether or not the position of a star's mean orbital radius (determined by its orbital angular momentum) is within the 'capture region', the location and shape of which can be derived from the capture criterion. We visualize and confirm this prediction via numerically integrated orbits. We then apply our capture criterion to snap shot models of disk galaxies to determine (1) the radial distribution of the fraction of stars initially trapped in horseshoe orbits, and (2) the dependence of the total fraction of captured stars in the disk on the radial component of the stellar velocity dispersion (σR) and the amplitude of the spiral perturbation to the underlying potential at corotation. We here present a model of an exponential disk with a flat rotation curve where the initial fraction of stars trapped in horseshoe orbits falls with increasing velocity dispersion as exp[-σR^2].

Photographic observations of six comets

NASA Astrophysics Data System (ADS)

de Sanctis, G.; Ferreri, W.; Zappala, V.

Sixty-nine positions of six comets are given as obtained from photographic observations made at the Observatory of Torino from October 1980 to September 1982. Positions are given for Comets Encke, Stephan-Oterma, Meier, Bradfield, Panther, and Austin. Plates were measured with a Zeiss two-coordinate measuring machine. The AGK3 catalog was used to obtain the positions of reference stars and the coordinates of an additional cataloged star near the position of the comet on the plate. The mean values of the differences between the cataloged positions were found to be 0.72 arcsec and 0.52 arcsec in right ascension and declination, respectively.

A detailed view of the gas shell around R Sculptoris with ALMA

NASA Astrophysics Data System (ADS)

Maercker, M.; Vlemmings, W. H. T.; Brunner, M.; De Beck, E.; Humphreys, E. M.; Kerschbaum, F.; Lindqvist, M.; Olofsson, H.; Ramstedt, S.

2016-02-01

Context. During the asymptotic giant branch (AGB) phase, stars undergo thermal pulses - short-lived phases of explosive helium burning in a shell around the stellar core. Thermal pulses lead to the formation and mixing-up of new elements to the stellar surface. They are hence fundamental to the chemical evolution of the star and its circumstellar envelope. A further consequence of thermal pulses is the formation of detached shells of gas and dust around the star, several of which have been observed around carbon-rich AGB stars. Aims: We aim to determine the physical properties of the detached gas shell around R Sculptoris, in particular the shell mass and temperature, and to constrain the evolution of the mass-loss rate during and after a thermal pulse. Methods: We analyse 12CO(1-0), 12CO(2-1), and 12CO(3-2) emission, observed with the Atacama Large Millimeter/submillimeter Array (ALMA) during Cycle 0 and complemented by single-dish observations. The spatial resolution of the ALMA data allows us to separate the detached shell emission from the extended emission inside the shell. We perform radiative transfer modelling of both components to determine the shell properties and the post-pulse mass-loss properties. Results: The ALMA data show a gas shell with a radius of 19.̋5 expanding at 14.3 km s-1. The different scales probed by the ALMA Cycle 0 array show that the shell must be entirely filled with gas, contrary to the idea of a detached shell. The comparison to single-dish spectra and radiative transfer modelling confirms this. We derive a shell mass of 4.5 × 10-3 M⊙ with a temperature of 50 K. Typical timescales for thermal pulses imply a pulse mass-loss rate of 2.3 × 10-5 M⊙ yr-1. For the post-pulse mass-loss rate, we find evidence for a gradual decline of the mass-loss rate, with an average value of 1.6 × 10-5 M⊙ yr-1. The total amount of mass lost since the last thermal pulse is 0.03 M⊙, a factor four higher compared to classical models, with a sharp decline in mass-loss rate immediately after the pulse. Conclusions: We find that the mass-loss rate after a thermal pulse has to decline more slowly than generally expected from models of thermal pulses. This may cause the star to lose significantly more mass during a thermal pulse cycle, which affects the lifetime on the AGB and the chemical evolution of the star, its circumstellar envelope, and the interstellar medium.

Cold induced mortality of the Burmese Python: An explanation via stochastic analysis

NASA Astrophysics Data System (ADS)

Quansah, Emmanuel; Parshad, Rana D.; Mondal, Sumona

2017-02-01

The Burmese python (Python bivitatus) is an invasive species, wreaking havoc on indigenous species in the Florida everglades. Data suggests an exponential growth in their population from 1995 to 2009, with a sharp decline however in 2010-2012 (Dorcas et al., 2012). In Mazzotti et al. (2011) an explanation is provided, citing the unusually cold winter that year, as the primary reason for this decline. We provide a first mathematical model, in the form of a system of stochastic differential equations, that supports the explanation in Mazzotti et al. (2011), by accurately matching the field data presented in Dorcas et al. (2012). More generally, our model provides a tool to predict the population dynamics of rapidly growing alien species, in the advent of climate change.

Evolution of X-ray activity of 1-3 Msun late-type stars in early post-main-sequence phases

NASA Astrophysics Data System (ADS)

Pizzolato, N.; Maggio, A.; Sciortino, S.

2000-09-01

We have investigated the variation of coronal X-ray emission during early post-main-sequence phases for a sample of 120 late-type stars within 100 pc, and with estimated masses in the range 1-3 Msun, based on Hipparcos parallaxes and recent evolutionary models. These stars were observed with the ROSAT/PSPC, and the data processed with the Palermo-CfA pipeline, including detection and evaluation of X-ray fluxes (or upper limits) by means of a wavelet transform algorithm. We have studied the evolutionary history of X-ray luminosity and surface flux for stars in selected mass ranges, including stars with inactive A-type progenitors on the main sequence and lower mass solar-type stars. Our stellar sample suggests a trend of increasing X-ray emission level with age for stars with masses M > 1.5 Msun, and a decline for lower-mass stars. A similar behavior holds for the average coronal temperature, which follows a power-law correlation with the X-ray luminosity, independently of their mass and evolutionary state. We have also studied the relationship between X-ray luminosity and surface rotation rate for stars in the same mass ranges, and how this relationships departs from the Lx ~ vrot2 law followed by main-sequence stars. Our results are interpreted in terms of a magnetic dynamo whose efficiency depends on the stellar evolutionary state through the mass-dependent changes of the stellar internal structure, including the properties of envelope convection and the internal rotation profile.

Sensitivity Monitoring of the SECCHI COR1 Telescopes on STEREO

NASA Astrophysics Data System (ADS)

Thompson, William T.

2018-03-01

Measurements of bright stars passing through the fields of view of the inner coronagraphs (COR1) on board the Solar Terrestrial Relations Observatory (STEREO) are used to monitor changes in the radiometric calibration over the course of the mission. Annual decline rates are found to be 0.648 ± 0.066%/year for COR1-A on STEREO Ahead and 0.258 ± 0.060%/year for COR1-B on STEREO Behind. These rates are consistent with decline rates found for other space-based coronagraphs in similar radiation environments. The theorized cause for the decline in sensitivity is darkening of the lenses and other optical elements due to exposure to high-energy solar particles and photons, although other causes are also possible. The total decline in the COR-B sensitivity when contact with Behind was lost on 1 October 2014 was 1.7%, while COR1-A was down by 4.4%. As of 1 November 2017, the COR1-A decline is estimated to be 6.4%. The SECCHI calibration routines will be updated to take these COR1 decline rates into account.

Detection of high Lyman continuum leakage from four low-redshift compact star-forming galaxies

NASA Astrophysics Data System (ADS)

Izotov, Y. I.; Schaerer, D.; Thuan, T. X.; Worseck, G.; Guseva, N. G.; Orlitová, I.; Verhamme, A.

2016-10-01

Following our first detection reported in Izotov et al., we present the detection of Lyman continuum (LyC) radiation of four other compact star-forming galaxies observed with the Cosmic Origins Spectrograph (COS) onboard the Hubble Space Telescope. These galaxies, at redshifts of z ˜ 0.3, are characterized by high emission-line flux ratios [O III] λ5007/[O II] λ3727 ≳ 5. The escape fractions of the LyC radiation fesc(LyC) in these galaxies are in the range of ˜6-13 per cent, the highest values found so far in low-redshift star-forming galaxies. Narrow double-peaked Ly α emission lines are detected in the spectra of all four galaxies, compatible with predictions for LyC leakers. We find escape fractions of Ly α, fesc(Ly α) ˜ 20-40 per cent, among the highest known for Ly α emitting galaxies. Surface brightness profiles produced from the COS acquisition images reveal bright star-forming regions in the centre and exponential discs in the outskirts with disc scalelengths α in the range ˜0.6-1.4 kpc. Our galaxies are characterized by low metallicity, ˜1/8-1/5 solar, low stellar mass ˜(0.2-4) × 109 M⊙, high star formation rates, SFR ˜ 14-36 M⊙ yr-1, and high SFR densities, Σ ˜ 2-35 M⊙ yr-1 kpc-2. These properties are comparable to those of high-redshift star-forming galaxies. Finally, our observations, combined with our first detection reported in Izotov et al., reveal that a selection for compact star-forming galaxies showing high [O III] λ5007/[O II] λ3727 ratios appears to pick up very efficiently sources with escaping LyC radiation: all five of our selected galaxies are LyC leakers.

Arm retraction dynamics of entangled star polymers: A forward flux sampling method study

NASA Astrophysics Data System (ADS)

Zhu, Jian; Likhtman, Alexei E.; Wang, Zuowei

2017-07-01

The study of dynamics and rheology of well-entangled branched polymers remains a challenge for computer simulations due to the exponentially growing terminal relaxation times of these polymers with increasing molecular weights. We present an efficient simulation algorithm for studying the arm retraction dynamics of entangled star polymers by combining the coarse-grained slip-spring (SS) model with the forward flux sampling (FFS) method. This algorithm is first applied to simulate symmetric star polymers in the absence of constraint release (CR). The reaction coordinate for the FFS method is determined by finding good agreement of the simulation results on the terminal relaxation times of mildly entangled stars with those obtained from direct shooting SS model simulations with the relative difference between them less than 5%. The FFS simulations are then carried out for strongly entangled stars with arm lengths up to 16 entanglements that are far beyond the accessibility of brute force simulations in the non-CR condition. Apart from the terminal relaxation times, the same method can also be applied to generate the relaxation spectra of all entanglements along the arms which are desired for the development of quantitative theories of entangled branched polymers. Furthermore, we propose a numerical route to construct the experimentally measurable relaxation correlation functions by effectively linking the data stored at each interface during the FFS runs. The obtained star arm end-to-end vector relaxation functions Φ (t ) and the stress relaxation function G(t) are found to be in reasonably good agreement with standard SS simulation results in the terminal regime. Finally, we demonstrate that this simulation method can be conveniently extended to study the arm-retraction problem in entangled star polymer melts with CR by modifying the definition of the reaction coordinate, while the computational efficiency will depend on the particular slip-spring or slip-link model employed.

The Sleeping Monster: NuSTAR Observations of SGR 1806-20, 11 Years After the Giant Flare

NASA Astrophysics Data System (ADS)

Younes, George; Baring, Matthew G.; Kouveliotou, Chryssa; Harding, Alice; Donovan, Sophia; Göğüş, Ersin; Kaspi, Victoria; Granot, Jonathan

2017-12-01

We report the analysis of five Nuclear Spectroscopic Telescope Array (NuSTAR) observations of SGR 1806-20 spread over a year from 2015 April to 2016 April, more than 11 years following its giant flare (GF) of 2004. The source spin frequency during the NuSTAR observations follows a linear trend with a frequency derivative \\dot{ν }=(-1.25+/- 0.03)× {10}-12 Hz s-1, implying a surface dipole equatorial magnetic field B≈ 7.7× {10}14 G. Thus, SGR 1806-20 has finally returned to its historical minimum torque level measured between 1993 and 1998. The source showed strong timing noise for at least 12 years starting in 2000, with \\dot{ν } increasing one order of magnitude between 2005 and 2011, following its 2004 major bursting episode and GF. SGR 1806-20 has not shown strong transient activity since 2009, and we do not find short bursts in the NuSTAR data. The pulse profile is complex with a pulsed fraction of ˜ 8 % with no indication of energy dependence. The NuSTAR spectra are well fit with an absorbed blackbody, {kT}=0.62+/- 0.06 {keV}, plus a power law, {{Γ }}=1.33+/- 0.03. We find no evidence for variability among the five observations, indicating that SGR 1806-20 has reached a persistent and potentially its quiescent X-ray flux level after its 2004 major bursting episode. Extrapolating the NuSTAR model to lower energies, we find that the 0.5-10 keV flux decay follows an exponential form with a characteristic timescale τ =543+/- 75 days. Interestingly, the NuSTAR flux in this energy range is a factor of ˜2 weaker than the long-term average measured between 1993 and 2003, a behavior also exhibited in SGR 1900+14. We discuss our findings in the context of the magnetar model.

Extremely Hard X-ray Emission from Eta Carinae observed with XMM-Newton and NuSTAR around Periastron in 2014.5

NASA Astrophysics Data System (ADS)

Hamaguchi, Kenji; Corcoran, Michael F.; Takahashi, Hiromitsu; Yuasa, Tadayuki; Groh, Jose H.; Russell, Christopher Michael Post; Pittard, Julian M.; Madura, Thomas; Owocki, Stanley P.; Grefenstette, Brian

2015-01-01

The super massive colliding wind binary system, Eta Carinae, experienced another periastron passage in the summer of 2014. We monitored this event using the multiple X-ray observatories, Chandra, XMM-Newton, NuSTAR, Suzaku and Swift. With a high eccentricity of its 5.5 year orbit, X-ray emission from the wind-wind collision (WWC) increases strongly toward periastron but then drops sharply by more than two orders of magnitude in two weeks around periastron due probably to an eclipse and an intrinsic activity decline of the WWC plasma. In this observing campaign, XMM-Newton and NuSTAR coordinated two simultaneous observations around the X-ray flux maximum on June 6 and just before the flux minimum on July 28. These two observations captured Eta Carinae with X-ray focusing telescopes in the extreme hard X-ray band above 10 keV for the first time.During the first observation, XMM and NuSTAR detected stable X-ray emission from the central binary system between 1 - 40 keV. A fit of a 1-temperature bremsstrahlung model to the high energy slope in the NuSTAR spectrum derives an electron temperature of ~6 keV, which is significantly higher than an ionization temperature at ~4.5 keV, measured from the Fe K emission lines resolved in the XMM spectrum.This result suggests the presence of very hot plasma and/or X-ray reflection at surrounding cold material. During the second observation, the X-ray flux between 5 - 10 keV declined steadily by a factor of ~2 in a day, while the other energy bands were rather stable. This variation may be explained by an increase of the line of sight absorption to emission from the plasma component that dominates above 5 keV. NuSTAR did not detect, in either observation, the very hard non-thermal component that dominated emission above 25 keV seen in earlier INTEGRAL and Suzaku observations. We discuss the plasma condition and the wind structure of Eta Carinae around periastron, and the nature of the non-thermal component.

The petroleum exponential (again)

NASA Astrophysics Data System (ADS)

Bell, Peter M.

The U.S. production and reserves of liquid and gaseous petroleum have declined since 1960, at least in the lower 48 states. This decline stems from decreased discovery rates, as predicted by M. King Hubbert in the mid-1950's. Hubbert's once unpopular views were based on statistical analysis of the production history of the petroleum industry, and now, even with inclusion of the statistical perturbation caused by the Prudhoe Bay-North Alaskan Slope discovery (the largest oil field ever found in the United States), it seems clear again that production is following the exponential curve to depletion of the resource—to the end of the ultimate yield of petroleum from wells in the United States.In a recent report, C. Hall and C. Cleveland of Cornell University show that large atypical discoveries, such as the Prudhoe Bay find, are but minor influences on what now appears to be the crucial intersection of two exponentials [Science, 211, 576-579, 1981]: the production-per-drilled-foot curve of Hubbert, which crosses zero production no later than the year 2005; the other, a curve that plots the energy cost of drilling and extraction with time; that is, the cost-time rate of how much oil is used to drill and extract oil from the ground. The intersection, if no other discoveries the size of the Prudhoe Bay field are made, could be as early as 1990, the end of the present decade. The inclusion of each Prudhoe-Bay-size find extends the year of intersection by only about 6 years. Beyond that point, more than one barrel of petroleum would be expended for each barrel extracted from the ground. The oil exploration-extraction and refining industry is currently the second most energy-intensive industry in the U.S., and the message seems clear. Either more efficient drilling and production techniques are discovered, or domestic production will cease well before the end of this century if the Hubbert analysis modified by Hall and Cleveland is correct.

Characterizing the reproduction number of epidemics with early subexponential growth dynamics

PubMed Central

Viboud, Cécile; Simonsen, Lone; Moghadas, Seyed M.

2016-01-01

Early estimates of the transmission potential of emerging and re-emerging infections are increasingly used to inform public health authorities on the level of risk posed by outbreaks. Existing methods to estimate the reproduction number generally assume exponential growth in case incidence in the first few disease generations, before susceptible depletion sets in. In reality, outbreaks can display subexponential (i.e. polynomial) growth in the first few disease generations, owing to clustering in contact patterns, spatial effects, inhomogeneous mixing, reactive behaviour changes or other mechanisms. Here, we introduce the generalized growth model to characterize the early growth profile of outbreaks and estimate the effective reproduction number, with no need for explicit assumptions about the shape of epidemic growth. We demonstrate this phenomenological approach using analytical results and simulations from mechanistic models, and provide validation against a range of empirical disease datasets. Our results suggest that subexponential growth in the early phase of an epidemic is the rule rather the exception. Mechanistic simulations show that slight modifications to the classical susceptible–infectious–removed model result in subexponential growth, and in turn a rapid decline in the reproduction number within three to five disease generations. For empirical outbreaks, the generalized-growth model consistently outperforms the exponential model for a variety of directly and indirectly transmitted diseases datasets (pandemic influenza, measles, smallpox, bubonic plague, cholera, foot-and-mouth disease, HIV/AIDS and Ebola) with model estimates supporting subexponential growth dynamics. The rapid decline in effective reproduction number predicted by analytical results and observed in real and synthetic datasets within three to five disease generations contrasts with the expectation of invariant reproduction number in epidemics obeying exponential growth. The generalized-growth concept also provides us a compelling argument for the unexpected extinction of certain emerging disease outbreaks during the early ascending phase. Overall, our approach promotes a more reliable and data-driven characterization of the early epidemic phase, which is important for accurate estimation of the reproduction number and prediction of disease impact. PMID:27707909

Documentation for the machine-readable version of the AGK3 Star Catalogue of Positions and Proper Motions North of -2 deg .5 declination (Dieckvoss and Collaborators 1975)

NASA Technical Reports Server (NTRS)

Warren, W. H., Jr.

1984-01-01

A detailed description of the machine-readable astronomical catalog as it is currently being distributed from the Astronomical Data Center is given. Stellar motions and positions are listed herein in tabular form.

First ultraviolet spectropolarimetry of Be stars from the Wisconsin Ultraviolet Photo-Polarimeter Experiment

NASA Technical Reports Server (NTRS)

Bjorkman, K. S.; Nordsieck, K. H.; Code, A. D.; Anderson, C. M.; Babler, B. L.; Clayton, G. C.; Magalhaes, A. M.; Meade, M. R.; Nook, M. A.; Schulte-Ladbeck, R. E.

1991-01-01

The first UV spectropolarimetric observations of Be stars are presented. They were obtained with the Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE) aboard the Astro-1 mission. WUPPE data on the Be stars Zeta Tau and Pi Aqr, along with near-simultaneous optical data obtained at the Pine Bluff Observatory (PBO). Combined WUPPE and PBO data give polarization as a function of wavelength across a very broad spectral region, from 1400 to 7600 A. Existing Be star models predicted increasing polarization toward shorter wavelengths in the UV, but this is not supported by the WUPPE observations. Instead, the observations show a constant or slightly declining continuum polarization shortward of the Balmer jump, and broad UV polarization dips around 1700 and 1900 A, which may be a result of Fe-line-attenuation effects on the polarized flux. Supporting evidence for this conclusion comes from the optical data, in which decreases in polarization across Fe II lines in Zeta Tau were discovered.

Fifth Fundamental Catalogue (FK5). Part 1: Basic fundamental stars (Fricke, Schwan, and Lederle 1988): Documentation for the machine-readable version

NASA Technical Reports Server (NTRS)

Warren, Wayne H., Jr.

1990-01-01

The machine-readable version of the catalog, as it is currently being distributed from the Astronomical Data Center, is described. The Basic FK5 provides improved mean positions and proper motions for the 1535 classical fundamental stars that had been included in the FK3 and FK4 catalogs. The machine version of the catalog contains the positions and proper motions of the Basic FK5 stars for the epochs and equinoxes J2000.0 and B1950.0, the mean epochs of individual observed right ascensions and declinations used to determine the final positions, and the mean errors of the final positions and proper motions for the reported epochs. The cross identifications to other designations used for the FK5 stars that are given in the published catalog were not included in the original machine versions, but the Durchmusterung numbers have been added at the Astronomical Data Center.

A Study of Nine High-Redshift Clusters of Galaxies. II. Photometry, Spectra, and Ages of Clusters 0023+0423 and 1604+4304

NASA Astrophysics Data System (ADS)

Postman, Marc; Lubin, Lori M.; Oke, J. B.

1998-08-01

We present an extensive photometric and spectroscopic study of two high-redshift clusters of galaxies based on data obtained from the Keck 10 m telescopes and the Hubble Space Telescope. The clusters Cl 0023+0423 (z = 0.84) and Cl 1604+4304 (z = 0.90) are part of a multiwavelength program of Oke, Postman & Lubin to study nine candidate clusters at z >~ 0.6. Based on these observations, we study in detail both the field and cluster populations. From the confirmed cluster members, we find that Cl 0023+0423 actually consists of two components separated by ~2900 km s^-1. A kinematic analysis indicates that the two components are a poor cluster with ~3 x 10^14 M_⊙ and a less massive group with ~10^13 M_⊙. Cl 1604+4304 is a centrally concentrated, rich cluster at z = 0.8967 with a velocity dispersion of 1226 km s^-1 and a mass of ~3 x 10^15 M_⊙. A large percentage of the cluster members show high levels of star formation activity. Approximately 57% and 50% of the galaxies are active in Cl 0023+0423 and Cl 1604+4304, respectively. These numbers are significantly larger than those found in intermediate-redshift clusters. We also observe many old, red galaxies. Found mainly in Cl 1604+4304, they have spectra consistent with passive stellar evolution, typical of the populations of early-type galaxies in low- and intermediate-redshift clusters. We have calculated their ages by comparing their spectral energy distributions to standard Bruzual & Charlot evolutionary models. We find that their colors are consistent with models having an exponentially decreasing star formation rate with a time constant of 0.6 Gyr. We also observe a significant luminosity brightening in our brightest cluster galaxies. Compared with brightest cluster galaxies at z ~ 0.1, we find a luminosity increase of ~1 mag in the rest M_B and ~0.8 mag in the rest M_V. In the field, we find that ~76% of the galaxies with z > 0.4 show emission-line activity. These numbers are consistent with previous studies. We find that an exponentially decaying star formation rate is required to produce the observed amount of star formation for the majority of the galaxies in our sample. A time constant of tau = 0.6 Gyr appears to be optimal. We also detect several interesting galaxies at z > 1. Two of these galaxies are extremely luminous, with strong Mg ii lambda2800 absorption and Fe ii resonance-line absorption. These lines are so strong that we conclude that they must be generated within the atmospheres of a large population of young, hot stars.

THE EVOLUTION OF POST-STARBURST GALAXIES FROM z  ∼ 1 TO THE PRESENT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pattarakijwanich, Petchara; Strauss, Michael A.; Ho, Shirley

Post-starburst galaxies are in the transitional stage between blue, star-forming galaxies and red, quiescent galaxies and therefore hold important clues for our understanding of galaxy evolution. In this paper, we systematically searched for and identified a large sample of post-starburst galaxies from the spectroscopic data set of the Sloan Digital Sky Survey (SDSS) Data Release 9. In total, we found more than 6000 objects with redshifts between z  ∼ 0.05 and z  ∼ 1.3, making this the largest sample of post-starburst galaxies in the literature. We calculated the luminosity function of the post-starburst galaxies using two uniformly selected subsamples: the SDSS mainmore » galaxy sample and the Baryon Oscillation Spectroscopic Survey CMASS sample. The luminosity functions are reasonably fit by half-Gaussian functions. The peak magnitudes shift as a function of redshift from M  ∼ −23.5 at z  ∼ 0.8 to M  ∼ −20.3 at z  ∼ 0.1. This is consistent with the downsizing trend, whereby more massive galaxies form earlier than low-mass galaxies. We compared the mass of the post-starburst stellar population found in our sample to the decline of the global star formation rate and found that only a small amount (∼1%) of all star formation quenching in the redshift range z  = 0.2–0.7 results in post-starburst galaxies in the luminosity range our sample is sensitive to. Therefore, luminous post-starburst galaxies are not the place where most of the decline in the star formation rate of the universe is happening.« less

DETECTION OF A COOL, ACCRETION-SHOCK-GENERATED X-RAY PLASMA IN EX LUPI DURING THE 2008 OPTICAL ERUPTION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Teets, William K.; Weintraub, David A.; Kastner, Joel H.

2012-11-20

EX Lupi is the prototype for a class of young, pre-main-sequence stars which are observed to undergo irregular, presumably accretion-generated, optical outbursts that result in a several magnitude rise of the optical flux. EX Lupi was observed to optically erupt in 2008 January, triggering Chandra ACIS Target of Opportunity observations shortly thereafter. We find very strong evidence that most of the X-ray emission in the first few months after the optical outburst is generated by accretion of circumstellar material onto the stellar photosphere. Specifically, we find a strong correlation between the decreasing optical and X-ray fluxes following the peak ofmore » the outburst in the optical, which suggests that these observed declines in both the optical and X-ray fluxes are the result of declining accretion rate. In addition, in our models of the X-ray spectrum, we find strong evidence for a {approx}0.4 keV plasma component, as expected for accretion shocks on low-mass, pre-main-sequence stars. From 2008 March through October, this cool plasma component appeared to fade as EX Lupi returned to its quiescent level in the optical, consistent with a decrease in the overall emission measure of accretion-shock-generated plasma. The overall small increase of the X-ray flux during the optical outburst of EX Lupi is similar to what was observed in previous X-ray observations of the 2005 optical outburst of the EX Lupi-type star V1118 Ori but contrasts with the large increase of the X-ray flux from the erupting young star V1647 Ori during its 2003 and 2008 optical outbursts.« less

THE CIRCUMSTELLAR ENVIRONMENT OF R CORONAE BOREALIS: WHITE DWARF MERGER OR FINAL-HELIUM-SHELL FLASH?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clayton, Geoffrey C.; Andrews, J. E.; Sugerman, Ben E. K.

2011-12-10

In 2007, R Coronae Borealis (R CrB) went into a historically deep and long decline. In this state, the dust acts like a natural coronagraph at visible wavelengths, allowing faint nebulosity around the star to be seen. Imaging has been obtained from 0.5 to 500 {mu}m with Gemini/GMOS, Hubble Space Telescope/WFPC2, Spitzer/MIPS, and Herschel/SPIRE. Several of the structures around R CrB are cometary globules caused by wind from the star streaming past dense blobs. The estimated dust mass of the knots is consistent with their being responsible for the R CrB declines if they form along the line of sightmore » to the star. In addition, there is a large diffuse shell extending up to 4 pc away from the star containing cool 25 K dust that is detected all the way out to 500 {mu}m. The spectral energy distribution of R CrB can be well fitted by a 150 AU disk surrounded by a very large diffuse envelope which corresponds to the size of the observed nebulosity. The total masses of the disk and envelope are 10{sup -4} and 2 M{sub Sun }, respectively, assuming a gas-to-dust ratio of 100. The evidence pointing toward a white dwarf merger or a final-helium-shell flash origin for R CrB is contradictory. The shell and the cometary knots are consistent with a fossil planetary nebula. Along with the fact that R CrB shows significant lithium in its atmosphere, this supports the final-helium-shell flash. However, the relatively high inferred mass of R CrB and its high fluorine abundance support a white dwarf merger.« less

Detection of a Cool, Accretion-Shock-Generated X-Ray Plasma in EX Lupi During the 2008 Optical Eruption

NASA Technical Reports Server (NTRS)

Teets, William K.; Weintraub, David A.; Kastner, Joel H.; Grosso, Nicholas; Hamaguchi, Kenji; Richmond, Michael

2012-01-01

EX Lupi is the prototype for a class of young, pre-main-sequence stars which are observed to undergo irregular, presumably accretion-generated, optical outbursts that result in a several magnitude rise of the optical flux. EX Lupi was observed to optically erupt in 2008 January, triggering Chandra ACIS Target of Opportunity observations shortly thereafter. We find very strong evidence that most of the X-ray emission in the first few months after the optical outburst is generated by accretion of circumstellar material onto the stellar photosphere. Specifically, we find a strong correlation between the decreasing optical and X-ray fluxes following the peak of the outburst in the optical, which suggests that these observed declines in both the optical and X-ray fluxes are the result of declining accretion rate. In addition, in our models of the X-ray spectrum, we find strong evidence for an approx 0.4 keV plasma component, as expected for accretion shocks on low-mass, pre-main-sequence stars. From 2008 March through October, this cool plasma component appeared to fade as EX Lupi returned to its quiescent level in the optical, consistent with a decrease in the overall emission measure of accretion-shock-generated plasma. The overall small increase of the X-ray flux during the optical outburst of EX Lupi is similar to what was observed in previous X-ray observations of the 2005 optical outburst of the EX Lupi-type star V1118 Ori but contrasts with the large increase of the X-ray flux from the erupting young star V1647 Ori during its 2003 and 2008 optical outbursts.

The Equatorial Coordinates and B-Magnitudes of the Stars in the Southern Hemisphere Zones Based on the Digitized Astronegatives of FON Project at the Ulugh Beg Astronomical Institute

NASA Astrophysics Data System (ADS)

Yuldoshev, Q. X.; Muminov, M. M.; Ehgamberdiev, Sh. A.; Usmanov, O. U.; Relke, H.; Protsyuk, Yu. I.; Kovylianska, O. E.; Protsyuk, S. V.; Andruk, V. N.

FON (Russian abbreviation of the Photographic Sky Survey) were carried out at 6 observatories. The Kitab Observatory (KO) of Ulugh Beg Astronomical Institute (UBAI) of the Uzbek Academy of Sciences (UzAS) was involved in this project from 1981 to 1996. For the observations the Double Astrograph of Zeiss (DAZ, D/F = 40/300, 69"/mm) was used. On the FON project about 2600 photographic plates were exposed. In October, 2015 digitization of these astroplates were started using EPSON Expression 10000XL flatbed scanner with the spatial resolution of 1200 dpi and completed in June, 2016. The first stage of the work is the processing of the 2000 photographic plates in zones of the southern hemisphere with the declination between 0 and -20 degrees. The 1704 plates have already been processed. The equatorial coordinates α, δ of stars and galaxies were determined in the system of the Tycho2 catalogue and the Bmagnitudes in the system of the photoelectric standards. UBAI UzAS, Tashkent (Uzbekistan), ASU, Andijan (Uzbekistan), WHO, Essen (Germany), RI NAO, Nikolaev (Ukraine), MAO NASU, Kyiv (Ukraine) have taken part in the processing of the digitized images. For the data reduction the MIDAS package and software, developed in the MAO NASU were used. Based on the results of the processing of the astronegatives in the sectors of right ascension from 0 hours to 24 hours and declination from - 20° to 0° the internal errors of the catalogue were estimated. The errors calculated for all stars are 0.17" and 0.18m respectively. For the stars brighter than 14 magnitude the errors are 0.08" and 0.07m for the equatorial coordinates and B-magnitudes respectively.

Response Characteristics of Dissolved Organic Carbon Flushing in a Subarctic Alpine Catchment

NASA Astrophysics Data System (ADS)

Carey, S. K.

2002-12-01

Dissolved organic carbon (DOC) is an important part of ecosystem-scale carbon balances and in the transport of contaminants as it interacts with other dissolved substances including trace metals. It also can be used as a surrogate hydrological tracer in permafrost regions as near-surface waters are often DOC enriched due to the presence of thick organic soils. In a small subarctic alpine catchment within the Wolf Creek Research Basin, Yukon, Canada, DOC was studied in the summer of 2001 and spring of 2002 to determine the role frost (both permanent and seasonal), snowmelt and summer storms on DOC flushing. Peak DOC concentrations occurred during the snowmelt period, approximately one week prior to peak discharge. However, peak discharge took place several weeks after snow on south facing exposures had melted. Within the hillslopes, DOC concentrations were three to five times greater in wells underlain with permafrost compared with seasonal frost. Groundwater DOC concentrations declined during snowmelt, yet remained at levels above the streamflow. After peaking, streamflow DOC concentrations declined exponentially suggesting a simple flushing mechanism, however there did not appear to be a relation between DOC and topographic position. Following melt, permafrost underlain slopes had near-surface water tables and retained elevated levels of DOC, whereas slopes without permafrost had rapidly declining water tables at upslope locations with low DOC concentrations at all positions except near-stream riparian zones. The influence of summer rainstorms on DOC was monitored on three occasions. In each case DOC peaked on the ascending limb of the runoff hydrograph and declined exponentially on the receding limb and hysteretic behavior occurred between discharge and DOC during all events. Patterns of DOC within the hillslopes and streams suggest that runoff from permafrost-underlain slopes control DOC flushing within the stream during both snowmelt and summer periods. This flushing mechanism conforms with conceptual models of runoff generation in discontinuous permafrost catchments whereby water tables within permafrost-underlain slopes rise into porous organic-layers, whereupon DOC is leached into the water and rapidly conveyed to the stream.

Time-dependent Models of Magnetospheric Accretion onto Young Stars

DOE Office of Scientific and Technical Information (OSTI.GOV)

Robinson, C. E.; Espaillat, C. C.; Owen, J. E.

Accretion onto Classical T Tauri stars is thought to take place through the action of magnetospheric processes, with gas in the inner disk being channeled onto the star’s surface by the stellar magnetic field lines. Young stars are known to accrete material in a time-variable manner, and the source of this variability remains an open problem, particularly on the shortest (∼day) timescales. Using one-dimensional time-dependent numerical simulations that follow the field line geometry, we find that for plausibly realistic young stars, steady-state transonic accretion occurs naturally in the absence of any other source of variability. However, we show that ifmore » the density in the inner disk varies smoothly in time with ∼day-long timescales (e.g., due to turbulence), this complication can lead to the development of shocks in the accretion column. These shocks propagate along the accretion column and ultimately hit the star, leading to rapid, large amplitude changes in the accretion rate. We argue that when these shocks hit the star, the observed time dependence will be a rapid increase in accretion luminosity, followed by a slower decline, and could be an explanation for some of the short-period variability observed in accreting young stars. Our one-dimensional approach bridges previous analytic work to more complicated multi-dimensional simulations and observations.« less

Up in arms: Immune and nervous system response to sea star wasting disease

USGS Publications Warehouse

Fuess, Lauren E; Eiselord, Morgan E.; Closek, Collin J.; Tracy, Allison M.; Mauntz, Ruth; Gignoux-Wolfsohn, Sarah; Moritsch, Monica M; Yoshioka, Reyn; Burge, Colleen A.; Harvell, Drew; Friedman, Carolyn S.; Hershberger, Paul K.; Roberts, Steven B.

2015-01-01

Echinoderms, positioned taxonomically at the base of deuterostomes, provide an important system for the study of the evolution of the immune system. However, there is little known about the cellular components and genes associated with echinoderm immunity. The 2013–2014 sea star wasting disease outbreak is an emergent, rapidly spreading disease, which has led to large population declines of asteroids in the North American Pacific. While evidence suggests that the signs of this disease, twisting arms and lesions, may be attributed to a viral infection, the host response to infection is still poorly understood. In order to examine transcriptional responses of the sea star Pycnopodia helianthoides to sea star wasting disease, we injected a viral sized fraction (0.2 μm) homogenate prepared from symptomatic P. helianthoides into apparently healthy stars. Nine days following injection, when all stars were displaying signs of the disease, specimens were sacrificed and coelomocytes were extracted for RNA-seq analyses. A number of immune genes, including those involved in Toll signaling pathways, complement cascade, melanization response, and arachidonic acid metabolism, were differentially expressed. Furthermore, genes involved in nervous system processes and tissue remodeling were also differentially expressed, pointing to transcriptional changes underlying the signs of sea star wasting disease. The genomic resources presented here not only increase understanding of host response to sea star wasting disease, but also provide greater insight into the mechanisms underlying immune function in echinoderms.

A method to estimate stellar ages from kinematical data

NASA Astrophysics Data System (ADS)

Almeida-Fernandes, F.; Rocha-Pinto, H. J.

2018-05-01

We present a method to build a probability density function (PDF) for the age of a star based on its peculiar velocities U, V, and W and its orbital eccentricity. The sample used in this work comes from the Geneva-Copenhagen Survey (GCS) that contains the spatial velocities, orbital eccentricities, and isochronal ages for about 14 000 stars. Using the GCS stars, we fitted the parameters that describe the relations between the distributions of kinematical properties and age. This parametrization allows us to obtain an age probability from the kinematical data. From this age PDF, we estimate an individual average age for the star using the most likely age and the expected age. We have obtained the stellar age PDF for the age of 9102 stars from the GCS and have shown that the distribution of individual ages derived from our method is in good agreement with the distribution of isochronal ages. We also observe a decline in the mean metallicity with our ages for stars younger than 7 Gyr, similar to the one observed for isochronal ages. This method can be useful for the estimation of rough stellar ages for those stars that fall in areas of the Hertzsprung-Russell diagram where isochrones are tightly crowded. As an example of this method, we estimate the age of Trappist-1, which is a M8V star, obtaining the age of t(UVW) = 12.50(+0.29 - 6.23) Gyr.

The rotation of very low mass objects

NASA Astrophysics Data System (ADS)

Scholz, Alexander

2004-10-01

This dissertation contains an investigation of the rotation of very low mass objects, i.e. Brown Dwarfs and stars with masses <0.4 MS. Today, it is well-established that there are large populations of such VLM objects in open clusters and in the field, but our knowledge about their physical properties and evolution is still very limited. Contrary to their solar-mass siblings, VLM objects are fully convective throughout their evolution. Thus, they are not able to form a large-scale magnetic field like for example the sun. The magnetic field, in turn, is crucial for the regulation of rotation: Magnetic interaction between star and circumstellar disk ("disk-locking") and angular momentum losses through stellar winds have dominant influence on the rotational evolution. Thus, we can expect major differences in the rotational behaviour of VLM objects and solar-mass stars. The best method to investigate stellar rotation is to measure rotation periods. If a star exhibits surface features which are asymmetrically distributed, its brightness may be modulated with the rotation period. Thus, this dissertation is based on the analysis of photometric time series. Open clusters are an ideal environment for such a project, since they enable one to follow many objects at the same time. Additionally, they allow one to investigate the age and mass dependence of rotation, because distance and age of the clusters are known in good approximation. For this thesis, five open clusters were observed, which span an age range from 3 to 750 Myr. In three of them (SigmaOri, EpsilonOri, IC4665), VLM objects were identified by means of colour magnitude diagrams. The candidate lists for these three regions comprise at least 100 objects, for which photometry in at least three wavelength bands is available. About a fifth to a third of these candidates could be contaminating field stars in the fore- or background of the clusters. For the remaining two clusters (Pleiades and Praesepe), objects from the literature were selected as targets for the variability study. Masses for all these candidates were estimated by comparing the photometry with stellar evolutionary tracks. For each of the clusters, at least one photometric monitoring campaign was carried out; three of them were observed twice. Subsequently, the magnitudes of the VLM objects were measured relative to non-variable stars in the same fields. The difference image analysis procedure was used to improve the precision for two time series. That way, a photometric precision between 5 and 20 mmag was reached for the brightest stars. A comparison of several period search techniques showed that periodogram analysis delivers by far the best results for the available time series data. Beside the Scargle and CLEAN periodogram, the period search includes several independent and robust control procedures, to assure the reliability of the results. Additionally, a test to identify even non-periodic variability was implemented. For 87 candidates, a photometric rotation period was determined, 80 of these objects have masses <0.4 MS. Thus, this work increases the number of known VLM rotation periods in the age range between 3 and 750 Myr by a factor of 14. Altogether, about 30-50% of the candidates are variable. In the two youngest clusters, several objects show variability with very high amplitudes between 0.2 and 1.1 mag. Their lightcurves contain in the most cases a periodic component, but additionally irregular brightness variations. For two VLM stars, a flare event was detected. The origin of the periodic variability is surface features co-rotating with the objects. In most cases, these surface features are cool magnetically induced spots. From the lightcurves, it can be concluded that the spot properties change on timescales of at most two or three weeks. The amplitudes of the lightcurves are in the VLM regime by a factor of 2.4 smaller than for solar-mass stars, indicating a change of the spot properties with mass. The best explanation for this phenomenon is a more symmetric spot distribution on VLM objects. Additionally, it is probable that the contrast between spots and photospheric environment is smaller than for more massive stars. The lightcurves of the highly variable objects in the youngest clusters cannot be understood only with cool spots. This kind of variability resembles very much the photometric behaviour of classical T Tauri stars, i.e. stars which accrete matter from a circumstellar disk. Thus, it is likely that the highly variable VLM objects possess accretion disks as well. This interpretation is confirmed by near-infrared photometry and optical spectroscopy. For VLM objects in the SigmaOri cluster, a disk frequency of 6-14% was estimated. From this value and the age of SigmaOri it follows that VLM objects loose their disk on shorter timescales than solar-mass stars, which could be an indication for a formation through ejection from a multiple system. This result, however, needs confirmation, since the derived disk frequency should only be considered as a lower limit. The majority of the periodic variable objects rotate with periods <2 d. Slow rotators, with periods longer than 2d, are rare, in contrast to solar-mass stars. For M<0.3 MS, a tendency of faster rotation with decreasing object mass is observed. The origin of this tendency lies very probably in the earliest phases of the rotational evolution. The lower limit of the periods is, within the statistical uncertainties, nearly independent of age and ranges from three to six hours. On the other hand, the upper period limit clearly evolves with time. Between ages of 3 and 100 Myr, it declines from at least ten days to about two days. Afterwards, it increases again up to at least four days. To investigate this behaviour in more detail, simple models were constructed which simulate the basic mechanisms of angular momentum regulation. It turns out that the basic aspects of the rotational evolution can be understood if one takes into account the contraction of the objects and exponential rotational braking through stellar winds. On the contrary, for solar-mass stars the angular momentum losses through stellar winds can be described with the Skumanich law, which predicts a period increase proportional to the squareroot of time. This Skumanich law is not applicable in the VLM regime. Moreover, in the considered age range, the influence of "disk-locking" is negligible. Many of these results can be understood by taking into account the fact that VLM objects are fully convective and cannot possess a large-scale magnetic field. This basic physical property could be responsible for the fast rotation, the breakdown of the Skumanich law, the exponential braking of the rotation, and a more symmetric spot distribution. Thus, main results of this thesis can be ascribed to the internal structure of VLM objects.

Boron Abundances Across the "Li-Be Dip" in the Hyades Cluster

NASA Astrophysics Data System (ADS)

Boesgaard, Ann Merchant; Lum, Michael G.; Deliyannis, Constantine P.; King, Jeremy R.; Pinsonneault, Marc H.

2015-08-01

Dramatic deficiencies of Li in the mid-F dwarf stars of the Hyades cluster were discovered by Boesgaard and Tripicco in 1986. Using high-resolution, high signal-to-noise spectra from the Keck 10-m telescope, Boesgaard and King discovered the corresponding, but smaller, deficiencies in Be in the same narrow temperature region in the Hyades. With the Space Telescope Imaging Spectrograph on HST we investigate B abundances in the Hyades F stars to look for a potential B dip. We use the resonance line of B I at 2497 A. These three elements are destroyed inside stars at increasingly hotter temperatures: 2.5 x 10$^6$, 3.5 x 10$^6$, and 5 x 10$^6$ K for Li, Be, B respectively. Consequently, these elements survive to increasingly greater depths in a star and their surface abundances act as a report on the depth and thoroughness of mixing in the star. We have used updated photometry from Hipparcos to find stellar parameters for the Hyades stars and have redetermined Li abundances (or upper limits) for 79 Hyades dwarfs, Be for 34 stars, and B in five stars. We find evidence for a small dip in the B abundance across the Li-Be dip. We have compared our nLTE B abundances for the three high B stars on either side of the Li-Be dip with those found by Duncan for the Hyades giants. This confirms the factor of ten decline in the B abundance in the Hyades giants as predicted by dilution due to the deepening of the surface convection zone.

Long-term radio and X-ray evolution of the tidal disruption event ASASSN-14li

NASA Astrophysics Data System (ADS)

Bright, J. S.; Fender, R. P.; Motta, S. E.; Mooley, K.; Perrott, Y. C.; van Velzen, S.; Carey, S.; Hickish, J.; Razavi-Ghods, N.; Titterington, D.; Scott, P.; Grainge, K.; Scaife, A.; Cantwell, T.; Rumsey, C.

2018-04-01

We report on late time radio and X-ray observations of the tidal disruption event candidate ASASSN-14li, covering the first 1000 d of the decay phase. For the first ˜200 d the radio and X-ray emission fade in concert. This phase is better fitted by an exponential decay at X-ray wavelengths, while the radio emission is well described by either an exponential or the canonical t-5/3 decay assumed for tidal disruption events. The correlation between radio and X-ray emission during this period can be fitted as L_R∝ L_X^{1.9± 0.2}. After 400 d the radio emission at 15.5 GHz has reached a plateau level of 244 ± 8 μJy which it maintains for at least the next 600 d, while the X-ray emission continues to fade exponentially. This steady level of radio emission is likely due to relic radio lobes from the weak AGN-like activity implied by historical radio observations. We note that while most existing models are based upon the evolution of ejecta which are decoupled from the central black hole, the radio-X-ray correlation during the declining phase is also consistent with core-jet emission coupled to a radiatively efficient accretion flow.

Extending the capability of GYRE to calculate tidally forced stellar oscillations

NASA Astrophysics Data System (ADS)

Guo, Zhao; Gies, Douglas R.

2016-01-01

Tidally forced oscillations have been observed in many eccentric binary systems, such as KOI-54 and many other 'heart beat stars'. The tidal response of the star can be calculated by solving a revised stellar oscillations equations.The open-source stellar oscillation code GYRE (Townsend & Teitler 2013) can be used to solve the free stellar oscillation equations in both adiabatic and non-adiabatic cases. It uses a novel matrix exponential method which avoids many difficulties of the classical shooting and relaxation method. The new version also includes the effect of rotation in traditional approximation.After showing the code flow of GYRE, we revise its subroutines and extend its capability to calculate tidallyforced oscillations in both adiabatic and non-adiabatic cases following the procedure in the CAFein code (Valsecchi et al. 2013). In the end, we compare the tidal eigenfunctions with those calculated from CAFein.More details of the revision and a simple version of the code in MATLAB can be obtained upon request.

Relativistic Jets from Collapsars

NASA Astrophysics Data System (ADS)

Aloy, M. A.; Müller, E.; Ibáñez, J. M.; Martí, J. M.; MacFadyen, A.

2000-03-01

Using a collapsar progenitor model of MacFadyen & Woosley, we have simulated the propagation of an axisymmetric jet through a collapsing rotating massive star with the GENESIS multidimensional relativistic hydrodynamic code. The jet forms as a consequence of an assumed (constant or variable) energy deposition in the range of 1050-1051 ergs s-1 within a 30 deg cone around the rotation axis. The jet flow is strongly beamed (approximately less than a few degrees), spatially inhomogeneous, and time dependent. The jet reaches the surface of the stellar progenitor (R*=2.98x1010 cm) intact. At breakout, the maximum Lorentz factor of the jet flow is 33. After breakout, the jet accelerates into the circumstellar medium, whose density is assumed to decrease exponentially and then become constant, ρext=10-5 g cm-3. Outside the star, the flow begins to expand laterally also (v~c), but the beam remains very well collimated. At a distance of 2.54 R*, where the simulation ends, the Lorentz factor has increased to 44.

The Star Formation History and Morphological Evolution of the Draco Dwarf Spheroidal Galaxy

NASA Astrophysics Data System (ADS)

Aparicio, Antonio; Carrera, Ricardo; Martínez-Delgado, David

2001-11-01

The photometric and morphological properties, as well as the star formation history, of the Draco dwarf spheroidal galaxy are analyzed on the basis of wide-field CCD photometry of the resolved stars covering about 1 deg2. Draco is at a distance of d=80+/-7 kpc and has a metallicity, [Fe/H], of -1.8+/-0.2. No metallicity gradient is detected. The star surface density distribution can be fitted by a single exponential law of scale length α=5.0‧+/-0.1‧. The central surface magnitude is μ''V''=24.4+/-0.5, and the core radius is rc=7.5‧+/-0.3‧ (equivalent to rc=175+/-7 pc). Within errors, the same scale lengths are found for the density profiles along the semimajor and semiminor axes (rescaled to semimajor-axis units, using the ellipticity of the galaxy) of Draco. There are hence no evidences of a tidal tail associated with Draco. The tidal radius of the galaxy is found to be rt~=42' (~=1 kpc). The possibility that the large mass-to-light relation in Draco could be accounted for by a convenient spatial orientation is tested. An upper limit to Draco's size along the line of sight is ~14 kpc. This is too small to account for the velocity dispersion of Draco if it were due to projection effects only, and it implies that other mechanisms (e.g., dark matter) are required. The stellar population of Draco is mainly old. Although some intermediate-age population is present in Draco, most of the star formation (up to 90%) took place before ~10 Gyr ago. No significant star formation activity is detected in the last ~2 Gyr. Two methods (partial model and subgiant) have been used to investigate the star formation history of Draco, both producing results in good qualitative agreement. No difference is found between the scale lengths of the distributions of old (>~9 Gyr) and young (~2-3 Gyr) stars, indicating either that both populations were formed under the same kinematic conditions, or that any initial difference was afterward erased.

Visual Spectroscopy of R Scuti (Poster abstract)

NASA Astrophysics Data System (ADS)

Undreiu, L.; Chapman, A.

2015-06-01

(Abstract only) We are currently conducting a visual spectral analysis of the brightest known RV Tauri variable star, R Scuti. The goal of our undergraduate research project is to investigate this variable star's erratic nature by collecting spectra at different times in its cycle. Starting in late June of 2014 and proceeding into the following four months, we have monitored the alterations in the spectral characteristics that accompany the progression of R Sct's irregular cycle. During this time, we were given the opportunity to document the star's most recent descent from maximum brightness V~5 to a relatively deep minimum of V~7.5. Analysis of the data taken during the star's period of declining magnitude has provided us with several interesting findings that concur with the observations of more technically sophisticated studies. Following their collection, we compared our observations and findings with archived material in the hopes of facilitating a better understanding of the physical state of RV Tauri stars and the perplexing nature of their evolution. Although identification of the elements in the star's bright phase proved to be challenging, documenting clear absorption features in its fainter stage was far less difficult. As previously reported in similar studies, we identified prominent TiO molecular absorption bands near R Sct's faintest state, typical of mid-M spectral type stars. In addition to these TiO absorption lines, we report the presence of many more metallic lines in the spectral profiles obtained near star's minimum. Supportive of previously published hypotheses regarding the causation of its variability, we observed significant variation in the star's spectral characteristics throughout different phases of its cycle. We are hopeful that our observations will make a meaningful contribution to existing databases and help advance our collective understanding of RV Tauri stars and their evolutionary significance.

The Effect of Star Formation History on the Inferred Stellar Initial Mass Function

NASA Astrophysics Data System (ADS)

Elmegreen, Bruce G.; Scalo, John

2006-01-01

Peaks and lulls in the star formation rate (SFR) over the history of the Galaxy produce plateaus and declines in the present-day mass function (PDMF) where the main-sequence lifetime overlaps the age and duration of the SFR variation. These PDMF features can be misinterpreted as the form of the intrinsic stellar initial mass function (IMF) if the star formation rate is assumed to be constant or slowly varying with time. This effect applies to all regions that have formed stars for longer than the age of the most massive stars, including OB associations, star complexes, and especially galactic field stars. Related problems may apply to embedded clusters. Evidence is summarized for temporal SFR variations from parsec scales to entire galaxies, all of which should contribute to inferred IMF distortions. We give examples of various star formation histories to demonstrate the types of false IMF structures that might be seen. These include short-duration bursts, stochastic histories with lognormal amplitude distributions, and oscillating histories with various periods and phases. The inferred IMF should appear steeper than the intrinsic IMF over mass ranges where the stellar lifetimes correspond to times of decreasing SFRs; shallow portions of the inferred IMF correspond to times of increasing SFRs. If field regions are populated by dispersed clusters and defined by their low current SFRs, then they should have steeper inferred IMFs than the clusters. The SFRs required to give the steep field IMFs in the LMC and SMC are determined. Structure observed in several determinations of the Milky Way field star IMF can be accounted for by a stochastic and bursty star formation history.

Chemical Mapping of the Milky Way with The Canada-France Imaging Survey: A Non-parametric Metallicity-Distance Decomposition of the Galaxy

NASA Astrophysics Data System (ADS)

Ibata, Rodrigo A.; McConnachie, Alan; Cuillandre, Jean-Charles; Fantin, Nicholas; Haywood, Misha; Martin, Nicolas F.; Bergeron, Pierre; Beckmann, Volker; Bernard, Edouard; Bonifacio, Piercarlo; Caffau, Elisabetta; Carlberg, Raymond; Côté, Patrick; Cabanac, Rémi; Chapman, Scott; Duc, Pierre-Alain; Durret, Florence; Famaey, Benoît; Fabbro, Sébastien; Gwyn, Stephen; Hammer, Francois; Hill, Vanessa; Hudson, Michael J.; Lançon, Ariane; Lewis, Geraint; Malhan, Khyati; di Matteo, Paola; McCracken, Henry; Mei, Simona; Mellier, Yannick; Navarro, Julio; Pires, Sandrine; Pritchet, Chris; Reylé, Celine; Richer, Harvey; Robin, Annie C.; Sánchez-Janssen, Rubén; Sawicki, Marcin; Scott, Douglas; Scottez, Vivien; Spekkens, Kristine; Starkenburg, Else; Thomas, Guillaume; Venn, Kim

2017-10-01

We present the chemical distribution of the Milky Way, based on 2900 {\\deg }2 of u-band photometry taken as part of the Canada-France Imaging Survey. When complete, this survey will cover 10,000 {\\deg }2 of the northern sky. By combing the CFHT u-band photometry together with Sloan Digital Sky Survey and Pan-STARRS g,r, and I, we demonstrate that we are able to reliably measure the metallicities of individual stars to ˜0.2 dex, and hence additionally obtain good photometric distance estimates. This survey thus permits the measurement of metallicities and distances of the dominant main-sequence (MS) population out to approximately 30 {kpc}, and provides a much higher number of stars at large extraplanar distances than have been available from previous surveys. We develop a non-parametric distance-metallicity decomposition algorithm and apply it to the sky at 30^\\circ < | b| < 70^\\circ and to the North Galactic Cap. We find that the metallicity-distance distribution is well-represented by three populations whose metallicity distributions do not vary significantly with vertical height above the disk. As traced in MS stars, the stellar halo component shows a vertical density profile that is close to exponential, with a scale height of around 3 {kpc}. This may indicate that the inner halo was formed partly from disk stars ejected in an ancient minor merger.

Does the HMXB IGR J18214-1318 contain a black hole or neutron star?

NASA Astrophysics Data System (ADS)

Fornasini, Francesca; Tomsick, John; Bachetti, Matteo; Fuerst, Felix; Natalucci, Lorenzo; Pottschmidt, Katja; Smith, David M.; Wilms, Joern

2015-01-01

Measuring the fraction of high-mass X-ray binaries (HMXBs) that harbors a black hole (BH) rather than a neutron star (NS) can improve our understanding of the role of stellar winds and mass transfer in the evolution of massive stars and help constrain estimates of the numbers of NS/BH and BH/BH binaries in the Galaxy, potential sources of gravitational waves that could be detected by Advanced-LIGO. Some population synthesis studies have shown that BHs are likely to be rare among the Be HMXB population (Belczynki & Ziolkowski, 2009, ApJ, 707, 870) and the one BH Be HMXB that has been discovered has very low X-ray luminosity (Casares et al., 2014, Nature, 505, 378), indicating that BH Be HMXBs may exist but remain undetected by current surveys. However, since luminous supergiant BH HMXBs are known to exist (i.e. Cyg X-1), it is possible that some of the supergiant HMXBs discovered by INTEGRAL may host BHs. Therefore, we are trying to identify the nature of the compact objects in the IGR HMXBs by using NuSTAR and XMM-Newton to search for NS signatures in these systems: pulsations, cyclotron absorption lines, and exponential cutoffs with e-folding energies below ~20 keV. The absence of such features would make an HMXB an excellent black hole candidate. We present the spectral and timing properties of our first target, IGR J18214-1318.

Effect of catalogues coordinate errors of a star onto determination of the physical libration of the Moon from the observations of stars

NASA Astrophysics Data System (ADS)

Petrova, Natalia; Kocoulin, Valerii; Nefediev, Yurii

2016-07-01

In the Kazan University computer simulation is carried out for observation of lunar physical libration in projects planned installation of measuring equipment on the lunar surface. One such project is the project of ILOM (Japan), in which on the lunar pole an optical telescope with CCD will be equipped. As a result, the determining the selenographic coordinates (x and y) of a star with an accuracy of 1 ms of arc will be achieved. On the basis of the analytical theory of physical libration we developed a technique for solving the inverse problem of the libration. And we have already shown, for example, that the error in determining selenographic coordinates about ɛ seconds does not lead to errors in the determination of the libration angles ρ and Iσ larger than the 1.414ɛ. Libration in longitude is not determined from observations of the polar star (Petrova et al., 2012). The accuracy of the libration in the inverse problem depends on accuracy of the coordinates of the stars - α and δ - taken from the star catalogs. Checking this influence is the task of the present study. To do simulation we have developed that allows to choose the stars, falling in the field of view of the lunar telescope on observation period. Equatorial coordinates of stars were chosen by us from several fundamental catalogs: UCAC2-BSS, Hipparcos, Tycho, FK6 (part I, III) and the Astronomical Almanac. An analysis of these catalogues from the point of view accuracy of coordinates of stars represented in them was performed by Nefediev et al., 2013. The largest error, 20-70 ms, found in the catalogues UCAC2 and Tycho, the others have an error about a millisecond of arc. We simulated the observations with mentioned errors and got the following results. 1. The error in the declination Δδ of the star causes the same order error in libration parameters ρ and Iσ , while the sensitivity of libration to errors in Δα is ten time smaller. Fortunately, due to statistics (30 to 70, depending on the time of observation), this error is reduced by an order, i.e. does not exceed the error of observation selenographic coordinates. 2. The worst thing - errors in coordinates of catalogue causes though a small but constant shift in the ρ and Iσ. So, when Δα, Δδ ˜0.01", then the shift reaches 0.0025". Moreover there is a trend, with a slight, but noticeable slope. 3. Effect of error in declination of a stars is substantially strong than the error in right ascension. Perhaps it is characteristic only for polar observations. For the required accuracy in determination of the physical libration these phenomena must be taken into account when processing the planned observations. Referencies. Nefediev et al., 2013. Uchenye zapiski Kazanskogo universiteta, v. 155, 1, p.188-194. Petrova, N., Abdulmyanov T., Hanada H. Some qualitative manifestations of the physical libration of the Moon by observing stars from the lunar surface. //J. Adv. Space Res., 2012a. V. 50, p. 1702-1711

The faint young Sun paradox: an observational test of an alternative solar model

NASA Technical Reports Server (NTRS)

Gaidos, E. J.; Gudel, M.; Blake, G. A.

2000-01-01

We report the results of deep observations at radio (3.6 cm) wavelengths of the nearby solar-type star pi 01 Ursa Majoris with the Very Large Array (VLA) intended to test an alternative theory of solar luminosity evolution. The standard model predicts a solar luminosity only 75% of the present value and surface temperatures below freezing on Earth and Mars at 4 Ga, seemingly in conflict with geologic evidence for liquid water on these planets. An alternative model invokes a compensatory mass loss through a declining solar wind that results in a more consistent early luminosity. The free-free emission from an enhanced wind around nearby young Sun-like stars should be detectable at microwave frequencies. Our observations of pi 01 UMa, a 300 million year-old solar-mass star, place an upper limit on the mass loss rate of 4-5 x 10(-11) M(solar) yr-1. Total mass loss from such a star over 4 Gyr would be less than 6%. If this star is indeed an analog of the early Sun, it casts doubt on the alternative model as a solution to the faint young Sun paradox, particularly for Mars.

Hipparchus' coordinate system

NASA Astrophysics Data System (ADS)

Duke, Dennis W.

2002-07-01

In his "Histoire de l'Astronomie Ancienne" Delambre concludes unequivocally that Hipparchus knew and used a definite system of celestial spherical coordinates, namely the right ascension and declination system that we use today. The basis of Delambre's conclusion was disarmingly simple: he pointed out that in the "Commentary to Aratus" Hipparchus actually quotes the positions of numerous stars directly in right ascension and declination (or more often its complement, polar distance). Nearly two centuries later, in his "A History of Ancient Mathematical Astronomy", Neugebauer not only completely ignores Delambre's conclusion on this issue, but goes further to propose his own, as we shall see quite fanciful, theory that begins "From the Commentary to Aratus, it is quite obvious that at Hipparchus' time a definite system of spherical coordinates for stellar positions did not yet exist." and concludes "...nowhere in Greek astronomy before the catalogue of stars in the Almagest is it attested that orthogonal spherical coordinates are used to determine stellar positions." Today it is clear that Neugebauer's theory is conventionally accepted. It is the purpose of this paper to offer fresh arguments that Delambre was correct.

Project Longshot

NASA Technical Reports Server (NTRS)

West, J. Curtis; Chamberlain, Sally A.; Stevens, Robert; Pagan, Neftali

1989-01-01

Project Longshot is an unmanned probe to our nearest star system, Alpha Centauri, 4.3 light years away. The Centauri system is a trinary system consisting of two central stars (A and B) orbiting a barycenter, and a third (Proxima Centauri) orbiting the two. The system is a declination of -67 degrees. The goal is to reach the Centauri system in 50 years. This time space was chosen because any shorter time would be impossible of the relativistic velocities involved, and any greater time would be impossible because of the difficulty of creating a spacecraft with such a long lifetime. Therefore, the following mission profile is proposed: (1) spacecraft is assembled in Earth orbit; (2) spacecraft escapes Earth and Sun in the ecliptic with a single impulse maneuver; (3) spacecraft changed declination to point toward Centauri system; (4) spacecraft accelerates to 0.1c; (5) spacecraft coasts at 0.1c for 41 years; (6) spacecraft decelerates upon reaching Centauri system; and (7) spacecraft orbits Centauri system, conducts investigations, and relays data to Earth. The total time to reach the Centauri system, taking into consideration acceleration and deceleration, will be approximately 50 years.

THE VERTICAL MOTIONS OF MONO-ABUNDANCE SUB-POPULATIONS IN THE MILKY WAY DISK

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bovy, Jo; Rix, Hans-Walter; Hogg, David W.

2012-08-20

We present the vertical kinematics of stars in the Milky Way's stellar disk inferred from Sloan Digital Sky Survey/Sloan Extension for Galactic Understanding and Exploration (SDSS/SEGUE) G-dwarf data, deriving the vertical velocity dispersion, {sigma}{sub z}, as a function of vertical height |z| and Galactocentric radius R for a set of 'mono-abundance' sub-populations of stars with very similar elemental abundances [{alpha}/Fe] and [Fe/H]. We find that all mono-abundance components exhibit nearly isothermal kinematics in |z|, and a slow outward decrease of the vertical velocity dispersion: {sigma}{sub z}(z, R | [{alpha}/Fe], [Fe/H]) Almost-Equal-To {sigma}{sub z}([{alpha}/Fe], [Fe/H]) Multiplication-Sign exp (- (R - R{submore » 0})/7 kpc). The characteristic velocity dispersions of these components vary from {approx}15 km s{sup -1} for chemically young, metal-rich stars with solar [{alpha}/Fe], to {approx}> 50 km s{sup -1} for metal-poor stars that are strongly [{alpha}/Fe]-enhanced, and hence presumably very old. The mean {sigma}{sub z} gradient (d{sigma}{sub z}/dz) away from the mid-plane is only 0.3 {+-} 0.2 km s{sup -1} kpc{sup -1}. This kinematic simplicity of the mono-abundance components mirrors their geometric simplicity; we have recently found their density distribution to be simple exponentials in both the z- and R-directions. We find a continuum of vertical kinetic temperatures ({proportional_to}{sigma}{sup 2}{sub z}) as a function of ([{alpha}/Fe], [Fe/H]), which contribute to the total stellar surface-mass density approximately as {Sigma}{sub R{sub 0}}({sigma}{sup 2}{sub z}){proportional_to} exp(-{sigma}{sup 2}{sub z}). This and the existence of isothermal mono-abundance populations with intermediate dispersions (30-40 km s{sup -1}) reject the notion of a thin-thick-disk dichotomy. This continuum of disk components, ranging from old, 'hot', and centrally concentrated ones to younger, cooler, and radially extended ones, argues against models where the thicker disk portions arise from massive satellite infall or heating; scenarios where either the oldest disk portion was born hot, or where internal evolution plays a major role, seem the most viable. In addition, the wide range of {sigma}{sub z}([{alpha}/Fe], [Fe/H]) combined with a constant {sigma}{sub z}(z) for each abundance bin provides an independent check on the precision of the SEGUE-derived abundances: {delta}{sub [{alpha}/Fe]} Almost-Equal-To 0.07 dex and {delta}{sub [Fe/H]} Almost-Equal-To 0.15 dex. The slow radial decline of the vertical dispersion presumably reflects the decrease in disk surface-mass density. This measurement constitutes a first step toward a purely dynamical estimate of the mass profile of the stellar and gaseous disk in our Galaxy.« less

UCAC3 Proper Motion Survey. 2. Discovery of New Proper Motion Stars in UCAC3 with 0.40 yr-1 micro or = 0.18 yr-1 between Declinations -47 deg and 00 deg

DTIC Science & Technology

2012-02-01

Micron All Sky Survey ( 2MASS ) infrared photometry. We find five new red dwarf systems estimated to be within 25 pc. These discoveries support results...re-reduction of the pixel data (Zacharias 2010). In addition, data from the Two Micron All Sky Survey ( 2MASS ) were used in UCAC3 to probe for and...errors ranging from 50 to 200 mas when compared to 2MASS data. To identify previously known high proper motion (HPM) stars in the UCAC3, a source list was

Fires of Galactic Youth Artist Animation

NASA Image and Video Library

2004-12-22

This artist's animation shows a typical young galaxy, teeming with hot, newborn stars and exploding supernovas. The supernovas are seen as white flashes of light. NASA's Galaxy Evolution Explorer spotted three-dozen young galaxies like the one shown here in our corner of the universe. It was able to see them with the help of its highly sensitive ultraviolet detectors. Because newborn stars radiate ultraviolet light, young galaxies light up brilliantly when viewed in ultraviolet wavelengths. The findings came as a surprise, because astronomers had thought that the universe's "birth-rate" had declined, and that massive galaxies were no longer forming. http://photojournal.jpl.nasa.gov/catalog/PIA07144

Photometry and polarimetry of V 1057 Cygni.

NASA Technical Reports Server (NTRS)

Rieke, G.; Lee, T.; Coyne, G.

1972-01-01

Evaluation of extensive photometric and polarimetric data over a six-month interval for V 1057 Cyg. The polarization appears to be constant and of interstellar origin; the photometry, which extends nearly six octaves from the ultraviolet to 22 microns in the infrared, indicates that the total observed luminosity is decreasing - having now declined about 10% from its earlier level. A model characterized by two circumstellar shells which absorb and reradiate short-wavelength stellar flux from an underlying A1-type star provides the best fit to the observational data. The present variability, however, cannot be due to circumstellar activity, but appears to originate in the star itself.

The US Naval Observatory Zodiacal Zone Catalog (Douglas and Harrington 1990): Documentation for the machine-readable version

NASA Technical Reports Server (NTRS)

Warren, Wayne H., Jr.

1990-01-01

The machine readable version of the catalog, as it is currently being distributed from the Astronomical Data Center, is described. The Zodiacal Zone Catalog is a catalog of positions and proper motions for stars in the magnitude range where m sub v is between 4 and 10, lying within 16 deg of the ecliptic and north of declination -30 deg. The catalog contains positions and proper motions, at epoch, for equator and equinox J2000.0, magnitudes and spectral types taken mostly from the Smithsonian Astrophysical Observatory Star Catalog, and reference positions and proper motions for equinox and epoch B1950.0.

The origin and evolution of short-period Miras in the solar neighborhood: Constraints on the life cycle of old stars

NASA Technical Reports Server (NTRS)

Jura, M.

1994-01-01

The spatial distribution of the short-period (P less than 300 days) oxygen-rich Miras in the solar neighborhood can be fitted with an exponential scale height above the Galactic plane of about 600 pc. Using the Gliese catalog of local main-sequence stars, we estimate that the density of suitable G-type progenitor dwarfs within 20 pc of the Sun for these short-period Miras is 6 x 10(exp -4)/cu pc. The portion of the H-R diagram near the main-sequence turnoff of these velocity-selected Gliese stars is intermediate between that of the old open cluster NGC 188 and that of the metal-rich globular cluster, 47 Tuc. We infer that the main-sequence progenitors of the short-period Miras have masses near 1.0 solar mass, and we estimate that these Miras have ages approximately 9 x 10(exp 9). We also identify a few old disk red giants in the neighborhood of the Sun. On the basis of very limited information, we estimate that the total amount of mass lost from these stars during their first ascent up the red giant branch is less than or equal to 0.1 solar mass. We derive a duration of the short-period Mira phase of close to 5 x 10(exp 5) yr. This estimate for the duration of the short period Mira phase is longer than our estimate of 2 x 10(exp 5) yr for the duration of the Mira phase for stars with periods longer than 300 days. From their infrared colors, we estimate a typical mass-loss rate from the short-period Miras of approximately 1 x 10(exp -7) solar mass/yr.

Star Formation at z = 2.481 in the Lensed Galaxy SDSS J1110 = 6459. I. Lens Modeling and Source Reconstruction

NASA Astrophysics Data System (ADS)

Johnson, Traci L.; Sharon, Keren; Gladders, Michael D.; Rigby, Jane R.; Bayliss, Matthew B.; Wuyts, Eva; Whitaker, Katherine E.; Florian, Michael; Murray, Katherine T.

2017-07-01

Using the combined resolving power of the Hubble Space Telescope and gravitational lensing, we resolve star-forming structures in a z˜ 2.5 galaxy on scales much smaller than the usual kiloparsec diffraction limit of HST. SGAS J111020.0+645950.8 is a clumpy, star-forming galaxy lensed by the galaxy cluster SDSS J1110+6459 at z=0.659, with a total magnification ˜ 30× across the entire arc. We use a hybrid parametric/non-parametric strong lensing mass model to compute the deflection and magnification of this giant arc, reconstruct the light distribution of the lensed galaxy in the source plane, and resolve the star formation into two dozen clumps. We develop a forward-modeling technique to model each clump in the source plane. We ray-trace the model to the image plane, convolve with the instrumental point-spread function (PSF), and compare with the GALFIT model of the clumps in the image plane, which decomposes clump structure from more extended emission. This technique has the advantage, over ray-tracing, of accounting for the asymmetric lensing shear of the galaxy in the image plane and the instrument PSF. At this resolution, we can begin to study star formation on a clump-by-clump basis, toward the goal of understanding feedback mechanisms and the buildup of exponential disks at high redshift. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program # 13003.

The MACHO Project 9 Million Star Color-Magnitude Diagram of the Large Magellanic Cloud: Probing the LMC Disk

NASA Astrophysics Data System (ADS)

Alves, D. R.; Alcock, C.; Allsman, R. A.; Axelrod, T. S.; Basu, A.; Becker, A. C.; Bennett, D. P.; Cook, K. H.; Drake, A. J.; Freeman, K. C.; Geha, M.; Griest, K.; King, L. J.; Lehner, M. J.; Marshall, S. L.; Minniti, D.; Peterson, B. A.; Popowski, P.; Pratt, M. R.; Quinn, P. J.; Rodgers, A. W.; Stubbs, C. W.; Sutherland, W.; Tomaney, A.; Vandehei, T.; Welch, D. L.; MACHO Collaboration

1998-12-01

We present a 9 million star color-magnitude diagram (9M CMD) of the Large Magellanic Cloud (LMC) bar. The 9M CMD reveals a complex superposition of different age and metallicity stellar populations. Young LMC stellar populations are prominent in the 9M CMD. Of these, the red and blue supergiants are potentially useful probes of the late stages of evolution in intermediate mass stars. Old LMC stellar populations are also evident in the 9M CMD. These are used to reconstruct the evolution of the LMC during cosmologically interesting epochs. We first build a plausible model for the old LMC populations consistent with features observed in the 9M CMD. We choose the 1.5 Gyr old cluster NGC 411 and the ancient globular cluster M3, with metal abundances of [Fe/H] = -0.7 and -1.5 dex respectively, as good representations of the giant branch and horizontal branch (HB) stars. The evolved asymptotic giant branch appears bimodal, which supports a model of two discrete older populations in the LMC field. We conclude the old populations in the LMC bar are likely a mix similar to NGC 411 and M3. Next, we infer the old and low metallicity LMC field population has a red HB morphology, which implies this population formed ~ 2 Gyr after the truly ancient LMC clusters formed. We find the surface density profile of this old LMC field population (traced by RRab variable stars) is exponential, favoring a disk-like rather than spheroidal distribution. We conclude the LMC disk formed ~ 10 Gyr ago, at the same time the Milky Way disk formed.

H II regions in the dwarf galaxy UGC-A 86

NASA Technical Reports Server (NTRS)

Miller, Bryan W.; Hodge, Paul

1993-01-01

The uncertain nature of the dwarf irregular galaxy UGC-A 86 (VIIZw009) makes it a very interesting object for studying star formation at the low end of the galaxy luminosity function. Saha and Hoessel (1991) find that this object is composed of two main parts, one of which appears more resolved than the other. The more resolved component has an excess of blue stars, suggesting that it is currently undergoing star formation. Thus, they argue that UGC-A 86 could be either a superposition of unrelated galaxies, two interacting galaxies, or a single galaxy. However, surface photometry performed by Richter et al. (1991) indicates that it is a single galaxy with an exponential luminosity profile. Richter et al. also find UGC-A 86 to be extremely dusty and to be associated with the infrared source IRAS 3550+6657. The uncertainty is compounded by the large ambiguity in the distance, though a heliocentric H1 velocity of 80 plus or minus 7 km s(sup -1) suggests that it is either a member of the Local Group or perhaps the IC 342 group. A distance of 1.5 Mpc and a reddening of E(B - V) = 0.65 is adopted. UGC-A 86 in H-alpha was observed in order to measure its current star formation rate. This is part of a larger project to study the star formation rates and histories of a complete sample of dwarf galaxies in the Local Group and other nearby groups. The H region luminosity function and size distribution for UGC-A 86 are presented and compared with previous observations of similar dwarf galaxies.

Tracing the Far-Infrared Roles of AGN in Dusty Star-Forming Galaxies

NASA Astrophysics Data System (ADS)

Brown, Arianna; Nayyeri, Hooshang; Cooray, Asantha R.; Mitchell-Wynne, Ketron

2017-01-01

Active galactic nuclei (AGNs) are suggested to play an important role in quenching their host galaxy’s star formation rate (SFR) by heating up and/or consuming the cool gas necessary to create stars. This mechanism is theorized as a critical step in AGN evolutionary models. The efforts to study this effect suffer in part from low-number statistics at high x-ray luminosities (LXR > 1044 ergs/s) for AGNs at z≈1-3, and a lack of separately estimated SFRs for AGN in dusty, star-forming galaxies (DSFGs). In this work, we extend our analysis to build a more complete picture using the variety of available multi-wavelength data in the XBoötes region. The Chandra XBoötes Survey is a 5-ks X-ray survey of the 9.3 square degree Boötes Field of the NOAO Deep Wide-Field Survey, a survey imaged from the optical to the near-IR. We estimate AGN spectral energy distributions and SFRs for ~400 x-ray sources using available data in all four Spitzer IRAC bands, the Spitzer MIPS 24µm band, all five Herschel SPIRE and PACS bands, along with NEWFIRM optical bands. Preliminary results show an exponential correlation between x-ray luminosity and star formation. As a comparison, we will use a stacking technique for the ~500 x-ray sources that were not detected at submillimeter wavelengths, where sources are binned by x-ray luminosity. We will compare these two samples and expect to see a difference in slope. Using these techniques, we hope to place tighter constraints on the mean SFRs of high-luminosity AGNs inside DSFGs, and determine if x-ray luminosities are independent of average SFRs for our sample in the Boötes field.

The origin and evolution of short-period Miras in the solar neighborhood: Constraints on the life cycle of old stars

NASA Astrophysics Data System (ADS)

Jura, M.

1994-02-01

The spatial distribution of the short-period (P less than 300 days) oxygen-rich Miras in the solar neighborhood can be fitted with an exponential scale height above the Galactic plane of about 600 pc. Using the Gliese catalog of local main-sequence stars, we estimate that the density of suitable G-type progenitor dwarfs within 20 pc of the Sun for these short-period Miras is 6 x 10-4/cu pc. The portion of the H-R diagram near the main-sequence turnoff of these velocity-selected Gliese stars is intermediate between that of the old open cluster NGC 188 and that of the metal-rich globular cluster, 47 Tuc. We infer that the main-sequence progenitors of the short-period Miras have masses near 1.0 solar mass, and we estimate that these Miras have ages approximately 9 x 109. We also identify a few old disk red giants in the neighborhood of the Sun. On the basis of very limited information, we estimate that the total amount of mass lost from these stars during their first ascent up the red giant branch is less than or equal to 0.1 solar mass. We derive a duration of the short-period Mira phase of close to 5 x 105 yr. This estimate for the duration of the short period Mira phase is longer than our estimate of 2 x 105 yr for the duration of the Mira phase for stars with periods longer than 300 days. From their infrared colors, we estimate a typical mass-loss rate from the short-period Miras of approximately 1 x 10-7 solar mass/yr.

Fundamental data on the desorption of pure interstellar ices

NASA Astrophysics Data System (ADS)

Brown, Wendy A.; Bolina, Amandeep S.

2007-01-01

The desorption of molecular ices from grain surfaces is important in a number of astrophysical environments including dense molecular clouds, cometary nuclei and the surfaces and atmospheres of some planets. With this in mind, we have performed a detailed investigation of the desorption of pure water, pure methanol and pure ammonia ices from a model dust-grain surface. We have used these results to determine the desorption energy, order of desorption and the pre-exponential factor for the desorption of these molecular ices from our model surface. We find good agreement between our desorption energies and those determined previously; however, our values for the desorption orders, and hence also the pre-exponential factors, are different to those reported previously. The kinetic parameters derived from our data have been used to model desorption on time-scales relevant to astrophysical processes and to calculate molecular residence times, given in terms of population half-life as a function of temperature. These results show the importance of laboratory data for the understanding of astronomical situations whereby icy mantles are warmed by nearby stars and by other dynamical events.

Estimating the decline in excess risk of cerebrovascular disease following quitting smoking--a systematic review based on the negative exponential model.

PubMed

Lee, Peter N; Fry, John S; Thornton, Alison J

2014-02-01

We attempted to quantify the decline in stroke risk following quitting using the negative exponential model, with methodology previously employed for IHD. We identified 22 blocks of RRs (from 13 studies) comparing current smokers, former smokers (by time quit) and never smokers. Corresponding pseudo-numbers of cases and controls/at risk formed the data for model-fitting. We tried to estimate the half-life (H, time since quit when the excess risk becomes half that for a continuing smoker) for each block. The method failed to converge or produced very variable estimates of H in nine blocks with a current smoker RR <1.40. Rejecting these, and combining blocks by amount smoked in one study where problems arose in model-fitting, the final analyses used 11 blocks. Goodness-of-fit was adequate for each block, the combined estimate of H being 4.78(95%CI 2.17-10.50) years. However, considerable heterogeneity existed, unexplained by any factor studied, with the random-effects estimate 3.08(1.32-7.16). Sensitivity analyses allowing for reverse causation or differing assumed times for the final quitting period gave similar results. The estimates of H are similar for stroke and IHD, and the individual estimates similarly heterogeneous. Fitting the model is harder for stroke, due to its weaker association with smoking. Copyright © 2013 The Authors. Published by Elsevier Inc. All rights reserved.

The Hydrodynamical Models of the Cometary Compact HII Region

NASA Astrophysics Data System (ADS)

Zhu, Feng-Yao; Zhu, Qing-Feng; Li, Juan; Zhang, Jiang-Shui; Wang, Jun-Zhi

2015-10-01

We have developed a full numerical method to study the gas dynamics of cometary ultracompact H ii regions, and associated photodissociation regions (PDRs). The bow-shock and champagne-flow models with a 40.9/21.9 M⊙ star are simulated. In the bow-shock models, the massive star is assumed to move through dense (n = 8000 cm-3) molecular material with a stellar velocity of 15 km s-1. In the champagne-flow models, an exponential distribution of density with a scale height of 0.2 pc is assumed. The profiles of the [Ne ii] 12.81 μm and H2 S(2) lines from the ionized regions and PDRs are compared for two sets of models. In champagne-flow models, emission lines from the ionized gas clearly show the effect of acceleration along the direction toward the tail due to the density gradient. The kinematics of the molecular gas inside the dense shell are mainly due to the expansion of the H ii region. However, in bow-shock models the ionized gas mainly moves in the same direction as the stellar motion. The kinematics of the molecular gas inside the dense shell simply reflects the motion of the dense shell with respect to the star. These differences can be used to distinguish two sets of models.

GRS 1739-278 Observed at Very Low Luminosity with XMM-Newton and NuSTAR

NASA Astrophysics Data System (ADS)

Fürst, F.; Tomsick, J. A.; Yamaoka, K.; Dauser, T.; Miller, J. M.; Clavel, M.; Corbel, S.; Fabian, A.; García, J.; Harrison, F. A.; Loh, A.; Kaaret, P.; Kalemci, E.; Migliari, S.; Miller-Jones, J. C. A.; Pottschmidt, K.; Rahoui, F.; Rodriguez, J.; Stern, D.; Stuhlinger, M.; Walton, D. J.; Wilms, J.

2016-12-01

We present a detailed spectral analysis of XMM-Newton and NuSTAR observations of the accreting transient black hole GRS 1739-278 during a very faint low hard state at ˜0.02% of the Eddington luminosity (for a distance of 8.5 kpc and a mass of 10 {M}⊙ ). The broadband X-ray spectrum between 0.5 and 60 keV can be well-described by a power-law continuum with an exponential cutoff. The continuum is unusually hard for such a low luminosity, with a photon index of Γ = 1.39 ± 0.04. We find evidence for an additional reflection component from an optically thick accretion disk at the 98% likelihood level. The reflection fraction is low, with {{ R }}{refl}={0.043}-0.023+0.033. In combination with measurements of the spin and inclination parameters made with NuSTAR during a brighter hard state by Miller et al., we seek to constrain the accretion disk geometry. Depending on the assumed emissivity profile of the accretion disk, we find a truncation radius of 15-35 {R}{{g}} (5-12 {R}{ISCO}) at the 90% confidence limit. These values depend strongly on the assumptions and we discuss possible systematic uncertainties.

Elemental Abundances and their Implications for the Chemical Enrichment of the Boötes I Ultrafaint Galaxy

NASA Astrophysics Data System (ADS)

Gilmore, Gerard; Norris, John E.; Monaco, Lorenzo; Yong, David; Wyse, Rosemary F. G.; Geisler, D.

2013-01-01

We present a double-blind analysis of high-dispersion spectra of seven red giant members of the Boötes I ultrafaint dwarf spheroidal galaxy, complemented with re-analysis of a similar spectrum of an eighth-member star. The stars cover [Fe/H] from -3.7 to -1.9 and include a CEMP-no star with [Fe/H] = -3.33. We conclude from our chemical abundance data that Boötes I has evolved as a self-enriching star-forming system, from essentially primordial initial abundances. This allows us uniquely to investigate the place of CEMP-no stars in a chemically evolving system, in addition to limiting the timescale of star formation. The elemental abundances are formally consistent with a halo-like distribution, with enhanced mean [α/Fe] and small scatter about the mean. This is in accord with the high-mass stellar initial mass function in this low-stellar-density, low-metallicity system being indistinguishable from the present-day solar neighborhood value. There is a non-significant hint of a decline in [α/Fe] with [Fe/H]; together with the low scatter, this requires low star formation rates, allowing time for supernova ejecta to be mixed over the large spatial scales of interest. One star has very high [Ti/Fe], but we do not confirm a previously published high value of [Mg/Fe] for another star. We discuss the existence of CEMP-no stars, and the absence of any stars with lower CEMP-no enhancements at higher [Fe/H], a situation that is consistent with knowledge of CEMP-no stars in the Galactic field. We show that this observation requires there be two enrichment paths at very low metallicities: CEMP-no and "carbon-normal." Based on observations collected at the European Southern Observatory, Paranal, Chile (Proposal P82.182.B-0372, PI: G. Gilmore).

VARIABLE WINDS AND DUST FORMATION IN R CORONAE BOREALIS STARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clayton, Geoffrey C.; Zhang Wanshu; Geballe, T. R., E-mail: gclayton@fenway.phys.lsu.edu, E-mail: wzhan21@lsu.edu, E-mail: tgeballe@gemini.edu

2013-08-01

We have observed P-Cygni and asymmetric, blue-shifted absorption profiles in the He I {lambda}10830 lines of 12 R Coronae Borealis stars over short (1 month) and long (3 yr) timescales to look for variations linked to their dust-formation episodes. In almost all cases, the strengths and terminal velocities of the line vary significantly and are correlated with dust formation events. Strong absorption features with blue-shifted velocities {approx}400 km s{sup -1} appear during declines in visible brightness and persist for about 100 days after recovery to maximum brightness. Small residual winds of somewhat lower velocity are present outside of the declinemore » and recovery periods. The correlations support models in which recently formed dust near the star is propelled outward at high speed by radiation pressure and drags the gas along with it.« less

WS1: one more new Galactic bona fide luminous blue variable★

NASA Astrophysics Data System (ADS)

Kniazev, A. Y.; Gvaramadze, V. V.; Berdnikov, L. N.

2015-04-01

In this Letter, we report the results of spectroscopic and photometric monitoring of the candidate luminous blue variable (LBV) WS1, which was discovered in 2011 through the detection of a mid-infrared circular shell and follow-up optical spectroscopy of its central star. Our monitoring showed that WS1 brightened in the B, V and I bands by more than 1 mag during the last three years, while its spectrum revealed dramatic changes during the same time period, indicating that the star became much cooler. The light curve of WS1 demonstrates that the brightness of this star has reached maximum in 2013 December and then starts to decline. These findings unambiguously proved the LBV nature of WS1 and added one more member to the class of Galactic bona fide LBVs, bringing their number to sixteen (an updated census of these objects is provided).

Dynamical Model for Spindown of Solar-type Stars

NASA Astrophysics Data System (ADS)

Sood, Aditi; Kim, Eun-jin; Hollerbach, Rainer

2016-12-01

After their formation, stars slow down their rotation rates by the removal of angular momentum from their surfaces, e.g., via stellar winds. Explaining how this rotation of solar-type stars evolves in time is currently an interesting but difficult problem in astrophysics. Despite the complexity of the processes involved, a traditional model, where the removal of angular momentum by magnetic fields is prescribed, has provided a useful framework to understand observational relations between stellar rotation, age, and magnetic field strength. Here, for the first time, a spindown model is proposed where loss of angular momentum by magnetic fields evolves dynamically, instead of being prescibed kinematically. To this end, we evolve the stellar rotation and magnetic field simultaneously over stellar evolution time by extending our previous work on a dynamo model which incorporates nonlinear feedback mechanisms on rotation and magnetic fields. We show that our extended model reproduces key observations and is capable of explaining the presence of the two branches of (fast and slow rotating) stars which have different relations between rotation rate Ω versus time (age), magnetic field strength | B| versus rotation rate, and frequency of magnetic field {ω }{cyc} versus rotation rate. For fast rotating stars we find that: (I) there is an exponential spindown {{Ω }}\\propto {e}-1.35t, with t measured in Gyr; (II) magnetic activity saturates for higher rotation rate; (III) {ω }{cyc}\\propto {{{Ω }}}0.83. For slow rotating stars we find: (I) a power-law spindown {{Ω }}\\propto {t}-0.52; (II) that magnetic activity scales roughly linearly with rotation rate; (III) {ω }{cyc}\\propto {{{Ω }}}1.16. The results obtained from our investigations are in good agreement with observations. The Vaughan-Preston gap is consistently explained in our model by the shortest spindown timescale in this transition from fast to slow rotators. Our results highlight the importance of self-regulation of magnetic fields and rotation by direct and indirect interactions involving nonlinear feedback in stellar evolution.

On the Kennicutt-Schmidt Relation of Low-Metallicity High-Redshift Galaxies

NASA Astrophysics Data System (ADS)

Gnedin, Nickolay Y.; Kravtsov, Andrey V.

2010-05-01

We present results of self-consistent, high-resolution cosmological simulations of galaxy formation at z ~ 3. The simulations employ a recently developed recipe for star formation based on the local abundance of molecular hydrogen, which is tracked self-consistently during the course of simulation. The phenomenological H2 formation model accounts for the effects of dissociating UV radiation of stars in each galaxy, as well as self-shielding and shielding of H2 by dust, and therefore allows us to explore effects of lower metallicities and higher UV fluxes prevalent in high-redshift galaxies on their star formation. We compare stellar masses, metallicities, and star formation rates of the simulated galaxies to available observations of the Lyman break galaxies (LBGs) and find a reasonable agreement. We find that the Kennicutt-Schmidt (KS) relation exhibited by our simulated galaxies at z ≈ 3 is substantially steeper and has a lower amplitude than the z = 0 relation at ΣH <~ 100 M odot pc-2. The predicted relation, however, is consistent with existing observational constraints for the z ≈ 3 damped Lyα and LBGs. Our tests show that the main reason for the difference from the local KS relation is lower metallicity of the interstellar medium in high-redshift galaxies. We discuss several implications of the metallicity-dependence of the KS relation for galaxy evolution and interpretation of observations. In particular, we show that the observed size of high-redshift exponential disks depends sensitively on their KS relation. Our results also suggest that significantly reduced star formation efficiency at low gas surface densities can lead to strong suppression of star formation in low-mass high-redshift galaxies and long gas consumption time scales over most of the disks in large galaxies. The longer gas consumption time scales could make disks more resilient to major and minor mergers and could help explain the prevalence of the thin stellar disks in the local universe.

Catalog of Positions and B Magnitudes of Stars in the Circumpolar Region of Northen Sky Survey (fon) Project

NASA Astrophysics Data System (ADS)

Andruk, V. M.; Pakuliak, L. K.; Golovnia, V. V.; Ivanov, G. A.; Yizhakevych, O. M.; Protsyuk, Yu. I.; Shatokhina, S. V.

The catalog of star positions and B-magnitudes for the circumpolar region (from 58° to 90° in declination) of Northern Sky Survey project has been created under the motto of the rational use of resources accumulated in UkrVO JDA (Joint Digital Archive) in MAO NASU. The total amount of processed plates is 477. Digitizing of astronegatives has been carried out using Microtek ScanMaker 9800XL TMA and Epson Expression 10000XL scanners, with the scanning mode - 1200 dpi, the linear size of the plates - 30x30 cm or 13000x13000 px. The catalog contains 1 975 967 stars and galaxies with B ≤ 16.5m for the epoch of 1985.28. The coordinates of stars and galaxies were obtained in the Tycho-2 reference system, and B-value in the system of photoelectric standards. The internal accuracy of the catalog for all the objects is σαδ = ± 0.23 "and σB = ± 0.12m (for stars in the range of B = 8m -14m errors are σαδ = ± 0.11" and σB = ± 0.06m). Convergence between the calculated and reference positions is σαδ = ± 0.06 "(for 171 124 stars from Tycho-2), and the convergence with photoelectric stellar B-magnitudes is σB = ± 0.15m (for 5130 stars). External accuracy from the comparison with UCAC-4 is σαδ = ± 0.33 "(1 928 367 stars and galaxies were cross identified).

Statistical power for detecting trends with applications to seabird monitoring

USGS Publications Warehouse

Hatch, Shyla A.

2003-01-01

Power analysis is helpful in defining goals for ecological monitoring and evaluating the performance of ongoing efforts. I examined detection standards proposed for population monitoring of seabirds using two programs (MONITOR and TRENDS) specially designed for power analysis of trend data. Neither program models within- and among-years components of variance explicitly and independently, thus an error term that incorporates both components is an essential input. Residual variation in seabird counts consisted of day-to-day variation within years and unexplained variation among years in approximately equal parts. The appropriate measure of error for power analysis is the standard error of estimation (S.E.est) from a regression of annual means against year. Replicate counts within years are helpful in minimizing S.E.est but should not be treated as independent samples for estimating power to detect trends. Other issues include a choice of assumptions about variance structure and selection of an exponential or linear model of population change. Seabird count data are characterized by strong correlations between S.D. and mean, thus a constant CV model is appropriate for power calculations. Time series were fit about equally well with exponential or linear models, but log transformation ensures equal variances over time, a basic assumption of regression analysis. Using sample data from seabird monitoring in Alaska, I computed the number of years required (with annual censusing) to detect trends of -1.4% per year (50% decline in 50 years) and -2.7% per year (50% decline in 25 years). At ??=0.05 and a desired power of 0.9, estimated study intervals ranged from 11 to 69 years depending on species, trend, software, and study design. Power to detect a negative trend of 6.7% per year (50% decline in 10 years) is suggested as an alternative standard for seabird monitoring that achieves a reasonable match between statistical and biological significance.

Influence of genetic background, salinity, and inoculum size on growth of the ichthyotoxic golden alga (Prymnesium parvum).

PubMed

Rashel, Rakib H; Patiño, Reynaldo

2017-06-01

Salinity (5-30) effects on golden alga growth were determined at a standard laboratory temperature (22°C) and one associated with natural blooms (13°C). Inoculum-size effects were determined over a wide size range (100-100,000cellsml -1 ). A strain widely distributed in the USA, UTEX-2797 was the primary study subject but another of limited distribution, UTEX-995 was used to evaluate growth responses in relation to genetic background. Variables examined were exponential growth rate (r), maximum cell density (max-D) and, when inoculum size was held constant (100cellsml -1 ), density at onset of exponential growth (early-D). In UTEX-2797, max-D increased as salinity increased from 5 to ∼10-15 and declined thereafter regardless of temperature but r remained generally stable and only declined at salinity of 25-30. In addition, max-D correlated positively with r and early-D, the latter also being numerically highest at salinity of 15. In UTEX-995, max-D and r responded similarly to changes in salinity - they remained stable at salinity of 5-10 and 5-15, respectively, and declined at higher salinity. Also, max-D correlated with r but not early-D. Inoculum size positively and negatively influenced max-D and r, respectively, in both strains and these effects were significant even when the absolute size difference was small (100 versus 1000 cells ml -1 ). When cultured under similar conditions, UTEX-2797 grew faster and to much higher density than UTEX-995. In conclusion, (1) UTEX-2797's superior growth performance may explain its relatively wide distribution in the USA, (2) the biphasic growth response of UTEX-2797 to salinity variation, with peak abundance at salinity of 10-15, generally mirrors golden alga abundance-salinity associations in US inland waters, and (3) early cell density - whether artificially manipulated or naturally attained - can influence UTEX-2797 bloom potential. Published by Elsevier B.V.

An unbiased study of debris discs around A-type stars with Herschel

NASA Astrophysics Data System (ADS)

Thureau, N. D.; Greaves, J. S.; Matthews, B. C.; Kennedy, G.; Phillips, N.; Booth, M.; Duchêne, G.; Horner, J.; Rodriguez, D. R.; Sibthorpe, B.; Wyatt, M. C.

2014-12-01

The Herschel DEBRIS (Disc Emission via a Bias-free Reconnaissance in the Infrared/Submillimetre) survey brings us a unique perspective on the study of debris discs around main-sequence A-type stars. Bias-free by design, the survey offers a remarkable data set with which to investigate the cold disc properties. The statistical analysis of the 100 and 160 μm data for 86 main-sequence A stars yields a lower than previously found debris disc rate. Considering better than 3σ excess sources, we find a detection rate ≥24 ± 5 per cent at 100 μm which is similar to the debris disc rate around main-sequence F/G/K-spectral type stars. While the 100 and 160 μm excesses slowly decline with time, debris discs with large excesses are found around some of the oldest A stars in our sample, evidence that the debris phenomenon can survive throughout the length of the main sequence (˜1 Gyr). Debris discs are predominantly detected around the youngest and hottest stars in our sample. Stellar properties such as metallicity are found to have no effect on the debris disc incidence. Debris discs are found around A stars in single systems and multiple systems at similar rates. While tight and wide binaries (<1 and >100 au, respectively) host debris discs with a similar frequency and global properties, no intermediate separation debris systems were detected in our sample.

The Type IIn Supernova SN 2010bt: The Explosion of a Star in Outburst

NASA Astrophysics Data System (ADS)

Elias-Rosa, Nancy; Van Dyk, Schuyler D.; Benetti, Stefano; Cappellaro, Enrico; Smith, Nathan; Kotak, Rubina; Turatto, Massimo; Filippenko, Alexei V.; Pignata, Giuliano; Fox, Ori D.; Galbany, Lluis; González-Gaitán, Santiago; Miluzio, Matteo; Monard, L. A. G.; Ergon, Mattias

2018-06-01

It is well known that massive stars (M > 8 M ⊙) evolve up to the collapse of the stellar core, resulting in most cases in a supernova (SN) explosion. Their heterogeneity is related mainly to different configurations of the progenitor star at the moment of the explosion and to their immediate environments. We present photometry and spectroscopy of SN 2010bt, which was classified as a Type IIn SN from a spectrum obtained soon after discovery and was observed extensively for about 2 months. After the seasonal interruption owing to its proximity to the Sun, the SN was below the detection threshold, indicative of a rapid luminosity decline. We can identify the likely progenitor with a very luminous star (log L/L ⊙ ≈ 7) through comparison of Hubble Space Telescope images of the host galaxy prior to explosion with those of the SN obtained after maximum light. Such a luminosity is not expected for a quiescent star, but rather for a massive star in an active phase. This progenitor candidate was later confirmed via images taken in 2015 (∼5 yr post-discovery), in which no bright point source was detected at the SN position. Given these results and the SN behavior, we conclude that SN 2010bt was likely a Type IIn SN and that its progenitor was a massive star that experienced an outburst shortly before the final explosion, leading to a dense H-rich circumstellar environment around the SN progenitor.

An Analytical Approach to the Evolution and Death of AGB Stars

NASA Astrophysics Data System (ADS)

Prager, Henry Alexander; Willson, Lee Anne M.; Marengo, Massimo; Creech-Eakman, Michelle J.

2017-01-01

Pop. I and II stars have a significant amount of metals throughout their structure, In the final stages of their evolution, intermediate mass stars (between 0.7 and 2 solar masses) ascend the Asymptotic Giant Branch (AGB). During their last few hundred thousand years on the AGB, these stars quickly lose their envelopes, recycling their metals as dust into the interstellar medium. The rate at which this happens consequently impacts the formation rate of stars, stellar systems, and the wider distribution of s-process isotopes.At the end of their life cycles, AGB stars experience a steep increase in mass loss rate. We can define the death line in two steps. First we define the critical mass loss rate to be where the mass loss rate equals the initial mass divided by the evolution time. Then the death line is where the rate of change of logMdot equals the rate of change of logL. Most of the stars we observe to be rapidly losing mass appear in the death zone between 0.1 and 10 times the critical mass loss rate.Assuming the mass loss rate increases exponentially with time, or, equivalently, the luminosity increases as a power of a characteristic exponent b, then the width of the death zone is the change in logL. This directly implies time is inversely proportional to b. This can be found for any mass-loss rate formula near the death line. By combining this with what we know about the initial-final mass relation and the core mass-luminosity relation, we can test for b with three observables — duration (width) of the death zone, the amplitude of mass loss variations (when L varies on an observable time scale such as a shell flash), and distributions of luminosity and pulsation period.By applying the initial mass function (IMF) and star formation rate (SFR) of an observed region, we can relate these observables to the characteristic exponent. We will need to look at nearby regions where we can see large numbers of AGB stars, such as the Magellanic clouds. We will show that by fixing the death line and the characteristic exponent that intermediate changes in the mass loss rate better fit observations than extreme values. This is consistent with dust-driven as opposed to pulsation-driven processes.

Simulation of the modulation transfer function dependent on the partial Fourier fraction in dynamic contrast enhancement magnetic resonance imaging.

PubMed

Takatsu, Yasuo; Ueyama, Tsuyoshi; Miyati, Tosiaki; Yamamura, Kenichirou

2016-12-01

The image characteristics in dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) depend on the partial Fourier fraction and contrast medium concentration. These characteristics were assessed and the modulation transfer function (MTF) was calculated by computer simulation. A digital phantom was created from signal intensity data acquired at different contrast medium concentrations on a breast model. The frequency images [created by fast Fourier transform (FFT)] were divided into 512 parts and rearranged to form a new image. The inverse FFT of this image yielded the MTF. From the reference data, three linear models (low, medium, and high) and three exponential models (slow, medium, and rapid) of the signal intensity were created. Smaller partial Fourier fractions, and higher gradients in the linear models, corresponded to faster MTF decline. The MTF more gradually decreased in the exponential models than in the linear models. The MTF, which reflects the image characteristics in DCE-MRI, was more degraded as the partial Fourier fraction decreased.

Resource acquisition, distribution and end-use efficiencies and the growth of industrial society

NASA Astrophysics Data System (ADS)

Jarvis, A.; Jarvis, S.; Hewitt, N.

2015-01-01

A key feature of the growth of industrial society is the acquisition of increasing quantities of resources from the environment and their distribution for end use. With respect to energy, growth has been near exponential for the last 160 years. We attempt to show that the global distribution of resources that underpins this growth may be facilitated by the continual development and expansion of near optimal directed networks. If so, the distribution efficiencies of these networks must decline as they expand due to path lengths becoming longer and more tortuous. To maintain long-term exponential growth the physical limits placed on the distribution networks appear to be counteracted by innovations deployed elsewhere in the system: namely at the points of acquisition and end use. We postulate that the maintenance of growth at the specific rate of ~2.4% yr-1 stems from an implicit desire to optimise patterns of energy use over human working lifetimes.

BORON ABUNDANCES ACROSS THE “Li–Be DIP” IN THE HYADES CLUSTER

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boesgaard, Ann Merchant; Lum, Michael G.; Deliyannis, Constantine P.

2016-10-10

Dramatic deficiencies of Li in the mid-F dwarf stars of the Hyades cluster were discovered by Boesgaard and Tripicco. Boesgaard and King discovered corresponding, but smaller, deficiencies in Be in the same narrow temperature region in the Hyades. Using the Space Telescope Imaging Spectrograph on the Hubble Space Telescope , we investigate B abundances in the Hyades F stars to look for a potential B dip using the B i resonance line at 2496.8 Å. The light elements Li, Be, and B are destroyed inside stars at increasingly hotter temperatures: 2.5, 3.5, and 5 × 10{sup 6} K, respectively. Consequently,more » these elements survive to increasingly greater depths in a star and their surface abundances indicate the depth and thoroughness of mixing in the star. We have (re)determined Li abundances/upper limits for 79 Hyades dwarfs, Be for 43 stars, and B for 5 stars. We find evidence for a small drop in the B abundance across the Li–Be dip. The B abundances for the four stars in the temperature range 6100–6730 K fit the B–Be correlation found previously by Boesgaard et al. Models of rotational mixing produce good agreement with the relative depletions of Be and B in the dip region. We have compared our nLTE B abundances for the three high B stars on either side of the Li–Be dip with those found by Duncan et al. for the two Hyades giants. This confirms the factor of 10 decline in the B abundance in the Hyades giants as predicted by dilution due to the deepening of the surface convection zone.« less

UIT: Ultraviolet surface photometry of the spiral galaxy M74 (NGC 628)

NASA Technical Reports Server (NTRS)

Cornett, Robert H.; O'Connell, Robert W.; Greason, Michael R.; Offenberg, Joel D.; Angione, Ronald J.; Bohlin, Ralph C.; Cheng, K. P.; Roberts, Morton S.; Smith, Andrew M.; Smith, Eric P.

1994-01-01

Ultraviolet photometry, obtained from Ultraviolet Imaging Telescope (UIT) images at 1520 A (far-UV; magnitudes m(152)) and 2490 A (near-UV; magnitudes m(249)), of the spiral galaxy M74 (NGC 628) is compared with H-alpha, R, V, and B surface photometry and with models. M74's surface brightness profiles have a central peak with an exponential falloff; the exponential scale lengths of the profiles increase with decreasing wavelength for the broad-band images. The slope of the continuum-subtracted H-alpha profile is intermediate between those of far-UV and near-UV profiles, consistent with the related origins of H-alpha and UV emission in extreme Population I material. M74's color profiles all become bluer with increasing radius. The (m(152) - m(249)) color as measured by UIT averages near 0.0 (the color of an A0 star) over the central 20 sec radius and decreases from approximately -0.2 to approximately -0.4 from 20 sec to 200 sec. The spiral arms are the dominant component of the surface photometry colors; interarm regions are slightly redder. In the UV, M74's nuclear region resembles its disk/spiral arm material in colors and morphology, unlike galaxies such as M81. No UV 'bulge' is apparent. The m(152) - m(249) colors and models of M74's central region clearly demonstrate that there is no significant population of O or B stars present in the central 10 sec. M74's UV morphology and (m(152) - m(249)) color profiles are similar to those of M33, although M74 is approximately 0.5 mag redder. M81 has a smooth UV bulge which is much redder than the nuclear regions of M74 and M33. M74 is approximately 0.4 mag bluer than M81 in its outer disk, although M81 has bright UV sources only in spiral arms more than 5 kpc from its center. We investigate possible explanations for the color profiles of the galaxies and the differences among the galaxies: abundances; reddening due to internal dust; interplanetary magnetic field (IMF) variations, and the history of formation of the dominant generations of stars. Abundance and IMF variations do not produce large enough m(152) - m(249) or UV - V color differences. Comparing model UV/optical colors with those of M74 shows that M74's disk has undergone significant star formation over the past 500 Myr, and that either the star-formation history or the extinction varies systematically across M74's disk. Comparison of M74, M33, and M81 (UV - V) colors shows that M74 colors range from the bluest of M33's colors to the bluest of M81's. The failure of reddening models to cover the range of colors, and the known abundance range in such material, leads to the conclusion that star-formation history varies significantly as a function of radius in these galaxies, and that such variation is required to explain the range of colors observed in M74, M33, and M81.

VizieR Online Data Catalog: Parenago Catalog of Stars in Orion Nebula (Parenago 1954)

NASA Astrophysics Data System (ADS)

Parenago, P. P.

1997-10-01

The present catalogue is a machine-readable version of the catalogue of stars in the area of the Orion nebula, published by P.P. Parenago (1954). The sky area between 5h 24m and 5h 36m in right ascension (1900.0) and between -4 and -7 degrees in declination (1900.0), containing the Orion nebula, has been investigated in that work. Ten of variable stars in original Parenago (1954) catalogue had CSV numbers (Kukarkin et al., 1951) but since that time all of them were confirmed as variables and included in GCVS (Kholopov et al., 1985a&b, 1987). We superseded CSV-numbers by GCVS-names in the machine-readable version for the following stars: ------------------------------------------------ Number in CSV-number GCVS-name the catalogue ------------------------------------------------ 1605 606 V372 ORI 1613 607 V373 ORI 1635 608 V374 ORI 1713 609 V375 ORI 1748 610 V387 ORI 1762 100569 V376 ORI 1974 617 V377 ORI 2183 625 V388 ORI 2393 630 V380 ORI 2478 634 V381 ORI ------------------------------------------------ (1 data file).

The onset of star formation 250 million years after the Big Bang

NASA Astrophysics Data System (ADS)

Hashimoto, Takuya; Laporte, Nicolas; Mawatari, Ken; Ellis, Richard S.; Inoue, Akio K.; Zackrisson, Erik; Roberts-Borsani, Guido; Zheng, Wei; Tamura, Yoichi; Bauer, Franz E.; Fletcher, Thomas; Harikane, Yuichi; Hatsukade, Bunyo; Hayatsu, Natsuki H.; Matsuda, Yuichi; Matsuo, Hiroshi; Okamoto, Takashi; Ouchi, Masami; Pelló, Roser; Rydberg, Claes-Erik; Shimizu, Ikkoh; Taniguchi, Yoshiaki; Umehata, Hideki; Yoshida, Naoki

2018-05-01

A fundamental quest of modern astronomy is to locate the earliest galaxies and study how they influenced the intergalactic medium a few hundred million years after the Big Bang1-3. The abundance of star-forming galaxies is known to decline4,5 from redshifts of about 6 to 10, but a key question is the extent of star formation at even earlier times, corresponding to the period when the first galaxies might have emerged. Here we report spectroscopic observations of MACS1149-JD16, a gravitationally lensed galaxy observed when the Universe was less than four per cent of its present age. We detect an emission line of doubly ionized oxygen at a redshift of 9.1096 ± 0.0006, with an uncertainty of one standard deviation. This precisely determined redshift indicates that the red rest-frame optical colour arises from a dominant stellar component that formed about 250 million years after the Big Bang, corresponding to a redshift of about 15. Our results indicate that it may be possible to detect such early episodes of star formation in similar galaxies with future telescopes.

The fraction of quiescent massive galaxies in the early Universe

NASA Astrophysics Data System (ADS)

Fontana, A.; Santini, P.; Grazian, A.; Pentericci, L.; Fiore, F.; Castellano, M.; Giallongo, E.; Menci, N.; Salimbeni, S.; Cristiani, S.; Nonino, M.; Vanzella, E.

2009-07-01

Aims: We attempt to compile a complete, mass-selected sample of galaxies with low specific star-formation rates, and compare their properties with theoretical model predictions. Methods: We use the f(24 μ m})/f(K) flux ratio and the SED fitting to the 0.35-8.0 μm spectral distribution, to select quiescent galaxies from z≃ 0.4 to z≃ 4 in the GOODS-MUSIC sample. Our observational selection can be translated into thresholds in specific star-formation rate dot{M}/M_*, which can be compared with theoretical predictions. Results: In the framework of the well-known global decline in quiescent galaxy fraction with redshift, we find that a non-negligible fraction {≃ 15-20% of massive galaxies with low specific star-formation rate exists up to z≃ 4, including a tail of “red and dead” galaxies with dot{M}/M_*<10-11 yr-1. Theoretical models vary to a large extent in their predictions for the fraction of galaxies with low specific star-formation rates, but are unable to provide a global match to our data.

Extraterrestrial Radio Noise and Its Effect on Radar Performance

DTIC Science & Technology

1983-08-01

by the function, Sa f-0.81. TABLE 1 EQUATORIAL COORDINATES OF MAJOR DISCRETE RADIO STARS Right Constellation Declination Ascension Andromeda 400 50...ASSIOPEIA( 4 - - -VIRGO(e• TAURU -, ,-,CYGNUS-Aia 0 ~PERSEUS(O)’i ANDROMEDA (a) 101 - z li izi ii- !liisl I I i 10-26 10-25 10-24 10-2 3 10-2 2

Magnetic Field Measurements of T Tauri Stars in the Orion Nebula Cluster

NASA Astrophysics Data System (ADS)

Yang, Hao; Johns-Krull, Christopher M.

2011-03-01

We present an analysis of high-resolution (R ~ 50, 000) infrared K-band echelle spectra of 14 T Tauri stars (TTSs) in the Orion Nebula Cluster. We model Zeeman broadening in three magnetically sensitive Ti I lines near 2.2 μm and consistently detect kilogauss-level magnetic fields in the stellar photospheres. The data are consistent in each case with the entire stellar surface being covered with magnetic fields, suggesting that magnetic pressure likely dominates over gas pressure in the photospheres of these stars. These very strong magnetic fields might themselves be responsible for the underproduction of X-ray emission of TTSs relative to what is expected based on main-sequence star calibrations. We combine these results with previous measurements of 14 stars in Taurus and 5 stars in the TW Hydrae association to study the potential variation of magnetic field properties during the first 10 million years of stellar evolution, finding a steady decline in total magnetic flux with age. Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (USA), the Science and Technology Facilities Council (UK), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciência e Tecnologia (Brazil), and SECYT (Argentina).

Cycle 22 COS/NUV Spectroscopic Sensitivity Monitor

NASA Astrophysics Data System (ADS)

Taylor, Jo

2016-09-01

Observations of HST spectrophotometric standard stars show that there is a significant time dependence of the COS NUV MAMA sensitivity (Debes et al. 2016). Time-dependent sensitivity (TDS) monitoring is necessary for accurate flux calibration. Regular calibration observations monitor the decline in sensitivity for all NUV gratings: G185M, G225M, G285M, and G230L. Results from the cycle 22 NUV TDS program show the reflectivity of the G225M and G285M gratings, which are coated in bare-aluminum, declines at a rate of -3 to -2.5%/year and -10.6 to -11.8%/year, respectively. The G185M and G230L gratings, which are coated in MgF2 over aluminum, show a decline of -0.3 to +0.6%/year and -0.4 to +0.9%/year, respectively.

A wavelet approach to binary blackholes with asynchronous multitasking

NASA Astrophysics Data System (ADS)

Lim, Hyun; Hirschmann, Eric; Neilsen, David; Anderson, Matthew; Debuhr, Jackson; Zhang, Bo

2016-03-01

Highly accurate simulations of binary black holes and neutron stars are needed to address a variety of interesting problems in relativistic astrophysics. We present a new method for the solving the Einstein equations (BSSN formulation) using iterated interpolating wavelets. Wavelet coefficients provide a direct measure of the local approximation error for the solution and place collocation points that naturally adapt to features of the solution. Further, they exhibit exponential convergence on unevenly spaced collection points. The parallel implementation of the wavelet simulation framework presented here deviates from conventional practice in combining multi-threading with a form of message-driven computation sometimes referred to as asynchronous multitasking.

Predicting functional decline and survival in amyotrophic lateral sclerosis.

PubMed

Ong, Mei-Lyn; Tan, Pei Fang; Holbrook, Joanna D

2017-01-01

Better predictors of amyotrophic lateral sclerosis disease course could enable smaller and more targeted clinical trials. Partially to address this aim, the Prize for Life foundation collected de-identified records from amyotrophic lateral sclerosis sufferers who participated in clinical trials of investigational drugs and made them available to researchers in the PRO-ACT database. In this study, time series data from PRO-ACT subjects were fitted to exponential models. Binary classes for decline in the total score of amyotrophic lateral sclerosis functional rating scale revised (ALSFRS-R) (fast/slow progression) and survival (high/low death risk) were derived. Data was segregated into training and test sets via cross validation. Learning algorithms were applied to the demographic, clinical and laboratory parameters in the training set to predict ALSFRS-R decline and the derived fast/slow progression and high/low death risk categories. The performance of predictive models was assessed by cross-validation in the test set using Receiver Operator Curves and root mean squared errors. A model created using a boosting algorithm containing the decline in four parameters (weight, alkaline phosphatase, albumin and creatine kinase) post baseline, was able to predict functional decline class (fast or slow) with fair accuracy (AUC = 0.82). However similar approaches to build a predictive model for decline class by baseline subject characteristics were not successful. In contrast, baseline values of total bilirubin, gamma glutamyltransferase, urine specific gravity and ALSFRS-R item score-climbing stairs were sufficient to predict survival class. Using combinations of small numbers of variables it was possible to predict classes of functional decline and survival across the 1-2 year timeframe available in PRO-ACT. These findings may have utility for design of future ALS clinical trials.

The bulge-disc decomposed evolution of massive galaxies at 1 < z < 3 in CANDELS

NASA Astrophysics Data System (ADS)

Bruce, V. A.; Dunlop, J. S.; McLure, R. J.; Cirasuolo, M.; Buitrago, F.; Bowler, R. A. A.; Targett, T. A.; Bell, E. F.; McIntosh, D. H.; Dekel, A.; Faber, S. M.; Ferguson, H. C.; Grogin, N. A.; Hartley, W.; Kocevski, D. D.; Koekemoer, A. M.; Koo, D. C.; McGrath, E. J.

2014-10-01

We present the results of a new and improved study of the morphological and spectral evolution of massive galaxies over the redshift range 1 < z < 3. Our analysis is based on a bulge-disc decomposition of 396 galaxies with M* > 1011 M⊙ uncovered from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) Wide Field Camera 3 (WFC3)/IR imaging within the Cosmological Evolution Survey (COSMOS) and UKIRT Infrared Deep Sky Survey (UKIDSS) UDS survey fields. We find that, by modelling the H160 image of each galaxy with a combination of a de Vaucouleurs bulge (Sérsic index n = 4) and an exponential disc (n = 1), we can then lock all derived morphological parameters for the bulge and disc components, and successfully reproduce the shorter-wavelength J125, i814, v606 HST images simply by floating the magnitudes of the two components. This then yields sub-divided four-band HST photometry for the bulge and disc components which, with no additional priors, is well described by spectrophotometric models of galaxy evolution. Armed with this information, we are able to properly determine the masses and star formation rates for the bulge and disc components, and find that: (i) from z = 3 to 1 the galaxies move from disc dominated to increasingly bulge dominated, but very few galaxies are pure bulges/ellipticals by z = 1; (ii) while most passive galaxies are bulge dominated, and most star-forming galaxies disc dominated, 18 ± 5 per cent of passive galaxies are disc dominated, and 11 ± 3 per cent of star-forming galaxies are bulge dominated, a result which needs to be explained by any model purporting to connect star formation quenching with morphological transformations; (iii) there exists a small but significant population of pure passive discs, which are generally flatter than their star-forming counterparts (whose axial ratio distribution peaks at b/a ≃ 0.7); (iv) flatter/larger discs re-emerge at the highest star formation rates, consistent with recent studies of sub-mm galaxies, and with the concept of a maximum surface density for star formation activity.

Was the Milky Way Bulge Formed from the Buckling Disk Instability, Hierarchical Collapse, Accretion of Clumps, or All of the Above?

NASA Astrophysics Data System (ADS)

Nataf, David M.

2017-09-01

The assembly of the Milky Way bulge is an old topic in astronomy, one now in a period of renewed and rapid development. That is due to tremendous advances in observations of bulge stars, motivating observations of both local and high-redshift galaxies, and increasingly sophisticated simulations. The dominant scenario for bulge formation is that of the Milky Way as a nearly pure disk galaxy, with the inner disk having formed a bar and buckled. This can potentially explain virtually all bulge stars with [Fe/H] ≳ -1.0, which comprise 95% of the stellar population. The evidence is the incredible success in N-body models of this type in making non-trivial, non-generic predictions, such as the rotation curve and velocity dispersion measured from radial velocities, and the spatial morphologies of the peanut/X-shape and the long bar. The classical bulge scenario, whereby the bulge formed from early dissipative collapse and mergers, remains viable for stars with [Fe/H] ≲ -1.0 and potentially a minority of the other stars. A classical bulge is expected from Λ-CDM cosmological simulations, can accentuate the properties of an existing bar in a hybrid system, and is most consistent with the bulge abundance trends such as [Mg/Fe], which are elevated relative to both the thin and thick disks. Finally, the clumpy-galaxy scenario is considered, as it is the correct description of most Milky Way precursors given observations of high-redshift galaxies. Simulations predict that these star-forming clumps will sometimes migrate to the centres of galaxies where they may form a bulge, and galaxies often include a bulge clump as well. They will possibly form a bar with properties consistent with those of the Milky Way, such as the exponential profile and metallicity gradient. Given the relative successes of these scenarios, the Milky Way bulge is plausibly of composite origin, with a classical bulge and/or inner halo numerically dominant for stars with [Fe/H] ≲ -1.0, a buckling thick disk for stars with - 1.0 ≲ [Fe/H

The Mass Distribution of Stellar-mass Black Holes

NASA Astrophysics Data System (ADS)

Farr, Will M.; Sravan, Niharika; Cantrell, Andrew; Kreidberg, Laura; Bailyn, Charles D.; Mandel, Ilya; Kalogera, Vicky

2011-11-01

We perform a Bayesian analysis of the mass distribution of stellar-mass black holes using the observed masses of 15 low-mass X-ray binary systems undergoing Roche lobe overflow and 5 high-mass, wind-fed X-ray binary systems. Using Markov Chain Monte Carlo calculations, we model the mass distribution both parametrically—as a power law, exponential, Gaussian, combination of two Gaussians, or log-normal distribution—and non-parametrically—as histograms with varying numbers of bins. We provide confidence bounds on the shape of the mass distribution in the context of each model and compare the models with each other by calculating their relative Bayesian evidence as supported by the measurements, taking into account the number of degrees of freedom of each model. The mass distribution of the low-mass systems is best fit by a power law, while the distribution of the combined sample is best fit by the exponential model. This difference indicates that the low-mass subsample is not consistent with being drawn from the distribution of the combined population. We examine the existence of a "gap" between the most massive neutron stars and the least massive black holes by considering the value, M 1%, of the 1% quantile from each black hole mass distribution as the lower bound of black hole masses. Our analysis generates posterior distributions for M 1%; the best model (the power law) fitted to the low-mass systems has a distribution of lower bounds with M 1%>4.3 M sun with 90% confidence, while the best model (the exponential) fitted to all 20 systems has M 1%>4.5 M sun with 90% confidence. We conclude that our sample of black hole masses provides strong evidence of a gap between the maximum neutron star mass and the lower bound on black hole masses. Our results on the low-mass sample are in qualitative agreement with those of Ozel et al., although our broad model selection analysis more reliably reveals the best-fit quantitative description of the underlying mass distribution. The results on the combined sample of low- and high-mass systems are in qualitative agreement with Fryer & Kalogera, although the presence of a mass gap remains theoretically unexplained.

Thermodynamic prediction of protein neutrality.

PubMed

Bloom, Jesse D; Silberg, Jonathan J; Wilke, Claus O; Drummond, D Allan; Adami, Christoph; Arnold, Frances H

2005-01-18

We present a simple theory that uses thermodynamic parameters to predict the probability that a protein retains the wild-type structure after one or more random amino acid substitutions. Our theory predicts that for large numbers of substitutions the probability that a protein retains its structure will decline exponentially with the number of substitutions, with the severity of this decline determined by properties of the structure. Our theory also predicts that a protein can gain extra robustness to the first few substitutions by increasing its thermodynamic stability. We validate our theory with simulations on lattice protein models and by showing that it quantitatively predicts previously published experimental measurements on subtilisin and our own measurements on variants of TEM1 beta-lactamase. Our work unifies observations about the clustering of functional proteins in sequence space, and provides a basis for interpreting the response of proteins to substitutions in protein engineering applications.

Thermodynamic prediction of protein neutrality

PubMed Central

Bloom, Jesse D.; Silberg, Jonathan J.; Wilke, Claus O.; Drummond, D. Allan; Adami, Christoph; Arnold, Frances H.

2005-01-01

We present a simple theory that uses thermodynamic parameters to predict the probability that a protein retains the wild-type structure after one or more random amino acid substitutions. Our theory predicts that for large numbers of substitutions the probability that a protein retains its structure will decline exponentially with the number of substitutions, with the severity of this decline determined by properties of the structure. Our theory also predicts that a protein can gain extra robustness to the first few substitutions by increasing its thermodynamic stability. We validate our theory with simulations on lattice protein models and by showing that it quantitatively predicts previously published experimental measurements on subtilisin and our own measurements on variants of TEM1 β-lactamase. Our work unifies observations about the clustering of functional proteins in sequence space, and provides a basis for interpreting the response of proteins to substitutions in protein engineering applications. PMID:15644440

Output of skeletal muscle contractions. a study of isokinetic plantar flexion in athletes.

PubMed

Fugl-Meyer, A R; Mild, K H; Hörnsten, J

1982-06-01

Maximum torques, total work and mean power of isokinetic plantar flexions were measured with simultaneous registrations. The integrated electromyograms (iEMG) were obtained by surface electrodes from all three heads of the m. triceps surae. The method applied offers possibilities for adequate description of dynamic muscular work which in the case of plantar flexion in trained man declines as a negative exponential function of angular motion velocity. The decline is parallel to that of maximum torques. The summed triceps surae iEMG was inversely proportional to the velocity and direct proportional to time suggesting that structural rather than neural factors determine the relationships between velocity of angular motion and maximum torque/total work of single Mmaneuvers. Moreover, the fact that maximum mean power as well as maximum electrical efficiency were reached at the functional velocity of toe-off during gait suggests an influence of pragmatic demands on plantar flexion mechanical output.

White Band Disease (type I) of endangered caribbean acroporid corals is caused by pathogenic bacteria.

PubMed

Kline, David I; Vollmer, Steven V

2011-01-01

Diseases affecting coral reefs have increased exponentially over the last three decades and contributed to their decline, particularly in the Caribbean. In most cases, the responsible pathogens have not been isolated, often due to the difficulty in isolating and culturing marine bacteria. White Band Disease (WBD) has caused unprecedented declines in the Caribbean acroporid corals, resulting in their listings as threatened on the US Threatened and Endangered Species List and critically endangered on the IUCN Red List. Yet, despite the importance of WBD, the probable pathogen(s) have not yet been determined. Here we present in situ transmission data from a series of filtrate and antibiotic treatments of disease tissue that indicate that WBD is contagious and caused by bacterial pathogen(s). Additionally our data suggest that Ampicillin could be considered as a treatment for WBD (type I).

A Multiplicity Census of Young Stars in Chamaeleon I

NASA Astrophysics Data System (ADS)

Lafrenière, David; Jayawardhana, Ray; Brandeker, Alexis; Ahmic, Mirza; van Kerkwijk, Marten H.

2008-08-01

We present the results of a multiplicity survey of 126 stars spanning ~0.1-3 M⊙ in the ~2 Myr old Chamaeleon I star-forming region, based on adaptive optics imaging with the ESO Very Large Telescope. Our observations have revealed 30 binaries and six triples, of which 19 and four, respectively, are new discoveries. The overall multiplicity fraction we find for Cha I (~30%) is similar to those reported for other dispersed young associations, but significantly higher than seen in denser clusters and the field, for comparable samples. Both the frequency and the maximum separation of Cha I binaries decline with decreasing mass, while the mass ratios approach unity; conversely, tighter pairs are more likely to be equal mass. We confirm that brown dwarf companions to stars are rare, even at young ages at wide separations. Based on follow-up spectroscopy of two low-mass substellar companion candidates, we conclude that both are likely background stars. The overall multiplicity fraction in Cha I is in rough agreement with numerical simulations of cloud collapse and fragmentation, but its observed mass dependence is less steep than predicted. The paucity of higher order multiples, in particular, provides a stringent constraint on the simulations, and seems to indicate a low level of turbulence in the prestellar cores in Cha I.

On the dispersion in brightness of far-ultraviolet emission lines of cool giant stars

NASA Technical Reports Server (NTRS)

Simon, T.

1984-01-01

Low-resolution spectra have been obtained with the short-wavelength camera of IUE for late-type giant stars of spectral type F5 III-G8 III. These stars are believed to be in their first crossing of the H-R diagram, as inferred from their location along the blue edge of the Hertzsprung gap or their high abundance of lithium. From the earliest spectral type observed along the blue edge of the gap, the normalized C IV flux, which is indicative of 100,000 K plasma, increases to a maximum at G0 and then falls with advancing spectral type. The total range in emission measure of 100,000 K gas is an order of magnitude or more among stars making their first appearance as yellow giants and averages about 25 times higher in these stars than in other G8-K0 yellow giants, the majority of which are probably He-burning post-red giants. The observations tentatively show that transition region emission, and by inference coronal emission, increases in intensity with the growth of convection zones in late-type giants and then declines at lower surface temperatures, perhaps because of rotational spin-down and a weakening of dynamo action.

Coevolution of Supermassive Black Holes and Galaxies across cosmic times

NASA Astrophysics Data System (ADS)

Aversa, Rossella

2015-10-01

Understanding how supermassive black holes (SMBHs) and galaxies coevolve within their host dark matter (DM) halos is a fundamental issue in astrophysics. This thesis is aimed to shed light on this topic. As a first step, we employ the recent wide samples of far-infrared (FIR) selected galaxies followed-up in X-rays, and of X-ray/optically selected active galactic nuclei (AGNs) followed-up in the FIR band, along with the classic data on AGN and stellar luminosity functions at redshift z & 1.5, to probe different stages in the coevolution of SMBHs and their host galaxies. The results of this analysis indicate the following scenario: (i) the star formation in the host galaxy proceeds within a heavily dust-enshrouded medium, at an almost constant rate, over a timescale . 0.5 - 1 Gyr, and then abruptly declines due to quasar feedback; (ii) part of the interstellar medium loses angular momentum, reaches the circum-nuclear regions, at a rate proportional to the star formation, and is temporarily stored into a massive reservoir/proto-torus, wherefrom it can be promptly accreted; (iii) the black hole (BH) grows by accretion in a self-regulated regime with radiative power that can slightly exceed the Eddington limit (L/LEdd . 4), particularly at the highest redshifts; (iv) the ensuing energy feedback from massive BHs, at its maximum, exceeds the stellar one and removes the interstellar gas, thus stopping the star formation and the fueling of the reservoir; (v) afterwards, if the gas stored in the reservoir is enough, a phase of supply-limited accretion follows, whose rate exponentially declines with a timescale of ∼3 e-folding times. We also discuss how the detailed properties and the specific evolution of the reservoir can be investigated via coordinated, high-resolution observations of starforming, strongly lensed galaxies in the (sub-)mm band with ALMA, and in the X-ray band with Chandra and the next generation of X-ray instruments. According to the scenario described above, we further investigate the coevolution of galaxies and hosted SMBHs throughout the history of the Universe by applying a statistical, model-independent approach, based on the continuity equation and the abundance matching technique. We present analytical solutions of the continuity equation without source term, to reconstruct the SMBH mass function (BHMF) at different redshifts iii from the AGN luminosity function. Such an approach includes the physically-motivated AGN lightcurves we have tested and discussed, which describe the evolution of both the Eddington ratio and the radiative efficiency from slim- to thin-disc conditions. We nicely reproduce the local estimates of the BHMF, the AGN duty cycle as a function of mass and redshift, along with the Eddington ratio function and the fraction of galaxies hosting an AGN with given Eddington ratio. We employ the same approach to reconstruct the observed stellar mass function (SMF) at different redshifts, starting from the ultraviolet (UV) and FIR luminosity functions associated to star formation in galaxies. Our results imply that the buildup of stars and BHs in galaxies occurs via in-situ processes, with dry mergers playing a marginal role, at least for stellar masses . 3×10^11 M⊙ and BH masses . 10^9 M⊙, where the statistical data are more secure and less biased by systematic errors. In addition, we develop an improved abundance matching technique, to link the stellar and BH content of galaxies to the gravitationally dominant DM component. The resulting relationships constitute a testbed for galaxy evolution models, highlighting the complementary role of stellar and AGN feedback in the star formation process. They may also be operationally implemented in numerical simulations to populate DM halos, or to gauge subgrid physics. Moreover, they can be exploited to investigate the galaxy/AGN clustering as a function of redshift, stellar/BH mass, and/or luminosity. The clustering properties of BHs and galaxies are found to be in full agreement with current observations, so further validating our results from the continuity equation. Finally, our analysis highlights that: (i) the fraction of AGNs observed in the slim-disc regime, where anyway most of the BH mass is accreted, increases with redshift; (ii) already at z & 6, a substantial amount of dust must have formed, over timescales . 10^8 yr, in strongly starforming galaxies, making these sources well within the reach of ALMA surveys in (sub-)millimeter bands.

A monitoring tool for performance improvement in plastic surgery at the individual level.

PubMed

Maruthappu, Mahiben; Duclos, Antoine; Orgill, Dennis; Carty, Matthew J

2013-05-01

The assessment of performance in surgery is expanding significantly. Application of relevant frameworks to plastic surgery, however, has been limited. In this article, the authors present two robust graphic tools commonly used in other industries that may serve to monitor individual surgeon operative time while factoring in patient- and surgeon-specific elements. The authors reviewed performance data from all bilateral reduction mammaplasties performed at their institution by eight surgeons between 1995 and 2010. Operative time was used as a proxy for performance. Cumulative sum charts and exponentially weighted moving average charts were generated using a train-test analytic approach, and used to monitor surgical performance. Charts mapped crude, patient case-mix-adjusted, and case-mix and surgical-experience-adjusted performance. Operative time was found to decline from 182 minutes to 118 minutes with surgical experience (p < 0.001). Cumulative sum and exponentially weighted moving average charts were generated using 1995 to 2007 data (1053 procedures) and tested on 2008 to 2010 data (246 procedures). The sensitivity and accuracy of these charts were significantly improved by adjustment for case mix and surgeon experience. The consideration of patient- and surgeon-specific factors is essential for correct interpretation of performance in plastic surgery at the individual surgeon level. Cumulative sum and exponentially weighted moving average charts represent accurate methods of monitoring operative time to control and potentially improve surgeon performance over the course of a career.

Steroidogenic acute regulatory protein (StAR) gene expression construct: Development, nanodelivery and effect on reproduction in air-breathing catfish, Clarias batrachus.

PubMed

Rathor, Pravesh Kumar; Bhat, Irfan Ahmad; Rather, Mohd Ashraf; Gireesh-Babu, Pathakota; Kumar, Kundan; Purayil, Suresh Babu Padinhate; Sharma, Rupam

2017-11-01

Steroidogenic acute regulatory protein (StAR) is responsible for the relocation of cholesterol across mitochondrial membrane in vertebrates and is, therefore, a key factor in regulating the rate and timing of steroidogenesis. In the present study, we developed chitosan nanoparticle (CNP) conjugated StAR gene construct (CNP-pcDNA4-StAR) in a eukaryotic expression vector, pcDNA4/HisMax A. CNPs of 135.4nm diameter, 26.7mV zeta potential and 0.381 polydispersity index were used for conjugation. The loading efficiency (LE) of pcDNA4-StAR construct with CNPs was found to be 86%. After the 24h of intramuscular injection, the CNP-pcDNA4-StAR plasmid could be detected from testis, brain, kidney and muscle tissues of Clarias batrachus. The transcript levels of important reproductive genes viz. cyp11a1, cyp17a1, 3β-hsd, 17β-hsd and cyp19a1 in CNP-pcDNA4-StAR treated group were initially low up to 24h, but significantly increased subsequently up to 120h. In naked pcDNA4-StAR treated group, the mRNA level of 3β-hsd, 17β-hsd and cyp19a1 increased initially up to 24h, while cyp11a1 and cyp17a1 increased up to 48h and then started declining. Similar results were obtained for 11-Ketotestosterone and 17β-estradiol. The results indicate relatively long lasting effects of nano-conjugated construct compared to the construct alone. Furthermore, the histopathology of gonads and liver authenticates its possible role in the gonadal development in fish without any adverse effect. Copyright © 2017 Elsevier B.V. All rights reserved.

VizieR Online Data Catalog: Spectral Classes in the Galaxy Anticenter (Chargeishsvili, 1988)

NASA Astrophysics Data System (ADS)

Chargeishvili, K.

2014-11-01

The catalogue is compiled on the basis of the spectral data obtained with the 70-cm meniscus telescope of Abastumani Astrophysical Observatory using the 8° objective prism (dispersion 166Å/mm near Hγ; in the short-wave region, the spectrum extends up to 3500Å).The field of the meniscus telescope is 4.5x4.5°.The area of 140 square degrees, under study, was overlapped by nine centers. Kodak IIa-O, Kodak IIIa-J and Kodak IIIa-F plates were used. A limiting apparent magnitude in V for the stars is between 12.5 photographic mag. and 15.0 photographic mag. for M stars. The errors of our determinations are: ±0.6 for spectral subtype and ±0.5 for luminosity class. The catalogue contains 558 objects with peculiarities in the spectrum Ap, Am, BaII and composite spectrum stars, 86 emission stars O, B, M and objects with Hα-emission as well as 453 M and 36 C-stars.Among 558 peculiar stars an overwhelming majority, namely 549, are first found. The stars in the Catalogue are arranged in the order of increasing right ascension. The stars are numbered according to zones of 1° in declination. The printed catalogue is provided with suitable stellar charts reproduced from the Lick Catalogue. The reference system on the charts refers to 1950 epoch and it is plotted according to the Smithsonian Astrophysical Observatory (SAO) catalogue. Clusters NGC 2168, NGC 1969 and OLC 0436 Whose sites in the charts are denoted with the circles, are supplies with the charts reproduced from relatively large-scale plates taken on the meniscus telescope. (1 data file).

WIYN Open Cluster Study. LXXVI. Li Evolution Among Stars of Low/Intermediate Mass: The Metal-deficient Open Cluster NGC 2506

NASA Astrophysics Data System (ADS)

Anthony-Twarog, Barbara J.; Lee-Brown, Donald B.; Deliyannis, Constantine P.; Twarog, Bruce A.

2018-03-01

HYDRA spectra of 287 stars in the field of NGC 2506 from the turnoff through the giant branch are analyzed. With previous data, 22 are identified as probable binaries; 90 more are classified as potential non-members. Spectroscopic analyses of ∼60 red giants and slowly rotating turnoff stars using line equivalent widths and a neural network approach lead to [Fe/H] = ‑0.27 ± 0.07 (s.d.) and [Fe/H] = ‑0.27 ± 0.06 (s.d.), respectively. Li abundances are derived for 145 probable single-star members, 44 being upper limits. Among turnoff stars outside the Li-dip, A(Li) = 3.04 ± 0.16 (s.d.), with no trend with color, luminosity, or rotation speed. Evolving from the turnoff across the subgiant branch, there is a well-delineated decline to A(Li) ∼1.25 at the giant branch base, coupled with the rotational spindown from between ∼20 and 70 km s‑1 to less than 20 km s‑1 for stars entering the subgiant branch and beyond. A(Li) remains effectively constant from the giant branch base to the red giant clump level. A new member above the clump redefines the path of the first-ascent red giant branch; its Li is 0.6 dex below the first-ascent red giants. With one exception, all post-He-flash stars have upper limits to A(Li), at or below the level of the brightest first-ascent red giant. The patterns are in excellent qualitative agreement with the model predictions for low/intermediate-mass stars which undergo rotation-induced mixing at the turnoff and subgiant branch, first dredge-up, and thermohaline mixing beyond the red giant bump.

Photographs of Stars, Star-Clusters and Nebulae 2 Volume Paperback Set

NASA Astrophysics Data System (ADS)

Roberts, Isaac

2010-10-01

Volume 1: Preface; Isaac Roberts' observatory, Crowborough Hill; Isaac Roberts' telescopes; List of the plates; List of the abbreviations; 1. The negatives; 2. Arrangement of the photographs; 3. Epoch of the Fiducial stars (A.D. 1900); 4. A table for converting measurements in right ascensions into intervals of time; 5. Illustrations of the method for determining the right ascensions and declinations of the stars; 6. Introduction; Utility of the photographic charts; 7. Refractors and reflectors as photo-instruments; 8. Requirements and adjustments of a reflector for celestial photography; 9. Collimation of the mirror; 10. Essentials of a photo-telescope; 11. Method for testing the stability of a photo-instrument; 12. Photographic plates: their exposures and development; 13. Description of the photographs and references concerning them; 14. Deductions from the photographs. Volume 2: Preface; List of the plates; Instruments; List of abbreviations adopted in this work; 1. The negatives; 2. Epoch of the Fiducial stars, A.D. 1900; 3. Table for converting the measured right ascensions; 4. Deterioration of the negatives; 5. Effects of atmospheric glare and of diffraction upon the films of photographic plates; 6. Arrangement of the plates; 7. Method for micro-puncturing the photographic discs of stars on plates; 8. Star catalogues and photographic charts; 9. Duration of the effective exposures given to photographic plates in the 20-inch reflector; 10. Are the millions of stars and the numerous nebulosities limited in number and extent; 11. The evolution of stellar systems; 12. Inferences suggested by examination of the photographs; 13. Description of the photographs; 14. M.31. Andromedae; 15. M.99 Virginis; 16. M.51 Canum Venaticorum; 17. Region of 7 Cassiopeiae; 18. Nebulae in the Pleiades; 19. M.42. Orionis; 20. General conclusions concerning the evolution of stellar systems.

The temperature of large dust grains in molecular clouds

NASA Technical Reports Server (NTRS)

Clark, F. O.; Laureijs, R. J.; Prusti, T.

1991-01-01

The temperature of the large dust grains is calculated from three molecular clouds ranging in visual extinction from 2.5 to 8 mag, by comparing maps of either extinction derived from star counts or gas column density derived from molecular observations to I(100). Both techniques show the dust temperature declining into clouds. The two techniques do not agree in absolute scale.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Horesh, Assaf; Kulkarni, Shrinivas R.; Corsi, Alessandra

Only a few cases of Type Ic supernovae (SNe) with high-velocity ejecta (≥0.2 c) have been discovered and studied. Here, we present our analysis of radio and X-ray observations of the Type Ic SN PTF 12gzk. The radio emission declined less than 10 days after explosion, suggesting SN ejecta expanding at high velocity (∼0.3 c). The radio data also indicate that the density of the circumstellar material (CSM) around the supernova is lower by a factor of ∼10 than the CSM around normal Type Ic SNe. PTF 12gzk may therefore be an intermediate event between a 'normal' SN Ic andmore » a gamma-ray-burst-SN-like event. Our observations of this rapidly declining radio SN at a distance of 58 Mpc demonstrates the potential to detect many additional radio SNe, given the new capabilities of the Very Large Array (improved sensitivity and dynamic scheduling), which are currently missed, leading to a biased view of radio SNe Ic. Early optical discovery followed by rapid radio observations would provide a full description of the ejecta velocity distribution and CSM densities around stripped massive star explosions as well as strong clues about the nature of their progenitor stars.« less

UCAC3: ASTROMETRIC REDUCTIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Finch, Charlie T.; Zacharias, Norbert; Wycoff, Gary L., E-mail: finch@usno.navy.mi

2010-06-15

Presented here are the details of the astrometric reductions from the x, y data to mean right ascension (R.A.), declination (decl.) coordinates of the third U.S. Naval Observatory CCD Astrograph Catalog (UCAC3). For these new reductions we used over 216,000 CCD exposures. The Two-Micron All-Sky Survey (2MASS) data are used extensively to probe for coordinate and coma-like systematic errors in UCAC data mainly caused by the poor charge transfer efficiency of the 4K CCD. Errors up to about 200 mas have been corrected using complex look-up tables handling multiple dependences derived from the residuals. Similarly, field distortions and sub-pixel phasemore » errors have also been evaluated using the residuals with respect to 2MASS. The overall magnitude equation is derived from UCAC calibration field observations alone, independent of external catalogs. Systematic errors of positions at the UCAC observing epoch as presented in UCAC3 are better corrected than in the previous catalogs for most stars. The Tycho-2 catalog is used to obtain final positions on the International Celestial Reference Frame. Residuals of the Tycho-2 reference stars show a small magnitude equation (depending on declination zone) that might be inherent in the Tycho-2 catalog.« less

Direct Measurement of Dust Attenuation in z approx. 1.5 Star-Forming Galaxies from 3D-HST: Implications for Dust Geometry and Star Formation Rates

NASA Technical Reports Server (NTRS)

Price, Sedona H.; Kriek, Mariska; Brammer, Gabriel B; Conroy, Charlie; Schreiber, Natascha M. Foerster; Franx, Marijn; Fumagalli, Mattia; Lundren, Britt; Momcheva, Ivelina; Nelson, Erica J.;

Stellar age spreads in clusters as imprints of cluster-parent clump densities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Parmentier, G.; Grebel, E. K.; Pfalzner, S.

2014-08-20

It has recently been suggested that high-density star clusters have stellar age distributions much narrower than that of the Orion Nebula Cluster, indicating a possible trend of narrower age distributions for denser clusters. We show this effect to likely arise from star formation being faster in gas with a higher density. We model the star formation history of molecular clumps in equilibrium by associating a star formation efficiency per free-fall time, ε{sub ff}, to their volume density profile. We focus on the case of isothermal spheres and we obtain the evolution with time of their star formation rate. Our modelmore » predicts a steady decline of the star formation rate, which we quantify with its half-life time, namely, the time needed for the star formation rate to drop to half its initial value. Given the uncertainties affecting the star formation efficiency per free-fall time, we consider two distinct values: ε{sub ff} = 0.1 and ε{sub ff} = 0.01. When ε{sub ff} = 0.1, the half-life time is of the order of the clump free-fall time, τ{sub ff}. As a result, the age distributions of stars formed in high-density clumps have smaller full-widths at half-maximum than those of stars formed in low-density clumps. When the star formation efficiency per free-fall time is 0.01, the half-life time is 10 times longer, i.e., 10 clump free-fall times. We explore what happens if the duration of star formation is shorter than 10τ{sub ff}, that is, if the half-life time of the star formation rate cannot be defined. There, we build on the invariance of the shape of the young cluster mass function to show that an anti-correlation between the clump density and the duration of star formation is expected. We therefore conclude that, regardless of whether the duration of star formation is longer than the star formation rate half-life time, denser molecular clumps yield narrower star age distributions in clusters. Published densities and stellar age spreads of young clusters and star-forming regions actually suggest that the timescale for star formation is of order 1-4τ{sub ff}. We also discuss how the age bin size and uncertainties in stellar ages affect our results. We conclude that there is no need to invoke the existence of multiple cluster formation mechanisms to explain the observed range of stellar age spreads in clusters.« less

A comprehensive HST BVI catalogue of star clusters in five Hickson compact groups of galaxies

NASA Astrophysics Data System (ADS)

Fedotov, K.; Gallagher, S. C.; Durrell, P. R.; Bastian, N.; Konstantopoulos, I. S.; Charlton, J.; Johnson, K. E.; Chandar, R.

2015-05-01

We present a photometric catalogue of star cluster candidates in Hickson compact groups (HCGs) 7, 31, 42, 59, and 92, based on observations with the Advanced Camera for Surveys and the Wide Field Camera 3 on the Hubble Space Telescope. The catalogue contains precise cluster positions (right ascension and declination), magnitudes, and colours in the BVI filters. The number of detected sources ranges from 2200 to 5600 per group, from which we construct the high-confidence sample by applying a number of criteria designed to reduce foreground and background contaminants. Furthermore, the high-confidence cluster candidates for each of the 16 galaxies in our sample are split into two subpopulations: one that may contain young star clusters and one that is dominated by globular older clusters. The ratio of young star cluster to globular cluster candidates varies from group to group, from equal numbers to the extreme of HCG 31 which has a ratio of 8 to 1, due to a recent starburst induced by interactions in the group. We find that the number of blue clusters with MV < -9 correlates well with the current star formation rate in an individual galaxy, while the number of globular cluster candidates with MV < -7.8 correlates well (though with large scatter) with the stellar mass. Analyses of the high-confidence sample presented in this paper show that star clusters can be successfully used to infer the gross star formation history of the host groups and therefore determine their placement in a proposed evolutionary sequence for compact galaxy groups.

The Catalina Surveys Southern periodic variable star catalogue

NASA Astrophysics Data System (ADS)

Drake, A. J.; Djorgovski, S. G.; Catelan, M.; Graham, M. J.; Mahabal, A. A.; Larson, S.; Christensen, E.; Torrealba, G.; Beshore, E.; McNaught, R. H.; Garradd, G.; Belokurov, V.; Koposov, S. E.

2017-08-01

Here, we present the results from our analysis of 6 yr of optical photometry taken by the Siding Spring Survey (SSS). This completes a search for periodic variable stars within the 30 000 deg2 of the sky covered by the Catalina Surveys. The current analysis covers 81 million sources with declinations between -20° and -75° with median magnitudes in the range 11 < V < 19.5. We find approximately 34 000 new periodic variable stars in addition to the ˜9000 RR Lyrae that we previously discovered in SSS data. This brings the total number of periodic variables identified in Catalina data to ˜110 000. The new SSS periodic variable stars mainly consist of eclipsing binaries, RR Lyrae, LPVs, RS CVn stars, δ Scutis, and Anomalous Cepheids. By cross-matching these variable stars with those from prior surveys, we find that ˜90 per cent of the sources are new discoveries and recover ˜95 per cent of the known periodic variables in the survey region. For the known sources, we find excellent agreement between our catalogue and prior values of luminosity, period, and amplitude. However, we find many variable stars that had previously been misclassified. Examining the distribution of RR Lyrae, we find a population associated with the Large Magellanic Cloud (LMC) that extends more than 20° from its centre confirming recent evidence for the existence of a very extended stellar halo in the LMC. By combining SSS photometry with Dark Energy Survey data, we identify additional LMC halo RR Lyrae, thus confirming the significance of the population.

Paper 5991: How Much Gas, Condensate, and Oil Will be Produced from Major Shale Plays in the U.S., and Why?

NASA Astrophysics Data System (ADS)

Marder, M. P.; Patzek, T. W.

2014-12-01

A one-dimensional universal model of gas inflow into the hydrofractured horizontal wells (Patzek, et al., PNAS, 110, 2013) was developed for the Barnett shale, and applied to explain historical production and predict future production in 8294 wells there. Subsequently, this model was extended and applied to 3756 wells in the Fayetteville shale, 2199 wells in the Haynesville shale, and 2764 wells in the Marcellus shale. Out of these, 2057, 703, 1515, and 1063 wells in the Barnett, Fayetteville, Haynesville, and Marcellus, respectively, show evidence of pressure interference between consecutive hydrofractures. For the interfering wells, we calculate their EURs and the distributions of effective gas permeability in the reservoir volumes influenced by these wells. For the non-interfering wells we calculate the lower and upper bounds on their EURs. We show that given the available data, a better field-wide prediction of EUR is impossible. The expected EURs vary between 0.4 and 4.3 Bscf in the Barnett, depending on the well quality. In the other shales the expected well EURs are 0.5 - 3.4 Bcf in the Fayetteville, 1.4 - 7.9 Bcf in the Haynesville, and 1 - 9 Bcf in the Marcellus. The respective mean effective gas permeabilities are 400, 1000, 230, and 800 nanodarcy for the same shales, much high than the core values. Work on the Eagle Ford shale is in progress and will be presented in December. In a shale- horizontal well system, we model rectilinear flow of natural gas as dimensionless nonlinear pseudo-pressure diffusion IVBP with gas sorption on the rock and the multiple planar hydrofractures acting as internal sorbing boundaries. After the initial choked flow, wells must decline as the inverse of the square root of time on production, until the gas pressure starts declining at the midplane of a reservoir cell between two consecutive hydrofractures. At this point of time production decline is exponential. The transition between the square-root-of-time and exponential decline is governed by the characteristic pressure diffusion time, τ, and gas mass in place, M. The dimensionless solution of this IVBP problem reduces the cumulative gas production in all wells to a single universal curve for each play. The ultimate recovery is about 15% of gas-in-place and less so for oil.

Longevity of acid discharges from underground mines located above the regional water table.

PubMed

Demchak, J; Skousen, J; McDonald, L M

2004-01-01

The duration of acid mine drainage flowing out of underground mines is important in the design of watershed restoration and abandoned mine land reclamation projects. Past studies have reported that acid water flows from underground mines for hundreds of years with little change, while others state that poor drainage quality may last only 20 to 40 years. More than 150 above-drainage (those not flooded after abandonment) underground mine discharges from Pittsburgh and Upper Freeport coal seams were located and sampled during 1968 in northern West Virginia, and we revisited 44 of those sites in 1999-2000 and measured water flow, pH, acidity, Fe, sulfate, and conductivity. We found no significant difference in flows between 1968 and 1999-2000. Therefore, we felt the water quality data could be compared and the data represented real changes in pollutant concentrations. There were significant water quality differences between year and coal seam, but no effect of disturbance. While pH was not significantly improved, average total acidity declined 79% between 1968 and 1999-2000 in Pittsburgh mines (from 66.8 to 14 mmol H+ L(-1)) and 56% in Upper Freeport mines (from 23.8 to 10.4 mmol H+ L(-1)). Iron decreased an average of about 80% across all sites (from an average of 400 to 72 mg L(-1)), while sulfate decreased between 50 and 75%. Pittsburgh seam discharge water was much worse in 1968 than Upper Freeport seam water. Twenty of our 44 sites had water quality information in 1980, which served as a midpoint to assess the slope of the decline in acidity and metal concentrations. Five of 20 sites (25%) showed an apparent exponential rate of decline in acidity and iron, while 10 of 20 sites (50%) showed a more linear decline. Drainage from five Upper Freeport sites increased in acidity and iron. While it is clear that surface mines and below-drainage underground mines improve in discharge quality relatively rapidly (20-40 years), above-drainage underground mines are not as easily predicted. In total, the drainage from 34 out of 44 (77%) above-drainage underground mines showed significant improvement in acidity over time, some exponentially and some linearly. Ten discharges showed no improvement and three of these got much worse.

Dose-response relationship between sleep duration and human psychomotor vigilance and subjective alertness

NASA Technical Reports Server (NTRS)

Jewett, M. E.; Dijk, D. J.; Kronauer, R. E.; Dinges, D. F.

1999-01-01

Although it has been well documented that sleep is required for human performance and alertness to recover from low levels after prolonged periods of wakefulness, it remains unclear whether they increase in a linear or asymptotic manner during sleep. It has been postulated that there is a relation between the rate of improvement in neurobehavioral functioning and rate of decline of slow-wave sleep and/or slow-wave activity (SWS/SWA) during sleep, but this has not been verified. Thus, a cross-study comparison was conducted in which dose-response curves (DRCs) were constructed for Stanford Sleepiness Scale (SSS) and Psychomotor Vigilance Task (PVT) tests taken at 1000 hours by subjects who had been allowed to sleep 0 hours, 2 hours, 5 hours or 8 hours the previous night. We found that the DRCs to each PVT metric improved in a saturating exponential manner, with recovery rates that were similar [time constant (T) approximately 2.14 hours] for all the metrics. This recovery rate was slightly faster than, though not statistically significantly different from, the reported rate of SWS/SWA decline (T approximately 2.7 hours). The DRC to the SSS improved much more slowly than psychomotor vigilance, so that it could be fit equally well by a linear function (slope = -0.26) or a saturating exponential function (T = 9.09 hours). We conclude that although SWS/SWA, subjective alertness, and a wide variety of psychomotor vigilance metrics may all change asymptotically during sleep, it remains to be determined whether the underlying physiologic processes governing their expression are different.

UCAC3 PROPER MOTION SURVEY. I. DISCOVERY OF NEW PROPER MOTION STARS IN UCAC3 WITH 0.''40 yr{sup -1} > {mu} {>=} 0.''18 yr{sup -1} BETWEEN DECLINATIONS -90{sup 0} AND -47{sup 0}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Finch, Charlie T.; Zacharias, Norbert; Henry, Todd J., E-mail: finch@usno.navy.mi

2010-09-15

This paper presents 442 new proper motion stellar systems in the southern sky between declinations -90{sup 0} and -47{sup 0} with 0.''40 yr{sup -1} > {mu} {>=} 0.''18 yr{sup -1}. These systems constitute a 25.3% increase in new systems for the same region of the sky covered by previous SuperCOSMOS RECONS (SCR) searches that used Schmidt plates as the primary source of discovery. Among the new systems are 25 multiples, plus an additional 7 new common proper motion (CPM) companions to previously known primaries. All stars have been discovered using the third U.S. Naval Observatory (USNO) CCD Astrograph Catalog (UCAC3).more » A comparison of the UCAC3 proper motions to those from the Hipparcos, Tycho-2, Southern Proper Motion (SPM4), and SuperCOSMOS efforts is presented and shows that UCAC3 provides similar values and precision to the first three surveys. The comparison between UCAC3 and SuperCOSMOS indicates that proper motions in R.A. are systematically shifted in the SuperCOSMOS data but are consistent in decl. data, while overall showing a significantly higher scatter. Distance estimates are derived for stars having SuperCOSMOS Sky Survey B{sub J} , R{sub 59F}, and I{sub IVN} plate magnitudes and Two-Micron All Sky Survey infrared photometry. We find 15 systems estimated to be within 25 pc, including UPM 1710-5300 our closest new discovery estimated at 13.5 pc. Such new discoveries suggest that more nearby stars are yet to be found in these slower proper motion regimes, indicating that more work is needed to develop a complete map of the solar neighborhood.« less

On the Nature and History of Blue Amorphous Galaxies

NASA Astrophysics Data System (ADS)

Marlowe, Amanda True

1998-07-01

Dwarf galaxies play an important role in our understanding of galaxy formation and evolution. We have embarked on a systematic study of 12 blue amorphous galaxies (BAGs) whose properties suggest that they are dwarf galaxies in a starburst or post-burst state. It seems likely that BAGs are related to other 'starburst' dwarfs such as blue compact dwarfs (BCDs) and HII galaxies. The BAGs in our sample, however, are considerably closer than BCDs and HII galaxies in other samples, and therefore easier to study. These galaxies may offer important insights into dwarf galaxy evolution. In an effort to clarify the role of BAGs in evolutionary scenarios for dwarf galaxies, we present and analyze Hα and UBVI data for our sample. BAGs, like BCDs and HII galaxies, have surface brightness profiles that are exponential in the outer regions but have a predominantly blue central blue excess, suggesting a young burst in an older, redder galaxy. Seven of the galaxies have the bubble or filamentary Hα morphology and double peaked emission lines that are the signature of superbubbles or superwind activity. These galaxies are typically the ones with the strongest central excesses. The starbursting regions are young events compared to the older underlying galaxy, which follow an exponential surface brightness law. Not all of the galaxies develop superwinds: the appearance of superwinds is most sensitive to the concentration and rate of star formation in the starbursting core. The underlying exponential galaxies are very similar to those found in BCDs and HII galaxies, though the 'burst' colors are slightly redder than those found in HII galaxies. BAGs are structurally similar to BCDs and HII galaxies. How BAGs fit into the dwarf galaxy evolutionary debate is less clear. While some compact dIs have properties similar to those of the underlying exponential galaxy in our sample, issues such as mass loss from superwinds, the impact of the starbursting core on the underlying galaxy, and fading complicate the search for BAG progenitor and evolved or faded BAG galaxy classes.

The Solar Neighborhood. XXV. Discovery of New Proper Motion Stars with 0.40 sec/yr > mu > or = 0.18 sec/yr Between Declinations -47 deg and 00 deg

NASA Technical Reports Server (NTRS)

Boyd, Mark R.; Winters, Jennifer G.; Henry, Todd J.; Jao, Wei-Chun; Finch, Charlie T.; Subasavage, John P.; Hambly, Nigel C.

2011-01-01

We present 2817 new southern proper motion systems with 0.40 sec/yr > mu > or = 0.18 sec/yr and declination between 47 deg and 00 deg. This is a continuation of the SuperCOSMOS-RECONS (SCR) proper motion searches of the southern sky. We use the same photometric relations as previous searches to provide distance estimates based on the assumption that the objects are single main-sequence stars. We find 79 new red dwarf systems predicted to be within 25 pc, including a few new components of previously known systems. Two systems--SCR 1731-2452 at 9.5 pc and SCR 1746-3214 at 9.9 pc--are anticipated to be within 10 pc. We also find 23 new white dwarf (WD) candidates with distance estimates of 15-66 pc, as well as 360 new red subdwarf candidates. With this search, we complete the SCR sweep of the southern sky for stars with mu > or = 0.18 sec/yr and R(sub 59F) < or = 16.5, resulting in a total of 5042 objects in 4724 previously unreported proper motion systems. Here we provide selected comprehensive lists from our SCR proper motion search to date, including 152 red dwarf systems estimated to be within 25 pc (9 within 10 pc), 46 WDs (10 within 25 pc), and 598 subdwarf candidates. The results of this search suggest that there are more nearby systems to be found at fainter magnitudes and lower proper motion limits than those probed so far.

Diffusion and Mixing in Globular Clusters

NASA Astrophysics Data System (ADS)

Meiron, Yohai; Kocsis, Bence

2018-03-01

Collisional relaxation describes the stochastic process with which a self-gravitating system near equilibrium evolves in phase-space due to the fluctuating gravitational field of the system. The characteristic timescale of this process is called the relaxation time. In this paper, we highlight the difference between two measures of the relaxation time in globular clusters: (1) the diffusion time with which the isolating integrals of motion (i.e., energy E and angular momentum magnitude L) of individual stars change stochastically and (2) the asymptotic timescale required for a family of orbits to mix in the cluster. More specifically, the former corresponds to the instantaneous rate of change of a star’s E or L, while the latter corresponds to the timescale for the stars to statistically forget their initial conditions. We show that the diffusion timescales of E and L vary systematically around the commonly used half-mass relaxation time in different regions of the cluster by a factor of ∼10 and ∼100, respectively, for more than 20% of the stars. We define the mixedness of an orbital family at any given time as the correlation coefficient between its E or L probability distribution functions and those of the whole cluster. Using Monte Carlo simulations, we find that mixedness converges asymptotically exponentially with a decay timescale that is ∼10 times the half-mass relaxation time.

THE HYDRODYNAMICAL MODELS OF THE COMETARY COMPACT H ii REGION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Feng-Yao; Zhu, Qing-Feng; Li, Juan

2015-10-10

We have developed a full numerical method to study the gas dynamics of cometary ultracompact H ii regions, and associated photodissociation regions (PDRs). The bow-shock and champagne-flow models with a 40.9/21.9 M{sub ⊙} star are simulated. In the bow-shock models, the massive star is assumed to move through dense (n = 8000 cm{sup −3}) molecular material with a stellar velocity of 15 km s{sup −1}. In the champagne-flow models, an exponential distribution of density with a scale height of 0.2 pc is assumed. The profiles of the [Ne ii] 12.81 μm and H{sub 2} S(2) lines from the ionized regionsmore » and PDRs are compared for two sets of models. In champagne-flow models, emission lines from the ionized gas clearly show the effect of acceleration along the direction toward the tail due to the density gradient. The kinematics of the molecular gas inside the dense shell are mainly due to the expansion of the H ii region. However, in bow-shock models the ionized gas mainly moves in the same direction as the stellar motion. The kinematics of the molecular gas inside the dense shell simply reflects the motion of the dense shell with respect to the star. These differences can be used to distinguish two sets of models.« less

Revival of the Magnetar PSR J1622–4950: Observations with MeerKAT, Parkes, XMM-Newton, Swift, Chandra, and NuSTAR

NASA Astrophysics Data System (ADS)

Camilo, F.; Scholz, P.; Serylak, M.; Buchner, S.; Merryfield, M.; Kaspi, V. M.; Archibald, R. F.; Bailes, M.; Jameson, A.; van Straten, W.; Sarkissian, J.; Reynolds, J. E.; Johnston, S.; Hobbs, G.; Abbott, T. D.; Adam, R. M.; Adams, G. B.; Alberts, T.; Andreas, R.; Asad, K. M. B.; Baker, D. E.; Baloyi, T.; Bauermeister, E. F.; Baxana, T.; Bennett, T. G. H.; Bernardi, G.; Booisen, D.; Booth, R. S.; Botha, D. H.; Boyana, L.; Brederode, L. R. S.; Burger, J. P.; Cheetham, T.; Conradie, J.; Conradie, J. P.; Davidson, D. B.; De Bruin, G.; de Swardt, B.; de Villiers, C.; de Villiers, D. I. L.; de Villiers, M. S.; de Villiers, W.; De Waal, C.; Dikgale, M. A.; du Toit, G.; du Toit, L. J.; Esterhuyse, S. W. P.; Fanaroff, B.; Fataar, S.; Foley, A. R.; Foster, G.; Fourie, D.; Gamatham, R.; Gatsi, T.; Geschke, R.; Goedhart, S.; Grobler, T. L.; Gumede, S. C.; Hlakola, M. J.; Hokwana, A.; Hoorn, D. H.; Horn, D.; Horrell, J.; Hugo, B.; Isaacson, A.; Jacobs, O.; Jansen van Rensburg, J. P.; Jonas, J. L.; Jordaan, B.; Joubert, A.; Joubert, F.; Józsa, G. I. G.; Julie, R.; Julius, C. C.; Kapp, F.; Karastergiou, A.; Karels, F.; Kariseb, M.; Karuppusamy, R.; Kasper, V.; Knox-Davies, E. C.; Koch, D.; Kotzé, P. P. A.; Krebs, A.; Kriek, N.; Kriel, H.; Kusel, T.; Lamoor, S.; Lehmensiek, R.; Liebenberg, D.; Liebenberg, I.; Lord, R. T.; Lunsky, B.; Mabombo, N.; Macdonald, T.; Macfarlane, P.; Madisa, K.; Mafhungo, L.; Magnus, L. G.; Magozore, C.; Mahgoub, O.; Main, J. P. L.; Makhathini, S.; Malan, J. A.; Malgas, P.; Manley, J. R.; Manzini, M.; Marais, L.; Marais, N.; Marais, S. J.; Maree, M.; Martens, A.; Matshawule, S. D.; Matthysen, N.; Mauch, T.; McNally, L. D.; Merry, B.; Millenaar, R. P.; Mjikelo, C.; Mkhabela, N.; Mnyandu, N.; Moeng, I. T.; Mokone, O. J.; Monama, T. E.; Montshiwa, K.; Moss, V.; Mphego, M.; New, W.; Ngcebetsha, B.; Ngoasheng, K.; Niehaus, H.; Ntuli, P.; Nzama, A.; Obies, F.; Obrocka, M.; Ockards, M. T.; Olyn, C.; Oozeer, N.; Otto, A. J.; Padayachee, Y.; Passmoor, S.; Patel, A. A.; Paula, S.; Peens-Hough, A.; Pholoholo, B.; Prozesky, P.; Rakoma, S.; Ramaila, A. J. T.; Rammala, I.; Ramudzuli, Z. R.; Rasivhaga, M.; Ratcliffe, S.; Reader, H. C.; Renil, R.; Richter, L.; Robyntjies, A.; Rosekrans, D.; Rust, A.; Salie, S.; Sambu, N.; Schollar, C. T. G.; Schwardt, L.; Seranyane, S.; Sethosa, G.; Sharpe, C.; Siebrits, R.; Sirothia, S. K.; Slabber, M. J.; Smirnov, O.; Smith, S.; Sofeya, L.; Songqumase, N.; Spann, R.; Stappers, B.; Steyn, D.; Steyn, T. J.; Strong, R.; Struthers, A.; Stuart, C.; Sunnylall, P.; Swart, P. S.; Taljaard, B.; Tasse, C.; Taylor, G.; Theron, I. P.; Thondikulam, V.; Thorat, K.; Tiplady, A.; Toruvanda, O.; van Aardt, J.; van Balla, T.; van den Heever, L.; van der Byl, A.; van der Merwe, C.; van der Merwe, P.; van Niekerk, P. C.; van Rooyen, R.; van Staden, J. P.; van Tonder, V.; van Wyk, R.; Wait, I.; Walker, A. L.; Wallace, B.; Welz, M.; Williams, L. P.; Xaia, B.; Young, N.; Zitha, S.

2018-04-01

New radio (MeerKAT and Parkes) and X-ray (XMM-Newton, Swift, Chandra, and NuSTAR) observations of PSR J1622–4950 indicate that the magnetar, in a quiescent state since at least early 2015, reactivated between 2017 March 19 and April 5. The radio flux density, while variable, is approximately 100× larger than during its dormant state. The X-ray flux one month after reactivation was at least 800× larger than during quiescence, and has been decaying exponentially on a 111 ± 19 day timescale. This high-flux state, together with a radio-derived rotational ephemeris, enabled for the first time the detection of X-ray pulsations for this magnetar. At 5%, the 0.3–6 keV pulsed fraction is comparable to the smallest observed for magnetars. The overall pulsar geometry inferred from polarized radio emission appears to be broadly consistent with that determined 6–8 years earlier. However, rotating vector model fits suggest that we are now seeing radio emission from a different location in the magnetosphere than previously. This indicates a novel way in which radio emission from magnetars can differ from that of ordinary pulsars. The torque on the neutron star is varying rapidly and unsteadily, as is common for magnetars following outburst, having changed by a factor of 7 within six months of reactivation.

Binary neutron star merger rate via the luminosity function of short gamma-ray bursts

NASA Astrophysics Data System (ADS)

Paul, Debdutta

2018-04-01

The luminosity function of short Gamma Ray Bursts (GRBs) is modelled by using the available catalogue data of all short GRBs (sGRBs) detected till October, 2017. The luminosities are estimated via the `pseudo-redshifts' obtained from the `Yonetoku correlation', assuming a standard delay distribution between the cosmic star formation rate and the production rate of their progenitors. While the simple powerlaw is ruled out to high confidence, the data is fit well both by exponential cutoff powerlaw and broken powerlaw models. Using the derived parameters of these models along with conservative values in the jet opening angles seen from afterglow observations, the true rate of short GRBs are derived. Assuming a short GRB is produced from each binary neutron star merger (BNSM), the rate of gravitational wave (GW) detections from these mergers are derived for the past, present and future configurations of the GW detector networks. Stringent lower limits of 1.87yr-1 for the aLIGO-VIRGO, and 3.11yr-1 for the upcoming aLIGO-VIRGO-KAGRA-LIGO/India configurations are thus derived for the BNSM rate at 68% confidence. The BNSM rates calculated from this work and that independently inferred from the observation of the only confirmed BNSM observed till date, are shown to have a mild tension; however the scenario that all BNSMs produce sGRBs cannot be ruled out.

High-functionality star-branched macromolecules: polymer size and virial coefficients.

PubMed

Randisi, Ferdinando; Pelissetto, Andrea

2013-10-21

We perform high-statistics Monte Carlo simulations of a lattice model to compute the radius of gyration Rg, the center-to-end distance, the monomer distribution, and the second and third virial coefficients of star polymers for a wide range of functionalities f, 6 ≤ f ≤ 120. We consider systems with a large number L of monomers per arm (100 is approximately < L is approximately < 1000 for f ≤ 40 and 100 is approximately < L is approximately < 400 for f = 80, 120), which allows us to determine accurately all quantities in the scaling regime. Results are extrapolated to determine the behavior of the different quantities in the limit f → ∞. Structural results are finally compared with the predictions of the Daoud-Cotton model. It turns out that the blob picture of a star polymer is essentially correct up to the corona radius Rc, which depends on f and which varies from 0.7Rg for f = 6 to 1.0Rg for f = 40. The outer region (r > Rc), in which the monomer distribution decays exponentially, shrinks as f increases, but it does not disappear in the scaling regime even in the limit f → ∞. We also consider the Daoud-Cotton scaling relation Rg (2)~f(1-ν)L(2ν), which is found to hold only for f > 100.

Binary neutron star merger rate via the luminosity function of short gamma-ray bursts

NASA Astrophysics Data System (ADS)

Paul, Debdutta

2018-07-01

The luminosity function of short gamma ray bursts (GRBs) is modelled by using the available catalogue data of all short GRBs (sGRBs) detected till 2017 October. The luminosities are estimated via the `pseudo-redshifts' obtained from the `Yonetoku correlation', assuming a standard delay distribution between the cosmic star formation rate and the production rate of their progenitors. While the simple power law is ruled out to high confidence, the data is fit well both by exponential cutoff power law and broken power law models. Using the derived parameters of these models along with conservative values in the jet opening angles seen from afterglow observations, the true rate of sGRBs is derived. Assuming a sGRB is produced from each binary neutron star merger (BNSM), the rate of gravitational wave (GW) detections from these mergers are derived for the past, present, and future configurations of the GW detector networks. Stringent lower limits of 1.87 { yr^{-1}} for the aLIGO-VIRGO, and 3.11 { yr^{-1}} for the upcoming aLIGO-VIRGO-KAGRA-LIGO/India configurations are thus derived for the BNSM rate at 68 per cent confidence. The BNSM rates calculated from this work and that independently inferred from the observation of the only confirmed BNSM observed till date are shown to have a mild tension; however, the scenario that all BNSMs produce sGRBs cannot be ruled out.

VizieR Online Data Catalog: Bayesian method for detecting stellar flares (Pitkin+, 2014)

NASA Astrophysics Data System (ADS)

Pitkin, M.; Williams, D.; Fletcher, L.; Grant, S. D. T.

2015-05-01

We present a Bayesian-odds-ratio-based algorithm for detecting stellar flares in light-curve data. We assume flares are described by a model in which there is a rapid rise with a half-Gaussian profile, followed by an exponential decay. Our signal model also contains a polynomial background model required to fit underlying light-curve variations in the data, which could otherwise partially mimic a flare. We characterize the false alarm probability and efficiency of this method under the assumption that any unmodelled noise in the data is Gaussian, and compare it with a simpler thresholding method based on that used in Walkowicz et al. We find our method has a significant increase in detection efficiency for low signal-to-noise ratio (S/N) flares. For a conservative false alarm probability our method can detect 95 per cent of flares with S/N less than 20, as compared to S/N of 25 for the simpler method. We also test how well the assumption of Gaussian noise holds by applying the method to a selection of 'quiet' Kepler stars. As an example we have applied our method to a selection of stars in Kepler Quarter 1 data. The method finds 687 flaring stars with a total of 1873 flares after vetos have been applied. For these flares we have made preliminary characterizations of their durations and and S/N. (1 data file).

A Bayesian method for detecting stellar flares

NASA Astrophysics Data System (ADS)

Pitkin, M.; Williams, D.; Fletcher, L.; Grant, S. D. T.

2014-12-01

We present a Bayesian-odds-ratio-based algorithm for detecting stellar flares in light-curve data. We assume flares are described by a model in which there is a rapid rise with a half-Gaussian profile, followed by an exponential decay. Our signal model also contains a polynomial background model required to fit underlying light-curve variations in the data, which could otherwise partially mimic a flare. We characterize the false alarm probability and efficiency of this method under the assumption that any unmodelled noise in the data is Gaussian, and compare it with a simpler thresholding method based on that used in Walkowicz et al. We find our method has a significant increase in detection efficiency for low signal-to-noise ratio (S/N) flares. For a conservative false alarm probability our method can detect 95 per cent of flares with S/N less than 20, as compared to S/N of 25 for the simpler method. We also test how well the assumption of Gaussian noise holds by applying the method to a selection of `quiet' Kepler stars. As an example we have applied our method to a selection of stars in Kepler Quarter 1 data. The method finds 687 flaring stars with a total of 1873 flares after vetos have been applied. For these flares we have made preliminary characterizations of their durations and and S/N.

Magnetic field amplification by the r-mode instability

NASA Astrophysics Data System (ADS)

Chugunov, A. I.; Friedman, J. L.; Lindblom, L.; Rezzolla, L.

2017-12-01

We discuss the magnetic field enhancement by unstable r-modes (driven by the gravitational radiation reaction force) in rotating stars. In the absence of a magnetic field, gravitational radiation exponentially increases the r-mode amplitude α, and accelerates differential rotation (secular motion of fluid elements). For a magnetized star, differential rotation enhances the magnetic field energy. Rezzolla et al (2000-2001) argued that if the magnetic energy grows faster than the gravitational radiation reaction force pumps energy into the r-modes, then the r-mode instability is suppressed. Chugunov (2015) demonstrated that without gravitational radiation, differential rotation can be treated as a degree of freedom decoupled from the r-modes and controlled by the back reaction of the magnetic field. In particular, the magnetic field windup does not damp r-modes. Here we discuss the effect of the back reaction of the magnetic field on differential rotation of unstable r-modes, and show that it limits the generated magnetic field and the magnetic energy growth rate preventing suppression of the r-mode instability by magnetic windup at low saturation amplitudes, α ≪ 1, predicted by current models.

The mass-loss return from evolved stars to the Large Magellanic Cloud. V. The GRAMS carbon-star model grid

NASA Astrophysics Data System (ADS)

Srinivasan, S.; Sargent, B. A.; Meixner, M.

2011-08-01

Context. Outflows from asymptotic giant branch (AGB) and red supergiant (RSG) stars inject dust into the interstellar medium. The total rate of dust return provides an important constraint to galactic chemical evolution models. However, this requires detailed radiative transfer (RT) modeling of individual stars, which becomes impractical for large data sets. An alternative approach is to select the best-fit spectral energy distribution (SED) from a grid of dust shell models, allowing for a faster determination of the luminosities and mass-loss rates for entire samples. Aims: We have developed the Grid of RSG and AGB ModelS (GRAMS) to measure the mass-loss return from evolved stars. The models span the range of stellar, dust shell and grain properties relevant to evolved stars. The GRAMS model database will be made available to the scientific community. In this paper we present the carbon-rich AGB model grid and compare our results with photometry and spectra of Large Magellanic Cloud (LMC) carbon stars from the SAGE (Surveying the Agents of Galaxy Evolution) and SAGE-Spec programs. Methods: We generate models for spherically symmetric dust shells using the 2Dust code, with hydrostatic models for the central stars. The model photospheres have effective temperatures between 2600 and 4000 K and luminosities from ~2000 L⊙ to ~40 000 L⊙. Assuming a constant expansion velocity, we explore five values of the inner radius Rin of the dust shell (1.5, 3, 4.5, 7 and 12 Rstar). We fix the outer radius at 1000 Rin. Based on the results from our previous study, we use amorphous carbon dust mixed with 10% silicon carbide by mass. The grain size distribution follows a power-law and an exponential falloff at large sizes. The models span twenty-six values of 11.3 μm optical depth, ranging from 0.001 to 4. For each model, 2Dust calculates the output SED from 0.2 to 200 μm. Results: Over 12 000 models have dust temperatures below 1800 K. For these, we derive synthetic photometry in optical, near-infrared and mid-infrared filters for comparison with available data. We find good agreement with magnitudes and colors observed for LMC carbon-rich and extreme AGB star candidates from the SAGE survey, as well as spectroscopically confirmed carbon stars from the SAGE-Spec study. Our models reproduce the IRAC colors of most of the extreme AGB star candidates, consistent with the expectation that a majority of these enshrouded stars have carbon-rich dust. Finally, we fit the SEDs of some well-studied carbon stars and compare the resulting luminosities and mass-loss rates with those from previous studies. The model grid is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/532/A54

M Stars in the TW Hydra Association: A Chandra Large Program Survey

NASA Astrophysics Data System (ADS)

Punzi, Kristina; Kastner, Joel; Principe, David; Stelzer, Beate; Gorti, Uma; Pascucci, Illaria; Argiroffi, Costanza

2018-01-01

We have conducted a Cycle 18 Chandra Large Program survey of very cool members of the $\\sim$ 8 Myr-old TW Hydra Association (TWA) to extend our previous study of the potential connections between M star disks and X-rays (Kastner et al. 2016, AJ, 152, 3) to the extreme low-mass end of the stellar initial mass function. The spectral types of our targets extend down to the M/L borderline. Thus we can further investigate the potential connection between the intense X-ray emission from young, low-mass stars and the lifetimes of their circumstellar planet-forming discs, as well as better constrain the age at which coronal activity declines for stellar masses approaching the H-burning limit of $\\sim$ 0.08 M$_{\\odot}$. We present preliminary results from the Cycle 18 survey, including X-ray detection statistics and measurements of relative X-ray luminosities and coronal (X-ray) temperatures for those TWA stars detected by Chandra. This research is supported by SAO/CXC grant GO7-18002A and NASA Astrophysics Data Analysis program grants NNX12AH37G and NNX16AG13G to RIT.

Submillimeter studies of main-sequence stars

NASA Technical Reports Server (NTRS)

Zuckerman, B.; Becklin, E. E.

1993-01-01

JCMT maps of the 800-micron emission from Vega, Fomalhaut, and Beta Pictoris are interpreted to indicate that they are not ringed by large reservoirs of distant orbiting dust particles that are too cold to have been detected by IRAS. A search for 800-micron emission from stars in the Pleiades and Ursa Majoris open clusters is reported. In comparison with the mass of dust particles near T Tauri and Herbig Ae stars, the JCMT data indicate a decline in dust mass during the initial 3 x 10 exp 8 yr that a star spends on the main sequence that is at least as rapid as (time) exp -2. It is estimated that in the Kuiper belt the ratio of total mass carried by small particles to that carried by comets is orders of magnitude smaller than this ratio is 1 AU from the sun. If 800-micron opacities calculated by Pollack et al. (1993) are correct, then the particles with radii less than 100 microns that dominate the FIR fluxes measured by IRAS cannot entirely account for the measured 800-micron fluxes at Vega, Beta Pic, and Fomalhaut; larger particles must be present as well.

R CORONAE BOREALIS STARS IN M31 FROM THE PALOMAR TRANSIENT FACTORY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tang Sumin; Bildsten, Lars; Cao Yi

2013-04-20

We report the discovery of R Coronae Borealis (RCB) stars in the Andromeda galaxy (M31) using the Palomar Transient Factory (PTF). RCB stars are rare hydrogen-deficient, carbon-rich supergiant variables, most likely the merger products of two white dwarfs. These new RCBs, including two confirmed ones and two candidates, are the first to be found beyond the Milky Way and the Magellanic Clouds. All of M31 RCBs showed >1.5 mag irregular declines over timescales of weeks to months. Due to the limiting magnitude of our data (R Almost-Equal-To 21-22 mag), these RCB stars have R Almost-Equal-To 19.5-20.5 mag at maximum light,more » corresponding to M{sub R} = -4 to -5, making them some of the most luminous RCBs known. Spectra of two objects show that they are warm RCBs, similar to the Milky Way RCBs RY Sgr and V854 Cen. We consider these results, derived from a pilot study of M31 variables, as an important proof-of-concept for the study of rare bright variables in nearby galaxies with the PTF or other synoptic surveys.« less

To the Galactic Virial Radius with Hyper Suprime-Cam

NASA Astrophysics Data System (ADS)

Deason, Alis J.; Belokurov, Vasily; Koposov, Sergey E.

2018-01-01

We exploit the exquisite, deep Hyper Suprime-Cam (HSC) imaging data to probe the Galactic halo out to 200 kpc. Using the ∼100 square degree, multiband photometry of the first HSC Wide survey data release, we identify blue horizontal branch (BHB) stars beyond 50 kpc in the halo. The presence of the Sagittarius (Sgr) stream in the HSC fields produces a notable excess of stars at the apocenter of the leading arm (∼50–60 kpc). For fields excluding Sgr, the BHB counts are consistent with a continuation of a ‑4 power law from the inner halo. However, we find that the majority of the non-Sgr BHB stars beyond 50 kpc reside in one 27 square degree HSC field called “VVDS.” Curiously, this field is located close to the Magellanic plane, and we hypothesize that the excess of stars between 50 and 200 kpc could be associated with distant Magellanic debris. Indeed, without the VVDS, there are very few BHBs in the remaining portions of the Galaxy probed by the HSC. Accordingly, this scarcity of tracers is consistent with a significant decline in stellar density beyond 50 kpc, with a power law of ‑4 or steeper.

The onset of star formation 250 million years after the Big Bang.

PubMed

Hashimoto, Takuya; Laporte, Nicolas; Mawatari, Ken; Ellis, Richard S; Inoue, Akio K; Zackrisson, Erik; Roberts-Borsani, Guido; Zheng, Wei; Tamura, Yoichi; Bauer, Franz E; Fletcher, Thomas; Harikane, Yuichi; Hatsukade, Bunyo; Hayatsu, Natsuki H; Matsuda, Yuichi; Matsuo, Hiroshi; Okamoto, Takashi; Ouchi, Masami; Pelló, Roser; Rydberg, Claes-Erik; Shimizu, Ikkoh; Taniguchi, Yoshiaki; Umehata, Hideki; Yoshida, Naoki

2018-05-01

A fundamental quest of modern astronomy is to locate the earliest galaxies and study how they influenced the intergalactic medium a few hundred million years after the Big Bang 1-3 . The abundance of star-forming galaxies is known to decline 4,5 from redshifts of about 6 to 10, but a key question is the extent of star formation at even earlier times, corresponding to the period when the first galaxies might have emerged. Here we report spectroscopic observations of MACS1149-JD1 6 , a gravitationally lensed galaxy observed when the Universe was less than four per cent of its present age. We detect an emission line of doubly ionized oxygen at a redshift of 9.1096 ± 0.0006, with an uncertainty of one standard deviation. This precisely determined redshift indicates that the red rest-frame optical colour arises from a dominant stellar component that formed about 250 million years after the Big Bang, corresponding to a redshift of about 15. Our results indicate that it may be possible to detect such early episodes of star formation in similar galaxies with future telescopes.

Kinematical evolution of tidally limited star clusters: rotational properties

NASA Astrophysics Data System (ADS)

Tiongco, Maria A.; Vesperini, Enrico; Varri, Anna Lisa

2017-07-01

We present the results of a set of N-body simulations following the long-term evolution of the rotational properties of star cluster models evolving in the external tidal field of their host galaxy, after an initial phase of violent relaxation. The effects of two-body relaxation and escape of stars lead to a redistribution of the ordered kinetic energy from the inner to the outer regions, ultimately determining a progressive general loss of angular momentum; these effects are reflected in the overall decline of the rotation curve as the cluster evolves and loses stars. We show that all of our models share the same dependence of the remaining fraction of the initial rotation on the fraction of the initial mass lost. As the cluster evolves and loses part of its initial angular momentum, it becomes increasingly dominated by random motions, but even after several tens of relaxation times, and losing a significant fraction of its initial mass, a cluster can still be characterized by a non-negligible ratio of the rotational velocity to the velocity dispersion. This result is in qualitative agreement with the recently observed kinematical complexity that characterizes several Galactic globular clusters.

Improvement of Accuracy of Proper Motions of Hipparcos Catalogue Stars Using Optical Latitude Observations

NASA Astrophysics Data System (ADS)

Damljanovic, G.

2009-09-01

Commission 19 (Earth Rotation) of the International Astronomical Union (IAU) established the Working Group on Earth Rotation in the Hipparcos Reference Frame (WG ERHRF) in 1995 to collect the optical observations of latitude and universal time variations, made during 1899.7 -- 1992.0 in line with the Earth orientation programmes (to derive Earth Orientation Parameters -- EOP), with Dr. Jan Vondrák (Astronomical Institute of Academy of Sciences of the Czech Republic, Prague) as the head of WG ERHRF. We participated in this international project using Belgrade Visual Zenith -- Telescope (BLZ) latitude data for the period 1949.0 -- 1986.0, after a new reduction of BLZ data made in my MSc thesis, finished in 1997 at the Faculty of Mathematics of University of Belgrade. Dr. Vondrák collected 4.4 million optical observations of latitude/universal time variations made at 33 observatories. The data were used for the EOP investigations, Hipparcos satellite Catalogue -- radio sources connection, etc. Nowadays, it is customary to correct the positions and proper motions of stars of Hipparcos Catalogue (as an optical reference frame) using ground -- based observations of some Hipparcos stars. In this PhD thesis we use the latitude observations made with several types of classical astrometric instruments: visual (ZT) and floating zenith -- telescope (FZT), visual zenith tube (VZT) and photographic zenith tube (PZT); 26 different instruments located at many observatories all over the world (used in the programs of monitoring the Earth orientation during the 20th century). We received the data from Dr. Vondrák via private communication. The observatories and instruments are: International Latitude Service -- ILS (Carloforte -- CA ZT, Cincinnati -- CI ZT, Gaithersburg -- GT ZT, Kitab -- KZ ZT, Mizusawa -- MZZ ZT, Tschardjui -- TS ZT and Ukiah -- UK ZT), Belgrade (BLZ ZT), Blagoveschtschensk (BK ZT), Irkutsk (IRZ ZT), Poltava (POL ZT), Pulkovo (PU and PUZ ZT), Varsovie (VJZ ZT), Mizusawa (MZL FZT), Tuorla -- Turku (TT VZT), Mizusawa (MZP and MZQ PZT), Mount Stromlo (MS PZT), Ondřejov (OJP PZT), Punta Indio (PIP PZT), Richmond (RCP and RCQ PZT) and Washington (WA, W and WGQ PZT). The task is to improve the proper motions in declination of the observed Hipparcos stars. The original method was developed, and it consists of removing from the instantaneous observed latitudes all known effects (polar motion and some local instrumental errors). The corrected latitudes are then used to calculate the corrections of the Hipparcos proper motions in declination (Damljanović 2005). The Least Squares Method (LSM) is used with the linear model. We compared the calculated results with ARIHIP and EOC-2 data, and found a good agreement. The newly obtained values of proper motions in declination are substantially more precise than those of the Hipparcos Catalogue. It is because the time interval covered by the latitude observations (tens of years) is much longer than the Hipparcos one (less than four years), and because of the great number of observations made during this interval (Damljanović et al. 2006). Our method is completely different from the one used to compute the EOC-2 catalogue (Vondrák 2004). It was also an almost independent check of the proper motions of EOC-2. The catalogue EOC-2 is used in this thesis to distinguish the corrections of the two stars of a pair observed by using the Horrebow -- Talcott method. The difference between the two proper motions is constrained by the difference in the EOC-2 and Hipparcos catalogues (Damljanović and Pejović 2006). The main result of the thesis is the catalogue of proper motions in declination of 2347 Hipparcos stars.

Digging in the coronal graveyard - A Rosat observation of the red giant Arcturus

NASA Technical Reports Server (NTRS)

Ayres, Thomas R.; Fleming, Thomas A.; Schmitt, Juergen H. M. M.

1991-01-01

A deep exposure of the bright star Arcturus (Alpha Bootis: K1 III) with the Roentgensatellit (Rosat) failed to detect soft X-ray emission from the archetype 'noncoronal' red giant. The 3-sigma upper limit in the energy band 0.1-2.4 keV corresponds to an X-ray luminosity of less than 3 x 10 to the 25th erg/s, equivalent to a coronal surface flux density of less than 0.0001 solar. The nondetection safely eliminates coronal irradiation as a possible mechanism to produce the highly variable He I 10830 feature and emphasizes the sharp decline in solarlike coronal activity that accompanies the evolution of low-mass single stars away from the main sequence. While the most conspicuous object in the Rosat field of view was not visible in X-rays, at least one fainter star is among the about 60 sources recorded: the Sigma Sct variable CN Boo, an A8 giant in the UMa Stream.

Star Formation in a Complete Spectroscopic Survey of Galaxies

NASA Astrophysics Data System (ADS)

Carter, B. J.; Fabricant, D. G.; Geller, M. J.; Kurtz, M. J.; McLean, B.

2001-10-01

The 15R-North galaxy redshift survey is a uniform spectroscopic survey (S/N~10) covering the range 3650-7400 Å for 3149 galaxies with median redshift 0.05. The sample is 90% complete to R=15.4. The median slit covering fraction is 24% of the galaxy, apparently sufficient to minimize the effects of aperture bias on the EW(Hα). Forty-nine percent of the galaxies in the survey have one or more emission lines detected at >=2 σ. In agreement with previous surveys, the fraction of absorption-line galaxies increases steeply with galaxy luminosity. We use Hβ, [O III], Hα, and [N II] to discriminate between star-forming galaxies and AGNs. At least 20% of the galaxies are star-forming, at least 17% have AGN-like emission, and 12% have unclassifiable emission. The unclassified 12% may include a ``hybrid'' population of galaxies with both star formation and AGN activity. The AGN fraction increases steeply with luminosity; the fraction of star-forming galaxies decreases. We use the EW(Hα+[N II]) to estimate the Scalo birthrate parameter, b, the ratio of the current star formation rate to the time averaged star formation rate. The median birthrate parameter is inversely correlated with luminosity in agreement with the conclusions based on smaller samples (Kennicutt, Tamblyn, & Congdon). Because our survey is large, we identify 33 vigorously star-forming galaxies with b>3. We confirm the conclusion of Jansen, Franx, & Fabricant that EW([O II]) must be used with caution as a measure of current star formation. Finally, we examine the way galaxies of different spectroscopic type trace the large-scale galaxy distribution. As expected the absorption-line fraction decreases and the star-forming emission-line fraction increases as the galaxy density decreases. The AGN fraction is insensitive to the surrounding galaxy density; the unclassified fraction declines slowly as the density increases. For the star-forming galaxies, the EW(Hα) increases very slowly as the galaxy number density decreases. Whether a galaxy forms stars or not is strongly correlated with the surrounding galaxy density averaged over a scale of a few Mpc. This dependence reflects, in large part, the morphology-density relation. However, for galaxies forming stars, the stellar birthrate parameter is remarkably insensitive to the galaxy density. This conclusion suggests that the triggering of star formation occurs on a smaller spatial scale.

Neutrino astronomy with supernova neutrinos

NASA Astrophysics Data System (ADS)

Brdar, Vedran; Lindner, Manfred; Xu, Xun-Jie

2018-04-01

Modern neutrino facilities will be able to detect a large number of neutrinos from the next Galactic supernova. We investigate the viability of the triangulation method to locate a core-collapse supernova by employing the neutrino arrival time differences at various detectors. We perform detailed numerical fits in order to determine the uncertainties of these time differences for the cases when the core collapses into a neutron star or a black hole. We provide a global picture by combining all the relevant current and future neutrino detectors. Our findings indicate that in the scenario of a neutron star formation, supernova can be located with precision of 1.5 and 3.5 degrees in declination and right ascension, respectively. For the black hole scenario, sub-degree precision can be reached.

Spectroscopic observations of V443 Herculis - A symbiotic binary with a low mass white dwarf

NASA Technical Reports Server (NTRS)

Dobrzycka, Danuta; Kenyon, Scott J.; Mikolajewska, Joanna

1993-01-01

We present an analysis of new and existing photometric and spectroscopic observations of the symbiotic binary V443 Herculis. This binary system consists of a normal M5 giant and a hot compact star. These two objects have comparable luminosities: about 1500 solar for the M5 giant and about 1000 solar for the compact star. We identify three nebular regions in this binary: a small, highly ionized volume surrounding the hot component, a modestly ionized shell close to the red giant photosphere, and a less dense region of intermediate ionization encompassing both binary components. The system parameters for V443 Her suggest the hot component currently declines from a symbiotic nova eruption.

The Wolf-Rayet star population in the dwarf galaxy NGC 625

NASA Astrophysics Data System (ADS)

Monreal-Ibero, A.; Walsh, J. R.; Iglesias-Páramo, J.; Sandin, C.; Relaño, M.; Pérez-Montero, E.; Vílchez, J.

2017-07-01

Context. Quantifying the number, type, and distribution of Wolf-Rayet (W-R) stars is a key component in the context of galaxy evolution, since they put constraints on the age of the star formation bursts. Nearby galaxies (distances ≲5 Mpc) are particularly relevant in this context since they fill the gap between studies in the Local Group, where individual stars can be resolved, and galaxies in the Local Volume and beyond. Aims: We intend to characterise the W-R star population in one of these systems, NGC 625, which is a low-metallicity dwarf galaxy suffering a currently declining burst of star formation. Methods: Optical integral field spectroscopy (IFS) data have been obtained with the VIMOS-IFU and the HR_Orange and HR_Blue gratings at the Very Large Telescope covering the starburst region of NGC 625. Ancillary Hubble Space Telescope (HST) images in the F555W and F814W bands are also used for comparison. We estimate the number of W-R stars using a linear combination of three W-R templates: one early-type nitrogen (WN) star, one late-type WN star, and one carbon-type (WC) star (or oxygen-type (WO) star). Fits using several ensembles of templates were tested. Results were confronted with I) high spatial resolution HST photometry; II) numbers of W-R stars in nearby galaxies; and III) model predictions. Results: The W-R star population is spread over the main body of the galaxy and is not necessarily coincident with the overall stellar distribution. Our best estimation for the number of W-R stars yields a total of 28 W-R stars in the galaxy, out of which 17 are early-type WN, six are late-type WN, and five are WC stars. The width of the stellar features nicely correlates with the dominant W-R type found in each aperture. The distribution of the different types of WR in the galaxy is roughly compatible with the way star formation has propagated in the galaxy, according to previous findings using high spatial resolution with the HST. Fits using templates at the metallicity of the Large Magellanic Cloud yield more reasonable number of W-R than those using templates at the metallicity of the Small Magellanic Cloud. Given the metallicity of NGC 625, this suggests a non-linear relation between the metallicity and luminosity of the W-R spectral features.

Relation between acute and long-term cognitive decline after surgery: Influence of metabolic syndrome.

PubMed

Gambús, P L; Trocóniz, I F; Feng, X; Gimenez-Milá, M; Mellado, R; Degos, V; Vacas, S; Maze, M

2015-11-01

The relationship between persistent postoperative cognitive decline and the more common acute variety remains unknown; using data acquired in preclinical studies of postoperative cognitive decline we attempted to characterize this relationship. Low capacity runner (LCR) rats, which have all the features of the metabolic syndrome, were compared postoperatively with high capacity runner (HCR) rats for memory, assessed by trace fear conditioning (TFC) on the 7th postoperative day, and learning and memory (probe trial [PT]) assessed by the Morris water-maze (MWM) at 3 months postoperatively. Rate of learning (AL) data from the MWM test, were estimated by non-linear mixed effects modeling. The individual rat's TFC result at postoperative day (POD) 7 was correlated with its AL and PT from the MWM data sets at postoperative day POD 90. A single exponential decay model best described AL in the MWM with LCR and surgery (LCR-SURG) being the only significant covariates; first order AL rate constant was 0.07 s(-1) in LCR-SURG and 0.16s(-1) in the remaining groups (p<0.05). TFC was significantly correlated with both AL (R=0.74; p<0.0001) and PT (R=0.49; p<0.01). Severity of memory decline at 1 week after surgery presaged long-lasting deteriorations in learning and memory. Copyright © 2015 Elsevier Inc. All rights reserved.

Adolescent Changes in Homeostatic Regulation of EEG Activity in the Delta and Theta Frequency Bands during NREM Sleep

PubMed Central

Campbell, Ian G.; Darchia, Nato; Higgins, Lisa M.; Dykan, Igor V.; Davis, Nicole M.; de Bie, Evan; Feinberg, Irwin

2011-01-01

Study Objectives: Slow wave EEG activity in NREM sleep decreases by more than 60% between ages 10 and 20 years. Slow wave EEG activity also declines across NREM periods (NREMPs) within a night, and this decline is thought to represent the dynamics of sleep homeostasis. We used longitudinal data to determine whether these homeostatic dynamics change across adolescence. Design: All-night sleep EEG was recorded semiannually for 6 years. Setting: EEG was recorded with ambulatory recorders in the subjects' homes. Participants: Sixty-seven subjects in 2 cohorts, one starting at age 9 and one starting at age 12 years. Measurements and Results: For NREM delta (1-4 Hz) and theta (4-8 Hz) EEG, we tested whether the proportion of spectral energy contained in the first NREMP changes with age. We also tested for age changes in the parameters of the process S exponential decline. For both delta and theta, the proportion of energy in the first NREMP declined significantly across ages 9 to 18 years. Process S parameters SWA0 and TWA0, respectively, represent slow wave (delta) activity and theta wave activity at the beginning of the night. SWA0 and TWA0 declined significantly (P < 0.0001) across ages 9 to 18. Conclusions: These declines indicate that the intensity of the homeostatic or restorative processes at the beginning of sleep diminished across adolescence. We propose that this change in sleep regulation is caused by the synaptic pruning that occurs during adolescent brain maturation. Citation: Campbell IG; Darchia N; Higgins LM; Dykan IV; Davis NM; de Bie E; Feinberg I. Adolescent changes in homeostatic regulation of EEG activity in the delta and theta frequency bands during NREM sleep. SLEEP 2011;34(1):83-91. PMID:21203377

Documentation for the machine-readable version of the catalogue of 20457 Star positions obtained by photography in the declination zone -48 deg to -54 deg (1950)

NASA Technical Reports Server (NTRS)

Warren, W. H., Jr.

1983-01-01

The machine readable catalog, as it is distributed from the Astronomical Data Center, is described. Some minor reformatting of the magnetic tape version is received to decrease the record size and conserve space; the data content is identical to the sample shown in Table VI of the source reference.

Boron Abundances Across the “Li-Be Dip” in the Hyades Cluster

NASA Astrophysics Data System (ADS)

Boesgaard, Ann Merchant; Lum, Michael G.; Deliyannis, Constantine P.; King, Jeremy R.; Pinsonneault, Marc H.; Somers, Garrett

2016-10-01

Dramatic deficiencies of Li in the mid-F dwarf stars of the Hyades cluster were discovered by Boesgaard & Tripicco. Boesgaard & King discovered corresponding, but smaller, deficiencies in Be in the same narrow temperature region in the Hyades. Using the Space Telescope Imaging Spectrograph on the Hubble Space Telescope, we investigate B abundances in the Hyades F stars to look for a potential B dip using the B I resonance line at 2496.8 Å. The light elements Li, Be, and B are destroyed inside stars at increasingly hotter temperatures: 2.5, 3.5, and 5 × 106 K, respectively. Consequently, these elements survive to increasingly greater depths in a star and their surface abundances indicate the depth and thoroughness of mixing in the star. We have (re)determined Li abundances/upper limits for 79 Hyades dwarfs, Be for 43 stars, and B for 5 stars. We find evidence for a small drop in the B abundance across the Li-Be dip. The B abundances for the four stars in the temperature range 6100-6730 K fit the B-Be correlation found previously by Boesgaard et al. Models of rotational mixing produce good agreement with the relative depletions of Be and B in the dip region. We have compared our nLTE B abundances for the three high B stars on either side of the Li-Be dip with those found by Duncan et al. for the two Hyades giants. This confirms the factor of 10 decline in the B abundance in the Hyades giants as predicted by dilution due to the deepening of the surface convection zone. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program #HST-G0-12294.

VizieR Online Data Catalog: G5 and later stars in a North Galactic Pole region (Upgren 1962)

NASA Astrophysics Data System (ADS)

Upgren, A. R., Jr.

2015-11-01

The catalog is an objective-prism survey of late-type stars in a region of 396 square degrees surrounding the north galactic pole. The objective-prism spectra employed have a dispersion of 58 nm/mm at H-γ and extend into the ultraviolet region. The catalog contains the magnitudes and spectral classes of 4027 stars of class G5 and later, complete to a limiting photographic magnitude of 13.0. The spectral classification of the stars is based on the Yerkes system. The catalog includes the serial numbers of the stars corresponding to the numbers on the identification charts in Upgren (1984), BD and HD numbers, B magnitudes, spectral classes, and letters designating the subregion and identification chart on which each star is located. This survey was undertaken to determine the space densities at varying distances from the galactic plane. Accurate separation of the surveyed stars of G5 and later into giants and dwarfs was achieved through the use of the UV region as well as conventional methods of classification. The resulting catalog of 4027 stars is probably complete over the region to a limiting photographic magnitude of 13.0. The region covered by the survey is the same as that discussed by Slettebak and Stock (1959) and is in the approximate range RA 11:30 to 13:00, Declination +25 to +50 (B1950.0). The catalog includes all M and Carbon stars previously published by Upgren (1960). For a discussion of the classification criteria, the combining of multiple classifications (each spectral image was classified twice), the determination of magnitudes, and additional details about the catalog, the source reference should be consulted. Corrections, accurate positions, more identifications, and remarks have been added in Nov. 2015 by B. Skiff in the file "positions.dat"; see the "History" section below for details. (3 data files).

On the Spatially Resolved Star Formation History in M51. I. Hybrid UV+IR Star Formation Laws and IR Emission from Dust Heated by Old Stars

NASA Astrophysics Data System (ADS)

Eufrasio, R. T.; Lehmer, B. D.; Zezas, A.; Dwek, E.; Arendt, R. G.; Basu-Zych, A.; Wiklind, T.; Yukita, M.; Fragos, T.; Hornschemeier, A. E.; Markwardt, L.; Ptak, A.; Tzanavaris, P.

2017-12-01

We present LIGHTNING, a new spectral energy distribution fitting procedure, capable of quickly and reliably recovering star formation history (SFH) and extinction parameters. The SFH is modeled as discrete steps in time. In this work, we assumed lookback times of 0-10 Myr, 10-100 Myr, 0.1-1 Gyr, 1-5 Gyr, and 5-13.6 Gyr. LIGHTNING consists of a fully vectorized inversion algorithm to determine SFH step intensities and combines this with a grid-based approach to determine three extinction parameters. We apply our procedure to the extensive far-UV-to-far-IR photometric data of M51, convolved to a common spatial resolution and pixel scale, and make the resulting maps publicly available. We recover, for M51a, a peak star formation rate (SFR) between 0.1 and 5 Gyr ago, with much lower star formation activity over the past 100 Myr. For M51b, we find a declining SFR toward the present day. In the outskirt regions of M51a, which includes regions between M51a and M51b, we recover an SFR peak between 0.1 and 1 Gyr ago, which corresponds to the effects of the interaction between M51a and M51b. We utilize our results to (1) illustrate how UV+IR hybrid SFR laws vary across M51 and (2) provide first-order estimates for how the IR luminosity per unit stellar mass varies as a function of the stellar age. From the latter result, we find that IR emission from dust heated by stars is not always associated with young stars and that the IR emission from M51b is primarily powered by stars older than 5 Gyr.

Insights on star-formation histories and physical properties of 1.2 ≤z ≲ 4 Herschel-detected galaxies

NASA Astrophysics Data System (ADS)

Sklias, P.; Schaerer, D.; Elbaz, D.; Pannella, M.; Schreiber, C.; Cava, A.

2017-09-01

Aims: We aim to test the impact of using variable star-forming histories (SFHs) and the IR luminosity as a constrain on the physical parameters of high redshift dusty star-forming galaxies. We explore in particular the properties (SFHs, ages, timescales) of galaxies depending on their belonging to the "main sequence" of star-forming galaxies (MS). Methods: We performed spectral energy distribution (SED) fitting of the UV-to-NIR and FIR emissions of a moderately large sample of GOODS-Herschel galaxies, for which rich multi-wavelength, optical to IR observations are available. We tested different SFHs and the impact of imposing energy conservation in the SED fitting process, to help with issues like the age-extinction degeneracy and produce SEDs consistent with observations. Results: Our simple models produce well constrained SEDs for the broad majority of the sample (84%), with the notable exception of the very high LIR end, for which we have indications that the energy conservation hypothesis cannot hold true for a single component population approach. We observe trends in the preferences in SFHs among our sources depending on stellar mass M⋆ and z. Trends also emerge in the characteristic timescales of the SED models depending on the location on the SFR - M⋆ diagram. We show that whilst using the same available observational data, we can produce galaxies less star-forming than classically inferred, if we allow rapidly declining SFHs, while properly reproducing their observables. These sources, representing 7% of the sample, can be post-starbursts undergoing quenching, and their SFRs are potentially overestimated if inferred from their LIR. Based on the trends observed in the rising SFH fits we explore a simple evolution model for stellar mass build-up over the considered time period. Conclusions: Our approach successfully breaks the age-extinction degeneracy, and enables to evaluate properly the SFRs of the sources in the SED fitting process. Fitting without the IR constrain leads to a strong preference for declining SFHs, while its inclusion increases the preference of rising SFHs, more so at high z, in tentative agreement with the cosmic star-formation history (CSFH), although this result suffers from poor statistics. Keeping in mind that the sample is biased toward high luminosities and intense star formation, the evolution shaped by our model appears as both bursty (in its early stages) and steady-lasting (later on). The SFH of the sample considered as a whole follows the CSFH with a surprisingly small scatter, and is compatible with other studies supporting that the more massive galaxies have built most of their mass earlier than lower mass galaxies.

Magnetorotational Mechanism of the Explosion of Core-Collapse Supernovae

NASA Astrophysics Data System (ADS)

Bisnovatyi-Kogan, G. S.; Moiseenko, S. G.; Ardelyan, N. V.

2018-03-01

The idea of the magnetorotational explosion mechanism is that the energy of rotation of the neutron star formed in the course of a collapse is transformed into the energy of an expanding shock wave by means of a magnetic field. In the two-dimensional case, the time of this transformation depends weakly on the initial strength of the poloidal magnetic field because of the development of a magnetorotational instability. Differential rotation leads to the twisting and growth of the toroidal magnetic-field component, which becomes much stronger than the poloidal component. As a result, the development of the instability and an exponential growth of all field components occur. The explosion topology depends on the structure of the magnetic field. In the case where the initial configuration of the magnetic field is close to a dipole configuration, the ejection of matter has a jet character, whereas, in the case of a quadrupole configuration, there arises an equatorial ejection. In either case, the energy release is sufficient for explaining the observed average energy of supernova explosion. Neutrinos are emitted as the collapse and the formation of a rapidly rotating neutron star proceeds. In addition, neutrino radiation arises in the process of magnetorotational explosion owing to additional rotational-energy losses. If the mass of a newborn neutron star exceeds the mass limit for a nonrotating neutron star, then subsequent gradual energy losses may later lead to the formation of a black hole. In that case, the energy carried away by a repeated flash of neutrino radiation increases substantially. In order to explain an interval of 4.5 hours between the two observed neutrino signals from SN 1987A, it is necessary to assume a weakening of the magnetorotional instability and a small initial magnetic field (109-1010 G) in the newly formed rotating neutron star. The existence of a black hole in the SN 1987A remnant could explain the absence of any visible pointlike source at the center of the explosion.

Detecting stellar-wind bubbles through infrared arcs in H II regions

NASA Astrophysics Data System (ADS)

Mackey, Jonathan; Haworth, Thomas J.; Gvaramadze, Vasilii V.; Mohamed, Shazrene; Langer, Norbert; Harries, Tim J.

2016-02-01

Mid-infrared arcs of dust emission are often seen near ionizing stars within H II regions. A possible explanations for these arcs is that they could show the outer edges of asymmetric stellar wind bubbles. We use two-dimensional, radiation-hydrodynamics simulations of wind bubbles within H II regions around individual stars to predict the infrared emission properties of the dust within the H II region. We assume that dust and gas are dynamically well-coupled and that dust properties (composition, size distribution) are the same in the H II region as outside it, and that the wind bubble contains no dust. We post-process the simulations to make synthetic intensity maps at infrared wavebands using the torus code. We find that the outer edge of a wind bubble emits brightly at 24 μm through starlight absorbed by dust grains and re-radiated thermally in the infrared. This produces a bright arc of emission for slowly moving stars that have asymmetric wind bubbles, even for cases where there is no bow shock or any corresponding feature in tracers of gas emission. The 24 μm intensity decreases exponentially from the arc with increasing distance from the star because the dust temperature decreases with distance. The size distribution and composition of the dust grains has quantitative but not qualitative effects on our results. Despite the simplifications of our model, we find good qualitative agreement with observations of the H II region RCW 120, and can provide physical explanations for any quantitative differences. Our model produces an infrared arc with the same shape and size as the arc around CD -38°11636 in RCW 120, and with comparable brightness. This suggests that infrared arcs around O stars in H II regions may be revealing the extent of stellar wind bubbles, although we have not excluded other explanations.

Halo Histories vs. Galaxy Properties at z=0, III: The Properties of Star-Forming Galaxies

NASA Astrophysics Data System (ADS)

Tinker, Jeremy L.; Hahn, ChangHoon; Mao, Yao-Yuan; Wetzel, Andrew R.

2018-05-01

We measure how the properties of star-forming central galaxies correlate with large-scale environment, δ, measured on 10 h-1Mpc scales. We use galaxy group catalogs to isolate a robust sample of central galaxies with high purity and completeness. The galaxy properties we investigate are star formation rate (SFR), exponential disk scale length Rexp, and Sersic index of the galaxy light profile, nS. We find that, at all stellar masses, there is an inverse correlation between SFR and δ, meaning that above-average star forming centrals live in underdense regions. For nS and Rexp, there is no correlation with δ at M_\\ast ≲ 10^{10.5} M⊙, but at higher masses there are positive correlations; a weak correlation with Rexp and a strong correlation with nS. These data are evidence of assembly bias within the star-forming population. The results for SFR are consistent with a model in which SFR correlates with present-day halo accretion rate, \\dot{M}_h. In this model, galaxies are assigned to halos using the abundance matching ansatz, which maps galaxy stellar mass onto halo mass. At fixed halo mass, SFR is then assigned to galaxies using the same approach, but \\dot{M}_h is used to map onto SFR. The best-fit model requires some scatter in the \\dot{M}_h-SFR relation. The Rexp and nS measurements are consistent with a model in which both of these quantities are correlated with the spin parameter of the halo, λ. Halo spin does not correlate with δ at low halo masses, but for higher mass halos, high-spin halos live in higher density environments at fixed Mh. Put together with the earlier installments of this series, these data demonstrate that quenching processes have limited correlation with halo formation history, but the growth of active galaxies, as well as other detailed galaxies properties, are influenced by the details of halo assembly.

Star-forming galaxies in intermediate-redshift clusters: stellar versus dynamical masses of luminous compact blue galaxies

NASA Astrophysics Data System (ADS)

Randriamampandry, S. M.; Crawford, S. M.; Bershady, M. A.; Wirth, G. D.; Cress, C. M.

2017-10-01

We investigate the stellar masses of the class of star-forming objects known as luminous compact blue galaxies (LCBGs) by studying a sample of galaxies in the distant cluster MS 0451.6-0305 at z ≈ 0.54 with ground-based multicolour imaging and spectroscopy. For a sample of 16 spectroscopically confirmed cluster LCBGs (colour B - V < 0.5, surface brightness μB < 21 mag arcsec-2 and magnitude MB < -18.5), we measure stellar masses by fitting spectral energy distribution (SED) models to multiband photometry, and compare with dynamical masses [determined from velocity dispersion in the range 10 < σv(km s- 1) < 80] we previously obtained from their emission-line spectra. We compare two different stellar population models that measure stellar mass in star-bursting galaxies, indicating correlations between the stellar age, extinction and stellar mass derived from the two different SED models. The stellar masses of cluster LCBGs are distributed similarly to those of field LCBGs, but the cluster LCBGs show lower dynamical-to-stellar mass ratios (Mdyn/M⋆ = 2.6) than their field LCBG counterparts (Mdyn/M⋆ = 4.8), echoing trends noted previously in low-redshift dwarf elliptical galaxies. Within this limited sample, the specific star formation rate declines steeply with increasing mass, suggesting that these cluster LCBGs have undergone vigorous star formation.

Morphology-based differences in the thermal response of freshwater phytoplankton.

PubMed

Segura, Angel M; Sarthou, Florencia; Kruk, Carla

2018-05-01

The thermal response of maximum growth rate in morphology-based functional groups (MBFG) of freshwater phytoplankton is analysed. Contrasting an exponential Boltzmann-Arrhenius with a unimodal model, three main features were evaluated: (i) the activation energy of the rise ( E r ), (ii) the presence of a break in the thermal response and (iii) the activation energy of the fall ( E f ). The whole dataset ( N = 563) showed an exponential increase ( E r ∼ 0.5), a break around 24°C and no temperature dependence after the breakpoint ( E f = 0). Contrasting thermal responses among MBFG were found. All groups showed positive activation energy ( E r > 0), four showed no evidence of decline in growth rate (temperature range = 0-35°C) and two presented a breakpoint followed by a sharp decrease in growth rate. Our results evidenced systematic differences between MBFG in the thermal response and a coherent response significantly related to morphological traits other than size (i.e. within MBFG). These results provide relevant information for water quality modelling and climate change predictions. © 2018 The Author(s).

Effects of anaerobic digestion on chlortetracycline and oxytetracycline degradation efficiency for swine manure.

PubMed

Yin, Fubin; Dong, Hongmin; Ji, Chao; Tao, Xiuping; Chen, Yongxing

2016-10-01

Manure containing antibiotics is considered a hazardous substance that poses a serious health risk to the environment and to human health. Anaerobic digestion (AD) could not only treatment animal waste but also generate valuable biogas. However, the interaction between antibiotics in manure and the AD process has not been clearly understood. In this study, experiments on biochemical methane potential (BMP) were conducted to determine the inhibition of the AD process from antibiotics and the threshold of complete antibiotic removal. The thresholds of the complete antibiotic removal were 60 and 40mg/kg·TS for CTC and OTC, respectively. CTC and OTC with concentrations below thresholds could increase the BMP of manure. When the CTC and OTC concentrations exceeded the thresholds, they inhibited manure fermentation, and the CTC removal rate declined exponentially with concentration (60-500mg/kg·TS). The relationship between OTC antibiotic concentration and its removal rate in AD treatment was described with exponential (40-100mg/kg·TS) and linear equations (100-500mg/kg·TS). Copyright © 2016 Elsevier Ltd. All rights reserved.

Regulation of StAR by the N-terminal Domain and Coinduction of SIK1 and TIS11b/Znf36l1 in Single Cells

PubMed Central

Lee, Jinwoo; Tong, Tiegang; Duan, Haichuan; Foong, Yee Hoon; Musaitif, Ibrahim; Yamazaki, Takeshi; Jefcoate, Colin

2016-01-01

The cholesterol transfer function of steroidogenic acute regulatory protein (StAR) is uniquely integrated into adrenal cells, with mRNA translation and protein kinase A (PKA) phosphorylation occurring at the mitochondrial outer membrane (OMM). The StAR C-terminal cholesterol-binding domain (CBD) initiates mitochondrial intermembrane contacts to rapidly direct cholesterol to Cyp11a1 in the inner membrane (IMM). The conserved StAR N-terminal regulatory domain (NTD) includes a leader sequence targeting the CBD to OMM complexes that initiate cholesterol transfer. Here, we show how the NTD functions to enhance CBD activity delivers more efficiently from StAR mRNA in adrenal cells, and then how two factors hormonally restrain this process. NTD processing at two conserved sequence sites is selectively affected by StAR PKA phosphorylation. The CBD functions as a receptor to stimulate the OMM/IMM contacts that mediate transfer. The NTD controls the transit time that integrates extramitochondrial StAR effects on cholesterol homeostasis with other mitochondrial functions, including ATP generation, inter-organelle fusion, and the major permeability transition pore in partnership with other OMM proteins. PKA also rapidly induces two additional StAR modulators: salt-inducible kinase 1 (SIK1) and Znf36l1/Tis11b. Induced SIK1 attenuates the activity of CRTC2, a key mediator of StAR transcription and splicing, but only as cAMP levels decline. TIS11b inhibits translation and directs the endonuclease-mediated removal of the 3.5-kb StAR mRNA. Removal of either of these functions individually enhances cAMP-mediated induction of StAR. High-resolution fluorescence in situ hybridization (HR-FISH) of StAR RNA reveals asymmetric transcription at the gene locus and slow RNA splicing that delays mRNA formation, potentially to synchronize with cholesterol import. Adrenal cells may retain slow transcription to integrate with intermembrane NTD activation. HR-FISH resolves individual 3.5-kb StAR mRNA molecules via dual hybridization at the 3′- and 5′-ends and reveals an unexpectedly high frequency of 1:1 pairing with mitochondria marked by the matrix StAR protein. This pairing may be central to translation-coupled cholesterol transfer. Altogether, our results show that adrenal cells exhibit high-efficiency StAR activity that needs to integrate rapid cholesterol transfer with homeostasis and pulsatile hormonal stimulation. StAR NBD, the extended 3.5-kb mRNA, SIK1, and Tis11b play important roles. PMID:27531991

Regulation of StAR by the N-terminal Domain and Coinduction of SIK1 and TIS11b/Znf36l1 in Single Cells.

PubMed

Lee, Jinwoo; Tong, Tiegang; Duan, Haichuan; Foong, Yee Hoon; Musaitif, Ibrahim; Yamazaki, Takeshi; Jefcoate, Colin

2016-01-01

The cholesterol transfer function of steroidogenic acute regulatory protein (StAR) is uniquely integrated into adrenal cells, with mRNA translation and protein kinase A (PKA) phosphorylation occurring at the mitochondrial outer membrane (OMM). The StAR C-terminal cholesterol-binding domain (CBD) initiates mitochondrial intermembrane contacts to rapidly direct cholesterol to Cyp11a1 in the inner membrane (IMM). The conserved StAR N-terminal regulatory domain (NTD) includes a leader sequence targeting the CBD to OMM complexes that initiate cholesterol transfer. Here, we show how the NTD functions to enhance CBD activity delivers more efficiently from StAR mRNA in adrenal cells, and then how two factors hormonally restrain this process. NTD processing at two conserved sequence sites is selectively affected by StAR PKA phosphorylation. The CBD functions as a receptor to stimulate the OMM/IMM contacts that mediate transfer. The NTD controls the transit time that integrates extramitochondrial StAR effects on cholesterol homeostasis with other mitochondrial functions, including ATP generation, inter-organelle fusion, and the major permeability transition pore in partnership with other OMM proteins. PKA also rapidly induces two additional StAR modulators: salt-inducible kinase 1 (SIK1) and Znf36l1/Tis11b. Induced SIK1 attenuates the activity of CRTC2, a key mediator of StAR transcription and splicing, but only as cAMP levels decline. TIS11b inhibits translation and directs the endonuclease-mediated removal of the 3.5-kb StAR mRNA. Removal of either of these functions individually enhances cAMP-mediated induction of StAR. High-resolution fluorescence in situ hybridization (HR-FISH) of StAR RNA reveals asymmetric transcription at the gene locus and slow RNA splicing that delays mRNA formation, potentially to synchronize with cholesterol import. Adrenal cells may retain slow transcription to integrate with intermembrane NTD activation. HR-FISH resolves individual 3.5-kb StAR mRNA molecules via dual hybridization at the 3'- and 5'-ends and reveals an unexpectedly high frequency of 1:1 pairing with mitochondria marked by the matrix StAR protein. This pairing may be central to translation-coupled cholesterol transfer. Altogether, our results show that adrenal cells exhibit high-efficiency StAR activity that needs to integrate rapid cholesterol transfer with homeostasis and pulsatile hormonal stimulation. StAR NBD, the extended 3.5-kb mRNA, SIK1, and Tis11b play important roles.

LOCAL TADPOLE GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Elmegreen, Debra Meloy; Putko, Joseph; Dewberry, Janosz

2012-05-10

Tadpole galaxies have a giant star-forming region at the end of an elongated intensity distribution. Here we use Sloan Digital Sky Survey data to determine the ages, masses, and surface densities of the heads and tails in 14 local tadpoles selected from the Kiso and Michigan surveys of UV-bright galaxies, and we compare them to tadpoles previously studied in the Hubble Ultra Deep Field. The young stellar mass in the head scales linearly with rest-frame galaxy luminosity, ranging from {approx}10{sup 5} M{sub Sun} at galaxy absolute magnitude U = -13 mag to 10{sup 9} M{sub Sun} at U = -20more » mag. The corresponding head surface density increases from several M {sub Sun} pc{sup -2} locally to 10-100 M{sub Sun} pc{sup -2} at high redshift, and the star formation rate (SFR) per unit area in the head increases from {approx}0.01 M{sub Sun} yr{sup -1} kpc{sup -2} locally to {approx}1 M{sub Sun} yr{sup -1} kpc{sup -2} at high z. These local values are normal for star-forming regions, and the increases with redshift are consistent with other cosmological SFRs, most likely reflecting an increase in gas abundance. The tails in the local sample look like bulge-free galaxy disks. Their photometric ages decrease from several Gyr to several hundred Myr with increasing z, and their surface densities are more constant than the surface densities of the heads. The far-outer intensity profiles in the local sample are symmetric and exponential. We suggest that most local tadpoles are bulge-free galaxy disks with lopsided star formation, perhaps from environmental effects such as ram pressure or disk impacts, or from a Jeans length comparable to half the disk size.« less

Can Geographical Factors Determine the Choices of Farmers in the Ethiopian Highlands to Trade in Livestock Markets?

PubMed Central

Ortiz-Pelaez, Angel; Ashenafi, Getaneh; Roger, Francois; Waret-Szkuta, Agnes

2012-01-01

Proximity and affiliation to the local market appear to be two of the most relevant factors to explain farmer's choices to select a particular trading point. Physical barriers may limit the options , especially in developing countries. A network of villages linked by traders/farmer-traders sharing livestock markets was built with field data collected in 75 villages from 8 kebelles in the Wassona Werna wereda of the Ethiopian Highlands. Two exponential random graph models were fitted with various geographical and demographic attributes of the nodes (dyadic independent model) and three internal network structures (dyadic dependent model). Several diagnostic methods were applied to assess the goodness of fit of the models. The odds of an edge where the distance to the main market Debre Behran and the difference in altitude between two connected villages are both large increases significantly so that villages far away from the main market and at different altitude are more likely to be linked in the network than randomly. The odds of forming an edge between two villages in Abamote or Gudoberet kebelles are approximately 75% lower than an edge between villages in any other kebelles (p<0.05). The conditional log-odds of two villages forming a tie that is not included in a triangle, a 2-star or a 3-star is extremely low, increasing the odds significantly (p<0.05) each time a node is in a 2-star structure and decreasing it when a node is in a 3-star (p<0.05) or in a triangle formation (p<0.05)), conditional on the rest of the network. Two major constraining factors, namely distance and altitude, are not deterrent for the potential contact of susceptible small ruminant populations in the Highlands of Ethiopia. PMID:22355324

An XMM-Newton and NuSTAR Study of IGR J18214-1318: A Non-pulsating High-mass X-Ray Binary with a Neutron Star

NASA Astrophysics Data System (ADS)

Fornasini, Francesca M.; Tomsick, John A.; Bachetti, Matteo; Krivonos, Roman A.; Fürst, Felix; Natalucci, Lorenzo; Pottschmidt, Katja; Wilms, Jörn

2017-05-01

IGR J18214-1318, a Galactic source discovered by the International Gamma-Ray Astrophysics Laboratory, is a high-mass X-ray binary (HMXB) with a supergiant O-type stellar donor. We report on the XMM-Newton and NuSTAR observations that were undertaken to determine the nature of the compact object in this system. This source exhibits high levels of aperiodic variability, but no periodic pulsations are detected with a 90% confidence upper limit of 2% fractional rms between 0.00003-88 Hz, a frequency range that includes the typical pulse periods of neutron stars (NSs) in HMXBs (0.1-103 s). Although the lack of pulsations prevents us from definitively identifying the compact object in IGR J18214-1318, the presence of an exponential cutoff with e-folding energy ≲ 30 {keV} in its 0.3-79 keV spectrum strongly suggests that the compact object is an NS. The X-ray spectrum also shows a Fe Kα emission line and a soft excess, which can be accounted for by either a partial-covering absorber with {N}{{H}}≈ {10}23 cm-2, which could be due to the inhomogeneous supergiant wind, or a blackbody component with {kT}={1.74}-0.05+0.04 keV and {R}{BB}≈ 0.3 km, which may originate from NS hot spots. Although neither explanation for the soft excess can be excluded, the former is more consistent with the properties observed in other supergiant HMXBs. We compare IGR J18214-1318 to other HMXBs that lack pulsations or have long pulsation periods beyond the range covered by our observations.

Metal enrichment of the intracluster medium: SN-driven galactic winds

NASA Astrophysics Data System (ADS)

Baumgartner, V.; Breitschwerdt, D.

2009-12-01

% We investigate the role of supernova (SN)-driven galactic winds in the chemical enrichment of the intracluster medium (ICM). Such outflows on galactic scales have their origin in huge star forming regions and expel metal enriched material out of the galaxies into their surroundings as observed, for example, in the nearby starburst galaxy NGC 253. As massive stars in OB-associations explode sequentially, shock waves are driven into the interstellar medium (ISM) of a galaxy and merge, forming a superbubble (SB). These SBs expand in a direction perpendicular to the disk plane following the density gradient of the ISM. We use the 2D analytical approximation by Kompaneets (1960) to model the expansion of SBs in an exponentially stratified ISM. This is modified in order to describe the sequence of SN-explosions as a time-dependent process taking into account the main-sequence life-time of the SN-progenitors and using an initial mass function to get the number of massive stars per mass interval. The evolution of the bubble in space and time is calculated analytically, from which the onset of Rayleigh-Taylor instabilities in the shell can be determined. In its further evolution, the shell will break up and high-metallicity gas will be ejected into the halo of the galaxy and even into the ICM. We derive the number of stars needed for blow-out depending on the scale height and density of the ambient medium, as well as the fraction of alpha- and iron peak elements contained in the hot gas. Finally, the amount of metals injected by Milky Way-type galaxies to the ICM is calculated confirming the importance of this enrichment process.

Limits on magnetic field amplification from the r -mode instability

NASA Astrophysics Data System (ADS)

Friedman, John L.; Lindblom, Lee; Rezzolla, Luciano; Chugunov, Andrey I.

2017-12-01

At second order in perturbation theory, the unstable r -mode of a rotating star includes growing differential rotation whose form and growth rate are determined by gravitational-radiation reaction. With no magnetic field, the angular velocity of a fluid element grows exponentially until the mode reaches its nonlinear saturation amplitude and remains nonzero after saturation. With a background magnetic field, the differential rotation winds up and amplifies the field, and previous work where large mode amplitudes were considered [L. Rezzolla, F. K. Lamb, and S. L. Shapiro, Astrophys. J. 531, L139 (2000)., 10.1086/312539], suggests that the amplification may damp out the instability. A background magnetic field, however, turns the saturated time-independent perturbations corresponding to adding differential rotation into perturbations whose characteristic frequencies are of order the Alfvén frequency. As found in previous studies, we argue that magnetic-field growth is sharply limited by the saturation amplitude of an unstable mode. In contrast to previous work, however, we show that if the amplitude is small, i.e., ≲10-4 , then the limit on the magnetic-field growth is stringent enough to prevent the loss of energy to the magnetic field from damping or significantly altering an unstable r -mode in nascent neutron stars with normal interiors and in cold stars whose interiors are type II superconductors. We show this result first for a toy model, and we then obtain an analogous upper limit on magnetic-field growth using a more realistic model of a rotating neutron star. Our analysis depends on the assumption that there are no marginally unstable perturbations, and this may not hold when differential rotation leads to a magnetorotational instability.

Multiwavelength Study of Quiescent States of Mrk 421 with Unprecedented Hard X-Ray Coverage Provided by NuSTAR in 2013

NASA Technical Reports Server (NTRS)

Balokovic, M.; Paneque, D.; Madejski, G.; Chiang, J.; Furniss, A.; Ajello, M.; Alexander, D. M.; Barret, D.; Blandford, R. D.; Boggs, S. E.;

K2 Ultracool Dwarfs Survey. III. White Light Flares Are Ubiquitous in M6-L0 Dwarfs

NASA Astrophysics Data System (ADS)

Paudel, Rishi R.; Gizis, John E.; Mullan, D. J.; Schmidt, Sarah J.; Burgasser, Adam J.; Williams, Peter K. G.; Berger, Edo

2018-05-01

We report the white light flare rates for 10 ultracool dwarfs using Kepler K2 short-cadence data. Among our sample stars, two have spectral type M6, three are M7, three are M8, and two are L0. Most of our targets are old low-mass stars. We identify a total of 283 flares in all of the stars in our sample, with Kepler energies in the range log E Kp ∼ (29–33.5) erg. Using the maximum-likelihood method of line fitting, we find that the flare frequency distribution (FFD) for each star in our sample follows a power law with slope ‑α in the range ‑(1.3–2.0). We find that cooler objects tend to have shallower slopes. For some of our targets, the FFD follows either a broken power law, or a power law with an exponential cutoff. For the L0 dwarf 2MASS J12321827-0951502, we find a very shallow slope (‑α = ‑1.3) in the Kepler energy range (0.82–130) × 1030 erg: this L0 dwarf has flare rates which are comparable to those of high-energy flares in stars of earlier spectral types. In addition, we report photometry of two superflares: one on the L0 dwarf 2MASS J12321827-0951502 and another on the M7 dwarf 2MASS J08352366+1029318. In the case of 2MASS J12321827-0951502, we report a flare brightening by a factor of ∼144 relative to the quiescent photospheric level. Likewise, for 2MASS J08352366+1029318, we report a flare brightening by a factor of ∼60 relative to the quiescent photospheric level. These two superflares have bolometric (ultraviolet/optical/infrared) energies 3.6 × 1033 erg and 8.9 × 1033 erg respectively, while the full width half maximum timescales are very short, ∼2 min. We find that the M8 star TRAPPIST-1 is more active than the M8.5 dwarf 2M03264453+1919309, but less active than another M8 dwarf (2M12215066-0843197).

An increase in the 12C + 12C fusion rate from resonances at astrophysical energies.

PubMed

Tumino, A; Spitaleri, C; La Cognata, M; Cherubini, S; Guardo, G L; Gulino, M; Hayakawa, S; Indelicato, I; Lamia, L; Petrascu, H; Pizzone, R G; Puglia, S M R; Rapisarda, G G; Romano, S; Sergi, M L; Spartá, R; Trache, L

2018-05-01

Carbon burning powers scenarios that influence the fate of stars, such as the late evolutionary stages of massive stars 1 (exceeding eight solar masses) and superbursts from accreting neutron stars 2,3 . It proceeds through the 12 C +  12 C fusion reactions that produce an alpha particle and neon-20 or a proton and sodium-23-that is, 12 C( 12 C, α) 20 Ne and 12 C( 12 C, p) 23 Na-at temperatures greater than 0.4 × 10 9 kelvin, corresponding to astrophysical energies exceeding a megaelectronvolt, at which such nuclear reactions are more likely to occur in stars. The cross-sections 4 for those carbon fusion reactions (probabilities that are required to calculate the rate of the reactions) have hitherto not been measured at the Gamow peaks 4 below 2 megaelectronvolts because of exponential suppression arising from the Coulomb barrier. The reference rate 5 at temperatures below 1.2 × 10 9 kelvin relies on extrapolations that ignore the effects of possible low-lying resonances. Here we report the measurement of the 12 C( 12 C, α 0,1 ) 20 Ne and 12 C( 12 C, p 0,1 ) 23 Na reaction rates (where the subscripts 0 and 1 stand for the ground and first excited states of 20 Ne and 23 Na, respectively) at centre-of-mass energies from 2.7 to 0.8 megaelectronvolts using the Trojan Horse method 6,7 and the deuteron in 14 N. The cross-sections deduced exhibit several resonances that are responsible for very large increases of the reaction rate at relevant temperatures. In particular, around 5 × 10 8 kelvin, the reaction rate is boosted to more than 25 times larger than the reference value 5 . This finding may have implications such as lowering the temperatures and densities 8 required for the ignition of carbon burning in massive stars and decreasing the superburst ignition depth in accreting neutron stars to reconcile observations with theoretical models 3 .

Optical observations of NGC 2915: A nearby blue compact dwarf galaxy

NASA Technical Reports Server (NTRS)

Meurer, G. R.; Mackie, G.; Carignan, C.

1994-01-01

This paper presents B and R band Charge Coupled Device (CCD) images and medium resolution spectroscopy of NGC 2915, a relatively isolated BCD (blue compact dwarf) galaxy at a distance of approximately 5 Mpc. NGC 2915 contains two stellar populations: a high surface brightness blue core population and a red diffuse population. The core population contains all of the H II, and numerous embedded objects. It is the locus of current high mass star formation. The brightest embedded objects are likely to be young ionizing clusters, while many of the fainter objects are likely to be individual supergiant stars with masses up to approximately 25 solar mass, or blends of a few such stars. Curious aligned structures on the SE side of the galaxy are seen and their nature discussed. The spectrum of the core is dominated by bright narrow emission lines like that of a high excitation and low metallicity (less than half solar) H II region. The continuum is flat, with Balmer and Ca II features seen in absorption. The velocity of the Ca II features suggest contamination by galactic interstellar absorption. There is a significant velocity gradient in the spectra, probably indicative of rotation. Outside of its core, NGC 2915 resembles a dE (dwarf elliptical) galaxy, in that it has an exponential surface brightness profile, is red ((B-R)(sub 0) = 1.65), and has a low extrapolated central surface brightness (B(0)(sub c) = 22.44). NGC 2915's properties are compared with other BCDs, concentrating on two morphologically similar BCDs that are near enough to resolve into stars: NGC 1705 and NGC 5253. It is noted that the presence of winds in BCDs invalidates closed box chemical evolution models and the remaining constraints on star formation duration are relatively weak. Some BCDs, including NGC 2915, may be able to maintain their present star formation rate for Gyr time scales. This suggests that the overall evolution of these BCDs may be much slower than the approximately 10 Myr burst time scales commonly quoted. However, shortly after the formation of a massive (10(exp 6) solar mass) cluster a BCD will have all the properties of strong starburst galaxy).

The infrared-radio correlation of spheroid- and disc-dominated star-forming galaxies to z ˜ 1.5 in the COSMOS field

NASA Astrophysics Data System (ADS)

Molnár, Dániel Cs; Sargent, Mark T.; Delhaize, Jacinta; Delvecchio, Ivan; Smolčić, Vernesa; Novak, Mladen; Schinnerer, Eva; Zamorani, Giovanni; Bondi, Marco; Herrera-Ruiz, Noelia; Murphy, Eric J.; Vardoulaki, Eleni; Karim, Alexander; Leslie, Sarah; Magnelli, Benjamin; Carollo, C. Marcella; Middelberg, Enno

2018-03-01

Using infrared data from the Herschel Space Observatory and Karl G. Jansky Very Large Array 3 GHz observations in the COSMOS field, we investigate the redshift evolution of the infrared-radio correlation (IRRC) for star-forming galaxies (SFGs) we classify as either spheroid- or disc-dominated based on their morphology. The sample predominantly consists of disc galaxies with stellar mass ≳ 1010 M⊙, and residing on the star-forming main sequence (MS). After the removal of AGN using standard approaches, we observe a significant difference between the redshift evolution of the median IR/radio ratio \\overline{q}_{TIR} of (i) a sample of ellipticals, plus discs with a substantial bulge component (`spheroid-dominated' SFGs) and, (ii) virtually pure discs and irregular systems (`disc-dominated' SFGs). The spheroid-dominated population follows a declining \\overline{q}_{TIR} versus z trend similar to that measured in recent evolutionary studies of the IRRC. However, for disc-dominated galaxies, where radio and IR emission should be linked to star formation in the most straightforward way, we measure very little change in \\overline{q}_{TIR}. This suggests that low-redshift calibrations of radio emission as a star formation rate (SFR) tracer may remain valid out to at least z ≃ 1-1.5 for pure star-forming systems. We find that the different redshift evolution of qTIR for the spheroid- and disc-dominated sample is mainly due to an increasing radio excess for spheroid-dominated galaxies at z ≳ 0.8, hinting at some residual AGN activity in these systems. This finding demonstrates that in the absence of AGN, the IRRC is independent of redshift, and that radio observations can therefore be used to estimate SFRs at all redshifts for genuinely star-forming galaxies.

Over the hill at 24: persistent age-related cognitive-motor decline in reaction times in an ecologically valid video game task begins in early adulthood.

PubMed

Thompson, Joseph J; Blair, Mark R; Henrey, Andrew J

2014-01-01

Typically studies of the effects of aging on cognitive-motor performance emphasize changes in elderly populations. Although some research is directly concerned with when age-related decline actually begins, studies are often based on relatively simple reaction time tasks, making it impossible to gauge the impact of experience in compensating for this decline in a real world task. The present study investigates age-related changes in cognitive motor performance through adolescence and adulthood in a complex real world task, the real-time strategy video game StarCraft 2. In this paper we analyze the influence of age on performance using a dataset of 3,305 players, aged 16-44, collected by Thompson, Blair, Chen & Henrey [1]. Using a piecewise regression analysis, we find that age-related slowing of within-game, self-initiated response times begins at 24 years of age. We find no evidence for the common belief expertise should attenuate domain-specific cognitive decline. Domain-specific response time declines appear to persist regardless of skill level. A second analysis of dual-task performance finds no evidence of a corresponding age-related decline. Finally, an exploratory analyses of other age-related differences suggests that older participants may have been compensating for a loss in response speed through the use of game mechanics that reduce cognitive load.

Over the Hill at 24: Persistent Age-Related Cognitive-Motor Decline in Reaction Times in an Ecologically Valid Video Game Task Begins in Early Adulthood

PubMed Central

Thompson, Joseph J.; Blair, Mark R.; Henrey, Andrew J.

2014-01-01

Typically studies of the effects of aging on cognitive-motor performance emphasize changes in elderly populations. Although some research is directly concerned with when age-related decline actually begins, studies are often based on relatively simple reaction time tasks, making it impossible to gauge the impact of experience in compensating for this decline in a real world task. The present study investigates age-related changes in cognitive motor performance through adolescence and adulthood in a complex real world task, the real-time strategy video game StarCraft 2. In this paper we analyze the influence of age on performance using a dataset of 3,305 players, aged 16-44, collected by Thompson, Blair, Chen & Henrey [1]. Using a piecewise regression analysis, we find that age-related slowing of within-game, self-initiated response times begins at 24 years of age. We find no evidence for the common belief expertise should attenuate domain-specific cognitive decline. Domain-specific response time declines appear to persist regardless of skill level. A second analysis of dual-task performance finds no evidence of a corresponding age-related decline. Finally, an exploratory analyses of other age-related differences suggests that older participants may have been compensating for a loss in response speed through the use of game mechanics that reduce cognitive load. PMID:24718593

Influence of genetic background, salinity, and inoculum size on growth of the ichthyotoxic golden alga (Prymnesium parvum)

USGS Publications Warehouse

Rashel, Rakib H.; Patino, Reynaldo

2017-01-01

Salinity (5–30) effects on golden alga growth were determined at a standard laboratory temperature (22 °C) and one associated with natural blooms (13 °C). Inoculum-size effects were determined over a wide size range (100–100,000 cells ml−1). A strain widely distributed in the USA, UTEX-2797 was the primary study subject but another of limited distribution, UTEX-995 was used to evaluate growth responses in relation to genetic background. Variables examined were exponential growth rate (r), maximum cell density (max-D) and, when inoculum size was held constant (100 cells ml−1), density at onset of exponential growth (early-D). In UTEX-2797, max-D increased as salinity increased from 5 to ∼10–15 and declined thereafter regardless of temperature but r remained generally stable and only declined at salinity of 25–30. In addition, max-D correlated positively with r and early-D, the latter also being numerically highest at salinity of 15. In UTEX-995, max-D and r responded similarly to changes in salinity − they remained stable at salinity of 5–10 and 5–15, respectively, and declined at higher salinity. Also, max-D correlated with r but not early-D. Inoculum size positively and negatively influenced max-D and r, respectively, in both strains and these effects were significant even when the absolute size difference was small (100 versus 1000 cells ml−1). When cultured under similar conditions, UTEX-2797 grew faster and to much higher density than UTEX-995. In conclusion, (1) UTEX-2797’s superior growth performance may explain its relatively wide distribution in the USA, (2) the biphasic growth response of UTEX-2797 to salinity variation, with peak abundance at salinity of 10–15, generally mirrors golden alga abundance-salinity associations in US inland waters, and (3) early cell density – whether artificially manipulated or naturally attained – can influence UTEX-2797 bloom potential.

The Suppression of Star Formation in Low-Mass Galaxies Caused by the Reionization of their Local Patch

NASA Astrophysics Data System (ADS)

Dawoodbhoy, Taha; Shapiro, Paul R.; Choi, Jun-Hwan; Ocvirk, Pierre; Gillet, Nicolas; Aubert, Dominique; Iliev, Ilian T.; Teyssier, Romain; Yepes, Gustavo; Sullivan, David; Knebe, Alexander; Gottloeber, Stefan; D'Aloisio, Anson; Park, Hyunbae; Hoffman, Yehuda; Stranex, Timothy

2017-01-01

The first stars and galaxies released enough ionizing radiation into the intergalactic medium (IGM) to ionize almost all the hydrogen atoms there by redshift z ~ 6. This process was "patchy" --- ionized zones grew in size over time until they overlapped to finish reionization.The photoheating associated with reionization caused a negative feedback on the galactic sources of reionization that suppressed star formation in low-mass galactic halos, especially those below 109 M⊙. To establish the causal connection between reionization and this suppression, we analyze the results of CoDa ("Cosmic Dawn"), the first fully-coupled radiation-hydrodynamical simulation of reionization and galaxy formation in the Local Universe, in a volume large enough to model reionization globally but with enough resolving power to follow all the atomic-cooling galactic halos in that volume. A 90 Mpc box was simulated from a constrained realization of primordial fluctuations, chosen to reproduce present-day features of the Local Group, including the Milky Way and M31, and the local universe beyond, including the Virgo cluster, with 40963 N-body particles for the dark matter and 40963 cells for the atomic gas and ionizing radiation. We use these results to show that the star formation rate in haloes below 109 M⊙ in different patches of the universe declined when each patch was reionized. Star formation in much more massive haloes continued, however. As a result, the earliest patches to develop structure and reionize ultimately produced more stars than they needed to reionize themselves, exporting their starlight to help reionize the regions that developed structure late.

The Suppression of Star Formation in Low-Mass Galaxies Caused by the Reionization of their Local Patch

NASA Astrophysics Data System (ADS)

Dawoodbhoy, Taha; Shapiro, Paul R.; Choi, Jun-Hwan; Ocvirk, Pierre; Gillet, Nicolas; Aubert, Dominique; Iliev, Ilian T.; Teyssier, Romain; Yepes, Gustavo; Sullivan, David; Knebe, Alexander; Gottloeber, Stefan; D'Aloisio, Anson; Park, Hyunbae; Hoffman, Yehuda; Stranex, Timothy

2017-06-01

The first stars and galaxies released enough ionizing radiation into the intergalactic medium (IGM) to ionize almost all the hydrogen atoms there by redshift z ~ 6. This process was "patchy" --- ionized zones grew in size over time until they overlapped to finish reionization. The photoheating associated with reionization caused a negative feedback on the galactic sources of reionization that suppressed star formation in low-mass galactic halos, especially those below 109 M⊙. To establish the causal connection between reionization and this suppression, we analyze the results of CoDa ("Cosmic Dawn"), the first fully-coupled radiation-hydrodynamical simulation of reionization and galaxy formation in the Local Universe, in a volume large enough to model reionization globally but with enough resolving power to follow all the atomic-cooling galactic halos in that volume. A 90 Mpc box was simulated from a constrained realization of primordial fluctuations, chosen to reproduce present-day features of the Local Group, including the Milky Way and M31, and the local universe beyond, including the Virgo cluster, with 40963 N-body particles for the dark matter and 40963 cells for the atomic gas and ionizing radiation. We use these results to show that the star formation rate in haloes below 109 M⊙ in different patches of the universe declined when each patch was reionized. Star formation in much more massive haloes continued, however. As a result, the earliest patches to develop structure and reionize ultimately produced more stars than they needed to reionize themselves, exporting their starlight to help reionize the regions that developed structure late.

The emerging planetary nebula CRL 618 and its unsettled central star(s)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Balick, B.; Riera, A.; Raga, A.

We report deep long-slit emission-line spectra, the line flux ratios, and Doppler profile shapes of various bright optical lines. The low-ionization lines (primarily [N I], [O I], [S II], and [N II]) originate in shocked knots, as reported by many previous observers. Dust-scattered lines of higher ionization are seen throughout the lobes but do not peak in the knots. Our analysis of these line profiles and the readily discernible stellar continuum shows that (1) the central star is an active symbiotic (whose spectrum resembles the central stars of highly bipolar and young planetary nebulae such as M2-9 and Hen2-437) whosemore » compact companion shows a WC8-type spectrum, (2) extended nebular lines of [O III] and He I originate in the heavily obscured nuclear H II region, and (3) the Balmer lines observed throughout the lobes are dominated by reflected Hα emission from the symbiotic star. Comparing our line ratios with those observed historically shows that (1) the [O III]/Hβ and He I/Hβ ratios have been steadily rising by large amounts throughout the nebula, (2) the Hα/Hβ ratio is steadily decreasing while Hγ/Hβ remains nearly constant, and (3) the low-ionization line ratios formed in the shocked knots have been in decline in different ways at various locations. We show that the first two of these results might be expected if the symbiotic central star has been active and if its bright Hα line has faded significantly in the past 20 years.« less

WHAT IS THE SHELL AROUND R CORONAE BOREALIS?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Montiel, Edward J.; Clayton, Geoffrey C.; Marcello, Dominic C.

2015-07-15

The hydrogen-deficient, carbon-rich R Coronae Borealis (RCB) stars are known for being prolific producers of dust which causes their large iconic declines in brightness. Several RCB stars, including R Coronae Borealis (R CrB), itself, have large extended dust shells seen in the far-infrared. The origin of these shells is uncertain but they may give us clues to the evolution of the RCB stars. The shells could form in three possible ways. (1) They are fossil Planetary Nebula (PN) shells, which would exist if RCB stars are the result of a final, helium-shell flash, (2) they are material left over frommore » a white-dwarf (WD) merger event which formed the RCB stars, or (3) they are material lost from the star during the RCB phase. Arecibo 21 cm observations establish an upper limit on the column density of H I in the R CrB shell implying a maximum shell mass of ≲0.3 M{sub ☉}. A low-mass fossil PN shell is still a possible source of the shell although it may not contain enough dust. The mass of gas lost during a WD merger event will not condense enough dust to produce the observed shell, assuming a reasonable gas-to-dust ratio. The third scenario where the shell around R CrB has been produced during the star’s RCB phase seems most likely to produce the observed mass of dust and the observed size of the shell. But this means that R CrB has been in its RCB phase for ∼10{sup 4} years.« less

On the Observability of Individual Population III Stars and Their Stellar-mass Black Hole Accretion Disks through Cluster Caustic Transits

NASA Astrophysics Data System (ADS)

Windhorst, Rogier A.; Timmes, F. X.; Wyithe, J. Stuart B.; Alpaslan, Mehmet; Andrews, Stephen K.; Coe, Daniel; Diego, Jose M.; Dijkstra, Mark; Driver, Simon P.; Kelly, Patrick L.; Kim, Duho

2018-02-01

We summarize panchromatic Extragalactic Background Light data to place upper limits on the integrated near-infrared surface brightness (SB) that may come from Population III stars and possible accretion disks around their stellar-mass black holes (BHs) in the epoch of First Light, broadly taken from z ≃ 7–17. Theoretical predictions and recent near-infrared power spectra provide tighter constraints on their sky signal. We outline the physical properties of zero-metallicity Population III stars from MESA stellar evolution models through helium depletion and of BH accretion disks at z≳ 7. We assume that second-generation non-zero-metallicity stars can form at higher multiplicity, so that BH accretion disks may be fed by Roche-lobe overflow from lower-mass companions. We use these near-infrared SB constraints to calculate the number of caustic transits behind lensing clusters that the James Webb Space Telescope and the next-generation ground-based telescopes may observe for both Population III stars and their BH accretion disks. Typical caustic magnifications can be μ ≃ {10}4{--}{10}5, with rise times of hours and decline times of ≲ 1 year for cluster transverse velocities of {v}T≲ 1000 km s‑1. Microlensing by intracluster-medium objects can modify transit magnifications but lengthen visibility times. Depending on BH masses, accretion-disk radii, and feeding efficiencies, stellar-mass BH accretion-disk caustic transits could outnumber those from Population III stars. To observe Population III caustic transits directly may require monitoring 3–30 lensing clusters to {AB}≲ 29 mag over a decade.

Can galaxy growth be sustained through HI-rich minor mergers?

NASA Astrophysics Data System (ADS)

Lehnert, M. D.; van Driel, W.; Minchin, R.

2016-05-01

Local galaxies with specific star-formation rates (star-formation rate per unit mass; sSFR ~ 0.2-10 Gyr-1) that are as high as distant galaxies (z ≈ 1-3), are very rich in Hi. Those with low stellar masses, M⋆ = 108-9 M⊙, for example, have MHI/M⋆ ≈ 5-30. Using continuity arguments, whereby the specific merger rate is hypothesized to be proportional to the specific star-formation rate, along with Hi gas mass measurements for local galaxies with high sSFR, we estimate that moderate-mass galaxies, M⋆ = 109-10.5 M⊙, can acquire enough gas through minor mergers (stellar mass ratios ~4-100) to sustain their star formation rates at z ~ 2. The relative fraction of the gas accreted through minor mergers declines with increasing stellar mass, and for the most massive galaxies considered, M⋆ = 1010.5-11 M⊙, this accretion rate is insufficient to sustain their star formation. We checked our minor merger hypothesis at z = 0 using the same methodology, but now with relations for local normal galaxies, and find that minor mergers cannot account for their specific growth rates, in agreement with observations of Hi-rich satellites around nearby spirals. We discuss a number of attractive features, such as a natural downsizing effect, in using minor mergers with extended Hi disks to support star formation at high redshift. The answer to the question posed by the title, "Can galaxy growth be sustained through Hi-rich minor mergers?", is "maybe", but only for relatively low-mass galaxies and at high redshift.

THE SOLAR NEIGHBORHOOD. XXV. DISCOVERY OF NEW PROPER MOTION STARS WITH 0.''40 yr{sup -1} > {mu} {>=} 0.''18 yr{sup -1} BETWEEN DECLINATIONS -47{sup 0} AND 00{sup 0}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boyd, Mark R.; Winters, Jennifer G.; Henry, Todd J.

2011-07-15

We present 2817 new southern proper motion systems with 0.''40 yr{sup -1} > {mu} {>=} 0.''18 yr{sup -1} and declination between -47{sup 0} and 00{sup 0}. This is a continuation of the SuperCOSMOS-RECONS (SCR) proper motion searches of the southern sky. We use the same photometric relations as previous searches to provide distance estimates based on the assumption that the objects are single main-sequence stars. We find 79 new red dwarf systems predicted to be within 25 pc, including a few new components of previously known systems. Two systems-SCR 1731-2452 at 9.5 pc and SCR 1746-3214 at 9.9 pc-are anticipatedmore » to be within 10 pc. We also find 23 new white dwarf (WD) candidates with distance estimates of 15-66 pc, as well as 360 new red subdwarf candidates. With this search, we complete the SCR sweep of the southern sky for stars with {mu} {>=} 0.''18 yr{sup -1} and R{sub 59F} {<=} 16.5, resulting in a total of 5042 objects in 4724 previously unreported proper motion systems. Here we provide selected comprehensive lists from our SCR proper motion search to date, including 152 red dwarf systems estimated to be within 25 pc (9 within 10 pc), 46 WDs (10 within 25 pc), and 598 subdwarf candidates. The results of this search suggest that there are more nearby systems to be found at fainter magnitudes and lower proper motion limits than those probed so far.« less

Extreme Wildlife Declines and Concurrent Increase in Livestock Numbers in Kenya: What Are the Causes?

PubMed Central

Ogutu, Joseph O.; Piepho, Hans-Peter; Said, Mohamed Y.; Ojwang, Gordon O.; Njino, Lucy W.; Kifugo, Shem C.; Wargute, Patrick W.

2016-01-01

There is growing evidence of escalating wildlife losses worldwide. Extreme wildlife losses have recently been documented for large parts of Africa, including western, Central and Eastern Africa. Here, we report extreme declines in wildlife and contemporaneous increase in livestock numbers in Kenya rangelands between 1977 and 2016. Our analysis uses systematic aerial monitoring survey data collected in rangelands that collectively cover 88% of Kenya’s land surface. Our results show that wildlife numbers declined on average by 68% between 1977 and 2016. The magnitude of decline varied among species but was most extreme (72–88%) and now severely threatens the population viability and persistence of warthog, lesser kudu, Thomson’s gazelle, eland, oryx, topi, hartebeest, impala, Grevy’s zebra and waterbuck in Kenya’s rangelands. The declines were widespread and occurred in most of the 21 rangeland counties. Likewise to wildlife, cattle numbers decreased (25.2%) but numbers of sheep and goats (76.3%), camels (13.1%) and donkeys (6.7%) evidently increased in the same period. As a result, livestock biomass was 8.1 times greater than that of wildlife in 2011–2013 compared to 3.5 times in 1977–1980. Most of Kenya’s wildlife (ca. 30%) occurred in Narok County alone. The proportion of the total “national” wildlife population found in each county increased between 1977 and 2016 substantially only in Taita Taveta and Laikipia but marginally in Garissa and Wajir counties, largely reflecting greater wildlife losses elsewhere. The declines raise very grave concerns about the future of wildlife, the effectiveness of wildlife conservation policies, strategies and practices in Kenya. Causes of the wildlife declines include exponential human population growth, increasing livestock numbers, declining rainfall and a striking rise in temperatures but the fundamental cause seems to be policy, institutional and market failures. Accordingly, we thoroughly evaluate wildlife conservation policy in Kenya. We suggest policy, institutional and management interventions likely to succeed in reducing the declines and restoring rangeland health, most notably through strengthening and investing in community and private wildlife conservancies in the rangelands. PMID:27676077

Extreme Wildlife Declines and Concurrent Increase in Livestock Numbers in Kenya: What Are the Causes?

PubMed

Ogutu, Joseph O; Piepho, Hans-Peter; Said, Mohamed Y; Ojwang, Gordon O; Njino, Lucy W; Kifugo, Shem C; Wargute, Patrick W

There is growing evidence of escalating wildlife losses worldwide. Extreme wildlife losses have recently been documented for large parts of Africa, including western, Central and Eastern Africa. Here, we report extreme declines in wildlife and contemporaneous increase in livestock numbers in Kenya rangelands between 1977 and 2016. Our analysis uses systematic aerial monitoring survey data collected in rangelands that collectively cover 88% of Kenya's land surface. Our results show that wildlife numbers declined on average by 68% between 1977 and 2016. The magnitude of decline varied among species but was most extreme (72-88%) and now severely threatens the population viability and persistence of warthog, lesser kudu, Thomson's gazelle, eland, oryx, topi, hartebeest, impala, Grevy's zebra and waterbuck in Kenya's rangelands. The declines were widespread and occurred in most of the 21 rangeland counties. Likewise to wildlife, cattle numbers decreased (25.2%) but numbers of sheep and goats (76.3%), camels (13.1%) and donkeys (6.7%) evidently increased in the same period. As a result, livestock biomass was 8.1 times greater than that of wildlife in 2011-2013 compared to 3.5 times in 1977-1980. Most of Kenya's wildlife (ca. 30%) occurred in Narok County alone. The proportion of the total "national" wildlife population found in each county increased between 1977 and 2016 substantially only in Taita Taveta and Laikipia but marginally in Garissa and Wajir counties, largely reflecting greater wildlife losses elsewhere. The declines raise very grave concerns about the future of wildlife, the effectiveness of wildlife conservation policies, strategies and practices in Kenya. Causes of the wildlife declines include exponential human population growth, increasing livestock numbers, declining rainfall and a striking rise in temperatures but the fundamental cause seems to be policy, institutional and market failures. Accordingly, we thoroughly evaluate wildlife conservation policy in Kenya. We suggest policy, institutional and management interventions likely to succeed in reducing the declines and restoring rangeland health, most notably through strengthening and investing in community and private wildlife conservancies in the rangelands.

First results from the oil sands passive air monitoring network for polycyclic aromatic compounds.

PubMed

Schuster, Jasmin K; Harner, Tom; Su, Ky; Mihele, Cristian; Eng, Anita

2015-03-03

Results are reported from an ongoing passive air monitoring study for polycyclic aromatic compounds (PACs) in the Athabasca oil sands region in Alberta, Canada. Polyurethane foam (PUF) disk passive air samplers were deployed for consecutive 2-month periods from November 2010 to June 2012 at 17 sites. Samples were analyzed for polycyclic aromatic hydrocarbons (PAHs), alkylated PAHs, dibenzothiophene and its alkylated derivatives (DBTs). Relative to parent PAHs, alkylated PAHs and DBTs are enriched in bitumen and therefore considered to be petrogenic markers. Concentrations in air were in the range 0.03-210 ng/m(3), 0.15-230 ng/m(3) and 0.01-61 ng/m(3) for ∑PAHs, ∑alkylated PAHs and ΣDBTs, respectively. An exponential decline of the PAC concentrations in air with distance from mining areas and related petrogenic sources was observed. The most significant exponential declines were for the alkylated PAHs and DBTs and attributed to their association with mining-related emissions and near-source deposition, due to their lower volatility and greater association with depositing particles. Seasonal trends in concentrations in air for PACs were not observed for any of the compound classes. However, a forest fire episode during April to July 2011 resulted in greatly elevated PAH levels at all passive sampling locations. Alkylated PAHs and DBTs were not elevated during the forest fire period, supporting their association with petrogenic sources. Based on the results of this study, an "Athabasca PAC profile" is proposed as a potential source marker for the oil sands region. The profile is characterized by ∑PAHs/∑Alkylated PAHs = ∼0.2 and ∑PAHs/∑DBTs = ∼5.

Occupational injuries in Italy: risk factors and long term trend (1951-98)

PubMed Central

Fabiano, B; Curro, F; Pastorino, R

2001-01-01

OBJECTIVES—Trends in the rates of total injuries and fatal accidents in the different sectors of Italian industries were explored during the period 1951-98. Causes and dynamics of injury were also studied for setting priorities for improving safety standards.
METHODS—Data on occupational injuries from the National Organisation for Labour Injury Insurance were combined with data from the State Statistics Institute to highlight the interaction between the injury frequency index trend and the production cycle—that is, the evolution of industrial production throughout the years. Multiple regression with log transformed rates was adopted to model the trends of occupational fatalities for each industrial group.
RESULTS—The ratios between the linked indices of injury frequency and industrial production showed a good correlation over the whole period. A general decline in injuries was found across all sectors, with values ranging from 79.86% in the energy group to 23.32% in the textile group. In analysing fatalities, the trend seemed to be more clearly decreasing than the trend of total injuries, including temporary and permanent disabilities; the fatalities showed an exponential decrease according to multiple regression, with an annual decline equal to 4.42%.
CONCLUSIONS—The overall probability of industrial fatal accidents in Italy tended to decrease exponentially by year. The most effective actions in preventing injuries were directed towards fatal accidents. By analysing the rates of fatal accident in the different sectors, appropriate targets and priorities for increased strategies to prevent injuries can be suggested. The analysis of the dynamics and the material causes of injuries showed that still more consideration should be given to human and organisational factors.


Keywords: labour injuries; severity; regression model PMID:11303083

The Galaxy mass function up to z =4 in the GOODS-MUSIC sample: into the epoch of formation of massive galaxies

NASA Astrophysics Data System (ADS)

Fontana, A.; Salimbeni, S.; Grazian, A.; Giallongo, E.; Pentericci, L.; Nonino, M.; Fontanot, F.; Menci, N.; Monaco, P.; Cristiani, S.; Vanzella, E.; de Santis, C.; Gallozzi, S.

2006-12-01

Aims.The goal of this work is to measure the evolution of the Galaxy Stellar Mass Function and of the resulting Stellar Mass Density up to redshift ≃4, in order to study the assembly of massive galaxies in the high redshift Universe. Methods: .We have used the GOODS-MUSIC catalog, containing 3000 Ks-selected galaxies with multi-wavelength coverage extending from the U band to the Spitzer 8 μm band, of which 27% have spectroscopic redshifts and the remaining fraction have accurate photometric redshifts. On this sample we have applied a standard fitting procedure to measure stellar masses. We compute the Galaxy Stellar Mass Function and the resulting Stellar Mass Density up to redshift ≃4, taking into proper account the biases and incompleteness effects. Results: .Within the well known trend of global decline of the Stellar Mass Density with redshift, we show that the decline of the more massive galaxies may be described by an exponential timescale of ≃6 Gyr up to z≃ 1.5, and proceeds much faster thereafter, with an exponential timescale of ≃0.6 Gyr. We also show that there is some evidence for a differential evolution of the Galaxy Stellar Mass Function, with low mass galaxies evolving faster than more massive ones up to z≃ 1{-}1.5 and that the Galaxy Stellar Mass Function remains remarkably flat (i.e. with a slope close to the local one) up to z≃ 1{-}1.3. Conclusions: .The observed behaviour of the Galaxy Stellar Mass Function is consistent with a scenario where about 50% of present-day massive galaxies formed at a vigorous rate in the epoch between redshift 4 and 1.5, followed by a milder evolution until the present-day epoch.

Suppression of invasive lake trout in an isolated backcountry lake in Glacier National Park

USGS Publications Warehouse

Fredenberg, C. R.; Muhlfeld, Clint C.; Guy, Christopher S.; D'Angelo, Vincent S.; Downs, Christopher C.; Syslo, John M.

2017-01-01

Fisheries managers have implemented suppression programmes to control non-native lake trout, Salvelinus namaycush (Walbaum), in several lakes throughout the western United States. This study determined the feasibility of experimentally suppressing lake trout using gillnets in an isolated backcountry lake in Glacier National Park, Montana, USA, for the conservation of threatened bull trout, Salvelinus confluentus (Suckley). The demographics of the lake trout population during suppression (2009–2013) were described, and those data were used to assess the effects of suppression scenarios on population growth rate (λ) using an age-structured population model. Model simulations indicated that the population was growing exponentially (λ = 1.23, 95% CI: 1.16–1.28) prior to suppression. However, suppression resulted in declining λ(0.61–0.79) for lake trout, which was concomitant with stable bull trout adult abundances. Continued suppression at or above observed exploitation levels is needed to ensure continued population declines.

VizieR Online Data Catalog: Adiabatic mass loss in binary stars. II. (Ge+, 2015)

NASA Astrophysics Data System (ADS)

Ge, H.; Webbink, R. F.; Chen, X.; Han, Z.

2016-02-01

In the limit of extremely rapid mass transfer, the response of a donor star in an interacting binary becomes asymptotically one of adiabatic expansion. We survey here adiabatic mass loss from Population I stars (Z=0.02) of mass 0.10M⊙-100M⊙ from the zero-age main sequence to the base of the giant branch, or to central hydrogen exhaustion for lower main sequence stars. The logarithmic derivatives of radius with respect to mass along adiabatic mass-loss sequences translate into critical mass ratios for runaway (dynamical timescale) mass transfer, evaluated here under the assumption of conservative mass transfer. For intermediate- and high-mass stars, dynamical mass transfer is preceded by an extended phase of thermal timescale mass transfer as the star is stripped of most of its envelope mass. The critical mass ratio qad (throughout this paper, we follow the convention of defining the binary mass ratio as q{equiv}Mdonor/Maccretor) above which this delayed dynamical instability occurs increases with advancing evolutionary age of the donor star, by ever-increasing factors for more massive donors. Most intermediate- or high-mass binaries with nondegenerate accretors probably evolve into contact before manifesting this instability. As they approach the base of the giant branch, however, and begin developing a convective envelope, qad plummets dramatically among intermediate-mass stars, to values of order unity, and a prompt dynamical instability occurs. Among low-mass stars, the prompt instability prevails throughout main sequence evolution, with qad declining with decreasing mass, and asymptotically approaching qad=2/3, appropriate to a classical isentropic n=3/2 polytrope. Our calculated qad values agree well with the behavior of time-dependent models by Chen & Han (2003MNRAS.341..662C) of intermediate-mass stars initiating mass transfer in the Hertzsprung gap. Application of our results to cataclysmic variables, as systems that must be stable against rapid mass transfer, nicely circumscribes the range in qad as a function of the orbital period in which they are found. These results are intended to advance the verisimilitude of population synthesis models of close binary evolution. (3 data files).

Van Gogh's Starry Nights, Lincoln's Moon, Shakespeare's Stars, and More: Tales of Astronomy in Art, History, and Literature

NASA Astrophysics Data System (ADS)

Olson, Donald

2009-10-01

How do astronomical methods make it possible to calculate dates and times for Vincent van Gogh's night-sky paintings? Why is there a blood-red sky in Edvard Munch's The Scream? On what dates did Ansel Adams create his moonrise photographs in Yosemite? How can the 18.6-year cycle of the lunar nodes and the Moon's declination on the night of August 29-30, 1857, explain a long-standing mystery about Abraham Lincoln's honesty in the murder case known as the almanac trial? Why is a bright star described in Act 1, Scene 1, of Hamlet? To answer questions like these, our Texas State group has published a series of articles over the last two decades, applying astronomy to art, history, and literature.

Giant Planets around FGK Stars Probably Form through Core Accretion

NASA Astrophysics Data System (ADS)

Wang, Wei; Wang, Liang; Li, Xiang; Chen, Yuqin; Zhao, Gang

2018-06-01

We present a statistical study of the planet–metallicity (P–M) correlation by comparing the 744 stars with candidate planets (SWPs) in the Kepler field that have been observed with LAMOST, and a sample of distance-independent, fake “twin” stars in the Kepler field with no planet reported (CKSNPs) yet. With well-defined and carefully selected large samples, we find for the first time a turnoff P–M correlation of Δ[Fe/H]SWPs–SNPs, which on average increases from ∼0.00 ± 0.03 dex to 0.06 ± 0.03 dex, and to 0.12 ± 0.03 for stars with Earth-, Neptune-, and Jupiter-sized planets successively, and then declines to ∼‑0.01 ± 0.03 dex for more massive planets or brown dwarfs. Moreover, the percentage of those systems with positive Δ[Fe/H] has the same turnoff pattern. We also find that FG-type stars follow this general trend, but K-type stars are different. Moderate metal enhancement (∼0.1–0.2 dex) for K-type stars with planets of radii between 2 and 4 R ⊕, compared to CKSNPs is observed, which indicates much higher metallicities are required for Super-Earths and Neptune-sized planets to form around K-type stars. We point out that the P–M correlation is actually metallicity-dependent, i.e., the correlation is positive at solar and supersolar metallicities, and negative at subsolar metallicities. No steady increase of Δ[Fe/H] against planet sizes is observed for rocky planets, excluding the pollution scenario as a major mechanism for the P–M correlation. All these clues suggest that giant planets probably form differently from rocky planets or more massive planets/brown dwarfs, and the core accretion scenario is highly favored, and high metallicity is a prerequisite for massive planets to form.

NuSTAR Discovery of a Cyclotron Line in KS 1947+300

NASA Technical Reports Server (NTRS)

Furst, Felix; Pottschmidt, Katja; Wilms, Jorn; Kennea, Jamie; Bachetti, Matteo; Bellm, Eric; Boggs, Steven E.; Chakrabarty, Deepto; Christensen, Finn E.; Craig, William W.;

Hubble Space Telescope Scattered-light Imaging and Modeling of the Edge-on Protoplanetary Disk ESO-Hα 569

NASA Astrophysics Data System (ADS)

Wolff, Schuyler G.; Perrin, Marshall D.; Stapelfeldt, Karl; Duchêne, Gaspard; Ménard, Francois; Padgett, Deborah; Pinte, Christophe; Pueyo, Laurent; Fischer, William J.

2017-12-01

We present new Hubble Space Telescope (HST) Advanced Camera for Surveys observations and detailed models for a recently discovered edge-on protoplanetary disk around ESO-Hα 569 (a low-mass T Tauri star in the Cha I star-forming region). Using radiative transfer models, we probe the distribution of the grains and overall shape of the disk (inclination, scale height, dust mass, flaring exponent, and surface/volume density exponent) by model fitting to multiwavelength (F606W and F814W) HST observations together with a literature-compiled spectral energy distribution. A new tool set was developed for finding optimal fits of MCFOST radiative transfer models using the MCMC code emcee to efficiently explore the high-dimensional parameter space. It is able to self-consistently and simultaneously fit a wide variety of observables in order to place constraints on the physical properties of a given disk, while also rigorously assessing the uncertainties in those derived properties. We confirm that ESO-Hα 569 is an optically thick nearly edge-on protoplanetary disk. The shape of the disk is well-described by a flared disk model with an exponentially tapered outer edge, consistent with models previously advocated on theoretical grounds and supported by millimeter interferometry. The scattered-light images and spectral energy distribution are best fit by an unusually high total disk mass (gas+dust assuming a ratio of 100:1) with a disk-to-star mass ratio of 0.16.

Economic growth and CO2 emissions: an investigation with smooth transition autoregressive distributed lag models for the 1800-2014 period in the USA.

PubMed

Bildirici, Melike; Ersin, Özgür Ömer

2018-01-01

The study aims to combine the autoregressive distributed lag (ARDL) cointegration framework with smooth transition autoregressive (STAR)-type nonlinear econometric models for causal inference. Further, the proposed STAR distributed lag (STARDL) models offer new insights in terms of modeling nonlinearity in the long- and short-run relations between analyzed variables. The STARDL method allows modeling and testing nonlinearity in the short-run and long-run parameters or both in the short- and long-run relations. To this aim, the relation between CO 2 emissions and economic growth rates in the USA is investigated for the 1800-2014 period, which is one of the largest data sets available. The proposed hybrid models are the logistic, exponential, and second-order logistic smooth transition autoregressive distributed lag (LSTARDL, ESTARDL, and LSTAR2DL) models combine the STAR framework with nonlinear ARDL-type cointegration to augment the linear ARDL approach with smooth transitional nonlinearity. The proposed models provide a new approach to the relevant econometrics and environmental economics literature. Our results indicated the presence of asymmetric long-run and short-run relations between the analyzed variables that are from the GDP towards CO 2 emissions. By the use of newly proposed STARDL models, the results are in favor of important differences in terms of the response of CO 2 emissions in regimes 1 and 2 for the estimated LSTAR2DL and LSTARDL models.

NuSTAR DISCOVERY OF A CYCLOTRON LINE IN KS 1947+300

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fürst, Felix; Bellm, Eric; Harrison, Fiona

2014-04-01

We present a spectral analysis of three simultaneous Nuclear Spectroscopy Telescope Array and Swift/XRT observations of the transient Be-neutron star binary KS 1947+300 taken during its outburst in 2013/2014. These broadband observations were supported by Swift/XRT monitoring snapshots every three days, which we use to study the evolution of the spectrum over the outburst. We find strong changes of the power-law photon index, which shows a weak trend of softening with increasing X-ray flux. The neutron star shows very strong pulsations with a period of P ≈ 18.8 s. The 0.8-79 keV broadband spectrum can be described by a power law with anmore » exponential cutoff and a blackbody component at low energies. During the second observation we detect a cyclotron resonant scattering feature at 12.5 keV, which is absent in the phase-averaged spectra of observations 1 and 3. Pulse phase-resolved spectroscopy reveals that the strength of the feature changes strongly with pulse phase and is most prominent during the broad minimum of the pulse profile. At the same phases the line also becomes visible in the first and third observation at the same energy. This discovery implies that KS 1947+300 has a magnetic field strength of B ≈ 1.1 × 10{sup 12}(1 + z) G, which is at the lower end of known cyclotron line sources.« less

The evolution of kicked stellar-mass black holes in star cluster environments

NASA Astrophysics Data System (ADS)

Webb, Jeremy J.; Leigh, Nathan W. C.; Singh, Abhishek; Ford, K. E. Saavik; McKernan, Barry; Bellovary, Jillian

2018-03-01

We consider how dynamical friction acts on black holes that receive a velocity kick while located at the centre of a gravitational potential, analogous to a star cluster, due to either a natal kick or the anisotropic emission of gravitational waves during a black hole-black hole merger. Our investigation specifically focuses on how well various Chandrasekhar-based dynamical friction models can predict the orbital decay of kicked black holes with mbh ≲ 100 M⊙ due to an inhomogeneous background stellar field. In general, the orbital evolution of a kicked black hole follows that of a damped oscillator where two-body encounters and dynamical friction serve as sources of damping. However, we find models for approximating the effects of dynamical friction do not accurately predict the amount of energy lost by the black hole if the initial kick velocity vk is greater than the stellar velocity dispersion σ. For all kick velocities, we also find that two-body encounters with nearby stars can cause the energy evolution of a kicked BH to stray significantly from standard dynamical friction theory as encounters can sometimes lead to an energy gain. For larger kick velocities, we find the orbital decay of a black hole departs from classical theory completely as the black hole's orbital amplitude decays linearly with time as opposed to exponentially. Therefore, we have developed a linear decay formalism, which scales linearly with black hole mass and v_k/σ in order to account for the variations in the local gravitational potential.

The young star cluster population of M51 with LEGUS - II. Testing environmental dependences

NASA Astrophysics Data System (ADS)

Messa, Matteo; Adamo, A.; Calzetti, D.; Reina-Campos, M.; Colombo, D.; Schinnerer, E.; Chandar, R.; Dale, D. A.; Gouliermis, D. A.; Grasha, K.; Grebel, E. K.; Elmegreen, B. G.; Fumagalli, M.; Johnson, K. E.; Kruijssen, J. M. D.; Östlin, G.; Shabani, F.; Smith, L. J.; Whitmore, B. C.

2018-06-01

It has recently been established that the properties of young star clusters (YSCs) can vary as a function of the galactic environment in which they are found. We use the cluster catalogue produced by the Legacy Extragalactic UV Survey (LEGUS) collaboration to investigate cluster properties in the spiral galaxy M51. We analyse the cluster population as a function of galactocentric distance and in arm and inter-arm regions. The cluster mass function exhibits a similar shape at all radial bins, described by a power law with a slope close to -2 and an exponential truncation around 105 M⊙. While the mass functions of the YSCs in the spiral arm and inter-arm regions have similar truncation masses, the inter-arm region mass function has a significantly steeper slope than the one in the arm region, a trend that is also observed in the giant molecular cloud mass function and predicted by simulations. The age distribution of clusters is dependent on the region considered, and is consistent with rapid disruption only in dense regions, while little disruption is observed at large galactocentric distances and in the inter-arm region. The fraction of stars forming in clusters does not show radial variations, despite the drop in the H2 surface density measured as a function of galactocentric distance. We suggest that the higher disruption rate observed in the inner part of the galaxy is likely at the origin of the observed flat cluster formation efficiency radial profile.

Multicolor photometry of the merging galaxy cluster A2319: Dynamics and star formation properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yan, Peng-Fei; Yuan, Qi-Rong; Zhang, Li

2014-05-01

Asymmetric X-ray emission and a powerful cluster-scale radio halo indicate that A2319 is a merging cluster of galaxies. This paper presents our multicolor photometry for A2319 with 15 optical intermediate filters in the Beijing-Arizona-Taiwan-Connecticut (BATC) system. There are 142 galaxies with known spectroscopic redshifts within the viewing field of 58' × 58' centered on this rich cluster, including 128 member galaxies (called sample I). A large velocity dispersion in the rest frame, 1622{sub −70}{sup +91} km s{sup –1}, suggests merger dynamics in A2319. The contour map of projected density and localized velocity structure confirm the so-called A2319B substructure, at ∼10'more » northwest to the main concentration A2319A. The spectral energy distributions (SEDs) of more than 30,000 sources are obtained in our BATC photometry down to V ∼ 20 mag. A u-band (∼3551 Å) image with better seeing and spatial resolution, obtained with the Bok 2.3 m telescope at Kitt Peak, is taken to make star-galaxy separation and distinguish the overlapping contamination in the BATC aperture photometry. With color-color diagrams and photometric redshift technique, 233 galaxies brighter than h {sub BATC} = 19.0 are newly selected as member candidates after an exclusion of false candidates with contaminated BATC SEDs by eyeball-checking the u-band Bok image. The early-type galaxies are found to follow a tight color-magnitude correlation. Based on sample I and the enlarged sample of member galaxies (called sample II), subcluster A2319B is confirmed. The star formation properties of cluster galaxies are derived with the evolutionary synthesis model, PEGASE, assuming a Salpeter initial mass function and an exponentially decreasing star formation rate (SFR). A strong environmental effect on star formation histories is found in the manner that galaxies in the sparse regions have various star formation histories, while galaxies in the dense regions are found to have shorter SFR time scales, older stellar ages, and higher interstellar medium metallicities. For the merging cluster A2319, local surface density is a better environmental indicator rather than the cluster-centric distance. Compared with the well-relaxed cluster A2589, a higher fraction of star-forming galaxies is found in A2319, indicating that the galaxy-scale turbulence stimulated by the subcluster merger might have played a role in triggering the star formation activity.« less

Impact of Intensive Summer Reading Intervention for Children With Reading Disabilities and Difficulties in Early Elementary School.

PubMed

Christodoulou, Joanna A; Cyr, Abigail; Murtagh, Jack; Chang, Patricia; Lin, Jiayi; Guarino, Anthony J; Hook, Pamela; Gabrieli, John D E

Efficacy of an intensive reading intervention implemented during the nonacademic summer was evaluated in children with reading disabilities or difficulties (RD). Students (ages 6-9) were randomly assigned to receive Lindamood-Bell's Seeing Stars program ( n = 23) as an intervention or to a waiting-list control group ( n = 24). Analysis of pre- and posttesting revealed significant interactions in favor of the intervention group for untimed word and pseudoword reading, timed pseudoword reading, oral reading fluency, and symbol imagery. The interactions mostly reflected (a) significant declines in the nonintervention group from pre- to posttesting, and (2) no decline in the intervention group. The current study offers direct evidence for widening differences in reading abilities between students with RD who do and do not receive intensive summer reading instruction. Intervention implications for RD children are discussed, especially in relation to the relevance of summer intervention to prevent further decline in struggling early readers.

Declining Rotation Curves at z = 2 in ΛCDM Galaxy Formation Simulations

NASA Astrophysics Data System (ADS)

Teklu, Adelheid F.; Remus, Rhea-Silvia; Dolag, Klaus; Arth, Alexander; Burkert, Andreas; Obreja, Aura; Schulze, Felix

2018-02-01

Selecting disk galaxies from the cosmological, hydrodynamical simulation Magneticum Pathfinder, we show that almost half of our poster child disk galaxies at z = 2 show significantly declining rotation curves and low dark matter fractions, very similar to recently reported observations. These galaxies do not show any anomalous behavior, they reside in standard dark matter halos, and they typically grow significantly in mass until z = 0, where they span all morphological classes, including disk galaxies matching present-day rotation curves and observed dark matter fractions. Our findings demonstrate that declining rotation curves and low dark matter fractions in rotation-dominated galaxies at z = 2 appear naturally within the ΛCDM paradigm and reflect the complex baryonic physics, which plays a role at the peak epoch of star formation. In addition, we find some dispersion-dominated galaxies at z = 2 that host a significant gas disk and exhibit similar shaped rotation curves as the disk galaxy population, rendering it difficult to differentiate between these two populations with currently available observation techniques.

SECULAR CHANGES IN ETA CARINAE'S WIND 1998-2011

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mehner, Andrea; Davidson, Kris; Humphreys, Roberta M.

2012-05-20

Stellar wind-emission features in the spectrum of eta Carinae have decreased by factors of 1.5-3 relative to the continuum within the last 10 years. We investigate a large data set from several instruments (STIS, GMOS, UVES) obtained between 1998 and 2011 and analyze the progression of spectral changes in direct view of the star, in the reflected polar-on spectra at FOS4, and at the Weigelt knots. We find that the spectral changes occurred gradually on a timescale of about 10 years and that they are dependent on the viewing angle. The line strengths declined most in our direct view ofmore » the star. About a decade ago, broad stellar wind-emission features were much stronger in our line-of-sight view of the star than at FOS4. After the 2009 event, the wind-emission line strengths are now very similar at both locations. High-excitation He I and N II absorption lines in direct view of the star strengthened gradually. The terminal velocity of Balmer P Cyg absorption lines now appears to be less latitude dependent, and the absorption strength may have weakened at FOS4. Latitude-dependent alterations in the mass-loss rate and the ionization structure of eta Carinae's wind are likely explanations for the observed spectral changes.« less

Star Streams and the Assembly History of the Galaxy

NASA Astrophysics Data System (ADS)

Carlberg, Raymond G.

2017-03-01

Thin halo star streams originate from the evaporation of globular clusters and therefore provide information about the early epoch globular cluster population. The observed tidal tails from halo globular clusters in the Milky Way are much shorter than expected from a star cluster orbiting for 10 Gyr. The discrepancy is likely the result of the assumptions that nearly nonevolving clusters have been orbiting in a nonevolving galactic halo for a Hubble time. As a first step toward more realistic stream histories, a toy model that combines an idealized merger model with a simplified model of the internal collisional relaxation of individual star clusters is developed. On average, the resulting stream velocity dispersion increases with distance, causing the density of the stream to decline with distance. The accretion time sets an upper limit to the length of the readily visible stream, with the internal evolution of the cluster usually playing the dominant role in limiting the sky visibility of the older parts of streams. Nevertheless, the high surface density segment of the stellar streams created from the evaporation of the more massive globular clusters should all be visible in low-obscuration parts of the sky if closer than about 30 kpc. The Pan-STARRS1 halo volume is used to compare the numbers of halo streams and globular clusters.

The All Sky Automated Survey. The Catalog of Bright Variable Stars in the I-band, South of Declination +28o

NASA Astrophysics Data System (ADS)

Sitek, M.; Pojmański, G.

2014-06-01

This paper presents the results of our extensive search for the bright variable stars in approximately 30 000 square degrees of the south sky in the I-band data collected by 9o×9o camera of the All Sky Automated Survey between 2002 and 2009. Lists of over 27 000 variable stars brighter than 9 mag at maximum light, with amplitudes ranging from 0.02 mag to 7 mag and variability time-scales from hours to years, as well as corresponding light curves are provided. Automated classification algorithm based on stellar properties (period, Fourier coefficients, 2MASS J, H, K, colors, ASAS V-band data) was used to roughly classify objects. Despite low spatial resolution of the ASAS data (≍15'') we cross-identified all objects with other available data sources. Coordinates of the most probable 2MASS counterparts are provided. 27 705 stars brighter than I=9 mag were found to be variable, of which 7842 objects were detected to be variable for the first time. Brief statistics and discussion of the presented data is provided. All the photometric data is available over the Internet at http://www.astrouw.edu.pl/ gp/asas/AsasBrightI.html

A UNIVERSAL NEUTRAL GAS PROFILE FOR NEARBY DISK GALAXIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bigiel, F.; Blitz, L., E-mail: bigiel@uni-heidelberg.de

2012-09-10

Based on sensitive CO measurements from HERACLES and H I data from THINGS, we show that the azimuthally averaged radial distribution of the neutral gas surface density ({Sigma}{sub HI}+ {Sigma}{sub H2}) in 33 nearby spiral galaxies exhibits a well-constrained universal exponential distribution beyond 0.2 Multiplication-Sign r{sub 25} (inside of which the scatter is large) with less than a factor of two scatter out to two optical radii r{sub 25}. Scaling the radius to r{sub 25} and the total gas surface density to the surface density at the transition radius, i.e., where {Sigma}{sub HI} and {Sigma}{sub H2} are equal, as wellmore » as removing galaxies that are interacting with their environment, yields a tightly constrained exponential fit with average scale length 0.61 {+-} 0.06 r{sub 25}. In this case, the scatter reduces to less than 40% across the optical disks (and remains below a factor of two at larger radii). We show that the tight exponential distribution of neutral gas implies that the total neutral gas mass of nearby disk galaxies depends primarily on the size of the stellar disk (influenced to some degree by the great variability of {Sigma}{sub H2} inside 0.2 Multiplication-Sign r{sub 25}). The derived prescription predicts the total gas mass in our sub-sample of 17 non-interacting disk galaxies to within a factor of two. Given the short timescale over which star formation depletes the H{sub 2} content of these galaxies and the large range of r{sub 25} in our sample, there appears to be some mechanism leading to these largely self-similar radial gas distributions in nearby disk galaxies.« less

Large and small-scale structures and the dust energy balance problem in spiral galaxies

NASA Astrophysics Data System (ADS)

Saftly, W.; Baes, M.; De Geyter, G.; Camps, P.; Renaud, F.; Guedes, J.; De Looze, I.

2015-04-01

The interstellar dust content in galaxies can be traced in extinction at optical wavelengths, or in emission in the far-infrared. Several studies have found that radiative transfer models that successfully explain the optical extinction in edge-on spiral galaxies generally underestimate the observed FIR/submm fluxes by a factor of about three. In order to investigate this so-called dust energy balance problem, we use two Milky Way-like galaxies produced by high-resolution hydrodynamical simulations. We create mock optical edge-on views of these simulated galaxies (using the radiative transfer code SKIRT), and we then fit the parameters of a basic spiral galaxy model to these images (using the fitting code FitSKIRT). The basic model includes smooth axisymmetric distributions along a Sérsic bulge and exponential disc for the stars, and a second exponential disc for the dust. We find that the dust mass recovered by the fitted models is about three times smaller than the known dust mass of the hydrodynamical input models. This factor is in agreement with previous energy balance studies of real edge-on spiral galaxies. On the other hand, fitting the same basic model to less complex input models (e.g. a smooth exponential disc with a spiral perturbation or with random clumps), does recover the dust mass of the input model almost perfectly. Thus it seems that the complex asymmetries and the inhomogeneous structure of real and hydrodynamically simulated galaxies are a lot more efficient at hiding dust than the rather contrived geometries in typical quasi-analytical models. This effect may help explain the discrepancy between the dust emission predicted by radiative transfer models and the observed emission in energy balance studies for edge-on spiral galaxies.

Cosmic Web of Galaxies in the COSMOS Field: Public Catalog and Different Quenching for Centrals and Satellites

NASA Astrophysics Data System (ADS)

Darvish, Behnam; Mobasher, Bahram; Martin, D. Christopher; Sobral, David; Scoville, Nick; Stroe, Andra; Hemmati, Shoubaneh; Kartaltepe, Jeyhan

2017-03-01

We use a mass complete (log(M/{M}⊙ ) ≥slant 9.6) sample of galaxies with accurate photometric redshifts in the COSMOS field to construct the density field and the cosmic web to z = 1.2. The comic web extraction relies on the density field Hessian matrix and breaks the density field into clusters, filaments, and the field. We provide the density field and cosmic web measures to the community. We show that at z ≲ 0.8, the median star formation rate (SFR) in the cosmic web gradually declines from the field to clusters and this decline is especially sharp for satellites (˜1 dex versus ˜0.5 dex for centrals). However, at z ≳ 0.8, the trend flattens out for the overall galaxy population and satellites. For star-forming (SF) galaxies only, the median SFR is constant at z ≳ 0.5 but declines by ˜0.3-0.4 dex from the field to clusters for satellites and centrals at z ≲ 0.5. We argue that for satellites, the main role of the cosmic web environment is to control their SF fraction, whereas for centrals, it is mainly to control their overall SFR at z ≲ 0.5 and to set their fraction at z ≳ 0.5. We suggest that most satellites experience a rapid quenching mechanism as they fall from the field into clusters through filaments, whereas centrals mostly undergo a slow environmental quenching at z ≲ 0.5 and a fast mechanism at higher redshifts. Our preliminary results highlight the importance of the large-scale cosmic web on galaxy evolution.

Modeling transitions in body composition: the approach to steady state for anthropometric measures and physiological functions in the Minnesota human starvation study

PubMed Central

Hargrove, James L; Heinz, Grete; Heinz, Otto

2008-01-01

Background This study evaluated whether the changes in several anthropometric and functional measures during caloric restriction combined with walking and treadmill exercise would fit a simple model of approach to steady state (a plateau) that can be solved using spreadsheet software (Microsoft Excel®). We hypothesized that transitions in waist girth and several body compartments would fit a simple exponential model that approaches a stable steady-state. Methods The model (an equation) was applied to outcomes reported in the Minnesota starvation experiment using Microsoft Excel's Solver® function to derive rate parameters (k) and projected steady state values. However, data for most end-points were available only at t = 0, 12 and 24 weeks of caloric restriction. Therefore, we derived 2 new equations that enable model solutions to be calculated from 3 equally spaced data points. Results For the group of male subjects in the Minnesota study, body mass declined with a first order rate constant of about 0.079 wk-1. The fractional rate of loss of fat free mass, which includes components that remained almost constant during starvation, was 0.064 wk-1, compared to a rate of loss of fat mass of 0.103 wk-1. The rate of loss of abdominal fat, as exemplified by the change in the waist girth, was 0.213 wk-1. On average, 0.77 kg was lost per cm of waist girth. Other girths showed rates of loss between 0.085 and 0.131 wk-1. Resting energy expenditure (REE) declined at 0.131 wk-1. Changes in heart volume, hand strength, work capacity and N excretion showed rates of loss in the same range. The group of 32 subjects was close to steady state or had already reached steady state for the variables under consideration at the end of semi-starvation. Conclusion When energy intake is changed to new, relatively constant levels, while physical activity is maintained, changes in several anthropometric and physiological measures can be modeled as an exponential approach to steady state using software that is widely available. The 3 point method for parameter estimation provides a criterion for testing whether change in a variable can be usefully modelled with exponential kinetics within the time range for which data are available. PMID:18840293

Responses of wind erosion to climate-induced vegetation changes on the Colorado Plateau.

PubMed

Munson, Seth M; Belnap, Jayne; Okin, Gregory S

2011-03-08

Projected increases in aridity throughout the southwestern United States due to anthropogenic climate change will likely cause reductions in perennial vegetation cover, which leaves soil surfaces exposed to erosion. Accelerated rates of dust emission from wind erosion have large implications for ecosystems and human well-being, yet there is poor understanding of the sources and magnitude of dust emission in a hotter and drier climate. Here we use a two-stage approach to compare the susceptibility of grasslands and three different shrublands to wind erosion on the Colorado Plateau and demonstrate how climate can indirectly moderate the magnitude of aeolian sediment flux through different responses of dominant plants in these communities. First, using results from 20 y of vegetation monitoring, we found perennial grass cover in grasslands declined with increasing mean annual temperature in the previous year, whereas shrub cover in shrublands either showed no change or declined as temperature increased, depending on the species. Second, we used these vegetation monitoring results and measurements of soil stability as inputs into a field-validated wind erosion model and found that declines in perennial vegetation cover coupled with disturbance to biological soil crust resulted in an exponential increase in modeled aeolian sediment flux. Thus the effects of increased temperature on perennial plant cover and the correlation of declining plant cover with increased aeolian flux strongly suggest that sustained drought conditions across the southwest will accelerate the likelihood of dust production in the future on disturbed soil surfaces.

Responses of wind erosion to climate-induced vegetation changes on the Colorado Plateau

USGS Publications Warehouse

Munson, Seth M.; Belnap, Jayne; Okin, Gregory S.

2011-01-01

Projected increases in aridity throughout the southwestern United States due to anthropogenic climate change will likely cause reductions in perennial vegetation cover, which leaves soil surfaces exposed to erosion. Accelerated rates of dust emission from wind erosion have large implications for ecosystems and human well-being, yet there is poor understanding of the sources and magnitude of dust emission in a hotter and drier climate. Here we use a two-stage approach to compare the susceptibility of grasslands and three different shrublands to wind erosion on the Colorado Plateau and demonstrate how climate can indirectly moderate the magnitude of aeolian sediment flux through different responses of dominant plants in these communities. First, using results from 20 y of vegetation monitoring, we found perennial grass cover in grasslands declined with increasing mean annual temperature in the previous year, whereas shrub cover in shrublands either showed no change or declined as temperature increased, depending on the species. Second, we used these vegetation monitoring results and measurements of soil stability as inputs into a field-validated wind erosion model and found that declines in perennial vegetation cover coupled with disturbance to biological soil crust resulted in an exponential increase in modeled aeolian sediment flux. Thus the effects of increased temperature on perennial plant cover and the correlation of declining plant cover with increased aeolian flux strongly suggest that sustained drought conditions across the southwest will accelerate the likelihood of dust production in the future on disturbed soil surfaces.

Responses of wind erosion to climate-induced vegetation changes on the Colorado Plateau

PubMed Central

Munson, Seth M.; Belnap, Jayne; Okin, Gregory S.

2011-01-01

Projected increases in aridity throughout the southwestern United States due to anthropogenic climate change will likely cause reductions in perennial vegetation cover, which leaves soil surfaces exposed to erosion. Accelerated rates of dust emission from wind erosion have large implications for ecosystems and human well-being, yet there is poor understanding of the sources and magnitude of dust emission in a hotter and drier climate. Here we use a two-stage approach to compare the susceptibility of grasslands and three different shrublands to wind erosion on the Colorado Plateau and demonstrate how climate can indirectly moderate the magnitude of aeolian sediment flux through different responses of dominant plants in these communities. First, using results from 20 y of vegetation monitoring, we found perennial grass cover in grasslands declined with increasing mean annual temperature in the previous year, whereas shrub cover in shrublands either showed no change or declined as temperature increased, depending on the species. Second, we used these vegetation monitoring results and measurements of soil stability as inputs into a field-validated wind erosion model and found that declines in perennial vegetation cover coupled with disturbance to biological soil crust resulted in an exponential increase in modeled aeolian sediment flux. Thus the effects of increased temperature on perennial plant cover and the correlation of declining plant cover with increased aeolian flux strongly suggest that sustained drought conditions across the southwest will accelerate the likelihood of dust production in the future on disturbed soil surfaces. PMID:21368143

The PHAT and SPLASH Surveys: Rigorous Structural Decomposition of the Andromeda Galaxy

NASA Astrophysics Data System (ADS)

Dorman, Claire; Guhathakurta, P.; Widrow, L.; Foreman-Mackey, D.; Seth, A.; Dalcanton, J.; Gilbert, K.; Lang, D.; Williams, B. F.; SPLASH Team; PHAT Team

2013-01-01

Traditional surface brightness profile (SBP) based structural decompositions of late-type galaxies into Sersic bulge, exponential disk, and power-law halo are often degenerate in the best-fit profiles. The Andromeda galaxy (M31) is the only large spiral close enough that the relative contributions of the subcomponents can be further constrained via their distinct signatures in resolved stellar population surveys. We make use of two such surveys. The SPLASH program has used the Keck/DEIMOS multiobject spectrograph to measure radial velocities of over 10,000 individual red giant branch stars in the inner 20kpc of M31. The PHAT survey, an ongoing Hubble Space Telescope Multicycle Treasury program, has so far obtained six-filter photometry of over 90 million stars in the same region. We use an MCMC algorithm to simultaneously fit a simple bulge/disk/halo structural model to the SBP, the disk fraction as measured from kinematics, and the PHAT luminosity function. We find that the additional constraints favor a larger bulge than expected from a pure SBP fit. Comparison to galaxy formation models will constrain the formation histories of large spiral galaxies such as the Milky Way and Andromeda.

Molecular maser flares in the high-mass star-forming region IRAS18566+0408

NASA Astrophysics Data System (ADS)

Halbe, Daniel M.

We report results of a long-termmonitoring study of 6cmformaldehyde (H 2CO), 6.035GHz hydroxyl (OH), and 6.7GHz methanol (CH3OH) masers in the young high-mass protostellar object IRAS18566+0408 (G37.55+0.20). This is the only high-mass star-forming region where correlated variability of three different maser species has been reported. The observations were conducted with the 305m Arecibo Radio Telescope, and together with data from the literature, we present H2CO flux density measurements from 2002 to 2014, CH3OH data from 2006 to 2013, and discuss OH observations obtained between 2008 and 2012. Our extended monitoring observations of the H2CO maser agree with the quasi-periodic flare phenomenon and exponential decrease in quiescent and flare flux densities proposed by Araya and collaborators in 2010. We also confirm the occurrence of 6.035GHz OH flares and a time delay with respect to the H2CO flares. An analysis between the variability behavior of different CH3OH maser components and the H2CO maser suggests that multiple variability mechanisms are responsible for CH3OH flux density changes.

On the Formation of Extended Galactic Disks by Tidally Disrupted Dwarf Galaxies

NASA Astrophysics Data System (ADS)

Peñarrubia, Jorge; McConnachie, Alan; Babul, Arif

2006-10-01

We explore the possibility that extended disks, such as that recently discovered in M31, are the result of a single dwarf (109-1010 Msolar) satellite merger. We conduct N-body simulations of dwarf NFW halos with embedded spheroidal stellar components on coplanar, prograde orbits in an M31-like host galaxy. As the orbit decays due to dynamical friction and the system is disrupted, the stellar particles relax to form an extended, exponential-disk-like structure that spans the radial range 30-200 kpc. The disk scale length Rd correlates with the initial extent of the stellar component within the satellite halo: the more embedded the stars, the smaller the resulting disk scale length. If the progenitors start on circular orbits, the kinematics of the stars that make up the extended disk have an average rotational motion that is 30-50 km s-1 lower than the host's circular velocity. For dwarf galaxies moving on highly eccentric orbits (e~=0.7), the stellar debris exhibits a much lower rotational velocity. Our results imply that extended galactic disks might be a generic feature of the hierarchical formation of spiral galaxies such as M31 and the Milky Way.

Revisiting the environmental Kuznets curve hypothesis in a tourism development context.

PubMed

de Vita, Glauco; Katircioglu, Salih; Altinay, Levent; Fethi, Sami; Mercan, Mehmet

2015-11-01

This study investigates empirically an extended version of the Environmental Kuznets Curve model that controls for tourism development. We find that international tourist arrivals into Turkey alongside income, squared income and energy consumption, cointegrate with CO2 emissions. Tourist arrivals, growth, and energy consumption exert a positive and significant impact on CO2 emissions in the long-run. Our results provide empirical support to EKC hypothesis showing that at exponential levels of growth, CO2 emissions decline. The findings suggest that despite the environmental degradation stemming from tourism development, policies aimed at environmental protection should not be pursued at the expense of tourism-led growth.

Impacts of biodiversity loss on ocean ecosystem services.

PubMed

Worm, Boris; Barbier, Edward B; Beaumont, Nicola; Duffy, J Emmett; Folke, Carl; Halpern, Benjamin S; Jackson, Jeremy B C; Lotze, Heike K; Micheli, Fiorenza; Palumbi, Stephen R; Sala, Enric; Selkoe, Kimberley A; Stachowicz, John J; Watson, Reg

2006-11-03

Human-dominated marine ecosystems are experiencing accelerating loss of populations and species, with largely unknown consequences. We analyzed local experiments, long-term regional time series, and global fisheries data to test how biodiversity loss affects marine ecosystem services across temporal and spatial scales. Overall, rates of resource collapse increased and recovery potential, stability, and water quality decreased exponentially with declining diversity. Restoration of biodiversity, in contrast, increased productivity fourfold and decreased variability by 21%, on average. We conclude that marine biodiversity loss is increasingly impairing the ocean's capacity to provide food, maintain water quality, and recover from perturbations. Yet available data suggest that at this point, these trends are still reversible.

Heavy Element Abundances in NGC 5846

NASA Technical Reports Server (NTRS)

Jones, Christine

2000-01-01

In this paper we analyze the diffuse X-ray coronae surrounding the elliptical galaxy NGC 5846, combining measurements from two observatories, ROSAT and the Advanced Satellite for Cosmology and Astrophysics. We map the gas temperature distribution and find a central cool region within an approximately isothermal gas halo extending to a radius of about 50 kpc and evidence for a temperature decrease at larger radii. With a radially falling temperature profile, the total mass converges to (9.6 +/- 1.0) x 10(exp 12) solar mass at 230 kpc radius. This corresponds to a total mass to blue light ratio of 53 +/- 5 solar mass/solar luminosity. As in other early type galaxies, the gas mass is only a few percent of the total mass. Using the spectroscopic measurements, we also derive radial distributions for the heavy elements silicon and iron and find that the abundances of both decrease with galaxy radius. The mass ratio of Si to Fe lies between the theoretical predictions for element production in SN Ia and SN II, suggesting an important role for SN Ia, as well as SN II, for gas enrichment in ellipticals. Using the 2 SN la yield of Si, we set an upper limit of 0.012 h(sup 2, sub 50) solar neutrino units (SNU) for the SN Ia rate at radii >50 kpc, which is independent of possible uncertainties in the iron L-shell modeling. We compare our observations with the theoretical predictions for the chemical evolution of ellipticals. We conclude that the metal content in stars, if explained by the star formation duration, requires a significant decline in the duration of star formation with galaxy radius, ranging from 1 Gyr at the center to 0.01 Gyr at 100 kpc radius. Alternatively, the decline in metallicity with galaxy radius may be caused by a similar drop with radius in the efficiency of star formation. Based on the Si and Fe measurements presented in this paper, we conclude that the latter scenario is preferred unless a dependence of the SN Ia rate on stellar metallicity is invoked.

Gamma rays, X-rays, and optical light from the cobalt and the neutron star in SN 1987A

NASA Technical Reports Server (NTRS)

Kumagai, Shiomi; Shigeyama, Toshikazu; Nomoto, Ken'ichi; Itoh, Masayuki; Nishimura, Jun

1989-01-01

Recent developments in modeling the X-ray and gamma-ray emission from SN 1987A are discussed by taking into account both the decaying cobalt and the buried neutron star. The light curve and the spectra evolution of X-rays and gamma-rays are well modeled up to day of about 300 if mixing of Co-56 into hydrogen-rich envelope is assumed. However, the 16-28 keV flux observed by Ginga declines very slowly, whereas the spherical mixing model predicts that the flux should have decreased by a large factor at t greater than 300d. It is shown that this problem can be solved if the photoelectric absorption of X-rays is effectively reduced as a result of the formation of chemically inhomogeneous clumps. Based on the adopted hydrodynamical model and the abundance distribution, predictions are offered for future optical, X-ray, and gamma-ray light curves by taking into account other radioactive sources and various types of the central source, e.g., a buried neutron star accreting the reinfalling material or an isolated pulsar.

Outbursts in Symbiotic Binaries

NASA Technical Reports Server (NTRS)

Sonneborn, George (Technical Monitor); Kenyon, Scott J.

2004-01-01

Two models have been proposed for the outbursts of symbiotic stars. In the thermonuclear model, outbursts begin when the hydrogen burning shell of a hot white dwarf reaches a critical mass. After a rapid increase in the luminosity and effective temperature, the white dwarf evolves at constant luminosity to lower effective temperatures, remains at optical maximum for several years, and then returns to quiescence along a white dwarf cooling curve. In disk instability models, the brightness rises when the accretion rate from the disk onto the central white dwarf abruptly increases by factors of 5-20. After a few month to several year period at maximum, both the luminosity and the effective temperature of the disk decline as the system returns to quiescence. If most symbiotic stars undergo thermonuclear eruptions, then symbiotics are probably poor candidates for type I supernovae. However, they can then provide approx. 10% of the material which stars recycle back into the interstellar medium. If disk instabilities are the dominant eruption mechanism, symbiotics are promising type Ia candidates but recycle less material into the interstellar medium.

The Magnetar Nature and the Outburst Mechanism of a Transient Anomalous X-ray Pulsar

NASA Technical Reports Server (NTRS)

Guver, Tolga; Ozel, Feryal; Gogus, Ersin; Kouveliotou, Chryssa

2007-01-01

Anomalous X-ray Pulsars (AXPs) belong to a class of neutron stars believed to harbor the strongest magnetic fields in the universe, as indicated by their energetic bursts and their rapid spindowns. However, a direct measurement of their surface field strengths has not been made to date. It is also not known whether AXP outbursts result from changes in the neutron star magnetic field or crust properties. Here we report the first, spectroscopic measurement of the surface magnetic field strength of an AXP, XTE J1810-197, and solidify its magnetar nature. The field strength obtained from detailed spectral analysis and modeling is remarkably close to the value inferred from the rate of spindown of this source and remains nearly constant during numerous observations spanning over two orders of magnitude in source flux. The surface temperature, on the other hand, declines steadily and dramatically following the 2003 outburst of this source. Our findings demonstrate that heating occurs in the upper neutron star crust during an outburst and sheds light on the transient behaviour of AXPs.

Detailed Physical Modeling Reveals the Magnetar Nature of a Transient Anomalous X-ray Pulsar

NASA Technical Reports Server (NTRS)

Guever, T.; Oezel, F.; Goegues, E.; Kouveliotou, C.

2007-01-01

Anomalous X-ray Pulsars (AXPs) belong to a class of neutron stars believed to harbor the strongest magnetic fields in the universe, as indicated by their energetic bursts and their rapid spindowns. However, a direct measurement of their surface field strengths has not been made to date. It is also not known whether AXP outbursts result from changes in the neutron star magnetic field or crust properties. Here we report the first, spectroscopic measurement of the surface magnetic field strength of an AXP, XTE J1810-197, and solidify its magnetar nature. The field strength obtained from detailed spectral analysis and modeling is remarkably close to the value inferred from the rate of spindown of this source and remains nearly constant during numerous observations spanning over two orders of magnitude in source flux. The surface temperature, on the other hand, declines steadily and dramatically following the 2003 outburst of this source. Our findings demonstrate that heating occurs in the upper neutron star crust during an outburst and sheds light on the transient behaviour of AXPs.

Metabolic Maturation of the Human Brain From Birth Through Adolescence: Insights From In Vivo Magnetic Resonance Spectroscopy

PubMed Central

Blüml, Stefan; Wisnowski, Jessica L.; Nelson, Marvin D.; Paquette, Lisa; Gilles, Floyd H.; Kinney, Hannah C.; Panigrahy, Ashok

2013-01-01

Between birth and late adolescence, the human brain undergoes exponential maturational changes. Using in vivo magnetic resonance spectroscopy, we determined the developmental profile for 6 metabolites in 5 distinct brain regions based on spectra from 309 children from 0 to 18 years of age. The concentrations of N-acetyl-aspartate (an indicator for adult-type neurons and axons), creatine (energy metabolite), and glutamate (excitatory neurotransmitter) increased rapidly between birth and 3 months, a period of rapid axonal growth and synapse formation. Myo-inositol, implicated in cell signaling and a precursor of membrane phospholipid, as well as an osmolyte and astrocyte marker, declined rapidly during this period. Choline, a membrane metabolite and indicator for de novo myelin and cell membrane synthesis, peaked from birth until approximately 3 months, and then declined gradually, reaching a plateau at early childhood. Similarly, taurine, involved in neuronal excitability, synaptic potentiation, and osmoregulation, was high until approximately 3 months and thereafter declined. These data indicate that the first 3 months of postnatal life are a critical period of rapid metabolic changes in the development of the human brain. This study of the developmental profiles of the major brain metabolites provides essential baseline information for future analyses of the pediatric health and disease. PMID:22952278

Decline in top predator body size and changing climate alter trophic structure in an oceanic ecosystem.

PubMed

Shackell, Nancy L; Frank, Kenneth T; Fisher, Jonathan A D; Petrie, Brian; Leggett, William C

2010-05-07

Globally, overfishing large-bodied groundfish populations has resulted in substantial increases in their prey populations. Where it has been examined, the effects of overfishing have cascaded down the food chain. In an intensively fished area on the western Scotian Shelf, Northwest Atlantic, the biomass of prey species increased exponentially (doubling time of 11 years) even though the aggregate biomass of their predators remained stable over 38 years. Concomitant reductions in herbivorous zooplankton and increases in phytoplankton were also evident. This anomalous trophic pattern led us to examine how declines in predator body size (approx. 60% in body mass since the early 1970s) and climatic regime influenced lower trophic levels. The increase in prey biomass was associated primarily with declines in predator body size and secondarily to an increase in stratification. Sea surface temperature and predator biomass had no influence. A regression model explained 65 per cent of prey biomass variability. Trait-mediated effects, namely a reduction in predator size, resulted in a weakening of top predation pressure. Increased stratification may have enhanced growing conditions for prey fish. Size-selective harvesting under changing climatic conditions initiated a trophic restructuring of the food chain, the effects of which may have influenced three trophic levels.

Shell-free biomass and population dynamics of dreissenids in offshore Lake Michigan, 2001-2003

USGS Publications Warehouse

French, J. R. P.; Adams, J.V.; Craig, J.; Stickel, R.G.; Nichols, S.J.; Fleischer, G.W.

2007-01-01

The USGS-Great Lakes Science Center has collected dreissenid mussels annually from Lake Michigan since zebra mussels (Dreissena polymorpha) became a significant portion of the bottom-trawl catch in 1999. For this study, we investigated dreissenid distribution, body mass, and recruitment at different depths in Lake Michigan during 2001-2003. The highest densities of dreissenid biomass were observed from depths of 27 to 46 m. The biomass of quagga mussels (Dreissena bugensis) increased exponentially during 2001-2003, while that of zebra mussels did not change significantly. Body mass (standardized for a given shell length) of both species was lowest from depths of 27 to 37m, highest from 55 to 64 m, and declined linearly at deeper depths during 2001-2003. Recruitment in 2003, as characterized by the proportion of mussels < 11 mm in the catch, varied with depth and lake region. For quagga mussels, recruitment declined linearly with depth, and was highest in northern Lake Michigan. For zebra mussels, recruitment generally declined non-linearly with depth, although the pattern was different for north, mid, and southern Lake Michigan. Our analyses suggest that quagga mussels could overtake zebra mussels and become the most abundant mollusk in terms of biomass in Lake Michigan.

The scaling of population persistence with carrying capacity does not asymptote in populations of a fish experiencing extreme climate variability.

PubMed

White, Richard S A; Wintle, Brendan A; McHugh, Peter A; Booker, Douglas J; McIntosh, Angus R

2017-06-14

Despite growing concerns regarding increasing frequency of extreme climate events and declining population sizes, the influence of environmental stochasticity on the relationship between population carrying capacity and time-to-extinction has received little empirical attention. While time-to-extinction increases exponentially with carrying capacity in constant environments, theoretical models suggest increasing environmental stochasticity causes asymptotic scaling, thus making minimum viable carrying capacity vastly uncertain in variable environments. Using empirical estimates of environmental stochasticity in fish metapopulations, we showed that increasing environmental stochasticity resulting from extreme droughts was insufficient to create asymptotic scaling of time-to-extinction with carrying capacity in local populations as predicted by theory. Local time-to-extinction increased with carrying capacity due to declining sensitivity to demographic stochasticity, and the slope of this relationship declined significantly as environmental stochasticity increased. However, recent 1 in 25 yr extreme droughts were insufficient to extirpate populations with large carrying capacity. Consequently, large populations may be more resilient to environmental stochasticity than previously thought. The lack of carrying capacity-related asymptotes in persistence under extreme climate variability reveals how small populations affected by habitat loss or overharvesting, may be disproportionately threatened by increases in extreme climate events with global warming. © 2017 The Author(s).

Satellite Ephemeris Correction via Remote Site Observation for Star Tracker Navigation Performance Improvement

DTIC Science & Technology

2016-03-01

squared RMS root mean squared GCRF Geocentric Celestial Reference Frame xi List of Figures Figure Page 1 Geometry of single observation...RA and DEC in the celestial sphere. The Geocentric Celestial Reference Frame (GCRF) is the standard geocentric frame that measures the RA east in the...Figure 2. Right ascension (α) and declination (δ) in the celestial sphere[6] 7 made between geocentric and topocentric angles. Geocentric is referred to

Astrometric Detection of Extrasolar Planets: Results of a Feasibility Study with the Palomar 5 Meter Telescope

NASA Technical Reports Server (NTRS)

Pravdo, Steven H.; Shaklan, Stuart B.

1996-01-01

The detection of extrasolar planets around stars like the Sun remains an important goal of astronomy. We present results from Palomar 5 m observations of the open cluster NGC 2420 in which we measure some of the sources of noise that will be present in an astrometric search for extrasolar planets. This is the first time that such a large aperture has been used for high-precision astrometry. We find that the atmospheric noise is 150 micro-arcsec hr(exp 1/2) across a 90 sec field of view and that differential chromatic refraction (DCR) can be calibrated to 128 micro-arcsec for observations within 1 hr of the meridian and 45 deg of zenith. These results confirm that a model for astrometric measurements can be extrapolated to large apertures. We demonstrate, based upon these results, that a large telescope achieves the sensitivity required to perform a statistically significant search for extra solar planets. We describe an astrometric technique to detect planets, the astrometric signals expected, the role of reference stars, and the sources of measurement noise: photometric noise, atmospheric motion between stars, sky background, instrumental noise, and DCR. For the latter, we discuss a method to reduce the noise further to 66 micro-arcsecond for observations within 1 hr of the meridian and 45 deg of zenith. We discuss optimal lists of target stars taken from the latest Gliese & Jahreiss catalog of nearby stars with the largest potential astrometric signals, declination limits for both telescope accessibility and reduced DCR, and galactic latitude limits for a sufficiant number of reference stars. Two samples are described from which one can perform statistically significant searches for gas giant planets around nearby stars. One sample contains 100 "solar class" stars with an average stellar mass of 0.82 solar mass; the other maximizes the number of stars, 574, by searching mainly low-mass M stars. We perform Monte Carlo simulations of the statistical significance of the expected results by using measured and estimated noise quantities. We show the semimajor axis parameter spaces that are searched for each star and how an increase in the length of the observing program expands these spaces. The search over semimajor axis parameter space relates to the theory of gas giant planet formation.

The Herschel Virgo Cluster Survey. XIX. Physical properties of low luminosity FIR sources at z < 0.5

NASA Astrophysics Data System (ADS)

Pappalardo, Ciro; Bizzocchi, Luca; Fritz, Jacopo; Boselli, Alessandro; Boquien, Mederic; Boissier, Samuel; Baes, Maarten; Ciesla, Laure; Bianchi, Simone; Clemens, Marcel; Viaene, Sebastien; Bendo, George J.; De Looze, Ilse; Smith, Matthew W. L.; Davies, Jonathan

2016-05-01

Context. The star formation rate is a crucial parameter for the investigation galaxy evolution. At low redshift the cosmic star formation rate density declines smoothly, and massive active galaxies become passive, reducing their star formation activity. This implies that the bulk of the star formation rate density at low redshift is mainly driven by low mass objects. Aims: We investigate the properties of a sample of low luminosity far-infrared sources selected at 250 μm. We have collected data from ultraviolet to far-infrared in order to perform a multiwavelengths analysis. The main goal is to investigate the correlation between star formation rate, stellar mass, and dust mass for a galaxy population with a wide range in dust content and stellar mass, including the low mass regime that most probably dominates the star formation rate density at low redshift. Methods: We define a main sample of ~800 sources with full spectral energy distribution coverage between 0.15 <λ< 500 μm and an extended sample with ~5000 sources in which we remove the constraints on the ultraviolet and near-infrared bands. We analyze both samples with two different spectral energy distribution fitting methods: MAGPHYS and CIGALE, which interpret a galaxy spectral energy distribution as a combination of different simple stellar population libraries and dust emission templates. Results: In the star formation rate versus stellar mass plane our samples occupy a region included between local spirals and higher redshift star forming galaxies. These galaxies represent the population that at z< 0.5 quenches their star formation activity and reduces their contribution to the cosmic star formation rate density. The subsample of galaxies with the higher masses (M∗> 3 × 1010 M⊙) do not lie on the main sequence, but show a small offset as a consequence of the decreased star formation. Low mass galaxies (M∗< 1 × 1010 M⊙) settle in the main sequence with star formation rate and stellar mass consistent with local spirals. Conclusions: Deep Herschel data allow the identification of a mixed galaxy population with galaxies still in an assembly phase or galaxies at the beginning of their passive evolution. We find that the dust luminosity is the parameter that allow us to discriminate between these two galaxy populations. The median spectral energy distribution shows that even at low star formation rate our galaxy sample has a higher mid-infrared emission than previously predicted. Herschel is an ESA space observatory with science instruments provided by a European-led principal investigator consortia and with an important participation from NASA.

Decline of radionuclides in the nearshore environment following nuclear reactor closure: A U.K. case study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cundy, A.B.; Croudace, I.W.; Warwick, P.E.

1999-09-01

Radioactive discharges from nuclear facilities are frequently made into the marine environment and their fate during and after cessation of discharges is a matter of interest and concern. This study examines the decline of the radionuclides {sup 60} and {sup 65}Zn along the southern UK. coast, over the per 1988--1998, following the closure of the steam-generating heavy water (SGHW) reactor at AEA Winfrith, Dorset, UK. {sup 60}Co and {sup 65}Zn (and other activation products such as {sup 63}Ni and {sup 55}Fe) were widely dispersed in the marine environment off the central south coast of England, due to authorized releases frommore » AEA Winfrith. Significant interaction occurred with clay-rich sediments and biota. A general exponential decline in {sup 60}Co activities (and in {sup 65}Zn activity) is found in intertidal mudflat sediments, seaweed and marine fauna in different areas along the south coast following closure of the reactor in 1990. Effective half-lives are determined which vary from 1 to 4 years in surface sediments ({sup 60}Co only), 1--4 years in seaweed and 0.5--2.5 years in crustaceans, bivalves and molluscs. Physical mixing and bioturbation largely control the rate at which {sup 60}Co declines in surface sediments. Both {sup 60}Co and {sup 65}Zn show a relatively slow rate of decline in seaweed and in marine fauna, showing that even after the virtual cessation of discharge from nuclear facilities, contamination of these organisms may persist for a number of years, albeit at reduced activities. Reasons for this persistence are likely to include absorption of radionuclides from sediment, and release and recycling of radionuclides via breakdown of contaminated organic material.« less

A M2FS Spectroscopic Study of Low-mass Young Stars in Orion OB1

NASA Astrophysics Data System (ADS)

Kaleida, Catherine C.; Briceno, Cesar; Calvet, Nuria; Mateo, Mario L.; Hernandez, Jesus

2015-01-01

Surveys of pre-main sequence stars in the ~4-10 Myr range provide a window into the decline of the accretion phase of stars and the formation of planets. Nearby star clusters and stellar associations allow for the study of these young stellar populations all the way down to the lowest mass members. One of the best examples of nearby 4-10 Myr old stellar populations is the Orion OB1 association. The CIDA Variability Survey of Orion OB1 (CVSO - Briceño et al. 2001) has used the variability properties of low-mass pre-main-sequence (PMS) stars to identify hundreds of K and M-type stellar members of the Orion OB1 association, a number of them displaying IR-excess emission and thought to be representative of more evolved disk-bearing young stars. Characterizing these young, low-mass objects using spectroscopy is integral to understanding the accretion phase in young stars. We present preliminary results of a spectroscopic survey of candidate and confirmed Orion OB1 low-mass members taken during November 2014 and February 2014 using the Michigan/Magellan Fiber Spectrograph (M2FS), a PI instrument on the Magellan Clay Telescope (PI: M. Matteo). Target fields located in the off-cloud regions of Orion were identified in the CVSO, and observed using the low and high-resolution modes of M2FS. Both low and high-resolution spectra are needed in order to confirm membership and derive masses, ages, kinematics and accretion properties. Initial analysis of these spectra reveal many new K and M-type members of the Orion OB1 association in these low extinction, off-cloud areas. These are the more evolved siblings of the youngest stars still embedded in the molecular clouds, like those in the Orion Nebula Cluster. With membership and spectroscopic indicators of accretion we are building the most comprehensive stellar census of this association, enabling us to derive a robust estimate of the fraction of young stars still accreting at a various ages, a key constraint for the end of accretion and the formation of giant planets.

DUST AROUND R CORONAE BOREALIS STARS. I. SPITZER/INFRARED SPECTROGRAPH OBSERVATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anibal Garcia-Hernandez, D.; Kameswara Rao, N.; Lambert, David L., E-mail: agarcia@iac.es, E-mail: nkrao@iiap.res.in, E-mail: dll@astro.as.utexas.edu

2011-09-20

Spitzer/infrared spectrograph (IRS) spectra from 5 to 37 {mu}m for a complete sample of 31 R Coronae Borealis stars (RCBs) are presented. These spectra are combined with optical and near-infrared photometry of each RCB at maximum light to compile a spectral energy distribution (SED). The SEDs are fitted with blackbody flux distributions and estimates are made of the ratio of the infrared flux from circumstellar dust to the flux emitted by the star. Comparisons for 29 of the 31 stars are made with the Infrared Astronomical Satellite (IRAS) fluxes from three decades earlier: Spitzer and IRAS fluxes at 12 {mu}mmore » and 25 {mu}m are essentially equal for all but a minority of the sample. For this minority, the IRAS to Spitzer flux ratio exceeds a factor of three. The outliers are suggested to be stars where formation of a dust cloud or dust puff is a rare event. A single puff ejected prior to the IRAS observations may have been reobserved by Spitzer as a cooler puff at a greater distance from the RCB. RCBs which experience more frequent optical declines have, in general, a circumstellar environment containing puffs subtending a larger solid angle at the star and a quasi-constant infrared flux. Yet, the estimated subtended solid angles and the blackbody temperatures of the dust show a systematic evolution to lower solid angles and cooler temperatures in the interval between IRAS and Spitzer. Dust emission by these RCBs and those in the LMC is similar in terms of total 24 {mu}m luminosity and [8.0]-[24.0] color index.« less

Variable rotational line broadening in the Be star Achernar

NASA Astrophysics Data System (ADS)

Rivinius, Th.; Baade, D.; Townsend, R. H. D.; Carciofi, A. C.; Štefl, S.

2013-11-01

Aims: The main theoretical problem for the formation of a Keplerian disk around Be stars is how angular momentum is supplied from the star to the disk, even more so since Be stars probably rotate somewhat subcritically. For instance, nonradial pulsation may transport angular momentum to the stellar surface until (part of) this excess supports the disk-formation/replenishment. The nearby Be star Achernar is presently building a new disk and offers an excellent opportunity to observe this process from relatively close-up. Methods: Spectra from various sources and epochs are scrutinized to identify the salient stellar parameters characterizing the disk life cycle as defined by Hα emission. The variable strength of the non-radial pulsation is confirmed, but does not affect the other results. Results: For the first time it is demonstrated that the photospheric line width does vary in a Be star, by as much as Δv sini ≲ 35 km s-1. However, unlike assumptions in which a photospheric spin-up accumulates during the diskless phase and then is released into the disk as it is fed, the apparent photospheric spin-up is positively correlated with the appearance of Hα line emission. The photospheric line widths and circumstellar emission increase together, and the apparent stellar rotation declines to the value at quiescence after the Hα line emission becomes undetectable. Based on observations collected at the European Southern Observatory at La Silla and Paranal, Chile, Prog. IDs: 62.H-0319, 64.H-0548, 072.C-0513, 073.C-0784, 074.C-0012, 073.D-0547, 076.C-0431, 077.D-0390, 077.D-0605, and the technical program IDs 60.A-9120 and 60.A-9036.Appendices are available in electronic form at http://www.aanda.org

Molecular cloud-scale star formation in NGC 300

DOE Office of Scientific and Technical Information (OSTI.GOV)

Faesi, Christopher M.; Lada, Charles J.; Forbrich, Jan

2014-07-01

We present the results of a galaxy-wide study of molecular gas and star formation in a sample of 76 H II regions in the nearby spiral galaxy NGC 300. We have measured the molecular gas at 250 pc scales using pointed CO(J = 2-1) observations with the Atacama Pathfinder Experiment telescope. We detect CO in 42 of our targets, deriving molecular gas masses ranging from our sensitivity limit of ∼10{sup 5} M {sub ☉} to 7 × 10{sup 5} M {sub ☉}. We find a clear decline in the CO detection rate with galactocentric distance, which we attribute primarily tomore » the decreasing radial metallicity gradient in NGC 300. We combine Galaxy Evolution Explorer far-ultraviolet, Spitzer 24 μm, and Hα narrowband imaging to measure the star formation activity in our sample. We have developed a new direct modeling approach for computing star formation rates (SFRs) that utilizes these data and population synthesis models to derive the masses and ages of the young stellar clusters associated with each of our H II region targets. We find a characteristic gas depletion time of 230 Myr at 250 pc scales in NGC 300, more similar to the results obtained for Milky Way giant molecular clouds than the longer (>2 Gyr) global depletion times derived for entire galaxies and kiloparsec-sized regions within them. This difference is partially due to the fact that our study accounts for only the gas and stars within the youngest star-forming regions. We also note a large scatter in the NGC 300 SFR-molecular gas mass scaling relation that is furthermore consistent with the Milky Way cloud results. This scatter likely represents real differences in giant molecular cloud physical properties such as the dense gas fraction.« less

Eta Carinae's Thermal X-Ray Tail Measured with XMM-Newton and NuStar

NASA Technical Reports Server (NTRS)

Hamaguchi, Kenji; Corcoran, Michael F.; Gull, Theodore R.; Takahashi, Hiromitsu; Grefenstette, Brian; Yuasa, Takayuki; Stuhlinger, Martin; Russell, Christopher; Moffat, Anthony F. J.; Madura, Thomas

2016-01-01

The evolved, massive highly eccentric binary system, Car, underwent a periastron passage in the summer of 2014. We obtained two coordinated X-ray observations with XMM-Newton and NuSTAR during the elevated X-ray flux state and just before the X-ray minimum flux state around this passage. These NuSTAR observations clearly detected X-ray emission associated with eta Car extending up to approx. 50 keV for the first time. The NuSTAR spectrum above 10 keV can be fit with the bremsstrahlung tail from a kT approx. 6 keV plasma. This temperature is delta kT 2 keV higher than those measured from the iron K emission line complex, if the shocked gas is in collisional ionization equilibrium. This result may suggest that the companion star's pre-shock wind velocity is underestimated. The NuSTAR observation near the X-ray minimum state showed a gradual decline in the X-ray emission by 40% at energies above 5 keV in a day, the largest rate of change of the X-ray flux yet observed in individual eta Car observations. The column density to the hardest emission component, N(sub H) approx. 10(exp24) H cm(exp-2), marked one of the highest values ever observed for eta Car, strongly suggesting the increased obscuration of the wind-wind colliding X-ray emission by the thick primary stellar wind prior to superior conjunction. Neither observation detected the power-law component in the extremely hard band that INTEGRAL and Suzaku observed prior to 2011. The power-law source might have faded before these observations.

The Average Star Formation Histories of Galaxies in Dark Matter Halos from z = 0-8

NASA Astrophysics Data System (ADS)

Behroozi, Peter S.; Wechsler, Risa H.; Conroy, Charlie

2013-06-01

We present a robust method to constrain average galaxy star formation rates (SFRs), star formation histories (SFHs), and the intracluster light (ICL) as a function of halo mass. Our results are consistent with observed galaxy stellar mass functions, specific star formation rates (SSFRs), and cosmic star formation rates (CSFRs) from z = 0 to z = 8. We consider the effects of a wide range of uncertainties on our results, including those affecting stellar masses, SFRs, and the halo mass function at the heart of our analysis. As they are relevant to our method, we also present new calibrations of the dark matter halo mass function, halo mass accretion histories, and halo-subhalo merger rates out to z = 8. We also provide new compilations of CSFRs and SSFRs; more recent measurements are now consistent with the buildup of the cosmic stellar mass density at all redshifts. Implications of our work include: halos near 1012 M ⊙ are the most efficient at forming stars at all redshifts, the baryon conversion efficiency of massive halos drops markedly after z ~ 2.5 (consistent with theories of cold-mode accretion), the ICL for massive galaxies is expected to be significant out to at least z ~ 1-1.5, and dwarf galaxies at low redshifts have higher stellar mass to halo mass ratios than previous expectations and form later than in most theoretical models. Finally, we provide new fitting formulae for SFHs that are more accurate than the standard declining tau model. Our approach places a wide variety of observations relating to the SFH of galaxies into a self-consistent framework based on the modern understanding of structure formation in ΛCDM. Constraints on the stellar mass-halo mass relationship and SFRs are available for download online.

Progenitors of low-luminosity Type II-Plateau supernovae

NASA Astrophysics Data System (ADS)

Lisakov, Sergey M.; Dessart, Luc; Hillier, D. John; Waldman, Roni; Livne, Eli

2018-01-01

The progenitors of low-luminosity Type II-Plateau supernovae (SNe II-P) are believed to be red supergiant (RSG) stars, but there is much disparity in the literature concerning their mass at core collapse and therefore on the main sequence. Here, we model the SN radiation arising from the low-energy explosion of RSG stars of 12, 25 and 27 M⊙ on the main sequence and formed through single star evolution. Despite the narrow range in ejecta kinetic energy (2.5-4.2 × 1050 erg) in our model set, the SN observables from our three models are significantly distinct, reflecting the differences in progenitor structure (e.g. surface radius, H-rich envelope mass and He-core mass). Our higher mass RSG stars give rise to Type II SNe that tend to have bluer colours at early times, a shorter photospheric phase, and a faster declining V-band light curve (LC) more typical of Type II-linear SNe, in conflict with the LC plateau observed for low-luminosity SNe II. The complete fallback of the CO core in the low-energy explosions of our high-mass RSG stars prevents the ejection of any 56Ni (nor any core O or Si), in contrast to low-luminosity SNe II-P, which eject at least 0.001 M⊙ of 56Ni. In contrast to observations, Type II SN models from higher mass RSGs tend to show an H α absorption that remains broad at late times (due to a larger velocity at the base of the H-rich envelope). In agreement with the analyses of pre-explosion photometry, we conclude that low-luminosity SNe II-P likely arise from low-mass rather than high-mass RSG stars.

Connection between Stellar Mass Distributions within Galaxies and Quenching Since z = 2

NASA Astrophysics Data System (ADS)

Mosleh, Moein; Tacchella, Sandro; Renzini, Alvio; Carollo, C. Marcella; Molaeinezhad, Alireza; Onodera, Masato; Khosroshahi, Habib G.; Lilly, Simon

2017-03-01

We study the history from z˜ 2 to z˜ 0 of the stellar mass assembly of quiescent and star-forming galaxies in a spatially resolved fashion. For this purpose, we use multi-wavelength imaging data from the Hubble Space Telescope (HST) over the GOODS fields and the Sloan Digital Sky Survey (SDSS) for the local population. We present the radial stellar mass surface density profiles of galaxies with {M}* > {10}10 {M}⊙ , corrected for mass-to-light ratio ({M}* /L) variations, and derive the half-mass-radius (R m ), central stellar mass surface density within 1 kpc ({{{Σ }}}1) and surface density at R m ({{{Σ }}}m) for star-forming and quiescent galaxies and study their evolution with redshift. At fixed stellar mass, the half-mass sizes of quiescent galaxies increase from z˜ 2 to z˜ 0 by a factor of ˜ 3-5, whereas the half-mass sizes of star-forming galaxies increase only slightly, by a factor of ˜2. The central densities {{{Σ }}}1 of quiescent galaxies decline slightly (by a factor of ≲ 1.7) from z˜ 2 to z˜ 0, while for star-forming galaxies {{{Σ }}}1 increases with time, at fixed mass. We show that the central density {{{Σ }}}1 has a tighter correlation with specific star-formation rate (sSFR) than {{{Σ }}}m and for all masses and redshifts galaxies with higher central density are more prone to be quenched. Reaching a high central density ({{{Σ }}}1≳ {10}10 {M}⊙ {{kpc}}2) seems to be a prerequisite for the cessation of star formation, though a causal link between high {{{Σ }}}1 and quenching is difficult to prove and their correlation can have a different origin.

Effect of temperature on life history parameters of adult Culicoides sonorensis (Diptera: Ceratopogonidae) in relation to geographic origin and vectorial capacity for bluetongue virus.

PubMed

Lysyk, T J; Danyk, T

2007-09-01

The effect of temperature on survival, oviposition, gonotrophic development, and a life history factor of vectorial capacity were examined in adult Culicoides sonorensis (Wirth & Jones) (Diptera: Ceratopogonidae) that originated from two geographic locations. Flies originating from the United States (Colorado) had slightly reduced survival after a bloodmeal compared with wild flies collected in southern Alberta (AB), Canada. Survival of AB flies declined in a curvilinear manner with temperature, whereas survival of U.S. flies showed a linear response to temperature. The survivorship curve of the AB flies more closely followed a Weibull distribution than an exponential, indicating survival was age-dependent. Survivorship of the U.S. flies followed an exponential distribution. Females from both sources laid similar numbers of eggs throughout their life. The first eggs were laid by females from both sources at 31.9 degree-day (DD)9.3. Dissections of blood-fed flies reared at various temperatures indicated that flies from both sources were 90% gravid at 32 DD9.3. Relationships among temperature and life history components of vectorial capacity were similar among flies from the two sources and indicated that vectorial capacity would be approximately 1.8-2.6-fold greater in a southern U.S. climate compared with southwestern Canada due solely to the effects of temperature on the life history of C. sonorensis. Using life history estimates derived from Weibull model had little effect on estimating vectorial capacity, whereas using estimates derived from the exponential model slightly overestimated vectorial capacity.

METALLICITY DISTRIBUTION FUNCTIONS, RADIAL VELOCITIES, AND ALPHA ELEMENT ABUNDANCES IN THREE OFF-AXIS BULGE FIELDS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, Christian I.; Rich, R. Michael; Kobayashi, Chiaki

2013-03-10

We present radial velocities and chemical abundance ratios of [Fe/H], [O/Fe], [Si/Fe], and [Ca/Fe] for 264 red giant branch stars in three Galactic bulge off-axis fields located near (l, b) = (-5.5, -7), (-4, -9), and (+8.5, +9). The results are based on equivalent width and spectrum synthesis analyses of moderate resolution (R Almost-Equal-To 18,000), high signal-to-noise ratio (S/N {approx} 75-300 pixel{sup -1}) spectra obtained with the Hydra spectrographs on the Blanco 4 m and WIYN 3.5 m telescopes. The targets were selected from the blue side of the giant branch to avoid cool stars that would be strongly affectedmore » by CN and TiO; however, a comparison of the color-metallicity distribution in literature samples suggests that our selection of bluer targets should not present a significant bias against metal-rich stars. We find a full range in metallicity that spans [Fe/H] Almost-Equal-To -1.5 to +0.5, and that, in accordance with the previously observed minor-axis vertical metallicity gradient, the median [Fe/H] also declines with increasing Galactic latitude in off-axis fields. The off-axis vertical [Fe/H] gradient in the southern bulge is estimated to be {approx}0.4 dex kpc{sup -1}; however, comparison with the minor-axis data suggests that a strong radial gradient does not exist. The (+8.5, +9) field exhibits a higher than expected metallicity, with a median [Fe/H] = -0.23, that might be related to a stronger presence of the X-shaped bulge structure along that line-of-sight. This could also be the cause of an anomalous increase in the median radial velocity for intermediate metallicity stars in the (+8.5, +9) field. However, the overall radial velocity and dispersion for each field are in good agreement with recent surveys and bulge models. All fields exhibit an identical, strong decrease in velocity dispersion with increasing metallicity that is consistent with observations in similar minor-axis outer bulge fields. Additionally, the [O/Fe], [Si/Fe], and [Ca/Fe] versus [Fe/H] trends are identical among our three fields, and are in good agreement with past bulge studies. We find that stars with [Fe/H] {approx}< -0.5 are {alpha}-enhanced, and that the [{alpha}/Fe] ratios decline at higher metallicity. At [Fe/H] {approx}< 0, the {alpha}-element trends are indistinguishable from the halo and thick disk, and the variations in the behavior of individual {alpha}-elements are consistent with production in massive stars and a rapid bulge formation timescale.« less

Tensile properties of craniofacial tendons in the mature and aged zebrafish

PubMed Central

Shah, Rishita R.; Nerurkar, Nandan L.; Wang, Calvin; Galloway, Jenna L.

2015-01-01

The zebrafish Danio rerio is a powerful model for the study of development, regenerative biology, and human disease. However, the analysis of load-bearing tissues such as tendons and ligaments has been limited in this system. This is largely due to technical limitations that preclude accurate measurement of their mechanical properties. Here, we present a custom tensile testing system that applies nano-Newton scale forces to zebrafish tendons as small as 1 mm in length. Tendon properties were remarkably similar to mammalian tendons, including stress-strain nonlinearity and a linear modulus (515±152 MPa) that aligned closely with mammalian data. Additionally, a simple exponential constitutive law used to describe tendon mechanics was successfully fit to zebrafish tendons; the associated material constants agreed with literature values for mammalian tendons. Finally, mature and aged zebrafish comparisons revealed a significant decline in mechanical function with age. Based on the exponential constitutive model, age related changes were primarily caused by a reduction in nonlinearity (e.g. changes in collagen crimp or fiber recruitment). These findings demonstrate the utility of zebrafish as a model to study tendon biomechanics in health and disease. Moreover, these findings suggest that tendon mechanical behavior is highly conserved across vertebrates. PMID:25665155

Resource acquisition, distribution and end-use efficiencies and the growth of industrial society

NASA Astrophysics Data System (ADS)

Jarvis, A. J.; Jarvis, S. J.; Hewitt, C. N.

2015-10-01

A key feature of the growth of industrial society is the acquisition of increasing quantities of resources from the environment and their distribution for end-use. With respect to energy, the growth of industrial society appears to have been near-exponential for the last 160 years. We provide evidence that indicates that the global distribution of resources that underpins this growth may be facilitated by the continual development and expansion of near-optimal directed networks (roads, railways, flight paths, pipelines, cables etc.). However, despite this continual striving for optimisation, the distribution efficiencies of these networks must decline over time as they expand due to path lengths becoming longer and more tortuous. Therefore, to maintain long-term exponential growth the physical limits placed on the distribution networks appear to be counteracted by innovations deployed elsewhere in the system, namely at the points of acquisition and end-use of resources. We postulate that the maintenance of the growth of industrial society, as measured by global energy use, at the observed rate of ~ 2.4 % yr-1 stems from an implicit desire to optimise patterns of energy use over human working lifetimes.

Evo-SETI SCALE to measure Life on Exoplanets

NASA Astrophysics Data System (ADS)

Maccone, Claudio

2016-04-01

Darwinian Evolution over the last 3.5 billion years was an increase in the number of living species from 1 (RNA?) to the current 50 million. This increasing trend in time looks like being exponential, but one may not assume an exactly exponential curve since many species went extinct in the past, even in mass extinctions. Thus, the simple exponential curve must be replaced by a stochastic process having an exponential mean value. Borrowing from financial mathematics (;Black-Scholes models;), this ;exponential; stochastic process is called Geometric Brownian Motion (GBM), and its probability density function (pdf) is a lognormal (not a Gaussian) (Proof: see ref. Maccone [3], Chapter 30, and ref. Maccone [4]). Lognormal also is the pdf of the statistical number of communicating ExtraTerrestrial (ET) civilizations in the Galaxy at a certain fixed time, like a snapshot: this result was found in 2008 by this author as his solution to the Statistical Drake Equation of SETI (Proof: see ref. Maccone [1]). Thus, the GBM of Darwinian Evolution may also be regarded as the extension in time of the Statistical Drake equation (Proof: see ref. Maccone [4]). But the key step ahead made by this author in his Evo-SETI (Evolution and SETI) mathematical model was to realize that LIFE also is just a b-lognormal in time: every living organism (a cell, a human, a civilization, even an ET civilization) is born at a certain time b (;birth;), grows up to a peak p (with an ascending inflexion point in between, a for adolescence), then declines from p to s (senility, i.e. descending inflexion point) and finally declines linearly and dies at a final instant d (death). In other words, the infinite tail of the b-lognormal was cut away and replaced by just a straight line between s and d, leading to simple mathematical formulae (;History Formulae;) allowing one to find this ;finite b-lognormal; when the three instants b, s, and d are assigned. Next the crucial Peak-Locus Theorem comes. It means that the GBM exponential may be regarded as the geometric locus of all the peaks of a one-parameter (i.e. the peak time p) family of b-lognormals. Since b-lognormals are pdf-s, the area under each of them always equals 1 (normalization condition) and so, going from left to right on the time axis, the b-lognormals become more and more ;peaky;, and so they last less and less in time. This is precisely what happened in human history: civilizations that lasted millennia (like Ancient Greece and Rome) lasted just centuries (like the Italian Renaissance and Portuguese, Spanish, French, British and USA Empires) but they were more and more advanced in the ;level of civilization;. This ;level of civilization; is what physicists call ENTROPY. Also, in refs. Maccone [3] and [4], this author proved that, for all GBMs, the (Shannon) Entropy of the b-lognormals in his Peak-Locus Theorem grows LINEARLY in time. The Molecular Clock, well known to geneticists since 50 years, shows that the DNA base-substitutions occur LINEARLY in time since they are neutral with respect to Darwinian selection. In simple words: DNA evolved by obeying the laws of quantum physics only (microscopic laws) and not by obeying assumed ;Darwinian selection laws; (macroscopic laws). This is Kimura's neutral theory of molecular evolution. The conclusion is that the Molecular Clock and the b-lognormal Entropy are the same thing. At last, we reach the new, original result justifying the publication of this paper. On exoplanets, molecular evolution is proceeding at about the same rate as it did proceed on Earth: rather independently of the physical conditions of the exoplanet, if the DNA had the possibility to evolve in water initially. Thus, Evo-Entropy, i.e. the (Shannon) Entropy of the generic b-lognormal of the Peak-Locus Theorem, provides the Evo-SETI SCALE to measure the evolution of life on exoplanets.

ETA CARINAE’S THERMAL X-RAY TAIL MEASURED WITH XMM-NEWTON AND NuSTAR

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hamaguchi, Kenji; Corcoran, Michael F.; Gull, Theodore R.

The evolved, massive highly eccentric binary system, η Car, underwent a periastron passage in the summer of 2014. We obtained two coordinated X-ray observations with XMM-Newton and NuSTAR during the elevated X-ray flux state and just before the X-ray minimum flux state around this passage. These NuSTAR observations clearly detected X-ray emission associated with η Car extending up to ∼50 keV for the first time. The NuSTAR spectrum above 10 keV can be fit with the bremsstrahlung tail from a kT ∼ 6 keV plasma. This temperature is ΔkT ∼ 2 keV higher than those measured from the iron K emission line complex, if the shockedmore » gas is in collisional ionization equilibrium. This result may suggest that the companion star's pre-shock wind velocity is underestimated. The NuSTAR observation near the X-ray minimum state showed a gradual decline in the X-ray emission by 40% at energies above 5 keV in a day, the largest rate of change of the X-ray flux yet observed in individual η Car observations. The column density to the hardest emission component, N{sub H} ∼ 10{sup 24} H cm{sup −2}, marked one of the highest values ever observed for η Car, strongly suggesting increased obscuration of the wind–wind colliding X-ray emission by the thick primary stellar wind prior to superior conjunction. Neither observation detected the power-law component in the extremely hard band that INTEGRAL and Suzaku observed prior to 2011. If the non-detection by NuSTAR is caused by absorption, the power-law source must be small and located very near the wind–wind collision apex. Alternatively, it may be that the power-law source is not related to either η Car or the GeV γ-ray source.« less

Star-forming brightest cluster galaxies at 0.25

DOE Office of Scientific and Technical Information (OSTI.GOV)

McDonald, M.; Stalder, B.; Bayliss, M.

2016-01-22

We present a multiwavelength study of the 90 brightest cluster galaxies (BCGs) in a sample of galaxy clusters selected via the Sunyaev Zel'dovich effect by the South Pole Telescope, utilizing data from various ground- and space-based facilities. We infer the star-formation rate (SFR) for the BCG in each cluster—based on the UV and IR continuum luminosity, as well as the [O ii]λλ3726,3729 emission line luminosity in cases where spectroscopy is available—and find seven systems with SFR > 100 M⊙ yr-1. We find that the BCG SFR exceeds 10 M⊙ yr-1 in 31 of 90 (34%) cases at 0.25 < z < 1.25, compared to ~1%–5% at z ~ 0 from the literature. At z gsim 1, this fraction increases tomore » $${92}_{-31}^{+6}$$%, implying a steady decrease in the BCG SFR over the past ~9 Gyr. At low-z, we find that the specific SFR in BCGs is declining more slowly with time than for field or cluster galaxies, which is most likely due to the replenishing fuel from the cooling ICM in relaxed, cool core clusters. At z gsim 0.6, the correlation between the cluster central entropy and BCG star formation—which is well established at z ~ 0—is not present. Instead, we find that the most star-forming BCGs at high-z are found in the cores of dynamically unrelaxed clusters. We use data from the Hubble Space Telescope to investigate the rest-frame near-UV morphology of a subsample of the most star-forming BCGs, and find complex, highly asymmetric UV morphologies on scales as large as ~50–60 kpc. The high fraction of star-forming BCGs hosted in unrelaxed, non-cool core clusters at early times suggests that the dominant mode of fueling star formation in BCGs may have recently transitioned from galaxy–galaxy interactions to ICM cooling.« less

Star-forming brightest cluster galaxies at 0.25 < z < 1.25: A transitioning fuel supply

DOE PAGES

McDonald, M.; Stalder, B.; Bayliss, M.; ...

2016-01-22

In this paper, we present a multiwavelength study of the 90 brightest cluster galaxies (BCGs) in a sample of galaxy clusters selected via the Sunyaev Zel'dovich effect by the South Pole Telescope, utilizing data from various ground- and space-based facilities. We infer the star-formation rate (SFR) for the BCG in each cluster—based on the UV and IR continuum luminosity, as well as the [O ii]λλ3726,3729 emission line luminosity in cases where spectroscopy is available—and find seven systems with SFR > 100 M ⊙ yr -1. We find that the BCG SFR exceeds 10 M ⊙ yr -1 in 31 of 90 (34%) cases at 0.25 < z < 1.25, compared to ~1%–5% at z ~ 0 from the literature. At z ≳ 1, this fraction increases tomore » $${92}_{-31}^{+6}$$%, implying a steady decrease in the BCG SFR over the past ~9 Gyr. At low-z, we find that the specific SFR in BCGs is declining more slowly with time than for field or cluster galaxies, which is most likely due to the replenishing fuel from the cooling ICM in relaxed, cool core clusters. At z ≳ 0.6, the correlation between the cluster central entropy and BCG star formation—which is well established at z ~ 0—is not present. Instead, we find that the most star-forming BCGs at high-z are found in the cores of dynamically unrelaxed clusters. We use data from the Hubble Space Telescope to investigate the rest-frame near-UV morphology of a subsample of the most star-forming BCGs, and find complex, highly asymmetric UV morphologies on scales as large as ~50–60 kpc. Finally, the high fraction of star-forming BCGs hosted in unrelaxed, non-cool core clusters at early times suggests that the dominant mode of fueling star formation in BCGs may have recently transitioned from galaxy–galaxy interactions to ICM cooling.« less

The Abundances of the Fe Group Elements in Early B Stars in the Magellanic Clouds and Bridge

NASA Astrophysics Data System (ADS)

Peters, Geraldine J.; Adelman, Saul J.

2016-01-01

The abundances of three Fe Group elements (V, Cr, and Fe) in 9 early main-sequence band B stars in the LMC, 7 in the SMC , and two in the Magellanic Bridge have been determined from archival FUSE observations and the Hubeny/Lanz NLTE programs TLUSTY/SYNSPEC. Lines from the Fe group elements, except for a few weak multiplets of Fe III, are not observable in the optical spectral region. The best set of lines in the FUSE spectral region are Fe III (UV1), V III 1150 Å, and Cr III 1137 Å. The abundances of these elements in early B stars are a marker for recent SNe Ia activity, as a single exploding white dwarf can deliver 0.5 solar masses of Ni-56 that decays into Fe to the ISM. The Fe group abundances in an older population of stars primarily reflect SNe II activity, in which a single explosion delivers only 0.07 solar masses of Ni-56 to the ISM (the rest remains trapped in the neutron star). The abundances of the Fe group elements in early B stars not only track SNe Ia activity but are also important for computing evolutionary tracks for massive stars. In general, the Fe abundance relative to the sun's value is comparable to the mean abundances for the lighter elements in the Clouds/Bridge but the values of [V,Cr/Fe]sun are smaller. This presentation will discuss the spatial distribution of the Fe Group elements in the Magellanic Clouds, and compare it with our galaxy in which the abundance of Fe declines with radial distance from the center. Support from NASA grants NAG5-13212, NNX10AD66G, STScI HST-GO-13346.22, and USC's Women in Science and Engineering (WiSE) program is greatly appreciated.

Cape Photographic Durchmusterung, volume 2

NASA Technical Reports Server (NTRS)

1993-01-01

The Cape Photographic Durchmusterung (CPD, Gill and Kapteyn 1895-1900) is a Photographic survey of southern stars in the declination range -18 to -90 degrees. This volume covers the declination range -53 through -89 degrees. Positions are given for 1875 equinox. The summary of the positional uncertainties quoted in the third volume of the published catalog gives +/- 0.28 sec (R.A.), +/- 0.044 arcmin (Dec.) for zones - 18 to -57 degrees, + 0.157 sec + 0.0764/cos(delta) sec (R.A.), +/- 0.056 arcmin (Dec.) for zones -58 to -85 degrees, +0.157 sec + 0.0353/cos (delta) sec (R.A.), + 0.0127 arcmin (Dec.) for the polar plate where, as explained in the introduction to the third volume, many positions were derived from rectangular coordinates (these are positions reported to 0.1 SCC (R.A.) and 0.001 arcmin (Dec.) in the -86 to -89 degree zones in the catalog). The probable error of a photographic magnitude, as determined by combining results for different magnitudes and weighting proportionately according to the numbers of stars in each class of magnitude, is given as +0.055 mag. From an analysis of the faint magnitude limits on the plates discussed in the third volume introduction, the catalog as a whole can be considered complete to photographic magnitude 9.2, but it is stated that it will be found practically complete, in or near the Milky Way, to magnitude 9.5.

Cape Photographic Durchmusterung, volume 3

NASA Technical Reports Server (NTRS)

1993-01-01

The Cape Photographic Durchmusterung (CPD, Gill and Kapleyn 1895-1900) is a photographic survey of southern stars in the declination range -18 to -90 degrees. This volume covers the declination range -53 through -89 degrees. Positions are given for the 1875 equinox. The summary of the positional uncertainties quoted in the third volume of the published catalog gives +/- 0.28 sec (R.A.), + 0.044 arcmin (Dec.) for zones -18 to -57 degrees, + 0.157 sec + 0.0764/cos(delta) sec (R.A.), +/- 0.056 arcmin (Dec.) for zones -58 to -85 degrees, +0.157 sec + 0.0353/cos(delta) sec (R.A.), +/- 0.0127 arcmin (Dec.) for the polar plate where, as explained in the introduction to the third volume, many positions were derived from rectangular coordinates (these are positions reported to 0.1 sec (R.A.) and 0.001 arcmin (Dec.) in the -86 to -89 degree zones in the catalog). The probable error of a photographic magnitude, as determined by combining results for different magnitudes and weighting proportionately according to the numbers of stars in each class of magnitude, is given as +0.055 mag. From an analysis of the faint magnitude limits on the plates discussed in the third volume introduction, the catalog as a whole can be considered complete to photographic magnitude 9.2, but it is stated that it will be found practically complete, in or near the Milky Way, to magnitude 9.5.

J-GEM observations of an electromagnetic counterpart to the neutron star merger GW170817

NASA Astrophysics Data System (ADS)

Utsumi, Yousuke; Tanaka, Masaomi; Tominaga, Nozomu; Yoshida, Michitoshi; Barway, Sudhanshu; Nagayama, Takahiro; Zenko, Tetsuya; Aoki, Kentaro; Fujiyoshi, Takuya; Furusawa, Hisanori; Kawabata, Koji S.; Koshida, Shintaro; Lee, Chien-Hsiu; Morokuma, Tomoki; Motohara, Kentaro; Nakata, Fumiaki; Ohsawa, Ryou; Ohta, Kouji; Okita, Hirofumi; Tajitsu, Akito; Tanaka, Ichi; Terai, Tsuyoshi; Yasuda, Naoki; Abe, Fumio; Asakura, Yuichiro; Bond, Ian A.; Miyazaki, Shota; Sumi, Takahiro; Tristram, Paul J.; Honda, Satoshi; Itoh, Ryosuke; Itoh, Yoichi; Kawabata, Miho; Morihana, Kumiko; Nagashima, Hiroki; Nakaoka, Tatsuya; Ohshima, Tomohito; Takahashi, Jun; Takayama, Masaki; Aoki, Wako; Baar, Stefan; Doi, Mamoru; Finet, Francois; Kanda, Nobuyuki; Kawai, Nobuyuki; Kim, Ji Hoon; Kuroda, Daisuke; Liu, Wei; Matsubayashi, Kazuya; Murata, Katsuhiro L.; Nagai, Hiroshi; Saito, Tomoki; Saito, Yoshihiko; Sako, Shigeyuki; Sekiguchi, Yuichiro; Tamura, Yoichi; Tanaka, Masayuki; Uemura, Makoto; Yamaguchi, Masaki S.

2017-12-01

GW170817 is the first detected gravitational wave source from a neutron star merger. We present the Japanese collaboration for gravitational-wave electro-magnetic (J-GEM) follow-up observations of SSS17a, an electromagnetic counterpart of GW170817. SSS17a shows a 2.5 mag decline in the z band during the period between 1.7 and 7.7 d after the merger. Such a rapid decline is not comparable with supernovae light curves at any epoch. The color of SSS17a also evolves rapidly and becomes redder during later epochs: the z - H color has changed by approximately 2.5 mag during the period between 0.7 and 7.7 d. The rapid evolutions of both the color and the optical brightness are consistent with the expected properties of a kilonova that is powered by the radioactive decay of newly synthesized r-process nuclei. Kilonova models with Lanthanide elements can reproduce the aforementioned observed properties well, which suggests that r-process nucleosynthesis beyond the second peak takes place in SSS17a. However, the absolute magnitude of SSS17a is brighter than the expected brightness of the kilonova models with an ejecta mass of 0.01 M⊙, which suggests a more intense mass ejection (˜0.03 M⊙) or possibly an additional energy source.

A minimalist feedback-regulated model for galaxy formation during the epoch of reionization

NASA Astrophysics Data System (ADS)

Furlanetto, Steven R.; Mirocha, Jordan; Mebane, Richard H.; Sun, Guochao

2017-12-01

Near-infrared surveys have now determined the luminosity functions of galaxies at 6 ≲ z ≲ 8 to impressive precision and identified a number of candidates at even earlier times. Here, we develop a simple analytic model to describe these populations that allows physically motivated extrapolation to earlier times and fainter luminosities. We assume that galaxies grow through accretion on to dark matter haloes, which we model by matching haloes at fixed number density across redshift, and that stellar feedback limits the star formation rate. We allow for a variety of feedback mechanisms, including regulation through supernova energy and momentum from radiation pressure. We show that reasonable choices for the feedback parameters can fit the available galaxy data, which in turn substantially limits the range of plausible extrapolations of the luminosity function to earlier times and fainter luminosities: for example, the global star formation rate declines rapidly (by a factor of ∼20 from z = 6 to 15 in our fiducial model), but the bright galaxies accessible to observations decline even faster (by a factor ≳ 400 over the same range). Our framework helps us develop intuition for the range of expectations permitted by simple models of high-z galaxies that build on our understanding of 'normal' galaxy evolution. We also provide predictions for galaxy measurements by future facilities, including James Webb Space Telescope and Wide-Field Infrared Survey Telescope.

Numerical Simulations of Wind Accretion in Symbiotic Binaries

NASA Astrophysics Data System (ADS)

de Val-Borro, M.; Karovska, M.; Sasselov, D.

2009-08-01

About half of the binary systems are close enough to each other for mass to be exchanged between them at some point in their evolution, yet the accretion mechanism in wind accreting binaries is not well understood. We study the dynamical effects of gravitational focusing by a binary companion on winds from late-type stars. In particular, we investigate the mass transfer and formation of accretion disks around the secondary in detached systems consisting of an asymptotic giant branch (AGB) mass-losing star and an accreting companion. The presence of mass outflows is studied as a function of mass-loss rate, wind temperature, and binary orbital parameters. A two-dimensional hydrodynamical model is used to study the stability of mass transfer in wind accreting symbiotic binary systems. In our simulations we use an adiabatic equation of state and a modified version of the isothermal approximation, where the temperature depends on the distance from the mass losing star and its companion. The code uses a block-structured adaptive mesh refinement method that allows us to have high resolution at the position of the secondary and resolve the formation of bow shocks and accretion disks. We explore the accretion flow between the components and formation of accretion disks for a range of orbital separations and wind parameters. Our results show the formation of stream flow between the stars and accretion disks of various sizes for certain orbital configurations. For a typical slow and massive wind from an AGB star the flow pattern is similar to a Roche lobe overflow with accretion rates of 10% of the mass loss from the primary. Stable disks with exponentially decreasing density profiles and masses of the order 10-4 solar masses are formed when wind acceleration occurs at several stellar radii. The disks are geometrically thin with eccentric streamlines and close to Keplerian velocity profiles. The formation of tidal streams and accretion disks is found to be weakly dependent on the mass loss from the AGB star. Our simulations of gravitationally focused wind accretion in symbiotic binaries show the formation of stream flows and enhanced accretion rates onto the compact component. We conclude that mass transfer through a focused wind is an important mechanism in wind accreting interacting binaries and can have a significant impact on the evolution of the binary itself and the individual components.

ADIABATIC MASS LOSS IN BINARY STARS. II. FROM ZERO-AGE MAIN SEQUENCE TO THE BASE OF THE GIANT BRANCH

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ge, Hongwei; Chen, Xuefei; Han, Zhanwen

2015-10-10

In the limit of extremely rapid mass transfer, the response of a donor star in an interacting binary becomes asymptotically one of adiabatic expansion. We survey here adiabatic mass loss from Population I stars (Z = 0.02) of mass 0.10 M{sub ⊙}–100 M{sub ⊙} from the zero-age main sequence to the base of the giant branch, or to central hydrogen exhaustion for lower main sequence stars. The logarithmic derivatives of radius with respect to mass along adiabatic mass-loss sequences translate into critical mass ratios for runaway (dynamical timescale) mass transfer, evaluated here under the assumption of conservative mass transfer. Formore » intermediate- and high-mass stars, dynamical mass transfer is preceded by an extended phase of thermal timescale mass transfer as the star is stripped of most of its envelope mass. The critical mass ratio q{sub ad} (throughout this paper, we follow the convention of defining the binary mass ratio as q ≡ M{sub donor}/M{sub accretor}) above which this delayed dynamical instability occurs increases with advancing evolutionary age of the donor star, by ever-increasing factors for more massive donors. Most intermediate- or high-mass binaries with nondegenerate accretors probably evolve into contact before manifesting this instability. As they approach the base of the giant branch, however, and begin developing a convective envelope, q{sub ad} plummets dramatically among intermediate-mass stars, to values of order unity, and a prompt dynamical instability occurs. Among low-mass stars, the prompt instability prevails throughout main sequence evolution, with q{sub ad} declining with decreasing mass, and asymptotically approaching q{sub ad} = 2/3, appropriate to a classical isentropic n = 3/2 polytrope. Our calculated q{sub ad} values agree well with the behavior of time-dependent models by Chen and Han of intermediate-mass stars initiating mass transfer in the Hertzsprung gap. Application of our results to cataclysmic variables, as systems that must be stable against rapid mass transfer, nicely circumscribes the range in q{sub ad} as a function of the orbital period in which they are found. These results are intended to advance the verisimilitude of population synthesis models of close binary evolution.« less

STARFIRE: The Spectroscopic Terahertz Airborne Receiver for Far-InfraRed Exploration

NASA Astrophysics Data System (ADS)

Aguirre, James; STARFIRE Collaboration

2018-01-01

Understanding the formation and evolution of galaxies is one of the foremost goals of astrophysics and cosmology today. The cosmic star formation rate has undergone a dramatic evolution over the course of the last seven billion years, with a peak in cosmic star formation near z ~ 1, largely in dust-obscured star forming galaxies (DSFGs), followed by a dramatic fall in both the star formation rate and the fraction of star formation occurring in DSFGs. A variety of unextincted diagnostic lines are present in the far-infrared (FIR) which can provide insight into the conditions of star formation in DSFGs. Spectroscopy in the far-infrared is thus scientifically crucial for understanding galaxy evolution, yet remains technically difficult, particularly for wavelengths shorter than those accessible to ALMA.STARFIRE (the Spectroscopic Terahertz Airborne Receiver for Far-InfraRed Exploration) is a proposed integral-field spectrometer using kinetic inductance detectors, operating from 240 - 420 μm and coupled to a 2.5 meter low-emissivity carbon-fiber balloon-borne telescope. Using dispersive spectroscopy and the stratospheric platform, STARFIRE can achieve better performance than SOFIA or Herschel-SPIRE FTS. STARFIRE is designed to study the ISM of galaxies from 0.5 < z < 1.5, primarily in the [CII](158 μm) line, and also in cross-correlation with [NII] (122 μm). This offers a view of the star-forming medium with minimal impact from dust extinction through the period of peak cosmic star formation and into the current epoch where the star formation rate begins to decline. STARFIRE will be capable of making a high significance detection of the [CII] power spectrum in at least 4 redshift bins and measuring the [CII] x [NII] power spectrum at z ~ 1. The intensity mapped power spectra will be sensitive to one- and two-halo clustering, as well as shot noise, and will relate the mean [CII] intensity as a function of redshift (a proxy for star formation rate density) to the large scale structure. In addition, STARFIRE will detect at least 50 galaxies directly in the [CII] line, and will also be able to stack on optical galaxies to below the SPIRE confusion limit to measure the [CII] luminosity of more typical galaxies.

Accretion and Magnetic Reconnection in the Pre-Main Sequence Binary DQ Tau as Revealed through High-Cadence Optical Photometry

NASA Astrophysics Data System (ADS)

Tofflemire, Benjamin M.; Mathieu, Robert D.; Ardila, David R.; Akeson, Rachel L.; Ciardi, David R.; Herczeg, Gregory; Johns-Krull, Christopher M.; Vodniza, Alberto

2016-01-01

Protostellar disks are integral to the formation and evolution of low-mass stars and planets. A paradigm for the star-disk interaction has been extensively developed through theory and observation in the case of single stars. Most stars, however, form in binaries or higher order systems where the distribution of disk material and mass flows are more complex. Pre-main sequence (PMS) binary stars can have up to three accretion disks: two circumstellar disks and a circumbinary disk separated by a dynamically cleared gap. Theory suggests that mass may periodically flow in an accretion stream from a circumbinary disk across the gap onto circumstellar disks or stellar surfaces.The archetype for this theory is the eccentric, PMS binary DQ Tau. Moderate-cadence broadband photometry (~10 observations per orbital period) has shown pulsed brightening events near most periastron passages, just as numerical simulations would predict for a binary of similar orbital parameters. While this observed behavior supports the accretion stream theory, it is not exclusive to variable accretion rates. Magnetic reconnection events (flares) during the collision of stellar magnetospheres at periastron (when separated by 8 stellar radii) could produce the same periodic, broadband behavior when observed at a one-day cadence. Further evidence for magnetic activity comes from gyrosynchrotron, radio flares (typical of stellar flares) observed near multiple periastron passages. To reveal the physical mechanism seen in DQ Tau's moderate-cadence observations, we have obtained continuous, moderate-cadence, multi-band photometry over 10 orbital periods (LCOGT 1m network), supplemented with 32 nights of minute-cadence photometry centered on 4 separate periastron passages (WIYN 0.9m; APO ARCSAT). With detailed lightcurve morphologies we distinguish between the gradual rise and fall on multi-day time-scales predicted by the accretion stream theory and the hour time-scale, rapid-rise and exponential-decay typical of flares. While both are present, accretion dominates the observed variability providing evidence for the accretion stream theory and detailed mass accretion rates for comparison with numerical simulations.

HST/WFC3 near-infrared spectroscopy of quenched galaxies at z ∼ 1.5 from the WISP survey: Stellar population properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bedregal, A. G.; Scarlata, C.; Rutkowski, M. J.

We combine Hubble Space Telescope (HST) G102 and G141 near-IR (NIR) grism spectroscopy with HST/WFC3-UVIS, HST/WFC3-IR, and Spitzer/IRAC [3.6 μm] photometry to assemble a sample of massive (log (M {sub star}/M {sub ☉}) ∼ 11.0) and quenched (specific star formation rate <0.01 Gyr{sup –1}) galaxies at z ∼ 1.5. Our sample of 41 galaxies is the largest with G102+G141 NIR spectroscopy for quenched sources at these redshifts. In contrast to the local universe, z ∼ 1.5 quenched galaxies in the high-mass range have a wide range of stellar population properties. We find that their spectral energy distributions (SEDs) are wellmore » fitted with exponentially decreasing star formation histories and short star formation timescales (τ ≤ 100 Myr). Quenched galaxies also show a wide distribution in ages, between 1 and 4 Gyr. In the (u – r){sub 0}-versus-mass space quenched galaxies have a large spread in rest-frame color at a given mass. Most quenched galaxies populate the z ∼ 1.5 red sequence (RS), but an important fraction of them (32%) have substantially bluer colors. Although with a large spread, we find that the quenched galaxies on the RS have older median ages (3.1 Gyr) than the quenched galaxies off the RS (1.5 Gyr). We also show that a rejuvenated SED cannot reproduce the observed stacked spectra of (the bluer) quenched galaxies off the RS. We derive the upper limit on the fraction of massive galaxies on the RS at z ∼ 1.5 to be <43%. We speculate that the young quenched galaxies off the RS are in a transition phase between vigorous star formation at z > 2 and the z ∼ 1.5 RS. According to their estimated ages, the time required for quenched galaxies off the RS to join their counterparts on the z ∼ 1.5 RS is of the order of ∼1 Gyr.« less