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Sample records for phoenicis stars revisited

  1. Discovery of 6 SX Phoenicis Stars in the Globular Cluster NGC 4833

    NASA Astrophysics Data System (ADS)

    Murphy, Brian W.; Darragh, A. N.

    2012-01-01

    We report the discovery of 6 SX Phoenicis stars in the globular cluster NGC 4833. Images were obtained from January through June 2011 with the Southeastern Association for Research in Astronomy (SARA) 0.6 meter telescope located at Cerro Tololo Interamerican Observatory. The image subtraction method of Alard & Lupton (1998) was used to search for variable stars in the cluster. We confirmed 16 previously known variables cataloged by Demers & Wehlau (1977). In addition to the previously known variables we have identified 11 new variables. Of the total number of confirmed variables in our 10x10 arc minute field, we classified 10 RRab variables, with a mean period of 0.69591 days, 9 RRc, with a mean period of 0.39555 days, a W Ursae Majoris contact binary, an Algol-type binary, and the 6 SX Phoenicis stars with a mean period of 0.05847 days. The periods and relative numbers of RRab and RRc variables are indicative of the cluster being of the Oosterhoff type II. We present the periods of previously known variables and the periods, classification, and multi-color light curves of the newly discovered variables, and their location on the color-magnitude diagram. This project was funded in part by the National Science Foundation Research Experiences for Undergraduates (REU) program through grant NSF AST-1004 872 and by a grant from the Butler Institute for Research and Scholarship.

  2. GLOBAL STAR FORMATION REVISITED

    SciTech Connect

    Silk, Joseph; Norman, Colin E-mail: norman@stsci.edu

    2009-07-20

    A general treatment of disk star formation is developed from a dissipative multiphase model, with the dominant dissipation due to cloud collisions. The Schmidt-Kennicutt (SK) law emerges naturally for star-forming disks and starbursts. We predict that there should be an inverse correlation between Tully-Fisher law and SK law residuals. The model is extended to include a multiphase treatment of supernova feedback that leads to a turbulent pressure-regulated generalization of the star formation law and is applicable to gas-rich starbursts. Enhanced pressure, as expected in merger-induced star formation, enhances star formation efficiency. An upper limit is derived for the disk star formation rate in starbursts that depends on the ratio of global ISM to cloud pressures. We extend these considerations to the case where the interstellar gas pressure in the inner galaxy is dominated by outflows from a central active galactic nucleus (AGN). During massive spheroid formation, AGN-driven winds trigger star formation, resulting in enhanced supernova feedback and outflows. The outflows are comparable to the AGN-boosted star formation rate and saturate in the super-Eddington limit. Downsizing of both SMBH and spheroids is a consequence of AGN-driven positive feedback. Bondi accretion feeds the central black hole with a specific accretion rate that is proportional to the black hole mass. AGN-enhanced star formation is mediated by turbulent pressure and relates spheroid star formation rate to black hole accretion rate. The relation between black hole mass and spheroid velocity dispersion has a coefficient (Salpeter time to gas consumption time ratio) that provides an arrow of time. Highly efficient, AGN-boosted star formation can occur at high redshift.

  3. A Vanishing Star Revisited

    NASA Astrophysics Data System (ADS)

    1999-07-01

    VLT Observations of an Unusual Stellar System Reinhold Häfner of the Munich University Observatory (Germany) is a happy astronomer. In 1988, when he was working at a telescope at the ESO La Silla observatory, he came across a strange star that suddenly vanished off the computer screen. He had to wait for more than a decade to get the full explanation of this unusual event. On June 10-11, 1999, he observed the same star with the first VLT 8.2-m Unit Telescope (ANTU) and the FORS1 astronomical instrument at Paranal [1]. With the vast power of this new research facility, he was now able to determine the physical properties of a very strange stellar system in which two planet-size stars orbit each other. One is an exceedingly hot white dwarf star , weighing half as much as the Sun, but only twice as big as the Earth. The other is a much cooler and less massive red dwarf star , one-and-a-half times the size of planet Jupiter. Once every three hours, the hot star disappears behind the other, as seen from the Earth. For a few minutes, the brightness of the system drops by a factor of more than 250 and it "vanishes" from view in telescopes smaller than the VLT. A variable star named NN Serpentis ESO PR Photo 30a/99 ESO PR Photo 30a/99 [Preview - JPEG: 400 x 468 pix - 152k] [Normal - JPEG: 800 x 936 pix - 576k] [High-Res - JPEG: 2304 x 2695 pix - 4.4M] Caption to ESO PR Photo 30a/99 : The sky field around the 17-mag variable stellar system NN Serpentis , as seen in a 5 sec exposure through a V(isual) filter with VLT ANTU and FORS1. It was obtained just before the observation of an eclipse of this unsual object and served to centre the telescope on the corresponding sky position. The field shown here measures 4.5 x 4.5 armin 2 (1365 x 1365 pix 2 ; 0.20 arcsec/pix). The field is somewhat larger than that shown in Photo 30b/99 and has the same orientation to allow comparison: North is about 20° anticlockwise from the top and East is 90° clockwise from that direction. The

  4. Two new pulsating low-mass pre-white dwarfs or SX Phoenicis stars?

    NASA Astrophysics Data System (ADS)

    Corti, M. A.; Kanaan, A.; Córsico, A. H.; Kepler, S. O.; Althaus, L. G.; Koester, D.; Sánchez Arias, J. P.

    2016-03-01

    Context. The discovery of pulsations in low-mass stars opens an opportunity to probe their interiors and determine their evolution by employing the tools of asteroseismology. Aims: We aim to analyse high-speed photometry of SDSS J145847.02+070754.46 and SDSS J173001.94+070600.25 and discover brightness variabilities. In order to locate these stars in the Teff - log g diagram, we fit optical spectra (SDSS) with synthetic non-magnetic spectra derived from model atmospheres. Methods: To carry out this study, we used the photometric data we obtained for these stars with the 2.15 m telescope at CASLEO, Argentina. We analysed their light curves and applied the discrete Fourier transform (FT) to determine the pulsation frequencies. Finally, we compare both stars in the Teff - log g diagram, with two known pre-white dwarfs and seven pulsating pre-ELM white dwarf stars, δ Scuti, and SX Phe stars Results: We report the discovery of pulsations in SDSS J145847.02+070754.46 and SDSS J173001.94+070600.25. We determine their effective temperature and surface gravity to be Teff = 7972 ± 200 K, log g = 4.25 ± 0.5 and Teff = 7925 ± 200 K, log g = 4.25 ± 0.5, respectively. With these parameters, these new pulsating low-mass stars can be identified with either ELM white dwarfs (with ~0.17 M⊙) or more massive SX Phe stars. We identified pulsation periods of 3278.7 and 1633.9 s for SDSS J145847.02+070754.46 and a pulsation period of 3367.1 s for SDSS J173001.94+070600.25. These two new objects, together with those of Maxted et al. (2013, 2014), indicate the possible existence of a new instability domain towards the late stages of evolution of low-mass white dwarf stars, although their identification with SX Phe stars cannot be discarded. Visiting Astronomer, Complejo Astronómico El Leoncito operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba, and San Juan.

  5. MC-17 Phoenicis Region

    NASA Technical Reports Server (NTRS)

    1994-01-01

    Mars digital-image mosaic merged with color of the MC-17 quadrangle, Phoenicis Lacus region of Mars. Two of the four largest shield volcanoes on Mars are within the northwestern part, the south half of Pavonis Mons and Arsia Mons. The eastern part includes Syria and Sinai Plana. Most of the quadrangle forms the Tharsis plateau--the highest plateau on Mars; its elevation, 10 km, is twice that of the Tibetan Plateau, the highest plateau on Earth. Also in the northeastern part is Noctis Labyrinthus, a complex system of fault valleys at the west end of Valles Marineris. The south-central part is marked by the large fault system, Claritas Fossae. Latitude range -30 to 0 degrees, longitude range 90 to 135 degrees.

  6. Brevipalpus Phoenicis (Geijskes) species complex – a closer look

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Brevipalpus phoenicis sensu stricto is redescribed and the species diagnosis established. Two former synonyms of B. phoenicis sensu lato, B. yothersi and B. papayensis, are resurrected and redescribed, and their species diagnoses established. Four new species, previously misidentified as B. phoeni...

  7. STATISTICAL PROPERTIES OF GALACTIC {delta} SCUTI STARS: REVISITED

    SciTech Connect

    Chang, S.-W.; Kim, D.-W.; Byun, Y.-I.; Protopapas, P. E-mail: kim@mpia-hd.mpg.de

    2013-05-15

    We present statistical characteristics of 1578 {delta} Scuti stars including nearby field stars and cluster member stars within the Milky Way. We obtained 46% of these stars (718 stars) from work by Rodriguez and collected the remaining 54% of stars (860 stars) from other literature. We updated the entries with the latest information of sky coordinates, color, rotational velocity, spectral type, period, amplitude, and binarity. The majority of our sample is well characterized in terms of typical period range (0.02-0.25 days), pulsation amplitudes (<0.5 mag), and spectral types (A-F type). Given this list of {delta} Scuti stars, we examined relations between their physical properties (i.e., periods, amplitudes, spectral types, and rotational velocities) for field stars and cluster members, and confirmed that the correlations of properties are not significantly different from those reported in Rodriguez's work. All the {delta} Scuti stars are cross-matched with several X-ray and UV catalogs, resulting in 27 X-ray and 41 UV-only counterparts. These counterparts are interesting targets for further study because of their uniqueness in showing {delta} Scuti-type variability and X-ray/UV emission at the same time. The compiled catalog can be accessed through the Web interface http://stardb.yonsei.ac.kr/DeltaScuti.

  8. Statistical Properties of Galactic δ Scuti Stars: Revisited

    NASA Astrophysics Data System (ADS)

    Chang, S.-W.; Protopapas, P.; Kim, D.-W.; Byun, Y.-I.

    2013-05-01

    We present statistical characteristics of 1578 δ Scuti stars including nearby field stars and cluster member stars within the Milky Way. We obtained 46% of these stars (718 stars) from work by Rodríguez and collected the remaining 54% of stars (860 stars) from other literature. We updated the entries with the latest information of sky coordinates, color, rotational velocity, spectral type, period, amplitude, and binarity. The majority of our sample is well characterized in terms of typical period range (0.02-0.25 days), pulsation amplitudes (<0.5 mag), and spectral types (A-F type). Given this list of δ Scuti stars, we examined relations between their physical properties (i.e., periods, amplitudes, spectral types, and rotational velocities) for field stars and cluster members, and confirmed that the correlations of properties are not significantly different from those reported in Rodríguez's work. All the δ Scuti stars are cross-matched with several X-ray and UV catalogs, resulting in 27 X-ray and 41 UV-only counterparts. These counterparts are interesting targets for further study because of their uniqueness in showing δ Scuti-type variability and X-ray/UV emission at the same time. The compiled catalog can be accessed through the Web interface http://stardb.yonsei.ac.kr/DeltaScuti.

  9. REVISITING THE FIRST GALAXIES: THE EPOCH OF POPULATION III STARS

    SciTech Connect

    Muratov, Alexander L.; Gnedin, Oleg Y.; Zemp, Marcel; Gnedin, Nickolay Y.

    2013-08-10

    We investigate the transition from primordial Population III (Pop III) star formation to normal Pop II star formation in the first galaxies using new cosmological hydrodynamic simulations. We find that while the first stars seed their host galaxies with metals, they cannot sustain significant outflows to enrich the intergalactic medium, even assuming a top-heavy initial mass function. This means that Pop III star formation could potentially continue until z Almost-Equal-To 6 in different unenriched regions of the universe, before being ultimately shut off by cosmic reionization. Within an individual galaxy, the metal production and stellar feedback from Pop II stars overtake Pop III stars in 20-200 Myr, depending on galaxy mass.

  10. Revisiting The First Galaxies: The Epoch of Population III Stars

    NASA Astrophysics Data System (ADS)

    Muratov, Alexander; Gnedin, O. Y.; Gnedin, N. Y.; Zemp, M. K.

    2013-01-01

    We study the formation of the first galaxies using new hydrodynamic cosmological simulations with the ART code. Our simulations feature a recently developed model for dust-based formation of molecular gas. Here, we develop and implement a new recipe for the formation of metal-free Pop III stars. We reach a spatial resolution of 2 pc at z=10 and resolve star-forming galaxies with the masses above 10^6 solar masses. We find the epoch during which Pop III stars dominate the energy and metal budget of the universe to be short-lived. While these stars seed their host galaxies with metals, they cannot drive significant outflows to enrich the IGM in our simulations. Feedback from pair instability supernovae causes Pop III star formation to self-terminate within their host galaxies, but is not strong enough to suppress star formation in external galaxies. Within any individual galaxy, Pop II stars overtake Pop III stars within ~50-150 Myr. A threshold of M = 3 * 10^6 solar masses separates galaxies that lose a significant fraction of their baryons due to Pop III feedback from those that do not. Understanding the nature of the transition between Pop III and Pop II star formation is of key importance for studying the dawn of galaxy formation.

  11. Orbital elements of S stars - Revisiting the evolutionary status of S stars

    NASA Astrophysics Data System (ADS)

    Jorissen, A.; Mayor, M.

    1992-07-01

    The hypothesis of an evolutionary link between barium stars and the non-Mira S stars is discussed. The hypothesis of an evolutionary link between the barium stars and the non-Mira S stars is confirmed. The mass function distribution of S stars, indicating that the companions are likely white dwarfs, as is the case for barium stars, supports this hypothesis. However, systems with periods shorter than 600 d appear to be lacking among S stars, although they are present among barium stars. Moreover, S stars appear to be less massive on the average than barium stars. It is suggested that these differences between the two families can be naturally explained by assuming that non-Mira S stars (without Tc) populate the first giant branch instead of the asymptotic branch. A synoptic view of the evolutionary paths followed by low- and intermediate-mass binary systems is presented, with special emphasis on the relationships between the families of peculiar red giants.

  12. REVISITING THE FIRST GALAXIES: THE EFFECTS OF POPULATION III STARS ON THEIR HOST GALAXIES

    SciTech Connect

    Muratov, Alexander L.; Gnedin, Oleg Y.; Zemp, Marcel; Gnedin, Nickolay Y.

    2013-08-01

    We revisit the formation and evolution of the first galaxies using new hydrodynamic cosmological simulations with the adaptive refinement tree code. Our simulations feature a recently developed model for H{sub 2} formation and dissociation, and a star formation recipe that is based on molecular rather than atomic gas. Here, we develop and implement a recipe for the formation of metal-free Population III (Pop III) stars in galaxy-scale simulations that resolve primordial clouds with sufficiently high density. We base our recipe on the results of prior zoom-in simulations that resolved the protostellar collapse in pre-galactic objects. We find the epoch during which Pop III stars dominated the energy and metal budget of the first galaxies to be short-lived. Galaxies that host Pop III stars do not retain dynamical signatures of their thermal and radiative feedback for more than 10{sup 8} years after the lives of the stars end in pair-instability supernovae, even when we consider the maximum reasonable efficiency of the feedback. Though metals ejected by the supernovae can travel well beyond the virial radius of the host galaxy, they typically begin to fall back quickly, and do not enrich a large fraction of the intergalactic medium. Galaxies with a total mass in excess of 3 Multiplication-Sign 10{sup 6} M{sub Sun} re-accrete most of their baryons and transition to metal-enriched Pop II star formation.

  13. The Variable Stars of the DRACO DWARF Spheroidal Glaxay: Revisited

    DTIC Science & Technology

    2008-11-01

    mag, those of Aparicio et al. (2001): 〈V (HB)〉 = 20.2±0.1 mag, and those of Bellazzini et al. (2002): 〈V (HB)〉 = 20.28± 0.10 mag, with a 2σ...254, 507 Aparicio , A., Carrera, R., & Martı́nez-Delgado, D. 2001, AJ, 122, 2524 No. 5, 2008 VARIABLE STARS IN DRACO 1939 Armandroff, T. E., Olszewski

  14. The near-contact binary star RZ Dra revisited

    NASA Astrophysics Data System (ADS)

    Erdem, A.; Zola, S.; Winiarski, M.

    2011-01-01

    This paper presents the absolute parameters of RZ Dra. New CCD observations were made at the Mt. Suhora Observatory in 2007. Two photometric data sets (1990 BV and 2007 BVRI) were analysed using modern light-curve synthesis methods. Large asymmetries in the light curves may be explained in terms of a dark starspot on the primary component, an A6 type star. Due to this magnetic activity, the primary component would appear to belong to the class of Ap-stars and would show small amplitude with δ Scuti-type pulsations. With this in mind, a time-series analysis of the residual light curves was made. However, we found no evidence of pulsation behaviour in RZ Dra. Combining the solutions of our light curves and Rucinski et al. (2000)'s radial velocity curves, the following absolute parameters of the components were determined: M1 = 1.63 ± 0.03 M ⊙, M2 = 0.70 ± 0.02 M ⊙, R1 = 1.65 ± 0.02R ⊙, R2 = 1.15 ± 0.02 R ⊙, L1 = 9.72 ± 0.30 L ⊙ and L2 = 0.74 ± 0.10 L ⊙. The distance to RZ Dra was calculated as 400 ± 25 pc, taking into account interstellar extinction. The orbital period of the system was studied using updated O- C information. It was found that the orbital period varied in its long-period sinusoidal form, superimposed on a downward parabola. The parabolic term shows a secular period decrease at a slow rate of 0.06 ± 0.02 s per century and is explained by the mass loss via magnetized wind of the Ap-star primary. The tilted sinusoidal form of the period variation may be considered as an apparent change and may be interpreted in terms of the light-time effect due to the presence of a third body.

  15. The Viscous Decretion Disk Model of the Classical Be Star β CMi Revisited

    NASA Astrophysics Data System (ADS)

    Klement, R.; Carciofi, A. C.; Rivinius, Th.

    2017-02-01

    We revisit the viscous decretion disk (VDD) model of the classical Be star β CMi as presented by Klemen et al. (2015) using an updated version of the radiative transfer code HDUST. A software bug was causing the mean intensities to be slightly underestimated in the equatorial region of the disk with small but detectable effects on the disk temperature and emergent spectrum. The new model fixes an unexplained feature of the original model, which was able to reproduce the observations only when considering a dual density behavior: a steep density fall-off in the very inner parts of the disk followed by a shallower density profile. The new model is able to reproduce all the observables reasonably well using a single power law for the density profile throughout the entire disk, as predicted by the VDD model. All the other original conclusions, most importantly the reported truncation of the disk at a distance of 35 stellar equatorial radii from the central star, remain unchanged.

  16. Effects of radiation (Cobalt-60) on the elimination of Brevipalpus phoenicis (Acari: Tenuipalpidae) Cardinum endosymbiont

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Brevipalpus phoenicis (Geijskes) (Acari: Tenuipalpidae) is a polyphagous mite with worldwide distribution and it is also a vector of several plant viruses. In citrus, B. phoenicis transmits Citrus leprosis virus (CiLV), the causal agent of leprosis, a disease that costs millions of dollars/year for ...

  17. FUV Spectra of Evolved Late-K and M Stars: Mass Loss Revisited and Stellar Activity

    NASA Technical Reports Server (NTRS)

    Harper, Graham M.

    2002-01-01

    This is the final report for the FUSE Cycle 1 program A100: FUV Spectra of Evolved Late-K and M Stars: Mass Loss revisited and Stellar Activity. Targets alpha TrA (K3 II) and gamma Cru (M3 III) were originally assigned 25 ksec each, to be observed in the medium aperture. Once the in-flight performance and telescope alignment problems were known, the observations were reprogrammed to optimized the scientific return of the program. Alpha TrA was scheduled for 25 ksec observations in both the medium and large apertures. The principle aim of this program was to measure the stellar FUV line and continuum emission, in order to estimate the photoionization radiation field and to determine the level of stellar activity through the fluxes in the collisionally excited high temperature diagnostics: C III 977Angstroms and O VI 1032,1038Angstrom doublet. The medium aperture observations were obtained successfully while the large aperture observations were thought by Johns Hopkins University (JHU)to be lost to satellite problems. There was insufficient signal-to- noise in the medium aperture short wavelength Sic channels to do quantitative science.

  18. Revisiting the Microlensing Event OGLE 2012-BLG-0026: A Solar Mass Star with Two Cold Giant Planets

    NASA Technical Reports Server (NTRS)

    Beaulieu, J.-P.; Bennett, D. P.; Batista, V.; Fukui, A.; Marquette, J.-B.; Brillant, S.; Cole, A. A.; Rogers, L. A.; Sumi, T.; Abe, F.

    2016-01-01

    Two cold gas giant planets orbiting a G-type main-sequence star in the galactic disk were previously discovered in the high-magnification microlensing event OGLE-2012-BLG-0026. Here, we present revised host star flux measurements and a refined model for the two-planet system using additional light curve data. We performed high angular resolution adaptive optics imaging with the Keck and Subaru telescopes at two epochs while the source star was still amplified. We detected the lens flux, H = 16.39 +/- 0.08. The lens, a disk star, is brighter than predicted from the modeling in the original study. We revisited the light curve modeling using additional photometric data from the B and C telescope in New Zealand and CTIO 1.3 m H-band light curve. We then include the Keck and Subaru adaptive optic observation constraints. The system is composed of an approximately 4-9 Gyr lens star of M(sub lens) = 1.06 +/- 0.05 solar mass at a distance of D(sub lens) = 4.0 +/- 0.3 kpc, orbited by two giant planets of 0.145 +/- 0.008 M(sub Jup) and 0.86 +/- 0.06 M(sub Jup), with projected separations of 4.0 +/- 0.5 au and 4.8 +/- 0.7 au, respectively. Because the lens is brighter than the source star by 16 +/- 8% in H, with no other blend within one arcsec, it will be possible to estimate its metallicity using subsequent IR spectroscopy with 8-10 m class telescopes. By adding a constraint on the metallicity it will be possible to refine the age of the system.

  19. Revisiting the Microlensing Event OGLE 2012-BLG-0026: A Solar Mass Star with Two Cold Giant Planets

    NASA Astrophysics Data System (ADS)

    Beaulieu, J.-P.; Bennett, D. P.; Batista, V.; Fukui, A.; Marquette, J.-B.; Brillant, S.; Cole, A. A.; Rogers, L. A.; Sumi, T.; Abe, F.; Bhattacharya, A.; Koshimoto, N.; Suzuki, D.; Tristram, P. J.; Han, C.; Gould, A.; Pogge, R.; Yee, J.

    2016-06-01

    Two cold gas giant planets orbiting a G-type main-sequence star in the galactic disk were previously discovered in the high-magnification microlensing event OGLE-2012-BLG-0026. Here, we present revised host star flux measurements and a refined model for the two-planet system using additional light curve data. We performed high angular resolution adaptive optics imaging with the Keck and Subaru telescopes at two epochs while the source star was still amplified. We detected the lens flux, H = 16.39 ± 0.08. The lens, a disk star, is brighter than predicted from the modeling in the original study. We revisited the light curve modeling using additional photometric data from the B&C telescope in New Zealand and CTIO 1.3 m H-band light curve. We then include the Keck and Subaru adaptive optic observation constraints. The system is composed of a ˜4-9 Gyr lens star of M lens = 1.06 ± 0.05 M ⊙ at a distance of D lens = 4.0 ± 0.3 kpc, orbited by two giant planets of 0.145 ± 0.008 M Jup and 0.86 ± 0.06 M Jup, with projected separations of 4.0 ± 0.5 au and 4.8 ± 0.7 au, respectively. Because the lens is brighter than the source star by 16 ± 8% in H, with no other blend within one arcsec, it will be possible to estimate its metallicity using subsequent IR spectroscopy with 8-10 m class telescopes. By adding a constraint on the metallicity it will be possible to refine the age of the system.

  20. Variables en la región central del cúmulo globular NGC 3201: descomposición de Fourier de las curvas de luz de las RR Lyrae y análisis de la relación período-luminosidad de las SX Phoenicis

    NASA Astrophysics Data System (ADS)

    Ahumada, J. A.; Arellano Ferro, A.; Calderón, J. H.; Kains, N.

    2015-08-01

    We present CCD time-series observations of the central region of the globular cluster NGC 3201, collected from CASLEO in March 2013, with the aim of performing the Fourier decomposition of the light curves of the RR Lyrae variables. This procedure, applied to the RRab-type stars, gave a mean value [Fe/H], for the cluster metallicity, and 5.00 0.22 kpc, for the cluster distance. The values found from two RRc stars are consistent with those derived previously. Because of differential reddening across the cluster field, individual reddenings for the RRab stars were estimated from their curves, resulting in an average value . An investigation of the light curves of stars in the blue straggler region led to the discovery of three new SX Phoenicis variables. The period-luminosity relation of the SX Phoenicis was used for an independent determination of the distance to the cluster and of the individual reddenings of these variables.

  1. Pulsating Blue Metal-poor Stars

    NASA Astrophysics Data System (ADS)

    Preston, George W.; Landolt, Arlo U.

    1999-12-01

    The blue metal-poor (BMP) star CS 22966-043 is an SX Phoenicis star and the primary of a spectroscopic binary with a provisional orbital period of ~430 days. Radial velocity and UBV photometric observations of this star made in 1998 require downward revision of the orbital period to 319 days. The BMP star CS 29499-057 also appears to be an SX Phoenicis star with small amplitude (ΔV~0.04 mag) and short period (P=0.0417 days), on the basis of photometric and radial velocity observations obtained in 1998. There is some indication that it too may be the primary of a spectroscopic binary. Three other BMP stars have radial velocity standard deviations greater than those of 17 BMP radial velocity standards. We suggest that they may be small-amplitude SX Phoenicis stars. Finally, the BMP star CS 29497-017 is shown to be a short-period velocity variable (P=0.302 days) on the basis of observations accumulated over an interval of 2200 days, but we were unable to detect a light variation in 1998 July. Therefore, the nature of the velocity variation of this object remains uncertain.

  2. Meteor Beliefs Project: Shakespeare revisited and the Elizabethan stage's `blazing star'

    NASA Astrophysics Data System (ADS)

    Gheorghe, Andrei Dorian; McBeath, Alastair

    2007-06-01

    Some fresh Shakespearean citations of meteors, further to those given previously in the Project, are presented, along with a discussion of the Elizabethan stage's use of the `blazing star', with especial reference to the great comet of 1577.

  3. Brevipalpus phoenicis (Geijskes) species complex – resurrection of E. W. Baker’s species (Acari: Tenuipalpidae)

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Brevipalpus phoenicis sensu lato has been identified from countries all over the world and has been associated with many different host plant species. As a taxon, it shows a degree of morphological variation. A combination such as this often indicates that the taxon actually represents a complex o...

  4. Revisiting Caroline Furness's An Introduction to the Study of Variable Stars on its Centenary (Poster abstract)

    NASA Astrophysics Data System (ADS)

    Larsen, K.

    2016-06-01

    (Abstract only) A century and one month ago (October 1915) Dr. Caroline Ellen Furness (1869-1936), Director of the Vassar College Observatory, published An Introduction to the Study of Variable Stars. Issued in honor of the fiftieth anniversary of the founding of Vassar College, the work was meant to fill a void in the literature, namely as both an introduction to the topic of variable stars and as a manual explaining how they should be observed and the resulting data analyzed. It was judged to be one of the hundred best books written by an American woman in the last hundred years at the 1933 World's Fair in Chicago. The book covers the relevant history of and background on types of variable stars, star charts, catalogs, and the magnitude scale, then describes observing techniques, including visual, photographic, and photoelectric photometry. The work finishes with a discussion of light curves and patterns of variability, with a special emphasis on eclipsing binaries and long period variables. Furness's work is a valuable snapshot of the state of astronomical knowledge, technology, and observing techniques from a century ago. This presentation will analyze both Furness's book and its reception in the scientific community, and draw parallels to current advice given to beginning variable star observers.

  5. Revisiting The Brightest RV Tauri Star: First Ionization Potential (FIP) Effect in R Sct

    NASA Astrophysics Data System (ADS)

    Yolalan, Gizay; Sahin, Timur

    2016-07-01

    We have derived elemental abundances of the brightest RV Tauri star, R Sct. The abundance analysis of the star is based on high resolution and high quality (S/N>300) echelle spectra, mainly obtained for radial velocity study of a large sample of IRAS like RV Tau sample stars, from the McDonald Observatory (R~48,000). Our analysis is based on optical spectra obtained at only one phase of the variation. The standard 1D LTE analysis provided a fresh determination of the atmospheric parameters: Teff=5000 K, logg=1.05 cgs, and a microturbulence velocity ξ=3.4 km/s and [Fe/H] = -0.33. We report on chemical abundances of 10 neutral and ionized species identified over 4800 - 5600 A wavelength region. In an effort to explain observed deficiency in abundances, possible scenarios including FIP is investigated.

  6. Interspecific interactions involving Neoseiulus californicus (Acari: Phytoseiidae) and Agistemus brasiliensis (Acari: Stigmaeidae) as predators of Brevipalpus phoenicis (Acari: Tenuipalpidae).

    PubMed

    da Silva, Marcos Zatti; Sato, Mário Eidi; de Oliveira, Carlos Amadeu Leite; Nicastro, Roberto Lomba

    2015-03-01

    Brevipalpus phoenicis (Geijskes) is associated with the transmission of Citrus leprosis which is considered the main viral disease for the Brazilian citrus production. Mites of the families Stigmaeidae and Phytoseiidae coexist in various agricultural crops, often promoting the biological control of pest mites. The aim of this work was to study the interactions of Neoseiulus californicus (McGregor) (Phytoseiidae) and Agistemus brasiliensis Matioli, Ueckermann & Oliveira (Stigmaeidae), in the presence or absence of B. phoenicis. Two experiments were carried out. In the first, a N. californicus female was placed in each leaf disc arena, with eggs of B. phoenicis and A. brasiliensis as food sources. In the second, an A. brasiliensis female was placed in each arena, with eggs of B. phoenicis and N. californicus as food sources. Adults of both predators were able to consume both types of eggs available as food sources, but they fed on considerably higher proportions of B. phoenicis than on eggs of the predator. Eggs of A. brasiliensis were not a suitable food source for N. californicus, which produced only 0.1 egg per female per day when only eggs of that species were present in the experimental unit. The results suggest that eggs of N. californicus were a suitable food source for A. brasiliensis, which oviposited 1.12 eggs per day, when only eggs of N. californicus were provided to the stigmaeid mite. The possible interactions among N. californicus, A. brasiliensis and B. phoenicis in citrus orchards are discussed.

  7. Binary Star Orbits. III. In which we Revisit the Remarkable Case of Tweedledum and Tweedledee

    DTIC Science & Technology

    2010-06-14

    from NOAO 4m telescopes, the Mt. Wilson 100in 1Visiting Astronomer , Kitt Peak National Observatory and Cerro Tololo Interamerican Observatories...a double by F.G.W. Struve in 1825 (Struve 1837). Since that time the system has been well observed by many double star astronomers , and has probably...give first and absolute priority to a programme of planetary photography , to the distress of van den Bos and myself . . . and this seems likely to ring

  8. Ribosomal RNA genes and deuterostome phylogeny revisited: more cyclostomes, elasmobranchs, reptiles, and a brittle star.

    PubMed

    Mallatt, Jon; Winchell, Christopher J

    2007-06-01

    This is an expanded study of the relationships among the deuterostome animals based on combined, nearly complete 28S and 18S rRNA genes (>3925 nt.). It adds sequences from 20 more taxa to the approximately 45 sequences used in past studies. Seven of the new taxa were sequenced here (brittle star Ophiomyxa, lizard Anolis, turtle Chrysemys, sixgill shark Hexanchus, electric ray Narcine, Southern Hemisphere lamprey Geotria, and Atlantic hagfish Myxine for 28S), and the other 13 were from GenBank and the literature (from a chicken, dog, rat, human, three lungfishes, and several ray-finned fishes, or Actinopterygii). As before, our alignments were based on secondary structure but did not account for base pairing in the stems of rRNA. The new findings, derived from likelihood-based tree-reconstruction methods and by testing hypotheses with parametric bootstrapping, include: (1) brittle star joins with sea star in the echinoderm clade, Asterozoa; (2) with two hagfishes and two lampreys now available, the cyclostome (jawless) fishes remain monophyletic; (3) Hexanchiform sharks are monophyletic, as Hexanchus groups with the frilled shark, Chlamydoselachus; (4) turtle is the sister taxon of all other amniotes; (5) bird is closer to the lizard than to the mammals; (6) the bichir Polypterus is in a monophyletic Actinopterygii; (7) Zebrafish Danio is the sister taxon of the other two teleosts we examined (trout and perch); (8) the South American and African lungfishes group together to the exclusion of the Australian lungfish. Other findings either upheld those of the previous rRNA-based studies (e.g., echinoderms and hemichordates group as Ambulacraria; orbitostylic sharks; batoids are not derived from any living lineage of sharks) or were obvious (monophyly of mammals, gnathostomes, vertebrates, echinoderms, etc.). Despite all these findings, the rRNA data still fail to resolve the relations among the major groups of deuterostomes (tunicates, Ambulacraria, cephalochordates

  9. BINARY STAR ORBITS. III. REVISITING THE REMARKABLE CASE OF TWEEDLEDUM AND TWEEDLEDEE

    SciTech Connect

    Mason, Brian D.; Hartkopf, William I.; McAlister, Harold A. E-mail: wih@usno.navy.mi

    2010-07-15

    Two of the most challenging objects for optical interferometry in the middle of the last century were the close components (FIN 332) of the wide visual binary STF2375 (= WDS 18455+0530 = HIP 92027 = ADS 11640). Each component of the wide pair was found to have subcomponents of approximately the same magnitude, position angle, and separation and, hence, were designated by the tongue-in-cheek monikers 'Tweedledum and Tweedledee' by the great visual interferometrist William S. Finsen in 1953. They were later included in a list of 'Double Stars that Vex the Observer' by W.H. van den Bos in 1958. While speckle interferometry has reaped a rich harvest investigating the close inteferometric binaries of Finsen, the 'Tweedles' have continued to both fascinate and exasperate due to both the great similarity of the close pairs and the inherent 180{sup 0} ambiguity associated with interferometry. Detailed analysis of all published observations of the system has revealed several errors which are here corrected, allowing for determination of these orbital elements which resolve the quadrant ambiguity. A unique software filter was developed which allowed subarrays from archival ICCD speckle data from 1982 to be re-reduced. Those data, combined with new and unpublished observations obtained in 2001-2009 from NOAO 4 m telescopes, the Mount Wilson 100 inch telescope and the Naval Observatory Flagstaff Station 61 inch telescope as well as high-quality unresolved measures all allow for the correct orbits to be determined. Co-planarity of the multiple system is also investigated.

  10. Binary Star Orbits. III. Revisiting the Remarkable Case of Tweedledum and Tweedledee

    NASA Astrophysics Data System (ADS)

    Mason, Brian D.; Hartkopf, William I.; McAlister, Harold A.

    2010-07-01

    Two of the most challenging objects for optical interferometry in the middle of the last century were the close components (FIN 332) of the wide visual binary STF2375 (= WDS 18455+0530 = HIP 92027 = ADS 11640). Each component of the wide pair was found to have subcomponents of approximately the same magnitude, position angle, and separation and, hence, were designated by the tongue-in-cheek monikers "Tweedledum and Tweedledee" by the great visual interferometrist William S. Finsen in 1953. They were later included in a list of "Double Stars that Vex the Observer" by W.H. van den Bos in 1958. While speckle interferometry has reaped a rich harvest investigating the close inteferometric binaries of Finsen, the "Tweedles" have continued to both fascinate and exasperate due to both the great similarity of the close pairs and the inherent 180° ambiguity associated with interferometry. Detailed analysis of all published observations of the system has revealed several errors which are here corrected, allowing for determination of these orbital elements which resolve the quadrant ambiguity. A unique software filter was developed which allowed subarrays from archival ICCD speckle data from 1982 to be re-reduced. Those data, combined with new and unpublished observations obtained in 2001-2009 from NOAO 4 m telescopes, the Mount Wilson 100 inch telescope and the Naval Observatory Flagstaff Station 61 inch telescope as well as high-quality unresolved measures all allow for the correct orbits to be determined. Co-planarity of the multiple system is also investigated.

  11. Passion fruit green spot virus vectored by Brevipalpus phoenicis (Acari: Tenuipalpidae) on passion fruit in Brazil.

    PubMed

    Kitajima, E W; Rezende, J A M; Rodrigues, J C V

    2003-01-01

    Passion fruit green spot disease was first identified in 1997 after a severe outbreak at Vera Cruz County, state of São Paulo, Brazil. Mature yellow fruits of Passiflora edulis Simms f. flavicarpa Degener showed characteristic green spots, 2-5 mm in diameter and patches of green tissues were present on senescent leaves. The devastating effect to passion flower is caused by necrotic lesions that encircle the stems and kill the plant. In severe cases, entire orchards of a few hectares in size have been completely destroyed. The disease was always preceded by heavy infestations of Brevipalpus phoenicis (Geijskes) (Acari: Tenuipalpidae). Transmission electron microscopy of affected tissues (fruits, leaves, and stems) consistently revealed the presence of short, bacilliform particles (50-70 nm x 100-120 nm) in the cisternae of the endoplasmic reticulum, as well as the presence of a dense viroplasm in the cytoplasm. This cytopathic effect has been found in several other Brevipalpus-transmitted or associated viruses and is classified as a cytoplasmic type of disease. Experimental reproduction of the leaf and stem symptoms was achieved by transferring B. phoenicis collected from affected field passion flower plants onto healthy plants. The evidence supports a viral etiology for the disease and the agent was named passion fruit green spot virus. Its relationship with other B. phoenicis related viruses continues to be studied. The disease was also found in the Brazilian states of Bahia, Sergipe, Rondonia, Minas Gerais, Rio de Janeiro, and in the Federal District. Use of one or more of the following acaricides (hexythiazox, fenbutatin-oxide, propargite, quinomethionate, or dicofol) has significantly reduced the incidence of the disease.

  12. Transmission of Citrus leprosis virus C by Brevipalpus phoenicis (Geijskes) to Alternative Host Plants Found in Citrus Orchards

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The equivalent of US$ 75 million is spent each year in Brazil to control Brevipalpus phoenicis, a mite vector of Citrus leprosis virus C (CiLV-C). In this study we investigated the possibility that hedgerows, windbreaks, and weeds normally found in citrus orchards could host CiLV-C. Mites reared on ...

  13. Absolute parameters for AI Phoenicis using WASP photometry

    NASA Astrophysics Data System (ADS)

    Kirkby-Kent, J. A.; Maxted, P. F. L.; Serenelli, A. M.; Turner, O. D.; Evans, D. F.; Anderson, D. R.; Hellier, C.; West, R. G.

    2016-06-01

    Context. AI Phe is a double-lined, detached eclipsing binary, in which a K-type sub-giant star totally eclipses its main-sequence companion every 24.6 days. This configuration makes AI Phe ideal for testing stellar evolutionary models. Difficulties in obtaining a complete lightcurve mean the precision of existing radii measurements could be improved. Aims: Our aim is to improve the precision of the radius measurements for the stars in AI Phe using high-precision photometry from the Wide Angle Search for Planets (WASP), and use these improved radius measurements together with estimates of the masses, temperatures and composition of the stars to place constraints on the mixing length, helium abundance and age of the system. Methods: A best-fit ebop model is used to obtain lightcurve parameters, with their standard errors calculated using a prayer-bead algorithm. These were combined with previously published spectroscopic orbit results, to obtain masses and radii. A Bayesian method is used to estimate the age of the system for model grids with different mixing lengths and helium abundances. Results: The radii are found to be R1 = 1.835 ± 0.014 R⊙, R2 = 2.912 ± 0.014 R⊙ and the masses M1 = 1.1973 ± 0.0037 M⊙, M2 = 1.2473 ± 0.0039 M⊙. From the best-fit stellar models we infer a mixing length of 1.78, a helium abundance of YAI = 0.26 +0.02-0.01 and an age of 4.39 ± 0.32 Gyr. Times of primary minimum show the period of AI Phe is not constant. Currently, there are insufficient data to determine the cause of this variation. Conclusions: Improved precision in the masses and radii have improved the age estimate, and allowed the mixing length and helium abundance to be constrained. The eccentricity is now the largest source of uncertainty in calculating the masses. Further work is needed to characterise the orbit of AI Phe. Obtaining more binaries with parameters measured to a similar level of precision would allow us to test for relationships between helium

  14. Production of cellulolytic enzymes by Aspergillus phoenicis in grape waste using response surface methodology.

    PubMed

    Dedavid e Silva, Lucas André; Lopes, Fernanda Cortez; Silveira, Silvana Terra; Brandelli, Adriano

    2009-02-01

    The production of cellulolytic enzymes by the fungus Aspergillus phoenicis was investigated. Grape waste from the winemaking industry was chosen as the growth substrate among several agro-industrial byproducts. A 2 x 2 central composite design was performed, utilizing the amount of grape waste and peptone as independent variables. The fungus was cultivated in submerged fermentation at 30 degrees C and 120 rpm for 120 h, and the activities of total cellulases, endoglucanases, and beta-glucosidases were measured. Total cellulases were positively influenced by the linear increase of peptone concentration and decrease at axial concentrations of grape waste and peptone. Maximum activity of endoglucanase was observed by a linear increase of both grape waste and peptone concentrations. Concentrations of grape waste between 5 and 15 g/L had a positive effect on the production of beta-glucosidase; peptone had no significant effects. The optimum production of the three cellulolytic activities was observed at values near the central point. A. phoenicis has the potential for the production of cellulases utilizing grape waste as the growth substrate.

  15. The ACS LCID project. X. the star formation history of IC 1613: Revisiting the over-cooling problem

    SciTech Connect

    Skillman, Evan D.; Hidalgo, Sebastian L.; Monelli, Matteo; Gallart, Carme; Aparicio, Antonio E-mail: shidalgo@iac.es E-mail: carme@iac.es [Instituto de Astrofísica de Canarias, Vía Láctea s and others

    2014-05-01

    We present an analysis of the star formation history (SFH) of a field near the half-light radius in the Local Group dwarf irregular galaxy IC 1613 based on deep Hubble Space Telescope Advanced Camera for Surveys imaging. Our observations reach the oldest main sequence turn-off, allowing a time resolution at the oldest ages of ∼1 Gyr. Our analysis shows that the SFH of the observed field in IC 1613 is consistent with being constant over the entire lifetime of the galaxy. These observations rule out an early dominant episode of star formation in IC 1613. We compare the SFH of IC 1613 with expectations from cosmological models. Since most of the mass is in place at early times for low-mass halos, a naive expectation is that most of the star formation should have taken place at early times. Models in which star formation follows mass accretion result in too many stars formed early and gas mass fractions that are too low today (the 'over-cooling problem'). The depth of the present photometry of IC 1613 shows that, at a resolution of ∼1 Gyr, the star formation rate is consistent with being constant, at even the earliest times, which is difficult to achieve in models where star formation follows mass assembly.

  16. Report on the Photometric Observations of the Variable Stars DH Pegasi, DY Pegasi, and RZ Cephei

    NASA Astrophysics Data System (ADS)

    Abu-Sharkh, I.; Fang, S.; Mehta, S.; Pham, D.

    2014-12-01

    We report 872 observations on two RR Lyrae variable stars, DH Pegasi and RZ Cephei, and on one SX Phoenicis variable, DY Pegasi. This paper discusses the methodology of our measurements, the light curves, magnitudes, epochs, and epoch prediction of the above stars. We also derived the period of DY Pegasi. All measurements and analyses are compared with prior publications and known values from multiple databases.

  17. Citrus leprosis virus vectored by Brevipalpus phoenicis (Acari: Tenuipalpidae) on citrus in Brazil.

    PubMed

    Rodrigues, J C V; Kitajima, E W; Childers, C C; Chagas, C M

    2003-01-01

    Citrus leprosis is caused by Citrus leprosis virus (CiLV) that is transmitted by mites in the genus Brevipalpus (Acari: Tenuipalpidae). This disease directly reduces production and the life span of the citrus plant. The main symptoms of the disease include lesions on fruits, leaves, and twigs or small branches, causing premature fruit drop, defoliation, and death of the twigs or branches leading to serious tree decline. Leprosis is a highly destructive disease of citrus, wherever it occurs. The Brazilian citrus industry spends over 100 million US dollars annually on acaricides to control the vector, Brevipalpus phoenicis (Geijskes). This review contains information about the history of the etiology of citrus leprosis, its geographical distribution, host range, the role of the mite vectors, viral morphology and relationships with the infected cell, and transmissibility of the virus by the mite. In addition, data on the mite-virus-plant relationship, disease damage, and strategies for controlling disease spread are presented.

  18. Revisiting CoRoT RR Lyrae stars: detection of period doubling and temporal variation of additional frequencies

    NASA Astrophysics Data System (ADS)

    Szabó, R.; Benkő, J. M.; Paparó, M.; Chapellier, E.; Poretti, E.; Baglin, A.; Weiss, W. W.; Kolenberg, K.; Guggenberger, E.; Le Borgne, J.-F.

    2014-10-01

    Context. High-precision, space-based photometric missions like CoRoT and Kepler have revealed new and surprising phenomena in classical variable stars. Such discoveries were the period doubling in RR Lyrae stars and the frequent occurrence of additional periodicities some of which can be explained by radial overtone modes, but others are discordant with the radial eigenfrequency spectrum. Aims: We search for signs of period doubling in CoRoT RR Lyrae stars. The occurrence of this dynamical effect in modulated RR Lyrae stars might help us to gain more information about the mysterious Blazhko effect. The temporal variability of the additional frequencies in representatives of all subtypes of RR Lyrae stars is also investigated. Methods: We preprocess CoRoT light curves by applying trend and jump correction and outlier removal. Standard Fourier technique is used to analyze the frequency content of our targets and follow the time-dependent phenomena. Results: The most comprehensive collection of CoRoT RR Lyrae stars, including new discoveries is presented and analyzed. We found alternating maxima and in some cases half-integer frequencies in four CoRoT Blazhko RR Lyrae stars, as clear signs of the presence of period doubling. This reinforces that period doubling is an important ingredient for understanding the Blazhko effect - a premise we derived previously from the Kepler RR Lyrae sample. As expected, period doubling is detectable only for short time intervals in most modulated RRab stars. Our results show that the temporal variability of the additional frequencies in all RR Lyrae subtypes is ubiquitous. The ephemeral nature and the highly variable amplitude of these variations suggest a complex underlying dynamics of and an intricate interplay between radial and possibly nonradial modes in RR Lyrae stars. The omnipresence of additional modes in all types of RR Lyrae - except in non-modulated RRab stars - implies that asteroseismology of these objects should be

  19. Revisiting the Trend of Debris Disks with regards to the Improved Ages of Early-Type Stars

    NASA Astrophysics Data System (ADS)

    Thomas, Brianna P.; Hillenbrand, Lynne

    2017-01-01

    Finding excess infrared emission around a star can indicate the presence of a debris disk, a collection of dust in orbit around a star as a result of large-body collisions (such as between asteroids). In order to see how these disks evolve, it is crucial to be able to define the ages of a large sample of stars. David and Hillenbrand (2015) were able to derive their own uniform technique for deriving the ages of 3,493 early-type stars using specialized photometry to derive parameters such as surface gravity and effective temperature. Correlating their sample of stars with infrared data from the Wide-field Infrared Survey Explorer (WISE) and 2 Micron All Sky Survey (2MASS) missions, we improved available trends among debris disk presence, stellar age, and spectral type. We did this by plotting different color-color and box-and-whisker diagrams in order to determine excess emission in the WISE and 2MASS bands. Colors ks-W3 and ks-W4 were chosen as our standard colors to detect circumstellar disk candidates after considering the reliability of the data. Stars above 1σ were considered to be stars with candidates. The percent frequency of sources with evidence of excess in ks-W3 is 6.4 ± 2.0% with ages <600 Myr and declines to 2% for older sources. The percent frequency of sources with evidence of excess in ks-W4 is 7.1 ± 2.1% with ages <600 Myr and declines to 4.4% for older sources.

  20. The Chemical Composition Contrast between M3 and M13 Revisited: New Abundances for 28 Giant Stars in M3

    NASA Astrophysics Data System (ADS)

    Sneden, Christopher; Kraft, Robert P.; Guhathakurta, Puragra; Peterson, Ruth C.; Fulbright, Jon P.

    2004-04-01

    We report new chemical abundances of 23 bright red giant members of the globular cluster M3, based on high-resolution (R~45,000) spectra obtained with the Keck I telescope. The observations, which involve the use of multislits in the HIRES Keck I spectrograph, are described in detail. Combining these data with a previously reported small sample of M3 giants obtained with the Lick 3 m telescope, we compare metallicities and [X/Fe] ratios for 28 M3 giants with a 35-star sample in the similar-metallicity cluster M13, and with Galactic halo field stars having [Fe/H]<-1. For elements having atomic number A>=A(Si), we derive little difference in [X/Fe] ratios in the M3, M13, or halo field samples. All three groups exhibit C depletion with advancing evolutionary state beginning at the level of the red giant branch ``bump,'' but the overall depletion of about 0.7-0.9 dex seen in the clusters is larger than that associated with the field stars. The behaviors of O, Na, Mg, and Al are distinctively different among the three stellar samples. Field halo giants and subdwarfs have a positive correlation of Na with Mg, as predicted from explosive or hydrostatic carbon burning in Type II supernova sites. Both M3 and M13 show evidence of high-temperature proton-capture synthesis from the ON, NeNa, and MgAl cycles, while there is no evidence for such synthesis among halo field stars. But the degree of such extreme proton-capture synthesis in M3 is smaller than it is in M13: the M3 giants exhibit only modest deficiencies of O and corresponding enhancements of Na, less extreme overabundances of Al, fewer stars with low Mg and correspondingly high Na, and no indication that O depletions are a function of advancing evolutionary state, as has been claimed for M13. We have also considered NGC 6752, for which Mg isotopic abundances have been reported by Yong et al. Giants in NGC 6752 and M13 satisfy the same anticorrelation of O abundances with the ratio (25Mg+26Mg)/24Mg, which measures the

  1. Revisiting Paine’s 1966 sea star removal experiment, the most-cited empirical article in the American Naturalist

    USGS Publications Warehouse

    Lafferty, Kevin D.; Suchanek, Tom

    2016-01-01

    “Food Web Complexity and Species Diversity” (Paine 1966) is the most-cited empirical article published in the American Naturalist. In short, Paine removed predatory sea stars (Pisaster ochraceus) from the rocky intertidal and watched the key prey species, mussels (Mytilus californianus), crowd out seven subordinate primary space-holding species. However, because these mussels are a foundational species, they provide three-dimensional habitat for over 300 associated species inhabiting the mussel beds; thus, removing sea stars significantly increases community-wide diversity. In any case, most ecologists cite Paine (1966) to support a statement that predators increase diversity by interfering with competition. Although detractors remained skeptical of top-down effects and keystone concepts, the paradigm that predation increases diversity spread. By 1991, “Food Web Complexity and Species Diversity” was considered a classic ecological paper, and after 50 years it continues to influence ecological theory and conservation biology.

  2. Revisiting the pre-main-sequence evolution of stars. I. Importance of accretion efficiency and deuterium abundance

    NASA Astrophysics Data System (ADS)

    Kunitomo, Masanobu; Guillot, Tristan; Takeuchi, Taku; Ida, Shigeru

    2017-02-01

    Context. Protostars grow from the first formation of a small seed and subsequent accretion of material. Recent theoretical work has shown that the pre-main-sequence (PMS) evolution of stars is much more complex than previously envisioned. Instead of the traditional steady, one-dimensional solution, accretion may be episodic and not necessarily symmetrical, thereby affecting the energy deposited inside the star and its interior structure. Aims: Given this new framework, we want to understand what controls the evolution of accreting stars. Methods: We use the MESA stellar evolution code with various sets of conditions. In particular, we account for the (unknown) efficiency of accretion in burying gravitational energy into the protostar through a parameter, ξ, and we vary the amount of deuterium present. Results: We confirm the findings of previous works that, in terms of evolutionary tracks on an Hertzprung-Russell (H-R) diagram, the evolution changes significantly with the amount of energy that is lost during accretion. We find that deuterium burning also regulates the PMS evolution. In the low-entropy accretion scenario, the evolutionary tracks in the H-R diagram are significantly different from the classical tracks and are sensitive to the deuterium content. A comparison of theoretical evolutionary tracks and observations allows us to exclude some cold accretion models (ξ 0) with low deuterium abundances. Conclusions: We confirm that the luminosity spread seen in clusters can be explained by models with a somewhat inefficient injection of accretion heat. The resulting evolutionary tracks then become sensitive to the accretion heat efficiency, initial core entropy, and deuterium content. In this context, we predict that clusters with a higher D/H ratio should have less scatter in luminosity than clusters with a smaller D/H. Future work on this issue should include radiation-hydrodynamic simulations to determine the efficiency of accretion heating and further

  3. Line-driven winds revisited in the context of Be stars: Ω-slow solutions with high k values

    SciTech Connect

    Silaj, J.; Jones, C. E.; Curé, M.

    2014-11-01

    The standard, or fast, solutions of m-CAK line-driven wind theory cannot account for slowly outflowing disks like the ones that surround Be stars. It has been previously shown that there exists another family of solutions—the Ω-slow solutions—that is characterized by much slower terminal velocities and higher mass-loss rates. We have solved the one-dimensional m-CAK hydrodynamical equation of rotating radiation-driven winds for this latter solution, starting from standard values of the line force parameters (α, k, and δ), and then systematically varying the values of α and k. Terminal velocities and mass-loss rates that are in good agreement with those found in Be stars are obtained from the solutions with lower α and higher k values. Furthermore, the equatorial densities of such solutions are comparable to those that are typically assumed in ad hoc models. For very high values of k, we find that the wind solutions exhibit a new kind of behavior.

  4. Coffee ringspot virus vectored by Brevipalpus phoenicis (Acari: Tenuipalpidae) in coffee.

    PubMed

    Chagas, C M; Kitajima, E W; Rodrigues, J C V

    2003-01-01

    Coffee ringspot is characterized by conspicuous ringspot symptoms on leaves, berries, and less frequently on twigs. It is caused by coffee ringspot virus (CoRSV), a short, bacilliform virus (40 nm x 100-110 nm). The virus is not seed borne and is transmitted by Brevipalpus phoenicis (Geijskes). Transovarial transmission within the mite does not occur. CoRSV has been mechanically transmitted to Chenopodium amaranticolor Coste and Reynaud, C. quinoa Wildenow, Beta vulgaris L., and Alternanthera tenella Colla resulting in local lesions. Systemic infection within both C. amaranticolor and C. quinoa occurs. Virions are found in the nucleus or cytoplasm of infected cells, commonly associated with membranes. Occasionally, membrane bounded particles are found within the cisternae of the endoplasmic reticulum. A characteristic electron lucent, nuclear inclusion is commonly found in many infected cells. These cytopathic effects place CoRSV among the nuclear type of Brevipalpus-borne viruses. The disease has been reported in several Brazilian states (São Paulo, Paraná, Minas Gerais, and Federal District) and recently found in Costa Rica. A similar disease is known in the Philippines, but no information exists about its relationship to CoRSV. Coffee ringspot had no economical significance until recently when a large scale infection was reported in Minas Gerais that resulted in yield loss.

  5. Chemical evaluation of African palm weevil, Rhychophorus phoenicis, larvae as a food source.

    PubMed

    Elemo, Babajide O; Elemo, Gloria N; Makinde, M A; Erukainure, Ochuko L

    2011-01-01

    The chemical properties of the African palm weevil, Rhychophorus phoenicis (F.) (Coleoptera: Curculionidae), larvae were evaluated using standard methodology. The chloroform-methanol extract yielded 37.12% on a dry basis. The oil was liquid at room temperature with a flash point of 36.0 °C. Analysis of the physical constants indicated values of 192.25 Wijs and 427.70 mg KOH/g as iodine and saponification, respectively. Fatty acid analysis of the extracted oil showed the presence of unsaturated fatty acids at low levels. Palmitic acid and stearic acid constituted 35.3 and 60.5% of the oil, respectively. The usual behaviour of the oil at room temperature, irrespective of the level of unsaturation of its constituent fatty acid was noted. The total protein content of the defatted palm weevil larva (dry basis) was estimated at 66.3%. The amino acid values compared favourably to FAO reference protein, except for tryptophan, which was limiting. All the other essential amino acids were adequate. Mineral analysis revealed high levels of potassium (1025 mg/100 g) and phosphorus (685 mg/100 g). The dried and defatted palm weevil lava represents a very good source of protein, and a good complement of essential amino acids.

  6. s-Processing in AGB Stars Revisited. II. Enhanced 13C Production through MHD-induced Mixing

    NASA Astrophysics Data System (ADS)

    Trippella, O.; Busso, M.; Palmerini, S.; Maiorca, E.; Nucci, M. C.

    2016-02-01

    Slow neutron captures are responsible for the production of about 50% of elements heavier than iron, mainly occurring during the asymptotic giant branch phase of low-mass stars (1 ≲ M/M⊙ ≲ 3), where the main neutron source is the 13C(α, n)16O reaction. This last reaction is activated from locally produced 13C, formed by partial mixing of hydrogen into the He-rich layers. We present here the first attempt to describe a physical mechanism for the formation of the 13C reservoir, studying the mass circulation induced by magnetic buoyancy without adding new free parameters to those already involved in stellar modeling. Our approach represents the application to the stellar layers relevant for s-processing of recent exact analytical 2D and 3D models for magneto-hydrodynamic processes at the base of convective envelopes in evolved stars in order to promote downflows of envelope material for mass conservation during the occurrence of a dredge-up phenomenon. We find that the proton penetration is characterized by small concentrations, but is extended over a large fractional mass of the He-layers, thus producing 13C reservoirs of several 10-3 M⊙. The ensuing 13C-enriched zone has an almost flat profile, while only a limited production of 14N occurs. In order to verify the effects of our new findings we show how the abundances of the main s-component nuclei can be accounted for in solar proportions and how our large 13C-reservoir allows us to solve a few so far unexplained features in the abundance distribution of post-AGB objects.

  7. s-PROCESSING IN AGB STARS REVISITED. II. ENHANCED {sup 13}C PRODUCTION THROUGH MHD-INDUCED MIXING

    SciTech Connect

    Trippella, O.; Busso, M.; Palmerini, S.; Maiorca, E.; Nucci, M. C.

    2016-02-20

    Slow neutron captures are responsible for the production of about 50% of elements heavier than iron, mainly occurring during the asymptotic giant branch phase of low-mass stars (1 ≲ M/M{sub ⊙} ≲ 3), where the main neutron source is the {sup 13}C(α, n){sup 16}O reaction. This last reaction is activated from locally produced {sup 13}C, formed by partial mixing of hydrogen into the He-rich layers. We present here the first attempt to describe a physical mechanism for the formation of the {sup 13}C reservoir, studying the mass circulation induced by magnetic buoyancy without adding new free parameters to those already involved in stellar modeling. Our approach represents the application to the stellar layers relevant for s-processing of recent exact analytical 2D and 3D models for magneto-hydrodynamic processes at the base of convective envelopes in evolved stars in order to promote downflows of envelope material for mass conservation during the occurrence of a dredge-up phenomenon. We find that the proton penetration is characterized by small concentrations, but is extended over a large fractional mass of the He-layers, thus producing {sup 13}C reservoirs of several 10{sup −3} M{sub ⊙}. The ensuing {sup 13}C-enriched zone has an almost flat profile, while only a limited production of {sup 14}N occurs. In order to verify the effects of our new findings we show how the abundances of the main s-component nuclei can be accounted for in solar proportions and how our large {sup 13}C-reservoir allows us to solve a few so far unexplained features in the abundance distribution of post-AGB objects.

  8. Variable stars in Local Group Galaxies - II. Sculptor dSph

    NASA Astrophysics Data System (ADS)

    Martínez-Vázquez, C. E.; Stetson, P. B.; Monelli, M.; Bernard, E. J.; Fiorentino, G.; Gallart, C.; Bono, G.; Cassisi, S.; Dall'Ora, M.; Ferraro, I.; Iannicola, G.; Walker, A. R.

    2016-11-01

    We present the identification of 634 variable stars in the Milky Way dwarf spheroidal (dSph) satellite Sculptor based on archival ground-based optical observations spanning ˜24 yr and covering ˜2.5 deg2. We employed the same methodologies as the `Homogeneous Photometry' series published by Stetson. In particular, we have identified and characterized one of the largest (536) RR Lyrae samples so far in a Milky Way dSph satellite. We have also detected four Anomalous Cepheids, 23 SX Phoenicis stars, five eclipsing binaries, three field variable stars, three peculiar variable stars located above the horizontal branch - near to the locus of BL Herculis - that we are unable to classify properly. Additionally, we identify 37 long period variables plus 23 probable variable stars, for which the current data do not allow us to determine the period. We report positions and finding charts for all the variable stars, and basic properties (period, amplitude, mean magnitude) and light curves for 574 of them. We discuss the properties of the RR Lyrae stars in the Bailey diagram, which supports the coexistence of subpopulations with different chemical compositions. We estimate the mean mass of Anomalous Cepheids (˜1.5 M⊙) and SX Phoenicis stars (˜1 M⊙). We discuss in detail the nature of the former. The connections between the properties of the different families of variable stars are discussed in the context of the star formation history of the Sculptor dSph galaxy.

  9. Draft Genome Sequences of Tersicoccus phoenicis DSM 30849(T), Isolated from a Cleanroom for Spacecraft Assembly, and Tersicoccus sp. Strain Bi-70, Isolated from a Freshwater Lake.

    PubMed

    Nakajima, Yu; Yoshizawa, Susumu; Nakamura, Keiji; Ogura, Yoshitoshi; Hayashi, Tetsuya; Kogure, Kazuhiro

    2017-03-30

    Here, we report the draft genome sequences of Tersicoccus phoenicis DSM 30849(T), isolated from a spacecraft assembly cleanroom at the National Aeronautics and Space Administration (NASA), and Tersicoccus sp. strain Bi-70, isolated from Lake Biwa, the largest lake in Japan. These genome sequences facilitate our understanding of the adaptation of these closely related strains to different habitats.

  10. Draft Genome Sequences of Tersicoccus phoenicis DSM 30849T, Isolated from a Cleanroom for Spacecraft Assembly, and Tersicoccus sp. Strain Bi-70, Isolated from a Freshwater Lake

    PubMed Central

    Yoshizawa, Susumu; Nakamura, Keiji; Ogura, Yoshitoshi; Hayashi, Tetsuya; Kogure, Kazuhiro

    2017-01-01

    ABSTRACT Here, we report the draft genome sequences of Tersicoccus phoenicis DSM 30849T, isolated from a spacecraft assembly cleanroom at the National Aeronautics and Space Administration (NASA), and Tersicoccus sp. strain Bi-70, isolated from Lake Biwa, the largest lake in Japan. These genome sequences facilitate our understanding of the adaptation of these closely related strains to different habitats. PMID:28360156

  11. Lakatos Revisited.

    ERIC Educational Resources Information Center

    Court, Deborah

    1999-01-01

    Revisits and reviews Imre Lakatos' ideas on "Falsification and the Methodology of Scientific Research Programmes." Suggests that Lakatos' framework offers an insightful way of looking at the relationship between theory and research that is relevant not only for evaluating research programs in theoretical physics, but in the social…

  12. A NEW CENSUS OF THE VARIABLE STAR POPULATION IN THE GLOBULAR CLUSTER NGC 2419

    SciTech Connect

    Di Criscienzo, M.; Greco, C.; Ripepi, V.; Dall' Ora, M.; Marconi, M.; Musella, I.; Clementini, G.; Federici, L.; Di Fabrizio, L.

    2011-03-15

    We present B, V, and I CCD light curves for 101 variable stars belonging to the globular cluster NGC 2419, 60 of which are new discoveries, based on data sets obtained at the Telescopio Nazionale Galileo, the Subaru telescope, and the Hubble Space Telescope. The sample includes 75 RR Lyrae stars (38 RRab, 36 RRc, and one RRd), one Population II Cepheid, 12 SX Phoenicis variables, two {delta} Scuti stars, three binary systems, five long-period variables, and three variables of uncertain classification. The pulsation properties of the RR Lyrae variables are close to those of Oosterhoff type II clusters, consistent with the low metal abundance and the cluster horizontal branch morphology, disfavoring (but not totally ruling out) an extragalactic hypothesis for the origin of NGC 2419. The observed properties of RR Lyrae and SX Phoenicis stars are used to estimate the cluster reddening and distance, using a number of different methods. Our final value is {mu}{sub 0} (NGC 2419) = 19.71 {+-} 0.08 mag (D = 87.5 {+-} 3.3 kpc), with E(B - V) = 0.08 {+-} 0.01 mag, [Fe/H] = -2.1 dex on the Zinn and West metallicity scale, and a value of M{sub V} that sets {mu}{sub 0} (LMC) = 18.52 mag. This value is in good agreement with the most recent literature estimates of the distance to NGC 2419.

  13. Conditions for HD cooling in the first galaxies revisited: interplay between far-ultraviolet and cosmic ray feedback in Population III star formation

    NASA Astrophysics Data System (ADS)

    Nakauchi, Daisuke; Inayoshi, Kohei; Omukai, Kazuyuki

    2014-08-01

    HD dominates the cooing of primordial clouds with enhanced ionization, e.g. shock-heated clouds in structure formation or supernova remnants, relic H II regions of Pop III stars and clouds with cosmic ray (CR) irradiation. There, the temperature decreases to several 10 K and the characteristic stellar mass decreases to ˜10 M⊙, in contrast with first stars formed from undisturbed pristine clouds (˜100 M⊙). However, without CR irradiation, even weak far-ultraviolet (FUV) irradiation suppresses HD formation/cooling. Here, we examine conditions for HD cooling in primordial clouds including both FUV and CR feedback. At the beginning of collapse, the shock-compressed gas cools with its density increasing, while the relic H II region gas cools at a constant density. Moreover, shocks tend to occur in denser environments than H II regions. Owing to the higher column density and the more effective shielding, the critical FUV intensity for HD cooling in a shock-compressed gas becomes ˜10 times higher than that in relic H II regions. Consequently, in the shock-compressed gas, the critical FUV intensity exceeds the background level for most of the redshift we consider (6 ≲ z ≲ 15), while in relic H II regions, HD cooling becomes effective after the CR intensity increases enough at z ≲ 10. Our result suggests that less massive (˜10 M⊙) Pop III stars may be more common than previously considered and could be the dominant population of Pop III stars.

  14. THE SWIFT UVOT STARS SURVEY. II. RR LYRAE STARS IN M3 AND M15

    SciTech Connect

    Siegel, Michael H.; Porterfield, Blair L.; Balzer, Benjamin G.; Hagen, Lea M. Z. E-mail: blp14@psu.edu E-mail: lea.zernow.hagen@gmail.com

    2015-10-15

    We present the first results of a near-ultraviolet (NUV) survey of RR Lyrae stars from the Ultraviolet Optical Telescope (UVOT) on board the Swift Gamma-ray Burst Mission. It is well-established that RR Lyrae stars have large amplitudes in the far- and near-ultraviolet. We have used UVOT’s unique wide-field NUV imaging capability to perform the first systematic NUV survey of variable stars in the Galactic globular clusters M3 and M15. We identify 280 variable stars, comprised of 275 RR Lyrae, 2 anomalous Cepheids, 1 classical Cepheid, 1 SX Phoenicis star, and 1 possible long-period or irregular variable. Only two of these are new discoveries. We compare our results to previous investigations and find excellent agreement in the periods with significantly larger amplitudes in the NUV. We map out, for the first time, an NUV Bailey diagram from globular clusters, showing the usual loci for fundamental mode RRab and first overtone RRc pulsators. We show the unique sensitivity of NUV photometry to both the temperatures and the surface gravities of RR Lyrae stars. Finally, we show evidence of an NUV period–metallicity–luminosity relationship. Future investigations will further examine the dependence of NUV pulsation parameters on metallicity and Oosterhoff classification.

  15. Non-linear hydrodynamical simulations of delta Scuti star pulsations

    NASA Astrophysics Data System (ADS)

    Templeton, M. R.; Guzik, J. A.; McNamara, B. J.

    1998-12-01

    We present the initial results of non-linear hydrodynamic simulations of the pulsation modes of delta Scuti stars. These models use the Ostlie and Cox (1993) Lagrangian hydrodynamic code, adapted to use the most recent OPAL (1996) opacities, the Stellingwerf (1974) periodic relaxation method of obtaining stable limit cycle pulsations, and time-dependent convection. Initial tests of first- and second-overtone pulsation models are consistent with the models of Bono, et al (1997) showing asymmetric lightcurves for first overtone rather than fundamental pulsations. Future modeling work will test several stellar models with varying masses, ages, metal and helium abundances and envelope abundance gradients. Ultimately, we hope to determine the role that abundances and, more specifically, helium abundance gradients in delta Scuti envelopes play in light curve shape. This work will be applied to a test sample of known radially-pulsating delta Scuti field stars and the newly-discovered delta Scuti/SX Phoenicis variables in the Galactic Bulge.

  16. s-processing in AGB stars revisited. I. Does the main component constrain the neutron source in the {sup 13}C pocket?

    SciTech Connect

    Trippella, O.; Busso, M.; Maiorca, E.; Käppeler, F.; Palmerini, S. E-mail: maurizio.busso@fisica.unipg.it

    2014-05-20

    Slow neutron captures at A ≳ 85 are mainly guaranteed by the reaction {sup 13}C(α,n){sup 16}O in asymptotic giant branch (AGB) stars, requiring proton injections from the envelope. These were so far assumed to involve a small mass (≲ 10{sup –3} M {sub ☉}), but models with rotation suggest that in such tiny layers excessive {sup 14}N hampers s-processing. Furthermore, s-element abundances in galaxies require {sup 13}C-rich layers substantially extended in mass (≳ 4 × 10{sup –3} M {sub ☉}). We therefore present new calculations aimed at clarifying those issues and at understanding whether the solar composition helps to constrain the {sup 13}C 'pocket' extension. We show that: (1) mixing 'from bottom to top' (as in magnetic buoyancy or other forced mechanisms) can form a {sup 13}C reservoir substantially larger than assumed so far, covering most of the He-rich layers; (2) on the basis of this idea, stellar models at a fixed metallicity reproduce the main s-component as accurately as before; and (3) they make nuclear contributions from unknown nucleosynthesis processes (LEPP) unnecessary, against common assumptions. These models also avoid problems of mixing at the envelope border and fulfil requirements from C-star luminosities. They yield a large production of nuclei below A = 100, so that {sup 86,} {sup 87}Sr may be fully synthesized by AGB stars, while {sup 88}Sr, {sup 89}Y, and {sup 94}Zr are contributed more efficiently than before. Finally, we suggest tests suitable for providing a final answer regarding the extension of the {sup 13}C pocket.

  17. Intelligence Revisited

    DTIC Science & Technology

    2005-05-01

    reasoning, rote memory , and the like.” Standardized tests also fall short in terms of assessing other important aspects of intelligence such as creativity...ipEngine made by BrightStar Engineering. Then in 2004 we further evolved to a Compulab 686 CORE with 128 megabytes of memory running at 266 mHz...driver runs in a continuous loop, timing sonar echoes on each pass, storing the resulting range values in memory for on-demand access by other

  18. IRAS 17423-1755 (HEN 3-1475) REVISITED: AN O-RICH HIGH-MASS POST-ASYMPTOTIC GIANT BRANCH STAR

    SciTech Connect

    Manteiga, M.; GarcIa-Hernandez, D. A.; Manchado, A.; GarcIa-Lario, P.

    2011-03-15

    The high-resolution (R {approx} 600) Spitzer/IRS spectrum of the bipolar protoplanetary nebula (PN) IRAS 17423-1755 is presented in order to clarify the dominant chemistry (C-rich versus O-rich) of its circumstellar envelope as well as to constrain its evolutionary stage. The high-quality Spitzer/IRS spectrum shows weak 9.7 {mu}m absorption from amorphous silicates. This confirms for the first time the O-rich nature of IRAS 17423-1755 in contradiction to a previous C-rich classification, which was based on the wrong identification of the strong 3.1 {mu}m absorption feature seen in the Infrared Space Observatory spectrum as due to acetylene (C{sub 2}H{sub 2}). The high-resolution Spitzer/IRS spectrum displays a complete lack of C-rich mid-IR features such as molecular absorption features (e.g., 13.7 {mu}m C{sub 2}H{sub 2}, 14.0 {mu}m HCN, etc.) or the classical polycyclic aromatic hydrocarbon infrared emission bands. Thus, the strong 3.1 {mu}m absorption band toward IRAS 17423-1755 has to be identified as water ice. In addition, an [Ne II] nebular emission line at 12.8 {mu}m is clearly detected, indicating that the ionization of its central region may be already started. The spectral energy distribution in the infrared ({approx}2-200 {mu}m) and other observational properties of IRAS 17423-1755 are discussed in comparison with the similar post-asymptotic giant branch (AGB) objects IRAS 19343+2926 and IRAS 17393-2727. We conclude that IRAS 17423-1755 is an O-rich high-mass post-AGB object that represents a link between OH/IR stars with extreme outflows and highly bipolar PN.

  19. Hubble Revisited

    NASA Astrophysics Data System (ADS)

    Fischer, Daniel; Duerbeck, Hilmar; Hawley, S. A.; Jenkner, H.

    Arguably the single most successful scientific instrument ever built, the Hubble Space telescope continues to dazzle. In recent months it has discovered the most distant known galaxy and the most massive known star, and has been at the front lines of all the most pressing questions in astrophysics: the age of the Universe, the nature of gamma-ray bursters, the discovery of extrasolar planets. In The Discovery Machine, the authors of the widely acclaimed Hubble: A New Window to the Universe bring you an exciting, detailed, gorgeously illustrated account of Hubble's breathtaking new discoveries. Acclaim for Hubble: A New Window to the Universe "Wonderful to behold. Buy it and feast your eyes." Scientific American "A wonderful volume...a clear and insightful explanation is included for each and every image." The Planetarian

  20. Variable stars in the globular cluster M 13

    NASA Astrophysics Data System (ADS)

    Kopacki, G.; Kołaczkowski, Z.; Pigulski, A.

    2003-02-01

    Results of a search for variable stars in the central region of the globular cluster M 13 are presented. Prior to this study, 36 variable and suspected variable stars were known in this cluster (Osborn \\cite{osborn00}; Clement et al. \\cite{clementetal01}). Of these stars, five were not observed by us. We find v3, v4, v10, v12, and v13 to be constant in light. Surprisingly, only two out of the ten variable star candidates of Kadla et al. (\\cite{kadlaetal80}) appear to be variable. Both are RRc variables. Additionally, three RR Lyrae stars and one SX Phoenicis variable are discovered. Three close frequencies are detected for an RRc star v36. It appears that this variable is another multi-periodic RR Lyrae star pulsating in non-radial modes. Light curves of the three known BL Herculis stars and all known RR Lyrae stars are presented. The total number of known RR Lyrae stars in M 13 is now nine. Only one is an RRab star. The mean period of RRc variables amounts to 0.36+/-0.05 d, suggesting that M 13 should be included in the group of Oosterhoff type II globular clusters. Mean V magnitudes and ranges of variation are derived for seven RR Lyrae and three BL Herculis variables. Almost all observed bright giants show some degree of variability. In particular, we confirm the variability of two red giants announced to be variable by Osborn (\\cite{osborn00}) and in addition find five new cases. The observations used in the paper are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/398/541

  1. Sloan Digital Sky Survey Photometric Calibration Revisited

    SciTech Connect

    Marriner, John; /Fermilab

    2012-06-29

    The Sloan Digital Sky Survey calibration is revisited to obtain the most accurate photometric calibration. A small but significant error is found in the flat-fielding of the Photometric telescope used for calibration. Two SDSS star catalogs are compared and the average difference in magnitude as a function of right ascension and declination exhibits small systematic errors in relative calibration. The photometric transformation from the SDSS Photometric Telescope to the 2.5 m telescope is recomputed and compared to synthetic magnitudes computed from measured filter bandpasses.

  2. Exploring the crowded central region of ten Galactic globular clusters using EMCCDs. Variable star searches and new discoveries

    NASA Astrophysics Data System (ADS)

    Figuera Jaimes, R.; Bramich, D. M.; Skottfelt, J.; Kains, N.; Jørgensen, U. G.; Horne, K.; Dominik, M.; Alsubai, K. A.; Bozza, V.; Calchi Novati, S.; Ciceri, S.; D'Ago, G.; Galianni, P.; Gu, S.-H.; Harpsøe, K. B. W.; Haugbølle, T.; Hinse, T. C.; Hundertmark, M.; Juncher, D.; Korhonen, H.; Mancini, L.; Popovas, A.; Rabus, M.; Rahvar, S.; Scarpetta, G.; Schmidt, R. W.; Snodgrass, C.; Southworth, J.; Starkey, D.; Street, R. A.; Surdej, J.; Wang, X.-B.; Wertz, O.

    2016-04-01

    Aims: We aim to obtain time-series photometry of the very crowded central regions of Galactic globular clusters; to obtain better angular resolution thanhas been previously achieved with conventional CCDs on ground-based telescopes; and to complete, or improve, the census of the variable star population in those stellar systems. Methods: Images were taken using the Danish 1.54-m Telescope at the ESO observatory at La Silla in Chile. The telescope was equipped with an electron-multiplying CCD, and the short-exposure-time images obtained (ten images per second) were stacked using the shift-and-add technique to produce the normal-exposure-time images (minutes). Photometry was performed via difference image analysis. Automatic detection of variable stars in the field was attempted. Results: The light curves of 12 541 stars in the cores of ten globular clusters were statistically analysed to automatically extract the variable stars. We obtained light curves for 31 previously known variable stars (3 long-period irregular, 2 semi-regular, 20 RR Lyrae, 1 SX Phoenicis, 3 cataclysmic variables, 1 W Ursae Majoris-type and 1 unclassified) and we discovered 30 new variables (16 long-period irregular, 7 semi-regular, 4 RR Lyrae, 1 SX Phoenicis and 2 unclassified). Fluxes and photometric measurements for these stars are available in electronic form through the Strasbourg astronomical Data Center. Based on data collected by the MiNDSTEp team with the Danish 1.54m telescope at ESO's La Silla observatory in Chile.Full Table 1 is only available at CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/588/A128

  3. A New Census of the Variable Star Population in the Globular Cluster NGC 2419

    NASA Astrophysics Data System (ADS)

    Di Criscienzo, M.; Greco, C.; Ripepi, V.; Clementini, G.; Dall'Ora, M.; Marconi, M.; Musella, I.; Federici, L.; Di Fabrizio, L.

    2011-03-01

    We present B, V, and I CCD light curves for 101 variable stars belonging to the globular cluster NGC 2419, 60 of which are new discoveries, based on data sets obtained at the Telescopio Nazionale Galileo, the Subaru telescope, and the Hubble Space Telescope. The sample includes 75 RR Lyrae stars (38 RRab, 36 RRc, and one RRd), one Population II Cepheid, 12 SX Phoenicis variables, two δ Scuti stars, three binary systems, five long-period variables, and three variables of uncertain classification. The pulsation properties of the RR Lyrae variables are close to those of Oosterhoff type II clusters, consistent with the low metal abundance and the cluster horizontal branch morphology, disfavoring (but not totally ruling out) an extragalactic hypothesis for the origin of NGC 2419. The observed properties of RR Lyrae and SX Phoenicis stars are used to estimate the cluster reddening and distance, using a number of different methods. Our final value is μ0 (NGC 2419) = 19.71 ± 0.08 mag (D = 87.5 ± 3.3 kpc), with E(B - V) = 0.08 ± 0.01 mag, [Fe/H] = -2.1 dex on the Zinn & West metallicity scale, and a value of MV that sets μ0 (LMC) = 18.52 mag. This value is in good agreement with the most recent literature estimates of the distance to NGC 2419. Based on data collected at the 3.5 m Telescopio Nazionale Galileo, operated by INAF, and the Subaru and Hubble Space Telescope archives.

  4. A catalog of 7000 optically faint periodic variable stars from the LINEAR survey

    NASA Astrophysics Data System (ADS)

    Ivezic, Zeljko; Palaversa, L.; Sesar, B.; Stuart, J.

    2014-01-01

    We present a catalog of about 7000 optically faint periodic variable stars with light curves obtained by the asteroid survey LINEAR across 10,000 sq.deg. of the northern sky. The majority of these variables have not been cataloged yet. The sample flux limit is several magnitudes fainter than most other wide-angle surveys; the photometric errors range from 0.03 mag at r = 15 to 0.20 mag at r = 18. Light curves include on average 250 data points, collected over about a decade. The sample is dominated by 3900 RR Lyrae stars and 2700 eclipsing binary stars of all subtypes and includes small fractions of relatively rare populations such as asymptotic giant branch stars and SX Phoenicis stars. These publicly available (from https://astroweb.lanl.gov/lineardb/) large samples of robustly classified variable stars will enable detailed statistical studies of the Galactic structure and physics of binary and other stars, and can be used for training automated light curve classification methods. Details about this catalog are available in Palaversa et al. (2013, AJ 146, 101).

  5. Anodic Polarization Curves Revisited

    ERIC Educational Resources Information Center

    Liu, Yue; Drew, Michael G. B.; Liu, Ying; Liu, Lin

    2013-01-01

    An experiment published in this "Journal" has been revisited and it is found that the curve pattern of the anodic polarization curve for iron repeats itself successively when the potential scan is repeated. It is surprising that this observation has not been reported previously in the literature because it immediately brings into…

  6. A Hydrostatic Paradox Revisited

    ERIC Educational Resources Information Center

    Ganci, Salvatore

    2012-01-01

    This paper revisits a well-known hydrostatic paradox, observed when turning upside down a glass partially filled with water and covered with a sheet of light material. The phenomenon is studied in its most general form by including the mass of the cover. A historical survey of this experiment shows that a common misunderstanding of the phenomenon…

  7. Parametric Resonance Revisited

    NASA Astrophysics Data System (ADS)

    van den Broeck, C.; Bena, I.

    The phenomenon of parametric resonance is revisited. Several physical examples are reviewed and an exactly solvable model is discussed. A mean field theory is presented for globally coupled parametric oscillators with randomly distributed phases. A new type of collective instability appears, which is similar in nature to that of noise induced phase transitions.

  8. Concept Image Revisited

    ERIC Educational Resources Information Center

    Bingolbali, Erhan; Monaghan, John

    2008-01-01

    Concept image and concept definition is an important construct in mathematics education. Its use, however, has been limited to cognitive studies. This article revisits concept image in the context of research on undergraduate students' understanding of the derivative which regards the context of learning as paramount. The literature, mainly on…

  9. Revisiting Bioaccumulation Criteria

    EPA Science Inventory

    The objective of workgroup 5 was to revisit the B(ioaccumulation) criteria that are currently being used to identify POPs under the Stockholm Convention and PBTs under CEPA, TSCA, REACh and other programs. Despite the lack of a recognized definition for a B substance, we defined ...

  10. The Linguistic Repertoire Revisited

    ERIC Educational Resources Information Center

    Busch, Brigitta

    2012-01-01

    This article argues for the relevance of poststructuralist approaches to the notion of a linguistic repertoire and introduces the notion of language portraits as a basis for empirical study of the way in which speakers conceive and represent their heteroglossic repertoires. The first part of the article revisits Gumperz's notion of a linguistic…

  11. Colloquial Hebrew Imperatives Revisited

    ERIC Educational Resources Information Center

    Bolozky, Shmuel

    2009-01-01

    In revisiting Bolozky's [Bolozky, Shmuel, 1979. "On the new imperative in colloquial Hebrew." "Hebrew Annual Review" 3, 17-24] and Bat-El's [Bat-El, Outi, 2002. "True truncation in colloquial Hebrew imperatives." "Language" 78(4), 651-683] analyses of colloquial Hebrew imperatives, the article argues for restricting Imperative Truncation to the…

  12. Revisiting Dialogues and Monologues

    ERIC Educational Resources Information Center

    Kvernbekk, Tone

    2012-01-01

    In educational discourse dialogue tends to be viewed as being (morally) superior to monologue. When we look at them as basic forms of communication, we find that dialogue is a two-way, one-to-one form and monologue is a one-way, one-to-many form. In this paper I revisit the alleged (moral) superiority of dialogue. First, I problematize certain…

  13. Clinical ethics revisited

    PubMed Central

    Singer, Peter A; Pellegrino, Edmund D; Siegler, Mark

    2001-01-01

    A decade ago, we reviewed the field of clinical ethics; assessed its progress in research, education, and ethics committees and consultation; and made predictions about the future of the field. In this article, we revisit clinical ethics to examine our earlier observations, highlight key developments, and discuss remaining challenges for clinical ethics, including the need to develop a global perspective on clinical ethics problems. PMID:11346456

  14. Mountain Rivers Revisited

    NASA Astrophysics Data System (ADS)

    Schultz, Colin

    2011-12-01

    Published in 2000, the original Mountain Rivers was written to provide a concise summary of the scientific understanding of the distinct subset of rivers that gave the book its name. Spurred by developments in the field in the past decade, the book's author, Ellen Wohl, produced Mountain Rivers Revisited, an updated edition aimed at graduate students and professional researchers. In this interview, Eos talks to Wohl about steep channels, climate change, and opportunities for future research.

  15. VARIABLE STARS IN LARGE MAGELLANIC CLOUD GLOBULAR CLUSTERS. II. NGC 1786

    SciTech Connect

    Kuehn, Charles A.; Smith, Horace A.; De Lee, Nathan; Catelan, Marcio; Pritzl, Barton J.; Borissova, Jura E-mail: smith@pa.msu.edu E-mail: mcatelan@astro.puc.cl E-mail: jura.borissova@uv.cl

    2012-12-01

    This is the second in a series of papers studying the variable stars in Large Magellanic Cloud globular clusters. The primary goal of this series is to study how RR Lyrae stars in Oosterhoff-intermediate systems compare to their counterparts in Oosterhoff I/II systems. In this paper, we present the results of our new time-series B-V photometric study of the globular cluster NGC 1786. A total of 65 variable stars were identified in our field of view. These variables include 53 RR Lyraes (27 RRab, 18 RRc, and 8 RRd), 3 classical Cepheids, 1 Type II Cepheid, 1 Anomalous Cepheid, 2 eclipsing binaries, 3 Delta Scuti/SX Phoenicis variables, and 2 variables of undetermined type. Photometric parameters for these variables are presented. We present physical properties for some of the RR Lyrae stars, derived from Fourier analysis of their light curves. We discuss several different indicators of Oosterhoff type which indicate that the Oosterhoff classification of NGC 1786 is not as clear cut as what is seen in most globular clusters.

  16. Numerical Simulations of High-Amplitude Delta Scuti Star Pulsations

    NASA Astrophysics Data System (ADS)

    Templeton, M. R.

    1999-12-01

    We present the results of a theoretical program to model high-amplitude delta Scuti (HADS) stars. We base this study on field HADS, and on the MACHO Project delta Scuti stars. We have generated a grid of evolution models with (X,Y,Z) = (0.76,0.24,0.0001) to (0.58,0.36,0.06) covering the delta Scuti/SX Phoenicis region of the instability strip. Linear pulsation tests were done to make theoretical Petersen diagrams for the double-mode pulsators, and to make period-luminosity relations. Petersen diagrams are consistent with previous observational and theoretical work, with all fundamental-first overtone pulsators having period ratios around 0.77. For a single metallicity, stars with masses separated by 0.1 Msun have distinct tracks in the Petersen diagram, which permits mass and age estimates for stars of known abundance. We also find that period ratios drop rapidly as these stars evolve toward the red giant branch. The two MACHO delta Scuti stars with period ratios around 0.75 may be highly evolved, cool (T = 6700 K) delta Scuti stars. Period-luminosity relations for stars of different masses but the same abundances have a large intrinsic scatter, indicating that a color term must be included in the P-L relation for delta Scuti stars. Hydrodynamic models of HADS have also been tested, using a variant of the Los Alamos DYNSTAR code (Ostlie and Cox, 1993, Astrophys. Space Sci 210, 311), modified to include the OPAL96 tabular opacities. We have obtained light curves that are similar to those of observed HADS, over a range of temperatures and masses. Our results are consistent with those of Bono et al. (1997; ApJ 477, 346) in that the light curves of fundamental mode pulsators are more sinusoidal than those of overtone pulsators. Work on the hydrodynamic models is being expanded to test the effects of helium enrichment on light curve shape, and to include convection in cooler HADS to better model the red edge of the instability strip.

  17. Strange stars

    NASA Technical Reports Server (NTRS)

    Alcock, Charles; Farhi, Edward; Olinto, Angela

    1986-01-01

    Strange matter, a form of quark matter that is postulated to be absolute stable, may be the true ground stage of the hadrons. If this hypothesis is correct, neutron stars may convert to 'strange stars'. The mass-radius relation for strange stars is very different from that of neutron stars; there is no minimum mass, and for mass of 1 solar mass or less, mass is proportional to the cube of the radius. For masses between 1 solar mass and 2 solar masses, the radii of strange stars are about 10 km, as for neutron stars. Strange stars may have an exposed quark surface, which is capable of radiating at rates greatly exceeding the Eddington limit, but has a low emissivity for X-ray photons. The stars may have a thin crust with the same composition as the preneutron drip outer layer of a conventional neutron star crust. Strange stars cool efficiently via neutrino emission.

  18. Quantum duel revisited

    NASA Astrophysics Data System (ADS)

    Schmidt, Alexandre G. M.; Paiva, Milena M.

    2012-03-01

    We revisit the quantum two-person duel. In this problem, both Alice and Bob each possess a spin-1/2 particle which models dead and alive states for each player. We review the Abbott and Flitney result—now considering non-zero α1 and α2 in order to decide if it is better for Alice to shoot or not the second time—and we also consider a duel where players do not necessarily start alive. This simple assumption allows us to explore several interesting special cases, namely how a dead player can win the duel shooting just once, or how can Bob revive Alice after one shot, and the better strategy for Alice—being either alive or in a superposition of alive and dead states—fighting a dead opponent.

  19. ``Robinson's sum rule'' revisited

    NASA Astrophysics Data System (ADS)

    Orlov, Yuri F.

    2010-02-01

    This discussion revisits two articles on synchrotron radiation damping published in 1958, one by this author and Evgeny K. Tarasov [Zh. Eksp. Teor. Fiz. 34, 651 (1958)ZETFA70044-4510; Sov. Phys. JETP 34, 449 (1958)SPHJAR0038-5646], and one by Kenneth W. Robinson [Phys. Rev. 111, 373 (1958)PHRVAO0031-899X10.1103/PhysRev.111.373]. The latter is the source of what is known as “Robinson’s sum rule.” Both present the familiar rule, but with very different proofs and calculations of concrete damping decrements. Comparative analysis of these differences reveals serious flaws in Robinson’s proof and calculations.

  20. Polite Theories Revisited

    NASA Astrophysics Data System (ADS)

    Jovanović, Dejan; Barrett, Clark

    The classic method of Nelson and Oppen for combining decision procedures requires the theories to be stably-infinite. Unfortunately, some important theories do not fall into this category (e.g. the theory of bit-vectors). To remedy this problem, previous work introduced the notion of polite theories. Polite theories can be combined with any other theory using an extension of the Nelson-Oppen approach. In this paper we revisit the notion of polite theories, fixing a subtle flaw in the original definition. We give a new combination theorem which specifies the degree to which politeness is preserved when combining polite theories. We also give conditions under which politeness is preserved when instantiating theories by identifying two sorts. These results lead to a more general variant of the theorem for combining multiple polite theories.

  1. Effective string theory revisited

    NASA Astrophysics Data System (ADS)

    Dubovsky, Sergei; Flauger, Raphael; Gorbenko, Victor

    2012-09-01

    We revisit the effective field theory of long relativistic strings such as confining flux tubes in QCD. We derive the Polchinski-Strominger interaction by a calculation in static gauge. This interaction implies that a non-critical string which initially oscillates in one direction gets excited in orthogonal directions as well. In static gauge no additional term in the effective action is needed to obtain this effect. It results from a one-loop calculation using the Nambu-Goto action. Non-linearly realized Lorentz symmetry is manifest at all stages in dimensional regularization. We also explain that independent of the number of dimensions non-covariant counterterms have to be added to the action in the commonly used zeta-function regularization.

  2. Stars and Star Myths.

    ERIC Educational Resources Information Center

    Eason, Oliver

    Myths and tales from around the world about constellations and facts about stars in the constellations are presented. Most of the stories are from Greek and Roman mythology; however, a few Chinese, Japanese, Polynesian, Arabian, Jewish, and American Indian tales are also included. Following an introduction, myths are presented for the following 32…

  3. Brevipalpus phoenicis: unraveling the complex

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The genus Brevipalpus has a long and complicated history, full of mystery, intrigue, and ultimately, confusion. With over 280 species in the genus, separating species has always proved challenging. Even sixty years ago, when only eight species had been recorded for the USA, there were already indi...

  4. Revisiting the Acanthamoeba species that form star-shaped cysts (genotypes T7, T8, T9, and T17): characterization of seven new Brazilian environmental isolates and phylogenetic inferences.

    PubMed

    Magliano, Ana C M; Teixeira, Marta M G; Alfieri, Silvia C

    2012-01-01

    Free-living amoebae of the genus Acanthamoeba are the agents of both opportunistic and non-opportunistic infections and are frequently isolated from the environment. Of the 17 genotypes (T1-T17) identified thus far, 4 (T7, T8, T9, and T17) accommodate the rarely investigated species of morphological group I, those that form large, star-shaped cysts. We report the isolation and characterization of 7 new Brazilian environmental Acanthamoeba isolates, all assigned to group I. Phylogenetic analyses based on partial (~1200 bp) SSU rRNA gene sequences placed the new isolates in the robustly supported clade composed of the species of morphological group I. One of the Brazilian isolates is closely related to A. comandoni (genotype T9), while the other 6, together with 2 isolates recently assigned to genotype T17, form a homogeneous, well-supported group (2·0% sequence divergence) that likely represents a new Acanthamoeba species. Thermotolerance, osmotolerance, and cytophatic effects, features often associated with pathogenic potential, were also examined. The results indicated that all 7 Brazilian isolates grow at temperatures up to 40°C, and resist under hyperosmotic conditions. Additionally, media conditioned by each of the new Acanthamoeba isolates induced the disruption of SIRC and HeLa cell monolayers.

  5. The Milton Bureau Revisited

    NASA Astrophysics Data System (ADS)

    Hoffleit, Dorrit

    2000-06-01

    Under the direction of Cecilia Payne-Gaposchkin and Sergei Gaposchkin, a program was subsidized by the Milton Fund of Harvard Observatory in 1937 for the study of all variable stars then known to be brighter than tenth photographic magnitude at maximum. This included some 1512 stars for which a grand total of 1,263,562 estimates of magnitude were made, ranging from a low of 16 (except for a few novae) to 4084 observations per star. The sky had been divided into 54 fields, and the results of the measurements presented field by field in two volumes of the Annals of Harvard Observatory. Then, in another volume, the results were discussed in four sections, each dealing with a particular class of variable: 1, those of RV Tauri type; 2, the eclipsing variables; 3, Cepheids and RR Lyrae variables, and 4, the red variables, especially Mira-type and semiregular variables. For the present paper, many of these results have been compared with modern determinations in the 1985-87 version of the "General Catalogue of Variable Stars (GCVS)". In particular, there are numerous instances of disagreement as to whether a star should be classified RV or SR. Although there are many instances where the Milton Bureau determinations of types of variability differ from the types given in modern catalogues, the reasons for the differences are generally understandable. For 17 RV Tauri type stars in this survey multiple periods have now been determined. Many of these still deserve continued observations in order to ascertain the constance of the periods and improve the accuracy of their longest reported periods.

  6. Pulsating Stars

    NASA Astrophysics Data System (ADS)

    Catelan, M.; Smith, H. A.

    2015-03-01

    This book surveys our understanding of stars which change in brightness because they pulsate. Pulsating variable stars are keys to distance scales inside and beyond the Milky Way galaxy. They test our understanding not only of stellar pulsation theory but also of stellar structure and evolution theory. Moreover, pulsating stars are important probes of the formation and evolution of our own and neighboring galaxies. Our understanding of pulsating stars has greatly increased in recent years as large-scale surveys of pulsating stars in the Milky Way and other Local Group galaxies have provided a wealth of new observations and as space-based instruments have studied particular pulsating stars in unprecedented detail.

  7. Long, cold, early r process? Neutrino-induced nucleosynthesis in He shells revisited.

    PubMed

    Banerjee, Projjwal; Haxton, W C; Qian, Yong-Zhong

    2011-05-20

    We revisit a ν-driven r-process mechanism in the He shell of a core-collapse supernova, finding that it could succeed in early stars of metallicity Z ≲ 10⁻³ Z(⊙), at relatively low temperatures and neutron densities, producing A ~ 130 and 195 abundance peaks over ~10-20 s. The mechanism is sensitive to the ν emission model and to ν oscillations. We discuss the implications of an r process that could alter interpretations of abundance data from metal-poor stars, and point out the need for further calculations that include effects of the supernova shock.

  8. Revisiting caspases in sepsis

    PubMed Central

    Aziz, M; Jacob, A; Wang, P

    2014-01-01

    Sepsis is a life-threatening illness that occurs due to an abnormal host immune network which extends through the initial widespread and overwhelming inflammation, and culminates at the late stage of immunosupression. Recently, interest has been shifted toward therapies aimed at reversing the accompanying periods of immune suppression. Studies in experimental animals and critically ill patients have demonstrated that increased apoptosis of lymphoid organs and some parenchymal tissues contributes to this immune suppression, anergy and organ dysfunction. Immediate to the discoveries of the intracellular proteases, caspases for the induction of apoptosis and inflammation, and their striking roles in sepsis have been focused elaborately in a number of original and review articles. Here we revisited the different aspects of caspases in terms of apoptosis, pyroptosis, necroptosis and inflammation and focused their links in sepsis by reviewing several recent findings. In addition, we have documented striking perspectives which not only rewrite the pathophysiology, but also modernize our understanding for developing novel therapeutics against sepsis. PMID:25412304

  9. Searle's"Dualism Revisited"

    SciTech Connect

    P., Henry

    2008-11-20

    A recent article in which John Searle claims to refute dualism is examined from a scientific perspective. John Searle begins his recent article 'Dualism Revisited' by stating his belief that the philosophical problem of consciousness has a scientific solution. He then claims to refute dualism. It is therefore appropriate to examine his arguments against dualism from a scientific perspective. Scientific physical theories contain two kinds of descriptions: (1) Descriptions of our empirical findings, expressed in an every-day language that allows us communicate to each other our sensory experiences pertaining to what we have done and what we have learned; and (2) Descriptions of a theoretical model, expressed in a mathematical language that allows us to communicate to each other certain ideas that exist in our mathematical imaginations, and that are believed to represent, within our streams of consciousness, certain aspects of reality that we deem to exist independently of their being perceived by any human observer. These two parts of our scientific description correspond to the two aspects of our general contemporary dualistic understanding of the total reality in which we are imbedded, namely the empirical-mental aspect and the theoretical-physical aspect. The duality question is whether this general dualistic understanding of ourselves should be regarded as false in some important philosophical or scientific sense.

  10. Cats protecting birds revisited.

    PubMed

    Fan, Meng; Kuang, Yang; Feng, Zhilan

    2005-09-01

    In this paper, we revisit the dynamical interaction among prey (bird), mesopredator (rat), and superpredator (cat) discussed in [Courchamp, F., Langlais, M., Sugihara, G., 1999. Cats protecting birds: modelling the mesopredator release effect. Journal of Animal Ecology 68, 282-292]. First, we develop a prey-mesopredator-superpredator (i.e., bird-rat-cat, briefly, BRC) model, where the predator's functional responses are derived based on the classical Holling's time budget arguments. Our BRC model overcomes several model construction problems in Courchamp et al. (1999), and admits richer, reasonable and realistic dynamics. We explore the possible control strategies to save or restore the bird by controlling or eliminating the rat or the cat when the bird is endangered. We establish the existence of two types of mesopredator release phenomena: severe mesopredator release, where once superpredators are suppressed, a burst of mesopredators follows which leads their shared prey to extinction; and mild mesopredator release, where the mesopredator release could assert more negative impact on the endemic prey but does not lead the endemic prey to extinction. A sharp sufficient criterion is established for the occurrence of severe mesopredator release. We also show that, in a prey-mesopredator-superpredator trophic food web, eradication of introduced superpredators such as feral domestic cats in the BRC model, is not always the best solution to protect endemic insular prey. The presence of a superpredator may have a beneficial effect in such systems.

  11. Twin Signature Schemes, Revisited

    NASA Astrophysics Data System (ADS)

    Schäge, Sven

    In this paper, we revisit the twin signature scheme by Naccache, Pointcheval and Stern from CCS 2001 that is secure under the Strong RSA (SRSA) assumption and improve its efficiency in several ways. First, we present a new twin signature scheme that is based on the Strong Diffie-Hellman (SDH) assumption in bilinear groups and allows for very short signatures and key material. A big advantage of this scheme is that, in contrast to the original scheme, it does not require a computationally expensive function for mapping messages to primes. We prove this new scheme secure under adaptive chosen message attacks. Second, we present a modification that allows to significantly increase efficiency when signing long messages. This construction uses collision-resistant hash functions as its basis. As a result, our improvements make the signature length independent of the message size. Our construction deviates from the standard hash-and-sign approach in which the hash value of the message is signed in place of the message itself. We show that in the case of twin signatures, one can exploit the properties of the hash function as an integral part of the signature scheme. This improvement can be applied to both the SRSA based and SDH based twin signature scheme.

  12. Dynamic causal modelling revisited.

    PubMed

    Friston, K J; Preller, Katrin H; Mathys, Chris; Cagnan, Hayriye; Heinzle, Jakob; Razi, Adeel; Zeidman, Peter

    2017-02-17

    This paper revisits the dynamic causal modelling of fMRI timeseries by replacing the usual (Taylor) approximation to neuronal dynamics with a neural mass model of the canonical microcircuit. This provides a generative or dynamic causal model of laminar specific responses that can generate haemodynamic and electrophysiological measurements. In principle, this allows the fusion of haemodynamic and (event related or induced) electrophysiological responses. Furthermore, it enables Bayesian model comparison of competing hypotheses about physiologically plausible synaptic effects; for example, does attentional modulation act on superficial or deep pyramidal cells - or both? In this technical note, we describe the resulting dynamic causal model and provide an illustrative application to the attention to visual motion dataset used in previous papers. Our focus here is on how to answer long-standing questions in fMRI; for example, do haemodynamic responses reflect extrinsic (afferent) input from distant cortical regions, or do they reflect intrinsic (recurrent) neuronal activity? To what extent do inhibitory interneurons contribute to neurovascular coupling? What is the relationship between haemodynamic responses and the frequency of induced neuronal activity? This paper does not pretend to answer these questions; rather it shows how they can be addressed using neural mass models of fMRI timeseries.

  13. Massive Stars

    NASA Astrophysics Data System (ADS)

    Livio, Mario; Villaver, Eva

    2009-11-01

    Participants; Preface Mario Livio and Eva Villaver; 1. High-mass star formation by gravitational collapse of massive cores M. R. Krumholz; 2. Observations of massive star formation N. A. Patel; 3. Massive star formation in the Galactic center D. F. Figer; 4. An X-ray tour of massive star-forming regions with Chandra L. K. Townsley; 5. Massive stars: feedback effects in the local universe M. S. Oey and C. J. Clarke; 6. The initial mass function in clusters B. G. Elmegreen; 7. Massive stars and star clusters in the Antennae galaxies B. C. Whitmore; 8. On the binarity of Eta Carinae T. R. Gull; 9. Parameters and winds of hot massive stars R. P. Kudritzki and M. A. Urbaneja; 10. Unraveling the Galaxy to find the first stars J. Tumlinson; 11. Optically observable zero-age main-sequence O stars N. R. Walborn; 12. Metallicity-dependent Wolf-Raynet winds P. A. Crowther; 13. Eruptive mass loss in very massive stars and Population III stars N. Smith; 14. From progenitor to afterlife R. A. Chevalier; 15. Pair-production supernovae: theory and observation E. Scannapieco; 16. Cosmic infrared background and Population III: an overview A. Kashlinsky.

  14. Benjamin Franklin and Mesmerism, revisited.

    PubMed

    McConkey, Kevin M; Perry, Campbell

    2002-10-01

    The authors revisit and update their previous historiographical note (McConkey & Perry, 1985) on Benjamin Franklin's involvement with and investigation of animal magnetism or mesmerism. They incorporate more recent literature and offer additional comment about Franklin's role in and views about mesmerism. Franklin had a higher degree of personal involvement with and a more detailed opinion of mesmerism than has been previously appreciated.

  15. Cultural Warping of Childbirth, Revisited

    PubMed Central

    Budin, Wendy C.

    2007-01-01

    In this column, the editor of The Journal of Perinatal Education revisits Doris Haire's classic 1972 article, “The Cultural Warping of Childbirth,” and describes the birth culture of today. The editor also describes the contents of this issue, which offer a broad range of resources, research, and inspiration for childbirth educators in their efforts to promote normal birth.

  16. The "Mushroom Cloud" Demonstration Revisited

    ERIC Educational Resources Information Center

    Panzarasa, Guido; Sparnacci, Katia

    2013-01-01

    A revisitation of the classical "mushroom cloud" demonstration is described. Instead of aniline and benzoyl peroxide, the proposed reaction involves household chemicals such as alpha-pinene (turpentine oil) and trichloroisocyanuric acid ("Trichlor") giving an impressive demonstration of oxidation and combustion reactions that…

  17. CH Stars and Barium Stars

    NASA Astrophysics Data System (ADS)

    Bond, H.; Sion, E.; Murdin, P.

    2000-11-01

    The classical barium (or `Ba II') stars are RED GIANT STARS whose spectra show strong absorption lines of barium, strontium and certain other heavy elements, as well as strong features due to carbon molecules. Together with the related class of CH stars, the Ba II stars were crucial in establishing the existence of neutron-capture reactions in stellar interiors that are responsible for the synt...

  18. Near-IR Period-Luminosity Relations for variable stars in ω Centauri

    NASA Astrophysics Data System (ADS)

    Navarrete, C.; Catelan, M.; Contreras Ramos, R.; Gran, F.; Alonso-García, J.; Dékány, I.

    2014-10-01

    We report on an extensive time-series study of the globular cluster ω Centauri (NGC 5139), obtained in the framework of the VVV Templates project (Catelan et al. 2013, arXiv: 1310.1996). This cluster was chosen for this project due to its large variable star content. A total of 42 and 100 epochs of the cluster in J and K_{S}, respectively, were taken using VIRCAM@VISTA, and PSF photometry was performed to derive light curves for 270 pulsating stars (RRab, RRc, type II Cepheids and SX Phoenicis) with an unprecedented phase coverage in the near-IR. Period-Luminosity (PL) relations in both bands were derived using Fourier fitted magnitudes for RR Lyrae and Type II Cepheids, while weighted-average magnitudes were used for SX Phe stars. Using the PL relation for RRab stars derived by Dékány et al. (2013, ApJ, 776, 19L) in the VISTA K_{S} system, we determine a distance modulus of (m-M)_{0} = 13.78 ± 0.04 mag, in good agreement with Del Principe et al. (2006, ApJ, 652, 362). From Type II Cepheids we derived a value of (m-M)_{0} = 13.67 ± 0.07 mag, similar to what was found by Matsunaga et al. (2006, MNRAS, 370, 1979). For SX Phe stars, we use the derived periods and magnitudes to infer their pulsation modes, and we confirm that at least 12 of them are fundamental-mode pulsators (Olech et al. 2005, MNRAS, 363, 40).

  19. Nutational Damping Revisited

    NASA Astrophysics Data System (ADS)

    Burns, J. A.; Sharma, I.

    2000-10-01

    Motivated by the recent detection of complex rotational states for several asteroids and comets, as well as by the ongoing and planned spacecraft missions to such bodies, which should allow their rotational states to be accurately determined, we revisit the problem of the nutational damping of small solar system bodies. The nutational damping of asteroids has been approximately analyzed by Prendergast (1958), Burns and Safronov (1973), and Efroimsky and Lazarian (2000). Many other similar dynamical studies concern planetary wobble decay (e.g., Peale 1973; Yoder and Ward 1979), interstellar dust grain alignment (e.g., Purcell 1979; Lazarian and Efroimsky 1999) and damping of Earth's Chandler wobble (Lambeck 1980). Recall that rotational energy loss for an isolated body aligns the body's angular momentum vector with its axis of maximum inertia. Assuming anelastic dissipation, simple dimensional analysis determines a functional form of the damping timescale, on which all the above authors agree. However, the numerical coefficients of published results are claimed to differ by orders of magnitude. Differences have been ascribed to absent physics, to solutions that fail to satisfy boundary conditions perfectly, and to unphysical choices for the Q parameter. The true reasons for the discrepancy are unclear since, despite contrary claims, the full 3D problem (nutational damping of an anelastic ellipsoid) is analytically intractable so far. To move the debate forward, we compare the solution of a related 2D problem to the expressions found previously, and we present results from a finite element model. On this basis, we feel that previous rates for the decay of asteroidal tumbling (Harris 1994), derived from Burns and Safronov (1973), are likely to be accurate, at least to a factor of a few. Funded by NASA.

  20. Enceladus' tidal dissipation revisited

    NASA Astrophysics Data System (ADS)

    Tobie, Gabriel; Behounkova, Marie; Choblet, Gael; Cadek, Ondrej; Soucek, Ondrej

    2016-10-01

    A series of chemical and physical evidence indicates that the intense activity at Enceladus' South Pole is related to a subsurface salty water reservoir underneath the tectonically active ice shell. The detection of a significant libration implies that this water reservoir is global and that the average ice shell thickness is about 20-25km (Thomas et al. 2016). The interpretation of gravity and topography data further predicts large variations in ice shell thickness, resulting in a shell potentially thinner than 5 km in the South Polar Terrain (SPT) (Cadek et al. 2016). Such an ice shell structure requires a very strong heat source in the interior, with a focusing mechanism at the SPT. Thermal diffusion through the ice shell implies that at least 25-30 GW is lost into space by passive diffusion, implying a very efficient dissipation mechanism in Enceladus' interior to maintain such an ocean/ice configuration thermally stable.In order to determine in which conditions such a large dissipation power may be generated, we model the tidal response of Enceladus including variable ice shell thickness. For the rock core, we consider a wide range of rheological parameters representative of water-saturated porous rock materials. We demonstrate that the thinning toward the South Pole leads to a strong increase in heat production in the ice shell, with a optimal thickness obtained between 1.5 and 3 km, depending on the assumed ice viscosity. Our results imply that the heat production in the ice shell within the SPT may be sufficient to counterbalance the heat loss by diffusion and to power eruption activity. However, outside the SPT, a strong dissipation in the porous core is required to counterbalance the diffusive heat loss. We show that about 20 GW can be generated in the core, for an effective viscosity of 1012 Pa.s, which is comparable to the effective viscosity estimated in water-saturated glacial tills on Earth. We will discuss the implications of this revisited tidal

  1. Dynamic Topography Revisited

    NASA Astrophysics Data System (ADS)

    Moresi, Louis

    2015-04-01

    Dynamic Topography Revisited Dynamic topography is usually considered to be one of the trinity of contributing causes to the Earth's non-hydrostatic topography along with the long-term elastic strength of the lithosphere and isostatic responses to density anomalies within the lithosphere. Dynamic topography, thought of this way, is what is left over when other sources of support have been eliminated. An alternate and explicit definition of dynamic topography is that deflection of the surface which is attributable to creeping viscous flow. The problem with the first definition of dynamic topography is 1) that the lithosphere is almost certainly a visco-elastic / brittle layer with no absolute boundary between flowing and static regions, and 2) the lithosphere is, a thermal / compositional boundary layer in which some buoyancy is attributable to immutable, intrinsic density variations and some is due to thermal anomalies which are coupled to the flow. In each case, it is difficult to draw a sharp line between each contribution to the overall topography. The second definition of dynamic topography does seem cleaner / more precise but it suffers from the problem that it is not measurable in practice. On the other hand, this approach has resulted in a rich literature concerning the analysis of large scale geoid and topography and the relation to buoyancy and mechanical properties of the Earth [e.g. refs 1,2,3] In convection models with viscous, elastic, brittle rheology and compositional buoyancy, however, it is possible to examine how the surface topography (and geoid) are supported and how different ways of interpreting the "observable" fields introduce different biases. This is what we will do. References (a.k.a. homework) [1] Hager, B. H., R. W. Clayton, M. A. Richards, R. P. Comer, and A. M. Dziewonski (1985), Lower mantle heterogeneity, dynamic topography and the geoid, Nature, 313(6003), 541-545, doi:10.1038/313541a0. [2] Parsons, B., and S. Daly (1983), The

  2. First Grade Writers Revisit Their Work

    ERIC Educational Resources Information Center

    Hansen, Jane A.

    2007-01-01

    In this article, the author focuses on first grade readers and writers who revisit their work and describes what first-graders do when they revisit their writing about science and literature and review collections of their work. The first-graders discussed here are in Elaine O'Connor's classroom at Clark Elementary School in Charlottesville. In a…

  3. Relativistic stars in beyond Horndeski theories

    NASA Astrophysics Data System (ADS)

    Babichev, Eugeny; Koyama, Kazuya; Langlois, David; Saito, Ryo; Sakstein, Jeremy

    2016-12-01

    This work studies relativistic stars in beyond Horndeski scalar-tensor theories that exhibit a breaking of the Vainshtein mechanism inside matter, focusing on a model based on the quartic beyond Horndeski Lagrangian. We self-consistently derive the scalar field profile for static spherically symmetric objects in asymptotically de Sitter space-time and show that the Vainshtein breaking branch of the solutions is the physical branch thereby resolving several ambiguities with non-relativistic frameworks. The geometry outside the star is shown to be exactly Schwarzschild-de Sitter and therefore the parameterised post-Newtonian parameter {β }{{PPN}}=1, confirming that the external screening works at the post-Newtonian level. The Tolman-Oppenheimer-Volkoff (TOV) equations are derived and a new lower bound on the Vainshtein breaking parameter {{{\\Upsilon }}}1\\gt -4/9 is found by requiring the existence of static spherically symmetric stars. Focusing on the unconstrained case where {{{\\Upsilon }}}1\\lt 0, we numerically solve the TOV equations for polytropic and realistic equations of state and find stars with larger radii at fixed mass. Furthermore, the maximum mass can increase dramatically and stars with masses in excess of 3{M}⊙ can be found for relatively small values of the Vainshtein breaking parameter. We re-examine white dwarf stars and show that post-Newtonian corrections are important in beyond Horndeski theories and therefore the bounds coming from previous analyses should be revisited.

  4. Asymptotic structure of electrodynamics revisited

    NASA Astrophysics Data System (ADS)

    Herdegen, Andrzej

    2017-03-01

    We point out that recently published analyses of null and timelike infinity and long-range structures in electrodynamics to large extent rediscover results present in the literature. At the same time, some of the conclusions these recent works put forward may prove controversial. In view of these facts, we find it desirable to revisit the analysis taken up more than two decades ago, starting from earlier works on null infinity by other authors.

  5. Variable Stars in Large Magellanic Cloud Globular Clusters. II. NGC 1786

    NASA Astrophysics Data System (ADS)

    Kuehn, Charles A.; Smith, Horace A.; Catelan, Márcio; Pritzl, Barton J.; De Lee, Nathan; Borissova, Jura

    2012-12-01

    This is the second in a series of papers studying the variable stars in Large Magellanic Cloud globular clusters. The primary goal of this series is to study how RR Lyrae stars in Oosterhoff-intermediate systems compare to their counterparts in Oosterhoff I/II systems. In this paper, we present the results of our new time-series B-V photometric study of the globular cluster NGC 1786. A total of 65 variable stars were identified in our field of view. These variables include 53 RR Lyraes (27 RRab, 18 RRc, and 8 RRd), 3 classical Cepheids, 1 Type II Cepheid, 1 Anomalous Cepheid, 2 eclipsing binaries, 3 Delta Scuti/SX Phoenicis variables, and 2 variables of undetermined type. Photometric parameters for these variables are presented. We present physical properties for some of the RR Lyrae stars, derived from Fourier analysis of their light curves. We discuss several different indicators of Oosterhoff type which indicate that the Oosterhoff classification of NGC 1786 is not as clear cut as what is seen in most globular clusters. Based on observations taken with the SMARTS 1.3 m telescope operated by the SMARTS Consortium and observations taken at the Southern Astrophysical Research (SOAR) telescope, which is a joint project of the Ministério da Ciência, Tecnologia, e Inovação (MCTI) da República Federativa do Brasil, the U.S. National Optical Astronomy Observatory (NOAO), the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU).

  6. Star Polymers.

    PubMed

    Ren, Jing M; McKenzie, Thomas G; Fu, Qiang; Wong, Edgar H H; Xu, Jiangtao; An, Zesheng; Shanmugam, Sivaprakash; Davis, Thomas P; Boyer, Cyrille; Qiao, Greg G

    2016-06-22

    Recent advances in controlled/living polymerization techniques and highly efficient coupling chemistries have enabled the facile synthesis of complex polymer architectures with controlled dimensions and functionality. As an example, star polymers consist of many linear polymers fused at a central point with a large number of chain end functionalities. Owing to this exclusive structure, star polymers exhibit some remarkable characteristics and properties unattainable by simple linear polymers. Hence, they constitute a unique class of technologically important nanomaterials that have been utilized or are currently under audition for many applications in life sciences and nanotechnologies. This article first provides a comprehensive summary of synthetic strategies towards star polymers, then reviews the latest developments in the synthesis and characterization methods of star macromolecules, and lastly outlines emerging applications and current commercial use of star-shaped polymers. The aim of this work is to promote star polymer research, generate new avenues of scientific investigation, and provide contemporary perspectives on chemical innovation that may expedite the commercialization of new star nanomaterials. We envision in the not-too-distant future star polymers will play an increasingly important role in materials science and nanotechnology in both academic and industrial settings.

  7. Radio stars.

    PubMed

    Hjellming, R M; Wade, C M

    1971-09-17

    Up to the present time six classes of radio stars have been established. The signals are almost always very faint and drastically variable. Hence their discovery has owed as much to serendipity as to the highly sophisticated equipment and techniques that have been used. When the variations are regular, as with the pulsars, this characteristic can be exploited very successfully in the search for new objects as well as in the detailed study of those that are already known. The detection of the most erratically variable radio stars, the flare stars and the x-ray stars, is primarily a matter of luck and patience. In the case of the novas, one at least knows where and oughly when to look for radio emission. A very sensitive interferometer is clearly the best instrument to use in the initial detection of a radio star. The fact that weak background sources are frequently present makes it essential to prove that the position of a radio source agrees with that of a star to within a few arc seconds. The potential of radio astronomy for the study of radio stars will not be realized until more powerful instruments than those that are available today can be utilized. So far, we have been able to see only the most luminous of the radio stars.

  8. Radiolytic Cryovolcanism Revisited

    NASA Astrophysics Data System (ADS)

    Cooper, J. F.; Cooper, P. D.; Sittler, E. C.; Wesenberg, R. P.

    2013-12-01

    Active geysers of water vapor and ice grains from the south pole of Enceladus are not yet definitively explained in terms of energy sources and processes. Other instances of hot (Io) and cold (Mars, Triton) volcanism beyond Earth are known if not fully understood. We revisit, in comparison to other models, the 'Old Faithful' theory of radiolytic gas-driven cryovolcanism first proposed by Cooper et al. [Plan. Sp. Sci. 2009]. In the energetic electron irradiation environment of Enceladus within Saturn's magnetosphere, a 10-percent duty cycle could be maintained for current geyser activity driven by gases from oxidation of ammonia to N2 and methane to CO2 in the thermal margins of a south polar sea. Much shorter duty cycles down to 0.01 percent would be required to account for thermal power output up to 16 GW, Steady accumulation of oxidant energy over four billion years could have powered all Enceladus emissions over the past four hundred thousand to four hundred million years. There could be separate energy sources driving mass flow and thermal emission over vastly different time scales. Since episodic tidal dissipation on 10 Myr time scales at 0.1 - 1 Gyr intervals [O'Neill and Nimmo, Nature 2010], and thus duty cycles 1 - 10 percent, could heat the polar sea to the current level, the radiolytic energy source could easily power and modulate the geyser mass flow on million-year time scales. Maximum thermal emission temperature 223 K [Abramov and Spencer, Icarus 2009] hints at thermal buffering in the basal and vent wall layers by a 1:1 H2O:H2O2 radiolytic eutectic, assuming deep ice crust saturation with H2O2 from long cumulative surface irradiation and downward ice convection. Due to density stratification the peroxide eutectic and salt water layers could separate, so that the denser peroxide layer (1.2 g/cc) descends to the polar sea while the lighter salt water (1.05 g/cc) rises along separate channels. Methane reservoirs could be found dissolved into the polar

  9. Lithium in the Pleiades Revisited

    NASA Astrophysics Data System (ADS)

    King, J. R.; Hobbs, L. M.; Schuler, S. C.; Pinsonneault, M. H.

    2003-12-01

    New Li abundances have been derived for some 15-20 Pleiades dwarfs using new high-resolution and high S/N spectroscopy from HET/HRS. Previous studies suggested that our objects, all modest (projected) rotators, evinced considerable scatter in their Li abundances. We revisit the question of this scatter and its origin. This work has been supported by NSF grants AST 00-86576 and 02-39518, a South Carolina Space Grant Scholarship award, a generous donation from the Curry Foundation of Seneca, SC, and the NOAO Public Access Program.

  10. Slowly rotating homogeneous masses revisited

    NASA Astrophysics Data System (ADS)

    Reina, Borja

    2016-02-01

    Hartle's model for slowly rotating stars has been extensively used to compute equilibrium configurations of slowly rotating stars to second order in perturbation theory in general relativity, given a barotropic equation of state. A recent study based on the modern theory of perturbed matchings concludes that the functions in the (first and second order) perturbation tensors can always be taken as continuous at the surface of the star, except for the second-order function m0. This function presents a jump at the surface of the star proportional to the discontinuity of the energy density there. This concerns only a particular outcome of the model: the change in mass δM. In this paper, the amended change in mass is calculated for the case of constant density stars.

  11. SLIM--An Early Work Revisited

    SciTech Connect

    Chao, Alex; /SLAC

    2008-07-25

    An early, but at the time illuminating, piece of work on how to deal with a general, linearly coupled accelerator lattice is revisited. This work is based on the SLIM formalism developed in 1979-1981.

  12. McLean's second variation formula revisited

    NASA Astrophysics Data System (ADS)

    Lê, Hông Vân; Vanžura, Jiří

    2017-03-01

    We revisit McLean's second variation formulas for calibrated submanifolds in exceptional geometries, and correct his formulas concerning associative submanifolds and Cayley submanifolds, using a unified treatment based on the (relative) calibration method and Harvey-Lawson's identities.

  13. Symbiotic stars

    NASA Technical Reports Server (NTRS)

    Kafatos, M.; Michalitsianos, A. G.

    1984-01-01

    The physical characteristics of symbiotic star systems are discussed, based on a review of recent observational data. A model of a symbiotic star system is presented which illustrates how a cool red-giant star is embedded in a nebula whose atoms are ionized by the energetic radiation from its hot compact companion. UV outbursts from symbiotic systems are explained by two principal models: an accretion-disk-outburst model which describes how material expelled from the tenuous envelope of the red giant forms an inwardly-spiralling disk around the hot companion, and a thermonuclear-outburst model in which the companion is specifically a white dwarf which superheats the material expelled from the red giant to the point where thermonuclear reactions occur and radiation is emitted. It is suspected that the evolutionary course of binary systems is predetermined by the initial mass and angular momentum of the gas cloud within which binary stars are born. Since red giants and Mira variables are thought to be stars with a mass of one or two solar mass, it is believed that the original cloud from which a symbiotic system is formed can consist of no more than a few solar masses of gas.

  14. Revisiting the Magnetic and Spin Evolution of Two Young X-ray Pulsars

    NASA Astrophysics Data System (ADS)

    Ferdman, Robert; Kaspi, Victoria M.; Archibald, Robert Frederic

    2014-08-01

    We present results from timing analysis of two young X-ray pulsars found in the large Magellanic Cloud: the Crab-like energetic pulsar PSR B0540-69 and the so-called "big glitcher", PSR J0537-6910. In both cases, we analyze data taken with the Rossi X-ray Timing Explorer. This work extends the published data sets for these pulsars by approximately doubling their respective data spans. We revisit the glitching activity of these neutron stars, particularly that of PSR J0537-6910, determine more precise glitch and spin parameters, and discuss the implications for the spin and magnetospheric evolution of these interesting pulsars.

  15. Revisiting Supernova 1987A constraints on dark photons

    NASA Astrophysics Data System (ADS)

    Chang, Jae Hyeok; Essig, Rouven; McDermott, Samuel D.

    2017-01-01

    We revisit constraints on dark photons with masses below ˜ 100 MeV from the observations of Supernova 1987A. If dark photons are produced in sufficient quantity, they reduce the amount of energy emitted in the form of neutrinos, in conflict with observations. For the first time, we include the effects of finite temperature and density on the kinetic-mixing parameter, ɛ, in this environment. This causes the constraints on ɛ to weaken with the dark-photon mass below ˜ 15 MeV. For large-enough values of ɛ, it is well known that dark photons can be reabsorbed within the supernova. Since the rates of reabsorption processes decrease as the dark-photon energy increases, we point out that dark photons with energies above the Wien peak can escape without scattering, contributing more to energy loss than is possible assuming a blackbody spectrum. Furthermore, we estimate the systematic uncertainties on the cooling bounds by deriving constraints assuming one analytic and four different simulated temperature and density profiles of the proto-neutron star. Finally, we estimate also the systematic uncertainty on the bound by varying the distance across which dark photons must propagate from their point of production to be able to affect the star. This work clarifies the bounds from SN1987A on the dark-photon parameter space.

  16. Rainbow's stars

    NASA Astrophysics Data System (ADS)

    Garattini, Remo; Mandanici, Gianluca

    2017-01-01

    In recent years, a growing interest in the equilibrium of compact astrophysical objects like white dwarf and neutron stars has been manifested. In particular, various modifications due to Planck-scale energy effects have been considered. In this paper we analyze the modification induced by gravity's rainbow on the equilibrium configurations described by the Tolman-Oppenheimer-Volkoff (TOV) equation. Our purpose is to explore the possibility that the rainbow Planck-scale deformation of space-time could support the existence of different compact stars.

  17. Chameleon stars

    SciTech Connect

    Dzhunushaliev, Vladimir; Folomeev, Vladimir; Singleton, Douglas

    2011-10-15

    We consider a gravitating spherically symmetric configuration consisting of a scalar field nonminimally coupled to ordinary matter in the form of a perfect fluid. For this system we find static, regular, asymptotically flat solutions for both relativistic and nonrelativistic cases. It is shown that the presence of the nonminimal interaction leads to substantial changes both in the radial matter distribution of the star and in the star's total mass. A simple stability test indicates that, for the choice of parameters used in the paper, the solutions are unstable.

  18. Star Power

    SciTech Connect

    2014-10-17

    The U.S. Department of Energy's Princeton Plasma Physics Laboratory has released ''Star Power,'' a new informational video that uses dramatic and beautiful images and thought-provoking interviews to highlight the importance of the Laboratory's research into magnetic fusion.

  19. Star Power

    ScienceCinema

    None

    2016-07-12

    The U.S. Department of Energy's Princeton Plasma Physics Laboratory has released ''Star Power,'' a new informational video that uses dramatic and beautiful images and thought-provoking interviews to highlight the importance of the Laboratory's research into magnetic fusion.

  20. Spectral Models of Neutron Star Magnetospheres

    NASA Technical Reports Server (NTRS)

    Romani, Roger W.

    1997-01-01

    We revisit the association of unidentified Galactic plane EGRET sources with tracers of recent massive star formation and death. Up-to-date catalogs of OB associations, SNR's, young pulsars, H2 regions and young open clusters were used in finding counterparts for a recent list of EGRET sources. It has been argued for some time that EGRET source positions are correlated with SNR's and OB associations as a class; we extend such analyses by finding additional counterparts and assessing the probability of individual source identifications. Among the several scenarios relating EGRET sources to massive stars, we focus on young neutron stars as the origin of the gamma-ray emission. The characteristics of the candidate identifications are compared to the known gamma-ray pulsar sample and to detailed Galactic population syntheses using our outer gap pulsar model of gamma-ray emission. Both the spatial distribution and luminosity function of the candidates are in good agreement with the model predictions; we infer that young pulsars can account for the bulk of the excess low latitude EGRET sources. We show that with this identification, the gamma-ray point sources provide an important new window into the history of recent massive star death in the solar neighborhood.

  1. Photoevaporation of Circumstellar Disks Revisited: The Dust-free Case

    NASA Astrophysics Data System (ADS)

    Tanaka, Kei E. I.; Nakamoto, Taishi; Omukai, Kazuyuki

    2013-08-01

    Photoevaporation by stellar ionizing radiation is believed to play an important role in the dispersal of disks around young stars. The mass-loss model for dust-free disks developed by Hollenbach et al. is currently regarded as the conventional one and has been used in a wide variety of studies. However, the rate in this model was derived using the crude so-called 1+1D approximation of ionizing radiation transfer, which assumes that diffuse radiation propagates in a direction vertical to the disk. In this study, we revisit the photoevaporation of dust-free disks by solving the two-dimensional axisymmetric radiative transfer for steady-state disks. Unlike that solved by the conventional model, we determine that direct stellar radiation is more important than the diffuse field at the disk surface. The radial density distribution at the ionization boundary is represented by a single power law with index -3/2 in contrast to the conventional double power law. For this distribution, the photoevaporation rate from the entire disk can be written as a function of the ionizing photon emissivity ΦEUV from the central star and the disk outer radius r d as follows: \\dot{M}_PE = 5.4 \\times 10^{-5} (\\Phi _EUV/10^{49}\\ s^{-1})^{1/2} (r_d/1000\\ AU)^{1/2} \\ M_\\odot \\ yr^{-1}. This new rate depends on the outer disk radius rather than on the gravitational radius as in the conventional model, because of the enhanced contribution to the mass loss from the outer disk annuli. In addition, we discuss its applications to present-day as well as primordial star formation.

  2. PHOTOEVAPORATION OF CIRCUMSTELLAR DISKS REVISITED: THE DUST-FREE CASE

    SciTech Connect

    Tanaka, Kei E. I.; Omukai, Kazuyuki; Nakamoto, Taishi

    2013-08-20

    Photoevaporation by stellar ionizing radiation is believed to play an important role in the dispersal of disks around young stars. The mass-loss model for dust-free disks developed by Hollenbach et al. is currently regarded as the conventional one and has been used in a wide variety of studies. However, the rate in this model was derived using the crude so-called 1+1D approximation of ionizing radiation transfer, which assumes that diffuse radiation propagates in a direction vertical to the disk. In this study, we revisit the photoevaporation of dust-free disks by solving the two-dimensional axisymmetric radiative transfer for steady-state disks. Unlike that solved by the conventional model, we determine that direct stellar radiation is more important than the diffuse field at the disk surface. The radial density distribution at the ionization boundary is represented by a single power law with index -3/2 in contrast to the conventional double power law. For this distribution, the photoevaporation rate from the entire disk can be written as a function of the ionizing photon emissivity {Phi}{sub EUV} from the central star and the disk outer radius r{sub d} as follows: M-dot{sub PE} = 5.4 x 10{sup -5} ({Phi}{sub EUV}/10{sup 49} s{sup -1}){sup 1/2} (r{sub d}/1000 AU){sup 1/2} M{sub Sun} yr{sup -1}. This new rate depends on the outer disk radius rather than on the gravitational radius as in the conventional model, because of the enhanced contribution to the mass loss from the outer disk annuli. In addition, we discuss its applications to present-day as well as primordial star formation.

  3. Gaia's view of the λ Boo star puzzle

    NASA Astrophysics Data System (ADS)

    Murphy, Simon J.; Paunzen, Ernst

    2017-04-01

    The evolutionary status of the chemically peculiar class of λ Boo stars has been intensely debated. It is now agreed that the λ Boo phenomenon affects A stars of all ages, from star formation to the terminal age main sequence, but the cause of the chemical peculiarity is still a puzzle. We revisit the debate of their ages and temperatures in order to shed light on the phenomenon, using the new parallaxes in Gaia Data Release 1 with existing Hipparcos parallaxes and multicolour photometry. We find that no single formation mechanism is able to explain all the observations, and suggest that there are multiple channels producing λ Boo spectra. The relative importance of these channels varies with age, temperature and environment.

  4. Converting neutron stars into strange stars

    NASA Technical Reports Server (NTRS)

    Olinto, A. V.

    1991-01-01

    If strange matter is formed in the interior of a neutron star, it will convert the entire neutron star into a strange star. The proposed mechanisms are reviewed for strange matter seeding and the possible strange matter contamination of neutron star progenitors. The conversion process that follows seeding and the recent calculations of the conversion timescale are discussed.

  5. Star clusters

    NASA Astrophysics Data System (ADS)

    Labhardt, Lukas; Binggeli, Bruno

    Star clusters are at the heart of astronomy, being key objects for our understanding of stellar evolution and galactic structure. Observations with the Hubble Space Telescope and other modern equipment have revealed fascinating new facts about these galactic building blocks. This book provides two comprehensive and up-to-date, pedagogically designed reviews on star clusters by two well-known experts in the field. Bruce Carney presents our current knowledge of the relative and absolute ages of globular clusters and the chemical history of our Galaxy. Bill Harris addresses globular clusters in external galaxies and their use as tracers of galaxy formation and cosmic distance indicators. The book is written for graduate students as well as professionals in astronomy and astrophysics.

  6. Exceptional Stars

    NASA Astrophysics Data System (ADS)

    Kulkarni, S. R.; Hansen, B.; van Kerkwijk, M.; Phinney, E. S.

    2005-12-01

    As part of our Interdisciplinary Scientist effort (PI, Kulkarni) for the Space Interferometry Mission (SIM) we proposed an investigation with SIM of a number of exceptional stars. With SIM we plan to observe dozens of nearby white dwarfs and search for planets surviving the evolution away from the main sequence as well as (newly formed) planets formed in the circumbinary disks of post-AGB binaries or as a result of white dwarf mergers. We propose to measure the proper motion of a sample of X-ray binaries and Be star binaries with the view of understanding the originof high latitude objects and inferring natal kicks and pre-supernova orbits. We plan to observe several compact object binaries to determine the mass of the compact star. Of particular importance is the proposed observation of SS 433 (for which we propose to use the spectrometer on SIM to measure the proper motion of the emission line clumps embedded in the relativistic jets). Separately we are investigating the issue of frame tie between SIM and the ecliptic frame (by observing binary millisecond pulsars with SIM; the position of these objects is very well determined by pulsar timing) and the degree to which highly precise visibility amplitude measurements can be inverted to infer binary parameters.

  7. Neutron Stars

    NASA Astrophysics Data System (ADS)

    van den Heuvel, Ed

    Radio pulsars are unique laboratories for a wide range of physics and astrophysics. Understanding how they are created, how they evolve and where we find them in the Galaxy, with or without binary companions, is highly constraining of theories of stellar and binary evolution. Pulsars' relationship with a recently discovered variety of apparently different classes of neutron stars is an interesting modern astrophysical puzzle which we consider in Part I of this review. Radio pulsars are also famous for allowing us to probe the laws of nature at a fundamental level. They act as precise cosmic clocks and, when in a binary system with a companion star, provide indispensable venues for precision tests of gravity. The different applications of radio pulsars for fundamental physics will be discussed in Part II. We finish by making mention of the newly discovered class of astrophysical objects, the Fast Radio Bursts, which may or may not be related to radio pulsars or neutron stars, but which were discovered in observations of the latter.

  8. Constraining the neutron star equation of state with gravitational wave signals from coalescing binary neutron stars

    NASA Astrophysics Data System (ADS)

    Agathos, M.; Meidam, J.; Del Pozzo, W.; Li, T. G. F.; Tompitak, M.; Veitch, J.; Vitale, S.; Van Den Broeck, C.

    2015-07-01

    Recently exploratory studies were performed on the possibility of constraining the neutron star equation of state (EOS) using signals from coalescing binary neutron stars, or neutron star-black hole systems, as they will be seen in upcoming advanced gravitational wave detectors such as Advanced LIGO and Advanced Virgo. In particular, it was estimated to what extent the combined information from multiple detections would enable one to distinguish between different equations of state through hypothesis ranking or parameter estimation. Under the assumption of zero neutron star spins both in signals and in template waveforms and considering tidal effects to 1 post-Newtonian (1PN) order, it was found that O (20 ) sources would suffice to distinguish between a stiff, moderate, and soft equation of state. Here we revisit these results, this time including neutron star tidal effects to the highest order currently known, termination of gravitational waveforms at the contact frequency, neutron star spins, and the resulting quadrupole-monopole interaction. We also take the masses of neutron stars in simulated sources to be distributed according to a relatively strongly peaked Gaussian, as hinted at by observations, but without assuming that the data analyst will necessarily have accurate knowledge of this distribution for use as a mass prior. We find that especially the effect of the latter is dramatic, necessitating many more detections to distinguish between different EOSs and causing systematic biases in parameter estimation, on top of biases due to imperfect understanding of the signal model pointed out in earlier work. This would get mitigated if reliable prior information about the mass distribution could be folded into the analyses.

  9. VizieR Online Data Catalog: Carbon-enhanced metal-poor stars (Placco+, 2014)

    NASA Astrophysics Data System (ADS)

    Placco, V. M.; Frebel, A.; Beers, T. C.; Stancliffe, R. J.

    2017-01-01

    We revisit the observed frequencies of carbon-enhanced metal-poor (CEMP) stars as a function of the metallicity in the Galaxy, using data from the literature with available high-resolution spectroscopy. Our analysis excludes stars exhibiting clear overabundances of neutron-capture elements and takes into account the expected depletion of surface carbon abundance that occurs due to CN processing on the upper red giant branch. This allows for the recovery of the initial carbon abundance of these stars, and thus for an accurate assessment of the frequencies of carbon-enhanced stars. The correction procedure we develop is based on stellar-evolution models and depends on the surface gravity, log g, of a given star. (2 data files).

  10. Binary stars.

    PubMed

    Paczynacuteski, B

    1984-07-20

    Most stars in the solar neighborhood are either double or multiple systems. They provide a unique opportunity to measure stellar masses and radii and to study many interesting and important phenomena. The best candidates for black holes are compact massive components of two x-ray binaries: Cygnus X-1 and LMC X-3. The binary radio pulsar PSR 1913 + 16 provides the best available evidence for gravitational radiation. Accretion disks and jets observed in close binaries offer a very good testing ground for models of active galactic nuclei and quasars.

  11. Gravity current jump conditions, revisited

    NASA Astrophysics Data System (ADS)

    Ungarish, Marius; Hogg, Andrew J.

    2016-11-01

    Consider the flow of a high-Reynolds-number gravity current of density ρc in an ambient fluid of density ρa in a horizontal channel z ∈ [ 0 , H ] , with gravity in - z direction. The motion is often modeled by a two-layer formulation which displays jumps (shocks) in the height of the interface, in particular at the leading front of the dense layer. Various theoretical models have been advanced to predict the dimensionless speed of the jump, Fr = U /√{g' h } ; g' , h are reduced gravity and jump height. We revisit this problem and using the Navier-Stokes equations, integrated over a control volume embedding the jump, derive balances of mass and momentum fluxes. We focus on understanding the closures needed to complete this model and we show the vital need to understand the pressure head losses over the jump, which we show can be related to the vorticity fluxes at the boundaries of the control volume. Our formulation leads to two governing equations for three dimensionless quantities. Closure requires one further assumption, depending on which we demonstrate that previous models for gravity current fronts and internal bores can be recovered. This analysis yield new insights into existing results, and also provides constraints for potential new formulae.

  12. Revisiting intracellular calcium signaling semantics.

    PubMed

    Haiech, Jacques; Audran, Emilie; Fève, Marie; Ranjeva, Raoul; Kilhoffer, Marie-Claude

    2011-12-01

    Cells use intracellular free calcium concentration changes for signaling. Signal encoding occurs through both spatial and temporal modulation of the free calcium concentration. The encoded message is detected by an ensemble of intracellular sensors forming the family of calcium-binding proteins (CaBPs) which must faithfully translate the message using a new syntax that is recognized by the cell. The cell is home to a significant although limited number of genes coding for proteins involved in the signal encoding and decoding processes. In a cell, only a subset of this ensemble of genes is expressed, leading to a genetic regulation of the calcium signal pathways. Calmodulin (CaM), the most ubiquitous expressed intracellular calcium-binding protein, plays a major role in calcium signal translation. Similar to a hub, it is central to a large and finely tuned network, receiving information, integrating it and dispatching the cognate response. In this review, we examine the different steps starting with an external stimulus up to a cellular response, with special emphasis on CaM and the mechanism by which it decodes calcium signals and translates it into exquisitely coordinated cellular events. By this means, we will revisit the calcium signaling semantics, hoping that we will ease communication between scientists dealing with calcium signals in different biological systems and different domains.

  13. Revisiting Bohr's semiclassical quantum theory.

    PubMed

    Ben-Amotz, Dor

    2006-10-12

    Bohr's atomic theory is widely viewed as remarkable, both for its accuracy in predicting the observed optical transitions of one-electron atoms and for its failure to fully correspond with current electronic structure theory. What is not generally appreciated is that Bohr's original semiclassical conception differed significantly from the Bohr-Sommerfeld theory and offers an alternative semiclassical approximation scheme with remarkable attributes. More specifically, Bohr's original method did not impose action quantization constraints but rather obtained these as predictions by simply matching photon and classical orbital frequencies. In other words, the hydrogen atom was treated entirely classically and orbital quantized emerged directly from the Planck-Einstein photon quantization condition, E = h nu. Here, we revisit this early history of quantum theory and demonstrate the application of Bohr's original strategy to the three quintessential quantum systems: an electron in a box, an electron in a ring, and a dipolar harmonic oscillator. The usual energy-level spectra, and optical selection rules, emerge by solving an algebraic (quadratic) equation, rather than a Bohr-Sommerfeld integral (or Schroedinger) equation. However, the new predictions include a frozen (zero-kinetic-energy) state which in some (but not all) cases lies below the usual zero-point energy. In addition to raising provocative questions concerning the origin of quantum-chemical phenomena, the results may prove to be of pedagogical value in introducing students to quantum mechanics.

  14. The Future of Engineering Education--Revisited

    ERIC Educational Resources Information Center

    Wankat, Phillip C.; Bullard, Lisa G.

    2016-01-01

    This paper revisits the landmark CEE series, "The Future of Engineering Education," published in 2000 (available free in the CEE archives on the internet) to examine the predictions made in the original paper as well as the tools and approaches documented. Most of the advice offered in the original series remains current. Despite new…

  15. Phenomenology of n - n ¯ oscillations revisited

    DOE PAGES

    Gardner, S.; Jafari, E.

    2015-05-22

    We revisit the phenomenology of n-n¯ oscillations in the presence of external magnetic fields, highlighting the role of spin. We show, contrary to long-held belief, that the n-n¯ transition rate need not be suppressed, opening new opportunities for its empirical study.

  16. Revisiting separation properties of convex fuzzy sets

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Separation of convex sets by hyperplanes has been extensively studied on crisp sets. In a seminal paper separability and convexity are investigated, however there is a flaw on the definition of degree of separation. We revisited separation on convex fuzzy sets that have level-wise (crisp) disjointne...

  17. The Rotating Morse-Pekeris Oscillator Revisited

    ERIC Educational Resources Information Center

    Zuniga, Jose; Bastida, Adolfo; Requena, Alberto

    2008-01-01

    The Morse-Pekeris oscillator model for the calculation of the vibration-rotation energy levels of diatomic molecules is revisited. This model is based on the realization of a second-order exponential expansion of the centrifugal term about the minimum of the vibrational Morse oscillator and the subsequent analytical resolution of the resulting…

  18. Topological string theory revisited I: The stage

    NASA Astrophysics Data System (ADS)

    Jia, Bei

    2016-08-01

    In this paper, we reformulate topological string theory using supermanifolds and supermoduli spaces, following the approach worked out by Witten (Superstring perturbation theory revisited, arXiv:1209.5461). We intend to make the construction geometrical in nature, by using supergeometry techniques extensively. The goal is to establish the foundation of studying topological string amplitudes in terms of integration over appropriate supermoduli spaces.

  19. Revisiting the Regenerative Possibilities of Ortiz

    ERIC Educational Resources Information Center

    Duques, Matthew

    2004-01-01

    The author of this article revisits Simon Ortiz's poem, "From Sand Creek," in which the latter can in so few words convey both the horrific tragedy of conquest and colonization, while at the same time find a space for possibility, a means for recovery that is never about forgetting but always occurs as a kind of recuperative remembering. Ortiz…

  20. Revisiting Basic Counseling Skills with Children

    ERIC Educational Resources Information Center

    Van Velsor, Patricia

    2004-01-01

    Counseling with children can be challenging for counselors whose training focused on adult clients. The purpose of this article is to offer information to counselors seeking to improve their skills with children, revisiting a topic discussed in an earlier Journal of Counseling & Development article by P. Erdman and R. Lampe (1996). Examples of…

  1. Revisiting the 1761 Transatlantic Tsunami

    NASA Astrophysics Data System (ADS)

    Baptista, Maria Ana; Wronna, Martin; Miranda, Jorge Miguel

    2016-04-01

    The tsunami catalogs of the Atlantic include two transatlantic tsunamis in the 18th century the well known 1st November 1755 and the 31st March 1761. The 31st March 1761 earthquake struck Portugal, Spain, and Morocco. The earthquake occurred around noontime in Lisbon alarming the inhabitants and throwing down ruins of the past 1st November 1755 earthquake. According to several sources, the earthquake was followed by a tsunami observed as far as Cornwall (United Kingdom), Cork (Ireland) and Barbados (Caribbean). The analysis of macroseismic information and its compatibility with tsunami travel time information led to a source area close to the Ampere Seamount with an estimated epicenter circa 34.5°N 13°W. The estimated magnitude of the earthquake was 8.5. In this study, we revisit the tsunami observations, and we include a report from Cadiz not used before. We use the results of the compilation of the multi-beam bathymetric data, that covers the area between 34°N - 38°N and 12.5°W - 5.5°W and use the recent tectonic map published for the Southwest Iberian Margin to select among possible source scenarios. Finally, we use a non-linear shallow water model that includes the discretization and explicit leap-frog finite difference scheme to solve the shallow water equations in the spherical or Cartesian coordinate to compute tsunami waveforms and tsunami inundation and check the results against the historical descriptions to infer the source of the event. This study received funding from project ASTARTE- Assessment Strategy and Risk Reduction for Tsunamis in Europe a collaborative project Grant 603839, FP7-ENV2013 6.4-3

  2. O stars and Wolf-Rayet stars

    NASA Technical Reports Server (NTRS)

    Conti, Peter S.; Underhill, Anne B.; Jordan, Stuart (Editor); Thomas, Richard (Editor)

    1988-01-01

    Basic information is given about O and Wolf-Rayet stars indicating how these stars are defined and what their chief observable properties are. Part 2 of the volume discussed four related themes pertaining to the hottest and most luminous stars. Presented are: an observational overview of the spectroscopic classification and extrinsic properties of O and Wolf-Rayet stars; the intrinsic parameters of luminosity, effective temperature, mass, and composition of the stars, and a discussion of their viability; stellar wind properties; and the related issues concerning the efforts of stellar radiation and wind on the immediate interstellar environment are presented.

  3. Lifestyles of the Stars.

    ERIC Educational Resources Information Center

    National Aeronautics and Space Administration, Cocoa Beach, FL. John F. Kennedy Space Center.

    Some general information on stars is provided in this National Aeronautics and Space Administration pamphlet. Topic areas briefly discussed are: (1) the birth of a star; (2) main sequence stars; (3) red giants; (4) white dwarfs; (5) neutron stars; (6) supernovae; (7) pulsars; and (8) black holes. (JN)

  4. Egyptian "Star Clocks"

    NASA Astrophysics Data System (ADS)

    Symons, Sarah

    Diagonal, transit, and Ramesside star clocks are tables of astronomical information occasionally found in ancient Egyptian temples, tombs, and papyri. The tables represent the motions of selected stars (decans and hour stars) throughout the Egyptian civil year. Analysis of star clocks leads to greater understanding of ancient Egyptian constellations, ritual astronomical activities, observational practices, and pharaonic chronology.

  5. The lithium content of the galactic halo stars

    NASA Astrophysics Data System (ADS)

    Charbonnel, C.; Primas, F.

    Thanks to the accurate determination of the baryon density of the Universe by the recent cosmic microwave background experiments, updated predictions of the standard model of Big Bang nucleosynthesis yield the initial abundances of the primordial light elements with an unprecedented precision (Bennet et al. 2003; Spergel et al. 2003; Coc et al. 2004; Cyburt 2004; Serpico et al. 2004). In the case of ^7Li, the CMB+SBBN value is significantly higher than the generally reported abundances for Pop II stars along the Spite plateau. Here, we report on the very recent results we obtained by revisiting a large sample of literature Li data in halo stars that we assembled following some strict criteria on the quality of the original analyses published from the early 90 s onwards. We put a strong emphasis on the temperature scale and reddening issues, and on the determination of the evolutionary status of each of our sample stars. Using our “best" (i.e. most consistent) set of temperatures we discuss the resulting mean Li value along the plateau for the dwarf stars on one hand and for the turnoff and subgiant stars on the other hand.

  6. Massive star formation by accretion. I. Disc accretion

    NASA Astrophysics Data System (ADS)

    Haemmerlé, L.; Eggenberger, P.; Meynet, G.; Maeder, A.; Charbonnel, C.

    2016-01-01

    Context. Massive stars likely form by accretion and the evolutionary track of an accreting forming star corresponds to what is called the birthline in the Hertzsprung-Russell (HR) diagram. The shape of this birthline is quite sensitive to the evolution of the entropy in the accreting star. Aims: We first study the reasons why some birthlines published in past years present different behaviours for a given accretion rate. We then revisit the question of the accretion rate, which allows us to understand the distribution of the observed pre-main-sequence (pre-MS) stars in the HR diagram. Finally, we identify the conditions needed to obtain a large inflation of the star along its pre-MS evolution that may push the birthline towards the Hayashi line in the upper part of the HR diagram. Methods: We present new pre-MS models including accretion at various rates and for different initial structures of the accreting core. We compare them with previously published equivalent models. From the observed upper envelope of pre-MS stars in the HR diagram, we deduce the accretion law that best matches the accretion history of most of the intermediate-mass stars. Results: In the numerical computation of the time derivative of the entropy, some treatment leads to an artificial loss of entropy and thus reduces the inflation that the accreting star undergoes along the birthline. In the case of cold disc accretion, the existence of a significant swelling during the accretion phase, which leads to radii ≳ 100 R⊙ and brings the star back to the red part of the HR diagram, depends sensitively on the initial conditions. For an accretion rate of 10-3M⊙ yr-1, only models starting from a core with a significant radiative region evolve back to the red part of the HR diagram. We also obtain that, in order to reproduce the observed upper envelope of pre-MS stars in the HR diagram with an accretion law deduced from the observed mass outflows in ultra-compact HII regions, the fraction of the

  7. Neutron Stars and NuSTAR

    NASA Astrophysics Data System (ADS)

    Bhalerao, Varun

    2012-05-01

    My thesis centers around the study of neutron stars, especially those in massive binary systems. To this end, it has two distinct components: the observational study of neutron stars in massive binaries with a goal of measuring neutron star masses and participation in NuSTAR, the first imaging hard X-ray mission, one that is extremely well suited to the study of massive binaries and compact objects in our Galaxy. The Nuclear Spectroscopic Telescope Array (NuSTAR) is a NASA Small Explorer mission that will carry the first focusing high energy X-ray telescope to orbit. NuSTAR has an order-of-magnitude better angular resolution and has two orders of magnitude higher sensitivity than any currently orbiting hard X-ray telescope. I worked to develop, calibrate, and test CdZnTe detectors for NuSTAR. I describe the CdZnTe detectors in comprehensive detail here - from readout procedures to data analysis. Detailed calibration of detectors is necessary for analyzing astrophysical source data obtained by the NuSTAR. I discuss the design and implementation of an automated setup for calibrating flight detectors, followed by calibration procedures and results. Neutron stars are an excellent probe of fundamental physics. The maximum mass of a neutron star can put stringent constraints on the equation of state of matter at extreme pressures and densities. From an astrophysical perspective, there are several open questions in our understanding of neutron stars. What are the birth masses of neutron stars? How do they change in binary evolution? Are there multiple mechanisms for the formation of neutron stars? Measuring masses of neutron stars helps answer these questions. Neutron stars in high-mass X-ray binaries have masses close to their birth mass, providing an opportunity to disentangle the role of "nature" and "nurture" in the observed mass distributions. In 2006, masses had been measured for only six such objects, but this small sample showed the greatest diversity in masses

  8. Revisiting the 1988 Pluto Occultation

    NASA Astrophysics Data System (ADS)

    Bosh, Amanda S.; Dunham, Edward W.; Young, Leslie A.; Slivan, Steve; Barba née Cordella, Linda L.; Millis, Robert L.; Wasserman, Lawrence H.; Nye, Ralph

    2015-11-01

    In 1988, Pluto's atmosphere was surmised to exist because of the surface ices that had been detected through spectroscopy, but it had not yet been directly detected in a definitive manner. The key to making such a detection was the stellar occultation method, used so successfully for the discovery of the Uranian rings in 1977 (Elliot et al. 1989; Millis et al. 1993) and before that for studies of the atmospheres of other planets.On 9 June 1988, Pluto occulted a star, with its shadow falling over the South Pacific Ocean region. One team of observers recorded this event from the Kuiper Airborne Observatory, while other teams captured the event from various locations in Australia and New Zealand. Preceding this event, extensive astrometric observations of Pluto and the star were collected in order to refine the prediction.We will recount the investigations that led up to this important Pluto occultation, discuss the unexpected atmospheric results, and compare the 1988 event to the recent 2015 event whose shadow followed a similar track through New Zealand and Australia.

  9. The flow along an external corner revisited

    NASA Astrophysics Data System (ADS)

    Denier, Jim; Jewell, Nathaniel

    2013-11-01

    We revisit the problem of the flow of an almost inviscid fluid along an external corner made from the junction of two quarter infinite plates joined at an angle 0 < α < π / 2 . The structure of the boundary layer which develops along the corner is explored using a computational approach based upon a spectral element discretisation of the steady two-dimensional boundary-layer equations. We pay particular attention to the case when the angle α is small, thus approximating the semi-infinte quarter plate problem considered by Stewartson (1961) and recently revisited by Duck & Hewitt (2012). Our results, which demonstrate a thickening of the boundary-layer near the sharp corner, will be discussed in the context of the asymptotic theory developed in the aforementioned papers.

  10. Revisiting Cementoblastoma with a Rare Case Presentation

    PubMed Central

    Narasimhan, Malathi; Ramalingam, Suganya; Anandan, Soumya; Ranganathan, Subhashini

    2017-01-01

    Cementoblastoma is a rare benign odontogenic neoplasm which is characterized by the proliferation of cellular cementum. Diagnosis of cementoblastoma is challenging because of its protracted clinical, radiographic features, and bland histological appearance; most often cementoblastoma is often confused with other cementum and bone originated lesions. The aim of this article is to overview/revisit, approach the diagnosis of cementoblastoma, and also present a unique radiographic appearance of a cementoblastoma lesion associated with an impacted tooth. PMID:28337352

  11. CCD star trackers

    NASA Technical Reports Server (NTRS)

    Goss, W. C.

    1975-01-01

    The application of CCDs to star trackers and star mappers is considered. Advantages and disadvantages of silicon CCD star trackers are compared with those of image dissector star trackers. It is concluded that the CCD has adequate sensitivity for most single star tracking tasks and is distinctly superior in multiple star tracking or mapping applications. The signal and noise figures of several current CCD configurations are discussed. The basic structure of the required signal processing is described, and it is shown that resolution in excess of the number of CCD elements may be had by interpolation.

  12. The Millennium Star Atlas

    NASA Astrophysics Data System (ADS)

    Sinnott, R. W.

    1997-08-01

    Derived from Hipparcos and Tycho observations, the Millennium Star Atlas is a set of 1548 charts covering the entire sky to about magnitude 11. It stands apart from all previous printed atlases in completeness to magnitude 10 and in uniformity around the sky. The generous chart scale has made possible a number of innovations never before seen in a star atlas: arrows on high-proper-motion stars, double-star ticks conveying separation and position angle for a specific modern epoch, distance labels for nearby stars, and variable stars coded by amplitude, period, and type. Among the nonstellar objects plotted, more than 8000 galaxies are shown with aspect ratio and orientation.

  13. Does radiative feedback by the first stars promote or prevent second generation star formation?

    NASA Astrophysics Data System (ADS)

    Ahn, Kyungjin; Shapiro, Paul R.

    2007-03-01

    response of the core to this shock front, which leads to molecular cooling and collapse that, when compared to the same halo without external radiation, is (a) expedited, or (b) delayed, or (c) unaltered, or (d) reversed or prevented, depending upon the flux (i.e. distance to the source) and the halo mass and evolutionary stage. When collapse is expedited, star formation in neighbouring minihaloes or in merging subhaloes within the host minihalo sometimes occurs within the lifetime of the first star. Roughly speaking, most haloes that were destined to cool, collapse and form stars in the absence of external radiation are found to do so even when exposed to the first Pop III star in their neighbourhood, while those that would not have done so are still not able to. A widely held view that the first Pop III stars must exert either positive or negative feedback on the formation of the stars in neighbouring minihaloes should, therefore, be revisited.

  14. BHQ revisited (2): Texture development

    NASA Astrophysics Data System (ADS)

    Kilian, Rüdiger; Heilbronner, Renée

    2016-04-01

    appears that grains can be unfavourably oriented for glide despite their c-axis direction falling in those positions which were used in the "classical" interpretation. Additionally, it turns out that grain-scale dispersion axes can be used to describe the kinematic behaviour in a more consistent way compared to the rotations axes obtained from intragranular misorientations in the range of 2-10°. The implications derived from the experimental data set will be compared to data obtained from natural quartz mylonites which formed in a comparable recrystallization regime. This is the companion poster to "BHQ revisited (I) looking at grain size" where the development of the dynamically recrystallized grain size is addressed. Reference cited: Heilbronner, R., and J. Tullis (2006), Evolution of c axis pole figures and grain size during dynamic recrystallization: Results from experimentally sheared quartzite, J. Geophys. Res., 111, B10202, doi:10.1029/2005JB004194.

  15. Astrophysics: Stars fight back

    NASA Astrophysics Data System (ADS)

    Hopkins, Philip F.

    2014-12-01

    Galaxies contain fewer stars than predicted. The discovery of a massive galactic outflow of molecular gas in a compact galaxy, which forms stars 100 times faster than the Milky Way, may help to explain why. See Letter p.68

  16. Star Formation in Galaxies

    NASA Technical Reports Server (NTRS)

    1987-01-01

    Topics addressed include: star formation; galactic infrared emission; molecular clouds; OB star luminosity; dust grains; IRAS observations; galactic disks; stellar formation in Magellanic clouds; irregular galaxies; spiral galaxies; starbursts; morphology of galactic centers; and far-infrared observations.

  17. Intrinsically variable stars

    NASA Technical Reports Server (NTRS)

    Bohm-Vitense, Erika; Querci, Monique

    1987-01-01

    The characteristics of intrinsically variable stars are examined, reviewing the results of observations obtained with the IUE satellite since its launch in 1978. Selected data on both medium-spectral-class pulsating stars (Delta Cep stars, W Vir stars, and related groups) and late-type variables (M, S, and C giants and supergiants) are presented in spectra, graphs, and tables and described in detail. Topics addressed include the calibration of the the period-luminosity relation, Cepheid distance determination, checking stellar evolution theory by the giant companions of Cepheids, Cepheid masses, the importance of the hydrogen convection zone in Cepheids, temperature and abundance estimates for Population II pulsating stars, mass loss in Population II Cepheids, SWP and LWP images of cold giants and supergiants, temporal variations in the UV lines of cold stars, C-rich cold stars, and cold stars with highly ionized emission lines.

  18. Dibaryons in neutron stars

    NASA Technical Reports Server (NTRS)

    Olinto, Angela V.; Haensel, Pawel; Frieman, Joshua A.

    1991-01-01

    The effects are studied of H-dibaryons on the structure of neutron stars. It was found that H particles could be present in neutron stars for a wide range of dibaryon masses. The appearance of dibaryons softens the equations of state, lowers the maximum neutron star mass, and affects the transport properties of dense matter. The parameter space is constrained for dibaryons by requiring that a 1.44 solar mass neutron star be gravitationally stable.

  19. Chromospheres of Coronal Stars

    NASA Technical Reports Server (NTRS)

    Linsky, Jeffrey L.; Wood, Brian E.

    1996-01-01

    We summarize the main results obtained from the analysis of ultraviolet emission line profiles of coronal late-type stars observed with the Goddard High Resolution Spectrograph (GHRS) on the Hubble Space Telescope. The excellent GHRS spectra provide new information on magnetohydrodynamic phenomena in the chromospheres and transition regions of these stars. One exciting new result is the discovery of broad components in the transition region lines of active stars that we believe provide evidence for microflare heating in these stars.

  20. America's Star Libraries

    ERIC Educational Resources Information Center

    Lyons, Ray; Lance, Keith Curry

    2009-01-01

    "Library Journal"'s new national rating of public libraries, the "LJ" Index of Public Library Service, identifies 256 "star" libraries. It rates 7,115 public libraries. The top libraries in each group get five, four, or three Michelin guide-like stars. All included libraries, stars or not, can use their scores to learn from their peers and improve…

  1. Origins of Hot Jupiters, Revisited

    NASA Astrophysics Data System (ADS)

    Batygin, Konstantin; Bodenheimer, Peter; Laughlin, Greg

    2016-05-01

    Hot Jupiters, giant extrasolar planets with orbital periods less than ~10 days, have long been thought to form at large radial distances (a > 2AU) in protoplanetary disks, only to subsequently experience large-scale inward migration to the small orbital radii at which they are observed. Here, we propose that a substantial fraction of the hot Jupiter population forms in situ, with the Galactically prevalent short-period super-Earths acting as the source population. Our calculations suggest that under conditions appropriate to the inner regions of protoplanetary disks, rapid gas accretion can be initiated for solid cores of 10-20 Earth masses, in line with the conventional picture of core-nucleated accretion. The planetary conglomeration process, coupled with subsequent gravitational contraction and spin down of the host star, drives sweeping secular resonances through the system, increasing the mutual inclinations of exterior, low-mass companions to hot Jupiters. Accordingly, this formation scenario leads to testable consequences, including the expectation that hot Jupiters should frequently be accompanied by additional non-transiting planets, reminiscent of those observed in large numbers by NASA’s Kepler Mission and Doppler velocity surveys. High-precision radial velocity monitoring provides the best prospect for their detection.

  2. The Galactic Nova Rate Revisited

    NASA Astrophysics Data System (ADS)

    Shafter, A. W.

    2017-01-01

    Despite its fundamental importance, a reliable estimate of the Galactic nova rate has remained elusive. Here, the overall Galactic nova rate is estimated by extrapolating the observed rate for novae reaching m≤slant 2 to include the entire Galaxy using a two component disk plus bulge model for the distribution of stars in the Milky Way. The present analysis improves on previous work by considering important corrections for incompleteness in the observed rate of bright novae and by employing a Monte Carlo analysis to better estimate the uncertainty in the derived nova rates. Several models are considered to account for differences in the assumed properties of bulge and disk nova populations and in the absolute magnitude distribution. The simplest models, which assume uniform properties between bulge and disk novae, predict Galactic nova rates of ∼50 to in excess of 100 per year, depending on the assumed incompleteness at bright magnitudes. Models where the disk novae are assumed to be more luminous than bulge novae are explored, and predict nova rates up to 30% lower, in the range of ∼35 to ∼75 per year. An average of the most plausible models yields a rate of {50}-23+31 yr‑1, which is arguably the best estimate currently available for the nova rate in the Galaxy. Virtually all models produce rates that represent significant increases over recent estimates, and bring the Galactic nova rate into better agreement with that expected based on comparison with the latest results from extragalactic surveys.

  3. On the evolutionary status of X-ray selected weak-line T Tauri star candidates in Taurus-Auriga

    NASA Astrophysics Data System (ADS)

    Martín, E. L.; Magazzù, A.

    1999-02-01

    We present lithium observations of 35 stars previously reported by Wichmann et al. (1996) to be possible new weak T Tauri stars (WTTS) discovered by ROSAT in the Taurus-Auriga star-forming region. These stars were identified on the basis of low-resolution optical spectra. We have used our higher resolution spectra for measuring the equivalent widths of the Li i 670.8 nm resonance line, and for revisiting the evolutionary status of these stars. Most ( ~ 85%) of the stars in our sample coming from ROSAT pointed observations are indeed confirmed to be new WTTS, but only a minority ( ~ 22%) of the stars coming from the ROSAT all-sky survey are confirmed as WTTS. There are two reasons why we reject some stars as WTTS. One is that seven of the stars do not have a detectable lithium line at all. The other is that we use a definition different from that Wichmann et al. (1996) for classifying stars as WTTS. In particular, we identify eight stars as post T Tauri stars (PTTS) on the basis of their moderate lithium depletion. Our results confirm that the widely dispersed RASS-selected candidate WTTS tend to be older than the T Tauri stars associated with dark molecular clouds. The presence of PTTS around central Taurus suggests that the clouds may have been forming stars for more than ~ 10 Myr, although at a very low rate. On the basis of the PTTS identified in this work we discuss possible differences between them and the WTTS. We find that PTTS seem to have slightly lower Hα emission equivalent width than WTTS, but the small number of known PTTS prevent us from making a strong conclusion. Based on observations made with the Isaac Newton and the William Herschel telescopes operated on the island of La~Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrof\\'\\i sica de Canarias

  4. Star field simulator

    NASA Technical Reports Server (NTRS)

    1985-01-01

    A Star Field Simulator has been developed to serve as a source of radiation for the ASTRO Star Tracker. The star tracker and simulator are components of a motion compensation test facility located at Marshall Space Flight Center in Huntsville, Alabama. Preflight tests and simulations using various levels of guide stars are performed in the test facility to establish performance of the motion compensation system before being used in a flight environment. The ASTRO Star Tracker operates over a wide dynamic range of irradiance corresponding to visual stellar magnitudes of -0.8 to 8. A minimum of three simulated guide stars with variable magnitudes are needed to fully test the Star Tracker performance under simulated mission conditions.

  5. Ponderable soliton stars

    NASA Technical Reports Server (NTRS)

    Chiu, Hong-Yee

    1990-01-01

    The theory of Lee and Pang (1987), who obtained solutions for soliton stars composed of zero-temperature fermions and bosons, is applied here to quark soliton stars. Model soliton stars based on a simple physical model of the proton are computed, and the properties of the solitons are discussed, including the important problem of the existence of a limiting mass and thus the possible formation of black holes of primordial origin. It is shown that there is a definite mass limit for ponderable soliton stars, so that during cooling a soliton star might reach a stage beyond which no equilibrium configuration exists and the soliton star probably will collapse to become a black hole. The radiation of ponderable soliton stars may alter the short-wavelength character of the cosmic background radiation, and may be observed as highly redshifted objects at z of about 100,000.

  6. Revisiting the texture zero neutrino mass matrices

    NASA Astrophysics Data System (ADS)

    Singh, Madan; Ahuja, Gulsheen; Gupta, Manmohan

    2016-12-01

    In the light of refined and large measurements of the reactor mixing angle θ, we have revisited the texture three- and two-zero neutrino mass matrices in the flavor basis. For Majorana neutrinos, it has been explicitly shown that all the texture three-zero mass matrices remain ruled out. Further, for both normal and inverted mass ordering, for the texture two-zero neutrino mass matrices one finds interesting constraints on the Dirac-like CP-violating phase δ and Majorana phases ρ and σ.

  7. The formation of the first galaxies and the transition to low-mass star formation

    NASA Astrophysics Data System (ADS)

    Greif, T. H.; Schleicher, D. R. G.; Johnson, J. L.; Jappsen, A.-K.; Klessen, R. S.; Clark, P. C.; Glover, S. C. O.; Stacy, A.; Bromm, V.

    2008-12-01

    The formation of the first galaxies at redshifts z ~ 10-15 signaled the transition from the simple initial state of the universe to one of ever increasing complexity. We here review recent progress in understanding their assembly process with numerical simulations, starting with cosmological initial conditions and modelling the detailed physics of star formation. In this context we emphasize the importance and influence of selecting appropriate initial conditions for the star formation process. We revisit the notion of a critical metallicity resulting in the transition from primordial to present-day initial mass functions and highlight its dependence on additional cooling mechanisms and the exact initial conditions. We also review recent work on the ability of dust cooling to provide the transition to present-day low-mass star formation. In particular, we highlight the extreme conditions under which this transition mechanism occurs, with violent fragmentation in dense gas resulting in tightly packed clusters.

  8. SUBSTELLAR OBJECTS IN NEARBY YOUNG CLUSTERS. VII. THE SUBSTELLAR MASS FUNCTION REVISITED

    SciTech Connect

    Scholz, Alexander; Geers, Vincent; Clark, Paul; Jayawardhana, Ray; Muzic, Koraljka

    2013-10-01

    The abundance of brown dwarfs (BDs) in young clusters is a diagnostic of star formation theory. Here we revisit the issue of determining the substellar initial mass function (IMF) based on a comparison between NGC 1333 and IC348, two clusters in the Perseus star-forming region. We derive their mass distributions for a range of model isochrones, varying distances, extinction laws, and ages with comprehensive assessments of the uncertainties. We find that the choice of isochrone and other parameters have significant effects on the results, thus we caution against comparing IMFs obtained using different approaches. For NGC 1333, we find that the star/BD ratio R is between 1.9 and 2.4 for all plausible scenarios, consistent with our previous work. For IC348, R is found to be between 2.9 and 4.0, suggesting that previous studies have overestimated this value. Thus the star-forming process generates about 2.5-5 substellar objects per 10 stars. The derived star/BD ratios correspond to a slope of the power-law mass function of α = 0.7-1.0 for the 0.03-1.0 M{sub ☉} mass range. The median mass in these clusters—the typical stellar mass—is between 0.13 and 0.30 M{sub ☉}. Assuming that NGC 1333 is at a shorter distance than IC348, we find a significant difference in the cumulative distribution of masses between the two clusters, resulting from an overabundance of very low mass objects in NGC 1333. Gaia astrometry will constrain the cluster distances better and will lead to a more definitive conclusion. Furthermore, the star/BD ratio is somewhat larger in IC348 compared with NGC 1333, although this difference is still within the margins of error. Our results indicate that environments with higher object density may produce a larger fraction of very low mass objects, in line with predictions for BD formation through gravitational fragmentation of filaments falling into a cluster potential.

  9. Substellar Objects in Nearby Young Clusters. VII. The Substellar Mass Function Revisited

    NASA Astrophysics Data System (ADS)

    Scholz, Alexander; Geers, Vincent; Clark, Paul; Jayawardhana, Ray; Muzic, Koraljka

    2013-10-01

    The abundance of brown dwarfs (BDs) in young clusters is a diagnostic of star formation theory. Here we revisit the issue of determining the substellar initial mass function (IMF) based on a comparison between NGC 1333 and IC348, two clusters in the Perseus star-forming region. We derive their mass distributions for a range of model isochrones, varying distances, extinction laws, and ages with comprehensive assessments of the uncertainties. We find that the choice of isochrone and other parameters have significant effects on the results, thus we caution against comparing IMFs obtained using different approaches. For NGC 1333, we find that the star/BD ratio R is between 1.9 and 2.4 for all plausible scenarios, consistent with our previous work. For IC348, R is found to be between 2.9 and 4.0, suggesting that previous studies have overestimated this value. Thus the star-forming process generates about 2.5-5 substellar objects per 10 stars. The derived star/BD ratios correspond to a slope of the power-law mass function of α = 0.7-1.0 for the 0.03-1.0 M ⊙ mass range. The median mass in these clusters—the typical stellar mass—is between 0.13 and 0.30 M ⊙. Assuming that NGC 1333 is at a shorter distance than IC348, we find a significant difference in the cumulative distribution of masses between the two clusters, resulting from an overabundance of very low mass objects in NGC 1333. Gaia astrometry will constrain the cluster distances better and will lead to a more definitive conclusion. Furthermore, the star/BD ratio is somewhat larger in IC348 compared with NGC 1333, although this difference is still within the margins of error. Our results indicate that environments with higher object density may produce a larger fraction of very low mass objects, in line with predictions for BD formation through gravitational fragmentation of filaments falling into a cluster potential.

  10. Massive Compact Stars as Quark Stars

    NASA Astrophysics Data System (ADS)

    Rodrigues, Hilário; Barbosa Duarte, Sérgio; de Oliveira, José Carlos T.

    2011-03-01

    High-mass compact stars have been reported recently in the literature, providing strong constraints on the properties of the ultra dense matter beyond the saturation nuclear density. In view of these results, the calculations of quark star or hybrid star equilibrium structure must be compatible with the provided observational data. But since the equations of state used in describing quark matter are in general too soft in comparison with the equation of states used to describe the hadronic or nuclear matter, the calculated quark star models presented in the literature are in general not suitable to explain the stability of highly-compact massive objects. In this work, we present the calculations of a spherically symmetric quark star structure by using an equation of state that takes into account the superconducting color-flavor locked phase of the strange quark matter. In addition, some fundamental aspects of QCD (asymptotic freedom and confinement) are considered by means of a phenomenological description of the deconfined quark phase, the density-dependent quark mass model. The quark matter behavior introduced by this model stiffens the corresponding equation of state. We thus investigate the influence of this model on the mass-radius diagram of quark stars. We obtain massive quark stars due to the stiffness of the equation of state, when a reasonable parameterization of the color superconducting gap is used. Models of quark stars enveloped by a nucleonic crust composed of a nuclear lattice embedded in an electron gas, with nuclei close to neutron drip line, are also discussed.

  11. Star Clusters within FIRE

    NASA Astrophysics Data System (ADS)

    Perez, Adrianna; Moreno, Jorge; Naiman, Jill; Ramirez-Ruiz, Enrico; Hopkins, Philip F.

    2017-01-01

    In this work, we analyze the environments surrounding star clusters of simulated merging galaxies. Our framework employs Feedback In Realistic Environments (FIRE) model (Hopkins et al., 2014). The FIRE project is a high resolution cosmological simulation that resolves star forming regions and incorporates stellar feedback in a physically realistic way. The project focuses on analyzing the properties of the star clusters formed in merging galaxies. The locations of these star clusters are identified with astrodendro.py, a publicly available dendrogram algorithm. Once star cluster properties are extracted, they will be used to create a sub-grid (smaller than the resolution scale of FIRE) of gas confinement in these clusters. Then, we can examine how the star clusters interact with these available gas reservoirs (either by accreting this mass or blowing it out via feedback), which will determine many properties of the cluster (star formation history, compact object accretion, etc). These simulations will further our understanding of star formation within stellar clusters during galaxy evolution. In the future, we aim to enhance sub-grid prescriptions for feedback specific to processes within star clusters; such as, interaction with stellar winds and gas accretion onto black holes and neutron stars.

  12. Dark stars: a review.

    PubMed

    Freese, Katherine; Rindler-Daller, Tanja; Spolyar, Douglas; Valluri, Monica

    2016-06-01

    Dark stars are stellar objects made (almost entirely) of hydrogen and helium, but powered by the heat from dark matter annihilation, rather than by fusion. They are in hydrostatic and thermal equilibrium, but with an unusual power source. Weakly interacting massive particles (WIMPs), among the best candidates for dark matter, can be their own antimatter and can annihilate inside the star, thereby providing a heat source. Although dark matter constitutes only [Formula: see text]0.1% of the stellar mass, this amount is sufficient to power the star for millions to billions of years. Thus, the first phase of stellar evolution in the history of the Universe may have been dark stars. We review how dark stars come into existence, how they grow as long as dark matter fuel persists, and their stellar structure and evolution. The studies were done in two different ways, first assuming polytropic interiors and more recently using the MESA stellar evolution code; the basic results are the same. Dark stars are giant, puffy (∼10 AU) and cool (surface temperatures  ∼10 000 K) objects. We follow the evolution of dark stars from their inception at  ∼[Formula: see text] as they accrete mass from their surroundings to become supermassive stars, some even reaching masses  >[Formula: see text] and luminosities  >[Formula: see text], making them detectable with the upcoming James Webb Space Telescope. Once the dark matter runs out and the dark star dies, it may collapse to a black hole; thus dark stars may provide seeds for the supermassive black holes observed throughout the Universe and at early times. Other sites for dark star formation may exist in the Universe today in regions of high dark matter density such as the centers of galaxies. The current review briefly discusses dark stars existing today, but focuses on the early generation of dark stars.

  13. Dark stars: a review

    NASA Astrophysics Data System (ADS)

    Freese, Katherine; Rindler-Daller, Tanja; Spolyar, Douglas; Valluri, Monica

    2016-06-01

    Dark stars are stellar objects made (almost entirely) of hydrogen and helium, but powered by the heat from dark matter annihilation, rather than by fusion. They are in hydrostatic and thermal equilibrium, but with an unusual power source. Weakly interacting massive particles (WIMPs), among the best candidates for dark matter, can be their own antimatter and can annihilate inside the star, thereby providing a heat source. Although dark matter constitutes only ≲ 0.1% of the stellar mass, this amount is sufficient to power the star for millions to billions of years. Thus, the first phase of stellar evolution in the history of the Universe may have been dark stars. We review how dark stars come into existence, how they grow as long as dark matter fuel persists, and their stellar structure and evolution. The studies were done in two different ways, first assuming polytropic interiors and more recently using the MESA stellar evolution code; the basic results are the same. Dark stars are giant, puffy (˜10 AU) and cool (surface temperatures  ˜10 000 K) objects. We follow the evolution of dark stars from their inception at  ˜1{{M}⊙} as they accrete mass from their surroundings to become supermassive stars, some even reaching masses  >{{10}6}{{M}⊙} and luminosities  >{{10}10}{{L}⊙} , making them detectable with the upcoming James Webb Space Telescope. Once the dark matter runs out and the dark star dies, it may collapse to a black hole; thus dark stars may provide seeds for the supermassive black holes observed throughout the Universe and at early times. Other sites for dark star formation may exist in the Universe today in regions of high dark matter density such as the centers of galaxies. The current review briefly discusses dark stars existing today, but focuses on the early generation of dark stars.

  14. Hershfield factor revisited: Correcting annual maximum precipitation

    NASA Astrophysics Data System (ADS)

    Papalexiou, Simon Michael; Dialynas, Yannis G.; Grimaldi, Salvatore

    2016-11-01

    The Hershfield factor (H) is a multiplier aiming to correct the error between fixed time interval maxima (F-maxima) and sliding maxima (S-maxima) as a direct consequence of temporal discretization of hydrometeorological time series. Rainfall is typically recorded over discrete intervals, e.g., over fixed 24-h intervals, and the historical series express average values over these intervals. This temporal discretization introduces an important systematic error on rainfall characteristics such as the annual maxima. Research to date suggests that our understanding of this error across different time scales is limited. In this study we revisit the probabilistic nature of the H-factor in an unprecedentedly large analysis comprising thousands of up-to-date hourly records across the US. We study the probabilistic behavior of F- and S-maxima of the historical records. We quantify the discretization error of the rainfall maxima and its statistical properties at different time scales. We revisit the classical definitions of the H-factor and we investigate the exact probability distribution of H-factor. We introduce a bounded exponential distribution with an atom at one, which closely depicts the empirical distribution of the H-factor. Notable is the result that the proposed mixed-type distribution is invariant across a range of time scales. This work clarifies the probabilistic nature of the rainfall maxima correction. The results may have wide use across a range of hydrological applications.

  15. STAR in CTO PCI: When is STAR not a star?

    PubMed

    Hira, Ravi S; Dean, Larry S

    2016-04-01

    Subintimal tracking and reentry (STAR) has been used as a bailout strategy and involves an uncontrolled dissection and recanalization into the distal lumen to reestablish vessel patency. In the current study, thrombolysis in myocardial infarction (TIMI) flow < 3 was the only variable which they found to be significantly associated with restenosis and reocclusion after stent placement. It may be reasonable to consider second generation drug eluting stent placement in patients receiving STAR that have TIMI 3 flow, however, this should only be done if there is no compromise of major side branches. If unsure, we recommend to perform balloon angioplasty without stenting.

  16. The First Stars

    NASA Astrophysics Data System (ADS)

    Yoshida, Naoki

    2010-10-01

    The standard cosmological model predicts that the first cosmological objects are formed when the age of the universe is a few hundred million years. Recent theoretical studies and numerical simulations consistently suggest that the first objects are very massive primordial stars. We introduce the key physics and explain why the first stars are thought to be massive, rather than to be low-mass stars. The state-of-the-art simulations include all the relevant atomic and molecular physics to follow the thermal evolution of a prestellar gas cloud to very high ``stellar'' densities. Evolutionary calculations of the primordial stars suggest the formation of massive blackholes in the early universe. Finally, we show the results from high-resolution simulations of star formation in a low-metallicity gas. Vigorous fragmentation is triggered in a star-forming gas cloud at a metallicity of as low as Z = 10-5Zsolar.

  17. Revisiting the Redshift Distribution of Gamma-Ray Bursts in the Swift Era

    NASA Astrophysics Data System (ADS)

    Le, Truong; Mehta, Vedant

    2017-03-01

    Le & Dermer developed a gamma-ray burst (GRB) model to fit the redshift and the jet opening angle distributions measured with pre-Swift and Swift missions and showed that GRBs do not follow the star formation rate. Their fitted results were obtained without the opening angle distribution from Swift with an incomplete Swift sample, and the calculated jet opening angle distribution was obtained by assuming a flat ν {F}ν spectrum. In this paper, we revisit the work done by Le & Dermer with an assumed broken power law GRB spectrum. Utilizing more than 100 GRBs in the Swift sample that include both the observed estimated redshifts and jet opening angles, we obtain a GRB burst rate functional form that gives acceptable fits to the pre-Swift and Swift redshift and jet opening angle distributions with an indication that an excess of GRBs exists at low redshift below z≈ 2. The mean redshifts and jet opening angles for pre-Swift (Swift) are < z> ∼ 1.3 (1.7) and < {θ }{{j}}> ∼ 7^\\circ (11^\\circ ), respectively. Assuming a GRB rate density (SFR9), similar to the Hopkins & Beacom star formation history and as extended by Li, the fraction of high-redshift GRBs is estimated to be below 10% and 5% at z≥slant 4 and z≥slant 5, respectively, and below 10% at z≤slant 1.

  18. Strange nonchaotic stars.

    PubMed

    Lindner, John F; Kohar, Vivek; Kia, Behnam; Hippke, Michael; Learned, John G; Ditto, William L

    2015-02-06

    The unprecedented light curves of the Kepler space telescope document how the brightness of some stars pulsates at primary and secondary frequencies whose ratios are near the golden mean, the most irrational number. A nonlinear dynamical system driven by an irrational ratio of frequencies generically exhibits a strange but nonchaotic attractor. For Kepler's "golden" stars, we present evidence of the first observation of strange nonchaotic dynamics in nature outside the laboratory. This discovery could aid the classification and detailed modeling of variable stars.

  19. SIRTF and star formation

    NASA Technical Reports Server (NTRS)

    Shu, Frank H.

    1988-01-01

    Four problems in the field of star formation that can be attacked to advantage with SIRTF are discussed: (1) the patterns of star formation in spiral galaxies, (2) the physical mechanism for bimodal star formation, (3) the nature of bipolar outflows from young stellar objects, and (4) the birth of brown dwarfs. In each case, SIRTF can provide the crucial combination of high angular resolution with great sensitivity over a broad range of wavelengths that is needed to address the relevant issues.

  20. Nagyszombat and the stars

    NASA Astrophysics Data System (ADS)

    Zsoldos, E.

    Péter Pázmány, founder of the University of Nagyszombat, considered stars in terms inherited from medieval times. The theses, connected to the university graduation, soon left this definition, and imagined stars as made from sublunar elements. The 1753 decree of the Empress Maria Theresia ordered university professors to publish textbooks. These textbooks, together with the theses showed a definite improvement, defining stars according to contemporary knowledge.

  1. Strange Nonchaotic Stars

    NASA Astrophysics Data System (ADS)

    Lindner, John F.; Kohar, Vivek; Kia, Behnam; Hippke, Michael; Learned, John G.; Ditto, William L.

    2015-08-01

    Exploiting the unprecedented capabilities of the planet-hunting Kepler space telescope, which stared at 150 000 stars for four years, we discuss recent evidence that certain stars dim and brighten in complex patterns with fractal features. Such stars pulsate at primary and secondary frequencies whose ratios are near the famous golden mean, the most irrational number. A nonlinear system driven by an irrational ratio of frequencies is generically attracted toward a “strange” behavior that is geometrically fractal without displaying the “butterfly effect” of chaos. Strange nonchaotic attractors have been observed in laboratory experiments and have been hypothesized to describe the electrochemical activity of the brain, but a bluish white star 16 000 light years from Earth in the constellation Lyra may manifest, in the scale-free distribution of its minor frequency components, the first strange nonchaotic attractor observed in the wild. The recognition of stellar strange nonchaotic dynamics may improve the classification of these stars and refine the physical modeling of their interiors. We also discuss nonlinear analysis of other RR Lyrae stars in Kepler field of view and discuss some toy models for modeling these stars.References: 1) Hippke, Michael, et al. "Pulsation period variations in the RRc Lyrae star KIC 5520878." The Astrophysical Journal 798.1 (2015): 42.2) Lindner, John F., et al. "Strange nonchaotic stars." Phys. Rev. Lett. 114, 054101 (2015)

  2. Charged Proca stars

    NASA Astrophysics Data System (ADS)

    Landea, Ignacio Salazar; García, Federico

    2016-11-01

    In this paper, we study gauged solutions associated with a massive vector field representing a spin-1 condensate, namely, the Proca field. We focus on regular spherically symmetric solutions which we construct either using a self-interaction potential or general relativity in order to glue the solutions together. We start generating nongravitating solutions—so-called Proca Q -balls and charged Proca Q -balls. Then we turn on backreaction on the metric, allowing gravity to hold together the Proca condensate, to study the so-called Proca stars, charged Proca stars, Proca Q -stars, and charged Proca Q -stars.

  3. Massive soliton stars

    NASA Astrophysics Data System (ADS)

    Chiu, Hong-Yee

    1990-05-01

    The structure of nontopological solutions of Einstein field equations as proposed by Friedberg, Lee, and Pang (1987) is examined. This analysis incorporates finite temperature effects and pair creation. Quarks are assumed to be the only species that exist in interior of soliton stars. The possibility of primordial creation of soliton stars in the incomplete decay of the degenerate vacuum in early universe is explored. Because of dominance of pair creation inside soliton stars, the luminosity of soliton stars is not determined by its radiative transfer characteristics, and the surface temperature of soliton stars can be the same as its interior temperature. It is possible that soliton stars are intense X-ray radiators at large distances. Soliton stars are nearly 100 percent efficient energy converters, converting the rest energy of baryons entering the interior into radiation. It is possible that a sizable number of baryons may also be trapped inside soliton stars during early epochs of the universe. In addition, if soliton stars exist they could assume the role played by massive black holes in galactic centers.

  4. Massive soliton stars

    NASA Technical Reports Server (NTRS)

    Chiu, Hong-Yee

    1990-01-01

    The structure of nontopological solutions of Einstein field equations as proposed by Friedberg, Lee, and Pang (1987) is examined. This analysis incorporates finite temperature effects and pair creation. Quarks are assumed to be the only species that exist in interior of soliton stars. The possibility of primordial creation of soliton stars in the incomplete decay of the degenerate vacuum in early universe is explored. Because of dominance of pair creation inside soliton stars, the luminosity of soliton stars is not determined by its radiative transfer characteristics, and the surface temperature of soliton stars can be the same as its interior temperature. It is possible that soliton stars are intense X-ray radiators at large distances. Soliton stars are nearly 100 percent efficient energy converters, converting the rest energy of baryons entering the interior into radiation. It is possible that a sizable number of baryons may also be trapped inside soliton stars during early epochs of the universe. In addition, if soliton stars exist they could assume the role played by massive black holes in galactic centers.

  5. Introduction to neutron stars

    SciTech Connect

    Lattimer, James M.

    2015-02-24

    Neutron stars contain the densest form of matter in the present universe. General relativity and causality set important constraints to their compactness. In addition, analytic GR solutions are useful in understanding the relationships that exist among the maximum mass, radii, moments of inertia, and tidal Love numbers of neutron stars, all of which are accessible to observation. Some of these relations are independent of the underlying dense matter equation of state, while others are very sensitive to the equation of state. Recent observations of neutron stars from pulsar timing, quiescent X-ray emission from binaries, and Type I X-ray bursts can set important constraints on the structure of neutron stars and the underlying equation of state. In addition, measurements of thermal radiation from neutron stars has uncovered the possible existence of neutron and proton superfluidity/superconductivity in the core of a neutron star, as well as offering powerful evidence that typical neutron stars have significant crusts. These observations impose constraints on the existence of strange quark matter stars, and limit the possibility that abundant deconfined quark matter or hyperons exist in the cores of neutron stars.

  6. Delta Scuti stars: Theory

    NASA Technical Reports Server (NTRS)

    Guzik, J. A.

    1998-01-01

    The purpose of asteroseismology is not only to derive the internal structure of individual stars from their observed oscillation frequencies, but also to test and extend one's understanding of the physics of matter under the extremes of temperature, density, and pressure found in stellar interiors. In this review, the author hopes to point out what one can learn about the Sun by studying (delta) Scuti stars, as well as what one can learn about stars more massive or evolved than the Sun. He discusses some of the difficulties in theoretical approaches to asteroseismology for (delta) Scuti stars, using FG Vir, (delta) Scuti, and CD-24(degree) 7599 as examples.

  7. Combinations of 148 navigation stars and the star tracker

    NASA Technical Reports Server (NTRS)

    Duncan, R.

    1980-01-01

    The angular separation of all star combinations for 148 nav star on the onboard software for space transportation system-3 flight and following missions is presented as well as the separation of each pair that satisfies the viewing constraints of using both star trackers simultaneously. Tables show (1) shuttle star catalog 1980 star position in M 1950 coordinates; (2) two star combination of 148 nav stars; and (3) summary of two star-combinations of the star tracker 5 deg filter. These 148 stars present 10,875 combinations. For the star tracker filters of plus or minus 5 deg, there are 875 combinations. Formalhaut (nav star 26) has the best number of combinations, which is 33.

  8. ɛ Ophiuchi: Revisiting a Red Giant

    NASA Astrophysics Data System (ADS)

    Kallinger, T.; Matthews, J. M.; Guenther, D. B.; Gruberbauer, M.; Kuschnig, R.; Weiss, W. W.; MOST Team

    2012-09-01

    In only a decade, seismology of red-giant stars has grown from infancy to adulthood in the study of stellar structure and evolution. The stimulants for this accelerated growth have been space observations, first provided by the WIRE star-tracker and MOST, and continuing with CoRoT and Kepler, having detected oscillations in thousands of cool giants. However, almost all of the stars in this impressive sample are faint, with little known about their basic properties. Even reliable spectral classifications are lacking for many of them. MOST is the only space-based photometer capable of continuous observations of bright red giants for which we have independent constraints (e.g., spectroscopy) essential to extract the internal structure from the stars' p-modes.

  9. Magneto-thermal evolution of neutron stars

    NASA Astrophysics Data System (ADS)

    Pons, J. A.; Miralles, J. A.; Geppert, U.

    2009-03-01

    Context: The presence of magnetic fields in the crust of neutron stars (NSs) causes a non-spherically symmetric temperature distribution. The strong temperature dependence of the magnetic diffusivity and thermal conductivity, together with the heat generated by magnetic dissipation, couple the magnetic and thermal evolution of NSs, which can no longer be formulated as separated one-dimensional problems. Aims: We study the mutual influence of thermal and magnetic evolution in a neutron star's crust in axial symmetry. Taking realistic microphysical inputs into account, we find the heat released by Joule effect consistent with the circulation of currents in the crust, and we incorporate its effects in 2D cooling calculations. Methods: We solve the induction equation numerically using a hybrid method (spectral in angles, but a finite-differences scheme in the radial direction), coupled to the thermal diffusion equation. To improve the boundary conditions, we also revisit the envelope stationary solutions updating the well known T_b-T_s-relations to include the effect of 2D heat transfer calculations and new microphysical inputs. Results: We present the first longterm 2D simulations of the coupled magneto-thermal evolution of neutron stars. This substantially improves previous works in which a very crude approximation in at least one of the parts (thermal or magnetic diffusion) has been adopted. Our results show that the feedback between Joule heating and magnetic diffusion is strong, resulting in a faster dissipation of the stronger fields during the first 10^5-106 years of an NS's life. As a consequence, all neutron stars born with fields over a critical value (>5 × 1013 G) reach similar field strengths (≈2-3 × 1013 G) at late times. Irrespective of the initial magnetic field strength, the temperature becomes so low after 106 years that the magnetic diffusion timescale becomes longer than the typical ages of radiopulsars, thus apparently resulting in no

  10. Visibility of stars, halos, and rainbows during solar eclipses.

    PubMed

    Können, Gunther P; Hinz, Claudia

    2008-12-01

    The visibility of stars, planets, diffraction coronas, halos, and rainbows during the partial and total phases of a solar eclipse is studied. The limiting magnitude during various stages of the partial phase is presented. The sky radiance during totality with respect to noneclipse conditions is revisited and found to be typically 1/4000. The corresponding limiting magnitude is +3.5. At totality, the signal-to-background ratio of diffraction coronas, halos, and rainbows has dropped by a factor of 250. It is found that diffraction coronas around the totally eclipsed Sun may nevertheless occur. Analyses of lunar halo observations during twilight indicate that bright halo displays may also persist during totality. Rainbows during totality seem impossible.

  11. THE FIRST FLUORINE ABUNDANCE DETERMINATIONS IN EXTRAGALACTIC ASYMPTOTIC GIANT BRANCH CARBON STARS

    SciTech Connect

    Abia, C.; Cristallo, S.; Dominguez, I.; Cunha, K.; Smith, V. V.; De Laverny, P.; Recio-Blanco, A.; Straniero, O.

    2011-08-10

    Fluorine ({sup 19}F) abundances (or upper limits) are derived in six extragalactic asymptotic giant branch (AGB) carbon stars from the HF(1-0) R9 line at 2.3358 {mu}m in high-resolution spectra. The stars belong to the Local Group galaxies, Large Magellanic Cloud, Small Magellanic Cloud, and Carina dwarf spheroidal, spanning more than a factor of 50 in metallicity. This is the first study to probe the behavior of F with metallicity in intrinsic extragalactic C-rich AGB stars. Fluorine could be measured only in four of the target stars, showing a wide range in F enhancements. Our F abundance measurements together with those recently derived in Galactic AGB carbon stars show a correlation with the observed carbon and s-element enhancements. The observed correlations, however, display a different dependence on the stellar metallicity with respect to theoretical predictions in low-mass, low-metallicity AGB models. We briefly discuss the possible reasons for this discrepancy. If our findings are confirmed in a larger number of metal-poor AGBs, the issue of F production in AGB stars will need to be revisited.

  12. Star Trek in the Schools

    ERIC Educational Resources Information Center

    Journal of Aerospace Education, 1977

    1977-01-01

    Describes specific educational programs for using the Star Trek TV program from kindergarten through college. For each grade level lesson plans, ideas for incorporating Star Trek into future classes, and reports of specific programs utilizing Star Trek are provided. (SL)

  13. Neutron Star Compared to Manhattan

    NASA Video Gallery

    A pulsar is a neutron star, the crushed core of a star that has exploded. Neutron stars crush half a million times more mass than Earth into a sphere no larger than Manhattan, as animated in this s...

  14. Observations of FK Comae stars

    NASA Technical Reports Server (NTRS)

    Bopp, B. W.

    1981-01-01

    Observations on the FK Comae stars are described. FK Com, UZ Lib and HD 199178 are compared and related as a group of stars. The crucial observational tests of the proposed evolutionary status of these stars are noted.

  15. Stars and Flowers, Flowers and Stars

    NASA Astrophysics Data System (ADS)

    Minti, Hari

    2012-12-01

    The author, a graduated from the Bucharest University (1964), actually living and working in Israel, concerns his book to variable stars and flowers, two domains of his interest. The analogies includes double stars, eclipsing double stars, eclipses, Big Bang. The book contains 34 chapters, each of which concerns various relations between astronomy and other sciences and pseudosciences such as Psychology, Religion, Geology, Computers and Astrology (to which the author is not an adherent). A special part of the book is dedicated to archeoastronomy and ethnoastronomy, as well as to history of astronomy. Between the main points of interest of these parts: ancient sanctuaries in Sarmizegetusa (Dacia), Stone Henge(UK) and other. The last chapter of the book is dedicated to flowers. The book is richly illustrated. It is designed for a wide circle of readers.

  16. Hybrid stars that masquerade as neutron stars

    SciTech Connect

    Mark Paris; Mark Alford; Matt Braby; Sanjay Reddy

    2004-11-01

    We show that a hybrid (nuclear + quark matter) star can have a mass-radius relationship very similar to that predicted for a star made of purely nucleonic matter. We show this for a generic parameterization of the quark matter equation of state, and also for an MIT bag model, each including a phenomenological correction based on gluonic corrections to the equation of state. We obtain hybrid stars as heavy as 2 M{sub solar} for reasonable values of the bag model parameters. For nuclear matter, we use the equation of state calculated by Akmal, Pandharipande, and Ravenhall using many-body techniques. Both mixed and homogeneous phases of nuclear and quark matter are considered.

  17. OB stars at the lowest Local Group metallicity. GTC-OSIRIS observations of Sextans A

    NASA Astrophysics Data System (ADS)

    Camacho, I.; Garcia, M.; Herrero, A.; Simón-Díaz, S.

    2016-01-01

    Context. Massive stars play an important role in the chemical and dynamical evolution of the Universe. The first metal-poor stars may have started the reionization of the Universe. To understand these early epochs it is necessary to know the behavior and the physical properties of massive stars in very metal-poor environments. We focus on the massive stellar content of the metal-poor irregular galaxy Sextans A. Aims: Our aim is to find and classify OB stars in Sextans A, so as to later determine accurate stellar parameters of these blue massive stars in this low-metallicity region (Z ~ 0.1 Z⊙). Methods: Using UBV photometry, the reddening-free index Q and GALEX imaging, we built a list of blue massive star candidates in Sextans A. We obtained low-resolution (R ~ 1000) GTC-OSIRIS spectra for a fraction of them and carried out spectral classification. For the confirmed O-stars, we derived preliminary stellar parameters. Results: The target selection criteria and observations were successful and have produced the first spectroscopic atlas of OB-type stars in Sextans A. From the whole sample of 18 observed stars, 12 were classified as early OB-types, including 5 O-stars. The radial velocities of all target stars are in agreement with their Sextans A membership, although three of them show significant deviations. We determined the stellar parameters of the O-type stars using the stellar atmosphere code FASTWIND and revisited the sub-SMC temperature scale. Two of the O-stars are consistent with relatively strong winds and enhanced helium abundances, although results are not conclusive. We discuss the position of the OB stars in the HRD. Initial stellar masses run from slightly below 20 up to 40 solar masses. Conclusions: The target selection method worked well for Sextans A. The stellar temperatures are consistent with findings in other galaxies. Some of the targets deserve follow-up spectroscopy because of indications of a runaway nature, an enhanced helium abundance

  18. Observing Double Stars

    NASA Astrophysics Data System (ADS)

    Genet, Russell M.; Fulton, B. J.; Bianco, Federica B.; Martinez, John; Baxter, John; Brewer, Mark; Carro, Joseph; Collins, Sarah; Estrada, Chris; Johnson, Jolyon; Salam, Akash; Wallen, Vera; Warren, Naomi; Smith, Thomas C.; Armstrong, James D.; McGaughey, Steve; Pye, John; Mohanan, Kakkala; Church, Rebecca

    2012-05-01

    Double stars have been systematically observed since William Herschel initiated his program in 1779. In 1803 he reported that, to his surprise, many of the systems he had been observing for a quarter century were gravitationally bound binary stars. In 1830 the first binary orbital solution was obtained, leading eventually to the determination of stellar masses. Double star observations have been a prolific field, with observations and discoveries - often made by students and amateurs - routinely published in a number of specialized journals such as the Journal of Double Star Observations. All published double star observations from Herschel's to the present have been incorporated in the Washington Double Star Catalog. In addition to reviewing the history of visual double stars, we discuss four observational technologies and illustrate these with our own observational results from both California and Hawaii on telescopes ranging from small SCTs to the 2-meter Faulkes Telescope North on Haleakala. Two of these technologies are visual observations aimed primarily at published "hands-on" student science education, and CCD observations of both bright and very faint doubles. The other two are recent technologies that have launched a double star renaissance. These are lucky imaging and speckle interferometry, both of which can use electron-multiplying CCD cameras to allow short (30 ms or less) exposures that are read out at high speed with very low noise. Analysis of thousands of high speed exposures allows normal seeing limitations to be overcome so very close doubles can be accurately measured.

  19. Nebraska STARS: Achieving Results

    ERIC Educational Resources Information Center

    Roschewski, Pat; Isernhagen, Jody; Dappen, Leon

    2006-01-01

    In 2000, the state of Nebraska passed legislation requiring the assessment of student performance on content standards, but its requirements were very different from those of any other state. Nebraska created what has come to be known as STARS (School-based Teacher-led Assessment and Reporting System). Under STARS, each of Nebraska's nearly 500…

  20. Science through ARts (STAR)

    ERIC Educational Resources Information Center

    Densmore, Marycay; Kolecki, Joseph C.; Miller, Allan; Petersen, Ruth; Terrell, Mike

    2005-01-01

    Science Through ARts (STAR) is a free, international, cross-curricular program thematically aligned with "The Vision for Space Exploration," a framework of goals and objectives published by NASA in February 2004. Through the STAR program, students in grades 5 through 12 are encouraged to apply their knowledge in creative ways as they approach a…

  1. Nuclear Star Clusters

    NASA Astrophysics Data System (ADS)

    Neumayer, Nadine

    2017-03-01

    The centers of galaxies host two distinct, compact components: massive black holes and nuclear star clusters. Nuclear star clusters are the densest stellar systems in the universe, with masses of ~ 107M⊙ and sizes of ~ 5pc. They are almost ubiquitous at the centres of nearby galaxies with masses similar to, or lower than the Milky Way. Their occurrence both in spirals and dwarf elliptical galaxies appears to be a strong function of total galaxy light or mass. Nucleation fractions are up to 100% for total galaxy magnitudes of M B = -19mag or total galaxy luminosities of about L B = 1010 L ⊙ and falling nucleation fractions for both smaller and higher galaxy masses. Although nuclear star clusters are so common, their formation mechanisms are still under debate. The two main formation scenarios proposed are the infall and subsequent merging of star clusters and the in-situ formation of stars at the center of a galaxy. Here, I review the state-of-the-art of nuclear star cluster observations concerning their structure, stellar populations and kinematics. These observations are used to constrain the proposed formation scenarios for nuclear star clusters. Constraints from observations show, that likely both cluster infall and in-situ star formation are at work. The relative importance of these two mechanisms is still subject of investigation.

  2. Revisiting Lepton Flavor Universality in B Decays.

    PubMed

    Feruglio, Ferruccio; Paradisi, Paride; Pattori, Andrea

    2017-01-06

    Lepton flavor universality (LFU) in B decays is revisited by considering a class of semileptonic operators defined at a scale Λ above the electroweak scale v. The importance of quantum effects, so far neglected in the literature, is emphasized. We construct the low-energy effective Lagrangian taking into account the running effects from Λ down to v through the one-loop renormalization group equations (RGEs) in the limit of exact electroweak symmetry and QED RGEs from v down to the 1 GeV scale. The most important quantum effects turn out to be the modification of the leptonic couplings of the vector boson Z and the generation of a purely leptonic effective Lagrangian. Large LFU breaking effects in Z and τ decays and visible lepton flavor violating effects in the processes τ→μℓℓ, τ→μρ, τ→μπ, and τ→μη^{(')} are induced.

  3. Revisiting instanton corrections to the Konishi multiplet

    NASA Astrophysics Data System (ADS)

    Alday, Luis F.; Korchemsky, Gregory P.

    2016-12-01

    We revisit the calculation of instanton effects in correlation functions in N=4 SYM involving the Konishi operator and operators of twist two. Previous studies revealed that the scaling dimensions and the OPE coefficients of these operators do not receive instanton corrections in the semiclassical approximation. We go beyond this approximation and demonstrate that, while operators belonging to the same N=4 supermultiplet ought to have the same conformal data, the evaluation of quantum instanton corrections for one operator can be mapped into a semiclassical computation for another operator in the same supermultiplet. This observation allows us to compute explicitly the leading instanton correction to the scaling dimension of operators in the Konishi supermultiplet as well as to their structure constants in the OPE of two half-BPS scalar operators. We then use these results, together with crossing symmetry, to determine instanton corrections to scaling dimensions of twist-four operators with large spin.

  4. Revisiting Lepton Flavor Universality in B Decays

    NASA Astrophysics Data System (ADS)

    Feruglio, Ferruccio; Paradisi, Paride; Pattori, Andrea

    2017-01-01

    Lepton flavor universality (LFU) in B decays is revisited by considering a class of semileptonic operators defined at a scale Λ above the electroweak scale v . The importance of quantum effects, so far neglected in the literature, is emphasized. We construct the low-energy effective Lagrangian taking into account the running effects from Λ down to v through the one-loop renormalization group equations (RGEs) in the limit of exact electroweak symmetry and QED RGEs from v down to the 1 GeV scale. The most important quantum effects turn out to be the modification of the leptonic couplings of the vector boson Z and the generation of a purely leptonic effective Lagrangian. Large LFU breaking effects in Z and τ decays and visible lepton flavor violating effects in the processes τ →μ ℓℓ, τ →μ ρ , τ →μ π , and τ →μ η(') are induced.

  5. Re-visiting the electrophysiology of language.

    PubMed

    Obleser, Jonas

    2015-09-01

    This editorial accompanies a special issue of Brain and Language re-visiting old themes and new leads in the electrophysiology of language. The event-related potential (ERP) as a series of characteristic deflections ("components") over time and their distribution on the scalp has been exploited by speech and language researchers over decades to find support for diverse psycholinguistic models. Fortunately, methodological and statistical advances have allowed human neuroscience to move beyond some of the limitations imposed when looking at the ERP only. Most importantly, we currently witness a refined and refreshed look at "event-related" (in the literal sense) brain activity that relates itself more closely to the actual neurobiology of speech and language processes. It is this imminent change in handling and interpreting electrophysiological data of speech and language experiments that this special issue intends to capture.

  6. Revisiting gravitino dark matter in thermal leptogenesis

    NASA Astrophysics Data System (ADS)

    Ibe, Masahiro; Suzuki, Motoo; Yanagida, Tsutomu T.

    2017-02-01

    In this paper, we revisit the gravitino dark matter scenario in the presence of the bilinear R-parity violating interaction. In particular, we discuss a consistency with the thermal leptogenesis. For a high reheating temperature required for the thermal leptogenesis, the gravitino dark matter tends to be overproduced, which puts a severe upper limit on the gluino mass. As we will show, a large portion of parameter space of the gravitino dark matter scenario has been excluded by combining the constraints from the gravitino abundance and the null results of the searches for the superparticles at the LHC experiments. In particular, the models with the stau (and other charged slepton) NLSP has been almost excluded by the searches for the long-lived charged particles at the LHC unless the required reheating temperature is somewhat lowered by assuming, for example, a degenerated right-handed neutrino mass spectrum.

  7. Olfactory pathogenesis of idiopathic Parkinson disease revisited.

    PubMed

    Lerner, Alicja; Bagic, Anto

    2008-06-15

    Idiopathic Parkinson disease (PD) is traditionally considered a movement disorder with hallmark lesions located in the substantia nigra pars compacta (SNpc). However, recent histopathological studies of some PD cases suggest the possibility of a multisystem disorder which progresses in a predictable sequence as described in Braak's staging criteria. The disease process starts in the dorsal motor nucleus of the vagus (dmX) and anterior olfactory nucleus and bulb, and from there, spreads through the brainstem nuclei to ultimately reach the SNpc, which then presents as symptomatic PD. In this article, we would like to revisit the olfactory pathogenesis of PD based on Braak's staging system and review anatomical pathways supporting such a possibility. We also suggest some biomarkers for early stages of PD. Additionally, we present and discuss the possibility that a prion-like process underlies the neurodegenerative changes in PD.

  8. Seasonal dating of Sappho's 'Midnight Poem' revisited

    NASA Astrophysics Data System (ADS)

    Cuntz, Manfred; Gurdemir, Levent; George, Martin

    2016-04-01

    Sappho was a Greek lyric poet who composed a significant array of pristine poetry. Although much of it has been lost, her reputation has endured thanks to numerous surviving fragments. One of her contributions includes the so-called 'Midnight Poem', which contains a line about the Pleiades, setting sometime before midnight, and supposedly observed from the island of Lesbos. This poem also refers to the setting of the Moon. Sappho's Midnight Poem thus represents a prime example of where ancient poetry and astronomy merge, and it also offers the possibility of seasonal dating. Previously, Herschberg and Mebius (1990) estimated that the poem was composed in late winter/early spring, a time frame that is not unusual for lyrics of an amorous nature. The aim of our paper is to revisit this earlier finding by using modern-day software. Our study confirms Herschberg and Mebius' result, but also conveys further information.

  9. Visser's massive graviton bimetric theory revisited

    SciTech Connect

    Roany, Alain de; Chauvineau, Bertrand; Freitas Pacheco, Jose A. de

    2011-10-15

    A massive gravity theory was proposed by Visser in the late 1990s. This theory, based on a background metric b{sub {alpha}{beta}} and on an usual dynamical metric g{sub {alpha}{beta}} has the advantage of being free of ghosts as well as discontinuities present in other massive theories proposed in the past. In the present investigation, the equations of Visser's theory are revisited with particular care on the related conservation laws. It will be shown that a multiplicative factor is missing in the graviton tensor originally derived by Visser, which has no incidence on the weak field approach but becomes important in the strong field regime when, for instance, cosmological applications are considered. In this case, contrary to some previous claims found in the literature, we conclude that a nonstatic background metric is required in order to obtain a solution able to mimic the {Lambda}CDM cosmology.

  10. Revisiting the R νMDM models

    NASA Astrophysics Data System (ADS)

    Cai, Yi; Schmidt, Michael A.

    2016-05-01

    Combining neutrino mass generation and a dark matter candidate in a unified model has always been intriguing. We revisit the class of R νMDM models, which incorporate minimal dark matter in radiative neutrino mass models based on the one-loop ultraviolet completions of the Weinberg operator. The possibility of an exact accidental Z 2 is completely ruled out in this scenario. We study the phenomenology of one of the models with an approximate Z 2 symmetry. In addition to the Standard Model particles, it contains two real scalar quintuplets, one vector-like quadruplet fermion and a fermionic quintuplet. The neutral component of the fermionic quintuplet serves as a good dark matter candidate which can be tested by the future direct and indirect detection experiments. The constraints from flavor physics and electroweak-scale naturalness are also discussed.

  11. Star spot location estimation using Kalman filter for star tracker.

    PubMed

    Liu, Hai-bo; Yang, Jian-kun; Wang, Jiong-qi; Tan, Ji-chun; Li, Xiu-jian

    2011-04-20

    Star pattern recognition and attitude determination accuracy is highly dependent on star spot location accuracy for the star tracker. A star spot location estimation approach with the Kalman filter for a star tracker has been proposed, which consists of three steps. In the proposed approach, the approximate locations of the star spots in successive frames are predicted first; then the measurement star spot locations are achieved by defining a series of small windows around each predictive star spot location. Finally, the star spot locations are updated by the designed Kalman filter. To confirm the proposed star spot location estimation approach, the simulations based on the orbit data of the CHAMP satellite and the real guide star catalog are performed. The simulation results indicate that the proposed approach can filter out noises from the measurements remarkably if the sampling frequency is sufficient.

  12. Activity Cycles in Stars

    NASA Technical Reports Server (NTRS)

    Hathaway, David H.

    2009-01-01

    Starspots and stellar activity can be detected in other stars using high precision photometric and spectrometric measurements. These observations have provided some surprises (starspots at the poles - sunspots are rarely seen poleward of 40 degrees) but more importantly they reveal behaviors that constrain our models of solar-stellar magnetic dynamos. The observations reveal variations in cycle characteristics that depend upon the stellar structure, convection zone dynamics, and rotation rate. In general, the more rapidly rotating stars are more active. However, for stars like the Sun, some are found to be inactive while nearly identical stars are found to be very active indicating that periods like the Sun's Maunder Minimum (an inactive period from 1645 to 1715) are characteristic of Sun-like stars.

  13. Producing Runaway Stars

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-07-01

    How are the hypervelocity stars weve observed in our galaxy produced? A recent study suggests that these escapees could be accelerated by a massive black hole in the center of the Large Magellanic Cloud.A Black Hole SlingshotSince their discovery in 2005, weve observed dozens of candidate hypervelocity stars stars whose velocity in the rest frame of our galaxy exceeds the local escape velocity of the Milky Way. These stars present a huge puzzle: how did they attain these enormous velocities?One potential explanation is known as the Hills mechanism. In this process, a stellar binary is disrupted by a close encounter with a massive black hole (like those thought to reside at the center of every galaxy). One member of the binary is flung out of the system as a result of the close encounter, potentially reaching very large velocities.A star-forming region known as LHA 120-N 11, located within the LMC. Some binary star systems within the LMC might experience close encounters with a possible massive black hole at the LMCs center. [ESA/NASA/Hubble]Blame the LMC?Usually, discussions of the Hills mechanism assume that Sagittarius A*, the supermassive black hole at the center of the Milky Way, is the object guilty of accelerating the hypervelocity stars weve observed. But what if the culprit isnt Sgr A*, but a massive black hole at the center of the Large Magellanic Cloud (LMC), one of the Milky Ways satellite galaxies?Though we dont yet have evidence of a massive black hole at the center of the LMC, the dwarf galaxy is large enough to potentially host one as large as 100,000 solar masses. Assuming that it does, two scientists at the University of Cambridge, Douglas Boubert and Wyn Evans, have now modeled how this black hole might tear apart binary star systems and fling hypervelocity stars around the Milky Way.Models for AccelerationBoubert and Evans determined that the LMCs hypothetical black hole could easily eject stars at ~100 km/s, which is the escape velocity of the

  14. The Carbon Star Phenomenon

    NASA Astrophysics Data System (ADS)

    Wing, Robert F.

    2000-06-01

    The atmospheres of many stars have chemical compositions that are significantly different from that of the interstellar medium from which they are formed. This symposium considered all kinds of late-type stars showing altered compositions, the carbon stars being simply the best-known of these. All stages of stellar evolution from the main sequence to the ejection of a planetary nebula were considered, with emphasis on the changes that occur on the asymptotic giant branch. The spectroscopic properties of the photospheres and circumstellar envelopes of chemically-peculiar red giant stars, their origins via single-star evolution or mass transfer in binary systems, and the methods currently used to study them were all discussed in detail. This volume includes the full texts of papers given orally at the symposium and abstracts of the posters. Link: http://www.wkap.nl/book.htm/0-7923-6347-7

  15. How Stars Form

    NASA Astrophysics Data System (ADS)

    McKee, Christopher F.

    2017-01-01

    Stars are the atoms of the universe. The process by which stars form is at the nexus of astrophysics since they are believed to be responsible for the re-ionization of the universe, they created the heavy elements, they play a central role in the formation and evolution of galaxies, and their formation naturally leads to the formation of planets. Whereas early work on star formation was based on the assumption that it is a quiescent process, it is now believed that turbulence plays a dominant role. In this overview, I shall discuss the evolution of our understanding of how stars form and current ideas about the stellar initial mass function and the rate of star formation.

  16. The Angular Momentum of Baryons and Dark Matter Halos Revisited

    NASA Technical Reports Server (NTRS)

    Kimm, Taysun; Devriendt, Julien; Slyz, Adrianne; Pichon, Christophe; Kassin, Susan A.; Dubois, Yohan

    2011-01-01

    Recent theoretical studies have shown that galaxies at high redshift are fed by cold, dense gas filaments, suggesting angular momentum transport by gas differs from that by dark matter. Revisiting this issue using high-resolution cosmological hydrodynamics simulations with adaptive-mesh refinement (AMR), we find that at the time of accretion, gas and dark matter do carry a similar amount of specific angular momentum, but that it is systematically higher than that of the dark matter halo as a whole. At high redshift, freshly accreted gas rapidly streams into the central region of the halo, directly depositing this large amount of angular momentum within a sphere of radius r = 0.1R(sub vir). In contrast, dark matter particles pass through the central region unscathed, and a fraction of them ends up populating the outer regions of the halo (r/R(sub vir) > 0.1), redistributing angular momentum in the process. As a result, large-scale motions of the cosmic web have to be considered as the origin of gas angular momentum rather than its virialised dark matter halo host. This generic result holds for halos of all masses at all redshifts, as radiative cooling ensures that a significant fraction of baryons remain trapped at the centre of the halos. Despite this injection of angular momentum enriched gas, we predict an amount for stellar discs which is in fair agreement with observations at z=0. This arises because the total specific angular momentum of the baryons (gas and stars) remains close to that of dark matter halos. Indeed, our simulations indicate that any differential loss of angular momentum amplitude between the two components is minor even though dark matter halos continuously lose between half and two-thirds of their specific angular momentum modulus as they evolve. In light of our results, a substantial revision of the standard theory of disc formation seems to be required. We propose a new scenario where gas efficiently carries the angular momentum generated

  17. Hydrodynamic limit of Wigner-Poisson kinetic theory: Revisited

    NASA Astrophysics Data System (ADS)

    Akbari-Moghanjoughi, M.

    2015-02-01

    In this paper, we revisit the hydrodynamic limit of the Langmuir wave dispersion relation based on the Wigner-Poisson model in connection with that obtained directly from the original Lindhard dielectric function based on the random-phase-approximation. It is observed that the (fourth-order) expansion of the exact Lindhard dielectric constant correctly reduces to the hydrodynamic dispersion relation with an additional term of fourth-order, beside that caused by the quantum diffraction effect. It is also revealed that the generalized Lindhard dielectric theory accounts for the recently discovered Shukla-Eliasson attractive potential (SEAP). However, the expansion of the exact Lindhard static dielectric function leads to a k4 term of different magnitude than that obtained from the linearized quantum hydrodynamics model. It is shown that a correction factor of 1/9 should be included in the term arising from the quantum Bohm potential of the momentum balance equation in fluid model in order for a correct plasma dielectric response treatment. Finally, it is observed that the long-range oscillatory screening potential (Friedel oscillations) of type cos ( 2 k F r ) / r 3 , which is a consequence of the divergence of the dielectric function at point k = 2kF in a quantum plasma, arises due to the finiteness of the Fermi-wavenumber and is smeared out in the limit of very high electron number-densities, typical of white dwarfs and neutron stars. In the very low electron number-density regime, typical of semiconductors and metals, where the Friedel oscillation wavelength becomes much larger compared to the interparticle distances, the SEAP appears with a much deeper potential valley. It is remarked that the fourth-order approximate Lindhard dielectric constant approaches that of the linearized quantum hydrodynamic in the limit if very high electron number-density. By evaluation of the imaginary part of the Lindhard dielectric function, it is shown that the Landau

  18. Catch a Star!

    NASA Astrophysics Data System (ADS)

    2006-11-01

    ESO and the European Association for Astronomy Education are launching today the 2007 edition of 'Catch a Star!', their international astronomy competition for school students. Now in its fifth year, the competition offers students the chance to win a once-in-a-lifetime trip to ESO's flagship observatory in Chile, as well as many other prizes. Students are invited to 'become astronomers' and embark on a journey to explore the Universe. ESO PR Photo 42/06 The competition includes separate categories - 'Catch a Star Researchers' and 'Catch a Star Adventurers' - to ensure that every student, whatever their level, has the chance to enter and win exciting prizes. For the artistically minded, 'Catch a Star!' also includes an artwork competition, 'Catch a Star Artists'. "'Catch a Star!' offers a unique opportunity for students to learn more about astronomy and about the methods scientists use to discover new things about the Universe", said Douglas Pierce-Price, Education Officer at ESO. In teams, students choose an astronomical topic to study and produce an in-depth report. An important part of the project for 'Catch a Star Researchers' is to think about how ESO's telescopes or a telescope of the future can contribute to their investigations of the subject. As well as the top prize - a trip to one of ESO's observatory sites in Chile - visits to observatories in Germany, Austria and Spain, and many other prizes are also available to be won. 'Catch a Star Researchers' winners will be chosen by an international jury, and 'Catch a Star Adventurers' will be awarded further prizes by lottery. Entries for 'Catch a Star Artists' will be displayed on the web and winners chosen with the help of a public online vote. The first editions of 'Catch a Star!' have attracted several hundred entries from more than 25 countries worldwide. Previous winning entries have included "Star clusters and the structure of the Milky Way" (Budapest, Hungary), "Vega" (Acqui Terme, Italy) and "Venus

  19. Making star teams out of star players.

    PubMed

    Mankins, Michael; Bird, Alan; Root, James

    2013-01-01

    Top talent is an invaluable asset: In highly specialized or creative work, for instance, "A" players are likely to be six times as productive as "B" players. So when your company has a crucial strategic project, why not multiply all that firepower and have a team of your best performers tackle it? Yet many companies hesitate to do this, believing that all-star teams don't work: Big egos will get in the way. The stars won't be able to work with one another. They'll drive the team Leader crazy. Mankins, Bird, and Root of Bain & Company believe it's time to set aside that thinking. They have seen all-star teams do extraordinary work. But there is a right way and a wrong way to organize them. Before you can even begin to assemble such a team, you need to have the right talent management practices, so you hire and develop the best people and know what they're capable of. You have to give the team appropriate incentives and leaders and support staffers who are stars in their own right. And projects that are ill-defined or small scale are not for all-star teams. Use them only for critical missions, and make sure their objectives are clear. Even with the right setup, things can still go wrong. The wise executive will take steps to manage egos, prune non-team-players, and prevent average coworkers from feeling completely undervalued. She will also invest a lot of time in choosing the right team Leader and will ask members for lots of feedback to monitor how that leader is doing.

  20. Dense Axion Stars

    NASA Astrophysics Data System (ADS)

    Braaten, Eric; Mohapatra, Abhishek; Zhang, Hong

    2016-09-01

    If the dark matter particles are axions, gravity can cause them to coalesce into axion stars, which are stable gravitationally bound systems of axions. In the previously known solutions for axion stars, gravity and the attractive force between pairs of axions are balanced by the kinetic pressure. The mass of these dilute axion stars cannot exceed a critical mass, which is about 10-14M⊙ if the axion mass is 10-4 eV . We study axion stars using a simple approximation to the effective potential of the nonrelativistic effective field theory for axions. We find a new branch of dense axion stars in which gravity is balanced by the mean-field pressure of the axion Bose-Einstein condensate. The mass on this branch ranges from about 10-20M⊙ to about M⊙ . If a dilute axion star with the critical mass accretes additional axions and collapses, it could produce a bosenova, leaving a dense axion star as the remnant.

  1. Dense Axion Stars

    NASA Astrophysics Data System (ADS)

    Mohapatra, Abhishek; Braaten, Eric; Zhang, Hong

    2016-03-01

    If the dark matter consists of axions, gravity can cause them to coalesce into axion stars, which are stable gravitationally bound Bose-Einstein condensates of axions. In the previously known axion stars, gravity and the attractive force between pairs of axions are balanced by the kinetic pressure. If the axion mass energy is mc2 =10-4 eV, these dilute axion stars have a maximum mass of about 10-14M⊙ . We point out that there are also dense axion stars in which gravity is balanced by the mean-field pressure of the axion condensate. We study axion stars using the leading term in a systematically improvable approximation to the effective potential of the nonrelativistic effective field theory for axions. Using the Thomas-Fermi approximation in which the kinetic pressure is neglected, we find a sequence of new branches of axion stars in which gravity is balanced by the mean-field interaction energy of the axion condensate. If mc2 =10-4 4 eV, the first branch of these dense axion stars has mass ranging from about 10-11M⊙ toabout M⊙.

  2. From stars to nuclei

    NASA Astrophysics Data System (ADS)

    Meynet, G.

    2008-04-01

    We recall the basic physical principles governing the evolution of stars with some emphasis on the role played by the nuclear reactions. We argue that in general it is not possible from observations of stars to deduce constraints on the nuclear reaction rates. This is the reason why precise measurements of nuclear reaction rates are a necessity in order to make progresses in stellar physics, nucleosynthesis and chemical evolution of galaxies. There are however some stars which provides useful constraints on nuclear processes. The Wolf-Rayet stars of the WN type present at their surface CNO equilibrium patterns. There is also the particular case of the abundance of 22Ne at the surface of WC stars. The abundance of this element is a measure of the initial CNO content. Very interestingly, recent determinations of its abundance at the surface of WC stars tend to confirm that massive stars in the solar neighborhood have initial metallicities in agreement with the Asplund et al. [1] solar abundances.

  3. Dense Axion Stars.

    PubMed

    Braaten, Eric; Mohapatra, Abhishek; Zhang, Hong

    2016-09-16

    If the dark matter particles are axions, gravity can cause them to coalesce into axion stars, which are stable gravitationally bound systems of axions. In the previously known solutions for axion stars, gravity and the attractive force between pairs of axions are balanced by the kinetic pressure. The mass of these dilute axion stars cannot exceed a critical mass, which is about 10^{-14}M_{⊙} if the axion mass is 10^{-4}  eV. We study axion stars using a simple approximation to the effective potential of the nonrelativistic effective field theory for axions. We find a new branch of dense axion stars in which gravity is balanced by the mean-field pressure of the axion Bose-Einstein condensate. The mass on this branch ranges from about 10^{-20}M_{⊙} to about M_{⊙}. If a dilute axion star with the critical mass accretes additional axions and collapses, it could produce a bosenova, leaving a dense axion star as the remnant.

  4. The AP spectroscopic binary HD 59435 revisited

    NASA Astrophysics Data System (ADS)

    Wade, G. A.; Mathys, G.; North, P.

    1999-07-01

    HD 59435 is a double-lined spectroscopic binary, one component of which is a magnetic Ap star and the other a G8 or K0 giant (Wade et al. 1996). Both components are very slowly rotating, and the Ap star exhibits spectral lines resolved into their magneti cally-split components. Herein we report additional measurements of the mean magnetic field modulus of the Ap star, measurements of the radial velocities of both components, and Geneva photometry of the system, and discuss their impact upon conclusions drawn previously. Based on observations collected at the European Southern Observatory (La Silla, Chile; ESO Programme Nos. 56.E-0688, 58.E-0159, 60.E-0565). Table 3 is available only in electronic form at the CDS via anonymous ftp 130.79.128.5

  5. Highly-evolved stars

    NASA Technical Reports Server (NTRS)

    Heap, S. R.

    1981-01-01

    The ways in which the IUE has proved useful in studying highly evolved stars are reviewed. The importance of high dispersion spectra for abundance analyses of the sd0 stars and for studies of the wind from the central star of NGC 6543 and the wind from the 0 type component of Vela X-1 is shown. Low dispersion spectra are used for absolute spectrophotometry of the dwarf nova, Ex Hya. Angular resolution is important for detecting and locating UV sources in globular clusters.

  6. Superradiance in stars

    NASA Astrophysics Data System (ADS)

    Cardoso, Vitor; Brito, Richard; Rosa, João L.

    2015-06-01

    It has long been known that dissipation is a crucial ingredient in the superradiant amplification of wave packets off rotating objects. We show that, once appropriate dissipation mechanisms are included, stars are also prone to superradiance and superradiant instabilities. In particular, ultralight dark matter with small interaction cross section with the star material or self-annihilation can trigger a superradiant instability. On long time scales, the instability strips the star of most of its angular momentum. Whether or not new stationary configurations surrounded by scalar condensates exist remains to be seen.

  7. Discovery of variable stars

    NASA Technical Reports Server (NTRS)

    Kurochkin, N. Y.

    1973-01-01

    Instrumented methods of discovering variable stars are reviewed, specifically the blink comparator, color contrast method, positive-negative method, and television method. Among the empirical methods discussed, the Van Gent method is the most important.

  8. Guide star probabilities

    NASA Technical Reports Server (NTRS)

    Soneira, R. M.; Bahcall, J. N.

    1981-01-01

    Probabilities are calculated for acquiring suitable guide stars (GS) with the fine guidance system (FGS) of the space telescope. A number of the considerations and techniques described are also relevant for other space astronomy missions. The constraints of the FGS are reviewed. The available data on bright star densities are summarized and a previous error in the literature is corrected. Separate analytic and Monte Carlo calculations of the probabilities are described. A simulation of space telescope pointing is carried out using the Weistrop north galactic pole catalog of bright stars. Sufficient information is presented so that the probabilities of acquisition can be estimated as a function of position in the sky. The probability of acquiring suitable guide stars is greatly increased if the FGS can allow an appreciable difference between the (bright) primary GS limiting magnitude and the (fainter) secondary GS limiting magnitude.

  9. Conformally symmetric relativistic star

    NASA Astrophysics Data System (ADS)

    Rahaman, Farook; Maharaj, Sunil D.; Sardar, Iftikar Hossain; Chakraborty, Koushik

    2017-03-01

    We investigate whether compact stars having Tolman-like interior geometry admit conformal symmetry. Taking anisotropic pressure along the two principal directions within the compact object, we obtain physically relevant quantities such as transverse and radial pressure, density and redshift function. We study the equation of state (EOS) for the matter distribution inside the star. From the relation between pressure and density function of the constituent matter, we explore the nature and properties of the interior matter. The redshift function and compactness parameter are found to be physically reasonable. The matter inside the star satisfies the null, weak and strong energy conditions. Finally, we compare the masses and radii predicted from the model with corresponding values in some observed stars.

  10. Cooling of neutron stars

    NASA Technical Reports Server (NTRS)

    Pethick, C. J.

    1992-01-01

    It is at present impossible to predict the interior constitution of neutron stars based on theory and results from laboratory studies. It has been proposed that it is possible to obtain information on neutron star interiors by studying thermal radiation from their surfaces, because neutrino emission rates, and hence the temperature of the central part of a neutron star, depend on the properties of dense matter. The theory predicts that neutron stars cool relatively slowly if their cores are made up of nucleons, and cool faster if the matter is in an exotic state, such as a pion condensate, a kaon condensate, or quark matter. This view has recently been questioned by the discovery of a number of other processes that could lead to copious neutrino emission and rapid cooling.

  11. Cosmology with hypervelocity stars

    SciTech Connect

    Loeb, Abraham

    2011-04-01

    In the standard cosmological model, the merger remnant of the Milky Way and Andromeda (Milkomeda) will be the only galaxy remaining within our event horizon once the Universe has aged by another factor of ten, ∼ 10{sup 11} years after the Big Bang. After that time, the only extragalactic sources of light in the observable cosmic volume will be hypervelocity stars being ejected continuously from Milkomeda. Spectroscopic detection of the velocity-distance relation or the evolution in the Doppler shifts of these stars will allow a precise measurement of the vacuum mass density as well as the local matter distribution. Already in the near future, the next generation of large telescopes will allow photometric detection of individual stars out to the edge of the Local Group, and may target the ∼ 10{sup 5±1} hypervelocity stars that originated in it as cosmological tracers.

  12. Sounds of a Star

    NASA Astrophysics Data System (ADS)

    2001-06-01

    Acoustic Oscillations in Solar-Twin "Alpha Cen A" Observed from La Silla by Swiss Team Summary Sound waves running through a star can help astronomers reveal its inner properties. This particular branch of modern astrophysics is known as "asteroseismology" . In the case of our Sun, the brightest star in the sky, such waves have been observed since some time, and have greatly improved our knowledge about what is going on inside. However, because they are much fainter, it has turned out to be very difficult to detect similar waves in other stars. Nevertheless, tiny oscillations in a solar-twin star have now been unambiguously detected by Swiss astronomers François Bouchy and Fabien Carrier from the Geneva Observatory, using the CORALIE spectrometer on the Swiss 1.2-m Leonard Euler telescope at the ESO La Silla Observatory. This telescope is mostly used for discovering exoplanets (see ESO PR 07/01 ). The star Alpha Centauri A is the nearest star visible to the naked eye, at a distance of a little more than 4 light-years. The new measurements show that it pulsates with a 7-minute cycle, very similar to what is observed in the Sun . Asteroseismology for Sun-like stars is likely to become an important probe of stellar theory in the near future. The state-of-the-art HARPS spectrograph , to be mounted on the ESO 3.6-m telescope at La Silla, will be able to search for oscillations in stars that are 100 times fainter than those for which such demanding observations are possible with CORALIE. PR Photo 23a/01 : Oscillations in a solar-like star (schematic picture). PR Photo 23b/01 : Acoustic spectrum of Alpha Centauri A , as observed with CORALIE. Asteroseismology: listening to the stars ESO PR Photo 23a/01 ESO PR Photo 23a/01 [Preview - JPEG: 357 x 400 pix - 96k] [Normal - JPEG: 713 x 800 pix - 256k] [HiRes - JPEG: 2673 x 3000 pix - 2.1Mb Caption : PR Photo 23a/01 is a graphical representation of resonating acoustic waves in the interior of a solar-like star. Red and blue

  13. Catch a Star 2008!

    NASA Astrophysics Data System (ADS)

    2007-10-01

    ESO and the European Association for Astronomy Education have just launched the 2008 edition of 'Catch a Star', their international astronomy competition for school students. Now in its sixth year, the competition offers students the chance to win a once-in-a-lifetime trip to ESO's flagship observatory in Chile, as well as many other prizes. CAS logo The competition includes separate categories - 'Catch a Star Researchers' and 'Catch a Star Adventurers' - to ensure that every student, whatever their level, has the chance to enter and win exciting prizes. In teams, students investigate an astronomical topic of their choice and write a report about it. An important part of the project for 'Catch a Star Researchers' is to think about how ESO's telescopes such as the Very Large Telescope (VLT) or future telescopes such as the Atacama Large Millimeter/submillimeter Array (ALMA) and the European Extremely Large Telescope (E-ELT) could contribute to investigations of the topic. Students may also include practical activities such as observations or experiments. For the artistically minded, 'Catch a Star' also offers an artwork competition, 'Catch a Star Artists'. Last year, hundreds of students from across Europe and beyond took part in 'Catch a Star', submitting astronomical projects and artwork. "'Catch a Star' gets students thinking about the wonders of the Universe and the science of astronomy, with a chance of winning great prizes. It's easy to take part, whether by writing about astronomy or creating astronomically inspired artwork," said Douglas Pierce-Price, Education Officer at ESO. As well as the top prize - a trip to ESO's Very Large Telescope in Chile - visits to observatories in Austria and Spain, and many other prizes, can also be won. 'Catch a Star Researchers' winners will be chosen by an international jury, and 'Catch a Star Adventurers' will be awarded further prizes by lottery. Entries for 'Catch a Star Artists' will be displayed on the web and winners

  14. Hypercritical accretion onto a magnetized neutron star surface: a numerical approach

    NASA Astrophysics Data System (ADS)

    Bernal, C. G.; Lee, W. H.; Page, D.

    2010-10-01

    The properties of a new-born neutron star, produced in a core-collapse supernova, can be strongly affected by the possible late fallback which occurs several hours after the explosion. This accretion occurs in the regime dominated by neutrino cooling, explored initially in this context by Chevalier (1989). Here we revisit this approach in a 1D spherically symmetric model and carry out numerical simulations in 2D in an accretion column onto a neutron star, considering detailed microphysics, neutrino cooling and the presence of magnetic fields in ideal MHD. We compare our numerical results with the analytic solutions and explore how the purely hydrodynamical as well as the MHD solutions differ from them, and begin to explore how this may affect the appearance of the remnant as a typical radio pulsar.

  15. Multiwavelength Diffraction-limited Imaging of the Evolved Carbon Star IRC +10216. II.

    NASA Astrophysics Data System (ADS)

    Tuthill, P. G.; Monnier, J. D.; Danchi, W. C.

    2005-05-01

    High angular resolution images of IRC +10216 taken at various bandpasses within the near-infrared H, K, and L bands are presented. The maps have the highest angular resolution yet recovered and were reconstructed from interferometric measurements obtained at the Keck I telescope in 1997 December and 1998 April, forming a subset of a seven-epoch monitoring program presented earlier by Tuthill and coworkers in Paper I. Systematic changes with observing wavelength are found and discussed in the context of present geometrical models for the circumstellar envelope. With these new high-resolution, multiwavelength data and contemporaneous photometry, we also revisit the hypothesis that the bright compact core of the nebula (component ``A'') marks the location of the central carbon star. We find that directly measured properties of the core (angular size, flux density, color temperature) are consistent with a reddened carbon star photosphere (line-of-sight τ2.2=5.3).

  16. Bubbly Little Star

    NASA Technical Reports Server (NTRS)

    2007-01-01

    In this processed Spitzer Space Telescope image, baby star HH 46/47 can be seen blowing two massive 'bubbles.' The star is 1,140 light-years away from Earth.

    The infant star can be seen as a white spot toward the center of the Spitzer image. The two bubbles are shown as hollow elliptical shells of bluish-green material extending from the star. Wisps of green in the image reveal warm molecular hydrogen gas, while the bluish tints are formed by starlight scattered by surrounding dust.

    These bubbles formed when powerful jets of gas, traveling at 200 to 300 kilometers per second, or about 120 to 190 miles per second, smashed into the cosmic cloud of gas and dust that surrounds HH 46/47. The red specks at the end of each bubble show the presence of hot sulfur and iron gas where the star's narrow jets are currently crashing head-on into the cosmic cloud's gas and dust material.

    Whenever astronomers observe a star, or snap a stellar portrait, through the lens of any telescope, they know that what they are seeing is slightly blurred. To clear up the blurring in Spitzer images, astronomers at the Jet Propulsion Laboratory developed an image processing technique for Spitzer called Hi-Res deconvolution.

    This process reduces blurring and makes the image sharper and cleaner, enabling astronomers to see the emissions around forming stars in greater detail. When scientists applied this image processing technique to the Spitzer image of HH 46/47, they were able to see winds from the star and jets of gas that are carving the celestial bubbles.

    This infrared image is a three-color composite, with data at 3.6 microns represented in blue, 4.5 and 5.8 microns shown in green, and 24 microns represented as red.

  17. Chaotic Star Birth

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site] [figure removed for brevity, see original site] Click on the image for Poster VersionClick on the image for IRAS 4B Inset

    Located 1,000 light years from Earth in the constellation Perseus, a reflection nebula called NGC 1333 epitomizes the beautiful chaos of a dense group of stars being born. Most of the visible light from the young stars in this region is obscured by the dense, dusty cloud in which they formed. With NASA's Spitzer Space Telescope, scientists can detect the infrared light from these objects. This allows a look through the dust to gain a more detailed understanding of how stars like our sun begin their lives.

    The young stars in NGC 1333 do not form a single cluster, but are split between two sub-groups. One group is to the north near the nebula shown as red in the image. The other group is south, where the features shown in yellow and green abound in the densest part of the natal gas cloud. With the sharp infrared eyes of Spitzer, scientists can detect and characterize the warm and dusty disks of material that surround forming stars. By looking for differences in the disk properties between the two subgroups, they hope to find hints of the star and planet formation history of this region.

    The knotty yellow-green features located in the lower portion of the image are glowing shock fronts where jets of material, spewed from extremely young embryonic stars, are plowing into the cold, dense gas nearby. The sheer number of separate jets that appear in this region is unprecedented. This leads scientists to believe that by stirring up the cold gas, the jets may contribute to the eventual dispersal of the gas cloud, preventing more stars from forming in NGC 1333.

    In contrast, the upper portion of the image is dominated by the infrared light from warm dust, shown as red.

  18. Star of Bethlehem

    NASA Astrophysics Data System (ADS)

    Hughes, D.; Murdin, P.

    2001-07-01

    The biblical Star of Bethlehem, which heralded the birth of Jesus Christ, is only mentioned in the Gospel of St Matthew 2. The astrologically significant 7 bc triple conjunction of Jupiter and Saturn in the constellation of Pisces is the most likely candidate, although a comet/nova in 5 bc and a comet in 4 bc cannot be ruled out. There is also the possibility that the star was simply fictitious....

  19. Matter accreting neutron stars

    NASA Technical Reports Server (NTRS)

    Meszaros, P.

    1981-01-01

    Some of the fundamental neutron star parameters, such as the mass and the magnetic field strength, were experimentally determined in accreting neutron star systems. Some of the relevant data and the models used to derive useful information from them, are reviewed concentrating mainly on X-ray pulsars. The latest advances in our understanding of the radiation mechanisms and the transfer in the strongly magnetized polar cap regions are discussed.

  20. Spectroscopic Binary Stars

    NASA Astrophysics Data System (ADS)

    Batten, A.; Murdin, P.

    2000-11-01

    Historically, spectroscopic binary stars were binary systems whose nature was discovered by the changing DOPPLER EFFECT or shift of the spectral lines of one or both of the component stars. The observed Doppler shift is a combination of that produced by the constant RADIAL VELOCITY (i.e. line-of-sight velocity) of the center of mass of the whole system, and the variable shift resulting from the o...

  1. Predator-prey interactions, resource depression and patch revisitation

    USGS Publications Warehouse

    Erwin, R.M.

    1989-01-01

    Generalist predators may be confronted by different types of prey in different patches: sedentary and conspicuous, cryptic (with or without refugia), conspicuous and nonsocial, or conspicuous and social. I argue that, where encounter rates with prey are of most importance, patch revisitation should be a profitable tactic where prey have short 'recovery' times (conspicuous, nonsocial prey), or where anti-predator response (e.g. shoaling) may increase conspicuousness. Predictions are made for how temporal changes in prey encounter rates should affect revisit schedules and feeding rates for the 4 different prey types.

  2. Seeing Stars in Serpens

    NASA Technical Reports Server (NTRS)

    2006-01-01

    Infant stars are glowing gloriously in this infrared image of the Serpens star-forming region, captured by NASA's Spitzer Space Telescope.

    The reddish-pink dots are baby stars deeply embedded in the cosmic cloud of gas and dust that collapsed to create it. A dusty disk of cosmic debris, or 'protoplanetary disk,' that may eventually form planets, surrounds the infant stars.

    Wisps of green throughout the image indicate the presence of carbon rich molecules called polycyclic aromatic hydrocarbons. On Earth, these molecules can be found on charred barbecue grills and in automobile exhaust. Blue specks sprinkled throughout the image are background stars in our Milky Way galaxy.

    The Serpens star-forming region is located approximately 848 light-years away in the Serpens constellation.

    The image is a three-channel, false-color composite, where emission at 4.5 microns is blue, emission at 8.0 microns is green, and 24 micron emission is red.

  3. A RE-EVALUATION OF THE EVOLVED STARS IN THE GLOBULAR CLUSTER M13

    SciTech Connect

    Sandquist, Eric L.; Gordon, Mark; Levine, Daniel; Bolte, Michael

    2010-06-15

    . These stars are brighter than other stars of similar color (either redder or bluer), and may be examples of 'early hot flashers' that ignite core helium fusion shortly after leaving the RGB. We used ultraviolet photometry to identify hot post-HB stars, and based on their numbers (relative to canonical AGB stars) we estimate the position on the HB where the morphology of the post-HB tracks change to I {approx} 17.3, between the two peaks in the HB distribution. Concerning the possibility of helium enrichment in M13, we revisited the helium-sensitive R ratio, applying a new method for correcting star counts for larger lifetimes of hot HB stars. We find that M13's R ratio is in agreement with theoretical values for primordial helium abundance Y{sub P} = 0.245 and inconsistent with a helium enhancement {Delta}Y = 0.04. The brightness of the HB (both in comparison to the end of the canonical HB and to the tip of the RGB) also appears to rule out the idea that the envelopes of the reddest HB stars have been significantly enriched in helium. The absolute colors of the turnoffs of M3 and M13 potentially may be used to look for differences in their mean helium abundances, but there are inconsistencies in current data sets between colors using different filters that prevent a solid conclusion. The numbers of stars on the lower RGB and in the red giant bump agree very well with recent theoretical models, although there are slight indications of a deficit of red giant stars above the bump. There is not convincing evidence that a large fraction of stars leave the RGB before undergoing a core helium flash.

  4. Collapsing Enormous Stars

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2015-09-01

    One of the big puzzles in astrophysics is how supermassive black holes (SMBHs) managed to grow to the large sizes weve observed in the very early universe. In a recent study, a team of researchers examines the possibility that they were formed by the direct collapse of supermassive stars.Formation MysterySMBHs billions of times as massive as the Sun have been observed at a time when the universe was less than a billion years old. But thats not enough time for a stellar-mass black hole to grow to SMBH-size by accreting material so another theory is needed to explain the presence of these monsters so early in the universes history. A new study, led by Tatsuya Matsumoto (Kyoto University, Japan), poses the following question: what if supermassive stars in the early universe collapsed directly into black holes?Previous studies of star formation in the early universe have suggested that, in the hot environment of these primordial times, stars might have been able to build up mass much faster than they can today. This could result in early supermassive stars roughly 100,000 times more massive than the Sun. But if these early stars end their lives by collapsing to become massive black holes in the same way that we believe massive stars can collapse to form stellar-mass black holes today this should result in enormously violent explosions. Matusmoto and collaborators set out to model this process, to determine what we would expect to see when it happens!Energetic BurstsThe authors modeled the supermassive stars prior to collapse and then calculated whether a jet, created as the black hole grows at the center of the collapsing star, would be able to punch out of the stellar envelope. They demonstrated that the process would work much like the widely-accepted collapsar model of massive-star death, in which a jet successfully punches out of a collapsing star, violently releasing energy in the form of a long gamma-ray burst (GRB).Because the length of a long GRB is thought to

  5. Hot Subluminous Stars

    NASA Astrophysics Data System (ADS)

    Heber, U.

    2016-08-01

    Hot subluminous stars of spectral type B and O are core helium-burning stars at the blue end of the horizontal branch or have evolved even beyond that stage. Most hot subdwarf stars are chemically highly peculiar and provide a laboratory to study diffusion processes that cause these anomalies. The most obvious anomaly lies with helium, which may be a trace element in the atmosphere of some stars (sdB, sdO) while it may be the dominant species in others (He-sdB, He-sdO). Strikingly, the distribution in the Hertzsprung-Russell diagram of He-rich versus He-poor hot subdwarf stars of the globular clusters ω Cen and NGC 2808 differ from that of their field counterparts. The metal-abundance patterns of hot subdwarfs are typically characterized by strong deficiencies of some lighter elements as well as large enrichments of heavy elements. A large fraction of sdB stars are found in close binaries with white dwarf or very low-mass main sequence companions, which must have gone through a common-envelope (CE) phase of evolution. Because the binaries are detached they provide a clean-cut laboratory to study this important but yet poorly understood phase of stellar evolution. Hot subdwarf binaries with sufficiently massive white dwarf companions are viable candidate progenitors of type Ia supernovae both in the double degenerate as well as in the single degenerate scenario as helium donors for double detonation supernovae. The hyper-velocity He-sdO star US 708 may be the surviving donor of such a double detonation supernova. Substellar companions to sdB stars have also been found. For HW Vir systems the companion mass distribution extends from the stellar into the brown dwarf regime. A giant planet to the acoustic-mode pulsator V391 Peg was the first discovery of a planet that survived the red giant evolution of its host star. Evidence for Earth-size planets to two pulsating sdB stars have been reported and circumbinary giant planets or brown dwarfs have been found around HW

  6. Revisiting the phase diagram of hard ellipsoids

    NASA Astrophysics Data System (ADS)

    Odriozola, Gerardo

    2012-04-01

    In this work, the well-known Frenkel-Mulder phase diagram of hard ellipsoids of revolution [D. Frenkel and B. M. Mulder, Mol. Phys. 55, 1171 (1985), 10.1080/00268978500101971] is revisited by means of replica exchange Monte Carlo simulations. The method provides good sampling of dense systems and so, solid phases can be accessed without the need of imposing a given structure. At high densities, we found plastic solids and fcc-like crystals for semi-spherical ellipsoids (prolates and oblates), and SM2 structures [P. Pfleiderer and T. Schilling, Phys. Rev. E 75, 020402 (2007)] for x : 1-prolates and 1 : x-oblates with x ≥ 3. The revised fluid-crystal and isotropic-nematic transitions reasonably agree with those presented in the Frenkel-Mulder diagram. An interesting result is that, for small system sizes (100 particles), we obtained 2:1- and 1.5:1-prolate equations of state without transitions, while some order is developed at large densities. Furthermore, the symmetric oblate cases are also reluctant to form ordered phases.

  7. Targeting Cancer Metabolism - Revisiting the Warburg Effects

    PubMed Central

    Tran, Quangdon; Lee, Hyunji; Park, Jisoo; Kim, Seon-Hwan; Park, Jongsun

    2016-01-01

    After more than half of century since the Warburg effect was described, this atypical metabolism has been standing true for almost every type of cancer, exhibiting higher glycolysis and lactate metabolism and defective mitochondrial ATP production. This phenomenon had attracted many scientists to the problem of elucidating the mechanism of, and reason for, this effect. Several models based on oncogenic studies have been proposed, such as the accumulation of mitochondrial gene mutations, the switch from oxidative phosphorylation respiration to glycolysis, the enhancement of lactate metabolism, and the alteration of glycolytic genes. Whether the Warburg phenomenon is the consequence of genetic dysregulation in cancer or the cause of cancer remains unknown. Moreover, the exact reasons and physiological values of this peculiar metabolism in cancer remain unclear. Although there are some pharmacological compounds, such as 2-deoxy-D-glucose, dichloroacetic acid, and 3-bromopyruvate, therapeutic strategies, including diet, have been developed based on targeting the Warburg effect. In this review, we will revisit the Warburg effect to determine how much scientists currently understand about this phenomenon and how we can treat the cancer based on targeting metabolism. PMID:27437085

  8. Revisiting the argument from fetal potential.

    PubMed

    Manninen, Bertha Alvarez

    2007-05-17

    One of the most famous, and most derided, arguments against the morality of abortion is the argument from potential, which maintains that the fetus' potential to become a person and enjoy the valuable life common to persons, entails that its destruction is prima facie morally impermissible. In this paper, I will revisit and offer a defense of the argument from potential.First, I will criticize the classical arguments proffered against the importance of fetal potential, specifically the arguments put forth by philosophers Peter Singer and David Boonin, by carefully unpacking the claims made in these arguments and illustrating why they are flawed.Secondly, I will maintain that fetal potential is morally relevant when it comes to the morality of abortion, but that it must be accorded a proper place in the argument. This proper place, however, cannot be found until we first answer a very important and complex question: we must first address the issue of personal identity, and when the fetus becomes the type of being who is relevantly identical to a future person. I will illustrate why the question of fetal potential can only be meaningfully addressed after we have first answered the question of personal identity and how it relates to the human fetus.

  9. Carbon emission from global hydroelectric reservoirs revisited.

    PubMed

    Li, Siyue; Zhang, Quanfa

    2014-12-01

    Substantial greenhouse gas (GHG) emissions from hydropower reservoirs have been of great concerns recently, yet the significant carbon emitters of drawdown area and reservoir downstream (including spillways and turbines as well as river reaches below dams) have not been included in global carbon budget. Here, we revisit GHG emission from hydropower reservoirs by considering reservoir surface area, drawdown zone and reservoir downstream. Our estimates demonstrate around 301.3 Tg carbon dioxide (CO2)/year and 18.7 Tg methane (CH4)/year from global hydroelectric reservoirs, which are much higher than recent observations. The sum of drawdown and downstream emission, which is generally overlooked, represents 42 % CO2 and 67 % CH4 of the total emissions from hydropower reservoirs. Accordingly, the global average emissions from hydropower are estimated to be 92 g CO2/kWh and 5.7 g CH4/kWh. Nonetheless, global hydroelectricity could currently reduce approximate 2,351 Tg CO2eq/year with respect to fuel fossil plant alternative. The new findings show a substantial revision of carbon emission from the global hydropower reservoirs.

  10. Hyperinflation in Brazil, Israel, and Nicaragua revisited

    NASA Astrophysics Data System (ADS)

    Szybisz, Martín A.; Szybisz, Leszek

    2017-01-01

    The aim of the present work is to address the description of hyperinflation regimens in economy. The spirals of hyperinflation developed in Brazil, Israel, and Nicaragua are revisited. This new analysis of data indicates that the episodes occurred in Brazil and Nicaragua can be understood within the frame of the model available in the literature, which is based on a nonlinear feedback (NLF) characterized by an exponent β > 0. In the NLF model the accumulated consumer price index carries a finite time singularity of the type 1 /(tc - t) (1 - β) / β determining a critical time tc at which the economy would crash. It is shown that in the case of Brazil the entire episode cannot be described with a unique set of parameters because the time series was strongly affected by a change of policy. This fact gives support to the "so called" Lucas critique, who stated that model's parameters usually change once policy changes. On the other hand, such a model is not able to provide any tc in the case of the weaker hyperinflation occurred in Israel. It is shown that in this case the fit of data yields β → 0. This limit leads to the linear feedback formulation which does not predict any tc. An extension for the NLF model is suggested.

  11. [What mirror neurons have revealed: revisited].

    PubMed

    Murata, Akira; Maeda, Kazutaka

    2014-06-01

    The first paper on mirror neurons was published in 1992. In the span of over two decades since then, much knowledge about the relationship between social cognitive function and the motor control system has been accumulated. Direct matching of visual actions and their corresponding motor representations is the most important functional property of mirror neuron. Many studies have emphasized intrinsic simulation as a core concept for mirror neurons. Mirror neurons are thought to play a role in social cognitive function. However, the function of mirror neurons in the macaque remains unclear, because such cognitive functions are limited or lacking in macaque monkeys. It is therefore important to discuss these neurons in the context of motor function. Rizzolatti and colleagues have stressed that the most important function of mirror neurons in macaques is recognition of actions performed by other individuals. I suggest that mirror neurons in the Macaque inferior pariental lobule might be correlated with body schema. In the parieto-premotor network, matching of corollary discharge and actual sensory feedback is an essential neuronal operation. Recently, neurons showing mirror properties were found in some cortical areas outside the mirror neuron system. The current work would revisit the outcomes of mirror neuron studies to discuss the function of mirror neurons in the monkey.

  12. No-scale ripple inflation revisited

    SciTech Connect

    Li, Tianjun; Li, Zhijin; Nanopoulos, Dimitri V. E-mail: lizhijin@physics.tamu.edu

    2014-04-01

    We revisit the no-scale ripple inflation model, where no-scale supergravity is modified by an additional term for the inflaton field in the Kähler potential. This term not only breaks one SU(N,1) symmetry explicitly, but also plays an important role for inflation. We generalize the superpotential in the no-scale ripple inflation model slightly. There exists a discrete Z{sub 2} symmetry/parity in the scalar potential in general, which can be preserved or violated by the non-canonical nomalized inflaton kinetic term. Thus, there are three inflation paths: one parity invariant path, and the left and right paths for parity violating scenario. We show that the inflations along the parity invariant path and right path are consistent with the Planck results. However, the gavitino mass for the parity invariant path is so large that the inflation results will be invalid if we consider the inflaton supersymmetry breaking soft mass term. Thus, only the inflation along the right path gives the correct and consistent results. Notably, the tensor-to-scalar ratio in such case can be large, with a value around 0.05, which may be probed by the future Planck experiment.

  13. The super-GUT CMSSM revisited

    NASA Astrophysics Data System (ADS)

    Ellis, John; Evans, Jason L.; Mustafayev, Azar; Nagata, Natsumi; Olive, Keith A.

    2016-11-01

    We revisit minimal supersymmetric SU(5) grand unification (GUT) models in which the soft supersymmetry-breaking parameters of the minimal supersymmetric Standard Model (MSSM) are universal at some input scale, M_in, above the supersymmetric gauge-coupling unification scale, M_GUT. As in the constrained MSSM (CMSSM), we assume that the scalar masses and gaugino masses have common values, m_0 and m_{1/2}, respectively, at M_in, as do the trilinear soft supersymmetry-breaking parameters A_0. Going beyond previous studies of such a super-GUT CMSSM scenario, we explore the constraints imposed by the lower limit on the proton lifetime and the LHC measurement of the Higgs mass, m_h. We find regions of m_0, m_{1/2}, A_0 and the parameters of the SU(5) superpotential that are compatible with these and other phenomenological constraints such as the density of cold dark matter, which we assume to be provided by the lightest neutralino. Typically, these allowed regions appear for m_0 and m_{1/2} in the multi-TeV region, for suitable values of the unknown SU(5) GUT-scale phases and superpotential couplings, and with the ratio of supersymmetric Higgs vacuum expectation values tan β ≲ 6.

  14. Post-inflationary gravitino production revisited

    SciTech Connect

    Ellis, John; Garcia, Marcos A.G.; Olive, Keith A.; Nanopoulos, Dimitri V.; Peloso, Marco E-mail: garciagarcia@physics.umn.edu E-mail: olive@physics.umn.edu

    2016-03-01

    We revisit gravitino production following inflation. As a first step, we review the standard calculation of gravitino production in the thermal plasma formed at the end of post-inflationary reheating when the inflaton has completely decayed. Next we consider gravitino production prior to the completion of reheating, assuming that the inflaton decay products thermalize instantaneously while they are still dilute. We then argue that instantaneous thermalization is in general a good approximation, and also show that the contribution of non-thermal gravitino production via the collisions of inflaton decay products prior to thermalization is relatively small. Our final estimate of the gravitino-to-entropy ratio is approximated well by a standard calculation of gravitino production in the post-inflationary thermal plasma assuming total instantaneous decay and thermalization at a time t ≅ 1.2/Γ{sub φ}. Finally, in light of our calculations, we consider potential implications of upper limits on the gravitino abundance for models of inflation, with particular attention to scenarios for inflaton decays in supersymmetric Starobinsky-like models.

  15. Revisiting the phase diagram of hard ellipsoids.

    PubMed

    Odriozola, Gerardo

    2012-04-07

    In this work, the well-known Frenkel-Mulder phase diagram of hard ellipsoids of revolution [D. Frenkel and B. M. Mulder, Mol. Phys. 55, 1171 (1985)] is revisited by means of replica exchange Monte Carlo simulations. The method provides good sampling of dense systems and so, solid phases can be accessed without the need of imposing a given structure. At high densities, we found plastic solids and fcc-like crystals for semi-spherical ellipsoids (prolates and oblates), and SM2 structures [P. Pfleiderer and T. Schilling, Phys. Rev. E 75, 020402 (2007)] for x : 1-prolates and 1 : x-oblates with x ≥ 3. The revised fluid-crystal and isotropic-nematic transitions reasonably agree with those presented in the Frenkel-Mulder diagram. An interesting result is that, for small system sizes (100 particles), we obtained 2:1- and 1.5:1-prolate equations of state without transitions, while some order is developed at large densities. Furthermore, the symmetric oblate cases are also reluctant to form ordered phases.

  16. Binocularity and visual search-Revisited.

    PubMed

    Zou, Bochao; Utochkin, Igor S; Liu, Yue; Wolfe, Jeremy M

    2017-02-01

    Binocular rivalry is a phenomenon of visual competition in which perception alternates between two monocular images. When two eye's images only differ in luminance, observers may perceive shininess, a form of rivalry called binocular luster. Does dichoptic information guide attention in visual search? Wolfe and Franzel (Perception & Psychophysics, 44(1), 81-93, 1988) reported that rivalry could guide attention only weakly, but that luster (shininess) "popped out," producing very shallow Reaction Time (RT) × Set Size functions. In this study, we have revisited the topic with new and improved stimuli. By using a checkerboard pattern in rivalry experiments, we found that search for rivalry can be more efficient (16 ms/item) than standard, rivalrous grating (30 ms/item). The checkerboard may reduce distracting orientation signals that masked the salience of rivalry between simple orthogonal gratings. Lustrous stimuli did not pop out when potential contrast and luminance artifacts were reduced. However, search efficiency was substantially improved when luster was added to the search target. Both rivalry and luster tasks can produce search asymmetries, as is characteristic of guiding features in search. These results suggest that interocular differences that produce rivalry or luster can guide attention, but these effects are relatively weak and can be hidden by other features like luminance and orientation in visual search tasks.

  17. Wolf-Rayet Stars

    NASA Astrophysics Data System (ADS)

    Hamann, Wolf-Rainer; Sander, Andreas; Todt, Helge

    Nearly 150 years ago, the French astronomers Charles Wolf and Georges Rayet described stars with very conspicuous spectra that are dominated by bright and broad emission lines. Meanwhile termed Wolf-Rayet Stars after their discoverers, those objects turned out to represent important stages in the life of massive stars. As the first conference in a long time that was specifically dedicated to Wolf-Rayet stars, an international workshop was held in Potsdam, Germany, from 1.-5. June 2015. About 100 participants, comprising most of the leading experts in the field as well as as many young scientists, gathered for one week of extensive scientific exchange and discussions. Considerable progress has been reported throughout, e.g. on finding such stars, modeling and analyzing their spectra, understanding their evolutionary context, and studying their circumstellar nebulae. While some major questions regarding Wolf-Rayet stars still remain open 150 years after their discovery, it is clear today that these objects are not just interesting stars as such, but also keystones in the evolution of galaxies. These proceedings summarize the talks and posters presented at the Potsdam Wolf-Rayet workshop. Moreover, they also include the questions, comments, and discussions emerging after each talk, thereby giving a rare overview not only about the research, but also about the current debates and unknowns in the field. The Scientific Organizing Committee (SOC) included Alceste Bonanos (Athens), Paul Crowther (Sheffield), John Eldridge (Auckland), Wolf-Rainer Hamann (Potsdam, Chair), John Hillier (Pittsburgh), Claus Leitherer (Baltimore), Philip Massey (Flagstaff), George Meynet (Geneva), Tony Moffat (Montreal), Nicole St-Louis (Montreal), and Dany Vanbeveren (Brussels).

  18. Compact Star Time Scales

    NASA Astrophysics Data System (ADS)

    Swank, J. H.

    1996-12-01

    A major goal of RXTE is to investigate the fastest timing signals from compact stars, especially neutron stars and black holes. Signals have now been found from many (at least nine) low mass X-ray binaries containing neutron stars in the frequency range (100-1200 Hz) expected for the rotation period of the neutron star after being spun up by accretion over a long period. The kilohertz frequency domain for these sources is simpler than the domain of oscillations below about 50 Hz in that a few isolated features can dominate over white noise. However there are three main features to consider (not all present at the same time) and at least two are quasiperiodic with varying widths and frequencies. Several models are pitting their predictions against the behavior of these features, but the bursters, especially, appear to be revealing the neutron stars's spin. It is consistent with our beliefs that no black hole candidate has shown the same complex of signals, although at least one QPO frequency of a few hundred Hz could be expected in black hole candidates by analogy to the 67 Hz observed from GRS 1915+105. The observations also provide critical tests of the interpretions of the lower frequency (5-50 Hz) QPO and the variable noise seen in both low magnetic field neutron stars and black hole candidates. The kilohertz features have not been seen from the accreting pulsars with relatively high magnetic fields, but high luminosity pulsars (such as last year's transient, GRO J1744-28) reveal signatures of the dynamic interaction between the accretion flow, the magnetic field, and perhaps the neutron star surface in addition to their coherent pulsations.

  19. Life Cycle of Stars

    NASA Technical Reports Server (NTRS)

    1999-01-01

    In this stunning picture of the giant galactic nebula NGC 3603, the crisp resolution of NASA's Hubble Space Telescope captures various stages of the life cycle of stars in one single view. To the upper left of center is the evolved blue supergiant called Sher 25. The star has a unique circumstellar ring of glowing gas that is a galactic twin to the famous ring around the supernova 1987A. The grayish-bluish color of the ring and the bipolar outflows (blobs to the upper right and lower left of the star) indicates the presence of processed (chemically enriched) material. Near the center of the view is a so-called starburst cluster dominated by young, hot Wolf-Rayet stars and early O-type stars. A torrent of ionizing radiation and fast stellar winds from these massive stars has blown a large cavity around the cluster. The most spectacular evidence for the interaction of ionizing radiation with cold molecular-hydrogen cloud material are the giant gaseous pillars to the right of the cluster. These pillars are sculptured by the same physical processes as the famous pillars Hubble photographed in the M16 Eagle Nebula. Dark clouds at the upper right are so-called Bok globules, which are probably in an earlier stage of star formation. To the lower left of the cluster are two compact, tadpole-shaped emission nebulae. Similar structures were found by Hubble in Orion, and have been interpreted as gas and dust evaporation from possibly protoplanetary disks (proplyds). This true-color picture was taken on March 5, 1999 with the Wide Field Planetary Camera 2.

  20. Threshold Concepts and Student Engagement: Revisiting Pedagogical Content Knowledge

    ERIC Educational Resources Information Center

    Zepke, Nick

    2013-01-01

    This article revisits the notion that to facilitate quality learning requires teachers in higher education to have pedagogical content knowledge. It constructs pedagogical content knowledge as a teaching and learning space that brings content and pedagogy together. On the content knowledge side, it suggests that threshold concepts, akin to a…

  1. Magnetic Braking Revisited: Activities for the Undergraduate Laboratory

    ERIC Educational Resources Information Center

    Ireson, Gren; Twidle, John

    2008-01-01

    This paper revisits the demonstration of Lenz by dropping magnets down a non-magnetic tube. Recent publications are reviewed and ideas for undergraduate laboratory investigations are suggested. Finally, an example of matching theory to observation is presented. (Contains 4 tables, 5 figures and 3 footnotes.)

  2. Revisiting Jack Goody to Rethink Determinisms in Literacy Studies

    ERIC Educational Resources Information Center

    Collin, Ross

    2013-01-01

    This article revisits Goody's arguments about literacy's influence on social arrangements, culture, cognition, economics, and other domains of existence. Whereas some of his arguments tend toward technological determinism (i.e., literacy causes change in the world), other of his arguments construe literacy as a force that shapes and is shaped by…

  3. Revisiting the Role of Communication in Adolescent Intimate Partner Violence

    ERIC Educational Resources Information Center

    Messinger, Adam M.; Rickert, Vaughn I.; Fry, Deborah A.; Lessel, Harriet; Davidson, Leslie L.

    2012-01-01

    A growing literature suggests that communication strategies can promote or inhibit intimate partner violence (IPV). Research on communication is still needed on a group ripe for early IPV intervention: high school-aged adolescents. This article revisits our previous analyses of young female reproductive clinic patients (Messinger, Davidson, &…

  4. College-Level Sheltered Instruction: Revisiting the Issue of Effectiveness

    ERIC Educational Resources Information Center

    Knoblock, Natalia; Youngquist, Judy

    2016-01-01

    Finding an effective instruction mode for ESL students in the US educational system has not been an easy task. The country's secondary and tertiary institutions continue to struggle to meet the needs of their large non-native student populations. The article revisits the debate whether sheltered instruction is an effective model to follow. In our…

  5. Revisiting Constructivist Teaching Methods in Ontario Colleges Preparing for Accreditation

    ERIC Educational Resources Information Center

    Schultz, Rachel A.

    2015-01-01

    At the time of writing, the first community colleges in Ontario were preparing for transition to an accreditation model from an audit system. This paper revisits constructivist literature, arguing that a more pragmatic definition of constructivism effectively blends positivist and interactionist philosophies to achieve both student centred…

  6. Educational Administration and the Management of Knowledge: 1980 Revisited

    ERIC Educational Resources Information Center

    Bates, Richard

    2013-01-01

    This paper revisits the thesis of a 1980 paper that suggested a new approach to educational administration based upon the New Sociology of Education. In particular it updates answers to the six key questions asked by that paper: what counts as knowledge; how is what counts as knowledge organised; how is what counts as knowledge transmitted; how is…

  7. Closing Achievement Gaps: Revisiting Benjamin S. Bloom's "Learning for Mastery"

    ERIC Educational Resources Information Center

    Guskey, Thomas R.

    2007-01-01

    The problem of achievement gaps among different subgroups of students has been evident in education for many years. This manuscript revisits the work of renowned educator Benjamin S. Bloom, who saw reducing gaps in the achievement of various groups of students as a simple problem of reducing variation in student learning outcomes. Bloom observed…

  8. Moral Judgment Development across Cultures: Revisiting Kohlberg's Universality Claims

    ERIC Educational Resources Information Center

    Gibbs, John C.; Basinger, Karen S.; Grime, Rebecca L.; Snarey, John R.

    2007-01-01

    This article revisits Kohlberg's cognitive developmental claims that stages of moral judgment, facilitative processes of social perspective-taking, and moral values are commonly identifiable across cultures. Snarey [Snarey, J. (1985). "The cross-cultural universality of social-moral development: A critical review of Kohlbergian research."…

  9. Literary Origins of the Term "School Psychologist" Revisited

    ERIC Educational Resources Information Center

    Fagan, Thomas K.

    2005-01-01

    Previous research on the literary origins of the term "school psychologist" is revisited, and conclusions are revised in light of new evidence. It appears that the origin of the term in the American literature occurred as early as 1898 in an article by Hugo Munsterberg, predating the usage by Wilhelm Stern in 1911. The early references to the…

  10. Girl Number 20 Revisited: Feminist Literacies in New Hard Times

    ERIC Educational Resources Information Center

    Gonick, Marnina

    2007-01-01

    This paper revisits the question of "voice" in the context of neo-liberal social and educational reform. "Voice" has been one of the key concepts of feminist and critical pedagogies in the theory and practice of producing social transformation. I argue in this paper, that the political effectiveness of this concept needs to be…

  11. Facilitating Grade Acceleration: Revisiting the Wisdom of John Feldhusen

    ERIC Educational Resources Information Center

    Culross, Rita R.; Jolly, Jennifer L.; Winkler, Daniel

    2013-01-01

    This article revisits the 1986 Feldhusen, Proctor, and Black recommendations on grade skipping. These recommendations originally appeared as 12 guidelines. In this article, the guidelines are grouped into three general categories: how to screen accelerant candidates, how to engage with the adults in the acceleration process (e.g., teachers,…

  12. Bohr’s ‘Light and Life’ revisited

    NASA Astrophysics Data System (ADS)

    Nussenzveig, H. M.

    2015-11-01

    I revisit Niels Bohr’s famous 1932 ‘Light and Life’ lecture, confronting it with current knowledge. Topics covered include: life origin and evolution, quantum mechanics and life, brain and mind, consciousness and free will, and light as a tool for biology, with special emphasis on optical tweezers and their contributions to biophysics. Specialized knowledge of biology is not assumed.

  13. Antidote for Zero Tolerance: Revisiting a "Reclaiming" School.

    ERIC Educational Resources Information Center

    Farner, Conrad D.

    2002-01-01

    Reports on a revisit to the Frank Lloyd Wright Middle School, which implemented strategies to deal with disciplinary problems. The school continues to progress towards creating the type of reclaiming environment necessary to ensure the needs of all students. Strategies used include alternatives to zero tolerance policy; smaller teams of students;…

  14. The Importance of Being a Complement: CED Effects Revisited

    ERIC Educational Resources Information Center

    Jurka, Johannes

    2010-01-01

    This dissertation revisits subject island effects (Ross 1967, Chomsky 1973) cross-linguistically. Controlled acceptability judgment studies in German, English, Japanese and Serbian show that extraction out of specifiers is consistently degraded compared to extraction out of complements, indicating that the Condition on Extraction domains (CED,…

  15. Revisiting the Trust Effect in Urban Elementary Schools

    ERIC Educational Resources Information Center

    Adams, Curt M.; Forsyth, Patrick B.

    2013-01-01

    More than a decade after Goddard, Tschannen-Moran, and Hoy (2001) found that collective faculty trust in clients predicts student achievement in urban elementary schools, we sought to identify a plausible link for this relationship. Our purpose in revisiting the trust effect was twofold: (1) to test the main effect of collective faculty trust on…

  16. Apollo Project- star projector

    NASA Technical Reports Server (NTRS)

    1964-01-01

    The specially designed star projector used in the Projection Planetarium. From A.W. Vogeley, 'Piloted Space-Flight Simulation at Langley Research Center,' Paper presented at the American Society of Mechanical Engineers, 1966 Winter Meeting, New York, NY, November 27 - December 1, 1966. 'Another approach to the scene-generation problem is the point-light-source projection technique. This technique has been used in the Langley Projection Planetarium,... to study Apollo launch-abort problems. This method was very effective in providing the required horizon-to-horizon view of Florida as seen from about 100,000 feet.' 'This projector operates on a concept developed by Spitz. It consists of a point-light source reflecting off a centrally located highly reflective sphere which directs the light outward through the many holes representing the stars. The size of the holes is varied to vary star magnitude. The star images are brought into focus on the inside of the planetarium by lenses glued to the surface of the projector and the diameter of the projection sphere govern the focal length required for these lenses. Although this type of projector does not have the precision required for the study of navigation problems it is very adequate for pilot control problems such as rendezvous where the star field is primarily used as an attitude reference.'

  17. Condensate dark matter stars

    SciTech Connect

    Li, X.Y.; Harko, T.; Cheng, K.S. E-mail: harko@hkucc.hku.hk

    2012-06-01

    We investigate the structure and stability properties of compact astrophysical objects that may be formed from the Bose-Einstein condensation of dark matter. Once the critical temperature of a boson gas is less than the critical temperature, a Bose-Einstein Condensation process can always take place during the cosmic history of the universe. Therefore we model the dark matter inside the star as a Bose-Einstein condensate. In the condensate dark matter star model, the dark matter equation of state can be described by a polytropic equation of state, with polytropic index equal to one. We derive the basic general relativistic equations describing the equilibrium structure of the condensate dark matter star with spherically symmetric static geometry. The structure equations of the condensate dark matter stars are studied numerically. The critical mass and radius of the dark matter star are given by M{sub crit} ≈ 2(l{sub a}/1fm){sup 1/2}(m{sub χ}/1 GeV){sup −3/2}M{sub s}un and R{sub crit} ≈ 1.1 × 10{sup 6}(l{sub a}/1 fm){sup 1/2}(m{sub χ}/1 GeV){sup −3/2} cm respectively, where l{sub a} and m{sub χ} are the scattering length and the mass of dark matter particle, respectively.

  18. Nursery of New Stars

    NASA Technical Reports Server (NTRS)

    1995-01-01

    This is a Hubble Space Telescope image (right) of a vast nebula called NGC 604, which lies in the neighboring spiral galaxy M33, located 2.7 million light-years away in the constellation Triangulum. This is a site where new stars are being born in a spiral arm of the galaxy. Though such nebulae are common in galaxies, this one is particularly large, nearly 1,500 light-years across. The nebula is so vast it is easily seen in ground-based telescopic images (left). At the heart of NGC 604 are over 200 hot stars, much more massive than our Sun (15 to 60 solar masses). They heat the gaseous walls of the nebula making the gas fluoresce. Their light also highlights the nebula's three-dimensional shape, like a lantern in a cavern. By studying the physical structure of a giant nebula, astronomers may determine how clusters of massive stars affect the evolution of the interstellar medium of the galaxy. The nebula also yields clues to its star formation history and will improve understanding of the starburst process when a galaxy undergoes a 'firestorm' of star formation. The image was taken on January 17, 1995 with Hubble's Wide Field and Planetary Camera 2. Separate exposures were taken in different colors of light to study the physical properties of the hot gas (17,000 degrees Fahrenheit, 10,000 degrees Kelvin

  19. Circulation of Stars

    NASA Astrophysics Data System (ADS)

    Boitani, P.

    2016-01-01

    Since the dawn of man, contemplation of the stars has been a primary impulse in human beings, who proliferated their knowledge of the stars all over the world. Aristotle sees this as the product of primeval and perennial “wonder” which gives rise to what we call science, philosophy, and poetry. Astronomy, astrology, and star art (painting, architecture, literature, and music) go hand in hand through millennia in all cultures of the planet (and all use catasterisms to explain certain phenomena). Some of these developments are independent of each other, i.e., they take place in one culture independently of others. Some, on the other hand, are the product of the “circulation of stars.” There are two ways of looking at this. One seeks out forms, the other concentrates on the passing of specific lore from one area to another through time. The former relies on archetypes (for instance, with catasterism), the latter constitutes a historical process. In this paper I present some of the surprising ways in which the circulation of stars has occurred—from East to West, from East to the Far East, and from West to East, at times simultaneously.

  20. Star Caught Smoking

    NASA Astrophysics Data System (ADS)

    2007-08-01

    VLTI Snapshots Dusty Puff Around Variable Star Using ESO's Very Large Telescope Interferometer, astronomers from France and Brazil have detected a huge cloud of dust around a star. This observation is further evidence for the theory that such stellar puffs are the cause of the repeated extreme dimming of the star. ESO PR Photo 34a/07 ESO PR Photo 34a/07 Dust Cloud in a R CrB Star (Artist's Impression) R Coronae Borealis stars are supergiants exhibiting erratic variability. Named after the first star that showed such behaviour [1], they are more than 50 times larger than our Sun. R Coronae Borealis stars can see their apparent brightness unpredictably decline to a thousandth of their nominal value within a few weeks, with the return to normal light levels being much slower. It has been accepted for decades that such fading could be due to obscuration of the stellar surface by newly formed dusty clouds. This 'Dust Puff Theory' suggests that mass is lost from the R Coronae Borealis (or R CrB for short) star and then moves away until the temperature is low enough for carbon dust to form. If the newly formed dust cloud is located along our line-of-sight, it eclipses the star. As the dust is blown away by the star's strong light, the 'curtain' vanishes and the star reappears. RY Sagittarii is the brightest member in the southern hemisphere of this family of weird stars. Located about 6,000 light-years away towards the constellation of Sagittarius (The Archer), its peculiar nature was discovered in 1895 by famous Dutch astronomer Jacobus Cornelius Kapteyn. In 2004, near-infrared adaptive optics observations made with NACO on ESO's Very Large Telescope allowed astronomers Patrick de Laverny and Djamel Mékarnia to clearly detect the presence of clouds around RY Sagittarii. This was the first direct confirmation of the standard scenario explaining the light variations of R CrB stars by the presence of heterogeneities in their envelope surrounding the star. ESO PR Photo 32e

  1. Origin of Neutron Stars

    NASA Astrophysics Data System (ADS)

    Brecher, K.

    1999-12-01

    The origin of the concept of neutron stars can be traced to two brief, incredibly insightful publications. Work on the earlier paper by Lev Landau (Phys. Z. Sowjetunion, 1, 285, 1932) actually predated the discovery of neutrons. Nonetheless, Landau arrived at the notion of a collapsed star with the density of a nucleus (really a "nucleus star") and demonstrated (at about the same time as, and independent of, Chandrasekhar) that there is an upper mass limit for dense stellar objects of about 1.5 solar masses. Perhaps even more remarkable is the abstract of a talk presented at the December 1933 meeting of the American Physical Society published by Walter Baade and Fritz Zwicky in 1934 (Phys. Rev. 45, 138). It followed the discovery of the neutron by just over a year. Their report, which was about the same length as the present abstract: (1) invented the concept and word supernova; (2) suggested that cosmic rays are produced by supernovae; and (3) in the authors own words, proposed "with all reserve ... the view that supernovae represent the transitions from ordinary stars to neutron stars (italics), which in their final stages consist of extremely closely packed neutrons." The abstract by Baade and Zwicky probably contains the highest density of new, important (and correct) ideas in high energy astrophysics ever published in a single paper. In this talk, we will discuss some of the facts and myths surrounding these two publications.

  2. Characterizing Retired A Stars

    NASA Astrophysics Data System (ADS)

    Ghezzi, Luan; Johnson, John

    2015-08-01

    A complete understanding of the formation and evolution of planetary systems depends on the precise characterization of the planets and their host stars. The stellar mass is particularly important because it might influence the planet occurrence and it is used to constrain the planetary masses, thus providing information about the systems' architectures. Single FGK stars on the main sequence usually have precise masses estimated from evolutionary tracks, but the results of this method for subgiants and giants have recently been called into question. In this work, we describe the ongoing efforts to precisely constrain the masses of evolved stars using benchmark subgiants and giants from the literature as well as the sample of retired A stars observed by the California Planet Search survey. Different input atmospheric parameters (from excitation and ionization equilibria, spectral synthesis, interferometry and photometry) and methods (evolutionary tracks, asteroseismology and lithium abundances) are used to critically evaluate the stellar masses and its uncertainties. Preliminary results are discussed and suggest that current mass determinations for evolved stars do not present any significant systematic errors.

  3. Memory for Star Trek: the role of prior knowledge in recognition revisited.

    PubMed

    Long, Debra L; Prat, Chantel S

    2002-11-01

    Prior studies have found robust knowledge effects on recall of text ideas but have seldom found comparable effects on recognition. This inconsistency was examined in light of recent research on the component processes that underlie recognition memory. Using the remember/know paradigm, the authors found that experts made more remember judgments than novices, but only in response to text ideas relevant to their domain of expertise. Using the process-dissociation procedure, the authors found knowledge effects on recollection estimates, but not on familiarity estimates. The authors contend that knowledge effects have been difficult to detect in recognition because knowledge primarily affects recollection, whereas familiarity gives rise to good performance even among novices.

  4. Binary Star Orbits. 3. Revisiting the Remarkable Case of Tweedledum and Tweedledee

    DTIC Science & Technology

    2010-06-11

    Observation Date 0.00 0.05 0.10 0.15 0.20 S ep ar at io n D iff er en ce FIN 332 Aa,Ab Unresolved Aa,Ab bB,aBdevlosernU bB,aB 233 NIF 1960 1970 1980 1990...2000 2010 Observation Date 0 50 100 150 200 P os iti on A ng le D iff er en ce FIN 332 Aa,Ab Unresolved Aa,Ab bB,aBdevlosernU bB,aB 233 NIF Figure

  5. Carbon-enhanced metal-poor star frequencies in the galaxy: corrections for the effect of evolutionary status on carbon abundances

    SciTech Connect

    Placco, Vinicius M.; Frebel, Anna; Beers, Timothy C.; Stancliffe, Richard J.

    2014-12-10

    We revisit the observed frequencies of carbon-enhanced metal-poor (CEMP) stars as a function of the metallicity in the Galaxy, using data from the literature with available high-resolution spectroscopy. Our analysis excludes stars exhibiting clear overabundances of neutron-capture elements and takes into account the expected depletion of surface carbon abundance that occurs due to CN processing on the upper red giant branch. This allows for the recovery of the initial carbon abundance of these stars, and thus for an accurate assessment of the frequencies of carbon-enhanced stars. The correction procedure we develop is based on stellar-evolution models and depends on the surface gravity, log g, of a given star. Our analysis indicates that for stars with [Fe/H] ≤–2.0, 20% exhibit [C/Fe] ≥+0.7. This fraction increases to 43% for [Fe/H] ≤–3.0 and 81% for [Fe/H] ≤–4.0, which is higher than have been previously inferred without taking the carbon abundance correction into account. These CEMP star frequencies provide important inputs for Galactic and stellar chemical evolution models, as they constrain the evolution of carbon at early times and the possible formation channels for the CEMP-no stars. We also have developed a public online tool with which carbon corrections using our procedure can be easily obtained.

  6. The lithium isotopic ratio in very metal-poor stars

    NASA Astrophysics Data System (ADS)

    Lind, K.; Melendez, J.; Asplund, M.; Collet, R.; Magic, Z.

    2013-06-01

    Context. Un-evolved, very metal-poor stars are the most important tracers of the cosmic abundance of lithium in the early universe. Combining the standard Big Bang nucleosynthesis model with Galactic production through cosmic ray spallation, these stars at [Fe / H] < - 2 are expected to show an undetectably small 6Li / 7Li isotopic signature. Evidence to the contrary may necessitate an additional pre-galactic production source or a revision of the standard model of Big Bang nucleosynthesis. It would also cast doubts on Li depletion from stellar atmospheres as an explanation for the factor 3-5 discrepancy between the predicted primordial 7Li from the Big Bang and the observed value in metal-poor dwarf/turn-off stars. Aims: We revisit the isotopic analysis of four halo stars, two with claimed 6Li-detections in the literature, to investigate the influence of improved model atmospheres and line formation treatment. Methods: For the first time, a combined 3D, non-local thermodynamic equilibrium (NLTE) modelling technique for Li, Na, and Ca lines is utilised to constrain the intrinsic line-broadening and to determine the Li isotopic ratio. We discuss the influence of 3D NLTE effects on line profile shapes and assess the realism of our modelling using the Ca excitation and ionisation balance. Results: By accounting for NLTE line formation in realistic 3D hydrodynamical model atmospheres, we can model the Li resonance line and other neutral lines with a consistency that is superior to LTE, with no need for additional line asymmetry caused by the presence of 6Li. Contrary to the results from 1D and 3D LTE modelling, no star in our sample has a significant (2σ) detection of the lighter isotope in NLTE. Over a large parameter space, NLTE modelling systematically reduces the best-fit Li isotopic ratios by up to five percentage points. As a bi-product, we also present the first ever 3D NLTE Ca and Na abundances of halo stars, which reveal significant departures from LTE

  7. Heavy Metal Stars

    NASA Astrophysics Data System (ADS)

    2001-08-01

    La Silla Telescope Detects Lots of Lead in Three Distant Binaries Summary Very high abundances of the heavy element Lead have been discovered in three distant stars in the Milky Way Galaxy . This finding strongly supports the long-held view that roughly half of the stable elements heavier than Iron are produced in common stars during a phase towards the end of their life when they burn their Helium - the other half results from supernova explosions. All the Lead contained in each of the three stars weighs about as much as our Moon. The observations show that these "Lead stars" - all members of binary stellar systems - have been more enriched with Lead than with any other chemical element heavier than Iron. This new result is in excellent agreement with predictions by current stellar models about the build-up of heavy elements in stellar interiors. The new observations are reported by a team of Belgian and French astronomers [1] who used the Coude Echelle Spectrometer on the ESO 3.6-m telescope at the La Silla Observatory (Chile). PR Photo 26a/01 : A photo of HD 196944 , one of the "Lead stars". PR Photo 26b/01 : A CES spectrum of HD 196944 . The build-up of heavy elements Astronomers and physicists denote the build-up of heavier elements from lighter ones as " nucleosynthesis ". Only the very lightest elements (Hydrogen, Helium and Lithium [2]) were created at the time of the Big Bang and therefore present in the early universe. All the other heavier elements we now see around us were produced at a later time by nucleosynthesis inside stars. In those "element factories", nuclei of the lighter elements are smashed together whereby they become the nuclei of heavier ones - this process is known as nuclear fusion . In our Sun and similar stars, Hydrogen is being fused into Helium. At some stage, Helium is fused into Carbon, then Oxygen, etc. The fusion process requires positively charged nuclei to move very close to each other before they can unite. But with increasing

  8. GRACE star camera noise

    NASA Astrophysics Data System (ADS)

    Harvey, Nate

    2016-08-01

    Extending results from previous work by Bandikova et al. (2012) and Inacio et al. (2015), this paper analyzes Gravity Recovery and Climate Experiment (GRACE) star camera attitude measurement noise by processing inter-camera quaternions from 2003 to 2015. We describe a correction to star camera data, which will eliminate a several-arcsec twice-per-rev error with daily modulation, currently visible in the auto-covariance function of the inter-camera quaternion, from future GRACE Level-1B product releases. We also present evidence supporting the argument that thermal conditions/settings affect long-term inter-camera attitude biases by at least tens-of-arcsecs, and that several-to-tens-of-arcsecs per-rev star camera errors depend largely on field-of-view.

  9. General Relativity&Compact Stars

    SciTech Connect

    Glendenning, Norman K.

    2005-08-16

    Compact stars--broadly grouped as neutron stars and white dwarfs--are the ashes of luminous stars. One or the other is the fate that awaits the cores of most stars after a lifetime of tens to thousands of millions of years. Whichever of these objects is formed at the end of the life of a particular luminous star, the compact object will live in many respects unchanged from the state in which it was formed. Neutron stars themselves can take several forms--hyperon, hybrid, or strange quark star. Likewise white dwarfs take different forms though only in the dominant nuclear species. A black hole is probably the fate of the most massive stars, an inaccessible region of spacetime into which the entire star, ashes and all, falls at the end of the luminous phase. Neutron stars are the smallest, densest stars known. Like all stars, neutron stars rotate--some as many as a few hundred times a second. A star rotating at such a rate will experience an enormous centrifugal force that must be balanced by gravity or else it will be ripped apart. The balance of the two forces informs us of the lower limit on the stellar density. Neutron stars are 10{sup 14} times denser than Earth. Some neutron stars are in binary orbit with a companion. Application of orbital mechanics allows an assessment of masses in some cases. The mass of a neutron star is typically 1.5 solar masses. They can therefore infer their radii: about ten kilometers. Into such a small object, the entire mass of our sun and more, is compressed.

  10. High Resolution Rapid Revisits Insar Monitoring of Surface Deformation

    NASA Astrophysics Data System (ADS)

    Singhroy, V.; Li, J.; Charbonneau, F.

    2014-12-01

    Monitoring surface deformation on strategic energy and transportation corridors requires high resolution spatial and temporal InSAR images for mitigation and safety purposes. High resolution air photos, lidar and other satellite images are very useful in areas where the landslides can be fatal. Recently, radar interferometry (InSAR) techniques using more rapid revisit images from several radar satellites are increasingly being used in active deformation monitoring. The Canadian RADARSAT Constellation (RCM) is a three-satellite mission that will provide rapid revisits of four days interferometric (InSAR) capabilities that will be very useful for complex deformation monitoring. For instance, the monitoring of surface deformation due to permafrost activity, complex rock slide motion and steam assisted oil extraction will benefit from this new rapid revisit capability. This paper provide examples of how the high resolution (1-3 m) rapid revisit InSAR capabilities will improve our monitoring of surface deformation and provide insights in understanding triggering mechanisms. We analysed over a hundred high resolution InSAR images over a two year period on three geologically different sites with various configurations of topography, geomorphology, and geology conditions. We show from our analysis that the more frequent InSAR acquisitions are providing more information in understanding the rates of movement and failure process of permafrost triggered retrogressive thaw flows; the complex motion of an asymmetrical wedge failure of an active rock slide and the identification of over pressure zones related to oil extraction using steam injection. Keywords: High resolution, InSAR, rapid revisits, triggering mechanisms, oil extraction.

  11. Pulsating Star Mystery Solved

    NASA Astrophysics Data System (ADS)

    2010-11-01

    By discovering the first double star where a pulsating Cepheid variable and another star pass in front of one another, an international team of astronomers has solved a decades-old mystery. The rare alignment of the orbits of the two stars in the double star system has allowed a measurement of the Cepheid mass with unprecedented accuracy. Up to now astronomers had two incompatible theoretical predictions of Cepheid masses. The new result shows that the prediction from stellar pulsation theory is spot on, while the prediction from stellar evolution theory is at odds with the new observations. The new results, from a team led by Grzegorz Pietrzyński (Universidad de Concepción, Chile, Obserwatorium Astronomiczne Uniwersytetu Warszawskiego, Poland), appear in the 25 November 2010 edition of the journal Nature. Grzegorz Pietrzyński introduces this remarkable result: "By using the HARPS instrument on the 3.6-metre telescope at ESO's La Silla Observatory in Chile, along with other telescopes, we have measured the mass of a Cepheid with an accuracy far greater than any earlier estimates. This new result allows us to immediately see which of the two competing theories predicting the masses of Cepheids is correct." Classical Cepheid Variables, usually called just Cepheids, are unstable stars that are larger and much brighter than the Sun [1]. They expand and contract in a regular way, taking anything from a few days to months to complete the cycle. The time taken to brighten and grow fainter again is longer for stars that are more luminous and shorter for the dimmer ones. This remarkably precise relationship makes the study of Cepheids one of the most effective ways to measure the distances to nearby galaxies and from there to map out the scale of the whole Universe [2]. Unfortunately, despite their importance, Cepheids are not fully understood. Predictions of their masses derived from the theory of pulsating stars are 20-30% less than predictions from the theory of the

  12. Really Hot Stars

    NASA Astrophysics Data System (ADS)

    2003-04-01

    Spectacular VLT Photos Unveil Mysterious Nebulae Summary Quite a few of the most beautiful objects in the Universe are still shrouded in mystery. Even though most of the nebulae of gas and dust in our vicinity are now rather well understood, there are some which continue to puzzle astronomers. This is the case of a small number of unusual nebulae that appear to be the subject of strong heating - in astronomical terminology, they present an amazingly "high degree of excitation". This is because they contain significant amounts of ions, i.e., atoms that have lost one or more of their electrons. Depending on the atoms involved and the number of electrons lost, this process bears witness to the strength of the radiation or to the impact of energetic particles. But what are the sources of that excitation? Could it be energetic stars or perhaps some kind of exotic objects inside these nebulae? How do these peculiar objects fit into the current picture of universal evolution? New observations of a number of such unusual nebulae have recently been obtained with the Very Large Telescope (VLT) at the ESO Paranal Observatory (Chile). In a dedicated search for the origin of their individual characteristics, a team of astronomers - mostly from the Institute of Astrophysics & Geophysics in Liège (Belgium) [1] - have secured the first detailed, highly revealing images of four highly ionized nebulae in the Magellanic Clouds, two small satellite galaxies of our home galaxy, the Milky Way, only a few hundred thousand light-years away. In three nebulae, they succeeded in identifying the sources of energetic radiation and to eludicate their exceptional properties: some of the hottest, most massive stars ever seen, some of which are double. With masses of more than 20 times that of the Sun and surface temperatures above 90 000 degrees, these stars are truly extreme. PR Photo 09a/03: Nebula around the hot star AB7 in the SMC. PR Photo 09b/03: Nebula near the hot Wolf-Rayet star BAT99

  13. Winds of low-metallicity OB-type stars: HST-COS spectroscopy in IC 1613

    SciTech Connect

    Garcia, Miriam; Najarro, Francisco; Herrero, Artemio; Urbaneja, Miguel Alejandro

    2014-06-10

    We present the first quantitative ultraviolet spectroscopic analysis of resolved OB stars in IC 1613. Because of its alleged very low metallicity (≲1/10 Z {sub ☉}, from H II regions), studies in this Local Group dwarf galaxy could become a significant step forward from the Small Magellanic Cloud (SMC) toward the extremely metal-poor massive stars of the early universe. We present HST-COS data covering the ∼1150-1800 Å wavelength range with resolution R ∼ 2500. We find that the targets do exhibit wind features, and these are similar in strength to SMC stars. Wind terminal velocities were derived from the observed P Cygni profiles with the Sobolev plus Exact Integration method. The v {sub ∞}-Z relationship has been revisited. The terminal velocity of IC 1613 O stars is clearly lower than Milky Way counterparts, but there is no clear difference between IC 1613 and SMC or LMC analog stars. We find no clear segregation with host galaxy in the terminal velocities of B-supergiants, nor in the v {sub ∞}/v {sub esc} ratio of the whole OB star sample in any of the studied galaxies. Finally, we present the first evidence that the Fe-abundance of IC 1613 OB stars is similar to the SMC, which is in agreement with previous results on red supergiants. With the confirmed ∼1/10 solar oxygen abundances of B-supergiants, our results indicate that IC 1613's α/Fe ratio is sub-solar.

  14. Weighing the Smallest Stars

    NASA Astrophysics Data System (ADS)

    2005-01-01

    VLT Finds Young, Very Low Mass Objects Are Twice As Heavy As Predicted Summary Thanks to the powerful new high-contrast camera installed at the Very Large Telescope, photos have been obtained of a low-mass companion very close to a star. This has allowed astronomers to measure directly the mass of a young, very low mass object for the first time. The object, more than 100 times fainter than its host star, is still 93 times as massive as Jupiter. And it appears to be almost twice as heavy as theory predicts it to be. This discovery therefore suggests that, due to errors in the models, astronomers may have overestimated the number of young "brown dwarfs" and "free floating" extrasolar planets. PR Photo 03/05: Near-infrared image of AB Doradus A and its companion (NACO SDI/VLT) A winning combination A star can be characterised by many parameters. But one is of uttermost importance: its mass. It is the mass of a star that will decide its fate. It is thus no surprise that astronomers are keen to obtain a precise measure of this parameter. This is however not an easy task, especially for the least massive ones, those at the border between stars and brown dwarf objects. Brown dwarfs, or "failed stars", are objects which are up to 75 times more massive than Jupiter, too small for major nuclear fusion processes to have ignited in its interior. To determine the mass of a star, astronomers generally look at the motion of stars in a binary system. And then apply the same method that allows determining the mass of the Earth, knowing the distance of the Moon and the time it takes for its satellite to complete one full orbit (the so-called "Kepler's Third Law"). In the same way, they have also measured the mass of the Sun by knowing the Earth-Sun distance and the time - one year - it takes our planet to make a tour around the Sun. The problem with low-mass objects is that they are very faint and will often be hidden in the glare of the brighter star they orbit, also when viewed

  15. Computational astrophysics: Pulsating stars

    NASA Astrophysics Data System (ADS)

    Davis, C. G.

    The field of computational astrophysics in pulsating star studies has grown considerably since the advent of the computer. Initially calculations were done on the IBM 704 with 32K of memory and now we use the CRAY YMP computers with considerably more memory. Our early studies were for models of pulsating stars using a 1D Lagrangian hydrodynamic code (SPEC) with radiation diffusion. The radiative transfer was treated in the equilibrium diffusion approximation and the hydrodynamics was done utilizing the approximation of artificial viscosity. The early calculations took many hours of 704 CPU time. Early in 1965 we decided to improve on the usual treatment of the radiative transfer used in our codes by utilizing the method of moments, the so-called variable Eddington approximation. In this approximation the material energy field is uncoupled from the radiation energy field and the angular dependence is introduced through the Eddington factor. A multigroup frequency dependent method may also be applied. The Eddington factor is determined by snapshots of the stars structure utilizing a y-line approximation. The full radiative transfer approximation appears necessary in order to understand the light curves for W Virginia stars and may be important for the light curves of RR Lyrae stars. A detailed radiative transfer method does not appear to be necessary for the understanding of Cepheid light curves. A recent improvement to our models for pulsating stars is in the use of an adaptive mesh scheme to resolve the sharp features in the nonlinear hydrodynamic structure. From these improved structures, better analysis of the radius, velocity, and light curves could be obtained.

  16. American Urban Star Fest

    NASA Astrophysics Data System (ADS)

    Pazmino, John

    2003-12-01

    Over the last couple of decades New York City implemented, and continues to carry out, several schemes of eradicating luminous graffiti. One result has been the gradual recovery of the natural night sky. By 1994 the normal clear sky transparency over Manhattan deepened to fourth magnitude and has been slowly creeping deeper, until in 2002 it is at magnitude 4 to 4.5. In the spring of 1995, during some lazing on a Manhattan rooftop under a sky full of stars, several New York astronomers hatched the idea of letting the whole people celebrate the renewed starry sky. In due course they, through the Amateur Astronomers Association, engaged the New York City Parks Department and the Urban Park Rangers in an evening of quiet picnicking to enjoy the stars in their natural sky. Thus the Urban Star Fest was born. The event thrilled about 3,000 visitors in Central Park's Sheep Meadow on Saturday 30 September 1995. This year's Fest, the eighth in the series demonstrated the City's upper skyline of stars on Saturday 5 October 2002 to about 2,200 enthused visitors. Although the Fest is always noted as cancelable for inclement weather, so far, it has convened every year, with attendance ranging from 4,000 down to a mere 1,000, this latter being under the smoke plume of the World Trade Center in 2001. Despite this swing in attendance, the American Urban Star Fest is America's largest regularly scheduled public astronomy event. Of course, special occasions, like comets or eclipses, can and do attract far larger interest both in the city and elsewhere. The presentation shows the setup and program of the American Urban Star Fest, to illustrate how the general public can actively become aware of the night sky and see for themselves the result of their very own efforts at removing light pollution--and note where improvement is yet to come.

  17. Morphodynamics of star dunes

    NASA Astrophysics Data System (ADS)

    Zhang, D.; Narteau, C.; Rozier, O.; Courrech du Pont, S.

    2012-04-01

    Star dunes are among the biggest and the most impressive dunes in Earth sand seas. Nonetheless, they remain poorly studied, probably because of their apparent complexity. They are massive pyramidal dunes with interlaced arms whose slip faces are oriented in various directions. Being large, they can integrate wind properties over a wide range of time scales. Thus, they are observed for wind regimes with multiple directions, and may result from the amalgamation of dunes or from the development of arms on a well-established dune pattern. In both cases, the roles of wind directional variability and secondary flow have been emphasized but not precisely quantified. Here, we report simulations where the star dune shape results from a a combination of longitudinal dunes, which form the star dune arms. These arms may radiate and so interact with the other dunes in the field. This mass exchange, controlled by the morphodynamics of star dunes arms, must play an important role in the large-scale arrangement of star dunes networks. We first demonstrate that star dune arms orientation maximizes the flux in the direction of crests. This is opposed to the usually admit dunes orientation, which maximizes the sediment transport perpendicular to the crest. Indeed, depending on sand availability, dunes development results from the growth of a wave on a sand bed or from a net transport of sediment, which grows and extends an isolated longitudinal dune over a non-erodible soil. These two different mechanisms lead to two different modes of crests orientation. Then, we show that the propagating arms reach a stationary state characterized by constant width, height and growth rate. These are controlled by the frequency at which the wind changes direction. Arm width and height increase, whereas the propagation speed decreases with a decreasing frequency. These morphodynamics properties are helpful to assess from pattern observation the variability of wind directionality over several time

  18. Orion revisited. III. The Orion Belt population

    NASA Astrophysics Data System (ADS)

    Kubiak, K.; Alves, J.; Bouy, H.; Sarro, L. M.; Ascenso, J.; Burkert, A.; Forbrich, J.; Großschedl, J.; Hacar, A.; Hasenberger, B.; Lombardi, M.; Meingast, S.; Köhler, R.; Teixeira, P. S.

    2017-02-01

    Aims: This paper continues our study of the foreground population to the Orion molecular clouds. The goal is to characterize the foreground population north of NGC 1981 and to investigate the star formation history in the large Orion star-forming region. We focus on a region covering about 25 square degrees, centered on the ɛ Orionis supergiant (HD 37128, B0 Ia) and covering the Orion Belt asterism. Methods: We used a combination of optical (SDSS) and near-infrared (2MASS) data, informed by X-ray (XMM-Newton) and mid-infrared (WISE) data, to construct a suite of color-color and color-magnitude diagrams for all available sources. We then applied a new statistical multiband technique to isolate a previously unknown stellar population in this region. Results: We identify a rich and well-defined stellar population in the surveyed region that has about 2000 objects that are mostly M stars. We infer the age for this new population to be at least 5 Myr and likely 10 Myr and estimate a total of about 2500 members, assuming a normal IMF. This new population, which we call the Orion Belt population, is essentially extinction-free, disk-free, and its spatial distribution is roughly centered near ɛ Ori, although substructure is clearly present. Conclusions: The Orion Belt population is likely the low-mass counterpart to the Ori OB Ib subgroup. Although our results do not rule out Blaauw's sequential star formation scenario for Orion, we argue that the recently proposed blue streams scenario provides a better framework on which one can explain the Orion star formation region as a whole. We speculate that the Orion Belt population could represent the evolved counterpart of an Orion nebula-like cluster. The catalog (Full Table A.1) is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/598/A124

  19. The spectroscopic orbit of Capella revisited

    NASA Astrophysics Data System (ADS)

    Weber, M.; Strassmeier, K. G.

    2011-07-01

    Context. Capella is among the few binary stars with two evolved giant components. The hotter component is a chromospherically active star within the Hertzsprung gap, while the cooler star is possibly helium-core burning. Aims: The known inclination of the orbital plane from astrometry in combination with precise radial velocities will allow very accurate masses to be determined for the individual Capella stars. This will constrain their evolutionary stage and possibly the role of the active star's magnetic field on the dynamical evolution of the binary system. Methods: We obtained a total of 438 high-resolution échelle spectra during the years 2007-2010 and used the measured velocities to recompute the orbital elements. Our double-lined orbital solution yields average residuals of 64 m s-1 for the cool component and 297 m s-1 for the more rapidly rotating hotter component. Results: The semi-amplitude of the cool component is smaller by 0.045 km s-1 than the orbit determination of Torres et al. from data taken during 1996-1999 but more precise by a factor of 5.5, while for the hotter component it is larger by 0.580 km s-1 and more precise by a factor of 3.6. This corresponds to masses of 2.573 ± 0.009 M⊙ and 2.488 ± 0.008 M⊙ for the cool and hot component, respectively. Their relative errors of 0.34% and 0.30% are about half of the values given in Torres et al. for a combined literature-data solution but with absolute values different by 4% and 2% for the two components, respectively. The mass ratio of the system is therefore q = MA/MB = 0.9673 ± 0.0020. Conclusions: Our orbit is the most precise and also likely to be the most accurate ever obtained for Capella. Based on data obtained with the STELLA robotic telescope in Tenerife, an AIP facility jointly operated by AIP and IAC.Full Table 1 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/531/A89

  20. A Star on Earth

    SciTech Connect

    Prager, Stewart; Zwicker, Andrew; Hammet, Greg; Tresemer, Kelsey; Diallo, Ahmed

    2014-03-05

    At the Energy Department's Princeton Plasma Physics Lab, scientists are trying to accomplish what was once considered the realm of science fiction: create a star on Earth. The National Spherical Torus Experiment (NSTX) is a magnetic fusion device that is used to study the physics principles of spherically shaped plasmas -- hot ionized gases in which, under the right conditions, nuclear fusion will occur. Fusion is the energy source of the sun and all of the stars. Not just limited to theoretical work, the NSTX is enabling cutting-edge research to develop fusion as a future energy source.

  1. The Drifting Star

    NASA Astrophysics Data System (ADS)

    2008-04-01

    By studying in great detail the 'ringing' of a planet-harbouring star, a team of astronomers using ESO's 3.6-m telescope have shown that it must have drifted away from the metal-rich Hyades cluster. This discovery has implications for theories of star and planet formation, and for the dynamics of our Milky Way. ESO PR Photo 09a/08 ESO PR Photo 09a/08 Iota Horologii The yellow-orange star Iota Horologii, located 56 light-years away towards the southern Horologium ("The Clock") constellation, belongs to the so-called "Hyades stream", a large number of stars that move in the same direction. Previously, astronomers using an ESO telescope had shown that the star harbours a planet, more than 2 times as large as Jupiter and orbiting in 320 days (ESO 12/99). But until now, all studies were unable to pinpoint the exact characteristics of the star, and hence to understand its origin. A team of astronomers, led by Sylvie Vauclair from the University of Toulouse, France, therefore decided to use the technique of 'asteroseismology' to unlock the star's secrets. "In the same way as geologists monitor how seismic waves generated by earthquakes propagate through the Earth and learn about the inner structure of our planet, it is possible to study sound waves running through a star, which forms a sort of large, spherical bell," says Vauclair. The 'ringing' from this giant musical instrument provides astronomers with plenty of information about the physical conditions in the star's interior. And to 'listen to the music', the astronomers used one of the best instruments available. The observations were conducted in November 2006 during 8 consecutive nights with the state-of-the-art HARPS spectrograph mounted on the ESO 3.6-m telescope at La Silla. Up to 25 'notes' could be identified in the unique dataset, most of them corresponding to waves having a period of about 6.5 minutes. These observations allowed the astronomers to obtain a very precise portrait of Iota Horologii: its

  2. The DQ Herculis stars

    NASA Technical Reports Server (NTRS)

    Patterson, Joseph

    1994-01-01

    We review the properties of the DQ Herculis stars: cataclysmic variables containing an accreting, magnetic, rapidly rotating white dwarf. These stars are characterized by strong X-ray emission, high-excitation spectra, and very stable optical and X-ray pulsations in their light curves. There is considerable resemblance to their more famous cousins, the AM Herculis stars, but the latter class is additionally characterized by spin-orbit synchronism and the presence of strong circular polarization. We list eighteen stars passing muster as certain or very likely DQ Her stars. The rotational periods range from 33 s to 2.0 hr. Additional periods can result when the rotating searchlight illuminates other structures in the binary. A single hypothesis explains most of the observed properties: magnetically channeled accretion within a truncated disk. Some accretion flow still seems to proceed directly to the magnetosphere, however. The white dwarfs' magnetic moments are in the range 10(sup 32) - 10(sup 34) G cc, slightly weaker than in AM Her stars but with some probable overlap. The more important reason why DQ Hers have broken synchronism is probably their greater accretion rate and orbital separation. The observed L(sub x)/L(sub V) values are surprisingly low for a radially accreting white dwarf, suggesting that most of the accretion energy is not radiated in a strong shock above the magnetic pole. The fluxes can be more satisfactorily explained if most of the radial infall energy manages to bypass the shock and deposit itse lf directly in the white dwarf photosphere, where it should emerge as extreme ultraviolet (EUV) radiation. This also provides an adequate source of ionizing photons to power the high-excitation optical and UV emission lines. This is probably the DQ Her analog to the famous 'soft X-ray excess' in AM Her stars. However, unlike the AM Her case, this radiation has not been directly observed, so the analogy must not (yet) be embraced too firmly. There is

  3. A Star on Earth

    ScienceCinema

    Prager, Stewart; Zwicker, Andrew; Hammet, Greg; Tresemer, Kelsey; Diallo, Ahmed

    2016-07-12

    At the Energy Department's Princeton Plasma Physics Lab, scientists are trying to accomplish what was once considered the realm of science fiction: create a star on Earth. The National Spherical Torus Experiment (NSTX) is a magnetic fusion device that is used to study the physics principles of spherically shaped plasmas -- hot ionized gases in which, under the right conditions, nuclear fusion will occur. Fusion is the energy source of the sun and all of the stars. Not just limited to theoretical work, the NSTX is enabling cutting-edge research to develop fusion as a future energy source.

  4. Synthetic guide star generation

    DOEpatents

    Payne, Stephen A [Castro Valley, CA; Page, Ralph H [Castro Valley, CA; Ebbers, Christopher A [Livermore, CA; Beach, Raymond J [Livermore, CA

    2008-06-10

    A system for assisting in observing a celestial object and providing synthetic guide star generation. A lasing system provides radiation at a frequency at or near 938 nm and radiation at a frequency at or near 1583 nm. The lasing system includes a fiber laser operating between 880 nm and 960 nm and a fiber laser operating between 1524 nm and 1650 nm. A frequency-conversion system mixes the radiation and generates light at a frequency at or near 589 nm. A system directs the light at a frequency at or near 589 nm toward the celestial object and provides synthetic guide star generation.

  5. Synthetic guide star generation

    DOEpatents

    Payne, Stephen A.; Page, Ralph H.; Ebbers, Christopher A.; Beach, Raymond J.

    2004-03-09

    A system for assisting in observing a celestial object and providing synthetic guide star generation. A lasing system provides radiation at a frequency at or near 938 nm and radiation at a frequency at or near 1583 nm. The lasing system includes a fiber laser operating between 880 nm and 960 nm and a fiber laser operating between 1524 nm and 1650 nm. A frequency-conversion system mixes the radiation and generates light at a frequency at or near 589 nm. A system directs the light at a frequency at or near 589 nm toward the celestial object and provides synthetic guide star generation.

  6. The neutron star zoo

    NASA Astrophysics Data System (ADS)

    Harding, Alice K.

    2013-12-01

    Neutron stars are a very diverse population, both in their observational and their physical properties. They prefer to radiate most of their energy at X-ray and gamma-ray wavelengths. But whether their emission is powered by rotation, accretion, heat, magnetic fields or nuclear reactions, they are all different species of the same animal whose magnetic field evolution and interior composition remain a mystery. This article will broadly review the properties of inhabitants of the neutron star zoo, with emphasis on their high-energy emission.

  7. A Real Shooting Star

    NASA Technical Reports Server (NTRS)

    2007-01-01

    [figure removed for brevity, see original site] Click on the image for movie of A Real Shooting Star

    This artist's animation illustrates a star flying through our galaxy at supersonic speeds, leaving a 13-light-year-long trail of glowing material in its wake. The star, named Mira (pronounced my-rah) after the latin word for 'wonderful,' sheds material that will be recycled into new stars, planets and possibly even life. NASA's Galaxy Evolution Explorer discovered the long trail of material behind Mira during its survey of the entire sky in ultraviolet light.

    The animation begins by showing a close-up of Mira -- a red-giant star near the end of its life. Red giants are red in color and extremely bloated; for example, if a red giant were to replace our sun, it would engulf everything out to the orbit of Mars. They constantly blow off gas and dust in the form of stellar winds, supplying the galaxy with molecules, such as oxygen and carbon, that will make their way into new solar systems. Our sun will mature into a red giant in about 5 billion years.

    As the animation pulls out, we can see the enormous trail of material deposited behind Mira as it hurls along between the stars. Like a boat traveling through water, a bow shock, or build up of gas, forms ahead of the star in the direction of its motion. Gas in the bow shock is heated and then mixes with the cool hydrogen gas in the wind that is blowing off Mira. This heated hydrogen gas then flows around behind the star, forming a turbulent wake.

    Why does the trailing hydrogen gas glow in ultraviolet light? When it is heated, it transitions into a higher-energy state, which then loses energy by emitting ultraviolet light - a process known as fluorescence.

    Finally, the artist's rendering gives way to the actual ultraviolet image taken by the Galaxy Evolution Explorer

    Mira is located 350 light-years from Earth in the constellation Cetus, otherwise known as the whale. Coincidentally, Mira

  8. Star cluster dynamics.

    PubMed

    Vesperini, Enrico

    2010-02-28

    Dynamical evolution plays a key role in shaping the current properties of star clusters and star cluster systems. A detailed understanding of the effects of evolutionary processes is essential to be able to disentangle the properties that result from dynamical evolution from those imprinted at the time of cluster formation. In this review, I focus my attention on globular clusters, and review the main physical ingredients driving their early and long-term evolution, describe the possible evolutionary routes and show how cluster structure and stellar content are affected by dynamical evolution.

  9. Stellar Dynamical Processes in Massive Star and Star Cluster Formation

    NASA Astrophysics Data System (ADS)

    Tan, Jonathan; Eyer, L.

    2009-01-01

    We study how high precision astrometric measurements by SIM and GAIA of stars involved in dynamical ejection events from star clusters can constrain theories of massive star and star cluster formation. We focus on the Orion Nebula Cluster (ONC). First, we investigate the scientific potential associated with an accurate measurement of the distance and proper motion of Theta 1 Ori C, which is the most massive star in the cluster and was recently involved (about 4000 years ago) in the ejection of a B star: the Becklin-Neugebauer (BN) star. The motion of the BN star has taken it close to a massive protostar, known as source I, where it appears to have influenced the accretion and outflow activity, most likely by a tidal interaction with the accretion disk. An accurate proper motion measurement of Theta 1 Ori C will constrain BN's initial motion, allowing us to search for deflections caused by the gravitational potential of the massive protostar. Second, we search the Hipparcos catalog for candidate runaway stars, i.e. that have been dynamically ejected from the cluster over the course of the last several Myr. SIM and GAIA observations of these stars will be needed to confirm their origin from the ONC. The results of this study will constrain the star cluster formation timescale and the statistics of the population of ejected stars. JCT acknowledges support from from NSF CAREER grant AST-0645412 and a grant from NASA for SIM Science Studies.

  10. Revisiting the conundrum of trehalose stabilization.

    PubMed

    Katyal, Nidhi; Deep, Shashank

    2014-12-28

    Protein aggregation and loss of protein's biological functionality are manifestations of protein instability. Cosolvents, in particular trehalose, are widely accepted antidotes against such destabilization. Although numerous theories have been promulgated in the literature with regard to its mechanism of stabilization, the present scenario is still elusive in view of the discrepancies existing in them. To this end, we have revisited the conundrum and attempted to rationalize the mechanism by conducting thorough investigation of the effect of trehalose on the native, partially unfolded and denatured states of protein "Lysozyme" by means of molecular dynamic (MD) simulations under different temperature and concentration regimes. Two-dimensional contour plots along with principal component analysis suggest that trehalose molecules offer on-pathway stabilization unaltering the principal direction of protein's motion, although it slows down protein dynamics so that the protein gets trapped in the homogeneous ensemble of conformations closer to the native state. Free energy landscape reveals higher population of native compared to intermediate and denatured states. Delphi results and calculation of the preferential interaction parameter demonstrate that this relative stabilization of the native state can be ascribed to be the consequence of favourable interactions of trehalose with side chains of certain loci on the protein surface encompassing polar flexible residues. Stability of protein results from the observed difference in binding affinity of trehalose for native and denatured states of protein. Our findings are at variance with the common conception of relative destabilization of the denatured state. Rather, we provide evidence for relative stabilization of the native state. This stabilization is due to interplay of protein-trehalose, water-trehalose, water-water, protein-water and trehalose-trehalose interactions.

  11. The coordinate coherent states approach revisited

    SciTech Connect

    Miao, Yan-Gang Zhang, Shao-Jun

    2013-02-15

    We revisit the coordinate coherent states approach through two different quantization procedures in the quantum field theory on the noncommutative Minkowski plane. The first procedure, which is based on the normal commutation relation between an annihilation and creation operators, deduces that a point mass can be described by a Gaussian function instead of the usual Dirac delta function. However, we argue this specific quantization by adopting the canonical one (based on the canonical commutation relation between a field and its conjugate momentum) and show that a point mass should still be described by the Dirac delta function, which implies that the concept of point particles is still valid when we deal with the noncommutativity by following the coordinate coherent states approach. In order to investigate the dependence on quantization procedures, we apply the two quantization procedures to the Unruh effect and Hawking radiation and find that they give rise to significantly different results. Under the first quantization procedure, the Unruh temperature and Unruh spectrum are not deformed by noncommutativity, but the Hawking temperature is deformed by noncommutativity while the radiation specturm is untack. However, under the second quantization procedure, the Unruh temperature and Hawking temperature are untack but the both spectra are modified by an effective greybody (deformed) factor. - Highlights: Black-Right-Pointing-Pointer Suggest a canonical quantization in the coordinate coherent states approach. Black-Right-Pointing-Pointer Prove the validity of the concept of point particles. Black-Right-Pointing-Pointer Apply the canonical quantization to the Unruh effect and Hawking radiation. Black-Right-Pointing-Pointer Find no deformations in the Unruh temperature and Hawking temperature. Black-Right-Pointing-Pointer Provide the modified spectra of the Unruh effect and Hawking radiation.

  12. Machining as a mechanical property test revisited

    NASA Astrophysics Data System (ADS)

    Smith, David L.

    There is much need for data on mechanical behavior of metals at high strains and strain rates. This need is dictated by modeling of processes like forming and machining, wherein the material in the deformation zone is subjected to severe deformation conditions atypical of conventional material property tests such as tension and torsion. Accurate flow stress data is an essential input for robust prediction of process outputs. Similar requirements arise from applications in high speed ballistic penetration and design of materials for armor. Since the deformation zone in cutting of metals is characterized by unique and extreme combinations of strain, strain rate and temperature, an opportunity exists for using plane-strain cutting as a mechanical property test for measuring flow properties of metals. The feasibility of using plane-strain cutting to measure flow properties of metals is revisited in the light of recent data showing controllability of the deformation conditions in chip formation by systematic variation of process input parameters. A method is outlined as to how the deformation conditions can be varied by changing the process parameters. The method is applied to cutting of commercially pure copper (FCC), iron (BCC) and zinc (HCP). Forces and chip geometries are measured, in conjunction with particle image velocimetry characterization of the deformation using high speed image sequences. The flow stresses are estimated from these measurements. The measured flow stress and its dependence on strain are shown to agree well with prior measurements of these parameters using conventional tests, and flow stress inferred from hardness characterization. The method is also demonstrated to be able to measure properties of metals that recrystallize at room temperature (zinc), wherein quasi-static tests predict much lower strength. Sources of variability and uncertainty in the application of this measurement technique are discussed. Future work in the context of further

  13. Revisiting mu suppression in autism spectrum disorder.

    PubMed

    Dumas, Guillaume; Soussignan, Robert; Hugueville, Laurent; Martinerie, Jacques; Nadel, Jacqueline

    2014-10-17

    Two aspects of the EEG literature lead us to revisit mu suppression in Autism Spectrum Disorder (ASD). First and despite the fact that the mu rhythm can be functionally segregated in two discrete sub-bands, 8-10 Hz and 10-12/13 Hz, mu-suppression in ASD has been analyzed as a homogeneous phenomenon covering the 8-13 Hz frequency. Second and although alpha-like activity is usually found across the entire scalp, ASD studies of action observation have focused on the central electrodes (C3/C4). The present study was aimed at testing on the whole brain the hypothesis of a functional dissociation of mu and alpha responses to the observation of human actions in ASD according to bandwidths. Electroencephalographic (EEG) mu and alpha responses to execution and observation of hand gestures were recorded on the whole scalp in high functioning subjects with ASD and typical subjects. When two bandwidths of the alpha-mu 8-13 Hz were distinguished, a different mu response to observation appeared for subjects with ASD in the upper sub-band over the sensorimotor cortex, whilst the lower sub-band responded similarly in the two groups. Source reconstructions demonstrated that this effect was related to a joint mu-suppression deficit over the occipito-parietal regions and an increase over the frontal regions. These findings suggest peculiarities in top-down response modulation in ASD and question the claim of a global dysfunction of the MNS in autism. This research also advocates for the use of finer grained analyses at both spatial and spectral levels for future directions in neurophysiological accounts of autism.

  14. The Death of a Star

    ERIC Educational Resources Information Center

    Thorne, Kip S.

    1971-01-01

    Theories associated with the gravitational collapse of a star into black holes" are described. Suggests that the collapse and compression might go through the stages from white dwarf star to neutron core to black hole." (TS)

  15. Photographic photometry of variable stars

    NASA Technical Reports Server (NTRS)

    Kholopov, P. N.

    1973-01-01

    Photographic methods of determining stellar magnitude and measuring brightness of variable stars on negatives include the photoelectric method and the contascope. Calibration curves are usually plotted by the UBV method. Magnitudes of comparison stars can be determined from photographs.

  16. Finding Planets around other stars

    NASA Video Gallery

    Just as the Earth revolves around the sun, our closest star, other planets might orbit the stars you see in the night sky. Think of all the planets in the universe that may be just the right distan...

  17. The Wolf-Rayet stars

    NASA Astrophysics Data System (ADS)

    Sahade, J.

    1981-12-01

    Aspects of the problems of the Wolf-Rayet stars related to their chemical composition, their evolutionary status, and their apparent dichotomy in two spectral sequences are discussed. Dogmas concerning WR stars are critically discussed, including the belief that WR stars lack hydrogen, that they are helium stars evolved from massive close binaries, and the existence of a second WR stage in which the star is a short-period single-lined binary. The relationship of WR stars with planetary nebulae is addressed, as is the membership of these stars in clusters and associations. The division of WR stars into WN and WC sequences is considered, questioning the reasonability of accounting for WR line formation in terms of abundance differences.

  18. Star Formation in Irregular Galaxies.

    ERIC Educational Resources Information Center

    Hunter, Deidre; Wolff, Sidney

    1985-01-01

    Examines mechanisms of how stars are formed in irregular galaxies. Formation in giant irregular galaxies, formation in dwarf irregular galaxies, and comparisons with larger star-forming regions found in spiral galaxies are considered separately. (JN)

  19. Radio Emission from Binary Stars

    NASA Astrophysics Data System (ADS)

    Hjellming, R.; Murdin, P.

    2000-11-01

    Stellar radio emission is most common in double star systems where each star provides something essential in producing the large amounts of radio radiation needed for it to be detectable by RADIO TELESCOPES. They transfer mass, supply energy or, when one of the stars is a NEUTRON STAR or BLACK HOLE, have the strong gravitational fields needed for the energetic particles and magnetic fields needed...

  20. Binary stars - Formation by fragmentation

    NASA Technical Reports Server (NTRS)

    Boss, Alan P.

    1988-01-01

    Theories of binary star formation by capture, separate nuclei, fission and fragmentation are compared, assessing the success of theoretical attempts to explain the observed properties of main-sequence binary stars. The theory of formation by fragmentation is examined, discussing the prospects for checking the theory against observations of binary premain-sequence stars. It is concluded that formation by fragmentation is successful at explaining many of the key properties of main-sequence binary stars.

  1. The evolution of massive stars

    NASA Technical Reports Server (NTRS)

    1982-01-01

    The hypotheses underlying theoretical studies of the evolution of massive model stars with and without mass loss are summarized. The evolutionary tracks followed by the models across theoretical Hertzsprung-Russell (HR) diagrams are compared with the observed distribution of B stars in an HR diagram. The pulsational properties of models of massive star are also described.

  2. Trek to the Stars

    ERIC Educational Resources Information Center

    Rubinstein, Robert E.

    1977-01-01

    "Star Trek", which was aired on television for three years, brought the creatures and conflicts of the "outer reaches" of space into our living rooms. Here its new episodes and reruns are analyzed by elementary students as part of a social studies/elementary science curriculum. (Author/RK)

  3. NuStar

    Integrated Risk Information System (IRIS)

    NuStar ; CASRN 85509 - 19 - 9 Human health assessment information on a chemical substance is included in the IRIS database only after a comprehensive review of toxicity data , as outlined in the IRIS assessment development process . Sections I ( Health Hazard Assessments for Noncarcinogenic Effects

  4. Pygmy stars: first pair.

    PubMed

    Zwicky, F

    1966-07-01

    The binary LP 101-15/16 having the proper motion of 1.62 seconds of arc per year has been studied with the prime-focus spectrograph of the 200-inch (508 cm) telescope. Indications are that LP 101-15/16 is the first pair of pygmy stars ever discovered. One of its components, LP 101-16, is probably a blue pygmy star which is at least four magnitudes fainter than the ordinary white dwarfs. Also, two of the Balmer lines in absorption appear to be displaced toward the red by amounts which indicate the existence of an Einstein gravitational red shift corresponding to about 1000 km sec-1. On the other hand LP 101-15 is red and shows an entirely new type of spectrum, which suggests that it may be a first representative of a type of red pygmy star which is 2.5 magnitudes fainter than the M-type dwarf stars of the main sequence.

  5. Reaching for the Stars

    ERIC Educational Resources Information Center

    Terry, Dorothy Givens

    2012-01-01

    Dr. Mae Jemison is the world's first woman astronaut of color who continues to reach for the stars. Jemison was recently successful in leading a team that has secured a $500,000 federal grant to make interstellar space travel a reality. The Dorothy Jemison Foundation for Excellence (named after Jemison's mother) was selected in June by the Defense…

  6. The Astounding Stars.

    ERIC Educational Resources Information Center

    Montgomery, Angela; And Others

    1983-01-01

    Studying about stellar constellations provides children with an opportunity to learn about ancient myths and mathematics at the same time. An interdisciplinary teaching unit combines information about myths associated with the zodiac signs and instructions for plotting the coordinates of stars. (PP)

  7. Reaching for the Stars.

    ERIC Educational Resources Information Center

    Roper-Davis, Sharon

    1999-01-01

    Describes "Reaching for the Stars," a program which develops teaming and mentoring skills in senior physics students. Phase 1 requires student pairs to design a rocket; Phase 2 pairs seniors with gifted second graders who build the rocket from written instructions; and in Phase 3, pairs of seniors create a children's storybook explaining…

  8. Chemical Compositions of Stars

    NASA Astrophysics Data System (ADS)

    Leckrone, D.; Murdin, P.

    2000-11-01

    In 1835, in a famously inaccurate forecast, the French philosopher Auguste Comte wrote of stars that, `We understand the possibility of determining their shapes, their distances, their sizes and their movements; whereas we would never know how to study by any means their chemical composition…'. At the close of the 20th century the accurate measurement of the abundances of the chemical elements in...

  9. Division Iv: Stars

    NASA Astrophysics Data System (ADS)

    Corbally, Christopher; D'Antona, Francesca; Spite, Monique; Asplund, Martin; Charbonnel, Corinne; Docobo, Jose Angel; Gray, Richard O.; Piskunov, Nikolai E.

    2012-04-01

    This Division IV was started on a trial basis at the General Assembly in The Hague 1994 and was formally accepted at the Kyoto General Assembly in 1997. Its broad coverage of ``Stars'' is reflected in its relatively large number of Commissions and so of members (1266 in late 2011). Its kindred Division V, ``Variable Stars'', has the same history of its beginning. The thinking at the time was to achieve some kind of balance between the number of members in each of the 12 Divisions. Amid the current discussion of reorganizing the number of Divisions into a more compact form it seems advisable to make this numerical balance less of an issue than the rationalization of the scientific coverage of each Division, so providing more effective interaction within a particular field of astronomy. After all, every star is variable to a certain degree and such variability is becoming an ever more powerful tool to understand the characteristics of every kind of normal and peculiar star. So we may expect, after hearing the reactions of members, that in the restructuring a single Division will result from the current Divisions IV and V.

  10. Sleeping under the stars

    NASA Astrophysics Data System (ADS)

    Zirkel, Jack

    Sherlock Holmes and Dr. Watson went on a camping trip. As they lay down for the night, Holmes said, “Watson, look up at the sky and tell me what you see.”Watson:“! see millions and millions of stars.”

  11. White Star technology.

    PubMed

    Olson, Randall J; Kumar, Rajiv

    2003-02-01

    White Star micropulse technology is a software modification that allows extremely short bursts of ultrasound energy. Studies have shown that this decreases wound heat build-up with the retained efficiency of continuous ultrasound. Decreased energy utilization with improved corneal function and improved nuclear fragment followability appear to be additional benefits.

  12. Multipath star switch controller

    NASA Technical Reports Server (NTRS)

    Anderson, T. O.

    1980-01-01

    Device concept permits parallel computers to scan several commonnetwork-connected data stations at maximum rate. Sequencers leap-frog to bypass ports already being serviced by another computer. Two-path system for 16-port star switch controller is cost effective if added bandwidth or increased reliability is desired. Triple-path system would be cost effective for 32-port controller.

  13. Molecules between the Stars.

    ERIC Educational Resources Information Center

    Verschuur, Gerrit L.

    1987-01-01

    Provides a listing of molecules discovered to date in the vast interstellar clouds of dust and gas. Emphasizes the recent discoveries of organic molecules. Discusses molecular spectral lines, MASERs (microwave amplification by stimulated emission of radiation), molecular clouds, and star birth. (TW)

  14. Physics of the Stars

    ERIC Educational Resources Information Center

    Haig, G. Y.

    1974-01-01

    Describes how astrophysics can be a do-it-yourself project within a school boy's budget and background, by giving detailed instruction on equipment construction. In addition, this article describes many experiments to undertake, with the equipment, such as determining color temperature, star spectra, chemical composition and others. (BR)

  15. Insight into star death

    SciTech Connect

    Talcott, R.

    1988-02-01

    Nineteen neutrinos, formed in the center of a supernova, became a theorist's dream. They came straight from the heart of supernova 1987A and landed in two big underground tanks of water. Suddenly a new chapter in observational astronomy opened as these two neutrino telescopes gave astronomers their first look ever into the core of a supernova explosion. But the theorists' dream almost turned into a nightmare. Observations of the presupernova star showed conclusively that the star was a blue supergiant, but theorists have long believed only red supergiant stars could explode as supernovae. Do astronomers understand supernovae better now than when supernova 1987A exploded in the Large Magellanic Cloud (LMC) one year ago Yes. The observations of neutrinos spectacularly confirmed a vital aspect of supernova theory. But the observed differences between 1987A and other supernovae have illuminated and advanced our perception of how supernovae form. By working together, observers and theorists are continuing to hone their ideas about how massive stars die and how the subsequent supernovae behave.

  16. First Star I See.

    ERIC Educational Resources Information Center

    Caffrey, Jaye Andras

    This children's novel tells the story of a young girl with attention deficit disorder (ADD) without hyperactivity and her younger brother who has ADD with hyperactivity. Trying to win a school writing contest on the topic of space and stars helps bright, imaginative Paige Bradley realize that fixing her "focusing knob" will compensate for her ADD.…

  17. StarLogo TNG

    NASA Astrophysics Data System (ADS)

    Klopfer, Eric; Scheintaub, Hal; Huang, Wendy; Wendel, Daniel

    Computational approaches to science are radically altering the nature of scientific investigatiogn. Yet these computer programs and simulations are sparsely used in science education, and when they are used, they are typically “canned” simulations which are black boxes to students. StarLogo The Next Generation (TNG) was developed to make programming of simulations more accessible for students and teachers. StarLogo TNG builds on the StarLogo tradition of agent-based modeling for students and teachers, with the added features of a graphical programming environment and a three-dimensional (3D) world. The graphical programming environment reduces the learning curve of programming, especially syntax. The 3D graphics make for a more immersive and engaging experience for students, including making it easy to design and program their own video games. Another change to StarLogo TNG is a fundamental restructuring of the virtual machine to make it more transparent. As a result of these changes, classroom use of TNG is expanding to new areas. This chapter is concluded with a description of field tests conducted in middle and high school science classes.

  18. Magnetic Dynamos and Stars

    SciTech Connect

    Eggleton, P P

    2007-02-15

    Djehuty is a code that has been developed over the last five years by the Lawrence Livermore National Laboratory (LLNL), from earlier code designed for programmatic efforts. Operating in a massively parallel environment, Djehuty is able to model entire stars in 3D. The object of this proposal was to continue the effort to introduce magneto-hydrodynamics (MHD) into Djehuty, and investigate new classes of inherently 3D problems involving the structure, evolution and interaction of stars and planets. However, towards the end of the second year we discovered an unexpected physical process of great importance in the evolution of stars. Consequently for the third year we changed direction and concentrated on this process rather than on magnetic fields. Our new process was discovered while testing the code on red-giant stars, at the 'helium flash'. We found that a thin layer was regularly formed which contained a molecular-weight inversion, and which led therefore to Rayleigh-Taylor instability. This in turn led to some deeper-than-expected mixing, which has the property that (a) much {sup 3}He is consumed, and (b) some {sup 13}C is produced. These two properties are closely in accord with what has been observed over the last thirty years in red giants, whereas what was observed was largely in contradiction to what earlier theoretical models predicted. Thus our new 3D models with Djehuty explain a previously-unexplained problem of some thirty years standing.

  19. Reading Stars. 2013 Report

    ERIC Educational Resources Information Center

    National Literacy Trust, 2013

    2013-01-01

    The National Literacy Trust's Premier League Reading Stars has now been running for 10 years. During this time, hundreds of thousands of children and families have been inspired by the power of football to develop a love of reading. Although the programme has grown and evolved over this period, the premise remains the same: harnessing the…

  20. Modular and scalable RESTful API to sustain STAR collaboration's record keeping

    NASA Astrophysics Data System (ADS)

    Arkhipkin, D.; Lauret, J.; Shanmuganathan, P. V.

    2015-12-01

    STAR collaboration's record system is a collection of heterogeneous and sparse information associated to each members and institutions. In its original incarnation, only flat information was stored revealing many restrictions such as the lack of historical change information, the inability to keep track of members leaving and re-joining STAR, or the ability to easily extend the saved information as new requirements appeared. In mid-2013, a new project was launched covering an extensive set of revisited requirements. The requirements led us to a design based on a RESTful API, back-end storage engine relying on key/value pair data representation model coupled with a tiered architecture design. This design was motivated by the fact that unifying many STAR tools, relying on the same business logic and storage engine, was a key and central feature for the maintainability and presentation of records. This central service API would leave no ambiguities and provide easy service integration between STAR tools. The new design stores the changes in records dynamically and allows tracking the changes chronologically. The storage engine is extensible as new field of information emerges (member specific or general) without affecting the presentation or the business logic layers. The new record system features a convenient administrative interface, fuzzy algorithms for data entry and search, and provides basic statistics and graphs. Finally, this modular approach is supplemented with access control, allowing private information and administrative operations to be hidden away from public eyes.

  1. Electromagnetic fields in the exterior of an oscillating relativistic star - II. Electromagnetic damping

    NASA Astrophysics Data System (ADS)

    Rezzolla, Luciano; Ahmedov, Bobomurat J.

    2016-07-01

    An important issue in the asteroseismology of compact and magnetized stars is the determination of the dissipation mechanism which is most efficient in damping the oscillations when these are produced. In a linear regime and for low-multipolarity modes, these mechanisms are confined to either gravitational-wave or electromagnetic losses. We here consider the latter and compute the energy losses in the form of Poynting fluxes, Joule heating and Ohmic dissipation in a relativistic oscillating spherical star with a dipolar magnetic field in vacuum. While this approach is not particularly realistic for rapidly rotating stars, it has the advantage that it is fully analytic and that it provides expressions for the electric and magnetic fields produced by the most common modes of oscillation both in the vicinity of the star and far away from it. In this way, we revisit and extend to a relativistic context the classical estimates of McDermott et al. Overall, we find that general-relativistic corrections lead to electromagnetic damping time-scales that are at least one order of magnitude smaller than in Newtonian gravity. Furthermore, with the only exception of g (gravity) modes, we find that f (fundamental), p (pressure), i (interface) and s (shear) modes are suppressed more efficiently by gravitational losses than by electromagnetic ones.

  2. H-cluster stars

    NASA Astrophysics Data System (ADS)

    Lai, X. Y.; Gao, C. Y.; Xu, R. X.

    2013-06-01

    The study of dense matter at ultrahigh density has a very long history, which is meaningful for us to understand not only cosmic events in extreme circumstances but also fundamental laws of physics. It is well known that the state of cold matter at supranuclear density depends on the non-perturbative nature of quantum chromodynamics (QCD) and is essential for modelling pulsars. A so-called H-cluster matter is proposed in this paper as the nature of dense matter in reality. In compact stars at only a few nuclear densities but low temperature, quarks could be interacting strongly with each other there. That might render quarks grouped in clusters, although the hypothetical quark clusters in cold dense matter have not been confirmed due to the lack of both theoretical and experimental evidence. Motivated by recent lattice QCD simulations of the H-dibaryons (with structure uuddss), we therefore consider here a possible kind of quark clusters, H-clusters, that could emerge inside compact stars during their initial cooling as the dominant components inside (the degree of freedom could then be H-clusters there). Taking into account the in-medium stiffening effect, we find that at baryon densities of compact stars H-cluster matter could be more stable than nuclear matter. We also find that for the H-cluster matter with lattice structure, the equation of state could be so stiff that it would seem to be `superluminal' in the most dense region. However, the real sound speed for H-cluster matter is in fact difficult to calculate, so at this stage we do not put constraints on our model from the usual requirement of causality. We study the stars composed of H-clusters, i.e. H-cluster stars, and derive the dependence of their maximum mass on the in-medium stiffening effect, showing that the maximum mass could be well above 2 M⊙ as observed and that the resultant mass-radius relation fits the measurement of the rapid burster under reasonable parameters. Besides a general

  3. Halo Star Lithium Depletion

    SciTech Connect

    Pinsonneault, M. H.; Walker, T. P.; Steigman, G.; Narayanan, Vijay K.

    1999-12-10

    The depletion of lithium during the pre-main-sequence and main-sequence phases of stellar evolution plays a crucial role in the comparison of the predictions of big bang nucleosynthesis with the abundances observed in halo stars. Previous work has indicated a wide range of possible depletion factors, ranging from minimal in standard (nonrotating) stellar models to as much as an order of magnitude in models that include rotational mixing. Recent progress in the study of the angular momentum evolution of low-mass stars permits the construction of theoretical models capable of reproducing the angular momentum evolution of low-mass open cluster stars. The distribution of initial angular momenta can be inferred from stellar rotation data in young open clusters. In this paper we report on the application of these models to the study of lithium depletion in main-sequence halo stars. A range of initial angular momenta produces a range of lithium depletion factors on the main sequence. Using the distribution of initial conditions inferred from young open clusters leads to a well-defined halo lithium plateau with modest scatter and a small population of outliers. The mass-dependent angular momentum loss law inferred from open cluster studies produces a nearly flat plateau, unlike previous models that exhibited a downward curvature for hotter temperatures in the 7Li-Teff plane. The overall depletion factor for the plateau stars is sensitive primarily to the solar initial angular momentum used in the calibration for the mixing diffusion coefficients. Uncertainties remain in the treatment of the internal angular momentum transport in the models, and the potential impact of these uncertainties on our results is discussed. The 6Li/7Li depletion ratio is also examined. We find that the dispersion in the plateau and the 6Li/7Li depletion ratio scale with the absolute 7Li depletion in the plateau, and we use observational data to set bounds on the 7Li depletion in main-sequence halo

  4. Morphodynamics of star dunes

    NASA Astrophysics Data System (ADS)

    Courrech du Pont, S.; Zhang, D.; Narteau, C.; Rozier, O.

    2011-12-01

    Star dunes are the bigger and most impressive dunes in Earth sand seas. Nonetheless, they remain poorly studied, probably because of their apparent complexity. They are massive pyramidal dunes with interlaced arms whose slip faces are oriented in various directions. Being large, they can integrate wind properties over a wide range of time scales. Thus, they are observed for wind regimes with multiple directions, and may result from the amalgamation of dunes or from the development of arms on a well-established dune pattern. In both cases, the roles of wind directional variability and secondary flow have been emphasized but not precisely quantified. As a matter of fact, although star dunes are ubiquitous in major sand seas, little is known about their formation and their evolution, essentially because of their size. We report simulations where the star dune shape results from a combination of longitudinal dunes, which form the star dune arms. These arms may radiate and so interact with the other dunes in the field. This mass exchange, controlled by the morphodynamics of star dunes arms, must play an important role in the large-scale arrangement of star dunes networks. We first demonstrate that star dune arms orientation maximizes the flux in the direction of crests. This is opposed to the usually admit dunes orientation, which maximizes the sediment transport perpendicular to the crest. Indeed, depending on sand availability, dunes development results from the growth of a wave on a sand bed or from a net transport of sediment, which grows and extends an isolated longitudinal dune over a non-erodible soil. These two different mechanisms lead to two different modes of crests orientation. Then, we show that the propagating arms reach a stationary state characterized by constant width, height and growth rate. These are controlled by the frequency at which the wind changes direction. Arm width and height increase, whereas the propagation speed decreases with a decreasing

  5. White Dwarf Stars

    NASA Astrophysics Data System (ADS)

    Kepler, S. O.

    2014-10-01

    White dwarfs are the evolutionary endpoint for nearly 95% of all stars born in our Galaxy, the final stages of evolution of all low- and intermediate mass stars, i.e., main sequence stars with masses below (8.5± 1.5) M_{odot}, depending on metallicity of the progenitor, mass loss and core overshoot. Massive white dwarfs are intrinsically rare objects, tand produce a gap in the determination of the initial vs. final mass relation at the high mass end (e.g. Weidemann 2000 A&A, 363, 647; Kalirai et al. 2008, ApJ, 676, 594; Williams, Bolte & Koester 2009, ApJ, 693, 355). Main sequences stars with higher masses will explode as SNII (Smartt S. 2009 ARA&A, 47, 63), but the limit does depend on the metallicity of the progenitor. Massive white dwarfs are probably SNIa progenitors through accretion or merger. They are rare, being the final product of massive stars (less common) and have smaller radius (less luminous). Kepler et al. 2007 (MNRAS, 375, 1315), Kleinman et al. 2013 (ApJS, 204, 5) estimate only 1-2% white dwarfs have masses above 1 M_{odot}. The final stages of evolution after helium burning are a race between core growth and loss of the H-rich envelope in a stellar wind. When the burning shell is exposed, the star rapidly cools and burning ceases, leaving a white dwarf. As they cool down, the magnetic field freezes in, ranging from a few kilogauss to a gigagauss. Peculiar type Ia SN 2006gz, SN 2007if, SN 2009dc, SN 2003fg suggest progenitors in the range 2.4-2.8 M_{odot}, and Das U. & Mukhopadhyay B. (2012, Phys. Rev. D, 86, 042001) estimate that the Chandrasekhar limit increases to 2.3-2.6 M_{odot} for extremely high magnetic field stars, but differential rotation induced by accretion could also increase it, according to Hachisu I. et al. 2012 (ApJ, 744, 69). García-Berro et al. 2012, ApJ, 749, 25, for example, proposes double degenerate mergers are the progenitors of high-field magnetic white dwarfs. We propose magnetic fields enhance the line broadening in

  6. Interstellar Abundances Toward X Per, Revisited

    NASA Technical Reports Server (NTRS)

    Valencic, Lynne A.; Smith, Randall K.

    2012-01-01

    The nearby X-ray binary X Per (HD 24534) provides a useful beacon with which to measure elemental abundances in the local ISM. We examine absorption features of O, Mg, and Si along this line of sight using spectra from the Chandra Observatory's LETG/ACIS-S and XMM-Newton's RGS instruments. In general, we find that the abundances and their ratios are similar to those of young F and G stars and the most recent solar values. We compare our results with abundances required by dust grain models.

  7. Interstellar Abundances Toward X Per, Revisited

    NASA Technical Reports Server (NTRS)

    Valencic, Lynne A.; Smith, Randall K.

    2014-01-01

    The nearby X-ray binary X Per (HD 24534) provides a useful beacon with which to measure elemental abundances in the local ISM. We examine absorption features of 0, Mg, and Si along this line of sight using spectra from the Chandra Observatory's LETG/ ACIS-S and XMM-Newton's RGS instruments. In general, we find that the abundances and their ratios are similar to those of young F and G stars and the most recent solar values. We compare our results with abundances required by dust grain models.

  8. The Stern-Gerlach experiment revisited

    NASA Astrophysics Data System (ADS)

    Schmidt-Böcking, Horst; Schmidt, Lothar; Lüdde, Hans Jürgen; Trageser, Wolfgang; Templeton, Alan; Sauer, Tilman

    2016-12-01

    experimental example for such directional quantization in scattering processes is shown. Last not least, the early history of the "almost" discovery of the electron spin in the SGE is revisited.

  9. Alkaline phosphatase revisited: hydrolysis of alkyl phosphates.

    PubMed

    O'Brien, Patrick J; Herschlag, Daniel

    2002-03-05

    Escherichia coli alkaline phosphatase (AP) is the prototypical two metal ion catalyst with two divalent zinc ions bound approximately 4 A apart in the active site. Studies spanning half a century have elucidated many structural and mechanistic features of this enzyme, rendering it an attractive model for investigating the potent catalytic power of bimetallic centers. Unfortunately, fundamental mechanistic features have been obscured by limitations with the standard assays. These assays generate concentrations of inorganic phosphate (P(i)) in excess of its inhibition constant (K(i) approximately 1 muM). This tight binding by P(i) has affected the majority of published kinetic constants. Furthermore, binding limits k(cat)/K(m) for reaction of p-nitrophenyl phosphate, the most commonly employed substrate. We describe a sensitive (32)P-based assay for hydrolysis of alkyl phosphates that avoids the complication of product inhibition. We have revisited basic mechanistic features of AP with these alkyl phosphate substrates. The results suggest that the chemical step for phosphorylation of the enzyme limits k(cat)/K(m). The pH-rate profile and additional results suggest that the serine nucleophile is active in its anionic form and has a pK(a) of < or = 5.5 in the free enzyme. An inactivating pK(a) of 8.0 is observed for binding of both substrates and inhibitors, and we suggest that this corresponds to ionization of a zinc-coordinated water molecule. Counter to previous suggestions, inorganic phosphate dianion appears to bind to the highly charged AP active site at least as strongly as the trianion. The dependence of k(cat)/K(m) on the pK(a) of the leaving group follows a Brønsted correlation with a slope of beta(lg) = -0.85 +/- 0.1, differing substantially from the previously reported value of -0.2 obtained from data with a less sensitive assay. This steep leaving group dependence is consistent with a largely dissociative transition state for AP-catalyzed hydrolysis of

  10. Revisiting the CALIOP Mineral Dust Optical Model

    NASA Astrophysics Data System (ADS)

    Winker, D. M.; Omar, A. H.; Liu, Z.

    2013-12-01

    The standard aerosol extinction retrieval applied to CALIOP observations relies heavily on a priori values of the lidar ratio (the ratio of extinction to 180-degree backscatter) for each of several aerosol types. The original CALIOP aerosol models were developed over 10 years ago, based on a combination of Aeronet retrievals, measurements from ground-based lidars, and theoretical scattering calculations. Both prior to and since the launch of CALIPSO, a number of studies using a variety of approaches have shown lidar ratios of around 40 sr for mineral dust. Ground-based Raman lidar measurements in Europe and Morroco, on the other hand, have consistently shown higher values of 50 to 60 sr. Reasons for this inconsistency have not been clearly identified, but may be due to geographical variability, mixtures of dust with fine-mode aerosol, multiple scattering effects on the CALIOP retrieval, other retrieval artifacts, or a combination of these. The simplest explanation for the difference between ground-based Raman and space-based retrievals of dust lidar ratio would be multiple scattering effects on the CALIOP signals. We have taken advantage of improvements in scattering codes and of recent field campaigns to re-evaluate the CALIOP optical model for mineral dust and to revisit multiple scattering effects. The original scattering phase functions used to predict multiple scattering were based on Dipole-Dipole Approximation (DDA) calculations of size-shape mixtures of irregular dust particles. At the time, the DDA calculations were limited to particles of less than 2 um diameter. Using current T-matrix codes, we are now able to compute scattering from particles as large as 10 um diameter. Applying T-matrix scattering calculations to spheroidal particles with size distributions consistent with those measured during the SAMUM campaign in Morroco, we find multiple scattering effects are similar to those predicted from the original DDA calculations. Thus multiple scattering

  11. Five years on: Revisiting GSN data quality

    NASA Astrophysics Data System (ADS)

    Gee, L. S.; Nettles, M.; Ekstrom, G.; Davis, J. P.; Ringler, A. T.; Storm, T. L.; Wilson, D.; Anderson, K. R.

    2014-12-01

    In 2010, the Lamont Waveform Quality Center (WQC) conducted an in-depth review of ten stations in the Global Seismographic Network (GSN). IU stations (CASY, DAV, KIP, KONO, WCI), IC stations (SSE, XAN), and II stations (ALE, DGAR, RPN) were analyzed using a scaling analysis based on data-synthetic comparisons, evaluation of noise levels, assessment of inter-sensor coherence, and polarization analysis. These reports (available from http://www.ldeo.columbia.edu/~ekstrom/Projects/WQC.html) highlighted a number of significant problems in GSN data quality, including the frequency-dependent loss of gain in the STS-1 seismometer (Ekström et al., 2006) that has been attributed to the presence of humidity in the electronics, cables, and connectors (Yuki and Ishihara, 2002; Hutt and Ringler, 2011). The reports from the WQC spurred a number of changes in the operation of the GSN, including the adoption of the policy of annual calibrations and the development of new tools and metrics to monitor, evaluate, and communicate data quality. In parallel, the USGS' Albuquerque Seismological Laboratory (ASL) and UCSD's Project IDA worked with the IRIS Consortium to upgrade GSN stations with new data acquisition systems, to refurbish the STS-1 seismometers with new electronics, and to expand the deployment of secondary broadband sensors. We revisit the 2010 reports, using the tools of the WQC as well as a number of newly developed tools such as the USGS' Data Quality Analyzer and IRIS' MUSTANG, and provide an update on GSN data quality. Our initial focus is on CASY and KIP, the first two stations reviewed by the WQC. Our goal is to evaluate progress in the last five years and assess our ability to quantify data quality as well as to identify potential problems that could compromise data quality in the future. Ekström, G., C. A. Dalton, and M. Nettles (2006). Observations of time-dependent errors in long-period instrument gain at global seismic stations. Seismological Research Letters

  12. Are Field OB Stars Alone?

    NASA Astrophysics Data System (ADS)

    Oey, Sally

    2005-07-01

    This SNAP program offers an inexpensive, simple program to search for low-mass companions of field OB stars. Do field OB stars exist in true isolation, as suggested by a recent Galactic study, or are they the tip of the iceberg on a small cluster of low-mass stars as predicted by the cluster mass function and stellar IMF? Short ACS/WFC V and I observations proposed here may easily resolve this issue for field OB stars in the Small Magellanic Cloud. Truly isolated OB stars represent a theoretical challenge and variation from clusters, in mode of star formation, and have important consequences for our understanding of the field stellar population in galaxies. Small clusters around the field OB stars, on the other hand, may confirm the universality of the stellar clustering law and IMF.

  13. Dead Star Rumbles

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site] Composite of Supernova Remnant Cassiopeia A This Spitzer Space Telescope composite shows the supernova remnant Cassiopeia A (white ball) and surrounding clouds of dust (gray, orange and blue). It consists of two processed images taken one year apart. Dust features that have not changed over time appear gray, while those that have changed are colored blue or orange. Blue represents an earlier time and orange, a later time.

    These observations illustrate that a blast of light from Cassiopeia A is waltzing outward through the dusty skies. This dance, called an 'infrared echo,' began when the remnant erupted about 50 years ago.

    Cassiopeia A is the remnant of a once massive star that died in a violent supernova explosion 325 years ago. It consists of a dead star, called a neutron star, and a surrounding shell of material that was blasted off as the star died. This remnant is located 10,000 light-years away in the northern constellation Cassiopeia.

    An infrared echo is created when a star explodes or erupts, flashing light into surrounding clumps of dust. As the light zips through the dust clumps, it heats them up, causing them to glow successively in infrared, like a chain of Christmas bulbs lighting up one by one. The result is an optical illusion, in which the dust appears to be flying outward at the speed of light. This apparent motion can be seen here by the shift in colored dust clumps.

    Echoes are distinct from supernova shockwaves, which are made up material that is swept up and hurled outward by exploding stars.

    This infrared echo is the largest ever seen, stretching more than 50 light-years away from Cassiopeia A. If viewed from Earth, the entire movie frame would take up the same amount of space as two full moons.

    Hints of an older infrared echo from Cassiopeia A's supernova explosion hundreds of years ago can also be seen.

    The earlier Spitzer image was taken on November 30

  14. Gaining Insight into Star Formation: Resolved Star Formation Laws

    NASA Astrophysics Data System (ADS)

    Liebst, Kelley; Scowen, Paul A.

    2014-06-01

    Until recently astronomers have used star formation laws to measure the star formation rate and star formation efficiency of galaxies only on global scales because of the poor resolution of available data. What I am now capable of producing is a spatially resolved star formation law that can provide direct insight into the physical processes that govern star formation and assess the short-term nature of bursts of star formation and the longer-term nature of larger-scale events that can dictate the global distribution of stars and the ultimate fate of a galaxy as a whole. I am using exquisite narrowband optical data from a variety of sources, including the Hubble Space Telescope, and Kitt Peak National Observatory, etc., in conjunction with infrared data from the Spitzer Infrared Nearby Galaxy Survey and the Spitzer Local Volume Legacy survey, neutral gas data from The HI Nearby Galaxy Survey, and molecular gas data from the Berkeley-Illinois-Maryland Association Survey of Nearby Galaxies, to provide star formation rates and star formation efficiencies on previously inaccessible small spatial scales across a suite of galaxies that represent a range of star formation environments and scales. My sample includes 18 spiral galaxies ranging from 2.1 to 15.1 Mpc in distance and offers a large range of morphological types (i.e. a large range of star formation environments). I am using these data to test different models of star formation modes under a variety of physical conditions and relate the variations I observe to the known local physical conditions and the associated star formation histories for each locale within each galaxy.This is the heart of the matter - that the nature and evolution of the local physical environment intimately influences how stars can form, how quickly and how massive those stars are allowed to form, and as a result how they shape the local conditions for subsequent star formation. It is this tracking of the stellar ecology that is vital for

  15. Neutron Star Science with the NuSTAR

    SciTech Connect

    Vogel, J. K.

    2015-10-16

    The Nuclear Spectroscopic Telescope Array (NuSTAR), launched in June 2012, helped scientists obtain for the first time a sensitive high-­energy X-­ray map of the sky with extraordinary resolution. This pioneering telescope has aided in the understanding of how stars explode and neutron stars are born. LLNL is a founding member of the NuSTAR project, with key personnel on its optics and science team. We used NuSTAR to observe and analyze the observations of different neutron star classes identified in the last decade that are still poorly understood. These studies not only help to comprehend newly discovered astrophysical phenomena and emission processes for members of the neutron star family, but also expand the utility of such observations for addressing broader questions in astrophysics and other physics disciplines. For example, neutron stars provide an excellent laboratory to study exotic and extreme phenomena, such as the equation of state of the densest matter known, the behavior of matter in extreme magnetic fields, and the effects of general relativity. At the same time, knowing their accurate populations has profound implications for understanding the life cycle of massive stars, star collapse, and overall galactic evolution.

  16. 14 CFR 1214.205 - Revisit and/or retrieval services.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 5 2011-01-01 2010-01-01 true Revisit and/or retrieval services. 1214.205... Substantial Investment in the STS Program § 1214.205 Revisit and/or retrieval services. These services will be... dedicated price will be charged. If the user's retrieval requirement is such that it can be accomplished...

  17. 14 CFR 1214.205 - Revisit and/or retrieval services.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 5 2010-01-01 2010-01-01 false Revisit and/or retrieval services. 1214.205... Substantial Investment in the STS Program § 1214.205 Revisit and/or retrieval services. These services will be... dedicated price will be charged. If the user's retrieval requirement is such that it can be accomplished...

  18. 14 CFR 1214.205 - Revisit and/or retrieval services.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 14 Aeronautics and Space 5 2012-01-01 2012-01-01 false Revisit and/or retrieval services. 1214.205... Substantial Investment in the STS Program § 1214.205 Revisit and/or retrieval services. These services will be... dedicated price will be charged. If the user's retrieval requirement is such that it can be accomplished...

  19. 14 CFR § 1214.205 - Revisit and/or retrieval services.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 5 2014-01-01 2014-01-01 false Revisit and/or retrieval services. § 1214... Have Made Substantial Investment in the STS Program § 1214.205 Revisit and/or retrieval services. These..., the full dedicated price will be charged. If the user's retrieval requirement is such that it can...

  20. 14 CFR 1214.205 - Revisit and/or retrieval services.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 14 Aeronautics and Space 5 2013-01-01 2013-01-01 false Revisit and/or retrieval services. 1214.205... Substantial Investment in the STS Program § 1214.205 Revisit and/or retrieval services. These services will be... dedicated price will be charged. If the user's retrieval requirement is such that it can be accomplished...

  1. Flattest Star Ever Seen

    NASA Astrophysics Data System (ADS)

    2003-06-01

    VLT Interferometer Measurements of Achernar Challenge Stellar Theory Summary To a first approximation, planets and stars are round. Think of the Earth we live on. Think of the Sun, the nearest star, and how it looks in the sky. But if you think more about it, you realize that this is not completely true. Due to its daily rotation, the solid Earth is slightly flattened ("oblate") - its equatorial radius is some 21 km (0.3%) larger than the polar one. Stars are enormous gaseous spheres and some of them are known to rotate quite fast, much faster than the Earth. This would obviously cause such stars to become flattened. But how flat? Recent observations with the VLT Interferometer (VLTI) at the ESO Paranal Observatory have allowed a group of astronomers [1] to obtain by far the most detailed view of the general shape of a fast-spinning hot star, Achernar (Alpha Eridani) , the brightest in the southern constellation Eridanus (The River). They find that Achernar is much flatter than expected - its equatorial radius is more than 50% larger than the polar one! In other words, this star is shaped very much like the well-known spinning-top toy, so popular among young children. The high degree of flattening measured for Achernar - a first in observational astrophysics - now poses an unprecedented challenge for theoretical astrophysics . The effect cannot be reproduced by common models of stellar interiors unless certain phenomena are incorporated, e.g. meridional circulation on the surface ("north-south streams") and non-uniform rotation at different depths inside the star. As this example shows, interferometric techniques will ultimately provide very detailed information about the shapes, surface conditions and interior structure of stars . PR Photo 15a/03 : The VLT Interferometer configuration for the Achernar measurements PR Photo 15b/03 : Achernar's "profile" , as measured by the VLTI. PR Photo 15c/03 : Models of Achernar's spatial shape. VLTI observations of Achernar

  2. Enthalpy-Entropy Compensation (EEC) Effect: A Revisit.

    PubMed

    Pan, Animesh; Biswas, Tapas; Rakshit, Animesh K; Moulik, Satya P

    2015-12-31

    A short account of the developments and perspectives of IKR (iso-kinetic relation) and EEC (enthalpy (H) - entropy (S) compensation) has been presented. The IKR and EEC are known to be extra thermodynamic or empirical correlations though linear H-S correlation can be thermodynamically deduced. Attempt has also been made to explain the phenomena in terms of statistical thermodynamics. In this study, we have briefly revisited the fundamentals of both IKR and EEC from kinetic and thermodynamic grounds. A detailed revisit of the EEC phenomenon on varied kinetic and equilibrium processes has been also presented. Possible correlations among the free energy (ΔG), enthalpy (ΔH), and entropy (ΔS) changes of different similar and nonsimilar chemical processes under varied conditions have been discussed with possible future projections.

  3. Hyperons and neutron stars

    SciTech Connect

    Vidaña, Isaac

    2015-02-24

    In this lecture I will briefly review some of the effects of hyperons on the properties of neutron and proto-neutron stars. In particular, I will revise the problem of the strong softening of the EoS, and the consequent reduction of the maximum mass, induced by the presence of hyperons, a puzzle which has become more intringuing and difficult to solve due the recent measurements of the unusually high masses of the millisecond pulsars PSR J1903+0327 (1.667±0.021M{sub ⊙}), PSR J1614–2230 (1.97±0.04M{sub ⊙}), and PSR J0348+0432 (2.01±0.04M{sub ⊙}). Finally, I will also examine the role of hyperons on the cooling properties of newly born neutron stars and on the so-called r-mode instability.

  4. Stars at Gammasphere

    NASA Astrophysics Data System (ADS)

    Bernstein, L. A.; Schiller, A.; Cooper, J. R.; Becker, J. A.; Fallon, P.; Macchiavelli, M. A.; McMahan, M. A.; Guttormsen, M.; Rekstad, J. B.; Siem, S.; Sarantites, D. G.; Sobotka, L. G.; Mitchell, G. E.; Tavukcu, E.

    2002-10-01

    STARS (Silicon Telescope Array for Reaction Studies) is a highly segmented array of particle telescope designed to allow for particle-gamma coincidence measurements in both forward and inverse kinematics at either forward or backward angles using GAMAMSPHERE. Two different arrays of Silicon surface barrier detectors can be employed depending on the configuration of the experiment. The first STARS experiment at GAMMASPHERE took place in April 2002. The ^157Gd(^3He,α)^156Gd reaction at E_α = 45 MeV was used to a) measure level densities and gamma-ray strength functions below the neutron binding energy, and b) to simulate neutron-induced reactions on ^155Gd. Preliminary results from this experiment will be presented. This work was funded by the US Department of Energy under contracts number W-7405-ENG-48 (LLNL), AC03-76SF00098 (LBNL) and the Norwegian Research Council (Oslo).

  5. Shooting Star Experiment

    NASA Technical Reports Server (NTRS)

    1997-01-01

    The Shooting Star Experiment (SSE) is designed to develop and demonstrate the technology required to focus the sun's energy and use the energy for inexpensive space Propulsion Research. Pictured is an engineering model (Pathfinder III) of the Shooting Star Experiment (SSE). This model was used to test and characterize the motion and deformation of the structure caused by thermal effects. In this photograph, alignment targets are being placed on the engineering model so that a theodolite (alignment telescope) could be used to accurately measure the deformation and deflections of the engineering model under extreme conditions, such as the coldness of deep space and the hotness of the sun as well as vacuum. This thermal vacuum test was performed at the X-Ray Calibration Facility because of the size of the test article and the capabilities of the facility to simulate in-orbit conditions

  6. O-star kinematics

    SciTech Connect

    Karimova, D.K.; Pavlovskaya, E.D.

    1984-01-01

    Proper motions determined by the authors are utilized to study the kinematics of 79 O-type stars at distance r< or =2.5 kpc. The sample is divided into two groups, having space-velocity dispersions tau/sub I/roughly-equal10 km/sec, sigma/sub II/roughly-equal35 km/sec. Solutions for the velocity-field parameters for group I yield a galactic angular rotation speed ..omega../sub 0/ = 24.9 km sec/sup -1/ kpc/sup -1/ at the sun (for R/sub 0/ = 10.0 kpc) and an Oort constant A = 12.2 km sec/sup -1/ kpc/sup -1/. Most of the O stars exhibit a small z-velocity directed away from the galactic plane. The velocity-ellipsoid parameters and box-orbit elements are calculated.

  7. White Dwarf Stars

    NASA Technical Reports Server (NTRS)

    1999-01-01

    Peering deep inside a cluster of several hundred thousand stars, NASA's Hubble Space Telescope has uncovered the oldest burned-out stars in our Milky Way Galaxy, giving astronomers a fresh reading on the age of the universe.

    Located in the globular cluster M4, these small, burned-out stars -- called white dwarfs -- are about 12 to 13 billion years old. By adding the one billion years it took the cluster to form after the Big Bang, astronomers found that the age of the white dwarfs agrees with previous estimates that the universe is 13 to 14 billion years old.

    The images, including some taken by Hubble's Wide Field and Planetary Camera 2, are available online at

    http://oposite.stsci.edu/pubinfo/pr/2002/10/ or

    http://www.jpl.nasa.gov/images/wfpc .

    The camera was designed and built by NASA's Jet Propulsion Laboratory, Pasadena, Calif.

    In the top panel, a ground-based observatory snapped a panoramic view of the entire cluster, which contains several hundred thousand stars within a volume of 10 to 30 light-years across. The Kitt Peak National Observatory's .9-meter telescope took this picture in March 1995. The box at left indicates the region observed by the Hubble telescope.

    The Hubble telescope studied a small region of the cluster. A section of that region is seen in the picture at bottom left. A sampling of an even smaller region is shown at bottom right. This region is only about one light-year across. In this smaller region, Hubble pinpointed a number of faint white dwarfs. The blue circles indicate the dwarfs. It took nearly eight days of exposure time over a 67-day period to find these extremely faint stars.

    Globular clusters are among the oldest clusters of stars in the universe. The faintest and coolest white dwarfs within globular clusters can yield a globular cluster's age. Earlier Hubble observations showed that the first stars formed less than 1 billion years after the universe's birth in the big bang. So, finding the

  8. What Is Inflammatory Breast Cancer? Revisiting the Case Definition

    DTIC Science & Technology

    2010-03-03

    Cancer? Revisiting the Case Definition Paul H. Levine 1 ,*, Ladan Zolfaghari 1 , Heather Young 1 , Muhannad Hafi 1 , Timothy Cannon 1 , Chitra Ganesan 1 ...Carmela Veneroso 1 , Rachel Brem 2 and Mark Sherman 3 1 The Department of Epidemiology and Biostatistics, George Washington University School of...gwumc.edu; Tel.: + 1 -202-994-4582; Fax: + 1 -202-994-0082. Received: 14 December 2009; in revised form: 10 February 2010 / Accepted: 1 March 2010

  9. Non linear evolution: revisiting the solution in the saturation region

    NASA Astrophysics Data System (ADS)

    Contreras, Carlos; Levin, Eugene; Meneses, Rodrigo

    2014-10-01

    In this paper we revisit the problem of the solution to Balitsky-Kovchegov equation deeply in the saturation domain. We find that solution has the form given in ref. [23] but it depends on variable and the value of Const is calculated in this paper. We propose the solution for full BFKL kernel at large in the entire kinematic region that satisfies the McLerran-Venugopalan-type [3-7] initial condition.

  10. Discussion of "Computational Electrocardiography: Revisiting Holter ECG Monitoring".

    PubMed

    Baumgartner, Christian; Caiani, Enrico G; Dickhaus, Hartmut; Kulikowski, Casimir A; Schiecke, Karin; van Bemmel, Jan H; Witte, Herbert

    2016-08-05

    This article is part of a For-Discussion-Section of Methods of Information in Medicine about the paper "Computational Electrocardiography: Revisiting Holter ECG Monitoring" written by Thomas M. Deserno and Nikolaus Marx. It is introduced by an editorial. This article contains the combined commentaries invited to independently comment on the paper of Deserno and Marx. In subsequent issues the discussion can continue through letters to the editor.

  11. Indoor air and human health revisited: A recent IAQ symposium

    SciTech Connect

    Gammage, R.B.

    1994-12-31

    Indoor Air and Human Health Revisited was a speciality symposium examining the scientific underpinnings of sensory and sensitivity effects, allergy and respiratory disease, neurotoxicity and cancer. An organizing committee selected four persons to chain the sessions and invite experts to give state-of-the-art presentations that will be published as a book. A summary of the presentations is made and some critical issues identified.

  12. Dilepton Measurements at STAR

    NASA Astrophysics Data System (ADS)

    Geurts, Frank; STAR Collaboration

    2013-08-01

    In the study of hot and dense nuclear matter, created in relativistic heavy-ion collisions, dilepton measurements play an essential role. Leptons, when compared to hadrons, have only little interaction with the strongly interacting system. Thus, dileptons provide ideal penetrating probes that allow the study of such a system throughout its space-time evolution. In the low mass range (Mll < 1.1 GeV/c2), the dominant source of dileptons originates from the decay of vector mesons which may see effects from chiral symmetry restoration. In the intermediate mass range (1.1 < Mll < 3.0 GeV/c2), the main contributions to the mass spectrum are expected to originate from the thermal radiation of a quark-gluon plasma as well as the decays of charm mesons. In the high mass range (Mll > 3.0 GeV/c2), dilepton measurements are expected to see contributions from primordial processes involving heavy quarks, and Drell-Yan production. With the introduction of the Time-of-Flight detector, the STAR detector has been able to perform large acceptance, high purity electron identification. In this contribution, we will present STAR's recent dielectron measurements in the low and intermediate mass range for RHIC beam energies ranging between 19.6 and 200 GeV. Compared to electrons, muon measurements have the advantage of reduced bremsstrahlung radiation in the surrounding detector materials. With the upcoming detector upgrades, specifically the muon detector (MTD), STAR will be able to include such measurements in its (di-)lepton studies. We will discuss the future dilepton program at STAR and the physics cases for these upgrades.

  13. Detector limitations, STAR

    SciTech Connect

    Underwood, D. G.

    1998-07-13

    Every detector has limitations in terms of solid angle, particular technologies chosen, cracks due to mechanical structure, etc. If all of the presently planned parts of STAR [Solenoidal Tracker At RHIC] were in place, these factors would not seriously limit our ability to exploit the spin physics possible in RHIC. What is of greater concern at the moment is the construction schedule for components such as the Electromagnetic Calorimeters, and the limited funding for various levels of triggers.

  14. The STAR PXL detector

    NASA Astrophysics Data System (ADS)

    Contin, G.

    2016-12-01

    The PiXeL detector (PXL) of the STAR experiment at RHIC is the first application of the state-of-the-art thin Monolithic Active Pixel Sensors (MAPS) technology in a collider environment. Designed to extend the STAR measurement capabilities in the heavy flavor domain, it took data in Au+Au collisions, p+p and p+Au collisions at 0√sNN=20 GeV at RHIC, during the period 2014-2016. The PXL detector is based on 50 μm-thin MAPS sensors with a pitch of 20.7 μm. Each sensor includes an array of nearly 1 million pixels, read out in rolling shutter mode in 185.6 μs. The 170 mW/cm2 power dissipation allows for air cooling and contributes to reduce the global material budget to 0.4% radiation length on the innermost layer. Experience and lessons learned from construction and operations will be presented in this paper. Detector performance and results from 2014 Au+Au data analysis, demonstrating the STAR capabilities of charm reconstruction, will be shown.

  15. A new family of magnetic stars: the Am stars

    NASA Astrophysics Data System (ADS)

    Blazère, A.; Neiner, C.; Petit, P.; Lignières, F.

    2016-12-01

    We presented the discovery of an ultra-weak field in three Am stars, β UMa, θ Leo, and Alhena, thanks to ultra-deep spectropolarimetric observations. Two of the three stars of this study shown peculiar magnetic signatures with prominent positive lobes like the one of Sirius A that are not expected in the standard theory of the Zeeman effect. Alhena, contrary to Sirius A, β UMa and θ Leo, show normal signatures. These detections of ultra-weak fields in Am stars suggest the existence of a new family of magnetic intermediate-mass stars: the Am stars. However the various shapes of the signatures required further observation to identify the physical processes at work in these stars. A preliminary explanation is based on microturbulence.

  16. Revisiting the revisit: added evidence for a social chemosignal in human emotional tears.

    PubMed

    Sobel, Noam

    2017-01-01

    In a study by Gelstein et al., we found that human emotional tears act as a social chemosignal. In the first of three different experiments in that study we observed that sniffing women's emotional tears reduced the sexual attractiveness attributed by men to pictures of women's faces. In a study partly titled "Chemosignaling effects of human tears revisited", Gračanin et al. claim failed replication of this effect in a series of experiments, one they described as "exactly the same procedure" as Gelstein. Given that Gračanin et al. refused our extended offer to jointly replicate the experiment at our expense, we can merely comment on their effort. We find that Gračanin, who are not a chemosignaling laboratory, used methodology that falls short of standards typically applied in chemosignaling research. Thus, their experiments were profoundly different from Gelstein. Finally, we found that in reanalysing their raw data we could in fact replicate the effect from Gelstein. Thus, we conclude that the failed replication in Gračanin is neither a replication nor failed.

  17. Star centroiding error compensation for intensified star sensors.

    PubMed

    Jiang, Jie; Xiong, Kun; Yu, Wenbo; Yan, Jinyun; Zhang, Guangjun

    2016-12-26

    A star sensor provides high-precision attitude information by capturing a stellar image; however, the traditional star sensor has poor dynamic performance, which is attributed to its low sensitivity. Regarding the intensified star sensor, the image intensifier is utilized to improve the sensitivity, thereby further improving the dynamic performance of the star sensor. However, the introduction of image intensifier results in star centroiding accuracy decrease, further influencing the attitude measurement precision of the star sensor. A star centroiding error compensation method for intensified star sensors is proposed in this paper to reduce the influences. First, the imaging model of the intensified detector, which includes the deformation parameter of the optical fiber panel, is established based on the orthographic projection through the analysis of errors introduced by the image intensifier. Thereafter, the position errors at the target points based on the model are obtained by using the Levenberg-Marquardt (LM) optimization method. Last, the nearest trigonometric interpolation method is presented to compensate for the arbitrary centroiding error of the image plane. Laboratory calibration result and night sky experiment result show that the compensation method effectively eliminates the error introduced by the image intensifier, thus remarkably improving the precision of the intensified star sensors.

  18. Insights on the First Stars from CEMP-no Stars

    NASA Astrophysics Data System (ADS)

    Choplin, Arthur; Meynet, Georges; Maeder, André; Hirschi, Raphael; Ekström, Sylvia; Chiappini, Cristina

    CEMP-no stars (Carbon-Enhanced metal-poor stars with no or few s- or r-elements) are long-lived low mass stars presenting a very low iron content and overabundances of carbon relatively to the sun. Their chemically peculiar abundance pattern could be inherited from a previous rotating massive star, also called the source star. Thanks to the rotational mixing at work in the source star, the chemical species transit from a hydrogen burning region to a helium burning region, leading to a varied and rich nucleosynthesis. Depending on the initial rotation of the source star, the internal mixing is more or less important, leading to a different nucleosynthesis. We suggest first that the observed 12C/13C ratio might constrain the mass cut of the source star. Then, we apply that constraint on a set of 20 M ȯ source stars models with various initial rotation rates. We show that the ejecta of these 20 M ȯ models match rather well the observed scatters of C/H, N/H, O/H, and Na/H of the CEMP-no sample. The impact of changing the reaction rate of 27Al(p, γ )28Si is also investigated.

  19. Astrophysics of Collapsing Axion Stars

    NASA Astrophysics Data System (ADS)

    Eby, Joshua; Leembruggen, Madelyn; Suranyi, Peter; Wijewardhana, L. C. R.

    2017-01-01

    Axion stars are condensed states of large numbers of axion particles, bound by self-gravitation and quantum self-interactions. The mass of weakly bound axion stars is limited by gravitational stability, with condensates exceeding the maximum mass subject to collapse. During the collapse process, the axion density increases and higher-order self-interactions become increasingly relevant. By taking these terms into account, we provide evidence that in spite of a leading attractive interaction, collapsing axion stars stabilize in a dense state which is larger than its Schwarzschild radius, and so do not form black holes. During the last moments of collapse, number changing processes take place in the axion star with a very large rate, leading to emission of many highly energetic axions which escape from galaxies and galaxy clusters. Finally, if axion stars are a significant fraction of cold dark matter, then frequent collisions with each other or with ordinary stars could catalyze this collapse process as well.

  20. The Birth of Stars and Planets

    NASA Astrophysics Data System (ADS)

    Bally, John; Reipurth, Bo

    2006-08-01

    Part I. Stars and Clusters: 1. Our Cosmic Backyard; 2. Looking up at the night sky; 3. The dark clouds of the Milky Way; 4. Infant stars; 5. Companions in birth: binary stars; 6. Outflows from young stars; 7. Towards adulthood; 8. The social life of stars: stellar groups; 9. Chaos in the nest: The brief lives of massive stars. Part II. Planetary Systems: 10. Solar systems in the making; 11. Messengers from the past; 12. Hazards to planet formation; 13. Planets around other stars; Part III. The Cosmic Context: 14. Cosmic cycles; 15. Star formation in galaxies; 16. The first stars and galaxies; 17. Astrobiology, origins, and SETI.

  1. Short-term variability and mass loss in Be stars. II. Physical taxonomy of photometric variability observed by the Kepler spacecraft

    NASA Astrophysics Data System (ADS)

    Rivinius, Th.; Baade, D.; Carciofi, A. C.

    2016-09-01

    Context. Classical Be stars have been established as pulsating stars. Space-based photometric monitoring missions contributed significantly to that result. However, whether Be stars are just rapidly rotating SPB or β Cep stars, or whether they have to be understood differently, remains debated in the view of their highly complex power spectra. Aims: Kepler data of three known Be stars are re-visited to establish their pulsational nature and assess the properties of additional, non-pulsational variations. The three program stars turned out to be one inactive Be star, one active, continuously outbursting Be star, and one Be star transiting from a non-outbursting into an outbursting phase, thus forming an excellent sample to distill properties of Be stars in the various phases of their life-cycle. Methods: The Kepler data was first cleaned from any long-term variability with Lomb-Scargle based pre-whitening. Then a Lomb-Scargle analysis of the remaining short-term variations was compared to a wavelet analysis of the cleaned data. This offers a new view on the variability, as it enables us to see the temporal evolution of the variability and phase relations between supposed beating phenomena, which are typically not visualized in a Lomb-Scargle analysis. Results: The short-term photometric variability of Be stars must be disentangled into a stellar and a circumstellar part. The stellar part is on the whole not different from what is seen in non-Be stars. However, some of the observed phenomena might be to be due to resonant mode coupling, a mechanism not typically considered for B-type stars. Short-term circumstellar variability comes in the form of either a group of relatively well-defined, short-lived frequencies during outbursts, which are called Štefl frequencies, and broad bumps in the power spectra, indicating aperiodic variability on a time scale similar to typical low-order g-mode pulsation frequencies, rather than true periodicity. Conclusions: From a

  2. The Orion nebula star cluster

    NASA Technical Reports Server (NTRS)

    Panek, R. J.

    1982-01-01

    Photography through filters which suppress nebular light reveal a clustering of faint red stars centered on the Trapezium, this evidences a distinct cluster within the larger OB1 association. Stars within about 20 ft of trapezium comprise the Orion Nebula star cluster are considered. Topics discussed re: (1) extinction by dust grains; (2) photometric peculiarities; (3) spectroscopic peculiarities; (4) young variables; (5) the distribution and motion of gas within the cluster.

  3. Massive star clusters in galaxies.

    PubMed

    Harris, William E

    2010-02-28

    The ensemble of all star clusters in a galaxy constitutes its star cluster system. In this review, the focus of the discussion is on the ability of star clusters, particularly the systems of old massive globular clusters (GCs), to mark the early evolutionary history of galaxies. I review current themes and key findings in GC research, and highlight some of the outstanding questions that are emerging from recent work.

  4. The Brightest Delta Scuti Star

    NASA Astrophysics Data System (ADS)

    Buzasi, D.; Bruntt, H.; Preston, H.; Mandeville, J.; Bedding, T.; Retter, A.; Kjeldsen, H.

    2003-12-01

    We present an analysis of observations of the bright star Altair (α Aql) obtained using the star camera on the Wide Field Infrared Explorer (WIRE) satellite. Although Altair lies within the δ Scuti instability strip, previous observations have not revealed the presence of oscillations. However, the WIRE observations show Altair to be a low amplitude (Δ m < 500 μ mag) δ Scuti star with at least 5 modes present. We further show that the detected frequencies are compatible with models for Altair.

  5. Strange Stars, Neutron Stars and Pulsar Emission

    NASA Astrophysics Data System (ADS)

    Benvenuto, O. G.; Horvath, J. E.

    1990-11-01

    RESUMEN. Se ha conjeturado que una partlecula de dieciocho quarks, sin Carga, sin espi'n y sin colar (quark-alfa) podri'a ser estable a ba5as tern peraturas y presiones aiTh COfl respecto a materia extrafla. Presentamos en este trabajo la estmctura de estrellas extraflas incluyendo los efectos y apariencia de parti'culas uark-alfa en las capas exteriores. La estruc tura interna ya no es hoinogenea del centro a la superficie, sino que muestra un centro de materia extrafla, capas s6lidas y una costra delgada de materia normal en la superficie. La superficie de materia nonnal permite la fornaci6n de una magnetosfera, la que se piensa sea el sitlo en donde ocurre la emisi6n del pulsar. La superficie de superflui'do ayuda a explicar el fen6rneno de `glitch', el cual ba sido observado en muchos pulsares. Se discute la ecuaci6n de estado para rnateria quark-alfa relevante en este regimen. ABSTIZACT:It has been conjectured that an quark, uncharged, spinless and colorless particle Cquark-alpha) could be stable at low pressures and temperatures even with respect to strange matter. We present in work tlie structure of stars including the effects of the appearance of quark-alpi' particles ii their outer layers. The internal structure is no longer from tlie center to the surface, but show a strange matter core, a solid and superfluid layers and a thin crust of normal matter at the surface. The normal matter surface allows tlie fon tion of a magnetosphere, whicl is to be tl place where pulsar emission occurs. A superfluid layer helps to explain tlie glitch , wlflch has been observed in . equation of state for quark-alpha matter relevant in regime is also discussed. Keq LA)OtL : ARY S - OF STATF - ?.ACT

  6. Space Science in Action: Stars [Videotape].

    ERIC Educational Resources Information Center

    1999

    This videotape recording shows students the many ways scientists look at the stars and how they can use what they see to answer questions such as What are stars made of?, How far away are they?, and How old are the stars? Students learn about the life span of stars and the various stages they pass through from protostar to main sequence star to…

  7. Apple Valley Double Star Workshop

    NASA Astrophysics Data System (ADS)

    Brewer, Mark

    2015-05-01

    The High Desert Astronomical Society hosts an annual double star workshop, where participants measure the position angles and separations of double stars. Following the New Generation Science Standards (NGSS), adopted by the California State Board of Education, participants are assigned to teams where they learn the process of telescope set-up and operation, the gathering of data, and the reduction of the data. Team results are compared to the latest epoch listed in the Washington Double Star Catalog (WDS) and papers are written for publication in the Journal of Double Star Observations (JDSO). Each team presents a PowerPoint presentation to their peers about actual hands-on astronomical research.

  8. Thermal instability in DAV stars

    NASA Astrophysics Data System (ADS)

    Labrador, J.; Falcon, N.

    2008-01-01

    The short period of the fluctuations of stars DAV, in the order of the hun dreds of seconds; the modes of luminosity oscillation's to constant radio, and the non existence of fusion processes in such stars invite elaboration of models in the formalism of Mixing Length Theory of Convection(MLT). In the present work a mechanism of luminosity variation in DAV stars based on thermodynamic processes of non balance with homogenous convection. The results of the model allow satisfactorily reproducing the light curves of DAV classic stars: G29- 38, GD 358, HL Tau- 76 and WD1647+1591.

  9. Optical filtering for star trackers

    NASA Technical Reports Server (NTRS)

    Wilson, R. E.

    1973-01-01

    The optimization of optical filtering was investigated for tracking faint stars, down to the fifth magnitude. The effective wavelength and bandwidth for tracking pre-selected guide stars are discussed along with the results of an all-electronic tracker with a star tracking photomultiplier, which was tested with a simulated second magnitude star. Tables which give the sum of zodiacal light and galactic background light over the entire sky for intervals of five degrees in declination, and twenty minutes in right ascension are included.

  10. Stellar populations in star clusters

    NASA Astrophysics Data System (ADS)

    Li, Cheng-Yuan; de Grijs, Richard; Deng, Li-Cai

    2016-12-01

    Stellar populations contain the most important information about star cluster formation and evolution. Until several decades ago, star clusters were believed to be ideal laboratories for studies of simple stellar populations (SSPs). However, discoveries of multiple stellar populations in Galactic globular clusters have expanded our view on stellar populations in star clusters. They have simultaneously generated a number of controversies, particularly as to whether young star clusters may have the same origin as old globular clusters. In addition, extensive studies have revealed that the SSP scenario does not seem to hold for some intermediate-age and young star clusters either, thus making the origin of multiple stellar populations in star clusters even more complicated. Stellar population anomalies in numerous star clusters are well-documented, implying that the notion of star clusters as true SSPs faces serious challenges. In this review, we focus on stellar populations in massive clusters with different ages. We present the history and progress of research in this active field, as well as some of the most recent improvements, including observational results and scenarios that have been proposed to explain the observations. Although our current ability to determine the origin of multiple stellar populations in star clusters is unsatisfactory, we propose a number of promising projects that may contribute to a significantly improved understanding of this subject.

  11. Fragmentation in massive star formation.

    PubMed

    Beuther, Henrik; Schilke, Peter

    2004-02-20

    Studies of evolved massive stars indicate that they form in a clustered mode. During the earliest evolutionary stages, these regions are embedded within their natal cores. Here we present high-spatial-resolution interferometric dust continuum observations disentangling the cluster-like structure of a young massive star-forming region. The derived protocluster mass distribution is consistent with the stellar initial mass function. Thus, fragmentation of the initial massive cores may determine the initial mass function and the masses of the final stars. This implies that stars of all masses can form via accretion processes, and coalescence of intermediate-mass protostars appears not to be necessary.

  12. Accretion Onto Magnetic Degenerate Stars

    NASA Technical Reports Server (NTRS)

    Frank, Juhan

    2000-01-01

    While the original objectives of this research program included the study of radiative processes in cataclysmic variables and the evolution of neutron star magnetic fields, the scope of the reported research expanded to other related topics as this project developed. This final report therefore describes the results of our research in the following areas: 1) Irradiation-driven mass transfer cycles in cataclysmic variables and low-mass X-ray binaries; 2) Propeller effect and magnetic field decay in isolated old neutron stars; 3) Decay of surface magnetic fields in accreting neutron stars and pulsars; 4) Finite-Difference Hydrodynamic simulations of mass transfer in binary stars.

  13. Revisiting Black Holes as Dark Matter

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2017-02-01

    Could dark matter be made of intermediate-mass black holes formed in the beginning of the universe? A recent study takes a renewed look at this question.Galactic LurkersThe nature of dark matter has long been questioned, but the recent discovery of gravitational waves by the Laser Interferometer Gravitational-Wave Observatory (LIGO) has renewed interest in the possibility that dark matter could consist of primordial black holes in the mass range of 101000 solar masses.The relative amounts of the different constituents of the universe. Dark matter makes up roughly 27%. [ESA/Planck]According to this model, the extreme density of matter present during the universes early expansion led to the formation of a large number of intermediate-mass black holes. These black holes now hide in the halos of galaxies, constituting the mass that weve measured dynamically but remains unseen.LIGOs first gravitational-wave detection revealed the merger of two black holes that were both tens of solar masses in size. If primordial black holes are indeed a major constituent of dark matter, then LIGOs detection is consistent with what we would expect to find: occasional mergers of the intermediate-mass black holes that formed in the early universe and now lurk in galactic halos.Quasar MicrolensingTheres a catch, however. If there truly were a large number of intermediate-mass primordial black holes hiding in galactic halos, they wouldnt go completely unnoticed: we would see signs of their presence in the gravitational microlensing of background quasars. Unseen primordial black holes in a foreground galaxy could cause an image of a background quasar to briefly brighten which would provide us with clear evidence of such black holes despite our not being able to detect them directly.A depiction of quasar microlensing (click for a closer look!). The microlensing object in the foreground galaxy could be a star (as depicted), a primordial black hole, or any other compact object. [NASA

  14. Stars with Extended Atmospheres

    NASA Astrophysics Data System (ADS)

    Sterken, C.

    2002-12-01

    This Workshop consisted of a full-day meeting of the Working Group "Sterren met Uitgebreide Atmosferen" (SUA, Working Group Stars with Extended Atmospheres), a discussion group founded in 1979 by Kees de Jager, Karel van der Hucht and Pik Sin The. This loose association of astronomers and astronomy students working in the Dutch-speaking part of the Low Countries (The Netherlands and Flanders) organised at regular intervals one-day meetings at the Universities of Utrecht, Leiden, Amsterdam and Brussels. These meetings consisted of the presentation of scientific results by junior as well as senior members of the group, and by discussions between the participants. As such, the SUA meetings became a forum for the exchange of ideas, and for asking questions and advice in an informal atmosphere. Kees de Jager has been chairman of the WG SUA from the beginning in 1979 till today, as the leading source of inspiration. At the occasion of Prof. Kees de Jager's 80th birthday, we decided to collect the presented talks in written form as a Festschrift in honour of this well-respected and much beloved scientist, teacher and friend. The first three papers deal with the personality of Kees de Jager, more specifically with his role as a supervisor and mentor of young researchers and as a catalyst in the research work of his colleagues. And also about his remarkable role in the establishment of astronomy education and research at the University of Brussels. The next presentation is a very detailed review of solar research, a field in which Cees was prominently active for many years. Then follow several papers dealing with stars about which Kees is a true expert: massive stars and extended atmospheres.

  15. Stars and Star Clusters: A Look at Intermediate-Mass Star-Forming Regions

    NASA Astrophysics Data System (ADS)

    Lundquist, Michael J.; Kobulnicky, Henry A.; Lau, Ryan M.

    2017-01-01

    Star-forming regions hosting intermediate-mass stars straddle the boundary separating the the low- and high-mass regimes. These intermediate-mass star-forming regions can be used to probe this transition from low- to high-mass star formation. Our team has assembled an all-sky catalog of 616 candidate intermediate-mass star forming regions (IMSFRs) selected by IRAS colors and refined by visual inspection of WISE imagery. We present here two outer-Galaxy star-forming regions, IRAS22451+6154 and IRAS23448+6010, that despite having similar IRAS colors and mid-infrared morphologies, have vastly different stellar content. We combine Gemini and IRTF NIR spectroscopy with WIYN and SOFIA imaging for a thorough look at the stellar content of these two regions.

  16. Sketching Star Clusters

    NASA Astrophysics Data System (ADS)

    Perez, Jeremy

    The next time you plan a quiet evening under a salted sky, with hopes of bathing your eyes in the ancient light of a majestic star cluster, be sure that your sketching kit comes with you! A casual glance at these celestial marvels will not give you a decent appreciation for an object whose history and character are as unique as the fingerprints you should be pressing into the side of your trusty pencil. I can think of no better way to connect with these stellar ballets, to understand their intricacies, and to recall your view later than to spend time sketching the soft glow or blazing pinpricks you see through the eyepiece.

  17. Adsorption of star polymers

    NASA Astrophysics Data System (ADS)

    Halperin, A.; Joanny, J. F.

    1991-06-01

    The adsorption of star polymers on a flat solid surface is analyzed by means of scalling arguments based on the Daoud-Cotton blob model. For the adsorption of a single star, consisting of f arms comprising each N monomers, we distinguish three regimes determined by the adsorption energy of a monomer at the surface, δ kT. 1) Strong adsorption characterized by the full adsorption of all arms occurs for δ > (f/N)^{3/5}. 2) A “Sombrero” like structure comprising f_ads fully adsorbed arms and f{-}f_ads free arms is obtained for (f/N)^{3/5}> δ > f^{9/20}/N^{3/5}. 3) Weakly adsorbed stars retain, essentially, the structure of a free star. This regime occurs for δ < f^{9/20}/N^{3/5}. The weakly adsorbed structure may also exist as a metastable state if δ > f^{9/5}/N^{3/5}. Nous étudions l'adsorption de polymères en étoile sur une surface solide en utilisant une approche de lois d'échelles basée sur le modèle de blobs de Daoud et Cotton. Pour une étoile formée de f bras contenant chacun N monomères, nous distinguons trois régimes suivant la valeur de l'énergie d'adsorption d'un monomère sur la surface δ kT. 1) L'adsorption forte caractérisée par une adsorption complète de tous les bras se produit lorsque δ > (f/N)^{3/5}. 2) Une structure en “sombrero” avec f_ads bras adsorbés et f{-}f_ads bras libres est obtenue si f^{9/20}/N^{3/5}δ < (f/N)^{3/5}. 3) Les étoiles faiblement adsorbées gardent une structure très similaire à celle des étoiles libres en solution. Ce régime existe si δ < f^{9/20}/N^{3/5}. La structure correspondant aux étoiles faiblement adsorbées peut aussi exister comme un état métastable si δ > f^{9/5}/N^{3/5}.

  18. The guide star catalog

    NASA Technical Reports Server (NTRS)

    Lasker, Barry M.; Jenkner, Helmut; Russell, Jane L.

    1987-01-01

    Part 1 of the catalog presents an astronomical overview of the Guide Star Catalog, together with its history, the properties of its current implementation, and the prospects for enhancement. Part 2 presents the algorithms used in photometric and astrometric calibration of the catalog, as well as the analyses of the related errors. Part 3 presents the current structure and content, as well as future enhancements in this area. An overview of the forthcoming publications is given, both with regard to scientific papers and electronic media.

  19. On magnetized neutron stars

    SciTech Connect

    Lopes, Luiz; Menezes, Debora E-mail: debora.p.m@ufsc.br

    2015-08-01

    In this work we review the formalism normally used in the literature about the effects of density-dependent magnetic fields on the properties of neutron and quark stars, expose some ambiguities that arise and propose a way to solve the related problem. Our approach explores more deeply the concept of pressure, yielding the so called chaotic magnetic field formalism for the stress tensor. We also use a different way of introducing a variable magnetic field, which depends on the energy density rather than on the baryonic density, which allows us to build a parameter free model.

  20. Isolation of the Paenibacillus phoenicis, a Spore-Forming Bacterium

    NASA Technical Reports Server (NTRS)

    Benardini, James N.; Vaishampayan, Parag A.; Venkateswaran, Kasthuri J.; Osman, Shariff; Satomi, Masataka

    2010-01-01

    A microorganism was isolated from the surfaces of the cleanroom facility in which the Phoenix lander was assembled. The isolated bacterial strain was subjected to a comprehensive polyphasic analysis to characterize its taxonomic position. Both phenotypic and phylogenetic analyses clearly indicate that this isolate belongs to the genus Paenibacillus and represents a novel species. Bacillus spores have been utilized to assess the degree and level of microbiological contamination on spacecraft and their associated spacecraft assembly facilities. Spores of Bacillus species are of particular concern to planetary protection due to the extreme resistance of some members of the genus to space environmental conditions such as UV and gamma radiation, vacuum, oxidation, and temperature fluctuation. These resistive spore phenotypes have enhanced potential for transfer, and subsequent proliferation, of terrestrial microbes on another solar body. Due to decreased nutrient conditions within spacecraft assembly facility clean rooms, the vegetative cells of Bacillus species and other spore-forming Paenibacillus species are induced to sporulate, thereby enhancing their survivability of bioreduction

  1. Triggered Star Formation Surrounding Wolf-Rayet Star HD 211853

    NASA Astrophysics Data System (ADS)

    Liu, Tie; Wu, Yuefang; Zhang, Huawei; Qin, Sheng-Li

    2012-05-01

    The environment surrounding Wolf-Rayet (W-R) star HD 211853 is studied in molecular, infrared, as well as radio, and H I emission. The molecular ring consists of well-separated cores, which have a volume density of 103 cm-3 and kinematic temperature ~20 K. Most of the cores are under gravitational collapse due to external pressure from the surrounding ionized gas. From the spectral energy distribution modeling toward the young stellar objects, the sequential star formation is revealed on a large scale in space spreading from the W-R star to the molecular ring. A small-scale sequential star formation is revealed toward core "A," which harbors a very young star cluster. Triggered star formations are thus suggested. The presence of the photodissociation region, the fragmentation of the molecular ring, the collapse of the cores, and the large-scale sequential star formation indicate that the "collect and collapse" process functions in this region. The star-forming activities in core "A" seem to be affected by the "radiation-driven implosion" process.

  2. Star-forming galaxy models: Blending star formation into TREESPH

    NASA Technical Reports Server (NTRS)

    Mihos, J. Christopher; Hernquist, Lars

    1994-01-01

    We have incorporated star-formation algorithms into a hybrid N-body/smoothed particle hydrodynamics code (TREESPH) in order to describe the star forming properties of disk galaxies over timescales of a few billion years. The models employ a Schmidt law of index n approximately 1.5 to calculate star-formation rates, and explicitly include the energy and metallicity feedback into the Interstellar Medium (ISM). Modeling the newly formed stellar population is achieved through the use of hybrid SPH/young star particles which gradually convert from gaseous to collisionless particles, avoiding the computational difficulties involved in creating new particles. The models are shown to reproduce well the star-forming properties of disk galaxies, such as the morphology, rate of star formation, and evolution of the global star-formation rate and disk gas content. As an example of the technique, we model an encounter between a disk galaxy and a small companion which gives rise to a ring galaxy reminiscent of the Cartwheel (AM 0035-35). The primary galaxy in this encounter experiences two phases of star forming activity: an initial period during the expansion of the ring, and a delayed phase as shocked material in the ring falls back into the central regions.

  3. The first stars: a classification of CEMP-no stars

    NASA Astrophysics Data System (ADS)

    Maeder, André; Meynet, Georges

    2015-08-01

    Aims: We propose and apply a new classification for the CEMP-no stars, which are carbon-enhanced metal-poor stars with no overabundance of s-elements and with [Fe/H] generally ≤-2.5. Methods: This classification is based on the changes in abundances for the elements and isotopes involved in the CNO, Ne-Na, and Mg-Al nuclear cycles. These abundances change very much owing to successive back and forth mixing motions between the He- and H-burning regions in massive stars (the "source stars" responsible for the chemical enrichment of the CEMP-no stars). Results: The wide variety of the ratios [C/Fe], 12C/13C, [N/Fe], [O/Fe], [Na/Fe], [Mg/Fe], [Al/Fe], [Sr/Fe], and [Ba/Fe], which are the main characteristics making the CEMP-no and low-s stars so peculiar, is described well in terms of the proposed nucleosynthetic classification. We note that the [(C+N+O)/Fe] ratios significantly increase for lower values of [Fe/H]. Conclusions: The classification of CEMP-no stars and the behavior of [(C+N+O)/Fe] support the presence, in the first stellar generations of the Galaxy, of fast-rotating massive stars experiencing strong mixing and mass loss (spinstars). This result has an impact on the early chemical and spectral evolution of the Galaxy.

  4. Stars For Citizens With Urban Star Parks and Lighting Specialists

    NASA Astrophysics Data System (ADS)

    Grigore, Valentin

    2015-08-01

    General contextOne hundred years ago, almost nobody imagine a life without stars every night even in the urban areas. Now, to see a starry sky is a special event for urban citizens.It is possible to see the stars even inside cities? Yes, but for that we need star parks and lighting specialists as partners.Educational aspectThe citizens must be able to identify the planets, constellations and other celestial objects in their urban residence. This is part of a basic education. The number of the people living in the urban area who never see the main constellations or important stars increase every year. We must do something for our urban community.What is an urban star park?An urban public park where we can see the main constellations can be considered an urban star park. There can be organized a lot of activities as practical lessons of astronomy, star parties, etc.Classification of the urban star parksA proposal for classification of the urban star parks taking in consideration the quality of the sky and the number of the city inhabitants:Two categories:- city star parks for cities with < 100.000 inhabitants- metropolis star parks for cities with > 100.000 inhabitantsFive levels of quality:- 1* level = can see stars of at least 1 magnitude with the naked eyes- 2* level = at least 2 mag- 3* level = at least 3 mag- 4* level= at least 4 mag- 5* level = at least 5 magThe urban star urban park structure and lighting systemA possible structure of a urban star park and sky-friend lighting including non-electric illumination are descripted.The International Commission on IlluminationA description of this structure which has as members national commissions from all over the world.Dark-sky activists - lighting specialistsNational Commissions on Illumination organize courses of lighting specialist. Dark-sky activists can become lighting specialists. The author shows his experience in this aspect as a recent lighting specialist and his cooperation with the Romanian National

  5. Wheeler & Feynman's Response of the Universe, revisited

    NASA Astrophysics Data System (ADS)

    Wolff, Milo

    2003-04-01

    In a famous 1945 paper Wheeler and Feynman (1) sought the cause of radiation from an accelerated electron. They assumed that acceleration produced an electromagnetic wave pulse from the electron that caused responding waves from static point-particle absorbers in the universe. Problems arose with possible violation of causality by waves that begin before their cause. This paper points out that a rigorous logical solution is obtained (2) when the electron is a dynamic structure of two scalar quantum waves. The scalar wave equation produces two such inward and outward spherical waves. The two waves combined have complete properties of positrons and electrons and the natural laws. Thus the problem is resolved by replacing the point particle with a scalar quantum wave structure (3). ... The conclusion: The universe and the laws of nature are inter-connected by co-mingled matter waves. Thus if the stars did not exist, it would be meaningless to think that we could exist. 1) Wheeler & Feynman, RMP, 17, 157 (1945). 2) Wolff, Gravition and Cosmology, Kluwer Acad. Publ. (2002). 3) www.QuantumMatter.com

  6. Al-Sufi's Investigation of Stars, Star Clusters and Nebulae

    NASA Astrophysics Data System (ADS)

    Hafez, Ihsan; Stephenson, F. R.; Orchiston, W.

    2011-01-01

    The distinguished Arabic astronomer, Al-Sufi (AD 903-986) is justly famous for his Book of the Fixed Stars, an outstanding Medieval treatise on astronomy that was assembled in 964. Developed from Ptolemy's Algamest, but based upon al-Sufi's own stellar observations, the Book of the Fixed Stars has been copied down through the ages, and currently 35 copies are known to exist in various archival repositories around the world. Among other things, this major work contains 55 astronomical tables, plus star charts for 48 constellations. For the first time a long-overdue English translation of this important early work is in active preparation. In this paper we provide biographical material about Al-Sufi and the contents of his Book of the Fixed Stars, before examining his novel stellar magnitude system, and his listing of star clusters and nebulae (including the first-ever mention of the Great Nebula in Andromeda).

  7. Clues about the first stars from CEMP-no stars

    NASA Astrophysics Data System (ADS)

    Choplin, A.; Meynet, G.; Maeder, A.

    2015-12-01

    The material used to form the CEMP-no stars presents signatures of material processed by the CNO cycle and by He-burning from a previous stellar generation called the source stars. In order to reproduce the relative abundance ratios like for instance C/N or ^{12}C/^{13}C, some mixing between the two burning regions must have occured in the source stars and only the outer layers of the stars, with modest amount coming from the CO core, must have been expelled either through stellar winds or at the time of the (faint) supernova event. With new models at low metallicity including rotational mixing, we shall discuss how the variety of abundances observed for CEMP-no stars can be reproduced.

  8. Stability of Rigidly Rotating Supermassive Stars against Gravitational Collapse

    NASA Astrophysics Data System (ADS)

    Shibata, Masaru; Uchida, Haruki; Sekiguchi, Yu-ichiro

    2016-02-01

    We revisit secular stability against quasi-radial collapse for rigidly rotating supermassive stars (SMSs) in general relativity. We suppose that the SMSs are in a nuclear-burning phase and can be modeled by polytropic equations of state with the polytropic index np slightly smaller than 3. The stability is determined in terms of the turning point method. We find a fitting formula of the stability condition for the plausible range of np (2.95≲ {n}{{p}}≲ 3) for SMSs. This condition reconfirms that while non-rotating SMSs with a mass of ˜ {10}5{M}⊙ -{10}6{M}⊙ may undergo a general relativistically induced quasi-radial collapse, rigidly rotating SMSs with a ratio of rotational to gravitational potential energy (β) of ˜ {10}-2 are likely to be stable against collapse unless they are able to accrete ˜5 times more mass during the (relatively brief) hydrogen-burning phase of their evolution. We discuss the implications of our results.

  9. The Star Cluster Mass-Galactocentric Radius Relation: Implications for Cluster Formation

    NASA Astrophysics Data System (ADS)

    Sun, Weijia; de Grijs, Richard; Fan, Zhou; Cameron, Ewan

    2016-01-01

    Whether or not the initial star cluster mass function is established through a universal, galactocentric-distance-independent stochastic process, on the scales of individual galaxies, remains an unsolved problem. This debate has recently gained new impetus through the publication of a study that concluded that the maximum cluster mass in a given population is not solely determined by size-of-sample effects. Here, we revisit the evidence in favor and against stochastic cluster formation by examining the young (≲ a few × {10}8 year old) star cluster mass-galactocentric radius relation in M33, M51, M83, and the Large Magellanic Cloud. To eliminate size-of-sample effects, we first adopt radial bin sizes containing constant numbers of clusters, which we use to quantify the radial distribution of the first- to fifth-ranked most massive clusters using ordinary least-squares fitting. We supplement this analysis with an application of quantile regression, a binless approach to rank-based regression taking an absolute-value-distance penalty. Both methods yield, within the 1σ to 3σ uncertainties, near-zero slopes in the diagnostic plane, largely irrespective of the maximum age or minimum mass imposed on our sample selection, or of the radial bin size adopted. We conclude that, at least in our four well-studied sample galaxies, star cluster formation does not necessarily require an environment-dependent cluster formation scenario, which thus supports the notion of stochastic star cluster formation as the dominant star cluster-formation process within a given galaxy.

  10. Stars Just Got Bigger - A 300 Solar Mass Star Uncovered

    NASA Astrophysics Data System (ADS)

    2010-07-01

    Using a combination of instruments on ESO's Very Large Telescope, astronomers have discovered the most massive stars to date, one weighing at birth more than 300 times the mass of the Sun, or twice as much as the currently accepted limit of 150 solar masses. The existence of these monsters - millions of times more luminous than the Sun, losing weight through very powerful winds - may provide an answer to the question "how massive can stars be?" A team of astronomers led by Paul Crowther, Professor of Astrophysics at the University of Sheffield, has used ESO's Very Large Telescope (VLT), as well as archival data from the NASA/ESA Hubble Space Telescope, to study two young clusters of stars, NGC 3603 and RMC 136a in detail. NGC 3603 is a cosmic factory where stars form frantically from the nebula's extended clouds of gas and dust, located 22 000 light-years away from the Sun (eso1005). RMC 136a (more often known as R136) is another cluster of young, massive and hot stars, which is located inside the Tarantula Nebula, in one of our neighbouring galaxies, the Large Magellanic Cloud, 165 000 light-years away (eso0613). The team found several stars with surface temperatures over 40 000 degrees, more than seven times hotter than our Sun, and a few tens of times larger and several million times brighter. Comparisons with models imply that several of these stars were born with masses in excess of 150 solar masses. The star R136a1, found in the R136 cluster, is the most massive star ever found, with a current mass of about 265 solar masses and with a birthweight of as much as 320 times that of the Sun. In NGC 3603, the astronomers could also directly measure the masses of two stars that belong to a double star system [1], as a validation of the models used. The stars A1, B and C in this cluster have estimated masses at birth above or close to 150 solar masses. Very massive stars produce very powerful outflows. "Unlike humans, these stars are born heavy and lose weight as

  11. Circular revisit orbits design for responsive mission over a single target

    NASA Astrophysics Data System (ADS)

    Li, Taibo; Xiang, Junhua; Wang, Zhaokui; Zhang, Yulin

    2016-10-01

    The responsive orbits play a key role in addressing the mission of Operationally Responsive Space (ORS) because of their capabilities. These capabilities are usually focused on supporting specific targets as opposed to providing global coverage. One subtype of responsive orbits is repeat coverage orbit which is nearly circular in most remote sensing applications. This paper deals with a special kind of repeating ground track orbit, referred to as circular revisit orbit. Different from traditional repeat coverage orbits, a satellite on circular revisit orbit can visit a target site at both the ascending and descending stages in one revisit cycle. This typology of trajectory allows a halving of the traditional revisit time and does a favor to get useful information for responsive applications. However the previous reported numerical methods in some references often cost lots of computation or fail to obtain such orbits. To overcome this difficulty, an analytical method to determine the existence conditions of the solutions to revisit orbits is presented in this paper. To this end, the mathematical model of circular revisit orbit is established under the central gravity model and the J2 perturbation. A constraint function of the circular revisit orbit is introduced, and the monotonicity of that function has been studied. The existent conditions and the number of such orbits are naturally worked out. Taking the launch cost into consideration, optimal design model of circular revisit orbit is established to achieve a best orbit which visits a target twice a day in the morning and in the afternoon respectively for several days. The result shows that it is effective to apply circular revisit orbits in responsive application such as reconnoiter of natural disaster.

  12. Stars and Planets

    NASA Astrophysics Data System (ADS)

    Neta, Miguel

    2014-05-01

    'Estrelas e Planetas' (Stars and Planets) project was developed during the academic year 2009/2010 and was tested on three 3rd grade classes of one school in Quarteira, Portugal. The aim was to encourage the learning of science and the natural and physical phenomena through the construction and manipulation of materials that promote these themes - in this case astronomy. Throughout the project the students built a small book containing three themes of astronomy: differences between stars and planets, the solar system and the phases of the Moon. To each topic was devoted two sessions of about an hour each: the first to teach the theoretical aspects of the theme and the second session to assembly two pages of the book. All materials used (for theoretical sessions and for the construction of the book) and videos of the finished book are available for free use in www.miguelneta.pt/estrelaseplanetas. So far there is only a Portuguese version but soon will be published in English as well. This project won the Excellency Prize 2011 of Casa das Ciências, a portuguese site for teachers supported by the Calouste Gulbenkian Fundation (www.casadasciencias.org).

  13. Morphogenesis of star dunes

    NASA Astrophysics Data System (ADS)

    Zhang, D.; Narteau, C.; Rozier, O.

    2010-12-01

    Dunes constantly adapt their shapes in response to the flow. Under multi-modal wind orientation, this permanent reorganization may result in the formation of star dunes, a highly complex structure with multiple arms, crests and slip faces oriented in different directions. Here, we show that this majestic dune feature can be described as a superposition of longitudinal dunes. In a 3D cellular automaton for sediment transport, star dunes form by amalgamation or by nucleation and growth of secondary longitudinal dunes. When the dune shape reaches a steady state, individual arms continue to propagate and detach from the main structure to feed other dunes in the neighborhood. From the sedimentary structures produced by the model we show that arm elongation is strongly dependent on the frequency at which the wind oscillates. This demonstrates that the elongation/propagation of dunes is a highly non-linear process that should account for crest reorientation over different time scales. We conclude that such a behavior needs to be taken into account when estimating climatic conditions from sedimentary structures on Earth or satellite images on other planetary bodies.

  14. Recovery Ship Freedom Star

    NASA Technical Reports Server (NTRS)

    1998-01-01

    Freedom Star, one of NASA's two solid rocket booster recovery ships, is towing a barge containing the third Space Shuttle Super Lightweight External Tank (SLWT) into Port Canaveral. This SLWT was slated for use to launch the orbiter Discovery on mission STS-95 in October 1998. This first time towing arrangement, part of a cost saving plan by NASA to prudently manage existing resources, began June 12 from the Michoud Assembly Facility in New Orleans where the Shuttle's external tanks were manufactured. The barge was transported up Banana River to the LC-39 turn basin using a conventional tug boat. Previously, NASA relied on an outside contractor to provide external tank towing services at a cost of about $120,000 per trip. The new plan allowed NASA's Space Flight Operations contractor, United Space Alliance (USA), to provide the same service to NASA using the recovery ships during their downtime between Shuttle launches. Studies showed a potential savings of about $50,000 per trip. The cost of the necessary ship modifications would be paid back by the fourteenth tank delivery. The other recovery ship, Liberty Star, also underwent deck strengthening enhancements and had the necessary towing wench installed.

  15. The Stars of Heaven

    NASA Astrophysics Data System (ADS)

    Pickover, Clifford A.

    2004-05-01

    Do a little armchair space travel, rub elbows with alien life forms, and stretch your mind to the furthest corners of our uncharted universe. With this astonishing guidebook, you don't have to be an astronomer to explore the mysteries of stars and their profound meaning for human existence. Clifford A. Pickover tackles a range of topics from stellar evolution to the fundamental reasons why the universe permits life to flourish. He alternates sections that explain the mysteries of the cosmos with sections that dramatize mind-expanding concepts through a fictional dialog between futuristic humans and their alien peers (who embark on a journey beyond the reader's wildest imagination). This highly accessible and entertaining approach turns an intimidating subject into a scientific game open to all dreamers. Told in Pickover's inimitable blend of fascinating state-of-the-art science and whimsical science fiction, and packed with numerous diagrams and illustrations, The Stars of Heaven unfolds a world of paradox and mystery, one that will intrigue anyone who has ever pondered the night sky with wonder.

  16. A Star on the Run

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2015-10-01

    Usually stars that are born together tend to move together but sometimes stars can go rogue and run away from their original birthplace. A pair of astronomers have now discovered the first runaway red supergiant (RSG) ever identified in another galaxy. With a radial velocity discrepancy of 300 km/s, its also the fastest runaway massive star known. Discrepant Speeds: When massive stars form in giant molecular clouds, they create what are known as OB associations: groups of hot, massive, short-lived stars that have similar velocities because theyre moving through space together. But sometimes stars that appear to be part of an OB association dont have the same velocity as the rest of the group. These stars are called runaways.What causes an OB star to run away is still debated, but we know that a fairly significant fraction of OB stars are runaways. In spite of this, surprisingly few runaways have been found that are evolved massive stars i.e., the post-main-sequence state of OB stars. This is presumably because these evolved stars have had more time to move away from their birthplace, and its more difficult to identify a runaway without the context of its original group. An Evolved Runaway: Difference between observed velocity and expected velocity, plotted as a function of expected velocity. The black points are foreground stars. The red points are expected RSGs, clustered around a velocity difference of zero. The green pentagon is the runaway RSG J004330.06+405258.4. [Evans Massey 2015]Despite this challenge, a recent survey of RSGs in the galaxy M31 has led to the detection of a massive star on the run! Kate Evans (Lowell Observatory and California Institute of Technology) and Philip Massey (Lowell Observatory and Northern Arizona University) discovered that RSG J004330.06+405258.4 is moving through the Andromeda Galaxy with a radial velocity thats off by about 300 km/s from the radial velocity expected for its location.Evans and Massey discovered this rogue star

  17. Revisiting impacts of nuclear burning for reviving weak shocks in neutrino-driven supernovae

    SciTech Connect

    Nakamura, Ko; Kotake, Kei; Takiwaki, Tomoya; Nishimura, Nobuya

    2014-02-20

    We revisit potential impacts of nuclear burning on the onset of the neutrino-driven explosions of core-collapse supernovae. By changing the neutrino luminosity and its decay time to obtain parametric explosions in one- and two-dimensional (1D and 2D, respectively) models with or without a 13 isotope α network, we study how the inclusion of nuclear burning could affect the postbounce dynamics for 4 progenitor models; 3 for 15.0 M {sub ☉} stars and 1 for an 11.2 M {sub ☉} star. We find that the energy supply due to the nuclear burning of infalling material behind the shock can energize the shock expansion, especially for models that produce only marginal explosions in the absence of nuclear burning. These models are energized by nuclear energy deposition when the shock front passes through the silicon-rich layer and/or later as it touches the oxygen-rich layer. Depending on the neutrino luminosity and its decay time, the diagnostic energy of the explosion increases up to a few times 10{sup 50} erg for models with nuclear burning compared to the corresponding models without. We point out that these features are most remarkable for the Limongi-Chieffi progenitor in both 1D and 2D because the progenitor model possesses a massive oxygen layer, with an inner-edge radius that is smallest among the employed progenitors, which means that the shock can touch the rich fuel on a shorter timescale after bounce. The energy difference is generally smaller (∼0.1-0.2 × 10{sup 51} erg) in 2D than in 1D (at most ∼0.6 × 10{sup 51} erg). This is because neutrino-driven convection and the shock instability in 2D models enhance the neutrino heating efficiency, which makes the contribution of nuclear burning relatively smaller compared to 1D models. Considering uncertainties in progenitor models, our results indicate that nuclear burning should remain one of the important ingredients to foster the onset of neutrino-driven explosions.

  18. Star formation in the multiverse

    SciTech Connect

    Bousso, Raphael; Leichenauer, Stefan

    2009-03-15

    We develop a simple semianalytic model of the star formation rate as a function of time. We estimate the star formation rate for a wide range of values of the cosmological constant, spatial curvature, and primordial density contrast. Our model can predict such parameters in the multiverse, if the underlying theory landscape and the cosmological measure are known.

  19. WhiteStar user's guide

    SciTech Connect

    Ezell, T.F.

    1990-08-01

    The WhiteStar project provides design engineers with needed part design data. WhiteStar encourages the use of preferred parts by providing a user-convenient parts database. This report shows selections the user makes in order to obtain information on a particular part. 15 figs.

  20. Stars Get Dizzy After Lunch

    NASA Astrophysics Data System (ADS)

    Zhang, Michael; Penev, Kaloyan

    2014-06-01

    Exoplanet searches have discovered a large number of "hot Jupiters"—high-mass planets orbiting very close to their parent stars in nearly circular orbits. A number of these planets are sufficiently massive and close-in to be significantly affected by tidal dissipation in the parent star, to a degree parameterized by the tidal quality factor Q *. This process speeds up their star's rotation rate while reducing the planet's semimajor axis. In this paper, we investigate the tidal destruction of hot Jupiters. Because the orbital angular momenta of these planets are a significant fraction of their star's rotational angular momenta, they spin up their stars significantly while spiraling to their deaths. Using the Monte Carlo simulation, we predict that for Q * = 106, 3.9 × 10-6 of stars with the Kepler Target Catalog's mass distribution should have a rotation period shorter than 1/3 day (8 hr) due to accreting a planet. Exoplanet surveys such as SuperWASP, HATnet, HATsouth, and KELT have already produced light curves of millions of stars. These two facts suggest that it may be possible to search for tidally destroyed planets by looking for stars with extremely short rotational periods, then looking for remnant planet cores around those candidates, anomalies in the metal distribution, or other signatures of the recent accretion of the planet.

  1. Comparable Habitable Zones of Stars

    NASA Video Gallery

    The habitable zone is the distance from a star where one can have liquid water on the surface of a planet. If a planet is too close to its parent star, it will be too hot and water would have evapo...

  2. Stars get dizzy after lunch

    SciTech Connect

    Zhang, Michael; Penev, Kaloyan

    2014-06-01

    Exoplanet searches have discovered a large number of {sup h}ot Jupiters{sup —}high-mass planets orbiting very close to their parent stars in nearly circular orbits. A number of these planets are sufficiently massive and close-in to be significantly affected by tidal dissipation in the parent star, to a degree parameterized by the tidal quality factor Q {sub *}. This process speeds up their star's rotation rate while reducing the planet's semimajor axis. In this paper, we investigate the tidal destruction of hot Jupiters. Because the orbital angular momenta of these planets are a significant fraction of their star's rotational angular momenta, they spin up their stars significantly while spiraling to their deaths. Using the Monte Carlo simulation, we predict that for Q {sub *} = 10{sup 6}, 3.9 × 10{sup –6} of stars with the Kepler Target Catalog's mass distribution should have a rotation period shorter than 1/3 day (8 hr) due to accreting a planet. Exoplanet surveys such as SuperWASP, HATnet, HATsouth, and KELT have already produced light curves of millions of stars. These two facts suggest that it may be possible to search for tidally destroyed planets by looking for stars with extremely short rotational periods, then looking for remnant planet cores around those candidates, anomalies in the metal distribution, or other signatures of the recent accretion of the planet.

  3. STARS: A Year in Review

    ERIC Educational Resources Information Center

    Association for the Advancement of Sustainability in Higher Education, 2011

    2011-01-01

    The Sustainability Tracking, Assessment & Rating System[TM] (STARS) is a program of AASHE, the Association for the Advancement of Sustainability in Higher Education. AASHE is a member-driven organization with a mission to empower higher education to lead the sustainability transformation. STARS was developed by AASHE with input and insight from…

  4. Mathematics Teaching with the Stars

    ERIC Educational Resources Information Center

    McKinney, Sueanne E.; Bol, Linda; Berube, Clair

    2010-01-01

    The mathematics instructional approaches of effective elementary teachers in urban high- poverty schools were investigated. Approximately 99 urban elementary teachers were administered the Star Teacher Selection Interview; a total of 31 were identified as star teachers. These teachers were then administered the Instructional Practices…

  5. Convective dynamos for rotating stars

    NASA Technical Reports Server (NTRS)

    Gilman, P. A.

    1981-01-01

    Global dynamo theory is applied to the problem of why some stars have field reversing dynamos, and others do not. It is argued that convectively driven dynamos are the most likely source of magnetic fields in stars that have convection zones.

  6. Socket stars: UBVRJIK radial profiles

    NASA Astrophysics Data System (ADS)

    Schaefer, Bradley E.

    1995-05-01

    Visual inspectin of stars embedded in H II nebulae has shown a significant fraction to be surrounded by nearly symmetric extended regions within which the nebular brightness is apparently significantly fainter than is typical for the surrounding area. These 'socket stars' might be caused by a bubble in the nebula blown out by a stellar wind or they might be caused by a circumstellar envelope of dust hiding the emission behind the star. As such, the sockets could be the first manifestation of a previously unknown component of pre-main-sequence stars. Unfortunately, no quantitative proof of the existence of sockets has been presented. To fill this need, I have imaged 10 socket stars and six background stars with CCD cameras and infrared array cameras. From these images, I have constructed radial plots which should reveal dips in brightness immediately outside the seeing disk. The radial plots do not show any evidence for the existence of sockets. A detailed examination of the photographs orginally used to identify the sockets show that the causes of these reports are (1) artifacts resulting from the photographic process of dodging and (2) random coincidence of stars with local minima in nebular brightness. Thus, I conclude that 'socket stars' do not exist.

  7. ENERGY STAR Certified Audio Video

    EPA Pesticide Factsheets

    Certified models meet all ENERGY STAR requirements as listed in the Version 3.0 ENERGY STAR Program Requirements for Audio Video Equipment that are effective as of May 1, 2013. A detailed listing of key efficiency criteria are available at http://www.energystar.gov/index.cfm?c=audio_dvd.pr_crit_audio_dvd

  8. ENERGY STAR Certified Pool Pumps

    EPA Pesticide Factsheets

    Certified models meet all ENERGY STAR requirements as listed in the Version 1.0 ENERGY STAR Program Requirements for Pool Pumps that are effective as of February 15, 2013. A detailed listing of key efficiency criteria are available at http://www.energystar.gov/index.cfm?c=poolpumps.pr_crit_poolpumps

  9. Dust near luminous ultraviolet stars

    NASA Technical Reports Server (NTRS)

    Henry, Richard C.

    1993-01-01

    This report describes research activities related to the Infrared Astronomical Satellite (IRAS) sky survey. About 745 luminous stars were examined for the presence of interstellar dust heated by a nearby star. The 'cirrus' discovered by IRAS is thermal radiation from interstellar dust at moderate and high galactic latitudes. The IRAS locates the dust which must (at some level) scatter ultraviolet starlight, although it was expected that thermal emission would be found around virtually every star, most stars shown no detectable emission. And the emission found is not uniform. It is not that the star is embedded in 'an interstellar medium', but rather what is found are discrete clouds that are heated by starlight. An exception is the dearth of clouds near the very hottest stars, implying that the very hottest stars play an active role with respect to destroying or substantially modifying the dust clouds over time. The other possibility is simply that the hottest stars are located in regions lacking in dust, which is counter-intuitive. A bibliography of related journal articles is attached.

  10. Hα observations of Be stars

    NASA Astrophysics Data System (ADS)

    Banerjee, D. P. K.; Rawat, S. D.; Janardhan, P.

    2000-12-01

    We present here the Hα spectra of 44 Be stars taken at a resolution of 0.5 Å. From the spectra, different emission line parameters have been deduced. A study of the correlations between different pairs of these parameters has been made with a view to understanding the mechanisms of line formation and shaping in Be stars.

  11. Astronomy: A truly embryonic star

    NASA Astrophysics Data System (ADS)

    Clarke, David A.

    2012-12-01

    The discovery of what may be the best example yet of a forming star caught in the moments just before birth provides a missing link in our understanding of how giant gas clouds collapse to form fully fledged stars. See Letter p.83

  12. Stars in the Tarantula Nebula

    NASA Technical Reports Server (NTRS)

    1999-01-01

    In the most active starburst region in the local universe lies a cluster of brilliant, massive stars, known to astronomers as Hodge 301. Hodge 301, seen in the lower right hand corner of this image, lives inside the Tarantula Nebula in our galactic neighbor, the Large Magellanic Cloud. This star cluster is not the brightest, or youngest, or most populous star cluster in the Tarantula Nebula, that honor goes to the spectacular R136. In fact, Hodge 301 is almost 10 times older than the young cluster R136. But age has its advantages; many of the stars in Hodge 301 are so old that they have exploded as supernovae. These exploded stars are blasting material out into the surrounding region at speeds of almost 200 miles per second. This high speed ejecta are plowing into the surrounding Tarantula Nebula, shocking and compressing the gas into a multitude of sheets and filaments, seen in the upper left portion of the picture. Hodge 301 contains three red supergiants - stars that are close to the end of their evolution and are about to go supernova, exploding and sending more shocks into the Tarantula. Also present near the center of the image are small, dense gas globules and dust columns where new stars are being formed today, as part of the overall ongoing star formation throughout the Tarantula region.

  13. Four Neglected Southern Mira Stars

    NASA Astrophysics Data System (ADS)

    Cragg, T. A.

    2006-06-01

    This paper is a continuation of the study of several southern Mira stars presented at the 1996 Fall Meeting of the AAVSO in Cambridge, Massachusetts. The four stars herein included are 0828-44, CT Vel; 1553-23, BK Sco; 1557-23, TY Sco; and 2011-52, X Tel. X Tel is now on the regular observing list of the RASNZ.

  14. A practical method of predicting client revisit intention in a hospital setting.

    PubMed

    Lee, Kyun Jick

    2005-01-01

    Data mining (DM) models are an alternative to traditional statistical methods for examining whether higher customer satisfaction leads to higher revisit intention. This study used a total of 906 outpatients' satisfaction data collected from a nationwide survey interviews conducted by professional interviewers on a face-to-face basis in South Korea, 1998. Analyses showed that the relationship between overall satisfaction with hospital services and outpatients' revisit intention, along with word-of-mouth recommendation as intermediate variables, developed into a nonlinear relationship. The five strongest predictors of revisit intention were overall satisfaction, intention to recommend to others, awareness of hospital promotion, satisfaction with physician's kindness, and satisfaction with treatment level.

  15. Physics of primordial star formation

    NASA Astrophysics Data System (ADS)

    Yoshida, Naoki

    2012-09-01

    The study of primordial star formation has a history of nearly sixty years. It is generally thought that primordial stars are one of the key elements in a broad range of topics in astronomy and cosmology, from Galactic chemical evolution to the formation of super-massive blackholes. We review recent progress in the theory of primordial star formation. The standard theory of cosmic structure formation posits that the present-day rich structure of the Universe developed through gravitational amplification of tiny matter density fluctuations left over from the Big Bang. It has become possible to study primordial star formation rigorously within the framework of the standard cosmological model. We first lay out the key physical processes in a primordial gas. Then, we introduce recent developments in computer simulations. Finally, we discuss prospects for future observations of the first generation of stars.

  16. Binary Stars in SBS Survey

    NASA Astrophysics Data System (ADS)

    Erastova, L. K.

    2016-06-01

    Thirty spectroscopic binary stars were found in the Second Byurakan Survey (SBS). They show composite spectra - WD(DA)+dM or dC (for example Liebert et al. 1994). They may have red color, if the radiation of the red star dominates, and blue one, if the blue star is brighter and have peculiar spectrum in our survey plate. We obtained slit spectra for most of such objects. But we often see the spectrum of one component, because our slit spectra did not cover all optical range. We examine by eye the slit spectra of all SBS stellar objects (˜700) in SDSS DR7, DR8 or DR9 independent on our observations. We confirmed or discovered the duplicity of 30 stars. Usually they are spectroscopic binaries, where one component is WD (DA) and the second one is a red star with or without emission. There also are other components combinations. Sometimes there are emission lines, probably, indicating variable ones.

  17. NSCool: Neutron star cooling code

    NASA Astrophysics Data System (ADS)

    Page, Dany

    2016-09-01

    NSCool is a 1D (i.e., spherically symmetric) neutron star cooling code written in Fortran 77. The package also contains a series of EOSs (equation of state) to build stars, a series of pre-built stars, and a TOV (Tolman- Oppenheimer-Volkoff) integrator to build stars from an EOS. It can also handle “strange stars” that have a huge density discontinuity between the quark matter and the covering thin baryonic crust. NSCool solves the heat transport and energy balance equations in whole GR, resulting in a time sequence of temperature profiles (and, in particular, a Teff - age curve). Several heating processes are included, and more can easily be incorporated. In particular it can evolve a star undergoing accretion with the resulting deep crustal heating, under a steady or time-variable accretion rate. NSCool is robust, very fast, and highly modular, making it easy to add new subroutines for new processes.

  18. Grand unification of neutron stars.

    PubMed

    Kaspi, Victoria M

    2010-04-20

    The last decade has shown us that the observational properties of neutron stars are remarkably diverse. From magnetars to rotating radio transients, from radio pulsars to isolated neutron stars, from central compact objects to millisecond pulsars, observational manifestations of neutron stars are surprisingly varied, with most properties totally unpredicted. The challenge is to establish an overarching physical theory of neutron stars and their birth properties that can explain this great diversity. Here I survey the disparate neutron stars classes, describe their properties, and highlight results made possible by the Chandra X-Ray Observatory, in celebration of its 10th anniversary. Finally, I describe the current status of efforts at physical "grand unification" of this wealth of observational phenomena, and comment on possibilities for Chandra's next decade in this field.

  19. The Visual Double Star Catalogs

    NASA Astrophysics Data System (ADS)

    Mason, Brian D.

    2015-08-01

    In visual double star work, production of the first comprehensive attempt to list all discovered pairs in his accessible sky was prepared by S.W. Burnham in 1906. A double star catalog for the southern hemisphere was prepared by R.T.A. Innes et al. in 1927 and the northern hemisphere catalog was updated by R.G. Aitken and E. Doolittle in 1932. Eventually, this led to Lick Observatory maintaining what became known as the Index Catalogue, an all-sky visual double star database.In 1964, under the aegis of Commission 26, the Lick double star database was transferred to the U.S. Naval Observatory where it was redesignated the Washington Double Star Catalog where it and it's ancillary catalogs, have been maintained for over half a century. The current statistics of the catalog and it's supplements are presented as are the enhancements currently under consideration.

  20. Grand unification of neutron stars

    PubMed Central

    Kaspi, Victoria M.

    2010-01-01

    The last decade has shown us that the observational properties of neutron stars are remarkably diverse. From magnetars to rotating radio transients, from radio pulsars to isolated neutron stars, from central compact objects to millisecond pulsars, observational manifestations of neutron stars are surprisingly varied, with most properties totally unpredicted. The challenge is to establish an overarching physical theory of neutron stars and their birth properties that can explain this great diversity. Here I survey the disparate neutron stars classes, describe their properties, and highlight results made possible by the Chandra X-Ray Observatory, in celebration of its 10th anniversary. Finally, I describe the current status of efforts at physical “grand unification” of this wealth of observational phenomena, and comment on possibilities for Chandra’s next decade in this field. PMID:20404205

  1. INTERSTELLAR ABUNDANCES TOWARD X Per, REVISITED

    SciTech Connect

    Valencic, Lynne A.; Smith, Randall K.

    2013-06-10

    The nearby X-ray binary X Per (HD 24534) provides a useful beacon with which to examine dust grain types and measure elemental abundances in the local interstellar medium (ISM). The absorption features of O, Fe, Mg, and Si along this line of sight were measured using spectra from the Chandra X-Ray Observatory's LETG/ACIS-S and XMM-Newton's RGS instruments, and the Spex software package. The spectra were fit with dust analogs measured in the laboratory. The O, Mg, and Si abundances were compared to those from standard references, and the O abundance was compared to that along lines of sight toward other X-ray binaries. The results are as follows. First, it was found that a combination of MgSiO{sub 3} (enstatite) and Mg{sub 1.6}Fe{sub 0.4}SiO{sub 4} (olivine) provided the best fit to the O K edge, with N(MgSiO{sub 3})/N(Mg{sub 1.6}Fe{sub 0.4}SiO{sub 4}) = 3.4. Second, the Fe L edge could be fit with models that included metallic iron, but it was not well described by the laboratory spectra currently available. Third, the total abundances of O, Mg, and Si were in very good agreement with that of recently re-analyzed B stars, suggesting that they are good indicators of abundances in the local ISM, and the depletions were also in agreement with expected values for the diffuse ISM. Finally, the O abundances found from X-ray binary absorption spectra show a similar correlation with Galactocentric distances as seen in other objects.

  2. Improved autonomous star identification algorithm

    NASA Astrophysics Data System (ADS)

    Luo, Li-Yan; Xu, Lu-Ping; Zhang, Hua; Sun, Jing-Rong

    2015-06-01

    The log-polar transform (LPT) is introduced into the star identification because of its rotation invariance. An improved autonomous star identification algorithm is proposed in this paper to avoid the circular shift of the feature vector and to reduce the time consumed in the star identification algorithm using LPT. In the proposed algorithm, the star pattern of the same navigation star remains unchanged when the stellar image is rotated, which makes it able to reduce the star identification time. The logarithmic values of the plane distances between the navigation and its neighbor stars are adopted to structure the feature vector of the navigation star, which enhances the robustness of star identification. In addition, some efforts are made to make it able to find the identification result with fewer comparisons, instead of searching the whole feature database. The simulation results demonstrate that the proposed algorithm can effectively accelerate the star identification. Moreover, the recognition rate and robustness by the proposed algorithm are better than those by the LPT algorithm and the modified grid algorithm. Project supported by the National Natural Science Foundation of China (Grant Nos. 61172138 and 61401340), the Open Research Fund of the Academy of Satellite Application, China (Grant No. 2014_CXJJ-DH_12), the Fundamental Research Funds for the Central Universities, China (Grant Nos. JB141303 and 201413B), the Natural Science Basic Research Plan in Shaanxi Province, China (Grant No. 2013JQ8040), the Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20130203120004), and the Xi’an Science and Technology Plan, China (Grant. No CXY1350(4)).

  3. StarGuides Plus

    NASA Astrophysics Data System (ADS)

    Heck, A.

    StarGuides Plus represents the most comprehensive and accurately validated collection of practical data on organizations involved in astronomy, related space sciences and other related fields. This invaluable reference source (and its companion volume, StarBriefs Plus) should be on the reference shelf of every library, organization or individual with any interest in these areas. The coverage includes relevant universities, scientific committees, institutions, associations, societies, agencies, companies, bibliographic services, data centers, museums, dealers, distributors, funding organizations, journals, manufacturers, meteorological services, national norms & standard institutes, parent associations & societies, publishers, software producers & distributors, and so on. Besides astronomy and associated space sciences, related fields such as aeronautics, aeronomy, astronautics, atmospheric sciences, chemistry, communications, computer sciences, data processing, education, electronics, engineering, energetics, environment, geodesy, geophysics, information handling, management, mathematics, meteorology, optics, physics, remote sensing, and so on, are also covered where appropriate. After some thirty years in continuous compilation, verification and updating, StarGuides Plus currently gathers together some 6,000 entries from 100 countries. The information is presented in a clear, uncluttered manner for direct and easy use. For each entry, all practical data are listed: city, postal and electronic-mail addresses, telephone and fax numbers, URLs for WWW access, foundation years, numbers of members and/or numbers of staff, main activities, publications titles (with frequencies, ISS-Numbers and circulations), names and geographical coordinates of observing sites, names of planetariums, awards (prizes and/or distinctions) granted, etc. The entries are listed alphabetically in each country. An exhaustive index gives a breakdown not only by different designations and

  4. Clues About the First Stars from CEMP-no Stars

    NASA Astrophysics Data System (ADS)

    Meynet, Georges; Maeder, André; Choplin, Arthur; Hirschi, Raphael; Ekström, Sylvia; Chiappini, Cristina

    2015-08-01

    The material used to form the CEMP-no stars presents signatures of material processed by the CNO cycle and by He-burning from a previous stellar generation called the source stars. In order to reproduce the absolute amounts of CNO elements observed at the surface of CEMP-no stars ([X/H] values), as well as the relative abundance ratios, for instance C/N, O/N or 12C/13C, some mixing between the two burning regions must have occured in the source stars and only the outer layers of the source stars, with modest amount coming from the CO core, must have been expelled either through stellar winds or at the time of the (faint) supernova event. With new models at low metallicity including rotational mixing, we shall discuss how the variety of abundances observed at the surface of CEMP-no stars can be reproduced. Some new results about the s-process nucleosynthesis by massive metal-poor rotating stars will also be presented.

  5. Rural-Nonrural Disparities in Postsecondary Educational Attainment Revisited

    PubMed Central

    Byun, Soo-yong; Meece, Judith L.; Irvin, Matthew J.

    2013-01-01

    Using data from the National Educational Longitudinal Study, this study revisited rural-nonrural disparities in educational attainment by considering a comprehensive set of factors that constrain and support youth's college enrollment and degree completion. Results showed that rural students were more advantaged in community social resources compared to nonrural students, and these resources were associated with a significant increase in the likelihood of bachelor's degree attainment. Yet results confirmed that rural students lagged behind nonrural students in attaining a bachelor's degree largely due to their lower socioeconomic background. The findings present a more comprehensive picture of the complexity of geographic residence in shaping college enrollment and degree attainment. PMID:24285873

  6. Nonlinear realization of spontaneously broken N = 1 supersymmetry revisited

    NASA Astrophysics Data System (ADS)

    Luo, Hui; Luo, Mingxing; Wang, Liucheng

    2010-02-01

    This paper revisits the nonlinear realization of spontaneously broken N = 1 supersymmetry. It is shown that the constrained superfield formalism as proposed in [6] can be reinterpreted in the language of standard realization of nonlinear supersymmetry via a new and simpler route. Explicit formulas of actions are presented for general renormalizable theories with or without gauge interactions. The nonlinearWess-Zumino gauge is discussed and relations are pointed out for different definitions of gauge fields. In addition, a general procedure is provided to deal with theories of arbitrary Kahler potentials.

  7. Revisiting a Constructive Classic: Wright's Physical Disability: A Psychosocial Approach

    PubMed Central

    Dunn, Dana S.; Elliott, Timothy R.

    2008-01-01

    Beatrice A. Wright's (1960) classic book, Physical Disability: A Psychological Approach is a landmark publication in rehabilitation psychology. The authors believe that Division 22's forthcoming 50th anniversary, the results of a recent survey on essential readings in rehabilitation psychology, and a public critique concerning the relevance of individuating language in psychology are compelling reasons for revisiting the influence of Physical Disability. After discussing these catalysts, the authors review the book's history, scholarly impact, and link to positive disciplinary directions. The authors conclude by encouraging rehabilitation psychologists and other members of the discipline to (re)acquaint themselves with this important book and the timeless concepts it espouses. PMID:19079791

  8. The Floor in the Solar Wind Magnetic Field Revisited

    DTIC Science & Technology

    2012-05-07

    Paper 3 . DATES COVERED (From - To) 1 Oct 2007 – 10 Nov 2010 4. TITLE AND SUBTITLE The Floor in the Solar Wind Magnetic Field Revisited...magnitude [B] had a floor of ≈ 4.6 nT in yearly averages, a value which the interplanetary magnetic - field [IMF] strength returned to, or approached, at...is implicit in the work of Owens and Crooker (2006, 2007) who simulated the interplanetary magnetic - field strength in terms of a constant open-flux

  9. Revisiting the deific-decree doctrine in Washington state.

    PubMed

    Leong, Gregory B

    2008-01-01

    The deific-decree exception to Washington's M'Naughten insanity standard first appeared in case law a quarter century ago in State v. Crenshaw. A few subsequent cases have attempted to refine the contours of the deific decree; however, the deific-decree doctrine has had only limited utility as a basis for the insanity defense. After about a decade of no activity in this area, the Washington courts have recently revisited the deific-decree doctrine in a case involving two defendants.

  10. HUBBLE FINDS THOUSANDS OF GASEOUS FRAGMENTS SURROUNDING DYING STAR

    NASA Technical Reports Server (NTRS)

    2002-01-01

    about one new one is created every year since this is the usual ending for the billions of sunlike stars inhabiting our Milky Way galaxy.' Hubble will be used to search more distant planetary nebulae for similar features. O'Dell hopes to revisit the Helix in a few years and take more images which might reveal the outward motion of the knots. * * * * The Space Telescope Science Institute is operated by the Association of Universities for Research in Astronomy, Inc. (AURA) for NASA, under contract with the Goddard Space Flight Center, Greenbelt, MD. The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency (ESA).

  11. Olber's Paradox Revisited in a Static and Finite Universe

    ERIC Educational Resources Information Center

    Couture, Gilles

    2012-01-01

    Building a Universe populated by stars identical to our Sun and taking into consideration the wave-particle duality of light, the biological limits of the human eye, the finite size of stars and the finiteness of our Universe, we conclude that the sky could very well be dark at night. Besides the human eye, the dominant parameter is the finite…

  12. Surface abundances of ON stars

    NASA Astrophysics Data System (ADS)

    Martins, F.; Simón-Díaz, S.; Palacios, A.; Howarth, I.; Georgy, C.; Walborn, N. R.; Bouret, J.-C.; Barbá, R.

    2015-06-01

    Context. Massive stars burn hydrogen through the CNO cycle during most of their evolution. When mixing is efficient or when mass transfer in binary systems occurs, chemically processed material is observed at the surface of O and B stars. Aims: ON stars show stronger lines of nitrogen than morphologically normal counterparts. Whether this corresponds to the presence of material processed through the CNO cycle is not known. Our goal is to answer this question. Methods: We performed a spectroscopic analysis of a sample of ON stars with atmosphere models. We determined the fundamental parameters as well as the He, C, N, and O surface abundances. We also measured the projected rotational velocities. We compared the properties of the ON stars to those of normal O stars. Results: We show that ON stars are usually rich in helium. Their CNO surface abundances are fully consistent with predictions of nucleosynthesis. ON stars are more chemically evolved and rotate - on average - faster than normal O stars. Evolutionary models including rotation cannot account for the extreme enrichment observed among ON main sequence stars. Some ON stars are members of binary systems, but others are single stars as indicated by stable radial velocities. Mass transfer is therefore not a simple explanation for the observed chemical properties. Conclusions: We conclude that ON stars show extreme chemical enrichment at their surface, consistent with nucleosynthesis through the CNO cycle. Its origin is not clear at present. Based on observations obtained 1) at the Anglo-Australian Telescope; 2) at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council (NRC) of Canada, the Institut National des Science de l'Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii; 3) at the ESO/La Silla Observatory under programs 081.D-2008, 083.D-0589, 086.D-0997; 4) the Nordic Optical Telescope, operated on the island of La

  13. The Destructive Birth of Massive Stars and Massive Star Clusters

    NASA Astrophysics Data System (ADS)

    Rosen, Anna; Krumholz, Mark; McKee, Christopher F.; Klein, Richard I.; Ramirez-Ruiz, Enrico

    2017-01-01

    Massive stars play an essential role in the Universe. They are rare, yet the energy and momentum they inject into the interstellar medium with their intense radiation fields dwarfs the contribution by their vastly more numerous low-mass cousins. Previous theoretical and observational studies have concluded that the feedback associated with massive stars' radiation fields is the dominant mechanism regulating massive star and massive star cluster (MSC) formation. Therefore detailed simulation of the formation of massive stars and MSCs, which host hundreds to thousands of massive stars, requires an accurate treatment of radiation. For this purpose, we have developed a new, highly accurate hybrid radiation algorithm that properly treats the absorption of the direct radiation field from stars and the re-emission and processing by interstellar dust. We use our new tool to perform a suite of three-dimensional radiation-hydrodynamic simulations of the formation of massive stars and MSCs. For individual massive stellar systems, we simulate the collapse of massive pre-stellar cores with laminar and turbulent initial conditions and properly resolve regions where we expect instabilities to grow. We find that mass is channeled to the massive stellar system via gravitational and Rayleigh-Taylor (RT) instabilities. For laminar initial conditions, proper treatment of the direct radiation field produces later onset of RT instability, but does not suppress it entirely provided the edges of the radiation-dominated bubbles are adequately resolved. RT instabilities arise immediately for turbulent pre-stellar cores because the initial turbulence seeds the instabilities. To model MSC formation, we simulate the collapse of a dense, turbulent, magnetized Mcl = 106 M⊙ molecular cloud. We find that the influence of the magnetic pressure and radiative feedback slows down star formation. Furthermore, we find that star formation is suppressed along dense filaments where the magnetic field is

  14. StarFISH: For Inferring Star-formation Histories

    NASA Astrophysics Data System (ADS)

    Harris, Jason; Zaritsky, Dennis

    2012-04-01

    StarFISH is a suite of programs designed to determine the star formation history (SFH) of a stellar population, given multicolor stellar photometry and a library of theoretical isochrones. It constructs a library of synthetic color-magnitude diagrams from the isochrones, which includes the effects of extinction, photometric errors and completeness, and binarity. A minimization routine is then used to determine the linear combination of synthetic CMDs that best matches the observed photometry. The set of amplitudes modulating each synthetic CMD describes the star formation history of the observed stellar population.

  15. Improving night sky star image processing algorithm for star sensors.

    PubMed

    Arbabmir, Mohammad Vali; Mohammadi, Seyyed Mohammad; Salahshour, Sadegh; Somayehee, Farshad

    2014-04-01

    In this paper, the night sky star image processing algorithm, consisting of image preprocessing, star pattern recognition, and centroiding steps, is improved. It is shown that the proposed noise reduction approach can preserve more necessary information than other frequently used approaches. It is also shown that the proposed thresholding method unlike commonly used techniques can properly perform image binarization, especially in images with uneven illumination. Moreover, the higher performance rate and lower average centroiding estimation error of near 0.045 for 400 simulated images compared to other algorithms show the high capability of the proposed night sky star image processing algorithm.

  16. Abundances in Przybylski's star

    NASA Astrophysics Data System (ADS)

    Cowley, C. R.; Ryabchikova, T.; Kupka, F.; Bord, D. J.; Mathys, G.; Bidelman, W. P.

    2000-09-01

    We have derived abundances for 54 elements in the extreme roAp star HD101065. ESO spectra with a resolution of about 80000, and S/N of 200 or more were employed. The adopted model has Teff=6600K, and log(g)=4.2. Because of the increased line opacity and consequent low gas pressure, convection plays no significant role in the temperature structure. Lighter elemental abundances through the iron group scatter about standard abundance distribution (SAD) (solar) values. Iron and nickel are about one order of magnitude deficient while cobalt is enhanced by 1.5dex. Heavier elements, including the lanthanides, generally follow the solar pattern but enhanced by 3 to 4dex. Odd-Z elements are generally less abundant than their even-Z neighbours. With a few exceptions (e.g. Yb), the abundance pattern among the heavy elements is remarkably coherent, and resembles a displaced solar distribution.

  17. Gaia and variable stars

    NASA Astrophysics Data System (ADS)

    Eyer, Laurent; Holl, Berry; Mowlavi, Nami

    2014-01-01

    The study of variable phenomena (periodic, irregular or transient) provides a unique way to acquire knowledge about objects in our Universe. Currently, we are going through a rapid expansion of time-domain astrophysics. One reason for this expansion is the technological developments materialised in small to medium size observational projects such as HAT, OGLE, Catalina, PTF and upcoming very large projects such as Gaia or LSST. In this article, we are focusing on the ESA cornerstone mission Gaia. This spacecraft will provide astrometric, photometric and spectroscopic measurements for one billion stars. Among the existing and planned multi-epoch projects Gaia is unique because it will provide exquisite astrometric measurements for all objects it observes. We provide a brief overview of the literature concerning this mission and its expected contribution to variability studies.

  18. StarCam

    NASA Technical Reports Server (NTRS)

    Swift, Wesley

    1999-01-01

    This project can be defined by it's three phases. The goals of Phase A of this contract are to (1) Determine the required dynamic range of the combined sky and stellar image and to (2) Specify camera and optics. That was accomplished and reported in the Phase A report attached. The goals of Phase B of this contract are to 1) Produce and demonstrate algorithms for starfield background removal, 2) Produce and demonstrate star tracking and centroiding algorithms, 3) Prepare and demonstrate pointing and auto- focus algorithms, and 4) Consult with those who develop flight software on above algorithms. We are pleased to report that the above has been accomplished and delivered to NASA via our contracting contact for this project, Cheryl Alexander and are attached here. We are proud to present this final report with the expectations that all should work as planned and under budget as well: two cameras for the expected price of one.

  19. Host's stars and habitability

    NASA Astrophysics Data System (ADS)

    Gallet, F.; Charbonnel, C.; Amard, L.

    2015-12-01

    With about 2000 exoplanets discovered within a large range of different configurations of distance from the star, size, mass, and atmospheric conditions, the concept of habitability cannot rely only on the stellar effective temperature anymore. In addition to the natural evolution of habitability with the intrinsic stellar parameters, tidal, magnetic, and atmospheric interactions are believed to have strong impact on the relative position of the planets inside the so-called habitable zone. Moreover, the notion of habitability itself strongly depends on the definition we give to the term ``habitable''. The aim of this talk is to provide a global and up-to-date overview of the work done during the last few years about the description and the modelling of the habitability, and to present the physical processes currently includes in this description.

  20. Shooting Star Experiment

    NASA Technical Reports Server (NTRS)

    1997-01-01

    The Shooting Star Experiment (SSE) is designed to develop and demonstrate the technology required to focus the Sun's energy and use the energy for inexpensive space propulsion research. Pictured is an engineering model (Pathfinder III) of SSE and its thermal vacuum test to simulate in-orbit conditions at the X-Ray Calibration Facility at the Marshall Space Flight Center (MSFC). This model was used to test and characterize the motion and deformation of the structure caused by thermal effects. In this photograph, alignment targets are being placed on the engineering model so that a theodolite (alignment telescope) could be used to accurately measure the deformation and deflection of the engineering model under extreme condition, such as the coldness of deep space and the hotness of the Sun, as well as vacuum.

  1. Neutron Star Mass Distribution in Binaries

    NASA Astrophysics Data System (ADS)

    Lee, Chang-Hwan; Kim, Young-Min

    2016-05-01

    Massive neutron stars with ∼ 2Mʘ have been observed in neutron star-white dwarf binaries. On the other hand, well-measured neutron star masses in double-neutron-star binaries are still consistent with the limit of 1.5Mʘ. These observations raised questions on the neutron star equations of state and the neutron star binary evolution processes. In this presentation, a hypothesis of super-Eddington accretion and its implications are discussed. We argue that a 2Mʘ neutron star is an outcome of the super-Eddington accretion during the evolution of neutron star-white dwarf binary progenitors. We also suggest the possibility of the existence of new type of neutron star binary which consists of a typical neutron star and a massive compact companion (high-mass neutron star or black hole) with M ≥ 2Mʘ.

  2. The Maximum Mass of Rotating Strange Stars

    NASA Astrophysics Data System (ADS)

    Szkudlarek, M.; Gondek-Rosiń; ska, D.; Villain, L.; Ansorg, M.

    2012-12-01

    Strange quark stars are considered as a possible alternative to neutron stars as compact objects (e.g. Weber 2003). A hot compact star (a proto-neutron star or a strange star) born in a supernova explosion or a remnant of neutron stars binary merger are expected to rotate differentially and be important sources of gravitational waves. We present results of the first relativistic calculations of differentially rotating strange quark stars for broad ranges of degree of differential rotation and maximum densities. Using a highly accurate, relativistic code we show that rotation may cause a significant increase of maximum allowed mass of strange stars, much larger than in the case of neutron stars with the same degree of differential rotation. Depending on the maximum allowed mass a massive neutron star (strange star) can be temporarily stabilized by differential rotation or collapse to a black hole.

  3. Regrowth of stellar disks in mature galaxies: The two component nature of NGC 7217 revisited with VIRUS-W† ⋄

    NASA Astrophysics Data System (ADS)

    Fabricius, Maximilian H.; Coccato, Lodovico; Bender, Ralf; Drory, Niv; Gössl, Claus; Landriau, Martin; Saglia, Roberto P.; Thomas, Jens; Williams, Michael J.

    2015-02-01

    We have obtained high spectral resolution (R ~ 9000), integral field observations of the three spiral galaxies NGC 3521, NGC 7217 and NGC 7331 using the new fiber-based Integral Field Unit instrument VIRUS-W at the 2.7 m telescope of the McDonald Observatory in Texas. Our data allow us to revisit previous claims of counter rotation in these objects. A detailed kinematic decomposition of NGC 7217 shows that no counter rotating stellar component is present. We find that NGC 7217 hosts a low dispersion, rotating disk that is embedded in a high velocity dispersion stellar halo or bulge that is co-rotating with the disk. Due to the very different velocity dispersions (~ 20 km s-1 vs. 150 km s-1) , we are further able to perform a Lick index analysis on both components separately which indicates that the two stellar populations are clearly separated in (Mgb,) space. The velocities and dispersions of the faster component are very similar to those of the interstellar gas as measured from the [O iii] emission. Morphological evidence of active star formation in this component further suggests that NGC 7217 may be in the process of (re)growing a disk inside a more massive and higher dispersion stellar halo.

  4. "Catch a Star !"

    NASA Astrophysics Data System (ADS)

    2002-05-01

    ESO and EAAE Launch Web-based Educational Programme for Europe's Schools Catch a star!... and discover all its secrets! This is the full title of an innovative educational project, launched today by the European Southern Observatory (ESO) and the European Association for Astronomy Education (EAAE). It welcomes all students in Europe's schools to an exciting web-based programme with a competition. It takes place within the context of the EC-sponsored European Week of Science and Technology (EWST) - 2002 . This unique project revolves around a web-based competition and is centred on astronomy. It is specifically conceived to stimulate the interest of young people in various aspects of this well-known field of science, but will also be of interest to the broad public. What is "Catch a Star!" about? [Go to Catch a Star Website] The programme features useful components from the world of research, but it is specifically tailored to (high-)school students. Younger participants are also welcome. Groups of up to four persons (e.g., three students and one teacher) have to select an astronomical object - a bright star, a distant galaxy, a beautiful comet, a planet or a moon in the solar system, or some other celestial body. Like detectives, they must then endeavour to find as much information as possible about "their" object. This information may be about the position and visibility in the sky, the physical and chemical characteristics, particular historical aspects, related mythology and sky lore, etc. They can use any source available, the web, books, newspaper and magazine articles, CDs etc. for this work. The group members must prepare a (short) summarising report about this investigation and "their" object, with their own ideas and conclusions, and send it to ESO (email address: eduinfo@eso.org). A jury, consisting of specialists from ESO and the EAAE, will carefully evaluate these reports. All projects that are found to fulfill the stipulated requirements, including a

  5. Star-forming Filament Models

    NASA Astrophysics Data System (ADS)

    Myers, Philip C.

    2017-03-01

    New models of star-forming filamentary clouds are presented in order to quantify their properties and to predict their evolution. These 2D axisymmetric models describe filaments that have no core, one low-mass core, and one cluster-forming core. They are based on Plummer-like cylinders and spheroids that are bounded by a constant-density surface of finite extent. In contrast to 1D Plummer-like models, they have specific values of length and mass, they approximate observed column density maps, and their distributions of column density (N-pdfs) are pole-free. Each model can estimate the star-forming potential of a core-filament system by identifying the zone of gas dense enough to form low-mass stars and by counting the number of enclosed thermal Jeans masses. This analysis suggests that the Musca central filament may be near the start of its star-forming life, with enough dense gas to make its first ∼3 protostars, while the Coronet filament is near the midpoint of its star formation, with enough dense gas to add ∼8 protostars to its ∼20 known stars. In contrast, L43 appears to be near the end of its star-forming life, since it lacks enough dense gas to add any new protostars to the two young stellar objectsalready known.

  6. Strange-quark-matter stars

    SciTech Connect

    Glendenning, N.K.

    1989-11-01

    We investigate the implications of rapid rotation corresponding to the frequency of the new pulsar reported in the supernovae remnant SN1987A. It places very stringent conditions on the equation of state if the star is assumed to be bound by gravity alone. We find that the central energy density of the star must be greater than 13 times that of nuclear density to be stable against the most optimistic estimate of general relativistic instabilities. This is too high for the matter to consist of individual hadrons. We conclude that it is implausible that the newly discovered pulsar, if its half-millisecond signals are attributable to rotation, is a neutron star. We show that it can be a strange quark star, and that the entire family of strange stars can sustain high rotation if strange matter is stable at an energy density exceeding about 5.4 times that of nuclear matter. We discuss the conversion of a neutron star to strange star, the possible existence of a crust of heavy ions held in suspension by centrifugal and electric forces, the cooling and other features. 34 refs., 10 figs., 1 tab.

  7. Rapidly rotating neutron star progenitors

    NASA Astrophysics Data System (ADS)

    Postnov, K. A.; Kuranov, A. G.; Kolesnikov, D. A.; Popov, S. B.; Porayko, N. K.

    2016-12-01

    Rotating proto-neutron stars can be important sources of gravitational waves to be searched for by present-day and future interferometric detectors. It was demonstrated by Imshennik that in extreme cases the rapid rotation of a collapsing stellar core may lead to fission and formation of a binary proto-neutron star which subsequently merges due to gravitational wave emission. In this paper, we show that such dynamically unstable collapsing stellar cores may be the product of a former merger process of two stellar cores in a common envelope. We applied population synthesis calculations to assess the expected fraction of such rapidly rotating stellar cores which may lead to fission and formation of a pair of proto-neutron stars. We have used the BSE (Binary Star Evolution) population synthesis code supplemented with a new treatment of stellar core rotation during the evolution via effective core-envelope coupling, characterized by the coupling time, τc. The validity of this approach is checked by direct MESA calculations of the evolution of a rotating 15 M⊙ star. From comparison of the calculated spin distribution of young neutron stars with the observed one, reported by Popov and Turolla, we infer the value τc ≃ 5 × 105 yr. We show that merging of stellar cores in common envelopes can lead to collapses with dynamically unstable proto-neutron stars, with their formation rate being ˜0.1-1 per cent of the total core collapses, depending on the common envelope efficiency.

  8. Gravitational Waves from Neutron Stars

    NASA Astrophysics Data System (ADS)

    Kokkotas, Konstantinos

    2016-03-01

    Neutron stars are the densest objects in the present Universe, attaining physical conditions of matter that cannot be replicated on Earth. These unique and irreproducible laboratories allow us to study physics in some of its most extreme regimes. More importantly, however, neutron stars allow us to formulate a number of fundamental questions that explore, in an intricate manner, the boundaries of our understanding of physics and of the Universe. The multifaceted nature of neutron stars involves a delicate interplay among astrophysics, gravitational physics, and nuclear physics. The research in the physics and astrophysics of neutron stars is expected to flourish and thrive in the next decade. The imminent direct detection of gravitational waves will turn gravitational physics into an observational science, and will provide us with a unique opportunity to make major breakthroughs in gravitational physics, in particle and high-energy astrophysics. These waves, which represent a basic prediction of Einstein's theory of general relativity but have yet to be detected directly, are produced in copious amounts, for instance, by tight binary neutron star and black hole systems, supernovae explosions, non-axisymmetric or unstable spinning neutron stars. The focus of the talk will be on the neutron star instabilities induced by rotation and the magnetic field. The conditions for the onset of these instabilities and their efficiency in gravitational waves will be presented. Finally, the dependence of the results and their impact on astrophysics and especially nuclear physics will be discussed.

  9. Hot stars in globular clusters.

    NASA Astrophysics Data System (ADS)

    Moehler, S.

    Globular clusters are ideal laboratories to study the evolution of low-mass stars. In this review, I shall concentrate on two types of hot stars observed in globular clusters: horizontal branch stars and UV bright stars. The third type, the white dwarfs, are covered by Bono in this volume. While the morphology of the horizontal branch correlates strongly with metallicity, it has been known for a long time that one parameter is not sufficient to describe the diversity of observed horizontal branch morphologies. A veritable zoo of candidates for this elusive ``2{nd} parameter'' has been suggested over the past decades, and the most prominent ones will be briefly discussed here. Adding to the complications, diffusion is active in the atmospheres of hot horizontal branch stars, which makes their analysis much more diffcult. The latest twist along the horizontal branch was added by the recent discovery of an extension to hotter temperatures and fainter magnitudes, the so-called ``blue hook''. The evolutionary origin of these stars is still under debate. I shall also give a brief overview of our current knowledge about hot UV bright stars and use them to illustrate the adverse effects of selection bias.

  10. Revisiting the block method for evaluating thermal conductivities of clay and granite

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Determination of thermal conductivities of porous media using the contact method is revisited and revalidated with consideration of thermal contact resistance. Problems that limit the accuracy of determination of thermal conductivities of porous media are discussed. Thermal conductivities of granite...

  11. Asteroseismology of EC14026 Stars

    NASA Astrophysics Data System (ADS)

    Charpinet, Stephane; Fontaine, G.; Brassard, P.; Billères, M.

    2001-05-01

    EC14026 stars form a class of pulsating stars which recent discovery originates back to 1997 (Kilkenny et al. 1997, MNRAS, 285,640). These are hot, relatively compact objets belonging to the class of subdwarf B (or sdB) stars and showing rapid multiperiodic (P 80-600 seconds), low amplitude (a few millimags) luminosity variations. These stars are identified to Extended Horizontal Branch (EHB) models, and thus are evolved, low mass (M 0.5 Modot) core helium burning objects (Dorman et al. 1993, ApJ, 415, 596). The theory of EC14026 stars, which origin is anterior to their "observational discovery" (their existence was predicted on these theoretical basis; Charpinet et al. 1996, ApJ, 471, L103), is nowadays in a relatively mature state. The mode driving mechanism identified is a kappa-mechanism caused by the formation, due to microscopic chemical diffusion processes, of a strongly overabundant reservoir of iron in the envelope of these stars. This theory has been remarkably consistent with the rapidly growing amounts of observational data so far, thus opening the way to a potentially very fruitful application of the tools of asteroseismology to probe the structure of these objects. In this context, I will present a method to constrain, with asteroseismology, the stellar parameters of EC14026 stars. This method is based on the construction of large grids of pulsating subdwarf B star models, each model being analysed with a linear nonadiabatic pulsation code, aimed at deriving the most appropriate set of model parameters that can best reproduce the observed periods of a given pulsating sdB star. With this method, fundamental quantities such as the effective temperature, the surface gravity, the total mass, and the mass of the H-rich envelope can be inferred.

  12. Precarious Stars — a Variety of Boson Stars

    NASA Astrophysics Data System (ADS)

    Hafizi, M.

    In this paper we study boson stars made up of real scalar λϕ4 self-interacting fields at finite temperature. For the reason of their equation of state, we call these configurations "precarious stars." The equation of state for these stars follows from the Gaussian approximation applied to real scalar λϕ4 self-interacting fields. We numerically calculate these configurations in the frame of general relativity. We obtain masses, radii, surface temperatures and other characteristics. After a numerical analysis of the thermal radiation emitted from their surface, we conclude that these stars radiate rapidly all their energy and mass. Nevertheless, we raise the question of the role these configurations may have played in formation of the large scale structures of the Universe.

  13. Neutron star structure from QCD

    NASA Astrophysics Data System (ADS)

    Fraga, Eduardo S.; Kurkela, Aleksi; Vuorinen, Aleksi

    2016-03-01

    In this review article, we argue that our current understanding of the thermodynamic properties of cold QCD matter, originating from first principles calculations at high and low densities, can be used to efficiently constrain the macroscopic properties of neutron stars. In particular, we demonstrate that combining state-of-the-art results from Chiral Effective Theory and perturbative QCD with the current bounds on neutron star masses, the Equation of State of neutron star matter can be obtained to an accuracy better than 30% at all densities.

  14. The Sun: Our Nearest Star

    NASA Technical Reports Server (NTRS)

    Adams, M. L.; Six, N. Frank (Technical Monitor)

    2002-01-01

    We have in our celestial backyard, a prime example of a variable star. The Sun, long thought to be "perfect" and unvarying, began to reveal its cycles in the early 1600s as Galileo Galilei and Christoph Scheiner used a telescope to study sunspots. For the past four hundred years, scientists have accumulated data, showing a magnetic cycle that repeats, on average, every eleven (or twenty-two) years. In addition, modern satellites have shown that the energy output at radio and x-ray wavelengths also varies with this cycle. This talk will showcase the Sun as a star and discuss how solar studies may be used to understand other stars.

  15. The formation of sunlike stars.

    PubMed

    Lada, C J; Shu, F H

    1990-05-04

    Understanding how stars like the sun formed constitutes one of the principal challenges confronting modern astrophysics. In recent years, advances in observational technology, particularly at infrared and millimeter wavelengths, have produced an avalanche of critical data and unexpected discoveries about the process of star formation, which is blocked from external view at optical and shorter wavelengths by an obscuring blanket of interstellar dust. Fueled by this new knowledge, a comprehensive empirical picture of stellar genesis is beginning to emerge, laying the foundations for a coherent theory of the birth of sunlike stars.

  16. The early evolution of stars

    NASA Technical Reports Server (NTRS)

    Strom, Stephen E.

    1995-01-01

    This review outlines the observational properties of young stellar objects as they evolve from their birth within dense rotating molecular cores to fully-formed pre-main sequence stars. Current work suggests that most of the mass which ultimately comprises a fully-formed star is transferred from a flattened infalling envelope (of size approximately several thousand AU) through a circumstellar accretion disk to the stellar surface. We summarize current estimates for the duration of the envelope infall and disk accretion phases and discuss the implication of these timescales for the formation of stars of different mass and of planetary systems.

  17. Spectroscopy of γ Doradus stars

    NASA Astrophysics Data System (ADS)

    Brunsden, E.; Pollard, K. R.; Cottrell, P. L.; Wright, D. J.; De Cat, P.; Kilmartin, P. M.

    2014-02-01

    The musician programme at the University of Canterbury has been successfully identifying pulsation modes in many γ Doradus stars using hundreds of ground-based spectroscopic observations. This paper describes some of the successful mode identifications and emerging patterns of the programme. The hybrid γ Doradus/δ Scuti star HD 49434 remains an enigma, despite the analysis of more than 1700 multi-site high-resolution spectra. A new result for this star is apparently distinct line-profile variations for the γ Doradus and δ Scuti frequencies.

  18. Revisiting the Capture of Mercury into Its 3:2 Spin-orbit Resonance

    DTIC Science & Technology

    2014-01-01

    well before differentiation. Keywords. celestial mechanics, planets and satellites: individual ( Mercury ) 1. Previous studies In the literature hitherto...2014 2. REPORT TYPE 3. DATES COVERED 00-00-2014 to 00-00-2014 4. TITLE AND SUBTITLE Revisiting the capture of Mercury into its 3:2 spin-orbit...Astronomical Union 2014 doi:10.1017/S1743921314007765 Revisiting the capture of Mercury into its 3:2 spin-orbit resonance Benôıt Noyelles1, Julien

  19. Tidal resonances in binary star systems. II - Slowly rotating stars

    NASA Astrophysics Data System (ADS)

    Alexander, M. E.

    1988-12-01

    The potential energy of tidal interactions in a binary system with rotating components is formulated as a perturbation Hamiltonian which self-consistently couples the dynamics of the rotating stars' oscillations and orbital motion. The action-angle formalism used to discuss tidal resonances in the nonrotating case (Alexander, 1987) is extended to rotating stars. The behavior of a two-mode system and the procedure for treating an arbitrary number of modes are discussed.

  20. Revisiting the Decision of Death in Hurst v. Florida.

    PubMed

    Cooke, Brian K; Ginory, Almari; Zedalis, Jennifer

    2016-12-01

    The United States Supreme Court has considered the question of whether a judge or a jury must make the findings necessary to support imposition of the death penalty in several notable cases, including Spaziano v. Florida (1984), Hildwin v. Florida (1989), and Ring v. Arizona (2002). In 2016, the U.S. Supreme Court revisited the subject in Hurst v. Florida Florida Statute § 921.141 allows the judge, after weighing aggravating and mitigating circumstances, to enter a sentence of life imprisonment or death. Before Hurst, Florida's bifurcated sentencing proceedings included an advisory sentence from jurors and a separate judicial hearing without juror involvement. In Hurst, the Court revisited the question of whether Florida's capital sentencing scheme violates the Sixth Amendment, which requires a jury, not a judge, to find each fact necessary to impose a sentence of death in light of Ring In an eight-to-one decision, the Court reversed the judgment of the Florida Supreme Court, holding that the Sixth Amendment requires a jury to find the aggravating factors necessary for imposing the death penalty. The role of Florida juries in capital sentencing proceedings was thereby elevated from advisory to determinative. We examine the Court's decision and offer commentary regarding this shift from judge to jury in the final imposition of the death penalty and the overall effect of this landmark case.

  1. Engineered nanoparticles: Revisiting safety concerns in light of ethno medicine.

    PubMed

    Palkhiwala, Suhani; Bakshi, Sonal R

    2014-01-01

    The nanoparticles are a miracle invention of the century that has opened novel avenues of applications in various fields. The safety aspect of exposure to nanoparticles for humans, plants, animals, soil micro-flora, and ecosystem at large has been questioned. The safety concern can be addressed by laboratory studies to assess the actual risk and recommend exposure limits and related regulation. There is also a suggestion for considering the nanoparticle form of conventional compounds as a new chemical and subject it to safety assessment in line with the chemical regulatory agencies. In the light of the current scenario of popularity and safety concerns regarding nanoparticles, the use of ancient metal based forms like, Bhasma is revisited in the present article. The current approach of green synthesis of nanoparticles is compared with the Ayurveda Rasayana Shastra guidelines of Bhasma preparation and modern preparation of engineered nanoparticles. Since the benefits of nanotechnology are undeniable, and safety concerns are also not ungrounded, there is a pressing need to revisit the ways nanoparticles are manufactured, and to carry out safety assessment by the techniques specially adapted for this novel compound.

  2. The Stars behind the Curtain

    NASA Astrophysics Data System (ADS)

    2010-02-01

    ESO is releasing a magnificent VLT image of the giant stellar nursery surrounding NGC 3603, in which stars are continuously being born. Embedded in this scenic nebula is one of the most luminous and most compact clusters of young, massive stars in our Milky Way, which therefore serves as an excellent "local" analogue of very active star-forming regions in other galaxies. The cluster also hosts the most massive star to be "weighed" so far. NGC 3603 is a starburst region: a cosmic factory where stars form frantically from the nebula's extended clouds of gas and dust. Located 22 000 light-years away from the Sun, it is the closest region of this kind known in our galaxy, providing astronomers with a local test bed for studying intense star formation processes, very common in other galaxies, but hard to observe in detail because of their great distance from us. The nebula owes its shape to the intense light and winds coming from the young, massive stars which lift the curtains of gas and clouds revealing a multitude of glowing suns. The central cluster of stars inside NGC 3603 harbours thousands of stars of all sorts (eso9946): the majority have masses similar to or less than that of our Sun, but most spectacular are several of the very massive stars that are close to the end of their lives. Several blue supergiant stars crowd into a volume of less than a cubic light-year, along with three so-called Wolf-Rayet stars - extremely bright and massive stars that are ejecting vast amounts of material before finishing off in glorious explosions known as supernovae. Using another recent set of observations performed with the SINFONI instrument on ESO's Very Large Telescope (VLT), astronomers have confirmed that one of these stars is about 120 times more massive than our Sun, standing out as the most massive star known so far in the Milky Way [1]. The clouds of NGC 3603 provide us with a family picture of stars in different stages of their life, with gaseous structures that are

  3. A Heavy Flavor Tracker for STAR

    SciTech Connect

    Xu, Z.; Chen, Y.; Kleinfelder, S.; Koohi, A.; Li, S.; Huang, H.; Tai, A.; Kushpil, V.; Sumbera, M.; Colledani, C.; Dulinski, W.; Himmi,A.; Hu, C.; Shabetai, A.; Szelezniak, M.; Valin, I.; Winter, M.; Miller,M.; Surrow, B.; Van Nieuwenhuizen G.; Bieser, F.; Gareus, R.; Greiner,L.; Lesser, F.; Matis, H.S.; Oldenburg, M.; Ritter, H.G.; Pierpoint, L.; Retiere, F.; Rose, A.; Schweda, K.; Sichtermann, E.; Thomas, J.H.; Wieman, H.; Yamamoto, E.; Kotov, I.

    2005-03-14

    We propose to construct a Heavy Flavor Tracker (HFT) for theSTAR experiment at RHIC. The HFT will bring new physics capabilities toSTAR and it will significantly enhance the physics capabilities of theSTAR detector at central rapidities. The HFT will ensure that STAR willbe able to take heavy flavor data at all luminosities attainablethroughout the proposed RHIC II era.

  4. A Heavy Flavor Tracker for STAR

    SciTech Connect

    Xu, Z.; Chen, Y.; Kleinfelder, S.; Koohi, A.; Li, S.; Huang, H.; Tai, A.; Kushpil, V.; Sumbera, M.; Colledani, C.; Dulinski, W.; Himmi,A.; Hu, C.; Shabetai, A.; Szelezniak, M.; Valin, I.; Winter, M.; Surrow,B.; Van Nieuwenhuizen, G.; Bieser, F.; Gareus, R.; Greiner, L.; Lesser,F.; Matis, H.S.; Oldenburg, M.; Ritter, H.G.; Pierpoint, L.; Retiere, F.; Rose, A.; Schweda, K.; Sichtermann, E.; Thomas, J.H.; Wieman, H.; Yamamoto, E.; Kotov, I.

    2005-03-14

    We propose to construct a Heavy Flavor Tracker (HFT) for the STAR experiment at RHIC. The HFT will bring new physics capabilities to STAR and it will significantly enhance the physics capabilities of the STAR detector at central rapidities. The HFT will ensure that STAR will be able to take heavy flavor data at all luminosities attainable throughout the proposed RHIC II era.

  5. Theoretical Considerations of Massive Star Formation

    NASA Technical Reports Server (NTRS)

    Yorke, Harold W.

    2006-01-01

    This viewgraph presentation reviews the formation of massive stars. The formation of massive stars is different in many ways from the formation of other stars. The presentation shows the math, and the mechanisms that must be possible for a massive star to form.

  6. Recovery From Giant Eruptions in Massive Stars

    NASA Astrophysics Data System (ADS)

    Kashi, A.; Davidson, K.; Humphreys, R. M.

    2015-12-01

    We perform radiation hydrodynamic simulations to study how very massive stars recover from giant eruptions. The post eruption star experience strong mass loss due to strong winds, driven by radial pulsations in the star*s interior, that operate by the κ-mechanism. The mass loss history obtained in our simulations resembles η Car*s history.

  7. The Neutron Star Zoo

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.

    2014-01-01

    Neutron stars are a very diverse population, both in their observational and their physical properties. They prefer to radiate most of their energy at X-ray and gamma-ray wavelengths. But whether their emission is powered by rotation, accretion, heat, magnetic fields or nuclear reactions, they are all different species of the same animal whose magnetic field evolution and interior composition remain a mystery. This article will broadly review the properties of inhabitants of the neutron star zoo, with emphasis on their high-energy emission. XXX Neutron stars are found in a wide variety of sources, displaying an amazing array of behavior. They can be isolated or in binary systems, accreting, heating, cooling, spinning down, spinning up, pulsing, flaring and bursting. The one property that seems to determine their behavior most strongly is their magnetic field strength, structure and evolution. The hot polar caps, bursts and flares of magnetars are likely due to the rapid decay and twisting of their superstrong magnetic fields, whose very existence requires some kind of early dynamo activity. The intermediate-strength magnetic fields of RPPs determines their spin-down behavior and radiation properties. However, the overlap of the magnetar and RPP populations is not understood at present. Why don't high-field RPPs burst or flare? Why don't lower-field magnetars sometimes behave more like RPPs? INS may be old magnetars whose high fields have decayed, but they do not account for the existence of younger RPPs with magnetar-strength fields. Not only the strength of the magnetic field but also its configuration may be important in making a NS a magnetar or a RPP. Magnetic field decay is a critical link between other NS populations as well. "Decay" of the magnetic field is necessary for normal RPPs to evolve into MSPs through accretion and spin up in LMXBs. Some kind of accretion-driven field reduction is the most likely mechanism, but it is controversial since it is not

  8. Chandra Captures Neutron Star Action

    NASA Video Gallery

    This movie from NASA's Chandra X-ray Observatory shows a fast moving jet of particles produced by a rapidly rotating neutron star, and may provide new insight into the nature of some of the densest...

  9. Coronal Structures in Cool Stars

    NASA Technical Reports Server (NTRS)

    Oliversen, Ronald (Technical Monitor); Duprec, Andrea K.

    2003-01-01

    Many papers have been published that further elucidate the structure of coronas in cool stars as determined from EUVE, HST, FUSE, Chandra, and XMM-Newton observations. Highlights of these are summarized including publications during this reporting period and presentations.

  10. Sleuthing the Isolated Compact Stars

    NASA Astrophysics Data System (ADS)

    Drake, J. J.

    2004-08-01

    In the early 1990's, isolated thermally-emitting neutron stars accreting from the interstellar medium were predicted to show up in their thousands in the ROSAT soft X-ray all-sky survey. The glut of sources would provide unprecedented opportunities for probing the equation of state of ultra-dense matter. Only seven objects have been firmly identified to date. The reasons for this discrepency are discussed and recent high resolution X-ray spectroscopic observations of these objects are described. Spectra of the brightest of the isolated neutron star candidates, RX J1856.5-3754, continue to present interpretational difficulties for current neutron star model atmospheres and alternative models are briefly discussed. RX J1856.5-3754 remains a valid quark star candidate.

  11. The star arboricity of graphs

    NASA Astrophysics Data System (ADS)

    Algor, Ilan

    1988-03-01

    The problem concerns the minimum time in which a number of messages can be transmitted through a communication network in which each node can transmit to many other nodes simultaneously but can receive only one message at a time. In the undirected version of the problem, the graphs, G, representing the messages are finite, undirected and simple; the messages transmitted in unit time form a subgraph which is a star. The star aboricity, st(G) of a graph G is the minimum number of star forests whose union covers all edges of G. A maximum value is derived for the star aboricity of any d-regular graph G, and is proved through probabilistic arguments.

  12. The STAR Vertex Position Detector

    NASA Astrophysics Data System (ADS)

    Llope, W. J.; Zhou, J.; Nussbaum, T.; Hoffmann, G. W.; Asselta, K.; Brandenburg, J. D.; Butterworth, J.; Camarda, T.; Christie, W.; Crawford, H. J.; Dong, X.; Engelage, J.; Eppley, G.; Geurts, F.; Hammond, J.; Judd, E.; McDonald, D. L.; Perkins, C.; Ruan, L.; Scheblein, J.; Schambach, J. J.; Soja, R.; Xin, K.; Yang, C.

    2014-09-01

    The 2×3 channel pseudo Vertex Position Detector (pVPD) in the STAR experiment at RHIC has been upgraded to a 2×19 channel detector in the same acceptance, called the Vertex Position Detector (VPD). This detector is fully integrated into the STAR trigger system and provides the primary input to the minimum-bias trigger in Au+Au collisions. The information from the detector is used both in the STAR Level-0 trigger and offline to measure the location of the primary collision vertex along the beam pipe and the event "start time" needed by other fast-timing detectors in STAR. The offline timing resolution of single detector channels in full-energy Au+Au collisions is ~100 ps, resulting in a start time resolution of a few tens of picoseconds and a resolution on the primary vertex location of ~1 cm.

  13. Starspots on Young pms Stars

    NASA Astrophysics Data System (ADS)

    Alekseev, I. Yu.

    2014-06-01

    Long-term, multiband photometric observations of 8 young PMS stars are used to construct models for their starspots. It is shown that the average density of starspots is up to 40 % of the total surface of a star (V824 Ara), while the difference in temperatures between a quiet photosphere and a spot ranges from 870 K (AB Dor) to 1700-1800 K (PZ Tel, V1321 Ori, V395 Cep). The spots lie at low (2-8°, V343 Nor) and medium (25-61°) latitudes, while the largest latitude of starspots is 16-80°. A cyclical activity that shows up as changes in the total area and average latitude of the starspots is observed in the stars PZ Tel, TY Col, V824 Ara, and AB Dor. A latitudinal drift of the starspots and differential rotation of the star are observed which are analogous to those of the sun.

  14. Neutron stars : Seen my way

    NASA Astrophysics Data System (ADS)

    Kundt, Wolfgang

    2001-09-01

    An unconventional survey is presented of the observable properties of neutron stars and of all astrophysical phenomena possibly related to them, such as their pulsing, clock irregularities, bursting, flickering, and occasional super-Eddington brightness, the generation of cosmic rays, of gamma-ray bursts, of jets, and of synchrotron nebulae, their birth, and their occasional transient appearance as 'supersoft' X-ray sources. The msec pulsars are argued to be born fast, the black-hole candidates to be neutron stars inside of massive disks, and the gamma-ray bursts to be sparks from dense 'blades' accreting spasmodically onto the surfaces of (generally old) neutron stars within " 0.3 Kpc from the Sun. Supernovae - the likely birth events of neutron stars - are thick-walled explosions, not to be described by Sedov-Taylor waves, which illuminate their gaseous environs via collisions of their 'splinters'.

  15. Star formation across galactic environments

    NASA Astrophysics Data System (ADS)

    Young, Jason

    I present here parallel investigations of star formation in typical and extreme galaxies. The typical galaxies are selected to be free of active galactic nuclei (AGN), while the extreme galaxies host quasars (the most luminous class of AGN). These two environments are each insightful in their own way; quasars are among the most violent objects in the universe, literally reshaping their host galaxies, while my sample of AGN-free star-forming galaxies ranges from systems larger than the Milky Way to small galaxies which are forming stars at unsustainably high rates. The current paradigm of galaxy formation and evolution suggests that extreme circumstances are key stepping stones in the assembly of galaxies like our Milky Way. To test this paradigm and fully explore its ramifications, this dual approach is needed. My sample of AGN-free galaxies is drawn from the KPNO International Spectroscopic Survey. This Halpha-selected, volume-limited survey was designed to detect star-forming galaxies without a bias toward continuum luminosity. This type of selection ensures that this sample is not biased toward galaxies that are large or nearby. My work studies the KISS galaxies in the mid- and far-infrared using photometry from the IRAC and MIPS instruments aboard the Spitzer Space Telescope. These infrared bands are particularly interesting for star formation studies because the ultraviolet light from young stars is reprocessed into thermal emission in the far-infrared (24mum MIPS) by dust and into vibrational transitions features in the mid-infrared (8.0mum IRAC) by polycyclic aromatic hydrocarbons (PAHs). The work I present here examines the efficiencies of PAH and thermal dust emission as tracers of star-formation rates over a wide range of galactic stellar masses. I find that the efficiency of PAH as a star-formation tracer varies with galactic stellar mass, while thermal dust has a highly variable efficiency that does not systematically depend on galactic stellar mass

  16. NGC 3293 revisited by the Gaia-ESO Survey

    NASA Astrophysics Data System (ADS)

    Semaan, Thierry; Morel, Thierry; Gosset, Eric; Zorec, Juan; Frémat, Yves; Blomme, Ronny; Lobel, Alex

    2015-01-01

    In the framework of the Gaia-ESO survey we have determined the fundamental parameters of a large number of B-type stars in the Galactic, young open cluster NGC 3293. The determination of the stellar parameters is based on medium-resolution spectra obtained with FLAMES/GIRAFFE at ESO-VLT. As a second step, we adopted the accurate parameters to determine the chemical abundances of these hot stars. We present a comparison of our results with those obtained by the 'VLT-FLAMES survey of massive stars' (Evans et al. 2005). Our study increases the number of objects analysed and provides an extended view of this cluster.

  17. GRBs from the First Stars

    SciTech Connect

    Iocco, Fabio; /Naples U. /KIPAC, Menlo Park

    2007-04-16

    We present an estimate of the Gamma Ray Bursts which should be expected from metal-free, elusive first generation of stars known as PopulationIII (PopIII). We derive the GRB rate from these stars from the Stellar Formation Rate obtained in several Reionization scenarios available in the literature. In all of the analyzed models we find that GRBs from PopIII are subdominant with respect to the ''standard'' (PopII) ones up to z {approx} 10.

  18. STAR Vertex Detector Upgrade Development

    SciTech Connect

    Greiner, Leo C.; Matis, Howard S.; Stezelberger, Thorsten; Vu,Chinh Q.; Wieman, Howard; Szelezniak, Michal; Sun, Xiangming

    2008-01-28

    We report on the development and prototyping efforts undertaken with the goal of producing a micro-vertex detector for the STAR experiment at the RHIC accelerator at BNL. We present the basic detector requirements and show a sensor development path, conceptual mechanical design candidates and readout architecture. Prototyping and beam test results with current generation MimoSTAR-2 sensors and a readout system featuring FPGA based on-the-fly hit finding and data sparsification are also presented.

  19. Neutron star news and puzzles

    NASA Astrophysics Data System (ADS)

    Prakash, Madappa

    2014-08-01

    Gerry Brown has had the most influence on my career in Physics, and my life after graduate studies. This article gives a brief account of some of the many ways in which Gerry shaped my research. Focus is placed on the significant strides on neutron star research made by the group at Stony Brook, which Gerry built from scratch. Selected puzzles about neutron stars that remain to be solved are noted.

  20. Laser Guide Star Operational Issues

    NASA Astrophysics Data System (ADS)

    Max, C. E.

    Introduction Operational Implications for the Laser System Rayleigh Scattering Focus Changes Variations in Sodium Column Density Requirement to Nod the Telescope for Infra-Red Observing Calibration of the Adaptive Optics System for Sodium Laser Guide - Star Operation Types of Internal Calibration Sources Static Calibration Auxiliary Wavefront Sensors Dynamic Calibration (Real-Time Point-Spread-Function Measurements) Safety Considerations Regarding Laser Guide Star Systems Laser Eye Safety Fire Safety Aircraft Avoidance Spacecraft Damage Avoidance Laser Coordination on Multi-Telescope Summits Conclusions