Physical Structure of Four Symbiotic Binaries

NASA Technical Reports Server (NTRS)

Kenyon, Scott J. (Principal Investigator)

1997-01-01

Disk accretion powers many astronomical objects, including pre-main sequence stars, interacting binary systems, and active galactic nuclei. Unfortunately, models developed to explain the behavior of disks and their surroundings - boundary layers, jets, and winds - lack much predictive power, because the physical mechanism driving disk evolution - the viscosity - is not understood. Observations of many types of accreting systems are needed to constrain the basic physics of disks and provide input for improved models. Symbiotic stars are an attractive laboratory for studying physical phenomena associated with disk accretion. These long period binaries (P(sub orb) approx. 2-3 yr) contain an evolved red giant star, a hot companion, and an ionized nebula. The secondary star usually is a white dwarf accreting material from the wind of its red giant companion. A good example of this type of symbiotic is BF Cygni: our analysis shows that disk accretion powers the nuclear burning shell of the hot white dwarf and also manages to eject material perpendicular to the orbital plane (Mikolajewska, Kenyon, and Mikolajewski 1989). The hot components in other symbiotic binaries appear powered by tidal overflow from a very evolved red giant companion. We recently completed a study of CI Cygni and demonstrated that the accreting secondary is a solar-type main sequence star, rather than a white dwarf (Kenyon et aL 1991). This project continued our study of symbiotic binary systems. Our general plan was to combine archival ultraviolet and optical spectrophotometry with high quality optical radial velocity observations to determine the variation of line and continuum sources as functions of orbital phase. We were very successful in generating orbital solutions and phasing UV+optical spectra for five systems: AG Dra, V443 Her, RW Hya, AG Peg, and AX Per. Summaries of our main results for these systems appear below. A second goal of our project was to consider general models for the outbursts of symbiotic stars, with an emphasis on understanding the differences between disk-driven and nuclear-powered eruptions.

Properties of evolved mass-losing stars in the Milky Way and variations in the interstellar dust composition

NASA Technical Reports Server (NTRS)

Thronson, Harley A., Jr.; Latter, William B.; Black, John H.; Bally, John; Hacking, Perry

1987-01-01

A large sample of evolved carbon-rich and oxygen-rich objects has been studied using data from the IRAS Point Source Catalog. The number density of infrared-emitting 'carbon' stars shows no variation with Galactocentric radius, while the evolved 'oxygen' star volume density can be well fitted by a given law. A law is given for the number of carbon stars; a total is found in the Galaxy of 48,000 highly evolved oxygen stars. The mass-return rate for all evolved stars is found to be 0.35 solar mass/yr, with a small percentage contribution from carbon stars. The mass-loss rates for both types of stars are dominated by the small number of objects with the smallest rates. A mean lifetime of about 200,000 yr is obtained for both carbon and oxygen stars. Main-sequence stars in the mass range of three to five solar masses are the probable precursors of the carbon stars.

Stellar structure and compact objects before 1940: Towards relativistic astrophysics

NASA Astrophysics Data System (ADS)

Bonolis, Luisa

2017-06-01

Since the mid-1920s, different strands of research used stars as "physics laboratories" for investigating the nature of matter under extreme densities and pressures, impossible to realize on Earth. To trace this process this paper is following the evolution of the concept of a dense core in stars, which was important both for an understanding of stellar evolution and as a testing ground for the fast-evolving field of nuclear physics. In spite of the divide between physicists and astrophysicists, some key actors working in the cross-fertilized soil of overlapping but different scientific cultures formulated models and tentative theories that gradually evolved into more realistic and structured astrophysical objects. These investigations culminated in the first contact with general relativity in 1939, when J. Robert Oppenheimer and his students George Volkoff and Hartland Snyder systematically applied the theory to the dense core of a collapsing neutron star. This pioneering application of Einstein's theory to an astrophysical compact object can be regarded as a milestone in the path eventually leading to the emergence of relativistic astrophysics in the early 1960s.

Probing Dust Formation Around Evolved Stars with Near-Infrared Interferometry

NASA Astrophysics Data System (ADS)

Sargent, B.; Srinivasan, S.; Riebel, D.; Meixner, M.

2014-09-01

Near-infrared interferometry holds great promise for advancing our understanding of the formation of dust around evolved stars. For example, the Magdalena Ridge Observatory Interferometer (MROI), which will be an optical/near-infrared interferometer with down to submilliarcsecond resolution, includes studying stellar mass loss as being of interest to its Key Science Mission. With facilities like MROI, many questions relating to the formation of dust around evolved stars may be probed. How close to an evolved star such as an asymptotic giant branch (AGB) or red supergiant (RSG) star does a dust grain form? Over what temperature ranges will such dust form? How does dust formation temperature and distance from star change as a function of the dust composition (carbonaceous versus oxygen-rich)? What are the ranges of evolved star dust shell geometries, and does dust shell geometry for AGB and RSG stars correlate with dust composition, similar to the correlation seen for planetary nebula outflows? At what point does the AGB star become a post-AGB star, when dust formation ends and the dust shell detaches? Currently we are conducting studies of evolved star mass loss in the Large Magellanic Cloud using photometry from the Surveying the Agents of a Galaxy's Evolution (SAGE; PI: M. Meixner) Spitzer Space Telescope Legacy program. We model this mass loss using the radiative transfer program 2Dust to create our Grid of Red supergiant and Asymptotic giant branch ModelS (GRAMS). For simplicity, we assume spherical symmetry, but 2Dust does have the capability to model axisymmetric, non-spherically-symmetric dust shell geometries. 2Dust can also generate images of models at specified wavelengths. We discuss possible connections of our GRAMS modeling using 2Dust of SAGE data of evolved stars in the LMC and also other data on evolved stars in the Milky Way's Galactic Bulge to near-infrared interferometric studies of such stars. By understanding the origins of dust around evolved stars, we may learn more about the later parts of the life of stardust; e.g., its residence in the interstellar medium, its time spent in molecular clouds, and its inclusion into solid bodies in future planetary systems.

Search for Close-in Planets around Evolved Stars with Phase-curve variations and Radial Velocity Measurements

NASA Astrophysics Data System (ADS)

Hirano, Teruyuki; Sato, Bun'ei; Masuda, Kento; Benomar, Othman Michel; Takeda, Yoichi; Omiya, Masashi; Harakawa, Hiroki

2016-10-01

Tidal interactions are a key process to understand the evolution history of close-in exoplanets. But tidals still have a large uncertainty in their prediction for the damping timescales of stellar obliquity and semi-major axis. We have worked on a search for transiting giant planets around evolved stars, for which few close-in planets were discovered. It has been reported that evolved stars lack close-in planets, which is often attributed to the tidal evolution and/or engulfment of close-in planets by the hosts. Meanwhile, Kepler has detected a certain fraction of transiting planet candidates around evolved stars. Confirming the planetary nature for these candidates is especially important since the comparison between the occurrence rates of close-in planets around main sequence stars and evolved stars provides a unique opportunity to discuss the final stage of close-in planets. With the aim of confirming KOI planet candidates around evolved stars, we measured precision radial velocities (RVs) for evolved stars with transiting planet candidates using Subaru/HDS. We also developed a new code which simultaneously models and fits the observed RVs and phase-curve variations in the Kepler data (e.g., transits, stellar ellipsoidal variations, and planet emission/reflected light). As a result of applying the global fit to KOI giants/subgiants, we confirmed two giant planets around evolved stars (Kepler-91 and KOI-1894), as well as revealed that KOI-977 is more likely a false positive.

Random forest classification of stars in the Galactic Centre

NASA Astrophysics Data System (ADS)

Plewa, P. M.

2018-05-01

Near-infrared high-angular resolution imaging observations of the Milky Way's nuclear star cluster have revealed all luminous members of the existing stellar population within the central parsec. Generally, these stars are either evolved late-type giants or massive young, early-type stars. We revisit the problem of stellar classification based on intermediate-band photometry in the K band, with the primary aim of identifying faint early-type candidate stars in the extended vicinity of the central massive black hole. A random forest classifier, trained on a subsample of spectroscopically identified stars, performs similarly well as competitive methods (F1 = 0.85), without involving any model of stellar spectral energy distributions. Advantages of using such a machine-trained classifier are a minimum of required calibration effort, a predictive accuracy expected to improve as more training data become available, and the ease of application to future, larger data sets. By applying this classifier to archive data, we are also able to reproduce the results of previous studies of the spatial distribution and the K-band luminosity function of both the early- and late-type stars.

KamLAND Sensitivity to Neutrinos from Pre-supernova Stars

NASA Astrophysics Data System (ADS)

Asakura, K.; Gando, A.; Gando, Y.; Hachiya, T.; Hayashida, S.; Ikeda, H.; Inoue, K.; Ishidoshiro, K.; Ishikawa, T.; Ishio, S.; Koga, M.; Matsuda, S.; Mitsui, T.; Motoki, D.; Nakamura, K.; Obara, S.; Oura, T.; Shimizu, I.; Shirahata, Y.; Shirai, J.; Suzuki, A.; Tachibana, H.; Tamae, K.; Ueshima, K.; Watanabe, H.; Xu, B. D.; Kozlov, A.; Takemoto, Y.; Yoshida, S.; Fushimi, K.; Piepke, A.; Banks, T. I.; Berger, B. E.; Fujikawa, B. K.; O'Donnell, T.; Learned, J. G.; Maricic, J.; Matsuno, S.; Sakai, M.; Winslow, L. A.; Efremenko, Y.; Karwowski, H. J.; Markoff, D. M.; Tornow, W.; Detwiler, J. A.; Enomoto, S.; Decowski, M. P.; KamLAND Collaboration

2016-02-01

In the late stages of nuclear burning for massive stars (M > 8 M⊙), the production of neutrino-antineutrino pairs through various processes becomes the dominant stellar cooling mechanism. As the star evolves, the energy of these neutrinos increases and in the days preceding the supernova a significant fraction of emitted electron anti-neutrinos exceeds the energy threshold for inverse beta decay on free hydrogen. This is the golden channel for liquid scintillator detectors because the coincidence signature allows for significant reductions in background signals. We find that the kiloton-scale liquid scintillator detector KamLAND can detect these pre-supernova neutrinos from a star with a mass of 25 M⊙ at a distance less than 690 pc with 3σ significance before the supernova. This limit is dependent on the neutrino mass ordering and background levels. KamLAND takes data continuously and can provide a supernova alert to the community.

Exposing Hierarchical Parallelism in the FLASH Code for Supernova Simulation on Summit and Other Architectures

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

Papatheodore, Thomas L.; Messer, Bronson

Since roughly 100 million years after the big bang, the primordial elements hydrogen (H), helium (He), and lithium (Li) have been synthesized into heavier elements by thermonuclear reactions inside of the stars. The change in stellar composition resulting from these reactions causes stars to evolve over the course of their lives. Although most stars burn through their nuclear fuel and end their lives quietly as inert, compact objects, whereas others end in explosive deaths. These stellar explosions are called supernovae and are among the most energetic events known to occur in our universe. Supernovae themselves further process the matter ofmore » their progenitor stars and distribute this material into the interstellar medium of their host galaxies. In the process, they generate ∼1051 ergs of kinetic energy by sending shock waves into their surroundings, thereby contributing to galactic dynamics as well.« less

STELLAR TIDAL DISRUPTION EVENTS BY DIRECT-COLLAPSE BLACK HOLES

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

Kashiyama, Kazumi; Inayoshi, Kohei, E-mail: kashiyama@berkeley.edu, E-mail: inayoshi@astro.columbia.edu

We analyze the early growth stage of direct-collapse black holes (DCBHs) with ∼10{sup 5} M {sub ⊙}, which are formed by collapse of supermassive stars in atomic-cooling halos at z ≳ 10. A nuclear accretion disk around a newborn DCBH is gravitationally unstable and fragments into clumps with a few × 10 M {sub ⊙} at ∼0.01–0.1 pc from the center. Such clumps evolve into massive Population III stars with a few × 10–10{sup 2} M {sub ⊙} via successive gas accretion, and a nuclear star cluster is formed. Radiative and mechanical feedback from an inner slim disk and themore » star cluster will significantly reduce the gas accretion rate onto the DCBH within ∼10{sup 6} yr. Some of the nuclear stars can be scattered onto the loss cone orbits also within ≲10{sup 6} yr and tidally disrupted by the central DCBH. The jet luminosity powered by such tidal disruption events can be L {sub j} ≳ 10{sup 50} erg s{sup 1}. The prompt emission will be observed in X-ray bands with a peak duration of δt {sub obs} ∼ 10{sup 5–6}(1 + z ) s followed by a tail ∝ t {sub obs} {sup 5/3}, which can be detectable by Swift BAT and eROSITA even from z ∼ 20. Follow-up observations of the radio afterglows with, e.g., eVLA and the host halos with James Webb Space Telescope could probe the earliest active galactic nucleus feedback from DCBHs.« less

SkyNet: A Modular Nuclear Reaction Network Library

NASA Astrophysics Data System (ADS)

Lippuner, Jonas; Roberts, Luke F.

2017-12-01

Almost all of the elements heavier than hydrogen that are present in our solar system were produced by nuclear burning processes either in the early universe or at some point in the life cycle of stars. In all of these environments, there are dozens to thousands of nuclear species that interact with each other to produce successively heavier elements. In this paper, we present SkyNet, a new general-purpose nuclear reaction network that evolves the abundances of nuclear species under the influence of nuclear reactions. SkyNet can be used to compute the nucleosynthesis evolution in all astrophysical scenarios where nucleosynthesis occurs. SkyNet is free and open source, and aims to be easy to use and flexible. Any list of isotopes can be evolved, and SkyNet supports different types of nuclear reactions. SkyNet is modular so that new or existing physics, like nuclear reactions or equations of state, can easily be added or modified. Here, we present in detail the physics implemented in SkyNet with a focus on a self-consistent transition to and from nuclear statistical equilibrium to non-equilibrium nuclear burning, our implementation of electron screening, and coupling of the network to an equation of state. We also present comprehensive code tests and comparisons with existing nuclear reaction networks. We find that SkyNet agrees with published results and other codes to an accuracy of a few percent. Discrepancies, where they exist, can be traced to differences in the physics implementations.

From hadrons to quarks in neutron stars: a review.

PubMed

Baym, Gordon; Hatsuda, Tetsuo; Kojo, Toru; Powell, Philip D; Song, Yifan; Takatsuka, Tatsuyuki

2018-05-01

In recent years our understanding of neutron stars has advanced remarkably, thanks to research converging from many directions. The importance of understanding neutron star behavior and structure has been underlined by the recent direct detection of gravitational radiation from merging neutron stars. The clean identification of several heavy neutron stars, of order two solar masses, challenges our current understanding of how dense matter can be sufficiently stiff to support such a mass against gravitational collapse. Programs underway to determine simultaneously the mass and radius of neutron stars will continue to constrain and inform theories of neutron star interiors. At the same time, an emerging understanding in quantum chromodynamics (QCD) of how nuclear matter can evolve into deconfined quark matter at high baryon densities is leading to advances in understanding the equation of state of the matter under the extreme conditions in neutron star interiors. We review here the equation of state of matter in neutron stars from the solid crust through the liquid nuclear matter interior to the quark regime at higher densities. We focus in detail on the question of how quark matter appears in neutron stars, and how it affects the equation of state. After discussing the crust and liquid nuclear matter in the core we briefly review aspects of microscopic quark physics relevant to neutron stars, and quark models of dense matter based on the Nambu-Jona-Lasinio framework, in which gluonic processes are replaced by effective quark interactions. We turn then to describing equations of state useful for interpretation of both electromagnetic and gravitational observations, reviewing the emerging picture of hadron-quark continuity in which hadronic matter turns relatively smoothly, with at most only a weak first order transition, into quark matter with increasing density. We review construction of unified equations of state that interpolate between the reasonably well understood nuclear matter regime at low densities and the quark matter regime at higher densities. The utility of such interpolations is driven by the present inability to calculate the dense matter equation of state in QCD from first principles. As we review, the parameters of effective quark models-which have direct relevance to the more general structure of the QCD phase diagram of dense and hot matter-are constrained by neutron star mass and radii measurements, in particular favoring large repulsive density-density and attractive diquark pairing interactions. We describe the structure of neutron stars constructed from the unified equations of states with crossover. Lastly we present the current equations of state-called 'QHC18' for quark-hadron crossover-in a parametrized form practical for neutron star modeling.

From hadrons to quarks in neutron stars: a review

NASA Astrophysics Data System (ADS)

Baym, Gordon; Hatsuda, Tetsuo; Kojo, Toru; Powell, Philip D.; Song, Yifan; Takatsuka, Tatsuyuki

2018-05-01

In recent years our understanding of neutron stars has advanced remarkably, thanks to research converging from many directions. The importance of understanding neutron star behavior and structure has been underlined by the recent direct detection of gravitational radiation from merging neutron stars. The clean identification of several heavy neutron stars, of order two solar masses, challenges our current understanding of how dense matter can be sufficiently stiff to support such a mass against gravitational collapse. Programs underway to determine simultaneously the mass and radius of neutron stars will continue to constrain and inform theories of neutron star interiors. At the same time, an emerging understanding in quantum chromodynamics (QCD) of how nuclear matter can evolve into deconfined quark matter at high baryon densities is leading to advances in understanding the equation of state of the matter under the extreme conditions in neutron star interiors. We review here the equation of state of matter in neutron stars from the solid crust through the liquid nuclear matter interior to the quark regime at higher densities. We focus in detail on the question of how quark matter appears in neutron stars, and how it affects the equation of state. After discussing the crust and liquid nuclear matter in the core we briefly review aspects of microscopic quark physics relevant to neutron stars, and quark models of dense matter based on the Nambu–Jona–Lasinio framework, in which gluonic processes are replaced by effective quark interactions. We turn then to describing equations of state useful for interpretation of both electromagnetic and gravitational observations, reviewing the emerging picture of hadron-quark continuity in which hadronic matter turns relatively smoothly, with at most only a weak first order transition, into quark matter with increasing density. We review construction of unified equations of state that interpolate between the reasonably well understood nuclear matter regime at low densities and the quark matter regime at higher densities. The utility of such interpolations is driven by the present inability to calculate the dense matter equation of state in QCD from first principles. As we review, the parameters of effective quark models—which have direct relevance to the more general structure of the QCD phase diagram of dense and hot matter—are constrained by neutron star mass and radii measurements, in particular favoring large repulsive density-density and attractive diquark pairing interactions. We describe the structure of neutron stars constructed from the unified equations of states with crossover. Lastly we present the current equations of state—called ‘QHC18’ for quark-hadron crossover—in a parametrized form practical for neutron star modeling.

ON POTASSIUM AND OTHER ABUNDANCE ANOMALIES OF RED GIANTS IN NGC 2419

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

Iliadis, C.; Karakas, A. I.; Prantzos, N.

2016-02-10

Globular clusters are of paramount importance for testing theories of stellar evolution and early galaxy formation. Strong evidence for multiple populations of stars in globular clusters derives from observed abundance anomalies. A puzzling example is the recently detected Mg–K anticorrelation in NGC 2419. We perform Monte Carlo nuclear reaction network calculations to constrain the temperature–density conditions that gave rise to the elemental abundances observed in this elusive cluster. We find a correlation between stellar temperature and density values that provide a satisfactory match between simulated and observed abundances in NGC 2419 for all relevant elements (Mg, Si, K, Ca, Sc,more » Ti, and V). Except at the highest densities (ρ ≳ 10{sup 8} g cm{sup −3}), the acceptable conditions range from ≈100 MK at ≈10{sup 8} g cm{sup −3} to ≈200 MK at ≈10{sup −4} g cm{sup −3}. This result accounts for uncertainties in nuclear reaction rates and variations in the assumed initial composition. We review hydrogen-burning sites and find that low-mass stars, asymptotic giant branch (AGB) stars, massive stars, or supermassive stars cannot account for the observed abundance anomalies in NGC 2419. Super-AGB stars could be viable candidates for the polluter stars if stellar model parameters can be fine-tuned to produce higher temperatures. Novae, involving either CO or ONe white dwarfs, could be interesting polluter candidates, but a current lack of low-metallicity nova models precludes firmer conclusions. We also discuss whether additional constraints for the first-generation polluters can be obtained by future measurements of oxygen, or by evolving models of second-generation low-mass stars with a non-canonical initial composition.« less

Studies of Evolved Star Mass Loss: GRAMS Modeling of Red Supergiant and Asymptotic Giant Branch Stars in the Magellanic Clouds

NASA Astrophysics Data System (ADS)

Sargent, Benjamin A.; Srinivasan, S.; Riebel, D.; Boyer, M.; Meixner, M.

2012-01-01

As proposed in our NASA Astrophysics Data Analysis Program (ADAP) proposal, my colleagues and I are studying mass loss from evolved stars. Such stars lose their own mass in their dying stages, and in their expelled winds they form stardust. To model mass loss from these evolved stars, my colleagues and I have constructed GRAMS: the Grid of Red supergiant and Asymptotic giant branch star ModelS. These GRAMS radiative transfer models are fit to optical through mid-infrared photometry of red supergiant (RSG) stars and asymptotic giant branch (AGB) stars. I will discuss our current studies of mass loss from AGB and RSG stars in the Small Magellanic Cloud (SMC), fitting GRAMS models to the photometry of SMC evolved star candidates identified from the SAGE-SMC (PI: K. Gordon) Spitzer Space Telescope Legacy survey. This work will be briefly compared to similar work we have done for the LMC. I will also discuss Spitzer Infrared Spectrograph (IRS) studies of the dust produced by AGB and RSG stars in the LMC. BAS is grateful for support from the NASA-ADAP grant NNX11AB06G.

Polarization and studies of evolved star mass loss

NASA Astrophysics Data System (ADS)

Sargent, Benjamin; Srinivasan, Sundar; Riebel, David; Meixner, Margaret

2012-05-01

Polarization studies of astronomical dust have proven very useful in constraining its properties. Such studies are used to constrain the spatial arrangement, shape, composition, and optical properties of astronomical dust grains. Here we explore possible connections between astronomical polarization observations to our studies of mass loss from evolved stars. We are studying evolved star mass loss in the Large Magellanic Cloud (LMC) by using photometry from the Surveying the Agents of a Galaxy's Evolution (SAGE; PI: M. Meixner) Spitzer Space Telescope Legacy program. We use the radiative transfer program 2Dust to create our Grid of Red supergiant and Asymptotic giant branch ModelS (GRAMS), in order to model this mass loss. To model emission of polarized light from evolved stars, however, we appeal to other radiative transfer codes. We probe how polarization observations might be used to constrain the dust shell and dust grain properties of the samples of evolved stars we are studying.

KamLAND Sensitivity to Neutrinos from Pre-Supernova Stars

DOE PAGES

Asakura, K.; Gando, A.; Gando, Y.; ...

2016-02-10

In the late stages of nuclear burning for massive stars (M > 8 M ⊙), the production of neutrino-antineutrino pairs through various processes becomes the dominant stellar cooling mechanism. Furthermore, as the star evolves, the energy of these neutrinos increases and in the days preceding the supernova a significant fraction of emitted electron anti-neutrinos exceeds the energy threshold for inverse beta decay on free hydrogen. This is the golden channel for liquid scintillator detectors because the coincidence signature allows for significant reductions in background signals. Here, we find that the kiloton-scale liquid scintillator detector KamLAND can detect these pre-supernova neutrinosmore » from a star with a mass of 25 M ⊙ at a distance less than 690 pc with 3σ significance before the supernova. This limit is dependent on the neutrino mass ordering and background levels. KamLAND takes data continuously and can provide a supernova alert to the community.« less

Mass return to the interstellar medium from highly-evolved carbon stars

NASA Technical Reports Server (NTRS)

Latter, W. B.; Thronson, H. A., Jr.; Hacking, P.; Bally, J.; Black, J.

1986-01-01

Data produced by the Infrared Astronomy Satellite (IRAS) was surveyed at the mid- and far-infrared wavelengths. Visually-identified carbon stars in the 12/25/60 micron color-color diagram were plotted, along with the location of a number of mass-losing stars that lie near the location of the carbon stars, but are not carbon rich. The final sample consisted of 619 objects, which were estimated to be contaminated by 7 % noncarbon-rich objects. The mass return rate was estimated for all evolved circumstellar envelopes. The IRAS Point Source Catalog (PSC) was also searched for the entire class of stars with excess emission. Mass-loss rates, lifetimes, and birthrates for evolved stars were also estimated.

VizieR Online Data Catalog: PTPS stars. III. The evolved stars sample (Niedzielski+, 2016)

NASA Astrophysics Data System (ADS)

Niedzielski, A.; Deka-Szymankiewicz, B.; Adamczyk, M.; Adamow, M.; Nowak, G.; Wolszczan, A.

2015-11-01

We present basic atmospheric parameters (Teff, logg, vt and [Fe/H]), rotation velocities and absolute radial velocities as well as luminosities, masses, ages and radii for 402 stars (including 11 single-lined spectroscopic binaries), mostly subgiants and giants. For 272 of them we present parameters for the first time. For another 53 stars we present estimates of Teff and log g based on photometric calibrations. We also present basic properties of the complete list of 744 stars that form the PTPS evolved stars sample. We examined stellar masses for 1255 stars in five other planet searches and found some of them likely to be significantly overestimated. Applying our uniformly determined stellar masses we confirm the apparent increase of companions masses for evolved stars, and we explain it, as well as lack of close-in planets with limited effective radial velocity precision for those stars due to activity. (5 data files).

Modern alchemy: Fred Hoyle and element building by neutron capture

NASA Astrophysics Data System (ADS)

Burbidge, E. Margaret

Fred Hoyle's fundamental work on building the chemical elements by nuclear processes in stars at various stages in their lives began with the building of elements around iron in the very dense hot interiors of stars. Later, in the paper by Burbidge, Burbidge, Fowler and Hoyle, we four showed that Hoyle's "equilibrium process" is one of eight processes required to make all of the isotopes of all the elements detected in the Sun and stars. Neutron capture reactions, which Fred had not considered in his epochal 1946 paper, but for which experimental data were just becoming available in 1957, are very important, in addition to the energy-generating reactions involving hydrogen, helium, carbon, nitrogen and oxygen, for building all of the elements. They are now providing clues to the late stages of stellar evolution and the earliest history of our Galaxy. I describe here our earliest observational work on neutron capture processes in evolved stars, some new work on stars showing the results of the neutron capture reactions, and data relating to processes ending in the production of lead, and I discuss where this fits into the history of stars in our own Galaxy.

Evolved stars in the Local Group galaxies - II. AGB, RSG stars and dust production in IC10

NASA Astrophysics Data System (ADS)

Dell'Agli, F.; Di Criscienzo, M.; Ventura, P.; Limongi, M.; García-Hernández, D. A.; Marini, E.; Rossi, C.

2018-06-01

We study the evolved stellar population of the Local Group galaxy IC10, with the aim of characterizing the individual sources observed and to derive global information on the galaxy, primarily the star formation history and the dust production rate. To this aim, we use evolutionary sequences of low- and intermediate-mass (M < 8 M⊙) stars, evolved through the asymptotic giant branch phase, with the inclusion of the description of dust formation. We also use models of higher mass stars. From the analysis of the distribution of stars in the observational planes obtained with IR bands, we find that the reddening and distance of IC10 are E(B - V) = 1.85 mag and d = 0.77 Mpc, respectively. The evolved stellar population is dominated by carbon stars, that account for 40% of the sources brighter than the tip of the red giant branch. Most of these stars descend from ˜1.1 - 1.3 M⊙ progenitors, formed during the major epoch of star formation, which occurred ˜2.5 Gyr ago. The presence of a significant number of bright stars indicates that IC10 has been site of significant star formation in recent epochs and currently hosts a group of massive stars in the core helium-burning phase. Dust production in this galaxy is largely dominated by carbon stars; the overall dust production rate estimated is 7 × 10-6 M⊙/yr.

Frontiers of stellar evolution

NASA Technical Reports Server (NTRS)

Lambert, David L. (Editor)

1991-01-01

The present conference discusses theoretical and observational views of star formation, spectroscopic constraints on the evolution of massive stars, very low mass stars and brown dwarfs, asteroseismology, globular clusters as tests of stellar evolution, observational tests of stellar evolution, and mass loss from cool evolved giant stars. Also discussed are white dwarfs and hot subdwarfs, neutron stars and black holes, supernovae from single stars, close binaries with evolved components, accretion disks in interacting binaries, supernovae in binary systems, stellar evolution and galactic chemical evolution, and interacting binaries containing compact components.

The UK Infrared Telescope M33 monitoring project - I. Variable red giant stars in the central square kiloparsec

NASA Astrophysics Data System (ADS)

Javadi, Atefeh; van Loon, Jacco Th.; Mirtorabi, Mohammad Taghi

2011-02-01

We have conducted a near-infrared monitoring campaign at the UK Infrared Telescope (UKIRT), of the Local Group spiral galaxy M33 (Triangulum). The main aim was to identify stars in the very final stage of their evolution, and for which the luminosity is more directly related to the birth mass than the more numerous less-evolved giant stars that continue to increase in luminosity. The most extensive data set was obtained in the K band with the UIST instrument for the central 4 × 4 arcmin2 (1 kpc2) - this contains the nuclear star cluster and inner disc. These data, taken during the period 2003-2007, were complemented by J- and H-band images. Photometry was obtained for 18 398 stars in this region; of these, 812 stars were found to be variable, most of which are asymptotic giant branch (AGB) stars. Our data were matched to optical catalogues of variable stars and carbon stars and to mid-infrared photometry from the Spitzer Space Telescope. In this first of a series of papers, we present the methodology of the variability survey and the photometric catalogue - which is made publicly available at the Centre de Données astronomiques de Strasbourg - and discuss the properties of the variable stars. The most dusty AGB stars had not been previously identified in optical variability surveys, and our survey is also more complete for these types of stars than the Spitzer survey.

Do Close-in Giant Planets Orbiting Evolved Stars Prefer Eccentric Orbits?

NASA Astrophysics Data System (ADS)

Grunblatt, Samuel K.; Huber, Daniel; Gaidos, Eric; Lopez, Eric D.; Barclay, Thomas; Chontos, Ashley; Sinukoff, Evan; Van Eylen, Vincent; Howard, Andrew W.; Isaacson, Howard T.

2018-07-01

The NASA Kepler and K2 Missions have recently revealed a population of transiting giant planets orbiting moderately evolved, low-luminosity red giant branch stars. Here, we present radial velocity (RV) measurements of three of these systems, revealing significantly non-zero orbital eccentricities in each case. Comparing these systems with the known planet population suggests that close-in giant planets around evolved stars tend to have more eccentric orbits than those around main sequence stars. We interpret this as tentative evidence that the orbits of these planets pass through a transient, moderately eccentric phase where they shrink faster than they circularize due to tides raised on evolved host stars. Additional RV measurements of currently known systems, along with new systems discovered by the recently launched NASA Transiting Exoplanet Survey Satellite (TESS) mission, may constrain the timescale and mass dependence of this process.

AN EVOLVING STELLAR INITIAL MASS FUNCTION AND THE GAMMA-RAY BURST REDSHIFT DISTRIBUTION

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

Wang, F. Y.; Dai, Z. G.

2011-02-01

Recent studies suggest that Swift gamma-ray bursts (GRBs) may not trace an ordinary star formation history (SFH). Here, we show that the GRB rate turns out to be consistent with the SFH with an evolving stellar initial mass function (IMF). We first show that the latest Swift sample of GRBs reveals an increasing evolution in the GRB rate relative to the ordinary star formation rate at high redshifts. We then assume only massive stars with masses greater than the critical value to produce GRBs and use an evolving stellar IMF suggested by Dave to fit the latest GRB redshift distribution.more » This evolving IMF would increase the relative number of massive stars, which could lead to more GRB explosions at high redshifts. We find that the evolving IMF can well reproduce the observed redshift distribution of Swift GRBs.« less

MODULES FOR EXPERIMENTS IN STELLAR ASTROPHYSICS (MESA): BINARIES, PULSATIONS, AND EXPLOSIONS

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

Paxton, Bill; Bildsten, Lars; Cantiello, Matteo

We substantially update the capabilities of the open-source software instrument Modules for Experiments in Stellar Astrophysics (MESA). MESA can now simultaneously evolve an interacting pair of differentially rotating stars undergoing transfer and loss of mass and angular momentum, greatly enhancing the prior ability to model binary evolution. New MESA capabilities in fully coupled calculation of nuclear networks with hundreds of isotopes now allow MESA to accurately simulate the advanced burning stages needed to construct supernova progenitor models. Implicit hydrodynamics with shocks can now be treated with MESA, enabling modeling of the entire massive star lifecycle, from pre-main-sequence evolution to themore » onset of core collapse and nucleosynthesis from the resulting explosion. Coupling of the GYRE non-adiabatic pulsation instrument with MESA allows for new explorations of the instability strips for massive stars while also accelerating the astrophysical use of asteroseismology data. We improve the treatment of mass accretion, giving more accurate and robust near-surface profiles. A new MESA capability to calculate weak reaction rates “on-the-fly” from input nuclear data allows better simulation of accretion induced collapse of massive white dwarfs and the fate of some massive stars. We discuss the ongoing challenge of chemical diffusion in the strongly coupled plasma regime, and exhibit improvements in MESA that now allow for the simulation of radiative levitation of heavy elements in hot stars. We close by noting that the MESA software infrastructure provides bit-for-bit consistency for all results across all the supported platforms, a profound enabling capability for accelerating MESA's development.« less

78 FR 4467 - UniStar Nuclear Energy, Combined License Application for Calvert Cliffs Power Plant, Unit 3...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-01-22

... NUCLEAR REGULATORY COMMISSION [Docket No. 52-016; NRC-2008-0250] UniStar Nuclear Energy, Combined License Application for Calvert Cliffs Power Plant, Unit 3, Exemption 1.0 Background UniStar Nuclear Energy (UNE), on behalf of Calvert Cliffs Nuclear Project, LLC and UniStar Nuclear Operating Services...

A massive, dead disk galaxy in the early Universe.

PubMed

Toft, Sune; Zabl, Johannes; Richard, Johan; Gallazzi, Anna; Zibetti, Stefano; Prescott, Moire; Grillo, Claudio; Man, Allison W S; Lee, Nicholas Y; Gómez-Guijarro, Carlos; Stockmann, Mikkel; Magdis, Georgios; Steinhardt, Charles L

2017-06-21

At redshift z = 2, when the Universe was just three billion years old, half of the most massive galaxies were extremely compact and had already exhausted their fuel for star formation. It is believed that they were formed in intense nuclear starbursts and that they ultimately grew into the most massive local elliptical galaxies seen today, through mergers with minor companions, but validating this picture requires higher-resolution observations of their centres than is currently possible. Magnification from gravitational lensing offers an opportunity to resolve the inner regions of galaxies. Here we report an analysis of the stellar populations and kinematics of a lensed z = 2.1478 compact galaxy, which-surprisingly-turns out to be a fast-spinning, rotationally supported disk galaxy. Its stars must have formed in a disk, rather than in a merger-driven nuclear starburst. The galaxy was probably fed by streams of cold gas, which were able to penetrate the hot halo gas until they were cut off by shock heating from the dark matter halo. This result confirms previous indirect indications that the first galaxies to cease star formation must have gone through major changes not just in their structure, but also in their kinematics, to evolve into present-day elliptical galaxies.

Presupernova Evolution of Differentially Rotating Massive Stars Including Magnetic Fields

NASA Astrophysics Data System (ADS)

Heger, A.; Woosley, S. E.; Spruit, H. C.

2005-06-01

As a massive star evolves through multiple stages of nuclear burning on its way to becoming a supernova, a complex, differentially rotating structure is set up. Angular momentum is transported by a variety of classic instabilities and also by magnetic torques from fields generated by the differential rotation. We present the first stellar evolution calculations to follow the evolution of rotating massive stars including, at least approximately, all these effects, magnetic and nonmagnetic, from the zero-age main sequence until the onset of iron-core collapse. The evolution and action of the magnetic fields is as described by Spruit in 2002, and a range of uncertain parameters is explored. In general, we find that magnetic torques decrease the final rotation rate of the collapsing iron core by about a factor of 30-50 when compared with the nonmagnetic counterparts. Angular momentum in that part of the presupernova star destined to become a neutron star is an increasing function of main-sequence mass. That is, pulsars derived from more massive stars rotate faster and rotation plays a more important role in the star's explosion. The final angular momentum of the core has been determined-to within a factor of 2-by the time the star ignites carbon burning. For the lighter stars studied, around 15 Msolar, we predict pulsar periods at birth near 15 ms, though a factor of 2 range is easily tolerated by the uncertainties. Several mechanisms for additional braking in a young neutron star, especially by fallback, are explored.

Planetary nebulae: 20 years of Hubble inquiry

NASA Astrophysics Data System (ADS)

Balick, Bruce

2012-08-01

The Hubble Space Telescope has served the critical roles of microscope and movie camera in the past 20 years of research on planetary nebulae (``PNe''). We have glimpsed the details of the evolving structures of neutral and ionized post-AGB objects, built ingenious heuristic models that mimic these structures, and constrained most of the relevant physical processes with careful observations and interpretation. We have searched for close physical binary stars with spatial resolution ~50 AU at 1 AU, located jets emerging from the nucleus at speeds up to 2000 km s-1 and matched newly discovered molecular and X-ray emission regions to physical substructures in order to better understand how stellar winds and ionizing radiation interact to form the lovely symmetries that are observed. Ultraviolet spectra of CNO in PNe help to uncover how stars process deep inside AGB stars with unstable nuclear burning zones. HST broadband imaging has been at the forefront of uncovering surprisingly complex wind morphologies produced at the tip of the AGB, and has led to an increasing realization of the potentially vital roles of close binary stars and emerging magnetic fields in shaping stellar winds.

Evolving R Coronae Borealis Stars with MESA

NASA Astrophysics Data System (ADS)

Clayton, Geoffrey C.; Lauer, Amber; Chatzopoulos, Emmanouil; Frank, Juhan

2018-01-01

R Coronae Borealis (RCB) stars form a small class of cool, carbon-rich supergiants that have almost no hydrogen. They undergo extreme, irregular declines in brightness of up to 8 magnitudes due to the formation of thick clouds of carbon dust. Two scenarios have been proposed for the origin of an RCB star: the merger of a CO/He white dwarf (WD) binary and a final helium-shell flash. We are using a combination of 3D hydrodynamics codes and the 1D MESA (Modules for Experiments in Stellar Astrophysics) stellar evolution code including nucleosynthesis to construct post-merger spherical models based on realistic merger progenitor models and on our hydrodynamical simulations, and then following the evolution into the region of the HR diagram where RCB stars are located. We are investigating nucleosynthesis in the dynamically accreting material of CO/He WD mergers which may provide a suitable environment for significant production of 18O and the very low 16O/18O values observed.Our MESA modeling consists of two steps: first mimicking the WD merger event using two different techniques, (a) by choosing a very high mass accretion rate with appropriate abundances and (b) by applying "stellar engineering" to an initial CO WD model to account for the newly merged material by applying an entropy adjusting procedure. Second, we follow the post-merger evolution using a large nuclear reaction network including the effects of convective and rotational instabilities to the mixing of material in order to match the observed RCB abundances. MESA follows the evolution of the merger product as it expands and cools to become an RCB star. We then examine the surface abundances and compare them to the observed RCB abundances. We also investigate how long fusion continues in the He shell near the core and how this processed material is mixed up to the surface of the star. We then model the later evolution of RCB stars to determine their likely lifetimes and endpoints when they have returned to being a WD. Solving the mystery of how the RCB stars evolve will lead to a better understanding of other important types of stellar merger events such as Type Ia SNe.

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.

76 FR 81994 - UniStar Nuclear Energy; Combined License Application for Calvert Cliffs Nuclear Power Plant, Unit...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-12-29

... NUCLEAR REGULATORY COMMISSION [Docket No. 52-016; NRC-2008-0250] UniStar Nuclear Energy; Combined License Application for Calvert Cliffs Nuclear Power Plant, Unit 3; Exemption 1.0 Background: UniStar Nuclear Energy (UNE) submitted to the U.S. Nuclear Regulatory Commission (NRC or the Commission ) a...

Trajectories of Cepheid variable stars in the Galactic nuclear bulge

NASA Astrophysics Data System (ADS)

Matsunaga, Noriyuki

2012-06-01

The central region of our Galaxy provides us with a good opportunity to study the evolution of galactic nuclei and bulges because we can observe various phenomena in detail at the proximity of 8 kpc. There is a hierarchical alignment of stellar systems with different sizes; from the extended bulge, the nuclear bulge, down to the compact cluster around the central supermassive blackhole. The nuclear bulge contains stars as young as a few Myr, and even hosts the ongoing star formation. These are in contrast to the more extended bulge which are dominated by old stars, 10Gyr. It is considered that the star formation in the nuclear bulge is caused by fresh gas provided from the inner disk. In this picture, the nuclear bulge plays an important role as the interface between the gas supplier, the inner disk, and the galactic nucleus. Kinematics of young stars in the nuclear bulge is important to discuss the star forming process and the gas circulation in the Galactic Center. We here propose spectroscopic observations of Cepheid variable stars, 25 Myr, which we recently discovered in the nuclear bulge. The spectra taken in this proposal will allow timely estimates of the systemic velocities of the variable stars.

Ultraviolet studies of O and B stars in the LMC cluster NGC 2100, the SMC cluster NGC 330 and the Galactic cluster NGC 6530

NASA Technical Reports Server (NTRS)

Boehm-Vitense, E.; Hodge, P.

1984-01-01

High-resolution and low-resolution IUE spectra of O and B stars in the LMC cluster NGC 2100, the SMC cluster NGC 330, and the young Galactic cluster NGC 6530 are investigated. Temperatures and luminosities are determined. In the LMC and SMC clusters, the most luminous stars are evolved stars on the horizontal supergiant branch, while in NGC 6530 the stars are all still on the main sequence. Extinction laws were determined. They confirm the known differences between LMC and Galactic extinctions. No mass loss was detected for the evolved B stars in the LMC and SMC clusters, while the high-luminosity stars in NGC 6530 show P Cygni profiles.

Mass Loss from Dusty AGB and Red Supergiant Stars in the Magellanic Clouds and in the Galaxy

NASA Astrophysics Data System (ADS)

Sargent, Benjamin A.; Srinivasan, Sundar; Meixner, Margaret; Kastner, Joel

2016-01-01

Asymptotic giant branch (AGB) and red supergiant (RSG) stars are evolved stars that eject large parts of their mass in outflows of dust and gas. As part of an ongoing effort to measure mass loss from evolved stars in our Galaxy and in the Magellanic Clouds, we are modeling mass loss from AGB and RSG stars in these galaxies. Our approach is twofold. We pursue radiative transfer modeling of the spectral energy distributions (SEDs) of AGB and RSG stars in the Large Magellanic Cloud (LMC), in the Small Magellanic Cloud (SMC), and in the Galactic bulge and in globular clusters of the Milky Way. We are also constructing detailed dust opacity models of AGB and RSG stars in these galaxies for which we have infrared spectra; e.g., from the Spitzer Space Telescope Infrared Spectrograph (IRS). Our sample of infrared spectra largely comes from Spitzer-IRS observations. The detailed dust modeling of spectra informs our choice of dust properties to use in radiative transfer modeling of SEDs. We seek to determine how mass loss from these evolved stars depends upon the metallicity of their host environments. BAS acknowledges funding from NASA ADAP grant NNX15AF15G.

Origin of the Elements

NASA Astrophysics Data System (ADS)

Truran, J. W., Jr.; Heger, A.

2003-12-01

Nucleosynthesis is the study of the nuclear processes responsible for the formation of the elements which constitute the baryonic matter of the Universe. The elements of which the Universe is composed indeed have a quite complicated nucleosynthesis history, which extends from the first three minutes of the Big Bang through to the present. Contemporary nucleosynthesis theory associates the production of certain elements/isotopes or groups of elements with a number of specific astrophysical settings, the most significant of which are: (i) the cosmological Big Bang, (ii) stars, and (iii) supernovae.Cosmological nucleosynthesis studies predict that the conditions characterizing the Big Bang are consistent with the synthesis only of the lightest elements: 1H, 2H, 3He, 4He, and 7Li (Burles et al., 2001; Cyburt et al., 2002). These contributions define the primordial compositions both of galaxies and of the first stars formed therein. Within galaxies, stars and supernovae play the dominant role both in synthesizing the elements from carbon to uranium and in returning heavy-element-enriched matter to the interstellar gas from which new stars are formed. The mass fraction of our solar system (formed ˜4.6 Gyr ago) in the form of heavy elements is ˜1.8%, and stars formed today in our galaxy can be a factor 2 or 3 more enriched (Edvardsson et al., 1993). It is the processes of nucleosynthesis operating in stars and supernovae that we will review in this chapter. We will confine our attention to three broad categories of stellar and supernova site with which specific nucleosynthesis products are understood to be identified: (i) intermediate mass stars, (ii) massive stars and associated type II supernovae, and (iii) type Ia supernovae. The first two of these sites are the straightforward consequence of the evolution of single stars, while type Ia supernovae are understood to result from binary stellar evolution.Stellar nucleosynthesis resulting from the evolution of single stars is a strong function of stellar mass (Woosley et al., 2002). Following phases of hydrogen and helium burning, all stars consist of a carbon-oxygen core. In the mass range of the so-called "intermediate mass" stars (1<˜M/M⊙<˜10), the temperatures realized in their degenerate cores never reach levels at which carbon ignition can occur. Substantial element production occurs in such stars during the asymptotic giant branch (AGB) phase of evolution, accompanied by significant mass loss, and they evolve to white dwarfs of carbon-oxygen (or, less commonly, oxygen-neon) composition. In contrast, the increased pressures that are experienced in the cores of stars of masses M>˜10M⊙ yield higher core temperatures that enable subsequent phases of carbon, neon, oxygen, and silicon burning to proceed. Collapse of an iron core devoid of further nuclear energy then gives rise to a type II supernova and the formation of a neutron star or black hole remnant (Heger et al., 2003). The ejecta of type IIs contain the ashes of nuclear burning of the entire life of the star, but are also modified by the explosion itself. They are the source of most material (by mass) heavier than helium.Observations reveal that binary stellar systems comprise roughly half of all stars in our galaxy. Single star evolution, as noted above, can leave in its wake compact stellar remnants: white dwarfs, neutron stars, and black holes. Indeed, we have evidence for the occurrence of all three types of condensed remnant in binaries. In close binary systems, mass transfer can take place from an evolving companion onto a compact object. This naturally gives rise to a variety of interesting phenomena: classical novae (involving hydrogen thermonuclear runaways in accreted shells on white dwarfs (Gehrz et al., 1998)), X-ray bursts (hydrogen/helium thermonuclear runaways on neutron stars (Strohmayer and Bildsten, 2003)), and X-ray binaries (accretion onto black holes). For some range of conditions, accretion onto carbon-oxygen white dwarfs will permit growth of the CO core to the Chandrasekhar limit MCh=1.4M⊙, and a thermonuclear runaway in to core leads to a type Ia supernova.In this chapter, we will review the characteristics of thermonuclear processing in the three environments we have identified: (i) intermediate-mass stars; (ii) massive stars and type II supernovae; and (iii) type Ia supernovae. This will be followed by a brief discussion of galactic chemical evolution, which illustrates how the contributions from each of these environments are first introduced into the interstellar media of galaxies. Reviews of nucleosynthesis processes include those by Arnett (1995), Trimble (1975), Truran (1984), Wallerstein et al. (1997), and Woosley et al. (2002). An overview of galactic chemical evolution is presented by Tinsley (1980).

Relaxation near Supermassive Black Holes Driven by Nuclear Spiral Arms: Anisotropic Hypervelocity Stars, S-stars, and Tidal Disruption Events

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

Hamers, Adrian S.; Perets, Hagai B., E-mail: hamers@ias.edu

Nuclear spiral arms are small-scale transient spiral structures found in the centers of galaxies. Similarly to their galactic-scale counterparts, nuclear spiral arms can perturb the orbits of stars. In the case of the Galactic center (GC), these perturbations can affect the orbits of stars and binaries in a region extending to several hundred parsecs around the supermassive black hole (SMBH), causing diffusion in orbital energy and angular momentum. This diffusion process can drive stars and binaries to close approaches with the SMBH, disrupting single stars in tidal disruption events (TDEs), or disrupting binaries, leaving a star tightly bound to themore » SMBH and an unbound star escaping the galaxy, i.e., a hypervelocity star (HVS). Here, we consider diffusion by nuclear spiral arms in galactic nuclei, specifically the Milky Way GC. We determine nuclear-spiral-arm-driven diffusion rates using test-particle integrations and compute disruption rates. Our TDE rates are up to 20% higher compared to relaxation by single stars. For binaries, the enhancement is up to a factor of ∼100, and our rates are comparable to the observed numbers of HVSs and S-stars. Our scenario is complementary to relaxation driven by massive perturbers. In addition, our rates depend on the inclination of the binary with respect to the Galactic plane. Therefore, our scenario provides a novel potential source for the observed anisotropic distribution of HVSs. Nuclear spiral arms may also be important for accelerating the coalescence of binary SMBHs and for supplying nuclear star clusters with stars and gas.« less

First results from the LIFE project: discovery of two magnetic hot evolved stars

NASA Astrophysics Data System (ADS)

Martin, A. J.; Neiner, C.; Oksala, M. E.; Wade, G. A.; Keszthelyi, Z.; Fossati, L.; Marcolino, W.; Mathis, S.; Georgy, C.

2018-04-01

We present the initial results of the Large Impact of magnetic Fields on the Evolution of hot stars (LIFE) project. The focus of this project is the search for magnetic fields in evolved OBA giants and supergiants with visual magnitudes between 4 and 8, with the aim to investigate how the magnetic fields observed in upper main-sequence (MS) stars evolve from the MS until the late post-MS stages. In this paper, we present spectropolarimetric observations of 15 stars observed using the ESPaDOnS instrument of the Canada-France-Hawaii Telescope. For each star, we have determined the fundamental parameters and have used stellar evolution models to calculate their mass, age, and radius. Using the least-squared deconvolution technique, we have produced averaged line profiles for each star. From these profiles, we have measured the longitudinal magnetic field strength and have calculated the detection probability. We report the detection of magnetic fields in two stars of our sample: a weak field of Bl = 1.0 ± 0.2 G is detected in the post-MS A5 star 19 Aur and a stronger field of Bl = -230 ± 10 G is detected in the MS/post-MS B8/9 star HR 3042.

IRAS observations of extended dust envelopes around evolved stars

NASA Technical Reports Server (NTRS)

Hawkins, George

1990-01-01

Deconvolved IRAS profiles, with resolution 2-3 time better than detector sizes 1.5 and 3 arcmin at 60 and 100 microns, are presented for a number of evolved stars with extended emission. These include VY UMa, Mu Cep, S Sct, U Hya, Y CVn, U Ant, alpha Ori, Y Pav, UU aur, IRC + 10216, RZ Sgr, and R Lyr. Simple models suggest that extended IRAS emission results from stars which greater mass loss rates in the past, rather than from stars with large current mass loss rates.

Chemical abundances and kinematics of 257 G-, K-type field giants. Setting a base for further analysis of giant-planet properties orbiting evolved stars

NASA Astrophysics Data System (ADS)

Adibekyan, V. Zh.; Benamati, L.; Santos, N. C.; Alves, S.; Lovis, C.; Udry, S.; Israelian, G.; Sousa, S. G.; Tsantaki, M.; Mortier, A.; Sozzetti, A.; De Medeiros, J. R.

2015-06-01

We performed a uniform and detailed abundance analysis of 12 refractory elements (Na, Mg, Al, Si, Ca, Ti, Cr, Ni, Co, Sc, Mn, and V) for a sample of 257 G- and K-type evolved stars from the CORALIE planet search programme. To date, only one of these stars is known to harbour a planetary companion. We aimed to characterize this large sample of evolved stars in terms of chemical abundances and kinematics, thus setting a solid base for further analysis of planetary properties around giant stars. This sample, being homogeneously analysed, can be used as a comparison sample for other planet-related studies, as well as for different type of studies related to stellar and Galaxy astrophysics. The abundances of the chemical elements were determined using an local thermodynamic equilibrium (LTE) abundance analysis relative to the Sun, with the spectral synthesis code MOOG and a grid of Kurucz ATLAS9 atmospheres. To separate the Galactic stellar populations, both a purely kinematical approach and a chemical method were applied. We confirm the overabundance of Na in giant stars compared to the field FGK dwarfs. This enhancement might have a stellar evolutionary character, but departures from LTE may also produce a similar enhancement. Our chemical separation of stellar populations also suggests a `gap' in metallicity between the thick-disc and high-α metal-rich stars, as previously observed in dwarfs sample from HARPS. The present sample, as most of the giant star samples, also suffers from the B - V colour cut-off, which excludes low-log g stars with high metallicities, and high-log g star with low [Fe/H]. For future studies of planet occurrence dependence on stellar metallicity around these evolved stars, we suggest to use a subsample of stars in a `cut-rectangle' in the log g-[Fe/H] diagram to overcome the aforementioned issue.

Building an Unusual White-Dwarf Duo

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2016-09-01

A new study has examined how the puzzling wide binary system HS 2220+2146 which consists of two white dwarfs orbiting each other might have formed. This system may be an example of a new evolutionary pathway for wide white-dwarf binaries.Evolution of a BinaryMore than 100 stellar systems have been discovered consisting of two white dwarfs in a wide orbit around each other. How do these binaries form? In the traditional picture, the system begins as a binary consisting of two main-sequence stars. Due to the large separation between the stars, the stars evolve independently, each passing through the main-sequence and giant branches and ending their lives as white dwarfs.An illustration of a hierarchical triple star system, in which two stars orbit each other, and a third star orbits the pair. [NASA/JPL-Caltech]Because more massive stars evolve more quickly, the most massive of the two stars in a binary pair should be the first to evolve into a white dwarf. Consequently, when we observe a double-white-dwarf binary, its usually a safe bet that the more massive of the two white dwarfs will also be the older and cooler of the pair, since it should have formed first.But in the case of the double-white-dwarf binary HS 2220+2146, the opposite is true: the more massive of the two white dwarfs appears to be the younger and hotter of the pair. If it wasnt created in the traditional way, then how did this system form?Two From Three?Led by Jeff Andrews (Foundation for Research and Technology-Hellas, Greece and Columbia University), a team of scientists recently examined this system more carefully, analyzing its spectra to confirm our understanding of the white dwarfs temperatures and masses.Based on their observations, Andrews and collaborators determined that there are no hidden additional companions that could have caused the unusual evolution of this system. Instead, the team proposed that this unusual binary might be an example of an evolutionary channel that involves three stars.The authors proposed formation scenario for H220+2146. In this picture, the inner binary merges to form a blue straggler. This star and the remaining main-sequence star then evolve independently into white dwarfs, forming the system observed today. [Andrews et al. 2016]An Early MergerIn the model the authors propose for HS 2220+2146, the binary system began as a hierarchical triple system of main-sequence stars. The innermost binary then merged to form a large star known as a blue straggler a star that, due to the merger, will evolve more slowly than its larger mass implies it should.The blue straggler and the remaining main-sequence star, still in a wide orbit, then continued to evolve independently of each other. The smaller star ended its main-sequence lifetime and became a white dwarf first, followed by the more massive but slowly evolving blue straggler thus forming the system we observe today.If the authors model is correct, then HS 2220+2146 would be the first binary double white dwarf known to have formed through this channel. ESAs Gaia mission, currently underway, is expected to discover up to a million new white dwarfs, many of which will likely be in wide binary systems. Among these, we may well find many other systems like HS 2220+2146 that formed in the same way.CitationJeff J. Andrews et al 2016 ApJ 828 38. doi:10.3847/0004-637X/828/1/38

Vibrationally excited water emission at 658 GHz from evolved stars

NASA Astrophysics Data System (ADS)

Baudry, A.; Humphreys, E. M. L.; Herpin, F.; Torstensson, K.; Vlemmings, W. H. T.; Richards, A. M. S.; Gray, M. D.; De Breuck, C.; Olberg, M.

2018-01-01

Context. Several rotational transitions of ortho- and para-water have been identified toward evolved stars in the ground vibrational state as well as in the first excited state of the bending mode (v2 = 1 in (0, 1, 0) state). In the latter vibrational state of water, the 658 GHz J = 11,0-10,1 rotational transition is often strong and seems to be widespread in late-type stars. Aims: Our main goals are to better characterize the nature of the 658 GHz emission, compare the velocity extent of the 658 GHz emission with SiO maser emission to help locate the water layers and, more generally, investigate the physical conditions prevailing in the excited water layers of evolved stars. Another goal is to identify new 658 GHz emission sources and contribute in showing that this emission is widespread in evolved stars. Methods: We have used the J = 11,0-10,1 rotational transition of water in the (0, 1, 0) vibrational state nearly 2400 K above the ground-state to trace some of the physical conditions of evolved stars. Eleven evolved stars were extracted from our mini-catalog of existing and potential 658 GHz sources for observations with the Atacama Pathfinder EXperiment (APEX) telescope equipped with the SEPIA Band 9 receiver. The 13CO J = 6-5 line at 661 GHz was placed in the same receiver sideband for simultaneous observation with the 658 GHz line of water. We have compared the ratio of these two lines to the same ratio derived from HIFI earlier observations to check for potential time variability in the 658 GHz line. We have compared the 658 GHz line properties with our H2O radiative transfer models in stars and we have compared the velocity ranges of the 658 GHz and SiO J = 2-1, v = 1 maser lines. Results: Eleven stars have been extracted from our catalog of known or potential 658 GHz evolved stars. All of them show 658 GHz emission with a peak flux density in the range ≈50-70 Jy (RU Hya and RT Eri) to ≈2000-3000 Jy (VY CMa and W Hya). Five Asymptotic Giant Branch (AGB) stars and one supergiant (AH Sco) are new detections. Three AGBs and one supergiant (VY CMa) exhibit relatively weak 13CO J = 6-5 line emission while o Ceti shows stronger 13CO emission. We have shown that the 658 GHz line is masing and we found that the 658 GHz velocity extent tends to be correlated with that of the SiO maser suggesting that both emission lines are excited in circumstellar layers close to the central star. Broad and stable line profiles are observed at 658 GHz. This could indicate maser saturation although we have tentatively provided first information on time variability at 658 GHz.

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

Pan, Kuo-Chuan; Ricker, Paul M.; Taam, Ronald E., E-mail: kpan2@illinois.edu, E-mail: pmricker@illinois.edu, E-mail: r-taam@northwestern.edu

The progenitor systems of Type Ia supernovae (SNe Ia) are still under debate. Based on recent hydrodynamics simulations, non-degenerate companions in the single-degenerate scenario (SDS) should survive the supernova (SN) impact. One way to distinguish between the SDS and the double-degenerate scenario is to search for the post-impact remnant stars (PIRSs) in SN Ia remnants. Using a technique that combines multi-dimensional hydrodynamics simulations with one-dimensional stellar evolution simulations, we have examined the post-impact evolution of helium-rich binary companions in the SDS. It is found that these helium-rich PIRSs (He PIRSs) dramatically expand and evolve to a luminous phase (L {approx}more » 10{sup 4} L{sub Sun }) about 10 yr after an SN explosion. Subsequently, they contract and evolve to become hot blue-subdwarf-like (sdO-like) stars by releasing gravitational energy, persisting as sdO-like stars for several million years before evolving to the helium red-giant phase. We therefore predict that a luminous OB-like star should be detectable within {approx}30 yr after the SN explosion. Thereafter, it will shrink and become an sdO-like star in the central regions of SN Ia remnants within star-forming regions for SN Ia progenitors evolved via the helium-star channel in the SDS. These He PIRSs are predicted to be rapidly rotating (v{sub rot} {approx}> 50 km s{sup -1}) and to have high spatial velocities (v{sub linear} {approx}> 500 km s{sup -1}). Furthermore, if SN remnants have diffused away and are not recognizable at a later stage, He PIRSs could be an additional source of single sdO stars and/or hypervelocity stars.« less

Determining Mass-Loss Rates of Evolved Stars in the Galactic Bulge from Infrared Surveys

NASA Astrophysics Data System (ADS)

Riley, Allyssa; Sargent, Benjamin A.; Srinivasan, Sundar; Meixner, Margaret; Kastner, Joel H.

2018-06-01

To investigate the relationship between mass loss from evolved stars and host galaxy metallicity, we are computing the dust mass loss budget due to red supergiant (RSG) and asymptotic giant branch (AGB) stars in the Galactic Bulge and comparing this result to that previously obtained for the Magellanic Clouds. We construct spectral energy distributions (SEDs) for our candidate RSG and AGB stars using observations from various infrared surveys, including the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE). Because Robitaille et al (2008, AJ, 136, 2413) have already identified Intrinsically Red Objects from the GLIMPSE I and II surveys, we use their method as a starting point and expand the study by using the GLIMPSE 3D survey. Because AGB stars can be variable, we also match the GLIMPSE I, II, and 3D sources to other surveys, such as DEEP GLIMPSE, WISE, VVV, and DENIS, in order to characterize the variability across the spectral energy distribution (SED) of each source. This allows us to determine the source’s average SED over multiple epochs. We use extinction curves derived from Spitzer studies of extinction in the Galaxy to determine the extinction corrections for our sample. To establish mass-loss rates of evolved stars in the Bulge, we use the Grid of Red supergiant and Asymptotic giant branch ModelS (GRAMS) of dust-enshrouded evolved stars (2011, A&A, 532, A54; 2011, ApJ, 728, 93). This allows us to determine the total mass return to the Bulge from these stars. This work has been supported by NASA ADAP grant 80NSSC17K0057.

Rapidly rotating single late-type giants: New FK Comae stars?

NASA Technical Reports Server (NTRS)

Fekel, Francis C.

1986-01-01

A group of rapidly rotating single late-type giants was found from surveys of chromospherically active stars. These stars have V sin I's ranging from 6 to 46 km/sec, modest ultraviolet emission line fluxes, and strong H alpha absorption lines. Although certainly chromospherically active, their characteristics are much less extreme than those of FK Com and one or two other similar systems. One possible explanation for the newly identified systems is that they have evolved from stars similar to FK Com. The chromospheric activity and rotation of single giant stars like FK Com would be expected to decrease with time as they do in single dwarfs. Alternatively, this newly identified group may have evolved from single rapidly rotating A, or early F stars.

Stellar photometry in the inner bulge of M31 using the Hubble Space Telescope wide field camera

NASA Technical Reports Server (NTRS)

Rich, R. M.; Mighell, K. J.

1995-01-01

We present photometry of two fields in the M31 bulge imaged with the Hubble Space Telescope (HST) Wide-Field Camara (WFC). The nuclear field (r less than 40 arcsecs = 150 pc) giant branch extends to I = 19.5, M(sub I) = -5 (Cousins system), a full 0.9 mag brighter than the giant-branch tips of metal-poor Galactic globular clusters and M31 halo fields. This is also approximately = 1.5 mag brighter than the giant branches of metal-rich Galactic globular clusters, but is no brighter than Mould's (1986) M31 bulge field 1 kpc from the nucleus. The data also suggest that the brighter stars may be preferentially concentrated to the center. The 648 luminous stars detected in 2 x 10(exp 9) solar luminosity is approximately = 25% that expected from a hypothetical population of evolved asymptotic giant branch (AGB) stars with lifetimes approximately = 10(exp 5) yr, with the cautionary note that we are near the detection limit. The number of bright stars is also consistent with the progeny of blue stragglers, if one uses a lifetime for the thermal-pulsing AGB of 2 x 10(exp 6) yr. We strongly caution that incompleteness becomes severe below I = 19.9 mag and that future surveys are likely to find numbers of bright stars too large to accomodate the blue straggler progeny hypothesis. We have imaged an additional field 2 arcmin = 500 pc south of the nucleus. The brightest stars in this field are also I = 19.5, but bright stars appear less numerous than in the nuclear field. If the population resembles that of the Galactic bulge, then M(sub bol) = -4.5 is a lower limit to the giant-branch tip luminosity; infrared studies should reveal stars 0.5 mag or more brighter. Either high-metallicity or (more likely) age approximately = 10 Gyr may be responsible for the presence of these luminous AGB stars. These observations confirm that previous ground-based infrared studies (e.g., Rich & Mould 1991) very likely detect an extended giant branch and not spurious luminous stars caused by crowding or disk contamination. However, published integrated colors for the M31 bulge/nucleus are extremely red, making it difficult to accomodate a young or intermediate-age population.

Calibration of Post-AGB Supergiants as Standard Extragalactic Candles for HST

NASA Technical Reports Server (NTRS)

Bond, Howard E.

1998-01-01

This report summarizes activities carried out with support from the NASA Ultraviolet, Visible, and Gravitational Astrophysics Research and Analysis Program. The aim of the program is to calibrate the absolute magnitudes of post-asymptotic-giant-branch (post-AGB or PAGB) stars, which we believe will be an excellent new "standard candle" for measuring extragalactic distances. The reason for this belief is that in old populations, the stars that are evolving through the PAGB region of the HR (Hertzsprung-Russell) diagram arise from only a single main-sequence turnoff mass. In addition, the theoretical PAGB evolutionary tracks show that they evolve through this region at constant luminosity; hence the PAGB stars should have an extremely narrow luminosity function. Moreover, as the PAGB stars evolve through spectral types F and A (en route from the AGB to hot stellar remnants and white dwarfs), they have the highest luminosities attained by old stars (both bolometrically and in the visual band). Finally, the PAGB stars of these spectral types are very easily identified, due to their large Balmer jumps, which are due to their very low surface gravities.

Luminous and Variable Stars in M31 and M33. V. The Upper HR Diagram

NASA Astrophysics Data System (ADS)

Humphreys, Roberta M.; Davidson, Kris; Hahn, David; Martin, John C.; Weis, Kerstin

2017-07-01

We present HR diagrams for the massive star populations in M31 and M33, including several different types of emission-line stars: the confirmed luminous blue variables (LBVs), candidate LBVs, B[e] supergiants, and the warm hypergiants. We estimate their apparent temperatures and luminosities for comparison with their respective massive star populations and evaluate the possible relationships of these different classes of evolved, massive stars, and their evolutionary state. Several of the LBV candidates lie near the LBV/S Dor instability strip that supports their classification. Most of the B[e] supergiants, however, are less luminous than the LBVs. Many are very dusty with the infrared flux contributing one-third or more to their total flux. They are also relatively isolated from other luminous OB stars. Overall, their spatial distribution suggests a more evolved state. Some may be post-RSGs (red supergiants) like the warm hypergiants, and there may be more than one path to becoming a B[e] star. There are sufficient differences in the spectra, luminosities, spatial distribution, and the presence or lack of dust between the LBVs and B[e] supergiants to conclude that one group does not evolve into the other.

A mysterious dust clump in a disk around an evolved binary star system.

PubMed

Jura, M; Turner, J

1998-09-10

The discovery of planets in orbit around the pulsar PSR1257+12 shows that planets may form around post-main-sequence stars. Other evolved stars, such as HD44179 (an evolved star which is part of the binary system that has expelled the gas and dust that make the Red Rectangle nebula), possess gravitationally bound orbiting dust disks. It is possible that planets might form from gravitational collapse in such disks. Here we report high-angular-resolution observations at millimetre and submillimetre wavelengths of the dusk disk associated with the Red Rectangle. We find a dust clump with an estimated mass near that of Jupiter in the outer region of the disk. The clump is larger than our Solar System, and far beyond where planet formation would normally be expected, so its nature is at present unclear.

Irradiation-driven Mass Transfer Cycles in Compact Binaries

NASA Astrophysics Data System (ADS)

Büning, A.; Ritter, H.

2005-08-01

We elaborate on the analytical model of Ritter, Zhang, & Kolb (2000) which describes the basic physics of irradiation-driven mass transfer cycles in semi-detached compact binary systems. In particular, we take into account a contribution to the thermal relaxation of the donor star which is unrelated to irradiation and which was neglected in previous studies. We present results of simulations of the evolution of compact binaries undergoing mass transfer cycles, in particular also of systems with a nuclear evolved donor star. These computations have been carried out with a stellar evolution code which computes mass transfer implicitly and models irradiation of the donor star in a point source approximation, thereby allowing for much more realistic simulations than were hitherto possible. We find that low-mass X-ray binaries (LMXBs) and cataclysmic variables (CVs) with orbital periods ⪉ 6hr can undergo mass transfer cycles only for low angular momentum loss rates. CVs containing a giant donor or one near the terminal age main sequence are more stable than previously thought, but can possibly also undergo mass transfer cycles.

Observations and modeling of cool, evolved stars: from chromospheric to wind regions

NASA Astrophysics Data System (ADS)

Rau, Gioia; Carpenter, Ken G.; Nielsen, Krister E.; Kober, Gladys V.; Josef Hron, Bernard Aringer, Kjell Eriksson, Paola Marigo, Claudia Paladini

2018-01-01

Evolved stars are fundamental contributors to the enrichment of the interstellar medium, via their mass loss, with heavy elements produced in their interior, and with the dust formed in their envelope. We present the results of the first systematic comparison (Rau et al. 2017, 2015) of multi-technique observations of a sample of C-rich Mira, semi-regular and irregular stars with the predictions from dynamic model atmospheres (Mattsson et al. 2010) and simpler models based on hydrostatic atmospheres combined with dusty envelopes. The chromosphere, located in the outer atmosphere of these stars, plays a crucial role in driving the mass loss in evolved K-M giant stars (see e.g. Carpenter et al. 2014, 1988). Despite recent efforts, details of the mass-loss scenario remain mysterious, as well as a complete understanding of the dynamic line formation regions, profiles, and structures. To solve these riddles, we present observation of flow and turbulent velocities, together with preliminary derivation of thermodynamic constraints for theoretical models (Rau, Carpenter, et al., in prep).

Habitable zones around low mass stars and the search for extraterrestrial life.

PubMed

Kasting, J F

1997-06-01

Habitable planets are likely to exist around stars not too different from the Sun if current theories about terrestrial climate evolution are correct. Some of these planets may have evolved life, and some of the inhabited planets may have evolved O2-rich atmospheres. Such atmospheres could be detected spectroscopically on planets around nearby stars using a space-based interferometer to search for the 9.6 micron band of O3. Planets with O2-rich atmospheres that lie within the habitable zone around their parent star are, in all probability, inhabited.

SALT Spectroscopy of Evolved Massive Stars

NASA Astrophysics Data System (ADS)

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

2017-06-01

Long-slit spectroscopy with the Southern African Large Telescope (SALT) of central stars of mid-infrared nebulae detected with the Spitzer Space Telescope and Wide-Field Infrared Survey Explorer (WISE) led to the discovery of numerous candidate luminous blue variables (cLBVs) and other rare evolved massive stars. With the recent advent of the SALT fiber-fed high-resolution echelle spectrograph (HRS), a new perspective for the study of these interesting objects is appeared. Using the HRS we obtained spectra of a dozen newly identified massive stars. Some results on the recently identified cLBV Hen 3-729 are presented.

Abundance differences among globular-cluster giants: Primordial versus evolutionary scenarios

NASA Astrophysics Data System (ADS)

Kraft, Robert P.

1994-06-01

Contrary to historical expectation, stars within a given globular cluster often exhibit wide variations in the abundance of C, N, and O as well as certain light metals, particularly Na and Al. Owing to flux limitations, studies have been confined to evolved stars, especially giants, but in few instances variations have been detected among main-sequence stars. Among giants, the variations are of two kinds. The abundances of C and N are often anticorrelated, and in the limited number of cases in which both have been measured, O and N abundances have also often proved to be anticorrelated (Pilachowski 1988; Sneden et al. 1991; Brown et al. 1991; Kraft et al. 1992). Following pioneering work by Cohen (1978) and Peterson (1980), strong evidence has recently emerged for the existence of a significant global anticorrelation between O and Na abundances (Drake et al. 1992, Kraft et al. 1993). The observations are discussed in terms of contrasting hypotheses: evolutionary versus primordial. In the former, the variations are attributed to the dredgeup of material that has been processed through the CNO cycle in the globular-cluster stars themselves. In the latter, the variations are attributed to primordial chemical inhomogeneities in the material out of which the cluster stars were formed, the composition of these 'clumps' having been determined by nuclear processing in a prior generation of more massive stars. Observational evidence supporting each of these scenarios is cited. Recent studies of stellar rotation among horizontal branch stars in certain clusters (Peterson et al. 1994) as well as new calculations of Na-23 and Al-27 production in the CNO processing regions of evolving low-mass giants (Langer et al. 1993) lend fresh support to the evolutionary hypothesis. However, such calculations do not explain the variation of C and N abundances found among cluster main-sequence stars (Suntzeff 1989; Briley et al. 1991) which therefore seem explicable only on the basis of a primordial scenario. Among mildly metal-poor giants, i.e., those in the range from solar metallicity to (Fe/H) approximately -1, recent observational evidence suggesting the existence of a substructure in the (el/Fe) ratios of the heavier alpha elements, e.g., Si, Mg, Ca, and Ti, is discussed. The possible influence of this effect on the interpretation of the integrated spectra of extragalactic globular clusters and E galaxies is noted.

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

Baines, Ellyn K.; Armstrong, J. Thomas; Schmitt, Henrique R.

Using the Navy Precision Optical Interferometer, we measured the angular diameters of 10 stars that have previously measured solar-like oscillations. Our sample covered a range of evolutionary stages but focused on evolved subgiant and giant stars. We combined our angular diameters with Hipparcos parallaxes to determine the stars' physical radii, and used photometry from the literature to calculate their bolometric fluxes, luminosities, and effective temperatures. We then used our results to test the scaling relations used by asteroseismology groups to calculate radii and found good agreement between the radii measured here and the radii predicted by stellar oscillation studies. Themore » precision of the relations is not as well constrained for giant stars as it is for less evolved stars.« less

The MACHO Project Sample of Galactic Bulge High-Amplitude δ Scuti Stars: Pulsation Behavior and Stellar Properties

NASA Astrophysics Data System (ADS)

Alcock, C.; Allsman, R. A.; Alves, D. R.; Axelrod, T. S.; Becker, A. C.; Bennett, D. P.; Cook, K. H.; Freeman, K. C.; Geha, M.; Griest, K.; Lehner, M. J.; Marshall, S. L.; McNamara, B. J.; Minniti, D.; Nelson, C.; Peterson, B. A.; Popowski, P.; Pratt, M. R.; Quinn, P. J.; Rodgers, A. W.; Sutherland, W.; Templeton, M. R.; Vandehei, T.; Welch, D. L.

2000-06-01

We have detected 90 objects with periods and light-curve structures similar to those of field δ Scuti stars using the Massive Compact Halo Object (MACHO) Project database of Galactic bulge photometry. If we assume similar extinction values for all candidates and absolute magnitudes similar to those of other field high-amplitude δ Scuti stars (HADS), the majority of these objects lie in or near the Galactic bulge. At least two of these objects are likely foreground δ Scuti stars, one of which may be an evolved nonradial pulsator, similar to other evolved, disk-population δ Scuti stars. We have analyzed the light curves of these objects and find that they are similar to the light curves of field δ Scuti stars and the δ Scuti stars found by the Optical Gravitational Lens Experiment (OGLE). However, the amplitude distribution of these sources lies between those of low- and high-amplitude δ Scuti stars, which suggests that they may be an intermediate population. We have found nine double-mode HADS with frequency ratios ranging from 0.75 to 0.79, four probable double- and multiple-mode objects, and another four objects with marginal detections of secondary modes. The low frequencies (5-14 cycles day-1) and the observed period ratios of ~0.77 suggest that the majority of these objects are evolved stars pulsating in fundamental or first overtone radial modes.

Evolved massive stars in W33 and in GMC 23.3-0.3

NASA Astrophysics Data System (ADS)

Messineo, Maria; Clark, J. Simon; Figer, Donald F.; Menten, Karl M.; Kudritzki, Rolf-Peter; Najarro, Francisco; Rich, Michael; Ivanov, Valentin D.; Valenti, Elena; Trombley, Christine; Chen, Rosie; Davies, Ben; MacKenty, John W.

2015-08-01

We have conducted an infrared spectroscopic survey for massive evolved stars and/or clusters in the Galactic giant molecular clouds G23.3-0.3 and W33. A large number of extraordinary sub-clumps/clusters of massive stars were detected. The spatial and temporal distribution of these massive stars yields information on the star formation history of the clouds.In G23.3-0.3, we discovered a dozen massive O-type stars, one candidate luminous blue variable, and several red supergiants. The O-type stars have masses from 25 to 50 Msun and ages of 5-8 Myr, while the RSGs belong to a burst that occurred 20-30 Myr ago. Therefore, GMC G23.3-0.3 has had one of the longest known histories of star formation (20-30 Myr). GMC G23.3-0.3 is rich in HII regions and supernova remnants; we detected massive stars in the cores of SNR W41 and of SNR G22.7-0.2.In W33, we detected a few evolved O-type stars and one Wolf-Rayet star, but none of the late-type objects has the luminosity of a red supergiant. W33 is characterized by discrete sources and has had at least 3-5 Myr of star formation history, which is now propagating from west to east. While our detections of massive evolved stars in W33 are made on the west side of the cloud, several dense molecular cores that may harbor proto clusters have recently been detected on the east side of the cloud by Immer et al. (2014).Messineo, Maria; Menten, Karl M.; Figer, Donald F.; Davies, Ben; Clark, J. Simon; Ivanov, Valentin D.Kudritzki, Rolf-Peter; Rich, R. Michael; MacKenty, John W.; Trombley, Christine 2014A&A...569A..20MMessineo, Maria; Clark, J. Simon; Figer, Donald F.; Kudritzki, Rolf-Peter; Francisco, Najarro; Rich, R. Michael; Menten, Karl M.; Ivanov, Valentin D.; Valenti, Elena; Trombley, Christine; Chen, C.H. Rosie; Davies, Ben; submitted to ApJ.

Reassessing the fundamentals: On the evolution, ages and masses of neutron stars

NASA Astrophysics Data System (ADS)

Kiziltan, Bulent

The evolution, ages and masses of neutron stars are the fundamental threads that make pulsars accessible to other sub-disciplines of astronomy and physics. A realistic and accurate determination of these indirectly probed features play an important role in understanding a very broad range of astrophysical processes that are, in many cases, not empirically accessible otherwise. For the majority of pulsars, the only observables are the rotational period (P), and its derivative (P˙) which gives the rate of change in the spin. I start with calculating the joint P-P˙ distributions of millisecond pulsars for the standard evolutionary model in order to assess whether millisecond pulsars are the unequivocal descendants of low mass X-ray binaries. We show that the P-P˙ density implied by the standard evolutionary model is inconsistent with observations, which suggests that it is unlikely that millisecond pulsars have evolved from a single coherent progenitor population. In the absence of constraints from the binary companion or supernova remnant, the standard method for estimating pulsar ages is to infer an age from the rate of spin-down. I parametrically incorporate constraints that arise from binary evolution and limiting physics to derive a "modified spin-down age" for millisecond pulsars. We show that the standard method can be improved by this approach to achieve age estimates closer to the true age. Then, I critically review radio pulsar mass measurements and present a detailed examination through which we are able to put stringent constraints on the underlying neutron star mass distribution. For the first time, we are able to analyze a sizable population of neutron star-white dwarf systems in addition to double neutron star systems with a technique that accounts for systematically different measurement errors. We find that neutron stars that have evolved through different evolutionary paths reflect distinctive signatures through dissimilar distribution peak and mass cutoff values. Neutron stars in double neutron star and neutron star-white dwarf systems show consistent respective peaks at 1.35 M⊙ and 1.50 M⊙ , which suggest significant mass accretion (Deltam ≈ 0.15 M⊙ ) has occurred during the spin up phase. We find a mass cutoff at 2 M⊙ for neutron stars with white dwarf companions which establishes a firm lower bound for the maximum neutron star mass. This rules out the majority of strange quark and soft equation of state models as viable configurations for neutron star matter. The lack of truncation close to the maximum mass cutoff suggests that the 2 M⊙ limit is set by evolutionary constraints rather than nuclear physics or general relativity, and the existence of rare super-massive neutron stars is possible.

Effect of nuclear stars gravity on quasar radiation feedback on the parsec-scale

NASA Astrophysics Data System (ADS)

Yang, Xiao-Hong; Bu, De-Fu

2018-05-01

It is often suggested that a super massive black hole is embedded in a nuclear bulge of size of a few 102 parsec . The nuclear stars gravity is not negligible near ˜10parsec. In order to study the effect of nuclear stars gravity on quasar radiation feedback on the parsec scale, we have simulated the parsec scale flows irradiated by a quasar by taking into account the gravitational potential of both the black hole and the nuclear star cluster. We find that the effect of nuclear stars gravity on the parsec-scale flows is related to the fraction of X-ray photons in quasar radiation. For the models in which the fraction of X-ray photons is not small (e.g. the X-ray photons contribute to 20% of the quasar radiation), the nuclear stars gravity is very helpful to collimate the outflows driven by UV photons, significantly weakens the outflow power at the outer boundary and significantly enhances the net accretion rate onto the black hole. For the models in which X-ray photons are significantly decreased (e.g. the X-ray photons contribute to 5% of the quasar radiation), the nuclear stars gravity can just slightly change properties of outflow and slightly enhance the net accretion rate onto the black hole.

New and updated stellar parameters for 71 evolved planet hosts. On the metallicity-giant planet connection

NASA Astrophysics Data System (ADS)

Mortier, A.; Santos, N. C.; Sousa, S. G.; Adibekyan, V. Zh.; Delgado Mena, E.; Tsantaki, M.; Israelian, G.; Mayor, M.

2013-09-01

Context. It is still being debated whether the well-known metallicity-giant planet correlation for dwarf stars is also valid for giant stars. For this reason, having precise metallicities is very important. Precise stellar parameters are also crucial to planetary research for several other reasons. Different methods can provide different results that lead to discrepancies in the analysis of planet hosts. Aims: To study the impact of different analyses on the metallicity scale for evolved stars, we compare different iron line lists to use in the atmospheric parameter derivation of evolved stars. Therefore, we use a sample of 71 evolved stars with planets. With these new homogeneous parameters, we revisit the metallicity-giant planet connection for evolved stars. Methods: A spectroscopic analysis based on Kurucz models in local thermodynamic equilibrium (LTE) was performed through the MOOG code to derive the atmospheric parameters. Two different iron line list sets were used, one built for cool FGK stars in general, and the other for giant FGK stars. Masses were calculated through isochrone fitting, using the Padova models. Kolmogorov-Smirnov tests (K-S tests) were then performed on the metallicity distributions of various different samples of evolved stars and red giants. Results: All parameters compare well using a line list set, designed specifically for cool and solar-like stars to provide more accurate temperatures. All parameters derived with this line list set are preferred and are thus adopted for future analysis. We find that evolved planet hosts are more metal-poor than dwarf stars with giant planets. However, a bias in giant stellar samples that are searched for planets is present. Because of a colour cut-off, metal-rich low-gravity stars are left out of the samples, making it hard to compare dwarf stars with giant stars. Furthermore, no metallicity enhancement is found for red giants with planets (log g < 3.0 dex) with respect to red giants without planets. The data presented here are based on observations collected at the La Silla Paranal Observatory, ESO (Chile) with the FEROS spectrograph at the 2.2 m telescope (ESO runs ID 70.C-0084, 088.C-0892, 089.C-0444, and 090.C-0146) and the HARPS spectrograph at the 3.6 m telescope (ESO run ID 72.C-0488); at the Paranal Observatory, ESO (Chile) with the UVES spectrograph at the VLT Kueyen telescope (ESO runs ID 074.C-0134, 079.C-0131, 380.C-0083, and 083.C-0174); at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias with the FIES spectrograph at the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden (program ID 44-210); and at the Observatoire de Haute-Provence (OHP, CNRS/OAMP), France with the SOPHIE spectrographs at the 1.93 m telescope (program ID 11B.DISC.SOUS).Tables 1, 5, 6 and Appendix A are available in electronic form at http://www.aanda.orgTables 5, 6, and A.1 are also available at the 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/557/A70

Revealing evolved massive stars with Spitzer

NASA Astrophysics Data System (ADS)

Gvaramadze, V. V.; Kniazev, A. Y.; Fabrika, S.

2010-06-01

Massive evolved stars lose a large fraction of their mass via copious stellar wind or instant outbursts. During certain evolutionary phases, they can be identified by the presence of their circumstellar nebulae. In this paper, we present the results of a search for compact nebulae (reminiscent of circumstellar nebulae around evolved massive stars) using archival 24-μm data obtained with the Multiband Imaging Photometer for Spitzer. We have discovered 115 nebulae, most of which bear a striking resemblance to the circumstellar nebulae associated with luminous blue variables (LBVs) and late WN-type (WNL) Wolf-Rayet (WR) stars in the Milky Way and the Large Magellanic Cloud (LMC). We interpret this similarity as an indication that the central stars of detected nebulae are either LBVs or related evolved massive stars. Our interpretation is supported by follow-up spectroscopy of two dozen of these central stars, most of which turn out to be either candidate LBVs (cLBVs), blue supergiants or WNL stars. We expect that the forthcoming spectroscopy of the remaining objects from our list, accompanied by the spectrophotometric monitoring of the already discovered cLBVs, will further increase the known population of Galactic LBVs. This, in turn, will have profound consequences for better understanding the LBV phenomenon and its role in the transition between hydrogen-burning O stars and helium-burning WR stars. We also report on the detection of an arc-like structure attached to the cLBV HD 326823 and an arc associated with the LBV R99 (HD 269445) in the LMC. Partially based on observations collected at the German-Spanish Astronomical Centre, Calar Alto, jointly operated by the Max-Planck-Institut für Astronomie Heidelberg and the Instituto de Astrofísica de Andalucía (CSIC). E-mail: vgvaram@mx.iki.rssi.ru (VVG); akniazev@saao.ac.za (AYK); fabrika@sao.ru (SF)

Nuclear pasta in protoneutron stars: simulations of neutrino emission from nucelar de-excitation

NASA Astrophysics Data System (ADS)

Witt, Matthew Charles; Newton, William

2017-01-01

Nuclear pasta is an exotic phase of matter with densities near ρ ≈ ρ0 = 1014 g cm-3 that consists of complex structures with geometries resembling spaghetti, lasagna, gnocchi, and other types of pasta. It is predicted to appear in the inner crust of neutron stars, protoneutron stars, and the collapsing cores of massive stars. It is hypothesized that nuclear pasta has a significant effect on transport and neutrino scattering properties of neutron and protoneutron stars. If this is true, then it is possible to find observational signatures of nuclear pasta. We present a calculation of neutrino emmissivity of pasta phases due to de-excitation of neutrons. We discuss observational implications on the neutrino signal of protoneutron stars.

FORCAST Observations of Galactic Evolved Stars: Measurements of Carbonaceous Dust, Crystalline Silicates, and Fullerenes from SOFIA

NASA Astrophysics Data System (ADS)

Kraemer, Kathleen; Sloan, G. C.; Keller, L. D.; Groenewegen, M. A. T.

2018-01-01

We present preliminary results from two projects to observe the mid-infrared spectra of evolved stars in the Milky Way using the FORCAST instrument on SOFIA. In the first project, we observed a set of 31 carbon stars over the course of three cycles (government shutdowns contributed to the delays in the program execution), covering a wavelength range of 5-13.7 μm, which includes prominent dust and gas diagnostics. The sources were selected to sample portions of period and flux phase space which were not covered in existing samples from older telescopes such as the Infrared Space Observatory (ISO) or Infrared Astronomical Satellite (IRAS). In the second project, we searched for fullerene emission (C60) at 18.9 μm in Galactic sources with crystalline silicate emission. Although most evolved stars are either carbon-rich or oxygen- (silicate-) rich, fullerenes, a carbon-rich molecule, have been observed in several oxygen-rich evolved stars whose silicate emission features are crystalline rather than the more usual amorphous types. None of our targets show clear signatures of fullerene emission.Support for this work was provided by NASA through awards SOF 03-0079, SOF 03-0104, and SOF 04-0129 issued by USRA.

Compact Stars with Sequential QCD Phase Transitions.

PubMed

Alford, Mark; Sedrakian, Armen

2017-10-20

Compact stars may contain quark matter in their interiors at densities exceeding several times the nuclear saturation density. We explore models of such compact stars where there are two first-order phase transitions: the first from nuclear matter to a quark-matter phase, followed at a higher density by another first-order transition to a different quark-matter phase [e.g., from the two-flavor color-superconducting (2SC) to the color-flavor-locked (CFL) phase]. We show that this can give rise to two separate branches of hybrid stars, separated from each other and from the nuclear branch by instability regions, and, therefore, to a new family of compact stars, denser than the ordinary hybrid stars. In a range of parameters, one may obtain twin hybrid stars (hybrid stars with the same masses but different radii) and even triplets where three stars, with inner cores of nuclear matter, 2SC matter, and CFL matter, respectively, all have the same mass but different radii.

Lithium abundance patterns of late-F stars: an in-depth analysis of the lithium desert

NASA Astrophysics Data System (ADS)

Aguilera-Gómez, Claudia; Ramírez, Iván; Chanamé, Julio

2018-06-01

Aims: We address the existence and origin of the lithium (Li) desert, a region in the Li-Teff plane sparsely populated by stars. Here we analyze some of the explanations that have been suggested for this region, including mixing in the late main sequence, a Li dip origin for stars with low Li abundances in the region, and a possible relation with the presence of planets. Methods: To study the Li desert, we measured the atmospheric parameters and Li abundance of 227 late-F dwarfs and subgiants, chosen to be in the Teff range of the desert and without previous Li abundance measurements. Subsequently, we complemented those with literature data to obtain a homogeneous catalog of 2318 stars, for which we compute masses and ages. We characterize stars surrounding the region of the Li desert. Results: We conclude that stars with low Li abundances below the desert are more massive and more evolved than stars above the desert. Given the unexpected presence of low Li abundance stars in this effective temperature range, we concentrate on finding their origin. We conclude that these stars with low Li abundance do not evolve from stars above the desert: at a given mass, stars with low Li (i.e., below the desert) are more metal-poor. Conclusions: Instead, we suggest that stars below the Li desert are consistent with having evolved from the Li dip, discarding the need to invoke additional mixing to explain this feature. Thus, stars below the Li desert are not peculiar and are only distinguished from other subgiants evolved from the Li dip in that their combination of atmospheric parameters locates them in a range of effective temperatures where otherwise only high Li abundance stars would be found (i.e., stars above the desert). Full Tables 1 and 3 are 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/614/A55This paper includes observations collected at The McDonald Observatory and observations gathered with the 6.5 meter Magellan Telescopes located at Las Campanas Observatory, Chile.

The Mass-loss Return from Evolved Stars to the Large Magellanic Cloud. VI. Luminosities and Mass-loss Rates on Population Scales

NASA Astrophysics Data System (ADS)

Riebel, D.; Srinivasan, S.; Sargent, B.; Meixner, M.

2012-07-01

We present results from the first application of the Grid of Red Supergiant and Asymptotic Giant Branch ModelS (GRAMS) model grid to the entire evolved stellar population of the Large Magellanic Cloud (LMC). GRAMS is a pre-computed grid of 80,843 radiative transfer models of evolved stars and circumstellar dust shells composed of either silicate or carbonaceous dust. We fit GRAMS models to ~30,000 asymptotic giant branch (AGB) and red supergiant (RSG) stars in the LMC, using 12 bands of photometry from the optical to the mid-infrared. Our published data set consists of thousands of evolved stars with individually determined evolutionary parameters such as luminosity and mass-loss rate. The GRAMS grid has a greater than 80% accuracy rate discriminating between oxygen- and carbon-rich chemistry. The global dust injection rate to the interstellar medium (ISM) of the LMC from RSGs and AGB stars is on the order of 2.1 × 10-5 M ⊙ yr-1, equivalent to a total mass injection rate (including the gas) into the ISM of ~6 × 10-3 M ⊙ yr-1. Carbon stars inject two and a half times as much dust into the ISM as do O-rich AGB stars, but the same amount of mass. We determine a bolometric correction factor for C-rich AGB stars in the K s band as a function of J - K s color, BC_{K_{s}} = -0.40(J-K_{s})^2 + 1.83(J-K_{s}) + 1.29. We determine several IR color proxies for the dust mass-loss rate (\\dot{M}_{d}) from C-rich AGB stars, such as log \\dot{M_{d}} = ({-18.90}/({(K_{s}-[8.0])+3.37}))-5.93. We find that a larger fraction of AGB stars exhibiting the "long-secondary period" phenomenon are more O-rich than stars dominated by radial pulsations, and AGB stars without detectable mass loss do not appear on either the first-overtone or fundamental-mode pulsation sequences.

Luminous and Variable Stars in M31 and M33. V. The Upper HR Diagram

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

Humphreys, Roberta M.; Davidson, Kris; Hahn, David

We present HR diagrams for the massive star populations in M31 and M33, including several different types of emission-line stars: the confirmed luminous blue variables (LBVs), candidate LBVs, B[e] supergiants, and the warm hypergiants. We estimate their apparent temperatures and luminosities for comparison with their respective massive star populations and evaluate the possible relationships of these different classes of evolved, massive stars, and their evolutionary state. Several of the LBV candidates lie near the LBV/S Dor instability strip that supports their classification. Most of the B[e] supergiants, however, are less luminous than the LBVs. Many are very dusty with themore » infrared flux contributing one-third or more to their total flux. They are also relatively isolated from other luminous OB stars. Overall, their spatial distribution suggests a more evolved state. Some may be post-RSGs (red supergiants) like the warm hypergiants, and there may be more than one path to becoming a B[e] star. There are sufficient differences in the spectra, luminosities, spatial distribution, and the presence or lack of dust between the LBVs and B[e] supergiants to conclude that one group does not evolve into the other.« less

Spatially-Resolved Observations of Giant Stars with SPHERE

NASA Astrophysics Data System (ADS)

Khouri, Theo

2018-04-01

SPHERE on the VLT is an extreme adaptive optics instrument that produces images with unprecedented angular resolution at visible and near-infrared wavelengths. Its primary goal is imaging, low-resolution spectroscopic, and polarimetric characterization of extra-solar planetary systems. Nonetheless, the high spatial resolution and the instrument design optimized for observations in a narrow field of view around bright targets make SPHERE the perfect instrument for obtaining spatially-resolved images of close-by giant, evolved stars. This is particularly true at the shortest wavelengths available with SPHERE, where the angular resolution is best (> 20 mas) and these stars appear larger (< 70 mas). In this talk, I will review how SPHERE has been used to study the surfaces and extended atmospheres of evolved stars and how these observations advance our understanding of the stellar pulsations and convective motions that shape these stars. Moreover, I will present recent results from a monitoring campaign of the star R Doradus using SPHERE with observations taken at twelve epochs over eight months that reveal features on the stellar disc varying on timescales of a few weeks. Finally, I will present quasi-simultaneous observations with SPHERE and ALMA that spatially resolve the stellar discs of two asymptotic giant branch stars, Mira and R Doradus, and discuss what such multi-wavelength observation campaigns can teach us about the processes that shape evolved stars.

Rotation and magnetism in intermediate-mass stars

NASA Astrophysics Data System (ADS)

Quentin, Léo G.; Tout, Christopher A.

2018-06-01

Rotation and magnetism are increasingly recognized as important phenomena in stellar evolution. Surface magnetic fields from a few to 20 000 G have been observed and models have suggested that magnetohydrodynamic transport of angular momentum and chemical composition could explain the peculiar composition of some stars. Stellar remnants such as white dwarfs have been observed with fields from a few to more than 109 G. We investigate the origin of and the evolution, on thermal and nuclear rather than dynamical time-scales, of an averaged large-scale magnetic field throughout a star's life and its coupling to stellar rotation. Large-scale magnetic fields sustained until late stages of stellar evolution with conservation of magnetic flux could explain the very high fields observed in white dwarfs. We include these effects in the Cambridge stellar evolution code using three time-dependant advection-diffusion equations coupled to the structural and composition equations of stars to model the evolution of angular momentum and the two components of the magnetic field. We present the evolution in various cases for a 3 M_{⊙} star from the beginning to the late stages of its life. Our particular model assumes that turbulent motions, including convection, favour small-scale field at the expense of large-scale field. As a result, the large-scale field concentrates in radiative zones of the star and so is exchanged between the core and the envelope of the star as it evolves. The field is sustained until the end of the asymptotic giant branch, when it concentrates in the degenerate core.

Towards a coherent view of mass loss in Betelgeuse from the photosphere to the interstellar medium

NASA Astrophysics Data System (ADS)

Montarges, Miguel; Kervella, Pierre; Perrin, Guy

2013-06-01

Massive evolved stars contribute to the chemical enrichment of the interstellar medium (ISM), the Galaxy and ultimately the Universe through their mass loss. From the photosphere to the ISM, large convective motions, low surface gravity and high brightness combine to trigger an intense stellar wind. The released material evolves chemically as the distance from the star increases, and eventually forms dust particles. The involved physical and chemical processes are central to apprehend the cosmic impact of massive evolved stars, but they are poorly understood: the surface convection remains essentially uncharacterized, as the composition of the wind, and the role of the magnetic field is unknown. Betelgeuse is the closest red supergiant and therefore it stands out as the best candidate to obtain detailed observations of the close circumstellar environment of a massive evolved star. We are currently running a high angular resolution observations program to obtain a multi-wavelength and multi-epoch characterisation of this star. Using the IOTA interferometer, Haubois et al. reconstructed an image of the photosphere of the star. Within 1 to 100 stellar radii, the VLT and VLTI allowed us to probe the compact molecular envelope of Betelgeuse (the MOLsphere) in the near-infrared, and the extended dusty envelope in the thermal infrared domain. They were recently completed with HST/STIS observations of the chromosphere in the UV, whose location is surprisingly coincident with the MOLsphere. We will present a brief review of our recent results and of our ongoing work on Betelgeuse.

Evolved Stars, Masers And Polarization Submm/mm/cm QUESO Workshop 2017 (QUESO2017), Centimetre-Sub-Millimetre Q&U (and V) European Southern Observatory Workshop, held 25-27 October, 2017 at ESO, Garching bei München, Germany. Online at https://www.eso.org/sci/meetings/2017/QUESO2017.html, id.35

NASA Astrophysics Data System (ADS)

Humphreys, Elizabeth

2017-11-01

Cool evolved stars on the Asymptotic Giant Branch (AGB) and Red Supergiants (RSG) often host strong masers, for example from SiO, water and OH. The maser emission can display high degrees of circular and linear polarization, potentially revealing information on magnetic field strength and morphology at different radii in the circumstellar envelopes. In this review, I will describe maser polarization theory and discuss was has been learnt so far from maser observations. I will also discuss dust polarization at (sub)mm wavelengths and the role that full polarization observations using ALMA is going to play in better characterizing evolved stars. Finally, I will talk about the potential impact of magnetic fields in the evolution of the stars, for example the shaping of AGB stars to often highly axisymmetric/aspherical Planetary Nebulae.queso2017queso2017

Mass-loss From Evolved Stellar Populations In The Large Magellanic Cloud

NASA Astrophysics Data System (ADS)

Riebel, David

2012-01-01

I have conducted a study of a sample of 30,000 evolved stars in the Large Magellanic Cloud (LMC) and 6,000 in the Small Magellanic Cloud (SMC), covering their variability, mass-loss properties, and chemistry. The initial stages of of my thesis work focused on the infrared variability of Asymptotic Giant Branch (AGB) stars in the LMC. I determined the period-luminosity (P-L) relations for 6 separate sequences of 30,000 evolved star candidates at 8 wavelengths, as a function of photometrically assigned chemistry, and showed that the P-L relations are different for different chemical populations (O-rich or C-rich). I also present results from the Grid of Red supergiant and Asymptotic giant branch star ModelS (GRAMS) radiative transfer (RT) model grid applied to the evolved stellar population of the LMC. GRAMS is a pre-computed grid of RT models of RSG and AGB stars and surrounding circumstellar dust. Best-fit models are determined based on 12 bands of photometry from the optical to the mid-infrared. Using a pre-computed grid, I can present the first reasonably detailed radiative transfer modeling for tens of thousands of stars, allowing me to make statistically accurate estimations of the carbon-star luminosity function and the global dust mass return to the interstellar medium from AGB stars, both key parameters for stellar population synthesis models to reproduce. In the SAGE-Var program, I used the warm Spitzer mission to take 4 additional epochs of observations of 7500 AGB stars in the LMC and SMC. These epochs, combined with existing data, enable me to derive mean fluxes at 3.6 and 4.5 microns, that will be used for tighter constraints for GRAMS, which is currently limited by the variability induced error on the photometry. This work is support by NASA NAG5-12595 and Spitzer contract 1415784.

New CO and HCN sources associated with IRAS carbon stars

NASA Technical Reports Server (NTRS)

NGUYEN-Q-RIEU; Epchtein, N.; TRUONG-BACH; Cohen, M.

1987-01-01

Emission of CO and HCN was detected in 22 out of a sample of 53 IRAS sources classified as unidentified carbon-rich objects. The sample was selected according to the presence of the silicon carbide feature as revealed by low-resolution spectra. The molecular line widths indicate that the CO and HCN emission arises from the circumstellar envelopes of very highly evolved stars undergoing mass loss. The visible stars tend to be deficient in CO as compared with unidentified sources. Most the detected CO and HCN IRAS stars are distinct and thick-shelled objects, but their infrared and CO luminosities are similar to those of IRC + 102156 AFGL and IRC-CO evolved stars. The 12 micron flux seems to be a good indicator of the distance, hence a guide for molecular searches.

A search for radio emission from exoplanets around evolved stars

NASA Astrophysics Data System (ADS)

O'Gorman, E.; Coughlan, C. P.; Vlemmings, W.; Varenius, E.; Sirothia, S.; Ray, T. P.; Olofsson, H.

2018-04-01

The majority of searches for radio emission from exoplanets have to date focused on short period planets, i.e., the so-called hot Jupiter type planets. However, these planets are likely to be tidally locked to their host stars and may not generate sufficiently strong magnetic fields to emit electron cyclotron maser emission at the low frequencies used in observations (typically ≥150 MHz). In comparison, the large mass-loss rates of evolved stars could enable exoplanets at larger orbital distances to emit detectable radio emission. Here, we first show that the large ionized mass-loss rates of certain evolved stars relative to the solar value could make them detectable with the LOw Frequency ARray (LOFAR) at 150 MHz (λ = 2 m), provided they have surface magnetic field strengths >50 G. We then report radio observations of three long period (>1 au) planets that orbit the evolved stars β Gem, ι Dra, and β UMi using LOFAR at 150 MHz. We do not detect radio emission from any system but place tight 3σ upper limits of 0.98, 0.87, and 0.57 mJy on the flux density at 150 MHz for β Gem, ι Dra, and β UMi, respectively. Despite our non-detections these stringent upper limits highlight the potential of LOFAR as a tool to search for exoplanetary radio emission at meter wavelengths.

Spectra from the IRS of Bright Oxygen-Rich Evolved Stars in the SMC

NASA Astrophysics Data System (ADS)

Kraemer, Kathleen E.; Sloan, Greg; Wood, Peter

2016-06-01

We have used Spitzer's Infrared Spectrograph (IRS) to obtain spectra of stars in the Small Magellanic Cloud (SMC). The targets were chosen from the Point Source Catalog of the Mid-Course Space Experiment (MSX), which detected the 243 brightest infrared sources in the SMC. Our SMC sample of oxygen-rich evolved stars shows more dust than found in previous samples, and the dust tends to be dominated by silicates, with little contribution from alumina. Both results may arise from the selection bias in the MSX sample and our sample toward more massive stars. Additionally, several sources show peculiar spectral features such as PAHs, crystalline silicates, or both carbon-rich and silicate features. The spectrum of one source, MSX SMC 145, is a combination of an ordinary AGB star and a background galaxy at z~0.16, rather than an OH/IR star as previously suggested.

Cannibals in the thick disk: the young α-rich stars as evolved blue stragglers

NASA Astrophysics Data System (ADS)

Jofré, P.; Jorissen, A.; Van Eck, S.; Izzard, R. G.; Masseron, T.; Hawkins, K.; Gilmore, G.; Paladini, C.; Escorza, A.; Blanco-Cuaresma, S.; Manick, R.

2016-10-01

Spectro-seismic measurements of red giants enabled the recent discovery of stars in the thick disk that are more massive than 1.4 M⊙. While it has been claimed that most of these stars are younger than the rest of the typical thick disk stars, we show evidence that they might be products of mass transfer in binary evolution, notably evolved blue stragglers. We took new measurements of the radial velocities in a sample of 26 stars from APOKASC, including 13 "young" stars and 13 "old" stars with similar stellar parameters but with masses below 1.2 M⊙ and found that more of the young starsappear to be in binary systems with respect to the old stars.Furthermore, we show that the young stars do not follow the expected trend of [C/H] ratios versus mass for individual stars. However, with a population synthesis of low-mass stars including binary evolution and mass transfer, we can reproduce the observed [C/N] ratios versus mass. Our study shows how asteroseismology of solar-type red giants provides us with a unique opportunity to study the evolution of field blue stragglers after they have left the main-sequence.

Starquakes, Heating Anomalies, and Nuclear Reactions in the Neutron Star Crust

NASA Astrophysics Data System (ADS)

Deibel, Alex Thomas

When the most massive stars perish, their cores may remain intact in the form of extremely dense and compact stars. These stellar remnants, called neutron stars, are on the cusp of becoming black holes and reach mass densities greater than an atomic nucleus in their centers. Although the interiors of neutron stars were difficult to investigate at the time of their discovery, the advent of modern space-based telescopes (e.g., Chandra X-ray Observatory) has pushed our understanding of the neutron star interior into exciting new realms. It has been shown that the neutron star interior spans an enormous range of densities and contains many phases of matter, and further theoretical progress must rely on numerical calculations of neutron star phenomena built with detailed nuclear physics input. To further investigate the properties of the neutron star interior, this dissertation constructs numerical models of neutron stars, applies models to various observations of neutron star high-energy phenomena, and draws new conclusions about the neutron star interior from these analyses. In particular, we model the neutron star's outermost ? 1 km that encompasses the neutron star's envelope, ocean, and crust. The model must implement detailed nuclear physics to properly simulate the hydrostatic and thermal structure of the neutron star. We then apply our model to phenomena that occur in these layers, such as: thermonuclear bursts in the envelope, g-modes in the ocean, torsional oscillations of the crust, and crust cooling of neutron star transients. A comparison of models to observations provides new insights on the properties of dense matter that are often difficult to probe through terrestrial experiments. For example, models of the quiescent cooling of neutron stars, such as the accreting transient MAXI J0556-332, at late times into quiescence probe the thermal transport properties of the deep neutron star crust. This modeling provides independent data from astronomical observations on the nature of neutron superfluidity and the thermal conductivity of nuclear pasta. Our neutron star modeling efforts also pose new questions. For instance, reaction networks find that neutrino emission from cycling nuclear reactions is present in the neutron star ocean and crust, and potentially cools an accreting neutron star. This is a theory we attempt to verify using observations of neutron star transients and thermonuclear bursts, although it remains unclear if this cooling occurs. Furthermore, on some accreting neutron stars, more heat than supplied by nuclear reactions is needed to explain their high temperatures at the outset of quiescence. Although the presence of heating anomalies seems common, the source of extra heating is difficult to determine.

The evolution of angular momentum among zero-age main-sequence solar-type stars

NASA Technical Reports Server (NTRS)

Soderblom, David R.; Stauffer, John R.; Macgregor, Keith B.; Jones, Burton F.

1993-01-01

We consider a survey of rotation among F, G, and K dwarfs of the Pleiades in the context of other young clusters (Alpha Persei and the Hyades) and pre-main-sequence (PMS) stars (in Taurus-Auriga and Orion) in order to examine how the angular momentum of a star like the sun evolves during its early life on the main sequence. The rotation of PMS stars can be evolved into distributions like those seen in the young clusters if there is only modest, rotation-independent angular momentum loss prior to the ZAMS. Even then, the ultrafast rotators (UFRs, or ZAMS G and K dwarfs with v sin i equal to or greater than 30 km/s) must owe their extra angular momentum to their conditions of formation and to different angular momentum loss rates above a threshold velocity, for it is unlikely that these stars had angular momentum added as they neared the ZAMS, nor can a spread in ages within a cluster account for the range of rotation seen. Only a fraction of solar-type stars are thus capable of becoming UFRs, and it is not a phase that all stars experience. Simple scaling relations (like the Skumanich relation) applied to the observed surface rotation rates of young solar-type stars cannot reproduce the way in which the Pleiades evolve into the Hyades. We argue that invoking internal differential rotation in these ZAMS stars can explain several aspects of the observations and thus can provide a consistent picture of ZAMS angular momentum evolution.

Planets around the evolved stars 24 Boötis and γ Libra: A 30 d-period planet and a double giant-planet system in possible 7:3 MMR

NASA Astrophysics Data System (ADS)

Takarada, Takuya; Sato, Bun'ei; Omiya, Masashi; Harakawa, Hiroki; Nagasawa, Makiko; Izumiura, Hideyuki; Kambe, Eiji; Takeda, Yoichi; Yoshida, Michitoshi; Itoh, Yoichi; Ando, Hiroyasu; Kokubo, Eiichiro; Ida, Shigeru

2018-05-01

We report the detection of planets around two evolved giant stars from radial velocity measurements at Okayama Astrophysical observatory. 24 Boo (G3 IV) has a mass of 0.99 M_{⊙}, a radius of 10.64 R_{⊙}, and a metallicity of [Fe/H] = -0.77. The star hosts one planet with a minimum mass of 0.91 MJup and an orbital period of 30.35 d. The planet has one of the shortest orbital periods among those ever found around evolved stars using radial-velocity methods. The stellar radial velocities show additional periodicity with 150 d, which can probably be attributed to stellar activity. The star is one of the lowest-metallicity stars orbited by planets currently known. γ Lib (K0 III) is also a metal-poor giant with a mass of 1.47 M_{⊙}, a radius of 11.1 R_{⊙}, and [Fe/H] = -0.30. The star hosts two planets with minimum masses of 1.02 MJup and 4.58 MJup, and periods of 415 d and 964 d, respectively. The star has the second-lowest metallicity among the giant stars hosting more than two planets. Dynamical stability analysis for the γ Lib system sets the minimum orbital inclination angle to be about 70° and suggests that the planets are in 7:3 mean-motion resonance, though the current best-fitting orbits for the radial-velocity data are not totally regular.

Mining the HST Treasury: The ASTRAL Reference Spectra for Evolved M Stars

NASA Technical Reports Server (NTRS)

Carpenter, K. G.; Ayres, T.; Harper, G.; Kober, G.; Wahlgren, G. M.

2012-01-01

The "Advanced Spectral Library (ASTRAL) Project: Cool Stars" (PI = T. Ayres) is an HST Cycle 18 Treasury Program designed to collect a definitive set of representative, high-resolution (R greater than 100,000) and high signal/noise (S/N greater than 100) UV spectra of eight F-M evolved cool stars. These extremely high-quality STIS UV echelle spectra are available from the HST archive and through the University of Colorado (http://casa.colorado.edu/ayres/ASTRAL/) portal and will enable investigations of a broad range of problems -- stellar, interstellar. and beyond -- for many years. In this current paper, we concentrate on producing a roadrnap to the very rich spectra of the two evolved M stars in the sample, the M3.4 giant Gamma Crucis (GaCrux) and the M2Iab supergiant Alpha Orionis (Betelgeuse) and illustrate the huge increase in coverage and quality that these spectra provide over that previously available from IUE and earlier HST observations. These roadmaps will facilitate the study of the spectra, outer atmospheres, and winds of not only these stars. but also numerous other cool, low-gravity stars and make a very interesting comparison to the already-available atlases of the K2III giant Arcturus.

THE MASS-LOSS RETURN FROM EVOLVED STARS TO THE LARGE MAGELLANIC CLOUD. VI. LUMINOSITIES AND MASS-LOSS RATES ON POPULATION SCALES

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

Riebel, D.; Meixner, M.; Srinivasan, S.

We present results from the first application of the Grid of Red Supergiant and Asymptotic Giant Branch ModelS (GRAMS) model grid to the entire evolved stellar population of the Large Magellanic Cloud (LMC). GRAMS is a pre-computed grid of 80,843 radiative transfer models of evolved stars and circumstellar dust shells composed of either silicate or carbonaceous dust. We fit GRAMS models to {approx}30,000 asymptotic giant branch (AGB) and red supergiant (RSG) stars in the LMC, using 12 bands of photometry from the optical to the mid-infrared. Our published data set consists of thousands of evolved stars with individually determined evolutionarymore » parameters such as luminosity and mass-loss rate. The GRAMS grid has a greater than 80% accuracy rate discriminating between oxygen- and carbon-rich chemistry. The global dust injection rate to the interstellar medium (ISM) of the LMC from RSGs and AGB stars is on the order of 2.1 Multiplication-Sign 10{sup -5} M{sub Sun} yr{sup -1}, equivalent to a total mass injection rate (including the gas) into the ISM of {approx}6 Multiplication-Sign 10{sup -3} M{sub Sun} yr{sup -1}. Carbon stars inject two and a half times as much dust into the ISM as do O-rich AGB stars, but the same amount of mass. We determine a bolometric correction factor for C-rich AGB stars in the K{sub s} band as a function of J - K{sub s} color, BC{sub K{sub s}}= -0.40(J-K{sub s}){sup 2} + 1.83(J-K{sub s}) + 1.29. We determine several IR color proxies for the dust mass-loss rate (M-dot{sub d}) from C-rich AGB stars, such as log M-dot{sub d} = (-18.90/((K{sub s}-[8.0])+3.37) - 5.93. We find that a larger fraction of AGB stars exhibiting the 'long-secondary period' phenomenon are more O-rich than stars dominated by radial pulsations, and AGB stars without detectable mass loss do not appear on either the first-overtone or fundamental-mode pulsation sequences.« less

GOODS-HERSCHEL: STAR FORMATION, DUST ATTENUATION, AND THE FIR–RADIO CORRELATION ON THE MAIN SEQUENCE OF STAR-FORMING GALAXIES UP TO z ≃ 4

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

Pannella, M.; Elbaz, D.; Daddi, E.

We use deep panchromatic data sets in the GOODS-N field, from GALEX to the deepest Herschel far-infrared (FIR) and VLA radio continuum imaging, to explore the evolution of star-formation activity and dust attenuation properties of star-forming galaxies to z ≃ 4, using mass-complete samples. Our main results can be summarized as follows: (i) the slope of the star-formation rate–M{sub *} correlation is consistent with being constant ≃0.8 up to z ≃ 1.5, while its normalization keeps increasing with redshift; (ii) for the first time we are able to explore the FIR–radio correlation for a mass-selected sample of star-forming galaxies: themore » correlation does not evolve up to z ≃ 4; (iii) we confirm that galaxy stellar mass is a robust proxy for UV dust attenuation in star-forming galaxies, with more massive galaxies being more dust attenuated. Strikingly, we find that this attenuation relation evolves very weakly with redshift, with the amount of dust attenuation increasing by less than 0.3 mag over the redshift range [0.5–4] for a fixed stellar mass; (iv) the correlation between dust attenuation and the UV spectral slope evolves with redshift, with the median UV slope becoming bluer with redshift. By z ≃ 3, typical UV slopes are inconsistent, given the measured dust attenuations, with the predictions of commonly used empirical laws. (v) Finally, building on existing results, we show that gas reddening is marginally larger (by a factor of around 1.3) than the stellar reddening at all redshifts probed. Our results support a scenario where the ISM conditions of typical star-forming galaxies evolve with redshift, such that at z ≥ 1.5 Main Sequence galaxies have ISM conditions moving closer to those of local starbursts.« less

Near-infrared variability study of the central 2.3 × 2.3 arcmin2 of the Galactic Centre - II. Identification of RR Lyrae stars in the Milky Way nuclear star cluster

NASA Astrophysics Data System (ADS)

Dong, Hui; Schödel, Rainer; Williams, Benjamin F.; Nogueras-Lara, Francisco; Gallego-Cano, Eulalia; Gallego-Calvente, Teresa; Wang, Q. Daniel; Rich, R. Michael; Morris, Mark R.; Do, Tuan; Ghez, Andrea

2017-11-01

Because of strong and spatially highly variable interstellar extinction and extreme source crowding, the faint (K ≥ 15) stellar population in the Milky Way's nuclear star cluster is still poorly studied. RR Lyrae stars provide us with a tool to estimate the mass of the oldest, relative dim stellar population. Recently, we analysed HST/WFC3/IR observations of the central 2.3 × 2.3 arcmin2 of the Milky Way and found 21 variable stars with periods between 0.2 and 1 d. Here, we present a further comprehensive analysis of these stars. The period-luminosity relationship of RR Lyrae is used to derive their extinctions and distances. Using multiple approaches, we classify our sample as 4 RRc stars, 4 RRab stars, 3 RRab candidates and 10 binaries. Especially, the four RRab stars show sawtooth light curves and fall exactly on to the Oosterhoff I division in the Bailey diagram. Compared to the RRab stars reported by Minniti et al., our new RRab stars have higher extinction (AK > 1.8) and should be closer to the Galactic Centre. The extinction and distance of one RRab stars match those for the Milky Way's nuclear star cluster given in previous works. We perform simulations and find that after correcting for incompleteness, there could be not more than 40 RRab stars within the Milky Way's nuclear star cluster and in our field of view. Through comparing with the known globular clusters of the Milky Way, we estimate that if there exists an old, metal-poor (-1.5 < [Fe/H] < -1) stellar population in the Milky Way nuclear star cluster on a scale of 5 × 5 pc, then it contributes at most 4.7 × 105 M⊙, I.e. ˜18 per cent of the stellar mass.

Obscured Active Galactic Nuclei in Luminous Infrared Galaxies

NASA Astrophysics Data System (ADS)

Shier, L. M.; Rieke, M. J.; Rieke, G. H.

1996-10-01

We examine the nature of the central power source in very luminous infrared galaxies. The infrared properties of the galaxies, including their far-infrared and 2.2 micron fluxes, CO indices, and Brackett line fluxes are compared to models of starburst stellar populations. Among seven galaxies we found two dominated by emission from young stars, two dominated by emission from an AGN, and three transition cases. Our results are consistent with evidence for active nuclei in the same galaxies at other wavelengths. Nuclear mass measurements obtained for the galaxies indicate an initial mass function biased toward high-mass stars in two galaxies. After demonstrating our methods in well-studied galaxies, we define complete samples of high luminosity and ultraluminous galaxies. We find that the space density of embedded and unembedded quasars in the local universe is similar for objects of similar luminosity. If quasars evolve from embedded sources to optically prominent objects, it appears that the lifetime of a quasar is no more than about 108 yr.

Supernova 1987A - the evolution from blue to red

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

Tuchman, Y.; Wheeler, J.C.

1989-09-01

The evolution of stars with mass comparable to that of the progenitor of SN 1987A from the main sequence to the Hayashi track is critically examined to determine why some models evolve to the red on nuclear time scales, some on thermal time scales, and some not at all. Thermal equilibrium solutions to a parametrized series of structural models with active hydrogen burning shells have two stable solutions with different T(eff) for the same helium core M(He) mass and a minimum M(He) below which no blue thermal equlibrium solution is possible. The dependence of the equilibrium solutions on stellar mass,more » envelope composition, and mass loss are investigated. The solutions quantitatively account for the 'gap' in the HR diagrams of massive stars in the Galaxy and LMC and suggest that the outer envelopes are not substantially enriched in helium during the first passage from the main sequence to the Hayashi track. 23 refs.« less

Connections between Star Cluster Populations and Their Host Galaxy Nuclear Rings

NASA Astrophysics Data System (ADS)

Ma, Chao; de Grijs, Richard; Ho, Luis C.

2018-04-01

Nuclear rings are excellent laboratories for probing diverse phenomena such as the formation and evolution of young massive star clusters and nuclear starbursts, as well as the secular evolution and dynamics of their host galaxies. We have compiled a sample of 17 galaxies with nuclear rings, which are well resolved by high-resolution Hubble and Spitzer Space Telescope imaging. For each nuclear ring, we identified the ring star cluster population, along with their physical properties (ages, masses, and extinction values). We also determined the integrated ring properties, including the average age, total stellar mass, and current star formation rate (SFR). We find that Sb-type galaxies tend to have the highest ring stellar mass fraction with respect to the host galaxy, and this parameter is correlated with the ring’s SFR surface density. The ring SFRs are correlated with their stellar masses, which is reminiscent of the main sequence of star-forming galaxies. There are striking correlations between star-forming properties (i.e., SFR and SFR surface density) and nonaxisymmetric bar parameters, appearing to confirm previous inferences that strongly barred galaxies tend to have lower ring SFRs, although the ring star formation histories turn out to be significantly more complicated. Nuclear rings with higher stellar masses tend to be associated with lower cluster mass fractions, but there is no such relation for the ages of the rings. The two youngest nuclear rings in our sample, NGC 1512 and NGC 4314, which have the most extreme physical properties, represent the young extremity of the nuclear ring age distribution.

Rings and arcs around evolved stars - I. Fingerprints of the last gasps in the formation process of planetary nebulae

NASA Astrophysics Data System (ADS)

Ramos-Larios, G.; Santamaría, E.; Guerrero, M. A.; Marquez-Lugo, R. A.; Sabin, L.; Toalá, J. A.

2016-10-01

Evolved stars such as asymptotic giant branch stars (AGB), post-AGB stars, proto-planetary nebulae (proto-PNe), and planetary nebulae (PNe) show rings and arcs around them and their nebular shells. We have searched for these morphological features in optical Hubble Space Telescope and mid-infrared Spitzer Space Telescope images of ˜650 proto-PNe and PNe and discovered them in 29 new sources. Adding those to previous detections, we derive a frequency of occurrence ≃8 per cent. All images have been processed to remove the underlying envelope emission and enhance outer faint structures to investigate the spacing between rings and arcs and their number. The averaged time lapse between consecutive rings and arcs is estimated to be in the range 500-1200 yr. The spacing between them is found to be basically constant for each source, suggesting that the mechanism responsible for the formation of these structures in the final stages of evolved stars is stable during time periods of the order of the total duration of the ejection. In our sample, this period of time spans ≤4500 yr.

MUSEing about the SHAPE of eta Car's outer ejecta

NASA Astrophysics Data System (ADS)

Mehner, A.; Steffen, W.; Groh, J.; Vogt, F. P. A.; Baade, D.; Boffin, H. M. J.; de Wit, W. J.; Oudmaijer, R. D.; Rivinius, T.; Selman, F.

2017-11-01

The role of episodic mass loss in evolved massive stars is one of the outstanding questions in stellar evolution theory. Integral field spectroscopy of nebulae around massive stars provide information on their recent mass-loss history. η Car is one of the most massive evolved stars and is surrounded by a complex circumstellar environment. We have conducted a three-dimensional morpho-kinematic analysis of η Car's ejecta outside its famous Homunculus nebula. SHAPE modelling of VLT MUSE data establish unequivocally the spatial cohesion of the outer ejecta and the correlation of ejecta with the soft X-ray emission.

Dissertation Award in Nuclear Physics Recipient: Astromaterials in Neutron Stars

NASA Astrophysics Data System (ADS)

Caplan, Matthew E.

2017-09-01

Stars freeze. As they age and cool white dwarfs and neutron stars crystallize, with remarkable materials forming in their interiors. These `astromaterials' have structures similar to terrestrial crystalline solids and liquid crystals, though they are over a trillion times denser. Notably, because their material properties affect the observable properties of the star, astromaterials must be understood to interpret observations of neutron stars. Thus, astromaterial science can be thought of as an interdisciplinary field, using techniques from material science to study nuclear physics systems with astrophysical relevance. In this talk, I will discuss recent results from simulations of astromaterials and how we use these results to interpret observations of neutron stars in X-ray binaries. In addition, I will discuss how nuclear pasta, in neutron stars, forms structures remarkably similar to biophysical membranes seen in living organisms.

Cosmic Feast of the Elements

NASA Astrophysics Data System (ADS)

Morisset, C.; Delgado-Inglada, G.; García-Rojas, J.

2017-11-01

In the past few decades most of our understanding of the history and chemical evolution of galaxies has been guided by the study of their stars and gaseous nebulae. Nebulae, thanks to their bright emission lines, are especially useful tracers of chemical elements from the very center to the outskirts of galaxies. In order to pin down the chemical abundances in nebulae, we must rely on careful analysis of emission lines combined with detailed models of the microscopic physical processes inside nebulae and state-of-the-art atomic data. Another important piece of the puzzle is the interplay between galaxy evolution and the activity of their central engines either as optical AGNs or radio jets. Last but not least, let us not forget the huge population of lineless, retired galaxies ionized by hot low-mass evolved stars: after nuclear and star formation activity quiets down, retired galaxies are the natural consequence of galaxy evolution. Grażyna Stasińska has made important contributions to each and every one of those aspects. This conference is to honor her work. We invite you to take part and share the latest news on this cosmic feast that transmutes chemical species, the onward journey of elements inside and outside galaxies either as lonely atoms or gregarious molecules and crystals, and their recycling in stars, which starts the cosmic feast all over again.

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

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

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

We have analyzed photometry from space- and ground-based cameras to identify all bright red giant branch (RGB), horizontal branch (HB), and asymptotic giant branch (AGB) stars within 10' of the center of the globular cluster M13. We identify a modest (7%) population of HB stars redder than the primary peak (including RR Lyrae variables at the blue end of the instability strip) that is somewhat more concentrated to the cluster core than the rest of the evolved stars. We find support for the idea that they are noticeably evolved and in the late stages of depleting helium in their cores.more » This resolves a disagreement between distance moduli derived from the tip of the RGB and from stars in or near the RR Lyrae instability strip. We identified disagreements between HB model sets on whether stars with T{sub eff} {approx}< 10, 000 K (near the 'knee' of the HB in optical CMDs) should evolve redward or blueward, and the differences may depend on the inclusion of diffusion in the stellar interior. The sharp cut at the red end of M13's HB provides strong evidence that stars from the dominant HB group still must be undergoing blue loops, which implies that diffusion is being inhibited. We argue that M13's HB is a somewhat pathological case-the dominant HB population occurs very near the 'knee' in optical CMDs, and evolved stars exclusively appear redward of that peak, leading to the incorrect appearance of a continuation of the unevolved HB. We identify two stars as 'blue hook' star candidates-the faintest stars in optical bands that remain significantly subluminous in the shortest ultraviolet wavelength photometry available. M13 also has a distinct group of stars previously identified with the 'second U jump'. Based on far-UV photometry, we find that these stars have genuinely high temperatures (probably 26,000 K {approx}

Infrared Spectroscopic Studies of the Properties of Dust in the Ejecta of Galactic Oxygen-Rich Asymptotic Giant Branch Stars

NASA Astrophysics Data System (ADS)

Sargent, Benjamin A.; Srinivasan, Sundar; Kastner, Joel; Meixner, Margaret; Riley, Allyssa

2018-06-01

We are conducting a series of infrared studies of large samples of mass-losing asymptotic giant branch (AGB) stars to explore the relationship between the composition of evolved star ejecta and host galaxy metallicity. Our previous studies focused on mass loss from evolved stars in the relatively low-metallicity Large and Small Magellanic Clouds. In our present study, we analyze dust in the mass-losing envelopes of AGB stars in the Galaxy, with special focus on the ejecta of oxygen-rich (O-rich) AGB stars. We have constructed detailed dust opacity models of AGB stars in the Galaxy for which we have infrared spectra from, e.g., the Spitzer Space Telescope Infrared Spectrograph (IRS). This detailed modeling of dust features in IRS spectra informs our choice of dust properties to use in radiative transfer modeling of the broadband SEDs of Bulge AGB stars. We investigate the effects of dust grain composition, size, shape, etc. on the AGB stars' infrared spectra, studying both the silicate dust and the opacity source(s) commonly attributed to alumina (Al2O3). BAS acknowledges funding from NASA ADAP grant 80NSSC17K0057.

A Runaway Yellow Supergiant Star in the Small Magellanic Cloud

NASA Astrophysics Data System (ADS)

Neugent, Kathryn; Massey, Phil; Morrell, Nidia

2018-01-01

Around 35% of OB stars are thought to be runaways formed through supernova explosions of companions, interactions with black holes, or close encounters with neighboring stars. Once these OB stars begin running away from their birthplace they eventually begin to evolve. However, few runaway evolved massive stars have been found, especially in galaxies other than the Milky Way. We recently stumbled across a Yellow Supergiant (YSG) in the Small Magellanic Cloud (SMC) with a heliocentric radial velocity ~150 km/s larger than expected. This velocity suggests that over the course of 10 million years, the YSG has moved 1.6 degrees across the plane of the SMC. A visual inspection of the locations of YSGs within the SMC shows that this star is on the outer edge of where the YSGs are located and not in an OB association. Runaway stars are also associated with bow shocks and this is primarily how such stars have been detected before. At a distance of the SMC, a bow shock would extend 2.8" away from the star and should be detectable using ground based telescopes. We have plans to search for such a bow shock and should know the results by the time of the meeting.

The QSE-Reduced Nuclear Reaction Network for Silicon Burning

NASA Astrophysics Data System (ADS)

Hix, W. Raphael; Parete-Koon, Suzanne T.; Freiburghaus, Christian; Thielemann, Friedrich-Karl

2007-09-01

Iron and neighboring nuclei are formed in massive stars shortly before core collapse and during their supernova outbursts, as well as during thermonuclear supernovae. Complete and incomplete silicon burning are responsible for the production of a wide range of nuclei with atomic mass numbers from 28 to 64. Because of the large number of nuclei involved, accurate modeling of silicon burning is computationally expensive. However, examination of the physics of silicon burning has revealed that the nuclear evolution is dominated by large groups of nuclei in mutual equilibrium. We present a new hybrid equilibrium-network scheme which takes advantage of this quasi-equilibrium in order to reduce the number of independent variables calculated. This allows accurate prediction of the nuclear abundance evolution, deleptonization, and energy generation at a greatly reduced computational cost when compared to a conventional nuclear reaction network. During silicon burning, the resultant QSE-reduced network is approximately an order of magnitude faster than the full network it replaces and requires the tracking of less than a third as many abundance variables, without significant loss of accuracy. These reductions in computational cost and the number of species evolved make QSE-reduced networks well suited for inclusion within hydrodynamic simulations, particularly in multidimensional applications.

Nuclear emulsion measurements of the dose contribution from tissue disintegration stars on the apollo-soyuz mission. Technical report No. 2, Jul 76--Mar 77

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

Schaefer, H.J.

1977-03-15

Analysis of the prong number distribution of a population of disintegration stars in nuclear emulsion allows a quantitative estimate of the fraction of stars originating in the gelatin matrix and thereby an assessment of the tissue-equivalent dose from stars. 996 stars were prong-counted in two 100 micron llford K.2 emulsions from the dosimeter of the Docking Pilot on Apollo-Soyuz and furnished a tissue star dose of 7.8 millirad or 45 millirem. Since star-produced neutrons do not leave visible prongs in emulsion, their dose contribution is not included. Nuclear theory as well as earlier measurements of galactic radiation in the Earth'smore » atmosphere indicate that the dose equivalent from neutrons is about equal to the one from all ionizing secondaries from stars. This would set the total tissue star dose for Apollo-Soyuz at approximately 90 millirem. (Author)« less

The shape of the cosmic X-ray background: nuclear starburst discs and the redshift evolution of AGN obscuration

NASA Astrophysics Data System (ADS)

Gohil, R.; Ballantyne, D. R.

2018-04-01

A significant number of active galactic nuclei (AGNs) are observed to be hidden behind dust and gas. The distribution of material around AGNs plays an important role in modelling the cosmic X-ray background (CXB), especially the fraction of type 2 AGNs (f2). One of the possible explanations for obscuration in Seyfert galaxies at intermediate redshifts is dusty starburst discs. We compute the two-dimensional (2D) hydrostatic structure of 768 nuclear starburst discs (NSDs) under various physical conditions and also the distribution of column density along the line of sight (NH) associated with these discs. Then the NH distribution is evolved with redshift by using the redshift-dependent distribution function of input parameters. Parameter f2 shows a strong positive evolution up to z = 2, but only a weak level of enhancement at higher z. The Compton-thin and Compton-thick AGN fractions associated with these starburst regions increase ∝ (1 + z)δ, where δ is estimated to be 1.12 and 1.45, respectively. The reflection parameter Rf associated with column density NH ≥ 1023.5 cm-2 extends from 0.13 at z = 0 to 0.58 at z = 4. A CXB model employing this evolving NH distribution indicates that more compact (Rout < 120 pc) NSDs provide a better fit to the CXB. In addition to `Seyfert-like' AGNs obscured by nuclear starbursts, we predict that 40-60 per cent of quasars must be Compton-thick to produce a peak of the CXB spectrum within the observational uncertainty. The predicted total number counts of AGNs in 8-24 keV bands are in fair agreement with observations from the Nuclear Spectroscopic Telescope Array (NuSTAR).

Nuclear Physics of neutron stars

NASA Astrophysics Data System (ADS)

Piekarewicz, Jorge

2015-04-01

One of the overarching questions posed by the recent community report entitled ``Nuclear Physics: Exploring the Heart of Matter'' asks How Does Subatomic Matter Organize Itself and What Phenomena Emerge? With their enormous dynamic range in both density and neutron-proton asymmetry, neutron stars provide ideal laboratories to answer this critical challenge. Indeed, a neutron star is a gold mine for the study of physical phenomena that cut across a variety of disciplines, from particle physics to general relativity. In this presentation--targeted at non-experts--I will focus on the essential role that nuclear physics plays in constraining the dynamics, structure, and composition of neutron stars. In particular, I will discuss some of the many exotic states of matter that are speculated to exist in a neutron star and the impact of nuclear-physics experiments on elucidating their fascinating nature. This material is based upon work supported by the U.S. Department of Energy Office of Science, Office of Nuclear Physics under Award Number DE-FD05-92ER40750.

Star-PAP Control of BIK Expression and Apoptosis Is Regulated by Nuclear PIPKIα and PKCδ Signaling

PubMed Central

Li, Weimin; Laishram, Rakesh S.; Ji, Zhe; Barlow, Christy A.; Tian, Bin; Anderson, Richard A.

2012-01-01

SUMMARY BIK protein is an initiator of mitochondrial apoptosis and BIK expression is induced by pro-apoptotic signals including DNA damage. Here we demonstrate that 3′-end processing and expression of BIK mRNA are controlled by the nuclear PI4,5P2-regulated poly(A) polymerase Star-PAP downstream of DNA damage. Nuclear PKCδ is a key mediator of apoptosis and DNA damage stimulates PKCδ association with the Star-PAP complex where PKCδ is required for Star-PAP-dependent BIK expression. PKCδ binds the PI4,5P2-generating enzyme PIPKIα, which is essential for PKCδ interaction with the Star-PAP complex and PKCδ activity is directly stimulated by PI4,5P2. Features in the BIK 3′-UTR uniquely define Star-PAP specificity and may block canonical PAP activity toward BIK mRNA. This reveals a nuclear phosphoinositide signaling nexus where PIPKIα, PI4,5P2 and PKCδ regulate Star-PAP control of BIK expression and induction of apoptosis. This pathway is distinct from the Star-PAP-mediated oxidative stress pathway indicating signal-specific regulation of mRNA 3′-end processing. PMID:22244330

RAPIDLY ROTATING, X-RAY BRIGHT STARS IN THE KEPLER FIELD

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

Howell, Steve B.; Mason, Elena; Boyd, Patricia

We present Kepler light curves and optical spectroscopy of twenty X-ray bright stars located in the Kepler field of view. The stars, spectral type F-K, show evidence for rapid rotation including chromospheric activity 100 times or more above the Sun at maximum and flaring behavior in their light curves. Eighteen of our objects appear to be (sub)giants and may belong to the class of FK Com variables, which are evolved rapidly spinning single stars with no excretion disk and high levels of chromospheric activity. Such stars are rare and are likely the result of W UMa binary mergers, a processmore » believed to produce the FK Com class of variable and their descendants. The FK Com stage, including the presence of an excretion disk, is short lived but leads to longer-lived stages consisting of single, rapidly rotating evolved (sub)giants with high levels of stellar activity.« less

Rapidly Rotating, X-Ray Bright Stars in the Kepler Field

NASA Technical Reports Server (NTRS)

Howell, Steve B.; Mason, Elena; Boyd, Patricia; Smith, Krista Lynne; Gelino, Dawn M.

2016-01-01

We present Kepler light curves and optical spectroscopy of twenty X-ray bright stars located in the Kepler field of view. The stars, spectral type F-K, show evidence for rapid rotation including chromospheric activity 100 times or more above the Sun at maximum and flaring behavior in their light curves. Eighteen of our objects appear to be (sub)giants and may belong to the class of FK Com variables, which are evolved rapidly spinning single stars with no excretion disk and high levels of chromospheric activity. Such stars are rare and are likely the result of W UMa binary mergers, a process believed to produce the FK Com class of variable and their descendants. The FK Com stage, including the presence of an excretion disk, is short lived but leads to longer-lived stages consisting of single, rapidly rotating evolved (sub)giants with high levels of stellar activity.

On the nature of upsilon Sagittarii

NASA Technical Reports Server (NTRS)

Schoenberner, D.; Drilling, J. S.

1982-01-01

An explanation for the nature and evolution of the extremely hydrogen deficient binary Upsilon Sagittarii which is consistent with all observational and theoretical facts. First, the system goes through a Case B mass exchange in which most of the hydrogen rich envelope of a massive primary (5 to 14 solar masses) is lost. The remaining envelope still contains about 50% hydrogen (by number), but is now of negligible mass, so that the star evolves like a pure helium star. If its mass is between 1 and 2 solar masses the star reaches low surface temperatures and becomes a supergiant before the onset of carbon burning. This star (the original primary) then fills its Roche lobe a second time, spilling its now helium rich envelope over onto the secondary (Case BB mass exchange). It is argued that Upsilon Sagrittarii is in this state at the present time, and that the visible star is an evolved helium star of about 1 solar mass with a degenerate carbon-oxygen core and a helium burning shell which provides the high luminosity.

Tracking Advanced Planetary Systems (TAPAS) with HARPS-N . I. A multiple planetary system around the red giant star TYC 1422-614-1

NASA Astrophysics Data System (ADS)

Niedzielski, A.; Villaver, E.; Wolszczan, A.; Adamów, M.; Kowalik, K.; Maciejewski, G.; Nowak, G.; García-Hernández, D. A.; Deka, B.; Adamczyk, M.

2015-01-01

Context. Stars that have evolved off the main sequence are crucial for expanding the frontiers of knowledge on exoplanets toward higher stellar masses and for constraining star-planet interaction mechanisms. These stars have an intrinsic activity, however, which complicates the interpretation of precise radial velocity (RV) measurements, and therefore they are often avoided in planet searches. Over the past ten years, we have monitored about 1000 evolved stars for RV variations in search for low-mass companions under the Penn State - Toruń Centre for Astronomy Planet Search program with the Hobby-Eberly Telescope. Selected prospective candidates that required higher RV precision measurements have been followed with HARPS-N at the 3.6 m Telescopio Nazionale Galileo. Aims: We aim to detect planetary systems around evolved stars, to be able to build sound statistics on the frequency and intrinsic nature of these systems, and to deliver in-depth studies of selected planetary systems with evidence of star-planet interaction processes. Methods: We obtained 69 epochs of precise RV measurements for TYC 1422-614-1 collected over 3651 days with the Hobby-Eberly Telescope, and 17 epochs of ultra-precise HARPS-N data collected over 408 days. We complemented these RV data with photometric time-series from the All Sky Automatic Survey archive. Results: We report the discovery of a multiple planetary system around the evolved K2 giant star TYC 1422-614-1. The system orbiting the 1.15 M⊙ star is composed of a planet with mass msini = 2.5 MJ in a 0.69 AU orbit, and a planet or brown dwarf with msini = 10 MJ in an orbit of 1.37 AU. The multiple planetary system orbiting TYC 1422-614-1 is the first finding of the TAPAS project, a HARPS-N monitoring of evolved planetary systems identified with the Hobby-Eberly Telescope. Based on observations obtained with the Hobby-Eberly Telescope, which is a joint project of the University of Texas at Austin, the Pennsylvania State University, Stanford University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen.Based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Fundación Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.Tables 2 and 3 are available in electronic form at http://www.aanda.org

Mass-losing M supergiants in the solar neighborhood

NASA Technical Reports Server (NTRS)

Jura, M.; Kleinmann, S. G.

1990-01-01

A list of the 21 mass-losing red supergiants (20 M type, one G type; L greater than 100,000 solar luminosities) within 2.5 kpc of the sun is compiled. These supergiants are highly evolved descendants of main-sequence stars with initial masses larger than 20 solar masses. The surface density is between about 1 and 2/sq kpc. As found previously, these stars are much less concentrated toward the Galactic center than W-R stars, which are also highly evolved massive stars. Although with considerable uncertainty, it is estimated that the mass return by the M supergiants is somewhere between 0.00001 and 0.00003 solar mass/sq kpc yr. In the hemisphere facing the Galactic center there is much less mass loss from M supergiants than from W-R stars, but, in the anticenter direction, the M supergiants return more mass than do the W-R stars. The duration of the M supergiant phase appears to be between 200,000 and 400,000 yr. During this phase, a star of initially at least 20 solar masses returns perhaps 3-10 solar masses into the interstellar medium.

On the nature of Upsilon Sagittarii

NASA Technical Reports Server (NTRS)

Schoenberner, D.; Drilling, J. S.

1983-01-01

An explanation for the nature and evolution of the extremely hydrogen deficient binary Upsilon Sagittarii which is consistent with all observational and theoretical facts. First, the system goes through a Case B mass exchange in which most of the hydrogen rich envelope of a massive primary (5 to 14 solar masses) is lost. The remaining envelope still contains about 50 percent hydrogen (by number), but is now of negligible mass, so that the star evolves like a pure helium star. If its mass is between 1 and 2 solar masses the star reaches low surface temperatures and becomes a supergiant before the onset of carbon burning. This star (the original primary) then fills its Roche lobe a second time,spilling its now helium rich envelope over onto the secondary (Case BB mass exchange). It is argued that Upsilon Sagittarii is in this state at the present time, and that the visible star is an evolved helium star of about 1 solar mass with a degenerate carbon-oxygen core and a helium burning shell which provides the high luminosity. Previously announced in Star as N26117

Mass-loss rates and luminosities of evolved stars in the Magellanic Clouds .

NASA Astrophysics Data System (ADS)

Groenewegen, M. A. T.; Sloan, G. C.

Stars on the asymptotic giant branch (AGB) stars play an important role in the chemical evolution of their host galaxies and the life cycle of dust in the interstellar medium. A detailed and quantitative understanding of they lose mass and eject their envelopes remains elusive, particularly how that process depends on metallicity. Groenewegen & Sloan (2017, hereafter GS17) recently presented dust radiative transfer models for 225 carbon stars and 171 oxygen-rich evolved stars in the Magellanic Clouds and four nearby dSphs which were observed with the Infrared spectrograph on the Spitzer Space Telescope. They applied a minimisation procedure to fit models to spectral energy distributions constructed from the infrared spectra and the available optical and infrared photometry for each star to determine its luminosity and dust mass-loss rate (MLR). In this contribution two items from that paper are highlighted: an update on MSX SMC 055, which Groenewegen et al. (2009) suggested could be a super-AGB star, and a discussion of synthetic colour-colour and colour-magnitude diagrams expected from the James Webb Space Telescope.

Finding evolved stars in the inner Galactic disk with Gaia

NASA Astrophysics Data System (ADS)

Quiroga-Nuñez, L. H.; van Langevelde, H. J.; Pihlström, Y. M.; Sjouwerman, L. O.; Brown, A. G. A.

2018-04-01

The Bulge Asymmetries and Dynamical Evolution (BAaDE) survey will provide positions and line-of-sight velocities of ~20, 000 evolved, maser bearing stars in the Galactic plane. Although this Galactic region is affected by optical extinction, BAaDE targets may have Gaia cross-matches, eventually providing additional stellar information. In an initial attempt to cross-match BAaDE targets with Gaia, we have found more than 5,000 candidates. Of these, we may expect half to show SiO emission, which will allow us to obtain velocity information. The cross-match is being refined to avoid false positives using different criteria based on distance analysis, flux variability, and color assessment in the mid- and near-IR. Once the cross-matches can be confirmed, we will have a unique sample to characterize the stellar population of evolved stars in the Galactic bulge, which can be considered fossils of the Milky Way formation.

Coronagraphic imaging of circumstellar material around evolved massive stars

NASA Astrophysics Data System (ADS)

Lomax, Jamie R.; Levesque, Emily; Wisniewski, John

2018-01-01

While many astronomical subfields (e.g. the solar, exoplanet, and disk communities) have been using coronagraphy to combat contrast ratio problems for years, the use of coronagraphic imaging techniques to probe the circumstellar environments of massive stars has been surprisingly underutilized. While current extreme adaptive optics coronagraphic imaging systems (e.g. GPI on Gemini South, SPHERE at the VLT, and SCExAO at Subaru) were built for the sole purpose of detecting exoplanets, their ability to provide large contrast ratios and small inner working angles means they can detect gas, dust, and companions that are closer to the central star than ever before. In this poster we present pilot studies of evolved massive stars using several coronagraphic imaging systems and summarize potential science gains this technique might provide.

The VLTI/MIDI view on the inner mass loss of evolved stars from the Herschel MESS sample

NASA Astrophysics Data System (ADS)

Paladini, C.; Klotz, D.; Sacuto, S.; Lagadec, E.; Wittkowski, M.; Richichi, A.; Hron, J.; Jorissen, A.; Groenewegen, M. A. T.; Kerschbaum, F.; Verhoelst, T.; Rau, G.; Olofsson, H.; Zhao-Geisler, R.; Matter, A.

2017-04-01

Context. The mass-loss process from evolved stars is a key ingredient for our understanding of many fields of astrophysics, including stellar evolution and the chemical enrichment of the interstellar medium (ISM) via stellar yields. Nevertheless, many questions are still unsolved, one of which is the geometry of the mass-loss process. Aims: Taking advantage of the results from the Herschel Mass loss of Evolved StarS (MESS) programme, we initiated a coordinated effort to characterise the geometry of mass loss from evolved red giants at various spatial scales. Methods: For this purpose we used the MID-infrared interferometric Instrument (MIDI) to resolve the inner envelope of 14 asymptotic giant branch stars (AGBs) in the MESS sample. In this contribution we present an overview of the interferometric data collected within the frame of our Large Programme, and we also add archive data for completeness. We studied the geometry of the inner atmosphere by comparing the observations with predictions from different geometric models. Results: Asymmetries are detected for the following five stars: R Leo, RT Vir, π1Gruis, omi Ori, and R Crt. All the objects are O-rich or S-type, suggesting that asymmetries in the N band are more common among stars with such chemistry. We speculate that this fact is related to the characteristics of the dust grains. Except for one star, no interferometric variability is detected, I.e. the changes in size of the shells of non-mira stars correspond to changes of the visibility of less than 10%. The observed spectral variability confirms previous findings from the literature. The detection of dust in our sample follows the location of the AGBs in the IRAS colour-colour diagram: more dust is detected around oxygen-rich stars in region II and in the carbon stars in region VII. The SiC dust feature does not appear in the visibility spectrum of the U Ant and S Sct, which are two carbon stars with detached shells. This finding has implications for the theory of SiC dust formation. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programmes 073.D-0711, 076.D-0620, 077.D-0294, 078.D-0122, 080.D-0801, 081.D-0021, 083.D-0234, 086.D-0737, 086.D-899, 187.D-0924, 089.D-0562, 090.D-410, 091.C-0468, 091.D-0344.

Double core evolution. 7: The infall of a neutron star through the envelope of its massive star companion

NASA Technical Reports Server (NTRS)

Terman, James L.; Taam, Ronald E.; Hernquist, Lars

1995-01-01

Binary systems with properties similar to those of high-mass X-ray binaries are evolved through the common envelope phase. Three-dimensional simulations show that the timescale of the infall phase of the neutron star depends upon the evolutionary state of its massive companion. We find that tidal torques more effectively accelerate common envelope evolution for companions in their late core helium-burning stage and that the infall phase is rapid (approximately several initial orbital periods). For less evolved companions the decay of the orbit is longer; however, once the neutron star is deeply embedded within the companion's envelope the timescale for orbital decay decreases rapidly. As the neutron star encounters the high-density region surrounding the helium core of its massive companion, the rate of energy loss from the orbit increases dramatically leading to either partial or nearly total envelope ejection. The outcome of the common envelope phase depends upon the structure of the evolved companion. In particular, it is found that the entire common envelope can be ejected by the interaction of the neutron star with a red supergiant companion in binaries with orbital periods similar to those of long-period Be X-ray binaries. For orbital periods greater than or approximately equal to 0.8-2 yr (for companions of mass 12-24 solar mass) it is likely that a binary will survive the common envelope phase. For these systems, the structure of the progenitor star is characterized by a steep density gradient above the helium core, and the common envelope phase ends with a spin up of the envelope to within 50%-60% of corotation and with a slow mass outflow. The efficiency of mass ejection is found to be approximately 30%-40%. For less evolved companions, there is insufficient energy in the orbit to unbind the common envelope and only a fraction of it is ejected. Since the timescale for orbital decay is always shorter than the mass-loss timescale from the common envelope, the two cores will likely merge to form a Thorne-Zytkow object. Implications for the origin of Cyg X-3, an X-ray source consisting of a Wolf-Rayet star and a compact companion, and for the fate of the remnant binary consisting of a helium star and a neutron star are briefly discussed.

Post-AGB Stars in Nearby Galaxies as Calibrators for HST

NASA Technical Reports Server (NTRS)

Bond, Howard E.

2003-01-01

This report summarizes activities carried out with support from the NASA Ultraviolet, Visible, and Gravitational Astrophysics Research and Analysis Program under Grant NAG 5-6821. The Principal Investigator is Howard E. Bond (Space Telescope Science Institute). STScI Postdoctoral Associates Laura K. Fullton (1998), David Alves (1998-2001), and Michael Siegel (2001) were partially supported by this grant. The aim of the program is to calibrate the absolute magnitudes of post-asymptotic- giant-branch (post-AGB or PAGB) stars, which we believe will be an excellent new "standard candle" for measuring extragalactic distances. The argument is that, in old populations, the stars that are evolving through the PAGB region of the HR diagram arise from only a single main-sequence turnoff mass. In addition, theoretical PAGB evolutionary tracks show that they evolve through this region at constant luminosity; hence the PAGB stars should have an extremely narrow luminosity function. Moreover, as the PAGB stars evolve through spectral types F and A (en route from the AGB to hot stellar remnants and white dwarfs), they have the highest luminosities attained by old stars (both bolometrically and in the visual band). Finally, PAGB stars of these spectral types are very easily identified. because of their large Balmer jumps, which are due to their very low surface gravities. Our approach is first to identify PAGB stars in Milky Way globular clusters and in other Local Group galaxies, which are at known distances, and thus to measure accurate absolute magnitudes for the PAGB stars. With this Milky Way and Local Group luminosity calibration, we will then be in a position to find PAGB stars in more distant galaxies from the ground, and ultimately from the Hubble Space Telescope. and thus derive distances. These PAGB stars are, as noted above, the visually brightest members of Population II, and hence will allow distance measurements to galaxies that do not contain Cepheids, such as elliptical galaxies, as well as distances to spirals using PAGB stars in their halos. Moreover, the method is entirely independent of Cepheids. and thus provides a direct test of the Cepheid distance scale. The program will also provide information on the evolutionary lifetimes of PAGB stars.

Many-particle theory of nuclear system with application to neutron-star matter and other systems

NASA Technical Reports Server (NTRS)

Yang, C. H.

1978-01-01

General problems in nuclear-many-body theory were considered. Superfluid states of neutron star matter and other strongly interacting many-fermion systems were analyzed by using the soft-core potential of Reid. The pion condensation in neutron star matter was also treated.

Equation of state of dense nuclear matter and neutron star structure from nuclear chiral interactions

NASA Astrophysics Data System (ADS)

Bombaci, Ignazio; Logoteta, Domenico

2018-02-01

Aims: We report a new microscopic equation of state (EOS) of dense symmetric nuclear matter, pure neutron matter, and asymmetric and β-stable nuclear matter at zero temperature using recent realistic two-body and three-body nuclear interactions derived in the framework of chiral perturbation theory (ChPT) and including the Δ(1232) isobar intermediate state. This EOS is provided in tabular form and in parametrized form ready for use in numerical general relativity simulations of binary neutron star merging. Here we use our new EOS for β-stable nuclear matter to compute various structural properties of non-rotating neutron stars. Methods: The EOS is derived using the Brueckner-Bethe-Goldstone quantum many-body theory in the Brueckner-Hartree-Fock approximation. Neutron star properties are next computed solving numerically the Tolman-Oppenheimer-Volkov structure equations. Results: Our EOS models are able to reproduce the empirical saturation point of symmetric nuclear matter, the symmetry energy Esym, and its slope parameter L at the empirical saturation density n0. In addition, our EOS models are compatible with experimental data from collisions between heavy nuclei at energies ranging from a few tens of MeV up to several hundreds of MeV per nucleon. These experiments provide a selective test for constraining the nuclear EOS up to 4n0. Our EOS models are consistent with present measured neutron star masses and particularly with the mass M = 2.01 ± 0.04 M⊙ of the neutron stars in PSR J0348+0432.

A possible origin of the Galactic Center magnetar SGR 1745-2900

NASA Astrophysics Data System (ADS)

Cheng, Quan; Zhang, Shuang-Nan; Zheng, Xiao-Ping

2017-05-01

Since there is a large population of massive O/B stars and putative neutron stars (NSs) located in the vicinity of the Galactic Center (GC), intermediate-mass X-ray binaries (IMXBs) constituted by an NS and a B-type star probably exist there. We investigate the evolutions of accreting NSs in IMXBs (similar to M82 X-2) with a ˜ 5.2 {M}⊙ companion and orbital period ≃ 2.53 d. By adopting a mildly super-Eddington rate \\dot{M}=6× {10}-8 {M}⊙ {{yr}}-1 for the early Case B Roche-lobe overflow (RLOF) accretion, we find that only in accreting NSs with quite elastic crusts (slippage factor s = 0.05) can the toroidal magnetic fields be amplified within 1 Myr, which is assumed to be the longest duration of the RLOF. These IMXBs will evolve into NS+white dwarf (WD) binaries if they are dynamically stable. However, before the formation of NS+WD binaries, the high stellar density in the GC will probably lead to frequent encounters between the NS+evolved star binaries (in post-early Case B mass transfer phase) and NSs or exchange encounters with other stars, which may produce single NSs. These NSs will evolve into magnetars when the amplified poloidal magnetic fields diffuse out to the NS surfaces. Consequently, our results provide a possible explanation for the origin of the GC magnetar SGR 1745-2900. Moreover, the accreting NSs with s> 0.05 will evolve into millisecond pulsars (MSPs). Therefore, our model reveals that the GC magnetars and MSPs could both originate from a special kind of IMXB.

Supernova 2007bi as a pair-instability explosion.

PubMed

Gal-Yam, A; Mazzali, P; Ofek, E O; Nugent, P E; Kulkarni, S R; Kasliwal, M M; Quimby, R M; Filippenko, A V; Cenko, S B; Chornock, R; Waldman, R; Kasen, D; Sullivan, M; Beshore, E C; Drake, A J; Thomas, R C; Bloom, J S; Poznanski, D; Miller, A A; Foley, R J; Silverman, J M; Arcavi, I; Ellis, R S; Deng, J

2009-12-03

Stars with initial masses such that 10M[symbol: see text] or= 140M[symbol: see text] (if such exist) develop oxygen cores with masses, M(core), that exceed 50M[symbol: see text], where high temperatures are reached at relatively low densities. Conversion of energetic, pressure-supporting photons into electron-positron pairs occurs before oxygen ignition and leads to a violent contraction which triggers a nuclear explosion that unbinds the star in a pair-instability supernova. Transitional objects with 100M[symbol: see text] < M(initial) < 140M[symbol: see text] may end up as iron-core-collapse supernovae following violent mass ejections, perhaps as a result of brief episodes of pair instability, and may already have been identified. Here we report observations of supernova SN 2007bi, a luminous, slowly evolving object located within a dwarf galaxy. We estimate the exploding core mass to be M(core) approximately 100M[symbol: see text], in which case theory unambiguously predicts a pair-instability supernova. We show that >3M[symbol: see text] of radioactive (56)Ni was synthesized during the explosion and that our observations are well fitted by models of pair-instability supernovae. This indicates that nearby dwarf galaxies probably host extremely massive stars, above the apparent Galactic stellar mass limit, which perhaps result from processes similar to those that created the first stars in the Universe.

UPDATED MASS SCALING RELATIONS FOR NUCLEAR STAR CLUSTERS AND A COMPARISON TO SUPERMASSIVE BLACK HOLES

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

Scott, Nicholas; Graham, Alister W.

2013-02-15

We investigate whether or not nuclear star clusters and supermassive black holes (SMBHs) follow a common set of mass scaling relations with their host galaxy's properties, and hence can be considered to form a single class of central massive object (CMO). We have compiled a large sample of galaxies with measured nuclear star cluster masses and host galaxy properties from the literature and fit log-linear scaling relations. We find that nuclear star cluster mass, M {sub NC}, correlates most tightly with the host galaxy's velocity dispersion: log M {sub NC} = (2.11 {+-} 0.31)log ({sigma}/54) + (6.63 {+-} 0.09), butmore » has a slope dramatically shallower than the relation defined by SMBHs. We find that the nuclear star cluster mass relations involving host galaxy (and spheroid) luminosity and stellar and dynamical mass, intercept with but are in general shallower than the corresponding black hole scaling relations. In particular, M {sub NC}{proportional_to}M {sup 0.55{+-}0.15} {sub Gal,dyn}; the nuclear cluster mass is not a constant fraction of its host galaxy or spheroid mass. We conclude that nuclear stellar clusters and SMBHs do not form a single family of CMOs.« less

VizieR Online Data Catalog: Common proper motion stars in the Kepler field (Janes, 2017)

NASA Astrophysics Data System (ADS)

Janes, K. A.

2017-08-01

In a search of proper motion catalogs for common proper motion stars in the field of the Kepler spacecraft I identified 93 likely binary systems. A comparison of their rotation periods is a test of the gyrochronology concept. To find their periods I calculated the autocorrelation function (ACF) of the Kepler mission photometry for each star. In most systems for which good periods can be found, the cooler star has a longer period than the hotter component, in general agreement with models. However, there is a wide range in the gradients of lines connecting binary pairs in a period-color diagram. Furthermore, near the solar color, only a few stars have longer periods than the Sun, suggesting that they, and their cooler companions, are not much older than the Sun. In addition, there is an apparent gap at intermediate periods in the period distribution of the late K and early M stars. Either star formation in this direction has been variable, or stars evolve in period at a non-uniform rate, or some stars evolve more rapidly than others at the same mass. Finally, using the ACF as a measure of the activity level, I found that while the F, G, and early K stars become less active as their periods increase, there is no correlation between period and activity for the mid K to early M stars. (1 data file).

Variational Theory of Hot Dense Matter

ERIC Educational Resources Information Center

Mukherjee, Abhishek

2009-01-01

We develop a variational theory of hot nuclear matter in neutron stars and supernovae. It can also be used to study charged, hot nuclear matter which may be produced in heavy-ion collisions. This theory is a generalization of the variational theory of cold nuclear and neutron star matter based on realistic models of nuclear forces and pair…

Colloquium: Astromaterial science and nuclear pasta

NASA Astrophysics Data System (ADS)

Caplan, M. E.; Horowitz, C. J.

2017-10-01

"Astromaterial science" is defined as the study of materials in astronomical objects that are qualitatively denser than materials on Earth. Astromaterials can have unique properties related to their large density, although they may be organized in ways similar to more conventional materials. By analogy to terrestrial materials, this study of astromaterials is divided into hard and soft and one example of each is discussed. The hard astromaterial discussed here is a crystalline lattice, such as the Coulomb crystals in the interior of cold white dwarfs and in the crust of neutron stars, while the soft astromaterial is nuclear pasta found in the inner crusts of neutron stars. In particular, how molecular dynamics simulations have been used to calculate the properties of astromaterials to interpret observations of white dwarfs and neutron stars is discussed. Coulomb crystals are studied to understand how compact stars freeze. Their incredible strength may make crust "mountains" on rotating neutron stars a source for gravitational waves that the Laser Interferometer Gravitational-Wave Observatory (LIGO) may detect. Nuclear pasta is expected near the base of the neutron star crust at densities of 1014 g /cm3 . Competition between nuclear attraction and Coulomb repulsion rearranges neutrons and protons into complex nonspherical shapes such as sheets (lasagna) or tubes (spaghetti). Semiclassical molecular dynamics simulations of nuclear pasta have been used to study these phases and calculate their transport properties such as neutrino opacity, thermal conductivity, and electrical conductivity. Observations of neutron stars may be sensitive to these properties and can be used to interpret observations of supernova neutrinos, magnetic field decay, and crust cooling of accreting neutron stars. This Colloquium concludes by comparing nuclear pasta shapes with some similar shapes seen in biological systems.

Quantifying the coexistence of massive black holes and dense nuclear star clusters

NASA Astrophysics Data System (ADS)

Graham, Alister W.; Spitler, Lee R.

2009-08-01

In large spheroidal stellar systems, such as elliptical galaxies, one invariably finds a 106-109Msolar supermassive black hole at their centre. In contrast, within dwarf elliptical galaxies one predominantly observes a 105-107Msolar nuclear star cluster. To date, few galaxies have been found with both types of nuclei coexisting and even less have had the masses determined for both central components. Here, we identify one dozen galaxies housing nuclear star clusters and supermassive black holes whose masses have been measured. This doubles the known number of such hermaphrodite nuclei - which are expected to be fruitful sources of gravitational radiation. Over the host spheroid (stellar) mass range 108-1011Msolar, we find that a galaxy's nucleus-to-spheroid (baryon) mass ratio is not a constant value but decreases from a few per cent to ~0.3 per cent such that log[(MBH + MNC)/Msph] = -(0.39 +/- 0.07) log[Msph/1010Msolar] - (2.18 +/- 0.07). Once dry merging commences and the nuclear star clusters disappear, this ratio is expected to become a constant value. As a byproduct of our investigation, we have found that the projected flux from resolved nuclear star clusters is well approximated with Sérsic functions having a range of indices from ~0.5 to ~3, the latter index describing the Milky Way's nuclear star cluster.

The fate of the Antennae galaxies

NASA Astrophysics Data System (ADS)

Lahén, Natalia; Johansson, Peter H.; Rantala, Antti; Naab, Thorsten; Frigo, Matteo

2018-04-01

We present a high-resolution smoothed particle hydrodynamic simulation of the Antennae galaxies (NGC 4038/4039) and follow the evolution 3 Gyr beyond the final coalescence. The simulation includes metallicity-dependent cooling, star formation, and both stellar feedback and chemical enrichment. The simulated best-match Antennae reproduce well both the observed morphology and the off-nuclear starburst. We also produce for the first time a simulated two-dimensional (2D) metallicity map of the Antennae and find good agreement with the observed metallicity of off-nuclear stellar clusters; however, the nuclear metallicities are overproduced by ˜0.5 dex. Using the radiative transfer code SKIRT, we produce multiwavelength observations of both the Antennae and the merger remnant. The 1-Gyr-old remnant is well fitted with a Sérsic profile of n = 7.07, and with an r-band effective radius of re = 1.6 kpc and velocity dispersion of σe = 180 km s-1 the remnant is located on the Fundamental Plane of early-type galaxies (ETGs). The initially blue Antennae remnant evolves on to the red sequence after ˜2.5 Gyr of secular evolution. The remnant would be classified as a fast rotator, as the specific angular momentum evolves from λRe ≈ 0.11 to 0.14 during its evolution. The remnant shows ordered rotation and a double peaked maximum in the mean 2D line-of-sight velocity. These kinematical features are relatively common amongst local ETGs and we specifically identify three local ETGs (NGC 3226, NGC 3379, and NGC 4494) in the atlas3D sample, whose photometric and kinematic properties most resemble the Antennae remnant.

Role of nuclear reactions on stellar evolution of intermediate-mass stars

NASA Astrophysics Data System (ADS)

Möller, H.; Jones, S.; Fischer, T.; Martínez-Pinedo, G.

2018-01-01

The evolution of intermediate-mass stars (8 - 12 solar masses) represents one of the most challenging subjects in nuclear astrophysics. Their final fate is highly uncertain and strongly model dependent. They can become white dwarfs, they can undergo electron-capture or core-collapse supernovae or they might even proceed towards explosive oxygen burning and a subsequent thermonuclear explosion. We believe that an accurate description of nuclear reactions is crucial for the determination of the pre-supernova structure of these stars. We argue that due to the possible development of an oxygen-deflagration, a hydrodynamic description has to be used. We implement a nuclear reaction network with ∼200 nuclear species into the implicit hydrodynamic code AGILE. The reaction network considers all relevant nuclear electron captures and beta-decays. For selected relevant nuclear species, we include a set of updated reaction rates, for which we discuss the role for the evolution of the stellar core, at the example of selected stellar models. We find that the final fate of these intermediate-mass stars depends sensitively on the density threshold for weak processes that deleptonize the core.

The UK Infrared Telescope M33 monitoring project - IV. Variable red giant stars across the galactic disc

NASA Astrophysics Data System (ADS)

Javadi, Atefeh; Saberi, Maryam; van Loon, Jacco Th.; Khosroshahi, Habib; Golabatooni, Najmeh; Mirtorabi, Mohammad Taghi

2015-03-01

We have conducted a near-infrared monitoring campaign at the UK InfraRed Telescope, of the Local Group spiral galaxy M33 (Triangulum). The main aim was to identify stars in the very final stage of their evolution, and for which the luminosity is more directly related to the birth mass than the more numerous less-evolved giant stars that continue to increase in luminosity. In this fourth paper of the series, we present a search for variable red giant stars in an almost square degree region comprising most of the galaxy's disc, carried out with the WFCAM (Wide Field CAMera) instrument in the K band. These data, taken during the period 2005-2007, were complemented by J- and H-band images. Photometry was obtained for 403 734 stars in this region; of these, 4643 stars were found to be variable, most of which are asymptotic giant branch (AGB) stars. The variable stars are concentrated towards the centre of M33, more so than low-mass, less-evolved red giants. Our data were matched to optical catalogues of variable stars and carbon stars and to mid-infrared photometry from the Spitzer Space Telescope. Most dusty AGB stars had not been previously identified in optical variability surveys, and our survey is also more complete for these types of stars than the Spitzer survey. The photometric catalogue is made publicly available at the Centre de Données astronomiques de Strasbourg.

Induced massive star formation in the trifid nebula?

PubMed

Cernicharo; Lefloch; Cox; Cesarsky; Esteban; Yusef-Zadeh; Mendez; Acosta-Pulido; Garcia Lopez RJ; Heras

1998-10-16

The Trifid nebula is a young (10(5) years) galactic HII region where several protostellar sources have been detected with the infrared space observatory. The sources are massive (17 to 60 solar masses) and are associated with molecular gas condensations at the edges or inside the nebula. They appear to be in an early evolutionary stage and may represent the most recent generation of stars in the Trifid. These sources range from dense, apparently still inactive cores to more evolved sources, undergoing violent mass ejection episodes, including a source that powers an optical jet. These observations suggest that the protostellar sources may have evolved by induced star formation in the Trifid nebula.

VizieR Online Data Catalog: MIPS 24um nebulae (Gvaramadze+, 2010)

NASA Astrophysics Data System (ADS)

Gvaramadze, V. V.; Kniazev, A. Y.; Fabrika, S.

2011-03-01

Massive evolved stars lose a large fraction of their mass via copious stellar wind or instant outbursts. During certain evolutionary phases, they can be identified by the presence of their circumstellar nebulae. In this paper, we present the results of a search for compact nebulae (reminiscent of circumstellar nebulae around evolved massive stars) using archival 24um data obtained with the Multiband Imaging Photometer for Spitzer. We have discovered 115 nebulae, most of which bear a striking resemblance to the circumstellar nebulae associated with luminous blue variables (LBVs) and late WN-type (WNL) Wolf-Rayet (WR) stars in the Milky Way and the Large Magellanic Cloud (LMC). (1 data file).

ROTATION PERIODS OF WIDE BINARIES IN THE KEPLER FIELD

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

Janes, K. A.

In a search of proper motion catalogs for common proper motion stars in the field of the Kepler spacecraft I identified 93 likely binary systems. A comparison of their rotation periods is a test of the gyrochronology concept. To find their periods I calculated the autocorrelation function (ACF) of the Kepler mission photometry for each star. In most systems for which good periods can be found, the cooler star has a longer period than the hotter component, in general agreement with models. However, there is a wide range in the gradients of lines connecting binary pairs in a period–color diagram.more » Furthermore, near the solar color, only a few stars have longer periods than the Sun, suggesting that they, and their cooler companions, are not much older than the Sun. In addition, there is an apparent gap at intermediate periods in the period distribution of the late K and early M stars. Either star formation in this direction has been variable, or stars evolve in period at a non-uniform rate, or some stars evolve more rapidly than others at the same mass. Finally, using the ACF as a measure of the activity level, I found that while the F, G, and early K stars become less active as their periods increase, there is no correlation between period and activity for the mid K to early M stars.« less

On the spectroscopic nature of the cool evolved Am star HD151878

NASA Astrophysics Data System (ADS)

Freyhammer, L. M.; Elkin, V. G.; Kurtz, D. W.

2008-10-01

Recently, Tiwari, Chaubey & Pandey detected the bright component of the visual binary HD151878 to exhibit rapid photometric oscillations through a Johnson B filter with a period of 6min (2.78mHz) and a high, modulated amplitude up to 22mmag peak-to-peak, making this star by far the highest amplitude rapidly oscillating Ap (roAp) star known. As a new roAp star, HD151878 is of additional particular interest as a scarce example of the class in the northern sky, and only the second known case of an evolved roAp star - the other being HD116114. We used the FIbre-fed Echelle Spectrograph at the Nordic Optical Telescope to obtain high time-resolution spectra at high dispersion to attempt to verify the rapid oscillations. We show here that the star at this epoch is spectroscopically stable to rapid oscillations of no more than a few tens of ms-1. The high-resolution spectra furthermore show the star to be of type Am rather than Ap and we show the star lacks most of the known characteristics for roAp stars. We conclude that this is an Am star that does not pulsate with a 6-min period. The original discovery of pulsation is likely to be an instrumental artefact. Based on observations collected at the Nordic Optical Telescope as part of programme 36-418. E-mail: lfreyham@gmail.com

Molecular Astrophysics from Space: the Physical and Chemical Effects of Star Formation and the Destruction of Planetary Systems around Evolved Stars

NASA Technical Reports Server (NTRS)

Neufeld, David

2005-01-01

The research conducted during the reporting period is grouped into three sections: 1) Warm molecular gas in the interstellar medium (ISM); 2) Absorption line studies of "cold" molecular clouds; 3) Vaporization of comets around the AGB star IRC+10216.

I-Love-Q: unexpected universal relations for neutron stars and quark stars.

PubMed

Yagi, Kent; Yunes, Nicolás

2013-07-26

Neutron stars and quark stars are not only characterized by their mass and radius but also by how fast they spin, through their moment of inertia, and how much they can be deformed, through their Love number and quadrupole moment. These depend sensitively on the star's internal structure and thus on unknown nuclear physics. We find universal relations between the moment of inertia, the Love number, and the quadrupole moment that are independent of the neutron and quark star's internal structure. These can be used to learn about neutron star deformability through observations of the moment of inertia, break degeneracies in gravitational wave detection to measure spin in binary inspirals, distinguish neutron stars from quark stars, and test general relativity in a nuclear structure-independent fashion.

Understand B-type stars

NASA Technical Reports Server (NTRS)

1982-01-01

When observations of B stars made from space are added to observations made from the ground and the total body of observational information is confronted with theoretical expectations about B stars, it is clear that nonthermal phenomena occur in the atmospheres of B stars. The nature of these phenomena and what they imply about the physical state of a B star and how a B star evolves are examined using knowledge of the spectrum of a B star as a key to obtaining an understanding of what a B star is like. Three approaches to modeling stellar structure (atmospheres) are considered, the characteristic properties of a mantle, and B stars and evolution are discussed.

TYC 3159-6-1: a runaway blue supergiant

NASA Astrophysics Data System (ADS)

Gvaramadze, V. V.; Miroshnichenko, A. S.; Castro, N.; Langer, N.; Zharikov, S. V.

2014-01-01

We report the results of optical spectroscopy of a candidate evolved massive star in the Cygnus-X region, TYC 3159-6-1, revealed via detection of its curious circumstellar nebula in archival data of the Spitzer Space Telescope. We classify TYC 3159-6-1 as an O9.5-O9.7 Ib star and derive its fundamental parameters by using the stellar atmosphere code FASTWIND. The He and CNO abundances in the photosphere of TYC 3159-6-1 are consistent with the solar abundances, suggesting that the star only recently evolved off the main sequence. Proper motion and radial velocity measurements for TYC 3159-6-1 show that it is a runaway star. We propose that Dolidze 7 is its parent cluster. We discuss the origin of the nebula around TYC 3159-6-1 and suggest that it might be produced in several successive episodes of enhanced mass-loss rate (outbursts) caused by rotation of the star near the critical Ω limit.

Star Shows It Has The Right Stuff

NASA Astrophysics Data System (ADS)

2004-01-01

Astronomers have used an observation by NASA's Chandra X-ray Observatory to make the best case yet that a star can be engulfed by its companion star and survive. This discovery will help astronomers better understand how closely coupled stars, and perhaps even stars and planets, evolve when one of the stars expands enormously in its red giant phase. The binary star system known as V471 Tauri comprises a white dwarf star (the primary) in a close orbit -- one thirtieth of the distance between Mercury and the Sun -- with a normal Sun-like star (the secondary). Chandra's data showed that the hot upper atmosphere of the secondary star has a deficit of carbon atoms relative to nitrogen atoms. "This deficit of carbon atoms is the first clear observational evidence that the normal star was engulfed by its companion in the past," according to Jeremy Drake of the Smithsonian Astrophysical Observatory in Cambridge, MA, who coauthored an article on V471 in The Astrophysical Journal Letters with Marek Sarna of the N. Copernicus Astronomical Center in Poland. The white dwarf star was once a star several times as massive as the Sun. Nuclear fusion reactions in the core of such a star convert carbon into nitrogen over a period of about a billion years. When the fuel in the core of the star is exhausted, the core collapses, triggering more energetic nuclear reactions that cause the star to expand and transform into a red giant before eventually collapsing to become a white dwarf. The carbon-poor material in the core of the red giant is mixed with outer part of the star, so its atmosphere shows a deficit of carbon, as compared with Sun-like stars. The X-ray spectra of a red giant star (top panel) and a Sun-like star (bottom panel) show the large difference in the peaks due to carbon atoms in the two stars. Theoretical calculations indicate that a red giant in a binary system can completely envelop its companion star and dramatically affect its evolution. During this common envelope phase, friction causes the companion star to spiral inward rapidly where it will either be destroyed by the red giant, or it will survive when much of the envelope is spun away. If the companion star manages to survive, it will bear the marks of its ordeal in the form of contamination by carbon-poor material that it accreted while it was inside the red giant envelope. The X-ray spectrum of V471 Tauri in the middle panel shows just this effect - the carbon peak is intermediate between that of a Sun-like star and an isolated red giant star. The data indicate that about 10 percent of the star's mass has been accreted from the red giant. In the future the companion star can return the favor when it expands and dumps material back onto the white dwarf. If enough material is dumped on the white dwarf, it could cause the white dwarf to explode as a supernova. "It's a dog-eat-dog world out there," observed Drake. V471 Tau was observed for approximately one day by Chandra using the Low Energy Transmission Grating and High Resolution Camera on January 24-25, 2002. NASA's Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for the Office of Space Science, NASA Headquarters, Washington. Northrop Grumman of Redondo Beach, Calif., formerly TRW, Inc., was the prime development contractor for the observatory. The Smithsonian Astrophysical Observatory controls science and flight operations from the Chandra X-ray Center in Cambridge, Mass.

Advanced Spectral Library (ASTRAL): Atomic Fluorescence in Cool, Evolved Stars

NASA Astrophysics Data System (ADS)

Carpenter, Ken G.; Nielsen, Krister E.; Kober, Gladys V.; Rau, Gioia

2018-01-01

The "Advanced Spectral Library (ASTRAL) Project: Cool Stars" (PI = T. Ayres) collected a definitive set of representative, high-resolution (R~46,000 in the FUV up to ~1700 Å, R~30,000 for 1700-2150 Å, and R~114,000 >2150 Å) and high signal/noise (S/N>100) UV spectra of eight F-M evolved cool stars. These extremely high-quality STIS UV echelle spectra are available from the HST archive and from the Univ. of Colorado (http://casa.colorado.edu/~ayres/ASTRAL/) and will enable investigations of a broad range of problems -- stellar, interstellar, and beyond -- for many years. In this paper, we extend our study of the very rich emission-line spectra of the four evolved K-M stars in the sample, Beta Gem (K0 IIIb), Gamma Dra (K5 III), Gamma Cru (M3.4 III), and Alpha Ori (M2 Iab), to study the atomic fluorescence processes operating in their outer atmospheres. We summarize the pumping transitions and fluorescent line products known on the basis of previous work (e.g. Carpenter 1988, etc.) and newly identified in our current, on-going analysis of these extraordinary ASTRAL STIS spectra.

Kinematical evolution of tidally limited star clusters: rotational properties

NASA Astrophysics Data System (ADS)

Tiongco, Maria A.; Vesperini, Enrico; Varri, Anna Lisa

2017-07-01

We present the results of a set of N-body simulations following the long-term evolution of the rotational properties of star cluster models evolving in the external tidal field of their host galaxy, after an initial phase of violent relaxation. The effects of two-body relaxation and escape of stars lead to a redistribution of the ordered kinetic energy from the inner to the outer regions, ultimately determining a progressive general loss of angular momentum; these effects are reflected in the overall decline of the rotation curve as the cluster evolves and loses stars. We show that all of our models share the same dependence of the remaining fraction of the initial rotation on the fraction of the initial mass lost. As the cluster evolves and loses part of its initial angular momentum, it becomes increasingly dominated by random motions, but even after several tens of relaxation times, and losing a significant fraction of its initial mass, a cluster can still be characterized by a non-negligible ratio of the rotational velocity to the velocity dispersion. This result is in qualitative agreement with the recently observed kinematical complexity that characterizes several Galactic globular clusters.

Constraints on the symmetry energy from neutron star observations

NASA Astrophysics Data System (ADS)

Newton, W. G.; Gearheart, M.; Wen, De-Hua; Li, Bao-An

2013-03-01

The modeling of many neutron star observables incorporates the microphysics of both the stellar crust and core, which is tied intimately to the properties of the nuclear matter equation of state (EoS). We explore the predictions of such models over the range of experimentally constrained nuclear matter parameters, focusing on the slope of the symmetry energy at nuclear saturation density L. We use a consistent model of the composition and EoS of neutron star crust and core matter to model the binding energy of pulsar B of the double pulsar system J0737-3039, the frequencies of torsional oscillations of the neutron star crust and the instability region for r-modes in the neutron star core damped by electron-electron viscosity at the crust-core interface. By confronting these models with observations, we illustrate the potential of astrophysical observables to offer constraints on poorly known nuclear matter parameters complementary to terrestrial experiments, and demonstrate that our models consistently predict L < 70 MeV.

Constraints on Bygone Nucleosynthesis of Accreting Neutron Stars

DOE PAGES

Meisel, Zach; Deibel, Alex

2017-03-06

Nuclear burning near the surface of an accreting neutron star produces ashes that, when compressed deeper by further accretion, alter the star’s thermal and compositional structure. Bygone nucleosynthesis can be constrained by the impact of compressed ashes on the thermal relaxation of quiescent neutron star transients. In particular, Urca cooling nuclei pairs in nuclear burning ashes that cool the neutron star crust via neutrino emission from e --capture/β --decay cycles and provide signatures of prior nuclear burning over the ~century timescales it takes to accrete to the e --capture depth of the strongest cooling pairs. By using crust cooling modelsmore » of the accreting neutron star transient MAXI J0556-332, we show that this source likely lacked Type I X-ray bursts and superbursts ≳120 years ago. Reduced nuclear physics uncertainties in rp-process reaction rates and e --capture weak transition strengths for low-lying transitions will improve nucleosynthesis constraints using this technique.« less

Circumnuclear star formation in Mrk 42 mapped with Gemini Near-infrared Integral Field Spectrograph

NASA Astrophysics Data System (ADS)

Hennig, Moiré G.; Riffel, Rogemar A.; Dors, O. L.; Riffel, Rogerio; Storchi-Bergmann, Thaisa; Colina, Luis

2018-06-01

We present Gemini Near-infrared Integral Field Spectrograph (NIFS) observations of the inner 1.5 × 1.5 kpc2 of the narrow-line Seyfert 1 galaxy Mrk 42 at a spatial resolution of 60 pc and spectral resolution of 40 km s^{-1}. The emission-line flux and equivalent width maps clearly show a ring of circumnuclear star formation regions surrounding the nucleus with radius of ˜500 pc. The spectra of some of these regions show molecular absorption features which are probably of CN, TiO, or VO, indicating the presence of massive evolved stars in the thermally pulsing asymptotic giant branch phase. The gas kinematics of the ring is dominated by rotation in the plane of the galaxy, following the large-scale disc geometry, while at the nucleus an additional outflowing component is detected blueshifted by 300-500 km s^{-1}, relative to the systemic velocity of the galaxy. Based on the equivalent width of Br γ we find pieces of evidence of gradients in the age of H II regions along the ring of Mrk 42, favouring the pearls on a string scenario of star formation. The broad component of Pa β emission line presents a Full Width at Half Maximum of ˜1480 km s^{-1}, implying in a mass of ˜2.5 × 106 M⊙ for the central supermassive black hole. Based on emission-line ratios we conclude that besides the active galactic nucleus, Mrk 42 presents nuclear Starburst activity.

The Novel Poly(A) Polymerase Star-PAP is a Signal-Regulated Switch at the 3′-end of mRNAs

PubMed Central

Li, Weimin; Laishram, Rakesh S.; Anderson, Richard A.

2013-01-01

The mRNA 3′-untranslated region (3′-UTR) modulates message stability, transport, intracellular location and translation. We have discovered a novel nuclear poly(A) polymerase termed Star-PAP (nuclear speckle targeted PIPKIα regulated-poly(A) polymerase) that couples with the transcriptional machinery and is regulated by the phosphoinositide lipid messenger phosphatidylinositol-4,5-bisphosphate (PI4,5P2), the central lipid in phosphoinositide signaling. PI4,5P2 is generated primarily by type I phosphatidylinositol phosphate kinases (PIPKI). Phosphoinositides are present in the nucleus including at nuclear speckles compartments separate from known membrane structures. PIPKs regulate cellular functions by interacting with PI4,5P2 effectors where PIPKs generate PI4,5P2 that then modulates the activity of the associated effectors. Nuclear PIPKIα interacts with and regulates Star-PAP, and PI4,5P2 specifically activates Star-PAP in a gene- and signaling-dependent manner. Importantly, other select signaling molecules integrated into the Star-PAP complex seem to regulate Star-PAP activities and processivities toward RNA substrates, and unique sequence elements around the Star-PAP binding sites within the 3′-UTR of target genes contribute to Star-PAP specificity for processing. Therefore, Star-PAP and its regulatory molecules form a signaling nexus at the 3′-end of target mRNAs to control the expression of select group of genes including the ones involved in stress responses. PMID:23306079

THROES: a caTalogue of HeRschel Observations of Evolved Stars. I. PACS range spectroscopy

NASA Astrophysics Data System (ADS)

Ramos-Medina, J.; Sánchez Contreras, C.; García-Lario, P.; Rodrigo, C.; da Silva Santos, J.; Solano, E.

2018-03-01

This is the first of a series of papers presenting the THROES (A caTalogue of HeRschel Observations of Evolved Stars) project, intended to provide a comprehensive overview of the spectroscopic results obtained in the far-infrared (55-670 μm) with the Herschel space observatory on low-to-intermediate mass evolved stars in our Galaxy. Here we introduce the catalogue of interactively reprocessed Photoconductor Array Camera and Spectrometer (PACS) spectra covering the 55-200 μm range for 114 stars in this category for which PACS range spectroscopic data is available in the Herschel Science Archive (HSA). Our sample includes objects spanning a range of evolutionary stages, from the asymptotic giant branch to the planetary nebula phase, displaying a wide variety of chemical and physical properties. The THROES/PACS catalogue is accessible via a dedicated web-based interface and includes not only the science-ready Herschel spectroscopic data for each source, but also complementary photometric and spectroscopic data from other infrared observatories, namely IRAS, ISO, or AKARI, at overlapping wavelengths. Our goal is to create a legacy-value Herschel dataset that can be used by the scientific community in the future to deepen our knowledge and understanding of these latest stages of the evolution of low-to-intermediate mass stars. The THROES/PACS catalogue is accessible at http://https://throes.cab.inta-csic.es/

Interferometric diameters of five evolved intermediate-mass planet-hosting stars measured with PAVO at the CHARA Array

NASA Astrophysics Data System (ADS)

White, T. R.; Huber, D.; Mann, A. W.; Casagrande, L.; Grunblatt, S. K.; Justesen, A. B.; Silva Aguirre, V.; Bedding, T. R.; Ireland, M. J.; Schaefer, G. H.; Tuthill, P. G.

2018-04-01

Debate over the planet occurrence rates around intermediate-mass stars has hinged on the accurate determination of masses of evolved stars, and has been exacerbated by a paucity of reliable, directly-measured fundamental properties for these stars. We present long-baseline optical interferometry of five evolved intermediate-mass (˜ 1.5 M⊙) planet-hosting stars using the PAVO beam combiner at the CHARA Array, which we combine with bolometric flux measurements and parallaxes to determine their radii and effective temperatures. We measured the radii and effective temperatures of 6 Lyncis (5.12±0.16 R⊙, 4949±58 K), 24 Sextantis (5.49±0.18 R⊙, 4908±65 K), κ Coronae Borealis (4.77±0.07 R⊙, 4870±47 K), HR 6817 (4.45±0.08 R⊙, 5013±59 K), and HR 8641 (4.91±0.12 R⊙, 4950±68 K). We find disagreements of typically 15 % in angular diameter and ˜ 200 K in temperature compared to interferometric measurements in the literature, yet good agreement with spectroscopic and photometric temperatures, concluding that the previous interferometric measurements may have been affected by systematic errors exceeding their formal uncertainties. Modelling based on BaSTI isochrones using various sets of asteroseismic, spectroscopic, and interferometric constraints tends to favour slightly (˜ 15 %) lower masses than generally reported in the literature.

Interferometric diameters of five evolved intermediate-mass planet-hosting stars measured with PAVO at the CHARA Array

NASA Astrophysics Data System (ADS)

White, T. R.; Huber, D.; Mann, A. W.; Casagrande, L.; Grunblatt, S. K.; Justesen, A. B.; Silva Aguirre, V.; Bedding, T. R.; Ireland, M. J.; Schaefer, G. H.; Tuthill, P. G.

2018-07-01

Debate over the planet occurrence rates around intermediate-mass stars has hinged on the accurate determination of masses of evolved stars, and has been exacerbated by a paucity of reliable, directly measured fundamental properties for these stars. We present long-baseline optical interferometry of five evolved intermediate-mass (˜ 1.5 M⊙) planet-hosting stars using the PAVO beam combiner at the CHARA Array, which we combine with bolometric flux measurements and parallaxes to determine their radii and effective temperatures. We measured the radii and effective temperatures of 6 Lyncis (5.12 ± 0.16 R⊙, 4949 ± 58 K), 24 Sextantis (5.49 ± 0.18 R⊙, 4908 ± 65 K), κ Coronae Borealis (4.77 ± 0.07 R⊙, 4870 ± 47 K), HR 6817 (4.45 ± 0.08 R⊙, 5013 ± 59 K), and HR 8461 (4.91 ± 0.12 R⊙, 4950 ± 68 K). We find disagreements of typically 15 per cent in angular diameter and ˜200 K in temperature compared to interferometric measurements in the literature, yet good agreement with spectroscopic and photometric temperatures, concluding that the previous interferometric measurements may have been affected by systematic errors exceeding their formal uncertainties. Modelling based on BaSTI isochrones using various sets of asteroseismic, spectroscopic, and interferometric constraints tends to favour slightly (˜15 per cent) lower masses than generally reported in the literature.

QUANTIFYING THE HEATING SOURCES FOR MID-INFRARED DUST EMISSIONS IN GALAXIES: THE CASE OF M 81

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

Lu, N.; Zhao, Y.; Bendo, G. J.

2014-12-20

With the newly available photometric images at 250 and 500 μm from the Herschel Space Observatory, we study quantitative correlations over a sub-kiloparsec scale among three distinct emission components in the interstellar medium of the nearby spiral galaxy M 81 (NGC 3031): (1) I {sub 8} or I {sub 24}, the surface brightness of the mid-infrared emission observed in the Spitzer Space Telescope 8 or 24 μm band, with I {sub 8} and I {sub 24} being dominated by the emissions from polycyclic aromatic hydrocarbons (PAHs) and very small grains (VSGs) of dust, respectively; (2) I {sub 500}, that of the coldmore » dust continuum emission in the Herschel Space Observatory 500 μm band, dominated by the emission from large dust grains heated by evolved stars; and (3) I {sub Hα}, a nominal surface brightness of the Hα line emission, from gas ionized by newly formed massive stars. The results from our correlation study, free from any assumption on or modeling of dust emissivity law or dust temperatures, present solid evidence for significant heating of PAHs and VSGs by evolved stars. In the case of M 81, about 67% (48%) of the 8 μm (24 μm ) emission derives its heating from evolved stars, with the remainder attributed to radiation heating associated with ionizing stars.« less

Building Blocks of Dust and Large Organic Molecules: a Coordinated Laboratory and Astronomical Study of AGB Stars

NASA Astrophysics Data System (ADS)

McCarthy, Michael C.; Gottlieb, Carl A.; Cernicharo, Jose

2017-06-01

The increased sensitivity and angular resolution of high-altitude ground-based interferometers in the sub-millimeter band has enabled the physics and chemistry of carbon- and oxygen-rich evolved stars to be re-examined at an unprecedented level of detail. Observations of rotational lines in the inner envelope - the region within a few stellar radii of the central star where the molecular seeds of dust are formed - allows one to critically assess models of dust growth. Interferometric observations of the outer envelope provide stringent tests of neutral and ionized molecule formation. All of the astronomical studies are crucially dependent on precise laboratory measurements of the rotational spectra of new species and of vibrationally excited levels of known molecules and their rare isotopic species. By means of a closely coordinated laboratory and astronomical program, a number of exotic species including the disilicon carbide SiCSi, titanium oxides TiO and TiO_2, and carbon chain anions ranging from CN^- to C_8H^- have recently been observed in evolved stars. This talk will provide overview of these findings, and how they impact current models of the ``chemical laboratories'' of evolved stars. Ongoing laboratory studies of small silicon-bearing molecules such as H_2SiO_2 and vibrationally excited SiC_2 will be highlighted.

Large Magellanic Cloud helium-rich peculiar blue supergiants and SN 1987A

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

Tuchman, Y.; Wheeler, J.C.

1990-11-01

The theoretical distribution of massive stars in the H-R diagram is compared to the revised data of Fitzpatrick and Garmany for the LMC. Preferred models of about 20 M solar masses undergo a thermal contraction at T(eff) about 35,000 K at the end of core hydrogen burning but reestablish thermal equilibrium to the red of the main sequence at T(eff) about 20,000 K after ignition of a hydrogen-burning shell. They then evolve on a nuclear time scale to T(eff) about 6000 K where they lose thermal equilibrium and jump to the Hayashi track. The theoretical and observed distributions agree withmore » two significant exceptions: the blue thermal contraction gap is overpopulated compared to the theory, and there is a ledge crossing the center of the H-R diagram. The hypothesis that some of the observed stars in the blue gap are secondaries that have accreted helium-rich matter from deep within the hydrogen envelope of a red supergiant primary is explored. Some preliminary observational justification is given. 27 refs.« less

ASTEROSEISMIC ANALYSIS OF THE PRE-MAIN-SEQUENCE STARS IN NGC 2264

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

Guenther, D. B.; Casey, M. P.; Kallinger, T.

2009-10-20

NGC 2264 is a young open cluster lying above the Galactic plane in which six variable stars have previously been identified as possible pre-main-sequence (PMS) pulsators. Their oscillation spectra are relatively sparse with each star having from 2 to 12 unambiguous frequency identifications based on Microvariability and Oscillations of Stars satellite and multi-site ground-based photometry. We describe our efforts to find classical PMS stellar models (i.e., models evolved from the Hayashi track) whose oscillation spectra match the observed frequencies. We find model eigenspectra that match the observed frequencies and are consistent with the stars' locations in the HR diagram formore » the three faintest of the six stars. Not all the frequencies found in spectra of the three brightest stars can be matched to classical PMS model spectra possibly because of effects not included in our PMS models such as chemical and angular momentum stratification in the outer layers of the star. All the oscillation spectra contain both radial and nonradial p-modes. We argue that the PMS pulsating stars divide into two groups depending on whether or not they have undergone complete mixing (i.e., have gone through a Hayashi phase). Lower mass stars that do evolve through a Hayashi phase have oscillation spectra predicted by classical PMS models, whereas more massive stars that do not, retain mass infall effects in their surface layers and are not well modeled by classical PMS models.« less

Mass, radius and composition of the outer crust of nonaccreting cold neutron stars

NASA Astrophysics Data System (ADS)

Hempel, Matthias; Schaffner-Bielich, Jürgen

2008-01-01

The properties and composition of the outer crust of nonaccreting cold neutron stars are studied by applying the model of Baym, Pethick and Sutherland, which was extended by including higher order corrections of the atomic binding, screening, exchange and zero-point energy. The most recent experimental nuclear data from the atomic mass table of Audi, Wapstra and Thibault from 2003 are used. Extrapolation to the drip line is utilized by various state-of-the-art theoretical nuclear models (finite range droplet, relativistic nuclear field and non-relativistic Skyrme Hartree Fock parameterizations). The different nuclear models are compared with respect to the mass and radius of the outer crust for different neutron star configurations and the nuclear compositions of the outer crust.

The evolution of red supergiants to supernovae

NASA Astrophysics Data System (ADS)

Beasor, Emma R.; Davies, Ben

2017-11-01

With red supergiants (RSGs) predicted to end their lives as Type IIP core collapse supernova (CCSN), their behaviour before explosion needs to be fully understood. Mass loss rates govern RSG evolution towards SN and have strong implications on the appearance of the resulting explosion. To study how the mass-loss rates change with the evolution of the star, we have measured the amount of circumstellar material around 19 RSGs in a coeval cluster. Our study has shown that mass loss rates ramp up throughout the lifetime of an RSG, with more evolved stars having mass loss rates a factor of 40 higher than early stage RSGs. Interestingly, we have also found evidence for an increase in circumstellar extinction throughout the RSG lifetime, meaning the most evolved stars are most severely affected. We find that, were the most evolved RSGs in NGC2100 to go SN, this extra extinction would cause the progenitor's initial mass to be underestimated by up to 9M⊙.

A VLT/UVES spectroscopy study of O2 stars in the LMC

NASA Astrophysics Data System (ADS)

Doran, Emile I.; Crowther, Paul A.

2011-01-01

We have analysed VLT/UVES spectra of six O2 stars within the Large Magellanic Cloud using the non-LTE atmospheric code CMFGEN. A range of physical properties was determined by employing a temperature calibration based upon N IV - N V diagnostics. Wind properties were also obtained from the Hα line, while CNO surface abundances were supplied through various diagnostics. Our results reveal effective temperatures in excess of T_{eff} ˜50 kK in all cases. We also addressed their evolutionary status and favour a mass dependent division. For lower masses ≤100 M⊙Mar, an O2 star follows the classical sequence, evolving from dwarf on to giant, through to supergiant. At higher masses, the dwarf phase may be circumvented and instead O2 stars begin their lives as giants or supergiants, evolving to the H-rich WN stage within ˜1.5 Myr.

Stacked Star Formation Rate Profiles of Bursty Galaxies Exhibit “Coherent” Star Formation

NASA Astrophysics Data System (ADS)

Orr, Matthew E.; Hayward, Christopher C.; Nelson, Erica J.; Hopkins, Philip F.; Faucher-Giguère, Claude-André; Kereš, Dušan; Chan, T. K.; Schmitz, Denise M.; Miller, Tim B.

2017-11-01

In a recent work based on 3200 stacked Hα maps of galaxies at z˜ 1, Nelson et al. find evidence for “coherent star formation”: the stacked star formation rate (SFR) profiles of galaxies above (below) the “star formation main sequence” (MS) are above (below) that of galaxies on the MS at all radii. One might interpret this result as inconsistent with highly bursty star formation and evidence that galaxies evolve smoothly along the MS rather than crossing it many times. We analyze six simulated galaxies at z˜ 1 from the Feedback in Realistic Environments (FIRE) project in a manner analogous to the observations to test whether the above interpretations are correct. The trends in stacked SFR profiles are qualitatively consistent with those observed. However, SFR profiles of individual galaxies are much more complex than the stacked profiles: the former can be flat or even peak at large radii because of the highly clustered nature of star formation in the simulations. Moreover, the SFR profiles of individual galaxies above (below) the MS are not systematically above (below) those of MS galaxies at all radii. We conclude that the time-averaged coherent star formation evident stacks of observed galaxies is consistent with highly bursty, clumpy star formation of individual galaxies and is not evidence that galaxies evolve smoothly along the MS.

The Universe at Ultraviolet Wavelengths: The first two years of International Ultraviolet Explorer

NASA Technical Reports Server (NTRS)

Chapman, R. D. (Editor)

1981-01-01

Highlights of the results obtained from the IUE satellite are addressed. specific topics discussed include the solar system, O-A stars, F-M stars, binary stars and highly evolved objects, nebulae and interstellar medium, and extragalactic objects. Data reduction techniques employed in the analysis of the varied data are also discussed.

BULGES OF NEARBY GALAXIES WITH SPITZER: THE GROWTH OF PSEUDOBULGES IN DISK GALAXIES AND ITS CONNECTION TO OUTER DISKS

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

Fisher, David B.; Drory, Niv; Fabricius, Maximilian H.

2009-05-20

We study star formation rates (SFRs) and stellar masses in bulges of nearby disk galaxies. For this we construct a new SFR indicator that linearly combines data from the Spitzer Space Telescope and the Galaxy Evolution Explorer. All bulges are found to be forming stars irrespective of bulge type (pseudobulge or classical bulge). At present-day SFR the median pseudobulge could have grown the present-day stellar mass in 8 Gyr. Classical bulges have the lowest specific SFR implying a growth times that are longer than a Hubble time, and thus the present-day SFR does not likely play a major role inmore » the evolution of classical bulges. In almost all galaxies in our sample the specific SFR (SFR per unit stellar mass) of the bulge is higher than that of the outer disk. This suggests that almost all galaxies are increasing their B/T through internal star formation. The SFR in pseudobulges correlates with their structure. More massive pseudobulges have higher SFR density, this is consistent with that stellar mass being formed by moderate, extended star formation. Bulges in late-type galaxies have similar SFRs as pseudobulges in intermediate-type galaxies, and are similar in radial size. However, they are deficient in mass; thus, they have much shorter growth times, {approx}2 Gyr. We identify a class of bulges that have nuclear morphology similar to pseudobulges, significantly lower specific SFR than pseudobulges, and are closer to classical bulges in structural parameter correlations. These are possibly composite objects, evolved pseudobulges or classical bulges experiencing transient, enhanced nuclear star formation. Our results are consistent with a scenario in which bulge growth via internal star formation is a natural, and near ubiquitous phenomenon in disk galaxies. Those galaxies with large classical bulges are not affected by the in situ bulge growth, likely because the majority of their stellar mass comes from some other phenomenon. Yet, those galaxies without a classical bulge, over long periods of extended star formation are able to growth a pseudobulge. Though cold accretion is not ruled out, for pseudobulge galaxies an addition of stellar mass from mergers or accretion is not required to explain the bulge mass. In this sense, galaxies with pseudobulges may very well be bulgeless (or 'quasi-bulgeless') galaxies, and galaxies with classical bulges are galaxies in which both internal evolution and hierarchical merging are responsible for the bulge mass by fractions that vary from galaxy to galaxy.« less

Effects of spiral arms on star formation in nuclear rings of barred-spiral galaxies

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

Seo, Woo-Young; Kim, Woong-Tae, E-mail: seowy@astro.snu.ac.kr, E-mail: wkim@astro.snu.ac.kr

2014-09-01

We use hydrodynamic simulations to study the effect of spiral arms on the star formation rate (SFR) in nuclear rings of barred-spiral galaxies. We find that spiral arms can be an efficient means of gas transport from the outskirts to the central parts, provided that the arms are rotating slower than the bar. While the ring star formation in models with no arms or corotating arms is active only during around the bar growth phase, arm-driven gas accretion both significantly enhances and prolongs the ring star formation in models with slow-rotating arms. The arm-enhanced SFR is larger by a factormore » of ∼3-20 than in the no-arm model, with larger values corresponding to stronger and slower arms. Arm-induced mass inflows also make dust lanes stronger. Nuclear rings in slow-arm models are ∼45% larger than in the no-arm counterparts. Star clusters that form in a nuclear ring exhibit an age gradient in the azimuthal direction only when the SFR is small, whereas no notable age gradient is found in the radial direction for models with arm-induced star formation.« less

Properties of Localized Protons in Neutron Star Matter at Finite Temperatures

NASA Astrophysics Data System (ADS)

Szmaglinski, A.; Kubis, S.; Wójcik, W.

2014-02-01

We study properties of the proton component of neutron star matter for realistic nuclear models. Vanishing of the nuclear symmetry energy implies proton-neutron separation in dense nuclear matter. Protons which form admixture tend to be localized in potential wells. Here, we extend the description of proton localization to finite temperatures. It appears that the protons are still localized at temperatures typical for hot neutron stars. That fact has important astrophysical consequences. Moreover, the temperature inclusion leads to unexpected results for the behavior of the proton localized state.

The chemistry in circumstellar envelopes of evolved stars: following the origin of the elements to the origin of life.

PubMed

Ziurys, Lucy M

2006-08-15

Mass loss from evolved stars results in the formation of unusual chemical laboratories: circumstellar envelopes. Such envelopes are found around carbon- and oxygen-rich asymptotic giant branch stars and red supergiants. As the gaseous material of the envelope flows from the star, the resulting temperature and density gradients create a complex chemical environment involving hot, thermodynamically controlled synthesis, molecule "freeze-out," shock-initiated reactions, and photochemistry governed by radical mechanisms. In the circumstellar envelope of the carbon-rich star IRC+10216, >50 different chemical compounds have been identified, including such exotic species as C(8)H, C(3)S, SiC(3), and AlNC. The chemistry here is dominated by molecules containing long carbon chains, silicon, and metals such as magnesium, sodium, and aluminum, which makes it quite distinct from that found in molecular clouds. The molecular composition of the oxygen-rich counterparts is not nearly as well explored, although recent studies of VY Canis Majoris have resulted in the identification of HCO(+), SO(2), and even NaCl in this object, suggesting chemical complexity here as well. As these envelopes evolve into planetary nebulae with a hot, exposed central star, synthesis of molecular ions becomes important, as indicated by studies of NGC 7027. Numerous species such as HCO(+), HCN, and CCH are found in old planetary nebulae such as the Helix. This "survivor" molecular material may be linked to the variety of compounds found recently in diffuse clouds. Organic molecules in dense interstellar clouds may ultimately be traced back to carbon-rich fragments originally formed in circumstellar shells.

Probing the formation history of the nuclear star cluster at the Galactic Centre with millisecond pulsars

NASA Astrophysics Data System (ADS)

Abbate, F.; Mastrobuono-Battisti, A.; Colpi, M.; Possenti, A.; Sippel, A. C.; Dotti, M.

2018-01-01

The origin of the nuclear star cluster in the centre of our Galaxy is still unknown. One possibility is that it formed after the disruption of stellar clusters that spiralled into the Galactic Centre due to dynamical friction. We trace the formation of the nuclear star cluster around the central black hole, using state-of-the-art N-body simulations, and follow the dynamics of the neutron stars born in the clusters. We then estimate the number of millisecond pulsars (MSPs) that are released in the nuclear star cluster during its formation. The assembly and tidal dismemberment of globular clusters lead to a population of MSPs distributed over a radius of about 20 pc, with a peak near 3 pc. No clustering is found on the subparsec scale. We simulate the detectability of this population with future radio telescopes like the MeerKAT radio telescope and SKA1, and find that about an order of 10 MSPs can be observed over this large volume, with a paucity of MSPs within the central parsec. This helps discriminating this scenario from the in situ formation model for the nuclear star cluster that would predict an overabundance of MSPs closer to the black hole. We then discuss the potential contribution of our MSP population to the gamma-ray excess at the Galactic Centre.

Nuclear ``pasta'' structures in low-density nuclear matter and properties of the neutron-star crust

NASA Astrophysics Data System (ADS)

Okamoto, Minoru; Maruyama, Toshiki; Yabana, Kazuhiro; Tatsumi, Toshitaka

2013-08-01

In the neutron-star crust, nonuniform structure of nuclear matter—called the “pasta” structure—is expected. From recent studies of giant flares in magnetars, these structures might be related to some observables and physical quantities of the neutron-star crust. To investigate the above quantities, we numerically explore the pasta structure with a fully three-dimensional geometry and study the properties of low-density nuclear matter, based on the relativistic mean-field model and the Thomas-Fermi approximation. We observe typical pasta structures for fixed proton number fraction and two of them for cold catalyzed matter. We also discuss the crystalline configuration of “pasta.”

Nuclear Star Formation in the Hot-Spot Galaxy NGC 2903

NASA Technical Reports Server (NTRS)

Alonso-Herrero, A.; Ryder, S. D.; Knapen, J. H.

1994-01-01

We present high-resolution near-infrared imaging obtained using adaptive optics and HST/NICMOS and ground-based spectroscopy of the hot-spot galaxy NGC 2903. Our near-infrared resolution imaging enables us to resolve the infrared hot spots into individual young stellar clusters or groups of these. The spatial distribution of the stellar clusters is not coincident with that of the bright H II regions, as revealed by the HST/NICMOS Pace image. Overall, the circumnuclear star formation in NGC 2903 shows a ring-like morphology with an approximate diameter of 625 pc. The SF properties of the stellar clusters and H II regions have been studied using the photometric and spectroscopic information in conjunction with evolutionary synthesis models. The population of bright stellar clusters shows a very narrow range of ages, 4 to 7 x 10(exp 6) yr after the peak of star formation, or absolute ages 6.5 to 9.5 x 10(exp 6) yr (for the assumed short-duration Gaussian bursts), and luminosities similar to the clusters found in the Antennae interacting galaxy. This population of young stellar clusters accounts for some 7 - 12% of the total stellar mass in the central 625 pc of NGC 2903. The H II regions in the ring of star formation have luminosities close to that of the super-giant H II region 30 Doradus, they are younger than the stellar clusters, and will probably evolve into bright infrared stellar clusters similar to those observed today. We find that the star formation efficiency in the central regions of NGC 2903 is higher than in normal galaxies, approaching the lower end of infrared luminous galaxies.

Massive black hole factories: Supermassive and quasi-star formation in primordial halos

NASA Astrophysics Data System (ADS)

Schleicher, Dominik R. G.; Palla, Francesco; Ferrara, Andrea; Galli, Daniele; Latif, Muhammad

2013-10-01

Context. Supermassive stars and quasi-stars (massive stars with a central black hole) are both considered as potential progenitors for the formation of supermassive black holes. They are expected to form from rapidly accreting protostars in massive primordial halos. Aims: We explore how long rapidly accreting protostars remain on the Hayashi track, implying large protostellar radii and weak accretion luminosity feedback. We assess the potential role of energy production in the nuclear core, and determine what regulates the evolution of such protostars into quasi-stars or supermassive stars. Methods: We followed the contraction of characteristic mass shells in rapidly accreting protostars, and inferred the timescales for them to reach nuclear densities. We compared the characteristic timescales for nuclear burning with those for which the extended protostellar envelope can be maintained. Results: We find that the extended envelope can be maintained up to protostellar masses of 3.6 × 108 ṁ3 M⊙, where ṁ denotes the accretion rate in solar masses per year. We expect the nuclear core to exhaust its hydrogen content in 7 × 106 yr. If accretion rates ṁ ≫ 0.14 can still be maintained at this point, a black hole may form within the accreting envelope, leading to a quasi-star. Alternatively, the accreting object will gravitationally contract to become a main-sequence supermassive star. Conclusions: Due to the limited gas reservoir in typical 107 M⊙ dark matter halos, the accretion rate onto the central object may drop at late times, implying the formation of supermassive stars as the typical outcome of direct collapse. However, if high accretion rates are maintained, a quasi-star with an interior black hole may form.

ON THE TIDAL DISSIPATION OF OBLIQUITY

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

Rogers, T. M.; Lin, D. N. C., E-mail: tami@lpl.arizona.edu, E-mail: lin@ucolick.org

2013-05-20

We investigate tidal dissipation of obliquity in hot Jupiters. Assuming an initial random orientation of obliquity and parameters relevant to the observed population, the obliquity of hot Jupiters does not evolve to purely aligned systems. In fact, the obliquity evolves to either prograde, retrograde, or 90 Degree-Sign orbits where the torque due to tidal perturbations vanishes. This distribution is incompatible with observations which show that hot Jupiters around cool stars are generally aligned. This calls into question the viability of tidal dissipation as the mechanism for obliquity alignment of hot Jupiters around cool stars.

DISCOVERY OF RR LYRAE STARS IN THE NUCLEAR BULGE OF THE MILKY WAY

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

Minniti, Dante; Ramos, Rodrigo Contreras; Zoccali, Manuela

Galactic nuclei, such as that of the Milky Way, are extreme regions with high stellar densities, and in most cases, the hosts of a supermassive black hole. One of the scenarios proposed for the formation of the Galactic nucleus is merging of primordial globular clusters. An implication of this model is that this region should host stars that are characteristically found in old Milky Way globular clusters. RR Lyrae stars are primary distance indicators, well known representatives of old and metal-poor stellar populations, and therefore are regularly found in globular clusters. Here we report the discovery of a dozen RRmore » Lyrae type ab stars in the vicinity of the Galactic center, i.e., in the so-called nuclear stellar bulge of the Milky Way. This discovery provides the first direct observational evidence that the Galactic nuclear stellar bulge contains ancient stars (>10 Gyr old). Based on this we conclude that merging globular clusters likely contributed to the build-up of the high stellar density in the nuclear stellar bulge of the Milky Way.« less

Witnessing Atmospheric Motions in Cool Evolved Stars with VLTI/Amber

NASA Astrophysics Data System (ADS)

Ohnaka, Keiichi

2018-04-01

Studies of the mass loss from stars in late evolutionary stages are of utmost importance for improving our understanding of not only stellar evolution but also the chemical enrichment of galaxies. Despite such importance, the mass loss from cool evolved stars is one of the long-standing problems in stellar astrophysics. Milliarcsecond resolution achieved by optical/infrared long-baseline interferometry provides a unique opportunity to spatially resolve this innermost key region. We have recently succeeded not only in imaging the surface of the red supergiant Antares in the 2.3 micron CO lines in unprecedented detail but also in witnessing, for the first time, the complex gas dynamics over the surface and atmosphere of the star. Our 2-D velocity field map of Antares reveals vigorous upwelling and downdrafting motions of large gas clumps in the atmosphere extending out to 1.7 stellar radii. This suggests that the mass loss in red supergiants may be launched in a turbulent, clumpy manner. We will also present preliminary results of the velocity-resolved imaging of an AGB star. Our work opens an entirely new window to observe stars just like in observations of the Sun.

The most luminous stars.

PubMed

Humphreys, R M; Davidson, K

1984-01-20

Stars with individual luminosities more than a million times that of the sun are now being studied in a variety of contexts. Observational and theoretical ideas about the most luminous stars have changed greatly in the past few years. They can be observed spectroscopically even in nearby galaxies. They are not very stable; some have had violent outbursts in which large amounts of mass were lost. Because of their instabilities, these stars do not evolve to become red superglants as less luminous stars do. Theoretical scenarios for the evolution of these most massive stars depend on the effects of turbulence and mixing combined with high radition densities.

Young Star Clusters: Keys to Understanding Massive Stars

NASA Astrophysics Data System (ADS)

Davies, B.

2012-12-01

Young, coeval clusters of stars provide the perfect laboratory in which to test our understanding of how massive stars evolve. Early optical observations limited us to a handful of low-mass clusters within 1kpc. However, thanks to the recent progress in infrared astronomy, the Milky Way's population of young massive star clusters is now beginning to be revealed. Here, I will review the recent progress made in this field, what it has told us about the evolution of massive stars to supernova and beyond, the prospects for this field, and some issues that should be taken into account when interpreting the results.

Sage Studies Of The Mass Return From AGB And RSG Stars In The Large Magellanic Cloud

NASA Astrophysics Data System (ADS)

Sargent, Benjamin A.; Srinivasan, S.; Meixner, M.

2011-01-01

The Surveying the Agents of a Galaxy's Evolution (SAGE; PI: M. Meixner) Spitzer Space Telescope Legacy project aims to further our understanding of the life cycle of matter in galaxies by studying this life cycle in our neighboring galaxy, the Large Magellanic Cloud (LMC). Combining SAGE mid-infrared photometry with that at shorter wavelengths from other catalogs, the spectral energy distribution (SED) for each of >25000 Asymptotic Giant Branch (AGB) and Red Supergiant (RSG) stars in the LMC has been assembled. To model mass loss from these stars, my colleagues and I have constructed the grid of RSG and AGB models (GRAMS) using the radiative transfer code 2Dust. I will discuss how GRAMS was constructed, and how we use it to determine the mass-loss rate for each evolved star studied, which gives the total mass-loss return to the LMC from AGB and RSG stars. In my talk, I show how this total mass-loss return is divided into oxygen-rich (O-rich) and carbon-rich (C-rich) dust using SED-fitting to identify O-rich versus C-rich AGB stars. Applications of this work to determining the mass return from evolved stars in other galaxies, including the Milky Way, will also be discussed.

I-Love-Q: Unexpected Universal Relations for Neutron Stars and Quark Stars

NASA Astrophysics Data System (ADS)

Yagi, Kent; Yunes, Nicolás

2013-07-01

Neutron stars and quark stars are not only characterized by their mass and radius but also by how fast they spin, through their moment of inertia, and how much they can be deformed, through their Love number and quadrupole moment. These depend sensitively on the star’s internal structure and thus on unknown nuclear physics. We find universal relations between the moment of inertia, the Love number, and the quadrupole moment that are independent of the neutron and quark star’s internal structure. These can be used to learn about neutron star deformability through observations of the moment of inertia, break degeneracies in gravitational wave detection to measure spin in binary inspirals, distinguish neutron stars from quark stars, and test general relativity in a nuclear structure-independent fashion.

Origin and stability of exomoon atmospheres: implications for habitability.

PubMed

Lammer, Helmut; Schiefer, Sonja-Charlotte; Juvan, Ines; Odert, Petra; Erkaev, Nikolai V; Weber, Christof; Kislyakova, Kristina G; Güdel, Manuel; Kirchengast, Gottfried; Hanslmeier, Arnold

2014-09-01

We study the origin and escape of catastrophically outgassed volatiles (H2O, CO2) from exomoons with Earth-like densities and masses of 0.1, 0.5 and 1 M⊕ orbiting an extra-solar gas giant inside the habitable zone of a young active solar-like star. We apply a radiation absorption and hydrodynamic upper atmosphere model to the three studied exomoon cases. We model the escape of hydrogen and dragged dissociation products O and C during the activity saturation phase of the young host star. Because the soft X-ray and EUV radiation of the young host star may be up to ~100 times higher compared to today's solar value during the first 100 Myr after the system's origin, an exomoon with a mass < 0.25 M⊕ located in the HZ may not be able to keep an atmosphere because of its low gravity. Depending on the spectral type and XUV activity evolution of the host star, exomoons with masses between ~0.25 and 0.5 M⊕ may evolve to Mars-like habitats. More massive bodies with masses >0.5 M⊕, however, may evolve to habitats that are a mixture of Mars-like and Earth-analogue habitats, so that life may originate and evolve at the exomoon's surface.

DISCOVERY OF TWIN WOLF-RAYET STARS POWERING DOUBLE RING NEBULAE

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

Mauerhan, Jon C.; Wachter, Stefanie; Van Dyk, Schuyler D.

We have spectroscopically discovered a pair of twin, nitrogen-type, hydrogen-rich, Wolf-Rayet stars (WN8-9h) that are both surrounded by circular, mid-infrared-bright nebulae detected with the Spitzer Space Telescope and MIPS instrument. The emission is probably dominated by a thermal continuum from cool dust, but also may contain contributions from atomic line emission. There is no counterpart at shorter Spitzer/IRAC wavelengths, indicating a lack of emission from warm dust. The two nebulae are probably wind-swept stellar ejecta released by the central stars during a prior evolutionary phase. The nebulae partially overlap on the sky and we speculate on the possibility that theymore » are in the early stage of a collision. Two other evolved massive stars have also been identified within the area subtended by the nebulae, including a carbon-type Wolf-Rayet star (WC8) and an O7-8 III-I star, the latter of which appears to be embedded in one of the larger WN8-9h nebulae. The derived distances to these stars imply that they are coeval members of an association lying 4.9 {+-} 1.2 kpc from Earth, near the intersection of the Galaxy's Long Bar and the Scutum-Centaurus spiral arm. This new association represents an unprecedented display of complex interactions between multiple stellar winds, outflows, and the radiation fields of evolved massive stars.« less

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2013-01-23

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Stellar Alchemy

NASA Astrophysics Data System (ADS)

Cassé, Michel; Lyle, Translated by Stephen

2003-08-01

Preface; 1. Nuclear astrophysics: defence and illustration; 2. Light from atoms, light from the sky; 3. Visions; 4. Contents of the sky: atomic sources and fountains; 5. Nuclear suns; 6. Sociology of stars and clouds; 7. Histories; 8. Ancient stars in the galactic halo; 9. Conclusion; Appendices.

Holographic Quark Matter and Neutron Stars.

PubMed

Hoyos, Carlos; Jokela, Niko; Rodríguez Fernández, David; Vuorinen, Aleksi

2016-07-15

We use a top-down holographic model for strongly interacting quark matter to study the properties of neutron stars. When the corresponding equation of state (EOS) is matched with state-of-the-art results for dense nuclear matter, we consistently observe a first-order phase transition at densities between 2 and 7 times the nuclear saturation density. Solving the Tolman-Oppenheimer-Volkov equations with the resulting hybrid EOSs, we find maximal stellar masses in excess of two solar masses, albeit somewhat smaller than those obtained with simple extrapolations of the nuclear matter EOSs. Our calculation predicts that no quark matter exists inside neutron stars.

Rapidly rotating polytropes in general relativity

NASA Technical Reports Server (NTRS)

Cook, Gregory B.; Shapiro, Stuart L.; Teukolsky, Saul A.

1994-01-01

We construct an extensive set of equilibrium sequences of rotating polytropes in general relativity. We determine a number of important physical parameters of such stars, including maximum mass and maximum spin rate. The stability of the configurations against quasi-radial perturbations is diagnosed. Two classes of evolutionary sequences of fixed rest mass and entropy are explored: normal sequences which behave very much like Newtonian evolutionary sequences, and supramassive sequences which exist solely because of relativistic effects. Dissipation leading to loss of angular momentum causes a star to evolve in a quasi-stationary fashion along an evolutionary sequence. Supramassive sequences evolve towards eventual catastrophic collapse to a black hole. Prior to collapse, the star must spin up as it loses angular momentum, an effect which may provide an observational precursor to gravitational collapse to a black hole.

A New Fokker-Planck Approach for the Relaxation-driven Evolution of Galactic Nuclei

NASA Astrophysics Data System (ADS)

Vasiliev, Eugene

2017-10-01

We present an approach for simulating the collisional evolution of spherical isotropic stellar systems based on the one-dimensional Fokker-Planck equation. A novel aspect is that we use the phase volume as the argument of the distribution function instead of the traditionally used energy, which facilitates the solution. The publicly available code PhaseFlow implements a high-accuracy finite-element method for the Fokker-Planck equation, and can handle multiple-component systems, optionally with the central black hole and taking into account loss-cone effects and star formation. We discuss the energy balance in the general setting, and in application to the Bahcall-Wolf cusp around a central black hole, for which we derive a perturbative solution. We stress that the cusp is not a steady-state structure, but rather evolves in amplitude while retaining an approximately ρ \\propto {r}-7/4 density profile. Finally, we apply the method to the nuclear star cluster of the milky Way, and illustrate a possible evolutionary scenario in which a two-component system of lighter main-sequence stars and stellar-mass black holes develops a Bahcall-Wolf cusp in the heavier component and a weaker ρ \\propto {r}-3/2 cusp in the lighter, visible component, over the period of several Gyr. The present-day density profile is consistent with the recently detected mild cusp inside the central parsec, and is weakly sensitive to initial conditions.

A Runaway Yellow Supergiant Star in the Small Magellanic Cloud

NASA Astrophysics Data System (ADS)

Neugent, Kathryn F.; Massey, Philip; Morrell, Nidia I.; Skiff, Brian; Georgy, Cyril

2018-05-01

We recently discovered a yellow supergiant (YSG) in the Small Magellanic Cloud (SMC) with a heliocentric radial velocity of ∼300 km s‑1, which is much larger than expected for a star at its location in the SMC. This is the first runaway YSG ever discovered and only the second evolved runaway star discovered in a galaxy other than the Milky Way. We classify the star as G5-8 I and use de-reddened broad-band colors with model atmospheres to determine an effective temperature of 4700 ± 250 K, consistent with what is expected from its spectral type. The star’s luminosity is then log L/L ⊙ ∼ 4.2 ± 0.1, consistent with it being a ∼30 Myr 9 M ⊙ star according to the Geneva evolution models. The star is currently located in the outer portion of the SMC’s body, but if the star’s transverse peculiar velocity is similar to its peculiar radial velocity, in 10 Myr the star would have moved 1.°6 across the disk of the SMC and could easily have been born in one of the SMC’s star-forming regions. Based on its large radial velocity, we suggest it originated in a binary system where the primary exploded as a supernovae, thus flinging the runaway star out into space. Such stars may provide an important mechanism for the dispersal of heavier elements in galaxies given the large percentage of massive stars that are runaways. In the future, we hope to look into additional evolved runaway stars that were discovered as part of our other past surveys. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

Large granulation cells on the surface of the giant star π1 Gruis

NASA Astrophysics Data System (ADS)

Paladini, C.; Baron, F.; Jorissen, A.; Le Bouquin, J.-B.; Freytag, B.; van Eck, S.; Wittkowski, M.; Hron, J.; Chiavassa, A.; Berger, J.-P.; Siopis, C.; Mayer, A.; Sadowski, G.; Kravchenko, K.; Shetye, S.; Kerschbaum, F.; Kluska, J.; Ramstedt, S.

2018-01-01

Convection plays a major part in many astrophysical processes, including energy transport, pulsation, dynamos and winds on evolved stars, in dust clouds and on brown dwarfs. Most of our knowledge about stellar convection has come from studying the Sun: about two million convective cells with typical sizes of around 2,000 kilometres across are present on the surface of the Sun—a phenomenon known as granulation. But on the surfaces of giant and supergiant stars there should be only a few large (several tens of thousands of times larger than those on the Sun) convective cells, owing to low surface gravity. Deriving the characteristic properties of convection (such as granule size and contrast) for the most evolved giant and supergiant stars is challenging because their photospheres are obscured by dust, which partially masks the convective patterns. These properties can be inferred from geometric model fitting, but this indirect method does not provide information about the physical origin of the convective cells. Here we report interferometric images of the surface of the evolved giant star π1 Gruis, of spectral type S5,7. Our images show a nearly circular, dust-free atmosphere, which is very compact and only weakly affected by molecular opacity. We find that the stellar surface has a complex convective pattern with an average intensity contrast of 12 per cent, which increases towards shorter wavelengths. We derive a characteristic horizontal granule size of about 1.2 × 1011 metres, which corresponds to 27 per cent of the diameter of the star. Our measurements fall along the scaling relations between granule size, effective temperature and surface gravity that are predicted by simulations of stellar surface convection.

BEYOND THE MAIN SEQUENCE: TESTING THE ACCURACY OF STELLAR MASSES PREDICTED BY THE PARSEC EVOLUTIONARY TRACKS

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

Ghezzi, Luan; Johnson, John Asher, E-mail: lghezzi@cfa.harvard.edu

2015-10-20

Characterizing the physical properties of exoplanets and understanding their formation and orbital evolution requires precise and accurate knowledge of their host stars. Accurately measuring stellar masses is particularly important because they likely influence planet occurrence and the architectures of planetary systems. Single main-sequence stars typically have masses estimated from evolutionary tracks, which generally provide accurate results due to their extensive empirical calibration. However, the validity of this method for subgiants and giants has been called into question by recent studies, with suggestions that the masses of these evolved stars could have been overestimated. We investigate these concerns using a samplemore » of 59 benchmark evolved stars with model-independent masses (from binary systems or asteroseismology) obtained from the literature. We find very good agreement between these benchmark masses and the ones estimated using evolutionary tracks. The average fractional difference in the mass interval ∼0.7–4.5 M{sub ⊙} is consistent with zero (−1.30 ± 2.42%), with no significant trends in the residuals relative to the input parameters. A good agreement between model-dependent and -independent radii (−4.81 ± 1.32%) and surface gravities (0.71 ± 0.51%) is also found. The consistency between independently determined ages for members of binary systems adds further support for the accuracy of the method employed to derive the stellar masses. Taken together, our results indicate that determination of masses of evolved stars using grids of evolutionary tracks is not significantly affected by systematic errors, and is thus valid for estimating the masses of isolated stars beyond the main sequence.« less

The chemistry in circumstellar envelopes of evolved stars: Following the origin of the elements to the origin of life

PubMed Central

Ziurys, Lucy M.

2006-01-01

Mass loss from evolved stars results in the formation of unusual chemical laboratories: circumstellar envelopes. Such envelopes are found around carbon- and oxygen-rich asymptotic giant branch stars and red supergiants. As the gaseous material of the envelope flows from the star, the resulting temperature and density gradients create a complex chemical environment involving hot, thermodynamically controlled synthesis, molecule “freeze-out,” shock-initiated reactions, and photochemistry governed by radical mechanisms. In the circumstellar envelope of the carbon-rich star IRC+10216, >50 different chemical compounds have been identified, including such exotic species as C8H, C3S, SiC3, and AlNC. The chemistry here is dominated by molecules containing long carbon chains, silicon, and metals such as magnesium, sodium, and aluminum, which makes it quite distinct from that found in molecular clouds. The molecular composition of the oxygen-rich counterparts is not nearly as well explored, although recent studies of VY Canis Majoris have resulted in the identification of HCO+, SO2, and even NaCl in this object, suggesting chemical complexity here as well. As these envelopes evolve into planetary nebulae with a hot, exposed central star, synthesis of molecular ions becomes important, as indicated by studies of NGC 7027. Numerous species such as HCO+, HCN, and CCH are found in old planetary nebulae such as the Helix. This “survivor” molecular material may be linked to the variety of compounds found recently in diffuse clouds. Organic molecules in dense interstellar clouds may ultimately be traced back to carbon-rich fragments originally formed in circumstellar shells. PMID:16894164

Interstellar Chemistry Special Feature: The chemistry in circumstellar envelopes of evolved stars: Following the origin of the elements to the origin of life

NASA Astrophysics Data System (ADS)

Ziurys, Lucy M.

2006-08-01

Mass loss from evolved stars results in the formation of unusual chemical laboratories: circumstellar envelopes. Such envelopes are found around carbon- and oxygen-rich asymptotic giant branch stars and red supergiants. As the gaseous material of the envelope flows from the star, the resulting temperature and density gradients create a complex chemical environment involving hot, thermodynamically controlled synthesis, molecule "freeze-out," shock-initiated reactions, and photochemistry governed by radical mechanisms. In the circumstellar envelope of the carbon-rich star IRC+10216, >50 different chemical compounds have been identified, including such exotic species as C8H, C3S, SiC3, and AlNC. The chemistry here is dominated by molecules containing long carbon chains, silicon, and metals such as magnesium, sodium, and aluminum, which makes it quite distinct from that found in molecular clouds. The molecular composition of the oxygen-rich counterparts is not nearly as well explored, although recent studies of VY Canis Majoris have resulted in the identification of HCO+, SO2, and even NaCl in this object, suggesting chemical complexity here as well. As these envelopes evolve into planetary nebulae with a hot, exposed central star, synthesis of molecular ions becomes important, as indicated by studies of NGC 7027. Numerous species such as HCO+, HCN, and CCH are found in old planetary nebulae such as the Helix. This "survivor" molecular material may be linked to the variety of compounds found recently in diffuse clouds. Organic molecules in dense interstellar clouds may ultimately be traced back to carbon-rich fragments originally formed in circumstellar shells.

Large granulation cells on the surface of the giant star π1 Gruis.

PubMed

Paladini, C; Baron, F; Jorissen, A; Le Bouquin, J-B; Freytag, B; Van Eck, S; Wittkowski, M; Hron, J; Chiavassa, A; Berger, J-P; Siopis, C; Mayer, A; Sadowski, G; Kravchenko, K; Shetye, S; Kerschbaum, F; Kluska, J; Ramstedt, S

2018-01-18

Convection plays a major part in many astrophysical processes, including energy transport, pulsation, dynamos and winds on evolved stars, in dust clouds and on brown dwarfs. Most of our knowledge about stellar convection has come from studying the Sun: about two million convective cells with typical sizes of around 2,000 kilometres across are present on the surface of the Sun-a phenomenon known as granulation. But on the surfaces of giant and supergiant stars there should be only a few large (several tens of thousands of times larger than those on the Sun) convective cells, owing to low surface gravity. Deriving the characteristic properties of convection (such as granule size and contrast) for the most evolved giant and supergiant stars is challenging because their photospheres are obscured by dust, which partially masks the convective patterns. These properties can be inferred from geometric model fitting, but this indirect method does not provide information about the physical origin of the convective cells. Here we report interferometric images of the surface of the evolved giant star π 1 Gruis, of spectral type S5,7. Our images show a nearly circular, dust-free atmosphere, which is very compact and only weakly affected by molecular opacity. We find that the stellar surface has a complex convective pattern with an average intensity contrast of 12 per cent, which increases towards shorter wavelengths. We derive a characteristic horizontal granule size of about 1.2 × 10 11 metres, which corresponds to 27 per cent of the diameter of the star. Our measurements fall along the scaling relations between granule size, effective temperature and surface gravity that are predicted by simulations of stellar surface convection.

Evolutionary status of isolated B[e] stars

NASA Astrophysics Data System (ADS)

Lee, Chien-De; Chen, Wen-Ping; Liu, Sheng-Yuan

2016-08-01

Aims: We study a sample of eight B[e] stars with uncertain evolutionary status to shed light on the origin of their circumstellar dust. Methods: We performed a diagnostic analysis on the spectral energy distribution beyond infrared wavelengths, and conducted a census of neighboring region of each target to ascertain its evolutionary status. Results: In comparison to pre-main sequence Herbig stars, these B[e] stars show equally substantial excess emission in the near-infrared, indicative of existence of warm dust, but much reduced excess at longer wavelengths, so the dusty envelopes should be compact in size. Isolation from star-forming regions excludes the possibility of their pre-main sequence status. Six of our targets, including HD 50138, HD 45677, CD-24 5721, CD-49 3441, MWC 623, and HD 85567, have been previously considered as FS CMa stars, whereas HD 181615/6 and HD 98922 are added to the sample by this work. We argue that the circumstellar grains of these isolated B[e] stars, already evolved beyond the pre-main sequence phase, should be formed in situ. This is in contrast to Herbig stars, which inherit large grains from parental molecular clouds. It has been thought that HD 98922, in particular, is a Herbig star because of its large infrared excess, but we propose it being in a more evolved stage. Because dust condenses out of stellar mass loss in an inside-out manner, the dusty envelope is spatially confined, and anisotropic mass flows, or anomalous optical properties of tiny grains, lead to the generally low line-of-sight extinction toward these stars.

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

Antonini, Fabio, E-mail: antonini@cita.utoronto.ca

We use N-body simulations as well as analytical techniques to study the long-term dynamical evolution of stellar black holes (BHs) at the Galactic center (GC) and to put constraints on their number and mass distribution. Starting from models that have not yet achieved a state of collisional equilibrium, we find that timescales associated with cusp regrowth can be longer than the Hubble time. Our results cast doubts on standard models that postulate high densities of BHs near the GC and motivate studies that start from initial conditions that correspond to well-defined physical models. For the first time, we consider themore » distribution of BHs in a dissipationless model for the formation of the Milky Way nuclear cluster (NC), in which massive stellar clusters merge to form a compact nucleus. We simulate the consecutive merger of ∼10 clusters containing an inner dense sub-cluster of BHs. After the formed NC is evolved for ∼5 Gyr, the BHs do form a steep central cusp, while the stellar distribution maintains properties that resemble those of the GC NC. Finally, we investigate the effect of BH perturbations on the motion of the GC S-stars as a means of constraining the number of the perturbers. We find that reproducing the quasi-thermal character of the S-star orbital eccentricities requires ≳ 1000 BHs within 0.1 pc of Sgr A*. A dissipationless formation scenario for the GC NC is consistent with this lower limit and therefore could reconcile the need for high central densities of BHs (to explain the S-stars orbits) with the 'missing-cusp' problem of the GC giant star population.« less

Spectral analysis of four surprisingly similar hot hydrogen-rich subdwarf O stars

NASA Astrophysics Data System (ADS)

Latour, M.; Chayer, P.; Green, E. M.; Irrgang, A.; Fontaine, G.

2018-01-01

Context. Post-extreme horizontal branch stars (post-EHB) are helium-shell burning objects evolving away from the EHB and contracting directly towards the white dwarf regime. While the stars forming the EHB have been extensively studied in the past, their hotter and more evolved progeny are not so well characterized. Aims: We perform a comprehensive spectroscopic analysis of four such bright sdO stars, namely Feige 34, Feige 67, AGK+81°266, and LS II+18°9, among which the first three are used as standard stars for flux calibration. Our goal is to determine their atmospheric parameters, chemical properties, and evolutionary status to better understand this class of stars that are en route to become white dwarfs. Methods: We used non-local thermodynamic equilibrium model atmospheres in combination with high quality optical and UV spectra. Photometric data were also used to compute the spectroscopic distances of our stars and to characterize the companion responsible for the infrared excess of Feige 34. Results: The four bright sdO stars have very similar atmospheric parameters with Teff between 60 000 and 63 000 K and log g (cm s-2) in the range 5.9 to 6.1. This places these objects right on the theoretical post-EHB evolutionary tracks. The UV spectra are dominated by strong iron and nickel lines and suggest abundances that are enriched with respect to those of the Sun by factors of 25 and 60. On the other hand, the lighter elements, C, N, O, Mg, Si, P, and S are depleted. The stars have very similar abundances, although AGK+81°266 shows differences in its light element abundances. For instance, the helium abundance of this object is 10 times lower than that observed in the other three stars. All our stars show UV spectral lines that require additional line broadening that is consistent with a rotational velocity of about 25 km s-1. The infrared excess of Feige 34 is well reproduced by a M0 main-sequence companion and the surface area ratio of the two stars suggests that the system is a physical binary. However, the lack of radial velocity variations points towards a low inclination and/or long orbital period. Spectroscopic and Hipparcos distances are in good agreement for our three brightest stars. Conclusions: We performed a spectroscopic analysis of four hot sdO stars that are very similar in terms of atmospheric parameters and chemical compositions. The rotation velocities of our stars are significantly higher than what is observed in their immediate progenitors on the EHB, suggesting that angular momentum may be conserved as the stars evolve away from the EHB.

Low-mass neutron stars: universal relations, the nuclear symmetry energy and gravitational radiation

NASA Astrophysics Data System (ADS)

O. Silva, Hector; Berti, Emanuele; Sotani, Hajime

2016-03-01

Compact objects such as neutron stars are ideal astrophysical laboratories to test our understanding of the fundamental interactions in the regime of supranuclear densities, unachievable by terrestrial experiments. Despite recent progress, the description of matter (i.e., the equation of state) at such densities is still debatable. This translates into uncertainties in the bulk properties of neutron stars, masses and radii for instance. Here we will consider low-mass neutron stars. Such stars are expected to carry important information on nuclear matter near the nuclear saturation point. It has recently been shown that the masses and surface redshifts of low-mass neutron stars smoothly depend on simple functions of the central density and of a characteristic parameter η associated with the choice of equation of state. Here we extend these results to slowly-rotating and tidally deformed stars and obtain empirical relations for various quantities, such as the moment of inertia, quadrupole moment and ellipticity, tidal and rotational Love numbers, and rotational apsidal constants. We discuss how these relations might be used to constrain the equation of state by future observations in the electromagnetic and gravitational-wave spectra.

SkyNet: Modular nuclear reaction network library

NASA Astrophysics Data System (ADS)

Lippuner, Jonas; Roberts, Luke F.

2017-10-01

The general-purpose nuclear reaction network SkyNet evolves the abundances of nuclear species under the influence of nuclear reactions. SkyNet can be used to compute the nucleosynthesis evolution in all astrophysical scenarios where nucleosynthesis occurs. Any list of isotopes can be evolved and SkyNet supports various different types of nuclear reactions. SkyNet is modular, permitting new or existing physics, such as nuclear reactions or equations of state, to be easily added or modified.

Starlight morphology of the interacting galaxy NGC 5195

NASA Astrophysics Data System (ADS)

Smith, J.; Gehrz, R. D.; Grasdalen, G. L.; Hackwell, John A.; Dietz, R. D.; Friedman, Scott D.

1990-10-01

We present near-infrared, red, and optical observations of NGC 5195, the interacting companion of NGC 5194 (M51). Three intrinsic components are suggested by the near-infrared data: a bright nuclear maximum, a low-contrast bar centered symmetrically on the nucleus, and a nearly face-on exponential disk. This organized near-infrared morphology contrasts strongly with the irregular appearance of optical images. Neither dust nor hot stars contribute much to the near-infrared emission, leaving cool stars probably of an evolved population as the main near-infrared sources. Optical (V) and red (R, I) images confirm the near-infrared morphology and imply that obscuration by an irregular distribution of dust causes the great difference between optical and near-infrared morphologies. Dust within a foreground spiral arm of M51 is an important source of obscuration. Dust internal to NGC 5195 gives an observed quantity of reradiation and perhaps contributes significant obscuration within 10" of the galactic nucleus. The nucleus itself lies at or near a local minimum in color produced by small obscuration or possibly hot emission from the galaxy's nuclear emission-line region or X-ray medium. When corrected for all spatial components of extinction, the body of NGC 5195 becomes much bluer and has a mean B - H color common to normal disk galaxies. Observations lead consistently to SB, but no further, as the best description of the NGC 5195 morphology. Images reveal no evidence of spiral arms which alone would imply a lenticular subtype. Yet the bulge-to-disk ratio of NGC 5195, evaluated from near-infrared observations, is far smaller than values inferred for noninteracting lenticular galaxies. Motivated by these difficulties in conventional classification, we proceed to discuss the possibility that certain attributes of NGC 5195, including its bar, are transient manifestations of the interaction with M51. Presented measurements support the galaxy mass ratio and type of NGC 5195 morphology assumed in a successful model of the gravitational interaction between stars of M51 and NGC 5195. Encouraged by this agreement between theory and experiment, we explore the consequences of an expanded version of the model, still premised on interaction via gravity but now including dynamics of both stars and interstellar clouds. Working within this theoretical context, we identify an interaction-induced component of star formation, an incipient starburst, within the disk of M51.

A comprehensive classification of galaxies in the Sloan Digital Sky Survey: how to tell true from fake AGN?

NASA Astrophysics Data System (ADS)

Cid Fernandes, R.; Stasińska, G.; Mateus, A.; Vale Asari, N.

2011-05-01

We use the WHα versus [N II]/Hα (WHAN) diagram introduced by us in previous work to provide a comprehensive emission-line classification of Sloan Digital Sky Survey galaxies. This classification is able to cope with the large population of weak line galaxies that do not appear in traditional diagrams due to a lack of some of the diagnostic lines. A further advantage of the WHAN diagram is to allow the differentiation between two very distinct classes that overlap in the low-ionization nuclear emission-line region (LINER) region of traditional diagnostic diagrams. These are galaxies hosting a weakly active galactic nucleus (wAGN) and 'retired galaxies' (RGs), i.e. galaxies that have stopped forming stars and are ionized by their hot low-mass evolved stars. A useful criterion to distinguish true from fake AGN (i.e. the RGs) is the value of ξ, which measures the ratio of the extinction-corrected Hα luminosity with respect to the Hα luminosity expected from photoionization by stellar populations older than 108 yr. We find that ξ follows a markedly bimodal distribution, with a ξ≫ 1 population composed by systems undergoing star formation and/or nuclear activity, and a peak at ξ˜ 1 corresponding to the prediction of the RG model. We base our classification scheme not on ξ but on a more readily available and model-independent quantity which provides an excellent observational proxy for ξ: the equivalent width of Hα. Based on the bimodal distribution of WHα, we set the practical division between wAGN and RGs at WHα= 3 Å. Five classes of galaxies are identified within the WHAN diagram: (i) pure star-forming galaxies: ? and WHα > 3 Å; (ii) strong AGN (i.e. Seyferts): ? and WHα > 6 Å; (iii) weak AGN: ? and WHα between 3 and 6 Å; (iv) RGs (i.e. fake AGN): WHα < 3 Å; (v) passive galaxies (actually, lineless galaxies): WHα and W[N II] < 0.5 Å. A comparative analysis of star formation histories and of other physical and observational properties in these different classes of galaxies corroborates our proposed differentiation between RGs and wAGN in the LINER-like family. This analysis also shows similarities between strong and weak AGN on the one hand, and retired and passive galaxies on the other.

Imaging of Stellar Surfacess Using Radio Facilities Including ALMA

NASA Astrophysics Data System (ADS)

O'Gorman, Eamon

2018-04-01

Until very recently, studies focusing on imaging stars at continuum radio wavelengths (here defined as submillimeter, millimeter, and centimeter wavelengths) has been scarce. These studies have mainly been carried out with the Very Large Array on a handful of evolved stars (i.e., Asymptotic Giant Branch and Red Supergiant stars) whereby their stellar disks have just about been spatially resolved. Some of these results however, have challenged our historical views on the nature of evolved star atmospheres. Now, the very long baselines of the Atacama Large Millimeter/submillimeter Array and the newly upgraded Karl G. Jansky Very Large Array provide a new opportunity to image these atmospheres at unprecedented spatial resolution and sensitivity across a much wider portion of the radio spectrum. In this talk I will first provide a history of stellar radio imaging and then discuss some recent exciting ALMA results. Finally I will present some brand new multi-wavelength ALMA and VLA results for the famous red supergiant Antares.

The distribution of stars most likely to harbor intelligent life.

PubMed

Whitmire, Daniel P; Matese, John J

2009-09-01

Simple heuristic models and recent numerical simulations show that the probability of habitable planet formation increases with stellar mass. We combine those results with the distribution of main-sequence stellar masses to obtain the distribution of stars most likely to possess habitable planets as a function of stellar lifetime. We then impose the self-selection condition that intelligent observers can only find themselves around a star with a lifetime greater than the time required for that observer to have evolved, T(i). This allows us to obtain the stellar timescale number distribution for a given value of T(i). Our results show that for habitable planets with a civilization that evolved at time T(i) = 4.5 Gyr the median stellar lifetime is 13 Gyr, corresponding approximately to a stellar type of G5, with two-thirds of the stars having lifetimes between 7 and 30 Gyr, corresponding approximately to spectral types G0-K5. For other values of T(i) the median stellar lifetime changes by less than 50%.

Winds from Luminous Late-Type Stars: II. Broadband Frequency Distribution of Alfven Waves

NASA Technical Reports Server (NTRS)

Airapetian, V.; Carpenter, K. G.; Ofman, L.

2010-01-01

We present the numerical simulations of winds from evolved giant stars using a fully non-linear, time dependent 2.5-dimensional magnetohydrodynamic (MHD) code. This study extends our previous fully non-linear MHD wind simulations to include a broadband frequency spectrum of Alfven waves that drive winds from red giant stars. We calculated four Alfven wind models that cover the whole range of Alfven wave frequency spectrum to characterize the role of freely propagated and reflected Alfven waves in the gravitationally stratified atmosphere of a late-type giant star. Our simulations demonstrate that, unlike linear Alfven wave-driven wind models, a stellar wind model based on plasma acceleration due to broadband non-linear Alfven waves, can consistently reproduce the wide range of observed radial velocity profiles of the winds, their terminal velocities and the observed mass loss rates. Comparison of the calculated mass loss rates with the empirically determined mass loss rate for alpha Tau suggests an anisotropic and time-dependent nature of stellar winds from evolved giants.

Galaxy And Mass Assembly (GAMA): blue spheroids within 87 Mpc

NASA Astrophysics Data System (ADS)

Mahajan, Smriti; Drinkwater, Michael J.; Driver, S.; Hopkins, A. M.; Graham, Alister W.; Brough, S.; Brown, Michael J. I.; Holwerda, B. W.; Owers, Matt S.; Pimbblet, Kevin A.

2018-03-01

In this paper, we test if nearby blue spheroid (BSph) galaxies may become the progenitors of star-forming spiral galaxies or passively evolving elliptical galaxies. Our sample comprises 428 galaxies of various morphologies in the redshift range 0.002 < z < 0.02 (8-87 Mpc) with panchromatic data from the Galaxy and Mass Assembly survey. We find that BSph galaxies are structurally (mean effective surface brightness, effective radius) very similar to their passively evolving red counterparts. However, their star formation and other properties such as colour, age, and metallicity are more like star-forming spirals than spheroids (ellipticals and lenticulars). We show that BSph galaxies are statistically distinguishable from other spheroids as well as spirals in the multidimensional space mapped by luminosity-weighted age, metallicity, dust mass, and specific star formation rate. We use H I data to reveal that some of the BSphs are (further) developing their discs, hence their blue colours. They may eventually become spiral galaxies - if sufficient gas accretion occurs - or more likely fade into low-mass red galaxies.

The d*(2380) in Neutron Stars - A New Degree of Freedom?

NASA Astrophysics Data System (ADS)

Vidaña, I.; Bashkanov, M.; Watts, D. P.; Pastore, A.

2018-06-01

Elucidating the appropriate microscopic degrees of freedom within neutron stars remains an open question which impacts nuclear physics, particle physics and astrophysics. The recent discovery of the first non-trivial dibaryon, the d* (2380), provides a new candidate for an exotic degree of freedom in the nuclear equation of state at high matter densities. In this paper a first calculation of the role of the d* (2380) in neutron stars is performed based on a relativistic mean field description of the nucleonic degrees of freedom supplemented by a free boson gas of d* (2380). The calculations indicate that the d* (2380) would appear at densities around three times normal nuclear matter saturation density and comprise around 20% of the matter in the centre of heavy stars with higher fractions possible in the higher densities of merger processes. The d* (2380) would also reduce the maximum star mass by around 15% and have significant influence on the fractional proton/neutron composition. New possibilities for neutron star cooling mechanisms arising from the d* (2380) are also predicted.

Equation of state for neutron stars. Some recent developments

NASA Astrophysics Data System (ADS)

Haensel, P.; Fortin, M.

2017-12-01

Calculations using the chiral effective field theory (ChEFT) indicate that the four-body force contribution to the equation of state (EOS) of pure neutron matter (PNM) at the nuclear density n 0 is negligibly small. However, the overall uncertainty in the EOS of PNM at n 0 remains ∼ 20%. Relativistic mean field (RMF) calculations with in-medium scaling, and including hyperons and Δ resonances, can be made consistent with recent nuclear and astrophysical constraints. Dirac-Brueckner-Hartree-Fock calculations with some medium dependence of the nuclear interaction yield neutron star (NS) models with hyperonic cores consistent with 2 M⊙ stars and agreeing with the saturation parameters of nuclear matter. Many unified EOS for the NS crust and core were calculated, and are reviewed here. The effect of the finite size of baryons on the EOS, its treatment via the excluded-volume approximation, and its relevance for the hypothetical hybrid-star twins at ∼ 2 M⊙ are dicussed.

Sub-saturation matter in compact stars: Nuclear modelling in the framework of the extended Thomas-Fermi theory

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

Aymard, François; Gulminelli, Francesca; Margueron, Jérôme

A recently introduced analytical model for the nuclear density profile [1] is implemented in the Extended Thomas-Fermi (ETF) energy density functional. This allows to (i) shed a new light on the issue of the sign of surface symmetry energy in nuclear mass formulas, as well as to (ii) show the importance of the in-medium corrections to the nuclear cluster energies in thermodynamic conditions relevant for the description of core-collapse supernovae and (proto)-neutron star crust.

Sub-saturation matter in compact stars: Nuclear modelling in the framework of the extended Thomas-Fermi theory

NASA Astrophysics Data System (ADS)

Aymard, François; Gulminelli, Francesca; Margueron, Jérôme

2015-02-01

A recently introduced analytical model for the nuclear density profile [1] is implemented in the Extended Thomas-Fermi (ETF) energy density functional. This allows to (i) shed a new light on the issue of the sign of surface symmetry energy in nuclear mass formulas, as well as to (ii) show the importance of the in-medium corrections to the nuclear cluster energies in thermodynamic conditions relevant for the description of core-collapse supernovae and (proto)-neutron star crust.

THE HOT R CORONAE BOREALIS STAR DY CENTAURI IS A BINARY

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

Kameswara Rao, N.; Lambert, David L.; McArthur, Barbara

2012-11-20

The remarkable hot R Coronae Borealis (RCB) star DY Cen is revealed to be the first and only binary system to be found among the RCB stars and their likely relatives, including the extreme helium stars and the hydrogen-deficient carbon stars. Radial velocity determinations from 1982 to 2010 have shown that DY Cen is a single-lined spectroscopic binary in an eccentric orbit with a period of 39.67 days. It is also one of the hottest and most H-rich member of the class of RCB stars. The system may have evolved from a common envelope to its current form.

MASSIVE STARS IN THE LOCAL GROUP: Implications for Stellar Evolution and Star Formation

NASA Astrophysics Data System (ADS)

Massey, Philip

The galaxies of the Local Group serve as important laboratories for understanding the physics of massive stars. Here I discuss what is involved in identifying various kinds of massive stars in nearby galaxies: the hydrogen-burning O-type stars and their evolved He-burning evolutionary descendants, the luminous blue variables, red supergiants, and Wolf-Rayet stars. Primarily I review what our knowledge of the massive star population in nearby galaxies has taught us about stellar evolution and star formation. I show that the current generation of stellar evolutionary models do well at matching some of the observed features and provide a look at the sort of new observational data that will provide a benchmark against which new models can be evaluated.

Observations of suspected low-mass post-T Tauri stars and their evolutionary status

NASA Technical Reports Server (NTRS)

Mundt, R.; Walter, F. M.; Feigelson, E. D.; Finkenzeller, U.; Herbig, G. H.; Odell, A. P.

1983-01-01

The results of a study of five X-ray discovered weak emission pre-main-sequence stars in the Taurus-Auriga star formation complex are presented. All are of spectral type K7-M0, and about 1-2 mag above the main sequence. One is a double-lined spectroscopic binary, the first spectroscopic binary PMS star to be confirmed. The ages, masses, and radii of these stars as determined by photometry and spectroscopy are discussed. The difference in emission strength between these and the T Tauri stars is investigated, and it is concluded that these 'post-T Tauri' stars do indeed appear more evolved than the T Tauri stars, although there is no evidence of any significant difference in ages.

p-capture reaction cycles in rotating massive stars and their impact on elemental abundances in globular cluster stars: A case study of O, Na and Al

NASA Astrophysics Data System (ADS)

Mahanta, Upakul; Goswami, Aruna; Duorah, Hiralal; Duorah, Kalpana

2017-08-01

Elemental abundance patterns of globular cluster stars can provide important clues for understanding cluster formation and early chemical evolution. The origin of the abundance patterns, however, still remains poorly understood. We have studied the impact of p-capture reaction cycles on the abundances of oxygen, sodium and aluminium considering nuclear reaction cycles of carbon-nitrogen-oxygen-fluorine, neon-sodium and magnesium-aluminium in massive stars in stellar conditions of temperature range 2×107 to 10×107 K and typical density of 102 gm cc-1. We have estimated abundances of oxygen, sodium and aluminium with respect to Fe, which are then assumed to be ejected from those stars because of rotation reaching a critical limit. These ejected abundances of elements are then compared with their counterparts that have been observed in some metal-poor evolved stars, mainly giants and red giants, of globular clusters M3, M4, M13 and NGC 6752. We observe an excellent agreement with [O/Fe] between the estimated and observed abundance values for globular clusters M3 and M4 with a correlation coefficient above 0.9 and a strong linear correlation for the remaining two clusters with a correlation coefficient above 0.7. The estimated [Na/Fe] is found to have a correlation coefficient above 0.7, thus implying a strong correlation for all four globular clusters. As far as [Al/Fe] is concerned, it also shows a strong correlation between the estimated abundance and the observed abundance for globular clusters M13 and NGC 6752, since here also the correlation coefficient is above 0.7 whereas for globular cluster M4 there is a moderate correlation found with a correlation coefficient above 0.6. Possible sources of these discrepancies are discussed.

Mass-losing peculiar red giants - The comparison between theory and observations

NASA Technical Reports Server (NTRS)

Jura, M.

1989-01-01

The mass loss from evolved red giants is considered. It seems that red giants on the Asymptotic Giant Branch (AGB) are losing between 0.0003 and 0.0006 solar mass/sq kpc yr in the solar neighborhood. If all the main sequence stars between 1 and 5 solar masses ultimately evolve into white dwarfs with masses of 0.7 solar mass, the predicted mass loss rate in the solar neighborhood from these stars is 0.0008 solar mass/sq kpc yr. Although there are still uncertainties, it appears that there is no strong disagreement between theory and observation.

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

Danchi, William C.; Lopez, Bruno, E-mail: william.c.danchi@nasa.gov, E-mail: bruno.lopez@oca.eu

During the course of stellar evolution, the location and width of the habitable zone changes as the luminosity and radius of the star evolves. The duration of habitability for a planet located at a given distance from a star is greatly affected by the characteristics of the host star. A quantification of these effects can be used observationally in the search for life around nearby stars. The longer the duration of habitability, the more likely it is that life has evolved. The preparation of observational techniques aimed at detecting life would benefit from the scientific requirements deduced from the evolutionmore » of the habitable zone. We present a study of the evolution of the habitable zone around stars of 1.0, 1.5, and 2.0 M{sub Sun} for metallicities ranging from Z = 0.0001 to Z = 0.070. We also consider the evolution of the habitable zone from the pre-main sequence until the asymptotic giant branch is reached. We find that metallicity strongly affects the duration of the habitable zone for a planet as well as the distance from the host star where the duration is maximized. For a 1.0 M{sub Sun} star with near solar metallicity, Z = 0.017, the duration of the habitable zone is >10 Gyr at distances 1.2-2.0 AU from the star, whereas the duration is >20 Gyr for high-metallicity stars (Z = 0.070) at distances of 0.7-1.8 AU, and {approx}4 Gyr at distances of 1.8-3.3 AU for low-metallicity stars (Z = 0.0001). Corresponding results have been obtained for stars of 1.5 and 2.0 solar masses.« less

Structural analysis of star-forming blue early-type galaxies. Merger-driven star formation in elliptical galaxies

NASA Astrophysics Data System (ADS)

George, Koshy

2017-02-01

Context. Star-forming blue early-type galaxies at low redshift can give insight to the stellar mass growth of L⋆ elliptical galaxies in the local Universe. Aims: We wish to understand the reason for star formation in these otherwise passively evolving red and dead stellar systems. The fuel for star formation can be acquired through recent accretion events such as mergers or flyby. The signatures of such events should be evident from a structural analysis of the galaxy image. Methods: We carried out structural analysis on SDSS r-band imaging data of 55 star-forming blue elliptical galaxies, derived the structural parameters, analysed the residuals from best-fit to surface brightness distribution, and constructed the galaxy scaling relations. Results: We found that star-forming blue early-type galaxies are bulge-dominated systems with axial ratio >0.5 and surface brightness profiles fitted by Sérsic profiles with index (n) mostly >2. Twenty-three galaxies are found to have n< 2; these could be hosting a disc component. The residual images of the 32 galaxy surface brightness profile fits show structural features indicative of recent interactions. The star-forming blue elliptical galaxies follow the Kormendy relation and show the characteristics of normal elliptical galaxies as far as structural analysis is concerned. There is a general trend for high-luminosity galaxies to display interaction signatures and high star formation rates. Conclusions: The star-forming population of blue early-type galaxies at low redshifts could be normal ellipticals that might have undergone a recent gas-rich minor merger event. The star formation in these galaxies will shut down once the recently acquired fuel is consumed, following which the galaxy will evolve to a normal early-type galaxy.

The Mass-loss Return from Evolved Stars to the Large Magellanic Cloud. IV. Construction and Validation of a Grid of Models for Oxygen-rich AGB Stars, Red Supergiants, and Extreme AGB Stars

NASA Astrophysics Data System (ADS)

Sargent, Benjamin A.; Srinivasan, S.; Meixner, M.

2011-02-01

To measure the mass loss from dusty oxygen-rich (O-rich) evolved stars in the Large Magellanic Cloud (LMC), we have constructed a grid of models of spherically symmetric dust shells around stars with constant mass-loss rates using 2Dust. These models will constitute the O-rich model part of the "Grid of Red supergiant and Asymptotic giant branch star ModelS" (GRAMS). This model grid explores four parameters—stellar effective temperature from 2100 K to 4700 K luminosity from 103 to 106 L sun; dust shell inner radii of 3, 7, 11, and 15 R star; and 10.0 μm optical depth from 10-4 to 26. From an initial grid of ~1200 2Dust models, we create a larger grid of ~69,000 models by scaling to cover the luminosity range required by the data. These models are available online to the public. The matching in color-magnitude diagrams and color-color diagrams to observed O-rich asymptotic giant branch (AGB) and red supergiant (RSG) candidate stars from the SAGE and SAGE-Spec LMC samples and a small sample of OH/IR stars is generally very good. The extreme AGB star candidates from SAGE are more consistent with carbon-rich (C-rich) than O-rich dust composition. Our model grid suggests lower limits to the mid-infrared colors of the dustiest AGB stars for which the chemistry could be O-rich. Finally, the fitting of GRAMS models to spectral energy distributions of sources fit by other studies provides additional verification of our grid and anticipates future, more expansive efforts.

New Galactic Candidate Luminous Blue Variables and Wolf-Rayet Stars

NASA Astrophysics Data System (ADS)

Stringfellow, Guy S.; Gvaramadze, Vasilii V.; Beletsky, Yuri; Kniazev, Alexei Y.

2012-04-01

We have undertaken a near-infrared spectral survey of stars associated with compact mid-IR shells recently revealed by the MIPSGAL (24 μm) and GLIMPSE (8 μm) Spitzer surveys, whose morphologies are typical of circumstellar shells produced by massive evolved stars. Through spectral similarity with known Luminous Blue Variable (LBV) and Wolf-Rayet (WR) stars, a large population of candidate LBVs (cLBVs) and a smaller number of new WR stars are being discovered. This significantly increases the Galactic cLBV population and confirms that nebulae are inherent to most (if not all) objects of this class.

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 via a photometric survey of RSGs in M31, followed up by spectroscopy with the Multiple Mirror Telescope. They determined that the star is also separated from other massive stars in the disk of the galaxy by about 4.6 kpc which is roughly the distance it would be expected to travel, given its discrepant motion, in an assumed age of about 10 Myr.The authors suggest that this star may be a high-mass analog of hypervelocity stars stars within the Milky Way that are moving fast enough to escape the galaxy. The authors demonstrate that the total discrepant speed of RSG J004330.06+405258.4 is probably comparable to the escape velocity of M31s disk.But whether or not this star is moving fast enough to escape turns out to be moot: it will only live another million years, which means it wont have enough time to leave the galaxy before ending its life in a spectacular supernova. Citation: Kate Anne Evans and Philip Massey 2015 AJ 150 149. doi:10.1088/0004-6256/150/5/149

LUNA, an underground nuclear astrophysics laboratory: recent results and future perspectives

NASA Astrophysics Data System (ADS)

Corvisiero, P.

2005-05-01

It is known that the chemical elements and their isotopes were created by nuclear fusion reactions in the hot interiors of remote and long-vanished stars over many billions of years. The present picture is that all elements from carbon to uranium have been produced entirely within stars during their fiery lifetimes and explosive deaths. The detailed understanding of the origin of the chemical elements and their isotopes combines astrophysics and nuclear physics, and forms what is called nuclear astrophysics. In turn, nuclear reactions are at the heart of nuclear astrophysics: they influence sensitively the nucleosynthesis of the elements in the earliest stages of the universe and in all the objects formed thereafter, and control the associated energy generation, neutrino luminosity, and evolution of stars. A good knowledge of the rates of these fusion reactions is essential to understanding this broad picture. Some of the most important experimental techniques to measure the corresponding cross sections, based both on direct and indirect methods, will be described in this paper.

From the sun to the Galactic Center: dust, stars and black hole(s)

NASA Astrophysics Data System (ADS)

Fritz, Tobias

2013-07-01

The centers of galaxies are their own ultimate gravitational sinks. Massive black holes and star clusters as well as gas are especially likely to fall into the centers of galaxies by dynamical friction or dissipation. Many galactic centers harbor supermassive black holes (SMBH) and dense nuclear (star) clusters which possibly arrived there by these processes. Nuclear clusters can be formed in situ from gas, or from smaller star clusters which fall to the center. Since the Milky Way harbors both an SMBH and a nuclear cluster, both can be studied best in the Galactic Center (GC), which is the closest galactic nucleus to us. In Chapter 1, I introduce the different components of the Milky Way, and put these into the context of the GC. I then give an overview of relevant properties (e.g. star content and distribution) of the GC. Afterwards, I report the results of four different studies about the GC. In Chapter 2, I analyze the limitations of astrometry, one of the most useful methods for the study of the GC. Thanks to the high density of stars and its relatively small distance from us it is possible to measure the motions of thousands of stars in the GC with images, separated by few years only. I find two main limitations to this method: (1) for bright stars the not perfectly correctable distortion of the camera limits the accuracy, and (2) for the majority of the fainter stars, the main limitation is crowding from the other stars in the GC. The position uncertainty of faint stars is mainly caused by the seeing halos of bright stars. In the very center faint unresolvable stars are also important for the position uncertainty. In Chapter 3, I evaluate the evidence for an intermediate mass black hole in the small candidate cluster IRS13E within the GC. Intermediate mass black holes (IMBHs) have a mass between the two types of confirmed black hole: the stellar remnants and the supermassive black holes in the centers of galaxies. One possibility for! their formation is the collision of stars in a dense young st! ar cluster. Such a cluster could sink to the GC by dynamical friction. There it would consist of few bright stars like IRS13E. Firstly, I analyze the SEDs of the objects in IRS13E. The SEDs of most objects can be explained by pure dust emission. Thus, most objects in IRS13E are pure dust clumps and only three young stars. This reduces the significance of the 'cluster' IRS13E compared to the stellar background. Secondly, I obtain acceleration limits for these three stars. The non-detection of accelerations makes an IMBH an unlikely scenario in IRS13E. However, since its three stars form a comoving association, which is unlikely to form by chance, the nature of IRS13E is not yet settled. In the third study (Chapter 4) I measure and analyze the extinction curve toward the GC. The extinction is a contaminant for GC observations and therefore it is necessary to know the extinction toward the GC to determine the luminosity properties of its stars. I obtain the extinction curve by measuring the flux of the HII region in the GC in several infrared HII lines and in the unextincted radio continuum. I compare these ratios with the ratios expected from recombination physics and obtain extinctions at 22 different lines between 1 and 19 micron. For the K-band I derive A_Ks=2.62+/-0.11. The extinction curve follows a power law with a steep slope of -2.11+/-0.06 shortward of 2.8 micron. At longer wavelengths the extinction is grayer and there are absorption features from ices. The extinction curve is a tool to constrain the properties of cosmic dust between the sun and the GC. The extinction curve cannot be explained by dust grains consisting of carbonaceous and silicate grains only. In addition composite particles, which also contain ices are necessary to fit the extinction curve. In the final part of this thesis (Chapter 5) I look at the properties of most of the stars in the GC. These are the old stars that form the nuclear cluster of the Milky Way. I obtain the mass distribution and the light distribution of these stars. I ! find that the flattening of the stellar distribution increases outside 70''. This indicates that inside a nearly spherical nuclear cluster dominates and that the surrounding light belongs mostly to the nuclear disk. I dissect the light in two components and obtain for the nuclear cluster L_Ks=2.7*10^7 L_sun. I obtain proper motions for more than 10000 stars and radial velocities for more than 2400 stars. Using Jeans modeling I combine velocities and the radial profile to obtain within 100'' (4 pc) a mass of 6.02*10^6 M_sun and a total nuclear cluster mass of 12.88*10^6 M_sun. The Jeans modeling and various other evidence weakly favor a core in the extended mass compared to a cusp. The old star light shows a similar core. The mass to light ratio of the old stars of the nuclear cluster is consistent with the usual initial mass function in the Galaxy. This suggests that most stars in GC formed in the usual way, in a mode different from the origin of the youngest stars there.

The Influence of Stellar Spin on Ignition of Thermonuclear Runaways

NASA Astrophysics Data System (ADS)

Galloway, Duncan K.; in ’t Zand, Jean J. M.; Chenevez, Jérôme; Keek, Laurens; Sanchez-Fernandez, Celia; Worpel, Hauke; Lampe, Nathanael; Kuulkers, Erik; Watts, Anna; Ootes, Laura; The MINBAR collaboration

2018-04-01

Runaway thermonuclear burning of a layer of accumulated fuel on the surface of a compact star provides a brief but intense display of stellar nuclear processes. For neutron stars accreting from a binary companion, these events manifest as thermonuclear (type-I) X-ray bursts, and recur on typical timescales of hours to days. We measured the burst rate as a function of accretion rate, from seven neutron stars with known spin rates, using a burst sample accumulated over several decades. At the highest accretion rates, the burst rate is lower for faster spinning stars. The observations imply that fast (>400 Hz) rotation encourages stabilization of nuclear burning, suggesting a dynamical dependence of nuclear ignition on the spin rate. This dependence is unexpected, because faster rotation entails less shear between the surrounding accretion disk and the star. Large-scale circulation in the fuel layer, leading to enhanced mixing of the burst ashes into the fuel layer, may explain this behavior; further numerical simulations are required to confirm this.

Mode extraction from time series: from the challenges of COROT to those of Eddington

NASA Astrophysics Data System (ADS)

Appourchaux, T.; Moreira, O.; Berthomieu, G.; Toutain, T.

2004-01-01

With more than 30 years of experience in extraction of eigenmodes from power spectra of solar signals, we are now almost ready to apply this knowledge onto the forecoming missions: COROT and Eddington. However the fitting task differs by 3 orders of magnitude; COROT will be able to get time series of stellar light for some 30 stars, while Eddington will be able to gather such data for about 50000 stars. While for COROT, our current tools can be applied by hand, the case of Eddington is significantly more complex. We are looking forward having automatic fitting procedures that will allow to recover mode parameters for about 90% of the solar-like stars. Unfortunately, about 10% of these stars will require some more delicate attention that will cost time to take care of. We will use the example of the infamous HD 57006, known to be quite evolved with a difficult eigenmode spectrum, to explain how a star can evolve from an easy-to-fit target (90% of the solar-like stars) to a difficult-to-fit (10% of the remaining stars). In the latter case, new techniques for detecting narrow peaks (g-mode like) out of broad peaks (p-mode like) has been devised in the context of the hare-and-hound exercise of COROT. This and other techniques will be used to implement the automatic fitting procedure for the remaining 10% of Eddington solar-like stars.

A Jupiter-mass planet around the K0 giant HD 208897

NASA Astrophysics Data System (ADS)

Yılmaz, M.; Sato, B.; Bikmaev, I.; Selam, S. O.; Izumiura, H.; Keskin, V.; Kambe, E.; Melnikov, S. S.; Galeev, A.; Özavcı, İ.; Irtuganov, E. N.; Zhuchkov, R. Ya.

2017-11-01

For over 10 years, we have carried out a precise radial velocity (RV) survey to find substellar companions around evolved G, K-type stars to extend our knowledge of planet formation and evolution. We performed high precision RV measurements for the giant star HD 208897 using an iodine (I2) absorption cell. The measurements were made at TÜBİTAK National Observatory (TUG; RTT150) and Okayama Astrophysical Observatory (OAO). For the origin of the periodic variation seen in the RV data of the star, we adopted a Keplerian motion caused by an unseen companion. We found that the star hosts a planet with a minimum mass of m2sini = 1.40 MJ, which is relatively low compared to those of known planets orbiting evolved intermediate-mass stars. The planet is in a nearly circular orbit with a period of P = 353 days at about 1 AU distance from the host star. The star is metal rich and located at the early phase of ascent along the red giant branch. The photometric observations of the star at Ankara University Kreiken Observatory (AUKR) and the Hipparcos photometry show no sign of variation with periods associated with the RV variation. Neither bisector velocity analysis nor analysis of the Ca II and Hα lines shows any correlation with the RV measurements. This work was supported by The Scientific and Technological Research Council of Turkey (TÜBİTAK), the project number of 114F099.

Cloud physics laboratory project science and applications working group

NASA Technical Reports Server (NTRS)

Hung, R. J.

1977-01-01

The conditions of the expansion chamber under zero gravity environment were simulated. The following three branches of fluid mechanics simulation under low gravity environment were accomplished: (1) oscillation of the water droplet which characterizes the nuclear oscillation in nuclear physics, bubble oscillation of two phase flow in chemical engineering, and water drop oscillation in meteorology; (2) rotation of the droplet which characterizes nuclear fission in nuclear physics, formation of binary stars and rotating stars in astrophysics, and breakup of the water droplet in meteorology; and (3) collision and coalescence of the water droplets which characterizes nuclear fusion in nuclear physics and processes of rain formation in meteorology.

Pox 186: A Nearby Protogalaxy?

NASA Astrophysics Data System (ADS)

Corbin, Michael

1999-07-01

Blue Compact Dwarf Galaxies {BCDGs} typically consist of clusters of early-type stars embedded in older, evolved stellar populations similar in size and shape to normal dwarf ellipticals. However, deep ground-based CCD images of one faint BCDG, Pox 186, reveal a very compact { 5" diameter} structure with no evidence of an underlying older population. Optical spectroscopy of this object also indicates that a large number of Wolf-Rayet stars are present, which implies that a burst of star formation must have occurred very recently {<=sssim 10^7 years ago}. It has thus been suggested that Pox 186 is a protogalaxy, forming its very first generation of stars. Further investigation of this possibility requires the high angular resolution and ultraviolet spectral coverage that only HST can provide. Using WFPC2, we propose to image the galaxy in the U, V, and I bands, in order to better test for the presence of an underlying evolved population and to reveal any substructure in its star-forming regions. Using STIS, we will obtain low-resolution ultraviolet spectra of the galaxy for combination with ground-based spectra covering the optical through near infrared. This will allow us to determine its spectral energy distribution, metallicity, and dust content, which will in turn constrain its age and star formation history.

Gravity modes as a way to distinguish between hydrogen- and helium-burning red giant stars.

PubMed

Bedding, Timothy R; Mosser, Benoit; Huber, Daniel; Montalbán, Josefina; Beck, Paul; Christensen-Dalsgaard, Jørgen; Elsworth, Yvonne P; García, Rafael A; Miglio, Andrea; Stello, Dennis; White, Timothy R; De Ridder, Joris; Hekker, Saskia; Aerts, Conny; Barban, Caroline; Belkacem, Kevin; Broomhall, Anne-Marie; Brown, Timothy M; Buzasi, Derek L; Carrier, Fabien; Chaplin, William J; Di Mauro, Maria Pia; Dupret, Marc-Antoine; Frandsen, Søren; Gilliland, Ronald L; Goupil, Marie-Jo; Jenkins, Jon M; Kallinger, Thomas; Kawaler, Steven; Kjeldsen, Hans; Mathur, Savita; Noels, Arlette; Aguirre, Victor Silva; Ventura, Paolo

2011-03-31

Red giants are evolved stars that have exhausted the supply of hydrogen in their cores and instead burn hydrogen in a surrounding shell. Once a red giant is sufficiently evolved, the helium in the core also undergoes fusion. Outstanding issues in our understanding of red giants include uncertainties in the amount of mass lost at the surface before helium ignition and the amount of internal mixing from rotation and other processes. Progress is hampered by our inability to distinguish between red giants burning helium in the core and those still only burning hydrogen in a shell. Asteroseismology offers a way forward, being a powerful tool for probing the internal structures of stars using their natural oscillation frequencies. Here we report observations of gravity-mode period spacings in red giants that permit a distinction between evolutionary stages to be made. We use high-precision photometry obtained by the Kepler spacecraft over more than a year to measure oscillations in several hundred red giants. We find many stars whose dipole modes show sequences with approximately regular period spacings. These stars fall into two clear groups, allowing us to distinguish unambiguously between hydrogen-shell-burning stars (period spacing mostly ∼ 50 seconds) and those that are also burning helium (period spacing ∼ 100 to 300 seconds).

An Adaptive QSE-reduced Nuclear Reaction Network for Silicon Burning

NASA Astrophysics Data System (ADS)

Parete-Koon, Suzanne; Hix, William Raphael; Thielemann, Friedrich-Karl

2010-02-01

The nuclei of the ``iron peak'' are formed late in the evolution of massive stars and during supernovae. Silicon burning during these events is responsible for the production of a wide range of nuclei with atomic mass numbers from 28 to 64. The large number of nuclei involved make accurate modeling of silicon burning computationally expensive. Examination of the physics of silicon burning reveals that the nuclear evolution is dominated by large groups of nuclei in mutual equilibrium. We present an improvement on our hybrid equilibrium-network scheme that takes advantage of this quasi-equilibrium (QSE) to reduce the number of independent variables calculated. Because the membership and number of these groups vary as the temperature, density and electron faction change, achieving maximal efficiency requires dynamic adjustment of group number and membership. The resultant QSE-reduced network is up to 20 times faster than the full network it replaces without significant loss of accuracy. These reductions in computational cost and the number of species evolved make QSE-reduced networks well suited for inclusion within hydrodynamic simulations, particularly in multi-dimensional applications. )

A catalog of rotational and radial velocities for evolved stars. V. Southern stars

NASA Astrophysics Data System (ADS)

De Medeiros, J. R.; Alves, S.; Udry, S.; Andersen, J.; Nordström, B.; Mayor, M.

2014-01-01

Rotational and radial velocities have been measured for 1589 evolved stars of spectral types F, G, and K and luminosity classes IV, III, II, and Ib, based on observations carried out with the CORAVEL spectrometers. The precision in radial velocity is better than 0.30 km s-1 per observation, whereas rotational velocity uncertainties are typically 1.0 km s-1 for subgiants and giants and 2.0 km s-1 for class II giants and Ib supergiants. Based on observations collected at the Haute-Provence Observatory, Saint-Michel, France, and at the European Southern Observatory, La Silla, Chile.Table 1 is only available at the 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/561/A126

OT2_nflagey_2: Capturing missing evolved stars in the Galactic plane

NASA Astrophysics Data System (ADS)

Flagey, N.

2011-09-01

We discovered more than 400 compact shells in the MIPSGAL 24 microns survey of the Galactic plane. About 15% of all these objects were already known as planetary nebulae, supernova remnants, Wolf-Rayet stars, and luminous blue variables. The unknown bubbles are expected to be envelopes of evolved stars that could account for the ``missing massive stars in the Galaxy. Indeed, recent spectroscopic follow-ups in the near-IR and mid-IR have revealed several dust-free planetary nebulae with very hot central white dwarf and significantly increased the number of WR and LBV candidates. Our OT1 Priority 1 proposal just provided us with a first observation in the PACS-SED B2A mode of one object, revealing only a strong [N II] 122 microns line. Without further spectral information, identification and modeling of the target are impossible. However, analysis of the PACS and SPIRE data from the HiGal survey has recently enabled us to measure much higher detection rates of the shells in the far-IR than with MIPS 70 microns. We are thus very confident that dust features and/or gas lines can be detected with the PACS and SPIRE spectrometers. Therefore, we request complementary PACS-SED B2B and SPIRE-FTS observations on our OT1 sample. The complete far-IR/submm spectrum of each target will allow its unequivocal identification thanks to comparison with spectra of known evolved stars from the MESS key program. We will also model with much detail the different phases of the envelopes, thanks to our expertise in circumstellar envelopes, dust models and photoionization codes.

On the Spatially Resolved Star Formation History in M51. II. X-Ray Binary Population Evolution

NASA Astrophysics Data System (ADS)

Lehmer, B. D.; Eufrasio, R. T.; Markwardt, L.; Zezas, A.; Basu-Zych, A.; Fragos, T.; Hornschemeier, A. E.; Ptak, A.; Tzanavaris, P.; Yukita, M.

2017-12-01

We present a new technique for empirically calibrating how the X-ray luminosity function (XLF) of X-ray binary (XRB) populations evolves following a star formation event. We first utilize detailed stellar population synthesis modeling of far-UV-to-far-IR photometry of the nearby face-on spiral galaxy M51 to construct maps of the star formation histories (SFHs) on subgalactic (≈400 pc) scales. Next, we use the ≈850 ks cumulative Chandra exposure of M51 to identify and isolate 2-7 keV detected point sources within the galaxy, and we use our SFH maps to recover the local properties of the stellar populations in which each X-ray source is located. We then divide the galaxy into various subregions based on their SFH properties (e.g., star formation rate (SFR) per stellar mass ({M}\\star ) and mass-weighted stellar age) and group the X-ray point sources according to the characteristics of the regions in which they are found. Finally, we construct and fit a parameterized XLF model that quantifies how the XLF shape and normalization evolves as a function of the XRB population age Our best-fit model indicates that the XRB XLF per unit stellar mass declines in normalization, by ˜3-3.5 dex, and steepens in slope from ≈10 Myr to ≈10 Gyr. We find that our technique recovers results from past studies of how XRB XLFs and XRB luminosity scaling relations vary with age and provides a self-consistent picture for how XRB XLFs evolve with age.

Nucleosynthesis in the first massive stars

NASA Astrophysics Data System (ADS)

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

2018-01-01

The nucleosynthesis in the first massive stars may be constrained by observing the surface composition of long-lived very iron-poor stars born around 10 billion years ago from material enriched by their ejecta. Many interesting clues on physical processes having occurred in the first stars can be obtained based on nuclear aspects. First, in these first massive stars, mixing must have occurred between the H-burning and the He-burning zone during their nuclear lifetimes; Second, only the outer layers of these massive stars have enriched the material from which the very iron-poor stars, observed today in the halo of the MilkyWay, have formed. These two basic requirements can be obtained by rotating stellar models at very low metallicity. In the present paper, we discuss the arguments supporting this view and illustrate the sensitivity of the results concerning the [Mg/Al] ratio on the rate of the reaction 23Na(p,γ)24Mg.

Super Star Clusters and H II Regions in Nuclear Rings

NASA Astrophysics Data System (ADS)

Filippenko, Alex

1996-07-01

We propose to obtain WFPC2 optical broad-band {F547M and F814W} and narrow-band Halpha+ionN2 {F658N} images of nuclear starburst rings in four nearby galaxies for which we already have ultraviolet {F220W} FOC data. Nuclear rings {or ``hot- spot'' regions} in barred spirals are some of the nearest and least obscured starburst regions, and HST images of nuclear rings in several galaxies show that the rings contain large populations of super star clusters similar to those recently discovered in other types of starburst systems. These compact clusters, many having luminosities exceeding that of the R136 cluster in 30 Doradus, represent a violent mode of star formation distinct from that seen in ordinary disk ionH2 regions, and the nuclear rings present us with an opportunity to study large numbers of these extreme clusters in relatively unobscured starburst environments. It has been suggested that super star clusters are present-day versions of young globular clusters. To evaluate this hypothesis, it is important to understand the physical properties and stellar contents of the clusters, but previous HST studies of nuclear ring galaxies have only used single-filter observations. Together with our UV data, new WFPC2 images will enable us to determine the H II region and cluster luminosity functions within nuclear rings, measure cluster radii, derive age and mass estimates for the clusters by comparison with evolutionary synthesis models, and study the structure and evolution of nuclear rings.

Common-envelope ejection in massive binary stars. Implications for the progenitors of GW150914 and GW151226

NASA Astrophysics Data System (ADS)

Kruckow, M. U.; Tauris, T. M.; Langer, N.; Szécsi, D.; Marchant, P.; Podsiadlowski, Ph.

2016-11-01

Context. The recently detected gravitational wave signals (GW150914 and GW151226) of the merger event of a pair of relatively massive stellar-mass black holes (BHs) calls for an investigation of the formation of such progenitor systems in general. Aims: We analyse the common-envelope (CE) stage of the traditional formation channel in binaries where the first-formed compact object undergoes an in-spiral inside the envelope of its evolved companion star and ejects the envelope in this process. Methods: We calculated envelope binding energies of donor stars with initial masses between 4 and 115M⊙ for metallicities of Z = ZMilky Way ≃ Z⊙/ 2 and Z = Z⊙/ 50, and derived minimum masses of in-spiralling objects needed to eject these envelopes. Results: In addition to producing double white dwarf and double neutron star binaries, CE evolution may also produce massive BH-BH systems with individual BH component masses of up to 50 - 60M⊙, in particular for donor stars evolved to giants beyond the Hertzsprung gap. However, the physics of envelope ejection of massive stars remains uncertain. We discuss the applicability of the energy-budget formalism, the location of the bifurcation point, the recombination energy, and the accretion energy during in-spiral as possible energy sources, and also comment on the effect of inflated helium cores. Conclusions: Massive stars in a wide range of metallicities and with initial masses of up to at least 115M⊙ may shed their envelopes and survive CE evolution, depending on their initial orbital parameters, similarly to the situation for intermediate- and low-mass stars with degenerate cores. In addition to being dependent on stellar radius, the envelope binding energies and λ-values also depend on the applied convective core-overshooting parameter, whereas these structure parameters are basically independent of metallicity for stars with initial masses below 60M⊙. Metal-rich stars ≳60M⊙ become luminous blue variables and do not evolve to reach the red giant stage. We conclude that based on stellar structure calculations, and in the view of the usual simple energy budget analysis, events like GW150914 and GW151226 might be produced by the CE channel. Calculations of post-CE orbital separations, however, and thus the estimated LIGO detection rates, remain highly uncertain.

Submillimeter Array reveals molecular complexity of dying stars

NASA Astrophysics Data System (ADS)

Tomasz

2018-01-01

The unique capabilities of the Submillimeter Array (SMA) have allowed unprecedented studies of cool evolved stars at submillimeter wavelengths. In particular, the SMA now offers the possibility to image multiple molecular transitions at once, owing to the 32-GHz wide instantaneous bandwidth of SWARM, the SMA’s new correlator. Molecular gas located far and very close to the photosphere of an asymptotic-giant branch (AGB) star, a red supergiant, or a pre-planetary nebula can now be examined in transitions observed simultaneously from a wide range of energy levels. This allows a very detailed quantitative investigation of physical and chemical conditions around these variable objects. Several imaging line surveys have been obtained with the SMA to reveal the beautiful complexity of these evolved systems. The surveys resulted in first submillimeter-wave identifications of molecules of prime astrophysical interest, e.g. of TiO, TiO2, and of rotational transitions at excited vibrational states of CO. An overview of recent SMA observations of cool evolved stars will be given with an emphasize on the interferometric line surveys. We will demonstrate their importance in unraveling the mass-loss phenomena, propagation of shocks in the circumstellar medium, and production of dust at elevated temperatures. The SMA studies of these molecular factories have a direct impact on our understanding of the chemical evolution of the Galaxy and stellar evolution at low and high masses.

Modelling Kepler red giants in eclipsing binaries: calibrating the mixing-length parameter with asteroseismology

NASA Astrophysics Data System (ADS)

Li, Tanda; Bedding, Timothy R.; Huber, Daniel; Ball, Warrick H.; Stello, Dennis; Murphy, Simon J.; Bland-Hawthorn, Joss

2018-03-01

Stellar models rely on a number of free parameters. High-quality observations of eclipsing binary stars observed by Kepler offer a great opportunity to calibrate model parameters for evolved stars. Our study focuses on six Kepler red giants with the goal of calibrating the mixing-length parameter of convection as well as the asteroseismic surface term in models. We introduce a new method to improve the identification of oscillation modes that exploits theoretical frequencies to guide the mode identification (`peak-bagging') stage of the data analysis. Our results indicate that the convective mixing-length parameter (α) is ≈14 per cent larger for red giants than for the Sun, in agreement with recent results from modelling the APOGEE stars. We found that the asteroseismic surface term (i.e. the frequency offset between the observed and predicted modes) correlates with stellar parameters (Teff, log g) and the mixing-length parameter. This frequency offset generally decreases as giants evolve. The two coefficients a-1 and a3 for the inverse and cubic terms that have been used to describe the surface term correction are found to correlate linearly. The effect of the surface term is also seen in the p-g mixed modes; however, established methods for correcting the effect are not able to properly correct the g-dominated modes in late evolved stars.

ACCURATE OH MASER POSITIONS FROM THE SPLASH PILOT REGION

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

Qiao, Hai-Hua; Shen, Zhi-Qiang; Walsh, Andrew J.

2016-12-01

We report on high spatial resolution observations, using the Australia Telescope Compact Array (ATCA), of ground-state OH masers. These observations were carried out toward 196 pointing centers previously identified in the Southern Parkes Large-Area Survey in Hydroxyl (SPLASH) pilot region, between Galactic longitudes of 334° and 344° and Galactic latitudes of −2° and +2°. Supplementing our data with data from the MAGMO (Mapping the Galactic Magnetic field through OH masers) survey, we find maser emission toward 175 of the 196 target fields. We conclude that about half of the 21 nondetections were due to intrinsic variability. Due to the superiormore » sensitivity of the followup ATCA observations, and the ability to resolve nearby sources into separate sites, we have identified 215 OH maser sites toward the 175 fields with detections. Among these 215 OH maser sites, 111 are new detections. After comparing the positions of these 215 maser sites to the literature, we identify 122 (57%) sites associated with evolved stars (one of which is a planetary nebula), 64 (30%) with star formation, two sites with supernova remnants, and 27 (13%) of unknown origin. The infrared colors of evolved star sites with symmetric maser profiles tend to be redder than those of evolved star sites with asymmetric maser profiles, which may indicate that symmetric sources are generally at an earlier evolutionary stage.« less

Magnetic Fields And The Formation Of Aspherical Planetary Nebulae

NASA Astrophysics Data System (ADS)

Leal Ferreira, Marcelo L.

2014-11-01

The general evolution of stars with initial mass between 0.8 and 8 solar masses is believed to be well understood until the last stages, when significant mass loss starts. However, an initially spherical star may evolve into an asymmetrical planetary nebula (PN), whereas the underlying mechanism to this process remains as a puzzle. Until about a decade ago, it was believed that stars in the asymptotic giant branch (AGB) phase were still spherically symmetric. Nevertheless, observations performed in the last years show that, for some sources, elongated and asymmetrical envelopes can already be detected during the AGB phase. In the following pre-PN and planetary nebula phases, a variety of morphologies is observed, and the sources are classified into round, elliptical/elongated, bipolar, quadrupolar, multipolar, spiral, collimated lobes and irregular. It is unknown which mechanism or set of mechanisms is responsible for this change of morphology, making this topic to be one of the most discussed by the evolved stars community. To shed some light on this problem, three AGB stars (IK Tau, R Scl, and V644 Sco) and one red supergiant (VY CMa) were observed at optical wavelengths. We analyzed their dust scattered emission and searched for signs of upcoming asymmetries in their circumstellar envelope. The observations in R band reveal that the dust envelope of the AGB star IK Tau has a global elliptical morphology, and the presence of a central waist is discussed. The observation of VY CMa shows a complex morphology in the very extended nebula that surrounds the source. Furthermore, for the first time the detached shell around the AGB star V644 Sco was imaged, allowing a better investigation of the mass-loss episodes of the source. The detached shell around R Scl was also imaged and analyzed. The results reported in this thesis add together with previous works, confirming that the loss of spherical symmetry in the circumstellar envelope of evolved stars can already start during the AGB phase. Moreover, we studied one of the mechanisms that can play a role in the shaping process of the circumstellar envelope of these sources: magnetic fields. For this purpose, we investigated 22 GHz H2O maser observations around five sources: four AGB stars (IK Tau, RT Vir, IRC+60370, and AP Lyn) and one pre-PN (OH231.8+4.2). By analyzing the linear and circular polarization in the masers, we detected the presence of magnetic field in four of these five sources. We measured the field strengths to be from a few tens up to a few hundreds of milligauss in the H2O maser region (at a few tens of astronomical units from the star). Comparing our results with magnetic field measurements from the literature, obtained at different distances with respect to the stars, we tried to determine the most plausible geometry of the magnetic fields for the observed sources. However, it is not yet definitive if the observed fields are toroidal, poloidal, or dipole. The influence of magnetic fields on the shaping process of the circumstellar envelope of evolved stars is still unclear, but their detection around AGB stars, pre-PNe and PNe supports that they might play a role in the process. More measurements of the strength of the fields, also at different distances to the stars, and the investigation of the geometry of the fields are fundamental for providing better constraints to models, and for the better understanding of this subject.

New capabilities in the HENP grand challenge storage access systemand its application at RHIC

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

Bernardo, L.; Gibbard, B.; Malon, D.

2000-04-25

The High Energy and Nuclear Physics Data Access GrandChallenge project has developed an optimizing storage access softwaresystem that was prototyped at RHIC. It is currently undergoingintegration with the STAR experiment in preparation for data taking thatstarts in mid-2000. The behavior and lessons learned in the RHIC MockData Challenge exercises are described as well as the observedperformance under conditions designed to characterize scalability. Up to250 simultaneous queries were tested and up to 10 million events across 7event components were involved in these queries. The system coordinatesthe staging of "bundles" of files from the HPSS tape system, so that allthe needed componentsmore » of each event are in disk cache when accessed bythe application software. The caching policy algorithm for thecoordinated bundle staging is described in the paper. The initialprototype implementation interfaced to the Objectivity/DB. In this latestversion, it evolved to work with arbitrary files and use CORBA interfacesto the tag database and file catalog services. The interface to the tagdatabase and the MySQL-based file catalog services used by STAR aredescribed along with the planned usage scenarios.« less

Nuclear Pasta: Topology and Defects

NASA Astrophysics Data System (ADS)

da Silva Schneider, Andre; Horowitz, Charles; Berry, Don; Caplan, Matt; Briggs, Christian

2015-04-01

A layer of complex non-uniform phases of matter known as nuclear pasta is expected to exist at the base of the crust of neutron stars. Using large scale molecular dynamics we study the topology of some pasta shapes, the formation of defects and how these may affect properties of neutron star crusts.

Nuclear Physical Uncertainties in Modeling X-Ray Bursts

NASA Astrophysics Data System (ADS)

Regis, Eric; Amthor, A. Matthew

2017-09-01

Type I x-ray bursts occur when a neutron star accretes material from the surface of another star in a compact binary star system. For certain accretion rates and material compositions, much of the nuclear material is burned in short, explosive bursts. Using a one-dimensional stellar model, Kepler, and a comprehensive nuclear reaction rate library, ReacLib, we have simulated chains of type I x-ray bursts. Unfortunately, there are large remaining uncertainties in the nuclear reaction rates involved, since many of the isotopes reacting are unstable and have not yet been studied experimentally. Some individual reactions, when varied within their estimated uncertainty, alter the light curves dramatically. This limits our ability to understand the structure of the neutron star. Previous studies have looked at the effects of individual reaction rate uncertainties. We have applied a Monte Carlo method ``-simultaneously varying a set of reaction rates'' -in order to probe the expected uncertainty in x-ray burst behaviour due to the total uncertainty in all nuclear reaction rates. Furthermore, we aim to discover any nonlinear effects due to the coupling between different reaction rates. Early results show clear non-linear effects. This research was made possible by NSF-DUE Grant 1317446, BUScholars Program.

Nuclear Phosphatidylinositol-Phosphate Type I Kinase α-Coupled Star-PAP Polyadenylation Regulates Cell Invasion

PubMed Central

A.P., Sudheesh

2017-01-01

ABSTRACT Star-PAP, a nuclear phosphatidylinositol (PI) signal-regulated poly(A) polymerase (PAP), couples with type I PI phosphate kinase α (PIPKIα) and controls gene expression. We show that Star-PAP and PIPKIα together regulate 3′-end processing and expression of pre-mRNAs encoding key anti-invasive factors (KISS1R, CDH1, NME1, CDH13, FEZ1, and WIF1) in breast cancer. Consistently, the endogenous Star-PAP level is negatively correlated with the cellular invasiveness of breast cancer cells. While silencing Star-PAP or PIPKIα increases cellular invasiveness in low-invasiveness MCF7 cells, Star-PAP overexpression decreases invasiveness in highly invasive MDA-MB-231 cells in a cellular Star-PAP level-dependent manner. However, expression of the PIPKIα-noninteracting Star-PAP mutant or the phosphodeficient Star-PAP (S6A mutant) has no effect on cellular invasiveness. These results strongly indicate that PIPKIα interaction and Star-PAP S6 phosphorylation are required for Star-PAP-mediated regulation of cancer cell invasion and give specificity to target anti-invasive gene expression. Our study establishes Star-PAP–PIPKIα-mediated 3′-end processing as a key anti-invasive mechanism in breast cancer. PMID:29203642

Nuclear Phosphatidylinositol-Phosphate Type I Kinase α-Coupled Star-PAP Polyadenylation Regulates Cell Invasion.

PubMed

A P, Sudheesh; Laishram, Rakesh S

2018-03-01

Star-PAP, a nuclear phosphatidylinositol (PI) signal-regulated poly(A) polymerase (PAP), couples with type I PI phosphate kinase α (PIPKIα) and controls gene expression. We show that Star-PAP and PIPKIα together regulate 3'-end processing and expression of pre-mRNAs encoding key anti-invasive factors ( KISS1R , CDH1 , NME1 , CDH13 , FEZ1 , and WIF1 ) in breast cancer. Consistently, the endogenous Star-PAP level is negatively correlated with the cellular invasiveness of breast cancer cells. While silencing Star-PAP or PIPKIα increases cellular invasiveness in low-invasiveness MCF7 cells, Star-PAP overexpression decreases invasiveness in highly invasive MDA-MB-231 cells in a cellular Star-PAP level-dependent manner. However, expression of the PIPKIα-noninteracting Star-PAP mutant or the phosphodeficient Star-PAP (S6A mutant) has no effect on cellular invasiveness. These results strongly indicate that PIPKIα interaction and Star-PAP S6 phosphorylation are required for Star-PAP-mediated regulation of cancer cell invasion and give specificity to target anti-invasive gene expression. Our study establishes Star-PAP-PIPKIα-mediated 3'-end processing as a key anti-invasive mechanism in breast cancer. Copyright © 2018 A.P. and Laishram.

Probabilistic HR Diagrams: A New Infrared and X-ray Chronometer for Very Young, Massive Stellar Clusters and Associations

NASA Astrophysics Data System (ADS)

Maldonado, Jessica; Povich, Matthew S.

2016-01-01

We present a novel method for constraining the duration of star formation in very young, massive star-forming regions. Constraints on stellar population ages are derived from probabilistic HR diagrams (pHRDs) generated by fitting stellar model spectra to the infrared (IR) spectral energy distributions (SEDs) of Herbig Ae/Be stars and their less-evolved, pre-main sequence progenitors. Stellar samples for the pHRDs are selected based on the detection of X-ray emission associated with the IR source, and the lack of detectible IR excess emission at wavelengths ≤4.5 µm. The SED model fits were used to create two-dimensional probability distributions of the stellar parameters, specifically bolometric luminosity versus temperature and mass versus evolutionary age. We present first results from the pHRD analysis of the relatively evolved Carina Nebula and the unevolved M17 SWex infrared dark cloud, which reveal the expected, strikingly different star formation durations between these two regions. In the future, we will apply this method to analyze available X-ray and IR data from the MYStIX project on other Galactic massive star forming regions within 3 kpc of the Sun.

The evolved central star of the planetary nebula ESO 166-PN 21.

NASA Astrophysics Data System (ADS)

Pena, M.; Ruiz, M. T.; Bergeron, P.; Torres-Peimbert, S.; Heathcote, S.

1997-02-01

Optical and UV spectrophotometric data of the nebula and the central star of the planetary nebula ESO 166-PN 21 are presented. The analysis of the nebular lines confirms that it is a He- and N-rich PN, with He/H=0.138+/-0.005 and N/O=0.58+/-0.08. The oxygen abundance is 12+logO/H=8.60+/-0.10. A distance of 1.2+/-0.2 kpc is derived for the nebula. The central star is very faint and blue, with an apparent magnitude V=17.94+/-0.03mag and a dereddened color index (B-V)_0_=-0.38mag. It shows faint wide H and He absorption lines typical of a DAO star. By modeling the line profiles we derived T_eff_=69200+/-8700K, logg=7.14+/-0.39 and logHe/H=-1.50+/-0.49 for the star. The position of the star in a HR diagram compared with evolutionary tracks indicates a stellar mass of ~0.55Msun_. The bolometric correction derived from the model atmosphere is -5.6mag which, combined with the mass, yields an absolute visual magnitude M_V_=6.95, a luminosity of 22Lsun_ and a distance of 1185+/-700pc, in good agreement with the nebular distance. Therefore, ESO 166-PN 21 central star is among the hottest and most helium-rich DAO stars and it is one of the most evolved PN nuclei known, similar to the central stars of S216 and NGC7293. A kinematical age of 16100yr is deduced for the nebula which is lower by about two orders of magnitude than the age of the central star. The possibility that this object is a member of a close binary system is suggested.

A theoretical study of alpha star populations in loaded nuclear emulsions

USGS Publications Warehouse

Senftle, F.E.; Farley, T.A.; Stieff, L.R.

1954-01-01

This theoretical study of the alpha star populations in loaded emulsions was undertaken in an effort to find a quantitative method for the analysis of less than microgram amounts of thorium in the presence of larger amounts of uranium. Analytical expressions for each type of star from each of the significantly contributing members of the uranium and thorium series as well as summation formulas for the whole series have been computed. The analysis for thorium may be made by determining the abundance of five-branched stars in a loaded nuclear emulsion and comparing of observed and predicted star populations. The comparison may also be used to check the half-lives of several members of the uranium and thorium series. ?? 1954.

The positive binding energy envelopes of low-mass helium stars

NASA Astrophysics Data System (ADS)

Hall, Philip D.; Jeffery, C. Simon

2018-04-01

It has been hypothesized that stellar envelopes with positive binding energy may be ejected if the release of recombination energy can be triggered and the calculation of binding energy includes this contribution. The implications of this hypothesis for the evolution of normal hydrogen-rich stars have been investigated, but the implications for helium stars - which may represent mass-transfer or merger remnants in binary star systems - have not. Making a set of model helium stars, we find that those with masses between 0.9 and 2.4 M⊙ evolve to configurations with positive binding energy envelopes. We discuss consequences of the ejection hypothesis for such stars, and possible observational tests of these predictions.

The SiO Masers of TX Camelopardalis

NASA Astrophysics Data System (ADS)

Marvel, Kevin B.; Diamond, P.; Kemball, A.

2001-06-01

Observations of evolved stars with the Very Long Baseline Array have shown that silicon monoxide masers are found just above the photospheres of these interesting objects. By observing many times over a few pulsation periods, researchers are now discovering complex motions in the extended photospheres of these bloated, old stars. We will present several dramatic "movies" of these sources and speculate on wat such observations can tell us about the physical conditions near the star.

Equation of state for nucleonic matter and its quark mass dependence from the nuclear force in lattice QCD.

PubMed

Inoue, Takashi; Aoki, Sinya; Doi, Takumi; Hatsuda, Tetsuo; Ikeda, Yoichi; Ishii, Noriyoshi; Murano, Keiko; Nemura, Hidekatsu; Sasaki, Kenji

2013-09-13

Quark mass dependence of the equation of state (EOS) for nucleonic matter is investigated, on the basis of the Brueckner-Hartree-Fock method with the nucleon-nucleon interaction extracted from lattice QCD simulations. We observe saturation of nuclear matter at the lightest available quark mass corresponding to the pseudoscalar meson mass ≃469  MeV. Mass-radius relation of the neutron stars is also studied with the EOS for neutron-star matter from the same nuclear force in lattice QCD. We observe that the EOS becomes stiffer and thus the maximum mass of neutron star increases as the quark mass decreases toward the physical point.

Strange mode instabilities and mass loss in evolved massive primordial stars

NASA Astrophysics Data System (ADS)

Yadav, Abhay Pratap; Kühnrich Biavatti, Stefan Henrique; Glatzel, Wolfgang

2018-04-01

A linear stability analysis of models for evolved primordial stars with masses between 150 and 250 M⊙ is presented. Strange mode instabilities with growth rates in the dynamical range are identified for stellar models with effective temperatures below log Teff = 4.5. For selected models, the final fate of the instabilities is determined by numerical simulation of their evolution into the non-linear regime. As a result, the instabilities lead to finite amplitude pulsations. Associated with them are acoustic energy fluxes capable of driving stellar winds with mass-loss rates in the range between 7.7 × 10-7 and 3.5 × 10-4 M⊙ yr-1.

Radio Imaging of Envelopes of Evolved Stars

NASA Astrophysics Data System (ADS)

Cotton, Bill

2018-04-01

This talk will cover imaging of stellar envelopes using radio VLBI techniques; special attention will be paid to the technical differences between radio and optical/IR interferomery. Radio heterodyne receivers allow a straightforward way to derive spectral cubes and full polarization observations. Milliarcsecond resolution of very bright, i.e. non thermal, emission of molecular masers in the envelopes of evolved stars can be achieved using VLBI techniques with baselines of thousands of km. Emission from SiO, H2O and OH masers are commonly seen at increasing distance from the photosphere. The very narrow maser lines allow accurate measurements of the velocity field within the emitting region.

Nuclear emulsion measurements of the dose contribution from tissue disintegration stars on the Apollo-Soyuz mission

NASA Technical Reports Server (NTRS)

Schaefer, H. J.

1977-01-01

A total of 996 disintegration stars were prong-counted in two 100 micron llford K.2 emulsions from the dosimeter of the Docking Pilot on Apollo-Soyuz. The change of slope of the distribution at a prong number of about 6 or 7 indicates 219 stars as originating in gelatin. Applying the QF values set forth in official regulations to the energy spectra of the proton and a alpha prongs of the gelatin stars leads to a tissue star dose of 7.8 millirad or 45 millirem. The quoted values do not include the dose contribution from star-produced neutrons since neutrons do not leave visible prongs in emulsion. Nuclear theory, in good agreement with measurements of galactic radiation in the earth's atmosphere, indicates that the dose equivalent from neutrons is about equal to the one from all ionizing secondaries of stars. Application of this proposition to the star prong spectrum found on Apollo-Soyuz would set the total tissue star dose for the mission at approximately 90 millirem.

Slow-blue nuclear hypervariables in PanSTARRS-1

DOE PAGES

Lawrence, A.; Bruce, A. G.; MacLeod, C.; ...

2016-09-08

We discuss 76 large amplitude transients (Δm > 1.5) occurring in the nuclei of galaxies, nearly all with no previously known active galactic nucleus (AGN). They have been discovered as part of the Pan-STARRS1 (PS1) 3π survey, by comparison with Sloan Digital Sky Survey (SDSS) photometry a decade earlier, and then monitored with the Liverpool Telescope, and studied spectroscopically with the William Herschel Telescope (WHT). Based on colours, light-curve shape, and spectra, these transients fall into four groups. A few are misclassified stars or objects of unknown type. Some are red/fast transients and are known or likely nuclear supernovae. Amore » few are either radio sources or erratic variables and so likely blazars. However the majority (~66 per cent) are blue and evolve slowly, on a time-scale of years. Spectroscopy shows them to be AGN at z ~0.3 – 1.4, which must have brightened since the SDSS photometry by around an order of magnitude. It is likely that these objects were in fact AGN a decade ago, but too weak to be recognized by SDSS; they could then be classed as ‘hypervariable’ AGN. By searching the SDSS Stripe 82 quasar database, we find 15 similar objects. We discuss several possible explanations for these slow-blue hypervariables – (i) unusually luminous tidal disruption events; (ii) extinction events; (iii) changes in accretion state; and (iv) large amplitude microlensing by stars in foreground galaxies. A mixture of explanations (iii) and (iv) seems most likely. As a result, both hold promise of considerable new insight into the AGN phenomenon.« less

Slow-blue nuclear hypervariables in PanSTARRS-1

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

Lawrence, A.; Bruce, A. G.; MacLeod, C.

We discuss 76 large amplitude transients (Δm > 1.5) occurring in the nuclei of galaxies, nearly all with no previously known active galactic nucleus (AGN). They have been discovered as part of the Pan-STARRS1 (PS1) 3π survey, by comparison with Sloan Digital Sky Survey (SDSS) photometry a decade earlier, and then monitored with the Liverpool Telescope, and studied spectroscopically with the William Herschel Telescope (WHT). Based on colours, light-curve shape, and spectra, these transients fall into four groups. A few are misclassified stars or objects of unknown type. Some are red/fast transients and are known or likely nuclear supernovae. Amore » few are either radio sources or erratic variables and so likely blazars. However the majority (~66 per cent) are blue and evolve slowly, on a time-scale of years. Spectroscopy shows them to be AGN at z ~0.3 – 1.4, which must have brightened since the SDSS photometry by around an order of magnitude. It is likely that these objects were in fact AGN a decade ago, but too weak to be recognized by SDSS; they could then be classed as ‘hypervariable’ AGN. By searching the SDSS Stripe 82 quasar database, we find 15 similar objects. We discuss several possible explanations for these slow-blue hypervariables – (i) unusually luminous tidal disruption events; (ii) extinction events; (iii) changes in accretion state; and (iv) large amplitude microlensing by stars in foreground galaxies. A mixture of explanations (iii) and (iv) seems most likely. As a result, both hold promise of considerable new insight into the AGN phenomenon.« less

Chandra and ALMA observations of the nuclear activity in two strongly lensed star-forming galaxies

NASA Astrophysics Data System (ADS)

Massardi, M.; Enia, A. F. M.; Negrello, M.; Mancuso, C.; Lapi, A.; Vignali, C.; Gilli, R.; Burkutean, S.; Danese, L.; Zotti, G. De

2018-02-01

Aim. According to coevolutionary scenarios, nuclear activity and star formation play relevant roles in the early stages of galaxy formation. We aim at identifying them in high-redshift galaxies by exploiting high-resolution and high-sensitivity X-ray and millimeter-wavelength data to confirm the presence or absence of star formation and nuclear activity and describe their relative roles in shaping the spectral energy distributions and in contributing to the energy budgets of the galaxies. Methods: We present the data, model, and analysis in the X-ray and millimeter (mm) bands for two strongly lensed galaxies, SDP.9 (HATLAS J090740.0-004200) and SDP.11 (HATLAS J091043.1-000322), which we selected in the Herschel-ATLAS catalogs for their excess emission in the mid-IR regime at redshift ≳1.5. This emission suggests nuclear activity in the early stages of galaxy formation. We observed both of them with Chandra ACIS-S in the X-ray regime and analyzed the high-resolution mm data that are available in the ALMA Science Archive for SDP.9. By combining the information available in mm, optical, and X-ray bands, we reconstructed the source morphology. Results: Both targets were detected in the X-ray, which strongly indicates highly obscured nuclear activity. ALMA observations for SDP.9 for the continuum and CO(6-5) spectral line with high resolution (0.02 arcsec corresponding to 65 pc at the distance of the galaxy) allowed us to estimate the lensed galaxy redshift to a better accuracy than pre-ALMA estimates (1.5753 ± 0.0003) and to model the emission of the optical, millimetric, and X-ray band for this galaxy. We demonstrate that the X-ray emission is generated in the nuclear environment, which strongly supports that this object has nuclear activity. On the basis of the X-ray data, we attempt an estimate of the black hole properties in these galaxies. Conclusions: By taking advantage of the lensing magnification, we identify weak nuclear activity associated with high-z galaxies with high star formation rates. This is useful to extend the investigation of the relationship between star formation and nuclear activity to two intrinsically less luminous high-z star-forming galaxies than was possible so far. Given our results for only two objects, they alone cannot constrain the evolutionary models, but provide us with interesting hints and set an observational path toward addressing the role of star formation and nuclear activity in forming galaxies. The reduced images and data cubes as FITS files are 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/610/A53

Wolf-Rayet stars as starting points or as endpoints of the evolution of massive stars?

NASA Technical Reports Server (NTRS)

Lamers, H. J. G. L. M.; Maeder, A.; Schmutz, W.; Cassinelli, J. P.

1991-01-01

The paper investigates the evidence for the two interpretations of Wolf-Rayet stars suggested in the literature: (1) massive premain-sequence stars with disks and (2) massive stars which have lost most of their H-rich layers in a stellar wind is investigated. The abundance determinations which are done in two different ways and which lead to different conclusions are discussed. The composition is solar, which would suggest interpretation (1), or the CNO abundances are strongly anomalous, which would suggest interpretation (2). Results from evolutionary calculations, stellar statistics, the existence of Ofpe/WN9 transition stars and W-R stars with evolved companions show overwhelming evidence that W-R stars are not premain-sequence stars but that they are in a late stage of evolution. Moreover, the fact that W-R stars are usually in clear regions of space, whereas massive premain-sequence stars are embedded in ultracompact H II regions also shows that W-R stars are not young premain-sequence stars.

The AAVSO as a Resource for Variable Star Research

NASA Astrophysics Data System (ADS)

Kafka, Stella

2016-07-01

The AAVSO was formed in 1911 as a group of US-based amateur observers obtaining data in support of professional astronomy projects. Now, it has evolved into an International Organization with members and observers from both the professional and non-professional astronomical community, contributing photometry to a public photometric database of about 22,000 variable objects, and using it for research projects. As such, the AAVSO's main claim to fame is that it successfully engages backyard Astronomers, educators, students and professional astronomers in astronomical research. I will present the main aspects of the association and how it has evolved with time to become a premium resource for variable star researchers. I will also discuss the various means that the AAVSO is using to support cutting-edge variable star science, and how it engages its members in projects building a stronger international astronomical community.

SI: The Stellar Imager

NASA Technical Reports Server (NTRS)

Carpenter, Kenneth G.; Schrijver, Carolus J.; Karovska, Margarita

2006-01-01

The ultra-sharp images of the Stellar Imager (SI) will revolutionize our view of many dynamic astrophysical processes: The 0.1 milliarcsec resolution of this deep-space telescope will transform point sources into extended sources, and simple snapshots into spellbinding evolving views. SI s science focuses on the role of magnetism in the Universe, particularly on magnetic activity on the surfaces of stars like the Sun. SI s prime goal is to enable long-term forecasting of solar activity and the space weather that it drives in support of the Living With a Star program in the Exploration Era by imaging a sample of magnetically active stars with enough resolution to map their evolving dynamo patterns and their internal flows. By exploring the Universe at ultra-high resolution, SI will also revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magnetohydrodynamically controlled structures and processes in the Universe.

Evolving Gravitationally Unstable Disks over Cosmic Time: Implications for Thick Disk Formation

NASA Astrophysics Data System (ADS)

Forbes, John; Krumholz, Mark; Burkert, Andreas

2012-07-01

Observations of disk galaxies at z ~ 2 have demonstrated that turbulence driven by gravitational instability can dominate the energetics of the disk. We present a one-dimensional simulation code, which we have made publicly available, that economically evolves these galaxies from z ~ 2 to z ~ 0 on a single CPU in a matter of minutes, tracking column density, metallicity, and velocity dispersions of gaseous and multiple stellar components. We include an H2-regulated star formation law and the effects of stellar heating by transient spiral structure. We use this code to demonstrate a possible explanation for the existence of a thin and thick disk stellar population and the age-velocity-dispersion correlation of stars in the solar neighborhood: the high velocity dispersion of gas in disks at z ~ 2 decreases along with the cosmological accretion rate, while at lower redshift the dynamically colder gas forms the low velocity dispersion stars of the thin disk.

Transport Properties in Nuclear Pasta

NASA Astrophysics Data System (ADS)

Caplan, Matthew; Horowitz, Charles; Berry, Donald; da Silva Schneider, Andre

2016-09-01

At the base of the inner crust of neutron stars, where matter is near the nuclear saturation density, nuclear matter arranges itself into exotic shapes such as cylinders and slabs, called `nuclear pasta.' Lepton scattering from these structures may govern the transport properties of the inner crust; electron scattering from protons in the pasta determines the thermal and electrical conductivity, as well as the shear viscosity of the inner crust. These properties may vary in pasta structures which form at various densities, temperatures, and proton fractions. In this talk, we report on our calculations of lepton transport in nuclear pasta and the implication for neutron star observables.

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

NASA Astrophysics Data System (ADS)

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

2013-01-01

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

GUM 48d: AN EVOLVED H II REGION WITH ONGOING STAR FORMATION

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

Karr, J. L.; Ohashi, N.; Manoj, P.

2009-05-20

High-mass star formation and the evolution of H II regions have a substantial impact on the morphology and star formation history of molecular clouds. The H II region Gum 48d, located in the Centaurus Arm at a distance of 3.5 kpc, is an old, well evolved H II region whose ionizing stars have moved off the main sequence. As such, it represents a phase in the evolution of H II regions that is less well studied than the earlier, more energetic, main-sequence phase. In this paper, we use multiwavelength archive data from a variety of sources to perform a detailedmore » study of this interesting region. Morphologically, Gum 48d displays a ring-like faint H II region associated with diffuse emission from the associated photodissociation region, and is formed from part of a large, massive molecular cloud complex. There is extensive ongoing star formation in the region, at scales ranging from low to high mass, which is consistent with triggered star formation scenarios. We investigate the dynamical history and evolution of this region, and conclude that the original H II region was once larger and more energetic than the faint region currently seen. The proposed history of this molecular cloud complex is one of multiple, linked generations of star formation, over a period of 10 Myr. Gum 48d differs significantly in morphology and star formation from the other H II regions in the molecular cloud; these differences are likely the result of the advanced age of the region, and its different evolutionary status.« less

ORIGIN: Metal Creation and Evolution From The Cosmic Dawn

NASA Astrophysics Data System (ADS)

Piro, L.; den Herder, J. W.; Ohashi, T.; Hartmann, D. H.; Kouveliotou, C.

2011-08-01

ORIGIN is a mission designed to use Gamma-Ray Bursts as a unique probe to study the cosmic history of baryons and the metal enrichment from the first stars up to the present Universe. Reconstructing the cosmic history of metals, from the first population of stars to the processes involved in the formation of galaxies and clusters of galaxies, is a key observational challenge. Observing any single star in the early Universe is in fact beyond the reach of presently planned mission. By measuring GRB redshifts and abundances in the circumburst medium deep into the era of re-ionization (z>6), ORIGIN will discover when star formation started and how it evolved into the present day structures. ORIGIN will collect 400 GRBs per year covering the full redshift distribution. About twice per month a GRB from the re-ionization era will trigger the instruments. The resulting multi-element abundance patterns derived from high resolution X-ray and IR observations will map the evolving chemical composition of the early Universe, ``fingerprint'' the elusive PopIII stars, and constrain the shape of the Initial Mass Function (IMF) of the first stars. While not observing GRB afterglows, ORIGIN will map element abundances in local structures (z<2) by determining the properties of the hot IGM in clusters and groups of galaxies and the Warm-Hot Intergalactic Medium (WHIM). In this paper we focus on the use of GRB to track the earliest star populations.

Neutrino Processes in Neutron Stars

NASA Astrophysics Data System (ADS)

Kolomeitsev, E. E.; Voskresensky, D. N.

2010-10-01

The aim of these lectures is to introduce basic processes responsible for cooling of neutron stars and to show how to calculate the neutrino production rate in dense strongly interacting nuclear medium. The formalism is presented that treats on equal footing one-nucleon and multiple-nucleon processes and reactions with virtual bosonic modes and condensates. We demonstrate that neutrino emission from dense hadronic component in neutron stars is subject of strong modifications due to collective effects in the nuclear matter. With the most important in-medium processes incorporated in the cooling code an overall agreement with available soft X ray data can be easily achieved. With these findings the so-called “standard” and “non-standard” cooling scenarios are replaced by one general “nuclear medium cooling scenario” which relates slow and rapid neutron star coolings to the star masses (interior densities). The lectures are split in four parts. Part I: After short introduction to the neutron star cooling problem we show how to calculate neutrino reaction rates of the most efficient one-nucleon and two-nucleon processes. No medium effects are taken into account in this instance. The effects of a possible nucleon pairing are discussed. We demonstrate that the data on neutron star cooling cannot be described without inclusion of medium effects. It motivates an assumption that masses of the neutron stars are different and that neutrino reaction rates should be strongly density dependent. Part II: We introduce the Green’s function diagram technique for systems in and out of equilibrium and the optical theorem formalism. The latter allows to perform calculations of production rates with full Green’s functions including all off-mass-shell effects. We demonstrate how this formalism works within the quasiparticle approximation. Part III: The basic concepts of the nuclear Fermi liquid approach are introduced. We show how strong interaction effects can be included within the Green’s function formalism. Softening of the pion mode with an baryon density increase is explicitly incorporated. We show examples of inconsistencies in calculations without inclusion of medium effects. Then we demonstrate calculations of different reaction rates in non-superfluid nuclear matter with taking into account medium effects. Many new reaction channels are open up in the medium and should be analyzed. Part IV: We discuss the neutrino production reactions in superfluid nuclear systems. The reaction rates of processes associated with the pair breaking and formation are calculated. Special attention is focused on the gauge invariance and the exact fulfillment of the Ward identities for the vector current. Finally we present comparison of calculations of neutron star cooling performed within nuclear medium cooling scenario with the available data.

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…

Physical Conditions of Eta Car Complex Environment Revealed From Photoionization Modeling

NASA Technical Reports Server (NTRS)

Verner, E. M.; Bruhweiler, F.; Nielsen, K. E.; Gull, T.; Kober, G. Vieira; Corcoran, M.

2006-01-01

The very massive star, Eta Carinae, is enshrouded in an unusual complex environment of nebulosities and structures. The circumstellar gas gives rise to distinct absorption and emission components at different velocities and distances from the central source(s). Through photoionization modeling, we find that the radiation field from the more massive B-star companion supports the low ionization structure throughout the 5.54 year period. The radiation field of an evolved O-star is required to produce the higher ionization . emission seen across the broad maximum. Our studies utilize the HST/STIS data and model calculations of various regimes from doubly ionized species (T= 10,000K) to the low temperature (T = 760 K) conditions conductive to molecule formation (CH and OH). Overall analysis suggests the high depletion in C and O and the enrichment in He and N. The sharp molecular and ionic absorptions in this extensively CNO - processed material offers a unique environment for studying the chemistry, dust formation processes, and nucleosynthesis in the ejected layers of a highly evolved massive star.

Nuclear Neutrino Spectra in Late Stellar Evolution

NASA Astrophysics Data System (ADS)

Misch, G. Wendell; Sun, Yang; Fuller, George

2018-05-01

Neutrinos are the principle carriers of energy in massive stars, beginning from core carbon burning and continuing through core collapse and after the core bounce. In fact, it may be possible to detect neutrinos from nearby pre-supernova stars. Therefore, it is of great interest to understand the neutrino energy spectra from these stars. Leading up to core collapse, beginning around core silicon burning, nuclei become dominant producers of neutrinos, particularly at high neutrino energy, so a systematic study of nuclear neutrino spectra is desirable. We have done such a study, and we present our sd-shell model calculations of nuclear neutrino energy spectra for nuclei in the mass number range A = 21 - 35. Our study includes neutrinos produced by charged lepton capture, charged lepton emission, and neutral current nuclear deexcitation. Previous authors have tabulated the rates of charged current nuclear weak interactions in astrophysical conditions, but the present work expands on this not only by providing neutrino energy spectra, but also by including the heretofore untabulated neutral current de-excitation neutrino pairs.

SDSS-IV MaNGA: the impact of diffuse ionized gas on emission-line ratios, interpretation of diagnostic diagrams and gas metallicity measurements

NASA Astrophysics Data System (ADS)

Zhang, Kai; Yan, Renbin; Bundy, Kevin; Bershady, Matthew; Haffner, L. Matthew; Walterbos, René; Maiolino, Roberto; Tremonti, Christy; Thomas, Daniel; Drory, Niv; Jones, Amy; Belfiore, Francesco; Sánchez, Sebastian F.; Diamond-Stanic, Aleksandar M.; Bizyaev, Dmitry; Nitschelm, Christian; Andrews, Brett; Brinkmann, Jon; Brownstein, Joel R.; Cheung, Edmond; Li, Cheng; Law, David R.; Roman Lopes, Alexandre; Oravetz, Daniel; Pan, Kaike; Storchi Bergmann, Thaisa; Simmons, Audrey

2017-04-01

Diffuse ionized gas (DIG) is prevalent in star-forming galaxies. Using a sample of 365 nearly face-on star-forming galaxies observed by Mapping Nearby Galaxies at APO, we demonstrate how DIG in star-forming galaxies impacts the measurements of emission-line ratios, hence the interpretation of diagnostic diagrams and gas-phase metallicity measurements. At fixed metallicity, DIG-dominated low ΣHα regions display enhanced [S II]/Hα, [N II]/Hα, [O II]/Hβ and [O I]/Hα. The gradients in these line ratios are determined by metallicity gradients and ΣHα. In line ratio diagnostic diagrams, contamination by DIG moves H II regions towards composite or low-ionization nuclear emission-line region (LI(N)ER)-like regions. A harder ionizing spectrum is needed to explain DIG line ratios. Leaky H II region models can only shift line ratios slightly relative to H II region models, and thus fail to explain the composite/LI(N)ER line ratios displayed by DIG. Our result favours ionization by evolved stars as a major ionization source for DIG with LI(N)ER-like emission. DIG can significantly bias the measurement of gas metallicity and metallicity gradients derived using strong-line methods. Metallicities derived using N2O2 are optimal because they exhibit the smallest bias and error. Using O3N2, R23, N2 = [N II]/Hα and N2S2Hα to derive metallicities introduces bias in the derived metallicity gradients as large as the gradient itself. The strong-line method of Blanc et al. (IZI hereafter) cannot be applied to DIG to get an accurate metallicity because it currently contains only H II region models that fail to describe the DIG.

THE K2 M67 STUDY: AN EVOLVED BLUE STRAGGLER IN M67 FROM K2 MISSION ASTEROSEISMOLOGY

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

Leiner, Emily; Mathieu, Robert D.; Stello, Dennis

Yellow straggler stars (YSSs) fall above the subgiant branch in optical color–magnitude diagrams (CMDs), between the blue stragglers and the red giants. YSSs may represent a population of evolved blue stragglers, but none have the direct and precise mass and radius measurements needed to determine their evolutionary states and formation histories. Here we report the first asteroseismic mass and radius measurements of such a star, the yellow straggler S1237 in the open cluster M67. We apply asteroseismic scaling relations to a frequency analysis of the Kepler K2 light curve and find a mass of 2.9 ± 0.2 M {sub ⊙}more » and a radius of 9.2 ± 0.2 R{sub ⊙}. This is more than twice the mass of the main-sequence turnoff in M67, suggesting that S1237 is indeed an evolved blue straggler. S1237 is the primary in a spectroscopic binary. We update the binary orbital solution and use spectral energy distribution fitting to constrain the CMD location of the secondary star. We find that the secondary is likely an upper main-sequence star near the turnoff, but a slightly hotter blue straggler companion is also possible. We then compare the asteroseismic mass of the primary to its mass from CMD fitting, finding that the photometry implies a mass and radius more than 2 σ below the asteroseismic measurement. Finally, we consider formation mechanisms for this star and suggest that S1237 may have formed from dynamical encounters resulting in stellar collisions or a binary merger.« less

Habitable zones around main sequence stars.

PubMed

Kasting, J F; Whitmire, D P; Reynolds, R T

1993-01-01

A one-dimensional climate model is used to estimate the width of the habitable zone (HZ) around our Sun and around other main sequence stars. Our basic premise is that we are dealing with Earth-like planets with CO2/H2O/N2 atmospheres and that habitability requires the presence of liquid water on the planet's surface. The inner edge of the HZ is determined in our model by loss of water via photolysis and hydrogen escape. The outer edge of the HZ is determined by the formation of CO2 clouds, which cool a planet's surface by increasing its albedo and by lowering the convective lapse rate. Conservative estimates for these distances in our own Solar System are 0.95 and 1.37 AU, respectively; the actual width of the present HZ could be much greater. Between these two limits, climate stability is ensured by a feedback mechanism in which atmospheric CO2 concentrations vary inversely with planetary surface temperature. The width of the HZ is slightly greater for planets that are larger than Earth and for planets which have higher N2 partial pressures. The HZ evolves outward in time because the Sun increases in luminosity as it ages. A conservative estimate for the width of the 4.6-Gyr continuously habitable zone (CHZ) is 0.95 to 1.15 AU. Stars later than F0 have main sequence lifetimes exceeding 2 Gyr and, so, are also potential candidates for harboring habitable planets. The HZ around an F star is larger and occurs farther out than for our Sun; the HZ around K and M stars is smaller and occurs farther in. Nevertheless, the widths of all of these HZs are approximately the same if distance is expressed on a logarithmic scale. A log distance scale is probably the appropriate scale for this problem because the planets in our own Solar System are spaced logarithmically and because the distance at which another star would be expected to form planets should be related to the star's mass. The width of the CHZ around other stars depends on the time that a planet is required to remain habitable and on whether a planet that is initially frozen can be thawed by modest increases in stellar luminosity. For a specified period of habitability, CHZs around K and M stars are wider (in log distance) than for our Sun because these stars evolve more slowly. Planets orbiting late K stars and M stars may not be habitable, however, b ecause they can become trapped in synchronous rotation as a consequence of tidal damping. F stars have narrower (log distance) CHZ's than our Sun because they evolve more rapidly. Our results suggest that mid-to-early K stars should be considered along with G stars as optimal candidates in the search for extraterrestrial life.

Theoretical Developments in Understanding Massive Star Formation

NASA Technical Reports Server (NTRS)

Yorke, Harold W.; Bodenheimer, Peter

2007-01-01

Except under special circumstances massive stars in galactic disks will form through accretion. The gravitational collapse of a molecular cloud core will initially produce one or more low mass quasi-hydrostatic objects of a few Jupiter masses. Through subsequent accretion the masses of these cores grow as they simultaneously evolve toward hydrogen burning central densities and temperatures. We review the evolution of accreting (proto-)stars, including new results calculated with a publicly available stellar evolution code written by the authors.

No surviving evolved companions of the progenitor of SN 1006.

PubMed

González Hernández, Jonay I; Ruiz-Lapuente, Pilar; Tabernero, Hugo M; Montes, David; Canal, Ramon; Méndez, Javier; Bedin, Luigi R

2012-09-27

Type Ia supernovae are thought to occur when a white dwarf made of carbon and oxygen accretes sufficient mass to trigger a thermonuclear explosion. The accretion could be slow, from an unevolved (main-sequence) or evolved (subgiant or giant) star (the single-degenerate channel), or rapid, as the primary star breaks up a smaller orbiting white dwarf (the double-degenerate channel). A companion star will survive the explosion only in the single-degenerate channel. Both channels might contribute to the production of type Ia supernovae, but the relative proportions of their contributions remain a fundamental puzzle in astronomy. Previous searches for remnant companions have revealed one possible case for SN 1572 (refs 8, 9), although that has been questioned. More recently, observations have restricted surviving companions to be small, main-sequence stars, ruling out giant companions but still allowing the single-degenerate channel. Here we report the results of a search for surviving companions of the progenitor of SN 1006 (ref. 14). None of the stars within 4 arc minutes of the apparent site of the explosion is associated with the supernova remnant, and we can firmly exclude all giant and subgiant stars from being companions of the progenitor. In combination with previous results, our findings indicate that fewer than 20 per cent of type Ia supernovae occur through the single-degenerate channel.

CstF-64 and 3'-UTR cis-element determine Star-PAP specificity for target mRNA selection by excluding PAPα.

PubMed

Kandala, Divya T; Mohan, Nimmy; A, Vivekanand; A P, Sudheesh; G, Reshmi; Laishram, Rakesh S

2016-01-29

Almost all eukaryotic mRNAs have a poly (A) tail at the 3'-end. Canonical PAPs (PAPα/γ) polyadenylate nuclear pre-mRNAs. The recent identification of the non-canonical Star-PAP revealed specificity of nuclear PAPs for pre-mRNAs, yet the mechanism how Star-PAP selects mRNA targets is still elusive. Moreover, how Star-PAP target mRNAs having canonical AAUAAA signal are not regulated by PAPα is unclear. We investigate specificity mechanisms of Star-PAP that selects pre-mRNA targets for polyadenylation. Star-PAP assembles distinct 3'-end processing complex and controls pre-mRNAs independent of PAPα. We identified a Star-PAP recognition nucleotide motif and showed that suboptimal DSE on Star-PAP target pre-mRNA 3'-UTRs inhibit CstF-64 binding, thus preventing PAPα recruitment onto it. Altering 3'-UTR cis-elements on a Star-PAP target pre-mRNA can switch the regulatory PAP from Star-PAP to PAPα. Our results suggest a mechanism of poly (A) site selection that has potential implication on the regulation of alternative polyadenylation. © The Author(s) 2015. Published by Oxford University Press on behalf of Nucleic Acids Research.

CstF-64 and 3′-UTR cis-element determine Star-PAP specificity for target mRNA selection by excluding PAPα

PubMed Central

Kandala, Divya T.; Mohan, Nimmy; A, Vivekanand; AP, Sudheesh; G, Reshmi; Laishram, Rakesh S.

2016-01-01

Almost all eukaryotic mRNAs have a poly (A) tail at the 3′-end. Canonical PAPs (PAPα/γ) polyadenylate nuclear pre-mRNAs. The recent identification of the non-canonical Star-PAP revealed specificity of nuclear PAPs for pre-mRNAs, yet the mechanism how Star-PAP selects mRNA targets is still elusive. Moreover, how Star-PAP target mRNAs having canonical AAUAAA signal are not regulated by PAPα is unclear. We investigate specificity mechanisms of Star-PAP that selects pre-mRNA targets for polyadenylation. Star-PAP assembles distinct 3′-end processing complex and controls pre-mRNAs independent of PAPα. We identified a Star-PAP recognition nucleotide motif and showed that suboptimal DSE on Star-PAP target pre-mRNA 3′-UTRs inhibit CstF-64 binding, thus preventing PAPα recruitment onto it. Altering 3′-UTR cis-elements on a Star-PAP target pre-mRNA can switch the regulatory PAP from Star-PAP to PAPα. Our results suggest a mechanism of poly (A) site selection that has potential implication on the regulation of alternative polyadenylation. PMID:26496945

Debris Disks Among the Shell Stars: Insights from Spitzer

NASA Technical Reports Server (NTRS)

Roberge, Aki; Weinberger, Alycia; Teske, Johanna

2008-01-01

Shell stars are a class of early-type stars that show narrow absorption lines in their spectra that appear to arise from circumstellar class. This observationally defined class contains a variety of objects, including evolved stars and classical Be stars. However, some of the main sequence shell stars harbor debris disks and younger protoplanetary disks, though this aspect of the class has been largely overlooked. We surveyed a set of main sequence stars for cool dust using Spitzer MIPS and found four additional systems with IR excesses at both 24 and 70 microns. This indicates that the stars have both circumstellar gas and dust, and are likely to be edge-on debris disks. Our estimate of the disk fraction among nearby main sequence shell stars is 48% +/- 14%. We discuss here the nature of the shell stars and present preliminary results from ground-based optical spectra of the survey target stars. We will also outline our planned studies aimed at further characterization of the shell star class.

Luminosity effect of O I 7771-5 triplet and atmospheric microturbulence in evolved A-, F-, and G-type stars

NASA Astrophysics Data System (ADS)

Takeda, Yoichi; Jeong, Gwanghui; Han, Inwoo

2018-01-01

It is known that the strength of neutral oxygen triplet lines at 7771-5 Å shows a luminosity effect in evolved A through G stars. However, its general behavior across the HR diagram is not yet well understood, since the applicability limit of the relations proposed by various previous work (tending to be biased toward supergiants) still remains unclear. Besides, our understanding on the nature of atmospheric micro-scale turbulence, which is considered to play a significant role (along with the non-LTE line intensification) for the cause of this effect, is still insufficient. Towards clarifying these problems, we carried out an extensive non-LTE spectrum-fitting analysis of O I 7771-5 lines for unbiased sample of 75 evolved A-, F,- and G-type stars over wide luminosity classes (from subgiants through supergiants) including rapid rotators, from which the total equivalent width (W77) was derived and the microturbulence (ξ) was determined by two different (profile- and abundance-based) methods for each star. While we confirmed that W77 tends to increase in the global sense as a star's absolute magnitude (MV) becomes more luminous, distinctly different trends were found between lower-gravity (log g ≲ 2.5) and higher-gravity (log g ≳ 2.5) stars, in the sense that the MV vs. W77 formulas proposed by past studies are applicable only to the former supergiant group. In case of using W77 for empirical MV evaluation by such simple formulas, it is recommended to confine only to supergiants of -5 ≳ MV ≳ -10. Regarding the microturbulence significantly controlling W77, it roughly shows an increasing tendency with a decrease in surface gravity. However, the trend is not monotonic but rather intricate (e.g., hump, stagnation, or discontinuously large increase) depending on the stellar type and evolutionary stage.

Dynamical Model for Spindown of Solar-type Stars

NASA Astrophysics Data System (ADS)

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

2016-12-01

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

EVOLUTION OF INTERMEDIATE-MASS X-RAY BINARIES DRIVEN BY THE MAGNETIC BRAKING OF AP/BP STARS. I. ULTRACOMPACT X-RAY BINARIES

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

Chen, Wen-Cong; Podsiadlowski, Philipp, E-mail: chenwc@pku.edu.cn

2016-10-20

It is generally believed that ultracompact X-ray binaries (UCXBs) evolved from binaries consisting of a neutron star accreting from a low-mass white dwarf (WD) or helium star where mass transfer is driven by gravitational radiation. However, the standard WD evolutionary channel cannot produce the relatively long-period (40–60 minutes) UCXBs with a high time-averaged mass-transfer rate. In this work, we explore an alternative evolutionary route toward UCXBs, where the companions evolve from intermediate-mass Ap/Bp stars with an anomalously strong magnetic field (100–10,000 G). Including the magnetic braking caused by the coupling between the magnetic field and an irradiation-driven wind induced bymore » the X-ray flux from the accreting component, we show that intermediate-mass X-ray binaries (IMXBs) can evolve into UCXBs. Using the MESA code, we have calculated evolutionary sequences for a large number of IMXBs. The simulated results indicate that, for a small wind-driving efficiency f = 10{sup −5}, the anomalous magnetic braking can drive IMXBs to an ultra-short period of 11 minutes. Comparing our simulated results with the observed parameters of 15 identified UCXBs, the anomalous magnetic braking evolutionary channel can account for the formation of seven and eight sources with f = 10{sup −3}, and 10{sup −5}, respectively. In particular, a relatively large value of f can fit three of the long-period, persistent sources with a high mass-transfer rate. Though the proportion of Ap/Bp stars in intermediate-mass stars is only 5%, the lifetime of the UCXB phase is ≳2 Gyr, producing a relatively high number of observable systems, making this an alternative evolutionary channel for the formation of UCXBs.« less

Wolf-Rayet stars in the Small Magellanic Cloud as testbed for massive star evolution

NASA Astrophysics Data System (ADS)

Schootemeijer, A.; Langer, N.

2018-03-01

Context. The majority of the Wolf-Rayet (WR) stars represent the stripped cores of evolved massive stars who lost most of their hydrogen envelope. Wind stripping in single stars is expected to be inefficient in producing WR stars in metal-poor environments such as the Small Magellanic Cloud (SMC). While binary interaction can also produce WR stars at low metallicity, it is puzzling that the fraction of WR binaries appears to be about 40%, independent of the metallicity. Aim. We aim to use the recently determined physical properties of the twelve known SMC WR stars to explore their possible formation channels through comparisons with stellar models. Methods: We used the MESA stellar evolution code to construct two grids of stellar models with SMC metallicity. One of these consists of models of rapidly rotating single stars, which evolve in part or completely chemically homogeneously. In a second grid, we analyzed core helium burning stellar models assuming constant hydrogen and helium gradients in their envelopes. Results: We find that chemically homogeneous evolution is not able to account for the majority of the WR stars in the SMC. However, in particular the apparently single WR star SMC AB12, and the double WR system SMC AB5 (HD 5980) appear consistent with this channel. We further find a dichotomy in the envelope hydrogen gradients required to explain the observed temperatures of the SMC WR stars. Shallow gradients are found for the WR stars with O star companions, while much steeper hydrogen gradients are required to understand the group of hot apparently single WR stars. Conclusions: The derived shallow hydrogen gradients in the WR component of the WR+O star binaries are consistent with predictions from binary models where mass transfer occurs early, in agreement with their binary properties. Since the hydrogen profiles in evolutionary models of massive stars become steeper with time after the main sequence, we conclude that most of the hot (Teff > 60 kK ) apparently single WR stars lost their envelope after a phase of strong expansion, e.g., as the result of common envelope evolution with a lower mass companion. The so far undetected companions, either main sequence stars or compact objects, are then expected to still be present. A corresponding search might identify the first immediate double black hole binary progenitor with masses as high as those detected in GW150914.

Hans Bethe, Powering the Stars, and Nuclear Physics

Science.gov Websites

dropdown arrow Site Map A-Z Index Menu Synopsis Hans Bethe, Energy Production in Stars, and Nuclear Physics physics, built atomic weapons, and called for a halt to their proliferation. Bethe's dual legacy is one of Laboratory] from 1943 to 1946. Prior to joining the Manhattan Project, Bethe taught physics at Cornell

High Resolution Three-Color Imaging of Spirals With Nuclear Star-Forming Rings

NASA Technical Reports Server (NTRS)

Mazzuca, Lisa; Obenschain, Arthur (Technical Monitor)

2001-01-01

Nuclear rings in barred spirals offer an opportunity to study starburst properties in order to develop an understanding of the evolution of star formation in galaxies. To achieve this understanding, a large scale imaging survey in the H alpha line and in the B and I broad bands has been performed. Analysis of all galaxies that reveal nuclear rings in the H alpha line will be compared to numerical models so that the relative ages between the starforming clumps can be estimated. The luminosity function of the starforming regions will be related to the measured properties of the associated star-cluster and the required ionizing flux. Also B - I color index images will be performed to indicate the location of the dust lanes.

Outer crust of nonaccreting cold neutron stars

NASA Astrophysics Data System (ADS)

Rüster, Stefan B.; Hempel, Matthias; Schaffner-Bielich, Jürgen

2006-03-01

The properties of the outer crust of nonaccreting cold neutron stars are studied by using modern nuclear data and theoretical mass tables, updating in particular the classic work of Baym, Pethick, and Sutherland. Experimental data from the atomic mass table from Audi, Wapstra, and Thibault of 2003 are used and a thorough comparison of many modern theoretical nuclear models, both relativistic and nonrelativistic, is performed for the first time. In addition, the influences of pairing and deformation are investigated. State-of-the-art theoretical nuclear mass tables are compared to check their differences concerning the neutron drip line, magic neutron numbers, the equation of state, and the sequence of neutron-rich nuclei up to the drip line in the outer crust of nonaccreting cold neutron stars.

Dynamics of Mass Transfer in Wide Symbiotic Systems

NASA Astrophysics Data System (ADS)

de Val-Borro, Miguel; Karovska, M.; Sasselov, D.

2010-01-01

We investigate the formation of accretion disks around the secondary in detached systems consisting of an Asymptotic Giant Branch (AGB) star and a compact accreting companion as a function of mass loss rate and orbital parameters. In particular, we study winds from late-type stars that are gravitationally focused by a companion in a wide binary system using hydrodynamical simulations. For a typical slow and massive wind from an evolved star there is a stream flow between the stars with accretion rates of a few percent of the mass loss from the primary. Mass transfer through a focused wind is an important mechanism for a broad range of interacting binary systems and can explain the formation of Barium stars and other chemically peculiar stars.

Unsolved problems. [the physics of B stars

NASA Technical Reports Server (NTRS)

1982-01-01

The level of understanding of the physics of single, isolated B stars is assessed and unresolved problems are defined. The significant observational results concerning the effective temperatures, radii, masses and mantles are summarized. The results of the theory of the evolution of massive stars are confronted with the observed luminosities and effective temperatures of B stars. In addition the implications of stellar spectra theory are compared with observed spectra and a heuristic model for a mantle is developed. The chief unresolved problems for B stars concern developing detailed models for (1) the internal structure of massive stars which are beginning to evolve rapidly as they complete burning hydrogen in their cores; (2) mantles; and (3) the transfer of radiation in high temperature inhomogeneous moving bodies of gas.

Luminous Infrared Sources in the Local Group: Identifying the Missing Links in Massive Star Evolution

NASA Astrophysics Data System (ADS)

Britavskiy, N.; Bonanos, A. Z.; Mehner, A.

2015-01-01

We present the first systematic survey of dusty massive stars (RSGs, LBVs, sgB[e]) in nearby galaxies, with the goal of understanding their importance in massive star evolution. Using the fact that these stars are bright in mid-infrared colors due to dust, we provide a technique for selecting and identifying dusty evolved stars based on the results of Bonanos et al. (2009, 2010), Britavskiy et al. (2014), and archival Spitzer/IRAC photometry. We present the results of our spectroscopic follow-up of luminous infrared sources in the Local Group dwarf irregular galaxies: Pegasus, Phoenix, Sextans A and WLM. The survey aims to complete the census of dusty massive stars in the Local Group.

Star formation in infrared bright and infrared faint starburst interacting galaxies

NASA Technical Reports Server (NTRS)

Lamb, Susan A.; Bushouse, Howard A.; Towns, John W.

1990-01-01

Short wavelength IUE spectra of Arp 248b and UGC 8315N are combined with optical spectra and interpreted using a combination of spectrum synthesis and spectral diagnostics to place constraints on the massive star populations of the central regions of these galaxies and to deduce information about the star formation histories in the last 10(exp 8) years. The authors find that both galaxies have substantial fractions of their optical light coming from massive stars and that Arp 248b may be dominated in the UV by WR stars. The UV spectra are dominated by radiation from evolved massive stars and the authors place and age on the burst in Arp 248b of a few tens of millions of years.

Sizzling Remains of a Dead Star

NASA Image and Video Library

2013-01-07

This new view of the historical supernova remnant Cassiopeia A, located 11,000 light-years away, was taken by NASA Nuclear Spectroscopic Telescope Array, or NuSTAR. While the star is long dead, its remains are still bursting with action.

Star trapping and metallicity enrichment in quasars and active galactic nuclei

NASA Technical Reports Server (NTRS)

Artymowicz, Pawel; Lin, D. N. C.; Wampler, E. J.

1993-01-01

Recent observational evidence suggests that the metallicity in quasars within a wide range of redshifts, in particular in gas flowing out of the nuclear regions, may be approximately redshift-independent and comparable with or larger than solar. It is plausible that the nuclear metallicity can be internally generated and maintained at approximately time-stationary values in quasars. We identify and estimate efficiency of a mechanism for rapid metallicity enrichment of quasar nuclear gas (in general, in active galactic nuclei) based on star-gas interactions and equivalent to an unusual mode of massive star formation. The mechanism involves capture of low-mass stars from the host galaxy's nucleus by the assemblages of clouds or by accretion disks orbiting the central massive objects (e.g., black holes). Trapping of stars within gaseous disks/clouds occurs through resonant density and bending wave excitation, as well as by hydrodynamical drag. The time scale for trapping stars with total mass equal to that of disk fragment/cloud is of order Hubble time and is remarkably model-independent. Our results show that the described mechanism can produce features suggested by observations, for example, the (super) solar gas metallicity in the nucleus. Thus the observed metallicities in high-redshift quasars do not necessarily imply that global star formation and efficient chemical changes have occurred in their host galaxies at very early cosmological epochs.

Approximate universal relations for neutron stars and quark stars

NASA Astrophysics Data System (ADS)

Yagi, Kent; Yunes, Nicolás

2017-04-01

Neutron stars and quark stars are ideal laboratories to study fundamental physics at supra nuclear densities and strong gravitational fields. Astrophysical observables, however, depend strongly on the star's internal structure, which is currently unknown due to uncertainties in the equation of state. Universal relations, however, exist among certain stellar observables that do not depend sensitively on the star's internal structure. One such set of relations is between the star's moment of inertia (I), its tidal Love number (Love) and its quadrupole moment (Q), the so-called I-Love-Q relations. Similar relations hold among the star's multipole moments, which resemble the well-known black hole no-hair theorems. Universal relations break degeneracies among astrophysical observables, leading to a variety of applications: (i) X-ray measurements of the nuclear matter equation of state, (ii) gravitational wave measurements of the intrinsic spin of inspiraling compact objects, and (iii) gravitational and astrophysical tests of General Relativity that are independent of the equation of state. We here review how the universal relations come about and all the applications that have been devised to date.

Identification of dusty massive stars in star-forming dwarf irregular galaxies in the Local Group with mid-IR photometry

NASA Astrophysics Data System (ADS)

Britavskiy, N. E.; Bonanos, A. Z.; Mehner, A.; Boyer, M. L.; McQuinn, K. B. W.

2015-12-01

Context. Increasing the statistics of spectroscopically confirmed evolved massive stars in the Local Group enables the investigation of the mass loss phenomena that occur in these stars in the late stages of their evolution. Aims: We aim to complete the census of luminous mid-IR sources in star-forming dwarf irregular (dIrr) galaxies of the Local Group. To achieve this we employed mid-IR photometric selection criteria to identify evolved massive stars, such as red supergiants (RSGs) and luminous blue variables (LBVs), by using the fact that these types of stars have infrared excess due to dust. Methods: The method is based on 3.6 μm and 4.5 μm photometry from archival Spitzer Space Telescope images of nearby galaxies. We applied our criteria to four dIrr galaxies: Pegasus, Phoenix, Sextans A, and WLM, selecting 79 point sources that we observed with the VLT/FORS2 spectrograph in multi-object spectroscopy mode. Results: We identified 13 RSGs, of which 6 are new discoveries, as well as two new emission line stars, and one candidate yellow supergiant. Among the other observed objects we identified carbon stars, foreground giants, and background objects, such as a quasar and an early-type galaxy that contaminate our survey. We use the results of our spectroscopic survey to revise the mid-IR and optical selection criteria for identifying RSGs from photometric measurements. The optical selection criteria are more efficient in separating extragalactic RSGs from foreground giants than mid-IR selection criteria, but the mid-IR selection criteria are useful for identifying dusty stars in the Local Group. This work serves as a basis for further investigation of the newly discovered dusty massive stars and their host galaxies. Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under programme IDs 090.D-0009 and 091.D-0010.Appendix A is available in electronic form at http://www.aanda.org

CHARACTERIZING THE POPULATION OF BRIGHT INFRARED SOURCES IN THE SMALL MAGELLANIC CLOUD

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

Kraemer, K. E.; Sloan, G. C.; Wood, P. R.

We have used the Infrared Spectrograph (IRS) on the Spitzer Space Telescope to observe stars in the Small Magellanic Cloud (SMC) selected from the Point Source Catalog of the Midcourse Space Experiment (MSX). We concentrate on the dust properties of the oxygen-rich evolved stars. The dust composition has smaller contributions from alumina compared to the Galaxy. This difference may arise from the lower metallicity in the SMC, but it could be a selection effect, as the SMC sample includes more stars that are brighter and thus more massive. The distribution of the SMC stars along the silicate sequence looks moremore » like the Galactic sample of red supergiants than asymptotic giant branch stars (AGBs). While many of the SMC stars are definitively on the AGB, several also show evidence of hot bottom burning. Three of the supergiants show PAH emission at 11.3 μ m. Two other sources show mixed chemistry, with both carbon-rich and oxygen-rich spectral features. One, MSX SMC 134, may be the first confirmed silicate/carbon star in the SMC. The other, MSX SMC 049, is a candidate post-AGB star. MSX SMC 145, previously considered a candidate OH/IR star, is actually an AGB star with a background galaxy at z  = 0.16 along the same line of sight. We consider the overall characteristics of all the MSX sources, the most infrared-bright objects in the SMC, in light of the higher sensitivity and resolution of Spitzer , and compare them with the object types expected from the original selection criteria. This population represents what will be seen in more distant galaxies by the upcoming James Webb Space Telescope ( JWST ). Color–color diagrams generated from the IRS spectra and the mid-infrared filters on JWST show how one can separate evolved stars from young stellar objects (YSOs) and distinguish among different classes of YSOs.« less

Characterizing the Population of Bright Infrared Sources in the Small Magellanic Cloud

NASA Astrophysics Data System (ADS)

Kraemer, K. E.; Sloan, G. C.; Wood, P. R.; Jones, O. C.; Egan, M. P.

2017-01-01

We have used the Infrared Spectrograph (IRS) on the Spitzer Space Telescope to observe stars in the Small Magellanic Cloud (SMC) selected from the Point Source Catalog of the Midcourse Space Experiment (MSX). We concentrate on the dust properties of the oxygen-rich evolved stars. The dust composition has smaller contributions from alumina compared to the Galaxy. This difference may arise from the lower metallicity in the SMC, but it could be a selection effect, as the SMC sample includes more stars that are brighter and thus more massive. The distribution of the SMC stars along the silicate sequence looks more like the Galactic sample of red supergiants than asymptotic giant branch stars (AGBs). While many of the SMC stars are definitively on the AGB, several also show evidence of hot bottom burning. Three of the supergiants show PAH emission at 11.3 μm. Two other sources show mixed chemistry, with both carbon-rich and oxygen-rich spectral features. One, MSX SMC 134, may be the first confirmed silicate/carbon star in the SMC. The other, MSX SMC 049, is a candidate post-AGB star. MSX SMC 145, previously considered a candidate OH/IR star, is actually an AGB star with a background galaxy at z = 0.16 along the same line of sight. We consider the overall characteristics of all the MSX sources, the most infrared-bright objects in the SMC, in light of the higher sensitivity and resolution of Spitzer, and compare them with the object types expected from the original selection criteria. This population represents what will be seen in more distant galaxies by the upcoming James Webb Space Telescope (JWST). Color-color diagrams generated from the IRS spectra and the mid-infrared filters on JWST show how one can separate evolved stars from young stellar objects (YSOs) and distinguish among different classes of YSOs.

Simulating star clusters with the AMUSE software framework. I. Dependence of cluster lifetimes on model assumptions and cluster dissolution modes

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

Whitehead, Alfred J.; McMillan, Stephen L. W.; Vesperini, Enrico

2013-12-01

We perform a series of simulations of evolving star clusters using the Astrophysical Multipurpose Software Environment (AMUSE), a new community-based multi-physics simulation package, and compare our results to existing work. These simulations model a star cluster beginning with a King model distribution and a selection of power-law initial mass functions and contain a tidal cutoff. They are evolved using collisional stellar dynamics and include mass loss due to stellar evolution. After studying and understanding that the differences between AMUSE results and results from previous studies are understood, we explored the variation in cluster lifetimes due to the random realization noisemore » introduced by transforming a King model to specific initial conditions. This random realization noise can affect the lifetime of a simulated star cluster by up to 30%. Two modes of star cluster dissolution were identified: a mass evolution curve that contains a runaway cluster dissolution with a sudden loss of mass, and a dissolution mode that does not contain this feature. We refer to these dissolution modes as 'dynamical' and 'relaxation' dominated, respectively. For Salpeter-like initial mass functions, we determined the boundary between these two modes in terms of the dynamical and relaxation timescales.« less

Dating the Tidal Disruption of Globular Clusters with GAIA Data on Their Stellar Streams

NASA Astrophysics Data System (ADS)

Bose, Sownak; Ginsburg, Idan; Loeb, Abraham

2018-05-01

The Gaia mission promises to deliver precision astrometry at an unprecedented level, heralding a new era for discerning the kinematic and spatial coordinates of stars in our Galaxy. Here, we present a new technique for estimating the age of tidally disrupted globular cluster streams using the proper motions and parallaxes of tracer stars. We evolve the collisional dynamics of globular clusters within the evolving potential of a Milky Way-like halo extracted from a cosmological ΛCDM simulation and analyze the resultant streams as they would be observed by Gaia. The simulations sample a variety of globular cluster orbits, and account for stellar evolution and the gravitational influence of the disk of the Milky Way. We show that a characteristic timescale, obtained from the dispersion of the proper motions and parallaxes of stars within the stream, is a good indicator for the time elapsed since the stream has been freely expanding away due to the tidal disruption of the globular cluster. This timescale, in turn, places a lower limit on the age of the cluster. The age can be deduced from astrometry using a modest number of stars, with the error on this estimate depending on the proximity of the stream and the number of tracer stars used.

Peculiar Abundances Observed in the Hot Subdwarf OB Star LB 3241

NASA Astrophysics Data System (ADS)

Chayer, Pierre; Dupuis, J.; Dixon, W. V.; Giguere, E.

2010-01-01

We present a spectral synthesis analysis of the hot subdwarf OB star LB 3241. The analysis is based on spectra obtained by the Far Ultraviolet Spectroscopic Explorer (FUSE). With an effective temperature of 41,000 K and a gravity of log g = 5.7, the position of LB 3241 in a Teff-log g diagram suggests that it has evolved from the extreme horizontal branch. Such stars evolve into white dwarfs without ascending the asymptotic giant branch after the helium core exhaustion. Arsenic (Z = 33), selenium (34), and tellurium (52) are observed in the atmosphere of LB 3241, and are a first for a hot subdwarf star. LB 3241 shows peculiar chemical abundances that exhibit trends observed in cooler sdB stars. The content of its atmosphere in light elements is about a factor ten lower than that of the Sun, except for nitrogen which has a solar abundance. The Fe abundance is consistent with a solar abundance, but abundances of elements beyond the iron peak (As, Se, Te, Pb) show enrichments over the solar values by factors ranging from 10 to 300. These observations suggest that competing mechanisms must counterbalance the effects of the downward diffusion. The FUSE observations also suggest that LB 3241 is a radial velocity variable.

Shedding light on baryonic dark matter.

PubMed

Silk, J

1991-02-01

Halo dark matter, if it is baryonic, may plausibly consist of compact stellar remnants. Jeans mass clouds containing 10(6) to 10(8) solar masses could have efficiently formed stars in the early universe and could plausibly have generated, for a suitably top-heavy stellar initial mass function, a high abundance of neutron stars as well as a small admixture of long-lived low mass stars. Within the resulting clusters of dark remnants, which eventually are tidally disrupted when halos eventually form, captures of neutron stars by non-degenerate stars resulted in formation of close binaries. These evolve to produce, by the present epoch, an observable x-ray signal associated with dark matter aggregations in galaxy halos and galaxy cluster cores.

VUV Spectroscopy of the Sun as a Star

NASA Astrophysics Data System (ADS)

Kankelborg, Charles; Philip, Judge; Winebarger, Amy R.; Kobayashi, Ken; Smart, Roy

2017-08-01

We describe a new sounding rocket mission to obtain the first high resolution, high quality VUV (100-200 nm) spectrum of the Sun-as-a-star. Our immediate science goal is to understand better the processes of chromospheric and coronal heating. HST data exist for a dozen or so Sun-like stars of a quality already beyond our ability to construct a comparable sun-as-a-star UV spectrum. The solar spectrum we obtain will enable us to understand the nature of magnetic energy dissipation as a Sun-like star evolves, and the dependence of magnetic activity on stellar mass and metallicity. This poster presents the instrument design, scientific prospects, and broader impacts of the proposed mission.

Stargazing: an integrative conceptual review, theoretical reconciliation, and extension for star employee research.

PubMed

Call, Matthew L; Nyberg, Anthony J; Thatcher, Sherry M B

2015-05-01

Stars--employees with disproportionately high and prolonged (a) performance, (b) visibility, and (c) relevant social capital--have garnered attention in economics, sociology, and management. However, star research is often isolated within these research disciplines. Thus, 3 distinct star research streams are evolving, each disconnected from the others and each bringing siloed theoretical perspectives, terms, and assumptions. A conceptual review of these perspectives reveals a focus on the expost effects that stars exert in organizations with little explanation of who a star is and how one becomes a star. To synthesize the stars literature across these 3 disciplines, we apply psychological theories, specifically motivation theories, to create an integrative framework for stars research. Thus, we present a unified stars definition and extend theory on the making, managing, and mobility of stars. We extend research about how and why employees may be motivated to become stars, how best to manage stars and their relationships with colleagues, and how to motivate star retention. We then outline directions for future research. (c) 2015 APA, all rights reserved.

The enrichment of the ISM: Evolved stars and meteorites

NASA Technical Reports Server (NTRS)

Jura, M.

1995-01-01

Small inclusions (diameters ranging from 0.001 microns to 10 microns) of isotopically anomalous material within meteorites were almost certainly produced in mass-losing stars. These solid particles preserved their individual identities as they passed through the interstellar medium and the pre-solar nebular. The relationship between studies of meteorites and mass-losing red giants is explored.

AGB and post-AGB objects in the outer Galaxy

NASA Astrophysics Data System (ADS)

Szczerba, Ryszard; Yung, Bosco H. K.; Sewiło, Marta; Siódmiak, Natasza; Karska, Agata

2017-10-01

We present the results of our search for low- and intermediate mass evolved stars in the outer Galaxy using AllWISE catalogue photometry. We show that the [3.4]-[12] vs. [4.6]-[22] colour-colour diagram is most suitable for separating C-rich/O-rich AGB and post-AGB star candidates. We are able to select 2,510 AGB and 24,821 post-AGB star candidates. However, the latter are severely mixed with the known young stellar objects in this diagram.

On the Maximum Mass of Differentially Rotating Neutron Stars

NASA Astrophysics Data System (ADS)

Baumgarte, Thomas W.; Shapiro, Stuart L.; Shibata, Masaru

2000-01-01

We construct relativistic equilibrium models of differentially rotating neutron stars and show that they can support significantly more mass than their nonrotating or uniformly rotating counterparts. We dynamically evolve such ``hypermassive'' models in full general relativity and show that there do exist configurations that are dynamically stable against radial collapse and bar formation. Our results suggest that the remnant of binary neutron star coalescence may be temporarily stabilized by differential rotation, leading to delayed collapse and a delayed gravitational wave burst.

RAPIDLY EVOLVING AND LUMINOUS TRANSIENTS DRIVEN BY NEWLY BORN NEUTRON STARS

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

Yu, Yun-Wei; Li, Shao-Ze; Dai, Zi-Gao, E-mail: yuyw@mail.ccnu.edu.cn

2015-06-10

We provide a general analysis on the properties of the emitting material of some rapidly evolving and luminous transients discovered recently with the Pan-STARRS1 Medium Deep Survey. It was found that these transients are probably produced by a low-mass non-relativistic outflow that is continuously powered by a newly born, rapidly spinning, and highly magnetized neutron star (NS). Such a system could originate from an accretion-induced collapse of a white dwarf or a merger of an NS–NS binary. Therefore, observations of these transients would be helpful for constraining white dwarf and NS physics and/or for searching and identifying gravitational wave signals frommore » the mergers.« less

Spectral Identification of New Galactic cLBV and WR Stars

NASA Astrophysics Data System (ADS)

Stringfellow, G. S.; Gvaramadze, V. V.; Beletsky, Y.; Kniazev, A. Y.

2012-12-01

We have undertaken a near-IR spectral survey of stars associated with compact nebulae recently revealed by the Spitzer and WISE imaging surveys. These circumstellar nebulae, produced by massive evolved stars, display a variety of symmetries and shapes and are often only evident at mid-IR wavelengths. Stars associated with ˜50 of these nebulae have been observed. We also obtained recent spectra of previously confirmed (known) luminous blue variables (LBVs) and candidate LBVs (cLBVs). The spectral similarity of the stars observed when compared directly to known LBVs and Wolf-Rayet (WR) stars indicate many are newly identified cLBVs, with a few being newly discovered WR stars, mostly of WN8-9h spectral type. These results suggest that a large population of previously unidentified cLBVs and related transitional stars reside in the Galaxy and confirm that circumstellar nebulae are inherent to most (c)LBVs.

Astromaterial Science

NASA Astrophysics Data System (ADS)

Caplan, Matthew E.

Recent work has used large scale molecular dynamics simulations to study the structures and phases of matter in the crusts of neutron stars, with an emphasis on applying techniques in material science to the study of astronomical objects. In the outer crust of an accreting neutron star, a mixture of heavy elements forms following an X-ray burst, which is buried and freezes. We will discuss the phase separation of this mixture, and the composition of the crust that forms. Additionally, calculations of the properties of the crust, such as diffusion coefficients and static structure factors, may be used to interpret observations. Deeper in the neutron star crust, at the base of the inner crust, nuclei are compressed until they touch and form structures which have come to be called 'nuclear pasta.' We study the phases of nuclear pasta with classical molecular dynamics simulations, and discuss how simulations at low density may be relevant to nucleosynthesis in neutron star mergers. Additionally, we discuss the structure factor of nuclear pasta and its impact on the properties of the crust, and use this to interpret observations of crust cooling in low mass X-ray binaries. Lastly, we discuss a correspondence between the structure of nuclear pasta and biophysics.

Effects of the nucleon radius on neutron stars in a quark mean field model

NASA Astrophysics Data System (ADS)

Zhu, Zhen-Yu; Li, Ang

2018-03-01

We study the effects of free space nucleon radius on nuclear matter and neutron stars within the framework of the quark mean field model. The nucleon radius is treated self-consistently with this model, where quark confinement is adjusted to fit different values of nucleon radius. Corrections due to center-of-mass motion, quark-pion coupling, and one gluon exchange are included to obtain the nucleon mass in vacuum. The meson coupling constants that describe the behavior of the many-body nucleonic system are constructed by reproducing the empirical saturation properties of nuclear matter, including the recent determinations of symmetry energy parameters. Our results show that the nucleon radius in free space has negligible effects on the nuclear matter equation of state and neutron star mass-radius relations, which is different from the conclusion drawn in previous studies. We further explore that the sensitivity of star radius on the nucleon radius found in earlier publications is actually from the symmetry energy and its slope.

Zodiacal Exoplanets in Time: Searching for Young Stars in K2

NASA Astrophysics Data System (ADS)

Morris, Nathan; Mann, Andrew W.

2017-06-01

Nearby young, open clusters such as the Hyades, Pleiades, and Praesepe provide an important reference point for the properties of stellar systems in general. In each cluster, all stars are of the same known age. As such, observations of planetary systems around these stars can be used to gain insight into the early stages of planetary system formation. K2, the revived Kepler mission, has provided a vast number of light curves for young stars in the and elsewhere in the K2 field. We aim to compute rotational periods from sunspot patterns for all K2 target stars and use gyrochronometric relationships derived from cluster stars to determine their ages. From there, we will search for planets around young stars outside the clusters with the ultimate goal of shedding light on how planets and planetary systems evolve with time.

The Contribution of Thermally-Pulsing Asymptotic Giant Branch and Red Supergiant Starts to the Luminosities of the Magellanic Clouds at 1-24 micrometers

NASA Technical Reports Server (NTRS)

Melbourne, J.; Boyer, Martha L.

2013-01-01

We present the near-through mid-infrared flux contribution of thermally-pulsing asymptotic giant branch (TP-AGB) and massive red supergiant (RSG) stars to the luminosities of the Large and Small Magellanic Clouds (LMC and SMC, respectively). Combined, the peak contribution from these cool evolved stars occurs at approx 3 - 4 micron, where they produce 32% of the SMC light, and 25% of the LMC flux. The TP-AGB star contribution also peaks at approx 3 - 4 micron and amounts to 21% in both galaxies. The contribution from RSG stars peaks at shorter wavelengths, 2.2 micron, where they provide 11% of the SMC flux, and 7% for the LMC. Both TP-AGB and RSG stars are short lived, and thus potentially impose a large stochastic scatter on the near-IR derived mass-to-light (M/L) ratios of galaxies at rest-frame 1 - 4 micron. To minimize their impact on stellar mass estimates, one can use the M/L ratio at shorter wavelengths (e.g., at 0.8 - 1 micron). At longer wavelengths (much > 8 micron), emission from dust in the interstellar medium dominates the flux. In the LMC, which shows strong polycyclic aromatic hydrocarbon (PAH) emission at 8 micron, TP-AGB and RSG contribute less than 4% of the 8 micron flux. However, 19% of the SMC 8 micron flux is from evolved stars, nearly half of which is produced by the rarest, dustiest, carbon-rich TP-AGB stars. Thus, star formation rates of galaxies, based on an 8 micron flux (e.g., observed-frame 24 micron at z = 2), may be biased modestly high, especially for galaxies with little PAH emission.

Westerlund 1: monolithic formation of a starburst cluster

NASA Astrophysics Data System (ADS)

Negueruela, Ignacio; Clark, J. Simon; Ritchie, Ben; Goodwin, Simon

2015-08-01

Westerlund 1 is in all likelihood the most massive young cluster in the Milky Way, with a mass on the order of 105 Msol. We have been observing its massive star population for ten years, measuring radial velocity changes for a substantial fraction of its OB stars and evolved supergiants. The properties of the evolved population are entirely consisting with a single burst of star formation, in excellent agreement with the results of studies based on the lower-mass population.Here we will present two new studies of the cluster: 1) A direct measurement of its average radial velocity and velocity dispersion based on individual measurements for several dozen stars with constant radial velocity and 2) A search for massive stars in its immediate neighbourhood using multi-object spectroscopy.The results of these two studies show that Westerlund 1 is decidedly subvirial and has a systemic radial velocity significantly different from that of nearby gas, which was assumed to provide a dynamical distance by previous authors. Moreover, the dynamical distance is inconsistent with the properties of the high-mass stellar population. In addition, we find that the cluster is completely isolated, with hardly any massive star in its vicinity that could be associated in terms of distance modulus or radial velocity. The cluster halo does not extend much further than five parsec away from the centre. All these properties are very unusual among starburst clusters in the Local Universe, which tend to form in the context of large star-forming regions.Westerlund 1 is thus the best example we have of a starburst cluster formed monolithically.

Outer crust of nonaccreting cold neutron stars

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

Ruester, Stefan B.; Hempel, Matthias; Schaffner-Bielich, Juergen

The properties of the outer crust of nonaccreting cold neutron stars are studied by using modern nuclear data and theoretical mass tables, updating in particular the classic work of Baym, Pethick, and Sutherland. Experimental data from the atomic mass table from Audi, Wapstra, and Thibault of 2003 are used and a thorough comparison of many modern theoretical nuclear models, both relativistic and nonrelativistic, is performed for the first time. In addition, the influences of pairing and deformation are investigated. State-of-the-art theoretical nuclear mass tables are compared to check their differences concerning the neutron drip line, magic neutron numbers, the equationmore » of state, and the sequence of neutron-rich nuclei up to the drip line in the outer crust of nonaccreting cold neutron stars.« less

Phosphorylation regulates the Star-PAP-PIPKIα interaction and directs specificity toward mRNA targets

PubMed Central

Mohan, Nimmy; AP, Sudheesh; Francis, Nimmy; Anderson, Richard; Laishram, Rakesh S.

2015-01-01

Star-PAP is a nuclear non-canonical poly(A) polymerase (PAP) that shows specificity toward mRNA targets. Star-PAP activity is stimulated by lipid messenger phosphatidyl inositol 4,5 bisphoshate (PI4,5P2) and is regulated by the associated Type I phosphatidylinositol-4-phosphate 5-kinase that synthesizes PI4,5P2 as well as protein kinases. These associated kinases act as coactivators of Star-PAP that regulates its activity and specificity toward mRNAs, yet the mechanism of control of these interactions are not defined. We identified a phosphorylated residue (serine 6, S6) on Star-PAP in the zinc finger region, the domain required for PIPKIα interaction. We show that S6 is phosphorylated by CKIα within the nucleus which is required for Star-PAP nuclear retention and interaction with PIPKIα. Unlike the CKIα mediated phosphorylation at the catalytic domain, Star-PAP S6 phosphorylation is insensitive to oxidative stress suggesting a signal mediated regulation of CKIα activity. S6 phosphorylation together with coactivator PIPKIα controlled select subset of Star-PAP target messages by regulating Star-PAP-mRNA association. Our results establish a novel role for phosphorylation in determining Star-PAP target mRNA specificity and regulation of 3′-end processing. PMID:26138484

Dust grains and gas in the circumstellar envelopes around luminous red giant stars

NASA Technical Reports Server (NTRS)

Zuckerman, B.; Dyck, H. M.

1986-01-01

Far-infrared color-color diagrams have been constructed for over 100 of the brightest evolved stars in the IRAS Point Source Catalog. The diagrams are used to deduce average values of the dust grain emissivity index (p) between 12 and 100 microns. Grains in C-rich and O-rich environments have similar values of p between 12 and 25 microns and between 60 and 100 microns, but between 25 and 60 microns p is larger by approximately 0.4 for the O-rich stars. Dust grains in envelopes around S-type stars seem to have 25 to 60 micron emissivities more nearly like grains in O-rich rather than C-rich environments. CO and HCN emissions from various stars are used to reclassify several stars as oxygen or carbon rich.

The mass-loss return from evolved stars to the Large Magellanic Cloud. V. The GRAMS carbon-star model grid

NASA Astrophysics Data System (ADS)

Srinivasan, S.; Sargent, B. A.; Meixner, M.

2011-08-01

Context. Outflows from asymptotic giant branch (AGB) and red supergiant (RSG) stars inject dust into the interstellar medium. The total rate of dust return provides an important constraint to galactic chemical evolution models. However, this requires detailed radiative transfer (RT) modeling of individual stars, which becomes impractical for large data sets. An alternative approach is to select the best-fit spectral energy distribution (SED) from a grid of dust shell models, allowing for a faster determination of the luminosities and mass-loss rates for entire samples. Aims: We have developed the Grid of RSG and AGB ModelS (GRAMS) to measure the mass-loss return from evolved stars. The models span the range of stellar, dust shell and grain properties relevant to evolved stars. The GRAMS model database will be made available to the scientific community. In this paper we present the carbon-rich AGB model grid and compare our results with photometry and spectra of Large Magellanic Cloud (LMC) carbon stars from the SAGE (Surveying the Agents of Galaxy Evolution) and SAGE-Spec programs. Methods: We generate models for spherically symmetric dust shells using the 2Dust code, with hydrostatic models for the central stars. The model photospheres have effective temperatures between 2600 and 4000 K and luminosities from ~2000 L⊙ to ~40 000 L⊙. Assuming a constant expansion velocity, we explore five values of the inner radius Rin of the dust shell (1.5, 3, 4.5, 7 and 12 Rstar). We fix the outer radius at 1000 Rin. Based on the results from our previous study, we use amorphous carbon dust mixed with 10% silicon carbide by mass. The grain size distribution follows a power-law and an exponential falloff at large sizes. The models span twenty-six values of 11.3 μm optical depth, ranging from 0.001 to 4. For each model, 2Dust calculates the output SED from 0.2 to 200 μm. Results: Over 12 000 models have dust temperatures below 1800 K. For these, we derive synthetic photometry in optical, near-infrared and mid-infrared filters for comparison with available data. We find good agreement with magnitudes and colors observed for LMC carbon-rich and extreme AGB star candidates from the SAGE survey, as well as spectroscopically confirmed carbon stars from the SAGE-Spec study. Our models reproduce the IRAC colors of most of the extreme AGB star candidates, consistent with the expectation that a majority of these enshrouded stars have carbon-rich dust. Finally, we fit the SEDs of some well-studied carbon stars and compare the resulting luminosities and mass-loss rates with those from previous studies. The model grid is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/532/A54

Low energy cross sections and underground laboratories

NASA Astrophysics Data System (ADS)

Corvisiero, P.; LUNA Collaboration

2005-04-01

It is known that the chemical elements and their isotopes were created by nuclear fusion reactions in the hot interiors of remote and long-vanished stars over many billions of years [C. Rolfs, W.S. Rodney, Cauldrons in the cosmos, University of Ghicago Press, Chicago (1988)]. The present picture is that all elements from carbon to uranium have been produced entirely within stars during their fiery lifetimes and explosive deaths. The detailed understanding of the origin of the chemical elements and their isotopes combines astrophysics and nuclear physics, and forms what is called nuclear astrophysics. In turn, nuclear reactions are at the heart of nuclear astrophysics: they influence sensitively the nucleosynthesis of the elements in the earliest stages of the universe and in all the objects formed thereafter, and control the associated energy generation, neutrino luminosity, and evolution of stars. A good knowledge of the rates of these fusion reactions is essential to understanding this broad picture. Some of the most important experimental techniques to measure the corresponding cross sections, based both on direct and indirect methods, will be described in this paper.

Constraints on CEMP-no progenitors from nuclear astrophysics

NASA Astrophysics Data System (ADS)

Choplin, Arthur; Maeder, André; Meynet, Georges; Chiappini, Cristina

2016-09-01

Context. The CEMP-no stars are long-lived small mass stars presenting a very low iron content and overabundances of carbon with no sign or only very weak signs of s- or r-elements. Although the origin of this abundance pattern is still a matter of debate, it was very likely inherited from a previous massive star, which we call the source star. Aims: We rely on a recent classification of CEMP-no stars arguing that some of them are made of a material processed by hydrogen burning that was enriched in products of helium burning during the nuclear life of the source star. We examine the possibility of forming CEMP-no stars with this material. Methods: We study the nucleosynthesis of the CNO cycle and the Ne-Na Mg-Al chains in a hydrogen burning single zone while injecting the helium burning products 12C, 16O, 22Ne, and 26Mg. We investigate the impact of changing density, temperature and the injection rate. The nuclear reaction rates involving the creation and destruction of 27Al are also examined. Results: 14N, 23Na, 24Mg, and 27Al are formed when injecting 12C, 16O, 22Ne, and 26Mg in the hydrogen burning zone. The 12C/13C ratio is constant under various conditions in the hydrogen burning zone. The predicted [Al/Fe] ratio varies up to ~ 2 dex depending on the prescription used for the reaction rates involving 27Al. Conclusions: The experiments we carried out support the view that some CEMP-no stars are made of a material processed by hydrogen burning that comes from a massive star experiencing mild to strong rotational mixing. During its burning, this material was likely enriched in helium burning products. No material coming from the carbon-oxygen rich core of the source star should be added to form the daughter star, otherwise the 12C/13C ratio would be largely above the observed range of values.

Evolved stars and the origin of abundance trends in planet hosts

NASA Astrophysics Data System (ADS)

Maldonado, J.; Villaver, E.

2016-04-01

Context. Detailed chemical abundance studies have revealed different trends between samples of planet and non-planet hosts. Whether these trends are related to the presence of planets or not is strongly debated. At the same time, tentative evidence that the properties of evolved stars with planets may be different from what we know for main-sequence hosts has recently been reported. Aims: We aim to test whether evolved stars with planets show any chemical peculiarity that could be related to the planet formation process. Methods: In a consistent way, we determine the metallicity and individual abundances of a large sample of evolved (subgiants and red giants) and main-sequence stars that are with and without known planetary companions, and discuss their metallicity distribution and trends. Our methodology is based on the analysis of high-resolution échelle spectra (R ≳ 57 000) from 2-3 m class telescopes. It includes the calculation of the fundamental stellar parameters, as well as individual abundances of C, O , Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, and Zn. Results: No differences in the ⟨[X/Fe]⟩ vs. condensation temperature (TC) slopes are found between the samples of planet and non-planet hosts when all elements are considered. However, if the analysis is restricted to only refractory elements, differences in the TC-slopes between stars with and without known planets are found. This result is found to be dependent on the stellar evolutionary stage, as it holds for main-sequence and subgiant stars, while there seems to be no difference between planet and non-planet hosts among the sample of giants. A search for correlations between the TC-slope and the stellar properties reveals significant correlations with the stellar mass and the stellar age. The data also suggest that differences in terms of mass and age between main-sequence planet and non-planet hosts may be present. Conclusions: Our results are well explained by radial mixing in the Galaxy. The sample of giants contains stars that are more massive and younger than their main-sequence counterparts. This leads to a sample of stars that are possibly less contaminated by stars that were not born in the solar neighbourhood, leading to no chemical differences between planet and non-planet hosts. The sample of main-sequence stars may contain more stars from the outer disc (specially the non-planet host sample) which might lead to the differences observed in the chemical trends. Based on observations made with the Mercator Telescope; on observations made with the Nordic Optical Telescope; on observations made with the Italian Telescopio Nazionale Galileo; on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto; and on data products from observations made with ESO Telescopes at the La Silla Paranal Observatory under programme ID 072.C-0488(E), 080.D-0347(A), 081.D-0870(A), 087.C-0831(A), and 183.C-0972(A).Tables B.1-B.3 are only available at the 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/A98

Unveiling the hearts of luminous and ultra-luminous infrared galaxy mergers with laser guide star adaptive optics

NASA Astrophysics Data System (ADS)

Medling, Anne M.

2013-03-01

Gas-rich galaxies across cosmic time exhibit one or both of two phenomena: ongoing star formation and an active galactic nucleus indicating current black hole accretion. These two processes are important mechanisms through which galaxies evolve and grow, but their effects are difficult to disentangle. Both will use up some available gas, and both are capable of producing winds strong enough to eject remaining gas from the galaxy. One must look at high spatial resolutions in order to separate the dynamical effects of star formation going on near the nucleus of a galaxy from the black hole growth going on in the nucleus. We present high spatial resolution integral field spectroscopy of fifteen nearby luminous and ultra-luminous infrared galaxies. These systems are extremely bright in the infrared exactly because they host powerful starbursts and active nuclei, which in turn heat the surrounding dust. Our data provide resolved stellar and gaseous kinematics of the central kiloparsec of each of these systems by removing atmospheric blurring with adaptive optics, an observing technique that measures the turbulence in the Earth's atmosphere and then uses a deformable mirror to correct the resulting distortions. Our kinematic maps reveal nuclear disks of gas and stars with radii ˜ a few hundred parsecs surrounding the central black holes. Because the stellar and gas kinematics match well, we conclude that the stars are forming in situ from the gas in the disks. These disks may be the progenitors of kinematically decoupled cores seen in many isolated elliptical galaxies, and may have a significant effect on the merger rate of binary black holes. Additionally, these disks may be used to measure black hole masses which, when combined with host galaxy properties and placed on scaling relations, indicate that black holes grow as or more quickly than their host galaxies during a merger. This suggests that a sudden burst of black hole growth at in the final stages of the merger is not likely to be responsible for shutting off star formation in these systems, unless a time delay is also present.

Microscopic calculations of nuclear and neutron matter, symmetry energy and neutron stars

DOE PAGES

Gandolfi, S.

2015-02-01

We present Quantum Monte Carlo calculations of the equation of state of neutron matter. The equation of state is directly related to the symmetry energy and determines the mass and radius of neutron stars, providing then a connection between terrestrial experiments and astronomical observations. As a result, we also show preliminary results of the equation of state of nuclear matter.

Orbital Decay in Binaries with Evolved Stars

NASA Astrophysics Data System (ADS)

Sun, Meng; Arras, Phil; Weinberg, Nevin N.; Troup, Nicholas; Majewski, Steven R.

2018-01-01

Two mechanisms are often invoked to explain tidal friction in binary systems. The ``dynamical tide” is the resonant excitation of internal gravity waves by the tide, and their subsequent damping by nonlinear fluid processes or thermal diffusion. The ``equilibrium tide” refers to non-resonant excitation of fluid motion in the star’s convection zone, with damping by interaction with the turbulent eddies. There have been numerous studies of these processes in main sequence stars, but less so on the subgiant and red giant branches. Motivated by the newly discovered close binary systems in the Apache Point Observatory Galactic Evolution Experiment (APOGEE-1), we have performed calculations of both the dynamical and equilibrium tide processes for stars over a range of mass as the star’s cease core hydrogen burning and evolve to shell burning. Even for stars which had a radiative core on the main sequence, the dynamical tide may have very large amplitude in the newly radiative core in post-main sequence, giving rise to wave breaking. The resulting large dynamical tide dissipation rate is compared to the equilibrium tide, and the range of secondary masses and orbital periods over which rapid orbital decay may occur will be discussed, as well as applications to close APOGEE binaries.

An Evolving Trio of Hybrid Stars: C 111

NASA Technical Reports Server (NTRS)

Oliversen, Ronald (Technical Monitor); Dupree, Andrea K.

2004-01-01

Our goal is to understand the behavior of the outer atmosphere in this intermediate stage to create a comprehensive picture of atmospheric evolution. In the hybrid phase, the large-scale magnetic dynamo activity decays and hydrodynamic processes assume importance. Some hot plasma is still confined close to the star by magnetic loops, yet the confining field is breaking open, the atmosphere can escape through these open field lines, and the diffuse corona may be warm. There may well be a more extended and variable transition process. It remains for FUSE to identify the controlling parameters of the hybrid stars. It shows the positions of our 3 targets in the color-magnitude diagram where it is seen that they are at the extreme end of the hybrid region. Originally we had been awarded the hybrid star Iota Aur, but due to newly imposed pointing constraints of FUSE, that target was not accessible. And so we substituted Iota Dra, a giant of mass similar to our other targets but less evolved. In addition, Iota Dra was recently found to harbor a sub-stellar objects, possibly a planet, and so it could reveal the stellar environment of the planet. This substitution was accepted.

Argonne Physics Division

Science.gov Websites

, nuclear structure and reaction research, nuclear theory, medium energy nuclear research and accelerator structure of baryonic matter in the universe - the matter that makes up stars, planets and human life itself

Synergies Between Asteroseismology and Exoplanetary Science

NASA Astrophysics Data System (ADS)

Huber, Daniel

Over the past decade asteroseismology has become a powerful method to systematically characterize host stars and dynamical architectures of exoplanet systems. In this contribution I review current key synergies between asteroseismology and exoplanetary science such as the precise determination of planet radii and ages, the measurement of orbital eccentricities, stellar obliquities and their impact on hot Jupiter formation theories, and the importance of asteroseismology on spectroscopic analyses of exoplanet hosts. I also give an outlook on future synergies such as the characterization of sub-Neptune-size planets orbiting solar-type stars, the study of planet populations orbiting evolved stars, and the determination of ages of intermediate-mass stars hosting directly imaged planets.

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

Suh, In-Saeng; Mathews, Grant J.; Haywood, J. Reese

The spatially conformally flat approximation (CFA) is a viable method to deduce initial conditions for the subsequent evolution of binary neutron stars employing the full Einstein equations. Here in this paper, we analyze the viability of the CFA for the general relativistic hydrodynamic initial conditions of binary neutron stars. We illustrate the stability of the conformally flat condition on the hydrodynamics by numerically evolving ~100 quasicircular orbits. We illustrate the use of this approximation for orbiting neutron stars in the quasicircular orbit approximation to demonstrate the equation of state dependence of these initial conditions and how they might affect themore » emergent gravitational wave frequency as the stars approach the innermost stable circular orbit.« less

Galaxy Formation from the Primordial Black Holes

NASA Astrophysics Data System (ADS)

Morikawa, Masahiro

2017-12-01

Supermassive black hole (SMBH) of size MBH = 106-10M⊙ is common in the Universe and it defines the center of the galaxy. A galaxy and the SMBH are generally thought to have co-evolved. However, the SMBH cannot evolve so fast as commonly observed even at redshift z > 6. Therefore, we explore a natural hypothesis that the SMBH has been already formed mature at z ⪆ 10 before stars and galaxies. The SMBH forms energetic jets and out-flows which trigger massive star formation in the ambient gas. They eventually construct globular clusters and classical bulge as well as the body of elliptical galaxies. We propose simple models which implement these processes. We point out that the globular clusters and classical bulges have a common origin but are in different phases. The same is true for the elliptical and spiral galaxies. Physics behind these phase division is the runaway star formation process with strong feedback to SMBH. This is similar to the forest-fire model that displays self-organized criticality.

NANOCOSMOS: a trip to the nanoworld

NASA Astrophysics Data System (ADS)

Ruiz Zelmanovitch, N.; Castellanos, M.

2017-03-01

Cosmic dust is made in evolved stars. However, the processes involved in the formation and evolution of dust remain unknown so far. The project ''Gas and dust from stars to the laboratory: exploring the NANOCOSMOS'', takes advantage of the new observational capabilities (increased angular resolution) of the Atacama Large Millimeter/submillimeter Array (ALMA) to unveil the physical and chemical conditions in the dust formation zone of evolved stars. These observations, in combination with novel top-level ultra-high vacuum experiments and astrophysical modelling, will provide a cutting-edge view of cosmic dust. The importance of publishing scientific results based on NANOCOSMOS in the scientific literature goes without saying. But it is also important and a stated NANOCOSMOS objective to disseminate the achievements of the project and its scientific and technological results to a wider audience. In this presentation we will discuss the tools used to spread them to the society. This presentation is structured as follows: 1. What is Astrochemistry?; 2. What is NANOCOSMOS?; 3. Outreach in the NANOCOSMOS programme; 4. Conclusions.

Near-infrared line and continuum emission from the blue dwarf galaxy II Zw 40

NASA Technical Reports Server (NTRS)

Joy, Marshall; Lester, Daniel F.

1988-01-01

A multicolor analysis of new near-infrared line and continuum measurements indicates that nebular recombination emission and photospheric radiation from young blue stars produce most of the near-infrared continuum emission in the central 6 arcsec of the dwarf galaxy II Zw 40. The derived nebular recombination level is in excellent agreement with independent observations of the radio free-free continuum. It is found that evolved stars, which dominate the near-infrared emission from normal galaxies, contribute no more than 25 percent of the total 2.2 micron flux in the central region of II Zw 40. It is concluded that the total mass of the evolved stellar population in the central 400 pc of the galaxy is less than about two hundred million solar. The total mass of recently formed stars is about two million solar, and the stellar mass ratio is exceptionally large. Thus, II Zw 40 is a quintessential starburst galaxy.

Ejection of the Massive Hydrogen-rich Envelope Timed with the Collapse of the Stripped SN 2014C

PubMed Central

Margutti, Raffaella; Kamble, A.; Milisavljevic, D.; Zapartas, E.; de Mink, S. E.; Drout, M.; Chornock, R.; Risaliti, G.; Zauderer, B. A.; Bietenholz, M.; Cantiello, M.; Chakraborti, S.; Chomiuk, L.; Fong, W.; Grefenstette, B.; Guidorzi, C.; Kirshner, R.; Parrent, J. T.; Patnaude, D.; Soderberg, A. M.; Gehrels, N. C.; Harrison, F.

2017-01-01

We present multi-wavelength observations of SN 2014C during the first 500 days. These observations represent the first solid detection of a young extragalactic stripped-envelope SN out to high-energy X-rays ~40 keV. SN 2014C shows ordinary explosion parameters (Ek ~ 1.8 × 1051 erg and Mej ~ 1.7 M⊙). However, over an ~1 year timescale, SN 2014C evolved from an ordinary hydrogen-poor supernova into a strongly interacting, hydrogen-rich supernova, violating the traditional classification scheme of type-I versus type-II SNe. Signatures of the SN shock interaction with a dense medium are observed across the spectrum, from radio to hard X-rays, and revealed the presence of a massive shell of ~1 M⊙of hydrogen-rich material at ~6 × 1016 cm. The shell was ejected by the progenitor star in the decades to centuries before collapse. This result challenges current theories of massive star evolution, as it requires a physical mechanism responsible for the ejection of the deepest hydrogen layer of H-poor SN progenitors synchronized with the onset of stellar collapse. Theoretical investigations point at binary interactions and/or instabilities during the last nuclear burning stages as potential triggers of the highly time-dependent mass loss. We constrain these scenarios utilizing the sample of 183 SNe Ib/c with public radio observations. Our analysis identifies SN 2014C-like signatures in ~10% of SNe. This fraction is reasonably consistent with the expectation from the theory of recent envelope ejection due to binary evolution if the ejected material can survive in the close environment for 103–104 years. Alternatively, nuclear burning instabilities extending to core C-burning might play a critical role. PMID:28684881

Hybrid Stars and Coronal Evolution

NASA Technical Reports Server (NTRS)

Mushotzky, Richard (Technical Monitor); Dupree, Andrea K.

2004-01-01

This program addresses the evolution of stellar coronas by comparing a solar-like corona in the supergiant Dra (G2 Ib-IIa) to the corona in the allegedly more evolved state of a hybrid star, TrA (K2 11-111). Because the hybrid star has a massive wind, it appears likely that the corona will be cooler and less dense as the magnetic loop structures are no longer closed. By analogy with solar coronal holes, when the topology of the magnetic field is configured with open magnetic structures, both the coronal temperature and density are lower than in atmospheres dominated by closed loops. The hybrid stars assume a pivotal role in the definition of coronal evolution, atmospheric heating processes and mechanisms to drive winds of cool stars.

Analysis of the Conformally Flat Approximation for Binary Neutron Star Initial Conditions

DOE PAGES

Suh, In-Saeng; Mathews, Grant J.; Haywood, J. Reese; ...

2017-01-09

The spatially conformally flat approximation (CFA) is a viable method to deduce initial conditions for the subsequent evolution of binary neutron stars employing the full Einstein equations. Here in this paper, we analyze the viability of the CFA for the general relativistic hydrodynamic initial conditions of binary neutron stars. We illustrate the stability of the conformally flat condition on the hydrodynamics by numerically evolving ~100 quasicircular orbits. We illustrate the use of this approximation for orbiting neutron stars in the quasicircular orbit approximation to demonstrate the equation of state dependence of these initial conditions and how they might affect themore » emergent gravitational wave frequency as the stars approach the innermost stable circular orbit.« less

Shedding light on baryonic dark matter

NASA Technical Reports Server (NTRS)

Silk, Joseph

1991-01-01

Halo dark matter, if it is baryonic, may plausibly consist of compact stellar remnants. Jeans mass clouds containing 10 to the 6th to 10 to the 8th solar masses could have efficiently formed stars in the early universe and could plausibly have generated, for a suitably top-heavy stellar initial mass function, a high abundance of neutron stars as well as a small admixture of long-lived low mass stars. Within the resulting clusters of dark remnants, which eventually are tidally disrupted when halos eventually form, captures of neutron stars by nondegenerate stars resulted in formation of close binaries. These evolve to produce, by the present epoch, an observable X-ray signal associated with dark matter aggregations in galaxy cluster cores.

Star Formation as Seen by the Infrared Array Camera on Spitzer

NASA Technical Reports Server (NTRS)

Smith, Howard A.; Allen, L.; Megeath, T.; Barmby, P.; Calvet, N.; Fazio, G.; Hartmann, L.; Myers, P.; Marengo, M.; Gutermuth, R.

2004-01-01

The Infrared Array Camera (IRAC) onboard Spitzer has imaged regions of star formation (SF) in its four IR bands with spatial resolutions of approximately 2"/pixel. IRAC is sensitive enough to detect very faint, embedded young stars at levels of tens of Jy, and IRAC photometry can categorize their stages of development: from young protostars with infalling envelopes (Class 0/1) to stars whose infrared excesses derive from accreting circumstellar disks (Class 11) to evolved stars dominated by photospheric emission. The IRAC images also clearly reveal and help diagnose associated regions of shocked and/or PDR emission in the clouds; we find existing models provide a good start at explaining the continuum of the SF regions IRAC observes.

Astrometric Planet Searches with SIM PlanetQuest

NASA Technical Reports Server (NTRS)

Beichman, Charles A.; Unwin, Stephen C.; Shao, Michael; Tanner, Angelle M.; Catanzarite, Joseph H.; March, Geoffrey W.

2007-01-01

SIM will search for planets with masses as small as the Earth's orbiting in the habitable zones' around more than 100 of the stars and could discover many dozen if Earth-like planets are common. With a planned 'Deep Survey' of 100-450 stars (depending on desired mass sensitivity) SIM will search for terrestrial planets around all of the candidate target stars for future direct detection missions such as Terrestrial Planet Finder and Darwin, SIM's 'Broad Survey' of 2010 stars will characterize single and multiple-planet systems around a wide variety of stellar types, including many now inaccessible with the radial velocity technique. In particular, SIM will search for planets around young stars providing insights into how planetary systems are born and evolve with time.

The ultraviolet-bright stars of Omega Centauri, M3, and M13

NASA Technical Reports Server (NTRS)

Landsman, Wayne B.; O'Connell, Robert W.; Whitney, Jonathan H.; Bohlin, Ralph C.; Hill, Robert S.; Maran, Stephen P.; Parise, Ronald A.; Roberts, Morton S.; Smith, Andrew A.; Stecher, Theodore P.

1992-01-01

Two new UV-bright stars detected within 2 arcmin of the center of Omega Cen are spectroscopically investigated with the short-wavelength spectrograph of the IUE. The IUE spectra of the UV-bright stars UIT-1 and UIT-2 in the core of Omega Cen superficially resemble those of Population I mid-B stars. The absorption lines of the core UV-bright stars are significantly weaker than in Population I stars, consistent with their membership in the cluster. Synthetic spectra calculated from low-metallicity Kurucz model stellar atmospheres are compared with the spectra. These objects are insufficiently luminous to be classical hydrogen-burning post-AGB stars. They may be evolved hot horizontal branch stars which have been brightened by more than 3 mag since leaving the zero-age horizontal branch. It is inferred from the spectra and luminosity of the core UV-bright stars that similar objects could provide the source of the UV light in elliptical galaxies.

Stars and Nuclei. Part II

ERIC Educational Resources Information Center

Ames, Oakes

1972-01-01

A brief review of the evidence that nuclear reactions are the main source of stellar energy, how nuclear reactions synthesize the elements, and how nuclear reactions determine the course of stellar evolution. (Author/CP)

Uncertainties in s-process nucleosynthesis in massive stars determined by Monte Carlo variations

NASA Astrophysics Data System (ADS)

Nishimura, N.; Hirschi, R.; Rauscher, T.; St. J. Murphy, A.; Cescutti, G.

2017-08-01

The s-process in massive stars produces the weak component of the s-process (nuclei up to A ˜ 90), in amounts that match solar abundances. For heavier isotopes, such as barium, production through neutron capture is significantly enhanced in very metal-poor stars with fast rotation. However, detailed theoretical predictions for the resulting final s-process abundances have important uncertainties caused both by the underlying uncertainties in the nuclear physics (principally neutron-capture reaction and β-decay rates) as well as by the stellar evolution modelling. In this work, we investigated the impact of nuclear-physics uncertainties relevant to the s-process in massive stars. Using a Monte Carlo based approach, we performed extensive nuclear reaction network calculations that include newly evaluated upper and lower limits for the individual temperature-dependent reaction rates. We found that most of the uncertainty in the final abundances is caused by uncertainties in the neutron-capture rates, while β-decay rate uncertainties affect only a few nuclei near s-process branchings. The s-process in rotating metal-poor stars shows quantitatively different uncertainties and key reactions, although the qualitative characteristics are similar. We confirmed that our results do not significantly change at different metallicities for fast rotating massive stars in the very low metallicity regime. We highlight which of the identified key reactions are realistic candidates for improved measurement by future experiments.

X-ray diagnostics of massive star winds

NASA Astrophysics Data System (ADS)

Oskinova, L. M.; Ignace, R.; Huenemoerder, D. P.

2017-11-01

Observations with powerful X-ray telescopes, such as XMM-Newton and Chandra, significantly advance our understanding of massive stars. Nearly all early-type stars are X-ray sources. Studies of their X-ray emission provide important diagnostics of stellar winds. High-resolution X-ray spectra of O-type stars are well explained when stellar wind clumping is taking into account, providing further support to a modern picture of stellar winds as non-stationary, inhomogeneous outflows. X-ray variability is detected from such winds, on time scales likely associated with stellar rotation. High-resolution X-ray spectroscopy indicates that the winds of late O-type stars are predominantly in a hot phase. Consequently, X-rays provide the best observational window to study these winds. X-ray spectroscopy of evolved, Wolf-Rayet type, stars allows to probe their powerful metal enhanced winds, while the mechanisms responsible for the X-ray emission of these stars are not yet understood.

Effects of stellar evolution and ionizing radiation on the environments of massive stars

NASA Astrophysics Data System (ADS)

Mackey, J.; Langer, N.; Mohamed, S.; Gvaramadze, V. V.; Neilson, H. R.; Meyer, D. M.-A.

2014-09-01

We discuss two important effects for the astrospheres of runaway stars: the propagation of ionizing photons far beyond the astropause, and the rapid evolution of massive stars (and their winds) near the end of their lives. Hot stars emit ionizing photons with associated photoheating that has a significant dynamical effect on their surroundings. 3-D simulations show that H ii regions around runaway O stars drive expanding conical shells and leave underdense wakes in the medium they pass through. For late O stars this feedback to the interstellar medium is more important than that from stellar winds. Late in life, O stars evolve to cool red supergiants more rapidly than their environment can react, producing transient circumstellar structures such as double bow shocks. This provides an explanation for the bow shock and linear bar-shaped structure observed around Betelgeuse.

Understanding r-process Nucleosynthesis through Nuclear Data

NASA Astrophysics Data System (ADS)

Surman, Rebecca

2018-06-01

The electromagnetic counterpart of the GW170817 neutron star merger provided the first direct evidence of the astrophysical formation of nuclei via rapid neutron capture (r-process) nucleosynthesis. Full understanding of this event from first principles and its role in galactic chemical evolution requires progress in a number of areas. One key area is nuclear physics. A neutron star merger r-process involves thousands of exotic nuclear species, the majority of which have never been studied in the laboratory. Here we will discuss r-process nuclear data needs and how nuclear physics uncertainties influence our interpretation of observed abundance patterns and kilonova signals. We will explore the promise of experimental campaigns at rare isotope beam facilities to reduce these uncertainties, and describe recent efforts to directly connect nuclear data to astrophysical environments via the ‘reverse-engineering’ of unknown nuclear properties from the r-process abundance pattern.

Tidal Disruption Events from Eccentric Nuclear Disks

NASA Astrophysics Data System (ADS)

Wernke, Heather N.; Madigan, Ann-Marie

2018-04-01

Stars that get too close to a supermassive black hole are in danger of being tidally disrupted. Stellar two-body relaxation is commonly assumed to be the main driver of these events. Recent work has shown, however, that secular gravitational torques from eccentric nuclear disks can push stars to extreme eccentricities at much higher rates than predicted by two-body relaxation. This work did not include the effects of general relativity, however, which could quench secular torques via rapid apsidal precession. Here we show that, for a star in danger of disruption, general relativity acts on a timescale of less than an orbital period. This short timescale means that general relativity does not have enough time to have a major effect on the orbit. When driven by secular torques from eccentric nuclear disks, tidal disruption event rates are not affected by general relativity.

NuSTAR Briefing

NASA Image and Video Library

2012-05-30

Yunjin Kim, NuSTAR project manager at the Jet Propulsion Laborartory (JPL), talks about NASA's Spectroscopic Telescope Array (NuStar) during a briefing, Wednesday, May 30, 2012, at NASA Headquarters in Washington. Imaging light in the high-energy, short-wavelength X-ray range, the telescope will aim to study how black holes form and evolve along with galaxies. The instrument, packed aboard an Orbital Sciences Pegasus XL rocket is set to launch from a plane in midair no earlier than June 13 from Kwajalein Atoll in the Marshall Islands. Photo Credit: (NASA/Paul E. Alers)

Dust clouds around red giant stars - Evidence of sublimating comet disks?

NASA Technical Reports Server (NTRS)

Matese, John J.; Whitmire, Daniel P.; Reynolds, Ray T.

1989-01-01

The dust production by disk comets around intermediate mass stars evolving into red giants is studied, focusing on AGB supergiants. The model of Iben and Renzini (1983) is used to study the observed dust mass loss for AGB stars. An expression is obtained for the comet disk net dust production rate and values of the radius and black body temperature corresponding to peak sublimation are calculated for a range of stellar masses. Also, the fractional amount of dust released from a cometesimal disk during a classical nova outburst is estimated.

History of Chandra X-Ray Observatory

NASA Image and Video Library

2003-01-22

This Chandra X-ray observatory image of M83 shows numerous point-like neutron stars and black hole x-ray sources scattered throughout the disk of this spiral galaxy. The bright nuclear region of the galaxy glows prominently due to a burst of star formation that is estimated to have begun about 20 million years ago in the galaxy's time frame. The nuclear region, enveloped by a 7 million degree Celsius gas cloud of carbon, neon, magnesium, silicon, and sulfur atoms, contains a much higher concentration of neutron stars and black holes than the rest of the galaxy. Hot gas with a slightly lower temperature of 4 million degrees observed along the spiral arms of the galaxy suggests that star formation in this region may be occurring at a more sedate rate.

The effect of photoionizing feedback on star formation in isolated and colliding clouds

NASA Astrophysics Data System (ADS)

Shima, Kazuhiro; Tasker, Elizabeth J.; Federrath, Christoph; Habe, Asao

2018-05-01

We investigate star formation occurring in idealized giant molecular clouds, comparing structures that evolve in isolation versus those undergoing a collision. Two different collision speeds are investigated and the impact of photoionizing radiation from the stars is determined. We find that a colliding system leads to more massive star formation both with and without the addition of feedback, raising overall star formation efficiencies (SFE) by a factor of 10 and steepening the high-mass end of the stellar mass function. This rise in SFE is due to increased turbulent compression during the cloud collision. While feedback can both promote and hinder star formation in an isolated system, it increases the SFE by approximately 1.5 times in the colliding case when the thermal speed of the resulting H II regions matches the shock propagation speed in the collision.

Population of the lower part of the instability strip: Delta Scuti stars and dwarf Cepheids (or AI Velorum)

NASA Technical Reports Server (NTRS)

Auvergne, M.; Baglin, A.; Lecontel, J. M.; Valtier, J. C.

1980-01-01

Some of the properties of the atmospheric variations in delta Scuti stars were investigated with emphasis on the amplitude and the shape of both light curves and radial velocity curves. It is shown that these curves are small and rapidly variable in the case of dwarf Scuti stars; for the evolved stars the situation is more complex. The relation between variables and nonvariables, and also the results on abundances in the atmospheres of these stars were surveyed with respect to the hydrodynamics of their envelopes. The abundance anomalies of Am stars were qualitatively examined. The coexistence of abundance anomalies and variability among giants were also studied. Attempts were made to relate the variability to the hydrogen ionization zone in an envelope deprived of helium. Specific results are reported.

Processing of presolar grains around post-AGB stars: SiC as the carrier of the ``21''μ m feature

NASA Astrophysics Data System (ADS)

Hofmeister, A. M.; Speck, A. K.

2003-12-01

Intermediate mass stars (0.8-8.0 Msolar) eventually evolve on the H-R diagram, up the asymptotic giant branch (AGB). The intensive mass loss which characterizes the AGB produces a circumstellar shell of dust and neutral gas. At the end of the AGB, mass loss virtually stops and the circumstellar shell begins to drift away from the star. At the same time the central star begins to shrink and heat up. This is the proto-planetary nebula (PPN) phase. Some PPNe exhibit an enigmatic feature in their infrared (IR) spectra at ˜21μ m. This feature is not seen in the spectra of either the precursors to PPNe, the AGB stars, or the successors of PPNe, ``normal'' planetary nebulae (PNe). However the ``21''μ m feature has been seen in the spectra of PNe with Wolf-Rayet central stars. Therefore the carrier of this feature is unlikely to be a transient species that only exists in the PPNe phase. This feature has been attributed to various molecular and solid state species, none of which satisfy all constraints, although titanium carbide (TiC) and polycyclic aromatic hydrocarbons (PAHs) have seemed the most viable. We present new laboratory data for silicon carbide (SiC) and show that it has a spectral feature which is a good candidate for the carrier of the 21μ m feature. The SiC spectral feature appears at approximately the same wavelength (depending on polytype/grain size) and has the same asymmetric profile as the observed astronomical feature. We suggest that processing and cooling of the SiC grains known to exist around carbon-rich AGB stars are responsible for the emergence of the enigmatic 21μ m feature. The emergence of this feature in the spectra of post-AGB stars demonstrates the processing of dust due to the changing physical environments around evolving stars.

Phosphorylation regulates the Star-PAP-PIPKIα interaction and directs specificity toward mRNA targets.

PubMed

Mohan, Nimmy; Sudheesh, A P; Francis, Nimmy; Anderson, Richard; Laishram, Rakesh S

2015-08-18

Star-PAP is a nuclear non-canonical poly(A) polymerase (PAP) that shows specificity toward mRNA targets. Star-PAP activity is stimulated by lipid messenger phosphatidyl inositol 4,5 bisphoshate (PI4,5P2) and is regulated by the associated Type I phosphatidylinositol-4-phosphate 5-kinase that synthesizes PI4,5P2 as well as protein kinases. These associated kinases act as coactivators of Star-PAP that regulates its activity and specificity toward mRNAs, yet the mechanism of control of these interactions are not defined. We identified a phosphorylated residue (serine 6, S6) on Star-PAP in the zinc finger region, the domain required for PIPKIα interaction. We show that S6 is phosphorylated by CKIα within the nucleus which is required for Star-PAP nuclear retention and interaction with PIPKIα. Unlike the CKIα mediated phosphorylation at the catalytic domain, Star-PAP S6 phosphorylation is insensitive to oxidative stress suggesting a signal mediated regulation of CKIα activity. S6 phosphorylation together with coactivator PIPKIα controlled select subset of Star-PAP target messages by regulating Star-PAP-mRNA association. Our results establish a novel role for phosphorylation in determining Star-PAP target mRNA specificity and regulation of 3'-end processing. © The Author(s) 2015. Published by Oxford University Press on behalf of Nucleic Acids Research.

Celestial paleontology: The legacy of dying stars

NASA Astrophysics Data System (ADS)

Hart, Alexa H.

2013-03-01

In their death throes, stars dole out their atmospheric material to the interstellar medium in dramatic stellar winds and spectacular explosions. The details of this profound metamorphosis, from star to remnant, play a key role in the next generation of star formation as well as the energetic and chemical evolution of galaxies and the universe as a whole. Dying stars are thought to be the source of all of the nuclei heavier than iron in the universe, as well as more complex molecules, such as carbon chains, which form the backbone of life as we know it. High mass Wolf-Rayet stars are likely progenitors of many types of Supernova, yet due to observational constraints we lack the most basic information about most of them: rather they are part of binary systems. This information is key to the determination of rather or not these stars will go supernova, since depending on its nature the companion can either draw mass off the Wolf-Rayet star, effectively quenching the march to explosion, or feed material onto the Wolf-Rayet star, speeding its demise as a supernova. Models of galactic evolution depend sensitively on the frequency of supernova for several reasons: they inject a great deal of energy into the Interstellar medium, they are the only known producers of nuclei heavier than nickel, and the shock waves that they create can stimulate star formation. In turn, the energy generated by supernova explosions drives the galactic wind, the heavier elements now present in the Interstellar Medium increase the efficiency of star formation, and the groups of new stars formed in the wake of a shock are thought to lead to the development of spiral arms in galaxies. In addition, because high mass stars are so short-lived, they can cycle through hundreds of generations in the time it takes one solar-type star's to evolve. Though intermediate mass stars merely fizzle out in comparison, they are pivotal to the evolution of the universe because they make up over 97% of the stars that have had enough time to evolve off the Main Sequence since the Big Bang. These stars produce more than half of the carbon in the universe as well as much of the nitrogen, oxygen, and more complex molecules such as aromatic rings of carbon. This process, often referred to as chemical enrichment, strongly affects the star formation rates and the characteristics of the next generation of stars. In this work, we explore the contributions of these two classes of stars to our own galaxy: we quantify the nature of the chemical enrichment to the Milky Way from a large sample of intermediate mass stars, and determine the binary status of a sample of Wolf-Rayet stars in the Milky Way.

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

Thilker, David A.; Bianchi, Luciana; Schiminovich, David

We have discovered recent star formation in the outermost portion ((1-4) x R {sub 25}) of the nearby lenticular (S0) galaxy NGC 404 using Galaxy Evolution Explorer UV imaging. FUV-bright sources are strongly concentrated within the galaxy's H I ring (formed by a merger event according to del RIo et al.), even though the average gas density is dynamically subcritical. Archival Hubble Space Telescope imaging reveals resolved upper main-sequence stars and conclusively demonstrates that the UV light originates from recent star formation activity. We present FUV, NUV radial surface brightness profiles, and integrated magnitudes for NGC 404. Within the ring,more » the average star formation rate (SFR) surface density ({Sigma}{sub SFR}) is {approx}2.2 x 10{sup -5} M {sub sun} yr{sup -1} kpc{sup -2}. Of the total FUV flux, 70% comes from the H I ring which is forming stars at a rate of 2.5 x 10{sup -3} M {sub sun} yr{sup -1}. The gas consumption timescale, assuming a constant SFR and no gas recycling, is several times the age of the universe. In the context of the UV-optical galaxy color-magnitude diagram, the presence of the star-forming H I ring places NGC 404 in the green valley separating the red and blue sequences. The rejuvenated lenticular galaxy has experienced a merger-induced, disk-building excursion away from the red sequence toward bluer colors, where it may evolve quiescently or (if appropriately triggered) experience a burst capable of placing it on the blue/star-forming sequence for up to {approx}1 Gyr. The green valley galaxy population is heterogeneous, with most systems transitioning from blue to red but others evolving in the opposite sense due to acquisition of fresh gas through various channels.« less

Tidal Dissipation In Rotating Low Mass Stars: Implications For The Orbital Evolution Of Close In Planets

NASA Astrophysics Data System (ADS)

Gallet, Florian; Bolmont, Emeline; Mathis, Stéphane; Charbonnel, Corinne; Amard, Louis; Alibert, Yann

2017-10-01

Close-in planets represent a large fraction of the population of confirmed exoplanets. To understand the dynamical evolution of these planets, star-planet interactions must be taken into account. In particular, the dependence of the tidal interactions on the structural parameters of the star, its rotation, and its metallicity should be treated in the models. We quantify how the tidal dissipation in the convective envelope of rotating low-mass stars evolves in time. We also investigate the possible consequences of this evolution on planetary orbital evolution. In Gallet et al. (2017) and Bolmont et al. (2017) we generalized the work of Bolmont & Mathis (2016) by following the orbital evolution of close-in planets using the new tidal dissipation predictions for advanced phases of stellar evolution and non-solar metallicity. We find that during the pre-main sequence the evolution of tidal dissipation is controlled by the evolution of the internal structure of the star through the stellar contraction. On the main-sequence tidal dissipation is strongly driven by the evolution of the surface rotation that is impacted by magnetized stellar winds braking. Finally, during the more evolved phases, the tidal dissipation sharply decreases as radiative core retreats in mass and radius towards the red-giant branch. Using an orbital evolution model, we also show that changing the metallicity leads to diUerent orbital evolutions (e.g., planets migrate farther out from an initially fast rotating metal rich star). By using this model, we qualitatively reproduced the observational trends of the population of hot Jupiters with the metallicity of their host stars. However, more work still remain to be do so as to be able to quantitatively fit our results to the observations.

Deep Imaging of Extremely Metal-Poor Galaxies

NASA Astrophysics Data System (ADS)

Corbin, Michael

2006-07-01

Conflicting evidence exists regarding whether the most metal-poor and actively star-forming galaxies in the local universe such as I Zw 18 contain evolved stars. We propose to help settle this issue by obtaining deep ACS/HRC U, narrow-V, I, and H-alpha images of nine nearby {z < 0.01} extremely metal-poor {12 + O/H < 7.65} galaxies selected from the Sloan Digital Sky Survey. These objects are only marginally resolved from the ground and appear uniformly blue, strongly motivating HST imaging. The continuum images will establish: 1.} If underlying populations of evolved stars are present, by revealing the objects' colors on scales 10 pc, and 2.} The presence of any faint tidal features, dust lanes, and globular or super star clusters, all of which constrain the objects' evolutionary states. The H-alpha images, in combination with ground-based echelle spectroscopy, will reveal 1.} Whether the objects are producing "superwinds" that are depleting them of their metals; ground-based images of some of them indeed show large halos of ionized gas, and 2.} The correspondence of their nebular and stellar emission on scales of a few parsecs, which is important for understanding the "feedback" process by which supernovae and stellar winds regulate star formation. One of the sample objects, CGCG 269-049, lies only 2 Mpc away, allowing the detection of individual red giant stars in it if any are present. We have recently obtained Spitzer images and spectra of this galaxy to determine its dust content and star formation history, which will complement the proposed HST observations. [NOTE: THIS PROPOSAL WAS REDUCED TO FIVE ORBITS, AND ONLY ONE OF THE ORIGINAL TARGETS, CGCG 269-049, AFTER THE PHASE I REVIEW

Bulgeless galaxies in the COSMOS field: environment and star formation evolution at z < 1

NASA Astrophysics Data System (ADS)

Grossi, Marco; Fernandes, Cristina A. C.; Sobral, David; Afonso, José; Telles, Eduardo; Bizzocchi, Luca; Paulino-Afonso, Ana; Matute, Israel

2018-03-01

Combining the catalogue of galaxy morphologies in the COSMOS field and the sample of H α emitters at redshifts z = 0.4 and z = 0.84 of the HiZELS survey, we selected ˜ 220 star-forming bulgeless systems (Sérsic index n ≤ 1.5) at both epochs. We present their star formation properties and we investigate their contribution to the star formation rate function (SFRF) and global star formation rate density (SFRD) at z < 1. For comparison, we also analyse H α emitters with more structurally evolved morphologies that we split into two classes according to their Sérsic index n: intermediate (1.5 < n ≤ 3) and bulge-dominated (n > 3). At both redshifts, the SFRF is dominated by the contribution of bulgeless galaxies and we show that they account for more than 60 per cent of the cosmic SFRD at z < 1. The decrease of the SFRD with redshift is common to the three morphological types, but it is stronger for bulge-dominated systems. Star-forming bulgeless systems are mostly located in regions of low to intermediate galaxy densities (Σ ˜ 1-4 Mpc-2) typical of field-like and filament-like environments and their specific star formation rates (sSFRs) do not appear to vary strongly with local galaxy density. Only few bulgeless galaxies in our sample have high (sSFR > 10-9 yr-1) and these are mainly low-mass systems. Above M* ˜ 1010 M⊙ bulgeless are evolving at a `normal' rate (10-9 yr-1 < sSFR < 10-10 yr-1) and in the absence of an external trigger (i.e. mergers/strong interactions) they might not be able to develop a central classical bulge.

Prior Knowledge Base of Constellations and Bright Stars among Non-Science Majoring Undergraduates and 14-15 Year Old Students

ERIC Educational Resources Information Center

Hintz, Eric G.; Hintz, Maureen L.; Lawler, M. Jeannette

2015-01-01

As part of an effort to improve students' knowledge of constellations and bright stars in an introductory level descriptive astronomy survey course, we measured the baseline knowledge that students bring to the class and how their score evolve over the course of the semester. This baseline is needed by the broader astronomy education research…

Eta Carinae and Other Luminous Blue Variables

NASA Technical Reports Server (NTRS)

Corcoran, M. F.

2006-01-01

Luminous Blue Variables (LBVs) are believed to be evolved, extremely massive stars close to the Eddington Limit and hence prone to bouts of large-scale, unstable mass loss. I discuss current understanding of the evolutionary state of these objects, the role duplicity may play and known physical characteristics of these stars using the X-ray luminous LBVs Eta Carinae and HD 5980 as test cases.

VizieR Online Data Catalog: A framework for empirical galaxy phenomenology (Munoz+, 2015)

NASA Astrophysics Data System (ADS)

Munoz, J. A.; Peeples, M. S.

2017-11-01

In this study, we develop a cohesive theoretical formalism for translating empirical relations into an understanding of the variations in galactic star formation histories. We achieve this goal by incorporating into the Main Sequence Integration (MSI) method the scatter suggested by the evolving fraction of quiescent galaxies and the spread in the observed stellar mass-star formation rate relation. (2 data files).

Magnetic field in IRC+10216 and other C-rich evolved stars

NASA Astrophysics Data System (ADS)

Duthu, A.; Herpin, F.; Wiesemeyer, H.; Baudry, A.; Lèbre, A.; Paubert, G.

2017-07-01

Context. During the transition from the asymptotic giant branch (AGB) to planetary nebulae (PN), the circumstellar geometry and morphology change dramatically. Another characteristic of this transition is the high mass-loss rate, that can be partially explained by radiation pressure and a combination of various factors, such as the stellar pulsation, the dust grain condensation, and opacity in the upper atmosphere. The magnetic field can also be one of the main ingredients that shapes the stellar upper atmosphere and envelope. Aims: Our main goal is to investigate for the first time the spatial distribution of the magnetic field in the envelope of IRC+10216. More generally we intend to determine the magnetic field strength in the circumstellar envelope (CSE) of C-rich evolved stars, compare this field with previous studies for O-rich stars, and constrain the variation of the magnetic field with r the distance to the star's centre. Methods: We use spectropolarimetric observations of the Stokes V parameter, collected with Xpol on the IRAM-30 m radiotelescope, observing the Zeeman effect in seven hyperfine components of the CN J = 1-0 line. We use the Crutcher et al. (1996, ApJ, 456, 217) method to estimate the magnetic field. For the first time, the instrumental contamination is investigated, through dedicated studies of the power patterns in Stokes V and I in detail. Results: For C-rich evolved stars, we derive a magnetic field strength (B) between 1.6 and 14.2 mG while B is estimated to be 6 mG for the proto-PN (PPN) AFGL618, and an upper value of 8 mG is found for the PN NGC 7027. These results are consistent with a decrease of B as 1/r in the environment of AGB objects, that is, with the presence of a toroidal field. But this is not the case for PPN and PN stars. Our map of IRC+10216 suggests that the magnetic field is not homogeneously strong throughout or aligned with the envelope and that the morphology of the CN emission might have changed with time.

Nuclear pasta phases within the quark-meson coupling model

NASA Astrophysics Data System (ADS)

Grams, Guilherme; Santos, Alexandre M.; Panda, Prafulla K.; Providência, Constança; Menezes, Débora P.

2017-05-01

In this work, the low-density regions of nuclear and neutron star matter are studied. The search for the existence of nuclear pasta phases in this region is performed within the context of the quark-meson coupling (QMC) model, which incorporates quark degrees of freedom. Fixed proton fractions are considered, as well as nuclear matter in β equilibrium at zero temperature. We discuss the recent attempts to better understand the surface energy in the coexistence phases regime and we present results that show the existence of the pasta phases subject to some choices of the surface energy coefficient. We also analyze the influence of the nuclear pasta on some neutron star properties. The equation of state containing the pasta phase will be part of a complete grid for future use in supernova simulations.

The Origin of Hot Subluminous Horizontal-Branch Stars in (omega) Centauri and NGC 2808

NASA Technical Reports Server (NTRS)

Sweigart, Allen V.; Brown, Thomas M.; Lanz, Thierry; Landsman, Wayne B.; Hubeny, Ivan

2001-01-01

Hot subluminous stars lying up to 0.7 mag below the extreme horizontal branch (EHB) are found in the ultraviolet (UV) color magnitude diagrams of both (omega) Cen and NGC 2808. In order to explore the evolutionary status of these subluminous stars, we have evolved a set of low-mass stars continuously from the main sequence through the helium-core flash to the HB (horizontal branch) for a wide range in the mass loss along the red-giant branch (RGB). Stars with the largest mass loss evolve off the RGB to high effective temperatures before igniting helium in their cores. Our results indicate that the subluminous EHB stars, as well as the gap within the EHB of NGC 2808, can be explained if these stars undergo a late helium-core flash while descending the white-dwarf cooling curve. Under these conditions the convection zone produced by the helium flash will penetrate into the stellar envelope, thereby mixing most, if not all, of the envelope hydrogen into the hot helium-burning interior, where it is rapidly consumed. This phenomenon is analogous to the 'born-again' scenario for producing hydrogen-deficient stars following a very late helium-shell flash. This 'flash mixing' of the stellar envelope greatly enhances the envelope helium and carbon abundances and, as a result, leads to a discontinuous jump in the HB effective temperature. We argue that the EHB gap in NGC 2808 is associated with this theoretically predicted dichotomy in the HB morphology. Using new helium- and carbon-rich stellar atmospheres, we show that these changes in the envelope abundances of the flash-mixed stars will suppress the UV flux by the amount needed to explain the hot subluminous EHB stars in (omega) Cen and NGC 2808. Moreover, we demonstrate that models without flash mixing lie, at most, only approximately 0.1 mag below the EHB, and hence fail to explain the observations. Flash mixing may also provide a new evolutionary channel for producing the high gravity, helium-rich sdO and sdB stars.

Identification of red supergiants in nearby galaxies with mid-IR photometry

NASA Astrophysics Data System (ADS)

Britavskiy, N. E.; Bonanos, A. Z.; Mehner, A.; García-Álvarez, D.; Prieto, J. L.; Morrell, N. I.

2014-02-01

Context. The role of episodic mass loss in massive-star evolution is one of the most important open questions of current stellar evolution theory. Episodic mass loss produces dust and therefore causes evolved massive stars to be very luminous in the mid-infrared and dim at optical wavelengths. Aims: We aim to increase the number of investigated luminous mid-IR sources to shed light on the late stages of these objects. To achieve this we employed mid-IR selection criteria to identity dusty evolved massive stars in two nearby galaxies. Methods: The method is based on mid-IR colors, using 3.6 μm and 4.5 μm photometry from archival Spitzer Space Telescope images of nearby galaxies and J-band photometry from 2MASS. We applied our criteria to two nearby star-forming dwarf irregular galaxies, Sextans A and IC 1613, selecting eight targets, which we followed-up with spectroscopy. Results: Our spectral classification and analysis yielded the discovery of two M-type supergiants in IC 1613, three K-type supergiants and one candidate F-type giant in Sextans A, and two foreground M giants. We show that the proposed criteria provide an independent way for identifying dusty evolved massive stars that can be extended to all nearby galaxies with available Spitzer/IRAC images at 3.6 μm and 4.5 μm. Based on observations made with the Gran Telescopio Canarias (GTC), installed in the Spanish Observatorio de El Roque de Los Muchachos of the Instituto de Astrofísica de Canarias, on the island of La Palma, and the 2.5 m du Pont telescope in operation at Las Campanas Observatory, Chile.Spectra are only available at the 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/562/A75

Minor Merger Origin for the Circumnuclear Starburst in NGC 7742

NASA Technical Reports Server (NTRS)

Mazzuca, Lisa M.; Sarzi, M.; Knapen, J. H.; Veilleux, S.; Swaters, R.

2006-01-01

We present an emission-line diagnostic analysis of integral-field spectroscopic observations that cover the central kiloparsec of NGC 7742. This Sa galaxy hosts a spectacular nuclear starburst ring and nuclear regions characterized by low-ionization emission. The gas in the ring rotates in the opposite sense to the stars in the galaxy, suggesting a recent merging or acquisition event. The combination of integral-field measurements for the H alpha+[N II] emission lines from DensePak and the H beta and [O 111] emission from SAURON allow the construction of diagnostic diagrams that highlight the transition from star formation in the nuclear ring to excitation by high-velocity shocks or by a central AGN towards the center. DensePak measurements for the [S II] line ratio reveal very low gas densities in the nuclear ring, N(sub e) less than 100 per cubic centimeters, characteristic of massive H II regions. Comparison with MAPPINGS III models for starbursts with low gas densities show that the ring is of roughly solar metallicity. This suggests that the gas in the nuclear ring originated in a stellar system capable of substantially enriching the gas metallicity through sustained star formation. We propose that NGC 7742 cannibalised a smaller galaxy rich in metal-poor gas, and that star formation episodes in the ring have since increased the metallicity to its present value. The techniques explored here can be widely used to study similar systems, including composite (AGN+starburst) galaxies.

Theory of winds in late-type evolved and pre-main-sequence stars

NASA Technical Reports Server (NTRS)

Macgregor, K. B.

1983-01-01

Recent observational results confirm that many of the physical processes which are known to occur in the Sun also occur among late-type stars in general. One such process is the continuous loss of mass from a star in the form of a wind. There now exists an abundance of either direct or circumstantial evidence which suggests that most (if not all) stars in the cool portion of the HR diagram possess winds. An attempt is made to assess the current state of theoretical understanding of mass loss from two distinctly different classes of late-type stars: the post-main-sequence giant/supergiant stars and the pre-main-sequence T Tauri stars. Toward this end, the observationally inferred properties of the wind associated with each of the two stellar classes under consideration are summarized and compared against the predictions of existing theoretical models. Although considerable progress has been made in attempting to identify the mechanisms responsible for mass loss from cool stars, many fundamental problems remain to be solved.

Hubble's Cosmic Atlas

NASA Image and Video Library

2017-12-08

Morphologies, masses, and structures - oh, my! This beautiful clump of glowing gas, dark dust and glittering stars is the spiral galaxy NGC 4248, located about 24 million light-years away in the constellation of Canes Venatici (The Hunting Dogs). This image was produced by the NASA/ESA Hubble Space Telescope as it embarked upon compiling the first Hubble ultraviolet “atlas,” for which the telescope targeted 50 nearby star-forming galaxies. The collection spans all kinds of different morphologies, masses, and structures. Studying this sample can help us to piece together the star-formation history of the Universe. By exploring how massive stars form and evolve within such galaxies, astronomers can learn more about how, when, and where star formation occurs, how star clusters change over time, and how the process of forming new stars is related to the properties of both the host galaxy and the surrounding interstellar medium (the gas and dust that fills the space between individual stars). This galaxy was imaged with observations from Hubble’s Wide Field Camera 3. Image credit: ESA/Hubble & NASA

Copernicus observations of the N v resonance doublet in 53 early-type stars

NASA Technical Reports Server (NTRS)

Abbott, D. C.; Bohlin, R. C.; Savage, B. D.

1982-01-01

UV spectra in the wavelength interval 1170-1270 A are presented for 53 early-type stars ranging in spectral type from O6.5 V to B2.5 IV. The sample includes four Wolf-Rayet stars, seven known Oe-Be stars, and six galactic halo OB stars. A qualitative analysis of the stellar N v doublet reveals that: (1) N v is present in all stars hotter and more luminous than type B0 for the main sequence, B1 for giants, and B2 for supergiants; (2) shell components of N v and an unidentified absorption feature at 1230 A are present in about half of the stars; (3) the column density of N v is well correlated with bolometric luminosity over the spectral range O6 to B2; and (4) the ratio of emission to absorption equivalent width is a factor of 2 smaller in the main sequence stars than in supergiants, which suggests that the wind structure changes as a star evolves. For several stars, this ratio is too small to be explained by traditional wind models.

A deep near-infrared spectroscopic survey of the Scutum-Crux arm for Wolf-Rayet stars

NASA Astrophysics Data System (ADS)

Rosslowe, C. K.; Crowther, Paul A.

2018-01-01

We present a New Technology Telescope/Son-of-Isaac spectroscopic survey of infrared selected Wolf-Rayet (WR) candidates in the Scutum-Crux spiral arm (298° ≤ l ≤ 340°, |b| ≤ 0.5°. We obtained near-IR spectra of 127 candidates, revealing 17 WR stars - a ∼13 per cent success rate - of which 16 are newly identified here. The majority of the new WR stars are classified as narrow-lined WN5-7 stars, with two broad-lined WN4-6 stars and three WC6-8 stars. The new stars, with distances estimated from previous absolute magnitude calibrations, have no obvious association with the Scutum-Crux arm. Refined near-infrared (YHJK) classification criteria based on over a hundred Galactic and Magellanic Cloud WR stars, providing diagnostics for hydrogen in WN stars, plus the identification of WO stars and intermediate WN/C stars. Finally, we find that only a quarter of WR stars in the survey region are associated with star clusters and/or H II regions, with similar statistics found for luminous blue variables (LBVs) in the Milky Way. The relative isolation of evolved massive stars is discussed, together with the significance of the co-location of LBVs and WR stars in young star clusters.

Starburst Galaxies. III. Properties of a Radio-selected Sample

NASA Astrophysics Data System (ADS)

Smith, Denise A.; Herter, Terry; Haynes, Martha P.

1998-02-01

We have analyzed the properties of the 20 most radio-luminous UGC starburst galaxies from Condon, Frayer, & Broderick. Near-infrared images, spectra, and optical rotation curves were presented in Smith et al. In this paper, we use these data and published radio data to assess the stellar populations, dust contents, ionizing conditions, and dynamics of the starbursts. Certain properties of the star formation occurring in these galaxies differ from those observed locally. The infrared excesses (IREs) are lower than and span a narrower range of values than those of Galactic H II regions. The starbursts appear to produce a higher proportion of ionizing photons than most Galactic H II regions. Consequently, the initial mass functions (IMFs) of the starbursts may be more strongly biased toward high-mass star formation. The starbursts may also contain fewer old H II regions than the Milky Way. Furthermore, the starburst IRE is likely to be influenced by the presence of large reservoirs of gas that absorb a larger fraction of the Lyman continuum photons. The OB stellar and far-infrared luminosities imply that the upper mass range of the starburst IMF (M > 10 M⊙) is characterized by a slope of 2.7 +/- 0.2. The starburst IMF thus bears a strong similarity to that observed in Magellanic OB associations. Optical line ratios indicate that a range of excitation conditions are present. We conclude that the near-infrared light from many of the starbursts is dominated by a heavily obscured mixture of emission from evolved red stars and young blue stars with small contributions (~5%) from thermal gas and hot dust, under the assumptions that a Galactic or SMC extinction law can be applied to these systems and that the true reddening curve follows one of the models currently existing in the literature. In some cases, larger amounts of emission from blue stars or hot dust may be required to explain the observed near-infrared colors. The amount of dust emission exceeds that predicted from comparisons with Galactic H II regions. The near-infrared colors of some of the systems may also be influenced by the presence of a low-luminosity active galactic nucleus (AGN). Emission from blue stars and hot dust, if present, dilutes the observed CO index. The activity in the redder, more luminous systems is strongly peaked. The galaxies hosting the starbursts exhibit a wide range of morphological and star-forming properties. While all of the host galaxies are interacting systems, the nuclear separations of the interacting nuclei range from <1 kpc to >1 Mpc. The dynamical behavior ranges from relaxed to strongly perturbed. The off-nuclear regions of the galaxies are sites of active star formation and are characterized by a range of excitation conditions. Spatially extended LINER emission is consistent with shock excitation produced by superwinds or galaxy-galaxy collisions. Violent star formation activity occurs over a larger physical scale in the most active starbursts. Systems containing mergers and widely separated nuclei possess similar colors and luminosities. The burst properties are most likely regulated by the internal structures of the interacting galaxies and not the separations of the interacting galaxies. Observations at the Palomar Observatory were made as part of a continuing collaborative agreement between the California Institute of Technology and Cornell University.

SiO maser polarization in evolved stars: magnetic field

NASA Astrophysics Data System (ADS)

Herpin, F.; Baudry, A.; Thum, C.; Morris, D.; Wiesemeyer, H.

The maser theory still needs to be improved, in particular in terms of polarization. The study of the maser geometry inside the circumstellar envelopes can also be achieved through polarization studies (e.g., VLBI observations). But the most exciting point is the determination of the magnetic field that can be made from polarization measurements: this is definitively a new field of investigation for these evolved objects. The magnetic field probably plays an important role in the AGB star's life and can be a major factor (magnetic rotator theory) on the origin of the high mass loss rates observed in evolved objects. Measurement of the magnetic field is thus essential to study the mass loss mechanisms and also the Alfven waves. During its transition most quasi spherical AGB stars (i.e. envelopes) become complicated aspherical objects. This shaping is well explained by the Interacting Stellar Winds theory (Kwok works), but the ISW model fails to reproduce very complicated structures with jets and ansae. A new model (Magnetized Wind Blown Bubble theory) was thus developed by Blackman et al. (2001) and A. Franck: a weak toroidal magnetic field, embedded in the stellar wind, acts as a collimating agent (cf. Garcia-Segura 1997) and can produce such structures. Three molecules can show polarized maser emission in the circumstellar envelopes: - OH traces the envelope far from the central star (1000-10000 AU) - H2O at intermediate distances (a few 100 AU) - SiO in the inner circumstellar layers (5-10 AU) Measurement of the polarization rate of the maser radiation emitted by these molecules can give us the averaged value B// of the magnetic field along the line of sight (for a single dish observation). We present here the first complete study of the SiO maser polarization in a large sample of evolved stars (more than 100). The 4 Stokes parameters I, U, Q, V were simultaneously measured with the polarimeter on the IRAM-30m telescope. From the Stokes parameters values we derive the linear (pL) and circular (pC) polarization rates and polarization angle. The circular polarization rate gives us directly the magnetic field B//: B// varies from 1 to 32 Gauss depending on the source, with an average value of 9 Gauss.

The innate origin of radial and vertical gradients in a simulated galaxy disc

NASA Astrophysics Data System (ADS)

Navarro, Julio F.; Yozin, Cameron; Loewen, Nic; Benítez-Llambay, Alejandro; Fattahi, Azadeh; Frenk, Carlos S.; Oman, Kyle A.; Schaye, Joop; Theuns, Tom

2018-05-01

We examine the origin of radial and vertical gradients in the age/metallicity of the stellar component of a galaxy disc formed in the APOSTLE cosmological hydrodynamical simulations. Some of these gradients resemble those in the Milky Way, where they have sometimes been interpreted as due to internal evolution, such as scattering off giant molecular clouds, radial migration driven by spiral patterns, or orbital resonances with a bar. Secular processes play a minor role in the simulated galaxy, which lacks strong spiral or bar patterns, and where such gradients arise as a result of the gradual enrichment of a gaseous disc that is born thick but thins as it turns into stars and settles into centrifugal equilibrium. The settling is controlled by the feedback of young stars; which links the star formation, enrichment, and equilibration time-scales, inducing radial and vertical gradients in the gaseous disc and its descendent stars. The kinematics of coeval stars evolve little after birth and provide a faithful snapshot of the gaseous disc structure at the time of their formation. In this interpretation, the age-velocity dispersion relation would reflect the gradual thinning of the disc rather than the importance of secular orbit scattering; the outward flaring of stars would result from the gas disc flare rather than from radial migration; and vertical gradients would arise because the gas disc gradually thinned as it enriched. Such radial and vertical trends might just reflect the evolving properties of the parent gaseous disc, and are not necessarily the result of secular evolutionary processes.

An evolving trio of hybrid stars: C111

NASA Technical Reports Server (NTRS)

Sonneborn, George (Technical Monitor); Dupree, Andrea K.

2005-01-01

Hybrid stars are a class of cool, luminous single stars originally identified based on the appearance of their ultraviolet IUE spectra. C IV emission is present (signifying temperatures of at least lo5 K), and asymmetric emission cores of Mg I1 are found, accompanied by absorption features at low and high velocities, indicating a massive stellar wind and circumstellar material. Many members of this class have been identified and X-rays have been detected from most hybrids. They represent the critical evolutionary state between coronal-like objects and the Alpha Ori-like objects and assume a pivotal role in the definition of coronal evolution, atmospheric heating processes, and mechanisms to drive winds of cool stars.

Talks also presented at the Symposium

NASA Astrophysics Data System (ADS)

Eldridge, J. J.; Bray, J. C.; McClelland, L. A. S.; Xiao, L.

2017-11-01

Internal rotation and magnetism are key ingredients that largely affect explosive stellar deaths (Supernovae and Gamma Ray Bursts) and the properties of stellar remnants (White Dwarfs, Neutron Stars and Black Holes). However, the study of these subtle internal stellar properties has been limited to very indirect proxies. In the last couple of years, exciting asteroseismic results have been obtained by the Kepler satellite. Among these results are 1) The direct measure of the degree of radial differential rotation in many evolved low-mass stars and in a few massive stars, and 2) The detection of strong (>105 G) internal magnetic fields in thousands of red giant stars that had convective cores during their main sequence. I will discuss the impact of these important findings for our understanding of massive star evolution.

Olivier Chesneau's Work on Low Mass Stars

NASA Astrophysics Data System (ADS)

Lagadec, E.

2015-12-01

During his too short career, Olivier Chesneau pioneered the study of the circumstellar environments of low mass evolved stars using very high angular resolution techniques. He applied state of the art high angular resolution techniques, such as optical interferometry and adaptive optics imaging, to the the study of a variety of objects, from AGB stars to Planetary Nebulae, via e.g. Born Again stars, RCB stars and Novae. I present here an overview of this work and most important results by focusing on the paths he followed and key encounters he made to reach these results. Olivier liked to work in teams and was very strong at linking people with complementary expertises to whom he would communicate his enthusiasm and sharp ideas. His legacy will live on through the many people he inspired.

Infrared Spectroscopy of Star Formation in Galactic and Extragalactic Regions

NASA Technical Reports Server (NTRS)

Smith, Howard A.; Hasan, Hashima (Technical Monitor)

2002-01-01

This report details work done in a project involving spectroscopic studies, including data analysis and modeling, of star-formation regions using an ensemble of archival space-based data including some from the Infrared Space Observatory's Long Wavelength Spectrometer and Short Wavelength Spectrometer, and other spectroscopic databases. We will include four kinds of regions: (1) disks around more evolved objects; (2) young, low or high mass pre-main sequence stars in star-formation regions; (3) star formation in external, bright IR (infrared) galaxies; and (4) the galactic center. During this period, work proceeded fully on track and on time. Details on workshops and conferences attended and research results are presented. A preprint article entitled 'The Far Infrared Lines of OH as Molecular Cloud Diagnostics' is included as an appendix.

Inside NuSTAR Nose Cone

NASA Image and Video Library

2012-03-02

A spacecraft technician is performing closeout work inside the fairing that will be installed around NASA Nuclear Spectroscopic Telescope Array NuSTAR spacecraft in a processing facility at Vandenberg Air Force Base in California.

Classic Galaxy with Glamour

NASA Image and Video Library

2005-04-11

Young hot blue stars dominate the outer spiral arms of nearby galaxy NGC 300, while the older stars congregate in the nuclear regions which appear yellow-green in this image from NASA Galaxy Evolution Explorer.

Electrically charged: An effective mechanism for soft EOS supporting massive neutron star

NASA Astrophysics Data System (ADS)

Jing, ZhenZhen; Wen, DeHua; Zhang, XiangDong

2015-10-01

The massive neutron star discoverer announced that strange particles, such as hyperons should be ruled out in the neutron star core as the soft Equation of State (EOS) can-not support a massive neutron star. However, many of the nuclear theories and laboratory experiments support that at high density the strange particles will appear and the corresponding EOS of super-dense matters will become soft. This situation promotes a challenge between the astro-observation and nuclear physics. In this work, we introduce an effective mechanism to answer this challenge, that is, if a neutron star is electrically charged, a soft EOS will be equivalently stiffened and thus can support a massive neutron star. By employing a representative soft EOS, it is found that in order to obtain an evident effect on the EOS and thus increasing the maximum stellar mass by the electrostatic field, the total net charge should be in an order of 1020 C. Moreover, by comparing the results of two kind of charge distributions, it is found that even for different distributions, a similar total charge: ~ 2.3 × 1020 C is needed to support a ~ 2.0 M ⊙ neutron star.

CNO isotopes in red giant stars

NASA Technical Reports Server (NTRS)

Wannier, P. G.

1985-01-01

The production and distribution of the CNO nuclides is discussed in light of observed abundance ratios in red giants and in the interstellar medium. Isotope abundances have been measured in the atmospheres and in the recent ejecta of cool giants, including carbon stars, S-type stars and red supergiants as well as in oxygen-rich giants making their first ascent of the giant branch. Several of the observations suggest revision of currently accepted nuclear cross-sections and of the mixing processes operating in giant envelopes. By comparing red giant abundances with high-quality observations of the interstellar medium, conclusions are reached about the contribution of intermediate-mass stars to galactic nuclear evolution. The three oxygen isotopes, O-16, -17 and -18, are particularly valuable for such comparison because they reflect three different stages of stellar nucleosynthesis. One remarkable result comes from observations of O-17/O-18 in several classes of red giant stars. The observed range of values for red giants excludes the entire range of values seen in interstellar molecular clouds. Furthermore, both the observations of stars and interstellar clouds exclude the isotopic ratio found in the solar system.

QPO Constraints on Neutron Stars

NASA Technical Reports Server (NTRS)

Miller, M. Coleman

2005-01-01

The kilohertz frequencies of QPOs from accreting neutron star systems imply that they are generated in regions of strong gravity, close to the star. This suggests that observations of the QPOs can be used to constrain the properties of neutron stars themselves, and in particular to inform us about the properties of cold matter beyond nuclear densities. Here we discuss some relatively model-insensitive constraints that emerge from the kilohertz QPOs, as well as recent developments that may hint at phenomena related to unstable circular orbits outside neutron stars.

Spallation processes and nuclear interaction products of cosmic rays.

PubMed

Silberberg, R; Tsao, C H

1990-08-01

Most cosmic-ray nuclei heavier than helium have suffered nuclear collisions in the interstellar gas, with transformation of nuclear composition. The isotopic and elemental composition at the sources has to be inferred from the observed composition near the Earth. The source composition permits tests of current ideas on sites of origin, nucleosynthesis in stars, evolution of stars, the mixing and composition of the interstellar medium and injection processes prior to acceleration. The effects of nuclear spallation, production of radioactive nuclides and the time dependence of their decay provide valuable information on the acceleration and propagation of cosmic rays, their nuclear transformations, and their confinement time in the Galaxy. The formation of spallation products that only decay by electron capture and are relatively long-lived permits an investigation of the nature and density fluctuations (like clouds) of the interstellar medium. Since nuclear collisions yield positrons, antiprotons, gamma rays and neutrinos, we shall discuss these topics briefly.

'Tertiary' nuclear burning - Neutron star deflagration?

NASA Technical Reports Server (NTRS)

Michel, F. Curtis

1988-01-01

A motivation is presented for the idea that dense nuclear matter can burn to a new class of stable particles. One of several possibilities is an 'octet' particle which is the 16 baryon extension of alpha particle, but now composed of a pair of each of the two nucleons, (3Sigma, Delta, and 2Xi). Such 'tertiary' nuclear burning (here 'primary' is H-He and 'secondary' is He-Fe) may lead to neutron star explosions rather than collapse to a black hole, analogous to some Type I supernovae models wherein accreting white dwarfs are pushed over the Chandrasekhar mass limit but explode rather than collapse to form neutron stars. Such explosions could possibly give gamma-ray bursts and power quasars, with efficient particle acceleration in the resultant relativistic shocks. The new stable particles themselves could possibly be the sought-after weakly interacting, massive particles (WIMPs) or 'dark' matter.

Many-particle theory of nuclear systems with application to neutron star matter

NASA Technical Reports Server (NTRS)

Chakkalakal, D. A.; Yang, C.

1973-01-01

The research is reported concerning energy-density relation for the normal state of neutron star matter, and the effects of superfluidity and polarization on neutron star matter. Considering constraints on variation, and the theory of quantum fluids, three methods for calculating the energy-density range are presented. The effects of polarization on neutron star structure, and polarization effects on condensation and superfluid-state energy are discussed.

On the Nature of the Enigmatic Object IRAS 19312+1950: A Rare Phase of Massive Star Formation?

NASA Technical Reports Server (NTRS)

Cordiner, M. A.; Boogert, A. C. A.; Charnley, S. B.; Justtanont, K.; Cox, N. L. J.; Smith, R. G.; Tielens, A. G. G. M.; Wirstrom, E. S.; Milam, S. N.; Keane, J. V.

2016-01-01

IRAS?19312+1950 is a peculiar object that has eluded firm characterization since its discovery, with combined maser properties similar to an evolved star and a young stellar object (YSO). To help determine its true nature, we obtained infrared spectra of IRAS?19312+1950 in the range 5-550 microns using the Herschel and Spitzer space observatories. The Herschel PACS maps exhibit a compact, slightly asymmetric continuum source at 170 microns, indicative of a large, dusty circumstellar envelope. The far-IR CO emission line spectrum reveals two gas temperature components: approx. = 0.22 Stellar Mass of material at 280+/-18 K, and ˜1.6 Me of material at 157+/-3 K. The OI 63 micron line is detected on-source but no significant emission from atomic ions was found. The HIFI observations display shocked, high-velocity gas with outflow speeds up to 90 km/s along the line of sight. From Spitzer spectroscopy, we identify ice absorption bands due to H2O at 5.8 microns and CO2 at 15 microns. The spectral energy distribution is consistent with a massive, luminous (approx. 2 × 10(exp 4) Stellar Luminosity) central source surrounded by a dense, warm circumstellar disk and envelope of total mass approx. 500-700 Stellar Mass with large bipolar outflow cavities. The combination of distinctive far-IR spectral features suggest that IRAS19312+1950 should be classified as an accreting, high-mass YSO rather than an evolved star. In light of this reclassification, IRAS19312+1950 becomes only the fifth high-mass protostar known to exhibit SiO maser activity, and demonstrates that 18 cm OH maser line ratios may not be reliable observational discriminators between evolved stars and YSOs.

77 FR 64501 - Combined Notice of Filings #1

Federal Register 2010, 2011, 2012, 2013, 2014

2012-10-22

.... Applicants: Calvert Cliffs Nuclear Power Plant, LLC, Nine Mile Point Nuclear Station, LLC, R.E. Ginna Nuclear Power Plant, LLC. Description: Notice of Non-Material Change in Status of Nine Mile Point Nuclear..., LLC, Shooting Star Wind Project, LLC, Safe Harbor Water Power Corporation, PECO Energy Company...

CORE-COLLAPSE SUPERNOVA EQUATIONS OF STATE BASED ON NEUTRON STAR OBSERVATIONS

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

Steiner, A. W.; Hempel, M.; Fischer, T.

2013-09-01

Many of the currently available equations of state for core-collapse supernova simulations give large neutron star radii and do not provide large enough neutron star masses, both of which are inconsistent with some recent neutron star observations. In addition, one of the critical uncertainties in the nucleon-nucleon interaction, the nuclear symmetry energy, is not fully explored by the currently available equations of state. In this article, we construct two new equations of state which match recent neutron star observations and provide more flexibility in studying the dependence on nuclear matter properties. The equations of state are also provided in tabularmore » form, covering a wide range in density, temperature, and asymmetry, suitable for astrophysical simulations. These new equations of state are implemented into our spherically symmetric core-collapse supernova model, which is based on general relativistic radiation hydrodynamics with three-flavor Boltzmann neutrino transport. The results are compared with commonly used equations of state in supernova simulations of 11.2 and 40 M{sub Sun} progenitors. We consider only equations of state which are fitted to nuclear binding energies and other experimental and observational constraints. We find that central densities at bounce are weakly correlated with L and that there is a moderate influence of the symmetry energy on the evolution of the electron fraction. The new models also obey the previously observed correlation between the time to black hole formation and the maximum mass of an s = 4 neutron star.« less

Combined Constraints on the Equation of State of Dense Neutron-rich Matter from Terrestrial Nuclear Experiments and Observations of Neutron Stars

NASA Astrophysics Data System (ADS)

Zhang, Nai-Bo; Li, Bao-An; Xu, Jun

2018-06-01

Within the parameter space of the equation of state (EOS) of dense neutron-rich matter limited by existing constraints mainly from terrestrial nuclear experiments, we investigate how the neutron star maximum mass M max > 2.01 ± 0.04 M ⊙, radius 10.62 km < R 1.4 < 12.83 km and tidal deformability Λ1.4 ≤ 800 of canonical neutron stars together constrain the EOS of dense neutron-rich nucleonic matter. While the 3D parameter space of K sym (curvature of nuclear symmetry energy), J sym, and J 0 (skewness of the symmetry energy and EOS of symmetric nuclear matter, respectively) is narrowed down significantly by the observational constraints, more data are needed to pin down the individual values of K sym, J sym, and J 0. The J 0 largely controls the maximum mass of neutron stars. While the EOS with J 0 = 0 is sufficiently stiff to support neutron stars as massive as 2.37 M ⊙, supporting the hypothetical ones as massive as 2.74 M ⊙ (composite mass of GW170817) requires J 0 to be larger than its currently known maximum value of about 400 MeV and beyond the causality limit. The upper limit on the tidal deformability of Λ1.4 = 800 from the recent observation of GW170817 is found to provide upper limits on some EOS parameters consistent with but far less restrictive than the existing constraints of other observables studied.

Interplay between Diffusion, Accretion and Nuclear Reactions in the Atmospheres of Sirius and Przybylski's Star

NASA Astrophysics Data System (ADS)

Yushchenko, A.; Gopka, V.; Goriely, S.; Lambert, D.; Shavrina, A.; Kang, Y. W.; Rostopchin, S.; Valyavin, G.; Lee, B.-C.; Kim, C.

2007-06-01

The abundance anomalies in chemically peculiar B-F stars are usually explained by diffusion of chemical elements in the stable atmospheres of these stars. But it is well known that peculiar stars with similar temperatures and gravities show very different chemical compositions. We show that the abundance patterns of several stars can be influenced by accretion and (or) nuclear reactions in stellar atmospheres. The first case is one of the hottest Am stars - Sirius. We determined the abundances of more than 50 chemical elements in the atmosphere of Sirius A and show that Sirius A was contaminated by s-process enriched matter from Sirius B (now a white dwarf). The second case is the well known Przybylski's star. The abundance pattern of this star is the second most studied one after the Sun with abundances determined for about 60 chemical elements. Spectral lines of radioactive elements with short decay times were found in the spectrum of this star. We report the results of our investigation on the stratification of chemical elements in the atmosphere of Przybylski's star and the new identification of lines corresponding to short-lived actinides in its spectrum. Possible explanations of the abundances pattern of Przybylski's star (as well as HR465 and HD965) can be the natural radioactive decays of thorium and uranium, the explosion of a companion as a supernova or the spallation reactions. These three hypotheses and (or) diffusion can possibly explain the abundance pattern of Przybylski's star and several similar objects such as HR465 and HD965.

Theoretical constraints on the properties of low-mass neutron stars from the equation of state of nuclear matter in the inner crust

NASA Astrophysics Data System (ADS)

Wen, Yong-Mei; Wen, De-Hua

2017-06-01

By employing four typical equation of states (EOSs) of nuclear matter in the inner crust, the properties of low-mass neutron stars are investigated theoretically. Based on the well-known fact that there is a big gap between the neutron stars and white dwarfs in the mass-radius sequence of compact stars, according to the mass-radius relations of the four adopted EOSs, we conclude that there is a rough forbidden region for the central density and stellar radius to form a compact star; that is, there is no compact star in nature having central density in the region from about 1012kgm-3 to 1017kgm-3 , and there is also no compact star having a radius in the region from about 400 km to 2000 km. Moreover, the properties of the low-mass neutron stars are also explored. It is shown that for a stable neutron star near the minimum mass point, the stellar size (with radius >200 km) is much larger than that of normal neutron stars, and there is a compact "core" concentrated at about 95% of the stellar mass in the inner core with a radius of about 13 km and density higher than the neutron-drip point (4.3 ×1014kgm-3) . This property totally differs from that of normal neutron stars and white dwarfs. Furthermore, the Keplerian period, the moment of inertia, and the surface gravitational redshift of the star near the minimum-mass point are also investigated.

Superfluidity in the Core of Neutron Stars

NASA Astrophysics Data System (ADS)

Page, Dany

2013-04-01

The year (1958) after the publication of the BCS theory, Bohr, Mottelson & Pines showed that nuclei should also contain superfluid neutrons and superconducting protons. In 1959, A. Migdal proposed that neutron superfluidity should also occur in the interior of neutron stars. Pairing in nuclei forms Cooper pairs with zero spin, but the relevant component of the nuclear interaction becomes repulsive at densities larger than the nuclear matter density. It has been proposed that neutron-neutron interaction in the spin-triplet state, and L=1 orbital angular momentum, that is known to be attractive from laboratory experiments, may result in a new form of neutron superfluidity in the neutron star interior. I will review our present understanding of the structure of neutron stars and describe how superfluidity strongly affects their thermal evolution. I will show how a ``Minimal Model'' that excludes the presence of ``exotic'' matter (Bose condensates, quarks, etc.) is compatible with most observations of the surface temperatures of young isolated neutron stars in the case this neutron superfluid exists. Compared to the case of isotropic spin-zero Cooper pairs, the formation of anisotropic spin-one Cooper pairs results in a strong neutrino emission that leads to an enhanced cooling of neutron stars after the onset of the pairing phase transition and allows the Minimal Cooling scenario to be compatible with most observations. In the case the pairing critical temperature Tc is less than about 6 x10^8 K, the resulting rapid cooling of the neutron star may be observable. It was recently reported that 10 years of Chandra observations of the 333 year young neutron star in the Cassiopeia A supernova remnant revealed that its temperature has dropped by about 5%. This result indicates that neutrons in this star are presently becoming superfluid and, if confirmed, provides us with the first direct observational evidence for neutron superfluidity at supra-nuclear densities.

The /a/m ratio of the baryonic matter and the black holes demography in galaxies

NASA Astrophysics Data System (ADS)

Curir, Anna; Mazzei, Paola

2001-06-01

The last years have seen a big progress in establishing the existence of supermassive black holes in the centers of galaxies. There are numerous very good cases [MNRAS 291 (1997) 219] where observations require a deep potential well. These observations raise the problem of when and how they formed and eventually when they gain most of their mass. The formation of a stationary black-hole is constrained by the conditions M>3 M ⊙ and cJ/ GM2≡ a/ m<1, J and M being the angular momentum and the total mass of the configuration which has collapsed to the hole. In this paper we analyze the behaviour of the a/ m ratio of the baryonic content in a protogalaxy, "primordial" scenario, and in a hot galaxy, "evolved" scenario, endowed with a suitable angular momentum distribution. In both the cases the baryonic matter is embedded in the gravitational potential generated by a cosmological Dark Matter (DM) halo. We deduce that the "primordial" scenario is less favourable to the black hole formation than the "evolved" one. Moreover, in the "evolved" scenario we find a twofold behaviour of the a/ m parameter which reflects the observed bimodal distribution of the central brightness in early-type galaxies and agrees with their corresponding degree of nuclear activity. As suggested by results of our SPH simulations of barred galaxies, the treatment of the dissipative processes and the inclusion of the star formation further improve the previous framework showing that barred galaxies provide very good environment for black hole formation.

SNR-shock impact on star formation

NASA Astrophysics Data System (ADS)

Sasaki, M.; Dincel, B.

2016-06-01

While stars form out of cores of molecular clouds due to gravitational collapse of the clouds, external pressure caused by shock waves of stellar winds or supernovae are believed to be responsible for triggering star formation. However, since massive stars evolve fast and their supernova remnants (SNRs) can only be observed up to an age of around 10^5 years, SNRs found near star-forming regions have most likely resulted from the same generation of stars as the young stellar objects (YSOs). Shock waves of these SNRs might show interaction with the existing YSOs and change their nature. We study YSO candidates in Galactic SNRs CTB 109, IC 443 and HB21, which are known to show interaction with molecular clouds and have associated infrared emission. By photometric and spectroscopic studies of YSOs in the optical and the near-infrared, we aim to find clear observational evidences for an interaction of SNR-shocks with YSOs.

Carbon stars with alpha-C:H emission

NASA Technical Reports Server (NTRS)

Gerbault, Florence; Goebel, John H.

1989-01-01

Many carbon stars in the IRS low resolution spectra (LRS) catalog were found which display emission spectra that compare favorable with the absorption spectrum of alpha-C:H. These stars have largely been classified as 4X in the LRS which has led to their interpretation by others in terms of displaying a mixture of the UIRF's 8.6 micron band and SiC at 11.5 microns. It was also found that many of these stars have a spectral upturn at 20+ microns which resembles the MgS band seen in carbon stars and planetary nebulae. It was concluded that this group of carbon stars will evolve into planetary nebulae like NGC 7027 and IC 418. In the presence of hard ultraviolet radiation the UIRF's will light up and be displayed as narrow emission bands on top of the broad alpha-C:H emission bands.

VLTI and KI Interferometric Observations of Massive Evolved Stars and Their Dusty Circumstellar Environments

NASA Astrophysics Data System (ADS)

Wallace, Debra J.; Danchi, W. C.; Rajagopal, J.; Chesneau, O.; Lopez, B.; Menut, J.; Monnier, J.; Tuthill, P.; Ireland, M.; Barry, R.; Richardson, L. J.

2007-12-01

Recent aperture-masking and interferometric observations of late-type WC Wolf-Rayet stars strongly support the theory that dust formation in these objects is a result of colliding winds in binary systems. To explore and quantify this possible explanation, we have conducted a high-resolution interferometric survey of late-type massive stars utilizing the VLTI, KI, IOTA, and FGS1r interferometers. We present here the motivation for this study. We also present the first results from the MIDI instrument on the VLTI, and the KI and IOTA observations. Our VLTI study is aimed primarily at resolving and characterizing the dust around the WC9 star WR 85a and the LBV WR 122, both dust-producing but at different phases of massive star evolution. Our IOTA and KI interferometric observations resolve the WR star WR 137 into a dust-producing binary system.

A Unified Equation of State on a Microscopic Basis : Implications for Neutron Stars Structure and Cooling

NASA Astrophysics Data System (ADS)

Burgio, G. F.

2018-03-01

We discuss the structure of Neutron Stars by modelling the homogeneous nuclear matter of the core by a suitable microscopic Equation of State, based on the Brueckner-Hartree-Fock many-body theory, and the crust, including the pasta phase, by the BCPM energy density functional which is based on the same Equation of State. This allows for a uni ed description of the Neutron Star matter over a wide density range. A comparison with other uni ed approaches is discussed. With the same Equation of State, which features strong direct Urca processes and using consistent nuclear pairing gaps as well as effective masses, we model neutron star cooling, in particular the current rapid cooldown of the neutron star Cas A. We nd that several scenarios are possible to explain the features of Cas A, but only large and extended proton 1 S 0 gaps and small neutron 3 PF 2 gaps can accommodate also the major part of the complete current cooling data.

Focused Study of Thermonuclear Bursts on Neutron Stars

NASA Astrophysics Data System (ADS)

Chenevez, Jérôme

2009-05-01

X-ray bursters form a class of Low Mass X-Ray Binaries where accreted material from a donor star undergoes rapid thermonuclear burning in the surface layers of a neutron star. The flux released can temporarily exceed the Eddington limit and drive the photosphere to large radii. Such photospheric radius expansion bursts likely eject nuclear burning ashes into the interstellar medium, and may make possible the detection of photoionization edges. Indeed, theoretical models predict that absorption edges from 58Fe at 9.2 keV, 60Zn and 62Zn at 12.2 keV should be detectable by the future missions Simbol-X and NuSTAR. A positive detection would thus probe the nuclear burning as well as the gravitational redshift from the neutron star. Moreover, likely observations of atomic X-ray spectral components reflected from the inner accretion disk have been reported. The high spectral resolution capabilities of the focusing X-ray telescopes may therefore make possible to differentiate between the potential interpretations of the X-ray bursts spectral features.

UNDERSTANDING THE EVOLUTION OF CLOSE BINARY SYSTEMS WITH RADIO PULSARS

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

Benvenuto, O. G.; De Vito, M. A.; Horvath, J. E., E-mail: obenvenu@fcaglp.unlp.edu.ar, E-mail: adevito@fcaglp.unlp.edu.ar, E-mail: foton@astro.iag.usp.br

We calculate the evolution of close binary systems (CBSs) formed by a neutron star (behaving as a radio pulsar) and a normal donor star, which evolve either to a helium white dwarf (HeWD) or to ultra-short orbital period systems. We consider X-ray irradiation feedback and evaporation due to radio pulsar irradiation. We show that irradiation feedback leads to cyclic mass transfer episodes, allowing CBSs to be observed in between episodes as binary radio pulsars under conditions in which standard, non-irradiated models predict the occurrence of a low-mass X-ray binary. This behavior accounts for the existence of a family of eclipsingmore » binary systems known as redbacks. We predict that redback companions should almost fill their Roche lobe, as observed in PSR J1723-2837. This state is also possible for systems evolving with larger orbital periods. Therefore, binary radio pulsars with companion star masses usually interpreted as larger than expected to produce HeWDs may also result in such quasi-Roche lobe overflow states, rather than hosting a carbon-oxygen WD. We found that CBSs with initial orbital periods of P{sub i} < 1 day evolve into redbacks. Some of them produce low-mass HeWDs, and a subgroup with shorter P{sub i} becomes black widows (BWs). Thus, BWs descend from redbacks, although not all redbacks evolve into BWs. There is mounting observational evidence favoring BW pulsars to be very massive (≳ 2 M {sub ☉}). As they should be redback descendants, redback pulsars should also be very massive, since most of the mass is transferred before this stage.« less

Secular Evolution of Galaxies

NASA Astrophysics Data System (ADS)

Falcón-Barroso, Jesús; Knapen, Johan H.

2013-10-01

Preface; 1. Secular evolution in disk galaxies John Kormendy; 2. Galaxy morphology Ronald J. Buta; 3. Dynamics of secular evolution James Binney; 4. Bars and secular evolution in disk galaxies: theoretical input E. Athanassoula; 5. Stellar populations Reynier F. Peletier; 6. Star formation rate indicators Daniela Calzetti; 7. The evolving interstellar medium Jacqueline van Gorkom; 8. Evolution of star formation and gas Nick Z. Scoville; 9. Cosmological evolution of galaxies Isaac Shlosman.

Massive stars in advanced evolutionary stages, and the progenitor of GW150914

NASA Astrophysics Data System (ADS)

Hamann, Wolf-Rainer; Oskinova, Lidia; Todt, Helge; Sander, Andreas; Hainich, Rainer; Shenar, Tomer; Ramachandran, Varsha

2017-11-01

The recent discovery of a gravitational wave from the merging of two black holes of about 30 solar masses each challenges our incomplete understanding of massive stars and their evolution. Critical ingredients comprise mass-loss, rotation, magnetic fields, internal mixing, and mass transfer in close binary systems. The imperfect knowledge of these factors implies large uncertainties for models of stellar populations and their feedback. In this contribution we summarize our empirical studies of Wolf-Rayet populations at different metallicities by means of modern non-LTE stellar atmosphere models, and confront these results with the predictions of stellar evolution models. At the metallicity of our Galaxy, stellar winds are probably too strong to leave remnant masses as high as ~30 M⊙, but given the still poor agreement between evolutionary tracks and observation even this conclusion is debatable. At the low metallicity of the Small Magellanic Cloud, all WN stars which are (at least now) single are consistent with evolving quasi-homogeneously. O and B-type stars, in contrast, seem to comply with standard evolutionary models without strong internal mixing. Close binaries which avoided early merging could evolve quasi-homogeneously and lead to close compact remnants of relatively high masses that merge within a Hubble time.

Study of nuclear multifragmentation induced by ultrarelativistic μ-mesons in nuclear track emulsion

NASA Astrophysics Data System (ADS)

Artemenkov, D. A.; Bradnova, V.; Firu, E.; Kornegrutsa, N. K.; Haiduc, M.; Mamatkulov, K. Z.; Kattabekov, R. R.; Neagu, A.; Rukoyatkin, P. A.; Rusakova, V. V.; Stanoeva, R.; Zaitsev, A. A.; Zarubin, P. I.; Zarubina, I. G.

2016-02-01

Exposures of test samples of nuclear track emulsion were analyzed. The formation of high-multiplicity nuclear stars was observed upon irradiating nuclear track emulsions with ultrarelativistic muons. Kinematical features studied in this exposure of nuclear track emulsions for events of the muon-induced splitting of carbon nuclei to three α-particles are indicative of the nuclear-diffraction interaction mechanism.

Rotating protoneutron stars: Spin evolution, maximum mass, and I-Love-Q relations

NASA Astrophysics Data System (ADS)

Martinon, Grégoire; Maselli, Andrea; Gualtieri, Leonardo; Ferrari, Valeria

2014-09-01

Shortly after its birth in a gravitational collapse, a protoneutron star enters in a phase of quasistationary evolution characterized by large gradients of the thermodynamical variables and intense neutrino emission. In a few tens of seconds, the gradients smooth out while the star contracts and cools down, until it becomes a neutron star. In this paper we study this phase of the protoneutron star life including rotation, and employing finite-temperature equations of state. We model the evolution of the rotation rate, and determine the relevant quantities characterizing the star. Our results show that an isolated neutron star cannot reach, at the end of the evolution, the maximum values of mass and rotation rate allowed by the zero-temperature equation of state. Moreover, a mature neutron star evolved in isolation cannot rotate too rapidly, even if it is born from a protoneutron star rotating at the mass-shedding limit. We also show that the I-Love-Q relations are violated in the first second of life, but they are satisfied as soon as the entropy gradients smooth out.

Chandra X-Ray Observatory Image NGC 3603

NASA Technical Reports Server (NTRS)

2001-01-01

NGC 3603 is a bustling region of star birth in the Carina spiral arm of the Milky Way galaxy, about 20,000 light-years from Earth. For the first time, this Chandra image resolves the multitude of individual x-ray sources in this star-forming region. (The intensity of the x-rays observed by Chandra are depicted by the various colors in this image. Green represents lower intensity sources, while purple and red indicate increasing x-ray intensity.) Specifically, the Chandra image reveals dozens of extremely massive stars born in a burst of star formation about 2 million years ago. This region's activities may be indicative of what is happening in other distant 'starburst' galaxies (bright galaxies flush with new stars). In the case of NGC 3603, scientists now believe that these x-rays are emitted from massive stars and stellar winds, since the stars are too young to have produced supernovae or have evolved into neutron stars. The Chandra observations of NGC 3603 may provide new clues about x-ray emission in starburst galaxies as well as star formation itself. (Photo credit: NASA/GSFC/M. Corcoran et al)

SDSS-IV MaNGA: Spatially Resolved Star Formation Main Sequence and LI(N)ER Sequence

NASA Astrophysics Data System (ADS)

Hsieh, B. C.; Lin, Lihwai; Lin, J. H.; Pan, H. A.; Hsu, C. H.; Sánchez, S. F.; Cano-Díaz, M.; Zhang, K.; Yan, R.; Barrera-Ballesteros, J. K.; Boquien, M.; Riffel, R.; Brownstein, J.; Cruz-González, I.; Hagen, A.; Ibarra, H.; Pan, K.; Bizyaev, D.; Oravetz, D.; Simmons, A.

2017-12-01

We present our study on the spatially resolved Hα and M * relation for 536 star-forming and 424 quiescent galaxies taken from the MaNGA survey. We show that the star formation rate surface density ({{{Σ }}}{SFR}), derived based on the Hα emissions, is strongly correlated with the M * surface density ({{{Σ }}}* ) on kiloparsec scales for star-forming galaxies and can be directly connected to the global star-forming sequence. This suggests that the global main sequence may be a consequence of a more fundamental relation on small scales. On the other hand, our result suggests that ∼20% of quiescent galaxies in our sample still have star formation activities in the outer region with lower specific star formation rate (SSFR) than typical star-forming galaxies. Meanwhile, we also find a tight correlation between {{{Σ }}}{{H}α } and {{{Σ }}}* for LI(N)ER regions, named the resolved “LI(N)ER” sequence, in quiescent galaxies, which is consistent with the scenario that LI(N)ER emissions are primarily powered by the hot, evolved stars as suggested in the literature.

History of Chandra X-Ray Observatory

NASA Image and Video Library

2001-01-01

NGC 3603 is a bustling region of star birth in the Carina spiral arm of the Milky Way galaxy, about 20,000 light-years from Earth. For the first time, this Chandra image resolves the multitude of individual x-ray sources in this star-forming region. (The intensity of the x-rays observed by Chandra are depicted by the various colors in this image. Green represents lower intensity sources, while purple and red indicate increasing x-ray intensity.) Specifically, the Chandra image reveals dozens of extremely massive stars born in a burst of star formation about 2 million years ago. This region's activities may be indicative of what is happening in other distant "starburst" galaxies (bright galaxies flush with new stars). In the case of NGC 3603, scientists now believe that these x-rays are emitted from massive stars and stellar winds, since the stars are too young to have produced supernovae or have evolved into neutron stars. The Chandra observations of NGC 3603 may provide new clues about x-ray emission in starburst galaxies as well as star formation itself. (Photo credit: NASA/GSFC/M. Corcoran et al)

On the absence of young white dwarf companions to five technetium stars

NASA Technical Reports Server (NTRS)

Smith, Verne V.; Lambert, David L.

1987-01-01

A search for hot companions to five stars of type MS and S has been carried out using the IUE satellite. No hot companions were detected for the MS stars HR 85, 4647, 6702, and 8062, and the S star HR 8714. Limits on the luminosities of possible white dwarf companions provide lower limits of 2-5x10 to the 8th yr to the ages of any degenerate companions. All five stars exhibit strong Tc I lines, and the presence of technetium, with a half-life of 2.1x10 to the 5th yr, signifies recent nucleosynthesis. The limits on the ages of possible white dwarf companions that are equal to or greater than 1000 half-lives of Tc exclude the possibility that the s-process elemental enhancement seen in these MS and S stars resulted from mass transfer from a more highly evolved companion (as is probably the mechanism by which barium stars are created). These MS and S stars represent a sample of true thermally pulsing asymptotic giant-branch stars.

Star formation histories in NGC 147 and NGC 185

NASA Astrophysics Data System (ADS)

Hamedani Golshan, R.; Javadi, A.; van Loon, J. Th

2017-06-01

NGC 147 and NGC 185 are two of the most massive satellites of the Andromeda galaxy (M 31). With similar mass and morphological type dE, they possess different amounts of interstellar gas and tidal distortion. The question therefore is, how do their histories compare? We present the first reconstruction of the star formation histories of NGC 147 and NGC 185 using long-period variable stars (LPVs). LPVs are low- to intermediate-mass stars at the asymptotic giant branch, which their luminosity is related to their birth mass. Combining near-infrared photometry with stellar evolution models, we construct the mass function and hence the star formation history. For NGC 185 we found that the main epoch of star formation occurred 8.3 Gyr ago, followed by a much lower, but relatively constant star formation rate. In the case of NGC 147, the star formation rate peaked only 7 Gyr ago, staying intense until ∼ 3 Gyr ago, but no star formation has occurred for at least 300 Myr. Despite their similar masses, NGC 147 has evolved more slowly than NGC 185 initially, but more dramatically in more recent times.

Rotational velocities of A-type stars. IV. Evolution of rotational velocities

NASA Astrophysics Data System (ADS)

Zorec, J.; Royer, F.

2012-01-01

Context. In previous works of this series, we have shown that late B- and early A-type stars have genuine bimodal distributions of rotational velocities and that late A-type stars lack slow rotators. The distributions of the surface angular velocity ratio Ω/Ωcrit (Ωcrit is the critical angular velocity) have peculiar shapes according to spectral type groups, which can be caused by evolutionary properties. Aims: We aim to review the properties of these rotational velocity distributions in some detail as a function of stellar mass and age. Methods: We have gathered vsini for a sample of 2014 B6- to F2-type stars. We have determined the masses and ages for these objects with stellar evolution models. The (Teff,log L/L⊙)-parameters were determined from the uvby-β photometry and the HIPPARCOS parallaxes. Results: The velocity distributions show two regimes that depend on the stellar mass. Stars less massive than 2.5 M⊙ have a unimodal equatorial velocity distribution and show a monotonical acceleration with age on the main sequence (MS). Stars more massive have a bimodal equatorial velocity distribution. Contrarily to theoretical predictions, the equatorial velocities of stars from about 1.7 M⊙ to 3.2 M⊙ undergo a strong acceleration in the first third of the MS evolutionary phase, while in the last third of the MS they evolve roughly as if there were no angular momentum redistribution in the external stellar layers. The studied stars might start in the ZAMS not necessarily as rigid rotators, but with a total angular momentum lower than the critical one of rigid rotators. The stars seem to evolve as differential rotators all the way of their MS life span and the variation of the observed rotational velocities proceeds with characteristic time scales δt ≈ 0.2 tMS, where tMS is the time spent by a star in the MS. 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/537/A120Appendices are available in electronic form at http://www.aanda.org

Unusual Metals in Galactic Center Stars

NASA Astrophysics Data System (ADS)

Hensley, Kerry

2018-03-01

Far from the galactic suburbs where the Sun resides, a cluster of stars in the nucleus of the Milky Way orbits a supermassive black hole. Can chemical abundance measurements help us understand the formation history of the galactic center nuclear star cluster?Studying Stellar PopulationsMetallicity distributions for stars in the inner two degrees of the Milky Way (blue) and the central parsec (orange). [Do et al. 2018]While many galaxies host nuclear star clusters, most are too distant for us to study in detail; only in the Milky Way can we resolve individual stars within one parsec of a supermassive black hole. The nucleus of our galaxy is an exotic and dangerous place, and its not yet clear how these stars came to be where they are were they siphoned off from other parts of the galaxy, or did they form in place, in an environment rocked by tidal forces?Studying the chemical abundances of stars provides a way to separate distinct stellar populations and discern when and where these stars formed. Previous studies using medium-resolution spectroscopy have revealed that many stars within the central parsec of our galaxy have very high metallicities possibly higher than any other region of the Milky Way. Can high-resolution spectroscopy tell us more about this unusual population of stars?Spectral Lines on DisplayTuan Do (University of California, Los Angeles, Galactic Center Group) and collaborators performed high-resolution spectroscopic observations of two late-type giant starslocated half a parsec from the Milky Ways supermassive black hole.Comparison of the observed spectra of the two galactic center stars (black) with synthetic spectra with low (blue) and high (orange) [Sc/Fe] values. Click to enlarge. [Do et al. 2018]In order to constrain the metallicities of these stars, Do and collaborators compared the observed spectra to a grid of synthetic spectra and used a spectral synthesis technique to determine the abundances of individual elements. They found that while one star is only slightly above solar metallicity, the other is likely more than four times as metal-rich as the Sun.The features in the observed and synthetic spectra generally matched well, but the absorption lines of scandium, vanadium, and yttrium were consistently stronger in the observed spectra than in the synthetic spectra. This led the authors to conclude that these galactic center stars are unusually rich in these metals trace elements that could reveal the formation history of the galactic nucleus.Old Stars, New Trends?Scandium to iron ratio versusiron abundance for stars in the disk of the Milky Way (blue) and the stars in this sample (orange). The value reported for this sample is a 95% lower limit. [Do et al. 2018]For stars in the disk of the Milky Way, the abundance of scandium relative to iron tends to decrease as the overall metallicity increases, but the stars investigated in this study are both iron-rich and anomalously high in scandium. This hints that the nuclear star cluster might represent a distinct stellar population with different metallicity trends.However, its not yet clear what could cause the elevated abundances of scandium, vanadium, and yttrium relative to other metals. Each of these elements is linked to a different source; scandium and vanadium are mainly produced in Type II and Type Ia supernovae, respectively, while yttrium is likely synthesized in asymptotic giant branch stars. Future observations of stars near the center of the Milky Way may help answer this question and further constrain the origin of our galaxys nuclear star cluster.CitationTuan Do et al 2018 ApJL 855 L5. doi:10.3847/2041-8213/aaaec3

Black-hole binaries as relics of gamma-ray burst/hypernova explosions

NASA Astrophysics Data System (ADS)

Moreno Mendez, Enrique

The Collapsar model, in which a fast-spinning massive star collapses into a Kerr black hole, has become the standard model to explain long-soft gamma-ray bursts and hypernova explosions (GRB/HN). However, stars massive enough (those with ZAMS mass ≳ (18--20) M⊙ ) to produce these events evolve through a path that loses too much angular momentum to produce a central engine capable of delivering the necessary energy. In this work I suggest that the soft X-ray transient sources are the remnants of GRBs/HNe. Binaries in which the massive primary star evolves a carbon-oxygen burning core, then start to transfer material to the secondary star (Case C mass transfer), causing the orbit to decay until a common-envelope phase sets in. The secondary spirals in, further narrowing the orbit of the binary and removing the hydrogen envelope of the primary star. Eventually the primary star becomes tidally locked and spins up, acquiring enough rotational energy to power up a GRB/HN explosion. The central engine producing the GRB/HN event is the Kerr black hole acting through the Blandford-Znajek mechanism. This model can explain not only the long-soft GRBs, but also the subluminous bursts (which comprise ˜ 97% of the total), the long-soft bursts and the short-hard bursts (in a neutron star, black hole merger). Because of our binary evolution through Case C mass transfer, it turns out that for the subluminous and cosmological bursts, the angular momentum O is proportional to m3/2D , where mD is the mass of the donor (secondary star). This binary evolution model has a great advantage over the Woosley Collapsar model; one can "dial" the donor mass in order to obtain whatever angular momentum is needed to drive the explosion. Population syntheses show that there are enough binaries to account for the progenitors of all known classes of GRBs.

Nucleosynthesis Predictions for Intermediate-Mass AGB Stars: Comparison to Observations of Type I Planetary Nebulae

NASA Technical Reports Server (NTRS)

Karakas, Amanda I.; vanRaai, Mark A.; Lugaro, Maria; Sterling, Nicholas C.; Dinerstein, Harriet L.

2008-01-01

Type I planetary nebulae (PNe) have high He/H and N/O ratios and are thought to be descendants of stars with initial masses of approx. 3-8 Stellar Mass. These characteristics indicate that the progenitor stars experienced proton-capture nucleosynthesis at the base of the convective envelope, in addition to the slow neutron capture process operating in the He-shell (the s-process). We compare the predicted abundances of elements up to Sr from models of intermediate-mass asymptotic giant branch (AGB) stars to measured abundances in Type I PNe. In particular, we compare predictions and observations for the light trans-iron elements Se and Kr, in order to constrain convective mixing and the s-process in these stars. A partial mixing zone is included in selected models to explore the effect of a C-13 pocket on the s-process yields. The solar-metallicity models produce enrichments of [(Se, Kr)/Fe] less than or approx. 0.6, consistent with Galactic Type I PNe where the observed enhancements are typically less than or approx. 0.3 dex, while lower metallicity models predict larger enrichments of C, N, Se, and Kr. O destruction occurs in the most massive models but it is not efficient enough to account for the greater than or approx. 0.3 dex O depletions observed in some Type I PNe. It is not possible to reach firm conclusions regarding the neutron source operating in massive AGB stars from Se and Kr abundances in Type I PNe; abundances for more s-process elements may help to distinguish between the two neutron sources. We predict that only the most massive (M grester than or approx.5 Stellar Mass) models would evolve into Type I PNe, indicating that extra-mixing processes are active in lower-mass stars (3-4 Stellar Mass), if these stars are to evolve into Type I PNe.

Nucleosynthesis Predictions for Intermediate-Mass Asymptotic Giant Branch Stars: Comparison to Observations of Type I Planetary Nebulae

NASA Astrophysics Data System (ADS)

Karakas, Amanda I.; van Raai, Mark A.; Lugaro, Maria; Sterling, N. C.; Dinerstein, Harriet L.

2009-01-01

Type I planetary nebulae (PNe) have high He/H and N/O ratios and are thought to be descendants of stars with initial masses of ~3-8 M sun. These characteristics indicate that the progenitor stars experienced proton-capture nucleosynthesis at the base of the convective envelope, in addition to the slow neutron capture process operating in the He-shell (the s-process). We compare the predicted abundances of elements up to Sr from models of intermediate-mass asymptotic giant branch (AGB) stars to measured abundances in Type I PNe. In particular, we compare predictions and observations for the light trans-iron elements Se and Kr, in order to constrain convective mixing and the s-process in these stars. A partial mixing zone is included in selected models to explore the effect of a 13C pocket on the s-process yields. The solar-metallicity models produce enrichments of [(Se, Kr)/Fe] lsim0.6, consistent with Galactic Type I PNe where the observed enhancements are typically lsim0.3 dex, while lower metallicity models predict larger enrichments of C, N, Se, and Kr. O destruction occurs in the most massive models but it is not efficient enough to account for the gsim0.3 dex O depletions observed in some Type I PNe. It is not possible to reach firm conclusions regarding the neutron source operating in massive AGB stars from Se and Kr abundances in Type I PNe; abundances for more s-process elements may help to distinguish between the two neutron sources. We predict that only the most massive (M gsim 5 M sun) models would evolve into Type I PNe, indicating that extra-mixing processes are active in lower-mass stars (3-4 M sun), if these stars are to evolve into Type I PNe. This paper includes data taken at The McDonald Observatory of The University of Texas at Austin.

KELT-12b: A P ˜ 5 day, Highly Inflated Hot Jupiter Transiting a Mildly Evolved Hot Star

NASA Astrophysics Data System (ADS)

Stevens, Daniel J.; Collins, Karen A.; Gaudi, B. Scott; Beatty, Thomas G.; Siverd, Robert J.; Bieryla, Allyson; Fulton, Benjamin J.; Crepp, Justin R.; Gonzales, Erica J.; Coker, Carl T.; Penev, Kaloyan; Stassun, Keivan G.; Jensen, Eric L. N.; Howard, Andrew W.; Latham, David W.; Rodriguez, Joseph E.; Zambelli, Roberto; Bozza, Valerio; Reed, Phillip A.; Gregorio, Joao; Buchhave, Lars A.; Penny, Matthew T.; Pepper, Joshua; Berlind, Perry; Calchi Novati, Sebastiano; Calkins, Michael L.; D'Ago, Giuseppe; Eastman, Jason D.; Bayliss, D.; Colón, Knicole D.; Curtis, Ivan A.; DePoy, D. L.; Esquerdo, Gilbert A.; Gould, Andrew; Joner, Michael D.; Kielkopf, John F.; Labadie-Bartz, Jonathan; Lund, Michael B.; Manner, Mark; Marshall, Jennifer L.; McLeod, Kim K.; Oberst, Thomas E.; Pogge, Richard W.; Scarpetta, Gaetano; Stephens, Denise C.; Stockdale, Christopher; Tan, T. G.; Trueblood, Mark; Trueblood, Patricia

2017-04-01

We announce the discovery of KELT-12b, a highly inflated Jupiter-mass planet transiting the mildly evolved, V = 10.64 host star TYC 2619-1057-1. We followed up the initial transit signal in the KELT-North survey data with precise ground-based photometry, high-resolution spectroscopy, precise radial velocity measurements, and high-resolution adaptive optics imaging. Our preferred best-fit model indicates that the host star has {T}{eff} = 6279 ± 51 K, {log}{g}\\star = 3.89 ± 0.05, [Fe/H] = {0.19}-0.09+0.08, {M}* = {1.59}-0.09+0.07 {M}⊙ , and {R}* = 2.37 ± 0.17 {R}⊙ . The planetary companion has {M}{{P}} = 0.95 ± 0.14 {M}{{J}}, {R}{{P}} = {1.78}-0.16+0.17 {R}{{J}}, {log}{g}{{P}} = {2.87}-0.10+0.09, and density {ρ }{{P}} = {0.21}-0.05+0.07 g cm-3, making it one of the most inflated giant planets known. Furthermore, for future follow-up, we report a high-precision time of inferior conjunction in {{BJD}}{TDB} of 2,457,083.660459 ± 0.000894 and period of P=5.0316216+/- 0.000032 days. Despite the relatively large separation of ˜0.07 au implied by its ˜5.03-day orbital period, KELT-12b receives significant flux of {2.38}-0.29+0.32× {10}9 erg s-1 cm-2 from its host. We compare the radii and insolations of transiting gas giant planets around hot ({T}{eff}≥slant 6250 K) and cool stars, noting that the observed paucity of known transiting giants around hot stars with low insolation is likely due to selection effects. We underscore the significance of long-term ground-based monitoring of hot stars and space-based targeting of hot stars with the Transiting Exoplanet Survey Satellite to search for inflated gas giants in longer-period orbits.

Reagan and the Nuclear Freeze: "Stars Wars" as a Rhetorical Strategy.

ERIC Educational Resources Information Center

Bjork, Rebecca S.

1988-01-01

Analyzes the interaction between nuclear freeze activists and proponents of a Strategic Defense Initiative (SDI). Argues that SDI strengthens Reagan's rhetorical position concerning nuclear weapons policy because it reduces the argumentative ground of the freeze movement by envisioning a defensive weapons system that would nullify nuclear weapons.…

Star-formation in the central kpc of the starburst/LINER galaxy NGC 1614

NASA Astrophysics Data System (ADS)

Olsson, E.; Aalto, S.; Thomasson, M.; Beswick, R.

2010-04-01

Aims: The aim is to investigate the star-formation and LINER (low ionization nuclear emission line region) activity within the central kiloparsec of the galaxy NGC 1614. In this paper the radio continuum morphology, which provides a tracer of both nuclear and star-formation activity, and the distribution and dynamics of the cold molecular and atomic gas feeding this activity, are studied. In particular, the nature of an R ≈ 300 pc nuclear ring of star-formation and its relationship to the LINER activity in NGC 1614 is addressed. Methods: A high angular resolution, multi-wavelength study of the LINER galaxy NGC 1614 has been performed. Deep observations of the CO 1-0 spectral line were performed using the Owens Valley Radio Observatory (OVRO). These data have been complemented by extensive multi-frequency radio continuum and Hi absorption observations using the Very Large Array (VLA) and Multi-Element Radio Linked Interferometer Network (MERLIN). Results: Toward the center of NGC 1614, we have detected a ring of radio continuum emission with a radius of 300 pc. This ring is coincident with previous radio and Paα observations. The dynamical mass of the ring based on Hi absorption is 3.1 × 109 M⊙. The peak of the integrated CO 1-0 emission is shifted by 1” to the north-west of the ring center. An upper limit to the molecular gas mass in the ring region is ~1.7 × 109 M⊙. Inside the ring, there is a north to south elongated 1.4 GHz radio continuum feature, with a nuclear peak. This peak is also seen in the 5 GHz radio continuum and in the CO. Conclusions: We suggest that the R = 300 pc star forming ring represents the radius of a dynamical resonance - as an alternative to the scenario that the starburst is propagating outwards from the center into a molecular ring. The ring-like appearance is probably part of a spiral structure. Substantial amounts of molecular gas have passed the radius of the ring and reached the nuclear region. The nuclear peak seen in 5 GHz radio continuum and CO is likely related to previous star formation, where all molecular gas was not consumed. The LINER-like optical spectrum observed in NGC 1614 may be due to nuclear starburst activity, and not to an active galactic nucleus (AGN). Although the presence of an AGN cannot be excluded.

Thermonuclear runaways in thick hydrogen rich envelopes of neutron stars

NASA Technical Reports Server (NTRS)

Starrfield, S. G.; Kenyon, S.; Truran, J. W.; Sparks, W. M.

1981-01-01

A Lagrangian, fully implicit, one dimensional hydrodynamic computer code was used to evolve thermonuclear runaways in the accreted hydrogen rich envelopes of 1.0 Msub solar neutron stars with radii of 10 km and 20 km. Simulations produce outbursts which last from about 750 seconds to about one week. Peak effective temeratures and luninosities were 26 million K and 80 thousand Lsub solar for the 10 km study and 5.3 millison and 600 Lsub solar for the 20 km study. Hydrodynamic expansion on the 10 km neutron star produced a precursor lasting about one ten thousandth seconds.

Radiation-driven winds of hot stars. V - Wind models for central stars of planetary nebulae

NASA Technical Reports Server (NTRS)

Pauldrach, A.; Puls, J.; Kudritzki, R. P.; Mendez, R. H.; Heap, S. R.

1988-01-01

Wind models using the recent improvements of radiation driven wind theory by Pauldrach et al. (1986) and Pauldrach (1987) are presented for central stars of planetary nebulae. The models are computed along evolutionary tracks evolving with different stellar mass from the Asymptotic Giant Branch. We show that the calculated terminal wind velocities are in agreement with the observations and allow in principle an independent determination of stellar masses and radii. The computed mass-loss rates are in qualitative agreement with the occurrence of spectroscopic stellar wind features as a function of stellar effective temperature and gravity.

28SiO v = 0 J = 1-0 emission from evolved stars

NASA Astrophysics Data System (ADS)

de Vicente, P.; Bujarrabal, V.; Díaz-Pulido, A.; Albo, C.; Alcolea, J.; Barcia, A.; Barbas, L.; Bolaño, R.; Colomer, F.; Diez, M. C.; Gallego, J. D.; Gómez-González, J.; López-Fernández, I.; López-Fernández, J. A.; López-Pérez, J. A.; Malo, I.; Moreno, A.; Patino, M.; Serna, J. M.; Tercero, F.; Vaquero, B.

2016-05-01

Aims: Observations of 28SiO v = 0J = 1-0 line emission (7-mm wavelength) from asymptotic giant branch (AGB) stars show in some cases peculiar profiles, composed of a central intense component plus a wider plateau. Very similar profiles have been observed in CO lines from some AGB stars and most post-AGB nebulae and, in these cases, they are clearly associated with the presence of conspicuous axial symmetry and bipolar dynamics. We aim to systematically study the profile shape of 28SiO v = 0J = 1-0 lines in evolved stars and to discuss the origin of the composite profile structure. Methods: We present observations of 28SiO v = 0J = 1-0 emission in 28 evolved stars, including O-rich, C-rich, and S-type Mira-type variables, OH/IR stars, semiregular long-period variables, red supergiants and one yellow hypergiant. Most objects were observed in several epochs, over a total period of time of one and a half years. The observations were performed with the 40 m radio telescope of the Instituto Geográfico Nacional (IGN) in Yebes, Spain. Results: We find that the composite core plus plateau profiles are systematically present in O-rich Miras, OH/IR stars, and red supergiants. They are also found in one S-type Mira (χ Cyg) and in two semiregular variables (X Her and RS Cnc) that are known to show axial symmetry. In the other objects, the profiles are simpler and similar to those observed in other molecular lines. The composite structure appears in the objects in which SiO emission is thought to come from the very inner circumstellar layers, prior to dust formation. The central spectral feature is found to be systematically composed of a number of narrow spikes, except for X Her and RS Cnc, in which it shows a smooth shape that is very similar to that observed in CO emission. These spikes show a significant (and mostly chaotic) time variation, while in all cases the smooth components remain constant within the uncertainties. The profile shape could come from the superposition of standard wide profiles and a group of weak maser spikes confined to the central spectral regions because of tangential amplification. Alternatively, we speculate that the very similar profiles detected in objects that are known to be conspicuously axisymmetric, such as X Her and RS Cnc, and in O-rich Mira-type stars, such as IK Tau and TX Cam, may be indicative of the systematic presence of a significant axial symmetry in the very inner circumstellar shells around AGB stars; such symmetry would be independent of the presence of weak maser effects in the central spikes.

Final Steps in Mating NuSTAR to its Rocket

NASA Image and Video Library

2012-02-23

Inside an environmental enclosure at Vandenberg Air Force Base processing facility in California, technicians complete the final steps in mating NASA Nuclear Spectroscopic Telescope Array NuSTAR and its Orbital Sciences Pegasus XL rocket.

Quantum nuclear pasta and nuclear symmetry energy

NASA Astrophysics Data System (ADS)

Fattoyev, F. J.; Horowitz, C. J.; Schuetrumpf, B.

2017-05-01

Complex and exotic nuclear geometries, collectively referred to as "nuclear pasta," are expected to appear naturally in dense nuclear matter found in the crusts of neutron stars and supernovae environments. The pasta geometries depend on the average baryon density, proton fraction, and temperature and are critically important in the determination of many transport properties of matter in supernovae and the crusts of neutron stars. Using a set of self-consistent microscopic nuclear energy density functionals, we present the first results of large scale quantum simulations of pasta phases at baryon densities 0.03 ≤ρ ≤0.10 fm-3 , proton fractions 0.05 ≤Yp≤0.40 , and zero temperature. The full quantum simulations, in particular, allow us to thoroughly investigate the role and impact of the nuclear symmetry energy on pasta configurations. We use the Sky3D code that solves the Skyrme Hartree-Fock equations on a three-dimensional Cartesian grid. For the nuclear interaction we use the state-of-the-art UNEDF1 parametrization, which was introduced to study largely deformed nuclei, hence is suitable for studies of the nuclear pasta. Density dependence of the nuclear symmetry energy is simulated by tuning two purely isovector observables that are insensitive to the current available experimental data. We find that a minimum total number of nucleons A =2000 is necessary to prevent the results from containing spurious shell effects and to minimize finite size effects. We find that a variety of nuclear pasta geometries are present in the neutron star crust, and the result strongly depends on the nuclear symmetry energy. The impact of the nuclear symmetry energy is less pronounced as the proton fractions increase. Quantum nuclear pasta calculations at T =0 MeV are shown to get easily trapped in metastable states, and possible remedies to avoid metastable solutions are discussed.

Origin of the high velocity gas in NGC 6231

NASA Astrophysics Data System (ADS)

Massa, Derck

2017-08-01

It is well known that clusters of massive stars are influenced by the presence of strong winds, that they are sources of diffuse X-rays from shocked gas, and that this gas can be vented into the surrounding region or the halo, forming a critical element in the process of galactic feedback. However, the details of how these different environments interact and evolve are far from complete. Recently, Massa (2017) showed that the peculiar C IV 1550 Ang absorption seen in several otherwise normal main sequence B stars in NGC 6231 is not intrinsic to the stars. Instead, this absorption, which extends to more than -2000 km/s, is due to intervening carbon rich, high speed gas in the cluster environment. In this proposal, we seek to identify the origin of the high speed gas. The proposed observations will enable us to determine whether it is due to the outer wind of the WC star WR79, or to a collective cluster wind, enriched by carbon from the wind of WR79. If it is due to the wind of WR79, then the new data will furnish a novel, less model dependent estimate of the mass loss rate of a WC star. If it is due to a collective wind from the cluster, then we could be witnessing an important stage of galactic feedback. In either case, the proposed observations will provide a unique and significant insight on how massive, open clusters evolve - insight that can only be obtained through UV spectroscopy.

Evidence of the evolved nature of the B[e] star MWC 137

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

Muratore, M. F.; Arias, M. L.; Cidale, L.

2015-01-01

The evolutionary phase of B[e] stars is difficult to establish due to the uncertainties in their fundamental parameters. For instance, possible classifications for the Galactic B[e] star MWC 137 include pre-main-sequence and post-main-sequence phases, with a large range in luminosity. Our goal is to clarify the evolutionary stage of this peculiar object, and to study the CO molecular component of its circumstellar medium. To this purpose, we modeled the CO molecular bands using high-resolution K-band spectra. We find that MWC 137 is surrounded by a detached cool (T=1900±100 K) and dense (N=(3±1)×10{sup 21} cm{sup −2}) ring of CO gas orbitingmore » the star with a rotational velocity, projected to the line of sight, of 84 ± 2 km s{sup −1}. We also find that the molecular gas is enriched in the isotope {sup 13}C, excluding the classification of the star as a Herbig Be. The observed isotopic abundance ratio ({sup 12}C/{sup 13}C = 25 ± 2) derived from our modeling is compatible with a proto-planetary nebula, main-sequence, or supergiant evolutionary phase. However, based on some observable characteristics of MWC 137, we propose that the supergiant scenario seems to be the most plausible. Hence, we suggest that MWC 137 could be in an extremely short-lived phase, evolving from a B[e] supergiant to a blue supergiant with a bipolar ring nebula.« less

A dusty, normal galaxy in the epoch of reionization.

PubMed

Watson, Darach; Christensen, Lise; Knudsen, Kirsten Kraiberg; Richard, Johan; Gallazzi, Anna; Michałowski, Michał Jerzy

2015-03-19

Candidates for the modest galaxies that formed most of the stars in the early Universe, at redshifts z > 7, have been found in large numbers with extremely deep restframe-ultraviolet imaging. But it has proved difficult for existing spectrographs to characterize them using their ultraviolet light. The detailed properties of these galaxies could be measured from dust and cool gas emission at far-infrared wavelengths if the galaxies have become sufficiently enriched in dust and metals. So far, however, the most distant galaxy discovered via its ultraviolet emission and subsequently detected in dust emission is only at z = 3.2 (ref. 5), and recent results have cast doubt on whether dust and molecules can be found in typical galaxies at z ≥ 7. Here we report thermal dust emission from an archetypal early Universe star-forming galaxy, A1689-zD1. We detect its stellar continuum in spectroscopy and determine its redshift to be z = 7.5 ± 0.2 from a spectroscopic detection of the Lyman-α break. A1689-zD1 is representative of the star-forming population during the epoch of reionization, with a total star-formation rate of about 12 solar masses per year. The galaxy is highly evolved: it has a large stellar mass and is heavily enriched in dust, with a dust-to-gas ratio close to that of the Milky Way. Dusty, evolved galaxies are thus present among the fainter star-forming population at z > 7.

Exact solution of equations for proton localization in neutron star matter

NASA Astrophysics Data System (ADS)

Kubis, Sebastian; Wójcik, Włodzimierz

2015-11-01

The rigorous treatment of proton localization phenomenon in asymmetric nuclear matter is presented. The solution of proton wave function and neutron background distribution is found by the use of the extended Thomas-Fermi approach. The minimum of energy is obtained in the Wigner-Seitz approximation of a spherically symmetric cell. The analysis of four different nuclear models suggests that the proton localization is likely to take place in the interior of a neutron star.

76 FR 81992 - PPL Bell Bend, LLC; Combined License Application for Bell Bend Nuclear Power Plant; Exemption

Federal Register 2010, 2011, 2012, 2013, 2014

2011-12-29

... License Application for Bell Bend Nuclear Power Plant; Exemption 1.0 Background PPL Bell Bend, LLC... for Nuclear Power Plants.'' This reactor is to be identified as Bell Bend Nuclear Power Plant (BBNPP... based upon the U.S. EPR reference COL (RCOL) application for UniStar's Calvert Cliffs Nuclear Power...

Physics of Neutron Star Crusts.

PubMed

Chamel, Nicolas; Haensel, Pawel

2008-01-01

The physics of neutron star crusts is vast, involving many different research fields, from nuclear and condensed matter physics to general relativity. This review summarizes the progress, which has been achieved over the last few years, in modeling neutron star crusts, both at the microscopic and macroscopic levels. The confrontation of these theoretical models with observations is also briefly discussed.

Gravitational waves from neutron star excitations in a binary inspiral

NASA Astrophysics Data System (ADS)

Parisi, Alessandro; Sturani, Riccardo

2018-02-01

In the context of a binary inspiral of mixed neutron star-black hole systems, we investigate the excitation of the neutron star oscillation modes by the orbital motion. We study generic eccentric orbits and show that tidal interaction can excite the f -mode oscillations of the star by computing the amount of energy and angular momentum deposited into the star by the orbital motion tidal forces via closed form analytic expressions. We study the f -mode oscillations of cold neutron stars using recent microscopic nuclear equations of state, and we compute their imprint into the emitted gravitational waves.

Wind accretion and formation of disk structures in symbiotic binary systems

NASA Astrophysics Data System (ADS)

de Val-Borro, M.; Karovska, M.; Sasselov, D. D.; Stone, J. M.

2015-05-01

We investigate gravitationally focused wind accretion in binary systems consisting of an evolved star with a gaseous envelope and a compact accreting companion. We study the mass accretion and formation of an accretion disk around the secondary caused by the strong wind from the primary late-type component using global 2D and 3D hydrodynamic numerical simulations. In particular, the dependence of the mass accretion rate on the mass loss rate, wind temperature and orbital parameters of the system is considered. For a typical slow and massive wind from an evolved star the mass transfer through a focused wind results in rapid infall onto the secondary. A stream flow is created between the stars with accretion rates of a 2--10% percent of the mass loss from the primary. This mechanism could be an important method for explaining periodic modulations in the accretion rates for a broad range of interacting binary systems and fueling of a large population of X-ray binary systems. We test the plausibility of these accretion flows indicated by the simulations by comparing with observations of the symbiotic variable system CH Cyg.

Investigating mass transfer in symbiotic systems with hydrodynamic simulations

NASA Astrophysics Data System (ADS)

de Val-Borro, Miguel; Karovska, Margarita; Sasselov, Dimitar D.

2014-06-01

We investigate gravitationally focused wind accretion in binary systems consisting of an evolved star with a gaseous envelope and a compact accreting companion. We study the mass accretion and formation of an accretion disk around the secondary caused by the strong wind from the primary late-type component using global 2D and 3D hydrodynamic numerical simulations. In particular, the dependence on the mass accretion rate on the mass loss rate, wind temperature and orbital parameters of the system is considered. For a typical slow and massive wind from an evolved star the mass transfer through a focused wind results in rapid infall onto the secondary. A stream flow is created between the stars with accretion rates of a 2-10% percent of the mass loss from the primary. This mechanism could be an important method for explaining periodic modulations in the accretion rates for a broad range of interacting binary systems and fueling of a large population of X-ray binary systems. We test the plausibility of these accretion flows indicated by the simulations by comparing with observations of the symbiotic CH Cyg variable system.

Formation of wide binaries by turbulent fragmentation

NASA Astrophysics Data System (ADS)

Lee, Jeong-Eun; Lee, Seokho; Dunham, Michael M.; Tatematsu, Ken'ichi; Choi, Minho; Bergin, Edwin A.; Evans, Neal J.

2017-08-01

Understanding the formation of wide-binary systems of very low-mass stars (M ≤ 0.1 solar masses, M⊙) is challenging 1,2,3 . The most obvious route is through widely separated low-mass collapsing fragments produced by turbulent fragmentation of a molecular core4,5. However, close binaries or multiples from disk fragmentation can also evolve to wide binaries over a few initial crossing times of the stellar cluster through tidal evolution6. Finding an isolated low-mass wide-binary system in the earliest stage of formation, before tidal evolution could occur, would prove that turbulent fragmentation is a viable mechanism for (very) low-mass wide binaries. Here we report high-resolution ALMA observations of a known wide-separation protostellar binary, showing that each component has a circumstellar disk. The system is too young7 to have evolved from a close binary, and the disk axes are misaligned, providing strong support for the turbulent fragmentation model. Masses of both stars are derived from the Keplerian rotation of the disks; both are very low-mass stars.

Atomic and molecular hydrogen in the circumstellar envelopes of late-type stars

NASA Technical Reports Server (NTRS)

Glassgold, A. E.; Huggins, P. J.

1983-01-01

The distribution of atomic and molecular hydrogen in the expanding circumstellar envelopes of cool evolved stars is discussed. The main concern is to evaluate the effects of photodestruction of H2 by galactic UV radiation, including shielding of the radiation by H2 itself and by dust in the envelope. One of the most important parameters is the H/H2 ratio which is frozen out in the upper atmosphere of the star. For stars with photospheric temperatures greater than about 2500 K, atmospheric models suggest that the outflowing hydrogen is mainly atomic, whereas cooler stars should be substantially molecular. In the latter case, photodissociation of H2 and heavy molecules contribute to the atomic hydrogen content of the outer envelope. The presented estimates indicate that atomic hydrogen is almost at the limit of detection in the C-rich star IRC + 10216, and may be detectable in warmer stars. Failure to detect it would have important implications for the general understanding of circumstellar envelopes.

RUNAWAY DWARF CARBON STARS AS CANDIDATE SUPERNOVA EJECTA

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

Plant, Kathryn A.; Margon, Bruce; Guhathakurta, Puragra

2016-12-20

The dwarf carbon (dC) star SDSS J112801.67+004034.6 has an unusually high radial velocity, 531 ± 4 km s{sup −1}. We present proper motion and new spectroscopic observations which imply a large Galactic rest frame velocity, 425 ± 9 km s{sup −1}. Several other SDSS dC stars are also inferred to have very high galactocentric velocities, again each based on both high heliocentric radial velocity and also confidently detected proper motions. Extreme velocities and the presence of C {sub 2} bands in the spectra of dwarf stars are both rare. Passage near the Galactic center can accelerate stars to such extreme velocities, but the largemore » orbital angular momentum of SDSS J1128 precludes this explanation. Ejection from a supernova in a binary system or disruption of a binary by other stars are possibilities, particularly as dC stars are thought to obtain their photospheric C {sub 2} via mass transfer from an evolved companion.« less

Evolution of massive stars in very young clusters and associations

NASA Technical Reports Server (NTRS)

Stothers, R. B.

1985-01-01

Statistics concerning the stellar content of young galactic clusters and associations which show well defined main sequence turnups have been analyzed in order to derive information about stellar evolution in high-mass galaxies. The analytical approach is semiempirical and uses natural spectroscopic groups of stars on the H-R diagram together with the stars' apparent magnitudes. The new approach does not depend on absolute luminosities and requires only the most basic elements of stellar evolution theory. The following conclusions are offered on the basis of the statistical analysis: (1) O-tupe main-sequence stars evolve to a spectral type of B1 during core hydrogen burning; (2) most O-type blue stragglers are newly formed massive stars burning core hydrogen; (3) supergiants lying redward of the main-sequence turnup are burning core helium; and most Wolf-Rayet stars are burning core helium and originally had masses greater than 30-40 solar mass. The statistics of the natural spectroscopic stars in young galactic clusters and associations are given in a table.

The evolution of rotating stars. III - Predicted surface rotation velocities for stars which conserve total angular momentum

NASA Technical Reports Server (NTRS)

Endal, A. S.; Sofia, S.

1979-01-01

Predicted surface rotation velocities for Population I stars at 10, 7, 5, 3, and 1.5 solar masses are presented. The surface velocities were computed for angular momentum with no radial redistribution, complete redistribution, and partial redistribution as predicted by consideration of circulation currents in rotating stars. Near the main sequence, rotational effects can reduce the moment of inertia of a star, so nonrotating models underestimate the expected velocities for evolving stars. On the red giant branch, angular momentum redistribution reduces the surface velocity by a factor of 2 or more, relative to the velocity expected for no radial redistribution. This removes the discrepancy between predicted and observed rotation rates for the K giants and makes it unlikely that these stars lose significant amounts of angular momentum by stellar winds. Calculations indicate that improved observations of the red giants in the Hyades cluster can be used to determine how angular momentum is redistributed by convection

Discovery of a parsec-scale bipolar nebula around MWC 349A

NASA Astrophysics Data System (ADS)

Gvaramadze, V. V.; Menten, K. M.

2012-05-01

We report the discovery of a bipolar nebula around the peculiar emission-line star MWC 349A using archival Spitzer Space Telescope 24 μm data. The nebula extends over several arcminutes (up to 5 pc) and has the same orientation and geometry as the well-known subarcsecond-scale (~400 times smaller) bipolar radio nebula associated with this star. We discuss the physical relationship between MWC 349A and the nearby B0 III star MWC 349B and propose that both stars were members of a hierarchical triple system, which was ejected from the core of the Cyg OB2 association several Myr ago and recently was dissolved into a binary system (now MWC 349A) and a single unbound star (MWC 349B). Our proposal implies that MWC 349A is an evolved massive star (likely a luminous blue variable) in a binary system with a low-mass star. A possible origin of the bipolar nebula around MWC 349A is discussed.

Spin-up of a rapidly rotating star by angular momentum loss - Effects of general relativity

NASA Technical Reports Server (NTRS)

Cook, Gregory B.; Shapiro, Stuart L.; Teukolsky, Saul A.

1992-01-01

It has recently been shown that a rapidly rotating Newtonian star can spin up by radiating angular momentum. Extremely fast pulsars losing energy and angular momentum by magnetic dipole radiation or gravitational radiation may exhibit this behavior. Here, we show that this phenomenon is more widespread for rapidly rotating stars in general relativity. We construct and tabulate polytropic sequences of fully relativistic rotating stars of constant rest mass and entropy. We find that the range of adiabatic indices allowing spin-up extends somewhat above 4/3 because of the nonlinear effects of relativistic gravity. In addition, there is a new class of 'supramassive' stars which will inevitably spin up by losing angular momentum regardless of their equation of state. A supramassive star, spinning up via angular momentum loss, will ultimately evolve until it becomes unstable to catastrophic collapse to a black hole. Spin-up in a rapidly rotating star may thus be an observational precursor to such collapse.

White Dwarfs in Star Clusters: The Initial-Final Mass Relation for Stars from 0.85 to 8 M$_\\odot$

NASA Astrophysics Data System (ADS)

Cummings, Jeffrey; Kalirai, Jason; Tremblay, P.-E.; Ramírez-Ruiz, Enrico

2018-01-01

The spectroscopic study of white dwarfs provides both their mass, cooling age, and intrinsic photometric properties. For white dwarfs in the field of well-studied star clusters, this intrinsic photometry can be used to determine if they are members of that star cluster. Comparison of a member white dwarf's cooling age to its total cluster's age provides the evolutionary timescale of its progenitor star, and hence the mass. This is the initial-final mass relation (IFMR) for stars, which gives critical information on how a progenitor star evolves and loses mass throughout its lifetime, and how this changes with progenitor mass. Our work, for the first time, presents a uniform analysis of 85 white dwarf cluster members spanning from progenitor masses of 0.85 to 8 M$_\\odot$. Comparison of our work to theoretical IFMRs shows remarkable consistency in their shape but differences remain. We will discuss possible explanations for these differences, including the effects of stellar rotation.

THE VERY MASSIVE STAR CONTENT OF THE NUCLEAR STAR CLUSTERS IN NGC 5253

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

Smith, L. J.; Crowther, P. A.; Calzetti, D.

2016-05-20

The blue compact dwarf galaxy NGC 5253 hosts a very young starburst containing twin nuclear star clusters, separated by a projected distance of 5 pc. One cluster (#5) coincides with the peak of the H α emission and the other (#11) with a massive ultracompact H ii region. A recent analysis of these clusters shows that they have a photometric age of 1 ± 1 Myr, in apparent contradiction with the age of 3–5 Myr inferred from the presence of Wolf-Rayet features in the cluster #5 spectrum. We examine Hubble Space Telescope ultraviolet and Very Large Telescope optical spectroscopy ofmore » #5 and show that the stellar features arise from very massive stars (VMSs), with masses greater than 100 M {sub ⊙}, at an age of 1–2 Myr. We further show that the very high ionizing flux from the nuclear clusters can only be explained if VMSs are present. We investigate the origin of the observed nitrogen enrichment in the circumcluster ionized gas and find that the excess N can be produced by massive rotating stars within the first 1 Myr. We find similarities between the NGC 5253 cluster spectrum and those of metal-poor, high-redshift galaxies. We discuss the presence of VMSs in young, star-forming galaxies at high redshift; these should be detected in rest-frame UV spectra to be obtained with the James Webb Space Telescope . We emphasize that population synthesis models with upper mass cutoffs greater than 100 M {sub ⊙} are crucial for future studies of young massive star clusters at all redshifts.« less

The Influence of Hyperons and Strong Magnetic Field in Neutron Star Properties

NASA Astrophysics Data System (ADS)

Lopes, L. L.; Menezes, D. P.

2012-12-01

Neutron stars are among of the most exotic objects in the universe and constitute a unique laboratory to study nuclear matter above the nuclear saturation density. In this work, we study the equation of state (EoS) of the nuclear matter within a relativistic model subject to a strong magnetic field. We then apply this EoS to study and describe some of the physical characteristics of neutron stars, especially the mass-radius relation and chemical compositions. To study the influence of the magnetic field and the hyperons in the stellar interior, we consider altogether four solutions: two different magnetic field to obtain a weak and a strong influence; and two configurations: a family of neutron stars formed only by protons, electrons, and neutrons and a family formed by protons, electrons, neutrons, muons, and hyperons. The limit and the validity of the results found are discussed with some care. In all cases, the particles that constitute the neutron star are in β equilibrium and zero total net charge. Our work indicates that the effect of a strong magnetic field has to be taken into account in the description of magnetars, mainly if we believe that there are hyperons in their interior, in which case the influence of the magnetic field can increase the mass by more than 10 %. We have also seen that although a magnetar can reach 2.48 M ⊙, a natural explanation of why we do not know pulsars with masses above 2.0 M ⊙ arises. We also discuss how the magnetic field affects the strangeness fraction in some standard neutron star masses, and to conclude our paper, we revisit the direct Urca process related to the cooling of the neutron stars and show how it is affected by the hyperons and the magnetic field.

THE ASTROPHYSICAL IMPLICATIONS OF DUST FORMATION DURING THE ERUPTIONS OF HOT, MASSIVE STARS

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

Kochanek, C. S.

2011-12-10

Dust formation in the winds of hot stars is inextricably linked to the classic eruptive state of luminous blue variables because it requires very high mass-loss rates, M-dot {approx}>10{sup -2.5} M{sub sun} year{sup -1}, for grains to grow and for the non-dust optical depth of the wind to shield the dust formation region from the true stellar photosphere. Thus, dusty shells around hot stars trace the history of 'great' eruptions, and the statistics of such shells in the Galaxy indicate that these eruptions are likely the dominant mass-loss mechanism for evolved, M{sub ZAMS} {approx}> 40 M{sub Sun} stars. Dust formationmore » at such high M-dot also explains why very large grains (a{sub max} {approx}> 1 {mu}m) are frequently found in these shells, since a{sub max}{proportional_to} M-dot . The statistics of these shells (numbers, ages, masses, and grain properties such as a{sub max}) provide an archaeological record of this mass-loss process. In particular, the velocities v{sub shell}, transient durations (where known), and ejected masses M{sub shell} of the Galactic shells and the supernova (SN) 'impostors' proposed as their extragalactic counterparts are very different. While much of the difference is a selection effect created by shell lifetimes {proportional_to}(v{sub shell}{radical}(M{sub shell})){sup -1}, more complete Galactic and extragalactic surveys are needed to demonstrate that the two phenomena share a common origin given that their observed properties are essentially disjoint. If even small fractions (1%) of SNe show interactions with such dense shells of ejecta, as is currently believed, then the driving mechanism of the eruptions must be associated with the very final phases of stellar evolution, suggestive of some underlying nuclear burning instability.« less

Constraints on pre-main-sequence evolution from stellar pulsations

NASA Astrophysics Data System (ADS)

Casey, M. P.; Zwintz, K.; Guenther, D. B.

2014-02-01

Pulsating pre-main-sequence (PMS) stars afford the earliest opportunity in the lifetime of a star to which the concepts of asteroseismology can be applied. PMS stars should be structurally simpler than their evolved counterparts, thus (hopefully!) making any asteroseismic analysis relatively easier. Unfortunately, this isn't necessarily the case. The majority of these stars (around 80) are δ Scuti pulsators, with a couple of γ Doradus, γ Doradus - δ Scuti hybrids, and slowly pulsating B stars thrown into the mix. The majority of these stars have only been discovered within the last ten years, with the community still uncovering the richness of phenomena associated with these stars, many of which defy traditional asteroseismic analysis. A systematic asteroseismic analysis of all of the δ Scuti PMS stars was performed in order to get a better handle on the properties of these stars as a group. Some strange results have been found, including one star pulsating up to the theoretical acoustic cut-off frequency of the star, and a number of stars in which the most basic asteroseismic analysis suggests problems with the stars' positions in the Hertzsprung-Russell diagram. From this we get an idea of the\\break constraints - or lack thereof - that these results can put on PMS stellar evolution.

Rejuvenation of the Innocent Bystander: Results from a Pilot X-ray Study of Dwarf Carbon Stars

NASA Astrophysics Data System (ADS)

Mazzoni, Fernando; Montez, Rodolfo; Green, Paul

2018-01-01

We present the results of a pilot study by the Chandra X-ray Observatory of X-ray emission from dwarf Carbon (dC) stars. Carbon stars were thought to be exclusively AGB stars but main sequence dwarfs showing carbon molecular bands appear to be the dominant variety. The existence of dC stars is surprising since dwarf stars cannot intrinsically produce carbon as an AGB star can. It is hypothesized that dC stars are polluted by an evolved companion star. Evidence of past pollution can appear in X-ray emission where increased coronal activity (“spin-up”) or mass accretion via a disk can be detected. Using the Chandra X-ray Observatory we detected X-ray photons in the vicinity of all the dC stars in our a pilot sample. For each detection we characterized the X-ray emission and compared to the emission expected from potential emission scenarios. Although the process that produces the X-ray emission from dC stars is presently unclear and our pilot sample is small, our results suggest that X-ray emission might be a universal characteristic of dC stars. Further examination of the X-ray emission plus future X-ray and multiwavelength observations will help us better understand the nature of these intriguing stars.

Characterizing the evolving K -band luminosity function using the UltraVISTA, CANDELS and HUDF surveys

NASA Astrophysics Data System (ADS)

Mortlock, Alice; McLure, Ross J.; Bowler, Rebecca A. A.; McLeod, Derek J.; Mármol-Queraltó, Esther; Parsa, Shaghayegh; Dunlop, James S.; Bruce, Victoria A.

2017-02-01

We present the results of a new study of the K-band galaxy luminosity function (KLF) at redshifts z ≤ 3.75, based on a nested combination of the UltraVISTA, Cosmic Assembly Near-infrared Deep Legacy Extragalactic Survey and HUDF surveys. The large dynamic range in luminosity spanned by this new data set (3-4 dex over the full redshift range) is sufficient to clearly demonstrate for the first time that the faint-end slope of the KLF at z ≥ 0.25 is relatively steep (-1.3 ≤ α ≤ -1.5 for a single Schechter function), in good agreement with recent theoretical and phenomenological models. Moreover, based on our new data set, we find that a double Schechter function provides a significantly improved description of the KLF at z ≤ 2. At redshifts z ≥ 0.25, the evolution of the KLF is remarkably smooth, with little or no evolution evident at faint (MK ≥ -20.5) or bright magnitudes (MK ≤ -24.5). Instead, the KLF is seen to evolve rapidly at intermediate magnitudes, with the number density of galaxies at MK ≃-23 dropping by a factor of ≃5 over the redshift interval 0.25 ≤ z ≤ 3.75. Motivated by this, we explore a simple description of the evolving KLF based on a double Schechter function with fixed faint-end slopes (α1 = -0.5, α2 = -1.5) and a shared characteristic magnitude (MK^{star }). According to this parametrization, the normalization of the component which dominates the faint end of the KLF remains approximately constant, with φ ^{star }2 decreasing by only a factor of ≃2 between z ≃0 and 3.25. In contrast, the component which dominates the bright end of the KLF at low redshifts evolves dramatically, becoming essentially negligible by z ≃3. Finally, we note that within this parametrization, the observed evolution of MK^{star } between z ≃0 and 3.25 is entirely consistent with MK^{star } corresponding to a constant stellar mass of M⋆ ≃5 × 1010 M⊙ at all redshifts.

Dwarf carbon stars are likely metal-poor binaries and unlikely hosts to carbon planets

NASA Astrophysics Data System (ADS)

Whitehouse, Lewis J.; Farihi, J.; Green, P. J.; Wilson, T. G.; Subasavage, J. P.

2018-06-01

Dwarf carbon stars make up the largest fraction of carbon stars in the Galaxy with ≈1200 candidates known to date primarily from the Sloan Digital Sky Survey. They either possess primordial carbon-enhancements, or are polluted by mass transfer from an evolved companion such that C/O is enhanced beyond unity. To directly test the binary hypothesis, a radial velocity monitoring survey has been carried out on 28 dwarf carbon stars, resulting in the detection of variations in 21 targets. Using Monte Carlo simulations,this detection fraction is found to be consistent with a 100% binary population and orbital periods on the order of hundreds of days. This result supports the post-mass transfer nature of dwarf carbon stars, and implies they are not likely hosts to carbon planets.

Dust Production and Mass Loss in Cool Evolved Stars

NASA Technical Reports Server (NTRS)

Boyer, M. L.

2013-01-01

Following the red giant branch phase and the subsequent core He-burning phase, the low- to intermediate-mass stars (0.8

Nuclear Reactions in the Crusts of Accreting Neutron Stars

NASA Astrophysics Data System (ADS)

Lau, R.; Beard, M.; Gupta, S. S.; Schatz, H.; Afanasjev, A. V.; Brown, E. F.; Deibel, A.; Gasques, L. R.; Hitt, G. W.; Hix, W. R.; Keek, L.; Möller, P.; Shternin, P. S.; Steiner, A. W.; Wiescher, M.; Xu, Y.

2018-05-01

X-ray observations of transiently accreting neutron stars during quiescence provide information about the structure of neutron star crusts and the properties of dense matter. Interpretation of the observational data requires an understanding of the nuclear reactions that heat and cool the crust during accretion and define its nonequilibrium composition. We identify here in detail the typical nuclear reaction sequences down to a depth in the inner crust where the mass density is ρ =2× {10}12 {{g}} {cm}}-3 using a full nuclear reaction network for a range of initial compositions. The reaction sequences differ substantially from previous work. We find a robust reduction of crust impurity at the transition to the inner crust regardless of initial composition, though shell effects can delay the formation of a pure crust somewhat to densities beyond ρ =2× {10}12 {{g}} {cm}}-3. This naturally explains the small inner crust impurity inferred from observations of a broad range of systems. The exception are initial compositions with A ≥ 102 nuclei, where the inner crust remains impure with an impurity parameter of Q imp ≈ 20 owing to the N = 82 shell closure. In agreement with previous work, we find that nuclear heating is relatively robust and independent of initial composition, while cooling via nuclear Urca cycles in the outer crust depends strongly on initial composition. This work forms a basis for future studies of the sensitivity of crust models to nuclear physics and provides profiles of composition for realistic crust models.

The Texas-Indiana Virtual STAR Center: Zebrafish Models for Developmental Toxicity Screening

EPA Pesticide Factsheets

The Texas-Indiana Virtual STAR Center: Zebrafish Models for Developmental Toxicity Screening (Presented by Maria Bondesson Bolin, Ph.D, University of Houston, Center for Nuclear Receptors and Cell Signaling) (3/22/2012)

Uniting of NuSTAR Spacecraft and Rocket

NASA Image and Video Library

2012-02-23

Inside an environmental enclosure at Vandenberg Air Force Base processing facility in California, solar panels line the sides of NASA Nuclear Spectroscopic Telescope Array NuSTAR, which was just joined to the Orbital Sciences Pegasus XL rocket.

STAR CLUSTERS IN A NUCLEAR STAR FORMING RING: THE DISAPPEARING STRING OF PEARLS

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

Väisänen, Petri; Barway, Sudhanshu; Randriamanakoto, Zara, E-mail: petri@saao.ac.za

2014-12-20

An analysis of the star cluster population in a low-luminosity early-type galaxy, NGC 2328, is presented. The clusters are found in a tight star forming nuclear spiral/ring pattern and we also identify a bar from structural two-dimensional decomposition. These massive clusters are forming very efficiently in the circumnuclear environment and they are young, possibly all less than 30 Myr of age. The clusters indicate an azimuthal age gradient, consistent with a ''pearls-on-a-string'' formation scenario, suggesting bar-driven gas inflow. The cluster mass function has a robust down turn at low masses at all age bins. Assuming clusters are born with a power-lawmore » distribution, this indicates extremely rapid disruption at timescales of just several million years. If found to be typical, it means that clusters born in dense circumnuclear rings do not survive to become old globular clusters in non-interacting systems.« less

Shell nebulae around luminous evolved stars

NASA Technical Reports Server (NTRS)

Dufour, Reginald J.

1989-01-01

Shell nebulae around luminous Population I Wolf-Rayet, Of, and P-Cygni stars are astrophysically interesting since they are indicators of pre-supernova mass loss and how such massive stars prepare their surrounding interstellar medium prior to explosion. Some twenty-odd such nebulae are known, for which detailed study of their morphological and spectroscopic characteristics have only begun in this decade. In this paper, some of these characteristics are reviewed in general, and new observations are reported. Emphasis has been placed on several 'prototype 'objects (NGC 7635, NGC 2359, NGC 6888, and the Eta Carinae condensations) to illustrate the varied massive-star mass-loss, the physics of their winds and shell ejecta, and related nucleosynthesis effects in the compositions of the winds and shells.

Burst Oscillations: Watching Neutron Stars Spin

NASA Technical Reports Server (NTRS)

Strohmayer, Tod

2010-01-01

It is now almost 15 years since the first detection of rotationally modulated emission from X-ray bursting neutron stars, "burst oscillations," This phenomenon enables us to see neutron stars spin, as the X-ray burst flux asymmetrically lights up the surface. It has enabled a new way to probe the neutron star spin frequency distribution, as well as to elucidate the multidimensional nature of nuclear burning on neutron stars. I will review our current observational understanding of the phenomenon, with an eye toward highlighting some of the interesting remaining puzzles, of which there is no shortage.

(Sub)millimeter emission lines of molecules in born-again stars

NASA Astrophysics Data System (ADS)

Tafoya, D.; Toalá, J. A.; Vlemmings, W. H. T.; Guerrero, M. A.; De Beck, E.; González, M.; Kimeswenger, S.; Zijlstra, A. A.; Sánchez-Monge, Á.; Treviño-Morales, S. P.

2017-04-01

Context. Born-again stars provide a unique possibility to study the evolution of the circumstellar envelope of evolved stars in human timescales. Up until now, most of the observations of the circumstellar material in these stars have been limited to studying the relatively hot gas and dust. In other evolved stars, the emission from rotational transitions of molecules, such as CO, is commonly used to study the cool component of their circumstellar envelopes. Thus, the detection and study of molecular gas in born-again stars is of great importance when attempting to understand their composition and chemical evolution. In addition, the molecular emission is an invaluable tool for exploring the physical conditions, kinematics, and formation of asymmetric structures in the circumstellar envelopes of these evolved stars. However, up until now, all attempts to detect molecular emission from the cool material around born-again stars have failed. Aims: We searched for emission from rotational transitions of molecules in the hydrogen-deficient circumstellar envelopes of born-again stars to explore the chemical composition, kinematics, and physical parameters of the relatively cool gas. Methods: We carried out observations using the APEX and IRAM 30 m telescopes to search for molecular emission toward four well-studied born-again stars, V4334 Sgr, V605 Aql, A30, and A78, that are thought to represent an evolutionary sequence. Results: For the first time, we detected emission from HCN and H13CN molecules toward V4334 Sgr, and CO emission in V605 Aql. No molecular emission was detected above the noise level toward A30 and A78. The detected lines exhibit broad linewidths ≳150 km s-1, which indicates that the emission comes from gas ejected during the born-again event, rather than from the old planetary nebula. A first estimate of the H12CN/H13CN abundance ratio in the circumstellar environment of V4334 Sgr is ≈3, which is similar to the value of the 12C/13C ratio measured from other observations. We derived a rotational temperature of Trot = 13 ± 1 K, and a total column density of NHCN = 1.6 ± 0.1 × 1016 cm-2 for V4334 Sgr. This result sets a lower limit on the amount of hydrogen that was ejected into the wind during the born-again event of this source. For V605 Aql, we obtained a lower limit for the integrated line intensities I12CO/I13CO> 4. This publication is based on data acquired with the Atacama Pathfinder Experiment (APEX) and IRAM 30 m telescopes. APEX is a collaboration between the Max-Planck-Institut für Radioastronomie, the European Southern Observatory, and the Onsala Space Observatory. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain).

Genetic polymorphisms of Echinococcus tapeworms in China as determined by mitochondrial and nuclear DNA sequences ✩

PubMed Central

Nakao, Minoru; Li, Tiaoying; Han, Xiumin; Ma, Xiumin; Xiao, Ning; Qiu, Jiamin; Wang, Hu; Yanagida, Tetsuya; Mamuti, Wulamu; Wen, Hao; Moro, Pedro L.; Giraudoux, Patrick; Craig, Philip S.; Ito, Akira

2009-01-01

The genetic polymorphisms of Echinococcus spp. in the eastern Tibetan Plateau and the Xinjiang Uyghur Autonomous Region were evaluated by DNA sequencing analyses of genes for mitochondrial cytochrome c oxidase subunit 1 (cox1) and nuclear elongation factor-1 alpha (ef1a). We collected 68 isolates of Echinococcus granulosus sensu stricto (s.s.) from Xinjiang and 113 isolates of E. granulosus s. s., 49 isolates of Echinococcus multilocularis and 34 isolates of Echinococcus shiquicus from the Tibetan Plateau. The results of molecular identification by mitochondrial and nuclear markers were identical, suggesting the infrequency of introgressive hybridization. A considerable intraspecific variation was detected in mitochondrial cox1 sequences. The parsimonious network of cox1 haplotypes showed star-like features in E. granulosus s. s. and E. multilocularis, but a divergent feature in E. shiquicus. The cox1 neutrality indexes computed by Tajima's D and Fu's Fs tests showed high negative values in E. granulosus s. s. and E. multilocularis, indicating significant deviations from neutrality. In contrast, the low positive values of both tests were obtained in E. shiquicus. These results suggest the following hypotheses: (i) recent founder effects arose in E. granulosus and E. multilocularis after introducing particular individuals into the endemic areas by anthropogenic movement or natural migration of host mammals, and (ii) the ancestor of E. shiquicus was segregated into the Tibetan Plateau by colonizing alpine mammals and its mitochondrial locus has evolved without bottleneck effects. PMID:19800346

An Astrophysical Laboratory: Understanding and Exploiting the Young Massive Cluster Westerlund 1

NASA Astrophysics Data System (ADS)

Clark, S.; Negueruela, I.; Ritchie, B.; Najarro, P.; Langer, N.; Crowther, P.; Bartlett, L.; Fenech, D.; González-Fernández, C.; Goodwin, S.; Lohr, M.; Prinja, R.

2015-03-01

Westerlund 1 provides a unique opportunity to probe the physics of massive stars, from birth to death and beyond, as well as the formation and evolution of a super star cluster that appears destined to evolve into a globular cluster. We highlight the result of current studies of this cluster, its diverse stellar constituents and immediate environment, concluding with a summary of future research avenues enabled by ESO facilities.

Ionization of the diffuse gas in galaxies: Hot low-mass evolved stars at work

NASA Astrophysics Data System (ADS)

Flores-Fajardo, N.; Morisset, C.; Stasinska, G.; Binette, L.

2011-10-01

The Diffuse Ionized Medium (DIG) is visible through its faint optical line emission outside classical HII regions (Reynolds 1971) and turns out to be a major component of the interstellar medium in galaxies. OB stars in galaxies likely represent the main source of ionizing photons for the DIG. However, an additional source is needed to explain the increase of [NII]/Hα, [SII]/Hα with galactic height.

Planetary Nebula NGC 7293 also Known as the Helix Nebula

NASA Image and Video Library

2005-05-05

This ultraviolet image from NASA Galaxy Evolution Explorer is of the planetary nebula NGC 7293 also known as the Helix Nebula. It is the nearest example of what happens to a star, like our own Sun, as it approaches the end of its life when it runs out of fuel, expels gas outward and evolves into a much hotter, smaller and denser white dwarf star. http://photojournal.jpl.nasa.gov/catalog/PIA07902

Post-main-sequence planetary system evolution.

PubMed

Veras, Dimitri

2016-02-01

The fates of planetary systems provide unassailable insights into their formation and represent rich cross-disciplinary dynamical laboratories. Mounting observations of post-main-sequence planetary systems necessitate a complementary level of theoretical scrutiny. Here, I review the diverse dynamical processes which affect planets, asteroids, comets and pebbles as their parent stars evolve into giant branch, white dwarf and neutron stars. This reference provides a foundation for the interpretation and modelling of currently known systems and upcoming discoveries.

Magnetic Fields in Evolved Stars: Imaging the Polarized Emission of High-frequency SiO Masers

NASA Astrophysics Data System (ADS)

Vlemmings, W. H. T.; Humphreys, E. M. L.; Franco-Hernández, R.

2011-02-01

We present Submillimeter Array observations of high-frequency SiO masers around the supergiant VX Sgr and the semi-regular variable star W Hya. The J = 5-4, v = 128SiO and v = 029SiO masers of VX Sgr are shown to be highly linearly polarized with a polarization from ~5% to 60%. Assuming the continuum emission peaks at the stellar position, the masers are found within ~60 mas of the star, corresponding to ~100 AU at a distance of 1.57 kpc. The linear polarization vectors are consistent with a large-scale magnetic field, with position and inclination angles similar to that of the dipole magnetic field inferred in the H2O and OH maser regions at much larger distances from the star. We thus show for the first time that the magnetic field structure in a circumstellar envelope can remain stable from a few stellar radii out to ~1400 AU. This provides further evidence supporting the existence of large-scale and dynamically important magnetic fields around evolved stars. Due to a lack of parallactic angle coverage, the linear polarization of masers around W Hya could not be determined. For both stars, we observed the 28SiO and 29SiO isotopologues and find that they have a markedly different distributions and that they appear to avoid each other. Additionally, emission from the SO 55-44 line was imaged for both sources. Around W Hya, we find a clear offset between the red- and blueshifted SO emission. This indicates that W Hya is likely host to a slow bipolar outflow or a rotating disk-like structure.

Retired A Stars Revisited: An Updated Giant Planet Occurrence Rate as a Function of Stellar Metallicity and Mass

NASA Astrophysics Data System (ADS)

Ghezzi, Luan; Montet, Benjamin T.; Johnson, John Asher

2018-06-01

Exoplanet surveys of evolved stars have provided increasing evidence that the formation of giant planets depends not only on stellar metallicity ([Fe/H]) but also on the mass ({M}\\star ). However, measuring accurate masses for subgiants and giants is far more challenging than it is for their main-sequence counterparts, which has led to recent concerns regarding the veracity of the correlation between stellar mass and planet occurrence. In order to address these concerns, we use HIRES spectra to perform a spectroscopic analysis on a sample of 245 subgiants and derive new atmospheric and physical parameters. We also calculate the space velocities of this sample in a homogeneous manner for the first time. When reddening corrections are considered in the calculations of stellar masses and a ‑0.12 {M}ȯ offset is applied to the results, the masses of the subgiants are consistent with their space velocity distributions, contrary to claims in the literature. Similarly, our measurements of their rotational velocities provide additional confirmation that the masses of subgiants with {M}\\star ≥slant 1.6 M ⊙ (the “retired A stars”) have not been overestimated in previous analyses. Using these new results for our sample of evolved stars, together with an updated sample of FGKM dwarfs, we confirm that giant planet occurrence increases with both stellar mass and metallicity up to 2.0 M ⊙. We show that the probability of formation of a giant planet is approximately a one-to-one function of the total amount of metals in the protoplanetary disk {M}\\star {10}[{Fe/{{H}}]}. This correlation provides additional support for the core accretion mechanism of planet formation.

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.

Genetic diversity and molecular evolution of Naga King Chili inferred from internal transcribed spacer sequence of nuclear ribosomal DNA.

PubMed

Kehie, Mechuselie; Kumaria, Suman; Devi, Khumuckcham Sangeeta; Tandon, Pramod

2016-02-01

Sequences of the Internal Transcribed Spacer (ITS1-5.8S-ITS2) of nuclear ribosomal DNAs were explored to study the genetic diversity and molecular evolution of Naga King Chili. Our study indicated the occurrence of nucleotide polymorphism and haplotypic diversity in the ITS regions. The present study demonstrated that the variability of ITS1 with respect to nucleotide diversity and sequence polymorphism exceeded that of ITS2. Sequence analysis of 5.8S gene revealed a much conserved region in all the accessions of Naga King Chili. However, strong phylogenetic information of this species is the distinct 13 bp deletion in the 5.8S gene which discriminated Naga King Chili from the rest of the Capsicum sp. Neutrality test results implied a neutral variation, and population seems to be evolving at drift-mutation equilibrium and free from directed selection pressure. Furthermore, mismatch analysis showed multimodal curve indicating a demographic equilibrium. Phylogenetic relationships revealed by Median Joining Network (MJN) analysis denoted a clear discrimination of Naga King Chili from its closest sister species (Capsicum chinense and Capsicum frutescens). The absence of star-like network of haplotypes suggested an ancient population expansion of this chili.

Clustering and pasta phases in nuclear density functional theory

DOE PAGES

Schuetrumpf, Bastian; Zhang, Chunli; Nazarewicz, Witold

2017-05-23

Nuclear density functional theory is the tool of choice in describing properties of complex nuclei and intricate phases of bulk nucleonic matter. It is a microscopic approach based on an energy density functional representing the nuclear interaction. An attractive feature of nuclear DFT is that it can be applied to both finite nuclei and pasta phases appearing in the inner crust of neutron stars. While nuclear pasta clusters in a neutron star can be easily characterized through their density distributions, the level of clustering of nucleons in a nucleus can often be difficult to assess. To this end, we usemore » the concept of nucleon localization. We demonstrate that the localization measure provides us with fingerprints of clusters in light and heavy nuclei, including fissioning systems. Furthermore we investigate the rod-like pasta phase using twist-averaged boundary conditions, which enable calculations in finite volumes accessible by state of the art DFT solvers.« less

Hiding in Plain Sight: The Low Mass Helium Star Companion of EL CVn

NASA Astrophysics Data System (ADS)

Gies, Douglas

2016-10-01

Binary stars with orbital periods of a decade or less are destined to interact during their evolution. The mass donor star among intermediate binaries may be stripped of its envelope by mass transfer to reveal its helium core. In cases that avoid merger, the low mass helium star will remain in a binary orbit but be lost in the glare of the mass gainer star.Thanks to photometric time series from Kepler and WASP, we now know of 27 such systems that are oriented to produce mutual eclipses. Althoughthe helium star companions are too small and faint in the optical bandfor spectroscopic detection, they contribute a larger fraction of the total flux in the ultraviolet. HST/COS measurements of one long period system, KOI-81, successfully detected the helium star's spectrum in the far-ultraviolet, leading to estimates of its mass and temperature. Here we propose to obtain new HST/COS FUV spectra of the prototype of this class of evolved binaries, EL CVn, and to determine the mass and physical properties of a star that barely escaped a merger.

Zodiacal Exoplanets in Time: Searching for Young Stars in K2

NASA Astrophysics Data System (ADS)

Morris, Nathan Ryan; Mann, Andrew; Rizzuto, Aaron

2018-01-01

Observations of planetary systems around young stars provide insight into the early stages of planetary system formation. Nearby young open clusters such as the Hyades, Pleiades, and Praesepe provide important benchmarks for the properties of stellar systems in general. These clusters are all known to be less than 1 Gyr old, making them ideal targets for a survey of young planetary systems. Few transiting planets have been detected around clusters stars, however, so this alone is too small of a sample. K2, the revived Kepler mission, has provided a vast number of light curves for young stars in clusters and elsewhere in the K2 field. This provides us with the opportunity to extend the sample of young systems to field stars while calibrating with cluster stars. We compute rotational periods from starspot patterns for ~36,000 K2 targets and use gyrochronological relationships derived from cluster stars to determine their ages. From there, we have begun searching for planets around young stars outside the clusters with the ultimate goal of shedding light on how planets and planetary systems evolve in their early, most formative years.

Three very cool degenerate stars in Luyten common proper motion binaries - Implications for the age of the galactic disk

NASA Technical Reports Server (NTRS)

Hintzen, Paul; Oswalt, Terry D.; Liebert, James; Sion, Edward M.

1989-01-01

During the course of a spectroscopic study of Luyten common proper motion (CPM) stars, spectrophotometric observations have been obtained of three binaries containing degenerate stars with estimated absolute magnitudes M(V) of about 16. Each of the three pairs consists of a yellow degenerate star primary and a DC 13 + secondary 1.4-2.3 mag fainter. One of the primary stars is spectral class DC 7, another is a sharp-lined DA 8, and the third shows peculiar broad absorption features which we interpret as pressure-shifted C2 Swan bands. The LP 701 - 69/70 system has survived for over 8 billion years without disruption by passing stars, despite its 1500 a.u. orbital major axis. The three cool degenerate companions nearly double the available sample of stars at the low-luminosity terminus of the white dwarf cooling sequence. These findings appear consistent with the conclusion that degenerate stars in the old disk population have not had time to evolve to a luminosity fainter than M(V) about 16.2.

From merging galaxies to quasars: The evolution of nuclear activity in luminous and ultraluminous infrared galaxies

NASA Astrophysics Data System (ADS)

Teng, Stacy H.

We present the largest X-ray survey (˜80 objects) of luminous and ultraluminous infrared galaxies (U/LIRGs) to date. The large infrared luminosities in these objects are thought to arise from either star formation triggered by the merging of disk galaxies or by nuclear activity. U/LIRGs have been purported to be the progenitors of some quasars. In this thesis, we utilize data from Chandra, XMM-Newton, and Suzaku X-ray observatories to quantify the contribution to the overall power of U/LIRGs by starbursts or active galactic nuclei (AGNs). A goal of this project is to statistically examine how the starburst-to-AGN ratio evolves as a function of merger stage. We find that a majority of U/LIRGs are X-ray faint. This may be a result of high obscuration or weak nuclear activity. The dearth of detected counts makes traditional fitting difficult. As a solution, we developed a method of using hardness ratios (HR) to estimate the spectral shapes of these weak sources. Both observational evidence and simulations show that this method is effective for sources with intrinsic column densities below ˜10 22 cm-2 and applicable to sources with only tens of detected counts. Applying the HR method and traditional spectral fitting to the U/LIRG data and that of 26 PG quasars, we find a correlation of AGN dominance with dust temperature, optical spectral type, and merger stage. The probability of having a powerful AGN increases along the merger sequence. However, the AGNs can turn on at any time, as evidenced by a large number of AGNs detected in binary U/LIRGs. Starburst dominates the total power in U/LIRGs prior to the merger. Then the black hole grows rapidly during coalescence. At this time, the AGN is likely to begin driving galactic scale winds which will quench star formation, resulting in a luminous quasar. These conclusions are in general agreement with results obtained at other wavelengths and current theoretical models.

Hot-Jupiter Breakfasts Realign Stars

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2015-08-01

Two researchers at the University of Chicago have recently developed a new theory to explain an apparent dichotomy in the orbits of planets around cool vs. hot stars. Their model proposes that the spins of cool stars are affected when they ingest hot Jupiters (HJs) early in their stellar lifetimes. A Puzzling Dichotomy: In exoplanet studies, there is a puzzling difference observed between planet orbits around cool and hot (those with Teff ≥ 6250 K) stars: the orbital planes of planets around cool stars are primarily aligned with the host star's spin, whereas the orbital planes of planets around hot stars seem to be randomly distributed. Previous attempts to explain this dichotomy have focused on tidal interactions between the host star and the planets observed in the system. Now Titos Matsakos and Arieh Königl have taken these models a step further — by including in their calculations not only the effects of observed planets, but also those of HJs that may have been swallowed by the star long before we observed the systems. Modeling Meals: Plots of the distribution of the obliquity λ for hot Jupiters around cool hosts (upper plot) and hot hosts (lower plot). The dashed line shows the initial distribution, the bins show the model prediction for the final distribution after the systems evolve, and the black dots show the current observational data. [Matsakos & Königl, 2015]" class="size-thumbnail wp-image-223" height="386" src="http://aasnova.org/wp-content/uploads/2015/08/fig22-260x386.png" width="260" /> Plots of the distribution of the obliquity λ for hot Jupiters around cool hosts (upper plot) and hot hosts (lower plot). The dashed line shows the initial distribution, the bins show the model prediction for the final distribution after the systems evolve, and the black dots show the current observational data. [Matsakos & Königl, 2015] The authors' model assumes that as HJs are formed and migrate inward through the protoplanetary disk, they stall out near the star (where they have periods of ~2 days) and get stranded as the gas disk evaporates around them. Tidal interactions can cause these planets to become ingested by the host star within 1 Gyr. Using Monte Carlo simulations, the authors model these star-planet tidal interactions and evolve a total of 10^6 systems: half with hot (Teff = 6400 K), main-sequence hosts, and half with cool (Teff = 5500 K), solar-type hosts. The initial obliquities — the angle between the stellar spin and the planets' orbital angular momentum vectors — are randomly distributed between 0° and 180°. The authors find that early stellar ingestion of planets might be very common: to match observations, roughly half of all stellar hosts must ingest an HJ early in their lifetimes! This scenario results in a good match with observational data: about 50% of cool hosts' spins become roughly aligned with the orbital plane of their planets after they absorb the orbital angular momentum of the HJ they ingest. Hot stars, on the other hand, generally retain their random distributions of obliquity, because their angular momentum is typically higher than the orbital angular momentum of the ingested planet. Citation: Titos Matsakos and Arieh Königl 2015, ApJ, 809, L20. doi: 10.1088/2041-8205/809/2/L20

Near--Infrared Imaging of the Starburst Ring in UGC12815

NASA Astrophysics Data System (ADS)

Smith, D. A.; Herter, T.; Haynes, M. P.; Neff, S. G.

1995-05-01

Starburst galaxies define an enigmatic class of objects undergoing a brief, intense episode of star formation. In order to investigate the nature of nearby starbursts, we have analyzed the 20 starburst galaxies with the highest 4.85 GHz luminosities from the survey of Condon, Frayer, & Broderick (1991, AJ, 101, 362) at infrared and optical wavelengths. As part of our study, we recently used the Cassegrain Infrared Camera at the Hale 5 m telescope to obtain high spatial resolution near--infrared images of the cores of 17 of these galaxies in order to better understand the starburst triggering mechanism. We find that one galaxy, UGC12815 (NGC7771), possesses a nucleus surrounded by a bright starburst ring. We present 1.25, 1.65, and 2.2 microns (J, H, and K band) images of the nuclear region of UGC12815 and a preliminary analysis of the properties of the starburst ring. The resolution of our K band image is 0.6('') FWHM. The ring is ~ 1.6 kpc (6('') ) in diameter assuming H_0=75 km/s/Mpc; several knots are detected in the ring at 2.2 microns. The spatial distribution of these knots is compared to that observed at 6 cm. The luminosities of the ring and nucleus, as mapped in the near--infrared and radio, are also discussed. Color maps (H-K and J-H) constructed from the near--infrared images trace the relative roles of extinction, and emission from evolved red stars, blue stars, thermal gas, and hot dust in the nucleus and starburst ring. A comparison between UGC12815 and other systems with circumnuclear starbursts is also made.

An evolutionary missing link? A modest-mass early-type galaxy hosting an oversized nuclear black hole

NASA Astrophysics Data System (ADS)

van Loon, Jacco Th.; Sansom, Anne E.

2015-11-01

SAGE1C J053634.78-722658.5 is a galaxy at redshift z = 0.14, discovered behind the Large Magellanic Cloud in the Spitzer Space Telescope`Surveying the Agents of Galaxy Evolution' Spectroscopy survey. It has very strong silicate emission at 10 μm but negligible far-IR and UV emission. This makes it a candidate for a bare active galactic nuclei (AGN) source in the IR, perhaps seen pole-on, without significant IR emission from the host galaxy. In this paper we present optical spectra taken with the Southern African Large Telescope to investigate the nature of the underlying host galaxy and its AGN. We find broad H α emission characteristic of an AGN, plus absorption lines associated with a mature stellar population (>9 Gyr), and refine its redshift determination to z = 0.1428 ± 0.0001. There is no evidence for any emission lines associated with star formation. This remarkable object exemplifies the need for separating the emission from any AGN from that of the host galaxy when employing IR diagnostic diagrams. We estimate the black hole mass, MBH = 3.5 ± 0.8 × 108 M⊙, host galaxy mass, M_stars=2.5^{2.5}_{1.2}× 10^{10} M⊙, and accretion luminosity, Lbol(AGN) = 5.3 ± 0.4 × 1045 erg s-1 (≈12 per cent of the Eddington luminosity), and find the AGN to be more prominent than expected for a host galaxy of this modest size. The old age is in tension with the downsizing paradigm in which this galaxy would recently have transformed from a star-forming disc galaxy into an early-type, passively evolving galaxy.

Homarine as a feeding deterrent in common shallow-water antarctic lamellarian gastropodMarseniopsis mollis: A rare example of chemical defense in a marine prosobranch.

PubMed

McClintock, J B; Baker, B J; Hamann, M T; Yoshida, W; Slattery, M; Heine, J N; Bryan, P J; Jayatilake, G S; Moon, B H

1994-10-01

The common bright yellow antarctic lamellarian gastropodMarseniopsis mollis was examined for the presence of defensive chemistry. Proton nuclear magnetic resonance (NMR) spectroscopy indicated that a major component of ethanolic extracts purified by reversed-phase column chromatography was homarine. Further high-performance liquid chromatography (HPLC) analysis of the mantle, foot, and viscera verified the presence of homarine in all body tissues at concentrations ranging from 6 to 24 mg/g dry tissue. A conspicuous macroinvertebrate predator of the shallow antarctic benthos, the sea starOdontaster validus, always rejected live individuals ofM. mollis, while readily feeding on pieces of fish tail muscle. Filter paper disks treated with shrimp elicited a broad range of feeding behaviors in the sea starO. validus (movement of disc to mouth, extrusion of cardiac stomach, humped feeding posture). Shrimp disks treated with homarine (0.4 and 4 mg/disk) were rejected byO. validus significantly more frequently than control disks treated with solvent carrier and shrimp or shrimp alone. The highest concentration of homarine tested not only caused feeding deterrence, but in several sea stars a flight response was noted. Homarine was not detected in the tunic of the antarctic ascidianCnemidocarpa verrucosa, a presumed primary prey ofM. mollis. Nonetheless, crude extracts of the epizooites that foul the tunic (primarily the bryozoans and hydroids) contain homarine, suggestingM. mollis may ingest and derive its chemistry from these organisms. This appears to be only the third example of chemical defense in a member of the Order Mesogastropoda. As the vestigial internalized shell ofM. mollis is considered a primitive condition, the findings of this study lend support to the hypothesis that chemical defense evolved prior to shell loss in shell-less gastropods.

THE HISTORY OF TIDAL DISRUPTION EVENTS IN GALACTIC NUCLEI

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

Aharon, Danor; Battisti, Alessandra Mastrobuono; Perets, Hagai B.

The tidal disruption of a star by a massive black hole (MBH) is thought to produce a transient luminous event. Such tidal disruption events (TDEs) may play an important role in the detection and characterization of MBHs, and in probing the properties and dynamics of their nuclear stellar cluster (NSC) hosts. Previous studies estimated the recent rates of TDEs in the local universe. However, the long-term evolution of the rates throughout the history of the universe has been little explored. Here we consider TDE history, using evolutionary models for the evolution of galactic nuclei. We use a 1D Fokker–Planck approachmore » to explore the evolution of MBH-hosting NSCs, and obtain the disruption rates of stars during their evolution. We complement these with an analysis of TDE history based on N -body simulation data, and find them to be comparable. We consider NSCs that are built up from close-in star formation (SF) or from far-out SF/cluster-dispersal, a few pc from the MBH. We also explore cases where primordial NSCs exist and later evolve through additional SF/cluster-dispersal processes. We study the dependence of the TDE history on the type of galaxy, as well as the dependence on the MBH mass. These provide several scenarios, with a continuous increase of the TDE rates over time for cases of far-out SF and a more complex behavior for the close-in SF cases. Finally, we integrate the TDE histories of the various scenarios to provide a total TDE history of the universe, which can be potentially probed with future large surveys (e.g., LSST).« less

General polytropic self-gravitating cylinder free-fall and accreting mass string with a chain of collapsed objects

NASA Astrophysics Data System (ADS)

Lou, Yu-Qing; Hu, Xu-Yao

2016-06-01

We present a theoretical model framework for general polytropic (GP) hydrodynamic cylinder under self-gravity of infinite length with axial uniformity and axisymmetry. For self-similar dynamic solutions, we derive valuable integrals, analytic asymptotic solutions, sonic critical curves, shock conditions, and global numerical solutions with or without expansion shocks. Among others, we investigate various dynamic solutions featured with central free-fall asymptotic behaviours, corresponding to a collapsed mass string with a sustained dynamic accretion from a surrounding mass reservoir. Depending on the allowed ranges of a scaling index a < -1, such cylindrical dynamic mass accretion rate could be steady, increasing with time and decreasing with time. Physically, such a collapsed mass string or filament would break up into a sequence of sub-clumps and segments as induced by gravitational Jeans instabilities. Depending on the scales involved, such sub-clumps would evolve into collapsed objects or gravitationally bound systems. In diverse astrophysical and cosmological contexts, such a scenario can be adapted on various temporal, spatial and mass scales to form a chain of collapsed clumps and/or compact objects. Examples include the formation of chains of proto-stars, brown dwarfs and gaseous planets along molecular filaments; the formation of luminous massive stars along magnetized spiral arms and circum-nuclear starburst rings in barred spiral galaxies; the formation of chains of compact stellar objects such as white dwarfs, neutron stars, and black holes along a highly condensed mass string. On cosmological scales, one can perceive the formation of chains of galaxies, chains of galaxy clusters or even chains of supermassive and hypermassive black holes in the Universe including the early Universe. All these chains referred to above include possible binaries.

Many-particle theory of nuclear systems with application to neutron star matter

NASA Technical Reports Server (NTRS)

Chakkalakal, D. A.; Yang, C. H.

1974-01-01

The energy-density relation was calculated for pure neutron matter in the density range relevant for neutron stars, using four different hard-core potentials. Calculations are also presented of the properties of the superfluid state of the neutron component, along with the superconducting state of the proton component and the effects of polarization in neutron star matter.

NuSTAR Inches Toward its Rocket

NASA Image and Video Library

2012-02-23

At Vandenberg Air Force Base processing facility in California, the separation ring on the aft end of NASA Nuclear Spectroscopic Telescope Array NuSTAR, at right, inches its way toward the third stage of an Orbital Sciences Pegasus XL rocket.

KSC-2012-3027

NASA Image and Video Library

2012-05-22

VANDENBERG AFB, Calif. – Technicians install the second half of the payload fairing over the NuSTAR spacecraft as they continue to process the spacecraft and its Pegasus rocket for launch. NuSTAR stands for Nuclear Spectroscopic Telescope Array. Photo credit: NASA/Randy Beaudoin

KSC-2012-3028

NASA Image and Video Library

2012-05-22

VANDENBERG AFB, Calif. – Technicians install the second half of the payload fairing over the NuSTAR spacecraft as they continue to process the spacecraft and its Pegasus rocket for launch. NuSTAR stands for Nuclear Spectroscopic Telescope Array. Photo credit: NASA/Randy Beaudoin

KSC-2012-3023

NASA Image and Video Library

2012-05-22

VANDENBERG AFB, Calif. – Technicians install one half of the payload fairing over the NuSTAR spacecraft as they continue to process the spacecraft and its Pegasus rocket for launch. NuSTAR stands for Nuclear Spectroscopic Telescope Array. Photo credit: NASA/Randy Beaudoin

KSC-2012-3026

NASA Image and Video Library

2012-05-22

VANDENBERG AFB, Calif. – Technicians install the second half of the payload fairing over the NuSTAR spacecraft as they continue to process the spacecraft and its Pegasus rocket for launch. NuSTAR stands for Nuclear Spectroscopic Telescope Array. Photo credit: NASA/Randy Beaudoin

KSC-2012-3022

NASA Image and Video Library

2012-05-22

VANDENBERG AFB, Calif. – Technicians install one half of the payload fairing over the NuSTAR spacecraft as they continue to process the spacecraft and its Pegasus rocket for launch. NuSTAR stands for Nuclear Spectroscopic Telescope Array. Photo credit: NASA/Randy Beaudoin

KSC-2012-3029

NASA Image and Video Library

2012-05-22

VANDENBERG AFB, Calif. – Technicians install the second half of the payload fairing over the NuSTAR spacecraft as they continue to process the spacecraft and its Pegasus rocket for launch. NuSTAR stands for Nuclear Spectroscopic Telescope Array. Photo credit: NASA/Randy Beaudoin

KSC-2012-3021

NASA Image and Video Library

2012-05-22

VANDENBERG AFB, Calif. – Technicians install one half of the payload fairing over the NuSTAR spacecraft as they continue to process the spacecraft and its Pegasus rocket for launch. NuSTAR stands for Nuclear Spectroscopic Telescope Array. Photo credit: NASA/Randy Beaudoin

KSC-2012-3024

NASA Image and Video Library

2012-05-22

VANDENBERG AFB, Calif. – Technicians install one half of the payload fairing over the NuSTAR spacecraft as they continue to process the spacecraft and its Pegasus rocket for launch. NuSTAR stands for Nuclear Spectroscopic Telescope Array. Photo credit: NASA/Randy Beaudoin

KSC-2012-3030

NASA Image and Video Library

2012-05-22

VANDENBERG AFB, Calif. – A technicians checks the installation of the payload fairing over the NuSTAR spacecraft as processing continues for the spacecraft and its Pegasus rocket for launch. NuSTAR stands for Nuclear Spectroscopic Telescope Array. Photo credit: NASA/Randy Beaudoin

The evolving magnetic topology of τ Boötis

NASA Astrophysics Data System (ADS)

Mengel, M. W.; Fares, R.; Marsden, S. C.; Carter, B. D.; Jeffers, S. V.; Petit, P.; Donati, J.-F.; Folsom, C. P.; BCool Collaboration

2016-07-01

We present six epochs of spectropolarimetric observations of the hot-Jupiter-hosting star τ Boötis that extend the exceptional previous multiyear data set of its large-scale magnetic field. Our results confirm that the large-scale magnetic field of τ Boötis varies cyclicly, with the observation of two further magnetic reversals; between 2013 December and 2014 May and between 2015 January and March. We also show that the field evolves in a broadly solar-type manner in contrast to other F-type stars. We further present new results which indicate that the chromospheric activity cycle and the magnetic activity cycles are related, which would indicate a very rapid magnetic cycle. As an exemplar of long-term magnetic field evolution, τ Boötis and this long-term monitoring campaign presents a unique opportunity for studying stellar magnetic cycles.

Infrared emission and mass loss from evolved stars in elliptical galaxies

NASA Technical Reports Server (NTRS)

Knapp, G. R.; Gunn, J. E.; Wynn-Williams, C. G.

1992-01-01

Small aperture 10.2-micron measurements of normal elliptical galaxies show that for almost all of these galaxies the 12-micron emission seen by IRAS is extended on the scale of the galaxy. NGC 1052 and NGC 3998 are exceptions to this; much of their 10-12-micron emission comes from the inner regions of the galaxies and may be associated with their active nuclei, as is the case for many radio galaxies. The distribution of the IR light and the IR colors of elliptical galaxies suggest that the most plausible source of the 12-micron emission is photospheric and circumstellear emission from cool evolved red giant stars. The 12-micron emission is well in excess of that expected from photospheric emission alone; about 40 percent of it probably comes from circumstellar dust.

A M2FS Spectroscopic Study of Low-mass Young Stars in Orion OB1

NASA Astrophysics Data System (ADS)

Kaleida, Catherine C.; Briceno, Cesar; Calvet, Nuria; Mateo, Mario L.; Hernandez, Jesus

2015-01-01

Surveys of pre-main sequence stars in the ~4-10 Myr range provide a window into the decline of the accretion phase of stars and the formation of planets. Nearby star clusters and stellar associations allow for the study of these young stellar populations all the way down to the lowest mass members. One of the best examples of nearby 4-10 Myr old stellar populations is the Orion OB1 association. The CIDA Variability Survey of Orion OB1 (CVSO - Briceño et al. 2001) has used the variability properties of low-mass pre-main-sequence (PMS) stars to identify hundreds of K and M-type stellar members of the Orion OB1 association, a number of them displaying IR-excess emission and thought to be representative of more evolved disk-bearing young stars. Characterizing these young, low-mass objects using spectroscopy is integral to understanding the accretion phase in young stars. We present preliminary results of a spectroscopic survey of candidate and confirmed Orion OB1 low-mass members taken during November 2014 and February 2014 using the Michigan/Magellan Fiber Spectrograph (M2FS), a PI instrument on the Magellan Clay Telescope (PI: M. Matteo). Target fields located in the off-cloud regions of Orion were identified in the CVSO, and observed using the low and high-resolution modes of M2FS. Both low and high-resolution spectra are needed in order to confirm membership and derive masses, ages, kinematics and accretion properties. Initial analysis of these spectra reveal many new K and M-type members of the Orion OB1 association in these low extinction, off-cloud areas. These are the more evolved siblings of the youngest stars still embedded in the molecular clouds, like those in the Orion Nebula Cluster. With membership and spectroscopic indicators of accretion we are building the most comprehensive stellar census of this association, enabling us to derive a robust estimate of the fraction of young stars still accreting at a various ages, a key constraint for the end of accretion and the formation of giant planets.

Kepler-432: A Red Giant Interacting with One of its Two Long-period Giant Planets

NASA Astrophysics Data System (ADS)

Quinn, Samuel N.; White, Timothy. R.; Latham, David W.; Chaplin, William J.; Handberg, Rasmus; Huber, Daniel; Kipping, David M.; Payne, Matthew J.; Jiang, Chen; Silva Aguirre, Victor; Stello, Dennis; Sliski, David H.; Ciardi, David R.; Buchhave, Lars A.; Bedding, Timothy R.; Davies, Guy R.; Hekker, Saskia; Kjeldsen, Hans; Kuszlewicz, James S.; Everett, Mark E.; Howell, Steve B.; Basu, Sarbani; Campante, Tiago L.; Christensen-Dalsgaard, Jørgen; Elsworth, Yvonne P.; Karoff, Christoffer; Kawaler, Steven D.; Lund, Mikkel N.; Lundkvist, Mia; Esquerdo, Gilbert A.; Calkins, Michael L.; Berlind, Perry

2015-04-01

We report the discovery of Kepler-432b, a giant planet ({{M}b}=5.41-0.18+0.32 {{M}Jup}, {{R}b}=1.145-0.039+0.036 {{R}Jup}) transiting an evolved star ({{M}\\star }=1.32-0.07+0.10 {{M}⊙ },{{R}\\star }=4.06-0.08+0.12 {{R}⊙ }) with an orbital period of {{P}b}=52.501129-0.000053+0.000067 days. Radial velocities (RVs) reveal that Kepler-432b orbits its parent star with an eccentricity of e=0.5134-0.0089+0.0098, which we also measure independently with asterodensity profiling (AP; e=0.507-0.114+0.039), thereby confirming the validity of AP on this particular evolved star. The well-determined planetary properties and unusually large mass also make this planet an important benchmark for theoretical models of super-Jupiter formation. Long-term RV monitoring detected the presence of a non-transiting outer planet (Kepler-432c; {{M}c}sin {{i}c}=2.43-0.24+0.22 {{M}Jup}, {{P}c}=406.2-2.5+3.9 days), and adaptive optics imaging revealed a nearby (0\\buildrel{\\prime\\prime}\\over{.} 87), faint companion (Kepler-432B) that is a physically bound M dwarf. The host star exhibits high signal-to-noise ratio asteroseismic oscillations, which enable precise measurements of the stellar mass, radius, and age. Analysis of the rotational splitting of the oscillation modes additionally reveals the stellar spin axis to be nearly edge-on, which suggests that the stellar spin is likely well aligned with the orbit of the transiting planet. Despite its long period, the obliquity of the 52.5 day orbit may have been shaped by star-planet interaction in a manner similar to hot Jupiter systems, and we present observational and theoretical evidence to support this scenario. Finally, as a short-period outlier among giant planets orbiting giant stars, study of Kepler-432b may help explain the distribution of massive planets orbiting giant stars interior to 1 AU.

A spectroscopic and photometric study of the unique pre- main sequence system KH 15D

NASA Astrophysics Data System (ADS)

Hamilton, Catrina Marie

2004-09-01

As a class, T Tauri stars are YSOs, some which are surrounded by circumstellar disks, and are recognized as the final stage of low-mass star formation. They also represent the earliest stage of stellar evolution that is optically visible, and, therefore, can be easily studied in detail. Understanding the processes through which these young stars interact with and eventually disperse their circumstellar disks is critical for understanding how they evolve from the T Tauri phase to the zero age main sequence (ZAMS), and how this affects the formation of planets, as well as their rotational evolution. KH 15D is a unique eclipsing system that could provide invaluable insight into the evolution of circumstellar disk material, as well as clues to the close stellar environment. Discovered in 1997, this star system has been observed to undergo an eclipse every 48 days in which the star's light is diminished by 3.5 magnitudes. What is so unusual about the eclipse is that the length of the eclipse has evolved over time, growing in length from 16 days initially, to ˜25 days in 2002/2003. Evolution of disk material on these timescales has never been observed before, and therefore provides us with a unique opportunity to refine our theories about remnant disks around young stars, how they transition, possibly into planets, and what role they play as the star matures and arrives on the zero age main sequence. Additionally, high resolution spectra obtained at specific phases during the December 2001 eclipse showed that as the obscuring matter cut across the star, dramatic spectral changes in the Hα and Hβ lines were seen. Its unique eclipse produces a “natural coronographic” effect in which the stellar photosphere is occulted, revealing details of its magnetosphere and surroundings during eclipse. There is evidence that the weak-lined T Tauri star (WTTS) central to the system is actively accreting gas, although probably not at the rate of a typical classical T Tauri star, calling into question the common practice of associating WTTS characteristics with the absence of an accretion disk. Here I present an investigation of the photometric and spectroscopic properties of the KH 15D eclipsing system, and discuss the implications that this system holds for the future research of T Tauri stars.

International trade and waste and fuel management issue, 2009

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

Agnihotri, Newal

The focus of the January-February issue is on international trade and waste and fuel managment. Major articles/reports in this issue include: Innovative financing and workforce planning, by Donna Jacobs, Entergy Nuclear; Nuclear power - a long-term need, by John C. Devine, Gerald Goldsmith and Michael DeLallo, WorleyParsons; Importance of loan guarantee program, by Donald Hintz; EPC contracts for new plants, by Dave Barry, Shaw Power Group; GNEP and fuel recycling, by Alan Hanson, AREVA NC Inc.; Safe and reliable reactor, by Kiyoshi Yamauchi, Mitsubishi Heavy Industries, Ltd.; Safe, small and simple reactors, by Yoshi Sakashita, Toshiba Corporation; Nuclear power inmore » Thailand, by Tatchai Sumitra, Thailand Institute of Nuclear Technology; and, Nuclear power in Vietnam, by Tran Huu Phat, Vietnam Atomic Energy Commission. The Industry Innovation article this issue is Rectifying axial-offset-anomaly problems, by Don Adams, Tennessee Valley Authority. The Plant Profile article is Star of Stars Excellence, by Tyler Lamberts, Entergy Nuclear Operations, Inc.« less

Hubble Observes One-of-a-Kind Star Nicknamed ‘Nasty’

NASA Image and Video Library

2015-03-21

Astronomers using NASA’s Hubble Space Telescope have uncovered surprising new clues about a hefty, rapidly aging star whose behavior has never been seen before in our Milky Way galaxy. In fact, the star is so weird that astronomers have nicknamed it “Nasty 1,” a play on its catalog name of NaSt1. The star may represent a brief transitory stage in the evolution of extremely massive stars. First discovered several decades ago, Nasty 1 was identified as a Wolf-Rayet star, a rapidly evolving star that is much more massive than our sun. The star loses its hydrogen-filled outer layers quickly, exposing its super-hot and extremely bright helium-burning core. But Nasty 1 doesn’t look like a typical Wolf-Rayet star. The astronomers using Hubble had expected to see twin lobes of gas flowing from opposite sides of the star, perhaps similar to those emanating from the massive star Eta Carinae, which is a Wolf-Rayet candidate. Instead, Hubble revealed a pancake-shaped disk of gas encircling the star. The vast disk is nearly 2 trillion miles wide, and may have formed from an unseen companion star that snacked on the outer envelope of the newly formed Wolf-Rayet. Based on current estimates, the nebula surrounding the stars is just a few thousand years old, and as close as 3,000 light-years from Earth. Credits: NASA/Hubble

The Magnetic Properties of Galactic OB Stars from the Magnetism in Massive Stars Project

NASA Astrophysics Data System (ADS)

Wade, Gregg A.; Grunhut, Jason; Petit, Veronique; Neiner, Coralie; Alecian, Evelyne; Landstreet, John; MiMeS Collaboration

2013-06-01

The Magnetism in Massive Stars (MiMeS) project represents the largest systematic survey of stellar magnetism ever undertaken. Comprising nearly 4500 high resolution polarised spectra of nearly 550 Galactic B and O-type stars, the MiMeS survey aims to address interesting and fundamental questions about the magnetism of hot, massive stars: How and when are massive star magnetic fields generated, and how do they evolve throughout stellar evolution? How do magnetic fields couple to and interact with the powerful winds of OB stars, and what are the consequences for the wind structure, momentum flux and energetics? What are the detailed physical mechanisms that lead to the anomalously slow rotation of many magnetic massive stars? What is the ultimate impact of stellar magnetic fields -- both direct and indirect -- on the evolution of massive stars? In this talk we report results from the analysis of the B-type stars observed within the MiMeS survey. The sample consists of over 450 stars ranging in spectral type from B9 to B0, and in evolutionary stage from the pre-main sequence to the post-main sequence. In addition to general statistical results concerning field incidence, strength and topology, we will elaborate our conclusions for subsamples of special interest, including the Herbig and classical Be stars, pulsating B stars and chemically peculiar B stars.

A spectroscopic survey of the WNL stars in the Large Magellanic Cloud: General properties and binary status

NASA Astrophysics Data System (ADS)

Schnurr, Olivier

2008-09-01

This thesis presents the results of an intense, spectroscopic survey of 41 of the 47 known, late-type, nitrogen-rich Wolf-Rayet (WR) stars in the Large Magellanic Cloud (LMC) which could be observed with ground-based, optical telescopes. For the study of the remaining 6 WNL located in the extremely dense central object of 30 Dor, R136, adaptive-optics assisted, near-infrared spectroscopy was required. The results of this study will be published elsewhere. Our survey concludes the decade-long effort of the Montreal Massive-Star Group to monitor all known WR stars in the Magellanic Clouds for radial-velocity (RV) variations due to binarity, a point which has been debated since the true, evolved nature of WR stars has been recognized in the late 1960s. From model calculations, it was expected that with decreasing metallicity, the binary frequency among WR stars increases, or otherwise the progenitor stars could not have turned into a WR star. Our survey set out to observationally test this assumption. After summarizing the general importance of massive stars, we describe the spectroscopic observations of our program stars. We then detail the data analysis process, which encompasses careful calibration and proper choice of RV standards. We also include publicly available, visible and X-ray photometric data in our analysis. We are able to identify four previously unknown binaries in our sample, bringing the total number of known WNL binaries in the LMC to only nine. As a direct result, we question the assumption that binarity is required to form WR stars at lower metallicity. At least some of the hydrogen-containing WNL stars in our sample seem not to be genuine, evolved, helium-burning WR stars, but rather unevolved, hydrogen- burning objects. There is ample evidence that some of these stars are the most massive stars known. As a second and most remarkable result, all but one of our nine binaries harbor such extreme objects; this greatly enlarges the sample of such known binaries, and paves the way for an independent mass determination via Keplerian orbits in further studies, some of which we have already initiated. The results of those studies will be crucial for calibrating stellar models. One of these binaries, R145, is then studied in greater detail, combining previously published and unpublished data with ours, to present, for the first time, a full set of orbital parameters for both components of the binary system. Since we also determine the orbital inclination angle, we are able to derive the absolute masses of this extreme object. It is found that R145 very likely harbors the most massive star known and properly "weighed" so far.

Ultra-stripped supernovae: progenitors and fate

NASA Astrophysics Data System (ADS)

Tauris, Thomas M.; Langer, Norbert; Podsiadlowski, Philipp

2015-08-01

The explosion of ultra-stripped stars in close binaries can lead to ejecta masses <0.1 M⊙ and may explain some of the recent discoveries of weak and fast optical transients. In Tauris et al., it was demonstrated that helium star companions to neutron stars (NSs) may experience mass transfer and evolve into naked ˜1.5 M⊙ metal cores, barely above the Chandrasekhar mass limit. Here, we elaborate on this work and present a systematic investigation of the progenitor evolution leading to ultra-stripped supernovae (SNe). In particular, we examine the binary parameter space leading to electron-capture (EC SNe) and iron core-collapse SNe (Fe CCSNe), respectively, and determine the amount of helium ejected with applications to their observational classification as Type Ib or Type Ic. We mainly evolve systems where the SN progenitors are helium star donors of initial mass MHe = 2.5-3.5 M⊙ in tight binaries with orbital periods of Porb = 0.06-2.0 d, and hosting an accreting NS, but we also discuss the evolution of wider systems and of both more massive and lighter - as well as single - helium stars. In some cases, we are able to follow the evolution until the onset of silicon burning, just a few days prior to the SN explosion. We find that ultra-stripped SNe are possible for both EC SNe and Fe CCSNe. EC SNe only occur for MHe = 2.60-2.95 M⊙ depending on Porb. The general outcome, however, is an Fe CCSN above this mass interval and an ONeMg or CO white dwarf for smaller masses. For the exploding stars, the amount of helium ejected is correlated with Porb - the tightest systems even having donors being stripped down to envelopes of less than 0.01 M⊙. We estimate the rise time of ultra-stripped SNe to be in the range 12 h-8 d, and light-curve decay times between 1 and 50 d. A number of fitting formulae for our models are provided with applications to population synthesis. Ultra-stripped SNe may produce NSs in the mass range 1.10-1.80 M⊙ and are highly relevant for LIGO/VIRGO since most (possibly all) merging double NS systems have evolved through this phase. Finally, we discuss the low-velocity kicks which might be imparted on these resulting NSs at birth.

Kepler sheds new and unprecedented light on the variability of a blue supergiant: Gravity waves in the O9.5Iab star HD 188209

NASA Astrophysics Data System (ADS)

Aerts, C.; Símon-Díaz, S.; Bloemen, S.; Debosscher, J.; Pápics, P. I.; Bryson, S.; Still, M.; Moravveji, E.; Williamson, M. H.; Grundahl, F.; Fredslund Andersen, M.; Antoci, V.; Pallé, P. L.; Christensen-Dalsgaard, J.; Rogers, T. M.

2017-06-01

Stellar evolution models are most uncertain for evolved massive stars. Asteroseismology based on high-precision uninterrupted space photometry has become a new way to test the outcome of stellar evolution theory and was recently applied to a multitude of stars, but not yet to massive evolved supergiants.Our aim is to detect, analyse and interpret the photospheric and wind variability of the O9.5 Iab star HD 188209 from Kepler space photometry and long-term high-resolution spectroscopy. We used Kepler scattered-light photometry obtained by the nominal mission during 1460 d to deduce the photometric variability of this O-type supergiant. In addition, we assembled and analysed high-resolution high signal-to-noise spectroscopy taken with four spectrographs during some 1800 d to interpret the temporal spectroscopic variability of the star. The variability of this blue supergiant derived from the scattered-light space photometry is in full in agreement with the one found in the ground-based spectroscopy. We find significant low-frequency variability that is consistently detected in all spectral lines of HD 188209. The photospheric variability propagates into the wind, where it has similar frequencies but slightly higher amplitudes. The morphology of the frequency spectra derived from the long-term photometry and spectroscopy points towards a spectrum of travelling waves with frequency values in the range expected for an evolved O-type star. Convectively-driven internal gravity waves excited in the stellar interior offer the most plausible explanation of the detected variability. Based on photometric observations made with the NASA Kepler satellite and on spectroscopic observations made with four telescopes: the Nordic Optical Telescope operated by NOTSA and the Mercator Telescope operated by the Flemish Community, both at the Observatorio del Roque de los Muchachos (La Palma, Spain) of the Instituto de Astrofísica de Canarias, the T13 2.0 m Automatic Spectroscopic Telescope (AST) operated by Tennessee State University at the Fairborn Observatory, and the Hertzsprung SONG telescope operated on the Spanish Observatorio del Teide on the island of Tenerife by the Aarhus and Copenhagen Universities and by the Instituto de Astrofísica de Canarias, Spain.

Tracking Advanced Planetary Systems (TAPAS) with HARPS-N. IV. TYC 3667-1280-1: The most massive red giant star hosting a warm Jupiter

NASA Astrophysics Data System (ADS)

Niedzielski, A.; Villaver, E.; Nowak, G.; Adamów, M.; Maciejewski, G.; Kowalik, K.; Wolszczan, A.; Deka-Szymankiewicz, B.; Adamczyk, M.

2016-05-01

Context. We present the latest result of the TAPAS project that is devoted to intense monitoring of planetary candidates that are identified within the PennState-Toruń planet search. Aims: We aim to detect planetary systems around evolved stars to be able to build sound statistics on the frequency and intrinsic nature of these systems, and to deliver in-depth studies of selected planetary systems with evidence of star-planet interaction processes. Methods: The paper is based on precise radial velocity measurements: 13 epochs collected over 1920 days with the Hobby-Eberly Telescope and its High-Resolution Spectrograph, and 22 epochs of ultra-precise HARPS-N data collected over 961 days. Results: We present a warm-Jupiter (Teq = 1350 K, m2 sin I = 5.4 ± 0.4 MJ) companion with an orbital period of 26.468 days in a circular (e = 0.036) orbit around a giant evolved (log g = 3.11 ± 0.09, R = 6.26 ± 0.86 R⊙) star with M⋆ = 1.87 ± 0.17 M⊙. This is the most massive and oldest star found to be hosting a close-in giant planet. Its proximity to its host (a = 0.21 au) means that the planet has a 13.9 ± 2.0% probability of transits; this calls for photometric follow-up study. Conclusions: This massive warm Jupiter with a near circular orbit around an evolved massive star can help set constraints on general migration mechanisms for warm Jupiters and, given its high equilibrium temperature, can help test energy deposition models in hot Jupiters. Based on observations obtained with the Hobby-Eberly Telescope, which is a joint project of the University of Texas at Austin, the Pennsylvania State University, Stanford University, Ludwig-Maximilians-Universität München, and Georg-August-Universität Göttingen.Based on observations made with the Italian Telescopio Nazionale Galileo (TNG) operated on the island of La Palma by the Fundación Galileo Galilei of the INAF (Istituto Nazionale di Astrofisica) at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.

Simultaneous 183 GHz H2O maser and SiO observations towards evolved stars using APEX SEPIA Band 5

NASA Astrophysics Data System (ADS)

Humphreys, E. M. L.; Immer, K.; Gray, M. D.; De Beck, E.; Vlemmings, W. H. T.; Baudry, A.; Richards, A. M. S.; Wittkowski, M.; Torstensson, K.; De Breuck, C.; Møller, P.; Etoka, S.; Olberg, M.

2017-07-01

Aims: The aim is to investigate the use of 183 GHz H2O masers for characterization of the physical conditions and mass loss process in the circumstellar envelopes of evolved stars. Methods: We used APEX SEPIA Band 5 (an ALMA Band 5 receiver on the APEX telescope) to observe the 183 GHz H2O line towards two red supergiant (RSG) and three asymptotic giant branch (AGB) stars. Simultaneously, we observed the J = 4-3 line for 28SiO v = 0, 1, 2 and 3, and for 29SiO v = 0 and 1. We compared the results with simulations and radiative transfer models for H2O and SiO, and examined data for the individual linear orthogonal polarizations. Results: We detected the 183 GHz H2O line towards all the stars with peak flux densities >100 Jy, including a new detection from VY CMa. Towards all five targets, the water line had indications of being caused by maser emission and had higher peak flux densities than for the SiO lines. The SiO lines appear to originate from both thermal and maser processes. Comparison with simulations and models indicate that 183 GHz maser emission is likely to extend to greater radii in the circumstellar envelopes than SiO maser emission and to similar or greater radii than water masers at 22, 321 and 325 GHz. We speculate that a prominent blue-shifted feature in the W Hya 183 GHz spectrum is amplifying the stellar continuum, and is located at a similar distance from the star as mainline OH maser emission. We note that the coupling of an SiO maser model to a hydrodynamical pulsating model of an AGB star yields qualitatively similar simulated results to the observations. From a comparison of the individual polarizations, we find that the SiO maser linear polarization fraction of several features exceeds the maximum fraction allowed under standard maser assumptions and requires strong anisotropic pumping of the maser transition and strongly saturated maser emission. The low polarization fraction of the H2O maser however, fits with the expectation for a non-saturated maser. Conclusions: 183 GHz H2O masers can provide strong probes of the mass loss process of evolved stars. Higher angular resolution observations of this line using ALMA Band 5 will enable detailed investigation of the emission location in circumstellar envelopes and can also provide information on magnetic field strength and structure.

The evolution of massive stars including mass loss - Presupernova models and explosion

NASA Technical Reports Server (NTRS)

Woosley, S. E.; Langer, Norbert; Weaver, Thomas A.

1993-01-01

The evolution of massive stars of 35, 40, 60, and 85 solar masses is followed through all stages of nuclear burning to the point of Fe core collapse. Critical nuclear reaction and mass-loss rates are varied. Efficient mass loss during the Wolf-Rayet (WR) stage is likely to lead to final masses as small as 4 solar masses. For a reasonable parameterization of the mass loss, there may be convergence of all WR stars, both single and in binaries, to a narrow band of small final masses. Our representative model, a 4.25 solar-mass WR presupernova derived from a 60 solar mass star, is followed through a simulated explosion, and its explosive nucleosynthesis and light curve are determined. Its properties are similar to those observed in Type Ib supernovae. The effects of the initial mass and mass loss on the presupernova structure of small mass WR models is also explored. Important properties of the presupernova star and its explosion can only be obtained by following the complete evolution starting on the main sequence.

NuSTAR on-ground calibration: II. Effective area

NASA Astrophysics Data System (ADS)

Brejnholt, Nicolai F.; Christensen, Finn E.; Westergaard, Niels J.; Hailey, Charles J.; Koglin, Jason E.; Craig, William W.

2012-09-01

The Nuclear Spectroscopic Telescope ARray (NuSTAR) was launched in June 2012 carrying the first focusing hard X-ray (5-80keV) optics to orbit. The multilayer coating was carried out at the Technical University of Denmark (DTU Space). In this article we introduce the NuSTAR multilayer reference database and its implementation in the NuSTAR optic response model. The database and its implementation is validated using on-ground effective area calibration data and used to estimate in-orbit performance.

Role of strangeness to the neutron star mass and cooling

NASA Astrophysics Data System (ADS)

Lee, Chang-Hwan; Lim, Yeunhwan; Hyun, Chang Ho; Kwak, Kyujin

2018-01-01

Neutron star provides unique environments for the investigation of the physics of extreme dense matter beyond normal nuclear saturation density. In such high density environments, hadrons with strange quarks are expected to play very important role in stabilizing the system. Kaons and hyperons are the lowest mass states with strangeness among meson and bayron families, respectively. In this work, we investigate the role of kaons and hyperons to the neutron star mass, and discuss their role in the neutron star cooling.

Neutron star moments of inertia

NASA Technical Reports Server (NTRS)

Ravenhall, D. G.; Pethick, C. J.

1994-01-01

An approximation for the moment of inertia of a neutron star in terms of only its mass and radius is presented, and insight into it is obtained by examining the behavior of the relativistic structural equations. The approximation is accurate to approximately 10% for a variety of nuclear equations of state, for all except very low mass stars. It is combined with information about the neutron-star crust to obtain a simple expression (again in terms only of mass and radius) for the fractional moment of inertia of the crust.

Yellow evolved stars in open clusters

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

Sowell, J.R.

1987-05-01

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

Non-Equilibrium Chemistry of O-Rich AGB Stars as Revealed by ALMA

NASA Astrophysics Data System (ADS)

Wong, Ka Tat

2018-04-01

Chemical models suggest that pulsation driven shocks propagating from the stellar surfaces of oxygen-rich evolved stars to the dust formation zone trigger non-equilibrium chemistry in the shocked gas near the star, including the formation of carbon-bearing molecules in the stellar winds dominated by oxygen-rich chemistry. Recent long-baseline ALMA observations are able to give us a detailed view of the molecular line emission and absorption at an angular resolution of a few stellar radii. I am going to present the latest results from the ALMA observations of IK Tau and o Cet in late 2017, with a particular focus on HCN.

Spots and the Activity of Stars in the Hyades Cluster from Observations with the Kepler Space Telescope (K2)

NASA Astrophysics Data System (ADS)

Savanov, I. S.; Dmitrienko, E. S.

2018-03-01

Observations of the K2 mission (continuing the program of the Kepler Space Telescope) are used to estimate the spot coverage S (the fractional area of spots on the surface of an active star) for stars of the Hyades cluster. The analysis is based on data on the photometric variations of 47 confirmed single cluster members, together with their atmospheric parameters, masses, and rotation periods. The resulting values of S for these Hyades objects are lower than those stars of the Pleiades cluster (on average, by Δ S 0.05-0.06). A comparison of the results of studies of cool, low-mass dwarfs in the Hyades and Pleiades clusters, as well as the results of a study of 1570 M stars from the main field observed in the Kepler SpaceMission, indicates that the Hyades stars are more evolved than the Pleiades stars, and demonstrate lower activity. The activity of seven solar-type Hyades stars ( S = 0.013 ± 0.006) almost approaches the activity level of the present-day Sun, and is lower than the activity of solar-mass stars in the Pleiades ( S = 0.031 ± 0.003). Solar-type stars in the Hyades rotate faster than the Sun (< P> = 8.6 d ), but slower than similar Pleiades stars.

X-ray technology behind NASA's black-hole hunter (NuSTAR)

ScienceCinema

Craig, Bill

2018-05-18

Livermore Lab astrophysicist Bill Craig describes his team's role in developing X-ray imaging technology for the NASA Nuclear Spectroscopic Telescope Array (NuSTAR) mission. The black-hole-hunting spacecraft bagged its first 10 supermassive black holes this week.