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Sample records for metal-poor binary star

  1. High-resolution spectroscopy of extremely metal-poor stars from SDSS/Segue. II. Binary fraction

    SciTech Connect

    Aoki, Wako; Suda, Takuma; Beers, Timothy C.; Honda, Satoshi E-mail: takuma.suda@nao.ac.jp E-mail: honda@nhao.jp

    2015-02-01

    The fraction of binary systems in various stellar populations of the Galaxy and the distribution of their orbital parameters are important but not well-determined factors in studies of star formation, stellar evolution, and Galactic chemical evolution. While observational studies have been carried out for a large sample of nearby stars, including some metal-poor Population II stars, almost no constraints on the binary nature for extremely metal-poor (EMP; [Fe/H] <−3.0) stars have yet been obtained. Here we investigate the fraction of double-lined spectroscopic binaries and carbon-enhanced metal-poor (CEMP) stars, many of which could have formed as pairs of low-mass and intermediate-mass stars, to estimate the lower limit of the fraction of binary systems having short periods. The estimate is based on a sample of very metal-poor stars selected from the Sloan Digital Sky Survey and observed at high spectral resolution in a previous study by Aoki et al. That survey reported 3 double-lined spectroscopic binaries and 11 CEMP stars, which we consider along with a sample of EMP stars from the literature compiled in the SAGA database. We have conducted measurements of the velocity components for stacked absorption features of different spectral lines for each double-lined spectroscopic binary. Our estimate indicates that the fraction of binary stars having orbital periods shorter than 1000 days is at least 10%, and possibly as high as 20% if the majority of CEMP stars are formed in such short-period binaries. This result suggests that the period distribution of EMP binary systems is biased toward short periods, unless the binary fraction of low-mass EMP stars is significantly higher than that of other nearby stars.

  2. High-Resolution Spectroscopy of Extremely Metal-Poor Stars from SDSS/SEGUE. II. Binary Fraction

    NASA Astrophysics Data System (ADS)

    Aoki, Wako; Suda, Takuma; Beers, Timothy C.; Honda, Satoshi

    2015-02-01

    The fraction of binary systems in various stellar populations of the Galaxy and the distribution of their orbital parameters are important but not well-determined factors in studies of star formation, stellar evolution, and Galactic chemical evolution. While observational studies have been carried out for a large sample of nearby stars, including some metal-poor Population II stars, almost no constraints on the binary nature for extremely metal-poor (EMP; [Fe/H] \\lt -3.0) stars have yet been obtained. Here we investigate the fraction of double-lined spectroscopic binaries and carbon-enhanced metal-poor (CEMP) stars, many of which could have formed as pairs of low-mass and intermediate-mass stars, to estimate the lower limit of the fraction of binary systems having short periods. The estimate is based on a sample of very metal-poor stars selected from the Sloan Digital Sky Survey and observed at high spectral resolution in a previous study by Aoki et al. That survey reported 3 double-lined spectroscopic binaries and 11 CEMP stars, which we consider along with a sample of EMP stars from the literature compiled in the SAGA database. We have conducted measurements of the velocity components for stacked absorption features of different spectral lines for each double-lined spectroscopic binary. Our estimate indicates that the fraction of binary stars having orbital periods shorter than 1000 days is at least 10%, and possibly as high as 20% if the majority of CEMP stars are formed in such short-period binaries. This result suggests that the period distribution of EMP binary systems is biased toward short periods, unless the binary fraction of low-mass EMP stars is significantly higher than that of other nearby stars.

  3. Modelling the observed properties of carbon-enhanced metal-poor stars using binary population synthesis

    NASA Astrophysics Data System (ADS)

    Abate, C.; Pols, O. R.; Stancliffe, R. J.; Izzard, R. G.; Karakas, A. I.; Beers, T. C.; Lee, Y. S.

    2015-09-01

    The stellar population in the Galactic halo is characterised by a large fraction of carbon-enhanced metal-poor (CEMP) stars. Most CEMP stars have enhanced abundances of s-process elements (CEMP-s stars), and some of these are also enriched in r-process elements (CEMP-s/r stars). In one formation scenario proposed for CEMP stars, the observed carbon excess is explained by invoking wind mass transfer in the past from a more massive thermally-pulsing asymptotic giant branch (AGB) primary star in a binary system.In this work we generate synthetic populations of binary stars at metallicity Z = 0.0001 ([Fe/H] ≈ - 2.3), with the aim of reproducing the observed fraction of CEMP stars in the halo. In addition, we aim to constrain our model of the wind mass-transfer process, in particular the wind-accretion efficiency and angular-momentum loss, and investigate under which conditions our model populations reproduce observed distributions of element abundances.We compare the CEMP fractions determined from our synthetic populations and the abundance distributions of many elements with observations. Several physical parameters of the binary stellar population of the halo are uncertain, in particular the initial mass function, the mass-ratio distribution, the orbital-period distribution, and the binary fraction. We vary the assumptions in our model about these parameters, as well as the wind mass-transfer process, and study the consequent variations of our synthetic CEMP population.The CEMP fractions calculated in our synthetic populations vary between 7% and 17%, a range consistent with the CEMP fractions among very metal-poor stars recently derived from the SDSS/SEGUE data sample. The resulting fractions are more than a factor of three higher than those determined with default assumptions in previous population-synthesis studies, which typically underestimated the observed CEMP fraction. We find that most CEMP stars in our simulations are formed in binary systems with periods

  4. Binary properties of CH and carbon-enhanced metal-poor stars

    NASA Astrophysics Data System (ADS)

    Jorissen, A.; Van Eck, S.; Van Winckel, H.; Merle, T.; Boffin, H. M. J.; Andersen, J.; Nordström, B.; Udry, S.; Masseron, T.; Lenaerts, L.; Waelkens, C.

    2016-02-01

    The HERMES spectrograph installed on the 1.2-m Mercator telescope has been used to monitor the radial velocity of 13 low-metallicity carbon stars, among which seven carbon-enhanced metal-poor (CEMP) stars and six CH stars (including HIP 53522, a new member of the family, as revealed by a detailed abundance study). All stars but one show clear evidence for binarity. New orbits are obtained for eight systems. The sample covers an extended range in orbital periods, extending from 3.4 d (for the dwarf carbon star HE 0024-2523) to about 54 yr (for the CH star HD 26, the longest known among barium, CH, and extrinsic S stars). Three systems exhibit low-amplitude velocity variations with periods close to 1 yr superimposed on a long-term trend. In the absence of an accurate photometric monitoring of these systems, it is not clear yet whether these variations are the signature of a very low-mass companion or of regular envelope pulsations. The period - eccentricity (P - e) diagram for the 40 low-metallicity carbon stars with orbits now available shows no difference between CH and CEMP-s stars (the latter corresponding to those CEMP stars enriched in s-process elements, as are CH stars). We suggest that they must be considered as one and the same family and that their different names only stem from historical reasons. Indeed, these two families have as well very similar mass-function distributions, corresponding to companions with masses in the range 0.5-0.7 M⊙, indicative of white-dwarf companions, adopting 0.8-0.9 M⊙ for the primary component. This result confirms that CH and CEMP-s stars obey the same mass-transfer scenario as their higher-metallicity analogues, barium stars. The P - e diagrams of barium, CH, and CEMP-s stars are indeed very similar. They reveal two different groups of systems: one with short orbital periods (P< 1000 d) and mostly circular or almost circular orbits, and another with longer period and eccentric (e> 0.1) orbits. These two groups either

  5. First stars XI. Chemical composition of the extremely metal-poor dwarfs in the binary CS 22876-032

    NASA Astrophysics Data System (ADS)

    González Hernández, J. I.; Bonifacio, P.; Ludwig, H.-G.; Caffau, E.; Spite, M.; Spite, F.; Cayrel, R.; Molaro, P.; Hill, V.; François, P.; Plez, B.; Beers, T. C.; Sivarani, T.; Andersen, J.; Barbuy, B.; Depagne, E.; Nordström, B.; Primas, F.

    2008-03-01

    Context: Unevolved metal-poor stars constitute a fossil record of the early Galaxy, and can provide invaluable information on the properties of the first generations of stars. Binary systems also provide direct information on the stellar masses of their member stars. Aims: The purpose of this investigation is a detailed abundance study of the double-lined spectroscopic binary CS 22876-032, which comprises the two most metal-poor dwarfs known. Methods: We used high-resolution, high-S/N ratio spectra from the UVES spectrograph at the ESO VLT telescope. Long-term radial-velocity measurements and broad-band photometry allowed us to determine improved orbital elements and stellar parameters for both components. We used OSMARCS 1D models and the turbospectrum spectral synthesis code to determine the abundances of Li, O, Na, Mg, Al, Si, Ca, Sc, Ti, Cr, Mn, Fe, Co and Ni. We also used the CO^5BOLD model atmosphere code to compute the 3D abundance corrections, notably for Li and O. Results: We find a metallicity of [Fe/H] ~ -3.6 for both stars, using 1D models with 3D corrections of ~-0.1 dex from averaged 3D models. We determine the oxygen abundance from the near-UV OH bands; the 3D corrections are large, -1 and -1.5 dex for the secondary and primary respectively, and yield [O/Fe] ~ 0.8, close to the high-quality results obtained from the [OI] 630 nm line in metal-poor giants. Other [ α/Fe] ratios are consistent with those measured in other dwarfs and giants with similar [Fe/H], although Ca and Si are somewhat low ([X/Fe] ⪉ 0). Other element ratios follow those of other halo stars. The Li abundance of the primary star is consistent with the Spite plateau, but the secondary shows a lower abundance; 3D corrections are small. Conclusions: The Li abundance in the primary star supports the extension of the Spite Plateau value at the lowest metallicities, without any decrease. The low abundance in the secondary star could be explained by endogenic Li depletion, due to its

  6. The role of binaries in the enrichment of the early Galactic halo. III. Carbon-enhanced metal-poor stars - CEMP-s stars

    NASA Astrophysics Data System (ADS)

    Hansen, T. T.; Andersen, J.; Nordström, B.; Beers, T. C.; Placco, V. M.; Yoon, J.; Buchhave, L. A.

    2016-04-01

    Context. Detailed spectroscopic studies of metal-poor halo stars have highlighted the important role of carbon-enhanced metal-poor (CEMP) stars in understanding the early production and ejection of carbon in the Galaxy and in identifying the progenitors of the CEMP stars among the first stars formed after the Big Bang. Recent work has also classified the CEMP stars by absolute carbon abundance, A(C), into high- and low-C bands, mostly populated by binary and single stars, respectively. Aims: Our aim is to determine the frequency and orbital parameters of binary systems among the CEMP-s stars, which exhibit strong enhancements of neutron-capture elements associated with the s-process. This allows us to test whether local mass transfer from a binary companion is necessary and sufficient to explain their dramatic carbon excesses. Methods: We have systematically monitored the radial velocities of a sample of 22 CEMP-s stars for several years with ~monthly, high-resolution, low S/N échelle spectra obtained at the Nordic Optical Telescope (NOT) at La Palma, Spain. From these spectra, radial velocities with an accuracy of ≈100 m s-1 were determined by cross-correlation with optimised templates. Results: Eighteen of the 22 stars exhibit clear orbital motion, yielding a binary frequency of 82 ± 10%, while four stars appear to be single (18 ± 10%). We thus confirm that the binary frequency of CEMP-s stars is much higher than for normal metal-poor giants, but not 100% as previously claimed. Secure orbits are determined for eleven of the binaries and provisional orbits for six long-period systems (P > 3000 days), and orbital circularisation timescales are discussed. Conclusions: The conventional scenario of local mass transfer from a former asymptotic giant branch (AGB) binary companion does appear to account for the chemical composition of most CEMP-s stars. However, the excess of C and s-process elements in some single CEMP-s stars was apparently transferred to their

  7. The role of binaries in the enrichment of the early Galactic halo. II. Carbon-enhanced metal-poor stars: CEMP-no stars

    NASA Astrophysics Data System (ADS)

    Hansen, T. T.; Andersen, J.; Nordström, B.; Beers, T. C.; Placco, V. M.; Yoon, J.; Buchhave, L. A.

    2016-02-01

    Context. The detailed composition of most metal-poor halo stars has been found to be very uniform. However, a fraction of 20-70% (increasing with decreasing metallicity) exhibit dramatic enhancements in their abundances of carbon; these are the so-called carbon-enhanced metal-poor (CEMP) stars. A key question for Galactic chemical evolution models is whether this non-standard composition reflects that of the stellar natal clouds or is due to local, post-birth mass transfer of chemically processed material from a binary companion; CEMP stars should then all be members of binary systems. Aims: Our aim is to determine the frequency and orbital parameters of binaries among CEMP stars with and without over-abundances of neutron-capture elements - CEMP-s and CEMP-no stars, respectively - as a test of this local mass-transfer scenario. This paper discusses a sample of 24 CEMP-no stars, while a subsequent paper will consider a similar sample of CEMP-s stars. Methods: High-resolution, low S/N spectra of the stars were obtained at roughly monthly intervals over a time span of up to eight years with the FIES spectrograph at the Nordic Optical Telescope. Radial velocities of ~100 m s-1 precision were determined by cross-correlation after each observing night, allowing immediate, systematic follow-up of any variable object. Results: Most programme stars exhibit no statistically significant radial-velocity variation over this period and appear to be single, while four are found to be binaries with orbital periods of 300-2000 days and normal eccentricity; the binary frequency for the sample is 17 ± 9%. The single stars mostly belong to the recently identified low-C band, while the binaries have higher absolute carbon abundances. Conclusions: We conclude that the nucleosynthetic process responsible for the strong carbon excess in these ancient stars is unrelated to their binary status; the carbon was imprinted on their natal molecular clouds in the early Galactic interstellar

  8. Carbon-enhanced metal-poor stars in SDSS/Segue. II. Comparison of CEMP-star frequencies with binary population-synthesis models

    SciTech Connect

    Lee, Young Sun; Suda, Takuma; Beers, Timothy C.; Stancliffe, Richard J.

    2014-06-20

    We present a comparison of the frequencies of carbon-enhanced metal-poor (CEMP) giant and main-sequence turnoff (MSTO) stars with predictions from binary population-synthesis models involving asymptotic giant-branch (AGB) mass transfer. The giant and MSTO stars are selected from the Sloan Digital Sky Survey and the Sloan Extension for Galactic Understanding and Exploration. We consider two initial mass functions (IMFs)—a Salpeter IMF, and a mass function with a characteristic mass of 10 M {sub ☉}. For giant stars, the comparison indicates a good agreement between the observed CEMP frequencies and the AGB binary model using a Salpeter IMF for [Fe/H] > – 1.5, and a characteristic mass of 10 M {sub ☉} for [Fe/H] < – 2.5. This result suggests that the IMF shifted from high- to low-mass dominated in the early history of the Milky Way, which appears to have occurred at a 'chemical time' between [Fe/H] =–2.5 and [Fe/H] =–1.5. The CEMP frequency for the turnoff stars with [Fe/H] < – 3.0 is much higher than the AGB model prediction from the high-mass IMF, supporting the previous assertion that one or more additional mechanisms, not associated with AGB stars, are required for the production of carbon-rich material below [Fe/H] =–3.0. We also discuss possible effects of first dredge-up and extra mixing in red giants and internal mixing in turnoff stars on the derived CEMP frequencies.

  9. THE BINARY FREQUENCY OF r-PROCESS-ELEMENT-ENHANCED METAL-POOR STARS AND ITS IMPLICATIONS: CHEMICAL TAGGING IN THE PRIMITIVE HALO OF THE MILKY WAY

    SciTech Connect

    Hansen, Terese; Andersen, Johannes; Nordstroem, Birgitta; Buchhave, Lars A.; Beers, Timothy C. E-mail: ja@astro.ku.dk E-mail: beers@pa.msu.edu

    2011-12-10

    A few rare halo giants in the range [Fe/H] {approx_equal} -2.9 {+-} 0.3 exhibit r-process element abundances that vary as a group by factors up to [r/Fe] {approx}80, relative to those of the iron peak and below. Yet, the astrophysical production site of these r-process elements remains unclear. We report initial results from four years of monitoring the radial velocities of 17 r-process-enhanced metal-poor giants to detect and characterize binaries in this sample. We find three (possibly four) spectroscopic binaries with orbital periods and eccentricities that are indistinguishable from those of Population I binaries with giant primaries, and which exhibit no signs that the secondary components have passed through the asymptotic giant branch stage of evolution or exploded as supernovae. The other 14 stars in our sample appear to be single-including the prototypical r-process-element-enhanced star CS 22892-052, which is also enhanced in carbon, but not in s-process elements. We conclude that the r-process (and potentially carbon) enhancement of these stars was not a local event due to mass transfer or winds from a binary companion, but was imprinted on the natal molecular clouds of these (single and binary) stars by an external source. These stars are thus spectacular chemical tracers of the inhomogeneous nature of the early Galactic halo system.

  10. Molybdenum Abundances in Metal-Poor Stars

    NASA Astrophysics Data System (ADS)

    Peterson, R. C.

    2012-08-01

    Peterson (2011) has analyzed HST spectra near 2000Å of five metal-poor turnoff stars with mild enhancements of heavy r-process elements. Two stars, HD 94028 and HD 160617, are unique in showing an extreme overabundance of the light trans-ironic element molybdenum (Z = 42), but less extreme enhancements of Zr (Z = 40) and Ru (Z = 44). Of several nucleosynthesis scenarios that can produce nuclei in this mass range in the oldest stars, a high-entropy wind (HEW) acting in a core-collapse supernova seems uniquely capable of a high overproduction confined to a narrow mass range. That this unusual elemental distribution is achieved only under very limited physical conditions suggests that very few individual nucleosynthesis events were responsible for the synthesis of the light trans-ironic elements in these stars, even though both are only moderately metal-poor.

  11. LITHIUM ABUNDANCES IN CARBON-ENHANCED METAL-POOR STARS

    SciTech Connect

    Masseron, Thomas; Johnson, Jennifer A.; Lucatello, Sara; Karakas, Amanda; Plez, Bertrand; Beers, Timothy C.; Christlieb, Norbert E-mail: jaj@astronomy.ohio-state.edu

    2012-05-20

    Carbon-enhanced metal-poor (CEMP) stars are believed to show the chemical imprints of more massive stars (M {approx}> 0.8 M{sub Sun }) that are now extinct. In particular, it is expected that the observed abundance of Li should deviate in these stars from the standard Spite lithium plateau. We study here a sample of 11 metal-poor stars and a double-lined spectroscopic binary with -1.8 < [Fe/H] < -3.3 observed with the Very Large Telescope/UVES spectrograph. Among these 12 metal-poor stars, there are 8 CEMP stars for which we measure or constrain the Li abundance. In contrast to previous arguments, we demonstrate that an appropriate regime of dilution permits the existence of 'Li-Spite plateau and C-rich' stars, whereas some of the 'Li-depleted and C-rich' stars call for an unidentified additional depletion mechanism that cannot be explained by dilution alone. We find evidence that rotation is related to the Li depletion in some CEMP stars. Additionally, we report on a newly recognized double-lined spectroscopic binary star in our sample. For this star, we develop a new technique from which estimates of stellar parameters and luminosity ratios can be derived based on a high-resolution spectrum alone, without the need for input from evolutionary models.

  12. Binarity in carbon-enhanced metal-poor stars

    NASA Astrophysics Data System (ADS)

    Starkenburg, Else; Shetrone, Matthew D.; McConnachie, Alan W.; Venn, Kim A.

    2014-06-01

    A substantial fraction of the lowest metallicity stars show very high enhancements in carbon. It is debated whether these enhancements reflect the stars' birth composition, or if their atmospheres were subsequently polluted, most likely by accretion from an asymptotic giant branch binary companion. Here we investigate and compare the binary properties of three carbon-enhanced subclasses: The metal-poor CEMP-s stars that are additionally enhanced in barium; the higher metallicity (sg)CH- and Ba II stars also enhanced in barium; and the metal-poor CEMP-no stars, not enhanced in barium. Through comparison with simulations, we demonstrate that all barium-enhanced populations are best represented by a ˜100 per cent binary fraction with a shorter period distribution of at maximum ˜20 000 d. This result greatly strengthens the hypothesis that a similar binary mass transfer origin is responsible for their chemical patterns. For the CEMP-no group we present new radial velocity data from the Hobby-Eberly Telescope for 15 stars to supplement the scarce literature data. Two of these stars show indisputable signatures of binarity. The complete CEMP-no data set is clearly inconsistent with the binary properties of the CEMP-s class, thereby strongly indicating a different physical origin of their carbon enhancements. The CEMP-no binary fraction is still poorly constrained, but the population resembles more the binary properties in the solar neighbourhood.

  13. The physics of carbon-enhanced metal-poor stars

    NASA Astrophysics Data System (ADS)

    Stancliffe, Richard

    2014-09-01

    A surprising fraction of metal-poor stars turn out to be rich in carbon. Of these, many show enhanced levels of heavy elements, particularly those formed by the slow neutron capture process. The proposed formation scenario for these objects involves mass transfer from an asymptotic giant branch star in a binary system. I will discuss (some) of the important (and uncertain!) physical processes that we must understand if we wish to learn the origin of these enigmatic, ancient objects.

  14. The role of binaries in the enrichment of the early Galactic halo. I. r-process-enhanced metal-poor stars

    NASA Astrophysics Data System (ADS)

    Hansen, T. T.; Andersen, J.; Nordström, B.; Beers, T. C.; Yoon, J.; Buchhave, L. A.

    2015-11-01

    Context. The detailed chemical composition of most metal-poor halo stars has been found to be highly uniform, but a minority of stars exhibit dramatic enhancements in their abundances of heavy neutron-capture elements and/or of carbon. The key question for Galactic chemical evolution models is whether these peculiarities reflect the composition of the natal clouds, or if they are due to later (post-birth) mass transfer of chemically processed material from a binary companion. If the former case applies, the observed excess of certain elements was implanted within selected clouds in the early ISM from a production site at interstellar distances. Aims: Our aim is to determine the frequency and orbital properties of binaries among these chemically peculiar stars. This information provides the basis for deciding whether local mass transfer from a binary companion is necessary and sufficient to explain their unusual compositions. This paper discusses our study of a sample of 17 moderately (r-I) and highly (r-II) r-process-element enhanced VMP and EMP stars. Methods: High-resolution, low signal-to-noise spectra of the stars were obtained at roughly monthly intervals over eight years with the FIES spectrograph at the Nordic Optical Telescope. From these spectra, radial velocities with an accuracy of ~100 m s-1 were determined by cross-correlation against an optimized template. Results: Fourteen of the programme stars exhibit no significant radial-velocity variation over this temporal window, while three are binaries with orbits of typical eccentricity for their periods, resulting in a normal binary frequency of ~18 ± 6% for the sample. Conclusions: Our results confirm our preliminary conclusion from 2011, based on partial data, that the chemical peculiarity of the r-I and r-II stars is not caused by any putative binary companions. Instead, it was imprinted on the natal molecular clouds of these stars by an external, distant source. Models of the ISM in early galaxies

  15. Toward ab initio extremely metal poor stars

    NASA Astrophysics Data System (ADS)

    Ritter, Jeremy S.; Safranek-Shrader, Chalence; Milosavljević, Miloš; Bromm, Volker

    2016-09-01

    Extremely metal poor stars have been the focus of much recent attention owing to the expectation that their chemical abundances can shed light on the metal and dust yields of the earliest supernovae. We present our most realistic simulation to date of the astrophysical pathway to the first metal enriched stars. We simulate the radiative and supernova hydrodynamic feedback of a 60 M⊙ Population III star starting from cosmological initial conditions realizing Gaussian density fluctuations. We follow the gravitational hydrodynamics of the supernova remnant at high spatial resolution through its freely-expanding, adiabatic, and radiative phases, until gas, now metal-enriched, has resumed runaway gravitational collapse. Our findings are surprising: while the Population III progenitor exploded with a low energy of 1051 erg and injected an ample metal mass of 6 M⊙, the first cloud to collapse after the supernova explosion is a dense surviving primordial cloud on which the supernova blast wave deposited metals only superficially, in a thin, unresolved layer. The first metal-enriched stars can form at a very low metallicity, of only 2 - 5 × 10-4 Z⊙, and can inherit the parent cloud's highly elliptical, radially extended orbit in the dark matter gravitational potential.

  16. RR Lyrae Stars, Metal-Poor Stars, and the Galaxy

    NASA Astrophysics Data System (ADS)

    McWilliam, Andrew

    2011-08-01

    This online book contains the proceedings of a meeting on "RR Lyrae Stars, Metal-Poor Stars, and the Galaxy" held at the Carnegie Observatories, Pasadena, California, in January 2011, to honor the 80th year of George W. Preston III. The book comprises the 5th volume of the Carnegie Observatories Astrophysics Series, and contains reviews and research articles on recent developments in the area of RR Lyrae stars, including results from the Kepler space mission. Review and research articles on metal-poor stars and Galactic structure are also included.

  17. Searching for dust around hyper metal poor stars

    SciTech Connect

    Venn, Kim A.; Divell, Mike; Starkenburg, Else; Puzia, Thomas H.; Côté, Stephanie; Lambert, David L.

    2014-08-20

    We examine the mid-infrared fluxes and spectral energy distributions for stars with iron abundances [Fe/H] <–5, and other metal-poor stars, to eliminate the possibility that their low metallicities are related to the depletion of elements onto dust grains in the formation of a debris disk. Six out of seven stars examined here show no mid-IR excesses. These non-detections rule out many types of circumstellar disks, e.g., a warm debris disk (T ≤ 290 K), or debris disks with inner radii ≤1 AU, such as those associated with the chemically peculiar post-asymptotic giant branch spectroscopic binaries and RV Tau variables. However, we cannot rule out cooler debris disks, nor those with lower flux ratios to their host stars due to, e.g., a smaller disk mass, a larger inner disk radius, an absence of small grains, or even a multicomponent structure, as often found with the chemically peculiar Lambda Bootis stars. The only exception is HE0107-5240, for which a small mid-IR excess near 10 μm is detected at the 2σ level; if the excess is real and associated with this star, it may indicate the presence of (recent) dust-gas winnowing or a binary system.

  18. Very Metal-poor Stars in the RAVE Spectroscopic Survey

    NASA Astrophysics Data System (ADS)

    Matijevic, Gal

    2015-08-01

    Metal-poor stars have been the cornerstone of the galactic and stellar archeology for decades. Due to their intact nature they offer a unique insight into the early stages of the galactic evolution and help us understand the nucleosynthesis processes responsible for the creation of chemical elements. The number of discovered very metal-poor stars (metallicity [Fe/H] < -2.0) is still relatively low and it drops sharply towards even lower metallicities. Only a handful of known stars have [Fe/H] < -4.0. RAVE spectroscopic survey enabled us to serendipitously discover many new metal-poor stars due to its large sample size and the fact that its wavelength range is centered around the infra-red CaII triplet which has been shown to be a good metallicity estimator for even the most metal-poor stars. The parameter estimation pipeline used on the survey data has trouble with accurately recovering the metallicities (they can be severely overestimated) and other parameters of the metal-poor stars. This is due to the lack of strong features in their spectra and sometimes humble signal-to-noise values. To cope with that we reanalyzed all metal-poor star spectra by measuring the equivalent widths of the CaII triplet lines. We devised a novel method employing Gaussian processes to model the continuum variations and also to account for the shallower and blended spectral lines that would otherwise add to the total equivalent width and lead to unwanted biases. New metallicity values for those stars were calibrated using the high resolution observations of the subset of stars and the available 8-band BVg'r'i'JHKS photometry. All sources of the uncertainty were taken into account which brought the final metallicity uncertainties to ~0.3dex, including for stars with lowest metal abundances. The study enabled us to discover many new very metal poor stars, several of which fall in the extremely metal-poor domain and some of which are possibly ultra metal-poor. For all stars in our sample

  19. Abundance analysis of extremely metal-poor stars

    NASA Astrophysics Data System (ADS)

    Hansen, T.; Hansen, C. J.; Christlieb, N.; Andersen, J.

    2016-01-01

    The outer atmosphere of the first generations of low-mass (M < 0.8 M⊙) stars retain to a great extent the original chemical composition of the interstellar medium (ISM) at the time and place of their birth. The composition of this pristine gas represents the nucleosynthesis of the very first massive stars, that produced and ejected the first heavy elements into the early ISM. Thus a detailed abundance analysis of low-mass, metal-poor stars can help us track these gasses and provide insight into the formation processes that took place in the very early stages of our Galaxy. Preliminary result of a 25-star homogeneously analysed sample of metal- poor candidates from the Hamburg/ESO survey is presented. The main focus is on the most metal-poor stars of the sample; stars with [Fe/H] < -4. The abundance pattern of these ultra metal-poor (UMP) stars is used to extract key information of the earliest ongoing formation processes (ranging from hydrostatic burning to neutron-capture processes).

  20. A Combined Astrometric and Spectroscopic Study of Metal-Poor Binaries

    NASA Astrophysics Data System (ADS)

    Benamati, L.; Sozzetti, A.; Santos, N. C.; Latham, D. W.

    2013-11-01

    In this work we present a study of binary systems in a metal-poor sample of solar type stars. The stars analyzed were rejected from two planet search samples because they were found to be binaries. Using available radial velocity and Hipparcos astrometric data, we apply different methods to find, for every binary system, a possible range of solutions for the mass of the companion and its orbital period. In one case we find that the solution depends on the Hipparcos data used: the old and new reductions give different results. Some candidate low-mass companions are found, including some close to the brown dwarf regime.

  1. Observing metal-poor stars with X-Shooter

    NASA Astrophysics Data System (ADS)

    Caffau, E.; Bonifacio, P.; Sbordone, L.; Monaco, L.; François; , P.

    The extremely metal-poor stars (EMP) hold in their atmospheres the fossil record of the chemical composition of the early phases of the Galactic evolution. The chemical analysis of such objects provides important constraints on these early phases. EMP stars are very rare objects; to dig them out large amounts of data have to be considered. With an automatic procedure, we analysed objects with colours of Turn-Off stars from the Sloan Digital Sky Survey to select a sample of good candidate EMP stars. During the French-Italian GTO of the spectrograph X-Shooter, we observed a sample of these candidates. We could confirm the low metallicity of our sample of stars, and we succeeded in finding a record metal-poor star.

  2. THE RAVE SURVEY: RICH IN VERY METAL-POOR STARS

    SciTech Connect

    Fulbright, Jon P.; Wyse, Rosemary F. G.; Ruchti, Gregory R.; Gilmore, G. F.; Grebel, Eva; Bienayme, O.; Siebert, A.; Binney, J.; Bland-Hawthorn, J.; Campbell, R.; Freeman, K. C.; Gibson, B. K.; Helmi, A.; Munari, U.; Navarro, J. F.; Siviero, A.; Parker, Q. A.; Reid, W.; Seabroke, G. M.; Steinmetz, M.

    2010-11-20

    Very metal-poor stars are of obvious importance for many problems in chemical evolution, star formation, and galaxy evolution. Finding complete samples of such stars which are also bright enough to allow high-precision individual analyses is of considerable interest. We demonstrate here that stars with iron abundances [Fe/H] <-2 dex, and down to below -4 dex, can be efficiently identified within the Radial Velocity Experiment (RAVE) survey of bright stars, without requiring additional confirmatory observations. We determine a calibration of the equivalent width of the calcium triplet lines measured from the RAVE spectra onto true [Fe/H], using high spectral resolution data for a subset of the stars. These RAVE iron abundances are accurate enough to obviate the need for confirmatory higher-resolution spectroscopy. Our initial study has identified 631 stars with [Fe/H] {<=}-2, from a RAVE database containing approximately 200,000 stars. This RAVE-based sample is complete for stars with [Fe/H] {approx_lt}-2.5, allowing statistical sample analysis. We identify three stars with [Fe/H] {approx_lt}-4. Of these, one was already known to be 'ultra metal-poor', one is a known carbon-enhanced metal-poor star, but we obtain [Fe/H] = -4.0, rather than the published [Fe/H] = -3.3, and derive [C/Fe] = +0.9, and [N/Fe] = +3.2, and the third is at the limit of our signal-to-noise ratio. RAVE observations are ongoing and should prove to be a rich source of bright, easily studied, very metal-poor stars.

  3. The Best and Brightest Metal-poor Stars

    NASA Astrophysics Data System (ADS)

    Schlaufman, Kevin C.; Casey, Andrew R.

    2014-12-01

    The chemical abundances of large samples of extremely metal-poor (EMP) stars can be used to investigate metal-free stellar populations, supernovae, and nucleosynthesis as well as the formation and galactic chemical evolution of the Milky Way and its progenitor halos. However, current progress on the study of EMP stars is being limited by their faint apparent magnitudes. The acquisition of high signal-to-noise spectra for faint EMP stars requires a major telescope time commitment, making the construction of large samples of EMP star abundances prohibitively expensive. We have developed a new, efficient selection that uses only public, all-sky APASS optical, 2MASS near-infrared, and WISE mid-infrared photometry to identify bright metal-poor star candidates through their lack of molecular absorption near 4.6 microns. We have used our selection to identify 11,916 metal-poor star candidates with V < 14, increasing the number of publicly available candidates by more than a factor of five in this magnitude range. Their bright apparent magnitudes have greatly eased high-resolution follow-up observations that have identified seven previously unknown stars with [Fe/H] <~ -3.0. Our follow-up campaign has revealed that 3.8+1.3-1.1% of our candidates have [Fe/H] <~ -3.0 and 32.5+3.0-2.9% have -3.0 <~ [Fe/H] <~ -2.0. The bulge is the most likely location of any existing Galactic Population III stars, and an infrared-only variant of our selection is well suited to the identification of metal-poor stars in the bulge. Indeed, two of our confirmed metal-poor stars with [Fe/H] <~ -2.7 are within about 2 kpc of the Galactic center. They are among the most metal-poor stars known in the bulge. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

  4. The best and brightest metal-poor stars

    SciTech Connect

    Schlaufman, Kevin C.; Casey, Andrew R. E-mail: arc@ast.cam.ac.uk

    2014-12-10

    The chemical abundances of large samples of extremely metal-poor (EMP) stars can be used to investigate metal-free stellar populations, supernovae, and nucleosynthesis as well as the formation and galactic chemical evolution of the Milky Way and its progenitor halos. However, current progress on the study of EMP stars is being limited by their faint apparent magnitudes. The acquisition of high signal-to-noise spectra for faint EMP stars requires a major telescope time commitment, making the construction of large samples of EMP star abundances prohibitively expensive. We have developed a new, efficient selection that uses only public, all-sky APASS optical, 2MASS near-infrared, and WISE mid-infrared photometry to identify bright metal-poor star candidates through their lack of molecular absorption near 4.6 microns. We have used our selection to identify 11,916 metal-poor star candidates with V < 14, increasing the number of publicly available candidates by more than a factor of five in this magnitude range. Their bright apparent magnitudes have greatly eased high-resolution follow-up observations that have identified seven previously unknown stars with [Fe/H] ≲ –3.0. Our follow-up campaign has revealed that 3.8{sub −1.1}{sup +1.3}% of our candidates have [Fe/H] ≲ –3.0 and 32.5{sub −2.9}{sup +3.0}% have –3.0 ≲ [Fe/H] ≲ –2.0. The bulge is the most likely location of any existing Galactic Population III stars, and an infrared-only variant of our selection is well suited to the identification of metal-poor stars in the bulge. Indeed, two of our confirmed metal-poor stars with [Fe/H] ≲ –2.7 are within about 2 kpc of the Galactic center. They are among the most metal-poor stars known in the bulge.

  5. The Best and Brightest Metal-Poor Stars

    NASA Astrophysics Data System (ADS)

    Schlaufman, Kevin

    2015-01-01

    The chemical abundances of large samples of extremely metal-poor (EMP) stars can be used to investigate metal-free stellar populations, supernovae, and nucleosynthesis as well as the formation and galactic chemical evolution of the Milky Way and its progenitor halos. However, current progress on the study of EMP stars is being limited by their faint apparent magnitudes. We have developed a new, efficient selection that uses only public, all-sky APASS optical, 2MASS near-infrared, and WISE mid-infrared photometry to identify bright metal-poor star candidates through their lack of molecular absorption near 4.6 microns. High-resolution follow up has revealed that 3.8% of our candidates have [Fe/H] < -3.0 and 32.5% have -3.0 < [Fe/H] < -2.0. We are using the Automated Planet Finder, Gemini, and Magellan to follow up all of our metal-poor candidates with V < 12 in both hemispheres with the goal of collecting the most information-rich sample of metal-poor stars ever assembled.

  6. Extremely metal-poor star candidates in the SDSS

    NASA Astrophysics Data System (ADS)

    Xu, Si-Yao; Zhang, Hua-Wei; Liu, Xiao-Wei

    2013-03-01

    For a sample of metal-poor stars (-3.3 <= [Fe/H] <= -2.2) that have high-resolution spectroscopic abundance determinations, we have measured equivalent widths of the Ca II K, Mg I b and near-infrared Ca II triplet lines using low-resolution spectra from the Sloan Digital Sky Survey (SDSS), calculated effective temperatures from (g - z)0 color, deduced stellar surface gravities by fitting stellar isochrones, and determined metallicities based on the aforementioned quantities. Metallicities thus derived from the Ca II K line are in much better agreement with the results determined from high-resolution spectra than the values given in the SDSS Data Release 7. The metallicities derived from the Mg I b lines have a large dispersion owing to the large measurement errors, whereas those deduced from the Ca II triplet lines are too high due to both non-local thermodynamical equilibrium (NLTE) effects and measurement errors. Abundances after correction for the NLTE effect for the Mg I b lines and Ca II triplet lines are also presented. Following this method, we have identified six candidates of ultra-metal-poor stars with [Fe/H] ~ -4.0 from a sample of 166 metal-poor star candidates. One of them, SDSS J102915+172927, was recently confirmed to be an ultra-metal-poor ([Fe/H] < -4.0) star with the lowest metallicity ever measured. Follow-up high-resolution spectroscopy for the other five ultra-metal-poor stars in our sample will therefore be of great interest.

  7. Very Metal-poor Stars Observed by the RAVE Survey

    NASA Astrophysics Data System (ADS)

    Matijevič, Gal

    2016-08-01

    Radial Velocity Experiment (RAVE) observed ~500,000 southern sky stars between 2003 and 2013 in the infra-red calcium triplet (CaII) spectral region. In this study we extended the analysis of RAVE very metal-poor stars ([Fe/H] < -2) presented by Fulbright et al. (2010). We employed a novel method for identifying the metal-poor stars and developed a tool for modeling CaII lines where we also modeled the background noise to avoid systematical biases in the equivalent width (EW) measurements. Final metallicity values were derived with a flexible calibration approach using only 2MASS photometric data and EW measurements obtained from the RAVE spectra.

  8. From C-Enhanced, Metal Poor Stars to AGB Nucleosynthesis

    NASA Astrophysics Data System (ADS)

    Lucatello, S.; Gratton, R.; Beers, T.; Carretta, E.

    The largest to date surveys for metal poor stars (i.e. HK survey Beers et al. 1992 and HES Christlieb et al. 2001) find that as many as ~25% of stars with [Fe/H]≤ -2.5 dex are have [C/Fe]>1 dex (CEMP stars). High resolution studies have revealed that the C-enhancements is accompanied by different abundance patterns, s and/or r-process enrichment, but there are also cases with no ncapture elements overabundance,and with or without extraordinary α elements enhancements. The mechanisms that originate the range of phenomena observed are far from being fully understood.

  9. LITHIUM ABUNDANCES OF EXTREMELY METAL-POOR TURNOFF STARS

    SciTech Connect

    Aoki, Wako; Inoue, Susumu; Barklem, Paul S.; Beers, Timothy C.; Christlieb, Norbert; Perez, Ana E. GarcIa; Norris, John E.; Carollo, Daniela E-mail: Paul.Barklem@physics.uu.se E-mail: N.Christlieb@lsw.uni-heidelberg.de E-mail: jen@mso.anu.edu.au E-mail: inoue@tap.scphys.kyoto-u.ac.jp

    2009-06-20

    We have determined Li abundances for eleven metal-poor turnoff stars, among which eight have [Fe/H] <-3, based on LTE analyses of high-resolution spectra obtained with the High Dispersion Spectrograph on the Subaru Telescope. The Li abundances for four of these eight stars are determined for the first time by this study. Effective temperatures are determined by a profile analysis of H{alpha} and H{beta}. While seven stars have Li abundances as high as the Spite Plateau value, the remaining four objects with [Fe/H] <-3 have A(Li) =log (Li/H)+ 12 {approx}< 2.0, confirming the existence of extremely metal-poor (EMP) turnoff stars having low Li abundances, as reported by previous work. The average of the Li abundances for stars with [Fe/H]<-3 is lower by 0.2 dex than that of the stars with higher metallicity. No clear constraint on the metallicity dependence or scatter of the Li abundances is derived from our measurements for the stars with [Fe/H]<-3. Correlations of the Li abundance with effective temperatures, with abundances of Na, Mg, and Sr, and with the kinematical properties are investigated, but no clear correlation is seen in the EMP star sample.

  10. La and Eu Abundances in Metal-poor Halo Stars

    NASA Astrophysics Data System (ADS)

    Cardillo, Harrison; Burris, Debra L.

    2016-01-01

    Elements with atomic number greater than Z=26 (the Iron Peak) cannot be formed through fusion in a star's core; the majority of these elements are produced through one of two neutron-capture processes. Early in the history of the Galaxy, the rapid neutron-capture process (r-process) is believed to be responsible for the production of elements Z=56 and beyond. These elements require at least one generation of stars to have completed their life cycle in order to be synthesized. Therefore, if we observe the heavy metal abundances in what are called Population II stars (metal-poor stars), then we can begin to make inferences about the chemistry of the earliest stars in the Galaxy. To contribute to this picture of the early universe, the Lanthanum and Europium abundances of low-metallicity stars will be measured and trends in these abundances based on comparisons to existing related literature will be sought.

  11. The chemical composition of TS 01, the most oxygen-deficient planetary nebula. AGB nucleosynthesis in a metal-poor binary star

    NASA Astrophysics Data System (ADS)

    Stasińska, G.; Morisset, C.; Tovmassian, G.; Rauch, T.; Richer, M. G.; Peña, M.; Szczerba, R.; Decressin, T.; Charbonnel, C.; Yungelson, L.; Napiwotzki, R.; Simón-Díaz, S.; Jamet, L.

    2010-02-01

    The planetary nebula TS 01 (also called PN G 135.9+55.9 or SBS 1150+599A) with its record-holding low oxygen abundance and its double degenerate close binary core (period 3.9 h) is an exceptional object located in the Galactic halo. We have secured observational data in a complete wavelength range to pin down the abundances of half a dozen elements in the nebula. The abundances are obtained via detailed photoionization modelling which takes into account all the observational constraints (including geometry and aperture effects) using the pseudo-3D photoionization code Cloudy_3D. The spectral energy distribution of the ionizing radiation is taken from appropriate model atmospheres. Incidentally we find from the new observational constraints that both stellar components contribute to the ionization: the “cool” one provides the bulk of hydrogen ionization, while the “hot” one is responsible for the presence of the most highly charged ions, which explains why previous attempts to model the nebula experienced difficulties. The nebular abundances of C, N, O, and Ne are found to be 1/3.5, 1/4.2, 1/70, and 1/11 of the solar value respectively, with uncertainties of a factor 2. Thus the extreme O deficiency of this object is confirmed. The abundances of S and Ar are less than 1/30 of solar. The abundance of He relative to H is 0.089 ± 0.009. Standard models of stellar evolution and nucleosynthesis cannot explain the abundance pattern observed in the nebula. To obtain an extreme oxygen deficiency in a star whose progenitor has an initial mass of about 1 M⊙ requires an additional mixing process, which can be induced by stellar rotation and/or by the presence of the close companion. We have computed a stellar model with an initial mass of 1 M⊙, appropriate metallicity, and initial rotation of 100 km s-1, and find that rotation greatly improves the agreement between the predicted and observed abundances. Based on observations obtained at the Canada

  12. Behavior of sulfur in extremely metal-poor stars

    NASA Astrophysics Data System (ADS)

    Takada-Hidai, Masahide; Sargent, Wallace L. W.

    The LTE abundances of sulfur (S) were explored in the sample of 15 metal-poor stars with the metallicity range of -4<[Fe/H]<-1.5, based on the equivalent widths of the S I(1) 9212 and 9237 Å lines measured on high-resolution spectra, which were observed by the Keck I HIRES. Combining our results and those of Takada-Hidai et al. (2005), we found that the behavior of [S/Fe] against [Fe/H] shows a nearly flat trend in the range of metallicity down to [Fe/H]˜-4.

  13. Chemical abundances of very metal-poor stars

    NASA Astrophysics Data System (ADS)

    Zhang, H. W.; Zhao, G.

    2005-12-01

    High-resolution and high signal-to-noise ratio spectra of 32 very metal-poor stars were obtained with the Coudé echelle spectrograph mounted on the 2.16-m telescope at the National Astronomical Observatories (Xinglong, China). Equivalent widths of FeI, FeII, OI, NaI, MgI, AlI, SiI, SiII, KI, CaI, ScII, TiI, VI, CrI, MnI, NiI, CuI and BaII lines were measured. Stellar effective temperatures were determined by colour indices. Stellar surface gravities were calculated from Hipparcos parallaxes and stellar evolutionary tracks. Photospheric abundances of 16 elements were derived by local thermodynamical equilibrium analysis. Stellar space motions (U, V, W) and Galactic orbital parameters were calculated. Based on kinematics, sample stars were separated into dissipative collapse and accretion components of halo population. The global kinematics of the two components were analysed. Element abundances were discussed as functions of metallicities. The results of oxygen and α-elements abundance confirmed the previous works. The [K/Fe] shows a gradual systematic increase toward a lower metallicity, such as in the case of α-elements. The [Ba/Fe] trend suggests that the s-process dominated Ba production at least for the metal-poor stars with [Fe/H]> -2.0.

  14. A Photometric Method for Discovering Extremely Metal Poor Stars

    NASA Astrophysics Data System (ADS)

    Miller, Adam

    2015-01-01

    I present a new non-parametric machine-learning method for predicting stellar metallicity ([Fe/H]) based on photometric colors from the Sloan Digital Sky Survey (SDSS). The method is trained using a large sample of ~150k stars with SDSS spectra and atmospheric parameter estimates (Teff, log g, and [Fe/H]) from the SEGUE Stellar Parameters Pipeline (SSPP). For bright stars (g < 18 mag) with 4500 K < Teff < 7000 K and log g > 2, corresponding to the stars for which the SSPP estimates are most reliable, the method is capable of predicting [Fe/H] with a typical scatter of ~0.16 dex. This scatter is smaller than the typical uncertainty associated with [Fe/H] measurements from a low-resolution spectrum. The method is suitable for the discovery of extremely metal poor (EMP) stars ([Fe/H] < -3), as high purity (P > 50%), but low efficiency (E ~ 10%), samples of EMP star candidates can be generated from the sources with the lowest predicted [Fe/H]. To improve the efficiency of EMP star discovery, an alternative machine-learning model is constructed where the number of non-EMP stars is down-sampled in the training set, and a new regression model is fit. This alternate model improves the efficiency of EMP candidate selection by a factor of ~2. To test the efficacy of the model, I have obtained low-resolution spectra of 56 candidate EMP stars. I measure [Fe/H] for these stars using the well calibrated Ca II K line method, and compare our spectroscopic measurements to those from the machine learning model. Once applied to wide-field surveys, such as SDSS, Pan-STARRS, and LSST, the model will identify thousands of previously unknown EMP stars.

  15. Automated Selection of Metal-Poor Stars in the Galaxy

    NASA Astrophysics Data System (ADS)

    Rhee, Jaehyon

    2000-08-01

    In this thesis I have developed algorithms for the efficient reduction and analysis of a large set of objective-prism data, and for the reliable selection of extremely metal-poor candidate stars in the Galaxy. Automated computer scans of the 308 photographic plates in the HK objective-prism / interference-filter survey of Beers and colleagues have been carried out with the Automatic Plate Measuring (APM) machine in Cambridge, England. Highly automated software tools have been developed in order to identify useful spectra and remove unusable spectra, to locate the positions of the Ca II H (3969 Å) and K (3933 Å) absorption lines, and to construct approximate continua. Equivalent widths of the Ca II H and K lines were then measured directly from these reduced spectra. A subset of 294,039 spectra from 87 of the HK survey plates (located within approximately 30 degrees of the South Galactic Pole) were extracted. Of these, 221,670 (75.4%) proved to be useful for subsequent analysis. I have explored new methodology, making use of an Artificial Neural Network (ANN) analysis approach, in order to select extremely metal-poor star candidates with high efficiency. The ANNs were trained to predict metallicity, [Fe/H], and to classify stars into 6 groups separated by temperature and metal abundance, based on two accurately measured parameters -- the de-reddened broadband (B-V)0 color for known HK survey stars with available photometric information, and the equivalent width of the Ca II K line in an 18 Å band, the K18 index, as measured from follow-up medium-resolution spectroscopy taken during the course of the HK survey. When provided with accurate input data, the trained networks were able to estimate [Fe/H] and to determine the class with high accuracy (with a robust estimated one-sigma scatter of SBI = 0.13 dex, and an overall correction rate of 91%). The ANN approach was then used in order to recover information on the K18 index and (B-V)0 color directly from the APM

  16. Inefficient star formation in extremely metal poor galaxies.

    PubMed

    Shi, Yong; Armus, Lee; Helou, George; Stierwalt, Sabrina; Gao, Yu; Wang, Junzhi; Zhang, Zhi-Yu; Gu, Qiusheng

    2014-10-16

    The first galaxies contain stars born out of gas with few or no 'metals' (that is, elements heavier than helium). The lack of metals is expected to inhibit efficient gas cooling and star formation, but this effect has yet to be observed in galaxies with an oxygen abundance (relative to hydrogen) below a tenth of that of the Sun. Extremely metal poor nearby galaxies may be our best local laboratories for studying in detail the conditions that prevailed in low metallicity galaxies at early epochs. Carbon monoxide emission is unreliable as a tracer of gas at low metallicities, and while dust has been used to trace gas in low-metallicity galaxies, low spatial resolution in the far-infrared has typically led to large uncertainties. Here we report spatially resolved infrared observations of two galaxies with oxygen abundances below ten per cent of the solar value, and show that stars formed very inefficiently in seven star-forming clumps in these galaxies. The efficiencies are less than a tenth of those found in normal, metal rich galaxies today, suggesting that star formation may have been very inefficient in the early Universe. PMID:25318522

  17. Inefficient star formation in extremely metal poor galaxies

    NASA Astrophysics Data System (ADS)

    Shi, Yong; Armus, Lee; Helou, George; Stierwalt, Sabrina; Gao, Yu; Wang, Junzhi; Zhang, Zhi-Yu; Gu, Qiusheng

    2014-10-01

    The first galaxies contain stars born out of gas with few or no `metals' (that is, elements heavier than helium). The lack of metals is expected to inhibit efficient gas cooling and star formation, but this effect has yet to be observed in galaxies with an oxygen abundance (relative to hydrogen) below a tenth of that of the Sun. Extremely metal poor nearby galaxies may be our best local laboratories for studying in detail the conditions that prevailed in low metallicity galaxies at early epochs. Carbon monoxide emission is unreliable as a tracer of gas at low metallicities, and while dust has been used to trace gas in low-metallicity galaxies, low spatial resolution in the far-infrared has typically led to large uncertainties. Here we report spatially resolved infrared observations of two galaxies with oxygen abundances below ten per cent of the solar value, and show that stars formed very inefficiently in seven star-forming clumps in these galaxies. The efficiencies are less than a tenth of those found in normal, metal rich galaxies today, suggesting that star formation may have been very inefficient in the early Universe.

  18. AGB nucleosynthesis at low metallicity: What can we learn from Carbon- and s-elements-enhanced metal-poor stars

    NASA Astrophysics Data System (ADS)

    Abate, C.; Pols, O. R.; Izzard, R. G.; Karakas, A. I.

    2013-02-01

    CEMP-s stars are very metal-poor stars with enhanced abundances of carbon and s-process elements. They form a significant proportion of the very metal-poor stars in the Galactic halo and are mostly observed in binary systems. This suggests that the observed chemical anomalies are due to mass accretion in the past from an asymptotic giant branch (AGB) star. Because CEMP-s stars have hardly evolved since their formation, the study of their observed abundances provides a way to probe our models of AGB nucleosynthesis at low metallicity. To this end we included in our binary evolution model the results of the latest models of AGB nucleosynthesis and we simulated a grid of 100 000 binary stars at metallicity Z = 0.0001 in a wide range of initial masses and separations. We compared our modelled stars with a sample of 60 CEMP-s stars from the SAGA database of metal-poor stars. For each observed CEMP-s star of the sample we found the modelled star that reproduces best the observed abundances. The result of this comparison is that we are able to reproduce simultaneously the observed abundance of the elements affected by AGB nucleosynthesis (e.g. C, Mg, s-elements) for about 60% of the stars in the sample.

  19. THE MOST METAL-POOR STARS. II. CHEMICAL ABUNDANCES OF 190 METAL-POOR STARS INCLUDING 10 NEW STARS WITH [Fe/H] {<=} -3.5 , ,

    SciTech Connect

    Yong, David; Norris, John E.; Bessell, M. S.; Asplund, M.; Christlieb, N.; Beers, Timothy C.; Barklem, P. S.; Frebel, Anna; Ryan, S. G. E-mail: jen@mso.anu.edu.au E-mail: martin@mso.anu.edu.au E-mail: beers@pa.msu.edu E-mail: afrebel@mit.edu

    2013-01-01

    We present a homogeneous chemical abundance analysis of 16 elements in 190 metal-poor Galactic halo stars (38 program and 152 literature objects). The sample includes 171 stars with [Fe/H] {<=} -2.5, of which 86 are extremely metal poor, [Fe/H] {<=} -3.0. Our program stars include 10 new objects with [Fe/H] {<=} -3.5. We identify a sample of 'normal' metal-poor stars and measure the trends between [X/Fe] and [Fe/H], as well as the dispersion about the mean trend for this sample. Using this mean trend, we identify objects that are chemically peculiar relative to 'normal' stars at the same metallicity. These chemically unusual stars include CEMP-no objects, one star with high [Si/Fe], another with high [Ba/Sr], and one with unusually low [X/Fe] for all elements heavier than Na. The Sr and Ba abundances indicate that there may be two nucleosynthetic processes at lowest metallicity that are distinct from the main r-process. Finally, for many elements, we find a significant trend between [X/Fe] versus T {sub eff}, which likely reflects non-LTE and/or three-dimensional effects. Such trends demonstrate that care must be exercised when using abundance measurements in metal-poor stars to constrain chemical evolution and/or nucleosynthesis predictions.

  20. A Model for Abundances in Metal-poor Stars

    NASA Astrophysics Data System (ADS)

    Qian, Y.-Z.; Wasserburg, G. J.

    2001-10-01

    A model is presented that seeks to explain quantitatively the stellar abundances of r-process elements and other elements associated with the r-process sites. It is argued that the abundances of all these elements in stars with -3<~[Fe/H]<-1 can be explained by the contributions of three sources. The sources are the first generations of very massive (>~100 Msolar) stars that are formed from big bang debris and are distinct from Type II supernovae (SNe II) and two types of SNe II, the H and L events, which can occur only at [Fe/H]>~-3. The H events are of high frequency and produce dominantly heavy (A>130) r-elements but no Fe (presumably leaving behind black holes). The L events are of low frequency and produce Fe and dominantly light (A<~130) r-elements (essentially none above Ba). By using the observed abundances in two ultra-metal-poor stars and the solar r-abundances, the initial or prompt inventory of elements produced by the first generations of very massive stars and the yields of H and L events can be determined. The abundances of a large number of elements in a star can then be calculated from the model by using only the observed Eu and Fe abundances. To match the model results and the observational data for stars with -3<[Fe/H]<-1 requires that the solar r-abundances for Sr, Y, Zr, and Ba must be significantly increased from the standard values. No such changes appear to be required for all other elements. If the changes in the solar r-abundances for Sr, Y, Zr, and Ba are not permitted, the model fails at -3<[Fe/H]<-1 but still works at [Fe/H]~-3 for these four elements. By using the corrected solar r-abundances for these elements, good agreement is obtained between the model results and data over the range -3<[Fe/H]<-1. No evidence of s-process contributions is found in this region, but all the observational data in this region now show regular increases of Ba/Eu above the standard solar r-process value. Whether the solar r-components of Sr, Y, Zr, and

  1. Improved Yttrium and Zirconium Abundances in Metal-Poor Stars

    NASA Astrophysics Data System (ADS)

    Violante, Renata; Biemont, E.; Cowan, J. J.; Sneden, C.

    2012-01-01

    Abstract We present new abundances of the lighter n-capture elements, Yttrium (Z=39) and Zirconium (Z=40) in the very metal poor, r-process rich stars BD+17 3248 and HD 221170. Very accurate abundances were obtained by use of the new transition probabilities for Y II published by Biémont et al. 2011, and Zr II by Malcheva et al. 2006, and by expanding the number of transitions employed for each element. For example, in BD+17 3248, we find log ɛπσιλον=-0.03 +/- 0.03 (σιγμα=0.15, from 23 lines) for Y II. As for Zr II, log ɛπσιλον = 0.65 +/- 0.03 (σɛγμα = 0.1, from 13 lines). The resulting abundance ratio is log ɛπσιλον [Y/Zr] = -0.68 +/- 0.05. The results for HD 221170 are in accord with those of BD+17 3248. The quantity of lines used to form the abundance means has increased significantly since the original studies of these stars, resulting in more trustworthy abundances. These observed abundance ratios are in agreement with an r-process-only value predicted from stellar models, but is under-abundant compared to an empirical model derived from direct analyses of meteoritic material. This ambiguity should stimulate further nucleosynthetic analysis to explain this abundance ratio. We would like to extend our gratitude to NSF grant AST-0908978 and the University of Texas Astronomy Department Rex G. Baker, Jr. Endowment for their financial support in this project.

  2. Abundances of 30 Elements in 23 Metal-Poor Stars

    NASA Astrophysics Data System (ADS)

    Johnson, Jennifer A.

    2002-03-01

    We report the abundances of 30 elements in 23 metal-poor ([Fe/H]<-1.7) giants. These are based on 7774 equivalent widths and spectral synthesis of 229 additional lines. Hyperfine splitting is taken into account when appropriate. Our choice of model atmospheres has the most influence on the accuracy of our abundances. We consider the effect of different model atmospheres on our results. In addition to the random errors in Teff, logg, and microturbulent velocity, there are several sources of systematic error. These include using Teff determined from Fe I lines rather than colors, ignoring non-LTE effects on the Fe I/Fe II ionization balance, using models with solar [α/Fe] ratios, and using Kurucz models with overshooting. Of these, only the use of models with solar [α/Fe] ratios had a negligible effect. However, while the absolute abundances can change by greater than 0.10 dex, the relative abundances, especially between closely allied atoms such as the rare earth group, often show only small (less than 0.03 dex) changes. We found that some strong lines of Fe I, Mn I, and Cr I consistently gave lower abundances by ~0.2 dex, a number larger than the quoted errors in the gf-values. After considering a model with depth-dependent microturbulent velocity and a model with hotter temperatures in the upper layers, we conclude that the latter did a better job of resolving the problem and agreeing with observational evidence for the structure of stars. The error analysis includes the effects of correlation of Teff, logg, and ξ errors, which is crucial for certain element ratios, such as [Mg/Fe]. The abundances presented here are being analyzed and discussed in a separate series of papers.

  3. Lithium evolution in metal-poor stars: from Pre-Main Sequence to the Spite Plateau

    NASA Astrophysics Data System (ADS)

    Fu, Xiaoting; Bressan, Alessandro; Molaro, Paolo; Marigo, Paola

    2015-08-01

    Lithium abundance derived in metal-poor main sequence stars is about three times lower than the value of primordial Li predicts by the standard Big Bang nucleosynthesis when the baryon density is taken from the CMB or the deuterium measurements. This disagreement is generally referred as the Li problem. We here reconsider the stellar Li evolution from the pre-main sequence to the end of the main sequence phase by introducing the effects of convective overshooting and residual mass accretion. We show that 7Li could be significantly depleted by convective overshooting in the PMS phase and then partially restored in the stellar atmosphere by a tail of matter accretion which follows the Li depletion phase and that could be regulated by EUV photo-evaporation. By considering the conventional nuclear burning and microscopic diffusion along the main sequence we can reproduce the Spite plateau for stars with m0 = 0.62 - 0.80 M⊙ and the Li decline branch for lower mass dwarfs e.g, m0 = 0.57 - 0.60 M⊙ for a wide range of metallicities (Z=0.00001 to Z=0.0005) starting from an initial 7Li abundance A(Li) = 2.72. This environmental Li evolution model offers the possibility to interpret the decreasing of Li abundance in extremely metal-poor stars, the Li disparities in spectroscopic binaries and low Li abundance in planet hosting stars.

  4. Lithium evolution in metal-poor stars: from pre-main sequence to the Spite plateau

    NASA Astrophysics Data System (ADS)

    Fu, Xiaoting; Bressan, Alessandro; Molaro, Paolo; Marigo, Paola

    2015-09-01

    Lithium abundance derived in metal-poor main-sequence (MS) stars is about three times lower than the value of primordial Li predicted by the standard big bang nucleosynthesis when the baryon density is taken from the cosmic microwave background or the deuterium measurements. This disagreement is generally referred as the lithium problem. We here reconsider the stellar Li evolution from the pre-main sequence (PMS) to the end of the MS phase by introducing the effects of convective overshooting (OV) and residual mass accretion. We show that 7Li could be significantly depleted by convective OV in the PMS phase and then partially restored in the stellar atmosphere by a tail of matter accretion which follows the Li-depletion phase and that could be regulated by EUV photoevaporation. By considering the conventional nuclear burning and microscopic diffusion along the MS, we can reproduce the Spite plateau for stars with initial mass m0 = 0.62-0.80 M⊙, and the Li declining branch for lower mass dwarfs, e.g. m0 = 0.57-0.60 M⊙, for a wide range of metallicities (Z = 0.00001 to Z = 0.0005), starting from an initial Li abundance A(Li) = 2.72. This environmental Li evolution model also offers the possibility to interpret the decrease of Li abundance in extremely metal-poor stars, the Li disparities in spectroscopic binaries and the low Li abundance in planet hosting stars.

  5. The Most Metal-poor Stars. II. Chemical Abundances of 190 Metal-poor Stars Including 10 New Stars with [Fe/H] <= -3.5

    NASA Astrophysics Data System (ADS)

    Yong, David; Norris, John E.; Bessell, M. S.; Christlieb, N.; Asplund, M.; Beers, Timothy C.; Barklem, P. S.; Frebel, Anna; Ryan, S. G.

    2013-01-01

    We present a homogeneous chemical abundance analysis of 16 elements in 190 metal-poor Galactic halo stars (38 program and 152 literature objects). The sample includes 171 stars with [Fe/H] <= -2.5, of which 86 are extremely metal poor, [Fe/H] <= -3.0. Our program stars include 10 new objects with [Fe/H] <= -3.5. We identify a sample of "normal" metal-poor stars and measure the trends between [X/Fe] and [Fe/H], as well as the dispersion about the mean trend for this sample. Using this mean trend, we identify objects that are chemically peculiar relative to "normal" stars at the same metallicity. These chemically unusual stars include CEMP-no objects, one star with high [Si/Fe], another with high [Ba/Sr], and one with unusually low [X/Fe] for all elements heavier than Na. The Sr and Ba abundances indicate that there may be two nucleosynthetic processes at lowest metallicity that are distinct from the main r-process. Finally, for many elements, we find a significant trend between [X/Fe] versus T eff, which likely reflects non-LTE and/or three-dimensional effects. Such trends demonstrate that care must be exercised when using abundance measurements in metal-poor stars to constrain chemical evolution and/or nucleosynthesis predictions. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile (proposal 281.D-5015).

  6. Seven new carbon-enhanced metal-poor RR Lyrae stars

    SciTech Connect

    Kennedy, Catherine R.; Stancliffe, Richard J.; Kuehn, Charles; Beers, Timothy C.; Kinman, T. D.; Placco, Vinicius M.; Reggiani, Henrique; Rossi, Silvia; Lee, Young Sun

    2014-05-20

    We report estimated carbon-abundance ratios, [C/Fe], for seven newly discovered carbon-enhanced metal-poor (CEMP) RR Lyrae stars. These are well-studied RRab stars that had previously been selected as CEMP candidates based on low-resolution spectra. For this pilot study, we observed eight of these CEMP RR Lyrae candidates with the Wide Field Spectrograph on the ANU 2.3 m telescope. Prior to this study, only two CEMP RR Lyrae stars had been discovered: TY Gru and SDSS J1707+58. We compare our abundances to new theoretical models of the evolution of low-mass stars in binary systems. These simulations evolve the secondary stars, post accretion from an asymptotic giant-branch (AGB) donor, all the way to the RR Lyrae stage. The abundances of CEMP RR Lyrae stars can be used as direct probes of the nature of the donor star, such as its mass, and the amount of material accreted onto the secondary. We find that the majority of the sample of CEMP RR Lyrae stars is consistent with AGB donor masses of around 1.5-2.0 M {sub ☉} and accretion masses of a few hundredths of a solar mass. Future high-resolution studies of these newly discovered CEMP RR Lyrae stars will help disentangle the effects of the proposed mixing processes that occur in such objects.

  7. Metal-poor stars: The fingerprints of the first stars and the early galaxy

    NASA Astrophysics Data System (ADS)

    Lai, David K.

    2008-10-01

    The chemical composition of metal-poor stars are fossil records of the first generations of stars and of the early Galactic environment. In this thesis I cover two of the main challenges in studying metal-poor stars. The first is finding metal-poor candidates, and the second is the high-resolution spectral follow-up study of a sample of metal-poor stars. In the first part of my thesis I explore one process to identify and study very metal-poor stars (VMP, [Fe/H] <= -2.0), using moderate-resolution spectra (R~7000) from the Echellete Spectrograph and Imager (ESI) instrument at the Keck Observatory. With ESI it is possible to obtain high signal-to-noise spectra efficiently ( V ~ 13 stars in ~ 15 minutes). Even at this moderate resolution I am able to derive abundances for Mg, Ca, Ti, Cr, and Ba. I also am able to derive C and Sr abundances through spectral synthesis. With the C abundances in hand, I also explore the phenomenon of carbon-enhanced metal-poor (CEMP) stars. A surprising discovery in the study of metal-poor stars is the number which are enhanced in carbon to levels of [C/Fe] >= 1.0. I explore how the metallicity distribution function of any particular sample is an important aspect in determining this fraction. The second part of this thesis is a detailed study of a sample of VMP stars using high-resolution spectral analysis. Most of the stars in the sample came from the ESI study. These observations were carried out with the High Resolution Echelle Spectrometer (HIRES) instrument at Keck, with spectral resolution of R~45,000. From these HIRES spectra, I have measured the abundances of up to 25 elements from C through Eu in 28 VMP stars. In this sample I have discovered a new star that is highly enhanced by r-process material, CS 31078-018, and a new [Fe/H]= -4.0 star, CS 30336-049. The abundance ratios in the stars in this sample may be the products of nucleosynthesis in the very first stars. With this in mind I have compared the abundance ratios of the

  8. The EMBLA survey - metal-poor stars in the Galactic bulge

    NASA Astrophysics Data System (ADS)

    Howes, Louise M.; Asplund, Martin; Keller, Stefan C.; Casey, Andrew R.; Yong, David; Lind, Karin; Frebel, Anna; Hays, Austin; Alves-Brito, Alan; Bessell, Michael S.; Casagrande, Luca; Marino, Anna F.; Nataf, David M.; Owen, Christopher I.; Da Costa, Gary S.; Schmidt, Brian P.; Tisserand, Patrick

    2016-07-01

    Cosmological models predict the oldest stars in the Galaxy should be found closest to the centre of the potential well, in the bulge. The Extremely Metal-poor BuLge stars with AAOmega survey (EMBLA) successfully searched for these old, metal-poor stars by making use of the distinctive SkyMapper photometric filters to discover candidate metal-poor stars in the bulge. Their metal-poor nature was then confirmed using the AAOmega spectrograph on the Anglo-Australian Telescope. Here we present an abundance analysis of 10 bulge stars with -2.8 < [Fe/H] < -1.7 from MIKE/Magellan observations, in total determining the abundances of 22 elements. Combining these results with our previous high-resolution data taken as part of the Gaia-ESO Survey, we have started to put together a picture of the chemical and kinematic nature of the most metal-poor stars in the bulge. The currently available kinematic data are consistent with the stars belonging to the bulge, although more accurate measurements are needed to constrain the stars' orbits. The chemistry of these bulge stars deviates from that found in halo stars of the same metallicity. Two notable differences are the absence of carbon-enhanced metal-poor bulge stars, and the α element abundances exhibit a large intrinsic scatter and include stars which are underabundant in these typically enhanced elements.

  9. Carbon-enhanced metal-poor stars: probes of nucleosynthesis from the first generation of stars in the Universe

    NASA Astrophysics Data System (ADS)

    Beers, T. C.

    CEMP-no stars are a subclass of very metal-poor (VMP; [Fe/H] < -2.0) and extremely metal-poor (EMP; [Fe/H] < -3.0) stars in the Milky Way (including the most iron-deficient stars known) with no strong enhancements of s-process elements (which might be attributed to mass transfer from a binary companion). In addition to C, these stars exhibit enhancements of N, O, and other light elements such as Na, Mg, Al, and Si, a pattern that may be uniquely produced by the first-generation stars in the early Universe. These stars have also been recently linked to the observed abundance pattern in a high redshift (z = 3.1), EMP damped Lyman-alpha cloud. I discuss the discovery of CEMP-no stars, connections with their progenitors in the outer-halo component of the Galaxy, new surveys that are expanding their numbers, and planned future spectroscopic exploration of these fascinating objects.

  10. Line Broadening in Field Metal-Poor Red Giant and Red Horizontal Branch Stars

    NASA Astrophysics Data System (ADS)

    Carney, Bruce W.; Latham, David W.; Stefanik, Robert P.; Laird, John B.

    2008-01-01

    We report 349 radial velocities for 45 metal-poor field red giant branch (RGB) and red horizontal branch (RHB) stars, with time coverage ranging from 1 to 21 years. We have identified one new spectroscopic binary, HD 4306, and one possible such system, HD 184711. We also provide 57 radial velocities for 11 of the 91 stars reported in our previous work. All but one of the 11 stars had been found to have variable radial velocities. New velocities for the long-period spectroscopic binaries BD-1 2582 and HD 108317 have extended the time coverage to 21.7 and 12.5 years, respectively, but in neither case have we yet completed a full orbital period. As was found in the previous study, radial velocity "jitter" is present in many of the most luminous stars. Excluding stars showing spectroscopic binary orbital motion, all 7 of the red giants with estimated MV values more luminous than -2.0 display jitter, as well as 3 of the 14 stars with -2.0 < MV <= -1.4. We have also measured the line broadening in all the new spectra, using synthetic spectra as templates. Comparison with results from high-resolution and higher signal-to-noise (S/N) spectra employed by other workers shows good agreement down to line-broadening levels of 3 km s-1, well below our instrumental resolution of 8.5 km s-1. As the previous work demonstrated, the majority of the most luminous red giants show significant line broadening, as do many of the red horizontal branch stars, and we briefly discuss possible causes. The line broadening appears related to velocity jitter, in that both appear primarily among the highest luminosity red giants.

  11. Radiative levitation in carbon-enhanced metal-poor stars with s-process enrichment

    NASA Astrophysics Data System (ADS)

    Matrozis, E.; Stancliffe, R. J.

    2016-07-01

    A significant fraction of all metal-poor stars are carbon-rich. Most of these carbon-enhanced metal-poor (CEMP) stars also show enhancement in elements produced mainly by the s-process (CEMP-s stars), and evidence suggests that the origin of these non-standard abundances can be traced to mass transfer from a binary asymptotic giant branch (AGB) companion. Thus, observations of CEMP-s stars are commonly used to infer the nucleosynthesis output of low-metallicity AGB stars. A crucial step in this exercise is understanding what happens to the accreted material after mass transfer ceases. Here we present models of the post-mass-transfer evolution of CEMP-s stars considering the physics of thermohaline mixing and atomic diffusion, including radiative levitation. We find that stars with typical CEMP-s star masses, M ≈ 0.85 M⊙, have very shallow convective envelopes (Menv ≲ 10-7 M⊙). Hence, the surface abundance variations arising from the competition between gravitational settling and radiative levitation should be orders of magnitude larger than observed (e.g. [C/Fe] < -1 or [C/Fe] > +4). Lower-mass stars (M ≈ 0.80 M⊙) retain thicker convective envelopes and thus show variations more in line with observations, but are generally too unevolved (log g > 4) when they reach the age of the Universe. We are therefore unable to reproduce the spread in the observed abundances with these models and conclude that some other physical process must largely suppress atomic diffusion in the outer layers of CEMP-s stars. We demonstrate that this could be achieved by some additional (turbulent) mixing process operating at the base of the convective envelope, as found by other authors. Alternatively, mass-loss rates around 10-13 M⊙yr-1 could also negate most of the abundance variations by eroding the surface layers and forcing the base of the convective envelope to move inwards in mass. Since atomic diffusion cannot have a substantial effect on the surface abundances of CEMP

  12. An Elemental Assay of Very, Extremely, and Ultra-metal-poor Stars

    NASA Astrophysics Data System (ADS)

    Hansen, T.; Hansen, C. J.; Christlieb, N.; Beers, T. C.; Yong, D.; Bessell, M. S.; Frebel, A.; García Pérez, A. E.; Placco, V. M.; Norris, J. E.; Asplund, M.

    2015-07-01

    We present a high-resolution elemental-abundance analysis for a sample of 23 very metal-poor ([Fe/H] < ‑2.0) stars, 12 of which are extremely metal-poor ([Fe/H] < ‑3.0), and 4 of which are ultra-metal-poor ([Fe/H] < ‑4.0). These stars were targeted to explore differences in the abundance ratios for elements that constrain the possible astrophysical sites of element production, including Li, C, N, O, the α-elements, the iron-peak elements, and a number of neutron-capture elements. This sample substantially increases the number of known carbon-enhanced metal-poor (CEMP) and nitrogen-enhanced metal-poor (NEMP) stars—our program stars include eight that are considered “normal” metal-poor stars, six CEMP-no stars, five CEMP-s stars, two CEMP-r stars, and two CEMP-r/s stars. One of the CEMP-r stars and one of the CEMP-r/s stars are possible NEMP stars. We detect lithium for three of the six CEMP-no stars, all of which are Li depleted with respect to the Spite plateau. The majority of the CEMP stars have [C/N] > 0. The stars with [C/N] < 0 suggest a larger degree of mixing; the few CEMP-no stars that exhibit this signature are only found at [Fe/H] < ‑3.4, a metallicity below which we also find the CEMP-no stars with large enhancements in Na, Mg, and Al. We confirm the existence of two plateaus in the absolute carbon abundances of CEMP stars, as suggested by Spite et al. We also present evidence for a “floor” in the absolute Ba abundances of CEMP-no stars at A(Ba) ∼ ‑2.0. Based on observations made with the European Southern Observatory telescopes.

  13. The EMBLA Survey - Metal-poor stars in the Galactic bulge

    NASA Astrophysics Data System (ADS)

    Howes, Louise M.; Asplund, Martin; Keller, Stefan C.; Casey, Andrew R.; Yong, David; Lind, Karin; Frebel, Anna; Hays, Austin; Alves-Brito, Alan; Bessell, Michael S.; Casagrande, Luca; Marino, Anna F.; Nataf, David M.; Owen, Christopher I.; Da Costa, Gary S.; Schmidt, Brian P.; Tisserand, Patrick

    2016-04-01

    Cosmological models predict the oldest stars in the Galaxy should be found closest to the centre of the potential well, in the bulge. The EMBLA Survey successfully searched for these old, metal-poor stars by making use of the distinctive SkyMapper photometric filters to discover candidate metal-poor stars in the bulge. Their metal-poor nature was then confirmed using the AAOmega spectrograph on the AAT. Here we present an abundance analysis of 10 bulge stars with -2.8 <[Fe/H]<- 1.7 from MIKE/Magellan observations, in total determining the abundances of 22 elements. Combining these results with our previous high-resolution data taken as part of the Gaia-ESO Survey, we have started to put together a picture of the chemical and kinematic nature of the most metal-poor stars in the bulge. The currently available kinematic data is consistent with the stars belonging to the bulge, although more accurate measurements are needed to constrain the stars' orbits. The chemistry of these bulge stars deviates from that found in halo stars of the same metallicity. Two notable differences are the absence of carbon-enhanced metal-poor bulge stars, and the alpha-element abundances exhibit a large intrinsic scatter and include stars which are underabundant in these typically enhanced elements.

  14. 2MASS J18082002-5104378: The brightest (V = 11.9) ultra metal-poor star

    NASA Astrophysics Data System (ADS)

    Meléndez, Jorge; Placco, Vinicius M.; Tucci-Maia, Marcelo; Ramírez, Iván; Li, Ting S.; Perez, Gabriel

    2016-01-01

    Context. The most primitive metal-poor stars are important for studying the conditions of the early galaxy and are also relevant to big bang nucleosynthesis. Aims: Our objective is to find the brightest (V< 14) most metal-poor stars. Methods: Candidates were selected using a new method, which is based on the mismatch between spectral types derived from colors and observed spectral types. They were observed first at low resolution with EFOSC2 at the NTT to obtain an initial set of stellar parameters. The most promising candidate, 2MASS J18082002-5104378 (V = 11.9), was observed at high resolution (R = 50 000) with UVES at the VLT, and a standard abundance analysis was performed. Results: We found that 2MASS J18082002-5104378 is an ultra metal-poor star with stellar parameters Teff = 5440 K, log g = 3.0 dex, vt = 1.5 km s-1, [Fe/H] = -4.1 dex. The star has [C/Fe] < +0.9 in a 1D analysis, or [C/Fe] ≲ +0.5 if 3D effects are considered; its abundance pattern is typical of normal (non-CEMP) ultra metal-poor stars. Interestingly, the star has a binary companion. Conclusions: 2MASS J1808-5104 is the brightest (V = 11.9) metal-poor star of its category, and it could be studied further with even higher S/N spectroscopy to determine additional chemical abundances, thus providing important constraints to the early chemical evolution of our Galaxy. Based on observations obtained at the European Southern Observatory (ESO) Very Large Telescope (VLT, observing program 293.D-5036) and New Technology Telescope (NTT, observing programs 091.D-0292 and 092.D-0308).

  15. Chemical Abundances of Metal-poor stars in Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Venn, Kim A.; Jablonka, Pascale; Hill, Vanessa; Starkenburg, Else; Lemasle, Bertrand; Shetrone, Matthew; Irwin, Mike; Norris, John; Yong, David; Gilmore, Gerry; Salvadori, Stephania; Skuladottir, Asa; Tolstoy, Eline

    2016-08-01

    Stars in low-mass dwarf galaxies show a larger range in their chemical properties than those in the Milky Way halo. The slower star formation efficiency make dwarf galaxies ideal systems for testing nucleosynthetic yields. Not only are alpha-poor stars found at lower metallicities, and a higher fraction of carbon-enhanced stars, but we are also finding stars in dwarf galaxies that appear to be iron-rich. These are compared with yields from a variety of supernova predictions.

  16. The Most Metal-poor Stars. III. The Metallicity Distribution Function and Carbon-enhanced Metal-poor Fraction

    NASA Astrophysics Data System (ADS)

    Yong, David; Norris, John E.; Bessell, M. S.; Christlieb, N.; Asplund, M.; Beers, Timothy C.; Barklem, P. S.; Frebel, Anna; Ryan, S. G.

    2013-01-01

    We examine the metallicity distribution function (MDF) and fraction of carbon-enhanced metal-poor (CEMP) stars in a sample that includes 86 stars with [Fe/H] <= -3.0, based on high-resolution, high signal-to-noise spectroscopy, of which some 32 objects lie below [Fe/H] = -3.5. After accounting for the completeness function, the "corrected" MDF does not exhibit the sudden drop at [Fe/H] = -3.6 that was found in recent samples of dwarfs and giants from the Hamburg/ESO survey. Rather, the MDF decreases smoothly down to [Fe/H] = -4.1. Similar results are obtained from the "raw" MDF. We find that the fraction of CEMP objects below [Fe/H] = -3.0 is 23% ± 6% and 32% ± 8% when adopting the Beers & Christlieb and Aoki et al. CEMP definitions, respectively. The former value is in fair agreement with some previous measurements, which adopt the Beers & Christlieb criterion. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile (proposal 281.D-5015).

  17. THE MOST METAL-POOR STARS. III. THE METALLICITY DISTRIBUTION FUNCTION AND CARBON-ENHANCED METAL-POOR FRACTION , ,

    SciTech Connect

    Yong, David; Norris, John E.; Bessell, M. S.; Asplund, M.; Christlieb, N.; Beers, Timothy C.; Barklem, P. S.; Frebel, Anna; Ryan, S. G. E-mail: jen@mso.anu.edu.au E-mail: martin@mso.anu.edu.au E-mail: beers@pa.msu.edu E-mail: afrebel@mit.edu

    2013-01-01

    We examine the metallicity distribution function (MDF) and fraction of carbon-enhanced metal-poor (CEMP) stars in a sample that includes 86 stars with [Fe/H] {<=} -3.0, based on high-resolution, high signal-to-noise spectroscopy, of which some 32 objects lie below [Fe/H] = -3.5. After accounting for the completeness function, the 'corrected' MDF does not exhibit the sudden drop at [Fe/H] = -3.6 that was found in recent samples of dwarfs and giants from the Hamburg/ESO survey. Rather, the MDF decreases smoothly down to [Fe/H] = -4.1. Similar results are obtained from the 'raw' MDF. We find that the fraction of CEMP objects below [Fe/H] = -3.0 is 23% {+-} 6% and 32% {+-} 8% when adopting the Beers and Christlieb and Aoki et al. CEMP definitions, respectively. The former value is in fair agreement with some previous measurements, which adopt the Beers and Christlieb criterion.

  18. Detailed Abundances of Two Very Metal-poor Stars in Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Kirby, Evan N.; Cohen, Judith G.

    2012-12-01

    The most metal-poor stars in dwarf spheroidal galaxies (dSphs) can show the nucleosynthetic patterns of one or a few supernovae (SNe). These SNe could have zero metallicity, making metal-poor dSph stars the closest surviving links to Population III stars. Metal-poor dSph stars also help to reveal the formation mechanism of the Milky Way (MW) halo. We present the detailed abundances from Keck/HIRES spectroscopy for two very metal-poor stars in two MW dSphs. One star, in the Sculptor dSph, has [Fe I/H] = -2.40. The other star, in the Ursa Minor dSph, has [Fe I/H] = -3.16. Both stars fall in the previously discovered low-metallicity, high-[α/Fe] plateau. Most abundance ratios of very metal-poor stars in these two dSphs are largely consistent with very metal-poor halo stars. However, the abundances of Na and some r-process elements lie at the lower end of the envelope defined by inner halo stars of similar metallicity. We propose that the metallicity dependence of SN yields is the cause. The earliest SNe in low-mass dSphs have less gas to pollute than the earliest SNe in massive halo progenitors. As a result, dSph stars at -3 < [Fe/H] < -2 sample SNe with [Fe/H] Lt -3, whereas halo stars in the same metallicity range sample SNe with [Fe/H] ~ -3. Consequently, enhancements in [Na/Fe] and [r/Fe] were deferred to higher metallicity in dSphs than in the progenitors of the inner halo. Data herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.

  19. DETAILED ABUNDANCES OF TWO VERY METAL-POOR STARS IN DWARF GALAXIES

    SciTech Connect

    Kirby, Evan N.; Cohen, Judith G.

    2012-12-01

    The most metal-poor stars in dwarf spheroidal galaxies (dSphs) can show the nucleosynthetic patterns of one or a few supernovae (SNe). These SNe could have zero metallicity, making metal-poor dSph stars the closest surviving links to Population III stars. Metal-poor dSph stars also help to reveal the formation mechanism of the Milky Way (MW) halo. We present the detailed abundances from Keck/HIRES spectroscopy for two very metal-poor stars in two MW dSphs. One star, in the Sculptor dSph, has [Fe I/H] = -2.40. The other star, in the Ursa Minor dSph, has [Fe I/H] = -3.16. Both stars fall in the previously discovered low-metallicity, high-[{alpha}/Fe] plateau. Most abundance ratios of very metal-poor stars in these two dSphs are largely consistent with very metal-poor halo stars. However, the abundances of Na and some r-process elements lie at the lower end of the envelope defined by inner halo stars of similar metallicity. We propose that the metallicity dependence of SN yields is the cause. The earliest SNe in low-mass dSphs have less gas to pollute than the earliest SNe in massive halo progenitors. As a result, dSph stars at -3 < [Fe/H] < -2 sample SNe with [Fe/H] << -3, whereas halo stars in the same metallicity range sample SNe with [Fe/H] {approx} -3. Consequently, enhancements in [Na/Fe] and [r/Fe] were deferred to higher metallicity in dSphs than in the progenitors of the inner halo.

  20. Possible evidence for metal accretion onto the surfaces of metal-poor main-sequence stars

    SciTech Connect

    Hattori, Kohei; Yoshii, Yuzuru; Beers, Timothy C.; Carollo, Daniela; Lee, Young Sun

    2014-04-01

    The entire evolution of the Milky Way, including its mass-assembly and star-formation history, is imprinted onto the chemo-dynamical distribution function of its member stars, f(x, v, [X/H]), in the multi-dimensional phase space spanned by position, velocity, and elemental abundance ratios. In particular, the chemo-dynamical distribution functions for low-mass stars (e.g., G- or K-type dwarfs) are precious tracers of the earliest stages of the Milky Way's formation, since their main-sequence lifetimes approach or exceed the age of the universe. A basic tenet of essentially all previous analyses is that the stellar metallicity, usually parameterized as [Fe/H], is conserved over time for main-sequence stars (at least those that have not been polluted due to mass transfer from binary companions). If this holds true, any correlations between metallicity and kinematics for long-lived main-sequence stars of different masses, effective temperatures, or spectral types must strictly be the same, since they reflect the same mass-assembly and star-formation histories. By analyzing a sample of nearby metal-poor halo and thick-disk stars on the main sequence, taken from Data Release 8 of the Sloan Digital Sky Survey, we find that the median metallicity of G-type dwarfs is systematically higher (by about 0.2 dex) than that of K-type dwarfs having the same median rotational velocity about the Galactic center. If it can be confirmed, this finding may invalidate the long-accepted assumption that the atmospheric metallicities of long-lived stars are conserved over time.

  1. SPECTROSCOPIC STUDIES OF EXTREMELY METAL-POOR STARS WITH THE SUBARU HIGH DISPERSION SPECTROGRAPH. V. THE Zn-ENHANCED METAL-POOR STAR BS 16920-017

    SciTech Connect

    Honda, Satoshi; Aoki, Wako; Beers, Timothy C.; Takada-Hidai, Masahide E-mail: aoki.wako@nao.ac.jp E-mail: hidai@apus.rh.u-tokai.ac.jp

    2011-04-01

    We report Zn abundances for 18 very metal-poor stars studied in our previous work, covering the metallicity range -3.2< [Fe/H] <-2.5. The [Zn/Fe] values of most stars show an increasing trend with decreasing [Fe/H] in this metallicity range, confirming the results found by previous studies. However, the extremely metal-poor star BS 16920-017([Fe/H] =-3.2) exhibits a significantly high [Zn/Fe] ratio ([Zn/Fe] = +1.0). Comparison of the chemical abundances of this object with HD 4306, which has similar atmospheric parameters to BS 16920-017, clearly demonstrates a deficiency of {alpha} elements and neutron-capture elements in this star, along with enhancements of Mn and Ni, as well as Zn. The association with a hypernova explosion that has been proposed to explain the high Zn abundance ratios found in extremely metal-poor stars is a possible explanation, although further studies are required to fully interpret the abundance pattern of this object.

  2. Lithium Abundances in Extremely Metal-Poor Turn-Off Stars

    SciTech Connect

    Aoki, W.; Barklem, P.; Christlieb, N.; Beers, T. C.; Inoue, S.

    2008-05-21

    The Lithium (Li) abundances measured for very metal-poor turn-off (unevolved) stars have been interpreted as the result of Big Bang nucleosynthesis. However, the value is lower by a factor of two or three than the prediction of standard Big Bang nucleosynthesis models, adopting the cosmological parameters determined by the measurements of cosmic microwave background radiation with the WMAP satellite. Moreover, the recent measurements for extremely metal-poor stars (objects having iron abundances less than 1/1000th solar) suggest a scatter of the Li abundance, or a possible decreasing trend with decreasing metallicity. In order to further investigate the Li production and destruction processes in the very early universe, we have determined Li abundances for extremely metal-poor stars based on high-resolution spectra for the resonance line of neutral Li. The result of our analysis, combined with previous measurements, indicates that the Li abundances of extremely metal-poor stars are, on average, lower than those of stars with higher metallicity, while the scatter or trend of the Li abundance remains unclear. We discuss possible reasons for the lower Li abundances in extremely metal-poor stars, such as depletion of Li in low-mass unevolved stars, or destruction of Li by the first generations of massive progenitors.

  3. Abundances of carbon-enhanced metal-poor stars as constraints on their formation

    NASA Astrophysics Data System (ADS)

    Hansen, C. J.; Nordström, B.; Hansen, T. T.; Kennedy, C. R.; Placco, V. M.; Beers, T. C.; Andersen, J.; Cescutti, G.; Chiappini, C.

    2016-04-01

    Context. An increasing fraction of carbon-enhanced metal-poor (CEMP) stars is found as their iron abundance, [Fe/H], decreases below [Fe/H] =-2.0. The CEMP-s stars have the highest absolute carbon abundances, [C/H], and are thought to owe their enrichment in carbon and the slow neutron-capture (s-process) elements to mass transfer from a former asymptotic giant branch (AGB) binary companion. The most Fe-poor CEMP stars are normally single, exhibit somewhat lower [C/H] than CEMP-s stars, but show no s-process element enhancement (CEMP-no stars). Abundance determinations of CNO offer clues to their formation sites. Aims: Our aim is to use the medium-resolution spectrograph X-Shooter/VLT to determine stellar parameters and abundances for C, N, Sr, and Ba in several classes of CEMP stars in order to further classify and constrain the astrophysical formation sites of these stars. Methods: Atmospheric parameters for our programme stars were estimated from a combination of V-K photometry, model isochrone fits, and estimates from a modified version of the SDSS/SEGUE spectroscopic pipeline. We then used X-Shooter spectra in conjunction with the 1D local thermodynamic equilibrium spectrum synthesis code MOOG, 1D ATLAS9 atmosphere models to derive stellar abundances, and, where possible, isotopic 12C/13C ratios. Results: Abundances (or limits) of C, N, Sr, and Ba are derived for a sample of 27 faint metal-poor stars for which the X-Shooter spectra have sufficient signal-to-noise ratios (S/N). These moderate resolution, low S/N (~10-40) spectra prove sufficient to perform limited chemical tagging and enable assignment of these stars into the CEMP subclasses (CEMP-s and CEMP-no). According to the derived abundances, 17 of our sample stars are CEMP-s and 3 are CEMP-no, while the remaining 7 are carbon-normal. For four CEMP stars, the subclassification remains uncertain, and two of them may be pulsating AGB stars. Conclusions: The derived stellar abundances trace the formation

  4. r-process enhanched metal-poor stars

    NASA Astrophysics Data System (ADS)

    Cowan, John; Sneden, Christopher; Lawler, James E.; Den Hartog, Elizabeth A.

    Abundance observations indicate the presence of rapid-neutron capture (i.e., r-process) elements in old Galactic halo and globular cluster stars. These observations provide insight into the nature of the earliest generations of stars in the Galaxy - the progenitors of the halo stars - responsible for neutron-capture synthesis of the heavy elements. The large star-to-star scatter observed in the abundances of neutron-capture element/iron ratios at low metallicities - which diminishes with in- creasing metallicity or [Fe/H] - suggests the formation of these heavy elements (presumably from certain types of supernovae) was rare in the early Galaxy. The stellar abundances also indicate a change from the r-process to the slow neutron capture (i.e., s-) process at higher metallicities in the Galaxy and provide insight into Galactic chemical evolution. Finally, the detection of thorium and uranium in halo and globular cluster stars offers an independent age-dating technique that can put lower limits on the age of the Galaxy, and hence the Universe.

  5. Identification of metal-poor stars using the artificial neural network

    NASA Astrophysics Data System (ADS)

    Giridhar, S.; Goswami, A.; Kunder, A.; Muneer, S.; Selvakumar, G.

    2013-08-01

    Context. Identification of metal-poor stars among field stars is extremely useful for studying the structure and evolution of the Galaxy and of external galaxies. Aims: We search for metal-poor stars using the artificial neural network (ANN) and extend its usage to determine absolute magnitudes. Methods: We have constructed a library of 167 medium-resolution stellar spectra (R ~ 1200) covering the stellar temperature range of 4200 to 8000 K, log g range of 0.5 to 5.0, and [Fe/H] range of -3.0 to +0.3 dex. This empirical spectral library was used to train ANNs, yielding an accuracy of 0.3 dex in [Fe/H] , 200 K in temperature, and 0.3 dex in log g. We found that the independent calibrations of near-solar metallicity stars and metal-poor stars decreases the errors in Teff and log g by nearly a factor of two. Results: We calculated Teff, log g, and [Fe/H] on a consistent scale for a large number of field stars and candidate metal-poor stars. We extended the application of this method to the calibration of absolute magnitudes using nearby stars with well-estimated parallaxes. A better calibration accuracy for MV could be obtained by training separate ANNs for cool, warm, and metal-poor stars. The current accuracy of MV calibration is ±0.3 mag. Conclusions: A list of newly identified metal-poor stars is presented. The MV calibration procedure developed here is reddening-independent and hence may serve as a powerful tool in studying galactic structure.

  6. High-resolution spectroscopic studies of ultra metal-poor stars found in the LAMOST survey

    NASA Astrophysics Data System (ADS)

    Li, Haining; Aoki, Wako; Zhao, Gang; Honda, Satoshi; Christlieb, Norbert; Suda, Takuma

    2015-10-01

    We report on the observations of two ultra metal-poor (UMP) stars with [Fe/H] ˜ -4.0, including one new discovery. The two stars are studied in the on-going and quite efficient project to search for extremely metal-poor (EMP) stars with LAMOST and Subaru. Detailed abundances or upper limits of abundances have been derived for 15 elements from Li to Eu based on high-resolution spectra obtained with the High Dispersion Spectrograph (HDS) mounted in the Subaru Telescope. The abundance patterns of both UMP stars are consistent with the "normal population" among the low-metallicity stars. Both of the two program stars show carbon-enhancement without any excess of heavy neutron-capture elements, indicating that they belong to the subclass of (carbon-enhanced metal-poor) CEMP-no stars, as is the case of most UMP stars previously studied. The [Sr/Ba] ratios of both CEMP-no UMP stars are above [Sr/Ba] ˜ -0.4, suggesting the origin of the carbon-excess is not compatible with the mass transfer from an asymptotic giant branch companion where the s-process has operated. Lithium abundance is measured in the newly discovered UMP star LAMOST J125346.09+075343.1, making it the second UMP turnoff star with Li detection. The Li abundance of LAMOST J125346.09+075343.1 is slightly lower than the values obtained for less metal-poor stars with similar temperatures, and provides a unique data point at [Fe/H] ˜ -4.2 to support the "meltdown" of the Li Spite plateau at extremely low metallicity. Comparison with the other two UMP and HMP (hyper metal-poor, with [Fe/H] < -5.0) turnoff stars suggests that the difference in lighter elements such as CNO and Na might cause notable difference in lithium abundances among CEMP-no stars.

  7. Observations of Very Metal-Poor Stars in the Galaxy

    SciTech Connect

    Beers, Timothy C.

    2008-05-21

    I report on recent results from observations of stars with metallicities [Fe/H]{<=}-2.0. These include a substantial new sample of objects with high-resolution observations obtained as part of a follow-up of the HK Survey, The Hamburg/ESO Survey, and the ongoing survey SEGUE: Sloan Extension for Galactic Understanding and Exploration. Perspectives on the next directions are also provided.

  8. Metal-poor Stars Observed with the Magellan Telescope. III. New Extremely and Ultra Metal-poor Stars from SDSS/SEGUE and Insights on the Formation of Ultra Metal-poor Stars

    NASA Astrophysics Data System (ADS)

    Placco, Vinicius M.; Frebel, Anna; Lee, Young Sun; Jacobson, Heather R.; Beers, Timothy C.; Pena, Jose M.; Chan, Conrad; Heger, Alexander

    2015-08-01

    We report the discovery of one extremely metal-poor (EMP; [{Fe}/{{H}}] \\lt -3) and one ultra metal-poor (UMP; [{Fe}/{{H}}] \\lt -4) star selected from the Sloan Digital Sky Survey/Sloan Extension for Galactic Understanding and Exploration survey. These stars were identified as EMP candidates based on their medium-resolution (R ˜ 2000) spectra, and were followed up with high-resolution (R ˜ 35,000) spectroscopy with the Magellan/Clay Telescope. Their derived chemical abundances exhibit good agreement with those of stars with similar metallicities. We also provide new insights on the formation of the UMP stars, based on comparisons with a new set of theoretical models of supernovae (SNe) nucleosynthesis. The models were matched with 20 UMP stars found in the literature, together with one of the program stars (SDSS J1204+1201), with [{Fe}/{{H}}]=-4.34. From fitting their abundances, we find that the SNe progenitors, for stars where carbon and nitrogen are measured, had masses ranging from 20.5 {M}⊙ to 28 {M}⊙ and explosion energies from 0.3 to 0.9× {10}51 {erg}. These results are highly sensitive to the carbon and nitrogen abundance determinations, which is one of the main drivers for a future high-resolution follow-up of UMP candidates. In addition, we are able to reproduce the different CNO abundance patterns found in UMP stars with a single progenitor type by varying its mass and explosion energy. Magellan Telescopes located at Las Campanas Observatory, Chile.

  9. First stars. XIII. Two extremely metal-poor RR Lyrae stars

    NASA Astrophysics Data System (ADS)

    Hansen, C. J.; Nordström, B.; Bonifacio, P.; Spite, M.; Andersen, J.; Beers, T. C.; Cayrel, R.; Spite, F.; Molaro, P.; Barbuy, B.; Depagne, E.; François, P.; Hill, V.; Plez, B.; Sivarani, T.

    2011-03-01

    Context. The chemical composition of extremely metal-poor stars (EMP stars; [Fe/H] < ~ -3) is a unique tracer of early nucleosynthesis in the Galaxy. As such stars are rare, we wish to find classes of luminous stars which can be studied at high spectral resolution. Aims: We aim to determine the detailed chemical composition of the two EMP stars CS 30317-056 and CS 22881-039, originally thought to be red horizontal-branch (RHB) stars, and compare it to earlier results for EMP stars as well as to nucleosynthesis yields from various supernova (SN) models. In the analysis, we discovered that our targets are in fact the two most metal-poor RR Lyrae stars known. Methods: Our detailed abundance analysis, taking into account the variability of the stars, is based on VLT/UVES spectra (R ≃ 43 000) and 1D LTE OSMARCS model atmospheres and synthetic spectra. For comparison with SN models we also estimate NLTE corrections for a number of elements. Results: We derive LTE abundances for the 16 elements O, Na, Mg, Al, Si, S, Ca, Sc, Ti, Cr, Mn, Fe, Co, Ni, Sr and Ba, in good agreement with earlier values for EMP dwarf, giant and RHB stars. Li and C are not detected in either star. NLTE abundance corrections are newly calculated for O and Mg and taken from the literature for other elements. The resulting abundance pattern is best matched by model yields for supernova explosions with high energy and/or significant asphericity effects. Conclusions: Our results indicate that, except for Li and C, the surface composition of EMP RR Lyr stars is not significantly affected by mass loss, mixing or diffusion processes; hence, EMP RR Lyr stars should also be useful tracers of the chemical evolution of the early Galactic halo. The observed abundance ratios indicate that these stars were born from an ISM polluted by energetic, massive (25-40 M⊙) and /or aspherical supernovae, but the NLTE corrections for Sc and certain other elements do play a role in the choice of model. Based on

  10. EXTREMELY METAL-POOR STARS AND A HIERARCHICAL CHEMICAL EVOLUTION MODEL

    SciTech Connect

    Komiya, Yutaka

    2011-07-20

    Early phases of the chemical evolution of the Galaxy and formation history of extremely metal-poor (EMP) stars are investigated using hierarchical galaxy formation models. We build a merger tree of the Galaxy according to the extended Press-Schechter theory. We follow the chemical evolution along the tree and compare the model results to the metallicity distribution function and abundance ratio distribution of the Milky Way halo. We adopt three different initial mass functions (IMFs). In a previous study, we argued that the typical mass, M{sub md}, of EMP stars should be high, M{sub md} {approx} 10 M{sub sun}, based on studies of binary origin carbon-rich EMP stars. In this study, we show that only the high-mass IMF can explain an observed small number of EMP stars. For relative element abundances, the high-mass IMF and the Salpeter IMF predict similar distributions. We also investigate dependence on nucleosynthetic yields of supernovae (SNe). The theoretical SN yields by Kobayashi et al. and Chieffi and Limongi show reasonable agreement with observations for {alpha}-elements. Our model predicts a significant scatter of element abundances at [Fe/H] < -3. We adopted the stellar yields derived in the work of Francois et al., which produce the best agreement between the observational data and the one-zone chemical evolution model. Their yields well reproduce a trend of the averaged abundances of EMP stars but predict much larger scatter than do the observations. The model with hypernovae predicts Zn abundance, in agreement with the observations, but other models predict lower [Zn/Fe]. Ejecta from the hypernovae with large explosion energy is mixed in large mass and decreases the scatter of the element abundances.

  11. Beryllium and boron in metal-poor stars

    NASA Astrophysics Data System (ADS)

    Primas, Francesca

    2010-04-01

    Knowledge of lithium, beryllium, and boron abundances in stars of the Galactic halo and disk plays a major role in our understanding of Big Bang nucleosynthesis, cosmic-ray physics, and stellar interiors. 9Be and 10B are believed to originate entirely from spallation reactions in the interstellar medium (ISM) between α-particles and protons and heavy nuclei like carbon, nitrogen, and oxygen (CNO), whereas 11B may have an extra production channel via neutrino-spallation. Beryllium and boron are both observationally challenging, with their main resonant doublets falling respectively at 313 nm and at 250 nm. The advent of 8-10m class telescopes equipped with highly sensitive (in the near-UV/blue) spectrographs has opened up a new era of Be abundance studies. Here, I will review and discuss the most interesting results of recent observational campaigns in terms of formation and evolution of these two light elements.

  12. Nucleosynthesis in Low Mass Very Metal Poor AGB Stars

    NASA Astrophysics Data System (ADS)

    Serenelli, A.

    The evolution of a 1.5 M⊙, Z= 10-5 stellar model has been followed starting at the ZAMS up to the thermally pulsating asymptotic giant branch (TP-AGB) phase. Calculations were done using the LPCODE [1], to which some changes were done. The most important and relevant to this work is the incorporation of a full nuclear network from H to Po, comprising about 525 isotopes and 910 nuclear reactions, appropriate for the computation of the s-process occurring in AGB stars. Convection is treated according to the mixing length theory (λMLT = 1.7) and convective mixing as a diffusive process. Diffusive overshooting is also included according to [2] and the free parameter f adopted is 0.015. Mass loss is given by the Reimers formula, with the parameter η = 1.

  13. Extremely metal-poor stars from the cosmic dawn in the bulge of the Milky Way.

    PubMed

    Howes, L M; Casey, A R; Asplund, M; Keller, S C; Yong, D; Nataf, D M; Poleski, R; Lind, K; Kobayashi, C; Owen, C I; Ness, M; Bessell, M S; Da Costa, G S; Schmidt, B P; Tisserand, P; Udalski, A; Szymański, M K; Soszyński, I; Pietrzyński, G; Ulaczyk, K; Wyrzykowski, Ł; Pietrukowicz, P; Skowron, J; Kozłowski, S; Mróz, P

    2015-11-26

    The first stars are predicted to have formed within 200 million years after the Big Bang, initiating the cosmic dawn. A true first star has not yet been discovered, although stars with tiny amounts of elements heavier than helium ('metals') have been found in the outer regions ('halo') of the Milky Way. The first stars and their immediate successors should, however, preferentially be found today in the central regions ('bulges') of galaxies, because they formed in the largest over-densities that grew gravitationally with time. The Milky Way bulge underwent a rapid chemical enrichment during the first 1-2 billion years, leading to a dearth of early, metal-poor stars. Here we report observations of extremely metal-poor stars in the Milky Way bulge, including one star with an iron abundance about 10,000 times lower than the solar value without noticeable carbon enhancement. We confirm that most of the metal-poor bulge stars are on tight orbits around the Galactic Centre, rather than being halo stars passing through the bulge, as expected for stars formed at redshifts greater than 15. Their chemical compositions are in general similar to typical halo stars of the same metallicity although intriguing differences exist, including lower abundances of carbon. PMID:26560034

  14. Extremely metal-poor stars from the cosmic dawn in the bulge of the Milky Way

    NASA Astrophysics Data System (ADS)

    Howes, L. M.; Casey, A. R.; Asplund, M.; Keller, S. C.; Yong, D.; Nataf, D. M.; Poleski, R.; Lind, K.; Kobayashi, C.; Owen, C. I.; Ness, M.; Bessell, M. S.; da Costa, G. S.; Schmidt, B. P.; Tisserand, P.; Udalski, A.; Szymański, M. K.; Soszyński, I.; Pietrzyński, G.; Ulaczyk, K.; Wyrzykowski, Ł.; Pietrukowicz, P.; Skowron, J.; Kozłowski, S.; Mróz, P.

    2015-11-01

    The first stars are predicted to have formed within 200 million years after the Big Bang, initiating the cosmic dawn. A true first star has not yet been discovered, although stars with tiny amounts of elements heavier than helium (‘metals’) have been found in the outer regions (‘halo’) of the Milky Way. The first stars and their immediate successors should, however, preferentially be found today in the central regions (‘bulges’) of galaxies, because they formed in the largest over-densities that grew gravitationally with time. The Milky Way bulge underwent a rapid chemical enrichment during the first 1-2 billion years, leading to a dearth of early, metal-poor stars. Here we report observations of extremely metal-poor stars in the Milky Way bulge, including one star with an iron abundance about 10,000 times lower than the solar value without noticeable carbon enhancement. We confirm that most of the metal-poor bulge stars are on tight orbits around the Galactic Centre, rather than being halo stars passing through the bulge, as expected for stars formed at redshifts greater than 15. Their chemical compositions are in general similar to typical halo stars of the same metallicity although intriguing differences exist, including lower abundances of carbon.

  15. Spectroscopic Analysis of Metal-poor Stars from LAMOST: Early Results

    NASA Astrophysics Data System (ADS)

    Li, Hai-Ning; Zhao, Gang; Christlieb, Norbert; Wang, Liang; Wang, Wei; Zhang, Yong; Hou, Yonghui; Yuan, Hailong

    2015-01-01

    We report on early results from a pilot program searching for metal-poor stars with LAMOST and follow-up high-resolution observation acquired with the MIKE spectrograph attached to the Magellan II telescope. We performed detailed abundance analysis for eight objects with iron abundances [Fe/H] < -2.0, including five extremely metal-poor (EMP; [Fe/H] < -3.0) stars with two having [Fe/H] < -3.5. Among these objects, three are newly discovered EMP stars, one of which is confirmed for the first time with high-resolution spectral observations. Three program stars are regarded as carbon-enhanced metal-poor (CEMP) stars, including two stars with no enhancement in their neutron-capture elements, which thus possibly belong to the class of CEMP-no stars; one of these objects also exhibits significant enhancement in nitrogen, and is thus a potential carbon and nitrogen-enhanced metal-poor star. The [X/Fe] ratios of the sample stars generally agree with those reported in the literature for other metal-poor stars in the same [Fe/H] range. We also compared the abundance patterns of individual program stars with the average abundance pattern of metal-poor stars and find only one chemically peculiar object with abundances of at least two elements (other than C and N) showing deviations larger than 0.5 dex. The distribution of [Sr/Ba] versus [Ba/H] agrees that an additional nucleosynthesis mechanism is needed aside from a single r-process. Two program stars with extremely low abundances of Sr and Ba support the prospect that both main and weak r-processes may have operated during the early phase of Galactic chemical evolution. The distribution of [C/N] shows that there are two groups of carbon-normal giants with different degrees of mixing. However, it is difficult to explain the observed behavior of the [C/N] of the nitrogen-enhanced unevolved stars based on current data.

  16. SPECTROSCOPIC ANALYSIS OF METAL-POOR STARS FROM LAMOST: EARLY RESULTS

    SciTech Connect

    Li, Hai-Ning; Zhao, Gang; Wang, Liang; Wang, Wei; Yuan, Hailong; Christlieb, Norbert; Zhang, Yong; Hou, Yonghui E-mail: gzhao@nao.cas.cn

    2015-01-10

    We report on early results from a pilot program searching for metal-poor stars with LAMOST and follow-up high-resolution observation acquired with the MIKE spectrograph attached to the Magellan II telescope. We performed detailed abundance analysis for eight objects with iron abundances [Fe/H] < -2.0, including five extremely metal-poor (EMP; [Fe/H] < -3.0) stars with two having [Fe/H] < -3.5. Among these objects, three are newly discovered EMP stars, one of which is confirmed for the first time with high-resolution spectral observations. Three program stars are regarded as carbon-enhanced metal-poor (CEMP) stars, including two stars with no enhancement in their neutron-capture elements, which thus possibly belong to the class of CEMP-no stars; one of these objects also exhibits significant enhancement in nitrogen, and is thus a potential carbon and nitrogen-enhanced metal-poor star. The [X/Fe] ratios of the sample stars generally agree with those reported in the literature for other metal-poor stars in the same [Fe/H] range. We also compared the abundance patterns of individual program stars with the average abundance pattern of metal-poor stars and find only one chemically peculiar object with abundances of at least two elements (other than C and N) showing deviations larger than 0.5 dex. The distribution of [Sr/Ba] versus [Ba/H] agrees that an additional nucleosynthesis mechanism is needed aside from a single r-process. Two program stars with extremely low abundances of Sr and Ba support the prospect that both main and weak r-processes may have operated during the early phase of Galactic chemical evolution. The distribution of [C/N] shows that there are two groups of carbon-normal giants with different degrees of mixing. However, it is difficult to explain the observed behavior of the [C/N] of the nitrogen-enhanced unevolved stars based on current data.

  17. Super and massive AGB stars - III. Nucleosynthesis in metal-poor and very metal-poor stars - Z = 0.001 and 0.0001

    NASA Astrophysics Data System (ADS)

    Doherty, Carolyn L.; Gil-Pons, Pilar; Lau, Herbert H. B.; Lattanzio, John C.; Siess, Lionel; Campbell, Simon W.

    2014-06-01

    We present a new grid of stellar models and nucleosynthetic yields for super-AGB stars with metallicities Z = 0.001 and 0.0001, applicable for use within galactic chemical evolution models. Contrary to more metal-rich stars where hot bottom burning is the main driver of the surface composition, in these lower metallicity models the effect of third dredge-up and corrosive second dredge-up also have a strong impact on the yields. These metal-poor and very metal-poor super-AGB stars create large amounts of 4He, 13C, 14N and 27Al as well as the heavy magnesium isotopes 25Mg and 26Mg. There is a transition in yield trends at metallicity Z ≈ 0.001, below which we find positive yields of 12C, 16O, 15N and 28Si, which is not the case for higher metallicities. We explore the large uncertainties derived from wind prescriptions in super-AGB stars, finding ≈2 orders of magnitude difference in yields of 22Ne, 23Na, 24, 25, 26Mg, 27Al and our s-process proxy isotope g. We find inclusion of variable composition low-temperature molecular opacities is only critical for super-AGB stars of metallicities below Z ≈ 0.001. We analyse our results, and those in the literature, to address the question: Are super-AGB stars the polluters responsible for extreme population in the globular cluster NGC 2808? Our results, as well as those from previous studies, seem unable to satisfactorily match the extreme population in this globular cluster.

  18. Mass-loss predictions for evolved very metal-poor massive stars

    NASA Astrophysics Data System (ADS)

    Muijres, L.; Vink, J. S.; de Koter, A.; Hirschi, R.; Langer, N.; Yoon, S.-C.

    2012-10-01

    Context. The first couple of stellar generations may have been massive, of order 100 M⊙, and to have played a dominant role in galaxy formation and the chemical enrichment of the early Universe. Some fraction of these objects may have died as pair-instability supernovae or gamma-ray bursts. The winds of these stars may have played an important role in determining these outcomes. As the winds are driven by radiation pressure on spectral lines, their strengths are expected to vary with metallicity. Until now, most mass-loss predictions for metal-poor O-type stars have assumed a scaled-down solar-abundance pattern. However, Population III evolutionary tracks show significant surface enrichment through rotational mixing of CNO-processed material, because even metal-poor stars switch to CNO-burning early on. Aims: We address the question of whether the CNO surface enhanced self-enrichment in the first few generations of stars could impact their mass-loss properties. Methods: We employ Monte Carlo simulations to establish the local line-force and solve for the momentum equation of the stellar outflow, testing whether an outflow can actually be established by assessing the net acceleration at the sonic point of the flow. Stellar evolution models of rotating metal-poor stars are used to specify the surface chemical composition, focussing on the phases of early enrichment. Results: We find that the mass-loss rates of CNO enhanced metal-poor stars are higher than those of non-enriched stars, but they are much lower than those rates where the CNO abundance is included in the total abundance Z. Metal-poor stars hotter than ~50 000 K, in the metallicity range investigated here (with an initial metallicity Z ≲ 10-4) are found to have no wind, as the high-ionization species of the CNO elements have too few strong lines to drive an outflow. We present a heuristic formula that provides mass-loss estimates for CNO-dominated winds in relation to scaled-down solar abundances

  19. CHEMICAL ABUNDANCES OF METAL-POOR RR LYRAE STARS IN THE MAGELLANIC CLOUDS

    SciTech Connect

    Haschke, Raoul; Grebel, Eva K.; Duffau, Sonia; Frebel, Anna; Hansen, Camilla J.; Koch, Andreas

    2012-09-01

    We present for the first time a detailed spectroscopic study of chemical element abundances of metal-poor RR Lyrae stars in the Large and Small Magellanic Cloud (LMC and SMC). Using the MagE echelle spectrograph at the 6.5 m Magellan telescopes, we obtain medium resolution (R {approx} 2000-6000) spectra of six RR Lyrae stars in the LMC and three RR Lyrae stars in the SMC. These stars were chosen because their previously determined photometric metallicities were among the lowest metallicities found for stars belonging to the old populations in the Magellanic Clouds. We find the spectroscopic metallicities of these stars to be as low as [Fe/H]{sub spec} = -2.7 dex, the lowest metallicity yet measured for any star in the Magellanic Clouds. We confirm that for metal-poor stars, the photometric metallicities from the Fourier decomposition of the light curves are systematically too high compared to their spectroscopic counterparts. However, for even more metal-poor stars below [Fe/H]{sub phot} < -2.8 dex this trend is reversed and the spectroscopic metallicities are systematically higher than the photometric estimates. We are able to determine abundance ratios for 10 chemical elements (Fe, Na, Mg, Al, Ca, Sc, Ti, Cr, Sr, and Ba), which extend the abundance measurements of chemical elements for RR Lyrae stars in the Clouds beyond [Fe/H] for the first time. For the overall [{alpha}/Fe] ratio, we obtain an overabundance of 0.36 dex, which is in very good agreement with results from metal-poor stars in the Milky Way halo as well as from the metal-poor tail in dwarf spheroidal galaxies. Comparing the abundances with those of the stars in the Milky Way halo we find that the abundance ratios of stars of both populations are consistent with another. Therefore, we conclude that from a chemical point of view early contributions from Magellanic-type galaxies to the formation of the Galactic halo as claimed in cosmological models are plausible.

  20. Hot, Massive Stars in the Extremely Metal-Poor Galaxy, I Zw 18

    NASA Technical Reports Server (NTRS)

    Heap, Sara R.; Malumuth, Eliot M.

    2010-01-01

    The extremely metal-poor galaxy I Zw 18, is the Rosetta Stone for understanding z=7-8 galaxies now being discovered by Hubb|e's Wide Field Camera 3 (HST/WFC3). Using HST/STIS images and recently obtained HST/COS ultraviolet spectra, we derive information about the hot, massive stars in this galaxy including stellar abundances, constraints on the stellar IMF and mass distribution of young clusters containing hot, massive stars.

  1. High-resolution analysis of carbon-enhanced metal-poor stars with Magellan

    NASA Astrophysics Data System (ADS)

    Kennedy, Catherine R.; Placco, Vinicius M.; Beers, Timothy C.

    2016-01-01

    We report chemical abundances for carbon-enhanced metal-poor stars observed with Magellan/MIKE. The various subclasses of CEMP stars are presented in the context of the astrophysical sites of production of the elements. Of particular importance are the new discoveries and analysis of CEMP-no stars with [Fe/H] < -3.5, which exhibit no neutron-capture-element enhancements. We find that the abundance patterns of the lowest-metallicity stars in the sample reveal new clues regarding the origin(s) of early CNO production in the Universe.

  2. VERY METAL-POOR STARS IN THE OUTER GALACTIC BULGE FOUND BY THE APOGEE SURVEY

    SciTech Connect

    Garcia Perez, Ana E.; Majewski, Steven R.; Hearty, Fred R.; Cunha, Katia; Shetrone, Matthew; Johnson, Jennifer A.; Zasowski, Gail; Smith, Verne V.; Beers, Timothy C.; Schiavon, Ricardo P.; Holtzman, Jon; Nidever, David; Allende Prieto, Carlos; Bizyaev, Dmitry; Ebelke, Garrett; Malanushenko, Elena; Malanushenko, Viktor; Eisenstein, Daniel J.; Frinchaboy, Peter M.; Girardi, Leo; and others

    2013-04-10

    Despite its importance for understanding the nature of early stellar generations and for constraining Galactic bulge formation models, at present little is known about the metal-poor stellar content of the central Milky Way. This is a consequence of the great distances involved and intervening dust obscuration, which challenge optical studies. However, the Apache Point Observatory Galactic Evolution Experiment (APOGEE), a wide-area, multifiber, high-resolution spectroscopic survey within Sloan Digital Sky Survey III, is exploring the chemistry of all Galactic stellar populations at infrared wavelengths, with particular emphasis on the disk and the bulge. An automated spectral analysis of data on 2403 giant stars in 12 fields in the bulge obtained during APOGEE commissioning yielded five stars with low metallicity ([Fe/H] {<=} -1.7), including two that are very metal-poor [Fe/H] {approx} -2.1 by bulge standards. Luminosity-based distance estimates place the 5 stars within the outer bulge, where 1246 of the other analyzed stars may reside. A manual reanalysis of the spectra verifies the low metallicities, and finds these stars to be enhanced in the {alpha}-elements O, Mg, and Si without significant {alpha}-pattern differences with other local halo or metal-weak thick-disk stars of similar metallicity, or even with other more metal-rich bulge stars. While neither the kinematics nor chemistry of these stars can yet definitively determine which, if any, are truly bulge members, rather than denizens of other populations co-located with the bulge, the newly identified stars reveal that the chemistry of metal-poor stars in the central Galaxy resembles that of metal-weak thick-disk stars at similar metallicity.

  3. The Extreme Overabundance of Molybdenum in Two Metal-poor Stars

    NASA Astrophysics Data System (ADS)

    Peterson, Ruth C.

    2011-11-01

    We report determinations of the molybdenum abundances in five mildly to extremely metal-poor turnoff stars using five Mo II lines near 2000 Å. In two of the stars, the abundance of molybdenum is found to be extremely enhanced, as high or higher than the neighboring even-Z elements ruthenium and zirconium. Of the several nucleosynthesis scenarios envisioned for the production of nuclei in this mass range in the oldest stars, a high-entropy wind acting in a core-collapse supernova seems uniquely capable of the twin aspects of a high molybdenum overproduction confined to a narrow mass range. Whatever the details of the nucleosynthesis mechanism, however, this unusual excess suggests that very few individual nucleosynthesis events were responsible for the synthesis of the light trans-Fe heavy elements in these cases, an unexpected result given that both are only moderately metal-poor.

  4. THE EXTREME OVERABUNDANCE OF MOLYBDENUM IN TWO METAL-POOR STARS

    SciTech Connect

    Peterson, Ruth C.

    2011-11-20

    We report determinations of the molybdenum abundances in five mildly to extremely metal-poor turnoff stars using five Mo II lines near 2000 A. In two of the stars, the abundance of molybdenum is found to be extremely enhanced, as high or higher than the neighboring even-Z elements ruthenium and zirconium. Of the several nucleosynthesis scenarios envisioned for the production of nuclei in this mass range in the oldest stars, a high-entropy wind acting in a core-collapse supernova seems uniquely capable of the twin aspects of a high molybdenum overproduction confined to a narrow mass range. Whatever the details of the nucleosynthesis mechanism, however, this unusual excess suggests that very few individual nucleosynthesis events were responsible for the synthesis of the light trans-Fe heavy elements in these cases, an unexpected result given that both are only moderately metal-poor.

  5. Is HE 0107-5240 A Primordial Star? The Characteristics of Extremely Metal-Poor Carbon-Rich Stars

    NASA Astrophysics Data System (ADS)

    Suda, Takuma; Aikawa, Masayuki; Machida, Masahiro N.; Fujimoto, Masayuki Y.; Iben, Icko, Jr.

    2004-08-01

    We discuss the origin of HE 0107-5240, which, with a metallicity of [Fe/H]=-5.3, is the most iron-poor star yet observed. Its discovery has an important bearing on the question of the observability of first-generation stars in our universe. In common with other stars of very small metallicity (-4<~[Fe/H]<~-2.5), HE 0107-5240 shows a peculiar abundance pattern, including large enhancements of C, N, and O, and a more modest enhancement of Na. The observed abundance pattern can be explained by nucleosynthesis and mass transfer in a first-generation binary star, which, after birth, accretes matter from a primordial cloud mixed with the ejectum of a supernova. We elaborate the binary scenario on the basis of our current understanding of the evolution and nucleosynthesis of extremely metal-poor, low-mass model stars and discuss the possibility of discriminating this scenario from others. In our picture, iron-peak elements arise in surface layers of the component stars by accretion of gas from the polluted primordial cloud, pollution occurring after the birth of the binary. To explain the observed C, N, O, and Na enhancements, as well as the 12C/ 13C ratio, we suppose that the currently observed star, once the secondary in a binary, accreted matter from a chemically evolved companion, which is now a white dwarf. To estimate the abundances in the matter transferred in the binary, we rely on the results of computations of model stars constructed with up-to-date input physics. Nucleosynthesis in a helium-flash-driven convective zone into which hydrogen has been injected is followed, allowing us to explain the origin in the primary of the observed O and Na enrichments and to discuss the abundances of s-process elements. From the observed abundances, we conclude that HE 0107-5240 has evolved from a wide binary (of initial separation ~20 AU) with a primary of initial mass in the range 1.2-3 Msolar. On the assumption that the system now consists of a white dwarf and a red giant

  6. A SEARCH FOR UNRECOGNIZED CARBON-ENHANCED METAL-POOR STARS IN THE GALAXY

    SciTech Connect

    Placco, Vinicius M.; Rossi, Silvia; Kennedy, Catherine R.; Beers, Timothy C.; Lee, Young Sun; Christlieb, Norbert; Sivarani, Thirupathi; Reimers, Dieter; Wisotzki, Lutz

    2010-03-15

    We have developed a new procedure to search for carbon-enhanced metal-poor (CEMP) stars from the Hamburg/ESO (HES) prism-survey plates. This method employs an extended line index for the CH G band, which we demonstrate to have superior performance when compared to the narrower G-band index formerly employed to estimate G-band strengths for these spectra. Although CEMP stars have been found previously among candidate metal-poor stars selected from the HES, the selection on metallicity undersamples the population of intermediate-metallicity CEMP stars (-2.5 {<=} [Fe/H] {<=} -1.0); such stars are of importance for constraining the onset of the s-process in metal-deficient asymptotic giant branch stars (thought to be associated with the origin of carbon for roughly 80% of CEMP stars). The new candidates also include substantial numbers of warmer carbon-enhanced stars, which were missed in previous HES searches for carbon stars due to selection criteria that emphasized cooler stars. A first subsample, biased toward brighter stars (B< 15.5), has been extracted from the scanned HES plates. After visual inspection (to eliminate spectra compromised by plate defects, overlapping spectra, etc., and to carry out rough spectral classifications), a list of 669 previously unidentified candidate CEMP stars was compiled. Follow-up spectroscopy for a pilot sample of 132 candidates was obtained with the Goodman spectrograph on the SOAR 4.1 m telescope. Our results show that most of the observed stars lie in the targeted metallicity range, and possess prominent carbon absorption features at 4300 A. The success rate for the identification of new CEMP stars is 43% (13 out of 30) for [Fe/H] < -2.0. For stars with [Fe/H] < -2.5, the ratio increases to 80% (four out of five objects), including one star with [Fe/H] < -3.0.

  7. Missing metal-poor stars from the HK and Hamburg/ESO Surveys

    NASA Astrophysics Data System (ADS)

    Beers, Timothy; Placco, Vinicius; Christlieb, Norbert; Rossi, Silvia; Santucci, Rafael

    2013-08-01

    The most metal-poor stars in the Galaxy retain the imprint of chemical evolution processes that took place during the earliest epochs of the Universe, and provide valuable kinematic probes of the hierachical assembly of the Milky Way. We propose to supplement the lists of known very metal-poor ([Fe/H] < -2.0) stars by obtaining follow-up medium-resolution spectroscopy of candidates selected from the HK and Hamburg/ESO prism surveys. We have prepared a list of several thousand candidates, with 10 < B < 18, and available at essentially all RAs in both hemispheres. We plan to use GMOS-N and GMOS-S to obtain spectra for the fainter candidates; brighter candidates will be acquired with other 4-m class telescopes. These medium-resolution spectra will be used to determine atmospheric parameters (Teff, logg, [Fe/H]), as well as estimates of [C/Fe] and [alpha/Fe] and accurate radial velocities, using our well-tested spectroscopic analysis pipeline. This information will enable the identification of many new very metal-poor stars, including representatives of the inner- and outer-halo populations, for which detailed chemodynamical analysis can be carried out. The most interesting stars identified during this project will be selected for later follow-up with the either existing or new high-resolution spectrographs being developed for Gemini-N, Gemini-S, and SOAR.

  8. Binary stars.

    PubMed

    Paczynacuteski, B

    1984-07-20

    Most stars in the solar neighborhood are either double or multiple systems. They provide a unique opportunity to measure stellar masses and radii and to study many interesting and important phenomena. The best candidates for black holes are compact massive components of two x-ray binaries: Cygnus X-1 and LMC X-3. The binary radio pulsar PSR 1913 + 16 provides the best available evidence for gravitational radiation. Accretion disks and jets observed in close binaries offer a very good testing ground for models of active galactic nuclei and quasars. PMID:17749544

  9. Metal-poor stars towards the Galactic bulge: A population potpourri⋆

    NASA Astrophysics Data System (ADS)

    Koch, Andreas; McWilliam, Andrew; Preston, George W.; Thompson, Ian B.

    2016-03-01

    We present a comprehensive chemical abundance analysis of five red giants and two horizontal branch (HB) stars towards the southern edge of the Galactic bulge, at (l, b) ~ (0°,-11°). Based on high-resolution spectroscopy obtained with the Magellan/MIKE spectrograph, we derived up to 23 chemical element abundances and identify a mixed bag of stars, representing various populations in the central regions of the Galaxy. Although cosmological simulations predict that the inner Galaxy was host to the first stars in the Universe, we see no chemical evidence of the ensuing massive supernova explosions: all of our targets exhibit halo-like, solar [Sc/Fe] ratios, which is in contrast to the low values predicted from Population III nucleosynthesis. One of the targets is a CEMP-s star at [Fe/H] = -2.52 dex, and another target is a moderately metal-poor ([Fe/H] = -1.53 dex) CH star with strong enrichment in s-process elements (e.g., [Ba/Fe] = 1.35). These individuals provide the first contenders of these classes of stars towards the bulge. Four of the carbon-normal stars exhibit abundance patterns reminiscent of halo star across a metallicity range spanning -2.0 to -2.6 dex, i.e., enhanced α-elements and solar Fe-peak and neutron-capture elements, and the remaining one is a regular metal-rich bulge giant. The position, distance, and radial velocity of one of the metal-poor HB stars coincides with simulations of the old trailing arm of the disrupted Sagittarius dwarf galaxy. While their highly uncertain proper motions prohibit a clear kinematic separation, the stars' chemical abundances and distances suggest that these metal-poor candidates, albeit located towards the bulge, are not of the bulge, but rather inner halo stars on orbits that make them pass through the central regions. Thus, we caution similar claims of detections of metal-poor stars as true habitants of the bulge. This paper includes data gathered with the 6.5 meter Magellan Telescopes located at Las Campanas

  10. OGLE-2009-BLG-076S: THE MOST METAL-POOR DWARF STAR IN THE GALACTIC BULGE

    SciTech Connect

    Bensby, T.; Feltzing, S.; Aden, D.; Simmerer, J.; Johnson, J. A.; Gould, A.; Gal-Yam, A.; Udalski, A.; Han, C. E-mail: sofia@astro.lu.se E-mail: jennifer@astro.lu.se E-mail: gould@astronomy.ohio-state.edu E-mail: udalski@astrouw.edu.pl

    2009-07-10

    Measurements based on a large number of red giant stars suggest a broad metallicity distribution function (MDF) for the Galactic bulge, centered on [Fe/H] {approx} -0.1. However, recently, a new opportunity emerged to utilize temporary flux amplification (by factors of {approx}100 or more) of faint dwarf stars in the Bulge which are gravitationally lensed, making them observable with high-resolution spectrographs during a short observational window. Surprisingly, of the first six stars measured, five have [Fe/H]> + 0.30, suggesting a highly skewed MDF, inconsistent with observations of giant stars. Here we present a detailed elemental abundance analysis of OGLE-2009-BLG-076S, based on a high-resolution spectrum obtained with the UVES spectrograph at the ESO Very Large Telescope. Our results indicate it is the most metal-poor dwarf star in the Bulge yet observed, with [Fe/H] = -0.76. Our results argue against a strong selection effect disfavoring metal-poor microlensed stars. It is possible that small number statistics is responsible for the giant/dwarf Bulge MDF discrepancy. Should this discrepancy survive when larger numbers of Bulge dwarf stars (soon to be available) are analyzed, it may require modification of our understanding of either Bulge formation models, or the behavior of metal-rich giant stars.

  11. Heavy-elements in metal-poor stars: an UV perspective

    NASA Astrophysics Data System (ADS)

    Siqueira-Mello, C.; Barbuy, B.

    2014-11-01

    The site(s) of the r-process(es) is(are) not completely defined, and several models have been proposed. Observed abundances are the best clues to bring some light to this field, especially the study of the extremely metal-poor (EMP) Galactic halo stars. Many elements can be measured using ground-based facilities already available, but the ultraviolet window also presents a rich opportunity in terms of chemical abundances of heavy elements. In fact, for some elements only the UV transitions are strong enough to be useful. Focusing on the project of the Cassegrain U-Band Brazilian Spectrograph (CUBES), we discuss the science case for heavy elements in metal-poor stars, describing the useful lines of trans-Fe elements present in the UV region. Lines in the far UV are also discussed.

  12. THE ORIGIN OF LOW [α/Fe] RATIOS IN EXTREMELY METAL-POOR STARS

    SciTech Connect

    Kobayashi, Chiaki; Ishigaki, Miho N.; Tominaga, Nozomu; Nomoto, Ken'ichi

    2014-04-10

    We show that the low ratios of α elements (Mg, Si, and Ca) to Fe recently found for a small fraction of extremely metal-poor stars can be naturally explained with the nucleosynthesis yields of core-collapse supernovae, i.e., 13-25 M {sub ☉} supernovae, or hypernovae. For the case without carbon enhancement, the ejected iron mass is normal, consistent with observed light curves and spectra of nearby supernovae. On the other hand, the carbon enhancement requires much smaller iron production, and the low [α/Fe] of carbon-enhanced metal-poor stars can also be reproduced with 13-25 M {sub ☉} faint supernovae or faint hypernovae. Iron-peak element abundances, in particular Zn abundances, are important to put further constraints on the enrichment sources from galactic archaeology surveys.

  13. The Origin of Low [α/Fe] Ratios in Extremely Metal-poor Stars

    NASA Astrophysics Data System (ADS)

    Kobayashi, Chiaki; Ishigaki, Miho N.; Tominaga, Nozomu; Nomoto, Ken'ichi

    2014-04-01

    We show that the low ratios of α elements (Mg, Si, and Ca) to Fe recently found for a small fraction of extremely metal-poor stars can be naturally explained with the nucleosynthesis yields of core-collapse supernovae, i.e., 13-25 M ⊙ supernovae, or hypernovae. For the case without carbon enhancement, the ejected iron mass is normal, consistent with observed light curves and spectra of nearby supernovae. On the other hand, the carbon enhancement requires much smaller iron production, and the low [α/Fe] of carbon-enhanced metal-poor stars can also be reproduced with 13-25 M ⊙ faint supernovae or faint hypernovae. Iron-peak element abundances, in particular Zn abundances, are important to put further constraints on the enrichment sources from galactic archaeology surveys.

  14. EXPLAINING THE Sr AND Ba SCATTER IN EXTREMELY METAL-POOR STARS

    SciTech Connect

    Aoki, W.; Suda, T.; Boyd, R. N.; Kajino, T.; Famiano, M. A. E-mail: takuma.suda@nao.ac.jp E-mail: kajino@nao.ac.jp

    2013-03-20

    Compilations of abundances of strontium and barium in extremely metal-poor stars show that an apparent cutoff is observed for [Sr/Ba] at [Fe/H] < -3.6 and large fluctuations for [Fe/H] > -3.6 with a clear upper bound depending on metallicity. We study the factors that place upper limits on the logarithmic ratio [Sr/Ba]. A model is developed in which the collapses of type II supernovae are found to reproduce many of the features seen in the data. This model is consistent with galactic chemical evolution constraints of light-element enrichment in metal-poor stars. Effects of turbulence in an explosive site have also been simulated, and are found to be important in explaining the large scatter observed in the [Sr/Ba] data.

  15. Stellar oxygen abundances. 3: The oxygen abundance of the very metal poor halo star BD -13 deg 3442

    NASA Technical Reports Server (NTRS)

    King, Jeremy R.

    1994-01-01

    A spectrum of the very metal poor ((Fe/H) approximately -3) halo star BD -13 deg 3442 is presented and used to determine this star's oxygen abundance. Our determination makes BD -13 deg 3442 the most metal poor dwarf (though a somewhat evolved one) with an O abundance determination. The O abundance (determined from the 7774 A O I triped) and (O/Fe) ratio is compared to that of two other metal-poor stars. The (O/Fe) ratio of BD -13 deg 3442 is found to be approximately 0.35 dex larger than that of the other two halo stars. Possible implications of this result are discussed.

  16. First high-precision differential abundance analysis of extremely metal-poor stars

    NASA Astrophysics Data System (ADS)

    Reggiani, Henrique; Meléndez, Jorge; Yong, David; Ramírez, Ivan; Asplund, Martin

    2016-02-01

    Context. Studies of extremely metal-poor stars indicate that chemical abundance ratios [X/Fe] have a root mean square scatter as low as 0.05 dex (12%). It remains unclear whether this reflects observational uncertainties or intrinsic astrophysical scatter arising from physical conditions in the interstellar medium at early times. Aims: We measure differential chemical abundance ratios in extremely metal-poor stars to investigate the limits of precision and to understand whether cosmic scatter or observational errors are dominant. Methods: We used high-resolution (R ~ 95 000) and high signal-to-noise (S/N = 700 at 5000 Å) HIRES/Keck spectra to determine high-precision differential abundances between two extremely metal-poor stars through a line-by-line differential approach. We determined stellar parameters for the star G64-37 with respect to the standard star G64-12. We performed EW measurements for the two stars for the lines recognized in both stars and performed spectral synthesis to study the carbon abundances. Results: The differential approach allowed us to obtain errors of σ(Teff) = 27 K, σ(log g) = 0.06 dex, σ( [Fe/H] ) = 0.02 dex and σ(vt) = 0.06 km s-1. We estimated relative chemical abundances with a precision as low as σ([X/Fe]) ≈ 0.01 dex. The small uncertainties demonstrate that there are genuine abundance differences larger than the measurement errors. The observed Li difference cannot be explained by the difference in mass because the less massive star has more Li. Conclusions: It is possible to achieve an abundance precision around ≈ 0.01-0.05 dex for extremely metal-poor stars, which opens new windows on the study of the early chemical evolution of the Galaxy. Table A.1 is 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/586/A67

  17. AN EXTREMELY CARBON-RICH, EXTREMELY METAL-POOR STAR IN THE SEGUE 1 SYSTEM

    SciTech Connect

    Norris, John E.; Yong, David; Gilmore, Gerard; Wyse, Rosemary F. G.; Frebel, Anna

    2010-10-10

    We report the analysis of high-resolution, high signal-to-noise ratio, spectra of an extremely metal-poor, extremely C-rich red giant, Seg 1-7, in Segue 1-described in the literature alternatively as an unusually extended globular cluster or an ultra-faint dwarf galaxy. The radial velocity of Seg 1-7 coincides precisely with the systemic velocity of Segue 1, and its chemical abundance signature of [Fe/H] = -3.52, [C/Fe] = +2.3, [N/Fe] = +0.8, [Na/Fe] = +0.53, [Mg/Fe] = +0.94, [Al/Fe] = +0.23, and [Ba/Fe] < -1.0 is similar to that of the rare and enigmatic class of Galactic halo objects designated CEMP-no (carbon-rich, extremely metal-poor with no enhancement (over solar ratios) of heavy neutron-capture elements). This is the first star in a Milky Way 'satellite' that unambiguously lies on the metal-poor, C-rich branch of the Aoki et al. bimodal distribution of field halo stars in the ([C/Fe], [Fe/H])-plane. Available data permit us only to identify Seg 1-7 as a member of an ultra-faint dwarf galaxy or as debris from the Sgr dwarf spheroidal galaxy. In either case, this demonstrates that at extremely low abundance, [Fe/H ] <-3.0, star formation and associated chemical evolution proceeded similarly in the progenitors of both the field halo and satellite systems. By extension, this is consistent with other recent suggestions that the most metal-poor dwarf spheroidal and ultra-faint dwarf satellites were the building blocks of the Galaxy's outer halo.

  18. The Discovery and Analysis of Very Metal-Poor Stars in the Galaxy

    NASA Astrophysics Data System (ADS)

    Beers, Timothy C.; Christlieb, Norbert

    2005-09-01

    We discuss the importance of very metal-poor stars to develop an understanding of the nature of the first stars that formed in the Universe and the nucleosynthesis events associated with them, as well as to refine models of galaxy formation, in particular for large spiral galaxies such as the Milky Way. After briefly reviewing the history of the search for very metal-deficient stars in the Galaxy, we summarize ongoing efforts, concentrating on the two large objective-prism surveys that have led to the discovery of the majority of stars with [Fe/H] < 2.0 known at present: the HK survey of Beers and collaborators and the Hamburg/ESO survey of Christlieb and collaborators. We then consider the wealth of information that can be gleaned from high-resolution spectroscopic study of very metal-poor stars. We close with a list of open questions and a discussion of new survey techniques that will expand the sample of recognized very metal-deficient stars in the Galaxy by several orders of magnitude.

  19. Very Metal-poor Outer-halo Stars with Round Orbits

    NASA Astrophysics Data System (ADS)

    Hattori, Kohei; Yoshii, Yuzuru; Beers, Timothy C.; Carollo, Daniela; Lee, Young Sun

    2013-01-01

    The orbital motions of halo stars in the Milky Way reflect the orbital motions of the progenitor systems in which they formed, making it possible to trace the mass-assembly history of the Galaxy. Direct measurement of three-dimensional velocities, based on accurate proper motions and line-of-sight velocities, has revealed that the majority of halo stars in the inner-halo region move in eccentric orbits. However, our understanding of the motions of distant, in situ halo-star samples is still limited, due to the lack of accurate proper motions for these stars. Here we explore a model-independent analysis of the line-of-sight velocities and spatial distribution of a recent sample of 1865 carefully selected halo blue horizontal-branch (BHB) stars within 30 kpc of the Galactic center. We find that the mean rotational velocity of the very metal-poor ([Fe/H] < -2.0) BHB stars significantly lags behind that of the relatively more metal-rich ([Fe/H] > -2.0) BHB stars. We also find that the relatively more metal-rich BHB stars are dominated by stars with eccentric orbits, as previously observed for other stellar samples in the inner-halo region. By contrast, the very metal-poor BHB stars are dominated by stars on rounder, lower-eccentricity orbits. Our results indicate that the motion of the progenitor systems of the Milky Way that contributed to the stellar populations found within 30 kpc correlates directly with their metal abundance, which may be related to their physical properties such as gas fractions. These results are consistent with the existence of an inner/outer halo structure for the halo system, as advocated by Carollo et al.

  20. Near-IR Observations Of Carbon-Enhanced Metal-Poor Stars With SOAR/OSIRIS

    NASA Astrophysics Data System (ADS)

    Kennedy, Catherine R.; Sivarani, T.; Beers, T.; Lee, Y.; Rossi, S.; Placco, V.

    2007-12-01

    We report on medium-resolution near-IR spectroscopy, obtained with SOAR/OSIRIS, of a sample of over 50 Carbon-Enhanced Metal-Poor (CEMP) stars selected from the HK survey of Beers and colleagues and the Hamburg/ESO Survey of Christlieb and colleagues. These stars are primarily cool (4000 K < Teff < 5000 K), metal-poor objects with previous optical observations that indicate carbon enhancement [C/Fe] > +1.0. The observations are used, in combination with information available from optical spectra, to derive estimates of the O abundance and 12C/13C ratios from the molecular lines of CO, which are very sensitive to oxygen abundances in such stars. The results are compared with abundances determined from high-resolution observations for a subset of these stars. Based the O abundances from CO lines, we revisit the estimation of C and N abundances from optical observations. The origin of the elemental abundance pattern for CEMP stars with s-process enhancement (CEMP-s stars) is very likely to be mass transfer from (now extinct) AGB companions. However, the [C/N] and 12C/13C ratios of CEMP-s stars are very different from solar-metallicity AGB stars. The [O/Fe] measurements provide additional constraints on the mass of these AGB companions. Another class, the CEMP-no stars (CEMP stars with no n-capture enhancement), could have either been polluted by AGB mass-transfer, winds from massive stars, or early supernovae. The 12C/13C and [O/Fe] abundances are crucial to distinguish their origin, and they are not easily available through optical observations due to the weakness of the [OI] 6300 A lines. TCB, YSL, CK, and TS acknowledge support from grant PHY 02-16783; Physics Frontier Center/Joint Institute for Nuclear Astrophysics (JINA), awarded by the U.S. National Science Foundation.

  1. VERY METAL-POOR OUTER-HALO STARS WITH ROUND ORBITS

    SciTech Connect

    Hattori, Kohei; Yoshii, Yuzuru; Beers, Timothy C.; Carollo, Daniela; Lee, Young Sun

    2013-01-20

    The orbital motions of halo stars in the Milky Way reflect the orbital motions of the progenitor systems in which they formed, making it possible to trace the mass-assembly history of the Galaxy. Direct measurement of three-dimensional velocities, based on accurate proper motions and line-of-sight velocities, has revealed that the majority of halo stars in the inner-halo region move in eccentric orbits. However, our understanding of the motions of distant, in situ halo-star samples is still limited, due to the lack of accurate proper motions for these stars. Here we explore a model-independent analysis of the line-of-sight velocities and spatial distribution of a recent sample of 1865 carefully selected halo blue horizontal-branch (BHB) stars within 30 kpc of the Galactic center. We find that the mean rotational velocity of the very metal-poor ([Fe/H] < -2.0) BHB stars significantly lags behind that of the relatively more metal-rich ([Fe/H] > -2.0) BHB stars. We also find that the relatively more metal-rich BHB stars are dominated by stars with eccentric orbits, as previously observed for other stellar samples in the inner-halo region. By contrast, the very metal-poor BHB stars are dominated by stars on rounder, lower-eccentricity orbits. Our results indicate that the motion of the progenitor systems of the Milky Way that contributed to the stellar populations found within 30 kpc correlates directly with their metal abundance, which may be related to their physical properties such as gas fractions. These results are consistent with the existence of an inner/outer halo structure for the halo system, as advocated by Carollo et al.

  2. Chemical composition of extremely metal-poor stars in the Sextans dwarf spheroidal galaxy

    NASA Astrophysics Data System (ADS)

    Aoki, W.; Arimoto, N.; Sadakane, K.; Tolstoy, E.; Battaglia, G.; Jablonka, P.; Shetrone, M.; Letarte, B.; Irwin, M.; Hill, V.; Francois, P.; Venn, K.; Primas, F.; Helmi, A.; Kaufer, A.; Tafelmeyer, M.; Szeifert, T.; Babusiaux, C.

    2009-08-01

    Context: Individual stars in dwarf spheroidal galaxies around the Milky Way Galaxy have been studied both photometrically and spectroscopically. Extremely metal-poor stars among them are very valuable because they should record the early enrichment in the Local Group. However, our understanding of these stars is very limited because detailed chemical abundance measurements are needed from high resolution spectroscopy. Aims: To constrain the formation and chemical evolution of dwarf galaxies, metallicity and chemical composition of extremely metal-poor stars are investigated. Methods: Chemical abundances of six extremely metal-poor ([Fe/H] < -2.5) stars in the Sextans dwarf spheroidal galaxy are determined based on high resolution spectroscopy (R=40 000) with the Subaru Telescope High Dispersion Spectrograph. Results: (1) The Fe abundances derived from the high resolution spectra are in good agreement with the metallicity estimated from the Ca triplet lines in low resolution spectra. The lack of stars with [Fe/H] ⪉ -3 in Sextans, found by previous estimates from the Ca triplet, is confirmed by our measurements, although we note that high resolution spectroscopy for a larger sample of stars will be necessary to estimate the true fraction of stars with such low metallicity. (2) While one object shows an overabundance of Mg (similar to Galactic halo stars), the Mg/Fe ratios of the remaining five stars are similar to the solar value. This is the first time that low Mg/Fe ratios at such low metallicities have been found in a dwarf spheroidal galaxy. No evidence for over-abundances of Ca and Ti are found in these five stars, though the measurements for these elements are less certain. Possible mechanisms to produce low Mg/Fe ratios, with respect to that of Galactic halo stars, are discussed. (3) Ba is under-abundant in four objects, while the remaining two stars exhibit large and moderate excesses of this element. The abundance distribution of Ba in this galaxy is

  3. Hot, Massive Stars in the Extremely Metal-Poor Galaxy, I Zw 18

    NASA Technical Reports Server (NTRS)

    Heap, Sara R.; Malumuth, Eliot M.

    2010-01-01

    The carbon-enhanced metal-poor galaxy, I Zw 18, is the Rosetta Stone for understanding galaxies in the early universe by providing constraints on the IMF of massive stars, the role of galaxies in reionization of the universe, mixing of newly synthesized material in the ISM, and gamma-ray bursts at low metallicity, and on the earliest generations of stars producing the observed abundance pattern. We describe these constraints as derived from analyses of HST/COS spectra of I Zw 18 including stellar atmosphere analysis and photo-ionization modeling of both the emission and absorption spectra of the nebular material and interstellar medium.

  4. Rotation and Macroturbulence in Metal-Poor Field Red Giant and Red Horizontal Branch Stars

    NASA Astrophysics Data System (ADS)

    Carney, Bruce W.; Gray, David F.; Yong, David; Latham, David W.; Manset, Nadine; Zelman, Rachel; Laird, John B.

    2008-03-01

    We report the results for rotational velocities, Vrot sin i, and macroturbulence dispersions, ζRT, for 12 metal-poor field red giant branch (RGB) stars and 7 metal-poor field red horizontal branch (RHB) stars. The results are based on Fourier transform analyses of absorption line profiles from high-resolution (R ≈ 120,000), high-S/N (≈215 per pixel; ≈345 per resolution element) spectra obtained with the Gecko spectrograph at the Canada-France-Hawaii Telescope (CFHT). The stars were selected from the authors' previous studies of 20 RHB and 116 RGB stars, based primarily on larger-than-average line-broadening values. We find that ζRT values for the metal-poor RGB stars are very similar to those for metal-rich disk giants studied earlier by Gray and his collaborators. Six of the RGB stars have small rotational values, less than 2.0 km s-1, while five show significant rotation/enhanced line broadening, over 3 km s-1. We confirm the rapid rotation rate for RHB star HD 195636, found earlier by Preston. This star's rotation is comparable to that of the fastest known rotating blue horizontal branch (BHB) stars, when allowance is made for differences in radii and moments of inertia. The other six RHB stars have somewhat lower rotation but show a trend to higher values at higher temperatures (lower radii). Comparing our results with those for BHB stars from Kinman et al., we find that the fraction of rapidly rotating RHB stars is somewhat lower than is found among BHB stars. The number of rapidly rotating RHB stars is also smaller than we would have expected from the observed rotation of the RGB stars. We devise two empirical methods to translate our earlier line-broadening results into Vrot sin i for all the RGB and RHB stars they studied. Binning the RGB stars by luminosity, we find that most metal-poor field RGB stars show no detectable sign, on average, of rotation, which is not surprising given the stars' large radii. However, the most luminous stars, with MV

  5. A giant planet around a metal-poor star of extragalactic origin.

    PubMed

    Setiawan, Johny; Klement, Rainer J; Henning, Thomas; Rix, Hans-Walter; Rochau, Boyke; Rodmann, Jens; Schulze-Hartung, Tim

    2010-12-17

    Stars in their late stage of evolution, such as horizontal branch stars, are still largely unexplored for planets. We detected a planetary companion around HIP 13044, a very metal-poor star on the red horizontal branch, on the basis of radial velocity observations with a high-resolution spectrograph at the 2.2-meter Max-Planck Gesellschaft-European Southern Observatory telescope. The star's periodic radial velocity variation of P = 16.2 days caused by the planet can be distinguished from the periods of the stellar activity indicators. The minimum mass of the planet is 1.25 times the mass of Jupiter and its orbital semimajor axis is 0.116 astronomical units. Because HIP 13044 belongs to a group of stars that have been accreted from a disrupted satellite galaxy of the Milky Way, the planet most likely has an extragalactic origin. PMID:21097905

  6. TOPoS: chemical study of extremely metal-poor stars.

    NASA Astrophysics Data System (ADS)

    Caffau, E.; Sbordone, L.; Bonifacio, P.; Cayrel, R.; Christlieb, N.; Clark, P.; François, P.; Glover, S.; Klessen, R.; Koch, A.; Ludwig, H.-G.; Monaco, L.; Plez, B.; Spite, F.; Spite, M.; Steffen, M.; Zaggia, S.

    The extremely metal-poor (EMP) stars hold in their atmospheres the fossil record of the chemical composition of the early phases of the Galactic evolution. The chemical analysis of such objects provides important constraints on these early phases. EMP stars are very rare objects; to dig them out, large amounts of data have to be processed. With an automatic procedure, we analysed objects with colours of Turn-Off stars from the Sloan Digital Sky Survey to select a sample of good candidate EMP stars. In the latest years, we observed a sample of these candidates with X-Shooter and UVES, and we have an ongoing ESO large programme to use these spectrographs to observe EMP stars. I will report here the results on metallicity and Strontium abundance. Based on observations obtained at ESO Paranal Observatory, programme 189.D-0165(A)

  7. The Synthetic-Oversampling Method: Using Photometric Colors to Discover Extremely Metal-poor Stars

    NASA Astrophysics Data System (ADS)

    Miller, A. A.

    2015-09-01

    Extremely metal-poor (EMP) stars ([Fe/H] ≤ ‑3.0 dex) provide a unique window into understanding the first generation of stars and early chemical enrichment of the universe. EMP stars are exceptionally rare, however, and the relatively small number of confirmed discoveries limits our ability to exploit these near-field probes of the first ∼500 Myr after the Big Bang. Here, a new method to photometrically estimate [Fe/H] from only broadband photometric colors is presented. I show that the method, which utilizes machine-learning algorithms and a training set of ∼170,000 stars with spectroscopically measured [Fe/H], produces a typical scatter of ∼0.29 dex. This performance is similar to what is achievable via low-resolution spectroscopy, and outperforms other photometric techniques, while also being more general. I further show that a slight alteration to the model, wherein synthetic EMP stars are added to the training set, yields the robust identification of EMP candidates. In particular, this synthetic-oversampling method recovers ∼20% of the EMP stars in the training set, at a precision of ∼0.05. Furthermore, ∼65% of the false positives from the model are very metal-poor stars ([Fe/H] ≤ ‑2.0 dex). The synthetic-oversampling method is biased toward the discovery of warm (∼F-type) stars, a consequence of the targeting bias from the Sloan Digital Sky Survey/Sloan Extension for Galactic Understanding survey. This EMP selection method represents a significant improvement over alternative broadband optical selection techniques. The models are applied to >12 million stars, with an expected yield of ∼600 new EMP stars, which promises to open new avenues for exploring the early universe.

  8. Identifying Bright Carbon-Enhanced Metal-Poor Stars in the RAVE Catalog

    NASA Astrophysics Data System (ADS)

    Placco, Vinicius; Beers, Timothy C.

    2016-01-01

    Bright metal-poor stars are of great importance for high-resolution spectroscopic follow-up, since their brightness allows for detailed studies of the chemical compositions of their atmospheres, obtainable with short integration times on 4m-8m class telescopes. We have carried out a medium-resolution spectroscopic follow-up survey of very metal-poor ([Fe/H] < -2.0) stars selected from the RAVE catalog.Over the course of four semesters we observed over 1,200 stars with the Gemini North, Gemini South, SOAR, KPNO/Mayall, and ESO/NTT telescopes. These spectra are used to confirm the estimated atmospheric parameters from RAVE, as well as to determine [C/Fe], using our spectroscopic analysis pipeline. This information has already enabled the identification of many new carbon-enhanced metal-poor (CEMP) stars, including representatives of the inner- and outer-halo populations of the Milky Way, for which high-resolution spectroscopy is in progress from the ground with the Magellan/Clay Telescope and with the South African Large Telescope (SALT). The most interesting stars from the high-resolution follow-up will be observed from space with HST/STIS or COS. In this talk I will present the results of the medium-resolution follow-up, and preliminary results from the high-resolution effort.We acknowledge partial support from the grant PHY 14-30152; Physics Frontier Center/JINA Center for the Evolution of the Elements (JINA-CEE), awarded by the US National Science Foundation.

  9. Chemistry of the Most Metal-poor Stars in the Bulge and the z ≳ 10 Universe

    NASA Astrophysics Data System (ADS)

    Casey, Andrew R.; Schlaufman, Kevin C.

    2015-08-01

    Metal-poor stars in the Milky Way are local relics of the epoch of the first stars and the first galaxies. However, a low metallicity does not prove that a star formed in this ancient era, as metal-poor stars form over a range of redshift in different environments. Theoretical models of Milky Way formation have shown that at constant metallicity, the oldest stars are those closest to the center of the Galaxy on the most tightly bound orbits. For that reason, the most metal-poor stars in the bulge of the Milky Way provide excellent tracers of the chemistry of the high-redshift universe. We report the dynamics and detailed chemical abundances of three stars in the bulge with [{Fe}/{{H}}]≲ -2.7, two of which are the most metal-poor stars in the bulge in the literature. We find that with the exception of scandium, all three stars follow the abundance trends identified previously for metal-poor halo stars. These three stars have the lowest [Sc ii/Fe] abundances yet seen in α-enhanced giant stars in the Galaxy. Moreover, all three stars are outliers in the otherwise tight [Sc ii/Fe]-[Ti ii/Fe] relation observed among metal-poor halo stars. Theoretical models predict that there is a 30% chance that at least one of these stars formed at z≳ 15, while there is a 70% chance that at least one formed at 10≲ z≲ 15. These observations imply that by z˜ 10, the progenitor galaxies of the Milky Way had both reached [{Fe}/{{H}}]˜ -3.0 and established the abundance pattern observed in extremely metal-poor stars. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

  10. Follow-up observations of extremely metal-poor stars identified from SDSS

    NASA Astrophysics Data System (ADS)

    Aguado, D. S.; Allende Prieto, C.; González Hernández, J. I.; Carrera, R.; Rebolo, R.; Shetrone, M.; Lambert, D. L.; Fernández-Alvar, E.

    2016-08-01

    Context. The most metal-poor stars in the Milky Way witnessed the early phases of formation of the Galaxy, and have chemical compositions that are close to the pristine mixture from Big Bang nucleosynthesis, polluted by one or few supernovae. Aims: Only two dozen stars with ([Fe/H] < -4) are known, and they show a wide range of abundance patterns. It is therefore important to enlarge this sample. We present the first results of an effort to identify new extremely metal-poor stars in the Milky Way halo. Methods: Our targets have been selected from low-resolution spectra obtained as part of the Sloan Digital Sky Survey, and followed-up with medium resolution spectroscopy on the 4.2 m William Herschel Telescope and, in a few cases, at high resolution on the 9.2 m Hobby-Eberly Telescope. Stellar parameters and the abundances of magnesium, calcium, iron, and strontium have been inferred from the spectra using classical model atmospheres. We have also derived carbon abundances from the G band. Results: We find consistency between the metallicities estimated from SDSS and those from new data at the level of 0.3 dex. The analysis of medium resolution data obtained with ISIS on the WHT allows us to refine the metallicities and in some cases measure other elemental abundances. Our sample contains 11 new metal-poor stars with [Fe/H] < -3.0, one of them with an estimated metallicity of [Fe/H] ~ -4.0. We also discuss metallicity discrepancies of some stars in common with previous works in the literature. Only one of these stars is found to be C-enhanced at about [C/Fe] ~ + 1, whereas the other metal-poor stars show C abundances at the level of [C/Fe] ~ + 0.45. 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.The reduced spectra as FITS files are only available at

  11. Armchair cartography - A map of the Galactic halo based on observations of local, metal-poor stars

    NASA Astrophysics Data System (ADS)

    Sommer-Larsen, Jesper; Zhen, Chen

    1990-01-01

    The velocity distribution of metal-poor halo stars in the solar neighborhood is studied to extract data on the global spatial and kinematic properties of the Galactic stellar halo. A global model of the solar neighborhood stars is constructed from observed positions and three-dimensional velocity of local, metal-poor halo stars in terms of a discrete sum of orbits. The characteristics of the reconstructed halo are examined and used to study the evolution of the halo subsystems.

  12. Determination of Physical Parameter Estimates for Metal-Poor Stars from the HK and HES Surveys

    NASA Astrophysics Data System (ADS)

    Beers, Timothy C.; Lee, Y.; Placco, V.; Carollo, D.; Christlieb, N.; Fiorenza, S.

    2013-06-01

    Over the past quarter century, well over ten thousand metal-poor star candidates selected during the course of the HK survey of Beers, Preston, and Shectman and the Hamburg/ESO survey of Christlieb and collaborators have had medium-resolution (R ~ 2500-3000) spectroscopy obtained, using a host of telescopes and spectrographs. During that time, we have refined the analysis tools at our disposal, and collected broadband photometry for many of these stars. Here we report on an application of the recently refined non-SEGUE Stellar Parameter Pipeline (n-SSPP) to obtain estimates of effective temperatures (Teff), surface gravities (log g), and metallicities ([Fe/H]) for many of these stars. In the case of some of the follow-up spectra, the wavelength coverage and S/N ratios also permit the determination of [C/Fe] and [alpha/Fe] ratios. Ongoing detailed analyses of the chemistry and kinematics of these stars will be described.

  13. The s-PROCESS Nucleosynthesis in Massive Metal-Poor Stars

    NASA Astrophysics Data System (ADS)

    Iwamoto, Nobuyuki

    2005-12-01

    We present the s-process nucleosynthesis in massive stars with a wide range of metallicity, using the recent sets of reaction rates and stellar input physics. The decreasing metallicity makes poisoning effects of primary 16O larger at the late phase of core He burning, at which the s-process occurs actively in solar metallicity stars, and prevents the synthesis of heavy elements from being efficient. However, we find that the s-process proceeds very efficiently via neutron source reaction of 13C(α,n)16O at the end of core H burning phase when the metallicity decreases below Z ~ 10-8. These massive, extremely low metallicity stars may have an important contribution of light s-elements to observed extremely metal-poor stars.

  14. Diversity of abundance patterns of neutron-capture elements in very metal-poor stars

    SciTech Connect

    Aoki, Misa; Ishimaru, Yuhri; Aoki, Wako; Wanajo, Shinya

    2014-05-02

    Observations of Very Metal-Poor stars indicate that there are at least two sites to r-process; “weak r-process” and “main r-process”. A question is whether these two are well separated or there exists a variation in the r-process. We present the results of abundance analysis of neutron-capture elements in the two Very Metal-Poor stars HD107752 and HD110184 in the Milky Way halo observed with the Subaru Telescope HDS. The abundance patterns show overabundace at light n-capture elements (e.g. Sr, Y), inferring the element yielding of weak r-process, while heavy neutron-capture elements (e.g. Ba, Eu) are deficient; however, the overabundance of light ones is not as significant as that previously found in stars representing the weak r-process (e.g. HD122563; Honda et al. 2006). Our study show diversity in the abundance patterns from light to heavy neutron-capture elements in VMP stars, suggesting a variation in r-process, which may depend on electron fraction of environment.

  15. Abundance profiling of extremely metal-poor stars and supernova properties in the early universe

    SciTech Connect

    Tominaga, Nozomu; Iwamoto, Nobuyuki; Nomoto, Ken'ichi E-mail: iwamoto.nobuyuki@jaea.go.jp

    2014-04-20

    After the big bang nucleosynthesis, the first heavy element enrichment in the universe was made by a supernova (SN) explosion of a population (Pop) III star (Pop III SN). The abundance ratios of elements produced from Pop III SNe are recorded in abundance patterns of extremely metal-poor (EMP) stars. The observations of the increasing number of EMP stars have made it possible to statistically constrain the explosion properties of Pop III SNe. We present Pop III SN models whose nucleosynthesis yields well reproduce, individually, the abundance patterns of 48 such metal-poor stars as [Fe/H] ≲ – 3.5. We then derive relations between the abundance ratios of EMP stars and certain explosion properties of Pop III SNe: the higher [(C + N)/Fe] and [(C + N)/Mg] ratios correspond to the smaller ejected Fe mass and the larger compact remnant mass, respectively. Using these relations, the distributions of the abundance ratios of EMP stars are converted to those of the explosion properties of Pop III SNe. Such distributions are compared with those of the explosion properties of present day SNe: the distribution of the ejected Fe mass of Pop III SNe has the same peak as that of the present day SNe but shows an extended tail down to ∼10{sup –2}-10{sup –5} M {sub ☉}, and the distribution of the mass of the compact remnant of Pop III SNe is as wide as that of the present-day, stellar-mass black holes. Our results demonstrate the importance of large samples of EMP stars obtained by ongoing and future EMP star surveys and subsequent high-dispersion spectroscopic observations in clarifying the nature of Pop III SNe in the early universe.

  16. Carbon-enhanced metal-poor stars: relics from the dark ages

    SciTech Connect

    Cooke, Ryan J.; Madau, Piero

    2014-08-20

    We use detailed nucleosynthesis calculations and a realistic prescription for the environment of the first stars to explore the first episodes of chemical enrichment that occurred during the dark ages. Based on these calculations, we propose a novel explanation for the increased prevalence of carbon-enhanced metal-poor (CEMP) stars with decreasing Fe abundance: the observed chemistry for the most metal-poor Galactic halo stars is the result of an intimate link between the explosions of the first stars and their host minihalo's ability to retain its gas. Specifically, high-energy supernovae produce a near solar ratio of C/Fe, but are effective in evacuating the gas from their host minihalo, thereby suppressing the formation of a second generation of stars. On the other hand, minihalos that host low-energy supernovae are able to retain their gas and form a second stellar generation, but, as a result, the second stars are born with a supersolar ratio of C/Fe. Our models are able to accurately reproduce the observed distributions of [C/Fe] and [Fe/H], as well as the fraction of CEMP stars relative to non-CEMP stars as a function of [Fe/H] without any free parameters. We propose that the present lack of chemical evidence for very massive stars (≳ 140 M {sub ☉}) that ended their lives as a highly energetic pair-instability supernova does not imply that such stars were rare or did not exist; the chemical products of these very massive first stars may have been evacuated from their host minihalos and were never incorporated into subsequent generations of stars. Finally, our models suggest that the most Fe-poor stars currently known may have seen the enrichment from a small multiple of metal-free stars, and need not have been exclusively enriched by a solitary first star. These calculations also add further support to the possibility that some of the surviving dwarf satellite galaxies of the Milky Way are the relics of the first galaxies.

  17. The chemical imprint of silicate dust on the most metal-poor stars

    SciTech Connect

    Ji, Alexander P.; Frebel, Anna; Bromm, Volker E-mail: afrebel@mit.edu

    2014-02-20

    We investigate the impact of dust-induced gas fragmentation on the formation of the first low-mass, metal-poor stars (<1 M {sub ☉}) in the early universe. Previous work has shown the existence of a critical dust-to-gas ratio, below which dust thermal cooling cannot cause gas fragmentation. Assuming that the first dust is silicon-based, we compute critical dust-to-gas ratios and associated critical silicon abundances ([Si/H]{sub crit}). At the density and temperature associated with protostellar disks, we find that a standard Milky Way grain size distribution gives [Si/H]{sub crit} = –4.5 ± 0.1, while smaller grain sizes created in a supernova reverse shock give [Si/H]{sub crit} = –5.3 ± 0.1. Other environments are not dense enough to be influenced by dust cooling. We test the silicate dust cooling theory by comparing to silicon abundances observed in the most iron-poor stars ([Fe/H] < -4.0). Several stars have silicon abundances low enough to rule out dust-induced gas fragmentation with a standard grain size distribution. Moreover, two of these stars have such low silicon abundances that even dust with a shocked grain size distribution cannot explain their formation. Adding small amounts of carbon dust does not significantly change these conclusions. Additionally, we find that these stars exhibit either high carbon with low silicon abundances or the reverse. A silicate dust scenario thus suggests that the earliest low-mass star formation in the most metal-poor regime may have proceeded through two distinct cooling pathways: fine-structure line cooling and dust cooling. This naturally explains both the carbon-rich and carbon-normal stars at extremely low [Fe/H].

  18. Abundance anomalies in metal-poor stars from Population III supernova ejecta hydrodynamics

    NASA Astrophysics Data System (ADS)

    Sluder, Alan; Ritter, Jeremy S.; Safranek-Shrader, Chalence; Milosavljević, Miloš; Bromm, Volker

    2016-02-01

    We present a simulation of the long-term evolution of a Population III supernova remnant in a cosmological minihalo. Employing passive Lagrangian tracer particles, we investigate how chemical stratification and anisotropy in the explosion can affect the abundances of the first low-mass, metal-enriched stars. We find that reverse shock heating can leave the inner mass shells at entropies too high to cool, leading to carbon enhancement in the recollapsing gas. This hydrodynamic selection effect could explain the observed incidence of carbon-enhanced metal-poor stars at low metallicity. We further explore how anisotropic ejecta distributions, recently seen in direct numerical simulations of core-collapse explosions, may translate to abundances in metal-poor stars. We find that some of the observed scatter in the Population II abundance ratios can be explained by an incomplete mixing of supernova ejecta, even in the case of only one contributing enrichment event. We demonstrate that the customary hypothesis of fully mixed ejecta clearly fails if post-explosion hydrodynamics prefers the recycling of some nucleosynthetic products over others. Furthermore, to fully exploit the stellar-archaeological programme of constraining the Pop III initial mass function from the observed Pop II abundances, considering these hydrodynamical transport effects is crucial. We discuss applications to the rich chemical structure of ultrafaint dwarf satellite galaxies, to be probed in unprecedented detail with upcoming spectroscopic surveys.

  19. Nucleosynthesis in Gamma-Ray Bursts and Supernovae: Constraints of Extremely Metal-Poor Stars

    NASA Astrophysics Data System (ADS)

    Tominaga, N.

    2012-08-01

    I present nucleosynthesis in explosions with relativistic jets or non- relativistic mildly aspherical components, assuming gamma-ray bursts (GRBs) or supernovae (SNe), and compare the abundance ratios of their yields with those of the extremely metal-poor (EMP) stars. The explosion with non-relativistic mildly aspherical energy deposition can explain [Mg/Fe], [Ca/Fe], and [Zn/Fe] but not [Ti/Fe], while the explosion with relativistic jets can explain [Ca/Fe], [Ti/Fe], and [Zn/Fe] but not [Mg/Fe]. This illustrates that the explosion with relativistic jets or non-relativistic mildly aspherical components cannot fully reproduce the EMP stars and implies that the explosion with relativistic jets and non-relativistic mildly aspherical components as in GRB-SNe could explain the abundance ratios of EMP stars simultaneously.

  20. Abundances of Extremely Metal-Poor Stars, aNnew HIRES Sample

    NASA Astrophysics Data System (ADS)

    Lai, David K.; Bolte, M.; Johnson, J. A.; Lucatello, S.

    2006-12-01

    We present the results of an abundance analysis for a sample of stars with -2>[Fe/H]> -4. The set includes 29 stars, with effective temperature ranging from 4800 K to 6300 K. The data were obtained with the HIRES spectrograph at Keck Observatory. For most objects our wavelength range reaches from about 3100 angstroms to 5800 angstroms. Our spectra allow us to further constrain the abundance scatter at low metallicities for the light elements including carbon and nitrogen, up through the iron group, and for many neutron-capture elements. Most of our objects have come from the Beers et al. HK survey (1992, AJ, 103, 1987) for metal-poor stars, and for many of them this is the first high-resolution study. This research is based on work supported by the National Science Foundation under the grant AST-0607770.

  1. THE MOST METAL-POOR STARS. I. DISCOVERY, DATA, AND ATMOSPHERIC PARAMETERS

    SciTech Connect

    Norris, John E.; Bessell, M. S.; Yong, David; Asplund, M.; Murphy, Simon J.; Christlieb, N.; Barklem, P. S.; Beers, Timothy C.; Frebel, Anna; Ryan, S. G. E-mail: bessell@mso.anu.edu.au E-mail: martin@mso.anu.edu.au E-mail: paul.barklem@physics.uu.se E-mail: afrebel@mit.edu

    2013-01-01

    We report the discovery of 34 stars in the Hamburg/ESO Survey for metal-poor stars and the Sloan Digital Sky Survey that have [Fe/H] {approx}< -3.0. Their median and minimum abundances are [Fe/H] = -3.1 and -4.1, respectively, while 10 stars have [Fe/H] < -3.5. High-resolution, high signal-to-noise spectroscopic data-equivalent widths and radial velocities-are presented for these stars, together with an additional four objects previously reported or currently being investigated elsewhere. We have determined the atmospheric parameters, effective temperature (T {sub eff}), and surface gravity (log g), which are critical in the determination of the chemical abundances and the evolutionary status of these stars. Three techniques were used to derive these parameters. Spectrophotometric fits to model atmosphere fluxes were used to derive T {sub eff}, log g, and an estimate of E(B - V); H{alpha}, H{beta}, and H{gamma} profile fitting to model atmosphere results provided the second determination of T {sub eff} and log g; and finally, we used an empirical T {sub eff}-calibrated H{delta} index, for the third, independent T {sub eff} determination. The three values of T {sub eff} are in good agreement, although the profile fitting may yield systematically cooler T {sub eff} values, by {approx}100 K. This collective data set will be analyzed in future papers in the present series to utilize the most metal-poor stars as probes of conditions in the early universe.

  2. DISCOVERY OF A SUPER-Li-RICH TURNOFF STAR IN THE METAL-POOR GLOBULAR CLUSTER NGC 6397

    SciTech Connect

    Koch, Andreas; Lind, Karin; Michael Rich, R.

    2011-09-10

    We report on the discovery of a super-Li-rich turnoff (TO) star in the old (12 Gyr), metal-poor ([Fe/H] = -2.1 dex) globular cluster (GC) NGC 6397, based on high-resolution MIKE/Magellan spectra. This star shows an unusually high lithium abundance of A(Li){sub NLTE} = 4.03 {+-} 0.06 {+-} 0.14 dex (or, 4.21, accounting for possible contamination from a binary companion) that lies above the canonical Li-plateau by a factor of 100. This is the highest Li enhancement found in a Galactic GC dwarf star to date. We discuss several enhancement mechanisms, but none can unambiguously explain such a high overabundance. The spectrum of the star shows a possible indication of binarity, but its line strengths and chemical element abundance ratios are fully compatible with other TO stars in this GC, seemingly ruling out mass transfer from an asymptotic giant branch companion as origin of the high A(Li). A possible cause is an interaction with a red giant that has undergone cool bottom processing.

  3. THE CHEMICAL ABUNDANCES OF STARS IN THE HALO (CASH) PROJECT. II. A SAMPLE OF 14 EXTREMELY METAL-POOR STARS ,

    SciTech Connect

    Hollek, Julie K.; Sneden, Christopher; Shetrone, Matthew; Frebel, Anna; Roederer, Ian U.; Beers, Timothy C.; Kang, Sung-ju; Thom, Christopher E-mail: chris@astro.as.utexas.edu E-mail: afrebel@cfa.harvard.edu E-mail: beers@pa.msu.edu E-mail: cthom@stsci.edu

    2011-11-20

    We present a comprehensive abundance analysis of 20 elements for 16 new low-metallicity stars from the Chemical Abundances of Stars in the Halo (CASH) project. The abundances have been derived from both Hobby-Eberly Telescope High Resolution Spectrograph snapshot spectra (R {approx}15, 000) and corresponding high-resolution (R {approx}35, 000) Magellan Inamori Kyocera Echelle spectra. The stars span a metallicity range from [Fe/H] from -2.9 to -3.9, including four new stars with [Fe/H] < -3.7. We find four stars to be carbon-enhanced metal-poor (CEMP) stars, confirming the trend of increasing [C/Fe] abundance ratios with decreasing metallicity. Two of these objects can be classified as CEMP-no stars, adding to the growing number of these objects at [Fe/H]< - 3. We also find four neutron-capture-enhanced stars in the sample, one of which has [Eu/Fe] of 0.8 with clear r-process signatures. These pilot sample stars are the most metal-poor ([Fe/H] {approx}< -3.0) of the brightest stars included in CASH and are used to calibrate a newly developed, automated stellar parameter and abundance determination pipeline. This code will be used for the entire {approx}500 star CASH snapshot sample. We find that the pipeline results are statistically identical for snapshot spectra when compared to a traditional, manual analysis from a high-resolution spectrum.

  4. TESTING THE ASTEROSEISMIC MASS SCALE USING METAL-POOR STARS CHARACTERIZED WITH APOGEE AND KEPLER

    SciTech Connect

    Epstein, Courtney R.; Johnson, Jennifer A.; Tayar, Jamie; Pinsonneault, Marc; Elsworth, Yvonne P.; Chaplin, William J.; Shetrone, Matthew; Mosser, Benoît; Hekker, Saskia; Harding, Paul; Silva Aguirre, Víctor; Basu, Sarbani; Beers, Timothy C.; Bizyaev, Dmitry; Bedding, Timothy R.; Frinchaboy, Peter M.; García, Rafael A.; and others

    2014-04-20

    Fundamental stellar properties, such as mass, radius, and age, can be inferred using asteroseismology. Cool stars with convective envelopes have turbulent motions that can stochastically drive and damp pulsations. The properties of the oscillation frequency power spectrum can be tied to mass and radius through solar-scaled asteroseismic relations. Stellar properties derived using these scaling relations need verification over a range of metallicities. Because the age and mass of halo stars are well-constrained by astrophysical priors, they provide an independent, empirical check on asteroseismic mass estimates in the low-metallicity regime. We identify nine metal-poor red giants (including six stars that are kinematically associated with the halo) from a sample observed by both the Kepler space telescope and the Sloan Digital Sky Survey-III APOGEE spectroscopic survey. We compare masses inferred using asteroseismology to those expected for halo and thick-disk stars. Although our sample is small, standard scaling relations, combined with asteroseismic parameters from the APOKASC Catalog, produce masses that are systematically higher (<ΔM > =0.17 ± 0.05 M {sub ☉}) than astrophysical expectations. The magnitude of the mass discrepancy is reduced by known theoretical corrections to the measured large frequency separation scaling relationship. Using alternative methods for measuring asteroseismic parameters induces systematic shifts at the 0.04 M {sub ☉} level. We also compare published asteroseismic analyses with scaling relationship masses to examine the impact of using the frequency of maximum power as a constraint. Upcoming APOKASC observations will provide a larger sample of ∼100 metal-poor stars, important for detailed asteroseismic characterization of Galactic stellar populations.

  5. Three New Planetary Systems Orbiting Metal-Poor Thick Disk Stars

    NASA Astrophysics Data System (ADS)

    Cochran, William D.; Endl, M.; Brugamyer, E. J.; MacQueen, P. J.

    2013-10-01

    We report the detection of Jovian mass planets orbiting three nearby metal-poor thick disk stars. These discoveries were all made using precise radial velocity measurements from the High Resolution Spectrograph of the Hobby-Eberly Telescope. All of the planets are of Jovian mass or larger, with orbital periods ranging from about a year to over six years. HIP 14342 shows two planetary companions with orbital periods near a 2:1 resonance. The other planets detected orbit HIP 13366 and HIP 109384. All three of these stars are kinematic members of the galactic "thick disk", which is a population of stars with a larger vertical scale height and a larger velocity dispersion that the thin disk to which the Sun belongs. The thick disk stars are of lower total metallicity than the Sun, and are also chemically different than thin disk stars, having the abundances of their alpha-capture elements (e.g. O, Ne, Mg, Si, S, Ca, Ti) enhanced by 0.2 to 0.4 dex over those of thin disk stars of the same [Fe/H]. The majority of planets found among stars with [Fe/H] < ~-0.2 orbit thick disk stars, even though thin disk stars significantly outnumber thick disk stars in this metallicity range. Thus, the enhanced abundance of the alpha-capture elements, which are also key elements in the chemistry of planet-forming materials, may be responsible for the large fraction of low-metallicity thick-disk stars with planetary companions.

  6. Carbon Abundance Plateaus among Carbon-Enhanced Metal-Poor Stars

    NASA Astrophysics Data System (ADS)

    Yoon, Jinmi; He, Siyu; Placco, Vinicius; Carollo, Daniela; Beers, Timothy C.

    2016-01-01

    A substantial fraction of low-metallicity stars in the Milky Way, the Carbon-Enhanced Metal-Poor (CEMP) stars, exhibit enhancements of their carbon-to-iron relative to the solar value ([C/Fe] > +0.7). They can be divided into several sub-classes, depending on the nature and degree of the observed enhancements of their neutron-capture elements, providing information on their likely progenitors. CEMP-s stars (which exhibit enhanced s-process elements) are thought to be enhanced by mass transfer from an evolved AGB companion, while CEMP-no stars (which exhibit no over-abundances of neutron-capture elements) appear to be associated with explosions of the very first generations of stars. High-resolution spectroscopic analyses are generally required in order to make these sub-classifications.Several recent studies have suggested the existence of bimodality in the distribution of absolute carbon abundances among CEMP stars -- most CEMP-no stars belong to a low-C band ((A(C) ˜ 6.5), while most CEMP-s stars reside on a high-C band (A(C) ˜ 8.25). The number of CEMP stars considered by individual studies is, however, quite small, so we have compiled all available high-resolution spectroscopic data for CEMP stars, in order to further investigate the existence of the claimed carbon bi-modality, and to consider what can be learned about the progenitors of CEMP-s and CEMP-no stars based on the observed distribution of A(C) on the individual plateaus.We acknowledge partial support from the grant PHY 14-30152; Physics Frontier Center/JINA Center for the Evolution of the Elements (JINA-CEE), awarded by the US National Science Foundation.

  7. EXTREMELY METAL-POOR STARS IN THE MILKY WAY: A SECOND GENERATION FORMED AFTER REIONIZATION

    SciTech Connect

    Trenti, Michele; Shull, J. Michael E-mail: michael.shull@colorado.ed

    2010-03-20

    Cosmological simulations of Population III star formation suggest an initial mass function (IMF) biased toward very massive stars (M {approx}> 100 M{sub sun}) formed in minihalos at redshift z {approx}> 20, when the cooling is driven by molecular hydrogen. However, this result conflicts with observations of extremely metal-poor (EMP) stars in the Milky Way (MW) halo, whose r-process elemental abundances appear to be incompatible with those expected from very massive Population III progenitors. We propose a new solution to the problem in which the IMF of second-generation stars formed at z {approx}> 10, before reionization, is deficient in sub-solar mass stars, owing to the high cosmic microwave background temperature floor. The observed EMP stars are formed preferentially at z {approx}< 10 in pockets of gas enriched to metallicity Z {approx}> 10{sup -3.5} Z{sub sun} by winds from Population II stars. Our cosmological simulations of dark matter halos like the MW show that current samples of EMP stars can only constrain the IMF of late-time Population III stars, formed at z {approx}< 13 in halos with virial temperature T{sub vir} {approx} 10{sup 4} K. This suggests that pair instability supernovae were not produced primarily by this population. To begin probing the IMF of Population III stars formed at higher redshift will require a large survey, with at least 500 and probably several thousand EMP stars of metallicities Z {approx} 10{sup -3.5} Z{sub sun}.

  8. Europium, Samarium, and Neodymium Isotopic Fractions in Metal-Poor Stars

    NASA Astrophysics Data System (ADS)

    Roederer, Ian U.; Lawler, James E.; Sneden, Christopher; Cowan, John J.; Sobeck, Jennifer S.; Pilachowski, Catherine A.

    2008-03-01

    We have derived isotopic fractions of europium (Eu), samarium (Sm), and neodymium (Nd) in two metal-poor giants with differing neutron-capture nucleosynthetic histories. These isotopic fractions were measured from new very high resolution (R~120,000), high signal-to-noise (S/N~160-1000) spectra obtained with the 2dCoudé spectrograph of McDonald Observatory's 2.7 m Smith telescope. Synthetic spectra were generated using recent high-precision laboratory measurements of hyperfine and isotopic subcomponents of several transitions of these elements and matched quantitatively to the observed spectra. We interpret our isotopic fractions by the nucleosynthesis predictions of the stellar model, which models s-process nucleosynthesis in the physical conditions expected in a low-mass, thermally-pulsing star on the AGB, and the classical method, which assumes that s-process nucleosynthesis can be approximated by a steady neutron flux impinging upon Fe-peak seed nuclei. These two approaches predict the relative contributions to the Solar System n-capture abundances from the s- and r-processes and, by extension, the relative contributions of these two process to material in metal-poor stars. Our Eu isotopic fraction in HD 175305 is consistent with an r-process origin by the classical method and is consistent with both an r-process and s-process origin by the stellar model. Our Sm isotopic fraction in HD 175305 is consistent with a predominantly r-process origin by both methods, and our Sm isotopic fraction in HD 196944 is consistent with a pure s-process origin by both methods as well. Our Nd isotopic fractions in both stars are consistent with either r-process and s-process origins by both methods. The Eu and Sm isotopic fraction estimates argue for an r-process origin for the rare-earth elements in HD 175305 and an s-process origin for them in HD 196944, in excellent agreement with previous studies of the elemental abundance distributions in these stars. This study for the

  9. DETECTION OF THE SECOND r-PROCESS PEAK ELEMENT TELLURIUM IN METAL-POOR STARS ,

    SciTech Connect

    Roederer, Ian U.; Lawler, James E.; Cowan, John J.; Beers, Timothy C.; Frebel, Anna; Ivans, Inese I.; Schatz, Hendrik; Sobeck, Jennifer S.; Sneden, Christopher

    2012-03-15

    Using near-ultraviolet spectra obtained with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope, we detect neutral tellurium in three metal-poor stars enriched by products of r-process nucleosynthesis, BD +17 3248, HD 108317, and HD 128279. Tellurium (Te, Z = 52) is found at the second r-process peak (A Almost-Equal-To 130) associated with the N = 82 neutron shell closure, and it has not been detected previously in Galactic halo stars. The derived tellurium abundances match the scaled solar system r-process distribution within the uncertainties, confirming the predicted second peak r-process residuals. These results suggest that tellurium is predominantly produced in the main component of the r-process, along with the rare earth elements.

  10. The r-Process in Metal Poor Stars and Black Hole Formation

    SciTech Connect

    Boyd, R N; Famiano, M A; Meyer, B S; Motizuki, Y; Kajino, T; Roederer, I U

    2011-11-30

    Nucleosynthesis of heavy nuclei in metal-poor stars is generally ascribed to the r-process, as the abundance pattern in many such stars agrees with the inferred Solar r-process abundances. Nonetheless, a significant number of these stars do not share this r-process template. they suggest that many such stars have begun an r-process, but it was prevented from running to completion in more massive stars by collapse to black holes, creating a 'truncated r-process,' or 'tr-process'. The observed fraction of tr-process stars is found to be consistent with expectations from the initial mass function (IMF), and they suggest that an apparent sharp truncation observed at around mass 160 could result from a combination of collapses to black holes and the difficulty of observing the higher mass rare earths. They test the tr-process hypothesis with calculations that are terminated before all r-process trajectories have been ejected. These produce qualitative agreement with observation when both black hole collapse and observational realities are taken into account.

  11. NEW HUBBLE SPACE TELESCOPE OBSERVATIONS OF HEAVY ELEMENTS IN FOUR METAL-POOR STARS

    SciTech Connect

    Roederer, Ian U.; Thompson, Ian B.; Lawler, James E.; Sobeck, Jennifer S.; Beers, Timothy C.; Cowan, John J.; Frebel, Anna; Ivans, Inese I.; Schatz, Hendrik; Sneden, Christopher

    2012-12-15

    Elements heavier than the iron group are found in nearly all halo stars. A substantial number of these elements, key to understanding neutron-capture nucleosynthesis mechanisms, can only be detected in the near-ultraviolet. We report the results of an observing campaign using the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope to study the detailed heavy-element abundance patterns in four metal-poor stars. We derive abundances or upper limits from 27 absorption lines of 15 elements produced by neutron-capture reactions, including seven elements (germanium, cadmium, tellurium, lutetium, osmium, platinum, and gold) that can only be detected in the near-ultraviolet. We also examine 202 heavy-element absorption lines in ground-based optical spectra obtained with the Magellan Inamori Kyocera Echelle Spectrograph on the Magellan-Clay Telescope at Las Campanas Observatory and the High Resolution Echelle Spectrometer on the Keck I Telescope on Mauna Kea. We have detected up to 34 elements heavier than zinc. The bulk of the heavy elements in these four stars are produced by r-process nucleosynthesis. These observations affirm earlier results suggesting that the tellurium found in metal-poor halo stars with moderate amounts of r-process material scales with the rare earth and third r-process peak elements. Cadmium often follows the abundances of the neighboring elements palladium and silver. We identify several sources of systematic uncertainty that must be considered when comparing these abundances with theoretical predictions. We also present new isotope shift and hyperfine structure component patterns for Lu II and Pb I lines of astrophysical interest.

  12. An Astrometric Companion to the Nearby Metal-Poor, Low-Mass Star LHS 1589

    NASA Astrophysics Data System (ADS)

    Lépine, Sébastien; Rich, R. Michael; Shara, Michael M.; Cruz, Kelle L.; Skemer, Andrew

    2007-10-01

    We report the discovery of a companion to the high proper motion star LHS 1589, a nearby high-velocity, low-mass subdwarf. The companion (LHS 1589B) is located 0.224''+/-0.004'' to the southwest of the primary (LHS 1589A), and is 0.5 mag fainter than the primary in the Ks band. The pair was resolved with the IRCAL infrared camera at Lick Observatory, operating with the Laser Guide Star Adaptive Optics system. A low-resolution spectrum of the unresolved pair obtained at the MDM observatory shows the source to be consistent with a cool subdwarf of spectral subtype sdK7.5. A photometric distance estimate places the metal-poor system at a distance d=81+/-18 pc from the Sun. We also measure a radial velocity Vrad=67+/-8 km s-1, which, together with the proper motion and estimated distance, suggests that the pair is roaming the inner Galactic halo on a highly eccentric orbit. With a projected orbital separation s=18.1+/-4.8 AU, and a crude estimate of the system's total mass, we estimate the orbital period of the system to be in the range 75 yr metal-poor, low-mass stars. Based on observations performed with the Laser Guide Star Adaptive Optics system at the Lick Observatory, operated by the University of California system. Based on observations conducted at the MDM observatory, operated jointly by the University of Michigan, Dartmouth College, the Ohio State University, Columbia University, and the University of Ohio.

  13. CHEMICAL ANALYSIS OF THE NINTH MAGNITUDE CARBON-ENHANCED METAL-POOR STAR BD+44 Degree-Sign 493

    SciTech Connect

    Ito, Hiroko; Aoki, Wako; Beers, Timothy C.; Tominaga, Nozomu; Honda, Satoshi; Carollo, Daniela E-mail: beers@noao.edu E-mail: honda@kwasan.kyoto-u.ac.jp

    2013-08-10

    We present detailed chemical abundances for the bright carbon-enhanced metal-poor (CEMP) star BD+44 Degree-Sign 493, previously reported on by Ito et al. Our measurements confirm that BD+44 Degree-Sign 493 is an extremely metal-poor ([Fe/H] =-3.8) subgiant star with excesses of carbon and oxygen. No significant excesses are found for nitrogen and neutron-capture elements (the latter of which place it in the CEMP-no class of stars). Other elements that we measure exhibit abundance patterns that are typical for non-CEMP extremely metal-poor stars. No evidence for variations of radial velocity has been found for this star. These results strongly suggest that the carbon enhancement in BD+44 Degree-Sign 493 is unlikely to have been produced by a companion asymptotic giant-branch star and transferred to the presently observed star, nor by pollution of its natal molecular cloud by rapidly-rotating, massive, mega metal-poor ([Fe/H] < - 6.0) stars. A more likely possibility is that this star formed from gas polluted by the elements produced in a ''faint'' supernova, which underwent mixing and fallback, and only ejected small amounts of elements of metals beyond the lighter elements. The Li abundance of BD+44 Degree-Sign 493 (A(Li) = log (Li/H)+12 =1.0) is lower than the Spite plateau value, as found in other metal-poor subgiants. The upper limit on Be abundance (A(Be) = log (Be/H)+12 < - 1.8) is as low as those found for stars with similarly extremely-low metallicity, indicating that the progenitors of carbon- (and oxygen-) enhanced stars are not significant sources of Be, or that Be is depleted in metal-poor subgiants with effective temperatures of {approx}5400 K.

  14. The low Sr/Ba ratio on some extremely metal-poor stars

    NASA Astrophysics Data System (ADS)

    Spite, M.; Spite, F.; Bonifacio, P.; Caffau, E.; François, P.; Sbordone, L.

    2014-11-01

    Context. It has been noted that, in classical extremely metal-poor (EMP) stars, the abundance ratio of two well-observed neutron-capture elements, Sr and Ba, is always higher than [Sr/Ba] = -0.5, which is the value of the solar r-only process; however, a handful of EMP stars have recently been found with a very low Sr/Ba ratio. Aims: We try to understand the origin of this anomaly by comparing the abundance pattern of the elements in these stars and in the classical EMP stars. Methods: For a rigorous comparison with previous data, four stars with very low Sr/Ba ratios were observed and analyzed in the same way as in the First Stars program: analysis within LTE approximation through 1D (hydrostatic) model atmosphere, providing homogeneous abundances of nine neutron-capture elements. Results: In CS 22950-173, the only turnoff star of the sample, the Sr/Ba ratio is, in fact, found to be higher than the r-only solar ratio, so the star is discarded. The remaining stars (CS 29493-090, CS 30322-023, HE 305-4520) are cool evolved giants. They do not present a clear carbon enrichment, but in evolved giants C is partly burned into N, and owing to their high N abundance, they could still have initially been carbon-rich EMP stars (CEMP). The abundances of Na to Mg present similar anomalies to those in CEMP stars. The abundance patterns of the neutron-capture elements in the three stars are strikingly similar to a theoretical s-process pattern. This pattern could at first be attributed to pollution by a nearby AGB, but none of the stars presents a clear variation in the radial velocity indicating the presence of a companion. The stellar parameters seem to exclude any internal pollution in a TP-AGB phase for at least two of these stars. The possibility that the stars are early-AGB stars polluted during the core He flash does not seem compatible with the theory. Based on observations obtained with the ESO Very Large Telescope at Paranal Observatory, Chile (ID 077.D-0299(A) PI

  15. Ultraviolet Spectral Synthesis and Oxygen in Metal-Poor Solar-Type Stars

    NASA Astrophysics Data System (ADS)

    Peterson, R. C.

    1999-05-01

    This report outlines the progress and pitfalls of calculating spectra from first principles in the 2300 -- 3400A region for metal-poor solar-type stars, and how they relate to the derivation of abundances of key species such as oxygen and magnesium. This work is part of a NASA-supported effort with Ben Dorman of Goddard Space Flight Center to develop ab initio spectra suitable for galaxy analysis, and also part of a HST-oriented program with Karel Schrijver of Lockheed Martin to characterize the chromospheric activity of the oldest solar-type stars. The first task has been a reanalysis of the basic stellar parameters of temperature, surface gravity, and metallicity for solar-temperature stars ranging from one-fifth to one-three hundredth solar metallicity, demanding agreement in line strengths and profiles of strong lines and weak, in both optical and ultraviolet, and in the ultraviolet flux distribution. These cross-checks are built in to ensure convergence to a unique solution, or to highlight where standard assumptions are breaking down. Once agreement is achieved for the most metal-deficient stars, the line list used for the spectral calculations is re-examined, and somewhat more metal-rich stars are matched. Abundance results for oxygen from various approaches will be described, from the near-UV OH, 6300A [O I], and near-IR O I lines, and from adopting laboratory versus theoretical versus astrophysical atomic and molecular constants.

  16. Linking dwarf galaxies to halo building blocks with the most metal-poor star in Sculptor.

    PubMed

    Frebel, Anna; Kirby, Evan N; Simon, Joshua D

    2010-03-01

    Current cosmological models indicate that the Milky Way's stellar halo was assembled from many smaller systems. On the basis of the apparent absence of the most metal-poor stars in present-day dwarf galaxies, recent studies claimed that the true Galactic building blocks must have been vastly different from the surviving dwarfs. The discovery of an extremely iron-poor star (S1020549) in the Sculptor dwarf galaxy based on a medium-resolution spectrum cast some doubt on this conclusion. Verification of the iron-deficiency, however, and measurements of additional elements, such as the alpha-element Mg, are necessary to demonstrate that the same type of stars produced the metals found in dwarf galaxies and the Galactic halo. Only then can dwarf galaxy stars be conclusively linked to early stellar halo assembly. Here we report high-resolution spectroscopic abundances for 11 elements in S1020549, confirming its iron abundance of less than 1/4,000th that of the Sun, and showing that the overall abundance pattern follows that seen in low-metallicity halo stars, including the alpha-elements. Such chemical similarity indicates that the systems destroyed to form the halo billions of years ago were not fundamentally different from the progenitors of present-day dwarfs, and suggests that the early chemical enrichment of all galaxies may be nearly identical. PMID:20203604

  17. A Chemical Abundance Analysis of Stars Believed to be Metal Poor Members of the Galactic Stellar Thick Disk

    NASA Astrophysics Data System (ADS)

    Simmerer, Jennifer Ann

    Galactic formation models have long sought to reproduce the observed chemical and kinematical properties of the Milky Way's stellar halo and disk. Recently it is the so-called ``intermediate population'', the stellarthick disk, that is driving advances in our understanding of the formation of spiral galaxies. The thick disk is kinematically more like the thin disk than the halo, for all the thick disk has a velocity dispersion twice that of the thin diskand rotates ~40 km/s more slowly. It is generally accepted that the thick disk's metallicity distribution function peaks at a lower metallicity than the thin disk but at higher metallicity than the halo. The lower bound of the thick disk is still uncertain, as many observational studies have found only a few thick disk candidate. stars or clusters that are more metal poor than [Fe/H]=--1. Beers et al. (2002) have so far proposed the largest sample of metal poor thick disk. candidates, presenting 9 stars at [Fe/H]=-1.2 or lower and 46 more stars at [Fe/H]=-1 or lower, all of which are believed to belong to the thick disk. Beers et al. (2002) present possible thick disk stars as metal poor as [Fe/H]~ -2.5, roughly 1 dex lower than is suggested by current Galactic formation models (Brook et al., 2005). This study is a high-resolution spectroscopic follow-up of 29 of the stars Beers et al. (2002) and Chiba & Beers (2000) identify as potiential metal poor members of the thick disk and an additional 40 stars from the cannonical thick disk, halo, and thin disk. None of the very metal-poor stars identified by Beers et al. (2002) can be confirmed as members of the thick disk and many are not metal poor at all. Only two stars more metal poor than [Fe/H]=--1.2 retain their thick disk membership. These two stars exhibit some of the. chemical characteristics of the cannonical thick disk: high alpha-element abundances and a relatively low s-/r- process element ratio. Also of interest are. six stars with thin disk kinematic

  18. Modeling Mid-Ultraviolet Spectra. I. Temperatures of Metal-poor Stars

    NASA Astrophysics Data System (ADS)

    Peterson, Ruth C.; Dorman, Ben; Rood, Robert T.

    2001-09-01

    Determining the properties of remote globular clusters and elliptical galaxies using evolutionary population synthesis requires a library of reliable model stellar fluxes. Empirical libraries are limited to spectra of stars in the solar neighborhood, with nearly solar abundances and abundance ratios. We report here a first step toward providing a flux library that includes nonsolar abundances, based on calculations from first principles that are calibrated empirically. Because the mid-ultraviolet spectrum of an old stellar system is dominated by the contribution from its main-sequence turnoff stars, we have started by modeling these. We have calculated mid-ultraviolet spectra for the Sun and nine nearby, near-main-sequence stars spanning metallicities from less than 1/100 solar to greater than solar, encompassing a range of light-element-abundance enhancements. We first determined temperatures of eight of the stars by analyzing optical echelle spectra together with the mid-ultraviolet. Both could be matched at the same time only when models with no convective overshoot were adopted and only when an approximate chromosphere was incorporated near the surface of relatively metal-rich models. Extensive modifications to mid-UV line parameters were also required, notably the manual assignment of approximate identifications for mid-UV lines missing from laboratory line lists. Without recourse to additional missing opacity, these measures suffice to reproduce in detail almost the entire mid-UV spectrum of solar-temperature stars up to 1/10 solar metallicity and the region from 2900 to 3100 Å throughout the entire metallicity range. Ramifications for abundance determinations in individual metal-poor stars and for age-metallicity determinations of old stellar systems are briefly discussed, with emphasis on the predictive power of the calculations. Based on observations obtained with the Hubble Space Telescope of the Space Telescope Science Institute, under contract with the

  19. High-resolution abundance analysis of very metal-poor r-I stars

    NASA Astrophysics Data System (ADS)

    Siqueira Mello, C.; Hill, V.; Barbuy, B.; Spite, M.; Spite, F.; Beers, T. C.; Caffau, E.; Bonifacio, P.; Cayrel, R.; François, P.; Schatz, H.; Wanajo, S.

    2014-05-01

    Context. Moderately r-process-enriched stars (r-I; +0.3 ≤ [Eu/Fe] ≤ +1.0) are at least four times as common as those that are greatly enriched in r-process elements (r-II; [Eu/Fe] > +1.0), and the abundances in their atmospheres are important tools for obtaining a better understanding of the nucleosynthesis processes responsible for the origin of the elements beyond the iron peak. Aims: The main aim of this work is to derive abundances for a sample of seven metal-poor stars with -3.4 ≤ [Fe/H] ≤ -2.4 classified as r-I stars, to understand the role of these stars for constraining the astrophysical nucleosynthesis event(s) that is (are) responsible for the production of the r-process, and to investigate whether they differ, in any significant way, from the r-II stars. Methods: We carried out a detailed abundance analysis based on high-resolution spectra obtained with the VLT/UVES spectrograph, using spectra in the wavelength ranges 3400-4500 Å, 6800-8200 Å, and 8700-10 000 Å, with resolving power R ~ 40 000 (blue arm) and R ~ 55 000 (red arm). The OSMARCS LTE 1D model atmosphere grid was employed, along with the spectrum synthesis code Turbospectrum. Results: We have derived abundances of the light elements Li, C, and N, the α-elements Mg, Si, S, Ca, and Ti, the odd-Z elements Al, K, and Sc, the iron-peak elements V, Cr, Mn, Fe, Co, and Ni, and the trans-iron elements from the first peak (Sr, Y, Zr, Mo, Ru, and Pd), the second peak (Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb), the third peak (Os and Ir, as upper limits), and the actinides (Th) regions. The results are compared with values for these elements for r-II and "normal" very and extremely metal-poor stars reported in the literature, ages based on radioactive chronometry are explored using different models, and a number of conclusions about the r-process and the r-I stars are presented. Hydrodynamical models were used for some elements, and general behaviors for the 3D corrections

  20. Erbium And The r-Process In The Sun And Metal-poor Stars

    NASA Astrophysics Data System (ADS)

    Lawler, James; Sneden, C.; Cowan, J. J.

    2007-12-01

    Recent laboratory radiative lifetimes accurate to 5% for 8 even-parity and 72 odd-parity levels of Er II (Stockett et al. 2007, J. Phys. B, in press) were combined with emission branching fractions from Fourier transform spectra to determine accurate absolute transition probabilities for 418 lines of Er II. The lines span the UV to IR wavelength range from 289.2 to 1984.1 nm. Our gf-values have been applied to refine the solar photospheric erbium abundance and to determine erbium abundances in 4 metal-poor giant stars with enhanced r-process abundances (those with [Fe/H] < -2, [Eu/Fe] > +0.5). For the Sun we derive log ɛ(Er) = 0.96 ± 0.02 (σ = 0.06 from 8 lines). This value is in excellent agreement with Lodders' (2003, ApJ, 591, 1220) recommended meteoritic abundance: log ɛ(Er) = 0.95 ± 0.03. Combining the new photospheric Er abundance with our earlier study of Eu (log ɛ(Er) = 0.52 ± 0.01; Lawler et al. 2001, ApJ, 563, 1075) yields log ɛ(Er/Eu) = 0.43 for the Sun. The origin of both Er and Eu are attributed predominantly to production in rapid neutron-capture synthesis (the r-process) in solar-system material, 83% and 97% respectively (Simmerer et al. 2004, ApJ, 617, 1091). We therefore applied the new transition data to the spectra of very metal-poor, r-process rich stars CS 22892-052, BD+17 3248, HD 115444, and HD 221170. Between 14 and 21 Er II features were usable in our abundance analyses in these stars. We derived = 0.43 for the four stars, obviously in excellent agreements with the solar value. This work has been supported by the National Science Foundations through grants AST-0506324 to JEL, AST-0607708 to CS, and AST-0707447 to JJC.

  1. New Hubble Space Telescope Observations of Heavy Elements in Four Metal-Poor Stars

    NASA Astrophysics Data System (ADS)

    Roederer, Ian U.; Lawler, James E.; Sobeck, Jennifer S.; Beers, Timothy C.; Cowan, John J.; Frebel, Anna; Ivans, Inese I.; Schatz, Hendrik; Sneden, Christopher; Thompson, Ian B.

    2012-12-01

    Elements heavier than the iron group are found in nearly all halo stars. A substantial number of these elements, key to understanding neutron-capture nucleosynthesis mechanisms, can only be detected in the near-ultraviolet. We report the results of an observing campaign using the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope to study the detailed heavy-element abundance patterns in four metal-poor stars. We derive abundances or upper limits from 27 absorption lines of 15 elements produced by neutron-capture reactions, including seven elements (germanium, cadmium, tellurium, lutetium, osmium, platinum, and gold) that can only be detected in the near-ultraviolet. We also examine 202 heavy-element absorption lines in ground-based optical spectra obtained with the Magellan Inamori Kyocera Echelle Spectrograph on the Magellan-Clay Telescope at Las Campanas Observatory and the High Resolution Echelle Spectrometer on the Keck I Telescope on Mauna Kea. We have detected up to 34 elements heavier than zinc. The bulk of the heavy elements in these four stars are produced by r-process nucleosynthesis. These observations affirm earlier results suggesting that the tellurium found in metal-poor halo stars with moderate amounts of r-process material scales with the rare earth and third r-process peak elements. Cadmium often follows the abundances of the neighboring elements palladium and silver. We identify several sources of systematic uncertainty that must be considered when comparing these abundances with theoretical predictions. We also present new isotope shift and hyperfine structure component patterns for Lu II and Pb I lines of astrophysical interest. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs 8111 and

  2. A high-resolution spectral analysis of three carbon-enhanced metal-poor stars

    NASA Astrophysics Data System (ADS)

    Goswami, Aruna; Aoki, Wako; Beers, Timothy C.; Christlieb, Norbert; Norris, John E.; Ryan, Sean G.; Tsangarides, Stelios

    2006-10-01

    We present results of an analysis of high-resolution spectra (R ~ 50000), obtained with the Subaru Telescope High Dispersion Spectrograph, of two carbon-enhanced metal-poor (CEMP) stars selected from the Hamburg/European Southern Observatory prism survey, HE 1305+0007 and HE 1152-0355, and of the classical CH star HD 5223. All these stars have relatively low effective temperatures (4000-4750K) and high carbon abundances, which result in the presence of very strong molecular carbon bands in their spectra. The stellar atmospheric parameters for these stars indicate that they all have surface gravities consistent with a present location on the red giant branch, and metallicities of [Fe/H] = -2.0 (HE 1305+0007, HD 5223) and [Fe/H] = -1.3 (HE 1152-0355). In addition to their large enhancements of carbon ([C/Fe] = +1.8, +1.6 and +0.6, respectively), all three stars exhibit strong enhancements of the s-process elements relative to iron. HE 1305+0007 exhibits a large enhancement of the third-peak s-process element, lead, with [Pb/Fe] = +2.37, as well as a high abundance of the r-process element europium, [Eu/Fe] = +1.97. The second-peak s-process elements, Ba, La, Ce, Nd and Sm, are found to be more enhanced than the first-peak s-process elements Zr, Sr and Y. Thus, HE 1305+0007 joins the growing class of the so-called `Lead stars', and also the class of objects that exhibit the presence of both r- and s-process elements, the CEMP-r/s stars. The large enhancements of neutron-capture (n-capture) elements exhibited by HE 1152-0355 and HD 5223 are more consistent with the abundance patterns generally noticed in CH stars, essentially arising from pure s-process nucleosynthesis. The elemental abundance distributions observed in these stars are discussed in light of existing theories of CH star formation, as well as the suggested formation scenarios of the CEMP-r/s group. Based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory

  3. New detections of arsenic, selenium, and other heavy elements in two metal-poor stars

    SciTech Connect

    Roederer, Ian U.; Schatz, Hendrik; Beers, Timothy C.; Lawler, James E.; Cowan, John J.; Frebel, Anna; Ivans, Inese I.; Sneden, Christopher; Sobeck, Jennifer S.

    2014-08-10

    We use the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope to obtain new high-quality spectra covering the 1900 ≤λ ≤ 2360 Å wavelength range for two metal-poor stars, HD 108317 and HD 128279. We derive abundances of Cu II, Zn II, As I, Se I, Mo II, and Cd II, which have not been detected previously in either star. Abundances derived for Ge I, Te I, Os II, and Pt I confirm those derived from lines at longer wavelengths. We also derive upper limits from the non-detection of W II, Hg II, Pb II, and Bi I. The mean [As/Fe] ratio derived from these two stars and five others in the literature is unchanged over the metallicity range –2.8 < [Fe/H] <–0.6, ([As/Fe]) = +0.28 ± 0.14 (σ = 0.36 dex). The mean [Se/Fe] ratio derived from these two stars and six others in the literature is also constant, ([Se/Fe]) = +0.16 ± 0.09 (σ = 0.26 dex). The As and Se abundances are enhanced relative to a simple extrapolation of the iron-peak abundances to higher masses, suggesting that this mass region (75 ≤A ≤ 82) may be the point at which a different nucleosynthetic mechanism begins to dominate the quasi-equilibrium α-rich freezeout of the iron peak. ([Cu II/Cu I]) = +0.56 ± 0.23 in HD 108317 and HD 128279, and we infer that lines of Cu I may not be formed in local thermodynamic equilibrium in these stars. The [Zn/Fe], [Mo/Fe], [Cd/Fe], and [Os/Fe] ratios are also derived from neutral and ionized species, and each ratio pair agrees within the mutual uncertainties, which range from 0.15 to 0.52 dex.

  4. [O/Fe] ESTIMATES FOR CARBON-ENHANCED METAL-POOR STARS FROM NEAR-INFRARED SPECTROSCOPY

    SciTech Connect

    Kennedy, Catherine R.; Beers, Timothy C.; Lee, Young Sun; Sivarani, Thirupathi; Placco, Vinicius M.; Rossi, Silvia; Christlieb, Norbert; Herwig, Falk; Plez, Bertrand E-mail: beers@pa.msu.edu E-mail: sivarani@iiap.res.in E-mail: rossi@astro.iag.usp.br E-mail: fherwig@uvic.ca

    2011-03-15

    We report on oxygen abundances determined from medium-resolution near-infrared spectroscopy for a sample of 57 carbon-enhanced metal-poor (CEMP) stars selected from the Hamburg/ESO Survey. The majority of our program stars exhibit oxygen-to-iron ratios in the range +0.5< [O/Fe]<+2.0. The [O/Fe] values for this sample are statistically compared to available high-resolution estimates for known CEMP stars as well as to high-resolution estimates for a set of carbon-normal metal-poor stars. Carbon, nitrogen, and oxygen abundance patterns for a sub-sample of these stars are compared to yield predictions for very metal-poor asymptotic giant branch (AGB) abundances in the recent literature. We find that the majority of our sample exhibit patterns that are consistent with previously studied CEMP stars having s-process-element enhancements and thus have very likely been polluted by carbon- and oxygen-enhanced material transferred from a metal-poor AGB companion.

  5. High-Resolution Spectroscopic Study of Extremely Metal-Poor Star Candidates from the SkyMapper Survey

    NASA Astrophysics Data System (ADS)

    Jacobson, Heather R.; Keller, Stefan; Frebel, Anna; Casey, Andrew R.; Asplund, Martin; Bessell, Michael S.; Da Costa, Gary S.; Lind, Karin; Marino, Anna F.; Norris, John E.; Peña, José M.; Schmidt, Brian P.; Tisserand, Patrick; Walsh, Jennifer M.; Yong, David; Yu, Qinsi

    2015-07-01

    The SkyMapper Southern Sky Survey is carrying out a search for the most metal-poor stars in the Galaxy. It identifies candidates by way of its unique filter set which allows for estimation of stellar atmospheric parameters. The set includes a narrow filter centered on the Ca ii K 3933 Å line, enabling a robust estimate of stellar metallicity. Promising candidates are then confirmed with spectroscopy. We present the analysis of Magellan Inamori Kyocera Echelle high-resolution spectroscopy of 122 metal-poor stars found by SkyMapper in the first two years of commissioning observations. Forty-one stars have [{Fe}/{{H}}]≤slant -3.0. Nine have [{Fe}/{{H}}]≤slant -3.5, with three at [{Fe}/{{H}}]∼ -4. A 1D LTE abundance analysis of the elements Li, C, Na, Mg, Al, Si, Ca, Sc, Ti, Cr, Mn, Co, Ni, Zn, Sr, Ba, and Eu shows these stars have [X/Fe] ratios typical of other halo stars. One star with low [X/Fe] values appears to be “Fe-enhanced,” while another star has an extremely large [Sr/Ba] ratio: \\gt 2. Only one other star is known to have a comparable value. Seven stars are “CEMP-no” stars ([{{C}}/{Fe}]\\gt 0.7, [{Ba}/{Fe}]\\lt 0). 21 stars exhibit mild r-process element enhancements (0.3≤slant [{Eu}/{Fe}]\\lt 1.0), while four stars have [{Eu}/{Fe}]≥slant 1.0. These results demonstrate the ability to identify extremely metal-poor stars from SkyMapper photometry, pointing to increased sample sizes and a better characterization of the metal-poor tail of the halo metallicity distribution function in the future. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

  6. METAL-POOR STARS OBSERVED WITH THE MAGELLAN TELESCOPE. I. CONSTRAINTS ON PROGENITOR MASS AND METALLICITY OF AGB STARS UNDERGOING s-PROCESS NUCLEOSYNTHESIS

    SciTech Connect

    Placco, Vinicius M.; Rossi, Silvia; Frebel, Anna; Beers, Timothy C.; Karakas, Amanda I.; Kennedy, Catherine R.; Christlieb, Norbert; Stancliffe, Richard J.

    2013-06-20

    We present a comprehensive abundance analysis of two newly discovered carbon-enhanced metal-poor (CEMP) stars. HE 2138-3336 is a s-process-rich star with [Fe/H] = -2.79, and has the highest [Pb/Fe] abundance ratio measured thus far, if non-local thermodynamic equilibrium corrections are included ([Pb/Fe] = +3.84). HE 2258-6358, with [Fe/H] = -2.67, exhibits enrichments in both s- and r-process elements. These stars were selected from a sample of candidate metal-poor stars from the Hamburg/ESO objective-prism survey, and followed up with medium-resolution (R {approx} 2000) spectroscopy with GEMINI/GMOS. We report here on derived abundances (or limits) for a total of 34 elements in each star, based on high-resolution (R {approx} 30, 000) spectroscopy obtained with Magellan-Clay/MIKE. Our results are compared to predictions from new theoretical asymptotic giant branch (AGB) nucleosynthesis models of 1.3 M{sub Sun} with [Fe/H] = -2.5 and -2.8, as well as to a set of AGB models of 1.0 to 6.0 M{sub Sun} at [Fe/H] = -2.3. The agreement with the model predictions suggests that the neutron-capture material in HE 2138-3336 originated from mass transfer from a binary companion star that previously went through the AGB phase, whereas for HE 2258-6358, an additional process has to be taken into account to explain its abundance pattern. We find that a narrow range of progenitor masses (1.0 {<=} M(M{sub Sun }) {<=} 1.3) and metallicities (-2.8 {<=} [Fe/H] {<=}-2.5) yield the best agreement with our observed elemental abundance patterns.

  7. Exploring the origin of lithium, carbon, strontium, and barium with four new ultra metal-poor stars

    SciTech Connect

    Hansen, T.; Hansen, C. J.; Christlieb, N. E-mail: cjhansen@lsw.uni-heidelberg.de; and others

    2014-06-01

    We present an elemental abundance analysis for four newly discovered ultra metal-poor stars from the Hamburg/ESO survey, with [Fe/H] ≤ –4. Based on high-resolution, high signal-to-noise spectra, we derive abundances for 17 elements in the range from Li to Ba. Three of the four stars exhibit moderate to large overabundances of carbon, but have no enhancements in their neutron-capture elements. The most metal-poor star in the sample, HE 0233–0343 ([Fe/H] = –4.68), is a subgiant with a carbon enhancement of [C/Fe] = +3.5, slightly above the carbon-enhancement plateau suggested by Spite et al. No carbon is detected in the spectrum of the fourth star, but the quality of its spectrum only allows for the determination of an upper limit on the carbon abundance ratio of [C/Fe] < +1.7. We detect lithium in the spectra of two of the carbon-enhanced stars, including HE 0233–0343. Both stars with Li detections are Li-depleted, with respect to the Li plateau for metal-poor dwarfs found by Spite and Spite. This suggests that whatever site(s) produced C either do not completely destroy lithium, or that Li has been astrated by early-generation stars and mixed with primordial Li in the gas that formed the stars observed at present. The derived abundances for the α elements and iron-peak elements of the four stars are similar to those found in previous large samples of extremely and ultra metal-poor stars. Finally, a large spread is found in the abundances of Sr and Ba for these stars, possibly influenced by enrichment from fast rotating stars in the early universe.

  8. A search for stars of very low metal abundance. VI. Detailed abundances of 313 metal-poor stars

    SciTech Connect

    Roederer, Ian U.; Preston, George W.; Thompson, Ian B.; Shectman, Stephen A.; Burley, Gregory S.; Kelson, Daniel D.; Sneden, Christopher

    2014-06-01

    We present radial velocities, equivalent widths, model atmosphere parameters, and abundances or upper limits for 53 species of 48 elements derived from high resolution optical spectroscopy of 313 metal-poor stars. A majority of these stars were selected from the metal-poor candidates of the HK Survey of Beers, Preston, and Shectman. We derive detailed abundances for 61% of these stars for the first time. Spectra were obtained during a 10 yr observing campaign using the Magellan Inamori Kyocera Echelle spectrograph on the Magellan Telescopes at Las Campanas Observatory, the Robert G. Tull Coudé Spectrograph on the Harlan J. Smith Telescope at McDonald Observatory, and the High Resolution Spectrograph on the Hobby-Eberly Telescope at McDonald Observatory. We perform a standard LTE abundance analysis using MARCS model atmospheres, and we apply line-by-line statistical corrections to minimize systematic abundance differences arising when different sets of lines are available for analysis. We identify several abundance correlations with effective temperature. A comparison with previous abundance analyses reveals significant differences in stellar parameters, which we investigate in detail. Our metallicities are, on average, lower by ≈0.25 dex for red giants and ≈0.04 dex for subgiants. Our sample contains 19 stars with [Fe/H] ≤–3.5, 84 stars with [Fe/H] ≤–3.0, and 210 stars with [Fe/H] ≤–2.5. Detailed abundances are presented here or elsewhere for 91% of the 209 stars with [Fe/H] ≤–2.5 as estimated from medium resolution spectroscopy by Beers, Preston, and Shectman. We will discuss the interpretation of these abundances in subsequent papers.

  9. Footprints of the weak s-process in the carbon-enhanced metal-poor star ET0097

    NASA Astrophysics Data System (ADS)

    Yang, Guochao; Li, Hongjie; Liu, Nian; Cui, Wenyuan; Liang, Yanchun; Zhang, Bo

    2016-09-01

    Historically, the weak s-process contribution to metal-poor stars is thought to be extremely small, due to the effect of the secondary-like nature of the neutron source 22Ne(α , n)25Mg in massive stars, which means that metal-poor "weak s-process stars" could not be found. ET0097 is the first observed carbon-enhanced metal-poor (CEMP) star in the Sculptor dwarf spheroidal galaxy. Because C is enriched and the elements heavier than Ba are not overabundant, ET0097 can be classified as a CEMP-no star. However, this star shows overabundances of lighter n-capture elements (i.e., Sr, Y and Zr). In this work, having adopted the abundance decomposition approach, we investigate the astrophysical origins of the elements in ET0097. We find that the light elements and iron-peak elements (from O to Zn) of the star mainly originate from the primary process of massive stars and the heavier n-capture elements (heavier than Ba) mainly come from the main r-process. However, the lighter n-capture elements such as Sr, Y and Zr should mainly come from the primary weak s-process. The contributed fractions of the primary weak s-process to the Sr, Y and Zr abundances of ET0097 are about 82 %, 84 % and 58 % respectively, suggesting that the CEMP star ET0097 should have the footprints of the weak s-process. The derived result should be a significant evidence that the weak s-process elements can be produced in metal-poor massive stars.

  10. New Detections of Arsenic, Selenium, and Other Heavy Elements in Two Metal-poor Stars

    NASA Astrophysics Data System (ADS)

    Roederer, Ian U.; Schatz, Hendrik; Lawler, James E.; Beers, Timothy C.; Cowan, John J.; Frebel, Anna; Ivans, Inese I.; Sneden, Christopher; Sobeck, Jennifer S.

    2014-08-01

    We use the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope to obtain new high-quality spectra covering the 1900 <=λ <= 2360 Å wavelength range for two metal-poor stars, HD 108317 and HD 128279. We derive abundances of Cu II, Zn II, As I, Se I, Mo II, and Cd II, which have not been detected previously in either star. Abundances derived for Ge I, Te I, Os II, and Pt I confirm those derived from lines at longer wavelengths. We also derive upper limits from the non-detection of W II, Hg II, Pb II, and Bi I. The mean [As/Fe] ratio derived from these two stars and five others in the literature is unchanged over the metallicity range -2.8 < [Fe/H] <-0.6, lang[As/Fe]rang = +0.28 ± 0.14 (σ = 0.36 dex). The mean [Se/Fe] ratio derived from these two stars and six others in the literature is also constant, lang[Se/Fe]rang = +0.16 ± 0.09 (σ = 0.26 dex). The As and Se abundances are enhanced relative to a simple extrapolation of the iron-peak abundances to higher masses, suggesting that this mass region (75 <=A <= 82) may be the point at which a different nucleosynthetic mechanism begins to dominate the quasi-equilibrium α-rich freezeout of the iron peak. lang[Cu II/Cu I]rang = +0.56 ± 0.23 in HD 108317 and HD 128279, and we infer that lines of Cu I may not be formed in local thermodynamic equilibrium in these stars. The [Zn/Fe], [Mo/Fe], [Cd/Fe], and [Os/Fe] ratios are also derived from neutral and ionized species, and each ratio pair agrees within the mutual uncertainties, which range from 0.15 to 0.52 dex. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs GO-12268 and GO-12976.

  11. EXAMINATION OF THE MASS-DEPENDENT Li DEPLETION HYPOTHESIS BY THE Li ABUNDANCES OF THE VERY METAL-POOR DOUBLE-LINED SPECTROSCOPIC BINARY G166-45

    SciTech Connect

    Aoki, Wako; Ito, Hiroko; Tajitsu, Akito

    2012-05-20

    The Li abundances of the two components of the very metal-poor ([Fe/H] -2.5) double-lined spectroscopic binary G166-45 (BD+26 Degree-Sign 2606) are determined separately based on high-resolution spectra obtained with the Subaru Telescope High Dispersion Spectrograph and its image slicer. From the photometric colors and the mass ratio, the effective temperatures of the primary and secondary components are estimated to be 6350 {+-} 100 K and 5830 {+-} 170 K, respectively. The Li abundance of the primary (A(Li) = 2.23) agrees well with the Spite plateau value, while that of the secondary is slightly lower (A(Li) = 2.11). Such a discrepancy of the Li abundances between the two components is previously found in the extremely metal-poor, double-lined spectroscopic binary CS 22876-032; however, the discrepancy in G166-45 is much smaller. The results agree with the trends found for Li abundance as a function of effective temperature (and of stellar mass) of main-sequence stars with -3.0 < [Fe/H] < -2.0, suggesting that the depletion of Li at T{sub eff} {approx} 5800 K is not particularly large in this metallicity range. The significant Li depletion found in CS 22876-032B is a phenomenon only found in the lowest metallicity range ([Fe/H] < -3).

  12. Deep SDSS optical spectroscopy of distant halo stars. III. Chemical analysis of extremely metal-poor stars

    NASA Astrophysics Data System (ADS)

    Fernández-Alvar, E.; Allende Prieto, C.; Beers, T. C.; Lee, Y. S.; Masseron, T.; Schneider, D. P.

    2016-09-01

    Aims: We present the results of an analysis of 107 extremely metal-poor (EMP) stars with metallicities lower than [Fe/H] =- 3.0, identified in medium-resolution spectra in the Sloan Digital Sky Survey (SDSS). Our analysis provides estimates of the stellar effective temperatures and surface gravities, as well as iron, calcium, and magnesium abundances. Methods: We followed the same method as in previous papers of this series. The method is based on comparisons of the observed spectra with synthetic spectra. The abundances of Fe, Ca, and Mg were determined by fitting spectral regions that are dominated by lines of each element. In addition, we present a technique to determine upper limits for elements whose features are not detected in a given spectrum. We also analyzed our sample with the SEGUE stellar parameter pipeline to obtain additional determinations of the atmospheric parameters and iron and alpha-element abundances, which we thend compare with ours. In addition, we used these parameters to infer [C/Fe] ratios. Results: Ca is typically the only element in these spectra with a moderate to low signal-to-noise ratio and medium resolution in this metallicity regime with lines that are sufficiently strong to reliably measure its abundance. Fe and Mg exhibit weaker features that in most cases only provide upper limits. We measured [Ca/Fe] and [Mg/Fe] for EMP stars in the SDSS spectra and conclude that most of the stars exhibit the typical enhancement level for α-elements, ~+0.4, although some stars for which only [Fe/H] upper limits could be estimated indicate higher [α/Fe] ratios. We also find that 26% of the stars in our sample can be classified as carbon-enhanced metal-poor (CEMP) stars and that the frequency of CEMP stars also increases with decreasing metallicity, as has been reported for previous samples. We identify a rare, bright (g = 11.90) EMP star, SDSS J134144.61+474128.6, with [Fe/H] =- 3.27, [C/Fe] = + 0.95, and elevated magnesium ([Mg/Fe] =+ 0

  13. Abundance analysis of SDSS J134338.67+484426.6; an extremely metal-poor star from the MARVELS pre-survey

    NASA Astrophysics Data System (ADS)

    Susmitha Rani, A.; Sivarani, T.; Beers, T. C.; Fleming, S.; Mahadevan, S.; Ge, J.

    2016-05-01

    We present an elemental-abundance analysis of an extremely metal-poor (EMP; [Fe/H] <-3.0) star, SDSS J134338.67+484426.6, identified during the course of the Multi-object Apache Point Observatory Radial Velocity Exoplanet Large-area Survey spectroscopic pre-survey of some 20 000 stars to identify suitable candidates for exoplanet searches. This star, with an apparent magnitude V = 12.14, is the lowest metallicity star found in the pre-survey, and is one of only ˜20 known EMP stars that are this bright or brighter. Our high-resolution spectroscopic analysis shows that this star is a subgiant with [Fe/H] = -3.42, having `normal' carbon and no enhancement of neutron-capture abundances. Strontium is underabundant, [Sr/Fe] = -0.47, but the derived lower limit on [Sr/Ba] indicates that Sr is likely enhanced relative to Ba. This star belongs to the sparsely populated class of α-poor EMP stars that exhibit low ratios of [Mg/Fe], [Si/Fe], and [Ca/Fe] compared to typical halo stars at similar metallicity. The observed variations in radial velocity from several epochs of (low- and high-resolution) spectroscopic follow-up indicate that SDSS J134338.67+484426.6 is a possible long-period binary. We also discuss the abundance trends in EMP stars for r-process elements, and compare with other magnesium-poor stars.

  14. Fe-Group Elements in the Metal-Poor Star HD 84937: Abundances and their Implications

    NASA Astrophysics Data System (ADS)

    Sneden, Chris; Cowan, John J.; Kobayashi, Chiaki; Pignatari, Marco; Lawler, James E.; Den Hartog, Elizabeth; Wood, Michael P.

    2016-01-01

    We have derived accurate relative abundances of the Fe-group elements Sc through Zn in the very metal-poor main-sequence turnoff star HD 84937. For this study we analyzed high resolution, high signal-to-noise HST/STIS and VLT/UVES spectra over a total wavelength range 2300-7000 Å. We employed only recent or newly-applied reliable laboratory transition data for all species. Abundances from more than 600 lines of non-Fe species were combined with about 550 Fe lines in HD 84937 to yield abundance ratios of high precision. From parallel analyses of solar photospheric spectra we also derived new solar abundances of these elements. This in turn yielded internally-consistent relative HD 84937 abundances with respect to the Sun. For seven of the ten Fe-group elements the HD 84937 abundances were from both neutral and ionized transitions. In all of these cases the neutral and ionized species yield the same abundances within the measurement uncertainties. Therefore standard Saha ionization balance appears to hold in the HD 84937 atmosphere. We derived metallicity [Fe/H] = -2.32 with sample standard deviation of 0.06. Solid evidence is seen for departures from the solar abundance mix in HD 84937, for example [Co/Fe] = +0.14, [Cu/Fe] = -0.83, and <[Sc,Ti,V/Fe]> = +0.31. Combining our Sc, Ti, and V abundances for this star with those from large-sample spectroscopic surveys suggests that these elements are positively correlated in stars with [Fe/H] < -2. HD 84937 is unusually enriched in Sc, Ti, and V. Our analysis strongly suggests that different types of supernovae with a large scatter of explosion energies and asymmetries contributed to the creation of the Fe-group elements early in the Galaxy's history.This work has been supported in part by NASA grant NNX10AN93G (J.E.L.), by NSF grants AST-1211055 (J.E.L.), AST-1211585 (C.S.), PHY-1430152 (through JINA, J.J.C. and M.P.), EU MIRGCT-2006-046520 (M.P.), and by the ``Lendlet-2014'' Programme of the Hungarian Academy of

  15. A Search for Stars of Very Low Metal Abundance. VI. Detailed Abundances of 313 Metal-poor Stars

    NASA Astrophysics Data System (ADS)

    Roederer, Ian U.; Preston, George W.; Thompson, Ian B.; Shectman, Stephen A.; Sneden, Christopher; Burley, Gregory S.; Kelson, Daniel D.

    2014-06-01

    We present radial velocities, equivalent widths, model atmosphere parameters, and abundances or upper limits for 53 species of 48 elements derived from high resolution optical spectroscopy of 313 metal-poor stars. A majority of these stars were selected from the metal-poor candidates of the HK Survey of Beers, Preston, and Shectman. We derive detailed abundances for 61% of these stars for the first time. Spectra were obtained during a 10 yr observing campaign using the Magellan Inamori Kyocera Echelle spectrograph on the Magellan Telescopes at Las Campanas Observatory, the Robert G. Tull Coudé Spectrograph on the Harlan J. Smith Telescope at McDonald Observatory, and the High Resolution Spectrograph on the Hobby-Eberly Telescope at McDonald Observatory. We perform a standard LTE abundance analysis using MARCS model atmospheres, and we apply line-by-line statistical corrections to minimize systematic abundance differences arising when different sets of lines are available for analysis. We identify several abundance correlations with effective temperature. A comparison with previous abundance analyses reveals significant differences in stellar parameters, which we investigate in detail. Our metallicities are, on average, lower by ≈0.25 dex for red giants and ≈0.04 dex for subgiants. Our sample contains 19 stars with [Fe/H] <=-3.5, 84 stars with [Fe/H] <=-3.0, and 210 stars with [Fe/H] <=-2.5. Detailed abundances are presented here or elsewhere for 91% of the 209 stars with [Fe/H] <=-2.5 as estimated from medium resolution spectroscopy by Beers, Preston, and Shectman. We will discuss the interpretation of these abundances in subsequent papers. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile, and The McDonald Observatory of The University of Texas at Austin. The Hobby-Eberly Telescope is a joint project of the University of Texas at Austin, the Pennsylvania State University, Stanford University

  16. Spectroscopic Studies of Very Metal-poor Stars with the Subaru High Dispersion Spectrograph. III. Light Neutron-Capture Elements

    NASA Astrophysics Data System (ADS)

    Aoki, Wako; Honda, Satoshi; Beers, Timothy C.; Kajino, Toshitaka; Ando, Hiroyasu; Norris, John E.; Ryan, Sean G.; Izumiura, Hideyuki; Sadakane, Kozo; Takada-Hidai, Masahide

    2005-10-01

    Elemental abundance measurements have been obtained for a sample of 18 very metal-poor stars using spectra obtained with the Subaru Telescope High Dispersion Spectrograph. Seventeen stars, among which 16 are newly analyzed in the present work, were selected from candidate metal-poor stars identified in the HK survey of Beers and colleagues. The metallicity range covered by our sample is -3.1<~[Fe/H]<~-2.4. The abundances of carbon, α-elements, and iron-peak elements determined for these stars confirm the trends found by previous work. One exception is the large overabundance of Mg, Al, and Sc found in BS 16934-002, a giant with [Fe/H]=-2.8. Interestingly, this is the most metal-rich star (by about 1 dex in [Fe/H]) known with such large overabundances in these elements. Furthermore, BS 16934-002 does not share the large overabundances of carbon that are associated with the two other, otherwise similar, extremely metal-poor stars CS 22949-037 and CS 29498-043. By combining our new results with those of previous studies, we investigate the distribution of neutron-capture elements in very metal-poor stars, focusing on the production of the light neutron-capture elements (e.g., Sr, Y, and Zr). Large scatter is found in the abundance ratios between the light and heavy neutron-capture elements (e.g., Sr/Ba, Y/Eu) for stars with low abundances of heavy neutron-capture elements. Most of these stars have extremely low metallicity ([Fe/H]<~-3). By contrast, the observed scatter in these ratios is much smaller in stars with excesses of heavy neutron-capture elements and with higher metallicity. These results can be naturally explained by assuming that two processes independently enriched the neutron-capture elements in the early Galaxy. One process increases both light and heavy neutron-capture elements and affects stars with [Fe/H]>~-3, while the other process contributes only to the light neutron-capture elements and affects most stars with [Fe/H]>~-3.5. Interestingly, the

  17. HIGH-RESOLUTION SPECTROSCOPY OF EXTREMELY METAL-POOR STARS FROM SDSS/SEGUE. I. ATMOSPHERIC PARAMETERS AND CHEMICAL COMPOSITIONS

    SciTech Connect

    Aoki, Wako; Suda, Takuma; Beers, Timothy C.; Lee, Young Sun; Honda, Satoshi; Ito, Hiroko; Takada-Hidai, Masahide; Frebel, Anna; Fujimoto, Masayuki Y.; Carollo, Daniela; Sivarani, Thirupathi E-mail: takuma.suda@nao.ac.jp E-mail: lee@pa.msu.edu E-mail: hidai@apus.rh.u-tokai.ac.jp E-mail: fujimoto@astro1.sci.hokudai.ac.jp E-mail: sivarani@iiap.res.in

    2013-01-01

    Chemical compositions are determined based on high-resolution spectroscopy for 137 candidate extremely metal-poor (EMP) stars selected from the Sloan Digital Sky Survey (SDSS) and its first stellar extension, the Sloan Extension for Galactic Understanding and Exploration (SEGUE). High-resolution spectra with moderate signal-to-noise (S/N) ratios were obtained with the High Dispersion Spectrograph of the Subaru Telescope. Most of the sample (approximately 80%) are main-sequence turnoff stars, including dwarfs and subgiants. Four cool main-sequence stars, the most metal-deficient such stars known, are included in the remaining sample. Good agreement is found between effective temperatures estimated by the SEGUE stellar parameter pipeline, based on the SDSS/SEGUE medium-resolution spectra, and those estimated from the broadband (V - K){sub 0} and (g - r){sub 0} colors. Our abundance measurements reveal that 70 stars in our sample have [Fe/H] < -3, adding a significant number of EMP stars to the currently known sample. Our analyses determine the abundances of eight elements (C, Na, Mg, Ca, Ti, Cr, Sr, and Ba) in addition to Fe. The fraction of carbon-enhanced metal-poor stars ([C/Fe] > +0.7) among the 25 giants in our sample is as high as 36%, while only a lower limit on the fraction (9%) is estimated for turnoff stars. This paper is the first of a series of papers based on these observational results. The following papers in this series will discuss the higher-resolution and higher-S/N observations of a subset of this sample, the metallicity distribution function, binarity, and correlations between the chemical composition and kinematics of extremely metal-poor stars.

  18. Clear Evidence for the Presence of Second-generation Asymptotic Giant Branch Stars in Metal-poor Galactic Globular Clusters

    NASA Astrophysics Data System (ADS)

    García-Hernández, D. A.; Mészáros, Sz.; Monelli, M.; Cassisi, S.; Stetson, P. B.; Zamora, O.; Shetrone, M.; Lucatello, S.

    2015-12-01

    Galactic globular clusters (GCs) are known to host multiple stellar populations: a first generation (FG) with a chemical pattern typical of halo field stars and a second generation (SG) enriched in Na and Al and depleted in O and Mg. Both stellar generations are found at different evolutionary stages (e.g., the main-sequence turnoff, the subgiant branch, and the red giant branch (RGB)). The non detection of SG asymptotic giant branch (AGB) stars in several metal-poor ([Fe/H] < -1) GCs suggests that not all SG stars ascend the AGB phase, and that failed AGB stars may be very common in metal-poor GCs. This observation represents a serious problem for stellar evolution and GC formation/evolution theories. We report fourteen SG-AGB stars in four metal-poor GCs (M13, M5, M3, and M2) with different observational properties: horizontal branch (HB) morphology, metallicity, and age. By combining the H-band Al abundances obtained by the Apache Point Observatory Galactic Evolution Experiment survey with ground-based optical photometry, we identify SG Al-rich AGB stars in these four GCs and show that Al-rich RGB/AGB GC stars should be Na-rich. Our observations provide strong support for present, standard stellar models, i.e., without including a strong mass-loss efficiency, for low-mass HB stars. In fact, current empirical evidence is in agreement with the predicted distribution of FG and SG stars during the He-burning stages based on these standard stellar models.

  19. SEARCHES FOR METAL-POOR STARS FROM THE HAMBURG/ESO SURVEY USING THE CH G BAND

    SciTech Connect

    Placco, Vinicius M.; Rossi, Silvia; Kennedy, Catherine R.; Beers, Timothy C.; Lee, Young Sun; Christlieb, Norbert; Sivarani, Thirupathi; Reimers, Dieter; Wisotzki, Lutz

    2011-12-15

    We describe a new method to search for metal-poor candidates from the Hamburg/ESO objective-prism survey (HES) based on identifying stars with apparently strong CH G-band strengths for their colors. The hypothesis we exploit is that large overabundances of carbon are common among metal-poor stars, as has been found by numerous studies over the past two decades. The selection was made by considering two line indices in the 4300 A region, applied directly to the low-resolution prism spectra. This work also extends a previously published method by adding bright sources to the sample. The spectra of these stars suffer from saturation effects, compromising the index calculations and leading to an undersampling of the brighter candidates. A simple numerical procedure, based on available photometry, was developed to correct the line indices and overcome this limitation. Visual inspection and classification of the spectra from the HES plates yielded a list of 5288 new metal-poor (and by selection, carbon-rich) candidates, which are presently being used as targets for medium-resolution spectroscopic follow-up. Estimates of the stellar atmospheric parameters, as well as carbon abundances, are now available for 117 of the first candidates, based on follow-up medium-resolution spectra obtained with the SOAR 4.1 m and Gemini 8 m telescopes. We demonstrate that our new method improves the metal-poor star fractions found by our pilot study by up to a factor of three in the same magnitude range, as compared with our pilot study based on only one CH G-band index. Our selection scheme obtained roughly a 40% success rate for identification of stars with [Fe/H] <-1.0; the primary contaminant is late-type stars with near-solar abundances and, often, emission line cores that filled in the Ca II K line on the prism spectrum. Because the selection is based on carbon, we greatly increase the numbers of known carbon-enhanced metal-poor stars from the HES with intermediate metallicities -2

  20. Far-ultraviolet energy distributions of the metal-poor A stars HD 109995 and HD 161817

    NASA Technical Reports Server (NTRS)

    Boehm-Vitense, E.

    1981-01-01

    Low-resolution IUE spectra at wavelengths between 1300 and 3400 A of the metal-poor stars HD 109995 (A1p) and HD 161817 (A4p) have been compared with model-atmosphere energy distributions computed by Kurucz (1979). Good overall agreement is found. Effective temperatures, metal abundances, and angular diameters could be determined. Assuming an absolute visual magnitude of 0.7, the previously determined gravity log = 3 yields masses of 0.5 solar masses for both stars. It is found that the theoretical UBV colors calculated earlier agree reaonably well with the ones observed for these stars.

  1. Nine new metal-poor stars on the subgiant and red horizontal branches with high levels of r-process enhancement

    NASA Astrophysics Data System (ADS)

    Roederer, Ian U.; Cowan, John J.; Preston, George W.; Shectman, Stephen A.; Sneden, Christopher; Thompson, Ian B.

    2014-12-01

    We report the discovery of nine metal-poor stars with high levels of r-process enhancement (+0.81 ≤ [Eu/Fe] ≤ +1.13), including six subgiants and three stars on the red horizontal branch. We also analyse four previously known r-process-enhanced metal-poor red giants. From this sample of 13 stars, we draw the following conclusions. (1) High levels of r-process enhancement are found in a broad range of stellar evolutionary states, reaffirming that this phenomenon is not associated with a chemical peculiarity of red giant atmospheres. (2) Only 1 of 10 stars observed at multiple epochs shows radial-velocity variations, reaffirming that stars with high levels of r-process enhancement are not preferentially found among binaries. (3) Only 2 of the 13 stars are highly enhanced in C and N, indicating that there is no connection between high levels of r-process enhancement and high levels of C and N. (4) The dispersions in [Sr/Ba] and [Sr/Eu] are larger than the dispersions in [Ba/Eu] and [Yb/Eu], suggesting that the elements below the second r-process peak do not always scale with those in the rare Earth domain, even within the class of highly-r-process-enhanced stars. (5) The light-element (12 ≤ Z ≤ 30) abundances of highly-r-process-enhanced stars are indistinguishable from those with normal levels of r-process material at the limit of our data, 3.5 per cent (0.015 dex) on average. The nucleosynthetic sites responsible for the large r-process enhancements did not produce any detectable light-element abundance signatures distinct from normal core-collapse supernovae.

  2. The HARPS search for southern extra-solar planets. XL. Searching for Neptunes around metal-poor stars

    NASA Astrophysics Data System (ADS)

    Faria, J. P.; Santos, N. C.; Figueira, P.; Mortier, A.; Dumusque, X.; Boisse, I.; Lo Curto, G.; Lovis, C.; Mayor, M.; Melo, C.; Pepe, F.; Queloz, D.; Santerne, A.; Ségransan, D.; Sousa, S. G.; Sozzetti, A.; Udry, S.

    2016-05-01

    Context. As a probe of the metallicity of proto-planetary disks, stellar metallicity is an important ingredient for giant planet formation, most likely through its effect on the timescales in which rocky or icy planet cores can form. Giant planets have been found to be more frequent around metal-rich stars, in agreement with predictions based on the core-accretion theory. In the metal-poor regime, however, the frequency of planets, especially low-mass planets, and the way it depends on metallicity are still largely unknown. Aims: As part of a planet search programme focused on metal-poor stars, we study the targets from this survey that were observed with HARPS on more than 75 nights. The main goals are to assess the presence of low-mass planets and provide a first estimate of the frequency of Neptunes and super-Earths around metal-poor stars. Methods: We performed a systematic search for planetary companions, both by analysing the periodograms of the radial-velocities and by comparing, in a statistically meaningful way, models with an increasing number of Keplerians. Results: A first constraint on the frequency of planets in our metal-poor sample is calculated considering the previous detection (in our sample) of a Neptune-sized planet around HD 175607 and one candidate planet (with an orbital period of 68.42 d and minimum mass Mpsini = 11.14 ± 2.47 M⊕) for HD 87838, announced in the present study. This frequency is determined to be close to 13% and is compared with results for solar-metallicity stars. Based on observations collected at ESO facilities under programs 082.C-0212, 085.C-0063, 086.C-0284, and 190.C-0027 (with the HARPS spectrograph at the ESO 3.6-m telescope, La Silla-Paranal Observatory).

  3. NEW RARE EARTH ELEMENT ABUNDANCE DISTRIBUTIONS FOR THE SUN AND FIVE r-PROCESS-RICH VERY METAL-POOR STARS

    SciTech Connect

    Sneden, Christopher; Lawler, James E.; Den Hartog, Elizabeth A.; Cowan, John J.; Ivans, Inese I. E-mail: jelawler@wisc.edu E-mail: cowan@nhn.ou.edu

    2009-05-15

    We have derived new abundances of the rare earth elements Pr, Dy, Tm, Yb, and Lu for the solar photosphere and for five very metal-poor, neutron-capture r-process-rich giant stars. The photospheric values for all five elements are in good agreement with meteoritic abundances. For the low-metallicity sample, these abundances have been combined with new Ce abundances from a companion paper, and reconsideration of a few other elements in individual stars, to produce internally consistent Ba, rare earth, and Hf (56 {<=} Z {<=} 72) element distributions. These have been used in a critical comparison between stellar and solar r-process abundance mixes.

  4. Metallicity inhomogeneities in local star-forming galaxies as a sign of recent metal-poor gas accretion

    SciTech Connect

    Sánchez Almeida, J.; Morales-Luis, A. B.; Muñoz-Tuñón, C.; Méndez-Abreu, J.; Elmegreen, D. M.; Elmegreen, B. G. E-mail: abml@iac.es E-mail: elmegreen@vassar.edu E-mail: jma20@st-andrews.ac.uk

    2014-03-01

    We measure the oxygen metallicity of the ionized gas along the major axis of seven dwarf star-forming galaxies. Two of them, SDSSJ1647+21 and SDSSJ2238+14, show ≅0.5 dex metallicity decrements in inner regions with enhanced star formation activity. This behavior is similar to the metallicity drop observed in a number of local tadpole galaxies by Sánchez Almeida et al., and was interpreted as showing early stages of assembling in disk galaxies, with the star formation sustained by external metal-poor gas accretion. The agreement with tadpoles has several implications. (1) It proves that galaxies other than the local tadpoles present the same unusual metallicity pattern. (2) Our metallicity inhomogeneities were inferred using the direct method, thus discarding systematic errors usually attributed to other methods. (3) Taken together with the tadpole data, our findings suggest a threshold around one-tenth the solar value for the metallicity drops to show up. Although galaxies with clear metallicity drops are rare, the physical mechanism responsible for them may sustain a significant part of the star formation activity in the local universe. We argue that the star formation dependence of the mass-metallicity relationship, as well as other general properties followed by most local disk galaxies, is naturally interpreted as side effects of pristine gas infall. Alternatives to the metal-poor gas accretion are examined as well.

  5. CARBON-ENHANCED METAL-POOR STARS IN SDSS/SEGUE. I. CARBON ABUNDANCE ESTIMATION AND FREQUENCY OF CEMP STARS

    SciTech Connect

    Lee, Young Sun; Beers, Timothy C.; Placco, Vinicius M.; Masseron, Thomas; Plez, Bertrand; Rockosi, Constance M.; Yanny, Brian; Lucatello, Sara; Sivarani, Thirupathi; Carollo, Daniela

    2013-11-01

    We describe a method for the determination of stellar [C/Fe] abundance ratios using low-resolution (R = 2000) stellar spectra from the Sloan Digital Sky Survey (SDSS) and its Galactic sub-survey, the Sloan Extension for Galactic Understanding and Exploration (SEGUE). By means of a star-by-star comparison with a set of SDSS/SEGUE spectra with available estimates of [C/Fe] based on published high-resolution analyses, we demonstrate that we can measure [C/Fe] from SDSS/SEGUE spectra with S/N ≥ 15 Å{sup –1} to a precision better than 0.35 dex for stars with atmospheric parameters in the range T {sub eff} = [4400, 6700] K, log g = [1.0, 5.0], [Fe/H] = [–4.0, +0.5], and [C/Fe] = [–0.25, +3.5]. Using the measured carbon-to-iron abundance ratios obtained by this technique, we derive the frequency of carbon-enhanced stars ([C/Fe] ≥ +0.7) as a function of [Fe/H], for both the SDSS/SEGUE stars and other samples from the literature. We find that the differential frequency slowly rises from almost zero to about 14% at [Fe/H] ∼ –2.4, followed by a sudden increase, by about a factor of three, to 39% from [Fe/H] ∼ –2.4 to [Fe/H] ∼ –3.7. Although the number of stars known with [Fe/H] < –4.0 remains small, the frequency of carbon-enhanced metal-poor (CEMP) stars below this value is around 75%. We also examine how the cumulative frequency of CEMP stars varies across different luminosity classes. The giant sample exhibits a cumulative CEMP frequency of 32% for [Fe/H] ≤ –2.5, 31% for [Fe/H] ≤ –3.0, and 33% for [Fe/H] ≤ –3.5; a roughly constant value. For the main-sequence turnoff stars, we obtain a lower cumulative CEMP frequency, around 10% for [Fe/H] ≤ –2.5, presumably due to the difficulty of identifying CEMP stars among warmer turnoff stars with weak CH G-bands. The dwarf population displays a large change in the cumulative frequency for CEMP stars below [Fe/H] = –2.5, jumping from 15% for [Fe/H] ≤ –2.5 to about 75% for [Fe/H] ≤ –3

  6. Carbon-enhanced Metal-poor Stars in SDSS/SEGUE. I. Carbon Abundance Estimation and Frequency of CEMP Stars

    NASA Astrophysics Data System (ADS)

    Lee, Young Sun; Beers, Timothy C.; Masseron, Thomas; Plez, Bertrand; Rockosi, Constance M.; Sobeck, Jennifer; Yanny, Brian; Lucatello, Sara; Sivarani, Thirupathi; Placco, Vinicius M.; Carollo, Daniela

    2013-11-01

    We describe a method for the determination of stellar [C/Fe] abundance ratios using low-resolution (R = 2000) stellar spectra from the Sloan Digital Sky Survey (SDSS) and its Galactic sub-survey, the Sloan Extension for Galactic Understanding and Exploration (SEGUE). By means of a star-by-star comparison with a set of SDSS/SEGUE spectra with available estimates of [C/Fe] based on published high-resolution analyses, we demonstrate that we can measure [C/Fe] from SDSS/SEGUE spectra with S/N >= 15 Å-1 to a precision better than 0.35 dex for stars with atmospheric parameters in the range T eff = [4400, 6700] K, log g = [1.0, 5.0], [Fe/H] = [-4.0, +0.5], and [C/Fe] = [-0.25, +3.5]. Using the measured carbon-to-iron abundance ratios obtained by this technique, we derive the frequency of carbon-enhanced stars ([C/Fe] >= +0.7) as a function of [Fe/H], for both the SDSS/SEGUE stars and other samples from the literature. We find that the differential frequency slowly rises from almost zero to about 14% at [Fe/H] ~ -2.4, followed by a sudden increase, by about a factor of three, to 39% from [Fe/H] ~ -2.4 to [Fe/H] ~ -3.7. Although the number of stars known with [Fe/H] < -4.0 remains small, the frequency of carbon-enhanced metal-poor (CEMP) stars below this value is around 75%. We also examine how the cumulative frequency of CEMP stars varies across different luminosity classes. The giant sample exhibits a cumulative CEMP frequency of 32% for [Fe/H] <= -2.5, 31% for [Fe/H] <= -3.0, and 33% for [Fe/H] <= -3.5 a roughly constant value. For the main-sequence turnoff stars, we obtain a lower cumulative CEMP frequency, around 10% for [Fe/H] <= -2.5, presumably due to the difficulty of identifying CEMP stars among warmer turnoff stars with weak CH G-bands. The dwarf population displays a large change in the cumulative frequency for CEMP stars below [Fe/H] = -2.5, jumping from 15% for [Fe/H] <= -2.5 to about 75% for [Fe/H] <= -3.0. When we impose a restriction with respect to

  7. Stellar Dust Production in Chemically Primitive Environments: Infrared Lightcurves and Mass Loss in Extremely Metal-poor AGB Stars

    NASA Astrophysics Data System (ADS)

    Sonneborn, George

    In their final stage of evolution, asymptotic giant branch (AGB) stars inject a substantial amount of dust into the surrounding interstellar medium, potentially dominating the total stellar dust budgets of their host galaxies. However, stellar models conflict over whether metal-poor AGB stars can condense enough dust to drive a strong stellar wind, so it is unclear what role AGB stars play in the early Universe compared to other dust sources, e.g., in high-redshift quasars that show evidence for massive dust reservoirs. Empirically, AGB stars that are massive enough to contribute in the early Universe are only well studied in the Milky Way and the nearby Magellanic Clouds; all three environments are relatively metal-rich and thus unlikely to be representative of high-redshift AGB stars. This lack of observations of metal-poor AGB stars motivated the survey of DUST in Nearby Galaxies with Spitzer (DUSTiNGS), which imaged 50 nearby dwarf galaxies in the infrared and identified 526 dusty "extreme" AGB stars. The DUSTiNGS stars confirm that dust can form at metallicities as low as 0.008 solar, more than an order of magnitude lower than had been previously observed. However, very little is known about the DUSTiNGS stars; among the unknowns are the photospheric chemistries, stellar masses, temperatures, luminosities, pulsation periods and amplitudes, dust-production rates, and even their statuses as bona fide AGB stars. To eliminate these unknowns, we were awarded 56 hours of Priority 1 observing time in Spitzer's cycle 11 to obtain 6 new epochs of imaging for a subset of the DUSTiNGS variables over an 18 month baseline. These will be the first infrared light curves of metal-poor, dust-producing AGB stars, allowing us to study the influence of metallicity on pulsation and dust production. Combined with additional archival data, our cycle-11 Spitzer program will allow estimates of all of the parameters listed above, enabling the first direct comparisons to models of AGB

  8. FORMATION OF CARBON-ENHANCED METAL-POOR STARS IN THE PRESENCE OF FAR-ULTRAVIOLET RADIATION

    SciTech Connect

    Bovino, S.; Schleicher, D. R. G.; Latif, M. A.; Grassi, T.

    2014-08-01

    Recent discoveries of carbon-enhanced metal-poor stars like SMSS J031300.36–670839.3 provide increasing observational insights into the formation conditions of the first second-generation stars in the universe, reflecting the chemical conditions after the first supernova explosion. Here, we present the first cosmological simulations with a detailed chemical network including primordial species as well as C, C{sup +}, O, O{sup +}, Si, Si{sup +}, and Si{sup 2+} following the formation of carbon-enhanced metal-poor stars. The presence of background UV flux delays the collapse from z = 21 to z = 15 and cool the gas down to the cosmic microwave background temperature for a metallicity of Z/Z {sub ☉} = 10{sup –3}. This can potentially lead to the formation of lower-mass stars. Overall, we find that the metals have a stronger effect on the collapse than the radiation, yielding a comparable thermal structure for large variations in the radiative background. We further find that radiative backgrounds are not able to delay the collapse for Z/Z {sub ☉} = 10{sup –2} or a carbon abundance as in SMSS J031300.36–670839.3.

  9. Abundance Results from the Las Campanas Observatory and McDonald Observatory High-Resolution Metal-Poor Star Survey

    NASA Astrophysics Data System (ADS)

    Roederer, Ian U.; Preston, G.; Shectman, S.; Thompson, I.; Sneden, C.

    2011-01-01

    We have undertaken a survey to collect high-resolution and high S/N spectra for more than 300 metal-poor stars. The majority of our sample was selected from the HK Survey of Beers, Preston, and Shectman, and nearly all stars with estimated [Fe/H] < -2.5 have been observed with the MIKE spectrograph on the Magellan-Clay Telescope at Las Campanas Observatory. Additional metal-poor targets were selected based on their kinematic properties and observed with the Tull spectrograph on the Smith Telescope at McDonald Observatory. Previous abundance analyses based on high-resolution and high S/N spectra have been performed for only about 20% of the sample. While this sample naturally allows us to reconfirm and expand upon previously-detected low metallicity abundance trends and identify new stars with unique abundance signatures, its real power is the ability to probe chemical dispersion in abundance ratios. We exploit this attribute by performing line-by-line differential abundance analyses for many elements in large numbers of stars at a single metallicity and evolutionary state. This allows us to assess the evolution of the cosmic scatter of the chemistry of the ISM at very early times in the halo of the Galaxy. Generous funding has been provided by the U.S. National Science Foundation (grant AST 09-08978 to C.S.).

  10. Radial Velocities of Very Metal-Poor Stars as Probes of the Dual Halo Model of the Milky Way

    NASA Astrophysics Data System (ADS)

    Beers, Timothy C.; Juric, M.; Carollo, D.; Lee, Y.; An, D.; Aoki, W.; Norris, J. E.; Yong, D.

    2012-05-01

    We consider the distribution of radial velocities (RVs) for a large sample of very metal-poor stars from SDSS/SEGUE (N > 25000 with [Fe/H]< -2.0, of which 900 have [Fe/H] < -3.0), and two smaller recent high-resolution spectroscopic studies of the most metal-poor stars known (N > 300, of which 150 have [Fe/H] < -3.0). The RVs are compared with the expected behavior obtained using the GALFAST code of Juric, under the assumption that the halo of the Milky Way comprises a single population with canonical kinematics (e.g., as described by Chiba & Beers 2000). We find clear evidence that the RVs of these stars are inconsistent with draws from such a model, and that they appear to require at least a two-component halo. This test is, by design, independent of questions related to assignment of estimated stellar distances, or selection criteria related to proper motions, and provides strong support of the dual halo model described by Carollo et al. (2007, 2010).

  11. The Chemical Compositions of Very Metal-poor Stars HD 122563 and HD 140283: A View from the Infrared

    NASA Astrophysics Data System (ADS)

    Afşar, Melike; Sneden, Christopher; Frebel, Anna; Kim, Hwihyun; Mace, Gregory N.; Kaplan, Kyle F.; Lee, Hye-In; Oh, Heeyoung; Sok Oh, Jae; Pak, Soojong; Park, Chan; Pavel, Michael D.; Yuk, In-Soo; Jaffe, Daniel T.

    2016-03-01

    From high resolution (R ≃ 45,000), high signal-to-noise ratio (S/N > 400) spectra gathered with the Immersion Grating Infrared Spectrograph (IGRINS) in the H and K photometric bands, we have derived elemental abundances of two bright, well-known metal-poor halo stars: the red giant HD 122563 and the subgiant HD 140283. Since these stars have metallicities approaching [Fe/H] = -3, their absorption features are generally very weak. Neutral-species lines of Mg, Si, S and Ca are detectable, as well as those of the light odd-Z elements Na and Al. The derived IR-based abundances agree with those obtained from optical-wavelength spectra. For Mg and Si the abundances from the infrared transitions are improvements to those derived from shorter wavelength data. Many useful OH and CO lines can be detected in the IGRINS HD 122563 spectrum, from which derived O and C abundances are consistent to those obtained from the traditional [O i] and CH features. IGRINS high resolutions H- and K-band spectroscopy offers promising ways to determine more reliable abundances for additional metal-poor stars whose optical features are either not detectable, or too weak, or are based on lines with analytical difficulties.

  12. Standard Stars for the High-velocity and Metal-poor project at San Pedro Mártir

    NASA Astrophysics Data System (ADS)

    Schuster, W. J.; Parrao, L.; Contreras, M. E.

    2016-04-01

    The main documentation for the primary and secondary standard stars used in the high-velocity and metal-poor stars project is presented. Observations were taken using the Strömgren-Crawford, uvby-Hβ, 6-channel, spectrophotometric equipment with the H.L. Johnson 1.5-m telescope at the Observatorio Astronómico Nacional, San Pedro Mártir, between 1987 and 2007. Standard photometric values from the literature are reported for our standard stars, as well as transformed standard values, errors in the instrumental system, the transformation coefficients obtained for the standard system, the transformation errors, and the methods used to obtain such photometric observations and their standard transformations.

  13. MOLYBDENUM, RUTHENIUM, AND THE HEAVY r-PROCESS ELEMENTS IN MODERATELY METAL-POOR MAIN-SEQUENCE TURNOFF STARS

    SciTech Connect

    Peterson, Ruth C.

    2013-05-01

    The ratios of elemental abundances observed in metal-poor stars of the Galactic halo provide a unique present-day record of the nucleosynthesis products of its earliest stars. While the heaviest elements were synthesized by the r- and s-processes, dominant production mechanisms of light trans-ironic elements were obscure until recently. This work investigates further our 2011 conclusion that the low-entropy regime of a high-entropy wind (HEW) produced molybdenum and ruthenium in two moderately metal-poor turnoff stars that showed extreme overabundances of those elements with respect to iron. Only a few, rare nucleosynthesis events may have been involved. Here we determine abundances for Mo, Ru, and other trans-Fe elements for 28 similar stars by matching spectral calculations to well-exposed near-UV Keck HIRES spectra obtained for beryllium abundances. In each of the 26 turnoff stars with Mo or Ru line detections and no evidence for s-process production (therefore old), we find Mo and Ru to be three to six times overabundant. In contrast, the maximum overabundance is reduced to factors of three and two for the neighboring elements zirconium and palladium. Since the overproduction peaks sharply at Mo and Ru, a low-entropy HEW is confirmed as its origin. The overabundance level of the heavy r-process elements varies significantly, from none to a factor of four, but is uncorrelated with Mo and Ru overabundances. Despite their moderate metallicity, stars in this group trace the products of different nucleosynthetic events: possibly very few events, possibly events whose output depended on environment, metallicity, or time.

  14. HIGH-RESOLUTION SPECTROSCOPY OF EXTREMELY METAL-POOR STARS IN THE LEAST EVOLVED GALAXIES: LEO IV

    SciTech Connect

    Simon, Joshua D.; McWilliam, Andrew; Thompson, Ian B.; Frebel, Anna; Kirby, Evan N. E-mail: andy@ociw.ed E-mail: afrebel@cfa.harvard.ed

    2010-06-10

    We present high-resolution Magellan/MIKE spectroscopy of the brightest star in the ultra-faint dwarf galaxy Leo IV. We measure an iron abundance of [Fe/H] = -3.2, adding to the rapidly growing sample of extremely metal-poor (EMP) stars being identified in Milky Way satellite galaxies. The star is enhanced in the {alpha} elements Mg, Ca, and Ti by {approx}0.3 dex, very similar to the typical Milky Way halo abundance pattern. All of the light and iron-peak elements follow the trends established by EMP halo stars, but the neutron-capture elements Ba and Sr are significantly underabundant. These results are quite similar to those found for stars in the ultra-faint dwarfs Ursa Major II, Coma Berenices, Booetes I, and Hercules, suggesting that the chemical evolution of the lowest-luminosity galaxies may be universal. The abundance pattern we observe is consistent with predictions for nucleosynthesis from a Population III supernova explosion. The extremely low metallicity of this star also supports the idea that a significant fraction ({approx}>10%) of the stars in the faintest dwarfs have metallicities below [Fe/H] = -3.0.

  15. Discovery of a strongly r-process enhanced extremely metal-poor star LAMOST J110901.22+075441.8

    NASA Astrophysics Data System (ADS)

    Li, Hai-Ning; Aoki, Wako; Honda, Satoshi; Zhao, Gang; Christlieb, Norbert; Suda, Takuma

    2015-08-01

    We report the discovery of an extremely metal-poor (EMP) giant, LAMOST J110901.22+075441.8, which exhibits a large excess of r-process elements with [Eu/Fe] ˜ +1.16. The star is one of the newly discovered EMP stars identified from the LAMOST low-resolution spectroscopic survey and a high-resolution follow-up observation with the Subaru Telescope. Stellar parameters and elemental abundances have been determined from the Subaru spectrum. Accurate abundances for a total of 23 elements including 11 neutron-capture elements from Sr through Dy have been derived for LAMOST J110901.22+075441.8. The abundance pattern of LAMOST J110901.22+075441.8 in the range of C through Zn is in line with the “normal” population of EMP halo stars, except that it shows a notable underabundance in carbon. The heavy element abundance pattern of LAMOST J110901.22+075441.8 is in agreement with other well studied cool r-II metal-poor giants such as CS 22892-052 and CS 31082-001. The abundances of elements in the range from Ba through Dy match the scaled solar r-process pattern well. LAMOST J110901.22+075441.8 provides the first detailed measurements of neutron-capture elements among r-II stars at such low metallicity with [Fe/H] ≲ -3.4, and exhibits similar behavior as other r-II stars in the abundance ratio of Zr/Eu as well as Sr/Eu and Ba/Eu.

  16. Preliminary determination of the Non-LTE Calcium abundance in a sample of extremely metal-poor stars*

    NASA Astrophysics Data System (ADS)

    Spite, M.; Spite, F.; Bonifacio, P.; Caffau, E.; Andrievsky, S.; Korotin, S.; Cayrel, R.; François, P.

    2011-12-01

    The abundance ratios of the elements found in the extremely metal-poor stars (EMP) are a test of the yields predicted by the models of supernovae. For precise comparisons, it is of course preferable to avoid the approximation of LTE. The difference of LTE and NLTE profiles is displayed for three strong lines. The NLTE abundances of Ca are derived from the profiles of about 15 Ca I lines in the EMP giants and about 10 lines in the turnoff stars. The improved abundance trends are consistent with a [Ca/Fe] ratio constant vs. [Fe/H], and with a [Ca/Mg] ratio slightly declining when [Mg/H] increases. Also [Ca/Mg] presents a scatter larger than [Ca/Fe]. As far as the comparison with sulfur (another alpha elment) is concerned we find that [S/Ca] presents a scatter smaller than [S/Mg].

  17. Detection of Phosphorus, Sulphur, and Zinc in the Carbon-enhanced Metal-poor Star BD+44 493

    NASA Astrophysics Data System (ADS)

    Roederer, Ian U.; Placco, Vinicius M.; Beers, Timothy C.

    2016-06-01

    The carbon-enhanced metal-poor star BD+44°493 ([Fe/H] = ‑3.9) has been proposed as a candidate second-generation star enriched by metals from a single Pop III star. We report the first detections of P and S and the second detection of Zn in any extremely metal-poor carbon-enhanced star, using new spectra of BD+44°493 collected by the Cosmic Origins Spectrograph on the Hubble Space Telescope. We derive [P/Fe] = ‑0.34 ± 0.21, [S/Fe] = +0.07 ± 0.41, and [Zn/Fe] = ‑0.10 ± 0.24. We increase by 10-fold the number of Si i lines detected in BD+44°493, yielding [Si/Fe] = +0.15 ± 0.22. The [S/Fe] and [Zn/Fe] ratios exclude the hypothesis that the abundance pattern in BD+44°493 results from depletion of refractory elements onto dust grains. Comparison with zero-metallicity supernova (SN) models suggests that the stellar progenitor that enriched BD+44°493 was massive and ejected much less than 0.07 M ⊙ of 56Ni, characteristic of a faint SN. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute (STScI), which is operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under NASA contract NAS 5-26555. These observations are associated with program GO-14231.

  18. The stellar content of the Hamburg/ESO survey. IV. Selection of candidate metal-poor stars

    NASA Astrophysics Data System (ADS)

    Christlieb, N.; Schörck, T.; Frebel, A.; Beers, T. C.; Wisotzki, L.; Reimers, D.

    2008-06-01

    We present the quantitative methods used for selecting candidate metal-poor stars in the Hamburg/ESO objective-prism survey (HES). The selection is based on the strength of the Ca II K line, B-V colors (both measured directly from the digital HES spectra), as well as J-K colors from the 2 Micron All Sky Survey. The KP index for Ca II K can be measured from the HES spectra with an accuracy of 1.0 Å, and a calibration of the HES B-V colors, using CCD photometry, yields a 1-σ uncertainty of 0.07 mag for stars in the color range 0.3 < B-V < 1.4. These accuracies make it possible to reliably reject stars with [Fe/H] > -2.0 without sacrificing completeness at the lowest metallicities. A test of the selection using 1121 stars of the HK survey of Beers, Preston, and Shectman present on HES plates suggests that the completeness at [Fe/H] < -3.5 is close to 100% and that, at the same time, the contamination of the candidate sample with false positives is low: 50% of all stars with [Fe/H] > -2.5 and 97% of all stars with [Fe/H] > -2.0 are rejected. The selection was applied to 379 HES fields, covering a nominal area of 8853 deg2 of the southern high Galactic latitude sky. The candidate sample consists of 20 271 stars in the magnitude range 10 ≲ B ≲ 18. A comparison of the magnitude distribution with that of the HK survey shows that the magnitude limit of the HES sample is about 2 mag fainter. Taking the overlap of the sky areas covered by both surveys into account, it follows that the survey volume for metal-poor stars has been increased by the HES by about a factor of 10 with respect to the HK survey. We have already identified several very rare objects with the HES, including, e.g., the three most heavy-element deficient stars currently known. Based on observations collected at the European Southern Observatory, Chile (Proposal ID 145.B-0009). Tables A.1 and A.2 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or

  19. The dust content of the most metal-poor star-forming galaxies

    NASA Astrophysics Data System (ADS)

    Schneider, Raffaella; Hunt, Leslie; Valiante, Rosa

    2016-04-01

    Although dust content is usually assumed to depend uniquely on metallicity, recent observations of two extremely metal-poor dwarf galaxies have suggested that this may not always be true. At a similar oxygen abundance of ˜3 per cent Z⊙, the dust-to-gas and dust-to-stellar mass ratios in SBS 0335-052 and I Zw 18 differ by a factor of 40-70 according to including molecular gas or excluding it. Here, we investigate a possible reason for this dramatic difference through models based on a semi-analytical formulation of chemical evolution including dust. Results suggest that the greater dust mass in SBS 0335-052 is due to the more efficient grain growth allowed by the high density in the cold interstellar medium (ISM), observationally inferred to be almost 20 times higher than in I Zw 18. Our models are able to explain the difference in dust masses, suggesting that efficient dust formation and dust content in galaxies, including those with the highest measured redshifts, depend sensitively on the ISM density, rather than only on metallicity.

  20. The frequency of carbon-enhanced metal-poor stars and the origin of carbon in the universe

    NASA Astrophysics Data System (ADS)

    Marsteller, Brian Elliott

    In recent large surveys of metal-poor stars, such as the HK survey (Beers et al., 1985, 1992), the Hamburg/ESO survey (HES, Christlieb et al., 2001), and recently the stellar component of the Sloan Digital Sky Survey (SDSS, Stoughton et al., 2002), a curiously large fraction of stars which show enhanced carbon abundances have been observed. In fact, this fraction seems to increase as metallicity decreases. Since these stars, the Carbon-Enhanced Metal-Poor (CEMP) stars, then play a significant role in the formation and evolution of the earliest stellar generations, and thus all following generations, it is of vital importance to fully understand their true fraction, so that they can be properly understood, and properly accounted for in models of galactic and nucleosynthetic evolution. In order to obtain this quantity, the frequency of carbon enhancement as a function of metallicity, a large quantity of metal-poor stars need to be analyzed to determine these important abundances. For this to occur from these large, pre-existing databases of low to medium resolution spectroscopy, an accurate method of quickly determining the metallicity and carbon abundance for a star is needed. Due to the limited data currently available in some of these extreme regions of parameter space, currently existing methods which rely on calibration samples do not prove sufficient. Thus, a new method, based solely on the physical properties of the stars and the information contained in their spectra, which is both relatively fast and accurate is needed. Here we outline the development of such a technique which generates synthetic spectra using the line index code MOOG, and automatically determines the required abundances. After verifying the validity of this technique using several samples, abundances are then determined for a large, unbiased sample of stars taken from SDSS. From these abundances, the frequency of carbon enhancement is derived. Although a true frequency cannot be determined

  1. Is There Plenty of Metal-poor Stars with Planets in the Galactic Thick Disk?

    NASA Astrophysics Data System (ADS)

    Adibekyan, V. Zh.; Santos, N. C.; Sousa, S. G.; Israelian, G.; Figueira, P.

    2013-04-01

    We performed an uniform spectroscopic analysis of 1111 FGK dwarfs observed as part of the HARPS GTO planet search program. We applied a purely chemical approach, based on [α/Fe] ratio, to distinguish the various stellar components in the Galaxy. Apart from the well known Galactic thick and thin disks, we separated an α-enhanced stellar family at super-solar metallicities. The metal-rich high-α stars have orbits similar to the thin disk stars, but they are similar to thick disk stars in terms of age. Our data indicate that the incidence of stars with planets are greater among the chemically separated “thick” disk stars with [Fe/H] ≤ -0.3 dex than they are among “thin” disk stars in the same [Fe/H] interval. Our results allow us to suppose that a certain chemical composition, and not the Galactic birth place of the stars, is the causative factor for that.

  2. VizieR Online Data Catalog: Fe Abundances in metal-poor stars (Sbordone+ 2010)

    NASA Astrophysics Data System (ADS)

    Sbordone, L.; Bonifacio, P.; Caffau, E.; Ludwig, H.-G.; Behara, N. T.; Gonzalez Hernandez, J. I.; Steffen, M.; Cayrel, R.; Freytag, B.; van't Veer, C.; Molaro, P.; Plez, B.; Sivarani, T.; Spite, M.; Spite, F.; Beers, T. C.; Christlieb, N.; Francois, P.; Hill, V.

    2010-08-01

    Line-by-line abundances for FeI and FeII lines used to estimate metallicity and gravity for the program stars. The first column lists the star name, then the ion (FeI or FeII) The the wavelength in nm, the loggf, the measured EW (pm) and the derived abundance assuming the four stellar parameter sets used in the article, respectively 3D, BA, ALI and IRFM. (3 data files).

  3. Spectroscopic Binary Stars

    NASA Astrophysics Data System (ADS)

    Batten, A.; Murdin, P.

    2000-11-01

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

  4. BOO-1137-AN EXTREMELY METAL-POOR STAR IN THE ULTRA-FAINT DWARF SPHEROIDAL GALAXY BOOeTES I

    SciTech Connect

    Norris, John E.; Yong, David; Gilmore, Gerard; Wyse, Rosemary F. G.

    2010-03-01

    We present high-resolution (R {approx} 40,000), high-signal-to-noise ratio (20-90) spectra of an extremely metal-poor giant star Boo-1137 in the 'ultra-faint' dwarf spheroidal galaxy (dSph) Booetes I, absolute magnitude M{sub V} {approx} -6.3. We derive an iron abundance of [Fe/H] = -3.7, making this the most metal-poor star as yet identified in an ultra-faint dSph. Our derived effective temperature and gravity are consistent with its identification as a red giant in Booetes I. Abundances for a further 15 elements have also been determined. Comparison of the relative abundances, [X/Fe], with those of the extremely metal-poor red giants of the Galactic halo shows that Boo-1137 is 'normal' with respect to C and N, the odd-Z elements Na and Al, the iron-peak elements, and the neutron-capture elements Sr and Ba, in comparison with the bulk of the Milky Way halo population having [Fe/H] {approx}<-3.0. The alpha-elements Mg, Si, Ca, and Ti are all higher by DELTA[X/Fe] {approx} 0.2 than the average halo values. Monte Carlo analysis indicates that DELTA[alpha/Fe] values this large are expected with a probability {approx}0.02. The elemental abundance pattern in Boo-1137 suggests inhomogeneous chemical evolution, consistent with the wide internal spread in iron abundances we previously reported. The similarity of most of the Boo-1137 relative abundances with respect to halo values, and the fact that the alpha-elements are all offset by a similar small amount from the halo averages, points to the same underlying galaxy-scale stellar initial mass function, but that Boo-1137 likely originated in a star-forming region where the abundances reflect either poor mixing of supernova (SN) ejecta, or poor sampling of the SN progenitor mass range, or both.

  5. Iron-group Abundances in the Metal-poor Main-Sequence Turnoff Star HD~84937

    NASA Astrophysics Data System (ADS)

    Sneden, Christopher; Cowan, John J.; Kobayashi, Chiaki; Pignatari, Marco; Lawler, James E.; Den Hartog, Elizabeth A.; Wood, Michael P.

    2016-01-01

    We have derived new, very accurate abundances of the Fe-group elements Sc through Zn (Z = 21-30) in the bright main-sequence turnoff star HD 84937 based on high-resolution spectra covering the visible and ultraviolet spectral regions. New or recent laboratory transition data for 14 species of seven elements have been used. Abundances from more than 600 lines of non-Fe species have been combined with about 550 Fe lines in HD 84937 to yield abundance ratios of high precision. The abundances have been determined from both neutral and ionized transitions, which generally are in agreement with each other. We find no substantial departures from the standard LTE Saha ionization balance in this [Fe/H] = -2.32 star. Noteworthy among the abundances are [Co/Fe] = +0.14 and [Cu/Fe] = -0.83, in agreement with past studies of abundance trends in this and other low-metallicity stars, and < [{{Sc,Ti,V/Fe}}]> = +0.31, which has not been noted previously. A detailed examination of scandium, titanium, and vanadium abundances in large-sample spectroscopic surveys reveals that they are positively correlated in stars with [Fe/H] < -2 HD 84937 lies at the high end of this correlation. These trends constrain the synthesis mechanisms of Fe-group elements. We also examine the Galactic chemical evolution abundance trends of the Fe-group elements, including a new nucleosynthesis model with jet-like explosion effects.

  6. Parameters and Kinematics of Carbon Enhanced Metal Poor (CEMP) Stars from the Hamburg/ESO Survey

    NASA Astrophysics Data System (ADS)

    Thirupathi, Sivarani; Beers, T. C.; Lee, Y. S.; Kennedy, C.; Carollo, D.; Masseron, T.; Plez, B.; Norris, J. E.; Bessell, M.; Rossi, S.

    2007-12-01

    Several hundred CEMP stars have been selected from the Christlieb et al (2001, A&A 375, 366) catalog of carbon-rich stars, which is based on the Hamburg/ESO objective prism survey. Medium resolution (R = 2000) optical spectra were obtained for these stars covering a wavelength range of 3800-4800 A. The estimates of Teff, [Fe/H], and [C/Fe] for this sample is already available, based on application of the Rossi et al. (2005, AJ 130, 2804 ), which uses the strength of the CaII K line, the CH G-band, and J-K colors. Here we present an automated method to estimate the full set of atmospheric parameters for these data (including logg) based on synthetic spectra and photometry. For this purpose, we have generated a set of synthetic grids with carbon enhanced atmospheres with the MARCS code (Plez et al. 1992, A&A 256,551; Asplund et al. 1997, A&A 318, 521; Gustafsson et al. 2003, ASP Conf. Ser. 288, 331), which is particularly important for cool CEMP stars (for which the atmospheric structure changes with increasing carbon abundance (Masseron et al. 2006 A&A 455, 1059). More than one hundred stars of our prpogram stars have already been observed at high spectral resolution (R = 20000-25000), during the course of the HERES survey (Barklem et al. 2005, A&A 439,129; Lucatello et al. 2006 ApJ 652, 37L), which allow us to calibrate our methods. Here we describe our new methods for estimation and validation of Teff, logg, [Fe/H], [C/Fe]. We also comment on the possible origin of CEMP stars in this sample based on these derived parameters and on the inferred kinematics. TS, TCB, YSL, and CK acknowledge support from grant PHY 02-16783; Physics Frontier Center/Joint Institute for Nuclear Astrophysics (JINA), awarded by the U.S. National Science Foundation and NSF grant AST 07-07776

  7. VizieR Online Data Catalog: Metal-poor stars towards the Galactic bulge (Koch+, 2016)

    NASA Astrophysics Data System (ADS)

    Koch, A.; McWilliam, A.; Preston, G. W.; Thompson, I. B.

    2015-11-01

    The stars studied here were identified in a search for EMP stars in the Galactic bulge (Preston et al. unpublished), near b=-10°, employing the 2.5-m du Pont and 1-m Swope telescopes at Las Campanas Observatory. Observations of seven EMP candidates presented here were taken spread over six nights in July 2007 with a median seeing of 0.95", while individual exposures reached as high as 2" and notably better conditions (~0.6") during several nights. Our chosen set-up included a 0.5" slit, 2x1 binning in spectral and spatial dimensions and resulted in a resolving power of R~45000. An observing log is given in Table 1. (3 data files).

  8. Precise Li abundances in metal-poor stars: depletion in the Spite plateau

    NASA Astrophysics Data System (ADS)

    Meléndez, J.; Casagrande, L.; Ramírez, I.; Asplund, M.

    2010-03-01

    We present Li abundances for 73 stars in the metallicity range -3.5 < [Fe/H] < -1.0 using improved IRFM temperatures (Casagrande et al. 2009) with precise E(B-V) values obtained mostly from interstellar NaI D lines, and high-quality equivalent widths (σEW ~ 3%). At all metallicities we uncover a fine-structure in the Li abundances of Spite plateau stars, which we trace to Li depletion that depends on both metallicity and mass. Models including atomic diffusion and turbulent mixing seem to reproduce the observed Li depletion assuming a primordial Li abundance ALi = 2.64 dex (MARCS models) or 2.72 (Kurucz overshooting models), in good agreement with current predictions (ALi = 2.72) from standard BBN.

  9. DISCOVERY OF MIRA VARIABLE STARS IN THE METAL-POOR SEXTANS DWARF SPHEROIDAL GALAXY

    SciTech Connect

    Sakamoto, Tsuyoshi; Matsunaga, Noriyuki; Nakada, Yoshikazu; Hasegawa, Takashi

    2012-12-10

    We report the discovery of two Mira variable stars (Miras) toward the Sextans dwarf spheroidal galaxy (dSph). We performed optical long-term monitoring observations for two red stars in the Sextans dSph. The light curves of both stars in the I{sub c} band show large-amplitude (3.7 and 0.9 mag) and long-period (326 {+-} 15 and 122 {+-} 5 days) variations, suggesting that they are Miras. We combine our own infrared data with previously published data to estimate the mean infrared magnitudes. The distances obtained from the period-luminosity relation of the Miras (75.3{sup +12.8}{sub -10.9} and 79.8{sup +11.5}{sub -9.9} kpc, respectively), together with the radial velocities available, support memberships of the Sextans dSph (90.0 {+-} 10.0 kpc). These are the first Miras found in a stellar system with a metallicity as low as [Fe/H] {approx} -1.9 than any other known system with Miras.

  10. DETECTION OF ELEMENTS AT ALL THREE r-PROCESS PEAKS IN THE METAL-POOR STAR HD 160617

    SciTech Connect

    Roederer, Ian U.; Lawler, James E. E-mail: jelawler@wisc.edu

    2012-05-01

    We report the first detection of elements at all three r-process peaks in the metal-poor halo star HD 160617. These elements include arsenic and selenium, which have not been detected previously in halo stars, and the elements tellurium, osmium, iridium, and platinum, which have been detected previously. Absorption lines of these elements are found in archive observations made with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. We present up-to-date absolute atomic transition probabilities and complete line component patterns for these elements. Additional archival spectra of this star from several ground-based instruments allow us to derive abundances or upper limits of 45 elements in HD 160617, including 27 elements produced by neutron-capture reactions. The average abundances of the elements at the three r-process peaks are similar to the predicted solar system r-process residuals when scaled to the abundances in the rare earth element domain. This result for arsenic and selenium may be surprising in light of predictions that the production of the lightest r-process elements generally should be decoupled from the heavier r-process elements.

  11. Metal-poor stars observed with the Magellan telescope. II. Discovery of four stars with [Fe/H] ≤ –3.5

    SciTech Connect

    Placco, Vinicius M.; Beers, Timothy C.; Frebel, Anna; Christlieb, Norbert; Lee, Young Sun; Kennedy, Catherine R.; Rossi, Silvia; Santucci, Rafael M.

    2014-01-20

    We report on the discovery of seven low-metallicity stars selected from the Hamburg/ESO Survey, six of which are extremely metal-poor (EMP, [Fe/H] ≤ –3.0), with four having [Fe/H] ≤ –3.5. Chemical abundances or upper limits are derived for these stars based on high-resolution (R ∼ 35,000) Magellan/MIKE spectroscopy, and are in general agreement with those of other very and extremely metal-poor stars reported in the literature. Accurate metallicities and abundance patterns for stars in this metallicity range are of particular importance for studies of the shape of the metallicity distribution function of the Milky Way's halo system, in particular for probing the nature of its low-metallicity tail. In addition, taking into account suggested evolutionary mixing effects, we find that six of the program stars (with [Fe/H] ≤ –3.35) possess atmospheres that were likely originally enriched in carbon, relative to iron, during their main-sequence phases. These stars do not exhibit overabundances of their s-process elements, and hence may be, within the error bars, additional examples of the so-called CEMP-no class of objects.

  12. Abundances of Sr, Y, and Zr in Metal-Poor Stars and Implications for Chemical Evolution in the Early Galaxy

    NASA Astrophysics Data System (ADS)

    Qian, Y.-Z.; Wasserburg, G. J.

    2008-11-01

    We have attributed the elements from Sr through Ag in stars of low metallicities ([ Fe/H ] lesssim - 1.5) to charged-particle reactions (CPRs) in neutrino-driven winds, which are associated with neutron star formation in low-mass and normal supernovae (SNe) from progenitors of ~8-11 M⊙ and ~12-25 M⊙, respectively. Using this rule and attributing all Fe production to normal SNe, we previously developed a phenomenological two-component model, which predicts that [ Sr/Fe ] >= - 0.32 for all metal-poor stars. This is in direct conflict with the high-resolution data now available, which show that there is a great shortfall of Sr relative to Fe in many stars with [ Fe/H ] lesssim - 3. The same conflict also exists for the CPR elements Y and Zr. We show that the data require a stellar source leaving behind black holes and that hypernovae (HNe) from progenitors of ~25-50 M⊙ are the most plausible candidates. If we expand our previous model to include three components (low-mass and normal SNe and HNe), we find that essentially all of the data are very well described by the new model. The HN yield pattern for the low-A elements from Na through Zn (including Fe) is inferred from the stars deficient in Sr, Y, and Zr. We estimate that HNe contributed ~24% of the bulk solar Fe inventory while normal SNe contributed only ~9% (not the usually assumed ~33%). This implies a greatly reduced role of normal SNe in the chemical evolution of the low-A elements.

  13. On 7LI Enrichment by Low-Mass Metal-Poor Red Giant Branch Stars

    NASA Astrophysics Data System (ADS)

    de la Reza, Ramiro; da Silva, Licio; Drake, Natalia A.; Terra, Marco A.

    2000-06-01

    First-ascent red giants with strong and very strong Li lines have just been discovered in globular clusters. Using the stellar internal prompt 7Li enrichment-mass-loss scenario, we explore the possibility of 7Li enrichment in the interstellar matter of the globular cluster M3 produced by these Li-rich giants. We found that enrichment as large as 70% or more compared to the initial 7Li content of M3 can be obtained during the entire life of this cluster. However, because M3 will cross into the Galactic plane several times, the new 7Li will be very probably removed by ram pressure into the disk. Globular clusters appear then as possible new sources of 7Li in the Galactic disk. It is also suggested that the known Na/Al variations in stars of globular clusters could be somehow related to the 7Li variations and that the cool bottom process mixing mechanism acting in the case of 7Li could also play a role in the case of Na and Al surface enrichments.

  14. EXTREME ENHANCEMENTS OF r-PROCESS ELEMENTS IN THE COOL METAL-POOR MAIN-SEQUENCE STAR SDSS J2357-0052

    SciTech Connect

    Aoki, Wako; Beers, Timothy C.; Honda, Satoshi; Carollo, Daniela E-mail: beers@pa.msu.ed E-mail: carollo@mso.anu.edu.a

    2010-11-10

    We report the discovery of a cool metal-poor, main-sequence star exhibiting large excesses of r-process elements. This star is one of the two newly discovered cool subdwarfs (effective temperatures of 5000 K) with extremely low metallicity ([Fe/H] < -3) identified from follow-up high-resolution spectroscopy of metal-poor candidates from the Sloan Digital Sky Survey. SDSS J2357-0052 has [Fe/H] = -3.4 and [Eu/Fe] = +1.9, and exhibits a scaled solar r-process abundance pattern of heavy neutron-capture elements. This is the first example of an extremely metal-poor, main-sequence star showing large excesses of r-process elements; all previous examples of the large r-process-enhancement phenomena have been associated with metal-poor giants. The metallicity of this object is the lowest, and the excess of Eu ([Eu/Fe]) is the highest, among the r-process-enhanced stars found so far. We consider possible scenarios to account for the detection of such a star and discuss techniques to enable searches for similar stars in the future.

  15. Numerical simulations of convection in low-mass metal-poor stars

    NASA Astrophysics Data System (ADS)

    Freytag, Bernd

    Based on detailed 2D numerical radiation hydrodynamics (RHD) calculations of time-dependent compressible convection, we have studied the dynamics and thermal structure of the convective surface layers of stars in the range of effective temperatures, gravities, and metallicities between 4300K <= Teff <= 7100K, 2.54 <= log g <= 4.74, and M/H=0.0, -0.5, -1.0, -2.0, respectively. Although our models describe only the shallow, strongly superadiabatic layers at the top of the convective stellar envelope, they provide information about the value of the entropy of the deeper, adiabatically stratified regions. This quantity can be translated into an effective mixing-length parameter alphaMLT for every single RHD model. A fit for all models with the same metallicity results in a function alpha=alphafit(Teff, log g) for each of the four metallicities. With the help of these functions, evolutionary tracks and isochrones with constant and calibrated alpha values have been computed and compared to investigate the significance of the variations in alphafit. The behavior of alphafit in the HRD region corresponding to Turn-Off, Subgiant Branch and base of the Red Giant Branch of globular clusters is of particular interest; a variable alpha may change the color (and even, at a lesser extent, the luminosity) of the Turn-Off and the color difference between Turn-Off and Red Giant Branch, as derived from theoretical isochrones, with respect to the case of constant alpha. This, in turn, might affect absolute and relative age determinations of globular clusters. Instead of the mixing-length parameter of the MLT it is possible to calibrate the free overshoot parameter of the turbulence theory of Canuto &\\ Mazzitelli in an analogous manner. The size of the variations of the free parameter of both theories is compared.

  16. CARBON-ENHANCED METAL-POOR STARS IN THE INNER AND OUTER HALO COMPONENTS OF THE MILKY WAY

    SciTech Connect

    Carollo, Daniela; Norris, John E.; Freeman, Ken C.; Beers, Timothy C.; Lee, Young Sun; Kennedy, Catherine R.; Bovy, Jo; Sivarani, Thirupathi; Aoki, Wako E-mail: kcf@mso.anu.edu.au E-mail: beers@pa.msu.edu E-mail: kenne257@msu.edu E-mail: sivarani@iiap.res.in

    2012-01-10

    Carbon-enhanced metal-poor (CEMP) stars in the halo components of the Milky Way are explored, based on accurate determinations of the carbon-to-iron ([C/Fe]) abundance ratios and kinematic quantities for over 30,000 calibration stars from the Sloan Digital Sky Survey. Using our present criterion that low-metallicity stars exhibiting [C/Fe] ratios ({sup c}arbonicity{sup )} in excess of [C/Fe] =+0.7 are considered CEMP stars, the global frequency of CEMP stars in the halo system for [Fe/H] <-1.5 is 8%, for [Fe/H] <-2.0 it is 12%, and for [Fe/H] <-2.5 it is 20%. We also confirm a significant increase in the level of carbon enrichment with declining metallicity, growing from ([C/Fe]) {approx}+1.0 at [Fe/H] =-1.5 to ([C/Fe]) {approx}+1.7 at [Fe/H] =-2.7. The nature of the carbonicity distribution function (CarDF) changes dramatically with increasing distance above the Galactic plane, |Z|. For |Z| <5 kpc, relatively few CEMP stars are identified. For distances |Z| >5 kpc, the CarDF exhibits a strong tail toward high values, up to [C/Fe] > +3.0. We also find a clear increase in the CEMP frequency with |Z|. For stars with -2.0 < [Fe/H] <-1.5, the frequency grows from 5% at |Z| {approx}2 kpc to 10% at |Z| {approx}10 kpc. For stars with [Fe/H] <-2.0, the frequency grows from 8% at |Z| {approx}2 kpc to 25% at |Z| {approx}10 kpc. For stars with -2.0 < [Fe/H] <-1.5, the mean carbonicity is ([C/Fe]) {approx}+1.0 for 0 kpc < |Z| < 10 kpc, with little dependence on |Z|; for [Fe/H] <-2.0, ([C/Fe]) {approx}+1.5, again roughly independent of |Z|. Based on a statistical separation of the halo components in velocity space, we find evidence for a significant contrast in the frequency of CEMP stars between the inner- and outer-halo components-the outer halo possesses roughly twice the fraction of CEMP stars as the inner halo. The carbonicity distribution also differs between the inner-halo and outer-halo components-the inner halo has a greater portion of stars with modest carbon

  17. Origins of the thick disk of the Milky Way Galaxy as traced by the elemental abundances of metal-poor stars

    NASA Astrophysics Data System (ADS)

    Ruchti, Gregory Randal

    2010-12-01

    Understanding the formation and evolution of disks in galaxies in the early universe is very important for understanding the forms of galaxies today. Recent studies of the Milky Way Galaxy, an ideal galaxy for analyzing individual stars within its disk, indicate that the formation of the Galactic disk is very complex. Most of these studies, however, contain very few stars at low metallicities. Metal-poor stars are important, because they are potential survivors of the earliest star formation in the disk of the Milky Way Galaxy. I therefore measured elemental abundances of a statistically significant sample of metal-poor ([Fe/H] ≲ - 1.0) stars in the disk of the Galaxy, chosen from the RAVE survey in order to study the early formation history of the Galactic disk. I report on a sample of 214 red giant branch, 31 red clump/horizontal branch, and 74 dwarf/sub-giant metal-poor thick-disk candidate stars. I found that the [alpha/Fe] ratios are enhanced implying that enrichment proceeded by purely core-collapse supernovae. This requires that star formation in each star forming region had a short duration. The relative lack of scatter in the [alpha/Fe] ratios implies good mixing in the interstellar medium prior to star formation. In addition, the ratios resemble that of the halo, indicating that the halo and thick disk share a similar massive star initial mass function. I further looked for radial or vertical gradients in metallicity or alpha-enhancement for the metal-poor thick disk, never before done for such a sample. I found no radial gradient and a moderate vertical gradient in my derived iron abundance, and only minimal-amplitude gradients in [alpha/Fe]. In addition, I show that the distribution of orbital eccentricities for my metal-poor thick-disk stars requires that the thick disk was formed primarily in situ, with direct accretion being extremely minimal. I conclude that the alpha-enhancement of the metal-poor thick disk, and the lack of obvious radial or

  18. Stellar Yields of Rotating First Stars: Yields of Weak Supernovae and Abundances of Carbon-enhanced Hyper Metal Poor Stars

    NASA Astrophysics Data System (ADS)

    Takahashi, Koh; Umeda, Hideyuki; Yoshida, Takashi

    2015-01-01

    The three most iron-poor stars known until now are also known to have peculiar enhancements of intermediate mass elements. Under the assumption that these iron-deficient stars reveal the nucleosynthesis result of Pop III stars, we show that a weak supernova model successfully reproduces the observed abundance patterns. Moreover, we show that the initial parameters of the progenitor, such as the initial masses and the rotational property, can be constrained by the model, since the stellar yields result from the nucleosynthesis in the outer region of the star, which is significantly affected by the initial parameters. The initial parameter of Pop III stars is of prime importance for the theoretical study of the early universe. Future observation will increase the number of such carbon enhanced iron-deficient stars, and the same analysis on the stars may give valuable information for the Pop III stars that existed in our universe.

  19. Carbon-enhanced metal-poor stars: CEMP-s and CEMP-no subclasses in the halo system of the Milky Way

    SciTech Connect

    Carollo, Daniela; Freeman, Ken; Beers, Timothy C.; Placco, Vinicius M.; Tumlinson, Jason; Martell, Sarah L. E-mail: kcf@mso.anu.edu.au E-mail: vplacco@gemini.edu E-mail: smartell@aao.gov.au

    2014-06-20

    We explore the kinematics and orbital properties of a sample of 323 very metal-poor stars in the halo system of the Milky Way, selected from the high-resolution spectroscopic follow-up studies of Aoki et al. and Yong et al. The combined sample contains a significant fraction of carbon-enhanced metal-poor (CEMP) stars (22% or 29%, depending on whether a strict or relaxed criterion is applied for this definition). Barium abundances (or upper limits) are available for the great majority of the CEMP stars, allowing for their separation into the CEMP-s and CEMP-no subclasses. A new method to assign membership to the inner- and outer-halo populations of the Milky Way is developed, making use of the integrals of motion, and applied to determine the relative fractions of CEMP stars in these two subclasses for each halo component. Although limited by small-number statistics, the data suggest that the inner halo of the Milky Way exhibits a somewhat higher relative number of CEMP-s stars than CEMP-no stars (57% versus 43%), while the outer halo possesses a clearly higher fraction of CEMP-no stars than CEMP-s stars (70% versus 30%). Although larger samples of CEMP stars with known Ba abundances are required, this result suggests that the dominant progenitors of CEMP stars in the two halo components were different; massive stars for the outer halo, and intermediate-mass stars in the case of the inner halo.

  20. uvby-β photometry of high-velocity and metal-poor stars. XI. Ages of halo and old disk stars

    NASA Astrophysics Data System (ADS)

    Schuster, W. J.; Moitinho, A.; Márquez, A.; Parrao, L.; Covarrubias, E.

    2006-01-01

    New uvby-β data are provided for 442 high-velocity and metal-poor stars; 90 of these stars have been observed previously by us, and 352 are new. When combined with our previous two photometric catalogues, the data base is now made up of 1533 high-velocity and metal-poor stars, all with uvby-β photometry and complete kinematic data, such as proper motions and radial velocities taken from the literature. Hipparcos, plus a new photometric calibration for Mv also based on the Hipparcos parallaxes, provide distances for nearly all of these stars; our previous photometric calibrations give values for E(b-y) and [Fe/H]. The [Fe/H], V(rot) diagram allows us to separate these stars into different Galactic stellar population groups, such as old-thin-disk, thick-disk, and halo. The X histogram, where X is our stellar-population discriminator combining V(rot) and [Fe/H], and contour plots for the [Fe/H], V(rot) diagram both indicate two probable components to the thick disk. These population groups and Galactic components are studied in the (b-y)0, Mv diagram, compared to the isochrones of Bergbusch & VandenBerg (2001, ApJ, 556, 322), to derive stellar ages. The two thick-disk groups have the mean characteristics: ([Fe/H], V(rot), Age, σW') ≈ (-0.7 dex, 120 km s-1, 12.5 Gyr, 62.0 km s-1), and ≈(-0.4, 160, 10.0, 45.8). The seven most metal-poor halo groups, -2.31 ≤ [Fe/H] ≤ -1.31, show a mean age of 13.0 ± 0.2 (mean error) Gyr, giving a mean difference from the WMAP results for the age of the Universe of 0.7 ± 0.3 Gyr. These results for the ages and components of the thick disk and for the age of the Galactic halo field stars are discussed in terms of various models and ideas for the formation of galaxies and their stellar populations.

  1. HIGH-RESOLUTION SPECTROSCOPY OF EXTREMELY METAL-POOR STARS IN THE LEAST EVOLVED GALAXIES: URSA MAJOR II and COMA BERENICES

    SciTech Connect

    Frebel, Anna; Simon, Joshua D.; Geha, Maria; Willman, Beth E-mail: jsimon@ociw.ed E-mail: bwillman@haverford.ed

    2010-01-01

    We present spectra of six metal-poor stars in two of the ultra-faint dwarf galaxies orbiting the Milky Way (MW), Ursa Major II, and Coma Berenices obtained with the Keck/High Resolution Echelle Spectrometer (HIRES). These observations include the first high-resolution spectroscopic observations of extremely metal-poor ([Fe/H] < -3.0) stars not belonging to the MW halo field star population. We obtain abundance measurements and upper limits for 26 elements between carbon and europium. The entire sample of stars spans a range of -3.2 < [Fe/H] < -2.3, and we confirm that each galaxy contains a large intrinsic spread of Fe abundances. A comparison with MW halo stars of similar metallicities reveals substantial agreement between the abundance patterns of the ultra-faint dwarf galaxies and the MW halo for the light, alpha, and iron-peak elements (C to Zn). This agreement contrasts with the results of earlier studies of more metal-rich stars (-2.5 approx< [Fe/H] approx< -1.0) in more luminous dwarf spheroidal galaxies, which found significant abundance discrepancies with respect to the MW halo data. The abundances of neutron-capture elements (Sr to Eu) in the ultra-faint dwarf galaxies are extremely low, consistent with the most metal-poor halo stars, but not with the typical halo abundance pattern at [Fe/H] approx> -3.0. Not only are our results broadly consistent with a galaxy formation model that predicts that massive dwarf galaxies are the source of the metal-rich component ([Fe/H]> - 2.5) of the MW halo, but they also suggest that the faintest known dwarfs may be the primary contributors to the metal-poor end of the MW halo metallicity distribution.

  2. Estimation of Carbon Abundances in Metal-Poor Stars. I. Application to the Strong G-Band Stars of Beers, Preston, and Shectman

    NASA Astrophysics Data System (ADS)

    Rossi, Silvia; Beers, Timothy C.; Sneden, Chris; Sevastyanenko, Tatiana; Rhee, Jaehyon; Marsteller, Brian

    2005-12-01

    We develop and test a method for the estimation of metallicities ([Fe/H]) and carbon abundance ratios ([C/Fe]) for carbon-enhanced metal-poor (CEMP) stars based on the application of artificial neural networks, regressions, and synthesis models to medium-resolution (1-2 Å) spectra and J-K colors. We calibrate this method by comparison with metallicities and carbon abundance determinations for 118 stars with available high-resolution analyses reported in the recent literature. The neural network and regression approaches make use of a previously defined set of line-strength indices quantifying the strength of the Ca II K line and the CH G band, in conjunction with J-K colors from the Two Micron All Sky Survey Point Source Catalog. The use of near-IR colors, as opposed to broadband B-V colors, is required because of the potentially large affect of strong molecular carbon bands on bluer color indices. We also explore the practicality of obtaining estimates of carbon abundances for metal-poor stars from the spectral information alone, i.e., without the additional information provided by photometry, as many future samples of CEMP stars may lack such data. We find that although photometric information is required for the estimation of [Fe/H], it provides little improvement in our derived estimates of [C/Fe], and hence, estimates of carbon-to-iron ratios based solely on line indices appear sufficiently accurate for most purposes. Although we find that the spectral synthesis approach yields the most accurate estimates of [C/Fe], in particular for the stars with the strongest molecular bands, it is only marginally better than is obtained from the line index approaches. Using these methods we are able to reproduce the previously measured [Fe/H] and [C/Fe] determinations with an accuracy of ~0.25 dex for stars in the metallicity interval -5.5<=[Fe/H]<=-1.0 and with 0.2<=(J-K)0<=0.8. At higher metallicity, the Ca II K line begins to saturate, especially for the cool stars in

  3. Metal-Poor, Strongly Star-Forming Galaxies in the DEEP2 Survey: The Relationship Between Stellar Mass, Temperature-Based Metallicity, and Star Formation Rate

    NASA Technical Reports Server (NTRS)

    Ly, Chun; Rigby, Jane R.; Cooper, Michael; Yan, Renbin

    2015-01-01

    We report on the discovery of 28 redshift (z) approximately 0.8 metal-poor galaxies in DEEP2. These galaxies were selected for their detection of the weak [O (sub III)] lambda 4363 emission line, which provides a "direct" measure of the gas-phase metallicity. A primary goal for identifying these rare galaxies is to examine whether the fundamental metallicity relation (FMR) between stellar mass, gas metallicity, and star formation rate (SFR) extends to low stellar mass and high SFR. The FMR suggests that higher SFR galaxies have lower metallicity (at fixed stellar mass). To test this trend, we combine spectroscopic measurements of metallicity and dust-corrected SFRs, with stellar mass estimates from modeling the optical photometry. We find that these galaxies are 1.05 plus or minus 0.61 decimal exponent (dex) above the redshift (z) approximately equal to 1 stellar mass-SFR relation, and 0.23 plus or minus 0.23 decimal exponent (dex) below the local mass-metallicity relation. Relative to the FMR, the latter offset is reduced to 0.01 decimal exponent (dex), but significant dispersion remains (0.29 decimal exponent (dex) with 0.16 decimal exponent (dex) due to measurement uncertainties). This dispersion suggests that gas accretion, star formation and chemical enrichment have not reached equilibrium in these galaxies. This is evident by their short stellar mass doubling timescale of approximately 100 (sup plus 310) (sub minus 75) million years that suggests stochastic star formation. Combining our sample with other redshift (z) of approximately 1 metal-poor galaxies, we find a weak positive SFR-metallicity dependence (at fixed stellar mass) that is significant at 97.3 percent confidence. We interpret this positive correlation as recent star formation that has enriched the gas, but has not had time to drive the metal-enriched gas out with feedback mechanisms.

  4. The history of chemical enrichment and the sites of early nucleosynthesis: CNO abundances of galactic carbon-enhanced metal-poor stars

    NASA Astrophysics Data System (ADS)

    Kennedy, Catherine R.

    This dissertation focuses on abundance analyses of carbon-enhanced metal-poor (CEMP) Galactic halo stars. Different methods for determining carbon, nitrogen, oxygen, and also some barium abundances are described. The study of these abundances in such stars serves to investigate the means by which the Universe became enriched in metals. Due to the different kinds of CEMP stars observed in the Milky Way, it can only be assumed that there is certainly more than one method of carbon-enhancement at early times. Complete abundance analyses for as many of these archaeological relics as possible are needed in order to constrain the astrophysical sites of early carbon production. There are three main parts of this dissertation. The first part describes new techniques to determine oxygen abundances from spectra of the near-infrared molecular CO bands. With the near-IR OSIRIS spectrograph on the SOAR 4.1-m telescope, 57 CEMP stars were observed. A wide range of oxygen abundances were estimated, and the results were statistically compared to high-resolution estimates for both carbon-enhanced and carbon-normal metal-poor stars. Abundance patterns of the sample stars were compared to yield predictions for very metal-poor asymptotic giant branch (AGB) stars. The majority of the sample exhibit patterns consistent with CEMP stars having s-process-element enhancements, and thus have very likely been polluted by carbon- and oxygen-enhanced material transferred from a metal-poor AGB companion. The second part delineates a new survey effort implemented in order to identify new CEMP stars. For the initial pilot study, a new selection technique was developed based solely on the strength of the CH G band at 4300 A. This technique eliminated previous temperature and metallicity biases present in other CEMP surveys. Observations of the pilot sample were carried out with the Goodman HTS spectrograph on the SOAR 4.1-m telescope. Of the over 120 candidate stars observed, over 35% were found to

  5. Stellar yields of rotating first stars. I. Yields of weak supernovae and abundances of carbon-enhanced hyper-metal-poor stars

    SciTech Connect

    Takahashi, Koh; Umeda, Hideyuki; Yoshida, Takashi

    2014-10-10

    We perform a stellar evolution simulation of first stars and calculate stellar yields from the first supernovae. The initial masses are taken from 12 to 140 M {sub ☉} to cover the whole range of core-collapse supernova progenitors, and stellar rotation is included, which results in efficient internal mixing. A weak explosion is assumed in supernova yield calculations, thus only outer distributed matter, which is not affected by the explosive nucleosynthesis, is ejected in the models. We show that the initial mass and the rotation affect the explosion yield. All the weak explosion models have abundances of [C/O] larger than unity. Stellar yields from massive progenitors of >40-60 M {sub ☉} show enhancement of Mg and Si. Rotating models yield abundant Na and Al, and Ca is synthesized in nonrotating heavy massive models of >80 M {sub ☉}. We fit the stellar yields to the three most iron-deficient stars and constrain the initial parameters of the mother progenitor stars. The abundance pattern in SMSS 0313–6708 is well explained by 50-80 M {sub ☉} nonrotating models, rotating 30-40 M {sub ☉} models well fit the abundance of HE 0107-5240, and both nonrotating and rotating 15-40 M {sub ☉} models explain HE 1327-2326. The presented analysis will be applicable to other carbon-enhanced hyper-metal-poor stars observed in the future. The abundance analyses will give valuable information about the characteristics of the first stars.

  6. Young and Waltzing Binary Stars

    NASA Astrophysics Data System (ADS)

    2001-10-01

    current ESO-ESA CERN educational programme on "Life in the Universe". [3] In the case of exoplanets, the planet itself is not visible, but the spectral lines from the star are seen to wobble due to the gravitational influence of the planet, cf. ESO PR 07/01. [4] Several ESO Press Releases concern observations of the element Lithium in stars, e.g., PR 03/99 (in a giant star), PR 08/00 (in a metal-poor star) and PR 10/01 (from a "swallowed" exoplanet).

  7. Modeling Binary Neutron Stars

    NASA Astrophysics Data System (ADS)

    Park, Conner; Read, Jocelyn; Flynn, Eric; Lockett-Ruiz, Veronica

    2016-03-01

    Gravitational waves, predicted by Einstein's Theory of Relativity, are a new frontier in astronomical observation we can use to observe phenomena in the universe. Laser Interferometer Gravitational wave Observatory (LIGO) is currently searching for gravitational wave signals, and requires accurate predictions in order to best extract astronomical signals from all other sources of fluctuations. The focus of my research is in increasing the accuracy of Post-Newtonian models of binary neutron star coalescence to match the computationally expensive Numerical models. Numerical simulations can take months to compute a couple of milliseconds of signal whereas the Post-Newtonian can generate similar signals in seconds. However the Post-Newtonian model is an approximation, e.g. the Taylor T4 Post-Newtonian model assumes that the two bodies in the binary neutron star system are point charges. To increase the effectiveness of the approximation, I added in tidal effects, resonance frequencies, and a windowing function. Using these observed effects from simulations significantly increases the Post-Newtonian model's similarity to the Numerical signal.

  8. AN INFRARED CENSUS OF DUST IN NEARBY GALAXIES WITH SPITZER (DUSTiNGS). II. DISCOVERY OF METAL-POOR DUSTY AGB STARS

    SciTech Connect

    Boyer, Martha L.; Sonneborn, George; McQuinn, Kristen B. W.; Gehrz, Robert D.; Skillman, Evan; Barmby, Pauline; Bonanos, Alceste Z.; Gordon, Karl D.; Meixner, Margaret; Groenewegen, M. A. T.; Lagadec, Eric; Lennon, Daniel; Marengo, Massimo; McDonald, Iain; Zijlstra, Albert; Sloan, G. C.; Van Loon, Jacco Th.

    2015-02-10

    The DUSTiNGS survey (DUST in Nearby Galaxies with Spitzer) is a 3.6 and 4.5 μm imaging survey of 50 nearby dwarf galaxies designed to identify dust-producing asymptotic giant branch (AGB) stars and massive stars. Using two epochs, spaced approximately six months apart, we identify a total of 526 dusty variable AGB stars (sometimes called ''extreme'' or x-AGB stars; [3.6]-[4.5] > 0.1 mag). Of these, 111 are in galaxies with [Fe/H] < –1.5 and 12 are in galaxies with [Fe/H] < –2.0, making them the most metal-poor dust-producing AGB stars known. We compare these identifications to those in the literature and find that most are newly discovered large-amplitude variables, with the exception of ≈30 stars in NGC 185 and NGC 147, 1 star in IC 1613, and 1 star in Phoenix. The chemical abundances of the x-AGB variables are unknown, but the low metallicities suggest that they are more likely to be carbon-rich than oxygen-rich and comparisons with existing optical and near-IR photometry confirm that 70 of the x-AGB variables are confirmed or likely carbon stars. We see an increase in the pulsation amplitude with increased dust production, supporting previous studies suggesting that dust production and pulsation are linked. We find no strong evidence linking dust production with metallicity, indicating that dust can form in very metal-poor environments.

  9. Chemical Evolution of Binary Stars

    NASA Astrophysics Data System (ADS)

    Izzard, R. G.

    2013-02-01

    Energy generation by nuclear fusion is the fundamental process that prevents stars from collapsing under their own gravity. Fusion in the core of a star converts hydrogen to heavier elements from helium to uranium. The signature of this nucleosynthesis is often visible in a single star only for a very short time, for example while the star is a red giant or, in massive stars, when it explodes. Contrarily, in a binary system nuclear-processed matter can captured by a secondary star which remains chemically polluted long after its more massive companion star has evolved and died. By probing old, low-mass stars we gain vital insight into the complex nucleosynthesis that occurred when our Galaxy was much younger than it is today. Stellar evolution itself is also affected by the presence of a companion star. Thermonuclear novae and type Ia supernovae result from mass transfer in binary stars, but big questions still surround the nature of their progenitors. Stars may even merge and one of the challenges for the future of stellar astrophysics is to quantitatively understand what happens in such extreme systems. Binary stars offer unique insights into stellar, galactic and extragalactic astrophysics through their plethora of exciting phenomena. Understanding the chemical evolution of binary stars is thus of high priority in modern astrophysics.

  10. The Hobby-Eberly Telescope Chemical Abundances of Stars in the Halo (CASH) Project. I. The Lithium-, s-, and r-enhanced Metal-poor Giant HKII 17435-00532

    NASA Astrophysics Data System (ADS)

    Roederer, Ian U.; Frebel, Anna; Shetrone, Matthew D.; Allende Prieto, Carlos; Rhee, Jaehyon; Gallino, Roberto; Bisterzo, Sara; Sneden, Christopher; Beers, Timothy C.; Cowan, John J.

    2008-06-01

    We present the first detailed abundance analysis of the metal-poor giant HKII 17435-00532. This star was observed as part of the University of Texas long-term project Chemical Abundances of Stars in the Halo (CASH). A spectrum was obtained with the High Resolution Spectrograph (HRS) on the Hobby-Eberly Telescope with a resolving power of R ~ 15,000. Our analysis reveals that this star may be located on the red giant branch, red horizontal branch, or early asymptotic giant branch. We find that this metal-poor ([Fe/H] = - 2.2) star has an unusually high lithium abundance [log ɛ (Li) = + 2.1], mild carbon ([C/Fe] = + 0.7) and sodium ([Na/Fe] = + 0.6) enhancement, as well as enhancement of both s-process ([Ba/Fe] = + 0.8) and r-process ([Eu/Fe] = + 0.5) material. The high Li abundance can be explained by self-enrichment through extra mixing that connects the convective envelope with the outer regions of the H-burning shell. If so, HKII 17435-00532 is the most metal-poor star in which this short-lived phase of Li enrichment has been observed. The Na and n-capture enrichment can be explained by mass transfer from a companion that passed through the thermally pulsing AGB phase of evolution with only a small initial enrichment of r-process material present in the birth cloud. Despite the current nondetection of radial velocity variations (over ~180 days), it is possible that HKII 17435-00532 is in a long-period or highly inclined binary system, similar to other stars with similar n-capture enrichment patterns. 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.

  11. METAL-POOR, COOL GAS IN THE CIRCUMGALACTIC MEDIUM OF A z = 2.4 STAR-FORMING GALAXY: DIRECT EVIDENCE FOR COLD ACCRETION?

    SciTech Connect

    Crighton, Neil H. M.; Hennawi, Joseph F.; Prochaska, J. Xavier

    2013-10-20

    In our current galaxy formation paradigm, high-redshift galaxies are predominantly fueled by accretion of cool, metal-poor gas from the intergalactic medium. Hydrodynamical simulations predict that this material should be observable in absorption against background sightlines within a galaxy's virial radius, as optically thick Lyman limit systems (LLSs) with low metallicities. Here we report the discovery of exactly such a strong metal-poor absorber at an impact parameter R = 58 kpc from a star-forming galaxy at z = 2.44. Besides strong neutral hydrogen (N{sub H{sup 0}}=10{sup 19.50±0.16} cm{sup -2}) we detect neutral deuterium and oxygen, allowing a precise measurement of the metallicity: log{sub 10}(Z/Z {sub ☉}) = –2.0 ± 0.17, or (7-15) × 10{sup –3} solar. Furthermore, the narrow deuterium linewidth requires a cool temperature <20,000 K. Given the striking similarities between this system and the predictions of simulations, we argue that it represents the direct detection of a high-redshift cold-accretion stream. The low-metallicity gas cloud is a single component of an absorption system exhibiting a complex velocity, ionization, and enrichment structure. Two other components have metallicities >0.1 solar, 10 times larger than the metal-poor component. We conclude that the photoionized circumgalactic medium (CGM) of this galaxy is highly inhomogeneous: the majority of the gas is in a cool, metal-poor and predominantly neutral phase, but the majority of the metals are in a highly ionized phase exhibiting weak neutral hydrogen absorption but strong metal absorption. If such inhomogeneity is common, then high-resolution spectra and detailed ionization modeling are critical to accurately appraise the distribution of metals in the high-redshift CGM.

  12. Improved Co I log(gf) & hfs data and Abundance Determinations in the Photospheres of the Sun & Metal-poor Star HD 84937

    NASA Astrophysics Data System (ADS)

    Lawler, James E.; Sneden, Chris; Cowan, John J.

    2016-01-01

    New emission branching fraction measurements for 898 lines of the first spectrum of cobalt (Co I) from hollow cathode lamp spectra recorded with a 1m Fourier transform spectrometer (FTS) and a high resolution echelle spectrometer are reported. Radiative lifetimes from laser induced fluorescence measurements are combined with the branching fractions to determine accurate log(gf)s for the 898 lines. Selected published hyperfine structure (hfs) constants for levels of neutral Co are used to generate complete hfs component patterns for 195 transitions of Co I. These new laboratory data are applied to determine the Co abundance in the Sun and metal-poor star HD 84937, yielding log eps(Co) = 4.955 ± 0.007 (sigma = 0.059) based on 82 Co I lines and log eps(Co) = 2.785 ± 0.008 (sigma = 0.065) based on 66 Co I lines respectively. A Saha balance test on the photosphere of HD 84937 is performed using 16 UV lines of Co II, and good agreement is found with the Co I result in this metal-poor ([Fe I /H] = -2.32, [Fe II /H] = -2.32) dwarf star. The resulting value of [Co/Fe] = +0.14 supports a rise of Co/Fe at low metallicity that has been suggested in other studies. These new Co I data are part of a continuing effort to explore the limits of 1D/LTE photospheric models in metal-poor stars and to determine the relative abundance of Fe-group elements at low metallicity. This work is supported in part by NASA grant NNX10AN93G (J.E.L.), by NSF grant AST-1211055 (J.E.L.), and by NSF grant AST-1211585 (C.S.).

  13. BINARIES AMONG DEBRIS DISK STARS

    SciTech Connect

    Rodriguez, David R.; Zuckerman, B.

    2012-02-01

    We have gathered a sample of 112 main-sequence stars with known debris disks. We collected published information and performed adaptive optics observations at Lick Observatory to determine if these debris disks are associated with binary or multiple stars. We discovered a previously unknown M-star companion to HD 1051 at a projected separation of 628 AU. We found that 25% {+-} 4% of our debris disk systems are binary or triple star systems, substantially less than the expected {approx}50%. The period distribution for these suggests a relative lack of systems with 1-100 AU separations. Only a few systems have blackbody disk radii comparable to the binary/triple separation. Together, these two characteristics suggest that binaries with intermediate separations of 1-100 AU readily clear out their disks. We find that the fractional disk luminosity, as a proxy for disk mass, is generally lower for multiple systems than for single stars at any given age. Hence, for a binary to possess a disk (or form planets) it must either be a very widely separated binary with disk particles orbiting a single star or it must be a small separation binary with a circumbinary disk.

  14. HST/STIS abundances in the uranium rich metal poor star CS 31082-001: Constraints on the r-Process

    NASA Astrophysics Data System (ADS)

    Siqueira-Mello, C.; Spite, M.; Barbuy, B.; Spite, F.; Caffau, E.; Hill, V.; Wanajo, S.; Primas, F.; Plez, B.; Cayrel, R.; Andersen, J.; Nordström, B.; Sneden, C.; Beers, T. C.; Bonifacio, P.; François, P.; Molaro, P.

    2016-01-01

    As a brief revision, the origin of heavy elements and the role of abundances in extremely metal-poor (EMP) stars are presented. Heavy element abundances in the EMP uranium-rich star CS 31082-001 based mainly on near-UV spectra from STIS/HST are presented. These results should be useful for a better characterisation of the neutron exposure(s) that produced the r-process elements in this star, as well as a guide for improving nuclear data and astrophysical site modelling, given that the new element abundances not available in previous works (Ge, Mo, Lu, Ta, W, Re, Pt, Au, and Bi) make CS 31082-001 the most completely well studied r-II object, with a total of 37 detections of n-capture elements.

  15. Explaining the Ba, Y, Sr, and Eu abundance scatter in metal-poor halo stars: constraints to the r-process

    NASA Astrophysics Data System (ADS)

    Cescutti, G.; Chiappini, C.

    2014-05-01

    Context. Thanks to the heroic observational campaigns carried out in recent years we now have large samples of metal-poor stars for which measurements of detailed abundances exist. In particular, large samples of stars with metallicities -5 < [Fe/H] <-1 and measured abundances of Sr, Ba, Y, and Eu are now available. These data hold important clues on the nature of the contribution of the first stellar generations to the enrichment of our Galaxy. Aims: We aim to explain the scatter in Sr, Ba, Y, and Eu abundance ratio diagrams unveiled by the metal-poor halo stars. Methods: We computed inhomogeneous chemical evolution models for the Galactic halo assuming different scenarios for the r-process site: the electron-capture (EC) supernovae and the magnetorotationally driven (MRD) supernovae scenarios. We also considered models with and without the contribution of fast-rotating massive stars (spinstars) to an early enrichment by the s-process. A detailed comparison with the now large sample of stars with measured abundances of Sr, Ba, Y, Eu, and Fe is provided (both in terms of scatter plots and number distributions for several abundance ratios). Results: The scatter observed in these abundance ratios of the very metal-poor stars (with [Fe/H] <-2.5) can be explained by combining the s-process production in spinstars, and the r-process contribution coming from massive stars. For the r-process we have developed models for both the EC and the MRD scenarios that match the observations. Conclusions: With the present observational and theoretical constraints we cannot distinguish between the EC and the MRD scenarios in the Galactic halo. Independently of the r-process scenarios adopted, the production of elements by an s-process in spinstars is needed to reproduce the spread in abundances of the light neutron capture elements (Sr and Y) over heavy neutron capture elements (Ba and Eu). We provide a way to test our suggestions by means of the distribution of the Ba isotopic

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

    SciTech Connect

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

    2014-12-10

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

  17. Non-LTE line formation of Fe in late-type stars - III. 3D non-LTE analysis of metal-poor stars

    NASA Astrophysics Data System (ADS)

    Amarsi, A. M.; Lind, K.; Asplund, M.; Barklem, P. S.; Collet, R.

    2016-08-01

    As one of the most important elements in astronomy, iron abundance determinations need to be as accurate as possible. We investigate the accuracy of spectroscopic iron abundance analyses using archetypal metal-poor stars. We perform detailed 3D non-LTE radiative transfer calculations based on 3D hydrodynamic STAGGER model atmospheres, and employ a new model atom that includes new quantum-mechanical neutral hydrogen collisional rate coefficients. With the exception of the red giant HD122563, we find that the 3D non-LTE models achieve Fe I/Fe II excitation and ionization balance as well as not having any trends with equivalent width to within modelling uncertainties of 0.05 dex, all without having to invoke any microturbulent broadening; for HD122563 we predict that the current best parallax-based surface gravity is overestimated by 0.5 dex. Using a 3D non-LTE analysis, we infer iron abundances from the 3D model atmospheres that are roughly 0.1 dex higher than corresponding abundances from 1D MARCS model atmospheres; these differences go in the same direction as the non-LTE effects themselves.We make available grids of departure coefficients, equivalent widths and abundance corrections, calculated on 1D MARCS model atmospheres and horizontally- and temporally-averaged 3D STAGGER model atmospheres.

  18. The Chemical Abundances of Stars in the Halo (CASH) Project. III. A New Classification Scheme for Carbon-enhanced Metal-poor Stars with s-process Element Enhancement

    NASA Astrophysics Data System (ADS)

    Hollek, Julie K.; Frebel, Anna; Placco, Vinicius M.; Karakas, Amanda I.; Shetrone, Matthew; Sneden, Christopher; Christlieb, Norbert

    2015-12-01

    We present a detailed abundance analysis of 23 elements for a newly discovered carbon-enhanced metal-poor (CEMP) star, HE 0414-0343, from the Chemical Abundances of Stars in the Halo Project. Its spectroscopic stellar parameters are Teff = 4863 K, {log}g=1.25,\\ξ = 2.20 km s-1, and [Fe/H] = -2.24. Radial velocity measurements covering seven years indicate HE 0414-0343 to be a binary. HE 0414-0343 has {{[C/Fe]}}=1.44 and is strongly enhanced in neutron-capture elements but its abundances cannot be reproduced by a solar-type s-process pattern alone. Traditionally, it could be classified as a “CEMP-r/s” star. Based on abundance comparisons with asymptotic giant branch (AGB) star nucleosynthesis models, we suggest a new physically motivated origin and classification scheme for CEMP-s stars and the still poorly understood CEMP-r/s. The new scheme describes a continuous transition between these two so-far distinctly treated subgroups: CEMP-sA, CEMP-sB, and CEMP-sC. Possible causes for a continuous transition include the number of thermal pulses the AGB companion underwent, the effect of different AGB star masses on their nucleosynthetic yields, and physics that is not well approximated in 1D stellar models such as proton ingestion episodes and rotation. Based on a set of detailed AGB models, we suggest the abundance signature of HE 0414-0343 to have arisen from a >1.3 M⊙ mass AGB star and a late-time mass transfer that transformed HE 0414-0343 into a CEMP-sC star. We also find that the [Y/Ba] ratio well parametrizes the classification and can thus be used to easily classify any future such stars. 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.

  19. First stars. XVI. HST/STIS abundances of heavy elements in the uranium-rich metal-poor star CS 31082-001

    NASA Astrophysics Data System (ADS)

    Siqueira Mello, C.; Spite, M.; Barbuy, B.; Spite, F.; Caffau, E.; Hill, V.; Wanajo, S.; Primas, F.; Plez, B.; Cayrel, R.; Andersen, J.; Nordström, B.; Sneden, C.; Beers, T. C.; Bonifacio, P.; François, P.; Molaro, P.

    2013-02-01

    Context. The origin and site(s) of the r-process nucleosynthesis is(are) still not known with certainty, but complete, detailed r-element abundances offer our best clues. The few extremely metal-poor (EMP) stars with large r-element excesses allow us to study the r-process signatures in great detail, with minimal interference from later stages of Galactic evolution. CS 31082-001 is an outstanding example of the information that can be gathered from these exceptional stars. Aims: Here we aim to complement our previous abundance determinations for third-peak r-process elements with new and improved results for elements of the first and second r-process peaks from near-UV HST/STIS and optical UVES spectra. These results should provide new insight into the nucleosynthesis of the elements beyond iron. Methods: The spectra were analyzed by a consistent approach based on an OSMARCS LTE model atmosphere and the Turbospectrum spectrum synthesis code to derive abundances of heavy elements in CS 31082-001, and using updated oscillator strengths from the recent literature. Synthetic spectra were computed for all lines of the elements of interest to check for proper line intensities and possible blends in these crowded spectra. Our new abundances were combined with the best previous results to provide reliable mean abundances for the first and second-peak r-process elements. Results: We present new abundances for 23 neutron-capture elements, 6 of which - Ge, Mo, Lu, Ta, W, and Re - have not been reported before. This makes CS 31082-001 the most completely studied r-II star, with abundances for a total of 37 neutron-capture elements. We also present the first NLTE+3D abundance of lead in this star, further constraining the nature of the r-process. Based on observations made with the NASA/ESA Hubble Space Telescope (HST) through the Space Telescope Science Institute, operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555; and

  20. Improved Co I log(gf) Values and Abundance Determinations in the Photospheres of the Sun and Metal-poor Star HD 84937

    NASA Astrophysics Data System (ADS)

    Lawler, J. E.; Sneden, C.; Cowan, J. J.

    2015-09-01

    New emission branching fraction measurements for 898 lines of the first spectrum of cobalt (Co i) are determined from hollow cathode lamp spectra recorded with the National Solar Observatory 1 m Fourier transform spectrometer on Kitt Peak, AZ and a high-resolution echelle spectrometer. Published radiative lifetimes from laser induced fluorescence measurements are combined with the branching fractions to determine accurate absolute atomic transition probabilities for the 898 lines. Hyperfine structure (hfs) constants for levels of neutral Co in the literature are surveyed and selected values are used to generate complete hfs component patterns for 195 transitions of Co i. These new laboratory data are applied to determine the Co abundance in the Sun and metal-poor star HD 84937, yielding log ɛ(Co) = 4.955 ± 0.007 (σ = 0.059) based on 82 Co i lines and log ɛ(Co) = 2.785 ± 0.008 (σ = 0.065) based on 66 Co i lines, respectively. A Saha or ionization balance test on the photosphere of HD 84937 is performed using 16 UV lines of Co ii, and good agreement is found with the Co i result in this metal-poor ([Fe i/H] = -2.32, [Fe ii/H] = -2.32) dwarf star. The resulting value of [Co/Fe] = +0.14 supports a rise of Co/Fe at low metallicity that has been suggested in other studies.

  1. Behavior of [S/Fe] in Very Metal-Poor Stars from the S I 1.046 µm Lines Revisited

    NASA Astrophysics Data System (ADS)

    Takeda, Yoichi; Takada-Hidai, Masahide

    2012-04-01

    With an aim to establish how the [S/Fe] ratios behave in the very low metallicity regime down to [Fe/H] ˜ -3, we conducted a non-LTE analysis of near-IR S I triplet lines (multiplet 3) at 10455-10459 Å for a dozen very metal-poor stars (-3.2 ≲ [Fe/H] ≲ -1.9) based on new observational data obtained with IRCS+AO188 of the Subaru Telescope. It turned out that the resulting [S/ Fe] values are only moderately supersolar at [S/Fe] ˜ +0.2-0.5, irrespective of the metallicity. While this ``flat'' tendency is consistent with a trend recently corroborated by Spite et al. (2011, A&A, 528, A9) based on the S I 9212/9228/9237 lines (multiplet 1), it disaffirms the possibility of a conspicuously large [S/Fe] (up to ˜ +0.8) at [Fe/H] ˜ -3 that we once suggested in our first report on the S abundances of disk/halo stars using S I 10455-10459 lines (Takeda & Takada-Hidai 2011, PASJ, 63, S537). Given these new observational facts, we withdraw our previous argument, since we consider that [S/Fe]'s of some most metal-poor objects were overestimated in that paper; the likely cause for this failure is also discussed.

  2. BDB: The Binary Star Database

    NASA Astrophysics Data System (ADS)

    Dluzhnevskaya, O.; Kaygorodov, P.; Kovaleva, D.; Malkov, O.

    2014-05-01

    Description of the Binary star DataBase (BDB, http://bdb.inasan.ru), the world's principal database of binary and multiple systems of all observational types, is presented in the paper. BDB contains data on physical and positional parameters of 100,000 components of 40,000 systems of multiplicity 2 to 20, belonging to various observational types: visual, spectroscopic, eclipsing, etc. Information on these types of binaries is obtained from heterogeneous sources of data - astronomical and. Organization of the information is based on the careful cross-identification of the objects. BDB can be queried by star identifier, coordinates, and other parameters.

  3. Uncovering multiple Wolf-Rayet star clusters and the ionized ISM in Mrk 178: the closest metal-poor Wolf-Rayet H II galaxy

    NASA Astrophysics Data System (ADS)

    Kehrig, C.; Pérez-Montero, E.; Vílchez, J. M.; Brinchmann, J.; Kunth, D.; García-Benito, R.; Crowther, P. A.; Hernández-Fernández, J.; Durret, F.; Contini, T.; Fernández-Martín, A.; James, B. L.

    2013-07-01

    New integral field spectroscopy (IFS) has been obtained for the nearby metal-poor Wolf-Rayet (WR) galaxy Mrk 178 to examine the spatial correlation between its WR stars and the neighbouring ionized interstellar medium (ISM). The strength of the broad WR features and its low metallicity make Mrk 178 an intriguing object. We have detected the blue and red WR bumps in different locations across the field of view (˜300 pc × 230 pc) in Mrk 178. The study of the WR content has been extended, for the first time, beyond its brightest star-forming knot uncovering new WR star clusters. Using Large/Small Magellanic Cloud-template WR stars, we empirically estimate a minimum of ˜20 WR stars within the region sampled. Maps of the spatial distribution of the emission lines and of the physical-chemical properties of the ionized ISM have been created and analysed. Here, we refine the statistical methodology by Pérez-Montero et al. (2011) to probe the presence of variations in the ISM properties. An error-weighted mean of 12+log(O/H) = 7.72 ± 0.01 is taken as the representative oxygen abundance for Mrk 178. A localized N and He enrichment, spatially correlated with WR stars, is suggested by this analysis. Nebular He II λ4686 emission is shown to be spatially extended reaching well beyond the location of the WR stars. This spatial offset between WRs and He II emission can be explained based on the mechanical energy input into the ISM by the WR star winds, and does not rule out WR stars as the He II ionization source. We study systematic aperture effects on the detection and measurement of the WR features, using Sloan Digital Sky Survey spectra combined with the power of IFS. In this regard, the importance of targeting low metallicity nearby systems is discussed.

  4. The Michigan Binary Star Program

    NASA Astrophysics Data System (ADS)

    Lindner, Rudi P.

    2007-07-01

    At the end of the nineteenth century, William J. Hussey and Robert G. Aitken, both at Lick Observatory, began a systematic search for unrecorded binary stars with the aid of the 12" and 36" refracting telescopes at Lick Observatory. Aitken's work (and book on binary stars) are well known, Hussey's contributions less so. In 1905 Hussey, a Michigan engineering graduate, returned to direct the Ann Arbor astronomy program, and immediately he began to design new instrumentation for the study of binary stars and to train potential observers. For a time, he spent six months a year at the La Plata Observatory, where he discovered a number of new pairs and decided upon a major southern hemisphere campaign. He spent a decade obtaining the lenses for a large refractor, through the vicissitudes of war and depression. Finally, he obtained a site in South Africa, a 26" refractor, and a small corps of observers, but he died in London en route to fulfill his dream. His right hand man, Richard Rossiter, established the observatory and spent the next thirty years discovering and measuring binary stars: his personal total is a record for the field. This talk is an account of the methods, results, and utility of the extraordinary binary star factory in the veldt.

  5. The Diverse Origins of Neutron-capture Elements in the Metal-poor Star HD 94028: Possible Detection of Products of i-Process Nucleosynthesis

    NASA Astrophysics Data System (ADS)

    Roederer, Ian U.; Karakas, Amanda I.; Pignatari, Marco; Herwig, Falk

    2016-04-01

    We present a detailed analysis of the composition and nucleosynthetic origins of the heavy elements in the metal-poor ([Fe/H] = ‑1.62 ± 0.09) star HD 94028. Previous studies revealed that this star is mildly enhanced in elements produced by the slow neutron-capture process (s process; e.g., [Pb/Fe] = +0.79 ± 0.32) and rapid neutron-capture process (r process; e.g., [Eu/Fe] = +0.22 ± 0.12), including unusually large molybdenum ([Mo/Fe] = +0.97 ± 0.16) and ruthenium ([Ru/Fe] = +0.69 ± 0.17) enhancements. However, this star is not enhanced in carbon ([C/Fe] = ‑0.06 ± 0.19). We analyze an archival near-ultraviolet spectrum of HD 94028, collected using the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope, and other archival optical spectra collected from ground-based telescopes. We report abundances or upper limits derived from 64 species of 56 elements. We compare these observations with s-process yields from low-metallicity AGB evolution and nucleosynthesis models. No combination of s- and r-process patterns can adequately reproduce the observed abundances, including the super-solar [As/Ge] ratio (+0.99 ± 0.23) and the enhanced [Mo/Fe] and [Ru/Fe] ratios. We can fit these features when including an additional contribution from the intermediate neutron-capture process (i process), which perhaps operated through the ingestion of H in He-burning convective regions in massive stars, super-AGB stars, or low-mass AGB stars. Currently, only the i process appears capable of consistently producing the super-solar [As/Ge] ratios and ratios among neighboring heavy elements found in HD 94028. Other metal-poor stars also show enhanced [As/Ge] ratios, hinting that operation of the i process may have been common in the early Galaxy. These data are associated with Program 072.B-0585(A), PI. Silva. Some data presented in this paper were obtained from the Barbara A. Mikulski Archive for Space Telescopes (MAST). The Space Telescope Science Institute

  6. The Diverse Origins of Neutron-capture Elements in the Metal-poor Star HD 94028: Possible Detection of Products of i-Process Nucleosynthesis

    NASA Astrophysics Data System (ADS)

    Roederer, Ian U.; Karakas, Amanda I.; Pignatari, Marco; Herwig, Falk

    2016-04-01

    We present a detailed analysis of the composition and nucleosynthetic origins of the heavy elements in the metal-poor ([Fe/H] = -1.62 ± 0.09) star HD 94028. Previous studies revealed that this star is mildly enhanced in elements produced by the slow neutron-capture process (s process; e.g., [Pb/Fe] = +0.79 ± 0.32) and rapid neutron-capture process (r process; e.g., [Eu/Fe] = +0.22 ± 0.12), including unusually large molybdenum ([Mo/Fe] = +0.97 ± 0.16) and ruthenium ([Ru/Fe] = +0.69 ± 0.17) enhancements. However, this star is not enhanced in carbon ([C/Fe] = -0.06 ± 0.19). We analyze an archival near-ultraviolet spectrum of HD 94028, collected using the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope, and other archival optical spectra collected from ground-based telescopes. We report abundances or upper limits derived from 64 species of 56 elements. We compare these observations with s-process yields from low-metallicity AGB evolution and nucleosynthesis models. No combination of s- and r-process patterns can adequately reproduce the observed abundances, including the super-solar [As/Ge] ratio (+0.99 ± 0.23) and the enhanced [Mo/Fe] and [Ru/Fe] ratios. We can fit these features when including an additional contribution from the intermediate neutron-capture process (i process), which perhaps operated through the ingestion of H in He-burning convective regions in massive stars, super-AGB stars, or low-mass AGB stars. Currently, only the i process appears capable of consistently producing the super-solar [As/Ge] ratios and ratios among neighboring heavy elements found in HD 94028. Other metal-poor stars also show enhanced [As/Ge] ratios, hinting that operation of the i process may have been common in the early Galaxy. These data are associated with Program 072.B-0585(A), PI. Silva. Some data presented in this paper were obtained from the Barbara A. Mikulski Archive for Space Telescopes (MAST). The Space Telescope Science Institute is

  7. Binary Stars in SBS Survey

    NASA Astrophysics Data System (ADS)

    Erastova, L. K.

    2016-06-01

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

  8. THE ORIGINS OF LIGHT AND HEAVY R-PROCESS ELEMENTS IDENTIFIED BY CHEMICAL TAGGING OF METAL-POOR STARS

    SciTech Connect

    Tsujimoto, Takuji; Shigeyama, Toshikazu

    2014-11-01

    Growing interests in neutron star (NS) mergers as the origin of r-process elements have sprouted since the discovery of evidence for the ejection of these elements from a short-duration γ-ray burst. The hypothesis of a NS merger origin is reinforced by a theoretical update of nucleosynthesis in NS mergers successful in yielding r-process nuclides with A > 130. On the other hand, whether the origin of light r-process elements are associated with nucleosynthesis in NS merger events remains unclear. We find a signature of nucleosynthesis in NS mergers from peculiar chemical abundances of stars belonging to the Galactic globular cluster M15. This finding combined with the recent nucleosynthesis results implies a potential diversity of nucleosynthesis in NS mergers. Based on these considerations, we are successful in the interpretation of an observed correlation between [light r-process/Eu] and [Eu/Fe] among Galactic halo stars and accordingly narrow down the role of supernova nucleosynthesis in the r-process production site. We conclude that the tight correlation by a large fraction of halo stars is attributable to the fact that core-collapse supernovae produce light r-process elements while heavy r-process elements such as Eu and Ba are produced by NS mergers. On the other hand, stars in the outlier, composed of r-enhanced stars ([Eu/Fe] ≳ +1) such as CS22892-052, were exclusively enriched by matter ejected by a subclass of NS mergers that is inclined to be massive and consist of both light and heavy r-process nuclides.

  9. KELT-6b: A P ~ 7.9 Day Hot Saturn Transiting a Metal-poor Star with a Long-period Companion

    NASA Astrophysics Data System (ADS)

    Collins, Karen A.; Eastman, Jason D.; Beatty, Thomas G.; Siverd, Robert J.; Gaudi, B. Scott; Pepper, Joshua; Kielkopf, John F.; Johnson, John Asher; Howard, Andrew W.; Fischer, Debra A.; Manner, Mark; Bieryla, Allyson; Latham, David W.; Fulton, Benjamin J.; Gregorio, Joao; Buchhave, Lars A.; Jensen, Eric L. N.; Stassun, Keivan G.; Penev, Kaloyan; Crepp, Justin R.; Hinkley, Sasha; Street, Rachel A.; Cargile, Phillip; Mack, Claude E.; Oberst, Thomas E.; Avril, Ryan L.; Mellon, Samuel N.; McLeod, Kim K.; Penny, Matthew T.; Stefanik, Robert P.; Berlind, Perry; Calkins, Michael L.; Mao, Qingqing; Richert, Alexander J. W.; DePoy, Darren L.; Esquerdo, Gilbert A.; Gould, Andrew; Marshall, Jennifer L.; Oelkers, Ryan J.; Pogge, Richard W.; Trueblood, Mark; Trueblood, Patricia

    2014-02-01

    We report the discovery of KELT-6b, a mildly inflated Saturn-mass planet transiting a metal-poor host. The initial transit signal was identified in KELT-North survey data, and the planetary nature of the occulter was established using a combination of follow-up photometry, high-resolution imaging, high-resolution spectroscopy, and precise radial velocity measurements. The fiducial model from a global analysis including constraints from isochrones indicates that the V = 10.38 host star (BD+31 2447) is a mildly evolved, late-F star with T eff = 6102 ± 43 K, log g_\\star =4.07_{-0.07}^{+0.04}, and [Fe/H] = -0.28 ± 0.04, with an inferred mass M sstarf = 1.09 ± 0.04 M ⊙ and radius R_\\star =1.58_{-0.09}^{+0.16} \\,R_\\odot. The planetary companion has mass MP = 0.43 ± 0.05 M Jup, radius R_{P}=1.19_{-0.08}^{+0.13} \\,R_Jup, surface gravity log g_{P}=2.86_{-0.08}^{+0.06}, and density \\rho _{P}=0.31_{-0.08}^{+0.07}\\,g\\,cm^{-3}. The planet is on an orbit with semimajor axis a = 0.079 ± 0.001 AU and eccentricity e=0.22_{-0.10}^{+0.12}, which is roughly consistent with circular, and has ephemeris of T c(BJDTDB) = 2456347.79679 ± 0.00036 and P = 7.845631 ± 0.000046 days. Equally plausible fits that employ empirical constraints on the host-star parameters rather than isochrones yield a larger planet mass and radius by ~4}-7}. KELT-6b has surface gravity and incident flux similar to HD 209458b, but orbits a host that is more metal poor than HD 209458 by ~0.3 dex. Thus, the KELT-6 system offers an opportunity to perform a comparative measurement of two similar planets in similar environments around stars of very different metallicities. The precise radial velocity data also reveal an acceleration indicative of a longer-period third body in the system, although the companion is not detected in Keck adaptive optics images. KELT is a joint project of The Ohio State University, Vanderbilt University, and Lehigh University.

  10. IMPROVED Ni I log(gf) VALUES AND ABUNDANCE DETERMINATIONS IN THE PHOTOSPHERES OF THE SUN AND METAL-POOR STAR HD 84937

    SciTech Connect

    Wood, M. P.; Lawler, J. E.; Sneden, C.; Cowan, J. J. E-mail: jelawler@wisc.edu E-mail: cowan@nhn.ou.edu

    2014-04-01

    Atomic transition probability measurements for 371 Ni I lines in the UV through near-IR are reported. Branching fractions from data recorded using a Fourier transform spectrometer and a new echelle spectrograph are combined with published radiative lifetimes to determine these transition probabilities. Generally good agreement is found in comparisons to previously reported Ni I transition probability measurements. Use of the new echelle spectrograph, independent radiometric calibration methods, and independent data analysis routines enable a reduction of systematic errors and overall improvement in transition probability uncertainty over previous measurements. The new Ni I data are applied to high-resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to derive new, more accurate Ni abundances. Lines covering a wide range of wavelength and excitation potential are used to search for non-LTE effects.

  11. Spectroscopic Binary Frequency among CNO Stars

    NASA Astrophysics Data System (ADS)

    Levato, H.; Malaroda, S.; Garcia, B.; Morell, N.

    1987-05-01

    ABSTRACT. Radial velocity variations are- analyzed through a sample of 35 OB stars with CH anomalies.Bolton and Rogers' proposal (1978) is con- firmed in the sense that the OBN stars appear preferably in short-period binary systems, in contrast to OBC stars. : STARS-BINARY - STARS-EARLY TYPE

  12. A New View of the Dwarf Spheroidal Satellites of the Milky Way From VLT/FLAMES: Where are the Very Metal Poor Stars?

    SciTech Connect

    Helmi, Amina; Irwin, M.J.; Tolstoy, E.; Battaglia, G.; Hill, V.; Jablonka, P.; Venn, K.; Shetrone, M.; Letarte, B.; Arimoto, N.; Abel, T.; Francois, P.; Kaufer, A.; Primas, F.; Sadakane, K.; Szeifert, T.; /Kapteyn Astron. Inst., Groningen /Cambridge U., Inst. of Astron. /Meudon Observ. /LASTRO Observ. /Victoria U. /Texas U., McDonald Observ. /Tokyo, Astron. Observ. /KIPAC, Menlo Park /European Southern Obs., Chile /European Southern Observ. /Osaka Kyoiku U.

    2006-11-20

    As part of the Dwarf galaxies Abundances and Radial-velocities Team (DART) Programme, we have measured the metallicities of a large sample of stars in four nearby dwarf spheroidal galaxies (dSph): Sculptor, Sextans, Fornax and Carina. The low mean metal abundances and the presence of very old stellar populations in these galaxies have supported the view that they are fossils from the early Universe. However, contrary to naive expectations, we find a significant lack of stars with metallicities below [Fe/H] {approx} -3 dex in all four systems. This suggests that the gas that made up the stars in these systems had been uniformly enriched prior to their formation. Furthermore, the metal-poor tail of the dSph metallicity distribution is significantly different from that of the Galactic halo. These findings show that the progenitors of nearby dSph appear to have been fundamentally different from the building blocks of the Milky Way, even at the earliest epochs.

  13. Gravity darkening in binary stars

    NASA Astrophysics Data System (ADS)

    Espinosa Lara, F.; Rieutord, M.

    2012-11-01

    Context. Interpretation of light curves of many types of binary stars requires the inclusion of the (cor)relation between surface brightness and local effective gravity. Until recently, this correlation has always been modeled by a power law relating the flux or the effective temperature and the effective gravity, namely Teff ∝ geffβ . Aims: We look for a simple model that can describe the variations of the flux at the surface of stars belonging to a binary system. Methods: This model assumes that the energy flux is a divergence-free vector anti-parallel to the effective gravity. The effective gravity is computed from the Roche model. Results: After explaining in a simple manner the old result of Lucy (1967, Z. Astrophys., 65, 89), which says that β ~ 0.08 for solar type stars, we first argue that one-dimensional models should no longer be used to evaluate gravity darkening laws. We compute the correlation between log Teff and log geff using a new approach that is valid for synchronous, weakly magnetized, weakly irradiated binaries. We show that this correlation is approximately linear, validating the use of a power law relation between effective temperature and effective gravity as a first approximation. We further show that the exponent β of this power law is a slowly varying function, which we tabulate, of the mass ratio of the binary star and the Roche lobe filling factor of the stars of the system. The exponent β remains mostly in the interval [0.20,0.25] if extreme mass ratios are eliminated. Conclusions: For binary stars that are synchronous, weakly magnetized and weakly irradiated, the gravity darkening exponent is well constrained and may be removed from the free parameters of the models.

  14. WASP-37b: A 1.8 M{sub J} EXOPLANET TRANSITING A METAL-POOR STAR

    SciTech Connect

    Simpson, E. K.; Faedi, F.; Barros, S. C. C.; Pollacco, D.; Todd, I.; McCormac, J.; Brown, D. J. A.; Cameron, A. Collier; Miller, G. R. M.; Hebb, L.; Smalley, B.; Anderson, D. R.; Butters, O. W.; Hebrard, G.; Boisse, I.; Santerne, A.; Street, R. A.; Skillen, I.; Triaud, A. H. M. J.; Bento, J.

    2011-01-15

    We report on the discovery of WASP-37b, a transiting hot Jupiter orbiting an m{sub v} = 12.7 G2-type dwarf, with a period of 3.577469 {+-} 0.000011 d, transit epoch T{sub 0} = 2455338.6188 {+-} 0.0006 (HJD; dates throughout the paper are given in Coordinated Universal Time (UTC)), and a transit duration 0.1304{sup +0.0018}{sub -0.0017} d. The planetary companion has a mass M{sub p} = 1.80 {+-} 0.17 M{sub J} and radius R{sub p} = 1.16{sup +0.07}{sub -0.06} R{sub J}, yielding a mean density of 1.15{sup +0.12}{sub -0.15} {rho}{sub J}. From a spectral analysis, we find that the host star has M{sub *} = 0.925 {+-} 0.120 M{sub sun}, R{sub *} = 1.003 {+-} 0.053 R{sub sun}, T{sub eff} = 5800 {+-} 150 K, and [Fe/H] = -0.40 {+-} 0.12. WASP-37 is therefore one of the lowest metallicity stars to host a transiting planet.

  15. KELT-6b: A P ∼ 7.9 day hot Saturn transiting a metal-poor star with a long-period companion

    SciTech Connect

    Collins, Karen A.; Kielkopf, John F.; Eastman, Jason D.; Beatty, Thomas G.; Gaudi, B. Scott; Siverd, Robert J.; Pepper, Joshua; Stassun, Keivan G.; Johnson, John Asher; Howard, Andrew W.; Fulton, Benjamin J.; Fischer, Debra A.; Manner, Mark; Bieryla, Allyson; Latham, David W.; Gregorio, Joao; Buchhave, Lars A.; Jensen, Eric L. N.; Penev, Kaloyan; Crepp, Justin R.; and others

    2014-02-01

    We report the discovery of KELT-6b, a mildly inflated Saturn-mass planet transiting a metal-poor host. The initial transit signal was identified in KELT-North survey data, and the planetary nature of the occulter was established using a combination of follow-up photometry, high-resolution imaging, high-resolution spectroscopy, and precise radial velocity measurements. The fiducial model from a global analysis including constraints from isochrones indicates that the V = 10.38 host star (BD+31 2447) is a mildly evolved, late-F star with T {sub eff} = 6102 ± 43 K, log g{sub ⋆}=4.07{sub −0.07}{sup +0.04}, and [Fe/H] = –0.28 ± 0.04, with an inferred mass M {sub *} = 1.09 ± 0.04 M {sub ☉} and radius R{sub ⋆}=1.58{sub −0.09}{sup +0.16} R{sub ⊙}. The planetary companion has mass M{sub P} = 0.43 ± 0.05 M {sub Jup}, radius R{sub P}=1.19{sub −0.08}{sup +0.13} R{sub Jup}, surface gravity log g{sub P}=2.86{sub −0.08}{sup +0.06}, and density ρ{sub P}=0.31{sub −0.08}{sup +0.07} g cm{sup −3}. The planet is on an orbit with semimajor axis a = 0.079 ± 0.001 AU and eccentricity e=0.22{sub −0.10}{sup +0.12}, which is roughly consistent with circular, and has ephemeris of T {sub c}(BJD{sub TDB}) = 2456347.79679 ± 0.00036 and P = 7.845631 ± 0.000046 days. Equally plausible fits that employ empirical constraints on the host-star parameters rather than isochrones yield a larger planet mass and radius by ∼4)-7). KELT-6b has surface gravity and incident flux similar to HD 209458b, but orbits a host that is more metal poor than HD 209458 by ∼0.3 dex. Thus, the KELT-6 system offers an opportunity to perform a comparative measurement of two similar planets in similar environments around stars of very different metallicities. The precise radial velocity data also reveal an acceleration indicative of a longer-period third body in the system, although the companion is not detected in Keck adaptive optics images.

  16. Young and Waltzing Binary Stars

    NASA Astrophysics Data System (ADS)

    2001-10-01

    ADONIS Observes Low-mass Eclipsing System in Orion Summary A series of very detailed images of a binary system of two young stars have been combined into a movie . In merely 3 days, the stars swing around each other. As seen from the earth, they pass in front of each other twice during a full revolution, producing eclipses during which their combined brightness diminishes . A careful analysis of the orbital motions has now made it possible to deduce the masses of the two dancing stars . Both turn out to be about as heavy as our Sun. But while the Sun is about 4500 million years old, these two stars are still in their infancy. They are located some 1500 light-years away in the Orion star-forming region and they probably formed just 10 million years ago . This is the first time such an accurate determination of the stellar masses could be achieved for a young binary system of low-mass stars . The new result provides an important piece of information for our current understanding of how young stars evolve. The observations were obtained by a team of astronomers from Italy and ESO [1] using the ADaptive Optics Near Infrared System (ADONIS) on the 3.6-m telescope at the ESO La Silla Observatory. PR Photo 29a/01 : The RXJ 0529.4+0041 system before primary eclipse PR Photo 29b/01 : The RXJ 0529.4+0041 system at mid-primary eclipse PR Photo 29c/01 : The RXJ 0529.4+0041 system after primary eclipse PR Photo 29d/01 : The RXJ 0529.4+0041 system before secondary eclipse PR Photo 29e/01 : The RXJ 0529.4+0041 system at mid-secondary eclipse PR Photo 29f/01 : The RXJ 0529.4+0041 system after secondary eclipse PR Video Clip 06/01 : Video of the RXJ 0529.4+0041 system Binary stars and stellar masses Since some time, astronomers have noted that most stars seem to form in binary or multiple systems. This is quite fortunate, as the study of binary stars is the only way in which it is possible to measure directly one of the most fundamental quantities of a star, its mass. The mass of a

  17. On the necessity of composition-dependent low-temperature opacity in models of metal-poor asymptotic giant branch stars

    SciTech Connect

    Constantino, Thomas; Campbell, Simon; Lattanzio, John; Gil-Pons, Pilar

    2014-03-20

    The vital importance of composition-dependent low-temperature opacity in low-mass (M ≤ 3 M {sub ☉}) asymptotic giant branch (AGB) stellar models of metallicity Z ≥ 0.001 has recently been demonstrated. Its significance to more metal-poor, intermediate-mass (M ≥ 2.5 M {sub ☉}) models has yet to be investigated. We show that its inclusion in lower-metallicity models ([Fe/H] ≤–2) is essential and that there exists no threshold metallicity below which composition-dependent molecular opacity may be neglected. We find it to be crucial in all intermediate-mass models investigated ([Fe/H] ≤–2 and 2.5 ≤ M/M {sub ☉} ≤ 5), because of the evolution of the surface chemistry, including the orders of magnitude increase in the abundance of molecule-forming species. Its effect on these models mirrors that previously reported for higher-metallicity models—increase in radius, decrease in T {sub eff}, faster mass loss, shorter thermally pulsing AGB lifetime, reduced enrichment in third dredge-up products (by a factor of 3-10), and an increase in the mass limit for hot bottom burning. We show that the evolution of low-metallicity models with composition-dependent low-temperature opacity is relatively independent of initial metal abundance because its contribution to the opacity is far outweighed by changes resulting from dredge-up. Our results imply a significant reduction in the expected number of nitrogen-enhanced metal-poor stars, which may help explain their observed paucity. We note that these findings are partially a product of the macrophysics adopted in our models, in particular, the Vassiliadis and Wood mass loss rate which is strongly dependent on radius.

  18. Contact binary stars

    NASA Astrophysics Data System (ADS)

    Mochnacki, S. W.

    1981-04-01

    Densities, corrected primary colors, minimum periods, inferred masses, luminosities, and specific angular momenta are computed from data on 37 W Ursae Majoris systems. A-type systems, having lower densities and angular momenta than the W-type systems, are shown to be evolved, and a new class of contact binary is identified, the OO Aquilae systems, whose members have evolved into contact. Evolutionary grids based on the contact condition agree with observation, except in that the evolved A-type systems have lost more angular momentum than predicted by gravitational radiation alone. This is accounted for by stellar wind magnetic braking, which is shown to be effective on a shorter time scale and to be important in other kinds of binaries containing a cool, tidally coupled component.

  19. Evolution and CNO yields of Z = 10-5 stars and possible effects on carbon-enhanced metal-poor production

    NASA Astrophysics Data System (ADS)

    Gil-Pons, P.; Doherty, C. L.; Lau, H.; Campbell, S. W.; Suda, T.; Guilani, S.; Gutiérrez, J.; Lattanzio, J. C.

    2013-09-01

    Aims: Our main goals are to get a deeper insight into the evolution and final fates of intermediate-mass, extremely metal-poor (EMP) stars. We also aim to investigate the C, N, and O yields of these stars. Methods: Using the Monash University Stellar Evolution code MONSTAR we computed and analysed the evolution of stars of metallicity Z = 10-5 and masses between 4 and 9 M⊙, from their main sequence until the late thermally pulsing (super) asymptotic giant branch, TP-(S)AGB phase. Results: Our model stars experience a strong C, N, and O envelope enrichment either due to the second dredge-up process, the dredge-out phenomenon, or the third dredge-up early during the TP-(S)AGB phase. Their late evolution is therefore similar to that of higher metallicity objects. When using a standard prescription for the mass loss rates during the TP-(S)AGB phase, the computed stars are able to lose most of their envelopes before their cores reach the Chandrasekhar mass (mCh), so our standard models do not predict the occurrence of SNI1/2 for Z = 10-5 stars. However, we find that the reduction of only one order of magnitude in the mass-loss rates, which are particularly uncertain at this metallicity, would prevent the complete ejection of the envelope, allowing the stars to either explode as an SNI1/2 or become an electron-capture SN. Our calculations stop due to an instability near the base of the convective envelope that hampers further convergence and leaves remnant envelope masses between 0.25 M⊙ for our 4 M⊙ model and 1.5 M⊙ for our 9 M⊙ model. We present two sets of C, N, and O yields derived from our full calculations and computed under two different assumptions, namely, that the instability causes a practically instant loss of the remnant envelope or that the stars recover and proceed with further thermal pulses. Conclusions: Our results have implications for the early chemical evolution of the Universe and might provide another piece for the puzzle of the carbon

  20. Neutron Star Mass Distribution in Binaries

    NASA Astrophysics Data System (ADS)

    Lee, Chang-Hwan; Kim, Young-Min

    2016-05-01

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

  1. Chemical compositions of six metal-poor stars in the ultra-faint dwarf spheroidal galaxy Boötes I

    NASA Astrophysics Data System (ADS)

    Ishigaki, M. N.; Aoki, W.; Arimoto, N.; Okamoto, S.

    2014-02-01

    Context. Ultra-faint dwarf galaxies recently discovered around the Milky Way (MW) contain extremely metal-poor stars, and might represent the building blocks of low-metallicity components of the MW. Among them, the Boötes I dwarf spheroidal galaxy is of particular interest because of its exclusively old stellar population. Detailed chemical compositions of individual stars in this galaxy are a key to understanding formation and chemical evolution in the oldest galaxies in the Universe and their roles in building up the MW halo. Aims: Previous studies of the chemical abundances of Boötes I show discrepancies in elemental abundances between different authors, and thus a consistent picture of its chemical enrichment history has not yet been established. In the present work, we independently determine chemical compositions of six red giant stars in Boötes I, some of which overlap with those analyzed in the previous studies. Based on the derived abundances, we re-examine trends and scatters in elemental abundances and make comparisons with MW field halo stars and other dwarf spheroidal galaxies in the MW. Methods: High-resolution spectra of a sample of stars were obtained with the High Dispersion Spectrograph mounted on the Subaru Telescope. Abundances of 12 elements, including C, Na, α, Fe-peak, and neutron capture elements, were determined for the sample stars. The abundance results were compared to those in field MW halo stars previously obtained using an abundance analysis technique similar to the present study. Results: We confirm the low metallicity of Boo-094 ([Fe/H] = -3.4). Except for this star, the abundance ratios ([X/Fe]) of elements lighter than zinc are generally homogeneous with small scatter around the mean values in the metallicities spanned by the other five stars (-2.7 < [Fe/H] < -1.8). Specifically, all of the sample stars with [Fe/H] > -2.7 show no significant enhancement of carbon. The [Mg/Fe] and [Ca/Fe] ratios are almost constant with a

  2. IMPROVED Ti II log(gf) VALUES AND ABUNDANCE DETERMINATIONS IN THE PHOTOSPHERES OF THE SUN AND METAL-POOR STAR HD 84937

    SciTech Connect

    Wood, M. P.; Lawler, J. E.; Sneden, C.; Cowan, J. J. E-mail: jelawler@wisc.edu E-mail: cowan@nhn.ou.edu

    2013-10-01

    Atomic transition probability measurements for 364 lines of Ti II in the UV through near-IR are reported. Branching fractions from data recorded using a Fourier transform spectrometer (FTS) and a new echelle spectrometer are combined with published radiative lifetimes to determine these transition probabilities. The new results are in generally good agreement with previously reported FTS measurements. Use of the new echelle spectrometer, independent radiometric calibration methods, and independent data analysis routines enables a reduction of systematic errors and overall improvement in transition probability accuracy over previous measurements. The new Ti II data are applied to high-resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to derive new, more accurate Ti abundances. Lines covering a range of wavelength and excitation potential are used to search for non-LTE effects. The Ti abundances derived using Ti II for these two stars match those derived using Ti I and support the relative Ti/Fe abundance ratio versus metallicity seen in previous studies.

  3. New high S/N observations of the (6Li) /(7) Li blend in HD 84937 and two other metal-poor stars

    NASA Astrophysics Data System (ADS)

    Cayrel, R.; Spite, M.; Spite, F.; Vangioni-Flam, E.; Cassé, M.; Audouze, J.

    1999-03-01

    High signal to noise ratio spectra have been obtained with the GECKO spectrograph at CFHT, at a spectral resolution of 100 000, for three metal-poor stars in order to obtain more accurate abundances of the very fragile element (6) Li. For two newly observed stars, BD +42 2667 and BD +36 2165 it appears that the first may have a detectable amount of (6) Li, whereas no (6) Li is found in the second one. The S/N ratio of only a few hundreds obtained for these two faint stars preclude however a firm conclusion. For the third star, the well known object HD84937, a very high S/N of 650 per pixel (over 1000 per resolved spectral element) was obtained, yielding greatly improved accuracy over previous determinations. A value of (6) Li / (7) Li = 0.052 +/- 0.019 (one sigma) is obtained. We also conclude that the no- (6) Li assumption is ruled out at the 95 per cent level, even in the most permissive case, when a variation of all the other free parameters (wavelength zero-point, continuum location, macroturbulent broadening, abundance of (7) Li) is allowed. The possibility that the (6) Li feature is an artifact due to a once suspected binarity of HD 84937 is discussed, with the conclusion that this assumption is ruled out by the extant data on the radial velocity of the object. The (6) Li abundance is compared with recent models of formation of the light elements Li, Be and B. This comparison shows that (6) Li is either undepleted, or only moderately depleted in HD 84937, from its initial value. Under the assumption that the atmospheric depletion of (6) Li and (7) Li in stars is by slow mixing with hot layers (underneath the convective zone), in which these elements can burn, we conclude that the depletion of (7) Li by this mechanism in HD 84937 is less than 0.1 dex. This new upper limit to the efficiency of the depletion of (7) Li by slow mixing burning, in a star located on the Spite plateau, leads to a more secure estimation of the primordial abundance of (7) Li. However

  4. Improved V II Log(gf) Values, Hyperfine Structure Constants, and Abundance Determinations in the Photospheres of the Sun and Metal-poor Star HD 84937

    NASA Astrophysics Data System (ADS)

    Wood, M. P.; Lawler, J. E.; Den Hartog, E. A.; Sneden, C.; Cowan, J. J.

    2014-10-01

    New experimental absolute atomic transition probabilities are reported for 203 lines of V II. Branching fractions are measured from spectra recorded using a Fourier transform spectrometer and an echelle spectrometer. The branching fractions are normalized with radiative lifetime measurements to determine the new transition probabilities. Generally good agreement is found between this work and previously reported V II transition probabilities. Two spectrometers, independent radiometric calibration methods, and independent data analysis routines enable a reduction in systematic uncertainties, in particular those due to optical depth errors. In addition, new hyperfine structure constants are measured for selected levels by least squares fitting line profiles in the FTS spectra. The new V II data are applied to high resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to determine new, more accurate V abundances. Lines covering a range of wavelength and excitation potential are used to search for non-LTE effects. Very good agreement is found between our new solar photospheric V abundance, log ɛ(V) = 3.95 from 15 V II lines, and the solar-system meteoritic value. In HD 84937, we derive [V/H] = -2.08 from 68 lines, leading to a value of [V/Fe] = 0.24.

  5. Improved V I Log(gf) Values and Abundance Determinations in the Photospheres of the Sun and Metal-poor Star HD 84937

    NASA Astrophysics Data System (ADS)

    Lawler, J. E.; Wood, M. P.; Den Hartog, E. A.; Feigenson, T.; Sneden, C.; Cowan, J. J.

    2014-12-01

    New emission branching fraction measurements for 836 lines of the first spectrum of vanadium (V I) are determined from hollow cathode lamp spectra recorded with the National Solar Observatory 1 m Fourier transform spectrometer (FTS) and a high-resolution echelle spectrometer. The branching fractions are combined with recently published radiative lifetimes from laser-induced fluorescence measurements to determine accurate absolute atomic transition probabilities for the 836 lines. The FTS data are also used to extract new hyperfine structure A coefficients for 26 levels of neutral vanadium. These new laboratory data are applied to determine the V abundance in the Sun and metal-poor star HD 84937, yielding log ɛ(V) = 3.956 ± 0.004 (σ = 0.037) based on 93 V I lines and log ɛ(V) = 1.89 ± 0.03 (σ = 0.07) based on nine V I lines, respectively, using the Holweger-Müller 1D model. These new V I abundance values for the Sun and HD 84937 agree well with our earlier determinations based upon V II.

  6. Improved log(gf) Values for Lines of V I and V II, New Vanadium Abundances in the Sun and the Metal-Poor Star HD 84937

    NASA Astrophysics Data System (ADS)

    Lawler, James E.; Wood, Michael P.; Den Hartog, Elizabeth; Feigenson, Thomas; Sneden, Chris; Cowan, John J.

    2015-01-01

    New emission branching fraction measurements for 836 lines of the first spectrum of vanadium (V I) and 203 lines of V II are determined from hollow cathode lamp spectra recorded with the National Solar Observatory 1m Fourier transform spectrometer (FTS) and a high resolution echelle spectrometer. The branching fractions are combined with new radiative lifetimes from laser induced fluorescence measurements to determine accurate absolute atomic transition probabilities for 1039 lines of V I and V II. The FTS data are also used to extract new hyperfine structure A coefficients for both spectra. These new laboratory data are applied to determine the V abundance in the Sun and metal-poor star HD 84937, yielding log ɛ(V) = 3.96 (σ = 0.04) based on 93 V I lines and log ɛ(V) = 1.89 (σ = 0.07) based on nine V I lines respectively, and yielding log ɛ(V) = 3.95 (σ = 0.05) based on 15 V II lines and log ɛ(V) = 1.87 (σ = 0.07) based on 68 V II lines respectively1-3.1. Wood et al., ApJS 214:18 (2014), 2. Den Hartog et al. ApJS in press (2014), 3. Lawler et al. ApJS submitted (2014). This work is supported by NASA grant NNX10AN93G (JEL), NSF AST-1211055 (EDH & JEL), and NSF AST-1211585 (CS).

  7. IMPROVED V I log(gf) VALUES AND ABUNDANCE DETERMINATIONS IN THE PHOTOSPHERES OF THE SUN AND METAL-POOR STAR HD 84937

    SciTech Connect

    Lawler, J. E.; Wood, M. P.; Den Hartog, E. A.; Feigenson, T.; Sneden, C.; Cowan, J. J. E-mail: mpwood@wisc.edu E-mail: tfeigenson@wisc.edu E-mail: cowan@nhn.ou.edu

    2015-01-01

    New emission branching fraction measurements for 836 lines of the first spectrum of vanadium (V I) are determined from hollow cathode lamp spectra recorded with the National Solar Observatory 1 m Fourier transform spectrometer (FTS) and a high-resolution echelle spectrometer. The branching fractions are combined with recently published radiative lifetimes from laser-induced fluorescence measurements to determine accurate absolute atomic transition probabilities for the 836 lines. The FTS data are also used to extract new hyperfine structure A coefficients for 26 levels of neutral vanadium. These new laboratory data are applied to determine the V abundance in the Sun and metal-poor star HD 84937, yielding log ε(V) = 3.956 ± 0.004 (σ = 0.037) based on 93 V I lines and log ε(V) = 1.89 ± 0.03 (σ = 0.07) based on nine V I lines, respectively, using the Holweger-Müller 1D model. These new V I abundance values for the Sun and HD 84937 agree well with our earlier determinations based upon V II.

  8. IMPROVED V II log(gf) VALUES, HYPERFINE STRUCTURE CONSTANTS, AND ABUNDANCE DETERMINATIONS IN THE PHOTOSPHERES OF THE SUN AND METAL-POOR STAR HD 84937

    SciTech Connect

    Wood, M. P.; Lawler, J. E.; Den Hartog, E. A.; Sneden, C.; Cowan, J. J. E-mail: jelawler@wisc.edu E-mail: chris@verdi.as.utexas.edu

    2014-10-01

    New experimental absolute atomic transition probabilities are reported for 203 lines of V II. Branching fractions are measured from spectra recorded using a Fourier transform spectrometer and an echelle spectrometer. The branching fractions are normalized with radiative lifetime measurements to determine the new transition probabilities. Generally good agreement is found between this work and previously reported V II transition probabilities. Two spectrometers, independent radiometric calibration methods, and independent data analysis routines enable a reduction in systematic uncertainties, in particular those due to optical depth errors. In addition, new hyperfine structure constants are measured for selected levels by least squares fitting line profiles in the FTS spectra. The new V II data are applied to high resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to determine new, more accurate V abundances. Lines covering a range of wavelength and excitation potential are used to search for non-LTE effects. Very good agreement is found between our new solar photospheric V abundance, log ε(V) = 3.95 from 15 V II lines, and the solar-system meteoritic value. In HD 84937, we derive [V/H] = –2.08 from 68 lines, leading to a value of [V/Fe] = 0.24.

  9. Recent Minima of 193 Eclipsing Binary Stars

    NASA Astrophysics Data System (ADS)

    Samolyk, G.

    2016-06-01

    This paper continues the publication of times of minima for eclipsing binary stars from observations reported to the AAVSO Eclipsing Binary section. Times of minima from CCD observations received by the author from November 2015 through January 2016 are presented.

  10. Massive Stars in Interactive Binaries

    NASA Astrophysics Data System (ADS)

    St.-Louis, Nicole; Moffat, Anthony F. J.

    Massive stars start their lives above a mass of ~8 time solar, finally exploding after a few million years as core-collapse or pair-production supernovae. Above ~15 solar masses, they also spend most of their lives driving especially strong, hot winds due to their extreme luminosities. All of these aspects dominate the ecology of the Universe, from element enrichment to stirring up and ionizing the interstellar medium. But when they occur in close pairs or groups separated by less than a parsec, the interaction of massive stars can lead to various exotic phenomena which would not be seen if there were no binaries. These depend on the actual separation, and going from wie to close including colliding winds (with non-thermal radio emission and Wolf-Rayet dust spirals), cluster dynamics, X-ray binaries, Roche-lobe overflow (with inverse mass-ratios and rapid spin up), collisions, merging, rejuventation and massive blue stragglers, black-hole formation, runaways and gamma-ray bursts. Also, one wonders whether the fact that a massive star is in a binary affects its parameters compared to its isolated equivalent. These proceedings deal with all of these phenomena, plus binary statistics and determination of general physical properties of massive stars, that would not be possible with their single cousins. The 77 articles published in these proceedings, all based on oral talks, vary from broad revies to the lates developments in the field. About a third of the time was spent in open discussion of all participants, both for ~5 minutes after each talk and 8 half-hour long general dialogues, all audio-recorded, transcribed and only moderately edited to yield a real flavour of the meeting. The candid information in these discussions is sometimes more revealing than the article(s) that preceded them and also provide entertaining reading. The book is suitable for researchers and graduate students interested in stellar astrophysics and in various physical processes involved when

  11. An ancient metal-poor population in M32, and halo satellite accretion in M31, identified by RR Lyrae stars

    NASA Astrophysics Data System (ADS)

    Sarajedini, Ata; Yang, S.-C.; Monachesi, A.; Lauer, Tod R.; Trager, S. C.

    2012-09-01

    We present time series photometry of two fields near M32 using archival observations from the Advanced Camera for Surveys Wide Field Channel on-board the Hubble Space Telescope. One field is centred about 2 arcmin from M32, while the other is located 15 arcmin to the south-east of M31. The imaging covers a time baseline sufficient for the identification and characterization of a total number of 1139 RR Lyrae variables of which 821 are ab-type and 318 are c-type. In the field near M32, we find a radial gradient in the density of RR Lyraes relative to the centre of M32. This gradient is consistent with the surface brightness profile of M32, suggesting that a significant number of the RR Lyraes in this region belong to M32. This provides further confirmation that M32 contains an ancient stellar population formed around the same time as the oldest population in M31 and the Milky Way. The RR Lyrae stars in M32 exhibit a mean metal abundance of <[Fe/H]> ≈ -1.42 ± 0.02, which is ≈15 times lower than the metal abundance of the overall M32 stellar population. Moreover, the abundance of RR Lyrae stars normalized to the luminosity of M32 in the field analysed further indicates that the ancient metal-poor population in M32 represents only a very minor component of this galaxy, consistent with the 1-4.5 per cent in mass inferred from the colour-magnitude diagram analysis of Monachesi et al. We also find that the measured reddening of the RR Lyrae stars is consistent with M32 containing little or no dust. In the other field, we find unprecedented evidence for two populations of RR Lyraes in M31 as shown by two distinct sequences among the ab-type variables in the Bailey diagram. When interpreted in terms of metal abundance, one population exhibits a peak at [Fe/H] ≈ -1.3 and the other is at [Fe/H] ≈ -1.9. One possible interpretation of this result is that the more metal-rich population represents the dominant M31 halo, while the metal-poorer group could be a disrupted

  12. Three-dimensional hydrodynamical CO5BOLD model atmospheres of red giant stars. IV. Oxygen diagnostics in extremely metal-poor red giants with infrared OH lines

    NASA Astrophysics Data System (ADS)

    Dobrovolskas, V.; Kučinskas, A.; Bonifacio, P.; Caffau, E.; Ludwig, H.-G.; Steffen, M.; Spite, M.

    2015-04-01

    Context. Although oxygen is an important tracer of Galactic chemical evolution, measurements of its abundance in the atmospheres of the oldest Galactic stars are still scarce and rather imprecise. This is mainly because only a few spectral lines are available for the abundance diagnostics. At the lowest end of the metallicity scale, oxygen can only be measured in giant stars and in most of cases such measurements rely on a single forbidden [O i] 630 nm line that is very weak and frequently blended with telluric lines. Although molecular OH lines located in the ultraviolet and infrared could also be used for the diagnostics, oxygen abundances obtained from the OH lines and the [O i] 630 nm line are usually discrepant to a level of ~ 0.3-0.4 dex. Aims: We study the influence of convection on the formation of the infrared (IR) OH lines and the forbidden [O i] 630 nm line in the atmospheres of extremely metal-poor (EMP) red giant stars. Our ultimate goal is to clarify whether a realistic treatment of convection with state-of-the-art 3D hydrodynamical model atmospheres may help to bring the oxygen abundances obtained using the two indicators into closer agreement. Methods: We used high-resolution (R = 50 000) and high signal-to-noise ratio (S/N ≈ 200-600) spectra of four EMP red giant stars obtained with the VLT CRIRES spectrograph. For each EMP star, 4-14 IR OH vibrational-rotational lines located in the spectral range of 1514-1548 and 1595-1632 nm were used to determine oxygen abundances by employing standard 1D local thermodynamic equilibrium (LTE) abundance analysis methodology. We then corrected the 1D LTE abundances obtained from each individual OH line for the 3D hydrodynamical effects, which was done by applying 3D-1D LTE abundance corrections that were determined using 3D hydrodynamical CO5BOLD and 1D hydrostatic LHD model atmospheres. Results: We find that the influence of convection on the formation of [O i] 630 nm line in the atmospheres of EMP giants

  13. Terrestrial Planet Formation Around Close Binary Stars

    NASA Technical Reports Server (NTRS)

    Lissauer, Jack J.; Quintana, Elisa V.

    2003-01-01

    Most stars reside in multiple star systems; however, virtually all models of planetary growth have assumed an isolated single star. Numerical simulations of the collapse of molecular cloud cores to form binary stars suggest that disks will form within such systems. Observations indirectly suggest disk material around one or both components within young binary star systems. If planets form at the right places within such circumstellar disks, they can remain in stable orbits within the binary star systems for eons. We are simulating the late stages of growth of terrestrial planets around close binary stars, using a new, ultrafast, symplectic integrator that we have developed for this purpose. The sum of the masses of the two stars is one solar mass, and the initial disk of planetary embryos is the same as that used for simulating the late stages of terrestrial planet growth within our Solar System and in the Alpha Centauri wide binary star system. Giant planets &are included in the simulations, as they are in most simulations of the late stages of terrestrial planet accumulation in our Solar System. When the stars travel on a circular orbit with semimajor axis of up to 0.1 AU about their mutual center of mass, the planetary embryos grow into a system of terrestrial planets that is statistically identical to those formed about single stars, but a larger semimajor axis and/or a significantly eccentric binary orbit can lead to significantly more dynamically hot terrestrial planet systems.

  14. Cool Star Binaries with ALEXIS

    NASA Technical Reports Server (NTRS)

    Stern, Robert A.

    1998-01-01

    We proposed to search for high-temperature, flare-produced Fe XXIII line emission from active cool star binary systems using the ALEXIS all-sky survey. Previous X-ray transient searches with ARIEL V and HEAO-1, and subsequent shorter duration monitoring with the GINGA and EXOSAT satellites demonstrated that active binaries can produce large (EM approximately equals 10(exp 55-56/cu cm) X-ray flares lasting several hours or longer. Hot plasma from these flares at temperatures of 10(exp 7)K or more should produce Fe XXIII line emission at lambda = 132.8 A, very near the peak response of ALEXIS telescopes 1A and 2A. Our primary goals were to estimate flare frequency for the largest flares in the active binary systems, and, if the data permitted, to derive a distribution of flare energy vs. frequency for the sample as a whole. After a long delay due to the initial problems with the ALEXIS attitude control, the heroic efforts on the part of the ALEXIS satellite team enabled us to carry out this survey. However, the combination of the higher than expected and variable background in the ALEXIS detectors, and the lower throughput of the ALEXIS telescopes resulted in no convincing detections of large flares from the active binary systems. In addition, vignetting-corrected effective exposure times from the ALEXIS aspect solution were not available prior to the end of this contract; therefore, we were unable to convert upper limits measured in ALEXIS counts to the equivalent L(sub EUV).

  15. Terrestrial Planet Formation in Binary Star Systems

    NASA Technical Reports Server (NTRS)

    Lissauer, Jack J.; Quintana, Elisa V.; Chambers, John; Duncan, Martin J.; Adams, Fred

    2003-01-01

    Most stars reside in multiple star systems; however, virtually all models of planetary growth have assumed an isolated single star. Numerical simulations of the collapse of molecular cloud cores to form binary stars suggest that disks will form within such systems. Observations indirectly suggest disk material around one or both components within young binary star systems. If planets form at the right places within such circumstellar disks, they can remain in stable orbits within the binary star systems for eons. We are simulating the late stages of growth of terrestrial planets within binary star systems, using a new, ultrafast, symplectic integrator that we have developed for this purpose. We show that the late stages of terrestrial planet formation can indeed take place in a wide variety of binary systems and we have begun to delineate the range of parameter space for which this statement is true. Results of our initial simulations of planetary growth around each star in the alpha Centauri system and other 'wide' binary systems, as well as around both stars in very close binary systems, will be presented.

  16. IMPROVED log(gf) VALUES FOR LINES OF Ti I AND ABUNDANCE DETERMINATIONS IN THE PHOTOSPHERES OF THE SUN AND METAL-POOR STAR HD 84937 (ACCURATE TRANSITION PROBABILITIES FOR Ti I)

    SciTech Connect

    Lawler, J. E.; Guzman, A.; Wood, M. P.; Sneden, C.; Cowan, J. J. E-mail: adrianaguzman2014@u.northwestern.edu E-mail: chris@verdi.as.utexas.edu

    2013-04-01

    New atomic transition probability measurements for 948 lines of Ti I are reported. Branching fractions from Fourier transform spectra and from spectra recorded using a 3 m echelle spectrometer are combined with published radiative lifetimes from laser-induced fluorescence measurements to determine these transition probabilities. Generally good agreement is found in comparisons to the NIST Atomic Spectra Database. The new Ti I data are applied to re-determine the Ti abundance in the photospheres of the Sun and metal-poor star HD 84937 using many lines covering a range of wavelength and excitation potential to explore possible non-local thermal equilibrium effects. The variation of relative Ti/Fe abundance with metallicity in metal-poor stars observed in earlier studies is supported in this study.

  17. Close binary stars in globular clusters

    NASA Technical Reports Server (NTRS)

    Margon, Bruce

    1991-01-01

    Although close binary stars are thought theoretically to play a major role in globular cluster dynamics, virtually no non-degenerate close binaries are known in clusters. We review the status of observations in this area, and report on two new programs which are finally yielding candidate systems suitable for further study. One of the objects, a close eclipsing system in omega Cen, is also a big straggler, thus finally proving firm evidence that globular cluster blue stragglers really are binary stars.

  18. Encounters between binaries and neutron stars

    NASA Technical Reports Server (NTRS)

    Davies, M. B.; Benz, W.; Hills, J. G.

    1993-01-01

    We simulated encounters between a neutron star and primordial and tidal-capture binaries. In the case of encounters involving a tidal-capture binary, comprising a white dwarf and a main-sequence star, we find that most exchange encounters will produce a single merged object with the white dwarf and neutron star engulfed in a common envelope of gas donated by the main-sequence primary of the original binary. A small fraction of exchanges induce a merger of the white dwarf and main-sequence star, with this object being unbound to the neutron star, and the two objects having a large relative speed at infinity. For encounters involving a primordial binary, fewer encounters require the inclusion of hydrodynamical effects. Those involving collisions or close encounters tend to produce a binary comprised of the two merged stars (now forming one star) and the third star. The binaries produced typically have large enough separations to prevent the formation of a single merged object until subsequent stellar evolution of one of the components causes it to fill its Roche lobe. Clean exchanges produce binaries with large eccentricities; they are typically sufficiently wide to avoid circularization.

  19. VVV SURVEY NEAR-INFRARED PHOTOMETRY OF KNOWN BULGE RR LYRAE STARS: THE DISTANCE TO THE GALACTIC CENTER AND ABSENCE OF A BARRED DISTRIBUTION OF THE METAL-POOR POPULATION

    SciTech Connect

    Dékány, I.; Minniti, D.; Catelan, M.; Zoccali, M.; Hempel, M.; Saito, R. K.

    2013-10-20

    We have combined optical and near-infrared data of known RR Lyrae (RRL) stars in the bulge in order to study the spatial distribution of its metal-poor component by measuring precise reddening values and distances of 7663 fundamental-mode RRL stars with high-quality photometry. We obtain a distance to the Galactic center of R {sub 0} = 8.33 ± 0.05 ± 0.14 kpc. We find that the spatial distribution of the RRL stars differs from the structures traced by the predominantly metal-rich red clump (RC) stars. Unlike the RC stars, the RRL stars do not trace a strong bar, but have a more spheroidal, centrally concentrated distribution, showing only a slight elongation in its very center. We find a hint of bimodality in the density distribution at high southern latitudes (b < –5°), which needs to be confirmed by extending the areal coverage of the current census. The different spatial distributions of the metal-rich and metal-poor stellar populations suggest that the Milky Way has a composite bulge.

  20. Terrestrial Planet Formation in Binary Star Systems

    NASA Technical Reports Server (NTRS)

    Lissauer, J. J.; Quintana, E. V.; Adams, F. C.; Chambers, J. E.

    2006-01-01

    Most stars reside in binary/multiple star systems; however, previous models of planet formation have studied growth of bodies orbiting an isolated single star. Disk material has been observed around one or both components of various young close binary star systems. If planets form at the right places within such disks, they can remain dynamically stable for very long times. We have simulated the late stages of growth of terrestrial planets in both circumbinary disks around 'close' binary star systems with stellar separations ($a_B$) in the range 0.05 AU $\\le a_B \\le$ 0.4 AU and binary eccentricities in the range $0 \\le e \\le 0.8$ and circumstellar disks around individual stars with binary separations of tens of AU. The initial disk of planetary embryos is the same as that used for simulating the late stages of terrestrial planet growth within our Solar System and around individual stars in the Alpha Centauri system (Quintana et al. 2002, A.J., 576, 982); giant planets analogous to Jupiter and Saturn are included if their orbits are stable. The planetary systems formed around close binaries with stellar apastron distances less than or equal to 0.2 AU with small stellar eccentricities are very similar to those formed in the Sun-Jupiter-Saturn, whereas planetary systems formed around binaries with larger maximum separations tend to be sparser, with fewer planets, especially interior to 1 AU. Likewise, when the binary periastron exceeds 10 AU, terrestrial planets can form over essentially the entire range of orbits allowed for single stars with Jupiter-like planets, although fewer terrestrial planets tend to form within high eccentricity binary systems. As the binary periastron decreases, the radial extent of the terrestrial planet systems is reduced accordingly. When the periastron is 5 AU, the formation of Earth-like planets near 1 AU is compromised.

  1. Population studies. XIII. A new analysis of the Bidelman-Macconnell 'weak-metal' stars - confirmation of metal-poor stars in the thick disk of the galaxy

    SciTech Connect

    Beers, Timothy C.; Norris, John E.; Placco, Vinicius M.; Lee, Young Sun; Rossi, Silvia; Carollo, Daniela; Masseron, Thomas E-mail: jen@mso.anu.edu.au E-mail: youngsun@cnu.ac.kr E-mail: daniela.carollo@mq.edu.au

    2014-10-10

    A new set of very high signal-to-noise (S/N > 100/1), medium-resolution (R ∼ 3000) optical spectra have been obtained for 302 of the candidate 'weak-metal' stars selected by Bidelman and MacConnell. We use these data to calibrate the recently developed generalization of the Sloan Extension for Galactic Exploration and Understanding and Exploration (SEGUE) Stellar Parameter Pipeline, and obtain estimates of the atmospheric parameters (T {sub eff}, log g, and [Fe/H]) for these non-Sloan Digital Sky Survey/SEGUE data; we also obtain estimates of [C/Fe]. The new abundance measurements are shown to be consistent with available high-resolution spectroscopic determinations, and represent a substantial improvement over the accuracies obtained from the previous photometric estimates reported in Paper I of this series. The apparent offset in the photometric abundances of the giants in this sample noted by several authors is confirmed by our new spectroscopy; no such effect is found for the dwarfs. The presence of a metal-weak thick-disk (MWTD) population is clearly supported by these new abundance data. Some 25% of the stars with metallicities –1.8 < [Fe/H] ≤–0.8 exhibit orbital eccentricities e < 0.4, yet are clearly separated from members of the inner-halo population with similar metallicities by their location in a Lindblad energy versus angular momentum diagram. A comparison is made with recent results for a similar-size sample of Radial Velocity Experiment stars from Ruchti et al. We conclude, based on both of these samples, that the MWTD is real, and must be accounted for in discussions of the formation and evolution of the disk system of the Milky Way.

  2. Radio Detection of Neutron Star Binary Mergers

    NASA Astrophysics Data System (ADS)

    Bear, Brandon; Cardena, Brett; Dispoto, Dana; Papadopoulos, Joanna; Kavic, Michael; Simonetti, John

    2011-10-01

    Neutron star binary systems lose energy through gravitational radiation, and eventually merge. The gravitational radiation from the merger can be detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO). It is expected that a transient radio pulse will also be produced during the merger event. Detection of such radio transients would allow for LIGO to search for signals within constrained time periods. We calculate the LWA-1 detection rate of transient events from neutron star binary mergers. We calculate the detection rate of transient events from neutron star binary mergers for the Long Wavelength Array and the Eight-meter-wavelength Transient Array.

  3. Binary stars in the Orion Nebula Cluster

    NASA Astrophysics Data System (ADS)

    Köhler, R.; Petr-Gotzens, M. G.; McCaughrean, M. J.; Bouvier, J.; Duchêne, G.; Quirrenbach, A.; Zinnecker, H.

    2006-11-01

    We report on a high-spatial-resolution survey for binary stars in the periphery of the Orion Nebula Cluster, at 5-15 arcmin (0.65-2 pc) from the cluster center. We observed 228 stars with adaptive optics systems, in order to find companions at separations of 0.13 arcsec-1.12 arcsec (60-500 AU), and detected 13 new binaries. Combined with the results of Petr (1998), we have a sample of 275 objects, about half of which have masses from the literature and high probabilities to be cluster members. We used an improved method to derive the completeness limits of the observations, which takes into account the elongated point spread function of stars at relatively large distances from the adaptive optics guide star. The multiplicity of stars with masses >2 M⊙ is found to be significantly larger than that of low-mass stars. The companion star frequency of low-mass stars is comparable to that of main-sequence M-dwarfs, less than half that of solar-type main-sequence stars, and 3.5 to 5 times lower than in the Taurus-Auriga and Scorpius-Centaurus star-forming regions. We find the binary frequency of low-mass stars in the periphery of the cluster to be the same or only slightly higher than for stars in the cluster core (<3 arcmin from θ^1C Ori). This is in contrast to the prediction of the theory that the low binary frequency in the cluster is caused by the disruption of binaries due to dynamical interactions. There are two ways out of this dilemma: Either the initial binary frequency in the Orion Nebula Cluster was lower than in Taurus-Auriga, or the Orion Nebula Cluster was originally much denser and dynamically more active.

  4. Binary Stars in the Orion Nebula Cluster

    NASA Astrophysics Data System (ADS)

    Köhler, Rainer; Petr-Gotzens, Monika G.; McCaughrean, Mark J.; Bouvier, Jerome; Duchêne, Gaspard; Quirrenbach, Andreas; Zinnecker, Hans

    2007-08-01

    We report on a high-spatial-resolution survey for binary stars in the periphery of the Orion Nebula Cluster, at 5 - 15 arcmin (0.65 - 2 pc) from the cluster center. We observed 228 stars with adaptive optics systems, in order to find companions at separations of 0.13 - 1.12 arcsec (60 - 500 AU), and detected 13 new binaries. Combined with the results of Petr (1998), we have a sample of 275 objects, about half of which have masses from the literature and high probabilities to be cluster members. We used an improved method to derive the completeness limits of the observations, which takes into account the elongated point spread function of stars at relatively large distances from the adaptive optics guide star. The multiplicity of stars with masses >2 Msun is found to be significantly larger than that of low-mass stars. The companion star frequency of low-mass stars is comparable to that of main-sequence M-dwarfs, less than half that of solar-type main-sequence stars, and 3.5 to 5 times lower than in the Taurus-Auriga and Scorpius-Centaurus star-forming regions. We find the binary frequency of low-mass stars in the periphery of the cluster to be the same or only slightly higher than for stars in the cluster core (<3 arcmin from θ1C Ori). This is in contrast to the prediction of the theory that the low binary frequency in the cluster is caused by the disruption of binaries due to dynamical interactions. There are two ways out of this dilemma: Either the initial binary frequency in the Orion Nebula Cluster was lower than in Taurus-Auriga, or the Orion Nebula Cluster was originally much denser and dynamically more active.

  5. Recent Minima of 171 Eclipsing Binary Stars

    NASA Astrophysics Data System (ADS)

    Samolyk, G.

    2015-12-01

    This paper continues the publication of times of minima for 171 eclipsing binary stars from observations reported to the AAVSO EB section. Times of minima from observations received by the author from March 2015 thru October 2015 are presented.

  6. Eclipsing Binary B-Star Mass Determinations

    NASA Astrophysics Data System (ADS)

    Townsend, Amanda; Eikenberry, Stephen S.

    2016-01-01

    B-stars in binary pairs provide a laboratory for key astrophysical measurements of massive stars, including key insights for the formation of compact objects (neutron stars and black holes). In their paper, Martayan et al (2004) find 23 Be binary star pairs in NGC2004 in the Large Magellanic Cloud, five of which are both eclipsing and spectroscopic binaries with archival data from VLT-Giraffe and photometric data from MACHO. By using the Wilson eclipsing binary code (e.g., Wilson, 1971), we can determine preliminary stellar masses of the binary components. We present the first results from this analysis. This study also serves as proof-of-concept for future observations with the Photonic Synthesis Telescope Array (Eikenberry et al., in prep) that we are currently building for low-cost, precision spectroscopic observations. With higher resolution and dedicated time for observations, we can follow-up observations of these Be stars as well as Be/X-ray binaries, for improved mass measurements of neutron stars and black holes and better constraints on their origin/formation.

  7. The X-Ray Luminosity Function of Low-mass X-Ray Binaries in Early-type Galaxies, Their Metal-rich, and Metal-poor Globular Clusters

    NASA Astrophysics Data System (ADS)

    Peacock, Mark B.; Zepf, Stephen E.

    2016-02-01

    We present the X-ray luminosity function (XLF) of low-mass X-ray binaries (LMXBs) in the globular clusters (GCs) and fields of seven early-type galaxies. These galaxies are selected to have both deep Chandra observations, which allow their LMXB populations to be observed to X-ray luminosities of 1037-1038 erg s-1, and Hubble Space Telescope optical mosaics that enable the X-ray sources to be separated into field LMXBs, GC LMXBs, and contaminating background and foreground sources. We find that at all luminosities the number of field LMXBs per stellar mass is similar in these galaxies. This suggests that the field LMXB populations in these galaxies are not effected by the GC specific frequency, and that properties such as binary fraction and the stellar initial mass function are either similar across the sample or change in a way that does not affect the number of LMXBs. We compare the XLF of the field LMXBs to that of the GC LMXBs and find that they are significantly different with a p-value of 3 × 10-6 (equivalent to 4.7σ for a normal distribution). The difference is such that the XLF of the GC LMXBs is flatter than that of the field LMXBs, with the GCs hosting relatively more bright sources and fewer faint sources. A comparison of the XLF of the metal-rich and metal-poor GCs hints that the metal-poor clusters may have more bright LMXBs, but the difference is not statistically significant.

  8. Contact binary stars as standard candles

    NASA Astrophysics Data System (ADS)

    Klagyivik, P.; Csizmadia, Sz.

    2004-06-01

    Rucinski (1996) suggested to use contact binary stars as standard candles. We investigated the properties of contact binary stars in order to search for possibility of their using as standard candles. For this purpose a catalogue of their light curve solution was compiled and on the basis of the catalogue data we calculated the rate of energy transfer between the two components. This allowed us to determine the mass-luminosity relation of the primary as well as secondary components in a contact binary and using Kepler's third law and the strict geometry a very reliable distance determination method was developed.

  9. Binary Star database BDB: datasets and services

    NASA Astrophysics Data System (ADS)

    Malkov, O. Yu.; Kaygorodov, P. V.; Koravleva, D. A.; Oblak, E.; Debray, B.

    Description of the Binary star DataBase (BDB, http://bdb.inasan.ru), the world's principal database of binary and multiple systems of all observational types, is presented in the paper. BDB contains data on physical and positional parameters of 100,000 components of 40,000 systems of multiplicity 2 to 20, belonging to various observational types: visual, spectroscopic, eclipsing, etc. Information on these types of binaries is obtained from heterogeneous sources of data astronomical catalogues and surveys. Organization of the information is based on the careful cross-identification of the objects. BDB can be queried by star identifier, coordinates, and other paramete

  10. IMPROVED LABORATORY TRANSITION PROBABILITIES FOR Ce II, APPLICATION TO THE CERIUM ABUNDANCES OF THE SUN AND FIVE r-PROCESS-RICH, METAL-POOR STARS, AND RARE EARTH LAB DATA SUMMARY

    SciTech Connect

    Lawler, J. E.; Den Hartog, E. A.; Sneden, C.; Cowan, J. J.; Ivans, I. I. E-mail: eadenhar@wisc.edu E-mail: cowan@nhn.ou.edu

    2009-05-15

    Recent radiative lifetime measurements accurate to {+-}5% using laser-induced fluorescence (LIF) on 43 even-parity and 15 odd-parity levels of Ce II have been combined with new branching fractions measured using a Fourier transform spectrometer (FTS) to determine transition probabilities for 921 lines of Ce II. This improved laboratory data set has been used to determine a new solar photospheric Ce abundance, log {epsilon} = 1.61 {+-} 0.01 ({sigma} = 0.06 from 45 lines), a value in excellent agreement with the recommended meteoritic abundance, log {epsilon} = 1.61 {+-} 0.02. Revised Ce abundances have also been derived for the r-process-rich metal-poor giant stars BD+17{sup 0}3248, CS 22892-052, CS 31082-001, HD 115444, and HD 221170. Between 26 and 40 lines were used for determining the Ce abundance in these five stars, yielding a small statistical uncertainty of {+-}0.01 dex similar to the solar result. The relative abundances in the metal-poor stars of Ce and Eu, a nearly pure r-process element in the Sun, matches r-process-only model predictions for solar system material. This consistent match with small scatter over a wide range of stellar metallicities lends support to these predictions of elemental fractions. A companion paper includes an interpretation of these new precision abundance results for Ce as well as new abundance results and interpretation for Pr, Dy, and Tm.

  11. Exploring the Birth of Binary Stars

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-08-01

    More than half of all stars are thought to be in binary or multiple star systems. But how do these systems form? The misaligned spins of some binary protostars might provide a clue.Two Formation ModelsIts hard to tell how multiple-star systems form, since these systems are difficult to observe in their early stages. But based on numerical simulations, there are two proposed models for the formation of stellar binaries:Turbulent fragmentationTurbulence within a single core leads to multiple dense clumps. These clumps independently collapse to form stars that orbit each other.Disk fragmentationGravitational instabilities in a massive accretion disk cause the formation of a smaller, secondary disk within the first, resulting in two stars that orbit each other.Log column density for one of the authors simulated binary systems, just after the formation of two protostars. Diamonds indicate the protostar positions. [Adapted from Offner et al. 2016]Outflows as CluesHow can we differentiate between these formation mechanisms? Led by Stella Offner (University of Massachusetts), a team of scientists has suggested that the key isto examine the alignment of the stars protostellar outflows jets that are often emitted from the poles of young, newly forming stars.Naively, wed expect that disk fragmentation would produce binary stars with common angular momentum. As the stars spins would be aligned, they would therefore also launch protostellar jets that were aligned with each other. Turbulent fragmentation, on the other hand, would cause the stars to have independent angular momentum. This would lead to randomly oriented spins, so the protostellar jets would be misaligned.Snapshots from the authors simulations. Left panel of each pair: column density; green arrows giveprotostellar spin directions. Right panel: synthetic observations produced from the simulations; cyan arrows giveprotostellar outflow directions. [Offner et al. 2016]Simulations of FragmentationIn order to better

  12. Last orbits of binary strange quark stars

    SciTech Connect

    Limousin, Francois; Gourgoulhon, Eric; Gondek-Rosinska, Dorota

    2005-03-15

    We present the first relativistic calculations of the final phase of inspiral of a binary system consisting of two stars built predominantly of strange quark matter (strange quark stars). We study the precoalescing stage within the Isenberg-Wilson-Mathews approximation of general relativity using a multidomain spectral method. A hydrodynamical treatment is performed under the assumption that the flow is either rigidly rotating or irrotational, taking into account the finite density at the stellar surface--a distinctive feature with respect to the neutron star case. The gravitational-radiation driven evolution of the binary system is approximated by a sequence of quasiequilibrium configurations at fixed baryon number and decreasing separation. We find that the innermost stable circular orbit (ISCO) is given by an orbital instability both for synchronized and irrotational systems. This contrasts with neutron stars for which the ISCO is given by the mass-shedding limit in the irrotational case. The gravitational wave frequency at the ISCO, which marks the end of the inspiral phase, is found to be {approx}1400 Hz for two irrotational 1.35 M{sub {center_dot}} strange stars and for the MIT bag model of strange matter with massless quarks and a bag constant B=60 MeV fm{sup -3}. Detailed comparisons with binary neutrons star models, as well as with third order post-Newtonian point-mass binaries are given.

  13. Chemical evolution of the Galactic bulge as traced by microlensed dwarf and subgiant stars. III. Detection of lithium in the metal-poor bulge dwarf MOA-2010-BLG-285S

    NASA Astrophysics Data System (ADS)

    Bensby, T.; Asplund, M.; Johnson, J. A.; Feltzing, S.; Meléndez, J.; Dong, S.; Gould, A.; Han, C.; Adén, D.; Lucatello, S.; Gal-Yam, A.

    2010-10-01

    Context. To study the evolution of Li in the Galaxy it is necessary to observe dwarf or subgiant stars. These are the only long-lived stars whose present-day atmospheric chemical composition reflects their natal Li abundances according to standard models of stellar evolution. Although Li has been extensively studied in the Galactic disk and halo, to date there has only been one uncertain detection of Li in an unevolved bulge star. Aims: Our aim with this study is to provide the first clear detection of Li in the Galactic bulge, based on an analysis of a dwarf star that has largely retained its initial Li abundance. Methods: We performed a detailed elemental abundance analysis of the bulge dwarf star MOA-2010-BLG-285S using a high-resolution and high signal-to-noise spectrum obtained with the UVES spectrograph at the VLT when the object was optically magnified during a gravitational microlensing event (visual magnification A~550 during observation). The Li abundance was determined through synthetic line profile fitting of the 7Li resonance doublet line at 670.8 nm. The results have been corrected for departures from LTE. Results: MOA-2010-BLG-285S is, at [Fe/H] = -1.23, the most metal-poor dwarf star detected so far in the Galactic bulge. Its old age (12.5 Gyr) and enhanced [α/Fe] ratios agree well with stars in the thick disk at similar metallicities. This star represents the first unambiguous detection of Li in a metal-poor dwarf star in the Galactic bulge. We find an NLTE corrected Li abundance of logɛ(Li) = 2.16, which is consistent with values derived for Galactic disk and halo dwarf stars at similar metallicities and temperatures. Conclusions: Our results show that there are no signs of Li enrichment or production in the Galactic bulge during its earliest phases. Observations of Li in other galaxies (ω Cen) and other components of the Galaxy suggest further that the Spite plateau is universal. Based on observations carried out at the European Southern

  14. Adiabatic Mass Loss Model in Binary Stars

    NASA Astrophysics Data System (ADS)

    Ge, H. W.

    2012-07-01

    Rapid mass transfer process in the interacting binary systems is very complicated. It relates to two basic problems in the binary star evolution, i.e., the dynamically unstable Roche-lobe overflow and the common envelope evolution. Both of the problems are very important and difficult to be modeled. In this PhD thesis, we focus on the rapid mass loss process of the donor in interacting binary systems. The application to the criterion of dynamically unstable mass transfer and the common envelope evolution are also included. Our results based on the adiabatic mass loss model could be used to improve the binary evolution theory, the binary population synthetic method, and other related aspects. We build up the adiabatic mass loss model. In this model, two approximations are included. The first one is that the energy generation and heat flow through the stellar interior can be neglected, hence the restructuring is adiabatic. The second one is that he stellar interior remains in hydrostatic equilibrium. We model this response by constructing model sequences, beginning with a donor star filling its Roche lobe at an arbitrary point in its evolution, holding its specific entropy and composition profiles fixed. These approximations are validated by the comparison with the time-dependent binary mass transfer calculations and the polytropic model for low mass zero-age main-sequence stars. In the dynamical time scale mass transfer, the adiabatic response of the donor star drives it to expand beyond its Roche lobe, leading to runaway mass transfer and the formation of a common envelope with its companion star. For donor stars with surface convection zones of any significant depth, this runaway condition is encountered early in mass transfer, if at all; but for main sequence stars with radiative envelopes, it may be encountered after a prolonged phase of thermal time scale mass transfer, so-called delayed dynamical instability. We identify the critical binary mass ratio for the

  15. A field guide to the binary stars

    NASA Astrophysics Data System (ADS)

    Trimble, V.

    1983-05-01

    Details and examples of the six phases of existence for a binary star system are described. The birth and pre-main-sequence contraction is generally obscured from observation by the presence of gas and dust clouds; it comprises 1/1000th of a system's lifetime. The main sequence, i.e., hydrogen burning, takes up to 90 pct of a star's lifetime, and has been detected in stars with masses ranging from 0.07-32 solar masses. In binary systems, the main sequence stars may or may not interact, or one companion may burn out before the other leaves the main sequence. The primary in a binary system expands to fill its Roche lobe before mass transfer begins, then continues on a Kelvin-Helmholtz time scale until the primary is smaller than the secondary, when transfer proceeds on a nuclear time scale. The depletion of hydrogen fuel or He ignition stops the mass transfer, leading to formation of a white dwarf, neutron star, or supernova that sends both the neutron star and the OB secondary off at high speeds. Back transfer can be initiated in a fifth phase and can produce black holes or dwarf novae, or supernovae. Finally, the system terminates when both stars are extinguished and fall into one another, which can also yield supernovae or black holes.

  16. Binary Origin of Blue Straggler Stars in Star Clusters

    NASA Astrophysics Data System (ADS)

    Xin, Yu

    2015-08-01

    Close-binary evolution is one of the major formation channels of blue straggler stars (BSSs). We present binary evolution models, including case-A and/or case-B mass transfer (MT) in the intermediate- and low-mass stars, to try to understand the binary origin of BSS populations in star clusters. With the help of Monte-Carlo simulations, we compared the distribution of our synthetic MT BSSs with observations in the color-magnitude diagram (CMD) of M67 and M30. The current results show that primordial binary MT can only contribute to a small part of BSSs in M67, and it can credibly explain the formation of the red-BSS sequence observed in the CMD of M30. We also analyzed the spectral properties of BSS populations in open clusters (OCs) based on the LAMOST data, and a small part of BSSs indeed present Carbon depletion compared with the main sequence stars, which indicate their binary origin. Unfortunately, a statistical resfult of how much the binary MT can contribute to BSS fomation in OCs still requires larger working sample.

  17. Interrupted Binary Mass Transfer in Star Clusters

    NASA Astrophysics Data System (ADS)

    Leigh, Nathan W. C.; Geller, Aaron M.; Toonen, Silvia

    2016-02-01

    Binary mass transfer (MT) is at the forefront of some of the most exciting puzzles of modern astrophysics, including SNe Ia, gamma-ray bursts, and the formation of most observed exotic stellar populations. Typically, the evolution is assumed to proceed in isolation, even in dense stellar environments such as star clusters. In this paper, we test the validity of this assumption via the analysis of a large grid of binary evolution models simulated with the SeBa code. For every binary, we calculate analytically the mean time until another single or binary star comes within the mean separation of the mass-transferring binary, and compare this timescale to the mean time for stable MT to occur. We then derive the probability for each respective binary to experience a direct dynamical interruption. The resulting probability distribution can be integrated to give an estimate for the fraction of binaries undergoing MT that are expected to be disrupted as a function of the host cluster properties. We find that for lower-mass clusters (≲ {10}4 {M}⊙ ), on the order of a few to a few tens of percent of binaries undergoing MT are expected to be interrupted by an interloping single, or more often binary, star, over the course of the cluster lifetime, whereas in more massive globular clusters we expect \\ll 1% to be interrupted. Furthermore, using numerical scattering experiments performed with the FEWBODY code, we show that the probability of interruption increases if perturbative fly-bys are considered as well, by a factor ˜2.

  18. Are All Dwarf Carbon Stars Binary?

    NASA Astrophysics Data System (ADS)

    Farihi, Jay; Harris, Hugh; Subasavage, John; Bergfors, Carolina; Green, Paul; Gansicke, Boris

    2014-08-01

    The origin of dwarf carbon stars is a persistent astrophysical curiosity dating back to 1977. Only giant stars dredge up interior carbon, and hence the discovery of an unevolved dwarf star with C/O >1 was a big surprise. Astronomers are no closer to understanding these rare and spectrally peculiar stars 37 years later(!). The bulk of dwarf carbon stars show no sign of an evolved companion necessary to account for their externally polluted atmospheres. These stars are sensitive tracers of Galactic chemical evolution and star formation, and provide strong constraints on the potential for carbon-dominated (single star) planetary systems. We propose to conclusively validate or refute the hypothetical binary nature of dwarf carbon stars, and hence their chemical and physical formation channel(s). For all binaries, we will initially constrain and eventually measure orbital periods. By determining their physical separation during the previous epoch of mass transfer, we will distinguish between the Roche lobe overflow and wind capture models for the creation of carbon dwarfs.

  19. The evolution of close binary stars

    NASA Astrophysics Data System (ADS)

    Tutukov, A. V.; Cherepashchuk, A. M.

    2016-05-01

    A review of our current understanding of the physics and evolution of close binary stars with various masses under the influence of the nuclear evolution of their components and their magnetic stellar winds is presented. The role of gravitational-wave radiation by close binaries on their evolution and the loss of their orbital angular momentum is also considered. The final stages in the evolution of close binary systems are described. The review also notes the main remaining tasks related to studies of the physics and evolution of various classes of close binaries, including analyses of collisions of close binaries and supermassive black holes in galactic nuclei. Such a collision could lead to the capture of one of the components by the black hole and the acceleration of the remaining component to relativistic speeds.

  20. Dynamics and Habitability in Binary Star Systems

    NASA Astrophysics Data System (ADS)

    Eggl, Siegfried; Georgakarakos, Nikolaos; Pilat-Lohinger, Elke

    2014-07-01

    Determining planetary habitability is a complex matter, as the interplay between a planet's physical and atmospheric properties with stellar insolation has to be studied in a self consistent manner. Standardized atmospheric models for Earth-like planets exist and are commonly accepted as a reference for estimates of Habitable Zones. In order to define Habitable Zone boundaries, circular orbital configurations around main sequence stars are generally assumed. In gravitationally interacting multibody systems, such as double stars, however, planetary orbits are forcibly becoming non circular with time. Especially in binary star systems even relatively small changes in a planet's orbit can have a large impact on habitability. Hence, we argue that a minimum model for calculating Habitable Zones in binary star systems has to include dynamical interactions.

  1. White dwarfs in Be star binary systems

    NASA Technical Reports Server (NTRS)

    Apparao, K. M. V.

    1991-01-01

    An evaluation is made of possible reasons for the persistent inability to identify white dwarf stars in the Be binary systems. It is noted that many Be stars exhibiting large optical enhancements may be Be + WD and Be + He systems, and that observations of pulsations in the H-alpha emission, as well as observation of time delays between enhancements of optical line and continuum, can identify such systems.

  2. Merger of Magnetized Binary Neutron Stars

    NASA Astrophysics Data System (ADS)

    Motl, Patrick M.; Anderson, Matthew; Lehner, Luis; Liebling, Steven L.; Hirschmann, Eric; Neilsen, David; Palenzuela, Carlos

    2016-01-01

    We present simulations of the merger of binary neutron star systems calculated with full general relativity and incorporating the global magnetic field structure for the stars evolved with resistive magnetohydrodynamics. We also incorporate the effects of neutrino transport and tabular equations of state to describe the degenerate matter. We gratefully acknowledge the support of NASA through the Astrophysics Theory Program grant NNX13AH01G.

  3. An electrically powered binary star?

    NASA Astrophysics Data System (ADS)

    Wu, Kinwah; Cropper, Mark; Ramsay, Gavin; Sekiguchi, Kazuhiro

    2002-03-01

    We propose a model for stellar binary systems consisting of a magnetic and a non-magnetic white dwarf pair which is powered principally by electrical energy. In our model the luminosity is caused by resistive heating of the stellar atmospheres arising from induced currents driven within the binary. This process is reminiscent of the Jupiter-Io system, but greatly increased in power because of the larger companion and stronger magnetic field of the primary. Electrical power is an alternative stellar luminosity source, following on from nuclear fusion and accretion. We find that this source of heating is sufficient to account for the observed X-ray luminosity of the 9.5-min binary RX J1914+24, and provides an explanation for its puzzling characteristics.

  4. Orbits of Six Binary Stars

    NASA Astrophysics Data System (ADS)

    Olevic, D.; Cvetkovic, Z.

    2005-04-01

    Preliminary orbital elements of binary systems WDS 03494-1956 = RST 2324, WDS 03513+2621 = A 1830, WDS 04093-2025 = RST 2333, WDS 06485-1226 = A 2935, WDS 07013-0906 = A 671, and WDS 18323-1439 = CHR 73 are presented. For all systems but WDS 18323-1439 the individual masses and dynamical parallaxes are derived.

  5. FU Orionis: A Binary Star?

    NASA Astrophysics Data System (ADS)

    Wang, Hongchi; Apai, Dániel; Henning, Thomas; Pascucci, Ilaria

    2004-01-01

    By using the Adaptive Optics with a Laser for Astronomy system at the 3.6 m telescope of the Calar Alto Observatory, we detected a faint red star in the apparent vicinity of FU Ori, the prototype of the FUor outburst stars. Independent confirmation of the detection is obtained from archival Probing the Universe with Enhanced Optics/Canada-France-Hawaii Telescope images. The separation between the companion candidate and FU Ori is 0.50", and their brightness contrast is around 4 mag. We discuss the possible nature of the newly detected star based on near-infrared photometry and its proper motion relative to FU Ori. The photometric data are consistent with a nearby late-type main-sequence star, a background giant star, and a pre-main-sequence star. On the basis of the proper motion and the stellar surface density in the direction toward FU Ori, we argue that the probabilities of the first two options are very low.

  6. Division G Commission 42: Close Binary Stars

    NASA Astrophysics Data System (ADS)

    Richards, Mercedes T.; Pribulla, Theodor; Ribas, Ignasi; Bradstreet, David H.; Dreschsel, Horst; Maceroni, Carla; Mikolajewska, Joanna; Munari, Ulisse; Prsa, Andrej; Scharfe, Colin; Southworth, John; Trimble, Virginia

    2016-04-01

    Commission 42 began life as Photometric Double Stars in 1948 at the 7th General Assembly in Zurich, under the presidency of Zdenek Kopal. As early as 1961, then General Secretary Lukas Plaut recommended a merger between C42 and C26, Double Stars, one of the original 32 commissions going back to 1919-22 (first president Aitken, assistant director at Lick). C42 became Close Binary Stars in 1970, at the 14th GA in Brighton (the first one I attended). Table 1 shows the presidents of C42, and vice presidents, from when the office started, through the history of the Commission.

  7. Nonparametric statistical modeling of binary star separations

    NASA Technical Reports Server (NTRS)

    Heacox, William D.; Gathright, John

    1994-01-01

    We develop a comprehensive statistical model for the distribution of observed separations in binary star systems, in terms of distributions of orbital elements, projection effects, and distances to systems. We use this model to derive several diagnostics for estimating the completeness of imaging searches for stellar companions, and the underlying stellar multiplicities. In application to recent imaging searches for low-luminosity companions to nearby M dwarf stars, and for companions to young stars in nearby star-forming regions, our analyses reveal substantial uncertainty in estimates of stellar multiplicity. For binary stars with late-type dwarf companions, semimajor axes appear to be distributed approximately as a(exp -1) for values ranging from about one to several thousand astronomical units. About one-quarter of the companions to field F and G dwarf stars have semimajor axes less than 1 AU, and about 15% lie beyond 1000 AU. The geometric efficiency (fraction of companions imaged onto the detector) of imaging searches is nearly independent of distances to program stars and orbital eccentricities, and varies only slowly with detector spatial limitations.

  8. Nonparametric statistical modeling of binary star separations

    NASA Astrophysics Data System (ADS)

    Heacox, William D.; Gathright, John

    1994-09-01

    We develop a comprehensive statistical model for the distribution of observed separations in binary star systems, in terms of distributions of orbital elements, projection effects, and distances to systems. We use this model to derive several diagnostics for estimating the completeness of imaging searches for stellar companions, and the underlying stellar multiplicities. In application to recent imaging searches for low-luminosity companions to nearby M dwarf stars, and for companions to young stars in nearby star-forming regions, our analyses reveal substantial uncertainty in estimates of stellar multiplicity. For binary stars with late-type dwarf companions, semimajor axes appear to be distributed approximately as a-1 for values ranging from about one to several thousand astronomical units. About one-quarter of the companions to field F and G dwarf stars have semimajor axes less than 1 AU, and about 15% lie beyond 1000 AU. The geometric efficiency (fraction of companions imaged onto the detector) of imaging searches is nearly independent of distances to program stars and orbital eccentricities, and varies only slowly with detector spatial limitations.

  9. THE STAR FORMATION HISTORY OF THE VERY METAL-POOR BLUE COMPACT DWARF I Zw 18 FROM HST/ACS DATA

    SciTech Connect

    Annibali, F.; Cignoni, M.; Tosi, M.; Clementini, G.; Contreras Ramos, R.; Fiorentino, G.; Van der Marel, R. P.; Aloisi, A.; Marconi, M.; Musella, I.

    2013-12-01

    We have derived the star formation history (SFH) of the blue compact dwarf galaxy I Zw 18 through comparison of deep HST/ACS data with synthetic color-magnitude diagrams (CMDs). A statistical analysis was implemented for the identification of the best-fit SFH and relative uncertainties. We confirm that I Zw 18 is not a truly young galaxy, having started forming stars earlier than ∼1 Gyr ago, and possibly at epochs as old as a Hubble time. In I Zw 18's main body we infer a lower limit of ≈2 × 10{sup 6} M {sub ☉} for the mass locked up in old stars. I Zw 18's main body has been forming stars very actively during the last ∼10 Myr, with an average star formation rate (SFR) as high as ≈1 M {sub ☉} yr{sup –1} (or ≈2 × 10{sup –5} M {sub ☉} yr{sup –1} pc{sup –2}). On the other hand, the secondary body was much less active at these epochs, in agreement with the absence of significant nebular emission. The high current SFR can explain the very blue colors and the high ionized gas content in I Zw 18, resembling primeval galaxies in the early universe. Detailed chemical evolution models are required to quantitatively check whether the SFH from the synthetic CMDs can explain the low measured element abundances, or if galactic winds with loss of metals are needed.

  10. Observational Investigations on Contact Binaries in Multiple-star Systems and Star Clusters

    NASA Astrophysics Data System (ADS)

    Liu, L.

    2013-01-01

    ER Cep is three times larger than that of the star at the turn-off point of the cluster's main-sequence, suggesting that ER Cep is at least a triple system. There is weak evidence showing that the system has another small cyclic oscillation with a period of 17.6 years. If this is true, ER Cep is likely to be a quadruple system. It is not surprise that such system can be found in an old open cluster like NGC 188. The periodic long-term increase of EQ Cep may be caused by mass transfer from the less massive component to the more massive one. As the mass ratio decreases, the system will evolve into a blue straggler. This conclusion is supported by the fact that 76% of the blue stragglers in NGC 188 are currently in binary systems. The values of the acceleration of gravity on the surface of V371 Cep reveal that this system is composed of two post main-sequence stars. It is the first example whose components are post main-sequence stars. Because of the short evolutionary time scale for the subgiants, V371 Cep is a rare object which will demonstrate a picture of a contact binary at the end of its evolution stage. (4) The contact binary QX And in the moderate-age open cluster NGC 752 has a very strong magnetic activity, with a period of about 2 years. (5) The contact binary V47 in the globular cluster M4 has an extreme mass ratio and a moderate contact factor. The mass ratio is the smallest one in this thesis. However, V53, which is also in the M4, is a system with a large mass ratio and a deep contact factor. It is meanwhile a blue straggler, which is a good target for the study of the merging binaries. (6) The contact binary V95 in the globular cluster 47 Tuc has an extreme mass ratio and a deep contact factor. The most interesting thing is that V95 shows strong magnetic activity in a metal poor cluster. (7) Through analyzing the data of the ASAS survey, we find that the distribution of the detached and semi-detached binaries tend to be located in the galactic plane

  11. Component Properties of T Tauri Star Binaries

    NASA Astrophysics Data System (ADS)

    Muzzio, Ryan; L. Prato, T. Allen, N. Wright-Garba, L. Biddle, J. McLane (Lowell Observatory), G. Schaefer (GSU & CHARA)

    2016-01-01

    This poster describes our study of the properties of individual components of young T Tauri binary stars. We observed about 100 multi-star systems in the near-infrared, within the relatively close star forming regions Taurus and Ophiuchus. Here we specifically focus on four systems in the Taurus sample, IS Tau, UZ Tau B, IW Tau, and Haro 6- 37 A. Their spectra were taken with the Keck 2 telescope's NIRSPEC spectrograph and the imaging data with the Keck 2 NIRC2 camera, both with adaptive optics. Properties that we determined include spectral type, radial velocity, vsini, veiling, and near-infrared colors. On the basis of these data, we estimate stellar and circumstellar disk properties for the subset of binaries presented here.

  12. The impact of IUE on binary star studies

    NASA Technical Reports Server (NTRS)

    Plavec, M. J.

    1981-01-01

    The use of IUE observations in the investigation of binary stars is discussed. The results of data analysis of several classes of binary systems are briefly reviewed including zeta Aurigae and VV Cephei stars, mu Sagittarii, epsilon Aurigae, beta Lyrae and the W Serpentis stars, symbiotic stars, and the Algols.

  13. A New Calibration of [Fe/H] and [C/Fe] Estimates for Medium-Resolution Spectra of Carbon-Enhanced Metal-Poor Stars

    NASA Astrophysics Data System (ADS)

    Kennedy, Catherine R.; Beers, T. C.; Marsteller, B.; Sivarani, T.; Rossi, S.; Plez, B.; Masseron, T.; Lucatello, S.

    2006-12-01

    In recent years it has become clear that a significant fraction (on the order of at least 20%) of Galactic halo stars with [Fe/H] < -2.0 exhibit strong enhancements of carbon, with [C/Fe] > +1.0. The availability of many thousands of medium-resolution spectra from previous (and ongoing) surveys such as the HK survey of Beers and colleagues, and the Hamburg/ESO Survey of Christlieb and collaborators, provide the opportunity to identify and quantify the distribution of [C/Fe] over a wide range of [Fe/H] and stellar evolutionary states. In order to quickly obtain this information, previous attempts have been made to develop a calibration of line index estimates of [Fe/H] and [C/Fe] based on the observed strengths of the CaII K line and the CH G-band feature. The methodology developed by Rossi et al. (2005) relied on a sample of some 120 stars with available high-resolution spectroscopic estimates of [Fe/H] and [C/Fe], as well as 2MASS J-K colors, to carry out such a calibration. Unfortunately, the sample of calibration objects did not include numerous stars with effective temperatures (and carbon abundances) over the full range that is required for some applications. Recently the numbers of potential calibration objects has increased dramatically, to over 500 stars, due to the completion of several large high-resolution spectroscopic studies (e.g., Barklem et al. 2005, Cohen et al. 2005, Spite et al. 2005, and Aoki et al. 2006). In addition, new carbon-enhanced model atmospheres from which synthetic spectra and colors can be estimated have become available. We explore the use of these new data and tools and develop a revised calibration that is expected to be superior in many respects to previous attempts.

  14. A Revised Calibration Of [Fe/H] And [C/Fe] Estimates For Medium Resolution Spectra Of Carbon Enhanced Metal Poor Stars

    NASA Astrophysics Data System (ADS)

    Kennedy, Catherine R.; Beers, T. C.; Marsteller, B.; Sivarani, T.; Rossi, S.; Plez, B.; Masseron, T.; Lucatello, S.

    2007-05-01

    In recent years it has become clear that a significant fraction (on the order of at least 20%) of Galactic halo stars with [Fe/H] < -2.0 exhibit strong enhancements of carbon, with [C/Fe] > +1.0. The availability of many thousands of medium-resolution spectra from previous (and ongoing) surveys such as the HK survey of Beers and colleagues, and the Hamburg/ESO Survey of Christlieb and collaborators, provide the opportunity to identify and quantify the distribution of [C/Fe] over a wide range of [Fe/H] and stellar evolutionary states. In order to quickly obtain this information, previous attempts have been made to develop a calibration of line index estimates of [Fe/H] and [C/Fe] based on the observed strengths of the CaII K line and the CH G-band feature. The methodology developed by Rossi et al. (2005) relied on a sample of some 120 stars with available high-resolution spectroscopic estimates of [Fe/H] and [C/Fe], as well as 2MASS J-K colors, to carry out such a calibration. Unfortunately, the sample of calibration objects did not include numerous stars with effective temperatures (and carbon abundances) over the full range that is required for some applications. Recently the numbers of potential calibration objects has increased dramatically, to over 500 stars, due to the completion of several large high-resolution spectroscopic studies (e.g., Barklem et al. 2005, Cohen et al. 2005, Spite et al. 2005, and Aoki et al. 2006). In addition, new carbon-enhanced model atmospheres from which synthetic spectra and colors can be estimated have become available. We explore the use of these new data and tools and develop a revised calibration that is expected to be superior in many respects to previous attempts.

  15. Transit Timing Variations In Binary Star Systems

    NASA Astrophysics Data System (ADS)

    Sansone, Eric; Haghighipour, N.

    2012-01-01

    We present the results of a study of the effect of a stellar companion on the transit timing variations (TTV) of a planetary system. The purpose of our study is to determine the ranges of the orbital elements of a secondary star for which the amplitude of a currently existing TTV is enhanced. We chose the system of Kepler 9 as this system represents the first planetary system detected by the transit timing variation method, and studied its TTVs by considering a hypothetical secondary star in this system. By varying the mass, semi-major axis, and eccentricity of the fictitious binary companion, we tested the stability of the known planets Kepler-9c and Kepler-9b and identified the region of the parameter-space for which the binary planetary system would be stable. We calculated TTVs for the two planets of the system for different values of the orbital elements of the secondary star and calculated its difference with the system's already existing TTVs. Results of our study indicate that the effect of the binary companion is significant only when the secondary star is in a highly eccentric orbit and/or the planets of the system are within the range of Super-Earth or terrestrial sizes. This work was funded by the National Science Foundation in the form of a Research Experience for Undergraduates program at the University of Hawaii at Manoa.

  16. The superwind mass-loss rate of the metal-poor carbon star LI-LMC 1813 in the LMC cluster KMHK 1603

    NASA Astrophysics Data System (ADS)

    van Loon, Jacco Th.; Marshall, Jonathan R.; Matsuura, Mikako; Zijlstra, Albert A.

    2003-06-01

    LI-LMC 1813 is a dust-enshrouded asymptotic giant branch (AGB) star, located in the small open cluster KMHK 1603 near the rim of the Large Magellanic Cloud (LMC). Optical and infrared photometry between 0.5 and 60 μm is obtained to constrain the spectral energy distribution of LI-LMC 1813. Near-infrared spectra unambiguously show it to be a carbon star. Modelling with the radiation transfer code DUSTY yields accurate values for the bolometric luminosity, L= 1.5 × 104 Lsolar, and mass-loss rate, . On the basis of colour-magnitude diagrams, the age of the cluster KMHK 1603 is estimated to be t= 0.9-1.0 Gyr, which implies a zero-age main-sequence mass for LI-LMC 1813 of MZAMS= 2.2 +/- 0.1 Msolar. This makes LI-LMC 1813 arguably the object with the most accurately and reliably determined (circum)stellar parameters amongst all carbon stars in the superwind phase.

  17. Light curves from binary neutron star coalescence

    NASA Astrophysics Data System (ADS)

    Ortiz, Nestor; Green, Stephen; Lehner, Luis; Ponce, Marcelo; HAD Collaboration

    2015-04-01

    Evolution of binary neutron stars, and the extraction of associated gravitational waveforms, have acquired certain maturity using numerical simulations. In this work we look to augment the observational predictions by extracting electromagnetic counterparts. That is, given results from a merger simulation, we produce a photon emission sky map. Our ray-tracing algorithm employ the two-pole caustic model of gamma-ray emission from the binary system's magnetosphere. The combined measurement of both gravitational and electromagnetic wave signals provides additional information to characterize the merger.

  18. Binary-binary collisions involving main-sequence stars, white dwarfs and neutron stars in globular clusters

    SciTech Connect

    Leonard, P.J.T.; Davies, M.B.

    1993-12-31

    We consider collisions between dynamically-evolved primordial binaries consisting of main-sequence stars, white dwarfs and neutron stars in globular clusters. In our four-body binary-binary scattering experiments, we allow stars to ``stick`` if they pass close enough to each other, which leads to the formation of a wide variety of exotic objects. Most of these objects have binary companions. Also, relatively clean exchange interactions can produce binaries containing neutron stars that eventually receive material from their companions. Such systems will be observable as X-ray binaries.

  19. On the formation of Be stars through binary interaction

    SciTech Connect

    Shao, Yong; Li, Xiang-Dong

    2014-11-20

    Be stars are rapidly rotating B-type stars. The origin of their rapid rotation is not certain, but binary interaction remains as a possibility. In this work, we investigate the formation of Be stars resulting from mass transfer in binaries in the Galaxy. We calculate binary evolution with both stars evolving simultaneously and consider different possible mass accretion histories for the accretor. From the calculated results, we obtain the critical mass ratios q {sub cr} that determine the stability of the mass transfer. We also numerically calculate the parameter λ in common envelope evolution and then incorporate both q {sub cr} and λ into the population synthesis calculations. We present the predicted numbers and characteristics of Be stars in binary systems with different types of companions, including helium stars, white dwarfs, neutron stars, and black holes. We find that in Be/neutron star binaries, the Be stars can have a lower mass limit ∼8 M {sub ☉} if they are formed by stable (i.e., without the occurrence of common envelope evolution) and nonconservative mass transfer. We demonstrate that isolated Be stars may originate from both mergers of two main-sequence stars and disrupted Be binaries during the supernova explosions of the primary stars, but mergers seem to play a much more important role. Finally, the fraction of Be stars that have involved binary interactions in all B-type stars can be as high as ∼13%-30%, implying that most Be stars may result from binary interaction.

  20. The temperatures of very metal-poor subdwarfs

    NASA Technical Reports Server (NTRS)

    Bell, R. A.

    1986-01-01

    The determination of ages for metal poor globular cluster stars using the relationship between stellar effective temperature and color, in order to transform isochrones from the L, Teff plane to the M(V), color plane is described. Estimates of the effective temperatures of metal-poor field subdwarfs deduced from the ratios of the integrated fluxes to the 12000 A fluxes of the 4 subdwarfs are in good agreement with published results. The stars are fainter than the models in the infrared, but the UV fluxes are in good agreement with model predictions.

  1. Binary neutron stars with arbitrary spins in numerical relativity

    NASA Astrophysics Data System (ADS)

    Tacik, Nick; Foucart, Francois; Pfeiffer, Harald P.; Haas, Roland; Ossokine, Serguei; Kaplan, Jeff; Muhlberger, Curran; Duez, Matt D.; Kidder, Lawrence E.; Scheel, Mark A.; Szilágyi, Béla

    2015-12-01

    We present a code to construct initial data for binary neutron star systems in which the stars are rotating. Our code, based on a formalism developed by Tichy, allows for arbitrary rotation axes of the neutron stars and is able to achieve rotation rates near rotational breakup. We compute the neutron star angular momentum through quasilocal angular momentum integrals. When constructing irrotational binary neutron stars, we find a very small residual dimensionless spin of ˜2 ×10-4 . Evolutions of rotating neutron star binaries show that the magnitude of the stars' angular momentum is conserved, and that the spin and orbit precession of the stars is well described by post-Newtonian approximation. We demonstrate that orbital eccentricity of the binary neutron stars can be controlled to ˜0.1 % . The neutron stars show quasinormal mode oscillations at an amplitude which increases with the rotation rate of the stars.

  2. Coalescence of Magnetized Binary Neutron Star Systems

    NASA Astrophysics Data System (ADS)

    Motl, Patrick M.; Anderson, Matthew; Lehner, Luis; Liebling, Steven L.; Neilsen, David; Palenzuela, Carlos; Ponce, Marcelo

    2015-01-01

    We present simulations of the merger of binary neutron star systems calculated with full general relativity and incorporating the global magnetic field structure for the stars evolved with resistive magnetohydrodynamics. Our simulation tools have recently been improved to incorporate the effects of neutrino cooling and have been generalized to allow for tabular equations of state to describe the degenerate matter. Of particular interest are possible electromagnetic counterparts to the gravitational radiation that emerges from these systems. We focus on magnetospheric interactions that ultimately tap into the gravitational potential energy of the binary to power a Poynting flux and deposition of energy through Joule heating and magnetic reconnection. We gratefully acknowledge the support of NASA through the Astrophysics Theory Program grant NNX13AH01G.

  3. Mergers of Binary Neutron Star Systems

    NASA Astrophysics Data System (ADS)

    Motl, Patrick M.; Anderson, Matthew; Lehner, Luis; Liebling, Steven; Neilsen, David; Palenzuela, Carlos

    2016-04-01

    We present results from fully relativistic simulations of binary neutron star mergers varying the tabular equation of state used to approximate the degenerate material and the mass ratio. The simulations incorporate both magnetic fields and the effects of neutrino cooling. In particular, we examine the amount and properties of material ejected from the merger. We gratefully acknowledge the support of NASA through the Astrophysics Theory Program grant NNX13AH01G.

  4. A Numerical Study of Boson Star Binaries

    NASA Astrophysics Data System (ADS)

    Mundim, Bruno C.

    2010-02-01

    This thesis describes a numerical study of binary boson stars within the context of an approximation to general relativity. The approximation we adopt places certain restrictions on the dynamical variables of general relativity (conformal flatness of the 3-metric), and on the time-slicing of the spacetime (maximal slicing). The resulting modeling problem requires the solution of a coupled nonlinear system of 4 hyperbolic, and 5 elliptic partial differential equations (PDEs) in three space dimensions and time. We approximately solve this system as an initial-boundary value problem, using finite difference techniques and well known, computationally efficient numerical algorithms such as the multigrid method in the case of the elliptic equations. Careful attention is paid to the issue of code validation, and a key part of the thesis is the demonstration that, as the basic scale of finite difference discretization is reduced, our numerical code generates results that converge to a solution of the continuum system of PDEs as desired. The thesis concludes with a discussion of results from some initial explorations of the orbital dynamics of boson star binaries. In particular, we describe calculations in which motion of such a binary is followed for more than two orbital periods, which is a significant advance over previous studies. We also present results from computations in which the boson stars merge, and where there is evidence for black hole formation.

  5. Nonlinear Tides in Coalescing Binary Neutron Stars

    NASA Astrophysics Data System (ADS)

    Weinberg, Nevin

    2016-03-01

    Coalescing binary neutron stars are among the most promising sources for ground-based gravitational wave detectors such as Advanced LIGO. Tidal interactions in such systems extract energy from the orbit and, at some level, modify the gravitational wave signal. Previous studies found that tidal effects are probably too small to be detected from individual systems with LIGO. However, these studies typically assumed that the tide can be treated as a linear perturbation to the star. I will show that the linear approximation is invalid even during the early stages of inspiral and that nonlinear fluid effects in the form of tide-internal wave interactions become important around the time the binary first enters LIGO's bandpass (at gravitational wave frequencies around 30 Hz). Although the precise influence of nonlinear fluid effects is not yet well constrained, I will show that they may significantly modify the gravitational wave signal and electromagnetic emission from coalescing binary neutron stars. This research was supported by NASA Grant NNX14AB40G.

  6. Binary interaction dominates the evolution of massive stars.

    PubMed

    Sana, H; de Mink, S E; de Koter, A; Langer, N; Evans, C J; Gieles, M; Gosset, E; Izzard, R G; Le Bouquin, J-B; Schneider, F R N

    2012-07-27

    The presence of a nearby companion alters the evolution of massive stars in binary systems, leading to phenomena such as stellar mergers, x-ray binaries, and gamma-ray bursts. Unambiguous constraints on the fraction of massive stars affected by binary interaction were lacking. We simultaneously measured all relevant binary characteristics in a sample of Galactic massive O stars and quantified the frequency and nature of binary interactions. More than 70% of all massive stars will exchange mass with a companion, leading to a binary merger in one-third of the cases. These numbers greatly exceed previous estimates and imply that binary interaction dominates the evolution of massive stars, with implications for populations of massive stars and their supernovae. PMID:22837522

  7. B-type stars in eclipsing binaries

    NASA Astrophysics Data System (ADS)

    Ratajczak, Milena; Pigulski, Andrzej

    2016-07-01

    B-type stars in eclipsing binary systems are unique astrophysical tools to test several aspects of stellar evolution. Such objects can be used e.g. to determine the masses of Beta Cephei variable stars, as well as help to place tighter constraints on the value of the convective core overshooting parameter α. Both precise photometry and high-resolution spectroscopy with high SNR are required to achieve these goals, but since many of the targets are bright enough, the challenge is fair. Following this assumption, we shall explain how we plan to examine both the aforementioned aspects of stellar evolution using observations of B-type stars obtained with a wide range of spectrographs, as well as BRITE-Constellation satellites.

  8. Coordinate System Issues in Binary Star Computations

    NASA Astrophysics Data System (ADS)

    Kaplan, George H.

    2015-08-01

    It has been estimated that half of all stars are components of binary or multiple systems. Yet the number of known orbits for astrometric and spectroscopic binary systems together is less than 7,000 (including redundancies), almost all of them for bright stars. A new generation of deep all-sky surveys such as Pan-STARRS, Gaia, and LSST are expected to lead to the discovery of millions of new systems. Although for many of these systems, the orbits may be undersampled initially, it is to be expected that combinations of new and old data sources will eventually lead to many more orbits being known. As a result, a revolution in the scientific understanding of these systems may be upon us.The current database of visual (astrometric) binary orbits represents them relative to the “plane of the sky”, that is, the plane orthogonal to the line of sight. Although the line of sight to stars constantly changes due to proper motion, aberration, and other effects, there is no agreed upon standard for what line of sight defines the orbital reference plane. Furthermore, the computation of differential coordinates (component B relative to A) for a given date must be based on the binary system’s direction at that date. Thus, a different “plane of the sky” is appropriate for each such date, i.e., each observation. However, projection effects between the reference planes, differential aberration, and the curvature of the sky are generally neglected in such computations. Usually the only correction applied is for the change in the north direction (position angle zero) due to precession (and sometimes also proper motion). This paper will present an algorithm for a more complete model of the geometry involved, and will show that such a model is necessary to avoid errors in the computed observables that are significant at modern astrometric accuracy. The paper will also suggest where conventions need to be established to avoid ambiguities in how quantities related to binary star

  9. Stellar and Binary Evolution in Star Clusters

    NASA Technical Reports Server (NTRS)

    McMillan, Stephen L. W.

    2001-01-01

    This paper presents a final report on research activities covered on Stellar and Binary Evolution in Star Clusters. Substantial progress was made in the development and dissemination of the "Starlab" software environment. Significant improvements were made to "kira," an N-body simulation program tailored to the study of dense stellar systems such as star clusters and galactic nuclei. Key advances include (1) the inclusion of stellar and binary evolution in a self-consistent manner, (2) proper treatment of the anisotropic Galactic tidal field, (3) numerous technical enhancements in the treatment of binary dynamics and interactions, and (4) full support for the special-purpose GRAPE-4 hardware, boosting the program's performance by a factor of 10-100 over the accelerated version. The data-reduction and analysis tools in Starlab were also substantially expanded. A Starlab Web site (http://www.sns.ias.edu/-starlab) was created and developed. The site contains detailed information on the structure and function of the various tools that comprise the package, as well as download information, "how to" tips and examples of common operations, demonstration programs, animations, etc. All versions of the software are freely distributed to all interested users, along with detailed installation instructions.

  10. Design and Implementation of BDB, the Binary Star Database

    NASA Astrophysics Data System (ADS)

    Kaygorodov, P.; Kovaleva, D.; Malkov, O.

    2013-02-01

    The Binary star DataBase (BDB, http://bdb.inasan.ru) is created to provide liasons between binary star catalogue data of various origin. Information on different observational types of binaries is obtained from heterogeneous sources of data - astronomical catalogues and surveys. The database allows a variety of query options useful for selected stars investigation purposes, for binary observations planning, and for construction and examination of binary datasets with certain characteristics.

  11. MAGNETIC INTERACTIONS IN COALESCING NEUTRON STAR BINARIES

    SciTech Connect

    Piro, Anthony L.

    2012-08-10

    It is expected on both evolutionary and empirical grounds that many merging neutron star (NS) binaries are composed of a highly magnetized NS in orbit with a relatively low magnetic field NS. I study the magnetic interactions of these binaries using the framework of a unipolar inductor model. The electromotive force generated across the non-magnetic NS as it moves through the magnetosphere sets up a circuit connecting the two stars. The exact features of this circuit depend on the uncertain resistance in the space between the stars R{sub space}. Nevertheless, I show that there are interesting observational and/or dynamical effects irrespective of its exact value. When R{sub space} is large, electric dissipation as great as {approx}10{sup 46} erg s{sup -1} (for magnetar-strength fields) occurs in the magnetosphere, which would exhibit itself as a hard X-ray precursor in the seconds leading up to merger. With less certainty, there may also be an associated radio transient. When R{sub space} is small, electric dissipation largely occurs in the surface layers of the magnetic NS. This can reach {approx}10{sup 49} erg s{sup -1} during the final {approx}1 s before merger, similar to the energetics and timescales of short gamma-ray bursts. In addition, for dipole fields greater than Almost-Equal-To 10{sup 12} G and a small R{sub space}, magnetic torques spin up the magnetized NS. This drains angular momentum from the binary and accelerates the inspiral. A faster coalescence results in less orbits occurring before merger, which would impact matched-filtering gravitational-wave searches by ground-based laser interferometers and could create difficulties for studying alternative theories of gravity with compact inspirals.

  12. Neutron star binaries, pulsars and burst sources

    NASA Technical Reports Server (NTRS)

    Lamb, F. K.

    1981-01-01

    Unresolved issues involving neutron star binaries, pulsars, and burst sources are described. Attention is drawn to the types of observations most likely to resolve them. Many of these observations are likely to be carried out during the next decade by one or more missions that have been approved or proposed. Flux measurements with an imaging detector and broad-band spectroscopic studies in the energy range 30-150 keV are discussed. The need for soft X-ray and X-ray observations with an instrument which has arcminute angular resolution and an effective area substantially greater than of ROSAT or EXOSAT is also discussed.

  13. Synchronization of magnetic stars in binary systems

    NASA Technical Reports Server (NTRS)

    Lamb, F. K.; Aly, J.-J.; Cook, M. C.; Lamb, D. Q.

    1983-01-01

    Asynchronous rotation of magnetic stars in close binary systems drives substantial field-aligned electrical currents between the magnetic star and its companion. The resulting magnetohydrodynamic torque is able to account for the heretofore unexplained synchronous rotation of the strongly magnetic degenerate dwarf component in systems like AM Her, VV Pup, AN UMa, and EF Eri as well as the magnetic A type component in systems like HD 98088 and 41 Tauri. The electric fields produced by even a small asynchronism are large and may accelerate some electrons to high energies, producing radio emission. The total energy dissipation rate in systems with degenerate dwarf spin periods as short as 1 minute may reach 10 to the 33rd ergs/s. Total luminosities of this order may be a characteristic feature of such systems.

  14. BINARY NEUTRON STARS IN QUASI-EQUILIBRIUM

    SciTech Connect

    Taniguchi, Keisuke; Shibata, Masaru

    2010-05-15

    Quasi-equilibrium sequences of binary neutron stars are constructed for a variety of equations of state in general relativity. Einstein's constraint equations in the Isenberg-Wilson-Mathews approximation are solved together with the relativistic equations of hydrostationary equilibrium under the assumption of irrotational flow. We focus on unequal-mass sequences as well as equal-mass sequences, and compare those results. We investigate the behavior of the binding energy and total angular momentum along a quasi-equilibrium sequence, the endpoint of sequences, and the orbital angular velocity as a function of time, changing the mass ratio, the total mass of the binary system, and the equation of state of a neutron star. It is found that the orbital angular velocity at the mass-shedding limit can be determined by an empirical formula derived from an analytic estimation. We also provide tables for 160 sequences, which will be useful as a guideline of numerical simulations for the inspiral and merger performed in the near future.

  15. The Lithium-, r- and s-Enhanced Metal-Poor Giant HK-II 17435-00532

    SciTech Connect

    Roederer, Ian U.; Prieto, Carlos Allende; Sneden, Christopher; Frebel, Anna; Shetrone, Matthew; Rhee, Jaehyon; Gallino, Roberto; Bisterzo, Sara; Beers, Timothy C.; Cowan, John J.

    2008-04-06

    We present the first detailed abundance analysis of the metal-poor giant HK-II 17435-00532. This star was observed as part of the University of Texas Long-Term Chemical Abundances of Stars in the Halo (CASH) Project. A spectrum was obtained with the High Resolution Spectrograph (HRS) on the Hobby-Eberly Telescope with a resolving power of R{approx}15000. Our analysis reveals that this star may be located on the red giant branch, red horizontal branch, or early asymptotic giant branch. We find that this metal-poor ([Fe/H] = -2.2) star has an unusually high lithium abundance (log{epsilon}(Li) = +2.1), mild carbon ([C/Fe] = +0.7) and sodium ([Na/Fe] = +0.6) enhancement, as well as enhancement of both s-process ([Ba/Fe] = +0.8) and r-process ([Eu/Fe] = +0.5) material. The high Li abundance can be explained by self-enrichment through extra mixing mechanisms that connect the convective envelope with the outer regions of the H-burning shell. If so, HK-II 17435-00532 is the most metal-poor starin which this short-lived phase of Li enrichment has been observed. The r- and s-process material was not produced in this star but was either present in the gas from which HK-II 17435-00532 formed or was transferred to it from a more massive binary companion. Despite the current non-detection of radial velocity variations (over a time span of {approx}180 days), it is possible that HK-II 17435-00532 is in a long-period binary system, similar to other stars with both r and s enrichment.

  16. VizieR Online Data Catalog: Binary properties of CH and CEMP stars (Jorissen+, 2016)

    NASA Astrophysics Data System (ADS)

    Jorissen, A.; van Eck, S.; van Winckel, H.; Merle, T.; Boffin, H. M. J.; Andersen, J.; Nordstroem, B.; Udry, S.; Masseron, T.; Lenaerts, L.; Waelkens, C.

    2015-11-01

    Radial velocities for 13 carbon-enhanced metal-poor and CH stars are listed. They were obtained mostly with the HERMES/Mercator spectrograph. These velocities made it possible to derive orbits for 8 systems. (2 data files).

  17. CALCULATING THE HABITABLE ZONE OF BINARY STAR SYSTEMS. II. P-TYPE BINARIES

    SciTech Connect

    Haghighipour, Nader; Kaltenegger, Lisa

    2013-11-10

    We have developed a comprehensive methodology for calculating the circumbinary habitable zone (HZ) in planet-hosting P-type binary star systems. We present a general formalism for determining the contribution of each star of the binary to the total flux received at the top of the atmosphere of an Earth-like planet and use the Sun's HZ to calculate the inner and outer boundaries of the HZ around a binary star system. We apply our calculations to the Kepler's currently known circumbinary planetary systems and show the combined stellar flux that determines the boundaries of their HZs. We also show that the HZ in P-type systems is dynamic and, depending on the luminosity of the binary stars, their spectral types, and the binary eccentricity, its boundaries vary as the stars of the binary undergo their orbital motion. We present the details of our calculations and discuss the implications of the results.

  18. Quasistatic Evolution of Binary Neutron Star Systems Before Merging

    NASA Astrophysics Data System (ADS)

    Eriguchi, Y.; Usui, F.

    Binary neutron star systems evolve due to the back reaction of gravitational wave emission. Although this evolution is essentially a time dependent phenomenon, most stages of the evolution can be regarded as if the system were in a stationary state. Consequently we can follow the evolution of binary neutron star systems quasistatically by connecting quasiequilibrium states of binary neutron stars. On the equilibrium sequences of congruent binary neutron star systems there are two important states of equilibrium configurations: 1) the minimum angular momentum state where some unstable phenomenon sets in and 2) the contact state from which a single body sequence will continue. Recent numerical results of quasiequilibrium approaches for the binary neutron star evolution are briefly reviewed and some problems in general relativistic treatments are discussed.

  19. Time markers in interstellar communication. [with binary star civilizations

    NASA Technical Reports Server (NTRS)

    Pace, G. W.; Walker, J. C. G.

    1975-01-01

    The chances that two civilizations establish contact with each other by means of interstellar radio communication are exceedingly small in the absence of time markers which will tell the two civilizations when to search for one another. In the case of binary stars, suitable time markers are provided by the apastron and the periastron. Single star civilization would transmit signals to binaries at the observation of apastron and periastron and the binary star civilization would scan single stars at the proper time for the reception of these signals.

  20. Planetary system disruption by Galactic perturbations to wide binary stars.

    PubMed

    Kaib, Nathan A; Raymond, Sean N; Duncan, Martin

    2013-01-17

    Nearly half the exoplanets found within binary star systems reside in very wide binaries with average stellar separations greater than 1,000 astronomical units (one astronomical unit (AU) being the Earth-Sun distance), yet the influence of such distant binary companions on planetary evolution remains largely unstudied. Unlike their tighter counterparts, the stellar orbits of wide binaries continually change under the influence of the Milky Way's tidal field and impulses from other passing stars. Here we report numerical simulations demonstrating that the variable nature of wide binary star orbits dramatically reshapes the planetary systems they host, typically billions of years after formation. Contrary to previous understanding, wide binary companions may often strongly perturb planetary systems, triggering planetary ejections and increasing the orbital eccentricities of surviving planets. Although hitherto not recognized, orbits of giant exoplanets within wide binaries are statistically more eccentric than those around isolated stars. Both eccentricity distributions are well reproduced when we assume that isolated stars and wide binaries host similar planetary systems whose outermost giant planets are scattered beyond about 10 AU from their parent stars by early internal instabilities. Consequently, our results suggest that although wide binaries eventually remove the most distant planets from many planetary systems, most isolated giant exoplanet systems harbour additional distant, still undetected planets. PMID:23292514

  1. ULTRA-LUMINOUS X-RAY SOURCES IN THE MOST METAL POOR GALAXIES

    SciTech Connect

    Prestwich, A. H.; Zezas, A.; Jackson, F.; Tsantaki, Maria; Roberts, T. P.; Foltz, R.; Linden, T.; Kalogera, V.

    2013-06-01

    Ultra-luminous X-ray sources (ULX) are X-ray binaries with L{sub x} >10{sup 39} erg s{sup -1}. The most spectacular examples of ULX occur in starburst galaxies and are now understood to be young, luminous high mass X-ray binaries. The conditions under which ULX form are poorly understood, but recent evidence suggests they may be more common in low metallicity systems. Here we investigate the hypothesis that ULX form preferentially in low metallicity galaxies by searching for ULX in a sample of extremely metal poor galaxies (XMPG) observed with the Chandra X-Ray Observatory. XMPG are defined as galaxies with log(O/H) + 12 < 7.65, or less than 5% solar. These are the most metal-deficient galaxies known, and a logical place to find ULX if they favor metal poor systems. We compare the number of ULX (corrected for background contamination) per unit of star formation (N{sub ULX}(SFR)) in the XMPG sample with N{sub ULX}(SFR) in a comparison sample of galaxies with higher metallicities taken from the Spitzer Infrared Galaxy Sample. We find that ULX occur preferentially in the metal poor sample with a formal statistical significance of 2.3{sigma}. We do not see strong evidence for a trend in the formation of ULX in the high metallicity sample: above 12+log(O/H) {approx} 8.0 the efficiency of ULX production appears to be flat. The effect we see is strongest in the lowest metallicity bin. We discuss briefly the implications of these results for the formation of black holes in low metallicity gas.

  2. STAR HOPPERS: PLANET INSTABILITY AND CAPTURE IN EVOLVING BINARY SYSTEMS

    SciTech Connect

    Kratter, Kaitlin M.; Perets, Hagai B.

    2012-07-01

    Many planets are observed in stellar binary systems, and their frequency may be comparable to that of planetary systems around single stars. Binary stellar evolution in such systems influences the dynamical evolution of the resident planets. Here, we study the evolution of a single planet orbiting one star in an evolving binary system. We find that stellar evolution can trigger dynamical instabilities that drive planets into chaotic orbits. This instability leads to planet-star collisions, exchange of the planet between the binary stars ('star hoppers'), and ejection of the planet from the system. The means by which planets can be recaptured is similar to the pull-down capture mechanism for irregular solar system satellites. Because planets often suffer close encounters with the primary on the asymptotic giant branch, captures during a collision with the stellar envelope are also possible for more massive planets. Such capture could populate the habitable zone around white dwarfs.

  3. Einstein observations of selected close binaries and shell stars

    NASA Technical Reports Server (NTRS)

    Guinan, E. F.; Koch, R. H.; Plavec, M. J.

    1984-01-01

    Several evolved close binaries and shell stars were observed with the IPC aboard the HEAO 2 Einstein Observatory. No eclipsing target was detected, and only two of the shell binaries were detected. It is argued that there is no substantial difference in L(X) for eclipsing and non-eclipsing binaries. The close binary and shell star CX Dra was detected as a moderately strong source, and the best interpretation is that the X-ray flux arises primarily from the corona of the cool member of the binary at about the level of Algol-like or RS CVn-type sources. The residual visible-band light curve of this binary has been modeled so as to conform as well as possible with this interpretation. HD 51480 was detected as a weak source. Substantial background information from IUE and ground scanner measurements are given for this binary. The positions and flux values of several accidentally detected sources are given.

  4. A New Eclipsing Binary Discovered in a Crowded Star Field

    NASA Astrophysics Data System (ADS)

    Larson, Jessica A.; Ranquist, E.; Hernandez, A.; Stoker, E.; Gaillard, C.

    2013-06-01

    Using the 0.9 meter telescope on West Mountain to follow-up possible transiting planets with ground based photometry, we discovered a previously unknown eclipsing binary system. This eclipsing binary is located in a crowded star field and so could not be reduced using photometry. In order to figure out which object in our field of view is the eclipsing binary, we learned how to use DAO phot. By using DAO phot we hope to be able to learn more about the individual stars that make up the binary system and their parameters.

  5. NIP of Stars: early results and new eclipsing binaries

    NASA Astrophysics Data System (ADS)

    Jaque Arancibia, M.; Barba, R.; Morrell, N.; Roman Lopes, A.; Torres Robledo, S.; Gunthardt, G.; Soto, M.; Ferrero, G.; Arias, J. I.; Gamen, R.; Fernadez Lajus, E.

    2014-10-01

    We have performed a near-infrared photometric monitoring of 39 galactic young star clusters and star-forming regions, known as NIP of Stars, between the years 2009-2011, using the Swope telescope at Las Campanas Observatory (Chile) and the RetroCam camera, in H- and Y-bands. This monitoring program is complementary to the Vista Variables in the Via Láctea (VVV), as the brightest sources observed in NIP of Stars are saturated in VVV. The aim of this campaign is to perform a census of photometric variability of such clusters and star-forming regions, with the main goal of discovering massive eclipsing binary stars. In this work, we present a preliminary analysis of this photometric monitoring program with the discovery of tens of candidates for variable stars, among them candidates for massive eclipsing binaries. We included also to the analysis of variability, a small set of images obtained in the Ks with the VISTA telescope in the framework of VVV survey (Minniti et al. 2010). In special, we announce the infrared discovering of four massive eclipsing binaries in the massive young cluster NGC 3603. The stars have been classified spectroscopically as O-type stars, and one of them, MTT 58, has a rare star with a spectral type of O2 If*/WN6, as one of its components. We present a preliminary analysis of the light-curves of these binaries.

  6. Identification and Spectral Classification of Close Red Dwarf Binary Stars

    NASA Astrophysics Data System (ADS)

    Chivers, James

    2015-01-01

    The position angle, angular and linear separation, distance, and spectral class of 713 red dwarf binary star systems are reported based on data-mining the Sloan Digital Sky Survey Data Release 10. 707 of these systems are new discoveries.

  7. Massive star evolution in close binaries. Conditions for homogeneous chemical evolution

    NASA Astrophysics Data System (ADS)

    Song, H. F.; Meynet, G.; Maeder, A.; Ekström, S.; Eggenberger, P.

    2016-01-01

    Aims: We investigate the impact of tidal interactions, before any mass transfer, on various properties of the stellar models. We study the conditions for obtaining homogeneous evolution triggered by tidal interactions, and for avoiding any Roche lobe overflow (RLOF) during the main-sequence phase. By homogeneous evolution, we mean stars evolving with a nearly uniform chemical composition from the centre to the surface. Methods: We consider the case of rotating stars computed with a strong core-envelope coupling mediated by an interior magnetic field. Models with initial masses between 15 and 60 M⊙, for metallicities between 0.002 and 0.014 and with initial rotation equal to 30% and 66% the critical rotation on the zero age main sequence, are computed for single stars and for stars in close binary systems. We consider close binary systems with initial orbital periods equal to 1.4, 1.6, and 1.8 days and a mass ratio equal to 3/2. Results: In models without any tidal interaction (single stars and wide binaries), homogeneous evolution in solid body rotating models is obtained when two conditions are realised: the initial rotation must be high enough, and the loss of angular momentum by stellar winds should be modest. This last point favours metal-poor fast rotating stars. In models with tidal interactions, homogeneous evolution is obtained when rotation imposed by synchronisation is high enough (typically a time-averaged surface velocities during the main-sequence phase above 250 km s-1), whatever the mass losses. We present plots that indicate for which masses of the primary and for which initial periods the conditions for the homogenous evolution and avoidance of the RLOF are met, for various initial metallicities and rotations. In close binaries, mixing is stronger at higher than at lower metallicities. Homogeneous evolution is thus favoured at higher metallicities. RLOF avoidance is favoured at lower metallicities because stars with less metals remain more

  8. BINARY STAR SYNTHETIC PHOTOMETRY AND DISTANCE DETERMINATION USING BINSYN

    SciTech Connect

    Linnell, Albert P.; DeStefano, Paul; Hubeny, Ivan E-mail: pdestefa@uw.edu

    2013-09-15

    This paper extends synthetic photometry to components of binary star systems. The paper demonstrates accurate recovery of single star photometric properties for four photometric standards, Vega, Sirius, GD153, and HD209458, ranging over the HR diagram, when their model synthetic spectra are placed in fictitious binary systems and subjected to synthetic photometry processing. Techniques for photometric distance determination have been validated for all four photometric standards.

  9. Phenomenological modelling of eclipsing binary stars

    NASA Astrophysics Data System (ADS)

    Andronov, I. L.; Tkachenko, M. G.; Chinarova, L. L.

    2016-03-01

    We review the method NAV ("New Algol Variable") first introduced in (2012Ap.....55..536A) which uses the locally-dependent shapes of eclipses in an addition to the trigonometric polynomial of the second order (which typically describes the "out-of-eclipse" part of the light curve with effects of reflection, ellipticity and O'Connell). Eclipsing binary stars are believed to show distinct eclipses only if belonging to the EA (Algol) type. With a decreasing eclipse width, the statistically optimal value of the trigonometric polynomial s(2003ASPC..292..391A) drastically increases from ~2 for elliptic (EL) variables without eclipses, ~6-8 for EW and up to ~30-50 for some EA with narrow eclipses. In this case of large number of parameters, the smoothing curve becomes very noisy and apparent waves (the Gibbs phenomenon) may be seen. The NAV set of the parameters may be used for classification in the GCVS, VSX and similar catalogs. The maximal number of parameters is m=12, which corresponds to s=5, if correcting both the period and the initial epoch. We have applied the method to few stars, also in a case of multi-color photometry (2015JASS...32..127A), when it is possible to use the phenomenological parameters from the NAV fit to estimate physical parameters using statistical dependencies. For the one-color observations, one may estimate the ratio of the surface brightnesses of the components. We compiled a catalog of phenomenological characteristics based on published observations. We conclude that the NAV approximation is better than the TP one even for the case of EW-type stars with much wider eclipses. It may also be used to determine timings (see 2005ASPC..335...37A for a review of methods) or to determine parameters in the case of variable period, using a complete light curve modeling the phase variations. The method is illustrated on 2MASS J11080447-6143290 (EA-type), USNO-B1.0 1265-0306001 and USNO-B1.01266-0313413 (EW-type) and compared to various other methods

  10. THE CLOSE BINARY FRACTION OF DWARF M STARS

    SciTech Connect

    Clark, Benjamin M.; Blake, Cullen H.; Knapp, Gillian R.

    2012-01-10

    We describe a search for close spectroscopic dwarf M star binaries using data from the Sloan Digital Sky Survey to address the question of the rate of occurrence of multiplicity in M dwarfs. We use a template-fitting technique to measure radial velocities from 145,888 individual spectra obtained for a magnitude-limited sample of 39,543 M dwarfs. Typically, the three or four spectra observed for each star are separated in time by less than four hours, but for {approx}17% of the stars, the individual observations span more than two days. In these cases we are sensitive to large-amplitude radial velocity variations on timescales comparable to the separation between the observations. We use a control sample of objects having observations taken within a four-hour period to make an empirical estimate of the underlying radial velocity error distribution and simulate our detection efficiency for a wide range of binary star systems. We find the frequency of binaries among the dwarf M stars with a < 0.4 AU to be 3%-4%. Comparison with other samples of binary stars demonstrates that the close binary fraction, like the total binary fraction, is an increasing function of primary mass.

  11. Compact Stellar Binary Assembly in the First Nuclear Star Clusters and r-process Synthesis in the Early Universe

    NASA Astrophysics Data System (ADS)

    Ramirez-Ruiz, Enrico; Trenti, Michele; MacLeod, Morgan; Roberts, Luke F.; Lee, William H.; Saladino-Rosas, Martha I.

    2015-04-01

    Investigations of elemental abundances in the ancient and most metal deficient stars are extremely important because they serve as tests of variable nucleosynthesis pathways and can provide critical inferences of the type of stars that lived and died before them. The presence of r-process elements in a handful of carbon-enhanced metal-poor (CEMP-r) stars, which are assumed to be closely connected to the chemical yield from the first stars, is hard to reconcile with standard neutron star mergers. Here we show that the production rate of dynamically assembled compact binaries in high-z nuclear star clusters can attain a sufficient high value to be a potential viable source of heavy r-process material in CEMP-r stars. The predicted frequency of such events in the early Galaxy, much lower than the frequency of Type II supernovae but with significantly higher mass ejected per event, can naturally lead to a high level of scatter of Eu as observed in CEMP-r stars.

  12. Binary nature of the HADS stars AN Lyn & BE Lyn

    NASA Astrophysics Data System (ADS)

    Peña, J. H.; Rentería, A.; Villarreal, C.; Pani, A.; Huepa, H.; Huepa, J. L.; Bernal, A.; Arenas, A.; García, C.; León, R.; Ramírez, E.; Trejo, O.; Colorado, E.; Sánchez-Cruces, M.; Rechy-García, J. S.

    2015-04-01

    From newly determined times of maxima from CCD photometry of the HADS stars AN Lyn & BE Lyn and a compilation of previous times of maxima, we are able to determine the binary nature of these stars. We determine their physical parameters by means of uvby-β photometry.

  13. The close-binary content of massive star clusters

    NASA Astrophysics Data System (ADS)

    van den Berg, Maureen C.

    2015-08-01

    The fates of star clusters and the binaries in them are closely intertwined. Close binaries support a cluster against core collapse, while stellar encounters in the dense cores of massive star clusters shape the properties and numbers of the binaries. Observations of massive globular clusters with the Chandra X-ray Observatory have revealed hundreds of close binaries. I will present new results from deep HST observations of massive star clusters including 47Tuc, M28, and M4, that are aimed at classifying the X-ray source populations. Besides exotic systems such as low-mass X-ray binaries and millisecond pulsars, more mundane systems such as magnetically active binaries and accreting white dwarfs have been found. I will discuss how a breakdown of sources by class has revealed how the various binary populations bear the imprints of stellar encounters: some are dominated by dynamical creation, others by dynamical destruction. I will also discuss the effects on the integrated X-ray emissivity of massive star clusters, which is suppressed compared to lower-density environments.

  14. MASS TRANSFER IN BINARY STARS USING SMOOTHED PARTICLE HYDRODYNAMICS. II. ECCENTRIC BINARIES

    SciTech Connect

    Lajoie, Charles-Philippe; Sills, Alison E-mail: asills@mcmaster.ca

    2011-01-10

    Despite numerous efforts to better understand binary star evolution, some aspects of it remain poorly constrained. In particular, the evolution of eccentric binaries has remained elusive mainly because the Roche lobe formalism derived for circular binaries does not apply. Here we report the results of our smoothed particle hydrodynamic simulations of mass transfer in eccentric binaries using an alternate method in which we model only the outermost layers of the stars with appropriate boundary conditions. Using this technique, along with properly relaxed model stars, we characterize the mass transfer episodes of binaries with various orbital parameters. In particular, we show that these episodes can be described by Gaussians with an FWHM of {approx}0.12P{sub orb} and that the peak rates occur after periastron, at an orbital phase of {approx}0.58, independently of the eccentricity and mass of the stars. The accreted material is observed to form a rather sparse envelope around either or both stars. Although the fate of this envelope is not modeled in our simulations, we show that a constant fraction ({approx}5%) of the material transferred is ejected from the systems. We discuss this result in terms of the non-conservative mass transfer scenario. We suggest that our results could be incorporated in analytical and binary population synthesis studies to help better understand the evolution of eccentric binaries and the formation of exotic stellar populations.

  15. Modelling of binary stars from observations. (Italian Title: Creare modelli di stelle binarie dalle osservazioni)

    NASA Astrophysics Data System (ADS)

    Marino, G.

    2011-08-01

    A review on basic physical parameters of closed binary stars introduces to modelling observational data. PHOEBE and other modelling software are described. As example of application, for the first time photometric elements of the eclipsing binary V400 Lyr are obtained.

  16. Milankovitch Cycles of Terrestrial Planets in Binary Star Systems

    NASA Astrophysics Data System (ADS)

    Forgan, Duncan

    2016-08-01

    The habitability of planets in binary star systems depends not only on the radiation environment created by the two stars, but also on the perturbations to planetary orbits and rotation produced by the gravitational field of the binary and neighbouring planets. Habitable planets in binaries may therefore experience significant perturbations in orbit and spin. The direct effects of orbital resonances and secular evolution on the climate of binary planets remain largely unconsidered. We present latitudinal energy balance modelling of exoplanet climates with direct coupling to an N Body integrator and an obliquity evolution model. This allows us to simultaneously investigate the thermal and dynamical evolution of planets orbiting binary stars, and discover gravito-climatic oscillations on dynamical and secular timescales. We investigate the Kepler-47 and Alpha Centauri systems as archetypes of P and S type binary systems respectively. In the first case, Earthlike planets would experience rapid Milankovitch cycles (of order 1000 years) in eccentricity, obliquity and precession, inducing temperature oscillations of similar periods (modulated by other planets in the system). These secular temperature variations have amplitudes similar to those induced on the much shorter timescale of the binary period. In the Alpha Centauri system, the influence of the secondary produces eccentricity variations on 15,000 year timescales. This produces climate oscillations of similar strength to the variation on the orbital timescale of the binary. Phase drifts between eccentricity and obliquity oscillations creates further cycles that are of order 100,000 years in duration, which are further modulated by neighbouring planets.

  17. Binary stars can provide the `missing photons' needed for reionization

    NASA Astrophysics Data System (ADS)

    Ma, Xiangcheng; Hopkins, Philip F.; Kasen, Daniel; Quataert, Eliot; Faucher-Giguère, Claude-André; Kereš, Dušan; Murray, Norman; Strom, Allison

    2016-07-01

    Empirical constraints on reionization require galactic ionizing photon escape fractions fesc ≳ 20 per cent, but recent high-resolution radiation-hydrodynamic calculations have consistently found much lower values ˜1-5 per cent. While these models include strong stellar feedback and additional processes such as runaway stars, they almost exclusively consider stellar evolution models based on single (isolated) stars, despite the fact that most massive stars are in binaries. We re-visit these calculations, combining radiative transfer and high-resolution cosmological simulations with detailed models for stellar feedback from the Feedback in Realistic Environments project. For the first time, we use a stellar evolution model that includes a physically and observationally motivated treatment of binaries (the Binary Population and Spectral Synthesis model). Binary mass transfer and mergers enhance the population of massive stars at late times (≳3 Myr) after star formation, which in turn strongly enhances the late-time ionizing photon production (especially at low metallicities). These photons are produced after feedback from massive stars has carved escape channels in the interstellar medium, and so efficiently leak out of galaxies. As a result, the time-averaged `effective' escape fraction (ratio of escaped ionizing photons to observed 1500 Å photons) increases by factors ˜4-10, sufficient to explain reionization. While important uncertainties remain, we conclude that binary evolution may be critical for understanding the ionization of the Universe.

  18. Evolution of binary stars in multiple-population globular clusters - II. Compact binaries

    NASA Astrophysics Data System (ADS)

    Hong, Jongsuk; Vesperini, Enrico; Sollima, Antonio; McMillan, Stephen L. W.; D'Antona, Franca; D'Ercole, Annibale

    2016-04-01

    We present the results of a survey of N-body simulations aimed at exploring the evolution of compact binaries in multiple-population globular clusters. We show that as a consequence of the initial differences in the structural properties of the first-generation (FG) and the second-generation (SG) populations and the effects of dynamical processes on binary stars, the SG binary fraction decreases more rapidly than that of the FG population. The difference between the FG and SG binary fraction is qualitatively similar to but quantitatively smaller than that found for wider binaries in our previous investigations. The evolution of the radial variation of the binary fraction is driven by the interplay between binary segregation, ionization and ejection. Ionization and ejection counteract in part the effects of mass segregation but for compact binaries the effects of segregation dominate and the inner binary fraction increases during the cluster evolution. We explore the variation of the difference between the FG and the SG binary fraction with the distance from the cluster centre and its dependence on the binary binding energy and cluster structural parameters. The difference between the binary fraction in the FG and the SG populations found in our simulations is consistent with the results of observational studies finding a smaller binary fraction in the SG population.

  19. Eccentricity boost of stars around shrinking massive black hole binaries

    NASA Astrophysics Data System (ADS)

    Iwasa, Mao; Seto, Naoki

    2016-06-01

    Based on a simple geometrical approach, we analyze the evolution of the Kozai-Lidov mechanism for stars around shrinking massive black hole binaries on circular orbits. We find that, due to a peculiar bifurcation pattern induced by the Newtonian potential of stellar clusters, the orbit of stars could become highly eccentric. This transition occurs abruptly for stars with small initial eccentricities. The approach presented in this paper may be useful for studying the Kozai-Lidov mechanism in various astrophysical contexts.

  20. Observations of hot stars and eclipsing binaries with FRESIP

    NASA Technical Reports Server (NTRS)

    Gies, Douglas R.

    1994-01-01

    The FRESIP project offers an unprecedented opportunity to study pulsations in hot stars (which vary on time scales of a day) over a several year period. The photometric data will determine what frequencies are present, how or if the amplitudes change with time, and whether there is a connection between pulsation and mass loss episodes. It would initiate a new field of asteroseismology studies of hot star interiors. A search should be made for selected hot stars for inclusion in the list of project targets. Many of the primary solar mass targets will be eclipsing binaries, and I present estimates of their frequency and typical light curves. The photometric data combined with follow up spectroscopy and interferometric observations will provide fundamental data on these stars. The data will provide definitive information on the mass ratio distribution of solar-mass binaries (including the incidence of brown dwarf companions) and on the incidence of planets in binary systems.

  1. Formation and Evolution of Binary Systems Containing Collapsed Stars

    NASA Technical Reports Server (NTRS)

    Rappaport, Saul; West, Donald (Technical Monitor)

    2003-01-01

    This research includes theoretical studies of the formation and evolution of five types of interacting binary systems. Our main focus has been on developing a number of comprehensive population synthesis codes to study the following types of binary systems: (i) cataclysmic variables (#3, #8, #12, #15), (ii) low- and intermediate-mass X-ray binaries (#13, #20, #21), (iii) high-mass X-ray binaries (#14, #17, #22), (iv) recycled binary millisecond pulsars in globular clusters (#5, #10, #ll), and (v) planetary nebulae which form in interacting binaries (#6, #9). The numbers in parentheses refer to papers published or in preparation that are listed in this paper. These codes take a new unified approach to population synthesis studies. The first step involves a Monte Carlo selection of the primordial binaries, including the constituent masses, and orbital separations and eccentricities. Next, a variety of analytic methods are used to evolve the primary star to the point where either a dynamical episode of mass transfer to the secondary occurs (the common envelope phase), or the system evolves down an alternate path. If the residual core of the primary is greater than 2.5 solar mass, it will evolve to Fe core collapse and the production of a neutron star and a supernova explosion. In the case of systems involving neutron stars, a kick velocity is chosen randomly from an appropriate distribution and added to the orbital dynamics which determine the state of the binary system after the supernova explosion. In the third step, all binaries which commence stable mass transfer from the donor star (the original secondary in the binary system) to the compact object, are followed with a detailed binary evolution code. Finally, we include all the relevant dynamics of the binary system. For example, in the case of LMXBs, the binary system, with its recoil velocity from the supernova explosion, is followed in time through its path in the Galactic potential. For our globular cluster

  2. Misaligned protoplanetary disks in a young binary star system.

    PubMed

    Jensen, Eric L N; Akeson, Rachel

    2014-07-31

    Many extrasolar planets follow orbits that differ from the nearly coplanar and circular orbits found in our Solar System; their orbits may be eccentric or inclined with respect to the host star's equator, and the population of giant planets orbiting close to their host stars suggests appreciable orbital migration. There is at present no consensus on what produces such orbits. Theoretical explanations often invoke interactions with a binary companion star in an orbit that is inclined relative to the planet's orbital plane. Such mechanisms require significant mutual inclinations between the planetary and binary star orbital planes. The protoplanetary disks in a few young binaries are misaligned, but often the measurements of these misalignments are sensitive only to a small portion of the inner disk, and the three-dimensional misalignment of the bulk of the planet-forming disk mass has hitherto not been determined. Here we report that the protoplanetary disks in the young binary system HK Tauri are misaligned by 60 to 68 degrees, such that one or both of the disks are significantly inclined to the binary orbital plane. Our results demonstrate that the necessary conditions exist for misalignment-driven mechanisms to modify planetary orbits, and that these conditions are present at the time of planet formation, apparently because of the binary formation process. PMID:25079553

  3. CALCULATING THE HABITABLE ZONE OF BINARY STAR SYSTEMS. I. S-TYPE BINARIES

    SciTech Connect

    Kaltenegger, Lisa; Haghighipour, Nader

    2013-11-10

    We have developed a comprehensive methodology for calculating the boundaries of the habitable zone (HZ) of planet-hosting S-type binary star systems. Our approach is general and takes into account the contribution of both stars to the location and extent of the binary HZ with different stellar spectral types. We have studied how the binary eccentricity and stellar energy distribution affect the extent of the HZ. Results indicate that in binaries where the combination of mass-ratio and orbital eccentricity allows planet formation around a star of the system to proceed successfully, the effect of a less luminous secondary on the location of the primary's HZ is generally negligible. However, when the secondary is more luminous, it can influence the extent of the HZ. We present the details of the derivations of our methodology and discuss its application to the binary HZ around the primary and secondary main-sequence stars of an FF, MM, and FM binary, as well as two known planet-hosting binaries α Cen AB and HD 196886.

  4. General relativistic models of binary neutron stars in quasiequilibrium

    NASA Astrophysics Data System (ADS)

    Baumgarte, T. W.; Cook, G. B.; Scheel, M. A.; Shapiro, S. L.; Teukolsky, S. A.

    1998-06-01

    We perform fully relativistic calculations of binary neutron stars in corotating, circular orbit. While Newtonian gravity allows for a strict equilibrium, a relativistic binary system emits gravitational radiation, causing the system to lose energy and slowly spiral inwards. However, since inspiral occurs on a time scale much longer than the orbital period, we can treat the binary to be in quasiequilibrium. In this approximation, we integrate a subset of the Einstein equations coupled to the relativistic equation of hydrostatic equilibrium to solve the initial value problem for binaries of arbitrary separation. We adopt a polytropic equation of state to determine the structure and maximum mass of neutron stars in close binaries for polytropic indices n=1, 1.5 and 2. We construct sequences of constant rest-mass and locate turning points along energy equilibrium curves to identify the onset of orbital instability. In particular, we locate the innermost stable circular orbit and its angular velocity. We construct the first contact binary systems in full general relativity. These arise whenever the equation of state is sufficiently soft (n>~1.5). A radial stability analysis reveals no tendency for neutron stars in close binaries to collapse to black holes prior to merger.

  5. Searching for pulsations in Kepler eclipsing binary stars

    NASA Astrophysics Data System (ADS)

    Gaulme, Patrick; Guzik, Joyce A.

    2014-02-01

    Eclipsing binaries can in principle provide additional constraints to facilitate asteroseismology of one or more pulsating components. We have identified 94 possible eclipsing binary systems in a sample of over 1800 stars observed in long cadence as part of the Kepler Guest Observer Program to search for γ Doradus and δ Scuti star candidates. We show the results of a procedure to fold the light curve to identify the potential binary period, subtract a fit to the binary light curve, and perform a Fourier analysis on the residuals to search for pulsation frequencies that may arise in one or both of the stellar components. From this sample, we have found a large variety of light curve types; about a dozen stars show frequencies consistent with δ Sct or γ Dor pulsations, or light curve features possibly produced by stellar activity (rotating spots). For several stars, the folded candidate `binary' light curve resembles more closely that of an RR Lyr, Cepheid, or high-amplitude δ Sct star. We show highlights of our results and discuss the potential for asteroseismology of the most interesting objects.

  6. Photometric binary stars in Praesepe and the search for globular cluster binaries

    NASA Technical Reports Server (NTRS)

    Bolte, Michael

    1991-01-01

    A radial velocity study of the stars which are located on a second sequence above the single-star zero-age main sequence at a given color in the color-magnitude diagram of the open cluster Praesepe, (NGC 2632) shows that 10, and possibly 11, of 17 are binary systems. Of the binary systems, five have full amplitudes for their velocity variations that are greater than 50 km/s. To the extent that they can be applied to globular clusters, these results suggests that (1) observations of 'second-sequence' stars in globular clusters would be an efficient way of finding main-sequence binary systems in globulars, and (2) current instrumentation on large telescopes is sufficient for establishing unambiguously the existence of main-sequence binary systems in nearby globular clusters.

  7. Changes in the orbital periods of close binary stars

    NASA Technical Reports Server (NTRS)

    Marsh, T. R.; Pringle, J. E.

    1990-01-01

    A number of close binary stars show erratic changes in their orbital periods on time scales of order 5-10 yr. Recently it has been proposed that the period changes are the result of changes in the quadrupole moment of one star, caused in turn by an alteration of the internal structure of that star. Magnetic pressure, which either distorts the shape of the star or changes its tidally induced quadrupole moment, is suggested as the driving force behind the alteration. Here, the amount of energy required to distort one component of a binary and match the observed period changes is estimated. The rate at which energy is produced or lost is governed by the thermal time scale of the star, and the estimates indicate that the observed period changes would take at least 1000 yr for the tidal quadrupole mechanism, and of order 60 yr to match a period change in V471 Tau which took only 4 yr.

  8. 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

  9. Binary Stars Can Provide the "Missing Photons" Needed for Reionization

    NASA Astrophysics Data System (ADS)

    Ma, Xiangcheng; Hopkins, Philip F.; Kasen, Daniel; Quataert, Eliot; Faucher-Giguère, Claude-André; Kereš, Dušan; Murray, Norman; Strom, Allison

    2016-04-01

    Empirical constraints on reionization require galactic ionizing photon escape fractions fesc ≳ 20%, but recent high-resolution radiation-hydrodynamic calculations have consistently found much lower values ˜1-5%. While these models include strong stellar feedback and additional processes such as runaway stars, they almost exclusively consider stellar evolution models based on single (isolated) stars, despite the fact that most massive stars are in binaries. We re-visit these calculations, combining radiative transfer and high-resolution cosmological simulations with detailed models for stellar feedback from the Feedback in Realistic Environments (FIRE) project. For the first time, we use a stellar evolution model that includes a physically and observationally motivated treatment of binaries (the BPASS model). Binary mass transfer and mergers enhance the population of massive stars at late times (≳ 3 Myr) after star formation, which in turn strongly enhances the late-time ionizing photon production (especially at low metallicities). These photons are produced after feedback from massive stars has carved escape channels in the ISM, and so efficiently leak out of galaxies. As a result, the time-averaged "effective" escape fraction (ratio of escaped ionizing photons to observed 1500 Å photons) increases by factors ˜4-10, sufficient to explain reionization. While important uncertainties remain, we conclude that binary evolution may be critical for understanding the ionization of the Universe.

  10. KOI-3278: A Self-Lensing Binary Star System

    NASA Astrophysics Data System (ADS)

    Kruse, Ethan; Agol, Eric

    2014-04-01

    Over 40% of Sun-like stars are bound in binary or multistar systems. Stellar remnants in edge-on binary systems can gravitationally magnify their companions, as predicted 40 years ago. By using data from the Kepler spacecraft, we report the detection of such a “self-lensing” system, in which a 5-hour pulse of 0.1% amplitude occurs every orbital period. The white dwarf stellar remnant and its Sun-like companion orbit one another every 88.18 days, a long period for a white dwarf-eclipsing binary. By modeling the pulse as gravitational magnification (microlensing) along with Kepler’s laws and stellar models, we constrain the mass of the white dwarf to be ~63% of the mass of our Sun. Further study of this system, and any others discovered like it, will help to constrain the physics of white dwarfs and binary star evolution.

  11. KOI-3278: a self-lensing binary star system.

    PubMed

    Kruse, Ethan; Agol, Eric

    2014-04-18

    Over 40% of Sun-like stars are bound in binary or multistar systems. Stellar remnants in edge-on binary systems can gravitationally magnify their companions, as predicted 40 years ago. By using data from the Kepler spacecraft, we report the detection of such a "self-lensing" system, in which a 5-hour pulse of 0.1% amplitude occurs every orbital period. The white dwarf stellar remnant and its Sun-like companion orbit one another every 88.18 days, a long period for a white dwarf-eclipsing binary. By modeling the pulse as gravitational magnification (microlensing) along with Kepler's laws and stellar models, we constrain the mass of the white dwarf to be ~63% of the mass of our Sun. Further study of this system, and any others discovered like it, will help to constrain the physics of white dwarfs and binary star evolution. PMID:24744369

  12. Optical and ultraviolet spectroscopy of three F + B binary stars

    NASA Astrophysics Data System (ADS)

    Bopp, Bernard W.; Dempsey, Robert C.; Parsons, Sidney B.

    1991-05-01

    Optical and ultraviolet spectroscopy is presented for three F + B objects that are members of the first group of strongly interacting, F II + B systems. The data obtained confirm that HD 59771, HD 242257, and CoD -30 5135 are all binary star systems consisting of a luminous F-type component and a B star. Strong, variable H-alpha emission is seen in all the stars. It is found that the UV spectrum of HD 59771 resembles the spectrum of HD 207739. CoD -30 5135 has the most dramatic mid-UV spectrum seen among the scores of observed cool + hot star systems.

  13. Magnetic field effects on gravitational waves from binary neutron stars

    NASA Astrophysics Data System (ADS)

    Anderson, Matthew; Hirschmann, Eric; Lehner, Luis; Liebling, Steven; Motl, Patrick; Neilsen, David; Palenzuela, Carlos; Tohline, Joel

    2008-04-01

    Observational evidence indicates that a fair number of neutron star binaries and neutron star-black hole binaries have a sizable magnetic field which can be responsible for powering pulsars and colimating jets. Magnetic field effects additionally can have a strong influence on the dynamics of the fluid by redistributing angular momentum through different mechanisms (magnetic winding and braking, magneto-rotational instabilities) depending on the strength of the magnetic field and the typical time scales involved in the process. These processes can affect the multipolar structure of the source and consequently the produced gravitational wave. We present results of neutron star binary mergers both with and without magnetic field and discuss the magnetic effects on the gravitational waves, fluid structure, and merger timescale.

  14. TRIPLE-STAR CANDIDATES AMONG THE KEPLER BINARIES

    SciTech Connect

    Rappaport, S.; Deck, K.; Sanchis-Ojeda, R.; Levine, A.; Borkovits, T.; Carter, J.; El Mellah, I.; Kalomeni, B. E-mail: kdeck@mit.edu E-mail: aml@space.mit.edu E-mail: jacarter@cfa.harvard.edu

    2013-05-01

    We present the results of a search through the photometric database of Kepler eclipsing binaries looking for evidence of hierarchical triple-star systems. The presence of a third star orbiting the binary can be inferred from eclipse timing variations. We apply a simple algorithm in an automated determination of the eclipse times for all 2157 binaries. The ''calculated'' eclipse times, based on a constant period model, are subtracted from those observed. The resulting O - C (observed minus calculated times) curves are then visually inspected for periodicities in order to find triple-star candidates. After eliminating false positives due to the beat frequency between the {approx}1/2 hr Kepler cadence and the binary period, 39 candidate triple systems were identified. The periodic O - C curves for these candidates were then fit for contributions from both the classical Roemer delay and so-called physical delay, in an attempt to extract a number of the system parameters of the triple. We discuss the limitations of the information that can be inferred from these O - C curves without further supplemental input, e.g., ground-based spectroscopy. Based on the limited range of orbital periods for the triple-star systems to which this search is sensitive, we can extrapolate to estimate that at least 20% of all close binaries have tertiary companions.

  15. Triple-star Candidates among the Kepler Binaries

    NASA Astrophysics Data System (ADS)

    Rappaport, S.; Deck, K.; Levine, A.; Borkovits, T.; Carter, J.; El Mellah, I.; Sanchis-Ojeda, R.; Kalomeni, B.

    2013-05-01

    We present the results of a search through the photometric database of Kepler eclipsing binaries looking for evidence of hierarchical triple-star systems. The presence of a third star orbiting the binary can be inferred from eclipse timing variations. We apply a simple algorithm in an automated determination of the eclipse times for all 2157 binaries. The "calculated" eclipse times, based on a constant period model, are subtracted from those observed. The resulting O - C (observed minus calculated times) curves are then visually inspected for periodicities in order to find triple-star candidates. After eliminating false positives due to the beat frequency between the ~1/2 hr Kepler cadence and the binary period, 39 candidate triple systems were identified. The periodic O - C curves for these candidates were then fit for contributions from both the classical Roemer delay and so-called physical delay, in an attempt to extract a number of the system parameters of the triple. We discuss the limitations of the information that can be inferred from these O - C curves without further supplemental input, e.g., ground-based spectroscopy. Based on the limited range of orbital periods for the triple-star systems to which this search is sensitive, we can extrapolate to estimate that at least 20% of all close binaries have tertiary companions.

  16. Black Hole - Neutron Star Binary Simulations at Georgia Tech

    NASA Astrophysics Data System (ADS)

    Haas, Roland

    2009-05-01

    Mixed compact object binaries consisting of a black hole and a neutron star are expected to be not only one of the primary sources of gravitational radiation to be observed by interferometric detectors but also the central engine of short gamma-ray bursts. We report on the status of our effort at Georgia Tech to model these mixed binary systems using the moving puncture method. The results are obtained with an enhanced version our vacuum MayaKranc code coupled to the hydrodynamics Whisky code. We present preliminary results of gravitational waveforms and the disruption of the neutron star for simple polytropic equations of state.

  17. Binary Neutron Star Mergers: Prospects for Multimessenger Observations

    NASA Astrophysics Data System (ADS)

    Neilsen, David; Anderson, Matthew; Lehner, Luis; Liebling, Steven; Palenzuela, Carlos

    2016-03-01

    Binary neutron star mergers are possible progenitors for short gamma-ray bursts. We evolve a binary system of two neutron stars using the fully relativistic Einstein equations from an initial quasi-circular orbit, through and past merger. We consider different finite-temperature, nuclear equations of state, which vary from soft to quite stiff, and allow for magnetization of the system and neutrino cooling via a leakage scheme. We focus on potential observables, other than gravitational waves, produced mainly by the hot, strongly magnetized matter resulting from the merger.

  18. The CHARA Catalog of Orbital Elements of Spectroscopic Binary Stars

    NASA Astrophysics Data System (ADS)

    Taylor, Stuart F.; Harvin, James A.; McAlister, Harold A.

    2003-05-01

    Optical interferometry is entering a new age, with several ground-based long-baseline observatories now making observations of unprecedented resolution. Interferometers bring a new level of resolution to bear on spectroscopic binaries, enabling the full extraction of the physical parameters for the component stars with high accuracy. In the case of double-lined systems, a geometrically determined orbital parallax becomes available as well. The first step in preparing to observe spectroscopic binaries is to list them, which has not been done since the 1989 publication of the Eighth Catalogue of the Orbital Elements of Spectroscopic Binaries by Batten et al. We present a new catalog with roughly half again as many listings as the Eighth Catalogue. Angular separation predictions are made for each catalog entry. The numbers of spectroscopic binaries available for study as a function of several important observational parameters are explored, and in particular, the number of spectroscopic binaries as a function of expected separation is discussed.

  19. The Binary Nature of CH-Like Stars

    NASA Astrophysics Data System (ADS)

    Sperauskas, J.; Začs, L.; Schuster, W. J.; Deveikis, V.

    2016-07-01

    Yamashita has described a group of early carbon stars with enhanced lines of barium that resemble the CH stars but have low radial velocities. It is not clear whether they represent a class of stars separate from early R stars. Radial-velocity measurements and abundance analyses are applied in order to clarify the evolutionary status of CH-like stars. Radial-velocity monitoring was performed over a time interval of about 10 years. Abundance analysis was carried out using high-resolution spectra and the method of atmospheric models for three CH-like candidate stars. The radial-velocity monitoring confirmed regular variations for all of the classified CH-like stars, except for two, in support of their binary nature. The calculated orbital parameters are similar to those observed for barium stars in the disk of the Galaxy and their counterparts in the halo, that is, the CH stars. The relatively low luminosity of CH-like stars and the overabundance of s-process elements in the atmospheres are in agreement with a mass-transfer scenario from the secondary—an AGB star in the past. The kinematic data and metallicities support the idea that CH-like stars are thin/thick-disk population objects.

  20. Observations of Disks Around Pre--Main-Sequence Binary Stars

    NASA Astrophysics Data System (ADS)

    Jensen, Eric L. N.

    1996-08-01

    This work is an observational study of disks around low-mass, pre--main-sequence binary stars. Its purpose is to study the extent of binary-disk interactions and to determine whether binaries modify the structure of their associated disks. We present 800 micron continuum photometry of pre--main-sequence binary stars with projected separations ap < 150 AU in the Scorpius-Ophiuchus and Taurus-Auriga star-forming regions. Combining our observations with published 1300 micron continuum photometry, we find that binaries with 1 < ap < 50--100 AU have lower submillimeter continuum fluxes than wider binaries or single stars with a confidence level of greater than 99%, implying reduced disk masses. Thus, binary companions with separations less than 50--100 AU significantly influence the nature of associated disks. A simple model suggests that large gaps in disks with surface densities typical of wide-binary or single-star disks can reduce submillimeter fluxes to levels consistent with the observed limits. This model shows that the present submillimeter flux upper limits do not necessarily imply a large reduction in disk surface densities outside of cleared gaps. IRAS 60 micron fluxes show that most binaries have at least one circumstellar disk, with typical lower limits of Mdisk = 10-5 Modot. Thus, circumstellar disk surface densities are no more than two orders of magnitude smaller than those of typical disks around single stars. Our upper limits on submillimeter fluxes place upper limits of 0.005 Modot on circumbinary disk masses among binaries with 1 < ap < 50--100 AU; however, circumbinary disks are found around some binaries with separations less than a few AU null. We then present λ = 1.3 and 3 mm aperture synthesis imaging of the multiple T Tauri system UZ Tauri. UZ Tau is a hierarchical quadruple composed of a sub-AU spectroscopic binary, UZ Tau E, 530 AU distant from a 50 AU binary, UZ Tau W null. Both dust and gas emission from the 50 AU binary are at least a

  1. Ring Planetary Nebulae Ejected from Close Binary Stars

    NASA Astrophysics Data System (ADS)

    Bond, H. E.; Ciardullo, R.; Webbink, R.

    1996-12-01

    We report photometric observations of the central stars of three planetary nebulae (PNe) which appear to be thin circular rings. All three central stars have proven to be close binaries, from CCD observations made at the CTIO and KPNO 0.9-m telescopes. The southern-hemisphere PN Sp 1 is a nearly perfect circular ring. Its central star has a light curve which is a low-amplitude sinusoid with a period of 2.9 days, suggesting a reflection effect in a binary system seen nearly pole-on. We therefore suggested (Bond & Livio, ApJ 355, 568, 1990) that the nebula must be a true toroidal annulus, likewise seen nearly pole-on. SuWt 2 is another southern PN, which appears as a thin ellipse. If it were an Sp 1-like PN, seen almost edge-on, and also ejected from a close binary, we might hope to detect actual stellar eclipses. This has proven to be the case: the central star is an eclipsing binary with a period of 4.8 days. WeBo 1 is a northern PN recently discovered by Webbink and Bond. Morphologically the nebula is extremely similar to SuWt 2, in being an almost mathematically perfect ellipse. Recent observations at KPNO reveal that its central star is also a close binary, with a sinusoidal light curve and a period of approximately 5 days. It is thus becoming clear that some close binaries can undergo a common-envelope interaction that results in a much shorter orbital period accompanied by ejection of a thin nebular ring. Parallels with other objects, including SN 1987A, should be explored.

  2. Hydrodynamical evolution of coalescing binary neutron stars

    NASA Technical Reports Server (NTRS)

    Rasio, Frederic A.; Shapiro, Stuart L.

    1992-01-01

    The hydrodynamics of the final merging of two neutron stars and the corresponding gravitational wave emission is studied in detail. Various test calculations are presented, including the compressible Roche and Darwin problems and the head-on collision of two polytropes. A complete coalescence calculation is presented for the simplest case of two identical neutron stars, represented by Gamma = 2 polytropes, in a circular orbit, with their spins aligned and synchronized with the orbital rotation.

  3. Binary star orbits from speckle interferometry. 5: A combined speckle/spectroscopic study of the O star binary 15 Monocerotis

    NASA Technical Reports Server (NTRS)

    Gies, Douglas R.; Mason, Brian D.; Hartkopf, William I.; Mcalister, Harold A.; Frazin, Richard A.; Hahula, Michael E.; Penny, Laura R.; Thaller, Michelle L.; Fullerton, Alexander W.; Shara, Michael M.

    1993-01-01

    We report on the discovery of a speckle binary companion to the O7 V (f) star 15 Monocerotis. A study of published radial velocities in conjunction with new measurements from Kitt Peak National Observatory (KPNO) and IUE suggests that the star is also a spectroscopic binary with a period of 25 years and a large eccentricity. Thus, 15 Mon is the first O star to bridge the gap between the spectroscopic and visual separation regimes. We have used the star's membership in the cluster NGC 2264 together with the cluster distance to derive masses of 34 and 19 solar mass for the primary and secondary, respectively. Several of the He I line profiles display a broad shallow component which we associate with the secondary, and we estimate the secondary's classification to be O9.5 Vn. The new orbit leads to several important predictions that can be tested over the next few years.

  4. HE 0017+0055: A probable pulsating CEMP-rs star and long-period binary

    NASA Astrophysics Data System (ADS)

    Jorissen, A.; Hansen, T.; Van Eck, S.; Andersen, J.; Nordström, B.; Siess, L.; Torres, G.; Masseron, T.; Van Winckel, H.

    2016-02-01

    Context. A large fraction of the carbon-enhanced, extremely metal-poor halo giants ([Fe/H] < -2.5) are also strongly enriched in neutron-capture elements from the s process (CEMP-s stars). The conventional explanation for the properties of these stars is mass transfer from a nearby binary companion on the asymptotic giant branch (AGB). This scenario leads to a number of testable predictions in terms of the properties of the putative binary system and the resulting abundance pattern. Among the CEMP stars, some stars further exhibit overabundances in r-process elements on top of the s-process enrichment, and are tagged CEMP-rs stars. Although the nucleosynthesis process responsible for this kind of mixed abundance pattern is still under debate, CEMP-rs stars seem to belong to binary systems as do CEMP-s stars. Aims: Our aim is to present and analyse in detail our comprehensive data set of systematic radial-velocity measurements and high-resolution spectroscopy of the CEMP star HE 0017+0055. Methods: Our precise radial-velocity monitoring of HE 0017+0055 over 2940 days (8 yr) with the Nordic Optical Telescope and Mercator telescopes exhibits variability, with a period of 384 d and amplitude of 540 ± 27 m s-1 superimposed on a nearly linear long-term decline of ~1 m s-1 day-1. We used high-resolution HERMES/Mercator and Keck/HIRES spectra to derive elemental abundances with 1D LTE MARCS models. A metallicity of [Fe/H] ~ -2.4 is found, along with s-process overabundances of the order of 2 dex (with the exception of [Y/Fe] ~ + 0.5), and most notably overabundances of r-process elements like Sm, Eu, Dy, and Er in the range 0.9-2.0 dex. With [Ba/Fe] > 1.9 dex and [Eu/Fe] = 2.3 dex, HE 0017+0055 is a CEMP-rs star. We used the derived atmospheric parameters and abundances to infer HE 0017+0055 evolutionary status from a comparison with evolutionary tracks. Results: HE 0017+0055 appears to be a giant star below the tip of the red giant branch. The s-process pollution must

  5. RADIAL VELOCITY STUDIES OF CLOSE BINARY STARS. XIV

    SciTech Connect

    Pribulla, Theodor; Rucinski, Slavek M.; DeBond, Heide; De Ridder, Archie; Karmo, Toomas; Thomson, J. R.; Croll, Bryce; Ogloza, Waldemar; Pilecki, Bogumil; Siwak, Michal E-mail: rucinski@astro.utoronto.ca E-mail: ridder@astro.utoronto.ca E-mail: croll@astro.utoronto.ca E-mail: pilecki@astrouw.edu.pl

    2009-03-15

    Radial velocity (RV) measurements and sine curve fits to the orbital RV variations are presented for 10 close binary systems: TZ Boo, VW Boo, EL Boo, VZ CVn, GK Cep, RW Com, V2610 Oph, V1387 Ori, AU Ser, and FT UMa. Our spectroscopy revealed two quadruple systems, TZ Boo and V2610 Oph, while three stars showing small photometric amplitudes, EL Boo, V1387 Ori, and FT UMa, were found to be triple systems. GK Cep is a close binary with a faint third component. While most of the studied eclipsing systems are contact binaries, VZ CVn and GK Cep are detached or semidetached double-lined binaries, and EL Boo, V1387 Ori, and FT UMa are close binaries of uncertain binary type. The large fraction of triple and quadruple systems found in this sample supports the hypothesis of formation of close binaries in multiple stellar systems; it also demonstrates that low photometric amplitude binaries are a fertile ground for further discoveries of multiple systems.

  6. Hydrodynamics of coalescing binary neutron stars: Ellipsoidal treatment

    NASA Technical Reports Server (NTRS)

    Lai, Dong; Shapiro, Stuart L.

    1995-01-01

    We employ an approximate treatment of dissipative hydrodynamics in three dimensions to study the coalescence of binary neutron stars driven by the emission of gravitational waves. The stars are modeled as compressible ellipsoids obeying a polytropic equation of state; all internal fluid velocities are assumed to be linear functions of the coordinates. The hydrodynamics equations then reduce to a set of coupled ordinary differential equations for the evolution of the principal axes of the ellipsoids, the internal velocity parameters, and the binary orbital parameters. Gravitational radiation reaction and viscous dissipation are both incorporated. We set up exact initial binary equilibrium configurations and follow the transition from the quasi-static, secular decay of the orbit at large separation to the rapid dynamical evolution of the configurations just prior to contact. A hydrodynamical instability resulting from tidal interactions significantly accelerates the coalescence at small separation, leading to appreciable radial infall velocity and tidal lag angles near contact. This behavior is reflected in the gravitational waveforms and may be observable by gravitational wave detectors under construction. In cases where the neutron stars have spins which are not aligned with the orbital angular momentum, the spin-induced quadrupole moment can lead to precession of the orbital plane and therefore modulation of the gravitational wave amplitude even at large orbital radius. However, the amplitude of the modulation is small for typical neutron star binaries with spins much smaller than the orbital angular momentum.

  7. The LIGO Scientific Collaboration search for inspiralling binary neutron stars

    NASA Astrophysics Data System (ADS)

    Brown, Duncan

    2006-04-01

    The three LIGO interferometers and the GEO600 interferometer operate as a network of detectors under the LIGO Scientific Collaboration (LSC). This network has now reached unprecedented levels of sensitivity. In this talk we will present the status and current results from the binary neutron star search in LIGO/GEO data.

  8. Electromagnetic and Gravitational Outputs from Binary-Neutron-Star Coalescence

    NASA Astrophysics Data System (ADS)

    Palenzuela, Carlos; Lehner, Luis; Ponce, Marcelo; Liebling, Steven L.; Anderson, Matthew; Neilsen, David; Motl, Patrick

    2013-08-01

    The late stage of an inspiraling neutron-star binary gives rise to strong gravitational wave emission due to its highly dynamic, strong gravity. Moreover, interactions between the stellar magnetospheres can produce considerable electromagnetic radiation. We study this scenario using fully general relativistic, resistive magnetohydrodynamic simulations. We show that these interactions extract kinetic energy from the system, dissipate heat, and power radiative Poynting flux, as well as develop current sheets. Our results indicate that this power can (i) outshine pulsars in binaries, (ii) display a distinctive angular- and time-dependent pattern, and (iii) radiate within large opening angles. These properties suggest that some binary neutron-star mergers are ideal candidates for multimessenger astronomy.

  9. Observations of binary stars by speckle interferometry. II

    NASA Astrophysics Data System (ADS)

    Morgan, B. L.; Beckmann, G. K.; Scaddan, R. J.

    1980-07-01

    This is the second paper in a series describing observations of binary stars using the technique of speckle interferometry. Observations were made using the 2.5-m Newton Telescope and the 1-m telescope of the Royal Greenwich Observatory and the 1.9-m telescope of the South African Astronomical Observatory. The classical Rayleigh diffraction limits are 0.050 arcsec for the 2.5-m telescope, 0.065 arcsec for the 1.9-m telescope and 0.125 arcsec for the 1-m telescope, at a wavelength of 500 nm. The results of 29 measurements of 26 objects are presented. The objects include long period spectroscopic binaries from the 6th Catalog of Batten, close visual binary systems from the 3rd Catalog of Finsen and Worley and variable stars. Nine of the objects have not been previously resolved by speckle interferometry. New members are detected in the systems Beta Cep, p Vel and Iota UMa.

  10. Cool and luminous transients from mass-losing binary stars

    NASA Astrophysics Data System (ADS)

    Pejcha, Ondřej; Metzger, Brian D.; Tomida, Kengo

    2016-07-01

    Motivated by the recently established link between luminous red novae (LRN) and catastrophic phases of binary star evolution, we perform smoothed particle hydrodynamic calculations of outflows from binary stars with realistic equation of state and opacities. We focus on the case of mass loss from the outer Lagrangian point (L2), where the resulting spiral stream experiences tidal torques from the binary and becomes unbound. As the individual spiral arms merge and collide near the binary, the outflow thermalizes about 5% of its kinetic energy. For reasonable binary parameters, the outflow can produce luminosities up to 106 L ⨀ with effective temperatures between 500 and 6000 K, depending on the optical depth through the outflow. This is compatible with many examples of the LRN such as V838 Mon and V1309 Sco. The luminosity and the expansion velocity are correlated, as is roughly observed in the known LRN. The outflow readily forms dust, leading to great variations of the appearance of the transient as a function of the viewing angle. Our results are relevant for a more general class of equatorial outflows with asymptotic velocity and heating rate near the binary proportional to its orbital speed.

  11. Orbital evolution of eccentric interacting binary star systems

    NASA Astrophysics Data System (ADS)

    Sepinsky, Jeremy Francis

    2009-06-01

    We provide a comprehensive description of the long-term (secular) orbital evolution of eccentric interacting binary systems. The evolution of circular interacting binary systems is a well studied phenomenon, but observations have shown the existence of a small but significant number of eccentric interacting binary systems. We begin by extending the commonly accepted Roche formalism for binary interacting to include eccentric orbits and asynchronously rotating stars. Using this, we calculate orbital trajectories for particles ejected from a Roche lobe-filling donor star at the periastron of the eccentric orbit. These particles admit of three possible trajectories: direct impact onto the secondary star, self accretion back onto the donor star, and the formation of a disk about the accretor. We provide a proscription for determining a priorithe trajectory of the particle given the initial system parameters, as well as describe the secular evolution of the system for each of the three cases described above. We find that these orbital evolution timescales are comparable to the mass transfer timescale which can be significantly longer than expected from the literature. Furthermore, while it is commonly assumed that any mass transfer interactions will act to circularize the orbit, we find that there are regimes of parameter space where mass transfer can cause an increase in eccentricity, and can do so at a timescale comparable to the circularization timescale created by tidal interactions. The formalism presented here can be incorporated into binary evolution and population synthesis models to create a self-consistent treatment of mass transfer in eccentric binaries.

  12. Active Longitudes and Flip-Flops in Binary Stars

    NASA Astrophysics Data System (ADS)

    Korhonen, Heidi; Järvinen, Silva P.

    2007-08-01

    In many active stars the spots concentrate on two permanent active longitudes which are 180 degrees apart. In some of these stars the dominant part of the spot activity changes the longitude every few years. This so-called flip-flop phenomenon was first reported in the early 1990's in the single, late type giant FK Com. Since then flip-flops have been reported also on binary stars, young solar type stars and the Sun itself. Even though this phenomenon has been detected on many different kinds of active stars, still less than ten stars are known to exhibit this effect. Therefore no statistically significant correlation between the stellar parameters and the flip-flop phenomenon can be carried out. Here we present results from investigation where we have studied the long-term photometry of several magnetically active RS CVn binaries to see whether or not they show permanent active longitudes and the flip-flop phenomenon. We find that it is very common for the active regions to occur on permanent active longitudes, and some of these stars also show clear flip-flop phenomenon.

  13. Binary stars and the UVX in early-type galaxies

    NASA Astrophysics Data System (ADS)

    Hernández-Pérez, Fabiola; Bruzual, Gustavo

    2014-11-01

    We use the Hernández-Pérez and Bruzual (HB13) stellar population synthesis models to study the role of interacting binary pairs as progenitors of extreme horizontal branch (EHB) stars. We assemble a sample of 3417 early-type galaxies observed both in the optical (SDSS-DR8) and the UV (GALEX-GR6). The galaxies in our sample can be classified according to their position in the colour-colour diagram as UV-weak or red-sequence galaxies (˜48 per cent), UV-strong or UVX galaxies (˜9 per cent), and recent star-forming galaxies (˜43 per cent). Analysing this sample using the HB13 models for various choices of basic model parameters, we conclude that (a) the UVr colours of UV-weak and UV-strong galaxies are reproduced by the models as long as the fraction of binary stars is at least 15 per cent. (b) Higher metallicity models (Z = 0.02 and 0.03) reproduce the colours of UV-weak and UV-strong galaxies better than lower Z models. The Z = 0.03 model is slightly bluer than the Z = 0.02 model in the UV-strong region, indicating a weak relationship between UVX and Z. (c) The strength of UVX increases with age in the model population. This is at variance with the results of other models that include binary stars as progenitors of EHB stars.

  14. Δ μ binaries among stars with large proper motions

    NASA Astrophysics Data System (ADS)

    Khovritchev, M. Yu.; Kulikova, A. M.

    2015-12-01

    Based on observations performed with the Pulkovo normal astrograph in 2008-2015 and data from sky surveys (DSS, 2MASS, SDSS DR12, WISE), we have investigated the motions of 1308 stars with proper motions larger than 300 mas yr-1 down to magnitude 17. The main idea of our search for binary stars based on this material is reduced to comparing the quasi-mean (POSS2-POSS1; an epoch difference of ≈50 yr) and quasi-instantaneous (2МASS, SDSS, WISE, Pulkovo; an epoch difference of ≈10 yr) proper motions. If the difference is statistically significant compared to the proper motion errors, then the object may be considered as a Δ μ-binary candidate. One hundred and twenty one stars from among those included in the observational program satisfy this requirement. Additional confirmations of binarity for a number of stars have been obtained by comparing the calculated proper motions with the data from several programs of stellar trigonometric parallax determinations and by analyzing the asymmetry of stellar images on sky-survey CCD frames. Analysis of the highly accurate SDSS photometric data for four stars (J0656+3827, J0838+3940, J1229+5332, J2330+4639) allows us to reach a conclusion about the probability that these Δ μ binaries are white dwarf +Mdwarf pairs.

  15. Nitrogen enhancement in metal-poor dwarfs - From inside or outside?

    NASA Astrophysics Data System (ADS)

    Spite, F.; Spite, M.

    1987-06-01

    The five known metal-poor dwarfs with an enhanced N/Fe ratio have been observed spectroscopically. Two of these dwarfs have no lithium line; the absence of lithium is most probably accounted for by the usual convective destruction. The three other dwrfs have the same lithium abundance as the normal metal-poor dwarfs (Spite, Maillard, and Spite, 1984). This excludes the deep mixing process as the general source of nitrogen enhancement, since lithium is destroyed in deep (hot) layers. Deep mixing had been previously found unlikely in metal-poor dwarfs (Da Costa and Demarque, 1982). The discussion stresses the remarkable uniformity of the lithium abundance in metal-poor dwarfs, and shows that the N-rich contaminating matter has a high N/H ratio. Finally, the Al abundance is not greatly enhanced in these five stars.

  16. Merger of binary neutron stars in numerical relativity

    NASA Astrophysics Data System (ADS)

    Shibata, Masaru

    2014-09-01

    The merger of binary neutron stars is one of most promising sources of gravitational waves. It is also a promising candidate for the central engine of short-hard gamma-ray bursts and a source of the strong transient electromagnetic signal that could be the counterpart of gravitational-wave signals. Numerical relativity is probably the unique tool for theoretically exploring the merger process, and now, it is powerful enough to provide us a wide variety of aspects of the binary-neutron-star merger. In this talk, I will summarize our current understanding of the entire merger event that is obtained by a large-scale numerical-relativity simulations. In particular, I focus on the relation between the neutron-star equation of state and gravitational waves emitted during the late inspiral and merger phase, and observable electromagnetic signal that is likely to be emitted by the dynamical ejecta through r-process nucleosynthesis.

  17. Photometric study of the active binary star V1430 Aquilae

    NASA Astrophysics Data System (ADS)

    Erdem, A.; Sürgit, D.

    2006-05-01

    New BVR light curves and a photometric analysis of the eclipsing binary star V1430 Aql are presented. The light curves were obtained at the Çanakkale Onsekiz Mart University Observatory in 2004. The light curves are generally those of detached eclipsing binaries, but there are large asymmetries between maxima. New BVR light curves were analysed with an ILOT procedure. Light curve asymmetries of the system were explained in terms of large dark starspots on the primary component. The primary star shows a long-lived and quasi-poloidal spot distribution with active longitudes in opposite hemispheres. Absolute parameters of the system were derived. We also discuss the evolution of the system: the components are likely to be pre-main sequence stars, but a post-main sequence stage cannot be ruled out. More observations are needed to decide this point.

  18. PRIMORDIAL r-PROCESS DISPERSION IN METAL-POOR GLOBULAR CLUSTERS

    SciTech Connect

    Roederer, Ian U.

    2011-05-01

    Heavy elements, those produced by neutron-capture reactions, have traditionally shown no star-to-star dispersion in all but a handful of metal-poor globular clusters (GCs). Recent detections of low [Pb/Eu] ratios or upper limits in several metal-poor GCs indicate that the heavy elements in these GCs were produced exclusively by an r-process. Re-examining GC heavy element abundances from the literature, we find unmistakable correlations between the [La/Fe] and [Eu/Fe] ratios in four metal-poor GCs (M5, M15, M92, and NGC 3201), only two of which were known previously. This indicates that the total r-process abundances vary from star to star (by factors of 2-6) relative to Fe within each GC. We also identify potential dispersion in two other GCs (M3 and M13). Several GCs (M12, M80, and NGC 6752) show no evidence of r-process dispersion. The r-process dispersion is not correlated with the well-known light element dispersion, indicating that it was present in the gas throughout the duration of star formation. The observations available at present suggest that star-to-star r-process dispersion within metal-poor GCs may be a common but not ubiquitous phenomenon that is neither predicted by nor accounted for in current models of GC formation and evolution.

  19. Magnetised winds in single and binary star systems

    NASA Astrophysics Data System (ADS)

    Johnstone, Colin

    2016-07-01

    Stellar winds are fundamentally important for the stellar magnetic activity evolution and for the immediate environment surrounding their host stars. Ionised winds travel at hundreds of km/s, impacting planets and clearing out large regions around the stars called astropheres. Winds influence planets in many ways: for example, by compressing the magnetosphere and picking up atmospheric particles, they can cause significant erosion of a planetary atmosphere. By removing angular momentum, winds cause the rotation rates of stars to decrease as they age. This causes the star's magnetic dynamo to decay, leading to a significant decay in the star's levels of X-ray and extreme ultraviolet emission. Despite their importance, little is currently known about the winds of other Sun-like stars. Their small mass fluxes have meant that no direct detections have so far been possible. What is currently known has either been learned indirectly or through analogies with the solar wind. In this talk, I will review what is known about the properties and evolution of the winds of other Sun-like stars. I will also review wind dynamics in binary star systems, where the winds from both stars impact each other, leading to shocks and compression regions.

  20. ADIABATIC MASS LOSS IN BINARY STARS. I. COMPUTATIONAL METHOD

    SciTech Connect

    Ge Hongwei; Chen Xuefei; Han Zhanwen; Webbink, Ronald F. E-mail: mshjell@gmail.co

    2010-07-10

    The asymptotic response of donor stars in interacting binary systems to very rapid mass loss is characterized by adiabatic expansion throughout their interiors. In this limit, energy generation and heat flow through the stellar interior can be neglected. We model this response by constructing model sequences, beginning with a donor star filling its Roche lobe at an arbitrary point in its evolution, holding its specific entropy and composition profiles fixed as mass is removed from the surface. The stellar interior remains in hydrostatic equilibrium. Luminosity profiles in these adiabatic models of mass-losing stars can be reconstructed from the specific entropy profiles and their gradients. These approximations are validated by comparison with time-dependent binary mass transfer calculations. We describe how adiabatic mass-loss sequences can be used to quantify threshold conditions for dynamical timescale mass transfer, and to establish the range of post-common envelope binaries that are allowed energetically. In dynamical timescale mass transfer, the adiabatic response of the donor star drives it to expand beyond its Roche lobe, leading to runaway mass transfer and the formation of a common envelope with its companion star. For donor stars with surface convection zones of any significant depth, this runaway condition is encountered early in mass transfer, if at all; but for main-sequence stars with radiative envelopes, it may be encountered after a prolonged phase of thermal timescale mass transfer, a so-called delayed dynamical instability. We identify the critical binary mass ratio for the onset of dynamical timescale mass transfer as that ratio for which the adiabatic response of the donor star radius to mass loss matches that of its Roche lobe at some point during mass transfer; if the ratio of donor to accretor masses exceeds this critical value, dynamical timescale mass transfer ensues. In common envelope evolution, the dissipation of orbital energy of the

  1. Synergies in Astrometry: Predicting Navigational Error of Visual Binary Stars

    NASA Astrophysics Data System (ADS)

    Gessner Stewart, Susan

    2015-08-01

    Celestial navigation can employ a number of bright stars which are in binary systems. Often these are unresolved, appearing as a single, center-of-light object. A number of these systems are, however, in wide systems which could introduce a margin of error in the navigation solution if not handled properly. To illustrate the importance of good orbital solutions for binary systems - as well as good astrometry in general - the relationship between the center-of-light versus individual catalog position of celestial bodies and the error in terrestrial position derived via celestial navigation is demonstrated. From the list of navigational binary stars, fourteen such binary systems with at least 3.0 arcseconds apparent separation are explored. Maximum navigational error is estimated under the assumption that the bright star in the pair is observed at maximum separation, but the center-of-light is employed in the navigational solution. The relationships between navigational error and separation, orbital periods, and observers' latitude are discussed.

  2. Ba STARS AND OTHER BINARIES IN FIRST AND SECOND GENERATION STARS IN GLOBULAR CLUSTERS

    SciTech Connect

    D'Orazi, Valentina; Gratton, Raffaele; Lucatello, Sara; Carretta, Eugenio; Bragaglia, Angela; Marino, Anna F.

    2010-08-20

    The determination of the Ba abundance in globular cluster (GC) stars is a very powerful test to address several issues in the framework of multiple population scenarios. We measured the Ba content for a sample of more than 1200 stars in 15 Galactic GCs, using high-resolution FLAMES/Giraffe spectra. We found no variation in [Ba/Fe] ratios for different stellar populations within each cluster; this means that low-mass asymptotic giant branch stars do not significantly contribute to the intracluster pollution. Very interestingly, we found that the fraction of Ba stars in first generation (FG) stars is close to the values derived for field stars ({approx}2%); on the other hand, second generation (SG) stars present a significantly lower fraction. An independent and successful test, based on radial velocity variations among giant stars in NGC 6121, confirms our finding: the binary fraction among FG stars is about {approx}12%, to be compared with {approx}1% of SG stars. This is an evidence that SG stars formed in a denser environment, where infant mortality of binary systems was particularly efficient.

  3. Electromagnetic field dynamics in Binary Neutron Stars

    NASA Astrophysics Data System (ADS)

    Palenzuela, Carlos; Anderson, Matthew; Hirschmann, Eric; Lehner, Luis; Liebling, Steven; Neilsen, David; Motl, Patrick

    2011-04-01

    Neutron star mergers represent one of the most promising sources of gravitational waves (GW) within the bandwidth of advLIGO. In addition to GW, strong magnetic fields may offer the possibility of a characteristic electromagnetic signature allowing for concurrent detection. In this talk we present results from numerical evolutions of such mergers, studying the dynamics of both the gravitational and electromagnetic degrees of freedom.

  4. The MACHO Project LMC variable star inventory. V. Classification and orbits of 611 eclipsing binary stars

    SciTech Connect

    The MACHO Collaboration

    1997-07-01

    We report the characteristics of 611 eclipsing binary stars in the Large Megallanic Cloud found by using the MACHO Project photometry database. The sample is magnitude limited, and extends down the main sequence to about spectral type A0. Many evolved binaries are also included. Each eclipsing binary is classified according to the traditional scheme of the {ital General Catalogue of Variable Stars} (EA and EB), and also according to a new decimal classification scheme defined in this paper. The new scheme is sensitive to the two major sources of variance in eclipsing binary star light curves{emdash}the sum of radii, and the surface-brightness ratio, and allow greater precision in characterizing the light curves. Examples of each type of light curve and their variations are given. Sixty-four of the eclipsing binaries have eccentric, rather than circular, orbits. The ephemeris and principal photometric characteristics of each eclipsing binary are listed in a table. Photometric orbits based on the Nelson{endash}Davis{endash}Etzel model have been fitted to all light curves. These data will be useful for planning future observations of these binaries. Plots of all data and fitted orbits and a table of the fitted orbital parameters are available on the AAS CD-ROM series, Vol. 9, 1997. These data are also available at the MACHO home page (http://wwwmacho.mcmaster.ca/). {copyright} {ital 1997 American Astronomical Society.}

  5. Resolving subdwarf B stars in binaries by HST imaging

    NASA Astrophysics Data System (ADS)

    Heber, U.; Moehler, S.; Napiwotzki, R.; Thejll, P.; Green, E. M.

    2002-03-01

    The origin of subluminous B stars is still an unsolved problem in stellar evolution. Single star as well as close binary evolution scenarios have been invoked but until now have met with little success. We have carried out a small survey of spectroscopic binary candidates (19 systems consisting of an sdB star and late type companion) with the Planetary Camera of the WFPC2 onboard Hubble Space Telescope to test these scenarios. Monte Carlo simulations indicate that by imaging the programme stars in the R-band about one third of the sample (6-7 stars) should be resolved at a limiting angular resolution of 0.1 arcsec if they have linear separations like main sequence stars (``single star evolution''). None should be resolvable if all systems were produced by close binary evolution. In addition we expect three triple systems to be present in our sample. Most of these, if not all, should be resolvable. Components were resolved in 6 systems with separations between 0.2 arcsec and 4.5 arcsec. However, only in the two systems TON 139 and PG 1718+519 (separations 0.32 arcsec and 0.24 arcsec, respectively) do the magnitudes of the resolved components match the expectations from the deconvolution of the spectral energy distribution. These two stars could be physical binaries whereas in the other cases the nearby star may be a chance projection or a third component. Radial velocity measurements indicate that the resolved system TON 139 is a triple system, with the sdB having a close companion that does not contribute detectably to the integrated light of the system. Radial velocity information for the second resolved system, PG 1718+519, is insufficient. Assuming that it is not a triple system, it would be the only resolved system in our sample. Accordingly the success rate would be only 5% which is clearly below the prediction for single star evolution. We conclude that the distribution of separations of sdB binaries deviates strongly from that of normal stars. Our results

  6. Unification of Binary Star Ephemeris Solutions

    NASA Astrophysics Data System (ADS)

    Wilson, R. E.; Van Hamme, W.

    2014-01-01

    Time-related binary system characteristics such as orbital period, its rate of change, apsidal motion, and variable light-time delay due to a third body, are measured in two ways that can be mutually complementary. The older way is via eclipse timings, while ephemerides by simultaneous whole light and velocity curve analysis have appeared recently. Each has its advantages, for example, eclipse timings typically cover relatively long time spans while whole curves often have densely packed data within specific intervals and allow access to systemic properties that carry additional timing information. Synthesis of the two information sources can be realized in a one step process that combines several data types, with automated weighting based on their standard deviations. Simultaneous light-velocity-timing solutions treat parameters of apsidal motion and the light-time effect coherently with those of period and period change, allow the phenomena to interact iteratively, and produce parameter standard errors based on the quantity and precision of the curves and timings. The logic and mathematics of the unification algorithm are given, including computation of theoretical conjunction times as needed for generation of eclipse timing residuals. Automated determination of eclipse type, recovery from inaccurate starting ephemerides, and automated data weighting are also covered. Computational examples are given for three timing-related cases—steady period change (XY Bootis), apsidal motion (V526 Sagittarii), and the light-time effect due to a binary's reflex motion in a triple system (AR Aurigae). Solutions for all combinations of radial velocity, light curve, and eclipse timing input show consistent results, with a few minor exceptions.

  7. Unification of binary star ephemeris solutions

    SciTech Connect

    Wilson, R. E.; Van Hamme, W. E-mail: vanhamme@fiu.edu

    2014-01-10

    Time-related binary system characteristics such as orbital period, its rate of change, apsidal motion, and variable light-time delay due to a third body, are measured in two ways that can be mutually complementary. The older way is via eclipse timings, while ephemerides by simultaneous whole light and velocity curve analysis have appeared recently. Each has its advantages, for example, eclipse timings typically cover relatively long time spans while whole curves often have densely packed data within specific intervals and allow access to systemic properties that carry additional timing information. Synthesis of the two information sources can be realized in a one step process that combines several data types, with automated weighting based on their standard deviations. Simultaneous light-velocity-timing solutions treat parameters of apsidal motion and the light-time effect coherently with those of period and period change, allow the phenomena to interact iteratively, and produce parameter standard errors based on the quantity and precision of the curves and timings. The logic and mathematics of the unification algorithm are given, including computation of theoretical conjunction times as needed for generation of eclipse timing residuals. Automated determination of eclipse type, recovery from inaccurate starting ephemerides, and automated data weighting are also covered. Computational examples are given for three timing-related cases—steady period change (XY Bootis), apsidal motion (V526 Sagittarii), and the light-time effect due to a binary's reflex motion in a triple system (AR Aurigae). Solutions for all combinations of radial velocity, light curve, and eclipse timing input show consistent results, with a few minor exceptions.

  8. A Binary Model for the Emission Line Star FX Velorum

    NASA Astrophysics Data System (ADS)

    Blake, M.; Hunter, M.

    2015-06-01

    FX Vel is a southern, young variable star which shows large variations in brightness. In examining the environments where planets may form, disks around young stars provide important clues as to how long such disks might last. We discuss several possible scenarios for the structure of FX Vel, including a binary model similar to EE Cep and the possibility that FX Vel may be a UXor variable, a class of young stars with disks. This could also explain the colors and irregular variation in brightness of the star. We suggest FX Vel may be a blue straggler member of the open cluster ASCC48 based upon its position on the cluster CMD and proper motions. More data is required examine the alternate possibility of FX Vel being a member of Teutsch 101. A spectroscopic study of FX Vel would be valuable.

  9. Gravitational and Electromagnetic Emission from Binary Neutron Star Mergers

    NASA Astrophysics Data System (ADS)

    Motl, Patrick M.; Palenzuela, C.; Lehner, L.; Ponce, M.; Liebling, S. L.; Anderson, M.; Neilsen, D.

    2013-06-01

    The inspiral of a neutron star - neutron star binary is a leading candidate for strong emission of gravitational waves. The interaction between the stellar magnetospheres may also give rise to electromagnetic emissions accompanying the gravity waves as the neutron stars inspiral and merge. We present results from a set of resistive magnetohydrodynamic simulations of mergers computed with full general relativity. We vary the initial magnetic field of the neutron stars including cases where the fields are initially aligned, anit-aligned and where one star’s field dominates over its companion. This presentation is based upon work supported by the National Aeronautics and Space Administration under grant No. NNX13AH01G through the astrophysics theory program.

  10. SPECTROSCOPIC METALLICITY DETERMINATIONS FOR W UMa-TYPE BINARY STARS

    SciTech Connect

    Rucinski, Slavek M.; Pribulla, Theodor; Budaj, Jan E-mail: pribulla@ta3.sk

    2013-09-15

    This study is the first attempt to determine the metallicities of W UMa-type binary stars using spectroscopy. We analyzed about 4500 spectra collected at the David Dunlap Observatory. To circumvent problems caused by the extreme spectral line broadening and blending and by the relatively low quality of the data, all spectra were subject to the same broadening function (BF) processing to determine the combined line strength in the spectral window centered on the Mg I triplet between 5080 A and 5285 A. All individual integrated BFs were subsequently orbital-phase averaged to derive a single line-strength indicator for each star. The star sample was limited to 90 W UMa-type (EW) binaries with the strict phase-constancy of colors and without spectral contamination by spectroscopic companions. The best defined results were obtained for an F-type sub-sample (0.32 < (B - V){sub 0} < 0.62) of 52 binaries for which integrated BF strengths could be interpolated in the model atmosphere predictions. The logarithmic relative metallicities, [M/H], for the F-type sub-sample indicate metal abundances roughly similar to the solar metallicity, but with a large scatter which is partly due to combined random and systematic errors. Because of the occurrence of a systematic color trend resulting from inherent limitations in our approach, we were forced to set the absolute scale of metallicities to correspond to that derived from the m{sub 1} index of the Stroemgren uvby photometry for 24 binaries of the F-type sub-sample. The trend-adjusted metallicities [M/H]{sub 1} are distributed within -0.65 < [M/H]{sub 1} < +0.50, with the spread reflecting genuine metallicity differences between stars. One half of the F-sub-sample binaries have [M/H]{sub 1} within -0.37 < [M/H]{sub 1} < +0.10, a median of -0.04 and a mean of -0.10, with a tail toward low metallicities, and a possible bias against very high metallicities. A parallel study of kinematic data, utilizing the most reliable and recently

  11. Spectroscopic Metallicity Determinations for W UMa-type Binary Stars

    NASA Astrophysics Data System (ADS)

    Rucinski, Slavek M.; Pribulla, Theodor; Budaj, Ján

    2013-09-01

    This study is the first attempt to determine the metallicities of W UMa-type binary stars using spectroscopy. We analyzed about 4500 spectra collected at the David Dunlap Observatory. To circumvent problems caused by the extreme spectral line broadening and blending and by the relatively low quality of the data, all spectra were subject to the same broadening function (BF) processing to determine the combined line strength in the spectral window centered on the Mg I triplet between 5080 Å and 5285 Å. All individual integrated BFs were subsequently orbital-phase averaged to derive a single line-strength indicator for each star. The star sample was limited to 90 W UMa-type (EW) binaries with the strict phase-constancy of colors and without spectral contamination by spectroscopic companions. The best defined results were obtained for an F-type sub-sample (0.32 < (B - V)0 < 0.62) of 52 binaries for which integrated BF strengths could be interpolated in the model atmosphere predictions. The logarithmic relative metallicities, [M/H], for the F-type sub-sample indicate metal abundances roughly similar to the solar metallicity, but with a large scatter which is partly due to combined random and systematic errors. Because of the occurrence of a systematic color trend resulting from inherent limitations in our approach, we were forced to set the absolute scale of metallicities to correspond to that derived from the m 1 index of the Strömgren uvby photometry for 24 binaries of the F-type sub-sample. The trend-adjusted metallicities [M/H]1 are distributed within -0.65 < [M/H]1 < +0.50, with the spread reflecting genuine metallicity differences between stars. One half of the F-sub-sample binaries have [M/H]1 within -0.37 < [M/H]1 < +0.10, a median of -0.04 and a mean of -0.10, with a tail toward low metallicities, and a possible bias against very high metallicities. A parallel study of kinematic data, utilizing the most reliable and recently obtained proper motion and radial

  12. Spectral Classification of Unresolved Binary Stars with Artificial Neural Networks

    NASA Astrophysics Data System (ADS)

    Weaver, Wm. Bruce

    2000-09-01

    An artificial neural network technique has been developed to perform two-dimensional spectral classification of the components of binary stars. The spectra are based on the 15 Å resolution near-infrared (NIR) spectral classification system described by Torres-Dodgen & Weaver. Using the spectrum with no manual intervention except wavelength registration, a single artificial neural network (ANN) can classify these spectra with Morgan-Keenan types with an average accuracy of about 2.5 types (subclasses) in temperature and about 0.45 classes in luminosity for up to 3 mag of difference in luminosity. The error in temperature classification does not increase substantially until the secondary contributes less than 10% of the light of the system. By following the coarse-classification ANN with a specialist ANN, the mean absolute errors are reduced to about 0.5 types in temperature and 0.33 classes in luminosity. The resulting ANN network was applied to seven binary stars.

  13. Cool and luminous transients from mass-losing binary stars

    NASA Astrophysics Data System (ADS)

    Pejcha, Ondřej; Metzger, Brian D.; Tomida, Kengo

    2016-02-01

    We study transients produced by equatorial disc-like outflows from catastrophically mass-losing binary stars with an asymptotic velocity and energy deposition rate near the inner edge which are proportional to the binary escape velocity vesc. As a test case, we present the first smoothed-particle radiation-hydrodynamics calculations of the mass loss from the outer Lagrange point with realistic equation of state and opacities. The resulting spiral stream becomes unbound for binary mass ratios 0.06 ≲ q ≲ 0.8. For synchronous binaries with non-degenerate components, the spiral-stream arms merge at a radius of ˜10a, where a is the binary semi-major axis, and the accompanying shock thermalizes about 10 per cent of the kinetic power of the outflow. The mass-losing binary outflows produce luminosities reaching up to ˜106 L⊙ and effective temperatures spanning 500 ≲ Teff ≲ 6000 K, which is compatible with many of the class of recently discovered red transients such as V838 Mon and V1309 Sco. Dust readily forms in the outflow, potentially in a catastrophic global cooling transition. The appearance of the transient is viewing angle-dependent due to vastly different optical depths parallel and perpendicular to the binary plane. We predict a correlation between the peak luminosity and the outflow velocity, which is roughly obeyed by the known red transients. Outflows from mass-losing binaries can produce luminous (105 L⊙) and cool (Teff ≲ 1500 K) transients lasting a year or longer, as has potentially been detected by Spitzer surveys of nearby galaxies.

  14. The Signature of Black Hole-Neutron Star Binaries

    NASA Astrophysics Data System (ADS)

    Liebling, Steven; Anderson, Matthew; Hirschmann, Eric; Lehner, Luis; Motl, Patrick; Neilsen, David; Palenzuela, Carlos

    2011-04-01

    Black hole-neutron star (BHNS) binaries are key gravitational wave sources, merging in the frequency band to which Earth-based GW detectors are most sensitive. Furthermore, as possible candidates for short-hard gamma ray bursts, combined observations in both gravitational and electromagnetic bands of BHNS mergers is thus an exciting possibility. This talk will discuss results from simulations that account for gravitational and magnetic effects as well as connections with processes capable of explaining key features of gamma ray bursts.

  15. NGC 1252: a high altitude, metal poor open cluster remnant

    NASA Astrophysics Data System (ADS)

    de la Fuente Marcos, R.; de la Fuente Marcos, C.; Moni Bidin, C.; Carraro, G.; Costa, E.

    2013-09-01

    If stars form in clusters but most stars belong to the field, understanding the details of the transition from the former to the latter is imperative to explain the observational properties of the field. Aging open clusters are one of the sources of field stars. The disruption rate of open clusters slows down with age but, as an object gets older, the distinction between the remaining cluster or open cluster remnant (OCR) and the surrounding field becomes less and less obvious. As a result, finding good OCR candidates or confirming the OCR nature of some of the best candidates still remain elusive. One of these objects is NGC 1252, a scattered group of about 20 stars in Horologium. Here we use new wide-field photometry in the UBVI passbands, proper motions from the Yale/San Juan SPM 4.0 catalogue and high-resolution spectroscopy concurrently with results from N-body simulations to decipher NGC 1252's enigmatic character. Spectroscopy shows that most of the brightest stars in the studied area are chemically, kinematically and spatially unrelated to each other. However, after analysing proper motions, we find one relevant kinematic group. This sparse object is relatively close (˜1 kpc), metal poor and is probably not only one of the oldest clusters (3 Gyr) within 1.5 kpc from the Sun but also one of the clusters located farthest from the disc, at an altitude of nearly -900 pc. That makes NGC 1252 the first open cluster that can be truly considered a high Galactic altitude OCR: an unusual object that may hint at a star formation event induced on a high Galactic altitude gas cloud. We also conclude that the variable TW Horologii and the blue straggler candidate HD 20286 are unlikely to be part of NGC 1252. NGC 1252 17 is identified as an unrelated, Population II cannonball star moving at about 400 km s-1.

  16. A catalogue of temperatures for Kepler eclipsing binary stars

    NASA Astrophysics Data System (ADS)

    Armstrong, D. J.; Gómez Maqueo Chew, Y.; Faedi, F.; Pollacco, D.

    2014-02-01

    We have combined the Kepler Eclipsing Binary Catalogue with information from the HES, KIS and 2MASS photometric surveys to produce spectral energy distribution fits to over 2600 eclipsing binaries in the catalogue over a wavelength range of 0.36-2.16 Å. We present primary (T1) and secondary (T2) stellar temperatures, plus information on the stellar radii and system distance ratios. The derived temperatures are on average accurate to 370 K in T1 and 620 K in T2. Our results improve on the similarly derived physical parameters of the Kepler Input Catalogue through consideration of both stars of the binary system rather than a single star model, and inclusion of additional U-band photometry. We expect these results to aid future uses of the Kepler eclipsing binary data, both in target selection and to inform users of the extremely high-precision light curves available. We do not include surface gravities or system metallicities, as these were found to have an insignificant effect on the observed photometric bands.

  17. RADIAL VELOCITY STUDIES OF CLOSE BINARY STARS. XV

    SciTech Connect

    Pribulla, Theodor; Rucinski, Slavek M.; Blake, R. M.; Lu, Wenxian; Thomson, J. R.; DeBond, Heide; Karmo, Toomas; De Ridder, Archie; Ogloza, Waldemar; Stachowski, Greg; Siwak, Michal E-mail: rucinski@astro.utoronto.ca E-mail: karmo@astro.utoronto.ca E-mail: ogloza@ap.krakow.pl E-mail: siwak@oa.uj.edu.pl

    2009-03-15

    Radial velocity (RV) measurements and sine curve fits to the orbital RV variations are presented for the last eight close binary systems analyzed in the same way as in the previous papers of this series: QX And, DY Cet, MR Del, HI Dra, DD Mon, V868 Mon, ER Ori, and Y Sex. For another seven systems (TT Cet, AA Cet, CW Lyn, V563 Lyr, CW Sge, LV Vir, and MW Vir), phase coverage is insufficient to provide reliable orbits but RVs of individual components were measured. Observations of a few complicated systems observed throughout the David Dunlap Observatory (DDO) close binary program are also presented; among them is an especially interesting multiple system V857 Her which-in addition to the contact binary-very probably contains one or more subdwarf components of much earlier spectral type. All suspected binaries which were found to be most probably pulsating stars are briefly discussed in terms of mean RVs and projected rotation velocities (vsin i) as well as spectral-type estimates. In two of them, CU CVn and V752 Mon, the broadening functions show a clear presence of nonradial pulsations. The previously missing spectral types for Paper I are given here in addition to such estimates for most of the program stars of this paper.

  18. Kitt Peak Speckle Interferometry of Close Visual Binary Stars (Abstract)

    NASA Astrophysics Data System (ADS)

    Gener, R.; Rowe, D.; Smith, T. C.; Teiche, A.; Harshaw, R.; Wallace, D.; Weise, E.; Wiley, E.; Boyce, G.; Boyce, P.; Branston, D.; Chaney, K.; Clark, R. K.; Estrada, C.; Estrada, R.; Frey, T.; Green, W. L.; Haurberg, N.; Jones, G.; Kenney, J.; Loftin, S.; McGieson, I.; Patel, R.; Plummer, J.; Ridgely, J.; Trueblood, M.; Westergren, D.; Wren, P.

    2014-12-01

    (Abstract only) Speckle interferometry can be used to overcome normal seeing limitations by taking many very short exposures at high magnification and analyzing the resulting speckles to obtain the position angles and separations of close binary stars. A typical speckle observation of a close binary consists of 1,000 images, each 20 milliseconds in duration. The images are stored as a multi-plane FITS cube. A portable speckle interferometry system that features an electron-multiplying CCD camera was used by the authors during two week-long observing runs on the 2.1-meter telescope at Kitt Peak National Observatory to obtain some 1,000 data cubes of close binaries selected from a dozen different research programs. Many hundreds of single reference stars were also observed and used in deconvolution to remove undesirable atmospheric and telescope optical effects. The database of well over one million images was reduced with the Speckle Interferometry Tool of platesolve3. A few sample results are provided. During the second Kitt Peak run, the McMath-Pierce 1.6- and 0.8-meter solar telescopes were evaluated for nighttime speckle interferometry, while the 0.8-meter Coude feed was used to obtain differential radial velocities of short arc binaries.

  19. VX Her: Eclipsing Binary System or Single Variable Star

    NASA Astrophysics Data System (ADS)

    Perry, Kathleen; Castelaz, Michael; Henson, Gary; Boghozian, Andrew

    2015-01-01

    VX Her is a pulsating variable star with a period of .4556504 days. It is believed to be part of an eclipsing binary system (Fitch et al. 1966). This hypothesis originated from Fitch seeing VX Her's minimum point on its light curve reaching a 0.7 magnitude fainter than normal and remaining that way for nearly two hours. If VX Her were indeed a binary system, I would expect to see similar results with a fainter minimum and a broader, more horizontal dip. Having reduced and analyzed images from the Southeastern Association for Research in Astronomy Observatory in Chile and Kitt Peak, as well as images from a 0.15m reflector at East Tennessee State University, I found that VX Her has the standard light curve of the prototype variable star, RR Lyrae. Using photometry, I found no differing features in its light curve to suggest that it is indeed a binary system. However, more observations are needed in case VX Her is a wide binary.

  20. Single versus binary star progenitors of Type IIb supernovae

    NASA Astrophysics Data System (ADS)

    Sravan, Niharika

    2016-07-01

    Stripped-envelope supernovae (SNe) represent a challenge to our understanding of massive star evolution. Wind mass loss and binary interactions are the leading candidates to explain observations. The latter has gained support in the recent years with growing evidence that mass-loss rates due to line-driven winds are, in reality, 2 - 3 times lower. Type IIb SNe retain a small amount of their Hydrogen envelope before undergoing core-collapse and are the only class of stripped-envelope SNe with identified progenitors. Thus they are powerful tools for testing our understanding of massive stellar evolution. To identify possible evolutionary pathways to Type IIb SNe, we use Modules for Experiments in Stellar Astrophysics (MESA) to model a large population of single and binary star sequences covering a broad parameter space with a wide range of component masses and initial orbital periods and identify those that undergo core-collapse with 0.01 to 0.5 solar masses of residual Hydrogen envelope. We find no single star Type IIb progenitors in the parameter space covered. We find a few Type IIb binary progenitors. These sequences have initial mass ratios greater than 0.6, wide orbital periods and undergo non-conservative mass transfer.

  1. Linking electromagnetic and gravitational radiation in coalescing binary neutron stars

    NASA Astrophysics Data System (ADS)

    Palenzuela, Carlos; Lehner, Luis; Liebling, Steven L.; Ponce, Marcelo; Anderson, Matthew; Neilsen, David; Motl, Patrick

    2013-08-01

    We expand on our study of the gravitational and electromagnetic emissions from the late stage of an inspiraling neutron star binary as presented in Palenzuela et al. [Phys. Rev. Lett. 111, 061105 (2013)]. Interactions between the stellar magnetospheres, driven by the extreme dynamics of the merger, can yield considerable outflows. We study the gravitational and electromagnetic waves produced during the inspiral and merger of a binary neutron star system using a full relativistic, resistive magnetohydrodynamics evolution code. We show that the interaction between the stellar magnetospheres extracts kinetic energy from the system and powers radiative Poynting flux and heat dissipation. These features depend strongly on the configuration of the initial stellar magnetic moments. Our results indicate that this power can strongly outshine pulsars in binaries and have a distinctive angular and time-dependent pattern. Our discussion provides more detail than Palenzuela et al., showing clear evidence of the different effects taking place during the inspiral. Our simulations include a few milliseconds after the actual merger and study the dynamics of the magnetic fields during the formation of the hypermassive neutron star. We also briefly discuss the possibility of observing such emissions.

  2. Neutron-Star-Black-Hole Binaries Produced by Binary-Driven Hypernovae

    NASA Astrophysics Data System (ADS)

    Fryer, Chris L.; Oliveira, F. G.; Rueda, J. A.; Ruffini, R.

    2015-12-01

    Binary-driven hypernovae (BdHNe) within the induced gravitational collapse paradigm have been introduced to explain energetic (Eiso≳1052 erg ), long gamma-ray bursts (GRBs) associated with type Ic supernovae (SNe). The progenitor is a tight binary composed of a carbon-oxygen (CO) core and a neutron-star (NS) companion, a subclass of the newly proposed "ultrastripped" binaries. The CO-NS short-period orbit causes the NS to accrete appreciable matter from the SN ejecta when the CO core collapses, ultimately causing it to collapse to a black hole (BH) and producing a GRB. These tight binaries evolve through the SN explosion very differently than compact binaries studied in population synthesis calculations. First, the hypercritical accretion onto the NS companion alters both the mass and the momentum of the binary. Second, because the explosion time scale is on par with the orbital period, the mass ejection cannot be assumed to be instantaneous. This dramatically affects the post-SN fate of the binary. Finally, the bow shock created as the accreting NS plows through the SN ejecta transfers angular momentum, braking the orbit. These systems remain bound even if a large fraction of the binary mass is lost in the explosion (well above the canonical 50% limit), and even large kicks are unlikely to unbind the system. Indeed, BdHNe produce a new family of NS-BH binaries unaccounted for in current population synthesis analyses and, although they may be rare, the fact that nearly 100% remain bound implies that they may play an important role in the compact merger rate, important for gravitational waves that, in turn, can produce a new class of ultrashort GRBs.

  3. Neutron-Star-Black-Hole Binaries Produced by Binary-Driven Hypernovae.

    PubMed

    Fryer, Chris L; Oliveira, F G; Rueda, J A; Ruffini, R

    2015-12-01

    Binary-driven hypernovae (BdHNe) within the induced gravitational collapse paradigm have been introduced to explain energetic (E_{iso}≳10^{52}  erg), long gamma-ray bursts (GRBs) associated with type Ic supernovae (SNe). The progenitor is a tight binary composed of a carbon-oxygen (CO) core and a neutron-star (NS) companion, a subclass of the newly proposed "ultrastripped" binaries. The CO-NS short-period orbit causes the NS to accrete appreciable matter from the SN ejecta when the CO core collapses, ultimately causing it to collapse to a black hole (BH) and producing a GRB. These tight binaries evolve through the SN explosion very differently than compact binaries studied in population synthesis calculations. First, the hypercritical accretion onto the NS companion alters both the mass and the momentum of the binary. Second, because the explosion time scale is on par with the orbital period, the mass ejection cannot be assumed to be instantaneous. This dramatically affects the post-SN fate of the binary. Finally, the bow shock created as the accreting NS plows through the SN ejecta transfers angular momentum, braking the orbit. These systems remain bound even if a large fraction of the binary mass is lost in the explosion (well above the canonical 50% limit), and even large kicks are unlikely to unbind the system. Indeed, BdHNe produce a new family of NS-BH binaries unaccounted for in current population synthesis analyses and, although they may be rare, the fact that nearly 100% remain bound implies that they may play an important role in the compact merger rate, important for gravitational waves that, in turn, can produce a new class of ultrashort GRBs. PMID:26684106

  4. The CHARA Catalog of Orbital Elements of Spectroscopic Binary Stars

    NASA Astrophysics Data System (ADS)

    Taylor, S. F.; McAlister, H. A.; Harvin, J. A.

    2003-12-01

    Optical interferometry is entering a new age with several ground-based longbaseline observatories now making observations of unprecedented resolution. Interferometers bring a new level of resolution to bear on spectroscopic binaries, enabling the full extraction of the physical parameters for the component stars with high accuracy. In the case of double-lined systems, a geometrically determined orbital parallax becomes available as well. The first step in preparing to observe spectroscopic binaries is to list them, which has not been done since the 1989 publication of the Eighth Catalogue of the Orbital Elements of Spectroscopic Binaries by Batten, et al. (1989). We present a new catalog with roughly half again as many listings as the Eighth Catalog. Angular separation predictions are made for each catalog entry. The numbers of spectroscopic binaries available for study as a function of several important observational parameters are explored, and in particular, the number of spectroscopic binaries as a function of expected separation is discussed. CHARA gratefully acknowledges the support of the National Science Foundation, the offices of the Dean of the College of Arts and Sciences, the Vice President for Research at Georgia State University, the W.M. Keck Foundation, and the David and Lucile Packard Foundation.

  5. Detailed chemical abundances in NGC 5824: another metal-poor globular cluster with internal heavy element abundance variations

    NASA Astrophysics Data System (ADS)

    Roederer, Ian U.; Mateo, Mario; Bailey, John I.; Spencer, Meghin; Crane, Jeffrey D.; Shectman, Stephen A.

    2016-01-01

    We present radial velocities, stellar parameters, and detailed abundances of 39 elements derived from high-resolution spectroscopic observations of red giant stars in the luminous, metal-poor globular cluster NGC 5824. We observe 26 stars in NGC 5824 using the Michigan/Magellan Fiber System (M2FS) and two stars using the Magellan Inamori Kyocera Echelle spectrograph. We derive a mean metallicity of [Fe/H] = -1.94 ± 0.02 (statistical) ±0.10 (systematic). The metallicity dispersion of this sample of stars, 0.08 dex, is in agreement with previous work and does not exceed the expected observational errors. Previous work suggested an internal metallicity spread only when fainter samples of stars were considered, so we cannot exclude the possibility of an intrinsic metallicity dispersion in NGC 5824. The M2FS spectra reveal a large internal dispersion in [Mg/Fe], 0.28 dex, which is found in a few other luminous, metal-poor clusters. [Mg/Fe] is correlated with [O/Fe] and anticorrelated with [Na/Fe] and [Al/Fe]. There is no evidence for internal dispersion among the other α- or Fe-group abundance ratios. 25 of the 26 stars exhibit a n-capture enrichment pattern dominated by r-process nucleosynthesis (<[Eu/Fe]> = +0.11 ± 0.12; <[Ba/Eu]> = -0.66 ± 0.05). Only one star shows evidence of substantial s-process enhancement ([Ba/Fe] = +0.56 ± 0.12; [Ba/Eu] = +0.38 ± 0.14), but this star does not exhibit other characteristics associated with s-process enhancement via mass transfer from a binary companion. The Pb and other heavy elements produced by the s-process suggest a time-scale of no more than a few hundred Myr for star formation and chemical enrichment, like the complex globular clusters M2, M22, and NGC 5286.

  6. Simulating binary neutron stars: Dynamics and gravitational waves

    NASA Astrophysics Data System (ADS)

    Anderson, Matthew; Hirschmann, Eric W.; Lehner, Luis; Liebling, Steven L.; Motl, Patrick M.; Neilsen, David; Palenzuela, Carlos; Tohline, Joel E.

    2008-01-01

    We model two mergers of orbiting binary neutron stars, the first forming a black hole and the second a differentially rotating neutron star. We extract gravitational waveforms in the wave zone. Comparisons to a post-Newtonian analysis allow us to compute the orbital kinematics, including trajectories and orbital eccentricities. We verify our code by evolving single stars and extracting radial perturbative modes, which compare very well to results from perturbation theory. The Einstein equations are solved in a first-order reduction of the generalized harmonic formulation, and the fluid equations are solved using a modified convex essentially non-oscillatory method. All calculations are done in three spatial dimensions without symmetry assumptions. We use the had computational infrastructure for distributed adaptive mesh refinement.

  7. Magnetic Energy Production by Turbulence in Binary Neutron Star Mergers

    NASA Astrophysics Data System (ADS)

    Zrake, Jonathan; MacFadyen, Andrew I.

    2013-06-01

    The simultaneous detection of electromagnetic and gravitational wave emission from merging neutron star binaries would greatly aid in their discovery and interpretation. By studying turbulent amplification of magnetic fields in local high-resolution simulations of neutron star merger conditions, we demonstrate that magnetar-level (gsim 1016 G) fields are present throughout the merger duration. We find that the small-scale turbulent dynamo converts 60% of the randomized kinetic energy into magnetic fields on a merger timescale. Since turbulent magnetic energy dissipates through reconnection events that accelerate relativistic electrons, turbulence may facilitate the conversion of orbital kinetic energy into radiation. If 10-4 of the ~1053 erg of orbital kinetic available gets processed through reconnection and creates radiation in the 15-150 keV band, then the fluence at 200 Mpc would be 10-7 erg cm-2, potentially rendering most merging neutron stars in the advanced LIGO and Virgo detection volumes detectable by Swift BAT.

  8. The Abundances of Neutron-capture Species in the Very Metal-poor Globular Cluster M15: A Uniform Analysis of Red Giant Branch and Red Horizontal Branch Stars

    NASA Astrophysics Data System (ADS)

    Sobeck, Jennifer S.; Kraft, Robert P.; Sneden, Christopher; Preston, George W.; Cowan, John J.; Smith, Graeme H.; Thompson, Ian B.; Shectman, Stephen A.; Burley, Gregory S.

    2011-06-01

    The globular cluster M15 is unique in its display of star-to-star variations in the neutron-capture elements. Comprehensive abundance surveys have been previously conducted for handfuls of M15 red giant branch (RGB) and red horizontal branch (RHB) stars. No attempt has been made to perform a single, self-consistent analysis of these stars, which exhibit a wide range in atmospheric parameters. In the current effort, a new comparative abundance derivation is presented for three RGB and six RHB members of the cluster. The analysis employs an updated version of the line transfer code MOOG, which now appropriately treats coherent, isotropic scattering. The apparent discrepancy in the previously reported values for the metallicity of M15 RGB and RHB stars is addressed and a resolute disparity of Δ(RHB - RGB) ≈ 0.1 dex in the iron abundance was found. The anti-correlative behavior of the light neutron-capture elements (Sr, Y, Zr) is clearly demonstrated with both Ba and Eu, standard markers of the s- and r-process, respectively. No conclusive detection of Pb was made in the RGB targets. Consequently for the M15 cluster, this suggests that the main component of the s-process has made a negligible contribution to those elements normally dominated by this process in solar system material. Additionally for the M15 sample, a large Eu abundance spread is confirmed, which is comparable to that of the halo field at the same metallicity. These abundance results are considered in the discussion of the chemical inhomogeneity and nucleosynthetic history of M15.

  9. Binary interactions with high accretion rates onto main sequence stars

    NASA Astrophysics Data System (ADS)

    Shiber, Sagiv; Schreier, Ron; Soker, Noam

    2016-07-01

    Energetic outflows from main sequence stars accreting mass at very high rates might account for the powering of some eruptive objects, such as merging main sequence stars, major eruptions of luminous blue variables, e.g., the Great Eruption of Eta Carinae, and other intermediate luminosity optical transients (ILOTs; red novae; red transients). These powerful outflows could potentially also supply the extra energy required in the common envelope process and in the grazing envelope evolution of binary systems. We propose that a massive outflow/jets mediated by magnetic fields might remove energy and angular momentum from the accretion disk to allow such high accretion rate flows. By examining the possible activity of the magnetic fields of accretion disks, we conclude that indeed main sequence stars might accrete mass at very high rates, up to ≈ 10‑2 M ⊙ yr‑1 for solar type stars, and up to ≈ 1 M ⊙ yr‑1 for very massive stars. We speculate that magnetic fields amplified in such extreme conditions might lead to the formation of massive bipolar outflows that can remove most of the disk's energy and angular momentum. It is this energy and angular momentum removal that allows the very high mass accretion rate onto main sequence stars.

  10. Observed rotational properties of the O-type stars in 30 Doradus: single stars and binaries

    NASA Astrophysics Data System (ADS)

    Hernan Ramirez Agudelo, Oscar; Sana, Hugues; de Koter, Alex; Tramper, Frank; de Mink, Selma; Vlt-Flames Tarantula Survey

    2015-01-01

    The initial distribution of the spin rates of massive stars is a fingerprint of their formation process. The stellar spin rate is also one of the main properties that control the evolution and ultimate fate of these objects.Using ground-based multi-object optical spectroscopy obtained in the framework of the VLT/FLAMES Tarantula Survey we established the projected rotational velocities, vsini, of a sample of ~330 O-type objects located in the 30 Doradus (30 Dor) region in the Large Magellanic Cloud. The sample is composed by ~200 spectroscopic single stars and ~110 stars in binary systems (~110 primaries and ~30 secondaries). The vsini values are derived from the most commonly used methods, i.e. full-width at half-maximum, Fourier transform, and line profile fitting, applied to a set of spectral lines.The most distinctive feature of the vsini distributions of the presumed-single stars, primaries, and secondaries in 30 Dor is a low-velocity peak at around 100 km/s. Stellar winds are not expected to have spun-down the bulk of the stars significantly since their arrival on the main sequence and therefore the peak of presumed-single stars is likely to represent the outcome of the formation process. Whereas the spin distribution of presumed-single stars shows a well developed tail of stars rotating more rapidly than 300 km/s, primaries and secondaries do not feature such a high-velocity tail. The tail of the presumed-single star distribution is attributed for the most part -- and could potentially be completely due -- to spun-up binary products that appear as single stars or that have merged. This would be consistent with the lack of such post-interaction products in the binary sample, that is expected to be dominated by pre-interaction systems. The peak in this distribution is broader and is shifted toward somewhat higher spin rates compared to the distribution of spectroscopic-single stars. Systems displaying large radial velocity variations, typical for short period

  11. Generalized Solution for Binary Star Ephemerides and Apsidal Motion

    NASA Astrophysics Data System (ADS)

    van Hamme, W. V.; Wilson, R. E.

    1998-12-01

    We demonstrate generalized determination of apsidal motion rates (domega /dt's), orbital periods (P's), and period changes (dP/dt's) in binary stars. Our method can use eclipses but is not restricted to eclipse data. A general binary star program solves for domega /dt and/or ephemeris parameters together with other binary star quantities, and combines radial velocities and light curves within a coherent analysis. We can use data that may have large timewise gaps and may be far less than optimally distributed over time. The method is particularly useful when the apsidal period is long and eclipse timings cover only a small part of the cycle. We show apsidal motion results for AS Cam and find a domega /dt of 18.20+/-0.66 arcdeg /100;yr. This result compares to a domega /dt of 13.2+/-1.8 arcdeg /100;yr obtained from a traditional weighted least squares fit to almost 100 years of times of minima, which is 3.3 times smaller than predicted by theory. Other published estimates for the apsidal motion rate are 15.0+/-5.3 arcdeg /100;yr by Maloney, Guinan & Mukherjee (1991, AJ, 102, 256), and 18.3+/-2.6 arcdeg /100;yr by Wolf, \\u{S}arounova & Diethelm (1996, A&AS, 116, 463). Apsidal motion determined from times of minima depends on the value of the eccentricity e. Our result is for e = 0.1633, obtained from the light and velocity solution. The new domega /dt from the general analysis is 2.4 times smaller than theory, with a standard error 3 times smaller than in the traditional method. Our apsidal period of 1978+/-71 year is based on only 30 years of light and velocity curves, or 1.5% of the cycle. The method also works well in measuring period changes in long period giant binaries (such as symbiotics), considering that these stars are typically observed in fragments and that very few show eclipses that are useful as timing ticks. Our dP/dt results for the symbiotic binary AG Peg have implications for its future evolution. Natural extensions of the idea can include other

  12. Estimating the Binary Fraction of Central Stars of Planetary Nebulae

    NASA Astrophysics Data System (ADS)

    Douchin, Dimitri

    2015-01-01

    Planetary nebulae are the end-products of intermediate-mass stars evolution, following a phase of expansion of their atmospheres at the end of their lives. Observationally, it has been estimated that 80% of them have non-spherical shapes. Such a high fraction is puzzling and has occupied the planetary nebula community for more than 30 years. One scenario that would allow to justify the observed shapes is that a comparable fraction of the progenitors of central stars of planetary nebula (CSPN) are not single, but possess a companion. The shape of the nebulae would then be the result of an interaction with this companion. The high fraction of non-spherical planetary nebulae would thus imply a high fraction of binary central stars of planetary nebulae, making binarity a preferred channel for planetary nebula formation. After presenting the current state of knowledge regarding planetary nebula formation and shaping and reviewing the diverse efforts to find binaries in planetary nebulae, I present my work to detect a near-infrared excess that would be the signature of the presence of cool companions. The first part of the project consists in the analysis of data and photometry acquired and conducted by myself. The second part details an attempt to make use of archived datasets: the Sloan Digital Sky Survey Data Release 7 optical survey and the extended database assembled by Frew (2008). I also present results from a radial velocity analysis of VLT/UVES spectra for 14 objects aiming to the detection of spectroscopic companions. Finally I give details of the analysis of optical photometry data from our observations associated to the detection of companions around central stars of planetary nebulae using the photometric variability technique. The main result of this thesis is from the near-infrared excess studies which I combine with previously published data. I conclude that if the detected red and NIR flux excess is indicative of a stellar companion then the binary

  13. Radial Velocity Studies of Close Binary Stars. XV

    NASA Astrophysics Data System (ADS)

    Pribulla, Theodor; Rucinski, Slavek M.; Blake, R. M.; Lu, Wenxian; Thomson, J. R.; DeBond, Heide; Karmo, Toomas; De Ridder, Archie; Ogłoza, Waldemar; Stachowski, Greg; Siwak, Michal

    2009-03-01

    Radial velocity (RV) measurements and sine curve fits to the orbital RV variations are presented for the last eight close binary systems analyzed in the same way as in the previous papers of this series: QX And, DY Cet, MR Del, HI Dra, DD Mon, V868 Mon, ER Ori, and Y Sex. For another seven systems (TT Cet, AA Cet, CW Lyn, V563 Lyr, CW Sge, LV Vir, and MW Vir), phase coverage is insufficient to provide reliable orbits but RVs of individual components were measured. Observations of a few complicated systems observed throughout the David Dunlap Observatory (DDO) close binary program are also presented; among them is an especially interesting multiple system V857 Her which—in addition to the contact binary—very probably contains one or more subdwarf components of much earlier spectral type. All suspected binaries which were found to be most probably pulsating stars are briefly discussed in terms of mean RVs and projected rotation velocities (vsin i) as well as spectral-type estimates. In two of them, CU CVn and V752 Mon, the broadening functions show a clear presence of nonradial pulsations. The previously missing spectral types for Paper I are given here in addition to such estimates for most of the program stars of this paper. Based on the data obtained at the David Dunlap Observatory, University of Toronto, Toronto, Canada.

  14. Spatially resolved dust emission of extremely metal-poor galaxies*

    NASA Astrophysics Data System (ADS)

    Zhou, Luwenjia; Shi, Yong; Diaz-Santos, Taino; Armus, Lee; Helou, George; Stierwalt, Sabrina; Li, Aigen

    2016-05-01

    We present infrared (IR) spectral energy distributions (SEDs) of individual star-forming regions in four extremely metal-poor (EMP) galaxies with metallicity Z ≲ Z⊙/10 as observed by the Herschel Space Observatory. With the good wavelength coverage of the SED, it is found that these EMP star-forming regions show distinct SED shapes as compared to those of grand design Spirals and higher metallicity dwarfs: they have on average much higher f70μm/f160 μm ratios at a given f160 μm/f250 μm ratio; single modified blackbody (MBB) fittings to the SED at λ ≥ 100 μm still reveal higher dust temperatures and lower emissivity indices compared to that of Spirals, while two MBB fittings to the full SED with a fixed emissivity index (β = 2) show that even at 100 μm, about half of the emission comes from warm (50 K) dust, in contrast to the cold (˜20 K) dust component. Our spatially resolved images furthermore reveal that the far-IR colours including f70 μm/f160 μm, f160 μm/f250 μm and f250 μm/f350 μm are all related to the surface densities of young stars as traced by far-UV, 24 μm and star formation rates (SFRs), but not to the stellar mass surface densities. This suggests that the dust emitting at wavelengths from 70 to 350 μm is primarily heated by radiation from young stars.

  15. The most metal-poor damped Lyα systems: insights into chemical evolution in the very metal-poor regime

    NASA Astrophysics Data System (ADS)

    Cooke, Ryan; Pettini, Max; Steidel, Charles C.; Rudie, Gwen C.; Nissen, Poul E.

    2011-10-01

    We present a high spectral resolution survey of the most metal-poor damped Lyα absorption systems (DLAs) aimed at probing the nature and nucleosynthesis of the earliest generations of stars. Our survey comprises 22 systems with iron abundance less than 1/100 solar; observations of seven of these are reported here for the first time. Together with recent measures of the abundances of C and O in Galactic metal-poor stars, we reinvestigate the trend of C/O in the very metal-poor (VMP) regime and we compare, for the first time, the O/Fe ratios in the most metal-poor DLAs and in halo stars. We confirm the near-solar values of C/O in DLAs at the lowest metallicities probed, and find that their distribution is in agreement with that seen in Galactic halo stars. We find that the O/Fe ratio in VMP DLAs is essentially constant, and shows very little dispersion, with a mean []=+0.39 ± 0.12, in good agreement with the values measured in Galactic halo stars when the oxygen abundance is measured from the [O I] λ6300 line. We speculate that such good agreement in the observed abundance trends points to a universal origin for these metals. In view of this agreement, we construct the abundance pattern for a typical VMP DLA and compare it to model calculations of Population II and Population III nucleosynthesis to determine the origin of the metals in VMP DLAs. Our results suggest that the most metal-poor DLAs may have been enriched by a generation of metal-free stars; however, given that abundance measurements are currently available for only a few elements, we cannot yet rule out an additional contribution from Population II stars. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile [VLT programme IDs 67.A-0078(A), 69.A-0613(A), 083.A-0042(A), 085.A-0109(A)], and at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of

  16. CHARACTERIZATION OF THE MOST LUMINOUS STAR IN M33: A SUPER SYMBIOTIC BINARY

    SciTech Connect

    Mikołajewska, Joanna; Iłkiewicz, Krystian; Caldwell, Nelson; Shara, Michael M.

    2015-01-30

    We present the first spectrum of the most luminous infrared star in M33, and use it to demonstrate that the object is almost certainly a binary composed of a massive O star and a dust-enshrouded red hypergiant. This is the most luminous symbiotic binary ever discovered. Its radial velocity is an excellent match to that of the hydrogen gas in the disk of M33, supporting our interpretation that it is a very young and massive binary star.

  17. Population Studies. XIII. A New Analysis of the Bidelman-MacConnell "Weak-metal" Stars—Confirmation of Metal-poor Stars in the Thick Disk of the Galaxy

    NASA Astrophysics Data System (ADS)

    Beers, Timothy C.; Norris, John E.; Placco, Vinicius M.; Lee, Young Sun; Rossi, Silvia; Carollo, Daniela; Masseron, Thomas

    2014-10-01

    A new set of very high signal-to-noise (S/N > 100/1), medium-resolution (R ~ 3000) optical spectra have been obtained for 302 of the candidate "weak-metal" stars selected by Bidelman & MacConnell. We use these data to calibrate the recently developed generalization of the Sloan Extension for Galactic Exploration and Understanding and Exploration (SEGUE) Stellar Parameter Pipeline, and obtain estimates of the atmospheric parameters (T eff, log g, and [Fe/H]) for these non-Sloan Digital Sky Survey/SEGUE data; we also obtain estimates of [C/Fe]. The new abundance measurements are shown to be consistent with available high-resolution spectroscopic determinations, and represent a substantial improvement over the accuracies obtained from the previous photometric estimates reported in Paper I of this series. The apparent offset in the photometric abundances of the giants in this sample noted by several authors is confirmed by our new spectroscopy; no such effect is found for the dwarfs. The presence of a metal-weak thick-disk (MWTD) population is clearly supported by these new abundance data. Some 25% of the stars with metallicities -1.8 < [Fe/H] <=-0.8 exhibit orbital eccentricities e < 0.4, yet are clearly separated from members of the inner-halo population with similar metallicities by their location in a Lindblad energy versus angular momentum diagram. A comparison is made with recent results for a similar-size sample of Radial Velocity Experiment stars from Ruchti et al. We conclude, based on both of these samples, that the MWTD is real, and must be accounted for in discussions of the formation and evolution of the disk system of the Milky Way.

  18. Equilibrium Structures of Differentially Rotating Primary Components of Binary Stars

    NASA Astrophysics Data System (ADS)

    Mohan, C.; Lal, A. K.; Singh, V. P.

    1997-11-01

    In this paper a method is proposed for computing the equilibrium structures and various other observable physical parameters of the primary components of stars in binary systems assuming that the primary is more massive than the secondary and is rotating differentially about its axis. Kippenhahn and Thomas averaging approach (1970) is used in a manner earlier used by Mohan, Saxena and Agarwal (1990) to incorporate the rotational and tidal effects in the equations of stellar structure. Explicit expressions for the distortional terms appearing in the stellar structure equations have been obtained by assuming a general law of differential rotation of the typeω2 = b 0+b 1 s 2+b 2 s 4, where ω is the angular velocity of rotation of a fluid element in the star at a distance s from the axis of rotation, and b 0, b 1, b 2 are suitably chosen numerical constants. The expressions incorporate the effects of differential rotation and tidal distortions up to second order terms. The use of the proposed method has been illustrated by applying it to obtain the structures and observable parameters of certain differentially rotating primary components of the binary stars assuming the primary components to have polytropic structures.

  19. Winds of Binary AGB Stars as Observed by Herschel

    NASA Astrophysics Data System (ADS)

    Mayer, A.; Jorissen, A.; Kerschbaum, F.; Ottensamer, R.; Mečina, M.; Paladini, C.; Cox, N. L. J.; Nowotny, W.; Aringer, B.; Pourbaix, D.; Mohamed, S.; Siopis, C.; Groenewegen, M. A. T.

    2015-08-01

    We present Herschel/PACS observations of the large-scale environments of binary AGB stars as part of the Mass-loss of Evolved StarS (MESS) sample. From the literature we found 18 of the objects to be members of physically bound multiple systems. Several show a large-scale far-IR emission which differs significantly from spherical symmetry. A probable cause is the gravitational force of the companion on the stellar AGB wind and the mass-losing star itself. A spiral pattern is thereby imprinted in the dusty stellar wind. The most remarkable structures are found around o Ceti, W Aquilæ, R Aquarii, and π1 Gruis. The environments of o Cet and W Aql show a spiral pattern while the symbiotic nature of R Aqr is revealed as two opposing arms which reflect a nova outburst. The emission around π1 Gru is dominated by two structures, a disk and an arc, which are presumably not caused by the same companion. We found evidence that π1 Gru is a hierarchical triple system in which a close companion attracts the AGB wind onto the orbital plane and the outer companion forms a spiral arm. These far-IR observations underline the role of a companion as a major external influence in creating asymmetric winds in the AGB phase, even before the star becomes a planetary nebula (PN).

  20. Phenomenological Modelling of a Group of Eclipsing Binary Stars

    NASA Astrophysics Data System (ADS)

    Andronov, Ivan L.; Tkachenko, Mariia G.; Chinarova, Lidia L.

    2016-03-01

    Phenomenological modeling of variable stars allows determination of a set of the parameters, which are needed for classification in the "General Catalogue of Variable Stars" and similar catalogs. We apply a recent method NAV ("New Algol Variable") to eclipsing binary stars of different types. Although all periodic functions may be represented as Fourier series with an infinite number of coefficients, this is impossible for a finite number of the observations. Thus one may use a restricted Fourier series, i.e. a trigonometric polynomial (TP) of order s either for fitting the light curve, or to make a periodogram analysis. However, the number of parameters needed drastically increases with decreasing width of minimum. In the NAV algorithm, the special shape of minimum is used, so the number of parameters is limited to 10 (if the period and initial epoch are fixed) or 12 (not fixed). We illustrate the NAV method by application to a recently discovered Algol-type eclipsing variable 2MASS J11080308-6145589 (in the field of previously known variable star RS Car) and compare results to that obtained using the TP fits. For this system, the statistically optimal number of parameters is 44, but the fit is still worse than that of the NAV fit. Application to the system GSC 3692-00624 argues that the NAV fit is better than the TP one even for the case of EW-type stars with much wider eclipses. Model parameters are listed.

  1. Cool and Luminous Transients from Mass-Losing Binary Stars

    NASA Astrophysics Data System (ADS)

    Pejcha, Ondrej; Metzger, Brian D.; Tomida, Kengo

    2016-01-01

    We study transients produced by equatorial disk-like outflows from catastrophically mass-losing binary stars with an asymptotic velocity and energy deposition rate near the inner edge which are proportional to the binary escape velocity. As a test case, we present the first smoothed-particle radiation-hydrodynamics calculations of the mass loss from the outer Lagrange point with realistic equation of state and opacities. The mass-losing binary outflows produce luminosities reaching up to 106 L⊙ and the effective temperatures are between 500 and 6000 K, which is compatible with those of many of the class of recently-discovered red transients such as V838 Mon and V1309 Sco. Dust readily forms in the outflow, potentially in a catastrophic global cooling transition. The appearance of the transient is viewing angle-dependent due to vastly different optical depths parallel and perpendicular to the binary plane. We predict a correlation between the peak luminosity and the outflow velocity, which is roughly obeyed by the known red transients.

  2. Electromagnetic Counterparts from Tilted Magnetized Binary Neutron-Stars Mergers

    NASA Astrophysics Data System (ADS)

    Ponce, Marcelo; Palenzuela, Carlos; Motl, Patrick M.; Anderson, Matthew; Hirschmann, Eric W.; Lehner, Luis; Liebling, Steven L.; Neilsen, David

    2014-03-01

    Recent studies have demonstrated that the interaction of magnetospheres in binary neutron star systems can radiate strongly electromagnetically. We study here a broader set of configurations accounting for tilted/misaligned dipoles in coalescing binaries and analyze the resulting Poynting flux and its correlation to the dynamics. In particular, the misalignment of the dipoles results in a very dynamic system with magnetic reconnections, sheer layers, and current sheets. The electromagnetic radiation displays a distinctive pulsating behaviour tied to the orbital dynamics and stellar dipole orientations and the overall power of this radiation. This work was supported by the NSF grants PHY-0969827 (LIU), PHY-0969811 (BYU), NASA's ATP grant NNX13AH01G, and NSERC through a Discovery Grant.

  3. Visual Measurements of the Binary Star S 654

    NASA Astrophysics Data System (ADS)

    Frey, Thomas; Achildiyev, Irina; Alduenda, Chandra; Bridgeman, Reid; Chamberlain, Rebecca; Hendrix, Alex

    2011-01-01

    A member of the faculty and students from The Evergreen State College, Olympia, Washington, participated in the 2010 summer astronomy workshop at Pine Mountain Observatory. They learned the proper techniques and skills required for measuring the separation and position angle of binary star S 654. They learned how to calibrate an astrometric eyepiece, make appropriate measurements, do a statistical analysis, and analyze the data. The separation and position angle values obtained were 69.9 arc seconds and 237 degrees, respectively. The percent difference for each value was less than 0.5% from the literature value.

  4. Quasiequilibrium sequences of binary neutron stars undergoing dynamical scalarization

    NASA Astrophysics Data System (ADS)

    Taniguchi, Keisuke; Shibata, Masaru; Buonanno, Alessandra

    2015-01-01

    We calculate quasiequilibrium sequences of equal-mass, irrotational binary neutron stars in a scalar-tensor theory of gravity that admits dynamical scalarization. We model neutron stars with realistic equations of state (notably through piecewise polytropic equations of state). Using these quasiequilibrium sequences we compute the binary's scalar charge and binding energy versus orbital angular frequency. We find that the absolute value of the binding energy is smaller than in general relativity, differing at most by ˜14 % at high frequencies for the cases considered. We use the newly computed binding energy and the balance equation to estimate the number of gravitational-wave (GW) cycles during the adiabatic, quasicircular inspiral stage up to the end of the sequence, which is the last stable orbit or the mass-shedding point, depending on which comes first. We find that, depending on the scalar-tensor parameters, the number of GW cycles can be substantially smaller than in general relativity. In particular, we obtain that when dynamical scalarization sets in around a GW frequency of ˜130 Hz , the sole inclusion of the scalar-tensor binding energy causes a reduction of GW cycles from ˜120 Hz up to the end of the sequence (˜1200 Hz ) of ˜11 % with respect to the general-relativity case. (The number of GW cycles from ˜120 Hz to the end of the sequence in general relativity is ˜270 .) We estimate that when the scalar-tensor energy flux is also included the reduction in GW cycles becomes of ˜24 %. Quite interestingly, dynamical scalarization can produce a difference in the number of GW cycles with respect to the general-relativity point-particle case that is much larger than the effect due to tidal interactions, which is on the order of only a few GW cycles. These results further clarify and confirm recent studies that have evolved binary neutron stars either in full numerical relativity or in post-Newtonian theory, and point out the importance of developing

  5. Binary Neutron Star Mergers: Prospects for Multimessenger Observations

    NASA Astrophysics Data System (ADS)

    Liebling, Steven; Anderson, Matthew; Lehner, Luis; Motl, Patrick; Neilsen, David; Palenzuela, Carlos; Ponce, Marcelo

    2015-04-01

    We evolve a binary system of two, equal-mass neutron stars in a quasi-circular orbit through and past merger. We consider different nuclear equations of state, which vary from soft to quite stiff, and allow for magnetization of the system and neutrino cooling via a leakage scheme. Here, I focus on potential observables, other than gravitational waves, produced mainly by the hot, strongly magnetized matter resulting from the merger and study their dependence on both the equation of state and the initial magnetic field strength.

  6. Gravitational radiation from primordial solitons and soliton-star binaries

    NASA Technical Reports Server (NTRS)

    Gleiser, Marcelo

    1989-01-01

    The possibility that both the formation of nontopological solitons in a primordial second-order phase transition and binary systems of soliton stars could generate a stochastic gravitational-wave background is examined. The present contribution of gravitational radiation to the energy density of the universe from these processes is estimated for a number of different models. The detectability of such contributions from the timing measurements of the millisecond pulsar and spaceborne laser interferometry is briefly discussed and compared to other cosmological and local sources of background gravitational waves.

  7. Systematic parameter errors in inspiraling neutron star binaries.

    PubMed

    Favata, Marc

    2014-03-14

    The coalescence of two neutron stars is an important gravitational wave source for LIGO and other detectors. Numerous studies have considered the precision with which binary parameters (masses, spins, Love numbers) can be measured. Here I consider the accuracy with which these parameters can be determined in the presence of systematic errors due to waveform approximations. These approximations include truncation of the post-Newtonian (PN) series and neglect of neutron star (NS) spin, tidal deformation, or orbital eccentricity. All of these effects can yield systematic errors that exceed statistical errors for plausible parameter values. In particular, neglecting spin, eccentricity, or high-order PN terms causes a significant bias in the NS Love number. Tidal effects will not be measurable with PN inspiral waveforms if these systematic errors are not controlled. PMID:24679276

  8. Systematic Parameter Errors in Inspiraling Neutron Star Binaries

    NASA Astrophysics Data System (ADS)

    Favata, Marc

    2014-03-01

    The coalescence of two neutron stars is an important gravitational wave source for LIGO and other detectors. Numerous studies have considered the precision with which binary parameters (masses, spins, Love numbers) can be measured. Here I consider the accuracy with which these parameters can be determined in the presence of systematic errors due to waveform approximations. These approximations include truncation of the post-Newtonian (PN) series and neglect of neutron star (NS) spin, tidal deformation, or orbital eccentricity. All of these effects can yield systematic errors that exceed statistical errors for plausible parameter values. In particular, neglecting spin, eccentricity, or high-order PN terms causes a significant bias in the NS Love number. Tidal effects will not be measurable with PN inspiral waveforms if these systematic errors are not controlled.

  9. Hybridizing Gravitationl Waveforms of Inspiralling Binary Neutron Star Systems

    NASA Astrophysics Data System (ADS)

    Cullen, Torrey; LIGO Collaboration

    2016-03-01

    Gravitational waves are ripples in space and time and were predicted to be produced by astrophysical systems such as binary neutron stars by Albert Einstein. These are key targets for Laser Interferometer and Gravitational Wave Observatory (LIGO), which uses template waveforms to find weak signals. The simplified template models are known to break down at high frequency, so I wrote code that constructs hybrid waveforms from numerical simulations to accurately cover a large range of frequencies. These hybrid waveforms use Post Newtonian template models at low frequencies and numerical data from simulations at high frequencies. They are constructed by reading in existing Post Newtonian models with the same masses as simulated stars, reading in the numerical data from simulations, and finding the ideal frequency and alignment to ``stitch'' these waveforms together.

  10. ABSOLUTE PROPERTIES OF THE ECLIPSING BINARY STAR V335 SERPENTIS

    SciTech Connect

    Lacy, Claud H. Sandberg; Fekel, Francis C.; Claret, Antonio E-mail: fekel@evans.tsuniv.edu

    2012-08-15

    V335 Ser is now known to be an eccentric double-lined A1+A3 binary star with fairly deep (0.5 mag) partial eclipses. Previous studies of the system are improved with 7456 differential photometric observations from the URSA WebScope and 5666 from the NFO WebScope, and 67 high-resolution spectroscopic observations from the Tennessee State University 2 m automatic spectroscopic telescope. From dates of minima, the apsidal period is about 880 years. Accurate (better than 2%) masses and radii are determined from analysis of the two new light curves and the radial velocity curve. Theoretical models match the absolute properties of the stars at an age of about 380 Myr, though the age agreement for the two components is poor. Tidal theory correctly confirms that the orbit should still be eccentric, but we find that standard tidal theory is unable to match the observed asynchronous rotation rates of the components' surface layers.

  11. ABSOLUTE PROPERTIES OF THE ECLIPSING BINARY STAR HY VIRGINIS

    SciTech Connect

    Sandberg Lacy, Claud H.; Fekel, Francis C. E-mail: fekel@evans.tsuniv.edu

    2011-12-15

    HY Vir is found to be a double-lined F0m+F5 binary star with relatively shallow (0.3 mag) partial eclipses. Previous studies of the system are improved with 7509 differential photometric observations from the URSA WebScope and 8862 from the NFO WebScope, and 68 high-resolution spectroscopic observations from the Tennessee State University 2 m automatic spectroscopic telescope, and the 1 m coude-feed spectrometer at Kitt Peak National Observatory. Very accurate (better than 0.5%) masses and radii are determined from analysis of the new light curves and radial velocity curves. Theoretical models match the absolute properties of the stars at an age of about 1.35 Gy.

  12. The Challenge of Observing the Zeta Aurigae Binary Stars

    NASA Astrophysics Data System (ADS)

    Melillo, Frank J.

    2013-07-01

    This author, in Holtsville, NY, has contributed to the observations of the Zeta Auriga binary stars, which included Zeta Aurigae itself and 32 Cygni. Both Zeta Aur and 32 Cygni were monitored in V and B bands during the most recent eclipses in the fall of 2011 and in late summer 2012, respectively. In addition, some spectra of both stars were captured to monitor the brightness in the near-UV section, that traces the hot companion being eclipsed. The lightcurves of both Zeta Aurigae and 32 Cygni show precise timing during the entire recent eclipses. The magnitude and duration of the eclipses in photometric V and B bands are described here, and forecasts made for future eclipses. This poster represents the work by Frank J Melillo and the observations were spaced closely enough to generate the true shape of the V and B lightcurves.

  13. Binary dynamics on star networks under external perturbations.

    PubMed

    Moreira, Carolina A; Schneider, David M; de Aguiar, Marcus A M

    2015-10-01

    We study a binary dynamical process that is a representation of the voter model with two candidates and opinion makers. The voters are represented by nodes of a network of social contacts with internal states labeled 0 or 1 and nodes that are connected can influence each other. The network is also perturbed by opinion makers, a set of external nodes whose states are frozen in 0 or 1 and that can influence all nodes of the network. The quantity of interest is the probability of finding m nodes in state 1 at time t. Here we study this process on star networks, which are simple representations of hubs found in complex systems, and compare the results with those obtained for networks that are fully connected. In both cases a transition from disordered to ordered equilibrium states is observed as the number of external nodes becomes small. For fully connected networks the probability distribution becomes uniform at the critical point. For star networks, on the other hand, we show that the equilibrium distribution splits in two peaks, reflecting the two possible states of the central node. We obtain approximate analytical solutions for the equilibrium distribution that clarify the role of the central node in the process. We show that the network topology also affects the time scale of oscillations in single realizations of the dynamics, which are much faster for the star network. Finally, extending the analysis to two stars we compare our results with simulations in simple scale-free networks. PMID:26565294

  14. Absolute properties of the eclipsing binary star V501 Herculis

    SciTech Connect

    Lacy, Claud H. Sandberg; Fekel, Francis C. E-mail: fekel@evans.tsuniv.edu

    2014-10-01

    V501 Her is a well detached G3 eclipsing binary star with a period of 8.597687 days for which we have determined very accurate light and radial-velocity curves using robotic telescopes. Results of these data indicate that the component stars have masses of 1.269 ± 0.004 and 1.211 ± 0.003 solar masses, radii of 2.001 ± 0.003 and 1.511 ± 0.003 solar radii, and temperatures of 5683 ± 100 K and 5720 ± 100 K, respectively. Comparison with the Yonsei-Yale series of evolutionary models results in good agreement at an age of about 5.1 Gyr for a somewhat metal-rich composition. Those models indicate that the more massive, larger, slightly cooler star is just beyond core hydrogen exhaustion while the less massive, smaller, slightly hotter star has not quite reached core hydrogen exhaustion. The orbit is not yet circularized, and the components are rotating at or near their pseudosynchronous velocities. The distance to the system is 420 ± 30 pc.

  15. Binary dynamics on star networks under external perturbations

    NASA Astrophysics Data System (ADS)

    Moreira, Carolina A.; Schneider, David M.; de Aguiar, Marcus A. M.

    2015-10-01

    We study a binary dynamical process that is a representation of the voter model with two candidates and opinion makers. The voters are represented by nodes of a network of social contacts with internal states labeled 0 or 1 and nodes that are connected can influence each other. The network is also perturbed by opinion makers, a set of external nodes whose states are frozen in 0 or 1 and that can influence all nodes of the network. The quantity of interest is the probability of finding m nodes in state 1 at time t . Here we study this process on star networks, which are simple representations of hubs found in complex systems, and compare the results with those obtained for networks that are fully connected. In both cases a transition from disordered to ordered equilibrium states is observed as the number of external nodes becomes small. For fully connected networks the probability distribution becomes uniform at the critical point. For star networks, on the other hand, we show that the equilibrium distribution splits in two peaks, reflecting the two possible states of the central node. We obtain approximate analytical solutions for the equilibrium distribution that clarify the role of the central node in the process. We show that the network topology also affects the time scale of oscillations in single realizations of the dynamics, which are much faster for the star network. Finally, extending the analysis to two stars we compare our results with simulations in simple scale-free networks.

  16. Rotating and binary relativistic stars with magnetic field

    NASA Astrophysics Data System (ADS)

    Markakis, Charalampos

    We develop a geometrical treatment of general relativistic magnetohydrodynamics for perfectly conducting fluids in Einstein--Maxwell--Euler spacetimes. The theory is applied to describe a neutron star that is rotating or is orbiting a black hole or another neutron star. Under the hypotheses of stationarity and axisymmetry, we obtain the equations governing magnetohydrodynamic equilibria of rotating neutron stars with poloidal, toroidal or mixed magnetic fields. Under the hypothesis of an approximate helical symmetry, we obtain the first law of thermodynamics governing magnetized equilibria of double neutron star or black hole - neutron star systems in close circular orbits. The first law is written as a relation between the change in the asymptotic Noether charge deltaQ and the changes in the area and electric charge of black holes, and in the vorticity, baryon rest mass, entropy, charge and magnetic flux of the magnetofluid. In an attempt to provide a better theoretical understanding of the methods used to construct models of isolated rotating stars and corotating or irrotational binaries and their unexplained convergence properties, we analytically examine the behavior of different iterative schemes near a static solution. We find the spectrum of the linearized iteration operator and show for self-consistent field methods that iterative instability corresponds to unstable modes of this operator. On the other hand, we show that the success of iteratively stable methods is due to (quasi-)nilpotency of this operator. Finally, we examine the integrability of motion of test particles in a stationary axisymmetric gravitational field. We use a direct approach to seek nontrivial constants of motion polynomial in the momenta---in addition to energy and angular momentum about the symmetry axis. We establish the existence and uniqueness of quadratic constants and the nonexistence of quartic constants for stationary axisymmetric Newtonian potentials with equatorial symmetry

  17. KEPLER ECLIPSING BINARY STARS. II. 2165 ECLIPSING BINARIES IN THE SECOND DATA RELEASE

    SciTech Connect

    Slawson, Robert W.; Doyle, Laurance R.; Prsa, Andrej; Engle, Scott G.; Conroy, Kyle; Coughlin, Jared; Welsh, William F.; Orosz, Jerome A.; Gregg, Trevor A.; Fetherolf, Tara; Short, Donald R.; Windmiller, Gur; Rucker, Michael; Batalha, Natalie; Fabrycky, Daniel C.; Jenkins, Jon M.; Mullally, F.; Seader, Shawn E.

    2011-11-15

    The Kepler Mission provides nearly continuous monitoring of {approx}156,000 objects with unprecedented photometric precision. Coincident with the first data release, we presented a catalog of 1879 eclipsing binary systems identified within the 115 deg{sup 2} Kepler field of view (FOV). Here, we provide an updated catalog augmented with the second Kepler data release which increases the baseline nearly fourfold to 125 days. Three hundred and eighty-six new systems have been added, ephemerides and principal parameters have been recomputed. We have removed 42 previously cataloged systems that are now clearly recognized as short-period pulsating variables and another 58 blended systems where we have determined that the Kepler target object is not itself the eclipsing binary. A number of interesting objects are identified. We present several exemplary cases: four eclipsing binaries that exhibit extra (tertiary) eclipse events; and eight systems that show clear eclipse timing variations indicative of the presence of additional bodies bound in the system. We have updated the period and galactic latitude distribution diagrams. With these changes, the total number of identified eclipsing binary systems in the Kepler FOV has increased to 2165, 1.4% of the Kepler target stars. An online version of this catalog is maintained at http://keplerEBs.villanova.edu.

  18. The VLT Unravels the Nature of the Fastest Binary Star

    NASA Astrophysics Data System (ADS)

    2002-03-01

    Two Hot White Dwarfs Perform a Tight Dance Summary Observations with ESO's Very Large Telescope (VLT) in Chile and the Italian Telescopio Nazionale Galileo (TNG) on the Canary Islands during the past two years have enabled an international group of astronomers [1] to unravel the true nature of an exceptional binary stellar system. This system, designated RX J0806.3+1527 , was first discovered as an X-ray source of variable brightness - once every five minutes, it "switches off" for a short moment. The new observations have shown beyond doubt that this period reflects the orbital motion of two "white dwarf" stars that revolve around each other at a distance of only 80,000 km . Each of the stars is about as large as the Earth and this is the shortest orbital period known for any binary stellar system. The VLT spectrum displays lines of ionized helium, indicating that the presence of an exceedingly hot area on one of the stars - a "hot spot" with a temperature of approx. 250,000 degrees. The system is currently in a rarely seen, transitory evolutionary state . PR Photo 10a/02 : U- and R-band images of RX J0806.3+1527. PR Photo 10b/02 : Spectrum of RX J0806.3+1527 An amazing stellar binary system ESO PR Photo 10a/02 ESO PR Photo 10a/02 [Preview - JPEG: 800 x 400 pix - 440k] [Normal - JPEG: 1600 x 800 pix - 1.1M] Caption : PR Photo 10a/02 shows U and R filter images of the sky field around RX J0806.3+1527 (at centre of circle), obtained with the FORS2 multi-mode instrument on VLT KUEYEN. The object is brightest at the shorter wavelength (U-band) - reflecting its very high temperature. Technical information about the photo is available below. One year is the time it takes the Earth to move once around the Sun, our central star. This may seem quite fast when measured on the scale of the Universe, but this is a snail's motion compared to the the speed of two recently discovered stars. They revolve around each other 100,000 times faster; one full revolution takes only 321

  19. Using stellar population models with binary stars to study the early type galaxies

    NASA Astrophysics Data System (ADS)

    Yu, Zhang

    2015-08-01

    The stellar mass, mean ages, metallicities and star formation histories of galaxy are now commonly determined via fitting multiband photometric properties of galaxies to the spectral energy distributions (SEDs) of stellar population models. The stellar population models are still poorly calibrated for certain stellar evolution stages, especially for the treatment of binary stars, which are very common in the Universe and their evolution is very different from single stars. In this work, we use the stellar population with and without binary stars to study the star formation histories (SFHs) for early type galaxies sample. Our results show that for the SFHs obtained by models with binary star are different from that without binary stars for 10% galaxy sample.

  20. New systemic radial velocities of suspected RR Lyrae binary stars

    NASA Astrophysics Data System (ADS)

    Guggenberger, E.; Barnes, T. G.; Kolenberg, K.

    2016-05-01

    Among the tens of thousands of known RR Lyrae stars there are only a handful that show indications of possible binarity. The question why this is the case is still unsolved, and has recently sparked several studies dedicated to the search for additional RR Lyraes in binary systems. Such systems are particularly valuable because they might allow to constrain the stellar mass. Most of the recent studies, however, are based on photometry by finding a light time effect in the timings of maximum light. This approach is a very promising and successful one, but it has a major drawback: by itself, it cannot serve as a definite proof of binarity, because other phenomena such as the Blazhko effect or intrinsic period changes could lead to similar results. Spectroscopic radial velocity measurements, on the other hand, can serve as definite proof of binarity. We have therefore started a project to study spectroscopically RR Lyrae stars that are suspected to be binaries. We have obtained radial velocity (RV) curves with the 2.1m telescope at McDonald observatory. From these we derive systemic RVs which we will compare to previous measurements in order to find changes induced by orbital motions. We also construct templates of the RV curves that can facilitate future studies. We also observed the most promising RR Lyrae binary candidate, TU UMa, as no recent spectroscopic measurements were available. We present a densely covered pulsational RV curve, which will be used to test the predictions of the orbit models that are based on the O - C variations.

  1. METAL-POOR LITHIUM-RICH GIANTS IN THE RADIAL VELOCITY EXPERIMENT SURVEY

    SciTech Connect

    Ruchti, Gregory R.; Fulbright, Jon P.; Wyse, Rosemary F. G.; Gilmore, Gerard F.; Grebel, Eva K.; Bienayme, Olivier; Siebert, Arnaud; Bland-Hawthorn, Joss; Freeman, Ken C.; Gibson, Brad K.; Munari, Ulisse; Navarro, Julio F.; Parker, Quentin A.; Watson, Fred G.; Reid, Warren; Seabroke, George M.; Siviero, Alessandro; Steinmetz, Matthias; Williams, Mary; Zwitter, Tomaz

    2011-12-20

    We report the discovery of eight lithium-rich field giants found in a high-resolution spectroscopic sample of over 700 metal-poor stars ([Fe/H] < -0.5) selected from the Radial Velocity Experiment survey. The majority of the Li-rich giants in our sample are very metal-poor ([Fe/H] {approx}< -1.9), and have a Li abundance (in the form of {sup 7}Li), A(Li) = log (n(Li)/n(H)) + 12, between 2.30 and 3.63, well above the typical upper red giant branch (RGB) limit, A(Li) < 0.5, while two stars, with A(Li) {approx} 1.7-1.8, show similar lithium abundances to normal giants at the same gravity. We further included two metal-poor, Li-rich globular cluster giants in our sample, namely the previously discovered M3-IV101 and newly discovered (in this work) M68-A96. This comprises the largest sample of metal-poor Li-rich giants to date. We performed a detailed abundance analysis of all stars, finding that the majority of our sample stars have elemental abundances similar to that of Li-normal halo giants. Although the evolutionary phase of each Li-rich giant cannot be definitively determined, the Li-rich phase is likely connected to extra mixing at the RGB bump or early asymptotic giant branch that triggers cool bottom processing in which the bottom of the outer convective envelope is connected to the H-burning shell in the star. The surface of a star becomes Li-enhanced as {sup 7}Be (which burns to {sup 7}Li) is transported to the stellar surface via the Cameron-Fowler mechanism. We discuss and discriminate among several models for the extra mixing that can cause Li production, given the detailed abundances of the Li-rich giants in our sample.

  2. MODELS FOR METAL-POOR STARS WITH ENHANCED ABUNDANCES OF C, N, O, Ne, Na, Mg, Si, S, Ca, AND Ti, IN TURN, AT CONSTANT HELIUM AND IRON ABUNDANCES

    SciTech Connect

    VandenBerg, Don A.; Dotter, Aaron; Bergbusch, Peter A.; Ferguson, Jason W.; Michaud, Georges; Richer, Jacques; Proffitt, Charles R. E-mail: Aaron.Dotter@gmail.com E-mail: proffitt@stsci.edu E-mail: michaudg@astro.umontreal.ca

    2012-08-10

    Recent work has shown that most globular clusters have at least two chemically distinct components, as well as cluster-to-cluster differences in the mean [O/Fe], [Mg/Fe], and [Si/Fe] ratios at similar [Fe/H] values. In order to investigate the implications of variations in the abundances of these and other metals for H-R diagrams and predicted ages, grids of evolutionary sequences have been computed for scaled solar and enhanced {alpha}-element metal abundances, and for mixtures in which the assumed [m/Fe] value for each of the metals C, N, O, Ne, Na, Mg, Si, S, Ca, and Ti has been increased, in turn, by 0.4 dex at constant [Fe/H]. These tracks, together with isochrones for ages from Almost-Equal-To 5 to 14 Gyr, have been computed for -3.0 {<=} [Fe/H] {<=}-0.6, with helium abundances Y = 0.25, 0.29, and 0.33 at each [Fe/H] value, using upgraded versions of the Victoria stellar structure program and the Regina interpolation code, respectively. Turnoff luminosity versus age relations from isochrones are found to depend almost entirely on the importance of the CNO cycle, and thereby mainly on the abundance of oxygen. Since C, N, and O, as well as Ne and S, do not contribute significantly to the opacities at low temperatures and densities, variations in their abundances do not impact the predicted T{sub eff} scale of red giants. The latter is a strong function of the abundances of only Mg and Si (and Fe, possibly to a lesser extent) because they are so abundant and because they are strong sources of opacity at low temperatures. For these reasons, Mg and Si also have important effects on the temperatures of main-sequence stars. Due to their low abundances, Na, Ca, and Ti are of little consequence for stellar models. The effects of varying the adopted solar metals mixture and the helium abundance at a fixed [Fe/H] are also briefly discussed.

  3. Investigating Binary Wolf-Rayet Binary Stars as Potential Gamma-Ray Source

    NASA Astrophysics Data System (ADS)

    Meadows, Jacqueline; Alexander, Michael J.; McSwain, M. Virginia

    2015-01-01

    Wolf-Rayets are massive, hot, and luminous evolved stars with strong stellar winds. When paired with another massive star emitting strong stellar winds, the region where their winds collide produces a bow shock that may emit gamma-rays. This work seeks to find such a colliding wind binary by correlating the orbital period of a binary Wolf-Rayet with periodic changes in flux in nearby gamma-ray sources observed by Fermi Gamma-ray Space Telescope Large Area Telescope (LAT). We selected three binary Wolf-Rayet stars for analysis. WR 39 and WR 48 are in close proximity to unassociated sources from the LAT 2-Year Point Source Catalog (2FGL). WR 140 was selected on the basis of being a double-lined spectroscopic binary; the close passage of the two stars may contribute to colliding winds that could produce gamma-rays. We first used the Fermi Science Tools to calculate average flux values. The orbital period of WR 39 has not been established; so rather than creating a folded light curve, photon data for its proposed 2FGL counterpart were next analyzed using seven-day time bins in an attempt to use periodic behavior in the 2FGL source to find the orbital period of WR 39. However, no periodic behavior was evident in the plotted data. Since WR 48 lies just outside error ellipse of its proposed 2FGL counterpart, we performed the six-year likelihood analysis twice. First, WR 48 was manually inserted as a point source; this resulted in a non-converging fit. Instead, we used the proposed 2FGL counterpart as the object of interest. After calculating the average flux, we separated the photon data into phase bins based on the 18.34 day period of WR 48. The resulting folded light curve does not show any periodic behavior. WR 140 was also manually inserted as a point source; the analysis of the six-year data set failed to establish the existence of a gamma-ray source at the location of WR 140 and no further analysis was performed on this source.This research took place at Lehigh

  4. Discovering metal-poor circumstellar OH masers

    NASA Astrophysics Data System (ADS)

    Goldman, Steve; Green, James; van Loon, Jacco; Wood, Peter; Imai, Hiroshi; Groenewegen, Martin; Nanni, Ambra

    2014-10-01

    OH masers are excellent signposts for a variety of phenomenon including winds of highly-evolved stars (1612 MHz). Using the superior angular resolution and sensitivity of the ATCA, high spectral resolution of the CABB backend, and close proximity to the LMC (with half solar metallicity), this observation will allow us to extend an important relation involving the evolution of red giants and supergiants in a lower metallicity (van Loon, 2012). With even fewer detections with clear double-peaked profiles, indicating an expansion velocity of the circumstellar envelope, successful observation is vital for the advancement of our stellar mass-loss models. By refining the metallicity dependence of the mass-loss of highly-evolved red giants and supergiants in their superwind phase, we can better understand the evolution of these stars and their feedback within galaxies.

  5. Dynamical mass ejection from binary neutron star mergers

    NASA Astrophysics Data System (ADS)

    Radice, David; Galeazzi, Filippo; Lippuner, Jonas; Roberts, Luke F.; Ott, Christian D.; Rezzolla, Luciano

    2016-08-01

    We present fully general-relativistic simulations of binary neutron star mergers with a temperature and composition dependent nuclear equation of state. We study the dynamical mass ejection from both quasi-circular and dynamical-capture eccentric mergers. We systematically vary the level of our treatment of the microphysics to isolate the effects of neutrino cooling and heating and we compute the nucleosynthetic yields of the ejecta. We find that eccentric binaries can eject significantly more material than quasi-circular binaries and generate bright infrared and radio emission. In all our simulations the outflow is composed of a combination of tidally- and shock-driven ejecta, mostly distributed over a broad $\\sim 60^\\circ$ angle from the orbital plane, and, to a lesser extent, by thermally driven winds at high latitudes. Ejecta from eccentric mergers are typically more neutron rich than those of quasi-circular mergers. We find neutrino cooling and heating to affect, quantitatively and qualitatively, composition, morphology, and total mass of the outflows. This is also reflected in the infrared and radio signatures of the binary. The final nucleosynthetic yields of the ejecta are robust and insensitive to input physics or merger type in the regions of the second and third r-process peaks. The yields for elements on the first peak vary between our simulations, but none of our models is able to explain the Solar abundances of first-peak elements without invoking additional first-peak contributions from either neutrino and viscously-driven winds operating on longer timescales after the mergers, or from core-collapse supernovae.

  6. Dynamical mass ejection from binary neutron star mergers

    NASA Astrophysics Data System (ADS)

    Radice, David; Galeazzi, Filippo; Lippuner, Jonas; Roberts, Luke F.; Ott, Christian D.; Rezzolla, Luciano

    2016-08-01

    We present fully general-relativistic simulations of binary neutron star mergers with a temperature and composition dependent nuclear equation of state. We study the dynamical mass ejection from both quasi-circular and dynamical-capture eccentric mergers. We systematically vary the level of our treatment of the microphysics to isolate the effects of neutrino cooling and heating and we compute the nucleosynthetic yields of the ejecta. We find that eccentric binaries can eject significantly more material than quasi-circular binaries and generate bright infrared and radio emission. In all our simulations the outflow is composed of a combination of tidally- and shock-driven ejecta, mostly distributed over a broad ˜60° angle from the orbital plane, and, to a lesser extent, by thermally driven winds at high latitudes. Ejecta from eccentric mergers are typically more neutron rich than those of quasi-circular mergers. We find neutrino cooling and heating to affect, quantitatively and qualitatively, composition, morphology, and total mass of the outflows. This is also reflected in the infrared and radio signatures of the binary. The final nucleosynthetic yields of the ejecta are robust and insensitive to input physics or merger type in the regions of the second and third r-process peaks. The yields for elements on the first peak vary between our simulations, but none of our models is able to explain the Solar abundances of first-peak elements without invoking additional first-peak contributions from either neutrino and viscously-driven winds operating on longer time-scales after the mergers, or from core-collapse supernovae.

  7. Dynamical Mass Ejection from Binary Neutron Star Mergers

    NASA Astrophysics Data System (ADS)

    Radice, David; Galeazzi, Filippo; Lippuner, Jonas; Roberts, Luke F.; Ott, Christian D.; Rezzolla, Luciano

    2016-05-01

    We present fully general-relativistic simulations of binary neutron star mergers with a temperature and composition dependent nuclear equation of state. We study the dynamical mass ejection from both quasi-circular and dynamical-capture eccentric mergers. We systematically vary the level of our treatment of the microphysics to isolate the effects of neutrino cooling and heating and we compute the nucleosynthetic yields of the ejecta. We find that eccentric binaries can eject significantly more material than quasi-circular binaries and generate bright infrared and radio emission. In all our simulations the outflow is composed of a combination of tidally- and shock-driven ejecta, mostly distributed over a broad ˜60° angle from the orbital plane, and, to a lesser extent, by thermally driven winds at high latitudes. Ejecta from eccentric mergers are typically more neutron rich than those of quasi-circular mergers. We find neutrino cooling and heating to affect, quantitatively and qualitatively, composition, morphology, and total mass of the outflows. This is also reflected in the infrared and radio signatures of the binary. The final nucleosynthetic yields of the ejecta are robust and insensitive to input physics or merger type in the regions of the second and third r-process peaks. The yields for elements on the first peak vary between our simulations, but none of our models is able to explain the Solar abundances of first-peak elements without invoking additional first-peak contributions from either neutrino and viscously-driven winds operating on longer timescales after the mergers, or from core-collapse supernovae.

  8. CARBON-RICH DUST PRODUCTION IN METAL-POOR GALAXIES IN THE LOCAL GROUP

    SciTech Connect

    Sloan, G. C.; Matsuura, M.; Lagadec, E.; Van Loon, J. Th.; Kraemer, K. E.; McDonald, I.; Zijlstra, A. A.; Groenewegen, M. A. T.; Wood, P. R.; Bernard-Salas, J.

    2012-06-20

    We have observed a sample of 19 carbon stars in the Sculptor, Carina, Fornax, and Leo I dwarf spheroidal galaxies with the Infrared Spectrograph on the Spitzer Space Telescope. The spectra show significant quantities of dust around the carbon stars in Sculptor, Fornax, and Leo I, but little in Carina. Previous comparisons of carbon stars with similar pulsation properties in the Galaxy and the Magellanic Clouds revealed no evidence that metallicity affected the production of dust by carbon stars. However, the more metal-poor stars in the current sample appear to be generating less dust. These data extend two known trends to lower metallicities. In more metal-poor samples, the SiC dust emission weakens, while the acetylene absorption strengthens. The bolometric magnitudes and infrared spectral properties of the carbon stars in Fornax are consistent with metallicities more similar to carbon stars in the Magellanic Clouds than in the other dwarf spheroidals in our sample. A study of the carbon budget in these stars reinforces previous considerations that the dredge-up of sufficient quantities of carbon from the stellar cores may trigger the final superwind phase, ending a star's lifetime on the asymptotic giant branch.

  9. The VLT Unravels the Nature of the Fastest Binary Star

    NASA Astrophysics Data System (ADS)

    2002-03-01

    Two Hot White Dwarfs Perform a Tight Dance Summary Observations with ESO's Very Large Telescope (VLT) in Chile and the Italian Telescopio Nazionale Galileo (TNG) on the Canary Islands during the past two years have enabled an international group of astronomers [1] to unravel the true nature of an exceptional binary stellar system. This system, designated RX J0806.3+1527 , was first discovered as an X-ray source of variable brightness - once every five minutes, it "switches off" for a short moment. The new observations have shown beyond doubt that this period reflects the orbital motion of two "white dwarf" stars that revolve around each other at a distance of only 80,000 km . Each of the stars is about as large as the Earth and this is the shortest orbital period known for any binary stellar system. The VLT spectrum displays lines of ionized helium, indicating that the presence of an exceedingly hot area on one of the stars - a "hot spot" with a temperature of approx. 250,000 degrees. The system is currently in a rarely seen, transitory evolutionary state . PR Photo 10a/02 : U- and R-band images of RX J0806.3+1527. PR Photo 10b/02 : Spectrum of RX J0806.3+1527 An amazing stellar binary system ESO PR Photo 10a/02 ESO PR Photo 10a/02 [Preview - JPEG: 800 x 400 pix - 440k] [Normal - JPEG: 1600 x 800 pix - 1.1M] Caption : PR Photo 10a/02 shows U and R filter images of the sky field around RX J0806.3+1527 (at centre of circle), obtained with the FORS2 multi-mode instrument on VLT KUEYEN. The object is brightest at the shorter wavelength (U-band) - reflecting its very high temperature. Technical information about the photo is available below. One year is the time it takes the Earth to move once around the Sun, our central star. This may seem quite fast when measured on the scale of the Universe, but this is a snail's motion compared to the the speed of two recently discovered stars. They revolve around each other 100,000 times faster; one full revolution takes only 321

  10. Time-Resolved Spectroscopy of Active Binary Stars

    NASA Technical Reports Server (NTRS)

    Brown, Alexander

    2000-01-01

    This NASA grant covered EUVE observing and data analysis programs during EUVE Cycle 5 GO observing. The research involved a single Guest Observer project 97-EUVE-061 "Time-Resolved Spectroscopy of Active Binary Stars". The grant provided funding that covered 1.25 months of the PI's salary. The activities undertaken included observation planning and data analysis (both temporal and spectral). This project was awarded 910 ksec of observing time to study seven active binary stars, all but one of which were actually observed. Lambda-And was observed on 1997 Jul 30 - Aug 3 and Aug 7-14 for a total of 297 ksec; these observations showed two large complex flares that were analyzed by Osten & Brown (1999). AR Psc, observed for 350 ksec on 1997 Aug 27 - Sep 13, showed only relatively small flares that were also discussed by Osten & Brown (1999). EUVE observations of El Eri were obtained on 1994 August 24-28, simultaneous with ASCA X-ray spectra. Four flares were detected by EUVE with one of these also observed simultaneously, by ASCA. The other three EUVE observations were of the stars BY Dra (1997 Sep 22-28), V478 Lyr (1998 May 18-27), and sigma Gem (1998 Dec 10-22). The first two stars showed a few small flares. The sigma Gem data shows a beautiful complete flare with a factor of ten peak brightness compared to quiescence. The flare rise and almost all the decay phase are observed. Unfortunately no observations in other spectral regions were obtained for these stars. Analysis of the lambda-And and AR Psc observations is complete and the results were published in Osten & Brown (1999). Analysis of the BY Dra, V478 Lyr and sigma Gem EUVE data is complete and will be published in Osten (2000, in prep.). The El Eri EUV analysis is also completed and the simultaneous EUV/X-ray study will be published in Osten et al. (2000, in prep.). Both these latter papers will be submitted in summer 2000. All these results will form part of Rachel Osten's PhD thesis.

  11. Merging binary stars and the magnetic white dwarfs

    NASA Astrophysics Data System (ADS)

    Briggs, Gordon P.; Ferrario, Lilia; Tout, Christopher A.; Wickramasinghe, Dayal T.; Hurley, Jarrod R.

    2015-02-01

    A magnetic dynamo driven by differential rotation generated when stars merge can explain strong fields in certain classes of magnetic stars, including the high field magnetic white dwarfs (HFMWDs). In their case the site of the differential rotation has been variously proposed to be within a common envelope, the massive hot outer regions of a merged degenerate core or an accretion disc formed by a tidally disrupted companion that is subsequently incorporated into a degenerate core. We synthesize a population of binary systems to investigate the stellar merging hypothesis for observed single HFMWDs. Our calculations provide mass distribution and the fractions of white dwarfs that merge during a common envelope phase or as double degenerate systems in a post-common-envelope phase. We vary the common envelope efficiency parameter α and compare with observations. We find that this hypothesis can explain both the observed incidence of magnetism and the mass distribution of HFMWDs for a wide range of α. In this model, the majority of the HFMWDs are of the carbon-oxygen type and merge within a common envelope. Less than about a quarter of a per cent of HFMWDs originate from double degenerate stars that merge after common envelope evolution and these populate the high-mass tail of the HFMWD mass distribution.

  12. MAGNETIC ENERGY PRODUCTION BY TURBULENCE IN BINARY NEUTRON STAR MERGERS

    SciTech Connect

    Zrake, Jonathan; MacFadyen, Andrew I.

    2013-06-01

    The simultaneous detection of electromagnetic and gravitational wave emission from merging neutron star binaries would greatly aid in their discovery and interpretation. By studying turbulent amplification of magnetic fields in local high-resolution simulations of neutron star merger conditions, we demonstrate that magnetar-level ({approx}> 10{sup 16} G) fields are present throughout the merger duration. We find that the small-scale turbulent dynamo converts 60% of the randomized kinetic energy into magnetic fields on a merger timescale. Since turbulent magnetic energy dissipates through reconnection events that accelerate relativistic electrons, turbulence may facilitate the conversion of orbital kinetic energy into radiation. If 10{sup -4} of the {approx}10{sup 53} erg of orbital kinetic available gets processed through reconnection and creates radiation in the 15-150 keV band, then the fluence at 200 Mpc would be 10{sup -7} erg cm{sup -2}, potentially rendering most merging neutron stars in the advanced LIGO and Virgo detection volumes detectable by Swift BAT.

  13. ellc: Light curve model for eclipsing binary stars and transiting exoplanets

    NASA Astrophysics Data System (ADS)

    Maxted, P. F. L.

    2016-03-01

    ellc analyzes the light curves of detached eclipsing binary stars and transiting exoplanet systems. The model represents stars as triaxial ellipsoids, and the apparent flux from the binary is calculated using Gauss-Legendre integration over the ellipses that are the projection of these ellipsoids on the sky. The code can also calculate the fluxweighted radial velocity of the stars during an eclipse (Rossiter-McLaghlin effect). ellc can model a wide range of eclipsing binary stars and extrasolar planetary systems, and can enable the use of modern Monte Carlo methods for data analysis and model testing.

  14. Dynamics of primordial binary stars in multiple-population globular clusters

    NASA Astrophysics Data System (ADS)

    Hong, Jongsuk; Vesperini, Enrico; Sollima, Antonio; McMillan, Steve; D'Antona, Franca; D'Ercole, Annibale

    2016-02-01

    We have performed a survey of N-body simulations to explore the dynamics of primordial binaries in multiple-population globular clusters. We show that, as a consequence of the initial differences between the spatial distribution of first-generation (FG) and second-generation (SG) stars, SG binaries are disrupted more efficiently than FG binaries. The effects of dynamical evolution on the surviving binaries produces a difference between the SG and the FG binary binding energy distribution with the SG population characterized by a larger fraction of high binding energy (more bound) binaries. We also explore the evolution of the radial variation of the SG-to-FG binary number ratio and find that although the global binary fraction decreases more rapidly for the SG population, the local binary fraction measured in the cluster inner regions may still be dominated by SG binaries.

  15. Are either X Her or g Her Binary Stars?

    NASA Astrophysics Data System (ADS)

    Shawl, Stephen J.; Scarfe, C.

    2007-12-01

    X Her (HD 144205) and g Her (HD 148783) were observed by Shawl (AJ, 80, 602, 1975) to exhibit polarization position angles that varied with time in peculiar ways. For example, for X Her, the variations in the B- and I-filters were significant and uncorrelated, while for g Her a possible periodic position angle variation was found. At the time of that work, a literature search found no papers indicating that either star was binary, which conceivably could explain the observed variations. For this reason, in spring 2001 these stars were placed on the observing list of the second author to obtain high precision radial velocities (2001-2003 using the DAO radial velocity scanner, while from 2004 onward using a CCD). The velocity errors are estimated to be les than 1 km/s. Nearly 100 observations were collected over a range of 2343 days. After we began collecting data, Hinkle et al. (AJ 123, 1002, 2002) published a paper that included radial velocity observations of both our program stars. For both stars they had 25 spectra during 1849 days between 1995 and 2000. X Her showed obvious velocity variations with a 666 day period. Lebzelter (Astron. Astrophys 351, 644, 1999) obtained a finer grid of data and found some complex short-period variations. For g Her, they found an 838 day period, which is consistent with the long-period variation in the V-band. We will present the interim results of our analysis of the more recent data. * Guest observer at the Dominion Astrophysical Observatory, Herzberg Institute of Astrophysics, National Research Council of Canada.

  16. Artificial neural network to search for metal-poor galaxies

    NASA Astrophysics Data System (ADS)

    Shi, Fei; Liu, Yu-Yan; Kong, Xu; Chen, Yang

    2014-02-01

    Aims: To find a fast and reliable method for selecting metal-poor galaxies (MPGs), especially in large surveys and huge databases, an artificial neural network (ANN) method is applied to a sample of star-forming galaxies from the Sloan Digital Sky Survey (SDSS) data release 9 (DR9) provided by the Max Planck Institute and the Johns Hopkins University (MPA/JHU). Methods: A two-step approach is adopted: (i) The ANN network must be trained with a subset of objects that are known to be either MPGs or metal rich galaxies (MRGs), treating the strong emission line flux measurements as input feature vectors in n-dimensional space, where n is the number of strong emission line flux ratios. (ii) After the network is trained on a sample of star-forming galaxies, the remaining galaxies are classified in the automatic test analysis as either MPGs or MRGs. We consider several random divisions of the data into training and testing sets; for instance, for our sample, a total of 70 percent of the data are involved in training the algorithm, 15 percent are involved in validating the algorithm, and the remaining 15 percent are used for blind testing the resulting classifier. Results: For target selection, we have achieved an acquisition rate for MPGs of 96 percent and 92 percent for an MPGs threshold of 12 + log (O/H) = 8.00 and 12 + log (O/H) = 8.39, respectively. Running the code takes minutes in most cases under the Matlab 2013a software environment. The ANN method can easily be extended to any MPGs target selection task when the physical property of the target can be expressed as a quantitative variable. The code in the paper is available on the web (http://fshi5388.blog.163.com).

  17. Database of candidates for RR Lyrae stars in binary systems - RRLyrBinCan

    NASA Astrophysics Data System (ADS)

    Liska, J.; Skarka, M.

    2016-05-01

    A new on-line database with RR Lyrae stars bound in binary systems is presented. Its purpose is to give a quick overview about known and suspected RR Lyrae stars in binaries on the basis of available literature. The first released version of the catalogue contains information about 61 double-star candidates, their orbital periods, method of detection, comments and active links to published papers.

  18. Gravitational lensing of gravitational waves from merging neutron star binaries

    SciTech Connect

    Wang, Yun; Stebbins, Albert; Turner, Edwin L.

    1996-05-01

    We discuss the gravitational lensing of gravitational waves from merging neutron star binaries, in the context of advanced LIGO type gravitational wave detectors. We consider properties of the expected observational data with cut on the signal-to-noise ratio \\rho, i.e., \\rho>\\rho_0. An advanced LIGO should see unlensed inspiral events with a redshift distribution with cut-off at a redshift z_{\\rm max} < 1 for h \\leq 0.8. Any inspiral events detected at z>z_{\\rm max} should be lensed. We compute the expected total number of events which are present due to gravitational lensing and their redshift distribution for an advanced LIGO in a flat Universe. If the matter fraction in compact lenses is close to 10\\%, an advanced LIGO should see a few strongly lensed events per year with \\rho >5.

  19. Observational Study of the Evolution of Massive Binary Stars

    NASA Astrophysics Data System (ADS)

    Burki, G.; Mayor, M.

    Six years ago an observational program on supergiant stars using CORAVEL was initiated at Geneva Observatory. About 1500 radial velocities were obtained out of a sample of 181 northern supergiants of F, G, K, M type. Nineteen new SB have been discovered and 16 others are suspected to be SB. From the catalogue of Batten et al. (1978) and the results of the authors' survey, the orbital elements are known for 25 SB having at least one supergiant component of type F to M. In each luminosity class all systems with Pcirc = P(1-e)3/2 (P, e are period and eccentricity of a binary system) shorter than a critical value have nearly circular orbits. The critical value is very well defined for class Ib: 350 - 440 days. This value is larger for classes Iab and Ia (1400 - 3900 days for class Ia).

  20. Absolute properties of the eclipsing binary star IM Persei

    SciTech Connect

    Lacy, Claud H. Sandberg; Torres, Guillermo; Fekel, Francis C.; Muterspaugh, Matthew W.; Southworth, John E-mail: gtorres@cfa.harvard.edu E-mail: matthew1@coe.tsuniv.edu

    2015-01-01

    IM Per is a detached A7 eccentric eclipsing binary star. We have obtained extensive measurements of the light curve (28,225 differential magnitude observations) and radial velocity curve (81 spectroscopic observations) which allow us to fit orbits and determine the absolute properties of the components very accurately: masses of 1.7831 ± 0.0094 and 1.7741 ± 0.0097 solar masses, and radii of 2.409 ± 0.018 and 2.366 ± 0.017 solar radii. The orbital period is 2.25422694(15) days and the eccentricity is 0.0473(26). A faint third component was detected in the analysis of the light curves, and also directly observed in the spectra. The observed rate of apsidal motion is consistent with theory (U = 151.4 ± 8.4 year). We determine a distance to the system of 566 ± 46 pc.

  1. Optical microflaring on the nearby flare star binary UV Ceti

    NASA Astrophysics Data System (ADS)

    Schmitt, J. H. M. M.; Kanbach, G.; Rau, A.; Steinle, H.

    2016-05-01

    We present extremely high time resolution observations of the visual flare star binary UV Cet obtained with the Optical Pulsar Timing Analyzer (OPTIMA) at the 1.3 m telescope at Skinakas Observatory (SKO) in Crete, Greece. OPTIMA is a fiber-fed optical instrument that uses Single Photon Avalanche Diodes to measure the arrival times of individual optical photons. The time resolution of the observations presented here was 4 μs, allowing to resolve the typical millisecond variability time scales associated with stellar flares. We report the detection of very short impulsive bursts in the blue band with well resolved rise and decay time scales of about 2 s. The overall energetics put these flares at the lower end of the known flare distribution of UV Cet.

  2. THE TERZAN 5 PUZZLE: DISCOVERY OF A THIRD, METAL-POOR COMPONENT

    SciTech Connect

    Origlia, L.; Massari, D.; Mucciarelli, A.; Ferraro, F. R.; Dalessandro, E.; Lanzoni, B.

    2013-12-10

    We report on the discovery of three metal-poor giant stars in Terzan 5, a complex stellar system in the Galactic bulge, known to have two populations at [Fe/H] = –0.25 and +0.3. For these three stars we present new echelle spectra obtained with NIRSPEC at Keck II, which confirm their radial velocity membership and provide an average [Fe/H] = –0.79 dex iron abundance and [α/Fe] = +0.36 dex enhancement. This new population extends the metallicity range of Terzan 5 to 0.5 dex more metal poor, and it has properties consistent with having formed from a gas polluted by core-collapse supernovae.

  3. SELF-REGULATED SHOCKS IN MASSIVE STAR BINARY SYSTEMS

    SciTech Connect

    Parkin, E. R.; Sim, S. A. E-mail: s.sim@qub.ac.uk

    2013-04-20

    In an early-type, massive star binary system, X-ray bright shocks result from the powerful collision of stellar winds driven by radiation pressure on spectral line transitions. We examine the influence of the X-rays from the wind-wind collision shocks on the radiative driving of the stellar winds using steady-state models that include a parameterized line force with X-ray ionization dependence. Our primary result is that X-ray radiation from the shocks inhibits wind acceleration and can lead to a lower pre-shock velocity, and a correspondingly lower shocked plasma temperature, yet the intrinsic X-ray luminosity of the shocks, L{sub X}, remains largely unaltered, with the exception of a modest increase at small binary separations. Due to the feedback loop between the ionizing X-rays from the shocks and the wind driving, we term this scenario as self-regulated shocks. This effect is found to greatly increase the range of binary separations at which a wind-photosphere collision is likely to occur in systems where the momenta of the two winds are significantly different. Furthermore, the excessive levels of X-ray ionization close to the shocks completely suppress the line force, and we suggest that this may render radiative braking less effective. Comparisons of model results against observations reveal reasonable agreement in terms of log (L{sub X}/L{sub bol}). The inclusion of self-regulated shocks improves the match for kT values in roughly equal wind momenta systems, but there is a systematic offset for systems with unequal wind momenta (if considered to be a wind-photosphere collision).

  4. THE HOT R CORONAE BOREALIS STAR DY CENTAURI IS A BINARY

    SciTech Connect

    Kameswara Rao, N.; Lambert, David L.; McArthur, Barbara; Garcia-Hernandez, D. A.; Woolf, Vincent M. E-mail: dll@astro.as.utexas.edu

    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.

  5. ABSOLUTE PROPERTIES OF THE ECLIPSING BINARY STAR BF DRACONIS