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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

An Ellipsometric Investigation of the Optical Properties of Ru{sub 2}Ge{sub 3} and Ru{sub 2}Sn{sub 3} Compounds

Ellipsometric investigations of the optical properties of Ru{sub 2}Ge{sub 3} and Ru{sub 2}Sn{sub 3} intermetallic compounds are carried out in the wavelength range from 0.22 to 15 μm. The nature of interband light absorption is analyzed based on a comparative analysis of the experimental and theoretical frequency dependences of an optical conductivity. The obtained results confirm the existence of energy gaps at the Fermi level in the electronic spectra of these materials predicted earlier by the band-structure calculations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

( Suzaku Suzaku) observation of the high-inclination binary EXO 0748-676 in the hard state

Utilizing archived Suzaku data acquired on 2007 December 25 for 46 ks, the X-ray spectroscopic properties of the dipping and eclipsing low-mass X-ray binary EXO 0748−676 were studied. At an assumed distance of 7.1 kpc, the data provided a persistent unabsorbed luminosity of 3.4×10{sup 36} erg cm{sup −2} s{sup −1} in 0.6−55 keV. The source was in a relatively bright low/hard state, wherein the 0.6−55 keV spectrum can be successfully explained by a “double-seed” Comptonization model incorporating a common corona with an electron temperature of ∼13 keV. The seed photons are thought to be supplied from both the neutron star surface and a cooler truncated disk. Compared to a sample of non-dipping, low-mass X-ray binaries in the low/hard state, the spectrum is subject to stronger Comptonization with a relatively larger Comptonizing y-parameter of ∼1.4 and a larger coronal optical depth of ∼5. This result, when attributed to the high inclination of EXO 0748−676, suggests that the Comptonizing corona may elongate along the disk plane and provide a longer path for the seed photons when viewed from edge-on inclinations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Zodiacal exoplanets in time (Zeit). I. A Neptune-sized planet orbiting an M4.5 dwarf in the Hyades star cluster

Studying the properties of young planetary systems can shed light on how the dynamics and structure of planets evolve during their most formative years. Recent K2 observations of nearby young clusters (10–800 Myr) have facilitated the discovery of such planetary systems. Here we report the discovery of a Neptune-sized planet transiting an M4.5 dwarf (K2-25) in the Hyades cluster (650–800 Myr). The light curve shows a strong periodic signal at 1.88 days, which we attribute to spot coverage and rotation. We confirm that the planet host is a member of the Hyades by measuring the radial velocity of the system with the high-resolution near-infrared spectrograph Immersion Grating Infrared Spectrometer. This enables us to calculate a distance based on K2-25's kinematics and membership to the Hyades, which in turn provides a stellar radius and mass to ≃5%–10%, better than what is currently possible for most Kepler M dwarfs (12%–20%). We use the derived stellar density as a prior on fitting the K2 transit photometry, which provides weak constraints on eccentricity. Utilizing a combination of adaptive optics imaging and high-resolution spectra, we rule out the possibility that the signal is due to a bound or background eclipsing binary, confirming the transits’ planetary origin. K2-25b has a radius (3.43{sub −0.31}{sup +0.95} R{sub ⊕}) much larger than older Kepler planets with similar orbital periods (3.485 days) and host-star masses (0.29 M{sub ⊙}). This suggests that close-in planets lose some of their atmospheres past the first few hundred million years. Additional transiting planets around the Hyades, Pleiades, and Praesepe clusters from K2 will help confirm whether this planet is atypical or representative of other close-in planets of similar age.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

STRUCTURE AND FEEDBACK IN 30 DORADUS. I. OBSERVATIONS

We have completed a new optical imaging and spectrophotometric survey of a 140 x 80 pc{sup 2} region of 30 Doradus centered on R136, covering key optical diagnostic emission lines including H{alpha}, H{beta}, H{gamma}, [O III] {lambda}{lambda}4363, 4959, 5007, [N II] {lambda}{lambda}6548, 6584, [S II] {lambda}{lambda}6717, 6731 [S III] {lambda}6312, and in some locations [S III] {lambda}9069. We present maps of fluxes and intensity ratios for these lines, and catalogs of isolated ionizing stars, elephant-trunk pillars, and edge-on ionization fronts. The final science-quality spectroscopic data products are available to the public. Our analysis of the new data finds that, while stellar winds and supernovae undoubtedly produce shocks and are responsible for shaping the nebula, there are no global spectral signatures to indicate that shocks are currently an important source of ionization. We conclude that the considerable region covered by our survey is well described by photoionization from the central cluster where the ionizing continuum is dominated by the most massive O stars. We show that if 30 Dor were viewed at a cosmological distance, its integrated light would be dominated by its extensive regions of lower surface brightness rather than by the bright, eye-catching arcs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

The early ALMA view of the FU Ori outburst system

We have obtained ALMA Band 7 observations of the FU Ori outburst system at a 0.″6 × 0.″5 resolution to measure the link between the inner disk instability and the outer disk through submillimeter continuum and molecular line observations. Our observations detect continuum emission that can be well-modeled by two unresolved sources located at the position of each binary component. The interferometric observations recover the entire flux reported in previous single-dish studies, ruling out the presence of a large envelope. Assuming that the dust is optically thin, we derive disk dust masses of 2 × 10{sup −4} M{sub ⊙} and 8×10{sup −5} M{sub ⊙} for the north and south components, respectively. We place limits on the disks’ radii of r < 45 AU. We report the detection of molecular emission from {sup 12}CO(3-2), HCO{sup +}(4-3), and from HCN(4-3). The {sup 12}CO appears widespread across the two binary components and is slightly more extended than the continuum emission. The denser gas tracer HCO{sup +} peaks close to the position of the southern binary component, while HCN appears to be peaked at the position of the northern component. This suggests that the southern binary component is embedded in denser molecular material, consistent with previous studies that indicate a heavily reddened object. At this angular resolution, any interaction between the two unresolved disk components cannot be disentangled. Higher-resolution images are vital for understanding the process of star formation via rapid accretion FU Ori-type episodes.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Tunable optical properties and stability of lead free all inorganic perovskites (Cs 2 SnI x Cl 6-x )

Organic–inorganic hybrid lead-based perovskites experience significant environmental instability under ambient moist air and are not environmentally benign due to the usage of toxic Pb. In this paper, we report a new approach to synthesize lead-free all inorganic perovskites (Cs 2 SnI x Cl 6-x ) using hydriodic acid (HI) demonstrating greatly enhanced environmental stability and tunable optical properties by controlling the I - /Cl - ratios. Single phase perovskites can be achieved with a low iodine or chlorine content, and a phase separation occurs in the binary system with closer iodine and chlorine dopings. UV-vis diffuse reflectance and photoluminescence measurements reveal tunable band gaps of Cs 2 SnI x Cl 6-x perovskites from the UV to the infrared region. The mixed halide perovskite with a lower chloride content shows significantly higher photoluminescence intensity. The thermal stability of mixed halide all-inorganic perovskites is continuously improved as the Cl content increases. Finally, the synthesis of Sn-based perovskites with tunable optical properties and environmental stability represents one step further toward the realization of the stable lead-free all inorganic perovskites.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Accretion and OH photodissociation at a nearby T Tauri system in the β Pictoris moving group

We present spectra of an M-type, binary star system (LDS 5606) that belongs to the nearby ∼20 Myr old β Pictoris moving group. Both stars are very dusty; the dustier member displays optical emission lines from eight elements indicative of ongoing mass accretion. The spectra of both stars contain oxygen forbidden line emission at 6302 and 5579 Å, consistent with a recent model of far ultraviolet photodissociation of OH molecules in a circumstellar disk. These are the oldest dwarf stars presently known to display such a phenomenon. The spectral energy distribution of the dustier star indicates substantial quantities of dust as hot as 900 K, and its fractional infrared luminosity (L {sub IR}/L {sub bol}) is almost as large as that of the main sequence record holder, V488 Per. The LDS 5606 binary joins a remarkable group of very dusty, old, T Tauri stars that belong to widely separated multiple systems.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Structural and optical properties of (Ag,Cu)(In,Ga)Se{sub 2} polycrystalline thin film alloys

The structural and optical properties of pentenary alloy (Ag,Cu)(In,Ga)Se{sub 2} polycrystalline thin films were characterized over the entire compositional range at a fixed (Cu + Ag)/(In + Ga) ratio. Films deposited at 550 °C on bare and molybdenum coated soda-lime glass by elemental co-evaporation in a single-stage process with constant incident fluxes exhibit single phase chalcopyrite structure, corresponding to 122 spacegroup (I-42d) over the entire compositional space. Unit cell refinement of the diffraction patterns show that increasing Ag substitution for Cu, the refined a{sub o} lattice constant, (Ag,Cu)-Se bond length, and anion displacement increase in accordance with the theoretical model proposed by Jaffe, Wei, and Zunger. However, the refined c{sub o} lattice constant and (In,Ga)-Se bond length deviated from theoretical expectations for films with mid-range Ag and Ga compositions and are attributed to influences from crystallographic bond chain ordering or cation electronegativity. The optical band gap, derived from transmission and reflection measurements, widened with increasing Ag and Ga content, due to influences from anion displacement and cation electronegativity, as expected from theoretical considerations for pseudo-binary chalcopyrite compounds.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Estimating the Contribution of Dynamical Ejecta in the Kilonova Associated with GW170817

The source of the gravitational-wave (GW) signal GW170817, very likely a binary neutron star merger, was also observed electromagnetically, providing the first multi-messenger observations of this type. The two-week-long electromagnetic (EM) counterpart had a signature indicative of an r-process-induced optical transient known as a kilonova. This Letter examines how the mass of the dynamical ejecta can be estimated without a direct electromagnetic observation of the kilonova, using GW measurements and a phenomenological model calibrated to numerical simulations of mergers with dynamical ejecta. Specifically, we apply the model to the binary masses inferred from the GW measurements, and use the resulting mass of the dynamical ejecta to estimate its contribution (without the effects of wind ejecta) to the corresponding kilonova light curves from various models. The distributions of dynamical ejecta mass range between ${M}_{\mathrm{ej}}={10}^{-3}-{10}^{-2}\,{M}_{\odot }$ for various equations of state, assuming that the neutron stars are rotating slowly. In addition, we use our estimates of the dynamical ejecta mass and the neutron star merger rates inferred from GW170817 to constrain the contribution of events like this to the r-process element abundance in the Galaxy when ejecta mass from post-merger winds is neglected. We find that if ≳10% of the matter dynamically ejected from binary neutron star (BNS) mergers is converted to r-process elements, GW170817-like BNS mergers could fully account for the amount of r-process material observed in the Milky Way.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

iPTF13bvn: The first evidence of a binary progenitor for a type Ib supernova

The recent detection in archival Hubble Space Telescope images of an object at the location of supernova (SN) iPTF13bvn may represent the first direct evidence of the progenitor of a Type Ib SN. The object's photometry was found to be compatible with a Wolf-Rayet pre-SN star mass of ≈11 M {sub ☉}. However, based on hydrodynamical models, we show that the progenitor had a pre-SN mass of ≈3.5 M {sub ☉} and that it could not be larger than ≈8 M {sub ☉}. We propose an interacting binary system as the SN progenitor and perform evolutionary calculations that are able to self-consistently explain the light curve shape, the absence of hydrogen, and the pre-SN photometry. We further discuss the range of allowed binary systems and predict that the remaining companion is a luminous O-type star of significantly lower flux in the optical than the pre-SN object. A future detection of such a star may be possible and would provide the first robust identification of a progenitor system for a Type Ib SN.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Hubble Space Telescope near-ultraviolet spectroscopy of bright CEMP-s stars

We present an elemental-abundance analysis, in the near-ultraviolet (NUV) spectral range, for the bright carbon-enhanced metal-poor (CEMP) stars HD 196944 (V=8.40, [Fe/H] = −2.41) and HD 201626 (V=8.16, [Fe/H] = −1.51), based on data acquired with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope. Both of these stars belong to the sub-class CEMP-s, and exhibit clear over-abundances of heavy elements associated with production by the slow neutron-capture process. HD 196944 has been well-studied in the optical region, but we add abundance results for six species (Ge, Nb, Mo, Lu, Pt, and Au) that are only accessible in the NUV. In addition, we provide the first determination of its orbital period, P = 1325 days. HD 201626 has only a limited number of abundance results based on previous optical work—here we add five new species from the NUV, including Pb. We compare these results with models of binary-system evolution and s-process element production in stars on the asymptotic giant branch, with the goal of explaining their origin and evolution. Our best-fitting models for HD 196944 (M{sub 1,i}=0.9M{sub ⊙}, M{sub 2,i}=0.86M{sub ⊙}, for [Fe/H] = −2.2), and HD 201626 (M{sub 1,i}=0.9M{sub ⊙}, M{sub 2,i}=0.76M{sub ⊙}, for [Fe/H] = −2.2; M{sub 1,i}=1.6M{sub ⊙}, M{sub 2,i}=0.59M{sub ⊙}, for [Fe/H] = −1.5) are consistent with the current accepted scenario for the formation of CEMP-s stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Identification of Faint Chandra X-Ray Sources in the Core-collapsed Globular Cluster NGC 6752

We have searched for optical identifications for 39 Chandra X-ray sources that lie within the 1.′9 half-mass radius of the nearby (d=4.0 kpc), core-collapsed globular cluster, NGC 6752, using deep Hubble Space Telescope ACS/WFC imaging in B {sub 435}, R{sub 625}, and Hα. Photometry of these images allows us to classify candidate counterparts based primarily on color–magnitude and color–color diagram location. The color–color diagram is particularly useful for quantifying the Hα-line equivalent width. In addition to recovering 11 previously detected optical counterparts, we propose 20 new optical IDs. In total, there are 16 likely or less certain cataclysmic variables (CVs), 9 likely or less certain chromospherically active binaries, 3 galaxies, and 3 active galactic nuclei. The latter three sources, which had been identified as likely CVs by previous investigations, now appear to be extragalactic objects based on their proper motions. As we previously found for NGC 6397, the CV candidates in NGC 6752 fall into a bright group that is centrally concentrated relative to the turnoff-mass stars and a faint group that has a spatial distribution that is more similar to that of the turnoff-mass stars. This is consistent with an evolutionary scenario in which CVs are produced by dynamical interactions near the cluster center and diffuse to larger radius orbits as they age.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Galaxies as High-resolution Telescopes

Recent observations show a population of active galaxies with milliarcsecond offsets between optical and radio emission. Such offsets can be an indication of extreme phenomena associated with supermassive black holes including relativistic jets, binary supermassive black holes, or even recoiling supermassive black holes. However, the multi-wavelength structure of active galaxies at a few milliarcseconds cannot be resolved with direct observations. We propose using strong gravitational lensing to elucidate the multi-wavelength structure of sources. When sources are located close to the caustic of a lensing galaxy, even a small offset in the position of the sources results in a drastic difference in the position and magnification of mirage images. We show that the angular offset in the position of the sources can be amplified more than 50 times in the observed position of mirage images. We find that at least 8% of the observed gravitationally lensed quasars will be in the caustic configuration. The synergy between SKA and Euclid will provide an ideal set of observations for thousands of gravitationally lensed sources in the caustic configuration, which will allow us to resolve the multi-wavelength structure for a large ensemble of sources and to study the physical origin of radio emissions, their connection to supermassive black holes, and their cosmic evolution.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Modified Closures in Monte Carlo Algorithms for Diffusive Binary Stochastic Media Transport Problems

In a stochastic medium, the material properties at a given spatial location are known only statistically. The most common approach to solving particle transport problems involving binary stochastic media (BSM) is to use the atomic mix approximation in which the transport problem is solved using homogenized (volume-averaged) material properties. A common deterministic model developed for solving BSM particle transport problems is the Levermore-Pomraning (LP) model. Zimmerman and Adams proposed a Monte Carlo algorithm (Algorithm A) that solves the LP equations and another Monte Carlo algorithm (Algorithm B) that locally preserves the sampled material realization; we refer to these Monte Carlo algorithms as the LP and LPLRP (LP local realization preserving) algorithms, respectively. One-dimensional (1D) planar geometry benchmark studies have shown that the LPLRP algorithm is often significantly more accurate than the LP algorithm for problems with an incident angular flux as well as for problems with an interior source. The LPLRP algorithm implementation in these benchmark comparisons made explicit use of the one-dimensional nature of the problem. The LP model is derived by assuming an 'upwind' closure in the coupling term relating the two materials in a binary stochastic medium. Su and Pomraning developed a modified form of this closure by considering the small correlation length limit and requiring the modified closure to produce the correct exponential decay for a source-free half-line albedo problem in rod geometry. They concluded that the modified closure is generally not inferior to the LP closure and in some cases is significantly better. Brantley investigated the use of the Su-Pomraning (SP) closure in the Monte Carlo LP algorithm (LP-SP) for the suite of benchmark problems and concluded that 1) the LP-SP algorithm was somewhat more accurate overall than the LP algorithm and somewhat less accurate overall than the LPLRP algorithm for an incident angular flux benchmark suite, and 2) the LP-SP algorithm was generally the least accurate of the algorithms for an interior source benchmark suite. Larsen et al. performed an asymptotic analysis of the transport equation in 1D planar geometry for the situation in which the physical system is 1) a random binary stochastic medium with material macroscopic total cross sections and mean slab width values of O(1) or smaller and 2) optically thick with weak absorption and sources at each spatial point and therefore globally diffusive. The asymptotic analysis demonstrates that, under these assumptions, the transport equation limits to the conventional diffusion equation with atomically-mixed (volume-averaged) material properties. Larsen et al. also demonstrate that, under these same assumptions, the LP equations asymptotically limit to an atomically-mixed diffusion equation with a diffusion coefficient that is too large, leading to an unphysical flattening of the ensemble-averaged scalar flux distribution. Vasques and Yadav recently performed an asymptotic analysis of an adjusted Levermore-Pomraning closure in which the Markovian transition functions are rescaled such that the equations asymptotically limit to the correct atomically-mixed diffusion equation; we refer to this model as LP-VY. In this paper, we demonstrate that the adjusted LP closure proposed by Vasques and Yadav is a special case of the SP closure obtained by assuming that the absorption cross sections in the two materials are equal. We further demonstrate that the Su-Pomraning closure has the correct asymptotic limit for the diffusive physical system and is therefore an appropriate closure for these problems. We also describe how to incorporate these various closures into the Monte Carlo LP and LPLRP particle transport algorithms, and we present numerical results comparing the accuracy of the Monte Carlo LP, LP-VY, LP-SP, LPLRP, and LPLRP-SP algorithms for the set of diffusive benchmark problems. We demonstrated that the SP closure has the correct asymptotic limit for the diffusive physical system under investigation in this paper and that the VY closure is a special case of the SP closure obtained by assuming equal absorption in the two materials. Both of these closures are readily implemented in the Monte Carlo LP and LPLRP algorithms for particle transport in BSM. Through numerical comparisons to a diffusive benchmark suite, we confirmed that 1) the LP and LPLRP algorithms do not limit to the appropriate diffusion solution and 2) the LP-VY, LP-SP, and LPLRP-SP algorithms limit to the appropriate diffusion solution and are of comparable accuracy. The LPLRP algorithm has been shown to be generally more accurate than the LP algorithm for non-diffusive problems. However, the numerical results in this paper indicate that the LPLRP algorithm does not limit to the correct diffusion equation for the asymptotic limit under consideration. The work in this paper demonstrates that the SP algorithm does limit to the correct diffusion equation for the asymptotic limit considered. Future work will investigate the possibility of whether the LPLRP-SP algorithm is accurate for both diffusive and non-diffusive problems.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2010

SPIDER. IV. OPTICAL AND NEAR-INFRARED COLOR GRADIENTS IN EARLY-TYPE GALAXIES: NEW INSIGHT INTO CORRELATIONS WITH GALAXY PROPERTIES

We present an analysis of stellar population gradients in 4546 early-type galaxies (ETGs) with photometry in grizYHJK along with optical spectroscopy. ETGs were selected as bulge-dominated systems, displaying passive spectra within the SDSS fibers. A new approach is described which utilizes color information to constrain age and metallicity gradients. Defining an effective color gradient, {nabla}{sub *}, which incorporates all of the available color indices, we investigate how {nabla}{sub *} varies with galaxy mass proxies, i.e., velocity dispersion, stellar (M{sub *}) and dynamical (M{sub dyn}) masses, as well as age, metallicity, and [{alpha}/Fe]. ETGs with M{sub dyn} larger than 8.5 x 10{sup 10} M{sub sun} have increasing age gradients and decreasing metallicity gradients with respect to mass, metallicity, and enhancement. We find that velocity dispersion and [{alpha}/Fe] are the main drivers of these correlations. ETGs with 2.5 x 10{sup 10} M{sub sun} {<=} M{sub dyn} {<=} 8.5 x 10{sup 10} M{sub sun} show no correlation of age, metallicity, and color gradients with respect to mass, although color gradients still correlate with stellar population parameters, and these correlations are independent of each other. In both mass regimes, the striking anti-correlation between color gradient and {alpha}-enhancement is significant at {approx}5{sigma} and results from the fact that metallicity gradient decreases with [{alpha}/Fe]. This anti-correlation may reflect the fact that star formation and metallicity enrichment are regulated by the interplay between the energy input from supernovae, and the temperature and pressure of the hot X-ray gas in ETGs. For all mass ranges, positive age gradients are associated with old galaxies (>5-7 Gyr). For galaxies younger than {approx}5 Gyr, mostly at low mass, the age gradient tends to be anti-correlated with the Age parameter, with more positive gradients at younger ages.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Two-epoch Orbit Estimation for Wide Binaries Resolved in Hipparcos and Gaia

The Hipparcos catalog and its Double and Multiple System Annex (DMSA) lists 4099 components with individual proper motions and coordinates on the epoch 1991.25. Many of these long-period binary stars are also present in Gaia Data Release 2 (DR2). Using the available relative positions and proper motions separated by 24.25 yr, the equations of relative orbital motion can be solved for the two epoch eccentric anomalies, orbital period, and eccentricity. This method employs elimination of the linear Thiele–Innes unknowns and nonlinear optimization of the remaining condition equations. The quality of these solutions is compromised by the insufficient condition and modest precision of the Hipparcos astrometric data, as revealed by Monte Carlo simulations with artificially perturbed data points. The presence of multiple systems and optical pairs can also perturb the results. Limited experiments with artificial data indicate that useful estimates can be obtained with a 25 yr epoch difference for wide binaries with orbital periods up to ~500 yr. The prospects of this method dramatically improve with the proposed next-generation space astrometry missions such as Gaia-NIR and Theia, especially when additional conditions are included from astrometric or spectroscopic measurements. An ancillary catalog of cross-identification and astrometric information for 1295 double-star pairs cross-matched in Gaia DR2 and Hipparcos is also published.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Cannibals in the thick disk II. Radial-velocity monitoring of the young α -rich stars

Determining ages of stars for reconstructing the history of the Milky Way remains one of the most difficult tasks in astrophysics. This involves knowing when it is possible to relate the stellar mass with its age and when it is not. The young α-rich (YAR) stars present such a case in which we are still not sure about their ages because they are relatively massive, implying young ages, but their abundances are α-enhanced, which implies old ages. We report the results from new observations from a long-term radial-velocity-monitoring campaign complemented with high-resolution spectroscopy, as well as new astrometry and seismology of a sample of 41 red giants from the third version of APOKASC, which includes YAR stars. The aim is to better characterize the YAR stars in terms of binarity, mass, abundance trends, and kinematic properties. The radial velocities of HERMES, APOGEE, and Gaia were combined to determine the binary fraction among YAR stars. In combination with their mass estimate, evolutionary status, chemical composition, and kinematic properties, it allowed us to better constrain the nature of these objects. We found that stars with M < 1 M ⊙ were all single, whereas stars with M > 1 M ⊙ could be either single or binary. This is in agreement with theoretical predictions of population synthesis models. Studying their [C/N], [C/Fe], and [N/Fe], trends with mass, it became clear that many YAR stars do not follow the APOKASC stars, favoring the scenario that most of them are the product of mass transfer. Our sample further includes two likely undermassive stars, that is to say of such as low mass that they cannot have reached the red clump within the age of the Universe, unless their low mass is the signature of mass loss in previous evolutionary phases. These stars do not show signatures of currently being binaries. Both YAR and undermassive stars might show some anomalous APOGEE abundances for the elements N, Na, P, K, and Cr; although, higher-resolution optical spectroscopy might be needed to confirm these findings. Considering the significant fraction of stars that are formed in pairs and the variety of ways that makes mass transfer possible, the diversity in properties in terms of binarity, and chemistry of the YAR and undermassive stars studied here implies that most of these objects are likely not young.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

GRAVITATIONAL PULSE ASTRONOMY

Thompson has argued that the Kozai mechanism is primarily responsible for driving white dwarf binary mergers and so generating type Ia supernovae (SNe). If so, the gravitational-wave signal from these systems will be characterized by isolated repeating pulses that are well approximated by parabolic encounters. I show that it is impossible to detect these with searches based on standard assumptions of circular binaries, nor could they be detected by analogs of the repeating-pulse searches that have been carried out at higher frequencies, even if these were modified to barycentric time as a function of putative sky position. Rather, new search algorithms are required that take account of the intrinsic three-body motion of the source as well as the motion of the Earth. If these eccentric binaries account for even a modest fraction of the observed SN rate, then there should be of order 1 pulse every 20 s coming from within 1 kpc, and there should be of order 200 detectable sources in this same volume. I outline methods of identifying these sources both to remove this very pernicious background to other signals and to find candidate SN Ia progenitors, and I sketch practical methods to find optical counterparts to these sources and so measure their masses and distances.

79 ASTRONOMY AND ASTROPHYSICS↗