Masses are one of the most difficult stellar properties to measure. In the case of the white-dwarf companions of Barium stars, the situation is worse. These stars are dim, cool, and difficult to observe via direct methods. However, Ba stars were polluted by the Asymptotic Giant Branch progenitors of these WDs with matter rich in heavy elements, and the properties of their WD companions contain key information about binary interaction processes involving AGB stars and about the slow-neutron-capture(s)-process of nucleosynthesis. We aim to determine accurate and assumption-free masses for the WD companions of as many Ba stars as possible. We want to provide new observational constraints that can help us learn about the formation and evolution of these post-interaction binary systems and about the nucleosynthesis processes that took place in the interiors of their AGB progenitors. We combined archival radial-velocity data with Hipparcos and Gaia astrometry using the software package orvara, a code designed to simultaneously fit a single Keplerian model to any combination of these types of data using a parallel-tempering Markov chain Monte Carlo method. We adopted Gaussian priors for the Ba star masses and for the parallaxes, and assumed uninformative priors for the orbital elements and the WD masses. We determined new orbital inclinations and companion masses for 60 Ba star systems, including a couple of new orbits and several improved orbits for the longest-period systems. We also unravelled a triple system that was not known before and constrained the orbits and the masses of the two companions. (Continued in the manuscript)
Barium stars are one of the important probes to understand the origin and evolution of slow neutron-capture process elements in the Galaxy. These are extrinsic stars, where the observed s-process element abundances are believed to have an origin in the now invisible companions that produced these elements at their Asymptotic Giant Branch phase of evolution. We have attempted to understand the s-process nucleosynthesis, as well as the physical properties of the companion stars through a detailed comparison of observed elemental abundances of 10 barium stars with the predictions from AGB nucleos…
This paper provides long-period and revised orbits for barium and S stars adding to previously published ones. The sample of barium stars with strong anomalies comprise all such stars present in the Lu et al. catalogue. We find orbital motion for all barium and extrinsic S stars monitored. We obtain the longest period known so far for a spectroscopic binary involving an S star, namely 57 Peg with a period of the order of 100 - 500 yr. We present the mass distribution for the barium stars, which ranges from 1 to 3 Msun, with a tail extending up to 5 Msun in the case of mild barium stars. This h…
The formation mechanism of the barium stars is thought to be well understood. Barium-rich material, lost in a stellar wind from a thermally-pulsing asymptotic-giant branch star in a binary system, is accreted by its companion main-sequence star. Now, many millions of years later, the primary is an unseen white dwarf and the secondary has itself evolved into a giant which displays absorption lines of barium in its spectrum and is what we call a barium star. A similar wind-accretion mechanism is also thought to form the low-metallicity CH and carbon-enhanced metal-poor stars. Qualitatively the p…
We report three new barium (Ba) dwarfs lying in Sirius-like systems, which provides direct evidence that Ba dwarfs are companions to white dwarfs (WDs). Atmospheric parameters, stellar masses, and chemical abundances of 25 elements, including light, $α$, Fe-peak and s-process elements, are derived from high resolution and high S/N spectra. Enhancement of s-process elements with [s/Fe] ratios between 0.4 and 0.6 confirm them as mild barium stars. The estimated metallicities ($-$0.31, $-$0.06, 0.13) of BD+68$^\circ$1027, RE~J0702+129 and BD+80$^\circ$670 are in the range of known Ba dwarfs and g…
We report the discovery of a spiral-like nebula with the Wide-field Infrared Survey Explorer (WISE) and the results of optical spectroscopy of its associated star TYC 8606-2025-1 with the Southern African Large Telescope (SALT). We find that TYC 8606-2025-1 is a G8 III star of $\approx3$ M$_\odot$, showing a carbon depletion by a factor of two and a nitrogen enhancement by a factor of three. We also derived an excess of s-process elements, most strongly for barium, which is a factor of three overabundant, indicating that TYC 8606-2025-1 is a mild barium star. We thereby add a new member to the…
Abell 70 is a planetary nebula (PN) whose nucleus at optical wavelengths is a G8 star with enhanced carbon and s-process abundances--a "barium star." The cool star is a binary companion of the true, hot central star. In several other members of this rare class, the cool star is known to rotate with a period of only a few days. This is attributed to a spin-up that occurred due to accretion from the wind of the central star during its post-AGB PN ejection; this also accounts for the unusual chemical composition of the companion's photosphere. We obtained photometry of the central star of Abell 7…
We examine the composition of barium stars in the context of mass transfer from an asymptotic giant branch (AGB) companion. We accrete between 0.01 and 0.5 M$_\odot$ of AGB ejecta on to low mass companions of [Fe/H] = -0.25 at the ages expected for the end of the lives of AGB stars of 2.5, 3 and 4M$_\odot$. In each case, we form a star of 2.5 M$_\odot$ which is thought to be a typical barium star mass. We discuss the extent of dilution of accreted material as the star evolves, and describe the impact on the surface abundances. For accretion from a 2.5\ms\ primary, if the secondary's initial ma…
The enrichment in s-process elements of barium stars is known to be due to pollution by mass transfer from a companion formerly on the thermally-pulsing asymptotic giant branch (AGB), now a carbon-oxygen white-dwarf (WD). This paper investigates the relationship between the s-process enrichment in the barium star and the mass of its WD companion. It is expected that helium WDs, which have masses smaller than about 0.5 Msun and never reached the AGB phase, should not pollute with s-process elements their giant companion, which should thus never turn into a barium star. Spectra with a resolution…
Barium (Ba) stars form via mass-transfer in binary systems, and can subsequently interact with their white dwarf companion in a second stage of binary interaction. We used observations of main-sequence Ba systems as input for our evolutionary models, and try to reproduce the orbits of the Ba giants. We show that to explain short and sometimes eccentric orbits, additional interaction mechanisms are needed along the RGB.
Barium (Ba) dwarfs and CH subgiants are the less-evolved analogues of Ba and CH giants. They are F- to G-type main-sequence stars polluted with heavy elements by a binary companion when the latter was on the Asymptotic Giant Branch (AGB). This companion is now a white dwarf that in most cases cannot be directly detected. We present a large systematic study of 60 objects classified as Ba dwarfs or CH subgiants. Combining radial-velocity measurements from HERMES and SALT high-resolution spectra with radial-velocity data from CORAVEL and CORALIE, we determine the orbital parameters of 27 systems.…
We present the barium surface abundance of 12 blue stragglers (BSs) and 18 main-sequence (MS) stars in the intermediate-age open cluster NGC 6819 (2.5 Gyr) based on spectra obtained from the Hydra Multi-object Spectrograph on the WIYN 3.5 m telescope. For the MS stars we find [Fe/H] = $+$0.05 $\pm$ 0.04 and [Ba/Fe] = $-$0.01 $\pm$ 0.10. The majority of the BS stars are consistent with these values. We identify five BSs with significant barium enhancement. These stars most likely formed through mass transfer from an asymptotic giant branch star that polluted the surface of the BS with the nucle…
Barium (Ba), CH, and extrinsic or Tc-poor S-type stars are evolved low- and intermediate-mass stars that show enhancement of slow-neutron-capture-process elements on their surface, an indication of mass accretion from a former asymptotic giant branch (AGB) companion, which is now a white dwarf (WD). Ba and CH stars can be found in the main-sequence (MS), the sub-giant, and the giant phase, while extrinsic S-type stars populate the giant branches only. As these polluted stars evolve, they might be involved in a second phase of interaction with their now white dwarf companion. In this paper, we …
Barium stars are thought to result from binary evolution in systems wide enough to allow the more massive component to reach the asymptotic giant branch and eventually become a CO white dwarf. While Ba stars were initially known only among giant or subgiant stars, some were subsequently discovered also on the main sequence (and known as dwarf Ba stars). We provide here the orbital parameters of three dwarf Ba stars, completing the sample of 27 orbits published recently by Escorza et al. with these three southern targets. We show that these new orbital parameters are consistent with those of ot…
In order to get a broader view of the s-process nucleosynthesis we study the abundance distribution of heavy elements of 35 barium stars and 24 CEMP-stars, including nine CEMP-s stars and 15 CEMP-r/s stars. The similar distribution of [Pb/hs] between CEMP-s and CEMP-r/s stars indicate that the s-process material of both CEMP-s and CEMP-r/s stars should have a uniform origin, i.e. mass transfer from their predominant AGB companions. For the CEMP-r/s stars, we found that the r-process should provide similar proportional contributes to the second s-peak and the third s-peak elements, and also be …
Barium stars have been studied extensively over the past few decades, yet our current understanding of how these intriguing objects formed leaves much to be desired. Many trends observed in systems containing barium stars cannot be satisfactorily explained by classical binary evolution models, naturally raising the question of whether triples and other higher-order multiples can give rise to such exotic objects. In this paper, we study the possibility that a Roche Lobe overflow from a tertiary in a hierarchical triple system can potentially lead to surface barium enrichment within the inner bi…
Barium stars are s-process enriched giants. They owe their chemical peculiarities to a past mass transfer phase. During which they were polluted by their binary companion, which at the time was an AGB star, but is now an extinct white dwarf. Barium stars are thus ideal targets for understanding and constraining the s-process in low and intermediate-mass AGB stars. We derive the abundances of a large number of heavy elements in order to shed light on the conditions of operation of the neutron source responsible for the production of s-elements in the former companions of the barium stars. Adopt…
Barium stars are extrinsic Asymptotic Giant Branch (AGB) stars. They present the s-enhancement characteristic for AGB and post-AGB stars, but are in an earlier evolutionary stage (main sequence dwarfs, subgiants, red giants). They are believed to form in binary systems, where a more massive companion evolved faster, produced the s-elements during its AGB phase, polluted the present barium star through stellar winds and became a white dwarf. The samples of barium stars of Allen & Barbuy (2006) and of Smiljanic et al. (2007) are analysed here. Spectra of both samples were obtained at high-resolu…
We present Spitzer IRAC photometry of white dwarf remnants of 14 stars with M = 3-5 Msol. We do not detect mid-infrared excess around any of our targets. By demanding a 3 sigma photometric excess at 4.5 micron for unresolved companions, we rule out planetary mass companions down to 5, 7, or 10 M_J for 13 of our targets based on the Burrows et al. (2003) substellar cooling models. Combined with previous IRAC observations of white dwarf remnants of intermediate-mass stars, we rule out \geq 10 M_J companions around 40 white dwarfs and \geq 5 M_J companions around 10 white dwarfs.
We present a detailed study of the barium star at the heart of the planetary nebula Abell 70. Time-series photometry obtained over a period of more than ten years demonstrates that the barium-contaminated companion is a rapid rotator with temporal variability due to spots. The amplitude and phasing of the photometric variability changes abruptly, however there is no evidence for a change in the rotation period (P = 2.06~d) over the course of the observations. The co-addition of 17 high-resolution spectra obtained with VLT-UVES allow us to measure the physical and chemical properties of the com…
Multiple channels have been proposed to produce Type Ia supernovae, with many scenarios suggesting that the exploding white dwarf accretes from a binary companion pre-explosion. In almost all cases, theory suggests that this companion will survive. However, no such companion has been unambiguously identified in ancient supernova remnants -- possibly falsifying the accretion scenario. Existing surveys, however, have only looked for stars as faint as $\approx 0.1 L_\odot$ and thus would have missed a surviving white dwarf companion. In this work, we present very deep DECAM imaging $(u, g, r, z)$…
Abell 70 (PN G038.1-25.4, hereafter A 70) is a planetary nebula (PN) known for its diamond ring appearance due a superposition with a background galaxy. The previously unstudied central star is found to be a binary consisting of a G8IV-V secondary at optical wavelengths and a hot white dwarf (WD) at UV wavelengths. The secondary shows Ba II and Sr II features enhanced for its spectral type that, combined with the chromospheric Halpha emission and possible 20-30 km/s radial velocity amplitude, firmly classifies the binary as a Barium star. The proposed origin of Barium stars is intimately linke…
For the spectral analysis of high-resolution and high-signal-to-noise (S/N) spectra of hot stars, state-of-the-art non-local thermodynamic equilibrium (NLTE) model atmospheres are mandatory. These are strongly dependent on the reliability of the atomic data that is used for their calculation. Reliable Ba V - VII oscillator strengths are used to identify Ba lines in the spectra of the DA-type white dwarf G191-B2B and the DO-type white dwarf RE0503-289 and to determine their photospheric Ba abundances. We newly calculated Ba V - VII oscillator strengths to consider their radiative and collisiona…
The number of spatially unresolved white dwarf plus main-sequence star binaries has increased rapidly in the last decade, jumping from only ~30 in 2003 to over 3000. However, in the majority of known systems the companion to the white dwarf is a low mass M dwarf, since these are relatively easy to identify from optical colours and spectra. White dwarfs with more massive FGK type companions have remained elusive due to the large difference in optical brightness between the two stars. In this paper we identify 934 main-sequence FGK stars from the Radial Velocity Experiment (RAVE) survey in the s…
The origin and evolution of neutron-capture elements in our Galaxy is poorly understood. In this work, we have attempted to understand the Galactic s-process nucleosynthesis using barium stars as probes. We have performed high resolution spectroscopic analysis for three barium stars HD 36650, HD 207585 and HD 219116. The analysis of HD 219116 is based on HCT/HESP data at a resolution of 60,000 covering a wavelength region 3530-9970 {\rm Å}. For HD 36650, we have used the FEROS spectrum at a resolution of 48,000 covering the wavelength region 3520-9200 {\rm Å}. For HD 207585, the spectrum from …
We present optical high-speed photometry of three millisecond pulsars with low-mass ($< 0.3 M_{\odot}$) white dwarf companions, bringing the total number of such systems with follow-up time-series photometry to five. We confirm the detection of pulsations in one system, the white dwarf companion to PSR J1738+0333, and show that the pulsation frequencies and amplitudes are variable over many months. A full asteroseismic analysis for this star is under-constrained, but the mode periods we observe are consistent with expectations for a $M_{\star} = 0.16 - 0.19 M_{\odot}$ white dwarf, as suggested…
In order to identify diagnostics distinguishing between pre- and post-mass-transfer systems, the mass-ratio distribution and period - eccentricity (P - e) diagram of barium and S stars are compared to those of the sample of binary red giants in open clusters from Mermilliod et al. (2007). From the analysis of the mass-ratio distribution for the cluster binary giants, we find an excess of systems with companion masses between 0.58 and 0.87 Msun, typical for white dwarfs. They represent 22% of the sample, which are thus candidate post-mass-transfer systems. Among these candidates which occupy th…
Classical barium stars are binary systems which consist of a late-type giant enriched in carbon and slow neutron capture (s-process) elements and an evolved white dwarf (WD) that is invisible at optical wavelengths. The youngest observed barium stars are surrounded by planetary nebulae (PNe), ejected soon after the wind accretion of polluted material when the WD was in its preceeding asymptotic giant branch (AGB) phase. Such systems are rare but powerful laboratories for studying AGB nucleosynthesis as we can measure the chemical abundances of both the polluted star and the nebula ejected by t…
Gaia Barium Dwarfs and Their Ostensibly Ordinary Counterparts
Weizmann Institute of Science（魏茨曼科学研究所）；Max-Planck-Institut für Astronomie（马克斯·普朗克天文学研究所）；Anton Pannekoek Institute for Astronomy, University of Amsterdam（阿姆斯特丹大学安东·潘内克天文研究所）
We present a near-infrared photometric search for unresolved substellar companions and debris disks around white dwarfs in the UKIRT Infrared Deep Sky Survey Large Area Survey. We cross-correlate the SDSS DR4 and McCook & Sion catalogues of white dwarfs with the UKIDSS DR8 producing 3109 and 163 unique matches respectively. Cooling models are fitted to the optical photometry of a subsample of DA white dwarfs and extended to the near-infrared. A comparison is then made with the observed photometry to identify those stars with a near-infrared excess consistent with the presence of a cool compani…
Abundance studies of solar-type stars revealed a small fraction of objects with extreme depletion of beryllium. We investigate the possible link between the beryllium depletion and the presence of companions. The classical methods (radial velocity, astrometry, imaging) used to search for binary companions were exploited. We also performed a chemical analysis to identify binaries by the alteration in abundances that is produced by the accretion of material lost by a former evolved companion. We found that all the four previously investigated stars that were found to be ultra--depleted in Be are…
2MASS J050051.85$-$093054.9 is the closest known low-mass helium-core white dwarf in a binary system. We used three high-band international LOFAR stations to perform a targeted search for a pulsar companion, reaching sensitivities of ~3 mJy for a 10-ms pulsar at a DM = 1 pc$\cdot$cm$^{-3}$. No pulsed signal was detected, confidently excluding the presence of a detectable radio pulsar in the system.
We report the optical discovery of the companion to the 2 M_sun millisecond pulsar PSR J1614-2230. The optical colors show that the 0.5 M_sun companion is a 2.2 Gyr old He-CO white dwarf. We infer that $\dot{M}$ during the accretion phase is <10^{-2}\dot{M}_{edd}. We show that the pulsar was born with a spin close to its current value, well below the rebirth line. The spin-down parameters, the mass of the pulsar, and the age of the system challenge the simple recycling model for the formation of millisecond pulsars.
We report photometric observations of the eclipsing close binary CSS21055 (SDSS J141126+200911) that strongly suggest that the companion to the carbon-oxygen white dwarf is a brown dwarf with a mass between 0.030 and 0.074 Msun. The measured orbital period is 121.73min and the totality of the eclipse lasts 125s. If confirmed, CSS21055 would be the first detached eclipsing WD+BD binary. Spectroscopy in the eclipse could provide information about the companion's evolutionary state and atmospheric structure.
In a search for eclipsing white dwarfs using the Zwicky Transient Facility lightcurves, we identified a deep eclipsing white dwarf with a dark, substellar companion. The lack of an infrared excess and an orbital period of 10 hours made this a potential exoplanet candidate. We obtained high-speed photometry and radial velocity measurements to characterize the system. The white dwarf has a mass of $0.50\pm0.02\,\mathrm{M_{\odot}}$ and a temperature of $10900\pm200\,$K. The companion has a mass of $0.059\pm0.004\,\mathrm{M_{\odot}}$ and a small radius of $0.0783\pm0.0013\,\mathrm{R_{\odot}}$. It …
[Abridged] Barium stars are moderately rare, chemically peculiar objects, which are believed to be the result of the pollution of an otherwise normal star by material from an evolved companion on the asymptotic giant branch (AGB). We aim to derive carbon, nitrogen, oxygen, and fluorine abundances for the first time from the infrared spectra of the barium red giant star HD 123396 to quantitatively test AGB nucleosynthesis models for producing barium stars via mass accretion. High-resolution and high S/N infrared spectra were obtained using the Phoenix spectrograph mounted at the Gemini South te…
We present the results of our Hubble Space Telescope far-ultraviolet survey of the blue lurkers (BLs) in M67. We find evidence for two white dwarf companions among the BLs that are indicative of mass transfer from an evolved companion, one in WOCS 14020 and the other in WOCS 3001. The cooling ages of the white dwarfs suggest that mass transfer in these systems occurred $\sim$300--540 Myr and $\sim$600--900 Myr ago, respectively. The rotation periods and cooling ages of the BLs are consistent with spin-up and subsequent single-star spin-down models, and binary evolution models yield plausible e…
Several possible formation pathways for blue straggler stars have been developed recently, but no one pathway has yet been observationally confirmed for a specific blue straggler. Here we report the first findings from a Hubble Space Telescope ACS/SBC far-UV photometric program to search for white dwarf companions to blue straggler stars. We find three hot and young white dwarf companions to blue straggler stars in the 7-Gyr open cluster NGC 188, indicating that mass transfer in these systems ended less than 300 Myr ago. These companions are direct and secure observational evidence that these …
SDSS J091709.55+463821.8 (hereafter J0917+4638) is the lowest surface gravity white dwarf (WD) currently known, with log g = 5.55 +/- 0.05 (M ~ 0.17 M_sun; Kilic et al. 2007a,b). Such low-mass white dwarfs (LMWDs) are believed to originate in binaries that evolve into WD/WD or WD/neutron star (NS) systems. An optical search for J0917+4638's companion showed that it must be a compact object with a mass >= 0.28 M_sun (Kilic 2007b). Here we report on Green Bank Telescope 820 MHz and XMM-Newton X-ray observations of J0917+4638 intended to uncover a potential NS companion to the LMWD. No convincing…
We report on the discovery of a white dwarf companion to the nearby late G dwarf star, HD 159062. The companion is detected in 14 years of precise radial velocity (RV) data, and in high-resolution imaging observations. RVs of HD 159062 from 2003-2018 reveal an acceleration of $-13.3\pm0.12\ \rm{m s}^{-1}$, indicating that it hosts a companion with a long-period orbit. Subsequent imaging observations with the ShaneAO system on the Lick Observatory 3-meter Shane telescope, the PHARO AO system on the Palomar Observatory 5-meter telescope, and the NIRC2 AO system at the Keck II 10-meter telescope …
Chemical Signatures of AGB Mass Transfer in Gaia White Dwarf Companions
California Institute of Technology（加州理工学院）；Gemini Observatory, NSF’s NOIRLab（双子座天文台，美国国家光学-红外天文研究实验室）；Max-Planck-Institut für Astronomie（马克斯·普朗克天文学研究所）
We present high time resolution SDSS-$g'$ and SDSS-$z'$ light curves of the primary eclipse in SDSS J141126.20+200911.1, together with time-resolved X-Shooter spectroscopy and near-infrared $JHK_{s}$ photometry. Our observations confirm the substellar nature of the companion, making SDSS J141126.20+200911.1 the first eclipsing white dwarf/brown dwarf binary known. We measure a (white dwarf model dependent) mass and radius for the brown dwarf companion of $M_{2} = 0.050 \pm 0.002$ $M_{\odot}$ and $R_{2} = 0.072 \pm 0.004$ $M_{\odot}$, respectively. The lack of a robust detection of the companio…
Results are presented for a Hubble Space Telescope Advanced Camera for Surveys high-resolution imaging campaign of 90 white dwarfs with known or suspected low mass stellar and substellar companions. Of the 72 targets which remain candidate and confirmed white dwarfs with near-infrared excess, 43 are spatially resolved into two or more components, and a total of 12 systems are potentially triples. There is a possible, slight deficit of earlier spectral types (bluer colors) among the spatially unresolved companions, exactly the opposite of expectations if significant mass is transferred to the c…
Binary companions to asymptotic giant branch (AGB) stars are an important aspect of their evolution. Few AGB companions have been detected, and in most cases it is difficult to distinguish between main-sequence and white dwarf companions. Detection of photometric flickering, a tracer of compact accretion disks around white dwarfs, can help identify the nature of these companions. In this work, we searched for flickering in four AGB stars suggested to have likely accreting companions. We found no signs for flickering in two targets: R~Aqr and V1016 Cyg. Flickering was detected in the other two …
The project Massive Unseen Companions to Hot Faint Underluminous Stars from SDSS (MUCHFUSS) aims at finding hot subdwarf stars with massive compact companions like massive white dwarfs (M>1.0 M$_\odot$), neutron stars, or stellar-mass black holes. We present orbital and atmospheric parameters and put constraints on the nature of the companions of 12 close hot subdwarf B star (sdB) binaries found in the course of the MUCHFUSS project. The systems show periods between 0.14 and 7.4 days. Three systems most likely have white dwarf companions. SDSS J083006.17+475150.3 is likely to be a rare example…
SDSSJ125733.63+542850.5 (hereafter SDSSJ1257+5428) is a compact white dwarf binary from the Sloan Digital Sky Survey that exhibits high-amplitude radial velocity variations on a period of 4.56 hours. While an initial analysis suggested the presence of a neutron star or black-hole binary companion, a follow-up study concluded that the spectrum was better understood as a combination of two white dwarfs. Here we present optical spectroscopy and ultraviolet fluxes which directly reveal the presence of the second white dwarf in the system. SDSSJ1257+5428's spectrum is a composite, dominated by the …
New elemental abundances for the neutron-capture elements Sr, Nb, Mo, Ru, La, Sm, and Eu are presented for a large sample of 180 barium (Ba) giant stars, a class of chemically peculiar objects that exhibit in their spectra enhancements of the elements created by the $s$-process, as a consequence of mass transfer between the components of a binary system. The content of heavy elements in these stars, in fact, points to nucleosynthesis mechanisms that took place within a former asymptotic giant branch (AGB) companion, now an invisible white dwarf. From high-resolution ($R=48000$) spectra in the …
Barium Stars Across the Milky Way: Probing Their Origins via the GALAH Survey
San Diego State University（圣地亚哥州立大学）；The University of Texas at Austin（德克萨斯大学奥斯汀分校）；University of Utah（犹他大学）；University of California Santa Cruz（加州大学圣克鲁兹分校）；Mullard Space Science Laboratory, University College London（伦敦大学学院穆拉德空间科学实验室）；Indiana University（印第安纳大学）；University of Wisconsin-Whitewater（威斯康星大学惠特沃分校）
During post-main-sequence evolution, radial expansion of the primary star, accompanied by intense winds, can significantly alter the binary orbit via tidal dissipation and mass loss. The fate of a given binary system is determined by the initial masses of the primary and companion, the initial orbit (taken to be circular), the Reimers mass-loss parameter, and the tidal prescription employed. For a range of these parameters, we determine whether the orbit expands due to mass loss or decays due to tidal torques. Where a common envelope (CE) phase ensues, we estimate the final orbital separation …
This paper is the third one in a series devoted to studying the properties of binaries involving M giants. We use a new set of orbits to construct the first (e-logP) diagram of an extensive sample of M giant binaries, to obtain their mass-function distribution, and to derive evolutionary constraints for this class of binaries and related systems. The orbital properties of binaries involving M giants were analysed and compared with those of related families of binaries (K giants, post-AGB stars, barium stars, Tc-poor S stars). The orbital elements of post-AGB stars and M giants are not differen…
Recent investigations of the WD + MS channel of Type Ia supernovae (SNe Ia) imply that this channel may be the main contribution to the old population (>1Gyr) of SNe Ia. In the WD + MS channel, the WD could accrete material from a main-sequence or a slightly evolved star until it reaches the Chandrasekhar mass limit. The companions in this channel would survive after SN explosion and show distinguishing properties. In this Letter, based on SN Ia production regions of the WD + MS channel and three formation channels of WD + MS systems, we performed a detailed binary population synthesis study t…
We report identification of the optical counterpart to the companion of the millisecond pulsar J2317+1439. At the timing position of the pulsar, we find an object with $g=22.96\pm0.05$, $r=22.86\pm0.04$ and $i=22.82\pm0.05$. The magnitudes and colors of the object are consistent with it being a white dwarf. By comparing with white dwarf cooling models, we estimate that it has a mass of $0.39^{+0.13}_{-0.10}$ M$_{\odot}$, an effective temperature of $8077^{+550}_{-470}$ K and a cooling age of $10.9\pm0.3$ Gyr. Combining our results with published constraints on the orbital parameters obtained t…
The recycled pulsar PSR J2222-0137 is one of the closest known neutron stars, with a parallax distance of $267_{-0.9}^{+1.2}\,$pc and an edge-on orbit. We measure the Shapiro delay in the system through pulsar timing with the Green Bank Telescope, deriving a low pulsar mass ($1.20\pm0.14$ $M_\odot$) and a high companion mass ($1.05\pm0.06$ $M_\odot$) consistent with either a low-mass neutron star or a high-mass white dwarf. We can largely reject the neutron star hypothesis on the basis of the system's extremely low eccentricity (3e-4) - too low to have been the product of two supernovae under …
Measuring the masses of companions to single-line spectroscopic binary stars is (in general) not possible because of the unknown orbital plane inclination. Even when the mass of the visible star can be measured, only a lower limit can be placed on the mass of the unseen companion. However, since these inclination angles should be isotropically distributed, for a large enough, unbiased sample, the companion mass distribution can be deconvolved from the distribution of observables. In this work, we construct a hierarchical probabilistic model to infer properties of unseen companion stars given o…
