Binary systems containing a magnetic white dwarf and a main-sequence star are considered extremely rare, perhaps non-existent. In the course of a search of magnetic fields in high-mass white dwarfs we have discovered a Sirius-like wide binary system composed of a main-sequence G0 star and a $M\sim 1.1\,M_\odot$ white dwarf with a huge (hundreds of MG) magnetic field. This star, WDS J03038+0608B, shows a circular polarisation amplitude of 5% in the continuum, with no evidence of variability in a 1d time-scale, little or no linear polarisation in the blue part of the spectrum, and about 2% linear polarisation in the red part of the optical spectrum. A search in the literature reveals the existence of at least four more binary systems that include a magnetic white dwarf and a non-degenerate companion - three such systems passed unremarked in previous studies. We estimate that up to a few percent of magnetic white dwarfs may be found to occur in wide binary pairs. However, at least four of the five known binary systems with a magnetic white dwarf are too widely separated to be expected to evolve into systems experiencing Roche lobe overflow, and cannot be considered as progenitors of magnetic cataclysmic variable (AM Her and DQ Her) systems.
Approximately 70 percent of the nearby white dwarfs appear to be single stars, with the remainder being members of binary or multiple star systems. The most numerous and most easily identifiable systems are those in which the main sequence companion is an M star, since even if the systems are unresolved the white dwarf either dominates or is at least competitive with the luminosity of the companion at optical wavelengths. Harder to identify are systems where the non-degenerate component has a spectral type earlier than M0 and the white dwarf becomes the less luminous component. Taking Sirius a…
Evidence is building that remnants of solar systems might orbit a large percentage of white dwarfs, as the polluted atmospheres of DAZ and DBZ white dwarfs indicate the very recent accretion of metal-rich material. (Zuckerman et al. 2010). Some of these polluted white dwarfs are found to have large mid-infrared excesses from close-in debris disks that are thought to be reservoirs for the metal accretion. These systems are coined DAZd white dwarfs (von Hippel et al. 2007). Here we investigate the claims of Bonnet-Bidaud & Pantin (2008) that Sirius B, the nearest white dwarf to the Sun, might ha…
The presence of a white dwarf in a resolved binary system, such as Sirius, provides an opportunity to combine dynamical information about the masses, from astrometry and spectroscopy, with a gravitational red-shift measurement and spectrophotometry of the white dwarf atmosphere to provide a test of theoretical mass-radius relations of unprecedented accuracy. We demonstrated this with the first Balmer line spectrum of Sirius B to be obtained free of contamination from the primary, with STIS on HST. However, we also found an unexplained discrepancy between the spectroscopic and gravitational red…
A New Sirius-like System at Only 21 Parsecs: An Elusive White Dwarf Companion to the Nearby K-dwarf HD 38230
Max Planck Institute for Astronomy（马克斯·普朗克天文学研究所）；Department of Astronomy, University of Michigan（密歇根大学天文学系）；Department of Physics, University of California Santa Barbara（加州大学圣塔芭芭拉分校物理系）；Department of Physics and Astronomy, Johns Hopkins University（约翰斯·霍普金斯大学物理与天文系）；SUPA, Institute for Astronomy, University of Edinburgh（爱丁堡大学天文学研究所（SUPA））；Department of Astronomy and Astrophysics, The University of California Santa Cruz（加州大学圣克鲁兹分校天文学与天体物理学系）
Einstein's theory of General Relativity predicts that the light from stars will be gravitationally shifted to longer wavelengths. We previously used this effect to measure the mass of the white dwarf Sirius B from the wavelength shift observed in its H-alpha line based on spectroscopic data from the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST), but found that the results did not agree with the dynamical mass determined from the visual-binary orbit. We have devised a new observing strategy using STIS where the shift is measured relative to the H-alpha line of …
Monitoring the long-term radial velocity (RV) and acceleration of nearby stars has proven an effective method for directly detecting binary and substellar companions. Some fraction of nearby RV trend systems are expected to be comprised of compact objects that likewise induce a systemic Doppler signal. In this paper, we report the discovery of a white dwarf companion found to orbit the nearby ($π= 28.297 \pm 0.066$ mas) G9 V star HD 169889. High-contrast imaging observations using NIRC2 at Keck and LMIRCam at the LBT uncover the ($ΔH = 9.76 \pm 0.16$, $ΔL' = 9.60 \pm 0.03$) companion at an ang…
We present Hubble Space Telescope imaging and spectroscopy of HD 217411, a G3 V star associated with the extreme ultraviolet excess source (EUV 2RE J2300-07.0). This star is revealed to be a triple system with a G 3V primary (HD 217411 A) separated by ~1.1" from a secondary that is in turn composed of an unresolved K0 V star (HD 217411 Ba) and a hot DA white dwarf (HD 217411 Bb). The hot white dwarf dominates the UV flux of the system. However; it is in turn dominated by the K0 V component beyond 3000 Å. A revised distance of 143 pc is estimated for the system. A low level photometric modulati…
We present deep imaging of Sirius B, the closest and brightest white dwarf, to constrain post-main-sequence planetary evolution in the Sirius system. We use Keck/NIRC2 in L'-band (3.776 $μ$m) across three epochs in 2020 using the technique of angular differential imaging. Our observations are speckle-limited out to 1 AU and background-limited beyond. The 5$σ$ detection limits from our best performing epoch are 17 to 20.4 L' absolute magnitude. We consider multiple planetary formation pathways in the context of Sirius B's evolution to derive mass sensitivity limits, and achieve sub-Jupiter sens…
We present new observations of the faint "Sirius-like" companion discovered to orbit HD 114174. Previous attempts to image HD 114174 B at mid-infrared wavelengths using NIRC2 at Keck have resulted in a non-detection. Our new L'-band observations taken with the Large Binocular Telescope and LMIRCam recover the companion ($ΔL$ = 10.15 $\pm$ 0.15 mag, $ρ$ = 0.675'' $\pm$ 0.016'') with a high signal-to-noise ratio (10 $σ$). This measurement represents the deepest L' high-contrast imaging detection at sub-arcsecond separations to date, including extrasolar planets. We confirm that HD 114174 B has n…
Sirius, the seventh-nearest stellar system, is a visual binary containing the metallic-line A1 V star Sirius A, brightest star in the sky, orbited in a 50.13-year period by Sirius B, the brightest and nearest white dwarf (WD). Using images obtained over nearly two decades with the Hubble Space Telescope (HST), along with photographic observations covering almost 20 years, and nearly 2300 historical measurements dating back to the 19th century, we determine precise orbital elements for the visual binary. Combined with the parallax and the motion of the A component, these elements yield dynamica…
White dwarfs (WDs) are powerful tools to study the evolutionary history of stars and binaries in the Galaxy. But do we understand their multiplicity from a theoretical point of view? This can be tested by a comparison with the sample of WDs within 20 pc, which is minimally affected by selection biases. From the literature, we compile the available information of the local WD sample with a particular emphasis on their multiplicity, and compare this to synthetic models of WD formation in single stars and binaries. As part of our population synthesis approach, we also study the effect of differen…
We have recently extended our ongoing survey of the local white dwarf population, effectively doubling the sample volume. Based upon the latest distance determinations, Holberg et al. (2016) estimated the present 20 pc and 25 pc samples were about 86 and 68 percent complete, respectively. Here we examine how the completeness of the 25 pc sample depends upon other observables such as apparent magnitude, proper motion, photometric color index, etc. The results may provide additional clues to why Sirius-Like systems are underrepresented in the extended 25 pc sample and how additional nearby singl…
White dwarf spectra have been widely used as a calibration source for X-ray and EUV instruments. The in-flight effective area calibration of the reflection grating spectrometers (RGS) of XMM-Newton depend upon the availability of reliable calibration sources. We investigate how well these white dwarf spectra can be used as standard candles at the lowest X-ray energies in order to gauge the absolute effective area scale of X-ray instruments. We calculate a grid of model atmospheres for Sirius B and HZ 43A, and adjust the parameters using several constraints until the ratio of the spectra of bot…
The absence of magnetic white dwarfs with a non-degenerate low-mass stellar companion in a wide binary is still very intriguing and at odds with the hypothesis that magnetic white dwarfs are the progenies of the magnetically peculiar Ap/Bp stars. On the other hand, we cannot resort to a process that impedes the generation of a strong magnetic field in the main or pre-main sequence progenitors of white dwarfs if they are in a multiple stellar system, because such a process would also prevent the formation of magnetic cataclysmic variables consisting of a magnetic white dwarf accreting mass from…
Observations of main sequence stars conducted over the last several decades have clearly shown that something like 50 per cent of stars of spectral types G and F occur in multiple systems. For earlier spectral types, the incidence of multiplicity is even higher. Thus, a volume limited sample of white dwarfs should reflect the percentage of binarity observed in stars of F to late B spectral types, which are their Main Sequence progenitors. However, a study of the local volume limited sample of white dwarfs (20 pc from the Sun) conducted by Holberg has shown that a white dwarf has a probability …
White dwarf stars have been used as flux standards for decades, thanks to their staid simplicity. We have empirically tested their photometric stability by analyzing the light curves of 398 high-probability candidates and spectroscopically confirmed white dwarfs observed during the original Kepler mission and later with K2 Campaigns 0-8. We find that the vast majority (>97 per cent) of non-pulsating and apparently isolated white dwarfs are stable to better than 1 per cent in the Kepler bandpass on 1-hr to 10-d timescales, confirming that these stellar remnants are useful flux standards. From t…
An ungravity-inspired model is employed to examine the astrophysical parameters of white dwarf stars (WDs) using polytropic and degenerate gas approaches. Based on the observed properties such as mass, radius, and luminosity of selected WDs, namely, Sirius B and $ε$ Reticulum, bounds on the characteristic length and scaling dimension of the ungravity (UG) model are estimated. The UG effect on the Chandrasekhar limit for WDs is shown. The UG model is examined in the study of ultra-massive WDs, e.g., EUVE J1746-706. In the contact of UG inspired model, a new location for some WDs on the Hertzspr…
Using Gaia DR2 data, we present an up-to-date sample of white dwarfs within 20 pc of the Sun. In total we identified 139 systems in Gaia DR2, nine of which are new detections, with the closest of these located at a distance of 13.05 pc. We estimated atmospheric parameters for all stellar remnants based on the Gaia parallaxes and photometry. The high precision and completeness of the Gaia astrometry allowed us to search for wide binary companions. We re-identified all known binaries where both components have accurate DR2 astrometry, and established the binarity of one of the nine newly identif…
We have extended our detailed survey of the local white dwarf population from 20 pc to 25 pc, effectively doubling the sample volume, which now includes 232 stars. In the process new stars within 20 pc have been added, a more uniform set of distance estimates as well as improved spectral and binary classifications are available. The present 25 pc sample is estimated to be about 68% complete (the corresponding 20 pc sample is now 86\% complete). The space density of white dwarfs is unchanged at 4.8 \pm 0.5 x 10^{-3} pc^{-3}. This new study includes a white dwarf mass distribution and luminosity…
We present a study of the dependence of the mass-radius relation for DA white dwarf stars on the hydrogen envelope mass and the impact on the value of log g, and thus the determination of the stellar mass. We employ a set of full evolutionary carbon-oxygen core white dwarf sequences with white dwarf mass between 0.493 and 1.05 Msun. Computations of the pre-white dwarf evolution uncovers an intrinsic dependence of the maximum mass of the hydrogen envelope with stellar mass, i.e., it decreases when the total mass increases. We find that a reduction of the hydrogen envelope mass can lead to a red…
Observational tests of the white dwarf mass-radius relationship have always been limited by the uncertainty in the available distance measurements. Most studies have focused on Balmer line spectroscopy because these spectra can be obtained from ground based observatories, while the Lyman lines are only accessible to space based UV telescopes. We present results using parallax data from Gaia DR2 combined with space based spectroscopy from HST and FUSE covering the Balmer and Lyman lines. We find that our sample supports the theoretical relation, although there is at least one star which is show…
Sirius-like systems are wide binaries composed of a white dwarf (WD) and a companion of a spectral type earlier than M0. The WD progenitor evolves in isolation, but its wind during the AGB phase pollutes the companion surface and transfers some angular momentum. Within SHINE survey that uses SPHERE at the VLT, we acquired images of HD2133, HD114174, and CD-567708 and combined this data with high resolution spectra of the primaries, TESS, and literature data. We performed accurate abundance analyses for the MS. We found brighter J and K magnitudes for HD114174B than obtained previously and exte…
We present the discovery of a white dwarf companion to the G1 V star 12 Psc found as part of a Keck adaptive optics imaging survey of long-term accelerating stars from the McDonald Observatory Planet Search Program. Twenty years of precise radial-velocity monitoring of 12 Psc with the Tull Spectrograph at the Harlan J. Smith telescope reveals a moderate radial acceleration ($\approx$10 m s$^{-1}$ yr $^{-1}$), which together with relative astrometry from Keck/NIRC2 and the astrometric acceleration between $Hipparcos$ and $Gaia$ DR2 yields a dynamical mass of $M_B$ = 0.605$^{+0.021}_{-0.022}$ $M…
Non-local Thermodynamic Equilibrium (NLTE) calculations of hot white dwarf (WD) model atmospheres are the cornerstone of modern flux calibrations for the Hubble Space Telescope (HST) and for the CALSPEC database. These theoretical spectral energy distributions (SEDs) provide the relative flux vs. wavelength, and only the absolute flux level remains to be set by reconciling the measured absolute flux of Vega in the visible with the Midcourse Space Experiment (MSX) values for Sirius in the mid-IR. The most recent SEDs calculated by the \textsc{tlusty} and \textsc{tmap} NLTE model atmosphere code…
We present the initial-final mass relation (IFMR) based on the self-consistent analysis of Sirius B and 79 white dwarfs from 13 star clusters. We have also acquired additional signal on eight white dwarfs previously analyzed in the NGC 2099 cluster field, four of which are consistent with membership. These reobserved white dwarfs have masses ranging from 0.72 to 0.97 M$_\odot$, with initial masses from 3.0 to 3.65 M$_\odot$, where the IFMR has an important change in slope that these new data help to observationally confirm. In total, this directly measured IFMR has small scatter ($σ$ = 0.06 M$…
On-Sky Single-photon Time resolution of 35 ps with White Rabbit synchronization: towards the measurement of the size of a White Dwarf star
Université Côte d’Azur（蔚蓝海岸大学）；CNRS, Institut de Physique de Nice（法国国家科学研究中心尼斯物理研究所）；Instituto de Ciencias Físicas (ICIFI, UNSAM - CONICET)（物理科学研究院（ICIFI，UNSAM-CONICET））；Universite Cote d’Azur, Observatoire de la Cote d’Azur, CNRS, Laboratoire Lagrange（蔚蓝海岸大学蔚蓝海岸天文台法国国家科学研究中心拉格朗日实验室）
The nearby Sun-like star HD 114174 exhibits a strong and persistent Doppler acceleration indicating the presence of an unseen distant companion. We have acquired high-contrast imaging observations of this star using NIRC2 at Keck and report the direct detection of the body responsible for causing the "trend". HD 114174 B has a projected separation of 692+/-9 mas (18.1 AU) and is 10.75+/-0.12 magnitudes (contrast of 5x10{-5}) fainter than its host in the K-band, requiring aggressive point-spread function subtraction to identify. Our astrometric time baseline of 1.4 years demonstrates physical a…
We present the results of a photometric and spectroscopic study of the white dwarf candidate members of the intermediate age open clusters NGC3532 and NGC2287. Of the nine objects investigated, it is determined that six are probable members of the clusters, four in NGC3532 and two in NGC2287. For these six white dwarfs we use our estimates of their cooling times together with the cluster ages to constrain the lifetimes and masses of their progenitor stars. We examine the location of these objects in initial mass-final mass space and find that they now provide no evidence for substantial scatte…
From a sample of spectra of 439 white dwarfs (WDs) from the ESO-VLT Supernova-Ia Progenitor surveY (SPY), we measure the maximal changes in radial-velocity (DRVmax) between epochs (generally two epochs, separated by up to 470d), and model the observed DRVmax statistics via Monte-Carlo simulations, to constrain the population characteristics of double WDs (DWDs). The DWD fraction among WDs is fbin=0.100+/-0.020 (1-sigma, random) +0.02 (systematic), in the separation range ~<4AU within which the data are sensitive to binarity. Assuming the distribution of binary separation, a, is a power-law, dN…
The connection between helium-rich hot subdwarfs of spectral types O and B (He-sdB) has been relatively unexplored since the latter were found in significant numbers in the 1980's. In order to explore this connection further, we have analysed the surface composition of six He-sdB stars, including LB 1766, LB 3229, SB 21 (= Ton-S 137 = BPS 29503-0009), BPS 22940-0009, BPS 29496-0010, and BPS 22956-0094. Opacity-sampled line-blanketed model atmospheres have been used to derive atmospheric properties and elemental abundances. All the stars are moderately metal-poor compared with the Sun ([Fe/H] ~…
A number of efforts are underway to detect close binary stars in planetary nebulae. The primary goal of these studies is to determine the binary fraction of central stars. The next stage is a detailed analysis of the binaries to determine physical parameters for the systems. These analyses can be combined with population synthesis models, common envelope evolution models, and observed properties of nebulae to further understand the impact of binarity on PN formation. I discuss the sample of known close binary central stars in relation to other close binaries with a white dwarf, cataclysmic var…
Increasing observations of white dwarf atmospheric pollution and disrupting planetesimals is driving increased studies into the fate of exo-asteroids around post-main-sequence stars. Planetesimal populations in the Solar System which are most likely to survive the violent post-main-sequence evolution, such as the Kuiper Belt, display a large binary fraction with a propensity for near equal-mass components and provide a previously unexplored population of planetesimals which are likely to exist around white dwarfs. Here we simulate the dynamical evolution of equal-mass binary asteroid systems a…
Binarity has been hypothesised to play an important, if not ubiquitous, role in the formation of planetary nebulae (PNe). Yet there remains a severe paucity of known binary central stars required to test the binary hypothesis and to place strong constraints on the physics of the common-envelope (CE) phase of binary stellar evolution. Large photometric surveys offer an unrivalled opportunity to efficiently discover many binary central stars. We have combined photometry from the OGLE microlensing survey with the largest sample of PNe towards the Galactic Bulge to systematically search for new bi…
The planet-hosting and Sirius-type binary system epsilon Reticulum (HD 27442) is examined from the perspective of its more evolved white dwarf secondary. The stellar parameters are determined from a combination of Balmer line spectroscopy, gravitational redshift, and solid angle. These three methods conspire to yield the most accurate physical description of the companion to date: Teff=15,310 \pm 350 K and M=0.60 \pm 0.02 Msol. Post-main sequence mass loss indicates the current binary separation has increased by a factor of 1.6 from its primordial state when the current primary was forming its…
This paper presents combined ${\it Spitzer}$ IRAC and ${\it Hubble}$ COS results for a double-blind survey of 195 single and 22 wide binary white dwarfs for infrared excesses and atmospheric metals. The selection criteria include cooling ages in the range 9 to 300 Myr, and hydrogen-rich atmospheres so that the presence of atmospheric metals can be confidently linked to ongoing accretion from a circumstellar disc. The entire sample has infrared photometry, whereas 168 targets have corresponding ultraviolet spectra. Three stars with infrared excesses due to debris discs are recovered, yielding a…
We present a detailed study based on infrared photometry of all Galactic RV Tauri stars from the General Catalogue of Variable Stars (GCVS). RV Tauri stars are the brightest among the population II Cepheids. They are thought to evolve away from the asymptotic giant branch (AGB) towards the white dwarf domain. IRAS detected several RV Tauri stars because of their large IR excesses and it was found that they occupy a specific region in the [12] - [25], [25] - [60] IRAS two-colour diagram. We used the all sky survey of WISE to extend these studies and compare the infrared properties of all RV Tau…
Measuring phase modulation in pulsating stars has proved to be a highly successful way of finding binary systems. The class of pulsating main-sequence A and F variables known as delta Scuti stars are particularly good targets for this, and the \textit{Kepler} sample of these has been almost fully exploited. However, some \textit{Kepler} $δ$ Scuti stars have incorrect temperatures in stellar properties catalogues, and were missed in previous analyses. We used an automated pulsation classification algorithm to find 93 new $δ$ Scuti pulsators among tens of thousands of F-type stars, which we then…
Binarity and beyond in A stars I. Survey description and first results of VLTI/GRAVITY observations of VAST targets with high Gaia-Hipparcos accelerations
Planetary Accretion Is Less Frequent in Wide Binaries: Evidence from Metal-Enriched White Dwarfs in DESI DR1
Gemini Observatory/NSF NOIRLab（吉米尼天文台/美国国家光学红外天文研究实验室）；Department of Physics, University of Warwick（华威大学物理系）；Institute for Astronomy, University of Edinburgh, Royal Observatory（爱丁堡大学天文研究所皇家天文台）；Institute of Astronomy, University of Cambridge（剑桥大学天文研究所）；Astrophysics Group, Department of Physics, Imperial College London（帝国理工学院物理系天体物理学组）；Department of Astronomy & Astrophysics, University of Toronto（多伦多大学天文学与天体物理系）；Department of Astronomy, School of Physics and Astronomy, Shanghai Jiao Tong Univer（上海交通大学物理与天文学院天文学系）
Although dwarf carbon (dC) stars are thought universally to be binaries to explain the presence of $C_2$ in their spectra while still near main sequence luminosity, direct observational evidence for binarity is remarkably scarce. Here we report the detection of a 2.92 d periodicity in both photometry and radial velocity of SDSS J125017.90+252427.6, an $r=16.4$ dC star. This is the first photometric binary dC, and only the second dC spectroscopic binary. The relative phase of the photometric period to the spectroscopic observations suggests that the photometric variations are a reflection effec…
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 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 $\approx$50 yr) and quasi-instantaneous (2MASS, SDSS, WISE, Pulkovo; an epoch difference of $\approx$10 yr) proper motions. If the difference is statistically significant compared to the proper motion errors…
HD 144941 is an extreme He (EHe) star, a rare class of subdwarf OB star formed from the merger of two white dwarf (WD) stars. Uniquely amongst EHe stars, its light curve has been reported to be modulated entirely by rotation, suggesting the presence of a magnetic field. Here we report the first high-resolution spectropolarimetric observations of HD 144941, in which we detect an extremely strong magnetic field both in circular polarization (with a line-of-sight magnetic field averaged over the stellar disk $\langle B_z \rangle \sim -8$ kG) and in Zeeman splitting of spectral lines (yielding a m…
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…
