Identification of white dwarfs (WD) with main-sequence (MS) companions and characterization of their properties can put important constraints on our understanding of binary stellar evolution and guide the theoretical predictions for a wide range of interesting transient events relevant for, e.g., Rubin Observatory (LSST), ZTF, and LISA. In this study, we combine ultraviolet (UV) and optical color-magnitude diagrams (CMDs) to identify unresolved WD--MS binaries. In particular, we combine high-precision astrometric and photometric data in the optical from \gaia\ -DR3 and UV data from GALEX GR6/7 to identify 93 WD--MS candidates within 100 pc. Of these, 80 are newly identified. Using the Virtual Observatory SED Analyzer (VOSA) we fit the spectral energy distributions (SEDs) of all our candidates and derive stellar parameters, such as effective temperature, bolometric luminosity, and radius for both companions. We find that our identification method helps identify hotter and smaller WD companions (majority with $\geq$10,000 K and $\leq$0.02 $R_\odot$) relative to the WDs identified by past surveys. We infer that these WDs are relatively more massive (median $\sim$ $0.76\,M_\odot$). We find that most of the MS companions in our binaries are of the $K$ and $M$ spectral types.
We predict the number of black holes with stellar companions that are potentially detectable with Gaia astrometry over the course of its five-year mission. Our model estimates that nearly 2$\times$10$^5$ astrometric binaries hosting black holes and stellar companions brighter than Gaia's detection threshold, G $\sim$ 20, should be discovered with 5$σ$ sensitivity. Among these detectable binaries, systems with longer orbital periods are favored, and black hole and stellar companion masses in the range M$_{BH} \sim$ 6-10 M$_\odot$ and M$_* \sim$ 1-2 M$_\odot$, respectively, are expected to domin…
We present Gemini-South observations of nine faint and extended planetary nebulae. Using direct images taken with the spectrograph GMOS, we built the $(u' - g')$ vs. $(g' - r')$ diagrams of the stars in the observed areas which allowed us, also considering their geometrical positions, to identify the probable central stars of the nebulae. Our stellar spectra of seven stars, also taken with GMOS, indicate that four (and probably two more) objects are white dwarfs of the DAO subtype. Moreover, the white dwarf status of the four stars is confirmed by the parameters $ T_{\mathrm{eff}}$ and $ \log …
We present UVIT/Astrosat UV photometry of the RSG population of the Small Cloud galaxy (SMC). As RSGs are extremely faint in the far-UV, these observations directly probe potential companion stars. From a sample of 861 SMC RSGs, we find 88 have detections at far-UV wavelengths: a clear signature of binarity. Stellar parameters are determined for both components, which allows us to study - for the first time - the mass-ratio (q) distribution of RSG binary systems. We find a flat mass-ratio distribution best describes the observations up to M{RSG}~15 Msun. We account for our main observing bias …
The determination of the brown dwarf binary fraction may contribute to the understanding of the substellar formation mechanisms. Unresolved brown dwarf binaries may be revealed through their peculiar spectra or the discrepancy between optical and near-infrared spectral type classification. We obtained medium-resolution spectra of 22 brown dwarfs with these characteristics using the X-Shooter spectrograph at the VLT. We aimed to identify brown dwarf binary candidates, and to test if the BT-Settl 2014 atmospheric models reproduce their observed spectra. To find binaries spanning the L-T boundary…
Hunting for millimeter flares from magnetic reconnection in pre-main sequence spectroscopic binaries
最近对低质量主序前偏心光谱双星DQ Tau和V773 Tau A的观测表明，它们的毫米光谱偶尔会被来自非热发射过程的耀斑所主导。瞬时活动被认为是同步加速的性质，由强大的磁重联事件引起，当双星组件的单独磁性结构能够相互作用并被迫重组时，通常在近星点附近。我们进行了第一次系统的研究，毫米的变化对样本的12 PMS光谱双星的目的是表征扩散的耀斑之间的来源可能会遇到类似的interbination事件。源样本包括短周期，近距离的双星，拥有一个高的轨道偏心率或圆形轨道。利用IRAM 30米望远镜上的MAMBO 2阵列，我们在1.25毫米处进行了连续4夜的监测，在此期间，所有的高偏心率双星接近近星点。我们还获得了同步光学VRI测量，因为恒星重联事件和光学增亮之间经常观察到强烈的联系。UZ Tau E是唯一一个在毫米波长下被探测到的光源：它表现出显著的变化;它也是唯一一个同时发生强烈光学变化的光源。这颗双星在目前的样本中拥有最大的轨道偏心率，这是恒星间磁相互作用事件的一个预测因素。由于轨道参数和可变吸积活动与DQ Tau相似，UZ Tau E的毫米行为与DQ Tau碰撞磁层模型有许多相似之处。然而，仅根据我们的观测，我们无法确定这种变化是否是重复性的，或者它是否也可能是由于电离风中的可变自由-自由发射。
Hunting for the progenitor of SN 1006: High resolution spectroscopic search with the FLAMES instrument
Ia型超新星在宇宙的演化中扮演着重要的角色，并且有着广泛的应用。人们普遍认为，这些事件是碳氧白矮星的热核爆炸，其质量接近1.38 M \odot。然而，CO白矮星出生时的质量远低于克拉塞卡极限，因此需要质量吸积才能成为Ia型超新星。吸积主要有两种情况。第一，两颗白矮星的合并，第二，来自伴星的稳定质量吸积。根据预测，这颗伴星（也被称为供体星）在爆炸中幸存下来，因此应该在Ia型遗迹的中心可见。在本文中，我们仔细检查了SN 1006残骸的中心恒星（共79颗），以寻找这种情况下预测的幸存的供体恒星。我们在SN 1006中没有发现与传统吸积方案一致的恒星。
We explore the long-term evolution of mass-transferring white dwarf binaries undergoing both direct-impact and disk accretion and explore implications of such systems to gravitational wave astronomy. We cover a broad range of initial component masses and show that these systems, the majority of which lie within the LISA sensitivity range, exhibit prominent negative orbital frequency evolution (chirp) for a significant fraction of their lifetimes. Using a galactic population synthesis, we predict ~$2700$ double white dwarfs will be observable by LISA with negative chirps less than $-0.1\ yr^{-2…
Recently, a large number of low-mass (<0.30 M_sun) helium white dwarfs (He WDs) have been discovered as a result of several surveys campaigns such as WASP, ELM, Kepler or SDSS. The far majority of them have as companion another compact object. There appears to be discrepancies between current theoretical modelling of low-mass He WDs and a number of key observational cases indicating that some details of their formation scenario yet remain to be understood.
Galactic binaries with orbital periods less than $\approx$1 hr are strong gravitational wave sources in the mHz regime, ideal for the Laser Interferometer Space Antenna (LISA). In fact, theory predicts that \emph{LISA} will resolve tens of thousands of Galactic binaries individually with a large fraction being bright enough for electromagnetic observations. This opens up a new window where we can study a statistical sample of compact Galactic binaries in both, the electromagnetic as well the gravitational wavebands. Using multi-messenger observations we can measure tidal effects in detached do…
Interacting binaries containing white dwarfs can lead to a variety of outcomes that range from powerful thermonuclear explosions, which are important in the chemical evolution of galaxies and as cosmological distance estimators, to strong sources of low frequency gravitational wave radiation, which makes them ideal calibrators for the gravitational low-frequency wave detector LISA mission. However, current theoretical evolution models still fail to explain the observed properties of the known populations of white dwarfs in both interacting and detached binaries. Major limitations are that the …
Neutron star-helium white dwarf (NS+He WD) binaries are important evolutionary products of close-orbit binary star systems. They are often observed as millisecond pulsars and may continue evolving into ultra-compact X-ray binaries (UCXBs) and continuous gravitational wave (GW) sources that will be detected by space-borne GW observatories, such as LISA, TianQin and Taiji. Nevertheless, the stability of NS+He WD binaries undergoing mass transfer is not well studied and still under debate. In this paper, we model the evolution of NS+He WD binaries with WD masses ranging from 0.17-0.45 $M_{\odot}$…
Evolution of binaries containing a hot subdwarf and a white dwarf to double white dwarfs, and double detonation supernovae with hypervelocity runaway stars
Max Planck Institut für Astrophysik（马克斯·普朗克天体物理学研究所）；Center for Astrophysics | Harvard & Smithsonian（哈佛-史密森尼天体物理中心）
We present an analysis of the second epoch HST WFC3 F110W near-Infrared (NIR) imaging data of the globular cluster M4. The new dataset suggests that one of the previously suggested four brown dwarf candidates in this cluster is indeed a high-probability cluster member. The position of this object in the NIR colour magnitude diagrams (CMDs) is in the white dwarf/brown dwarf area. The source is too faint to be a low-mass main sequence star, but, according to theoretical considerations, also most likely somewhat too bright to be a bona-fide brown dwarf. Since we know that the source is a cluster …
Tidal interactions can play an important role as compact white dwarf (WD) binaries are driven together by gravitational waves (GWs). This will modify the strain evolution measured by future space-based GW detectors and impact the potential outcome of the mergers. Surveys now and in the near future will generate an unprecedented population of detached WD binaries to constrain tidal interactions. Motivated by this, I summarize the deviations between a binary evolving under the influence of only GW emission and a binary that is also experiencing some degree of tidal locking. I present analytic re…
Black holes in binary star systems are vital for understanding the process of pr oducing gravitational wave sources, understanding how supernovae work, and for p roviding fossil evidence for the high mass stars from earlier in the Universe. At the present time, sample sizes of these objects, and especially of black hole s in binaries, are quite limited. Furthermore, more precise measurements of the binary parameters are needed, as well. With improvements primarily in X-ray an d radio astronomy capabilities, it should be possible to build much larger sampl es of much better measured black hole …
We study the evolution and gravitational wave emission of white dwarf -- black hole accreting binaries with a semi-analytical model. These systems will evolve across the mHz gravitational wave frequency band and potentially be detected by the Laser Interferometer Space Antenna (LISA). We identify new universal relations for this class of binaries, which relate the component masses to the gravitational wave frequency and its first derivative. Combined with the high precision measurements possible with LISA, these relations could allow us to infer the component masses and the luminosity distance…
Although not nearly as numerous as binaries with two white dwarfs, eccentric neutron star-white dwarf (NS-WD) binaries are important gravitational-wave (GW) sources for the next generation of space-based detectors sensitive to low frequency waves. Here we investigate periastron precession in these sources as a result of general relativistic, tidal, and rotational effects; such precession is expected to be detectable for at least some of the detected binaries of this type. Currently, two eccentric NS-WD binaries are known in the galactic field, PSR J1141-6545 and PSR B2303+46, both of which hav…
Binary population synthesis (BPS) study provides a comprehensive way to understand evolutions of binaries and their end products. Close white dwarf (WD) binaries have crucial characteristics in examining in uence of yetunresolved physical parameters on the binary evolution. In this paper, we perform Monte Carlo BPS simulations, investigating the population of WD/main sequence (WD/MS) binaries and double WD binaries, with a publicly available binary star evolution code under 37 different assumptions on key physical processes and binary initial conditions. We considered different combinations of…
The prime candidate sources for the upcoming space-borne gravitational wave (GW) observatory LISA are the numerous Galactic tight binaries of white dwarfs (WDs) and neutron stars (NSs), many of which will coalesce and undergo mass transfer, leading to simultaneous emission of X-rays and GWs. Here, detailed and coherent numerical stellar models are explored for the formation and evolution of these systems, including finite-temperature effects and complete calculations of mass transfer from a WD to a NS accretor. Evolutionary tracks of characteristic strain amplitude are computed, and the unique…
We investigate the effects of mass transfer and gravitational wave (GW) radiation on the orbital evolution of contact neutron-star-white-dwarf (NS-WD) binaries, and the detectability of these binaries by space GW detectors (e.g., Laser Interferometer Space Antenna, LISA; Taiji; Tianqin). A NS-WD binary becomes contact when the WD component fills its Roche lobe, at which the GW frequency ranges from ~0.0023 to 0.72 Hz for WD with masses ~0.05-1.4 Msun. We find that some high-mass NS-WD binaries may undergo direct coalescence after unstable mass transfer. However, the majority of NS-WD binaries …
Gaia provided the largest-ever catalogue of white dwarf stars. We use this catalogue, along with the third public data release of the Zwicky Transient Facility (ZTF), to identify new eclipsing white dwarf binaries. Our method exploits light curve statistics and the Box Least Squares algorithm to detect periodic light curve variability. The search revealed 18 new binaries, of which 17 are eclipsing. We use the position in the Gaia H-R diagram to classify these binaries and find that the majority of these white dwarfs have main sequence companions. We identify one system as a candidate eclipsing…
Common envelope (CE) evolution, which is crucial in creating short period binaries and associated astrophysical events, can be constrained by reverse modeling of such binaries' formation histories. Through analysis of a sample of well-constrained white dwarf (WD) binaries with low-mass primaries (7 eclipsing double WDs, 2 non-eclipsing double WDs, 1 WD-brown dwarf), we estimate the CE energy efficiency $α_{\rm{CE}}$ needed to unbind the hydrogen envelope. We use grids of He- and CO-core WD models to determine the masses and cooling ages that match each primary WD's radius and temperature. Assu…
Virtually all binaries consisting of a white dwarf with a non-degenerate companion can be classified as either close post-interaction systems (with orbital periods of a few days or less), or wide systems (with periods longer than decades), in which both components have effectively evolved as single stars. Binaries with periods between these two extremes can help constrain common envelope efficiency, or highlight alternative pathways towards the creation of compact binaries. To date such binaries have remained mostly elusive. Here we present three white dwarfs in binaries with evolved subgiant …
Galactic short-period close white dwarf binaries (CWDBs) are important objects for space-borne gravitational-wave (GW) detectors in the millihertz frequency bands. Due to the intrinsically low luminosity, only about 25 identified CWDBs are detectable by the Laser Interferometer Space Antenna (LISA), which are also known as verification binaries (VBs). The Gaia Early Data Release 3 (EDR3) provids a catalog containing a large number of CWDB candidates, which also includes parallax and photometry measurements. We crossmatch the Gaia EDR3 and Zwicky Transient Facility public data release 8, and ap…
We estimate the merger rate of double degenerate binaries containing extremely low mass (ELM) <0.3 Msun white dwarfs in the Galaxy. Such white dwarfs are detectable for timescales of 0.1 Gyr -- 1 Gyr in the ELM Survey; the binaries they reside in have gravitational wave merger times of 0.001 Gyr -- 100 Gyr. To explain the observed distribution requires that most ELM white dwarf binary progenitors detach from the common envelope phase with <1 hr orbital periods. We calculate the local space density of ELM white dwarf binaries and estimate a merger rate of 3e-3/yr over the entire disk of the Mil…
The ELM Survey. V. Merging Massive White Dwarf Binaries
我们在短周期P<1天的双星中发现了17颗低质量白矮星。我们的样本包括四个对象显着的log（g）~5表面重力和轨道的解决方案，要求他们是双退化双星。所有最低的表面重力WD在其光谱中都有金属线，这意味着长的重力沉降时间或正在进行的吸积。值得注意的是，在我们的样本中的六个WD具有二进制合并时间<10 Gyr. Four have >=0.9 Msun同伴。如果伴星是大质量的WD，这四个双星将演化成稳定的质量转移AM CVn系统，并可能爆炸为暗超新星。如果伴星是中子星，那么它们可能是毫秒脉冲星双星。这些发现使ELM巡天中分离的双简并双星的数量增加到54个;其中31个将在哈勃时间内合并。
We present the discovery of 15 extremely low mass (5 < log{g} < 7) white dwarf candidates, 9 of which are in ultra-compact double-degenerate binaries. Our targeted ELM Survey sample now includes 76 binaries. The sample has a lognormal distribution of orbital periods with a median period of 5.4 hr. The velocity amplitudes imply that the binary companions have a normal distribution of mass with 0.76 Msun mean and 0.25 Msun dispersion. Thus extremely low mass white dwarfs are found in binaries with a typical mass ratio of 1:4. Statistically speaking, 95% of the white dwarf binaries have a total m…
Close white dwarf binaries play an important role across a range of astrophysics, including thermonuclear supernovae, the Galactic low-frequency gravitational wave signal, and the chemical evolution of the Galaxy. Progress in developing a detailed understanding of the complex, multi-threaded evolutionary pathways of these systems is limited by the lack of statistically sound observational constraints on the relative fractions of various sub-populations, and their physical properties. The available samples are small, heterogeneous, and subject to a multitude of observational biases. Our overarc…
The Post-Merger Magnetized Evolution of White Dwarf Binaries: The Double-Degenerate Channel of Sub-Chandrasekhar Type Ia Supernovae and the Formation of Magnetized White Dwarfs
Magnitude-limited samples have shown that 20-25 per cent of cataclysmic variables contain white dwarfs with magnetic fields of Mega Gauss strength, in stark contrast to the approximately 5 per cent of single white dwarfs with similar magnetic field strengths. Moreover, the lack of identifiable progenitor systems for magnetic cataclysmic variables leads to considerable challenges when trying to understand how these systems form and evolve. Here we present a sample of six magnetic white dwarfs in detached binaries with low-mass stellar companions where we have constrained the stellar and binary …
Context. White dwarf-main sequence (WDMS) binaries are used to study several different important open problems in modern astrophysics. Aims. The Sloan Digital Sky Survey (SDSS) identified the largest catalogue of WDMS binaries currently known. However, this sample is seriously affected by selection effects and the population of systems containing cool white dwarfs and early-type companions is under-represented.Here we search for WDMS binaries within the spectroscopic data release 1 of the LAMOST (Large sky Area Multi-Object fiber Spectroscopic Telescope) survey. LAMOST and SDSS follow differen…
Post-common envelope binaries from SDSS - VII: A catalogue of white dwarf-main sequence binaries
我们提出了一个目录的1602白矮星主序星（WDMS）的光谱斯隆数字巡天数据发布6（SDSS DR 6）。其中，我们确定440作为新的WDMS二进制文件。我们从拟合所有127万个DR 6光谱的模板中选择WDMS二进制候选者，使用$χ^{2}$和信噪比中的组合约束。此外，我们使用星系演化探测器（GALEX）和UKIRT红外巡天（UKIDSS）的大小搜索的对象，其中两个组件之一占主导地位的SDSS光谱。我们使用分解/拟合技术来测量有效温度，表面重力，质量和距离的白矮星，以及光谱类型和距离的同伴在我们的目录。从这些恒星参数的分布和密度图，然后被用来研究的一般性质和选择效应的WDMS双星SDSS。我们还利用SDSS-GALEX-UKIDSS星等研究了WDMS双星在紫外到红外色空间的分布，以及它们的白矮星有效温度和伴星光谱类型。我们表明，WDMS双星可以非常有效地从单一的主序星和白矮星分离时，使用组合的紫外，光学和红外颜色选择。最后，我们还提供了径向速度为1068系统测量的\Lines{Na}{I}{8183.27,8194.81}吸收双峰和/或H $α$发射线。在具有多个SDSS光谱的系统中，我们发现了五个新的系统表现出显着的径向速度变化，将其确定为后共同包络二进制候选人。
We present the data release (DR) 5 catalogue of white dwarf-main sequence (WDMS) binaries from the Large Area Multi-Object fiber Spectroscopic Telescope (LAMOST). The catalogue contains 876 WDMS binaries, of which 757 are additions to our previous LAMOST DR1 sample and 357 are systems that have not been published before. We also describe a LAMOST-dedicated survey that aims at obtaining spectra of photometrically-selected WDMS binaries from the Sloan Digital Sky Survey (SDSS) that are expected to contain cool white dwarfs and/or early type M dwarf companions. This is a population under-represen…
We have presented 309 new white-dwarf (WD) + main-sequence (MS) star binaries identified from the Sloan Digital Sky Survey (SDSS) Tenth Data Release (DR10). The majority of them consist of a white dwarf and a low-mass secondary (typically M dwarf) companion. The SDSS spectra of the newly found WDMS binaries with a DA/DB white dwarf and an M/late-K dwarf companion are analyzed based on a spectral decomposition/fitting method. White dwarf effective temperatures, surface gravities and masses together with the secondary star spectral types are obtained, and the stellar parameters of DA WDs with $T…
We present an updated version of the spectroscopic catalogue of white dwarf-main sequence (WDMS) binaries from the Sloan Digital Sky Survey (SDSS). We identify 939 WDMS binaries within the data releases (DR) 9-12 of SDSS plus 40 objects from DR 1-8 that we missed in our previous works, 646 of which are new. The total number of spectroscopic SDSS WDMS binaries increases to 3294. This is by far the largest and most homogeneous sample of compact binaries currently available. We use a decomposition/fitting routine to derive the stellar parameters of all systems identified here (white dwarf effecti…
