Using a population synthesis technique, we have calculated detailed models of the present-day field population of objects that have resulted from the merger of a giant primary and a main-sequence or brown dwarf secondary during common-envelope evolution. We used a grid of 116 stellar and 32 low-mass/brown dwarf models, a crude model of the merger process, and followed the angular momentum evolution of the binary orbit and the primary's rotation prior to merger, as well as the merged object's rotation after the merger. We find that present-day merged objects that are observable as giant stars or core-helium burning stars in our model population constitute between 0.24% and 0.33% of the initial population of ZAMS binaries, depending upon the input parameters chosen. The median projected rotational velocity of these merged objects is ~16 km/sec, an order of magnitude higher than the median projected rotational velocity in a model population of normal single stars calculated using the same stellar models and initial mass function. The masses of the merged objects are typically less than ~2 solar masses, with a median mass of 1.28 solar masses, which is slightly more than, but not significantly different from, their normal single star counterparts. The luminosities in our merged object population range from ~10-100 solar luminosities, with a strong peak in the luminosity distribution at ~60 solar luminosities, since the majority of the merged objects (57%) lie on the horizontal branch at the present epoch. The results of our population synthesis study are discussed in terms of possible observational counterparts either directly involving the high rotational velocity of the merger product or indirectly, via the effect of rotation on envelope abundances and on the amount and distribution of circumstellar matter.
Non-Detection of the Putative Substellar Companion to HD 149382
有人认为，一个亚恒星的同伴可能会显着影响sdB星的祖先的演化。最近，明亮的sdB恒星HD 149382被声称拥有一颗周期为2.391天的亚恒星（可能是行星）伴星。这对sdB星的祖先的演化以及椭圆星系中紫外线过量的来源具有重要意义。为了验证这颗行星的存在，我们在17天内用Hobby-Eberly望远镜的高分辨率光谱仪对HD 149382进行了10次径向速度测量。我们的数据最终证明了假定的亚恒星伴星并不存在，并且排除了几乎所有具有P ~ 1 Mjup的亚恒星伴星的存在< 28 days and Msin i >。
On the formation of subdwarf B stars via engulfment of substellar companions I. Conditions for and occurrence of envelope ejection events
Space sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège（列日大学空间科学、技术与天体物理研究研究所）；Institut d’Astronomie et d’Astrophysique, Université Libre de Bruxelles (ULB)（布鲁塞尔自由大学天文与天体物理研究所）
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 …
About a dozen substellar companions orbiting young stellar objects or pre-main sequence stars at several hundred au have been identified in the last decade. These objects are interesting both due to the uncertainties surrounding their formation, and because their large separation from the host star offers the potential to study the atmospheres of young giant planets and brown dwarfs. Here, we present X-shooter spectroscopy of SR 12 C, a $\sim\,2\,$Myrs young brown dwarf orbiting SR 12 at an orbital separation of 1083 au. We determine the spectral type, gravity, and effective temperature via co…
Common envelope (CE) phases in binary systems where the primary star reaches the tip of the red giant branch are discussed as a formation scenario for hot subluminous B-type (sdB) stars. For some of these objects, observations point to very low-mass companions. In hydrodynamical CE simulations with the moving-mesh code AREPO, we test whether low-mass objects can successfully unbind the envelope. The success of envelope removal in our simulations critically depends on whether or not the ionization energy released by recombination processes in the expanding material is taken into account. If thi…
White dwarfs in the UKIDSS Large Area Survey: The Substellar Companion Fraction
我们提出了一个近红外测光搜索未解决的亚恒星同伴和碎片盘周围的白矮星在UKIRT红外深空大面积调查。我们交叉相关SDSS DR 4和McCook & Sion目录的白矮星与UKIDSS DR 8生产3109和163个独特的匹配分别。冷却模型适用于DA白矮星子样本的光学测光，并推广到近红外。然后与观测到的测光进行比较，以确定那些具有与冷伴星或碎片盘的存在相一致的近红外过量的恒星。在存在的地方，我们已经估计了任何假定的伴星的近似光谱类型，或者碎片盘温度的上限。我们总共确认了14-16个新的候选白矮星+极低质量恒星系统，9-11个候选白矮星+棕矮星系统，3个候选白矮星+碎片盘。我们对所有DA白矮星的未解决（<2英寸）伴星设定了下限，从而评估UKIDSS对此类物体的敏感性。我们使用该结果来估计f（WD+dL）>0.4+/-0.3%，f（WD+dT）>0.2%和f（WD+BD）>0.5+/-0.3%的未分辨二元分数。
A Long-period Eccentric Substellar Companion to the Evovled Intermediate-Mass Star HD 14067
本文报道了用精密多普勒技术探测到一颗围绕中等质量演化恒星HD 14067（G9 III）运行的亚恒星伴星。这颗恒星的径向速度可以很好地拟合成一个具有线性速度下降趋势的开普勒周期变化（P=1455天，$K_1=92.2$ m s $^{-1}$，$e=0.533$，和$\dotγ=-22.4$ m s $^{-1}$ yr $^{-1}$）或一个没有线性趋势的开普勒轨道（P=2850天，$K_1=100.1$ m s $^{-1}$，和$e=0.697$）。最小质量（$m_2\sin{i}=7.8\,M_{\rm J}$是有线性趋势的模型，$m_2\sin{i}=9.0\,M_{\rm J}$是没有线性趋势的模型）表明有一颗长周期的巨行星围绕着一颗演化中的中等质量恒星。它的轨道偏心率是已知在演化恒星周围探测到的行星中最高的。
Hot subdwarfs (sdO/Bs) are the helium-burning cores of red giants, which lost almost all of their hydrogen envelopes. This mass loss is often triggered by common envelope interactions with close stellar or even substellar companions. Cool companions like late-type stars or brown dwarfs are detectable via characteristic light curve variations like reflection effects and often also eclipses. To search for such objects we obtained multi-band light curves of 26 close sdO/B binary candidates from the MUCHFUSS project with the BUSCA instrument. We discovered a new eclipsing reflection effect system …
A recent study using $Hubble$ $Space$ $Telescope$ observations found periodic, high-speed, collimated ejections (or "bullets") from the star V Hya. The authors of that study proposed a model associating these bullets with the periastron passage of an unseen, substellar companion in an eccentric orbit and with an orbital period of $\sim8$ yrs. Here we propose that V Hya is part of a triple system, with a substellar companion having an orbital period of $\sim8$ yrs, and a tertiary object on a much wider orbit. In this model, the more distant object causes high-eccentricity excitations on the sub…
The substellar companion HD206893b has recently been discovered by direct imaging of its disc-bearing host star with the SPHERE instrument. We investigate the atypical properties of the companion, which has the reddest near-infrared colours among all known substellar objects, either orbiting a star or isolated, and we provide a comprehensive characterisation of the host star-disc-companion system. We conducted a follow-up of the companion with adaptive optics imaging and spectro-imaging with SPHERE, and a multiinstrument follow-up of its host star. We obtain a R=30 spectrum from 0.95 to 1.64 m…
We have measured stellar parameters, [Fe/H], lithium abundances, rotation, and 12C/13C in a small sample of red giants in three open clusters that are each home to a red giant star that hosts a substellar companion (NGC2423 3, NGC4349 127, and BD+12 1917 in M67). Our goal is to explore whether the presence of substellar companions influences the Li content. Both 12C/13C and stellar rotation are measured as additional tracers of stellar mixing. One of the companion hosts, NGC2423 3, is found to be Li-rich with A(Li)_NLTE=1.56 dex, and this abundance is significantly higher than the A(Li) of the…
Model-independent masses of substellar companions are critical tools to validate models of planet and brown dwarf cooling, test their input physics, and determine the formation and evolution of these objects. In this work, we measure the dynamical mass and orbit of the young substellar companion HD 984 B. We obtained new high-contrast imaging of the HD 984 system with Keck/NIRC2 which expands the baseline of relative astrometry from 3 to 8 years. We also present new radial velocities of the host star with the Habitable-Zone Planet Finder spectrograph at the Hobby-Eberly Telescope. Furthermore,…
We find a new substellar companion to the Pleiades member star, Pleiades HII 3441, using the Subaru telescope with adaptive optics. The discovery is made as part of the high-contrast imaging survey to search for planetary-mass and substellar companions in the Pleiades and young moving groups. The companion has a projected separation of 0".49 +/- 0".02 (66 +/- 2 AU) and a mass of 68 +/- 5 M_J based on three observations in the J-, H-, and K_S-band. The spectral type is estimated to be M7 (~2700 K), and thus no methane absorption is detected in the H band. Our Pleiades observations result in the…
Context. Identification of planetary companions of giant stars is made difficult because of the astrophysical noise, that may produce radial velocity (RV) variations similar to those induced by a companion. On the other hand any stellar signal is wavelength dependent, while signals due to a companion are achromatic. Aims. Our goal is to determine the origin of the Doppler periodic variations observed in the thick disk K giant star TYC 4282-605-1 by HARPS-N at the Telescopio Nazionale Galileo (TNG) and verify if they can be due to the presence of a substellar companion. Methods. Several methods…
The census of stellar and substellar companions of nearby stars is largely incomplete. It is, however, fundamentally important in the understanding of the stellar and planetary formation and evolution mechanisms. We aim to characterize the presence of physical companions in orbit around nearby stars. Orbiting secondary bodies influence the proper motion (PM) of their parent star through their gravitational reflex motion. Using the Hipparcos catalog and Gaia's second data release (GDR2), we determined the long-term PM of the stars common to these two catalogs. We then searched for a PM anomaly …
Fates of the sub-stellar objects (FOSSO) II. Evidence for Suppression of Metal Pollution in White Dwarfs by Close Substellar Companions
School of Physics and Astronomy, Sun Yat-sen University（中山大学物理学院）；CSST Science Center for the Guangdong-Hong Kong-Macau Great Bay Area, Sun Yat-sen University（中山大学粤港澳大湾区子午线工程科学中心）；School of Astronomy and Space Science, Nanjing University（南京大学天文与空间科学学院）
The relationship between luminosity and mass is of fundamental importance for direct imaging studies of brown dwarf and planetary companions to stars. In principle this can be inferred from theoretical mass-luminosity models; however, these relations have not yet been thoroughly calibrated, since there is a lack of substellar companions for which both the brightness and mass have been directly measured. One notable exception is GJ 758 B, a brown dwarf companion in a $\sim$20 AU orbit around a nearby Sun-like star, which has been both directly imaged and dynamically detected through a radial ve…
Using data from the extended Kepler mission in K2 Campaign 10 we identify two eclipsing binaries containing white dwarfs with cool companions that have extremely short orbital periods of only 71.2 min (SDSS J1205-0242, a.k.a. EPIC 201283111) and 72.5 min (SDSS J1231+0041, a.k.a. EPIC 248368963). Despite their short periods, both systems are detached with small, low-mass companions, in one case a brown dwarf, and the other case either a brown dwarf or a low-mass star. We present follow-up photometry and spectroscopy of both binaries, as well as phase-resolved spectroscopy of the brighter system…
Deep optical imaging is used to study time-domain properties of young brown dwarfs in sigma Orionis over typical rotational time-scales and to search for new substellar and planetary-mass cluster members. We used VIMOS at the VLT to monitor a 24 arcmin x 16 arcmin field in the I-band. Using the individual images from this run we investigated the photometric time series of nine substellar cluster members with masses from 10 to 60 Mj. The deep stacked image shows cluster members down to $\approx$ 5 Mj. We search for new planetary mass objects by combining our deep I-band photometry with public J…
OASIS Survey Direct Imaging and Astrometric Discovery of HIP 71618 B: A Substellar Companion Suitable for the Roman Coronagraph Technology Demonstration
The DODO Survey II: A Gemini Direct Imaging Search for Substellar and Planetary Mass Companions around Nearby Equatorial and Northern Hemisphere White Dwarfs
简并天体周围的简并天体巡天（DODO）的目的是通过直接成像在白矮星周围的宽轨道上寻找质量很低的棕矮星和太阳系外行星。直接探测到这样的伴星将允许光谱研究温度比目前观测到的最冷的褐矮星低得多（< 500 K）的物体。这些超低质量的亚恒星天体的光谱型可能大于T8.5，因此可能属于Y矮星光谱序列。探测到白矮星周围的行星将证明这种物体可以在恒星演化的最后阶段幸存下来，并限制其祖先周围的行星系的频率（质量在1.5 - 8个太阳质量之间，即，早B到中F）。本文介绍了对23颗赤道附近和北半球白矮星进行的多历元J波段共同自行巡天观测结果。我们排除了任何常见的自行同伴的存在，从每次观察的完整性极限确定的限制质量，18个白矮星。对于剩下的五个目标，白矮星的运动与每个视场中不运动的背景物体没有充分分离。这些目标需要额外的观测，以最终排除任何共同的自行同伴的存在。从我们的完整性限制，我们初步建议，< 5% of white dwarfs have substellar companions with effective temperatures >500 K之间的预计物理分离60 - 200 AU。
We present results from the Large Adaptive optics Survey for Substellar Objects (LASSO), where the goal is to directly image new substellar companions (<70 M$_{Jup}$) at wide orbital separations ($\gtrsim$50 AU) around young ($\lesssim$300 Myrs), nearby (<100 pc), low-mass ($\approx$0.1-0.8 M$_{\odot}$) stars. We report on 427 young stars imaged in the visible (i') and near-infrared (J or H) simultaneously with Robo-AO on the Kitt Peak 2.1-m telescope and later the Maunakea University of Hawaii 2.2-m telescope. To undertake the observations, we commissioned a new infrared camera for Robo-AO th…
Multi-wavelength observations provide a complementary view of the formation of young directly-imaged planet-mass companions. We report the ALMA 1.3 mm and Magellan adaptive optics (MagAO) H-alpha, i', z', and Ys observations of the GQ Lup system, a classical T Tauri star with a 10-40 Mjup substellar companion at ~110 AU projected separation. We estimate the accretion rates for both components from the observed H-alpha fluxes. In our 0.05 arcsec resolution ALMA map, we resolve GQ Lup A's disk in dust continuum, but no signal is found from the companion. The disk is compact, with a radius of ~22…
Eclipsing post-common envelope binaries are highly important for resolving the poorly understood, very short-lived common envelope phase. Most hot subdwarfs (sdO/Bs) are the bare He-burning cores of red giants which have lost almost all of their hydrogen envelopes. This mass loss is often triggered by common envelope interactions with close stellar or even sub-stellar companions. In the recently published catalog of eclipsing binaries in the Galactic Bulge and in the ATLAS survey, we discovered 161 new eclipsing systems showing a reflection effect by visual inspection of the light curves and u…
We present a detailed characterization of 2MASS J04435750+3723031, a low-mass companion orbiting the young M2 star, 2MASS J04435686+3723033, at 7.6 arcseconds (550 AU) with potential membership in the 23 Myr $β$ Pictoris moving group ($β$PMG). Using near-infrared spectroscopy of the companion from IRTF/SpeX we have found a spectral type of M6 $\pm$ 1 and indications of youth through age-sensitive absorption lines and a low surface gravity index (VL-G). A young age is supported by H$α$ emission and lithium absorption in the host. We re-evaluate the membership of this system and find that it is …
We present new near-infrared Gemini Planet Imager (GPI) spectroscopy of HD 206893 B, a substellar companion orbiting within the debris disk of its F5V star. The $J$, $H$, $K1$, and $K2$ spectra from GPI demonstrate the extraordinarily red colors of the object, confirming it as the reddest substellar object observed to date. The significant flux increase throughout the infrared presents a challenging atmosphere to model with existing grids. Best-fit values vary from 1200 K to 1800 K for effective temperature and from 3.0 to 5.0 for log($g$), depending on which individual wavelength band is fit …
Statistics on the population of distant substellar companions to nearby stars
Université Joseph Ki-Zerbo（约瑟夫·基泽尔博大学）；Université Côte d’Azur, Observatoire de la Côte 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）；Institut Trottier de recherche sur les exoplanètes, Département de Physique, Université de Montréal（特罗蒂埃系外行星研究所，物理系，蒙特利尔大学）；Observatoire du Mont-Mégantic（梅冈蒂克山天文台）；SUPA, Institute for Astronomy, University of Edinburgh（苏格兰天体物理学联盟，爱丁堡大学天文学研究所）
We present the new results of our long-term observational project to detect the small variations in the orbital periods of low-mass and short-period eclipsing binaries. About 120 new precise mid-eclipse times were obtained for three relatively well-known dwarf eclipsing binaries: SDSS J143547.87+373338.5 (P = 0.126 d), NSVS 07826147 (0.162 d), and NSVS 14256825 (0.110 d). Observed-minus-calculated (O-C) diagrams of these systems were analyzed using all accurate timings, and, where possible, new parameters of the light-time effect were calculated. For the first time, we derive (or improve upon …
Very Low-Mass Stellar and Substellar Companions to Solar-Like Stars from MARVELS I: A Low Mass Ratio Stellar Companion to TYC 4110-01037-1 in a 79-day Orbit
Connections Between Tilted Accretion Disks Around White Dwarfs and Substellar Companions
白矮星系统中的吸积盘被认为是倾斜的。在最近的出版物中，升力被认为是盘倾斜的一个来源，一个可能与所有吸积盘系统相关的来源。升力是由在亮点处流过圆盘上方和下方的超音速气流速度略有不同而产生的。在这次会议的过程中，我们集中在是否有足够的质量，以有助于磁盘倾斜吸积到一个白矮星主要的棕矮星捐助星。我们也想知道一个白矮星-棕矮星密近双星系统是否有足够的质量来诱导和维持四度的盘倾斜。我们采用SDSS 103533.03+055158.4作为我们的模型系统，其传质速率为（（10 \pm 2）\times 10^{-12}）M $_{\odot}$ yr $^{-1}$。我们发现SDSS 1035中的褐矮星没有足够的质量来贡献盘倾斜。我们发现最小质量传递速率的总量为$\sim10^{-10}$ M $_{\odot}$ yr $^{-1}$。我们的结论是，SDSS 1035似乎没有足够高的传质速率，诱导和维持可观察到的磁盘倾斜。因此，褐矮星供体系统如此难以找到的一个原因可能是由于它们的低质量传递速率，这不会引起白矮星-红矮星CV中典型的可观察到的动力学效应。
Planet searches using the radial velocity technique show a paucity of companions to solar-type stars within ~5 AU in the mass range of ~10 - 80 M$_{\text{Jup}}$. This deficit, known as the brown dwarf desert, currently has no conclusive explanation. New substellar companions in this region help asses the reality of the desert and provide insight to the formation and evolution of these objects. Here we present 10 new brown dwarf and two low-mass stellar companion candidates around solar-type stars from the Multi-object APO Radial-Velocity Exoplanet Large-Area Survey (MARVELS) of the Sloan Digit…
