Several observational pieces of evidence indicate that specific evolutionary channels which involve Roche lobe overflow are not correctly accounted for by the classical Roche model. We generalize the concept of Roche lobe in the presence of extra forces (caused by radiation pressure or pulsations). By computing the distortion of the equipotential surfaces, we are able to evaluate the impact of these perturbing forces on the stability of Roche-lobe overflow (RLOF). Radiative forces are parametrized through the constant reduction factor that they impose on the gravitational force from the radiating star (neglecting any shielding in case of large optical thickness). Forces imparted by pulsations are derived from the velocity profile of the wind that they trigger. We provide analytical expressions to compute the generalized Roche radius. Depending on the extra force, the Roche-lobe radius may either stay unchanged, become smaller, or even become meaningless (in the presence of a radiatively- or pulsation-driven wind). There is little impact on the RLOF stability.
In compact stellar triple systems, an evolved tertiary star can overflow its Roche lobe around the inner binary. Subsequently, the tertiary star can transfer mass to the inner binary in a stable manner, or Roche lobe overflow (RLOF) can be unstable and lead to common-envelope (CE) evolution. In the latter case, the inner binary enters the extended envelope of the tertiary star and spirals in towards the donor's core, potentially leading to mergers or ejections. Although studied in detail for individual systems, a comprehensive statistical view on the various outcomes of triple RLOF is lacking.…
Common-envelope (CE) evolution is an outstanding open problem in stellar evolution, critical to the formation of compact binaries including gravitational-wave sources. In the ``classical'' isolated binary evolution scenario for double compact objects, the CE is usually the second mass transfer phase. Thus, the donor star of the CE is the product of a previous binary interaction, often stable Roche-lobe overflow (RLOF). Because of the accretion of mass during the first RLOF, the main-sequence core of the accretor star grows and is ``rejuvenated''. This modifies the core-envelope boundary region…
The first ultracompact Roche lobe-filling hot subdwarf binary
我们报告发现的第一个短周期的双星中，一个热的亚矮星（sdOB）填充其洛希叶，并开始质量转移到它的同伴。该天体是在一项名为“茨维基瞬变设施”的专门高节奏银河平面调查中发现的，其周期为$P_{\rm orb}=39.3401(1)$ min，是目前已知的最紧凑的热亚矮星双星。光谱观测结果与中间He-sdOB恒星一致，有效温度为$T_{\rm eff}=42,400\pm300$ K，表面重力为$\log(g)=5.77\pm0.05$。高信噪比的GTC+HiPERCAM光变曲线主要由sdOB星的椭球形变形和吸积盘对sdOB的蚀。我们推断一个低质量的热亚矮星施主的质量为$M_{\rm sdOB}=0.337\pm0.015$ M $_\odot$和一个白矮星吸积体的质量为$M_{\rm WD}=0.545\pm0.020$ M $_\odot$。理论双星模型表明，当$2.5-2.8$ M $_\odot$恒星在穿越赫兹斯普林隙时失去了它的包络线时，在一个共同的包络线阶段形成了热的亚矮星。为了匹配其当前的$P_{\rm orb}$，$T_{\rm eff}$，$\log(g)$和质量，我们估计后共同包络周期$P_{\rm orb}\approx150$分钟，并发现sdOB星目前正在进行氢壳燃烧。我们估计，热亚矮星将成为一个白矮星与厚氦层的$\approx0.1$ M $_\odot$和将合…
Revisiting atmospheric Roche lobe overflow in symbiotic binaries
Yunnan Observatories, Chinese Academy of Sciences (CAS)（中国科学院云南天文台）；International Centre of Supernovae (ICESUN), Yunnan Key Laboratory of Supernova Research（超新星国际中心（ICESUN），云南省超新星研究重点实验室）；University of Chinese Academy of Sciences（中国科学院大学）；Department of Physics, University of Alberta（阿尔伯塔大学物理系）；London Institute of Stellar Astrophysics（伦敦恒星天体物理学研究所）；University of Oxford, St Edmund Hall（牛津大学圣埃德蒙学堂）；Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences（波兰科学院尼古拉·哥白尼天文中心）
FQ Circini: An Ordinary Nova with a High-mass B1 V(n)(e) Companion Whose Decretion Disk Transfers Mass to the White Dwarf via Roche-Lobe Overflow
Louisiana State University（路易斯安那州立大学）；American Association of Variable Star Observers（变星观测者协会）；Variable Stars South, Royal Astronomical Society of New Zealand（南半球变星，新西兰皇家天文学会）；Centre for Astrophysics, University of Southern Queensland（南昆士兰大学天体物理中心）；Department of Astrophysics, American Museum of Natural History（美国自然历史博物馆天体物理学系）；South African Astronomical Observatory（南非天文台）；Southern African Large Telescope（南非大型望远镜）；University of Southern Queensland（南昆士兰大学）；Vatican Observatory Research Group, University of Arizona（亚利桑那大学梵蒂冈天文台研究组）
We present ULTRACAM multiband optical photometry of two transitional millisecond pulsars, PSR J1023+0038 and PSR J1227$-$4853, taken while both were in their radio pulsar states. The light curves show significant asymmetry about the flux maxima in all observed bands, suggesting an asymmetric source of heating in the system. We model the light curves using the Icarus binary code, using models with an additional "hot spot" heating contribution and an anisotropic heat redistribution model to treat the asymmetry. Our modelling reveals companion stars with under-filled Roche lobes in both PSRs J102…
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 …
We present the discovery of the second binary with a Roche lobe-filling hot subdwarf transferring mass to a white dwarf (WD) companion. This 56 minute binary was discovered using data from the Zwicky Transient Facility. Spectroscopic observations reveal an He-sdOB star with an effective temperature of $T_{\rm eff}=33,700\pm1000$ K and a surface gravity of $log(g)=5.54\pm0.11$. The GTC+HiPERCAM light curve is dominated by the ellipsoidal deformation of the He-sdOB star and shows an eclipse of the He-sdOB by an accretion disk as well as a weak eclipse of the WD. We infer a He-sdOB mass of $M_{\r…
Binaries consisting of a hot subdwarf star and an accreting white dwarf (WD) are sources of gravitational wave radiation at low frequencies and possible progenitors of type Ia supernovae if the WD mass is large enough. Here, we report the discovery of the third binary known of this kind: it consists of a hot subdwarf O (sdO) star and a WD with an orbital period of 3.495 hours and an orbital shrinkage of 0.1 s in 6 yr. The sdO star overfills its Roche lobe and likely transfers mass to the WD via an accretion disk. From spectroscopy, we obtain an effective temperature of $T_{\mathrm{eff}}=54\,24…
In our earlier Paper I we showed that the accretion disc radius of the dwarf nova HT Cas in its quiescent state has not changed significantly during many years of observations. It has remained consistently large, close to the tidal truncation radius. This result is inconsistent with the modern understanding of the evolution of the disc radius through an outburst cycle. Here we present a new set of time-resolved spectra of HT Cas obtained in the middle of its 2017 superoutburst. We used Doppler tomography to map emission structures in the system, which we compared with those detected in quiesce…
Eta Carinae's historical light curve: evidence for cyclic Roche lobe overflow from the primary star
Instituto de Astr., Geofísica e Ciências Atmosf. da USP（圣保罗大学天文、地球物理和大气科学研究所）；Escola de Ciências e Tecnologia, Universidade Federal do Rio Grande do Norte（北里奥格兰德联邦大学科学与技术学院）；Instituto Nac. de Pesq. Espaciais/MCTI（国家空间研究院/科技部）；Instituto de Astrofísica de La Plata (CCT La Plata - CONICET/UNLP)（拉普拉塔天体物理研究所（拉普拉塔中心-阿根廷国家科学研究委员会/拉普拉塔国立大学））；Laboratório Nacional de Astrofísica（国家天体物理实验室）；Max Planck Institute for Radio Astronomy（马克斯·普朗克射电天文研究所）
WOCS 4540 is the longest orbital period ($P_{\rm orb}=3030$ days) blue straggler (BSS) - white dwarf (WD) pair in the old open cluster NGC 188 . It also contains one of the most luminous BSS in the cluster. Prior \textit{Hubble Space Telescope} COS spectroscopy measured a WD mass of 0.53 $M_{\odot}$, indicative of a carbon-oxygen WD and suggesting previous mass transfer from an asymptotic branch giant (AGB). Detailed modeling of the system evolution, including red giant branch phase wind mass transfer, AGB wind Roche-lobe overflow and regular Roche-lobe overflow, is done with Modules for Exper…
We explore the effect of anisotropic wind driving on the properties of accretion onto black holes in close binaries. We specifically focus on line-driven winds, which are common in high-mass X-ray binaries. In close binary systems, the tidal force from the companion star can modify the wind structure in two different ways. One is the reduction of wind terminal velocity due to the weaker effective surface gravity. The other is the reduction in mass flux due to gravity darkening. We incorporate these effects into the so-called CAK theory in a simple way and investigate the wind flow around the a…
The role of mass transfer efficiency in stability criteria: Implementation in SEVN and a test on blue stragglers and binary compact objects
INAF – Osservatorio Astrofisico di Arcetri（意大利国家天体物理研究所阿切尔西天文台）；Instituto de Astrofísica de Canarias（加那利群岛天体物理研究所）；Universidad de La Laguna（拉古纳大学）；Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (UB)（巴塞罗那大学宇宙科学研究所）；Universität Heidelberg, Zentrum für Astronomie (ZAH), Institut für Theoretische Astrophysik（海德堡大学天文学中心理论天体物理研究所）；Universität Heidelberg, Interdiszipliäres Zentrum für Wissenschaftliches Rechnen（海德堡大学跨学科科学计算中心）；Dipartimento di Fisica e Astronomia Galileo Galilei, Università di Padova（帕多瓦大学伽利略·伽利莱物理与天文学系）；INFN, Sezione di Padova（意大利国家核物理研究所帕多瓦分部）；Dipartimento di Fisica e Astronomia, Università degli Studi di Bologna（博洛尼萨大学物理与天文学系）
