分类： 天文学 >> 天文学 提交时间： 2023-02-19
Matthew J. Green
Dan Maoz
Tsevi Mazeh
Simchon Faigler
Sahar Shahaf
Roy Gomel
Kareem El-Badry
Hans-Walter Rix
摘要： We present a homogeneously-selected sample of 15779 candidate binary systems with main sequence primary stars and orbital periods shorter than 5 days. The targets were selected from TESS full-frame image lightcurves on the basis of their tidally-induced ellipsoidal modulation. Spectroscopic follow-up suggests a sample purity of $83 \pm 13$ per cent. Injection-recovery tests allow us to estimate our overall completeness as $28 \pm 3$ per cent with $P_\mathrm{orb} < 3$ days and to quantify our selection effects. We estimate that $39 \pm 4$ per cent of our sample are contact binary systems, and we disentangle the period distributions of the contact and detached binaries. We derive the orbital period distribution of the main sequence binary population at short orbital periods, finding a distribution continuous with the log-normal distribution previously found for solar-type stars at longer periods, but with a significant steepening at $P_\mathrm{orb} \lesssim 3$ days, and a pile-up of contact binaries at $P_\mathrm{orb} \approx 0.4$ days. Companions in the period range 1--5 days are found to be an order of magnitude more frequent around stars hotter than $\approx 6250 K$ (the Kraft break) when compared to cooler stars, suggesting that magnetic braking plays an important role in shaping the temperature and period distributions. We detect resolved tertiary companions to $9.0 \pm 0.2$ per cent of our binaries with a median separation of 3200 AU. The frequency of tertiary companions rises to $29 \pm 5$ per cent among the systems with the shortest ellipsoidal periods. This large binary sample with quantified selection effects will be a powerful resource for future studies of detached and contact binary systems with $P_\mathrm{orb} < 5$ days.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Tsevi Mazeh
Simchon Faigler
Dolev Bashi
Sahar Shahaf
Niv Davidson
Matthew Green
Roy Gomel
Dan Maoz
Amitay Sussholz
Subo Dong
Haotong Zhang
Jifeng Liu
Song Wang
Ali Luo
Zheng Zheng
Na'ama Hallakoun
Volker Perdelwitz
David W. Latham
Ignasi Ribas
David Baroch
摘要： We have identified 2XMM J125556.57+565846.4, at a distance of 600 pc, as a binary system consisting of a normal star and a probable dormant neutron star. Optical spectra exhibit a slightly evolved F-type single star, displaying periodic Doppler shifts with a 2.76-day Keplerian circular orbit, with no indication of light from a secondary component. Optical and UV photometry reveal ellipsoidal variations with half the orbital period, due to the tidal deformation of the F star. The mass of the unseen companion is constrained to the range $1.1$--$2.1\,M_{\odot}$ at $3\sigma$ confidence, with the median of the mass distribution at $1.4\,M_{\odot}$, the typical mass of known neutron stars. A main-sequence star cannot masquerade as the dark companion. The distribution of possible companion masses still allows for the possibility of a very massive white dwarf. The companion itself could also be a close pair consisting of a white dwarf and an M star, or two white dwarfs, although the binary evolution that would lead to such a close triple system is unlikely. Similar ambiguities regarding the certain identification of a dormant neutron star are bound to affect most future discoveries of this type of non-interacting system. If the system indeed contains a dormant neutron star, it will become, in the future, a bright X-ray source and afterwards might even host a millisecond pulsar.
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