分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： A mass paucity of compact objects in the range of $\sim 2-5 ~M_\odot$ has been suggested by X-ray binary observations, namely, the "lower mass gap". Gravitational wave detections have unlocked another mass measurement method, and aLIGO/Virgo has observed some candidates in the gap. We revisit the numerical simulations on the core-collapse supernovae (CCSNe) for $\sim 20-40~M_\odot$ progenitor stars with differently initial explosion energies. As a result, the lower explosion energy naturally causes more efficient fallback accretion for low-metallicity progenitors, and then the newborn black holes (BHs) in the center of the CCSNe can escape from the gap, but neutron stars cannot easily collapse into BHs in the gap; nevertheless, the final remnants of the solar-metallicity progenitors stick to the gap. If we consider that only drastic CCSNe can be observed and that those with lower explosion energies are universal, the lower mass gap can be reasonably built. The width and depth of the gap are mainly determined by the typical CCSN initial explosion energy and metallicity. One can expect that the future multi-messenger observations of compact objects delineate the shape of the gap, which might constrain the properties of the CCSNe and their progenitors.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Time-domain (TD) spectroscopic data from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) can provide accurate and high-cadence radial velocities (RVs). In this work, we search for binaries with compact components with RV monitoring method by using the LAMOST TD survey of four $K$2 plates. Three binary systems including an unseen white dwarf or neutron star are found. For each binary system, we estimate the stellar parameters of the visible star and orbital parameters, and finally calculate the binary mass function and the minimum mass of the unseen star. No obvious double-lined feature is seen from the LAMOST medium-resolution spectra of the three sources. In addition, we found no X-ray counterpart for all these sources but UV companions for two of them. Spectral disentangling also shows no additional component with optical absorption spectra, supporting that these systems contain compact objects.
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