分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jie Lin
Chengyuan Wu
Xiaofeng Wang
Péter Németh
Herang Xiong
Tao Wu
Alexei Filippenko
Yongzhi Cai
Thomas Brink
Shengyu Yan
Xiangyun Zeng
Yangpin Luo
Danfeng Xiang
Jujia Zhang
Weikang Zheng
Yi Yang
Jun Mo
Gaobo Xi
Jicheng Zhang
Abdusamatjan Iskandar
摘要： Blue large-amplitude pulsators (BLAPs) represent a new and rare class of hot pulsating stars with unusually large amplitudes and short periods. Up to now, only 24 confirmed BLAPs have been identified from more than one billion monitored stars, including a group with pulsation period longer than $\sim 20$ min (classical BLAPs, hereafter) and the other group with pulsation period below $\sim 8$ min. The evolutionary path that could give rise to such kinds of stellar configurations is unclear. Here we report on a comprehensive study of the peculiar BLAP discovered by the Tsinghua University - Ma Huateng Telescopes for Survey (TMTS), TMTS J035143.63+584504.2 (TMTS-BLAP-1). This new BLAP has an 18.9 min pulsation period and is similar to the BLAPs with a low surface gravity and an extended helium-enriched envelope, suggesting that it is a low-gravity BLAP at the shortest-period end. In particular, the long-term monitoring data reveal that this pulsating star has an unusually large rate of period change, P_dot/P=2.2e-6/yr. Such a significant and positive value challenges its origins from both helium-core pre-white-dwarfs and core helium-burning subdwarfs, but is consistent with that derived from shell helium-burning subdwarfs. The particular pulsation period and unusual rate of period change indicate that TMTS-BLAP-1 is at a short-lived (~10^6 yr) phase of shell-helium ignition before the stable shell-helium burning; in other words, TMTS-BLAP-1 is going through a "Hertzsprung gap" of hot subdwarfs.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We present the first results from our ongoing project to study extremely low mass (ELM) white dwarfs (WDs) ($M$ $\leq$ 0.3$M_{\sun}$) with the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) spectra. Based on the LAMOST DR8 spectral database, we analyzed 136 ELM WD candidates selected from $\it Gaia$ DR2 data and 12 known objects previously identified by the ELM Survey. The atmospheric parameters and radial velocities of these stars were obtained by fitting the LAMOST low-resolution spectra. After comparing the atmospheric parameters of the 12 known objects from this work to the results reported by the ELM Survey, we demonstrated the potential of LAMOST spectra in probing into the nature of ELM WDs. Based on the atmospheric parameters and $\it Gaia$ EDR3 data, we identified 21 new high-probability ELM WDs with masses $M$ $\leq$ 0.3$M_{\sun}$ and parallax estimates that agree to within a factor of 3. Two of them, J0338+4134 and J1129+4715, show significant radial velocity variability and are very likely to be binary systems containing at least one ELM WD.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jiangdan Li
Christopher A. Onken
Christian Wolf
Péter Németh
Mike Bessell
Zhenwei Li
Xiaobin Zhang
Jiao Li
Luqian Wang
Lifang Li
Yangping Luo
Hailiang Chen
Kaifan Ji
Xuefei Chen
Zhanwen Han
摘要： 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 $T_{\mathrm{eff}}=54\,240\pm1\,840$ K and a surface gravity of $\log{g}=4.841\pm0.108$ for the sdO star. From the light curve analysis, we obtain a sdO mass of $M_{\mathrm{sdO}}=0.55$ ${\mathrm{M_{\odot}}}$ and a mass ratio of $q=M_{\mathrm{WD}}/M_{\mathrm{sdO}}=0.738\pm0.001$. Also, we estimate that the disk has a radius of $\sim 0.41R_\odot$ and a thickness of $\sim 0.18R_\odot$. The origin of this binary is probably a common envelope ejection channel, where the progenitor of the sdO star is either an RGB star or, more likely, an early AGB star; the sdO star will subsequently evolve into a WD and merge with its WD companion, likely resulting in an R CrB star. The outstanding feature in the spectrum of this object is strong Ca H&K lines, which are blueshifted by $\sim$200 km/s and likely originate from the recently ejected common envelope, and we estimated that the remnant CE material in the binary system has a density $\sim 6\times 10^{-10} {\rm g/cm^3}$.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jie Lin
Chengyuan Wu
Xiaofeng Wang
Péter Németh
Herang Xiong
Tao Wu
Alexei Filippenko
Yongzhi Cai
Thomas Brink
Shengyu Yan
Xiangyun Zeng
Yangpin Luo
Danfeng Xiang
Jujia Zhang
Weikang Zheng
Yi Yang
Jun Mo
Gaobo Xi
Jicheng Zhang
Abdusamatjan Iskandar
摘要： Blue large-amplitude pulsators (BLAPs) represent a new and rare class of hot pulsating stars with unusually large amplitudes and short periods. Up to now, only 24 confirmed BLAPs have been identified from more than one billion monitored stars, including a group with pulsation period longer than $\sim 20$ min (classical BLAPs, hereafter) and the other group with pulsation period below $\sim 8$ min. The evolutionary path that could give rise to such kinds of stellar configurations is unclear. Here we report on a comprehensive study of the peculiar BLAP discovered by the Tsinghua University - Ma Huateng Telescopes for Survey (TMTS), TMTS J035143.63+584504.2 (TMTS-BLAP-1). This new BLAP has an 18.9 min pulsation period and is similar to the BLAPs with a low surface gravity and an extended helium-enriched envelope, suggesting that it is a low-gravity BLAP at the shortest-period end. In particular, the long-term monitoring data reveal that this pulsating star has an unusually large rate of period change, P_dot/P=2.2e-6/yr. Such a significant and positive value challenges its origins from both helium-core pre-white-dwarfs and core helium-burning subdwarfs, but is consistent with that derived from shell helium-burning subdwarfs. The particular pulsation period and unusual rate of period change indicate that TMTS-BLAP-1 is at a short-lived (~10^6 yr) phase of shell-helium ignition before the stable shell-helium burning; in other words, TMTS-BLAP-1 is going through a "Hertzsprung gap" of hot subdwarfs.
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