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arXiv 2001.02253astro-ph.SR
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特殊造父变星V473 Lyr的X射线观测确定了一个低质量的伴星

X-ray Observations of the Peculiar Cepheid V473 Lyr Identify A Low-Mass Companion

Nancy Remage Evans, Ignazio Pillitteri, Laszlo Molnar, Laszlo Szabados, Emese Plachy, Robert Szabo, Scott Engle, Ed Guinan, Scott Wolk, H. Moritz Guenther, Hild… 展开作者

Nancy Remage Evans, Ignazio Pillitteri, Laszlo Molnar, Laszlo Szabados, Emese Plachy, Robert Szabo, Scott Engle, Ed Guinan, Scott Wolk, H. Moritz Guenther, Hilding Neilson, Massimo Marengo, Lynn D. Matthews, Sofia Moschou, Jeremy J. Drake, Vinay Kashyap, Pierre Kervella, Tamas Tordai, Peter Somogyi, Gilbert Burki

摘要:

天琴座V473是一颗典型的造父变星,其独特之处在于它的振幅变化周期约为3.3年,被认为与天琴座RR型星的Blazhko变化相似。我们获得了这颗恒星的{ \it XMM-Newton}观测,以跟踪先前的X射线探测。与造父星$δ$本身在最大半径附近看到的X射线爆发和快速下降不同,V473 Lyr中的X射线通量在观测所涵盖的脉动周期的三分之一内保持恒定。因此,X射线很可能不是由脉动周期周围的变化产生的。X射线光谱是软的(kT = 0.6 keV),X射线的性质与年轻的低质量伴星一致。以前没有证据表明在径向速度或{ \it盖亚}和{ \it依巴谷}自行中有伴星存在。虽然这排除了非常接近或非常遥远的伴星,但距离在30到300 AU之间的双星伴星是可能的。这是一个X射线观测的例子,揭示了低质量伴星的证据,这对完成造父变星的质量比统计很重要。此外,一颗年轻的X射线亮伴星的发现进一步表明造父变星(主星)是一颗第I星族恒星,尽管它的脉动行为与其他经典造父变星不同。

英文摘要:

V473 Lyr is a classical Cepheid which is unique in having substantial amplitude variations with a period of approximately 3.3 years, thought to be similar to the Blazhko variations in RR Lyrae stars. We obtained an {\it XMM-Newton} observation of this star to followup a previous detection in X-rays. Rather than the X-ray burst and rapid decline near maximum radius seen in $δ$ Cephei itself, the X-ray flux in V473 Lyr remained constant for a third of the pulsation cycle covered by the observation. Thus the X-rays are most probably not produced by the changes around the pulsation cycle. The X-ray spectrum is soft (kT = 0.6 keV), with X-ray properties which are consistent with a young low mass companion. Previously there was no evidence of a companion in radial velocities or in {\it Gaia} and {\it Hipparcos} proper motions. While this rules out companions which are very close or very distant, a binary companion at a separation between 30 and 300 AU is possible. This is an example of an X-ray observation revealing evidence of a low mass companion, which is important in completing the mass ratio statistics of binary Cepheids. Furthermore, the detection of a young X-ray bright companion is a further indication that the Cepheid (primary) is a Population I star, even though its pulsation behavior differs from other classical Cepheids.

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