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arXiv 2402.03584astro-ph.SRastro-ph.HE
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周期下限以下、具有热伴星的贫氦ER UMa型矮新星

Helium-deficient ER UMa-type dwarf nova below the period minimum with a hot secondary

Youngdae Lee, Dae-Sik Moon, Sang Chul Kim, Hong Soo Park, Yuan Qi Ni

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12 pages, 5 figures, accepted for publication in ApJ
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AI总结：

发现周期下限以下、具有热伴星的贫氦ER UMa型矮新星KSP-OT-201712a，其爆发行为与伴星温度首次被测量，表明跨越周期下限的演化伴随大量质量转移。

摘要：

我们利用韩国微引力透镜望远镜网络的高频次、多色观测，发现了一颗特殊的矮新星KSP-OT-201712a。KSP-OT-201712a在静止期表现出罕见的爆发，以及对于轨道周期为58.75 ± 0.02分钟的周期下限以下的矮新星而言，具有强烈的Hα发射。爆发周期在静止期内约为6.6天，但在静止期外增加到约15天。在静止期内的爆发中，B-V和V-I颜色分别随着爆发光度的增加和减少而变蓝和变红，而在静止期外则呈相反方向演化。源中存在的强双峰Hα和弱He I发射线（He/H通量比为0.27），以及Mg b和Na D吸收线，使得我们估算出其伴星的Teff约为4570 ± 40 K，[Fe/H]约为0.06 ± 0.15 dex，log g约为4.5 ± 0.1。KSP-OT-201712a是周期下限以下第二颗贫氦矮新星，而其伴星的温度是此类天体首次被测量。我们将其认定为ER UMa型矮新星，这表明矮新星跨越周期下限的演化伴随着大量的质量转移。伴星的高温度表明，该系统在其伴星处于主序年龄约93%时开始了质量转移。该系统将在其氢包层耗尽后，在爆炸为Ia型超新星之前，演化为氦激变变星或AM CVn型天体。

英文摘要：

We present the discovery of a peculiar dwarf nova KSP-OT-201712a using high-cadence, multi-color observations made with the Korea Microlensing Telescope Network. KSP-OT-201712a exhibits a rare presence of outbursts during standstills as well as strong H$α$ emission for a dwarf nova below the period minimum with an orbital period of 58.75 $\pm$ 0.02 minutes. The outburst cycles are ~ 6.6 days within standstills but increase to ~ 15 days outside of them. Both B-V and V-I colors become bluer and redder as the outburst luminosities increase and decrease, respectively, for the outburst within standstill, while they evolve in the opposite directions outside of the standstills. The presence of strong double-peaked H$α$ and weak He I emission lines with He/H flux ratio of 0.27, together with absorption lines of Mg b and Na D in the source, leads to the estimation Teff ~ 4570 $\pm$ 40 K, [Fe/H] ~ 0.06 $\pm$ 0.15 dex, and log g ~ 4.5 $\pm$ 0.1 for its secondary. KSP-OT-201712a is the second He-deficient dwarf nova below the period minimum, while the temperature of the secondary is measured for the first time in such objects. We identify it to be an ER UMa type dwarf nova suggesting that the evolution of dwarf novae across the period minimum is accompanied by large mass transfers. The high temperature of the secondary indicates that the system started its mass transfer when the secondary was about 93$\%$ of its main sequence age. The system will evolve to a helium cataclysmic variable or to AM CVn once its hydrogen envelope is exhausted before it explodes as a Type Ia supernova.

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