arXiv 1602.001422016-02astro-ph.SR

两个新的脉动低质量前白矮星或SX凤凰星？*

Two new pulsating low-mass pre-white dwarfs or SX Phenix stars?*

M. A. Corti, A. Kanaan, A. H. Córsico, S. O. Kepler, L. G. Althaus, D. Koester, J. P. Sánchez Arias

备注：: 5 pages, 5 figures, 1 table, accepted for publication in A&AL
DOI：: 10.1051/0004-6361/201527458

摘要：

上下文在低质量恒星中发现脉动，为利用星震学工具探测其内部并确定其演变提供了机会。目标。我们的目的是分析SDSSJ 145847.02 $+$ 070754.46和SDSSJ 173001.94 $+$ 070600.25的高速测光，并发现亮度变化。为了在$T_{\rm eff} - \log g$图中定位这些恒星，我们将光学光谱（SDSS）与来自模型大气的合成非磁性光谱相匹配。方法.为了进行这项研究，我们使用了我们在阿根廷CASLEO的2.15米望远镜获得的这些恒星的光度数据。我们分析了它们的光变曲线，并应用离散傅里叶变换来确定脉动频率。最后，我们在$T_{\rm eff} - \log g$图中比较了这两颗恒星，与已知的两颗前白矮星，七颗脉动前ELM白矮星，$δ$ Scuti和SX Phe星。结果我们报告了在SDSSJ 145847.02 $+$ 070754.46和SDSSJ 173001.94 $+$ 070600.25中发现的脉动。计算出它们的有效温度和表面重力分别为：$T_{\rm eff}$ = 7 972 $\pm$ 200 K，$\log g$ = 4.25 $\pm$ 0.5和$T_{\rm eff}$ = 7 925 $\pm$ 200 K，$\log g$ = 4.25 $\pm$ 0.5。根据这些参数，这些新的脉动低质量恒星可以被识别为ELM白矮星（~ 0.17 Mo）或更大质量的SX Phe恒星。我们确定SDSSJ 145847.02 $+$ 070754.46的脉动周期为3 278.7和1 633.9 s，SDSSJ 173001.94 $+$ 070600.25的脉动周期为3 367.1 s。这两个新天体与Maxted等人（2013，2014）的天体一起表明，在低质量白矮星演化的后期可能存在一个新的不稳定域，尽管它们与SX Phe星的一致性不能被排除。

英文摘要：

Context. The discovery of pulsations in low-mass stars opens an opportunity for probing their interiors and to determine their evolution, by employing the tools of asteroseismology. Aims. We aim to analyze high-speed photometry of SDSSJ145847.02$+$070754.46 and SDSSJ173001.94$+$070600.25 and discover brightness variabilities. In order to locate these stars in the $T_{\rm eff} - \log g$ diagram we fit optical spectra (SDSS) with synthetic non-magnetic spectra derived from model atmospheres. Methods. To carry out this study, we used the photometric data obtained by us for these stars with the 2.15m telescope at CASLEO, Argentina. We analyzed their light curves and we apply the Discrete Fourier Transform to determine the pulsation frequencies. Finally, we compare both stars in the $T_{\rm eff} - \log g$ diagram, with known two pre-white dwarfs, seven pulsating pre-ELM white dwarf stars, $δ$ Scuti and SX Phe stars. Results. We report the discovery of pulsations in SDSSJ145847.02$+$070754.46 and SDSSJ173001.94$+$070600.25. We determine their effective temperature and surface gravity to be $T_{\rm eff}$ = 7 972 $\pm$ 200 K, $\log g$ = 4.25 $\pm$ 0.5 and $T_{\rm eff}$ = 7 925 $\pm$ 200 K, $\log g$ = 4.25 $\pm$ 0.5, respectively. With these parameters these new pulsating low-mass stars can be identified with either ELM white dwarfs (with ~ 0.17 Mo) or more massive SX Phe stars. We identified pulsation periods of 3 278.7 and 1 633.9 s for SDSSJ145847.02$+$070754.46 and a pulsation period of 3 367.1 s for SDSSJ173001.94$+$070600.25. These two new objects together with those of Maxted et al. (2013, 2014) indicate the possible existence of a new instability domain towards the late stages of evolution of low-mass white dwarf stars, although their identification with SX Phe stars cannot be discarded.

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