[论文解读] Hot subdwarf binaries from the MUCHFUSS project - Analysis of 12 new systems and a study of the short-period binary population

Thomas Kupfer, S. Geier+7 more|Keele Research Repository (Keele University)|Jan 15, 2015

Stellar, planetary, and galactic studies参考文献 120被引用 47

一句话总结

本研究基于MUCHFUSS巡天发现了12个新的热亚矮星B型双星系统，给出了其轨道与大气参数，识别出其中三个系统可能拥有白矮星伴星，包括一颗罕见的低质量氦核心白矮星。研究揭示了伴星质量分布呈双峰特征，分别在0.1 M⊙（棕矮星/次恒星伴星）和0.4 M⊙（白矮星）处达到峰值，预测有16个系统将在一个哈勃时标内演化为激变双星，12个白矮星双星系统将在该时标内发生合并，其中包括潜在的Ia型超新星前身体和AM CVn型系统。

ABSTRACT

The project Massive Unseen Companions to Hot Faint Underluminous Stars from SDSS (MUCHFUSS) aims at finding hot subdwarf stars with massive compact companions like massive white dwarfs (M>1.0 M$_\odot$), neutron stars, or stellar-mass black holes. We present orbital and atmospheric parameters and put constraints on the nature of the companions of 12 close hot subdwarf B star (sdB) binaries found in the course of the MUCHFUSS project. The systems show periods between 0.14 and 7.4 days. Three systems most likely have white dwarf companions. SDSS J083006.17+475150.3 is likely to be a rare example of a low-mass helium-core white dwarf. SDSS J095101.28+034757.0 shows an excess in the infrared that probably originates from a third companion in a wide orbit. SDSS J113241.58-063652.8 is the first helium deficient sdO star with a confirmed close companion. This study brings to 142 the number of sdB binaries with orbital periods of less than 30 days and with measured mass functions. We present an analysis of the minimum companion mass distribution and show that it is bimodal. One peak around 0.1 M$_\odot$ corresponds to the low-mass main sequence and substellar companions. The other peak around 0.4 M$_\odot$ corresponds to the white dwarf companions. The derived masses for the white dwarf companions are significantly lower than the average mass for single carbon-oxygen white dwarfs. In a T$_{ m eff}$-log(g) diagram of sdB+dM companions, we find signs that the sdB components are more massive than the rest of the sample. The full sample was compared to the known population of extremely low-mass white dwarf binaries as well as short-period white dwarfs with main sequence companions. Both samples show a significantly different companion mass distribution. We calculate merger timescales and timescales when the companion will fill its Roche Lobe and the system evolves into a cataclysmic variable.

研究动机与目标

• 通过光谱分析识别并表征具有大质量致密伴星（包括白矮星、中子星或黑洞）的热亚矮星B型星。
• 测定12个新发现的周期在0.14至7.4天之间的sdB双星系统的轨道与大气参数。
• 研究这些系统中不可见伴星的性质，特别关注白矮星和低质量恒星伴星。
• 分析短周期sdB双星中伴星最小质量的分布特征，并评估其对双星演化及合并路径的启示。
• 识别将在一个哈勃时标内演化为激变双星、AM CVn型星或RCrB型星的系统，并评估其作为Ia型超新星前身体的潜力。

提出的方法

• 对SDSS巡天中12个热亚矮星B型星进行光谱监测，测量径向速度变化并推导轨道元素。
• 利用高分辨率光谱测定大气参数，获得有效温度（Teff）、表面重力（log g）和金属丰度。
• 根据径向速度振幅计算质量函数，以约束不可见伴星的最小质量。
• 将观测到的伴星质量分布与双星演化理论模型及已知的白矮星与激变双星种群进行比较。
• 通过红外测光及过量辐射分析，搜寻宽轨道中的第三颗伴星。
• 进行演化 timescale 建模，预测未来的演化路径，包括洛希瓣溢出与双星合并。

Figure 1: Radial velocity plotted against orbital phase. The RV data were phase folded with the most likely orbital periods and are plotted twice for better visualisation. The residuals are plotted below. The RVs were measured from spectra obtained with SDSS (squares), CAHA3.5m/TWIN (upward triangle

实验结果

研究问题

• RQ1 12个新发现的短周期热亚矮星B型双星系统中不可见伴星的性质是什么？
• RQ2 sdB双星中伴星最小质量的分布如何为双星演化模型提供信息，特别是关于白矮星和低质量恒星存在的影响？
• RQ3 在所识别的系统中，哪些系统有望在哈勃时标内演化为激变双星、AM CVn系统或RCrB型星？
• RQ4 是否存在潜在的Ia型超新星前身体系统？它们对单简并通道有何约束？
• RQ5 是否存在支持存在分级三合星系统的证据，如SDSS J095101.28+034757.0？它们如何影响轨道与演化建模？

主要发现

• 12个系统中有9个的伴星无法被明确分类，另有3个系统极有可能拥有白矮星伴星，包括SDSS J083006.17+475150.3，其伴星为罕见的低质量氦核心白矮星。
• 伴星最小质量分布呈双峰特征，分别在约0.1 M⊙（棕矮星/次恒星伴星）和约0.4 M⊙（白矮星伴星）处达到峰值，表明存在截然不同的演化路径。
• 推导出的白矮星伴星质量显著低于单个碳氧白矮星的平均值，暗示其具有独特的形成机制。
• 预测有16个系统将在一个哈勃时标内演化为激变双星，其中2个将具有棕矮星供体。
• 12个确认拥有白矮星伴星的系统将在一个哈勃时标内发生合并，其中包括2个可能演化为稳定AM CVn型双星的系统，以及2个潜在的Ia型超新星前身体系统。
• 另有8个系统预计会合并并形成RCrB型星或大质量C/O白矮星，具体取决于白矮星伴星的内部结构。

Figure 2: Radial velocity plotted against orbital phase (see Fig 1 ).