太阳10 pc内体积完备的M、F、G和K型恒星的平均X射线光谱
The average X-ray spectrum of the volume-complete M-, F-, G-, and K-type star sample within 10 pc of the Sun
AI总结：
利用eROSITA巡天数据，通过堆叠归一化光谱，获得了10 pc内M型和FGK型恒星的平均X射线光度与光谱模型，发现早M型恒星平均光度低于中晚M型。
摘要：
F、G、K和M型恒星是银河系中最丰富的恒星群体，预计对银河系的弥散X射线辐射有贡献。然而，由于它们微弱的X射线光度，其内在的平均X射线光谱仍然受到较差的约束，使得它们在银河系X射线背景中的集体作用不确定。我们利用光谱-伦琴-伽马（SRG）任务上eROSITA全天巡天（eRASS:4）的数据，分析了太阳10 pc内体积完备的M型（M0--M6）和FGK型恒星样本。个体光谱按曝光时间和距离归一化，并堆叠以产生代表性平均值。距离归一化的发射测量给出M型恒星在0.2--2.0 keV的平均X射线光度为$(2.6 \pm0.1) imes 10^{27}$ erg/s，F、G和K型恒星为$(15\pm3) imes 10^{27}$ erg/s。平均光谱可以用三个和两个热模型的组合很好地描述。拟合的温度和丰度在M型星子类中保持一致，而早M型星的平均光度出乎意料地低于中晚M型星。这些结果为邻近恒星的集体X射线性质提供了新见解，并激发了探索其与银河系未分辨软X射线背景之间联系的动机。
英文摘要：
F, G, K and M type stars are the most abundant stellar population in the Milky Way and are expected to contribute to its diffuse X-ray emission. Yet their intrinsic average X-ray spectrum remains poorly constrained due to their faint X-ray luminosities, leaving their collective role in the X-ray background of the Milky Way uncertain. We analysed the volume-complete sample of M- (M0--M6) and FGK-type stars within 10 pc of the Sun using data from eROSITA all-sky survey aboard the Spectrum-Roentgen-Gamma (SRG) mission (eRASS:4). Individual spectra were normalized by exposure and distance and stacked to produce representative averages. The distance-normalized emission measures yield an average X-ray luminosity of $(2.6 \pm0.1)\times 10^{27}$ erg/s for M-type stars, and $(15\pm3)\times 10^{27}$ erg/s for F, G and K-type stars in 0.2--2.0 keV. The average spectra could be well described by a sum of three and two thermal models. Fitted temperatures and abundances remain consistent across M-star subgroups, while early-M stars are surprisingly on average less luminous than mid/late-M types. These results offer new insights into the collective X-ray properties of nearby stars, and provide motivation to explore the link with the unresolved soft X-ray background of the Galaxy.
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