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arXiv 2005.05539astro-ph.SRastro-ph.GA
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碳星作为标准蜡烛：I.麦哲伦星云中碳星的光度函数

Carbon stars as standard candles: I. The luminosity function of carbon stars in the Magellanic Clouds

Paul Ripoche, Jeremy Heyl, Javiera Parada, Harvey Richer

备注：
10 pages, 12 figures. Accepted for publication in MNRAS. Results unchanged. Correction of some uncertainty values in Eq. (24) and Eq. (25). Added some acknowledgements. Minor changes to the text. Codes and catalogues available on GitLab, see https://gitlab.com/pripoche/using-carbon-stars-as-standard-candles
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摘要：

本文的目标是推导出一个碳星光度函数，它最终将被用来确定星系到$50$ - $60$ Mpc的距离，从而得出哈勃常数的值。冷的N型碳星比富氧星呈现出更红的近红外颜色。利用2微米全天巡天近红外测光和盖亚数据发布2，我们确定了麦哲伦云（MC）和银河系（MW）中的碳星。MC中的碳星在近红外（$(J-K_s)_0$，$M_J$）色星等图中呈现出明显的水平特征。我们建立了一个色选模型（$1.4 < (J-K_s)_0 < 2$），并推导了色选碳星的光度函数。我们发现大麦云和小麦哲伦云在J波段的绝对星等和色散的中值分别为（$\bar{M_J} = -6.284 \pm 0.004$，$σ= 0.352 \pm 0.005$）和（$\bar{M_J} = -6.160 \pm 0.015$，$σ= 0.365 \pm 0.014$）。MC之间的差异可以用小麦哲伦云较低的金属丰度来解释，但在任何情况下，它都提供了可以用这种技术确定距离的星系类型的限制。为了解释金属丰度效应，我们开发了一个复合星等，命名为C，其中两个MC的误差加权平均C星等相等。多亏了下一代望远镜（JWST、ELT、TMT），才能在距离$50$ - $60$ Mpc的MC型星系中探测到碳星。最终的目标是最终尝试和改进哈勃常数的测量，同时探索与其价值相关的当前紧张局势。

英文摘要：

Our goal in this paper is to derive a carbon-star luminosity function that will eventually be used to determine distances to galaxies at $50$-$60$ Mpc and hence yield a value of the Hubble constant. Cool N-type carbon stars exhibit redder near-infrared colours than oxygen-rich stars. Using Two Micron All Sky Survey near-infrared photometry and the Gaia Data Release 2, we identify carbon stars in the Magellanic Clouds (MC) and the Milky Way (MW). Carbon stars in the MC appear as a distinct horizontal feature in the near-infrared ($(J-K_s)_0$, $M_J$) colour-magnitude diagram. We build a colour selection ($1.4 < (J-K_s)_0 < 2$) and derive the luminosity function of the colour-selected carbon stars. We find the median absolute magnitude and the dispersion, in the J band, for the Large Magellanic Cloud and the Small Magellanic Cloud to be, respectively, ($\bar{M_J} = -6.284 \pm 0.004$, $σ= 0.352 \pm 0.005$) and ($\bar{M_J} = -6.160 \pm 0.015$, $σ= 0.365 \pm 0.014$). The difference between the MC may be explained by the lower metallicity of the Small Magellanic Cloud, but in any case it provides limits on the type of galaxy whose distance can be determined with this technique. To account for metallicity effects, we developed a composite magnitude, named C, for which the error-weighted mean C magnitude of both the MC are equal. Thanks to the next generation of telescopes (JWST, ELT, TMT), carbon stars could be detected in MC-type galaxies at distances out to $50$-$60$ Mpc. The final goal is to eventually try and improve the measurement of the Hubble constant while exploring the current tensions related to its value.

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