AI 中文总结
本研究基于盖亚DR3碳星星表，分析银河系及近邻星系的碳巨星，测得相关空间密度、标高，区分碳AGB星与低光度碳巨星的分布特征，为碳星的起源与应用提供关键观测依据。
AI 中文摘要
经典碳星（大气C/O >1）是渐近巨星分支（AGB）恒星，在热脉冲AGB阶段通过第三次 dredge-up 过程变得富碳。不过碳星也存在于红巨星和主序星中，这类碳星的碳被认为来自前身AGB伴星的双星质量转移。我们使用Roulston等人（2025）提供的盖亚DR3中G<16.5等的全天碳星星表，研究银河系、其球状星团及近邻本星系群星系中均匀、高置信度的碳巨星样本。我们在大麦哲伦云（LMC）中识别出6937颗碳巨星，小麦哲伦云（SMC）中2148颗，与人马座矮椭球星系相关的有219颗，后者已知样本量几乎增至原来的四倍。我们通过X射线对应体识别出多个候选碳共生星。LMC中碳AGB星的绝对J波段星等均值M⁰_J=-6.30，SMC中为-6.15，与Ripoche等人（2020）通过测光推导的值吻合度很高，进一步证实碳AGB星可作为距离指示器的实用性。从4276颗M_G<0且|b|>5°的银河系碳巨星，我们测得本地银盘空间密度n₀=11±0.5×10⁻⁸ pc⁻³，标高H_z=257±4 pc。低光度碳巨星的盖亚DR3 RUWE值显著高于碳AGB星，这有力证明它们大多是外禀的质量转移后系统，可能是演化后的矮碳星。碳AGB星更紧密地分布在银盘内，且在R≲7 kpc内罕见，与银河系年龄和金属丰度梯度一致；而低光度碳巨星标高更大，需要额外的银晕成分。
英文摘要
Classical carbon stars (atmospheric C/O >1) are asymptotic giant branch (AGB) stars that become carbon-rich through third dredge-up during the thermally pulsing AGB phase. However, carbon stars also occur among red giants and main-sequence stars, where the carbon is thought to originate from binary mass transfer from a former AGB companion. Using the all-sky catalog of G<16.5 mag Gaia DR3 carbon stars from Roulston et al. (2025), we investigate a uniform, high-confidence sample of carbon giants in the Milky Way, its globular clusters, and nearby Local Group galaxies. We identify 6937 carbon giants in the Large Magellanic Cloud, 2148 in the Small Magellanic Cloud, and 219 associated with the Sagittarius dwarf spheroidal, nearly quadrupling the previously known sample in the latter. We identify several candidate carbon symbiotic stars through their X-ray counterparts. The mean absolute C-AGB magnitude, $M^0_J=-6.30$ in the LMC and -6.15 in the SMC, agrees closely with the photometrically derived values of Ripoche et al. (2020), reinforcing the utility of carbon AGB stars as distance indicators. From 4276 Galactic carbon giants with $M_G<0$ and $|b|>5^\circ$, we measure a local disk space density of $n_0=11\pm0.5\times10^{-8},\mathrm{pc}^{-3}$ and a scale height of $H_z=257\pm4$ pc. Lower-luminosity carbon giants exhibit significantly larger Gaia DR3 RUWE values than C-AGB stars, providing strong evidence that most are extrinsic post-mass-transfer systems, likely evolved dwarf carbon stars. C-AGB stars are more tightly confined to the Galactic disk and are rare inside $R\lesssim7$ kpc, consistent with Galactic age and metallicity gradients, whereas the lower-luminosity carbon giants have a larger scale height and require an additional halo component.
Comments27 pages, 12 figures, 3 tables, submitted to ApJ. Comments welcome
