发表机构
Universidad de La Serena; Universidad Bernardo O’Higgins; University of North Florida; Zentrum für Astronomie der Universität Heidelberg, Astronomisches Rechen-Institut; Instituto de Astronomía, Universidad Nacional Autónoma de México; Universidad Andrés Bello; Instituto de Astronomía, Universidad Católica del Norte（拉塞雷纳大学; 贝尔纳多·奥希金斯大学; 北佛罗里达大学; 海德堡大学天文学中心，天文计算研究所; 墨西哥国立自治大学天文学研究所; 安德烈斯·贝略大学; 天主教学院北部天文学研究所）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究利用SDSS-V/BOSS光谱重新评估LMC中三个源，通过视向速度、等值宽度和SED拟合确认了新的O2型恒星，揭示了蓝色覆盖不足和星表关联模糊会隐藏最热大质量恒星。
AI 中文摘要
O2型恒星定义了正常O型恒星序列中最热的一端，但它们的识别需要蓝色光学氮诊断线，而许多巡天缺少这些诊断线。我们利用斯隆数字巡天V（SDSS-V）项目中使用重子振荡光谱巡天（BOSS）光谱仪获取的多历元光谱，重新评估了大麦哲伦云（LMC）中的三个明亮源：\wsi、\lh和\sk。我们测量了每次访问分辨的视向速度以及H、He和N的等值宽度（EWs），在共同的有效分辨率下与LMC O2模板进行稳健组合比较，并使用OSTAR2002光谱能量分布（SED）拟合和Gaia颜色-星等图（CMD）作为宽带检查。\wsi、\lh和\sk的加权$\log|{\rm EW}(\niv~\lambda4058)/{\rm EW}(\niii~\lambda4640)|$值分别为$0.64\pm0.29$、$0.48\pm0.23$和$0.34\pm0.44$。检测到\nv~$\lambda\lambda4604,4620$支持分别对\wsi和\lh采用的O2~If$^\ast$和O2~V--III分类。对于\sk，不确定的\niv/\niii比值和未检测到\nv表明其为O2--3~V--III型。弱的\hei~$\lambda4471$可能表明\wsi和\sk中存在未分辨的晚期型污染。\sk的视向速度显示出暗示性但非显著的变异性。OSTAR2002在45--55~kK范围内的拟合和Gaia CMD将所有三个源置于明亮的极早O型星区域；\wsi显示出强的中红外（MIR）过量，\lh几乎完全是光球层辐射，而\sk仅显示出适度的$3$--$8\\,\mu$m过量。BOSS光谱将\wsi和\lh添加到LMC极早O型星种群中，并将\sk识别为额外的O2--3源。这些案例表明，不完整的蓝色覆盖和模糊的星表关联如何隐藏最热的大质量恒星。
英文摘要
{O2 stars define the hottest end of the normal O-star sequence, but their identification requires blue-optical nitrogen diagnostics absent from many surveys.} {We reassess three luminous Large Magellanic Cloud (LMC) sources with multi-epoch Sloan Digital Sky Survey V (SDSS-V) spectroscopy obtained with the Baryon Oscillation Spectroscopic Survey (BOSS) spectrographs: \wsi, \lh, and \sk.} {We measure visit-resolved radial velocities and H, He, and N equivalent widths (EWs), compare robust combinations with LMC O2 templates at a common effective resolution, and use OSTAR2002 spectral energy distribution (SED) fits and a Gaia colour--magnitude diagram (CMD) as broad-band checks.} {The weighted $\log|{\rm EW}(\niv~\lambda4058)/{\rm EW}(\niii~\lambda4640)|$ values are $0.64\pm0.29$, $0.48\pm0.23$, and $0.34\pm0.44$ for \wsi, \lh, and \sk. The detection of \nv~$λ\lambda4604,4620$ supports the O2~If$^\ast$ and O2~V--III classifications adopted for \wsi\ and \lh, respectively. For \sk, the uncertain \niv/\niii\ ratio and non-detection of \nv\ motivate O2--3~V--III. Weak \hei~$\lambda4471$ may indicate unresolved later-type contamination in \wsi\ and \sk. The radial velocities of \sk\ show suggestive but non-significant variability. OSTAR2002 fits over 45--55~kK and the Gaia CMD place all three sources in the luminous very-early-O regime; \wsi\ shows a strong mid-infrared (MIR) excess, \lh\ is nearly photospheric, and \sk\ shows only a modest $3$--$8\,μ$m excess.} {The BOSS spectra add \wsi\ and \lh\ to the LMC very-early-O population and identify \sk\ as an additional O2--3 source. These cases show how incomplete blue coverage and ambiguous catalogue associations can conceal the hottest massive stars.}
CommentsLetter to the A&A Editor - Accepted for publication - 4 pages, 2 figures
