A Survey of Local Group Galaxies Currently Forming Stars. I. UBVRI Photometry of Stars in M31 and M33
A Survey of Local Group Galaxies Currently Forming Stars. I. UBVRI Photometry of Stars in M31 and M33
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DOI：
10.1086/503256
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发表时间：
2006-02
期刊：
影响因子：
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通讯作者：
P. Massey;P. Massey;Kirsty Olsen;P. Hodge;Shay Strong;Shay Strong;G. Jacoby;W. Schlingman;R. C. Smith
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文献类型：
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作者：
P. Massey;P. Massey;Kirsty Olsen;P. Hodge;Shay Strong;Shay Strong;G. Jacoby;W. Schlingman;R. C. Smith
我们展示使用 Kitt Peak 国家天文台 4 m 望远镜从 M31 和 M33 的马赛克图像获得的 UBVRI 光度测量。我们将详细描述我们的数据缩减和自动测光技术，因为我们很快将对其他本星系群进行类似的分析。本研究覆盖了沿 M31 长轴的 2.2 deg2 和 M33 上的 0.8 deg2，选择该范围是为了包括目前活跃于形成大质量恒星的所有区域。我们使用 Lowell 1.1 m 望远镜的光度测量来校准我们的数据，这种外部方法导致重叠视场的光度测量存在毫数量级的差异，从而在一定程度上保证了我们的光度测量的可靠性。最终目录分别包含 M31 和 M33 中的 371,781 颗恒星和 146,622 颗恒星，其中每颗恒星在（至少）B、V 和 R 通带中都有对应的恒星。我们的调查足够深入，在 21 星等（对应于质量大于 20 M⊙ 的恒星）下实现了 1%-2% 的光度测量，并在 U ∼ B ∼ V ∼ R ∼ I ∼ 23 星等下实现了 <10% 的误差。尽管按照某些标准，我们的典型视宁度仅为中等（0.″8-1.″4，中位数为 1.″0），但我们发现我们的星表来源与我们在 OB48（M31 中的一个拥挤区域）的哈勃太空望远镜 ACS 数据中看到的数据之间存在极好的对应关系。我们将我们的最终光度测定结果与其他人的光度测定结果进行比较，发现与 Magnier 等人的 M31 恒星 CCD 目录非常吻合，尽管我们的研究覆盖了两倍的面积，深度大约为 2 星等。与 M31 和 M33 的 CCD“直接”测量也非常吻合。其他人的摄影研究表现不佳，特别是在 V 的微弱末端，需要精确的背景扣除才能获得良好的光度测量。我们提供了通过光谱学确认为成员的恒星的交叉引用，并将这些恒星的位置与颜色星等图中的完整恒星集进行比较。虽然许多项目都需要后续光谱学，但我们证明了我们的光度测定法在区分 M31/M33 成员和前景银河系恒星方面的成功。最后，我们展示了 WIYN 3.5 m 望远镜一晚的光谱结果，检查了 M31 中可能最亮的成员。光谱确定了 34 个新确认的成员，包括 B-A 超巨星、M31 中已知最早的 O 星，以及光谱与天鹅座 P 相似的两个新的发光蓝色变星候选者。
We present UBVRI photometry obtained from Mosaic images of M31 and M33 using the Kitt Peak National Observatory 4 m telescope. We describe our data reduction and automated photometry techniques in some detail, as we will shortly perform a similar analysis of other Local Group galaxies. The present study covered 2.2 deg2 along the major axis of M31 and 0.8 deg2 on M33, chosen so as to include all of the regions currently active in forming massive stars. We calibrated our data using photometry from the Lowell 1.1 m telescope, and this external method resulted in millimagnitude differences in the photometry of overlapping fields, providing some assurance that our photometry is reliable. The final catalog contains 371,781 and 146,622 stars in M31 and M33, respectively, where every star has a counterpart in (at least) the B, V, and R passbands. Our survey goes deep enough to achieve 1%-2% photometry at 21 mag (corresponding to stars more massive than 20 M⊙) and achieves <10% errors at U ∼ B ∼ V ∼ R ∼ I ∼ 23 mag. Although our typical seeing was only modest (0.″8-1.″4, with median 1.″0) by some standards, we find excellent correspondence between our catalog sources and those we see in our Hubble Space Telescope ACS data for OB48, a crowded region in M31. We compare our final photometry with that of others and find good agreement with the CCD catalog of M31 stars by Magnier et al., although our study covers twice the area and goes about 2 mag deeper. There is also excellent agreement with the CCD "DIRECT" surveys of M31 and M33. The photographic studies of others fare less well, particularly at the faint end in V, where accurate background subtraction is needed for good photometry. We provide cross-references to the stars confirmed as members by spectroscopy and compare the locations of these to the complete set in color-magnitude diagrams. While follow-up spectroscopy is needed for many projects, we demonstrate the success of our photometry in being able to distinguish M31/M33 members from foreground Galactic stars. Finally, we present the results of a single night of spectroscopy on the WIYN 3.5 m telescope, examining the brightest likely members of M31. The spectra identify 34 newly confirmed members, including B-A supergiants, the earliest O star known in M31, and two new luminous blue variable candidates whose spectra are similar to that of P Cygni.