The WFC3 Galactic Bulge Treasury Program: A First Look at Resolved Stellar Population Tools
Thomas M. Brown, Kailash Sahu, Manuela Zoccali, Alvio Renzini, Henry C. Ferguson, Jay Anderson, Ed Smith, Howard E. Bond, Dante Minniti, Jeff A. Valenti, Stefan… 展开作者
Thomas M. Brown, Kailash Sahu, Manuela Zoccali, Alvio Renzini, Henry C. Ferguson, Jay Anderson, Ed Smith, Howard E. Bond, Dante Minniti, Jeff A. Valenti, Stefano Casertano, Mario Livio, Nino Panagia, Don A. VandenBerg, Elena Valenti
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Accepted for publication in The Astronomical Journal. 9 pages, 8 figures, latex, AJ format
[Abridged] When WFC3 is installed on HST, the community will have powerful new tools for investigating resolved stellar populations. The WFC3 Galactic Bulge Treasury program will obtain deep imaging on 4 low-extinction fields. These non-proprietary data will enable a variety of science investigations not possible with previous data sets. To aid in planning for the use of these data and for future proposals, we provide an introduction to the program, its photometric system, and the associated calibration effort.
The observing strategy is based upon a new 5-band photometric system spanning the UV, optical, and near-infrared. With these broad bands, one can construct reddening-free indices of Teff and [Fe/H]. Besides the 4 bulge fields, the program will target 6 fields in well-studied star clusters, spanning a wide range of [Fe/H]. The cluster data serve to calibrate the indices, provide population templates, and correct the transformation of isochrones into the WFC3 photometric system. The bulge data will shed light on the bulge formation history, and will also serve as population templates for other studies. One of the fields includes 12 candidate hosts of extrasolar planets.
CMDs are the most popular tool for analyzing resolved stellar populations. However, due to degeneracies among Teff, [Fe/H], and reddening in traditional CMDs, it can be difficult to draw robust conclusions from the data. The 5-band system used for the bulge Treasury observations will provide indices that are roughly orthogonal in Teff and [Fe/H], and we argue that model fitting in an index-index diagram will make better use of the information than fitting separate CMDs. We provide simulations to show the expected data quality and the potential for differentiating between different star-formation histories.
The ACS Nearby Galaxy Survey Treasury I. The Star Formation History of the M81 Outer Disk
ACS邻近星系巡天金库（英语：ACS Nearby Galaxy Survey Treasury，缩写：ANGST）是一个大型的哈勃太空望远镜巡天高级照相机（英语：Advanced Camera for Survey，缩写：ACS）金库计划，目的是获得体积有限的星系样本的恒星光度测量结果。作为该计划的一部分，我们已经获得了大螺旋星系M81外盘的深ACS成像。这个区域包含一个旋臂的外围，以及一个没有当前恒星形成的区域。我们的成像结果在颜色星等图（CMD）达到F814 W = 28.8和F606 W = 29.5，一个比红色团暗的星等。通过详细的建模的完整CMD，我们量化的年龄和金属丰度分布的恒星星族包含在字段。磁场中的平均金属丰度为-1<[M/H]<0，只有一小部分恒星的年龄<~1 Gyr。结果表明，在这个外盘场中的大多数恒星都是由z~1形成的，并且在这个半径处的臂结构的寿命>~ 1亿年。我们讨论了测量的高红移盘星系的调查和其他附近星系的深恒星测光的背景下，M81磁盘的演变。这些都表明，大规模的螺旋盘主要是由z~1形成的，它们经历了快速的金属富集。
X-Ray Properties of the Point Source Population in the Spiral Galaxy NGC 5055 (M63) with Chandra
By analyzing the Chandra ACIS S3 data we studied the X-ray properties of the low-mass and high-mass X-ray binary populations in the nearby spiral galaxy NGC 5055. A total of 43 X-ray point sources were detected within the 2 effective radii, with 31 sources located on the disk and the rest 12 sources in the bulge. The resolved point sources dominate the total X-ray emission of the galaxy by accounting for about 80% of the total counts in 0.3--10 keV. By carrying out the spectral fittings we calculated the 0.3--10.0 keV luminosities of all the detected X-ray point sources and found that they spa…
