A new method of determining distances to dark globules. : The distance to B 335
A new method of determining distances to dark globules. : The distance to B 335
复制标题
一种确定暗球距离的新方法。
DOI：
10.1051/0004-6361/200811574
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发表时间：
2009
影响因子：
6.5
通讯作者：
G. Olofsson
中科院分区：
文献类型：
--
作者：
S. Olofsson;G. Olofsson
上下文一个孤立的暗球的距离通常是未知的，但对于理解它的性质，特别是它的质量至关重要。本文提出了一种新的解决这一问题的方法。本文的目的是研究如何以及更多或更少的红化场星的距离可以确定使用多色成像。方法.我们观察到一个测试球，B 335在U，B，g，r，a ndI，并与2 MASS的调查，这个数据集给出了一个定义明确的光谱能量分布（SED）的大量恒星。每颗星星的SED取决于星际消光、到星星的距离以及它的内在SED。由于我们有充分的理由怀疑消光（红化）的波长依赖性从球状体的外围到中心部分发生变化，因此我们没有假设任何特定的红化定律。相反，我们使用一个方案，允许独立确定的消光在每个视线所确定的相邻恒星群。该方法是基于使用恒星大气模型来表示恒星的固有SED。从形式上讲，这样就可以确定每颗星星的光谱类别，从而确定它的距离。对于一些恒星，我们有光谱，使我们能够比较光度分类和光谱分类。结果正如预期的那样，主要的问题是，有几个恒星发现在每个距离箱的小领域的大小定义一个典型的黑暗球状体。然而，消光的特征和光度分类给出了一致的结果，我们可以确定一个星星在前面的球状体。它的光度距离为90 pc。在B 335球状体后面最近的星星距离只有120 pc，因此我们确定到B 335的距离为90 - 120 pc。我们的深U图像显示了一个相对明亮的球状体西南边缘，我们调查它是否可能是由于辐射场的局部增强。一个候选源，位于1.5弧分以外的领域，将是领域的星星，HD 184982。这颗星星在依巴谷星表中有一个条目，它的距离是140 - 200 pc。然而，我们得出的结论是，明亮的SW边缘更可能是由于这颗星星的点扩散函数（PSF）的翅膀。
Context. The distance to an isolated dark globule is often unknown and yet crucial for understanding its properties, in particular its mass. A new approach to this problem is discussed Aims. The purpose of the present paper is to investigate how well the distances of more or less reddened field stars can be determined by using multi-colour imaging. Methods. We observed a test globule, B 335 in U, B, g, r ,a ndI, and together with the 2MASS survey, this data set gives a well-defined spectral energy distribution (SED) of a large number of stars. The SED of each star depends on the interstellar extinction, the distance to the star, and its intrinsic SED. As we had good reasons to suspect that the wavelength dependence of the extinction (the reddening) changes from the outskirts of the globule to the central parts, we did not assume any specific reddening law. Instead, we use a scheme that allows independent determination of the extinction in each line of sight as determined by groups of adjacent stars. The method is based on the use of stellar atmospheric models to represent the intrinsic SEDs of the stars. Formally, it is then possible to determine the spectral class of each star and thereby its distance. For some of the stars we have optical spectra, allowing us to compare the photometric classification to the spectrometric. Results. As expected, the main problem is that there are few stars found within each distance bin for the small field size defining a typical dark globule. However, the characterisation of the extinction and photometric classification give consistent results and we can identify one star at the front side of the globule. It has a photometric distance of 90 pc. The closest star behind the B 335 globule has a distance of only ≈120 pc and we therefore determine the distance to B 335 as 90−120 pc. Our deep U image shows a relatively bright south-western rim of the globule, and we investigate whether it might be due to a local enhancement of the radiation field. A candidate source, located 1.5 arcmin outside our field, would be the field star, HD 184982. This star has an entry in the Hipparcos Catalogue and its distance is 140−200 pc. However, we come to the conclusion that the bright SW rim is more likely due to the wing of the point-spread-function (PSF) of this star.