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RESOLVING THE 47 TUCANAE DISTANCE PROBLEM

机译:解决47个TUCANAE距离问题

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摘要

We present new B-, V-, and I-band photometry for a sample of 43 local subdwarfs with Hipparcos parallax errors less than 13%, in the metallicity range - 1.0 < [Fe/H] < -0.3, which we use to perform main-sequence (MS) fitting to the Galactic globular cluster 47 Tuc. This sample is many times larger than those used in previous MS-fitting studies and also enables us to fit in two color planes, V/(B-V) and V/(V-I). With this enlarged subdwarf sample we investigate whether the current discrepancy in empirical distance estimates for 47 Tuc, arising from recent MS-fitting and white dwarf fitting results, is due to inaccuracies in the MS-fitting method. Comparison of published photometries for 47 Tuc has revealed systematic offsets, which means that the (B-V) main line used in previous studies may be too blue by ~0.02 mag, which would have the effect of making any derived distance modulus too large by around 0.1 mag. Preliminary work has also highlighted discrepancies between results obtained in the two color planes, V/(B-V) and V/(V-I). We have derived main lines in V/(B-V) and V/(V-I) from the data of Kaluzny et al., which we have recalibrated from the " secondary " standards in 47 Tuc of Stetson (2000). Using an assumed cluster reddening of E(B-V] = 0.04, our best-fit apparent distance modulus is (m - M)_v = 13.37_(-0.11)_~(0.10) in both color planes, which implies a cluster age of 11.0 +- 1.4 Gyr and leads to a dereddened distance modulus of (m - M)_0 = 13.25_(-0.07)~(+0.06). Comparison with previous work shows that our apparent distance modulus is ~0.2 mag smaller than those derived in previous MS-fitting studies. The difference is accounted for by our preferred cluster reddening and the recalibra-tion of the cluster photometry, which has made the main line redder by an average of 0.02 mag in (B-V). Our derived distance modulus is also now plausibly consistent with the short distance recently derived from white dwarf fitting. Independent support for our MS-fitting distance comes from consideration of the red clump in the cluster, from which we derive a dereddened distance modulus of (m - M)_0 = 13.31 +- 0.05, which is in agreement with the MS-fitting result.
机译:我们为43个局部Hipparcos视差误差小于13%的局部亚矮小样本提供了新的B波段,V波段和I波段光度法,在金属度范围内-1.0 <[Fe / H] <-0.3对银河系球状星团47 Tuc执行主序列(MS)拟合。该样本比以前的MS拟合研究中使用的样本大许多倍,也使我们能够拟合到两个颜色平面V /(B-V)和V /(V-I)中。利用这个扩大的亚矮样本,我们调查了由于最近的MS拟合和白矮拟合结果导致的47 Tuc的经验距离估计当前差异是否是由于MS拟合方法的不准确性所致。比较已发表的47个Tuc的测光图,可以发现系统的偏移,这意味着以前的研究中使用的(BV)主线在约0.02 mag时可能会太蓝,这将导致派生的距离模数过大约0.1。 MAG。初步工作还强调了在两个颜色平面V /(B-V)和V /(V-I)中获得的结果之间的差异。我们从Kaluzny等人的数据中得出了V /(B-V)和V /(V-I)的主线,这些数据已根据Stetson(47)的47 Tuc中的“次要”标准进行了重新校准。使用假定的群集发红E(BV] = 0.04,我们最适合的视在距离模量在两个颜色平面中均为(m-M)_v = 13.37 _(-0.11)_〜(0.10),这意味着群集年龄为11.0 +-1.4 Gyr并导致递减的距离模量(m-M)_0 = 13.25 _(-0.07)〜(+0.06)。与先前的工作比较表明,我们的视在距离模量比导出的模量小〜0.2 mag在先前的MS拟合研究中,差异是由我们首选的群集变红和群集光度法的重新校准造成的,这使主线平均变红了0.02 mag in(BV),我们得出的距离模量为也可能与最近从白矮星拟合得出的短距离保持一致,对我们的MS拟合距离的独立支持来自对星团中红色团块的考虑,由此得出了一个递减的距离模数(m-M)_0 = 13.31±0.05,与质谱拟合结果一致。

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