Resolving the 47 Tucanae Distance Problem
Resolving the 47 Tucanae Distance Problem
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解决 47 Tucanae 距离问题
DOI：
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发表时间：
2002
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影响因子：
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通讯作者：
D. Kilkenny
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作者：
S. Percival;M. Salaris;F. van Wyk;D. Kilkenny
我们提出了一个新的B-，V-和I-波段测光的43个本地亚矮星的依巴谷视差误差小于13%，在金属丰度范围-1.0 < [Fe/H] <-0.3，我们使用它来执行主序星（MS）的银河系球状星团47 Tuc的拟合。这个样本比以前的MS拟合研究中使用的样本大很多倍，也使我们能够拟合两个颜色平面，V/（B-V）和V/（V-I）。这个扩大的亚矮星样本，我们调查是否目前的差异，经验距离估计47图克，所产生的最近MS拟合和白色矮星拟合结果，是由于MS拟合方法的不准确性。对47 Tuc的已发表光度测定结果进行比较，发现存在系统性偏移，这意味着以前研究中使用的（B-V）主线可能偏蓝约0.02 mag，这将导致任何推导出的距离模数偏大约0.1 mag。初步工作还强调了在两个彩色平面V/（B-V）和V/（V-I）中获得的结果之间的差异。我们从Kaluzny等人的数据中导出了V/（B-V）和V/（V-I）的主线，这是我们从Stetson的47 Tuc（2000）中的“二级”标准重新校准的。使用假设的E（B-V）= 0.04的簇红化，我们在两个颜色平面中的最佳拟合表观距离模量是（m-M）V = 13.37，这意味着11.0 ± 1.4 Gyr的簇年龄，并导致（m-M）0 = 13.25的去红化距离模量。与以前的工作比较表明，我们的表观距离模量是~0.2兆比以前的MS拟合研究中得出的。这种差异是由我们喜欢的星系团红化和星系团测光的重新校准造成的，这使得主线在（B-V）中平均红了0.02等。我们推导出的距离模量也与最近从白色矮星拟合中推导出的短距离一致。对我们的MS拟合距离的独立支持来自于对簇中的红色团块的考虑，由此我们推导出去红化的距离模量（m-M）0 = 13.31 ± 0.05，这与MS拟合结果一致。
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 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. 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 recalibration 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.