疏散星團UBV光度之紅化與消光研究

Abstract

為了精確地由UBV光度推算疏散星團的距離與年齡，恆星光度必須加以紅化、消光修正。以往文獻關於紅化與消光的修正大多以OB星作為依據。而OB星在TCD中之分佈可視為線性。本研究試圖以在TCD上也可視為線性之G6V-K3V型恆星，套用OB星之紅化、消光修正模式，但從文獻中取適合的常數數值。共挑選了五個具有UBV光度的疏散星團，包括NGC 2168、NGC 2422、NGC 2516、Pleiades與Hyades，作為探討紅化、消光的樣本。從這五個疏散星團之本質光度CMD圖中，推估距離模數與文獻符合，除了NGC 2168比文獻數值大了約200 pc。由於只有Pleiades與NGC 2168同時具有OB星與G6V-K3V兩部分，因而可由其等時曲線擬合判斷兩疏散星團之年齡分別Pleiades為1.26×108(108.1)年與NGC 2168為1.58×108 (108.2)年，也與文獻之數據吻合。For estimating accurately the distance and age of an open cluster with UBV photometry, the photometry of each member should be corrected by means of reddening and extinction. But the correction of reddening and extinction is usually done for the OB type stars only, the distribution on the TCD is looks likely linear. In this work, the correction of reddening and extinction is tried to G6V-K3V stars using the corrective processes as same as that for OB stars with the value of constants of equations for reddening and extinction taken from literature. The total five open clusters with all UBV photometric data, NGC 2168, NGC 2422, NGC 2516, Pleiades, and Hyades are chosen for the correction of reddening and extinction. From the CMD of these five open clusters in photometry of V and color index (B-V) of free reddening and extinction, the value of distance modulus of four open clusters except NGC 2168 are nearly same as the data taken from the literature. Furthermore, there are only two open clusters, Pleiades and NGC 2168, posse the data of OB stars and G6V-K3V stars on their CMD. From the isochrones fitting with different ages, the age of these two open clusters are 1.26×108 years for Pleiades and1.58×108 years for NGC 2168, respectively, and these values are also the same with literature