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The VELA star cloud. III - The B8 to A0 stars and interstellar reddening

1986; Institute of Physics; Volume: 92; Linguagem: Inglês

10.1086/114238

1538-3881

O. J. Eggen,

Stellar, planetary, and galactic studies

Intermediate-band and Hβ observations of 360 HD stars of types B8 - A0 in a 10°×10° region in Vela, and all the CPD stars in a small adjacent region, are discussed. The interstellar absorption in this and in a neighboring region can be understood as a combination of three absorbing clouds with A V (1 kpc) = 1.50, 0.50, and 0.17 mag. The density of B8 to A0 stars is near 13×10 -5 pc -3 and slightly increases at the distance of the "Vela Sheet" (350 - 450 pc), where these objects are apparently coeval at 2 to 3×10 8 yr. The stars of mid B type and earlier in the Sheet are considerably younger at 2 to 5×10 7 yr, a situation that is also obtained in the Pleiades and α Persei clusters that border the Taurus dark cloud. The major difference in the two environments is the presence of numerous T Tauri stars in Taurus. The B8 to A0 stars more distant then the Vela Sheet (550 - 700 pc) show a very large range of ages. Several clusters in the Vela region are discussed: Cr 173, NGC 2451, NGC 2547, and Tr 10.