Optical and infrared properties of the newly formed stars in Canis Major R1

UBVRIJHKL photometry and MK spectral types have been obtained for stars illuminating nebulae in the CMa RI association. Five stars, including the two classical Herbig emission stars Z CMa and HD 53367, have K - L excesses and/or emission-line spectra indicating the presence of circumstellar matter. A number of stars also have V - K indices larger than expected on the basis of their spectral types and B - V indices, suggesting that a steeper than normal extinction law applies to these stars. The color-magnitude diagram for the association is unusual; many stars over the entire spectral range of the association (B0 to Al) lie more than 1 mag above the zero-age main sequence (ZAMS) in V. The middle and early-type B stars with this property are all variable stars and most have rotationally broadened spectra and/or shell indicators. The stars with K - L excesses all lie well above the ZAMS. An age of 3 x 10 years is suggested for most of the stars, compatible with the suggestion that a supernova explosion triggered star formation in this region. A comparison is made between the observations and theoretical models of pre-main-sequence stars. Some of the latest-type stars (A0-Al) lie close to the ZAMS, suggesting that either (1) star formation in the association was not coeval, or (2) isochrones derived from Iben's pre-main-sequence models do not represent real stellar groups. A bolometric luminosity of Mbol < - 4.3 is derived for Z CMa, implying a core mass of M> 10 M0 and a spectral type of B 1, if the star is on the ZAM S. Subject headings: clusters: associations - stars: early-type - stars: emission-line

Перевод пока недоступен