Some Results of an H Survey in the Taurus Dark Clouds

Discussion

The spatial distribution of the new H stars in the TDC region is shown in Fig.1. The solid lines represent the contours of the dark clouds with visual absorption A(V) 2.0. The intermittent ones outline the fields surveyed. As seen in Fig.1 the new H emission line stars are concentrated in the clouds themselves and have the same type of location as known H emission line stars and Pre-Main-Sequence (thereafter PMS) stars in general. Consideration of known and newly discovered stars shows a grouping effect to the local centers.

  
Figure 1: Spatial distribution of the new H stars in the Taurus Dark Cloud region.

Many previously discovered stars with H emission (Joy,1949;Haro et al, 1953) have turned out to be PMS stars with stochastic or irregular variability (Cohen Kuhi,1979; Kholopov et al,1987; Herbig Bell,1988 and so on). Some of the H line stars discovered during our research, for example BV 5 (Hojaev,1986), B 41 and SB 33(Hojaev,1984), B 4 (Hojaev,1983), are also such stars. It is clear the spectral variability of these young stars has a connection with their photometric variability and is irregular in nature. The latter allows us to apply the method for an estimation of the total number of irregular variable stars in the clusters suggested by Ambartsumian(1977) and Parsamian (1981) in order to calculate the total number of the H emission line stars in the TDC region. We have used 36 stars having evaluations of H line intensities for four periods: 1952(Haro et al,1953), 1958-62(Dolidze,1975), 1970 and 1983-84(this work). We evaluated the expected total number of the TDC's stars with H line emission according to the formulae given in Parsamian& Hojaev (1985) as N = 77. The total number of stars with H emission which can be revealed from our plates should be about 80 for the surveyed TDC area (i.e. about 1.6 per sq.deg.).

In summary, 20 new stars with H line emission were found in the TDC region. The fact that the H line emission of these stars was not discovered earlier can be explained as either variability of the line intensity or the weakness of the line in the studied stars. We can assume that these stars do not differ from the Orion population stars by the nature of the H emission line variability.

The existence of the large number of young stars and related objects as well as the other indicators of youth (e.g. infrared sources, molecular clouds, cometary nebulae, Herbig-Haro objects, flare stars, T Tauri stars and other PMS stars) allows us to presume that the associations of SFR in the TDC, including this sample, have the same age as the associations in Orion's and Monocerotis' SFRs.

© Copyright Astronomical Society of Australia 1997