Astron. Astrophys. 331, 977-988 (1998)

2. The sample

This work is based on the results of Wichmann et al. (1996), who searched for hitherto undiscovered T Tauri stars on the basis of the ROSAT All-Sky Survey and additional pointed ROSAT observations. Their identification of ROSAT sources by means of optical spectroscopy revealed a total of 76 new T Tauri stars in the Taurus region, located between and in right ascension and between and in declination. 68 of these sources are in the All-Sky Survey, the remaining 8 were found with pointed observations. 72 were classified as weak-line T Tauri stars (WTTS) based on an equivalent width of the emission line Å, 4 as classical T Tauri star (CTTS). The complete object list can be found in Wichmann et al. (1996).

One star of this sample (RXJ0422.9+2310) turned out to be too faint for speckle observations. We observed it in October 1995 and September 1996 and were forced to use an integration time of 3 seconds to obtain a signal of only a few hundred counts. This is much too long for speckle imaging, so we decided to exclude this star from our survey. Two other stars (RXJ0437.4+1851A and B) are only separated from each other, so we count them as one binary. Therefore, we start our survey with a sample of 74 systems, where "system" means either a single star, a binary, or a multiple.

This sample supplements the work of Leinert et al. (1993), who surveyed all the young stars contained in the Herbig-Bell catalogue which are located in the same region and are brighter than , i. e. the T Tauri stars known before ROSAT. Their sample contained 104 systems, 59 classical, 36 weak-line, and 9 unclassified T Tauri stars. The spatial distribution of both samples is shown in Fig. 1. It is obvious from this figure that the TTS known before ROSAT cluster on the CO maxima, while the ROSAT-discovered sources do not and thus probably represent an independent population.

Fig. 1. Spatial distribution of T Tauri stars known prior to ROSAT (left panel) and the new T Tauri stars discovered by Wichmann et al. (1996, right panel). Our combined sample consists of the stars in the left plus the stars in the right panel. Classical T Tauri stars are marked by "C", weak-line T Tauri stars by "W", and unclassified T Tauri stars by crosses. The dotted contours represent the integrated CO J=1-0 line brightness (Ungerechts & Thadeus 1987)

© European Southern Observatory (ESO) 1998

Online publication: March 3, 1998
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