Absorption of X-Ray Emission of T Tauri Stars by Circumstellar Material

Detections of Rovibrational H2Emission from the Disks of T Tauri Stars

“…Historically, we know that most wTTSs are strong X-ray emitters, with many wTTSs having been discovered through extensive X-ray surveys of star-forming regions (e.g., Casanova et al 1995;Neuhäuser et al 1995). The apparent bimodal distribution of TTSs as X-ray sources, in which wTTSs were almost always detected and cTTSs were much less often detected, led to widespread acceptance that the X-ray emission mechanism was related to the evolution of the star/disk system.…”

Newly discovered candidate weak-line T Tauri stars in the surrounding area of the Taurus-Auriga region

“…Within our sample area of about 10 3 square degrees, 219 X-ray sources were selected based on the RASS-BSC and the selection criteria developed by Neuhäuser et al (1995a), −0.15 ≤ HR1 ≤ 1 and −0.3 ≤ HR2 ≤ 0.5 where the HRs represent hardness ratios computed with count rates of five different energy bands of the ROSAT detection. The X-ray sources thus selected all, except one, have optical counterparts in the Digital Sky Survey(DSS) within the RASS error box of 20 ; their E magnitudes have been estimated from the DSS with a routine developed by Cao et al (1997) with an accuracy of 0.5 mag, and a sample of 164 X-ray sources with at least one counterpart brighter than E = 16 was obtained.…”

“…About 150 TTS were known prior to the ROSAT mission in the surrounding area of the T association, most of which are listed in the HerbigBell catalog (Herbig & Bell 1988), and nearly all CTTS have been previously discovered by their conspicuous optical characteristics. Since WTTS are intrinsically more X-ray luminous than CTTS (Neuhäuser et al 1995a) and thus are much easier detected by the spatially unbiased ROSAT All Sky Survey (RASS), the advent of the RASS offers for the first time the opportunity to extend the search for X-ray active WTTS in nearby SFRs, with a flux limit comparable with typical EO pointed observations. So far, ∼70 previously unknown WTTS candidates have been uncovered in the central part of the Taurus-Auriga SFR (Wichmann et al 1996).…”

“…So far, ∼70 previously unknown WTTS candidates have been uncovered in the central part of the Taurus-Auriga SFR (Wichmann et al 1996). Furthermore, 15 WTTS candidates (Neuhäuser et al 1995c) and later 30 more WTTS candidates (Magazzú et al 1997) have been identified to the south of the Taurus molecular clouds on the basis of RASS data and follow-up optical observations. A few TTS candidates have also been discovered sporadically in deep ROSAT pointed observations in Taurus-Auriga (Strom & Strom 1994;Carkner et al 1996;Wichmann et al 1996).…”

“…Within a sky coverage of about 10 3 square degrees, 219 X-ray sources fulfil the criteria for selecting program sources suggested by Neuhäuser et al (1995a), and 164 of these X-ray sources were found to have at least one optical counterpart with E magnitude brighter than 16. Low-resolution spectroscopic observation has been carried out in order to discard early type stars and galaxies from the sample, additional intermediate-resolution spectra of a sub-sample of 156 late type optical counterparts were obtained for spectral classification and for the calculation of the equivalent width of H α emission and LiI line absorption at 6707Å.…”