New weak-line T Tauri stars in Orion from the ROSAT all-sky survey

Abstract

Abstract. -We present results of the spectroscopic and photometric follow-up observations of the ROSAT allsky survey in the direction of the Orion cloud complex. The main goal of these observations is the search for X-ray emitting pre-main sequence stars. 820 X-ray sources were detected with high confidence in about 450 square degrees. The mean density of X-ray sources in this region is a factor of about two higher than that of the whole RASS. 5% of the RASS sources in this region are identified with previously known and likely pre-main sequence stars. We have investigated spectroscopically 181 new RASS sources widely distributed over the entire cloud complex. On the basis of the presence of strong Li I λ6707 absorption, spectral type later than F0 and chromospheric emission, 112 new weak-line T Tauri stars could be found. We present coordinates, X-ray count-rates and finding charts of the new PMS. Optical UBV (RI)KC, near-infrared JHKLM and uvby-β photometry for the new WTTS is also provided. In addition 24 dKe-dMe stars were also found on the basis of the RASS data.

XMM-Newtonobservations of the young open cluster aroundλ Orionis

“…1). This star, first detected in X-rays with Einstein (Stone & Taam 1985), has been classified as a weak-lined T Tauri star, due to its strong Li i absorption and weak Hα emission (Fernandez et al 1995;Alcalá et al 1996Alcalá et al , 2000Li & Hu 1998). However, as mentioned in Sect.…”

“…The ROSAT All-Sky Survey detected several X-ray sources identified with new T Tauri stars Neuhäuser et al 1995Neuhäuser et al , 1997Alcalá et al 1996;Magazzu et al 1997). The central hot star was observed with ASCA by Corcoran et al (1994) who found a hard spectrum with temperatures of 0.3 and 2.3 keV.…”

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

“…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). 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.…”

“…We present results of an extensive search for weak-line T Tauri stars (WTTS) in the outskirts of the Taurus-Auriga molecular cloud on the basis of the ROSAT All-Sky Survey Bright Source Catalog. Our surveyed region extends from 2 h 40 m to 5 h 40 m in right ascension and from 10• to 40• in declination, with the central part of Taurus-Auriga (4 h < α < 5 h , 15 Wichmann et al (1996), excluded. 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.…”

“…• in declination, with the central part of Taurus-Auriga (4 h < α < 5 h , 15 Wichmann et al (1996), excluded. 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.…”