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An XMM-Newton-based X-ray survey of pre-main sequence stellar emission in the L1551 star-forming complex
We present a study of the X-ray sources present in the nearby L1551 starforming region, based on a deep XMM-Newton observation complemented withChandra data for the brightest sources. Most known pre-main sequencestars in the region have been detected, most of them with sufficientstatistics to allow a detailed study of the temporal and spectralcharacteristics of their X-ray emission. Significant temporal (andspectral) variability on both short and long time scales is visible formost of the stars. In particular XZ Tau shows large-amplitude variationson time scales of several hours with large changes in the interveningabsorption, suggestive of the X-ray emission being eclipsed by theaccretion stream (and thus of the X-ray emission being partly or totallyaccretion-induced). The coronal metal abundance of the WTTS sources isclustered around Z =~ 0.2, while the CTTS sources span almost twoorders of magnitudes in coronal Z, even though the photosphericabundance of all stars in the L1551 is likely to be very similar. Someindividual elements (notably Ne) appear to be systematically enhancedwith respect to Fe in the WTTS stars. The significant differencesbetween the spectral and temporal characteristics of the CTTS and WTTSpopulations suggest that a different emission mechanism is (at leastpartly) responsible for the X-ray emission of the two types of stars.
| The Henry Draper Extension Charts: A catalogue of accurate positions, proper motions, magnitudes and spectral types of 86933 stars
The Henry Draper Extension Charts (HDEC), published in the form offinding charts, provide spectral classification for some 87000 starsmostly between 10th and 11th magnitude. This data, being highlyvaluable, as yet was practically unusable for modern computer-basedastronomy. An earlier pilot project (Roeser et al. 1991) demonstrated apossibility to convert this into a star catalogue, using measurements ofcartesian coordinates of stars on the charts and positions of theAstrographic Catalogue (AC) for subsequent identification. We presenthere a final HDEC catalogue comprising accurate positions, propermotions, magnitudes and spectral classes for 86933 stars of the HenryDraper Extension Charts.
| A search for weak H-alpha emission line pre-main-sequence stars
A spectroscopic survey of 177 stars brighter than about 12.5 in R nearfour dark clouds in an effort to find pre-main-sequence (PMS) stars withweak H-alpha emission is reported. A number of such stars have beenfound previously in X-ray images of star formation clouds. Six newcandidate PMS stars with EW (H-alpha) between 0.4 and 4.2 A, in additionto four X-ray discovered stars, are found in the L1551 and L1529 cloudsin the Taurus-Auriga complex. The total number of pre-main-sequencestars in these clouds appears to be about two times the number of strongemission line T Tauri stars.
| Interstellar extinction in the Taurus dark clouds. II
The results of photoelectric photometry of 89 stars in the Vilniusseven-color system in the area of the Taurus dark clouds withcoordinates (1950) 4h16m-4h33m, +16 deg-+20 deg are presented.Photometric spectral types, absolute magnitudes, color excesses,interstellar extinctions and distances of the stars are determined. Thedistance of the dark nebula is found to be 140 pc and is in goodagreement with the distance determined by Straizys and Meistas (1980)for the dark nebula Khavtassi 286, 278. The average extinction in theinvestigated area is of the order of 1.4.
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| Takýmyýldýz: | Boga |
| Sað Açýklýk: | 04h32m21.57s |
| Yükselim: | +18°12'58.5" |
| Görünürdeki Parlaklýk: | 10.751 |
| özdevim Sað Açýklýk: | -18.4 |
| özdevim Yükselim: | 7.7 |
| B-T magnitude: | 11.216 |
| V-T magnitude: | 10.79 |
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