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Search for associations containing young stars (SACY). I. Sample and searching method
We report results from a high-resolution optical spectroscopic surveyaimed to search for nearby young associations and young stars amongoptical counterparts of ROSAT All-Sky Survey X-ray sources in theSouthern Hemisphere. We selected 1953 late-type (B-V~≥~0.6),potentially young, optical counterparts out of a total of 9574 1RXSsources for follow-up observations. At least one high-resolutionspectrum was obtained for each of 1511 targets. This paper is the firstin a series presenting the results of the SACY survey. Here we describeour sample and our observations. We describe a convergence method in the(UVW) velocity space to find associations. As an example, we discuss thevalidity of this method in the framework of the β Pic Association.
| Newly-discovered young stars in Carina and Vela
Recent observations have shown that a substantial population ofpre-main-sequence stars exists within 100 pc of the Sun. Such stars areuseful for constraining disk evolution timescales, given their relativeproximity and their ages in the 10--50 Myr range, filling the gapbetween nearby low-mass star-forming regions with ages of a few Myr andZAMS stars at ages of 100 Myr. We present here the latest results fromour continuing search for such stars.In this work, we have undertaken a search for young stars too faint tobe included in the Hipparcos catalog by looking for x-ray bright Tycho-2stars with kinematics similar to the young Hipparcos stars HIP 33111,33455, 46063, and 48558. These stars lie in the vicinity of (but outsidethe conventional boundaries of) the Lower Centaurus Crux (LCC) OBassociation and the ˜30 Myr-old open cluster IC 2391. There issignificant overlap between the stars selected here and those proposedby Makarov & Urban (2000) as the Carina-Vela moving group, thoughthe stars around HIP 33111 and 33455 lie outside the proposed movinggroup, and also farther from LCC.We present high-resolution optical spectra of more than 60 such stars,from which we derive Li abundances, surface gravities, and preciseradial velocities. Many of these stars are late-type pre-main-sequencestars, showing strong x-ray emission (logLx}/L{bol > -4) and strong Li absorption atlevels similar to the late-type stars in IC 2602 and IC 2391. Most ofthe stars that show strong Li absorption also share similar radialvelocities, clustering around vhelio ? +20 km/s.We present a detailed analysis of these stars' ages and kinematics, andwe discuss their relationship to the other young stars and knownstar-forming regions in the vicinity.We gratefully acknowledge the support of this work by the NationalScience Foundation, through grant AST-0307830.
| Two-colour photometry for 9473 components of close Hipparcos double and multiple stars
Using observations obtained with the Tycho instrument of the ESAHipparcos satellite, a two-colour photometry is produced for componentsof more than 7 000 Hipparcos double and multiple stars with angularseparations 0.1 to 2.5 arcsec. We publish 9473 components of 5173systems with separations above 0.3 arcsec. The majority of them did nothave Tycho photometry in the Hipparcos catalogue. The magnitudes arederived in the Tycho B_T and V_T passbands, similar to the Johnsonpassbands. Photometrically resolved components of the binaries withstatistically significant trigonometric parallaxes can be put on an HRdiagram, the majority of them for the first time. Based on observationsmade with the ESA Hipparcos satellite.
| Optical identification of EUV sources from the ROSAT Wide Field Camera all-sky survey
Optical identifications for 195 EUV sources located in the ROSAT WideField Camera all-sky survey are presented. We list 69 previously unknownEUV-emitting white dwarfs, 114 active stars, 7 new magnetic cataclysmicvariables and 5 active galaxies. Several of the white dwarfs haveresolved M-type companions, while five are unresolved white dwarf/M-starpairs. Finding charts are given for the optical counterparts.
| The ROSAT Wide Field Camera all-sky survey of extreme-ultraviolet sources - II. The 2RE Source Catalogue
During 1990-1991 the Wide Field Camera (WFC) on the ROSAT satelliteperformed the first all-sky survey at EUV wavelengths. The survey wasconducted in two `colours' using broad-band filters to define wavebandscovering the ranges 60-140 A and 112-200 A. It was fully imaging, witheffective spatial resolution of about 3 arcmin FWHM, and point sourcelocation accuracy of typically better than 1 arcmin. From an initialanalysis, Pounds et al. published the WFC Bright Source Catalogue (BSC)of 383 sources. In this paper we report results from reprocessing of thecomplete survey database; the resulting list of sources is the `2RE'Catalogue. It contains 479 sources, of which 387 are detected in bothsurvey wavebands, a significant advance on the BSC (80 per cent versus60 per cent). Improvements over the original BSC include: (i) betterrejection of poor aspect periods, and smaller random errors in theaspect reconstruction; (ii) improved background screening; (iii)improved methods for source detection; (iv) inclusion of atime-variability test for each source; (v) more extensive investigationof the survey sensitivity. We define the catalogue selection criteria,and present the catalogue contents in terms of tables and sky maps. Wealso discuss the sky coverage, source number-flux relations, opticalidentifications and source variability.
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Pozíciós és asztrometriai adatok
| Csillagkép: | Hajófar |
| Rektaszcenzió: | 06h53m47.37s |
| Deklináció: | -43°06'50.9" |
| Vizuális fényesség: | 8.933 |
| Távolság: | 87.951 parszek |
| RA sajátmozgás: | 5.6 |
| Dec sajátmozgás: | 12.1 |
| B-T magnitude: | 9.661 |
| V-T magnitude: | 8.994 |
Katalógusok és elnevezések:
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