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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.
| XMM-Newton Archival Study of the Ultraluminous X-Ray Population in Nearby Galaxies
We present the results of an archival XMM-Newton study of the brightX-ray point sources (LX>1038 ergss-1) in 32 nearby galaxies. From our list of approximately100 point sources, we attempt to determine if there is a low-statecounterpart to the ultraluminous X-ray (ULX) population, searching for asoft-hard state dichotomy similar to that known for Galactic X-raybinaries and testing the specific predictions of the intermediate-massblack hole (IMBH) hypothesis. To this end, we searched for ``low-state''objects, which we defined as objects within our sample that had aspectrum well fitted by a simple absorbed power law, and ``high-state''objects, which we defined as objects better fitted by a combinedblackbody and a power law. Assuming that low-state objects accrete atapproximately 10% of the Eddington luminosity (as found by Done &Gierlinski) and that high-state objects accrete near the Eddingtonluminosity, we further divided our sample of sources into low- andhigh-state ULX sources. We classify 16 sources as low-state ULXs and 26objects as high-state ULXs. As in Galactic BH systems, the spectralindices, Γ, of the low-state objects, as well as the luminosities,tend to be lower than those of the high-state objects. The observedrange of blackbody temperatures for the high state is 0.1-1 keV, withthe most luminous systems tending toward the lowest temperatures. Wetherefore divide our high-state ULXs into candidate IMBHs (withblackbody temperatures of approximately 0.1 keV) and candidate stellarmass BHs (with blackbody temperatures of approximately 1.0 keV). Asubset of the candidate stellar mass BHs have spectra that are wellfitted by a Comptonization model, a property similar to Galactic BHsradiating in the ``very high'' state near the Eddington limit.
| The 78th Name-List of Variable Stars
We present the next regular Name-List of variable stars containinginformation on 1706 variable stars recently designated in the system ofthe General Catalogue of Variable Stars.
| Ultraluminous X-Ray Sources in Nearby Galaxies from ROSAT High Resolution Imager Observations I. Data Analysis
X-ray observations have revealed in other galaxies a class ofextranuclear X-ray point sources with X-ray luminosities of1039-1041 ergs s-1, exceeding theEddington luminosity for stellar mass X-ray binaries. Theseultraluminous X-ray sources (ULXs) may be powered by intermediate-massblack holes of a few thousand Msolar or stellar mass blackholes with special radiation processes. In this paper, we present asurvey of ULXs in 313 nearby galaxies withD25>1' within 40 Mpc with 467 ROSAT HighResolution Imager (HRI) archival observations. The HRI observations arereduced with uniform procedures, refined by simulations that help definethe point source detection algorithm employed in this survey. A sampleof 562 extragalactic X-ray point sources withLX=1038-1043 ergs s-1 isextracted from 173 survey galaxies, including 106 ULX candidates withinthe D25 isophotes of 63 galaxies and 110 ULX candidatesbetween 1D25 and 2D25 of 64 galaxies, from which aclean sample of 109 ULXs is constructed to minimize the contaminationfrom foreground or background objects. The strong connection betweenULXs and star formation is confirmed based on the striking preference ofULXs to occur in late-type galaxies, especially in star-forming regionssuch as spiral arms. ULXs are variable on timescales over days to yearsand exhibit a variety of long term variability patterns. Theidentifications of ULXs in the clean sample show some ULXs identified assupernovae (remnants), H II regions/nebulae, or young massive stars instar-forming regions, and a few other ULXs identified as old globularclusters. In a subsequent paper, the statistic properties of the surveywill be studied to calculate the occurrence frequencies and luminosityfunctions for ULXs in different types of galaxies to shed light on thenature of these enigmatic sources.
| New Elements for 80 Eclipsing Binaries
This research presents new elements for 80 eclipsing binaries found withthe help of the ASAS-3, Hipparcos and TASS databases.
| X-ray emission from the Sculptor galaxy NGC 300
We report here the results of a full analysis of all the ROSAT PSPCspectral imaging observations and all the ROSAT HRI high resolutionimaging observations of the very nearby (D=2.1 Mpc) Sculptor galaxy, NGC300. Many point sources are detected within the field, several of themshowing evidence for variability, and we present full source listsdetailing their X-ray properties, and attempt to classify them on thebasis of their temporal, spectral and multi-wavelength characteristics.A black hole X-ray binary candidate, a supersoft source and severalsupernova remnants and H ii regions are detected in X-rays, as isunresolved, possibly diffuse emission, accounting for perhaps ~ 20% ofthe total NGC 300 X-ray (0.1-2.4 keV) luminosity (5.8*E38 ergs-1). We compare the X-ray source luminosity distribution ofNGC 300 with that of other nearby galaxies, and we also compare NGC 300with its Sculptor neighbours, concluding that it is a quite anunremarkable system, showing no unusual X-ray (or othermulti-wavelength) properties. It may be one of the best examples of acompletely typical normal quiescent late-type spiral galaxy.
| F, G and K stars in the ROSAT all-sky survey. I. Photometry
We present accurate BV(RI)_c photometry for a sample of F, G and K starsdetected in selected areas of the ROSAT all-sky survey (RASS). We haveused the photometry, in addition to low-resolution spectroscopy, toestimate spectral classifications, distances and X-ray luminosities. Thelog (L_X / L_V) in the sample lies below -2. Although the samplecontains also nearby, inactive stars, it is dominated by active objects.The median X-ray luminosity in our sample is < L_X > = 29.88 andthe mean value of the hardness ratios = 0.13 +/- 0.35. Wecompare the derived X-ray luminosity function with similar functionsobtained from the serendipitous samples of the Einstein Observatorymedium sensitivity survey (EMSS) and EXOSAT. Our sample is completelyconsistent with the EMSS sample of solar type stars, indicating thatboth our sources and the EMSS sources are representative of the highgalactic latitude X-ray stellar population. We do not find extremelyactive stars (log (L_X) >= 32), as are found in the EMSS sample, andwe argue that these objects are rare. Table 3 is also available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
| Longterm Photometry of Variables at ESO - Part Two - the Second Data Catalogue 1986-1990
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1993A&AS..102...79S&db_key=AST
| H II regions in NGC 300
The authors present a catalogue of 176 H II regions in the nearby Sdgalaxy NGC 300. Positions, dimensions, and absolute Hα fluxes aregiven for most of the regions, and new spectrophotometry for some. Theluminosity function and the radial distribution of H II regions arediscussed. At least four H II regions exhibit Wolf-Rayet spectralfeatures. The metallicity gradient in NGC 300 is rediscussed in thelight of these new observations.
| Spectral Classification of Red Variables Along the Galactic Equator.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1956ApJ...124..346C&db_key=AST
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