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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

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Dades d'Observació i Astrometria

Constel·lació:Pictor
Ascensió Recta:05h49m41.23s
Declinació:-59°50'22.2"
Magnitud Aparent:9.417
Distancia:141.443 parsecs
Moviment propi RA:0.5
Moviment propi Dec:32.7
B-T magnitude:10.031
V-T magnitude:9.468

Catàlegs i designacions:
Noms Propis   (Edit)
HD 1989HD 39579
TYCHO-2 2000TYC 8532-1541-1
USNO-A2.0USNO-A2 0300-01901509
HIPHIP 27524

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