Photometric and spectroscopic studies of cool stars discovered in EXOSAT X-ray images. III. Photometric properties J/A+AS/115/41 J/A+AS/115/41 UBV Photometric and spectroscopic studies of cool stars discovered in EXOSAT X-ray images. III. Photometric properties G Cutispoto G Tagliaferri R Pallavicini L Pasquini M Rodono Astron. Astrophys. Suppl. Ser. 115 41 1996 1996A&AS..115...41C Photometry, UBVRI Stars, late-type X-ray sources stars: activity stars: late-type stars: variables: general X-rays: stars We present high-precision UBV(RI)_c_ photometry for a sample of active stars detected serendipitously by the EXOSAT satellite. Fourteen objects, out of 47 likely optical counterparts, turned out to be clearly variable, with periods in the range 1-8 days, including a newly discovered eclipsing binary. For most of them the optical variability is consistent with the presence of photospheric cool spots. We have used our multicolour photometry to estimate spectral classifications and distances. The derived distances indicate that some of the observed stars are previously unidentified nearby (d<=25pc) M dwarfs. When combined with the results of high resolution spectroscopy, our photometric observations allow us to investigate the stellar content of the selected X-ray sample. Young stars and RS CVn-type binaries appear to constitute a large fraction of the selected sample. For a description of the UBV and (RI)c photometric systems, see e.g. <http://obswww.unige.ch/gcpd/ph01.html> and <http://obswww.unige.ch/gcpd/ph54.html>.
Photometric data for the observed stars Id Identification number --- Name EXOSAT name (Catalogue <VI/43>) --- ObsSeason Code for the observing season number=1 The code is composed by the initial of the month followed by the two last numbers of the year. --- n_ObsSeason When "o": data from Paper I: Cutispoto G. et al 1991 --- Vmax V magnitude at maximum luminosity mag U-B U-B color index mag B-V B-V color index mag V-Rc V-R_c_ color index (Cousins) mag V-Ic V-I_c_ color index (Cousins) mag Qual Quality of the data --- Var Variability flag --- n_Var Uncertainty on variability flag --- Photometric data Id Identification number --- EXOSAT EXOSAT name --- Other Other catalogue number --- Sp Spectral type --- Dist Distance pc n_Dist Uncertainty on distance --- Var Variability flag --- Period Period of variability d n_Period Uncertainty on period of variability --- l_DeltaV Limit flag on amplitude in V-band --- DeltaV Amplitude in the V-band mag Simona Mei CDS 1995Sep25 J_A+AS_115_41.xml