Doppler imaging of stellar surface structure. XIII. The flaring RS CVn-binary HD 291095 = V1355 Orionis
We present the first Doppler images of the newly discovered RS CVnbinary HD 291095. The star is a synchronuously rotating subgiant in a4-day spectroscopic binary with an unseen companion and is particularlyinteresting because it is one of the few evolved stars that show largeflares. Three consecutive years of moderate-resolution KPNO spectra andcontinuous VI and by photometry with our APTs reveal a large, cool, andlong-living asymmetric polar spot. Its temperature is approximately 1100K below the average photospheric temperature. Several low latitude andeven equatorial spots were evident at the same time. We interpret thislatitudinal spot bimodality to be due to a combination of polewardmeridional circulation and more frequent magnetic reconnections near thepole than near the equator. During the 1998 Doppler-imagingobservations, a strong flare in Hα was detected which coincidedwith a meridian passage of the most asymmetric part of the polar spot.We estimate a total flare energy of 5x1034 erg typical forflares on very active RS CVn systems. No photospheric heating is evidentin our surface maps from optically thin spectral lines of varioustemperature sensitivities.
|
Starspot photometry with robotic telescopes. UBV(RI)_C and by light curves of 47 active stars in 1996/97
We present continuous multicolor photometry for 47 stars from October1996 through June 1997. Altogether, 7073 V(RI)_c, UBV, and by datapoints, each the average of three individual readings, were acquiredwith three automatic photoelectric telescopes (APTs) at FairbornObservatory in southern Arizona. Most of our targets arechromospherically active single and binary stars of spectral type G to Kbut there are also four pre-main-sequence objects and three pulsatingstars in our sample. The light variability is generally due torotational modulation of an asymmetrically spotted stellar surface andtherefore precise rotational periods and their seasonal variations aredetermined from Fourier analysis. We also report on photometricvariations of gamma CrB (A0V) with a period of 0.44534 days. All dataare available in numerical form. All data are available from CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
|
Photometry of cool stars detected in extreme-ultraviolet (EUV) all-sky surveys.
We present high-precision UBV(RI)_c_ photometry for a small sample ofcool stars detected at EUV wavelengths by the ROSAT WFC and/or the EUVEall-sky survey. Four out of the five stars observed are variable and oneof them is an eclipsing binary. Amplitudes up to 0.38 magnitudes in theV band have been observed and clear colour variations have been found.We have computed the photometric periods and deduced approximatespectral classifications and distances.
|
The photometric variability of K giants
We have photometrically monitored 49 of the more than 200 K giants inthe Yale Catalog of Bright Stars (YCBS) which are named or suspectedvariable stars. Only two (HR 3275 and HR 5219) are clearly variable; afew more program stars and K- and M-giant comparison stars aremarginally variable. Most of these appear to be RS Canum Venaticorum orSR variables.
|
Evolved GK stars near the sun. I - The old disk population
A sample of nearly two thousand GK giants with intermediate band, (R,I),DDO and Geneva photometry has been assembled. Astrometric data is alsoavailable for most of the stars. The some 800 members of the old diskpopulation in the sample yield accurate luminosities (from two sources),reddening values and chemical abundances from calibrations of thephotometric parameters. Less than one percent of the objects arepeculiar in the sense that the flux distribution is abnormal. Thepeculiarity is signaled by strong CH (and Ba II) and weak CH. The CH+stars are all spectroscopic binaries, probably with white dwarfcompanions, whereas the CH- stars are not. A broad absorption band,centered near 3500 A, is found in the CH+ stars whereas the CH- objectshave a broad emission feature in the same region. The intensity of theseabsorptions and emissions are independent of the intensity of abnormalspectral features. Ten percent of the old disk sample have a heavyelement abundance from one and a half to three times the solar value.The distribution of the heavy element abundances is nearly a normal onewith a peak near solar abundance and ranges three times to one sixthsolar. The distribution of the (U, V) velocities is independent of theheavy element abundance and does not appear to be random. Ten percent ofthe old disk stars show a CN anomaly, equally divided between CN strongand CN weak. Several stars of individual astrometric or astrophysicalimportance are isolated.
|
Large and kinematically unbiased samples of G- and K-type stars. IV - Evolved stars of the old disk population
Modified Stromgren and (R,I) photometry, along with DDO and Genevaphotometry, are presented for a complete sample of evolved old-disk Gand K giants in the Bright Star Catalogue. Stars with ages of between1.5 x 10 to the 9th and 10 to the 10th yr are found to have anear-normal distribution of heavy element abundances, centered on anFe/H abundance ratio of -0.1 dex. The old disk clusters NGC 3680 and IC4651 contain red-straggler young-disk giants that are probablycontemporaries of the blue stragglers in the clusters.
|
Large and kinematically unbiased samples of G- and K-type stars. II - Observations of evolved stars in the Bright Star sample. III - Evolved young disk stars in the Bright Star sample
Four color and RI observations were obtained for a large sample ofG-type and K-type stars in the Bright Star Catalogue. Data are firstpresented for 110 evolved stars. Photometry of evolved young diskpopulation stars have then been calibrated for luminosity, reddening,and metallicity on the basis of results for members of the Hyades andSirius superclusters. New DDO results are given for 120 stars.
|
Differential population synthesis of early-type galaxies. I - Spectrophotometric atlas of synthesis standard spectra
Continuous spectrophotometry has been obtained for 200 objects at aresolution of 10-17 A over the wavelength region 3600-10,000 A.Kron-Cousins BVRI colors are computed from the spectra and compared withpublished photoelectric photometry. The (V - R)C color index is used togroup the individual observations to form synthesis standard spectra for48 common spectral types. The standard groups include a solar abundancesequence of most spectral types and luminosity classes, metal-rich andmetal weak G - K giant-branch sequences, and horizontal-branch giants.The variations with color, luminosity, and metallicity of severalprominent line strengths are discussed. The spectral atlas is availableas a FITS magnetic tape.
|
Photoelectric radial velocities. V. 69 southern HR stars.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972MNRAS.155..449G&db_key=AST
|
Strong-Cyanogen Stars: Photometry and Kinematics
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1971ApJ...165..561J&db_key=AST
|
