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Spot activity in the RS CVn binary DM Ursae Majoris
We present extensive UBVRI photometry of the active RS CVn binary DM UMaobtained at two different observatories over 1988-2008. We find thelight curve of the star to be highly variable. The long-term photometryshows no evidence of any cyclic spot activity. On one occasion, theamplitude of modulation in V band was 0.30 mag, a rather high value foran active star in a binary seen at a comparatively low orbitalinclination. The mean V magnitude of DM UMa during 1993-94 was brighterthan that over 1979-85 by about 0.35 mag. We interpret the monotonicincrease in mean brightness from 1984 onwards as due to the steadydisappearance of star-spots in the near-polar latitudes of the star. TheV-band data clearly show evidence for the presence of two distinctregions of enhanced spot activity on the visible primary, which arefixed in the orbital frame of reference, one facing the companion starand the other away from it. It appears that the nearby companion starsuppresses the natural tendency of the active star for differentialrotation and modifies the physical processes leading to the formation ofspots, besides spinning it up by locking its rotation with the orbitalmotion. The variations in (V - R) and (V - I) colours with the Vmagnitudes clearly indicate that star-spots about 800 K cooler than theunspotted photosphere are responsible for the rotational modulation oflight in DM UMa. The spot-filling factors derived from TiO-bandstrengths, which are available in the literature, are found to show theexpected anticorrelation with the V magnitudes of the star. Apparently,there is excess flux in U and B bands, which increases as the starbecomes fainter, partly compensating for the reduction of flux in thosebands due to spot activity. The excess flux, probably, originates fromplages or facular regions associated with the spot activity, andindicates that the simple two-component spot model with spotted andunspotted photospheric regions is not adequate to represent thestar-spot activity in DM UMa.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
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| Effective temperature scale and bolometric corrections from 2MASS photometry
We present a method to determine effective temperatures, angularsemi-diameters and bolometric corrections for population I and II FGKtype stars based on V and 2MASS IR photometry. Accurate calibration isaccomplished by using a sample of solar analogues, whose averagetemperature is assumed to be equal to the solar effective temperature of5777 K. By taking into account all possible sources of error we estimateassociated uncertainties to better than 1% in effective temperature andin the range 1.0-2.5% in angular semi-diameter for unreddened stars.Comparison of our new temperatures with other determinations extractedfrom the literature indicates, in general, remarkably good agreement.These results suggest that the effective temperaure scale of FGK starsis currently established with an accuracy better than 0.5%-1%. Theapplication of the method to a sample of 10 999 dwarfs in the Hipparcoscatalogue allows us to define temperature and bolometric correction (Kband) calibrations as a function of (V-K), [m/H] and log g. Bolometriccorrections in the V and K bands as a function of T_eff, [m/H] and log gare also given. We provide effective temperatures, angularsemi-diameters, radii and bolometric corrections in the V and K bandsfor the 10 999 FGK stars in our sample with the correspondinguncertainties.
| Mesures de vitesses radiales. VII. Accompagnement AU sol DU programme d'observation DU satellite Hipparcos. Radial velocities. VII. Ground based measurements for Hipparcos.
We publish 734 radial velocities of stars distributed in 28 fields of4x4deg. We continue the PPO series (Fehrenbach et al. 1987; Duflot etal. 1990 and 1992), using the Fehrenbach objective prism method.
| Evolution of starspot regions in DM UMa
An analysis of B and V photometry obtained over January 1980-June 1984for DM UMa yields a mean photometric period of 7.478 + or - 0.010 days,compared to the known orbital period of 7.492 + or - 0.009 days. Thelight curves obtained during any two seasons are noted to dissagree inshape, phases of maxima and minima, mean light level, or minima andmaxima light brightness. In light of the star spot model presentlyapplied, the separation of light minima phases into two groups withdifferent slopes indicates that two respective centers of activity weresituated at different longitudes and latitudes on a differentiallyrotating star.
| Meridian observations made with the Carlsberg Automatic Meridian Circle at Brorfelde (Copenhagen University Observatory) 1981-1982
The 7-inch transit circle instrument with which the present position andmagnitude catalog for 1577 stars with visual magnitudes greater than11.0 was obtained had been equipped with a photoelectric moving slitmicrometer and a minicomputer to control the entire observationalprocess. Positions are reduced relative to the FK4 system for each nightover the whole meridian rather than the usual narrow zones. Thepositions of the FK4 stars used in the least squares solution are alsogiven in the catalog.
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