A Spectroscopic and Photometric Study of 12 BM Camelopardalis
Abstract
Radial velocities from 1916.95 to 1991.95 and photometry from l979.25, both published and new in this paper, are presented and analyzed. A new solution of the radial velocity curve reveals a new period of 80.90 days and an eccentricity of e = 0.05 +/ 0.02, both very different from the 80.17 days and 0.35 found by Abt et al. (1969). An alternative solution with e = 0 is given because we cannot decide firmly whether or not the small eccentricity is real. We find V sin i = 11.3 +/ 0.3 km/s from Maidanak and 10 unequal depth. 0.048 mins and 0.026 mins. The orbital ephemeris for conjunction (K gisnt behind) is JD(hel.) 2,448,111.1 (+/ 0.4 days ) + 80.898 days (+/ 0.004 days ) E, consistent with both the radial velocities and the photometry. With the ellipticity effect removed, the light curve shows residual variability which we fit with a twospot model. During the 13 years covered by photometry there were nine different starspots, the largest one producing a light loss of 0.19 mins. Rotation periods for the nine spots ranged from 78.6 +/ 0.5 days to 83.7 +/ 0.4 days from which we concluded that the K giant does rotate synchronously but with a differential rotation coefficient of k = 0.06 +/ 0.01. Lifetimes for the nine spots ranged from 1.1 to greater than 4.2 yr and were consistent with the empirical spot lifetime laws of Hall & Henry (1994). Use of the mass function, the orbital period, the V sin i, the two different ellipticity effect amplitudes, and various logical constraints led to ranges of possible masses, radii and inclinations. The most believable solution was around i = 90 deg, R_{1} = 24 solar radii, M_{1} = 1.1 solar mass, and M_{2} = 0.6 solar mass. THe Rossby number for the K giant is 0.48, small enough compared to the critical value of 0.65 to explain why, though rotating 'slowly', it does have large spots.
 Publication:

The Astronomical Journal
 Pub Date:
 March 1995
 DOI:
 10.1086/117360
 Bibcode:
 1995AJ....109.1277H
 Keywords:

 Binary Stars;
 Light Curve;
 Radial Velocity;
 Starspots;
 Stellar Magnitude;
 Stellar Orbits;
 Stellar Rotation;
 Variability;
 Data Correlation;
 Ellipticity;
 Ephemerides;
 Orbital Elements;
 Periodic Variations;
 Stellar Spectrophotometry;
 Astronomy;
 STARS: GIANT;
 STARS: ROTATION