A Spectroscopic and Photometric Study of 12 BM Camelopardalis
Document Type
Article
Publication Date
1-1-1995
Description
Radial velocities from 1916.95 to 1991.95 and photometry from 1979.25 to 1992.40, both published and new in this paper, are presented and analyzed. A new solution of the radial velocity curve reveals a new period of 80d.90 and an eccentricity of e=0.05±0.02, both very different from the 80d.17 and 0.35 found by Abt et al. [ApJ, 157, 717 (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 km/s from Kitt Peak. Fourier analysis of the V-band photometry shows the ellipticity effect with minima of unequal depth, 0m.048 and 0m.026. The orbital ephemeris for conjunction (K giant behind) is JD(hel.) 2,448,111.1 (±0d.4) + 80d.898 (±0s.004) 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 two-spot model. During the 13 years covered by photometry there were nine different starspots, the largest one producing a light loss of 0m.19. Rotation periods for the nine spots ranged from 78d.6±0d.5 to 83d.7±0d.4, 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 >4.2 yr and were consistent with the empirical spot lifetime laws of Hall and Henry [IAPPP Comm. No. 55, 51 (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°, R1=24 R⊙,ℳ1=1.1 ℳ⊙, and ℳ2=0.6 ℳ⊙. 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.
Citation Information
Hall, Douglas S.; Fekel, Francis C.; Henry, Gregory W.; Eaton, Joel A.; Barksdale, William S.; Dadonas, Virgilijus; Eker, Zeki; Kalv, Peep; Chambliss, Carlson R.; Fried, Robert E.; Fortier, George L.; Landis, Howard J.; Louth, Howard P.; Powell, Harry D.; Mcfaul, Thomas G.; Miles, Richard; Nielsen, Paul; Renner, Thomas R.; Robb, Stephen P.; Slauson, Douglas M.; Stelzer, Harold J.; Wasson, Rick; and Wood, James E.. 1995. A Spectroscopic and Photometric Study of 12 BM Camelopardalis. Astronomical Journal. Vol.109(3). 1277-1288. https://doi.org/10.1086/117360 ISSN: 0004-6256