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Stellar rotation in lower main-sequence stars measured from time variations in H and K emission-line fluxes. II - Detailed analysis of the 1980 observing season data
Baliunas, S. L.; Hartmann, L.; Noyes, R. W.; Vaughan, H.; Preston, G. W.; Frazer, J.; Lanning, H.; Middelkoop, F.; Mihalas, D.
AA(Harvard-Smithsonian Center for Astrophyics, Cambridge, MA), AB(Harvard-Smithsonian Center for Astrophyics, Cambridge, MA), AC(Harvard-Smithsonian Center for Astrophyics, Cambridge, MA), AD(Mount Wilson and Las Campanas Observatoires, Pasadena, CA), AE(Mount Wilson and Las Campanas Observatoires, Pasadena, CA), AF(Mount Wilson and Las Campanas Observatoires, Pasadena, CA), AG(Mount Wilson and Las Campanas Observatoires, Pasadena, CA), AH(Sterrewacht, Sonnenborgh, Utrecht, Netherlands), AI(Sacramento Peak Observatory, Sunspot, NM)
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 275, Dec. 15, 1983, p. 752-772. Research supported by the Smithsonian Institution and Nederlandse Organisatie voor Zuiver-Wetenschappelijk, Onderzoek. (ApJ Homepage)
Publication Date:
NASA/STI Keywords:
Calcium, Chromosphere, Late Stars, Main Sequence Stars, Stellar Rotation, Stellar Spectrophotometry, Autocorrelation, Giant Stars, Light Curve, Secular Variations, Stellar Radiation, Stellar Spectra, Time Series Analysis
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For a sample of 47 lower main-sequence stars, including the Sun, and eight evolved stars, the relative strength of the Ca II H and K emission cores has been measured daily over a nearly continuous interval during 1980 July through October at Mount Wilson. From these time series measurements of chromospheric emission, rotation rates have been inferred with quantitative estimates of both the reality and precision of the rotation periods. We find rotation rates easily for the main-sequence stars with strong emission or those later than about spectral type K0. With this technique, rotation rates can be measured precisely for the first time for equatorial velocities as slow as 1 km s-1 and independently of the aspect of the rotation axis. In a limited range of spectral type, a small sample of stars indicates that chromospheric emission decreases smoothly as a function of rotation period. No conclusion can be drawn on the question of the reality of a discontinuity in chromospheric emission as a function of time (the "Vaughan-Preston" gap for stars in the solar neighborhood).

In our sample of giant stars, the G2 III star HD 218658 shows a persistent fluctuation of 4.6 days, a period that is inconsistent with stellar rotation. The G0 III star HD 6903 is a previously unreported FK Comae-type star.

For a few main-sequence stars, measurements continued beyond 1980 October suggest the presence of active longitudes (if not individual active regions) persisting through the observing season 1981.

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