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Title:
Chromospheric Variability in Early F-Type Stars
Authors:
Rachford, Brian L.; Foight, Dillon R.
Affiliation:
AA(Visiting Astronomer, Kitt Peak National Observatory, National Optical Astronomy Observatories, which is operated by the Association of Universities for Research in Astronomy Inc., under cooperative agreement with the National Science Foundation. ), AB(Department of Physics, Embry-Riddle Aeronautical University, 3700 Willow Creek Road, Prescott, AZ 86301, USA )
Publication:
The Astrophysical Journal, Volume 698, Issue 1, pp. 786-802 (2009). (ApJ Homepage)
Publication Date:
06/2009
Origin:
IOP
ApJ Keywords:
stars: abundances, stars: activity, stars: chromospheres
DOI:
10.1088/0004-637X/698/1/786
Bibliographic Code:
2009ApJ...698..786R

Abstract

Using precise measurements of the helium D3 line, we have searched for statistically significant variations in the strength of chromospheric activity in 13 early F-type stars and two late F-type stars. In two early F-type stars, we find short-term (hours to days) variability based on ~25 observations over the course of a week. In an additional two cases we find significant differences between observations taken years apart, but we can most likely explain this apparent long-term variation as an artifact of probable short-term variations. The evidence suggests that pure rotational modulation of discrete active regions is not responsible for the short-term variations in the early F-type stars and that either a more global process is at work or we are seeing large number of small active regions spread across the star. In contrast, the two late F-type stars in the sample show strength and/or wavelength variations that are consistent with "solar-type" activity typified by the rotational modulation of active regions. Our results suggest that variability does not cause the wide range in activity levels observed within the early F-type stars.
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