期刊
ASTROPHYSICAL JOURNAL
卷 698, 期 1, 页码 786-802出版社
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/698/1/786
关键词
stars: abundances; stars: activity; stars: chromospheres
Using precise measurements of the helium D-3 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 similar to 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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