期刊
ASTRONOMY & ASTROPHYSICS
卷 566, 期 -, 页码 -出版社
EDP SCIENCES S A
DOI: 10.1051/0004-6361/201322697
关键词
stars: activity; stars: chromospheres; stars: solar-type; planetary systems
资金
- European Research Council/European Community [PTDT/CTE-AST/098528/2008]
- Fundacao para a Ciencia e a Tecnologia (FCT), Portugal
- FCT [SFRH/BD/64722/2009, SFRH/BPD/81084/2011]
- FCT - FCT/MCTES (Portugal)
- POPH/FSE (EC)
- Fundação para a Ciência e a Tecnologia [SFRH/BPD/81084/2011, SFRH/BD/64722/2009] Funding Source: FCT
The re-emission in the cores of the Ca II H & K and H alpha lines are well known proxies of stellar activity. However, these activity indices probe different activity phenomena: the first is more sensitive to plage variation, while the other is more sensitive to filaments. In this paper, we study the long-term correlation between log R'(HK) and log I-H alpha, two indices based on the Ca II H & K and H alpha lines, respectively, for a sample of 271 FGK stars using measurements obtained over a similar to 9 year time span. Because stellar activity is one of the main obstacles to the detection of low-mass and long-period planets, understanding this activity index correlation further can give us some hints about the optimal target to focus on ways to correct for these activity effects. We found a great variety of long-term correlations between log R'(HK) and log I-H alpha. Around 20% of our sample has a strong positive correlation between the indices while about 3% show strong negative correlation. These fractions are compatible with those found for the case of early-M dwarfs. Stars exhibiting a positive correlation have a tendency to be more active when compared to the median of the sample, while stars showing a negative correlation are more present among higher metallicity stars. There is also a tendency for the positively correlated stars to be more present among the coolest stars, a result which is probably due to the activity level effect on the correlation. Activity level and metallicity therefore seem to be playing a role on the correlation between log R'(HK) and log I-H alpha. Possible explanations based on the influence of filaments for the diversity in the correlations between these indices are discussed in this paper. As a parallel result, we show a way to estimate the effective temperature of FGK dwarfs that exhibit a low activity level by using the H alpha index.
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