Comparing the Ca ii H and K Emission Lines in Red Giant Stars
Abstract
Measurements of the asymmetry of the emission peaks in the core of the Ca ii H line for 105 giant stars are reported. The asymmetry is quantified with the parameter V/R, defined as the ratio between the maximum number of counts in the blueward peak and the redward peak of the emission profile. The Ca ii H and K emission lines probe the differential motion of certain chromospheric layers in the stellar atmosphere. Data on V/R for the Ca ii K line are drawn from previous papers and compared to the analogous H-line ratio, the H and K spectra being from the same sets of observations. It is found that the H-line (V/R)H value is +0.04 larger, on average, than the equivalent K-line ratio, however, the difference varies with B - V color. Red giants cooler than B - V = 1.2 are more likely to have (V/R)H > (V/R)K, whereas the opposite is true for giants hotter than B - V = 1.2. The differences between the Ca ii H and K-line asymmetries could be caused by the layers of chromospheric material from which these emission features arise moving with different velocities in an expanding outflow.
- Publication:
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Publications of the Astronomical Society of the Pacific
- Pub Date:
- August 2009
- DOI:
- 10.1086/605456
- arXiv:
- arXiv:0907.3346
- Bibcode:
- 2009PASP..121..842R
- Keywords:
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- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 36 pages, 12 figures, 2 tables. Accepted to PASP. Corrected a typo in Table 2