Bibcode
Garcia Lopez, R. J.; Crivellari, L.; Beckman, J. E.; Rebolo, R.
Bibliographical reference
Astronomy and Astrophysics (ISSN 0004-6361), vol. 262, no. 1, p. 195-208.
Advertised on:
8
1992
Citations
7
Refereed citations
6
Description
We have used high-resolution spectra of the Ca II H resonance line in
late-type dwarfs, obtained with high S:N ratios, over a period of four
years to widen our understanding of the dynamical behavior of the Ca II
emission cores. All of the stars dealt with in this article, which are
chromospherically active, show variability both in core emission flux
and line width. They also show significant wavelength shifts with time
of order hundreds of meters per second in the mean core wavelength, and
with lower amplitude in the H3 self-absorption, compared to the
photospheric rest wavelength of Ca II H. Comparing the emission core
shifts with those observed in the H3 features, we find, for the first
time, direct prima facie evidence for vertical chromospheric velocity
fields, which show stability in sense over periods of years in a given
star, with notable modulation in gradient, and which differ in gradient
from star to star. We present evidence to show that the observed effects
are almost certainly not due to projected rotational modulation, and
offer new prospects, given spectral measurements closely sampled in
time, for investigating the vertical velocity structures of
chromospheres.