GHRS Observations of the M-giant gamma CRU

Details GHRS Observations of the M-giant gamma CRU GHRS Observations of the M-giant gamma CRU

May 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993aas...182.4613c&link_type=abstract

American Astronomical Society, 182nd AAS Meeting, #46.13; Bulletin of the American Astronomical Society, Vol. 25, p.875

Astronomy and Astrophysics

Astronomy

1

Scientific paper

The Goddard High Resolution Spectrograph (GHRS) on the Hubble Space Telescope has been used to obtain medium (R=20,000) and high (R=85,000) resolution UV spectra of chromospheric emission features for the M3.4 III star gamma Cru. Large Science Aperture (LSA), medium resolution spectra were obtained to survey the 1980 - 2200 Angstroms region with good signal-to-noise. Small Science Aperture (SSA) G270M and Echelle-B spectra of selected longer wavelength regions were obtained to allow the measurement of velocity flows and turbulence for a variety of ions, including C II, Fe II, Co II, Si I/II, Ni II, Mn II, and Mg II. Gaussian fits to the optically thin C II (UV 0.01) intercombination lines and fluorescently-excited lines of Co II, Ni II, Fe II, and Si I indicate average turbulent velocities (Doppler FWHM) of 30.2 and 28.6 km/s, respectively. For comparison, the C II turbulent velocity previously measured for the K5 giant alpha Tau is ~ 24 km/s. The measured radial velocities of the fluorescent lines average 21.5 km/s, which places them basically at rest relative to the radial velocity of the star (21 km/s), while the C II lines average 23.1 km/s, a modest inflow of a couple of km/s. A subset of the collisionally-excited Fe II emission lines show an average radial velocity of 22.6 km/s, also a very modest inflow, at best. The stronger Fe II lines exhibit a more complex profile which consists of a broad emission line with an ~ 40 km/s FWHM, on which are superposed two absorption components. The stronger component appears at relatively low radial velocity (in the 7 - 15 km/s range) in each line, with a mean value over the sample of ~ 10.5 km/s, while the weaker component appears at relatively high radial velocity in each line (in the range from 25 to 34 km/s), with a mean value of ~ 31.3 km/s. The first represents an outflow of about 10 km/s, while the second an inflow of about 10 km/s. The Mg II h and k emission lines also show the dual-absorption structure seen in the Fe II lines. However, both the emission and absorption components in the k-line are red-shifted by 7 to 9.5 km/s, relative to their equivalent components in the h-line.

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