Astronomy and Astrophysics – Astronomy
Scientific paper
May 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994aas...184.0506e&link_type=abstract
American Astronomical Society, 184th AAS Meeting, #05.06; Bulletin of the American Astronomical Society, Vol. 26, p.863
Astronomy and Astrophysics
Astronomy
Scientific paper
Ultraviolet spectra from the first Hubble Space Telescope observations of a carbon star are presented, as well as line identifications and an initial analysis of the velocity structure of the emitting region. Two spectra of UU Aur (HD 46687, type N3; C5,3) have been obtained. In the lower-resolution FOS spectrum (2310 -- 3275 Angstroms), UV emission lines of Mg I, Mg II, and Fe II, fluoresced lines of Fe I and II, semi-forbidden emission from C II, Si II, and Al II, absorption lines of Fe I and Ti II, and absorption by CH and CaCl have been identified. In the high resolution GHRS spectrum, which covers a 50 Angstroms region around the Mg II h and k emission lines, overlying Mg II and Mn I absorption and two fluoresced Fe I lines have been resolved. The Mg II, and perhaps the Ti II, absorption appears to be interstellar. UV emission lines of predominantly singly ionized metals indicate the existence of a chromosphere at ~ 5000 K. In UU Aur, the Mg II emission clearly arises in material which is flowing away from the star at 35--60 km/s. Shifts of the Fe II emission lines support the conclusion that the chromosphere is expanding at highly supersonic velocities. However, overlying Mn I absorption must be due to stationary material further out. The forbidden and fluoresced lines also come from a region(s) with negligible velocity. These data imply that shocks may form in the atmospheres of carbon stars and thus be a mechanism for chromospheric heating and mass loss. In fact, previous semi-empirical chromospheric models of the carbon star TX Psc (Luttermoser, Johnson, Avrett, and Loeser 1989) indicate a similar shock-like velocity field. Luttermoser, D., Johnson, H. R., Avrett, G., and Loeser, R. 1989, ApJ 345, 543.
Carpenter Kenneth G.
Ensman Lisa M.
Johnson Hollis R.
Luttermoser Don
Robinson Richard D.
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