Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004apj...612.1140c&link_type=abstract
The Astrophysical Journal, Volume 612, Issue 2, pp. 1140-1146.
Astronomy and Astrophysics
Astronomy
6
Atomic Data, Stars: Activity, Stars: Atmospheres, Stars: Individual: Alphanumeric: Gj 551, Stars: Late-Type, Ultraviolet: Stars
Scientific paper
We present far-UV and UV spectroscopic observations of Proxima Centauri obtained as part of our continued investigation into the optically thin approximation assumed for the transition regions of late-type stars. Significant opacity is found in the C III lines during both the quiescent and flaring states of Proxima Cen, with up to 70% of the expected flux being lost in the latter. Our findings cast some doubt on the suitability of the C III λ977 line for estimating the electron density in stellar atmospheres. However, the opacity has no significant effect on the observed line widths. We calculate optical depths for homogeneous and inhomogeneous geometries and estimate an electron density of 6×1010 cm-3 for the transition region using the O IV line ratios at 1400 Å. The combination of electron density and optical depth indicates path lengths as low as ~10 km, which are in excellent agreement with estimates of the small-scale structure seen in the solar transition region.
Bloomfield Shaun D.
Christian Damian Joseph
Dupuis Jean
Keenan Francis P.
Mathioudakis Michail
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