Coronal C⁺³ in the Large Magellanic Cloud: Evidence for a Hot Halo

Abstract

Based on the detection of C IV absorption in five Large Magellanic Cloud (LMC) stars observed with the Goddard High-Resolution Spectrograph on the Hubble Space Telescope, we present the first unambiguous evidence that C⁺³ exists in the LMC away from regions where it could have been locally produced. We can exclude that this C⁺³ is associated with hot early-type stars or active regions. Significant differences between the Hα and C⁺³ velocities toward our probes indicate that H⁺ and C⁺³ are not cospatial. Large column density variations show that the distribution of C⁺³ is not uniform. The properties of the LMC C IV lines are similar but not identical to those found for the Milky Way: 45 km s^-1 versus 73 km s^-1 for the average FWHM, (8-12) × 10¹³ cm^-2 versus (9-16) × 10¹³ cm^-2 for the average column density. The Hα versus C IV velocity differences and the similarity of the properties of the LMC and Milky Way C IV absorption suggest that at least some of the C⁺³ in the LMC is in a hot corona and that it has been produced by processes similar to those in the Milky Way. Our results show the feasibility of detecting high-ionization absorption in faint LMC stars, but more observations will be necessary before we can understand the distribution and properties of 10⁵ K gas in the LMC.

Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Also based on observations with the IUE satellite, sponsored and operated by NASA, by the Science and Engineering Research Council, and by the European Space Agency.