Astronomy and Astrophysics – Astrophysics
Scientific paper
Jul 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...274...37v&link_type=abstract
Astronomy and Astrophysics, Vol. 274, NO. 1/JUL(I), P. 37, 1993
Astronomy and Astrophysics
Astrophysics
17
Scientific paper
We present a study of the interstellar gas in a ~30'x30' region of the Large Magellanic Cloud centered around SN 1987A and including the core of the 30 Doradus nebula. The study is based on high-resolution NaI (FWHM ~ 3-7 km s^-1^) and CaII (FWHM ~ 5-7 km s^-1^) spectra of early-type LMC supergiants, collected as part of a coordinated investigation of selected regions in the Magellanic Clouds. From the analysis of the optical absorptions by means of multiple- component line fitting techniques we have obtained the most complete data base of interstellar NaI and CaII column densities and radial velocities for the LMC. The gas structure is more complex than expected on the basis of 21-cm emission surveys of the LMC, which identified just two main components in our field: in several lines of sight the absorption profiles show at least five absorption components spanning the range of radial velocities +260 km s^-1^ <~ V_hel_ <~ +300 km s^-1^. The most intense absorptions are seen between V_hel_ ~ +280 and ~ +290 km s^-1^; the gas at these velocities can be seen as a sort of galactic H I disk disrupted in several components. Absorptions at V_hel_ ~+271 km s^-1^ show a good coincidence in radial velocity and sky distribution with the most intense H I emission component in the field, which is widespread over at least several 102 pc in the plane of the sky; however, these absorptions are quite weak, suggesting that the 271 km s^-1^ gas lies in large part beyond our stars or it has a relatively high degree of NaI ionization. The behaviour of the NaI/CaII ratios as a function of radial velocity is very similar to that originally found by Routly & Spitzer in our Galaxy, the bulk velocity of the LMC absorption in our field (V_hel_ ~280 km s^-1^) playing the same role of the rest LSR velocity in the Galactic Routly-Spitzer effect. The interstellar HI/NaI abundance ratio in the LMC appears to be higher than in our Galaxy by ~0.5 dex, a result consistent with the known metal deficiency of the LMC.
D'Odorico Sandro
Dennefeld Michel
Ferlet Roger
Madjar Vidal A.
Molaro Paolo P.
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