Interstellar CAII and NAI in the Supernova 1987A Field - Part One - Foreground and Intermediate Velocity Gas

Details Interstellar CAII and NAI in the Supernova 1987A Field - Part One - Foreground and Intermediate Velocity Gas Interstellar CAII and NAI in the Supernova 1987A Field - Part One - Foreground and Intermediate Velocity Gas

Jul 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...274..505m&link_type=abstract

Astronomy and Astrophysics, Vol. 274, NO. 2/JUL(II), P. 505, 1993

Astronomy and Astrophysics

Astrophysics

14

Scientific paper

High-resolution (3-7km s^-1^) interstellar NaI and CaII spectra for a total of 13 lines of sight in a field of 30x30 arcminutes centered on SN 1987A and including 30 Dor, have been analyzed to study the local and the intermediate velocity gas (V_hel_ <= 240 km s^-1^). Along this direction ( l = 281^deg^, b = -33^deg^) the Milky Way gas is characterized by a composite structure with two major components falling at V_hel_ = 10.3 +/- 0.6 and at V_hel_ = 24.9 +/- 1.1 km s^-1^, plus some other material with lower column density and velocities in between these two. All the components show variations in column density in the field; in particular, the 10-km s^-1^ component shows variations exceeding two orders of magnitude in the sodium column density along lines of sight separated by only ~8 arcminutes. This gas is probably located within 100 pc and therefore the variations occur on a linear scale smaller than 0.23 pc. The foreground reddening is also found to vary on the same angular scale, with E_(B-V)_ in the range from 0.05 to 0.13 mag. Intermediate velocity clouds (IVCs) are detected in almost all CaII spectra and only seldom in NaI. The direction of the two close stars Sk-69^deg^ 211 and Sk-69^deg^ 216 is rather peculiar, with a number of components comparable to that observed towards SN 1987A, which is ~8' away. The clouds at V_hel_ ~ 64km s^-1^, ~90km s^-1^ and ~170km s^-1^ are shared by more than one line of sight and show different intensities. Thus the IVCs in our field show a clumpy morphology on scales of a few arcminutes. Some IVCs are detected towards LMC stars that do not show the main LMC components at V_hel_ > 240km s^-1^, showing that this material is located in front of, and not within, the bulk of the LMC gas. The 64km s^-1^ cloud shows remarkable constancy in the radial velocity, within +/- 0.3km s^-1^ over 20 arcminutes on the sky, providing additional evidence that it is located close to our Galaxy. The CaII/NaI ratios for the IVCs are always > 10 and in a few cases even higher than 30 showing the Routly-Spitzer effect at its limiting value, thus suggesting that these IVCs are free from dust. We show that the evaluation of the abundances of the IVCs may be seriously affected by their clumpy structure. For the clouds at 55km s^-1^, 64km s^-1^ and 120km s^-1^, a calcium abundance lower by 1.0 dex than the solar value is derived.

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