Observations of SK -69 203 and the Interstellar Extinction Toward SN 1987A
Abstract
We have obtained optical and UV spectroscopic observations of the Large Magellanic Cloud (LMC) star Sk - 69^deg^ 203, which is located in the 30 Doradus region of the LMC, approximately 2.2 arcmin north of the position of SN 1987A. The optical data reveal Sk - 69^deg^ 203 to be a B0.7 Ia supergiant with a moderate nitrogen enhancement. The UV spectrum is consistent with this classification. Sk - 69^deg^ 203 is reddened by E(B - V)_total_ = 0.19, which is made up of a Galactic foreground component (~ 0.06) and a LMC component (~ 0.13). We construct UV interstellar extinction curves for Sk - 69^deg^ 203 using two lightly reddened LMC supergiants, which bracket Sk - 69^deg^ 203's spectral type, as flux standards. The resultant extinction curves are consistent with the extinction law derived in previous studies for the 30 Doradus region. The results for Sk - 69^deg^ 203 suggest that the general 30 Doradus extinction law is appropriate for dereddening the observed fluxes of SN 1987A. Assuming a spectral type of B3 for the supernova precursor, Sk - 69^deg^ 202, and the intrinsic colors for a LMC B3 Ia supergiant, we find a total reddening along the supernova line of sight of E(B - V) = 0.16, also consisting of Galactic and LMC components. We tabulate the total extinction affecting SN 1987A observations at a number of UV and optical wavelengths. The LMC component of the reddening [E(B - V) ~0.10] and the 30 Doradus gas- to-dust ratio imply a column density of N(H I) ~ 2.4 x 10^21^ cm^-2^ for LMC neutral hydrogen in front of SN 1987A. Published H I 21 cm observations show that SN 1987A is located in a region with a strong E-W gradient in the total hydrogen content. Comparison with the H I column density implied by the reddening indicates that the supernova is imbedded approximately in the middle of the main H I complex.
- Publication:
-
The Astronomical Journal
- Pub Date:
- May 1990
- DOI:
- 10.1086/115432
- Bibcode:
- 1990AJ.....99.1483F
- Keywords:
-
- Interstellar Extinction;
- Supernova 1987a;
- B Stars;
- Cosmic Dust;
- Magellanic Clouds;
- Supergiant Stars;
- Ultraviolet Spectroscopy;
- Astronomy;
- STARS: SUPERNOVAE