A. Crotts, Columbia University; and S. Heathcote, Cerro Tololo Interamerican Observatory (CTIO), report on data obtained with the CTIO 4-m telescope on 1996 Dec. 5 and 1998 Feb. 17 UT (echelle spectrograph), and on 1997 Sept. 23 (RC spectrograph): "The increase in strength of the blue wing of the H-alpha emission line, as reported on IAUC 6831, is difficult to confirm with certainty in our data. Some weak emission lines have formed in the near- infrared portion of the spectrum, particularly [Fe II] at 768.6, 889.1, and 905.1 nm, and appear offset to the northeast of the supernova by about 0".5 (for the slit at p.a. 50o). (Stronger lines due to [Fe II] at 715.5, 717.2, 738.8, 745.2, and 861.7 nm are detected also in RC spectrograph data obtained on 1997 Jan. 15 by J. Maza and M. Phillips, while [Fe II] 768.6, 889.1, and 905.1 nm would have been detected at the strength found on 1997 Sept. 23, but were not.) Previously detected lines over the range 570-1080 nm are the H I Paschen series (all terms 7 to 17); [Fe VII] 608.7 nm; [Ar III] 713.5 and 775.1 nm; [Ar V] 700.5 nm; [Cl II] 857.9 nm; and [Ca II] 729.1 and 732.3 nm; [Ni II] 737.8 nm; [Cr II] 812.5, 822.9, and 830.8 nm; and perhaps [C I] 984.9 nm and [Ar IV] 723.7 and 726.2 nm. Also seen are the usual strong lines of [N II], He I, [O I], [O II], [S II], [S III] and H-alpha. New, unidentified, very weak lines are also seen at rest wavelengths 704.56, 710.37, and 711.98 nm (with a typical accuracy of +/- 0.02 nm and calculated for the supernova's redshift of 289 km/s). All of the above lines have narrow components with velocity widths less than about 100 km/s. This spectrum appears to be dominated by low- density, low-ionization shock excitation, especially to the northeast of the supernova (consistent in position with the previously reported 'hot spot'; cf. IAUC 6665, 6710)."
International Astronomical Union Circular
- Pub Date:
- March 1998