Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005jrasc..99q.145w&link_type=abstract
Journal of the Royal Astronomical Society of Canada, Vol. 99, No. 4, p.145
Astronomy and Astrophysics
Astronomy
Scientific paper
Over 50% of dust production in the Galaxy is from old stellar systems (AGB stars & Type Ia SNe). However, the origin of dust in high-redshift galaxies is expected to be much different. Such galaxies have been observed to contain abundant dust even though they are quite young. After only 1 Gyr, there has not been time for low-mass stars to evolve to the AGB. Using estimates from our Galaxy, the timescale for injection of stardust into the ISM by AGB stars is about 2.5 Gyr. Evidence from pre-solar dust grains implies that Type Ia SNe are also significant sources for interstellar dust locally, but these too are old systems that may not have had time to evolve by the epoch of our observations of high-redshift galaxies. Dust production in high-redshift galaxies therefore is expected to be dominated by Type II SNe. The condensation of dust in SN ejecta is still not well understood. One reason is that detection of newly-formed dust in SNe in nearby galaxies has been extremely rare. In August 2004, we began a program with Gemini/GMOS to study dust formation in Type II SNe. We were able to obtain spectra, as well as VRI photometry, of 14 Type II SNe with ages of 200 to 650 days. Dust formation in the SNe ejecta is indicated by a sudden decrease in continuum brightness in the visible due to increased dust extinction. This is accompanied by the development of asymmetric, blue-shifted emission-line profiles, caused by dust forming in the ejecta, and preferentially extinguishing redshifted emission from material on the far side of the SN. We will present early results from this study as well as the late-time evolution of the spectrum of the Type II supernova 2002hh in NGC 6946 obtained in August, October, and December 2004 with Gemini North and GMOS.
Clayton Geoff
Welch Doug
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