No abstract

We have obtained high signal-to-noise spectra along the major axes of 28 S0 galaxies in order to search for the presence of disk stars on retrograde orbits. Full line-of-sight velocity distributions were extracted from the data, and the velocity distributions were modelled as arising from the superposition of populations of stars on prograde and retrograde orbits. We find no new cases in which a significant fraction of disk stars lie on retrograde orbits; an identical analysis of NGC 4550 does reveal the previouslyknown counter-rotating stellar disk in this system. Upper limits determined for each object indicate that no more than ∼ 5% of the observed disk star light could arise from counter-rotating stellar components. These results suggest that previously-discovered disk galaxies with counter-rotating stars are exceptional and that (at 95% confidence) at most 10% of S0 galaxies contain significant counter-rotating populations. The most likely value for the fraction of such S0 galaxies lies closer to 1%. This result contrasts with the prevalence of counter-rotating gas in these systems; combining our new observations with existing data, we find that 24 ± 8% (1-σ error) of the gas disks in S0 galaxies counter-rotate relative to their stellar components.

We present 42 low-resolution spectra of supernova (SN) 1993J, our complete collection from the Lick and Keck observatories, from day 3 after explosion to day 2454, as well as one Keck high-dispersion spectrum from day 383. SN 1993J began as an apparent SN II, albeit an unusual one. After a few weeks, a dramatic transition took place, as prominent helium lines emerged in the spectrum. SN 1993J had metamorphosed from a SN II to a SN IIb. Nebular spectra of SN 1993J closely resemble those of SNe Ib and Ic, but with a persistent Ha line. At very late times, the Ha emission line dominated the spectrum, but with an unusual, boxlike proÐle. This is interpreted as an indication of circumstellar interaction.

No abstract

No abstract