Optical Observations of Core-Collapse Supernovae

I present an overview of optical observations (mostly spectra) of Type II, Ib, and Ic supernovae (SNe). SNe II are defined by the presence of hydrogen, and exhibit a very wide variety of properties. SNe II-L tend to show evidence of late-time interaction with circumstellar material. SNe IIn are distinguished by relatively narrow emission lines with little or no P-Cygni absorption component and (quite often) slowly declining light curves; they probably have unusually dense circumstellar gas with which the ejecta interact. Some SNe IIn, however, might not be genuine SNe, but rather are ``impostors'' --- specifically, super-outbursts of luminous blue variables. SNe Ib do not exhibit the deep 6150 Angstrom absorption characteristic of ``classical'' SNe Ia; instead, their early-time spectra have He I absorption lines. SNe Ic appear similar to SNe Ib, but lack the helium lines as well. Spectra of SNe IIb initially exhibit hydrogen, yet gradually evolve to resemble those of SNe Ib; their progenitors seem to contain only a low-mass skin of hydrogen. Spectropolarimetry thus far indicates large asymmetries in the ejecta of SNe IIn, but much smaller ones in SNe II-P. As one peers deeper into the ejecta of core-collapse SNe, the asymmetry (indicated by the amount of polarization) seems to increase. There is intriguing, but inconclusive, evidence that some peculiar SNe IIn might be associated with gamma-ray bursts. The rates of different kinds of SNe as a function of Hubble type are still relatively poorly known, although there are good prospects for future improvement.Comment: 19 pages, 10 figures. To appear in "Young Supernova Remnants," ed. S. S. Holt (New York: American Institute of Physics), 200

Optical Observations of Type II Supernovae

I present an overview of optical observations (mostly spectra) of Type II supernovae. SNe II are defined by the presence of hydrogen, and exhibit a very wide variety of properties. SNe II-L tend to show evidence of late-time interaction with circumstellar material. SNe IIn are distinguished by relatively narrow emission lines with little or no P-Cygni absorption component and (quite often) slowly declining light curves; they probably have unusually dense circumstellar gas with which the ejecta interact. Some SNe IIn, however, might not be genuine SNe, but rather are super-outbursts of luminous blue variables. The progenitors of SNe IIb contain only a low-mass skin of hydrogen; their spectra gradually evolve to resemble those of SNe Ib. Limited spectropolarimetry thus far indicates large asymmetries in the ejecta of SNe IIn, but much smaller ones in SNe II-P. There is intriguing, but still inconclusive, evidence that some peculiar SNe IIn might be associated with gamma-ray bursts. SNe II-P are useful for cosmological distance determinations with the Expanding Photosphere Method, which is independent of the Cepheid distance scale.Comment: 18 pages, 10 embedded figures, latex with aipproc style file included, to appear in "Cosmic Explosions" -- eds. S. Holt and W. W. Zhang (New York: American Institute of Physics), 200

Spectropolarimetry of Core-Collapse Supernovae

We briefly review the young field of spectropolarimetry of core-collapse supernovae (SNe). Spectropolarimetry provides the only direct known probe of early-time supernova (SN) geometry. The fundamental result is that asphericity is a ubiquitous feature of young core-collapse SNe. However, the nature and degree of the asphericity vary considerably. The best predictor of core-collapse SN polarization seems to be the mass of the hydrogen envelope that is intact at the time of the explosion: those SNe that arise from progenitors with large, intact envelopes (e.g., Type II-plateau) have very low polarization, while those that result from progenitors that have lost part (SN IIb, SN IIn) or all (SN Ib) of their hydrogen (or even helium; SN Ic) layers prior to the explosion tend to show substantial polarization. Thus, the deeper we probe into core-collapse events, the greater the asphericity seems to be, suggesting a fundamentally asymmetric explosion with the asymmetry damped by the addition of envelope material.Comment: Invited review at Supernovae as Cosmological Lighthouses, 16-19 June, Padua, IT. 6 page

Probing black hole X-ray binaries with the Keck telescopes

The advent of the large effective apertures of the Keck telescopes has resulted in the determination with unprecedented accuracy of the mass functions and mass ratios of faint (R ~ 21 mag) X-ray transients (GS 2000+25, GRO J0422+32, Nova Oph 1977, Nova Vel 1993), as well as constraining the main-sequence companion star parameters and producing images of the accretion disks around the black holes.Comment: 7 pages, 4 figures, SPIE Symposium 4005, in pres