Supernova Environments in Hubble Space Telescope Images

The locations of supernovae in the local stellar and gaseous environment in galaxies contain important clues to their progenitor stars. Access to this information, however, has been hampered by the limited resolution achieved by ground-based observations. High spatial resolution Hubble Space Telescope (HST) images of galaxy fields in which supernovae had been observed can improve the situation considerably. We have examined the immediate environments of a few dozen supernovae using archival post-refurbishment HST images. Although our analysis is limited due to signal-to-noise ratio and filter bandpass considerations, the images allow us for the first time to resolve individual stars in, and to derive detailed color-magnitude diagrams for, several environments. We are able to place more rigorous constraints on the masses of these supernovae. A search was made for late-time emission from supernovae in the archival images, and for the progenitor stars in presupernova images of the host galaxies. In particular, we highlight the results for the Type II SN 1979C in M100. In addition, we have identified the progenitor of the Type IIn SN 1997bs in NGC 3627. We also add to the statistical inferences that can be made from studying the association of SNe with recent star-forming regions

Radio Detection of SN 1986E in NGC 4302

Radio observations of SN 1986E have shown a clear detection of emission at 6 cm wavelength about 8 months after optical discovery. Combined with a number of new upper limits and a study of the possible models, it appears that SN 1986E was probably a fairly normal Type IIL supernova, somewhat similar to SN 1980K, with radio emission at roughly expected levels. This detection continues the correlation between radio detection and late time optical emission.Comment: 14 pages, LaTeX (AASTeX), 2 PostScript figures, to appear in ApJ (Letters

Radio emission from SNe and young SNRs

Study of radio supernovae (RSNe), the earliest stages of supernova remnant (SNR) formation, over the past 20 years includes two dozen detected objects and more than 100 upper limits. From this work we are able to identify classes of radio properties, demonstrate conformance to and deviations from existing models, estimate the density and structure of the circumstellar material and, by inference, the evolution of the presupernova stellar wind, and reveal the last stages of stellar evolution before explosion. It is also possible to detect ionized hydrogen along the line of sight, to demonstrate binary properties of the stellar system, and to show clumpiness of the circumstellar material. More speculatively, it may be possible to provide distance estimates to RSNe

Early-time Spitzer observations of the type II-Plateau supernova, 2004dj

We present mid-infrared observations with the Spitzer Space Telescope of the nearby type II-P supernova, SN 2004dj, at epochs of 89 to 129 days. We have obtained the first mid-IR spectra of any supernova apart from SN 1987A. A prominent [NiII] 6.64 micron line is observed, from which we deduce that the mass of stable nickel must be at least 2.2e10(-4) Msun. We also observe the red wing of the CO-fundamental band. We relate our findings to possible progenitors and favour an evolved star, most likely a red supergiant, with a probable initial mass between ~10 and 15 Msun.Comment: ApJ Letters (accepted

HST Scattered Light Imaging and Modeling of the Edge-on Protoplanetary Disk ESO-Hα\alpha 569

We present new HST ACS observations and detailed models for a recently discovered edge-on protoplanetary disk around ESO H$\alpha$ 569 (a low-mass T Tauri star in the Cha I star forming region). Using radiative transfer models we probe the distribution of the grains and overall shape of the disk (inclination, scale height, dust mass, flaring exponent and surface/volume density exponent) by model fitting to multiwavelength (F606W and F814W) HST observations together with a literature compiled spectral energy distribution. A new tool set was developed for finding optimal fits of MCFOST radiative transfer models using the MCMC code emcee to efficiently explore the high dimensional parameter space. It is able to self-consistently and simultaneously fit a wide variety of observables in order to place constraints on the physical properties of a given disk, while also rigorously assessing the uncertainties in those derived properties. We confirm that ESO H$\alpha$ 569 is an optically thick nearly edge-on protoplanetary disk. The shape of the disk is well described by a flared disk model with an exponentially tapered outer edge, consistent with models previously advocated on theoretical grounds and supported by millimeter interferometry. The scattered light images and spectral energy distribution are best fit by an unusually high total disk mass (gas+dust assuming a ratio of 100:1) with a disk-to-star mass ratio of 0.16.Comment: Accepted for publication in Ap

Radio Emission from SN 2001gd in NGC 5033

We present the results of monitoring the radio emission from the Type IIb supernova SN 2001gd between 2002 February 8 and 2002 October 28. Most of the data were obtained using the Very Large Array at the five wavelengths of $\lambda \lambda$1.3 cm (22.4 GHz), 2.0 cm (14.9 GHz), 3.6 cm (8.44 GHz), 6.2 cm (4.86 GHz), and 21 cm (1.4 GHz). Observations were also made with Giant Meterwave Radio Telescope at $\lambda$21 cm (1.4 GHz). The object was discovered optically well after maximum light, making any determination of the early radio evolution difficult. However, subsequent observations indicate that the radio emission has evolved regularly in both time and frequency and is well described by the SN shock/circumstellar medium interaction model.Comment: 16 pages 2 figures to appear in Astrophysical Journa

The Light Echo Around Supernova 2003gd in Messier 74

We confirm the discovery of a light echo around the Type II-plateau Supernova 2003gd in Messier 74 (NGC 628), seen in images obtained with the High Resolution Channel of the Advanced Camera for Surveys on-board the Hubble Space Telescope (HST), as part of a larger Snapshot program on the late-time emission from supernovae. The analysis of the echo we present suggests that it is due to the SN light pulse scattered by a sheet of dust grains located about 113 pc in front of the SN, and that these grains are not unlike those assumed to be in the diffuse Galactic interstellar medium, both in composition and in size distribution. The echo is less consistent with scattering off carbon-rich grains, and, if anything, the grains may be somewhat more silicate-rich than the Galactic dust composition. The echo also appears to be more consistent with a SN distance closer to 7 Mpc than 9 Mpc. This further supports the conclusion we reached elsewhere that the initial mass for the SN progenitor was relatively low (about 8--9 M_suns). HST should be used to continue to monitor the echo in several bands, particularly in the blue, to better constrain its origin.Comment: 8 pages, 4 figures, To appear in PASP (2006 March); disregard previous versio

Detection of Pre-Shock Dense Circumstellar Material of SN 1978K

The supernova SN 1978K has been noted for its lack of emission lines broader than a few thousand km/s since its discovery in 1990. Modeling of the radio spectrum of the peculiar SN 1978K indicates the existence of HII absorption along the line of sight. To determine the nature of this absorbing region, we have obtained a high-dispersion spectrum of SN 1978K at the wavelength range 6530--6610 \AA. The spectrum shows not only the moderately broad H-alpha emission of the supernova ejecta but also narrow nebular H-alpha and [N II] emission. The high [N II]6583/H-alpha ratio, 0.8-1.3, suggests that this radio absorbing region is a stellar ejecta nebula. The expansion velocity and emission measure of the nebula are consistent with those seen in ejecta nebulae of luminous blue variables. Previous low-dispersion spectra have detected a strong [N II]5755 line, indicating an electron density of 3-12x10^5 cm^{-3}. We argue that this stellar ejecta nebula is probably part of the pre-shock dense circumstellar envelope of SN 1978K. We further suggest that SN 1997ab may represent a young version of SN 1978K.Comment: 12 pages, 1 figure, accepted for publication in the ApJ Letter

Radio Observations of SN 1980K: Evidence for Rapid Presupernova Evolution

New observations of SN 1980K made with the VLA at 20 and 6 cm from 1994 April through 1996 October show that the supernova (SN) has undergone a significant change in its radio emission evolution, dropping by a factor of ~2 below the flux density S \propto t^{-0.73} power-law decline with time t observed earlier. However, although S at all observed frequencies has decreased significantly, its current spectral index of \alpha= -0.42\pm0.15 (S \propto \nu^{+\alpha}) is consistent with the previous spectral index of \alpha=-0.60_{-0.07}^{+0.04}. It is suggested that this decrease in emission may be due to the SN shock entering a new region of the circumstellar material which has a lower density than that expected for a constant speed (w), constant mass-loss rate (Mdot) wind from the progenitor. If such an interpretation is correct, the difference in wind and shock speeds appears to indicate a significant evolution in the mass-loss history of the SN progenitor ~10^4 years before explosion, with a change in circumstellar density (\propto Mdot/w) occurring over a time span of \lesssim 4 kyr. Such features could be explained in terms of a fast ``blue-loop'' evolutionary phase of a relatively massive pre-SN progenitor star. If so, we may, for the first time, provide a stringent constraint on the mass of the SN progenitor based solely on the SN's radio emission.Comment: 22 pages, 3 figures, to appear in Ap