56Ni dredge-up in Supernova 1987A

We use early-time observations of He I 10830 \AA to measure the extent of upward mixing of radioactive material in SN 1987A. This work develops and extends the work of Graham (1988), and places constraints on actual explosion models. The presence of the He I 10830 \AA (2s^{3}S--2p^{3}P) line at $\geq 10$ days post-explosion implies re-ionisation by $\gamma$-rays from upwardly-mixed radioactive material produced during the explosion. Using the unmixed explosion model 10H (Woosley 1988) as well as mixed versions of it, we estimated the $\gamma$-ray energy deposition by applying a purely absorptive radiative transfer calculation. The deposition energy was used to find the ionisation balance as a function of radius, and hence the 2s$^{3}$S population density profile. This was then applied to a spectral synthesis model and the synthetic spectra were compared with the observations. Neither model 10H nor the mixed version, 10HMM, succeeded in reproducing the observed He I 10830 \AA line. The discrepancy with the data found for 10HMM is particularly significant, as this model has successfully reproduced the X-ray and $\gamma$-ray observations and the UVOIR light curve. We find that a match to the He I line profile is achieved by reducing the extent of mixing in 10HMM. Our reduced-mixing models also reproduce the observed $\gamma$-ray line light curves and the iron-group velocities deduced from late-time infrared line profiles. We suggest that the He I line method provides a more sensitive measure of the extent of mixing in a type II supernova explosion.Comment: 18 pages, 5 figures, accepted for publication in MNRAS (uses epsf.sty - included

Supernovae in the nuclear regions of starburst galaxies

The feasibility of using near-infrared observations to discover supernovae in the nuclear and circumnuclear regions of nearby starburst galaxies is investigated. We provide updated estimates of the intrinsic core-collapse supernova rates in these regions. We discuss the problem of extinction, and present new estimates of the extinction towards 33 supernova remnants in the starburst galaxy M 82. This is done using H I and H_2 column density measurements. We estimate the molecular to atomic hydrogen mass ratio to be 7.4 +- 1.0 in M 82. We have assembled near-infrared photometric data for a total of 13 core-collapse supernovae, some unpublished hitherto. This constitutes the largest database of IR light curves for such events. We show that the IR light curves fall into two classes, ``ordinary'' and ``slow-declining''. Template JHKL light curves are derived for both classes. For ordinary core-collapse supernovae, the average peak JHKL absolute magnitudes are -18.4, -18.6, -18.6, and -19.0 respectively. The slow-declining core-collapse SNe are found to be significantly more luminous than the ordinary events, even at early times, having average peak JHKL absolute magnitudes of -19.9, -20.0, -20.0, and -20.4 respectively. We investigate the efficiency of a computerised image subtraction method in supernova detection. We then carry out a Monte Carlo simulation of a supernova search using K-band images of NGC 5962. The effects of extinction and observing strategy are discussed. We conclude that a modest observational programme will be able to discover a number of nuclear supernovae.Comment: 19 pages, 7 figures; accepted in MNRA

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

Spectroscopically Peculiar Type Ia Supernovae and Implications for Progenitors

In a recent paper Li et al. (2000) reported that 36 percent of 45 Type Ia supernovae (SNe Ia) discovered since 1997 in two volume-limited supernova searches were spectroscopically peculiar, and they suggested that because this peculiarity rate is higher than that reported for an earlier observational sample by Branch et al. (1993), it is now more likely that SNe Ia are produced by more than one kind of progenitor. In this paper I discuss and clarify the differences between the results of Li et al. and Branch et al. and I suggest that multiple progenitor systems are now less likely than they were before.Comment: 11 pages; accepted by PASP; several minor changes, 2 references added, main conclusions unchange

A Spitzer Space Telescope Study of SN 2003gd: Still No Direct Evidence that Core-Collapse Supernovae are Major Dust Factories

We present a new, detailed analysis of late-time mid-infrared (IR) observations of the Type II-P supernova (SN) 2003gd. At about 16 months after the explosion, the mid-IR flux is consistent with emission from 4 x 10^(-5) M(solar) of newly condensed dust in the ejecta. At 22 months emission from point-like sources close to the SN position was detected at 8 microns and 24 microns. By 42 months the 24 micron flux had faded. Considerations of luminosity and source size rule out the ejecta of SN 2003gd as the main origin of the emission at 22 months. A possible alternative explanation for the emission at this later epoch is an IR echo from pre-existing circumstellar or interstellar dust. We conclude that, contrary to the claim of Sugerman et al. (2006, Science, 313, 196), the mid-IR emission from SN 2003gd does not support the presence of 0.02 M(solar) of newly formed dust in the ejecta. There is, as yet, no direct evidence that core-collapse supernovae are major dust factories.Comment: 26 pages, 2 figures, 2 tables, accepted for publication in Astrophysical Journa

A Spitzer Space Telescope study of SN 2002hh: an infrared echo from a Type IIP supernova

We present late-time (590-994 d) mid-IR photometry of the normal, but highly-reddened Type IIP supernova SN 2002hh. Bright, cool, slowly-fading emission is detected from the direction of the supernova. Most of this flux appears not to be driven by the supernova event but instead probably originates in a cool, obscured star-formation region or molecular cloud along the line-of-sight. We also show, however, that the declining component of the flux is consistent with an SN-powered IR echo from a dusty progenitor CSM. Mid-IR emission could also be coming from newly-condensed dust and/or an ejecta/CSM impact but their contributions are likely to be small. For the case of a CSM-IR echo, we infer a dust mass of as little as 0.036 M(solar) with a corresponding CSM mass of 3.6(0.01/r(dg))M(solar) where r(dg) is the dust-to-gas mass ratio. Such a CSM would have resulted from episodic mass loss whose rate declined significantly about 28,000 years ago. Alternatively, an IR echo from a surrounding, dense, dusty molecular cloud might also have been responsible for the fading component. Either way, this is the first time that an IR echo has been clearly identified in a Type IIP supernova. We find no evidence for or against the proposal that Type IIP supernovae produce large amounts of dust via grain condensation in the ejecta. However, within the CSM-IR echo scenario, the mass of dust derived implies that the progenitors of the most common of core-collapse supernovae may make an important contribution to the universal dust content.Comment: 41 pages, 11 figures, 4 tables, accepted for publication in Astrophysical Journal (References corrected

On the High--Velocity Ejecta of the Type Ia Supernova 1994D

Synthetic spectra generated with the parameterized supernova synthetic-spectrum code SYNOW are compared to spectra of the Type Ia SN 1994D that were obtained before the time of maximum brightness. Evidence is found for the presence of two-component Fe II and Ca II features, forming in high velocity ($\ge 20,000$ \kms) and lower velocity ($\le 16,000$ \kms) matter. Possible interpretations of these spectral splits, and implications for using early--time spectra of SNe Ia to probe the metallicity of the progenitor white dwarf and the nature of the nuclear burning front in the outer layers of the explosion, are discussed.Comment: 15 pages, 3 figures, 3 tables, Astrophysical Journal, in pres