Interacting supernovae and supernova impostors. SN 2007sv: the major eruption of a massive star in UGC 5979

We report the results of the photometric and spectroscopic monitoring campaign of the transient SN 2007sv. The observables are similar to those of type IIn supernovae, a well-known class of objects whose ejecta interact with pre-existing circum-stellar material. The spectra show a blue continuum at early phases and prominent Balmer lines in emission, however, the absolute magnitude at the discovery of SN 2007sv (M_R = - 14.25 +/- 0.38) indicate it to be most likely a supernova impostor. This classification is also supported by the lack of evidence in the spectra of very high velocity material as expected in supernova ejecta. In addition we find no unequivocal evidence of broad lines of alpha - and/or Fe-peak elements. The comparison with the absolute light curves of other interacting objects (including type IIn supernovae) highlights the overall similarity with the prototypical impostor SN 1997bs. This supports our claim that SN 2007sv was not a genuine supernova, and was instead a supernova impostor, most likely similar to the major eruption of a luminous blue variable.Comment: Accepted for publication in MNRAS. 15 pages, 11 figures, 5 table

Luminous Blue Variable eruptions and related transients: Diversity of progenitors and outburst properties

We present new light curves and spectra for a number of extragalactic optical transients or "SN impostors" related to giant eruptions of LBVs, and we provide a comparative discussion of LBV-like giant eruptions known to date. New data include photometry and spectroscopy of SNe1999bw, 2000ch, 2001ac, 2002bu, 2006bv, and 2010dn. SN2010dn resembles SN2008S and NGC 300-OT, whereas SN2002bu shows spectral evolution from a normal LBV at early times to a twin of these cooler transients at late times. SN2008S, NGC300-OT, and SN2010dn appear to be special cases of a broader eruptive phenomenon where the progenitor star was enshrouded by dust. Examining the full sample, SN impostors have range of timescales from a day to decades, potentially suffering multiple eruptions. The upper end of the luminosity distribution overlaps with the least luminous SNe. The low end of the luminosity distribution is poorly defined, and a distinction between various eruptions is not entirely clear. We discuss observational clues concerning winds or shocks as the relevant mass-loss mechanism, and we evaluate possible ideas for physical mechanisms. Although examples of these eruptions are sufficient to illustrate their diversity, their statistical distribution will benefit greatly from upcoming transient surveys. Based on the distribution of eruptions, we propose that SN1961V was not a member of this class of impostors, but was instead a true core-collapse SNIIn preceded by a giant LBV eruption. (abridged)Comment: 36(!) journal pages, 16 figures. submitted to MNRAS on october 12. coments welcome. updated reference

A New Class of Luminous Transients and A First Census of Their Massive Stellar Progenitors

The progenitors of SN 2008S and the 2008 transient in NGC300 were dust-enshrouded, with extremely red mid-infrared (MIR) colors and relatively low luminosities. The transients were optically faint (-13 < M_V < -15) compared to normal core-collapse supernovae (SNe), and their spectra exhibited narrow emission lines. These events are unique among transient-progenitor pairs and hence constitute a new class. Whether they are true SNe or bright massive-star eruptions, we argue that their rate is ~20% of the SN rate. This fact is remarkable in light of the observation that a very small fraction of all massive stars have the MIR colors of the SN 2008S and NGC300 progenitors, as we show using MIR and optical luminosity, color, and variability properties of massive stars in M33. We find that the fraction of massive stars with colors consistent with these progenitors is 1/10000. In fact, only < 10 similar objects exist in M33 - all of which lie at the luminous red extremum of the AGB sequence. That these transients are relatively common with respect to SNe, while their progenitors are rare compared to the massive star population, implies that the dust-enshrouded phase is a short-lived phase in the lives of many massive stars. This shrouded epoch can occur only in the last ~10^4 yr before explosion, be it death or merely eruption. We discuss the implications of this finding for the evolution and census of ``low-mass'' massive stars (8-12 Msun), and we connect it with theoretical discussions of electron-capture SNe and the explosive birth of white dwarfs. A systematic census with (warm) Spitzer of galaxies in the local universe for analogous progenitors would significantly improve our knowledge of this channel to massive stellar explosions, and potentially to others with obscured progenitors. (Abridged)Comment: 24 pages; revised in response to referee's comments; conclusions unchanged, discussion update

A Systematic Study of Mid-Infrared Emission from Core-Collapse Supernovae with Spirits

The American Astronomical Society. All rights reserved.We present a systematic study of mid-infrared emission from 141 nearby supernovae (SNe) observed with Spitzer/IRAC as part of the ongoing SPIRITS survey. We detect 8 Type Ia and 36 core-collapse SNe. All Type Ia/Ibc SNe become undetectable within three years of explosion, whereas 22 ± 11% of Type II SNe continue to be detected. Five Type II SNe are detected even two decades after discovery (SN 1974E, 1979C, 1980K, 1986J, and 1993J). Warm dust luminosity, temperature, and a lower limit on mass are obtained by fitting the two IRAC bands, assuming an optically thin dust shell. We derive warm dust masses between 10-6 and 10-2 M o and dust color temperatures between 200 and 1280 K. This observed warm dust could be pre-existing or newly created, but in either case represents a lower limit to the dust mass because cooler dust may be present. We present three case studies of extreme SNe. SN 2011ja (II-P) was over-luminous ([4.5] = -15.6 mag) at 900 days post explosion with increasing hot dust mass, suggesting either an episode of dust formation or intensifying circumstellar material (CSM) interactions heating up pre-existing dust. SN 2014bi (II-P) showed a factor of 10 decrease in dust mass over one month, suggesting either dust destruction or reduced dust heating. The IR luminosity of SN 2014C (Ib) stayed constant over 800 days, possibly due to strong CSM interaction with an H-rich shell, which is rare among stripped-envelope SNe. The observations suggest that this CSM shell originated from an LBV-like eruption roughly 100 years pre-explosion. The observed diversity demonstrates the power of mid-IR observations of a large sample of SNe. © 2017

Continuous medial representation for anatomical structures.

The m-rep approach pioneered by Pizer et al. (2003) is a powerful morphological tool that makes it possible to employ features derived from medial loci (skeletons) in shape analysis. This paper extends the medial representation paradigm into the continuous realm, modeling skeletons and boundaries of three-dimensional objects as continuous parametric manifolds, while also maintaining the proper geometric relationship between these manifolds. The parametric representation of the boundary-medial relationship makes it possible to fit shape-based coordinate systems to the interiors of objects, providing a framework for combined statistical analysis of shape and appearance. Our approach leverages the idea of inverse skeletonization, where the skeleton of an object is defined first and the object's boundary is derived analytically from the skeleton. This paper derives a set of sufficient conditions ensuring that inverse skeletonization is well-posed for single-manifold skeletons and formulates a partial differential equation whose solutions satisfy the sufficient conditions. An efficient variational algorithm for deformable template modeling using the continuous medial representation is described and used to fit a template to the hippocampus in 87 subjects from a schizophrenia study with sub-voxel accuracy and 95% mean overlap