The 2012 explosion of SN 2009ip raises questions about our understanding of the late stages of massive star evolution. Here we present a comprehensive study of SN 2009ip during its remarkable re-brightening(s). Highcadence photometric and spectroscopic observations from the GeV to the radio band obtained from a variety of ground-based and space facilities (including the VLA, Swift, Fermi, HST and XMM) constrain SN 2009ip to be a low energy (E ∼ 10 50 erg for an ejecta mass ∼ 0.5 M ) and likely asymmetric explosion in a complex medium shaped by multiple eruptions of the restless progenitor star. Most of the energy is radiated as a result of the shock breaking out through a dense shell of material located at ∼ 5 × 10 14 cm with M ∼ 0.1 M , ejected by the precursor outburst ∼ 40 days before the major explosion. We interpret the NIR excess of emission as signature of dust vaporization of material located further out (R > 4 × 10 15 cm), the origin of which has to be connected with documented mass loss episodes in the previous years. Our modeling predicts bright neutrino emission associated with the shock break-out if the cosmic ray energy is comparable to the radiated energy. We connect this phenomenology with the explosive ejection of the outer layers of the massive progenitor star, that later interacted with material deposited in the surroundings by previous eruptions. Future observations will reveal if the luminous blue variable (LBV) progenitor star survived. Irrespective of whether the explosion was terminal, SN 2009ip brought to light the existence of new channels for sustained episodic mass-loss, the physical origin of which has yet to be identified.

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Wolf-Rayet stars (WRs) are evolved massive stars, and the relative number of WC-type and WN-type WRs should vary with metallicity, providing a sensitive test of stellar evolutionary theory. The observed WC/WN ratio is much higher than that predicted by theory in some galaxies but this could be due to observational incompleteness for WN-types, which have weaker lines. Previous studies of M33's WR content show a galactocentric gradient in the relative numbers of WCs and WNs, but only small regions have been surveyed with sufficient sensitivity to detect all of the WNs. Here we present a sensitive survey for WRs covering all of M33, finding 55 new WRs, mostly of WN type. Our spectroscopy also improves the spectral types of many previously known WRs, establishing in one case that the star is actually a background quasar. The total number of spectroscopically confirmed WRs in M33 is 206, a number we argue is complete to ∼5%, with most WRs residing in OB associations, although ∼2% are truly isolated. The WC/WN ratio in the central regions (<2 kpc) of M33 is much higher than that predicted by the current Geneva evolutionary models, while the WC/WN ratios in the outer regions are in good accord, as are the values in the SMC and LMC. The WC/WN ratio and the WC subtype distribution both argue that the oxygen abundance gradient in M33 is significantly larger than found by some recent studies, but are consistent with the two-component model proposed by Magrini et al.

Wolf-Rayet stars are evolved massive stars, and the relative number of WCtype and WN-type WRs should vary with the metallicity of the host galaxy, providing a sensitive test of stellar evolutionary theory. However, past studies of the WR content of M31 have been biased towards detecting WC stars, as their emission line signatures are much stronger than those of WNs. Here we present the results of a survey covering all of M31's optical disk (2.2 deg 2 ), with sufficient sensitivity to detect the weaker-lined WN-types. We identify 107 newly found WR stars, mostly of WN-type. This brings the total number of spectroscopically confirmed WRs in M31 to 154, a number we argue is complete to ∼ 95%, except in regions of unusually high reddening. This number is consistent with what we expect from the integrated Hα luminosity compared to that of M33. The majority of these WRs formed in OB associations around the Population I ring, although 5% are truly isolated. Both the relative number of WC to WN-type stars as well as the WC subtype distribution suggest that most WRs exist in environments with higher-than-solar metallicities, which is consistent with studies of M31's metallicity. Although the WC-to-WN ratio we find for M31 is much lower than that found by previous studies, it is still higher than what the Geneva evolutionary models predict. This may suggest that Roche-lobe overflow produces the excess of WC stars observed at high metallicity, or that the assumed rotational velocities in the models are too high.

We describe our spectroscopic follow-up to the Local Group Galaxy Survey (LGGS) photometry of M31 and M33. We have obtained new spectroscopy of 1895 stars, allowing us to classify 1496 of them for the first time. Our study has identified many foreground stars, and established membership for hundreds of early-and mid-type supergiants. We have also found nine new candidate luminous blue variables and a previously unrecognized Wolf-Rayet star. We republish the LGGS M31 and M33 catalogs with improved coordinates, and including spectroscopy from the literature and our new results. The spectroscopy in this paper is responsible for the vast majority of the stellar classifications in these two nearby spiral neighbors. The most luminous (and hence massive) of the stars in our sample are early-type B supergiants, as expected; the more massive O stars are more rare and fainter visually, and thus mostly remain unobserved so far. The majority of the unevolved stars in our sample are in the 20-40 M e range.