1Dept. of Astronomy, The Ohio State University, 140 W. 18th Ave., Columbus, OH 43210; khan, kstanek, ckochanek@astronomy.ohio-state.edu

2Center for Cosmology and AstroParticle Physics, The Ohio State University, 191 W. Woodruff Ave., Columbus, OH 43210

Finding $\Eta$ Car

Khan et al. 2011

Abstract:

The late-stage evolution of the most massive stars such as $\eta$Carinae is controlled by the effects of mass loss, which may be dominated by poorly understood eruptive mass ejections. Understanding this population is challenging because no true analogs of $\eta$Car have been clearly identified in the Milky Way or other galaxies. We utilize Spitzer IRAC images of 7 nearby ($\lesssim4$Mpc) galaxies to search for such analogs. We find 34 candidates with a flat or rising mid-IR spectral energy distributions towards longer mid-infrared wavelengths that emit $>10^5$L$_\odot$ in the IRAC bands (3.6 to 8.0$\micron$) and are not known to be background sources. Based on our estimates for the expected number of background sources, we expect that follow-up observations will show that most of these candidates are not dust enshrouded massive stars, with an expectation of only $6\pm6$ surviving candidates. Since we would detect true analogs of $\eta$Car for roughly 200 years post-eruption, this implies that the rate of eruptions like $\eta$Car is less than the ccSN rate. It is possible, however, that every M$>40$M$_\odot$ star undergoes such eruptions given our initial results. In PaperII we will characterize the candidates through further analysis and follow-up observations, and there is no barrier to increasing the galaxy sample by an order of magnitude.

stars: evolution, mass-loss, winds, outflows -- stars: individual: Eta Carinae -- galaxies: individual (M33, M81, NGC247, NGC300, NGC2403, NGC6822, NGC7793)

Finding $\eta$ Car Analogs in Nearby Galaxies Using Spitzer:
I. Candidate Selection

Rubab Khan1, K. Z. Stanek1,2, C. S. Kochanek1,2