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A new link in the causal mapping between massive stars and potentially fatalexplosive transients opened with the 2008 discovery of the dust-obscuredprogenitors of the luminous outbursts in NGC 6946 and NGC 300. Here we carryout a systematic mid-IR photometric search for massive, luminous, self-obscuredstars in four nearby galaxies: M33, NGC 300, M81, and NGC 6946. For detection,we use only the 3.6 micron and 4.5 micron IRAC bands, as these can still beused for multi-epoch Spitzer surveys of nearby galaxies (=<10 Mpc). We combinefamiliar PSF and aperture-photometry with an innovative application of imagesubtraction to catalog the self-obscured massive stars in these galaxies. Inparticular, we verify that stars analogous to the progenitors of the NGC 6946(SN 2008S) and NGC 300 transients are truly rare in all four galaxies: theirnumber may be as low as ~1 per galaxy at any given moment. This resultempirically supports the idea that the dust-enshrouded phase is a veryshort-lived phenomenon in the lives of many massive stars and that theseobjects constitute a natural extension of the AGB sequence. We also providemid-IR catalogs of sources in NGC 300, M81, and NGC 6946.

Census of Self-Obscured Massive Stars in Nearby Galaxies with Spitzer: Implications for Understanding the Progenitors of SN 2008S-Like Transients