| Popis: |
Although small in number, massive stars are critical to the formation and evolution of galaxies. They shape the interstellar medium ofgalaxies through their strong winds and ultra-violet radiation, are amajor source of the heavy elements enriching the interstellar medium,and are the progenitors of core-collapse supernovae and gamma-raybursts, which are among the most energetic explosions in the Universeand mark the death of a massive star. Still, our understanding of theconnection between massive stars and supernovae from observations isfairly limited. In this dissertation, I present new observationalevidence that shows the importance of metallicity, mass-loss, andbinarity in the lives and deaths of massive stars.We investigate how the different types of supernovae are relativelyaffected by the metallicity of their host galaxy. We take advantage ofthe large number of spectra of star-forming galaxies obtained by theSloan Digital Sky Survey and their overlap with supernova hostgalaxies. We find strong evidence that type Ib/c supernovae areoccurring in higher-metallicity host galaxies than type IIsupernovae. We discuss various implications of our findings forunderstanding supernova progenitors and their host galaxies, includinginteresting supernovae found in low-metallicity hosts.We present the discovery of the progenitors of SN 2008S and the luminoustransient in NGC 300 in archival data obtained with the Spitzer SpaceTelescope. They are deeply dust-enshrouded massive stars, with extremelyred mid-infrared colors compared to other massive stars, and relativelylow bolometric luminosities ≈5x104 L☉. We discuss the implications ofthese findings for the evolution and census of “low-mass” massivestars (i.e., ~8-12 M☉), and we connect it with theoretical discussionsof electron-capture supernovae near this mass range, explosive birth ofmassive white dwarfs, and massive star outbursts.We present a Spitzer low-resolution mid-infrared spectrum of theluminous transient in NGC 300. The spectrum shows that the transient isvery luminous in the mid-infrared and most of the pre-existingprogenitor dust survived the explosion. Furthermore, the spectrum showsstrong, broad emission features that are observed in Galacticcarbon-rich proto-planetary nebulae. These observations support ourconclusions of an explosive event on a massive carbon-rich AGB orpost-AGB star as the origin of the transient in NGC 300 and SN 2008S.We present extensive ugriz YHJKs photometry and optical spectroscopy of SN2005gj. These data show that SN 2005gj is the second possible case,after SN 2002ic, of a thermonuclear explosion in a dense circumstellarenvironment. The interaction of the supernova ejecta with the densecircumstellar medium is stronger than in SN 2002ic.Finally, we present the discovery of a peculiar eclipsing binary in avariability survey of the dwarf galaxy Holmberg IX undertaken with theLarge Binocular Telescope. The binary has a period of 271 days, and iscomposed of two yellow supergiants that are overflowing their Rochelobes. Such systems must be rare, and indeed we only note one similarsystem in the Small Magellanic Cloud. We propose that these systems maybe the progenitors of supernovae that appeared to have yellow-supergiantprogenitors. |
