GeminiFocus January 2019 - Page 10

John Blakeslee Science Highlights GNIRS time-sequence spectra trace onset of dust and CO production in a nearby core-collapse supernova, GMOS-South monitors orbital motion to determine the mass of a record- setting ultra metal-poor star, and archival NICI data provide first epoch observations of the first exoplanet found within the gap of a transition disk. Nearby Supernova Illuminates Early Origins of Distant Dust Interstellar dust constitutes about 1% of the mass of interstellar matter in the Milky Way. Most of this dust is thought to originate in intermediate-mass evolved stars that ejected their outer layers as red giants or thermally pulsating asymptotic giant branch stars. Once the ejecta cool to temperatures lower than about 2,000 K, dust particles inevitably start to form from carbon and other elements. However, this process cannot explain the large amounts of dust observed in some galaxies in the early Universe, since such stars would not have had time to evolve to the dust-producing stage. The only viable explanation for the dust observed in such galaxies is production in the ejecta of core-collapse super- novae (ccSNe), and this can be tested through careful observations of ccSNe in the local Universe. Until now, detailed evolution of dust production in such supernovae, which can take place over several years, has only been followed in one object, SN 1987A in the Large Magellanic Cloud. However, the recent explosion of SN 2017eaw in the nearby galaxy NGC 6946 has provided another excellent opportunity to follow that evolution in detail over an extended period. NGC 6946 is only about 7 megaparsecs away and is popularly known as the Fireworks Gal- axy because it is a prodigious producer of supernovae, all of the core-collapse variety. SN 2017eaw was discovered in May 2017, just as its host galaxy became observable in the east- 8 GeminiFocus January 2019