Browsing by Author "Graham, Matthew"
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- ItemDiscovery of 30,000 Periodic Variables in the Southern Sky(2016) Drake, Andrew J.; Djorgovski, Stanislav G.; Graham, Matthew; Catelan, Márcio; Torrealba, Gabriel; Mahabal, Ashish A.; Christensen, Eric J.; Larson, Stephen M.; McNaught, Robert; Garradd, GordonWe have completed a search for periodic variable stars within the 30,000 square degrees of the sky covered by the Catalina Surveys. Here we present the results from our analysis of six years of optical photometry taken by the Siding Spring Survey (SSS). This data covers 200 million sources at declinations between -20 and -75 degrees in the magnitude range 11 < V < 19. In addition to the 10,000 RR Lyrae that we previously discovered in this data, we find approximately 30,000 new periodic variable stars. These sources include, eclipsing binaries, RR Lyrae, LPVs, RSCVn stars, delta Scutis and Anomalous Cepheids.As part of our ongoing search for structure within the Galactic halo we determine the distances to each of the type-ab RR Lyrae. We discover that many of these stars appear to belong to the old stellar halo of the LMC. Our analysis suggests that the stellar halo of the LMC extends far beyond the limits previously observed....
- ItemPeriodic Variable Stars Across the Southern Sky(2015) Drake, Andrew J.; Graham, Matthew; Djorgovski, Stanislav G.; Catelan, Márcio; Torrealba, Gabriel; Mahabal, Ashish A.; Donalek, Ciro; Christensen, Eric J.; Larson, Stephen M.; McNaught, Robert; Garradd, GordonWe continue our search for periodic variables within the ~30,000 square degrees of the sky covered by the Catalina Surveys. Here we analyze six years of optical photometry taken by the Siding Spring Survey (SSS), which is sensitive to sources in the range 11 < V < 19. In all, this new analysis covers ten thousand square degrees on the sky at declinations between -20 and -75 degrees. Due to the very large number of periodic variable candidates found, we perform automated classification of the stars using multivariate kernel density estimation based on features selected from previously classified northern data. We test the accuracy of the results by visually validating a large sample of the objects. We also compare the classifications with those from other automated methods. The final SSS catalog contains tens of thousands of new periodic variable stars including eclipsing binaries, RR Lyrae, LPVs, delta Scuti's and Cepheids. By combining the newly discovered LPVs and RR Lyrae with our previous discoveries, we trace the path of the Sagittarius tidal streams system across the entire sky....
- ItemSupernovae in Extreme Environments(2012) Drake, Andrew J.; Prieto, Jose; Djorgovski, George; Mahabal, Ashish; Beshore, Edward; Graham, Matthew; Catelan, Marcio; Christensen, Eric; Stoll, RebeccaThe Catalina Real-time Transient Survey (CRTS) currently covers 33,000 square degrees of the sky in search of transient astrophysical events. Data provided by the Catalina Sky Survey provides an unequaled baseline against which more than 4000 unique optical transient events have been discovered and openly published in real-time. Of the more than 800 supernovae discovered among these are distinct classes of previously undetected extremely luminous type-Ic and type-IIn supernovae. These events appear to reside predominately in very faint, low-metalicity, star-forming galaxies. Similar to the environments that have been associated with so called hypernova explosions. However, the recent discovery of what was very likely the most luminous and optically energetic supernova ever discovered, CSS100217, within the AGN disk of a bright NLS1 galaxy, demonstrates that extreme supernova can occur in a variety of extreme environments. Here we propose to use Gemini observations to continue our study of the extreme supernova populations discovered by CRTS....