Browsing by Author "Drake, Andrew J."
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- ItemAn Updated Catalog of 4680 Northern Eclipsing Binaries with Algol-type Light-curve Morphology in the Catalina Sky Surveys(2018) Papageorgiou, Athanasios; Catelan, Márcio; Christopoulou, Panagiota-Eleftheria; Drake, Andrew J.; Djorgovski, S. G.
- ItemCRTS: An Open Optical Transient Survey(2011) Drake, Andrew J.; Djorgovski, S. G.; Mahabal, A.; Williams, R.; Graham, M. J.; Donalek, C.; Prieto, J. L.; Catelan, Márcio; Beshore, E.; Larson, S.; Christensen, E.The Catalina Real-time Transient Survey (CRTS) is an open optical transient survey that covers 3/4 of the entire sky in a search of transient astrophysical phenomena occurring on timescales of minutes to years. Observational data is derived from the three telescopes of the Catalina Sky Survey which cover up to 2,500 square degrees of sky each night. CRTS has so far discovered more that 2000 transient sources including 600 supernovae, 500 dwarf novae and more than 100 Blazars and UV Ceti variables. All data is processed within minutes of observation and discoveries are openly distributed using SkyAlert and VOEvent technologies as well as iPhone, html tables, RSS and Twitter feeds. Events are classified utilizing data from virtual observatory enabled archives, machine learning, and collaborative Citizen science....
- ItemDetection of period variations of eclipsing binaries in the Catalina Sky Survey(2021) Papageorgiou, Athanasios; Catelan, Márcio; Christopoulou, Panagiota-Eleftheria; Drake, Andrew J.; Djorgovski, S. G.
- 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....
- ItemDiscovery of Thousands of RR Lyrae by the Catalina Surveys(2013) Drake, Andrew J.; Djorgovski, S. G.; Catelan, Márcio; Torrealba, G.; Graham, M.; Mahabal, A. A.; Donalek, C.; Prieto, J.; McNaught, R.; Larson, S. M.; Christensen, E.; Beshore, E. C.We have performed an extensive search for RR Lyrae among the 500 million sources observed by the Catalina Surveys. We detect 23,000 type-ab RR Lyrae (of which 18,700 are new discoveries) from a region spanning 3/4 of the sky. By combining calibrated Catalina photometry with RR Lyrae absolute magnitude estimates, we derive accurate distances and investigate the spatial distribution of structures within the Galactic halo. We identify hundreds of new RR Lyrae belonging to the Sagittarius tidal streams system and compare their observed properties with predictions from existing N-body models. We discover significant evidence that firmly establishes the existence of a tidal stream reaching Galactocentric distances beyond 100 kpc. This stream remains to be explained by any Sagittarius model. For 1,500 of the RR Lyrae we find matches with targets observed by past SDSS spectroscopic surveys. Combining the radial velocities and metallicity estimates from the SDSS spectra, with photometric distances, we investigate the kinematics and abundances of halo tidal stream populations....
- ItemEclipsing binary stars in the era of massive surveys first results and future prospects(2017) Papageorgiou, Athanasios; Catelan, Márcio; Ramos Contreras, Rodrigo; Drake, Andrew J.Our thinking about eclipsing binary stars has undergone a tremendous change in the last decade. Eclipsing binary stars are one of nature's best laboratories for determining the fundamental physical properties of stars and thus for testing the predictions of theoretical models. Some of the largest ongoing variable star surveys include the Catalina Real-time Transient Survey (CRTS) and the VISTA Variables in the Vía Láctea survey (VVV). They both contain a large amount of photometric data and plenty of information about eclipsing binaries that wait to be extracted and exploited. Here we briefly describe our efforts in this direction....
- ItemNew low mass ratio contact binaries in the Catalina Sky Survey(2022) Christopoulou, Panagiota-Eleftheria; Lalounta, Eleni; Papageorgiou, Athanasios; Ferreira Lopes, C. E.; Catelan, Márcio; Drake, Andrew J.
- 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....
- ItemPhysical Parameters of Northern Eclipsing Binaries in the Catalina Sky Survey(2019) Papageorgiou, Athanasios; Catelan, Márcio; Christopoulou, Panagiota-Eleftheria; Drake, Andrew J.; Djorgovski, S. G.
- ItemResults from the Catalina Real-time Transient Survey(2009) Drake, Andrew J.; Djorgovski, S. G.; Mahabal, A. A.; Graham, M.; Williams, R.; Catelan, Marcio; Beshore, E.; Larson, S.; Christensen, E.The Catalina Real-time Transient Survey (CRTS) is a collaborative effort between Caltech and LPL that uses data from Catalina Sky Survey's 0.7m Schmidt telescope to search for optical transients. This survey currently covers a total of 26,000 square degrees on the sky between declinations -30 and 70. Observations covering 1200 square degrees are taken 21 nights per lunation and reach magnitudes of 19 to 20. CRTS is sensitive to transients with timescales from minutes to years since images are taken in sequences separated by 10 minutes and past observations date back over four years. Transient classification is performed using follow up imaging and spectroscopy in combination with VO-enabled archival analysis of CSS and Palomar Quest synoptic datasets and DSS, 2MASS, SDSS, GALEX and UKIDSS surveys. To date more than 600 unique transients have been identified by CRTS. These include more than 200 newly discovered Supernovae, Cataclysmic Variables and Blazars. Initial results of note include in the discovery of hyper-luminous supernovae, as well as a high rate of supernovae associated with intrinsically faint galaxies. In the near future we expect to expand the survey area and depth by utilizing data from two additional operational Catalina Sky Survey telescopes. All CRTS transients are discovered and distributed openly within minutes of observation using VOEvent technology as well as html tables, RSS feeds and GoogleSky (from VOEventNet.org). Astronomers will soon be able to automatically select transients of particular interest by using the personalized event selection available via the SkyAlert system....
- ItemResults From The First Year Of The Catalina Real-time Transient Survey(2009) Drake, Andrew J.; Djorgovski, S. G.; Mahabal, A.; Graham, M. J.; Williams, R.; Catelan, Marcio; Beshore, E.; Larson, S.; Christensen, E.The Catalina Real-time Transient Survey (CRTS) is a collaborative effort between Caltech and LPL that uses data from Catalina Sky Survey's 0.76m Schmidt telescope to search for optical transients (OTs) varying by more than two magnitudes between past and current data. The survey covers 26,000 square degrees on the sky between declination -30 and 70 at Galactic latitudes |b| > 10 deg. Sequences of four observations are taken separated by 10 minutes and cover 1200 square degrees each night for 21 nights per lunation. Observations reach transients at unfiltered magnitudes of 19 to 20. To date more than 400 unique OTs have been identified by CRTS. These transients include more than 150 supernovae and dwarf novae, as well as UV Ceti flares, high proper motion stars, comets, Miras and currently unidentified transients. Classification is carried out using follow up imaging and spectroscopy in combination with VO-enabled archival analysis of CSS and Palomar Quest synoptic datasets and DSS, 2MASS, SDSS, GALEX and UKIDSS surveys. All candidate OTs are published within 5 mins of observation and are openly accessible as VOEvents, html tables and RSS feeds (from VOEventNet.org). As part of our public outreach program, the CRTS event stream is also published in the event layer of Google Sky....
- ItemSearching for fossil remnants in the Galactic halo: photometric follow-up of southern CRTScandidates(2015) Chan, Siukuen Josephine; Navarrete, Camila; Catelan, Marcio; Duffau, Sonia; Torrealba, Gabriel. I.; Drake, Andrew J.; Belokurov, Vasily; Koposov, SergeyObservations of the fossil record of the early formation stages of the Milky Way galaxy provide important constraints on cosmological scenarios for the formation of large galaxies like our own. While the northern celestial hemisphere has been extensively examined for the presence and degree of halo substructure, the southern halo has until recently remained "terra incognita" for such studies. However, based on RR Lyrae stars detected in the course of the Catalina Real-time Transients Survey (CRTS), our team has identified a number of new candidate overdensities in the southern Galactic halo (Torrealba et al. 2015, MNRAS, 446, 2251). Here we describe some preliminary results of a deeper search for the Torrealba et al. overdensity candidates, using photometric data from selected wide-field surveys that have mapped the immediate vicinity of some of the more promising among these candidates....
- ItemSixty Thousand Periodic Variables from the Catalina Surveys(2014) Drake, Andrew J.; Graham, M.; Djorgovski, S. G.; Catelan, Marcio; Mahabal, A. A.; Prieto, J.; Donalek, C.; Christensen, E. J.; Larson, S. M.; Boattini, A.; Gibbs, A.; Grauer, A. D.; Hill, R.; Kowalski, R.; Johnson, J.; Shelly, F.; Torrealba, G.We have performed an in-depth search for periodic variable stars within the photometry from the Catalina Surveys Data Releases. Our analysis reveals ~40,000 new periodic variable stars with brightness ranging from V=11 to 20, from a region covering ~20,000 square degrees on the sky. Each source is classified based on lightcurve morphology and multi-color photometry from WISE and SDSS. The variable stars discovered include eclipsing binaries, such as Algol, beta Lyrae, W UMa and WD+dM types, and pulsators including delta Scuti's, SX Phe, LPVs, RR Lyrae and Cepheids. We combine these sources with type-ab RR Lyrae from our prior analysis to produce a periodic variable catalog containing 60,000 stars. Using ~5,500 optical spectra from SDSS DR10 we determine the metallicities, surface gravities and radial velocities of the major types. The photometry, classifications and periods will all be made publicly available through the Catalina Surveys data release website....
- 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....
- ItemThe First Data Release of the Catalina Surveys(2012) Drake, Andrew J.; Beshore, E.; Djorgovski, S. G.; Larson, S.; Boattini, A.; Catelan, Marcio; Christensen, E.; Donalek, C.; Gibbs, A.; Graham, M.; Grauer, A.; Hill, R.; Kowalski, R.; Mahabal, A.; Prieto, J. L.; Williams, R.The Catalina Surveys consists of the Catalina Sky Survey (CSS) and the Catalina Real-time Transient Survey (CRTS). These two surveys work synergistically to extract the maximum scientific return from the data gathered by Catalina telescopes. In order to further facility the wealth of time-domain science that is possible with this data, the Catalina Surveys are now releasing Catalina Schmidt telescope photometry for 200 million objects. Each source has been measured over a period of six years and comes from a 24,000 square degree region between declination -30 and +70 degrees (with 10 degree avoidance of the galactic plane). On average each location in the data release has been observed more than 200 times to a depth of V=19.5. We will provide the details of the open-access data services as well as future data releases and recent discoveries....