A. J. Drake

Discovery of ∼9000 new RR Lyrae in the southern Catalina surveys

We present the results of a deep, wide-area variability survey in the Southern hemisphere, the first of its kind. As part of the Catalina Sky Surveys, the Siding Spring Survey (SSS) has covered 14,800 square degrees in the declination range of 75 ◦ 6 � 6 15 ◦ . To mine the enormous SSS dataset efficiently we have developed two algorithms: Automatic Period Selection (APS) and Automatic Fourier Decomposition (AFD), which aim to sharpen the period estimation and produce robust lightcurve models. Armed with the APS and AFD outputs we classify 10,540 ab-type RR Lyrae (RRab) stars (�90% of which are new) across the Southern sky. As well as the positional information we supply photometric metallicities, and unreddened distances. For the RRab stars in the halo, a study of the photometric metallicity distribution reveals a nearly Gaussian shape with a mean metallicity of [Fe/H] = 1.4 dex and a dispersion of 0.3 dex. A spatial study of the RRab metallicities shows no significant radial gradient in the first � 7 kpc from the Galaxy center. However, further out, a small negative gradient is clearly present. This is complemented by a very obvious correlation of the mean RR Lyrae metallicity with distance above the Galactic plane, z. We have also carried out an initial substructure search using the discovered RRab, and present the properties of the candidates with significance greater than 2 �. Most prominent among these is a southern extension of the Sagittarius dwarf galaxy’s stream system, reaching down to declinations � 40deg.

Multiwavelength observations of the γ-ray-emitting narrow-line Seyfert 1 PMN J0948+0022 in 2011

We report on radio-to-gamma-ray observations during 2011 May-September of PMN J0948+0022, the first narrow-line Seyfert 1 (NLSy1) galaxy detected in gamma-rays by Fermi-Large Area Telescope. Strong variability was observed in gamma-rays, with two flaring periods peaking on 2011 June 20 and July 28. The variability observed in optical and near-infrared seems to have no counterpart in gamma-rays. This different behaviour could be related to a bending and inhomogeneous jet or a turbulent extreme multicell scenario. The radio spectra showed a variability pattern typical of relativistic jets. The XMM spectrum shows that the emission from the jet dominates above similar to 2 keV, while a soft X-ray excess is evident in the low-energy part of the X-ray spectrum. Models where the soft emission is partly produced by blurred reflection or Comptonization of the thermal disc emission provide good fits to the data. The X-ray spectral slope is similar to that found in radio-quiet NLSy1, suggesting that a standard accretion disc is present, as expected from the high accretion rate. Except for the soft X-ray excess, unusual in jet-dominated active galactic nuclei, PMN J0948+0022, shows all characteristics of the blazar class.

New RR Lyrae variables in binary systems

Despite their importance, very few RR Lyrae (RRL) stars have been known to reside in binary systems. We report on a search for binary RRL in the OGLE-III Galactic bulge data. Our approach consists in the search for evidence of the light-travel time effect in so-called observed minus calculated (O−C) diagrams. Analysis of 1952 well-observed fundamental-mode RRL in the OGLE-III data revealed an initial sample of 29 candidates. We used the recently released OGLE-IV data to extend the baselines up to 17 years, leading to a final sample of 12 firm binary candidates. We provide O−C diagrams and binary parameters for this final sample, and also discuss the properties of 8 additional candidate binaries whose parameters cannot be firmly determined at present. We also estimate that ≳4 per cent of the RRL reside in binary systems.

A SERENDIPITOUS ALL SKY SURVEY FOR BRIGHT OBJECTS IN THE OUTER SOLAR SYSTEM

We use seven yearʼs worth of observations from the Catalina Sky Survey and the Siding Spring Survey covering most of the northern and southern hemisphere at galactic latitudes higher than 20° to search for serendipitously imaged moving objects in the outer solar system. These slowly moving objects would appear as stationary transients in these fast cadence asteroids surveys, so we develop methods to discover objects in the outer solar system using individual observations spaced by months, rather than spaced by hours, as is typically done. While we independently discover eight known bright objects in the outer solar system, the faintest having V = 19.8 ± 0.1, no new objects are discovered. We find that the survey is nearly 100% efficient at detecting objects beyond 25 AU for V ≾ 19.1 V ≾ 18.6 in the southern hemisphere) and that the probability that there is one or more remaining outer solar system object of this brightness left to be discovered in the unsurveyed regions of the galactic plane is approximately 32%.

Flashes in a star stream: Automated classification of astronomical transient events

An automated, rapid classification of transient events detected in the modern synoptic sky surveys is essential for their scientific utility and effective follow-up using scarce resources. This presents some unusual challenges: the data are sparse, heterogeneous and incomplete; evolving in time; and most of the relevant information comes not from the data stream itself, but from a variety of archival data and contextual information (spatial, temporal, and multi-wavelength). We are exploring a variety of novel techniques, mostly Bayesian, to respond to these challenges, using the ongoing CRTS sky survey as a testbed. The current surveys are already overwhelming our ability to effectively follow all of the potentially interesting events, and these challenges will grow by orders of magnitude over the next decade as the more ambitious sky surveys get under way. While we focus on an application in a specific domain (astrophysics), these challenges are more broadly relevant for event or anomaly detection and knowledge discovery in massive data streams.

Supernovae 2016bdu and 2005gl, and their link with SN 2009ip-like transients: another piece of the puzzle

PRIN-INAF; MIUR PRIN; Royal Society - Science Foundation Ireland University Research Fellowship; European Union through ERC [320360]; US National Science Foundation (NSF) [AST-1515876, AST-1515927]; NSFC [11573003]; Chinese Academy of Sciences [XDB09000000]; National Aeronautics and Space Administration (NASA) - Space Telescope Science Institute (STScI) [HST-HF-51348.001]; NASA [NAS 5-26555, NN12AR55G, NNX08AR22G, NNX12AR65G, NNX14AM74G]; NSF [AST-1515927, AST-1211916, PHY-1607611, AST-1313422, AST-1413600]; TABASGO Foundation; Christopher R. Redlich Fund; Miller Institute for Basic Research in Science (U.C. Berkeley); STScI [HST-AR-14295]; DOE [DE-FG02-97ER25308]; FONDECYT [1151445]; Ministry of Economy, Development, and Tourisms Millennium Science Initiative [IC120009]; ERCgrant [291222]; Emil Aaltonen Foundation; Finnish Cultural Foundation; Vilho, Yrjo and Kalle Vaisala Foundation of the Finnish Academy of Science and Letters; EU via ERCgrant [307260]; Quantum Universe I-Core program by Israeli Committee for Planning and Budgeting; ISF; Kimmel award; Israel Science Foundation, Minerva; I-CORE Program of the Planning and Budgeting Committee; Israel Science Foundation; Danish Agency for Science and Technology and Innovation through Sapere Aude; Villum foundation; Instrument Center for Danish Astrophysics (IDA); Gordon and Betty Moore Foundation [GBMF5490]; Center for Cosmology and Astro-Particle Physics (CCAPP) at OSU; Chinese Academy of Sciences South America Center for Astronomy (CASSACA); Mt Cuba Astronomical Foundation; US NSF [AST-1238877]; UK Science and Technology Facilities Council; NASA; NSF

Real-time data mining of massive data streams from synoptic sky surveys

The nature of scientific and technological data collection is evolving rapidly: data volumes and rates grow exponentially, with increasing complexity and information content, and there has been a transition from static data sets to data streams that must be analyzed in real time.?Interesting or anomalous phenomena must be quickly characterized and followed up with additional measurements via optimal deployment of limited assets.?Modern astronomy presents a variety of such phenomena in the form of transient events in digital synoptic sky surveys, including cosmic explosions (supernovae, gamma ray bursts), relativistic phenomena (black hole formation, jets), potentially hazardous asteroids, etc. We have been developing a set of machine learning tools to detect, classify and plan a response to transient events for astronomy applications, using the Catalina Real-time Transient Survey (CRTS) as a scientific and methodological testbed. The ability to respond rapidly to the potentially most interesting events is a key bottleneck that limits the scientific returns from the current and anticipated synoptic sky surveys.?Similar challenge arises in other contexts, from environmental monitoring using sensor networks to autonomous spacecraft systems.?Given the exponential growth of data rates, and the time-critical response, we need a fully automated and robust approach.?We describe the results obtained to date, and the possible future developments. Advances in the automated classification of transient events in synoptic sky surveys.Innovative methods for the analysis of irregularly sampled, heterogeneous time series.Novel approach to the machine-assisted discovery using a symbolic regression.Approaches to an automated decision making based on the automated classification.

Unmixing the Galactic Halo with RR Lyrae tagging

We show that tagging RR Lyrae stars according to their location in the period-amplitude diagram can be used to shed light on the genesis of the Galactic stellar halo. The mixture of RR Lyrae of ab type, separated into classes along the lines suggested by Oosterhoff, displays a strong and coherent evolution with Galactocentric radius. The change in the RR Lyrae composition appears to coincide with the break in the halo’s radial density profile at ∼25 kpc. Using simple models of the stellar halo, we establish that at least three different types of accretion events are necessary to explain the observed RRab behavior. Given that there exists a correlation between the RRab class fraction and the total stellar content of a dwarf satellite, we hypothesize that the field halo RRab composition is controlled by the mass of the progenitor contributing the bulk of the stellar debris at the given radius. This idea is tested against a suite of cosmological zoom-in simulations of Milky Way-like stellar halo formation. Finally, we study some of the most prominent stellar streams in the Milky Way halo and demonstrate that their RRab class fractions follow the trends established previously.

Exploring the Time Domain With Synoptic Sky Surveys

Synoptic sky surveys are becoming the largest data generators in astronomy, and they are opening a new research frontier that touches practically every field of astronomy. Opening the time domain to a systematic exploration will strengthen our understanding of a number of interesting known phenomena, and may lead to the discoveries of as yet unknown ones. We describe some lessons learned over the past decade, and offer some ideas that may guide strategic considerations in the planning and execution of future synoptic sky surveys.

Results of a systematic search for outburst events in 1.4 million galaxies

We present an analysis of nine years of Catalina Surveys optical photometry for 1.4 million spectroscopically confirmed SDSS galaxies. We find 717 outburst events that were not reported by ongoing transient surveys. These events have timescales ranging from weeks to years. More than two thirds of these new events are found in starforming galaxies, while such galaxies only constitute ~20% of our sample. Based on the properties of the hosts and events, we find that almost all of the new events are likely to be associated with regular supernovae. However, a small number of long-timescale events are found among the galaxies containing AGN. These events have similar properties to those recently found in the analyses of light curves of large samples of AGN. Given the lack of such events among the more than a million passive galaxies in the sample, we suggest that the long outbursts are associated with super-massive black holes or their environments.