-
A. J. Drake,
M. Catelan,
S. G. Djorgovski,
G. Torrealba,
M. J. Graham,
A. A. Mahabal,
J. L. Prieto,
C. Donalek, R. Williams,
S. Larson,
E. Christensen,
E. Beshore
[show abstract]
[hide abstract]
ABSTRACT: We present the analysis of 1,207 RR Lyrae found in photometry taken by the
Catalina Survey's Mount Lemmon telescope. By combining accurate distances for
these stars with measurements for ~14,000 type-AB RR Lyrae from the Catalina
Schmid telescope, we reveal an extended association that reaches Galactocentric
distances beyond 100 kpc and overlaps the Sagittarius streams system. This
result confirms earlier evidence for the existence of an outer halo tidal
stream resulting from a disrupted stellar system. By comparing the RR Lyrae
source density with that expected based on halo models, we find the detection
has ~8 sigma significance. We investigate the distances, radial velocities,
metallicities, and period-amplitude distribution of the RR Lyrae. We find that
both radial velocities and distances are inconsistent with current models of
the Sagittarius stream. We also find tentative evidence for a division in
source metallicities for the most distant sources. Following prior analyses, we
compare the locations and distances of the RR Lyrae with photometrically
selected candidate horizontal branch stars and find supporting evidence that
this structure spans at least 60 deg of the sky. We investigate the prospects
of an association between the stream and unusual globular cluster NGC 2419.
The Astrophysical Journal 03/2013; 765(2):154. · 6.02 Impact Factor
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A. J. Drake,
M. Catelan,
S. G. Djorgovski,
G. Torrealba,
M. J. Graham,
V. Belokurov,
S. E. Koposov,
A. Mahabal,
J. L. Prieto,
C. Donalek, R. Williams,
S. Larson E. Christensen,
E. Beshore
[show abstract]
[hide abstract]
ABSTRACT: We present the analysis of 12227 type-ab RR Lyrae found among the 200 million
public lightcurves in the Catalina Surveys Data Release 1 (CSDR1). These stars
span the largest volume of the Milky Way ever surveyed with RR Lyrae, covering
~20,000 square degrees of the sky (0 < RA < 360, -22 < Dec < 65 deg) to
heliocentric distances of up to 60kpc. Each of the RR Lyrae are observed
between 60 and 419 times over a six-year period. Using period finding and
Fourier fitting techniques we determine periods and apparent magnitudes for
each source. We find that the periods at generally accurate to sigma = 0.002%
by comparison with 2842 previously known RR Lyrae and 100 RR Lyrae observed in
overlapping survey fields. We photometrically calibrate the light curves using
445 Landolt standard stars and show that the resulting magnitudes are accurate
to ~0.05 mags using SDSS data for ~1000 blue horizontal branch stars and 7788
of the RR Lyrae. By combining Catalina photometry with SDSS spectroscopy, we
analyze the radial velocity and metallicity distributions for > 1500 of the RR
Lyrae. Using the accurate distances derived for the RR Lyrae, we show the paths
of the Sagittarius tidal streams crossing the sky at heliocentric distances
from 20 to 60 kpc. By selecting samples of Galactic halo RR Lyrae, we compare
their velocity, metallicity, and distance with predictions from a recent
detailed N-body model of the Sagittarius system. We find that there are some
significant differences between the distances and structures predicted and our
observations.
The Astrophysical Journal 01/2013; 763(1):32. · 6.02 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: 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 problem will grow by orders of magnitude
with the next generation of surveys. We are exploring a variety of novel
automated classification techniques, mostly Bayesian, to respond to these
challenges, using the ongoing CRTS sky survey as a testbed. We describe briefly
some of the methods used.
11/2011;
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A. J. Drake,
S. G. Djorgovski,
A. Mahabal,
J. L. Prieto,
E. Beshore,
M. J. Graham,
M. Catalan,
S. Larson,
E Christensen,
C. Donalek, R Williams
[show abstract]
[hide abstract]
ABSTRACT: The Catalina Real-time Transient Survey (CRTS) currently covers 33,000 deg^2
of the sky in search of transient astrophysical events, with time baselines
ranging from 10 minutes to ~7 years. Data provided by the Catalina Sky Survey
provides an unequaled baseline against which >4,000 unique optical transient
events have been discovered and openly published in real-time. Here we
highlight some of the discoveries of CRTS.
11/2011;
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[show abstract]
[hide abstract]
ABSTRACT: Synoptic sky surveys are becoming the largest data generators in astronomy,
and they are opening a new research frontier, that touches essentially every
field of astronomy. Opening of 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 planning and execution of the future synoptic sky surveys.
11/2011;
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A. J. Drake,
S. G. Djorgovski,
A. Mahabal,
J Anderson,
R Roy,
V Mohan,
S. Ravindranath,
D. Frail,
S. Gezari,
James D. Neill, [......],
Yogesh Wadadekar,
Brijesh Kumar,
A. D. Myers,
E. S. Phinney, R Williams,
M. J. Graham,
M. Catelan,
E. Beshore,
S. Larson,
E Christensen
[show abstract]
[hide abstract]
ABSTRACT: We report on the discovery and observations of the extremely luminous optical
transient CSS100217:102913+404220 (CSS100217 hereafter). Spectroscopic
observations show this transient was coincident with a galaxy at redshift
z=0.147, and reached an apparent magnitude of V ~ 16.3. After correcting for
foreground Galactic extinction we determine the absolute magnitude to be M_V
=-22.7 approximately 45 days after maximum light. Based on our unfiltered
optical photometry the peak optical emission was L = 1.3 x 10^45 erg s^-1, and
over a period of 287 rest-frame days had an integrated bolometric luminosity of
1.2 x 10^52 erg. Analysis of the pre-outburst SDSS spectrum of the source shows
features consistent with a Narrow-line Seyfert1 (NLS1) galaxy. High-resolution
HST and Keck followup observations show the event occurred within 150pc of
nucleus of the galaxy, suggesting a possible link to the active nuclear region.
However, the rapid outburst along with photometric and spectroscopic evolution
are much more consistent with a luminous supernova. Line diagnostics suggest
that the host galaxy is undergoing significant star formation. We use extensive
follow-up of the event along with archival CSS and SDSS data to investigate the
three most likely sources of such an event; 1) an extremely luminous supernova;
2) the tidal disruption of a star by the massive nuclear black hole; 3)
variability of the central AGN. We find that CSS100217 was likely an extremely
luminous type IIn supernova that occurred within range of the narrow-line
region of an AGN. We discuss how similar events may have been missed in past
supernova surveys because of confusion with AGN activity.
The Astrophysical Journal 03/2011; 705(2):106. · 6.02 Impact Factor
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Central Bureau Electronic Telegrams. 02/2011; 2666:1.
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S. G. Djorgovski,
A. J. Drake,
A. A. Mahabal,
M. J. Graham,
C. Donalek, R Williams,
E. C. Beshore,
S. M. Larson,
J. Prieto,
M. Catelan,
E Christensen,
R. H. McNaught
[show abstract]
[hide abstract]
ABSTRACT: Catalina Real-Time Transient Survey (CRTS) is a synoptic sky survey uses data
streams from 3 wide-field telescopes in Arizona and Australia, covering the
total area of ~30,000 deg2, down to the limiting magnitudes ~ 20 - 21 mag per
exposure, with time baselines from 10 min to 6 years (and growing); there are
now typically ~ 200 - 300 exposures per pointing, and coadded images reach
deeper than 23 mag. The basic goal of CRTS is a systematic exploration and
characterization of the faint, variable sky. The survey has detected ~ 3,000
high-amplitude transients to date, including ~ 1,000 supernovae, hundreds of
CVs (the majority of them previously uncatalogued), and hundreds of blazars /
OVV AGN, highly variable and flare stars, etc. CRTS has a complete open data
philosophy: all transients are published immediately electronically, with no
proprietary period at all, and all of the data (images, light curves) will be
publicly available in the near future, thus benefiting the entire astronomical
community. CRTS is a scientific and technological testbed and precursor for the
grander synoptic sky surveys to come.
02/2011;
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A. A. Mahabal,
A. J. Drake,
S. G. Djorgovski,
M. J. Graham, R. Williams,
C. Donalek,
D. Stern,
J. Prieto,
M. Catelan,
E. Christensen,
E. C. Beshore,
S. M. Larson,
R. H. McNaught
[show abstract]
[hide abstract]
ABSTRACT: We report the discovery of several flaring radio sources and blazars by
the Catalina Real-time Transient Survey (CRTS) during the period from
2010-09-15 to 2010-10-15 UT. All these were announced in real-time on
the CRTS website.
The Astronomer's Telegram. 09/2010; 2955:1.
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A. J. Drake,
S. G. Djorgovski,
A. A. Mahabal,
M. J. Graham, R. Williams,
J. Prieto,
M. Catelan,
E. Christensen,
E. C. Beshore,
S. M. Larson,
R. H. McNaught
[show abstract]
[hide abstract]
ABSTRACT: We report the discovery of supernova candidates by the Catalina
Real-time Transient Survey (CRTS) in data from the Catalina Sky Survey
during the period from 2010-09-29 to 2010-10-17 UT.
The Astronomer's Telegram. 09/2010; 2978:1.
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[show abstract]
[hide abstract]
ABSTRACT: Although white dwarfs are believed to be the end point of most stellar evolution, unlike main sequence stars, they have not yet been the subject of dedicated time-domain surveys for exoplanets. We discuss how their size and distinctive colour make them excellent targets for wide-field searches for exoplanets. In particular, we note that planets of Earth-size can give rise to multi-magnitude eclipses of massive white dwarfs. Such a large signal is almost unmistakable and would be detectable even with very low-precision photometry. For objects of smaller size, the high accuracy photometry currently being used to detect Super-Earth and smaller planets transiting Sun-sized stars, is capable of revealing minor planets down to R~100km as they transit white dwarfs. Such observations can be used to test current evidence for asteroid-size objects being the cause for dust rings which have recently been observed for a number of white dwarfs. No other current exoplanet search method is capable of detecting such exo-asteroids. As an initial test of this search strategy, we combine synoptic data from the Catalina Sky Survey with multi-colour photometry and spectra from the Sloan Digital Sky Survey to search ~12,000 white dwarf lightcurves for eclipsing events. We find 20 new eclipsing white dwarf binary systems with low-mass companions. This doubles the number of known eclipsing white dwarfs and is expected to enable the determination of accurate white dwarf radii. Three of the discoveries have radii consistent with substellar systems and show no evidence of flux from the eclipsing object in their SDSS optical spectra, or near-IR data. Comment: Submitted ApJ Aug 2009
09/2010;
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[show abstract]
[hide abstract]
ABSTRACT: We report on the discovery and initial observations of the energetic type IIn supernova 2008fz. This object was discovered at redshift z = 0.133 and reached an apparent magnitude of V ~ 17. After correcting for Galactic extinction and redshift, we determine the peak absolute magnitude of the event to be MV = –22.3, placing it among the most luminous supernovae discovered. The optical energy emitted by SN 2008fz (based on the light curve over an 88 day period) is possibly the most ever observed for a supernova (>1.4 × 1051 erg). The event was more luminous than the type IIn SN 2006gy, but exhibited the same smooth, slowly evolving light curve. As is characteristic of type IIn supernova, the early spectra of SN 2008fz initially exhibited narrow Balmer lines which were replaced by a broader component at later times. The spectra also show a blue continuum with no signs of Ca or Na absorption, suggesting that there is little extinction due to dust in the host or circumstellar material. No host galaxy is identified in prior co-added images reaching R ~ 22. From the supernova's redshift, we place an upper limit on the brightness of the host of MR ~ –17 (similar to the brightness of the Small Magellanic Cloud). The presence of the supernova within such a faint galaxy follows the majority of recently discovered highly luminous supernovae. A possible reason for this is the combination of a high star formation rate in low-mass galaxies with a low-metallicity environment.
The Astrophysical Journal Letters 07/2010; 718(2):L127. · 5.53 Impact Factor
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A. A. Mahabal,
A. J. Drake,
S. G. Djorgovski,
M. J. Graham, R. Williams,
Adam Myers,
J. Prieto,
M. Catelan,
E. Christensen,
Vijay Mohan,
Swara Ravindranath,
E. C. Beshore,
S. M. Larson
[show abstract]
[hide abstract]
ABSTRACT: We report the discovery of supernova candidates by the Catalina
Real-time Transient Survey (CRTS) between 2010-03-04 and 2010-03-18 UT
as well as spectroscopic observations taken with Palomar 5m+DSBS on 2010
Mar 15 UT.
The Astronomer's Telegram. 02/2010; 2490:1.
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P. Wils,
J. Greaves,
M. Catelan,
S. G. Djorgovski,
A. J. Drake,
M. J. Graham,
A. A. Mahabal, R. Williams,
E. C. Beshore,
S. M. Larson,
E. Christensen
[show abstract]
[hide abstract]
ABSTRACT: We report the discovery of a possible FU-Ori-type eruption. The object
CSS091110:060919-064155
located at R.A. = 06h09m19.32s, Decl. = -06d41'55.4" (equinox 2000.0)
and coincident with the infrared source IRAS 06068-0641, was detected
by the Catalina Real-time Transient Survey (CRTS) on 10 November 2009.
It has been continuously brightening from at least early 2005 (when it
was mag 14.8 on unfiltered CCD images) to the present mag 12.6, and may
possibly brighten further.
The Astronomer's Telegram. 10/2009; 2307:1.
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A. J. Drake,
S. G. Djorgovski,
A. A. Mahabal, R. Williams,
M. Catelan,
E. C. Beshore,
S. M. Larson,
A. Boattini,
A. Gibbs,
R. Hill,
R. Kowaski,
E. Christensen
The Astronomer's Telegram. 05/2009; 2087:1.
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A. J. Drake,
S. G. Djorgovski,
A. Mahabal,
E. Beshore,
S. Larson,
M. J. Graham, R. Williams,
E. Christensen,
M. Catelan,
A. Boattini,
A. Gibbs,
R. Hill,
and R. Kowalski
[show abstract]
[hide abstract]
ABSTRACT: We report on the results from the first six months of the Catalina Real-Time Transient Survey (CRTS). In order to search for optical transients (OTs) with timescales of minutes to years, the CRTS analyses data from the Catalina Sky Survey which repeatedly covers 26,000 of square degrees on the sky. The CRTS provides a public stream of transients that are bright enough to be followed up using small telescopes. Since the beginning of the survey, all CRTS transients have been made available to astronomers around the world in real time using HTML tables,RSS feeds, and VOEvents. As part of our public outreach program, the detections are now also available in Keyhole Markup Language through Google Sky. The initial discoveries include over 350 unique OTs rising more than 2 mag from past measurements. Sixty two of these are classified as supernovae (SNe), based on light curves, prior deep imaging and spectroscopic data. Seventy seven are due to cataclysmic variables (CVs; only 13 previously known), while an additional 100 transients were too infrequently sampled to distinguish between faint CVs and SNe. The remaining OTs include active galactic nucleus, blazars, high-proper-motions stars, highly variable stars (such as UV Ceti stars), and transients of an unknown nature. Our results suggest that there is a large population of SNe missed by many current SN surveys because of selection biases. These objects appear to be associated with faint host galaxies. We also discuss the unexpected discovery of white dwarf binary systems through dramatic eclipses.
The Astrophysical Journal 04/2009; 696(1):870. · 6.02 Impact Factor
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Stanislav G. Djorgovski,
A. Mahabal,
A. Drake,
C. Donalek,
E. Glikman,
M. Graham, R. Williams,
T. Morton,
A. Bauer,
C. Baltay,
D. Rabinowitz,
R. Scalzo,
P. Nugent,
Palomar-Quest Survey Team
[show abstract]
[hide abstract]
ABSTRACT: Palomar-Quest (PQ) digital synoptic sky survey, conducted at the Samuel
Oschin 48-inch telescope at Palomar Observatory, using the Yale Quest-2,
161-Megapixel, 112-CCD camera, is now complete. The survey covered >
15,000 deg2 multiple times (up to several tens of pointings), spanning a
range of time baselines from minutes to years. The data were taken in a
drift scan mode, in Johnson UBRI or Gunn griz filters. They are now
supplemented by an even larger data set taken in the traditional
point-and-stare mode, with a broad red bandpass, much of it taken by the
JPL NEAT team, and processed at LBNL Nearby Supernova Factory. This
joint data set offers unprecedented opportunities for exploration of
time domain in astronomy. All transient sources detected in the course
of real-time processing of the drift scan survey have been published
immediately, using the VOEventNet system. In addtion to a very
productive supernova search conducted in collaboration with the LBNL
Nearby Supernova Factory, we have conducted several studies: (1) a
real-time detection of transients and strong variables; (2) a systematic
study of QSO variability; (3) studies of blazar variability, and blazar
discovery using variability alone; (4) the astrophysical nature of the
most variable sources on the high-latitude sky. Follow-up spectroscopy
was obtained at the Palomar 200-inch Hale telescope for a number of
sources. We will report preliminary results from some of these studies.
Experience gained in the course of this survey should be useful for
future synoptic sky surveys.
12/2008; 41:258.
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[show abstract]
[hide abstract]
ABSTRACT: Digital synoptic sky surveys pose several new object classification challenges. In surveys where real-time detection and classification of transient events is a science driver, there is a need for an effective elimination of instrument-related artifacts which can masquerade as transient sources in the detection pipeline, e.g., unremoved large cosmic rays, saturation trails, reflections, crosstalk artifacts, etc. We have implemented such an Artifact Filter, using a supervised neural network, for the real-time processing pipeline in the Palomar-Quest (PQ) survey. After the training phase, for each object it takes as input a set of measured morphological parameters and returns the probability of it being a real object. Despite the relatively low number of training cases for many kinds of artifacts, the overall artifact classification rate is around 90%, with no genuine transients misclassified during our real-time scans. Another question is how to assign an optimal star-galaxy classification in a multi-pass survey, where seeing and other conditions change between different epochs, potentially producing inconsistent classifications for the same object. We have implemented a star/galaxy multipass classifier that makes use of external and a priori knowledge to find the optimal classification from the individually derived ones. Both these techniques can be applied to other, similar surveys and data sets. Comment: 5 pages, 5 figures. To appear in proceedings of the Class2008 conference (Classification and Discovery in Large Astronomical Surveys, Ringberg Castle, 14-17 October 2008)
10/2008;
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A. Mahabal,
S. G. Djorgovski, R Williams,
A. Drake,
C. Donalek,
M. Graham,
B. Moghaddam,
M. Turmon,
J. Jewell,
A. Khosla,
B. Hensley
[show abstract]
[hide abstract]
ABSTRACT: Exploration of time domain is now a vibrant area of research in astronomy, driven by the advent of digital synoptic sky surveys. While panoramic surveys can detect variable or transient events, typically some follow-up observations are needed; for short-lived phenomena, a rapid response is essential. Ability to automatically classify and prioritize transient events for follow-up studies becomes critical as the data rates increase. We have been developing such methods using the data streams from the Palomar-Quest survey, the Catalina Sky Survey and others, using the VOEventNet framework. The goal is to automatically classify transient events, using the new measurements, combined with archival data (previous and multi-wavelength measurements), and contextual information (e.g., Galactic or ecliptic latitude, presence of a possible host galaxy nearby, etc.); and to iterate them dynamically as the follow-up data come in (e.g., light curves or colors). We have been investigating Bayesian methodologies for classification, as well as discriminated follow-up to optimize the use of available resources, including Naive Bayesian approach, and the non-parametric Gaussian process regression. We will also be deploying variants of the traditional machine learning techniques such as Neural Nets and Support Vector Machines on datasets of reliably classified transients as they build up. Comment: 7 pages, 3 figures, to appear in proceedings of the Class2008 conference (Classification and Discovery in Large Astronomical Surveys, Ringberg Castle, 14-17 October 2008)
10/2008;
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S. G. Djorgovski,
T. Morton,
A. J. Drake,
A. Mahabal,
E. Glikman,
P. Nugent,
C. Baltay,
D. Rabinowitz,
E. C. Beshore,
S. M. Larson, R. Williams,
D. Gopal,
C. Donalek,
M. Graham,
A. Bauer,
N. Ellman,
R. Scalzo,
J. Jerke,
E. Christensen
[show abstract]
[hide abstract]
ABSTRACT: We compiled archival light curves for the blazar 3C454.3, which is
currently dominating the extragalactic gamma-ray sky as seen by the
early GLAST/ Fermi observations. One data set is from the
Palomar-Quest (PQ) survey, a combination of exposures taken in the drift
scan and point-and-stare modes, supplemented by a few early observations
from the JPL NEAT team. These data were obtained at Palomar 48-inch
Schmidt Samuel Oschin Telescope, span a time range of about 6 years,
from 04 Aug 2002 UT, through 22 June 2008 UT, and consist of 69
exposures taken on 32 separate dates.
The Astronomer's Telegram. 07/2008; 1684:1.
