J/ApJ/892/112 CTIO/DECam LCs for Galactic bulge variable stars (Soraisam+, 2020)
A classification algorithm for time-domain novelties in preparation for LSST
alerts. Application to variable stars and transients detected with DECam in the
Galactic Bulge.
Soraisam M.D., Saha A., Matheson T., Lee C.-H., Narayan G., Vivas A.K.,
Scheidegger C., Oppermann N., Olszewski E.W., Sinha S., Desantis S.R.,
(The ANTARES Collaboration)
<Astrophys. J., 892, 112-112 (2020)>
=2020ApJ...892..112S 2020ApJ...892..112S (SIMBAD/NED BibCode)
ADC_Keywords: Stars, variable; Galactic plane; Photometry, ugriz; Surveys
Keywords: Astronomy databases; Surveys; Catalogs; Time domain astronomy
Astrostatistics; Algorithms; Variable stars
Abstract:
With the advent of the Legacy Survey of Space and Time, time-domain
astronomy will be faced with an unprecedented volume and rate of data.
Real-time processing of variables and transients detected by such
large-scale surveys is critical to identifying the more unusual events
and allocating scarce follow-up resources efficiently. We develop an
algorithm to identify these novel events within a given population of
variable sources. We determine the distributions of magnitude changes
(dm) over time intervals (dt) for a given passband f, pf(dm|dt),
and use these distributions to compute the likelihood of a test source
being consistent with the population or being an outlier. We
demonstrate our algorithm by applying it to the DECam multiband
time-series data of more than 2000 variable stars identified by
Saha+ (2019, J/ApJ/874/30) in the Galactic Bulge that are largely
dominated by long-period variables and pulsating stars. Our algorithm
discovers 18 outlier sources in the sample, including a microlensing
event, a dwarf nova, and two chromospherically active RS CVn stars, as
well as sources in the blue horizontal branch region of the
color-magnitude diagram without any known counterparts. We compare the
performance of our algorithm for novelty detection with the
multivariate Kernel Density Estimator and Isolation Forest on the
simulated PLAsTiCC data set. We find that our algorithm yields
comparable results despite its simplicity. Our method provides an
efficient way for flagging the most unusual events in a real-time
alert-broker system.
Description:
The time-series data we use here are obtained from an NOAO observing
program for conducting a deep synoptic survey of the Galactic Bulge
(2013A-0719; PI: A. Saha) using the DECam imager mounted atop the
Victor M. Blanco 4m telescope at the Cerro Tololo Inter-American
Observatory. The program imaged six separate fields (each of area
3deg2, corresponding to the imager's field of view) toward the
Galactic center, named B1-B6, in five passbands u, g, r, i, z over
multiple epochs extending from 2013 until 2015 (seven nights in 2013
and three nights in 2015).
Saha+ (2019, J/ApJ/874/30) presented an analysis of the data for the
field B1. See Section 2.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
stars.dat 30 2266 List of variable stars; table added by CDS
table1.dat 58 520801 Light curve data
--------------------------------------------------------------------------------
See also:
II/213 : OGLE Galactic Bulge periodic variables (Udalski+ 1996)
J/AcA/52/129 : DIA OGLE2 candidate variable stars catalog (Wozniak+, 2002)
J/MNRAS/364/117 : OGLE2 Mira variables in the Galactic bulge (Matsunaga+, 2005)
J/AJ/131/1044 : Chromospherically active stars in the Bulge (Drake, 2006)
J/AcA/61/1 : VI light curves of Galactic Bulge RR Lyrae (Soszynski+, 2011)
J/ApJS/194/4 : Classification of CCCP X-ray sources (Broos+, 2011)
J/AcA/61/285 : VI light curves of Galactic Bulge Cepheids (Soszynski+, 2011)
J/ApJ/778/150 : Microlensing events toward the Bulge from MOA-II (Sumi+, 2013)
J/A+A/572/A29 : Asteroids for a targeted spectrosc. survey (Oszkiewicz+, 2014)
J/AcA/65/313 : One thousand new dwarf novae from the OGLE Survey (Mroz+, 2015)
J/AcA/66/405 : Galactic bulge eclipsing & ellipsoidal bin. (Soszynski+, 2016)
J/A+A/605/A89 : Abund. of microlensed Bulge dwarf stars. VI. (Bensby+, 2017)
J/ApJ/874/30 : RRab toward Baade's window with Blanco/DECam (Saha+, 2019)
Byte-by-byte Description of file: stars.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Name Star name (B1-NNNNNNN)
12- 20 F9.5 deg RAdeg [269.65/272.13] Right Ascension (J2000)
22- 30 F9.5 deg DEdeg [-31/-29] Declination (J2000)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Name Star name
12- 20 F9.5 deg RAdeg Right Ascension in decimal degrees (J2000)
22- 30 F9.5 deg DEdeg Declination in decimal degrees (J2000)
32- 43 F12.6 d HJD [56423.65/57116.91] Heliocentric Julian Date,
HJD-2400000.0
45 A1 --- Band Passband used (u, g, r, i or z)
47- 52 F6.3 mag mag [9.85/21.5] Observed magnitude in Band
54- 58 F5.3 mag e_mag [0.01/0.85] Uncertainty in mag
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 17-Aug-2021