J/AJ/146/21 LINEAR. II. Catalog of RR Lyrae stars (Sesar+, 2013)
Exploring the variable sky with LINEAR. II. Halo structure and substructure
traced by RR Lyrae stars to 30 kpc.
Sesar B., Ivezic Z., Stuart J.S., Morgan D.M., Becker A.C., Sharma S.,
Palaversa L., Juric M., Wozniak P., Oluseyi H.
<Astron. J., 146, 21 (2013)>
=2013AJ....146...21S 2013AJ....146...21S
ADC_Keywords: Surveys ; Stars, variable ; Stars, halo ; Stars, distances ;
Photometry
Keywords: Galaxy: halo - Galaxy: stellar content - Galaxy: structure -
stars: variables: RR Lyrae
Abstract:
We present a sample of ∼5000 RR Lyrae stars selected from the
recalibrated LINEAR data set and detected at heliocentric distances
between 5kpc and 30kpc over ∼8000 deg2 of sky. The coordinates and
light curve properties, such as period and Oosterhoff type, are made
publicly available. We analyze in detail the light curve properties
and Galactic distribution of the subset of ∼4000 type ab RR Lyrae
(RRab) stars, including a search for new halo substructures and the
number density distribution as a function of Oosterhoff type. We find
evidence for the Oosterhoff dichotomy among field RR Lyrae stars, with
the ratio of the type II and I subsamples of about 1:4, but with a
weaker separation than for globular cluster stars. The wide sky
coverage and depth of this sample allow unique constraints for the
number density distribution of halo RRab stars as a function of
galactocentric distance: it can be described as an oblate ellipsoid
with an axis ratio q=0.63 and with either a single or a double power
law with a power-law index in the range -2 to -3. Consistent with
previous studies, we find that the Oosterhoff type II subsample has a
steeper number density profile than the Oosterhoff type I subsample.
Using the group-finding algorithm EnLink, we detected seven candidate
halo groups, only one of which is statistically spurious. Three of
these groups are near globular clusters (M53/NGC 5053, M3, M13), and
one is near a known halo substructure (Virgo Stellar Stream); the
remaining three groups do not seem to be near any known halo
substructures or globular clusters and seem to have a higher ratio of
Oosterhoff type II to Oosterhoff type I RRab stars than what is found
in the halo. The extended morphology and the position (outside the
tidal radius) of some of the groups near globular clusters are
suggestive of tidal streams possibly originating from globular
clusters. Spectroscopic follow-up of detected halo groups is
encouraged.
Description:
The MIT Lincoln Laboratory (MITLL) has operated the Lincoln Near-Earth
Asteroid Research (LINEAR) program since 1998 to search for asteroids.
The focus of the program is to discover and track near-Earth asteroids
(NEAs) larger than 1km in diameter, but LINEAR has also discovered and
tracked many main-belt asteroids and smaller NEAs. Since late 2002,
the LINEAR program has maintained an archive of all of its imagery
data. The LINEAR program operates two telescopes (each of them is
equipped with a CCD camera) at the Experimental Test Site located
within the US Army White Sands Missile Range in central New Mexico at
an altitude of 1506m above sea level and a latitude of 33.8°N. The
program uses two essentially identical equatorial-mounted telescopes
of the Ground-based Electro-Optical Deep Space Surveillance (GEODSS)
type. Public access to the recalibrated LINEAR data is provided
through the SkyDOT Web site (https://astroweb.lanl.gov/lineardb/).
This paper is the second one in a series based on light curve data
collected by the LINEAR survey. Here, we searched the LINEAR data set
for variable RR Lyrae stars. In total, we have selected 4067 RRab and
834 RRc stars from the recalibrated LINEAR data set. These stars probe
∼8000deg2 of sky to 30kpc from the Sun.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 101 5684 Positions and light curve parameters of LINEAR
RR Lyrae stars
table2.dat 71 7 Halo substructures detected in LINEAR
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See also:
V/139 : The SDSS Photometric Catalog, Release 9 (Adelman-McCarthy+, 2012)
VII/233 : The 2MASS Extended sources (IPAC/UMass, 2003-2006)
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
VII/202 : Globular Clusters in the Milky Way (Harris, 1997)
J/ApJ/731/4 : Galactic halo as seen by the CFHTLS (Sesar+, 2011)
J/ApJ/708/717 : Light curve templates of RR Lyrae stars (Sesar+, 2010)
J/ApJ/678/865 : LONEOS-I RR Lyrae stars (Miceli+, 2008)
J/ApJ/678/851 : RR Lyrae survey in the Galactic Halo (Keller+, 2008)
J/AJ/132/1202 : RR Lyrae in Northern Sky Variability Survey (Kinemuchi+, 2006)
J/AJ/129/267 : RR Lyrae variables in NGC 5272 (Cacciari+, 2005)
https://astroweb.lanl.gov/lineardb/ : SkyDOT Web site
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 I8 --- LINEAR [29848/24264172] LINEAR object identifier (1)
9 A1 --- f_LINEAR [*] RR Lyrae star from the LINEAR Catalog of
Variable Stars (Palaversa et al.,
2013AJ....146..101P 2013AJ....146..101P; Paper III)
11- 20 F10.6 deg RAdeg Right Ascension in decimal degrees (J2000)
22- 31 F10.6 deg DEdeg Declination in decimal degrees (J2000)
33- 34 A2 --- Type [abc ] RR Lyrae type (ab or c=first overtone)
36- 43 F8.6 d Per [0.1130/1.1915]?=9 Period
45- 56 F12.6 d T0 HJD-2400000 of maximum brightness
58- 62 F5.3 mag Amp [0.067/1.54] Amplitude (3)
64- 69 F6.3 mag mag Best-fit LINEAR template maximum brightness (4)
71- 78 I8 --- Templ [32086/24262387] Best-fit LINEAR template number
80- 84 F5.3 mag Ar Extinction in the SDSS r band (5)
86- 91 F6.3 mag [13.235/18.497] Flux-average magnitude (6)
93- 97 F5.2 kpc Dist Heliocentric distance; see Section 3.2 (7)
99 I1 --- Cl [0/2] Oosterhoff class (1 or 2 for RRab stars
and 0 for RRc stars)
101 I1 --- Gr [0/7] Substructure halo group identifier (0 for
stars not associated with a substructure)
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Note (1): Identification number referencing this object in the LINEAR database
(https://astroweb.lanl.gov/lineardb/). in Simbad.
Note (3): Measured from the best-fit LINEAR template.
Note (4): Not corrected for interstellar medium extinction.
Note (5): Ar=2.751E(B-V), where E(B-V) color excess is provided by the
Schlegel et al. (1998ApJ...500..525S 1998ApJ...500..525S) dust map.
Note (6): Corrected for interstellar medium extinction as
= (not-corrected)-Ar.
Note (7): Dist=10(<mag>-Mrr)/5/100 (Eq. 14 in Section 3.2), where
Mrr is the absolute magnitude of RR Lyrae stars in the LINEAR bandpass.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1 I1 --- Gr [1/7] Substructure halo group identifier (1)
3- 12 F10.6 deg RAdeg Right Ascension in decimal degrees (J2000) (2)
14- 22 F9.6 deg DEdeg Declination in decimal degrees (J2000) (2)
24- 27 F4.1 kpc Dist [6/15.7] Heliocentric distance (2)
29- 31 F3.1 kpc Rad Radius of the group (3)
33- 34 I2 --- Ns [10/35] Number of stars in the group
36- 39 F4.2 --- Signi Significance of a group (4)
41- 66 A26 --- GC Globular cluster (M53/NGC 5053, M3, M13) or
halo substructure (Virgo Stellar Stream) near
the group (5)
68- 71 F4.2 --- OII/OI Ratio of Oosterhoff type II to Oosterhoff
type I RRab stars in a group (6)
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Note (1): We use a group-finding algorithm EnLink (Sharma & Johnston,
2009ApJ...703.1061S 2009ApJ...703.1061S) to identify significant clusters of RR Lyrae stars
(halo substructures). The search for halo substructures is done using
LINEAR RRab stars that pass Equations (22)-(28). See Section 6 for details.
Note (2): Of the peak in number density, where the number density has been
measured by the group-finding algorithm EnLink.
Note (3): Estimated as the median distance of stars from the peak in number
density.
Note (4): As measured by the group-finding algorithm EnLink.
Note (5): Groups 1, 2, and 7 do not seem to be near any known halo substructures
Note (6): This ratio may provide additional clues on the nature of detected
groups. For the full LINEAR RRab sample, this ratio is 0.25. For group 4,
this ratio is close to zero (0.05), indicating that the group 4 is
dominated by Oosterhoff type I RRab stars. This result is interesting
because M3 is classified as an Oosterhoff I-type globular cluster (Catelan,
2009Ap&SS.320..261C 2009Ap&SS.320..261C) and is located within group 4 (see Table2). Thus, the
fact that the group 4 and the globular cluster M3 have the same Oosterhoff
type may indicate their common origin.
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History:
From electronic version of the journal
References:
Paper I, Sesar et al., 2011AJ....142..190S 2011AJ....142..190S
Paper III, Palaversa et al., 2013AJ....146..101P 2013AJ....146..101P, Cat. J/AJ/146/101
(End) Greg Schwarz [AAS], Sylvain Guehenneux [CDS] 06-Jun-2014