J/AJ/150/27 New catalog of variable stars in M37 field (Chang+, 2015)
A new catalog of variable stars in the field of the open cluster M37.
Chang S.-W., Byun Y.-I., Hartman J.D.
<Astron. J., 150, 27 (2015)>
=2015AJ....150...27C 2015AJ....150...27C (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, open ; Stars, variable ; Binaries, eclipsing ;
Stars, flare ; Photometry, ugriz
Keywords: binaries: eclipsing - catalogs -
open clusters and associations: individual: M37 - stars: flare -
stars: oscillations - stars: variables: general
Abstract:
We present a comprehensive re-analysis of stellar photometric
variability in the field of the open cluster M37 following the
application of a new photometry and de-trending method to the
MMT/Megacam image archive. This new analysis allows a rare opportunity
to explore photometric variability over a broad range of timescales,
from minutes to a month. The intent of this work is to examine the
entire sample of more than 30000 objects for periodic, aperiodic, and
sporadic behaviors in their light curves. We show a modified version
of the fast χ2 periodogram algorithm (Fχ2) and
change-point analysis as tools for detecting and assessing the
significance of periodic and non-periodic variations. The benefits of
our new photometry and analysis methods are evident. A total of 2306
stars exhibit convincing variations that are induced by flares,
pulsations, eclipses, starspots, and unknown causes in some cases.
This represents a 60% increase in the number of variables known in
this field. Moreover, 30 of the previously identified variables are
found to be false positives resulting from time-dependent systematic
effects. The new catalog includes 61 eclipsing binary systems, 92
multiperiodic variable stars, 132 aperiodic variables, and 436 flare
stars, as well as several hundreds of rotating variables. Based on
extended and improved catalog of variables, we investigate the basic
properties (e.g., period, amplitude, type) of all variables. The
catalog can be accessed through the web interface
(http://stardb.yonsei.ac.kr/).
Description:
Hartman et al. 2008 (cat. J/ApJ/675/1233) have conducted a study to
find Neptune-sized planets transiting solar-like stars in the rich
open cluster M37. In paper I (Chang et al., 2015AJ....149..135C 2015AJ....149..135C), we
used the same data set on the open cluster M37. A detailed discussion
of the observations, original data reduction, and light curve
production is described in Hartman et al. 2008 (cat. J/ApJ/675/1233,
cat. J/ApJ/675/1254). The data archive consists of approximately 5000
r'-filter images taken over 24 nights with the wide-field mosaic
imager (Megacam) mounted at the f/5 Cassegrain focus of the 6.5m MMT
telescope. Note that Megacam is made up of 36 2048*4608 pixel CCD
chips in a 9*4 pattern, covering a 24'*24' FOV. This instrument has an
unbinned pixel scale of 0.08'', but it was used in binning mode for
readout. The observation logs are summarized in Table1 of Hartman et
al. 2008 (cat. J/ApJ/675/1233). In brief, the r'-bandtime-series
observations were undertaken between 2005 December 21 and 2006 January
21, with a median FWHM of 0.89±0.39arcsec.
In this paper, we cataloged and investigated a variety of photometric
variables in the field of M37 using our new light curves, which were
obtained from the archival imaging data of the one-month long
exo-planet transit survey with the 6.5m MMT telescope. We refer the
reader to Paper I (Chang et al., 2015AJ....149..135C 2015AJ....149..135C) for a detailed
description of our photometric reduction and light curve production
We provide a catalog of the total 2306 stars that exhibit convincing
variations that are induced by flares, pulsations, eclipses,
starspots, or in some cases, unknown causes. This catalog is made
available in electronic form at http://stardb.yonsei.ac.kr/. Table1
gives the basic information about previously known and new variable
stars that we detected in the field of M37.
We find 61 eclipsing binary systems (EB), 92 multiperiodic variable
stars (mp; see Table5), 132 aperiodic variables (A; see Table6), and
436 flare stars (F; see Table7), as well as several hundreds of
rotating variables (R). Our work has increased the number of known
variable stars in this field by 60%.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 119 2306 New catalog of 2306 variable stars in M37 field
table2.dat 45 30 List of 30 stars whose variability turns out to
be false
table3.dat 117 22 Parameters for 22 detached and semi-detached
eclipsing binary (EB) systems
table4.dat 60 34 List of new 15 eclipsing binary candidates from
the Change-Point Analysis (CPA) analysis
table5.dat 85 524 Candidate frequencies identified in 92
multiperiodic light curves
table6.dat 68 132 Long-term 132 aperiodic variable candidates
with timescales of >1 month
table7.dat 65 625 436 flare stars
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See also:
V/139 : The SDSS Photometric Catalog, Release 9 (Adelman-McCarthy+, 2012)
II/294 : The SDSS Photometric Catalog, Release 7 (Adelman-McCarthy+, 2009)
J/ApJ/809/161 : X-ray obs. and membership probabilities of M37 (Nunez+, 2015)
J/ApJ/691/342 : griBVI photometry in M37 (Hartman+, 2009)
J/ApJ/675/1254 : M37 variable stars (Hartman+, 2008)
J/ApJ/675/1233 : gri photometry in M37 (NGC 2099) (Hartman+, 2008)
J/A+A/483/253 : BV photometry of NGC 2099 variables (Messina+, 2008)
J/ApJ/628/411 : Eclipsing binaries identification and analysis (Devor+, 2005)
http://stardb.yonsei.ac.kr/ : Our catalog in electronic form
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1 A1 --- --- [V]
2- 5 I4 --- Star [1/2306] Variable star identifier (G1)
7- 25 A19 --- Name Star identifier (HHMMSS.ss+DDMMSS.ss, J2000)
27- 33 F7.4 d Per [0/24.2]? Period (1)
35- 39 F5.3 mag Amp [0/2.1]? Amplitude (1)
41- 46 F6.3 mag umag [13.1/26.7]? SDSS u band magnitude (2)
48- 53 F6.3 mag rmag [13.2/24.5]? SDSS r band magnitude (3)
55- 60 F6.3 mag g-r [-2.6/3.6]? The (g-r) color index (3)
62- 67 F6.3 mag r-i [-1.8/6.2]? The (r-i) color index (3)
69- 74 F6.3 mag zmag [13/23.3]? SDSS z band magnitude (2)
76- 81 F6.3 mag Vmag [13.2/24.2]? V band magnitude (4)
83- 88 F6.3 mag B-V [-0.1/3.3]? The (B-V) color index (4)
90- 95 F6.3 mag Jmag [12.2/17.3]? 2MASS J band magnitude (5)
97-102 F6.3 mag J-H [-1.1/1.7]? The 2MASS (J-H) color index (5)
104-109 F6.3 mag H-Ks [-1.9/1.6]? The 2MASS (H-Ks) color index (5)
111-119 A9 --- Type ? Variable Type (6)
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Note (1): Dominant period and its full amplitude. All blank fields are
non-periodic variables. In cases where the periodicity analysis is
affected by a large scatter of light curves due to photometric bias or
source blending, we used the already known period in that source from the
previous catalog (Harman et al. 2008, cat. J/ApJ/675/1254).
Note (2): The u and z magnitudes are from the Sloan Digital Sky Survey (SDSS)
DR7 (cat. II/294).
Note (3): The g, r, and i magnitudes are from Hartman et al. 2008
(cat. J/ApJ/675/1233) and SDSS DR7 catalog (cat. II/294).
Note (4): The B and V photometry is from Kalirai et al. (2001AJ....122.3239K 2001AJ....122.3239K).
Note (5): The J, H, and Ks photometry from the Two Micron All Sky
Survey (2MASS) Point Source Catalog (Cutri et al. 2003, cat. II/246).
Note (6): The types of variability were assigned as:
F = Flare star;
P = Pulsating variable;
mp = Multi-periodic variable;
R = Rotating variable;
EB = Eclipsing Binary system;
A = Aperiodic variable;
: = Variable candidate;
var = Variable;
non = Non-variable listed in Table2;
U = Variable object fell on chip gap and was not observed.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Seq [1/30] Running sequence number
4 A1 --- --- [V]
5- 8 I4 --- Star [27/1423] Variable star identifier (G1)
10- 28 A19 --- Name Star identifier (HHMMSS.ss+DDMMSS.ss, J2000)
30- 31 I2 --- Chip [3/35] Chip number
33- 38 F6.3 mag rmag [15.5/21.9] The r band magnitude
40- 45 F6.3 d Per [1.6/16.6]? Period obtained by Hartman et al.
2008 (cat. J/ApJ/675/1254)
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Seq [1/22] Running sequence number
4 A1 --- --- [V]
5- 8 I4 --- Star [1/2297] Variable star identifier (G1)
10- 15 F6.3 mag rmag [13.6/22.6] The r band magnitude
17- 22 F6.4 d Per [0.6/6]? Orbital period
24- 25 A2 --- l_e [≤] Upper limit flag on eccentricity
26- 29 F4.2 --- e [0/0.7]? Orbital eccentricity (1)
31- 34 F4.2 --- Rad1 [0.04/0.43]? Radius of large star (in units of
semimajor axis)
36- 39 F4.2 --- Rad2 [0.01/0.34]? Radius of small star (in units of
semimajor axis)
41- 45 F5.2 mag mag1 [14.2/22.9]? Brightness of large star
47- 51 F5.2 mag mag2 [16.8/24.6]? Brightness of small star
53- 56 F4.2 --- sini [0.98/1]? Sine of inclination
58- 61 F4.2 --- t0 [0.01/0.9]? Phased epoch of periastron (2)
63- 67 F5.1 deg omega [73/357]? Argument of periastron, ω
69- 95 A27 --- EB Type of Eclipsing Binary (EB) system (D, SD,
or RM) (3)
97-117 A21 --- Note Note about the system
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Note (1): For the cases where the errors are larger than e, we show the best-fit
value plus the error as an upper limit.
Note (2): Modified Julian date folded by the period (see Table4 in Devor 2005,
cat. J/ApJ/628/411).
Note (3): Defined as follows:
D = Detached eclipsing binary system;
SD = Semi-detached eclipsing binary system;
RM = Rotational modulation.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- Seq [1/15] Running sequence number
4 A1 --- --- [V]
5- 8 I4 --- Star [791/2214] Variable star identifier (G1)
10- 28 A19 --- Name Star identifier (HHMMSS.ss+DDMMSS.ss, J2000)
30- 35 F6.3 mag rmag [13.2/21.2] The r band magnitude
37 I1 --- N [1/8] Number of the event
39- 49 F11.5 d t0 [53725.1/53756.3] First time of dimming points
that were detected by the Change-Point Analysis
(CPA) (1)
51- 53 F3.1 h dt [0/4.7] Duration between the start time of the
eclipse and the end, Δt
55 A1 --- l_d [<] Upper limit flag on d
56- 60 F5.3 mag d [0.01/0.3] Depth of the observed dimming points
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Note (1): In units of Modified Julian Date (MJD).
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- Seq [1/92] Number identifier
4 A1 --- --- [V]
5- 8 I4 --- Star [5/2284] Variable star identifier (G1)
10- 28 A19 --- Name Star identifier (HHMMSS.ss+DDMMSS.ss, J2000)
30- 35 F6.3 mag rmag [14.5/22.3]? The r band magnitude
37- 43 F7.4 --- Freq [0.04/52.2]Frequency in units of cycles/day
45- 49 A5 --- FName Frequency name (1)
51- 56 F6.1 mmag Amp [0.6/1092] Amplitude (2)
58- 63 F6.4 deg Phase [0/1] Phase
65- 70 F6.1 --- S/N [3.3/1730.4]? The signal to noise ratio (3)
72- 85 A14 --- Note ? Close frequency (4)
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Note (1): All the detected frequencies are classified as independent modes (f1,
f2, f3, ...), combination modes (afi±bfj), and harmonic mode (hfj).
Note (2): We doubled amplitudes derived by PERIOD04 since this program gives
half of the full amplitudes.
Note (3): The signal-to-noise ratio (S/N) was calculated by PERIOD04. Each noise
level was computed from the prewhitened periodogram as a running mean over
boxes of 5 cycles/day in frequency.
Note (4): We note the frequency values at which the close pairs occur with a
separation less than 0.1cycles/day.
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq [1/132] Running sequence number
5 A1 --- --- [V]
6- 9 I4 --- Star [58/2305] Variable star identifier (G1)
11- 29 A19 --- Name Star identifier (HHMMSS.ss+DDMMSS.ss, J2000)
31- 36 F6.3 mag rmag [13.9/21.8]? The r band magnitude
38- 42 F5.3 mag rms [0.002/0.4] Light curve rms, σm (1)
44- 48 F5.3 mag Amp [0.01/2.1] Light curve amplitude, Δm (2)
50- 56 F7.1 --- chi2 [0.9/11220.4] Reduced χ2 statistic,
χ2v (3)
58- 61 I4 --- Np [135/4730] Number of data points
63- 68 F6.3 d Per [3.7/21.6]? Previously known period (4)
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Note (1): The measured standard deviation of 3σ-clipped light curve.
Note (2): The peak-to-trough amplitude of 3σ-clipped light curve
(Amp=mmax-mmin).
Note (3): The reduced chi-square chi2 (χ2v of the magnitudes is to
test the significance of variability for individual objects against the
null hypothesis of no variation.
Note (4): For the objects that were previously recognized as periodic variables,
we fill the column with the period value using the catalog of Hartman et
al. 2008 (cat. J/ApJ/675/1254).
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Byte-by-byte Description of file: table7.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq [1/436] Running sequence number
5 A1 --- --- [V]
6- 9 I4 --- Star [42/2306] Variable star identifier (G1)
11- 29 A19 --- Name Star identifier (HHMMSS.ss+DDMMSS.ss, J2000)
31- 36 F6.3 mag rmag [15.1/24.5]? The r band magnitude
38 I1 --- N [1/6] Number of the flare event
40- 50 F11.5 d Tpeak [53725.1/53756.3] The time at flare peak
52- 56 F5.3 mag FAmp [0.006/3.8] The incremental magnitude at
flare peak, Δmpeak
58- 61 F4.2 h tau [0/2.9] The flare duration, τ0.2 (1)
63- 65 A3 --- Var [Var] Indicates spot-induced variability (2)
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Note (1): We define the flare duration (τ0.2=t0.2,rise+t0.2,decay) as
the time-scales of flare events at 80% of its peak level (see Chang et al.,
Paper III).
Note (2): These stars show periodic brightness variations with a near or
distorted sinusoidal shape.
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Global Notes:
Note (G1): The variable star identifiers for the first 1483 stars are from the
numbering system of Hartman et al. 2008 (cat. J/ApJ/675/1254). New variable
identifier numbers are given in ascending order by their right ascension
from V1484 to V2306.
History:
From electronic version of the journal
References:
Chang et al., Paper I 2015AJ....149..135C 2015AJ....149..135C
Chang et al., Paper III
(End) Prepared by [AAS]; Sylvain Guehenneux [CDS] 24-Nov-2015