J/AJ/145/113 JHK photometry in Cyg OB7. II. Variable stars (Wolk+, 2013)
Near-infrared periodic and other variable field stars in the field of the
Cygnus OB7 star-forming region.
Wolk S.J., Rice T.S., Aspin C.A.
<Astron. J., 145, 113 (2013)>
=2013AJ....145..113W 2013AJ....145..113W
ADC_Keywords: Binaries, eclipsing ; Photometry, infrared ; Stars, variable
Keywords: binaries: eclipsing - infrared: stars - stars: variables: general
Abstract:
We present a subset of the results of a three-season, 124 nights,
near-infrared monitoring campaign of the dark clouds Lynds 1003 and
Lynds 1004 in the Cygnus OB7 star-forming region. In this paper, we
focus on the field star population. Using three seasons of UKIRT J, H,
and K-band observations spanning 1.5 years, we obtained high-quality
photometry on 9200 stars down to J=17mag, with photometric uncertainty
better than 0.04mag. After excluding known disk-bearing stars we
identify 149 variables-1.6% of the sample. Of these, about 60 are
strictly periodic, with periods predominantly <2days. We conclude this
group is dominated by eclipsing binaries. A few stars have long period
signals of between 20 and 60 days. About 25 stars have weak modulated
signals, but it was not clear if these were periodic. Some of the
stars in this group may be diskless young stellar objects with
relatively large variability due to cool starspots. The remaining ∼60
stars showed variations which appear to be purely stochastic.
Description:
J, H, and K observations of the Cygnus OB7 region were obtained using
the Wide-Field Camera (WFCAM) instrument on the United Kingdom
InfraRed Telescope (UKIRT), an infrared-optimized 3.8m telescope atop
Mauna Kea, Hawaii at 4200m elevation. Our data consist of WFCAM
observations taken from 2008 May to 2009 October in three observing
seasons (Season 1 from 2008 Apr 26 to 2008 May 22; Season 2 from 2008
Sep 19 to 2008 Nov 27; Season 3 from 2009 Aug 28 to 2009 Oct 13) as
part of a special observation program. Data were taken on a total of
124 nights during this period. The data set used here was fully
described in Paper I (Rice et al., 2012ApJ...755...65R 2012ApJ...755...65R).
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table3.dat 110 65 Strongly periodic stars in the monitored field
table4.dat 110 62 Stochastically variable stars in the monitored field
table5.dat 110 24 Other possibly periodic stars in the monitored field
--------------------------------------------------------------------------------
See also:
B/gcvs : General Catalogue of Variable Stars (Samus+ 2007-2013)
J/AJ/142/160 : Kepler Mission. II. 2165 eclipsing binaries (Slawson+, 2011)
J/A+A/503/651 : Variable stars in a Carina VLT/VIMOS field (Pietrukowicz+ 2009)
J/AJ/124/1001 : JHKs photometry of Cha I variables (Carpenter, 2002)
J/AJ/121/3160 : JHK photometry near the Trapezium region (Carpenter+, 2001)
Byte-by-byte Description of file: table[345].dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 16 A16 --- Group Group of stars (Simple eclipse, continual
change, other periodic, lower quality, long
period, moderate period) (1)
18- 19 I2 h RAh Hour of Right Ascension (J2000)
21- 22 I2 min RAm Minute of Right Ascension (J2000)
24- 29 F6.3 s RAs Second of Right Ascension (J2000)
31 A1 --- DE- Sign of the Declination (J2000)
32- 33 I2 deg DEd Degree of Declination (J2000)
35- 36 I2 arcmin DEm Arcminute of Declination (J2000)
38- 41 F4.1 arcsec DEs Arcsecond of Declination (J2000)
43- 47 F5.2 mag Jmag UKIRT J-band magnitude (2)
49- 53 F5.2 mag Hmag UKIRT H-band magnitude (2)
55- 59 F5.2 mag Kmag UKIRT K-band magnitude (2)
61- 64 F4.2 mag DJmag Range seen in the J filter (2)
66- 69 F4.2 mag DKmag Range seen in the K filter (2)
71- 74 F4.2 mag D(J-H) Peak to floor change in the J-H color index (2)
76- 79 F4.2 mag D(H-K) Peak to floor change in the H-K color index (2)
81- 85 F5.2 mag S Stetson variability index for the star (3)
87- 91 A5 --- f_Per Flag on Per (a=star with no unique period
identified; b=period only in Season2; multi)
92- 96 F5.2 d Per ? Period of the star (only for Tables 3 and 5)
98-103 F6.2 d Per2 ? Second period identified (only in Table5)
104 A1 --- f_Type [?] Uncertainty on Type (?)
105-108 A4 --- Type ? Binary classification (E, EA, EB, EW, P, RRab,
or dScu; only in Table3) (4)
110 I1 --- G [1/5]? Period grade (0-5; only in Table5) (5)
--------------------------------------------------------------------------------
Note (1): Details about the group of stars:
Simple eclipse = Eclipsing systems showing clean, sharp eclipses, in which
the star deviated from its nominal flux level for a fixed time
period in which it dropped sharply and then returned to the original
flux. These are detached systems where the separation of both
components is large compared to their radii. The stars interact
gravitationally, but the distortion of their surfaces due to tidal
deformation and rotation is minimal (see additional details in
Section 4.1).
Other periodic = Stars showing very strong periodic light curves which
corresponded to neither eclipse events nor symmetric signals
(see Section 4.4 for further details).
Moderate period = Stars showing sinusoidal variations on timescales of
about 2-25 days (more details in Section 4.3).
Note (2): Typical photometric errors are ∼2%. UKIRT is the United Kingdom
InfraRed Telescope (UKIRT), an infrared-optimized 3.8m telescope atop
Mauna Kea, Hawaii at 4200m elevation.
Note (3): Used to quantify variability for all sources in the field (Stetson,
1996PASP..108..851S 1996PASP..108..851S; this index is referred to by the letter J in the
original article; we have relabeled S to avoid confusion with the filter
band). This is a method for quantifying variability within a sample which
includes multiple colors each with different error characteristics. The
resultant value is zero for a constant source and exceeds 1 for a source
with significant correlated variability; high values indicate greater
variability. Carpenter et al. (2001, cat. J/AJ/121/3160) compared the
Stetson index to χ2 fits and concluded that S>0.55 was sufficient to
confirm variability. In Paper I (Rice et al., 2012ApJ...755...65R 2012ApJ...755...65R) we
concluded that S>1.0 was preferable for our analysis because the more
conservative value prevented false detections in large samples.
Note (4): The General Catalog of Variable Stars (GCVS; cat. B/gcvs) divides
eclipsing binary systems into four observational classes based on the shape
of their light curves. General classes are as follows:
E = Eclipsing systems in which the stars are well separated with very
sharp eclipses;
EA = Algol-like systems in which we can note some rounding of the edges
near the time of the eclipses;
EB = β Lyrae-like system in which the eclipse edges are so rounded
as to make it difficult to tell when the eclipses begin and end, and
they have one minimum much deeper than the other;
EW = W UMa-like near contact systems with nearly sinusoidal signals and
period ≲1day;
P = Stars identified as Pulsators;
RRab = RR Lyrae sub-type known as an RRab star which has a large
amplitude, hours long, asymmetric light curve;
dScu = δ Scuti star.
Note (5): Even when it appears that a period is present, the algorithms often
disagree on the preferred period. To deal with this, we manually graded the
light curves of each star on a five-point empirical scale.
Grade as follows:
1 = Cases in which the rise and fall in the data were clear, but no period
could be established, perhaps simply due to unlucky sampling;
2 = The various methods returned different periods of similar quality and hence
the period list was not considered to be reliable;
3 = The various techniques returned clear aliases of each other an hence the
positive determination of the true period was not possible. Periods longer
than 60 days often fall into this category;
4 = Stars with periods of similar consistency in results, but in which the
noise in the individual measurements was nearly at the level of the signal
and hence less reliable;
5 = Subset of periods which appeared beyond question; usually these were clear
eclipsing systems or other systems which varied sinusoidally with periods
under a day.
--------------------------------------------------------------------------------
Nomenclature note:
In Tables 3-5, variable stars are <[WRA2013] JHHMMSS.ss+DDMMSS.s> in Simbad.
History:
From electronic version of the journal
References:
Rice et al., Paper I, 2012ApJ...755...65R 2012ApJ...755...65R
Wolk et al., Paper III, 2013ApJ...773..145W 2013ApJ...773..145W
(End) Sylvain Guehenneux [CDS] 16-May-2014