J/AJ/155/116 The globular cluster M14.II. Variable stars (Contreras Pena+, 2018)
The globular cluster NGC 6402 (M14).
II. Variable stars.
Contreras Pena C., Catelan M., Grundahl F., Stephens A.W., Smith H.A.
<Astron. J., 155, 116 (2018)>
=2018AJ....155..116C 2018AJ....155..116C (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Clusters, globular ; Stars, variable ;
Photometry, UBVRI ; Abundances, [Fe/H] ; Effective temperatures
Keywords: galaxies: dwarf - galaxies: star clusters: general -
globular clusters: individual (NGC 6402, M14) -
Hertzsprung-Russell and C-M diagrams - stars: variables: RR Lyrae
Abstract:
We present time-series BVI photometry for the Galactic globular cluster
NGC 6402 (M14). The data consist of ∼137 images per filter, obtained
using the 0.9 and 1.0 m SMARTS telescopes at the Cerro Tololo
Inter-American Observatory. The images were obtained during two observing
runs in 2006-2007. The image-subtraction package ISIS, along with
DAOPHOT II/ALLFRAME, was used to perform crowded-field photometry and
search for variable stars. We identified 130 variables, eight of which
are new discoveries. The variable star population is comprised of
56 ab-type RR Lyrae stars, 54 c-type RR Lyrae, 6 type II Cepheids,
1 W UMa star, 1 detached eclipsing binary, and 12 long-period variables.
We provide Fourier decomposition parameters for the RR Lyrae, and discuss
the physical parameters and photometric metallicity derived therefrom.
The M14 distance modulus is also discussed, based on different approaches
for the calibration of the absolute magnitudes of RR Lyrae stars. The
possible presence of second-overtone RR Lyrae in M14 is critically
addressed, with our results arguing against this possibility. By
considering all of the RR Lyrae stars as members of the cluster, we derive
<Pab≥0.589 days. This, together with the position of the RR Lyrae stars
of both Bailey types in the period-amplitude diagram, suggests an
Oosterhoff-intermediate classification for the cluster. Such an
intermediate Oosterhoff type is much more commonly found in nearby
extragalactic systems, and we critically discuss several other possible
indications that may point to an extragalactic origin for this cluster.
Description:
Time-series B, V, and I photometry was obtained for M14 using two different
telescopes. The first set was obtained with the SMARTS 1.0 m telescope
at the Cerro Tololo Inter-American Observatory (CTIO) for seven consecutive
nights between 2006 August 10-16 and five nights between September 28-
October 3, comprising a total of 75, 72, and 80 images in the B, V, and I
filters, respectively. Typical exposure times corresponded to 300 s (B),
150 s (V), and 100 s (I). The typical seeing level was 1.6". The telescope
was equipped with the Y4KCam 4064x4064 CCD detector, with a pixel scale of
0.289"/pixel, producing a 20'x20' field of view (FOV). The second set
of time-series B, V, and I photometry was obtained with the SMARTS 0.9 m
telescope at CTIO during 16 nights between 2007 June 22-July 12,
comprising a total of 67, 65, and 62 images in B, V, and I, respectively.
Typical exposure times of 600 s in B, V and 150 s in I were used, and
the typical seeing was 1.8". A 2048x2046 CCD detector with a pixel scale
of 0.369"/pixel, equivalent to a field size of 13.5'x13.5', was used for
image acquisition.
Objects:
---------------------------------------------
RA (ICRS) DE Designation(s)
---------------------------------------------
17 37 36.15 -03 14 45.3 NGC 6402 = M 14
---------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 53 130 Properties of variable stars found in M14
table3.dat 91 130 Properties of variable stars found in M14
table4.dat 47 34 Amplitude ratios and phase differences from
Fourier analysis for c-type RR Lyrae stars
table5.dat 47 50 Amplitude ratios and phase differences for RRab
stars
table6.dat 30 13 Derived parameters for c-type RR Lyrae stars
table7.dat 30 12 *Physical parameters of ab-type RR Lyrae
table8.dat 107 27 Mean physical parameters of RR Lyrae stars
in GCs
table1.dat 33 35892 Light curves of variable stars of M14
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Note on table7.dat: Derived from Fourier parameters of stars with Dm<5.
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See also:
VII/202 : Globular Clusters in the Milky Way (Harris, 1997)
V/150 : Updated catalog of variable stars in globular clusters
(Clement+ 2001)
B/gcvs : General Catalogue of Variable Stars (Samus+, 2007-2017)
J/A+A/312/111 : [Fe/H] from RR Lyrae light curves (Jurcsik+, 1996)
J/PASP/121/1378 : Positions of variable stars in globular clusters
(Samus+, 2009)
J/A+A/548/A92 : VrI light curves of NGC1904 variables (Kains+, 2012)
J/AJ/146/57 : NGC 6402. I. BV photometry (Contreras+, 2013)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- Star Star identifier (VNNN) (G1)
6- 7 I2 h RAh Hour of Right Ascension (J2000)
9- 10 I2 min RAm Minute of Right Ascension (J2000)
12- 16 F5.2 s RAs Second of Right Ascension (J2000)
18 A1 --- DE- Sign of the Declination (J2000)
19- 20 I2 deg DEd Degree of Declination (J2000)
22- 23 I2 arcmin DEm Arcminute of Declination (J2000)
25- 29 F5.2 arcsec DEs Arcsecond of Declination (J2000)
31- 38 F8.5 d Per [0.25209/18.76018]? Period of the variable star;
when applicable
40- 45 F6.3 mag E(B-V) [-0.07/0.016] Differential reddening,
ΔE(B-V), derived in Contreras Pena et al.
(2013, J/AJ/146/57)
47- 53 A7 --- Type Variable star classification
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- Star Star identifier (VNNN) (G1)
6- 9 F4.2 mag AB [0.24/1.72]? Amplitude of the B light curve
11- 14 F4.2 mag AV [0.11/1.34]? Amplitude of the V light curve
16- 19 F4.2 mag AI [0.04/0.95]? Amplitude of the I light curve
21- 26 F6.3 mag Bmag [15.563/18.623] Magnitude-weighted mean B
magnitude (1)
28- 33 F6.3 mag Vmag [14.08/17.702] Magnitude-weighted mean V magnitude
(1)
35- 40 F6.3 mag Imag [11.647/16.691]? Magnitude-weighted mean I
magnitude (1)
42- 47 F6.3 mag Bint [15.429/18.55]? Intensity-weighted mean B
magnitude (1)
49- 54 F6.3 mag Vint [14.21/17.695]? Intensity-weighted mean V
magnitude (1)
56- 61 F6.3 mag Iint [12.633/16.688]? Intensity-weighted mean I
magnitude (1)
63- 67 F5.3 mag B-Vmag [0.601/2.417] Magnitude-weighted mean B-V color
(1)
69- 73 F5.3 mag B-Vint [0.604/1.351]? Intensity-weighted mean B-V color
(1)
75- 79 F5.3 mag B-Vstat [0.596/1.362]? B-V color of the equivalent static
star (1)
81- 85 F5.3 mag V-Imag [0.942/2.952]? Magnitude-weighted mean V-I color
(1)
87- 91 F5.3 mag V-Iint [0.937/2.902]? Intensity-weighted mean V-I color
(1)
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Note (1): For further details on the difference between magnitude- and
intensity-weighted means, and how they compare with the corresponding
quantities for the so-called "equivalent static star", the reader is referred
to Bono et al. (1995ApJS...99..263B 1995ApJS...99..263B).
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Byte-by-byte Description of file: table4.dat table5.dat
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Bytes Format Units Label Explanations
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1- 4 A4 --- Star Star identifier (VNNN) (G1)
5 A1 --- u_Star [:] Uncertainty flag on Star (1)
7- 11 F5.3 --- A21 [0.038/0.612] Amplitude ratio A2/A1
13- 17 F5.3 --- A31 [0.023/0.423] Amplitude ratio A3/A1
19- 23 F5.3 --- A41 [0.011/0.352] Amplitude ratio A4/A1
25- 29 F5.3 --- Phi21 [2.088/6.174] Phase difference Φ2-2Φ1
31- 35 F5.3 --- Phi31 [0.079/6.203] Phase difference Φ3-3Φ1
37- 41 F5.3 --- Phi41 [0.04/6.207] Phase difference Φ4-4Φ1
43- 47 F5.1 --- Dm [1.4/143.3]? Deviation parameter Dm (not in
Table 4) (2)
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Note (1): Flag as follows:
: = Star with uncertain values, which we do not use in the subsequent
analysis.
Note (2): The Dm parameter was introduced by Jurcsik & Kovacs (1996,
J/A+A/312/111) and is defined as the maximum of nine deviation parameters,
{DF}, defined as DF=(|Fobs-Fjk|)/σF, where Fobs is the
observed value of the given Fourier parameter, Fjk is its predicted value
using the other observed parameters, and σF is the standard deviation
of Fjk (Jurcsik & Kovacs 1996, J/A+A/312/111). Jurcsik & Kovacs (1996,
J/A+A/312/111) argue that light curves showing Dm=<3 satisfy the
compatibility condition, and the physical parameters derived from these stars
can be accounted as reliable estimates of such parameters.
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Byte-by-byte Description of file: table6.dat table7.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- Star Star identifier (VNNN) (G1)
5 A1 --- u_Star [*] Uncertainty flag on Star (not in Table 6) (1)
7- 12 F6.3 [-] [Fe/H] [-1.666/-0.523] Metallicity (in the UVES scale
in Table 6; in the Jurcsik (1995AcA....45..653J 1995AcA....45..653J)
scale in Table 7) (2)
14- 18 F5.3 [-] e_[Fe/H] [0.062/3.079] Uncertainty in [Fe/H]U (2)
20- 24 F5.3 mag VMag [0.467/0.661] Intensity-averaged absolute V
magnitude (from Kovacs 1998MmSAI..69...49K 1998MmSAI..69...49K) (3)
26- 30 F5.3 mag e_VMag [0.013/0.025] Uncertainty in VMag (3)
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Note (1): Flag as follows:
* = Variable star with uncertain parameters.
Note (2): Mean [Fe/H] is equal to -1.202±0.268 dex in Table 6 and is equal to
-1.105±0.093 in Table 7. Mean values are derived excluding variable stars
with uncertain parameters.
Note (3): Mean VMag is equal to 0.518±0.040 in Table 6 and is equal to
0.572±0.048 in Table 7. Mean values are derived excluding variable stars
with uncertain parameters.
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Byte-by-byte Description of file: table8.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- Cluster Cluster name
10- 13 A4 --- OCluster Other name for the cluster
15- 20 A6 --- OoType Oosterhoff classification (Int=Intermediate)
22- 26 F5.2 [-] [Fe/H] [-2.37/-0.46] Metallicity (in the
Carretta et al. 2009A&A...508..695C 2009A&A...508..695C;
UVES scale)
28- 31 F4.2 Msun M [0.47/0.76]? Mass (1)
33- 36 F4.2 [Lsun] logL [1.41/1.81]? Log luminosity (1)
38- 41 I4 K Teff [6282/7495]? Effective temperature (1)
43- 46 F4.2 --- Y [0.24/0.29]? Helium abundance parameter (1)
48- 51 F4.2 mag VMag [0.38/0.68]? Absolute V band magnitude (2)
(3)
53 I1 --- n_VMag [1/3]? Note on VMag (4)
55- 58 I4 K Teff(V-K) [6160/6633]? Effective temperature derived
from V-K color index (2)
60- 87 A28 --- Ref Reference
89-107 A19 --- Bibcode Bibcode of the reference
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Note (1): From Fourier decomposition of RRc light curves.
As explained in the text, the mass, luminosity, Y, and Teff values derived
from Fourier parameters should be treated with great caution, which is the
reason they are not provided for each individual M14 variable in our paper.
However, mean values are still listed in this table, though solely for the
purpose of comparing M14 with other GCs for which such values had been
previously obtained in the literature, using the same technique.
Note (2): From Fourier decomposition of RRab light curves.
Note (3): Following Kains et al. (2012, J/A+A/548/A92; see their Table 10), the
listed absolute magnitudes, VMag, are converted to values consistent with the
distance scale of Cacciari et al. (2005AJ....129..267C 2005AJ....129..267C). If the Kovacs
(1998ASPC..135...52K 1998ASPC..135...52K) scale is used in the original publication, then 0.2 mag
are subtracted from VMag.
Note (4): Note as follows:
1 = GCs where original values were calculated using the Kovacs
(1998ASPC..135...52K 1998ASPC..135...52K) scale;
2 = GCs where VMag was derived using the scale of Cacciari et al.
(2005AJ....129..267C 2005AJ....129..267C);
3 = Indicates cases where VMag was left the same as the original value, given
that the shift suggested by Cacciari et al. (2005AJ....129..267C 2005AJ....129..267C) might
not be applicable to metal-rich GCs (Kains et al. 2012A&A...548A..92K 2012A&A...548A..92K).
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 A4 --- Star Star identifier (VNNN) (G1)
6 A1 --- Filt [BVI] Filter
8- 20 F13.5 d HJD Heliocentric Julian Date of observation
22- 27 F6.3 mag mag [11.483/19.585] Apparent magnitude in Filt
29- 33 F5.3 mag e_mag [0.001/0.48] Error in mag
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Global notes:
Note (G1): Variable name from Clement et al. 2017, Cat. V/150 (cluster
C1735-032).
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History:
From electronic version of the journal
References:
Contreras Pena et al. Paper I. 2013AJ....146...57C 2013AJ....146...57C, Cat. J/AJ/146/57
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 31-Oct-2018