J/A+A/668/A59 Time-series photometry of variables in NGC 6441 (Bhardwaj+, 2022)
Near-infrared observations of RR Lyrae and Type II Cepheid variables in the
metal-rich bulge globular cluster NGC 6441.
Bhardwaj A., Kanbur S.M., Rejkuba M., Marconi M., Catelan M., Ripepi V.,
Singh H.P.
<Astron. Astrophys. 668, A59 (2022)>
=2022A&A...668A..59B 2022A&A...668A..59B (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Clusters, globular ; Stars, variable ;
Photometry, infrared
Keywords: stars: variables: RR Lyrae - stars: variables: Cepheids -
globular clusters: globulars - stars: oscillations - distance scale
Abstract:
NGC 6441 is a bulge globular cluster with an unusual horizontal branch
morphology and a rich population of RR Lyrae (RRL) and Type II Cepheid
(T2C) variables that is unexpected for its relatively high
metallicity.
Our goal is to characterize the pulsation properties of the population
II RRL and T2C variables in this metal-rich GC and compare them with a
sample of variables in more metal-poor clusters, as well as with
theoretical predictions.
We present near-infrared (NIR, JHKs) time-series observations of 42
RRL, 8 T2Cs, and 10 eclipsing binary candidate variables in NGC 6441.
The multi-epoch observations were obtained using the FLAMINGOS-2
instrument on the 8-m Gemini South telescope. Multiband data are used
to investigate pulsation properties of RRL and T2C variables including
their light curves, instability strip, period--amplitude diagrams, and
period--luminosity and period--wesenheit relations (PLRs and PWRs) in
JHKs filters.
The near-infrared (NIR) pulsation properties of RRL variables are well
fitted with theoretical models that have canonical helium content and
the mean-metallicity of NGC 6441 ([Fe/H]=-0.44±0.07dex).
The helium-enhanced RRL models predict brighter NIR magnitudes and
bluer colors than the observations of RRL in the cluster. We find that
the empirical slopes of the RRL PLRs and PWRs in NGC 6441 are
statistically consistent with those of RRLs in more metal-poor GCs, as
well as the theoretical models. Therefore, we use theoretical
calibrations of RRL period-luminosity-metallicity (PLZ) relations
to simultaneously estimate the mean reddening,
E(J-Ks)=0.26±0.06mag, and the distance, d=12.67±0.09kpc, to NGC
6441. Our mean reddening value is consistent with an independent
estimate from the bulge reddening map based on red clump stars. The
RRL-based distance agrees well with similar literature measurements
based on the PLZ relations, and the Gaia and other independent
methods. Our distance and reddening values provide a very good
agreement between the PLRs of T2Cs in NGC 6441 and those for RRLs and
T2Cs in Galactic GCs that span a broad range of metallicity.
We conclude that the NIR colour-magnitude diagrams, pulsation
properties, and PLRs for RRLs and T2Cs in NGC 6441 are in good
agreement with the predictions of RRL pulsation models with canonical
helium content. This suggests that these population II variables are
either not significantly helium enhanced, as previously thought, or
the impact of such enhancement is smaller in NIR than the predictions
of the pulsation models.
Description:
Near-infrared time-series photometry of 42 RR Lyrae variables, eight
Type II Cepheids and 10 eclipsing binary candidates in NGC 6441.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 140 60 NIR pulsation properties of variable stars
in NGC 6441
table2.dat 35 3297 Time-series photometry of variables
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See also:
V/150 : Updated catalog of variable stars in globular clusters
(Clement+ 2017)
J/AcA/64/177 : VI light curves of Galactic Bulge RR Lyrae (Soszynski+, 2014)
J/A+A/651/A47 : Variable stars in VVV globulars. II. (Alonso-Garcia+, 2021)
J/A+A/644/A140 : VVVEXMAP-BULGE High resolution reddening map (Surot+, 2020)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Name Star identifier (1)
11- 19 F9.5 deg RAdeg Rigth ascension (J2000) (1)
21- 29 F9.5 deg DEdeg Declination (J2000) (1)
31- 38 F8.5 d Per Period (1)
40- 43 A4 --- Type Variable type (1) (2)
45- 50 F6.3 mag Jmag Intensity-averaged mean J magnitude
52- 57 F6.3 mag Hmag ?=- Intensity-averaged mean H magnitude
59- 64 F6.3 mag Ksmag Intensity-averaged mean Ks magnitude
66- 70 F5.3 mag e_Jmag rms uncertainty on Jmag
72- 76 F5.3 mag e_Hmag ?=- rms uncertainty on Hmag
78- 82 F5.3 mag e_Ksmag rms uncertainty on Ksmag
84- 88 F5.3 mag AmpJ Peak-to-peak amplitude of variation in J band
90- 94 F5.3 mag AmpH ?=- Peak-to-peak amplitude of variation
in H band
96-100 F5.3 mag AmpKs Peak-to-peak amplitude of variation in Ks band
102-106 F5.3 mag e_AmpJ rms uncertainty on AmpJ
108-112 F5.3 mag e_AmpH rms uncertainty on AmpH
114-118 F5.3 mag e_AmpKs rms uncertainty on AmpKs
120-124 F5.3 mag E(J-Ks) Reddening (3)
126-130 F5.3 mag e_E(J-Ks) rms uncertainty on E(J-Ks) (3)
132-140 A9 --- OName Other name (4)
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Note (1): Star ID, coordinates (epoch J2000), period, variable type, and the
pulsation mode are adopted from the literature:
VNNN from Clement et al., 2001AJ....122.2587C 2001AJ....122.2587C, Cat. V/150
RRL-, T2C-, EC- from Soszynski et al., 2014AcA....64..177S 2014AcA....64..177S, Cat. J/AcA/64/177
CNN from Alonso-Garcia et al., 2021A&A...651A..47A 2021A&A...651A..47A, Cat. J/A+A/651/A47.
Note (2): Type as follows:
RRab = fundamental-mode RRL
RRc = overtone-mode RRL
T2C = Type II Cepheids
EC = Eclipsing binary
EC? = Eclipsing binary candidates
Note (3): reddening values and their errors taken from the reddening maps
of Surot et al. (2020A&A...644A.140S 2020A&A...644A.140S, Cat. J/A+A/644/A140).
Note (4): alternate ID of the variable which was taken from the OGLE catalog
of variable stars or the aforementioned references.
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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- 9 A9 --- Name Star identifier
11- 12 A2 --- Filt [J H Ks] Filter in which the magnitude
was obtained
14- 22 F9.3 d MJD Modified Julian Date of observation
(JD-2400000.5)
24- 29 F6.3 mag mag Near-infrared magnitude in Filt
31- 35 F5.3 mag e_mag Uncertainty in mag
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Acknowledgements:
Anupam Bhardwaj, anupam.bhardwaj(at)inaf.it
(End) Anupam Bhardwaj [INAF-OACN, Italy], Patricia Vannier [CDS] 13-Oct-2022