J/A+A/695/A164 Population II Cepheids in Galactic GC (Cruz Reyes+, 2025)
Variable stars in Galactic globular clusters. II. Population II Cepheids.
Cruz Reyes M., Anderson I.R., Das S.
<Astron. Astrophys. 695, A164 (2025)>
=2025A&A...695A.164C 2025A&A...695A.164C (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Stars, variable ; Stars, population II
Keywords: catalogs - stars: Population II - stars: variables: Cepheids
Abstract:
We have identified a sample of 88 bona fide population II Cepheids
(henceforth: Cepheids) and 44 candidates in Galactic globular clusters
(GCs). Seventy-eight of the Cepheids in the sample align within
2σ of the period-luminosity relation for Milky Way Type II
Cepheids (T2CEP). Nine align with the period-luminosity relation for
fundamental-mode Anomalous Cepheids (ACEPs), and only one (BL Bootis)
follows the relation for first-overtone ACEPs determined using the
Large Magellanic Cloud. For sources in common between our catalog and
the OGLE catalog, the classification agrees in 94% of cases. In
comparison, for sources shared between Gaia SOS and OGLE, the
agreement is 74%. In the dense environments of GCs, our analysis
shows that the completeness of the Gaia catalogs for Cepheids is
64% for the SOS (Specific Object Study) and 74% for the classifier
of variable stars. Using linear MESA-RSP models, we determined the red
and blue edges of the instability strip for T2CEPs. We found that the
models providing the best fit to the observations are able to fit
90% of the stars in our sample. They have the following parameters:
M=0.6M☉, Z=0.0003, and this percentage does not change
for two different values of the helium abundance (Y=0.220 and
0.245). Higher values of Y lower this percentage, and the same
effect is observed with lower values of Z. In the future, combining
the sample of T2CEPs with the precise parallaxes obtained from GCs
will strengthen the geometric calibration of a distance ladder based
on Population II stars. This will be useful for determining distances
within the Milky Way and for cross-checking distances to Local Group
galaxies determined through other methods.
Description:
Our approach is analogous to the membership analysis of RRLs in GCs
presented in Paper I, which is largely based on the sample of 170 GCs
and their cluster members compiled by Vasiliev & Baumgardt
(2021MNRAS.505.5978V 2021MNRAS.505.5978V, Cat. J/MNRAS/505/5978). Paper I lists the
astrometric parameters adopted in our analysis, while the
ellipticities of GCs, essential for constructing the membership prior,
were obtained from Cruz Reyes & Anderson (2024A&A...689A.232C 2024A&A...689A.232C, Cat.
J/A+A/689/A232), and the reddening values were taken from the catalog
of cluster parameters by Harris (2010, arXiv e-prints
[1012.3224]).
We compiled our sample of variable stars using five different
catalogs. The first, the Gaia Specific Object Study (SOS), contains
15021 Cepheids (Ripepi et al., 2023A&A...674A..17R 2023A&A...674A..17R, Cat.
J/A+A/674/A17). The second catalog, the Gaia classifier of variable
sources, includes 16141 Cepheids. The third catalog, Gavras et al.
(2023A&A...674A..22G 2023A&A...674A..22G, Cat. J/A+A/674/A22: henceforth: G23),
incorporates 19482 Cepheids. The fourth catalog combines the OGLE
collection of T2CEPs in the Galactic disk (Udalski et al.,
2018AcA....68..315U 2018AcA....68..315U, Cat. J/AcA/68/315) and the Galactic bulge
(Soszynski et al., 2017AcA....67..297S 2017AcA....67..297S, Cat. J/AcA/67/297). After
merging the Cepheids from the Clement (2017EPJWC.15201021C 2017EPJWC.15201021C)
catalog with the previous ones, we had a total of 21252 unique
Cepheids. It is important to note that all ACEPs observed by Ngeow et
al. (2022AJ....164..191N 2022AJ....164..191N) and all T2CEPs from Ngeow et al.
(2022AJ....164..154N 2022AJ....164..154N) are included in the sample.
Table A.1 provides details about the sample of Cepheids analyzed in
Sect. 4. Table A.2 lists the identifiers for all Cepheids in clusters
from the Gaia, Clement (2017EPJWC.15201021C 2017EPJWC.15201021C), and OGLE
catalogs, along with their assigned classifications.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tablea1.dat 129 158 Cepheids in globular clusters
tablea2.dat 83 88 Cepheid identifiers and their assigned
classification in other catalogs
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See also:
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
J/AcA/70/101 : OGLE IV Galactic Cepheids (Soszynski+, 2020)
Byte-by-byte Description of file: tablea1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 A19 --- GaiaDR3 Gaia DR3 source_id
21- 38 F18.14 deg RAdeg Gaia DR3 Barycentric right ascension (ICRS)
at Ep=2016.0
40- 59 F20.16 deg DEdeg Gaia DR3 Barycentric declination (ICRS)
at Ep=2016.0
61- 73 A13 --- Cluster Cluster name
75- 80 F6.4 --- Like ? Likelihood
82- 87 F6.4 --- Prior [0/1] Prior probability
89- 94 F6.4 --- Posterior [0/1]? Posterior probability
96-100 A5 --- Final [False True] A Boolean column that specifies
whether the star is part of Final sample of
Cepheids in clusters
102-108 A7 --- Class Classification assigned in this study
110-114 A5 deg Cand [False True] A Boolean column identifying
Cepheids whose membership could not be
confirmed
116-123 F8.4 d Period ? Pulsation period used to determine the
classification
125-129 A5 --- SOS [False True] Boolean column indicating whether
SOS photometry is available in the
Gaia archive
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Byte-by-byte Description of file: tablea2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 A19 --- GaiaDR3 Gaia DR3 source_id
21- 33 A13 --- Cluster Cluster name
35- 41 A7 --- C17 Identifier in the Clement
(2017EPJWC.15201021C 2017EPJWC.15201021C) catalog
43- 61 A19 --- OGLE Identifier in the OGLE IV catalog,
OGLE-BLG-T2CEP-NNNN or OGLE-GD-T2CEP-NNN
63- 67 A5 --- ClassSOS Classification assigned in the SOS catalog
69- 73 A5 --- ClassC17 Classification assigned in the C17 catalog
75- 77 A3 --- Class Classification assigned by the classifier of
variable sources of Gaia (DR3)
79- 83 A5 --- G23 Primary classification assigned in the G23
catalog
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Acknowledgements:
Mauricio Cruz Reyes, mauricio.cruzre(at)gmail.com
(End) Patricia Vannier [CDS] 11-Feb-2025