J/A+A/706/A87 High-accuracy distances of 93 globular clusters (Lengen+, 2026)
A joint 1% calibration of the RR Lyrae type-II Cepheid Leavitt laws yields
homogeneous distances to 93 Galactic globular clusters.
Lengen B., Anderson I.R., Cruz Reyes M., Viviani G.
<Astron. Astrophys. 706, A87 (2026)>
=2026A&A...706A..87L 2026A&A...706A..87L (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Stars, variable ; Stars, population II
Keywords: stars: Population II - stars: variables: Cepheids -
stars: variables: RR Lyrae - Galaxy: clusters: general
Abstract:
Recent work has established large samples of astrometrically confirmed
RR Lyrae and type-II Cepheid members of Galactic globular clusters
(GCs). Any given GC can contain multiple such stars at once, notably
RR Lyrae stars pulsating in the fundamental mode (RRab) or the first
overtone (RRc), and type-II Cepheids (T2Cep) of BL Her and W Vir
types. Here, we present the first joint calibration of the Leavitt
laws (LL) exhibited by 802 RRab, 345 RRc, and 21 T2Cep stars anchored
to trigonometric parallaxes. Using the third data release of the ESA
Gaia mission (GDR3), we have calibrated the intercepts of the RRab and
RRc Leavitt laws in the reddening-free Gaia Wesenheit magnitude, MWG,
to better than 1.0% in distance, and that of T2Cep to 1.3%, using a
global fit to all data. The absolute scale is set by 37 nearby GCs
with high- accuracy parallaxes while 56 additional GCs provide
constraints on LL slopes as well as the LL intercept differences of
RRc and T2Cep relative to RRab stars. Our global fit yields
homogeneous high-accuracy distances of 93 GCs that show no evidence of
bias for Gaia parallaxes of distant GCs. Control of systematics was
demonstrated by 30 alternative fit variants, notably involving
different treatments of metallicity effects, as well as by Markov
Chain Monte Carlo analysis. Our results suggest that photometric
metallicities of RR Lyrae stars require further improvements while
also exhibiting possible signs of intra-cluster chemical
inhomogeneity. This work lays the foundation for exploiting RRab, RRc,
and T2Cep stars as high-accuracy standard candles for near-field
cosmology and the extragalactic distance scale.
Description:
Table e2 lists the anchor globular clusters, providing the number of
Gaia member stars used to determine the GC parallax, the baseline fit
distance modulus and parallax from the global Leavitt-law calibration,
the literature distance modulus from Baumgardt & Vasiliev
(2021MNRAS.505.5957B 2021MNRAS.505.5957B), and the Gaia DR3 mean cluster parallax from
Cruz Reyes et al. (2024A&A...684A.173C 2024A&A...684A.173C, Cat. J/A+A/684/A173),
together with the numbers of RRab, RRc, and Type II Cepheid members;
Table e3 lists the host clusters with the same columns, noting that
the Gaia DR3 mean cluster parallaxes from Cruz Reyes et al.
(2024A&A...684A.173C 2024A&A...684A.173C,, Cat. J/A+A/684/A173) are not used as
constraints in the fit for these GCs.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablee2.dat 189 37 Anchor GCs used in the baseline fit
tablee3.dat 189 56 Host GCs used in the baseline fit
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See also:
J/A+A/684/A173 : RR Lyrae stars in Galactic Globular Clusters
(Cruz Reyes+, 2024)
Byte-by-byte Description of file: tablee2.dat tablee3.dat
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Bytes Format Units Label Explanations
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1- 15 A15 --- GC Cluster name
17- 21 I5 --- Nstars Number of member stars used to determine
the cluster parallax
23- 24 I2 --- NRRab Number of RRab stars belonging to
the cluster used in the baseline fit
26- 27 I2 --- NRRc Number of RRc stars belonging to the cluster
used in the baseline fit
29 I1 --- NT2Cep Number of T2Cep stars belonging to
the cluster used in the baseline fit
31- 48 F18.15 mag mufit Distance modulus determined by the baseline
fit
50- 69 F20.18 mag e_mufit Uncertainty in the distance modulus
determined by the baseline fit
71- 88 F18.15 mag muBV21 Distance modulus from Baumgardt & Vasiliev
(2021MNRAS.505.5957B 2021MNRAS.505.5957B)
90-109 F20.18 mag e_muBV21 Uncertainty in the distance modulus from
Baumgardt & Vasiliev (2021MNRAS.505.5957B 2021MNRAS.505.5957B)
111-129 F19.15 uarcsec plxfit Parallax determined by the baseline fit
131-149 F19.16 uarcsec e_plxfit Uncertainty in the parallax determined by
the baseline fit
152-170 F19.15 uarcsec plxgaia GC mean parallax from Cruz Reyes et al.
(2024A&A...684A.173C 2024A&A...684A.173C, Cat. J/A+A/684/A173)
172-189 F18.15 uarcsec e_plxgaia Uncertainty in the GC mean parallax from
Cruz Reyes et al. (2024A&A...684A.173C 2024A&A...684A.173C,
Cat. J/A+A/684/A173)
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Acknowledgements:
Bastian Lengen, bastianlengen(at)gmail.com
(End) Patricia Vannier [CDS] 24-Nov-2025