J/A+A/712/A150 RGB surface brightness-color relation (Xiong+, 2026)
Surface brightness-colour relations for red giant branch stars:
Observational constraints on metallicity effects using the ARD method
Xiong J., Chen X., Li J., Cheng Q., Zhang X., Liu C., Han Z., Chen X.
<Astron. Astrophys. 712, A150 (2026)>
=2026A&A...712A.150X 2026A&A...712A.150X (SIMBAD/NED BibCode)
ADC_Keywords: Stars, giant ; Stars, distances ; Photometry
Keywords: asteroseismology - stars: distances - stars: fundamental parameters -
stars: late-type
Abstract:
The surface brightness-color relation (SBCR) links stellar color to
angular diameter and is a key ingredient of geometric distance
measurements on the first rung of the cosmic distance ladder. However,
previous RGB-based calibrations were limited by small samples and did
not observeably constrain the role of metallicity.
We aim to quantify the metallicity dependence of the SBCR for red
giant branch (RGB) stars and to test the robustness of the relation
using asteroseismic radii, Gaia distances, and atmospheric parameters
from APOGEE.
We selected more than 2000 RGB stars from APOKASC-3 to calibrate and
validate the SBCR. Johnson V magnitudes were synthesized from Gaia XP
spectra and homogenized to widely used SBCR photometric systems, while
Ks photometry was taken from 2MASS. Angular diameters derived from
asteroseismic radii and Gaia distances (ARD) were used to construct
the SBCR. We explored three fitting strategies: metallicity-free,
metallicity-binned, and global metallicity-dependent relations.
Over the range V-Ks, the SBCR shows only a weak metallicity
dependence. A change of 1dex in [Fe/H] modifies the predicted angular
diameter by less than 1%, well below the intrinsic scatter of the
calibration (∼0.05mag). This result is consistent with theoretical
expectations. Comparison with the interferometric sample reveals a
systematic offset of ∼1.5% toward smaller angular diameters in our
SBCR predictions, with a mild color dependence.
The metallicity effect on the SBCR is small in the color range
explored here, but it becomes relevant for sub-percent distance
measurements. Our results show that large RGB samples with
asteroseismic radii and Gaia distances provide a powerful
observational route for SBCR calibration, with clear potential for
extension to cooler and redder giants as the precision and parameter
coverage of the input data improve.
Description:
This catalogue contains two tables. The first table contains the RGB
stars used to calibrate the SBCRs. The second table contains an
independent RGB sample used to validate the derived relations. Angular
diameters were derived from Gaia geometric distances and asteroseismic
stellar radii using the ARD method.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
fitsamp.dat 352 429 Fitting sample, RGB stars used to calibrate
the SBCRs
testsamp.dat 352 2075 Testing sample, independent RGB sample used
to validate the derived relations
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See also:
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
V/133 : Kepler Input Catalog (Kepler Mission Team, 2009)
Byte-by-byte Description of file: fitsamp.dat testsamp.dat
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Bytes Format Units Label Explanations
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1- 19 I19 --- GaiaDR3 Gaia DR3 source identifier
21- 28 I8 --- KIC Kepler Input Catalog identifier
30- 40 F11.7 deg RAdeg Right ascension (J2000)
42- 50 F9.6 deg DEdeg Declination (J2000)
52- 57 A6 --- EvolState Asteroseismic evolutionary state
59- 65 F7.4 Rsun Radius Asteroseismic stellar radius
67- 72 F6.4 Rsun e_Radius Uncertainty on Radius
74- 80 F7.4 --- [Fe/H] Stellar metallicity [Fe/H]
82- 86 F5.3 --- e_[Fe/H] Uncertainty on [Fe/H]
88- 98 F11.6 pc rgeo Gaia geometric distance (Bailer-Jones et al.,
2021, Cat. I/352)
100-110 F11.6 pc b_rgeo Lower confidence limit of rgeo
112-122 F11.6 pc B_rgeo Upper confidence limit of rgeo
124-129 F6.3 mag Kmag 2MASS Ks-band magnitude
131-135 F5.3 mag e_Kmag Uncertainty on Kmag
137-158 E22.16 mag E(B-V)3d Three-dimensional reddening E(B-V)
160-181 E22.16 mag e_E(B-V)3d Uncertainty on E(B-V)
183-200 F18.15 mag VmagXP Johnson V magnitude synthesized from Gaia XP
spectra (corrected)
202-219 F18.16 mag e_VmagXP Uncertainty on Vmag_xp
221-238 F18.16 --- SvXP Surface brightness parameter S_V
240-257 F18.16 --- E_SvXP Upper uncertainty on S_V
259-276 F18.16 --- e_SvXP Lower uncertainty on S_V
278-295 F18.16 mag (V-Ks)XP Extinction-corrected colour (V-Ks)0
297-314 F18.16 mag e_(V-Ks)XP Uncertainty on (V-Ks)0
316-333 F18.16 mas LD Limb-darkened angular diameter (LD) derived
from the ARD (Gaia distance + asteroseismic
stellar radius) method
335-352 F18.16 mas e_LD Uncertainty on LD
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Acknowledgements:
Jianping Xiong, xiongjianping(at)ynao.ac.cn
License: CC-BY-4.0
(End) Patricia Vannier [CDS] 18-Jun-2026