J/A+A/708/A100 Ultra-faint dwarf Bootes I using JWST and HST (Muratore+, 2026)
Exploring the ultra-faint dwarf Bootes I using JWST and HST:
Metallicity distribution and binaries.
Muratore F., Legnardi M.V., Milone A.P., Mastrobuono-Battisti A.,
Cordoni G., Gorza L.N., Lagioia E.P., Bortolan E., Dondoglio E.,
Marino A.F., Ziliotto T.
<Astron. Astrophys. 708, A100 (2026)>
=2026A&A...708A.100M 2026A&A...708A.100M (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Photometry ; Optical ; Infrared
Keywords: stars: abundances - binaries: close -
Hertzsprung-Russell and C-M diagrams - galaxies: abundances -
galaxies: dwarf
Abstract:
Ultra-faint dwarf galaxies (UFDs) are among the oldest and most
metal-poor stellar systems in the Universe. Their metallicity
distribution encodes the fossil record of the earliest star formation,
feedback, and chemical enrichment, providing crucial tests of models
of the first stars, galaxy assembly, and dark matter halos. However,
due to their faint luminosities and the limited number of bright
giants, spectroscopic studies of UFDs typically probe only small
stellar samples. Here, we present an analysis of multi-epoch Hubble
Space Telescope and James Webb Space Telescope observations of the UFD
Bootes I. Using deep color-magnitude diagram in the F606W and
F322W2 bands, extending from the subgiant branch to the M-dwarfs, and
stellar proper motions to identify likely members, we obtained an
unprecedentedly clean census of the system. The exquisite quality of
the diagram, combined with the sensitivity of M-dwarf colors to
metallicity, allowed us to constrain the metallicity distribution in a
large stellar sample. As a first step, we then exploited the
metallicity sensitivity of M-dwarf colors to derive the metallicity
distribution function. We find that most of the stars ∼85% have
[Fe/H]←2, and that roughly ∼17% have [Fe/H]←3. Then, we derived the
binary fraction in Bootes I. This is crucial, since binaries can bias
kinematic mass estimates, affect stellar population analyses, and
shape the photometric signatures used to infer metallicity. We find
that 20±2% of stellar systems in Bootes I are binaries with mass
ratios larger than 0.4, corresponding to a total binary fraction of
∼30%. This value is comparable to the binary fractions observed in
globular clusters of similar stellar mass, suggesting that the
presence of dark matter does not significantly affect the binary
properties of Bootes I.
Description:
Metallicity distribution and binaries in Bootes I dwarf galaxy.
Objects:
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RA (2000) DE Designation(s)
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14 00 00.00 +14 30 00.0 Bootes I = NAME Bootes Dwarf Galaxy
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table.dat 61 33908 Stellar positions and photometry
(32859 sources without photometry)
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Byte-by-byte Description of file: table.dat
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Bytes Format Units Label Explanations
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1- 10 F10.4 pix Xpos X position on CCD
12- 21 F10.4 pix Ypos Y position on CCD
23- 40 F18.15 mag F606W ?=0 Magnitude in F606W HST filter
42- 59 F18.15 mag F322W2 ?=0 Magnitude in F322W2 (3.247um) JWST filter
61 I1 --- Qual [0/1] Membership flag from proper motions
+ photometric quality flag
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Acknowledgements:
Fabrizio Muratore, Fabrizio.muratore(at)phd.unipd.it,
Fabrizio.muratore98(at)gmail.com
License: CC-BY-4.0 [see https://spdx.org/licenses/]
(End) Patricia Vannier [CDS] 11-Mar-2026