J/MNRAS/516/2348 Spectroscopy of metal-poor stars in Bootes I (Longeard+, 2022)
The Pristine dwarf galaxy survey - IV. Probing the outskirts of the dwarf
galaxy Bootes I.
Longeard N., Jablonka P., Arentsen A., Thomas G.F., Aguado D.S.,
Carlberg R.G., Lucchesi R., Malhan K., Martin N., Mcconnachie A.W.,
Navarro J.F., Sanchez-Janssen R., Sestito F., Starkenburg E., Yuan Z.
<Mon. Not. R. Astron. Soc. 516, 2348-2362 (2022)>
=2022MNRAS.516.2348L 2022MNRAS.516.2348L (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Galaxies, dwarf ; Stars, metal-deficient ;
Populations, stellar ; Spectroscopy ; Spectrophotometry ;
Optical ; Positional data ; Line Profiles ; Photometry ;
Proper motions ; Abundances, [Fe/H]
Keywords: galaxies: dwarf - galaxies: individual: Bootes I - Local Group
Abstract:
We present a new spectroscopic study of the dwarf galaxy Bootes I
(Boo I) with data from the Anglo-Australian Telescope and its AAOmega
spectrograph together with the Two Degree Field multi-object system.
We observed 36 high-probability Boo I stars selected using Gaia Early
Data Release 3 proper motions and photometric metallicities from the
Pristine survey. Out of those, 27 are found to be Boo I stars,
resulting in an excellent success rate of 75 per cent at finding new
members. Our analysis uses a new pipeline developed to estimate radial
velocities and equivalent widths of the calcium triplet lines from
Gaussian and Voigt line profile fits. The metallicities of 16 members
are derived, including 3 extremely metal-poor stars ([Fe/H] < -3.0),
which translates into a success rate of 25 per cent at finding them
with the combination of Pristine and Gaia. Using the large spatial
extent of our new members that spans up to 4.1 half-light radii and
spectroscopy from the literature, we find a systemic velocity gradient
of 0.40 ± 0.10 km.s-1.arcmin-1 and a small but resolved
metallicity gradient of -0.008 ± 0.003 dex.arcmin-1. Finally, we
show that Boo I is more elongated than previously thought with an
ellipticity of ε = 0.68 ± 0.15. Its velocity and metallicity
gradients as well as its elongation suggest that Boo I may have been
affected by tides, a result supported by direct dynamical modelling.
Description:
We present here a new set of spectroscopic observations of the faint
UFD Bootes I (Boo I). This exceptionally large FoV combined with the
Gaia Data Release 3 and the Pristine survey enables us to probe the
outskirts of Boo I. Metallicity measurements for the stars beyond 1rh
only represent about 17 per cent of all Boo I members with a known
[Fe/H]. Therefore, Boo I is a good target for such a study. Our target
selection relies on data from the Pristine survey which is a
photometric survey based on a narrow-band, metallicity-sensitive
photometry centred on the calcium H&K doublet and has proven to be
efficient at identifying metal-poor stars such as those characteristic
of the UFDs stellar population. We constrained our stars selection
with SDSS (g-i,i), photometric metallicity above -1.0 dex and PM gaia
DR3 within 2σ from Boo I PM.
Finally, no stars previously observed in the literature at the time
were targeted by these observations. In total, the final target list
was composed of 92 stars including 36 probable Boo I red giant branch
(RGB) members, 18 potential horizontal branch (HB) stars, and 12
potentially very metal-poor halo stars. Data were observed with AAT
and its AAOmega spectrograph for low resolution optical spectra
(3700-5500 Å and R ∼ 1300) and for calcium triplet spectra with
high resolution R ∼ 11000 located in red part around 8400-8800 Å.
Spectral and Ca H&K reductions are done with AAT 2DFDR package.
This pipeline allows to proceed to EWs and RVs estimations for CaT
with fitting line profiles method and a bayesian approach. We use
empirical calibration for spectroscopy to estimate [Fe/H] according to
EWs from gaussian and voigt profiles. Also, pristine photometry
centred on Ca H&K doublet and SDSS photometry allows us to retreive
[Fe/H] values. More, we computed membership probabilities from
dynamical parameters (RV and proper motions) and CMD. These results
are available for 81 stars in table1.dat and also 21 stars identified
as members by previous studies have too low PM or dynamical
probability membership to be considered members of the satellite,
their properties are in table2.dat.
Objects:
----------------------------------------------------------------------------
RA (2000) DE Designation(s)
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14 00 00.00 +14 30 00.0 NAME Bootes Dwarf Spheroidal Galaxy = NAME Boo dS
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File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 118 81 Properties and estimated metallicities of the
new AAT spectroscopic Boo I sample
table2.dat 61 21 Previous literature members that are found not
to be Boo I members after reanalysis
--------------------------------------------------------------------------------
See also:
J/MNRAS/380/281 : Faint galactic satellites spectroscopic survey
(Martin+, 2007)
J/MNRAS/490/2241 : Spectroscopy of Pristine EMP star candidates (Aguado+, 2019)
J/MNRAS/472/2963 : Metallicities of Pristine stars (Youakim+, 2017)
J/MNRAS/490/3508 : The Southern Stellar Stream Sp. Survey (S5) (Li+, 2019)
J/MNRAS/383/183 : CaII triplet of RGB from VLT/FLAMES obs. (Battaglia+, 2008)
J/MNRAS/491/356 : Sagittarius II study with the Pristine survey
(Longeard+, 2020)
J/MNRAS/458/L59 : Draco II stars gi magnitude & radial velocities
(Martin+, 2016)
J/MNRAS/466/2006 : Phoenix dwarf galaxy RV and [Fe/H] catalog (Kacharov+, 2017)
J/MNRAS/434/1681 : Extremely metal-poor stars CaII triplet (Carrera+, 2013)
J/A+A/623/A129 : New satellites of the LMC search (Fritz+, 2019)
J/A+A/562/A146 : Chemical abundances of 8 metal-poor stars (Ishigaki+, 2014)
J/A+A/657/A54 : Local Group Gaia eDR3 systemic motions (Battaglia+, 2022)
J/A+A/608/A89 : Very metal poor stars in MW halo (Mashonkina+, 2017)
J/A+A/544/A73 : BVI photometry of Fornax dSph galaxy (de Boer+, 2012)
J/ApJ/770/16 : Spectroscopic members of Segue 2 galaxy (Kirby+, 2013)
J/ApJ/920/92 : VLT Spectroscopy of Ultra-faint Dwarf Galaxies
(Jenkins+, 2021)
J/ApJ/723/1632 : Abundance spreads in Bootes I and Segue 1 (Norris+, 2010)
J/ApJ/826/110 : Boo-127 and Boo-980 high-resolution spectra (Frebel+, 2016)
J/ApJ/763/61 : Abundances of 7 red giant members of BootesI (Gilmore+,2013)
J/ApJ/711/350 : Metal-poor giant Boo-1137 abundances (Norris+, 2010)
J/ApJ/736/146 : Radial velocities of stars in Bootes I (Koposov+, 2011)
J/AJ/144/4 : Properties of dwarf galaxies in the Local Group
(McConnachie+, 2012)
II/349 : The Pan-STARRS release 1 (PS1) Survey - DR1 (Chambers+,2016)
I/350 : Gaia EDR3 (Gaia Collaboration, 2020)
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 F9.5 deg RAdeg Right ascension (J2000) (RA)
11- 18 F8.5 deg DEdeg Declination (J2000) (Dec)
20- 23 F4.1 mag g0mag Extinction corrected SDSS g magnitude (g0)
25- 27 F3.1 mag e_g0mag Uncertainty of g0mag (errg0)
29- 32 F4.1 mag i0mag Extinction corrected SDSS i magnitude (i0)
34- 36 F3.1 mag e_i0mag Uncertainty of i0mag (erri0)
38- 41 F4.1 mag CaHK0mag Extinction corrected of calcium H&K lines
magnitude centered around ∼3933 Å and
∼3968 Å from AAT pristine obs. (CaHK0)
43- 45 F3.1 mag e_CaHK0mag Uncertainty of CaHK0mag (errCaHK0)
47- 52 F6.1 km/s RV Radial velocity computed from observed
spectrum (vr)
54- 57 F4.1 km/s e_RV Uncertainty of RV (errvr)
59- 64 F6.2 mas/yr pmRA ? Proper motion in right ascension direction
from observed spectrum and GaiaDR3
(µ*α)
66- 69 F4.2 mas/yr e_pmRA ? Uncertainty of pmRA (errµ*α)
71- 76 F6.2 mas/yr pmDE ? Proper motion in declination direction
from observed spectrum and GaiaDR3
(µδ)
78- 81 F4.2 mas/yr e_pmDE ? Uncertainty of pmDE (errµδ)
83- 86 F4.1 --- S/N Signal to noise ratio from observations (S/N)
88- 91 F4.1 [Sun] [Fe/H]G ? Iron to hydrogen abundance ratio from EWs
translation ([Fe/H]G,spectro) (1)
93- 95 F3.1 [Sun] e_[Fe/H]G ? Uncertainty of [Fe/H]G
(err[Fe/H]G,spectro)
97-100 F4.1 [Sun] [Fe/H]V ? Iron to hydrogen abundance ratio from EWs
translation ([Fe/H]V,spectro) (2)
102-104 F3.1 [Sun] e_[Fe/H]V ? Uncertainty of [Fe/H]V
(err[Fe/H]V,spectro)
106-110 F5.2 [Sun] [Fe/H]P ? Iron to hydrogen abundance ratio with
pristine photometry ([Fe/H]Pristine) (3)
112-115 F4.2 [Sun] e_[Fe/H]P ? Uncertainty of [Fe/H]P
(err[Fe/H]Pristine)
117-118 A2 --- Member Flag of Boo I membership according to CMD and
dynamical probabilities (Member) (4)
--------------------------------------------------------------------------------
Note (1): Obtained by Ca triplet lines fitted with gaussian line profiles around
850nm reported with S/N => 10.
Note (2): Obtained by Ca triplet lines fitted with Voigt line profiles around
850nm reported with S/N => 10.
Note (3): From metallicity-sensitive photometry centered on Ca H&K lines and
SDSS colours comparisons.
Note (4): There is 26 spectroscopically confirmed and 1 probable Boo I members
in our sample.
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Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 F9.5 deg RAdeg Right ascension (J2000) (RA)
11- 18 F8.5 deg DEdeg Declination (J2000) (Dec)
20- 24 F5.1 km/s RV Radial velocity computed from observed
spectrum (vr)
26- 29 F4.1 km/s e_RV Uncertainty of RV (errvr)
31- 36 F6.2 mas/yr pmRA ? Proper motion in right ascension direction
from observed spectrum and GaiaDR3
(µ*α)
38- 41 F4.2 mas/yr e_pmRA ? Uncertainty of pmRA (errµ*α)
43- 47 F5.2 mas/yr pmDE ? Proper motion in declination direction
from observed spectrum and GaiaDR3
(µδ)
49- 52 F4.2 mas/yr e_pmDE ? Uncertainty of pmDE (errµδ)
54- 57 F4.1 [Sun] [Fe/H] ? Iron to hydrogen abundance ratio from
spectroscopy observations ([Fe/H]spectro)
59- 61 F3.1 [Sun] e_[Fe/H] ? Uncertainty of [Fe/H] (err[Fe/H]spectro)
--------------------------------------------------------------------------------
History:
From electronic version of the journal
References:
Longeard et al., Paper I 2018MNRAS.480.2609L 2018MNRAS.480.2609L
Longeard et al., Paper II 2020MNRAS.491..356L 2020MNRAS.491..356L, Cat. J/MNRAS/491/356
Longeard et al., Paper III 2021MNRAS.503.2754L 2021MNRAS.503.2754L
Longeard et al., Paper V 2023MNRAS.525.3086L 2023MNRAS.525.3086L
Longeard et al., Paper VI 2025A&A...698A..63L 2025A&A...698A..63L
(End) Luc Trabelsi [CDS] 24-Jul-2025