J/MNRAS/497/1236 Chemo-dynamics of outer halo dwarf stars (Monty+, 2020)
Chemo-dynamics of outer halo dwarf stars, including Gaia-Sausage and
Gaia-Sequoia candidates.
Monty S., Venn K.A., Lane J.M.M., Lokhorst D., Yong D.
<Mon. Not. R. Astron. Soc., 497, 1236-1255 (2020)>
=2020MNRAS.497.1236M 2020MNRAS.497.1236M (SIMBAD/NED BibCode)
ADC_Keywords: Stars, halo ; Milky Way ; Local group ; Abundances, peculiar ;
Parallaxes, trigonometric ; Proper motions ; Radial velocities ;
Space velocities ; Optical
Keywords: stars: stellar parameters - stars: abundances - Galaxy: halo -
Galaxy: stellar content - Galaxy: kinematics and dynamics -
Local Group - stellar abundances
Abstract:
The low-metallicity, kinematically interesting dwarf stars studied by
Stephens & Boesgaard (2002AJ....123.1647S 2002AJ....123.1647S, SB02) are re-examined using
Gaia DR2 astrometry, and updated model atmospheres and atomic line
data. New stellar parameters are determined based on the Gaia DR2
parallactic distances and Dartmouth Stellar Evolution Database
isochrones. These are in excellent agreement with spectroscopically
determined stellar parameters for stars with [Fe/H]>-2; however, large
disagreements are found for stars with [Fe/H]=←2, with offsets as
large as ΔTeff~+500K and Δlogg~+1.0. A subset of six
stars (test cases) are analysed ab initio using high-resolution
spectra with Keck HIRES and Gemini GRACES. This sub-sample is found to
include two α-challenged dwarf stars, suggestive of origins in a
low-mass, accreted dwarf galaxy. The orbital parameters for the entire
SB02 sample are re-determined using Gaia DR2 data. We find 11 stars
that are dynamically coincident with the Gaia-Sausage accretion event
and another 17 with the Gaia-Sequoia event in action space. Both
associations include low-mass, metal-poor stars with isochrone ages
older than 10Gyr. Two dynamical subsets are identified within
Gaia-Sequoia. When these subsets are examined separately, a common
knee in [α/Fe] is found for the Gaia-Sausage and low orbital
energy Gaia-Sequoia stars. A lower metallicity knee is tentatively
identified in the Gaia-Sequoia high orbital energy stars. If the
metal-poor dwarf stars in these samples are true members of the
Gaia-Sausage and Gaia-Sequoia events, then they present a unique
opportunity to probe the earlier star formation histories of these
systems.
Description:
Stephens & Boesgaard (2002AJ....123.1647S 2002AJ....123.1647S) selected their original
sample from the Carney et al. (1994AJ....107.2240C 1994AJ....107.2240C, Cat.
J/AJ/107/2240) catalogue of high proper motion stars. The Carney et
al. (1994AJ....107.2240C 1994AJ....107.2240C, Cat. J/AJ/107/2240) catalogue was compiled
over many years using photometry and radial velocities for almost 500
stars from the Lowell Proper Motion Catalog along with estimates of
stellar distances. Orbital parameters including apocentric radii
(Rapo) and maximum height from the disc (Zmax) were determined in
the catalogue using the two component MW model of Bahcall, Soneira &
Schmidt (1983ApJ...265..730B 1983ApJ...265..730B).
SB02 selected 56 dwarf stars that satisfy one of three orbital
criterion: Outer halo (Rapo>16kpc); High halo (Zmax>5kpc); Extreme
retrograde orbit (V←400km/s).
We re-examine these 56 stars given the new Gaia DR2 astrometry. In
particular, we calculate new stellar parameters by combining the Gaia
DR2 parallactic distances with isochrones from the x-z Dartmouth
Stellar Evolution Database (DSED; Dotter et al. 2008ApJS..178...89D 2008ApJS..178...89D).
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tablea5.dat 87 17 Sample of the updated abundances for the low
metallicity ([Fe/H]←2) stars in the SB02
sample, bins (iii) and (iv)
tablea6.dat 106 17 Sample of the updated abundances for the low
metallicity ([Fe/H]←2) stars in the SB02
sample, bins (iii) and (iv) continued
tableb1.dat 82 52 A sample of the basic astrometric parameters
from Gaia and radial velocities from this work
and SB02
tableb2.dat 85 52 A sample of the orbital properties for the SB02
stars
tableb3.dat 104 52 A sample of additional kinematic parameters
used to classify the stars as being dynamically
coincident with the Gaia-Sausage (Saug.) and
Gaia-Sequoia (Seq. G1 and Seq. G2) events
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
J/AJ/107/2240 : Proper motion stars survey. XII. (Carney+, 1994)
Byte-by-byte Description of file: tablea5.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- Name Star name
10- 12 A3 --- Bin Subsample (G1)
14- 18 F5.2 [-] [Na/Fe] ? Na/Fe abundance ratio (G2)
20- 23 F4.2 [-] e_[Na/Fe] ? Error on [Na/Fe] (G3)
25 I1 --- o_[Na/Fe] Number of lines used to determine [Na/Fe]
27- 30 F4.2 [-] [Mg/Fe] Mg/Fe abundance ratio (G2)
32- 35 F4.2 [-] e_[Mg/Fe] Error on [Mg/Fe] (G3)
37 I1 --- o_[Mg/Fe] Number of lines used to determine [Mg/Fe]
39- 42 F4.2 [-] [Si/Fe] ? Si/Fe abundance ratio (G2)
44- 47 F4.2 [-] e_[Si/Fe] ? Error on [Si/Fe] (G3)
49 I1 --- o_[Si/Fe] Number of lines used to determine [Si/Fe]
51- 54 F4.2 [-] [Ca/Fe] Ca/Fe abundance ratio (G2)
56- 59 F4.2 [-] e_[Ca/Fe] Error on [Ca/Fe] (G3)
61- 62 I2 --- o_[Ca/Fe] Number of lines used to determine [Ca/Fe]
64- 67 F4.2 [-] [TiI/Fe] TiI/Fe abundance ratio (G2)
69- 72 F4.2 [-] e_[TiI/Fe] Error on [TiI/Fe] (G3)
74- 75 I2 --- o_[TiI/Fe] Number of lines used to determine [TiI/Fe]
77- 80 F4.2 [-] [TiII/Fe] TiII/Fe abundance ratio (G2)
82- 85 F4.2 [-] e_[TiII/Fe] Error on [TiII/Fe] (G3)
87 I1 --- o_[TiII/Fe] Number of lines used to determine [TiII/Fe]
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Byte-by-byte Description of file: tablea6.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- Name Star name
10- 12 A3 --- Bin Subsample (G1)
14- 18 F5.2 [-] [CrI/Fe] CrI/Fe abundance ratio (G2)
20- 23 F4.2 [-] e_[CrI/Fe] Error on [CrI/Fe] (G3)
25- 26 I2 --- o_[CrI/Fe] Number of lines used to determine [CrI/Fe]
28- 31 F4.2 [-] [CrII/Fe] ? CrII/Fe abundance ratio (G2)
33- 36 F4.2 [-] e_[CrII/Fe] ? Error on [CrII/Fe] (G3)
38 I1 --- o_[CrII/Fe] Number of lines used to determine [CrII/Fe]
40- 44 F5.2 [-] [FeI/H] FeI/H abundance ratio (G2)
46- 49 F4.2 [-] e_[FeI/H] Error on [FeI/H] (G3)
51- 52 I2 --- o_[FeI/H] Number of lines used to determine [FeI/H]
54- 58 F5.2 [-] [FeII/H] FeII/H abundance ratio (G2)
60- 63 F4.2 [-] e_[FeII/H] Error on [FeII/H] (G3)
65- 66 I2 --- o_[FeII/H] Number of lines used to determine [FeII/H]
68- 72 F5.2 [-] [NiI/Fe] NiI/Fe abundance ratio (G2)
74- 77 F4.2 [-] e_[NiI/Fe] Error on [NiI/Fe] (G3)
79- 80 I2 --- o_[NiI/Fe] Number of lines used to determine [NiI/Fe]
82- 86 F5.2 [-] [YII/Fe] ? YII/Fe abundance ratio (G2)
88- 91 F4.2 [-] e_[YII/Fe] ? Error on [YII/Fe] (G3)
93 I1 --- o_[YII/Fe] Number of lines used to determine [YII/Fe]
95- 99 F5.2 [-] [BaII/Fe] ? BaII/Fe abundance ratio (G2)
101- 104 F4.2 [-] e_[BaII/Fe] ? Error on [BaII/Fe] (G3)
106 I1 --- o_[BaII/Fe] Number of lines used to determine [BaII/Fe]
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Byte-by-byte Description of file: tableb1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- Name Star name
10- 15 F6.2 deg RAdeg Right ascension (ICRS) at Ep=2015.5
17- 20 F4.2 deg e_RAdeg Error on RAdeg
22- 27 F6.2 deg DEdeg Declination (ICRS) at Ep=2015.5
29- 32 F4.2 deg e_DEdeg Error on DEdeg
34- 39 F6.2 mas plx Parallax
41- 44 F4.2 mas e_plx Error on plx
46- 52 F7.2 mas/yr pmRA Proper motion in right ascension
54- 57 F4.2 mas/yr e_pmRA Error on pmRA
59- 66 F8.2 mas/yr pmDE Proper motion in declination
68- 71 F4.2 mas/yr e_pmDE Error on pmDE
73- 78 F6.1 km/s RV Radial velocity
80- 82 F3.1 km/s e_RV Error on RV
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Byte-by-byte Description of file: tableb2.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- Name Star name
10- 13 F4.2 kpc Rperi Pericentric radius
15- 19 F5.3 kpc e_Rperi Error on Rperi
21- 26 F6.3 kpc Rapo Apocentric radius
28- 31 F4.2 kpc e_Rapo Error on Rapo
33- 38 F6.1 Myr Trad Radiation temperature
40- 45 F6.2 Myr e_Trad Error on Trad
47- 53 F7.2 km/s U U component of space velocity
55- 58 F4.2 km/s e_U Error on U
60- 66 F7.2 km/s V V component of space velocity
68- 72 F5.2 km/s e_V Error on V
74- 80 F7.2 km/s W W component of space velocity
82- 85 F4.2 km/s e_W Error on W
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Byte-by-byte Description of file: tableb3.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- Name Star name
10- 14 A5 --- Subgroup Subgroup (1)
16- 23 F8.2 kpc.km/s Jphi Orbital azimuthal action
25- 30 F6.2 kpc.km/s e_Jphi Error on Jphi
32- 38 F7.2 kpc.km/s Jr Radial action
40- 46 F7.3 kpc.km/s e_Jr Error on Jr
48- 54 F7.2 kpc.km/s Jz Vertical action
56- 60 F5.2 kpc.km/s e_Jz Error on Jz
62- 67 F6.4 --- e Eccentricity
69- 74 F6.4 --- e_e Error on e
76- 81 F6.3 kpc Zmax Maximum height from the disc
83- 87 F5.3 kpc e_Zmax Error on Zmax
89- 97 F9.1 km2/s2 E Orbital energy
99- 104 F6.1 km2/s2 e_E Error on E
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Note (1): Subgroup as follows:
None = No association to a merger event (24/52)
Saug = Star belonging to the Gaia-Sausage event (11/52)
SeqG1 = Star belonging to the Gaia-Sequoia event and to the G1 subgroup (see
Section 4.2.1) (8/52)
SeqG2 = Star belonging to the Gaia-Sequoia event and to the G2 subgroup (see
Section 4.2.1) (9/52)
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Global Notes:
Note (G1): We split the SB02 sample into smaller sub-samples using the same
metallicity bins used in Stephens & Boesgaard (2002AJ....123.1647S 2002AJ....123.1647S).
Those bins are as follows:
i = [Fe/H]>-1.0, [α/Fe]=0
ii = -2.0<[Fe/H]=←1.0, [α/Fe]=0.2
iii = -3.0<[Fe/H]=←2.0, [α/Fe]=0.4
iv = [Fe/H]=←3.0, [α/Fe]=0.4
Note (G2): Abundances were calculated from combining the original SB02 stellar
parameters with the updated line list and atomic data used in this
study
Note (G3): Uncertainties in abundances were calculated from the line-to-line
abundance dispersion (σEW) alone
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History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 25-Jul-2023