J/AJ/156/179 Highly r-process-enhanced field stars kinematics (Roederer+, 2018)
Kinematics of highly r-process-enhanced field stars: evidence for an accretion
origin and detection of several groups from disrupted satellites.
Roederer I.U., Hattori K., Valluri M.
<Astron. J., 156, 179-179 (2018)>
=2018AJ....156..179R 2018AJ....156..179R (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Stars, metal-deficient ; Abundances ;
Parallaxes, trigonometric ; Proper motions ; Stars, distances ;
Radial velocities ; Stars, diameters
Keywords: galaxies: dwarf - Galaxy: halo - stars: abundances -
stars: kinematics and dynamics - stars: Population II
Abstract:
We present the kinematics of 35 highly r-process-enhanced ([Eu/Fe]≥+0.7)
metal-poor (-3.8<[Fe/H]< -1.4) field stars. We calculate six-dimensional
positions and velocities, evaluate energies and integrals of motion,
and compute orbits for each of these stars using parallaxes and proper
motions from the second Gaia data release (Cat. I/345) and published radial
velocities. All of these stars have halo kinematics. Most stars (66%)
remain in the inner regions of the halo (<13 kpc), and many (51%) have
orbits that pass within 2.6 kpc of the Galactic center. Several stars (20%)
have orbits that extend beyond 20 kpc, including one with an orbital
apocenter larger than the Milky Way virial radius. We apply three
clustering methods to search for structure in phase space, and we identify
eight groups. No abundances are considered in the clustering process,
but the [Fe/H] dispersions of the groups are smaller than would be expected
by random chance. The orbital properties, clustering in phase space and
metallicity, and the lack of highly r-process-enhanced stars on disk-like
orbits, indicate that such stars likely were accreted from disrupted
satellites. Comparison with the galaxy luminosity-metallicity relation
suggests MV≳-9 for most of the progenitor satellites, characteristic
of ultra-faint or low-luminosity classical dwarf spheroidal galaxies.
Environments with low rates of star formation and Fe production, rather
than the nature of the r-process site, may be key to obtaining the [Eu/Fe]
ratios found in highly r-process-enhanced stars.
Description:
Many highly r-process-enhanced stars have been identified and analyzed
individually over the last 25 years. Our sample includes stars from
the literature that show at least moderately high levels of r-process
enhancement relative to Fe, [Eu/Fe]≥+0.7; i.e., enhanced by a factor
of 5 relative to the solar ratio. Europium (Eu, Z=63) is commonly used
as a proxy for the overall level of r-process enhancement in a star.
A large fraction (∼94%-98%; Sneden et al. 2008ARA&A..46..241S 2008ARA&A..46..241S;
Bisterzo et al. 2011, J/MNRAS/418/284) of the Eu in the solar system
originated via the r-process, despite the fact that both the r-process
and the s-process (slow neutron-capture process) contributed roughly equal
amounts to the total mass of elements heavier than the Fe group in the
solar system. We also require that the heavy-element abundance pattern
in each star has been scrutinized in sufficient detail to determine that
the r-process was the dominant source of the heavy elements (e.g.,
Sneden et al. 1996ApJ...467..819S 1996ApJ...467..819S). We only include field stars in our
sample, so r-process-enhanced stars in dwarf galaxies and globular
clusters are not considered.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 87 83 List of known highly r-process-enhanced field
stars, sorted by decreasing [Eu/Fe] ratios
table2.dat 207 35 Parallaxes, proper motions, distances,
and radial velocities
table3.dat 92 35 Calculated velocities in a cylindrical
coordinate system
table4.dat 103 35 Calculated orbital energies and angular momenta
table5.dat 97 35 Calculated orbital parameters
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
I/347 : Distances to 1.33 billion stars in Gaia DR2 (Bailer-Jones+, 2018)
J/AJ/119/2866 : Proper motions of metal-poor stars (Beers+, 2000)
J/ApJ/681/1524 : Detailed abundances for 28 metal-poor stars (Lai+, 2008)
J/AJ/137/272 : Space velocities orbits in the Milky Way halo
(Roederer+ 2009)
J/MNRAS/418/284 : s-process in low-metallicity stars. II. (Bisterzo+, 2011)
J/ApJ/794/58 : Metal-poor stars in the thick disk of the Galaxy
(Beers+, 2014)
J/A+A/586/A49 : r- and s- process elements in Milky Way disk
(Battistini+, 2016)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 25 A25 --- Star Star name
27- 31 F5.2 [-] [Fe/H] [-3.71/-1.47] Metallicity
33- 36 F4.2 [-] [Eu/Fe] [0.7/1.92] Europium-to-iron ratio
38- 42 F5.2 [-] [Eu/H] [-2.71/-0.14] Europium-to-hydrogen ratio
44- 67 A24 --- Ref Reference
69- 87 A19 --- Bibcode Bibcode of the reference
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 24 A24 --- Star Star name
26- 44 I19 --- Gaia Gaia DR2 (Cat. I/345) source identifier
46- 51 F6.4 mas Plx [0.1779/6.7911] Gaia DR2 parallax
53- 58 F6.4 mas e_Plx [0.0141/0.0587] 1σ uncertainty in Plx
60- 67 F8.3 mas/yr pmRA [-228.893/211.493] Gaia DR2 proper motion
along RA (pmRA*cosDE)
69- 73 F5.3 mas/yr e_pmRA [0.026/0.095] Uncertainty in pmRA
75- 82 F8.3 mas/yr pmDE [-212.06/9.317] Gaia DR2 proper motion along
DE
84- 88 F5.3 mas/yr e_pmDE [0.022/0.067] 1σ uncertainty in pmDE
90- 94 F5.3 kpc Dist [0.147/4.595] Distance adopted from
Bailer-Jones et al. (2018, Cat. I/347) and
based on Gaia DR2 parallax
96-100 F5.3 kpc Dist16 [0.001/0.381] 16th percentile distance
confidence interval
102-106 F5.3 kpc Dist84 [0.001/0.453] 84th percentile distance
confidence interval
108-113 F6.1 km/s HRV [-377.1/372.8] Heliocentric radial velocity
115-117 F3.1 km/s e_HRV [0.1/3] 1σ uncertainty in HRV
119-165 A47 --- r_HRV Reference(s) for HRV
166 A1 --- nrHRV [a] Note on HRV reference (1)
168-207 A40 --- Bibcode Bibcode of the reference(s)
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Note (1): Note as follows:
a = The median RV from this source is adopted as the systemic RV.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 24 A24 --- Star Star name
26- 31 F6.1 km/s VR [-274.9/246.9] Calculated median velocity in
a cylindrical coordinate system VR (1)
33- 36 F4.1 km/s VR16 [0.4/67.4] 16th percentile VR confidence
interval
38- 42 F5.1 km/s VR84 [0.4/125] 84th percentile VR confidence
interval
44- 49 F6.1 km/s VPhi [-262.2/336.1] Calculated median velocity in
a cylindrical coordinate system VΦ (2)
51- 54 F4.1 km/s VPhi16 [0.5/87] 16th percentile VΦ confidence
interval
56- 59 F4.1 km/s VPhi84 [0.4/55.3] 84th percentile VΦ confidence
interval
61- 66 F6.1 km/s Vz [-230.3/271.5] Calculated median velocity in
a cylindrical coordinate system Vz (3)
68- 71 F4.1 km/s Vz16 [0.3/28.8] 16th percentile Vz confidence
interval
73- 76 F4.1 km/s Vz84 [0.3/45.4] 84th percentile Vz confidence
interval
78- 82 F5.1 km/s Vperp [18.1/338.3] Tangential velocity V⊥ (4)
84- 87 F4.1 km/s Vperp16 [0.2/35.7] 16th percentile V⊥ confidence
interval
89- 92 F4.1 km/s Vperp84 [0.2/85.4] 84th percentile V⊥ confidence
interval
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Note (1): There are roughly equal numbers of stars moving toward (VR<0) and
away from the Galactic center (VR>0).
Note (2): There are roughly equal numbers of stars on prograde (VΦ>0) and
retrograde (VΦ<0) orbits.
Note (3): There are roughly equal numbers of stars moving north (Vz>0) and
south (Vz<0) as they pass through the Galactic disk.
Note (4): Defined as (VR2+Vz2)1/2.
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Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 24 A24 --- Star Star name
26- 31 F6.1 10+3km2/s2 E [-132/-13.4] Orbital energy
33- 36 F4.1 10+3km2/s2 E16 [0.1/17.4] 16th percentile E confidence
interval
38- 41 F4.1 10+3km2/s2 E84 [0.1/37] 84th percentile E confidence interval
43- 49 F7.1 kpc.km/s Jr [21.3/24200] Calculated median radial action
Jr
51- 56 F6.1 kpc.km/s Jr16 [1.7/7770] 16th percentile Jr confidence
interval
58- 64 F7.1 kpc.km/s Jr84 [2/31300] 84th percentile Jr confidence
interval
66- 72 F7.1 kpc.km/s JPhi [-2360/2670] Calculated median azimuthal action
JΦ
74- 78 F5.1 kpc.km/s JPhi16 [3.5/745] 16th percentile JΦ confidence
interval
80- 84 F5.1 kpc.km/s JPhi84 [3.2/605] 84th percentile JΦ confidence
interval
86- 91 F6.1 kpc.km/s Jz [6.1/1080] Calculated median vertical action
Jz
93- 97 F5.1 kpc.km/s Jz16 [0.1/164] 16th percentile Jz confidence
interval
99-103 F5.1 kpc.km/s Jz84 [0.1/407] 84th percentile Jz confidence
interval
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Byte-by-byte Description of file: table5.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 24 A24 --- Star Star name
26- 29 F4.2 kpc rperi [0.13/8.67] Calculated median pericentric radius
rperi
31- 34 F4.2 kpc rperi16 [0.01/1.41] 16th percentile rperi confidence
interval
36- 39 F4.2 kpc rperi84 [0.02/1.31] 84th percentile rperi confidence
interval
41- 46 F6.2 kpc rapo [6.05/434] Calculated median apocentric radius
rapo
48- 53 F6.2 kpc rapo16 [0/138] 16th percentile rapo confidence interval
55- 60 F6.2 kpc rapo84 [0/140] 84th percentile rapo confidence interval
62- 67 F6.2 kpc Zmax [0.69/151] Calculated median maximum distance
above or below the Galactic plane Zmax
69- 73 F5.2 kpc Zmax16 [0.01/53] 16th percentile Zmax confidence
interval
75- 79 F5.2 kpc Zmax84 [0.01/60.9] 84th percentile Zmax confidence
interval
81- 85 F5.3 --- e [0.173/0.975] Eccentricity
87- 91 F5.3 --- e16 [0.003/0.168] 16th percentile e confidence
interval
93- 97 F5.3 --- e84 [0.002/0.213] 84th percentile e confidence
interval
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History:
From electronic version of the journal
(End) Tiphaine Pouvreau [CDS] 21-Mar-2019