J/ApJ/946/48 r-II stars in the solar neighborhood with Gaia DR3 (Hattori+, 2023)
Finding r-II sibling stars in the Milky Way with the greedy optimistic
clustering algorithm.
Hattori K., Okuno A., Roederer I.U.
<Astrophys. J., 946, 48 (2023)>
=2023ApJ...946...48H 2023ApJ...946...48H
ADC_Keywords: Abundances; Space velocities; Stars, halo; Milky Way;
Associations, stellar; Optical
Keywords: Milky Way dynamics ; Galactic archaeology ; Milky Way stellar halo ;
Astroinformatics ; R-process ; Clustering ; Stellar dynamics
Abstract:
R-process enhanced stars with [Eu/Fe]≥+0.7 (so-called r-II stars) are
believed to have formed in an extremely neutron-rich environment in
which a rare astrophysical event (e.g., a neutron-star merger)
occurred. This scenario is supported by the existence of an
ultra-faint dwarf galaxy, Reticulum II, where most of the stars are
highly enhanced in r-process elements. In this scenario, some small
fraction of dwarf galaxies around the Milky Way were r enhanced. When
each r-enhanced dwarf galaxy accreted to the Milky Way, it deposited
many r-II stars in the Galactic halo with similar orbital actions. To
search for the remnants of the r-enhanced systems, we analyzed the
distribution of the orbital actions of N=161 r-II stars in the solar
neighborhood by using Gaia EDR3 data. Since the observational
uncertainty is not negligible, we applied a newly developed greedy
optimistic clustering method to the orbital actions of our sample
stars. We found six clusters of r-II stars that have similar orbits
and chemistry, one of which is a new discovery. Given the apparent
phase-mixed orbits of the member stars, we interpret that these
clusters are good candidates for remnants of completely disrupted
r-enhanced dwarf galaxies that merged with the ancient Milky Way.
Description:
We extend the sample in Roederer+ 2018, J/AJ/156/179 and construct a
catalog of r-II stars for which reliable measurements of chemical
abundances and the line-of-sight velocity vlos are available from
high-resolution spectra. In constructing the catalog, we select N=161
stars from the literature (published before the end of 2020) that
satisfy the criteria given in Section 2.
We combine the literature data on ([Fe/H], [Eu/Fe], [Eu/H], vlos) and
the astrometric data from Gaia EDR3 (Gaia Col. 2021, I/350) to
construct the catalog analyzed in this paper.
We note that our catalog based on Gaia EDR3 supersedes the catalog in
Roederer+ (2018), which is based on Gaia DR2.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 129 30 Properties of the clusters
table2.dat 99 161 Basic properties of the member stars of the clusters
table3.dat 98 161 Kinematics of the member stars of the clusters
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
I/350 : Gaia EDR3 (Gaia Collaboration, 2020)
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
J/ApJ/530/783 : The r-process enriched giant HD 115444 (Westin+, 2000)
J/A+A/416/1117 : Abundances in the early Galaxy (Cayrel+, 2004)
J/A+A/439/129 : HERES II. Spectroscopic analysis (Barklem+, 2005)
J/ApJ/645/613 : Abundances of HD 221170 (Ivans+, 2006)
J/ApJ/681/1524 : Detailed abundances for 28 metal-poor stars (Lai+, 2008)
J/A+A/516/A46 : HE 2327-5642 abundance analysis (Mashonkina+, 2010)
J/ApJ/742/54 : CASH project II. Extremely metal-poor stars (Hollek+, 2011)
J/A+A/548/A34 : Abund. of carbon-enhanced metal-poor stars (Allen+, 2012)
J/ApJ/753/64 : Abundances for 97 metal-poor stars (Ishigaki+, 2012)
J/ApJ/778/56 : Hamburg/ESO Survey extremely metal-poor stars (Cohen+, 2013)
J/ApJ/771/67 : Abundances for 97 metal-poor stars. II. (Ishigaki+, 2013)
J/ApJ/775/L27 : Abundances in a metal-poor RGB star (Johnson+, 2013)
J/ApJ/779/102 : Metallicities of RGB stars in dwarf galaxies (Kirby+, 2013)
J/ApJ/767/134 : Abund. of red giant stars in UFD galaxies (Vargas+, 2013)
J/A+A/569/A43 : HE 2252-4225 abundance analysis (Mashonkina+, 2014)
J/AJ/147/136 : Stars of very low metal abundance. VI. (Roederer+, 2014)
J/ApJ/807/171 : SkyMapper Survey metal-poor star sp. (Jacobson+, 2015)
J/MNRAS/450/815 : Red giants in NGC 5286 (Marino+, 2015)
J/ApJ/808/103 : Kapteyn moving group star abundances (Navarrete+, 2015)
J/MNRAS/449/3889 : Abundances of 15 stars in NGC 4833 (Roederer+, 2015)
J/ApJ/808/108 : M2FS stellar spectroscopy of Reticulum 2 (Walker+, 2015)
J/MNRAS/460/884 : EMBLA survey. Galactic bulge metal-poor stars (Howes+, 2016)
J/ApJ/823/157 : LOS velocities & [Fe/H] of Pal 5 (Ishigaki+, 2016)
J/AJ/151/82 : The 4 brightest red giants in Ret 2 (Roederer+, 2016)
J/A+A/607/A91 : CS 29497-004 abundances (Hill+, 2017)
J/ApJ/844/18 : RAVE J203843.2-002333 high-res. spectroscopy (Placco+, 2017)
J/ApJ/864/43 : Abund. of 3 bright extremely metal-poor giants (Cain+, 2018)
J/ApJ/858/92 : RPA Southern Pilot Search of 107 Stars (Hansen+, 2018)
J/AJ/156/179 : r-process-enhanced field stars kinematics (Roederer+, 2018)
J/ApJ/865/129 : Abundance analysis of HD 222925 (Roederer+, 2018)
J/ApJ/868/110 : R-Process Alliance: 1st release in Gal. halo (Sakari+, 2018)
J/MNRAS/485/4726 : An all-sky view of the Orphan Stream (Koposov+, 2019)
J/ApJ/874/74 : Local stellar halo member stars from Gaia/LAMOST (Li+, 2019)
J/ApJ/874/148 : Metal-poor star RAVE J093730.5-062655 abund. (Sakari+, 2019)
J/A+A/627/A173 : Abundances for 4 metal-poor stars (Valentini+, 2019)
J/ApJ/898/40 : 2MASSJ15213995-3538094 abundances from sp. (Cain+, 2020)
J/ApJ/898/150 : High-res. MIKE obs. of metal-poor stars (Ezzeddine+, 2020)
J/A+A/635/A104 : Chemical abundance analysis of HD 20 (Hanke+, 2020)
J/A+A/643/A49 : Linelist (Hansen+, 2020)
J/ApJS/249/30 : R-Process Alliance: metal-poor star sp. (Holmbeck+, 2020)
J/AJ/160/181 : Chemical abundances in red giants with Magellan (Ji+, 2020)
J/ApJ/903/88 : Ions individual abund. in LAMOST J1109+0754 (Mardini+, 2020)
J/ApJ/905/20 : Metal-poor stars observed with SALT/HRS (Rasmussen+, 2020)
J/ApJ/891/39 : LAMOST DR3 very metal-poor stars of Gal. halo (Yuan+, 2020)
J/ApJ/908/79 : The r-process Alliance; abund. in 519 stars (Gudin+, 2021)
J/ApJ/915/103 : Oscillator strength for Indus_0 & Indus_13 (Hansen+, 2021)
J/ApJ/914/123 : Gaia DR2 and EDR3 stars with sp. follow-up (Ibata+, 2021)
J/MNRAS/505/5978 : Gaia EDR3 view on Gal. globular clusters (Vasiliev+, 2021)
J/ApJ/931/147 : Very metal-poor stars with LAMOST & Subaru. II. (Li+, 2022)
J/A+A/665/A57 : The stellar halo near the Sun. I. (Lovdal+, 2022)
J/ApJS/260/27 : R-Process Alliance: UV sp. of HD 222925 (Roederer+, 2022)
J/ApJ/926/26 : Groups of metal-poor stars. I. (Shank+, 2022)
J/ApJ/927/13 : Metal-poor stars observed with SALT/HRS. II. (Zepeda+, 2022)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- --- [H22:DTC-]
9- 10 I2 --- DTC [1/30] Cluster identification (H22:DTC-)
running sequence number (k) (1)
12- 13 I2 --- Nm [1/18] Number of members in cluster
15- 18 I4 kpc.km/s Jr [67/8014] Radial orbital action of
cluster center
20- 23 I4 kpc.km/s Jz [52/3390] Vertical orbital action of
cluster center
25- 29 I5 kpc.km/s Jphi [-3751/1757] Azimuthal orbital action of
cluster center
31- 33 I3 kpc.km/s sigJr [8/153]? Dispersion of Jr in cluster
35- 37 I3 kpc.km/s sigJz [4/193]? Dispersion of Jz in cluster
39- 41 I3 kpc.km/s sigJphi [0/233]? Dispersion of Jphi in cluster
43- 45 I3 kpc.km/s sigk [24/150]? Average of Jr, Jz, & Jphi
dispersions
47- 51 F5.2 [Sun] [Fe/H]Avg [-3.71/-1.39] Average log Fe/H number
abundance
53- 56 F4.2 [Sun] sig[Fe/H] [0.05/0.83]? Dispersion of log Fe/H
number abundance
58- 62 F5.2 --- q[Fe/H] [0.56/97.7]? Percentile rank of
σ<[Fe/H]>, see Section 7.1
64- 68 F5.2 [Sun] [Eu/H]Avg [-2.71/-0.39] Average log Eu/H number
abundance
70- 73 F4.2 [Sun] sig[Eu/H] [0.01/0.9]? Dispersion of log Eu/H number
abundance
75- 79 F5.2 --- q[Eu/H] [0.78/98]? Percentile rank of
σ[Eu/H], see Section 7.1
81- 129 A49 --- Comm Comment (2)
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Note (1): Following recent convention (Yuan+ 2020, J/ApJ/891/39;
<[YMB2020] DTG-NN> in Simbad and Gudin+ 2021, J/ApJ/908/79;
<[GSB2021] CDTG-NN> in Simbad), in the paper, we label the kth r-II
cluster as H22:DTC-k, where "DTC" stands for dynamically tagged
cluster. We use dynamically tagged clusters rather than dynamically
tagged groups, in order to not to be confused with the merger groups.
Note (2): R18 denotes Roederer+ 2018, J/AJ/156/179 and Y20 denotes
Yuan+ 2020, J/ApJ/891/39. The group C in R18 contains 4 member stars,
among which 3 stars are included in our cluster H22:DTC-4. This is why
we put a comment "C3/4 (R18)" for our cluster H22:DTC-4.
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Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- DTC [1/30] The cluster identifier
4- 31 A28 --- Name Star name
33- 37 F5.2 [Sun] [Fe/H] [-3.71/-0.94] log Fe/H number abundance
39- 43 F5.2 [Sun] [Eu/H] [-2.71/-0.14] log Eu/H number abundance
45- 48 F4.2 [Sun] [Eu/Fe] [0.7/2.23] log Eu/Fe number abundance
50- 68 A19 --- Ref Reference bibcode
70- 73 I4 kpc.km/s Jr [0/8014] Radial orbital action
75- 78 I4 kpc.km/s Jz [2/3462] Vertical orbital action
80- 84 I5 kpc.km/s Jphi [-3751/1757] Azimuthal orbital action
86- 91 F6.3 10+5km2/s2 Energy [-2.2/-0.56] Orbital energy
93- 99 F7.3 --- plx/err [0.14/640] Gaia parallax/error value
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Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- DTC [1/30] The cluster identifier
4- 31 A28 --- Name Star name
33- 38 F6.2 kpc x [-16.1/3.1] Galactic X coordinate
40- 44 F5.2 kpc y [-7.1/4.6] Galactic Y coordinate
46- 51 F6.2 kpc z [-16.1/16.1] Galactic Z coordinate
53- 59 F7.2 km/s Vx [-372.1/346.4] Velocity along the X coordinate
61- 67 F7.2 km/s Vy [-294/439.1] Velocity along the Y coordinate
69- 75 F7.2 km/s Vz [-434.4/408.2] Velocity along the Z coordinate
77- 80 F4.2 kpc rperi [0.1/9.6] Perigalactic radius
82- 87 F6.2 kpc rapo [3.27/129.5] Apogalactic radius
89- 93 F5.2 kpc Zmax [0.4/77.6] Maximum height above the Galactic plane
95- 98 F4.2 --- e [0.04/0.99] Eccentricity
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 27-Feb-2025