J/AJ/165/100 Stellar parameters and abundances in Reticulum II (Ji+, 2023)
Metal Mixing in the r-process Enhanced Ultrafaint Dwarf Galaxy Reticulum II
Ji A.P., Simon J.D., Roederer I.U., Magg E., Frebel A., Johnson C.I.,
Klessen R.S., Magg M., Cescutti G., Mateo M., Bergemann M., Bailey J.I.I.
<Astron. J., 165, 100 (2023)>
=2023AJ....165..100J 2023AJ....165..100J
ADC_Keywords: Galaxies, dwarf; Spectra, optical; Abundances; Proper motions;
Radial velocities; Effective temperatures
Keywords: Dwarf galaxies ; Local Group ; R-process ; Chemical abundances
; Galaxy chemical evolution
Abstract:
The ultrafaint dwarf galaxy ReticulumII was enriched by a single rare
and prolific r-process event. The r-process content of ReticulumII
thus provides a unique opportunity to study metal mixing in a relic
first galaxy. Using multi-object high-resolution spectroscopy with
VLT/GIRAFFE and Magellan/M2FS, we identify 32 clear spectroscopic
member stars and measure abundances of Mg, Ca, Fe, and Ba where
possible. We find 72-12+10% of the stars are r-process-enhanced,
with a mean <Ba/H≥-1.68±0.07 and unresolved intrinsic dispersion
σ[Ba/H]<0.20. The homogeneous r-process abundances imply that
RetII's metals are well mixed by the time the r-enhanced stars form,
which simulations have shown requires at least 100Myr of metal mixing
in between bursts of star formation to homogenize. This is the first
direct evidence of bursty star formation in an ultrafaint dwarf
galaxy. The homogeneous dilution prefers a prompt and high-yield
r-process site, such as collapsar disk winds or prompt neutron star
mergers. We also find evidence from [Ba/H] and [Mg/Ca] that the
r-enhanced stars in RetII formed in the absence of substantial
pristine gas accretion, perhaps indicating that ∼70% of RetII stars
formed after reionization.
Description:
The Fibre Large Array Multi Element Spectrograph (FLAMES/GIRAFFE)
setup on the Very Large Telescope (VLT) UT2 provides high-resolution
spectra of ∼100 stars over a field of view of diameter 0.4deg.
Observations were taken in visitor mode on 2017 October 26-27 with
excellent weather. We used the HR14A setting, covering one order from
6300-6500Å with R∼18000.
We obtained high-resolution spectra of Ret II stars with
Michigan/Magellan Fiber System (M2FS) on 2017 November 16-17. We used
the HiRes mode with 180µm slits, providing R∼18000 at
6100-6700Å.
Objects:
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RA (ICRS) DE Designation(s)
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03 35 42.10 -54 02 56.9 Reticulum II = NAME Reticulum II
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 140 129 Observations
table2.dat 32 38 *Stellar parameters
table4.dat 91 40 *Abundances
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Note on table2.dat: We adopt [M/H]=-2.5 and [α/Fe]=+0.4 for all stars.
Note on table4.dat: Ba/H-NLTE refers to our fiducial Ba abundances
derived from MULTI/MARCS, Ba/H-LTE is the Ba abundance derived from
MOOG/ATLAS, and Ba/H-MR is the MOOG/ATLAS abundance from the 4554Å
line derived from the medium-resolution M2FS observations.
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See also:
B/simbad : Simbad objects catalogue (M.Wenger 2000)
I/337 : Gaia DR1 (Gaia Collaboration, 2016)
II/357 : The Dark Energy Survey (DES): Data Release 1 (Abbott+, 2018)
J/AJ/128/1177 : Galactic stellar abundances (Venn+, 2004)
J/A+A/439/129 : HERES II. Spectroscopic analysis (Barklem+, 2005)
J/ApJ/645/613 : Abundances of HD 221170 (Ivans+, 2006)
J/MNRAS/383/183 : CaII triplet of RGB from VLT/FLAMES obs. (Battaglia+, 2008)
J/A+A/490/625 : Abundances of NGC 6121 red giants (Marino+, 2008)
J/ApJ/708/560 : Spectroscopy of UMa II and Coma Ber (Frebel+, 2010)
J/AJ/141/175 : Abundances in M15 RGB/RHB stars (Sobeck+, 2011)
J/ApJ/778/56 : Hamburg/ESO Survey extremely metal-poor stars (Cohen+, 2013)
J/ApJ/769/57 : Equivalent widths of metal-poor stars (Frebel+, 2013)
J/ApJ/778/149 : Abundances for 3 stars in Sgr dSph (McWilliam+, 2013)
J/ApJ/767/134 : Abundances of red giant stars in UFD galaxies (Vargas+, 2013)
J/MNRAS/444/392 : Synthetic Stellar Photometry. I. (Casagrande+, 2014)
J/ApJ/786/74 : EW measurements of 6 Segue 1 red giants (Frebel+, 2014)
J/A+A/569/A43 : HE 2252-4225 abundance analysis (Mashonkina+, 2014)
J/AJ/147/136 : Stars of low metal abundance VI. Abundances (Roederer+, 2014)
J/ApJ/789/147 : Star formation histories of LG dwarf galaxies (Weisz+, 2014)
J/ApJ/807/171 : SkyMapper Survey metal-poor star spectro. (Jacobson+, 2015)
J/ApJ/808/95 : Spectroscopy of Reticulum II (Simon+, 2015)
J/ApJ/808/108 : M2FS stellar spectroscopy of Reticulum 2 (Walker+, 2015)
J/ApJ/826/110 : Boo-127 and Boo-980 high-resolution spectra (Frebel+, 2016)
J/ApJ/830/93 : Abundances of Ret II brightest red giant members (Ji+, 2016)
J/ApJ/817/41 : Abundances of 4 metal-poor red giants in BooII (Ji+, 2016)
J/AJ/151/82 : 4 brightest red giants in UFD galaxy Ret 2 (Roederer+, 2016)
J/ApJ/838/44 : Abundances of the brightest member of Tuc III (Hansen+, 2017)
J/ApJ/838/11 : Member stars in the MW satellite Tucana III (Simon+, 2017)
J/MNRAS/479/5343 : Nearby dwarf galaxy in Magellanic bridge (Koposov+, 2018)
J/ApJ/857/145 : MagLiteS Carina II and Carina III spectroscopy (Li+, 2018)
J/ApJS/237/13 : Models & yields of 13-120Msun massive stars (Limongi+, 2018)
J/ApJ/863/25 : Magellan/Megacam obs of 4 MW satellites (Mutlu-Pakdil+, 2018)
J/A+A/631/A80 : Mn lines 3D NLTE formation late-type stars (Bergemann+, 2019)
J/A+A/626/A15 : Sculptor Red Giant Branch stars abundances (Hill+, 2019)
J/ApJ/882/40 : Lanthanide fraction distribution metal-poor stars (Ji+, 2019)
J/ApJ/870/83 : Abundances in ultra-faint dwarf gal. GruI & TriII (Ji+, 2019)
J/MNRAS/490/3508 : The Southern Stellar Stream Sp. Survey (S5) (Li+, 2019)
J/ApJ/897/183 : Chemical abundances 3 stars in Grus II galaxy (Hansen+, 2020)
J/AJ/160/181 : Chemical abundances in red giants with Magellan (Ji+, 2020)
J/ApJ/889/27 : Abundances of 11 stars in Carina II and III (Ji+, 2020)
J/AJ/159/46 : Elemental abundances416 stars in 5 M31 dSphs (Kirby+, 2020)
J/ApJ/892/137 : Spectroscopy of Grus II, Tuc IV and Tuc V (Simon+, 2020)
J/A+A/642/A176 : Chemical evolution of dSph galaxy Sextans (Theler+, 2020)
J/ApJ/906/96 : Dwarfs galaxies in DC Justice League Simul (Applebaum+, 2021)
J/ApJ/921/67 : High-dispersion sp. 8 Phoenix stream redgiants (Casey+, 2021)
J/A+A/657/A54 : Local Group Gaia eDR3 systemic motions (Battaglia+, 2022)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- ID [1/200] Internal index identifier
5- 6 I2 h RAh [3/3] Hour of Right Ascension (J2000)
8- 9 I2 min RAm Minute of Right Ascension (J2000)
11- 14 F4.1 s RAs Second of Right Ascension (J2000)
16- 16 A1 --- DE- [-] Sign of the Declination (J2000)
17- 18 I2 deg DEd [53/54] Degree of Declination (J2000)
20- 21 I2 arcmin DEm Arcminute of Declination (J2000)
23- 27 F5.2 arcsec DEs Arcsecond of Declination (J2000)
29- 33 F5.2 mag gmag [16/21] Extinction corrected, apparent g band
35- 39 F5.2 mag rmag [15.6/20.7] Extinction corrected, apparent r
band magnitude
41- 44 F4.2 --- re/rh [0.23/4.78] Elliptical distance divided by
half-light radius
46- 51 F6.1 km/s RVel [-492/345] Heliocentric radial velocity
53- 57 F5.2 km/s e_RVel [0.1/12] Uncertainty in RVel
59- 63 F5.2 mas/yr pmRA [-3.73/35.2] Proper motion along RA*cos(DEC)
65- 70 F6.2 mas/yr pmDE [-23/22.1] Proper motion along DEC
72 I1 --- Mem [0/1] Member? 1=True and 0=False
74 I1 --- CanMem [0/1] Candidate member? 1=True and 0=False
76 I1 --- Bin [0/1] Binary? 1=True and 0=False
78- 82 A5 --- VLT-SN VLT Signal-to-Noise Ratio, per pixel
84- 84 A1 --- M2FS M2FS filter used; b or r
86- 89 F4.1 --- highSN [2/40]? M2FS hi-resolution Signal-to-Noise
Ratio, per pixel
91- 92 I2 --- medSN [22/94]? M2FS medium-resolution
Signal-to-Noise, per pixel
94-112 I19 --- Gaia Gaia EDR3 identifier
114-119 F6.1 km/s VLT-RVel [-490/348]? VLT heliocentric velocity
from Hα
121-124 F4.2 km/s e_VLT-RVel [0.6/3]? Uncertainty in VLT-Ha
126-130 F5.1 km/s highRVel [0/133]? M2FS high-resolution heliocentric
velocity
132-135 F4.2 km/s e_highRVel [0/4.25]? Uncertainty in M2FS-vHel
137-140 F4.1 km/s medRVel [45.1/66.9]? M2FS medium-resolution
heliocentric velocity
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- ID [1/195] Internal index identifier
5- 8 I4 K Teff [4584/6645] Effective temperature
10- 12 I3 K e_Teff [49/130] Error on Teff
14- 17 F4.2 [-] logg [1.24/3.81] Surface gravity
19- 22 F4.2 [-] e_logg [0.1/0.2] Error on logg
24- 27 F4.2 km/s Vt [1.26/1.61] Turbulence velocity
29- 32 F4.2 km/s e_Vt [0.1/0.2] Error on Vt
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- ID [1/195] Internal index identifier
5 A1 --- Mem Membership (1)
7- 9 I3 --- VLT-SN [7/140]? Very Large Telescope signal-to-noise
11- 22 A12 --- M2FS-SN M2FS signal-to_noise
24- 28 F5.2 [-] Mg/H [-2.84/-2.03]? log Mg ratio
30- 33 F4.2 [-] e_Mg/H [0.11/0.22]? Error on Mg/H
35- 39 F5.2 [-] Ca/H [-2.98/0.34]? log Ca ratio
41- 44 F4.2 [-] e_Ca/H [0.06/0.23]? Error on Ca/H
46 A1 --- f_Ca/H [*] Flag on Ca/H (2)
48- 52 F5.2 [-] Fe/H [-3.28/-0.37]? log Fe ratio
54- 57 F4.2 [-] e_Fe/H [0.08/0.44]? Error on Fe/H
59 A1 --- f_Fe/H [*] Flag on Fe/H (2)
61- 65 F5.2 [-] Ba/H-NLTE [-3.46/0.79]? log Ba ratio, NLTE
67- 70 F4.2 [-] e_Ba/H-NLTE [0.15/0.71]? Error on Ba/H-NLTE
72 A1 --- f_Ba/H-NLTE [*] Flag on Ba/H-NLTE (2)
74- 78 F5.2 [-] Ba/H-LTE [-3.46/0.79]? log Ba ratio, LTE
80- 84 F5.2 [-] Ba/H-MR [-1.82/-0.83]? log Ba ration, MR
86- 89 F4.2 [-] e_Ba/H-MR [0.16/0.87]? Error on Ba/H-MR
91 A1 --- f_Ba/H-MR [*] Flag on Ba/H-MR (2)
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Note (1): Codes as follows:
M = clear member (32 occurrences)
C = candidate member (8 occurrences)
Note (2): Flag as follows:
* = For the error, indicated value is a 99% upper limit
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History:
From electronic version of the journal
(End) Prepared by [AAS], Coralie Fix [CDS], 02-Jun-2023