J/AJ/165/55 Chemical abundances for 5 stars in Tucana II (Chiti+, 2023)
Detailed Chemical Abundances of Stars in the Outskirts of the Tucana II
Ultrafaint Dwarf Galaxy.
Chiti A., Frebel A., Ji A.P., Mardini M.K., Ou X., Simon J.D., Jerjen H.,
Kim D., Norris J.E.
<Astron. J., 165, 55 (2023)>
=2023AJ....165...55C 2023AJ....165...55C
ADC_Keywords: Galaxies, dwarf; Stars, population II; Spectra, optical;
Abundances; Radial velocities; Effective temperatures
Keywords: Dwarf galaxies ; Local Group ; Population II stars
Abstract:
We present chemical abundances and velocities of five stars between
0.3 and 1.1kpc from the center of the TucanaII ultrafaint dwarf galaxy
(UFD) from high-resolution Magellan/MIKE spectroscopy. We find that
every star is deficient in metals (-3.6<[Fe/H]←1.9) and in
neutron-capture elements as is characteristic of UFD stars,
unambiguously confirming their association with TucanaII. Other
chemical abundances (e.g., C, iron peak) largely follow UFD trends and
suggest that faint core-collapse supernovae (SNe) dominated the early
evolution of TucanaII. We see a downturn in [α/Fe] at
[Fe/H]~-2.8, indicating the onset of Type Ia SN enrichment and
somewhat extended chemical evolution. The most metal-rich star has
strikingly low [Sc/Fe]=-1.29±0.48 and [Mn/Fe]=-1.33±0.33,
implying significant enrichment by a sub-Chandrasekhar mass Type Ia
SN. We do not detect a radial velocity gradient in TucanaII
(dvhelio/dθ1=-2.6-2.9+3.0km/s/kpc), reflecting a lack of
evidence for tidal disruption, and derive a dynamical mass of
M1/2(rh)=1.6-0.7+1.1x106M☉. We revisit formation
scenarios of the extended component of TucanaII in light of its
stellar chemical abundances. We find no evidence that TucanaII had
abnormally energetic SNe, suggesting that if SNe drove in situ stellar
halo formation, then other UFDs should show similar such features.
Although not a unique explanation, the decline in [α/Fe] is
consistent with an early galactic merger triggering later star
formation. Future observations may disentangle such formation channels
of UFD outskirts.
Description:
We used Magellan Inamori Kyocera Echelle (Magellan/MIKE) to obtain
high-resolution spectra of five Tucana II member stars.
The MIKE spectra in this study were obtained using the 1.0" slit and
2x2 binning, which provided wavelength coverage between 3500 and
9000Å with a resolution of R∼28000 on the blue echelle orders and
R∼22000 on the red echelle orders. The observations took place in 2020
October and December and in 2021 June, July, and October.
Objects:
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RA (ICRS) DE Designation(s)
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22 51 55.10 -58 34 08.0 Tucana II = NAME Tuc 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 101 5 Observations
table2.dat 49 5 Stellar parameters
table3.dat 47 84 Chemical abundances
table4.dat 44 79 Uncertainties
table5.dat 47 557 Line measurements
table6.dat 58 60 *Velocity measurements
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Note on table6.dat: For velocities reported in Walker+, 2016, J/ApJ/819/53,
we list the MJD derived from Table1 in that study.
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See also:
I/337 : Gaia DR1 (Gaia Collaboration, 2016)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
J/ApJ/612/447 : Draco 119 and HD 88609 equivalent widths (Fulbright+, 2004)
J/ApJ/645/613 : Abundances of HD 221170 (Ivans+, 2006)
J/ApJS/162/227 : Transition probabilities for SmII (Lawler+, 2006)
J/ApJ/655/492 : Equivalent widths of 26 metal-poor stars (Aoki+, 2007)
J/ApJS/182/51 : Transition probabilities rare earth elements (Lawler+, 2009)
J/ApJS/182/80 : Rare earth abundances (Sneden+, 2009)
J/ApJ/708/560 : Spectroscopy of UMa II and Coma Ber (Frebel+, 2010)
J/ApJ/724/341 : Nucleosynthesis of massive metal-free stars (Heger+, 2010)
J/ApJ/723/1632 : Abundance spreads in Bootes I and Segue 1 (Norris+, 2010)
J/ApJ/711/350 : Metal-poor giant Boo-1137 abundances (Norris+, 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/763/61 : Abundances of 7 red giant members of BootesI (Gilmore+, 2013)
J/ApJ/778/149 : Abundances for 3 stars in Sgr dSph (McWilliam+, 2013)
J/ApJ/786/74 : EW measurements of 6 Segue 1 red giants (Frebel+, 2014)
J/A+A/562/A146 : Chemical abundances of 8 metal-poor stars (Ishigaki+, 2014)
J/A+A/571/A47 : Extensive linelist CH in stellar atmospheres (Masseron+, 2014)
J/ApJ/797/21 : Carbon-enhanced metal-poor stars (Placco+, 2014)
J/MNRAS/440/2665 : SDSS J021933.13+200830.2 spectroscopy (Roederer+, 2014)
J/AJ/147/136 : Stars of low metal abundance. VI. Abundances (Roederer+, 2014)
J/ApJ/801/125 : Carbon in red giants in GCs and dSph galaxies (Kirby+, 2015)
J/ApJ/802/93 : Chemical abundance analysis 5 stars in Sculptor (Simon+, 2015)
J/A+A/574/A129 : The First CEMP star in the Sculptor dSph (Skuladottir+, 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/A+A/586/A120 : Grid of 1D models for Mg line formation (Osorio+, 2016)
J/AJ/151/82 : 4 brightest red giants in UFD galaxy Ret 2 (Roederer+, 2016)
J/ApJ/819/53 : Magellan/M2FS spectroscopy of Tucana2 & Grus1 (Walker+, 2016)
J/ApJ/838/44 : Abundances of the brightest member of Tuc III (Hansen+, 2017)
J/ApJ/838/83 : RVel, abundances & membership in TriII (Kirby+, 2017)
J/A+A/606/A112 : Abundance analysis of ALW Carina 8 (Susmitha+, 2017)
J/ApJ/857/74 : Abundances of 7 new member stars in Tucana II (Chiti+, 2018)
J/ApJ/856/142 : Abundances of metal-poor stars in Sculptor (Chiti+, 2018)
J/ApJ/855/83 : Abundances of metal-poor stars in Sagittarius (Hansen+, 2018)
J/ApJ/866/22 : Spectroscopic analysis of Tuc III stream (Li+, 2018)
J/ApJ/852/99 : Abundances 3 metal-poor starsHorologium I (Nagasawa+, 2018)
J/ApJ/863/89 : Gaia DR2 PMs stars in ultra-faint MW satellites (Simon, 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/870/83 : Abundances in ultra-faint dwarf gal. GruI & TriII (Ji+, 2019)
J/ApJ/882/177 : Abundances of 4 member stars of Tucana III (Marshall+, 2019)
J/ApJ/891/85 : Mn abundances in GC & dSph galaxies (de los Reyes+, 2020)
J/ApJ/898/150 : High-res. MIKE obs. of metal-poor stars (Ezzeddine+, 2020)
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/ApJ/909/192 : HST/ACS photometry of Eridanus II (Gallart+, 2021)
J/ApJ/908/18 : HST stellar photometry of Eridanus II (Simon+, 2021)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 A9 --- Name Name from Chiti+, 2021NatAs...5..392C 2021NatAs...5..392C
11- 12 I2 h RAh [22] Hour of right ascension (J2000)
14- 15 I2 min RAm [49/57] Minute of right ascension (J2000)
17- 22 F6.3 s RAs Second of right ascension (J2000)
24 A1 --- DE- [-] Sign of declination (J2000)
26- 27 I2 deg DEd [57/58] Degree of declination (J2000)
29- 30 I2 arcmin DEm Arcminute of declination (J2000)
32- 37 F6.3 arcsec DEs Arcsecond of declination (J2000)
39- 70 A32 --- Obs UT date(s) of observation
72- 74 F3.1 s Slit [1] Slit size
76- 80 F5.2 mag gmag [18.3/18.9] g-band magnitude
82- 84 I3 min Texp [150/365] Exposure time
86- 87 I2 --- S/N4500 [12/19] Signal-to-noise ratio at 4500Å
89- 90 I2 --- S/N6500 [22/40] Signal-to-noise ratio at 6500Å
92- 97 F6.1 km/s RVel [-129/-119] Heliocentric radial velocity
99-101 F3.1 km/s e_RVel [0.9] Error on RVel
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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- 9 A9 --- Name Name from Chiti+, 2021NatAs...5..392C 2021NatAs...5..392C
11- 14 I4 K Teff [4810/5071] Effective temperature
16- 18 I3 K e_Teff [160/241] Error on Teff
20- 23 F4.2 [-] logg [1.55/1.75] log surface gravity
25- 28 F4.2 [-] e_logg [0.3/0.9] Error on logg
30- 33 F4.2 km/s nu [1.73/2.3] microturbulence velocity
35- 38 F4.2 km/s e_nu [0.2/0.3] Error on nu
40- 44 F5.2 [-] [Fe/H] [-3.59/-1.93] log metallicity
46- 49 F4.2 [-] e_[Fe/H] [0.1/0.3] Error on [Fe/H]
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Name Star identifier
11- 15 A5 --- Species Species identifier
17 A1 --- f_Species [b] Flag on Species (1)
19- 21 I3 --- N [1/126] Number of lines used
23- 26 F4.2 [-] logeX [0.52/8.43] log solar number abundance
28 A1 --- l_[X/H] Limit flag on [X/H]
29- 33 F5.2 [-] [X/H] [-4.99/-1.29] log abundance relative to Hydrogen
34 A1 --- u_[X/H] [:] Uncertainty flag on [X/H] (9 occurrences) (2)
36 A1 --- l_[X/Fe] Limit flag on [X/Fe]
37- 41 F5.2 [-] [X/Fe] [-2.09/1.45] log abundance relative to Iron
42 A1 --- u_[X/Fe] [:] Uncertainty in [X/Fe] (9 occurrences) (2)
44- 47 F4.2 --- sigma [0.17/0.65]? Random uncertainty in abundances (3)
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Note (1): Flag as follows:
b = Corrected for the evolutionary status of the star following
Placco+, 2014, J/ApJ/797/21 (5 occurrences).
Note (2): A large uncertainty despite the detection of a line feature.
Note (3): See Table 4 for total uncertainties.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Name Star identifier
11- 15 A5 --- Species Species identifier
17- 19 I3 --- N [1/126] Number of lines used
21- 24 F4.2 [-] sigma [0.17/0.65]? Random uncertainty
26- 29 F4.2 [-] [X/H]sys [0.09/0.79]? log systematic abundance
uncertainty relative to Hydrogen
31- 34 F4.2 [-] [X/H]tot [0.25/0.82]? log total abundance uncertainty
relative to Hydrogen
36- 39 F4.2 [-] [X/Fe]sys [0.01/0.65]? log systematic abundance
uncertainty relative to Iron
41- 44 F4.2 [-] [X/Fe]tot [0.17/0.71]? log total abundance uncertainty
relative to Iron
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Name Star identifier
11- 17 F7.2 0.1nm Wave [3787/6979] Rest wavelength; Angstroms
19- 23 A5 --- Species Species identifier
25- 28 F4.2 eV ExPot [0/4.45]? Excitation potential (1)
30- 34 F5.2 --- loggf [-5.69/0.65]? Oscillator strength (1)
36- 40 F5.1 10-13m EW [22.3/244]? Equivalent width; mÅ (1)
42 A1 --- l_logeX Limit flag on loge(X)
43- 47 F5.2 [-] logeX [-2.56/7.02] log number abundance
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Note (1): A blank indicates a synthetic spectrum was used to derive loge(X).
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Name Star identifier
11- 19 F9.5 deg RAdeg [342/345] Degree of Right Ascension (J2000)
21- 29 F9.5 deg DEdeg [-59/-57] Degree of Declination (J2000)
31- 37 F7.1 d MJD [57221/59494] Modified Julian Date at midpoint of
the observation (JD-2400000.5)
39- 43 A5 --- Inst Instrument used (1)
45- 50 F6.1 km/s RVel [-136/-115] Heliocentric radial velocity
52 A1 --- f_RVel [b] Flag on RVel (2)
54- 56 F3.1 km/s e_RVel [0.5/9] Error on RVel
58 I1 --- Ref [1/5] Reference used (3)
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Note (1): Instruments as follows:
IMACS = Inamori-Magellan Areal Camera and Spectrograph (15 occurrences)
M2FS = Michigan/Magellan Fiber System (14 occurrences)
MIKE = Magellan Inamori Kyocera Echelle (21 occurrences)
MagE = Magellan Echellette spectrograph (10 occurrences)
Note (2): Flag as follows:
b = Offset of 2.5km/s has been applied to account for a zero-point
offset between M2FS and MIKE velocities (see paragraph 4 in Section
3.1) (13 occurrences).
Note (3): References as follows:
1 = This work
2 = Walker+, 2016, J/ApJ/819/53
3 = Chiti+, 2021NatAs...5..392C 2021NatAs...5..392C
4 = Remeasured from Ji+, 2016ApJ...832L...3J 2016ApJ...832L...3J
5 = Remeasured from Chiti+, 2018, J/ApJ/857/74
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History:
From electronic version of the journal
(End) Prepared by [AAS], Coralie Fix [CDS], 26-May-2023