J/ApJ/897/183 Chemical abundances of 3 stars in Grus II galaxy (Hansen+, 2020)
Chemical Analysis of the Ultrafaint Dwarf Galaxy Grus II. Signature of High-mass
Stellar Nucleosynthesis.
Hansen T.T., Marshall J.L., Simon J.D., Li T.S., Bernstein R.A., Pace A.B.,
Ferguson P., Nagasawa D.Q., Kuehn K., Carollo D., Geha M., James D.,
Walker A., Diehl H.T., Aguena M., Allam S., Avila S., Bertin E., Brooks D.,
Buckley-Geer E., Burke D.L., Rosell A.C., Kind M.C., Carretero J.,
Costanzi M., Da Costa L.N., Desai S., De Vicente J., Doel P., Eckert K.,
Eifler T.F., Everett S., Ferrero I., Frieman J., Garcia-Bellido J.,
Gaztanaga E., Gerdes D.W., Gruen D., Gruendl R.A., Gschwend J.,
Gutierrez G., Hinton S.R., Hollowood D.L., Honscheid K., Kuropatkin N.,
Maia M.A.G., March M., Miquel R., Palmese A., Paz-Chinchon F., Plazas A.A.,
Sanchez E., Santiago B., Scarpine V., Serrano S., Smith M., Soares-
Santos M., Suchyta E., Swanson M.E.C., Tarle G., Varga T.N., Wilkinson R.
<Astrophys. J., 897, 183 (2020)>
=2020ApJ...897..183H 2020ApJ...897..183H
ADC_Keywords: Galaxies; Stars, peculiar; Abundances; Optical
Keywords: Chemical abundances ; Dwarf galaxies ; Chemically peculiar stars ;
Stellar abundances
Abstract:
We present a detailed abundance analysis of the three brightest member
stars at the top of the giant branch of the ultrafaint dwarf (UFD)
galaxy GrusII. All stars exhibit a higher than expected [Mg/Ca] ratio
compared to metal-poor stars in other UFD galaxies and in the Milky
Way (MW) halo. Nucleosynthesis in high-mass (≥20M☉) core-collapse
supernovae has been shown to create this signature. The abundances of
this small sample (three) stars suggests the chemical enrichment of
GrusII could have occurred through substantial high-mass stellar
evolution, and is consistent with the framework of a top-heavy initial
mass function. However, with only three stars it cannot be ruled out
that the abundance pattern is the result of a stochastic chemical
enrichment at early times in the galaxy. The most metal-rich of the
three stars also possesses a small enhancement in rapid
neutron-capture (r-process) elements. The abundance pattern of the
r-process elements in this star matches the scaled r-process pattern
of the solar system and r-process enhanced stars in other dwarf
galaxies and in the MW halo, hinting at a common origin for these
elements across a range of environments. All current proposed
astrophysical sites of r-process element production are associated
with high- mass stars, thus the possible top-heavy initial mass
function of GrusII would increase the likelihood of any of these
events occurring. The time delay between the α and r-process
element enrichment of the galaxy favors a neutron star merger as the
origin of the r-process elements in GrusII.
Description:
A total sample of five stars were observed with the Magellan Inamori
Kyocera Echelle (MIKE) spectrograph at the Magellan-Clay Telescope at
Las Campanas Observatory. Table1 lists the targets, observing dates,
and exposure times.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 127 6 Observing Log
table3.dat 48 274 EW and atomic data for FeI and FeII lines used for
parameter determination
table4.dat 48 101 EW measurements and atomic data for lines used for
abundance determination
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See also:
II/357 : The Dark Energy Survey (DES): Data Release 1 (Abbott+, 2018)
J/A+A/439/129 : HERES II. Spectroscopic analysis (Barklem+, 2005)
J/ApJ/655/492 : Equivalent widths of 26 metal-poor stars (Aoki+, 2007)
J/A+A/512/A54 : Teff and Fbol from Infrared Flux Method (Casagrande+, 2010)
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/AJ/141/175 : Abundances in M15 RGB/RHB stars (Sobeck+, 2011)
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/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 low metal abundance. VI. Abundances (Roederer+, 2014)
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/857/74 : Abundances of 7 new member stars in Tucana II (Chiti+, 2018)
J/ApJ/858/92 : RPA Southern Pilot Search of 107 Stars (Hansen+, 2018)
J/ApJ/866/22 : Spectroscopic analysis of Tuc III stream (Li+, 2018)
J/ApJ/852/99 : Abundances of 3 metal-poor stars Horologium I (Nagasawa+,2018)
J/ApJ/882/40 : Lanthanide fraction distrib. of metal-poor stars (Ji+, 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/875/77 : Proper motions of MW satellites with Gaia & DES (Pace+, 2019)
J/ApJ/889/27 : Abundances of 11 stars in Carina II and III (Ji+, 2020)
J/ApJ/892/137 : Spectroscopy of Grus II, Tuc IV and Tuc V (Simon+, 2020)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 23 A23 --- Name Star identifier
25- 26 I2 h RAh [22] Hour of right ascension (J2000)
28- 29 I2 min RAm [02/04] Minute of right ascension (J2000)
31- 35 F5.2 s RAs Second of right ascension (J2000)
37 A1 --- DE- [-] Sign of declination (J2000)
39- 40 I2 deg DEd [46] Degree of declination (J2000)
42- 43 I2 arcmin DEm [21/41] Arcminute of declination (J2000)
45- 49 F5.2 arcsec DEs Arcsecond of declination (J2000)
51- 56 F6.3 mag gmag [17.5/19.4] g-band magnitude
58- 63 F6.3 mag rmag [16.7/18.9]? r-band magnitude
65- 70 F6.3 mag imag [16.4/18.7]? i-band magnitude
72- 77 F6.3 mag zmag [16.2/18.6]? z-band magnitude
79- 83 I5 d MJD [57605/58433] Modified Juliand Date of
observation; MJD-2400000.5
85- 94 A10 s Texp Exposure time for each observation
96- 97 I2 --- S/N4100 [3/12] Signal-to-noise ration at 4100Å
99 A1 --- f_S/N4100 [a] Flag means S/N of the combined spectrum
per pixel
101-102 I2 --- S/N5500 [5/32] Signal-to-noise ration at 5500Å
104 A1 --- f_S/N5500 [a] Flag means S/N of the combined spectrum
per pixel
106-111 F6.1 km/s RVel [-107/77] Heliocentric radial velocity
113-115 F3.1 km/s e_RVel [0.6/1.1] Error on RVel
117-119 A3 --- Memb Member? Yes or No
121-127 A7 --- ID Identifier used in this work
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Byte-by-byte Description of file: table[34].dat
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Bytes Format Units Label Explanations
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1- 7 A7 --- ID Stellar ID
9- 12 A4 --- Species Species
14- 20 F7.2 0.1nm lambda Wavelength
22- 26 F5.3 eV ExPot Excitation potential
28- 32 F5.2 [-] loggf Log of the oscillator strength
34- 38 F5.1 10-13m EW Equivalent width of species line
40- 43 F4.1 10-13m e_EW Uncertainty in EW
45- 48 F4.2 [-] [Abd] Abundance, log
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History:
From electronic version of the journal
(End) Prepared by [AAS], Coralie Fix [CDS], 30-Sep-2021