J/MNRAS/500/889 S2 stream. Shreds of a primitive dwarf galaxy (Aguado+, 2021)
The S2 stream: the shreds of a primitive dwarf galaxy.
Aguado D.S., Myeong G.C., Belokurov V., Evans N.W., Koposov S.E.,
Allende Prieto C., Lanfranchi G.A., Matteucci F., Shetrone M., Sbordone L.,
Navarrete C., Gonzalez Hernandez J.I., Chaname J., Peralta de Arriba L.,
Yuan Z.
<Mon. Not. R. Astron. Soc., 500, 889-910 (2021)>
=2021MNRAS.500..889A 2021MNRAS.500..889A (SIMBAD/NED BibCode)
ADC_Keywords: Stars, halo ; Galaxies, dwarf ; Milky Way ; Abundances, [Fe/H] ;
Abundances, peculiar ; Effective temperatures ; Spectra, optical
Keywords: stars: abundances - Galaxy: evolution - Galaxy: formation -
Galaxy: halo - Galaxy: kinematics and dynamics
Abstract:
The S2 stream is a kinematically cold stream that is plunging
downwards through the Galactic disc. It may be part of a hotter and
more diffuse structure called the Helmi stream. We present a
multi-instrument chemical analysis of the stars in the metal-poor S2
stream using both high- and low-resolution spectroscopy, complemented
with a re-analysis of the archival data to give a total sample of 62
S2 members. Our high-resolution program provides α-elements (C,
Mg, Si, Ca, and Ti), iron-peak elements (V, Cr, Mn, Fe, Ni), n-capture
process elements (Sr, Ba), and other elements such as Li, Na, Al, and
Sc for a subsample of S2 objects. We report coherent abundance
patterns over a large metallicity spread (∼1dex) confirming that the
S2 stream was produced by a disrupted dwarf galaxy. The combination of
S2's α-elements displays a mildly decreasing trend with
increasing metallicity, which can be tentatively interpreted as a
'knee' at [Fe/H]←2. At the low-metallicity end, the n-capture
elements in S2 may be dominated by r-process production; however,
several stars are Ba-enhanced but unusually poor in Sr. Moreover, some
of the low-[Fe/H] stars appear to be carbon-enhanced. We interpret the
observed abundance patterns with the help of chemical evolution models
that demonstrate the need for modest star formation efficiency and low
wind efficiency confirming that the progenitor of S2 was a primitive
dwarf galaxy.
Description:
The identification of S2 candidate stars in Myeong et al.
(2018MNRAS.475.1537M 2018MNRAS.475.1537M) and Myeong et al. (2018MNRAS.478.5449M 2018MNRAS.478.5449M) was made
from the SDSS-Gaia catalogue, which is a crossmatch between Gaia Data
Release (DR) 1 (Gaia Collaboration 2016A&A...595A...2G 2016A&A...595A...2G, Cat. I/337),
SDSS DR9 (Ahn et al. 2012ApJS..203...21A 2012ApJS..203...21A, Cat. V/139), and LAMOST DR3
(Luo et al. 2015RAA....15.1095L 2015RAA....15.1095L, Cat. V/146). These stars were
re-analysed with later released Gaia DR2 proper motions, and 52 stars
were reconfirmed as high-quality members based on their revised action
variables (O'Hare et al. 2020PhRvD.101b3006O 2020PhRvD.101b3006O).
Our spectroscopic follow-up sample is built from three different
sources. The first is Very Large Telescope (VLT) observations with the
Ultraviolet and Visual Echelle Spectrograph (UVES) (Dekker et al.
2000SPIE.4008..534D 2000SPIE.4008..534D) and X-SHOOTER (Vernet et al.
2011A&A...536A.105V 2011A&A...536A.105V). This sample comprises five S2 members, albeit
with lower signal-to-noise (S/N) ratio than originally anticipated
because of weather conditions. We took advantage of the recent
start-up of operations of the new High Optical Resolution Spectrograph
(HORuS Penate et al. 2014SPIE.9147E..8JP) at the Gran Telescopio
Canarias (GTC) to obtain data on two further objects. Finally, we
re-observed one S2 object with the second-generation Low Resolution
Spectrograph (LRS2-B Chonis et al. 2014SPIE.9147E..0AC) at the
Hobby-Eberly Telescope (HET).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tableb1.dat 97 52 Coordinates and stellar parameters from
low-resolution analysis
tableb2.dat 106 7 APOGEE abundances for S2 members from ASPCAP
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See also:
I/337 : Gaia DR1 (Gaia Collaboration, 2016)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
V/139 : The SDSS Photometric Catalog, Release 9 (Adelman-McCarthy+, 2012)
V/146 : LAMOST DR1 catalogs (Luo+, 2015)
Byte-by-byte Description of file: tableb1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 A6 --- Survey Survey name (SDSS or LAMOST)
8- 17 A10 --- Name Source name (JHHMM-DDMM)
19- 22 F4.1 mag Vmag V-band magnitude
24- 25 I2 h RAh Right ascension (J2000)
27- 28 I2 min RAm Right ascension (J2000)
30- 34 F5.2 s RAs Right ascension (J2000)
36 A1 --- DE- Declination sign (J2000)
37- 38 I2 deg DEd Declination (J2000)
40- 41 I2 arcmin DEm Declination (J2000)
43- 46 F4.1 arcsec DEs Declination (J2000)
48- 51 I4 K Teff Effective temperature
53- 55 I3 K e_Teff Error on Teff
57- 60 F4.2 [cm/s2] logg Surface gravity
62- 65 F4.2 [cm/s2] e_logg Error on logg
67- 71 F5.2 [-] [Fe/H] Fe/H abundance ratio
73- 76 F4.2 [-] e_[Fe/H] Error on [Fe/H]
78- 82 F5.2 [-] [C/Fe] C/Fe abundance ratio
84- 87 F4.2 [-] e_[C/Fe] Error on [C/Fe]
89- 91 I3 --- S/N Signal to noise ratio
93- 97 A5 --- Flag Flag (1)
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Note (1): Flag as follows:
1 = Objects with high-resolution analysis
2 = Objects with positive vz motion
3 = Objects with tentative [Fe/H] and [C/Fe] from low-resolution analysis
4 = Objects with tentative [C/Fe] from low-resolution analysis
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Byte-by-byte Description of file: tableb2.dat
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Bytes Format Units Label Explanations
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1- 18 A18 --- Name APOGEE name (2MHHMMSSss+DDMMSSs)
20- 23 I4 K Teff Effective temperature
25- 26 I2 K e_Teff Error on Teff
28- 30 F3.1 [cm/s2] logg Surface gravity
32- 34 F3.1 [cm/s2] e_logg Error on logg
36- 39 F4.1 [-] [Fe/H] Fe/H abundance ratio
41- 43 F3.1 [-] e_[Fe/H] Error on [Fe/H]
45- 48 F4.1 [-] [C/Fe] C/Fe abundance ratio
50- 52 F3.1 [-] e_[C/Fe] Error on [C/Fe]
54- 57 F4.1 [-] [Mg/Fe] Mg/Fe abundance ratio
59- 61 F3.1 [-] e_[Mg/Fe] Error on [Mg/Fe]
63- 66 F4.1 [-] [Al/Fe] Al/Fe abundance ratio
68- 70 F3.1 [-] e_[Al/Fe] Error on [Al/Fe]
72- 74 F3.1 [-] [Si/Fe] Si/Fe abundance ratio
76- 78 F3.1 [-] e_[Si/Fe] Error on [Si/Fe]
80- 82 F3.1 [-] [Ca/Fe] Ca/Fe abundance ratio
84- 86 F3.1 [-] e_[Ca/Fe] Error on [Ca/Fe]
88- 91 F4.1 [-] [Mn/Fe] ? Mn/Fe abundance ratio
93- 95 F3.1 [-] e_[Mn/Fe] ? Error on [Mn/Fe]
97- 100 F4.1 [-] [Ni/Fe] ? Ni/Fe abundance ratio
102- 104 F3.1 [-] e_[Ni/Fe] ? Error on [Ni/Fe]
106 I1 --- Flag ? Flag (1)
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Note (1): Flag as follows:
1 = Objects discarded by Gaia DR2 kinematics
2 = Objects flagged by ASPCAP and not used in this work
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History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 28-Sep-2023