J/ApJ/856/142 Abundances of metal-poor stars in Sculptor (Chiti+, 2018)
Detection of a population of carbon-enhanced metal-poor stars in the Sculptor
dwarf spheroidal galaxy.
Chiti A., Simon J.D., Frebel A., Thompson I.B., Shectman S.A., Mateo M.,
Bailey J.I., Crane J.D., Walker M.
<Astrophys. J., 856, 142 (2018)>
=2018ApJ...856..142C 2018ApJ...856..142C
ADC_Keywords: Stars, metal-deficient; Abundances; Spectra, optical;
Effective temperatures
Keywords: galaxies: dwarf ; galaxies: individual (Sculptor dSph) ;
galaxies: stellar content ; stars: abundances ; stars: carbon
Abstract:
The study of the chemical abundances of metal-poor stars in dwarf
galaxies provides a venue to constrain paradigms of chemical
enrichment and galaxy formation. Here we present metallicity and
carbon abundance measurements of 100 stars in Sculptor from
medium-resolution (R∼2000) spectra taken with the Magellan/Michigan
Fiber System mounted on the Magellan-Clay 6.5m telescope at Las
Campanas Observatory. We identify 24 extremely metal-poor star
candidates ([Fe/H]<-3.0) and 21 carbon-enhanced metal-poor (CEMP)
star candidates. Eight carbon-enhanced stars are classified with at
least 2σ confidence, and five are confirmed as such with
follow-up R∼6000 observations using the Magellan Echellette
Spectrograph on the Magellan-Baade 6.5m telescope. We measure a CEMP
fraction of 36% for stars below [Fe/H]=-3.0, indicating that the
prevalence of carbon-enhanced stars in Sculptor is similar to that of
the halo (∼43%) after excluding likely CEMP-s and CEMP-r/s stars from
our sample. However, we do not detect that any CEMP stars are strongly
enhanced in carbon ([C/Fe]>1.0). The existence of a large number of
CEMP stars both in the halo and in Sculptor suggests that some halo
CEMP stars may have originated from accreted early analogs of dwarf
galaxies.
Description:
We first obtained low-resolution (R∼700) spectroscopy of eight fields
in Sculptor using the IMACS spectrograph at the Magellan-Baade
telescope at Las Campanas Observatory.
IMACS targets were selected from the photometric catalog of Coleman+
(2005, J/AJ/130/1065 ; <[CDB2005] FF-N-NNNN> in Simbad).
We then obtained R∼4000 and 6000 optical spectra of 22 of the best
candidates using the MagE spectrograph at the Magellan telescopes.
We observed an additional 10 Sculptor stars using the MagE
spectrograph on the Magellan-Baade telescope in 2016 September.
We also observed two partially overlapping 29.5' diameter fields in
Sculptor using the Michigan/Magellan Fiber System (M2FS) on the
Magellan-Clay telescope. We employed the low-resolution mode of M2FS,
producing R=2000 spectra covering 3700-5700Å.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table5.dat 131 27 Stellar parameters and abundances
from Magellan/MagE spectra
table6.dat 99 100 Magellan-Clay/M2FS measurements
--------------------------------------------------------------------------------
See also:
V/65 : Spectroscopically Selected Halo K Giants (Ratnatunga+ 1989)
J/AJ/103/1987 : Stars of very low metal abundance (Beers+ 1992)
J/AJ/117/981 : Estimation of stellar metal abundance. II. (Beers+, 1999)
J/AJ/130/1065 : Sculptor dwarf spheroidal galaxy members (Coleman+, 2005)
J/AJ/130/2804 : Carbon abundances in metal-poor stars (Rossi+, 2005)
J/ApJ/655/492 : Equivalent widths of 26 metal-poor stars (Aoki+, 2007)
J/ApJ/682/1217 : Abundances in red giants in 7 GCs (Kirby+, 2008)
J/ApJ/705/328 : Abundance measurements in Sculptor dSph (Kirby+, 2009)
J/ApJS/182/80 : Rare earth abundances (Sneden+, 2009)
J/AJ/137/3100 : Radial velocities of 4 dSph galaxies (Walker+, 2009)
J/ApJ/724/341 : Nucleosynthesis of massive metal-free stars (Heger+, 2010)
J/ApJS/191/352 : Abundances in stars of MW dwarf satellites (Kirby+, 2010)
J/ApJ/711/350 : Metal-poor giant Boo-1137 abundances (Norris+, 2010)
J/AJ/144/168 : Spectroscopy of Scl 1019417 and UMi 20103 (Kirby+, 2012)
J/ApJ/779/102 : Metallicities of RGB stars in dwarf galaxies (Kirby+, 2013)
J/ApJS/210/23 : Line intensities in CN transitions (Brooke+, 2014)
J/A+A/571/A47 : Linelist of 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 very low metal abundance. VI. (Roederer+, 2014)
J/ApJS/214/26 : Line lists for CN isotopes transitions (Sneden+, 2014)
J/ApJ/807/171 : SkyMapper Survey metal-poor star spectro. (Jacobson+, 2015)
J/ApJ/801/125 : Carbon in red giants in GCs and dSph galaxies (Kirby+, 2015)
J/ApJ/802/93 : Abundance analysis of 5 stars in Sculptor (Simon+, 2015)
J/A+A/580/A129 : Sulphur in the Sculptor dSph (Skuladottir+, 2015)
J/A+A/574/A129 : First CEMP star in the Sculptor dSph (Skuladottir+, 2015)
J/ApJ/817/53 : Fe-group abundance analysis in HD84937 (Sneden+, 2016)
J/ApJ/833/20 : Carbon-enhanced metal-poor star abundances (Yoon+, 2016)
J/A+A/606/A71 : dSph RGB abundance and velocities (Skuladottir+, 2017)
Byte-by-byte Description of file: table5.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 A11 --- ID Source name
13- 17 A5 --- f_ID [abd, ] Flag(s) on ID (1)
19- 21 F3.1 arcsec Slit [0.7/1.0] Slit width
23- 26 F4.2 [cm/s2] log(g) [1/3.6] log surface gravity
28- 31 I4 K Teff [4513/5518] Effective temperature
33 A1 --- l_[Fe/H]KP Limit flag on [Fe/H]KP
35- 39 F5.2 [Sun] [Fe/H]KP [-4/-2.1]? log Fe/H number abundance
from the KP index
41- 44 F4.2 [Sun] e_[Fe/H]KP [0.1/0.4]? Uncertainty in [Fe/H]KP
46 A1 --- l_A(C) Limit flag on A(C)
48- 51 F4.2 [Sun] A(C) [4.8/8.3] Absolute carbon abundance
53- 56 F4.2 [Sun] e_A(C) [0.1/0.4]? Uncertainty in A(C)
58 A1 --- l_[C/Fe] Limit flag on [C/Fe]
59- 63 F5.2 [Sun] [C/Fe] [-0.6/2.6]? log C/Fe number abundance
65- 68 F4.2 [Sun] e_[C/Fe] [0.1/0.3]? Uncertainty in [C/Fe]
70- 73 F4.2 [Sun] [C/Fe]c [0/0.8]? log Fe/H number abundance correction
75 A1 --- l_[C/Fe]c Limit flag on [C/Fe]corr
76- 80 F5.2 [Sun] [C/Fe]f [-0.5/2.7]? Final log C/Fe number abundance
82- 85 F4.2 [Sun] e_[C/Fe]f [0.1/0.3]? Uncertainty in [C/Fe]final
87- 91 F5.2 [Sun] [Ba/H] [-0.7/0.8]? log Ba/H number abundance
92 A1 --- u_[Ba/H] Uncertainty flag on [Ba/H] (2)
94-111 F18.15 deg RAdeg Right ascension (J2000) (3)
113-131 F19.15 deg DEdeg Declination (J2000) (3)
--------------------------------------------------------------------------------
Note (1): Flag as follows:
a = Stellar parameters and [Fe/H] for CS29497-034 are from
Aoki+ (2007, J/ApJ/655/492).
b = The first 11 stars were observed as a follow-up to M2FS observations to
confirm [C/Fe] measurements; and stars without this flag were observed
immediately after the initial IMACS observations as EMP candidates.
d = The S/N over the Ca II K feature was too low to estimate a [Fe/H]
from the KP index. The M2FS [Fe/H] was assumed when calculating
[C/Fe] (See Table 6).
Note (2): Indicates large and uncertain error bars.
Note (3): Coordinates sent by the author, except for CS29497-034 from SIMBAD.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table6.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 15 A15 --- Type Object type (1)
17- 25 A9 --- ID Source name
27 A1 --- f_ID [d] Flag on ID (2)
29- 30 I2 h RAh [0/1] Hour of Right Ascension (J2000)
32- 33 I2 min RAm Minute of Right Ascension (J2000)
35- 39 F5.2 s RAs Second of Right Ascension (J2000)
41- 41 A1 --- DE- [-] Sign of the Declination (J2000)
42- 43 I2 deg DEd [33] Degree of Declination (J2000)
45- 46 I2 arcmin DEm [31/59] Arcminute of Declination (J2000)
48- 52 F5.2 arcsec DEs Arcsecond of Declination (J2000)
54- 57 F4.2 [cm/s2] log(g) [0.9/3.6] log surface gravity
59- 62 I4 K Teff [4451/5493] Effective temperature
64 A1 --- l_[Fe/H] Limit flag on [Fe/H]
66- 70 F5.2 [Sun] [Fe/H] [-3.8/-0.6] log Fe/H number abundance
72- 75 F4.2 [Sun] e_[Fe/H] [0.1/0.9]? Uncertainty in [Fe/H]
77 A1 --- l_[C/Fe] Limit flag on [C/Fe]
78- 82 F5.2 [Sun] [C/Fe] [-1.4/0.9]? log C/Fe number abundance
84- 87 F4.2 [Sun] e_[C/Fe] [0.2/0.7]? Uncertainty in [C/Fe]
89- 92 F4.2 [Sun] [C/Fe]c [0/0.8]? log Fe/H number abundance correction
94 A1 --- l_[C/Fe]f Limit flag on [C/Fe]final
95- 99 F5.2 [Sun] [C/Fe]f [-0.9/1.1]? Final log C/Fe number abundance
--------------------------------------------------------------------------------
Note (1): The "RGB" stars lie on the RGB of Sculptor and stars in the "Blueward
of RGB" lie blueward of the RGB (see Figure 1).
Note (2):
d = The star is classified as likely CH-strong, Ba-strong, or CEMP-s star
due to the presence of saturated carbon features
(see Sections 4.6 and 5.1).
--------------------------------------------------------------------------------
History:
From electronic version of the journal -
Coordinates of Table 5 sent by the author (except for BPS CS29497-034).
Acknowledgements:
Ani Chiti [Massachusetts Institute of Technology, Cambridge]
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 13-Feb-2019