J/ApJ/802/93 Chemical abundance analysis of 5 stars in Sculptor (Simon+, 2015)
Chemical signatures of the first supernovae in the Sculptor dwarf spheroidal
galaxy.
Simon J.D., Jacobson H.R., Frebel A., Thompson I.B., Adams J.J.,
Shectman S.A.
<Astrophys. J., 802, 93 (2015)>
=2015ApJ...802...93S 2015ApJ...802...93S
ADC_Keywords: Abundances ; Equivalent widths ; Stars, metal-deficient ;
Keywords: galaxies: dwarf; galaxies: individual: Sculptor dSph;
galaxies: stellar content; stars: abundances
Abstract:
We present a homogeneous chemical abundance analysis of five of the
most metal-poor stars in the Sculptor dwarf spheroidal galaxy. We
analyze new and archival high resolution spectroscopy from
Magellan/MIKE and VLT/UVES and determine stellar parameters and
abundances in a consistent way for each star. Two of the stars in our
sample, at [Fe/H]=-3.5 and [Fe/H]=-3.8, are new discoveries from our
Ca K survey of Sculptor, while the other three were known in the
literature. We confirm that Scl 07-50 is the lowest metallicity star
identified in an external galaxy, at [Fe/H]=-4.1. The two most
metal-poor stars both have very unusual abundance patterns, with
striking deficiencies of the α elements, while the other three
stars resemble typical extremely metal-poor Milky Way halo stars. We
show that the star-to-star scatter for several elements in Sculptor is
larger than that for halo stars in the same metallicity range. This
scatter and the uncommon abundance patterns of the lowest metallicity
stars indicate that the oldest surviving Sculptor stars were enriched
by a small number of earlier supernovae, perhaps weighted toward
high-mass progenitors from the first generation of stars the galaxy
formed.
Description:
We obtained spectra centered on the CaK line of ∼2000 stars with the
IMACS spectrograph from 2009-2011. Scl 66402 and Scl 1114296 were
two of the stars with the smallest CaK equivalent widths (EWs) in the
sample, marking them as likely extremely meta-poor (EMP) stars. We
obtained medium resolution Magellan/MagE spectra of them in 2010
December, confirming their extremely low metallicity. We then observed
the two stars with Magellan/MIKE at over a wavelength range of
346-941nm on 10 nights between 2013 October and 2014 June,
accumulating a total of 20hr of integration time on Scl 66402 and
9.7hr on Scl 1114296.
Two other EMP stars in Sculptor, Scl 07-49 and Scl 07-50, were
identified by T10 (Tafelmeyer+, 2010A&A...524A..58T 2010A&A...524A..58T) who obtained
R∼40000 spectra of these stars with VLT/UVES. S1020549 was confirmed
as an EMP star by Frebel et al. (2010Natur.464...72F 2010Natur.464...72F) with an R∼33000
Magellan/MIKE spectrum.
To ensure that the full sample can be placed on a common abundance
scale we downloaded the reduced spectra from the ESO archive and
re-determine the stellar parameters and chemical abundances.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 90 5 Coordinates and stellar parameters
table2.dat 54 1255 Equivalent widths
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See also:
J/A+A/574/A129 : The First CEMP star in the Sculptor dSph (Skuladottir+, 2015)
J/AJ/147/136 : Stars of very low metal abundance. VI. (Roederer+, 2014)
J/A+A/562/A146 : Chemical abundances of 8 metal-poor stars (Ishigaki+, 2014)
J/ApJ/779/102 : Metallicities of RGB stars in dwarf galaxies (Kirby+, 2013)
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/A+A/541/A143 : NLTE Corrections of the Ca lines (Spite+, 2012)
J/MNRAS/414/3492 : JHKs photometry of Sculptor dSph galaxy (Menzies+, 2011)
J/ApJ/724/341 : Nucleosynthesis of massive metal-free stars (Heger+, 2010)
J/AJ/137/3100 : Radial velocities of 4 dSph galaxies (Walker+, 2009)
J/ApJ/705/328 : Abundance measurements in Sculptor dSph (Kirby+, 2009)
J/ApJ/681/1524 : Detailed abundances for 28 metal-poor stars (Lai+, 2008)
J/ApJ/652/1585 : Bright metal-poor stars from HES survey (Frebel+, 2006)
J/AJ/131/375 : Phot. & vel. of Sculptor dSph giants (Westfall+, 2006)
J/AJ/130/1065 : Members of the Sculptor dSph galaxy (Coleman+, 2005)
J/A+AS/142/467 : Broadening of metallic lines by H collisions (Barklem+ 2000)
J/AJ/110/2747 : Stars in Sculptor dwarf spheroidal galaxy (Schweitzer+ 1995)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 13 A13 --- Name Star name
15- 16 I2 h RAh [0/1] Hour of Right Ascension (J2000) (1)
18- 19 I2 min RAm Minute of Right Ascension (J2000) (1)
21- 25 F5.2 s RAs Second of Right Ascension (J2000) (1)
27 A1 --- DE- [-] Sign of the Declination (J2000) (1)
28- 29 I2 deg DEd [33/34] Degree of Declination (J2000) (1)
31- 32 I2 arcmin DEm Arcminute of Declination (J2000) (1)
34- 37 F4.1 arcsec DEs Arcsecond of Declination (J2000) (1)
39- 43 F5.2 mag Vmag [18.3/19.2] V-band magnitude (1)
45- 48 F4.2 mag V-I V-I color index (1)
50- 53 F4.2 mag V-Ks V-Ks color index (1)(2)
55- 58 I4 K Teff [4495/4945] Derived stellar effective
temperature
60- 62 I3 K e_Teff [150] Uncertainty in Teff
64- 67 F4.2 [cm/s2] log(g) [0.8/2] Log derived stellar surface gravity
69- 71 F3.1 [cm/s2] e_log(g) [0.3] Uncertainty in log(g)
73- 76 F4.2 km/s Vt [1.8/2.7] Microturbulence velocity
78- 80 F3.1 km/s e_Vt [0.3] Uncertainty in Vt
82- 86 F5.2 [Sun] [Fe/H] [-4.1/-3.3] Iron to hydrogen abundance ratio
relative to the Sun
88- 90 I3 --- S/N [76/204] 535nm signal to noise ratio (3)
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Note (1): Coordinates and optical (V, I) magnitudes are taken from
Coleman et al. (2005, J/AJ/130/1065).
Note (2): Ks magnitudes from Menzies et al. (2011, J/MNRAS/414/3492).
Note (3): The signal-to-noise ratio is given per Angstrom, measured
at a wavelength of 5350 Angstrom.
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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- 13 A13 --- Name Star name
15- 19 A5 --- Ion Species identifier
21- 27 F7.2 0.1nm lambda [3727.6/6767.8] Wavelength in Angstroms
29- 32 F4.2 eV ExPot [0/4.4]? Excitation Potential χ
34- 38 F5.2 [-] log(gf) [-5/0.7]? Log of the oscillator strength
40- 44 F5.1 10-13m EW [8/196]? Equivalent width (mÅ)
46 A1 --- f_log(A) [s] Abundance derived from sythetic spectrum
48 A1 --- l_log(A) Limit flag on log(A)
50- 54 F5.2 [-] log(A) [-3.4/5.5]? Log number abundance logε
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 24-Jul-2015