J/ApJ/801/125 Carbon in red giants in GCs and dSph galaxies (Kirby+, 2015)
Carbon in red giants in globular clusters and dwarf spheroidal galaxies.
Kirby E.N., Guo M., Zhang A.J., Deng M., Cohen J.G., Guhathakurta P.,
Shetrone M.D., Lee Y.S., Rizzi L.
<Astrophys. J., 801, 125 (2015)>
=2015ApJ...801..125K 2015ApJ...801..125K
ADC_Keywords: Abundances ; Stars, carbon ; Stars, giant ; Spectroscopy
Keywords: galaxies: abundances; galaxies: dwarf; Local Group; stars: abundances;
stars: evolution
Abstract:
We present carbon abundances of red giants in Milky Way (MW) globular
clusters and dwarf spheroidal galaxies (dSphs). Our sample includes
measurements of carbon abundances for 154 giants in the clusters
NGC2419, M68, and M15 and 398 giants in the dSphs Sculptor, Fornax,
Ursa Minor, and Draco. This sample doubles the number of dSph stars
with measurements of [C/Fe]. The [C/Fe] ratio in the clusters
decreases with increasing luminosity above (L/L☉)~=1.6, which
can be explained by deep mixing in evolved giants. The same decrease
is observed in dSphs, but the initial [C/Fe] of the dSph giants is not
uniform. Stars in dSphs at lower metallicities have larger [C/Fe]
ratios. We hypothesize that [C/Fe] (corrected to the initial carbon
abundance) declines with increasing [Fe/H] due to the metallicity
dependence of the carbon yield of asymptotic giant branch stars and
due to the increasing importance of SNe Ia at higher metallicities. We
also identified 11 very carbon-rich giants (eight previously known) in
three dSphs. However, our selection biases preclude a detailed
comparison to the carbon-enhanced fraction of the MW stellar halo.
Nonetheless, the stars with [C/Fe]<+1 in dSphs follow a different
[C/Fe] track with [Fe/H] than the halo stars. Specifically, [C/Fe] in
dSphs begins to decline at lower [Fe/H] than in the halo. The
difference in the metallicity of the [C/Fe] "knee" adds to the
evidence from [α/Fe] distributions that the progenitors of the
halo had a shorter timescale for chemical enrichment than the
surviving dSphs.
Description:
We obtained Keck/DEIMOS spectra of the carbon G band in red giants in
Milky Way (MW) globular clusters (GCs) and dwarf spheroidal galaxies
(dSphs) between 2011 Jul 29 and 2012 Mar 19. The GCs are NGC 2419, NGC
4590 (M68), and NGC 7078 (M15). The dSphs are Sculptor, Fornax, Ursa
Minor, and Draco. See table 1.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 65 16 DEIMOS observations
table2.dat 30 31809 Linelist
table4.dat 144 745 Carbon Abundances
--------------------------------------------------------------------------------
See also:
VII/202 : Globular Clusters in the Milky Way (Harris, 1997)
J/A+A/572/A88 : Measured EWs for Fornax RGB stars (Lemasle+, 2014)
J/A+A/571/A47 : Extensive linelist of CH in atmospheres (Masseron+, 2014)
J/MNRAS/440/1095 : Chemical analysis of CH stars (Karinkuzhi+, 2014)
J/ApJ/762/27 : Most metal-poor stars. III. [Fe/H]≤-3.0 stars (Yong+, 2013)
J/ApJ/760/86 : Equivalent widths for 13 NGC2419 RGB stars (Cohen+, 2012)
J/A+A/544/A73 : BVI photometry of Fornax dSph galaxy (de Boer+, 2012)
J/ApJ/740/60 : EWs for NGC2419 and NGC7099 RGB stars (Cohen+, 2011)
J/AJ/141/175 : Abundances in M15 RGB/RHB stars (Sobeck+, 2011)
J/ApJS/191/352 : Abundances in stars of MW dwarf satellites (Kirby+, 2010)
J/ApJ/719/931 : Chemical evolution of the UMi dSph (Cohen+, 2010)
J/MNRAS/403/1413 : Updated stellar yields from AGB models (Karakas, 2010)
J/ApJ/705/328 : Abundance measurements in Sculptor dSph (Kirby+, 2009)
J/ApJ/701/1053 : Abundances of 8 stars in the Draco dSph (Cohen+, 2009)
J/ApJ/682/1217 : Abundances in red giants in 7 GCs (Kirby+, 2008)
J/AJ/135/1993 : JHK mag of Sculptor dSph RR Lyrae (Pietrzynski+, 2008)
J/MNRAS/375/831 : Draco MegaCam, INT and HST photometry (Segall+, 2007)
J/ApJ/655/492 : Equivalent widths of 26 metal-poor stars (Aoki+, 2007)
J/ApJ/652/1585 : Bright metal-poor stars from HES survey (Frebel+, 2006)
J/A+A/459/423 : VI and [Fe/H] of Fornax dSph RGB stars (Battaglia+, 2006)
J/AJ/132/137 : Extremely metal-poor carbon stars abundances (Cohen+, 2006)
J/AJ/131/375 : Photometry & vel. of Sculptor dSph giants (Westfall+, 2006)
J/AJ/128/1177 : Galactic stellar abundances (Venn+, 2004)
J/AJ/124/3222 : VI photometry of Draco and UMi galaxies (Bellazzini+, 2002)
J/A+A/354/169 : Metal-poor field stars abundances (Gratton+, 2000)
J/PASP/110/533 : BR photometry of Fornax bright stars (Stetson+ 1998)
J/AJ/110/2131 : M/L for Draco and UMi. I. (Armandroff+ 1995)
J/AJ/108/555 : BVI photometry in globular cluster M68 (Walker, 1994)
J/AJ/103/1987 : Stars of very low metal abundance (Beers+ 1992)
J/AJ/99/1831 : M 68 BVRI photometry (Alcaino+ 1990)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Syst Globular cluster or dwarf galaxy
12- 17 A6 --- Slit Slitmask identifier
19- 21 I3 --- Nt [86/169]? Targets number
23- 33 A11 "YYYY/MMM/DD" Date Observation date
35- 37 F3.1 --- AirM [1/1.9] Airmass
39- 41 F3.1 arcsec Seeing [0.6/1.3] Seeing
43- 60 A18 s Exposures Individual exposure time(s)
62- 65 I4 s tExp [1800/6360]? Total exposure time
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 F8.3 0.1nm lambda [4100/4500] Air wavelength
10- 11 I2 --- A [12/13]? Isotope of carbon
12- 13 A2 --- El Name of atom or molecule
15- 16 A2 --- Ion ? Ionization state of atom
18- 23 F6.3 eV EP [0/38.3] Excitation potential
25- 30 F6.3 --- log(gf) [-9/1.5] Logarithm of oscillator strength
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 --- Syst Globular cluster or dwarf galaxy (1)
12- 24 A13 --- Name Object name
26- 27 I2 h RAh Hour of Right Ascension (J2000) (4)
29- 30 I2 min RAm Minute of Right Ascension (J2000) (4)
32- 36 F5.2 s RAs Second of Right Ascension (J2000) (4)
38 A1 --- DE- Sign of the Declination (J2000) (4)
39- 40 I2 deg DEd Degree of Declination (J2000) (4)
42- 43 I2 arcmin DEm Arcminute of Declination (J2000) (4)
45- 48 F4.1 arcsec DEs Arcsecond of Declination (J2000) (4)
50 A1 --- n_mag1 [Bg]? First filter (B or g)
52- 56 F5.2 mag mag1 [13.4/22]? Extinction-corrected magnitude
in Filt1
58 A1 --- n_mag2 [MRVr] Second filter (M, V, R or r)
60- 64 F5.2 mag mag2 [12/22] Extinction-corrected magnitude in Filt2
66 A1 --- n_mag3 [ITi]? Third filter (T, I or i)
68- 72 F5.2 mag mag3 [11/21.3]? Extinction-corrected magnitude
in Filt3
74- 77 F4.2 [Lsun] logL [0.6/3.6] Log of luminosity relative to sun
79- 81 I3 0.1nm-1 S/N [0/225]? Spectral signal-to-noise ratio
per Angstrom
83- 86 I4 K Teff [3743/5966]? Effective temperature
88- 91 F4.2 [cm/s2] log(g) [0.1/3.6]? Surface gravity
93- 97 F5.2 [Sun] [Fe/H] [-3.3/-0.4]? Iron abundance relative to the Sun
99-102 F4.2 [Sun] e_[Fe/H] [0.1/0.4]? Uncertainty in [Fe/H]
104-108 F5.2 [Sun] [a/Fe] [-0.8/1.2]? [α/Fe], α-to-iron ratio
relative to the Sun
110-113 F4.2 [Sun] e_[a/Fe] [0.01/1]? Uncertainty in [a/Fe]
115 A1 --- l_[C/Fe] ? Upper limit flag for [C/Fe]
116-120 F5.2 [Sun] [C/Fe] [-1.6/1.1]? Carbon-to-iron ratio
relative to the Sun
122-125 F4.2 [Sun] e_[C/Fe] [0.1/0.4]? Uncertainty in [C/Fe]
127 A1 --- l_[C/Fe]c ? Upper limit flag for [C/Fe]c
128-132 F5.2 [Sun] [C/Fe]c [-1.3/1.1]? [C/Fe] corrected for
evolutionary state (2)
134-137 F4.2 mag S2CH [0.2/2.4]? S2(CH) index (3)
139-142 F4.2 mag e_S2CH [0/0.51]? Uncertainty in S2(CH)
144 A1 --- C [C] "C" indicates a Carbon star
--------------------------------------------------------------------------------
Note (1): Photometry comes from the following sources:
* NGC 2419 and M15: Stetson (2000PASP..112..925S 2000PASP..112..925S),
* M68: Alcaino et al. 1990 (J/AJ/99/1831); Walker 1994 (J/AJ/108/555);
Stetson (2000PASP..112..925S 2000PASP..112..925S),
* Sculptor: Westfall et al. 2006 (J/AJ/131/375),
* Fornax: Stetson et al. 1998 (J/PASP/110/533),
* Ursa Minor: Bellazzini et al. 2002 (J/AJ/124/3222),
* Draco: Segall et al. 2007 (J/MNRAS/375/831).
Note (2): According to Placco et al. (2014ApJ...797...21P 2014ApJ...797...21P).
Note (3): index defined following Martell et al. (2008PASP..120..839M 2008PASP..120..839M),
as the ratio of G-band (4297-4317Å) to 2 side-band fluxes
(4212-4242Å and 4330-4375Å) in continuum-corrected spectrum.
Note (4): the positions for the stars in M68 named "Wal94-"* are in error
by ∼30arcsec (the position reported in the table is 30"S of actual position)
[Note added at CDS in 2016-Aug]
--------------------------------------------------------------------------------
History:
* 06-Jul-2015: From electronic version of the journal
* 13-Aug-2016: added Note(4) about the positions of stars in M68 from
Wal94 (1994AJ....108..555W 1994AJ....108..555W)
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 06-Jul-2015