J/ApJ/872/137 Abundances of red clump & RGB stars with APOGEE (Shetrone+, 2019)
Constraining metallicity-dependent mixing and extra mixing using [C/N] in alpha-
rich field giants.
Shetrone M., Tayar J., Johnson J.A., Somers G., Pinsonneault M.H.,
Holtzman J.A., Hasselquist S., Masseron T., Meszaros S., Jonsson H.,
Hawkins K., Sobeck J., Zamora O., Garcia-Hernandez D.A.
<Astrophys. J., 872, 137 (2019)>
=2019ApJ...872..137S 2019ApJ...872..137S
ADC_Keywords: Abundances; Spectra, infrared; Stars, giant
Keywords: infrared: stars ; stars: abundances
Abstract:
Internal mixing on the giant branch is an important process which
affects the evolution of stars and the chemical evolution of the
galaxy. While several mechanisms have been proposed to explain this
mixing, better empirical constraints are necessary. Here, we use [C/N]
abundances in 26097 evolved stars from the SDSS-IV/APOGEE-2 DR14 to
trace mixing and extra mixing in old field giants with
-1.7<[Fe/H]<0.1. We show that the APOGEE [C/N] ratios before any
dredge-up occurs are metallicity dependent, but that the change in
[C/N] at the first dredge-up is metallicity independent for stars
above [Fe/H]~-1. We identify the position of the red giant branch
(RGB) bump as a function of metallicity, note that a
metallicity-dependent extra mixing episode takes place for
low-metallicity stars ([Fe/H]<-0.4) 0.14dex in logg above the bump,
and confirm that this extra mixing is stronger at low metallicity,
reaching Δ[C/N]=0.58dex at [Fe/H]=-1.4. We show evidence for
further extra mixing on the upper giant branch, well above the bump,
among the stars with [Fe/H]<-1.0. This upper giant branch mixing is
stronger in the more metal-poor stars, reaching 0.38 dex in [C/N] for
each 1.0dex in logg. The APOGEE [C/N] ratios for red clump (RC) stars
are significantly higher than for stars at the tip of the RGB,
suggesting additional mixing processes occur during the helium flash
or that unknown abundance zero points for C and N may exist among the
RC sample. Finally, because of extra mixing, we note that current
empirical calibrations between [C/N] ratios and ages cannot be naively
extrapolated for use in low-metallicity stars specifically for those
above the bump in the luminosity function.
Description:
APOGEE-2 is a part of the Sloan Digital Sky Survey IV
(Blanton+ 2017AJ....154...28B 2017AJ....154...28B) and is collecting high-resolution
(R=22500) spectra of ∼300000 stars across the Milky Way
(Zasowski+ 2017AJ....154..198Z 2017AJ....154..198Z) using the Sloan Foundation Telescope
at Apache Point Observatory.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 67 26097 Sample data
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See also:
VII/202 : Globular Clusters in the Milky Way (Harris, 1997)
V/147 : The SDSS Photometric Catalogue, Release 12 (Alam+, 2015)
III/284 : APOGEE-2 data from DR16 (Majewski+, 2017)
J/A+A/354/169 : Metal-poor field stars abundances (Gratton+, 2000)
J/ApJS/215/19 : APOKASC catalog of Kepler red giants (Pinsonneault+, 2014)
J/ApJ/797/21 : Carbon-enhanced metal-poor stars (Placco+, 2014)
J/A+A/580/A24 : Abundances in dwarfs, subgiants, and giants (da Silva+, 2015)
J/ApJ/801/125 : Carbon in red giants in GCs and dSph galaxies (Kirby+, 2015)
J/ApJS/225/32 : Extended abundance analysis of cool stars (Brewer+, 2016)
J/AJ/151/144 : ASPCAP weights for APOGEE chemical elements (Garcia+, 2016)
J/MNRAS/456/3655 : Masses and ages of red giants (Martig+, 2016)
J/ApJ/823/114 : The Cannon: a new approach to determine masses (Ness+, 2016)
J/MNRAS/466/3344 : Red-giant stars classification (Elsworth+, 2017)
J/AJ/156/126 : Stellar param. & abund. from BACCHUS analysis (Jonsson+, 2018)
J/ApJS/239/32 : APOKASC-2 catalog of Kepler evolved stars (Pinsonneault+, 2018)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 18 A18 --- ID APOGEE identifier (2MHHMMSSss+DDMMSSs)
20- 25 F6.3 [Sun] [Fe/H] [-1.7/0.1] Metallicity
27- 31 F5.3 [Sun] [A/M] [0.14/0.7] log α/Fe abundance ratio
33- 37 F5.3 [cm/s2] log(g) [0.8/3.7] log surface gravity
39- 44 F6.3 [Sun] [C/Fe] [-0.8/1] log C/Fe abundance ratio
46- 50 F5.3 [Sun] e_[C/Fe] [0.009/0.2] The 1σ uncertainty in [C/Fe]
52- 57 F6.3 [Sun] [N/Fe] [-0.96/1.1] log N/Fe abundance ratio
59- 63 F5.3 [Sun] e_[N/Fe] [0.013/0.3] The 1σ uncertainty in [N/Fe]
65- 67 A3 --- Class Classification (1)
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Note (1): Class as follows:
RC = red clump stars (5624 occurrences);
RGB = red giant branch (20473 occurrences).
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 05-Aug-2020