J/AJ/159/50 Identifying multiple populations in M71 using CN (Gerber+, 2020)
Identifying multiple populations in M71 using CN.
Gerber J.M., Friel E.D., Vesperini E.
<Astron. J., 159, 50 (2020)>
=2020AJ....159...50G 2020AJ....159...50G
ADC_Keywords: Clusters, globular; Effective temperatures; Magnitudes, absolute;
Radial velocities; Stars, giant; Abundances;
Stars, horizontal branch; Spectra, optical
Keywords: Globular star clusters ; Stellar astronomy ; Spectroscopy
Abstract:
We have observed their cyanogen CN features at ∼3800 and 4120Å as
well as the CH band at ∼4300Å for 145 evolved stars in the Galactic
globular cluster M71 using the multi-object spectrograph, Hydra, on
the Wisconsin-Indiana-Yale- NOAO-3.5 m telescope. We use these
measurements to create two δCN indices finding that both
distributions are best fit by two populations: a CN-enhanced and
CN-normal. We find that 42%±4% of the red giant branch stars in
our sample are CN-enhanced. The percentage of CN-enhanced is
40%±13% for the asymptotic giant branch and 33%±9% for the
horizontal branch stars (HB stars), which suggests there are no
missing second generation stars at these stages of stellar evolution.
The two generations also separate in magnitude and color on the HB,
which allows us to find the difference in He abundance between the two
populations by fitting appropriate zero-age horizontal branches. The
broad range of distances from the cluster's center covered by our
sample allows us to study the dependence of the ratio of the number of
first to second population stars on the distance from the cluster's
center, and we find that this ratio does not vary radially and that
the two populations are spatially mixed. Finally, we compare our
identification of multiple populations with the classification based
on the Na-O anti-correlation and the Hubble Space Telescope UV
photometry, and we find good agreement with both methods.
Description:
In this paper, we continue our previous work on multiple populations
in globular clusters (GCs) (Gerberi+, 2018, J/AJ/156/6) with a sample
size of approximately 150 stars in M71.
We obtained 171 combined spectra of stars within a 18' by 18' grid
around the center of M71 between four observation runs in 2014 August,
2015 June, 2016 June, and 2017 June using the
Wisconsin-Indiana-Yale-NOAO (WIYN) 3.5m Telescope and Hydra, a
multi-object, fiber-fed bench spectrograph. The Bench Spectrograph was
used with the "600@10.1" grating, which resulted in spectra with a
∼4.5Å/pixel dispersion covering a range of ∼2800Å. The spectra
taken during the 2014 run are centered on a wavelength of 4900Å,
while the spectra taken in subsequent runs are centered on a
wavelength of 5100Å. Ten different configurations of fibers were
necessary to obtain our full sample size.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 151 151 Stars measured in M71
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See also:
VII/195 : Globular Clusters in the Milky Way (Harris, 1996)
VII/202 : Globular Clusters in the Milky Way (Harris, 1997)
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+, 2003)
J/A+AS/144/227 : BV photometry of M71 (Geffert+, 2000)
J/AJ/125/197 : CN abundances of the 47 Tuc main sequence (Harbeck+, 2003)
J/AJ/127/1588 : 47 Tuc main-sequence star abundances (Briley+, 2004)
J/ApJ/638/1018 : Equivalent widths for giant stars in M13 and M71 (Yong+, 2006)
J/A+A/486/941 : Abundances in M71 (NGC 6838) (Alves-Brito+, 2008)
J/ApJ/687/1019 : Chandra X-ray observations of M71 (Elsner+, 2008)
J/A+A/505/139 : Abundances red giants 17 globular clusters (Carretta+, 2009)
J/A+A/505/117 : Abundances red giants 15 globular clusters (Carretta+, 2009)
J/ApJ/754/L38 : Abundances & radial velocities of M13 giants (Johnson+, 2012)
J/other/Nat/498.198 : Na abundances in NGC6752 (Campbell+, 2013)
J/ApJ/810/148 : Red giant abundances in NGC 2808 (Carretta, 2015)
J/AJ/149/53 : Rad. velocities 12 Milky Way globular clusters (Kimmig+, 2015)
J/ApJ/801/125 : Carbon in red giants in GCs and dSph galaxies (Kirby+, 2015)
J/A+A/573/A70 : UBVI photometry in 3 globular clusters (Nardiello+, 2015)
J/ApJ/824/5 : Chemical abundances in NGC 5024 (M53) (Boberg+, 2016)
J/AJ/151/7 : Globular & open clusters observed SDSS/SEGUE (Morrison+, 2016)
J/AJ/156/6 : Light element abundances RGB & AGB stars in M10 (Gerber+,2018)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- ID [2/2299] Index number (1)
6- 18 F13.9 deg RAdeg [298.36/298.52] Right Ascension (J2000) (1)
20- 32 F13.10 deg DEdeg [18.72/18.85] Declination (J2000) (1)
34- 37 I4 km/s HRV [-112/30] Heliocentric radial velocity
39- 43 F5.2 mag Vmag [12/18] Apparent V band magnitude (1)
45- 48 F4.2 mag B-V [0.75/1.9] The (B-V) color (1)
50- 54 F5.2 mag VMAG [-1.7/4.2] Absolute V band magnitude
assuming (m-M)v=13.728
56- 71 A16 --- 2MASS 2MASS identifier (HHMMSSss+DDMMSSs; J2000)
if any
73- 76 I4 K Teff [3485/6084] Effective temperature
78- 81 F4.2 [cm/s2] logg [0.19/4.4] log surface gravity
83- 88 F6.3 --- S3839 [-0.7/0.5]?=99.99 The S(3839) index
90- 95 F6.3 --- CN4216 [-0.07/0.5]?=99.99 The CN(4216) index
97-102 F6.3 --- CH4300 [0.08/0.4]?=99.99 The CH(4300) index
104-110 F7.3 --- DS3839 [-0.7/0.5]?=100.144 The δS(3839) index
112-117 F6.3 --- DCN4216 [-0.2/0.3]?=99.838 The δCN(4216) index
119-124 F6.3 [-] [Na/Fe] [-0.1/0.9]?=99.999 log Na/Fe abundance ratio
126-131 F6.3 [-] [O/Fe] [0.05/0.8]?=99.999 log O/Fe abundance ratio
133-138 A6 --- r_[Na/Fe] ? Source reference for [Na/Fe] (2)
140-145 A6 --- r_[O/Fe] ? Source reference for [O/Fe] (2)
147-149 A3 --- OType Branch (3)
151-151 A1 --- Mm [y/n] Membership y=yes (146 occurrences),
n=no (5 occurrences)
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Note (1): Cudworth, 1985AJ.....90...65C 1985AJ.....90...65C (<Cl* NGC 6838 KC NNN> in Simbad)
and private communication.
Note (2): References as follows:
Ram = Ramirez & Cohen 2002AJ....123.3277R 2002AJ....123.3277R (6 occurrences),
Car09a = Carretta+ 2009, J/A+A/505/117 (20 occurrences),
Car09b = Carretta+ 2009, J/A+A/505/139 (2 occurrences),
Cord = Cordero+, 2015ApJ...800....3C 2015ApJ...800....3C (33 occurrences).
Note (3): Branch as follows:
AGB = massive asymptotic giant branch stars (16 occurrences)
HB = horizontal-branch stars (27 occurrences)
RGB = red giant branch stars (105 occurrences)
M = star with spectral type M (3 occurrences)
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History:
From electronic version of the journal
References:
Gerber et al. M10. 2018AJ....156....6G 2018AJ....156....6G Cat. J/AJ/156/6
(End) Prepared by [AAS], Coralie Fix, 05-Mar-2020