J/MNRAS/481/373 Spectroscopic observations on M4 AGB stars (MacLean+, 2018)
On the AGB stars of M 4: a robust disagreement between spectroscopic
observations and theory.
MacLean B.T., Campbell S.W., Amarsi A.M., Nordlander T., Cottrell P.L.,
De Silva G.M., Lattanzio J., Constantino T., D'Orazi V., Casagrande L.
<Mon. Not. R. Astron. Soc., 481, 373-395 (2018)>
=2018MNRAS.481..373M 2018MNRAS.481..373M (SIMBAD/NED BibCode)
ADC_Keywords: Abundances ; Clusters, globular ; Stars, giant ;
Photometry, UBVRI ; Photometry, infrared
Keywords: stars: abundances - stars: AGB and post-AGB - Galaxy: abundances -
Galaxy: formation - Galaxy: globular clusters: general
Abstract:
Several recent spectroscopic investigations have presented conflicting
results on the existence of Na-rich asymptotic giant branch (AGB)
stars in the Galactic globular cluster M 4 (NGC 6121). The studies
disagree on whether or not Na-rich red giant branch (RGB) stars evolve
to the AGB. For a sample of previously published HERMES/AAT AGB and
RGB stellar spectra, we present a re-analysis of O, Na, and Fe
abundances, and a new analysis of Mg and Al abundances; we also
present CN band strengths for this sample, derived from low-resolution
AAOmega spectra. Following a detailed literature comparison, we find
that the AGB samples of all studies consistently show lower abundances
of Na and Al, and are weaker in CN, than RGB stars in the cluster.
This is similar to recent observations of AGB stars in NGC 6752 and
M 62. In an attempt to explain this result, we present new
theoretical stellar evolutionary models for M 4; however, these
predict that all stars, including Na-rich RGB stars, evolve on to the
AGB. We test the robustness of our abundance results using a variety
of atmospheric models and spectroscopic methods; however, we do not
find evidence that systematic modelling uncertainties can explain the
apparent lack of Na-rich AGB stars in M 4. We conclude that an
unexplained, but robust, discordance between observations and theory
remains for the AGB stars in M 4.
Description:
The reduced M 4 high-resolution spectra and photometry used in this
study are the same as those used in ML16 (2016MNRAS.460L..69M 2016MNRAS.460L..69M).
Spectra were collected in 2014 August and 2015 July, using 2dF+HERMES
on the AAT which provides R=28000 resolution spectra in four narrow
spectral windows (Sheinis et al. 2015JATIS...1c5002S 2015JATIS...1c5002S). In total, 121
targets were observed with average signal-to-noise ratio (SNR) of 70.
The software package 2dfdr (AAO Software Team 2015ascl.soft05015A,
v6.5) was used to reduce the spectral data for analysis. Photometry was
taken from Momany et al. (2003A&A...407..303M 2003A&A...407..303M, UBVI photometry and
target IDs) and 2MASS (JHK photometry; Skrutskie et al.
2006AJ....131.1163S 2006AJ....131.1163S, Cat. VII/233).
M 4 suffers from significant differential reddening, however constant
reddening values were used in ML16. Here we improve upon this, with
each star corrected using the reddening map of Hendricks et al.
(2012AJ....144...25H 2012AJ....144...25H). Individual corrections are included in Table 1.
We found an average reddening value of E(B-V)=0.37 and a 1σ
star-to-star scatter of ±0.02. This differential reddening map,
however, does not cover our entire sample, and some stars were only
adjusted according to the average reddening value.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 80 121 M4 target details
table3.dat 38 121 Stellar parameters for each star in our M4 sample
table5.dat 69 121 Chemical abundances for each star in our
M4 sample
--------------------------------------------------------------------------------
See also:
VII/233 : The Two Micron All Sky Survey (2MASS)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- ID Target ID (1)
7- 9 A3 --- Type Star type (AGB : asymptotic giant branch star
or RGB : red giant branch star)
11- 33 A23 --- 2MASS 2MASS Name (2MASS JHHMMSSss+DDMMSSsA)
35- 39 F5.2 mag Vmag V-band magnitude (1)
41- 45 F5.2 mag Bmag B-band magnitude (1)
47- 51 F5.2 mag Umag ? U-band magnitude (1)
53- 57 F5.2 mag Imag ? I-band magnitude (1)
59- 63 F5.2 mag Jmag ? J-band magnitude (2)
65- 69 F5.2 mag Hmag ? H-band magnitude (2)
71- 75 F5.2 mag Kmag ? K-band magnitude (2)
77- 80 F4.2 mag E(B-V) ? Reddening value (3)
--------------------------------------------------------------------------------
Note (1): UBVI photometry and target ID from Momany et al. (2003A&A...407..303M 2003A&A...407..303M)
Note (2): 2MASS JHK photometry taken Skrutskie et al. (2006AJ....131.1163S 2006AJ....131.1163S,
Cat. VII/233). Gaps in 2MASS data represent targets with low-quality
flags.
Note (3): Stars for which no reddening value is listed were outside the
reddening map of Hendricks et al. (2012AJ....144...25H 2012AJ....144...25H), and were
corrected according to the average reddening value of E(B-V)=0.37
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- ID Target ID
7- 9 A3 --- Type Star type (AGB : asymptotic giant branch star
or RGB : red giant branch star)
11- 14 I4 K Teffsp Spectroscopic effective temperatures (1)
16- 18 I3 K e_Teffsp Error on Teffsp (1)
20- 23 F4.2 [cm/s2] logg Surface gravity (2)
25- 28 F4.2 km/s vt Microturbulence values (1)
30- 33 F4.2 km/s e_vt Error on vt (1)
35- 38 I4 K Teffph Effective temperatures estimated from
photometric colour-Teff relations used
in the PHOBOS test
--------------------------------------------------------------------------------
Note (1): Values determined using PHOBOS version 2.
Note (2): logg values were calculated based on the empirical relation from
Alonso et al. (1999A&AS..140..261A 1999A&AS..140..261A)
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table5.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- ID Target ID
7- 9 A3 --- Type Star type (AGB : asymptotic giant branch star
or RGB : red giant branch star)
11- 14 F4.2 [-] loge(FeI) FeI abundance (1)
16- 19 F4.2 [-] e_loge(FeI) Error on loge(FeI) (2)
21- 24 F4.2 [-] loge(FeII) FeII abundance (1)
26- 29 F4.2 [-] e_loge(FeII) Error on loge(FeII) (2)
31- 34 F4.2 [-] loge(O) O abundance (1)
36- 39 F4.2 [-] e_loge(O) Error on loge(O) (2)
41- 44 F4.2 [-] loge(Na) Na abundance (1)
46- 49 F4.2 [-] e_loge(Na) Error on loge(Na) (2)
51- 54 F4.2 [-] loge(Mg) Mg abundance (1)
56- 59 F4.2 [-] e_loge(Mg) Error on loge(Mg) (2)
61- 64 F4.2 [-] loge(Al) Al abundance (1)
66- 69 F4.2 [-] e_loge(Al) Error on loge(Al) (2)
--------------------------------------------------------------------------------
Note (1): We present all abundances as logε(X)=log10(NX/NH)+12.0,
where NX represents the number density of atoms of an element X.
This eliminates many systematic offsets that may exist in [X/Fe]
and [X/H] ratios.
O, Na, and Al abundances were corrected for non-LTE effects.
Note (2): Abundance uncertainties reflect line-to-line scatter (1σ), and
do not take atmospheric sensitivities into account
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 03-Jun-2022