2020A&A...640A..87M


C.D.S. - SIMBAD4 rel 1.7 - 2020.10.26CET13:42:31

2020A&A...640A..87M - Astronomy and Astrophysics, volume 640A, 87-87 (2020/8-1)

Facing problems in the determination of stellar temperatures and gravities: Galactic globular clusters.

MUCCIARELLI A. and BONIFACIO P.

Abstract (from CDS):

We analysed red giant branch stars in 16 Galactic globular clusters, computing their atmospheric parameters both from the photometry and from excitation and ionisation balances. The spectroscopic parameters are lower than the photometric ones and this discrepancy increases with decreasing metallicity, reaching differences of ∼350K in effective temperature and ∼1dex in surface gravity at [Fe/H]~-2.5dex. We demonstrate that the spectroscopic parameters are inconsistent with the position of the stars in the colour-magnitude diagram, providing overly low temperatures and gravities, and predicting that the stars are up to about 2.5 magnitudes brighter than the observed magnitudes. The parameter discrepancy is likely due to inadequacies in the adopted physics; in particular the assumption of a one-dimensional geometry could be the origin of the observed slope between iron abundances and excitation potential that leads to low temperatures. However, the current modelling of 3D/NLTE radiative transfer for giant stars seems to be unable to totally erase this slope. We conclude that the spectroscopic parameters are incorrect for metallicity lower than -1.5dex and that photometric temperatures and gravities should be adopted for these red giant stars. We provide a simple relation to correct the spectroscopic temperatures in order to put them onto a photometric scale.

Abstract Copyright: © ESO 2020

Journal keyword(s): globular clusters: general - stars: abundances - stars: atmospheres - techniques: spectroscopic

CDS comments: stars NGC 4590-3584, NGC 5904-900073, NGC 7099-7414 and NGC 904-171 not identified.

Simbad objects: 23

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Number of rows : 23

N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2020
#notes
1 NGC 104 GlC 00 24 05.359 -72 04 53.20   5.78 4.09     ~ 3575 0
2 CD-38 245 Pe* 00 46 36.1954714218 -37 39 33.555736375   12.733 11.929 13.39 10.996 KIIvw 204 0
3 NGC 288 GlC 00 52 45.24 -26 34 57.4   10 8.13     ~ 931 0
4 NAME Magellanic Clouds GrG 03 00 -71.0           ~ 5762 1
5 HE 0305-4520 Pe* 03 07 02.1830662441 -45 09 00.544178397   14.791 13.979 13.473 12.973 ~ 9 0
6 NGC 1851 GlC 05 14 06.76 -40 02 47.6   8.80 7.23     ~ 1252 0
7 M 79 GlC 05 24 10.59 -24 31 27.3   9.21 8.16     ~ 722 0
8 NGC 2808 GlC 09 12 03.10 -64 51 48.6   7.77 5.69     ~ 1254 0
9 TYC 4928-1438-1 Pe* 11 18 35.8833462324 -06 50 45.017807583   12.577 11.606 10.822 10.099 CEMP-no 15 0
10 M 68 GlC 12 39 27.98 -26 44 38.6   10.26 7.96     ~ 886 0
11 HD 122563 Pe* 14 02 31.8456299772 +09 41 09.942736952 7.47 7.10 6.19 5.37 4.79 G8:III:Fe-5 760 0
12 * alf Boo RG* 14 15 39.67207 +19 10 56.6730 2.46 1.18 -0.05 -1.03 -1.68 K1.5IIIFe-0.5 2148 0
13 NGC 5634 GlC 14 29 37.28 -05 58 35.1   10.69 10.05     ~ 249 0
14 NGC 5694 GlC 14 39 36.52 -26 32 18.0   11.58 10.89     ~ 269 0
15 NGC 5824 GlC 15 03 58.612 -33 04 06.70   10.28 9.56     ~ 344 0
16 M 5 GlC 15 18 33.22 +02 04 51.7   7.34 5.95     ~ 1782 0
17 M 80 GlC 16 17 02.41 -22 58 33.9           ~ 623 0
18 NGC 6397 GlC 17 40 42.09 -53 40 27.6   7.39 5.17     ~ 1808 1
19 NGC 6752 GlC 19 10 52.11 -59 59 04.4   6.96 6.28     ~ 1817 0
20 M 55 GlC 19 39 59.71 -30 57 53.1     6.49     ~ 764 0
21 M 15 GlC 21 29 58.33 +12 10 01.2   3       ~ 2922 0
22 M 30 GlC 21 40 22.12 -23 10 47.5     7.10     ~ 925 0
23 HE 2141-3741 Pe* 21 44 51.1647173336 -37 27 55.017357431   14.10 13.47     CEMP-no 53 0

    Equat.    Gal    SGal    Ecl

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2020.10.26-13:42:31

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