Query : 2005A&A...440..901G

2005A&A...440..901G - Astronomy and Astrophysics, volume 440, 901-908 (2005/9-4)

Precise reddening and metallicity of NGC 6752 from FLAMES spectra.


Abstract (from CDS):

Accurate reddenings for Globular Clusters could be obtained by comparing the colour-temperature relation obtained using temperatures from a reddening-free indicator (Hα) with that given by standard colour-temperature calibrations. The main difficulty in such derivations is the large errors in temperatures for individual stars due to uncertainties on the removal of instrumental signature for each individual star. The large multiplexing opportunity offered by FLAMES at VLT2 allowed us to obtain spectra centred on Hα at a resolution of R=6000 and 5<S/N<50 for 120 stars near the turn-off of NGC 6752 with GIRAFFE from a single 1300 seconds exposure. This set of spectra was used to derive effective temperatures from fittings of Hα profiles with typical errors of about ±200K and reddening estimates with individual errors of 0.05mag. Averaging all individual reddenings, a high precision reddening estimate was obtained for the cluster: E(B-V)=0.046±0.005. The same exposure provided UVES spectra of seven stars near the red giant branch bump at a resolution of 40000 and 20<S/N<40. These spectra, combined with temperatures from colours (corrected for our high precision reddening value), provided Fe abundances with internal errors of 0.026dex and with average metallicity [Fe/H]=-1.48±0.01±0.06dex (random + systematic). Abundances were obtained for several other elements, allowing e.g. an accurate estimate of the ratio between the α-elements and Fe ([α/Fe]=+0.27±0.01). The O-Na anticorrelation is evident from our UVES data, in agreement with past results. This analysis shows the power of FLAMES for analysis of globular clusters: the accurate reddenings and metal abundances obtained by a procedure like that described here, combined with distance determinations from cluster dynamics or main sequence fitting, and high quality colour-magnitude diagrams, could allow derivation of ages with errors below 1Gyr for individual globular clusters.

Abstract Copyright:

Journal keyword(s): stars: abundances - stars: evolution - stars: Population II - Galaxy: globular clusters: general - Galaxy: formation

VizieR on-line data: <Available at CDS (J/A+A/440/901): table3.dat table4.dat table7.dat>

Nomenclature: Tables: Cl* NGC 6752 GBC NNNNN N=120 among (Nos 1538-49342).

Errata: erratum vol. 442, p. 947 (2005)

Status at CDS : All or part of tables of objects will not be ingested in SIMBAD.

Simbad objects: 3

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Number of rows : 3
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
1 NGC 104 GlC 00 24 05.359 -72 04 53.20   5.78 4.09     ~ 3722 0
2 NGC 6397 GlC 17 40 42.09 -53 40 27.6   7.39 5.17     ~ 1876 1
3 NGC 6752 GlC 19 10 52.11 -59 59 04.4   6.96 6.28     ~ 1894 0

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