2018A&A...610A..66C


Query : 2018A&A...610A..66C

2018A&A...610A..66C - Astronomy and Astrophysics, volume 610A, 66-66 (2018/2-1)

NGC 6705 a young α-enhanced open cluster from OCCASO data.

CASAMIQUELA L., CARRERA R., BALAGUER-NUNEZ L., JORDI C., CHIAPPINI C., ANDERS F., ANTOJA T., MIRET-ROIG N., ROMERO-GOMEZ M., BLANCO-CUARESMA S., PANCINO E., AGUADO D.S., DEL PINO A., DIAZ-PEREZ L. and GALLART C.

Abstract (from CDS):

Context. The stellar [α/Fe] abundance is sometimes used as a proxy for stellar age, following standard chemical evolution models for the Galaxy, as seen by different observational results.
Aim. In this work, we aim to show that the open cluster NGC 6705/M 11 has a significant α-enhancement [α/Fe]>0.1dex, despite its young age (∼300Myr), challenging the current paradigm.
Methods. We used high resolution (R>65000) high signal-to-noise (∼70) spectra of eight red clump stars, acquired within the OCCASO survey. We determined very accurate chemical abundances of several α elements, using an equivalent width methodology (Si, Ca and Ti), and spectral synthesis fits (Mg and O).
Results. We obtain [Si/Fe]=0.13±0.05, [Mg/Fe]=0.14±0.07, [O/Fe]=0.17±0.07, [Ca/Fe]=0.06±0.05, and [Ti/Fe]=0.03±0.03. Our results place these clusters within the group of young [α/Fe]-enhanced field stars recently found by several authors in the literature. The ages of our stars have an uncertainty of around 50 Myr, much more precise than for field stars. By integrating the cluster's orbit in several non-axisymmetric Galactic potentials, we establish the M 11's most likely birth radius as lying between 6.8-7.5kpc from the Galactic centre, not far from its current position.
Conclusions. With the robust open cluster age scale, our results prove that a moderate [α/Fe]-enhancement is no guarantee for a star to be old, and that not all α-enhanced stars can be explained with an evolved blue straggler scenario. Based on our orbit calculations, we further argue against a Galactic bar origin of M 11.

Abstract Copyright: © ESO 2018

Journal keyword(s): Stars: abundances - open clusters and associations: individual: NGC 6705 (M 11)

VizieR on-line data: <Available at CDS (J/A+A/610/A66): table1.dat table2.dat>

Simbad objects: 11

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Number of rows : 11
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2024
#notes
1 NAME Galactic Center reg 17 45 39.60213 -29 00 22.0000           ~ 14383 0
2 NGC 6705 1423 * 18 50 55.8201141624 -06 18 14.788090512   13.041 11.414     KIII: 36 0
3 NGC 6705 1256 * 18 51 00.2328335592 -06 16 59.365374420   13.319 11.586     ~ 31 0
4 NGC 6705 1184 * 18 51 02.0070991104 -06 17 26.535767388   13.030 11.426     ~ 37 0
5 NGC 6705 OpC 18 51 03.8 -06 16 19   6.32 5.8     ~ 410 0
6 NGC 6705 916 RG* 18 51 07.8670021944 -06 17 11.897493432   13.084 11.60     ~ 43 0
7 NGC 6705 779 * 18 51 11.1565074360 -06 14 34.000633752   13.200 11.468     ~ 38 0
8 NGC 6705 686 RG* 18 51 14.5257257232 -06 16 55.182562356   13.403 11.923     ~ 43 0
9 NGC 6705 669 * 18 51 15.3452793144 -06 18 35.967625128   13.527 11.974     K0III: 34 0
10 NGC 6705 660 RG* 18 51 15.7117781616 -06 18 14.698776960   13.297 11.807     ~ 44 0
11 NAME Galactic Bar reg ~ ~           ~ 1215 0

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