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J/A+A/604/A41       ESO452-SC11 Stellar parameters and abundances  (Koch+, 2017)

Spectroscopic study of the elusive globular cluster ESO452-SC11 and its surroundings. Koch A., Hansen C.J., Kunder A.M. <Astron. Astrophys. 604, A41 (2017)> =2017A&A...604A..41K (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Radial velocities ; Abundances Keywords: stars: abundances - Galaxy: abundances - Galaxy: structure - globular clusters: individual: ESO452-SC11 - Galaxy: disk - Galaxy: bulge Abstract: Globular clusters (GCs) have long been recognized as being amongst the oldest objects in the Galaxy. As such, they have the potential of playing a pivotal role in deciphering the Milky Way's early history. Here we present the first spectroscopic study of the low-mass system ESO452-SC11 using the AAOmega multifibre spectrograph at medium resolution. Given the stellar sparsity of this object and the high degree of foreground contamination due to its location toward the Galactic bulge, very few details are known for this cluster - there is no consensus, for instance, about its age, metallicity, or its association with the disk or bulge. We identify five member candidates based on common radial velocity, calcium-triplet metallicity, and position within the GC. Using spectral synthesis, the measurement of accurate Fe-abundances from Fe-lines, and abundances of several α-, Fe-peak, and neutron-capture elements (Si, Ca, Ti,Cr, Co, Ni, Sr, and Eu) is carried out, albeit with large uncertainties. We find that two of the five cluster candidates are likely non-members, as they have deviating iron abundances and [alpha/Fe] ratios. The cluster mean heliocentric velocity is 19±2km/s with a velocity dispersion of 2.8±3.4km/s, a low value in line with its sparse nature and low mass. The mean Fe-abundance from spectral fitting is -0.88±0.03dex, where the spread is driven by observational errors. Furthermore, the alpha-elements of the GC candidates are marginally lower than expected for the bulge at similar metallicities. As spectra of hundreds of stars were collected in a 2-degree field centered on ESO452-SC11, a detailed abundance study of the surrounding field was also enabled. The majority of the non-members have slightly higher [Fe] ratios, in line with the typical nearby bulge population. A subset of the spectra with measured Fe-peak abundance ratios shows a large scatter around solar values, albeit with large uncertainties. Furthermore, our study provides the first systematic measurements of strontium abundances in a Galactic bulge GC. Here, the Eu and Sr abundances of the GC candidates are broadly consistent with a disk or bulge association. Recent proper motions and our orbital calculations place ESO452 on an elliptical orbit in the central 3kpc of the Milky Way, establishing a firm connection with the bulge. Finally, while the radial velocities and preferential position of a dozen of stars outside the GC radius appear to imply the presence of extra-tidal stars, their significantly different chemical composition refutes this hypothesis. Description: All our data were taken on June 08, 2013,with the AAOmega multifibre spectrograph at the 3.9 m Anglo-Australian Telescope (Siding Spring, Australia). Objects: ------------------------------------------------------- RA (2000) DE Designation(s) ------------------------------------------------------- 16 39 25.50 -28 23 52.0 ESO452-SC1 = ESO 452-11 ------------------------------------------------------- File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table2.dat 71 363 Properties of the target stars table3.dat 67 289 Stellar parameters from our photometric analysis and from SP_ACE table4.dat 93 289 Stellar abundances from SP_ACE (Fe, Si, Ca, Ti) table5.dat 96 289 Stellar abundances from SP_ACE (Cr, Co, Ni, Sr, Eu)
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1 A1 --- Note [M] M for member candidates, else fore- and background candidates 3- 5 I3 --- Star Star identifier 8- 9 I2 h RAh Right ascension (J2000) 11- 12 I2 min RAm Right ascension (J2000) 14- 17 F4.1 s RAs Right ascension (J2000) 19 A1 --- DE- Declination sign (J2000) 20- 21 I2 deg DEd Declination (J2000) 23- 24 I2 arcmin DEm Declination (J2000) 26- 29 F4.1 arcsec DEs Declination (J2000) 32- 36 F5.2 arcmin r Radial distance from cluster center 39- 44 F6.1 km/s HRV Heliocentric radial velocity 46- 48 F3.1 km/s e_HRV Error on HRV 51- 54 F4.2 10-13m SigmaEW ? Reduced equivalent width 56- 59 F4.2 10-13m e_SigmaEW ? Error on SigmaEW 62- 66 F5.2 [-] [Fe/H]CaT ?=- Calcium triplet metallicity 68- 71 F4.2 [-] e_[Fe/H]CaT ?=- Error on [Fe/H]CaT
Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
1 A1 --- Note [M] M for member candidates, else fore- and background candidates 3- 5 I3 --- Star Star identifier 9- 13 F5.3 mag J-K 2MASS J-K color index (reddened) 17- 20 I4 K Teff(A) ?=- Effective temperature from Alonso calibration 22- 25 I4 K Teff(S) Effective temperature from SP_ACE pipeline 27- 30 I4 K e_Teff Lower error bound on Teff(SP_ACE) 32- 35 I4 K E_Teff Upper error bound on Teff(SP_ACE) 38- 41 F4.2 [cm/s2] logg Survace gravity 43- 46 F4.2 [cm/s2] e_logg Lower error bound on logg 48- 51 F4.2 [cm/s2] E_logg Upper error bound on logg 54- 57 F4.2 km/s vmic Microturbulence velocity 60- 62 I3 --- SNR Signal-t-Noise ratio 64- 67 F4.2 --- chi2 Chi2 value of spectral fitting
Byte-by-byte Description of file: table4.dat
Bytes Format Units Label Explanations
1 A1 --- Note [M] M for member candidates, else fore- and background candidates 3- 5 I3 --- Star Star identifier 8- 12 F5.2 [-] [Fe/H] ?=- Iron abundance from SP_ACE 15- 18 F4.2 [-] e_[Fe/H] ?=- Lower error bound on [Fe/H] 21- 24 F4.2 [-] E_[Fe/H] ?=- Upper error bound on [Fe/H] 27 I1 --- nFe Number of Fe lines 30- 34 F5.2 [-] [Si/Fe] ?=- [Si/Fe] abundance ratio from SP_ACE 37- 40 F4.2 [-] e_[Si/Fe] ?=- Lower error bound on [Si/Fe] 43- 46 F4.2 [-] E_[Si/Fe] ?=- Upper error bound on [Si/Fe] 49 I1 --- nSi Number of Si lines 52- 56 F5.2 [-] [Ca/Fe] ?=- [Ca/Fe] abundance ratio from SP_ACE 59- 62 F4.2 [-] e_[Ca/Fe] ?=- Lower error bound on [Ca/Fe] 65- 68 F4.2 [-] E_[Ca/Fe] ?=- Upper error bound on [Ca/Fe] 71 I1 --- nCa Number of Ca lines 74- 78 F5.2 [-] [Ti/Fe] ?=- [Ti/Fe] abundance ratio from SP_ACE 81- 84 F4.2 [-] e_[Ti/Fe] ?=- Lower error bound on [Ti/Fe] 87- 90 F4.2 [-] E_[Ti/Fe] ?=- Upper error bound on [Ti/Fe] 93 I1 --- nTi Number of Ti lines
Byte-by-byte Description of file: table5.dat
Bytes Format Units Label Explanations
1 A1 --- Note [M] M for member candidates, else fore- and background candidates 3- 5 I3 --- Star Star identifier 8- 12 F5.2 [-] [Cr/Fe] ?=- [Cr/Fe] abundance ratio from SP_ACE 15- 18 F4.2 [-] e_[Cr/Fe] ?=- Lower error bound on [Cr/Fe] 21- 24 F4.2 [-] E_[Cr/Fe] ?=- Upper error bound on [Cr/Fe] 27 I1 --- nCr Number of Cr lines 30- 34 F5.2 [-] [Co/Fe] ?=- [Co/Fe] abundance ratio from SP_ACE 37- 40 F4.2 [-] e_[Co/Fe] ?=- Lower error bound on [Co/Fe] 43- 46 F4.2 [-] E_[Co/Fe] ?=- Upper error bound on [Co/Fe] 49 I1 --- nCo Number of Co lines 52- 56 F5.2 [-] [Ni/Fe] ?=- [Ni/Fe] abundance ratio from SP_ACE 59- 62 F4.2 [-] e_[Ni/Fe] ?=- Lower error bound on [Ni/Fe] 65- 68 F4.2 [-] E_[Ni/Fe] ?=- Upper error bound on [Ni/Fe] 71 I1 --- nNiFe Number of Ni lines 75- 78 F4.2 [-] [Sr/Fe] ?=- [Sr/Fe] abundance ratio from SP_ACE 80- 83 F4.2 [-] e_[Sr/Fe] ?=- Error on [Sr/Fe] 86 A1 --- l_[Eu/Fe] Limit flag on [Eu/Fe] 87- 91 F5.2 [-] [Eu/Fe] ?=- [Sr/Fe] abundance ratio from SP_ACE 93- 96 F4.2 [-] e_[Eu/Fe] ?=- Error on [Eu/Fe]
Acknowledgements: Andreas Koch, a.koch1(at)lancaster.ac.uk
(End) Patricia Vannier [CDS] 05-May-2017
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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