High-resolution CRIRES spectra of Terzan 1: a metal-poor globular cluster toward the inner bulge
Journal
Date Issued
2015
Author(s)
Description
E.V. warmly thanks the telescope operators and night astronomers of Paranal working on UT1, for their competence and dedication while doing observations for this program. R.M.R. acknowledges support from grants AST-1212095, AST-1413755 from the National Science Foundation. The authors thank Ivo Saviane and Sergio Vasquez for sharing information on their results on Terzan 1 radial velocity measurements that will be presented in a forthcoming paper (Vasquez et al., in prep.). NSO/Kitt Peak FTS data used here were produced by NSF/NOAO.
Abstract
Aims: Containing the oldest stars in the Galaxy, globular clusters toward the bulge can be used to trace its dynamical and chemical evolution. In the bulge direction, there are ~50 clusters, but only about 20% have been subject of high-resolution spectroscopic investigations. So far, the sample observed at high resolution spans a moderate-to-high metallicity regime. In this sample, however, very few are located in the innermost region (RGC ≤ 1.5 Kpc and | l,b | ≤ 5°). To constrain the chemical evolution enrichment of the innermost region of Galaxy, accurate abundances and abundance patterns of key elements based on high-resolution spectroscopy are necessary. Here we present the results we obtained for Terzan 1, a metal-poor cluster located in the innermost bulge region. Methods: Using the near-infrared spectrograph CRIRES at ESO/VLT, we obtained high-resolution (R ≈ 50 000) H-band spectra of 16 bright giant stars in the innermost region (r ≤ 60'') of Terzan 1. Full spectral synthesis techniques and equivalent width measurements of selected lines, isolated and free of significant blending and/or contamination by telluric lines, allowed accurate chemical abundances and radial velocities to be derived. Results: Fifteen out of 16 observed stars are likely cluster members, with an average heliocentric radial velocity of +57 ± 1.8 km s-1 and mean iron abundance of [ Fe/H ] = -1.26 ± 0.03 dex. For these stars we measured some [α/Fe] abundance ratios, finding average values of [ O/Fe ] = +0.39 ± 0.02 dex, [ Mg/Fe ] = +0.42 ± 0.02 dex, [ Si/Fe ] = +0.31 ± 0.04 dex, and [ Ti/Fe ] = +0.15 ± 0.04 dex Conclusions: The α enhancement (≈+0.4 dex) found in the observed giant stars of Terzan 1 is consistent with previous measurements on other, more metal-rich bulge clusters, which suggests a rapid chemical enrichment.
Based on data taken at the ESO/VLT Telescope, within the observing program 093.D-0179(A).
Volume
574
Start page
A80
Issn Identifier
0004-6361
Ads BibCode
2015A&A...574A..80V
Rights
open.access
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