The near-infrared Ca ii triplet as a metallicity indicator – II. Extension to extremely metal-poor metallicity regimes★

Carrera, R.; Pancino, E.; Gallart, Carme; Pino, Andrés del

doi:10.1093/mnras/stt1126

Cited by 102 publications

(192 citation statements)

References 85 publications

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“…Many authors have confirmed the accuracy and repeatability of CaT abundance measurements in combination with broad-band optical photometry and shown its very high sensitivity to metallicity and insensitivity to age (e.g., Cole et al 2004). Additionally, as reported by Carrera et al (2013), the strength of the CaT lines depends mainly on iron abundances, and not on the Ca abundance, as has been pointed out also by several other investigations (e.g. Idiart et al 1997;Battaglia et al 2008).…”

Section: Introductionmentioning

confidence: 55%

Deriving metallicities from calcium triplet spectroscopy in combination with near-infrared photometry

Mauro

Bidin

Geisler

et al. 2014

A&A

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Context. When they are established with sufficient precision, the ages, metallicities and kinematics of Galactic globular clusters (GGCs) can shed much light on the dynamical and chemical evolution of the Galactic halo and bulge. While the most fundamental way of determining GC abundances is by means of high-resolution spectroscopy, in practice this method is limited to only the brighter stars in the nearest and less reddened objects. This restriction has, over the years, led to the development of a large number of techniques that measure the overall abundance indirectly from parameters that correlate with overall metallicity. One of the most efficient methods is measuring the equivalent width (EW) of the calcium II triplet (CaT) at λ ≈ 8500 Å in red giants, which are corrected for the luminosity and temperature effects using the V magnitude differences from the horizontal branch (HB). Aims. We establish a similar method in the near-infrared (NIR), by combining the power of the differential magnitudes technique with the advantages of NIR photometry to minimize differential reddening effects. Methods. We used the K s magnitude difference between the star and the reddest part of the HB (RHB) or of the red clump (RC) to generate reduced equivalent widths (rEW) from previously presented datasets. Then we calibrated these rEW against three previously reported different metallicity scales; one of which we corrected using high-resolution spectroscopic metallicities. Results. We calculated the calibration relations for the two datasets and the three metallicity scales and found that they are approximately equivalent, with almost negligible differences. We compared our NIR calibrations with the corresponding optical ones, and found them to be equivalent, which shows that the luminosity-corrected rEW using the K s magnitude is compatible with the one obtained from the V magnitude. We then used the metallicities obtained from the calibration to investigate the internal metallicity distributions of the GCs. Conclusions. We have established that the ([Fe/H]:rEW) relation is independent of the magnitude used for the luminosity correction and find that the calibration relations change only slightly for different metallicity scales. The CaT technique using NIR photometry is thus a powerful tool to derive metallicities. In particular, it can be used to study the internal metallicity spread of a GC. We confirm the presence of at least two metallicity populations in NGC 6656 and find that several other GCs present peculiar metallicity distributions.

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Section: Introductionmentioning

confidence: 55%

Deriving metallicities from calcium triplet spectroscopy in combination with near-infrared photometry

Mauro

Bidin

Geisler

et al. 2014

A&A

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“…We prefer to use that calibration because it is based on moderate-resolution near-IR spectroscopy in the K band, which is similar to our spectral database. Moreover, the later work of Carrera et al (2013) shows that the metallicity vs. spectral index relation of globular and open clusters can be successfully combined and thus the range A24, page 4 of 25 Gray circles are all stars within the estimated cluster radius, dark circles are probable cluster members that remained after statistical decontamination. Stars with spectra are denoted by red circles and are labeled.…”

Section: Cluster Search and Methods Of Analysismentioning

confidence: 99%

New galactic star clusters discovered in the VVV survey. Candidates projected on the inner disk and bulge

Borissova

Chené

Alegría

et al. 2014

A&A

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Context. VISTA Variables in the Vía Láctea (VVV) is one of six ESO Public Surveys using the 4 meter Visible and Infrared Survey Telescope for Astronomy (VISTA). The VVV survey covers the Milky Way bulge and an adjacent section of the disk, and one of the principal objectives is to search for new star clusters within previously unreachable obscured parts of the Galaxy. Aims. The primary motivation behind this work is to discover and analyze obscured star clusters in the direction of the inner Galactic disk and bulge. Methods. Regions of the inner disk and bulge covered by the VVV survey were visually inspected using composite JHK S color images to select new cluster candidates on the basis of apparent overdensities. DR1, DR2, CASU, and point spread function photometry of 10 × 10 arcmin fields centered on each candidate cluster were used to construct color-magnitude and color-color diagrams. Follow-up spectroscopy of the brightest members of several cluster candidates was obtained in order to clarify their nature. Results. We report the discovery of 58 new infrared cluster candidates. Fundamental parameters such as age, distance, and metallicity were determined for 20 of the most populous clusters.

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“…However, Starkenburg et al (2010) have demonstrated that this assumption is not valid, particularly for metal-poor regimes. For this reason, Carrera et al (2013) recomputed the Carrera et al (2007) relationships, introducing two additional terms to account for the non-linearity effects. In any case, these authors have demonstrated that both calibrations produce similar results, within ±0.2 dex, in the range of metallicities expected for open clusters.…”

Section: Membership Selection Radial Velocity and Metallicity Determmentioning

confidence: 99%

Radial velocities and metallicities from infrared Ca ii triplet spectroscopy of open clusters

Carrera

Casamiquela

Ospina

et al. 2015

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Context. Open clusters are key to studying the formation and evolution of the Galactic disc. However, there is a deficiency of radial velocity and chemical abundance determinations for open clusters in the literature. Aims. We intend to increase the number of determinations of radial velocities and metallicities from spectroscopy for open clusters. Methods. We acquired medium-resolution spectra (R ∼ 8000) in the infrared region Ca ii triplet lines (∼8500 Å) for several stars in five open clusters with the long-slit IDS spectrograph on the 2.5 m Isaac Newton Telescope (Roque de los Muchachos Observatory, Spain). Radial velocities were obtained by cross-correlation fitting techniques. The relationships available in the literature between the strength of infrared Ca ii lines and metallicity were also used to derive the metallicity for each cluster. Results. We obtain V r = 48.6 ± 3.4, −58.4 ± 6.8, 26.0 ± 4.3, and −65.3 ± 3.2 km s −1 for Berkeley 23, NGC 559, NGC 6603, and NGC 7245, respectively. We found [Fe/H] = −0.25 ± 0.14 and −0.15 ± 0.18 for NGC 559 and NGC 7245, respectively. Berkeley 23 has low metallicity, [Fe/H] = −0.42 ± 0.13, which is similar to other open clusters in the outskirts of the Galactic disc. In contrast, we derived high metallicity ([Fe/H] = +0.43 ± 0.15) for NGC 6603, which places this system among the most metal-rich known open clusters. To our knowledge, this is the first determination of radial velocities and metallicities from spectroscopy for these clusters, except NGC 6603, for which radial velocities had been previously determined. We have also analysed ten stars in the line of sight to King 1. Because of the large dispersion obtained in both radial velocity and metallicity, we cannot be sure that we have sampled true cluster members.

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The near-infrared Ca ii triplet as a metallicity indicator – II. Extension to extremely metal-poor metallicity regimes★

Cited by 102 publications

References 85 publications

Deriving metallicities from calcium triplet spectroscopy in combination with near-infrared photometry

Deriving metallicities from calcium triplet spectroscopy in combination with near-infrared photometry

New galactic star clusters discovered in the VVV survey. Candidates projected on the inner disk and bulge

Radial velocities and metallicities from infrared Ca ii triplet spectroscopy of open clusters

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