The infrared CA II triplet - A luminosity indicator for stellar population synthesis

Jones, Jeryl C.; Alloin, D.; Jones, Bernard J. T.

doi:10.1086/162325

Cited by 68 publications

(75 citation statements)

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“…Alkali atoms in general are all extremely sensitive to density because the sole valence electron can easily be perturbed by small changes in pressure (Schlieder et al 2012), making sodium transitions good surface gravity (and age) indicators. Lastly, the equivalent width of the calcium triplet around 8600 Å is known to be larger in giants than in dwarfs (Jones et al 1984), which our spectra show in the the bottom left panel. shows the zoomed-in region around the Ca II triplet.…”

Section: The Spectramentioning

confidence: 55%

“…To spectroscopically distinguish dwarfs from giant stars, we focused on the gravity-sensitive features, Na I (8200 Å) and the calcium triplet (∼8600 Å). The Na I doublet is extremely sensitive to gravity (Schlieder et al 2012) and is only strong in dwarf stars, while the calcium triplet is more prominent in giant stars (Jones et al 1984). After our spectroscopic classification, we conservatively removed~75% of the selected stars, and we expect that the vast majority of our remaining spectra are true M giants.…”

Section: Late-type K All M Starsmentioning

confidence: 99%

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An Empirical Template Library of Stellar Spectra for a Wide Range of Spectral Classes, Luminosity Classes, and Metallicities Using SDSS BOSS Spectra

Kesseli

West

Veyette

et al. 2017

ApJS

118

124

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We present a library of empirical stellar spectra created using spectra from the Sloan Digital Sky Survey's Baryon Oscillation Spectroscopic Survey. The templates cover spectral types O5 through L3, are binned by metallicity from −2.0 dex through +1.0 dex, and are separated into main-sequence (dwarf) stars and giant stars. With recently developed M dwarf metallicity indicators, we are able to extend the metallicity bins down through the spectral subtype M8, making this the first empirical library with this degree of temperature and metallicity coverage. The wavelength coverage for the templates is from 3650 to 10200 Å at a resolution of better than R∼2000. Using the templates, we identify trends in color space with metallicity and surface gravity, which will be useful for analyzing large data sets from upcoming missions like the Large Synoptic Survey Telescope. Along with the templates, we are releasing a code for automatically (and/or visually) identifying the spectral type and metallicity of a star.

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Section: The Spectramentioning

confidence: 55%

Section: Late-type K All M Starsmentioning

confidence: 99%

An Empirical Template Library of Stellar Spectra for a Wide Range of Spectral Classes, Luminosity Classes, and Metallicities Using SDSS BOSS Spectra

Kesseli

West

Veyette

et al. 2017

ApJS

118

124

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“…Early investigations of the CaT concentrated mainly on their sensitivity to surface gravity (Spinrad & Taylor 1969, 1971Cohen 1978;Jones et al 1984). It was realized by Armandroff & Zinn (1988) that a more metal-rich RGB star should have stronger CaT lines, because it has both a greater abundance of Fe (and also Ca) in its atmosphere and a lower surface gravity.…”

Section: Introduction and Outlinementioning

confidence: 99%

The NIR Ca ii triplet at low metallicity

Starkenburg¹,

Hill

Tolstoy³

et al. 2010

A&A

228

432

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The NIR Ca ii triplet absorption lines have proven to be an important tool for quantitative spectroscopy of individual red giant branch stars in the Local Group, providing a better understanding of metallicities of stars in the Milky Way and dwarf galaxies and thereby an opportunity to constrain their chemical evolution processes. An interesting puzzle in this field is the significant lack of extremely metal-poor stars, below [Fe/H] = −3, found in classical dwarf galaxies around the Milky Way using this technique. The question arises whether these stars are really absent, or if the empirical Ca ii triplet method used to study these systems is biased in the lowmetallicity regime. Here we present results of synthetic spectral analysis of the Ca ii triplet, that is focused on a better understanding of spectroscopic measurements of low-metallicity giant stars. Our results start to deviate strongly from the widely-used and linear empirical calibrations at [Fe/H] < −2. We provide a new calibration for Ca ii triplet studies which is valid for −0.5 ≥ [Fe/H] ≥ −4. We subsequently apply this new calibration to current data sets and suggest that the classical dwarf galaxies are not so devoid of extremely low-metallicity stars as was previously thought.

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“…The CaT method can also be applied to derive the metallicity for red giants in any stellar population for which V HB is known, for instance dwarf spheroidal galaxies, the Magellanic Clouds, extragalactic globular clusters, or even M31 (Battaglia et al 2011;Parisi et al 2010;Foster et al 2010;Jones et al 1984;Cenarro et al 2008). Adapting the technique to the IR allows us to apply it to any stellar population where reddening is problematic, which adds many targets for detailed study.…”

Section: Introductionmentioning

confidence: 99%

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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The infrared CA II triplet - A luminosity indicator for stellar population synthesis

Cited by 68 publications

References 0 publications

An Empirical Template Library of Stellar Spectra for a Wide Range of Spectral Classes, Luminosity Classes, and Metallicities Using SDSS BOSS Spectra

An Empirical Template Library of Stellar Spectra for a Wide Range of Spectral Classes, Luminosity Classes, and Metallicities Using SDSS BOSS Spectra

The NIR Ca ii triplet at low metallicity

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

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