Volume 641, September 2020
|Number of page(s)||55|
|Published online||07 September 2020|
The Infrared Telescope Facility (IRTF) spectral library
II. New indices in Y, J, H, and L atmospheric windows⋆
Instituto de Astronomía y Ciencias Planetarias, Universidad de Atacama, Copiapó, Chile
2 European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
3 Dipartimento di Fisica e Astronomia “G. Galilei”, Università di Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
4 INAF–Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
5 GEPI, Observatoire de Paris, PSL Research University, CNRS, Univ. Paris Diderot, Sorbonne Paris Cité, 61 Avenue de l’Observatoire, 75014 Paris, France
6 Independent Scholar, Viale degli Aironi 4, 30021 Caorle, VE, Italy
Accepted: 17 June 2020
Context. Stellar population studies in the infrared (IR) wavelength range have two main advantages with respect to the optical regime: they probe different populations, because most of the light in the IR comes from redder and generally older stars, and they allow us to see through dust because IR light is less affected by extinction. Unfortunately, IR modeling work was halted by the lack of adequate stellar libraries, but this has changed in the recent years.
Aims. Our project investigates the sensitivity of various spectral features in the 1−5 μm wavelength range to the physical properties of stars (Teff, [Fe/H], log g) and aims to objectively define spectral indices that can characterize the age and metallicity of unresolved stellar populations.
Methods. We implemented a method that uses derivatives of the indices as functions of Teff, [Fe/H] or log g across the entire available wavelength range to reveal the most sensitive indices to these parameters and the ranges in which these indices work.
Results. Here, we complement the previous work in the I and K bands, reporting a new system of 14, 12, 22, and 12 indices for Y, J, H, and L atmospheric windows, respectively, and describe their behavior. We list the equivalent widths of these indices for the Infrared Telescope Facility (IRTF) spectral library stars.
Conclusions. Our analysis indicates that features sensitive to the effective temperature are present and measurable in all the investigated atmospheric windows at the spectral resolution and in the metallicity range of the IRTF library for a signal-to-noise ratio greater than 20−30. The surface gravity is more challenging and only indices in the H and J windows are best suited for this. The metallicity range of the stars with available spectra is too narrow to search for suitable diagnostics. For the spectra of unresolved galaxies, the defined indices are valuable tools in tracing the properties of the stars in the IR-dominant stellar populations.
Key words: infrared: stars / line: identification / stars: abundances / supergiants / stars: late-type / stars: fundamental parameters
Full Tables E.1−E.6 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (188.8.131.52) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/641/A44
© ESO 2020
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