Fe i Lines in 0.91–1.33 μm Spectra of Red Giants for Measuring the Microturbulence and Metallicities

Abstract

For a detailed analysis of stellar chemical abundances, high-resolution spectra in the optical have mainly been used, while the development of near-infrared (NIR) spectrograph has opened new wavelength windows. Red giants have a large number of resolved absorption lines in both the optical and NIR wavelengths, but the characteristics of the lines in different wave passbands are not necessarily the same. We present a selection of Fe I lines in the z ′ , Y , and J bands (0.91-1.33 µm). On the basis of two different lists of lines in this range, the Vienna Atomic Line Database (VALD) and the catalog published by Meléndez & Barbuy in 1999 (MB99), we selected sufficiently strong lines that are not severely blended and compiled lists with 107 Fe I lines in total (97 and 75 lines from VALD and MB99, respectively). Combining our lists with high-resolution (λ/∆λ = 28, 000) and high signalto-noise (> 500) spectra taken with a NIR spectrograph, WINERED, we present measurements of the iron abundances of two prototype red giants: Arcturus and µ Leo. A bootstrap method for determining the microturbulence and abundance together with their errors is demonstrated. The standard deviations of log ǫ Fe values from individual Fe I lines are significantly smaller when we use the lines from MB99 instead of those from VALD. With the MB99 list, we obtained ξ = 1.20 ± 0.11 km s −1 and log ǫ Fe = 7.01 ± 0.05 dex for Arcturus, and ξ = 1.54 ± 0.17 km s −1 and log ǫ Fe = 7.73 ± 0.07 dex for µ Leo. These final values show better agreements with previous values in the literature than the corresponding values we obtained with VALD.

Stellar population astrophysics (SPA) with the TNG

“…It is also interesting to compare our results on stellar parameters and iron abundances with those obtained by the NIR studies of Kondo et al (2019) in the in the 9300−13100 Å spectral range and of Smith et al (2013) in the 15000 − 17000 Å spectral range, at about half the spectral resolution of our study. Kondo et al (2019) 6 7 8 9 1 1 1 2 1 3 1 4 1 5 1 6 1 9 2 0 2 1 2 2 2 3 2 4 2 5 2 6 2 7 2 8 2 9 3 0 3 9 5 8 6 0 6 6 Atomic Number Table 1 and in Sect. 1.…”

“…Our list has 48 lines in common with the Kondo et al (2019) VALD3 line list. Our and the Kondo et al (2019) VALD3 abundances are similar, although we adopted a 0.4 kms −1 higher microturbulence velocity. The other 20 lines in the Kondo et al (2019) VALD3 line list have not been used in our analysis because they are blended or contaminated by nearby strong photospheric or telluric lines.…”

“…Our and the Kondo et al (2019) VALD3 abundances are similar, although we adopted a 0.4 kms −1 higher microturbulence velocity. The other 20 lines in the Kondo et al (2019) VALD3 line list have not been used in our analysis because they are blended or contaminated by nearby strong photospheric or telluric lines. These rejected lines give an average abundances that differs by more than 0.1 dex and has a significantly larger (>0.2 dex) dispersion.…”

“…These rejected lines give an average abundances that differs by more than 0.1 dex and has a significantly larger (>0.2 dex) dispersion. We also used 30 lines in the YJ bands that are not in the VALD3 Kondo et al (2019) line list. On average, they provide abundances that are a few hundredths dex higher than those from the the lines in common.…”

Stellar population astrophysics (SPA) with the TNG

“…These Sc data were vital, for example, in the discussion on K-band Sc abundances in the Nuclear Star Cluster by Thorsbro et al (2018). Other examples are the works on WINERED spectra by Kondo et al (2019), who investigated Fe lines at 0.9−1.3 µm in spectra of red giants and their usefulness for determining the metallicity and microturbulence, and the work by Fukue et al (2015) on the development of the line-depth ratio method to determine effective temperatures of classical Cepheids in the H band. Furthermore, in the K band, not many measurements on relevant atomic data, such as wavelengths and lines strengths, exist at all from laboratory spectra, and the line wavelengths in the Vienna Atomic Line Database (VALD; e.g.…”