Determination of Sodium Abundance Ratio from Low-resolution Stellar Spectra and Its Applications
Abstract
We present a method to determine sodium abundance ratios ([Na/Fe]) using the Na I D doublet lines in low-resolution (R ~ 2000) stellar spectra. As stellar Na I D lines are blended with those produced by the interstellar medium, we developed a technique for removing the interstellar Na I D lines using the relationship between extinction, which is proportional to E(B - V), and the equivalent width of the interstellar Na I D absorption lines. When measuring [Na/Fe], we also considered corrections for nonlocal thermodynamic equilibrium (NLTE) effects. Comparisons with data from high-resolution spectroscopic surveys suggest that the expected precision of [Na/Fe] from low-resolution spectra is better than 0.3 dex for stars with [Fe/H] > -3.0. We also present a simple application employing the estimated [Na/Fe] values for a large number of stellar spectra from the Sloan Digital Sky Survey (SDSS). After classifying the SDSS stars into Na-normal, Na-high, and Na-extreme, we explore their relation to stars in Galactic globular clusters (GCs). We find that while the Na-high SDSS stars exhibit a similar metallicity distribution function (MDF) to that of the GCs, indicating that the majority of such stars may have originated from GC debris, the MDF of the Na-normal SDSS stars follows that of typical disk and halo stars. As there is a high fraction of carbon-enhanced metal-poor stars among the Na-extreme stars, they may have a non-GC origin, perhaps due to mass-transfer events from evolved binary companions.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- January 2022
- DOI:
- 10.3847/1538-4357/ac3423
- arXiv:
- arXiv:2109.00142
- Bibcode:
- 2022ApJ...925...35K
- Keywords:
-
- 1060;
- 1622;
- 1671;
- 656;
- 1054;
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- 13 pages, 9 figures, submitted to ApJ