Determination of Sodium Abundance Ratio from Low-resolution Stellar Spectra and Its Applications

Journal Article · 24 January 2022 · The Astrophysical Journal

DOI: https://doi.org/10.3847/1538-4357/ac3423 · OSTI ID:1983205

Koo, Jae-Rim  ^[1]; Sun Lee, Young  ^[2]; Park, Hye-Jin ^[3]; Kwang Kim, Young  ^[2]; Beers, Timothy C.  ^[4]

---

1. Chungnam National Univ., Daejeon (Korea, Republic of); Kyungpook National Univ., Daegu (Korea, Republic of)
2. Chungnam National Univ., Daejeon (Korea, Republic of)
3. Sejong Univ., Seoul (Korea, Republic of)
4. University of Notre Dame, IN (United States)

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.

• Research Organization: US Department of Energy (USDOE), Washington, DC (United States). Office of Science, Sloan Digital Sky Survey (SDSS)
• Sponsoring Organization: USDOE Office of Science (SC)
• OSTI ID: 1983205
• Journal Information: The Astrophysical Journal, Journal Name: The Astrophysical Journal Journal Issue: 1 Vol. 925; ISSN 0004-637X
• Publisher: IOP PublishingCopyright Statement
• Country of Publication: United States
• Language: English