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 ($R\sim$ 2000) stellar spectra. As stellar Na I D lines are blended with those produced by the interstellar medium (ISM), 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 (EW) of the interstellar Na I D absorption lines. When measuring [Na/Fe], we also considered corrections for non-local 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.

13 pages, 9 figures, submitted to ApJ

References in corpus (29)

• Array Programming with NumPy
• galpy: A Python Library for Galactic Dynamics
• Gaia Early Data Release 3: The astrometric solution
• The mass distribution and gravitational potential of the Milky Way
• The GALAH+ Survey: Third Data Release
• The SEGUE Stellar Parameter Pipeline. I. Description and Initial Validation Tests
• Carbon Enhanced Metal-Poor Stars. I. Chemical Compositions of 26 Stars
• Evidence for Two Early Accretion Events That Built the Milky Way Stellar Halo
• The SEGUE Stellar Parameter Pipeline. II. Validation with Galactic Globular and Open Clusters
• The SEGUE Stellar Parameter Pipeline. III. Comparison with High-Resolution Spectroscopy of SDSS/SEGUE Field Stars
• Observational Constraints on First-Star Nucleosynthesis. I. Evidence for Multiple Progenitors of CEMP-no Stars
• An Elemental Assay of Very, Extremely, and Ultra Metal-Poor Stars
• The SEGUE Stellar Parameter Pipeline. IV. Validation with an Extended Sample of Galactic Globular and Open Clusters
• The GALAH Survey: Non-LTE departure coefficients for large spectroscopic surveys
• A New Catalog of Globular Clusters in the Milky Way
• APOGEE Chemical Abundances of Globular Cluster Giants in the Inner Galaxy
• The tidal remnant of an unusually metal-poor globular cluster
• The contribution of N-rich stars to the Galactic stellar halo using APOGEE red giants
• Calcium H & K and sodium D absorption induced by the interstellar and circumgalactic media of the Milky Way
• The hidden past of M92: Detection and characterization of a newly formed 17° long stellar stream using the Canada-France Imaging Survey
• The low Sr/Ba ratio on some extremely metal-poor stars
• GRACES: Gemini remote access to CFHT ESPaDOnS Spectrograph through the longest astronomical fiber ever made (Experimental phase completed.)
• The Globular Cluster Origin of the Milky Way Outer Bulge: Evidence from Sodium Bimodality
• The Age-Metallicity-Specific Orbital Energy Relation for the Milky Way's Globular Cluster System Confirms the Importance of Accretion for Its Formation
• Difference in chemical composition between the bright and faint red clump stars in the Milky Way bulge
• APOGEE-2 Discovery of a Large Population of Relatively High-Metallicity Globular Cluster Debris
• Multiple populations in low mass globular clusters: Palomar 13
• Spectroscopic evidence of Multiple Stellar Populations in Globular Clusters
• Observational evidence points at AGB stars as possible progenitors of CEMP-s & r/s stars

Cited by in corpus (5)

• Galactic ArchaeoLogIcaL ExcavatiOns (GALILEO) I. An updated census of APOGEE N-rich giants across the Milky Way
• Phase-space Properties and Chemistry of the Sagittarius Stellar Stream Down to the Extremely Metal-poor ($[Fe/H]\lesssim -3$) Regime
• Search for Extremely Metal-Poor Stars with GEMINI-N/GRACES I. Chemical-Abundance Analysis
• Chemodynamical Analysis of Metal-rich High-eccentricity Stars in the Milky Way's Disk
• Detection of Ubiquitous Circumbinary Matter in Hot Subdwarfs Formed from Common-Envelope Ejections