M67 Blue Stragglers with High-resolution Infrared Spectroscopy

TL;DR

This study presents the first high-resolution infrared chemical analysis of five blue straggler binary stars in M67, revealing their elemental abundances and rotational velocities, and comparing them to turnoff star abundances.

Contribution

It provides novel infrared spectral data and chemical abundance measurements for blue stragglers in M67, expanding understanding of their composition and evolution.

Findings

Abundances of key elements are consistent with turnoff stars.

Three stars show high rotational velocities (v sin i ≥ 25 km/s).

Detection of carbon enrichment or depletion is limited by measurement uncertainties.

Abstract

We report on the first detailed infrared chemical analysis of five binary members (S277, S997, S975, S1031, and S1195) in the open cluster M67 (NGC 2682). These stars are located outside (bluer and/or brighter than) the main-sequence turnoff region in M67. High-resolution (R ~ 45,000) near-infrared spectra were obtained with the Immersion GRating INfrared Spectrograph (IGRINS) at the McDonald Observatory 2.7 m Harlan J. Smith Telescope, providing full spectral coverage of the H and K bands. The abundances of C, Na, Mg, Al, Si, S, Ca, Fe, and Ni are measured using neutral atomic absorption lines. We detect v sin i greater than or equal to 25 km s-1 in three of our program stars: S1031, S975, and S1195. We find our derived abundances to be in good agreement with turnoff star abundances, similar to published analyses of blue straggler stars in M67 from optical spectra. Detection of a carbon enhancement or depletion resulting from mass transfer is difficult due to the uncertainties in the carbon abundance and the relatively modest changes that may occur through red giant and asymptotic giant branch evolution.