FUSE, STIS, and Keck spectroscopic analysis of the UV-bright star vZ 1128 in M3 (NGC 5272)

TL;DR

This paper presents a detailed spectroscopic analysis of the UV-bright star vZ 1128 in M3, revealing its physical parameters, photospheric composition, and stellar wind features, and comparing its abundances to cluster red giants.

Contribution

It provides the first comprehensive UV and optical spectroscopic analysis of vZ 1128, determining its physical parameters and chemical abundances, and comparing them to cluster stars to infer its evolutionary history.

Findings

Teff = 36,600 K, log g = 3.95, He/H ratio = -0.84

Photospheric abundances match cluster red giants, with little change since RGB phase

Detection of weak stellar wind via P Cygni profiles in N V 1240

Abstract

We present a spectral analysis of the UV-bright star vZ 1128 in M3 based on observations with the Far Ultraviolet Spectroscopic Explorer (FUSE), the Space Telescope Imaging Spectrograph (STIS), and the Keck HIRES echelle spectrograph. By fitting the H I, He I, and He II lines in the Keck spectrum with non-LTE H-He models, we obtain Teff = 36,600 K, log g = 3.95, and log N(He)/N(H) = -0.84. The star's FUSE and STIS spectra show photospheric absorption from C, N, O, Al, Si, P, S, Fe, and Ni. No stellar features from elements beyond the iron peak are observed. Both components of the N V 1240 doublet exhibit P~Cygni profiles, indicating a weak stellar wind, but no other wind features are seen. The star's photospheric abundances appear to have changed little since it left the red giant branch (RGB). Its C, N, O, Al, Si, Fe, and Ni abundances are consistent with published values for the red-giant stars in M3, and the relative abundances of C, N, and O follow the trends seen on the cluster RGB. In particular, its low C abundance suggests that the star left the asymptotic giant branch before the onset of third dredge-up.