A FEROS spectroscopic study of the extreme O supergiant He 3-759

TL;DR

This study characterizes the extreme O supergiant He 3-759 using high-resolution spectroscopy, revealing its physical properties, wind characteristics, and chemical composition, and compares it with similar stars to understand its evolutionary status.

Contribution

First detailed spectroscopic analysis of He 3-759, establishing its physical parameters and wind properties, and comparing it with similar stars to infer its evolutionary context.

Findings

He 3-759 is a near twin of HD 151804 in spectral properties.

He 3-759 is located at ~6.5 kpc in the Sagittarius-Carina arm.

He 3-759 has a temperature of 30.5 kK, luminosity log L/L_sun = 5.9, and a wind mass-loss rate of 10^-5.17 M_sun/yr.

Abstract

We present a study of the extreme O-type supergiant He 3-759 using new high-resolution FEROS data, revealing that it is a near spectroscopic twin of HD 151804 (O8 Iaf). We investigate the extinction towards He 3-759 using a variety of methods, revealing A_V ~ 4.7 mag. If we assume He 3-759 has an identical absolute K-band magnitude to HD 151804 we find that it lies in the Sagittarius-Carina spiral arm at a distance of ~6.5 kpc. We derive the physical and wind properties for He 3-759, revealing T* = 30.5 kK, log L/L(sun) = 5.9 and dM/dt = 10^-5.17 M(sun)/yr for a clumped wind whose terminal velocity is estimated at 1000 km/s. The atmosphere of He 3-759 is enriched in helium (X_He = 49%) and nitrogen (X_N = 0.3%). A reanalysis of HD 151804 and HD 152408 (WN9ha) reveals similar parameters except that the WN9ha star possesses a stronger wind and reduced surface hydrogen content. HD 151804 and HD 152408 lie within the Sco OB1 association, with initial masses of ~60 M(sun) and ages ~2.7 Myr, consistent with NGC 6231 cluster members using standard Geneva isochrones. Improved agreement with observed surface abundances are obtained for similar initial masses with more recent Geneva group predictions from which higher ages of ~3.75 Myr are obtained. No young, massive star cluster is known to be associated with He 3-759.