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

Abstract

Translate Article

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