A STUDY OF THE LUMINOUS BLUE VARIABLE CANDIDATE HE 3-519 AND ITS SURROUNDING NEBULA.
833 - 854.
He 3-519 is 20' away from the well-known LBV AG Car and is surrounded by a ring nebula 1' in diameter. In this paper, we present the first detailed study of He 3-519 and its surrounding nebula based on high resolution spectra obtained at the AAT with the UCL echelle spectrograph for several epochs. The optical spectrum of He 3-519 is dominated by H I, He I and N II P Cygni profiles and contains weak He II lambda4686 emission. The SWP IUE spectrum consists mainly of Fe II absorption plus a Si IV lambda1400 stellar wind feature. Two strong emission lines possibly due to Fe II and Fe III are present in the LWP spectrum. We find that dramatic optical line profile variability is present in our spectra and comparison with earlier epochs back to 1989 shows that the Balmer P Cygni absorption components disappear and reappear over timescales of weeks. We compare the spectral characteristics of He 3-519 with those of related stars and find that they are most similar to AG Car at, and just after, minimum. We further find that He 3-519 and AG Car at minimum have spectral features that are not consistent with a Ofpe/WN9 spectral type. We instead assign a new spectral class of WN11 to these two stars.We derive E(B-V)= 1.14 +/- 0.10 from the nebular lines, the strengths of diff-use interstellar bands and the 2200 angstrom feature. The measured nebular systemic velocity and the profiles of the Na I and Ca II interstellar lines give a kinematic distance of 8.0 +/- 1.0 kpc. The corresponding M(V) of He 3-519 is -7.1 +/- 0.6.We derive various stellar parameters by fitting the He and H line profiles of He 3-519 using the Hillier non-LTE model atmosphere code. We find T* = 27 500 +/- 1000 K; log L/L. = 5.66(-0.19)+0.22, M = 1.3(-0.4)+0.8 10(-4) M. yr-1, upsilon(infinity) = 365 km s-1, and Y = 0.67 +/- 0.02. We also perform a similar analysis for AG Car and derive its parameters at minimum in 1989 March. We find that both stars have lower temperatures than WN7-8 stars but similar low hydrogen contents, in line with their new WN11 classifications. The position of He 3-519 on the HR diagram is just consistent with the upper luminosity/stability limit.Finally, we consider the nature of the nebula surrounding He 3-519. The shell shows deviations from spherical symmetry but overall is expanding at 61 km s-1 and has an ionized mass of approximately 2 M.. The nebular parameters we derive and its similarity to the AG Car nebula indicate that it was probably ejected from He 3-519 approximately 2 10(4) yr ago.The overall properties of He 3-519 and its nebula lead us to conclude that it should be considered as a new LBV. Moreover, the evolved status of both He 3-519 and AG Car indicate that they should properly be considered as cool WN11 stars i.e. they are WR stars which are members of the LBV class because of their proximity to the upper luminosity boundary in the HR diagram. Similarly, their nebulae should be considered as examples of WR ring nebulae.
|Title:||A STUDY OF THE LUMINOUS BLUE VARIABLE CANDIDATE HE 3-519 AND ITS SURROUNDING NEBULA|
|Keywords:||STARS, HE 3-519, AG CAR, WOLF-RAYET, FUNDAMENTAL PARAMETERS, MASS-LOSS, CIRCUMSTELLAR MATTER, WOLF-RAYET STARS, EMISSION-LINE STARS, LARGE MAGELLANIC CLOUD, AG CARINAE, ELECTRON-SCATTERING, MILKY-WAY, P-CYGNI, WIND, SPECTROSCOPY, CAR|
|UCL classification:||UCL > School of BEAMS > Faculty of Maths and Physical Sciences > Physics and Astronomy|
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