He IIλ4686 emission from the massive binary system in η Car: Constraints to the orbital elements and the nature of the periodic minima

Journal Article · Thu Mar 10 04:00:00 EST 2016 · Astrophysical Journal

DOI:https://doi.org/10.3847/0004-637X/819/2/131· OSTI ID:22890142

Teodoro, M.; Russell, C.; Gull, T. R.; Madura, T. I. ^[1]; Damineli, A. ^[2]; Heathcote, B. ^[3]; Richardson, N. D.; Moffat, A. F. J.; St-Jean, L. ^[4]; Pollard, K. R. ^[5]; Walter, F. ^[6]; Coimbra, A.; Prates, R. ^[7]; Fernández-Lajús, E.; Gamen, R. C. ^[8]; Hickel, G. ^[9]; others, and

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1. Astrophysics Science Division, NASA Goddard Space Flight Center, Code 667, Greenbelt, MD 20771 (United States)
2. Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, R. do Matão 1226, Cidade Universitária, São Paulo 05508-900 (Brazil)
3. SASER Team, 269 Domain Road, South Yarra, Vic 3141 (Australia)
4. Départment de Physique, Université de Montréal, CP 6128, Succursale: Centre-Ville, Montréal, QC H3C 3J7 (Canada)
5. Department of Physics and Astronomy, University of Canterbury, Christchurch (New Zealand)
6. Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794-3800 (United States)
7. Laboratório Nacional de Astrofíca, R. Estados Unidos, 154, Bairro das Nações, Itajubá 37504-364 (Brazil)
8. Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, Paseo del Bosque s/n, La Plata, BA, B1900FWA (Argentina)
9. Instituto de Física and Química, Universidade Federal de Itajubá, Av. BPS, 1303, Pinheirinho, Itajubá 37500-062 (Brazil)

Eta Carinae (η Car) is an extremely massive binary system in which rapid spectrum variations occur near periastron. Most notably, near periastron the He ii λ4686 line increases rapidly in strength, drops to a minimum value, then increases briefly before fading away. To understand this behavior, we conducted an intense spectroscopic monitoring of the He ii λ4686 emission line across the 2014.6 periastron passage using ground- and space-based telescopes. Comparison with previous data confirmed the overall repeatability of the line equivalent width (EW), radial velocities, and the timing of the minimum, though the strongest peak was systematically larger in 2014 than in 2009 by 26%. The EW variations, combined with other measurements, yield an orbital period of 2022.7 ± 0.3 days. The observed variability of the EW was reproduced by a model in which the line flux primarily arises at the apex of the wind–wind collision and scales inversely with the square of the stellar separation, if we account for the excess emission as the companion star plunges into the hot inner layers of the primary’s atmosphere, and including absorption from the disturbed primary wind between the source and the observer. This model constrains the orbital inclination to 135°–153°, and the longitude of periastron to 234°–252°. It also suggests that periastron passage occurred on T{sub 0}=2456874.4 (±1.3 days). Our model also reproduced EW variations from a polar view of the primary star as determined from the observed He ii λ4686 emission scattered off the Homunculus nebula.

• OSTI ID: 22890142
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 819; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United Kingdom
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABSORPTION
COMPARATIVE EVALUATIONS
EMISSION
H2 REGIONS
INTERSTELLAR SPACE
NEBULAE
PERIODICITY
RADIAL VELOCITY
SPECTRA
STARS
STELLAR ATMOSPHERES
TELESCOPES