He II {lambda}4686 IN {eta} CARINAE: COLLAPSE OF THE WIND-WIND COLLISION REGION DURING PERIASTRON PASSAGE
- Instituto de Astronomia, Geofisica e Ciencias Atmosfericas, Universidade de Sao Paulo, Rua do Matao 1226, Cidade Universitaria, Sao Paulo 05508-900 (Brazil)
- Departamento de Fisica, Universidad de La Serena, Av. Cisternas 1200 Norte, La Serena (Chile)
- Observatorio Nacional, Rua General Jose Cristino 77, Sao Cristovao, Rio de Janeiro 20921-400 (Brazil)
- Instituto de Ciencias Astronomicas, de la Tierra, y del Espacio (ICATE-CONICET), Avenida Espana Sur 1512, J5402DSP San Juan (Argentina)
- CRESST and X-ray Astrophysics Laboratory, NASA/Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
- Facultad de Ciencias Astronomicas y Geofisicas, Universidad Nacional de La Plata, Paseo del Bosque s/n, La Plata, BA, B1900FWA (Argentina)
- Southern Observatory for Astrophysical Research, Colina El Pino s/n, Casilla 603, La Serena (Chile)
- Max-Planck-Institute fuer Radioastronomie, Auf dem Huegel 69, D-53121 Bonn (Germany)
- Department of Physics and Astronomy, Texas A and M University, College Station, TX 77843-4242 (United States)
- Research School of Astronomy and Astrophysics (RSAA), Mount Stromlo Observatory, Cotter Road, Weston, ACT 2611 (Australia)
The periodic spectroscopic events in {eta} Carinae are now well established and occur near the periastron passage of two massive stars in a very eccentric orbit. Several mechanisms have been proposed to explain the variations of different spectral features, such as an eclipse by the wind-wind collision (WWC) boundary, a shell ejection from the primary star or accretion of its wind onto the secondary. All of them have problems explaining all the observed phenomena. To better understand the nature of the cyclic events, we performed a dense monitoring of {eta} Carinae with five Southern telescopes during the 2009 low-excitation event, resulting in a set of data of unprecedented quality and sampling. The intrinsic luminosity of the He II {lambda}4686 emission line (L {approx} 310 L{sub Sun }) just before periastron reveals the presence of a very luminous transient source of extreme UV radiation emitted in the WWC region. Clumps in the primary's wind probably explain the flare-like behavior of both the X-ray and He II {lambda}4686 light curves. After a short-lived minimum, He II {lambda}4686 emission rises again to a new maximum, when X-rays are still absent or very weak. We interpret this as a collapse of the WWC onto the 'surface' of the secondary star, switching off the hard X-ray source and diminishing the WWC shock cone. The recovery from this state is controlled by the momentum balance between the secondary's wind and the clumps in the primary's wind.
- OSTI ID:
- 22011795
- Journal Information:
- Astrophysical Journal, Vol. 746, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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