Browsing by Subject "stars: massive"

Now showing 1 - 4 of 4
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    Open Access
    Multi-epoch VLTI-PIONIER imaging of the supergiant V766 Cen: Image of the close companion in front of the primary
    (2017) Wittkowski, M; Abellán, F J; Arroyo-Torres, B; Chiavassa, A; Guirado, J C; Marcaide, J M; Alberdi, A; de Wit, W J; Hofmann, K-H; Meilland, A; Millour, F; Mohamed, S; Sanchez-Bermudez, J
    Context. The star V766 Cen (=HR 5171A) was originally classified as a yellow hypergiant but lately found to more likely be a 27−36 M⊙ red supergiant (RSG). Recent observations indicated a close eclipsing companion in the contact or common-envelope phase.
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    Open Access
    Near-infrared evidence for a sudden temperature increase in Eta Carinae
    (2014) Mehner, Andrea; Ishibashi, Kazunori; Whitelock, Patricia; Nagayama, Takahiro; Feast, Michael; van Wyk, Francois; de Wit, Willem-Jan
    Aims. Eta Car's ultra-violet, optical, and X-ray light curves and its spectrum suggest a physical change in its stellar wind over the last decade. It was proposed that the mass-loss rate decreased by a factor of about 2 in the last 15 years. We complement these recent results by investigating the past evolution and the current state of eta Car in the near-infrared (IR). Methods. We present JHKL photometry of eta Car obtained at SAAO Sutherland from 2004-2013 with the Mk II photometer at the 0.75-m telescope and JHKs photometry with SIRIUS at the 1.4-m IRSF telescope from 2012-2013. The near-IR light curves since 1972 are analyzed. Results. The long-term brightening trends in eta Car's JHKL light curves were discontinuous around the 1998 periastron passage. After 1998, the star shows excess emission above the extrapolated trend from earlier dates, foremost in J and H, and the blueward, cyclical progression in its near-IR colors is accelerated. The near-IR color evolution is strongly correlated with the periastron passages. After correcting for the secular trend we find that the color evolution matches an apparent increase in blackbody temperature of an optically thick near-IR emitting plasma component from about 3500 to 6000 K over the last 20 years. Conclusions. We suggest that the changing near-IR emission may be caused by variability in optically thick bremsstrahlung emission. Periastron passages play a key role in the observed excess near-IR emission after 1998 and the long-term color evolution. We thus propose as a hypothesis that angular momentum transfer (via tidal acceleration) during periastron passages leads to sudden changes in eta Car's atmosphere resulting in a long-term decrease in the mass-loss rate.
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    Open Access
    SN 2006oz: rise of a super-luminous supernova observed by the SDSS-II SN Survey
    (2012) Leloudas, G; Chatzopoulos, E; Dilday, B; Gorosabel, J; Vinko, J; Gallazzi, A; Wheeler, J C; Bassett, B; Fischer, J A; Frieman, J A; Fynbo, J P U; Goobar, A; Jelínek, M; Malesani, D; Nichol, R C; Nordin, J; Östman, L; Sako, M; Schneider, D P; Smith, M; Sollerman, J; Stritzinger, M D; Thöne, C C; de Ugarte Postigo, A
    Context. A new class of super-luminous transients has recently been identified. These objects reach absolute luminosities of M-u < -21, lack hydrogen in their spectra, and are exclusively discov ...
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    Open Access
    The yellow hypergiant HR 5171 A: Resolving a massive interacting binary in the common envelope phase
    (2014) Chesneau, O; Meilland, A; Chapellier, E; Millour, F; van Genderen, A M; Nazé, Y; Smith, N; Spang, A; Smoker, J V; Dessart, L; Kanaan, S; Bendjoya, Ph; Feast, M W; Groh, J H; Lobel, A; Nardetto, N; Otero, S; Oudmaijer, R D; Tekola, A G; Whitelock, P A; Arcos, C; Curé, M; Vanzi, L
    Context. Only a few stars are caught in the very brief and often crucial stages when they quickly traverse the Hertzsprung-Russell diagram, and none has yet been spatially resolved in the mass transfer phase.