Browsing by Subject "outflows"

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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
    The ALMA detection of CO rotational line emission in AGB stars in the Large Magellanic Cloud
    (2016) Groenewegen, M A T; Vlemmings, W H T; Marigo, P; Sloan, G C; Decin, L; Feast, M W; Goldman, S R; Justtanont, K; Kerschbaum, F; Matsuura, M; McDonald, I; Olofsson, H; Sahai, R; van Loon, J Th; Wood, P R; Zijlstra, A A; Bernard-Salas, J; Boyer, M L; Guzman-Ramirez, L; Jones, O C; Lagadec, E; Meixner, M; Rawlings, M G; Srinivasan, S
    Context. Low- and intermediate-mass stars lose most of their stellar mass at the end of their lives on the asymptotic giant branch (AGB). Determining gas and dust mass-loss rates (MLRs) is important in quantifying the contribution of evolved stars to the enrichment of the interstellar medium.
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    Open Access
    X-ray pulsations from the region of the supergiant fast X-ray transient IGR J17544−2619
    (2012) Drave, S P; Bird, A J; Townsend, L J; Hill, A B; McBride, V A; Sguera, V; Bazzano, A; Clark, D J
    Phase-targeted RXTE observations have allowed us to detect a transient 71.49 pm 0.02 s signal that is most likely to be originating from the supergiant fast X-ray transient IGR J17544-2619. The phase-folded light curve shows a possible double-peaked structure with a pulsed flux of ~4.8*10-12 erg cm-2 s-1 (3-10 keV). Assuming the signal to indicate the spin period of the neutron star in the system, the provisional location of IGR J17544-2619 on the Corbet diagram places the system within the classical wind-fed supergiant XRB region. Such a result illustrates the growing trend of supergiant fast X-ray transients to span across both of the original classes of HMXB in Porb - Pspin space.