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Post Info TOPIC: HD 5980
Blobrana


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RE: HD 5980
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The predicted primary eclipses are on the following JDs:

2456220.8 (2012 Oct 20)
2456240.0 (2012 Nov 8)
2456259.3 (2012 Nov 27)
2456278.5 (2012 Dec 17)
2456297.8 (2013 Jan 5)
2456317.0 (2013 Jan 24)

The predicted secondary eclipses are on the following JDs:

2456227.7 (2012 Oct 27)
2456246.9 (2012 Nov 15)
2456266.2 (2012 Dec 4)
2456285.4 (2012 Dec 24)
2456304.7 (2013 Jan 12)
2456323.9 (2013 Jan 31)"

Position (J2000): R.A. 00 59 26.57  |  Dec. -72° 09' 53.9''

Information on submitting observations to the AAVSO



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Blobrana


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Title: Wind structure and luminosity variations in the WR/LBV HD 5980
Authors: Leonid N Georgiev, Gloria Koenigsberger, D John Hillier, Nidia Morrell, Rodolfo Barba, Roberto Gamen

Over the past 40 years, the massive LBV/WR system HD 5980 in the Small Magellanic Cloud has undergone a long-term S Doradus type variability cycle and two brief and violent eruptions in 1993 and 1994. In this paper we analyse a collection of UV and optical spectra obtained between 1979 and 2009 and perform CMFGEN model fits to spectra of 1994, 2000, 2002 and 2009. The results are as follows: a) The long term S Dor-type variability is associated with changes of the hydrostatic radius; b) The 1994 eruption involved changes in its bolometric luminosity and wind structure; c) the emission-line strength, the wind velocity and the continuum luminosity underwent correlated variations in the sense that a decreasing V_\infty is associated with increasing emission line and continuum levels; and d) The spectrum of the third star in the system (Star C) is well-fit by a T_{eff}=32 K model atmosphere with SMC chemical abundances.
For all epochs, the wind of the erupting star is optically thick at the sonic point and is thus driven mainly by the continuum opacity. We speculate that the wind switches between two stable regimes driven by the "hot" (during the eruption) and the "cool" (post-eruption) iron opacity bumps as defined by Lamers & Nugis (2002) and Grafener and Hamann (2008), and thus the wind may undergo a bi-stability jump of a different nature from that which occurs in OB-stars.

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Blobrana


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Title: New insights into the nature of the SMC WR/LBV binary HD 5980
Authors: C. Foellmi, G. Koenigsberger, L. Georgiev, O. Toledano, S.V. Marchenko, P. Massey, T.H. Dall, A.F.J. Moffat, N. Morrell, M. Corcoran, A. Kaufer, Y. Naze, J. Pittard, N. St.-Louis, A. Fullerton, D. Massa, A.M.T. Pollock

We present the results of optical wavelength observations of the unusual SMC eclipsing binary system HD 5980 obtained in 1999 and 2004--2005. Radial velocity curves for the erupting LBV/WR object (star A) and its close WR-like companion (star B) are obtained by deblending the variable emission-line profiles of N IV and N V lines under the simplistic assumption that these lines originate primarily in the winds of star A and star B. The derived masses M_A=58--79 Mo and M_B=51--67 Mo, are more consistent with the stars' location near the top of the HRD than previous estimates. The presence of a wind-wind interaction region is inferred from the orbital phase-dependent behaviour of He I P Cygni absorption components. The emission-line intensities continued with the declining trend previously seen in UV spectra. The behaviour of the photospheric absorption lines is consistent with the results of Schweickhardt (2002) who concludes that the third object in the combined spectrum, star C, is also a binary system with P(starC)~96.5 days, e=0.83. The data used in this paper will be made publicly available for further analysis.

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Blobrana


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Posts: 131433
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Extraordinary LBV/WR system
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Title: The extraordinary LBV/WR system HD 5980
Authors: Gloria Koenigsberger, Edmundo Moreno

The LBV/WR system HD 5980 contains a short-period, eccentric binary system with interacting stellar winds. In this paper we summarise results from model calculations of the tidal flows on the LBV component showing that energy dissipation rates, E-dot, associated with turbulent viscosity are orbital-phase dependent as well as variable over the stellar surface. We speculate that if E-dot contributes towards driving mass-loss, the strongest wind-wind interaction effects may occur after periastron passage. In addition, the model suggests the presence of stronger outflows localised at polar angles theta~30 --50 degrees during part of the orbital cycle. Thus, the analysis of wind-wind interactions in this system requires that models be revised to incorporate non-stationary and asymmetric wind structures.

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Blobrana


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Posts: 131433
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HD5980
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Title: First detection of phase-dependent colliding wind X-ray emission outside the Milky Way
Authors: Yael Naze (IAGL, ULg), Michael F. Corcoran (GSFC), Gloria Koenisgberger (UNAM), Anthony F.J. Moffat (UMontreal)

After having reported the detection of X-rays emitted by the peculiar system HD5980, we assess here the origin of this high-energy emission from additional X-ray observations obtained with XMM-Newton. This research provides the first detection of apparently periodic X-ray emission from hot gas produced by the collision of winds in an evolved massive binary outside the Milky Way. It also provides the first X-ray monitoring of a Luminous Blue Variable only years after its eruption and shows that the dominant source of the X-rays is not associated with the ejecta.

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Blobrana


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Posts: 131433
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HD 5980
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Imagine two stars with winds so powerful that they eject an Earth's worth of material roughly once every month. Next, imagine those two winds colliding head-on. Such titanic collisions produce multimillion-degree gas, which radiates brilliantly in X-rays. Astronomers have conclusively identified the X-rays from about two-dozen of these systems in our Milky Way. But they have never seen one outside our galaxy — until now.
The binary system, known as HD 5980, contains two extremely massive stars, 'weighing' about 50 and 30 times the mass of the Sun. Each star radiates more than a million times as much light as the Sun, meaning they put out more light in one minute than our host star generates in an entire year.

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