October 19, 2012: Dr. Noel Richardson (Universite de Montreal, formerly at Georgia State University) has requested monitoring of the Small Magellanic Cloud eclipsing binary HD 5980 (in Tucana) as part of a multiwavelength campaign he is coordinating to study this unusual system. Dr. Richardson writes:
"HD 5980 is an eclipsing binary in the Small Magellanic Cloud. The system consists of two massive, stars that both have a strong wind. The primary star is a luminous blue variable (LBV) and is unstable, having erupted in the 1990s to become the visually brightest star in the SMC. The secondary star is a nitrogen-enriched Wolf-Rayet star (WN). The orbit is slightly eccentric with a short 19.3 d period. As the stars orbit each other, their strong winds collide, bringing about changes in multiple spectral lines, small changes in the brightness of the system, and strong X-ray modulation.
"We have been awarded time with the CTIO 1.5 m telescope to further study this system in the upcoming months (October -- January). It would be incredibly useful to have simultaneous ground-based photometry from the expert observers of the AAVSO with preference to filtered CCD measurements (UBVRI or any subset of these). This will allow us to fully update the orbital ephemeris. It will be great to have high cadence observations on the nights of the eclipses (given below), as well as good coverage (a few points per night) on the remaining nights through January. We thank the southern observers in advance for their contributions. With enough good photometry, there is a chance that we might be able to detect a period change in this system, expected with the various high mass-loss stages, both constant and eruptive. Such a period change will inform us of how much mass the system is losing, a key parameter for massive, luminous stars that tend to be dominated by their strong winds.
"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)"
Beginning immediately, visual and photometric observations are requested on a nightly basis, with higher cadence on the nights of the eclipses. BVRI photometry would be ideal, but any filter(s) would be very helpful. According to observations in the AAVSO International Database, HD 5980 is currently at visual magnitude ~11.6.
Coordinates: RA = 00 59 26.57 Dec = -72 09 53.9 (2000.0)
Charts may be created using VSP (http://www.aavso.org/vsp).
Please submit observations to the AAVSO International Database using the name HD 5980.
This campaign is described on the AAVSO Observing Campaigns page.
Your observations are very important to the success of this campaign. If you have been observing HD 5980, please continue. If you have not, and if you can observe this far south, please add HD 5980 to your nightly list. Many thanks!
This AAVSO Alert Notice was prepared by Elizabeth O. Waagen.
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