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Alert Notice 548: AR Sco observing campaign

August 18, 2016: Dr. Thomas Marsh (University of Warwick) and colleagues have requested AAVSO coverage of the intriguing binary AR Sco in support of upcoming Newton-XMM observations.

The XMM observations of AR Sco have been scheduled for:
2016 September 10 15:41 - September 11 02:26 UT

As with all satellite observations, there is always the chance that Target of Opportunity (TOO) observations of a transient object may cause the schedule to change. If this should happen, observers will be alerted via an AAVSO Special Notice and the Campaigns and Observing Reports Forum.

This fascinating binary system is the subject of an exciting paper in the July 2016 issue of Nature ( A pre-print version is available at arXiv ( The article is titled "A radio-pulsing white dwarf binary star" and the authors are T. R. Marsh, B. T. Gaensicke, S. Huemmerich, F.-J. Hambsch, K. Bernhard, C. Lloyd, E. Breedt, E. R. Stanway, D. T. Steeghs, S. G. Parsons, O. Toloza, M. R. Schreiber, P. G. Jonker, J. van Roestel, T. Kupfer, A. F. Pala, V. S. Dhillon, L. K. Hardy, S. P. Littlefair, A. Aungwerojwit, S. Arjyotha, D. Koester, J. J. Bochinski, C. A. Haswell, P. Frank, and P. J. Wheatley. A press release from the European Southern Observatory is available at .

Dr. Marsh writes of their research on AR Sco: " was down to [the amateurs [who are co-authors] on the paper that we got onto it in the first place ...It's already past best visibility for this year, but there will be plenty of opportunity in the future. I think many observers will find it a fascinating object to study and it could be accessible to quite a number of them I think (at its very brightest it gets to V=13.6 although a more typical magnitude is V=14.8).

"Coverage immediately before, after and (especially) during [the XMM observations] would be great. The most challenging aspect is the time resolution: ideally one wants a cadence < 29 seconds because of the strong harmonic of the basic 2 minute period, and the faster the better. Observers should use whatever filter (including clear/white light) is needed to allow them to match this constraint. If they can't follow it this fast or faster, then it might not be worth their trying. They need to have accurate timing as well, i.e. they need to know the centres of the exposures to better than +/- 2 seconds, and preferably better."

Please observe AR Sco beginning now (one to a few times per night), then switch to the cadence Dr. Marsh requests long enough before the XMM observations begin to establish a good baseline. Continue at this cadence through the XMM observations and beyond for at least another hour.

A page of materials on AR Sco related to the Nature paper may be found at    Item #9 on that page is a YouTube video of a fascinating movie Dr. Marsh made of AR Sco from their data. The direct link to the video is (

Coordinates (2000.0):  R.A. 16 21 47.29   Dec. -22 53 10.4

Charts: Charts with a comparison star sequence for AR Sco may be created using the AAVSO Variable Star Plotter (VSP).

Please submit observations to the AAVSO International Database using the name AR SCO.

This campaign is being monitored on the AAVSO Observing Campaigns webpage and is being followed on the Campaigns and Observation Reports Forum under the thread AR Sco Campaign.

This AAVSO Alert Notice was compiled by Elizabeth O. Waagen.


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