Alert Notice 608: TT Ari monitoring requested for VLA observations

December 1, 2017: Dr. Deanne Coppejans (Northwestern University) and colleagues have requested AAVSO assistance in monitoring the cataclysmic variable TT Ari in support of observations scheduled to be made with the Very Large Array (VLA) in December 2017.

Dr. Coppejans writes:

"Background  -  Cataclysmic Variables (CVs, binary stars in which one star is stripping material off of its close companion star) have been observed at optical wavelengths for hundreds of years. It is only recently, however, that we have had radio telescopes that are sensitive enough to detect CVs at radio wavelengths. With the AAVSO, we showed that CVs produce significant radio emission (light). Currently we do not know how the radio emission is produced or where it comes from in CVs. One of the main ideas for its origin is that it comes from jets of matter that the CV launches out into the universe. If this is the case, then it is an important finding that can help us understand the details of how material and energy are transferred between stars and then out into space. This was the science case we were testing in previous AAVSO campaigns." [see, for example, AAVSO Alert Notices 505 and 539]

"In this campaign, we are testing alternative theories. The CV TT Ari shows unusual flaring radio emission that is different from other CVs and is not from a jet. Why is it different from other CVs? Where does the radio emission come from? At the moment we don't have the well-sampled radio light curves necessary to answer these questions. Over 10-12 December 2017 the Very Large Array telescope in New Mexico will take high-cadence radio observations to help us answer these questions. To help pinpoint the source of the emission, we are arranging a campaign to get simultaneous observations at many different wavelengths. Different parts of the CV predominantly emit light at different wavelengths, so multi-wavelength observations will help us isolate the source of the emission.

"AAVSO observations  -  The VLA will observe TT Ari twice for four hours (a total of 8 hours) over the period 10-12 December 2017. The exact timing depends on the weather, and we will likely only have a day or two advance notice of the exact time. In preparation for these observations, we ask for increased monitoring of TT Ari over the period 3 - 19 December so that we know the state during the observations. Additionally, during the VLA observations, we need as many observations as possible (in any filter). If you are able to take photometry (as high cadence as possible) in a single filter, that will be extremely useful. V-band data are preferred. Otherwise, U-band if possible, or else any other band.

"Thank you in advance for all your observations. This will be the first really high cadence radio campaign on a CV with simultaneous multi-wavelength data. With your help we will have optical light curves in a range of bands that will be extremely important to determine the source of the radio emission in TT Ari."

Observers are requested to observe TT Ari a few times per night beginning now and continuing through at least December 19, and to observe in a single filter at as high a cadence as possible December 10-12. V photometry is preferred, then U, then any other band. Visual observations are welcome.

TT Ari has a V range of 10.2 - 16.5. Observations in the AAVSO International Database from 2017 November 29-30 show it at visual magnitude 10.8 (BRJ, J. Bortle; HSP, S. Hovell; PYG, G. Poyner).

Coordinates (2000.0): R.A. 02 06 53.09   Dec. +15 17 41.8

Finder charts with a comparison star sequence for TT Ari may be created using the AAVSO Variable Star Plotter (VSP).

Please submit observations to the AAVSO International Database using the name TT ARI.

This multiwavelength observing campaign is being followed on the AAVSO Campaigns and Observing Reports online forum at

This AAVSO Alert Notice was compiled by Elizabeth O. Waagen using material supplied by Dr. Coppejans.


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