Alert Notice 459: Monitoring of RU Peg requested for Swift observations

6 June 2012: Dr. Koji Mukai (Universities Space Research Association/NASA Goddard Space Flight Center) has requested AAVSO observers' assistance in monitoring the SS Cyg-type dwarf nova RU Peg in support of target-of-opportunity observations with the NASA Swift satellite during an outburst.

His observations will be targeted during the rise to outburst and during late decline from outburst. Thus, your prompt notification to AAVSO Headquarters of activity in RU Peg will be crucial to the success of this campaign.

The campaign will run from now through March 31, 2013. According to Dr. Mukai, although RU Peg is observable with Swift from mid-April to mid-January, the best time of the year for Swift is late June through late October. However, he notes, there are ~3 days every month when it is too close to the Moon (around July 7, August 4, August 31, September 27, and October 25).

According to observations in the AAVSO International Database, the last outburst of RU Peg occurred 2012 April 7, reached visual magnitude 10.1, and was brighter than magnitude 12.0 for 12 days. Around 12.9 at minimum, it is currently at magnitude 13.1 (M. Komorous, London, ONT, Canada). The next outburst is expected to occur mid-June through mid-July.

Visual and CCD observations (filtered preferred to unfiltered) are appropriate for this campaign. Observers are requested to monitor RU Peg duning minimum, throughout the next outburst, and after return to minimym, and report their observations in a timely manner. If RU Peg appears to be brightening from minimum, please report your observations immediately to the AAVSO. If it is brighter than magnitude 12.3, please also send an email report to Elizabeth Waagen ( and Matthew Templeton (  

Please be aware that there is a ~12.5-magnitude star 11" NE of RU Peg. Be sure to use a chart that goes deep enough to clearly show the locations of both RU Peg and the 12.5 star, and please be careful not to push your telescope too far.

Dr. Mukai writes: "In the famous AAVSO/EUVE/RXTE campaign on SS Cyg (Mattei et al. 2000JAVSO..28..160M), the hard X-ray flux went up (with a delay) during the rise, then suddenly dropped; there was a corresponding flux enhancement episode during the decline.  We know that, during the peak of the outburst, many dwarf novae are hard X-ray fainter than in quiescence (with a few exceptions, like U Gem). However, the hard X-ray enhancement episodes seen in SS Cyg have never been observed in other dwarf novae. We have proposed a hypothesis that this is related to the mass of the accreting white dwarf; only dwarf novae with a relatively massive white dwarf show the hard X-ray enhancement. If that's true, we may well see similar enhancement in RU Peg, which is thought to have a massive white dwarf. Even if this hypothesis is completely wrong, RU Peg is a good target for an SS Cyg-like campaign, since it's X-ray bright during quiescence."

Coordinates: RA 22 14 02.58  Dec +12 42 11.4  (2000.0)

Charts for RU Peg may be created using the AAVSO Variable Star Plotter (

Please submit observations promptly to the AAVSO International Database using the name RU PEG.

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


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