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Alert Notice 580: ASASSN-17fp rebrightening event and ongoing monitoring

May 24, 2017: ASASSN-17fp, discovered on 2017 April 28 and classified as a helium dwarf nova, was observed to be in outburst again on May 16 after fading 2.5 magnitudes from its original outburst. Dr. Tom Marsh (University of Warwick) and Dr. Elme Breedt (University of Cambridge) requested immediate time-series coverage.

Dr. Breedt wrote: "The transient was identified as a helium dwarf nova (also known as an AMCVn star) from a spectrum taken by the PESSTO survey and reported in ATel #10334. Since then, we have been observing the target using the New Technology Telescope on La Silla in Chile. We measured a photometric period of 51 minutes in the first few nights during which the object was bright at g=16.03 (Marsh et al., ATel #10354), and then it faded to about g~18. However last night [ May 16] it brightened back to g~16 again, apparently starting a second outburst.

"Time series observations during this bright state would be very valuable to determine whether the 51 min period we saw in earlier data returns, and whether it is the orbital period of the binary or related to the distortion of the accretion disc in outburst (superhumps). If the 51 min signal is the orbital period or close to it, this would be the helium dwarf nova with the longest orbital period known. Multiple successive outbursts are not uncommon in binaries like this..."

Dr. Breedt also requested that observers continue to monitor ASASSN-17fp with nightly snapshots for two weeks after it fades, in case it rebrightens again. It appears to have faded, according to an observation in the AAVSO International Database by F.-J. Hambsch (HMB, Mol, Belgium), who observed it remotely from Chile on 2017 May 24.2252 UT at magnitude 19.944 CV +/- 0.595.

Please continue nightly snapshots through June 6 at least, and if it brightens again, resume time series.
     
Coordinates (2000.0):  R.A. 18 08 51.11  Dec. -73 04 04.2

Finder charts with a comparison star sequence for ASASSN-17fp may be created using the AAVSO Variable Star Plotter (VSP). To see the sequence, choose an 'e', 'f', or 'g' scale chart.

Observations should be submitted to the AAVSO International Database using the name ASASSN-17fp.

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

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