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AAVSO Alert Notice 558

October 19, 2016

CI Aql monitoring needed to support HST observations

Dr. Edward Sion (Villanova University) has requested AAVSO 
observers' assistance in monitoring the recurrent nova CI Aql in
support of observations with the Hubble Space Telescope Cosmic 
Origins Spectrograph scheduled for October 31 - November 2, 2016,
and November 3 - November 5, 2016. These observations are part of 
a study on short orbital period recurrent novae as Supernovae
Type Ia progenitors.

It is essential to know 24 hours prior to the HST COS observations 
that CI Aql is not in outburst, in order to protect the
instrumentation. Observers are asked to keep an eye on CI Aql with 
nightly snapshot images (V preferred) from now until November 12,
and to report their observations promptly. It will be especially 
important to know the brightness of CI Aql each night for October
28 through November 7 UT. Visual observations are welcome.

CI Aql (Nova Aql 1917) has had recurrent outbursts in 1941 and 
2000, brightening to V~8.5. At minimum it is V~16-16.5 or fainter.

Coordinates (2000.0): R.A. 18 52 03.57  Dec.  -01 28 39.4

Charts with a comparison star sequence for CI Aql may be created 
using the AAVSO Variable Star Plotter (VSP, 
Observers need to be aware that the field of view is complicated 
by some comparison stars appearing as close doubles.

Please submit observations to the AAVSO International Database 
using the name CI AQL.

This campaign is being followed on the AAVSO Observing Campaigns 
webpage ( A thread has 
been created on the Campaigns and Observation Reports forum at 

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

When does an old nova become a dwarf nova? Kinematics and age of the nova shell of the dwarf nova AT Cnc

Authors: Michael M. Shara, Laurent Drissen, Thomas Martin, Alexandre Alarie

The Z Cam-type dwarf nova AT Cnc displays a classical nova (CN) shell, demonstrating that mass transfer in cataclysmic binaries decreases substantially after a CN eruption. The hibernation scenario of cataclysmic binaries predicts such a decrease, on a timescale of a few centuries. In order to measure the time since AT Cnc's last CN eruption, we have measured the radial velocities of a hundred clumps in its ejecta with SITELLE, CFHT's recently commissioned imaging Fourier transform spectrometer. These range from -455 to +490 km/s. Coupled with the known distance to AT Cnc of 460 pc (Shara 2012), the size of AT Cnc's shell, and a simple model of nova ejecta deceleration, we determine that the last CN eruption of this system occurred 330+135−90 years ago. This is the most rapid transition from a high mass transfer rate, novalike variable to a low mass transfer rate, dwarf nova yet measured, and in accord with the hibernation scenario of cataclysmic binaries. We conclude by noting the similarity in deduced outburst date (within a century of 1686 CE) of AT Cnc with a "guest star" reported in the constellation Cancer by Korean observers in 1645 CE.

It’s all about the  standstills, those episodes where the star gets stuck at a mid-point between maximum and minimum. If it doesn’t exhibit standstills it isn’t a Z Cam star.

AM Her stars in need of further investigation

Data from Catalina Real Time Survey 
Drake et al. 2009, ApJ, 696, 87

Northern CVs brighter than 17th magnitude here.

Southern CV's brighter than 17th magnitude here.


New outbursts and unusual activity reported in the last 72 hours

Last updated 10:55 October 24 2016



KU Cas
U Gem
CY Lyr

# indicates a noteworthy or unusual outburst
:  indicates confirmation required
'Activity At A Glance' is gleaned from observations reported to AAVSO MyNewsFlash, BAAVSS-Alert, CVnet-Outburst, VSObs-share and VSNET-outburst. We sincerely thank all the observers who contribute timely observations and reports of activity to these email lists.


Authors: Artur Rutkowski, Waclaw Waniak, George W. Preston, Wojciech Pych

Authors: Andrey Semena, Mikhail Revnivtsev, David Buckley, Alexander Lutovinov, Hannes Breytenbach

Authors:  T. Kato et al

Authors: T.V. Tomov, K.A. Stoyanov, R.K. Zamanov