Alert Notice 767: Coverage needed now for CSS_J024048.5+195227 in support of HST observations

January 30, 2022

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Dr. Peter Garnavich (University of Notre Dame) and colleagues request AAVSO observers' assistance in monitoring the cataclysmic variable CSS_J024048.5+195227 in support of HST observations scheduled for:

2022 03 February 01:32:35 - 08:47:50 UT

Time-series coverage is requested beginning immediately and continuing through February 4 UT.

Dr. Garnavich writes: "CSS_J024048.5+195227 is the second known “propeller” cataclysmic variable (AE Aqr is the other). In a propeller CV, gas donated by the cool secondary star is prevented from forming an accretion disk by the spinning, magnetic white dwarf. Instead, the drag force of the spinning field accelerates the donated gas and ejects it from the system ( J0240 has recently been found to have the fastest spinning white dwarf in a CV system. As with AE Aqr, the target is seen to have ~1 mag flares thought to be caused by the donated gas being shocked as it runs into the white dwarf propeller. Hubble Space Telescope will observe the target in the ultraviolet (COS). We request optical observations around the time of the HST visit to confirm its photometric state and flaring characteristics. Observations that are simultaneous with the HST visit are particularly useful to correlate optical flares with the UV data.

"CCD time-series observations are most valuable. The longer the time-series the better. A cadence between 10s to 60s is best. Time-series should be done in a single filter. Unfiltered observations are fine (CV or CR), but filtered observations should aim for a blue wavelengths (g,V, or B) as the flaring amplitude is strongest in the blue. The signal/noise ratio (SNR) of a single exposure should be >5. If the SNR in each exposure is greater than 25, then exposure times should be shortened and a faster cadence used. That is, it is better to get a high-cadence time-series than high SNR in each exposure.

"DSLR observations are acceptable if the required SNR level can be reached over a long time-series."

For this campaign, visual observations are not requested. Spectroscopy is also not requested.

Dr. Garnavich adds: "It looks like the visit is well placed for North American observers...[to obtain] simultaneous photometry with the HST visit.  [Also, we] predict that an eclipse for J0240 will occur during the HST visit at:

2022 February 03 02:07:23.714 UT

which is in darkness over the East Coast but twilight in the West."

Dr. Garnavich also notes that observers contributing significant data will be considered for co-authorship.

Coordinates for CSS_J024048.5+195227 (2000.0): R.A. 02 40 48.54   Dec. +19 52 27.1 (from VSX page for CSS_J024048.5+195227)
Range: 16.4 - 18.5 V
Variability Type: DQ/AE+E   [AE is a new subtype]

Charts with comparison stars for CSS_J024048.5+195227 may be created using the AAVSO Variable Star Plotter (VSP).

Please submit observations using the name CSS_J024048.5+195227 to the AAVSO International Database.

This AAVSO Alert Notice was compiled by Elizabeth O. Waagen using material provided by Dr. Garnavich.


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