Alert Notice 754: Monitoring requested for 15 VY Scl cataclysmic variables in support of HST observations

Note: Please continue to monitor these targets per the instructions below.  -  Elizabeth O. Waagen, October 31, 2022

September 14, 2021

AAVSO Forum threads (scroll to the bottom of a thread for latest posts):
- Campaigns and Observing Reports:
- Cataclysmic Variables:
- Spectroscopy:

Please subscribe to these threads if you are participating in the campaign so you can be updated by the astronomers and by HQ. Join in the discussion or ask questions there!

Drs. Anna Francesca Pala (European Space Agency, ESAC, Spain) and Thomas Kupfer (Texas Tech University), on behalf of a large consortium of astronomers, have requested AAVSO observers' assistance in monitoring 15 VY Scl novalike cataclysmic variables in support of Target of Opportunity (ToO) observations with the Hubble Space Telescope.

Coverage is requested to begin immediately and continue through September 2024.

This campaign on VY Scl stars is the first part of a larger campaign which includes a substantial number of dwarf novae to be observed by HST. The parts of the campaign related to the dwarf novae will be announced in separate Alert Notices.

Dr. Pala writes: "VY Scl [systems] are typically characterised by high average accretion rates which keep the disc in a stable hot state, equivalent to a permanent outburst. Occasionally the accretion rate drastically drops (“low state”), unveiling the white dwarf. These low states provide a window in which we can directly observe the underlying accreting white dwarf and measure its temperature, mass and accretion rate. For this reason, we have to make absolutely sure that the HST observations are obtained during a low state, when the white dwarf is the dominant source of light in the ultraviolet. Moreover, this observing strategy will protect the detectors of the Cosmic Origin Spectrograph against exposure to too much light which, during high states, could result in their permanent damages."

"...A continuous nightly monitoring over the entire visible period would be useful to detect the occurrence of a low state, which we will use to trigger the HST observations via ToOs."

Dr. Pala further informs us that a website that includes all the information on the progam is in preparation. When it is ready, the link will be posted in the forum threads given above. [Note from October 2023: this website was not created.]

Nightly observations in V of the targets in the table below are requested. A minimum SNR~20 is recommended. If the target is too faint to obtain the minimum SNR in V, switch to CV. It is important to cover the targets for as long as they are observable, including dusk and dawn twilight at the ends of the observing season. If a target is observed going into its faint state, please submit your observation(s) as soon as possible, and begin obtaining multiple observations per night.

If time-series observations are made, an uninterrupted light curve in a single filter (preferably B or V) would be better than alternating with different filters. CV observations can still be useful but V-filter observations should be the priority (whenever possible).

DSLR observations, particularly if they are transformed to V, will be useful and are welcome. Visual observations will also be very valuable.

Regarding spectroscopy, observations during the low state of these VY Scl systems would be very valuable (but probably challenging) since they can provide the detection of both the white dwarf and the donor star. Spectra during high states are not necessary since these should already be available in the literature (and the spectral appearance of these objects is not expected to change significantly over time during high states). If spectroscopy is possible for a target in its low state, any resolution up to ~10000 and covering the wavelength range between ~4000-10000 A would be appropriate. For those observers doing both photometry and spectroscopy, the photometry is of much higher priority.

Name (primary name in VSX) Alternate Name R.A. (2000) Dec (2000) Range Priority
1SWASP J022916.91-395901.4 (Eri) 1RXS J022917.1-395851 02 29 16.94 -39 59 01.6 12.8 - 16.7: V first
HS 0506+7725 (Cam)   05 13 36.57 +77 28 42.8 14.6 V - 18.5 B first
KR Aur   06 15 43.92 +28 35 08.6 12.7 - 19.5: V first
V442 Oph   17 32 15.14 -16 15 22.1 13.45 V - 16.4 CV first
GS Pav   20 08 07.62 -69 48 58.7 14.8 - 18.6 CV first
V794 Aql   20 17 33.92 -03 39 51.0 13.4 - 18.6 V first
VY Scl GD 1662 23 29 00.47 -29 46 46.0 11.8 - 18.6 V first
1RXS J233801.0+430852 (And) 2MASS J23375921+4308509 23 37 59.22 +43 08 51.1 16.05 - 20.6 V first
V704 And   23 44 57.51 +43 31 22.3 12.6 - 19.5 CV first
HS 0220+0603 (Cet)   02 23 01.66 +06 16 49.6 15.7 - 19.7 CV second
WX Ari   02 47 36.22 +10 35 37.7 14.5 - 18.6 V second
V1024 Cep HS 0455+8315 05 06 48.28 +83 19 23.3 14.7 V - 20.7 CV second
LN UMa   10 04 34.73 +66 29 14.9 14.6 - 18 V second
V380 Oph   17 50 13.63 +06 05 29.3 14.3 V - 19.0 CV second
V425 Cas   23 03 46.66 +53 17 14.8 14.4 - 18.0 V second

Among these targets, GS Pav and WX Ari are eclipsing. Their elements are:

Name Period (d) Zero phase (HJD)
GS Pav 0.1552699235 2457567.83273
WX Ari 0.1393512 2452500.139

Charts with comparison stars for the targets may be created using the AAVSO Variable Star Plotter (VSP).

Please submit observations in a timely manner, and as soon as possible if a star is seen going into its faint state. Use the primary name given in the above table.
  - Photometry and visual observations: AAVSO International Database
  - Spectroscopy: AAVSO Spectroscopy Database
(links at the end of this Alert Notice)

Observers are encouraged to subscribe to the forum threads above and use them to report any interesting observations and post questions or comments for Dr. Pala and Dr. Kupfer.

Dr. Pala writes that "Our team deeply values the support from AAVSO observers and significant contributors will be invited to join the papers as co-authors."

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



Information on submitting observations to the AAVSO may be found at:
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 - Spectroscopy:


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