Alert Notice 838: Monitoring requested for 11 dwarf novae in support of HST observations in 2023-2024

Note: KZ Gem has been put on hold by HST, and likely won't be observed until next year, if at all.  -  Elizabeth O. Waagen, January 2, 2024

October 26, 2023

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

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 11 dwarf nova cataclysmic variables in support of observations with the Hubble Space Telescope.

Coverage is requested to begin immediately and continue through September 2024. The month each star is scheduled to be observed by HST is given in the table below. When specific HST dates are announced, they will be posted in the forum threads (above) related to this campaign. The webpage for this Alert Notice will also be updated.

This 2023-2024 campaign on dwarf novae is the fourth part of a larger campaign which includes 11 dwarf novae observed in 2022-2023 (AAVSO Alert Notice 796 and related follow-up Alert Notices), 11 dwarf novae observed in 2021-2022 (AAVSO Alert Notice 758 and related follow-up Alert Notices), and 15 VY Scl stars for which coverage (2021-2024) was requested in AAVSO Alert Notice 754 (and related follow-up Alert Notices).

Dr. Pala writes: "In the last 20 years, the study of compact interacting binaries has led to two major breakthroughs in astrophysics: the discovery of dark energy and the first detection of gravitational waves. Although binaries are critically important to probe the properties of the Universe and to test fundamental physical theories, our understanding of their evolution and final fate is still far from being complete.

"Accreting white dwarfs are ideal laboratories in which to test the models of compact binary evolution. We are carrying out a large program with the Cosmic Origin Spectrograph (COS), onboard the Hubble Space Telescope (HST), to obtain ultraviolet spectroscopy of 43 accreting white dwarfs, with the aim to accurately measure their effective temperatures, masses and accretion rates. These fundamental parameters will provide firm observational constraints on the angular momentum loss mechanisms driving the evolution of all types of binaries, and on the formation channel of the brightest gravitational wave sources. Moreover, we will unveil the intimate connection between accreting white dwarfs and Type Ia Supernova explosions.  
"Because of the extremely variable nature of accreting white dwarfs, we have to make absolutely sure that the HST observations are obtained during quiescence, as the detectors of the Cosmic Origin Spectrograph can be damaged by exposure to too much light. The outstanding support from the AAVSO observers is crucial to ensure the success of this program, which entirely relies on ground-based observers who can monitor the targets in the weeks prior to the HST observations."

INSTRUCTIONS: To assess the quiescent state of each target, nightly observations in V starting at least three weeks before the HST observations are requested, then a more intensive monitoring the week before the observations, and then nightly monitoring again for two/three weeks after the observations. As with all targets for HST, it will be crucial to have a positive V measurement 24 hours before the scheduled HST time so the HST team can make a go-nogo decision.

Please begin observing BF Eri immediately. Because the specific HST dates of the targets are not known, it would be prudent to begin nightly coverage of each of them the month before the HST window given in the table. For example, begin observing KZ Gem (scheduled for December) on November 1. Please focus your efforts on the next upcoming target, but if you have time, it would be good also to make observations of the later targets in order to give good long-term coverage for the HST planners.

A minimum SNR~20 is requested. If the target is too faint to obtain the minimum SNR in V, switch to CV. If a target is observed going into outburst, please submit your observation(s) as soon as possible and begin obtaining multiple observations per night.

Dr. Pala adds: "We know that some observers carry out time-series observations and also spectroscopy, and we welcome any additional contributions. Nonetheless the monitoring to assess quiescence should have the highest priority since, without it, there is the risk to lose the allocated orbits.

"In case of time-series observations, 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."

Targets: November 2023 – September 2024

Name (primary VSX name) R.A. (2000) Dec (2000) Range CV type HST window Scheduled for/Completed
BF Eri 04 39 29.95 -04 35 58.9 12.3 - 15.2 V UG November 2023 November 10 postponed to 2024
KZ Gem 06 53 02.45 +16 39 58.7 14.0 - 17.6 V UGSS+ELL December 2023 suspended or postponed to late 2024
ASASSN-18dg  (Eri) 04 07 49.30 -00 07 16.7 15.5 - 21.3 g UGSU/IBWD+E January 2024 January 11 completed
SDSS J080449.49+161624.8  (Cnc) 08 04 49.49 +16 16 24.9 17.8 - 19.1 r IBWD February 2024 February 16 completed
ASASSN-20pv  (Vel) 10 40 19.50 -49 51 29.7 12.3 g - 17.4 V UGSU/IBWD March 2024 May 30-31 cancelled due to technical issues with HST, hopefully to be rescheduled
SDSS J080846.19+313106.0  (Cnc) 08 08 46.19 +31 31 06.0 14.1 - 20.4 g UG April 2024 April 5-6 completed
ASASSN-19ct  (Cen) 11 33 15.36 -37 10 20.0 13.4 - 17.8 V UGSU/IBWD May 2024 May 18 completed
TW Vul 20 39 34.48 +27 15 55.8 12.8 - 18.4 V UG June 2024 June 28
LL Lyr 18 35 12.82 +38 20 04.3 12.9 - 18.5 V UG July 2024  
CS Ind 21 59 54.56 -68 50 36.6 11.5 V - 17.6 CV UGSU August 2024  
SDSS J152509.57+360054.5  (Boo) 15 25 09.57 +36 00 54.7 13.4 - 20.0 V UG/IBWD September 2024  

This table and corresponding tables in the AAVSO forums (see links above) will be updated as each target is scheduled, and as observations are carried out.

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 outburst. 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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