Alert Notice 758: Monitoring requested for 11 dwarf novae in support of HST observations in 2021-2022

Note:  RY Ser was scheduled for May and for June but was in outburst or too close to outburst to be a safe target. It may be rescheduled. GP Com observations did take place.  -  Elizabeth O. Waagen, July 5, 2022

GP Com observations will take place April 29-30, 2022; coverage is needed until May 20. See Alert Notice 775.  -  Elizabeth O. Waagen, April 27, 2022

SDSS J154453.60+255348.8 will not be observed by HST during April. V1239 Her and V493 Gem have been observed and observations of them are no longer needed.   -  Elizabeth O. Waagen, April 5, 2022

GP Com is being observed with HST on January 21, 2022.   YZ LMi observations are no longer needed.  -  Elizabeth O. Waagen, January 3, 2022

YZ LMi is to be observed with HST on December 30, 2021. CH UMa observations are no longer needed.  -  Elizabeth O. Waagen,  December 21, 2021

October 26, 2021

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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 2022. 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 2021-2022 campaign on dwarf novae is the second part of a larger campaign which includes additional dwarf novae to be observed in 2022-2023 and 2023-2024 (to be announced later), and 15 VY Scl stars for which coverage (2021-2024) was requested in AAVSO Alert Notice 754.

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 CH UMa immediately. Because the specific HST dates are not known, it would be prudent to begin nightly coverage of the other targets the month before the HST window given in the table. For example, begin observing YZ LMi (scheduled for December) on November 1.

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."

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.

Targets: November 2021 – September 2022

Name (primary VSX name) Alternate Name R.A. (2000) Dec (2000) Range CV type HST window

Scheduled for/Completed

CH UMa   10 07 00.72 +67 32 47.5 10.7-15.3 V  UG November 2021 completed
YZ LMi   09 26 38.73 +36 24 02.5 16.3 g-20.5 CV UGSU/IBWD+E December 2021 completed
GP Com   13 05 42.40 +18 01 03.8 15.7-16.2 V IBWD January 2022 completed
V1239 Her   17 02 13.25 +32 29 54.2 13.7 CR-19.1 V UGSU+E February 2022 completed
V493 Gem ASASSN-14mv 07 13 27.28 +20 55 53.3 11.7 - 18.2 V UG/IBWD March 2022 completed
SDSS J154453.60+255348.8 (CrB) 2MASS J15445360+2553488 15 44 53.60 +25 53 49.0 16.0 - 19.7 g NL+E April 2022 removed from targets
RY Ser   17 23 07.18 -12 48 09.7 13.6 - 16.6 V UG May 2022 not observed May or June
SDSS J190817.07+394036.4 (Lyr) KIC 4547333 19 08 17.08 +39 40 36.4 16.2 - 16.3 V IBWD June 2022  
UU Aql   19 57 18.77 -09 19 21.1 11.0 - 17.0 V UGSS July 2022 completed
V485 Aqr SDSS J204448.92-045928.8 20 44 48.92 -04 59 28.8 14.3 - 17.1 V UG August 2022 completed
ASASSN-14cn (Dra)   16 11 33.95 +63 08 32.0 13.6 - 18.7 V UG/IBWD+E September 2022 completed

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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