Alert Notice 845: HST schedule set for ASSN-18dg

January 2, 2024

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!

Further to AAVSO Alert Notice 838, Dr. Anna Francesca Pala (European Space Agency, ESAC, Spain) informs us that observations of the cataclysmic variable ASASSN-18dg have been scheduled with the Hubble Space Telescope for:

2024 January 11 UT

When the exact time is announced, it will be reported in the above forum threads.

Beginning immediately, please observe ASASSN-18dg in V one to a few times per night from now through January 11, then nightly through January 27. 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; the nights of January 8-9, 9-10, and 10-11 will be critical.

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 writes: "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."

ASASSN-18dg has a range of 15.5 - 21.3 g and spectral type UGSU/IBWD+E. The most recent observations of it in the AAVSO International Database show it at magnitude <20 V on 2023 Dec. 31.10383 UT (T. Rutherford, Blountville, TN).

Coordinates: R.A. 04 07 49.30  Dec. -00 07 16.7 (from VSX entry for ASASSN-18dg)

Charts with comparison stars for ASASSN-18dg may be created using the AAVSO Variable Star Plotter (VSP).

Please report all photometry observations to the AAVSO International Database using the name ASASSN-18dg. Include the hyphen and do not include any spaces in the name. Reduce and submit observations as soon as possible after making them.

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


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


An Alert Notice archive is available at the following URL:

Subscribing and Unsubscribing may be done at the following URL:


Please support the AAVSO and its mission -- Join or donate today: