Alert Notice 618: Monitoring SDSS J153817.35+512338.0 for HST observations

March 5, 2018: Anna Pala (Ph.D. candidate, University of Warwick) has requested AAVSO observers' assistance in monitoring the faint polar cataclysmic variable SDSS J153817.35+512338.0 in support of Hubble Space Telescope observations scheduled for late March-early April 2018.

The HST observing window is 2018 March 28 - April 9. Once the exact time of the HST observations is known, it will be announced on the AAVSO discussion forum thread for this campaign given below.

Pala writes: "...SDSS J153817.35+512338.0 [is] a short period CV (Porb = 93.11 min) that hosts an unexpectedly hot white dwarf (T ~ 30000K). This high temperature could be a clue of a nova eruption within the past few 1000 years and the HST observations will help us in identifying possible ashes and the expanding circumstellar gas shell expected in this case."

It is essential to know the brightness of the target just prior to the HST observations in order to protect the satellite equipment. A go/nogo decision will be made 24 hours prior to the observation time based on positive magnitude reports from AAVSO observers.

Beginning immediately, nightly V/CV (unfiltered) observations are requested. From March 28 through April 9, multiple observations per night (not time series) in V/CV are requested, then nightly observations again through April 30.

SDSS J153817.35+512338.0 has a range of 17.5 - 19.1 CV. In its current low (quiescent) state it is magnitude ~18.6 V.

Coordinates (2000.0):  R.A. 15 38 17.34   Dec.  +51 23 38.0

Charts with a comparison star sequence for SDSS J153817.35+512338.0 may be plotted using the AAVSO Variable Star Plotter (VSP). Be sure to include the space between SDSS and J. It is recommended to select the option to display a DSS chart so that all of the comp star images will show.

Please submit observations to the AAVSO International Database using the name SDSS J153817.35+512338.0. Again, please be sure to put a space between SDSS and J.

This observing campaign is being followed on the AAVSO Campaigns and Observing Reports online forum at

This AAVSO Alert Notice was compiled by Elizabeth O. Waagen.

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