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AAVSO Alert Notice 365

Request to Monitor EF Eri for Hubble Space Telescope Observations
January 6, 2008

Dr. Paula Szkody (University of Washington) has requested our help in monitoring the magnetic cataclysmic variable EF Eri for upcoming Hubble Space Telescope observations. Confirming observations are requested to ensure that EF Eri is fainter than the safe observing threshold during the HST observing window on 2008 January 17 UT.

EF Eri is at RA = 03:14:13.20 , Dec = -22:35:43.0 (J2000).

EF Eri is an intermediate polar. Time-resolved spectroscopy with the Hubble Space Telescope will be used to investigate the physical origin of ultraviolet variability observed with the GALEX satellite in 2004 (also by Szkody et al). HST can only observe objects fainter than 14th magnitude due to the sensitivity of its instruments, and so observations of EF Eri can only be made if it is known that the star is fainter than those limits. AAVSO observers are asked to begin monitoring this star nightly beginning immediately, and to monitor this object intensely immediately prior to and during the observing window beginning 2008 January 17 01:30 UT (JD 2454482.5625) and continuing through the closing of the observing window at 2008 January 17 16:15 UT (JD 2454483.1771).

Both positive and "fainter-than" observations are useful for this campaign. Visual observers are asked to report the faintest comparison star they can reliably detect, with the two nearby stars at m(V) = 14.5 and m(V) = 14.8 being ideal. CCD observers should observe such that they obtain a signal to noise of 10 in the faintest comparison star they can reliably detect in reasonable time. EF Eri is currently around m(V) = 18.1; if you are able to detect EF Eri with S/N of 10 in reasonable time using a CCD, please do so. Filtered CCD observations are not required, but please indicate which if any filters you are using when submitting observations. Please report all observations promptly via WebObs.

Please note that EF Eri is approximately 20 arcseconds East of the m(V) = 14.8 comparison star, so please make sure you are measuring (and reporting) EF Eri rather than this comparison. For those of you who print charts from DSS using VSP, be aware the DSS plates for this field were taken when EF Eri was in a high state -- it will appear much fainter now.

Charts for EF Eri are available through VSP at the following URL:


Recent observations are available here:


Please report all observations to the AAVSO as "EF ERI" (AAVSO 0309-22).

This Alert Notice was prepared by Dr. Matthew Templeton.


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