April 8, 2013: Further to AAVSO Alert Notice 471 (http://www.aavso.org/aavso-alert-notice-471) and AAVSO Special Notice #345 (http://www.aavso.org/aavso-special-notice-345), HST/COS is scheduled to observe the eclipsing SU UMa-type dwarf nova RZ Leo:
RZ Leo 2013 Apr 11 07:18:24 through 14:15:5 UT
The HST team will be making a final decision on observing RZ Leo based on the observations of April 9/10, and observations from the following night will also be essential. Close monitoring of RZ Leo through April 12 is requested to be sure it is below the threshold brightness and to have a good magnitude value for correlation with the HST observations. RZ Leo is V=18.7 at minimum and can be as bright as V=11.1 at maximum.
After RZ Leo, the next target will be the dwarf nova IU Leo (HS 1055+0939):
IU Leo 2013 April 18 9:30:11 through 12:05:05 UT
Giving RZ Leo highest priority, please begin covering IU Leo now; close monitoring through April 19 is essential. IU Leo went into outburst between April 1 and 4, according to Gordon Myers of Hillsborough, CA. Dr. Szkody points out that its outbursts usually last about two weeks, and it appears to be declining a bit faster than usual this time, so it should be faint enough for HST by April 18, but your observations will be absolutely critical to the HST planners. IU Leo is V=15.5 at minimum and can be as bright as V=12.9 at maximum.
Also regarding IU Leo, Dr. Szkody points out that it has a faint companion about 2 arcsec to the NE - separated well with <1 arcsec seeing but likely included in AAVSO measurements. Please note in your observations whether this companion is included in your estimates of IU Leo.
As instructed in AAVSO Alert Notice 471, for CCD observers, simultaneous photometry [shortly before, during, and after the HST observations] would be ideal. For the magnitude estimates, a nightly V measurement from now through the HST observations and a day beyond would be best. If positive visual observations are possible, they are welcome, as are visual fainter-than observations fainter than magnitude 15.0.
RZ Leo R.A. 11 37 22.27 Dec. +01 48 58.6
IU Leo R.A. 10 57 56.29 Dec. +09 23 14.8
Charts may be created using the AAVSO Variable Star Plotter (http://www.aavso.org/vsp).
Please report observations as soon as possible to the AAVSO International Database using the names RZ LEO and IU LEO, respectively. If an outburst is detected, please report observations immediately. Many thanks!
This AAVSO Special Notice was compiled by Elizabeth O. Waagen.
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