March 25, 2013: Further to AAVSO Alert Notice 471 (http://www.aavso.org/aavso-alert-notice-471) and AAVSO Special Notice #342 (http://www.aavso.org/aavso-special-notice-342), HST/COS is scheduled to observe the eclipsing SU UMa-type dwarf nova IY UMa:
IY UMa 2013 March 29 23:43:52 through March 30 02:18:13 UT
IY UMa went into outburst in early March but has returned to minumum. Nevertheless, close monitoring through March 31 is important to be sure it is below the threshold brightness and to have a good magnitude value for correlation with the HST observations. IY UMa is V=18.4 at minimum and can be as bright as V=13 at maximum.
After IY UMa, the next target will be the eclipsing SU UMa-type dwarf nova MR UMa:
MR UMa 2013 April 4 04:12:40 through 08:44:27 UT
Note that THIS DATE IS REVISED from that published in AAVSO Special Notice #342. MR UMa also went into outburst in early March but is returning to minumum. Nevertheless, close monitoring through April 5 is important to be sure it is below the threshold brightness and to have a good magnitude value for correlation with the HST observations. IY UMa is V=16.7 at minimum and can be as bright as V=12.3 at maximum.
Observations are crucial beginning now and continuing through one night after the HST observations. About 24-36 hours before the planned observations the HST/COS scheduling team will make the final decision whether to observe each system.
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.
IY UMa R.A. 10 43 56.74 Dec. +58 07 32.1
MR UMa R.A. 11 31 22.39 Dec. +43 22 38.5
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 IY UMa and MR UMa, 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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