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Special Notice #91: BZ UMa Monitoring for Polarization Measurements

January 14, 2008: Photometric and visual observations of the dwarf novae BZ UMa are

requested this week in support of an observing run using the new Dual-Beam Imaging Polarimeter (DBIP) on the University of Hawaii's 88-inch telescope (2.2m) on Mauna Kea.

Operators of the telescope and instrument have agreed to include BZ UMa in observations planned during DBIP engineering tests on January 17, 2008 (UT). Currently, BZ UMa is in quiescence but is approaching the end of its typical supercycle, meaning an outburst may occur soon. Nightly visual and photometric observations until January 16 (UT) are needed to confirm that BZ UMa is not in outburst.

Also, time series photometric observations are needed from 05:00 - 16:00 UT on January 17, 2008. The polarimeter measurements will take place sometime during that window, with increasing likelihood towards the latter half of the window. We would like to have precise observations with high temporal resolution during the polarimeter exposures. Since BZ UMa will be faint and we will be looking for short period fluctuations, a filter is not needed. So feel free to remove it to lower your exposure time, which should be as short as possible to get an SNR>100.

Recent positive observations of BZ UMa:

Date Mag Band Observer

2008 Jan. 13.2086, 16.097 +/-0.106 V KQR (Richard Kinne)

2008 Jan. 10.1951, 16.058 +/-0.114 V KQR (Richard Kinne )

2007 Dec. 15.3679, 16.19 +/-0.07 V MDW (Walter J. MacDonald II)

2007 Nov. 24.4212, 16.36 +/-0.02 Unf. BXS (Steve Brady)

Charts and a table of photometric measurements for comparison stars can be drawn via the Variable Star Plotter. Just put in "BZ UMa" in the form at the URL below: http://www.aavso.org/observing/charts/vsp/

BZ UMa is an enigmatic dwarf novae with properties of both a UGSU system and an intermediate polar. The AAVSO ran observing campaigns in 2004 and 2005 that revealed new, but inconclusive behavior. Last year it underwent a rare superoutburst that had previously not been observed since consistent observations of BZ UMa began in 1976. But there is still the question of the origin of its X-Rays, peculiar emission lines and a possible polarization detection in 1980. We hope this polarization measurement using modern and more sensitive equipment will help shed light on this system.

As per policy for AAVSO originated campaigns, if a paper results from these observations then observers will be thanked in the paper and significant contributors will be included as coauthors.

This Special Notice was prepared by: A. Price

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