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            THE AMERICAN ASSOCIATION OF VARIABLE STAR OBSERVERS
                  25 Birch Street, Cambridge, MA 02138 USA
                        aavso@aavso.org
                  Tel. 617-354-0484       Fax 617-354-0665

AAVSO ALERT NOTICE 332 (January 18, 2006)

SUBJECT: REQUEST TO MONITOR V426 OPH FOR XMM-NEWTON OBSERVATIONS

Dr. Darren Baskill, University of Leicester, has requested optical observations of the cataclysmic variable star V426 Oph to coincide with upcoming XMM-Newton observations.

1803+05 V426 Oph is located at RA: 18:07:51.7 and Decl.: +05:51:48. (J2000)

Both visual and CCD observations are needed. For visual observers, make an observation once per night from now until April 6, 2006. For CCD observations, please observe in B and V using the following observing schedule. Please aim for 0.01 magnitude precision. This is a relatively bright object for CCD observers, but it rises in the early morning hours so, if possible, please plan ahead of time (remember, sleep is a luxury)!

Please observe during the following windows:

January 17 - February 26, 2006: At least once per night.
February 26 - March 6, 2006: Time series for as long as possible each night.
March 7 - April 6, 2006: At least once per night.

The XMM Newton observing run is scheduled for February 26 - March 6. A detailed schedule of their observations will be available in approximately 2-3 weeks. The AAVSO web page and AAVSO-Photometry discussion group will be updated with this schedule when it is available.

An AAVSO web page for this campaign has been created at the following URL. It will be updated with light curves and more information as this campaign gets underway. Discussion will take place on the AAVSO-Photometry discussion group.

http://www.aavso.org/news/v426oph.shtml

AAVSO charts with B & V CCD photometry from A. Henden are available at this URL:

http://www.aavso.org/cgi-bin/searchcharts3.pl?name=v426%20oph

The latest observation in the AAVSO International Database, as reported by ASAS-3:

V426 OPH OCT 20.993 2005 12.585 V Err: 0.072

A light curve is available here:

http://tinyurl.com/8x3yv

V426 Oph is suspected to be an intermediate polar (IP). However, in previous X-Ray observations by the ASCA satellite the period modulation usually found in polars was absent. The XMM-Newton observations hope to either find the modulation or an explanation for their absence.

According to Dr. Baskill:

"Our XMM-Newton observation of V426 Oph will allow us to carry out phase-resolved spectrometry; that is, we will be able to compare the Xray spectra of the numerous viewing angles that we naturally have as the two stars orbit each other. This, along with V426 Ophiuchi's relatively high inclination of 60 degrees, will allow us to search for vertical structure above and around the accretion disc. But the primary question is this: will we clearly see the periodic modulation that was hinted at in the ASCA observation? If we do, it could settle the published claims and counterclaims that this system is indeed an intermediate polar. "

Optical observations before, during and after the observing run are needed to correlate the X-Ray data with optical because "...as the gas falls through the disc, it changes colour from optical through to the X-ray."

This campaign will be coordinated by Aaron P. (aaronp@aavso.org).
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This Alert Notice was prepared by: Aaron P.
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Many thanks for your valuable astronomical contributions and your efforts.

Good observing!

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