Alert Notice 601: V902 Mon observations needed to support XMM-Newton observation

October 10, 2017: Dr. Hauke Wörpel (Leibniz-Institut für Astrophysik Potsdam (AIP)) has requested AAVSO assistance in obtaining observations of the eclipsing intermediate polar (IP) candidate V902 Mon in support of an XMM-Newton observation scheduled for 2017 October 14, 14:42 UT (duration 43,000s).

Dr. Wörpel writes: “The goal of this campaign is to verify its nature as an IP by verifying modulations at the white dwarf spin period (~37 min) in multiple wavelengths. If confirmed, V902 Mon would be the eclipsing IP with the longest known orbital period (8.162 hours). Based on a Swift observation it is also X-ray underluminous compared to other IPs, making it potentially a member of an X-ray faint population believed to be numerous but for which only two other examples (DQ Her and AE Aqr) are definitely known.

“The most useful observations will be a continuous series with exposures of moderate length. For instance, a previous AAVSO observing run on 17-18 Feb 2016 of this object used 90s V-band exposures and observed it continuously on two nights for several hours each, and this data was nearly perfect for our purposes. Similar runs in BVRI, beginning three or four nights before the XMM observation and extending to three or four nights afterward, will be very helpful. It will not matter if the exposure lengths are a bit longer, and it is not critical that the cadence be the same before and after the XMM observation. White light photometry [unfiltered] will be handy for timing purposes and to get the shape of the eclipse profile.

“Timing accuracy is important…to match the orbital and spin phases in the optical to those in the XMM observation. We therefore request that CCD observations be synchronised via NTP.

“Observations of the eclipses will be especially helpful. Previous observations show a variable eclipse shape, at times displaying the flat-based profile of a point-like emitter and at other times the rounded shape given by an extended emitting source. Determining which state V902 Mon is in during the XMM-Newton observation will shed more light onto the accretion geometry.”

Dr. Wörpel’s eclipse ephemeris is: BJD 2453340.50674(3) + 0.34008278(5) x E.

There is also a published eclipse ephemeris for V902 Mon in VSX (

Dr. Wörpel indicates that either ephemeris may be used. The difference between the two ephemerides in October 2017 will be only 4 minutes; he hopes to use the observations from the current observing campaign to refine his ephemeris further.

Beginning now and continuing through 2017 October 19 UT, V, and BVRI if possible, time series observations are requested according to the instructions given above. Unfiltered photometry reduced to a V sequence is also welcome. Be sure the timing is synchronized via NTP. Since V902 Mon is faint (V~17, and 18.5-19.0 in eclipse) and has slow rotation and orbital periods, cadence faster than 90 seconds for photometry is not necessary.

Coordinates (2000):  RA  06 27 46.40   Dec.  +01 48 11.2

Charts with a comparison star sequence for V902 Mon may be created using the AAVSO Variable Star Plotter (VSP).

Please submit observations to the AAVSO International Database using the name V902 MON.

This campaign is being followed on the Campaigns and Observation Reports Forum at

This AAVSO Alert Notice was compiled by Elizabeth O. Waagen.


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