Alert Notice 824: AR UMa photometry requested in support of XMM-Newton observations

May 5, 2023

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Dr. Axel Schwope (Leibniz-Institut für Astrophysik Potsdam) has requested the assistance of AAVSO observers in obtaining multicolor photometry on the magnetic cataclysmic variable AR UMa in support of observations with XMM-Newton scheduled for

2023 May 09 20:31:40 - May 10 08:51:40 UT

Dr. Schwope writes: "I'm looking for the support of AAVSO astronomers for a triggered and just scheduled XMM-Newton observation of the magnetic cataclysmic variable AR UMa. This object is of high interest because it is the magnetic CV with the highest magnetic field. X-ray observations are key to understanding the energy release in such a high field environment, but can be triggered only if the source is shown to be in a high state. The object was in a low state for many years but seemed to be in a stable high state (according to ASAS-SN and ATLAS); now I have triggered my hibernating XMM-Newton observation on the source. I would be excited if your fellow astronomers could support the campaign with time-resolved optical photometry."

Beginning now and continuing through May 13, time-series BVRI photometry is requested. Unfiltered observations reduced to a V or Rc zero point (CV or CR) will also be valuable, as will DSLR photometry.

The orbital period of AR UMa is 116 minutes, and observers are asked to make their time-series runs at least that long if possible. A cadence of one minute (allowing for a good S/N) would be very helpful. AR UMa has a range of 13.9-16.7 V. The most recent observation in the AAVSO International Database shows it at magnitude 14.319 CV +/- 0.096 on 2023 May 4.002847 UT (F.-J. Hambsch, Mol, Belgium, remotely).

Coordinates (J2000): R.A. 11 15 44.59   Dec. +42 58 22.4   (from VSX entry for AR UMa)

Charts with comparison stars for AR UMa may be created using the AAVSO Variable Star Plotter (VSP).

Please report observations to the AAVSO International Database using the name AR UMA.

This Alert Notice was compiled by Elizabeth O. Waagen using information provided by Dr. Schwope.


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