Alert Notice 517: Monitoring of AM Her urgently requested in support of XMM-Newton and NuSTAR observations

April 2, 2015: Dr. Axel Schwope (Leibniz Institute for Astrophysics Potsdam, Germany) has requested AAVSO observers' assistance in monitoring the magnetic variable AM Her in support of upcoming XMM-Newton plus NuSTAR (Nuclear Spectroscopic Telescope Array) observations.

The XMM-Newton observations are scheduled for 2015 April 06 02:37:02-15:07:02 UT. The NuSTAR observations have not been made final yet but are expected to run longer. A Special Notice will be issued when the NuSTAR schedule is known.

Observers are requested to observe AM Her using standard standard BVRI filters (V filter preferred). The preferred manner of observing is to use only one filter and observe with the highest possible time resolution (aiming for a S/N=10). Dr. Schwope writes that timing accuracy is an issue for these observations and all CCD clocks need to be synchronized via NTP.

Observations are requested nightly from now until April 4, then time series observations through April 8, and then nightly observations through April 16.

The prototype of the class of magnetic cataclysmic variables known as polars, AM Her has "high" and "low" states, ranging approximately V=12.7-13.8 in its high state and V=15.3-15.7 in its low state. Currently it is in its high state at visual magnitude 13.2 on 2015 March 30.107 UT (JD 2457111.607, G. Poyner, Birmingham, England). Its orbital period is 3.1 hours.

To learn more about polars and AM Her, see the AAVSO Variable Star of the Season web presentation "AM Herculis" (

Coordinates:  R.A. 18 16 13.34   Dec. +49 52 04.1  (2000.0)

Charts with a comparison star sequence for AM Her may be created using the AAVSO Variable Star Plotter (VSP,

Please submit observations to the AAVSO International Database using the name AM HER.

This campaign is being followed on the AAVSO Observing Campaigns page (

Your filtered photometry is extremely important for these observations, and your contributions are greatly appreciated.

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


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