Alert Notice 452: Simultaneous observations of SU Aur and AB Aur requested for XMM-Newton

8 February 2012:  Dr. Hans Moritz Guenther, Harvard-Smithsonian Center for Astrophysics, has requested bracketing and simultaneous observations in support of XMM-Newton x-ray observations of the classical T Tauri star SU Aur and the close-by Herbig Ae star AB Aur scheduled for February 15 - 17, 2012. The targets are too bright to use the XMM optical monitor for simultaneous monitoring, so your observing assistance is essential for correlation of the x-ray data.

Dr. Guenther writes, "The scientific goal of the observation is to study the rise and decay of flares in classical T Tauri stars at a relatively high time resolution (less than minutes). Because T Tauri stars are surrounded by an accretion disk and actively accrete matter from the star, there is reason to believe that flares on T Tauri stars behave differently compared to flares on older stars like our sun."

At visual magnitude ~9.5 and ~7.0, respectively, SU Aur and AB Aur are bright. Thus, this campaign is best suited to observers with smaller telescopes, as large instruments will saturate very quickly. AB Aur is located about 3 arcmin from SU Aur, and there is a magnitude 7.6 comparison nearby that is suitable for both stars.

The XMM-observations are scheduled for UT 20:31:13 2012 February 15 - 01:27:53 February 17. Optical observations starting a few hours before and lasting a few hours longer would be ideal, but the main focus is the time of the XMM-Newton observation. SU Aur flares often and Dr. Guenther expects it will exhibit optical brightening.

Photometry should be carried out with exposure times of 1 minute or less (and timing of the telescope clock accurate to the same level). V filter is preferred but any filter is acceptable. Unfiltered observations are not recommended as both stars are red. It would be helpful if the filter and zero point were calibrated, but since Dr. Guenther is most concerned about relative changes, it is not required.

Nightly observations are also requested from now through February 24 to provide a good context for the simultaneous and bracketing observations.

Coordinates (2000.0):
SU Aur R.A. 04 55 59.38  Dec. +30 34 01.5
AB Aur R.A. 04 55 45.84  Dec. +30 33 04.3

Charts may be created using VSP (

Please report observations to the AAVSO International Database using the names SU AUR and AB AUR.

Your observations are crucial to the success of this campaign! Many thanks!

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


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