Alert Notice 490: Optical monitoring of T Ori requested

August 30, 2013: Dr. William Herbst (Wesleyan University) and Rachel Pedersen (Bates College) have requested AAVSO assistance in monitoring the Orion variable T Ori in support of spectroscopy they will be obtaining during September 2013. AAVSO nightly coverage (visual or electronic, not time series) of this star is crucial throughout the month of September.

Dr. Herbst writes: "T Ori is one of the first variable stars discovered, varies by up to several magnitudes, and remains a mysterious object. The cause of its variability is not fully known more than a century after its discovery!

"To help address this issue, my student Rachel Pedersen and I will be obtaining high resolution spectra with the SMARTS 1.5m telescope at the Cerro Tololo Interamerican Observatory in Chile during the month of September, 2013. We hope to observe spectral changes accompanying the brightness variations that will shed light on their cause. It is critical that we be able to assign a magnitude to each spectrum. Amateur astronomers could make a terrific contribution to this project by more intensively monitoring the star during September.

"For visual observers: Estimates of the brightness using the AAVSO charts will be helpful. Since the star changes brightness by up to several magnitudes, an accuracy of 0.1 or even 0.2 mag as can be achieved by (careful!) visual observers will be sufficient. Observations made with care by experienced observers will be most helpful to us.

"For CCD observers: V magnitude or even unfiltered observations will be most useful. If colors can be obtained (e.g. UBVRI) they could be helpful, but we primarily need a magnitude estimate.

"Of course, during this time period T Ori is an early morning -  pre-dawn - object. There is no need for time series during the short window that the star is high enough in the sky for accurate measurement. We really need just one observation per night - it generally does not change significantly on the time scale of minutes or even an hour.

"...We look forward to unveiling some of the mysteries of this star -- or at least trying!"

When the variable is relatively bright, as in the case of T Ori, a filtered observation is always preferred to an unfiltered one as it is much easier to integrate with data from other observers. Observations in the AAVSO International Database show T Ori with a visual range of magnitude 9.3-~12.6; recent visual and V magnitudes show it between ~9.7 and 11.9. Because of the nebulosity associated with the area around T Ori, observations need to be made very carefully and consistently.

Coordinates: 05 35 50.44 -05 28 34.9 (2000.0)

Finder charts for T Ori may be created using the AAVSO International Variable Star Plotter (VSP,

Please report observations to the AAVSO International Database using the name T ORI.

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

Many thanks for your help with this campaign. You are key to its success!

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


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