Alert Notice 474: Multiwavelength campaign on delta Ori (Mintaka)

December 14, 2012:  An international team of astronomers, including Drs. Tony Moffat (University of Montreal), Michael Corcoran (NASA GSFC), and Noel Richardson (University of Montreal), has requested AAVSO photometry and spectroscopy of delta Ori (Mintaka) in support of their multiwavelength campaign on this hot binary star in Orion's Belt. Satellite observations will include x-ray via NASA's Chandra and precision optical photometry via Canada's MOST.

***Chandra and MOST observations will be carried out

                                 2012 DECEMBER 17 through 2013 JANUARY 7

so coverage is critical throughout this period, and is also needed before and after this period.***

The astronomers write: "...we make a plea to the astronomical community to obtain simultaneous complementary ground‐based optical observations of the key bright hot binary star delta Orionis (Mintaka, one of the belt stars) in the period between mid December 2012 and early January 2013. Both multi‐band photometry and especially spectroscopy would be most welcome."

They write further: "Massive O‐type stars, though rare, are a primary driver behind the chemical, ionization and pressure evolution of the interstellar medium. Evolution of these stars from main sequence to supernova is driven significantly by stellar‐wind mass loss. Understanding this important connection in individual stars requires a good understanding of the physical stellar parameters...combined with detailed understanding of the outflowing wind... Because massive stars are rare, and massive binaries rarer still...dynamical determinations of stellar parameters are only known for a few systems. Our uncertainties regarding mass loss are even worse... Important questions...have not yet been answered." For a more complete description of this campaign, please see the file Mintaka.pdf.

Del Ori (Mintaka, 2.41V, (B‐V) ‐0.40) is the belt star closest to gam Ori (Bellatrix) and bet Ori (Rigel). The del Ori system contains multiple stars and visually is a double star, so be careful not to include the fainter star when making observations.

Photometry: At second magnitude (visual), del Ori is ideally suited to multicolor and near-infrared photoelectric photometry and DSLR photometry, and is a candidate for successful CCD photometry. The extremely small range of this system (2.20-2.32 V) makes visual detection of the brightness changes very difficult.

BVRIJH photometry is requested, ideally 100 data points per night obtained from an average of three measurements per data point. Be sure to include the standard deviation for each set of three measurements (i.e., each data point). Magnitudes should be measured to 0.001, and the JD reported to four places.

Gam Ori (Bellatrix, 1.64V, (B-V) -0.22) should be used as the comparison star.

Spectroscopy: Spectroscopy is strongly encouraged. Observers are requested to use S/N >= 200, R >=10000, integration < 30 min, and range 4000-7000 Å. Observations of Hydrogen alpha (6563 Å) and Helium I (6678 Å) are also requested.

Coordinates for del Ori: RA 05 32 00.40  Dec ‐00:17:56.7  (2000.0)

Charts for del Ori may be created using the AAVSO Variable Star Plotter ( Best results will be obtained by specifying an 'A' scale chart and including no other variables on the chart. Photometrists should use the table accompanying this chart.

Please use the name "DEL ORI" when reporting observations and submit photometric observations to the AAVSO International Database. Spectroscopy should be submitted directly to Dr. Noel Richardson at <>.

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

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


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