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Alert Notice 358: Monitoring of Mira (omi Cet) in support of HST Observations

Due to the New England winter storm currently affecting the area, phone coverage at the AAVSO may be much reduced until Wednesday. The staff is still available via email, and we suggest using that method to contact us if you need assistance.

September 17, 2007: Dr. Margarita Karovska (Harvard-Smithsonian Center for Astrophysics) and
collaborators are performing a comprehensive study of the Mira AB interacting system, using the WFPC2 camera on the Hubble Space Telescope. Mira AB is composed of the prototype Mira variable omi Cet and its companion VZ Cet, separated by about 0.5 arcsecond. As part of this project they plan to obtain a large number of high-angular resolution images at wavelengths ranging from UV to optical.  The main objectives of the HST/WFPC2 observations are:

 - to determine the properties of the material ejected in December 2004 in the Mira AB system as it flows throughout the binary and interacts with the Mira A (omi Cet, Mira) circumstellar material and wind; 

 - to determine the physical characteristics of mass transfer in this system and especially the role of the accretion stream between Mira A and its accreting companion Mira B (VZ Cet); 

 - to determine the response of the system to the increased accretion rate onto Mira B following the outburst.

The HST observations are scheduled for September 23, from 1900 to 2300 hours UT.  Both visual and instrumental observers are requested to observe this object, currently at omi Cet's pulsational minimum around visual magnitude 9 - 9.5.  The observing window for this program consists of the approximately two weeks on either side of the September 23 observation date. 

Visual Observers: If you currently observe omi Cet as part of your visual observing program, please continue your observations as you normally do. If you do not typically observe omi Cet, all visual observers are encouraged to make at least one but *no more than three* observations of omi Cet during this time, preferably spaced approximately 10 days apart. 

CCD and PEP observers: filtered observations are strongly encouraged, particularly at the bluest wavelengths for which you have filters. Observers are requested to perform nightly observations of omi Cet in the 2 weeks centered on the HST observing window, and intensive observations during the window itself. Also very helpful will be observations in UBV and RIJH. Note that omi Cet and VZ Cet are separated by only 0.5 arcsecond, and will appear blended in all telescopes. Please use an aperture that covers both objects when performing photometry of CCD images.

We are currently working to establish a suitable CCD sequence, and this sequence will be uploaded to VSP for plotting on CCD-appropriate charts. Please make CCD observations, but do not upload data until comparison stars have been given.  Visual observers, please use the existing sequence for visual magnitude estimates.

Please be aware that the m(V) ~ 9.5 star HD 14411 located at RA 02:19:28.47, Dec= -02:57:57.5 is a variable, and should not be used as a comparison.

Omi Cet is located at RA=02:19:20.7927, Dec=-02:58:39.513 (J2000). Please report all observations to the AAVSO as "OMI CET" (designation 0214-03).

Charts may be generated using the AAVSO Variable Star Plotter (VSP).

This Alert Notice was composed by Dr. Margarita Karovska (CfA) and Dr. Matthew Templeton (AAVSO).



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