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AAVSO Alert Notice 358

Monitoring of Mira (omi Cet) in support of HST Observations
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

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

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


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