Doublestar analysis of lunar occultation of SAO77494 on Apr.1 2009

Observed by Masayuki Ishida

Analized by Kazuhisa Miyashita

Fig.1    Brightness of main star only.

M. Ishida observed lunar occultation of SAO77494(=XZ7500=WDS A496) and he confirmed a step change on the light curve.

Catalogue details (Washington Doublestar Catalog)

    WDS   Discovr Comp  EPOCH      #  THETA       RHO     Magnitudes Spectral  Prop Mot  2nd PM   DM Desig Note     Precise       
Identifier             Frst Last      Fst Lst First  Last  Pri   Sec  Type      RA" DEC" RA" DEC"                 Coordinate      
05449+2621A   496      1903 2004   22  11   7   0.2   0.3  7.91  8.35 B9        -001-007          +26  937      054455.56+262032.7


Place name  Moriyama, Shiga, Japan
Observer Masayuki Ishida

coming soon..


Fig.2    Limovie analysis
A step is visible clearly at 80% of full brightness.

Diffraction fitting and photometry

Fig.3    Fitting observation to diffraction simulation.


(1) Timming data and component's magnitude
Object Phenomenon Timemagnitude
Component B  Appearance 11h40m00.51s +/- 0.017sec 9.01
Component A Appearance   11h40m00.61s +/- 0.017sec7.60
Time difference 0.101 sec
It is assuming combined magnitude is 7.34 mag.
(2) Compare with catalogues
This observation 1.41 mag
Wasington Doublestar Catalog 0.44 mag
XZ Doublestar File 0.5 mag


Elements of separation to the radial direction of lunar is ..
Radial Velocity * Time Difference = 0.472 * 0.101 = 0.048 (arcsec)
Expected time difference from catalogue and prediction is ..
Dp: Position angle around lunar limb - Position angle of component = 94-7= 87 degree
Expected time difference = separation(catalogue) * cos(DP) = 0.3*cos(87) = 0.016 arcsec

Assuming, the lunar has a complete spherical surface, and the position angle on catalogue is correct, it is expected that the primary star disappears first. However, at this observed event, the secondary star disappeared first. An accurate lunar limb chart become to necessary to solve this issue.

As an other solution of this issue, it is possible to think that a discovery of a new (tertiary) component was done. Because the observed magnitude drop is much smaller than expected by disappearance of secondary star. It is difficult to think that previous photometrical observations have large error on component's magnitude. And also, the possibility of which the CCD camera indicates such a large error on luminous intensity is very small.
If these are correct, it is presumed that the situation was below.
The line passed primary star with secondary star is parallel to the lunar limb, and a new tertiary component is distant from the line passed other two stars by 48 milliarcsecond.