Diameter solutions from VINCI

NOTE:
The latest results pointed to from this page were from "solution #18" produced in January 2006.
I hope to soon post updated results following improvements of the solution algorithm, changes to the visibility estimator, and an external redetermination of the "zero-point" calibration (affects solutions for stars with diameters < 3 mas)
Do check back soon for the latest results....

From this page you may go to the latest solution of the VINCI diameter solutions. A similar list was presented at the April 2005 VLTI conference in Garching. This was part of a poster presented there entitled
Diameter determinations from VINCI using global calibration solutions

Current diameter solutions were computed in January 2006.

Previous solution sets:

Solution #1 (as presented at conference):
View the April 2005 diameter results here (these are the results as first presented at the VLTI conference).
Or in plain text form.

Solution #2, August 2005:
View the August 2005 diameter results as a text file.

Solution #2, November 2005:
View the November 2005 diameter results as a text file.

Proper Calibration
A number of diameter solutions include a "proper calibration" solution in addition, or instead of, the normal diameter. This is a determination of the so-called "zero-baseline" visibility being less than unity, perhaps because of circumstellar emmission which is over-resolved at all baselines.

A number of Mira stars, in particular, have visibility curves which cannot be fit by a normal visibility curve, but can be reasonably fit by one corresponding to a normal visibility curve multiplied by a constant A, the "proper calibration." This may actually describe the portion of the power that is emanating from the photosphere of the star with the remainder 1 - A being attributable to a circumstellar envelope which has close to zero visibility at the baselines considered. However the actual visibility curve could well be more complex, and this is simply a good interpolation fitting the baselines observed. In other cases, the "detection" of a non-unity zero-baseline power is simply an artifact of another complication regarding the star's visibility curve. When these cases are spotted, the result has been marked with the 'I' flag ("invalid result").

Uniform Disk Diameter Solutions:
A few caveats:

• These are not the final results! They are the raw output of the algorithm at its current stage of development.
• A good number of the stars cannot be described by a single "diameter" (for instance, pulsating stars observed at a limited number of epochs, elliptical stars observed at a limited range of position angles, and stars with an undetected proper calibration) and the numbers reported are invalid. A few invalid results have been spotted and marked with an 'I'. But there are many more.
• Many of the solutions smaller than 2 mas must be considered unresolved. The non-zero diameter printed is simply a maximum-likelihood solution, but a diameter of zero is not excluded with any degree of confidence. In these cases a 'U' has been supplied to indicate "unresolved."
• The error bars may be too optimistic in many cases due to shortcomings of the solution algorithm (which is continually being worked on). However any error bars of less than about 1% of the diameter itself should not be taken seriously. That is because of likely systematic errors due to uncertainties in the piezo calibration (leading to errors in the effective wavelength applying to visibilities) which add an (undetected) error of order .5% to the diameters. This applies more to the diameters of larger stars (> 10 mas) whereas the diameters of smaller stars (< 5 mas) have net errors which are usually dominated by noise in the visibility data itself.