VLTI Calibrator Selector
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Important notes and bug reports

Note: Point like telescopes are assumed. These tools are only provided for the technical assessment of the feasibility of observations. Variations of the atmospheric conditions can strongly affect the fringe visibility. Users are advised to apply caution in the interpretation of the results and are kindly requested to report any results which may appear inconsistent.

General description

The VLTI Calibrator Selector Tool is a tool intended to assist in the selection of suitable interferometric calibrators for VLTI observations with MIDI and AMBER. It uses a model of the VLTI and its instruments to assess the fringe visibility, given the observed bandpass, the geometry, spectrum, and coordinates of the target and the time at which the observations are to be made. It also takes into account shadowing by telescope structures and the maximum available stroke of the delay lines for the feasibility assessment of the observations.

The tool offers an HTML/Java based interface and consists of two pages. The observation parameters page presents the entry fields and widgets for the target spectrum and geometry, time of observation, instrument configuration and results selection. A "Submit" button submits the parameters to the model executed on the ESO Web server. The results page presents the computed results. The optional graphs are displayed within Java applets allowing interactive manipulation. The results are also provided in ASCII and GIF formats for further analysis and printing. Finally, a summary of the input parameters is appended to the result page.

In this section, the instrument and mode must be selected. Instrument description and additional information is available for VLTI.

• Midi

  Mid-Infrared Instrument.

• Amber

  Astronomical Multi-BEam Recombiner.

• Instrument Mode

  • Disperser

    Disperser Description.

  • Beam Combiner

    Beam combiner description.

  • Fringe Tracking

    Fringe Sensor description.

In this section, the spectrum and geometry of the target to be observed must be defined.

• Target Coordinates

  • Right Ascension (2000.0)

    Given in hours, minutes, and seconds, or in decimal degrees

  • Declination (2000.0)

    Given in degrees, arc-minutes, and arc-seconds, or in decimal degrees between -90 and +90 degrees.

  • Target Name

    The target name is resolved by Simbad. This service determines the coordinates of the target automatically.

• Target Magnitude

  Here you specify the target magnitudes, as needed.

  • Magnitude in band of observation

    J, H, K, or N band, needed to find matching calibrator.

  • Magnitude in H band

    Only needed if FINITO is to be used (fringe tracking in H band).

  • Magnitude in V band

    Magnitude of the target itself or its Coude offset guide star in V band to check feasibility of guiding.

• Target Diameter

  Here you specify the uniform disk equivalent diameter of your target. This value is needed to predict visibility amplitudes of the target. A suitable calibrator would have amplitudes significantly larger than these to provide a reliable calibration.

  • Single disc diameter

    Given in mas. For binaries, specify for the larger component.

• Universal Time

  Best suited for planning visitor mode observations on a specific date. In service mode, January is best for RA of 8h, then advance RA by 2h for each month, e.g. April for RA of 14h, July for RA of 20, October for RA of 2h.

  • Date

    UT Date on which the observation shall take place

  • UT Start

    Time at which the observation shall start. Measured in Universal Time (UT).

  • UT End

    The length of time the observation shall take.

• Local Sidereal Time

  Best suited for planning service mode observations on any date.

  • LST Start

    LST at which the observation shall start.

  • LST End

    LST at which the observation shall end.

• Hour Angle

  Best suited for planning service mode observations on any date.

  • HA Start

    HA at which the observation shall start.

  • HA End

    HA at which the observation shall end.

• Baseline Configuration

  Please select the telescopes of a baseline individually.

• Angular Distance

  Range of angular distances to the target (in degrees).

• Magnitude Difference

  Range of magnitude difference to target.

• Calibrator Diameter

  Range of calibrator diameters.

• Spectral Type

  Various constraints on the calibrator spectral types.

• Luminosity Class

  Range of calibrator luminosity classes.

• Quality Flag

  Quality 1: Stars that are listed in JSDC, and in either of the Borde, Merand, or MIDI consortium calibrator catalogues (but diameters are all given based on the JSDC method)

  Quality 2: Stars that are only listed in JSDC, and not known in the Borde, Merand, or MIDI consortium catalogues.

  Quality 3: Stars that were added from the MIDI consortium catalogue, but are not listed in JSDC.

• Normalized Visibility

  Range of normalized visibilities. NB: Experimental!

Using the default values in the html input page an example of the calculations can be seen using the 'MAPLE' application

• Calculating normalised visibilities

  The web page takes into account the filter transmission, and uniform, blackbody and spectral target fluxes in calculating a weight average curve which is used to calculate the final visibility value.

  • General (common parameters)

    	Units: 
    	aU aV [metres]
    	lambda [metres]
    	
    	double uCoord = aU/lambda;
    	double vCoord = aV/lambda;
    	double rho = sqrt(uCoord*uCoord + vCoord*vCoord);
    	

  • Single Disc

    	Units: 
    	singleDiscDiam [radians]
    	
    	double uda = _pi*singleDiscDiam*fabs(rho);
    	double vis = 2* fabs(j1(uda))/uda;
    	

  ---

• Version Information

  • Version 3.1.2 (19 December 2011)

    JMMC provided calibrator list (released 06 December 2011) is implemented.
    It is now based on JSDC catalogue.

    New interface for plots - the calibrator observability windows
    are displayed as coloured background at any plot.

    "Astrometric" mode is implemented. It gives access to the proper motions and paralaxes.

    The algorithm to compute U,V,W has been made more accurate due to the use of CPL matrix multiplication.

  • Version 3.1.1 (22 August 2011)

    Bugfix. All visible calibrators are displayed inside the table.

    The new format of the observable time intervals is implemented.
    A list of the intervals is displayed in the corresponding column.

  • Version 3.1.0 (20 July 2011)

    JMMC provided data moved to the database.

    New javascript-based visualization technology introduced to show the plots.

    Position astronomy algorithms re-implemented using SLALIB.

    Result page layout changed to fit VLT-SPE-ESO-19600-4654.

  • Version 3.0.0 (14 January 2011)

    New release based on calibrator catalog provided by JMMC.

  • Version 2.0.2 (07 March 2008)

    Corrected average visibilities values.

    Displaying "NOT VISIBLE" instead of data when a calibrator is not visible.

    Corrected the formula computing the loss of correlated magnitude.

  • Version 2.0.1 (30 November 2007)

    Fixed layout problem of results.

  • Version 2.0.0 (29 November 2007)

    Added user configuarble text files which are parsed for suitable search criteria for the current experiment period.

    Also added a text file with a range of minimum magnitude limits which are dependent on the user input.
    This text file is also configurable and can be altered for each call for proposals period.

  • Version 1.5.0 (01 December 2006)

    Added FINITO visibility calculations.

    Calc Engine now uses XY and user input is North East angle orientation.

    Simbad link added so that calibrator can be viewed in Simbad.

    Magnitude criteria 'ticked' and put in 2nd place.

  • Version 1.0.3 (23 Apr 2003)

    Added a third configuration for the auxiliary positions. The graphs have been given a second axis showing the HourAngle in addition to the Universal Time

  • Version 1.0.2 (12 Mar 2003)

    Updated the demo.fits file so that the file is stored internally to the application.

  • Version 1.0.1 (3 Mar 2003)

    Updated calculation of visibilities on uploaded FITS files and frequency scale calculation

  • Version 1.0.0 (17 Feb 2003)

Send comments on this document to User Support Group/DMD<usg-help@eso.org> Last modified: 20 July 2011