VLTI Calibrator Selector

General description

The VLTI Calibrator Selector Tool is a tool intended to assist in the selection of suitable interferometric calibrators for VLTI observations with PIONIER and GRAVITY. 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.

Instrument

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

• PIONIER

  Precision Integrated-Optics Near-infrared Imaging ExpeRiment.

• GRAVITY

• Instrument Mode

  • Disperser

    Disperser Description.

  • Beam Combiner

    Beam combiner description.

  • Fringe Tracking

    Fringe Sensor description.

Target Definition

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.

Observation Setup

• 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.

User Search Criteria

• 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

  MATISSE

  The quality flag is a bit field:

  • bit zero is set if LDD_CHI is above 5;
  • bit 1 is set if the star is a known double in WDS (Cat. B/wds/wds) with separation inferior to 1 arcsec;
  • bit 2 is set if the star is, according to Simbad's OTYPEs, one of the following codes: "C*", "S*", "Pu*", "RR*", "Ce*", "dS*", "RV*", "WV*", "bC*", "cC*", "gD*", "SX*", "Mi*", "SB*", "Al*", which signals a possible binarity or pulsating stars.

  Although none of these bit flags prevent the LDD estimate to be accurate, they imply some caution in choosing this star as a calibrator star for Optical Long-Baseline Interferometry.

  Other instruments

  The quality flag depends on LDD_chi2.

  • Quality flag 1: LDD_chi2 less than 1;
  • Quality flag 2: LDD_chi2 between 1 and 2;
  • Quality flag 3: LDD_chi2 between 2 and 3;
  • Quality flag 4: LDD_chi2 between 3 and 4;
  • Quality flag 5: LDD_chi2 between 4 and 5;
  • Quality flag 6: LDD_chi2 larger than 5.

• Normalized Visibility

  Range of normalized visibilities. NB: Experimental!

Formulas

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;
    	

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  Version Information

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