How to create Finding Charts for Service Mode

In general, a finding chart has to be attached to each OB. Exceptions are given in the instrument-specific rules. Please read the P2PP3 User Manual for a detailed description on attaching finding charts to OBs.

General Finding Chart Requirements

Regardless of the instrument, finding charts must have all the following characteristics:

  • Clearly indicate the Observing Run ID.
  • Clearly indicate the PI Name.
  • Clearly indicate the OB Name or Target Name, as used in the OB to which it is attached.
  • The target(s) position(s) must be clearly indicated.
  • The entire instrument field-of-view must be shown.
  • North and East must be clearly indicated.
  • The scale must be indicated by drawing a bar and writing the bar length in arcseconds or arcminutes.
  • The wavelength range of the image must be indicated. Whenever possible, finding charts should have similar central wavelength to observations (e.g. DSS charts are often inappropriate for IR observations near the galactic equator).
  • The images should be negative, i.e. dark objects on light background.
  • The output files must be in JPEG format and their size must be less than 1 Mbyte.
  • Positions of spectroscopic acquisition reference stars, if any, should be marked.
  • Spectroscopic finding charts must indicate the slit(s) position(s) clearly (unless slits are aligned along parallactic angle)

Please verify that finding charts have sufficient quality and resolution. This can be easily done from within P2PP by using the View Finding Chart option in the Finding Charts menu of the main P2PP interface (see also the P2PP User Manual).

Skycat Finding Chart tool

Although in most cases valid finding charts can be produced with any software tool able to produce output files in JPEG format, ESO recommends the use of the SkyCat-based finding chart tool. This tool provides a user-friendly interface to easily produce finding charts with the general characteristics described above.

Additional rules for CRIRES finding charts

In addition to the general requirements for finding charts, the following requirements should be fulfilled:

  • Finding charts should be provided for a field size of 50" x 50", with a clear indication of field orientation. The target should be clearly marked by an arrow. If observations are performed with the derotator in SKY mode, the slit orientation should be clearly drawn.
  • For high proper motion stars (>1"/year) the present day position should be indicated by an arrow pointing from the target in the chart to the present day position (especially if similar bright sources are around).
  • Finding charts are to be provided based on existing infrared images obtained in J, H or K-band. Typically, 2MASS or DENIS images are acceptable, although higher spatial resolution is preferable, especially for crowded fields. The finding charts have to show the field in the NIR band closest to the observing wavelength, λOBS:
    • in J band, if 950 nm < λOBS < 1300 nm,
    • in H band, if 1300 nm < λOBS < 2000 nm, or for very bright targets,
    • in K band, if 2000 nm < λOBS < 5400 nm.
    Note that the ESO infrared digitized sky II actually corresponds to the I band and should not be used if other infrared images are available.
  • If the wavelength at which the finding chart has been taken is different from that of the science observation, the user has to clearly describe in the README file section Programme Description how to identify the target at the wavelength of acquisition. Adequate examples of such comments could be:
    • the source is the brightest object in the field of view in H-band, or
    • two bright sources are expected in our field of view. The science target is the southernmost of the two.
  • In crowded fields, a second finding chart should be attached to the corresponding OB, with a zoom-in on the science target(s).
  • For observations using AO it is mandatory to indicate the location of the AO guide star on the finding-chart, because the AO system is operated blindly (i.e. the instrument operator has no image of the field in the optical bandpass used by the AO).
  • It is mandatory to indicate the location of the SV guide star, if different from the AO guide star and/or science target.
  • If the AO guide star or the SV guide star are less than 15 arcsec from the edge of the finding chart (centered on the target), another 2' by 2' finding chart should be provided.

In general, a finding chart has to be attached to each science and standard star (telluric or spectro-photometric) OB. Only under certain circumstances, the finding chart might be skipped (see the Additional Conditions for Waiver Requests).

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