1. VLT calibration issues Optical instruments
Martino Romaniello (ESO – HQ)
on behalf of a lot of people

2. Why this meeting? or The fundamental importance of calibrations
The end user of the data are more and more detached from the observatories (space-based telescopes, service mode, etc.)
The increasing importance of archival research (aka Virtual Observatory) requires excellent archival calibrations, even beyond the scope of the original program
It is not the individual dataset that should be calibrated, but, rather, the instrument
Calibration are an integral part of the operations of an instrument and should maximize the scientific return and ensure sustainable operations

3. Today’s menu VLT/VLTI Optical Infrared (Nancy Ageorges)
VLTI (Christian Hummel)
VST/VISTA (Dietrich Baade, Fernando Selman)
Space telescopes
HST (Jeremy Walsh)
JWST (Harald Kuntschner)
Alma (Robert Laing)
OWL (Nancy Ageorges)

4. The basics: photometric standards
The Landolt (1992) standard stars are used for the VLT, Keck and Gemini

5. The basics: photometric standards
The Landolt (1992) standard stars are used for the VLT, Keck and Gemini

6. The Landolt standards Data obtained at the CTIO’s 1.5m telescope
298 stars with an average of 29 measures each on 19 nights
Photometric errors of a few millimags

7. The Landolt standards: problems
Too sparse for typical FOVs (few stars, narrow color range, etc.)
Too bright for 8m class telescopes (saturation, scintillation, etc.)
Equatorial: don’t cover the same azimuth range as science targets

8. The Stetson standards: better, but…
No U band
BVRI not available in all fields

9. The FORS Faint Standards Project
By Appointment to the FORS Instrument Operations Team
The Goal: define a homogeneous set of standard stars in the optical, suitable for large telescopes, with high photometric accuracy
The FSSP Working Group:
Stefano Bagnulo, Wolfram Freudling, Arto Järvinen, Emmanuel Jehin, Kieran O'Brien, Roberto Mignani, Palle Møller, Ferdinando Patat, Monika Petr-Gotzens, Martino Romaniello, Gero Rupprecht, Thomas Szeifert, Mario Van Den Ancker…

10. The FORS Faint Standards Project
Status: proof of concept, is it possible to achieve extreme photometric precision with FORS?
Dataset: B and R rotated and shifted images of a mildly crowded stellar field, plus 3 Landolt fields, plus tons of biases and sky flats

11. Optical polarimetry
An open issue is the intrinsic variations with time of the polarization characteristics of polarimetric standards
Exploit the FORS1 archive to obtain repeated polarization measurements of commonly-used polarization standards: Stefano Bagnulo, Elena Mason (PSO), plus DGDF (??)
The archival data are mostly adequate for the project
Gaps or missing data can be obtained virtually for free in the context of the FORS Calibration Plan

12. Optical polarimetry
Instrumental polarization across the field is obviously an issue:
Patat & Romaniello (2004)
FORS1 instrumental polarization map

13. And also: Spectrophotometric standards Radial velocity standards
Lick standards
Astrometric calibration …

14. Finally:
Need for an official channel for calibration proposals, similar to the HST:
STScI does not have the resources to calibrate fully all potential capabilities of all instruments. On the other hand, the astronomical community has expressed interest in receiving support to perform calibrations for certain uncalibrated or poorly calibrated modes, or to develop specialized software for certain HST calibration and data reduction tasks. [HST Call for Proposals, section 3.6]
Zum Beispiel:
• Faint photometric standards for WFPC2
• Creation of a coronagraphic and spectroscopic PSF library for STIS/CCD
• NICMOS polarimetric calibrations
• ACS photometric zero point verification
• Calibration of the ACS emission line filters

15. Finally:
Need for an official channel for calibration proposals, similar to the HST:
STScI does not have the resources to calibrate fully all potential capabilities of all instruments. On the other hand, the astronomical community has expressed interest in receiving support to perform calibrations for certain uncalibrated or poorly calibrated modes, or to develop specialized software for certain HST calibration and data reduction tasks. [HST Call for Proposals, section 3.6]
Monitoring of atmospheric conditions (sky transparency and seeing in the pointing direction, extinction coefficients, etc.)