Calibrations

This page describes the suite of calibration frames routinely taken for GSAOI. Applicants are encouraged to review the information in the instrument and GeMS pages in order to understand the level of precision that can be achieved with the standard set of calibrations.

Applicants should not include time for baseline calibrations in their Phase I proposals. If additional calibrations are deemed necessary, for example to achieve a precision beyond that provided by the baseline set, then these must be included explicitly as part of the Phase I proposal and Phase II science program. Any time used between the hours of nautical sunset and sunrise to obtain baseline calibrations will not be explicitly charged to the program but will be charged to the partner country whose NTAC recommended time (i.e. it is part of the time accounting used to balance partner usage). The time will be charged in proportion to the number of programs that receive the calibration data. Any time required for additional calibrations requested by the PI will be charged to that particular program.

Baseline calibrations will be obtained for all observations, and shared between programs. GSAOI calibrations are associated to a particular science data through the Gemini Observatory Archive (GOA). Instructions on how to retrieve the science data and associated baseline calibrations required for a program are given in the GOA Help web page. Calibrations requested outside the baseline set are included with the program data.

• Baseline Calibrations
• Photometric Standards and zero points
• Download data from the Gemini Observatory Archive (GOA)
• Pre-defined queries for Flats (Dome and Twilight) and Photometric standards for each GeMS/GSAOI run

Baseline calibrations

For all queue observations, a set of standard calibrations (the "baseline calibrations") will be taken by Gemini Staff to ensure the long-term utility of data in the archive. The baseline calibration set varies from instrument to instrument and from mode to mode. The table below describes the GSAOI baseline calibrations, as well as provides information on how and when to request additional frames.

All GSAOI baseline calibrations are taken from the GS-CALYYYYMMDD (shared) program, and not from the individual science programs. In the new Gemini Observatory Archive, the calibrations are associated automatically when you search for the science data by clicking the tab "Load Associated Calibrations". See the Gemini Observatory Archive Help page for detailed instructions on the procedures to search for data and associated calibrations.

Photometric Standards and zero points

• Photometric Standard Stars
• Photometric Zero Points and Sky Background

Photometric Standard Stars

The photometric standard stars are selected from the Photometric Standard star catalogues listed in the NIR Resources web page. The photometric standards are observed as part of Baseline Calibrations for GSAOI. The observations are taken from the GS-CAL (shared) program, and not from the individual science programs. The observations of standard stars are only obtained in the J, H, K_p, K_s and K broadband filters. A more limited set of standards include the Z filter. The observations are obtained under natural seeing conditions (NO AO correction). If applicants would like to observe photometric standard stars with the AO loop closed, the coordinates of the selected standard stars and the time for observation have to be included in the Phase I proposal. Note that when the GeMS loops are closed, the standard stars may saturate even with the shorter exposure time allowed (5.3 seconds). Therefore, users should be careful to select standards which will NOT saturate in the fully corrected images. More detailed information is given in the GSAOI Baseline Calibration web page.

Photometric Zero Points and Sky Background

Approximate photometric zero points in the J, H and K_s broadband filters were measured from data collected during April 2012 GeMS/GSAOI commissioning run. The instrumental magnitudes in the GeMS/GSAOI system were calculated as follows:

m_λ  = - 2.5 log F_λ

where m_λ is the instrumental magnitude and F_λ is the flux in ADU/s. The resulting values for the instrumental magnitudes were then compared with the 2MASS standard magnitudes to define the zero points. Note that airmass effects were not considered in the calculation of the zero points (the observations were assumed to be taken at a “typical” airmass). The table below contains the approximate zero points for GeMS/GSAOI system. Extinction values were taken from Nikolaev et al. (2000, AJ, 120, 3340) . The sky brightness values, converted from the average counts in the sky frames, are also listed in the table.

A comparison of the values listed in the table with the values derived from the January 2012 and February 2012 commissioning runs indicates that the photometric zero-points are reasonably stable (within 3%). More detailed information about the photometric zero-points, including information about the color terms for each detector, will be posted in this web page as commissioning progresses. In the near future, more detailed information about the GeMS/GSAOI zero points will be provided through the Instrument Performance Monitoring project web page.

GSAOI Photometric Zero Points

Description and Goals

Every night with GSAOI science, we take images of photometric standards in the same filters as the science for that night. The photometric zero-point is added to these tables and graphs the next morning. Photometric conditions are required, but observations can be collected during twilight.

Status

First results available.  More details in iPoster, presented at AAS 233, January 2019

GSAOI Quick links for Calibration Searches

The links below allow for quick search and download of GSAOI calibrations since semester 2012B from the Gemini Observatory Archive (GOA). Information on how to modify or use different queries for other calibrations can be found here. 

NOTE: the links in the table will open in a new window.

• 2016B Semester
• 2016A Semester
• 2015A Semester
• 2014B Semester
• 2014A Semester
• 2013B Semester
• 2013A Semester
• 2012B Semester