A standards observation programme similar to that previously used with
RATCam is in operation. Broad-band images of calibration fields drawn
from the SDSS Extended
Northern+Equatorial u'g'r'i'z' Standards are obtained every 2-3
hours. They are spaced every few
hours of RA and are observed in all bands on photometric nights, and in r' & i' on non-photometric nights to autonomously monitor the seeing.
These data are available to all observers via the LT data
archive under the Proposal ID
IOOStand or, for observations obtained within the
past month, from the Recent
If you require standards beyond those routinely taken by the robotic system, you must request them explicitly in your Phase 1 proposal and include the appropriate observations in your Phase 2 sequence definition. The time needed for these observations should also be included in your application.
Zero-polarised and polarised standards are observed for RINGO3, selected from the same list as used by RINGO2, every night. Users do not need to request poliarmetric standards in their Phase 1 proposal, nor schedule them in their Phase 2 submission.
Two types of standard are necessary to reduce RINGO3 data; unpolarised stars, and objects with known polarisation. The unpolarised standards are necessary to remove the instrumental polarisation from the data. The polarised standards allow you to calibrate the effect of instrumental depolarisation.
These standards are used to remove the instrumental signature in the polarimetry measurements, they are not primarily intended for photometric calibration and are not effected by issues such as airmass. This, and the fact that instrumental components are stable on timescales of many months, mean there is no need to observe the same standard multiple times through the night. Our tests have demonstrated that better calibration is obtained by using a variety of different reference stars observed over a few nights either side of the science observation rather than a single standard observed multiple times on the night of the science frame. Our automated standard scheduling takes this into account and follows a different strategy than, for example, the photmetric standards on IO:O. We are in the process of developing a calibration procedure document, but in the mean time interested observers who need assistance should contact us to discuss Ringo3 calibrations.
In general we recommend using a MOUNT position angle of zero for all RINGO3 observations. Calculation of a true sky position angle for your data (and hence polarisation angle) is possible by using FITS keywords. In the FITS headers the sky position angle is stored in ROTSKYPA and the mechanical mount position in ROTANGLE.
Because these standards are used for polarimetric calibration and not photometric calibration there are no particular actions required, but be aware that the very bright and fainter stadards are observed using a different camera gain settings to prevent saturation.
Standards currently being observed with RINGO3 are taken from:
Schmidt, Elston and Lupie 1992,
The HST Northern Hemisphere Grid of Stellar Polarimetric Standards,
AJ, 104, 1563.
Hough et al. 2007, Low Polarisation Standards, ASP Conf. Ser. 364, 523.
As the majority of RISE data are taken for the purpose of relative photometry using secondary standards within the field of view, no routine nightly photometric standards are obtained with this instrument. If you require standards you must request them explicitly in your Phase 1 proposal (and include the time needed for these in your time request); you should also upload observing groups for them in your Phase 2 submission.
Please note that we do not routinely observe standard stars for telluric correction or photometric callibration of spectroscopic data. If you require standards for these purposes, you must request them explicitly in your Phase 1 proposal (and include the time needed for these in your time request); you should also upload observing groups for them in your Phase 2 submission.