Bright-Moon sky as a wide-field linear Polarimetric flat source for calibration
Abstract
Context. Next-generation wide-field optical polarimeters such as Wide-Area Linear Optical Polarimeters (WALOPs) have a field of view (FoV) of tens of arcminutes. Wide-field polarimetric flat sources are essential to the efficient and accurate calibration of these instruments. However, no established wide-field polarimetric standard or flat sources exist at present.
Aims: This study tests the feasibility of using the polarized sky patches of the size of around 10 × 10 arcminutes2, at a distance of up to 20° from the Moon, on bright-Moon nights as a wide-field linear polarimetric flat source.
Methods: We observed 19 patches of the sky adjacent to the bright-Moon with the RoboPol instrument in the SDSS-r broadband filter. These patches were observed on five nights within two days of the full-Moon across two RoboPol observing seasons.
Results: We find that for 18 of the 19 patches, the uniformity in the measured normalized Stokes parameters q and u is within 0.2%, with 12 patches exhibiting uniformity within 0.07% or better for both q and u simultaneously, making them reliable and stable wide-field linear polarization flats.
Conclusions: We demonstrate that the sky on bright-Moon nights is an excellent wide-field linear polarization flat source. Various combinations of the normalized Stokes parameters q and u can be obtained by choosing suitable locations of the sky patch with respect to the Moon.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- November 2023
- DOI:
- 10.1051/0004-6361/202346830
- arXiv:
- arXiv:2305.04270
- Bibcode:
- 2023A&A...679A..68M
- Keywords:
-
- instrumentation: polarimeters;
- techniques: polarimetric;
- Moon;
- atmospheric effects;
- Astrophysics - Instrumentation and Methods for Astrophysics
- E-Print:
- 8 pages including appendix, 6 figures and 3 tables. Submitted to Astronomy and Astrophysics for review. Comments are welcome