Pan-STARRS Photometric and Astrometric Calibration (1612.05242v3)

Abstract: We present the details of the photometric and astrometric calibration of the Pan-STARRS1 $3\pi$ Survey. The photometric goals were to reduce the systematic effects introduced by the camera and detectors, and to place all of the observations onto a photometric system with consistent zero points over the entire area surveyed, the ~30,000 square degrees north of $\delta$ = -30 degrees. The astrometric calibration compensates for similar systematic effects so that positions, proper motions, and parallaxes are reliable as well. The Pan-STARRS Data Release 2 (DR2) astrometry is tied to the Gaia DR1 release.

Overview of Pan-STARRS Photometric and Astrometric Calibration

The paper provides a detailed description of the photometric and astrometric calibration processes employed in the Pan-STARRS\,1 $3\pi$ Survey, targeting systematic effects to achieve reliable positional and flux measurements across a large swath of the northern sky. The survey uses a wide-field telescope system and imaging data to support various scientific endeavors such as mapping the Milky Way and identifying transient astronomical events.

Calibration Goals

The primary objective of the photometric calibration was to mitigate systematic errors introduced by the camera and detectors, achieving uniform zero-point photometry across 30,000 square degrees north of declination -30. Astrometric calibration aimed to eliminate similar systematic errors to produce reliable positions, proper motions, and parallaxes.

Methodology

• Photometric Calibration: Photometric calibration employed an "ubercal" methodology, which minimized systematic errors via nightly zero-point determinations and a low-resolution grid of flat-field corrections. These outcomes linked exposures across photometric nights, tying them to a previously defined photometric system using comparison with reference standards.
• Astrometric Calibration: Multiple systematic effects were addressed, such as the Koppenh\"ofer Effect, Differential Chromatic Refraction (DCR), and static deviations in camera response. Each measurement's raw coordinates were corrected based on these factors to enhance the positional accuracy delivered by the astrometric model.

Results

The analysis yielded robust calibration models, consistently tying the PV3 photometric data to external standards with a systematic error floor below 7 millimagnitudes, and astrometric accuracy refined to $\sim$22 milliarcseconds for bright-object measurements. Additionally, Gaia DR1 data provided an external astrometric reference, strengthening calibration models through the inclusion of Gaia position data.

Implications and Future Developments

The demonstrated precision in photometric and astrometric calibration enhances the usability of Pan-STARRS data for multi-epoch and multi-band surveys. Moving forward, the anticipated integration of Gaia DR2 data promises further improvements in astrometric solutions, offering enhanced understanding of stellar dynamics and improved celestial navigation for transient extragalactic sources. The continued refinement of these calibration processes will underpin more accurate mapping of the Milky Way's structure and facilitate detection of potentially hazardous near-Earth objects.

Concluding Remarks

The paper represents a significant advancement in survey calibration techniques, underscoring the critical importance of addressing systematic errors for reliable astronomical observations. The detailed discussion of calibration methodologies offers valuable insights into the complexity and precision required for large-scale astronomical surveys. As such, the implications are far-reaching in observing standards and methodologies for future astronomical projects.