The astrometric precision and accuracy of an imaging camera is often limited by geometric optical distortions. These must be calibrated and removed to measure precise proper motions, orbits, and gravitationally lensed positions of interesting astronomical objects. Here, we derive a distortion solution for the OSIRIS Imager fed by the Keck I adaptive optics system at the W. M. Keck Observatory. The distortion solution was derived from images of the dense globular clusters M15 and M92 taken with OSIRIS in 2020 and 2021. The set of 403 starlists, each containing ∼1000 stars, were compared to reference Hubble catalogs to measure the distortion-induced positional differences. OSIRIS was opened and optically realigned in 2020 November and the distortion solutions before and after the opening show slight differences at the ∼20 mas level. We find that the OSIRIS distortion closely matches the designed optical model: large, reaching 20 pixels at the corners, but mostly low order, with the majority of the distortion in the 2nd-order mode. After applying the new distortion correction, we find a median residual of [
Smartphone Screens as Astrometric Calibrators
Geometric optical distortion is a significant contributor to the astrometric error budget in large telescopes using adaptive optics. To increase astrometric precision, optical distortion calibration is necessary. We investigate using smartphone Organic Light-Emitting Diode (OLED) screens as astrometric calibrators. Smartphones are low-cost, have stable illumination, and can be quickly reconfigured to probe different spatial frequencies of an optical system’s geometric distortion. In this work, we characterize the astrometric accuracy of a Samsung S20 smartphone, with a view towards providing large format, flexible astrometric calibrators for the next generation of astronomical instruments. We find the placement error of the pixels to be 189[Formula: see text]nm ± 15[Formula: see text]nm Root Mean Square (RMS). At this level of error, milliarcsecond astrometric accuracy can be obtained on modern astronomical instruments.
more »
« less
- Award ID(s):
- 2108185
- NSF-PAR ID:
- 10447771
- Date Published:
- Journal Name:
- Journal of Astronomical Instrumentation
- ISSN:
- 2251-1717
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract x, y ] = [0.052, 0.056] pixels ([0.51, 0.56] mas) for the 2020 solution, and [x, y ] = [0.081, 0.071] pixels ([0.80, 0.71] mas) for the 2021 solution. Comparison between NIRC2 images and OSIRIS images of the Galactic center show that the mean astrometric difference between the two instruments reduces from 10.7 standard deviations to 1.7 standard deviations when the OSIRIS distortion solution is applied. The distortion model is included in the Keck AO Imaging data-reduction pipeline and is available for use on OSIRIS data. -
Schmidt, Dirk ; Schreiber, Laura ; Vernet, Elise (Ed.)We calculate an optical distortion solution for the OSIRIS Imager on the Keck I telescope, by matching observations of globular clusters to a Hubble reference catalogue. This solution can be applied to correct astrometric distortions in OSIRIS frames, improving the astrometric accuracy of observations. We model the distortion with a 5th order Legendre polynomial. The distortion we find matches the expected OSIRIS distortion, and has a fit error of 0.6 mas, but has large residuals of 7 mas. We are currently iterating on an improved reference frame to improve the residual. Additionally, we have installed the Precision Calibration Unit (PCU) on the Keck I optical bench, which will generates an artificial grid of stars for use in future distortion calculations.more » « less
-
We consider the topological and geometric reconstruction of a geodesic subspace of [Formula: see text] both from the Čech and Vietoris-Rips filtrations on a finite, Hausdorff-close, Euclidean sample. Our reconstruction technique leverages the intrinsic length metric induced by the geodesics on the subspace. We consider the distortion and convexity radius as our sampling parameters for the reconstruction problem. For a geodesic subspace with finite distortion and positive convexity radius, we guarantee a correct computation of its homotopy and homology groups from the sample. This technique provides alternative sampling conditions to the existing and commonly used conditions based on weak feature size and [Formula: see text]–reach, and performs better under certain types of perturbations of the geodesic subspace. For geodesic subspaces of [Formula: see text], we also devise an algorithm to output a homotopy equivalent geometric complex that has a very small Hausdorff distance to the unknown underlying space.more » « less
-
The noise performance of a high sensitivity, wide-field astronomical phased array feed receiver can be characterized by measurements using the antenna Y factor method. These measurements are used to determine figures of merit for an active array receiver. Antenna elements for the Advanced L Band Phased Array Camera for Astronomy (ALPACA) were measured using the antenna Y factor method to determine the active array and receiver noise figure, the antenna loss, receiver equivalent noise temperature, and radiation efficiency of the system over its 500[Formula: see text]MHz operating bandwidth. The completed ALPACA instrument will feature a fully cryogenic design with both the low-noise amplifiers and array elements cryogenically cooled. The uncooled performance measurements from the antenna Y factor method are used to extrapolate the elements cryogenic radiation efficiency and antenna loss showing that it is expected that the elements will contribute less than 1 K to the overall system noise temperature. These results validate the antenna Y factor method to measure key antenna parameters such as the antenna radiation efficiency and show that the instruments front-end array and electronics meets expected performance targets.more » « less
-
This paper presents the experimental position and force testing of a 3-armed 6-DOF Parallel Robot, Robossis, that is specifically designed for the application of long-bone femur fracture surgery. Current surgical techniques require a significant amount of time and effort to restore the fractured femur fragments’ length, alignment and rotation. To address these issues, the Robossis system will facilitate the femur fracture surgical procedure and oppose the large traction forces/torques of the muscle groups surrounding the femur. As such, Robossis would subsequently improve patient outcomes by eliminating intraoperative injuries, reducing radiation exposure from X-rays during surgery and decreasing the likelihood of follow-up operations. Specifically, in this paper, we study the accuracy of the Robossis system while moving in the operational workspace under free and simulated traction loads of ([Formula: see text]–1100[Formula: see text]N). Experimental testing in this study demonstrates that Robossis can reach the most extreme points in the workspace, as defined by the theoretical workspace, while maintaining minimal deviation from those points with an average deviation of 0.324[Formula: see text]mm. Furthermore, the force testing experiment shows that Robossis can counteract loads that are clinically relevant to restoring the fractured femur fragments’ length, alignment and rotation. In addition, we study the accuracy of Robossis motion while coupled with the master controller Sigma 7. The results show that Robossis can follow the desired trajectory in real-time with an average error of less than 1[Formula: see text]mm. To conclude, these results further establish the ability of the Robossis system to facilitate the femur fracture surgical procedure and eliminate limitations faced with the current surgical techniques.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1142/S2251171723500095
