arXiv subjects

Robert Hill

Publications and source records attributed to Robert Hill.

4 recordsLinked to original sources

arXiv2026

Gravitational Redshift of Light and the Heisenberg Uncertainty Principle

Empirical observations together with theoretical analyses are being used to argue that the classical phenomenon of gravitational redshift -- namely, the redshift of light in a static gravitational potential -- may be in tension with the Heisenberg uncertainty principle. In particular, in the Pound-Rebka experiment, the emitter-absorber pair interact with each other by exchanging a Mossbauer photon, a process that is fully describable within quantum mechanics but how the photon interacts with the spacetime metric remains unclear. Since the uncertainty principle is incompatible with local realism, as per general relativity, we propose to study continuous-variable photonic entanglement within the Einstein-Podolsky-Rosen (EPR) framework in a weak gravitational field. We outline a thought experiment, realizable on the surface of the Earth, that could shed further light on this problematic seamline between general relativity and quantum mechanics in the weak-field regime.

physics.gen-ph↗

arXiv2026

The Nancy Grace Roman Space Telescope Wide Field Instrument: Characterization of the Brighter-Fatter Effect in a Roman H4RG-10 Detector using the Talbot Effect

The Nancy Grace Roman Space Telescope will conduct several community-driven surveys using its Wide Field Instrument (WFI), which contains 18 Teledyne H4RG-10 near-infrared detectors in the focal plane. Roman's wide area survey to measure weak gravitational lensing places particularly stringent requirements on point spread function (PSF) precision for the WFI. The brighter-fatter effect (BFE) is a nonlinear detector effect caused by the deflection of new charge away from pixels with previously accumulated charge during an exposure. As a result, the PSF measured at the detector depends on the charge contrast between pixels, and therefore the effective PSF for astronomical sources is a function of flux contrast and integration time. We present characterization of the BFE observed in a non-flight H4RG by projecting a grid of bright point sources onto the detector using the Talbot Illuminator at the NASA Goddard Space Flight Center Detector Characterization Lab. We find that the effective area of a pixel decreases by $(-2.18\pm0.04) \times 10^{-6}$ per electron of charge contrast with its neighbors, corresponding to a measurable increase in the effective PSF size over the course of an exposure. Despite charge migration, the total signal detected in the vicinity of a bright source is roughly conserved. We also analyze flat field statistics for the same detector to measure the total inter-pixel nonlinearity (IPNL), which is dominated by BFE. We present a method to correct BFE in H4RG images using the flat field IPNL results, adapted from an extant optical correction technique. The correction reduces the observed BFE by about a factor of 25 as measured by the effective pixel area change, but there is remaining nonlinearity in the corrected data. We discuss possible sources of residual nonlinearity and suggest avenues to investigate optimal BFE correction in Roman survey images.

astro-ph.IM↗

arXiv2024

Ground-based Cislunar Space Surveillance Demonstrations at Los Alamos National Laboratory

Surveillance of objects in the cislunar domain is challenging due primarily to the large distances (10x the Geosynchronous orbit radius) and total volume of space to be covered. Ground-based electro-optical observations are further hindered by high background levels due to scattered moonlight. In this paper, we report on ground-based demonstrations of space surveillance for targets in the cislunar domain exploiting the remarkable performance of 36cm, F2.2 class telescopes equipped with current generation, back-side illuminated, full-frame CMOS imager. The demonstrations leverage advantageous viewing conditions for the Artemis Orion vehicle during its return to earth, and the total lunar eclipse of November 8th 2022 for viewing the CAPSTONE vehicle. Estimated g-band magnitudes for vehicles were 19.57 at a range of 4.4e5 km and 15.53 at a range of 3.2e5 km for CAPSTONE and Artemis Orion, respectively. In addition to observations, we present reflectance signature modeling implemented in the LunaTK space-sensing simulation framework and compare calculated apparent magnitudes to observed. Design of RApid Telescopes for Optical Response (RAPTOR) instruments, observing campaigns of Artemis Orion and CAPSTONE missions, and initial comparisons to electro-optical modeling are reviewed.

astro-ph.IM↗

arXiv1998

The Hubble Space Telescope Extragalactic Distance Scale Key Project. X. The Cepheid Distance to NGC 7331

The distance to NGC 7331 has been derived from Cepheid variables observed with HST/WFPC2, as part of the Extragalactic Distance Scale Key Project. Multi-epoch exposures in F555W (V) and F814W (I), with photometry derived independently from DoPHOT and DAOPHOT/ALLFRAME programs, were used to detect a total of 13 reliable Cepheids, with periods between 11 and 42 days. The relative distance moduli between NGC 7331 and the LMC, imply an extinction to NGC 7331 of A_V = 0.47+-0.15 mag, and an extinction-corrected distance modulus to NGC 7331 of 30.89+-0.14(random) mag, equivalent to a distance of 15.1 Mpc. There are additional systematic uncertainties in the distance modulus of +-0.12 mag due to the calibration of the Cepheid Period-Luminosity relation, and a systematic offset of +0.05+-0.04 mag if we applied the metallicity correction inferred from the M101 results of Kennicutt et al 1998.

astro-ph↗