arXiv subjects

Theodore A. Grosson

Publications and source records attributed to Theodore A. Grosson.

4 recordsLinked to original sources

arXiv2026

96 kHz on-sky imaging on an adaptive optics system with a single-photon avalanche diode

Astronomical observations requiring extremely high angular resolution necessitate advanced adaptive optics (AO) systems to overcome blurring caused by the atmosphere. In addition to obtaining much sharper point-spread functions (PSFs) with these systems, it is beneficial to be able to characterize the behaviour of the resulting PSF across time and wavelength. We have installed a commercially-available Single-photon avalanche diode (SPAD) array on the focal plane of the REVOLT AO testbench at the Dominion Astrophysical Observatory, allowing us to observe the visible PSF of the system at rates up to 96 kHz. This provides a time-resolved view of the PSF at $\sim$100 times the frequency of the AO system itself. We use this detector to analyze the high-frequency behaviour of the PSF of the AO system, including residual tip/tilt and deformable mirror response. We also explore the performance of AO-assisted lucky imaging, in which we average together only the frames which result in the best image quality. We find that high-framerate imaging can significantly improve the PSF beyond the native capabilities of the AO system.

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arXiv2026

Exploring the trade-space of distributed aperture telescopes for faint-object spectroscopy

Scientific programs targeting the faintest objects push modern telescopes to increasingly large sizes, high costs and complex designs. Obtaining spectra of low surface brightness galaxies, for example, requires hours of observations on state-of-the art instruments. Increasing telescope diameters beyond 40 m raises potentially insurmountable challenges for design and funding. An innovative strategy for combating these costs is to use many small telescopes in place of a single large aperture. For observations in which high angular resolution is not necessary, this can be equivalent to a large diameter telescope in terms of sensitivity, while diffraction limited by the individual aperture. Improvements in commercial off-the-shelf (COTS) components have made this concept a possibility, as demonstrated by instruments such as the Dragonfly Telephoto Array, the Huntsman Telescope, and the Argus Array. In this work, we discuss the merits of "distributed aperture telescopes" as applied to the use case of spectroscopic observations of ultra-diffuse galaxies (UDGs). We compare the cost and simulated scientific performance of different configurations of apertures, detectors, and other components for this purpose, finding that an array of half-metre telescopes can obtain comparable observations to large telescopes for a fraction of the cost. Finally, we discuss the path to prototyping an array which will enable a spectroscopic survey of UDGs.

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arXiv2025

Bright Region Reset: an on-detector strategy for minimizing the impacts of atmospheric emission lines on spectral observations

Observations in the near-infrared using large ground-based telescopes are adversely impacted by bright atmospheric emission lines, particularly the OH Meinel bands. These lines can saturate a moderate-resolution spectrograph on the order of minutes, resulting in information loss at the wavelengths of the lines. OH lines also vary on similar timescales, requiring frequent sky exposures to be able to subtract the sky spectrum from that of the target. In this paper we present a new method, which we call bright region reset (BRR), to prevent the saturation of these lines in near-infrared spectra while simultaneously improving information about their variability. This is accomplished by periodically resetting pixels that contain bright lines on a detector capable of sub-window readout while the rest of the detector continues integrating. This method is demonstrated on the McKellar Spectrograph in the 1.2 m telescope at the Dominion Astrophysical Observatory in Victoria, Canada. Using a Teledyne H2RG detector, we reset the emission lines produced by an arc lamp while still recording their flux. We show no degradation in the resulting spectrum compared to a conventional observing mode. Unlike other OH line mitigation strategies, the BRR method not only avoids loss of information at wavelengths containing the lines, but also provides higher-cadence information on sky line variability, making it a promising technique for implementation at observatories. We advocate demonstrating this method on sky at existing 8--10 m class facilities with near-infrared spectrographs equipped with HxRG detectors in order to test its feasibility for use in sky subtraction schemes for premier modern spectrographs, including the upcoming generation of instruments for the Extremely Large Telescopes.

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arXiv2023

Fat cosmic ray tracks in charge-coupled devices

Cosmic rays are particles from the upper atmosphere which often leave bright spots and trails in images from telescope CCDs. We investigate so-called ``fat" cosmic rays seen in images from Vera C. Rubin Observatory and the Subaru Telescope. These tracks are much wider and brighter than typical cosmic ray tracks, and therefore are more capable of obscuring data in science images. By understanding the origins of these tracks, we can better ensure that they do not interfere with on-sky data. We compare the properties of these tracks to simulated and theoretical models in order to identify both the particles causing these tracks as well as the reason for their excess spread. We propose that the origin of these tracks is cosmic ray protons, which deposit much greater charge in the CCDs than typical cosmic rays due to their lower velocities. The generated charges then repel each other while drifting through the detector, resulting in a track which is much wider than typical tracks.

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