arXiv subjects

Ky Huynh

Publications and source records attributed to Ky Huynh.

5 recordsLinked to original sources

arXiv2026

Updates to the WFC3/IR Photometric Stability Stellar Cluster Study

The WFC3/IR channel has been shown to lose sensitivity over time. The sensitivity loss rate has been quantified in past works and we extend those measurements into 2026 using photometry of uncrowded regions of star clusters 47 Tucanae and Messier 4 in the F110W and F160W filters. This study adds 4-7 additional visits since Bajaj et al. (2022) for each target/filter combination. Using F160W data of 47Tuc, we find that the IR channel continues to lose sensitivity at a rate of -0.07% $\pm$ 0.01% per year using the full dataset, and -0.06% $\pm$ 0.02% per year using only the first exposure of every visit. Using M4 data observed in F110W, we find a sensitivity loss rate of -0.13% $\pm$ 0.02% per year using the full dataset, and -0.07% $\pm$ 0.03% per year using just the first exposure of every visit. We find that the rate of sensitivity loss has decreased since the previous study. This likely stems from the inclusion of more recent visits that were designed to mitigate persistence effects. These results suggest that earlier observations, which were not intended for sensitivity measurements, may have overestimated the IR channel's sensitivity due to the effects of persistence from bright sources. The IMPHTTAB reference file that contains the correction to the time-dependent sensitivity remains unchanged from the sensitivity measurements of this report.

astro-ph.IM↗

arXiv2026

A Look at Eight Outbursts of Comet 7P/Pons-Winnecke

Cometary outbursts may be used as a means to infer the physical processes occurring on cometary nuclei. To that end, we studied eight outbursts of comet 7P/Pons-Winnecke identified between 2021 June 3 and 2021 August 31. The data analyzed consisted of optical images and derived photometry of the comet from the Las Cumbres Observatory network of telescopes. The outburst strengths relative to the ambient coma ranged from -0.2 to -1.1 mag, and the ejecta themselves had apparent brightnesses ranging from 17.4 to 13.3 mag. The morphologies of the ejecta varied, suggesting that the events may have originated from different sources across the nucleus. An order of magnitude estimation of the ejecta masses ranged from 10$^{5}$ - 10$^{6}$ kg, similar to other mini-outbursts of comets. The surface-area normalized outburst rate estimated during this time period is similar to comets 41P/Tuttle-Giacobini-Kres\'ak, 9P/Tempel 1 and 46P/Wirtanen, but 10 times larger than that observed at comet 49P/Arend-Rigaux. However, a comparison to the mini-outburst rate of comet 67P/Churyumov-Gerasimenko reveals significant discrepancies between Rosetta spacecraft results and those from ground-based telescopes. We also investigate whether or not cometary outbursts from 7P in the 19th century are needed to explain outbursts in meteor shower rates observed in the 20th century.

astro-ph.EP↗

arXiv2025

Pixel-Based Non-Linearity Correction for the WFC3 IR Detector

The current non-linearity correction for the Wide Field Camera 3 Infrared (WFC3/IR) channel is based on ground-based data acquired during WFC3's Thermal Vacuum 3 (TV3) testing campaign. In the current reference file, the correction coefficients derived for each pixel are averaged over each of the four detector quadrants. In this work, we compute a new pixel-based non-linearity correction using in-flight calibration observations with the internal tungsten lamp flats acquired between 2011 and 2013. We derive the new correction coefficients by fitting a third-order polynomial to the accumulated signal ``up-the-ramp" for each pixel. Approximately 2\% of IR detector pixels are flagged as bad, and a solution cannot be computed. For these, we use the quadrant averages of the new correction coefficients. An accompanying report (\cite{huynh2025}) provides detailed testing results using both internal flats and external science targets acquired in a variety of observing modes. The report highlights improvements in photometry derived from ``\_flt.fits" data products calibrated using the new reference file, with the largest improvement for pixels with fluence levels approaching the full well limit of $\sim$80,000 $e^- $. A new NLINFILE reference file was delivered in October 2025 and will be used to reprocess all WFC3/IR imaging and grism observations in the MAST archive.

astro-ph.IM↗

arXiv2024

The Local Ultraviolet to Infrared Treasury I. Survey Overview of the Broadband Imaging

The Local Ultraviolet to Infrared Treasury (LUVIT) is a Hubble Space Telescope program that combines newly acquired data in the near ultraviolet (NUV), optical, and near infrared (NIR) with archival optical and NIR imaging to produce multiband panchromatic resolved stellar catalogs for 23 pointings in 22 low-mass, star-forming galaxies ranging in distance from the outskirts of the Local Group to ~3.8 Mpc. We describe the survey design, detail the LUVIT broadband filter observations and the archival datasets included in the LUVIT reductions, and summarize the simultaneous multiband data reduction steps. The spatial distributions and color-magnitude diagrams (CMDs) from the resulting stellar catalogs are presented for each target, from the NUV to the NIR. We demonstrate in which regions of the CMDs stars with NUV and optical, optical and NIR, and NUV through NIR detections reside. For each target, we use the results from artificial star tests to measure representative completeness, bias, and total photometric uncertainty as a function of magnitude in each broadband filter. We also assess which LUVIT targets have significant spatial variation in the fraction of stars recovered at a given magnitude. The panchromatic LUVIT stellar catalogs will provide a rich legacy dataset for a host of resolved stellar population studies.

astro-ph.GA↗

arXiv2022

The LCO Outbursting Objects Key Project: Overview and Year 1 Status

The LCO Outbursting Objects Key (LOOK) Project uses the telescopes of the Las Cumbres Observatory (LCO) Network to: (1) to systematically monitor a sample of Dynamically New Comets over the whole sky, and (2) use alerts from existing sky surveys to rapidly respond to and characterize detected outburst activity in all small bodies. The data gathered on outbursts helps to characterize each outburst's evolution with time, assess the frequency and magnitude distribution of outbursts in general, and contributes to the understanding of outburst processes and volatile distribution in the Solar System. The LOOK Project exploits the synergy between current and future wide-field surveys such as ZTF, PanSTARRS, and LSST as well as rapid-response telescope networks such as LCO, and serves as an excellent testbed for what will be needed the much larger number of objects coming from Rubin Observatory. We will describe the LOOK Project goals, the planning and target selection (including the use of NEOexchange as a Target and Observation Manager or "TOM"), and results from the first phase of observations, including the detection of activity and outbursts on the giant comet C/2014 UN271 (Bernardinelli-Bernstein) and the discovery and follow-up of outbursts on comets. Within these outburst discoveries, we present a high cadence of 7P/Pons-Winnecke with days, a large outburst on 57P/duToit-Neujmin-Delporte, and evidence that comet P/2020 X1 (ATLAS) was in outburst when discovered.

astro-ph.EP↗