Identifying Cosmic Ray Over-Flagging in STIS CCD Spectroscopic Observations
Abstract
The standard method for rejecting cosmic rays in CCD data taken by the Hubble Space Telescope's Space Telescope Imaging Spectrograph (STIS) instrument relies on combining multiple sub-exposures while flagging outliers. A known caveat of this method is that when the sub-exposures are not well registered, large portions of valid spectroscopic data can be flagged as cosmic rays. In this work we discuss the new ocrreject_exam() task in the stistools Python package designed to quickly identify datasets impacted by this misregistration-induced over-flagging. We demonstrate its effectiveness on known cases of over-flagged data, introduce a new monitoring website which automatically runs the tool on STIS CCD spectroscopic data, and analyze the tool's output on STIS CCD spectroscopic data from 1997 through 2025. From this analysis we estimate that ~31% of datasets will exhibit cosmic ray over-flagging. Lastly, we discuss various methods of recalibrating impacted data to mitigate the effects of over-flagging.
Related
- Simultaneous photometric, spectroscopic, and FAST radio observations of AD Leo
- Tracing the Cosmic web across Cosmic time through SKA observations of radio galaxies
- Atmosphere mitigation in cosmic microwave background observations using multifrequency time-domain component separation
- Analysis of Aditya-L1/VELC [Fe XIV ] 5303 Å Spectroscopic Observations of the Solar Corona: Development of a Data-processing Pipeline
- geko : A tool for modelling galaxy kinematics and morphology in JWST /NIRCam slitless spectroscopic observations
BibTeX
@misc{dallas2026identifying,
title = {{Identifying Cosmic Ray Over-Flagging in STIS CCD Spectroscopic Observations}},
author = {Matthew M. Dallas and Sean Lockwood},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.33184},
eprint = {2610.33184},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.33184},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Identifying Cosmic Ray Over-Flagging in STIS CCD Spectroscopic Observations
AU - Matthew M. Dallas
AU - Sean Lockwood
PY - 2026
DA - 2026/10/23
PB - arXiv
DO - 10.48550/arxiv.2610.33184
UR - https://arxiv.org/abs/2610.33184
AB - The standard method for rejecting cosmic rays in CCD data taken by the Hubble Space Telescope's Space Telescope Imaging Spectrograph (STIS) instrument relies on combining multiple sub-exposures while flagging outliers. A known caveat of this method is that when the sub-exposures are not well registered, large portions of valid spectroscopic data can be flagged as cosmic rays. In this work we discuss the new ocrreject_exam() task in the stistools Python package designed to quickly identify datasets impacted by this misregistration-induced over-flagging. We demonstrate its effectiveness on known cases of over-flagged data, introduce a new monitoring website which automatically runs the tool on STIS CCD spectroscopic data, and analyze the tool's output on STIS CCD spectroscopic data from 1997 through 2025. From this analysis we estimate that ~31% of datasets will exhibit cosmic ray over-flagging. Lastly, we discuss various methods of recalibrating impacted data to mitigate the effects of over-flagging.
ER -