Current Cosmic Ray Monitor: 2025 STIS CR Table
CCD exposures taken with the Space Telescope Imaging Spectrograph (STIS) are split into multiple subexposures (CR-SPLITS) which are later combined for the purpose of rejecting cosmic rays. This monitor runs daily on STIS CCD spectroscopic datasets that have both a calibrated cosmic ray rejected image (_crj.fits) and a 1d extracted spectrum (_sx1.fits or _x1d.fits) available on MAST. The monitor provides basic information about the exposures from the public Phase II and MAST, as well as the pixels identified as cosmic rays by the pipeline. The pixels identified as cosmic rays are also presented visually in two interactive plots (STACK_PLOT and SPLIT_PLOT). The first is an image of the detector or subarray with each pixel color coded to the number of times across all subexposures it was flagged as a cosmic ray. The second is a zoomed image of each CR-SPLIT showing which pixels are flagged as cosmic rays in and around the extraction box. These are particularly useful for quickly identifying cases of cosmic ray over-flagging, discussed below. For a full list of available columns, see the Column Definitions section below.
Cosmic Ray Over-Flagging
There is a known issue when the target is not spatially well aligned in the aperture between CR-SPLITS. In these cases, the default cosmic ray rejection algorithm can identify valid spectral data in one or more of the cr-splits as cosmic rays, leading to an underestimation of the counts in the spectrum after combining. STIS ISR 2019-02 and the caveats section of STIS ISR 1998-22
As a simple check for cosmic ray over-flagging, the Cosmic Ray Monitor provides the fraction of pixels identified as cosmic rays inside (AVG_EXTR_FRAC) and outside (AVG_OUTSIDE_FRAC) the default spectral extraction box. Ideally, the ratio of these fractional rejection rates (AVG_RATIO) is equal to one, but in cases where the cosmic ray rejection algorithm preferentially flags data within the extraction box it will be > 1. Datasets with AVG_RATIO > 1.47 are highlighted in orange as they likely have valid data being flagged in one or more subexposures. STIS ISR STIS ISR 2019-02 provides suggestions for custom cosmic ray rejection that can help mitigate this overflagging.
- 2024 STIS CR table
- 2023 STIS CR table
- 2022 STIS CR table
- 2021 STIS CR table
- 2020 STIS CR table
- 2019 STIS CR table
- 2018 STIS CR table
- 2017 STIS CR table
- 2016 STIS CR table
- 2015 STIS CR table
- 2014 STIS CR table
- 2013 STIS CR table
- 2012 STIS CR table
- 2011 STIS CR table
- 2010 STIS CR table
- 2009 STIS CR table
- 2004 STIS CR table
- 2003 STIS CR table
- 2002 STIS CR table
- 2001 STIS CR table
- 2000 STIS CR table
- 1999 STIS CR table
- 1998 STIS CR table
- 1997 STIS CR table
Column Definitions
| Column Name | Description |
|---|---|
| OBSID | Dataset name |
| PROPOSID | ID number assigned to the proposal |
| LINENUM | Proposal logsheet line number. First two values usually indicate visit ID, remaining values indicate the line of the exposure in the Phase II file |
| TARGNAME | Target name designated by the observer |
| TARDESCR | Target description designated by the observer |
| APERTURE | Aperture configuration |
| OBS_TIME | UT start time of first exposure |
| POSTARG1 | X component of the offset of the target from the aperture fiducial point (perpendicular to slit) in arcseconds |
| POSTARG2 | Y component of the offset of the target from the aperture fiducial point (parallel to slit) in arcseconds |
| PATTERN1 | Primary pattern type |
| CRSPLIT | Number of cosmic ray split exposures |
| NRPTEXP | Number of specified identical repeat exposures in set (default is 1 if CRSPLIT is specified, usually used to obtain time-resolved images) |
| AVG_EXTR_FRAC | Average cosmic ray rejection rate (n cosmic ray flags/ n pixels) in the extraction box across all subexposures |
| AVG_OUTSIDE_FRAC | Average cosmic ray rejection rate (n cosmic ray flags/ n pixels) outside the extraction box across all subexposures |
| AVG_RATIO | The ratio between the average cosmic ray rate of the extraction box and the average cosmic ray rate outside of the extraction box across all subexposures. Values >1 indicate preferential flagging of cosmic rays within the extraction box. Values >1.47 are highlighted in orange as they have a high likelihood of valid spectroscopic data being flagged as cosmic rays. |
| QUALITY | Procedural Data Quality comments from MAST (e.g., LOCKLOST, RECENTER, TDF-DOWN, SLEWING), as well as custom quality comments in cases where a dataset could not be processed by the monitor. |
| STACK_PLOT | Image of the detector or subarray with each pixel color-coded based on the number of times it was flagged as a cosmic ray across all subexposures |
| SPLIT_PLOT | Zoomed image of each subexposure around the extraction box showing which pixels are flagged as cosmic rays |