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### CEERS Data Release 0.7 ###
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Date Released: 3 October, 2023

Here we provide our team's reductions of the CEERS NIRCam WFSS observations.
These CEERS Epoch 2 observations are of pointings 5, 7, 8 and 9, and were 
obtained as prime observations in December 2022 with MIRI imaging in parallel. 


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### Summary

Instrument: NIRCam
Mode: Wide Field Slitless Spectroscopy
Calibration Pipeline Used: jwst v1.10.2 (Stages 1 and 2, custom procedures 
    used for spectral calibration and extraction)
CRDS Context pmap: 1089
Target: NIRCam Pointings 5, 7, 8, 9
Filters: F356W
Readout: SHALLOW4
Observation specification: 6 groups, 1 integration
Dithers: 4-point dithers, optimized for NIRCam+MIRI-F1500W


Contact: Nor Pirzkal (npirzkal@stsci.edu)


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### CEERS NIRCam WFSS observations

This data release includes CEERS NIRCam WFSS pointings 5, 7, 8 and 9, obtained
as prime observations with MIRI imaging in parallel. These pointings were 
chosen to maximize the overlap between the NIRCam grism and NIRSpec MSA 
observations. Each pointing is observed with the F356W filter, covering 
~3.1-4.0 um with R~1600, using both the row (GRISMR) and column (GRISMC)
grisms. 

Grism observations were accompanied by direct imaging with F356W, including 
two out-of-field dithered parallel to the dispersion direction to identify 
off-image sources with dispersed spectra in the grism FOV. All LW observations 
were paired with F115W imaging. The imaging was included in our NIRCam imaging 
data release DR0.6. 


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### Data reduction and calibration

We processed the raw data through Stages 1 and 2 of the JWST Calibration 
Pipeline (Bushouse et al. 2023, DOI:10.5281/zenodo.7829329) to perform 
detector-level corrections and create output countrate images. The WFSS data 
are then processed through custom procedures designed to optimize the modeling 
and extraction of slitless spectroscopic data. We briefly summarize these steps 
below, but see Pirzkal et al. 2017 for details.
(https://ui.adsabs.harvard.edu/abs/2017ApJ...846...84P/abstract)

Imaging mosaics were created from running the direct imaging through Stages 2 
and 3 of the Calibration Pipeline to create mosaics in F356W. These mosaics 
were not GAIA corrected as to not break relative astrometry to the WFSS
observations. 

The extraction catalog and segmentation map were generated from the full CEERS
imaging mosaics (including all NIRCam imaging from CEERS data releases DR0.5 
and DR0.6), and affine transformations were computed between the F356W direct 
imaging mosaics and the full extraction catalog. 

We used the full extraction catalog including all available NIRCam LW bands   
to pre-compute and model contamination from overlapping spectra. We extract 
spectra down to the detection limit of the F356W mosaic in order to get as 
complete a model of contamination as possible. However, we release here 
spectra extracted down to F356W = 25 (AB mag), as contamination in slitless 
data is of increasing concern for fainter targets. Extractions of fainter 
sources will be included in a future release.

The WFSS calibration was derived using commissioning data from PID01076. 
This calibration is current as of June 2023, though it is not yet included in 
CRDS. A new and improved calibration will be available soon.


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### Directory Contents

Spectra for each pointing are stored in separated directories. The filenames 
are of the form:
  [pointing]/[grism]/[module]_F356W_[grism]_[obj]_dr0.7_[ext].fits
where:
  - [pointing] is one of 'nircam5', 'nircam7', 'nircam8' or 'nircam9' 
  - [grism] is either 'GRISMR' or 'GRISMC'
  - [module] refers to the NIRCam module and is either 'A' or 'B'
  - [obj] is the source ID number 
  - [ext] is one of:
    - 's2d': rectified 2D spectrum in units of DN/pixel
    - 'x1d': extracted 1D spectrum in units of erg/s/cm^2/A

Auxiliary files:
  - CEERS_NIRCam_WFSS_catalog.csv - F356W catalog proviging source ID number, 
        RA and Dec, and F356W magnitude. It also specifies which CEERS pointing 
        and NIRCam module (A or B) each source is in, and whether the source 
        is covered by the GRISMR and/or GRISMC observations.
  - [pointing]/plots/individual_grisms/[module]_F356W_[grism]_[obj]_dr0.7.pdf - 
        diagnostic plot showing 2D and 1D spectra for the individual grisms as 
        well as an image stamp of the source in F356W. The 1D plot shows the 
        flux extracted using both a box extraction and our optimal extraction
  - [pointing]/plots/combined_grisms/[pointing]_[module]_[obj].pdf - diagnostic 
        plot combinging both GRISMR and GRISMC observations (where available) 
        of the source
  

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### File structure

Rectified 2D spectra (*_s2d.fits) are multi-extension fits files with 7 
extensions:
  0. PRIMARY header
  1. 2D_COUNT  - 2D data array (DN/s)
  2. 2D_ERR  - 2D error array
  3. 2D_TCOUNT  - 2D array of total counts
  4. 2D_CCOUNT  - 2D array of estimated contamination counts 
  5. 2D_MCOUNT  - 2D model estimated counts (based on photometry)
  6. 2D_WAVE  - 2D wavelength array (um)


Extracted 1D spectra (*_x1d.fits) are single-extension fits files containing 
a table with the following columns:
  - WAVELENGTH  (um)
  - OPTFLUX, flux using optimal extraction as described above (erg/s/cm^2/A)
  - FLUXERR, flux error from optimal extraction (erg/s/cm^2/A)