Description of the HST UV Slitless Reflectance Spectra of (1) Ceres bundle V1.0
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Bundle Generation Date: 2021-10-27
Peer Review: 2020_Asteroid_Review
Discipline node: Small Bodies Node


Content description for the HST UV Slitless Reflectance Spectra of (1) Ceres bundle
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This data set is part of the Repository for UV Spectral Data of Small Bodies (https://sbn.psi.edu/pds/resource/uvspec.html).

This archive package includes five data products. Average Ceres reflectance spectrum (avg_refl.csv) is the final data product. Three intermediate data products are: Ceres UV raw spectrum (subdirectory dn/) contains the raw spectra of Ceres extracted from the three 2D spectral images from the HST data archive (MAST); Ceres UV radiance spectrum (subdirectory radiance/) contains the radiance spectra derived from the raw spectra; Ceres UV reflectance spectrum (subdirectory reflectance/) contains the reflectance spectra of Ceres based on the radiance spectra. The fifth data product in the package is a list of the observation information for all original HST images (observations_list.csv), such as the exposure times, UTC, the geometry of the target, etc.  The derivation of intermediate data products and the final average Ceres reflectance spectrum, as well as the quality assessment of the data, are summarized in description_v4.pdfa.pdf in the document/ subdirectory.

All spectral tables, except for the final average spectrum, have 5 columns: Column 1 is the center wavelength of each spectral channel; Column 2 is the raw counts, radiance, or reflectance spectrum; Column 3 is the error; Column 4 is the spectral width of the channel from center wavelength to the short wavelength boundary; Column 5 is the spectral width of the channel from center wavelength to the long wavelength boundary. The Final reflectance spectrum table has three columns: Column 1 is the effective wavelength of each spectral channel; Column 2 is the reflectance spectrum; Column 3 is the error.


Caveats to the data user
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Because Ceres was spatially resolved, the slitless spectra of Ceres are degraded in spectral resolution compared to point sources, and the flux calibration is also affected and is not accurate.

Ceres was resolved to about 21 pixels in diameter in the observations. The spectra of Ceres extracted for any pixel inside the disk of Ceres will be affected by the spatial width of Ceres along the direction of dispersion. The spectral resolution degradation varies with the width of Ceres at the corresponding locations.

The flux of each spectrum also contains the flux from all the spectra of locations on the chord along the direction of dispersion, albeit at various wavelengths. Therefore, the flux calibration for point source cannot calibrate the flux of slitless spectrum for an extended source. The overall flux level of the radiance spectrum calibrated this way will be overestimated.

We did not attempt to restore the spectral resolution and correct for flux level for the data archived in this package. The spectral resolution and flux correction requires complicated deconvolution techniques and are not covered in the original project.