Data Release 1

Data Release 1 (DR1) was published November 5, 2020. This release consists of both coadded and abutted COS and STIS spectra for 115 of the approved ULLYSES targets. For a complete description of how High Level Science Products (HLSPs) are produced, see Data Product Description.

DR1 Targets

Included in DR-1 are 53 massive stars located in the LMC and 62 massive stars located in the SMC. Data products for these targets are available from this website (HLSPs and contributing data), the MAST Data Discovery Portal (HLSPs and contributing data), or directly as a High-Level Science Product collection using the DOI.

Products not included in this release:

Known Issues and Caveats

  1. The selection of the transition wavelength from one abutted spectrum to the next is defined in this release to be the middle of the overlap region. In future releases the transition wavelengths will be selected such that the signal-to-noise ratio in the input spectra is very similar.
  2. The computation of the error arrays includes contributions from the flat-field uncertainty and background contribution for COS data, but only from the celestial target+background counts for STIS data. This calculation is a good approximation in the high signal limit which applies to nearly all data in DR-1.
  3. For STIS data, all Data Quality (DQ) flags in the standard CALSTIS Serious Data Quality Flags (SDQFlags) definition are used with the exception of DQ=16 (pixels with dark rate >5-sigma times the median dark level) as this DQ flag was not deemed to have significant impact on the computed flux.
  4. The output flux is weighted by:
    • GCOUNTS for COS
    • GROSS counts times the expusure duration for STIS. For STIS the GROSS counts arrays include some negative values due to the subtraction of the scattered light contribution in the CALSTIS pipeline. Therefore, for STIS data only, we currently weight input flux by absolute gross counts multiplied by the exposure duration.
  5. For COS G130M/1096 data of FP-POS setting 1 only: a flux calibration issue at the reddest ~1.5 Angstroms of both FUVA and FUVB segment spectra causes incorrect flux measurements. As a temporary solution until new sensitivity curves are implemented, the discrepant flux is currently being excluded from coaddition.

Charting young stars’ ultraviolet light with Hubble.

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