Data Release 5

June 28, 2022

NOTE: Due to problems with MAST ingestion, products for SSTC2DJ161344.1-373646 are not available through the MAST portal. However, products can still be downloaded from the ULLYSES download page.

ULLYSES Data Release 5 (DR5) consists of high-level science products (HLSPs) for 75 new ULLYSES targets and updated HLSPs for 250 targets previously released in DRs 1-4, for a total of 325 ULLYSES targets to date. Products are also provided for 9 companion targets present in STIS long-slit observations. Updated HLSPs from previous DRs include recent COS and STIS pipeline and/or calibration improvements. HLSPs from previous DRs should be replaced with newly downloaded products that incorporate these upgrades.

DR5 Target Breakdown

325 ULLYSES targets: 9 non-ULLYSES targets Finally, HST/WFC3 imaging HLSPs exist for both low-metallicity galaxies, NGC 3109 and Sextans A.

T Tauri Star Companions

One survey T Tauri star new to DR5 had a companion in the STIS slit, and another is suspected to have a companion. Details are provided below.
  1. RXJ0438.6+1546: 1 unexpected companion. This companion was identified as 2MASSJ04383885+1546045, located approximately 9.6” away from the ULLYSES target. The 2MASS identifier was adopted as this companion’s name. HLSPs are produced for this companion.
  2. V-VZ-CHA: 1 suspected companion. The cross-dispersion profiles appear slightly asymmetric and acquisition images show a slightly elongated PSF. While no nearby companions were found in catalogs, it is suspected that there is actually a companion to this ULLYSES target. Users should be aware that if there is a companion, the spectra for V-VZ-CHA will include contributions from this companion.

HLSP Creation Code

DR5 includes the public release of the ULLYSES HLSP creation code through the ULLYSES git repository. The public release includes an installation guide and instructions for creating the four main types of ULLYSES HLSPs:
  1. coadded and abutted spectra
  2. timeseries spectra
  3. re-packaged drizzled images
  4. custom-calibrated individual spectra, or level0 HLSPs
Contributions and feedback on this project are welcome! Contribution guidelines are included in the repository. If you have questions or concerns regarding the software, please open an issue or contact the HST Help Desk.

Changes to the ULLYSES Sample

A few notable updates to the ULLYSES sample are included below.
  1. Previously, the ULLYSES name for the target HD-5980 was defined as AV229. HD-5980 is the generally agreed upon name of this target, so documentation and products have now been updated to reflect this.
  2. Archival STIS spectra for the target NGC346-ELS-22 have been delivered since DR3, however, it was recently discovered that the MAST target name of this target was incorrect. The actual target was NGC346-MPG-346 which is not in the ULLYSES sample. Instead, archival COS data was discovered, and the previous STIS data was removed. From DR5 onwards, this target only includes COS data, and previous products should not be used.
  3. SMC target AV255 was dropped from the ULLYSES sample, given its uncertain flux and the fact that its spectral type and luminosity class (O8 V) have already been well covered by previous ULLYSES observations.
  4. The LMC target VFTS180 was mistakenly included in DRs 3 and 4, even though all expected data have not been acquired. While archival STIS data is currently available for this target, the S/N is quite low. As such, this target will be observed by the ULLYSES team with COS to improve its S/N. Therefore, the partial STIS product is removed in DR5 and this target will be redelivered once the ULLYSES program has executed.

Time-series Spectra

Spectroscopic time-series products are available for both survey and monitoring T Tauri stars. For survey stars, only exposure level time-series with LCOGT data (with extension “_tss.fits”) are available. It should be noted that LCOGT time-series “spectra” consist of only two wavelength samples corresponding to the central wavelengths of each imaging filter used. HST COS and STIS UV data are time-tagged, which allows for sub-exposure time-series spectra. Sub-exposure products (with extension “_split-tss.fits”) are only generated from HST data of monitoring stars. HST exposure-level time-series spectra are also created for monitoring stars. The data formats of both exposure- and sub-exposure-level products are identical regardless of input data type (LCOGT or HST) or target type (survey or monitoring star), but the input data calibration and exact methods of creation differ. See the Data Description webpage for complete details.

In DR5, new LCOGT exposure-level products are available for: New HST exposure- and sub-exposure-level products are available for: New HST exposure-level products only are available for: Additionally, updated DR4 time-series products are available for download. These products benefit from updated calibration and processing.

Time and Wavelength Sampling

The time and wavelength sampling for sub-exposure time-series spectra are optimized to probe the smallest time interval possible while maintaining a S/N ≥ 5 per resolution element at the peak of the most important emission lines: C IV (1548 Å), and Mg II (2800 Å). The final sampling is also chosen to ensure that products are ready for use out-of-the-box and require no additional binning for most scientific goals. However, if a higher S/N is required, data can be binned further in time or wavelength by the user.

For all NUV observations, the optimal time sampling and wavelength sampling were determined to be, respectively, 10s and the native wavelength grid (i.e. no wavelength binning, or ~0.415 Å). For FUV spectra, the following time and wavelength bins have been adopted for the four monitoring T Tauri stars: For reference, the COS/FUV resolution element is 6 pixels, or ~0.073 Å, in the dispersion direction.

Targets Requiring Special Calibration


A subset of the available exposures were used to create the coadded products for target RECX-6. This target was found to be variable on short timescales, and only exposures of the same flux state were coadded together. Users wishing to explore the variability of this target may do so by consulting its timeseries product.

Survey T Tauri Stars

As in previous DRs, all STIS/G230L, G430L, and G750L data of T Tauri stars continue to require tailored calibrations. Special calibration steps taken for these observations can include: custom hot pixel identification and flagging, defringing for G750L observations, and customized spectral extraction parameters for T Tauri stars and any companions. Level0 HLSPs (manually calibrated 1-D spectra) are provided for these stars.

DR5 Caveats and Known Issues

Data Description & Download

A full description of the ULLYSES data products and how they are created can be found here. Data may be downloaded from this website (HLSPs and their contributing data), the MAST Data Discovery Portal (HLSPs and their contributing data), or directly as a High-Level Science Product collection using the DOI.


A description of the ULLYSES observations and data products is given in:

For more information on how to cite ULLYSES data, see ULLYSES References.

Charting young stars’ ultraviolet light with Hubble.

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