June 28, 2022
Due to problems with MAST ingestion, products for SSTC2DJ161344.1-373646
are not available through the MAST portal. However, products can still be downloaded
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:
- 233 massive stars from the LMC and SMC
- 122 massive stars also have FUSE spectra
- 3 massive stars in NGC3109
- 85 Survey T Tauri stars
- 36 stars have LCOGT (Las Cumbres Observatory Global Telescope) imaging observations
- 41 stars have HST COS/FUV, STIS/NUV, and STIS/Optical spectra
- 4 Monitoring T Tauri stars
- All monitoring stars have LCOGT imaging observations in the u’, V, and i’ bands
9 non-ULLYSES targets
- These targets are present in STIS long-slit observations of T Tauri stars
- Products for these companions may be used to disentangle their
contributions to the spectra of primary ULLYSES T Tauri stars
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.
- 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
- 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:
- coadded and abutted spectra
- timeseries spectra
- re-packaged drizzled images
- 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
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.
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.
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.
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.
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.
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:
- 5 survey T Tauri stars
- All 4 monitoring T Tauri stars in u’, V, and i’ bands (previously only V and i’ bands)
New HST exposure- and sub-exposure-level products are available for:
- The second epoch of TW Hya
- 6 additional visits for the first epoch of GM Aur
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:
- TW Hya: time = 30s, wavelength = 3 pixels
- RU Lup: time = 30s, wavelength = 6 pixels
- BP Tau: time = 30s, wavelength = 6 pixels
- GM Aur: time = 90s, wavelength = 6 pixels
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
For regions where all contributing datasets have data quality issues, flux is set to 0.
The selection of the transition wavelength from one abutted spectrum to
the next is currently defined to be the middle of the overlap region.
In future releases, the transition wavelengths will be selected to ensure
the signal-to-noise ratio is similar at the transition wavelength.
Twenty of the T Tauri stars introduced in DR3 include archival data only.
While low-resolution STIS spectra (G230L, G430L, and/or G750L) exist for
these targets, these modes require careful manual calibration. As such,
these modes will be included in a future DR.
The STScI STIS team is in the process of re-deriving
As of June 2022, the following modes have been completed: G140L, E140M,
G230L, G230LB, and G430L. Until the remaining modes are completed, there
may be slight mismatches between the flux of adjacent modes (e.g. between
G430L and G750L or between E140M and E230M).
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
A description of the ULLYSES observations and data products is given in:
For more information on how to cite ULLYSES data, see