ULLYSES LOW-Z

Low-Metallicity Galaxy OB Stars

The ULLYSES sample for stars in low-metallicity galaxies consists of two parts. The core sample (Table 1) includes six high-mass stars in the low-metallicity galaxies Sextans A and NGC 3109 with spectroscopic data that is consistent with the design goals in terms of wavelength coverage and signal-to-noise. The HST UV spectroscopy for the core sample is a mixture of new data collected during HST Cycles 27–29 and archival data. Additionally, pre-imaging data was obtained of NGC 3109 and Sextans A with WFC3/UVIS (Table 3).

The core sample is augmented by a subset of stars with purely archival data that meet many, though not necessarily all, of the project’s design goals, but nevertheless provides supplementary material that contributes directly to the scientific goals of ULLYSES. These "extra" targets and their HST UV spectroscopic material are summarized in Table 2.

In both Tables, successive columns record:

• a commonly used name for the target that can be resolved by Simbad
• the name that has been adopted by the ULLYSES project and is used in the ULLYSES catalog
• the name that appears in the Phase II files, which can be used for separate queries to MAST. The name used in the ULLYSES products appears in bold face.
• Gaia DR3 coordinates
• the adopted spectral type
• the Johnson V magnitude
• the estimated reddening, E(B-V), which is usually derived from the observed (B-V) color and a calibration of intrinsic color (B-V)₀ as a function of spectral type

Table 1 also contains photometry for 5 WFC3 filters (F225W, F275W, F336W, F475W, F814W) listed in units of STmag with errors on the order of 0.05-0.1mag. Simbad target names are hyperlinked to their entry in Simbad, which provides a complete list of aliases, while the ULLYSES target names are hyperlinked to the specific entry in the ULLYSES catalog. References to the source of observational information are also linked.

Four additional columns summarize the HST spectra held by MAST by providing:

• the proposal ID(s) that collected the data. Each ID is linked to its Phase II proposal.
• the instrumental configurations that were used
• the date of the first HST observation of the target
• the current status of the data collection. "In progress" implies that additional visits await scheduling.

Clicking anywhere in a row will also open a table that provides more detailed information about the observations in each visit.

Tables 1 and 2 contain a subset of the information accessible from the ULLYSES search form, which supports querying targets and datasets based on both observational and astrophysical parameters. The "Simbad Resolvable Name" should aid in querying specific targets in the search form. In addition to specialized search parameters, the form also:

• enables direct data file downloads
• allows customized API script to be generated
• provides complete metadata for selected targets to be exported in a variety of file formats

Information for all ULLYSES targets in low-metallicity galaxies can be accessed directly via this predefined query.

Table 1: ULLYSES Core Sample

Table 2: Additional Archival Stars Included in the ULLYSES sample

Table 3: ULLYSES Imaging