ULLYSES Observing Strategies and Technical Specifications

The ULLYSES program is divided into two primary observational campaigns of high- and low-mass stars. The focus on high-mass stars includes observations of 70 OB stars in each of the Large (50% solar metallicity) and Small (20% solar metallicity) Magellanic Clouds, prioritizing the latter, as well as five to ten additional stars, which are accessible in the even lower metallicity Local Group galaxies NGC 3109 (10 to 20% solar metallicity), and Sextans A (10% solar metallicity). For low-mass stars, observations will focus on about 40 K- and M-type T Tauri stars and brown dwarfs within the Milky Way, including time-domain monitoring of four prototypical T Tauri stars with well-known rotation periods and magnetic configurations.

Observations of high-mass stars will consist of 200 orbits on the LMC targets, 250 orbits for those in the SMC, and 50 orbits for other low-metallicity Local Group galaxies. For low-mass stars, the grid will sample mass, age, and accretion rate over 400 orbits. 100 additional orbits will be allocated to the time-domain variability aspect of ULLYSES.

UV spectrum of Sk-68 26
Example of UV spectrum (FUV+NUV) of LMC massive star Sk-68 26, a BC2 Ia supergiant. For this star, archival coverage exists with FUSE, but this spectral range could be observed as part of ULLYSES with the COS/G130M/1096 setting. The STIS E140M or COS G130M+G160M gratings will cover the longest wavelengths in the FUV, while massive stars in the LMC and SMC will be observed with STIS E230M/1978 (and E230M/2707 for the the brightest late B supergiant).
Full spectral coverage of TW Hya
Example of full spectral coverage of T Tauri star TW Hya. The FUV part of the spectrum has been observed with STIS E140M. Similar objects selected in the ULLYSES samples will be observed in the FUV with either STIS E140M or COS G130M+G160M. The NUV, optical, and NIR parts of the spectrum of T Tauri stars in ULLYSES will be observed with STIS G230L, G430L, and G750L, respectively.

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