Arcus is a high-resolution soft X-ray and far-ultraviolet spectroscopy mission submitted to the National Aeronautics and Space Administration’s inaugural Astrophysics Probe solicitation. Arcus makes simultaneous observations in these two critical wavelength regimes to address a broad range of science questions highlighted by the 2020 Astronomy and Astrophysics Decadal Survey, from the temperature and composition of the missing baryons in the intergalactic medium to the evolution of stars and their influence on orbiting planets. We present the science motivation for and performance of the Arcus ultraviolet spectrograph (UVS). UVS comprises a 60-cm, off-axis Cassegrain telescope feeding an imaging spectrograph operating over the 970- to 1580-Å bandpass. The instrument employs two interchangeable diffraction gratings to provide medium-resolution spectroscopy (R>20,000 in two grating modes centered at ∼1110 and 1390 Å). The spectra are recorded on an open-face, photon-counting microchannel plate detector. The instrument design achieves an end-to-end sensitivity >10 times that of the Far-Ultraviolet Spectroscopic Explorer over the key 1020- to 1150-Å range and offers arcsecond-level angular resolution spectral imaging over a 6-arcminute-long slit for observations of extended sources. We describe the example science investigations for far-ultraviolet spectroscopy on Arcus, the resultant instrument design and predicted performance, and simulated data from potential General Observer programs with Arcus.
The Arcus Probe mission addresses a wide range of Astro2020 Decadal and NASA Science Mission Directorate Priority science areas, and is designed to explore astrophysical feedback across all mass scales. Arcus' three baseline science goals include: (i) Characterizing the drivers of accretion-powered feedback in supermassive black holes, (ii) Quantifying how feedback at all scales drives galaxy evolution and large-scale structure, including the tenuous cosmic web, and (iii) Analyzing stellar feedback from exoplanetary to galactic scales, including its effects on exoplanet environments targeted by current and future NASA missions. These science goals, along with a robust General Observer program, will be achieved using a mission that provides a high-sensitivity soft (10-60Å) X-ray spectrometer (XRS), working simultaneously with a co-aligned UV spectrometer (UVS; 970-1580Å). Arcus enables compelling baseline science and provides the broader astronomy community a revolutionary tool to characterize the full ionization range of warm and hot plasmas - including hydrogen, helium, and all abundant metals - in the Universe, from the halos of galaxies and clusters to the coronae of stars.
The Hydrogen Emission Line Interferometric eXplorer (HELIX) is a SmallSat mission concept to study the vertical distribution and transport flux of geocoronal hydrogen that is transitioning from Earth’s upper atmosphere into the exosphere. This investigation is conducted using a dual channel, all-reflective Spatial Heterodyne Spectrometer (SHS). A SHS is a type of Fourier Transform Spectrometer that divides incoming light into 2-beams with a diffraction grating that interfere to produce a linear fringe pattern from which spectral power is obtained. The HELIX SHS has a dual ruled grating that is can be simultaneously aligned to observe the Ly-α and Ly-β transitions of hydrogen. It has a spectral resolving power of ~200000 that separates the geocoronal lines from contaminating background emissions and allows exploration of the thermal and non-thermal populations of hydrogen. HELIX is designed for incorporation into a high-heritage SmallSat spacecraft platform that would be launched into low Earth orbit for a 12-month mission. This presentation describes the SHS concept, the mission requirements for HELIX, and the top-level on-orbit performance of the instrument.
Arcus is a high-resolution soft X-ray and far-ultraviolet spectroscopy mission being developed for submission to NASA’s inaugural Astrophysics Probe solicitation. Arcus makes simultaneous observations in these two critical wavelength regimes to address a broad range of science questions highlighted by the 2020 Astronomy and Astrophysics Decadal Survey, from the temperature and composition of the missing baryons in the intergalactic medium to the evolution of stars and their influence on orbiting planets. This proceeding presents the science motivation for and performance of the Arcus UltraViolet spectrograph (UVS). UVS comprises a 60 cm, off-axis Cassegrain telescope feeding an imaging spectrograph operating over the 970 – 1580 ˚A bandpass. The instrument employs two interchangeable diffraction gratings to provide medium-resolution spectroscopy (R ⪆ 20,000 in two grating modes centered at approximately 1110 and 1390 ˚A, respectively). The spectra are recorded on an open-face, photon-counting microchannel plate detector. The instrument design achieves an end-to-end sensitivity ⪆ 10 times that of the Far-Ultraviolet Spectroscopic Explorer over the key 1020 – 1150 ˚A range and offers arcsecond-level angular resolution spectral imaging over a six arcminute long slit for observations of extended sources. We describe example science investigations for FUV spectroscopy on Arcus, the resultant instrument design and predicted performance, and simulated data from potential Guest Observer programs with Arcus.
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