We present a set of isochrone-tailored spectral libraries for analyzing composite spectra of low-metallicity galaxies. Specifically, we have computed synthetic spectra for stars of all initial masses for isochrones at metallicities Z=0.002 and Z=0.0004, with and without considering rotation, constructed by the Geneva group (Ekström et al., 2011; Georgy et al.. 2013; Groh et al., 2019). We also present a Python program for integrating the individual spectra with a given initial mass function.

The Lyman-UV Imaging Spectrograph (LUVIS) is a NASA SMEX mission concept. Here, we describe the basic scientific requirements of LUVIS and instrumental requirements derived from the scientific requirements. Other papers in this conference by Woodruff et al. and Kendrick et al. describe the LUVIS instrument in detail.

We are developing the design for the Lyman-Ultraviolet (LUV) Imaging Spectrograph, LUVIS to propose for a small explorer (SMEX) mission. LUVIS will provide true long slit (six arc minute) imaging spectroscopic capability with large spectral resolving power, R. Minimizing the number of optical components to the required minimum of three enables large spectral throughput. The design uses a two-mirror Cassegrain Ritchey-Chretien Optical Telescope assembly (OTA), a single optic Rowland-like spectrometer, and a windowless 50 x 127 mm curved microchannel plate (MCP). The design is optimized over the 102 to 140 nm spectral range providing spectral imaging at R ~ 20K in a single exposure. Lyman-β enhanced Al + LiF mirror and grating coatings with the LiF protected with an atomic layer deposition (ALD) fluoride encapsulating overcoat provide high throughput over that spectral range. Line-of-sight (LOS) jitter control utilizes time-tag photon arrival to compensate field position jitter by re-registering pixel location in post-processing as well as tip/tilt active control of the secondary mirror of the OTA. This paper will describe the design as well as some of the key design trades that defined the design.

The Lyman UV imaging spectrograph (LUVIS) accomplishes priority UV science contained in the budget of a SMEXclass mission. LUVIS consists of a 0.5-m f/24 Cassegrain optical telescope assembly feeding a UV/ far-UV spectrometer. LUVIS has a long 6 arcmin slit enabling spectral imaging and is optimized for 102-140 nm with a resolving power of 20,000 on a micro-channel plate detector with a CsI photocathode. The light gathering power is designed to reach galaxies with near-UV fluxes as low as 10-14 erg/s/cm2 /Å (and lower with long time exposures). The design approach encompasses a simple but elegant optical design, minimum number of reflective surfaces, limited mechanisms, and an orbit minimizing fuel requirements while offering operational advantages. All components are already at a high technology readiness level further reducing technical and cost risk to meet a SMEX budget with healthy cost reserves.

We report on a study of 9 nearby star-forming, very low-metallicity galaxies observed by Hubble's COS far-UV spectrograph that can serve as templates of high-z galaxies to be observed by JWST. We find that the nebular spectra of these primitive galaxies show evidence of irradiation by X-ray emitters. Following Thuan et al. (2004), we identify the sources of X-ray emission as massive X-ray binaries containing a massive accreting stellar black hole. We further find that the lower the metallicity, the higher the probability of strong X-irradiation. Following Heger et al. (2003), we suggest that these accreting black holes are produced by direct collapse of stars having initial masses greater than ∼50 M_⊙. Our models of young star clusters with an embedded stellar black hole produce effects on the surrounding gaseous medium that are consistent with the observed spectra. We conclude that primitive galaxies are qualitatively different from more metal-rich galaxies in showing evidence of hard radiation that can best be explained by the presence of one or more embedded stellar black holes.

We report on the status of CETUS, an all-UV, Probe-class mission concept to be evaluated by the Astro2020 Steering Panel. This report expands and updates the scientific uses of CETUS and CETUS technology as described earlier by Kendrick et al. (2019). The major updates derive form technological advances that promise to make CETUS a scientifically more powerful and long-lived space observatory than originally proposed. A long, useful lifetime will be needed to fulfill the future needs of the astronomical and planetary-science community.

Aerobee rocket experiment intended to survey a larger region of sky than was observed in the 1955 flight and at higher spatial resolution.The objective was to measure the intensity of sources in the same wavelength band as in 1955 and to determine what the objects were.It revealed many bright extended regions tending to occur near O and B stars [4].The 1957 rocket payload also included three wide-band photometers operating in the 2700-Å band.Forty-nine stars of spectral types from about O to F were measured and analyzed by Boggess and Lawrence Dunkleman [5].

Measurements on astronomical survey data are the link between scientific questions and scientific findings that help to answer these questions. In acknowledgement of their importance, NASA requires proposers to specify what measurements their space mission concept can make and what physical properties or processes can be derived from those measurements. NASA is now requiring a plan for actually making these measurements and how they will be made available in useable form to astronomical community. We will explore the benefits and issues involved in having a NASA mission take responsibility for making and distributing astronomical measurements. We use as a case study the NASA Probe mission concept, CETUS (Cosmic Evolution Through UV Surveys) posted at arXiv:1909.10437.

This contribution summarizes the status and capabilities of current and future UV facilities for the investigation of the origin of life. The main operational project for UV astronomy is the Hubble Space Telescope with versatile instrumentation for astrobiological research. ASTROSAT/UVIT is also operational and providing useful information on the magnetic activity and flaring frequency of M-type stars. There are three projects currently under development: a cubesat mission, Colorado Ultraviolet Transit Experiment (CUTE), devoted to the detection of extended exospheres from giant planets orbiting M-type stars; and two medium size missions: Spektr-UF/WSO-UV and the telescope that will be operated in association with the China Space Station. The instrumentation for Spektr-UF/WSO-UV is very versatile and include imaging and spectroscopic capabilities; the mission is getting ready for a launch in 2025. Finally, there is section devoted to the coming projects and their foreseen impact. The section includes from flagship scale missions such as LUVOIR to small cubesat projects devoted to the investigation of the interstellar and interplanetary compounds through their impact in the UV extinction curve.

From studying the fossil records of stars to exploring the circumgalactic medium, UV astronomy is a field rife with scientific opportunity. CETUS is a proposed next-generation UV space telescope equipped with a suite of instruments tailored to the study of UV phenomena in our galaxy. To achieve diffraction-limited imaging and spectroscopy performance at short wavelengths, a high-performance and resolution optical design is necessary. We describe the telescope design options including a trade study between a traditional on-axis TMA and freeform off-axis TMA solution considering their alignment sensitivity and tolerances. Different secondary support structures are explored for the on-axis design to analyze the irradiance distribution of the point-spread function (PSF) due to the pupil obscuration and how it influences the simulated starfield at the telescope focal planes. With rigorous analysis we aim to enable the next spaceborne observatory for UV astronomy.

This whitepaper shows ozone to be the best potential biosignature gas for an early exoplanet imaging mission. While oxygen is not detectable at Earth until about 0.5 Ga, its proxy ozone is detectable for about half of that history. Ozone’s pronounced UV feature yields a small starshade and telescope and a simple photometer instrument.

A Probe-class ultraviolet (UV) telescope having capabilities not available to Hubble can help answer many outstanding Key Science Questions posed by Astro2010. Measurements of the processed UV data will increase the scientific yield and impact of this telescope.

I Zw 18 is a star-forming dwarf galaxy having a very low metal content, O/H similar to 1/50 solar (Skillman & Kennicutt 1993). While galaxies with such low metallicity are rare in the low-redshift universe, they are likely to be common in galaxies at cosmic dawn. Thus, I Zw 18 is a "living" template for z > 6 galaxies. We have obtained HST/COS far-UV spectra of the northwest star cluster in I Zw 18 and have compared them to SYNSPEC model spectra by Lanz & Hubeny (2003, 2007) in order to determine the properties of the stellar population. We have also compared the observed spectra of I Zw 18-NW to the CLOUDSPEC models (Hubeny et al. 2000) of the stellar cluster with an embedded ultra-luminous X-ray source (ULX). This comparison reveals feedback of the stellar black hole in the form of photoionization and heating. Such models can be used as starting points to explore the physical conditions in which stars and black holes form and evolve in an extremely low-metallicity environment at high redshift.

CETUS is a 1.5-m, wide-field UV observatory that will be a worthy successor to Hubble. Its distinguishing characteristics include multi-object slit spectroscopy, long-slit spectroscopy, spectroscopy in the Lyman-UV, prompt-response observations, and detection of low-surface brightness objects. These new capabilities ensure future discoveries.

The mission concept, Cosmic Origins Through UV Surveys (CETUS) is an all-UV space mission concept that was selected and funded by NASA for study in 2017. The main capabilities of CETUS that even Hubble doesn't have are: (1) wide-field (17.4'x17.4') imaging and spectroscopy of astronomical sources with <0.5'' resolution; (2) spectral sensitivity to UV radiation at wavelengths as short as 1000 Å; (3) near-UV multi-object slit spectroscopy; and (4) rapid-response UV spectroscopy and deep imaging of transients like GW 170817; and (5) 23 times higher sensitivity to extended sources. The main purposes of this CETUS Final Report are to describe the CETUS scientific program and to demonstrate the maturity of its instrumentation, which forms the basis of its estimated cost. While there are similarities of this Final Report to that submitted to NASA in March 2019 by the Goddard Space Flight Center, there are important differences including the following. * Science. The science case has been refreshed, deepened, and expanded as a result of ideas and recommendations expressed in the Astro2020 science white papers. * Instrumentation. Detailed investigations including a high-level error budget for focus with implications for thermal management, target acquisition in the MOS micro-shutter array, contamination control have been carried out. * Mission Design. The spacecraft and mission operations concepts as developed by NGIS Gilbert (formerly Orbital ATK) rather than the output of Goddard's Mission Design Lab have been adopted.. * Technology. Technology maturation plans have been updated.

We describe the impact of atomic spectroscopy on astrophysics and future requirements for atomic data. These requirements cannot be met with current levels of funding for laboratory astrophysics. The situation could be substantially improved with relatively small investment from the funding agencies.

CETUS ("Cosmic Evolution Through Ultraviolet Spectroscopy") is a mission concept that was selected by NASA for study as a Probe-class mission, meaning a mission whose full life-cycle cost to NASA is between $400M and $1.0B. CETUS has a wide-field UV telescope that will work with other survey telescopes observing at gamma-rays to radio waves to help solve major problems in galaxy and stellar astrophysics. CETUS features a 1.5-m telescope and two wide-field survey instruments, a near-UV multi-object slit spectrograph (MOS), a near-UV/far-UV camera. It also has a near-UV/far-UV imaging spectrograph to survey classes of astronomical objects one at a time. In this paper, we describe how CETUS will address questions posed by the 2010 Astrophysics Decadal Survey panel (Astro-2010) including: what are the drivers of galaxy evolution at the peak rate of star formation; what are the path(s) of evolution from the blue cloud to the red sequence; and how does the circumgalactic medium influence galaxy evolution and vice versa.

NASA has funded the Cosmic Evolution Through Ultraviolet Spectroscopy (CETUS) mission study in preparation for the Decadal Survey, ASTRO2020. CETUS is developed as a Probe Class Mission, a new NASA category for astrophysics cost capped at 1B USD. This enables larger and more sophisticated observatories than under NASA’s Explorer Programs, but less ambitious than under NASA Flagship Missions. The NASA CETUS Study has resulted in a wide-field-of-view (WFOV) telescope of 1.5m aperture, with the colleting area by solid angle product A*Ω substantially higher than that for HST. CETUS will include a wide field camera, a multi-object spectrograph of the same field, and also a point source spectrometer reaching down to 100nm wavelength.

The Cosmic Evolution Through UV Spectroscopy (CETUS) concept1-3 enables parallel observations by the UV multiobject spectrometer (MOS) and near-UV/far-UV camera which operate simultaneously but independently with their separate field of views. The near-UV MOS can target up to 100 objects at a time without confusion with nearby sources or background zodiacal light. This multiplexing will allow over 100,000 galaxies to be observed over a typical mission lifetime. The MOS includes a next-generation micro-shutter array (NGMSA), an efficient aspheric Offner-like spectrometer design with a convex grating, and nanotube light traps for suppressing unwanted wavelengths. The NUV/FUV Camera has the capability to image in a range of sub-bands from 115-400 nm at the same time the MOS is operating at 180-350 nm. The UV camera has a similar Offner-like relay, selectable filters, and two separate detectors to optimize observing in either the far-UV (115-175 nm) or the near-UV (180-400 nm) utilizing a CsI Micro-Channel Plate detector (MCP) and a CCD respectively.