The existence, properties, and dynamics of the dark sectors of our universe pose fundamental challenges to our current model of physics, and large-scale astronomical surveys may be our only hope to unravel these long-standing mysteries. In this white paper, we describe the science motivation, instrumentation, and survey plan for the next-generation spectroscopic observatory, the Stage-5 Spectroscopic Experiment (Spec-S5). Spec-S5 is a new all-sky spectroscopic instrument optimized to efficiently carry out cosmological surveys of unprecedented scale and precision. The baseline plan for Spec-S5 involves upgrading two existing 4-m telescopes to new 6-m wide-field facilities, each with a highly multiplexed spectroscopic instrument capable of simultaneously measuring the spectra of 13,000 astronomical targets. Spec-S5, which builds and improves on the hardware used for previous cosmology experiments, represents a cost-effective and rapid approach to realizing a more than 10× gain in spectroscopic capability compared to the current state-of-the-art represented by the Dark Energy Spectroscopic Instrument project (DESI). Spec-S5 will provide a critical scientific capability in the post-Rubin and post-DESI era for advancing cosmology, fundamental physics, and astrophysics in the 2030s.

A wide-field near-infrared survey of the Galactic disk and bulge/bar(s) is supported by a large representation of the community of Galactic astronomers. The combination of sensitivity, angular resolution and large field of view make Roman uniquely able to study the crowded and highly extincted lines of sight in the Galactic plane. A 1000 deg2 survey of the bulge and inner Galactic disk would yield an impressive dataset of 120 billion sources and map the structure of our Galaxy. The effort would foster subsequent expansions in numerous dimensions (spatial, depth, wavelengths, epochs). Importantly, the survey would benefit from early defintion by the community, namely because the Galactic disk is a complex environment, and different science goals will require trade offs.

In May 2019 SpaceX launched its first batch of 60 Starlink communication satellites, which surprised astronomers and laypeople with their appearance in the night sky. Astronomers have only now, a little over a year later, accumulated enough observations of constellation satellites like those being launched by SpaceX and OneWeb, and run computer simulations of their likely impact when fully deployed, to thoroughly understand the magnitude and complexity of the problem. This research informed the discussion at the Satellite Constellations 1 (SATCON1) workshop held virtually 29 June to 2 July 2020 and led to recommendations for observatories and constellation operators. The SATCON1 report concludes that the effects on astronomical research and on the human experience of the night sky range from "negligible" to "extreme."

The Dark Energy Spectroscopic Instrument (DESI) is a Stage IV ground-based dark energy experiment that will measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 35 million galaxies and quasars over 14000 square degrees will be measured during the life of the experiment. We describe the installation of the major elements of the instrument at the Mayall 4m telescope, completed in late 2019. The previous prime focus corrector, spider vanes, and upper rings were removed from the Mayall's Serrurier truss and replaced with the newly-constructed DESI ring, vanes, cage, hexapod, and optical corrector. The new corrector was optically aligned with the primary mirror using a laser tracker system. The DESI focal plane system was integrated to the corrector, with each of its ten 500-fiber-positioner petal segments installed using custom installation hardware and the laser tracker. Ten DESI spectrographs with 30 cryostats were installed in a newly assembled clean room in the Large Coude Room. The ten cables carrying 5000 optical fibers from the positioners in the focal plane were routed down the telescope through cable wraps at the declination and hour angle axes, and their integral slitheads were integrated with the ten spectrographs. The fiber view camera assembly was installed to the Mayall's primary mirror cell. Servers for the instrument control system replaced existing computer equipment. The fully integrated instrument has been commissioned and is ready to start its operations phase.

We explore the relation between the stellar mass surface density and the mass surface density of molecular hydrogen gas in 12 nearby molecular clouds that are located at <1.5 kpc distance. The sample clouds span an order-of-magnitude range in mass, size, and star formation rates. We use thermal dust emission from Herschel maps to probe the gas surface density and the young stellar objects from the most recent Spitzer Extended Solar Neighborhood Archive catalog to probe the stellar surface density. Using a star-sampled nearest neighbor technique to probe the star–gas surface density correlations at the scale of a few parsecs, we find that the stellar mass surface density varies as a power law of the gas mass surface density, with a power-law index of ∼2 in all the clouds. The consistent power-law index implies that star formation efficiency is directly correlated with gas column density, and no gas column density threshold for star formation is observed. We compare the observed correlations with the predictions from an analytical model of thermal fragmentation and with the synthetic observations of a recent hydrodynamic simulation of a turbulent star-forming molecular cloud. We find that the observed correlations are consistent for some clouds with the thermal fragmentation model and can be reproduced using the hydrodynamic simulations.

The degree to which the properties of protostars are affected by environment remains an open question. To investigate this, we look at the Orion A and B molecular clouds, home to most of the protostars within 500 pc. At 400 pc, Orion is close enough to distinguish individual protostars across a range of environments in terms of both the stellar and gas projected densities. As part of the Herschel Orion Protostar Survey (HOPS), we used the Photodetector Array Camera and Spectrometer (PACS) to map 108 partially overlapping square fields with edge lengths of 5 arcmin or 8 arcmin and measure the 70 micron and 160 micron flux densities of 338 protostars within them. In this paper we examine how these flux densities and their ratio depend on evolutionary state and environment within the Orion complex. We show that Class 0 protostars occupy a region of the 70 micron flux density versus 160 micron to 70 micron flux density ratio diagram that is distinct from their more evolved counterparts. We then present evidence that the Integral-Shaped Filament (ISF) and Orion B contain protostars with more massive envelopes than those in the more sparsely populated LDN 1641 region. This can be interpreted as evidence for increasing star formation rates in the ISF and Orion B or as a tendency for more massive envelopes to be inherited from denser birth environments. We also provide technical details about the map-making and photometric procedures used in the HOPS program.

Using radial velocity data from the Habitable Zone Planet Finder, we have measured the mass of the Neptune-sized planet K2-25b, as well as the obliquity of its M4.5 dwarf host star in the 600-800 Myr Hyades cluster. This is one of the youngest planetary systems for which both of these quantities have been measured and one of the very few M dwarfs with a measured obliquity. Based on a joint analysis of the radial velocity data, time-series photometry from the K2 mission, and new transit light curves obtained with diffuser-assisted photometry, the planet's radius and mass are 3.44 +/- 0.12 R-circle plus and 24.5(-5.2)(+5.7) M-circle plus. These properties are compatible with a rocky core enshrouded by a thin hydrogen-helium atmosphere (5% by mass). We measure an orbital eccentricity of e = 0.43 +/- 0.05. The sky-projected stellar obliquity is lambda = 3 degrees +/- 16 degrees, compatible with spin-orbit alignment, in contrast to other "hot Neptunes" that have been studied around older stars.

Context.The study of star formation is extremely challenging, due to the lack of complete and clean samples of young nearby clusters and star-forming regions. The recentGaiaDR2 catalogue complemented with the deep ground-based COSMIC DANCe catalogue offers a new database of unprecedented accuracy to revisit the membership of clusters and star-forming regions. The 30 Myr open cluster IC 4665 is one of the few well-known clusters of this age and it is an excellent target where evolutionary models can be tested and planetary formation studied.Aims.We provide a comprehensive membership analysis of IC 4665 and study the following properties: empirical isochrones, distance, magnitude distribution, present-day system mass function, and spatial distribution.Methods.We used theGaiaDR2 catalogue together with the DANCe catalogue to look for members via a probabilistic model of the distribution of the observable quantities in both the cluster and background populations.Results.We obtained a final list of 819 candidate members that cover a 12.4 magnitude range (7 < J < 19.4). We find that 50% are new candidates, and we estimate a conservative contamination rate of 20%. This unique sample of members allows us to obtain a present-day system mass function in the range of 0.02–6M⊙, which reveals a number of details not seen in previous studies. In addition, we find that a spherically symmetric spatial distribution is favoured by our final list of members for this young open cluster.Conclusions.Our membership analysis represents a significant increase in the quantity and quality (low contamination) with respect to previous studies. It offers an excellent opportunity to revisit other fundamental parameters such as age.

L3Harris Corporation is providing this white paper on the fabrication and test of the HabEx primary mirror. This mirror is a 4 meter off-axis monolith with challenging surface figure requirements. The development challenges to achieving the surface figure error (SFE) include smoothing processes, mirror metrology accuracy, and 1-G to 0-G shift.

Ultra-Stable Large Telescope Research and Analysis (ULTRA) is a system study performed by an industry consortium led by Ball Aerospace to evaluate potential architectures, perform trade studies, and identify technology gaps that must be addressed to enable picometer-level optical stability in space to support the LUVOIR/HabEx concepts.

Industry capabilities are emerging to enable LUVOIR-class space telescope performance and to significantly mitigate cost, schedule and risk. This report establishes the activities and technologies which will advance LUVOIR Wavefront Error (WFE) stability aligned to producing a cost-effective design.

The DESI Legacy Imaging Surveys are a combination of three public projects (the Dark Energy Camera Legacy Survey, the Beijing-Arizona Sky Survey, and the Mayall z-band Legacy Survey) that will jointly image approximately 14,000 deg^2 of the extragalactic sky visible from the northern hemisphere in three optical bands (g, r, and z) using telescopes at the Kitt Peak National Observatory and the Cerro Tololo Inter-American Observatory. The combined survey footprint is split into two contiguous areas by the Galactic plane. The optical imaging is conducted using a unique strategy of dynamically adjusting the exposure times and pointing selection during observing that results in a survey of nearly uniform depth. In addition to calibrated images, the project is delivering a catalog, constructed by using a probabilistic inference-based approach to estimate source shapes and brightnesses. The catalog includes photometry from the grz optical bands and from four mid-infrared bands (at 3.4, 4.6, 12 and 22 micorons) observed by the Wide-field Infrared Survey Explorer (WISE) satellite during its full operational lifetime. The project plans two public data releases each year. All the software used to generate the catalogs is also released with the data. This paper provides an overview of the Legacy Surveys project.

With the goal to study the physical and chemical evolution of ices in solar-mass systems, a spectral survey is conducted of a sample of 41 low luminosity YSOs (L ∼ 0.1− 10 L⊙) using 5–38 μm Spitzer Space Telescope and 3–4 μm ground-based spectra. The sample is complemented with previously published Spitzer spectra of background stars and with ISO spectra of well studied massive YSOs (L ∼ 10 L⊙). This paper focuses on the origin of the prominent absorption features in the 5-8 μm spectral region. The long-known 6.0 and 6.85 μm bands are detected toward all sources, with the Class 0-type low mass YSOs showing the deepest bands ever observed. In almost all sources the 6.0 μm band is deeper, by up to a factor of 3, than expected from the bending mode of pure solid H2O, based on the optical depths of the 3.0 μm stretching and 13 μm libration modes. The depth and shape variations of the remaining 5–7 μm absorption indicate that it consists of 5 independent components, which, by comparison to laboratory studies, must be from at least 8 different carriers. Together with information from the 3-4 μm spectra and the additionally detected weak 7.25, 7.40, 9.0, and 9.7 μm features it is argued that overlapping bands of simple species are responsible for much of the absorption in the 5-7 μm region, at abundances of 1-30% for CH3OH, 3-8% for NH3, 1-5% for HCOOH, ∼6% for H2CO, and ∼0.3% for HCOO − with respect to solid H2O. The 6.85 μm band likely consists of one or two carriers, of which one is less volatile than H2O because its abundance relative to H2O is enhanced at lower H2O/τ9.7 ratios. It does not survive in the diffuse interstellar medium (ISM), however. The similarity of the 6.85 μm bands for YSOs and background stars indicates that its carrier(s) must be formed early in the molecular cloud evolution. If an NH4 salt is the carrier its abundance with respect to solid H2O is typically 7%, and low temperature acid-base chemistry or cosmic ray induced reactions must have been involved in its formation. Possible origins are discussed for the carrier of an enigmatic, very broad absorption between 5 and 8 μm. It shows large depth variations toward both lowand high-mass YSOs. Weak evidence is found that it correlates with temperature tracers. Finally, all the phenomena observed for ices toward massive YSOs are also observed toward low mass YSOs, indicating that processing of the ices by internal ultraviolet radiation fields is a minor factor in the early chemical evolution of the ices. Subject headings: infrared: ISM — ISM: molecules — ISM: abundances — stars: formation — infrared: stars— astrochemistry 1 Some of the data presented herein were obtained at the W.M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W.M. Keck Foundation. 2 The VLT/ISAAC spectra were obtained at the European Southern Observatory, Paranal, Chile, within the observing programs 164.I-0605, 69.C-0441, and 272.C-5008 3 Division of PMA, Mail Code 105-24, California Institute of Technology, Pasadena, CA 91125, USA 4 AURA/NOAO-South, Gemini Science Center, Casilla 603, La Serena, Chile 5 current address: IPAC, NASA Herschel Science Center, Mail Code 100-22, California Institute of Technology, Pasadena, CA 91125, USA (email: aboogert@ipac.caltech.edu) 6 Division of GPS, Mail Code 150-21, California Institute of Technology, Pasadena, CA 91125, USA 7 Hubble Fellow 8 Department of Astronomy, University of Maryland, College Park, MD 20742, USA 9 Leiden Observatory, PO Box 9513, 2300 RA Leiden, the Netherlands 10 SRON, PO Box 800, 9700 AV Groningen, the Netherlands 11 Department of Astronomy, University of Texas at Austin, 1

Massively multiplexed spectroscopic surveys of Milky Way stars will revolutionize our understanding of our Galaxy's structural components, revealing their past history and the small-scale structure of its dark matter halo. A spectroscopic survey of 108 stars, previously unimaginable, is now within reach of new instruments in the coming decade.

Time domain and multi-messenger astrophysics are growing and important modes of observational astronomy that will help define astrophysics in the 2020s. Significant effort is being put into developing the components of a follow-up system for dynamically turning survey alerts into data. This system consists of: 1) brokers that will aggregate, classify, and filter alerts; 2) Target Observation Managers (TOMs) for prioritizing targets and managing observations and data; and 3) observatory interfaces, schedulers, and facilities along with data reduction software and science archives. These efforts need continued community support and funding in order to complete and maintain them. Many of the efforts can be community open-source software projects but they will benefit from the leadership of professional software developers. The coordination should be done by institutions that are involved in the follow-up system such as the national observatories (e.g. LSST/Gemini/NOAO Mid-scale/Community Science and Data Center) or a new MMA institute. These tools will help the community to produce the most science from new facilities and will provide new capabilities for all users of the facilities that adopt them.

In this white paper, we will outline threats to astronomy in the areas of light pollution, radio interference, and space debris, and we will specify key principles and policy points that the AAS and other advocates can use in mitigating these threats.

Wide-field survey spectroscopy is essential to realizing the astrophysics potential of LSST and other imaging surveys. We review the strong case for this capability, summarize available options to meet the need, and provide strategic recommendations to enable national scientific progress and leadership in this area in the coming decade.

Low strain mounting of the Lynx mirrors is essential to the telescope image quality. Mount strain must be managed during assembly with precision fixturing, environmental control, and knowledge of adhesive cure shrinkage. The large number of segment and modules for Lynx necessitates a time-efficient, deterministic, and high-quality process.