The After Sloan-V Project
With the fifth generation of the Sloan Digital Sky Survey (SDSS-V) expected to wrap up in 2027, the astronomical community has an exciting opportunity to develop a new and ambitious program. The After Sloan-V (AS5) program, expected to begin observations in 2027, will leverage existing and new instrumentation to conduct multiple surveys that advance wide-field spectroscopic science into the 2030s. The proposed AS5 program, and its 4 defining programs, will transform our understanding of the dynamic Universe (from quasars to stellar transients) providing complimentary spectroscopic followup of photometrically varying sources (through the Dynamic Universe Explorer), investigate the chemistry and dynamics of the Milky Way’s unexplored regions (through the Hidden Galaxy Explorer), map stars and gas at star-formation scales across Local Group galaxies (through the Local Group Explorer/Local Volume Mapper-2), and probe the key nucleosynthetic pathways that produce the elements of the periodic table with high precision (through the Atomic Genesis Explorer).
Below we describe each of the science programs proposed for AS5.
If you or your institution would like to get involved and join the exciting AS5 program, please contact the AS5 Director Keith Hawkins (University of Texas at Austin, email: keithhawkins@utexas.edu) and the AS5 Project Scientist, Peter Frinchaboy (Texas Christian University, email : p.frinchaboy@tcu.edu).
For more general announcements and to stay up to date on the AS5 project, we invite you to join/subscribe to our as5-general mailing list.
Dynamic Universe Explorer
Program Heads : Kate Grier (University of Wisconsin), Marina Kounkel (University of North Florida)
The Dynamic Universe Explorer (DUE) will deliver spectroscopic follow-up of interesting events and variable sources as well as high-cadence monitoring of a range of variable sources. DUE will observe these phenomena with the BOSS and APOGEE spectrographs, which respectively operate in optical and near-IR. This program has three distinct components/subsurveys and is designed to complement ongoing photometric surveys by building a transformative spectroscopic dataset.
TRIGGER (Transient Rapid-response Investigation of Galactic and extraGalactic Events):
DUE will carry out rapid-response spectroscopy of short-lived phenomena such as supernovae, cataclysmic variables, tidal disruption events, and others. By dynamically allocating telescope time, the program anticipates obtaining 1,000+ transient spectra, offering collaboration members the flexibility to prioritize targets of greatest scientific interest. This effort will establish a large, homogeneous spectroscopic dataset for transient classification and physical interpretation, significantly enhancing our understanding of dynamic processes in both galactic and extragalactic environments.
RHYTHM (Repeated High-Cadence Yield for Temporal Horizon Monitoring):
DUE will conduct weekly spectroscopic observations of select fields for 3–5 years.
Inside the Milky Way, DUE will deliver spectroscopic light curves tracking changes in radial velocities, emission and absorption line profiles, chemical abundances, and other fundamental properties of stars. It will support investigations such as rotational modulation and disk occultation in young stellar objects, astroseismology, multiplicity, and more.
Outside our galaxy, DUE will monitor hundreds of active galactic nuclei (AGN) to constrain black hole masses using reverberation mapping, map the structure of the broad-line region, and examine the variability of AGN on long (>10-year) and short (~weekly) timescales.
SCOPE (Single-epoch Classification of Photometric Events):
DUE will obtain single-epoch spectra for large samples of variable sources across the sky to classify and further investigate interesting objects. This program will target variable stars, compact binaries, changing-look active galactic nuclei, and other SMBH accretion events, among others. By building a comprehensive spectroscopic catalog, this effort will improve population statistics, refine variability taxonomies, and enable the discovery of rare or previously unrecognized classes of variable phenomena.
Hidden Galaxy Explorer
Program Head : David Nidever (Montana State University)
The Motivation and Driving Questions:
The Hidden Galaxy Explorer (HGE) aims to reveal and characterize the “hidden half” of the Milky Way: regions on the far side of the bulge and bar and deep within the Galactic midplane that remain poorly explored due to dust extinction and stellar crowding. Using dual-hemisphere, high-resolution near-infrared spectroscopy, HGE addresses several fundamental questions:
• How symmetric is the Milky Way disk and spiral structure when the obscured far side is mapped at the same fidelity as the near side?
• What are the three-dimensional structure, chemistry, and dynamics of the far-side bar and inner bulge, including spherical and X-shaped components?
• Are there measurable kinematic or chemical asymmetries in the inner disk and bulge that reflect recent or ongoing interactions (e.g., with the Sagittarius dwarf or the Magellanic Clouds)?
• Can we measure the full 360-degree Galactic rotation curve and identify non-axisymmetric perturbations such as bar-driven streaming motions or interaction-induced corrugations?
• Are there significant stellar substructures, clusters, or satellite remnants preferentially hidden behind the bulge and midplane?
Science Goals, Deliverables and Uniqueness:
HGE is designed to provide the first comprehensive chemo-dynamical map of the Milky Way’s far disk, bulge and bar. It exploits the unique capabilities of the dual-hemisphere SDSS/APOGEE spectrographs to observe dust-obscured regions inaccessible to optical surveys. Key elements that distinguish HGE from all other current or planned surveys:
• Dual-hemisphere coverage combined with wide-area, high-resolution near-infrared spectroscopy, enabling contiguous mapping of the inner and far side of the Galaxy.
• Depth and sensitivity optimized for the far disk and midplane, reaching faint luminous giants (H ≈ 14.5) with long integrations and multi-visit cohort strategies.
• Étendue and survey efficiency unmatched by other facilities targeting similar science.
• Strong synergy with NASA’s Roman Galactic Plane Survey and asteroseismic targets.
By filling the most critical spatial gap in our current Galactic maps, HGE transforms our view of the Milky Way from a near-side-biased picture into a truly global one.
HGE will deliver a lasting legacy dataset for Galactic astronomy, including:
A contiguous Milky Way chemo-dynamical map spanning the far disk, bulge and bar, enabling definitive tests of Galactic symmetry, bar structure, and inner-disk dynamics.
• A million star sample observed at high spectral resolution in the most heavily obscured regions of the Galaxy.
• Spectroscopic products that directly support Roman bulge and Galactic plane programs.
• Fully reduced spectra and homogeneously derived stellar parameters and abundances.
Together, these deliverables will enable transformative advances in our understanding of the Milky Way’s structure, formation history, and dynamical evolution.
Local Volume Mapper 2
Program Heads : Niv Drory (University of Texas at Austin/McDonald Observatory), Guillermo Blanc (Carnegie Observatories/Las Campanas Observatory)
The Local Volume Mapper 2 (LVM2) program will extend the capabilities of LVM in SDSS-V (Drory et al. 2024, Kollmeier et al. 2025) to the Northern Hemisphere, to conduct an unprecedented new IFU survey of the Local Group. It will also push the limits of the existing Southern LVM instrument to do the deepest optical spectroscopic characterization ever of selected regions of the Milky Way ISM. The ongoing SDSS-V LVM program demonstrated the power of high spatial resolution ultra-wide-field IFU spectroscopy, by producing the first optical IFU data set of the entire southern Milky Way plane and the Magellanic Clouds, covering ~4000 square degrees of sky.
The LVM2-South survey will dramatically expand the sources in which critical “extremely-faint emission line science” can be carried out, and will produce the first comprehensive spectral characterization of low surface brightness emission in our Galaxy. The LVM2-North survey (also known as the Local Group Explorer) will create IFU maps of M31, M33 and a sample of dwarf galaxies within 5 Mpc, providing a view into stellar feedback physics, linking stars and gas, as well as stellar populations and star formation histories across a wide range of physical conditions and local environments. LVM2 will link the galactic and extragalactic regimes, exploring star forming regions over a range of scales and environments unattainable before now. LVM2 is being conducted with 2 primary subsurveys:
LVM2 North Survey/Local Group Explorer:
In LVM2 North, we will mount a new wide-field (2×2 arcmin) IFU on a 2.5-m class telescope in the Northern hemisphere, feeding a twin cluster of LVM spectrographs, and use it to map M31 and M33, matching the coverage of the HST-PHAT+PHAST and PHATTER surveys. This enables a spaxel size of 2.5 arcsec and spatial resolutions of <0.1 pc within our Galaxy, ~10 pc (within the local group) and up to ~50pc (for more distant galaxies). We will also map a sample of 57 local dwarf galaxies at <5 Mpc distance. Following a strategy well-proven in the ongoing SDSS-V LVM survey of the LMC/SMC.
LVM2 South Survey/The Interstellar Explorer (ISE) Survey:
In LVM2 South, deeper observations with the LVM-I at LCO in selected areas, together with an expansion of the spatial coverage, will enable the exploration of previously unstudied regions of the Milky Way, mapping low–surface-brightness Galactic structures, particularly toward the Galactic center. The increased depth will enable the detection of extremely faint emission lines from HII regions, planetary nebulae, and supernova remnants, providing key diagnostics of ionized gas. In particular, measurements of extremely faint heavy-element recombination lines will allow robust, largely temperature-independent determinations of chemical abundances.
Atomic Genesis Explorer
Program Head : Melissa Ness (Australia National University)
The dual-hemisphere AS5 Atomic Genesis Explorer (AGE) will provide a benchmark sample for tracing the origin of the elements over time. AGE will be the first high-resolution (R ≥ 70,000) program in the SDSS ecosystem and aims to provide the precision in stellar atmospheric parameters and detailed chemical abundances to understand how elements form & evolve across the Milky Way disk.
The Motivation and Driving Science Questions:
We have learned from SDSS-V, and other large scale spectroscopic surveys, that stars across the disk have chemical abundances that can be generated by different combinations of shared patterns. These patterns are intimately connected to the nucleosynthetic pathways that create the elements and their isotopes and the star formation history of the Galaxy. The specific observed chemical abundance patterns in stars enable us to answer key astrophysical questions which include:
-What built the elements in our Galaxy?
-How does Galactic chemistry connect to its structure and evolution over time?
-How do we unlock the information in large stellar survey maps?
To answer these questions, a high quality, high resolution set of SNR > 100 spectra, that enables the measurement of a large number of elements at high precision (< 0.05 dex) is required. This set of elements, including light, odd-z, alpha, Fe=peak, and r- and s-process, across the periodic table, will complete the genetic map of the Milky Way disk and provide key missing information about its enrichment pathways.
Using facilities in both hemispheres, AGE will obtain high-quality, high resolution (R > 70,000) , SNR > 100 spectra of ~2000 stars in a restricted evolutionary state, uniformly sampling disk metallicity. A targeted set of Kepler asteroseismic benchmarks as well as TESS continuous viewing zone stars delivers exceptional spectral quality tied to precise ages and stellar structure. The high quality of the collected spectra will enable measurements of ~30 element abundances (across nearly all element families) at ~0.01-0.02 dex precision (using differential analysis approaches) and will provide the first systematic isotopic-ratio survey for a large sample of stars that will be a key tracer of stellar physics.