Themes & early results
Each theme below draws on the same data product — a medium-band spectral energy distribution for every source in a 1.25 square degree field.
The 7DS science program
- 01
Multi-messenger Astronomy
The mission 7DT was built for. A kilonova peaks near absolute magnitude −15 to −17 and fades by roughly half a magnitude per day, inside a gravitational-wave localization of hundreds to thousands of square degrees — where even a single 100 deg² patch is expected to hold of order a hundred unrelated transients over a seven-day window. 7DT answers with wide-field tiling, sub-minute response to an alert, and enough spectral information in a single visit to reject the contaminants without follow-up spectroscopy.
- 02
Transients
Medium-band spectral sampling gives direct color and continuum information for a transient from one epoch of imaging. A hybrid classification framework built on 7DT spectral energy distributions — an unsupervised anomaly detector coupled to a supervised multiclass classifier — reaches macro F1 ≈ 0.80 across eight common transient types and recovers more than 90 percent of optically detectable kilonovae, including AT2017gfo, without ever being trained on one.
- 03
Galaxy Formation & Evolution
Medium-band mapping over 1.25 square degrees is IFU-like data at survey scale. Star-forming clumps are identified through Hα emission in stellar-continuum-subtracted images, and pilot studies indicate that pixel-based SED fitting of 7DT and SPHEREx data can recover spatially resolved stellar populations approaching the quality of high-resolution IFU spectroscopy — for galaxies that would otherwise demand dedicated campaigns on much larger telescopes. Both studies are as yet unpublished (Shim et al., submitted; Lee et al., in prep).
- 04
Cosmology & Photometric Redshifts
At R = 30–70 across 0.4–0.9 µm, 7DT straddles the boundary between broadband photometry and low-resolution spectroscopy, capturing the 4000 Å break and prominent emission lines at a resolution that lifts much of the color–redshift degeneracy inherent to broadband surveys. Forecasts give σ_NMAD = 0.003–0.007 at 19 < m625 < 22 for the five-year stacked WTS, with strong gains when combined with SPHEREx all-sky data.
- 05
Active Galactic Nuclei
Repeated medium-band visits measure how an AGN spectrum changes, not merely how its brightness does. The 10–14 day cadence of WTS over five years is matched to reverberation mapping through long-term spectral variability, while the nightly cadence of IMS reaches variability on timescales of a single night.
- 06
Galactic Science
Two-epoch 7DT photometry with sixteen medium bands across 400–825 nm identified 110 variable young stellar objects in the central region of Orion A — 14 percent of 769 candidates — including seven extreme cases varying by more than 0.5 mag. The wavelength dependence of the variability distinguishes extinction-like, gray and spot-like mechanisms on day timescales, which otherwise requires rapid filter cycling or simultaneous multi-band instrumentation.
- 07
Solar System Objects
Medium-band imaging of the main-belt asteroids 13 Egeria and 10 Hygiea targets the 0.7 µm absorption feature characteristic of Ch-type bodies, a tracer of their thermal history. Time-series observations of the third interstellar object, 3I/ATLAS, followed the emergence of extended CN emission as it fell inside 3 au — behavior resembling that of 2I/Borisov at comparable heliocentric distance.
Results from commissioning and first survey data
Photometric redshifts at survey scale
Forecasts using EAZY on EL-COSMOS mock catalogs give σ_NMAD = 0.003–0.007 and catastrophic failure fractions of 0.8–8.1 percent for the five-year stacked WTS with 40 medium bands at 19 < m625 < 22. Combining 7DS with SPHEREx all-sky data reduces the failure fraction to 0.4 percent for fainter sources by breaking color–redshift degeneracies with near-infrared coverage. Extending the analysis to six independent methods — four template-fitting codes and two machine-learning approaches — gives σ_NMAD ≲ 0.005 for bright GAMA-like galaxies and ≈ 0.01 for fainter COSMOS-like galaxies, with the combined dataset consistently outperforming either survey alone.
Resolved star formation in nearby galaxies
Spatially resolved maps of star formation rate and 3.3 µm PAH emission were constructed for a nearby galaxy from 7DT and SPHEREx data. Dust-corrected star formation rates agree with those derived for H ii regions from higher-resolution spectroscopy, correlate tightly with PAH luminosity, and reveal the inside-out growth of the galactic disk together with the suppression of PAH emission in intensely star-forming regions. A companion study of NGC 3627 used VLT/MUSE observations as reference and found that pixel-wise SED fitting of combined 7DT and SPHEREx data improves stellar-age precision significantly over broadband photometry alone, with global and radial trends agreeing with MUSE apart from a minor metallicity offset in the central region. Both studies are unpublished as yet (Shim et al., submitted; Lee et al., in prep).
Single-epoch transient classification
A framework coupling an Isolation Forest anomaly detector to an XGBoost multiclass classifier, trained on realistically simulated 7DT photometry, achieves macro F1 ≈ 0.80 across eight common transient types while recovering more than 90 percent of simulated and observed optically detectable kilonovae at low contamination. Feature analysis shows that the top-ranked half of the 40 medium bands combined with a single LSST band reproduces the full-model accuracy to within 1–2 percent, which points directly at practical follow-up strategies for the Rubin alert stream.
Follow-up of transient alerts
7DT searched for the optical counterpart of the bright X-ray transient EP240219a and reported upper limits in several medium bands, and covered approximately 170 deg² in Sloan r and the medium-band suite in follow-up of the LVK gravitational-wave event S240422ed. Since RTCSpy took over nightly operation in August 2024 the array has carried out about 100 follow-up observations and some ten gravitational-wave event campaigns.
Figures quoted above are drawn from the 7DT status report and the associated early science papers. See Publications for the full list.
Working with 7DT data
7DT data products are medium-band images and matched source catalogs on a fixed tile grid, calibrated against Gaia DR3 synthetic photometry and flux-scaled so that pixel values carry units of microjansky. That makes them directly usable for pixel-based SED fitting without further conversion.
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