TITAN DR1: An Improved, Validated, and Systematically Controlled Recalibration of ATLAS Photometry toward Type Ia Supernova Cosmology

Journal article

ATLAS (Asteroid Terrestrial Last Alert System) is a time-domain survey using four telescopes, covering the entire sky. It has observed 8378 spectroscopically confirmed Type Ia supernovae (SNe Ia), with thousands of cosmology-grade light curves (to be released as TITAN DR1). To prepare this massive, low-redshift dataset for cosmology, we evaluate and cross-calibrate ATLAS forced photometry using tertiary stars from the DES (Dark Energy Survey) Y6 release. The 5000 deg2 DES footprint overlaps regions both in and out of the PS1 (Pan-STARRS DR1) footprint, allowing tests of the primary calibrator for the ATLAS Refcat2 catalog. Initial offsets are at the ∼40 mmag scale. To improve this, we determine Δ zero-point offsets for two cases: (1) pixel-to-pixel offsets within individual CCDs (reduced from ∼8 to ∼4 mmag rms) and (2) chip-to-chip offsets across the nine CCDs and filters (reduced from ∼17 to ∼3 mmag rms). We also identify the largest systematic uncertainty as a transmission-function color dependence, requiring shifts in the assumed ATLAS filters at the ∼30 mmag level if uncorrected. We validate our calibration using (a) CALSPEC standards, (b) an independent tertiary catalog, and (c) distance moduli of cross-matched SNe Ia, all showing improved consistency. Overall, we estimate combined calibration-related systematics at the ∼5–10 mmag level, supporting competitive cosmological constraints with the TITAN SN Ia dataset.

Authors: Marlin, EG; Murakami, YS; Brout, D; Tweddle, JW; Popovic, B

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: American Astronomical Society
• Journal: The Astrophysical Journal
• Volume: 1004
• Issue: 2
• Pages: 173
• Article number: 173
• Publication date: 2026-06-12
• Acceptance date: 2026-05-05
• DOI: 10.3847/1538-4357/ae69cc
• EISSN: 1538-4357
• ISSN: 0004637X, 0004-637X
• Language: English
• Keywords: Tertiary stars; Broad band photometry; Optical astronomy; Hubble diagram; Type Ia supernovae; Transient sources; Cosmology