AstroNote 2025-211

ATLAS has been operating as a quadruple 0.5m telescope system with two units in Hawaii (Haleakala and Mauna Loa), and one each in Chile (El Sauce) and South Africa (Sutherland), see  Tonry et al. 2018, (PASP,130:064505),  robotically surveying the whole sky with a cadence of 1 day between -50 and +50 and 2 days in the polar regions, weather permitting. Two filters are used, cyan and orange (denoted c and o; all mags quoted are in the AB system). While carrying out the primary mission for Near-Earth Objects, we search for and publicly report stationary transients to the IAU Transient Name Server.  Automated data processing is described in Smith et al. (2020, PASP, 132:08500), which combines spatial cross-matching with astronomical catalogues (Young 2023) and a machine learning model that performs real-bogus classification on the images (Weston et al. 2024, RASTI 3, 385). Finally, the ATLAS Virtual Research Assistant prioritises alerts using multi-modal information present in the stream (Stevance 2025).   More information is on the ATLAS homepage.

A fith unit, ATLAS-Teide in Tenerife, Canary Islands, is now being brought into service. ATLAS-Teide is a different optical design but provides similar field-of-view and depth to the other four units. ATLAS-Teide consisits of 4 modules, each module being four RASA 11 telescopes (each of 28cm aperture) mounted together on a L-series PlaneWave equatorial mount, each one equipped with a QHY600 CMOS camera (Licandro et al. 2022 https://doi.org/10.5194/epsc2022-634). All 4 telescopes of one module point to the same field and the 7.3 sq degree images are stacked together.  Four modules (16 RASA 11 telescopes and cameras in total) then give a combined FOV per pointing similar to the previous ATLAS units. The ATLAS-Teide data are unfiltered (TNS designation wide-ATLAS), but the CMOS detector response is similar to the cyan-ATLAS filter response curve. During telescope commissioning we are differencing data against the cyan-ATLAS reference images until the wide-ATLAS reference sky is built later in 2025. We are also using the the ML codes for real-bogus as trained on the other ATLAS cameras as we build new training sets for the different ATLAS-Teide data. 

We report a new transient source, most likely a supernova in the galaxy SDSS J120634.98+625915.6. This is the first supernova candidate to be submitted to TNS from ATLAS-Teide (observatory code R17). We discovered ATLAS25hnz (AT2025qzy) on MJD 60863.89 == 2025-07-07.89, at m_w = 18.50 +/- 0.13. There was no detection by ATLAS on MJD 60859.94 == 2025-07-03.94 and recent forced photometry indicates the transient is rising (see attached forced photometry plot). ATLAS25hnz is offset by 0.4 arcsec north, 10.1 arcsec east from SDSS J120634.98+625915.6, which is at z = 0.039 or d = 168 Mpc (from NED), implying an absolute magnitude of M = -17.7 (assuming m-M = 36.13 and A_g = 0.06 and A_r = 0.05). Followup observations are encouraged.

The Asteroid Terrestrial-impact Last Alert System [ATLAS] project is primarily funded to search for Near-Earth asteroids through NASA grants NN12AR55G, 80NSSC18K0284, and 80NSSC18K1575; byproducts of the NEO search include images and catalogs from the survey area. This work was partially funded by Kepler/K2 grant J1944/80NSSC19K0112 and HST GO-15889,  STFC grants ST/Y001605/1, ST/X001253/1, the Royal Society and Schmidt Sciences. The ATLAS science products have been made possible through the contributions of the University of Hawaii Institute for Astronomy,  Queen's University Belfast, University of Oxford, the Space Telescope Science Institute, the South African Astronomical Observatory, The Millennium Institute of Astrophysics (MAS), Chile, and the Instituto de Astrofisica De Canarias.

ATLAS-Teide is an IAC instrument included in the present “Strategic plan of the Canarian Observatories”, funded by the European Union  NextGenerationEU  EQC2021-007122-P  and ICT2022-007828 projects.