ATLAS photometry of interstellar object 3I/ATLAS

John L. Tonry; Larry Denneau; Miguel R. Alarcón; Alejandro Clocchiatti; Nicolas Erasmus; Alan Fitzsimmons; Javier Licandro; Karen J. Meech; Robert Siverd; Henry Weiland

doi:10.3847/2041-8213/ae1f12

ATLAS photometry of interstellar object 3I/ATLAS

John L. Tonry^*
, Larry Denneau
, Miguel R. Alarcón
, Alejandro Clocchiatti
, Nicolas Erasmus
, Alan Fitzsimmons
, Javier Licandro
, Karen J. Meech
, Robert Siverd
, Henry Weiland

^*Corresponding author for this work

Research output: Contribution to journal › Article › peer-review

Abstract

We present calibrated Asteroid Terrestrial-impact Last Alert System (ATLAS) photometry of the interstellar comet 3I/ATLAS (C/2025 N1) from March 28 through 2025 August 29, obtained with the five-site, robotic ATLAS network in the c (420–650 nm), o (560–820 nm), and Teide w (420–720 nm) bands. Stacked difference images yield reliable light curves measured in four fixed apertures that capture the evolving coma. We observe 3I/ATLAS transitioning in color from red (c − o) ≈ 0.7 before MJD 60860 to near-solar (c − o) ≈ 0.3 after MJD 60870, coincident with the appearance of a prominent antisolar tail. The absolute magnitude curve H(t) shows a slope break near MJD 60890 at r ∼ 3.3 au from −0.035 to −0.012 mag day−1, or in terms of coma cross section as a function of heliocentric distance, r−3.9 to r−1.1. We release the aperture photometry with geometry and uncertainties to enable cross-instrument synthesis of 3I/ATLAS activity and color evolution.

Original language	English
Article number	L15
Number of pages	6
Journal	The Astrophysical Journal Letters
Volume	995
Issue number	1
DOIs	https://doi.org/10.3847/2041-8213/ae1f12
Publication status	Published - 04 Dec 2025

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ATLAS photometry of interstellar object 3I/ATLAS
Copyright 2025 the authors. This is an open access article published under a Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution and reproduction in any medium, provided the author and source are cited.
Final published version, 639 KBLicence: CC BY

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@article{54b60ae5eabc4814b5696aa6b7cc4af7,

title = "ATLAS photometry of interstellar object 3I/ATLAS",

abstract = "We present calibrated Asteroid Terrestrial-impact Last Alert System (ATLAS) photometry of the interstellar comet 3I/ATLAS (C/2025 N1) from March 28 through 2025 August 29, obtained with the five-site, robotic ATLAS network in the c (420–650 nm), o (560–820 nm), and Teide w (420–720 nm) bands. Stacked difference images yield reliable light curves measured in four fixed apertures that capture the evolving coma. We observe 3I/ATLAS transitioning in color from red (c − o) ≈ 0.7 before MJD 60860 to near-solar (c − o) ≈ 0.3 after MJD 60870, coincident with the appearance of a prominent antisolar tail. The absolute magnitude curve H(t) shows a slope break near MJD 60890 at r ∼ 3.3 au from −0.035 to −0.012 mag day−1, or in terms of coma cross section as a function of heliocentric distance, r−3.9 to r−1.1. We release the aperture photometry with geometry and uncertainties to enable cross-instrument synthesis of 3I/ATLAS activity and color evolution.",

author = "Tonry, \{John L.\} and Larry Denneau and Alarc{\'o}n, \{Miguel R.\} and Alejandro Clocchiatti and Nicolas Erasmus and Alan Fitzsimmons and Javier Licandro and Meech, \{Karen J.\} and Robert Siverd and Henry Weiland",

year = "2025",

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doi = "10.3847/2041-8213/ae1f12",

language = "English",

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journal = "The Astrophysical Journal Letters",

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TY - JOUR

T1 - ATLAS photometry of interstellar object 3I/ATLAS

AU - Tonry, John L.

AU - Denneau, Larry

AU - Alarcón, Miguel R.

AU - Clocchiatti, Alejandro

AU - Erasmus, Nicolas

AU - Fitzsimmons, Alan

AU - Licandro, Javier

AU - Meech, Karen J.

AU - Siverd, Robert

AU - Weiland, Henry

PY - 2025/12/4

Y1 - 2025/12/4

N2 - We present calibrated Asteroid Terrestrial-impact Last Alert System (ATLAS) photometry of the interstellar comet 3I/ATLAS (C/2025 N1) from March 28 through 2025 August 29, obtained with the five-site, robotic ATLAS network in the c (420–650 nm), o (560–820 nm), and Teide w (420–720 nm) bands. Stacked difference images yield reliable light curves measured in four fixed apertures that capture the evolving coma. We observe 3I/ATLAS transitioning in color from red (c − o) ≈ 0.7 before MJD 60860 to near-solar (c − o) ≈ 0.3 after MJD 60870, coincident with the appearance of a prominent antisolar tail. The absolute magnitude curve H(t) shows a slope break near MJD 60890 at r ∼ 3.3 au from −0.035 to −0.012 mag day−1, or in terms of coma cross section as a function of heliocentric distance, r−3.9 to r−1.1. We release the aperture photometry with geometry and uncertainties to enable cross-instrument synthesis of 3I/ATLAS activity and color evolution.

AB - We present calibrated Asteroid Terrestrial-impact Last Alert System (ATLAS) photometry of the interstellar comet 3I/ATLAS (C/2025 N1) from March 28 through 2025 August 29, obtained with the five-site, robotic ATLAS network in the c (420–650 nm), o (560–820 nm), and Teide w (420–720 nm) bands. Stacked difference images yield reliable light curves measured in four fixed apertures that capture the evolving coma. We observe 3I/ATLAS transitioning in color from red (c − o) ≈ 0.7 before MJD 60860 to near-solar (c − o) ≈ 0.3 after MJD 60870, coincident with the appearance of a prominent antisolar tail. The absolute magnitude curve H(t) shows a slope break near MJD 60890 at r ∼ 3.3 au from −0.035 to −0.012 mag day−1, or in terms of coma cross section as a function of heliocentric distance, r−3.9 to r−1.1. We release the aperture photometry with geometry and uncertainties to enable cross-instrument synthesis of 3I/ATLAS activity and color evolution.

U2 - 10.3847/2041-8213/ae1f12

DO - 10.3847/2041-8213/ae1f12

M3 - Article

SN - 2041-8205

VL - 995

JO - The Astrophysical Journal Letters

JF - The Astrophysical Journal Letters

IS - 1

M1 - L15

ER -

ATLAS photometry of interstellar object 3I/ATLAS

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