arXiv · 2507.13409
NSF-DOE Vera C. Rubin Observatory Observations of Interstellar Comet 3I/ATLAS (C/2025 N1)
Abstract
We report on the observation and measurement of astrometry, photometry, morphology, and activityof the interstellar object 3I/ATLAS, also designated C/2025 N1 (ATLAS) with the NSF-DOE Vera C. Rubin Observatory. Comet 3I/ATLAS, the third known interstellar object, was discovered on UT 2025 July 1. Rubin Observatory had coincidentally collected images of the object's region of the sky during routine commissioning. Facilitated by Rubin's high resolution and large aperture, we successfully recovered object detections from Rubin observations spanning UT 2025 June 21 (10 days before discovery, when 3I/ATLAS was 4.5 au from the Sun) through the date of discovery, and we acquired additional images through UT 2025 July 20 as part of commissioning. We measure on-sky locations of 3I/ATLAS in Rubin ugrizy bands, with a typical precision of about 70 mas, and briefly describe the reason this is coarser than our measured static source astrometric precision of about 3 mas in Rubin images. We measure grizy magnitudes of 3I/ATLAS photometry at about 0.01 mag precision, detecting no short-term photometric variability above 0.01 mag. We derive an estimated near-nucleus dust-to-nucleus scattering cross-section ratio of eta >= 13 on UT 2025 July 2 based on Rubin photometry and an upper limit nucleus size computed from Hubble Space Telescope observations. We find Rubin colors of g - r = (0.657 +/- 0.013) mag, r - i = (0.235 +/- 0.018) mag, i - z = (0.147 +/- 0.042) mag, z - y = (0.047 +/- 0.052) mag. These data represent the earliest observations of this object by a large (>=8-meter class) telescope and illustrate the type of measurements (and discoveries) Rubin's Legacy Survey of Space and Time (LSST) will begin to provide after it begins in early 2026.
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Colin Orion Chandler, Pedro H. Bernardinelli, Mario Jurić, Devanshi Singh, Henry H. Hsieh, Ian Sullivan, R. Lynne Jones, Jacob A. Kurlander, Dmitrii Vavilov, Siegfried Eggl, Matthew Holman, Federica Spoto, Megan E. Schwamb, Lauren A. MacArthur, Rahil Makadia, Marco Micheli, Aren Heinze, Eric J. Christensen, Wilson Beebe, Aaron Roodman, Kian-Tat Lim, Tim Jenness, James Bosch, Brianna M. Smart, Eric Bellm, Sean MacBride, Meredith L. Rawls, Sarah Greenstreet, Colin Slater, Željko Ivezić, Robert D. Blum, Andrew Connolly, Gregory Daues, Michelle Gower, J. Bryce Kalmbach, Michele T. Bannister, Luke Dones, Rosemary C. Dorsey, Davide Farnocchia, Wesley C. Fraser, John C. Forbes, Cesar Fuentes, Carrie E. Holt, Laura Inno, Geraint H. Jones, Matthew M. Knight, Chris J. Lintott, Tim Lister, Robert Lupton, Mark Jesus M. Magbanua, Renu Malhotra, Beatrice E. A. Mueller, Joseph Murtagh, Nitya Pandey, William T. Reach, Nalin H. Samarasinha, Darryl Z. Seligman, Colin Snodgrass, Michael Solontoi, Gyula M. Szabó, Peter Vereš, Ellie White, Maria Womack, Leslie A. Young, Russ Allbery, Shreya Anand, Roberto Armellin, Éric Aubourg, Chrysa Avdellidou, Farrukh Azfar, James Bauer, Keith Bechtol, Valerie Becker, Matthew Belyakov, Susan D. Benecchi, Ivano Bertini, Dennis Bodewits, Patricia Boeshaar, Bryce T. Bolin, Maitrayee Bose, Alexandre Boucaud, Rodrigo C. Boufleur, Dominique Boutigny, Andrew Bradshaw, Felipe Braga-Ribas, Johan Bregeon, Laura E. Buchanan, Daniel Calabrese, J. I. B. Camargo, Neven Caplar, Jeffrey L. Carlin, Benoit Carry, Juan Pablo Carvajal, Ross Ceballo, Hsin-Fang Chiang, Yumi Choi, Céline Combet, Luiz da Costa, Preeti Cowan, John Franklin Crenshaw. 2025-07-17. NSF-DOE Vera C. Rubin Observatory Observations of Interstellar Comet 3I/ATLAS (C/2025 N1). https://doi.org/10.3847/2041-8213%2Fae4b3a
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