University of Hawaii 88-inch Telescope Observations of the Interstellar Comet 3I/ATLAS: Spectrophotometric Blue-Sensitive Spectral Time Series Spanning Two Months from Discovery

@article{hoogendam2026university,
  title = {{University of Hawaii 88-inch Telescope Observations of the Interstellar Comet 3I/ATLAS: Spectrophotometric Blue-Sensitive Spectral Time Series Spanning Two Months from Discovery}},
  author = {W. B. Hoogendam and D. Kuesters and Benjamin J. Shappee and Gregory S. Aldering and James J. Wray and B. Yang and Karen J. Meech and Michael A. Tucker and M. E. Huber and Katie Auchettl and C. R. Angus and D. Desai and J. T. Hinkle and J. Kiyokawa and Gregory S. H. Paek and S. Romagnoli and J. Shi and A. Syncatto and Chris Ashall and M. E. Dixon and Kevin Hart and A. M. Hoffman and D. O. Jones and K. Medler and C. M. Pfeffer},
  journal = {The Open Journal of Astrophysics},
  year = {2026},
  month = jul,
  doi = {10.33232/001c.165099},
  url = {https://doi.org/10.33232/001c.165099},
  note = {CC BY},
}

TY  - JOUR
TI  - University of Hawaii 88-inch Telescope Observations of the Interstellar Comet 3I/ATLAS: Spectrophotometric Blue-Sensitive Spectral Time Series Spanning Two Months from Discovery
AU  - W. B. Hoogendam
AU  - D. Kuesters
AU  - Benjamin J. Shappee
AU  - Gregory S. Aldering
AU  - James J. Wray
AU  - B. Yang
AU  - Karen J. Meech
AU  - Michael A. Tucker
AU  - M. E. Huber
AU  - Katie Auchettl
AU  - C. R. Angus
AU  - D. Desai
AU  - J. T. Hinkle
AU  - J. Kiyokawa
AU  - Gregory S. H. Paek
AU  - S. Romagnoli
AU  - J. Shi
AU  - A. Syncatto
AU  - Chris Ashall
AU  - M. E. Dixon
AU  - Kevin Hart
AU  - A. M. Hoffman
AU  - D. O. Jones
AU  - K. Medler
AU  - C. M. Pfeffer
PY  - 2026
DA  - 2026/07/15
JO  - The Open Journal of Astrophysics
DO  - 10.33232/001c.165099
UR  - https://doi.org/10.33232/001c.165099
AB  - Interstellar objects are the ejected building blocks of other solar systems. As such, they enable the acquisition of otherwise inaccessible information about nascent extrasolar systems. The discovery of the third interstellar object, 3I/ATLAS, provides an opportunity to explore the properties of a small body from another solar system and to compare it to the small bodies in our own. To that end, we present spectrophotometric observations of 3I/ATLAS taken using the SuperNova Integral Field Spectrograph on the University of Hawaii 2.2-m telescope. Our data includes the earliest λ ≤ 3800 A spectrum of 3I/ATLAS, obtained ∼ 12.5 hours after the discovery announcement. Later spectra confirm previously reported cometary activity, including Ni and CN emission. The data show wavelength-varying spectral slopes ( S ≈ ( 0%-29%)/1000 A, depending on wavelength range) throughout the pre-perihelion ( r h = 4.4 – 2.5 au) approach of 3I/ATLAS. We perform synthetic photometry on our spectra and find 3I/ATLAS shows mostly stable color evolution over the period of our observations, with g − r colors ranging from ∼ 0.69-0.75 mag, r − i colors ranging from ∼ 0.26-0.30 mag, and c − o colors ranging from ∼ 0.50-0.55 mag. Ongoing post-perihelion observations of 3I/ATLAS will provide further insight into its potentially extreme composition.
SN  - 2565-6120
ER  -