SN 2022acko: The First Early Far-ultraviolet Spectra of a Type IIP Supernova

K. Azalee Bostroem, Luc Dessart, D. John Hillier, Michael Lundquist, Jennifer E. Andrews, David J. Sand, Yize Dong, Stefano Valenti, Joshua Haislip, Emily T. Hoang, Griffin Hosseinzadeh, Daryl Janzen, Jacob E. Jencson, Saurabh W. Jha, Vladimir Kouprianov, Jeniveve Pearson, Nicolas E. Meza Retamal, Daniel E. Reichart, Manisha Shrestha, Christopher AshallE. Baron, Peter J. Brown, James M. DerKacy, Joseph Farah, Lluís Galbany, J. I.González Hernández, Elizabeth Green, Peter Hoeflich, D. Andrew Howell, Lindsey A. Kwok, Curtis McCully, Tomás E. Müller-Bravo, Megan Newsome, Estefania Padilla Gonzalez, Craig Pellegrino, Jeonghee Rho, Micalyn Rowe, Michaela Schwab, Melissa Shahbandeh, Nathan Smith, Jay Strader, Giacomo Terreran, Schuyler D. Van Dyk, Samuel Wyatt

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


We present five far- and near-ultraviolet spectra of the Type II plateau supernova, SN 2022acko, obtained 5, 6, 7, 19, and 21 days after explosion, all observed with the Hubble Space Telescope/Space Telescope Imaging Spectrograph. The first three epochs are earlier than any Type II plateau supernova has been observed in the far-ultraviolet revealing unprecedented characteristics. These three spectra are dominated by strong lines, primarily from metals, which contrasts with the featureless early optical spectra. The flux decreases over the initial time series as the ejecta cool and line blanketing takes effect. We model this unique data set with the non-local thermodynamic equilibrium radiation transport code CMFGEN, finding a good match to the explosion of a low-mass red supergiant with energy E kin = 6 × 1050 erg. With these models we identify, for the first time, the ions that dominate the early ultraviolet spectra. We present optical photometry and spectroscopy, showing that SN 2022acko has a peak absolute magnitude of V = − 15.4 mag and plateau length of ∼115 days. The spectra closely resemble those of SN 2005cs and SN 2012A. Using the combined optical and ultraviolet spectra, we report the fraction of flux as a function of bluest wavelength on days 5, 7, and 19. We create a spectral time-series of Type II supernovae in the ultraviolet, demonstrating the rapid decline of flux over the first few weeks of evolution. Future observations of Type II supernovae are required to map out the landscape of exploding red supergiants, with and without circumstellar material, which is best revealed in high-quality ultraviolet spectra.

Original languageEnglish (US)
Article numberL18
JournalAstrophysical Journal Letters
Issue number2
StatePublished - Aug 1 2023

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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