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Published December 1, 2023 | Published
Journal Article Open

RNO 54: A Previously Unappreciated FU Ori Star

  • 1. ROR icon California Institute of Technology


We present evidence in support of the hypothesis that the young stellar object RNO 54 is a mature-stage FU Ori type source. The star was first cataloged as a "red nebulous object" in the 1980s but appears to have undergone its outburst prior to the 1890s. Present-day optical and near-infrared spectra are consistent with those of other FU Ori-type stars, both in the details of spectral line presence and shape, and in the overall change in spectral type from an FGK-type in the optical, to the M-type presented in the near-infrared. In addition, the spectral energy distribution of RNO 54 is well-fit by a pure-accretion disk model with parameters: Ṁ = 10 − 3.45 ± 0.06 M_⊙ yr⁻¹, M* = 0.23 ± 0.06 M_⊙, and R_(inner) = 3.68 ± 0.76 R_⊙, though we believe R inner is likely close to its upper range of 4.5 R_⊙ in order to produce a Tₘₐₓ = 7000 K that is consistent with the optical to near-infrared spectra. The resulting L_(acc) is ∼265 L_⊙. To find these values, we adopted a source distance d = 1400 pc and extinction Aᵥ = 3.9 mag, along with disk inclination i = 50 deg based on the consideration of confidence intervals from our initial disk model, and in agreement with observational constraints. The new appreciation of a well-known source as an FU Ori-type object suggests that other such examples may be lurking in extant samples.

Copyright and License

© 2023. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.


We thank our referee for detailed comments that helped improve the manuscript, and Tigran Magakian for reminding us of the distinction between cometary and conical nebulae when describing YSOs.


Keck:II(ESI) - KECK II Telescope, IRTF(SpeX) - Infrared Telescope Facility.


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Additional details

January 3, 2024
January 3, 2024