Abstract 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: <?CDATA $\dot{M}={10}^{-3.45\pm 0.06}$?> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>̇</mml:mo> </mml:mrow> </mml:mover> <mml:mo>=</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3.45</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.06</mml:mn> </mml:mrow> </mml:msup> </mml:math> 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 <?CDATA ${T}_{\max }=7000$?> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>max</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>7000</mml:mn> </mml:math> 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 A V = 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. 

pdf/rno-54-a-previously-unappreciated-fu-ori-star-4agjmsd00u.pdf

RNO 54: A Previously Unappreciated FU Ori Star

As presented in Annenkov&Shrira (2009), when a surface gravity wave field is subjected to an abrupt perturbation of external forcing, its spectrum evolves on a ``fast'' dynamic time scale of $O(\varepsilon^{-2})$, with $\varepsilon$ a measure of wave steepness. This observation poses a challenge to wave turbulence theory that predicts an evolution with a kinetic time scale of $O(\varepsilon^{-4})$. We revisit this unresolved problem by studying the same situation in the context of a one-dimensional Majda-McLaughlin-Tabak (MMT) equation with gravity wave dispersion relation. Our results show that the kinetic and dynamic time scales can both be realised, with the former and latter occurring for weaker and stronger forcing perturbations, respectively. The transition between the two regimes corresponds to a critical forcing perturbation, with which the spectral evolution time scale drops to the same order as the linear wave period (of some representative mode). Such fast spectral evolution is mainly induced by a far-from-stationary state after a sufficiently strong forcing perturbation is applied. We further develop a set-based interaction analysis to show that the inertial-range modal evolution in the studied cases is dominated by their (mostly non-local) interactions with the low-wavenumber ``condensate'' induced by the forcing perturbation. The results obtained in this work should be considered to provide significant insight into the original gravity wave problem.

pdf/on-the-time-scales-of-spectral-evolution-of-nonlinear-waves-1idvfpz3.pdf

On the time scales of spectral evolution of nonlinear waves

pdf/spectral-transfers-of-sign-definite-invariants-in-wave-igi3ghypw1xq.pdf

Spectral transfers of sign-definite invariants in wave turbulence

We study the spectral energy transfer due to wave-triad interactions in the Garrett-Munk spectrum of internal gravity waves (IGWs) based on a numerical evaluation of the collision integral in the wave kinetic equation. Our numerical evaluation builds on the reduction of the collision integral on the resonant manifold for an horizontally isotropic spectrum. We directly evaluate the downscale energy flux available for ocean mixing, whose value is in close agreement with the empirical finescale parameterization. We further decompose the energy transfer into contributions from different mechanisms, including local interactions and three types of nonlocal interactions, namely parametric subharmonic instability (PSI), elastic scattering (ES) and induced diffusion (ID). Through analysis on the role of each type of interaction, we resolve two long-standing paradoxes regarding the mechanism for forward cascade in frequency and zero ID flux for GM76 spectrum. In addition, our analysis estimates the contribution of each mechanism to the energy transfer in each spectral direction, and reveals new understanding of the importance of local interactions and ES in the energy transfer.

pdf/energy-cascade-in-the-garrett-munk-spectrum-of-internal-1ingpx2r.pdf

Energy cascade in the Garrett-Munk spectrum of internal gravity waves

Aims. The aim of the present study is to analyze the spectra of an unusual pre-main sequence star in the cometary nebula RNO 54, which is suspected by several researchers to be a FUori-like object.
Methods. We performed long-slit spectroscopy of the star using the 6m telescope with the SCORPIO-2 multi-mode focal reducer.
Results. We discover a short (~4″ or ~6000 AU) and faint emission shock-excited jet from this star, probably oriented toward the long axis of the nebular ellipse. The spectral type of the star is estimated as G0-2 II; we confirm the split of the Li I absorption line, which is a typical sign indicating a FUori-like spectrum. Our analysis of the available data reveals an almost null photometric variability over at least the last 20 years. The lower limit of the bolometric luminosity of the star is estimated as 300 L⊙. Our study supports the classification of RNO 54 as a FUor-like star in the long post-outburst stage.

/pdf/the-star-in-rno-54-a-possible-post-fuor-with-a-short-faint-kfes2jm5.pdf

The star in RNO 54: A possible post-FUor with a short faint jet

We develop a theory of turbulence of weak random gravity waves on surface of deep water in which the main nonlinear process at high-frequency part of the spectrum is a nonlocal interaction with a strong low-frequency component. The latter component, which we call ``condensate", may appear in the system due to, e.g., the finite size effects which lead to an energy stagnation at waves whose wavelength is comparable to the size of the retaining flume. Our theory assumes the form of a linear spectral diffusion equation. We find a scaling solution of this equation and propose it as a possible explanation of recent numerical results for the gravity wave spectrum.

https://export.arxiv.org/pdf/2305.01930v1.pdf

Nonlocal gravity wave turbulence in presence of condensate

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The star in RNO 54: A possible post-FUor with a short faint jet

Nonlocal gravity wave turbulence in presence of condensate