RNO 54: A Previously Unappreciated FU Ori Star

Abstract

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: <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 <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.

Topics & Concepts