RNO 54: A Previously Unappreciated FU Ori Star

Hillenbrand, Lynne A.; Carvalho, Adolfo; van Roestel, Jan; De, Kishalay

doi:10.3847/2041-8213/ad0be0

Cited by 4 publications

(1 citation statement)

References 36 publications

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“…The O I 7773 triplet, which has an EP = 9.1 eV, is typically only present in higher-temperature atmospheres or high-T max FU Ori objects (Hillenbrand et al 2023). Here, it appears almost entirely in excess of the disk model, which predicts a maximum depth of ∼5% for the line.…”

Section: Appendix B Line Profiles Of O I Wind Linesmentioning

confidence: 99%

An Expanding Accretion Disk and a Warm Disk Wind as Seen in the Spectral Evolution of HBC 722

Carvalho,

Hillenbrand,

Seebeck

et al. 2024

ApJ

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We present a comprehensive analysis of the post-outburst evolution of the FU Ori object HBC 722 in optical/near-infrared (NIR) photometry and spectroscopy. Using a modified viscous accretion disk model, we fit the outburst epoch spectral energy distribution to determine the physical parameters of the disk, including M ̇ acc = 10 − 4.0 M ⊙ yr−1, R inner = 3.65 R ⊙, i = 79°, and a maximum disk temperature of T max = 5700 K. We then use a decade of optical/NIR spectra to demonstrate a changing accretion rate drives the visible-range photometric variation, while the NIR shows the outer radius of the active accretion disk expands outward as the outburst progresses. We also identify the major components of the disk system: a plane-parallel disk atmosphere in Keplerian rotation and a two-part warm disk wind that is collimated near the star and wide-angle at larger radii. The wind is traced by classic wind lines, and appears as a narrow, low-velocity, deep absorption component in several atomic lines spanning the visible spectrum and in the CO 2.29 μm band. We compare the wind lines to those computed from wind models for other FU Ori systems and rapidly accreting young stellar disks and find a 4000–6000 K wind can explain the observed line profiles. Fitting the progenitor spectrum, we find M * = 0.2 M ⊙ and M ̇ progenitor = 7.8 × 10 − 8 M ⊙ yr − 1 . Finally, we discuss HBC 722 relative to V960 Mon, another FU Ori object we have previously studied in detail.

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Section: Appendix B Line Profiles Of O I Wind Linesmentioning

confidence: 99%

An Expanding Accretion Disk and a Warm Disk Wind as Seen in the Spectral Evolution of HBC 722

Carvalho,

Hillenbrand,

Seebeck

et al. 2024

ApJ

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Episodic eruptions of young accreting stars: the key role of disc thermal instability due to Hydrogen ionization

Nayakshin,

Cruz Sáenz de Miera,

Kóspál

et al. 2024

Monthly Notices of the Royal Astronomical Society

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In the classical grouping of large magnitude episodic variability of young accreting stars, FUORs outshine their stars by a factor of ∼100, and can last for up to centuries; EXORs are dimmer, and last months to a year. A disc Hydrogen ionisation Thermal Instability (TI) scenario was previously proposed for FUORs but required unrealistically low disc viscosity. In the last decade, many intermediate type objects, e.g., FUOR-like in luminosity and spectra but EXOR-like in duration were found. Here we show that the intermediate type bursters Gaia20eae, PTF14jg, Gaia19bey and Gaia21bty may be naturally explained by the TI scenario with realistic viscosity values. We argue that TI predicts a dearth (desert) of bursts with peak accretion rates between 10−6 ${\rm {\rm M}_{\odot }}$ yr−1 $\lesssim \dot{M}_{\rm burst} \lesssim 10^{-5}$ ${\rm {\rm M}_{\odot }}$ yr−1, and that this desert is seen in the sample of all the bursters with previously determined $\dot{M}_{\rm burst}$. Most classic EXORs (FUORs) appear to be on the cold (hot) branch of the S-curve during the peak light of their eruptions; thus TI may play a role in this class differentiation. At the same time, TI is unable to explain how classic FUORs can last for up to centuries, and over-predicts the occurrence rate of short FUORs by at least an order of magnitude. We conclude that TI is a required ingredient of episodic accretion operating at R ≲ 0.1 au, but additional physics must play a role at larger scales. Knowledge of TI inner workings from related disciplines may enable its use as a tool to constrain the nature of this additional physics.

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WTP 10aaauow: discovery of a new FU Ori outburst towards the RCW 49 star-forming region in NEOWISE data

Tran,

De,

Hillenbrand

2024

Monthly Notices of the Royal Astronomical Society

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Large-amplitude accretion outbursts in young stars are expected to play a central role in proto-stellar assembly. Outburst identification historically has taken place using optical techniques, but recent, systematic infrared searches are enabling their discovery in heavily dust-obscured regions of the Galactic plane. Here, we present the discovery of WTP 10aaauow, a large-amplitude mid-infrared (MIR) outburst identified in a systematic search of NEOWISE data using new image subtraction techniques. The source is located towards the RCW 49 star-forming region, and estimated to be at a distance of ≈4 kpc via Gaia parallax measurement. Concurrent with the MIR brightening, the source underwent a ≳ 5 mag outburst in the optical and near-infrared (NIR) bands, reaching a peak luminosity of ≈260 L⊙ in 2014-2015, followed by a slow decline over the next 7 years. Analysis of the pre- and post-outburst spectral energy distributions reveal a pre-outburst stellar photosphere at a temperature of 3600 − 4000 K, surrounded by a likely two-component dust structure similar to a flat-spectrum or Class I type YSO. We present optical and NIR spectroscopy that show a GK-type spectrum in the optical bands exhibiting complex line profiles in strong absorption features, and evidence for a wind reaching a terminal velocity of ≈400 km s−1. The NIR bands are characterized by a cooler M-type spectrum exhibiting a forest of atomic and molecular features. All together, the spectra demonstrate that WTP 10aaauow is an FU Ori type outburst. Ongoing systematic infrared searches will continue to reveal the extent of this population in the Galactic disk.

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RNO 54: A Previously Unappreciated FU Ori Star

Cited by 4 publications

References 36 publications

An Expanding Accretion Disk and a Warm Disk Wind as Seen in the Spectral Evolution of HBC 722

An Expanding Accretion Disk and a Warm Disk Wind as Seen in the Spectral Evolution of HBC 722

Episodic eruptions of young accreting stars: the key role of disc thermal instability due to Hydrogen ionization

WTP 10aaauow: discovery of a new FU Ori outburst towards the RCW 49 star-forming region in NEOWISE data

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