Application of a Steady-state Accretion Disk Model to Spectrophotometry and High-resolution Spectra of Two Recent FU Ori Outbursts
Abstract
We apply a conventional accretion disk model to the FU Ori–type objects HBC 722 and Gaia 17bpi. Our base model is a steady-state, thin Keplerian disk featuring a modified Shakura–Sunyaev temperature profile, with each annulus radiating as an area-weighted spectrum given by a NextGen atmosphere at the appropriate temperature. We explore departures from the standard model by altering the temperature distribution in the innermost region of the disk to account for "boundary region"–like effects. We consider the overall spectral energy distribution as well as medium- and high-resolution spectra in evaluating best-fit models to the data. Parameter degeneracies are studied via a Markov Chain Monte Carlo parameter estimation technique. Allowing all parameters to vary, we find accretion rates for HBC 722 of M˙ = 10^(−4.90) M_⊙ yr⁻¹^ (+0.99)_(−0.40) dex and for Gaia 17bpi of M˙ = 10^(−6.70) M_⊙ yr⁻¹ ^(+0.46)_(−0.36) dex the corresponding maximum disk temperatures are 7100⁺³⁰⁰₋₅₀₀ K and 7900⁺⁹⁰⁰₋₄₀₀ K, respectively. While the accretion rate of HBC 722 is on the same order as other FU Ori–type objects, Gaia 17bpi has a lower rate than previously reported as typical, commensurate with its lower luminosity. Alternate models that fix some disk or stellar parameters are also presented, with tighter confidence intervals on the remaining fitted parameters. In order to improve upon the somewhat large credible intervals for the values, and to make progress on boundary layer characterization, flux-calibrated ultraviolet spectroscopy is needed.
Additional Information
© 2022 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. Received 2021 July 7; revised 2022 January 4; accepted 2022 January 5; published 2022 March 10. We are grateful for the allocation of observing time on the Palomar 200'' telescope through the Caltech SURF Observing Program. We appreciate the observatory staff at both Palomar and WMKO for excellent operations that enabled the new optical spectroscopic data presented here. We thank Ágnes Kóspál for providing her published infrared spectrum of HBC 722. We also thank Mike Connelley for use of his infrared spectrum of Gaia 17bpi, which is of higher quality than the one published in our discovery paper. We acknowledge useful discussions with Roger W. Romani and his research group, as well as early discussions with Michael Kuhn. We thank Lee Hartmann for constructive feedback regarding accretion disk fundamentals. We additionally thank the anonymous referee for insightful comments and feedback that helped improve the final manuscript.Attached Files
Published - Rodriguez_2022_ApJ_927_144.pdf
Submitted - 2112.01549.pdf
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Additional details
- Eprint ID
- 113004
- Resolver ID
- CaltechAUTHORS:20220119-233943041
- Caltech Summer Undergraduate Research Fellowship (SURF)
- Created
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2022-01-20Created from EPrint's datestamp field
- Updated
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2022-03-22Created from EPrint's last_modified field
- Caltech groups
- Astronomy Department