Millimeter-sized Dust Grains Surviving the Water-sublimating Temperature in the Inner 10 au of the FU Ori Disk

Author(s): Hauyu Baobab Liu, An-Li Tsai, Wen-Ping Chen, Jin Zhong Liu, Xuan Zhang, Eduard Vorobiev
Abstract: Previous observations have shown that the ≲10 au, ≳400 K hot inner disk of the archetypal accretion outburst young stellar object, FU Ori, is dominated by viscous heating. To constrain dust properties in this region, we have performed radio observations toward this disk using the Karl G. Jansky Very Large Array in 2020 June-July, September, and November. We also performed complementary optical photometric monitoring observations. We found that the dust thermal emission from the hot inner disk mid-plane of FU Ori has been approximately stationary and the maximum dust grain size is ≳1.6 mm in this region. If the hot inner disk of FU Ori, which is inward of the 150-170 K water snowline, is turbulent (e.g., corresponding to a Sunyaev & Shakura viscous α_t ≳ 0.1), or if the actual maximum grain size is still larger than the lower limit we presently constrain, then as suggested by the recent analytical calculations and the laboratory measurements, water-ice-free dust grains may be stickier than water-ice-coated dust grains in protoplanetary disks. Additionally, we find that the free-free emission and the Johnson B- and V-band magnitudes of these binary stars were brightening in 2016-2020. The optical and radio variability might be related to the dynamically evolving protostellar- or disk-accretion activities. Our results highlight that the hot inner disks of outbursting objects are important laboratories for testing models of dust grain growth. Given the active nature of such systems, to robustly diagnose the maximum dust grain sizes, it is important to carry out coordinated multiwavelength radio observations.
Organisation(s): Department of Astrophysics
External organisation(s): National Central University, Chinese Academy of Sciences (CAS), Southern Federal University, Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), No. 1, Section 4, Roosevelt Road
Journal: The Astrophysical Journal
Volume: 923
No. of pages: 20
ISSN: 0004-637X
DOI: https://doi.org/10.3847/1538-4357/ac31b9
Publication date: 12-2021
Peer reviewed: Yes
Austrian Fields of Science 2012: 103003 Astronomy, 103004 Astrophysics
Keywords
ASJC Scopus subject areas: Astronomy and Astrophysics, Space and Planetary Science
Portal url: https://ucrisportal.univie.ac.at/en/publications/3106905b-80a1-4999-be03-97815cf330b8

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