A Study of Millimeter Variability in FUor Objects

TL;DR

This study investigates millimeter wavelength variability in FU Orionis objects, revealing first evidence of flux changes at 2.7 mm likely caused by jet/wind activity, which impacts disk mass estimations and understanding of FUor outbursts.

Contribution

First detection of millimeter flux variability in FUor objects, highlighting the role of free-free emission from jets/winds in these systems.

Findings

Detected variability at 2.7 mm in V1735 Cyg.

Free-free emission may significantly affect millimeter flux measurements.

Variability likely due to jet/wind activity, not disk changes.

Abstract

FU Orionis objects (FUors) are rapidly-accreting, pre-main sequence objects that are known to exhibit large outbursts at optical and near-infrared wavelengths, with post-eruption, small-scale photometric variability superimposed on longer-term trends. In contrast, little is known about the variability of FUors at longer wavelengths. To explore this further, we observed six FUor objects using the NOrthern Extended Millimeter Array (NOEMA) and for a subset of three objects we obtained coordinated observations with NOEMA and the Lowell Discovery Telescope (LDT). In combination with previously published NOEMA observations from 2014, our 2017 observations of V1735 Cyg provide the first detection of variability in an FUor object at 2.7 mm. In the absence of significant optical variability, we discount the possibility that the mm flux density changed as a result of irradiation from the central disk. In addition, a change in the dust mass due to infall is highly unlikely. A plausible explanation for the change in 2.7 mm flux density is variability in free-free emission due to changes in the object's jet/wind. Thus, it may be that free-free emission in some FUor objects is significant at $\sim$3 mm and must be considered when deriving disk masses in order to help constrain the mechanism responsible for triggering FUor outbursts.