Radio multiwavelength analysis of the compact disk CX Tau: Presence of strong free-free variability or anomalous microwave emission

Abstract

Protoplanetary disks emit radiation across a broad range of wavelengths, requiring a multiwavelength approach to fully understand their physical mechanisms and how they form planets. Observations at sub-millimeter to centimeter wavelengths can provide insights into the thermal emission from dust, free-free emission from ionized gas, and possible gyro-synchrotron emission from the stellar magnetosphere. This work is focused on CX Tau, a $\sim 0.4M_{\odot }$ star with an extended gas emission and a compact and apparently structureless dust disk, with an average millimeter flux when compared to Class II sources in Taurus. We present observations from the Karl G. Jansky Very Large Array (VLA) across four bands (between 9.0 mm and 6.0 cm) and combine them with archival data from the Atacama Large Millimeter/submillimeter Array (ALMA), the Submillimeter Array (SMA) and the Plateau de Bure Interferometer (PdBI). This multiwavelength approach allows us to separate the dust continuum from other emissions. After isolating the dust thermal emission, we derived an upper limit of the dust disk extent at 1.3 cm which is consistent with theoretical predictions of a radial drift-dominated disk. Centimeter data show a peculiar behavior: deep observations at 6.0 cm did not detect the source, while at 1.3 cm the flux density is anomalously higher than adjacent bands. Intraband spectral indices suggest a dominant contribution from free-free emission, whereas gyro-synchrotron emission is excluded. To explain these observations, we propose a strong variability among the free-free emission with timescales shorter than a month. Another possible interpretation is the presence of anomalous microwave emission from spinning dust grains.

Accepted for publication in A&A; 13 pages, 13 figures, 1 table

References in corpus (16)

• Estimating distances from parallaxes. V: Geometric and photogeometric distances to 1.47 billion stars in Gaia Early Data Release 3
• CASA, the Common Astronomy Software Applications for Radio Astronomy
• Demographics of Transition Objects
• The Radial Distribution of Dust Particles in the HL Tau Disk from ALMA and VLA Observations
• Characterizing the dust content of disk substructures in TW Hya
• The time evolution of dusty protoplanetary disc radii: observed and physical radii differ
• High gas/dust size ratio indicating efficient radial drift in the mm-faint CX Tau disk
• Distribution of solids in the rings of the HD 163296 disk: a multiwavelength study
• Dynamical Masses of Low Mass Stars in the Taurus and Ophiuchus Star Forming Regions
• Low EUV Luminosities Impinging on Protoplanetary Disks
• On the secular evolution of the ratio between gas and dust radii in protoplanetary discs
• Imaging the photoevaporating disk and radio jet of GM Aur
• A 1.3 cm wavelength radio flare from a deeply embedded source in the Orion BN/KL region
• The ALMA view of MP Mus (PDS 66): a protoplanetary disk with no visible gaps down to 4 au scales
• Revealing the Star-Disk-Jet Connection in GM Aur using Multiwavelength Variability
• A VLA Survey For Faint Compact Radio Sources in the Orion Nebula Cluster