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Abstract This article presents the latest results of our Atacama Large Millimeter/submillimeter Array (ALMA) program to study circumstellar disk characteristics as a function of orbital and stellar properties in a sample of young binary star systems known to host at least one disk. Optical and infrared observations of the eccentric, ∼48 yr period binary DF Tau indicated the presence of only one disk around the brighter component. However, our 1.3 mm ALMA thermal continuum maps show two nearly equal-brightness components in this system. We present these observations within the context of updated stellar and orbital properties, which indicate that the inner disk of the secondary is absent. Because the two stars likely formed together, with the same composition, in the same environment, and at the same time, we expect their disks to be co-eval. However the absence of an inner disk around the secondary suggests uneven dissipation. We consider several processes that have the potential to accelerate inner disk evolution. Rapid inner disk dissipation has important implications for planet formation, particularly in the terrestrial-planet-forming region. 

Abstract Close binary systems present challenges to planet formation. As binary separations decrease, so do the occurrence rates of protoplanetary disks in young systems and planets in mature systems. For systems that do retain disks, their disk masses and sizes are altered by the presence of the binary companion. Through the study of protoplanetary disks in binary systems with known orbital parameters, we seek to determine the properties that promote disk retention and therefore planet formation. In this work, we characterize the young binary−disk system FO Tau. We determine the first full orbital solution for the system, finding masses of ${0.35}_{-0.05}^{+0.06}{M}_{\odot }$and 0.34 ± 0.05M_⊙for the stellar components, a semimajor axis of $22{(}_{-1}^{+2})$au, and an eccentricity of $0.21{(}_{-0.03}^{+0.04})$. With long-baseline Atacama Large Millimeter/submillimeter Array interferometry, we detect 1.3 mm continuum and¹²CO (J= 2–1) line emission toward each of the binary components; no circumbinary emission is detected. The protoplanetary disks are compact, consistent with being truncated by the binary orbit. The dust disks are unresolved in the image plane, and the more extended gas disks are only marginally resolved. Fitting the continuum and CO visibilities, we determine the inclination of each disk, finding evidence for alignment of the disk and binary orbital planes. This study is the first of its kind linking the properties of circumstellar protoplanetary disks to a precisely known binary orbit. In the case of FO Tau, we find a dynamically placid environment (coplanar, low eccentricity), which may foster its potential for planet formation. 

Most young stellar objects in nearby star forming regions reside in binary and multiple systems. Although circumstellar disks in these configurations are less massive and evolve more rapidly than their single star disk counterparts, many nevertheless persist for millions of years and have been shown to host young planets. Disks around the stars in the closest resolved young binaries, with separations of a few to tens of AU, are truncated at outer radii of ~1/3 the binary semi-major axis. Component-resolved, high-resolution spectra of the He I 10830A line show evidence for accretion plus winds from the stars and disks, launched over a range of radii and betraying the inner disk structure and activity. I will present results from recent He I 10830A observations, complemented with high-angular resolution data from ALMA and other facilities, for several binary systems in the Taurus region. 

Understanding the inclinations of stellar spin axes is fundamental for studying planet formation and young binary star evolution. Obliquities between exoplanet orbits and their host stars can be traced to the misalignment of circumstellar disks and stellar rotation. In both single and binary systems, these misalignments can impact disk lifetimes and hinder the formation of planets altogether. Our goal is to derive the inclinations for single and binary systems in the Taurus star-forming region using a unique method that relies on estimates of stellar radii. We first identify rotation periods from TESS and K2 light curves for over a hundred sources. In order to test that these periods reflect the stellar rotation of CTTSs, we model the impact of accretion and other activity on our ability to extract the underlying sinusoidal signal we expect from rotation. We combine these data with projected stellar rotation velocities and effective temperatures derived by fitting a synthetic model grid to IGRINS spectra of our sources. Alongside all of these parameters, we use stellar ages and evolutionary track models from the literature to determine inclination. We present the details of this novel approach and the results from our derived distribution of stellar inclinations. 

Young binary systems offer a unique opportunity to study the fragility of circumstellar disks in dynamically tumultuous environments. In this talk, I will present preliminary ALMA continuum and 12CO emission for several systems, including the puzzling DF Tau. DF Tau is a close visual binary with a semi-major axis of only 14 AU; we find circumstellar disks around both the primary and secondary star. Other disk signatures, i.e. accretion measurements and H-band veiling, indicate only a disk around the primary star. Because the two stars likely formed together, with the same composition, in the same environment, and at the same time, we expect their disks to be co-eval. However the absence of an inner disk around the secondary suggests uneven dissipation. We resolve this contradiction by proposing that the inner disk of DF Tau B is, at minimum, beyond ~0.06 AU and consider several processes which have the potential to accelerate inner disk evolution.