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The accretion/ejection processes in T Tauri stars are fundamental to their physical evolution, while also impacting the properties and evolution of the circumstellar material at a time when planet formation takes place. To date, the characterization of ongoing accretion processes in stellar pairs at 5–50 au scales has been challenging as high-angular resolution spectrographs are required to extract the spectral features of each component. We present the analysis of spectroscopic observations of the tight (160 mas, 25 au) T Tauri system HT Lup A/B, obtained with MUSE at the Very Large Telescope in 2021 March and July. We focus on constraining the accretion/ejection processes and variability of the secondary component HT Lup B by searching for accretion tracers by applying high-resolution spectral differential imaging techniques. We retrieve strong (signal-to-noise ratio > 5) H α, H β, and [O i ] λ 6300 emission in both epochs. The H α and H β line fluxes showcase high variability, with variations up to 200%–300% between epochs. The fluxes are consistent with accretion rates of 3× 10−9 M ⊙ yr−1 and 8 × 10−10 M ⊙ yr−1 for the first and second epochs, respectively. We attribute the increased accretion activity during the first night to a "burst-like" event, followed by a relaxation period more representative of the common accretion activity of the system. The [O i ] λ 6300 line profiles remain relatively similar between epochs and suggest ejection rates on the order of 10−9−10−10 M ⊙ yr−1, compatible with moderate disk wind emission. Our results also indicate that the accretion processes of HT Lup B are compatible with Classical T Tauri stars, unlike previous classifications. [ABSTRACT FROM AUTHOR]

The gas dissipation from a protoplanetary disk is one of the key processes affecting planet formation, and it is widely accepted that it happens on timescales of a few million years for disks around single stars. In recent years, several protoplanetary disks have been discovered in multiple-star systems, and despite the complex environment in which they find themselves, some of them seem to be quite old, a situation that may favor planet formation. A clear example of this is the disk around HD 98800 B, a binary in a hierarchical quadruple stellar system, which at an ∼10 Myr age seems to still be holding significant amounts of gas. Here we present a 1D+1D model to compute the vertical structure and gas evolution of circumbinary disks in hierarchical triple-star systems considering different stellar and disk parameters. We show that tidal torques due to the inner binary, together with the truncation of the disk due to the external companion, strongly reduce the viscous accretion and expansion of the disk. Even allowing viscous accretion by tidal streams, disks in these kind of environments can survive for more than 10 Myr, depending on their properties, with photoevaporation being the main gas dissipation mechanism. We particularly apply our model to the circumbinary disk around HD 98800 B and confirm that its longevity, along with the current nonexistence of a disk around the companion binary HD 98800 A, can be explained with our model and by this mechanism. [ABSTRACT FROM AUTHOR]

We present sensitive ALMA observations of TWA 3, a nearby, young (∼10 Myr) hierarchical system composed of three pre-main-sequence M3–M4.5 stars. For the first time, we detected 12CO and 13CO J = 2–1 emissions from the circumbinary protoplanetary disk around TWA 3A. We jointly fit the protoplanetary disk velocity field, stellar astrometric positions, and stellar radial velocities to infer the architecture of the system. The Aa and Ab stars (0.29 ± 0.01 M⊙ and 0.24 ± 0.01 M⊙, respectively) comprising the tight (P = 35 days) eccentric (e = 0.63 ± 0.01) spectroscopic binary are coplanar with their circumbinary disk (misalignment <6° with 68% confidence), similar to other short-period binary systems. From models of the spectral energy distribution, we found the inner radius of the circumbinary disk (rinner = 0.50–0.75 au) to be consistent with theoretical predictions of dynamical truncation rcav/ainner ≈ 3. The outer orbit of the tertiary star B (0.40 ± 0.28 M⊙, a ∼ 65 ± 18 au, e = 0.3 ± 0.2) is not as well constrained as the inner orbit; however, orbits coplanar with the A system are still preferred (misalignment < 20°). To better understand the influence of the B orbit on the TWA 3A circumbinary disk, we performed SPH simulations of the system and found that the outer edge of the gas disk (router = 8.5 ± 0.2 au) is most consistent with truncation from a coplanar, circular, or moderately eccentric orbit, supporting the preference from the joint orbital fit. [ABSTRACT FROM AUTHOR]

Planets form in young circumstellar disks called protoplanetary disks. However, it is still difficult to catch planet formation in situ. Nevertheless, from recent ALMA/SPHERE data, encouraging evidence of the direct and indirect presence of embedded planets has been identified in disks around young stars: co-moving point sources, gravitational perturbations, rings, cavities, and emission dips or shadows cast on disks. The interpretation of these observations needs a robust physical framework to deduce the complex disk geometry. In particular, protoplanetary disk models usually assume the gas pressure scale height given by the ratio of the sound speed over the azimuthal velocity H/r = cs/vk. By doing so, radiative pressure fields are often ignored, which could lead to a misinterpretation of the real vertical structure of such disks. We follow the evolution of a gaseous disk with an embedded Jupiter-mass planet through hydrodynamical simulations, computing the disk scale height including radiative pressure, which was derived from a generalization of the stellar atmosphere theory. We focus on the vertical impact of the radiative pressure in the vicinity of circumplanetary disks, where temperatures can reach ≳1000 K for an accreting planet and radiative forces can overcome gravitational forces from the planet. The radiation pressure effects create a vertical, optically thick column of gas and dust at the protoplanet location, casting a shadow in scattered light. This mechanism could explain the peculiar illumination patterns observed in some disks around young stars such as HD 169142 where a moving shadow has been detected or the extremely high aspect ratio H/r ∼ 0.2 observed in systems like AB Aur and CT Cha. [ABSTRACT FROM AUTHOR]