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Planet formation imprints signatures on the physical structures of disks. In this paper, we present high-resolution ($\sim$50 mas, 8 au) Atacama Large Millimeter/submillimeter Array (ALMA) observations of 1.3 mm dust continuum and CO line emission toward the disk around the M3.5 star 2MASS J04124068+2438157. The dust disk consists only of two narrow rings at radial distances of 0.47 and 0.78 arcsec ($\sim$70 and 116 au), with Gaussian $\sigma$ widths of 5.6 and 8.5 au, respectively. The width of the outer ring is smaller than the estimated pressure scale height by $\sim25\%$, suggesting dust trapping in a radial pressure bump. The dust disk size, set by the location of the outermost ring, is significantly larger (by $3\sigma$) than other disks with similar millimeter luminosity, which can be explained by an early formation of local pressure bump to stop radial drift of millimeter dust grains. After considering the disk's physical structure and accretion properties, we prefer planet--disk interaction over dead zone or photoevaporation models to explain the observed dust disk morphology. We carry out high-contrast imaging at $L'$ band using Keck/NIRC2 to search for potential young planets, but do not identify any source above $5\sigma$. Within the dust gap between the two rings, we reach a contrast level of $\sim$7 mag, constraining the possible planet below $\sim$2--4 $M_{\rm Jup}$. Analyses of the gap/ring properties suggest a $\sim$Saturn mass planet at $\sim$90 au is likely responsible for the formation of the outer ring, which can be potentially revealed with JWST., Comment: 15 pages, 5 figures. Accepted for publication in ApJ

We map the planetary wake associated with the embedded protoplanet creating the CO kink in the disk of HD~163296. We show that the wake can be traced by a series of correlated perturbations in the peak velocity map. The sign change of the perturbations across the disk major axis confirm that the wake induces predominantly radial motion, as predicted by models of planet-disk interaction. These results provide the first direct confirmation of planet wakes generated by Lindblad resonances. Mapping the wake provides a constraint on the disk aspect ratio, which is required to measure the mass of the planet., Comment: 10 Pages, 6 figures. Accepted in ApJL

Rings are the most frequently revealed substructure in ALMA dust observations of protoplanetary disks, but their origin is still hotly debated. In this paper, we identify dust substructures in 12 disks and measure their properties to investigate how they form. This subsample of disks is selected from a high-resolution ($\sim0.12''$) ALMA 1.33 mm survey of 32 disks in the Taurus star-forming region, which was designed to cover a wide range of sub-mm brightness and to be unbiased to previously known substructures. While axisymmetric rings and gaps are common within our sample, spiral patterns and high contrast azimuthal asymmetries are not detected. Fits of disk models to the visibilities lead to estimates of the location and shape of gaps and rings, the flux in each disk component, and the size of the disk. The dust substructures occur across a wide range of stellar mass and disk brightness. Disks with multiple rings tend to be more massive and more extended. The correlation between gap locations and widths, the intensity contrast between rings and gaps, and the separations of rings and gaps could all be explained if most gaps are opened by low-mass planets (super-Earths and Neptunes) in the condition of low disk turbulence ($\alpha=10^{-4}$). The gap locations are not well correlated with the expected locations of CO and N$_2$ ice lines, so condensation fronts are unlikely to be a universal mechanism to create gaps and rings, though they may play a role in some cases., Comment: 23 pages, 11 figures, ApJ accepted

We present ALMA observations of the 2M1207 system, a young binary made of a brown dwarf with a planetary-mass companion at a projected separation of about 40 au. We detect emission from dust continuum at 0.89 mm and from the $J = 3 - 2$ rotational transition of CO from a very compact disk around the young brown dwarf. The small radius found for this brown dwarf disk may be due to truncation from the tidal interaction with the planetary-mass companion. Under the assumption of optically thin dust emission, we estimated a dust mass of 0.1 $M_{\oplus}$ for the 2M1207A disk, and a 3$\sigma$ upper limit of $\sim 1~M_{\rm{Moon}}$ for dust surrounding 2M1207b, which is the tightest upper limit obtained so far for the mass of dust particles surrounding a young planetary-mass companion. We discuss the impact of this and other non-detections of young planetary-mass companions for models of planet formation, which predict the presence of circum-planetary material surrounding these objects., Comment: 10 pages, 6 figures, accepted for publication in AJ

The present observational understanding of the evolution of the mass accretion rates (Ṁ_acc) in pre-main-sequence stars is limited by the lack of accurate measurements of Ṁ_acc over homogeneous and large statistical samples of young stars. Such observational effort is needed to properly constrain the theory of star formation and disk evolution. Based on Hubble Space Telescope/WFPC2 observations, we present a study of Ṁ_acc for a sample of ~700 sources in the Orion Nebula Cluster, ranging from the hydrogen-burning limit to M_* ~ 2 M_☉. We derive Ṁ_acc from both the U-band excess and the Hα luminosity (L_Hα), after determining empirically both the shape of the typical accretion spectrum across the Balmer jump and the relation between the accretion luminosity (L acc) and L_Hα, which is L_acc/L_☉ = (1.31 ± 0.03) ⋅ L_Hα/L_☉ + (2.63 ± 0.13). Given our large statistical sample, we are able to accurately investigate relations between Ṁ_acc and the parameters of the central star such as mass and age. We clearly find Ṁ_acc to increase with stellar mass and decrease over evolutionary time, but we also find strong evidence that the decay of Ṁ_acc with stellar age occurs over longer timescales for more massive PMS stars. Our best-fit relation between these parameters is given by log(Ṁ_acc)/M_☉ yr) = (–5.12 ± 0.86) – (0.46 ± 0.13) ⋅ log(t/yr) – (5.75 ± 1.47) ⋅ log(M */M ☉) + (1.17 ± 0.23) ⋅ log(t/yr) ⋅ log(M_*/M_☉). These results also suggest that the similarity solution model could be revised for sources with M_* ≳ 0.5 M_☉. Finally, we do not find a clear trend indicating environmental effects on the accretion properties of the sources.

We examine the tidal disruption event scenario to explain Sw 1644+57, a powerful and persistent X-ray source which suddenly became active as GRB 110328A. The precise localization at the center of a z=0.35 galaxy argues for activity of the central engine as the underlying cause. We look at the suggestion by Bloom et al of the possibility of a tidal disruption event (TDE). We argue that Sw 1644+57 cannot be explained by the traditional TDE model in which the periastron distance is close to the tidal disruption radius - three independent lines of argument indicate the orbit must be deeply plunging or else the powerful jet we are observing could not be produced. These arguments stem from (i) comparing the early X-ray light curve to the expected theoretical fallback rate, (ii) looking at the time of transition to disk-dominated decay, and (iii) considering the TDE rate. Due to the extreme excess in the tidal force above that which would be required minimally to disrupt the star in a deeply plunging orbit at periastron, we suggest this scenario might be referred to more descriptively as a TOE (tidal obliteration event) rather than a TDE., 7 pages, 2 figures, accepted by the Astrophysical Journal, major revisions since vers. [1]; corrupted file in vers. [2] replaced