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Planetesimal belts are ubiquitous around nearby stars, and their spatial properties hold crucial information for planetesimal and planet formation models. We present resolved dust observations of 74 planetary systems as part of the REsolved ALMA and SMA Observations of Nearby Stars (REASONS) survey and archival reanalysis. We uniformly modelled interferometric visibilities for the entire sample to obtain the basic spatial properties of each belt, and combined these with constraints from multi-wavelength photometry. We report key findings from a first exploration of this legacy dataset: (1) Belt dust masses are depleted over time in a radially dependent way, with dust being depleted faster in smaller belts, as predicted by collisional evolution. (2) Most belts are broad discs rather than narrow rings, with much broader fractional widths than rings in protoplanetary discs. We link broad belts to either unresolved substructure or broad planetesimal discs produced if protoplanetary rings migrate. (3) The vertical aspect ratios (h = H/R) of 24 belts indicate orbital inclinations of 1-20 degrees, implying relative particle velocities of 0.1-4 km/s, and no clear evolution of heights with system age. This could be explained by early stirring within the belt by large bodies (with sizes of at least 140 km to the size of the Moon), by inheritance of inclinations from the protoplanetary disc stage, or by a diversity in evolutionary pathways and gravitational stirring mechanisms. We release the REASONS legacy multidimensional sample of millimetre-resolved belts to the community as a valuable tool for follow-up multi-wavelength observations and population modelling studies., Comment: Published in A&A, 693, A151. 27 pages, 15 figures, 3 tables

Substructures in disc density are ubiquitous in the bright extended discs that are observed with high resolution. These substructures are intimately linked to the physical mechanisms driving planet formation and disc evolution. Surveys of star-forming regions find that most discs are in fact compact, less luminous, and do not exhibit these same substructures. It remains unclear whether compact discs also have similar substructures or if they are featureless. This suggests that different planet formation and disc evolution mechanisms operate in these discs. We investigated evidence of substructure within two compact discs around the stars Sz 65 and Sz 66 using high angular resolution observations with ALMA at 1.3 mm. The two stars form a wide-binary system with 6.36 arcsec separation. The continuum observations achieve a synthesised beam major axis of 0.026 arcsec, equivalent to about 4.0 au, enabling a search for substructure on these spatial scales and a characterisation of the gas and dust disc sizes with high precision. We analysed the data in the image plane through an analysis of reconstructed images, as well as in the uv plane by modelling the visibilities and by an analysis of the 12CO emission line. Comparisons were made with high-resolution observations of compact discs and radially extended discs. We find evidence of substructure in the dust distribution of Sz 65, namely a shallow gap centred at approximately 20 au, with an emission ring exterior to it. Ninety percent of the measured continuum flux is found within 27 au, and the distance for 12CO is 142 au. The observations show that Sz 66 is very compact: 90 per cent of the continuum flux is contained within 16 au, and 48 au for the gas. While the overall prevalence and diversity of substructure in compact discs relative to larger discs is yet to be determined, we find evidence that substructures can exist in compact discs.

Understanding the formation of substructures in protoplanetary disks is vital for gaining insights into dust growth and the process of planet formation. Studying these substructures in highly embedded Class 0 objects using the Atacama Large Millimeter/submillimeter Array (ALMA), however, poses significant challenges. Nonetheless, it is imperative to do so to unravel the mechanisms and timing behind the formation of these substructures. In this study, we present high-resolution ALMA data at Bands 6 and 4 of the NGC1333 IRAS4A Class 0 protobinary system. This system consists of two components, A1 and A2, separated by 1.8" and located in the Perseus molecular cloud at $\sim$293 pc distance. To gain a comprehensive understanding of the dust properties and formation of substructures in the early stages, we conducted a multi-wavelength analysis of IRAS4A1. Additionally, we sought to address whether the lack of observed substructures in very young disks, could be attributed to factors such as high degrees of disk flaring and large scale heights. To explore this phenomenon, we employed radiative transfer models using RADMC-3D. Our multi-wavelength analysis of A1 discovered characteristics such as high dust surface density, substantial dust mass within the disk, and elevated dust temperatures. These findings suggest the presence of large dust grains compared to the ones in the interstellar medium (ISM), greater than 100 microns in size within the region. Furthermore, while there's no direct detection of any substructure, our models indicate that some, such as a small gap, must be present. In summary, this result implies that disk substructures may be masked or obscured by a large scale height in combination with a high degree of flaring in Class 0 disks. [Abridged], Comment: Accepted for publication in A&A, 13 pages, 7 figures

[abridged] We present new scattered light and millimeter observations of the protoplanetary disk around LkH$\alpha\,330$, using SPHERE/VLT and ALMA, respectively. The scattered-light SPHERE observations reveal an asymmetric ring at around 45au from the star in addition to two spiral arms with similar radial launching points at around 90au. The millimeter observations from ALMA (resolution of 0.06''$\times$0.04'') mainly show an asymmetric ring located at 110au from the star. In addition to this asymmetry, there are two faint symmetric rings at 60au and 200au. The $^{12}$CO, $^{13}$CO, and C$^{18}$O lines seem to be less abundant in the inner disk (these observations have a resolution of 0.16''$\times$0.11''). The $^{13}$CO peaks at a location similar to the inner ring observed with SPHERE, suggesting that this line is optically thick and traces variations of disk temperature instead of gas surface-density variations, while the C$^{18}$O peaks slightly further away at around 60au. We compare our observations with hydrodynamical simulations that include gas and dust evolution, and conclude that a 10$M_{\rm{Jup}}$ mass planet at 60au and in an eccentric orbit ($e=0.1$) can qualitatively explain most of the observed structures. A planet in a circular orbit leads to a much narrower concentration in the millimeter emission, while a planet in a more eccentric orbit leads to a very eccentric cavity as well. In addition, the outer spiral arm launched by the planet changes its pitch angle along the spiral due to the eccentricity and when it interacts with the vortex, potentially appearing in observations as two distinct spirals. Our observations and models show that LkH$\alpha\,330$ is an interesting target to search for (eccentric-) planets while they are still embedded in their parental disk, making it an excellent candidate for studies on planet-disk interaction., Comment: Accepted for publication in A&A, minor changes after language edition

We present \textit{ALMA} 1.3 mm and 0.86 mm observations of the nearby (17.34 pc) F9V star q1 Eri (HD 10647, HR 506). This system, with age ${\sim}1.4$ Gyr, hosts a ${\sim}2$ au radial velocity planet and a debris disc with the highest fractional luminosity of the closest 300 FGK type stars. The \textit{ALMA} images, with resolution ${\sim}0.5''$, reveal a broad (34{-}134 au) belt of millimeter emission inclined by $76.7{\pm}1.0$ degrees with maximum brightness at $81.6{\pm}0.5$ au. The images reveal an asymmetry, with higher flux near the southwest ansa, which is also closer to the star. Scattered light observed with the Hubble Space Telescope is also asymmetric, being more radially extended to the northeast. We fit the millimeter emission with parametric models and place constraints on the disc morphology, radius, width, dust mass, and scale height. We find the southwest ansa asymmetry is best fitted by an extended clump on the inner edge of the disc, consistent with perturbations from a planet with mass $8 M_{\oplus} {-} 11 M_{\rm Jup}$ at ${\sim}60$ au that may have migrated outwards, similar to Neptune in our Solar System. If the measured vertical aspect ratio of $h{=}0.04{\pm}0.01$ is due to dynamical interactions in the disc, then this requires perturbers with sizes ${>}1200$ km. We find tentative evidence for an 0.86 mm excess within 10 au, $70{\pm}22\, \mu$Jy, that may be due to an inner planetesimal belt. We find no evidence for CO gas, but set an upper bound on the CO gas mass of $4{\times}10^{-6}$ M$_{\oplus}$ ($3\,\sigma$), consistent with cometary abundances in the Solar System., Comment: Accepted for publication in MNRAS. Paper: 21 pages, appendix: 4 pages. 16 figures

The radio spectra of main-sequence stars remain largely unconstrained due to the lack of observational data to inform stellar atmosphere models. As such, the dominant emission mechanisms at long wavelengths, how they vary with spectral type, and how much they contribute to the expected brightness at a given radio wavelength are still relatively unknown for most spectral types. We present radio continuum observations of Altair, a rapidly rotating A-type star. We observed Altair with NOEMA in 2018 and 2019 at 1.34 mm, 2.09 mm, and 3.22 mm and with the VLA in 2019 at 6.7 mm and 9.1 mm. In the radio spectra, we see a brightness temperature minimum at millimeter wavelengths followed by a steep rise to temperatures larger than the optical photosphere, behavior that is unexpected for A-type stars. We use these data to produce the first sub-millimeter to centimeter spectrum of a rapidly rotating A-type star informed by observations. We generated both PHOENIX and KINICH-PAKAL model atmospheres and determine the KINICH-PAKAL model better reproduces Altair's radio spectrum. The synthetic spectrum shows a millimeter brightness temperature minimum followed by significant emission over that of the photosphere at centimeter wavelengths. Together, these data and models show how the radio spectrum of an A-type star can reveal the presence of a chromosphere, likely induced by rapid rotation, and that a Rayleigh Jean's extrapolation of the stellar photosphere is not an adequate representation of a star's radio spectrum., Comment: 11 pages, 3 figures, accepted to ApJL

To determine the origin of the spiral structure observed in the dust continuum emission of Elias 2-27 we analyze multi-wavelength continuum ALMA data with a resolution of $\sim$0.2 arcsec ($\sim$23au) at 0.89, 1.3 and 3.3mm. We also study the kinematics of the disk with $^{13}$CO and C$^{18}$O ALMA observations in the $J=$3-2 transition. The spiral arm morphology is recovered at all wavelengths in the dust continuum observations, where we measure contrast and spectral index variations along the spiral arms and detect subtle dust-trapping signatures. We determine that the emission from the midplane is cold and interpret the optical depth results as signatures of a higher disk mass than previous constraints. From the gas data, we search for deviations from Keplerian motion and trace the morphology of the emitting surfaces and the velocity profiles. We find an azimuthally varying emission layer height in the system, large-scale emission surrounding the disk, and strong perturbations in the channel maps, co-located with the spirals. Additionally, we develop multigrain dust and gas SPH simulations of a gravitationally unstable disk and compare them to the observations. Given the large scale emission and highly perturbed gas structure, together with the comparison of continuum observations to theoretical predictions, we propose infall-triggered gravitational instabilities as origin for the observed spiral structure., Comment: Accepted for publication in ApJ, 38 pages, 23 Figures

We present new Jansky Very Large Array (VLA) images of the central region of the W49A star-forming region at 3.6~cm and at 7~mm at resolutions of 0\farcs15 (1650 au) and 0\farcs04 (440 au), respectively. The 3.6~cm data reveal new morphological detail in the ultracompact \ion{H}{2} region population, as well as several previously unknown and unresolved sources. In particular, source A shows elongated, edge-brightened, bipolar lobes, indicative of a collimated outflow, and source E is resolved into three spherical components. We also present VLA observations of radio recombination lines at 3.6~cm and 7~mm, and IRAM Northern Extended Millimeter Array (NOEMA) observations at 1.2~mm. Three of the smallest ultracompact \ion{H}{2} regions (sources A, B2 and G2) all show broad kinematic linewidths, with $\Delta$V$_{FWHM}\gtrsim$40~km~s$^{-1}$. A multi-line analysis indicates that broad linewidths remain after correcting for pressure broadening effects, suggesting the presence of supersonic flows. Substantial changes in linewidth over the 21 year time baseline at both 3.6 cm and 7 mm are found for source G2. At 3.6 cm, the linewidth of G2 changed from 31.7$\pm$1.8 km s$^{-1}$ to 55.6$\pm$2.7 km s$^{-1}$, an increase of $+$23.9$\pm$3.4 km s$^{-1}$. The G2 source was previously reported to have shown a 3.6~cm continuum flux density decrease of 40\% between 1994 and 2015. This source sits near the center of a very young bipolar outflow whose variability may have produced these changes., Comment: 18 pages, 7 figures, Accepted for publication in The Astronomical Journal

The spectrum of stars in the submillimeter to centimeter wavelength range remains poorly constrained due to a lack of data for most spectral types. An accurate characterization of stellar emission in this regime is needed to test stellar atmosphere models, and is also essential for revealing emission associated with unresolved circumstellar debris. We present ALMA observations of the three nearby, main-sequence, debris-poor, F-type stars $\gamma$ Lep, $\gamma$ Vir A, and $\gamma$ Vir B at 0.87 and 1.29 millimeters. We use these data to constrain semi-empirical atmospheric models. We discuss the atmospheric structure of these stars, explore potential short term variability, and the potential impact on debris disk studies. These results are part of an ongoing campaign to obtain long wavelength observations of debris-poor stars, entitled Measuring the Emission of Stellar Atmospheres at Submillimeter/millimeter wavelengths (MESAS)., Comment: Accepted to ApJ, 13 pages, 7 figures

Observations of young stellar objects (YSOs) in centimeter bands can probe the continuum emission from growing dust grains, ionized winds, and magnetospheric activity, which are intimately connected to the evolution of protoplanetary disks and the formation of planets. We have carried out sensitive continuum observations toward the Ophiuchus A star-forming region using the Karl G. Jansky Very Large Array (VLA) at 10 GHz over a field-of-view of 6$'$ with a spatial resolution of $\theta_{maj}$ $\times$ $\theta_{min}$ $\sim$ 0.4$''$ $\times$ 0.2$''$. We achieved a 5 $\mu$Jy beam$^{-1}$ root-mean-square noise level at the center of our mosaic field of view. Among the eighteen sources we detected, sixteen are YSOs (three Class 0, five Class I, six Class II, and two Class III) and two are extragalactic candidates. We find that thermal dust emission generally contributes less that 30% of the emission at 10 GHz. The radio emission is dominated by other types of emission such as gyro-synchrotron radiation from active magnetospheres, free-free emission from thermal jets, free-free emission from the outflowing photo-evaporated disk material, and/or synchrotron emission from accelerated cosmic-rays in jet or protostellar surface shocks. These different types of emission could not be clearly disentangled. Our non-detections towards Class II/III disks suggest that extreme UV-driven photoevaporation is insufficient to explain the disk dispersal, assuming that the contribution of UV photoevaporating stellar winds to radio flux does not evolve with time. The sensitivity of our data cannot exclude photoevaporation due to X-ray photons as an efficient mechanism for disk dispersal. Deeper surveys with the Square Kilometre Array will be able to provide strong constraints on disk photoevaporation., Comment: Accepted in A&A

We present observations of the HD 15115 debris disk from ALMA at 1.3 mm that capture this intriguing system with the highest resolution ($0.\!\!^{\prime\prime}6$ or $29$ AU) at millimeter wavelengths to date. This new ALMA image shows evidence for two rings in the disk separated by a cleared gap. By fitting models directly to the observed visibilities within a MCMC framework, we are able to characterize the millimeter continuum emission and place robust constraints on the disk structure and geometry. In the best-fit model of a power law disk with a Gaussian gap, the disk inner and outer edges are at $43.9\pm5.8$ AU ($0.\!\!^{\prime\prime}89\pm0.\!\!^{\prime\prime}12$) and $92.2\pm2.4$ AU ($1.\!\!^{\prime\prime}88\pm0.\!\!^{\prime\prime}49$), respectively, with a gap located at $58.9\pm4.5$~AU ($1.\!\!^{\prime\prime}2\pm0.\!\!^{\prime\prime}10$) with a fractional depth of $0.88\pm0.10$ and a width of $13.8\pm5.6$ AU ($0.\!\!^{\prime\prime}28\pm0.\!\!^{\prime\prime}11$). Since we do not see any evidence at millimeter wavelengths for the dramatic east-west asymmetry seen in scattered light, we conclude that this feature most likely results from a mechanism that only affects small grains. Using dynamical modeling and our constraints on the gap properties, we are able to estimate a mass for the possible planet sculpting the gap to be $0.16\pm0.06$ $M_\text{Jup}$., Comment: 9 pages, 4 figures, accepted to ApJL on May 15, 2019

We write in response to the call from the 2020 Decadal Survey to submit white papers illustrating the most pressing scientific questions in astrophysics for the coming decade. We propose exploration as the central question for the Decadal Committee's discussions.The history of astronomy shows that paradigm changing discoveries are not driven by well formulated scientific questions, based on the knowledge of the time. They were instead the result of the increase in discovery space fostered by new telescopes and instruments. An additional tool for increasing the discovery space is provided by the analysis and mining of the increasingly larger amount of archival data available to astronomers. Revolutionary observing facilities, and the state of the art astronomy archives needed to support these facilities, will open up the universe to new discovery. Here we focus on exploration for compact objects and multi messenger science. This white paper includes science examples of the power of the discovery approach, encompassing all the areas of astrophysics covered by the 2020 Decadal Survey.

We present ALMA 1.3 mm (230 GHz) observations of the HD 32297 and HD 61005 debris disks, two of the most iconic debris disks due to their dramatic swept-back wings seen in scattered light images. These observations achieve sensitivities of 14 and 13 $\mu$Jy beam$^{-1}$ for HD 32297 and HD 61005, respectively, and provide the highest resolution images of these two systems at millimeter wavelengths to date. By adopting a MCMC modeling approach, we determine that both disks are best described by a two-component model consisting of a broad ($\Delta R/R> 0.4$) planetesimal belt with a rising surface density gradient, and a steeply falling outer halo aligned with the scattered light disk. The inner and outer edges of the planetesimal belt are located at $78.5\pm8.1$ AU and $122\pm3$ AU for HD 32297, and $41.9\pm0.9$ AU and $67.0\pm0.5$ AU for HD 61005. The halos extend to $440\pm32$ AU and $188\pm8$ AU, respectively. We also detect $^{12}$CO J$=2-1$ gas emission from HD 32297 co-located with the dust continuum. These new ALMA images provide observational evidence that larger, millimeter-sized grains may also populate the extended halos of these two disks previously thought to only be composed of small, micron-sized grains. We discuss the implications of these results for potential shaping and sculpting mechanisms of asymmetric debris disks., Comment: 17 pages, 5 figures, published in ApJ

The presence of a debris disc around the Gyr-old solar-type star $\zeta^2\,\mathrm{Reticuli}$ was suggested by the $\mathit{Spitzer}$ infrared excess detection. Follow-up observations with $\mathit{Herschel}$/PACS revealed a double-lobed feature, that displayed asymmetries both in brightness and position. Therefore, the disc was thought to be edge-on and significantly eccentric. Here we present ALMA/ACA observations in Band 6 and 7 which unambiguously reveal that these lobes show no common proper motion with $\zeta^2\,\mathrm{Reticuli}$. In these observations, no flux has been detected around $\zeta^2\,\mathrm{Reticuli}$ that exceeds the $3\sigma$ levels. We conclude that surface brightness upper limits of a debris disc around $\zeta^2\,\mathrm{Reticuli}$ are $5.7\,\mathrm{\mu Jy/arcsec^2}$ at 1.3 mm, and $26\,\mathrm{\mu Jy/arcsec^2}$ at 870 microns. Our results overall demonstrate the capability of the ALMA/ACA to follow-up $\mathit{Herschel}$ observations of debris discs and clarify the effects of background confusion., Comment: 6 pages, 2 figures, 2 tables

A number of ultracompact H II regions in Galactic star forming environments have been observed to vary significantly in radio flux density on timescales of 10-20 years. Theory predicted that such variations should occur when the accretion flow that feeds a young massive star becomes unstable and clumpy. We have targeted the massive star-forming region W49A with the Karl G. Jansky Very Large Array (VLA) for observations at 3.6 cm with the B-configuration at 0.8'' resolution, to compare to nearly identical observations taken almost 21 years earlier (February 2015 and August 1994). Most of the sources in the crowded field of ultracompact and hypercompact H II regions exhibit no significant changes over this time period. However, one source, W49A/G2, decreased by 20% in peak intensity (from 71+/-4 mJy/beam to 57+/-3 mJy/beam), and 40% in integrated flux (from 0.109+/-0.011 Jy to 0.067+/-0.007 Jy), where we cite 5 sigma errors in peak intensity, and 10% errors in integrated flux. We present the radio images of the W49A region at the two epochs, the difference image that indicates the location of the flux density decrease, and discuss explanations for the flux density decrease near the position of W49A/G2., Comment: 9 pages, 2 figures, accepted for publication, The Astrophysical Journal Letters, July 26, 2018

We present a suite of ALMA interferometric molecular line and continuum images that elucidate, on linear size scales of $\sim$30--40 AU, the chemical structure of the nearby, evolved, protoplanetary disk orbiting the close binary system V4046 Sgr. The observations were undertaken in the 1.1--1.4 mm wavelength range (ALMA Bands 6 and 7) with antenna configurations involving maximum baselines of several hundred meters, yielding subarcsecond-resolution images in more than a dozen molecular species and isotopologues. Isotopologues of CO and HCN display centrally peaked morphologies of integrated emission line intensity, whereas the line emission from complex nitrile group molecules (HC$_3$N, CH$_3$CN), deuterated molecules (DCN, DCO$^+$), hydrocarbons (as traced by C$_2$H), and potential CO ice line tracers (N$_2$H$^+$, and H$_2$CO) appears as a sequence of sharp and diffuse rings. The dimensions and morphologies of HC$_3$N and CH$_3$CN emission are suggestive of photodesorption of organic ices from the surfaces of dust grains, while the sequence of increasing radius of peak intensity represented by DCN (smallest), DCO$^+$, N$_2$H$^+$, and H$_2$CO (largest) is qualitatively consistent with the expected decline of midplane gas temperature with increasing disk radius. Empirical modeling indicates that the sharp-edged C$_2$H emission ring lies at relatively deep disk layers, leaving open the question of the origin of C$_2$H abundance enhancements in evolved disks. This study of the "molecular anatomy" of V4046 Sgr should serve as motivation for additional subarcsecond ALMA molecular line imaging surveys of nearby, evolved protoplanetary disks aimed at addressing major uncertainties in protoplanetary disk physical and chemical structure and molecular production pathways., Comment: 32 pages, 10 figures; accepted 26 June 2018 by The Astrophysical Journal

We aim to reproduce the DCO$^+$ emission in the disk around HD163296 using a simple 2D chemical model for the formation of DCO$^+$ through the cold deuteration channel and a parametric treatment of the warm deuteration channel. We use data from ALMA in band 6 to obtain a resolved spectral imaging data cube of the DCO$^+$ $J$=3--2 line in HD163296 with a synthesized beam of 0."53$\times$ 0."42. We adopt a physical structure of the disk from the literature that reproduces the spectral energy distribution. We then apply a simplified chemical network for the formation of DCO$^+$ that uses the physical structure of the disk as parameters along with a CO abundance profile, a constant HD abundance and a constant ionization rate. Finally, from the resulting DCO$^+$ abundances, we calculate the non-LTE emission using the 3D radiative transfer code LIME. The observed DCO$^+$ emission is reproduced by a model with cold deuteration producing abundances up to $1.6\times 10^{-11}$. Warm deuteration, at a constant abundance of $3.2\times 10^{-12}$, becomes fully effective below 32 K and tapers off at higher temperatures, reproducing the lack of DCO$^+$ inside 90 AU. Throughout the DCO$^+$ emitting zone a CO abundance of $2\times 10^{-7}$ is found, with $\sim$99\% of it frozen out below 19 K. At radii where both cold and warm deuteration are active, warm deuteration contributes up to 20\% of DCO$^+$, consistent with detailed chemical models. The decrease of DCO$^+$ at large radii is attributed to a temperature inversion at 250 AU, which raises temperatures above values where cold deuteration operates. Increased photodesorption may also limit the radial extent of DCO$^+$. The corresponding return of the DCO$^+$ layer to the midplane, together with a radially increasing ionization fraction, reproduces the local DCO$^+$ emission maximum at $\sim$260 AU., Comment: 9 pages, 5 figures, accepted 7th July 2018

Resolved observations of millimetre-sized dust, tracing larger planetesimals, have pinpointed the location of 26 Edgeworth-Kuiper belt analogs. We report that a belt's distance $R$ to its host star correlates with the star's luminosity $L_{\star}$, following $R\propto L^{0.19}_{\star}$ with a low intrinsic scatter of $\sim$17%. Remarkably, our Edgeworth-Kuiper belt in the Solar System and the two CO snow lines imaged in protoplanetary disks lie close to this $R$-$L_{\star}$ relation, suggestive of an intrinsic relationship between protoplanetary disk structures and belt locations. To test the effect of bias on the relation, we use a Monte Carlo approach and simulate uncorrelated model populations of belts. We find that observational bias could produce the slope and intercept of the $R$-$L_{\star}$ relation, but is unable to reproduce its low scatter. We then repeat the simulation taking into account the collisional evolution of belts, following the steady state model that fits the belt population as observed through infrared excesses. This significantly improves the fit by lowering the scatter of the simulated $R$-$L_{\star}$ relation; however, this scatter remains only marginally consistent with the one observed. The inability of observational bias and collisional evolution alone to reproduce the tight relationship between belt radius and stellar luminosity could indicate that planetesimal belts form at preferential locations within protoplanetary disks. The similar trend for CO snow line locations would then indicate that the formation of planetesimals and/or planets in the outer regions of planetary systems is linked to the volatility of their building blocks, as postulated by planet formation models., Comment: Accepted for publication in ApJ. 23 pages, 9 figures

We present Atacama Large Millimeter/sub-millimeter Array (ALMA) Cycle 2 observations of the 1.3 mm dust continuum emission of the protoplanetary disc surrounding the T Tauri star Elias 24 with an angular resolution of $\sim 0.2"$ ($\sim 28$ au). The dust continuum emission map reveals a dark ring at a radial distance of $0.47"$ ($\sim 65$ au) from the central star, surrounded by a bright ring at $0.58"$ ($\sim 81$ au). In the outer disc, the radial intensity profile shows two inflection points at $0.71"$ and $0.87"$ ($\sim 99$ and $121$ au respectively). We perform global three-dimensional smoothed particle hydrodynamic gas/dust simulations of discs hosting a migrating and accreting planet. Combining the dust density maps of small and large grains with three dimensional radiative transfer calculations, we produce synthetic ALMA observations of a variety of disc models in order to reproduce the gap- and ring-like features observed in Elias 24. We find that the dust emission across the disc is consistent with the presence of an embedded planet with a mass of $\sim 0.7\, \mathrm{M_{\mathrm{J}}}$ at an orbital radius of $\sim$ 60 au. Our model suggests that the two inflection points in the radial intensity profile are due to the inward radial motion of large dust grains from the outer disc. The surface brightness map of our disc model provides a reasonable match to the gap- and ring-like structures observed in Elias 24, with an average discrepancy of $\sim$ 5% of the observed fluxes around the gap region., Comment: 17 pages, 11 figures. Accepted for publication in MNRAS

The exocometary origin of CO gas has been confirmed in several extrasolar Kuiper belts, with CO ice abundances consistent with Solar System comets. We here present a molecular survey of the $\beta$ Pictoris belt with the Submillimeter Array (SMA), reporting upper limits for CN, HCN, HCO$^+$, N$_2$H$^+$ and H$_2$CO, as well as for H$_2$S, CH$_3$OH, SiO and DCN from archival ALMA data. Non-detections can be attributed to rapid molecular photodissociation due to the A-star's strong UV flux. CN is the longest-lasting and most easily detectable molecule after CO in this environment. We update our NLTE excitation model to include UV fluorescence, finding it plays a key role in CO and CN excitation, and use it to turn the SMA CN/CO flux ratio constraint into an upper limit of $<2.5$% on the HCN/(CO+CO$_2$) ratio of outgassing rates. This value is consistent with, but at the low end of, the broad range observed in Solar System comets. If sublimation dominates outgassing, then this low value may be caused by decreased outgassing for the less volatile molecule HCN compared to CO. If instead UV photodesorption or collisional vaporization of unbound grains dominates outgassing, then this low ratio of rates would imply a low ice abundance ratio, which would in turn indicate a variation in cometary cyanide abundances across planetary systems. To conclude, we make predictions for future molecular surveys and show that CN and HCN should be readily detectable with ALMA around $\beta$ Pictoris for Solar-System-like exocometary compositions., Comment: Accepted for publication in ApJ. 19 pages, 7 figures

We present VLA 9 mm (33 GHz) observations of the HD 141569 system from semester 16A. The observations achieve a resolution of 0.25 arcsec ($\sim28$ au) and a sensitivity of $4.7~\mu \rm Jy~beam^{-1}$. We find (1) a $52\pm 5~\mu$Jy point source at the location of HD 141569A that shows potential variability, (2) the detected flux is contained within the SED-inferred central clearing of the disc meaning the spectral index of the dust disc is steeper than previously inferred, and (3) the M dwarf companions are also detected and variable. Previous lower-resolution VLA observations (semester 14A) found a higher flux density, interpreted as solely dust emission. When combined with ALMA observations, the VLA 14A observations suggested the spectral index and grain size distribution of HD 141569's disc was shallow and an outlier among debris systems. Using archival ALMA observations of HD 141569 at 0.87 mm and 2.9 mm we find a dust spectral index of $\alpha_{\rm mm} = 1.81\pm 0.20$. The VLA 16A flux corresponds to a brightness temperature of $\sim5\times10^{6}$ K, suggesting strong non-disc emission is affecting the inferred grain properties. The VLA 16A flux density of the M2V companion HD 141569B is $149\pm9~\mu$Jy, corresponding to a brightness temperature of $\sim2\times10^{8}$ K and suggesting significant stellar variability when compared to the VLA14A observations, which are smaller by a factor of $\sim6$., Comment: Accepted for publication in MNRAS, 8 pages, 6 figures

The formation pathways of deuterated species trace different regions of protoplanetary disks and may shed light into their physical structure. We aim to constrain the radial extent of main deuterated species; we are particularly interested in spatially characterizing the high and low temperature pathways for enhancing deuteration of these species. We observed the disk surrounding the Herbig Ae star HD 163296 using ALMA in Band 6 and obtained resolved spectral imaging data of DCO$^+$ ($J$=3-2), DCN ($J$=3-2) and N$_2$D$^+$ ($J$=3-2). We model the radial emission profiles of DCO$^+$, DCN and N$_2$D$^+$, assuming their emission is optically thin, using a parametric model of their abundances and radial excitation temperature estimates. DCO$^+$ can be described by a three-region model, with constant-abundance rings centered at 70 AU, 150 AU and 260 AU. The DCN radial profile peaks at about ~60 AU and N$_2$D$^+$ is seen in a ring at ~160 AU. Simple models of both molecules using constant abundances reproduce the data. Assuming reasonable average excitation temperatures for the whole disk, their disk-averaged column densities (and deuterium fractionation ratios) are 1.6-2.6$\times 10^{12}$ cm$^{-2}$ (0.04-0.07), 2.9-5.2$\times 10^{12}$ cm$^{-2}$ ($\sim$0.02) and 1.6-2.5 $\times 10^{11}$ cm$^{-2}$ (0.34-0.45) for DCO$^+$, DCN and N$_2$D$^+$, respectively. Our simple best-fit models show a correlation between the radial location of the first two rings in DCO$^+$ and the DCN and N$_2$D$^+$ abundance distributions that can be interpreted as the high and low temperature deuteration pathways regimes. The origin of the third DCO$^+$ ring at 260 AU is unknown but may be due to a local decrease of ultraviolet opacity allowing the photodesorption of CO or due to thermal desorption of CO as a consequence of radial drift and settlement of dust grains.

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

Several studies support the existence of a link between the AGN and star formation activity. Radio jets have been argued to be an ideal mechanism for direct interaction between the AGN and the host galaxy. A drawback of previous surveys of AGN is that they are fundamentally limited by the degeneracy between redshift and luminosity in flux-density limited samples. To overcome this limitation, we present far-infrared Herschel observations of 74 radio-loud quasars (RLQs), 72 radio-quiet quasars (RQQs) and 27 radio galaxies (RGs), selected at 0.9

Three formaldehyde lines were observed (H$_2$CO 3$_{03}$--2$_{02}$, H$_2$CO 3$_{22}$--2$_{21}$, and H$_2$CO 3$_{21}$--2$_{20}$) in the protoplanetary disk around the Herbig Ae star HD 163296 with ALMA at 0.5 arcsecond (60 AU) spatial resolution. H$_2$CO 3$_{03}$--2$_{02}$ was readily detected via imaging, while the weaker H$_2$CO 3$_{22}$--2$_{21}$ and H$_2$CO 3$_{21}$--2$_{20}$ lines required matched filter analysis to detect. H$_2$CO is present throughout most of the gaseous disk, extending out to 550 AU. An apparent 50 AU inner radius of the H$_2$CO emission is likely caused by an optically thick dust continuum. The H$_2$CO radial intensity profile shows a peak at 100 AU and a secondary bump at around 300 AU, suggesting increased production in the outer disk. Different parameterizations of the H$_2$CO abundance were compared to the observed visibilities with $\chi^2$ minimization, using either a characteristic temperature, a characteristic radius or a radial power law index to describe the H$_2$CO chemistry. Similar models were applied to ALMA Science Verification data of C$^{18}$O. In all modeling scenarios, fits to the H$_2$CO data show an increased abundance in the outer disk. The overall best-fit H$_2$CO model shows a factor of two enhancement beyond a radius of 270$\pm$20 AU, with an inner abundance of $2\!-\!5 \times 10^{-12}$. The H$_2$CO emitting region has a lower limit on the kinetic temperature of $T > 20$ K. The C$^{18}$O modeling suggests an order of magnitude depletion in the outer disk and an abundance of $4\!-\!12 \times 10^{-8}$ in the inner disk. The increase in H$_2$CO outer disk emission could be a result of hydrogenation of CO ices on dust grains that are then sublimated via thermal desorption or UV photodesorption, or more efficient gas-phase production beyond about 300 AU if CO is photodisocciated in this region.

Recent ALMA observations present mounting evidence for the presence of exocometary gas released within Kuiper belt analogues around nearby main sequence stars. This represents a unique opportunity to study their ice reservoir at the younger ages when volatile delivery to planets is most likely to occur. We here present the detection of CO J=2-1 emission co-located with dust emission from the cometary belt in the 440 Myr-old Fomalhaut system. Through spectro-spatial filtering, we achieve a 5.4$\sigma$ detection and determine that the ring's sky-projected rotation axis matches that of the star. The CO mass derived ($0.65-42 \times10^{-7}$ M$_{\oplus}$) is the lowest of any circumstellar disk detected to date, and must be of exocometary origin. Using a steady state model, we estimate the CO+CO$_2$ mass fraction of exocomets around Fomalhaut to be between 4.6-76%, consistent with Solar System comets and the two other belts known to host exocometary gas. This is the first indication of a similarity in cometary compositions across planetary systems that may be linked to their formation scenario and is consistent with direct ISM inheritance. In addition, we find tentative evidence that $(49\pm 27)$% of the detected flux originates from a region near the eccentric belt's pericentre. If confirmed, the latter may be explained through a recent impact event or CO pericentre glow due to exocometary release within a steady state collisional cascade. In the latter scenario, we show how the azimuthal dependence of the CO release rate leads to asymmetries in gas observations of eccentric exocometary belts., Comment: Accepted for publication in ApJ. 17 pages, 8 figures

The GW Ori system is a pre-main sequence triple system (GW Ori A/B/C) with companions (GW Ori B/C) at $\sim$1 AU and $\sim$8 AU, respectively, from the primary (GW Ori A). The primary of the system has a mass of 3.9 $M_{\odot}$, but shows a spectral type of G8. Thus, GW Ori A could be a precursor of a B star, but it is still at an earlier evolutionary stage than Herbig Be stars. GW Ori provides us an ideal target for experiments and observations (being a "blown-up" upscaled Solar System with a very massive "sun" and at least two "upscaled planets"). We present the first spatially-resolved millimeter interferometric observations of the disk around the triple pre-main-sequence system GW Ori, obtained with the the Submillimeter Array, both in continuum and in the $^{12}{\rm CO} J=2-1$, $^{13}{\rm CO} J=2-1$, and ${\rm C^{18}O} J=2-1$ lines. These new data reveal a huge, massive, and bright disk in the GW Ori system. The dust continuum emission suggests a disk radius around 400 AU. But, the $^{12}{\rm CO} J=2-1$ emission shows much more extended disk with a size around 1300 AU. Due to the spatial resolution ($\sim$1$"$), we cannot detect the gap in the disk which is inferred from spectral energy distribution (SED) modeling. We characterize the dust and gas properties in the disk by comparing the observations with the predictions from the disk models with various parameters calculated with a Monte Carlo radiative transfer code RADMC-3D. The disk mass is around 0.12 $M_{\odot}$, and the disk inclination with respect to the line of sight is around $\sim$ 35$^\circ$. The kinematics in the disk traced by the CO line emission strongly suggest that the circumstellar material in the disk is in Keplerian rotation around GW Ori. Tentatively substantial ${\rm C^{18}O}$ depletion in gas phase is required to explain the characteristics of the line emission from the disk., Comment: 10 pages, 8 Figure, 3 tables, Accepted by A&A

We present ~0.4 resolution images of CO(3-2) and associated continuum emission from the gas-bearing debris disk around the nearby A star 49 Ceti, observed with the Atacama Large Millimeter/Submillimeter Array (ALMA). We analyze the ALMA visibilities in tandem with the broad-band spectral energy distribution to measure the radial surface density profiles of dust and gas emission from the system. The dust surface density decreases with radius between ~100 and 310 au, with a marginally significant enhancement of surface density at a radius of ~110 au. The SED requires an inner disk of small grains in addition to the outer disk of larger grains resolved by ALMA. The gas disk exhibits a surface density profile that increases with radius, contrary to most previous spatially resolved observations of circumstellar gas disks. While ~80% of the CO flux is well described by an axisymmetric power-law disk in Keplerian rotation about the central star, residuals at ~20% of the peak flux exhibit a departure from axisymmetry suggestive of spiral arms or a warp in the gas disk. The radial extent of the gas disk (~220 au) is smaller than that of the dust disk (~300 au), consistent with recent observations of other gas-bearing debris disks. While there are so far only three broad debris disks with well characterized radial dust profiles at millimeter wavelengths, 49 Ceti's disk shows a markedly different structure from two radially resolved gas-poor debris disks, implying that the physical processes generating and sculpting the gas and dust are fundamentally different., Comment: 20 pages, 8 figures, accepted for publication in ApJ March 31, 2017 (submitted Nov 2016)

The presence of dusty debris around main sequence stars denotes the existence of planetary systems. Such debris disks are often identified by the presence of excess continuum emission at infrared and (sub-)millimetre wavelengths, with measurements at longer wavelengths tracing larger and cooler dust grains. The exponent of the slope of the disk emission at sub-millimetre wavelengths, `q', defines the size distribution of dust grains in the disk. This size distribution is a function of the rigid strength of the dust producing parent planetesimals. As part of the survey `PLAnetesimals around TYpical Pre-main seqUence Stars' (PLATYPUS) we observed six debris disks at 9-mm using the Australian Telescope Compact Array. We obtain marginal (~3-\sigma) detections of three targets: HD 105, HD 61005, and HD 131835. Upper limits for the three remaining disks, HD20807, HD109573, and HD109085, provide further constraint of the (sub-)millimetre slope of their spectral energy distributions. The values of q (or their limits) derived from our observations are all smaller than the oft-assumed steady state collisional cascade model (q = 3.5), but lie well within the theoretically expected range for debris disks q ~ 3 to 4. The measured q values for our targets are all < 3.3, consistent with both collisional modelling results and theoretical predictions for parent planetesimal bodies being `rubble piles' held together loosely by their self-gravity., Comment: 7 pages, 5 tables, 2 figures, accepted for publication in MNRAS

In order to look for signs of on-going planet formation in young disks, we carried out the first J-band polarized emission imaging of the Herbig Ae/Be stars HD 150193, HD 163296, and HD 169142 using the Gemini Planet Imager (GPI), along with new H band observations of HD 144432. We confirm the complex "double ring" structure for the nearly face-on system HD 169142 first seen in H-band, finding the outer ring to be substantially redder than the inner one in polarized intensity. Using radiative transfer modeling, we developed a physical model that explains the full spectral energy distribution (SED) and J- and H-band surface brightness profiles, suggesting that the differential color of the two rings could come from reddened starlight traversing the inner wall and may not require differences in grain properties. In addition, we clearly detect an elongated, off-center ring in HD 163296 (MWC 275), locating the scattering surface to be 18 AU above the midplane at a radial distance of 77 AU, co-spatial with a ring seen at 1.3mm by ALMA linked to the CO snow line. Lastly, we report a weak tentative detection of scattered light for HD 150193 (MWC 863) and a non-detection for HD 144432; the stellar companion known for each of these targets has likely disrupted the material in the outer disk of the primary star. For HD 163296 and HD 169142, the prominent outer rings we detect could be evidence for giant planet formation in the outer disk or a manifestation of large-scale dust growth processes possibly related to snow-line chemistry., Comment: Accepted Astrophysical Journal

Protoplanetary disc systems observed at radio wavelengths often show excess emission above that expected from a simple extrapolation of thermal dust emission observed at short millimetre wavelengths. Monitoring the emission at radio wavelengths can be used to help disentangle the physical mechanisms responsible for this excess, including free-free emission from a wind or jet, and chromospheric emission associated with stellar activity. We present new results from a radio monitoring survey conducted with Australia Telescope Compact Array over the course of several years with observation intervals spanning days, months and years, where the flux variability of 11 T Tauri stars in the Chamaeleon and Lupus star forming regions was measured at 7 and 15 mm and 3 and 6 cm. Results show that for most sources are variable to some degree at 7 mm, indicating the presence of emission mechanisms other than thermal dust in some sources. Additionally, evidence of grain growth to cm-sized pebbles was found for some sources that also have signs of variable flux at 7 mm. We conclude that multiple processes contributing to the emission are common in T Tauri stars at 7 mm and beyond, and that a detection at a single epoch at radio wavelengths should not be used to determine all processes contributing to the emission., Comment: Accepted 2017 January 4, Monthly Notices of the Royal Astronomical Society

While most of the known debris discs present cold dust at tens of AU, a few young systems exhibit hot dust analogous to the Zodiacal dust. $\eta$ Corvi is particularly interesting as it is old and it has both, with its hot dust significantly exceeding the maximum luminosity of an in-situ collisional cascade. Previous work suggested that this system could be undergoing an event similar to the Late Heavy Bombardment (LHB) soon after or during a dynamical instability. Here we present ALMA observations of $\eta$ Corvi with a resolution of 1."2 (~22au) to study its outer belt. The continuum emission is consistent with an axisymmetric belt, with a mean radius of 152au and radial FWHM of 46au, which is too narrow compared to models of inward scattering of an LHB-like scenario. Instead, the hot dust could be explained as material passed inwards in a rather stable planetary configuration. We also report a 4sigma detection of CO at ~ 20au. CO could be released in situ from icy planetesimals being passed in when crossing the H$_2$O or CO$_2$ ice lines. Finally, we place constraints on hidden planets in the disc. If a planet is sculpting the disc's inner edge, this should be orbiting at 75-100au, with a mass of 3-30 M$_\oplus$ and an eccentricity < 0.08. Such a planet would be able to clear its chaotic zone on a timescale shorter than the age of the system and scatter material inwards from the outer belt to the inner regions, thus feeding the hot dust., Comment: 22 pages, 16 figures. Accepted for publication in MNRAS

We present Chandra X-ray Observatory and Submillimeter Array (SMA) imaging of HBC 515, a system consisting of multiple young stellar objects (YSOs). The five members of HBC 515 represent a remarkably diverse array of YSOs, ranging from the low-mass Class I/II protostar HBC 515B, through Class II and transition disk objects (HBC 515D and C, respectively), to the "diskless", intermediate- mass, pre-main sequence binary HBC 515A. Our Chandra/ACIS imaging establishes that all five components are X-ray sources, with HBC 515A - a subarcsecond-separation binary that is partially resolved by Chandra - being the dominant X-ray source. We detect an X-ray flare associated with HBC 515B. In the SMA imaging, HBC 515B is detected as a strong 1.3 mm continuum emission source; a second, weaker mm continuum source is coincident with the position of the transition disk object HBC 515C. These results strongly support the protostellar nature of HBC 515B, and firmly establish HBC 515A as a member of the rare class of relatively massive, X-ray luminous "weak-lined T Tauri stars" that are binaries and have shed their disks at very early stages of pre-MS evolution. The coexistence of two such disparate objects within a single, presumably coeval multiple YSO system highlights the influence of pre- MS star mass, binarity, and X-ray luminosity in regulating the lifetimes of circumstellar, planet-forming disks and the timescales of star-disk interactions., Comment: Accepted for publication in A&A; 11 pages, 5 figures

Recent ALMA observations unveiled the structure of CO gas in the 23 Myr-old $\beta$ Pictoris planetary system, a component that has been discovered in many similarly young debris disks. We here present ALMA CO J=2-1 observations, at an improved spectro-spatial resolution and sensitivity compared to previous CO J=3-2 observations. We find that 1) the CO clump is radially broad, favouring the resonant migration over the giant impact scenario for its dynamical origin, 2) the CO disk is vertically tilted compared to the main dust disk, at an angle consistent with the scattered light warp. We then use position-velocity diagrams to trace Keplerian radii in the orbital plane of the disk. Assuming a perfectly edge-on geometry, this shows a CO scale height increasing with radius as $R^{0.75}$, and an electron density (derived from CO line ratios through NLTE analysis) in agreement with thermodynamical models. Furthermore, we show how observations of optically thin line ratios can solve the primordial versus secondary origin dichotomy in gas-bearing debris disks. As shown for $\beta$ Pictoris, subthermal (NLTE) CO excitation is symptomatic of H$_2$ densities that are insufficient to shield CO from photodissociation over the system's lifetime. This means that replenishment from exocometary volatiles must be taking place, proving the secondary origin of the disk. In this scenario, assuming steady state production/destruction of CO gas, we derive the CO+CO$_2$ ice abundance by mass in $\beta$ Pic's exocomets to be at most $\sim$6%, consistent with comets in our own Solar System and in the coeval HD181327 system., Comment: 21 pages, 13 figures, Accepted for publication in MNRAS

Transitional discs are a class of circumstellar discs around young stars with extensive clearing of dusty material within their inner regions on 10s of au scales. One of the primary candidates for this kind of clearing is the formation of planet(s) within the disc that then accrete or clear their immediate area as they migrate through the disc. Our sample included eight transitional discs. Using the Keck/NIRC2 instrument we utilised the Sparse Aperture Masking (SAM) interferometry technique to search for asymmetries indicative of ongoing planet formation. We searched for close-in companions using both model fitting and interferometric image reconstruction techniques. Using simulated data, we derived diagnostics that helped us to distinguish between point sources and extended asymmetric disc emission. In addition, we investigated the degeneracy between the contrast and separation that appear for marginally resolved companions. We found FP Tau to contain a previously unseen disc wall, and DM Tau, LkHa 330, and TW Hya to contain an asymmetric signal indicative of point source-like emission. We placed upper limits on the contrast of a companion in RXJ1842.9-3532 and V2246 Oph. We ruled the asymmetry signal in RXJ1615.3-3255 and V2062 Oph to be false positives. In the cases where our data indicated a potential companion we computed estimates for the value of $M_c \dot M_c$ and found values in the range of $10^{-5} - 10^{-3} M^2_J yr^{-1}$. We found significant asymmetries in four targets. Of these, three were consistent with companions. We resolved a previously unseen gap in the disc of FP Tau extending inwards from approximately 10 au., Comment: 14 pages, 12 figures, A&A, accepted

We present ALMA band 7 (345 GHz) continuum and $^{12}$CO(J = 3-2) observations of the circumstellar disk surrounding HD141569. At an age of about 5 Myr, the disk has a complex morphology that may be best interpreted as a nascent debris system with gas. Our $870\rm~\mu m$ ALMA continuum observations resolve a dust disk out to approximately $ 56 ~\rm au$ from the star (assuming a distance of 116 pc) with $0."38$ resolution and $0.07 ~ \rm mJy~beam^{-1}$ sensitivity. We measure a continuum flux density for this inner material of $3.8 \pm 0.4 ~ \rm mJy$ (including calibration uncertainties). The $^{12}$CO(3-2) gas is resolved kinematically and spatially from about 30 to 210 au. The integrated $^{12}$CO(3-2) line flux density is $15.7 \pm 1.6~\rm Jy~km~s^{-1}$. We estimate the mass of the millimeter debris and $^{12}$CO(3-2) gas to be $\gtrsim0.04~\rm M_{\oplus}$ and $\sim2\times 10^{-3}~\rm M_{\oplus}$, respectively. If the millimeter grains are part of a collisional cascade, then we infer that the inner disk ($<50$ au) has $\sim 160~\rm M_{\oplus}$ contained within objects less than 50 km in radius, depending on the planetesimal size distribution and density assumptions. MCMC modeling of the system reveals a disk morphology with an inclination of $53.4^{\circ}$ centered around a $\rm M=2.39~ M_{\odot}$ host star ($\rm Msin(i)=1.92~ M_{\odot}$). We discuss whether the gas in HD141569's disk may be second generation. If it is, the system can be used to study the clearing stages of planet formation., Comment: 35 pages, 7 figures, submitted to ApJ

To characterize the mechanisms of planet formation it is crucial to investigate the properties and evolution of protoplanetary disks around young stars, where the initial conditions for the growth of planets are set. Our goal is to study grain growth in the disk of the young, intermediate mass star HD163296 where dust processing has already been observed, and to look for evidence of growth by ice condensation across the CO snowline, already identified in this disk with ALMA. Under the hypothesis of optically thin emission we compare images at different wavelengths from ALMA and VLA to measure the opacity spectral index across the disk and thus the maximum grain size. We also use a Bayesian tool based on a two-layer disk model to fit the observations and constrain the dust surface density. The measurements of the opacity spectral index indicate the presence of large grains and pebbles ($\geq$1 cm) in the inner regions of the disk (inside $\sim$50 AU) and smaller grains, consistent with ISM sizes, in the outer disk (beyond 150 AU). Re-analysing ALMA Band 7 Science Verification data we find (radially) unresolved excess continuum emission centered near the location of the CO snowline at $\sim$90 AU. Our analysis suggests a grain size distribution consistent with an enhanced production of large grains at the CO snowline and consequent transport to the inner regions. Our results combined with the excess in infrared scattered light found by Garufi et al. (2014) suggests the presence of a structure at 90~AU involving the whole vertical extent of the disk. This could be evidence for small scale processing of dust at the CO snowline., Comment: 12 pages, 17 figures. Accepted for publication in A\&A

We present new ALMA observations of CO $J$=2$-$1 line emission from the DQ Tau circumbinary disk. These data are used to tomographically reconstruct the Keplerian disk velocity field in a forward-modeling inference framework, and thereby provide a dynamical constraint on the mass of the DQ Tau binary of $M_\ast = 1.27_{-0.27}^{+0.46} \,M_\odot$. Those results are compared with an updated and improved orbital solution for this double-lined system based on long-term monitoring of its stellar radial velocities. Both of these independent dynamical constraints on the binary mass are in excellent agreement: taken together, they demonstrate that the DQ Tau system mass is $1.21\pm0.26\,M_\odot$ and that the disk and binary orbital planes are aligned within $3^\circ$ (at 3$\sigma$ confidence). The predictions of various theoretical models for pre-main sequence stellar evolution are also consistent with these masses, although more detailed comparisons are difficult due to lingering uncertainties in the photospheric properties of the individual components. DQ Tau is the third nearly equal-mass double-lined spectroscopic binary with a circumbinary disk that has been dynamically "weighed" with these two independent techniques: all show consistent results, validating the overall accuracy of the disk-based approach and demonstrating that it can be robustly applied to large samples of young, single stars as ALMA ramps up to operations at full capacity., Comment: Accepted to The Astrophysical Journal. 9 pages, 5 figures

Theoretical models of grain growth predict dust properties to change as a function of protoplanetary disk radius, mass, age and other physical conditions. We lay down the methodology for a multi-wavelength analysis of (sub-)mm and cm continuum interferometric observations to constrain self-consistently the disk structure and the radial variation of the dust properties. The computational architecture is massively parallel and highly modular. The analysis is based on the simultaneous fit in the uv-plane of observations at several wavelengths with a model for the disk thermal emission and for the dust opacity. The observed flux density at the different wavelengths is fitted by posing constraints on the disk structure and on the radial variation of the grain size distribution. We apply the analysis to observations of three protoplanetary disks (AS 209, FT Tau, DR Tau) for which a combination of spatially resolved observations in the range ~0.88mm to ~10mm is available (from SMA, CARMA, and VLA), finding evidence of a decreasing maximum dust grain size (a_max) with radius. We derive large a_max values up to 1 cm in the inner disk between 15 and 30 AU and smaller grains with a_max~1 mm in the outer disk (R > 80AU). In this paper we develop a multi-wavelength analysis that will allow this missing quantity to be constrained for statistically relevant samples of disks and to investigate possible correlations with disk or stellar parameters., Comment: 19 pages, 15 figures, accepted for publication in A&A

We have recently published observations of significant flux density variations at 1.3 cm in HII regions in the star forming regions Sgr B2 Main and North (De Pree et al. 2014). To further study these variations, we have made new 7 mm continuum and recombination line observations of Sgr B2 at the highest possible angular resolution of the Karl G. Jansky Very Large Array (VLA). We have observed Sgr B2 Main and North at 42.9 GHz and at 45.4 GHz in the BnA configuration (Main) and the A configuration (North). We compare these new data to archival VLA 7 mm continuum data of Sgr B2 Main observed in 2003 and Sgr B2 North observed in 2001. We find that one of the 41 known ultracompact and hypercompact HII regions in Sgr B2 (K2-North) has decreased $\sim$27% in flux density from 142$\pm$14 mJy to 103$\pm$10 mJy (2.3$\sigma$) between 2001 and 2012. A second source, F3c-Main has increased $\sim$30% in flux density from 82$\pm$8 mJy to 107 $\pm$11 mJy (1.8$\sigma$) between 2003 and 2012. F3c-Main was previously observed to increase in flux density at 1.3 cm over a longer time period between 1989 and 2012 (De Pree et al. 2014). An observation of decreasing flux density, such as that observed in K2-North, is particularly significant since such a change is not predicted by the classical hypothesis of steady expansion of HII regions during massive star accretion. Our new observations at 7 mm, along with others in the literature, suggest that the formation of massive stars occurs through time-variable and violent accretion., Comment: 20 pages, 5 figures, Accepted for publication in The Astrophysical Journal

We present ATCA continuum observations at a wavelength of 6.8 mm of five debris disks: $\beta$ Pictoris, q$^1$ Eridani, HD 107146, HD 181327, and HD 95086. These observations provide the detection at the longest wavelengths obtained to date for all these debris disks. By combining our 6.8 mm data with previous detections at shorter sub-millimeter/millimeter wavelengths we measure the long wavelength spectral index of these sources. We then use previous estimates for the temperature of the emitting dust to derive the spectral index of the dust emissivity. Under the assumption that all the detected flux comes from dust only, we constrain the slope of the solid size distribution, assumed to be a power-law. The values that we infer for the slope of the size distribution range between about 3.36 and 3.50. We compare our findings with the case of the Fomalhaut debris disk and use these results to test the predictions of collisional cascades of planetesimal belts., Comment: 7 pages, 3 figures, accepted for publication on ApJ

We have used the Submillimeter Array to image, at ~1" resolution, C2H(3-2) emission from the molecule-rich circumstellar disks orbiting the nearby, classical T Tauri star systems TW Hya and V4046 Sgr. The SMA imaging reveals that the C2H emission exhibits a ring-like morphology within each disk, the inner hole radius of the C2H ring within the V4046 Sgr disk (~70 AU) is somewhat larger than than of its counterpart within the TW Hya disk (~45 AU). We suggest that, in each case, the C2H emission likely traces irradiation of the tenuous surface layers of the outer disks by high-energy photons from the central stars., Comment: 2 pages, 2 figures, to appear in "Young Stars and Planets Near the Sun", Proceedings of IAU Symposium No. 314 (Cambridge University Press), J.H. Kastner, B. Stelzer, S.A. Metchev, eds

Measuring redshifted CO line emission is an unambiguous method for obtaining an accurate redshift and total cold gas content of optically faint, dusty starburst systems. Here, we report the first successful spectroscopic redshift determination of AzTEC J095942.9+022938 ("COSMOS AzTEC-1"), the brightest 1.1mm continuum source found in the AzTEC/JCMT survey (Scott et al. 2008), through a clear detection of the redshifted CO (4-3) and CO (5-4) lines using the Redshift Search Receiver on the Large Millimeter Telescope. The CO redshift of $z=4.3420\pm0.0004$ is confirmed by the detection of the redshifted 158 micron [C II] line using the Submillimeter Array. The new redshift and Herschel photometry yield $L_{FIR}=(1.1\pm0.1)\times 10^{13} L_\odot$ and $SFR = 1300\, M_\odot$ yr$^{-1}$. Its molecular gas mass derived using the ULIRG conversion factor is $1.4\pm0.2 \times 10^{11} M_\odot$ while the total ISM mass derived from the 1.1mm dust continuum is $3.7\pm0.7 \times 10^{11} M_\odot$ assuming dust temperature of 35 K. Our dynamical mass analysis suggests that the compact gas disk ($r\approx 1.1$ kpc, inferred from dust continuum and SED analysis) has to be nearly face-on, providing a natural explanation for the uncommonly bright, compact stellar light seen by the HST. The [C II] line luminosity $L_{[C~II]} = 7.8\pm1.1 \times 10^9 L_\odot$ is remarkably high, but it is only 0.04 per cent of the total IR luminosity. AzTEC COSMOS-1 and other high redshift sources with a spatially resolved size extend the tight trend seen between [C II]/FIR ratio and $\Sigma_{FIR}$ among IR-bright galaxies reported by Diaz-Santos et al. (2013) by more than an order of magnitude, supporting the explanation that the higher intensity of the IR radiation field is responsible for the "[C II] deficiency" seen among luminous starburst galaxies., Comment: 16 pages, 12 figures, accepted for publication in the Monthly Notices of the Royal Astronomical Society

We report detections of two candidate distant submillimeter galaxies (SMGs), MM J154506.4$-$344318 and MM J154132.7$-$350320, which are discovered in the AzTEC/ASTE 1.1 mm survey toward the Lupus-I star-forming region. The two objects have 1.1 mm flux densities of 43.9 and 27.1 mJy, and have Herschel/SPIRE counterparts as well. The Submillimeter Array counterpart to the former SMG is identified at 890 $\mu$m and 1.3 mm. Photometric redshift estimates using all available data from the mid-infrared to the radio suggest that the redshifts of the two SMGs are $z_{\rm photo} \simeq$ 4-5 and 3, respectively. Near-infrared objects are found very close to the SMGs and they are consistent with low-$z$ ellipticals, suggesting that the high apparent luminosities can be attributed to gravitational magnification. The cumulative number counts at $S_{\rm 1.1mm} \ge 25$ mJy, combined with other two 1.1-mm brightest sources, are $0.70 ^{+0.56}_{-0.34}$ deg$^{-2}$, which is consistent with a model prediction that accounts for flux magnification due to strong gravitational lensing. Unexpectedly, a $z > 3$ SMG and a Galactic dense starless core (e.g., a first hydrostatic core) could be similar in the mid-infrared to millimeter spectral energy distributions and spatial structures at least at $\gtrsim 1"$. This indicates that it is necessary to distinguish the two possibilities by means of broad band photometry from the optical to centimeter and spectroscopy to determine the redshift, when a compact object is identified toward Galactic star-forming regions., Comment: Accepted for publication in ApJ. 16 pages, 9 figures, 2 tables

We present Early Science observations with the Large Millimeter Telescope, AzTEC 1.1 mm continuum images and wide bandwidth spectra (73-111 GHz) acquired with the Redshift Search Receiver, towards four bright lensed submillimetre galaxies identified through the Herschel Lensing Survey-snapshot and the SCUBA-2 Cluster Snapshot Survey. This pilot project studies the star formation history and the physical properties of the molecular gas and dust content of the highest redshift galaxies identified through the benefits of gravitational magnification. We robustly detect dust continuum emission for the full sample and CO emission lines for three of the targets. We find that one source shows spectroscopic multiplicity and is a blend of three galaxies at different redshifts (z=2.040, 3.252 and 4.680), reminiscent of previous high-resolution imaging follow-up of unlensed submillimetre galaxies, but with a completely different search method, that confirm recent theoretical predictions of physically unassociated blended galaxies. Identifying the detected lines as 12CO (J_up=2-5) we derive spectroscopic redshifts, molecular gas masses, and dust masses from the continuum emission. The mean H_2 gas mass of the full sample is (2.0 +- 0.2) x 10^11 M_sun/\mu, and the mean dust mass is (2.0+-0.2) x 10^9 M_sun/\mu, where \mu=2-5 is the expected lens amplification. Using these independent estimations we infer a gas-to-dust ratio of \delta_GDR=55-75, in agreement with other measurements of submillimetre galaxies. Our magnified high-luminosity galaxies fall on the same locus as other high-redshift submillimetre galaxies, extending the L'_CO - L_FIR correlation observed for local luminous and ultraluminous infrared galaxies to higher FIR and CO luminosities., Comment: Minor changes to match the published version

Resolved submillimeter imaging of transitional disks is increasingly revealing the complexity of disk structure. Here we present the first high-resolution submillimeter image of a recently identified transitional disk around IRAS 04125+2902 in the Taurus star-forming region. We measure an inner disk hole of ~20 AU around IRAS 04125+2902 by simultaneously modeling new 880 micron Submillimeter Array (SMA) data along with an existing spectral energy distribution supplemented by new Discovery Channel Telescope (DCT) photometry. We also constrain the outer radius of the dust disk in IRAS~04125+2902 to ~50-60 AU. Such a small dust disk could be attributed to initial formation conditions, outward truncation by an unseen companion, or dust evolution in the disk. Notably, the dust distribution of IRAS 04125+2902 resembles a narrow ring (delta R ~ 35 AU) composed of large dust grains at the location of the disk wall. Such narrow dust rings are also seen in other transitional disks and may be evidence of dust trapping in pressure bumps, possibly produced by planetary companions. More sensitive submillimeter observations of the gas are necessary to further probe the physical mechanisms at work in shaping the spatial distribution of large dust in this disk. Interestingly, the IRAS 04125+2902 disk is significantly fainter than other transitional disks that have been resolved at submillimeter wavelengths, hinting that more objects with large disk holes may exist at the faint end of the submillimeter luminosity distribution that await detection with more sensitive imaging telescopes., Comment: accepted to ApJ

The study of the planet-debris disk connection can shed light on the formation and evolution of planetary systems, and may help predict the presence of planets around stars with certain disk characteristics. In preliminary analyses of the Herschel DEBRIS and DUNES surveys, Wyatt et al. (2012) and Marshall et al. (2014) identified a tentative correlation between debris and low-mass planets. Here we use the cleanest possible sample out these surveys to assess the presence of such a correlation, discarding stars without known ages, with ages < 1 Gyr and with binary companions <100 AU, to rule out possible correlations due to effects other than planet presence. In our sample of 204 FGK stars, we do not find evidence that debris disks are more common or more dusty around stars harboring high-mass or low-mass planets compared to a control sample without identified planets, nor that debris disks are more or less common (or more or less dusty) around stars harboring multiple planets compared to single-planet systems. Diverse dynamical histories may account for the lack of correlations. The data show the correlation between the presence of high-mass planets and stellar metallicity, but no correlation between the presence of low-mass planets or debris and stellar metallicity. Comparing the observed cumulative distribution of fractional luminosity to those expected from a Gaussian distribution, we find that a distribution centered on the Solar system's value fits well the data, while one centered at 10 times this value can be rejected. This is of interest in the context of future terrestrial planet characterization because it indicates that there are good prospects for finding a large number of debris disk systems (i.e. with evidence of harboring the building blocks of planets) with exozodiacal emission low enough to be appropriate targets for an ATLAST-type mission to search for biosignatures., Comment: Accepted for publication in ApJ. 31 pages, 13 figures, 9 tables

$\tau$ Ceti is a nearby, mature G-type star very similar to our Sun, with a massive Kuiper Belt analogue (Greaves et al. 2004) and possible multiplanet system (Tuomi et al. 2013) that has been compared to our Solar System. We present Herschel Space Observatory images of the debris disk, finding the disk is resolved at 70 and 160 microns, and marginally resolved at 250 microns. The Herschel images and infrared photometry from the literature are best modelled using a wide dust annulus with an inner edge between 1-10 AU and an outer edge at ~55 AU, inclined from face-on by 35$\pm$10 degrees, and with no significant azimuthal structure. We model the proposed tightly-packed planetary system of five super-Earths and find that the innermost dynamically stable disk orbits are consistent with the inner edge found by the observations. The photometric modelling, however, cannot rule out a disk inner edge as close to the star as 1 AU, though larger distances produce a better fit to the data. Dynamical modelling shows that the 5 planet system is stable with the addition of a Neptune or smaller mass planet on an orbit outside 5 AU, where the Tuomi et al. analysis would not have detected a planet of this mass., Comment: accepted to MNRAS

We carried out a 12CO(3-2) survey of 52 southern stars with a wide range of IR excesses (LIR/L*) using the single dish telescopes APEX and ASTE. The main aims were (1) to characterize the evolution of molecular gas in circumstellar disks using LIR/L* values as a proxy of disk dust evolution, and (2) to identify new gas-rich disk systems suitable for detailed study with ALMA. About 60% of the sample (31 systems) have LIR/L* > 0.01 typical of T-Tauri or Herbig AeBe stars, and the rest (21 systems) have LIR/L* < 0.01 typical of debris disks. We detect CO(3-2) emission from 20 systems, and 18 (90%) of these have LIR/L* > 0.01. However, the spectra of only four of the newly detected systems appear free of contamination from background or foreground emission from molecular clouds. These include the early-type stars HD 104237 (A4/5V, 116 pc) and HD 98922 (A2 III, 507 pc, as determined in this work), where our observations reveal the presence of CO-rich circumstellar disks for the first time. Of the other detected sources, many could harbor gaseous circumstellar disks, but our data are inconclusive. For these two newly discovered gas-rich disks, we present radiative transfer models that simultaneously reproduce their spectral energy distributions and the 12CO(3-2) line profiles. For both of these systems, the data are fit well by geometrically flat disks, placing them in the small class of non-flaring disks with significant molecular gas reservoirs., Comment: 73 pages, 23 figures