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Invited talk on ALMA and circumstellar disks in connection with Gaia DR3 at the MW-Gaia Aarhus conference 2022.

Transition disks with small inner dust cavities are interesting targets for the study of disk clearing mechanisms. Such disks have been identified through a deficit in the infrared part of their SED, but spatially resolved millimeter imaging is required to confirm the presence of an inner dust cavity. We use high-resolution ALMA observations of 30 mas resolution in Band 6 continuum and $^{12}$CO 2--1 emission of 10 transition disk candidates in the Lupus star forming region, in order to confirm the presence of inner dust cavities and infer the responsible mechanism. The continuum data are analyzed using visibility modeling and the SEDs are compared with radiative transfer models. Out of the six transition disk candidates selected from their SED, only one disk revealed an inner dust cavity of 4 au in radius. Three of the other disks are highly inclined, which limits the detectability of an inner dust cavity but it is also demonstrated to be the possible cause for the infrared deficit in their SED. The two remaining SED-selected disks are very compact, with dust radii of only $\sim$3 au. From the four candidates selected from low-resolution images, three new transition disks with large inner cavities $>$20 au are identified, bringing the total number of transition disks with large cavities in Lupus to 13. SED-selected transition disks with small cavities are biased towards highly inclined and compact disks, which casts doubt on the use of their occurrence rates in estimating dispersal timescales of photoevaporation. Using newly derived disk dust masses and radii, we re-evaluate the size-luminosity and $M_{\rm dust}-M_{\rm star}$ relations. These relations can be understood if the bright disks are dominated by disks with substructure whereas faint disks are dominated by drift-dominated disks. (Abridged), Submitted to A&A. Currently in revision. 28 pages, 13 figures

Protoplanetary disks with large inner dust cavities are thought to host massive planetary or substellar companions. These disks show asymmetries and rings in the millimeter continuum, caused by dust trapping in pressure bumps, and potentially vortices or horseshoes. The origin of the asymmetries and their diversity remains unclear. We present a comprehensive study of 16 disks for which the gas surface density profile has been constrained by CO isotopologue data. We compare the azimuthal extents of the dust continuum profiles with the local gas surface density in each disk, and find that the asymmetries correspond to higher Stokes numbers or low gas surface density. We discuss which asymmetric structures can be explained by a horseshoe, a vortex or spiral density waves. Second, we reassess the gas gap radii from the 13CO maps, which are about a factor 2 smaller than the dust ring radii, suggesting that companions in these disks are in the brown dwarf mass regime or in the Super-Jovian mass regime on eccentric orbits. This is consistent with the estimates from contrast curves on companion mass limits. These curves rule out (sub)stellar companions for the majority of the sample at the gap location, but it remains possible at even smaller radii. Third, we find that spiral arms in scattered light images are primarily detected around high luminosity stars with disks with wide gaps, which can be understood by the dependence of the spiral arm pitch angle on disk temperature and companion mass.

Transition disks with large inner dust cavities are thought to host massive companions. However, the disk structure inside the companion orbit and how material flows toward an actively accreting star remain unclear. We present a high resolution continuum study of inner disks in the cavities of 38 transition disks. Measurements of the dust mass from archival Atacama Large Millimeter/Submillimeter Array observations are combined with stellar properties and spectral energy distributions to assemble a detailed picture of the inner disk. An inner dust disk is detected in 18 of 38 disks in our sample. Of the 14 resolved disks, 9 are significantly misaligned with the outer disk. The near-infrared excess is uncorrelated with the mm dust mass of the inner disk. The size-luminosity correlation known for protoplanetary disks is recovered for the inner disks as well, consistent with radial drift. The inner disks are depleted in dust relative to the outer disk and their dust mass is uncorrelated with the accretion rates. This is interpreted as the result of radial drift and trapping by planets in a low $\alpha$ ($\sim 10^{-3}$) disk, or a failure of the $\alpha$-disk model to describe angular momentum transport and accretion. The only disk in our sample with confirmed planets in the gap, PDS 70, has an inner disk with a significantly larger radius and lower inferred gas-to-dust ratio than other disks in the sample. We hypothesize that these inner disk properties and the detection of planets are due to the gap having only been opened recently by young, actively accreting planets., Comment: 31 pages, 14 figures, accepted for publication in the Astrophysical Journal, minor corrections

Protoplanetary disk surveys by the Atacama Large Millimeter/sub-millimeter Array (ALMA) are now probing a range of environmental conditions, from low-mass star-forming regions like Lupus to massive OB clusters like $��$ Orionis. Here we conduct an ALMA survey of protoplanetary disks in $��$ Orionis, a ~5 Myr old OB cluster in Orion, with dust mass sensitivities comparable to the surveys of nearby regions (~0.4 $M_\oplus$). We assess how massive OB stars impact planet formation, in particular from the supernova that may have occurred ~1 Myr ago in the core of $��$ Orionis; studying these effects is important as most planetary systems, including our Solar System, are likely born in cluster environments. We find that the effects of massive stars, in the form of pre-supernova feedback and/or a supernova itself, do not appear to significantly reduce the available planet-forming material otherwise expected at the evolved age of $��$ Orionis. We also compare a lingering massive "outlier" disk in $��$ Orionis to similar systems in other evolved regions, hypothesizing that these outliers host companions in their inner disks that suppress disk dispersal to extend the lifetimes of their outer primordial disks. We conclude with numerous avenues for future work, highlighting how $��$ Orionis still has much to teach us about perhaps one of the most common types of planet-forming environments in the Galaxy., 21 pages, 8 figures, 3 tables. Accepted to AAS Journals

This white paper submitted for the 2020 Canadian Long-Range Planning process (LRP2020) presents the prospects for Canada and the Square Kilometre Array (SKA) from 2020-2030, focussing on the first phase of the project (SKA1) scheduled to begin construction early in the next decade. SKA1 will make transformational advances in our understanding of the Universe across a wide range of fields, and Canadians are poised to play leadership roles in several. Canadian key SKA technologies will ensure a good return on capital investment in addition to strong scientific returns, positioning Canadian astronomy for future opportunities well beyond 2030. We therefore advocate for Canada's continued scientific and technological engagement in the SKA from 2020-2030 through participation in the construction and operations phases of SKA1., Comment: 14 pages, 4 figures, 2020 Canadian Long-Range Plan (LRP2020) white paper

Star formation involves the flow of gas and dust within molecular clouds into protostars and young stellar objects (YSOs) due to gravity. Along the way, these flows are shaped significantly by many other mechanisms, including pressure, turbulent motions, magnetic fields, stellar feedback, jets, and angular momentum. How all these mechanisms interact nonlinearly with each other on various length scales leads to the formation and evolution of substructures within clouds, including filaments, clumps, cores, disks, outflows, the protostars/YSOs themselves, and planets. In this white paper, prepared for the 2020 Long Range Plan panel which will recommend Canada's future directions for astronomy, we describe the observational and theoretical leadership in the star formation field that Canada's vibrant community has demonstrated over the past decade. Drawing from this extensive background, we identify five key questions that must be addressed for further progress to be made in understanding star formation in the next decade. Addressing these questions will improve our understanding of the dynamics of the dense gas and the role of the magnetic field in star formation, the optical properties of the dust used to trace mass and magnetic fields, the sources of variability in star-forming objects on short timescales, and the physical processes that specifically promote the clustering of stars. We further highlight key facilities in which Canada should become involved to continue making progress in this field. Single-dish facilities we recommend include LSST, trans-atmospheric far-infrared telescopes like BLAST-TNG and SPICA, and ground-based telescopes like JCMT, GBT, and CCAT-p. Interferometric facilities we recommend include ALMA, ngVLA, and SKA1., 11 pages, a contributed white paper prepared for Canada's 2020 Long Range Plan decadal process

The Square Kilometre Array (SKA), an exciting new world observatory that will enable transformational science at metre and centimetre wavelengths for years to come, is rapidly becoming reality. The SKA will be built in two phases, with the first phase (SKA1) representing ~10% of the full facility (SKA2). The SKA1 Design Baseline development is almost complete, and construction is set to begin early in the next decade. When constructed, it will be the largest and most powerful general-purpose radio telescope operating from 50 MHz - 15 GHz for years to come. Scientific and technological participation in the SKA has been identified as a top priority for the Canadian astronomical community for almost twenty years. This white paper advocates for Canada’s continued scientific and technological participation in the SKA project, focussing on Canadian prospects for SKA1 from 2020-2030. SKA1 is poised to make fundamental advances across a broad range of fields by virtue of its combination of sensitivity, angular resolution, imaging quality and frequency coverage. SKA1 scientific goals align well with the strengths of Canadian researchers. Canada is a world leader in studies of pulsars, cosmic magnetism and transients, as well as in low-frequency cosmology. Our multi-wavelength expertise in galaxy evolution, multi-messenger astronomy and planetary system formation – in which radio observations play a critical role – is also a key strength. The Canadian community therefore has the potential to carry out important PI science with SKA1, as well as to play world-leading roles in a number of the transformational Key Science Projects (KSPs) that are anticipated to take up the majority of available telescope time. An examination of the KSP leadership opportunities afforded by a decade of full operations implies that a 6% participation in the SKA1 Design Baseline is well-matched to Canadian scientific capacity and ambitions. Canada is a leader in technological development for the SKA through effective partnerships between universities, the National Research Council (NRC) and industry. Our key SKA1 technological capabilities include the design and fabrication of correlators and beamformers, digitisers, low-noise amplifiers, signal processing, and monitor & control. These technologies provide a suite of possible in-kind contributions to offset construction costs for good return on the capital investment required to participate in SKA1 at a level commensurate with our scientific ambitions. Canada also has the computing platform and archive development expertise to make important contributions to the SKA Regional Centre (SRC) network that will deliver global SKA1 scientific computing capability. A Canadian SRC would leverage our national compute strength to provide processing, storage, and user support tailored to Canadian SKA1 needs while also fulfilling our SKA1 participation requirements. Canadian contributions to the SKA now span two decades, marked by scientific and technological leadership that persists today within a vibrant metre and centimetre-wave radio community. SKA1 is happening now. Canada at last has the opportunity to reap the scientific benefits of our contributions, while an early commitment to construction would maximize our impact on this phase and our technological benefits as well. The 2020 Canadian Long-Range Planning process (LRP2020) will determine the future of the SKA in Canada for the next decade and beyond. We make the following recommendations: Canada should participate in the construction and operations phases of SKA1. SKA1 Design Baseline construction, operations and a staged technology development program should be funded at a 6% level, commensurate with Canadian scientific ambitions. This commitment is estimated to cost $160M CAD over the period 2021-2030. Canada should participate in the SKA regional centre (SRC) network to ensure community access to the processing, storage and user support required to scientifically exploit SKA1. The cost of this participation at a level commensurate with Canadian scientific ambitions, and in accordance with SRC network guidelines, is estimated to be $45M CAD over the period 2021-2030 in addition to construction and operations funding. To meet its SKA1 compute needs, Canada should leverage its established strength in scientific computing platforms and archive development by hosting a Canadian SRC. The membership model through which Canada participates in the intergovernmental organisation (IGO) that will build and operate SKA1 should provide full scientific and technological access as well as leadership rights for Canadian researchers and industry. An agreement for Canadian participation in the IGO should be finalized as early as possible in the next decade in order to maximize our impact on the construction phase as well as to maximize opportunities for technological tender and procurement., White paper identifier W046

Many of the facilities and missions that Canada is or will be involved in as well as the diverse science programs that drive these missions rely on the astronomical detection and characterization of atomic and molecular gas as well as dust grains across the electromagnetic spectrum. Molecular bands and dust features have been observed in almost all astrophysical environments—from exoplanet atmospheres to interstellar clouds and star forming regions to AGN winds. Indeed, to date, over 200 molecules and a handful of minerals have been identified in space, and the Universe is aglow with the widespread and abundant emission of Polycyclic Aromatic Hydrocarbons (PAHs). Molecules and dust grains can be powerful probes for the physical conditions in the environment in which they reside, and their presence can help elucidate chemical evolution. However, the vast majority of the known molecular spectral features remain unidentified, and for many identified species, we do not have enough information to turn their spectral appearance into diagnostic probes. Support from laboratory experiments, theoretical calculations and detailed observational data analysis will be crucial to fully exploit astronomical observations in the next decade. This white paper describes the current expertise in Canada in the fields of molecular astrophysics and astrochemistry, detail the key science questions to address within the next decade, and describe the expected needs from laboratory astrophysics and computational chemistry to establish a unique Canadian expertise center in molecular astrophysics and astrochemistry to support upcoming astronomical missions and facilities.&nbsp

Debris disks represent the longest lived example of circumstellar disks, generated by collisions of planetesimals before, throughout and beyond the main sequence lifetime of a star. Such disks are typically faint and most were detected via infrared or submm excess above the expected photospheric emission. Looking forward, the most fundamental progress on debris disksrequires large single dish capabilities in the mid-IR, the far-IR and the submm/mm. A strong concept in the submm is the Atacama Large Aperture Submillimetre Telescope (AtLAST), which will be able to detect statistically significant numbers of new disks (1000s rather than 100s), including those around M-stars,to a fractional luminosity level at or below that of the Kuiper Belt. Such a telescope would have 2'' resolution at 350μm, meaning that belts comparable scale to the Edgeworth-Kuiper Belt would be resolvable to a distance of 30-40 pc. AtLAST would be a particularly compatible facility with ALMA, which, although powerful, is not an optimal facility for imaging of nearby debris disks since even in its lowest resolution configuration, large scale emission is filtered out. A facility like AtLAST would also have access to the molecular spectra from these 1000s of detected disks to characterize the kinematics via gas emission. Emission from the cold dust components of debris disks peaks in the far-infrared. SPICA will have some capability at this wavelength, but its size limits debris disk imaging to only the nearest disks, and its sensitivity will be severely hindered by confusion with the extragalactic background. The far-IR facility that best meets our requirements is the Origins Space Telescope. At 9m in diameter, the full scope mission would provide images at 100μm imaging at the 2'' scale, comparable to AtLAST. In the mid-infrared, SPICA also has some capability, particularly with respect to spectroscopy, which will be excellent for the detection of solid state features and detection of atomic and molecular species in the gas phase. JWST is the only mission in the next decade, however, that will be able to resolve those spectral features for disks in the near-IR and mid-IR, as well as thermal emission across a large fraction of known disks (up to 50%), though most of the resolved imaging will be of cold belts, rather than any warm components that may be present. To resolve warm belt components, a mid-IR facility larger than JWST or an interferometer in space would be required. Satellites in the mid- to far-IR will be able to measure spectra and detect atomic and molecular species in the gas phase. These single dish facilities are essential to map out signatures of long period planets on their debris disks, probe dust grain properties over a statistically significant number of disks, and reach the sensitivities needed to detect true solar system analogues in the debris disk population. They will also have enough sensitivity to detect cold, small disks around low-mass stars. The ability of interferometers to conduct blind surveys for disks is very limited due to sensitivity and the need to tailor configurations for disk properties. While we can make a decent statistical distribution of disk mean radii, the width of individual disks is likely very tuned to the planetary architecture of the system. For known disks, mm and cm interferometers like ALMA and ngVLA will provide the high resolution, high sensitivity mapping that will image known dust emission in exquisite detail. We will also have sensitivity to detect CO and CI(ALMA) emission, and potentially OH or HI in the disks, which would likely be sourced by photodissociation of H2O outgassing from the planetesimals. Both these gaseous species will be detectable to ngVLA and SKA. The next generation of optical/near-IR ELTs will add significantly to our ability to image more disks in scattered light via extreme AO, detecting asymmetries in disks, while polarization data will provide a measure of dust grain porosity and thereby constrain composition. Our ability to detect variability due to terrestrial planet formation will likely be limited for the near future to a fraction of the known young disks. Frequent monitoring of a small number of disks with JWST, or with upgraded SOFIA instrumentation may be possible. From the ground, instruments like MATISSE on VLTI could frequently visit high-priority targets, potentially several times a year. Canada’s access to such instruments will be limited. LSST’s continuous monitoring will no doubt detect more systems like Tabby’s star, with continuous occultations of the star due to intermediary planetesimals, including clustered groups of planetesimals, such as analogues to the Trojans in our own Solar system., White paper identifier W066

Successful exoplanet surveys in the last decade have revealed that planets are ubiquitous throughout the Milky Way, and show a large diversity in mass, location and composition. At the same time, new facilities such as the Atacama Large Millimeter/submillimeter Array (ALMA) and optical/infrared facilities including Gemini/GPI have provided us with sharper images than ever before of protoplanetary disks around young stars, the birth cradles of planets. The high spatial resolution has revealed astonishing structures in disks, such as rings, gaps, asymmetries and spiral arms, and the enormous jump in sensitivity has provided the tools for both large, statistically relevant surveys and deep, sensitive molecular line studies. These observations have revolutionized our view of planet formation, disk formation and disk evolution, bringing model simulations and observations closer to the same level of detail, with many contributions from Canadian researchers on theoretical, observational and technological sides. The new results have inevitably led to a range of new questions, which require next generation instruments such as the Next Generation Very Large Array (ngVLA) and large scale optical infrared facilities. In this white paper we will discuss the current transformation in our understanding of planet formation and the next steps and challenges in connecting theory with exoplanet demographics and protoplanetary disk observations for Canadian research., White paper identifier W005

The search for life outside our solar system is one of the great frontiers in astronomy.Confirming life and habitability of planets will require a detailed spectroscopic analysis to search for biomarkers over a wide range of wavelengths, from the visible to the thermal infrared. While many observing techniques are being pursued towards that goal, the exoplanet imaging technique, consisting of directly detecting the exoplanet light against the bright diffracted stellar halo, offers several advantages, including the detection and characterization of Earth-sized planets, orbiting around a wide range of stellar hosts without requiring any special orbital alignments. Exoplanet imaging requires overcoming two main challenges, (1) the telescope resolution limit, motivating a strong interest by the community to operate on the largest possible telescopes, and (2) contrast—planets can be 10^5 (gas giants) to 10^10 (rocky planets) times fainter than the host star. High-contrast imaging instruments on ground-based telescopes typically include an adaptive optics system to measure and correct (at kHz speeds) the turbulent atmosphere, a coronagraph to block the bright central star, and an imaging spectrograph. Many breakthrough scientific discoveries were achieved in exoplanet imaging by Canadians during the last decade, from new gas giant planets to leading international campaigns using both ground- and space-based observatories. With the deployment of the Gemini Planet Imager (GPI) at the Gemini South observatory, an instrument part of the first generation of facility-class high-contrast imaging instruments, Canadians are at the forefront of the field. While GPI has achieved a contrast gain of more than 100x compared to previous instruments, new techniques must be developed if we are to detect rocky planets. Imaging rocky planets will require new solutions to overcome the “speckle noise” contrast challenge, improving sensitivity by 10^3 for M dwarfs to 10^5 for Sun-like stars. The NRC, the Canadian Universities, and industry have been developing key technologies that are crucial for high-contrast imaging. New developments in speckle subtraction include the invention of new adaptive optics systems and coronagraphic masks, powerful focal plane wavefront sensors, and promising new observing methods, such as the high-dispersion spectroscopic technique. The community is ready to integrate all the latest promising technologies into facility-class instruments, but how to integrate such complex approaches is still an open question. The first high-contrast imaging Canadian laboratory, NEW EARTH, has been recently set up at NRC to test and validate new technologies. The University of Laval-led HiCIBaS’ stratospheric telescope was also developed to validate space technologies. With these foundations now in place, the Canadian community is now in a position to develop and test the new technologies needed to directly image rocky exoplanets. The next decade will see new science capabilities and exciting exoplanet science discoveries with new instruments, including from a first set of GPI upgrades and the launch of the JWST and WFIRST. ELT telescopes should see their first light before the end of the decade, and their dedicated high-contrast imaging instruments should be well in their design/construction phase. Large flagship exoplanet imaging space missions, such as HABEX and LUVOIR, are being studied in the US, but it is still unclear if Canada will be a partner of these. Canadians are now well-positioned to develop and contribute key hardware to these initiatives, but some challenges still remain. We make important recommendations to support the essential high-contrast imaging R&D in the next decade for: developing technologies to reach contrast levels sufficient to image rocky planets and find life for both ground- and space-based telescopes, strategic hires in the field, keeping Gemini/GPI access for the next decade, modifying the funding system to better prepare for large Canadian instrument infrastructures, securing an ELT early access, and the development of long term commitments (pathfinders like HiCIBaS, to flagship missions) by CSA. With this emphasis, Canadians will be positioned at the forefront of the search for life elsewhere in the Universe for decades to come., White paper identifier W059

Star formation involves the flow of gas and dust within molecular clouds into protostars and young stellar objects (YSOs) due to gravity. Along the way, these flows are shaped significantly by many other mechanisms, including pressure, turbulent motions, magnetic fields, stellar feedback, jets, and angular momentum. How all these mechanisms interact nonlinearly with each other on various length scales leads to the formation and evolution of substructures within clouds, including filaments, clumps, cores, disks, outflows, the protostars/YSOs themselves, and planets. In this LRP2020 white paper, we describe the observational and theoretical leadership in the star formation field that Canada’s vibrant community has demonstrated over the past decade. Drawing from this extensive background, we identify five key questions that must be addressed for further progress to be made in understanding star formation in the next decade. Addressing these questions will improve our understanding of the dynamics of the dense gas and the role of the magnetic field in star formation, the optical properties of the dust used to trace mass and magnetic fields, the sources of variability in star-forming objects on short timescales, and the physical processes that specifically promote the clustering of stars. We further highlight key facilities in which Canada should become involved to continue making progress in this field. Single-dish facilities we recommend include LSST, trans-atmospheric far-infrared telescopes like BLAST-TNG and SPICA, and ground-based telescopes like JCMT, GBT, and CCAT-p. Interferometric facilities we recommend include ALMA, ngVLA, and SKA1., White paper identifier W063

The Atacama Large Millimeter/submillimeter Array (ALMA) was the top-ranked priority for a new ground-based facility in the 2000 Long Range Plan. Ten years later, at the time of LRP2010, ALMA construction was well underway, with first science observations anticipated for 2011. In the past 8 years, ALMA has proved itself to be a high-impact, high-demand observatory, with record numbers of proposals submitted to the past few annual calls (more proposals than are submitted annually to HST) and large numbers of highly cited scientific papers across fields from protoplanetary disks to high-redshift galaxies and quasars. Since Cycle 4, ALMA has also begun to carry out large programs using more than 60 hours of observing time on the 12-m array or more than 200 hours of time on the Atacama Compact Array (ACA). ALMA’s scientific impact reaches into nearly every area of astronomy. Highlights include the first image of a supermassive black hole in the centre of M87 by the Event Horizon Telescope Collaboration; Canadians led the analysis that extracted the physics, such as black hole mass and spin, from that image. A Canadian-led collaboration has shown that radio galaxies located in clusters and groups can drive molecular gas flows (both inflows and outflows) up to 10s of kpc in altitude. Canadians are also leading innovative studies of proto-stellar and proto-planetary disks, including the first systematic study of their morpohologies and the location of gaps that can signal unseen planets. VERTICO (PI. T. Brown) is the first Canadian-led ALMA large program. VERTICO will map 51 spiral galaxies in the nearby Virgo cluster and use a multi-wavelength approach to quantify the effect of cluster environment on the star-forming molecular gas. The LRP2010 ALMA white paper laid out 8 specific metrics for ALMA and the Canadian ALMA user community that could be used to judge the success of Canada’s participation in ALMA. These metrics ranged from publications (number; impact) to collaborations (international; multi-wavelength) to student training and leadership in ALMA operations, as well as the successful completion of the Band 3 (3mm, 100 GHz) receivers and ALMA development projects. All 8 metrics argue for Canada’s involvement in ALMA over the past decade to be judged a success. The successful achievement of these wide-ranging goals argues strongly for Canada’s continuing participation in operating and developing ALMA over the next decade and beyond. To call out one particular success metric, Canadians are making excellent use of ALMA in training graduate students and postdocs. For example, 12 of 23 Canadian first-author papers published as of June 2018 were led by a graduate student, and a further 4 papers were led by postdocs. As of that date, the Canadian-led paper with the highest number of citations was by a graduate student. The first Canadian-led ALMA large program (VERTICO) is led by postdoc T. Brown at McMaster University. The ALMA observatory has identified a set of short and medium-term development goals that will keep ALMA at the cutting-edge of astronomy and allow it to continue producing transformational scientific results in future decades. Over the next decade, the focus is on expanding the spectral bandwidth of ALMA by a factor of at least two. This increase in bandwidth requires upgrades to ALMA’s receivers, electronics, and correlator. These increases in bandwidth will reduce the integration time required for a variety of scientific programs, such as blind redshift surveys, spectral scans, and sensitive continuum imaging, by a factor of two. High-resolution spectral scans, for example of proto-planetary disks, will see an increase in speed by a factor of 8 or more. Improvements to the ALMA Archive is another important focus, particularly in the area of applying data mining to large spectral datasets. There are opportunities for Canadian participation and/or leadership in many of these development areas. Looking forward to the next decade of ALMA operations, our community needs to: maintain Canadian access to ALMA and our competitiveness in using ALMA; preserve full Canadian funding for our share of ALMA operations; identify components of ALMA development in which Canada can play a significant role, including stimulating expertise in submillimetre instrumentation to capitalize on future opportunities; and keep Canadians fully trained and engaged in ALMA, as new capabilities become available, reaching the widest possible community of potential users., White paper identifier W019

The next generation Very Large Array (ngVLA) is a transformational radio observatory being designed by the U.S. National Radio Astronomy Observatory (NRAO). It will provide order of magnitude improvements in sensitivity, resolution, and uv coverage over the current Jansky Very Large Array (VLA) at ~1.2-50 GHz and extend the frequency range up to 70-115 GHz. The ngVLA will consist of three arrays working in parallel: i) a Main Array of 214 x 18-m antennas clustered at the current VLA site but spread within and beyond New Mexico that will provide baselines of 0.01-1000 km; ii) a Short Baseline Array of 19 x 6-m antennas located at the Main Array centre (+ 4 MA antennas with total-power capabilities) for high sensitivity to low surface brightness emission, and; iii) a Long Baseline Array of 30 x 18-m antennas located across the U.S. from Hawaii to the Virgin Islands, as well as western Canada, for extremely high resolution imaging with a maximum ~8,800 km baseline. The ngVLA concept has been submitted for consideration to the U.S. Astro2020 decadal survey panel, and soon thereafter it will be submitted to the U.S. National Science Foundation’s Major Research Equipment and Facility Construction program. The goal is to have early science with ngVLA as early as 2028 and full operations by 2034. The ngVLA will be a PI-proposal driven observatory and will tackle a wide range of high-impact key science projects that shaped its overall design. For example, the ngVLA will probe the innermost “terrestrial” zones of nearby circumstellar disks for forming planets, search for interstellar signals from key prebiotic molecules such as simple amino acids, trace the evolution of gas within galaxies across cosmic time, plumb the Galactic Centre for pulsars that will test General Relativity in new regimes, and explore the growth and evolution of black holes within and beyond our Galaxy in the era of multi-messenger astronomy. The ngVLA’s versatile design will also enable many other fundamental advances, as detailed in the recently published, topically diverse ngVLA Science Book. NRAO is seeking international partnerships at the 25% level to build and operate the ngVLA. Since Canadians have been historically major users of the VLA and have been valued partners with NRAO for ALMA, our participation is welcome. Canadians have been actually involved in ngVLA discussions for the past five years, and have played leadership roles in the ngVLA Science and Technical Advisory Councils. Canadian technologies are also very attractive for the ngVLA, in particular our designs for radio antennas, receivers, correlators, and data archives, and our industrial capacities to realize them. Indeed, the Canadian designs for the ngVLA antennas and correlator/beamformer are presently the baseline models for the project. Five other countries have also expressed interest in participating in ngVLA. Given the size of Canada’s radio community and earlier use of the VLA (and ALMA), we recommend Canadian participation in the ngVLA at the 7% level. Such participation would be significant enough to allow Canadian leadership in ngVLA’s construction and usage. Canada’s participation in ngVLA should not preclude its participation in SKA; access to both facilities is necessary to meet Canada’s radio astronomy needs. Indeed, ngVLA will fill the gap between those radio frequencies observable with the SKA and ALMA at high sensitivities and resolutions. Canada’s partnership in ngVLA will make it a major player in global radio astronomy, with access to cutting-edge facilities together covering approximately three orders of magnitude in frequency., White paper identifier W032

Many of the facilities and missions that Canada is or will be involved in as well as the diverse science programs that drive these missions rely on the astronomical detection and characterization of atomic and molecular gas as well as dust grains across the electromagnetic spectrum. Molecular bands and dust features have been observed in almost all astrophysical environments—from exoplanet atmospheres to interstellar clouds and star forming regions to AGN winds. Indeed, to date, over 200 molecules and a handful of minerals have been identified in space, and the Universe is aglow with the widespread and abundant emission of Polycyclic Aromatic Hydrocarbons (PAHs). Molecules and dust grains can be powerful probes for the physical conditions in the environment in which they reside, and their presence can help elucidate chemical evolution. However, the vast majority of the known molecular spectral features remain unidentified, and for many identified species, we do not have enough information to turn their spectral appearance into diagnostic probes. Support from laboratory experiments, theoretical calculations and detailed observational data analysis will be crucial to fully exploit astronomical observations in the next decade. This white paper describes the current expertise in Canada in the fields of molecular astrophysics and astrochemistry, detail the key science questions to address within the next decade, and describe the expected needs from laboratory astrophysics and computational chemistry to establish a unique Canadian expertise center in molecular astrophysics and astrochemistry to support upcoming astronomical missions and facilities., White paper identifier W056

The Square Kilometre Array (SKA), an exciting new world observatory that will enable transformational science at metre and centimetre wavelengths for years to come, is rapidly becoming reality. The SKA will be built in two phases, with the first phase (SKA1) representing ~10% of the full facility (SKA2). The SKA1 Design Baseline development is almost complete, and construction is set to begin early in the next decade. When constructed, it will be the largest and most powerful general-purpose radio telescope operating from 50 MHz - 15 GHz for years to come. Scientific and technological participation in the SKA has been identified as a top priority for the Canadian astronomical community for almost twenty years. This white paper advocates for Canada’s continued scientific and technological participation in the SKA project, focussing on Canadian prospects for SKA1 from 2020-2030. SKA1 is poised to make fundamental advances across a broad range of fields by virtue of its combination of sensitivity, angular resolution, imaging quality and frequency coverage. SKA1 scientific goals align well with the strengths of Canadian researchers. Canada is a world leader in studies of pulsars, cosmic magnetism and transients, as well as in low-frequency cosmology. Our multi-wavelength expertise in galaxy evolution, multi-messenger astronomy and planetary system formation – in which radio observations play a critical role – is also a key strength. The Canadian community therefore has the potential to carry out important PI science with SKA1, as well as to play world-leading roles in a number of the transformational Key Science Projects (KSPs) that are anticipated to take up the majority of available telescope time. An examination of the KSP leadership opportunities afforded by a decade of full operations implies that a 6% participation in the SKA1 Design Baseline is well-matched to Canadian scientific capacity and ambitions. Canada is a leader in technological development for the SKA through effective partnerships between universities, the National Research Council (NRC) and industry. Our key SKA1 technological capabilities include the design and fabrication of correlators and beamformers, digitisers, low-noise amplifiers, signal processing, and monitor & control. These technologies provide a suite of possible in-kind contributions to offset construction costs for good return on the capital investment required to participate in SKA1 at a level commensurate with our scientific ambitions. Canada also has the computing platform and archive development expertise to make important contributions to the SKA Regional Centre (SRC) network that will deliver global SKA1 scientific computing capability. A Canadian SRC would leverage our national compute strength to provide processing, storage, and user support tailored to Canadian SKA1 needs while also fulfilling our SKA1 participation requirements. Canadian contributions to the SKA now span two decades, marked by scientific and technological leadership that persists today within a vibrant metre and centimetre-wave radio community. SKA1 is happening now. Canada at last has the opportunity to reap the scientific benefits of our contributions, while an early commitment to construction would maximize our impact on this phase and our technological benefits as well. The 2020 Canadian Long-Range Planning process (LRP2020) will determine the future of the SKA in Canada for the next decade and beyond. We make the following recommendations: Canada should participate in the construction and operations phases of SKA1. SKA1 Design Baseline construction, operations and a staged technology development program should be funded at a 6% level, commensurate with Canadian scientific ambitions. This commitment is estimated to cost $160M CAD over the period 2021-2030. Canada should participate in the SKA regional centre (SRC) network to ensure community access to the processing, storage and user support required to scientifically exploit SKA1. The cost of this participation at a level commensurate with Canadian scientific ambitions, and in accordance with SRC network guidelines, is estimated to be $45M CAD over the period 2021-2030 in addition to construction and operations funding. To meet its SKA1 compute needs, Canada should leverage its established strength in scientific computing platforms and archive development by hosting a Canadian SRC. The membership model through which Canada participates in the intergovernmental organisation (IGO) that will build and operate SKA1 should provide full scientific and technological access as well as leadership rights for Canadian researchers and industry. An agreement for Canadian participation in the IGO should be finalized as early as possible in the next decade in order to maximize our impact on the construction phase as well as to maximize opportunities for technological tender and procurement.

The submillimeter is a crucial part of the electromagnetic spectrum for studies of the cold universe, essential to understand the origins of galaxies, and the physical and chemical conditions within the interstellar medium in the dense and cold molecular clouds in which stars and planetary systems form. A next generation of single dish telescopes are uniquely poised to deliver accurate measurements of fundamental astrophysical processes that govern stellar birth and evolution, galaxy formation, and the coming-of-age of the universe itself. The submillimeter regime is accessible in several atmospheric windows from the ground, where single dish telescopes are able to exploit a rapidly growing detector technology to implement powerful instruments which can survey vast regions of the sky to unprecedented depths.In this white paper we will discuss key research areas that require ground-based Submillimeter Wave observatories, exploiting the crucial submillimeter diagnostics of the molecular ISM, and the redshifted dust and strong ISM cooling lines from all galaxies at z>1 — the first half of the history of our Universe, when galaxies were actively assembling and building their stellar populations. At the moment there are no submillieter single dish telescopes funded in Canada. Those that Canadian astronomers use are funded through individual academic grants, or through external collaborations. This white paper will bring together discussions of the science cases, and descriptions of the proposed facilities, along with prospects for Canadian involvement and timelines of single dish mm/submm facilities: CCAT-prime, JCMT upgrades, APEX upgrades, SPT, ACT, Polarbear, Simon’s Observatory, CCAT-25, and AtLAST., White paper identifier W048

Successful exoplanet surveys in the last decade have revealed that planets are ubiquitous throughout the Milky Way, and show a large diversity in mass, location and composition. At the same time, new facilities such as the Atacama Large Millimeter/submillimeter Array (ALMA) and optical/infrared facilities including Gemini/GPI have provided us with sharper images than ever before of protoplanetary disks around young stars, the birth cradles of planets. The high spatial resolution has revealed astonishing structures in disks, such as rings, gaps, asymmetries and spiral arms, and the enormous jump in sensitivity has provided the tools for both large, statistically relevant surveys and deep, sensitive molecular line studies. These observations have revolutionized our view of planet formation, disk formation and disk evolution, bringing model simulations and observations closer to the same level of detail, with many contributions from Canadian researchers on theoretical, observational and technological sides. The new results have inevitably led to a range of new questions, which require next generation instruments such as the Next Generation Very Large Array (ngVLA) and large scale optical infrared facilities. In this white paper we will discuss the current transformation in our understanding of planet formation and the next steps and challenges in connecting theory with exoplanet demographics and protoplanetary disk observations for Canadian research., White paper E013 submitted to the Canadian Long Range Plan 2020

Modern astronomy has finally been able to observe protoplanetary disks in reasonable resolution and detail, unveiling the processes happening during planet formation. These observed processes are understood under the framework of disk-planet interaction, a process studied analytically and modeled numerically for over 40 years. Long a theoreticians' game, the wealth of observational data has been allowing for increasingly stringent tests of the theoretical models. Modeling efforts are crucial to support the interpretation of direct imaging analyses, not just for potential detections but also to put meaningful upper limits on mass accretion rates and other physical quantities in current and future large-scale surveys. This white paper addresses the questions of what efforts on the computational side are required in the next decade to advance our theoretical understanding, explain the observational data, and guide new observations. We identified the nature of accretion, ab initio planet formation, early evolution, and circumplanetary disks as major fields of interest in computational planet formation. We recommend that modelers relax the approximations of alpha-viscosity and isothermal equations of state, on the grounds that these models use flawed assumptions, even if they give good visual qualitative agreement with observations. We similarly recommend that population synthesis move away from 1D hydrodynamics. The computational resources to reach these goals should be developed during the next decade, through improvements in algorithms and the hardware for hybrid CPU/GPU clusters. Coupled with high angular resolution and great line sensitivity in ground based interferometers, ELTs and JWST, these advances in computational efforts should allow for large strides in the field in the next decade., White paper submitted to the Astro2020 decadal survey

Planet formation is thought to begin with the growth of dust particles in protoplanetary disks from micrometer to millimeter and centimeter sizes. Dust growth is hindered by a number of growth barriers, according to dust evolution theory, while observational evidence indicates that somehow these barriers must have been overcome. The observational evidence of dust traps, in particular the Oph IRS 48 disk, with the Atacama Large Millimeter/submillimeter Array (ALMA) has changed our view of the dust growth process. In this article I review the history of dust trapping in models and observations., Perspective article in Star Formation Newsletter 308, August 2018 (http://www.ifa.hawaii.edu/~reipurth/newsletter/newsletter308.pdf). arXiv admin note: substantial text overlap with arXiv:1809.06403

(abridged) The Atacama Large Millimeter/submillimeter Array (ALMA) was the top-ranked priority for a new ground-based facility in the 2000 Canadian Long Range Plan. Ten years later, at the time of LRP2010, ALMA construction was well underway, with first science observations anticipated for 2011. In the past 8 years, ALMA has proved itself to be a high-impact, high-demand observatory, with record numbers of proposals submitted to the annual calls and large numbers of highly cited scientific papers across fields from protoplanetary disks to high-redshift galaxies and quasars. The LRP2010 ALMA white paper laid out 8 specific metrics that could be used to judge the success of Canada's participation in ALMA. Among these metrics were publications (number; impact), collaborations (international; multi-wavelength), and student training. To call out one particular metric, Canadians are making excellent use of ALMA in training graduate students and postdocs: as of June 2018, 12 of 23 Canadian first-author papers were led by a graduate student, and a further 4 papers were led by postdocs. All 8 metrics argue for Canada's involvement in ALMA over the past decade to be judged a success. The successful achievement of these wide-ranging goals argues strongly for Canada's continuing participation in ALMA over the next decade and beyond. Looking forward, our community needs to: (1) maintain Canadian access to ALMA and our competitiveness in using ALMA; (2) preserve full Canadian funding for our share of ALMA operations; (3) identify components of ALMA development in which Canada can play a significant role, including stimulating expertise in submillimetre instrumentation to capitalize on future opportunities; and (4) keep Canadians fully trained and engaged in ALMA, as new capabilities become available, reaching the widest possible community of potential users., Comment: White paper E004 submitted to the Canadian Long Range Plan 2020

The next generation Very Large Array (ngVLA) is a transformational radio observatory being designed by the U.S. National Radio Astronomy Observatory (NRAO). It will provide order of magnitude improvements in sensitivity, resolution, and uv coverage over the current Jansky Very Large Array (VLA) at ~1.2-50 GHz and extend the frequency range up to 70-115 GHz. This document is a white paper written by members of the Canadian community for the 2020 Long Range Plan panel, which will be making recommendations on Canada's future directions in astronomy. Since Canadians have been historically major users of the VLA and have been valued partners with NRAO for ALMA, Canada's participation in ngVLA is welcome. Canadians have been actually involved in ngVLA discussions for the past five years, and have played leadership roles in the ngVLA Science and Technical Advisory Councils. Canadian technologies are also very attractive for the ngVLA, in particular our designs for radio antennas, receivers, correlates, and data archives, and our industrial capacities to realize them. Indeed, the Canadian designs for the ngVLA antennas and correlator/beamformer are presently the baseline models for the project. Given the size of Canada's radio community and earlier use of the VLA (and ALMA), we recommend Canadian participation in the ngVLA at the 7% level. Such participation would be significant enough to allow Canadian leadership in gVLA's construction and usage. Canada's participation in ngVLA should not preclude its participation in SKA; access to both facilities is necessary to meet Canada's radio astronomy needs. Indeed, ngVLA will fill the gap between those radio frequencies observable with the SKA and ALMA at high sensitivities and resolutions. Canada's partnership in ngVLA will give it access to cutting-edge facilities together covering approximately three orders of magnitude in frequency., Comment: 11 pages; a contributed white paper for Canada's 2020 Long Range Plan decadal process

This white paper submitted for the 2020 Canadian Long-Range Planning process (LRP2020) presents the prospects for Canada and the Square Kilometre Array (SKA) from 2020-2030, focussing on the first phase of the project (SKA1) scheduled to begin construction early in the next decade. SKA1 will make transformational advances in our understanding of the Universe across a wide range of fields, and Canadians are poised to play leadership roles in several. Canadian key SKA technologies will ensure a good return on capital investment in addition to strong scientific returns, positioning Canadian astronomy for future opportunities well beyond 2030. We therefore advocate for Canada's continued scientific and technological engagement in the SKA from 2020-2030 through participation in the construction and operations phases of SKA1., 14 pages, 4 figures, 2020 Canadian Long-Range Plan (LRP2020) white paper

ALMA has revolutionized our view of protoplanetary disks, revealing structures such as gaps, rings and asymmetries that indicate dust trapping as an important mechanism in the planet formation process. However, the high resolution images have also shown that the optically thin assumption for millimeter continuum emission may not be valid and the low values of the spectral index may be related to optical depth rather than dust growth. Longer wavelength observations are essential to properly disentangle these effects. The high sensitivity and spatial resolution of the next-generation Very Large Array (ngVLA) will open up the possibilities to spatially resolve disk continuum emission at centimeter wavelengths and beyond, which allows the study of dust growth in disks in the optically thin regime and further constrain models of planet formation.

Protoplanetary disks of gas and dust around young stars are the birth cradles of planets. Of particular interest are the so-called transition disks with large inner dust cavities, a sign of active evolution and potential early planet formation. The arrival of ALMA has revolutionized our view of the structure of these disks. ALMA observations in the last few years have revealed rings, asymmetries, dust/gas segregation, gas dynamics, evidence for dust trapping and vortices, and many more exciting phenomena that have been predicted for decades in disk models. Using new physical-chemical modeling tools it is now possible to constrain gas and dust densities and compare these with planet-disk interaction model predictions. Larger disk surveys allow us to compare disk results with exoplanet statistics. In this talk I will discuss several recent ALMA discoveries and the next steps in planet formation studies.

ALMA has revolutionized our view of protoplanetary disks, revealing structures such as gaps, rings and asymmetries that indicate dust trapping as an important mechanism in the planet formation process. However, the high resolution images have also shown that the optically thin assumption for millimeter continuum emission may not be valid and the low values of the spectral index may be related to optical depth rather than dust growth. Longer wavelength observations are essential to properly disentangle these effects. The high sensitivity and spatial resolution of the next-generation Very Large Array (ngVLA) will open up the possibilities to spatially resolve disk continuum emission at centimeter wavelengths and beyond, which allows the study of dust growth in disks in the optically thin regime and further constrain models of planet formation., Comment: To be published in the ASP Monograph Series, "Science with a Next-Generation VLA", ed. E. J. Murphy (ASP, San Francisco, CA)

The $��$ Orionis cluster is important for studying protoplanetary disk evolution, as its intermediate age ($\sim$3-5 Myr) is comparable to the median disk lifetime. We use ALMA to conduct a high-sensitivity survey of dust and gas in 92 protoplanetary disks around $��$ Orionis members with $M_{\ast}\gtrsim0.1 M_{\odot}$. Our observations cover the 1.33 mm continuum and several CO $J=2-1$ lines: out of 92 sources, we detect 37 in the mm continuum and six in $^{12}$CO, three in $^{13}$CO, and none in C$^{18}$O. Using the continuum emission to estimate dust mass, we find only 11 disks with $M_{\rm dust}\gtrsim10 M_{\oplus}$, indicating that after only a few Myr of evolution most disks lack sufficient dust to form giant planet cores. Stacking the individually undetected continuum sources limits their average dust mass to 5$\times$ lower than that of the faintest detected disk, supporting theoretical models that indicate rapid dissipation once disk clearing begins. Comparing the protoplanetary disk population in $��$ Orionis to those of other star-forming regions supports the steady decline in average dust mass and the steepening of the $M_{\rm dust}$-$M_{\ast}$ relation with age; studying these evolutionary trends can inform the relative importance of different disk processes during key eras of planet formation. External photoevaporation from the central O9 star is influencing disk evolution throughout the region: dust masses clearly decline with decreasing separation from the photoionizing source, and the handful of CO detections exist at projected separations $>1.5$ pc. Collectively, our findings indicate that giant planet formation is inherently rare and/or well underway by a few Myr of age., 16 pages, 9 figures; published in AJ; The full machine readable tables can be obtained by downloading and extracting the gzipped tar source file listed under "Other formats."

In recent years spiral structures and vortices (potentially signs of planets) are seen in disks. I present ALMA mm-data of the HD135344B disk, revealing that the dust disk in fact consists of a ring and an asymmetry. This can be understood as triggered formation of a secondary vortex by a planet at 30 AU. The 2 spiral arms seen in PDI are fit to originate from that same planet and from the vortex.

Simple molecules like H2CO and CH3OH in protoplanetary disks are the starting point for the production of more complex organic molecules. So far, the observed chemical complexity in disks has been limited due to freeze out of molecules onto grains in the bulk of the cold outer disk. Complex molecules can be studied more directly in transitional disks with large inner holes, as these have a higher potential of detection, through UV heating of the outer disk and the directly exposed midplane at the wall. We use Atacama Large Millimeter/submillimeter Array (ALMA) Band 9 (~680 GHz) line data of the transitional disk Oph IRS 48, previously shown to have a large dust trap, to search for complex molecules in regions where planetesimals are forming. We report the detection of the H2CO 9(1,8)-8(1,7) line at 674 GHz, which is spatially resolved as a semi-ring at ~60 AU radius centered south from the star. The inferred H2CO abundance is ~10^{-8} derived by combining a physical disk model of the source with a non-LTE excitation calculation. Upper limits for CH3OH lines in the same disk give an abundance ratio H2CO/CH3OH>0.3, which points to both ice formation and gas-phase routes playing a role in the H2CO production. Upper limits on the abundances of H13CO+, CN and several other molecules in the disk are also derived and found to be consistent with full chemical models. The detection of the H2CO line demonstrates the start of complex organic molecules in a planet-forming disk. Future ALMA observations should be able to push down the abundance detection limits of other molecules by 1-2 orders of magnitude and test chemical models of organic molecules in (transitional) disks., Updated references and minor changes to text, approved by language editor