Publication Search Results

ID: 158658
Type: article
Authors: Benac, Peyton; Matrà, Luca; Wilner, David J.; Jimènez-Donaire, Marìa J.; Monnier, J. D.; Harries, Tim J.; Laws, Anna; Rich, Evan A.; Zhang, Qizhou
Abstract: Millimeter observations of disks around young stars reveal substructures indicative of gas pressure traps that may aid grain growth and planet formation. We present Submillimeter Array observations of HD 34700: two Herbig Ae stars in a close binary system (Aa/Ab, ˜0.25 au), surrounded by a disk presenting a large cavity and spiral arms seen in scattered light, and two distant, lower-mass companions. These observations include 1.3 mm continuum emission and the ¹²CO 2-1 line at ˜0"5 (178 au) resolution. They resolve a prominent azimuthal asymmetry in the continuum and Keplerian rotation of a circumbinary disk in the ¹²CO line. The asymmetry is located at a radius of 155⁺¹¹_-7 au, consistent with the edge of the scattered-light cavity, being resolved in both radius (72 ⁺¹⁴_-15 au) and azimuth (FWHM = 64^°+8_-7). The strong asymmetry in millimeter continuum emission could be evidence for a dust trap, together with the more symmetric morphology of ¹²CO emission and small grains. We hypothesize an unseen circumbinary companion responsible for the cavity in scattered light and creating a vortex at the cavity edge that manifests in dust trapping. The disk mass has limitations imposed by the detection of ¹²CO and nondetection of ¹³CO. We discuss its consequences for the potential past gravitational instability of this system, likely accounting for the rapid formation of a circumbinary companion. We also report the discovery of resolved continuum emission associated with HD 34700B (projected separation ˜1850 au), which we explain through a circumstellar disk.

ID: 158100
Type: article
Authors: Kral, Quentin; Matrà, Luca; Kennedy, Grant M.; Marino, Sebastian; Wyatt, Mark C.
Abstract: Gas detection around main-sequence stars is becoming more common with around 20 systems showing the presence of CO. However, more detections are needed, especially around later spectral type stars to better understand the origin of this gas and refine our models. To do so, we carried out a survey of 10 stars with predicted high likelihoods of secondary CO detection using ALMA in band 6. We looked for continuum emission of mm-dust as well as gas emission (CO and CN transitions). The continuum emission was detected in 9/10 systems for which we derived the discs' dust masses and geometrical properties, providing the first mm-wave detection of the disc around HD 106906, the first mm-wave radius for HD 114082, 117214, HD 15745, HD 191089, and the first radius at all for HD 121191. A crucial finding of our paper is that we detect CO for the first time around the young 10-16 Myr old G1V star HD 129590, similar to our early Sun. The gas seems colocated with its planetesimal belt and its total mass is likely in the range of (2-10) × 10^-5 M_⊕. This first gas detection around a G-type main-sequence star raises questions as to whether gas may have been released in the Solar system as well in its youth, which could potentially have affected planet formation. We also detected CO gas around HD 121191 at a higher signal-to-noise ratio than previously and find that the CO lies much closer-in than the planetesimals in the system, which could be evidence for the previously suspected CO viscous spreading owing to shielding preventing its photodissociation. Finally, we make estimates for the CO content in planetesimals and the HCN/CO outgassing rate (from CN upper limits), which we find are below the level seen in Solar system comets in some systems.

ID: 156466
Type: article
Authors: Marino, S.; Flock, M.; Henning, Th; Kral, Q.; Matrà, Luca; Wyatt, M. C.
Abstract: The presence of CO gas around 10-50 Myr old A stars with debris discs has sparked debate on whether the gas is primordial or secondary. Since secondary gas released from planetesimals is poor in H₂, it was thought that CO would quickly photodissociate never reaching the high levels observed around the majority of A stars with bright debris discs. Kral et al. showed that neutral carbon produced by CO photodissociation can effectively shield CO and potentially explain the high CO masses around 9 A stars with bright debris discs. Here, we present a new model that simulates the gas viscous evolution, accounting for carbon shielding and how the gas release rate decreases with time as the planetesimal disc loses mass. We find that the present gas mass in a system is highly dependant on its evolutionary path. Since gas is lost on long time-scales, it can retain a memory of the initial disc mass. Moreover, we find that gas levels can be out of equilibrium and quickly evolving from a shielded on to an unshielded state. With this model, we build the first population synthesis of gas around A stars, which we use to constrain the disc viscosity. We find a good match with a high viscosity (α ∼ 0.1), indicating that gas is lost on time-scales ∼1-10 Myr. Moreover, our model also shows that high CO masses are not expected around FGK stars since their planetesimal discs are born with lower masses, explaining why shielded discs are only found around A stars. Finally, we hypothesize that the observed carbon cavities could be due to radiation pressure or accreting planets.

ID: 156381
Type: article
Authors: Marino, S.; Wyatt, M. C.; Kennedy, G. M.; Kama, M.; Matrà, Luca; Triaud, A. H. M. J.; Henning, Th
Abstract: Low-mass stars might offer today the best opportunities to detect and characterize planetary systems, especially those harbouring close-in low-mass temperate planets. Among those stars, TRAPPIST-1 is exceptional since it has seven Earth-sized planets, of which three could sustain liquid water on their surfaces. Here we present new and deep ALMA observations of TRAPPIST-1 to look for an exo-Kuiper belt which can provide clues about the formation and architecture of this system. Our observations at 0.88 mm did not detect dust emission, but can place an upper limit of 23 µJy if the belt is smaller than 4 au, and 0.15 mJy if resolved and 100 au in radius. These limits correspond to low dust masses of ∼10^-5 to 10^-2 M_⊕, which are expected after 8 Gyr of collisional evolution unless the system was born with a >20 M_⊕ belt of 100 km-sized planetesimals beyond 40 au or suffered a dynamical instability. This 20 M_⊕ mass upper limit is comparable to the combined mass in TRAPPIST-1 planets, thus it is possible that most of the available solid mass in this system was used to form the known planets. A similar analysis of the ALMA data on Proxima Cen leads us to conclude that a belt born with a mass ≳1 M_⊕ in 100 km-sized planetesimals could explain its putative outer belt at 30 au. We recommend that future characterizations of debris discs around low-mass stars should focus on nearby and young systems if possible.

ID: 157701
Type: article
Authors: Matrà, Luca; Dent, William R. F.; Wilner, David J.; Marino, Sebastián; Wyatt, Mark C.; Marshall, Jonathan P.; Su, Kate Y. L.; Chavez, Miguel; Hales, Antonio; Hughes, A. Meredith; Greaves, Jane S.; Corder, Stuartt A.
Abstract: The Vega planetary system hosts the archetype of extrasolar Kuiper belts and is rich in dust from the sub-astronomical unit region out to hundreds of astronomical units, suggesting intense dynamical activity. We present Atacama Large Millimeter/submillimeter Array (ALMA) millimeter observations that detect and resolve the outer dust belt from the star for the first time. The interferometric visibilities show that the belt can be fit by a Gaussian model or by power-law models with a steep inner edge (at 60-80 au). The belt is very broad, extending out to at least 150-200 au. We strongly detect the star and set a stringent upper limit to warm dust emission previously detected in the infrared. We discuss three scenarios that could explain the architecture of Vega's planetary system, including the new ALMA constraints: no outer planets, a chain of low-mass planets, and a single giant planet. The planetless scenario is only feasible if the outer belt was born with the observed sharp inner edge. If, instead, the inner edge is currently being truncated by a planet, then the planet must be $\gtrsim 6$ ${M}_{\oplus }$ and at $\lesssim 71\,\mathrm{au}$ to have cleared its chaotic zone within the system age. In the planet chain scenario, outward planet migration and inward scattering of planetesimals could produce the hot and warm dust observed in the inner regions of the system. In the single giant planet scenario, an asteroid belt could be responsible for the warm dust, and mean motion resonances with the planet could put asteroids on star-grazing orbits, producing the hot dust.

ID: 155674
Type: article
Authors: Rosotti, G. P.; Benisty, M.; Juhász, A.; Teague, Richard; Clarke, C.; Dominik, C.; Dullemond, C. P.; Klaassen, P. D.; Matrà, Luca; Stolker, T.
Abstract: Scattered light high-resolution imaging of the protoplanetary disc orbiting HD100453 shows two symmetric spiral arms, possibly launched by an external stellar companion. In this paper, we present new, sensitive high-resolution (∼30 mas) Band 7 ALMA observations of this source. This is the first source where we find counterparts in the sub-mm continuum to both scattered light spirals. The CO J = 3-2 emission line also shows two spiral arms; in this case, they can be traced over a more extended radial range, indicating that the southern spiral arm connects to the companion position. This is clear evidence that the companion is responsible for launching the spirals. The pitch angle of the submillimetre continuum spirals (∼6°) is lower than the one in scattered light (∼16°). We show that hydrodynamical simulations of binary-disc interaction can account for the difference in pitch angle only if one takes into account that the mid-plane is colder than the upper layers of the disc, as expected for the case of externally irradiated discs.

ID: 157796
Type: article
Authors: Tanner, Angelle; Plavchan, Peter; Bryden, Geoff; Kennedy, Grant; Matrá, Luca; Cronin-Coltsmann, Patrick; Lowrance, Patrick; Henry, Todd; Riaz, Basmah; Gizis, John E.; Riedel, Adric; Choquet, Elodie
Abstract: A set of twenty late-type (K5-M5) stars were observed with the Herschel Space Observatory at 100 and 160 microns with the goal of searching for far-infrared excesses indicative of the presence of circumstellar disks. Out of this sample, four stars (TYC 7443-1102-1, TYC 9340-437-1, GJ 784 and GJ 707) have infrared excesses above their stellar photospheres at either 100 or 160 μm or both. At 100 microns TYC 9340-437-1 is spatially resolved with a shape that suggests it is surrounded by a face-on disk. The 100 μm excess flux associated with GJ 707 is marginal at around 3σ. The excess flux associated with GJ 784 is most likely due to a background galaxy as the dust radius estimated from the spectral energy fit implies that any associated dust disk should have been resolved in the Herschel images but is not. TYC 7443-1102-1 has been observed with ALMA which resolves the emission at its location into two distinct sources making the Herschel excess most likely also due to a background galaxy. It is worth noting that this star is in the 23 Myr old β Pic association. With a disk luminosity on the order of 10^-3 L_*, this system is an ideal follow-up target for high-contrast imaging and ALMA.

ID: 154182
Type: article
Authors: Bayo, A.; Olofsson, J.; Matrà, L.; Beamín, J. C.; Gallardo, J.; De Gregorio-Monsalvo, I.; Booth, M.; Zamora, C.; Iglesias, D.; Henning, Th; Schreiber, M. R.; Cáceres, C.
Abstract: Debris discs can be seen as the leftovers of giant planet formation and the possible nurseries of rocky planets. While M-type stars outnumber more massive stars we know very little about the time evolution of their circumstellar discs at ages older than ̃10 Myr. Sub-millimetre observations are best to provide first order estimates of the available mass reservoir and thus better constrain the evolution of such discs. Here, we present ALMA Cycle 3 Band 7 observations of the debris disc around the M2 star TWA 7, which had been postulated to harbour two spatially separated dust belts, based on unresolved far-infrared and sub-millimetre data. We show that most of the emission at wavelengths longer than ̃300 μm is in fact arising from a contaminant source, most likely a sub-mm galaxy, located at about 6.6 arcsec east of TWA 7 (in 2016). Fortunately, the high resolution of our ALMA data allows us to disentangle the contaminant emission from that of the disc and report a significant detection of the disc in the sub-millimetre for the first time with a flux density of 2.1 ± 0.4 mJy at 870 {μ m}. With this detection, we show that the spectral energy distribution can be reproduced with a single dust belt.

ID: 150453
Type: article
Authors: Booth, Mark; Matrà, Luca; Su, Kate Y. L.; Kral, Quentin; Hales, Antonio S.; Dent, William R. F.; Hughes, A. Meredith; MacGregor, Meredith A.; Löhne, Torsten; Wilner, David J.
Abstract: One of the defining properties of debris discs compared to protoplanetary discs used to be their lack of gas, yet small amounts of gas have been found around an increasing number of debris discs in recent years. These debris discs found to have gas tend to be both young and bright. In this paper, we conduct a deep search for CO gas in the system HD 95086 - a 17 Myr old, known planet host that also has a debris disc with a high fractional luminosity of 1.5 × 10^-3. Using the Atacama Large Millimeter/submillimeter Array (ALMA), we search for CO emission lines in bands 3, 6, and 7. By implementing a spectro-spatial filtering technique, we find tentative evidence for CO J = 2-1 emission in the disc located at a velocity, 8.5 ± 0.2 km s^-1, consistent with the radial velocity of the star. The tentative detection suggests that the gas on the east side of the disc is moving towards us. In the same region where continuum emission is detected, we find an integrated line flux of 9.5 ± 3.6 mJy km s^-1, corresponding to a CO mass of (1.4-13) × 10^-6 M_⊕. Our analysis confirms that the level of gas present in the disc is inconsistent with the presence of primordial gas in the system and is consistent with second generation production through the collisional cascade.

ID: 154639
Type: article
Authors: Faramaz, Virginie; Krist, John; Stapelfeldt, Karl R.; Bryden, Geoffrey; Mamajek, Eric E.; Matrà, Luca; Booth, Mark; Flaherty, Kevin; Hales, Antonio S.; Hughes, A. Meredith; Bayo, Amelia; Casassus, Simon; Cuadra, Jorge; Olofsson, Johan; Su, Kate Y. L.; Wilner, David J.
Abstract: We present here new observations of the eccentric debris ring surrounding the Gyr-old solar-type star HD 202628: at millimeter wavelengths with ALMA, at far-infrared wavelengths with Herschel, and in scattered light with the Hubble Space Telescope (HST). The ring inner edge is found to be consistent between ALMA and HST data. As radiation pressure affects small grains seen in scattered-light, the ring appears broader at optical than at millimeter wavelengths. The best fit to the ring seen with ALMA has inner and outer edges at 143.1 ± 1.7 au and 165.5 ± 1.4, respectively, and an inclination of 57.°4 ± 0.4 from face- on. The offset of the ring center of symmetry from the star allows us to quantify its eccentricity to be e={0.09}_-0.01^+0.02. This eccentric feature is also detected in low resolution Herschel/PACS observations, under the form of a pericenter-glow. Combining the infrared and millimeter photometry, we retrieve a disk grain size distribution index of ̃-3.4, and therefore exclude in situ formation of the inferred belt-shaping perturber, for which we provide new dynamical constraints. Finally, ALMA images show four point-like sources that exceed 100 μJy, one of them being just interior to the ring. Although the presence of a background object cannot be excluded, we cannot exclude either that this source is circumplanetary material surrounding the belt-shaper, in which case degeneracies between its mass and orbital parameters could be lifted, allowing us to fully characterize such a distant planet in this mass and age regime for the very first time.

ID: 155464
Type: article
Authors: Kennedy, Grant M.; Matrà, Luca; Facchini, Stefano; Milli, Julien; Panić, Olja; Price, Daniel; Wilner, David J.; Wyatt, Mark C.; Yelverton, Ben M.
Abstract: Nearly all young stars are initially surrounded by `protoplanetary' disks of gas and dust, and in the case of single stars at least 30% of these disks go on to form planets<sup>1</sup>. The process of protoplanetary disk formation can result in initial misalignments, where the disk orbital plane is different from the stellar equator in single- star systems, or different from the binary orbital plane in systems with two stars<sup>2</sup>. A quirk of the dynamics means that initially misaligned `circumbinary' disks-those that surround two stars-are predicted to evolve to one of two possible stable configurations: one where the disk and binary orbital planes are coplanar and one where they are perpendicular (a `polar' configuration)^3-5. Previous work has found coplanar circumbinary disks⁶, but no polar examples were known until now. Here, we report the first discovery of a protoplanetary circumbinary disk in the polar configuration, supporting the predictions that such disks should exist. The disk shows some characteristics that are similar to disks around single stars, and that are attributed to dust growth. Thus, the first stages of planet formation appear able to proceed in polar circumbinary disks.

ID: 154597
Type: article
Authors: Kral, Quentin; Marino, Sebastian; Wyatt, Mark C.; Kama, Mihkel; Matrà, Luca
Abstract: Despite being >10 Myr, there are ∼10 debris discs with as much CO gas as in protoplanetary discs. Such discs have been assumed to be 'hybrid', i.e. with secondary dust but primordial gas. Here, we show that both the dust and gas in such systems could instead be secondary, with the high CO content caused by accumulation of neutral carbon (C⁰) that shields CO from photodissociating; i.e. these could be 'shielded secondary discs'. New ALMA observations are presented of HD131835 that detect ∼3 × 10^-3 M_⊕ of C⁰, the majority 40-200 au from the star, in sufficient quantity to shield the previously detected CO. A simple semi-analytic model for the evolution of CO, C, and O originating in a volatile-rich planetesimal belt shows how CO shielding becomes important when the viscous evolution is slow (low α parameter) and/or the CO production rate is high. Shielding by C⁰ may also cause the CO content to reach levels at which CO self-shields, and the gas disc may become massive enough to affect the dust evolution. Application to the HD 131835 observations shows these can be explained if α ∼ 10^-3; an inner cavity in C⁰ and CO may also mean the system has yet to reach steady state. Application to other debris discs with high CO content finds general agreement for α = 10^-3 to 0.1. The shielded secondary nature of these gas discs can be tested by searching for C⁰, as well as CN, N₂, and CH⁺, which are also expected to be shielded by C⁰.

ID: 154579
Type: article
Authors: Macri, Lucas M.; Kraan-Korteweg, Renée C.; Lambert, Trystan; Alonso, María Victoria; Berlind, Perry; Calkins, Michael; Erdoğdu, Pirin; Falco, Emilio E.; Jarrett, Thomas H.; Mink, Jessica D.
Abstract: The Two Micron All-Sky Survey (2MASS) Redshift Survey was started two decades ago with the goal of mapping the three-dimensional distribution of an all-sky flux-limited (K _s < 11.75 mag) sample of ∼45,000 galaxies. Our first data release presented an unprecedented uniform coverage for most of the celestial sphere, with redshifts for ∼98% of our sample. However, we were missing redshifts for ∼18% of the catalog entries that were located within the "Zone of Avoidance" (| b| < 10^\circ )-an important region of the sky for studies of the large- scale structure and cosmic flows. In this second and final data release, we present redshifts for all 1041 2MRS galaxies that previously lacked this information, as well as updated measurements for 27 others.

ID: 150913
Type: article
Authors: Marino, S.; Yelverton, B.; Booth, M.; Faramaz, V.; Kennedy, G. M.; Matrà, Luca; Wyatt, M. C.
Abstract: In the last few years, multiwavelength observations have revealed the ubiquity of gaps/rings in circumstellar discs. Here we report the first ALMA observations of HD 92945 at 0.86 mm, which reveal a gap at about 73 ± 3 au within a broad disc of planetesimals that extends from 50 to 140 au. We find that the gap is 20^{+10}_{-8} au wide. If cleared by a planet in situ, this planet must be less massive than 0.6 M_Jup, or even lower if the gap was cleared by a planet that formed early in the protoplanetary disc and prevented planetesimal formation at that radius. By comparing opposite sides of the disc, we also find that the disc could be asymmetric. Motivated by the asymmetry and the fact that planets might be more frequent closer to the star in exoplanetary systems, we show that the gap and asymmetry could be produced by two planets interior to the disc through secular resonances. These planets excite the eccentricity of bodies at specific disc locations, opening radial gaps in the planetesimal distribution. New observations are necessary to confirm if the disc is truly asymmetric, thus favouring the secular resonance model, or if the apparent asymmetry is due to a background galaxy, favouring the in situ planet scenario. Finally, we also report the non-detection of CO and HCN gas, confirming that no primordial gas is present. The CO and HCN non-detections are consistent with the destruction of volatile-rich Solar system-like comets.

ID: 150914
Type: article
Authors: Matrà, Luca; Öberg, Karin I.; Wilner, David James; Olofsson, J.; Bayo, Amelia
Abstract: Millimeter observations of CO gas in planetesimal belts show a high detection rate around A stars, but few detections for later type stars. We present the first CO detection in a planetesimal belt around an M star, TWA 7. The optically thin CO (J = 3-2) emission is colocated with previously identified dust emission from the belt, and the emission velocity structure is consistent with Keplerian rotation around the central star. The detected CO is not well shielded against photodissociation, and must thus be continuously replenished by gas release from exocomets within the belt. We analyze in detail the process of exocometary gas release and destruction around young M dwarfs and how this process compares to earlier type stars. Taking these differences into account, we find that CO generation through exocometary gas release naturally explains the increasing CO detection rates with stellar luminosity, mostly because the CO production rate from the collisional cascade is directly proportional to stellar luminosity. More luminous stars will therefore on average host more massive (and hence more easily detectable) exocometary CO disks, leading to the higher detection rates observed. The current CO detection rates are consistent with a ubiquitous release of exocometary gas in planetesimal belts, independent of spectral type.

ID: 155310
Type: article
Authors: Matrà, Luca; Wyatt, M. C.; Wilner, David J.; Dent, W. R. F.; Marino, S.; Kennedy, G. M.; Milli, J.
Abstract: The inclination distribution of the Kuiper Belt provides unique constraints on its origin and dynamical evolution, motivating vertically resolved observations of extrasolar planetesimal belts. We present ALMA observations of millimeter emission in the near edge-on planetesimal belt around β Pictoris, finding that the vertical distribution is significantly better described by the sum of two Gaussians compared to a single Gaussian. This indicates that, as for the Kuiper Belt, the inclination distribution of β Pic's belt is better described by the sum of dynamically hot and cold populations, rather than a single component. The hot and cold populations have rms inclinations of {8.9}_-0.5^+0.7 and {1.1}_-0.5^+0.5 degrees. We also report that an axisymmetric belt model provides a good fit to new and archival ALMA visibilities, and confirm that the midplane is misaligned with respect to β Pic b's orbital plane. However, we find no significant evidence for either the inner disk tilt observed in scattered light and CO emission or the southwest/northeast asymmetry previously reported for millimeter emission. Finally, we consider the origin of the belt's inclination distribution. Secular perturbations from β Pic b are unlikely to provide sufficient dynamical heating to explain the hot population throughout the belt's radial extent, and viscous stirring from large bodies within the belt alone cannot reproduce the two populations observed. This argues for an alternative or additional scenario, such as planetesimal being born with high inclinations, or the presence of a "β Pic c" planet, potentially migrating outward near the belt's inner edge.

ID: 154264
Type: article
Authors: Sepulveda, Aldo G.; Matrà, Luca; Kennedy, Grant M.; del Burgo, Carlos; Öberg, Karin I.; Wilner, David J.; Marino, Sebastián; Booth, Mark; Carpenter, John M.; Davies, Claire L.; Dent, William R. F.; Ertel, Steve; Lestrade, Jean-Francois; Marshall, Jonathan P.; Milli, Julien; Wyatt, Mark C.; MacGregor, Meredith A.; Matthews, Brenda C.
Abstract: Debris disks are extrasolar analogs to our own Kuiper Belt and they are detected around at least 17% of nearby Sun-like stars. The morphology and dynamics of a disk encode information about its history, as well as that of any exoplanets within the system. We used the Atacama Large Millimeter/submillimeter Array (ALMA) to obtain 1.3 mm observations of the debris disk around the nearby F5V star HD 170773. We image the face-on ring and determine its fundamental parameters by forward-modeling the interferometric visibilities through a Markov Chain Monte Carlo approach. Using a symmetric Gaussian surface density profile, we find a 71 ± 4 au wide belt with a radius of {193}_-3⁺² au, a relatively large radius compared with most other millimeter-resolved belts around late A/early F type stars. This makes HD 170773 part of a group of four disks around A and F stars with radii larger than expected from the recently reported planetesimal belt radius-stellar luminosity relation. Two of these systems are known to host directly imaged giant planets, which may point to a connection between large belts and the presence of long-period giant planets. We also set upper limits on the presence of CO and CN gas in the system, which imply that the exocomets that constitute this belt have CO and HCN ice mass fractions of <77% and <3%, respectively. This is consistent with solar system comets and other exocometary belts.

ID: 147048
Type: article
Authors: Kennedy, Grant M.; Marino, Sebastian; Matrà, Luca; Panic, Olja; Wilner, David; Wyatt, Mark C.; Yelverton, Ben
Abstract: The young A0V star HR 4796A is host to a bright and narrow ring of dust, thought to originate in collisions between planetesimals within a belt analogous to the Solar system's Edgeworth-Kuiper belt. Here we present high spatial resolution 880 mum continuum images from the Atacama Large Millimeter Array. The 80 au radius dust ring is resolved radially with a characteristic width of 10 au, consistent with the narrow profile seen in scattered light. Our modelling consistently finds that the disc is also vertically resolved with a similar extent. However, this extent is less than the beam size, and a disc that is dynamically very cold (i.e. vertically thin) provides a better theoretical explanation for the narrow scattered light profile, so we remain cautious about this conclusion. We do not detect ¹²CO J=3-2 emission, concluding that unless the disc is dynamically cold the CO+CO₂ ice content of the planetesimals is of order a few per cent or less. We consider the range of semi-major axes and masses of an interior planet supposed to cause the ring's eccentricity, finding that such a planet should be more massive than Neptune and orbit beyond 40 au. Independent of our ALMA observations, we note a conflict between mid-IR pericentre-glow and scattered light imaging interpretations, concluding that models where the spatial dust density and grain size vary around the ring should be explored.

ID: 149370
Type: article
Authors: Marino, S.; Carpenter, J.; Wyatt, M. C.; Booth, M.; Casassus, S.; Faramaz, V.; Guzman, V.; Hughes, A. M.; Isella, A.; Kennedy, G. M.; Matrà, L.; Ricci, L.; Corder, S.
Abstract: While detecting low-mass exoplanets at tens of au is beyond current instrumentation, debris discs provide a unique opportunity to study the outer regions of planetary systems. Here, we report new ALMA observations of the 80-200 Myr old Solar analogue HD 107146 that reveal the radial structure of its exo-Kuiper belt at wavelengths of 1.1 and 0.86 mm. We find that the planetesimal disc is broad, extending from 40 to 140 au, and it is characterized by a circular gap extending from 60 to 100 au in which the continuum emission drops by about 50 per cent. We also report the non-detection of the CO J = 3-2 emission line, confirming that there is not enough gas to affect the dust distribution. To date, HD 107146 is the only gas-poor system showing multiple rings in the distribution of millimetre sized particles. These rings suggest a similar distribution of the planetesimals producing small dust grains that could be explained invoking the presence of one or more perturbing planets. Because the disc appears axisymmetric, such planets should be on circular orbits. By comparing N-body simulations with the observed visibilities we find that to explain the radial extent and depth of the gap, it would require the presence of multiple low-mass planets or a single planet that migrated through the disc. Interior to HD 107146's exo-Kuiper belt we find extended emission with a peak at ˜20 au and consistent with the inner warm belt that was previously predicted based on 22 μm excess as in many other systems. This warm belt is the first to be imaged, although unexpectedly suggesting that it is asymmetric. This could be due to a large belt eccentricity or due to clumpy structure produced by resonant trapping with an additional inner planet.

ID: 145805
Type: article
Authors: Matrà, L.; Wilner, D. J.; Öberg, K. I.; Andrews, S. M.; Loomis, R. A.; Wyatt, M. C.; Dent, W. R. F.
Abstract: 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 ? Pictoris belt with the Submillimeter Array (SMA), reporting upper limits for CN, HCN, HCO⁺, N₂H⁺, and H₂CO, as well as for H₂S, CH₃OH, SiO, and DCN from archival ALMA data. Nondetections 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 nonlocal thermodynamic equilibrium excitation model to include UV fluorescence, finding it plays a key role in CO and