Browsing by Author "Andrews, Sean M."

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    ALMA Detection of Dust Trapping around Lagrangian Points in the LkCa 15 Disk
    (IOP Publishing, 2022) Long, Feng; Andrews, Sean M.; Zhang, Shangjia; Qi, Chunhua; Benisty, Myriam; Facchini, Stefano; Isella, Andrea; Wilner, David J.; Bae, Jaehan; Huang, Jane; Loomis, Ryan A.; Öberg, Karin I.; Zhu, Zhaohuan
    We present deep high-resolution (∼50 mas, 8 au) Atacama Large Millimeter/submillimeter Array (ALMA) 0.88 and 1.3 mm continuum observations of the LkCa 15 disk. The emission morphology shows an inner cavity and three dust rings at both wavelengths, but with slightly narrower rings at the longer wavelength. Along a faint ring at 42 au, we identify two excess emission features at ∼10σ significance at both wavelengths: one as an unresolved clump and the other as an extended arc, separated by roughly 120° in azimuth. The clump is unlikely to be a circumplanetary disk (CPD) as the emission peak shifts between the two wavelengths even after accounting for orbital motion. Instead, the morphology of the 42 au ring strongly resembles the characteristic horseshoe orbit produced in planet–disk interaction models, where the clump and the arc trace dust accumulation around Lagrangian points L 4 and L 5, respectively. The shape of the 42 au ring, dust trapping in the outer adjacent ring, and the coincidence of the horseshoe ring location with a gap in near-IR scattered light, are all consistent with the scenario of planet sculpting, with the planet likely having a mass between those of Neptune and Saturn. We do not detect pointlike emission associated with a CPD around the putative planet location (0.″27 in projected separation from the central star at a position angle of ∼60°), with upper limits of 70 and 33 μJy at 0.88 and 1.3 mm, respectively, corresponding to dust mass upper limits of 0.02–0.03 M ⊕.
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    CO and Dust Properties in the TW Hya Disk from High-resolution ALMA Observations
    (IOP Publishing, 2018) Huang, Jane; Andrews, Sean M.; Cleeves, L. Ilsedore; Öberg, Karin I.; Wilner, David J.; Bai, Xuening; Birnstiel, Til; Carpenter, John; Hughes, A. Meredith; Isella, Andrea; Pérez, Laura M.; Ricci, Luca; Zhu, Zhaohuan
    We analyze high angular resolution ALMA observations of the TW Hya disk to place constraints on the CO and dust properties. We present new, sensitive observations of the 12CO J = 3 − 2 line at a spatial resolution of 8 au (0farcs14). The CO emission exhibits a bright inner core, a shoulder at r ≈ 70 au, and a prominent break in slope at r ≈ 90 au. Radiative transfer modeling is used to demonstrate that the emission morphology can be reasonably reproduced with a 12CO column density profile featuring a steep decrease at r ≈ 15 au and a secondary bump peaking at r ≈ 70 au. Similar features have been identified in observations of rarer CO isotopologues, which trace heights closer to the midplane. Substructure in the underlying gas distribution or radially varying CO depletion that affects much of the disk's vertical extent may explain the shared emission features of the main CO isotopologues. We also combine archival 1.3 mm and 870 μm continuum observations to produce a spectral index map at a spatial resolution of 2 au. The spectral index rises sharply at the continuum emission gaps at radii of 25, 41, and 47 au. This behavior suggests that the grains within the gaps are no larger than a few millimeters. Outside the continuum gaps, the low spectral index values of α ≈ 2 indicate either that grains up to centimeter size are present or that the bright continuum rings are marginally optically thick at millimeter wavelengths.
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    Gemini-LIGHTS: Herbig Ae/Be and Massive T Tauri Protoplanetary Disks Imaged with Gemini Planet Imager
    (IOP Publishing, 2022) Rich, Evan A.; Monnier, John D.; Aarnio, Alicia; Laws, Anna S. E.; Setterholm, Benjamin R.; Wilner, David J.; Calvet, Nuria; Harries, Tim; Miller, Chris; Davies, Claire L.; Adams, Fred C.; Andrews, Sean M.; Bae, Jaehan; Espaillat, Catherine; Greenbaum, Alexandra Z.; Hinkley, Sasha; Kraus, Stefan; Hartmann, Lee; Isella, Andrea; McClure, Melissa; Oppenheimer, Rebecca; Pérez, Laura M.; Zhu, Zhaohuan
    We present the complete sample of protoplanetary disks from the Gemini- Large Imaging with the Gemini Planet Imager Herbig/T Tauri Survey, which observed bright Herbig Ae/Be stars and T Tauri stars in near-infrared polarized light to search for signatures of disk evolution and ongoing planet formation. The 44 targets were chosen based on their near- and mid-infrared colors, with roughly equal numbers of transitional, pre-transitional, and full disks. Our approach explicitly did not favor well-known, “famous” disks or those observed by the Atacama Large Millimeter/submillimeter Array, resulting in a less-biased sample suitable to probe the major stages of disk evolution during planet formation. Our optimized data reduction allowed polarized flux as low as 0.002% of the stellar light to be detected, and we report polarized scattered light around 80% of our targets. We detected point-like companions for 47% of the targets, including three brown dwarfs (two confirmed, one new), and a new super-Jupiter-mass candidate around V1295 Aql. We searched for correlations between the polarized flux and system parameters, finding a few clear trends: the presence of a companion drastically reduces the polarized flux levels, far-IR excess correlates with polarized flux for nonbinary systems, and systems hosting disks with ring structures have stellar masses <3 M⊙. Our sample also included four hot, dusty “FS CMa” systems, and we detected large-scale ( >100 au) scattered light around each, signs of extreme youth for these enigmatic systems. Science-ready images are publicly available through multiple distribution channels using a new FITS file standard that has been jointly developed with members of the Very Large Telescope Spectro-polarimetric High-contrast Exoplanet Research team.
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    Mapping Protoplanetary Disk Vertical Structure with CO Isotopologue Line Emission
    (IOP Publishing, 2023) Law, Charles J.; Teague, Richard; Öberg, Karin I.; Rich, Evan A.; Andrews, Sean M.; Bae, Jaehan; Benisty, Myriam; Facchini, Stefano; Flaherty, Kevin; Isella, Andrea; Jin, Sheng; Hashimoto, Jun; Huang, Jane; Loomis, Ryan A.; Long, Feng; Muñoz-Romero, Carlos E.; Paneque-Carreño, Teresa; Pérez, Laura M.; Qi, Chunhua; Schwarz, Kamber R.; Stadler, Jochen; Tsukagoshi, Takashi; Wilner, David J.; Plas, Gerrit van der
    High-spatial-resolution observations of CO isotopologue line emission in protoplanetary disks at mid-inclinations (≈30°–75°) allow us to characterize the gas structure in detail, including radial and vertical substructures, emission surface heights and their dependencies on source characteristics, and disk temperature profiles. By combining observations of a suite of CO isotopologues, we can map the two-dimensional (r, z) disk structure from the disk upper atmosphere, as traced by CO, to near the midplane, as probed by less abundant isotopologues. Here, we present high-angular-resolution (≲0.″1 to ≈0.″2; ≈15–30 au) observations of CO, 13CO, and C18O in either or both J = 2–1 and J = 3–2 lines in the transition disks around DM Tau, Sz 91, LkCa 15, and HD 34282. We derived line emission surfaces in CO for all disks and in 13CO for the DM Tau and LkCa 15 disks. With these observations, we do not resolve the vertical structure of C18O in any disk, which is instead consistent with C18O emission originating from the midplane. Both the J = 2–1 and J = 3–2 lines show similar heights. Using the derived emission surfaces, we computed radial and vertical gas temperature distributions for each disk, including empirical temperature models for the DM Tau and LkCa 15 disks. After combining our sample with literature sources, we find that 13CO line emitting heights are also tentatively linked with source characteristics, e.g., stellar host mass, gas temperature, disk size, and show steeper trends than seen in CO emission surfaces.
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    On the radio detectability of circumplanetary discs
    (Oxford University Press, 2018) Zhu, Zhaohuan; Andrews, Sean M.; Isella, Andrea
    Discs around young planets, so-called circumplanetary discs (CPDs), are essential for planet growth, satellite formation, and planet detection. We study the millimetre and centimetre emission from accreting CPDs by using the simple α disc model. We find that it is easier to detect CPDs at shorter radio wavelengths (e.g. λ ≲ 1 mm). For example, if the system is 140 pc away from us, deep observations (e.g. 5 h) at ALMA Band 7 (0.87 mm) are sensitive to as small as 0.03 lunar mass of dust in CPDs. If the CPD is around a Jupiter mass planet 20 au away from the host star and has a viscosity parameter α ≲ 0.001, ALMA can detect this disc when it accretes faster than 10−10M⊙yr−1⁠. ALMA can also detect the 'minimum mass sub-nebulae' disc if such a disc exists around a young planet in young stellar objects. However, to distinguish the embedded compact CPD from the circumstellar disc material, we should observe circumstellar discs with large gaps/cavities using the highest resolution possible. We also calculate the CPD fluxes at VLA bands, and discuss the possibility of detecting radio emission from jets/winds launched in CPDs. Finally we argue that, if the radial drift of dust particles is considered, the drifting time-scale for millimetre dust in CPDs can be extremely short. It only takes 102–103 yr for CPDs to lose millimetre dust. Thus, for CPDs to be detectable at radio wavelengths, mm-sized dust in CPDs needs to be replenished continuously, or the disc has a significant fraction of micron-sized dust or a high gas surface density so that the particle drifting time-scale is long, or the radial drift is prevented by other means (e.g. pressure traps).
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    The Millimeter Continuum Size–Frequency Relationship in the UZ Tau E Disk
    (IOP, 2018) Tripathi, Anjali; Andrews, Sean M.; Birnstiel, Tilman; Chandler, Claire J.; Isella, Andrea; Pérez, Laura M.; Harris, R.J.; Ricci, Luca; Wilner, David J.; Carpenter, John M.; Calvet, N.; Corder, S.A.; Deller, A.T.; Dullemond, C.P.; Greaves, J.S.; Henning, Th.; Kwon, W.; Lazio, J.; Linz, H.; Testi, L.
    We present high spatial resolution observations of the continuum emission from the young multiple star system UZ Tau at frequencies from 6 to 340 GHz. To quantify the spatial variation of dust emission in the UZ Tau E circumbinary disk, the observed interferometric visibilities are modeled with a simple parametric prescription for the radial surface brightnesses at each frequency. We find evidence that the spectrum steepens with radius in the disk, manifested as a positive correlation between the observing frequency and the radius that encircles a fixed fraction of the emission (R eff ∝ ν 0.34±0.08). The origins of this size–frequency relation are explored in the context of a theoretical framework for the growth and migration of disk solids. While that framework can reproduce a similar size–frequency relation, it predicts a steeper spectrum than that observed. Moreover, it comes closest to matching the data only on timescales much shorter (≤1 Myr) than the putative UZ Tau age (~2–3 Myr). These discrepancies are direct consequences of the rapid radial drift rates predicted by models of dust evolution in a smooth gas disk. One way to mitigate that efficiency problem is to invoke small-scale gas pressure modulations that locally concentrate drifting solids. If such particle traps reach high-continuum optical depths at 30–340 GHz with a ~30%–60% filling fraction in the inner disk (r lesssim 20 au), they can also explain the observed spatial gradient in the UZ Tau E disk spectrum.