Browsing by Author "Long, Feng"

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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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    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.