Browsing by Author "Pegues, Jamila"

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    An ALMA Survey of H2CO in Protoplanetary Disks
    (IOP PUBLISHING LTD, 2020) Pegues, Jamila; Oberg, Karin I.; Bergner, Jennifer B.; Loomis, Ryan A.; Qi, Chunhua; Le Gal, Romane; Cleeves, L. Ilsedore; Guzman, Viviana V.; Huang, Jane; Jorgensen, Jes K.; Andrews, Sean M.; Blake, Geoffrey A.; Carpenter, John M.; Schwarz, Kamber R.; Williams, Jonathan P.; Wilner, David J.
    H2CO is one of the most abundant organic molecules in protoplanetary disks and can serve as a precursor to more complex organic chemistry. We present an Atacama Large Millimeter/submillimeter Array survey of H2CO toward 15 disks covering a range of stellar spectral types, stellar ages, and dust continuum morphologies. H2CO is detected toward 13 disks and tentatively detected toward a fourteenth. We find both centrally peaked and centrally depressed emission morphologies, and half of the disks show ring-like structures at or beyond expected CO snowline locations. Together these morphologies suggest that H2CO in disks is commonly produced through both gas-phase and CO-ice-regulated grain-surface chemistry. We extract disk-averaged and azimuthally-averaged H2CO excitation temperatures and column densities for four disks with multiple H2CO line detections. The temperatures are between 20-50 K, with the exception of colder temperatures in the DM Tau disk. These temperatures suggest that H2CO emission in disks generally emerges from the warm molecular layer, with some contributions from the colder midplane. Applying the same H2CO excitation temperatures to all disks in the survey, we find that H2CO column densities span almost three orders of magnitude (similar to 5 x 10(11) -5 x 10(14) cm(-2)). The column densities appear uncorrelated with disk size and stellar age, but Herbig Ae disks may have less H2CO compared to T Tauri disks, possibly because of less CO freeze-out. More H2CO observations toward Herbig Ae disks are needed to confirm this tentative trend, and to better constrain under which disk conditions H2CO and other oxygen-bearing organics efficiently form during planet formation.
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    An Atacama Large Millimeter/submillimeter Array Survey of Chemistry in Disks around M4-M5 Stars
    (2021) Pegues, Jamila; Oberg, Karin I.; Bergner, Jennifer B.; Huang, Jane; Pascucci, Ilaria; Teague, Richard; Andrews, Sean M.; Bergin, Edwin A.; Cleeves, L. Ilsedore; Guzman, Viviana V.; Long, Feng; Qi, Chunhua; Wilner, David J.
    M-stars are the most common hosts of planetary systems in the Galaxy. Protoplanetary disks around M-stars thus offer a prime opportunity to study the chemistry of planet-forming environments. We present an Atacama Large Millimeter/submillimeter Array survey of molecular line emission toward a sample of five protoplanetary disks around M4-M5 stars (FP Tau, J0432+1827, J1100-7619, J1545-3417, and Sz 69). These observations can resolve chemical structures down to tens of astronomical units. Molecular lines of (CO)-C-12, (CO)-C-13, (CO)-O-18, C2H, and HCN are detected toward all five disks. Lines of H2CO and DCN are detected toward 2/5 and 1/5 disks, respectively. For disks with resolved (CO)-O-18, C2H, HCN, and H2CO emission, we observe substructures similar to those previously found in disks around solar-type stars (e.g., rings, holes, and plateaus). C2H and HCN excitation conditions estimated interior to the pebble disk edge for the bright disk J1100-7619 are consistent with previous measurements around solar-type stars. The correlation previously found between C2H and HCN fluxes for solar-type disks extends to our M4-M5 disk sample, but the typical C2H/HCN ratio is higher for the M4-M5 disk sample. This latter finding is reminiscent of the hydrocarbon enhancements found by previous observational infrared surveys in the innermost (<10 au) regions of M-star disks, which is intriguing since our disk-averaged fluxes are heavily influenced by flux levels in the outermost disk, exterior to the pebble disk edge. Overall, most of the observable chemistry at 10-100 au appears similar for solar-type and M4-M5 disks, but hydrocarbons may be more abundant around the cooler stars.