An ALMA Survey of H₂CO in Protoplanetary Disks

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 (~5 × 10¹¹–5 × 10¹⁴ 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

Dynamical masses and stellar evolutionary model predictions of M stars

Funding: J.P. gratefully acknowledges the support of the National Science Foundation (NSF) Graduate Research Fellowship through grant Nos. DGE1144152 and DGE1745303. K.I.Ö. gratefully acknowledges the support of the Simons Foundation through a Simons Collaboration on the Origins of Life (SCOL) PI grant (No. 321183). G.J.H. is supported by general grant 11773002 awarded by the National Science Foundation of China. L.I.C. gratefully acknowledges support from the David and Lucille Packard Foundation, the Virginia Space Grant Consortium, and Johnson & Johnson’s WiSTEM2D Award. V.V.G. gratefully acknowledges support from FONDECYT Iniciación 11180904. Support for this work was also provided by NASA through the NASA Hubble Fellowship grant Nos. HST-HF2-51460.001-A, HST-HF2-51405.001-A, and HST-HF2-51429.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555.In this era of Gaia and ALMA, dynamical stellar mass measurements, derived from spatially and spectrally resolved observations of the Keplerian rotation of circumstellar disks, provide benchmarks that are independent of observations of stellar characteristics and their uncertainties. These benchmarks can then be used to validate and improve stellar evolutionary models, the latter of which can lead to both imprecise and inaccurate mass predictions for pre-main-sequence, low-mass (≤0.5 M⊙) stars. We present the dynamical stellar masses derived from disks around three M stars (FP Tau, J0432+1827, and J1100-7619) using ALMA observations of 12CO (J = 2-1) and 13CO (J = 2-1) emission. These are the first dynamical stellar mass measurements for J0432+1827 and J1100-7619 (0.192 ± 0.005 M⊙ and 0.461 ± 0.057 M⊙, respectively) and the most precise measurement for FP Tau (0.395 ± 0.012 M⊙). Fiducial stellar evolutionary model tracks, which do not include any treatment of magnetic activity, agree with the dynamical stellar mass measurement of J0432+1827 but underpredict the mass by ∼60% for FP Tau and by ∼80% for J1100-7619. Possible explanations for the underpredictions include inaccurate assumptions of stellar effective temperature, undetected binarity for J1100-7619, and that fiducial stellar evolutionary models are not complex enough to represent these stars. In the former case, the stellar effective temperatures would need to be increased by amounts ranging from ∼40 to ∼340 K to reconcile the fiducial stellar evolutionary model predictions with the dynamically measured masses. In the latter case, we show that the dynamical masses can be reproduced using results from stellar evolutionary models with starspots, which incorporate fractional starspot coverage to represent the manifestation of magnetic activity. Folding in low-mass M stars from the literature and assuming that the stellar effective temperatures are imprecise but accurate, we find tentative evidence of a relationship between fractional starspot coverage and observed effective temperature for these young, cool stars.Publisher PDFPeer reviewe

An Unbiased ALMA Spectral Survey of the LkCa 15 and MWC 480 Protoplanetary Disks

The volatile contents of protoplanetary disks both set the potential for planetary chemistry and provide valuable probes of defining disk system characteristics such as stellar mass, gas mass, ionization, and temperature structure. Current disk molecular inventories are fragmented, however, giving an incomplete picture: unbiased spectral line surveys are needed to assess the volatile content. We present here an overview of such a survey of the protoplanetary disks around the Herbig Ae star MWC 480 and the T Tauri star LkCa 15 in ALMA Band 7, spanning ~36 GHz from 275 to 317 GHz and representing an order of magnitude increase in sensitivity over previous single-dish surveys. We detect 14 molecular species (including isotopologues), with five species (C34S, 13CS, H2CS, DNC, and C2D) detected for the first time in protoplanetary disks. Significant differences are observed in the molecular inventories of MWC 480 and LkCa 15, and we discuss how these results may be interpreted in light of the different physical conditions of these two disk systems

Vancomycin-intermediate Staphylococcus aureus in a home health-care patient.

In June 2000, vancomycin-intermediate Staphylococcus aureus (VISA) was isolated from a 27-year-old home health-care patient following a complicated cholecystectomy. Two VISA strains were identified with identical MICs to all antimicrobials tested except oxacillin and with closely related pulsed-field gel electrophoresis types. The patient was treated successfully with antimicrobial therapy, biliary drainage, and reconstruction. Standard precautions in the home health setting appear successful in preventing transmission

An unbiased ALMA spectral survey of the LkCa 15 and MWC 480 protoplanetary disks

Funding: R.A.L. gratefully acknowledges funding from ALMA Student Observing Support and a Jansky Fellowship. K.I.O. acknowledges funding from the David and Lucile Packard Foundation and from the Simons Foundation (SCOL #321183). J.H. acknowledges support from the National Science Foundation Graduate Research Fellowship under grant No. DGE-1144152. E.A.B. acknowledges funding through NSF grant AST-1514670 and NASA NNX16AB48G. C.W. acknowledges financial support from STFC (grant reference ST/R000549/1) and the University of Leeds.The volatile contents of protoplanetary disks both set the potential for planetary chemistry and provide valuable probes of defining disk system characteristics such as stellar mass, gas mass, ionization, and temperature structure. Current disk molecular inventories are fragmented, however, giving an incomplete picture: unbiased spectral line surveys are needed to assess the volatile content. We present here an overview of such a survey of the protoplanetary disks around the Herbig Ae star MWC 480 and the T Tauri star LkCa 15 in ALMA Band 7, spanning ∼36 GHz from 275 to 317 GHz and representing an order of magnitude increase in sensitivity over previous single-dish surveys. We detect 14 molecular species (including isotopologues), with five species (C34S, 13CS, H2CS, DNC, and C2D) detected for the first time in protoplanetary disks. Significant differences are observed in the molecular inventories of MWC 480 and LkCa 15, and we discuss how these results may be interpreted in light of the different physical conditions of these two disk systems.PostprintPeer reviewe

An ALMA Survey of H₂CO in Protoplanetary Disks

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 (~5 × 10¹¹–5 × 10¹⁴ 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