DSpace Angular :: Browsing by Author "Oberg, Karin I."

Browsing by Author "Oberg, Karin I."

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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.
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.
Chemistry in Externally FUV-irradiated Disks in the Outskirts of the Orion Nebula Cluster
(2024) Diaz-Berrios, Javiera K.; Guzman, Viviana V.; Walsh, Catherine; Oberg, Karin I.; Cleeves, L. Ilsedore; de la Villarmois, Elizabeth Artur; Carpenter, John
Most stars are born in stellar clusters, and their protoplanetary disks, which are the birthplaces of planets, can, therefore, be affected by the radiation of nearby massive stars. However, little is known about the chemistry of externally irradiated disks, including whether or not their properties are similar to the so-far better-studied isolated disks. Motivated by this question, we present ALMA Band 6 observations of two irradiated Class II protoplanetary disks in the outskirts of the Orion Nebula Cluster to explore the chemical composition of disks exposed to (external) far-ultraviolet (FUV) radiation fields: the 216-0939 disk and the binary system 253-1536A/B, which are exposed to radiation fields of 102-103 times the average interstellar radiation field. We detect lines from CO isotopologues, HCN, H2CO, and C2H toward both protoplanetary disks. Based on the observed disk-integrated line fluxes and flux ratios, we do not find significant differences between isolated and irradiated disks. The observed differences seem to be more closely related to the different stellar masses than to the external radiation field. This suggests that these disks are far enough away from the massive Trapezium stars, that their chemistry is no longer affected by external FUV radiation. Additional observations toward lower-mass disks and disks closer to the massive Trapezium stars are required to elucidate the level of external radiation required to make an impact on the chemistry of planet formation in different kinds of disks.
Cold Deuterium Fractionation in the Nearest Planet-forming Disk
(2023) Munoz-Romero, Carlos E.; Oberg, Karin I.; Law, Charles J.; Teague, Richard; Aikawa, Yuri; Bergner, Jennifer B.; Wilner, David J.; Huang, Jane; Guzman, Viviana V.; Cleeves, L. Ilsedore
Deuterium fractionation provides a window into the thermal history of volatiles in the solar system and protoplanetary disks. While evidence of active molecular deuteration has been observed toward a handful of disks, it remains unclear whether this chemistry affects the composition of forming planetesimals due to limited observational constraints on the radial and vertical distribution of deuterated molecules. To shed light on this question, we introduce new Atacama Large Millimeter/submillimeter Array observations of DCO+ and DCN J = 2-1 at an angular resolution of 0.'' 5 (30 au) and combine them with archival data of higher energy transitions toward the protoplanetary disk around TW Hya. We carry out a radial excitation analysis assuming both LTE and non-LTE to localize the physical conditions traced by DCO+ and DCN emission in the disk, thus assessing deuterium fractionation efficiencies and pathways at different disk locations. We find similar disk-averaged column densities of 1.9 x 10(12) and 9.8 x 10(11) cm(-2) for DCO+ and DCN, with typical kinetic temperatures for both molecules of 20-30 K, indicating a common origin near the comet- and planet-forming midplane. The observed DCO+/DCN abundance ratio, combined with recent modeling results, provide tentative evidence of a gas-phase C/O enhancement within <40 au. Observations of DCO+ and DCN in other disks, as well as HCN and HCO+, will be necessary to place the trends exhibited by TW Hya in context, and fully constrain the main deuteration mechanisms in disks.
JWST-MIRI Spectroscopy of Warm Molecular Emission and Variability in the AS 209 Disk
(2024) Munoz-Romero, Carlos E.; Oberg, Karin I.; Banzatti, Andrea; Pontoppidan, Klaus M.; Andrews, Sean M.; Wilner, David J.; Bergin, Edwin A.; Czekala, Ian; Law, Charles J.; Salyk, Colette; Teague, Richard; Qi, Chunhua; Bergner, Jennifer B.; Huang, Jane; Walsh, Catherine; Guzman, Viviana V.; Cleeves, L. Ilsedore; Aikawa, Yuri; Bae, Jaehan; Booth, Alice S.; Cataldi, Gianni; Ilee, John D.; Le Gal, Romane; Long, Feng; Loomis, Ryan A.; Menard, Francois; Liu, Yao
We present MIRI Medium-resolution Spectrograph observations of the large, multi-gapped protoplanetary disk around the T Tauri star AS 209. The observations reveal hundreds of water vapor lines from 4.9-25.5 mu m toward the inner similar to 1 au in the disk, including the first detection of rovibrational water emission in this disk. The spectrum is dominated by hot (similar to 800 K) water vapor and OH gas, with only marginal detections of CO2, HCN, and a possible colder water vapor component. Using slab models with a detailed treatment of opacities and line overlap, we retrieve the column density, emitting area, and excitation temperature of water vapor and OH, and provide upper limits for the observable mass of other molecules. Compared to MIRI spectra of other T Tauri disks, the inner disk of AS 209 does not appear to be atypically depleted in CO2 nor HCN. Based on Spitzer Infrared Spectrograph observations, we further find evidence for molecular emission variability over a 10 yr baseline. Water, OH, and CO2 line luminosities have decreased by factors of 2-4 in the new MIRI epoch, yet there are minimal continuum emission variations. The origin of this variability is yet to be understood.
Molecules with ALMA at Planet-forming Scales (MAPS). II. CLEAN Strategies for Synthesizing Images of Molecular Line Emission in Protoplanetary Disks
(2021) Czekala, Ian; Loomis, Ryan A.; Teague, Richard; Booth, Alice S.; Huang, Jane; Cataldi, Gianni; Ilee, John D.; Law, Charles J.; Walsh, Catherine; Bosman, Arthur D.; Guzman, Viviana V.; Gal, Romane Le; Oberg, Karin I.; Yamato, Yoshihide; Aikawa, Yuri; Andrews, Sean M.; Bae, Jaehan; Bergin, Edwin A.; Bergner, Jennifer B.; Cleeves, L. Ilsedore; Kurtovic, Nicolas T.; Menard, Francois; Nomura, Hideko; Perez, Laura M.; Qi, Chunhua; Schwarz, Kamber R.; Tsukagoshi, Takashi; Waggoner, Abygail R.; Wilner, David J.; Zhang, Ke
The Molecules with ALMA at Planet-forming Scales Large Program (MAPS LP) surveyed the chemical structures of five protoplanetary disks across more than 40 different spectral lines at high angular resolution (0.'' 15 and 0.'' 30 beams for Bands 6 and 3, respectively) and sensitivity (spanning 0.3-1.3 mJy beam(-1) and 0.4-1.9 mJy beam(-1) for Bands 6 and 3, respectively). In this article, we describe the multistage workflow-built around the CASA tclean image deconvolution procedure-that we used to generate the core data product of the MAPS LP: the position-position-velocity image cubes for each spectral line. Owing to the expansive nature of the survey, we encountered a range of imaging challenges: some are familiar to the submillimeter protoplanetary disk community, like the need to use an accurate CLEAN mask, and others are less well known, like the incorrect default flux scaling of the CLEAN residual map first described by Jorsater & van Moorsel (the "JvM effect"). We distill lessons learned into recommended workflows for synthesizing image cubes of molecular emission. In particular, we describe how to produce image cubes with accurate fluxes via "JvM correction," a procedure that is generally applicable to any image synthesized via CLEAN deconvolution but is especially critical for low signal-to-noise ratio (S/N) emission. We further explain how we used visibility tapering to promote a common, fiducial beam size and contextualize the interpretation of S/N when detecting molecular emission from protoplanetary disks. This paper is part of the MAPS special issue of the Astrophysical Journal Supplement.
Molecules with ALMA at Planet-forming Scales (MAPS). VI. Distribution of the Small Organics HCN, C₂H, and H₂CO
(2021) Guzman, Viviana V.; Bergner, Jennifer B.; Law, Charles J.; Oberg, Karin I.; Walsh, Catherine; Cataldi, Gianni; Aikawa, Yuri; Bergin, Edwin A.; Czekala, Ian; Huang, Jane; Andrews, Sean M.; Loomis, Ryan A.; Zhang, Ke; Le Gal, Romane; Alarcon, Felipe; Ilee, John D.; Teague, Richard; Cleeves, L. Ilsedore; Wilner, David J.; Long, Feng; Schwarz, Kamber R.; Bosman, Arthur D.; Perez, Laura M.; Menard, Francois; Liu, Yao
Small organic molecules, such as C2H, HCN, and H2CO, are tracers of the C, N, and O budget in protoplanetary disks. We present high-angular-resolution (10-50 au) observations of C2H, HCN, and H2CO lines in five protoplanetary disks from the Molecules with ALMA at Planet-forming Scales (MAPS) ALMA Large Program. We derive column density and excitation temperature profiles for HCN and C2H, and find that the HCN emission arises in a temperate (20-30 K) layer in the disk, while C2H is present in relatively warmer (20-60 K) layers. In the case of HD 163296, we find a decrease in column density for HCN and C2H inside one of the dust gaps near similar to 83 au, where a planet has been proposed to be located. We derive H2CO column density profiles assuming temperatures between 20 and 50 K, and find slightly higher column densities in the colder disks around T Tauri stars than around Herbig Ae stars. The H2CO column densities rise near the location of the CO snowline and/or millimeter dust edge, suggesting an efficient release of H2CO ices in the outer disk. Finally, we find that the inner 50 au of these disks are rich in organic species, with abundances relative to water that are similar to cometary values. Comets could therefore deliver water and key organics to future planets in these disks, similar to what might have happened here on Earth. This paper is part of the MAPS special issue of the Astrophysical Journal Supplement.
Molecules with ALMA at Planet-forming Scales (MAPS). VII. Substellar O/H and C/H and Superstellar C/O in Planet-feeding Gas
(2021) Bosman, Arthur D.; Alarcon, Felipe; Bergin, Edwin A.; Zhang, Ke; Van't Hoff, Merel L. R.; Oberg, Karin I.; Guzman, Viviana V.; Walsh, Catherine; Aikawa, Yuri; Andrews, Sean M.; Bergner, Jennifer B.; Booth, Alice S.; Cataldi, Gianni; Cleeves, L. Ilsedore; Czekala, Ian; Furuya, Kenji; Huang, Jane; Ilee, John D.; Law, Charles J.; Le Gal, Romane; Liu, Yao; Long, Feng; Loomis, Ryan A.; Menard, Francois; Nomura, Hideko; Qi, Chunhua; Schwarz, Kamber R.; Teague, Richard; Tsukagoshi, Takashi; Yamato, Yoshihide; Wilner, David J.
The elemental composition of the gas and dust in a protoplanetary disk influences the compositions of the planets that form in it. We use the Molecules with ALMA at Planet-forming Scales (MAPS) data to constrain the elemental composition of the gas at the locations of potentially forming planets. The elemental abundances are inferred by comparing source-specific gas-grain thermochemical models with variable C/O ratios and small-grain abundances from the DALI code with CO and C2H column densities derived from the high-resolution observations of the disks of AS 209, HD 163296, and MWC 480. Elevated C/O ratios (similar to 2.0), even within the CO ice line, are necessary to match the inferred C2H column densities over most of the pebble disk. Combined with constraints on the CO abundances in these systems, this implies that both the O/H and C/H ratios in the gas are substellar by a factor of 4-10, with the O/H depleted by a factor of 20-50, resulting in the high C/O ratios. This necessitates that even within the CO ice line, most of the volatile carbon and oxygen is still trapped on grains in the midplane. Planets accreting gas in the gaps of the AS 209, HD 163296, and MWC 480 disks will thus acquire very little carbon and oxygen after reaching the pebble isolation mass. In the absence of atmosphere-enriching events, these planets would thus have a strongly substellar O/H and C/H and superstellar C/O atmospheric composition. This paper is part of the MAPS special issue of the Astrophysical Journal Supplement.
Molecules with ALMA at Planet-forming Scales (MAPS). XI. CN and HCN as Tracers of Photochemistry in Disks
(2021) Bergner, Jennifer B.; Oberg, Karin I.; Guzman, Viviana V.; Law, Charles J.; Loomis, Ryan A.; Cataldi, Gianni; Bosman, Arthur D.; Aikawa, Yuri; Andrews, Sean M.; Bergin, Edwin A.; Booth, Alice S.; Cleeves, L. Ilsedore; Czekala, Ian; Huang, Jane; Ilee, John D.; Le Gal, Romane; Long, Feng; Nomura, Hideko; Menard, Francois; Qi, Chunhua; Schwarz, Kamber R.; Teague, Richard; Tsukagoshi, Takashi; Walsh, Catherine; Wilner, David J.; Yamato, Yoshihide
UV photochemistry in the surface layers of protoplanetary disks dramatically alters their composition relative to previous stages of star formation. The abundance ratio CN/HCN has long been proposed to trace the UV field in various astrophysical objects; however, to date the relationship between CN, HCN, and the UV field in disks remains ambiguous. As part of the ALMA Large Program MAPS (Molecules with ALMA at Planet-forming Scales), we present observations of CN N = 1-0 transitions at 0.'' 3 resolution toward five disk systems. All disks show bright CN emission within similar to 50-150 au, along with a diffuse emission shelf extending up to 600 au. In all sources we find that the CN/HCN column density ratio increases with disk radius from about unity to 100, likely tracing increased UV penetration that enhances selective HCN photodissociation in the outer disk. Additionally, multiple millimeter dust gaps and rings coincide with peaks and troughs, respectively, in the CN/HCN ratio, implying that some millimeter substructures are accompanied by changes to the UV penetration in more elevated disk layers. That the CN/HCN ratio is generally high (>1) points to a robust photochemistry shaping disk chemical compositions and also means that CN is the dominant carrier of the prebiotically interesting nitrile group at most disk radii. We also find that the local column densities of CN and HCN are positively correlated despite emitting from vertically stratified disk regions, indicating that different disk layers are chemically linked. This paper is part of the MAPS special issue of the Astrophysical Journal Supplement.
Molecules with ALMA at Planet-forming Scales (MAPS): Complex Kinematics in the AS 209 Disk Induced by a Forming Planet and Disk Winds
(2023) Galloway-Sprietsma, Maria; Bae, Jaehan; Teague, Richard; Benisty, Myriam; Facchini, Stefano; Aikawa, Yuri; Alarcon, Felipe; Andrews, Sean M.; Bergin, Edwin; Cataldi, Gianni; Cleeves, L. Ilsedore; Czekala, Ian; Guzman, Viviana V.; Huang, Jane; Law, Charles J.; Le Gal, Romane; Liu, Yao; Long, Feng; Menard, Francois; Oberg, Karin I.; Walsh, Catherine; Wilner, David J.
We study the kinematics of the AS 209 disk using the J = 2-1 transitions of (CO)-C-12, (CO)-C-13, and (CO)-O-18. We derive the radial, azimuthal, and vertical velocity of the gas, taking into account the lowered emission surface near the annular gap at similar or equal to 1.'' 7 (200 au) within which a candidate circumplanetary-disk-hosting planet has been reported previously. In (CO)-C-12 and (CO)-C-13, we find a coherent upward flow arising from the gap. The upward gas flow is as fast as 150 m s(-1) in the regions traced by (CO)-C-12 emission, which corresponds to about 50% of the local sound speed or 6% of the local Keplerian speed. Such an upward gas flow is difficult to reconcile with an embedded planet alone. Instead, we propose that magnetically driven winds via ambipolar diffusion are triggered by the low gas density within the planet-carved gap, dominating the kinematics of the gap region. We estimate the ambipolar Elsasser number, Am, using the HCO+ column density as a proxy for ion density and find that Am is similar to 0.1 at the radial location of the upward flow. This value is broadly consistent with the value at which numerical simulations find that ambipolar diffusion drives strong winds. We hypothesize that the activation of magnetically driven winds in a planet-carved gap can control the growth of the embedded planet. We provide a scaling relationship that describes the wind-regulated terminal mass: adopting parameters relevant to 100 au from a solar-mass star, we find that the wind-regulated terminal mass is about one Jupiter mass, which may help explain the dearth of directly imaged super-Jovian-mass planets.
The Disk Substructures at High Angular Resolution Program (DSHARP). VIII. The Rich Ringed Substructures in the AS 209 Disk
(2018) Guzman, Viviana V.; Huang, Jane; Andrews, Sean M.; Isella, Andrea; Perez, Laura M.; Carpenter, John M.; Dullemond, Cornelis P.; Ricci, Luca; Birnstiel, Tilman; Zhang, Shangjia; Zhu, Zhaohuan; Bai, Xue-Ning; Benisty, Myriam; Oberg, Karin I.; Wilner, David J.
We present a detailed analysis of the high angular resolution (0.'' 037, corresponding to 5 au) observations of the 1.25. mm continuum and (CO)-C-12 2 - 1 emission from the disk around the T. Tauri star AS. 209. AS. 209 hosts one of the most unusual disks from the Disk Substructures at High Angular Resolution Project sample, the first high angular resolution Atacama Large Millimeter Array survey of disks, as nearly all of the emission can be explained with concentric Gaussian rings. In particular, the dust emission consists of a series of narrow and closely spaced rings in the inner similar to 60 au, two well-separated bright rings in the outer disk, centered at 74 and 120 au, and at least two fainter emission features at 90 and 130 au. We model the visibilities with a parametric representation of the radial surface brightness profile, consisting of a central core and seven concentric Gaussian rings. Recent hydrodynamical simulations of low-viscosity disks show that super-Earth planets can produce the multiple gaps seen in AS. 209 millimeter continuum emission. The (CO)-C-12 line emission is centrally peaked and extends out to similar to 300 au, much farther than the millimeter dust emission. We find axisymmetric, localized deficits of CO emission around four distinct radii, near 45, 75, 120, and 210 au. The outermost gap is located well beyond the edge of the millimeter dust emission, and therefore cannot be due to dust opacity and must be caused by a genuine CO surface density reduction, due either to chemical effects or depletion of the overall gas content.
The TW Hya Rosetta Stone Project. II. Spatially Resolved Emission of Formaldehyde Hints at Low-temperature Gas-phase Formation
(2021) Terwisscha van Scheltinga, Jeroen; Hogerheijde, Michiel R.; Cleeves, L. Ilsedore; Loomis, Ryan A.; Walsh, Catherine; Oberg, Karin I.; Bergin, Edwin A.; Bergner, Jennifer B.; Blake, Geoffrey A.; Calahan, Jenny K.; Cazzoletti, Paolo; van Dishoeck, Ewine F.; Guzman, Viviana V.; Huang, Jane; Kama, Mihkel; Qi, Chunhua; Teague, Richard; Wilner, David J.
Formaldehyde (H2CO) is an important precursor to organics like methanol (CH3OH). It is important to understand the conditions that produce H2CO and prebiotic molecules during star and planet formation. H2CO possesses both gas-phase and solid-state formation pathways, involving either UV-produced radical precursors or CO ice and cold (less than or similar to 20 K) dust grains. To understand which pathway dominates, gaseous H2CO's ortho-to-para ratio (OPR) has been used as a probe, with a value of 3 indicating "warm" conditions and <3 linked to cold formation in the solid state. We present spatially resolved Atacama Large Millimeter/submillimeter Array observations of multiple ortho- and para-H2CO transitions in the TW Hya protoplanetary disk to test H2CO formation theories during planet formation. We find disk-averaged rotational temperatures and column densities of 33 2 K, (1.1 +/- 0.1) x 10(12) cm(-2) and 25 +/- 2 K, (4.4 +/- 0.3) x 10(11) cm(-2) for ortho- and para-H2CO, respectively, and an OPR of 2.49 +/- 0.23. A radially resolved analysis shows that the observed H2CO emits mostly at rotational temperatures of 30-40 K, corresponding to a layer with z/R >= 0.25. The OPR is consistent with 3 within 60 au, the extent of the pebble disk, and decreases beyond 60 au to 2.0 +/- 0.5. The latter corresponds to a spin temperature of 12 K, well below the rotational temperature. The combination of relatively uniform emitting conditions, a radial gradient in the OPR, and recent laboratory experiments and theory on OPR ratios after sublimation, led us to speculate that gas-phase formation is responsible for the observed H2CO across the TW Hya disk.

Browsing by Author "Oberg, Karin I."

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