The Evolution of Inner Disk Gas in Transition Disks

Hoadley, Keri; Alexander, R. D.; McJunkin, Matthew; Schneider, P. C.

doi:10.1088/0004-637x/812/1/41

Cited by 24 publications

(100 citation statements)

References 125 publications

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“…All of these observations have been described previously in studies of H 2 (e.g. France et al 2012b;Hoadley et al 2015), hot gas (e.g. Ardila et al 2013), and UV radiation (e.g.…”

supporting

confidence: 57%

“…To explore the behavior of H 2 populations simultaneously in all PPD sightlines, we normalize each H 2 rotation diagram to the column density in the [v = 2,J = 1] level. We include thermal models of warm/hot distributions of H 2 populations, drawn through the normalization rovibrational level [v = 2,J = 1], which range from the expected thermal populations of fluorescent H 2 in PPDs (Herczeg et al 2002(Herczeg et al , 2006France et al 2012b;Hoadley et al 2015) to the dissociation limit of the molecule (red dashed line for T diss ≈ 4500 K; Shull & Beckwith 1982;Williams & Murdin 2000).…”

Section: Analysis and Resultsmentioning

confidence: 99%

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Signatures of Hot Molecular Hydrogen Absorption from Protoplanetary Disks. I. Non-thermal Populations

Hoadley

Arulanantham

Loyd

et al. 2017

ApJ

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The environment around protoplanetary disks (PPDs) regulates processes which drive the chemical and structural evolution of circumstellar material. We perform a detailed empirical survey of warm molecular hydrogen (H 2 ) absorption observed against H I-Lyα (Lyα: λ 1215.67Å) emission profiles for 22 PPDs, using archival Hubble Space Telescope (HST ) ultraviolet (UV) spectra to identify H 2 absorption signatures and quantify the column densities of H 2 ground states in each sightline. We compare thermal equilibrium models of H 2 to the observed H 2 rovibrational level distributions. We find that, for the majority of targets, there is a clear deviation in high energy states (T exc 20,000 K) away from thermal equilibrium populations (T(H 2 ) 3500 K). We create a metric to estimate the total column density of non-thermal H 2 (N(H 2 ) nLTE ) and find that the total column densities of thermal (N(H 2 )) and N(H 2 ) nLTE correlate for transition disks and targets with detectable C IV-pumped H 2 fluorescence. We compare N(H 2 ) and N(H 2 ) nLTE to circumstellar observables and find that N(H 2 ) nLTE correlates with X-ray and FUV luminosities, but no correlations are observed with the luminosities of discrete emission features (e.g., Lyα, C IV). Additionally, N(H 2 ) and N(H 2 ) nLTE are too low to account for the H 2 fluorescence observed in PPDs, so we speculate that this H 2 may instead be associated with a diffuse, hot, atomic halo surrounding the planet-forming disk. We create a simple photon-pumping model for each target to test this hypothesis and find that Lyα efficiently pumps H 2 levels with T exc ≥ 10,000 K out of thermal equilibrium.

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“…All of these observations have been described previously in studies of H 2 (e.g. France et al 2012b;Hoadley et al 2015), hot gas (e.g. Ardila et al 2013), and UV radiation (e.g.…”

supporting

confidence: 57%

Section: Analysis and Resultsmentioning

confidence: 99%

Signatures of Hot Molecular Hydrogen Absorption from Protoplanetary Disks. I. Non-thermal Populations

Hoadley

Arulanantham

Loyd

et al. 2017

ApJ

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“…The thermal models at 1500 and 2500 K are unable to reproduce the flux in the (1 -4) R(12) line. It appears that the 3000 K spectrum can approximately describe the line complex near 1186Å, however this spectrum significantly overpredicts the observed data at other wavelengths, which is reflected in the results of previous fits to the H 2 spectrum, T (H 2 ) ≤ 2000K for V4046 Sgr (Hoadley et al 2015;McJunkin et al 2016). Emission from non-thermal H 2 is able to augment the dominant thermal population and present a better overall fit to the observed spectrum.…”

Section: Comparison Of the Synthetic H2o Dissociation Spectra With Thmentioning

confidence: 70%

The 1600 Å Emission Bump in Protoplanetary Disks: A Spectral Signature of H₂O Dissociation^∗

France

Roueff

Abgrall

2017

ApJ

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The FUV continuum spectrum of many accreting pre-main sequence stars, Classical T Tauri Stars (CTTSs), does not continue smoothly from the well-studied Balmer continuum emission in the NUV, suggesting that additional processes contribute to the short-wavelength emission in these objects. The most notable spectral feature in the FUV continuum of some CTTSs is a broad emission approximately centered at 1600Å, which has been referred to as the "1600Å Bump". The origin of this feature remains unclear. In an effort to better understand the molecular properties of planet-forming disks and the UV spectral properties of accreting protostars, we have assembled archival FUV spectra of 37 disk-hosting systems observed by the Hubble Space Telescope-Cosmic Origins Spectrograph. Clear 1600Å Bump emission is observed above the smooth, underlying 1100 -1800Å continuum spectrum in 19/37 Classical T Tauri disks in the HST -COS sample, with the detection rate in transition disks (8/8) being much higher than in primordial or non-transition sources (11/29). We describe a spectral deconvolution analysis to separate the Bump (spanning 1490 -1690Å) from the underlying FUV continuum, finding an average Bump luminosity, L(Bump) ≈ 7 × 10 29 erg s −1 . Parameterizing the Bump with a combination of Gaussian and polynomial components, we find that the 1600Å Bump is characterized by a peak wavelength λ o = 1598.6 ± 3.3Å, with FWHM = 35.8 ± 19.1Å.Contrary to previous studies, we find that this feature is inconsistent with models of H 2 excited by electron-impact. We show that this Bump makes up between 5 -50% of the total FUV continuum emission in the 1490 -1690Å band and emits roughly 10 -80% of the total fluorescent H 2 luminosity for stars with well-defined Bump features. Energetically, this suggests that the carrier of the 1600Å Bump emission is powered by Lyα photons. We argue that the most likely mechanism is Lyα-driven dissociation of H 2 O in the inner disk, r 2 AU. We demonstrate that non-thermally populated H 2 O fragments can qualitatively account for the observed emission (discrete and continuum), and find that the average Lyα-driven H 2 O dissociation rate is 1.7 × 10 42 water molecules s −1 .

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“…found evidence for an insideout depletion sequence where CO gas is progressively removed from ∼0.1 out to ∼20 au, providing a new probe of gaps over a radial disk region that extends the region probed by millimeter interferometers (typically limited to 5 10 au -, depending on the distance from Earth). By tracing H 2 emission at ultraviolet wavelengths, Hoadley et al (2015) found similar evidence for a removal of molecular gas at small radii in transitional disks. The combination of dust and gas studies of small to large gaps bears the potential for a comprehensive understanding of the physical and chemical evolution of inner disks during planet formation.…”

Section: Introductionmentioning

confidence: 71%

The Depletion of Water During Dispersal of Planet-Forming Disk Regions

Banzatti

Pontoppidan

Salyk

et al. 2017

ApJ

121

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We present a new velocity-resolved survey of 2.9 μm spectra of hot H 2 O and OH gas emission from protoplanetary disks, obtained with the Cryogenic Infrared Echelle Spectrometer at the VLT (R ∼ 96,000). With the addition of archival Spitzer-IRS spectra, this is the most comprehensive spectral data set of water vapor emission from disks ever assembled. We provide line fluxes at 2.9-33 μm that probe from the dust sublimation radius at ∼0.05 au out to the region of the water snow line. With a combined data set for 55 disks, we find a new correlation between H 2 O line fluxes and the radius of CO gas emission, as measured in velocity-resolved 4.7 μm spectra (Rco), which probes molecular gaps in inner disks. We find that H 2 O emission disappears from 2.9 μm (hotter water) to 33 μm (colder water) as R co increases and expands out to the snow line radius. These results suggest that the infrared water spectrum is a tracer of inside-out water depletion within the snow line. It also helps clarify an unsolved discrepancy between water observations and models by finding that disks around stars ofgenerally have inner gaps with depleted molecular gas content. We measure radial trends in H 2 O, OH, and CO line fluxes that can be used as benchmarks for models to study the chemical composition and evolution of planet-forming disk regions at 0.05-20 au. We propose that JWST spectroscopy of molecular gas may be used as a probe of inner disk gas depletion, complementary to the larger gaps and holes detected by direct imaging and by ALMA.

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The Evolution of Inner Disk Gas in Transition Disks

Cited by 24 publications

References 125 publications

Signatures of Hot Molecular Hydrogen Absorption from Protoplanetary Disks. I. Non-thermal Populations

Signatures of Hot Molecular Hydrogen Absorption from Protoplanetary Disks. I. Non-thermal Populations

The 1600 Å Emission Bump in Protoplanetary Disks: A Spectral Signature of H₂O Dissociation^∗

The Depletion of Water During Dispersal of Planet-Forming Disk Regions

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The Evolution of Inner Disk Gas in Transition Disks

Cited by 24 publications

References 125 publications

Signatures of Hot Molecular Hydrogen Absorption from Protoplanetary Disks. I. Non-thermal Populations

Signatures of Hot Molecular Hydrogen Absorption from Protoplanetary Disks. I. Non-thermal Populations

The 1600 Å Emission Bump in Protoplanetary Disks: A Spectral Signature of H2O Dissociation∗

The Depletion of Water During Dispersal of Planet-Forming Disk Regions

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The 1600 Å Emission Bump in Protoplanetary Disks: A Spectral Signature of H₂O Dissociation^∗