Total transition probability and spontaneous radiative
 dissociation of B, C, B′ and D
 states of molecular hydrogen

Abgrall, H.; Roueff, E.; Drira, I.

doi:10.1051/aas:2000121

Cited by 129 publications

(147 citation statements)

References 19 publications

Supporting

Mentioning

143

Contrasting

Order By: Relevance

“…Such occurrences can produce resonances in the spectrum and theoretical calculations are required to predict the width and relative fluxes of such features. We refer the reader to previous work (e.g., Abgrall et al 1993Abgrall et al , 2000 to recover the full theoretical treatments.…”

Section: Calculations Of the H2 Dissociation Continuummentioning

confidence: 99%

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

France

Roueff

Abgrall

2017

ApJ

View full text Add to dashboard Cite

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 .

show abstract

Section: Calculations Of the H2 Dissociation Continuummentioning

confidence: 99%

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

France

Roueff

Abgrall

2017

ApJ

View full text Add to dashboard Cite

show abstract

“…The H 2 line positions and oscillator strengths were adopted from Abgrall et al (1994). The total transition probabilities that include the transitions to continuum (dissociating) states were taken from Abgrall et al (2000).…”

Section: Column Densitiesmentioning

confidence: 99%

Interstellar H₂toward HD 37903

Gnaciński

2011

A&A

View full text Add to dashboard Cite

We present an analysis of interstellar H 2 toward HD 37903, which is a hot B 1.5 V star located in the NGC 2023 reflection nebula. Meyer et al. (2001, ApJ, 553, L59) used a rich spectrum of vibrationally excited H 2 observed by the HST to calculate a model of the interstellar cloud toward HD 37903. We extend their analysis by including the ν = 0 vibrational level observed by the FUSE satellite. The temperature calculated from the two lowest rotational levels (J = 0, 1) of the H 2 molecule should not be interpreted as a "rotational temperature", but rather as a temperature of thermal equilibrium between the ortho and para H 2 . The ortho-to-para H 2 ratio is lower for the lowest rotational levels than for the higher levels populated by fluorescence. The PDR model of the cloud located in front of HD 37903 points to a gas kinetic temperature ranging from 110 K on the observer side of the cloud to 377 K on the star side. The hydrogen density changes from n H = 1874 cm −3 on the observer side to 544 cm −3 on the star side. The star-cloud distance in our model is 0.45 pc.

show abstract

“…Meanwhile, the rotational and rovibrational collisional excitation of HD by H, He and H 2 has been studied with quantal close coupling techniques and new molecular potential surfaces (Roueff & Zeippen 1999Flower & Roueff 1999). Transition and photodissociation probabilities of H 2 and HD have been improved (Abgrall et al 2000;Abgrall & Roueff 2002) taking into account the rotational coupling and new transition moments calculations.Article published by EDP Sciences and available at …”

mentioning

confidence: 99%

D/HD transition in Photon Dominated Regions (PDR)

Petit¹,

Roueff²,

Bourlot³

2002

A&A

Self Cite

128

View full text Add to dashboard Cite

Abstract. We present the basic features of a steady state chemical model of Photon Dominated Regions (PDR), where the deuterium chemistry is explicitly introduced. The model is an extension of a previous PDR model (Abgrall et al. 1992;Le Bourlot et al. 1993; in which the microscopic processes relative to HD have been incorporated. The J-dependent photodissociation probabilities have been calculated and included in the statistical equilibrium of the rotational levels of HD where the latest collision molecular data are also introduced. The thermal balance is calculated from the equilibrium between the different heating and cooling processes. We introduce a standard model of density n H = 500 cm −3 embedded in the Interstellar Standard Radiation Field (ISRF) from which we derive the main properties of HD in PDR. The D/HD transition does not depend only on the density, radiation field but also on the chemical processes and especially on the dust formation efficiency. In standard radiation field conditions, the D/HD transition occurs in a narrow range of visual extinctions as long as density is less than 1000 cm −3 and HD is formed through the D + + H 2 reaction. At higher densities a logarithmic dependence of the location of the transition is derived. The model is applied both to ultraviolet absorption observations from the ground rotational state of HD performed in diffuse and translucent clouds and infrared emission detectable at high densities and for high ultraviolet radiation fields coming from the bright surrounding stars.Key words. astrochemistry -molecular processes -ISM: molecules IntroductionSince deuterium has been formed only at the early beginning of the universe, the elemental deuterium to hydrogen ratio is one pivotal parameter to understand the evolution of astrophysical media. In the interstellar medium (ISM), deuterium may be present in atomic but also in molecular form and over 20 single D-bearing molecules and two doubly deuterated ones have been found in cold molecular clouds and star forming regions Loinard et al. 2000). Last but not least, the triply deuterated ammonia has been detected towards two dense cold clouds (Lis et al. 2002;van der Tak et al. 2002). However, chemical fractionation processes and mantle desorption from grains take place in these molecular clouds and it is not straightforward to derive the elemental deuterium abundance from such observations (Roberts & Millar 2000a,b).Atomic deuterium has first been observed with the Copernicus satellite in the local interstellar medium and in diffuse clouds in absorption towards bright stars where HD has also been detected (see Lemoine et al. 1999 for a review). The successful launch of the FUSE (Far Ultraviolet Spectroscopy Explorer) mission allows to search for molecular HD towards fainter sources, in translucent clouds which are intermediate between diffuse and molecular clouds. FUSE detections Send offprint requests to: E. Roueff, e-mail: Evelyne.Roueff@obspm.fr of interstellar HD have been reported in a variety of galactic lines o...

show abstract

Total transition probability and spontaneous radiative dissociation of B, C, B′ and D states of molecular hydrogen

Cited by 129 publications

References 19 publications

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

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

Interstellar H₂toward HD 37903

D/HD transition in Photon Dominated Regions (PDR)

Contact Info

Product

Resources

About

Total transition probability and spontaneous radiative dissociation of B, C, B′ and D states of molecular hydrogen

Cited by 129 publications

References 19 publications

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

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

Interstellar H2toward HD 37903

D/HD transition in Photon Dominated Regions (PDR)

Contact Info

Product

Resources

About

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

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

Interstellar H₂toward HD 37903