Fluorescent Molecular Hydrogen Emission in IC 63:<i>FUSE</i>, Hopkins Ultraviolet Telescope, and Rocket Observations

Andersson, B. G.; McCandliss, Stephan R.; Feldman, P. D.

doi:10.1086/430878

Cited by 37 publications

(39 citation statements)

References 28 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Models of UV pumping that incorporate X-ray irradiation and dust grain evolution (which regulates the penetration depth of FUV photons into the disk) show similar, high-v, low-J excitation diagrams (Nomura et al 2007). H 2 dissociation spectra in from these populations will be similar to the hot-star pumped H 2 fluorescence spectrum observed in photodissociation regions, where the continuum peak is clearly established at λ ≈ 1575 -1580Å (Witt et al 1989;France et al 2005), in contrast to the observed spectra in our CTTS survey. There may be other pathways to the formation of the highly non-thermal population distributions that give rise to the quasi-continuous and discrete emission lines observed in the CTTS sample, including the dissociation products of other molecular species and formationpumping of H 2 molecules newly formed on dust grains.…”

Section: Comparison With Infrared Spectrasupporting

confidence: 73%

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: Comparison With Infrared Spectrasupporting

confidence: 73%

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

“…4 of France et al (2005), which means that the VUV-spectrum that interacts with the ice sample mimicks the molecular hydrogen photoexcitation Fig. 8.…”

Section: Astrophysical Implicationsmentioning

confidence: 92%

Vacuum-UV spectroscopy of interstellar ice analogs

Cruz-Díaz

Muñoz

Chen

et al. 2014

A&A

110

View full text Add to dashboard Cite

Context. The vacuum-UV (VUV) absorption cross sections of most molecular solids present in interstellar ice mantles with the exception of H 2 O, NH 3 , and CO 2 have not been reported yet. Models of ice photoprocessing depend on the VUV absorption cross section of the ice to estimate the penetration depth and radiation dose, and in the past, gas phase cross section values were used as an approximation. Aims. We aim to estimate the VUV absorption cross section of molecular ice components. Methods. Pure ices composed of CO, H 2 O, CH 3 OH, NH 3 , or H 2 S were deposited at 8 K. The column density of the ice samples was measured in situ by infrared spectroscopy in transmittance. VUV spectra of the ice samples were collected in the 120−160 nm (10.33−7.74 eV) range using a commercial microwave-discharged hydrogen flow lamp. Results. We provide VUV absorption cross sections of the reported molecular ices. Our results agree with those previously reported for H 2 O and NH 3 ices. Vacuum-UV absorption cross section of CH 3 OH, CO, and H 2 S in solid phase are reported for the first time. H 2 S presents the highest absorption in the 120−160 nm range. Conclusions. Our method allows fast and readily available VUV spectroscopy of ices without the need to use a synchrotron beamline. We found that the ice absorption cross sections can be very different from the gas-phase values, and therefore, our data will significantly improve models that simulate the VUV photoprocessing and photodesorption of ice mantles. Photodesorption rates of pure ices, expressed in molecules per absorbed photon, can be derived from our data.

show abstract

“…The nebula is illuminated by the star γ Cassiopeia located at projected distance d ⋆,sky = 1.3 pc from the star and the attenuated ISRF. Physical parameters adopted for IC 63, including gas density n(H2), temperature Tgas, dust temperature T d (Jansen et al 1994;Jansen et al 1996;France et al 2005) and the parameters of γ Cas are listed in Table 1. Based on the geometry of the diffuse emission, Andersson et al (2013) found that IC 63 and γ Cas are offset from each other along the sightline, with the line between γ Cas and IC 63 making an angle of γ⋆ = 58 • with respect to the plane of the sky (henceforth POS).…”

Section: Physical Model Of Ic 63 and Model Set Upmentioning

confidence: 99%

Modelling grain alignment by radiative torques and hydrogen formation torques in reflection nebula

Hoang

Lazarían

Andersson

2015

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

Reflection nebulae-dense cores-illuminated by surrounding stars offer a unique opportunity to directly test our quantitative model of grain alignment based on radiative torques (RATs) and to explore new effects arising from additional torques. In this paper, we first perform detailed modeling of grain alignment by RATs for the IC 63 reflection nebula illuminated both by a nearby γ Cas star and the diffuse interstellar radiation field. We calculate linear polarization p λ of background stars by radiatively aligned grains and explore the variation of fractional polarization (p λ /A V ) with visual extinction A V across the cloud. Our results show that the variation of p V /A V versus A V from the dayside of IC 63 to its center can be represented by a power-law (p V /A V ∝ A η V ) with different slopes depending on A V . We find a shallow slope η ∼ −0.1 for A V < 3 and a very steep slope η ∼ −2 for A V > 4. We then consider the effects of additional torques due to H 2 formation and model grain alignment by joint action of RATs and H 2 torques. We find that p V /A V tends to increase with an increasing magnitude of H 2 torques. In particular, the theoretical predictions obtained for p V /A V and peak wavelength λ max in this case show an improved agreement with the observational data. Our results reinforce the predictive power of the RAT alignment mechanism in a broad range of environmental conditions and show the effect of pinwheel torques in environments with efficient H 2 formation. Physical parameters involved in H 2 formation may be constrained using detailed modeling of grain alignment combined with observational data. In addition, we discuss implications of our modeling for interpreting latest observational data by Planck and other ground-based instruments.

show abstract

Fluorescent Molecular Hydrogen Emission in IC 63:FUSE, Hopkins Ultraviolet Telescope, and Rocket Observations

Cited by 37 publications

References 28 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^∗

Vacuum-UV spectroscopy of interstellar ice analogs

Modelling grain alignment by radiative torques and hydrogen formation torques in reflection nebula

Contact Info

Product

Resources

About

Fluorescent Molecular Hydrogen Emission in IC 63:FUSE, Hopkins Ultraviolet Telescope, and Rocket Observations

Cited by 37 publications

References 28 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∗

Vacuum-UV spectroscopy of interstellar ice analogs

Modelling grain alignment by radiative torques and hydrogen formation torques in reflection nebula

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^∗