Compression and ablation of the photo-irradiated molecular cloud the Orion Bar

Goicoechea, J. R.; Pety, J.; Cuadrado, S.; Cernicharo, J.; Chapillon, E.; Fuente, A.; Gérin, M.; Joblin, C.; Marcelino, N.; Pilleri, P.

doi:10.1038/nature18957

Cited by 127 publications

(229 citation statements)

References 53 publications

(128 reference statements)

Supporting

Mentioning

197

Contrasting

Order By: Relevance

“…The impinging FUV radiation field at the edge of the Bar is approximatley 4 × 10 4 times the mean interstellar radiation field (e.g., Goicoechea et al 2016, and references therein). We observed three positions of the Bar characterized by a decreasing FUV photon flux.…”

Section: Source Selection and Observationsmentioning

confidence: 99%

“…In order to estimate the most realistic ξ tc and ξ ct rates for the FUV-irradiation conditions in the Orion Bar, we used the Meudon PDR code (Le Petit et al 2006) and calculate N ph (λ) at different cloud depth A V values. Following our previous studies of the Bar (Cuadrado et al 2015;Goicoechea et al 2016) we run a model of an isobaric PDR (P th /k = 10 8 K cm −3 ) illuminated by χ = 4 × 10 4 times the mean interstellar radiation field (Draine 1978). For photons in the λ = 2000−3000 Å range, we adopt N ph (λ) = 4 × 10 4 × 732 × λ 0.7 photon cm −2 s −1 Å −1 at the PDR edge (A V = 0) (van Dishoeck & Black 1982).…”

Section: Appendix B: Estimation Of the Photoisomerization Rate In Thementioning

confidence: 99%

“…We observed three prototypical interstellar sources known to display a very rich chemistry and bright molecular line emission: (i) the Orion Bar photodissociation region (PDR): the edge of the Orion cloud irradiated by ultraviolet (UV) photons from nearby massive stars (e.g., Goicoechea et al 2016); (ii) the Orion hot core: warm gas around massive protostars (e.g., Tercero et al 2010); and (iii) Barnard 1-b (B1-b): a cold dark cloud (e.g., Cernicharo et al 2012). The two latter sources are shielded from strong UV radiation fields.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Trans-cismolecular photoswitching in interstellar space

Cuadrado

Goicoechea

Roncero

et al. 2016

A&A

View full text Add to dashboard Cite

As many organic molecules, formic acid (HCOOH) has two conformers (trans and cis). The energy barrier to internal conversion from trans to cis is much higher than the thermal energy available in molecular clouds. Thus, only the most stable conformer (trans) is expected to exist in detectable amounts. We report the first interstellar detection of cis-HCOOH. Its presence in ultraviolet (UV) irradiated gas exclusively (the Orion Bar photodissociation region), with a low trans-to-cis abundance ratio of 2.8 ± 1.0, supports a photoswitching mechanism: a given conformer absorbs a stellar photon that radiatively excites the molecule to electronic states above the interconversion barrier. Subsequent fluorescent decay leaves the molecule in a different conformer form. This mechanism, which we specifically study with ab initio quantum calculations, was not considered in Space before but likely induces structural changes of a variety of interstellar molecules submitted to UV radiation.

show abstract

Section: Source Selection and Observationsmentioning

confidence: 99%

Section: Appendix B: Estimation Of the Photoisomerization Rate In Thementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Trans-cismolecular photoswitching in interstellar space

Cuadrado

Goicoechea

Roncero

et al. 2016

A&A

View full text Add to dashboard Cite

show abstract

“…The blue contours in e) and f) represent the CH + 119.8 µm (≈9 resolution) and OH 84.6 µm (≈6 ) lines mapped by Herschel (Parikka et al 2017). few 10 4 times the mean interstellar radiation field. Because of its proximity (∼414 pc, Menten et al 2007) and nearly edge-on orientation, the Bar is a template to investigate the dynamics and chemistry in strongly FUV-irradiated gas (e.g., Pellegrini et al 2009;Cuadrado et al 2015;Goicoechea et al 2016).…”

Section: Introductionmentioning

confidence: 99%

Spatially resolved images of reactive ions in the Orion Bar

Goicoechea

Cuadrado

Pety

et al. 2017

A&A

Self Cite

View full text Add to dashboard Cite

We report high angular resolution (4.9 × 3.0 ) images of reactive ions SH + , HOC + , and SO + toward the Orion Bar photodissociation region (PDR). We used ALMA-ACA to map several rotational lines at 0.8 mm, complemented with multi-line observations obtained with the IRAM 30 m telescope. The SH + and HOC + emission is restricted to a narrow layer of 2 -to 10 -width (≈800 to 4000 AU depending on the assumed PDR geometry) that follows the vibrationally excited H * 2 emission. Both ions efficiently form very close to the H/H 2 transition zone, at a depth of A V 1 mag into the neutral cloud, where abundant C + , S + , and H * 2 coexist. SO + peaks slightly deeper into the cloud. The observed ions have low rotational temperatures (T rot ≈ 10−30 K T k ) and narrow line-widths (∼2−3 km s −1 ), a factor of 2 narrower that those of the lighter reactive ion CH + . This is consistent with the higher reactivity and faster radiative pumping rates of CH + compared to the heavier ions, which are driven relatively more quickly toward smaller velocity dispersion by elastic collisions and toward lower T rot by inelastic collisions. We estimate column densities and average physical conditions from an excitation model (n(H 2 ) ≈ 10 5 −10 6 cm −3 , n(e − ) ≈ 10 cm −3 , and T k ≈ 200 K). Regardless of the excitation details, SH + and HOC + clearly trace the most exposed layers of the UV-irradiated molecular cloud surface, whereas SO + arises from slightly more shielded layers.

show abstract

“…Others, such as Parmar et al (1991), Goicoechea et al (2016), and Salgado et al (2016), argue that the Orion Bar is not in hydrostatic equilibrium but instead represents a slow moving (< 4 km s −1 ) magnetohydrodynamic shock front of swept-up molecular material supported by a strong compressed magnetic field. Observations of the Orion Bar find that complex molecules in the far-IR, sub-millimeter, and radio (Danby et al 1988;Simon et al 1997;Young Owl et al 2000;Batrla & Wilson 2003;Lis & Schilke 2003;Parise et al 2009;Goicoechea et al 2011Goicoechea et al , 2016 trace relatively cool dense gas (T = 50 to 250 K, n H = 10 5 to 10 7 cm −3 ).…”

mentioning

confidence: 99%

Excitation of Molecular Hydrogen in the Orion Bar PhotodissociationRegion from a Deep Near-infrared IGRINS Spectrum

Kaplan

Dinerstein

et al. 2017

ApJ

View full text Add to dashboard Cite

We present a deep near-infrared spectrum of the Orion Bar Photodissociation Region (PDR) taken with the Immersion Grating INfrared Spectrometer (IGRINS) on the 2.7 m telescope at the McDonald Observatory. IGRINS has high spectral resolution (R ∼ 45000) and instantaneous broad wavelength coverage (1.45-2.45 µm), enabling us to detect 87 emission lines from rovibrationally excited molecular hydrogen (H 2 ) that arise from transitions out of 69 upper rovibration levels of the electronic ground state. These levels cover a large range of rotational and vibrational quantum numbers and excitation energies, making them excellent probes of the excitation mechanisms of H 2 and physical conditions within the PDR. The Orion Bar PDR is thought to consist of cooler high density clumps or filaments (T = 50 to 250 K, n H = 10 5 to 10 7 cm −3 ) embedded in a warmer lower density medium (T = 250 to 1000 K, n H = 10 4 to 10 5 cm −3 ). We fit a grid of constant temperature and density Cloudy models, which recreate the observed H 2 level populations well, to constrain the temperature to a range of 600 to 650 K and the density to n H = 2.5 × 10 3 to 10 4 cm −3 . The best-fit model gives T = 625 K and n H = 5 × 10 3 cm −3 . This well-constrained warm temperature is consistent with kinetic temperatures found by other studies for the Orion Bar's lower density medium. However, the range of densities well fit by the model grid is marginally lower than those reported by other studies. We could be observing lower density gas than the surrounding medium, or perhaps a density-sensitive parameter in our models is not properly estimated.

show abstract

Compression and ablation of the photo-irradiated molecular cloud the Orion Bar

Cited by 127 publications

References 53 publications

Trans-cismolecular photoswitching in interstellar space

Trans-cismolecular photoswitching in interstellar space

Spatially resolved images of reactive ions in the Orion Bar

Excitation of Molecular Hydrogen in the Orion Bar PhotodissociationRegion from a Deep Near-infrared IGRINS Spectrum

Contact Info

Product

Resources

About