H2 infrared line emission across the bright side of the rho Ophiuchi main cloud

Details H2 infrared line emission across the bright side of the rho Ophiuchi main cloud H2 infrared line emission across the bright side of the rho Ophiuchi main cloud

Jan 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003a%26a...397..623h&link_type=abstract

Astronomy and Astrophysics, v.397, p.623-634 (2003)

Astronomy and Astrophysics

Astrophysics

36

Ism: Clouds, Ism: Dust, Extinction, Atomic Processes, Molecular Processes, Radiative Transfer

Scientific paper

We present imaging and spectroscopic observations of dust and gas (H2) emission, obtained with ISO, from the western edge of the rho Ophiuchi molecular cloud illuminated by the B2 star HD147889 (chi ~ 400). This photodissociation region (PDR) is one of the nearest PDRs to the Sun (d = 135 +/- 15 pc from the stellar parallax) and the layer of UV light penetration and of H2 emission is spatially resolved. It is therefore an ideal target to test the prediction of models on the integrated fluxes but also on the spatial distribution. The emission from dust heated by the external UV radiation, from collisionally excited and fluorescent H2 are observed to coincide spatially. The spectroscopic data, obtained with ISO-SWS, allows us to estimate the gas temperature to be 300-345 K in the H2 emitting layer, in which the ortho-to-para H2 ratio is about 1 or significantly smaller than the equilibrium ratio ( ~ 3 at that temperature). We interpret this data with an equilibrium PDR model. In this low excitation PDR, the gas heat budget is dominated by the contribution of the photoelectric heating from very small grains and polycyclic aromatic hydrocarbons (PAHs). With the standard PAH abundance ([C/H]PAH =~ 5 x 10-5), we find that the H2 formation rate Rf must be high in warm gas ( ~ 6 times the rate derived by Jura, 1975), in order to account for the observed H2 emission. This result and the spatial coincidence between the PAHs and H2 emission suggest that H2 forms efficiently by chemisorption on the PAHs surface. If the latter interpretation is correct, the enhancement in Rf may also result from an increased PAH abundance: assuming that Rf scales with the PAH abundance, the observed H2 excitation is well explained with Rf =~ 1x 10-16 cm3 s-1 at Tgas=330 K ( ~ 3 times the rate derived by Jura 1975) and [C/H]PAH =~ 7.5 x 10-5. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with the participation of ISAS and NASA.

Affiliated with

Also associated with

No associations

Rating

H2 infrared line emission across the bright side of the rho Ophiuchi main cloud does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with H2 infrared line emission across the bright side of the rho Ophiuchi main cloud, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and H2 infrared line emission across the bright side of the rho Ophiuchi main cloud will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1524266