Gas and dust in the star-forming regionρ Oph A

Abstract

Aims. We aim at determining the spatial distribution of the gas and dust in star-forming regions and address their relative abundances in quantitative terms. We also examine the dust opacity exponent β for spatial and/or temporal variations. Methods. Using mapping observations of the very dense ρ Oph A core, we examined standard 1D and non-standard 3D methods to analyse data of far-infrared and submillimetre (submm) continuum radiation. The resulting dust surface density distribution can be compared to that of the gas. The latter was derived from the analysis of accompanying molecular line emission, observed with Herschel from space and with APEX from the ground. As a gas tracer we used N 2 H + , which is believed to be much less sensitive to freeze-out than CO and its isotopologues. Radiative transfer modelling of the N 2 H + (J = 3−2) and (J = 6−5) lines with their hyperfine structure explicitly taken into account provides solutions for the spatial distribution of the column density N(H 2 ), hence the surface density distribution of the gas. Results. The gas-to-dust mass ratio is varying across the map, with very low values in the central regions around the core SM 1. The global average, =88, is not far from the canonical value of 100, however. In ρ Oph A, the exponent β of the power-law description for the dust opacity exhibits a clear dependence on time, with high values of 2 for the envelope-dominated emission in starless Class -1 sources to low values close to 0 for the disk-dominated emission in Class III objects. β assumes intermediate values for evolutionary classes in between. Conclusions. Since β is primarily controlled by grain size, grain growth mostly occurs in circumstellar disks. The spatial segregation of gas and dust, seen in projection toward the core centre, probably implies that, like C 18 O, also N 2 H + is frozen onto the grains.

ALMA view of the circumstellar environment of the post-common-envelope-evolution binary system HD 101584

“…The 12 CO channel maps confirm the conclusion by Olofsson & Nyman (1999) of an E-W oriented high-velocity outflow, but also show additional considerable complexity, Fig. 3.…”

“…where B 230 is the blackbody brightness at 230 GHz, with S 230 = 112 mJy, D = 0.7 kpc, the dust opacity κ 230 = 0.5 cm 2 g −1 (Liseau et al 2015), and an adopted dust temperature of 45 K (from the SED in Bakker et al 1996b) gives M d ≈ 0.007 M (with an uncertainty of, at least, a factor of four). This suggests about a solar mass of gas in the central region, assuming a dustto-gas ratio of 200.…”

“…Olofsson & Nyman (1999) obtained 12 CO and 13 CO J = 1-0 and 2-1 single-dish map data. They found at least three kinematic components: a low-velocity, an intermediatevelocity, and a high-velocity component of total widths ≈15, ≈100, and ≈300 km s −1 , respectively.…”

Deuterium fractionation in the Ophiuchus molecular cloud

“…Lada et al 2013). The higher average densities, together with the generally higher molecular cloud temperatures (Pattle et al 2015;Liseau et al 2015), imply larger pressures that may accelerate the formation of denser cores and the rate of star formation (e.g. Kennicutt & Evans 2012) compared to the other nearby molecular cloud complexes.…”

Calibrating Column Density Tracers With Gamma-Ray Observations of the Ρ Ophiuchi Molecular Cloud

“…The dust properties of the ρ Oph cloud are notoriously unusual (Liseau et al 2015), which calls into question standard scaling relations between A V , A λ , CO emission, dust emission, and gas column density. The ρ Oph dark core harbors the star-forming region L1688, which exhibits radio and X-ray emission (Dzib et al 2013) potentially indicative of locally accelerated CRs.…”