Observations of 6 - 200 μm emission of the Ophiuchus cloud LDN 1688

Abstract

We examine two positions, ON1 and ON2, within the Ophiuchus cloud LDN 1688 using observations made with the ISOPHOT instrument aboard the ISO satellite. The data include mid-IR spectra (~6-12μm) and several photometric bands up to 200μm. The data probe the emission from molecular PAH-type species, transiently-heated Very Small Grains (VSGs), and large classical dust grains. We compare the observations to earlier studies, especially those carried out towards an isolated translucent cloud in Chamaeleon (Paper I). The spectra towards the two LDN 1688 positions are very similar to each other, in spite of position ON1 having a larger column density and probably being subjected to a stronger radiation field. The ratios of the mid-IR features are similar to those found in other diffuse and translucent clouds. Compared to paper I, the 7.7/11.3μm band ratios are lower, ~2.0, at both LDN 1688 positions. A continuum is detected in the ~10μm region. This is stronger towards the position ON1 but still lower than on any of the sightlines in Paper I. The far-infrared opacities are higher than for diffuse medium. The value of the position ON2, τ200/N(H) = 3.9 x 10^{-25} cm^2/H, is twice the value found for ON1. The radiation field of LDN 1688 is dominated by the two embedded B type double stars, ρ Oph AB and HD 147889, with an additional contribution from the Upper Sco OB association. The strong heating is reflected in the high colour temperature, ~24 K, of the large grain emission. Radiative transfer modelling confirms a high level of the radiation field and points to an increased abundance of PAH grains. However, when the hardening of the radiation field caused by the local B-stars is taken into account, the observations can be fitted with almost no change to the standard dust models. However, all the examined models underestimate the level of the mid-IR continuum.

12 pages, 7 figures, 3 tables. Accepted for publication in MNRAS

References in corpus (8)

• The Wide-field Infrared Survey Explorer (WISE): Mission Description and Initial On-orbit Performance
• Herschel Space Observatory - An ESA facility for far-infrared and submillimetre astronomy
• The Photodetector Array Camera and Spectrometer (PACS) on the Herschel Space Observatory
• Variations of the Mid-IR Aromatic Features Inside and Among Galaxies
• 2MASS wide field extinction maps: II. The Ophiuchus and the Lupus cloud complexe
• Evidence for Environmental Changes in the Submillimeter Dust Opacity
• The Spitzer c2d Survey of Large, Nearby, Interstellar Clouds: VII. Ophiuchus Observed with MIPS
• Centimeter-wave continuum radiation from the rho Ophiuchi molecular cloud

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• Assessing the Performance of a Machine Learning Algorithm in Identifying Bubbles in Dust Emission
• Families and Clusters of Diffuse Interstellar Bands: a Data-Driven Correlation Analysis