* Astronomy

Title: The role of theta Oph in the formation and evolution of the Pipe Nebula - is star formation ever isolated?
Authors: Matthias Gritschneder, Douglas N. C. Lin

We propose that the Pipe Nebula is an HII region shell swept up by the B2 IV beta Cephei star theta Ophiuchi. After reviewing the morphological evidence by recent observations, we perform a series of analytical calculations. We use realistic HII region parameters derived with the radiative transfer code Cloudy from observed stellar parameters. We are able to show that the current size, mass and pressure of the region can be explained in this scenario. We investigate the configuration today and come to the conclusion that the Pipe Nebula can be best described by a three phase medium in pressure equilibrium. The pressure support is provided by the ionised gas and mediated by an atomic component to confine the cores at the observed current pressure. In the future, star formation in these cores is likely to be either triggered by feedback of the most massive, gravitationally bound cores as soon as they collapse or by the supernova explosion of theta Ophiuchi itself.

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Title: The Pipe Nebula as seen with Herschel: Formation of filamentary structures by large-scale compression ?
Authors: N. Peretto, Ph. Andre, V. Konyves, N. Schneider, D. Arzoumanian, P. Palmeirim, P. Didelon, M. Attard, J.P. Bernard, J. Di Francesco, D. Elia, M. Hennemann, T. Hill, J. Kirk, A. Men'shchikov, F. Motte, Q. Nguyen Luong, H. Roussel, T. Sousbie, L. Testi, D. Ward-Thompson, G. J. White, A. Zavagno

A growing body of evidence indicates that the formation of filaments in interstellar clouds is a key component of the star formation process. In this paper, we present new Herschel PACS and SPIRE observations of the B59 and Stem regions in the Pipe Nebula complex, revealing a rich, organized network of filaments. The asymmetric column density profiles observed for several filaments, along with the bow-like edge of B59, indicates that the Pipe Nebula is being compressed from its western side, most likely by the winds from the nearby Sco OB2 association. We suggest that this compressive flow has contributed to the formation of some of the observed filamentary structures. In B59, the only region of the entire Pipe complex showing star formation activity, the same compressive flow has likely enhanced the initial column density of the clump, allowing it to become globally gravitationally unstable. Although more speculative, we propose that gravity has also been responsible for shaping the converging filamentary pattern observed in B59. While the question of the relative impact of large-scale compression and gravity remains open in B59, large-scale compression appears to be a plausible mechanism for the initial formation of filamentary structures in the rest of the complex

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Title: Chemical Differentiation toward the Pipe Nebula Starless Cores
Authors: P. Frau (1), J.M. Girart (1), M. T. Beltran (2) ((1) Institut de Ciències de l'Espai (CSIC-IEEC), (2) INAF-Osservatorio Astrofisico di Arcetri)

We used the new IRAM 30-m FTS backend to perform an unbiased ~15 GHz wide survey at 3 mm toward the Pipe Nebula young diffuse starless cores. We found an unexpectedly rich chemistry. We propose a new observational classification based on the 3 mm molecular line emission normalised by the core visual extinction (Av). Based on this classification, we report a clear differentiation in terms of chemical composition and of line emission properties, which served to define three molecular core groups. The "diffuse" cores, Av~22, show typical evolved chemistry prior to the onset of the star formation process, with nitrogenated and deuterated species, as well as carbon chain molecules. Based on these categories, one of the "diffuse" cores (Core 47) has the spectral line properties of the "oxo-sulfurated" ones, which suggests that it is a possible failed core.

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