Linking pre- and proto-stellar objects in the intermediate-/high-mass star forming region IRAS 05345+3157 ^*,**,***

¹ ISDC, Ch. d'Ecogia 16, 1290 Versoix, Switzerland e-mail: Francesco.Fontani@unige.ch
² Observatoire de Genève, University of Geneva, Ch. de Maillettes 51, 1290 Sauverny, Switzerland
³ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
⁴ School of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, UK

Received: 2 January 2009
Accepted: 25 February 2009

Abstract

Context. To better understand the initial conditions of the high-mass star formation process, it is crucial to study at high angular resolution the morphology, the kinematics, and the interactions of the coldest condensations associated with intermediate-/high-mass star forming regions.

Aims. This paper studies the cold condensations in the intermediate-/high-mass proto-cluster IRAS 05345+3157, focusing on the interaction with the other objects in the cluster.

Methods. We performed millimeter high-angular resolution observations, both in the continuum and several molecular lines, with the PdBI and the SMA. In a recent paper, we published part of these data. The main finding of that work was the detection of two cold and dense gaseous condensations, called N and S (masses ∼2 and  ), characterised by high values of deuterium fractionation (∼0.1 in both cores) obtained from the column density ratio N(N₂D⁺)/N(N₂H⁺). In this paper, we present a full report of the observations, and a complete analysis of the data obtained.

Results. The millimeter maps reveal the presence of 3 cores inside the interferometer primary beam, called C1-a, C1-b and C2. None of them are associated with cores N and S. C1-b is very likely associated with a newly formed early-B ZAMS star embedded inside a hot core, while C1-a is more likely associated with a class 0 intermediate-mass protostar. The nature of C2 is unclear. Both C1-a and C1-b are good candidates as driving sources of a powerful ¹²CO outflow, which strongly interacts with N, as demonstrated by the velocity gradient of the gas along this condensation. The N₂H⁺ linewidths are between ∼1 and 2 km s^-1 in the region where the continuum cores are located, and smaller (∼0.5–1.5 km s^-1) towards N and S, indicating that the gas in the deuterated condensations is more quiescent than that associated with the continuum sources. This is consistent with the fact that they are still in the pre-stellar phase and hence the star formation process has not yet taken place there.

Conclusions. The study of the gas kinematics across the source indicates a tight interaction between deuterated condensations and the sources embedded in millimeter cores. For the nature of N and S, we propose two scenarios: they can be low-mass pre-stellar condensations or “seeds” of future high-mass star(s). However, from these data it is not possible to establish how the turbulence triggered by the neghbouring cluster of protostars can influence the evolution of the condensations.