Unveiling the nature and interaction of the intermediate/high-mass YSOs in IRAS 20343+4129^*

¹ Laboratorio de Astrofísica Espacial y Física Fundamental, INTA, Apartado 78, 28691 Villanueva de la Cañada, Madrid, Spain e-mail: apalau@laeff.inta.es
² Departament d'Astronomia i Meteorologia, Universitat de Barcelona, Av. Diagonal 647, 08028 Barcelona, Catalunya, Spain
³ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
⁴ Academia Sinica, Institute of Astronomy and Astrophysics, PO Box 23-141, Taipei, 106, Taiwan
⁵ Max-Planck-Institut for Astronomy, Koenigstuhl 17, 69117 Heidelberg, Germany

Received: 23 April 2007
Accepted: 23 August 2007

Abstract

Context.IRAS 20343+4129 was suggested to harbor one of the most massive and embedded stars in the Cygnus OB2 association, IRS 1, which seemed to be associated with a north-south molecular outflow. However, the dust emission peaks do not coincide with the position of IRS 1, but lie on either side of another massive Young Stellar Object (YSO), IRS 3, which is associated with centimeter emission.

Aims.The goal of this work is to elucidate the nature of IRS 1 and IRS 3, and study their interactions with the surrounding medium.

Methods.The Submillimeter Array (SMA) was used to observe with high angular resolution the 1.3 mm continuum and CO (2–1) emission of the region, and we compared this millimeter emission with the infrared emission from 2MASS.

Results.Faint millimeter dust continuum emission was detected toward IRS 1, and we derived an associated gas mass of ~0.8 . The IRS 1 Spectral Energy Distribution (SED) agrees with IRS 1 being an intermediate-mass Class I source of about 1000 , whose circumstellar material is producing the observed large infrared excess. We have discovered a high-velocity CO (2–1) bipolar outflow in the east-west direction, which is clearly associated with IRS 1. Its outflow parameters are similar to those of intermediate-mass YSOs. Associated with the blue large-scale CO (2–1) outflow lobe, detected with single-dish observations, we only found two elongated low-velocity structures on either side of IRS 3. The large-scale outflow lobe is almost completely resolved out by the SMA. Our detected low-velocity CO structures are coincident with elongated H₂ emission features. The strongest millimeter continuum condensations in the region are found on either side of IRS 3, where the infrared emission is extremely weak. The CO and H₂ elongated structures follow the border of the millimeter continuum emission that is facing IRS 3. All these results suggest that the dust is associated with the walls of an expanding cavity driven by IRS 3, estimated to be a B2 star from both the centimeter and the infrared continuum emission.

Conclusions.IRS 1 seems to be an intermediate-mass Class I YSO driving a molecular outflow in the east-west direction, while IRS 3 is most likely a more evolved intermediate/high-mass star that is driving a cavity and accumulating dust in its walls. Within and beyond the expanding cavity, the millimeter continuum sources can be sites of future low-mass star formation.