Volume 529, May 2011
|Number of page(s)||12|
|Section||Interstellar and circumstellar matter|
|Published online||06 April 2011|
Hot HCN around young massive stars at 0.1′′ resolution
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
2 I. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany
3 Institut für Theoretische Astrophysik, Universität Heidelberg, Albert-Ueberle-Str. 2, 69120 Heidelberg, Germany
4 Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
Received: 19 January 2011
Accepted: 3 March 2011
Massive stars form deeply embedded in dense molecular gas, which they stir and heat up and ionize. During an early phase, the ionization is confined to hypercompact Hii regions, and the stellar radiation is entirely absorbed by dust, giving rise to a hot molecular core. To investigate the innermost structure of such high-mass star-forming regions, we observed vibrationally excited HCN (via the direct ℓ-type transition of v2 = 1, ΔJ = 0, J = 13, which lies 1400 K above ground) toward the massive hot molecular cores G10.47+0.03, SgrB2-N, and SgrB2-M with the Very Large Array (VLA) at 7 mm, reaching a resolution of about 1000 AU (0.1′′). We detect the line both in emission and in absorption against Hii regions. The latter allows to derive lower limits on the column densities of hot HCN, which are several times 1019 cm-2. We see indication of expansion motions in G10.47+0.03 and detect velocity components in SgrB2-M at 50, 60, and 70 km s-1 relative to the Local Standard of Rest. The emission originates in regions of less than 0.1 pc diameter around the hypercompact Hii regions G10.47+0.03 B1 and SgrB2-N K2, and reaches brightness temperatures of more than 200 K. Using the three-dimensional radiative transfer code RADMC-3D, we model the sources as dense dust cores heated by stars in the Hii regions, and derive masses of hot (>300 K) molecular gas of more than 100 solar masses (for an HCN fractional abundance of 10-5), challenging current simulations of massive star formation. Heating only by the stars in the Hii regions is sufficient to produce such large quantities of hot molecular gas, provided that dust is optically thick to its own radiation, leading to high temperatures through diffusion of radiation.
Key words: ISM: molecules / ISM: structure / ISM: clouds / stars: formation
© ESO, 2011
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.