Near- and far-infrared counterparts of millimeter dust cores in the Vela molecular ridge cloud D ^*,**

¹ INAF - Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monte Porzio Catone (Roma), Italy e-mail: [deluca;giannini;lorenzetti;nisini]@oa-roma.inaf.it
² Dipartimento di Fisica - Università di Roma “Tor Vergata”, via della Ricerca Scientifica 1, 00133 Roma, Italy
³ INAF - Osservatorio Astrofisico di Arcetri, Largo E.Fermi 5, 50125 Firenze, Italy e-mail: fmassi@arcetri.astro.it
⁴ Dipartimento di Fisica - Università di Lecce, CP 193, 73100 Lecce, Italy

Received: 5 February 2007
Accepted: 24 April 2007

Abstract

Aims.Identify the young protostellar counterparts associated with dust millimeter cores of the Vela Molecular Ridge Cloud D through new IR observations (H₂ narrow-band at 2.12 μm and N broad band at 10.4 μm) along with an investigation performed on the existing IR catalogues.

Methods.The association of mm continuum emission with infrared sources from catalogues (IRAS, MSX, 2MASS), JHK data from the literature, and new observations, was established according to spatial coincidence, infrared colours and spectral energy distributions.

Results.Only 7 out of 29 resolved mm cores (and 16 out of the 26 unresolved ones) do not exhibit signposts of star formation activity. The other ones are clearly associated with: far-IR sources, H₂ jets pointing back to embedded objects not (yet) detected or near-IR objects showing a high intrinsic colour excess. The distribution of the spectral indices pertaining to the associated sources is peaked at values typical of Class I objects, while three objects are signalled as candidates Class 0 sources. Objects with far-IR colours similar to those of T-Tauri and Herbig Ae/Be stars seem to be very few. An additional population of young objects exists associated not with the mm-cores, but with both the diffuse warm dust emission and the gas filaments. We point out the high detection rate (30%) of H₂ jets driven by sources located inside the mm-cores. They do not appear to be driven by the most luminous objects in the field, but rather by less luminous objects in young clusters, testifying the co-existence of both low- and intermediate-mass star formation.

Conclusions.The presented results reliably describe the young population of VMR-D. However, the statistical evaluation of activity vs. inactivity of the investigated cores, even in good agreement with results found for other star forming regions, seems to reflect the limiting sensitivity of the available facilities rather than any property intrinsic to the mm-condensations.