We present the first results from the science demonstration phase for the Hi-GAL survey, the Herschel key program that will map the inner Galactic plane of the Milky Way in 5 bands. We outline our data reduction strategy and present some science highlights on the two observed 2° × 2° tiles approximately centered at l = 30° and l = 59°. The two regions are extremely rich in intense and highly structured extended emission which shows a widespread organization in filaments. Source SEDs can be built for hundreds of objects in the two fields, and physical parameters can be extracted, for a good fraction of them where the distance could be estimated. The compact sources (which we will call cores' in the following) are found for the most part to be associated with the filaments, and the relationship to the local beam-averaged column density of the filament itself shows that a core seems to appear when a threshold around A V ~ 1 is exceeded for the regions in the l = 59° field; a A V value between 5 and 10 is found for the l = 30° field, likely due to the relatively higher distances of the sources. This outlines an exciting scenario where diffuse clouds first collapse into filaments, which later fragment to cores where the column density has reached a critical level. In spite of core L/M ratios being well in excess of a few for many sources, we find core surface densities between 0.03 and 0.5 g cm-2. Our results are in good agreement with recent MHD numerical simulations of filaments forming from large-scale converging flows.

International audienceHi-GAL, the Herschel infrared Galactic Plane Survey, is an Open Time Key Project of the Herschel Space Observatory. It will make an unbiased photometric survey of the inner Galactic plane by mapping a wide strip in the longitude range in five wavebands between 70 μm and 500 μm. The aim of Hi-GAL is to detect the earliest phases of the formation of molecular clouds and high-mass stars and to use the optimum combination of Herschel wavelength coverage, sensitivity, mapping strategy, and speed to deliver a homogeneous census of star-forming regions and cold structures in the interstellar medium. The resulting representative samples will yield the variation of source temperature, luminosity, mass and age in a wide range of Galactic environments at all scales from massive YSOs in protoclusters to entire spiral arms, providing an evolutionary sequence for the formation of intermediate and high-mass stars. This information is essential to the formulation of a predictive global model of the role of environment and feedback in regulating the star-formation process. Such a model is vital to understanding star formation on galactic scales and in the early universe. Hi-GAL will also provide a science legacy for decades to come with incalculable potential for systematic and serendipitous science in a wide range of astronomical fields, enabling the optimum use of future major facilities such as JWST and ALMA

We present SEST-SIMBA 1.2-mm continuum maps and ESO-NTT SOFI JHK S images of the Galactic H ii region RCW 79. The millimetre continuum data reveal the presence of massive fragments located in a dust emission ring surrounding the ionized gas. The two most massive fragments are diametrically opposite each other in the ring. The near-IR data, centred on the compact H ii region located at the south-eastern border of RCW 79, show the presence of an IR-bright cluster containing massive stars along with young stellar objects with near-IR excesses. A bright near- and mid-IR source is detected towards maser emissions, 1.2 pc north-east of the compact H ii region centre. Additional information extracted from the Spitzer GLIMPSE survey is used to discuss the nature of the bright IR sources observed towards RCW 79. Twelve luminous Class I sources are identified towards the most massive millimetre fragments. All these facts strongly indicate that the massive-star formation observed at the border of the H ii region RCW 79 has been triggered by its expansion, most probably by the collect and collapse process.

Astronomy & Astrophysics (A&A) is an international journal which publishes papers on all aspects of astronomy and astrophysics

Aims. We present one-dimensional aperture synthesis imaging of the red supergiant Betelgeuse (α Ori) with VLTI/AMBER. We reconstructed for the first time one-dimensional images in the individual CO first overtone lines. Our aim is to probe the dynamics of the inhomogeneous atmosphere and its time variation. Methods. Betelgeuse was observed between 2.28 and 2.31 μm with VLTI/AMBER using the 16-32-48 m telescope configuration with a spectral resolution up to 12 000 and an angular resolution of 9.8 mas. The good nearly one-dimensional uv coverage allows us to reconstruct one-dimensional projection images (i.e., one-dimensional projections of the object’s two-dimensional intensity distributions). Results. The reconstructed one-dimensional projection images reveal that the star appears differently in the blue wing, line center, and red wing of the individual CO lines. The one-dimensional projection images in the blue wing and line center show a pronounced, asymmetrically extended component up to ~1.3 R ⋆, while those in the red wing do not show such a component. The observed one-dimensional projection images in the lines can be reasonably explained by a model in which the CO gas within a region more than half as large as the stellar size is moving slightly outward with 0–5 km s-1, while the gas in the remaining region is infalling fast with 20–30 km s-1. A comparison between the CO line AMBER data taken in 2008 and 2009 shows a significant time variation in the dynamics of the CO line-forming region in the photosphere and the outer atmosphere. In contrast to the line data, the reconstructed one-dimensional projection images in the continuum show only a slight deviation from a uniform disk or limb-darkened disk. We derive a uniform-disk diameter of 42.05 ± 0.05 mas and a power-law-type limb-darkened disk diameter of 42.49 ± 0.06 mas and a limb-darkening parameter of (9.7 ± 0.5) × 10-2. This latter angular diameter leads to an effective temperature of 3690 ± 54 K for the continuum-forming layer. These diameters confirm that the near-IR size of Betelgeuse was nearly constant over the last 18 years, in marked contrast to the recently reported noticeable decrease in the mid-IR size. The continuum data taken in 2008 and 2009 reveal no or only marginal time variations, much smaller than the maximum variation predicted by the current three-dimensional convection simulations.Conclusions. Our two-epoch AMBER observations show that the outer atmosphere extending to ~1.3–1.4 R ⋆ is asymmetric and its dynamics is dominated by vigorous, inhomogeneous large-scale motions, whose overall nature changes drastically within one year. This is likely linked to the wind-driving mechanism in red supergiants.

Complete flux-calibrated spectra covering the spectral range from 6000 Å to 2.5 μm have been obtained along the HH1 jet and analysed in order to explore the potential of a combined optical/near-IR diagnostic applied to jets from young stellar objects. The main physical parameters (visual extinction, electron temperature and density, ionization fraction and total density) have been derived along the jet using various diagnostic line ratios. This multi-line analysis shows, in each spatially unresolved knot, the presence of zones at different excitation conditions, as expected from the cooling layers behind a shock front. In particular, a density stratification in the jet is evident from ratios of various lines of different critical density. We measure electron densities in the range 6 $\times$ 102–3 $\times$ 103 cm-3 with the [$\ion{S}{ii}$] optical doublet lines, 4 $\times$ 103–104 cm-3 with the near-IR [$\ion{Fe}{ii}$] lines, and 105–106 cm-3 with optical [$\ion{Fe}{ii}$] and CaII lines. The electron temperature also shows variations, with values between 8000–11 000 K derived from optical/near-IR [$\ion{Fe}{ii}$] lines and 11 000–20 000 K from a combined diagnostic employing optical [$\ion{O}{i}$] and [$\ion{N}{ii}$] lines. Thus [$\ion{Fe}{ii}$] lines originate in a cooling layer located at larger distances from the shock front than that generating the optical lines, where the compression is higher and the temperature is declining. The derived parameters were used to measure the mass flux along the jet, adopting different procedures, the advantages and limitations of which are discussed. The [$\ion{Fe}{ii}$] 1.64 μm line luminosity turns out to be more suitable to measure $\dot{M}_{{\rm jet}}$ than the optical lines, since it samples a fraction of the total mass flowing through a knot larger than the [$\ion{O}{i}$] or [$\ion{S}{ii}$] lines. $\dot{M}_{{\rm jet}}$ is high in the initial part of the flow (~2.2 $\times$ 10$^{-7}~M_{\odot}$ yr-1) but decreases by about an order of magnitude further out. Conversely, the mass flux associated with the warm molecular material is low, $\dot{M}_{{\rm H2}}$ ~ 10$^{-9}~M_{\odot}$ yr-1, and does not show appreciable variations along the jet. We suggest that part of the mass flux in the external regions is not revealed in optical and IR lines because it is associated with a colder atomic component, which may be traced by the far-IR [$\ion{O}{i}$]63 μm line. Finally, we find that the gas-phase abundance of refractory species, such as Fe, C, Ca, and Ni, is lower than the solar value, with the lowest values (between 10 and 30% of solar) derived in the inner and densest regions. This suggests a significant fraction of dust grains may still be present in the jet beam, imposing constraints on the efficiency of grain destruction by multiple low-velocity shock events.