16173830
Single-dish monitoring of circumstellar water masers
We present an overview of the long-term water maser monitoring program of a sample of late-type stars, carried out with the Medicina 32-m and Effelsberg 100-m telescopes, and describe the results in some detail. The role the SRT (Sardinia Radio Telescope) could play in this program is outlined.
18606865
Galactic interstellar 18 O/ 17 O ratios - a radial gradient?
Context. The determination of interstellar abundances is essential for a better understanding of stellar nucleosynthesis and the “chemical” evolution of the Galaxy. Aims. The aim is to determine 18 O/ 17 O abundance ratios across the entire Galaxy. These provide a measure of the amount of enrichment by high-mass versus intermediate-mass stars. Methods. Such ratios, derived from the C 18 O and C 17 O $J = 1$–0 lines alone, may be affected by systematic errors. Therefore, the C 18 O and C 17 O (1–0), (2–1), and (3–2), as well as the 13 CO(1–0) and (2–1) lines, were observed towards 18 prominent galactic targets (a total of 25 positions). The combined dataset was analysed with a large velocity gradient model, accounting for optical depth effects. Results. The data cover galactocentric radii between 0.1 and 16.9 kpc (solar circle at 8.5 kpc). Near the centre of the Galaxy, 18 O/ 17 O = 2.88  ±  0.11. For the galactic disc out to a galactocentric distance of ~10 kpc, 18 O/ 17 O = 4.16  ±  0.09. At ~16.5 kpc from the galactic centre, 18 O/ 17 O = 5.03  ±  0.46. Assuming that 18 O is synthesised predominantly in high-mass stars ($M >8$ $M_{\odot}$), while C 17 O is mainly a product of lower mass stars, the ratio from the inner Galaxy indicates a dominance of CNO-hydrogen burning products that is also apparent in the carbon and nitrogen isotope ratios. The high 18 O/ 17 O value of the solar system (5.5) relative to that of the ambient interstellar medium suggests contamination by nearby high-mass stars during its formation. The outer Galaxy poses a fundamental problem. High values in the metal-poor environment of the outer Galaxy are not matched by the low values observed towards the even more metal-poor Large Magellanic Cloud. Apparently, the outer Galaxy cannot be considered as an intermediate environment between the solar neighbourhood and the interstellar medium of small metal-poor galaxies. The apparent 18 O/ 17 O gradient along the galactic disc and the discrepancy between outer disc and LMC isotope ratios may be explained by different ages of the respective stellar populations. More data from the central and far outer parts of the Galaxy are, however, needed to improve the statistical significance of our results.
118239150
The exciting future of (sub-)millimeter interferometry: ALMA
The Atacama Large Millimeter/submillimeter Array (ALMA), presently under construction, is a revolutionary astronomical interferometer, that will operate at (sub)millimeter wavelengths. With unprecedented sensitivity, resolution, and imaging capability, ALMA will explore the (sub-)mm Universe, one of astronomy's last frontiers. ALMA is expected to provide insight in star- and galaxy formation in the early Universe and to image local star- and planet formation in great detail. The ALMA Commissioning and Science Verification phase is currently in course, preparing the path for Early Science. The Call for ALMA Early Science proposals is expected to be released before the end of 2010. In this contribution we will describe the ALMA project, the array and its receivers, its science goals, and its scientific and technological potential. We will outline the organizational structure of the ALMA Regional Centres, that will play an important role in providing support to the users, with particular attention to the Italian ALMA Regional Centre in Bologna. Finally, we will illustrate what ALMA can contribute to the specific science case of AGN fueling.
15829595
Monitoring Water Masers in Star-Forming Regions
An overview is given of the analysis of more than a decade of H2O maser data from our monitoring program. We find the maser emission to generally depend on the luminosity of the YSO as well as on the geometry of the SFR. There appears to be a threshold luminosity of a few times 104L⊙ above and below which we find different maser characteristics.
14067221
Search for massive protostar candidates in the southern hemisphere - II. Dust continuum emission
In an ongoing effort to identify and study high-mass protostellar candidates we have observed in various tracers a sample of 235 sources selected from the IRAS Point Source Catalog, mostly with $\delta Low sources and 93 High , which are believed to be in different evolutionary stages. Both sub-samples have been studied in detail by comparing their physical properties and morphologies. Massive dust clumps have been detected in all but 8 regions, with usually more than one clump per region. The dust emission shows a variety of complex morphologies, sometimes with multiple clumps forming filaments or clusters. The mean clump has a linear size of ~$ 0.5$ pc, a mass of ~$ 320~M_\odot$ for a dust temperature $T_{\rm d} = 30$ K, an H 2 density of $9.5\times10^5$ cm -3 , and a surface density of 0.4 g cm -2 . The median values are 0.4 pc, $102~M_\odot$, $4\times10^4$ cm -3 , and 0.14 g cm -2 , respectively. The mean value of the luminosity-to-mass ratio, $L/M \simeq 99~L_\odot/M_\odot$, suggests that the sources are in a young, pre-ultracompact Hii  phase. We have compared the millimeter continuum maps with images of the mid-IR MSX emission, and have discovered 95 massive millimeter clumps non-MSX emitters, either diffuse or point-like, that are potential prestellar or precluster cores. The physical properties of these clumps are similar to those of the others, apart from the mass that is ~3 times lower than for clumps with MSX counterpart. Such a difference could be due to the potential prestellar clumps having a lower dust temperature. The mass spectrum of the clumps with masses above $M \sim 100~M_\odot$ is best fitted with a power-law d$N/{\rm d}M \propto M^{-\alpha}$ with $\alpha = 2.1$, consistent with the Salpeter (1955) stellar IMF, with $\alpha=2.35$. On the other hand, the mass function of clumps with masses $10~M_\odot\la M \la 120~M_\odot$ is better fitted with a power law of slope $\alpha = 1.5$, more consistent with the mass function of molecular clouds derived from gas observations.
5428392
Search for massive protostellar candidates in the southern hemisphere: I. Association with dense gas
We have observed two rotational transitions of both CS and C 17 O, and the 1.2 mm continuum emission towards a sample of 130 high-mass protostellar candidates with δ δ ≥ $-30^{\circ}$, we have selected from the IRAS Point Source Catalogue 429 sources which potentially are compact molecular clouds on the basis of their IR colours. The sample has then been divided into two groups according to the colour indices [25–12] and [60–12]: the 298 sources with [25–12]  ≥ 0.57 and [60–12]  ≥ 1.30 have been called High sources, the remaining 131 have been called Low sources. In this paper, we check the association with dense gas and dust in 130 Low sources. We have obtained a detection rate of ~$85\%$ in CS, demonstrating a tight association of the sources with dense molecular clumps. Among the sources detected in CS, ~$76\%$ have also been detected in C 17 O  and ~$93\%$ in the 1.2 mm continuum. Millimeter-continuum maps show the presence of clumps with diameters in the range $0.2{-}2$ pc and masses from a few $M_{\odot}$ to $10^{5}~M_{\odot}$; H 2  volume densities computed from CS line ratios lie between ~10 4.5 and 10 5.5  cm -3 . The bolometric luminosities of the sources, derived from IRAS data, are in the range $10^{3}{-}10^{6}~L_{\odot}$, consistent with embedded high-mass objects. Based on our results and those found in the literature for other samples of high-mass young stellar objects, we conclude that our sources are massive objects in a very early evolutionary stage, probably prior to the formation of an Hii region. We propose a scenario in which High and Low sources are both made of a massive clump hosting a high-mass protostellar candidate and a nearby stellar cluster. The difference might be due to the fact that the 12  μ m IRAS flux, the best discriminant between the two groups, is dominated by the emission from the cluster in Lows and from the massive protostellar object in Highs .
120833712
Subterranean ground motion studies for the Einstein Telescope
Seismic motion limits the low-frequency sensitivity of ground-based gravitational wave detectors. A conceptual design study into the feasibility of a future-generation gravitational wave observatory, coined the Einstein Telescope, has been completed. As part of this design phase, we performed a ground motion study to determine the seismic noise characteristics at various sites across the globe. This investigation focused on underground sites and encompassed a variety of geologies, including clay, salt, and hard rock, at 15 locations in nine European countries, the USA, and Japan. In addition, we analyzed data from the Virtual European Broadband Seismograph Network to characterize European seismic motion. We show that, in the region of interest for future-generation gravitational wave detectors (1–10 Hz), seismic motion is dominated by activity from anthropogenic sources. A number of sites were found that exhibited a reduction in seismic power of several orders of magnitude with respect to current detector sites, thus making it possible to set requirements for the Einstein Telescope seismic noise environment.
123641202
Seismic Attenuation System (SAS) in the Kamioka Mine