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.
115454830
Clouds, filaments, and protostars: TheHerschel Hi-GAL Milky Way
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 AV ~ 1 is exceeded for the regions in the l = 59° field; a AV 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.
12498400
A molecular-line study of clumps with embedded high-mass protostar candidates
We present molecular line observations made with the IRAM 30-m telecopes of the immediate surroundings of a sample of 11 candidate high-mass protostars. These observations are part of an effort to clarify the evolutionary status of a set of objects which we consider to be precursors of UC HII regions. In a preceding series of papers we have studied a sample of objects, which on the basis of their IR colours are likely to be associated with compact molecular clouds. The original sample of 260 objects was divided approximately evenly into a High group, with IR colour indices [25-12] ≥ 0.57 and [60-12] ≥ 1.3, and a Low group with complementary colours. The FIR luminosity of the Low sources, their distribution in the IR colour-colour diagram, and their lower detection rate in H_2O maser emission compared to the High sources, led to the hypothesis that the majority of these objects represent an earlier stage in the evolution than the members of the High group, which are mostly identifiable with UC HII regions. Subsequent observations led to the selection of 12 Low sources that have FIR luminosities indicating the presence of B2.5 to O8.5 V0 stars, are associated with dense gas and dust, have (sub-)mm continuum spectra indicating temperatures of ~30 K, and have no detectable radio continuum emission. One of these sources has been proposed by us to be a good candidate for the high-mass equivalent of a Class 0 object. In the present paper we present observations of the molecular environment of 11 of these 12 objects, with the aim to derive the physical parameters of the gas in which they are embedded, and to find further evidence in support of our hypothesis that these sources are the precursors to UC HII regions. We find that the data are consistent with such an interpretation. All observed sources are associated with well-defined molecular clumps. Masses, sizes, and other parameters depend on the tracer used, but typically the cores have average diameters of ~0.5-1 pc (with a range of 0.2 to 2.2 pc), and masses of a few tens to a few thousand solar masses. Compared to a similar analysis of High sources, the present sample has molecular clumps that are more massive, larger, cooler, and less turbulent. They also tend to have a smaller ratio of virial-to-luminous mass, indicating they are less dynamically stable than their counterparts in which the High sources are embedded. The large sizes suggest these clumps should still undergo substantial contraction (their densities are ~10 times smaller than those of the High sources). The lower temperatures and small linewidths are also expected in objects in an earlier evolutionary state. In various sources indications are found for outflowing gas, though its detection is hampered by the presence of multiple emission components in the line spectra. There are also signs of self-absorption, especially in the spectra of ^(13)CO and HCO+. We find that the masses of the molecular clumps associated with our objects increase with L_(fir) (M_(clump) ∝ L^(1.17)_(fir)), and that there is a (weak) relation between the clump mass and the mass of the embedded protostellar object M_(proto) ∝ M^(0.30)_(clump). The large amount of observational data is necessarily presented in a compact, reduced form. Yet we supply enough information to allow further study. These data alone cannot prove or disprove the hypothesis that among these objects a high-mass protostar is truly present. More observations, at different wavelenghts and spatial resolutions are needed to provide enough constraints on the number of possible interpretations.
59289400
Molecular gas and stars in the translucent cloud MBM 18 (LDN 1569)
Context. We investigate star formation in translucent, high-latitu de clouds. Aims. Our aim is to understand the star-formation history and rate in the solar neighbourhood. Methods. We used spectroscopic observations of newly found candidate Hα emission-line stars to establish their pre-main-sequence nature. The environment was studied through molecular line observations of the cloud (MBM 18/LDN 1569) in which the stars are presumably embedded. Results. Ten candidate Hα emission-line stars were found in an objective grism survey of a∼ 1 square degree region in MBM 18, of which seven have been observed spectroscopically in this study. Four of these have weak (| W(Hα)|< 5 A) Hα emission, and six out of seven have spectral types M1−M4 V. One star is of type F7-G1 V, and has Hα in absorption. The spectra of three of the M-stars may show an absorption line of LiI, although none of these is an unambiguous detection. The M-stars lie at distances between∼60 pc and 250 pc, while most distance determinations of MBM 18 found in the literature agree on 120− 150 pc. For the six M-stars a good fit is obtained with pre-main-sequence isochrones indi cating ages between 7.5 and 15 Myr. The mass of the molecular material, derived from the integrated 12 CO(1‐0) emission, is∼ 160 M⊙ (for a distance of 120 pc). This is much smaller than the viria l mass (∼ 10 3 M⊙), and the cloud is not gravitationally bound. Using a clump-finding routine, we identify 12 clumps from the CO-data, with masses between 2.2 and 22 M⊙. All clumps have a virial mass at least six times higher than t heir CO-mass, and thus none are in gravitational equilibrium. A similar situation is found fr om higher-resolution CO-observations of the northern part of the cloud. Conclusions. Considering the relative weakness or absence of the Hα emission, the absence of other emission lines, and the lack of clear LiI absorption, the targets are not T Tauri stars. Wi th ages between 7.5 and 15 Myr they are old enough to explain the lack of lithium in their spectra. Based on the derived distances, some of the stars may lie inside the molecular cloud. From the fact that the cloud as a whole, as well as the individual clumps, are not gravitationally bound, in combination with the ages of the stars we conclude that it is not likely that (these) stars were formed in MBM 18.
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.
10224110
IRAS 23385+6053: A Prototype Massive Class 0 Object
IRAS 23385+6053 is a young stellar object with a luminosity of ~1.6 × 10 -->4 L☉${s}$ -->$t SUBgt {s}t/SUBgt $ --> at a kinematic distance of 4.9 kpc. This candidate precursor of an ultracompact H II region is associated with a millimeter source detected at the James Clerk Maxwell Telescope but is undetected at centimeter wavelengths with the VLA. We observed this source with the Owens Valley Radio Observatory millimeter array at 3.4 mm in the continuum, HCO -->+ (1→0), H -->13CO -->+ (1→0), and SiO (v=0, 2→1) line emission and with CAM aboard the Infrared Space Observatory at 6.75 and 15 μm. The IRAS source is coincident with a 3.4 mm compact (rcore${r core}$ -->$t SUBgt {r core}t/SUBgt $ --> 0.048 pc) and massive (M 370 M☉${s}$ -->$t SUBgt {s}t/SUBgt $ -->) core, which is undetected at 15 μm to a 3 σ level of 6 mJy; this is compatible with the derived H -->2 column density of ~2 × 10 -->24 cm -->−2 and the estimated visual extinction A -->V ~2000 mag. We find Lsubmm${r submm}$ -->$t SUBgt {r submm}t/SUBgt $ -->/Lbol${r bol}$ -->$t SUBgt {r bol}t/SUBgt $ --> ~3 × 10 -->−3 and Menv${r env}$ -->$t SUBgt {r env}t/SUBgt $ -->/M${s}$ -->$t SUBgt {s}t/SUBgt $ -->1, which is typical of class 0 objects. The source is also associated with a compact outflow characterized by a size rcore, a dynamical timescale of 7 × 10 -->3 yr, and a mass-loss rate ${u{M}{"705F}}$ -->${u{M}{"705F}}$ --> 10 -->−3 M☉$$ -->$t SUBgt {s}t/SUBgt $ --> yr -->−1. The axis of the outflow is oriented nearly perpendicular to the plane of the sky, ruling out the possibility that the nondetection at 15 μm is the result of a geometric effect. All these properties suggest that IRAS 23385+6053 is the first example of a bona fide massive class 0 object.
123641202
Seismic Attenuation System (SAS) in the Kamioka Mine