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MACHO-96-BLG-5 was a microlensing event observed toward the bulge of the Galaxy with an exceptionally long duration of ~970 days. The microlensing parallax fit parameters were used to estimate a lens mass M = 6 M☉, corresponding to a distance d in the range 0.5-2 kpc. The upper limit on the absolute brightness for main-sequence stars of the same mass is less than 1 L☉, so the lens is a good black hole candidate. Such a black hole would accrete from the interstellar medium, thereby emitting in the X-ray band. Here we report the analysis of a deep XMM-Newton observation toward the MACHO-96-BLG-5 lens position. Only an upper limit (99.8% confidence level) to the X-ray flux from the lens position, 9.10 × 10-15 to 1.45 × 10-14 ergs cm-2 s-1 in the 0.2-10 keV energy band, is obtained, allowing us to constrain the putative black hole's accretion parameters.

In this paper, we present and discuss an infrared two-colour diagram built with the 60, 100, and 170 μm photometry of the whole sample of Herbig Ae/Be stars observed by the spectrometers on board of ISO satellite. An overview of this diagram reveals a certain degree of homogeneity in the behaviour of these stars and their IR-emitting environments, with some exceptions. In particular, we account for the objects located to the left of the blackbody line. In addition, the infrared colours obtained with ISO gave us the opportunity to compare with the IRAS measurements, which generally appear in good agreement. Finally, a simple spherically symmetric model of pre-ZAMS circumstellar environment is used to obtain the two-colour diagram, as a diagnostic tool complementary to the best-fit of the spectra in investigating the distribution of matter around these stars.

The interstellar medium (ISM), gas and dust, appears to be arranged in clouds, whose dimensions, masses and densities span a large range of scales: from giant molecular clouds to small isolated globules. The structure of these objects show a high degree of complexity appearing, in the range of the observed scales, as a non-homogeneous ("clumpy") distribution of matter. The arrangement of the ISM is clearly relevant for the study of the fragmentation of the clouds and then of the star formation processes. To quantify observationally the ISM structure, many methods have been developed and our study is focused on some of them, exploiting multiwavelength observations of IS objects. The investigations presented here have been carried out by considering both the dust absorption (in optical and near IR wavelengths) and the gas emission (in the submm-radio spectral range). We present the maps obtained from the reduction of raw data and a first tentative analysis by means of methods as the structure function, the autocorrelation, and the Δ-variance. These are appropriate tools to highlight the complex structure of the ISM with reference to the paradigm given by the supersonic turbulence. Three observational cases are briefly discussed. In order to analyse the structure of objects characterized by different sizes, we applied the above-mentioned algorithms to the extinction map of the dark globule CB 107 and to the CO(J = 1-0) integrated intensity map of Vela Molecular Ridge, D Cloud. Finally we compare the results obtained with synthetic fractal maps known as "fractional Brownian motion" fBm images.

This paper presents the near-IR imaging observations of CB 107, a small dark globule projected against a rich stellar background. By means of accurate photometry, the near-IR two-color diagram J - H versus H - K was obtained for the stellar background. This information was used to estimate the color excesses of the detected stars so that, given the reddening curve, it was possible to derive the extinction map of the cloud. The structural properties of the dark globule were investigated by plotting the extinction dispersion σ, obtained in a given spatial box, as a function of the mean extinction AV. This relationship has shown quite a definite linear behavior, with the slope increasing with the box size. The results of the present analysis, compared with those obtained by other authors on larger dark clouds, suggest that for a given spatial scale the slope of the σ versus AV relation is greater in CB 107 than in larger clouds. The so-called Δ-variance method was also used to investigate the structure of the dark globule by evaluating the drift behavior of its extinction map. In this way, we have found that the power spectrum of the extinction map is characterized by a power law with exponent β ~ 2.7. This value is lower than expected, for the same range of spatial scales, on the basis of previous work on large molecular clouds.

This paper discusses a model for the continuum emission of the Herbig Ae/Be stars in the light of an updated set of observational data spanning 5 orders of magnitude in wavelength and including the low-resolution spectra obtained with the Short Wavelength Spectrometer and Long Wavelength Spectrometer on board the Infrared Space Observatory (ISO). The model is used to reproduce the continuum emission of the 36 Herbig Ae/Be stars included in the list by The and coworkers and observed by ISO. The circumstellar matter responsible for the observed spectral energy distributions has been investigated by comparing the set of the observations with the model spectra computed for different possible distributions of circumstellar matter. Cases have been considered with the circumstellar regions partially evacuated along the polar axis by the action of the stellar wind, a phenomenon that is quite common in these pre-main-sequence objects. The inclusion of the polar cavities indirectly allows geometries in which a small-scale disklike structure around the central star is present. The possible coexistence of two different density profiles, in the inner and the outer region of the envelope, respectively, has been also considered. The comparison of the computed models with the observed spectral energy distributions selects the parameter values in such a way that the larger dust grains are preferentially associated with the later spectral types. We find that 17 objects are reasonably fitted, eight of which with a purely spherical model and the remaining nine with the inclusion of the polar cavities. For 10 further objects the fit is worse, and for the remaining nine, almost all associated to IR companions, our model is clearly inappropriate. A linear relationship is suggested between the logarithm of the initial density n0 and the exponent p of the power law n(r) = n0(R*/r)p adopted for the circumstellar density distribution.

We present a study of the infrared variability of young stellar objects by means of two Spitzer-IRAC images of the Vela Molecular Cloud D (VMR-D) obtained in observations separated in time by about six months. By using the same space-born IR instrumentation, this study eliminates all the unwanted effects usually unavoidable when comparing catalogs obtained from different instruments. The VMR-D map covers about 1.5 square deg. of a site where star formation is actively ongoing. We are interested in accreting pre-main sequence variables whose luminosity variations are due to intermittent events of disk accretion (i.e. active T Tauri stars and EXor type objects). The variable objects have been selected from a catalog of more than 170,000 sources detected at a S/N ratio > 5. We searched the sample of variables for ones whose photometric properties are close to those of known EXor's. These latter are monitored in a more systematic way than T Tauri stars and the mechanisms that regulate the observed phenomenology are exactly the same. Hence the modalities of the EXor behavior is adopted as driving criterium for selecting variables in general. We selected 19 bona fide candidates that constitute a well-defined sample of new variable targets for further investigation. Out of these, 10 sources present a Spitzer MIPS 24 micron counterpart, and have been classified as 3 Class I, 5 flat spectrum and 2 Class II objects, while the other 9 sources have spectral energy distribution compatible with phases older than Class I. This is consistent with what is known about the small sample of known EXor's, and suggests that the accretion flaring or EXor stage might come as a Class I/II transition. We present also new prescriptions that can be useful in future searches for accretion variables in large IR databases., 35 pages, 12 figures To appear in ApJ

We present the preliminary results of a statistical analysis carried out on a 1° × 1° CO(1-0) map of the intermediate mass star forming region Vela-D Cloud. Our goal is to determine statistical parameters suitable to quantify the structure of the observed cloud, in particular the power-law exponent of the map power spectrum. Furthermore, to help in removing the degeneracy implied in using a single parameter, we also resort to the multifractal approach.

A new, unbiased Spitzer-MIPS imaging survey (~1.8 square degs) of the young stellar content of the Vela Molecular Cloud-D is presented. The survey is complete down to 5mJy and 250mJy at 24micron (mu) and 70mu, respectively. 849 sources are detected at 24mu and 52 of them also have a 70mu counterpart. The VMR-D region is one that we have already partially mapped in dust and gas millimeter emission, and we discuss the correlation between the Spitzer compact sources and the mm contours. About half of the 24mu sources are located inside the region delimited by the 12CO(1-0) contours (corresponding to only one third of the full area mapped with MIPS) with a consequent density increase of about 100% of the 24mu sources [four times for 70mu ones] moving from outside to inside the CO contours. About 400 sources have a 2MASS counterpart. So we have constructed a Ks vs. Ks-[24] diagram and identified the protostellar population. We find an excess of Class I sources in VMR-D in comparison with other star forming regions. This result is reasonably biased by the sensitivity limits, or, alternatively, may reflect a very short lifetime (, 29 pages, 14 figures. To appear in Ap.J

We present a comparative study of three dark globules CB52, CB107, and DC267.407.5. By means of an accurate photometry, near-IR two-colour diagrams were derived for the stellar backgrounds and used to determine the colour excesses of the reddened stars (Campeggio et al. 2004). By assuming a normal interstellar reddening law (Rieke & Lebofsky 1985), the visual extinction can be obtained as AV = 15.87E(H −K). We sampled the three images with a spatial grid, computing, for each box, the mean extinction AV and the relative dispersion σAV . It is noteworthy that the extinction maps, obtained by means of this information, closely follow the shapes of the globules with values increasing from the boundary to the innermost dark regions. To analyze the structural properties of these globules we investigated the extinction dispersion σAV as a function of AV (Lada et al. 1994; Padoan et al. 1997), pointing out three different behaviours: parabolic (increasing up to a maximum and then decreasing), linear and fanlike for CB52, CB107, and DC267.4-07.5 respectively. For the globules DC267.4-07.5 and CB107, the scatter plots can be fitted with a linear function, while, for comparison purpose, we adopted for CB52 the tangent slope to the fitting parabola in the point AV =2. To give a physical interpretation of these trends we also developed a code to simulate clouds. In this model a given volume of space is filled with a collection of small spheres (clumps) randomly distributed and characterized by different positions, central densities, and density profiles. Our simulations are completed by considering artificial stellar backgrounds, characterized by density, magnitude and colour distributions similar to those actually observed in the unreddened regions of the observed fields. We applied to these synthetic backgrounds the same procedures used for the analysis of the observations. Our results point out that such a kind of simulation can account for the different behaviours of the σAV vs. AV scatter plots observed in clouds with different internal structures (Maiolo et al. 2006). We also extended this analysis to a range of angular scales to study the non-homogeneity of these clouds for different spatial scales. We note that in each case the slope decreases with increasing angular resolution, pointing out that the globules, particularly CB107 and DC267.4-07.5, appear more structured toward the larger scales. Similar evidence was given by Lada et al. 1999 for the cloud IC 5146. In conclusion, our investigation suggests different internal structures for the studied clouds.

We present the 12CO(1-0) and 13CO(2-1) line maps obtained observing with the SEST a $\sim 1\degr \times 1\degr$ region of the Vela Molecular Ridge, Cloud D. This cloud is part of an intermediate-mass star forming region that is relatively close to the Sun. Our observations reveal, over a wide range of spatial scales (from $\sim 0.1$ to a few parsecs), a variety of dense structures such as arcs, filaments and clumps, that are in many cases associated with far-IR point-like sources, recognized as young stellar objects and embedded star clusters. The velocity field analysis highlights the presence of possible expanding shells, extending over several parsecs, probably related to the star forming activity of the cloud. Furthermore, the analysis of the line shapes in the vicinity of the far-IR sources allowed the detection of 13 molecular outflows. Considering a hierarchical scenario for the gas structure, a cloud decomposition was obtained for both spectral lines by means of the CLUMPFIND algorithm. The CLUMPFIND output has been discussed critically and a method is proposed to reasonably correct the list of the identified clumps. We find that the corresponding mass spectrum shows a spectral index $\alpha\sim1.3 \div 2.0$ and the derived clump masses are below the corresponding virial masses. The mass-radius and velocity dispersion-radius relationships are also briefly discussed for the recovered clump population., Comment: 43 pages, 16 figures. Accepted by Astrophysical Journal

We discuss some methods for characterizing the mass distribution in the interstellar clouds. This is done in the light of available observational techniques and of appropriate statistical tools capable to highlight the structural properties of the astronomical images. The potentialities of the optical and near-IR imaging of dark clouds as well as of their far-IR and millimetric mapping are also discussed with respect to the analysis in terms of statistical characterization. We briefly address the hypothesis that the origin of the structure observed in interstellar clouds is the turbulence which could be a natural consequence of the physical status of the interstellar medium. We finally discuss how the fractal geometry offers an interesting tool for characterizing the structure of the interstellar clouds introducing the so called multifractal spectrum. The physical interpretation of this spectrum can offer a further tool in discriminating among different possible kind of internal dynamics.

We present the first results from the science demonstration phase for the Hi-GAL survey, the Herschel key-project 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{\deg} x 2{\deg} tiles approximately centered at l=30{\deg} and l=59{\deg}. 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 of about 1 is exceeded for the regions in the l=59{\deg} field; a A_V value between 5 and 10 is found for the l=30{\deg} field, likely due to the relatively larger 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., Comment: A&A, accepted

We present a first study of the star-forming compact dust condensations revealed by Herschel in the two 2 \times 2 \degr Galactic Plane fields centered at [l;b] = [30\degr; 0 \degr] and [l;b] = [59\degr; 0 \degr], respectively, and observed during the Science Demonstration Phase for the Herschel infrared Galactic Plane survey (Hi-GAL) Key-Project. Compact source catalogs extracted for the two fields in the five Hi-GAL bands (70, 160, 250, 350 and 500 $\mu$m) were merged based on simple criteria of positional association and spectral energy distribution (SED) consistency into a final catalog which contains only coherent SEDs with counterparts in at least three adjacent Herschel bands. These final source lists contain 528 entries for the l = 30\degr field, and 444 entries for the l = 59\degr field. The SED coverage has been augmented with ancillary data at 24 $\mu$m and 1.1 mm. SED modeling for the subset of 318 and 101 sources (in the two fields, respectively) for which the distance is known was carried out using both a structured star/disk/envelope radiative transfer model and a simple isothermal grey-body. Global parameters like mass, luminosity, temperature and dust properties have been estimated. The Lbol/Menv ratio spans four orders of magnitudes from values compatible with the pre-protostellar phase to embedded massive zero-age main sequence stars. Sources in the l = 59\degr field have on average lower L/M, possibly outlining an overall earlier evolutionary stage with respect to the sources in the l = 30\degr field. Many of these cores are actively forming high-mass stars, although the estimated core surface densities appear to be an order of magnitude below the 1 g cm$^{-2}$ critical threshold for high-mass star formation., Comment: To appear in A&A

In Herschel images of the Galactic plane and many star forming regions, a major factor limiting our ability to extract faint compact sources is cirrus confusion noise, operationally defined as the "statistical error to be expected in photometric measurements due to confusion in a background of fluctuating surface brightness". The histogram of the flux densities of extracted sources shows a distinctive faint-end cutoff below which the catalog suffers from incompleteness and the flux densities become unreliable. This empirical cutoff should be closely related to the estimated cirrus noise and we show that this is the case. We compute the cirrus noise directly, both on Herschel images from which the bright sources have been removed and on simulated images of cirrus with statistically similar fluctuations. We connect these direct estimates with those from power spectrum analysis, which has been used extensively to predict the cirrus noise and provides insight into how it depends on various statistical properties and photometric operational parameters. We report multi-wavelength power spectra of diffuse Galactic dust emission from Hi-GAL observations at 70 to 500 microns within Galactic plane fields at l= 30 degrees and l= 59 degrees. We find that the exponent of the power spectrum is about -3. At 250 microns, the amplitude of the power spectrum increases roughly as the square of the median brightness of the map and so the expected cirrus noise scales linearly with the median brightness. Generally, the confusion noise will be a worse problem at longer wavelengths, because of the combination of lower angular resolution and the rising power spectrum of cirrus toward lower spatial frequencies, but the photometric signal to noise will also depend on the relative spectral energy distribution of the source compared to the cirrus., Comment: 4 pages (in journal), 3 figures, Astronomy and Astrophysics, accepted for publication 13 May 2010