Analysis of the fraction of clear sky at the La Palma and Mt Graham sites

The fraction of available telescope time is one of the most important requirements for selecting astronomical sites affecting the performance of ground based telescopes. A quantitative survey of clouds coverage at La Palma and Mt.Graham is presented using both ground and satellite based data. The aim of this work is deriving clear nights for the satellite infrared channels and verifying the results using ground based observations. At La Palma we found a mean percentage of clear nights of 62.6% from ground and 71.9% from satellite. Taking into account the fraction of common nights we found a concordance of 80.7% clear nights from ground and satellite. At Mt.Graham we found a 97% of agreement between Columbine heliograph and night time observing log. From Columbine heliograph and TOMS-OMI satellite we found about 45% of clear nights, while satellite data (GOES, TOMS) are much more dispersed than those ones of La Palma. Setting a statistical threshold we retried a comparable seasonal trend between heliograph and satellite.Comment: 14 pages, 18 figures, 6 tables, MNRAS accepted on September 23 200

Fraction of clear skies above astronomical sites: a new analysis from the GOES12 satellite

Comparing the number of clear nights (cloud free) available for astronomical observations is a critical task because it should be based on homogeneous methodologies. Current data are mainly based on different judgements based on observer logbooks or on different instruments. In this paper we present a new homogeneous methodology on very different astronomical sites for modern optical astronomy, in order to quantify the available night time fraction. The data are extracted from night time GOES12 satellite infrared images and compared with ground based conditions when available. In this analysis we introduce a wider average matrix and 3-Bands correlation in order to reduce the noise and to distinguish between clear and stable nights. Temporal data are used for the classification. In the time interval 2007-2008 we found that the percentage of the satellite clear nights is 88% at Paranal, 76% at La Silla, 72.5% at La Palma, 59% at Mt. Graham and 86.5% at Tolonchar. The correlation analysis of the three GOES12 infrared bands B3, B4 and B6 indicates that the fraction of the stable nights is lower by 2% to 20% depending on the site

Spitzer-IRAC survey of molecular jets in Vela-D

We present a survey of H2 jets from young protostars in the Vela-D molecular cloud (VMR-D), based on Spitzer -IRAC data between 3.6 and 8.0 micron. Our search has led to the identification of 15 jets and about 70 well aligned knots within 1.2 squared degree. We compare the IRAC maps with observations of the H2 1-0 S(1) line at 2.12 micron, with a Spitzer-MIPS map at 24 and 70 micron, and with a map of the dust continuum emission at 1.2 mm. We find a association between molecular jets and dust peaks. The jet candidate exciting sources have been searched for in the published catalog of the Young Stellar Objects of VMR-D. We selected all the sources of Class II or earlier which are located close to the jet center and aligned with it.The association between jet and exciting source was validated by estimating the differential extinction between the jet opposite lobes. We are able to find a best-candidate exciting source in all but two jets. Four exciting sources are not (or very barely) observed at wavelengths shorter than 24 micron, suggesting they are very young protostars. Three of them are also associated with the most compact jets. The exciting source Spectral Energy Distributions have been modeled by means of the photometric data between 1.2 micron and 1.2 mm. From SEDs fits we derive the main source parameters, which indicate that most of them are low-mass protostars. A significant correlation is found between the projected jet length and the [24] - [70] color, which is consistent with an evolutionary scenario according to which shorter jets are associated with younger sources. A rough correlation is found between IRAC line cooling and exciting source bolometric luminosity, in agreement with the previous literature. The emerging trend suggests that mass loss and mass accretion are tightly related phenomena and that both decrease with time.Comment: Accepted by The Astrophysical Journa

Characterizing the structure of diffuse emission in Hi-GAL maps

We present a study of the structure of the Galactic interstellar medium through the Delta-variance technique, related to the power spectrum and the fractal properties of infrared/sub-mm maps. Through this method, it is possible to provide quantitative parameters which are useful to characterize different morphological and physical conditions, and to better constrain the theoretical models. In this respect, the Herschel Infrared Galactic Plane Survey carried out at five photometric bands from 70 to 500 \mu m constitutes an unique database for applying statistical tools to a variety of regions across the Milky Way. In this paper, we derive a robust estimate of the power-law portion of the power spectrum of four contiguous 2{\deg}x2{\deg} Hi-GAL tiles located in the third Galactic quadrant (217{\deg} < l < 225{\deg}, -2{\deg} < b < 0{\deg}). The low level of confusion along the line of sight testified by CO observations makes this region an ideal case. We find very different values of the power spectrum slope from tile to tile but also from wavelength to wavelength (2 < \beta < 3), with similarities between fields attributable to components located at the same distance. Thanks to the comparison with models of turbulence, an explanation of the determined slopes in terms of the fractal geometry is also provided, and possible relations with the underlying physics are investigated. In particular, an anti-correlation between ISM fractal dimension and star formation efficiency is found for the two main distance components observed in these fields. A possible link between the fractal properties of the diffuse emission and the resulting clump mass function is discussed.Comment: Accepted by Ap

The YSO Population in the Vela-D Molecular Cloud

We investigate the young stellar population in the Vela Molecular Ridge, Cloud-D (VMR-D), a star forming (SF) region observed by both Spitzer/NASA and Herschel/ESA space telescope. The point source, band-merged, Spitzer-IRAC catalog complemented with MIPS photometry previously obtained is used to search for candidate young stellar objects (YSO), also including sources detected in less than four IRAC bands. Bona fide YSO are selected by using appropriate color-color and color-magnitude criteria aimed to exclude both Galatic and extragalactic contaminants. The derived star formation rate and efficiency are compared with the same quantities characterizing other SF clouds. Additional photometric data, spanning from the near-IR to the submillimeter, are used to evaluate both bolometric luminosity and temperature for 33 YSOs located in a region of the cloud observed by both Spitzer and Herschel. The luminosity-temperature diagram suggests that some of these sources are representative of Class 0 objects with bolometric temperatures below 70 K and luminosities of the order of the solar luminosity. Far IR observations from the Herschel/Hi-GAL key project for a survey of the Galactic plane are also used to obtain a band-merged photometric catalog of Herschel sources aimed to independently search for protostars. We find 122 Herschel cores located on the molecular cloud, 30 of which are protostellar and 92 starless. The global protostellar luminosity function is obtained by merging the Spitzer and Herschel protostars. Considering that 10 protostars are found in both Spitzer and Herschel list it follows that in the investigated region we find 53 protostars and that the Spitzer selected protostars account for approximately two-thirds of the total.Comment: 40 pages, 12 figures, accepted for publication in Ap

A characterization of the NGC 4051 soft X-ray spectrum as observed by XMM-Newton

Soft X-rays high resolution spectroscopy of obscured AGNs shows the existence of a complex soft $X$-ray spectrum dominated by emission lines of He and H-like transitions of elements from Carbon to Neon, as well as L-shell transitions due to iron ions. In this paper we characterize the XMM-Newton RGS spectrum of the Seyfert 1 galaxy NGC 4051 observed during a low flux state and infer the physical properties of the emitting and absorbing gas in the soft X-ray regime. X-ray high-resolution spectroscopy offers a powerful diagnostic tool since the observed spectral features strongly depend on the physical properties of matter (ionization parameter U, electron density n_e, hydrogen column density N_H), which in turn are tightly related to the location and size of the X-ray emitting clouds. We carried out a phenomenological study to identify the atomic transitions detected in the spectra. This study suggests that the spectrum is dominated by emission from a photoionised plasma. Then, we used the photoionization code Cloudy to produce synthetic models for the emission line component and the warm absorber observed during phases of high intrinsic luminosity. The low state spectrum cannot be described by a single photoionization component. A multi-ionization phase gas with ionization parameter in the range log U = 0.63-1.90 and column density log N_H = 22.10-22.72 cm^-2 is required, while the electron density n_e remains unconstrained. A warm absorber medium is required by the fit with parameters log U = 0.85, log N_H = 23.40 and log n_e \ut< 5. The model is consistent with an X-ray emitting regions at a distance > 5 x 10^-2 pc from the central engine.Comment: Accepted for publication on section 4 "Extragalactic astronomy" of Astronomy and Astrophysics, 2010, 12 pages, 8 Figures, 4 Tables, in printer format. A few typos corrected

The First Hi-GAL Observations of the Outer Galaxy: A Look at Star Formation in the Third Galactic Quadrant in the Longitude Range 216.º5 ≾ ℓ ≾ 225.º5

We present the first Herschel PACS and SPIRE photometric observations in a portion of the outer Galaxy (216.º5≾ℓ≾ 225.º5 and –2°≾b≾0°) as a part of the Hi-GAL survey. The maps between 70 and 500 μm, the derived column density and temperature maps, and the compact source catalog are presented. NANTEN CO(1-0) line observations are used to derive cloud kinematics and distances so that we can estimate distance-dependent physical parameters of the compact sources (cores and clumps) having a reliable spectral energy distribution that we separate into 255 proto-stellar and 688 starless sources. Both typologies are found in association with all the distance components observed in the field, up to ~5.8 kpc, testifying to the presence of star formation beyond the Perseus arm at these longitudes. Selecting the starless gravitationally bound sources, we identify 590 pre-stellar candidates. Several sources of both proto- and pre-stellar nature are found to exceed the minimum requirement for being compatible with massive star formation based on the mass-radius relation. For the pre-stellar sources belonging to the Local arm (d ≾ 1.5 kpc) we study the mass function whose high-mass end shows a power law N(log M)∝M^(–1.0 ± 0.2). Finally, we use a luminosity versus mass diagram to infer the evolutionary status of the sources, finding that most of the proto-stellar sources are in the early accretion phase (with some cases compatible with a Class I stage), while for pre-stellar sources, in general, accretion has not yet started

The first Hi-GAL observations of the outer Galaxy: a look to star formation in the third Galactic quadrant in the longitude range 216.5 < l < 225.5

We present the first Herschel PACS and SPIRE photometric observations in a portion of the outer Galaxy ($216.5^{\circ} \lesssim \ell \lesssim 225.5^{\circ}$ and $-2^{\circ} \lesssim b \lesssim 0^{\circ}$) as a part of the Hi-GAL survey. The maps between 70 and 500 $\mu$m, the derived column density and temperature maps, and the compact source catalog are presented. NANTEN CO(1-0) line observations are used to derive cloud kinematics and distances, so that we can estimate distance-dependent physical parameters of the compact sources (cores and clumps) having a reliable spectral energy distribution, that we separate in 255 proto-stellar and 688 starless. Both typologies are found in association with all the distance components observed in the field, up to $\sim 5.8$ kpc, testifying the presence of star formation beyond the Perseus arm at these longitudes. Selecting the starless gravitationally bound sources we identify 590 pre-stellar candidates. Several sources of both proto- and pre-stellar nature are found to exceed the minimum requirement for being compatible with massive star formation, based on the mass-radius relation. For the pre-stellar sources belonging to the Local arm ($d\lesssim1.5$ kpc) we study the mass function, whose high-mass end shows a power-law $N(\log M) \propto M^{-1.0 \pm 0.2}$. Finally, we use a luminosity vs mass diagram to infer the evolutionary status of the sources, finding that most of the proto-stellar are in the early accretion phase (with some cases compatible with a Class I stage), while for pre-stellar sources, in general, accretion has not started yet.Comment: Accepted by Ap

The Hi-GAL compact source catalogue – I. The physical properties of the clumps in the inner Galaxy (−71. ◦ 0 < ℓ < 67.◦ 0)

Hi-GAL (Herschel InfraRed Galactic Plane Survey) is a large-scale survey of the Galactic plane, performed with Herschel in five infrared continuum bands between 70 and 500 µm. We present a band-merged catalogue of spatially matched sources and their properties derived from fits to the spectral energy distributions (SEDs) and heliocentric distances, based on the photometric catalogues presented in Molinari et al., covering the portion of Galactic plane −71.◦ 0 < ℓ < 67.◦ 0. The band-merged catalogue contains 100 922 sources with a regular SED, 24 584 of which show a 70-µm counterpart and are thus considered protostellar, while the remainder are considered starless. Thanks to this huge number of sources, we are able to carry out a preliminary analysis of early stages of star formation, identifying the conditions that characterize different evolutionary phases on a statistically significant basis. We calculate surface densities to investigate the gravitational stability of clumps and their potential to form massive stars. We also explore evolutionary status metrics such as the dust temperature, luminosity and bolometric temperature, finding that these are higher in protostellar sources compared to pre-stellar ones. The surface density of sources follows an increasing trend as they evolve from pre-stellar to protostellar, but then it is found to decrease again in the majority of the most evolved clumps. Finally, we study the physical parameters of sources with respect to Galactic longitude and the association with spiral arms, finding only minor or no differences between the average evolutionary status of sources in the fourth and first Galactic quadrants, or between 'on-arm' and 'interarm' positions