Cloud chemistry at the Puy de Dôme: variability and relationships with environmental factors

The chemical composition of cloud water was investigated during the winter-spring months of 2001 and 2002 at the Puy de D&#244;me station (1465 m above sea level, 45&deg;46&prime;22&prime;&prime; N, 2&deg;57&prime;43&prime;&prime; E) in an effort to characterize clouds in the continental free troposphere. Cloud droplets were sampled with single-stage cloud collectors (cut-off diameter approximately 7 &micro;m) and analyzed for inorganic and organic ions, as well as total dissolved organic carbon. Results show a very large variability in chemical composition and total solute concentration of cloud droplets, ranging from a few mg l^-1 to more than 150 mg l^-1. Samplings can be classified in three different categories with respect to their total ionic content and relative chemical composition: background continental (BG, total solute content lower than 18 mg l^-1), anthropogenic continental (ANT, total solute content from 18 to 50 mg l^-1), and special events (SpE, total solute content higher than 50 mg l^-1). The relative chemical composition shows an increase in anthropogenic-derived species (NO₃^-, SO₄^2- and NH₄⁺) from BG to SpE, and a decrease in dissolved organic compounds (ionic and non-ionic) that are associated with the anthropogenic character of air masses. <P style='line-height: 20px;'> We observed a high contribution of solute in cloud water derived from the dissolution of gas phase species in all cloud events. This was evident from large solute fractions of nitrate, ammonium and mono-carboxylic acids in cloud water, relative to their abundance in the aerosol phase. The comparison between droplet and aerosol composition clearly shows the limited ability of organic aerosols to act as cloud condensation nuclei. The strong contribution of gas-phase species limits the establishment of direct relationships between cloud water solute concentration and LWC that are expected from nucleation scavenging

Nearby Optical Galaxies: Selection of the Sample and Identification of Groups

In this paper we describe the Nearby Optical Galaxy (NOG) sample, which is a complete, distance-limited ($cz\leq$6000 km/s) and magnitude-limited (B$\leq$14) sample of $\sim$7000 optical galaxies. The sample covers 2/3 (8.27 sr) of the sky ($|b|>20^{\circ}$) and appears to have a good completeness in redshift (98%). We select the sample on the basis of homogenized corrected total blue magnitudes in order to minimize systematic effects in galaxy sampling. We identify the groups in this sample by means of both the hierarchical and the percolation {\it friends of friends} methods. The resulting catalogs of loose groups appear to be similar and are among the largest catalogs of groups presently available. Most of the NOG galaxies ($\sim$60%) are found to be members of galaxy pairs ($\sim$580 pairs for a total of $\sim$15% of objects) or groups with at least three members ($\sim$500 groups for a total of $\sim$45% of objects). About 40% of galaxies are left ungrouped (field galaxies). We illustrate the main features of the NOG galaxy distribution. Compared to previous optical and IRAS galaxy samples, the NOG provides a denser sampling of the galaxy distribution in the nearby universe. Given its large sky coverage, the identification of groups, and its high-density sampling, the NOG is suited for the analysis of the galaxy density field of the nearby universe, especially on small scales

Geometrical tests of cosmological models. II. Calibration of rotational widths and disc scaling relations

This series of papers is dedicated to a new technique to select galaxies that can act as standard rods and standard candles in order to perform geometrical tests on large samples of high redshift galaxies to constrain different cosmological parameters. The goals of this paper are (1) to compare different rotation indicators in order to understand the relation between rotation velocities extracted from observations of the Halpha line and the [OII]3727 line, and (2) determine the scaling relations between physical size, surface brightness and magnitude of galaxies and their rotation velocity using the SFI++, a large catalog of nearby galaxies observed at I-band. A good correlation is observed between the rotation curve-derived velocities of the Halpha and [OII] observations, as well as between those calculated from velocity histograms, justifying the direct comparison of velocities measured from Halpha rotation curves in nearby galaxies and from [OII] line widths at higher redshifts. To provide calibration for the geometrical tests, we give expressions for the different scaling relations between properties of galaxies (size, surface brightness, magnitude) and their rotation speeds. Apart from the Tully-Fisher relation, we derive the size-rotation velocity and surface brightness-rotation velocity relations with unprecedentedly small scatters. We show how the best size-rotation velocity relation is derived when size is estimated not from disc scale lengths but from the isophotal diameter r23.5, once these have been corrected for inclination and extinction effects.Comment: 14 pages and 10 figures. A&A submitte

The double RGB in M 2: C, N, Sr and Ba abundances

The globular cluster M 2 has a photometrically detected double red giant branch (RGB) sequence. We investigate here the chemical differences between the two RGBs in order to gain insight in the star formation history of this cluster. The low-resolution spectra, covering the blue spectral range, were collected with the MODS spectrograph on the LBT, and analyzed via spectrum synthesis technique. The high quality of the spectra allows us to measure C, N, Ba, and Sr abundances relative to iron for 15 RGB stars distributed along the two sequences. We add to the MODS sample C and N measurements for 35 additional stars belonging to the blue RGB sequence, presented in Lardo et al. (2012). We find a clear separation between the two groups of stars in s-process elements as well as C and N content. Both groups display a C-N anti-correlation and the red RGB stars are on average richer in C and N with respect to the blue RGB. Our results reinforce the suggestion that M2 belongs to the family of globular clusters with complex star formation history, together with Omega Cen, NGC 1851, and M 22.Comment: 11 pages, 8 figures. Accepted for publication in MNRA

Studying the evolution of AGB stars in the Gaia epoch

We present asymptotic giant branch (AGB) models of solar metallicity, to allow the interpretation of observations of Galactic AGB stars, whose distances should be soon available after the first release of the Gaia catalogue. We find an abrupt change in the AGB physical and chemical properties, occurring at the threshold mass to ignite hot bottom burning,i.e. $3.5M_{\odot}$. Stars with mass below $3.5 M_{\odot}$ reach the C-star stage and eject into the interstellar medium gas enriched in carbon , nitrogen and $^{17}O$. The higher mass counterparts evolve at large luminosities, between $3\times 10^4 L_{\odot}$ and $10^5 L_{\odot}$. The mass expelled from the massive AGB stars shows the imprinting of proton-capture nucleosynthesis, with considerable production of nitrogen and sodium and destruction of $^{12}C$ and $^{18}O$. The comparison with the most recent results from other research groups are discussed, to evaluate the robustness of the present findings. Finally, we compare the models with recent observations of galactic AGB stars, outlining the possibility offered by Gaia to shed new light on the evolution properties of this class of objects.Comment: 21 pages, 11 figure, 3 tables, accepted for publication in MNRAS (2016 July 11

A quasi 3D approach for the modelling of an automotive turbocharger's compressor

In this work the 3DCell method has been extended to the thermo-fluid dynamic simulation of an automotive turbocharger's compressor. The 3DCell, an approach continuously developed by the authors at Politecnico di Milano, is based on a pseudo-staggered leapfrog method that allows to decompose a generic 3D problem in a set of 1D scalar equation arbitrarily oriented in space. The system of equations has been solved referring to a relative rotating framework for the moving components, whereas to an absolute reference elsewhere. The domain has been discretized on a basis of a polar coordinate system, identifying five macro sub-domains, namely the inlet pipe, impeller, vaneless diffuser, volute, outlet pipe, each treated numerically in a specific way. The diffuser's momentum in the tangential direction has been modelled resorting to the conservation of the angular momentum, while the rotor channels are modelled as rotating pipes that exchange work and momentum with the blades as they experience a relative source term due to the centrifugal force field and its potential. The model has been validated against measurements carried out on a steady state flow test bench at University of Genoa