Dehydrogenated coronene molecules have been proposed as the carrier of the interstellar UV extinction bump and of some diffuse interstellar bands. To test this hypothesis, we have undertaken a combined a) theoretical and b) experimental work on the subject. a) We use the (time–dependent) density functional theory to study the effect of hydrogenation on the UV absorption cross–section of neutral and ionised coronene molecules. b) For the visible and near–UV, these calculations provide useful guidelines to analyse and interpret the electronic spectra obtained with the PIRENEA experimental set-up dedicated to astrochemistry.

The International Heliophysical Year (IHY) is an international program of scientific research and collaboration to understand the external drivers of the space environment and climate. Its activities were centered on the year 2008, the 50th anniversary of the International Geophysical Year. The IHY involves utilizing the existing assets from space and ground as a distributed Great Observatory and the deployment of new instrumentation, new observations from the ground and in space, and public and student education. The IHY officially was launched in February 2007 with an opening ceremony and workshop in Vienna. Many IHY activities, both scientific and educational, have occurred since then. In practice, these activities have taken place over the last several years, and the programs that have been established through the IHY will continue into the future as ‘legacies’ of the IHY.

Observations show that MHD waves are one of the most important universal processes in the heliosphere. These waves are likely to play an important role in energy transfer in the heliosphere, and they can be used as a diagnostic tool of the properties of the local magneto-fluid environment. Recent observations by TRACE and Hinode satellites provide ample evidence of oscillations in coronal active region loops. The oscillations were interpreted as fast (kink), slow, and Alfvén modes, and the properties of the waves were used for coronal seismology. However, due to the complex interactions of the various modes in the inhomogeneous active region plasma, and due to nonlinearity, idealized linear theory is inadequate to properly describe the waves. To overcome this theoretical shortcoming we developed 3D MHD models of waves in active region loops. We investigated the effects of 3D active region magnetic and density structure on the oscillations and the wave dissipation, and we investigated the oscillation of individual loops. Some loops were constructed to contain several threads and twist. Here, we present the results of our models, and show how they can be used to understand better the properties of the waves, and of the active regions.

In this paper, we use a parametric model of the asymptotic giant branch (AGB) stars, in which the 13C neutron source is activated in radiative conditions during the interpulse periods, to calculate the nucleosynthesis in 29 very metal-poor double-enhanced stars (i.e. s+r stars) and 26 barium stars (i.e. Ba stars), respectively. Through a statistical analyzing on the corresponding parameters obtained for the above stars, we get the possible conditions which the s+r stars formed in. We find that the value of neutron exposures of most s+r stars is greater than that of Ba stars. In the very metal-poor stars, the Ba stars stars should belong to the binary systems with large initial orbital separation, by comparing the s-process-component coefficient (Cs) values with those of s+r stars. For s+r stars, there is strong correlation between their Cs and Cr (r-process-component coefficient) but no correlation for Ba stars. This strongly confirms the possibility that the s+r stars should form through the accretion-induced collapse (AIC) or type 1.5 supernova mechanism.

Eclipsing binary stars provide highly accurate measurements of the fundamental physical properties of stars. They therefore serve as stringent tests of the predictions of evolutionary models upon which most stellar age determinations are based. Models generally perform very well in predicting coeval ages for eclipsing binaries with main-sequence components more massive than ≈1.2 M⊙; relative ages are good to ~5% or better in this mass regime. Low-mass main-sequence stars (M < 0.8 M⊙) reveal large discrepancies in the model predicted ages, primarily due to magnetic activity in the observed stars that appears to inhibit convection and likely causes the radii to be 10–20% larger than predicted. In mass-radius diagrams these stars thus appear 50–90% older or younger than they really are. Aside from these activity-related effects, low-mass pre–main-sequence stars at ages ~1 Myr can also show non-coevality of ~30% due to star formation effects, however these effects are largely erased after ~10 Myr.

Magnetic fields are supposed to play an important role in the formation and support of self-gravitating clouds and the formation and evolution of protostars in such clouds. We used R-band linear polarimetry collected for about 12000 stars in 46 fields with lines of sight toward the Pipe nebula to investigate the properties of the magnetic fields acting on this dark cloud complex.

The increasing number of transiting planets raises the possibility of finding changes in their transit time, duration and depth that could be indicative of further planets in the system. Experience from eclipsing binaries indeed shows that such changes may be expected. A first obvious candidate to look for a perturbing planet is GJ 436, which hosts a hot transiting Neptune-mass planet in an eccentric orbit. Ribas et al. (2008) suggested that such eccentricity and a possible change in the orbital inclination might be due to a perturbing small planet in a close-in orbit. A radial velocity signal of a 5 M⊕ planet close to the 2:1 mean-motion resonance seemed to provide the perfect candidate. Recent new radial velocities have deemed such signal spurious. Here we put all the available information in context and we evaluate the possibility of a small perturber to GJ 436 b to explain its eccentricity and possible inclination change. In particular, we discuss the constraints provided by the transit time variation data. We conclude that, given the current data, the close-in perturber scenario still offers a plausible explanation to the observed orbital and physical properties of GJ 436 b.

We present our recent results on the cosmic evolution of the outskirts of disk galaxies. In particular we focus on disk–like galaxies with stellar disk truncations. Using UDF, GOODS and SDSS data we show how the position of the break (i.e. a direct estimator of the size of the stellar disk) evolves with time since z~1. Our findings agree with an evolution on the radial position of the break by a factor of 1.3 ± 0.1 in the last 8 Gyr for galaxies with similar stellar masses. We also present radial color gradients and how they evolve with time. At all redshifts we find a radial inside-out bluing reaching a minimum at the position of the break radius, this minimum is followed by a reddening outwards. Our results constraint several galaxy disk formation models and favour a scenario where stars are formed inside the break radius and are relocated in the outskirts of galaxies through secular processes.

I use high resolution N-body/SPH simulations to model the new proper motion of the Large Magellanic Cloud (LMC) within the Milky Way (MW) halo and investigate the effects of gravitational and hydrodynamical forces on the formation of the Magellanic Stream (MS). Both the LMC and the MW are fully self consistent galaxy models embedded in extended cuspy ΛCDM dark matter halos. I find that ram-pressure from a low density ionized halo is sufficient to remove a large amount of gas from the LMC's disk forming a trailing Stream that extends more than 120 degrees from the Cloud. Tidal forces elongate the satellite's disk but do not affect its vertical structure. No stars become unbound showing that tidal stripping is almost effectless.

I report on observations of the z=t 0.01 dwarf galaxy SBS1543+593 which is projected onto the background QSO HS1543+5921. As a star-forming galaxy first noted in emission, this dwarf is playing a pivotal role in our understanding of high-redshift galaxy populations, because it also gives rise to a Damped Lyman Alpha system. This enabled us to analyze, for the first time, the chemical abundance of α elements in a Damped Lyman Alpha galaxy using both, emission and absorption diagnostics. We find that the abundances agree with one another within the observational uncertainties. I discuss the implications of this result for the interpretation of high-redshift galaxy observations. A catalog of dwarf-galaxy–QSO projections culled from the Sloan Digital Sky Survey is provided to stimulate future work.

We briefly overview our newly developed radiation transport module for MHD simulations and two actual applications. The method combines the advantage of the speed of the Flux-Limited Diffusion approximation and the high accuracy obtained in ray-tracing methods.

Age constraints are most often placed on globular clusters by comparing their CMDs with theoretical isochrones. The recent discoveries of detached, eclipsing binaries in such systems by the Cluster AgeS Experiment (CASE) provide new insights into their ages and, at the same time, provide much-needed tests of stellar evolution models. We describe efforts to model the properties of the detached, eclipsing binary V69 in 47 Tuc and compare age constraints derived from stellar evolution models of V69A and B with ages obtained from fitting isochrones to the cluster CMD. We determine whether or not, under reasonable assumptions of distance, reddening, and metallicity, it is possible to simultaneously constrain the age and He content of 47 Tuc.

Division III's activities focus on a broad range of astronomical research on bodies in the solar system (excluding the Sun), on extrasolar planets, and on the search for life in the Universe.

In this work we present the first results of study and comparison of the parameters of quasi-periodic long-term oscillations of microwave emission of large (>0.7 arcmin) sunspots as a result of simultaneous observations with two radioheliographs – NoRH (17 GHz) and Siberian Solar Radio Telescope (SSRT) (5.7 GHz) with 1 minute cadence. Radioheliographs have been working with quite large time overlap (about 5 hours) and have the high spatial resolution: 10 arcsec (NoRH) and 20 arcsec (SSRT). We have found that quasi-periodic long-term oscillations are surely observed at both frequencies with the periods in the range of 20–150 min. We detected common periods for common time of observations with two radioheliographs and interpret this as the consequence of the vertical-radial quasi-periodic displacements of sunspot as a whole structure.

We use discrete dipole approximation (DDA) to study the scattering properties of composite grains made up of host silicate spheroids and graphite inclusions. We calculate the extinction cross sections of the composite grains in the wavelength region 0.20–0.55 μm and study the extinction of the composite grains as a function of graphite inclusions. We present the composite grain model and discuss the results.

We present evidence that the accretion of warm gas onto the Galaxy today is at least as important as cold gas accretion. For more than a decade, the source of the bright Hα emission (up to 750 mR†) along the Magellanic Stream has remained a mystery. We present a hydrodynamical model that explains the known properties of the Hα emission and provides new insights on the lifetime of the Stream clouds. The upstream clouds are gradually disrupted due to their interaction with the hot halo gas. The clouds that follow plough into gas ablated from the upstream clouds, leading to shock ionisation at the leading edges of the downstream clouds. Since the following clouds also experience ablation, and weaker Hα (100–200 mR) is quite extensive, a disruptive cascade must be operating along much of the Stream. In order to light up much of the Stream as observed, it must have a small angle of attack (≈ 20°) to the halo, and this may already find support in new H i observations. Another prediction is that the Balmer ratio (Hα/Hβ) will be substantially enhanced due to the slow shock; this will soon be tested by upcoming WHAM observations in Chile. We find that the clouds are evolving on timescales of 100–200 Myr, such that the Stream must be replenished by the Magellanic Clouds at a fairly constant rate (≳ 0.1 M⊙ yr−1). The ablated material falls onto the Galaxy as a warm drizzle; diffuse ionized gas at 104 K is an important constituent of galactic accretion. The observed Hα emission provides a new constraint on the rate of disruption of the Stream and, consequently, the infall rate of metal-poor gas onto the Galaxy. When the ionized component of the infalling gas is accounted for, the rate of gas accretion is ≳ 0.4 M⊙ yr−1, roughly twice the rate deduced from H i observations alone.

Chemical evolution models for dwarf metal poor galaxies, including dwarf irregulars and dwarf spheroidals will be presented. The main ingredients necessary to build detailed models of chemical evolution including stellar nucleosynthesis, supernova progenitors, stellar lifetimes and stellar feedback will be discussed. The stellar feedback will be analysed in connection with the development of galactic winds in dwarf galaxies and their effects on the predicted abundances and abundance ratios. Model results concerning α-elements (O, Mg, Si, Ca), Fe and s-and r-process elements will be discussed and compared with the most recent observational data for metal poor galaxies of the Local Group. We will show how the study of abundance ratios versus abundances can represent a very powerful tool to infer constraints on galaxy formation mechanisms. In this framework, we will discuss whether, on the basis of their chemical properties, the dwarf galaxies of the Local Group could have been the building blocks of the Milky Way.

The long term goal of large-scale chemical tagging is to use stellar elemental abundances as a tracer of dispersed substructures of the Galactic disk. The identification of such lost stellar aggregates and exploring their chemical properties will be key in understanding the formation and evolution of the disk. Present day stellar structures such as open clusters and moving groups are the ideal testing grounds for the viability of chemical tagging, as they are believed to be the remnants of the original larger star-forming aggregates. We examine recent high resolution abundance studies of open clusters to explore the various abundance trends and reassess the prospects of large-scale chemical tagging.

Asteroseismology, as a tool to use the indirect information contained in stellar oscillations to probe the stellar interiors, is an active field of research presently. Stellar age, as a fundamental property of star apart from its mass, is most difficult to estimate. In addition, the estimating of stellar age can provide the chance to study the time evolution of astronomical phenomena. In our poster, we summarize our previous work and further present a method to determine age of low-mass main-sequence star.

The TEDI (TripleSpec - Exoplanet Discovery Instrument) is a dedicated instrument for the near-infrared radial velocity search for planetary companions to low-mass stars with the goal of achieving meters-per-second radial velocity precision. Heretofore, such planet searches have been limited almost entirely to the optical band and to stars that are bright in this band. Consequently, knowledge about planetary companions to the populous but visibly faint low-mass stars is limited. In addition to the opportunity afforded by precision radial velocity searches directly for planets around low mass stars, transits around the smallest M dwarfs offer a chance to detect the smallest possible planets in the habitable zones of the parent stars. As has been the the case with followup of planet candidates detected by the transit method requiring radial velocity confirmation, the capability to undertake efficient precision radial velocity measurements of mid-late M dwarfs will be required. TEDI has been commissioned on the Palomar 200” telescope in December 2007, and is currently in a science verification phase.