We investigate the NIR spectra of 24 Seyfert galaxies observed with the instrument SpeX at the NASA Infrared Telescope Facility (ITRF) in the short cross-dispersed mode. The results of the spectral synthesis fitting procedure are presented and discussed in details by Riffel et al. (2009). The approach followed here is based on the starlight code (see Cid Fernandes et al. 2005). The spectral synthesis shows that the NIR continuum of active galaxies can be explained in terms of at least three components: a non-thermal continuum, dust emission, and the stellar population of the circumnuclear region. The study of the stellar population is a critical step in the analysis of the continuum emission of Seyfert galaxies. Moreover, our results are consistent with the predictions of the unified model for AGNs, as the non-thermal continuum and the hot dust emission are present in all Sy 1 sources and only in a small fraction of the Sy 2s. Regarding the stellar population component, our results point to a mean metallicity solar to above solar, if we consider the light-weighted values, while for the mass-weighted mean metallicity our results indicate a sub-solar value. We associate this discrepancy with the well known age–metallicity degeneracy: i.e., for a fixed mass, a high-metallicity stellar population looks cooler — and older — than a low-metallicity population, thus resulting in a higher M/L ratio. Moreover, this is consistent with a galaxy chemical enrichment scenario in which the young population is enriched by the evolution of the early massive stars. In this context, the light-weighted metallicity is more sensitive to the young component, while the mass-weighted metallicity to the old stellar population.

Approximately 20% of very metal-poor stars ([Fe/H] < −2.0) are strongly enhanced in carbon ([C/Fe] > +1.0). Such stars are referred to as carbon-enhanced metal-poor (CEMP) stars. We present a chemical abundance analysis based on high resolution spectra acquired with UVES at the VLT of three dwarf CEMP stars: SDSS J1349-0229, SDSS J0912+0216 and SDSS J1036+1212. These very metal-poor stars, with [Fe/H] < −2.5, were selected from our ongoing survey of extremely metal-poor dwarf candidates from the SDSS.

Among these CEMPs, SDSS J1349-0229 has been identified as a carbon star ([C/O] > +1.0). First and second peak s-process elements, as well as second peak r-process elements have been detected in all stars. In addition, elements from the third r-process peak were detected in one of the stars, SDSS J1036+1212. We present the abundance results of these stars in the context of neutron-capture nucleosynthesis theories.

Broad absorption lines (BALs), seen in a small fraction of both the radio-quiet and radio-loud quasar populations, are probably caused by the outflow of gas with high velocities and are part of the accretion process. The presence of BALs is due to a geometrical effect and/or it is connected with the quasar evolution. Using the final release of FIRST survey combined with a catalog of BAL QSOs from SDSS/DR3, we have constructed a new sample of compact radio-loud BAL QSOs, which constitutes the majority of radio-loud BAL QSOs. The main goal of this project is to study the origin of BALs by analysis of the BAL QSOs radio morphology, orientation, and jet evolution using the European VLBI Network (EVN) at 1.6 GHz and the Very Long Baseline Array (VLBA) at 5 and 8.4 GHz.

We study the dynamics of stellar-mass black holes (BHs) in star clusters, with particular attention to the formation of BH–BH binaries, which are interesting as sources of gravitational waves (GWs). We examine the properties of these BH–BH binaries through direct N-body simulations of Plummer clusters of N ≤ 105 low-mass stars with an initial population of stellar-mass BHs, using the nbody6 code. We find that the stellar-mass BHs segregate rapidly into the cluster core and form a dense subcluster of BHs in which BH–BH binaries form through three-body encounters. While most BH binaries are ejected from the cluster by recoils due to superelastic encounters with the single BHs, we find that for clusters with N ≳ 5 × 104, typically a few of them harden sufficiently so that they can merge via GW emission within the cluster. Also, for each of such clusters there are a few escaping BH binaries that merge within a Hubble time, with most merger times being within a few Gyr. These results imply that the intermediate-age massive clusters constitute the most important class of star cluster candidates that can produce dynamical BH–BH mergers at the present epoch. The BH–BH merger rates obtained from our computations imply a significant detection rate (~30 yr−1) for the proposed Advanced LIGO GW detector.

By means of a simple non-gravitational force model of the cometary nucleus, which relies on the observed light curves assumed to be a good representation of the water sublimation rate, we estimate the masses of a sample of long-period comets (LPCs).

A critical issue of our method is the assumption of a correlation between visual heliocentric magnitudes and water production rates. This is a necessary assumption because of the sparse observational data of gas production rates (with the exception of very few comets like Hale-Bopp or Hyakutake). In this regard we present here a new correlation for LPCs. We also present the preliminary results for the masses of comets Hale-Bopp and Hyakutake.

The Indian National Large Solar Telescope (NLST) will be a state-of-the-art 2-m class telescope for carrying out high resolution studies of the solar atmosphere. Sites in the Himalayan region at altitudes greater than 4000-m that have extremely low water vapor content and are unaffected by monsoons are under evaluation. This project is led by the Indian Institute of Astrophysics and has national and international partners.

NLST is an on-axis alt-azimuth Gregorian multi-purpose open telescope with the provision of carrying out night time stellar observations using a spectrograph. The telescope utilizes an innovative design with low number of reflections to achieve a high throughput and low instrumental polarization. High order adaptive optics is integrated into the design that works with a modest Fried's parameter of 7-cm to give diffraction limited performance. The telescope will be equipped with a suite of post-focus instruments including a high resolution spectrograph and a polarimeter. A detailed concept design of the telescope is presently being finalized and fabrication is expected to begin in 2010 with first light in 2014.

We observed a volume-limited sample of 19 luminous type 1 QSO host galaxies at MV ~ −23 mag and redshift 0.06 < z < 0.2 (Jahnke et al. 2004) using the VLT/VIMOS Integral Field Spectrograph. After removal of the QSO contribution (using the method of Husemann et al. 2008), we construct 2D intensity maps and gas velocity fields of the host galaxies in the Hα and [O iii] emission lines. Two representative cases are shown in Figure 1.

The rapid neutron-capture process (r-process), which produces some of the heaviest elements, is not well understood. Obtaining accurate abundances of these heavy elements (Z > 38) is important, both in the context of the chemical evolution of the Galaxy and for understanding the site(s) and process(es) of formation of those elements. We have determined elemental abundances for several r-process elements, notably silver, from high resolution VLT/UVES spectra. Silver was chosen because it is predominantly a light r-process element (38 < Z < 50), and little is known about its formation and evolution in the Galaxy. Here, we present our preliminary results.

We present a short summary of several 2D hydrodynamic calculations that suggest that upon the collision of galaxies two physical mechanisms lead to the formation of proto-super star clusters. These are condensation, induced by radiative cooling, and implosion caused by the shocked intercloud medium. Even in the absence of gravity, these lead to storage and compression of the dense cloud component into massive and compact gravitationally unstable condensations. The resulting entities exhibit enhanced surface densities that are several hundred times higher than their initial values. These are here postulated as the cradles of very efficient and rapid star-formation episodes, able to withstand the negative feedback effects associated with star formation, while leading to the formation of massive and compact super star clusters.

The solar-terrestrial energy transfer, due to the total solar irradiance (TSI), solar wind and interplanetary magnetic field, has 11-year modulation during the sunspot cycles. Other oscillations of solar-terrestrial energy transfer are with periods of 22 and 45 year due to the magnetic reversal and equatorial solar asymmetry, which cause corresponding oscillations of all Earth systems, including climate and weather, atmosphere and ocean circulations, geomagnetic field and core processes. A part of this energy variation is transformed to oscillations of the Earth rotation. A model of indirect mechanism of Earth rotation excitation during sunspot cycles is proposed, which is based on global water circulation and periodical mass transfer between oceans and polar ice caps. The oscillations of the mean sea level (MSL) with periods 11, 22 and 45 years are determined by sea level data for the last two centuries from 13 maregraph stations. The necessary energy of water evaporation, corresponding to the observed MSL variations is provided by TSI oscillations with amplitudes between 0.2-0.5W/m2, determined by means of reconstructed time series of the TSI since 1610. The determined mean Universal Time (UT1) amplitudes, corresponding to the 22-year and 45-year cycles of the solar activity are 185ms and 310ms.

We describe the behavior of the rotational velocity in metal-poor stars ([Fe/H] ~ −0.5 dex) at different evolutionary stages, based on v sin i values from the literature. Our sample is composed of stars in the field and in some Galactic globular clusters, including stars on the main sequence (MS), red-giant branch (RGB), and horizontal branch (HB). The metal-poor stars are mainly slow rotators, and their v sin i distribution along the Hertzsprung–Russell diagram is quite homogeneous. Nevertheless, a few moderate to high values of v sin i are found for stars located on the MS and the HB. We show that the overall distribution of v sin i values is basically independent of metallicity for the stars in our sample. In particular, the fast-rotating MS stars in our sample exhibit similar rotation rates as their metal-rich counterparts, suggesting that some may actually be fairly young, in spite of their low metallicity, or else that at least some would be better classified as blue straggler stars. We do not find significant evidence of evolution in v sin i values as a function of position on the RGB. In particular, we do not confirm previous suggestions that stars close to the RGB tip rotate faster than their less-evolved counterparts. While the presence of fast rotators among moderately cool blue-HB stars has been suggested as due to angular-momentum transport from a stellar core that has retained significant angular momentum during its prior evolution, we find that any such transport mechanisms must likely operate very fast as the star arrives on the zero-age HB (ZAHB), since we do not find a link between evolution off the ZAHB and v sin i values.

We summarise recent results form direct numerical simulations of both non-rotating helically forced and rotating convection driven MHD equations in spherical wedge-shape domains. In the former, using perfect-conductor boundary conditions along the latitudinal boundaries we observe oscillations, polarity reversals and equatorward migration of the large-scale magnetic fields. In the latter we obtain angular velocity with cylindrical contours and large-scale magnetic field which shows oscillations, polarity reversals but poleward migration. The occurrence of these behviours in direct numerical simulations is clearly of interest. However the present models as they stand are not directly applicable to the solar dynamo problem. Nevertheless, they provide general insights into the operation of turbulent dynamos.

One major topic in studying stellar activity is to explain how phenomena seen on the Sun and stars, and specially magnetic phenomena, depend on stellar properties such as rotation and age. Differential rotation is an important physical process in theories of stellar magnetic field generation. The solar surface differential rotation was initially discovered via the simple method of tracking the rotation rates of individual starspots at different latitudes. Adopting a similar principle, high accuracy light curves of active stars observed with the CoRoT satellite are analyzed using a model based on the rotational modulation of the visibility of active regions.

NGC 205 is a small galaxy (M/M⊙ = 0.7 × 109; MV = −16.6) currently located 36′ NW of M31. It is classified as dE because in ground-based images it appears as an elliptical body. However past investigations have revealed characteristics that are more typical of a disk galaxy: the specific frequency of globular clusters is 1.8; the large scale dynamics shows partial rotational support; there is a significant amount (106M⊙) of rotating gas (molecular and atomic) and dust; the central regions harbor a fairly complex stellar population, including a 100–500 Myr old nucleus surrounded by 50- and 100-Myr old stellar associations (see references in Monaco et al. 2009; M09). Very recently, thanks to hst/acs imaging we have been able to reveal a young central ‘field’ population (M09), extending out to ~40″ in radius (~160 pc). The luminosity function of the main sequence can be fitted with Saviane et al. (2004) model of continuous star formation (SF) from at least ~600 Myr ago to ~60 Myr ago. We found that 1.5 × 105M⊙ in stars were produced from ~300 Myr to ~60 Myr ago, with a SF rate of 7 × 10−4M⊙ yr−1. A continuous SF seems to support the latest simulations of NGC 205 orbit: Howley et al. (2008) found that the galaxy must be moving with a velocity 300–500 km s−1 (comparable to the escape velocity) along an almost radial orbit, and it should be approaching M31 for the first time. An episodic SF triggered by passages through M31 disk every ~300 Myr in a bound orbit (Cepa & Beckman 1988) is excluded by our data.

As part of our near-infrared photometric survey of nearby dwarf galaxies, we present recent results for Leo I and Leo II dwarf spheroidal galaxies. We selected O- and C-rich AGB stellar populations using two-color diagrams and compared their luminosity functions and star counts with the predictions of the most recent AGB theoretical models.

A long-term project, aiming at systematic search for variable stars in Galactic Open Clusters (OCs), was started at the Geneva Observatory in 2002. We have been observing regularly a sample of twenty-seven Galactic Open Clusters in the U, B, V Geneva filters (hereafter U, B, V). The goal is to identify and to study their variable stars, as well as the connection between the variable stars in a cluster and the cluster properties. We present the status of this work in progress, and show preliminary results for one of these clusters, IC 4651.

We present the largest sample available to date of lithium abundances in extremely metal poor (EMP) Halo dwarfs. Four Teff estimators are used, including IRFM and Hα wings fitting against 3D hydrodynamical synthetic profiles. Lithium abundances are computed by means of 1D and 3D-hydrodynamical NLTE computations. Below [Fe/H]~−3, a strong positive correlation of A(Li) with [Fe/H] appears, not influenced by the choice of the Teff estimator. A linear fit finds a slope of about 0.30 dex in A(Li) per dex in [Fe/H], significant to 2–3 σ, and consistent within 1 σ among all the Teff estimators. The scatter in A(Li) increases significantly below [Fe/H]~−3. Above, the plateau lies at 〈A(Li)3D, NLTE〉 = 2.199 ± 0.086. If the primordial A(Li) is the one derived from standard Big Bang Nucleosynthesis (BBN), it appears difficult to envision a single depletion phenomenon producing a thin, metallicity independent plateau above [Fe/H] = −2.8, and a highly scattered, metallicity dependent distribution below.

We performed numerical simulations of dynamical encounters between hard, massive binaries and a very massive star (VMS; formed through runaway mergers of ordinary stars in the dense core of a young massive star cluster) to explore the hypothesis that this dynamical process could be responsible for the origin of high-velocity (≥ 200 − 400 km s−1) early or late B-type stars. We estimated the typical velocities produced in encounters between very tight massive binaries and VMSs (of mass of ≥ 200 M⊙) and found that about 3 − 4% of all encounters produce velocities ≥ 400 km s−1, while in about 2% of encounters the escapers attain velocities exceeding the Milky Ways's escape velocity. We therefore argue that the origin of high-velocity (≥ 200 − 400 km s−1) runaway stars and at least some so-called hypervelocity stars could be associated with dynamical encounters between the tightest massive binaries and VMSs formed in the cores of star clusters. We also simulated dynamical encounters between tight massive binaries and single ordinary 50 − 100 M⊙ stars. We found that from 1 to ≃ 4% of these encounters can produce runaway stars with velocities of ≥ 300 − 400 km s−1 (typical of the bound population of high-velocity halo B-type stars) and occasionally (in less than 1% of encounters) produce hypervelocity (≥ 700 km s−1) late B-type escapers.

Using the Hyperz code (Bolzonella et al. 2000) we present photometric redshift estimates for a random sample of galaxies selected from the SDSS/DR7 and GALEX/DR4, for which spectroscopic redshifts are also available.

We confirm that the inclusion of ultraviolet photometry improves the accuracy of photo-zs for those galaxies with g* – r* ≤ 0.7 and zspec ≤ 0.2. We also address the problem of how binary interactions can affect photo-z estimates, and find that their effect is negligible.

We report on the method developed by Zibetti, Charlot & Rix (2009) to construct resolved stellar mass maps of galaxies from optical and NIR imaging. Accurate pixel-by-pixel colour information (specifically g – i and i – H) is converted into stellar mass-to-light ratios with typical accuracy of 30%, based on median likelihoods derived from a Monte Carlo library of 50,000 stellar population synthesis models that include dust and updated TP-AGB phase prescriptions. Hence, surface mass densities are computed. In a pilot study, we analyze 9 galaxies spanning a broad range of morphologies. Among the main results, we find that: i) galaxies appear much smoother in stellar mass maps than at any optical or NIR wavelength; ii) total stellar mass estimates based on unresolved photometry are biased low with respect to the integral of resolved stellar mass maps, by up to 40%, due to dust obscured regions being under-represented in global colours; iii) within a galaxy, on local scales colours correlate with surface stellar mass density; iv) the slope and tightness of this correlation reflect/depend on the morphology of the galaxy.