We present a mid-infrared 3D view of the central parsec using ISAAC spectrograph (ESO/VLT) with its spectroscopic mode. We mapped the central parsec in L- and M-bands by using 27 and 21 slit positions, respectively, that allowed us to build two data cubes of the region in these spectral domains. We also use an original method to distinguish the contribution of the foreground extinction to the absorbed spectra from that of the local extinction in both wavelength ranges. We find that there are residual water and CO ices in the central parsec as well as hydrocarbons and gaseous CO implying very low temperatures of the order of tens of Kelvin in the local environment of Sgr A*.

The electronic spectroscopy of various polycyclic aromatic hydrocarbon (PAH) molecules has been studied in the laboratory at low temperatures using both molecular beam and matrix isolation spectroscopy techniques. While molecular beam spectra can be readily compared to astronomical observations, the band positions measured in Ne and Ar matrices are extrapolated to obtain rather good estimates for the same transitions in the gas phase. Absolute absorption cross sections are determined for gas-phase and matrix spectra by comparing them with calibrated solution spectra. All laboratory results are analyzed and discussed in view of the role that PAHs can play as carriers of the diffuse interstellar bands (DIBs). Our studies suggest that regular neutral PAHs are not responsible for any of the known strong DIBs.

Solar oxygen abundance is a key parameter for the studies of solar physics. Oxygen abundances of cool stars with different metallicities are important for understanding the galactic chemical evolution. We present non-LTE calculations for O I with the classical plane-parallel (1D) model atmospheres for a set of stellar parameters corresponding to stars of spectral types from A to K. Non-LTE leads to strengthening the O I lines, and the difference between the non-LTE and LTE abundances (non-LTE correction) is negative. The departures from LTE grow toward higher effective temperature and lower surface gravity. In the entire temperature range and log g = 4, the non-LTE correction does not exceed 0.05 dex in absolute value for lines of O I in the visible spectral range. The non-LTE corrections are significantly larger for the infrared O I 7771-5, 8446 Å lines and reach an order of magnitude for A-type stars. To differentiate the effects of inelastic collisions with electrons and neutral hydrogen atoms on the statistical equilibrium (SE) of O I, we derived the oxygen abundance for the five well studied A-type stars. For each star, non-LTE largely removes the difference between the infrared and visible lines found in LTE. In the case of cool stars (Sun and Procyon), inelastic collisions with H I affect the SE of O I, and agreement between the abundances from different lines is achieved when using the Drawin's formalism for collisional rates calculations. The solar mean oxygen abundance from the six lines is ϵ = 8.74 ± 0.05, when using the MAFAGS-OS solar model atmosphere and ϵ = 8.78 ± 0.03, when applying the 3D corrections taken from the literature. The non-LTE abundances of oxygen are derived for the sample of cool dwarfs with various metallicities on high-resolution spectra observed in the Lick observatory.

The XMM-Newton spectral-fit database is an ongoing ESA funded project aimed to construct a catalogue of spectral-fitting results for all the sources within the XMM-Newton serendipitous source catalogue for which spectral data products have been pipeline-extracted (≳ 120,000 X-ray source detections). The fundamental goal of this project is to provide the astronomical community with a tool to construct large and representative samples of X-ray sources by allowing source selection according to spectral properties.

Polycyclic aromatic hydrocarbon (PAH) molecules have been long considered promising candidates for the carriers of the diffuse interstellar bands (DIBs). The PAH-DIB hypothesis, however, raises two major issues. First, the number of interstellar PAH species is potentially orders of magnitude larger than the number of DIBs. Second, the absorption spectrum of a PAH is in general dominated by bands found at UV wavelengths while, conversely, DIBs are absent from the UV wavelength domain and arise at visible and near IR wavelengths. These issues do not necessarily weaken the PAH-DIB hypothesis and can actually allow us to refine it. In that context, we analyze the UV/vis absorption spectra of PAH molecules isolated in Ne matrices and propose that polyynyl-substituted PAHs, or similar species, are valid candidates for the carriers of the DIBs. Finally, a possible lifecycle for DIB-carrying PAHs is presented.

We determined NLTE abundances of Na in the atmospheres of 80 red giants including the 33 stars of the thin disk, 35 stars of the thick disk and 12 stars of Hercules stream.

Milagro has recently reported an extended TeV γ-ray source MGRO J2019+37 in the Cygnus region. It is the second brightest TeV source after Crab nebula in their source catalogue. No confirmed counterparts of this source are known although possible associations with several known sources have been suggested. We study leptonic as well as hadronic models of TeV emission within the context of Pulsar Wind Nebulae (PWN) and Supernova Remnant (SNR) type sources, using constraints from multi-wavelength data from observations made on sources around MGRO J2019+37. These include radio upper limit given by GMRT, GeV observations by Fermi-LAT, EGRET and AGILE and very high energy data taken from Milagro. We find that, within the PWN scenario, while both leptonic as well as hadronic models can explain the TeV flux from this source, the GMRT upper limit imposes a stringent upper limit on the size of the emission region in the case of leptonic model. In the SNR scenario, on the other hand, a purely leptonic origin of TeV flux is inconsistent with the GMRT upper limit. At the same time, a dominantly hadronic origin of the TeV flux is consistent with all observations, and the required hadronic energy budget is comparable to that of typical supernovae explosions.

We present the first systematic study of 4646 spectroscopically confirmed early-type massive stars in the Small Magellanic Cloud (SMC), using variability as a tool to confine the physics of OB-type massive stars. We report the discovery of ∼100 massive eclipsing systems which are useful for the accurate determination of the fundamental parameters of massive stars and we evaluate the frequency of multiplicity. In addition, we explore the occurrence of the Oe/Be phenomenon and provide a large number of candidate non-radial pulsators, which can be further studied via asteroseismology. The results of this work (Kourniotis et al. 2014) will contribute to a better understanding of the role of metallicity in triggering processes associated to matter ejections and/or disk formation, which in turn affect mass loss and stellar rotation.

We explore quantitatively the low but sufficient sensitivity of oscillation modes to probe both the core composition and the details of the chemical stratification of pulsating white dwarfs. Until recently, applications of asteroseismic methods to pulsating white dwarfs have been far and few, and have generally suffered from an insufficient exploration of parameter space. To remedy this situation, we apply to white dwarfs the same double-optimization technique that has been used quite successfully in the context of pulsating hot B subdwarfs. Based on the frequency spectrum of the pulsating white dwarf R548, we are able to unravel in a robust way the unique onion-like stratification and the chemical composition of the star. Independent confirmations from both spectroscopic analyses and detailed evolutionary calculations including diffusion provide crucial consistency checks and add to the credibility of the inferred seismic model. More importantly, these results boost our confidence in the reliability of the forward method for sounding white dwarf internal structure with asteroseismology.

The advent of precision space-based photometric missions such as MOST, CoRoT and Kepler has revealed stellar magnetic activity in unprecedented detail. These observations enable new investigations into the fundamental nature of stellar magnetism by furthering our understanding of the stellar rotation and differential rotation that generate the field, and the photometric variability caused by the surface manifestations of the field. In the case of stars with planetary candidates, these data also offer synergy between studies of stars and planets. Here, I review the possibilities and challenges for deepening our understanding of magnetism in solar-like stars in the era of space-based precision photometry.

Planar motions of a triangular body and a massive point under the action of mutual Newtonian attraction are studied. For the first formulation the triangle is assumed to be composed of three massive points. For the second formulation it is constructed with three homogeneous rods. Some partial solutions are observed within the analysis of the geometry of mass distribution.

The investigation is motivated by the problem of motion of spacecrafts near asteroid-like celestial objects possessing irregular mass distribution. Comparison of dynamical effects for two types of mass distribution is another goal of the research.

Problems appearing because of irregularities in mass distributions have been known for a long time. Certain approaches to the description of motions under attraction as well as qualitative particulars of dynamics are discussed by Demin (1963), Burov & Karapetyan (1995), Buchin & Burov & Troger (2008), Burov & Guerman & Sulikashvili (2010), Kholshevnikov & Kuznetsov (2011), Beletsky & Rodnikov (2011) and Scheeres (2012).

High-velocity compact clouds (HVCCs) are a population of molecular clouds which have compact appearance (d < 10 pc) and large velocity width (Δ V > 50 km s−1), and are found in the central molecular zone of our Galaxy. We performed a 3 mm band line survey toward CO−0.40−0.22, a spatially unresolved HVCC with an extremely large velocity width (Δ V ≃ 90 km s−1), using the Mopra 22 m telescope. We surveyed the frequency range between 76 GHz and 116 GHz with a 0.27 MHz frequency resolution. We detect at least 54 lines from 32 molecules. Many line profiles show a prominent peak at vLSR ∼ 70 km s−1 with very large velocity width, indicating they are emitted by the HVCC. Detections of largish molecules are indicative of non-equilibrium chemistry. We extracted some prominent lines based on velocity structure, intensity ratios, and PCA analyses. Shock diagnostic lines (SiO, SO, CH3OH, HNCO) and dense gas probes (HCN, HCO+) appear to be prominent. Excitation analysis of CH3OH lines show an enhancement in Trot in the negative high-velocity end of the profile. These results suggest that CO−0.40−0.22 has experienced a shock, acceleration, compression, and heating in the recent past.

We derive the pattern speed of the Galactic bar from the analysis of the kinematics of the Hercules stream at different Galactocentric radii with RAVE, assuming that Hercules is caused by the bar. We find a well constrained pattern speed of Ωb=1.98+0.04−0.08 Ωo, where Ω0 is the local circular frequency.

In the circular case of the coplanar Restricted Three-body Problem, we studied how the family of quasi-satellite (QS) periodic orbits allows to define an associated libration center. Using the averaged problem, we highlighted a validity limit of this one: for QS orbits with low eccentricities, the averaged problem does not correspond to the real problem. We do the same procedure to L3, L4 and L5 emerging periodic orbits families and remarked that for very high eccentricities ${\cal F}_{L_4}$ and ${\cal F}_{L_5}$ merge with ${\cal F}_{L_3}$ which bifurcates to a stable family.

Supernova remnants have long been considered to be the dominant sources of Galactic cosmic rays. For a long time the prime evidence consisted of radio synchrotron radiation from supernova remnants, indicating the presence of electrons with energies of several GeV. However, in order to explain the cosmic ray energy density and spectrum in the Galaxy supernova remnant should use 10% of the explosion energy to accelerate particles, and about 99% of the accelerated particles should be protons and other atomic nuclei.

Over the last decade a lot of progress has been made in providing evidence that supernova remnant can accelerate protons to very high energies. The evidence consists of, among others, X-ray synchrotron radiation from narrow regions close to supernova remnant shock fronts, indicating the presence of 10-100 TeV electrons, and providing evidence for amplified magnetic fields, gamma-ray emission from both young and mature supernova remnants. The high magnetic fields indicate that the condition for accelerating protons to >1015 eV are there, whereas the gamma-ray emission from some mature remnants indicate that protons have been accelerated.

A new and sensitive set-up to swiftly test proposed carriers of the diffuse interstellar bands (DIBs), over a relatively broad spectral range, is described. The instrument utilizes broad-band cavity enhanced absorption spectroscopy (BBCEAS) and incorporates an optomechanical shutter to modulate light from a continuous incoherent light source. A pulsed supersonically expanding planar plasma expansion is used to mimic conditions in translucent interstellar clouds. Measurements of plasma durations as low as 400 μs are possible. The sensitivity is estimated to be better than 10 ppm/pass, measured with an effective exposure time of only ca. 1 s. The performance and potential of the instrument is demonstrated on spectra of C5H, C6H and C9H3 recorded through expanding hydrocarbon plasma.

We have calculated the pulsations of massive stars using a nonlinear hydrodynamic code including time-dependent convection. The basic structure models are based on a standard grid published by Meynet et al. (1994). Using the basic structure, we calculated envelope models, which include the outer few percent of the star. These models go down to depths of at least 2 million K. These models, which range from 40 to 85 solar masses, show a range of pulsation behaviours. We find models with very long period pulsations (> 100 d), resulting in high amplitude changes in the surface properties. We also find a few models that show outburst-like behaviour. The details of this behaviour are discussed, including calculations of the resulting wind mass-loss rates.

Sgr B2 is an active high mass star forming region in the Galactic center and the pre-eminent interstellar source of organic chemistry. Newly available broad bandwidth radio interferometry data enables a spatially resolved study of the chemical environments within the Sgr B2(N) core. We present selections from a 30 - 50 GHz spectral line survey conducted with the ATCA.

With the precise, nearly-continuous photometry from the Kepler satellite and the sub-milliarcsecond resolving capabilities of the CHARA Array, astronomy is entering a new age for the imaging and understanding of stellar magnetic activity. We present first results from our Guest Observer Program, where 180 single-epoch surface image reconstructions of KIC 5110407 have revealed differential rotation and hints of magnetic activity cycles based on both spot and flare variations. Analysis of our larger, full dataset will establish in unprecedented detail how surface magnetic activity correlates with stellar age and spectral type. In addition to Kepler work, we have harnessed the power of the world's largest infrared interferometer to “directly” image the spotted surfaces of a few of the closest RS CVn systems, allowing a comparison of contemporaneous Doppler and light-curve inversion imaging techniques.

In this work, we investigated the correlation between the γ-ray luminosity, logLγ and the core-dominance parameter, log (1+R), for a sample of 124 Fermi blazars with available core and extended radio emissions. Our analysis shows that there is no correlation between the γ-ray luminosity, log Lγ and the core-dominance parameter, log (1+R). However, there is a closely linear correlation between log Lγ − log LExt and log (1+R), log Lγ−log LExt = (0.95 ± 0.08) log (1+R) + (2.72 ± 0.11), for the whole sample. The result suggests that the γ-ray emissions are composed of two components, one is beamed, the other is unbeamed.