We construct rotating boson stars in (4+1)-dimensional asymptotically Anti-de Sitter space-time (aAdS) with two equal angular momenta that are composed out of a massive and self-interacting scalar field. These solutions possess a single Killing vecto
r field. We construct explicit solutions of the equations in the case of a fixed AdS background and vanishing self-coupling of the scalar field. These are the generalizations of the oscillons discussed in the literature previously now taking the mass of the scalar field into account. We study the evolution of the spectrum of massive oscillons when taking backreaction and/or the self-coupling into account numerically. We observe that very compact boson stars possess an ergoregion.
We construct electrically charged Q-balls and boson stars in a model with a scalar self-interaction potential resulting from gauge mediated supersymmetry breaking. We discuss the properties of these solutions in detail and emphasize the differences t
o the uncharged case. We observe that Q-balls can only be constructed up to a maximal value of the charge of the scalar field, while for boson stars the interplay between the attractive gravitational force and the repulsive electromagnetic force determines their behaviour. We find that the vacuum is stable with respect to pair production in the presence of our charged boson stars. We also study the motion of charged, massive test particles in the space-time of boson stars. We find that in contrast to charged black holes the motion of charged test particles in charged boson star space-times is planar, but that the presence of the scalar field plays a crucial role for the qualitative features of the trajectories. Applications of this test particle motion can be made in the study of extreme-mass ratio inspirals (EMRIs) as well as astrophysical plasmas relevant e.g. in the formation of accretion discs and polar jets of compact objects.
We study the stability of static as well as of rotating and charged black holes in (4+1)-dimensional Anti-de Sitter space-time which possess spherical horizon topology. We observe a non-linear instability related to the condensation of a charged, tac
hyonic scalar field and construct hairy black hole solutions of the full system of coupled Einstein, Maxwell and scalar field equations. We observe that the limiting solution for small horizon radius is either a hairy soliton solution or a singular solution that is not a regular extremal solution. Within the context of the gauge/gravity duality the condensation of the scalar field describes a holographic conductor/superconductor phase transition on the surface of a sphere.
The spectral predictions of stellar population models are not as accurate in the ultra-violet (UV) as in the optical wavelength domain. One of the reasons is the lack of high-quality stellar libraries. The New Generation Stellar Library (NGSL), recen
tly released,represents a significant step towards the improvement of this situation. To prepare NGSL for population synthesis, we determined the atmospheric parameters of its stars, we assessed the precision of the wavelength calibration and characterised its intrinsic resolution. We also measured the Galactic extinction for each of the NGSL stars. For our analyses we used ULySS, a full spectrum fitting package, fitting the NGSL spectra against the MILES interpolator. We find that the wavelength calibration is precise up to 0.1 px, after correcting a systematic effect in the optical range. The spectral resolution varies from 3{AA} in the UV to 10{AA} in the near-infrared (NIR), corresponding to a roughly constant reciprocal resolution R ~ 1000 and an instrumental velocity dispersion $sigma_{ins}$ ~ 130 km/s. We derived the atmospheric parameters homogeneously. The precision for the FGK stars is 42K, 0.24 and 0.09 dex for Teff, logg and [Fe/H], respectively. The corresponding mean errors are 29K, 0.50 and 0.48 dex for theMstars, and for the OBA stars they are 4.5 percent, 0.44 and 0.18 dex. The comparison with the literature shows that our results are not biased.
Many early-type stars are in binary systems. A number of them shows radio emissivity with periodic variability. This variability is associated with non-thermal synchrotron radiation emitted by relativistic electrons. The strong shocks necessary to ac
celerate the electrons up to high energies are produced by the collision of the radiatively-driven stellar winds. A study of the non-thermal emission is necessary in order to investigate O-star colliding wind binaries. Here preliminary results of our modeling of the colliding winds in Cyg OB2 No.9 are presented.
We develop a new method to determine oscillator strength values of atomic absorption lines with state-of-the-art detailed spectral synthesis calculations of the optical spectrum of the Sun and of standard spectral reference stars. We update the log(g
f)-values of 911 neutral lines observed in the KPNO-FTS flux spectrum of the Sun and high-resolution echelle spectra (R=80,000) of Procyon (F5 IV-V) and {epsilon} Eri (K2 V) observed with large signal-to-noise (S/N) ratios of ~2,000 using the new Mercator-Hermes spectrograph at La Palma Observatory (Spain). We find for 483 Fe I, 85 Ni I, and 51 Si I absorption lines in the sample a systematic over-estimation of the literature log(gf)-values with central line depths below 15 %. We employ a curve-of-growth analysis technique to test the accuracy of the new oscillator strength values and compare calculated equivalent line widths to the Moore, Minnaert, & Houtgast atlas of the Sun. The online SpectroWeb database at http://spectra.freeshell.org interactively displays the observed and synthetic spectra and provides the new log(gf)-values together with important atomic line data. The graphical database is under development for stellar reference spectra of every spectral sub-class observed with large spectral resolution and S/N ratios.
The aims of this paper are: 1) to revisit the Tc content of a sample of oxygen-rich asymptotic giant branch (AGB) variables and 2) to increase the number of such stars for which the Li abundance has been measured to provide constraints on theoretical
models of extra-mixing processes. To this end, we analysed high-resolution spectra of 18 sample stars for the presence of absorption lines of Tc and Li. The abundance of the latter was determined by comparing the observed spectra to hydrostatic MARCS model spectra. Bolometric magnitudes were established from near-IR photometry and pulsation periods. We reclassify the star V441 Cyg as Tc-rich, and the unusual Mira star R Hya, as well as W Eri, as Tc-poor. The abundance of Li, or an upper limit to it, was determined for all of the sample stars. In all stars with Tc we also detected Li. Most of them have a Li content slightly below the solar photospheric value, except for V441 Cyg, which has ~1000 times the solar abundance. We also found that, similar to Tc, a lower luminosity limit seems to exist for the presence of Li. We conclude that the higher Li abundance found in the cooler and higher luminosity objects could stem from a Li production mechanism operating on the AGB. The stellar mass might have a crucial influence on this (extra-mixing) production mechanism. It was speculated that the declining pulsation period of R Hya is caused by a recent thermal pulse (TP). While not detecting Tc does not rule out a TP, it indicates that the TPs are not strong enough to drive dredge-up in R Hya. V441 Cyg, on the other hand, could either be a low-mass, intrinsic S-star that produced its large amount of Li by extra-mixing processes, or an intermediate-mass star (M>=M_sun) undergoing Li production due to hot bottom burning.
The James Webb Space Telescope (JWST), due to launch in 2014, shall provide an unprecedented wealth of information in the near and mid-infrared wavelengths, thanks to its high-sensitivity instruments and its 6.5 m primary mirror, the largest ever lau
nched into space. NIRSpec and MIRI, the two spectrographs onboard JWST, will play a key role in the study of the spectral features of Active Galactic Nuclei in the 0.6-28 micron wavelength range. This talk aims at presenting an overview of the possibilities provided by these two instruments, in order to prepare the astronomical community for the JWST era.
We study angularly excited as well as interacting non-topological solitons, so-called Q-balls and their gravitating counterparts, so-called boson stars in 3+1 dimensions. Q-balls and boson stars carry a non-vanishing Noether charge and arise as solut
ions of complex scalar field models in a flat space-time background and coupled minimally to gravity, respectively. We present examples of interacting Q-balls that arise due to angular excitations, which are closely related to the spherical harmonics. We also construct explicit examples of rotating boson stars that interact with non-rotating boson stars. We observe that rotating boson stars tend to absorb the non-rotating ones for increasing, but reasonably small gravitational coupling. This is a new phenomenon as compared to the flat space-time limit and is related to the negative contribution of the rotation term to the energy density of the solutions. In addition, our results indicate that a system of a rotating and non-rotating boson star can become unstable if the direct interaction term in the potential is large enough. This instability is related to the appearance of ergoregions.
We study Abelian strings in a fixed de Sitter background. We find that the gauge and Higgs fields extend smoothly across the cosmological horizon and that the string solutions have oscillating scalar fields outside the cosmological horizon for all cu
rrently accepted values of the cosmological constant. If the gauge to Higgs boson mass ratio is small enough, the gauge field function has a power-like behaviour, while it is oscillating outside the cosmological horizon if Higgs and gauge boson mass are comparable. Moreover, we observe that Abelian strings exist only up to a maximal value of the cosmological constant and that two branches of solutions exist that meet at this maximal value. We also construct radially excited solutions that only exist for non-vanishing values of the cosmological constant and are thus a novel feature as compared to flat space-time. Considering the effect of the de Sitter string on the space-time, we observe that the deficit angle increases with increasing cosmological constant. Lensed objects would thus be separated by a larger angle as compared to asymptotically flat space-time.
