Recently a formalism for solving the open set of non-local hydrodynamic moment equations has been applied to the envelopes of A-stars by Kupka & Montgomery (2002). Tests on numerical simulations and selected properties derived from stellar spectra such as average surface velocities and velocity skewness have shown the applicability of this RSM approach. In addition, a variety of improvements over existing modeling standards have been developed within and around the AMS group at the Institute for Astronomy in Vienna during the last couple of years. For example, individual elemental abundance patterns (Piskunov & Kupka 2001) or stratification as an observed parameter (Shuliak et al. 2004) can be taken into account in our model atmospheres. Once the underlying programs, which currently operate as stand alone applications, are combined with a model atmosphere code, we will obtain a powerful and efficient tool that will allow us the investigation of a number of open problems in the physics of A-stars, such as more realistic models of the temperature gradients of cool CP2 stars.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We reanalyzed high quality spectra of 158 stars of spectral types A0–F1 and $v\,\sin{i}$ values between 60 and 150 km s$^{-1}$. Using a least squares deconvolution technique we extracted high $S/N$ broadening profiles and determined the loci of the Fourier transform zeros $q_{1}$ and $q_{2}$ where the $S/N$-ratio was high enough. For 78 stars $q_{2}$ could be determined and the ratio $q_{2}/q_{1}$ was used as a shape parameter sensitive to solar-like differential rotation (the equatorial velocity is faster than the near polar velocities). Seventy-four of the 78 stars have values of $q_{2}/q_{1}$ consistent with solid body rotation; in four of the 78 cases, values of $q_{2}/q_{1}$ are not consistent with rigid rotation. Although these stars may be binaries, none of their profiles shows any signatures of a companion. The Fourier transforms do not indicate any distortions and the broadening profiles can be considered due to single objects. One of these candidates may be an extremely rapid rotator seen pole-on, but for the other three stars of spectral types as early as A6, differential rotation seems to be the most plausible explanation for the peculiar profiles.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The gravitational lensing constraints on the small mass end of the $\Lambda$CDM mass function are discussed. Here a conservative approach is taken where the most difficult to explain image flux anomalies in strong lenses are emphasized. Numerical simulations are performed to compare predictions for the $\Lambda$CDM small scale mass function with the observed flux ratios. It is found that the cusp caustic lens anomalies and the disagreements between monochromatic flux ratios and simple lens models can be explained without any substructure in the primary lenses' dark matter halos. Extragalactic $\Lambda$CDM halos are enough to naturally explain these cases. This does not mean that substructure within the host lens is not contributing. In fact, it could be dominating the lensing. It should also be noted that this extragalactic population has not been directly observed either.

Spectroscopic gravitational lensing provides more information on the nature of these substructures. In the one relevant case in which this technique has been used so far, observations of Q2237+0305, there is evidence that there are more small mass halos ($\sim 10^6\msun$) than is expected in the $\Lambda$CDM model.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present our cosmic shear analysis of the Galaxy Evolution from Morphology and SEDs (GEMS) survey. Imaged with the Advanced Camera for Surveys (ACS) on HST, GEMS provides high resolution imaging spanning some 800 square arcmins in the Chandra Deep Field South (CDFS). We discuss the benefits of using space-based data for weak lensing studies and show that the ACS is a very powerful instrument in this regard. We find that we are not limited by systematic errors arising from the anisotropic ACS point spread function distortion and use our cosmic shear results to place joint constraints on the matter density parameter $\Omega_m$ and the amplitude of the matter power spectrum $\sigma_8$, finding $\sigma_8(\Omega_m/0.3)^{0.62}=0.73 \pm 0.12$.

To investigate the impact of atmospheric seeing on weak lensing analysis we compare the shear measured from CDFS galaxies resolved by the COMBO-17 survey and imaged by GEMS. We find good agreement between the two surveys and a higher dispersion in the intrinsic ellipticity distribution of COMBO-17. This dispersion implies that a space-based cosmic shear analysis would yield higher signal-to-noise results compared to a ground-based cosmic shear analysis of the same galaxy sample.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We discuss two methods for constraining the equation of state of dark energy using strong gravitational lensing by galaxy clusters. In the so called “arc statistics” approach, we compare the cluster efficiency for producing giant arcs in several dark-energy cosmologies and in the “standard” $\Lambda$CDM and OCDM models. We find that the expected abundance of gravitational arcs depends on the equation of state of dark energy and reflects the dependence of halo concentrations on cosmology. In agreement with results in previous works, the lensing cross section is very sensitive to dynamical processes occurring in the lenses. Then we use gravitational arcs for tracing the position of the lens critical curves and we measure their scaling with the source redshift in a variety of cosmological models. We find that there is a degeneracy between several lens properties and the equation of state of dark energy which can be broken only after an extremely precise modeling of the lens. Instead of using this “golden lens” approach, we check whether combining the information from a statistical sample of clusters we can distinguish among the various cosmologies. We test the method on a sample of numerically simulated clusters and we reproduce the results expected from the analytic models.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present preliminary results of a photometric multisite campaign on the $\delta$ Scuti-type Pre–Main-Sequence star IP Per. Nine telescopes have been involved in the observations, with a total of about 173 hour of observations over around 40 nights. Our current data permitted us to confirm the multiperiodic nature of this star and to determine at least 9 pulsational frequencies. A preliminary nonradial theoretical analysis seems to show that the star pulsates in a mixture of $l=0, 1, 2$ modes.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

A rapidly oscillating Ap star pulsates in high-order p-modes under the influence of a strong magnetic field. The strong field distorts spatially the angluar and the radial pulsation amplitude (eigenfunction). To study the effect of the magnetic field on the radiative excitation and the damping of p-modes, we performed a fully nonadiabatic analysis including the effect of a dipole magnetic field. A magnetic field always tends to stabilize low order p-modes. In the presence of a magnetic field stronger than $\sim 1{\rm kG}$, all $\delta$ Scuti type pulsations are stabilized. For high-order p-modes, on the other hand, the magnetic field enhances $\kappa$-mechanism excitation in some range of the field strength, depending on the pulsation frequency.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Young A-type stars in the pre–main-sequence (PMS) evolutionary phase are particularly interesting objects since they cover the mass range ($\sim$1.5-4 $M_\odot$) which is most sensitive to the internal conditions inherited from the protostellar phase. In particular, they undergo a process of thermal relaxation from which they emerge as fully radiative objects contracting towards the Main Sequence. A-type stars also show intense surface activity (including winds, accretion, pulsations) whose origin is still not completely understood, and infrared excesses related to the presence of circumstellar disks and envelopes. Disks display significant evolution in the dust properties, likely signalling the occurrence of protoplanetary growth. Finally, A-type stars are generally found in multiple systems and small aggregates with lower mass companions.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The study of detached eclipsing binaries is one of the most powerful ways to investigate the properties of individual stars and stellar systems. We present preliminary masses, radii and effective temperatures for the eclipsing binary WW Aurigae, which is composed of two metallic-lined A-type stars. We also reanalyse the data on HD 23642, an A-type eclipsing binary member of the Pleiades open cluster with a metallic-lined component, and determine its distance to be $139 \pm 4$ pc. This is in agreement with the traditional Pleiades distance, but in disagreement with distance to the Pleiades, and to HD 23642 itself, derived from Hipparcos trigonometrical parallaxes.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present results of stratification analyses for Mg, Si, Ca, Cr and Fe in the atmospheres of two Cr-type sharp-lined peculiar stars HD 133792 and HD 204411. Even in the absence of strong magnetic fields their atmospheres are stable which is confirmed by zero microturbulence. Both stars are slightly evolved, their $\log g \approx 3.5$, whereas their effective temperatures are 9200 and 8400 K, respectively. We find a moderate Cr and Fe stratification. However the abundances of these elements do not fall below the solar value throughout the atmosphere. Si and Ca are strongly stratified, in particular in HD 133792, with large underabundances in the outer atmospheric layers. Abundance stratifications derived for weakly magnetic Ap stars are compared with the empirically determined stratification in the atmospheres of strongly magnetic Ap stars in the same temperature range.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present a new method of phenomenologically modelling light curves of variable stars using Principal Component Analysis techniques that provide a realistic description of the variability with a minimum of free parameters. Examples of this method are demonstrated for the magnetic CP stars HD 90044 and HD 125248.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

In stars with sufficiently small projected rotational velocities (less than a few ${\rm km\,s}^{-1}$), it is often possible to detect signatures of the atmospheric velocity field in line profiles. These signatures may be as subtle as small asymmetries in the profile (“line bisector curvature”) or as obvious as profile shapes that strongly depart from those predicted by simple microturbulence models. We have recently carried out a high resolution survey of sharp-line stars to search for these symptoms of local velocity fields. We report the first results of a comparison of models with the observed profiles.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We consider the CMB bispectrum signal induced by structure formation through the correlation between the Integrated Sachs-Wolfe and the weak lensing effect. We investigate how the bispectrum knowledge can improve our knowledge of the most important cosmological parameters, focusing on the dark energy ones. The bispectrum signal arises at intermediate redshifts, being null at present and infinity, and is characterized by a large scale regime (dominated by linear dynamics of cosmological perturbation) and a small scale one (dominated by density perturbations in a non-linear regime); on the other hand, the effect induced by dark energy on the power spectrum is mostly geometrical and imprinted at redshift close to the present. Because of this, the knowledge of power spectrum and bispectrum yield two complementary informations at very different cosmological epochs, particularly suitable to extract informations about the onset of the cosmic acceleration and dark energy properties that provide it. In order to quantify how much the bispectrum can help the power spectrum in constraining the dark energy parameters, we choose a fiducial model on a three-dimensional space including the following dark energy parameters: dark energy density $\Omega_V$; dark energy equation of state today $w_0$ and dark energy equation of state in the past $w_\infty$ ($w_\infty - w_0$ is related to the first derivative of equation of state). Then we simulate a likelihood analysis showing how contour levels become narrower when bispectrum is included. Preliminary results suggest a consistent improvement on the estimation of dark energy abundance and on dynamical properties of the equation of state. This indicates that the knowledge of the bispectrum in future high resolution and high sensitivity CMB observations could yield a substantial improvement with respect to the traditional analysis based on the power spectrum only.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Some highlights of Symposium 224 on “The A-Star Puzzle” are reviewed and transcribed from the author's ad hoc oral presentation on the final day of the meeting. Articles referred to are all contained in this volume, hence there are no figures or references. Topics include theory and observations of normal A stars, HgMn, Am, and Ap stars, $\lambda$ Boo stars, magnetic fields, rotation, convection, pulsations, supergiant stars, and observational methods including polarimetry, spectroscopy, and photometry.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html