The current status of our knowledge of magnetic fields in A-type stars is reviewed with special emphasis on the progress achieved for “classical” Ap stars over the last four years. For those stars, the distribution of the strength of the field, its three-dimensional structure, and its relation with rotation and evolution are discussed.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present the first results of the CP star observations in the spectral regions of the Li I lines at $\lambda 6708$ and $\lambda 6104$ obtained with the 6-m BTA telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We calculate the synthetic spectra of TT Hya, an Algol-type eclipsing binary system which contains an A-type primary surrounded by a disc, and an evolved secondary which fills its Roche lobe. A new code SHELLSPEC was developed to solve the simple radiative transfer along the line of sight propagating through the 3D moving medium in LTE. The synthetic spectra are then compared with the observed ones which enable us to derive independent constraints on the behavior of the state quantities, the velocity field and the geometry of the disc.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Important results of magnetic CP star research in the last decade from photometric and spectroscopic observations are discussed. Hipparcos parallaxes confirm CP stars are Main Sequence stars. Photometric monitoring of the rapidly rotating stars provides evidences for the rotational braking on the Main Sequence. High signal-to-noise spectra with high resolution and time-resolution give strong support for chemical separation processes operating in stellar atmospheres (abundance stratification). There are also observational evidences for the departure of the temperature structure of cool CP star atmospheres from that for normal stars.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present the results of a search for gravitational lensing of the cosmic microwave background (CMB) in cross-correlation with the projected density of luminous red galaxies (LRGs). The CMB lensing reconstruction is performed using the first year of Wilkinson Microwave Anisotropy Probe (WMAP) data, and the galaxy maps are obtained using the Sloan Digital Sky Survey (SDSS) imaging data. We find no detection of lensing; our constraint on the galaxy bias derived from the galaxy-convergence cross-spectrum is $b_g=1.81\pm 1.92$ ($1\sigma$, statistical), as compared to the expected result of $b_g\sim 1.7$ for this sample. We discuss possible instrument-related systematic errors and show that the Galactic foregrounds are not important. We do not find any evidence for point source or thermal Sunyaev-Zel'dovich effect contamination.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present a new model of the lensing cluster of galaxies MS2137-23. By incorporating strong and weak lensing data in a fully elliptical lens modeling, we show that the total density profile must be close to the predictions of numerical simulations with an inner slope well consistent with a NFW profile. The model that best fits the lensing constraints is used to infer to line-of-sight velocity distribution (LOSVD) of stars in the central cD galaxy. This distribution is found to be far from Maxwellian. The important non-Gaussian tails produce a significant low-bias when measuring the velocity dispersion by assuming Gaussian absorption lines. In the case of MS2137, most of the information comes from multiples arcs. Internal kinematics of stars only help modeling the innermost kiloparsecs. However, in clusters with fewer constraints (no radial arcs for instance), a detailed modeling of both strong lensing and internal kinematics is crucial.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Recent spectroscopic observations of roAp stars with high spectral resolution and high time resolution show line profile variations (LPV) which seem to be similar to those seen in rapidly rotating B-type line-profile variables. At first glance these line profile variations seem to be in disagreement with the mode identification based on the photometric observations. We propose an interpretation according to which the observed line profile variations are a manifestation of a shock wave in the high atmosphere near the magnetic polar regions, and show that the line profile variations can be still understood in the framework of the oscillation mode being consistent with the photometric observations.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present the theory of weak gravitational lensing in cosmologies with generalized gravity, described in the Lagrangian by a generic function depending on the Ricci scalar and a non-minimally coupled scalar field.

We work out the generalized Poisson equations relating the dynamics of the fluctuating components to the two gauge invariant scalar gravitational potentials, fixing the new contributions from the modified background expansion and fluctuations.

We show how the lensing observables are affected by the cosmic expansion as well as by the presence of the anisotropic stress, which is non-null at the linear level both in scalar-tensor gravity and in theories where the gravitational Lagrangian term features a non-minimal dependence on the Ricci scalar. We derive the generalized expressions for the convergence power spectrum, and illustrate phenomenologically the new effects in Extended Quintessence scenarios, where the scalar field coupled to gravity plays the role of the dark energy.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

New pulsating pre-main sequence (PMS) stars have been discovered in the young open clusters IC 4996 and NGC 6383 using CCD time series photometry in Johnson B and V filters. As the cluster ages are both smaller than 10 million years, all members later than spectral type A0 are still contracting towards the ZAMS, hence providing ideal candidates for searches of pulsation. A dozen stars in NGC 6383 and 35 stars in IC 4996 lie within the boundaries of the classical instability region in the Hertzsprung-Russell (HR) diagram, but pulsation was detected for only two of them in each cluster.

For the well-studied cluster NGC 2264, the two already known PMS pulsating members, V 588 Mon and V 589 Mon, have been analysed using new data from a multi-site campaign. All data collected since their discovery in 1972 build the basis for the first measurements of period changes in PMS pulsators.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

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