Components of multiple systems generally originate from the same protostellar environment. Their similarities or differences in surface chemical composition therefore relates to their individual evolutionary paths (stellar evolution, rotation) and the possible influence of a close companion.

DG Leo is a spectroscopic hierarchical triple system with almost equal-mass late-A type components. Observations with high time and high spectral resolution were used to disentangle the spectrum of each component from the composite spectra. A detailed abundance analysis of the component spectra reveals that the wide companion has a nearly solar-like composition, while both components in the close binary show Am type peculiarities.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We calculated the energy distributions of A-star atmospheres (${{T}_\text{eff}=10 000}\,{\rm K},{\log g=4.0}$) for ranges of the abundances of silicon and other light chemical elements using adequate model atmospheres. We discuss the reasons for and the magnitudes of the calculated departures of the stellar energy distribution and uvby magnitudes from those of normal stars.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

This article reviews the methods of measurement which allow us to infer the presence of magnetic fields in (A) stars. Beginning with the basic observational consequences of the Zeeman effect, we describe various modern spectroscopic and polarimetric techniques which allow us to directly detect and characterise magnetic fields in stellar photospheres. Sometimes, nature conspires to make such detections difficult, forcing us to rely on indirect (proxy) indicators of magnetism. This talk will also briefly discuss a number of these indirect field indicators, some of which demand space-based observations.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Scalar-tensor (ST) theories of gravity are the best motivated alternative to general relativity (GR), arising in every high-energy theory attempting to unify all the fundamental interactions. Furthermore, accomodating an arbitrary number of scalar fields, ST theories yield to cosmological scenarios with a dynamical realization of the dark energy. Solar-System experiments and binary-pulsars observations are compatible with very small departures from GR on the local universe ($z\simeq 0$); on cosmological scales, big-bang nucleosynthesis and cosmic microwave background (CMB) observables can admit larger deviations from the predictions of GR. Weak lensing could provide a test for ST theories of gravity on intermediate scales. Based on a code developed to study ST theories on CMB observables, we implemented a plug-in code to compute the convergence power spectrum and some 2-points statistics. Preliminary results using a simple model of ST theory are presented. This study is aimed to constraint classes of ST models.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

KUBÁT: What are the differences between both codes for convection simulations without magnetic fields which we have just seen?

FREYTAG: Both codes solve the same set of basic equations and rely on very similar fundamental assumptions. However, the algorithms used to solve the hydrodynamics or the radiation transport equations differ. The codes have no routines in common. There is an ongoing project to perform a simulation of solar granulation with both codes, relying on the very same settings (grid, model extension, equation of state, opacities, ray system, etc.). The remaining differences are tiny, for example, much smaller than the difference between the 2D and the 3D models. Both codes have some extensions (for instance dust or magnetic field) not (yet) found in the other.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We briefly review the traditional classifications of CP stars. The current availability of large numbers of abundances now make it possible to use multivariate techniques, both to supplement traditional classification methods and probe the abundance patterns. We discuss cluster analysis and correlation matrices for sample material. We review the historical resistance to the notion that CP stars were indeed chemically peculiar. Modern work shows that while these objects do indeed have atmospheric anomalies, they are nevertheless chemically peculiar.

Abundance patterns are an important clue to the origin of the abundance peculiarities. We contrast patterns due to nuclear and chemical differentiation processes. The roAp and related stars show vertical as well as horizontal abundance variations, and abnormal line profiles. Photospheric abundances in these stars are surely abnormal (nonsolar), but as long as the models are uncertain the derived abundances will be very crude.

For more than two decades, observations of CP stars in the X-ray and radio regimes have been made with increasing sensitivity and pointing accuracy. We discuss the current evidence linking magnetic and nonmagnetic CP stars to sources of galactic X-rays and radio radiation. There seems no doubt that high energy phenomena are associated with, if not produced by, some CP stars. This circumstance admits the possibility that the release of high energy particles (p's, n's and $\alpha$'s) during such events may initiate nuclear reactions on the surfaces of the CP stars. We briefly reconsider the viability of such processes for producing exotic species like Pm by proton bombardment using recent data for solar and stellar flares.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Ultra-high signal-to-noise, high dispersion spectroscopy over the wavelength range \mbox{$\lambda 4487 - 4553$} shows Vega to be a rapidly rotating star $(V_{\rm eq}\sim 160\,{\rm km\,s^{-1}})$ seen almost pole-on. These data, analyzed anew, are combined with analyses of the hydrogen lines (${\rm H}\gamma, {\rm H}\beta$ and ${\rm H}\alpha$) and the latest absolute continuum flux for Vega to yield the following results: $V \sin i=21.9\pm 0.1\,{\rm km\,s^{-1}}$, polar $T_{\rm eff}=9680\pm 10\,{\rm K}$, polar $\log g=4.00\pm 0.02\,{\rm dex}$, $V_{\rm eq}=160\pm 10\,{\rm km\,s^{-1}}$, $\xi_{\rm T}=1.08\pm 0.02\,{\rm km\, s^{-1}}$ and $i=7.9\pm 0.5^{\circ}$. The variations in $T_{\rm eff}$ and $\log g$ over the photosphere total 350 K and 0.06 dex, respectively. The mean $T_{\rm eff}=9510\pm 10\,{\rm K}$ and mean $\log g=3.97\pm 0.02\,{\rm dex}$ agree with the spherical model values derived here and by others.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Both components of the composite-spectrum binary o Leo have Am characteristics, even though the primary is an evolving giant ($\log g=3.25$) with $T_{\rm eff} \sim 6100\,{\rm K}$. This is believed to be the first isolation of such a cool Am star. The finding challenges the theories of diffusion which are widely accepted as the cause of metallicism. The primary component (o Leo A) appears to be deficient in Ca and Sc, as are classical Am stars. Its unusual state may be attributable either to its current state of rapid evolution, or to regular Am-star evolution that is difficult to recognize spectroscopically. A full account of this research appeared in AJ 123, 988-1001, 2002.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We report irregular changes in the line profiles of Deneb, and suggest that they represent part of the mechanism causing the stellar wind.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The Hubble Deep Field (North) and the flanking fields are used investigate the occurrence of multiple weak lensing deflections along the line of sight in relatively deep imaging data ($z_{\rm lens} \sim 0.6$, $z_{\rm source} \sim 1.2$). Ray tracing simulations of galaxy–galaxy lensing in the HDF-North show that proper inclusion of multiple weak deflections is important for a correct prediction of the net shear for most sources, and for a given source redshift the number of multiple weak deflections is largely insensitive to the cosmography. The effects of multiple weak deflections on the magnitude of the weak lensing signal are, of course, strong functions of the adopted halo parameters. Independent of the halo parameters, however, the closest lens to a source (in projection on the sky) is not the strongest lens in the case of more than 50% of the sources which acquire a net shear of $\gamma \lo 0.01$. In addition, multiple weak deflections result in a tangential shear about the lens centers that is greater than the tangential shear that would occur if source galaxies were lensed solely by the closest lens. Further, multiple weak deflections give rise to correlated image ellipticities and account for a substantial amount of the total cosmic shear signal on small angular scales in $\Lambda$CDM and open CDM models.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Two topics concerning A-type stars are discussed: starspots associated with the strong magnetic fields and the prospects for asteroseismology. Considering starspots as analogous to sunspots is misleading. The photosphere of starspots of a magnetic A-star is higher than the normal photosphere, contrary to sunspots. As for the prospects of asteroseismology, it is demonstrated how well (or poorly) we can probe the internal structure of the distant stars using a limited number of p-mode frequencies. Although the detectable eigenmodes must be limited to be $\ell \leq 4$, if the observational error is of the order of $10^{-3}$, inversion has still some hope.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Lenses acting on the Cosmic Microwave Background can potentially be a very efficient and robust probe of the large-scale matter distribution in the Universe. Their most immediate signature is the way they affect the statistical properties of both the temperature and the polarization fields, in particular they both induce non-Gaussian properties that can be explicitly computed.

Investigations of those effects led to the elaboration of specific reconstruction procedures that aim at mapping the projected mass responsible of the lens effects. These techniques are now on solid ground and are remarkably efficient. However it is likely that our best chance to detect a lensing signal in CMB data in the coming years will be through the cross-correlation patterns they induce between CMB data and tracers of the large-scale structure. Clearly the detection of such an effect would be very fruitful in scrutinizing the gravitational instability picture.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

In the pre-WMAP, pre-Supernova-Ia-Hubble-diagram era, quasar lensing statistics stubbornly indicated low values of $\Omega_{\Lambda}$. In contrast, a number of recent lensing statistics studies either find the data support the standard $\Lambda$CDM picture, or simply take the standard cosmological parameters as a given. Have the data or the analyses changed or improved, and how? I review several of the “historical” and the more recent studies, and show that there is no particular measurement, assumption, or model parameter in the old studies that was grossly wrong. Instead, at least several effects, operating together, are likely required in order to achieve agreement between the observations and the currently standard cosmology. Most likely among these effects are: a somewhat lower lensing cross section for elliptical galaxies than assumed in the past; some loss of lensed quasars in optical samples due to extinction by the lenses; and a somewhat lower-than-standard value of $\Omega_{\Lambda}\sim 0.6$. The agreement between recent model calculations and the results of radio lens surveys may be fortuitous, and due to a cancellation between the errors in the input parameters for the lens population and the cosmology, on the one hand, and for the source population, on the other hand.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We present results from an SED analysis of two lensed high-$z$ objects, the $z=6.56$ galaxy HCM6A behind the cluster Abell 370 discovered by Hu et al. (2002) and the triple arc at $z \sim 7$ behind Abell 2218 found by Kneib et al. (2004). For HCM 6A we find indications for the presence of dust in this galaxy, and we estimate the properties of its stellar populations (SFR, age, etc.), and the intrinsic ly$\alpha$ emission. From the “best fit” reddening ($E(B-V) \sim 0.25$) its estimated luminosity is $L \sim (1-4) \times 10^{11} \lsun$, in the range of luminous infrared galaxies. For the arc behind Abell 2218 we find a most likely redshift of $z \sim$ 6.0–7.2 taking into account both our photometric determination and lensing considerations. SED fits indicate generally a low extinction but do not strongly constrain the SF history. Best fits have typical ages of $\sim$ 3 to 400 Myr. The apparent 4000 Å break observed recently by Egami et al. (2004) from combination of IRAC/Spitzer and HST observations can also well be reproduced with templates of young populations ($\sim$ 15 Myr or even younger) and does not necessarily imply old ages. Finally, we briefly examine the detectability of dusty lensed high-z galaxies with Herschel and ALMA.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Period04, a reworked and extended version of Period98 (Sperl 1998) and PERIOD/PERDET (Breger 1990), is a new software package especially dedicated to the statistical analysis of large astronomical data sets containing gaps. It offers tools to extract the individual frequencies from the multiperiodic content of time series and provides a flexible interface to perform multiple-frequency fits. A review of the functions of Period04 is given.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Double-lined-eclipsing binaries are the essential systems for the measurement of stellar masses and radii. About 50-60 systems have components (mostly A-stars) for which these values are known with an uncertainty less than 1-2%. Therefore, these systems are very suitable to improve our understanding of stellar structure and evolution. In this paper, special attention is given to the assessment of the role of internal rotation of the early-type stars in selected double-lined binaries (i.e., EK Cep, PV Cas, and $\theta^2$ Tau): it is shown that adoption of rapidly rotating cores for such stars permits the models to be in very good agreement with the observational results including the apsidal advance rates.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Elemental abundance analysis are derived for the Mercury-Manganese stars HR 4817 (B8 II/III) and $\mu$ Lep (B9 IV) using CCD recorded exposures obtained at the EBASIM echelle spectrograph at the 2.1-m CASLEO (Complejo Astronómico El Leoncito) telescope in Argentina. The spectra coverage is 390-900 nm. The results are compared with previous analyses made with spectra taken using the REOSC echelle spectrograph at CASLEO, the coudé feed telescope at Kitt Peak National Observatory, and/or with the Dominion Astrophysical Observatory coudé spectrograph. As these new spectra go farther into the red and have better resolution than those obtained with the REOSC, we could make better abundance determinations.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The single-lined 51.420d spectroscopic binary $\alpha$ Dra (HD 123299, Thuban, spectral type A0 III) is a slightly metal poor star. First orbital elements were obtained by Harper in 1907. Mizar A (HD 116656, spectral type A2 V) is a double-lined 20.53 d spectroscopic binary first reported by Pickering in 1890. Its orbital elements were determined by Vogel in 1901. The redetermination of the orbital elements for these two binaries used the spectrum disentangling computer code KOREL (Hadrava 1995, 1997). We present revised orbital elements based on new electronic spectra taken at the Ondřejov Observatory between 1994 and 2003.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

We derived the chemical abundances in the photosphere of $\delta$ Scuti, the prototype of the class of pulsating variables, from the analysis of a spectrum obtained at the Terskol Observatory 2-m telescope with a resolution $R=52000$ and $S/N=250$. VLT and IUE spectra were also used. The abundance pattern of $\delta$ Sct consists of 49 chemical elements. The abundances of Be, P, Ge, Nb, Mo, Ru, Er, Tb, Dy, Tm, Yb, Lu, Hf, Ta, Os, Pt, and Th were not investigated previously. The lines of third spectra of Pr and Nd also are investigated for the first time. The abundances of heavy elements show overabundances with respect to the Sun up to 1 dex. The abundance pattern of $\delta$ Sct is similar to that of the Am-Fm stars.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

The subject of gravitational lensing is now a mature discipline, with an automatic place in cosmology. The robust mass measures provided by lensing are one of the key reasons for having confidence in the standard model of structure formation. For the future, things are more challenging: the next set of interesting questions requires the measurement of small effects with non-trivial systematics. The real question will be whether lensing can overcome these problems rapidly enough that it becomes the most precise probe of the cosmological parameters, in particular the equation of state of the vacuum and its evolution.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html