arXiv subjects

M. Rainer

Publications and source records attributed to M. Rainer.

At least 145 records · Page 8Linked to original sources

arXiv2009

HD 50844: the new look of Delta Sct stars from CoRoT space photometry

It has also been suggested that the detection of a wealth of very low amplitude modes in Delta Sct stars was only a matter of signal--to--noise ratio. Access to this treasure, impossible from the ground, is one of the scientific aims of the space mission CoRoT, a space mission developed and operated by CNES. This work presents the results obtained on HD 50844: the 140,016 datapoints were analysed using independent approaches and several checks performed. A level of 10^{-5} mag was reached in the amplitude spectra of the CoRoT timeseries. The frequency analysis of the CoRoT timeseries revealed hundreds of terms in the frequency range 0--30 d^{-1}. All the cross--checks confirmed this new result. The initial guess that Delta Sct stars have a very rich frequency content is confirmed. The spectroscopic mode identification gives theoretical support since very high--degree modes (up to ell=14) are identified. We also prove that cancellation effects are not sufficient in removing the flux variations associated to these modes at the noise level of the CoRoT measurements. The ground--based observations indicate that HD 50844 is an evolved star that is slightly underabundant in heavy elements, located on the Terminal Age Main Sequence. Probably due to this unfavourable evolutionary status, no clear regular distribution is observed in the frequency set. The predominant term (f_1=6.92 d^{-1}) has been identified as the fundamental radial mode combining ground-based photometric and spectroscopic data. This work is also based on observations made with ESO telescopes under the ESO Large Programme LP178.D-0361 and on data collected at the Observatorio de Sierra Nevada, at the Observatorio Astronomico Nacional San Pedro Martir, and at the Piszkesteto Mountain Station of Konkoly Observatory.

astro-ph.SR↗

arXiv2008

Close-up of primary and secondary asteroseismic CoRoT targets and the ground-based follow-up observations

To optimise the science results of the asteroseismic part of the CoRoT satellite mission a complementary simultaneous ground-based observational campaign is organised for selected CoRoT targets. The observations include both high-resolution spectroscopic and multi-colour photometric data. We present the preliminary results of the analysis of the ground-based observations of three targets. A line-profile analysis of 216 high-resolution FEROS spectra of the delta Sct star HD 50844 reveals more than ten pulsation frequencies in the frequency range 5-18 c/d, including possibly one radial fundamental mode (6.92 c/d). Based on more than 600 multi-colour photometric datapoints of the beta Cep star HD180642, spanning about three years and obtained with different telescopes and different instruments, we confirm the presence of a dominant radial mode nu1=5.48695 c/d, and detect also its first two harmonics. We find evidence for a second mode nu2=0.3017 c/d, possibly a g-mode, and indications for two more frequencies in the 7-8 c/d domain. From Stromgren photometry we find evidence for the hybrid delta Sct/gamma Dor character of the F0 star HD 44195, as frequencies near 3 c/d and 21 c/d are detected simultaneously in the different filters.

astro-ph↗

arXiv2008

The gamma Dor CoRoT target HD49434. I-Results from the ground-based campaign

Context: We present the results of an extensive ground-based photometric and spectroscopic campaign on the gamma Dor CoRoT target HD49434. This campaign was preparatory to the CoRoT satellite observations, which took place from October 2007 to March 2008. Results: The frequency analysis clearly shows the presence of four frequencies in the 0.2-1.7 c/d interval, as well as six frequencies in the 5-12 c/d domain. The low frequencies are typical for gamma Dor variables while the high frequencies are common for delta Sct pulsators. We propose the frequency 2.666 c/d as a possible rotational frequency. All modes, for which an identification was possible, seem to be high-degree modes (3 <= l <= 8). We did not find evidence for a possible binary nature of HD49434. The element abundances we derived are consistent with the values obtained in previous analyses. Conclusions: We classify the gamma Dor star HD49434 as a hybrid pulsator, which pulsates simultaneously in p- and g-modes. This finding makes HD49434 an extremely interesting target for asteroseismic modelling. Observations: Based on observations made with the 2.2m ESO/MPI telescope at the La Silla Observatory under the ESO Large Programme: LP178.D-0361. Also based on observations obtained at Observatorio de Sierra Nevada (Spain), at the Centro Astronomico Hispano Aleman at Calar Alto (Spain), at Observatorio Astronomico Nacional San Pedro Martir (Mexico), at the Piszkesteto Mountain Station of Konkoly Observatory (Hungary), at Observatoire de Haute Provence (France) and at Mount John University Observatory (New Zealand).

astro-ph↗

arXiv2005

Probable nonradial g-mode pulsation in early A-type stars

A survey for line profile variability in early A-type stars has been performed in order to detect nonradial pulsation signatures. The star HR 6139, with spectral type A2V and estimated T_eff=8800 K, shows evident line profile variations that can be explained by oscillations in prograde g-modes. This feature and the known photometric variability are similar to those observed in the Slowly Pulsating B-type stars. However HR 6139 is much cooler than the cool border of the instability strip of such variables, and it is hotter than the blue edge of the delta Scuti instability strip. There are indications of a tiny variability also in other four objects, whose nature is not yet clear.

astro-ph↗

arXiv2005

Preparing the COROT space mission: new variable stars in the galactic Anticenter direction

The activities related to the preparation of the asteroseismic, photometric space mission COROT are described. Photoelectric observations, wide--field CCD photometry, uvbyB calibrations and further time--series have been obtained at different observatories and telescopes. They have been planned to complete the COROT programme in the direction of the galactic Anticenter. In addition to suitable asteroseismic targets covering the different evolutionary stages between ZAMS and TAMS, we discovered several other variable stars, both pulsating and geometrical. We compared results on the incidence of variability in the galactic Center and Anticenter directions. Physical parameters have been obtained and evolutionary tracks fitting them have been calculated. The peculiarities of some individual stars alre pointed out. Paper based on observations collected at the San Pedro Martir, Sierra Nevada, Teide, La Silla, Haute-Provence and Roque de Los Muchachos (Telescopio Nazionale Galileo and Mercator telescopes) observatories.

astro-ph↗

arXiv2004

GAUDI: a preparatory archive for the COROT mission

The GAUDI database (Ground-based Asteroseismology Uniform Database Interface, http://sdc.laeff.esa.es/gaudi/) is a preparatory archive for the COROT (COnvection, ROtation and planetary Transits, http://www.astrsp-mrs.fr/projets/corot/) mission developed at LAEFF (Laboratory for Space Astrophysics and Theoretical Physics, http://www.laeff.esa.es). Its intention is to make the ground-based observations obtained in the preparation of the asteroseismology programme available in a simple and efficient way. It contains spectroscopic and photometric data together with inferred physical parameters for more than 1500 objects gathered since January 1998 in 6 years of observational campaigns. In this paper, the main functionalities and characteristics of the system are described. The observations have been collected at ESO-La Silla, Telescopio Nazionale Galileo, Observatoire de Haute-Provence, South African Astronomical Observatory, Tautenberg Observatory and Sierra Nevada Observatory.

astro-ph↗

arXiv1999

The effective sigma-model of multidimensional gravity

The properties of the effective sigma-model for D-dimensional Einstein gravity based on multidimensional geometries is analyzed. Besides pure geometry, additional minimally coupled scalars and (p+2)-forms are considered which yield an extended target space after reduction to the effective D_0-dimensional geometry. In any case the target space is a homogeneous space. The orthobrane condition guarantees the existence of exact solutions. Geometrically, it makes the target space a locally symmetric one. New solutions with scalar fields are found, which may inflate not only in time-like but in also in additional spatial directions of the effective geometry. Static spherically symmetric solutions with a particular configuration of intersecting electric and magnetic branes are investigated both, for the orthobrane case and for degenerated charges. In both cases T_H depends critically on the intersection dimension of the p-branes. Finally, the role of the Einstein frame for 4-geometries is addressed, and the physical frame transformation for cosmological geometries is given.

gr-qc↗

arXiv1999

On the fundamental length of quantum geometry and the black hole entropy

The geometric operators of area, volume, and length, depend on a fundamental length l of quantum geometry which is a priori arbitrary rather than equal to the Planck length l_P. The fundamental length l and the Immirzi parameter $γ$ determine each other. With any l the entropy formula is rendered most naturally in units of the length gap sqrt{{sqrt 3}/2} (sqrt{gamma} l). Independently of the choice of l, the black hole entropy derived from quantum geometry in the limit of classical geometry is completely consistent with the Bekenstein-Hawking form. The extremal limit of 1-puncture states of the quantum surface geometry corresponds rather to an extremal string than to a classical horizon.

gr-qc↗

arXiv1999

The role of dilations in diffeomorphism covariant algebraic quantum field theory

The quantum analogue of general relativistic geometry should be implementable on smooth manifolds without an a priori metric structure, the kinematical covariance group acting by diffeomorphisms. Here I approach quantum gravity (QG) in the view of constructive, algebraic quantum field theory (QFT). Comparing QG with usual QFT, the algebraic approach clarifies analogies and peculiarities. As usual, an isotonic net of *-algebras is taken to encode the quantum field operators. For QG, the kinematical covariance group acts via diffeomorphisms on the open sets of the manifold, and via algebraic isomorphisms on the algebras. In general, the algebra of observables is covariant only under a (dynamical) subgroup of the general diffeomorphism group. After an algebraic implementation of the dynamical subgroup of dilations, small and large scale cutoffs may be introduced algebraically. So the usual a priori conflict of cutoffs with general covariance is avoided. Even more, these cutoffs provide a natural local cobordism for topological quantum field theory. A new commutant duality between the minimal and maximal algebra allows to extract the modular structure from the net of algebras. The outer modular isomorphisms are then again related to dilations, which (under certain conditions) may provide a notion of time.

gr-qc↗

arXiv1998

Einstein and Brans-Dicke frames in multidimensional cosmology

Inhomogeneous multidimensional cosmological models with a higher dimensional space-time manifold M= M_0 x M_1 ...x M_n are investigated under dimensional reduction to a D_0-dimensional effective non-minimally coupled sigma-model which generalizes the familiar Brans-Dicke model. It is argued that the Einstein frame should be considered as the physical one. The general prescription for the Einstein frame reformulation of known solutions in the Brans-Dicke frame is given. As an example, the reformulation is demonstrated explicitly for the generalized Kasner solutions where it is shown that in the Einstein frame there are no solutions with inflation of the external space.

gr-qc↗

arXiv1998

Toda chains with type A_m Lie algebra for multidimensional m-component perfect fluid cosmology

We consider a D-dimensional cosmological model describing an evolution of Ricci-flat factor spaces, M_1,...M_n (n > 2), in the presence of an m-component perfect fluid source (n > m > 1). We find characteristic vectors, related to the matter constants in the barotropic equations of state for fluid components of all factor spaces. We show that, in the case where we can interpret these vectors as the root vectors of a Lie algebra of Cartan type A_m=sl(m+1,C), the model reduces to the classical open m-body Toda chain. Using an elegant technique by Anderson (J. Math. Phys. 37 (1996) 1349) for solving this system, we integrate the Einstein equations for the model and present the metric in a Kasner-like form.

gr-qc↗

arXiv1997

Multidimensional sigma-models with composite electric p-branes

We consider a gravitational model on a manifold M = M_0 x M_1 x...x M_n with oriented connected Einstein internal spaces M_1,...,M_n. The matter part of the action contains several scalar fields and antisymmetric forms. With Ricci-flat internal spaces, the model has a midisuperspace representation in form of a sigma-model on M_0. The latter can be used to determine exact composite electric p-brane solutions, which depend on a set of harmonic functions on M_0.

gr-qc↗

arXiv1997

A regularizing commutant duality for a kinematically covariant partial ordered net of observables

We consider a net of *-algebras, locally around any point of observation, equipped with a natural partial order related to the isotony property. Assuming the underlying manifold of the net to be a differentiable, this net shall be kinematically covariant under general diffeomorphisms. However, the dynamical relations, induced by the physical state defining the related net of (von Neumann) observables, are in general not covariant under all diffeomorphisms, but only under the subgroup of dynamical symmetries. We introduce algebraically both, IR and UV cutoffs, and assume that these are related by a commutant duality. The latter, having strong implications on the net, allows us to identify a 1-parameter group of the dynamical symmetries with the group of outer modular automorphisms. For thermal equilibrium states, the modular dilation parameter may be used locally to define the notions of both, time and a causal structure.

gr-qc↗

arXiv1997

Intersecting electric and magnetic p-branes: spherically symmetric solutions

We consider a D-dimensional self-gravitating spherically symmetric configuration of a generalized electro-magnetic n-form F and a dilatonic scalar field, admitting an interpretation in terms of intersecting p-branes. For theories with multiple times, selection rules are obtained, which obstruct the existence of p-branes in certain subspaces. General static solutions are obtained under a specific restriction on the model parameters, which corresponds to the known "intersection rules". More special families of solutions (with equal charges for some of the F-field components) are found with weakened restrictions on the input parameters. Black-hole solutions are determined, and it is shown that in the extreme limit the Hawking temperature may tend to zero, a finite value, or infinity, depending on the p-brane intersection dimension. A kind of no-hair theorem is obtained, claiming that black holes cannot coexist with a quasiscalar component of the F-field.

gr-qc↗

arXiv1997

Regularized Algebraic Nets for General Covariant QFT on Differentiable Manifolds

Quantum general relativity may be considered as generally covariant QFT on differentiable manifolds, without any a priori metric structure. The kinematically covariance group acts by general diffeomorphisms on the manifold and by automorphisms on the isotonic net of *-algebras encoding the QFT, while the algebra of observables is covariant under the dynamical subgroup of the general diffeomorphism group. Here, I focus on an algebraic implementation of the dynamical subgroup of dilations. Introducing an small and large scale cutoffs algebraically, their usual a priori conflict with general covariance is avoided. Thereby, a commutant duality between the minimal and maximal algebra is proposed. This allows to extract the modular structure, which is again related to the dilations.

gr-qc↗

arXiv1997

Integrable Multicomponent Perfect Fluid Multidimensional Cosmology II: Scalar Fields

We consider anisotropic cosmological models with an universe of dimension 4 or more, factorized into n>1 Ricci-flat spaces, containing an m-component perfect fluid of m non-interacting homogeneous minimally coupled scalar fields under special conditions. We describe the dynamics of the universe: It has a Kasner-like behaviour near the singularity and isotropizes during the expansion to infinity. Some of the considered models are integrable, and classical as well as quantum solutions are found. Some solutions produce inflation from "nothing". There exist classical asymptotically anti-de Sitter wormholes, and quantum wormholes with discrete spectrum.

gr-qc↗

arXiv1996

Tensor-multi-scalar theories from multidimensional cosmology

Inhomogeneous multidimensional cosmological models with a higher dimensional space-time manifold M=M_0 x M_1 x ... M_n are investigated under dimensional reduction to tensor-multi-scalar theories. In the Einstein conformal frame, these theories take the shape of a flat sigma-model. For the singular case where M_0 is 2-dimensional, the dimensional reduction to dilaton gravity is preformed with different distinguished representations of the action.

gr-qc↗

arXiv1996

The moduli space of local homogeneous 3-geometries

For a canonical formulation of quantum gravity, the superspace of all possible 3-geometries on a Cauchy hypersurface of a 3+1-dimensional Lorentzian manifold plays a key role. While in the analogous 2+1-dimensional case the superspace of all Riemannian 2-geometries is well known, the structure of the superspace of all Riemannian 3-geometries has not yet been resolved at present. In this paper, an important subspace of the latter is disentangled: The superspace of local homogenous Riemannian 3-geometries. It is finite dimensional and can be factored by conformal scale dilations, with the flat space as the center of projection. The corresponding moduli space can be represented by homothetically normalized 3-geometries. By construction, this moduli space of the local homogenous 3-geometries is an algebraic variety. An explicit parametrization is given by characteristic scalar invariants of the Riemannian 3-geometry. Although the moduli space is not locally Euclidean, it is a Hausdorff space. Nevertheless, its topology is compatible with the non-Hausdorffian topology of the space of all Bianchi-Lie algebras, which characterize the moduli modulo differences in their anisotropy.

gr-qc↗