Astronomy

Noether gauge symmetry of Dirac field in $2+1$ dimensional gravity
In this paper, we consider a gravitational theory including a Dirac fieldthat is non-minimal coupled to gravity in $2+1$ dimensions. Noether gaugesymmetry approach can be used to fix the form of coupling function $F(Psi)$and the potential $V(Psi)$ of the Dirac field and to obtain a constant ofmotion for the dynamical equations. In the context of $2+1$ dimensions gravity,we investigate cosmologi...


A symmetric scalar constraint for loop quantum gravity
In the framework of loop quantum gravity, we define a new Hilbert space ofstates which are solutions of a large number of components of thediffeomorphism constraint. On this Hilbert space, using the methods ofThiemann, we obtain a family of gravitational scalar constraints. They preservethe Hilbert space for every choice of lapse function. Thus adjointness andcommutator properties of the constr...
Dirac fields in massive conformal gravity
In this article we show that the gravitational field in massive conformalgravity couples consistently with Dirac spinor fields. We solve the problem ofconsistency by considering that the Dirac spinor fields couple with both themetric field and a scalar field, which are the gravitational field variables ofmassive conformal gravity.


Dynamical compact elastic bodies in general relativity
We prove the local existence of solutions to the Einstein-Elastic equationsthat represent self-gravitating, relativistic elastic bodies with compactsupport.
Properties of Polycyclic Aromatic Hydrocarbons in the Northwest Photon Dominated Region of NGC 7023. II. Traditional PAH Analysis Using k-means as a Visualization Tool
Polycyclic aromatic hydrocarbon (PAH) emission in the Spitzer -IRS spectral map of the northwest photon dominated region (PDR) in NGC 7023 is analyzed using the "traditional" approach in which the PAH bands and plateaus between 5.2-19.5 μm are isolated by subtracting the underlying continuum and removing H 2 emission lines. The spectra are organized into seven spectroscopic bins by using k -m...


Investigating Nearby Star-forming Galaxies in the Ultraviolet with HST/COS Spectroscopy. I. Spectral Analysis and Interstellar Abundance Determinations
This is the first in a series of three papers describing a project with the Cosmic Origins Spectrograph on the Hubble Space Telescope to measure abundances of the neutral interstellar medium (ISM) in a sample of nine nearby star-forming galaxies. The goal is to assess the (in)homogeneities of the multiphase ISM in galaxies where the bulk of metals can be hidden in the neutral phase, yet the met...
Evidence for Wave Heating of the Quiet-Sun Corona
We have measured the energy and dissipation of Alfvénic waves in the quiet Sun. A magnetic field model was used to infer the location and orientation of the magnetic field lines along which the waves are expected to travel. The waves were measured using spectral lines to infer the wave amplitude. The waves cause a non-thermal broadening of the spectral lines, which can be expressed as a non-th...

New insights on Saturn's formation from its nitrogen isotopic composition
The recent derivation of a lower limit for the $^{14}$N/$^{15}$N ratio inSaturn's ammonia, which is found to be consistent with the Jovian value,prompted us to revise models of Saturn's formation using as constraints thesupersolar abundances of heavy elements measured in its atmosphere. Here wefind that it is possible to account for both Saturn's chemical and isotopiccompositions if one assumes...
Resonance capture at arbitrary inclination
Resonance capture is studied numerically in the three-body problem forarbitrary inclinations. Massless particles are set to drift from outside the1:5 resonance with a Jupiter-mass planet thereby encountering the web of theplanet's diverse mean motion resonances. Randomly constructed samples exploreparameter space for inclinations from 0 to 180 deg with 5deg incrementstotalling nearly 6x10^5 num...

A self-consistent and time-dependent hybrid blazar emission model - Properties and application
A time-dependent emission model for blazar jets, taking acceleration due toFermi-I and Fermi-II processes for electrons and protons as well as allrelevant radiative processes self-consistently into account, is presented. Thepresence of highly relativistic protons within the jet extends the simplesynchrotron self-Compton case not only in the very high energy radiation ofblazars, but also in the ...
Close stellar binary systems by grazing envelope evolution
I suggest a spiral-in process by which a stellar companion graze the envelopeof a giant star while both the orbital separation and the giant radius shrinksimultaneously, and a close binary system is formed. The binary system might beviewed as evolving in a constant state of `just entering a common envelope (CE)phase'. In cases where this process takes place it can be an alternative to theCE evo...

Discriminant analysis of solar bright points and faculae II. Contrast and morphology analysis
Taken at a high spatial resolution of 0.1 arcsec, Bright Points (BPs) arefound to coexist with faculae in images and the latter are often resolved asadjacent striations. Understanding the properties of these different featuresis fundamental to carrying out proxy magnetometry. To shed light on therelationship between BPs and faculae, we studied them separately after theapplication of a classific...
How accurate are stellar ages based on stellar models? II. The impact of asteroseismology
Accurate and precise stellar ages are best determined for stars which arestrongly observationally constrained, that is which are intrinsicallyoscillating. We review here the seismic diagnostics which are sensitive tostellar ages and provide some illustrating examples of seismically age-datedstars.
How accurate are stellar ages based on stellar models ? I. The impact of stellar models uncertainties
Among the various methods used to age-date stars, methods based on stellarmodel predictions are widely used, for nearly all kind of stars in large rangesof masses, chemical compositions and evolutionary stages. The precision andaccuracy on the age determination depend on both the precision and number ofobservational constraints, and on our ability to correctly describe the stellarinterior and e...
On the characterization of transiting exoplanets and magnetic spots with optical interferometry
Stellar activity causes difficulties in the characterization of transitingexoplanets. Studies have been performed to quantify its impact on infraredinterferometry, but not in the visible domain, which however allows reachingbetter angular resolution and is also the one mostly used for spectroscopic andphotometric measurements. We use a textbook case to make a complete analysis of the impact of ...