We report monitoring observations of the T Tauri star EX Lupi during its outburst in 2008 in the CO fundamental band at 4.6-5.0 um. The observations were carried out at the VLT and the Subaru Telescope at six epochs from April to August 2008, covering the plateau of the outburst and the fading phase to a quiescent state. The line flux of CO emission declines with the visual brightness of the star and the continuum flux at 5 um, but composed of two subcomponents that decay with different rates. The narrow line emission (50 km s-1 in FWHM) is near the systemic velocity of EX Lupi. These emission lines appear exclusively in v=1-0. The line widths translate to a characteristic orbiting radius of 0.4 AU. The broad line component (FWZI ~ 150 km s-1) is highly excited upto v<=6. The line flux of the component decreases faster than the narrow line emission. Simple modeling of the line profiles implies that the broad-line emitting gas is orbiting around the star at 0.04-0.4 AU. The excitation state, the decay speed of the line flux, and the line profile, indicate that the broad-line emission component is physically distinct from the narrow-line emission component, and more tightly related to the outburst event.
We report a measurement of intergalactic magnetic fields using combined data from Atmospheric Cherenkov Telescopes and Fermi Gamma-Ray Space Telescope, based on the spectral data alone. If blazars are assumed to produce both gamma rays and cosmic rays, the observed spectra are not sensitive to the intrinsic spectrum of the source, because, for a distant blazar, secondary photons produced in line-of-sight cosmic-ray interactions dominate the signal. In this case, we set a robust limit 0.01 fG < B < 30 fG. If one excludes the cosmic-ray component, the robust 0.01 fG lower limit remains, but the upper limit depends on the spectral properties of the source. We present the allowed ranges for a variety of model parameters.
We present a study of the small-scale structure of the interstellar medium in the Milky Way. We used HST STIS data to measure N(HI) in a pencil-beam toward 59 AGNs and compared the results with the values seen at 9 arcmin - 36 arcmin resolution in the same directions using radio telescopes (GBT, Green Bank 140-ft and LAB survey). The distribution of ratios N(Lya)/N(HI) has an average of 1 and a dispersion of about 10%. Our analysis also revealed that spectra from the Leiden-Argentina-Bonn (LAB) all-sky HI survey need to be corrected, taking out a broad gaussian component (peak brightness temperature 0.048 K, FWHM 167 km/s, and central velocity -22 km/s). The column density ratios have a distribution showing similarities to simple descriptions of hierarchical structure in the neutral ISM, as well as to a more sophisticated 3D MHD simulation. From the comparison with such models, we find that the sonic Mach number of the local ISM should lie between 0.6 and 0.9. However, none of the models yet matches the observed distribution in all details, but with many more sightlines (as will be provided by COS) our approach can be used to constrain the properties of interstellar turbulence.
Simulations of the moon-forming impact suggest that most of the lunar material derives from the impactor rather than the Earth. Measurements of lunar samples, however, reveal an oxygen isotope composition that is indistinguishable from terrestrial samples, and clearly distinct from meteorites coming from Mars and Vesta. Here we explore the possibility that the silicate Earth and impactor were compositionally distinct with respect to oxygen isotopes, and that the terrestrial magma ocean and lunar-forming material underwent turbulent mixing and equilibration in the energetic aftermath of the giant impact. This mixing may arise in the molten disk epoch between the impact and lunar accretion, lasting perhaps 10^2-10^3 yr. The implications of this idea for the geochemistry of the Moon, the origin of water on Earth, and constraints on the giant impact are discussed.
We present spectroscopic observations obtained with the infrared Spitzer Space Telescope, which provide insight into the H$_2$ physics and gas energetics in photodissociation Regions (PDRs) of low to moderate far-ultraviolet (FUV) fields and densities. We analyze data on six well known Galactic PDRs (L1721, California, N7023E, Horsehead, rho Oph, N2023N), sampling a poorly explored range of excitation conditions ($\chi \sim 5-10^3$), relevant to the bulk of molecular clouds in galaxies. Spitzer observations of H$_2$ rotational lines are complemented with H$_2$ data, including ro-vibrational line measurements, obtained with ground-based telescopes and ISO, to constrain the relative contributions of ultraviolet pumping and collisions to the H$_2$ excitation. The data analysis is supported by model calculations with the Meudon PDR code. The observed column densities of rotationally excited H$_2$ are observed to be much higher than PDR model predictions. In the lowest excitation PDRs, the discrepancy between the model and the data is about one order of magnitude for rotational levels $J \ge $3. We discuss whether an enhancement in the H$_2$ formation rate or a local increase in photoelectric heating, as proposed for brighter PDRs in former ISO studies, may improve the data-model comparison. We find that an enhancement in the H$_2$ formation rates reduces the discrepancy, but the models still fall short of the data. This large disagreement suggests that our understanding of the formation and excitation of H$_2$ and/or of PDRs energetics is still incomplete. We discuss several explanations, which could be further tested using the Herschel Space Telescope
Despite its importance to questions of lunar origin, the chemical composition of the Moon is not precisely known. In recent years, however, the isotopic composition of lunar samples has been determined to high precision and found to be indistinguishable from the terrestrial mantle despite widespread isotopic heterogeneity in the Solar System. In the context of the giant-impact hypothesis, this level of isotopic homogeneity can evolve if the proto-lunar disk and post-impact Earth undergo turbulent mixing into a single uniform reservoir while the system is extensively molten and partially vaporized. In the absence of liquid-vapor separation, such a model leads to the lunar inheritance of the chemical composition of the terrestrial magma ocean. Hence, the turbulent mixing model raises the question of how chemical differences arose between the silicate Earth and Moon. Here we explore the consequences of liquid-vapor separation in one of the settings relevant to the lunar composition: the silicate vapor atmosphere of the post-giant-impact Earth. We use a model atmosphere to quantify the extent to which rainout can generate chemical differences by enriching the upper atmosphere in the vapor, and show that plausible parameters can generate the postulated enhancement in the FeO/MgO ratio of the silicate Moon relative to the Earth's mantle. Moreover, we show that liquid-vapor separation also generates measurable mass-dependent isotopic offsets between the silicate Earth and Moon and that precise silicon isotope measurements can be used to constrain the degree of chemical fractionation during this earliest period of lunar history. An approach of this kind has the potential to resolve long-standing questions on the lunar chemical composition.
Recent radio observations reveal the existence of mini radio lobes in active galaxies with their scales of $\sim 10 {\rm pc}$. The lobes are expected to be filled with shock accelerated electrons and protons. In this work, we examine the photon spectra from the mini lobes, properly taking the hadronic processes into account. We find that the resultant broadband spectra contain the two distinct hadronic bumps in $\gamma$-ray bands, i.e., the proton synchrotron bump at $\sim$ MeV and the synchrotron bump at $\sim$ GeV due to the secondary electrons/positrons produced via photo-pion cascade. Especially when the duration of particle injection is shorter than the lobe age, radio-dark $\gamma$-ray lobes are predicted. The existence of the $\gamma$-ray lobes could be testable with the future TeV-$\gamma$ telescope {\it CTA}.
A model-independent reconstruction of the cosmic expansion rate is essential to a robust analysis of cosmological observations. Our goal is to demonstrate that current data are able to provide reasonable constraints on the behavior of the Hubble parameter with redshift, independently of any cosmological model or underlying gravity theory. Using type Ia supernova data, we show that it is possible to analytically calculate the Fisher matrix components in a Hubble parameter analysis without assumptions about the energy content of the Universe. We used a principal component analysis to reconstruct the Hubble parameter as a linear combination of the Fisher matrix eigenvectors (principal components). To suppress the bias introduced by the high redshift behavior of the components, we considered the value of the Hubble parameter at high redshift as a free parameter. We first tested our procedure using a mock sample of type Ia supernova observations, we then applied it to the real data compiled by the Sloan Digital Sky Survey (SDSS) group. In the mock sample analysis, we demonstrate that it is possible to drastically suppress the bias introduced by the high redshift behavior of the principal components. Applying our procedure to the real data, we show that it allows us to determine the behavior of the Hubble parameter with reasonable uncertainty, without introducing any ad-hoc parameterizations. Beyond that, our reconstruction agrees with completely independent measurements of the Hubble parameter obtained from red-envelope galaxies.
An analytical solution for the discrepancy between observed core-like profiles and predicted cusp profiles in dark matter halos is studied. We calculate the distribution function for Navarro-Frenk-White halos and extract energy from the distribution, taking into account the effects of baryonic physics processes. We show with a simple argument that we can reproduce the evolution of a cusp to a flat density profile by a decrease of the initial potential energy.
Rankine-Hugoniot condition has been solved to study phase transition in astrophysical scenario mainly in the case of phase transition from neutron star (NS) to quark star (QS). The phase transition is brought about by a combustion front, which travels from the center to the surface. The equations of state and temperature plays a huge role in determining the nature of the front propagation, which brings about the phase transition in neutron stars (NSs). Magnetic field has been introduced and the modified conservation condition for the perpendicular and oblique shocks is obtained. Numerical solution of the perpendicular shock has been shown in the figures, which finds that the magnetic field helps in shock generation. It indirectly hints at the instability of the matter and thereby the NS for very high magnetic field, implying that NSs can only support finite magnetic field strength.
We present the preliminary results of a survey of the open clusters NGC3532 and NGC2287 for new white dwarf members which can help improve understanding of the form of the upper end of the stellar initial mass-final mass relation. We identify four objects with cooling times, distances and proper motions consistent with membership of these clusters. We find that despite a range in age of ~100Myr the masses of the four heaviest white dwarfs in NGC3532 span the narrow mass interval M~0.9-1.0Msolar suggesting that the initial mass-final mass relation is relatively flatter over 4.5Msolar <~ M_init <~ 6.5Msolar than at immediately lower masses. Additionally, we have unearthed WD J0646-203 which is possibly the most massive cluster white dwarf identified to date. With M~1.1Msolar it seems likely to be composed of ONe and has a cooling time consistent with it having evolved from a single star.
We study the impact of modifying the vector sector of gravity on the CMB polarization. We employ the Einstein-aether theory as a concrete example. The Einstein-aether theory admits dynamical vector perturbations generated during inflation, leaving imprints on the CMB polarization. We derive the perturbation equations of the aether vector field in covariant formalism and compute the CMB B-mode polarization using the modified CAMB code. It is found that the amplitude of the B-mode signal from the aether field can surpass the one from the inflationary gravitational waves. The shape of the spectrum is clearly understood in an analytic way using the tight coupling approximation.
In this letter, we introduce a new method of image stacking to directly study the undetected but possible gamma-ray point sources. Applying the method to the Australia Telescope 20 GHz Survey (AT20G) sources which have not been detected by LAT on Fermi, we find that the sources contribute (10.5+/-1.1)% and (4.3+/-0.9)% of the extragalactic gamma-ray background (EGB) and have a very soft spectrum with the photon indexes of 3.09+/-0.23 and 2.61+/-0.26, in the 1-3 and 3-300GeV energy ranges. In the 0.1-1GeV range, they probably contribute more large faction to the EGB, but it is not quite sure. It maybe not appropriate to assume that the undetected sources have the similar property to the detected sources.
We are now exploring the inner region of Type 1 AGNs with the Keck interferometer in the near-infrared. Here we report further measurements of K-band (2.2 um) visibilities on four more targets, namely AKN120, IC4329A, Mrk6, and the radio-loud QSO 3C273 at z=0.158. The observed visibilities are quite high for all the targets. We interpret these as an indication of partially resolving the dust sublimation region. The effective ring radii derived from the observed visibilities approximately scale with L^1/2 where L is the AGN luminosity. Comparing the radii with those from independent optical-infrared reverberation measurements, the new data further support our previous claim that the interferometric ring radius is either roughly equal to or slightly larger than the reverberation radius. We interpret the ratio of these two radii for a given L as an approximate probe for the radial distribution of the inner accreting material. We show tentative evidence that this inner radial structure might closely be related to the radio-loudness of the central engine. Finally, we re-observed the brightest Seyfert 1 galaxy NGC4151. The marginally higher visibility at a shorter projected baseline, compared to our previous measurements obtained one year before, supports the partial resolution of the inner structure. We did not detect any significant change in the implied emission size when the K-band flux is brightened up by a factor of 1.5 over a time interval of one year.
We present parsec-scale resolution observations of the atomic and molecular ISM in two Galactic supershells, GSH 287+04-17 and GSH 277+00+36. HI synthesis images from the Australia Telescope Compact Array are combined with 12CO(J=1-0) data from the NANTEN telescope to reveal substantial quantities of molecular gas closely associated with both shells. These data allow us to confirm an enhanced level of molecularization over the volumes of both objects, providing the first direct observational evidence of increased molecular cloud production due to the influence of supershells. We find that the atomic shell walls are dominated by cold gas with estimated temperatures and densities of T ~ 100 K and n0 ~ 10 cm-3. Locally, the shells show rich substructure in both tracers, with molecular gas seen elongated along the inner edges of the atomic walls, embedded within HI filaments and clouds, or taking the form of small CO clouds at the tips of tapering atomic `fingers'. We discuss these structures in the context of different formation scenarios, suggesting that molecular gas embedded within shell walls is well explained by in-situ formation from the swept up medium, whereas CO seen at the ends of fingers of HI may trace remnants of molecular clouds that pre-date the shells. A preliminary assessment of star formation activity within the shells confirms ongoing star formation in the molecular gas of both GSH 287+04-17 and GSH 277+00+36.
Aims. The goal of our survey is to provide accurate and multi-epoch radial velocities, atmospheric parameters (Teff, log g and [M/H]), distances and space velocities of faint Red Clump stars. Methods. We recorded high signal-to-noise (S/N >= 200) spectra of Red Clump stars, over the 4750-5950 Ang range, at a resolving power 5500. The target stars are distributed over the great circle of the celestial equator. Radial velocities were obtained via cross-correlation against IAU radial velocity standards. Atmospheric parameters were derived via chi^2 fit to a synthetic spectral library. A large number of RC stars from other surveys were re-observed to check the consistency of our results. Results. A total of 245 Red Clump stars were observed (60 of them with a second epoch observation separated in time by about three months), and the results are presented in an output catalog. None of them is already present in other surveys of Red Clump stars. In addition to astrometric and photometric support data from external sources, the catalog provides radial velocities (accuracy sigma(RV)=1.3 km/s), atmospheric parameters (sigma(Teff)=88 K, sigma(log g)=0.38 dex and sigma([M/H])=0.17 dex), spectro-photometric distances, (X,Y,Z) galacto-centric positions and (U,V,W) space velocities.
The respective contribution of disk and jet components to the total emission in low luminosity active galactic nuclei (LLAGNs) is an open question. This paper suggests that $\gamma$-rays emitted from electrons accelerated in jets could be a direct diagnostic tool for a jet component to the total emission. We demonstrate $\gamma$-ray flux from jets based on a synchrotron self-compton (SSC) model on the assumption that radio and X-rays are dominantly produced from jets in the case of a high state of a nearby LLAGN, NGC 4278. We also survey parameter space in the model. Observational properties of LLAGNs in radio and X-ray bands allow to constrain physical parameters in an emission region. The size of the emission region $R$ is limited to $10^{16}$ cm $\leq R \leq 10^{17.5}$ cm if the observed tight correlation between radio and X-ray emission originates from the same jet component. If the beaming factor of the emission region is close to the observed parsec scale jet of NGC 4278 and $R \sim 10^{16}$ cm, the $\gamma$-rays may be detected by Cherenkov Telescope Array, and the jet domination can be tested in the near future.
We investigate the motion of neutral test particles in the gravitational field of a mass $M$ with charge $Q$ described by the Reissner-Nordstr\"om (RN) spacetime. We focus on the study of circular stable and unstable orbits around configurations describing either black holes or naked singularities. We show that at the classical radius, defined as $Q^2/M$, there exist orbits with zero angular momentum due to the presence of repulsive gravity. The analysis of the stability of circular orbits indicates that black holes are characterized by a continuous region of stability. In the case of naked singularities, the region of stability can split into two non-connected regions inside which test particles move along stable circular orbits.
Using ab initio simulations we investigate whether water ice is stable in the cores of giant planets, or whether it dissolves into the layer of metallic hydrogen above. By Gibbs free energy calculations we find that for pressures between 10 and 40 Mbar the ice-hydrogen interface is unstable at temperatures above approximately 3000 K, far below the temperature of the core-mantle boundaries in Jupiter and Saturn that are of the order of 10000 K. This implies that the cores of solar and extrasolar giant planets are at least partially eroded.
The Newtonian Euler-Poisson equations with attractive forces are the classical models for the evolution of gaseous stars and galaxies in astrophysics. In this paper, we use the integration method to study the blowup problem of the $N$-dimensional system with adiabatic exponent $\gamma>1$, in radial symmetry. We could show that the $C^{1}$ non-trivial classical solutions $(\rho,V)$, with compact support in $[0,R]$, where $R>0$ is a positive constant with $\rho(t,r)=0$ and $V(t,r)=0$ for $r\geq R$, under the initial condition H_{0}=\int_{0}^{R}r^{n}V_{0}dr>\sqrt{\frac{2R^{2n-N+4}M}{n(n+1)(n-N+2)}}% with an arbitrary constant $n>\max(N-2,0),$ blow up before a finite time $T$ for pressureless fluids or $\gamma>1.$ Our results could fill some gaps about the blowup phenomena to the classical $C^{1}$ solutions of that system.
Boltzmann equations and their matrix valued generalisations are commonly used to describe nonquilibrium phenomena in cosmology. On the other hand, it is known that in gauge theories at high temperature processes involving many quanta, which naively are of higher order in the coupling, contribute to the relaxation rate at leading order. How does this accord with the use of single particle distribution functions in the kinetic equations? When can these effects be parametrised in an effective quasiparticle description? And what is the kinematic role of their thermal masses? We address these questions in the framework of nonequilibrium quantum field theory and develop an intuitive picture in which contributions from higher order processes are parametrised by the widths of resonances in the plasma. In the narrow width limit we recover the quasiparticle picture, with the additional processes giving rise to off-shell parts of quasiparticles that appear to violate energy conservation. In this regime we give analytic expressions for the scalar and fermion nonequilibrium propagators in a medium. We compare the efficiency of decays and scatterings involving real quasiparticles, computed from analytic expressions for the relaxation rates via trilinear scalar and Yukawa interactions for all modes, to off-shell contributions and find that the latter can be significant even for moderate widths. Our results apply to various processes including thermal production of particles from a plasma, dissipation of fields in a medium and particle propagation in dense matter. We discuss cosmological implications, in particular for the maximal temperature achieved during reheating by perturbative inflaton decay.
As we shall briefly recall, Nordstr\"om's theory of gravity is observationally ruled out. It is however an interesting example of non-minimal coupling of matter to gravity and of the role of conformal transformations. We show in particular that they could be useful to extend manifolds through curvature singularities.
Neutrino energy losses through neutral weak currents in the triplet-spin superfluid neutron liquid are studied for the case of condensate involving several magnetic quantum numbers. Low-energy excitations of the multicomponent condensate in the timelike domain of the energy and momentum are analyzed. Along with the well-known excitations in the form of broken Cooper pairs, the theoretical analysis predicts the existence of collective waves of spin density at very low energy. Because of a rather small excitation energy of spin waves, their decay leads to a substantial neutrino emission at the lowest temperatures, when all other mechanisms of neutrino energy loss are killed by a superfluidity. Neutrino energy losses caused by the pair recombination and spin-wave decays are examined in all of the multicomponent phases that might represent the ground state of the condensate, according to modern theories, and for the case when a phase transition occurs in the condensate at some temperature. Our estimate predicts a sharp increase in the neutrino energy losses followed by a decrease, along with a decrease in the temperature, that takes place more rapidly than it would without the phase transition. We demonstrate the important role of the neutrino radiation caused by the decay of spin waves in the cooling of neutron stars.
A new calculation of the propagation direction of light in a 3-parameter family of static, spherically symmetric space-times within the post-post-Newtonian framework is presented. The solution for an emitter and an observer both located at a finite distance is simply obtained by differentiating the time-delay function. The case of a ray emitted at infinity is also treated, enabling us to confirm a recent analysis by S. Klioner and S. Zschocke in the context of the Gaia mission.
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We report monitoring observations of the T Tauri star EX Lupi during its outburst in 2008 in the CO fundamental band at 4.6-5.0 um. The observations were carried out at the VLT and the Subaru Telescope at six epochs from April to August 2008, covering the plateau of the outburst and the fading phase to a quiescent state. The line flux of CO emission declines with the visual brightness of the star and the continuum flux at 5 um, but composed of two subcomponents that decay with different rates. The narrow line emission (50 km s-1 in FWHM) is near the systemic velocity of EX Lupi. These emission lines appear exclusively in v=1-0. The line widths translate to a characteristic orbiting radius of 0.4 AU. The broad line component (FWZI ~ 150 km s-1) is highly excited upto v<=6. The line flux of the component decreases faster than the narrow line emission. Simple modeling of the line profiles implies that the broad-line emitting gas is orbiting around the star at 0.04-0.4 AU. The excitation state, the decay speed of the line flux, and the line profile, indicate that the broad-line emission component is physically distinct from the narrow-line emission component, and more tightly related to the outburst event.
We report a measurement of intergalactic magnetic fields using combined data from Atmospheric Cherenkov Telescopes and Fermi Gamma-Ray Space Telescope, based on the spectral data alone. If blazars are assumed to produce both gamma rays and cosmic rays, the observed spectra are not sensitive to the intrinsic spectrum of the source, because, for a distant blazar, secondary photons produced in line-of-sight cosmic-ray interactions dominate the signal. In this case, we set a robust limit 0.01 fG < B < 30 fG. If one excludes the cosmic-ray component, the robust 0.01 fG lower limit remains, but the upper limit depends on the spectral properties of the source. We present the allowed ranges for a variety of model parameters.
We present a study of the small-scale structure of the interstellar medium in the Milky Way. We used HST STIS data to measure N(HI) in a pencil-beam toward 59 AGNs and compared the results with the values seen at 9 arcmin - 36 arcmin resolution in the same directions using radio telescopes (GBT, Green Bank 140-ft and LAB survey). The distribution of ratios N(Lya)/N(HI) has an average of 1 and a dispersion of about 10%. Our analysis also revealed that spectra from the Leiden-Argentina-Bonn (LAB) all-sky HI survey need to be corrected, taking out a broad gaussian component (peak brightness temperature 0.048 K, FWHM 167 km/s, and central velocity -22 km/s). The column density ratios have a distribution showing similarities to simple descriptions of hierarchical structure in the neutral ISM, as well as to a more sophisticated 3D MHD simulation. From the comparison with such models, we find that the sonic Mach number of the local ISM should lie between 0.6 and 0.9. However, none of the models yet matches the observed distribution in all details, but with many more sightlines (as will be provided by COS) our approach can be used to constrain the properties of interstellar turbulence.
Simulations of the moon-forming impact suggest that most of the lunar material derives from the impactor rather than the Earth. Measurements of lunar samples, however, reveal an oxygen isotope composition that is indistinguishable from terrestrial samples, and clearly distinct from meteorites coming from Mars and Vesta. Here we explore the possibility that the silicate Earth and impactor were compositionally distinct with respect to oxygen isotopes, and that the terrestrial magma ocean and lunar-forming material underwent turbulent mixing and equilibration in the energetic aftermath of the giant impact. This mixing may arise in the molten disk epoch between the impact and lunar accretion, lasting perhaps 10^2-10^3 yr. The implications of this idea for the geochemistry of the Moon, the origin of water on Earth, and constraints on the giant impact are discussed.
We present spectroscopic observations obtained with the infrared Spitzer Space Telescope, which provide insight into the H$_2$ physics and gas energetics in photodissociation Regions (PDRs) of low to moderate far-ultraviolet (FUV) fields and densities. We analyze data on six well known Galactic PDRs (L1721, California, N7023E, Horsehead, rho Oph, N2023N), sampling a poorly explored range of excitation conditions ($\chi \sim 5-10^3$), relevant to the bulk of molecular clouds in galaxies. Spitzer observations of H$_2$ rotational lines are complemented with H$_2$ data, including ro-vibrational line measurements, obtained with ground-based telescopes and ISO, to constrain the relative contributions of ultraviolet pumping and collisions to the H$_2$ excitation. The data analysis is supported by model calculations with the Meudon PDR code. The observed column densities of rotationally excited H$_2$ are observed to be much higher than PDR model predictions. In the lowest excitation PDRs, the discrepancy between the model and the data is about one order of magnitude for rotational levels $J \ge $3. We discuss whether an enhancement in the H$_2$ formation rate or a local increase in photoelectric heating, as proposed for brighter PDRs in former ISO studies, may improve the data-model comparison. We find that an enhancement in the H$_2$ formation rates reduces the discrepancy, but the models still fall short of the data. This large disagreement suggests that our understanding of the formation and excitation of H$_2$ and/or of PDRs energetics is still incomplete. We discuss several explanations, which could be further tested using the Herschel Space Telescope
Despite its importance to questions of lunar origin, the chemical composition of the Moon is not precisely known. In recent years, however, the isotopic composition of lunar samples has been determined to high precision and found to be indistinguishable from the terrestrial mantle despite widespread isotopic heterogeneity in the Solar System. In the context of the giant-impact hypothesis, this level of isotopic homogeneity can evolve if the proto-lunar disk and post-impact Earth undergo turbulent mixing into a single uniform reservoir while the system is extensively molten and partially vaporized. In the absence of liquid-vapor separation, such a model leads to the lunar inheritance of the chemical composition of the terrestrial magma ocean. Hence, the turbulent mixing model raises the question of how chemical differences arose between the silicate Earth and Moon. Here we explore the consequences of liquid-vapor separation in one of the settings relevant to the lunar composition: the silicate vapor atmosphere of the post-giant-impact Earth. We use a model atmosphere to quantify the extent to which rainout can generate chemical differences by enriching the upper atmosphere in the vapor, and show that plausible parameters can generate the postulated enhancement in the FeO/MgO ratio of the silicate Moon relative to the Earth's mantle. Moreover, we show that liquid-vapor separation also generates measurable mass-dependent isotopic offsets between the silicate Earth and Moon and that precise silicon isotope measurements can be used to constrain the degree of chemical fractionation during this earliest period of lunar history. An approach of this kind has the potential to resolve long-standing questions on the lunar chemical composition.
Recent radio observations reveal the existence of mini radio lobes in active galaxies with their scales of $\sim 10 {\rm pc}$. The lobes are expected to be filled with shock accelerated electrons and protons. In this work, we examine the photon spectra from the mini lobes, properly taking the hadronic processes into account. We find that the resultant broadband spectra contain the two distinct hadronic bumps in $\gamma$-ray bands, i.e., the proton synchrotron bump at $\sim$ MeV and the synchrotron bump at $\sim$ GeV due to the secondary electrons/positrons produced via photo-pion cascade. Especially when the duration of particle injection is shorter than the lobe age, radio-dark $\gamma$-ray lobes are predicted. The existence of the $\gamma$-ray lobes could be testable with the future TeV-$\gamma$ telescope {\it CTA}.
A model-independent reconstruction of the cosmic expansion rate is essential to a robust analysis of cosmological observations. Our goal is to demonstrate that current data are able to provide reasonable constraints on the behavior of the Hubble parameter with redshift, independently of any cosmological model or underlying gravity theory. Using type Ia supernova data, we show that it is possible to analytically calculate the Fisher matrix components in a Hubble parameter analysis without assumptions about the energy content of the Universe. We used a principal component analysis to reconstruct the Hubble parameter as a linear combination of the Fisher matrix eigenvectors (principal components). To suppress the bias introduced by the high redshift behavior of the components, we considered the value of the Hubble parameter at high redshift as a free parameter. We first tested our procedure using a mock sample of type Ia supernova observations, we then applied it to the real data compiled by the Sloan Digital Sky Survey (SDSS) group. In the mock sample analysis, we demonstrate that it is possible to drastically suppress the bias introduced by the high redshift behavior of the principal components. Applying our procedure to the real data, we show that it allows us to determine the behavior of the Hubble parameter with reasonable uncertainty, without introducing any ad-hoc parameterizations. Beyond that, our reconstruction agrees with completely independent measurements of the Hubble parameter obtained from red-envelope galaxies.
An analytical solution for the discrepancy between observed core-like profiles and predicted cusp profiles in dark matter halos is studied. We calculate the distribution function for Navarro-Frenk-White halos and extract energy from the distribution, taking into account the effects of baryonic physics processes. We show with a simple argument that we can reproduce the evolution of a cusp to a flat density profile by a decrease of the initial potential energy.
Rankine-Hugoniot condition has been solved to study phase transition in astrophysical scenario mainly in the case of phase transition from neutron star (NS) to quark star (QS). The phase transition is brought about by a combustion front, which travels from the center to the surface. The equations of state and temperature plays a huge role in determining the nature of the front propagation, which brings about the phase transition in neutron stars (NSs). Magnetic field has been introduced and the modified conservation condition for the perpendicular and oblique shocks is obtained. Numerical solution of the perpendicular shock has been shown in the figures, which finds that the magnetic field helps in shock generation. It indirectly hints at the instability of the matter and thereby the NS for very high magnetic field, implying that NSs can only support finite magnetic field strength.
We present the preliminary results of a survey of the open clusters NGC3532 and NGC2287 for new white dwarf members which can help improve understanding of the form of the upper end of the stellar initial mass-final mass relation. We identify four objects with cooling times, distances and proper motions consistent with membership of these clusters. We find that despite a range in age of ~100Myr the masses of the four heaviest white dwarfs in NGC3532 span the narrow mass interval M~0.9-1.0Msolar suggesting that the initial mass-final mass relation is relatively flatter over 4.5Msolar <~ M_init <~ 6.5Msolar than at immediately lower masses. Additionally, we have unearthed WD J0646-203 which is possibly the most massive cluster white dwarf identified to date. With M~1.1Msolar it seems likely to be composed of ONe and has a cooling time consistent with it having evolved from a single star.
We study the impact of modifying the vector sector of gravity on the CMB polarization. We employ the Einstein-aether theory as a concrete example. The Einstein-aether theory admits dynamical vector perturbations generated during inflation, leaving imprints on the CMB polarization. We derive the perturbation equations of the aether vector field in covariant formalism and compute the CMB B-mode polarization using the modified CAMB code. It is found that the amplitude of the B-mode signal from the aether field can surpass the one from the inflationary gravitational waves. The shape of the spectrum is clearly understood in an analytic way using the tight coupling approximation.
In this letter, we introduce a new method of image stacking to directly study the undetected but possible gamma-ray point sources. Applying the method to the Australia Telescope 20 GHz Survey (AT20G) sources which have not been detected by LAT on Fermi, we find that the sources contribute (10.5+/-1.1)% and (4.3+/-0.9)% of the extragalactic gamma-ray background (EGB) and have a very soft spectrum with the photon indexes of 3.09+/-0.23 and 2.61+/-0.26, in the 1-3 and 3-300GeV energy ranges. In the 0.1-1GeV range, they probably contribute more large faction to the EGB, but it is not quite sure. It maybe not appropriate to assume that the undetected sources have the similar property to the detected sources.
We are now exploring the inner region of Type 1 AGNs with the Keck interferometer in the near-infrared. Here we report further measurements of K-band (2.2 um) visibilities on four more targets, namely AKN120, IC4329A, Mrk6, and the radio-loud QSO 3C273 at z=0.158. The observed visibilities are quite high for all the targets. We interpret these as an indication of partially resolving the dust sublimation region. The effective ring radii derived from the observed visibilities approximately scale with L^1/2 where L is the AGN luminosity. Comparing the radii with those from independent optical-infrared reverberation measurements, the new data further support our previous claim that the interferometric ring radius is either roughly equal to or slightly larger than the reverberation radius. We interpret the ratio of these two radii for a given L as an approximate probe for the radial distribution of the inner accreting material. We show tentative evidence that this inner radial structure might closely be related to the radio-loudness of the central engine. Finally, we re-observed the brightest Seyfert 1 galaxy NGC4151. The marginally higher visibility at a shorter projected baseline, compared to our previous measurements obtained one year before, supports the partial resolution of the inner structure. We did not detect any significant change in the implied emission size when the K-band flux is brightened up by a factor of 1.5 over a time interval of one year.
We present parsec-scale resolution observations of the atomic and molecular ISM in two Galactic supershells, GSH 287+04-17 and GSH 277+00+36. HI synthesis images from the Australia Telescope Compact Array are combined with 12CO(J=1-0) data from the NANTEN telescope to reveal substantial quantities of molecular gas closely associated with both shells. These data allow us to confirm an enhanced level of molecularization over the volumes of both objects, providing the first direct observational evidence of increased molecular cloud production due to the influence of supershells. We find that the atomic shell walls are dominated by cold gas with estimated temperatures and densities of T ~ 100 K and n0 ~ 10 cm-3. Locally, the shells show rich substructure in both tracers, with molecular gas seen elongated along the inner edges of the atomic walls, embedded within HI filaments and clouds, or taking the form of small CO clouds at the tips of tapering atomic `fingers'. We discuss these structures in the context of different formation scenarios, suggesting that molecular gas embedded within shell walls is well explained by in-situ formation from the swept up medium, whereas CO seen at the ends of fingers of HI may trace remnants of molecular clouds that pre-date the shells. A preliminary assessment of star formation activity within the shells confirms ongoing star formation in the molecular gas of both GSH 287+04-17 and GSH 277+00+36.
Aims. The goal of our survey is to provide accurate and multi-epoch radial velocities, atmospheric parameters (Teff, log g and [M/H]), distances and space velocities of faint Red Clump stars. Methods. We recorded high signal-to-noise (S/N >= 200) spectra of Red Clump stars, over the 4750-5950 Ang range, at a resolving power 5500. The target stars are distributed over the great circle of the celestial equator. Radial velocities were obtained via cross-correlation against IAU radial velocity standards. Atmospheric parameters were derived via chi^2 fit to a synthetic spectral library. A large number of RC stars from other surveys were re-observed to check the consistency of our results. Results. A total of 245 Red Clump stars were observed (60 of them with a second epoch observation separated in time by about three months), and the results are presented in an output catalog. None of them is already present in other surveys of Red Clump stars. In addition to astrometric and photometric support data from external sources, the catalog provides radial velocities (accuracy sigma(RV)=1.3 km/s), atmospheric parameters (sigma(Teff)=88 K, sigma(log g)=0.38 dex and sigma([M/H])=0.17 dex), spectro-photometric distances, (X,Y,Z) galacto-centric positions and (U,V,W) space velocities.
The respective contribution of disk and jet components to the total emission in low luminosity active galactic nuclei (LLAGNs) is an open question. This paper suggests that $\gamma$-rays emitted from electrons accelerated in jets could be a direct diagnostic tool for a jet component to the total emission. We demonstrate $\gamma$-ray flux from jets based on a synchrotron self-compton (SSC) model on the assumption that radio and X-rays are dominantly produced from jets in the case of a high state of a nearby LLAGN, NGC 4278. We also survey parameter space in the model. Observational properties of LLAGNs in radio and X-ray bands allow to constrain physical parameters in an emission region. The size of the emission region $R$ is limited to $10^{16}$ cm $\leq R \leq 10^{17.5}$ cm if the observed tight correlation between radio and X-ray emission originates from the same jet component. If the beaming factor of the emission region is close to the observed parsec scale jet of NGC 4278 and $R \sim 10^{16}$ cm, the $\gamma$-rays may be detected by Cherenkov Telescope Array, and the jet domination can be tested in the near future.
We investigate the motion of neutral test particles in the gravitational field of a mass $M$ with charge $Q$ described by the Reissner-Nordstr\"om (RN) spacetime. We focus on the study of circular stable and unstable orbits around configurations describing either black holes or naked singularities. We show that at the classical radius, defined as $Q^2/M$, there exist orbits with zero angular momentum due to the presence of repulsive gravity. The analysis of the stability of circular orbits indicates that black holes are characterized by a continuous region of stability. In the case of naked singularities, the region of stability can split into two non-connected regions inside which test particles move along stable circular orbits.
Using ab initio simulations we investigate whether water ice is stable in the cores of giant planets, or whether it dissolves into the layer of metallic hydrogen above. By Gibbs free energy calculations we find that for pressures between 10 and 40 Mbar the ice-hydrogen interface is unstable at temperatures above approximately 3000 K, far below the temperature of the core-mantle boundaries in Jupiter and Saturn that are of the order of 10000 K. This implies that the cores of solar and extrasolar giant planets are at least partially eroded.
The Newtonian Euler-Poisson equations with attractive forces are the classical models for the evolution of gaseous stars and galaxies in astrophysics. In this paper, we use the integration method to study the blowup problem of the $N$-dimensional system with adiabatic exponent $\gamma>1$, in radial symmetry. We could show that the $C^{1}$ non-trivial classical solutions $(\rho,V)$, with compact support in $[0,R]$, where $R>0$ is a positive constant with $\rho(t,r)=0$ and $V(t,r)=0$ for $r\geq R$, under the initial condition H_{0}=\int_{0}^{R}r^{n}V_{0}dr>\sqrt{\frac{2R^{2n-N+4}M}{n(n+1)(n-N+2)}}% with an arbitrary constant $n>\max(N-2,0),$ blow up before a finite time $T$ for pressureless fluids or $\gamma>1.$ Our results could fill some gaps about the blowup phenomena to the classical $C^{1}$ solutions of that system.
Boltzmann equations and their matrix valued generalisations are commonly used to describe nonquilibrium phenomena in cosmology. On the other hand, it is known that in gauge theories at high temperature processes involving many quanta, which naively are of higher order in the coupling, contribute to the relaxation rate at leading order. How does this accord with the use of single particle distribution functions in the kinetic equations? When can these effects be parametrised in an effective quasiparticle description? And what is the kinematic role of their thermal masses? We address these questions in the framework of nonequilibrium quantum field theory and develop an intuitive picture in which contributions from higher order processes are parametrised by the widths of resonances in the plasma. In the narrow width limit we recover the quasiparticle picture, with the additional processes giving rise to off-shell parts of quasiparticles that appear to violate energy conservation. In this regime we give analytic expressions for the scalar and fermion nonequilibrium propagators in a medium. We compare the efficiency of decays and scatterings involving real quasiparticles, computed from analytic expressions for the relaxation rates via trilinear scalar and Yukawa interactions for all modes, to off-shell contributions and find that the latter can be significant even for moderate widths. Our results apply to various processes including thermal production of particles from a plasma, dissipation of fields in a medium and particle propagation in dense matter. We discuss cosmological implications, in particular for the maximal temperature achieved during reheating by perturbative inflaton decay.
As we shall briefly recall, Nordstr\"om's theory of gravity is observationally ruled out. It is however an interesting example of non-minimal coupling of matter to gravity and of the role of conformal transformations. We show in particular that they could be useful to extend manifolds through curvature singularities.
Neutrino energy losses through neutral weak currents in the triplet-spin superfluid neutron liquid are studied for the case of condensate involving several magnetic quantum numbers. Low-energy excitations of the multicomponent condensate in the timelike domain of the energy and momentum are analyzed. Along with the well-known excitations in the form of broken Cooper pairs, the theoretical analysis predicts the existence of collective waves of spin density at very low energy. Because of a rather small excitation energy of spin waves, their decay leads to a substantial neutrino emission at the lowest temperatures, when all other mechanisms of neutrino energy loss are killed by a superfluidity. Neutrino energy losses caused by the pair recombination and spin-wave decays are examined in all of the multicomponent phases that might represent the ground state of the condensate, according to modern theories, and for the case when a phase transition occurs in the condensate at some temperature. Our estimate predicts a sharp increase in the neutrino energy losses followed by a decrease, along with a decrease in the temperature, that takes place more rapidly than it would without the phase transition. We demonstrate the important role of the neutrino radiation caused by the decay of spin waves in the cooling of neutron stars.
A new calculation of the propagation direction of light in a 3-parameter family of static, spherically symmetric space-times within the post-post-Newtonian framework is presented. The solution for an emitter and an observer both located at a finite distance is simply obtained by differentiating the time-delay function. The case of a ray emitted at infinity is also treated, enabling us to confirm a recent analysis by S. Klioner and S. Zschocke in the context of the Gaia mission.
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