Posts Tagged observational result

Recent Postings from observational result

The effects of stellar dynamics on the X-ray emission of flat early-type galaxies

Observational and numerical studies gave hints that the hot gaseous haloes of ETGs may be sensitive to the galaxy internal kinematics. By using high resolution 2D hydro simulations, and realistic two-component (stars plus dark matter) axisymmetric galaxy models, we study the evolution of the hot haloes in a suite of flat ETGs of fixed mass distribution, but with variable amounts of azimuthal velocity dispersion and rotational support, including the possibility of a counter-rotating inner stellar disc. The hot halo is fed by stellar mass losses and heated by SNIa explosions and thermalization of stellar motions. We measure the value of the thermalization parameter gamma (the ratio between the heating due to the relative velocity between the stellar streaming and the ISM bulk flow, and the heating attainable by complete thermalization of the stellar streaming motions). We find that 1) the X-ray emission and the average temperature are larger in fully velocity dispersion supported systems; 2) 0.1<gamma<0.2 for isotropic rotators (with a trend for being larger for lower dark mass models); 3) systems that are isotropic rotators at large radii with an inner counter-rotating disc, or fully velocity dispersion supported systems with an inner rotating disc, have gamma=1, again with a trend to increase for lower dark mass contents. We also find that the lower X-ray luminosities of isotropic rotators cannot be explained just by their low gamma, but are due to the complicated flow structure, consequence of the angular momentum stored at large radii. X-ray emission weighted temperatures and luminosities nicely match observed values; the X-ray isophotes are boxy in case of significant galaxy rotation. Overall, it is found that rotation has an important role to explain the observational result that more rotationally supported ETGs on average show a lower X-ray emission [abridged].

Higher order statistics of curvature perturbations in IFF model and its Planck constraints [Replacement]

We compute the power spectrum P_\zeta, and non-linear parameters f_nl and \tau_nl of the curvature perturbation induced during inflation by the electromagnetic fields in the kinetic coupling model (IFF model). By using the observational result of P_\zeta, f_nl and \tau_nl reported by the Planck collaboration, we study the constraint on the model comprehensively. Interestingly, if the single slow-rolling inflaton is responsible for the observed P_\zeta, the constraint from \tau_nl is most stringent. We also find a general relationship between f_nl and \tau_nl generated in this model. Even if f_nl \sim O(1), a detectable \tau_nl can be produced.

Higher order statistics of curvature perturbations in IFF model and its Planck constraints

We compute the power spectrum P_\zeta, and non-linear parameters f_nl and \tau_nl of the curvature perturbation induced during inflation by the electromagnetic fields in the kinetic coupling model (IFF model). By using the observational result of P_\zeta, f_nl and \tau_nl reported by the Planck collaboration, we study the constraint on the model comprehensively. Interestingly, if the single slow-rolling inflaton is responsible for the observed P_\zeta, the constraint from \tau_nl is most stringent. We also find a general relationship between f_nl and \tau_nl generated in this model. Even if f_nl \sim O(1), a detectable \tau_nl can be produced.

Higher order statistics of curvature perturbations in IFF model and its Planck constraints [Replacement]

We compute the power spectrum P_\zeta, and non-linear parameters f_nl and \tau_nl of the curvature perturbation induced during inflation by the electromagnetic fields in the kinetic coupling model (IFF model). By using the observational result of P_\zeta, f_nl and \tau_nl reported by the Planck collaboration, we study the constraint on the model comprehensively. Interestingly, if the single slow-rolling inflaton is responsible for the observed P_\zeta, the constraint from \tau_nl is most stringent. We also find a general relationship between f_nl and \tau_nl generated in this model. Even if f_nl \sim O(1), a detectable \tau_nl can be produced.

Warping of accretion disk and launching of jet by a spinning black hole in NGC 4258 [Replacement]

We fit the most updated broadband spectral energy distribution from radio to X-rays for NGC 4258 with a coupled accretion-jet model that surrounding a Kerr black hole (BH), where both the jet and the warped H_2O maser disk are assumed to be triggered by a spinning BH through Blandford-Znajek mechanism and Bardeen-Petterson effect respectively. The accretion flow consists with an inner radiatively inefficient accretion flow (RIAF) and an outer truncated standard thin disk, where the transition radius R_tr~3*10^3Rg for NGC 4258 based on the width and variability of its narrow Fe K$\alpha$ line. The hybrid jet formation model, as a variant of Blandford-Znajek model, is used to model the jet power. Therefore, we can estimate the accretion rate and BH spin through the two observed quantities–X-ray emission and jet power, where the observed jet power is estimated from the low-frequency radio emission. Through this method, we find that the BH of NGC 4258 should be mildly spinning with dimensionless spin parameter a_*=0.7\pm0.2. The outer thin disk mainly radiates at near infrared waveband and the jet contributes predominantly at radio waveband. Using above estimated BH spin and the inferred accretion rate at the region of the maser disk based on the physical existence of the H_2 O maser, we find that the warp radius is ~8.6*10^4 R_g if it is driven by the Bardeen-Petterson effect, which is consistent with the observational result very well.

Warping of accretion disk and launching of jet by a spinning black hole in NGC 4258

We model the spectral energy distribution of NGC 4258 with updated broadband observations from radio to X-rays and a coupled accretion-jet model that surrounding a Kerr black hole (BH). The observed radio jet and the warped water maser disk are assumed to be triggered by a spinning BH through Blandford-Znajek mechanism and Bardeen-Petterson effect respectively. The accretion flow is modeled as an inner radiatively inefficient accretion flow (RIAF) and an outer truncated standard thin disk, where the transition radius is ~10^3R_g based on the width and variability of narrow Fe K_alpha line. We find that the RIAF surrounding a mildly spinning BH with dimensionless spin parameter a_*~0.73 can well reproduce the observed X-ray emission and jet power, where the observational jet power is estimated from its low-frequency radio emission. The outer thin disk mainly radiates at near infrared waveband, while the jet contributes predominantly at radio waveband. We propose that the accretion flow initially may consists a two-phase disk that the cold maser disk is sandwiched by substantial hot plasma, since that Bondi radius for the diffused hot plasma is much larger than the size of the observed maser disk. This can naturally explain why the accretion rate of inner RIAF is larger than that of outer maser disk. Using above estimated BH spin and the inferred accretion rate in maser disk based on the physical existence of the water maser, we find that the warp radius of the maser disk that driven by the Bardeen-Petterson effect is ~8.8*10^4 R_g, which is consistent with the observational result very well.

Spin-orbit alignment in the very low mass binary regime: The L dwarf tight binary 2MASSW J0746425+200032AB

Studies of solar-type binaries have found coplanarity between the equatorial and orbital planes of systems with $<$40 AU separation. By comparison, the alignment of the equatorial and orbital axes in the substellar regime, and the associated implications for formation theory, are relatively poorly constrained. Here we present the discovery of the rotation period of 3.32 $\pm$ 0.15 hours from 2MASS J0746+20A – the primary component of a tight (2.7 AU) ultracool dwarf binary system (L0+L1.5). The newly discovered period, together with the established period via radio observations of the other component, and the well constrained orbital parameters and rotational velocity measurements, allow us to infer alignment of the equatorial planes of both components with the orbital plane of the system to within 10 degrees. This result suggests that solar-type binary formation mechanisms may extend down into the brown dwarf mass range, and we consider a number of formation theories that may be applicable in this case. This is the first such observational result in the very low mass binary regime. In addition, the detected period of 3.32 $\pm$ 0.15 hours implies that the reported radio period of 2.07 $\pm$ 0.002 hours is associated with the secondary star, not the primary, as was previously claimed. This in turn refutes the claimed radius of 0.78 $\pm$ 0.1 $R_{J}$ for 2MASS J0746+20A, which we demonstrate to be 0.99 $\pm$ 0.03 $R_{J}$.

Reexamination of inflation in noncommutative space-time after Planck results [Replacement]

An inflationary model in the framework of noncommutative space-time may generate a nontrivial running of the scalar spectral index, but usually induces a large tensor-to-scalar ratio simultaneously. With the latest observational data from the Planck mission, we reexamine the inflationary scenarios in a noncommutative space-time. We find that either the running of the spectral index is tiny compared with the recent observational result, or the tensor-to-scalar ratio is too large to allow a sufficient number of $e$-folds. As examples, we show that the chaotic and power-law inflation models with the noncommutative effects are not favored by the current Planck data.

Reexamination of inflation in noncommutative space-time after Planck results

An inflationary model in the framework of noncommutative space-time may generate a nontrivial running of the scalar spectral index, but usually induces a large tensor-to-scalar ratio simultaneously. With the latest observational data from the Planck mission, we reexamine the inflationary scenarios in a noncommutative space-time. We find that either the running of the spectral index is tiny compared with the recent observational result, or the tensor-to-scalar ratio is too large to allow a sufficient number of $e$-folds. As examples, we show that the chaotic and power-law inflation models with the noncommutative effects are not favored by the current Planck data.

Reexamination of inflation in noncommutative space-time after Planck results [Replacement]

An inflationary model in the framework of noncommutative space-time may generate a nontrivial running of the scalar spectral index, but usually induces a large tensor-to-scalar ratio simultaneously. With the latest observational data from the Planck mission, we reexamine the inflationary scenarios in a noncommutative space-time. We find that either the running of the spectral index is tiny compared with the recent observational result, or the tensor-to-scalar ratio is too large to allow a sufficient number of $e$-folds. As examples, we show that the chaotic and power-law inflation models with the noncommutative effects are not favored by the current Planck data.

The dependence of the mass-size relation of early-type galaxies on environment in the local Universe

The early–type galaxy (ETG) mass–size relation has been largely studied to understand how these galaxies have assembled their mass. One key observational result of the last years is that massive galaxies increased their size by a factor of a few at fixed stellar mass from z~2. Minor mergers have been put forward in hierarchical models as a plausible driver of this size growth. Some of these models, predict a significant environmental dependence in the sense that galaxies residing in more massive halos tend to be larger than galaxies in lower mass halos, at fixed stellar mass and redshift. At present, observational results of this environmental dependence have been contradictory. In this paper we revisit this issue in the local Universe, by carefully investigating how the sizes of massive ETGs depend on large-scale environment using an updated and accurate sample of massive ETGs (>10^{11}) in different environments – field, group, clusters – from the Sloan Digital Sky Survey DR7. Observations do not show any environmental dependence of the sizes of central and satellites ETGs at fixed stellar mass. The size-mass relation of early-type galaxies seems to be universal, i.e., independent of the mass of the host halo and of the position of the galaxy in that halo (central or satellite). We compare our observational results with two hierarchical models built from the Millennium Simulation. Once observational errors are properly included in model predictions, we find our results to broadly agree (at 1-2 sigma level) with one of the models, but strongly disagree with the other (at ~3sigma level), proving how useful environment is in testing galaxy evolution models.

Parameters of rotating neutron stars with and without hyperons

The discovery of a 2 Msun neutron star provided a robust constraint for the theory of exotic dense matter, questioning the existence of strange baryons in the interiors of neutron stars. With many theories failing to reproduce this observational result, several equations of state containing hyperons are consistent with it. We study global properties of stars using equations of state containing hyperons, and compare them to those without hyperons in order to find similarities, differences and limits that can be compared with the astrophysical observations. Rotating, axisymmetric and stationary stellar configurations in General Relativity are obtained, and their global parameters are studied. Approximate formulae describing the behavior of the maximum and minimum stellar mass, compactness, surface redshifts and moments of inertia as functions of spin frequency are provided. We also study the thin disk accretion and compare the spin-up evolution of stars with different moments of inertia.

Parameters of rotating neutron stars with and without hyperons [Replacement]

The discovery of a 2 Msun neutron star provided a robust constraint for the theory of exotic dense matter, bringing into question the existence of strange baryons in the interiors of neutron stars. Although many theories fail to reproduce this observational result, several equations of state containing hyperons are consistent with it. We study global properties of stars using equations of state containing hyperons, and compare them to those without hyperons to find similarities, differences, and limits that can be compared with the astrophysical observations. Rotating, axisymmetric, and stationary stellar configurations in general relativity are obtained, and their global parameters are studied. Approximate formulae describing the behavior of the maximum and minimum stellar mass, compactness, surface redshifts, and moments of inertia as functions of spin frequency are provided. We also study the thin disk accretion and compare the spin-up evolution of stars with different moments of inertia.

Differential Emission Measure Analysis of Multiple Structural Components of Coronal Mass Ejections in the Inner Corona

In this paper, we study the temperature and density properties of multiple structural components of coronal mass ejections (CMEs) using differential emission measure (DEM) analysis. The DEM analysis is based on the six-passband EUV observations of solar corona from the Atmospheric Imaging Assembly onboard the \emph{Solar Dynamic Observatory}. The structural components studied include the hot channel in the core region (presumably the magnetic flux rope of the CME), the bright loop-like leading front (LF), and coronal dimming in the wake of the CME. We find that the presumed flux rope has the highest average temperature ($>$8 MK) and density ($\sim$1.0 $\times10^{9}$ cm$^{-3}$), resulting in an enhanced emission measure (EM) over a broad temperature range (3 $\leq$ T(MK) $\leq$ 20). On the other hand, the CME LF has a relatively cool temperature ($\sim$2 MK) and a narrow temperature distribution similar to the pre-eruption coronal temperature (1 $\leq$ T(MK) $\leq$ 3). The density in the LF, however, is increased by 2% to 32% compared with that of the pre-eruption corona, depending on the event and location. In coronal dimmings, the temperature is more broadly distributed (1 $\leq$ T(MK) $\leq$ 4), but the density decreases by $\sim$35% to $\sim$40%. These observational results show that: (1) CME core regions are significantly heated, presumably through magnetic reconnection, (2) CME LFs are a consequence of compression of ambient plasma caused by the expansion of the CME core region, and (3) the dimmings are largely caused by the plasma rarefaction associated with the eruption.

Rotational periods and evolutionary models for subgiant stars observed by CoRoT

We present rotation period measurements for subgiants observed by CoRoT. Interpreting the modulation of stellar light that is caused by star-spots on the time scale of the rotational period depends on knowing the fundamental stellar parameters. Constraints on the angular momentum distribution can be extracted from the true stellar rotational period. By using models with an internal angular momentum distribution and comparing these with measurements of rotation periods of subgiant stars we investigate the agreement between theoretical predictions and observational results. With this comparison we can also reduce the global stellar parameter space compatible with the rotational period measurements from subgiant light curves. We can prove that an evolution assuming solid body rotation is incompatible with the direct measurement of the rotational periods of subgiant stars. Measuring the rotation periods relies on two different periodogram procedures, the Lomb-Scargle algorithm and the Plavchan periodogram. Angular momentum evolution models were computed to give us the expected rotation periods for subgiants, which we compared with measured rotational periods. We find evidence of a sinusoidal signal that is compatible in terms of both phase and amplitude with rotational modulation. Rotation periods were directly measured from light curves for 30 subgiant stars and indicate a range of 30 to 100 d for their rotational periods. Our models reproduce the rotational periods obtained from CoRoT light curves. These new measurements of rotation periods and stellar models probe the non-rigid rotation of subgiant stars.

Data analysis challenges in transient gravitational-wave astronomy [Cross-Listing]

Gravitational waves are radiative solutions of space-time dynamics predicted by Einstein’s theory of General Relativity. A world-wide array of large-scale and highly-sensitive interferometric detectors constantly scrutinizes the geometry of the local space-time with the hope to detect deviations that would signal an impinging gravitational wave from a remote astrophysical source. Finding the rare and weak signature of gravitational waves buried in non-stationary and non-Gaussian instrument noise is a particularly challenging problem. We will give an overview of the data-analysis techniques and associated observational results obtained so far by Virgo (in Europe) and LIGO (in the US), along with the prospects offered by the up-coming advanced versions of those detectors.

Fermi Limit of the Neutrino Flux from Gamma-ray Bursts

If gamma-ray bursts (GRBs) produce high energy cosmic rays, neutrinos are expected to be generated in GRBs due to photo-pion productions. However we stress that the same process also generates electromagnetic (EM) emission induced by the production of secondary electrons and photons, and that the EM emission is expected to be correlated to the neutrino flux. Using the Fermi observational results on gamma-ray flux from GRBs, the GRB neutrino emission is limited to be below ~20 GeV/m^2 per GRB event on average, which is independent of the unknown GRB proton luminosity. This neutrino limit suggests that the full IceCube needs stacking more than 370 GRBs in order to detect one GRB muon neutrino. The Fermi observations of GRBs also imply that the ratio between energy in the accelerated protons and electrons is f_p<~10.

Cross-correlating cosmic IR and X-ray background fluctuations: evidence of significant black hole populations among the CIB sources

In order to understand the nature of the sources producing the recently uncovered CIB fluctuations, we study cross-correlations between the fluctuations in the source-subtracted Cosmic Infrared Background (CIB) from Spitzer/IRAC data and the unresolved Cosmic X-ray Background (CXB) from deep Chandra observations. Our study uses data from the EGS/AEGIS field, where both datasets cover an ~8′x45′ region of the sky. Quantitatively, our measurement is the cross-power spectrum between the IR and X-ray data which we detect to be statistically significant and positive at angular scales >20" where the source-subtracted CIB fluctuations in the Spitzer data are dominated by the clustering component. The cross-power signal between the IRAC maps at 3.6 um and 4.5 um and the Chandra [0.5-2] keV data has been detected with the overall significance of ~3.5 sigma and ~5 sigma respectively. At the same time we find no evidence of significant cross-correlations at the harder Chandra bands. The cross-correlation signal is produced by individual IR sources with 3.6 um and 4.5 um magnitudes m_AB>25-26 and [0.5-2] keV X-ray fluxes <<7×10^-17 cgs. We determine that at least 15-25% of the large scale power of CIB fluctuations is correlated with the spatial power spectrum of the X-ray fluctuations. If this correlation is attributed to emission from accretion processes at both IR and X-ray wavelengths, this implies a much higher fraction of the accreting black holes than among the known populations. We discuss the various possible low- and high-z suspects for the discovered cross-power and show that neither local foregrounds, nor the known remaining normal galaxies and active galactic nuclei (AGN) can reproduce the measurements. These observational results are an important new constraint on theoretical modeling of the near-IR CIB fluctuations.

Low-Resolution Spectroscopy of the Recurrent Nova T Pyxidis at its Early Stage of 2011 Outburst

We present our observational results of the recurrent nova T Pyxidis at its early stage of 2011 outburst, using a low-resolution spectrograph ($R\approx400$) attached to a 28cm telescope. Total nights of our observation are 11, among which 9 nights are during the pre-maximum stage. As a result we have obtained a detailed evolutional feature of this recurrent nova on the way to its maximum light. At first, on the earliest three nights ($-25 \sim -21$ days before maximum), broad and prominent emission lines such as Balmer series, He I, He II, N II, N III and O I together with P Cygni profile are seen on the spectra. The blueshifted absorption minima of H$\alpha$ yields a maximum expansion velocity of approximately 2200 km s$^{-1}$, and the velocity gradually decreases. Then, Helium and Nitrogen lines are weakened day by day. After that (18 days before maximum light), Fe II (multiplets) lines emerge on the spectra. These lines are then strengthened day by day, and the P Cygni profiles also become more prominent. Accordingly, the expansion velocities turns to be gradual increase. In addition, during the pre-maximum stage, nova spectral type of T Pyx is thought to evolve from He/N type to Fe II one.

Maser emission during post-AGB evolution

This contribution reviews recent observational results concerning astronomical masers toward post-AGB objects with a special attention to water fountain sources and the prototypical source OH231.8+4.2. These sources represent a short transition phase in the evolution between circumstellar envelopes around asymptotic giant branch stars and planetary nebulae. The main masing species are considered and key results are summarized.

Determination of the stars fundamental parameters using seismic scaling relations

Seismology of stars that exhibit solar-like oscillations develops a growing interest with the wealth of observational results obtained with the CoRoT and Kepler space-borne missions. In this framework, relations between asteroseismic quantities and stellar parameters provide a unique opportunity to derive model-independent determinations of stellar parameters (e.g., masses and radii) for a large sample of stars. I review those scaling relations with particular emphasis on the underlying physical processes governing those relations, as well as their uncertainties.

Physical and dynamical characterisation of low Delta-V NEA (190491) 2000 FJ10

We investigated the physical properties and dynamical evolution of Near Earth Asteroid (NEA) (190491) 2000 FJ10 in order to assess the suitability of this accessible NEA as a space mission target. Photometry and colour determination were carried out with the 1.54 m Kuiper Telescope and the 10 m Southern African Large Telescope during the object’s recent favourable apparition in 2011-12. During the earlier 2008 apparition, a spectrum of the object in the 6000-9000 Angstrom region was obtained with the 4.2 m William Herschel Telescope. Interpretation of the observational results was aided by numerical simulations of 1000 dynamical clones of 2000 FJ10 up to 10^6 yr in the past and in the future. The asteroid’s spectrum and colours determined by our observations suggest a taxonomic classification within the S-complex although other classifications (V, D, E, M, P) cannot be ruled out. On this evidence, it is unlikely to be a primitive, relatively unaltered remnant from the early history of the solar system and thus a low priority target for robotic sample return. Our photometry placed a lower bound of 2 hrs to the asteroid’s rotation period. Its absolute magnitude was estimated to be 21.54+-0.1 which, for a typical S-complex albedo, translates into a diameter of 130+-20 m. Our dynamical simulations show that it has likely been an Amor for the past 10^5 yr. Although currently not Earth-crossing, it will likely become so during the period 50 – 100 kyr in the future. It may have arrived from the inner or central Main Belt > 1 Myr ago as a former member of a low-inclination S-class asteroid family. Its relatively slow rotation and large size make it a suitable destination for a human mission. We show that ballistic Earth-190491-Earth transfer trajectories with Delta-V < 2 km s^-1 at the asteroid exist between 2052 and 2061.

High-Resolution Spectroscopy of Extremely Metal-Poor Stars from SDSS/SEGUE: I. Atmospheric Parameters and Chemical Compositions

Chemical compositions are determined based on high-resolution spectroscopy for 137 candidate extremely metal-poor (EMP) stars selected from the Sloan Digital Sky Survey (SDSS) and its first stellar extension, the Sloan Extension for Galactic Understanding and Exploration (SEGUE). High-resolution spectra with moderate signal-to-noise (S/N) ratios were obtained with the High Dispersion Spectrograph of the Subaru Telescope. Most of the sample (approximately 80%) are main-sequence turn-off stars, including dwarfs and subgiants. Four cool main-sequence stars, the most metal-deficient such stars known, are included in the remaining sample. Good agreement is found between effective temperatures estimated by the SEGUE stellar parameter pipeline, based on the SDSS/SEGUE medium-resolution spectra, and those estimated from the broadband $(V-K)_0$ and $(g-r)_0$ colors. Our abundance measurements reveal that 70 stars in our sample have [Fe/H] $ < -3$, adding a significant number of EMP stars to the currently known sample. Our analyses determine the abundances of eight elements (C, Na, Mg, Ca, Ti, Cr, Sr, and Ba) in addition to Fe. The fraction of carbon-enhanced metal-poor stars ([C/Fe]$> +0.7$) among the 25 giants in our sample is as high as 36%, while only a lower limit on the fraction (9%) is estimated for turn-off stars. This paper is the first of a series of papers based on these observational results. The following papers in this series will discuss the higher-resolution and higher-S/N observations of a subset of this sample, the metallicity distribution function, binarity, and correlations between the chemical composition and kinematics of extremely metal-poor stars.

Testing Hadronic Models of Gamma Ray Production at the Core of Cen A

Pierre Auger experiment has observed a few cosmic ray events above 55 EeV from the direction of the core of Cen A.These cosmic rays might have originated from the core of Cen A. High energy gamma ray emission has been observed by HESS from the radio core and inner kpc jets of Cen A. We are testing whether pure hadronic interactions of protons or heavy nuclei with the matter at the core or photo-disintegration of heavy nuclei at the core can explain the cosmic ray and high energy gamma ray observations from the core of Cen A. The scenario of $p-\gamma$ interactions followed by photo-pion decay has been tested earlier by Sahu et al. (2012) and found to be consistent with the observational results. In this paper we have considered some other possibilities (i) the primary cosmic rays at the core of Cen A are protons and the high energy gamma rays are produced in $p-p$ interactions,(ii) the primary cosmic rays are Fe nuclei and the high energy gamma rays are produced in $Fe-p$ interactions and (iii) the primary cosmic rays are Fe nuclei and they are photo-disintegrated at the core. The daughter nuclei de-excite and high energy gamma rays are produced. The high energy gamma ray fluxes expected in each of these cases are compared with the flux observed by HESS experiment to normalise the spectrum of the primary cosmic rays at the core. We have calculated the expected number of cosmic ray nucleon events between 55 EeV and 150 EeV in each of these cases to verify the consistencies of the different scenarios with the observations by Pierre Auger experiment. We find that if the primary cosmic rays are Fe nuclei then their photo-disintegration followed by de-excitation of daughter nuclei can explain the observed high energy particle emissions from the core of Cen A.

Baryon Census in Hydrodynamical Simulations of Galaxy Clusters

We carry out an analysis of a set of cosmological SPH hydrodynamical simulations of galaxy clusters and groups aimed at studying the total baryon budget in clusters, and how this budget is shared between the hot diffuse component and the stellar component. Using the TreePM+SPH GADGET-3 code, we carried out one set of non-radiative simulations, and two sets of simulations including radiative cooling, star formation and feedback from supernovae (SN), one of which also accounting for the effect of feedback from active galactic nuclei (AGN). The analysis is carried out with the twofold aim of studying the implication of stellar and hot gas content on the relative role played by SN and AGN feedback, and to calibrate the cluster baryon fraction and its evolution as a cosmological tool. We find that both radiative simulation sets predict a trend of stellar mass fraction with cluster mass that tends to be weaker than the observed one. However this tension depends on the particular set of observational data considered. Including the effect of AGN feedback alleviates this tension on the stellar mass and predicts values of the hot gas mass fraction and total baryon fraction to be in closer agreement with observational results. We further compute the ratio between the cluster baryon content and the cosmic baryon fraction, Y_b, as a function of cluster-centric radius and redshift. At R_500 we find for massive clusters with M_500>2\times10^{14} h^{-1} M_sun that Y_b is nearly independent of the physical processes included and characterized by a negligible redshift evolution: Y_{b,500}=0.85+/-0.05 with the error accounting for the intrinsic r.m.s. scatter within the set of simulated clusters. At smaller radii, R_2500, the typical value of Y_b slightly decreases, by an amount that depends on the physics included in the simulations, while its scatter increases by about a factor of two.

Investigating Supergiant Fast X-ray Transients with LOFT

Supergiant Fast X-ray Transients (SFXT) are a class of High-Mass X-ray Binaries whose optical counterparts are O or B supergiant stars, and whose X-ray outbursts are ~ 4 orders of magnitude brighter than the quiescent state. LOFT, the Large Observatory For X-ray Timing, with its coded mask Wide Field Monitor (WFM) and its 10 m^2 class collimated X-ray Large Area Detector (LAD), will be able to dramatically deepen the knowledge of this class of sources. It will provide simultaneous high S/N broad-band and time-resolved spectroscopy in several intensity states, and long term monitoring that will yield new determinations of orbital periods, as well as spin periods. We show the results of an extensive set of simulations performed using previous observational results of these sources obtained with Swift and XMM-Newton. The WFM will detect all SFXT flares within its field of view down to a 15-20 mCrab in 5ks. Our simulations describe the outbursts at several intensities (F_(2-10keV)=5.9×10^-9 to 5.5×10^-10 erg cm^-2 s^-1), the intermediate and most common state (10^-11 erg cm^-2 s^-1), and the low state (1.2×10^-12 to 5×10^-13 erg cm^-2 s^-1). We also considered large variations of N_H and the presence of emission lines, as observed by Swift and XMM-Newton.

Identifying Contaminated K-band Globular Cluster RR Lyrae Photometry

Acquiring near-infrared K-band (2.2 um) photometry for RR Lyrae variables in globular clusters and nearby galaxies is advantageous since the resulting distances are less impacted by reddening and metallicity. However, K-band photometry for RR Lyrae variables in M5, Reticulum, M92, omega Cen, and M15 display clustercentric trends. HST ACS data imply that multiple stars in close proximity to RR Lyrae variables located near the cluster core, where the stellar density increases markedly, are generally unresolved in ground-based images. RR Lyrae variables near the cluster cores appear to suffer from photometric contamination, thereby yielding underestimated cluster distances and biased ages. The impact is particularly pernicious since the contamination propagates a systematic uncertainty into the distance scale, and hinders the quest for precision cosmology. The clustercentric trends are probably unassociated with variations in chemical composition since an empirical K-band period-magnitude relation inferred from Araucaria/VLT data for RR Lyrae variables in the Sculptor dSph exhibits a negligible metallicity dependence: (0.059+-0.095)[Fe/H], a finding that supports prior observational results. A future multi-epoch high-resolution near-infrared survey, analogous to the optical HST ACS Galactic Globular Cluster Survey, may be employed to establish K-band photometry for the contaminating stars discussed here.

Gravitational lensing with $ f(\chi)=\chi^{3/2} $ gravity in accordance with astrophysical observations

In this article we perform a second order perturbation analysis of the gravitational metric theory of gravity $ f(\chi) = \chi^{3/2} $ developed by Bernal et al. (2011). We show that the theory is capable to account exactly for two observational facts: (1) the phenomenology of flattened rotation curves through the Tully-Fisher relation observed in spiral galaxies, and (2) the details of observations of gravitational lensing in galaxies and groups of galaxies, without the need of any dark matter. We show how all dynamical observations on flat rotation curves and gravitational lensing can be synthesised in terms of the empirically required metric coefficients of any metric theory of gravity. We construct the corresponding metric components for the theory presented at second order in perturbation, which are shown to be perfectly compatible with the empirically derived ones. It is also shown that, in order to obtain a complete full agreement with the observational results, a specific signature of Riemann’s tensor has to be chosen. This signature corresponds to the one most widely used nowadays in relativity theory. Also, a computational program, the MEXICAS (Metric EXtended-gravity Incorporated through a Computer Algebraic System) code, developed for its usage in the Computer Algebraic System (CAS) Maxima for working out perturbations on a metric theory of gravity is presented and made publicly available.

Metallicity Effect on LMXB Formation in Globular Clusters [Replacement]

We present comprehensive observational results of the metallicity effect on the fraction of globular clusters (GC) that contain low-mass X-ray binaries (LMXB), by utilizing all available data obtained with Chandra for LMXBs and HST ACS for GCs. Our primary sample consists of old elliptical galaxies selected from the ACS Virgo and Fornax surveys. To improve statistics at both the lowest and highest X-ray luminosity, we also use previously reported results from other galaxies. It is well known that the LMXB fraction is considerably higher in red, metal-rich, than in blue, metal-poor GCs. In this paper, we test whether this metallicity effect is X-ray luminosity-dependent, and find that the effect holds uniformly in a wide luminosity range. This result is statistically significant (at >= 3 sigma) in LMXBs with luminosities in the range LX = 2 x 10^37 – 5 x 10^38 erg s-1, where the ratio of LMXB fractions in metal-rich to metal-poor GCs is R = 3.4 +- 0.5. A similar ratio is also found at lower (down to 10^36 erg s-1) and higher luminosities (up to the ULX regime), but with less significance (~2 sigma confidence). Because different types of LMXBs dominate in different luminosities, our finding requires a new explanation for the metallicity effect in dynamically formed LMXBs. We confirm that the metallicity effect is not affected by other factors such as stellar age, GC mass, stellar encounter rate, and galacto-centric distance.

Metallicity Effect on LMXB Formation in Globular Clusters

We present comprehensive observational results of the metallicity effect on the fraction of globular clusters (GC) that contain low-mass X-ray binaries (LMXB), by utilizing all available data obtained with Chandra for LMXBs and HST ACS for GCs. Our primary sample consists of old elliptical galaxies selected from the ACS Virgo and Fornax surveys. To improve statistics at both the lowest and highest X-ray luminosity, we also use previously reported results from other galaxies. It is well known that the LMXB fraction is considerably higher in red, metal-rich, than in blue, metal-poor GCs. In this paper, we test whether this metallicity effect is X-ray luminosity-dependent, and find that the effect holds uniformly in a wide luminosity range. This result is statistically significant (at >= 3 sigma) in LMXBs with luminosities in the range LX = 2 x 10^37 – 5 x 10^38 erg s-1, where the ratio of LMXB fractions in metal-rich to metal-poor GCs is R = 3.4 +- 0.5. A similar ratio is also found at lower (down to 10^36 erg s-1) and higher luminosities (up to the ULX regime), but with less significance (~2 sigma confidence). Because different types of LMXBs dominate in different luminosities, our finding requires a new explanation for the metallicity effect in dynamically formed LMXBs. We confirm that the metallicity effect is not affected by other factors such as stellar age, GC mass, stellar encounter rate, and galacto-centric distance.

A unified picture of breaks and truncations in spiral galaxies from SDSS and S^{4}G imaging

The mechanism causing breaks in the radial surface brightness distribution of spiral galaxies is not yet well known. Despite theoretical efforts, there is not a unique explanation for these features and the observational results are not conclusive. In an attempt to address this problem, we have selected a sample of 34 highly inclined spiral galaxies present both in the Sloan Digital Sky Survey and in the Spitzer Survey of Stellar Structure in Galaxies. We have measured the surface brightness profiles in the five Sloan optical bands and in the 3.6$\mu m$ Spitzer band. We have also calculated the color and stellar surface mass density profiles using the available photometric information, finding two differentiated features: an innermost break radius at distances of $\sim 8 \pm 1$ kpc [$0.77 \pm 0.06$ $R_{25}$] and a second characteristic radius, or truncation radius, close to the outermost optical extent ($\sim 14 \pm 2$ kpc [$1.09 \pm 0.05$ $R_{25}$]) of the galaxy. We propose in this work that the breaks might be a phenomena related to a threshold in the star formation, while truncations are more likely a real drop in the stellar mass density of the disk associated with the maximum angular momentum of the stars.

A unified picture of breaks and truncations in spiral galaxies from SDSS and S^{4}G imaging [Replacement]

The mechanism causing breaks in the radial surface brightness distribution of spiral galaxies is not yet well known. Despite theoretical efforts, there is not a unique explanation for these features and the observational results are not conclusive. In an attempt to address this problem, we have selected a sample of 34 highly inclined spiral galaxies present both in the Sloan Digital Sky Survey and in the Spitzer Survey of Stellar Structure in Galaxies. We have measured the surface brightness profiles in the five Sloan optical bands and in the 3.6$\mu m$ Spitzer band. We have also calculated the color and stellar surface mass density profiles using the available photometric information, finding two differentiated features: an innermost break radius at distances of $\sim 8 \pm 1$ kpc [$0.77 \pm 0.06$ $R_{25}$] and a second characteristic radius, or truncation radius, close to the outermost optical extent ($\sim 14 \pm 2$ kpc [$1.09 \pm 0.05$ $R_{25}$]) of the galaxy. We propose in this work that the breaks might be a phenomena related to a threshold in the star formation, while truncations are more likely a real drop in the stellar mass density of the disk associated with the maximum angular momentum of the stars.

Phase transitions of Neutron stars and its connection with high energetic bursts in astrophysics

Neutron stars (NS) can be made of normal hadronic matter (generally called NS) or they can have exotic states of matter in their interiors, like quark matter or color superconducting matter. Stars can have such exotic states up to their surface (called strange stars (SS)) or they can only have a quark core surrounded by hadronic matter, known as hybrid stars (HS). The hybrid stars is likely to have a mixed phase, such as both hadron and quark phases, in the intermediate region. Observational results also suggest huge surface magnetic field in certain compact stars called magnetars. The conversion of NS to SS/HS is a highly energetic process, in such conversion, the equations of state (EOS) of matter changes, resulting in the change in their masses. Special theory of relativity relates mass to energy, therefore such conversion leads to huge energy release, of the order of $10^{53}$ ergs. In this work we study the energy released by such conversion process. We also study the energy released by normal pulsars and magnetars. The final state of the star after conversion may be a SS or a HS, we have calculated the energy released for these final states. The energy released in the conversion of NS to SS is greater than the energy released in the conversion of NS to HS. We study the effect of magnetic field in the EOS. We find that if the magnetic field strength is of the order of $10^{14}$G or more, the effect in the EOS is significant and thereby the effect of the conversion process. The energy released by magnetars is found to be more than that of normal pulsars, for NS to SS conversion process, whereas for the conversion of NS to HS the energy released by magnetars is less than normal pulsars. The amount of energy released by such conversion may only be compared to the energy observed in the gamma ray bursts (GRB).

High cadence spectropolarimetry of moving magnetic features observed around a pore

Moving magnetic features (MMFs) are small-size magnetic elements that are seen to stream out from sunspots, generally during their decay phase. Several observational results presented in the literature suggest them to be closely related to magnetic filaments that extend from the penumbra of the parent spot. Nevertheless, few observations of MMFs streaming out from spots without penumbra have been reported. The literature still lacks of analyses of the physical properties of these features. We investigate physical properties of monopolar MMFs observed around a small pore that had developed penumbra in the days preceding our observations and compare our results with those reported in the literature for features observed around sunspots. We analyzed NOAA 11005 during its decay phase with data acquired at the Dunn Solar Telescope in the FeI 617.3$ nm and the CaII 854.2$ nm spectral lines with IBIS, and in the G-band. The field of view showed monopolar MMFs of both polarities streaming out from the leading negative polarity pore of the observed active region. Combining different analyses of the data, we investigated the temporal evolution of the relevant physical quantities associated with the MMFs as well as the photospheric and chromospheric signatures of these features. We show that the characteristics of the investigated MMFs agree with those reported in the literature for MMFs that stream out from spots with penumbrae. Moreover, observations of at least two of the observed features suggest them to be manifestations of emerging magnetic arches.

Making Galaxies in a Cosmological Context: The Need for Early Stellar Feedback [Replacement]

We introduce the Making Galaxies in a Cosmological Context (MaGICC) program of smoothed particle hydrodynamics (SPH) simulations. We describe a parameter study of galaxy formation simulations of an L* galaxy that uses early stellar feedback combined with supernova feedback to match the stellar mass–halo mass relationship. While supernova feedback alone can reduce star formation enough to match the stellar mass–halo mass relationship, the galaxy forms too many stars before z=2 to match the evolution seen using abundance matching. Our early stellar feedback is purely thermal and thus operates like a UV ionization source as well as providing some additional pressure from the radiation of massive, young stars. The early feedback heats gas to >10^6 K before cooling to 10^4 K. The pressure from this hot gas creates a more extended disk and prevents more star formation prior to z=1 than supernovae feedback alone. The resulting disk galaxy has a flat rotation curve, an exponential surface brightness profile, and matches a wide range of disk scaling relationships. The disk forms from the inside-out with an increasing exponential scale length as the galaxy evolves. Overall, early stellar feedback helps to simulate galaxies that match observational results at low and high redshifts.

Making Galaxies in a Cosmological Context: The Need for Early Stellar Feedback

We introduce the Making Galaxies in a Cosmological Context (MaGICC) program of smoothed particle hydrodynamics (SPH) simulations. We describe a parameter study of galaxy formation simulations of an L* galaxy that uses early stellar feedback combined with supernova feedback to match the stellar mass–halo mass relationship. While supernova feedback alone can reduce star formation enough to match the stellar mass–halo mass relationship, the galaxy forms too many stars before z=2 to match the evolution seen using abundance matching. Our early stellar feedback is purely thermal and thus operates in a fundamentally different way than radiation pressure. The main effect of our implementation of early stellar feedback is to preheat the interstellar medium so that supernovae can drive outflows. The stronger feedback reduces the star formation efficiency beyond what supernovae alone can accomplish. As a result of the early stellar feedback, simulations produce a disk galaxy with a flat rotation curve, an exponential surface brightness profile that are also able to match a wide range of disk scaling relationships. The disk forms from the inside-out with an increasing exponential scale length as the galaxy evolves. Overall, early stellar feedback helps to simulate galaxies that match observational results at low and high redshifts.

The influence of superstructures on bright galaxy environments: clustering properties

We analyse the dependence of clustering properties of galaxies as a function of their large-scale environment. In order to characterize the environment on large scales, we use the catalogue of future virialized superstructures (FVS) by Luparello (2011) and separate samples of luminous galaxies according to whether or not they belong to FVS. In order to avoid biases in the selection of galaxies, we have constructed different subsamples so that the distributions of luminosities and masses are comparable outside and within FVS. As expected, at large scales, there is a strong difference between the clustering of galaxies inside and outside FVS. However, this behaviour changes at scales r $\le$ 1 $h^{-1}$ Mpc, where the correlations have similar amplitudes. The amplitude of the two-halo term of the correlation function for objects inside FVS does not depend on their mass, but rather on that of the FVS. This is confirmed by comparing this amplitude with that expected from extended Press-Schechter fits. In order to compare these observational results with current models for structure formation, we have performed a similar analysis using a semi-analytic implementation in a $\Lambda$CDM cosmological model. We find that the cross-correlation functions from the mock catalogue depend on the large-scale structures in a similar way to the observations. From our analysis, we conclude that the clustering of galaxies within the typical virialized regions of groups, mainly depends on the halo mass, irrespective of the large-scale environment.

The influence of superstructures on bright galaxy environments: clustering properties [Replacement]

We analyse the dependence of clustering properties of galaxies as a function of their large-scale environment. In order to characterize the environment on large scales, we use the catalogue of future virialized superstructures (FVS) by Luparello et al. and separate samples of luminous galaxies according to whether or not they belong to FVS. In order to avoid biases in the selection of galaxies, we have constructed different subsamples so that the distributions of luminosities and masses are comparable outside and within FVS. As expected, at large scales, there is a strong difference between the clustering of galaxies inside and outside FVS. However, this behaviour changes at scales r < 1 Mpc/h, where the correlations have similar amplitudes. The amplitude of the two-halo term of the correlation function for objects inside FVS does not depend on their mass, but rather on that of the FVS. This is confirmed by comparing this amplitude with that expected from extended Press-Schechter fits. In order to compare these observational results with current models for structure formation, we have performed a similar analysis using a semi-analytic implementation in a LCDM cosmological model. We find that the cross-correlation functions from the mock catalogue depend on the large-scale structures in a similar way to the observations. From our analysis, we conclude that the clustering of galaxies within the typical virialized regions of groups, mainly depends on the halo mass, irrespective of the large-scale environment.

Mixed phase in a compact star with strong magnetic field

Compact stars can have either hadronic matter or can have exotic states of matter like strange quark matter or color superconducting matter. Stars also can have a quark core surrounded by hadronic matter, known as hybrid stars (HS). The HS is likely to have a mixed phase in between the hadron and quark phase. Observational results suggest huge surface magnetic field in certain neutron stars (NS) called magnetars. Here we study the effect of strong magnetic field on the respective EOS of matter under extreme conditions. We further study the hadron-quark phase transition in the interiors of NS giving rise to hybrid stars (HS) in presence of strong magnetic field. The hadronic matter EOS is described based on relativistic mean field theory and we include the effect of strong magnetic fields leading to Landau quantization of the charged particles. For the quark phase we use the simple MIT bag model. We assume density dependent bag pressure and magnetic field. The magnetic field strength increases going from the surface to the center of the star. We construct the intermediate mixed phase using Glendenning conjecture. The magnetic field softens the EOS of both the matter phases. The effect of magnetic field is insignificant unless the field strength is above $10^{14}$G. A varying magnetic field, with surface field strength of $10^{14}$G and the central field strength of the order of $10^{17}$G has significant effect on both the stiffness and the mixed phase regime of the EOS. We finally study the mass-radius relationship for such type of mixed HS, calculating their maximum mass, and compare them with the recent observation of pulsar PSR J1614-2230, which is about 2 solar mass. The observations puts a severe constraint on the EOS of matter at extreme conditions. The maximum mass with our EOS can reach the limit set by the observation.

Mixed phase in a compact star with strong magnetic field [Replacement]

Compact stars can have either hadronic matter or can have exotic states of matter like strange quark matter or color superconducting matter. Stars also can have a quark core surrounded by hadronic matter, known as hybrid stars (HS). The HS is likely to have a mixed phase in between the hadron and quark phase. Observational results suggest huge surface magnetic field in certain neutron stars (NS) called magnetars. Here we study the effect of strong magnetic field on the respective EOS of matter under extreme conditions. We further study the hadron-quark phase transition in the interiors of NS giving rise to hybrid stars (HS) in presence of strong magnetic field. The hadronic matter EOS is described based on relativistic mean field theory and we include the effect of strong magnetic fields leading to Landau quantization of the charged particles. For the quark phase we use the simple MIT bag model. We assume density dependent bag pressure and magnetic field. The magnetic field strength increases going from the surface to the center of the star. We construct the intermediate mixed phase using Glendenning conjecture. The magnetic field softens the EOS of both the matter phases. The effect of magnetic field is insignificant unless the field strength is above $10^{14}$G. A varying magnetic field, with surface field strength of $10^{14}$G and the central field strength of the order of $10^{17}$G has significant effect on both the stiffness and the mixed phase regime of the EOS. We finally study the mass-radius relationship for such type of mixed HS, calculating their maximum mass, and compare them with the recent observation of pulsar PSR J1614-2230, which is about 2 solar mass. The observations puts a severe constraint on the EOS of matter at extreme conditions. The maximum mass with our EOS can reach the limit set by the observation.

CID: Chemistry In Disks VII. First detection of HC3N in protoplanetary disks

Molecular line emission from protoplanetary disks is a powerful tool to constrain their physical and chemical structure. Nevertheless, only a few molecules have been detected in disks so far. We take advantage of the enhanced capabilities of the IRAM 30m telescope by using the new broad band correlator (FTS) to search for so far undetected molecules in the protoplanetary disks surrounding the TTauri stars DM Tau, GO Tau, LkCa 15 and the Herbig Ae star MWC 480. We report the first detection of HC3N at 5 sigma in the GO Tau and MWC 480 disks with the IRAM 30-m, and in the LkCa 15 disk (5 sigma), using the IRAM array, with derived column densities of the order of 10^{12}cm^{-2}. We also obtain stringent upper limits on CCS (N < 1.5 x 10^{12} cm^{-3}). We discuss the observational results by comparing them to column densities derived from existing chemical disk models (computed using the chemical code Nautilus) and based on previous nitrogen and sulfur-bearing molecule observations. The observed column densities of HC3N are typically two orders of magnitude lower than the existing predictions and appear to be lower in the presence of strong UV flux, suggesting that the molecular chemistry is sensitive to the UV penetration through the disk. The CCS upper limits reinforce our model with low elemental abundance of sulfur derived from other sulfur-bearing molecules (CS, H2S and SO).

GREGOR Fabry-Perot Interferometer - status report and prospects

The GREGOR Fabry-Perot Interferometer (GFPI) is one of three first-light instruments of the German 1.5-meter GREGOR solar telescope at the Observatorio del Teide, Tenerife, Spain. The GFPI allows fast narrow-band imaging and post-factum image restoration. The retrieved physical parameters will be a fundamental building block for understanding the dynamic Sun and its magnetic field at spatial scales down to 50 km on the solar surface. The GFPI is a tunable dual-etalon system in a collimated mounting. It is designed for spectropolarimetric observations over the wavelength range from 530-860 nm with a theoretical spectral resolution of R ~ 250,000. The GFPI is equipped with a full-Stokes polarimeter. Large-format, high-cadence CCD detectors with powerful computer hard- and software enable the scanning of spectral lines in time spans equivalent to the evolution time of solar features. The field-of-view of 50" x 38" covers a significant fraction of the typical area of active regions. We present the main characteristics of the GFPI including advanced and automated calibration and observing procedures. We discuss improvements in the optical design of the instrument and show first observational results. Finally, we lay out first concrete ideas for the integration of a second FPI, the Blue Imaging Solar Spectrometer, which will explore the blue spectral region below 530 nm.

The influence of cosmic rays in the circumnuclear molecular gas of NGC1068

We surveyed the circumnuclear disk of the Seyfert galaxy NGC1068 between the frequencies 86.2 GHz and 115.6 GHz, and identified 17 different molecules. Using a time and depth dependent chemical model we reproduced the observational results, and show that the column densities of most of the species are better reproduced if the molecular gas is heavily pervaded by a high cosmic ray ionization rate of about 1000 times that of the Milky Way. We discuss how molecules in the NGC1068 nucleus may be influenced by this external radiation, as well as by UV radiation fields.

Ionization Parameter as a Diagnostic of Radiation and Wind Pressures in H II Regions and Starburst Galaxies

The ionization parameter U is potentially useful for measuring radiation pressure feedback from massive star clusters, as it reflects the radiation-to-gas-pressure ratio and is readily derived from mid-infrared line ratios. We consider several effects which determine the apparent value of U in HII regions and galaxies. An upper limit is set by the compression of gas by radiation pressure. The pressure from stellar winds and the presence of neutral clumps both reduce U for a given radiation intensity. The most intensely irradiated regions are selectively dimmed by internal dust absorption of ionizing photons, inducing observational bias on galactic scales. We explore these effects analytically and numerically, and use them to interpret previous observational results. We find that radiation confinement sets the upper limit log_10 U = -1 seen in individual regions. Unresolved starbursts display a maximum value of ~ -2.3. While lower, this is also consistent with a large portion of their HII regions being radiation dominated, given the different technique used to interpret unresolved regions, and given the bias caused by dust absorption. We infer that many individual, strongly illuminated regions cannot be dominated by stellar winds, and that even when averaged on galactic scales, shocked wind pressures cannot be large compared to radiation pressure. Therefore, most HII regions cannot be adiabatic wind bubbles. Our models imply a metallicity dependence in the physical structure and dust attenuation of radiation-dominated regions, both of which should vary strongly across a critical metallicity of about one-twentieth solar.

Magnetization of cloud cores and envelopes and other observational consequences of reconnection diffusion [Replacement]

Recent observational results for magnetic fields in molecular clouds reviewed by Crutcher (2012) seem to be inconsistent with the predictions of the ambipolar diffusion theory of star formation. These include the measured decrease in mass to flux ratio between envelopes and cores, the failure to detect any self-gravitating magnetically subcritical clouds, the determination of the flat PDF of the total magnetic field strengths implying that there are many clouds with very weak magnetic fields, and the observed scaling $B \propto \rho^{2/3}$ that implies gravitational contraction with weak magnetic fields. We consider the problem of magnetic field evolution in turbulent molecular clouds and discuss the process of magnetic field diffusion mediated by magnetic reconnection. For this process that we termed "reconnection diffusion" we provide a simple physical model and explain that this process is inevitable in view of the present day understanding of MHD turbulence. We address the issue of the expected magnetization of cores and envelopes in the process of star formation and show that reconnection diffusion provides an efficient removal of magnetic flux that depends only on the properties of MHD turbulence in the core and the envelope. As a result, the magnetic flux trapped during the collapse in the envelope is being released faster than the flux trapped in the core, resulting in much weaker fields in envelopes than in cores, as observed. We provide simple semi-analytical model calculations which support this conclusion and qualitatively agree with the observational results. We argue that magnetic reconnection provides a solution to the magnetic flux problem of star formation that agrees better with observations than the long-standing ambipolar diffusion paradigm.

Magnetization of cloud cores and envelopes and other observational consequences of reconnection diffusion

Recent observational results for magnetic fields in molecular clouds reviewed by Crutcher (2012) seem to be inconsistent with the predictions of the ambipolar diffusion theory of star formation. These include the measured decrease in mass to flux ratio between envelopes and cores, the failure to detect any self-gravitating magnetically subcritical clouds, the determination of the flat PDF of the total magnetic field strengths implying that there are many clouds with very weak magnetic fields, and the observed scaling $B \propto \rho^{2/3}$ that implies gravitational contraction with weak magnetic fields. We consider the problem of magnetic field evolution in turbulent molecular clouds and discuss the process of magnetic field diffusion mediated by magnetic reconnection. For this process that we termed "reconnection diffusion" we provide a simple physical model and explain that this process is inevitable in view of the present day understanding of MHD turbulence. We address the issue of the expected magnetization of cores and envelopes in the process of star formation and show that reconnection diffusion provides an efficient removal of magnetic flux that depends only on the properties of MHD turbulence in the core and the envelope. As a result, the magnetic flux trapped during the collapse in the envelope is being released faster than the flux trapped in the core, resulting in much weaker fields in envelopes than in cores, as observed. We provide simple semi-analytical model calculations which support this conclusion and qualitatively agree with the observational results. We argue that magnetic reconnection provides a solution to the magnetic flux problem of star formation that agrees better with observations than the long-standing ambipolar diffusion paradigm.

Investigation of the Forces that Govern the Three-Dimensional Propagation and Expansion of Coronal Mass Ejections from Sun to Earth

In this study, we analyze nine CMEs from the Sun to Earth as observed in both the remote sensing and in situ data sets. To date, this is the largest study of Earth impacting CMEs using the multi-view point remote sensing and in situ data. However, the remote sensing and in situ data of the same CME cannot be directly compared. Thus, we use several models to parameterize the two data sets. With the model results, we are able to compare the arrival time, Earth impact speed, internal magnetic field, size and orientation as derived from the remote sensing and in situ methods. From the derived kinematics, we compare the predicted arrival times and impact velocities with the in situ data. We find that even with nearly continuous observations and the best available model of the CME structure, there is still a significant error in the predicted values. We estimate the various forces acting on the CME as predicted by three theoretical models of CME propagation and expansion and compare these results with the observational results. We find that the flux rope model of Chen (1989) provides the best agreement with the observations. With the flux rope model, we are able to predict the internal magnetic field of the CME near Earth from the remote sensing data to an order of magnitude. Finally, we compare the size and orientation of the CMEs as predicted from the remote sensing and in situ data. We find very little agreement between the values derived from the two data sets.

The Structure and Spectral Features of a Thin Disk and Evaporation-Fed Corona in High-Luminosity AGNs

We investigate the accretion process in high-luminosity AGNs (HLAGNs) in the scenario of the disk evaporation model. Based on this model, the thin disk can extend down to the innermost stable circular orbit (ISCO) at accretion rates higher than $0.02\dot{M}_{\rm Edd}$; while the corona is weak since part of the coronal gas is cooled by strong inverse Compton scattering of the disk photons. This implies that the corona cannot produce as strong X-ray radiation as observed in HLAGNs with large Eddington ratio. In addition to the viscous heating, other heating to the corona is necessary to interpret HLAGN. In this paper, we assume that a part of accretion energy released in the disk is transported into the corona, heating up the electrons and thereby radiated away. We for the first time, compute the corona structure with additional heating, taking fully into account the mass supply to the corona and find that the corona could indeed survive at higher accretion rates and its radiation power increases. The spectra composed of bremsstrahlung and Compton radiation are also calculated. Our calculations show that the Compton dominated spectrum becomes harder with the increase of energy fraction ($f$) liberating in the corona, and the photon index for hard X-ray($2-10 \rm keV$) is $2.2 < \Gamma < 2.7 $. We discuss possible heating mechanisms for the corona. Combining the energy fraction transported to the corona with the accretion rate by magnetic heating, we find that the hard X-ray spectrum becomes steeper at larger accretion rate and the bolometric correction factor ($L_{\rm bol}/L_{\rm 2-10keV}$) increases with increasing accretion rate for $f<8/35$, which is roughly consistent with the observational results.

Afterglows after Swift

Since their discovery by the Beppo-SAX satellite in 1997, gamma-ray burst afterglows have attracted an ever-growing interest. They have allowed redshift measurements that have confirmed that gamma-ray bursts are located at cosmological distances. Their study covers a huge range both in time (from one minute to several months after the trigger) and energy (from the GeV to radio domains). The purpose of this review is first to give a short historical account of afterglow research and describe the main observational results with a special attention to the early afterglow revealed by Swift. We then present the standard afterglow model as it has been developed in the pre-Swift era and show how it is challenged by the recent Swift and Fermi results. We finally discuss different options (within the standard framework or implying a change of paradigm) that have been proposed to solve the current problems.

Afterglows after Swift [Replacement]

Since their discovery by the Beppo-SAX satellite in 1997, gamma-ray burst afterglows have attracted an ever-growing interest. They have allowed redshift measurements that have confirmed that gamma-ray bursts are located at cosmological distances. Their study covers a huge range both in time (from one minute to several months after the trigger) and energy (from the GeV to radio domains). The purpose of this review is first to give a short historical account of afterglow research and describe the main observational results with a special attention to the early afterglow revealed by Swift. We then present the standard afterglow model as it has been developed in the pre-Swift era and show how it is challenged by the recent Swift and Fermi results. We finally discuss different options (within the standard framework or implying a change of paradigm) that have been proposed to solve the current problems.

 

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