Using the 2004 Venus transit of the Sun to constrain a semi-empirical point-spread function for the TRACE EUV solar telescope, we have measured the effect of stray light in that telescope. We find that 43% of 171A EUV light that enters TRACE is scattered, either through diffraction off the entrance filter grid or through other nonspecular effects. We carry this result forward, via known-PSF deconvolution of TRACE images, to identify its effect on analysis of TRACE data. Known-PSF deconvolution by this derived PSF greatly reduces the effect of visible haze in the TRACE 171A images, enhances bright features, and reveals that the smooth background component of the corona is considerably less bright (and hence much more rarefied) than commonly supposed. Deconvolution reveals that some prior conlclusions about the Sun appear to have been based on stray light in the images. In particular, the diffuse background "quiet corona" becomes consistent with hydrostatic support of the coronal plasma; feature contrast is greatly increased, possibly affecting derived parameters such as the form of the coronal heating function; and essentially all existing differential emission measure studies of small features appear to be affected by contamination from nearby features. We speculate on further implications of stray light for interpretation of EUV images from TRACE and similar instruments, and advocate deconvolution as a standard tool for image analysis with future instruments such as SDO/AIA.
We present multi-color optical observations of long-duration gamma-ray bursts (GRBs) made over a three year period with the robotic Palomar 60 inch telescope (P60). Our sample consists of all 29 events discovered by Swift for which P60 began observations less than one hour after the burst trigger. We were able to recover 80% of the optical afterglows from this prompt sample, and we attribute this high efficiency to our red coverage. Like Melandri et al. (2008), we find that a significant fraction (~ 50%) of Swift events show a suppression of the optical flux with regards to the X-ray emission (so-called "dark" bursts). Our multi-color photometry demonstrates this is likely due in large part to extinction in the host galaxy. We argue that previous studies, by selecting only the brightest and best-sampled optical afterglows, have significantly underestimated the amount of dust present in typical GRB environments.
We present Suzaku spectra of X-ray emission in the fields just off the LMC X-3 sight line. OVII, OVIII, and NeIX emission lines are clearly detected, suggesting the presence of an optically thin thermal plasma with an average temperature of 2.4E6. This temperature is significantly higher than that inferred from existing X-ray absorption line data obtained with Chandra grating observations of LMC X-3, strongly suggesting that the gas is not isothermal. We then jointly analyze these data to characterize the spatial and temperature distributions of the gas. Assuming a vertical exponential Galactic disk model, we estimate the gas temperature and density at the Galactic plane and their scale heights as 3.6(2.9, 4.7)E6 K and 1.4(0.3, 3.4)E-3 cm^{-3} and 1.4(0.2, 5.2) kpc and $2.8(1.0, 6.4)$ kpc, respectively. This characterization can account for all the \ovi line absorption, as observed in a FUSE spectrum of LMC X-3, but only predicts less than one tenth of the OVI line emission intensity typically detected at high Galactic latitudes. The bulk of the OVI emission most likely arises at interfaces between cool and hot gases.
It has long been known that the C-14 calibration curve, which relates the
known age of tree rings to their apparent C-14 ages, includes a number of
"wiggles" which clearly are not experimental errors or other random effects. A
reasonable interpretation of these wiggles is that they indicate that the Sun's
fusion "furnace" is pulsating, perhaps for reasons similar to that of the
Cepheid variables, albeit under a very different regime of pressure and
temperature. If this speculation is correct, we are seeing the heartbeat of the
Sun-the C-14 calibration curve is the Sun's "neutrino-cardiogram." Elevated
neutrino flux during a relatively brief period would have two effects: (1) a
surge in C-14 fraction in the atmosphere, which would make biological samples
that were alive during the surge appear to be "too young" (2) depletion of C-14
in the biotic matter already dead at the time of the surge; this is a
consequence of the recently discovered Jenkins-Fischbach effect, which is an
observed correlation between nuclear decay rates and solar activity or
Earth-Sun distance.
In addition, the precise value at any given time of the "half-life" of any
unstable isotope-including C-14-must now be considered in doubt, since the
Jenkins-Fischbach effect implies that we may no longer view the decay rate of
an isotope as intrinsically governed and therefore a constant of Nature.
Transiting planets like HD209458b offer a unique opportunity to scrutinize their atmospheric composition and structure. Transit spectroscopy probes the transition region between the day and night sides, called limb. We present a re-analysis of existing archived HST/STIS transmission spectra of HD209458b's atmosphere. From these observations we: Identify H2 Rayleigh scattering, derive the absolute Sodium abundance and quantify its depletion in the upper atmosphere, extract a stratospheric T-P profile with a temperature inversion and explain broad band absorptions with the presence of TiO and VO molecules in the atmosphere of this planet.
One of the current opportunities for stellar atmospheric modeling is the interpretation of optical interferometric data of stars. Starting from the robust, open source ATLAS atmospheric code (Kururc, 1979), we have developed a spherically symmetric code, SATLAS, as a new option for modeling stellar atmospheres of low gravity stars. The SATLAS code is tested against both interferometric observations of M giants by Wittkowski and collaborators, and spherically symmetric M giant NextGen models from the PHOENIX code. The SATLAS models predict interferometric visibilities that agree with the observed visibilities and with predicted visibilities, and the SATLAS atmospheric structures also agree with those from spherical PHOENIX models, with just small differences in temperature and pressure at large depths in the atmospheres.
The purpose of this preliminary work is to determine if Large Magellanic Cloud (LMC) Cepheids have stellar winds. If a Cepheid undergoes mass loss then at some distance from the star, a fraction of the gas becomes dust, which causes an infrared excess. Mass loss is tested using OGLE II optical observations and SAGE infrared observations for a sample of 488 Cepheids. The resultant mass-loss rates range from $10^{-12}$ to $10^{-7}$ $M_\odot/yr$. Using the mass--loss model we compute infrared stellar luminosities for the sample of Cepheids and compare predicted infrared PL relations with observed relations. The predicted relations not only vary from the observed relations, implying mass loss plays a significant role, but also show evidence for non-linearity. It is determined that mass loss is important for LMC Cepheids.
We report the first discovery of the emergence of a high-velocity broad-line outflow in a luminous quasar, J105400.40+034801.2 at redshift z ~ 2.1. The outflow is evident in ultraviolet CIV and SiIV absorption lines with velocity shifts v ~ 26,300 km/s and deblended widths FWHM ~ 4000 km/s. These features are marginally strong and broad enough to be considered broad absorption lines (BALs), but their large velocities exclude them from the standard BAL definition. The outflow lines appeared between two observations in the years 2002.18 and 2006.96. A third observation in 2008.48 showed the lines becoming ~40% weaker and 10% to 15% narrower. There is no evidence for acceleration or for any outflow gas at velocities <23,000 km/s. The lines appear to be optically thick, with the absorber covering just 20% of the quasar continuum source. This indicates a characteristic absorber size of ~4 x 10^15 cm, but with a BAL-like total column density log N_H (cm^-2) > 21.2 and average space density n_H > 2 x 10^5 cm^-3. We attribute the emergence of the outflow lines to a substantial flow structure moving across our line of sight, possibly near the ragged edge of the main BAL flow or possibly related to the onset of a BAL evolutionary phase.
We determine the mass of the black hole at the center of the spiral galaxy NGC 4258 by constructing axisymmetric dynamical models of the galaxy. These models are constrained by high spatial resolution imaging and long-slit spectroscopy of the nuclear region obtained with the {\em Hubble Space Telescope}, complemented by ground-based observations extending to larger radii. Our best mass estimate is $\MBH = (3.3 \pm 0.2) \times 10^7 \MSun $ for a distance of 7.28 Mpc (statistical errors only). This is within 15% of $ (3.82\pm 0.01) \times 10^7 \MSun$, the mass determined from the kinematics of water masers (rescaled to the same distance) assuming they are in Keplerian rotation in a warped disk. The construction of accurate dynamical models of NGC 4258 is somewhat compromised by an unresolved active nucleus and color gradients, the latter caused by variations in the stellar population and/or obscuring dust. These problems are not present in the $\sim 30$ other black hole mass determinations from stellar dynamics that have been published by us and other groups; thus, the relatively close agreement between the stellar dynamical mass and the maser mass in NGC 4258 enhances our confidence in the black hole masses determined in other galaxies from stellar dynamics using similar methods and data of comparable quality.
The near future of astrophysics involves many large solid-angle, multi-epoch, multi-band imaging surveys. These surveys will, at their faint limits, have data on large numbers of sources that are too faint to be detected at any individual epoch. Here we show that it is possible to measure in multi-epoch data not only the fluxes and positions, but also the parallaxes and proper motions of sources that are too faint to be detected at any individual epoch. The method involves fitting a model of a moving point source simultaneously to all imaging, taking account of the noise and point-spread function in each image. By this method it is possible to measure the proper motion of a point source with an uncertainty close to the minimum possible uncertainty given the information in the data, which is limited by the point-spread function, the distribution of observation times (epochs), and the total signal-to-noise in the combined data. We demonstrate our technique on multi-epoch Sloan Digital Sky Survey imaging of the SDSS Southern Stripe. We show that we can distinguish very red brown dwarfs by their proper motions from very high-redshift quasars more than $1.6\mag$ fainter than with traditional technique on these SDSS data, and with better better fidelity than by multi-band imaging alone. We re-discover all 10 known brown dwarfs in our sample and present 9 new candidate brown dwarfs, identified on the basis of high proper motion.
We suggest that non-thermal emission can be produced by multiple scatterings of the photons between the supernova ejecta and pre-shock material in supernova shock breakout. Such bulk-Comptonization process may significantly change the original thermal photon spectrum, forming a power-law non-thermal component at higher energies. We then show that the luminous X-ray outburst XRO081009 associated with SN2008D is likely to be such shock breakout emission from an ordinary type Ib/c supernova.
It has long been known that a large fraction of disc galaxies are lopsided. We simulate three different mechanisms that can induce lopsidedness: flyby interactions, gas accretion from cosmological filaments and ram pressure from the intergalactic medium. Comparing the morphologies, HI spectrum and m=1 Fourier components, we find that all of these mechanisms can induce lopsidedness in the gaseous component of disc galaxies. In particular, we estimate that flybys can contribute to ~20 per cent of lopsided galaxies. We compare our simulations with the observations of NGC 891, a lopsided, edge-on galaxy with a nearby companion (UGC 1807). We find that the main properties of NGC 891 favour a flyby event for the origin of lopsidedness in this galaxy.
We present an updated spectroscopic orbit and a new visual orbit for the double-lined spectroscopic binary \sigma^2 Coronae Borealis based on radial velocity measurements at the Oak Ridge Observatory in Harvard, Massachusetts and interferometric visibility measurements at the CHARA Array on Mount Wilson. \sigma^2 CrB is composed of two Sun-like stars of roughly equal mass in a circularized orbit with a period of 1.14 days. The long baselines of the CHARA Array have allowed us to resolve the visual orbit for this pair, the shortest period binary yet resolved interferometrically, enabling us to determine component masses of 1.137 \pm 0.037 M_sun and 1.090 \pm 0.036 M_sun. We have also estimated absolute V-band magnitudes of MV (primary) = 4.35 \pm 0.02 and MV(secondary) = 4.74 \pm 0.02. A comparison with stellar evolution models indicates a relatively young age of 1-3 Gyr, consistent with the high Li abundance measured previously. This pair is the central component of a quintuple system, along with another similar-mass star, \sigma^1 CrB, in a ~ 730-year visual orbit, and a distant M-dwarf binary, \sigma CrB C, at a projected separation of ~ 10 arcmin. We also present differential proper motion evidence to show that components C & D (ADS 9979C & D) listed for this system in the Washington Double Star Catalog are optical alignments that are not gravitationally bound to the \sigma CrB system.
HIZOA J0836-43 is an extreme gas-rich ($M_{\rm{HI}}$=7.5$\times10^{10} M_{\sun}$) disk galaxy which lies hidden behind the strongly obscuring Vela region of the Milky Way. Utilizing observations from the {\it Spitzer Space Telescope}, we have found it to be a luminous infrared starburst galaxy with a star formation rate of $\sim 21 M_{\sun} \rm{yr^{-1}}$, arising from exceptionally strong molecular PAH emission ($L_{7.7\micron} = 1.50 \times 10^{9} L_{\odot}$) and far-infrared emission from cold dust. The galaxy exhibits a weak mid-infrared continuum compared to other starforming galaxies and U/LIRGs. This relative lack of emission from small grains suggests atypical interstellar medium conditions compared to other starbursts. We do not detect significant $[$Ne {\sc v}$]$ or $[$O {\sc iv}$]$, which implies an absent or very weak AGN. The galaxy possesses a prominent bulge of evolved stars and a stellar mass of 4.4($\pm$1.4)$\times10^{10} M_{\sun}$. With its plentiful gas supply and current star formation rate, a doubling of stellar mass would occur on a timescale of $\sim$2 Gyr. Compared to local galaxies, HIZOA J0836-43 appears to be a "scaled-up" spiral undergoing inside-out formation, possibly resembling stellar disk building processes at intermediate redshifts.
We compare the detection rates and redshift distributions of low-luminosity (LL) GRBs localized by Swift with those expected to be observed by the new generation satellite detectors on GLAST (now Fermi) and, in future, EXIST. Although the GLAST burst telescope will be less sensitive than Swift's in the 15--150 keV band, its large field-of-view implies that it will double Swift's detection rate of LL bursts. We show that Swift, GLAST and EXIST should detect about 1, 2 & 30 LL GRBs, respectively, over a 5-year operational period. The burst telescope on EXIST should detect LL GRBs at a rate of more than an order of magnitude greater than that of Swift's BAT. We show that the detection horizon for LL GRBs will be extended from $z \simeq 0.4$ for Swift to $z \simeq 1.1$ in the EXIST era. Also, the contribution of LL bursts to the observed GRB redshift distribution will contribute to an identifiable feature in the distribution at $z \simeq 1$.
This Letter is to investigate the physics of a newly discovered phenomenon -- contracting flare loops in the early phase of solar flares. In classical flare models, which were constructed based on the phenomenon of expansion of flare loops, an energy releasing site is put above flare loops. These models can predict that there is a vertical temperature gradient in the top of flare loops due to heat conduction and cooling effects. Therefore, the centroid of an X-ray looptop source at higher energy bands will be higher in altitude, for which we can define as normal temperature distribution. With observations made by {\it RHESSI}, we analyzed 10 M- or X-class flares (9 limb flares). For all these flares, the movement of looptop sources shows an obvious U-shaped trajectory, which we take as the signature of contraction-to-expansion of flare loops. We find that, for all these flares, normal temperature distribution does exist, but only along the path of expansion. The temperature distribution along the path of contraction is abnormal, showing no spatial order at all. The result suggests that magnetic reconnection processes in the contraction and expansion phases of these solar flares are different.
We report the gamma-ray activity from the intermediate BL Lac S5 0716+714 during observations acquired by the AGILE satellite in September and October 2007. These detections of activity were contemporaneous with a period of intense optical activity, which was monitored by GASP-WEBT. This simultaneous optical and gamma-ray coverage allows us to study in detail the light curves, time lags, gamma-ray photon spectrum, and Spectral Energy Distributions (SEDs) during different states of activity. AGILE observed the source with its two co-aligned imagers, the Gamma-Ray Imaging Detector (GRID) and the hard X-ray imager (Super-AGILE), which are sensitive to the 30 MeV-50 GeV and 18-60 keV energy ranges, respectively. Observations were completed in two different periods, the first between 2007 September 4-23, and the second between 2007 October 24-November 1. Over the period 2007 September 7-12, AGILE detected gamma-ray emission from the source at a significance level of 9.6-sigma with an average flux (E>100 MeV) of (97 +/- 15) x 10^{-8} photons cm^{-2} s^{-1}, which increased by a factor of at least four within three days. No emission was detected by Super-AGILE for the energy range 18-60 keV to a 3-sigma upper limit of 10 mCrab in 335 ksec. In October 2007, AGILE repointed toward S5 0716+714 following an intense optical flare, measuring an average flux of (47 +/- 11) x 10^{-8} photons cm^{-2} s^{-1} at a significance level of 6.0-sigma. The gamma-ray flux of S5 0716+714 detected by AGILE is the highest ever detected for this blazar and one of the most intense gamma-ray fluxes detected from a BL Lac object. The SED of mid-September appears to be consistent with the synchrotron self-Compton (SSC) emission model, but only by including two SSC components of different variabilities.
Based on 2MASS J and Ks photometry for the open star clusters NGC 2383, NGC 2384,Pismis 6, Pismis 8 and using color magnitude diagrams with isochrones fit, we found an age of $\log ({age})$ = 8.3 (200 $\pm$ 6 Myr) for NGC 2383 and $\log ({age})$ = 6.9 (8 $\pm$ 6 Myr) for NGC 2384. For Pismis 6 and Pismis 8 we adopted a range of $\log ({age})$ = 6 - 7 (1 - 10 Myr). Because they similar ages, Pismis 6 and Pismis 8 may have been formed in the same Giant Molecular Cloud, and we concluded they are a good candidate for a binary system. In the case of NGC 2383 and NGC 2384, because the big age difference found we conclude that most probably they are born in different environments and as well are not physically connected.
We reanalyze the broadband optical/UV/X-ray Swift spectra of the outburst of the black hole binary XTE J1817--330. We build a simple physical model of an X-ray irradiated disc, and use this to show that the optical/UV emission in the soft state is consistent with a reprocessing of a constant fraction of the bolometric X-ray luminosity. This argues against a scattering origin for the illumination, as the optical depth/solid angle of a wind/corona over the disc should decrease as the source luminosity declines. Instead it is much more likely that the outer disc is directly illuminated by the central source, and maintains a constant opening angle throughout the soft state. However, the constant reprocessed fraction also requires that the fraction of bolometric flux absorbed and thermalized in the disc remains constant. This is easiest to do if the disc has an ionized skin. The reprocessed fraction increases very significantly as the source enters the hard state though this change is masked by bandpass effects in simple plots of the UV versus 2--10 keV flux. It does not necessarily signal a change in emission e.g. the emergence of the jet dominating the optical/UV flux. While there should indeed be some contribution from the jet, the majority of the optical/UV emission is probably still from reprocessing.
Employing the perturbative treatment of gravitational clustering, we discuss possible effects of primordial non-Gaussianity on the matter power spectrum. As the gravitational clustering develops, the coupling between different Fourier modes of density perturbations becomes important and the primordial non-Gaussianity which intrinsically possesses the non-trivial mode-correlation can affect the late-time evolution of the power spectrum. We quantitatively estimate the non-Gaussian effect of power spectrum from the perturbation theory. The potential impacts on the cosmological parameter estimations using power spectrum are investigated based on the Fisher-matrix formalism. Also, on the basis of local biasing prescription, non-Gaussian effect on galaxy power spectrum is considered, showing that the scale-dependent biasing arises from a local-type primordial non-Gaussianity. On the other hand, an equilateral-type non-Gaussianity does not induce such scale-dependence because of weaker mode-correlations between small and large Fourier modes.
We describe a new method for measuring the extragalactic background light (EBL) through the detection of $\gamma$-ray inverse Compton (IC) emission due to scattering of the EBL photons off relativistic electrons in the lobes of radio galaxies. Our method has no free physical parameters and is a powerful tool when the lobes are characterized by a high energy sharp break or cutoff in their electron energy distribution (EED). We show that such a feature will produce a high energy IC `imprint' of the EBL spectrum in which the radio lobes are embedded, and show how this imprint can be used to derive the EBL. We apply our method to the bright nearby radio galaxy Fornax A, for which we demonstrate, using WMAP and EGRET observations, that the EED of its lobes is characterized by a conveniently located cutoff, bringing the IC EBL emission into the {\sl Fermi} energy range. We show that {\sl Fermi} will set upper limits to the optical EBL and measure the more elusive infrared EBL.
We have made a new compilation of observations of maximum stellar mass versus cluster membership number from the literature, which we analyse for consistency with the predictions of a simple random drawing hypothesis for stellar mass selection in clusters. Previously, Weidner and Kroupa have suggested that the maximum stellar mass is lower, in low mass clusters, than would be expected on the basis of random drawing, and have pointed out that this could have important implications for steepening the integrated initial mass function of the Galaxy (the IGIMF) at high masses. Our compilation demonstrates how the observed distribution in the plane of maximum stellar mass versus membership number is affected by the method of target selection; in particular, rather low n clusters with large maximum stellar masses are abundant in observational datasets that specifically seek clusters in the environs of high mass stars. Although we do not consider our compilation to be either complete or unbiased, we discuss the method by which such data should be statistically analysed. Our very provisional conclusion is that the data is not indicating any striking deviation from the expectations of random drawing.
The various scenarios proposed for the origin of the multiple, helium-enriched populations in massive globular clusters are critically compared to the relevant constraining observations. Among accretion of helium-rich material by pre-existing stars, star formation out of ejecta from massive AGB stars or from fast rotating massive stars, and pollution by Population III stars, only the AGB option appears to be viable. Accretion or star formation out of outflowing disks would result in a spread of helium abundances, thus failing to produce the distinct, chemically homogeneous sub-populations such as those in the clusters $\omega$ Cen and NGC 2808. Pollution by Population III stars would fail to produce sub-populations selectively enriched in helium, but maintaining the same abundance of heavy elements. Still, it is argued that for the AGB option to work two conditions should be satisfied: i) AGB stars experiencing the hot bottom burning process (i.e., those more massive than $\sim 3 \msun$) should rapidly eject their envelope upon arrival on the AGB, thus experiencing just a few third dredge-up episodes, and ii) clusters with multiple, helium enriched populations should be the remnants of much more massive systems, such as nucleated dwarf galaxies, as indeed widely assumed.
We have compared the optical emission line ratios of type 2 quasars from
Zakamska et al. with standard AGN photoionization model predictions, Seyfert
2s, HII galaxies, and narrow line FRII radio galaxies. Moderate to high
ionization narrow line radio galaxies and Seyfert 2s are indistinguishable from
type 2 quasars based on their optical line ratios.
The standard AGN photoionization models, widely discussed for other type 2
AGNs, can reproduce successfully the loci and trends of type 2 quasars in some
of the main diagnostic diagrams. These models are not exempt of problems and
the discrepancies with the data are the same encountered for other type 2 AGNs.
As for these, realistic models must take into account a range of cloud
properties, as widely demonstrated in the literature.
We also study the possible impact of stellar photoionization.
Using a hydrodynamics plus N-body simulation of galaxy cluster formation within a large volume and mock Chandra X-ray observations, we study the form and evolution of the intrinsic scatter about the best-fit X-ray temperature-mass relation for clusters. We investigate the physical origin of the scatter by correlating it with quantities that are closely related to clusters' formation and merging histories. We also examine the distribution of the scatter for merging and nonmerging populations, identified using halo merger trees derived from the simulation as well as X-ray substructure measures. We find a strong correlation between the scatter in the M-T_X relation and the halo concentration, in the sense that more concentrated clusters tend to be cooler than clusters with similar masses. No bias is found between the merging and relaxed clusters, but merging clusters generally have greater scatter. The amount of scatter is smaller at z=1 than at z=0 for both populations. We show that the above trends can be explained by the properties of the distribution of halo concentrations. We also detect a signature of non-lognormality in the distribution of scatter for our simulated clusters both at z=0 and at z=1. We conclude that, when cooling-related effects are neglected, the intrinsic scatter in the M-T_X relation is primarily driven by variations in halo concentrations, and only secondarily by departures from hydrostatic equilibrium due to cluster mergers.
Giant low surface brightness galaxies (GLSBs) have flat discs extending up to ~100 kpc. Their formation is a puzzle for cosmological simulations in the cold dark matter scenario. We suggest that GLSBs might be the final product of the evolution of collisional ring galaxies. In fact, our simulations show that, approximately 0.5-1.5 Gyr after the collision which led to the formation of the ring galaxy, the ring keeps expanding and fades, while the disc becomes very large (~100 kpc) and flat. At this stage, our simulated galaxies match many properties of GLSBs (surface brightness profile, morphology, HI spectrum and rotation curve).
We present grids of stellar models and their associated oscillation frequencies that have been used by the CoRoT Seismology Working Group during the scientific preparation of the CoRoT mission. The stellar models have been calculated with the CESAM stellar internal structure and evolution code while the oscillation frequencies have been obtained from the CESAM models by means of the ADIPLS adiabatic oscillation programme. The grids cover a range of masses, chemical compositions and evolutionary stages corresponding to those of the CoRoT primary targets. The stellar models and oscillation frequencies are available on line through the Evolution and Seismic Tools Activity (ESTA) web site.
The red spectral shape of the visible to near infrared reflectance spectrum of the sharply-edged ring-like disk around the young main sequence star HR 4796A was recently interpreted as the presence of tholin-like complex organic materials which are seen in the atmosphere and surface of Titan and the surfaces of icy bodies in the solar system. However, we show in this Letter that porous grains comprised of common cosmic dust species (amorphous silicate, amorphous carbon, and water ice) also closely reproduce the observed reflectance spectrum, suggesting that the presence of complex organic materials in the HR 4796 disk is still not definitive.
Although it is well recognized that gamma-ray burst (GRB) afterglows are obscured and reddened by dust in their host galaxies, the wavelength-dependence and quantity of dust extinction are still poorly known. Current studies on this mostly rely on fitting the afterglow spectral energy distributions (SEDs) with template extinction models. The inferred extinction (both quantity and wavelength-dependence) and dust-to-gas ratios are often in disagreement with that obtained from dust depletion and X-ray spectroscopy studies. We argue that this discrepancy could result from the prior assumption of a template extinction law. We propose an analytical formula to approximate the GRB host extinction law. With the template extinction laws self-contained, and the capability of revealing extinction laws differing from the conventional ones, it is shown that this is a powerful approach in modeling the afterglow SEDs to derive GRB host extinction.
Dust plays an essential role in the unification theory of active galactic nuclei (AGNs). This review summarizes our current understanding of the extinction and infrared emission properties of the circumnuclear dust in AGNs as well as the inferred dust composition and size distribution.
The recent Spitzer detections of the 9.7 micron Si--O silicate emission in type 1 AGNs provide support for the AGN unification scheme. The properties of the silicate dust are of key importance to understanding the physical, chemical and evolutionary properties of the obscuring dusty torus around AGNs. Compared to that of the Galactic interstellar medium (ISM), the 10 micron silicate emission profile of type 1 AGNs is broadened and has a clear shift of peak position to longer wavelengths. In literature this is generally interpreted as an indication of the deviations of the silicate composition, size, and degree of crystallization of AGNs from that of the Galactic ISM. In this Letter we show that the observed peak shift and profile broadening of the 9.7 micron silicate emission feature can be explained in terms of porous composite dust consisting of ordinary interstellar amorphous silicate, amorphous carbon and vacuum. Porous dust is naturally expected in the dense circumnuclear region around AGNs, as a consequence of grain coagulation.
Except in a few cases cosmic dust can be studied in situ or in terrestrial laboratories, essentially all of our information concerning the nature of cosmic dust depends upon its interaction with electromagnetic radiation. This chapter presents the theoretical basis for describing the optical properties of dust -- how it absorbs and scatters starlight and reradiates the absorbed energy at longer wavelengths.
The carrier of the 2175 Angstrom interstellar extinction feature remains unidentified since its first detection over 40 years ago. In recent years carbon buckyonions have been proposed as a carrier of this feature, based on the close similarity between the electronic transition spectra of buckyonions and the 2175 Angstrom interstellar feature. We examine this hypothesis by modeling the interstellar extinction with buckyonions as a dust component. It is found that dust models containing buckyonions (in addition to amorphous silicates, polycyclic aromatic hydrocarbon molecules, graphite) can closely reproduce the observed interstellar extinction curve. To further test this hypothesis, we call for experimental measurements and/or theoretical calculations of the infrared vibrational spectra of hydrogenated buckyonions. By comparing the infrared emission spectra predicted for buckyonions vibrationally excited by the interstellar radiation with the observed emission spectra of the diffuse interstellar medium, we will be able to derive (or place an upper limit on) the abundance of interstellar buckyonions.
An accurate knowledge of the mineralogy (chemical composition and crystal structure) of the silicate dust in the interstellar medium (ISM) is crucial for understanding its origin in evolved stars, the physical and chemical processing in the ISM, and its subsequent incorporation into protostellar nebulae, protoplanetary disks and cometary nuclei where it is subjected to further processing. While an appreciable fraction of silicate dust in evolved stars, in protoplanetary disks around pre-main sequence stars, in debris disks around main sequence stars, and in cometary nuclei is found to be in crystalline form, very recent infrared spectroscopic studies of the dust along the sightline toward the Galactic center source Sgr A* placed an upper limit of ~1.1% on the silicate crystalline fraction, well below the previous estimates of ~5% or ~60% derived from the observed 10 micron absorption profile for the local ISM toward Cyg OB2 No.12. Since the sightline toward SgrA contains molecular cloud materials as revealed by the detection of the 3.1 and 6.0 micron water ice absorption features, we argue that by taking into account the presence of ice mantles on silicate cores, the upper limit on the degree of silicate crystallinity in the ISM is increased to ~3--5%.
We report a multi-week sequence of B-band photometric measurements of the dwarf planet Eris using the {\it Swift} satellite. The use of an observatory in low-Earth orbit provides better temporal sampling than is available with a ground-based telescope. We find no compelling evidence for an unusually slow rotation period of multiple days, as has been suggested previously. A $\sim$1.08 day rotation period is marginally detected at a modest level of statistical confidence ($\sim$97%). Analysis of the combination of the $Swift$ data with the ground-based B-band measurements of \citet{2007AJ....133...26R} returns the same period ($\sim$1.08 day) at a slightly higher statistical confidence ($\sim$99%).
We propose an explanation to the appearance of a wide blue absorption wing in the He I 10830A P Cygni profile of the massive binary star Eta Carinae several months before periastron. We assume that the mixing regions of the two wind is accelerated by the secondary's wind to ~1800 km s^{-1}, and is responsible for the absorption. We also assume that the secondary star is toward the observer at periastron passage. With a toy-model we achieve two significant results. (1) We show that the orientation we use can account for the appearance and evolution of the wide blue wing. (2)We predict that the Doppler shift (the edge of the absorption profile) will reach a maximum 5-15 days before periastron passage. We encourage a nightly observation of Eta Carinae in this line to start December 28, 2008, and continue to several days after periastron.
We present 2D hydrodynamic simulations of the long-time accretion phase of a 15 solar mass star after core bounce and before the launch of a supernova explosion. Our simulations are performed with the Prometheus-Vertex code, employing multi-flavor, energy-dependent neutrino transport and an effective relativistic gravitational potential. Testing the influence of a stiff and a soft equation of state for hot neutron star matter, we find that the non-radial mass motions in the supernova core due to the standing accretion shock instability (SASI) and convection impose a time variability on the neutrino and gravitational-wave signals. These variations have larger amplitudes as well as higher frequencies in the case of a more compact nascent neutron star. After the prompt shock-breakout burst of electron neutrinos, a more compact accreting remnant radiates neutrinos with higher luminosities and larger mean energies. The observable neutrino emission in the direction of SASI shock oscillations exhibits a modulation of several 10% in the luminosities and ~1 MeV in the mean energies with most power at typical SASI frequencies of 20-100 Hz. At times later than 50-100 ms after bounce the gravitational-wave amplitude is dominated by the growing low-frequency (<200 Hz) signal associated with anisotropic neutrino emission. A high-frequency wave signal is caused by nonradial gas flows in the outer neutron star layers, which are stirred by anisotropic accretion from the SASI and convective regions. The gravitational-wave power then peaks at about 300-800 Hz with distinctively higher spectral frequencies originating from the more compact and more rapidly contracting neutron star. (abridged)
We study the stability of standing shock waves in advection-dominated accretion flows into a Schwarzschild black hole by 2D general relativistic hydrodynamic simulations as well as linear analysis in the equatorial plane. We demonstrate that the accretion shock is stable against axisymmetric perturbations but becomes unstable to non-axisymmetric perturbations. The results of dynamical simulations show good agreement with linear analysis on the stability, oscillation and growing time scales. The comparison of different wave-travel times with the growth time scales of the instability suggests that the instability is likely to be of the Papaloizou-Pringle type, induced by the repeated propagations of acoustic waves. However, the wavelengths of perturbations are too long to clearly define the reflection point. By analyzing the non-linear phase in the dynamical simulations, it is shown that quadratic mode couplings precede the non-linear saturation. It is also found that not only short-term random fluctuations by turbulent motions but also quasi periodic oscillations take place on longer time scales in the non-linear phase. We give some possible implications of the instability for quasi periodic oscillations (QPOs) and the central engine for gamma ray bursts (GRBs).
A class of modified gravity, known as $f(R)$-gravity, has presently been applied to Cosmology as a realistic alternative to dark energy. In this paper we use the most recent Type-Ia Supernova (SNe Ia) data, the so-called \emph{Union} sample of 307 SNe Ia, to place bounds on a theory of the form $f(R)=R - \beta/R^n$ within the Palatini approach. Given the complementarity of SNe Ia data with other cosmological observables, a joint analysis with measurements of baryon acoustic oscillation peak and estimates of the {\rm CMB} shift parameter is also performed. We show that, for the allowed intervals of $n$, $\Omega_{mo}$, and $\beta$, models based on $f(R) = R - \beta/R^{n}$ gravity in the Palatini approach can produce the sequence of radiation-dominated, matter-dominated, and accelerating periods without need of dark energy.
Polycyclic aromatic hydrocarbon (PAH) molecules, ubiquitously seen in the interstellar medium (ISM) of our own and external galaxies, might have been incorporated into comets if they are formed from relatively unprocessed interstellar matter. The detection of PAHs in comets would be an important link between the ISM and comets. This review compiles our current knowledge on cometary PAHs, based on ground-based and space-borne observations of infrared vibrational and ultraviolet fluorescence spectra of comets, and laboratory analysis of interplanetary dust particles possibly of cometary origin and cometary samples returned to Earth by the Stardust spacecraft. The latter provided the most unambiguous evidence for the presence of PAHs in cometary nuclei.
We have studied the relationship between the high- and low-ionization [O IV] lambda 25.89 micron, [Ne III] lambda 15.56 micron and [Ne II] lambda 12.81 micron emission lines with the aim of constraining the active galactic nuclei (AGN) and star formation contributions for a sample of 103 Seyfert galaxies. We used the [O IV] and [Ne II] emission as tracers for the AGN power and star formation to investigate the ionization state of the emission-line gas. We find that Seyfert 2 galaxies have, on average, lower [O IV]/[Ne II] ratios than those of Seyfert 1 galaxies. This result suggests two possible scenarios: 1) Seyfert 2 galaxies have intrinsically weaker AGN, or 2) Seyfert 2 galaxies have relatively higher star formation rates than Seyfert 1 galaxies. We estimate the fraction of [Ne II] directly associated with the AGN and find that Seyfert 2 galaxies have a larger contribution from star formation, by a factor of ~1.5 on average, than what is found in Seyfert 1 galaxies. Using the stellar component of [Ne II] as a tracer of the current star formation we found similar star formation rates in Seyfert 1 and Seyfert 2 galaxies. We examined the mid- and far-infrared continua and find that [Ne II] is well correlated with the continuum luminosity at 60 micron and that both [Ne III] and [O IV] are better correlated with the 25 micron luminosities than with the continuum at longer wavelengths, suggesting that the mid-infrared continuum luminosity is dominated by the AGN, while the far-infrared luminosity is dominated by star formation. Overall, these results test the unified model of AGN, and suggest that the differences between Seyfert galaxies cannot be solely due to viewing angle dependence.
We examine variability of absorption line strength of intervening systems along the line of sight to GRB 060206 at z=4.05, by the low-resolution optical spectra obtained by the Subaru telescope from six to ten hours after the burst. Although strong variabilities of Fe II and Mg II lines at z=1.48 during t=5-8 hours have been reported for this GRB (Hao et al. 2007), our spectra with higher signal-to-noise ratio do not show any evidence for variability in t=6-10 hours. There is a clear discrepancy between our data and Hao et al. data in the overlapping time interval. Furthermore, the line strengths in our data are in good agreement with those observed at t~2 hours by Thone et al.(2008). We also detected Fe II and Mg II absorption lines for a system at z=2.26, and these lines do not show evidence for variability either. Therefore we conclude that there is no evidence for variability of intervening absorption lines toward GRB 060206. The intervening line variability has been used to support the idea of clumpy Mg II cloudlets that was originally proposed to explain the anomalously high incidence of Mg II absorbers in GRB spectra compared with quasars, but this Mg II incidence anomaly should be explained by other effects.
Ten accretion-powered millisecond pulsars are now known. We show that many properties of their X-ray oscillations can be understood if the X-ray emitting regions of most are near their spin axes but wander. This is to be expected if their magnetic poles are close to their spin axes, so that accreting gas is channeled there. As the accretion rate and structure of the inner disk vary, gas will be channeled to different locations on the stellar surface, causing the X-ray emitting regions to move with respect to the magnetic field. This model can explain the small amplitudes and nearly sinusoidal waveforms of most of these pulsars and the large, rapid phase variations of several. It may also explain why accretion-powered millisecond pulsars are difficult to detect, why all found so far are transients, and why the oscillations of a few are intermittent. The model can be tested by comparing with observations the correlated waveform changes that it predicts, including changes with accretion rate.
In this work we discuss the time-evolution of nonspherical perturbations of a nonrotating neutron star described by a realistic Equation of State (EOS). We analyze 10 different EOS for a large sample of neutron star models. Various kind of generic initial data are evolved and the corresponding gravitational wave signals are computed. We focus on the dynamical excitation of fluid and spacetime modes and extract the corresponding frequencies. We employ a constrained numerical algorithm based on standard finite differencing schemes which permits stable and long term evolutions. Our code provides accurate waveforms and allows to capture, via Fourier analysis of the energy spectra, the frequencies of the fluid modes with an accuracy comparable to that of frequency domain calculations. The results we present here are useful for provindig comparisons with simulations of nonlinear oscillations of (rotating) neutron star models as well as testbeds for 3D nonlinear codes.
We propose a class of models in which the $\eta$-problem of supersymmetric hybrid inflation is resolved using a Heisenberg symmetry, where the associated modulus field is stabilized and made heavy with the help of the large vacuum energy during inflation without any fine-tuning. The proposed class of models is well motivated both from string theory considerations, since it includes the commonly encountered case of no-scale supergravity Kaehler potential, and from the perspective of particle physics since a natural candidate for the inflaton in this class of models is the right-handed sneutrino which is massless during the inflationary epoch, and subsequently acquires a large mass at the end of inflation. We study a specific example motivated by sneutrino hybrid inflation with no-scale supergravity in some detail, and show that the spectral index may lie within the latest WMAP range, while the tensor-to-scalar ratio is very small.
We generate an explicit four-fold infinity of physically acceptable exact perfect fluid solutions of Einstein's equations by way of conformal transformations of physically unacceptable solutions (one way to view the use of isotropic coordinates). Special cases include the Schwarzschild interior solution and the Einstein static universe. The process we consider involves solving two equations of the Riccati type coupled by a single generating function rather than a specification of one of the two metric functions.
In continuation of previous work, numerical results are presented, concerning relativistically counter-streaming plasmas. Here, the relativistic mixed mode instability evolves through, and beyond, the linear saturation -- well into the nonlinear regime. Besides confirming earlier findings, that wave power initially peaks on the mixed mode branch, it is observed that, during late time evolution wave power is transferred to other wave numbers. It is argued that the isotropization of power in wavenumber space may be a consequence of weak turbulence. Further, some modifications to the ideal weak turbulence limit is observed. Development of almost isotropic predominantly electrostatic -- partially electromagnetic -- turbulent spectra holds relevance when considering the spectral emission signatures of the plasma, namely bremsstrahlung, respectively magneto-bremsstrahlung (synchrotron radiation and jitter radiation) from relativistic shocks in astrophysical jets and shocks from gamma-ray bursts and active galactic nuclei.
We investigated the light propagation by means of the Robertson-McVittie solution which is considered to be the spacetime around the gravitating body embedded in the FLRW (Friedmann-Lema{\^i}tre-Robertson-Walker) background metric. We concentrated on the time delay and derived the correction terms with respect to the Shapiro's formula. To relate with the actual observation and its reduction process, we also took account of the time transformations; coordinate time to proper one, and conversely, proper time to coordinate one. We applied these results to the problem of increase of astronomical unit reported by Krasinsky and Brumberg (2004). However, we found the influence of the cosmological expansion on the light propagation does not give an explanation of observed value, $d{\rm AU}/dt = 15 \pm 4$ [m/century] in the framework of Robertson-McVittie metric.
We discuss the bounds on the mass of Dark Matter (DM) particles, coming from the analysis of DM phase-space distribution in dwarf spheroidal galaxies (dSph's). After reviewing existing approaches, we choose two methods to derive such a bound. The first method depends on the information about the current phase space distribution of DM particles only, while the second one uses both the initial and final distributions. We discuss the recent data on dSph's as well as astronomical uncertainties in relevant parameters. As an application, we present lower bounds on the mass of DM particles, coming from various dSph's, using both methods. The model-independent bound holds for any type of fermionic DM. Stronger, model-dependent bounds are quoted for several DM models (thermal relics, non-resonantly and resonantly produced sterile neutrinos, etc.). The latter bounds rely on the assumption that baryonic feedback cannot significantly increase the maximum of a distribution function of DM particles. Combining these results with the X-ray bounds of DM decay lines, we conclude that the scenario when DM is made of sterile neutrinos produced via non-resonant oscillations with the active neutrinos, is disfavored. The results of this work allow to reach this conclusion without relying on the Lyman-alpha analysis. The model of DM sterile neutrinos resonantly produced in the presence of lepton asymmetry remains viable. Within minimal neutrino extension of the Standard Model (the nuMSM) both mass and the mixing angle of the DM sterile neutrino are bounded from above and below, which suggests a possibility for its experimental search.
We apply phase-space density considerations to obtain lower bounds on the mass of sterile neutrino as dark matter candidate. The bounds are different for non-resonant production, resonant production in the presence of lepton asymmetry and production in decays of heavier particles. In the former case our bound is comparable to, but independent of the Lyman-alpha bound, and together with X-ray upper limit it disfavors non-resonantly produced sterile neutrino dark matter. An interesting feature of the latter case is that warm dark matter may be composed of heavy particles.
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[Abridged] We present an 8.5-hour simultaneous radio, X-ray, UV, and optical observation of the L dwarf binary 2MASSW J0746+20. We detect strong radio emission, dominated by short-duration periodic pulses at 4.86 GHz with P=124.32+/-0.11 min. The stability of the pulse profiles and arrival times demonstrates that they are due to the rotational modulation of a B~1.7 kG magnetic field. A quiescent non-variable component is also detected, likely due to emission from a uniform large-scale field. The H-alpha emission exhibits identical periodicity, but unlike the radio pulses it varies sinusoidally and is offset by exactly 1/4 of a phase. The sinusoidal variations require chromospheric emission from a large-scale field structure, with the radio pulses likely emanating from the magnetic poles. While both light curves can be explained by a rotating mis-aligned magnetic field, the 1/4 phase lag rules out a symmetric dipole topology since it would result in a phase lag of 1/2 (poloidal field) or zero (toroidal field). We therefore conclude that either (i) the field is dominated by a quadrupole configuration, which can naturally explain the 1/4 phase lag; or (ii) the H-alpha and/or radio emission regions are not trivially aligned with the field. Regardless of the field topology, we use the measured period along with the known rotation velocity (vsini=27 km/s), and the binary orbital inclination (i=142 deg), to derive a radius for the primary star of 0.078+/-0.010 R_sun. This is the first measurement of the radius of an L dwarf, and along with a mass of 0.085+/-0.010 M_sun it provides a constraint on the mass-radius relation below 0.1 M_sun. We find that the radius is about 30% smaller than expected from theoretical models, even for an age of a few Gyr.
We report about the detection of 10 clusters of galaxies in the ongoing Swift/BAT all-sky survey. This sample, which comprises mostly merging clusters, was serendipitously detected in the 15--55 keV band. We use the BAT sample to investigate the presence of excess hard X-rays above the thermal emission. The BAT clusters do not show significant (e.g. >2 $\sigma$) non-thermal hard X-ray emission. The only exception is represented by Perseus whose high-energy emission is likely due to NGC 1275. Using XMM-Newton, Swift/XRT, Chandra and BAT data, we are able to produce upper limits on the Inverse Compton (IC) emission mechanism which are in disagreement with most of the previously claimed hard X-ray excesses. The coupling of the X-ray upper limits on the IC mechanism to radio data shows that in some clusters the magnetic field might be larger than 0.5 $\mu$G. We also derive the first logN-logS and luminosity function distribution of galaxy clusters above 15 keV.
We apply spherical needlets to the Wilkinson Microwave Anisotropy Probe 5-year cosmic microwave background (CMB) dataset, to search for imprints of non-isotropic features in the CMB sky. We use the needlets localization properties to resolve peculiar features in the CMB sky and to study how these features contribute to the anisotropy power spectrum of the CMB. In addition to the now well-known "cold spot" of the CMB map in the southern hemisphere, we also find two hot spots at greater than 99% confidence level, again in the southern hemisphere and closer to the Galactic plane. While the cold spot contributes to the anisotropy power spectrum in the multipoles between l=6 to l=33, the hot spots are found to be dominating the anisotropy power in the range between l=6 and l=18. Masking both the cold and the two hot spots results in a reduction by about 15% in the amplitude of the angular power spectrum of CMB around l=10. The resulting changes to the cosmological parameters when the power spectrum is estimated masking these features (in addition to the WMAP team's KQ85 mask) are within the 1$\sigma$ errors published with the WMAP mask only. We also study the asymmetry between the angular power spectra evaluated on the northern and southern hemispheres. When the features detected by needlets are masked, we find that the difference in the power, measured in terms of the anisotropy variance between l=4 and l=18, is reduced by a factor 2. We make available a mask related to needlet features for more detailed studies on asymmetries in the CMB anisotropy sky.
The transfer of polarized radiation in magnetized and non-magnetized relativistic plasmas is an area of research with numerous flaws and gaps. The present paper is aimed at filling some gaps and eliminating the flaws. Starting from a Trubnikov's linear response tensor for a vacuum wave with ${\bf k}=\omega/c$ in thermal plasma, the analytic expression for the dielectric tensor is found in the limit of high frequencies. The Faraday rotation and Faraday conversion measures are computed in their first orders in the ratio of the cyclotron frequency $\Omega_0$ to the observed frequency $\omega$. The computed temperature dependencies of propagation effects bridge the known non-relativistic and ultra-relativistic limiting formulas. The fitting expressions are found for high temperatures, where the higher orders in $\Omega_0/\omega$ cannot be neglected. The plasma eigenmodes are found to become linearly polarized at much larger temperatures than thought before. The results are applied to the diagnostics of the hot ISM, hot accretion flows, and jets.
The small separation (delta nu 01, delta nu 02 and delta nu 13) between the oscillations with low degree l is dependent primarily on the sound speed profile within the stellar core, where nuclear evolution occurs. The detection of such oscillations for a star offers a very good opportunity to determine the stage of its nuclear evolution, and hence its age. In this context, we investigate the Sun and alpha Cen A and B. For alpha Cen A and B, each of the small separations delta nu 01, delta nu 02 and delta nu 13 gives a different age. Therefore, in our fitting process, we also employ the second difference, defined as nu n2 - 2 nu n1 + nu n0, which is 2 delta nu 01- delta nu 02. In addition to this, we also use frequency ratio (nu n0/ nu n2). For the Sun, these expressions areequivalent and give an age of about 4.9-5.0 Gyr. For alpha Cen A and B, however, the small separation and the second difference give very different ages. This conflict may be solved by the detection of oscillation frequencies that can be measured much more precisely than the current frequencies. When we fit the models to the observations, we find (i) Z 0=0.020, t=3.50 Gyr and M B=1.006 Msun from the small separations delta nu 01, delta nu 02 and delta nu 13 of alpha Cen B; and (ii) a variety of solutions from the non-seismic constraints and delta nu 02 of alpha Cen A and B, in which the masses of alpha Cen A and B are slightly modified and the age of the system is about 5.2-5.3 Gyr. For Z=0.025, the closest masses we find to the observed masses are M B=0.922 Msun and M A=1.115 Msun.The differences between these masses and the corresponding observed masses are about 0.01 Msun.
We report deep Sub-Millimeter Array observations of 26 pre-main-sequence (PMS) stars with evolved inner disks. These observations measure the mass of the outer disk (r ~20-100 AU) across every stage of the dissipation of the inner disk (r < 10 AU) as determined by the IR spectral energy distributions (SEDs). We find that only targets with high mid-IR excesses are detected and have disk masses in the 1-5 M_Jup range, while most of our objects remain undetected to sensitivity levels of M_DISK ~0.2-1.5 M_Jup. To put these results in a more general context, we collected publicly available data to construct the optical to millimeter wavelength SEDs of over 120 additional PMS stars. We find that the near-IR and mid-IR emission remain optically thick in objects whose disk masses span 2 orders of magnitude (~0.5-50 M_Jup). Taken together, these results imply that, in general, inner disks start to dissipate only after the outer disk has been significantly depleted of mass. This provides strong support for photoevaporation being one of the dominant processes driving disk evolution.
A brief overview on the current status of the census of the early universe population is given. Observational surveys of high redshift galaxies provide direct opportunities to witness the cosmic dawn and to have better understanding of how and when infant galaxies evolve into mature ones. It is a much more astronomical approach in contrast to the physical approach of to study the spatial fluctuation of cosmic microwave radiation. Recent findings in these two areas greatly advanced our understanding of the early Universe. I will describe the basic properties of several target objects we are looking for and the concrete methods astronomers are using to discover those objects in early Universe. My talk starts with Lyman alpha emitters and Lyman break galaxies, then introduces a clever approach to use gravitational lensing effect of clusters of galaxies to detect distant faint galaxies behind the clusters. Finally I will touch on the status and prospects of surveys for quasars and gamma-ray bursts.
The Australia Telescope Compact Array (ATCA) has been used at 1.38 and 2.38 GHz to survey seven southern Abell clusters of galaxies with high X-ray luminosities: A2746, A2837, A3126, A3216, A3230, A3827 and A3836. The clusters have also been surveyed at 0.843 GHz with the Molonglo Observatory Synthesis Telescope (MOST). We have listed a complete 1.38-GHz sample of 149 radio sources within the Abell circles centred on their X-ray centroids. We compare their identification fractions, emitted 1.38-GHz and optical powers, radio spectral indices and radial variation in projected source density with those of the radio-selected samples of Slee et al. (1998). We compare our fractional radio luminosity function with that of the radio-selected samples of Ledlow and Owen (1996) and Slee et al. (1998). Three significant differences are noted between X-ray and radio-selected samples of clusters; (1) the X-ray sample has an excess of flat-spectrum radio sources; (2) the fractional radio luminosity function for the FR I sources in the X-ray selected sample is much steeper, implying that fewer of their cluster galaxies become hosts for the stronger FR I radio galaxies; (3) a complete absence of FR II radio galaxies in the X-ray selected sample. The average excess projected density of radio sources near our cluster centres is approx. 5 times the background source density.
In this note, we consider the observational constraints on some cosmological models by using the 307 Union type Ia supernovae (SNIa), the 32 calibrated Gamma-Ray Bursts (GRBs) at $z>1.4$, the updated shift parameter $R$ from WMAP 5-year data (WMAP5), and the distance parameter $A$ of the measurement of baryon acoustic oscillation (BAO) peak in the distribution of SDSS luminous red galaxies with the updated scalar spectral index $n_s$ from WMAP5. The tighter constraints obtained here update the ones obtained previously in the literature.
The young $\sigma$-Orionis cluster is an important location for understanding the formation and evolution of stars, brown dwarfs, and planetary-mass objects. Its metallicity, although being a fundamental parameter, has not been well determined yet. We present the first determination of the metallicity of nine young late-type stars in $\sigma$-Orionis. Using the optical and near-infrared broadband photometry available in the literature we derive the effective temperatures for these nine cluster stars, which lie in the interval 4300--6500 K (1--3 \Msuno). These parameters are employed to compute a grid of synthetic spectra based on the code MOOG and Kurucz model atmospheres. We employ a $\chi^2$-minimization procedure to derive the stellar surface gravity and atmospheric abundances of Al, Ca, Si, Fe, Ni and Li, using multi-object optical spectroscopy taken with WYFFOS+AF2 at at the William Herschel Telescope ($\lambda/\delta\lambda\sim7500$). The average metallicity of the $\sigma$-Orionis cluster is [Fe/H] $ = -0.02\pm0.09\pm0.13$ (random and systematic errors). The abundances of the other elements, except lithium, seem to be consistent with solar values. Lithium abundances are in agreement with the "cosmic" $^7$Li abundance, except for two stars which show a $\log \epsilon(\mathrm{Li})$ in the range 3.6--3.7 (although almost consistent within the error bars). There are also other two stars with $\log \epsilon(\mathrm{Li})\sim 2.75$. We derived an average radial velocity of the $\sigma$-Orionis cluster of $28\pm4$km/s. The $\sigma$-Orionis metallicity is roughly solar.
Suzaku observation of the edge-on spiral galaxy NGC 4631 confirmed its X-ray halo extending out to about 10 kpc from the galactic disk. The XIS spectra yielded the temperature and metal abundance for the disk and the halo regions. The observed abundance pattern for O, Ne, Mg, Si and Fe is consistent with the metal yield from type II supernovae, with an O mass of about 1E6 Msun contained in the halo. These features imply that metal-rich gas produced by type II supernova is brought into the halo region very effectively, most likely through a galactic wind. Temperature and metal abundance may be affected by charge exchange and dust. An upper limit for the hard X-ray flux was obtained, corresponding to a magnetic field higher than 0.5 uG.
It is widely written and believed that Edwin Hubble introduced the terms `early' and `late types' to suggest an evolutionary sequence for galaxies. This is incorrect. Hubble took these terms from spectral classification of stars to signify a sequence related to complexity of appearance, albeit based on images rather than spectra. The temporal connotations of the terms had been abandoned prior to his 1926 paper on classification of galaxies.
Using RHESSI and some auxiliary observations we examine possible connections between spatial and temporal morphology of the sources of non-thermal hard X-ray (HXR) emission which revealed minute quasi-periodic pulsations (QPPs) during the two-ribbon flares on 2003 May 29 and 2005 January 19. Microwave emission also reveals the same quasi-periodicity. The sources of non-thermal HXR emission are situated mainly inside the footpoints of the flare arcade loops observed by the TRACE and SOHO instruments. At least one of the sources moves systematically both during the QPP-phase and after it in each flare that allows to examine the sources velocities and the energy release rate via the process of magnetic reconnection. The sources move predominantly parallel to the magnetic inversion line or the appropriate flare ribbon during the QPP-phase whereas the movement slightly changes to more perpendicular regime after the QPPs. Each QPP is emitted from its own position. It is also seen that the velocity and the energy release rate don't correlate well with the flux of the HXR emission calculated from the sources. The sources of microwaves and thermal HXRs are situated near the apex of the loop arcade and are not stationary either. Almost all QPPs and some spikes of HXR emission during the post-QPP-phase reveal the soft-hard-soft spectral behavior indicating separate acts of electrons acceleration and injection, rather than modulation of emission flux by some kinds of magnetohydrodynamic (MHD) oscillations of coronal loops. In all likelihood, the flare scenarios based on the successively firing arcade loops are more preferable to interpret the observations, although we can not conclude exactly what mechanism forces these loops to flare up.
The radial-orbit instability is a collective phenomenon that has heretofore only been observed in spherical systems. We find that this instability occurs also in triaxial systems, as we checked by performing extensive N-body simulations whose initial conditions were obtained by sampling a self-consistent triaxial model of a cuspy galaxy composed of luminous and dark matter. N-body simulations show a time evolution of the galaxy that is not due to the development of chaotic motions but, rather, to the collective instability induced by an excess of box-like orbits. The instability quickly transforms such models into a more prolate configuration, with 0.64<b/a<0.77 and 0.6<c/a<0.7 for the dark halo and 0.64<b/a<0.77 and 0.59<c/a<0.67 for the luminous matter. Stable triaxial, cuspy galaxies with dark matter halos are obtained when the contribution of radially-biased orbits to the solution is reduced. These results constitute the first evidence of the radial-orbit instability in triaxial galaxy models.
Precision Doppler velocity measurements from the Anglo-Australian Tele- scope reveal a planet with a 9.4+/-0.4 year period orbiting the M1.5 dwarf GJ 832. Within measurement uncertainty the orbit is circular, and the minimum mass (m sin i) of the planet is 0.64+/-0.06 MJUP. GJ 832 appears to be depleted in met- als by at least 50% relative to the Sun, as are a significant fraction of the M dwarfs known to host exoplanets. GJ 832 adds another Jupiter-mass planet to the known census of M dwarf exoplanets, which currently includes a significant number of Neptune-mass planets. GJ 832 is an excellent candidate for astromet- ric orbit determination with alpha sin i = 0.95 mas. GJ 832b has the second largest angular distance from its star among radial velocity detected exoplanets (0.69 arc sec) making it a potentially interesting target for future direct detection.
We present a preliminary analysis of the photospheric activity of CoRoT-Exo-2a, a young G7V star accompanied by a transiting hot Jupiter recently discovered by CoRoT. We apply spot modelling techniques developed for the analysis of the Sun as a star and capable to extract from CoRoT high precision light curves information on the variation of the total spotted area and the longitude of active regions along the 142 days of the observations. This preliminary analysis shows that the active regions form within two active longitudes separated by about 180 degrees and rotating with periods of 4.5221 and 4.5543 days, respectively, and that the total spotted area oscillates with a period of about 28.9 days.
We performed the first systematic search for the minimum variability time scale between 0.3 and 10 keV studying the 28 brightest early (<3000 s) afterglows detected by Swift-XRT up to March 2008. We adopt the power spectrum analysis in the time domain: unlike the Fourier spectrum, this is suitable to study the rms variations at different time-scales. We find that early XRT afterglows show variability in excess of the Poissonian noise level on time-scales as short as about 1 s (rest frame value), with the shortest t_{min} associated with the highest energy band. The gamma-ray prompt emission of GRB080319B shows a characteristic average variability time-scale t_{var} of about 1s; this parameter undergoes a remarkable evolution during the prompt emission (BAT observation).
The concept of "age" as a parameter for the description of the state of development of high energy showers in the atmosphere has been in use in cosmic ray studies for several decades. In this work we briefly discuss how this concept, originally introduced to describe the average behavior of electromagnetic cascades, can be fruitfully applied to describe individual showers generated by primary particles of different nature, including protons, nuclei and neutrinos. Showers with the same age share three different important properties: (i) their electron size has the same fractional rate of change with increasing depth, (ii) the bulk of the electrons and photons in the shower (excluding high energy particles) have energy spectra with shapes and relative normalization uniquely determined by the age parameter, (iii) the electrons and photons in the shower have also the same angular and lateral distributions sufficiently far from the shower axis. In this work we discuss how the properties associated with the shower age can be understood with simple arguments, and how the shapes of the electron and photon spectra and the relative normalization that correspond to a certain age can be calculated analytically.
We report the identification of a source coincident with the position of the nearby type II-P supernova (SN) 2008bk in high quality optical and near-infrared pre-explosion images from the ESO Very Large Telescope (VLT). The SN position in the optical and near-infrared pre-explosion images is identified to within about +-70 and +-40 mas, respectively, using post-explosion Ks-band images obtained with the NAOS CONICA adaptive optics system on the VLT. The pre-explosion source detected in four different bands is precisely coincident with SN 2008bk and is consistent with being dominated by a single point source. We determine the nature of the point source using the STARS stellar evolutionary models and find that its colours and luminosity are consistent with the source being a red supergiant progenitor of SN 2008bk with an initial mass of 8.5 +- 1.0 Msun.
Radio astronomical observations have very poor signal to noise ratios, unlike in other disciplines. On the other hand, it is possible to observe the object of interest for long time intervals as well as using a wider bandwidth. Traditionally, by averaging in time and in frequency, it has been possible to improve the signal to noise ratio of astronomical observations to improve the dynamic range. This is possible due to the inherent assumption that the object of interest in the sky is invariant over time and the frequency range of observation. However, in reality this assumption does not hold, due to intrinsic variation of the sky as well as due to errors generated by the instrument. In this paper, we shall discuss an alternative to averaging of images, without ignoring subtle changes in the observed data over time and frequency, using subspace decomposition. By separation of data to signal and noise subspaces, not only would this improve the quality of the data, but also enable us to detect faint artifacts due to calibration errors, interference etc.
Searching for planets in the atmosphere of AGB stars is difficult, due to confusion with the stellar wind and pulsations. The aim here is to provide a strategy for planet search in such a dense environment.The polarization properties of SiO masers, especially their circular polarization, are, under certain conditions, good tracers for rapid magnetospheric events. A Jovian planet with a magnetosphere whose dipole axis is misaligned with its rotation axis, naturally provides such conditions. Both VLBI techniques and single-dish observations with a carefully calibrated polarimeter are suited, with a sufficiently dense time sampling, to detect a periodic modulation of the circular polarization due to a precessing Jovian magnetosphere. Linear polarization, though exhibiting similar signatures, will probably suffer more from confusion due to beam dilution, even in VLBI observations.
We study the inverse problem of deducing the dynamical characteristics (such as the potential field) of large systems from kinematic observations. We show that, for a class of steady-state systems, the solution is unique even with fragmentary data, dark matter, or selection (bias) functions. Using spherically symmetric models for simulations, we investigate solution convergence and the roles of data noise and regularization in the inverse problem. We also present a method, analogous to tomography, for comparing the observed data with a model probability distribution such that the latter can be determined.
Using recent polarimetric observations of the Crab Nebula in the hard X-ray band by INTEGRAL, we show that the absence of vacuum birefringence effects constrains O(E/M) Lorentz violation in QED to the level |\xi| < 9x10^{-10} at three sigma CL, tightening by more than three orders of magnitude previous constraints. We show that planned X-ray polarimeters have the potential the potential to probe |\xi|~ 10^{-16} by detecting polarization in active galaxies at red-shift ~1.
The $^{92}$Mo($\alpha,n$)$^{95}$Ru, $^{94}$Mo($\alpha,n$)$^{97}$Ru, and $^{112}$Sn($\alpha,\gamma$)$^{116}$Te cross sections were measured at the upper end of the $p$-process Gamow window between 8.2 MeV and 11.1 MeV. Our results are slightly lower than global Hauser-Feshbach calculations from the code NON-SMOKER, but still within the uncertainty of the prediction. The $^{112}$Sn($\alpha,\gamma$)$^{116}$Te cross section agrees well with a recently measured thick-target cross section in the same energy range. For the $^{92,94}$Mo($\alpha,n$) reactions the present data close to the reaction thresholds could eliminate previous uncertainties within a factor of 20, and we can present now useful comparisons to statistical model calculations with different optical potentials.
The hypothesis is rapidly gaining popularity that the dark energy pervading
our universe is extra-repulsive ($-p>\rho$). The density of such a
substance(usually called phantom energy) grows with the cosmological expansion
and may become infinite in a finite time producing a Big Rip. In this paper we
analyze the late stages of the universe evolution and demonstrate that the
presence of the phantom energy in the universe is not enough in itself to
produce the Big Rip. This singularity occurrence requires the fulfillment of
some additional, rather strong conditions. A more probable outcome of the
cosmological evolution is the decay of the phantom field into 'normal' matter.
The second, more intriguing consequence of the presence of the phantom field
is the possibility to introduce a cosmological scenario that does not contain a
Big Bang. In the framework of this model the universe eternally expands, while
its density and other physical parameters oscillate over a wide range, never
reaching the Plank values. Thus, the universe evolution has no singularities at
all.
We present observational constraints on the nature of the different core-collapse supernova types through an investigation of the association of their explosion sites with recent star formation, as traced by H-alpha +[NII] line emission. We discuss results on the analysed data of the positions of 168 core-collapse supernovae with respect to the H-alpha emission within their host galaxies. From our analysis we find that overall the type II progenitor population does not trace the underlying star formation. Our results are consistent with a significant fraction of SNII arising from progenitor stars of less than 10 solar masses. We find that the supernovae of type Ib show a higher degree of association with HII regions than those of type II (without accurately tracing the emission), while the type Ic population accurately traces the H-alpha emission. This implies that the main core-collapse supernova types form a sequence of increasing progenitor mass, from the type II, to Ib and finally Ic. We find that the type IIn sub-class display a similar degree of association with the line emission to the overall SNII population, implying that at least the majority of these SNe do not arise from the most massive stars. We also find that the small number of SN `impostors' within our sample do not trace the star formation of their host galaxies, a result that would not be expected if these events arise from massive Luminous Blue Variable star progenitors.
The orbital dynamics of most planetary satellites is governed by the quadrupole moment from the equatorial bulge of the host planet and the tidal field from the Sun. On the Laplace surface, the long-term orbital evolution driven by the combined effects of these forces is zero, so that orbits have a fixed orientation and shape. The "classical" Laplace surface is defined for circular orbits, and coincides with the planet's equator at small planetocentric distances and with its orbital plane at large distances. A dissipative circumplanetary disk should settle to this surface, and hence satellites formed from such a disk are likely to orbit in or near the classical Laplace surface. This paper studies the properties of Laplace surfaces. Our principal results are: (i) if the planetary obliquity exceeds 68.875 deg there is a range of semimajor axes in which the classical Laplace surface is unstable; (ii) at some obliquities and planetocentric distances there is a distinct Laplace surface consisting of nested eccentric orbits, which bifurcates from the classical Laplace surface at the point where instability sets in; (iii) there is also a "polar" Laplace surface perpendicular to the line of nodes of the planetary equator on the planetary orbit; (iv) for circular orbits, the polar Laplace surface is stable at small planetocentric distances and unstable at large distances; (v) at the onset of instability this polar Laplace surface bifurcates into two polar Laplace surfaces composed of nested eccentric orbits.
Central peaks in the iron abundance of intracluster plasma are a common feature of cooling-core galaxy clusters. These abundance peaks have a much broader profile than the stars of the central brightest cluster galaxy (BCG), which produce the excess iron, indicating that metal-enriched plasma is transported out of the BCG by some process such as turbulent diffusion. At the same time, cooling-core clusters are likely heated by central active galactic nuclei (AGNs) by means of jets, cosmic-ray bubbles, and convection. The recent AGN-driven convection model of Chandran&Rasera predicts the turbulent velocity profile in a steady-state cluster in which radiative cooling is balanced by heating from a combination of AGN-driven convection and thermal conduction. We use the velocity profiles as input into an advection/diffusion model for the transport of metals in the intracluster medium, taking the iron to be injected by the BCG. We compare the results of our model to XMM and Chandra observations of eight clusters. Assuming a constant turbulence level over a cluster's lifetime, the turbulent velocities in the model can explain the observed abundance profiles in only five of the eight clusters. However, we go on to develop an analytic fit of the turbulent velocity profile as a function of the AGN power. We then deduce for each cluster the average AGN power (during the past 10 Gyr) required to match the abundance profiles. The required average values are between 10^43 and 2.10^44 erg/s, while the present AGN powers span a much larger range from 6.10^41 (Virgo) to 2.10^44 erg/s (Hydra A). Our results suggest that AGN-driven convection can account for the observed abundance profiles if the AGN power varies over a cluster's lifetime between Virgo-like and Hydra-A-like values, with average values in the above-quoted range.
We present the 3.5m SPICA space telescope, a proposed Japanese-led JAXA-ESA mission scheduled for launch around 2017. The actively cooled (<5 K), single aperture telescope and monolithic mirror will operate from ~3.5 to ~210 um and will provide superb sensitivity in the mid- and far-IR spectral domain (better than JWST at lambda > 18 um). SPICA is one of the few space missions selected to go to the next stage of ESA's Cosmic Vision 2015-2025 selection process. In this White Paper we present the main specifications of the three instruments currently baselined for SPICA: a mid-infrared (MIR) coronagraph (~3.5 to ~27 um) with photometric and spectral capabilities (R~200), a MIR wide-field camera and high resolution spectrometer (R~30,000), and a far-infrared (FIR ~30 to ~210 um) imaging spectrometer - SAFARI - led by a European consortium. We discuss their capabilities in the context of MIR direct observations of exo-planets (EPs) and multiband photometry/high resolution spectroscopy observations of transiting exo-planets. We conclude that SPICA will be able to characterize the atmospheres of transiting exo-planets down to the super-Earth size previously detected by ground- or space-based observatories. It will also directly detect and characterize Jupiter/Neptune-size planets orbiting at larger separation from their parent star (>5-10 AU), by performing quantitative atmospheric spectroscopy and studying proto-planetary and debris disks. In addition, SPICA will be a scientific and technological precursor for future, more ambitious, IR space missions for exo-planet direct detection as it will, for example, quantify the prevalence exo-zodiacal clouds in planetary systems and test coronographic techniques, cryogenic systems and lightweight, high quality telescopes. (abridged)
Studying the internal structure of exoplanet-host stars compared to that of similar stars without detected planets is particularly important for the understanding of planetary formation. The observed average overmetallicity of stars with planets is an interesting point in that respect. In this framework, asteroseismic studies represent an excellent tool to determine the structural differences between stars with and without detected planets. It also leads to more precise values of the stellar parameters like mass, gravity, effective temperature, than those obtained from spectroscopy alone. Interestingly enough, the detection of stellar oscillations is obtained with the same instruments as used for the discovery of exoplanets, both from the ground and from space. The time scales however are very different, as the oscillations of solar type stars have periods around five to ten minutes, while the exoplanets orbits may go from a few days up to many years. Here I discuss the asteroseismology of exoplanet-host stars, with a few examples.
Following Prendergast we study the relativistically expanding electromagnetic fields generated by an axisymmetric explosion of magnetic energy in a small volume. The magnetic field expands uniformly either within a cone or in all directions and it is therefore accompanied by an electric field. In the highly conducting plasma the charges move to annul the electric field in the frame of the moving plasma. The solutions presented are analytical and semi-analytical. We find that the time-scale for the winding up of the initial magnetic field is crucial, as short time-scales lead to strong radiant fields. Assuming a magnetic field of $10^{13}Gauss$ emerging from a magnetosphere of $10^{9}cm$ we end with a jet when confined by a pressure environment that falls more slowly than $r^{-4}$. The jet carries energy of $10^{51}erg$, which is mostly due to differential rotation at the base.
Starting from a complete sample of type I AGN observed by INTEGRAL in the 20-40 keV band, we have selected a set of 8 AGN which can be classified as radio loud objects according to their 1.4 GHz power density, radio to hard X-ray flux flux density ratio and radio morphology. The sample contains 6 Broad Line Radio Galaxies and 2 candidate ones. Most of the objects in our sample display a double lobe morphology, both on small and large scales. For all the objects, we present broad-band (1-110 keV) spectral analysis using INTEGRAL observations together with archival XMM-Newton, Chandra, Swift/XRT and Swift/BAT data. We constrain the primary continuum (photon index and cut-off energy), intrinsic absorption and reprocessing features (iron line and reflection) in most of the objects. The sources analysed here show remarkable similarities to radio quiet type 1 AGN with respect to most of the parameters analysed; we only find marginal evidence for weaker reprocessing features in our objects compared to their radio quiet counterparts. Similarly we do not find any correlation between the spectral parameters studied and the source core dominance or radio to 20-100 keV flux density ratios, suggesting that what makes our objects radio loud has no effect on their high energy characteristics.
We study the degree to which non-radiative gas dynamics affects the merger histories of haloes along with subsequent predictions from a semi-analytic model (SAM) of galaxy formation. To this aim, we use a sample of dark matter only and non-radiative SPH simulations of four massive clusters. The presence of gas-dynamical processes (e.g. ram-pressure from the hot ICM) makes haloes more fragile in the runs which include gas. This results in a 25 per cent decrease in the total number of subhaloes at z = 0. The impact on the galaxy population predicted by SAMs is complicated by the presence of "orphan" galaxies, i.e. galaxies whose parent substructures are reduced below the resolution limit of the simulation. In the model employed in our study, these galaxies survive for a residual merging time that is computed using a variation of the Chandrasekhar formula. Due to ram-pressure stripping, haloes in gas simulations tend to be less massive than their counterparts in the dark matter simulations. The resulting merging times for satellite galaxies are then longer in these simulations. On the other hand, the presence of gas influences the orbits of haloes making them on average more circular and therefore reducing the estimated merging times with respect to the dark matter only simulation. This effect is particularly significant for the most massive satellites and is (at least in part) responsible for the fact that brightest cluster galaxies in runs with gas have stellar masses which are about 25 per cent larger than those obtained from dark matter only simulations. Our results show that gas-dynamics has only a marginal impact on the statistical properties of the galaxy population, but that its impact on the orbits and merging times of haloes strongly influences the assembly of the most massive galaxies.
This paper is the 4th in a series describing the latest additions to the BaSTI stellar evolution database, which consists of a large set of homogeneous models and tools for population synthesis studies. Here we present a new set of low and high resolution synthetic spectra based on the BaSTI stellar models, covering a large range of simple stellar populations (SSPs) for both scaled solar and alpha-enhanced metal mixtures. This enables a completely consistent study of the photometric and spectroscopic properties of both resolved and unresolved stellar populations, and allows us to make detailed tests on their integrated properties. Our low resolution spectra are suitable for deriving broadband magnitudes and colors in any photometric system. These spectra cover the full wavelength range (9-160000nm) and include all evolutionary stages up to the end of AGB evolution. Our high resolution spectra are suitable for studying the behaviour of line indices and we have tested them against a large sample of Galactic globular clusters. We find that the range of ages, iron abundances [Fe/H], and degree of alpha-enhancement predicted by the models matches observed values very well. We have also tested the global consistency of the BaSTI models by making detailed comparisons between ages and metallicities derived from isochrone fitting to observed CMDs, and from line index strengths, for the Galactic globular cluster 47Tuc and the open cluster M67. For 47Tuc we find reasonable agreement between the 2 methods, within the estimated errors. From the comparison with M67 we find non-negligible effects on derived line indices caused by statistical fluctuations, which are a result of the specific method used to populate an isochrone and assign appropriate spectra to individual stars. (abridged)
The ANTARES detector was operated in a configuration with 5 lines for a period of 10 months from February until November 2007. The duty cycle was better than 80% during this period and almost 2*10**7 atmospheric muon triggers were collected. This large sample was used to test Monte Carlo simulation programs and to evaluate possible systematic effects due to uncertainties on environmental parameters and detector description. First results are presented and discussed.
We present here additional results of a spectropolarimetric survey of a small
sample of stars ranging from spectral type M0 to M8 aimed at investigating
observationally how dynamo processes operate in stars on both sides of the full
convection threshold (spectral type M4).
The present paper focuses on early M stars (M0--M3), i.e. above the full
convection threshold. Applying tomographic imaging techniques to time series of
rotationally modulated circularly polarised profiles collected with the NARVAL
spectropolarimeter, we determine the rotation period and reconstruct the
large-scale magnetic topologies of 6 early M dwarfs. We find that early-M stars
preferentially host large-scale fields with dominantly toroidal and
non-axisymmetric poloidal configurations, along with significant differential
rotation (and long-term variability); only the lowest-mass star of our
subsample is found to host an almost fully poloidal, mainly axisymmetric
large-scale field ressembling those found in mid-M dwarfs.
This abrupt change in the large-scale magnetic topologies of M dwarfs
(occuring at spectral type M3) has no related signature on X-ray luminosities
(measuring the total amount of magnetic flux); it thus suggests that underlying
dynamo processes become more efficient at producing large-scale fields (despite
producing the same flux) at spectral types later than M3. We suspect that this
change relates to the rapid decrease in the radiative cores of low-mass stars
and to the simultaneous sharp increase of the convective turnover times (with
decreasing stellar mass) that models predict to occur at M3; it may also be (at
least partly) responsible for the reduced magnetic braking reported for
fully-convective stars.
The usual procedure for estimating the significance of a peak in a power spectrum is to calculate the probability of obtaining that value or a larger value by chance, on the assumption that the time series contains only noise (e.g. that the measurements were derived from random samplings of a Gaussian distribution). However, it is known that one should regard this P-Value approach with caution. As an alternative, we here examine a Bayesian approach to estimating the significance of a peak in a power spectrum. This approach requires that we consider explicitly the hypothesis that the time series contains a periodic signal as well as noise. The challenge is to identify a probability distribution function for the power that is appropriate for this hypothesis. We propose what seem to be reasonable conditions to require of this function, and then propose a simple function that meets these requirements. We also propose a consistency condition, and check to see that our function satisfies this condition. We find that the Bayesian significance estimates are considerably more conservative than the conventional estimates. We apply this procedure to three recent analyses of solar neutrino data: (a) bimodality of GALLEX data; (b) power spectrum analysis of Super-Kamiokande data; and (c) the combined analysis of radiochemical neutrino data and irradiance data.
We use 2D numerical simulations and eikonal approximation to study properties of magneto-acoustic gravity waves traveling below the solar surface through the magnetic structure of sunspots. We consider a series of magnetostatic models of sunspots of different magnetic field strengths, from the deep interior to the chromosphere. The purpose of these studies is to quantify the effect of the magnetic field on local helioseismology measurements. Waves are excited by a sub-photospheric source located in the region beta slightly larger than 1. Time-distance diagrams and travel times are calculated for various frequency intervals and compared to the non-magnetic case. The results confirm that the observed time-distance helioseismology signals in sunspot regions correspond to fast MHD waves. The slow MHD waves form a distinctly different pattern in the time-distance diagram, which has not been detected in observations. The numerical results are in good agreement with the solution in the short-wavelength (eikonal) approximation, providing its validation. The frequency dependence of the travel times is in a good qualitative agreement with observations.
We have studied the sensitivity of s-process nucleosynthesis in massive stars to +/- 2sigma variations in the rates of the triple alpha and 12C(a,g)16O reactions. We simulated the evolution of massive stars from H-burning through Fe-core collapse, followed by a supernova explosion. We found that: the production factors of s-process nuclides between 58Fe and 96Zr change strongly with changes in the He burning reaction rates; using the Lodders (2003) solar abundances rather than those of Anders and Grevesse (1989) reduces s-process nucleosynthesis; later burning phases beyond core He burning and the shell C burning have a significant effect on post-explosive production factors. We also discuss the implications of the uncertainties in the helium burning rates for evidence of a new primary neutron capture process (LEPP) in massive stars.
Although most young massive stars appear to be part of multiple systems, it is poorly understood how this multiplicity influences the formation of massive stars. The high-mass star-forming region W3 IRS5 is a prime example of a young massive cluster where the cluster center is resolved into multiple subsources at cm and infrared wavelengths, a potential proto-Trapezium system. The region W3 IRS5 was mapped with the PdBI at 1.4mm and 3.4mm in the AB configurations, observing shock-tracing SiO and SO_2 emission. In the continuum we detect five sources, one of them for the first time, while counterparts were detected in the NIR, MIR or at radio wavelengths for the remaining four sources. Three of the detected sources are within the inner 2100AU, where the protostellar number density exceeds 10^6 protostars pc^-3 assuming spherical symmetry. Lower limits for the circumstellar masses of the detected sources were calculated, although they were strongly affected by the spatial filtering of the interferometer. However, the projected separations of the sources ranging between ~750 and ~4700AU indicate a multiple, Trapezium-like system. We detected five molecular outflows in SiO, two of them nearly in the line of sight direction, which allowed us to see the collapsing protostars in the NIR through the cavities carved by the outflows. The SO_2 velocity structure indicates a rotating, bound system, and we find tentative signatures of converging flows as predicted by the gravoturbulent star formation and converging flow theories. The obtained data strongly indicate that the clustered environment has a major influence on the formation of high-mass stars; however, our data do not clearly allow us to distinguish whether the ongoing star-forming process follows a monolithic collapse or a competitive accretion mechanism.
The Gaia satellite is a high-precision astrometry, photometry and spectroscopic ESA cornerstone mission, currently scheduled for launch in late 2011. Its primary science drivers are the composition, formation and evolution of the Galaxy. Gaia will achieve its scientific requirements with detailed calibration and correction for radiation damage. Microscopic models of Gaia's CCDs are being developed to simulate the charge trapping effect of radiation damage, which causes charge transfer inefficiency. The key to calculating the probability of a photoelectron being captured by a trap is the 3D electron density within each CCD pixel. However, this has not been physically modelled for Gaia CCD pixels. In this paper, the first of a series, we motivate the need for such specialised 3D device modelling and outline how its future results will fit into Gaia's overall radiation calibration strategy.
In supersymmetric models with a long-lived stau being the lightest Standard Model superpartner, the stau abundance during primordial nucleosynthesis is tightly constrained. Considering the complete set of stau annihilation channels in the minimal supersymmetric Standard Model (MSSM) with real parameters for scenarios in which sparticle coannihilations are negligible, we calculate the decoupling of the lighter stau from the primordial plasma and identify processes which are capable to deplete the resulting stau abundance significantly. We find particularly efficient stau annihilation at the resonance of the heavy CP-even Higgs boson and for a lighter stau with a sizeable left-right mixing due to enhanced stau-Higgs couplings. Even within the constrained MSSM, we encounter both effects leading to exceptionally small values of the resulting stau abundance. Prospects for collider phenomenology are discussed and possible implications of our findings are addressed with emphasis on gravitino dark matter scenarios.
We provide a systematic treatment of possible corrections to the inflaton potential for D-brane inflation in the warped deformed conifold. We consider the D3-brane potential in the presence of the most general possible corrections to the throat geometry sourced by coupling to the bulk of a compact Calabi-Yau space. This corresponds to the potential on the Coulomb branch of the dual gauge theory, in the presence of arbitrary perturbations of the Lagrangian. The leading contributions arise from perturbations by the most relevant operators that do not destroy the throat geometry. We find a generic contribution from a non-chiral operator of dimension $\Delta=2$ associated with a global symmetry current, resulting in a negative contribution to the inflaton mass-squared. If the Calabi-Yau preserves certain discrete symmetries, this is the dominant correction to the inflaton potential, and fine-tuning of the inflaton mass is possible. In the absence of such discrete symmetries, the dominant contribution comes from a chiral operator with $\Delta=3/2$, corresponding to a $\phi^{3/2}$ term in the inflaton potential. The resulting inflationary models are phenomenologically identical to the inflection point scenarios arising from specific D7-brane embeddings, but occur under far more general circumstances. Our strategy extends immediately to other warped geometries, given sufficient knowledge of the Kaluza-Klein spectrum.
Proposing new solution problems of the hierarchy and smallness of the cosmological constant using the Tev scale of the Standard Model in new framework of the higher-order gravity.
The main aim of this study is the comparison of gravitational waveforms obtained from numerical simulations which employ different numerical evolution approaches and different wave-extraction techniques. For this purpose, we evolve an oscillating, non-rotating polytropic neutron-star model with two different approaches: a full nonlinear relativistic simulation (in three dimensions) and a linear simulation based on perturbation theory. The extraction of the gravitational-wave signal is performed with three methods: The gauge-invariant curvature-perturbation theory based on the Newman-Penrose scalar $\psi_4$; The gauge-invariant Regge-Wheeler-Zerilli-Moncrief metric-perturbation theory of a Schwarzschild space-time; Some generalization of the quadrupole emission formula.
In a recent note, arXiv:0808.1415, it was argued that a hypothetical metastable black hole scenario could pose collider risk not excluded by our previous study. We comment on inconsistency of this proposed scenario.
In view of the imminent start of the LHC experimental programme, we use the available indirect experimental and cosmological information to estimate the likely range of parameters of the constrained minimal supersymmetric extension of the Standard Model (CMSSM), using a Markov-chain Monte Carlo (MCMC) technique to sample the parameter space. The 95% confidence-level area in the (m_0, m_1/2) plane of the CMSSM lies largely within the region that could be explored with 1/fb of integrated luminosity at 14 TeV, and much of the 68% confidence-level area lies within the region that could be explored with 50/pb of integrated luminosity at 10 TeV. A same-sign dilepton signal could well be visible in most of the 68% confidence-level area with 1/fb of integrated luminosity at 14 TeV. We discuss the sensitivities of the preferred ranges to variations in the most relevant indirect experimental and cosmological constraints and also to deviations from the universality of the supersymmetry-breaking contributions to the masses of the Higgs bosons.
We consider the prospects for testing the dark matter interpretation of the DAMA/LIBRA signal with the Super-Kamiokande experiment. The DAMA/LIBRA signal favors dark matter with low mass and high scattering cross section. We show that these characteristics imply that the scattering cross section that enters the DAMA/LIBRA event rate determines the annihilation rate probed by Super-Kamiokande. Current limits from Super-Kamiokande through-going events do not probe the DAMA/LIBRA favored region. We show, however, that upcoming analyses including fully-contained events with sensitivity to dark matter masses from 5 to 10 GeV may corroborate the DAMA/LIBRA signal. We conclude by considering three specific dark matter candidates, neutralinos, WIMPless dark matter, and mirror dark matter, which illustrate the various model-dependent assumptions entering our analysis.
Several aspects of mathematical astrobiology are discussed. It is argued that around the time of the origin of life the handedness of biomolecules must have established itself through an instability. Possible pathways of producing a certain handedness include mechanisms involving either autocatalysis or, alternatively, epimerization as governing effects. Concepts for establishing hereditary information are discussed in terms of the theory of hypercycles. Instabilities toward parasites and possible remedies by invoking spatial extent are reviewed. Finally, some effects of early life are discussed that contributed to modifying and regulating atmosphere and climate of the Earth, and that could have contributed to the highly oxidized state of its crust.
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To obtain an accurate description of broad-band photometric star cluster evolution, certain effects should be accounted for, such as the preferential loss of low-mass stars and the retain of stellar remnants. Moreover, the IMF and metallicity affect photometry as well. Due to their advanced evolutionary state, globular clusters (GCs) are interesting test cases for cluster models describing these effects. In this paper we describe cluster models in which the above effects are included. The photometric evolution of clusters is predicted, and the results are applied to Galactic GCs. The presented cluster models represent an analytical description of the evolution of the underlying stellar mass function due to stellar evolution and dynamical cluster dissolution. Stellar remnants are included by using initial-remnant mass relations, while cluster photometry is computed from the Padova 1999 isochrones. Our study shows that the preferential loss of low-mass stars, the retain of stellar remnants, as well as IMF and metallicity variations strongly influence the magnitude, colour and mass-to-light ratio evolution of clusters. The different effects can be clearly separated with our models. The models are applied to the Galactic GC population, of which the magnitude, colour and mass-to-light ratio ranges are well reproduced. We also show that the mass-to-light ratios of clusters of similar ages and metallicities cannot be assumed to be constant for all cluster luminosities. Instead, mass-to-light ratio increases with cluster luminosity and mass. These models underline the importance of detailed cluster models when considering cluster photometry. With the analytic framework provided in this paper, observed cluster properties can be interpreted in a more complete perspective. (Abridged)
We apply simple optical and SZ cluster finders to mock galaxy catalogues and SZ flux maps created from dark matter halos in a (1 Gpc/h)^3 dark matter simulation, at redshifts 0.5 and 0.9. At each redshift, the two catalogues are then combined to assess how well they can improve each other, and compared to several variants of catalogues made using SZ flux and galaxy information simultaneously. We use several different criteria to compare the catalogues, and illustrate some of the tradeoffs which arise in tuning the galaxy cluster finders with respect to these criteria. We detail many of the resulting improvements and issues which arise in comparing and combining these two types of data sets.
We use HST/ACS images and a photometric catalog of the COSMOS field to analyze morphologies of the host galaxies of approximately 400 AGN candidates at redshifts 0.3 < z < 1.0. We compare the AGN hosts with a sample of non-active galaxies drawn from the COSMOS field to match the magnitude and redshift distribution of the AGN hosts. We perform 2-D surface brightness modeling with GALFIT to yield host galaxy and nuclear point source magnitudes. X-ray selected AGN host galaxy morphologies span a substantial range that peaks between those of early-type, bulge-dominated and late-type, disk-dominated systems. We also measure the asymmetry and concentration of the host galaxies. Unaccounted for, the nuclear point source can significantly bias results of these measured structural parameters, so we subtract the best-fit point source component to obtain images of the underlying host galaxies. Our concentration measurements reinforce the findings of our 2-D morphology fits, placing X-ray AGN hosts between early- and late-type inactive galaxies. AGN host asymmetry distributions are consistent with those of control galaxies. Combined with a lack of excess companion galaxies around AGN, the asymmetry distributions indicate that strong interactions are no more prevalent among AGN than normal galaxies. In light of recent work, these results suggest that the host galaxies of AGN at these X-ray luminosities may be in a transition from disk-dominated to bulge-dominated, but that this transition is not typically triggered by major mergers.
Using a one-dimensional $\alpha\omega$-dynamo model appropriate to galaxies, we study the possibility of dynamo action driven by a stochastic alpha effect and shear. To determine the field evolution, one needs to examine a large number of different realizations of the stochastic component of $\alpha$. The net growth or decay of the field depends not only on the dynamo parameters but also on the particular realization, the correlation time of the stochastic $\alpha$ compared to turbulent diffusion timescale and the time over which the system is evolved. For dynamos where both a coherent and fluctuating $\alpha$ are present, the stochasticity of $\alpha$ can help alleviate catastrophic dynamo quenching, even in the absence of helicity fluxes. One can obtain final field strengths up to a fraction $\sim 0.01$ of the equipartition field $ B_{eq}$ for dynamo numbers $| D| \sim 40$, while fields comparable to $ B_{eq}$ require much larger degree of $\alpha$ fluctuations or shear. This type of dynamo may be particularly useful for amplifying fields in the central regions of disk galaxies.
[ABRIDGED] We study supermassive black hole binary mergers driven by angular momentum loss to small-scale gas discs. Such binaries form after major galaxy mergers, but their fate is unclear since hardening through stellar scattering becomes very inefficient at sub-parsec distances. Gas discs may dominate binary dynamics on these scales, and promote mergers. Using numerical simulations, we investigate the evolution of the orbits of binaries embedded within geometrically thin gas discs. Our simulations directly resolve angular momentum transport within the disc, which at the radii of interest is likely dominated by disc self-gravity. We show that the binary decays at a rate which is in good agreement with analytical estimates, while the eccentricity grows. Saturation of eccentricity growth is not observed up to values e > 0.35. Accretion onto the black holes is variable, and is roughly modulated by the binary orbital frequency. Scaling our results, we analytically estimate the maximum rate of binary decay that is possible without fragmentation occuring within the surrounding gas disc, and compare that rate to an estimate of the stellar dynamical hardening rate. For binary masses in the range 10^5 < M/Msun < 10^8 we find that decay due to gas discs may dominate for separations below a ~ 0.01--0.1 pc, where the disc is optically thick. The minimum merger time scale is shorter than the Hubble time for M < 10^7 Msun. This implies that gas discs could commonly attend relatively low mass black hole mergers, and that a significant population of binaries might exist at separations of a few hundredths of a pc, where the combined decay rate is slowest. For more massive binaries, we suggest that scattering of stars formed within a fragmenting gas disc could act as a significant additional sink of binary angular momentum.
We have derived a model of the Kuiper belt luminosity function exhibited by a broken power-law size distribution. This model allows direct comparison of the observed luminosity function to the underlying size distribution. We discuss the importance of the radial distribution model in determining the break diameter. We determine a best-fit break-diameter of the Kuiper belt size-distribution of 30<Db<90 km via a maximum-likelihood fit of our model to the observed luminosity function. We also confirm that the observed luminosity function for m(R) ~ 21-28 is consistent with a broken power-law size distribution, and exhibits a break at m(R)=26.0+0.7-1.8.
We present results from deep radio observations taken with the VLA at a center frequency of 1400 MHz cover a region of the SWIRE Spitzer Legacy survey, centered at 10 46 00, 59 01 00 (J2000). The reduction and cataloging of the radio sources are described. The survey presented is the deepest so far in terms of the radio source density on the sky. Perhaps surprisingly, the sources down to the bottom of the catalog have median angular sizes greater than 1 arcsecond, like their cousins 10-100 times stronger. If the log N - log S normalization remains constant at the lowest flux densities, there are about 6 sources per square arcminute down to 15 microJy at 20cm. Given the finite source sizes this implies we may reach the natural confusion limit near 1 microJy.
Star forming regions are expected to show linear proper motions due to the relative motion of the Sun with respect to the region. These proper motions appear superposed to the proper motions expected in features associated with mass ejection from the young stellar objects embedded in them. Therefore, it is necessary to have a good knowledge of the proper motions of the region as a whole in order to correctly interpret the motions associated with mass ejection. In this paper we present the first direct measurement of proper motions of the NGC 1333 star forming region. This region harbors one of the most studied Herbig-Haro systems, HH 7-11, whose exciting source remains unclear. Using VLA A configuration data at 3.6 cm taken over 10 years, we have been able to measure the absolute proper motions of four thermal sources embedded in NGC 1333. From our results we have derived the mean proper motions of the NGC 1333 star forming region to be mu(alpha)cos(delta) = 9 +- 1 mas/yr and mu(delta) = -10 +- 2 mas/yr. In this paper, we also discuss the possible implications of our results in the identification of the outflow exciting sources.
I model profiles of the [NeII] forbidden emission line at 12.81um, emitted by photoevaporative winds from discs around young, solar-mass stars. The predicted line luminosities (~ 1E-6 Lsun) are consistent with recent data, and the line profiles vary significantly with disc inclination. Edge-on discs show broad (30-40km/s) double-peaked profiles, due to the rotation of the disc, while in face-on discs the structure of the wind results in a narrower line (~10km/s) and a significant blue-shift (5-10km/s). These results suggest that observations of [NeII] line profiles can provide a direct test of models of protoplanetary disc photoevaporation.
Evolutionary trends in the surface abundances of heavier elements have recently been identified in the globular cluster NGC 6397 ([Fe/H]=-2), indicating the operation of atomic diffusion in these stars. Such trends constitute important constraints for the extent to which diffusion modifies the internal structure and surface abundances of solar-type, metal-poor stars. We perform an independent check of the reality and size of abundance variations within this metal-poor globular cluster. Observational data covering a large stellar sample, located between the cluster turn-off point and the base of the red giant branch, are homogeneously analysed. The spectroscopic data were obtained with the medium-high resolution spectrograph FLAMES/GIRAFFE on VLT-UT2. We derive independent effective-temperature scales from profile fitting of Balmer lines and by applying colour-temperature calibrations to Str\"omgren uvby and broad-band BVI photometry. An automated spectral analysis code is used together with a grid of MARCS model atmospheres to derive stellar surface abundances of Mg, Ca, Ti, and Fe. We identify systematically higher iron abundances for more evolved stars. The turn-off point stars are found to have 0.13dex lower surface abundances of iron compared to the coolest, most evolved stars in our sample. There is a strong indication of a similar trend in magnesium, whereas calcium and titanium abundances are more homogeneous. Within reasonable error limits, the obtained abundance trends are in agreement with the predictions of stellar structure models including diffusive processes (sedimentation, levitation), if additional turbulent mixing below the outer convection zone is included.
We present new radial velocity measurements of 586 stars in a one-degree field centered on the open cluster M46, and the planetary nebula NGC 2438 located within a nuclear radius of the cluster. The data are based on medium-resolution optical and near-infrared spectra taken with the AAOmega spectrograph on the Anglo-Australian Telescope. We find a velocity difference of about 30 km/s between the cluster and the nebula, thus removing all ambiguities about the cluster membership of the planetary nebula caused by contradicting results in the literature. The line-of-sight velocity dispersion of the cluster is 3.9+/-0.3 km/s, likely to be affected by a significant population of binary stars.
Disk galaxies in compact galaxy groups exhibit a remarkable shortfall of neutral hydrogen compared to both isolated spirals and spirals in more loose groups, but the origin of this HI deficiency remains unclear. Based on a sample of highly HI deficient compact galaxy groups, here updated to also include HCG 58 and HCG 93, we summarise the first results of a multi-wavelength campaign aimed at understanding the processes responsible for modifying the HI content of galaxy disks in these environments. While tidal stripping, ram pressure stripping by hot intragroup gas, and star-formation induced strangulation could individually be affecting the ISM in some of the group members, these processes each face specific difficulties in explaining the inferred deficiency of HI for the sample as a whole. A complete picture of the mechanisms driving the ISM evolution in the disk galaxies of these groups has thus yet to emerge, but promising avenues for further progress in this field are briefly discussed on the basis of the present sample.
We consider radiation emitted by the jitter mechanism in a Blandford-McKee self-similar blastwave. We assume the magnetic field configuration throughout the whole blastwave meets the condition for the emission of jitter radiation and we compute the ensuing images, light curves and spectra. The calculations are performed for both a uniform and a wind environment. We compare our jitter results to synchrotron results. We show that jitter radiation produces slightly different spectra than synchrotron, in particular between the self-absorption and the peak frequency, where the jitter spectrum is flat, while the synchrotron spectrum grows as \nu^{1/3}. The spectral difference is reflected in the early decay slope of the light curves. We conclude that jitter and synchrotron afterglows can be distinguished from each other with good quality observations. However, it is unlikely that the difference can explain the peculiar behavior of several recent observations, such as flat X-ray slopes and uncorrelated optical and X-ray behavior.
Inhomogeneous cosmological models have recently become a very interesting alternative to standard cosmology. This is because these models are able to fit cosmological observations without the need for dark energy. However, due to inhomogeneity and pressure-less matter content, these models can suffer from shell crossing singularities. These singularities occur when two shell of dust collide with each other leading to infinite values of the density. In this Letter we show that if inhomogeneous pressure is included then these singularities can be prevented from occurring over the period of structure formation. Thus, a simple incorporation of a gradient of pressure allows for more comprehensive studies of inhomogeneous cosmological models and their application to cosmology.
DDSCAT 7.0 is an open-source Fortran-90 software package applying the
discrete dipole approximation to calculate scattering and absorption of
electromagnetic waves by targets with arbitrary geometries and complex
refractive index. The targets may be isolated entities (e.g., dust particles),
but may also be 1-d or 2-d periodic arrays of "target unit cells", allowing
calculation of absorption, scattering, and electric fields around arrays of
nanostructures.
The theory of the DDA and its implementation in DDSCAT is presented in Draine
(1988) and Draine & Flatau (1994), and its extension to periodic structures
(and near-field calculations) in Draine & Flatau (2009). DDSCAT 7.0 includes
support for MPI, OpenMP, and the Intel Math Kernel Library (MKL). DDSCAT
supports calculations for a variety of target geometries. Target materials may
be both inhomogeneous and anisotropic. It is straightforward for the user to
"import" arbitrary target geometries into the code. DDSCAT automatically
calculates total cross sections for absorption and scattering and selected
elements of the Mueller scattering intensity matrix.
A Fortran-90 code DDfield to calculate E and B at user-selected locations
near the target is included in the distribution. This User Guide explains how
to use DDSCAT 7.0 to carry out electromagnetic scattering calculations.
The discrete-dipole approximation (DDA) is a powerful method for calculating absorption and scattering by targets that have sizes smaller than or comparable to the wavelength of the incident radiation. The DDA can be extended to targets that are singly- or doubly-periodic. We generalize the scattering amplitude matrix and the 4 x 4 Mueller matrix to describe scattering by singly- and doubly-periodic targets, and show how these matrices can be calculated using the DDA. The accuracy of DDA calculations using the open-source code DDSCAT is demonstrated by comparison to exact results for infinite cylinders and infinite slabs. A method for using the DDA solution to obtain fields within and near the target is presented, with results shown for infinite slabs.
We propose that a sufficiently advanced civilization may employ Cepheid variable stars as beacons to transmit all-call information throughout the galaxy and beyond. One can construct many scenarios wherein it would be desirable for such a civilization of star ticklers to transmit data to anyone else within viewing range. The beauty of employing Cepheids is that these stars can be seen from afar(we monitor them out through the Virgo cluster), and any developing technological society would seem to be likely to closely observe them as distance markers. Records exist of Cepheids for well over one hundred years. We propose that these (and other regularly variable types of stars) be searched for signs of phase modulation (in the regime of short pulse duration) and patterns, which could be indicative of intentional signaling.
We review X-ray flux modulation from X-ray binaries on time scales corresponding to the orbital period and those at longer time scales (so called superorbital). Those modulations provide a powerful tool to constrain geometry of the accretion flow. The most common cause of the superorbital variability appears to be precession. We then discuss two specific examples of discoveries of a coupling between the two types of variability and their physical interpretation. One is Cyg X-1, a black-hole binary with a high-mass companion, in which case we find the presence of an accretion bulge formed by collision of the stellar wind with the outer edge of the precessing accretion disc. The other is 4U 1820-303, a neutron star accreting from a low-mass white dwarf, in which case we interpret the superorbital variability as accretion rate modulation induced by interactions in a triple stellar system. Then, the varying accretion rate leads to changes of the size of the accretion bulge in that system, obscuring the centrally-emitted X-rays.
In clusters of galaxies, the specific entropy of intracluster plasma increases outwards. Nevertheless, a number of recent studies have shown that the intracluster medium is subject to buoyancy instabilities due to the effects of cosmic rays and anisotropic thermal conduction. In this paper, we present a new numerical algorithm for simulating such instabilities. This numerical method treats the cosmic rays as a fluid, accounts for the diffusion of heat and cosmic rays along magnetic field lines, and enforces the condition that the temperature and cosmic-ray pressure remain positive. We carry out several tests to ensure the accuracy of the code, including the detailed matching of analytic results for the eigenfunctions and growth rates of linear buoyancy instabilities. This numerical scheme will be useful for simulating convection driven by cosmic-ray buoyancy in galaxy cluster plasmas and may also be useful for other applications, including fusion plasmas, the interstellar medium, and supernovae remnants.
During the phase when stars appear in the Hertzsprung-Russell-Diagram in the upper asymptotic giant branch (AGB), they loose, due to a wind driven by pulsations, at least half of their mass. The inner part of the envelop thus formed, also called extended atmosphere, is expected to bear complex magneto-hydrodynamic phenomena, due to the interaction of the wind with the previously expulsed matter and, possibly, with Jovian or terrestial planets. As in the solar system, fluctuations of the magnetic field ("space weather" about a mean value can be expected, but the observational evidence is still lacking. Here we show that for a narrow range of velocities the circular polarization of SiO masers, tracing the magnetic field in the extended atmosphere of AGB stars, varies in two stars with a period of a few hours. Previous multi-epoch observations of SiO masers were neither polarimetric nor critically sampled to detect such intraday magnetic fluctuations. Because statistically significant fluctuations are seemingly rare and localized in the extended atmosphere, they are expected to be due to a variety of phenomena. Coronal flux loops, magnetic clouds or Jovian magnetospheres provide suitable explanations. Our study opens the way to future observations combining intensive full polarization monitoring of SiO masers, sampling at least once per hour, with high spatial resolution. This will ultimately allow us to distinguish between the proposed scenarios and to investigate the fate of inner planetary systems around solar-type stars entering their AGB phase.
[abbreviated] Long-lived, large-scale magnetic field configurations exist in upper main sequence, white dwarf, and neutron stars. Externally, these fields are roughly dipolar, while their internal structure and evolution are uncertain, but highly relevant for several problems in stellar and high-energy astrophysics. We discuss the main properties expected for the stable magnetic configurations in these stars from physical arguments, and how these properties may determine the modes of decay of these configurations. Stable magneto-hydrostatic equilibria appear to exist in stars whenever the matter in their interior is stably stratified (not barotropic). These equilibria are not force-free and not required to satisfy the Grad-Shafranov equation, but they do involve both toroidal and poloidal field components. We argue that the main mode of decay for these configurations are processes that lift the constraints set by stable stratification, such as heat diffusion in main-sequence envelopes and white dwarfs, and beta decays or particle diffusion in neutron stars. In the former, heat diffusion is not fast enough to make these equilibria evolve over the stellar lifetime. In neutron stars, a strong enough field might decay by overcoming the compositional stratification through beta decays (at the highest field strengths) or through ambipolar diffusion (for somewhat weaker fields). These processes convert magnetic energy to thermal energy, and they occur at significant rates only once the latter is smaller than the former, and therefore they substantially delay the cooling of the neutron star, while slowly decreasing its magnetic energy.
We consider a technique of calculating deflection of the light passing through wormholes (from one universe to another). We find fundamental and characteristic features of electromagnetic radiation passing through the wormholes. Making use of this, we propose new methods of observing distinctive differences between wormholes and other objects as well as methods of determining characteristic parameters for different wormhole models.
The emission from neutral hydrogen (HI) clouds in the post-reionization era (z < 6), too faint to be individually detected, is present as a diffuse background in all low frequency radio observations below 1420 MHz. The angular and frequency fluctuations of this radiation (~ 1 mK) is an important future probe of the large scale structures in the Universe. We show that such observations are a very effective probe of the background cosmological model and the perturbed Universe. In our study we focus on the possibility of determining the redshift space distortion parameter, coordinate distance and its derivative with redshift. Using reasonable estimates for the observational uncertainties and configurations representative of the ongoing and upcoming radio interferometers, we predict parameter estimation at a precision comparable with supernova Ia observations and galaxy redshift surveys, across a wide range in redshift that is only partially accessed by other probes. Future HI observations of the post-reionization era present a new technique, complementing several existing one, to probe the expansion history and to elucidate the nature of the dark energy.
We based on 2MASS J and Ks photometry for the open star clusters King 14 and NGC 146, and using color magnitude diagrams with isochrones fit we have found an age of log(age) = 7.8 (63 $\pm$8 Myr) for King 14 and log(age) = 7.5 (32 $\pm$8 Myr) for NGC 146. Our age determination is bigger than given in Lynga [5] (log(age) = 7.2 for King 14 and log(age) = 7.1 for NGC 146) and less than Dias [6] (log(age) = 7.9 for King 14 and log(age) = 7.8 for NGC 146)
We investigate whether it is possible that viable microbes could have been transported to Earth from the planets in extra-solar systems by means of natural vehicles such as ejecta expelled by comet or asteroid impacts on such planets. The probabilities of close encounters with other solar systems are taken into account as well as the limitations of bacterial survival times inside ejecta in space, caused by radiation and DNA decay. The conclusion is that no potentially DNA/RNA life-carrying ejecta from another solar system in the general Galactic star field landed on Earth before life already existed on Earth, not even if microbial survival time in space is as long as tens of millions of years. However, if the Sun formed initially as a part of a star cluster, as is commonly assumed, we cannot rule out the possibility of transfer of life from one of the sister systems to us. Likewise, there is a possibility that some extra-solar planets carry life that originated in our solar system. It will be of great interest to identify the members of the Sun's birth cluster of stars and study them for evidence for planets and life on the planets. The former step may be accomplished by the GAIA mission, the latter step by the SIM and DARWIN missions. Therefore it may not be too long until we have experimental knowledge on the question whether the natural transfer of life from one solar system to another has actually taken place.
The application of the virial theorem provides a tool to estimate supermassive black hole (BH) masses in large samples of active galactic nuclei (AGN) with broad emission lines at all redshifts and luminosities, if the broad line region (BLR) is gravitationally bound. In this paper we discuss the importance of radiation forces on BLR clouds arising from the deposition of momentum by ionizing photons. Such radiation forces counteract gravitational ones and, if not taken into account, BH masses can be severely underestimated. We provide virial relations corrected for the effect of radiation pressure and we discuss their physical meaning and application. If these corrections to virial masses, calibrated with low luminosity objects, are extrapolated to high luminosities then the BLRs of most quasars might be gravitationally unbound. The importance of radiation forces in high luminosity objects must be thoroughly investigated to assess the reliability of quasar BH masses.
We present Very Large Array (VLA) observations of the water maser emission towards IRAS 16552-3050. The maser emission shows a velocity spread of ~170 km/s, and a bipolar distribution with a separation between the red and blueshifted groups of ~0.08". These observations and the likely post-AGB nature of the source indicate that IRAS 16552-3050 can be considered as a member of the "water fountain" class of sources (evolved stars showing H2O maser emission with a velocity spread $\ga$ 100 km/s, probably tracing collimated jets). The water maser emission in IRAS 16552-3050 does not seem to be associated with with any known optical counterpart. Moreover, this source does not have a near-IR 2MASS counterpart, as it happens in about half of the water fountains known. This suggests that these sources tend to be heavily obscured objects, probably with massive precursors ($\ga 4-5$ M$_\odot$). We suggest that the water maser emission in IRAS 16552-3050 could be tracing a rapidly precessing bipolar jet.
Planetary systems are angular momentum reservoirs generated during star
formation. This accretion process produces very powerful engines able to drive
the optical jets and the molecular outflows. A fraction of the engine energy is
released into heating thus the temperature of the engine ranges from the 3000K
of the inner disk material to the 10MK in the areas where magnetic reconnection
occurs. There are important unsolved problems concerning the nature of the
engine, its evolution and the impact of the engine in the chemical evolution of
the inner disk. Of special relevance is the understanding of the shear layer
between the stellar photosphere and the disk; this layer controls a significant
fraction of the magnetic field building up and the subsequent dissipative
processes ougth to be studied in the UV.
This contribution focus on describing the connections between 1 Myr old suns
and the Sun and the requirements for new UV instrumentation to address their
evolution during this period. Two types of observations are shown to be needed:
monitoring programmes and high resolution imaging down to, at least,
milliarsecond scales.
We present the results of a 10.5 yr, volume limited (28 Mpc) search for supernova (SN) progenitor stars. We compile all SNe discovered within this volume (132, of which 27% are type Ia) and determine the relative rates of each sub-type from literature studies : II-P (59%), Ib/c (29%), IIb (5%), IIn (4%) and II-L (3%). Twenty II-P SNe have high quality optical or near-IR pre-explosion images that allow a meaningful search for the progenitor stars. In four cases they are clearly red supergiants, one case is unconstrained, two fall on compact coeval star clusters and the other 13 have no progenitor detected. We review and update all the available data for the host galaxies (distance, metallicity and extinction) and determine masses and upper mass estimates using the STARS stellar evolutionary code and a single consistent homogeneous method. A maximum likelihood calculation suggests that the minimum stellar mass for a type II-P to form is m(min)=8.5 +1/-1.5 Msol and the maximum mass for II-P progenitors is m(max)=16.5 +/- 1.5 Msol, assuming a Salpeter initial mass function (in the range Gamma = -1.35 +0.3/-0.7). The minimum mass is consistent with current estimates for white dwarf progenitor masses, but the maximum mass does not appear consistent with massive star populations. Red supergiants in the Local Group have masses up to 25Msol and the minimum mass to produce a Wolf-Rayet star in single star evolution (between solar and LMC metallicity) is similarly 25-30 Msol. We term this discrepancy the "red supergiant problem" and speculate that these stars could have core masses high enough to form black holes and SNe which are too faint to have been detected. Low luminosity SNe with low 56Ni production seem to arise from explosions of low mass progenitors near the mass threshold for core-collapse. (abridged).
Aims: Solar radio type II bursts are rarely seen at frequencies higher than a few hundred MHz. Since metric type II bursts are thought to be signatures of propagating shock waves, it is of interest to know how these shocks, and the type II bursts, are formed. In particular, how are high-frequency, fragmented type II bursts created? Are there differences in shock acceleration or in the surrounding medium that could explain the differences to the "typical" metric type IIs? Methods: We analyse one unusual metric type II event in detail, with comparison to white-light, EUV, and X-ray observations. As the radio event was associated with a flare and a coronal mass ejection (CME), we investigate their connection. We then utilize numerical MHD simulations to study the shock structure induced by an erupting CME in a model corona including dense loops. Results: Our simulations show that the fragmented part of the type II burst can be formed when a coronal shock driven by a mass ejection passes through a system of dense loops overlying the active region.To produce fragmented emission, the conditions for plasma emission have to be more favourable inside the loop than in the interloop area. The obvious hypothesis, consistent with our simulation model, is that the shock strength decreases significantly in the space between the denser loops. The later, more typical type II burst appears when the shock exits the dense loop system and finally, outside the active region, the type II burst dies out when the changing geometry no longer favours the electron shock-acceleration.
We summarize observational results on the stellar population and star formation history of the Scorpius-Centaurus OB Association (Sco OB2), the nearest region of recent massive star formation. It consists of three subgroups, Upper Scorpius (US), Upper Centaurus-Lupus (UCL), and Lower Centaurus-Crux (LCC) which have ages of about 5, 17, and 16 Myr. In Upper Scorpius, numerous studies have recently revealed hundreds of low-mass association members, including dozens of brown dwarfs. The empirical mass function could be established over the full stellar mass range from 0.1 M_sun up to 20 M_sun, and was found to be consistent with recent determinations of the field initial mass function. A narrow range of ages around 5 Myr was found for the low-mass stars, the same age as had previously (and independently) been derived for the high-mass members. This supports earlier indications that the star formation process in US was triggered, and agrees with previous conjectures that the triggering event was a supernova- and wind-driven shock-wave originating from the nearby UCL group. In the older UCL and LCC regions, large numbers of low-mass members have recently been identified among X-ray and proper-motion selected candidates. In both subgroups, low-mass members have also been serendipitously discovered through investigations of X-ray sources in the vicinity of better known regions (primarily the Lupus and TW Hya associations). While both subgroups appear to have mean ages of ~16 Myr, they both show signs of having substructure. Their star-formation histories may be more complex than that of the younger, more compact US group. ... (abstract abbreviated; see paper for full abstract).
We present the results of optical panoramic and long-slit spectroscopy of the nebula MF16 associated with the Ultraluminous X-ray Source NGC6946 ULX-1. More than 20 new emission lines are identified in the spectra. Using characteristic line ratios we find the electron density n_e ~ 600cm^{-3}, electron temperature in the range from ~9000K to ~20 000K (for different diagnostic lines) and the total emitting gas mass M ~ 900 Msolar. We also estimate the interstellar extinction towards the nebula as A_V = 1.m54 somewhat higher than the Galactic absorption. Observed line luminosities and ratios appear to be inconsistent with excitation and ionization by shock waves so we propose the central object responsible for powering the nebula. We estimate the parameters of the ionizing source using photon number estimates and Cloudy modelling. Required EUV luminosity ($\sim 10^{40}$\ergl) is high even if compared with the X-ray luminosity. We argue that independently of their physical nature ULXs are likely to be bright UV and EUV sources. It is shown that the UV flux expected in the GALEX spectral range (1000-3000Angstroms) is quite reachable for UV photometry. Measuring the luminosities and spectral slopes in the UV range may help to distinguish between the two most popular ULX models.
An attempt is made for a new type of analysis of the time-variability of the fine-structure constant trying to fit the recent result from the laboratory measurements, the Oklo constraint and the data from the QSO absorption lines all in consistency with the accelerating universe.
Toroidal magnetic fields subject to the Tayler instability can transport angular momentum. We show that the Maxwell and Reynolds stress of the nonaxisymmetric field pattern depend linearly on the shear in the cylindrical gap geometry. Resulting angular momentum transport also scales linear with shear. It is directed outwards for astrophysical relevant flows and directed inwards for superrotating flows with dOmega/dR>0. We define an eddy viscosity based on the linear relation between shear and angular momentum transport and show that its maximum for given Prandtl and Hartmann number depends linear on the magnetic Reynolds number Rm. For Rm=1000 the eddy viscosity is of the size of 30 in units of the microscopic value.
Thermal emission from the accretion disc around a black hole can be
polarized, due to Thomson scattering in a disc atmosphere. In Newtonian space,
the polarization angle must be either parallel or perpendicular to the
projection of the disc axis on the sky. As first pointed out by Stark and
Connors in 1977, General Relativity effects strongly modify the polarization
properties of the thermal radiation as observed at infinity. Among these
effects, the rotation of the polarization angle with energy is particularly
useful as a diagnostic tool.
In this paper, we extend the Stark and Connors calculations by including the
spectral hardening factor, several values of the optical depth of the
scattering atmosphere and rendering the results to the expected performances of
planned X-ray polarimeters. In particular, to assess the perspectives for the
next generation of X-ray polarimeters, we consider the expected sensitivity of
the detectors onboard the planned POLARIX and IXO missions. We assume the two
cases of a Schwarzschild and an extreme Kerr black hole with a standard thin
disc and a scattering atmosphere. We compute the expected polarization degree
and the angle as functions of the energy as they could be measured for
different inclinations of the observer, optical thickness of the atmosphere and
different values of the black hole spin. We assume the thermal emission
dominates the X-ray band. Using the flux level of the microquasar GRS 1915+105
in the thermal state, we calculate the observed polarization.
Using the linearly polarized intensity and polarization angle data at 3.6, 6.2 and 20 cm, we determine variations of Faraday rotation and depolarization across the nearby galaxy M33. A 3-D model of the regular magnetic field is fitted to the observed azimuthal distribution of polarization angles. Faraday rotation, measured between 3.6 and 6.2 cm at a linear resolution of 0.7 kpc, shows more variation in the south than in the north of the galaxy. About 10% of the nonthermal emission from M33 at 3.6 cm is polarized. We estimate the average total and regular magnetic field strengths in M33 as ~ 6.4 and 2.5 $\mu$G, respectively. Under the assumption that the disk of M33 is flat, the regular magnetic field consists of horizontal and vertical components: however the inferred vertical field may be partly due to a galactic warp. The horizontal field is represented by an axisymmetric (m=0) mode from 1 to 3 kpc radius and a superposition of axisymmetric and bisymmetric (m=0+1) modes from 3 to 5 kpc radius. An excess of differential Faraday rotation in the southern half together with strong Faraday dispersion in the southern spiral arms seem to be responsible for the north-south asymmetry in the observed wavelength dependent depolarization. The presence of an axisymmetric m=0 mode of the regular magnetic field in each ring suggests that a galactic dynamo is operating in M33. The pitch angles of the spiral regular magnetic field are generally smaller than the pitch angles of the optical spiral arms but are twice as big as simple estimates based on the mean-field dynamo theory and M33's rotation curve. Generation of interstellar magnetic fields from turbulent gas motions in M33 is indicated by the equipartition of turbulent and magnetic energy densities.
The PICsIT detector aboard the INTEGRAL satellite was planned to provide information on the emission in the soft gamma-ray band for many bright sources. Because of strong and variable instrumental background only 4 objects were detected so far using the standard software. The moderate sensitivity of PICsIT can be compensated for many objects by a very long exposure time, thanks to INTEGRAL's large field of view and the observing strategy focusing on the Galactic plane. Moreover, with angular resolution much better than that of all other instruments operating in a similar energy band, PICsIT is very suitable for fields too crowded or affected by the Galactic diffuse emission. The new PICsIT spectral extraction method, presented here, is based on three elements: careful modelling of the background, energy-dependent pixel illumination function and sophisticated technique used for extraction of the source count rate. The new method was tested extensively on a large real data set as well as on simulated data. Results assumed in simulations are reproduced perfectly, without any bias and with a high precision. Count rates extracted for Crab are much more stable than those obtained with the standard software. For weaker sources the new method produces much better spectra and allows to detect at least 7 additional objects. Comparison with other INTEGRAL instruments shows that PICsIT is well calibrated and provides the best information on the continuum emission in the 250 keV -- 1 MeV band, covered currently only by INTEGRAL.
We consider an extreme case of disc accretion onto a gravitating centre when the viscosity in the disc is negligible. The angular momentum and the rotational energy of the accreted matter is carried out by a magnetized wind outflowing from the disc. The outflow of matter from the disc occurs due to the Blandford & Payne(1982) centrifugal mechanism. The disc is assumed to be cold. Accretion and outflow are connected by the conservation of the energy, mass and the angular momentum. The basic properties of the outflow, angular momentum flux and energy flux per particle in the wind, do not depend on the details of the structure of the accretion disc. In the case of selfsimilar accretion/outflow, the dependence of the rate of accretion $\dot M$ in the disc depends on the disc radius $r$ on the law $\dot M \sim r^{{1\over2(\alpha^2-1)}}$, where $\alpha$ is a dimensionless Alfvenic radius. In the case of $\alpha \gg 1$, the accretion in the disc is provided by very weak matter outflow from the disc and the outflow predominantly occurs from the very central part of the disc. The solution obtained in the work provides mechanism which transforms the gravitational energy of the accreted matter into the energy of the outflowing wind with efficiency close to 100%. The final velocity can essentially exceed Kepler velocity at the site of the wind launch. This mechanism allows us to understand the nature of the astrophysical objects with low luminosity discs and energetic jet-like outflows.
Radiation from accretion discs in Cataclysmic Variable stars (CVs) provides fundamental information about the properties of these close binary systems and about the physics of accretion in general. Of particular interest are dwarf-nova outburst cycles during which variations of the disc properties allow detailed study of the physical processes in accretion flows. The detailed diagnostics of of accretion disc structure can be achieved by including into its description all the relevant heating and cooling physical mechanism, in particular the convective energy transport. We constructed a radiative transfer code coupled with a code determining the disc vertical structure. We have obtained for the first time model spectra of cold, convective accretion discs. As expected, these spectra are mostly flat in the optical, with no contribution from the UV, which in quiescence must be emitted by the white dwarf. The disc structures obtained with our radiative-transfer code compares well with the solutions of equations used to describe the dwarf-nova outburst cycle according to the thermal-viscous disc instability model thus allowing combining the two. For high temperatures our spectra are compatible with models obtained with Hubeny's code TLUSTY. Our code therefore allows calculating the spectral evolution of dwarf nova stars through their whole outburst cycle, providing a new tool for testing models of accretion discs in cataclysmic variables.
All slightly extended sources were identified on deep K-band maps of 46
spiral galaxies reaching at least K=20.3 mag/arcsec2 at a signal-to-noise level
of 3. The galaxies had inclination angles <65 deg and linear resolutions <100
pc with seeing better than 1". The sample includes both barred and normal
spirals with a wide spread in types. We also analyzed J- and H-band colors for
4 galaxies for which such images were available. An apparent magnitude limit of
K = 19 mag was used for the sources analyzed in order to avoid marginal
detections. Furthermore, we derived the source distributions of magnitudes and
relative locations with respect to the spiral patterns.
Almost 70% (15/22) of the grand-design spiral galaxies show significant
concentration of bright K-band knots in their arm regions corresponding to 30%
(15/46) of the full sample. Color-color diagrams for the 4 spirals with JHK
photometry suggest that a significant fraction of the diffuse sources found in
the arms are complexes of young stellar clusters with ages <10 Myr and reddened
with several magnitudes of visual extinction. The brightest knots reach an
absolute K-band magnitude Mk of -15.5 mag corresponding to stellar clusters or
complexes with total masses up to at least 10^5 Mo. Brightest magnitude and
number of knots correlate with the total absolute magnitude of the host galaxy.
More knots are seen in galaxies with high far-infrared flux and strong
two-armed spiral perturbations. The bright knots constitute up to a few percent
of the total K-band flux from their parent galaxy and account for a star
formation rate of ~1 Mo/yr for the brightest grand-design spiral galaxies.
We reexamine the limits on charged dark matter particles. We show that if their mass and charge fall in the range 100(q_X/e)^2< m_X < 10^8(q_X/e) TeV, then magnetic fields prevent particles in the halo from entering the galactic disk, while those initially trapped inside are accelerated through the Fermi mechanism and ejected within about 0.1-1 Gyrs. Consequently, previous constraints on charged dark matter based on terrestrial non-observation are invalid within that range. Further, we find that charged massive particles may simultaneously solve several long-standing astrophysical problems, including the underabundance of dwarf galaxies, the shallow density profiles in the cores of the LSB galaxies, the absence of cooling flows in the cores of galaxy clusters, and several others.
We report a serendipitous detection of rapid, large amplitude flux density variations in the highly core-dominated, flat-spectrum radio quasar 1156+295 during an observing session at the Very Long Baseline Array (VLBA). The source was observed as a part of the MOJAVE survey programme with the VLBA at 15 GHz on February 5, 2007. Large amplitude variability in the correlated flux density, unexplainable in terms of the source structure, was first discovered while processing the data, and later confirmed by calibrating the antenna gains using 24 other sources observed in the experiment. The source shows variations in the correlated flux density as high as 40% on a timescale of only 2.7 hours. This places 1156+295 between the classical IDV sources and the so-called intra-hour variables. The observed variability timescale and the modulation index of 13% are consistent with interstellar scintillation by a nearby, highly turbulent scattering screen. The large modulation index at 15 GHz implies a scattering measure that is atypically high for a high galactic latitude source such as 1156+295.
Observations of the 2008 February outburst of V452 Cas show that the profile, duration and magnitude at maximum were very similar to the previous superoutburst in 2007 September. Low-amplitude variations consistent with previously observed superhumps were also seen.
We report on low-spectral resolution observations of comet 9P/Tempel 1 from 1983, 1989, 1994 and 2005 using the 2.7m Harlan J. Smith telescope of McDonald Observatory. This comet was the target of NASA's Deep Impact mission and our observations allowed us to characterize the comet prior to the impact. We found that the comet showed a decrease in gas production from 1983 to 2005, with the the decrease being different factors for different species. OH decreased by a factor 2.7, NH by 1.7, CN by 1.6, C$_{3}$ by 1.8, CH by 1.4 and C$_{2}$ by 1.3. Despite the decrease in overall gas production and these slightly different decrease factors, we find that the gas production rates of OH, NH, C$_{3}$, CH and C$_{2}$ ratioed to that of CN were constant over all of the apparitions. We saw no change in the production rate ratios after the impact. We found that the peak gas production occurred about two months prior to perihelion. Comet Tempel 1 is a "normal" comet.
We present high-quality J, H and K photometry of four Small Magellanic Cloud stellar clusters with intermediate ages in the 1-7 Gyr range (namely NGC 339, 361, 416 and 419) . We obtained deep Color-Magnitude Diagrams to study the evolved sequences and providing a detailed census of the Red Giant Branch (RGB), Asymptotic Giant Branch (AGB) and Carbon star populations in each cluster and their contribution to the total cluster light. We find that in the 5-7 Gyr old clusters AGB stars account for ~6 % of the total light in K-band, Carbon stars are lacking and RGB stars account for ~45 % of the total bolometric luminosity. These empirical findings are in good agreement with the theoretical predictions. Finally, we derived photometric metallicities computed by using the properties of the RGB and finding an iron content of [Fe/H]=-1.18, -1.08, -0.99 and -0.96 dex for NGC 339, 361, 416 and 419 respectively.
Caustics are a generic feature of the nonlinear growth of structure in the dark matter distribution. If the dark matter were absolutely cold, its mass density would diverge at caustics, and the integrated annihilation probability would also diverge for individual particles participating in them. For realistic dark matter candidates, this behaviour is regularised by small but non-zero initial thermal velocities. We present a mathematical treatment of evolution from Hot, Warm or Cold Dark Matter initial conditions which can be directly implemented in cosmological N-body codes. It allows the identification of caustics and the estimation of their annihilation radiation in fully general simulations of structure formation.
We present two series of MOST (Microvariability & Oscillations of STars) space-based photometry, covering nearly continuously 10 days in 2004 and 30 days in 2007, of selected variable stars in the upper Main Sequence of the old open cluster M67. New high-precision light curves were obtained for the blue-straggler binary/triple systems AH Cnc, ES Cnc and EV Cnc. The precision and phase coverage of ES Cnc and EV Cnc is by far superior to any previous observations. The light curve of ES Cnc is modelled in detail, assuming two dark photospheric spots and Roche geometry. An analysis of the light curve of AH Cnc indicates a low mass ratio (q about 0.13) and a high inclination angle for this system. Two new long-period eclipsing binaries, GSC 814-323 and HD75638 (non-members of M67) were discovered. We also present ground-based DDO spectroscopy of ES Cnc and of the newly found eclipsing binaries. Especially interesting is HD75638, a member of a visual binary, which must itself be a triple or a higher-multiplicity system. New light curves of two delta Scuti pulsators, EX Cnc and EW Cnc, have been analyzed leading to detection of 26 and 8 pulsation frequencies of high temporal stability.
We present a code for solving the coupled Einstein-hydrodynamics equations to evolve relativistic, self-gravitating fluids. The Einstein field equations are solved in generalized harmonic coordinates on one grid using pseudospectral methods, while the fluids are evolved on another grid using shock-capturing finite difference or finite volume techniques. We show that the code accurately evolves equilibrium stars and accretion flows. Then we simulate an equal-mass nonspinning black hole-neutron star binary, evolving through the final four orbits of inspiral, through the merger, to the final stationary black hole. The gravitational waveform can be reliably extracted from the simulation.
Assuming that the positron excess in PAMELA data is a consequence of annihilations of cold dark matter lighter than the top quark, we consider from a model-independent perspective if the data show a preference for the spin of dark matter.
Since that very memorable day at the Beijing 2008 Olympics, a big question on every sports commentator's mind has been "What would the 100 meter dash world record have been, had Usain Bolt not celebrated at the end of his race?" Glen Mills, Bolt's coach suggested at a recent press conference that the time could have been 9.52 seconds or better. We revisit this question by measuring Bolt's position as a function of time using footage of the run, and then extrapolate into the last two seconds based on two different assumptions. First, we conservatively assume that Bolt could have maintained Richard Thompson's, the runner-up, acceleration during the end of the race. Second, based on the race development prior to the celebration, we assume that he could also have kept an acceleration of 0.5 m/s^2 higher than Thompson. In these two cases, we find that the new world record would have been 9.61 +/- 0.04 and 9.55 +/- 0.04 seconds, respectively, where the uncertainties denote 95% statistical errors.
Warm dark matter (WDM) may resolve the conflict between observed galaxy halos and singular halos produced in cold dark matter (CDM) simulations. Here we extend the MSSM to include WDM by adding a gauge singlet fermion, \bar{\chi}, with a portal-like coupling to the MSSM Higgs doublets. In the case where M_{\bar{\chi}} is mainly due to electroweak symmetry breaking, the \bar{\chi} mass is completely determined by its relic density and the reheating temperature, T_R. For 10^2 GeV ^{<}_{\sim} T_{R} ^{<}_{\sim} 10^6 GeV, the range allowed by thermal \bar{chi} production via Higgs scattering and the gravitino upper bound, the \bar{\chi} mass is in the range 0.1-4 keV. Remarkably, this is the range required for WDM. The primordial phase-space density, Q, can account for that observed in dwarf spheroidal galaxies, Q \approx 5 \times 10^6, when the reheating temperature is in the range T_R \approx 10-100 TeV, in which case M_{\bar{\chi}} \approx 0.36 keV. The corresponding free-streaming length is approximately 1 Mpc.
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We use a Press-Schechter-like calculation to study how the abundance of voids changes in models with non-Gaussian initial conditions. While a positive skewness increases the cluster abundance, a negative skewness does the same for the void abundance. We determine the dependence of the void abundance on the non-Gaussianity parameter fnl for the local-model bispectrum-which approximates the bispectrum in some multi-field inflation models-and for the equilateral bispectrum, which approximates the bispectrum in e.g. string-inspired DBI models of inflation. We show that the void abundance in large-scale-structure surveys currently being considered should probe values as small as fnl < 10 and fnl^eq < 30, over distance scales ~10 Mpc.
We present an analysis of the spectral energy distribution (SED) of the galaxy ESO 184-G82, the host of the closest known long gamma-ray burst (GRB) 980425 and its associated supernova SN 1998bw. We use our observations obtained at the Australia Telescope Compact Array (the third >3 sigma radio detection of a GRB host) as well as archival infrared (IR) and ultraviolet (UV) observations to estimate its star formation state. We find that ESO 184-G82 has a UV star formation rate (SFR) and stellar mass consistent with the population of cosmological GRB hosts and of local dwarf galaxies. It has however a higher specific SFR (per unit stellar mass) and lower molecular gas-to-dust ratio than luminous spiral galaxies. The mass of ESO 184-G82 is dominated by an older stellar population in contrast to the majority of GRB hosts. The Wolf-Rayet region ~800 pc from the supernova site experienced a starburst episode during which the majority of its stellar population was built up. Unlike that of the entire galaxy, its SED is similar to those of cosmological submillimeter/radio-bright GRB hosts with hot dust content. These findings add to the picture that in general, the environments of GRBs on 1-3 kpc scales are associated with high specific SFR and hot dust.
We investigate the dependence of pulse amplitudes of accreting millisecond pulsars on the masses of the neutron stars. Because the pulsation amplitudes are suppressed as the neutron stars become more massive, the probability of detection of pulsations decreases in systems that have been accreting for a long time. However, the probability of detectable pulsations is higher in transient systems where the mass accretion is sporadic and the neutron star is likely to have a low mass. We propose this mechanism as the explanation of the small number of millisecond X-ray pulsars found to date, as well as their emergence as fast pulsars mostly in transient, low-Mdot systems. This mechanism can also quantitatively explain the lack of pulsars in the majority of LMXBs.
The progenitors of SN 2008S and the luminous 2008 transient in NGC 300 were dust-enshrouded, with extremely red mid-infrared (MIR) colors. In addition, the MIR luminosities of the M85 transient and SN 1999bw suggest that their progenitors were also highly obscured. As a class, these events were optically-faint (-13 < M_V < -15) compared to normal core-collapse supernovae (SNe). Whether they are true SNe or a new class of massive star eruptions, we argue that their rate is of order (but likely less than) the rate of normal SN. This fact is remarkable because very few massive stars in any galaxy, at any moment, have the characteristics of the progenitors of SN 2008S and NGC 300. We show this by extracting mid-infrared and optical luminosity, color, and variability properties of massive stars in M33 using archival imaging. We find that the fraction of all massive stars with colors consistent with the SN 2008S and NGC 300 progenitors is < 1/2000. Only ~10 similar objects, all at the red, high luminosity extremum of the AGB sequence, exist in M33. That these transients are relatively common relative to SNe, while their progenitors are remarkably rare compared to massive stars, implies that the dust-enshrouded phase is a short-lived phenomenon in the lives of many massive stars. This shrouded epoch can occur only in the last < 10^4 yr before explosion, be it death or merely eruption. We discuss the implications of this finding for the evolution and census of "low-mass" massive stars (i.e., 8-11M_sun), and we connect it with theoretical discussions of electron-capture SNe. A survey with (warm) Spitzer of local galaxies for analogous progenitors would significantly improve our knowledge of this channel to massive stellar explosions. (Abridged)
Context. Recent studies have suggested that moving groups have a dynamic or "resonant" origin. Under this hypothesis, these kinematic structures become a powerful tool for studying the large-scale structure and dynamics of the Milky Way. Aims. We aim to characterize these structures in the U-V-age-[Fe/H] space and establish observational constraints that will allow us to study their origin and evolution. Methods. We apply multiscale techniques -wavelet denoising (WD)- to an extensive compendium of more than 24000 stars in the solar neighbourhood with the best available astrometric, photometric and spectroscopic data. Results. We confirm that the dominant structures in the U-V plane are the branches of Sirius, Coma Berenices, Hyades-Pleiades and Hercules, which are nearly equidistant in this kinematic plane and show a negative slope. The abrupt drops in the velocity distribution are characterized. We find a certain dependence of these kinematic structures on Galactic position with a significant change of contrast among substructures inside the branches. A large spread of ages is observed for all branches. The Hercules branch is detected in all subsamples with ages older than ~ 2 Gyr and the set of the other three branches is well established for stars > 400 Myr. The age-metallicity relation of each branch is examined and the relation between kinematics and metallicity is studied. Conclusions. Not all of these observational constraints are successfully explained by the recent models proposed for the formation of such kinematic structures. Simulations incorporating stellar ages and metallicities are essential for future studies. The comparison of the observed and simulated distributions obtained by WD will provide a physical interpretation of the existence of the branches in terms of local or large-scale dynamics. [Abridged]
Global star formation is the key to understanding galaxy disk formation. This in turn depends on gravitational instability of disks and continuing gas accretion as well as minor merging. A key component is feedback from supernovae. Primary observational constraints on disk galaxy formation and evolution include the Schmidt-Kennicutt law, the Tully-Fisher relation and the galaxy luminosity function. I will review how theory confronts phenomenology, and discuss future prospects for refining our understanding of disk formation.
We simulate anisotropic outflows of AGN, and investigate the large-scale impact of the cosmological population of AGN outflows over the Hubble time by performing N-body LambdaCDM simulations. Using the observed quasar luminosity function to get the redshift and luminosity distribution, and analytical models for the outflow expansion, AGNs are allowed to evolve in a cosmological volume. By the present epoch, 13 - 25% of the total volume is found to be pervaded by AGN outflows, with 10^{-9} G magnetic field.
We describe possible scenarios of quark deconfinement in compact stars and we analyze their astrophysical implications. The quark deconfinement process can proceed rapidly, as a strong deflagration, releasing a huge amount of energy in a short time and generating an extra neutrino burst. If energy is transferred efficiently to the surface, like e.g. in the presence of convective instabilities, this burst could contribute to revitalize a partially failed SN explosion. We discuss how the neutrino observations from SN1987A would fit in this scenario. Finally, we focus on the fate of massive and rapidly rotating progenitors, discussing possible time separations between the moment of the core collapse and the moment of quark deconfinement. This mechanism can be at the basis of the interpretation of gamma ray bursts in which lines associated with heavy elements are present in the spectrum.
We have imaged 45 quasars from the Sloan Digital Sky Survey (SDSS) with redshifts 1.85 < z < 4.26 in JHKs with the KPNO SQIID imager. By combining these data with optical magnitudes from the SDSS we have computed the restframe optical spectral indices of this sample and investigate their relation to quasar redshift. We find a mean spectral index of <alpha_o> = -0.55+/-0.42 with a large spread in values. We also find possible evolution of the form alpha_o = (0.148+/-0.068)z - (0.964+/-0.200)$ in the luminosity range -28.0 < M_i < -26.5. Such evolution suggests changes in the accretion process in quasars with time and is shown to have an effect on computed quasar luminosity functions.
The supernova (SN) neutronization phase produces mainly electron ($\nu_e$) neutrinos, the oscillations of which must take place within a few mean-free-paths of their resonance surface located nearby their neutrinosphere. The state-of-the-art on the SN dynamics suggests that a significant part of these $\nu_e$ can convert into right-handed neutrinos in virtue of the interaction of the electrons and the protons flowing with the SN outgoing plasma, whenever the Dirac neutrino magnetic moment be of strength $\mu_\nu < 10^{-11} \mu_{\rm B}$, with $\mu_{\rm B}$ being the Bohr magneton. In the supernova envelope, part of these neutrinos can flip back to the left-handed flavors due to the interaction of the neutrino magnetic moment with the magnetic field in the SN expanding plasma (Kuznetsov & Mikheev 2007; Kuznetsov, Mikheev & Okrugin 2008), a region where the field strength is currently accepted to be $B \gtrsim 10^{13}$ ~G. This type of $\nu$ oscillations were shown to generate powerful gravitational wave (GW) bursts (Mosquera Cuesta 2000, Mosquera Cuesta 2002, Mosquera Cuesta & Fiuza 2004, Loveridge 2004). If such double spin-flip mechanism does run into action inside the SN core, then the release of both the oscillation-produced $\nu_\mu$s, $\nu_\tau$s and the GW pulse generated by the coherent $\nu$ spin-flips provides a unique emission offset $\Delta T^{emission}_{\rm GW} \leftrightarrow \nu = 0$ for measuring the $\nu$ travel time to Earth. As massive $\nu$s get noticeably delayed on its journey to Earth with respect to the Einstein GW they generated during the reconversion transient, then the accurate measurement of this time-of-flight delay by SNEWS + LIGO, VIRGO, BBO, DECIGO, etc., might readily assess the absolute $\nu$ mass spectrum.
We aim to obtain a complete sample of redshift > 3.6 radio QSOs from FIRST sources having star-like counterparts in the SDSS DR5 photometric survey (r<=20.2). We found that simple supervised neural networks, trained on sources with SDSS spectra, and using optical photometry and radio data, are very effective for identifying high-z QSOs without spectra. The technique yields a completeness of 96 per cent and an efficiency of 62 per cent. Applying the trained networks to 4415 sources without DR5 spectra we found 58 z>=3.6 QSO candidates. We obtained spectra of 27 of them, and 17 are confirmed as high-z QSOs. Spectra of 13 additional candidates from the literature and from SDSS DR6 revealed 7 more z>=3.6 QSOs, giving and overall efficiency of 60 per cent. None of the non-candidates with spectra from NED or DR6 is a z>=3.6 QSO, consistently with a high completeness. The initial sample of z>=3.6 QSOs is increased from 52 to 76, i.e. by a factor 1.46. From the new identifications and candidates we estimate an incompleteness of SDSS for the spectroscopic classification of FIRST 3.6<=z<=4.6 QSOs of 15 percent for r<=20.2.
We report basic far-infrared (FIR) properties of eight blue compact dwarf galaxies (BCDs) observed by AKARI. We measure the fluxes at the four FIS bands (wavelengths of 65 um, 90 um, 140 um, and 160 um). Based on these fluxes, we estimate basic quantities about dust: dust temperature, dust mass, and total FIR luminosity. We find that the typical dust temperature of the BCD sample is systematically higher than that of normal spiral galaxies, although there is a large variety. The interstellar radiation field estimated from the dust temperature ranges up to 100 times of the Galactic value. This confirms the concentrated star-forming activity in BCDs. The star formation rate can be evaluated from the FIR luminosity as 0.01--0.5 $M_\odot$ yr$^{-1}$. Combining this quantity with gas mass taken from the literature, we estimate the gas consumption timescales (gas mass divided by the star formation rate), which prove to span a wide range from 1 Gyr to 100 Gyr. A natural interpretation of this large variety can be provided by intermittent star formation activity. We finally show the relation between dust-to-gas ratio and metallicity (we utilize our estimate of dust mass, and take other necessary quantities from the literature). There is a positive correlation between dust-to-gas ratio and metallicity as expected from chemical evolution models.
The recent discovery of the 2003EL61 collisional family in the Kuiper belt (Brown et al., 2007) is surprising because the formation of such a family is a highly improbable event in today's belt. Assuming Brown et al.'s estimate of the size of progenitors, we find that the probability that a Kuiper belt object was involved in such a collision since primordial times is less than roughly 0.001. In addition, it is not possible for the collision to have occurred in a massive primordial Kuiper belt because the dynamical coherence of the family would not have survived whatever event produced the currently observed orbital excitation. Here we suggest that the family is the result of a collision between two scattered disk objects. We show that the probability that a collision occurred between two such objects with sizes similar to those advocated in Brown et al. (2007) and that the center of mass of the resulting family is on an orbit typical of the Kuiper belt can be as large as 47%. Given the large uncertainties involved in this estimate, this result is consistent with the existence of one such family. If true, this result has implications far beyond the origin of a single collisional family, because it shows that collisions played an important role in shaping the dynamical structure of the small body populations that we see today.
We present results on the modelling of the ejection of a superluminal component in the jet of 3C111. We propose that the component is generated by an injection of dense material followed by a decrease in the injection rate of bulk particles in the jet. Our model is supported by 1D relativistic hydrodynamics and emission simulations, and is capable of reproducing the brightness evolution of two features, as revealed by 15 GHz VLBA observations. We show that other scenarios, such as an increase of the Lorentz factor in the material of the perturbation, fails to reproduce the observed evolution of this flare.
Many studies assume that the solar irradiance in the EUV can be decomposed into different contributions, which makes the modelling of the spectral variability considerably easier. We consider a different approach, in which these contributions are not imposed a priori but are effectively and robustly inferred from spectral irradiance measurements. This is a source separation problem with a positivity constraint, for which we use a Bayesian solution. Using five years of daily EUV spectra recorded by the TIMED/SEE satellite, we show that the spectral irradiance can be decomposed into three elementary spectra. Our results suggest that they describe different layers of the solar atmosphere rather than specific regions. The temporal variability of these spectra is discussed.
Distances of galaxies in the Hubble Space Telescope Key Project are based on the Cepheid period-luminosity relation. An alternative basis is the tip of the red giant branch. Using archival HST data, we calibrate the infrared Tully-Fisher relation using 14 galaxies with tip of the red giant branch measurements. Compared with the Key Project, a higher value of the Hubble Constant by 10% +/- 7% is inferred. Within the errors the two distance scales are therefore consistent. We describe the additional data required for a conclusive tip of the red giant branch measurement of H_0.
The results of speckle interferometric observations of 115 metal-poor stars [m/H]<-1 within 250 pc from the Sun and with proper motions mu <= 0.2"/yr, made with the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences, are reported. Close companions with separations ranging from 0.034" to 1" were observed for 12 objects - G76-21, G59-1, G63-46, G135-16, G168-42, G141-47, G142-44, G190-10, G28-43, G217-8, G130-7, and G89-14 - eight of them are astrometrically resolved for the first time. The newly resolved systems include one triple star - G190-10. If combined with spectroscopic and visual data, our results imply a single:binary:triple:quadruple star ratio of 147:64:9:1 for a sample of 221 primary components of halo and thick-disk stars.
The H.E.S.S. survey of the Galactic plane has established the existence of a substantial number (~40) of Galactic TeV gamma-ray sources, a large fraction of which remain unidentified. HESS J0632+057 is one of a small fraction of these objects which is point-like in nature(<2' rms), and is one of only two point-like sources that remain unidentified. Follow-up observations of this object with XMM-Newton have revealed an X-ray source coincident with the TeV source and with the massive star MWC 148, of spectral type B0pe. This source exhibits a hard spectrum, consistent with an absorbed power-law with Gamma = 1.26 +/- 0.04, and shows significant variability on hour timescales. We discuss this spatial coincidence and the implied spectral energy distribution of this object and argue that it is likely a new gamma-ray binary system with a close resemblance to the three known members of this class, and in particular to LS I +61 303. Further X-ray, radio and optical observations of this system are needed to firmly establish HESS J0632+057 as a new member of this rare class of Galactic objects.
In this chapter we review the properties of the Orion outlying clouds at b < -21 degrees. These clouds are located far off the Orion giant molecular cloud complex and are in most cases small cometary-shaped clouds, with their head pointing back towards the main Orion clouds. A wealth of data indicate that star formation is ongoing in many of these clouds. The star formation in these regions might have been triggered due to the strong impact of the massive stars in the Orion OB association. Some of the clouds discussed here may be part of the Orion-Eridanus bubble. An overview on each individual cloud is given. A synthesis of the Pre-Main Sequence stars discovered in these clouds is presented. We also discuss the millimeter and centimeter data and present a review of the outflows and Herbig-Haro objects so far discovered in these clouds.
A simple method to compute numerically the lowest eigenmodes of the Laplacian in compact orientable hyperbolic spaces of dimension 3 is presented. It is applied to the Thurston manifold, the Weber-Seifert manifold, and to the spaces whose fundamental domain is a regular icosahedron.
We observed the southwestern region of the Cygnus Loop in two pointings with \textit{XMM-Newton}. The region observed is called the "blow-out" region that is extended further in the south. The origin of the "blow-out" is not well understood while it is suggested that there is another supernova remnant here in radio observation. To investigate the detail structure of this region in X-ray, we divided our fields of view into 33 box regions. The spectra are well fitted by a two-component nonequilibrium ionization model. The emission measure distributions of heavy elements decrease from the inner region to the outer region of the Loop. Then, we also divided our fields of view into 26 annular sectors to examine the radial plasma structure. Judging from metal abundances obtained, it is consistent with that the X-ray emission is the Cygnus Loop origin and we concluded that high-$kT_{e}$ component ($\sim$0.4 keV) originates from the ejecta while low-$kT_{e}$ component ($\sim$0.2 keV) is derived from the swept-up interstellar medium. The flux of low-$kT_{e}$ component is much less than that of high-$kT_{e}$ component, suggesting the ISM component is very thin. Also, the relative abundances in the ejecta component shows similar values to those obtained from previous observations of the Cygnus Loop. We find no evidence in X-ray that the nature of the "blow-out" region originated from the extra supernova remnant. From the ejecta component, we calculated the masses for various metals and estimated the origin of the Cygnus Loop as the core-collapse explosion rather than the Type Ia supernova.
The nearby long GRB 060614 was not accompanied by a supernova, challenging the collapsar model for long-duration GRBs and the traditional classification scheme for GRBs. However, Cobb et al. have argued that the association of GRB 060614 and its host galaxy could be chance coincidence. In this work we calculate the probability for a GRB to be randomly coincident with a galaxy on the sky, using a galaxy luminosity function obtained from current galaxy surveys. We find that, with a magnitude limit that current telescopes can reach and an evolving galaxy luminosity function obtained from VVDS, the probability for chance coincidence of a GRB with a galaxy of redshift <1.5 is about several percent. These results agree with previous estimates based on observed galaxies. For the case of GRB 060614, the probability for it to be coincident with a z<0.125 galaxy by angular separation <0.5" is ~0.03, indicating that the association of GRB 060614 and its host galaxy is secure. If the telescope magnitude limit is significantly improved in future, the probability for GRB-galaxy association will be considerably large, making it very problematic to identify a GRB host based only on the superposition of a GRB and a galaxy on the sky.
A new search result of the Tokyo axion helioscope is presented. The axion helioscope consists of a dedicated cryogen-free 4T superconducting magnet with an effective length of 2.3 m and PIN photodiodes as x-ray detectors. Solar axions, if exist, would be converted into X-ray photons through the inverse Primakoff process in the magnetic field. Conversion is coherently enhanced even for massive axions by filling the conversion region with helium gas. The present third phase measurement sets a new limit of g_{a\gamma\gamma}<(5.6--13.4)\times10^{-10} GeV^{-1} for the axion mass of 0.84<m_a<1.0 eV at 95% confidence level.
We present an analysis of the chemical abundances of the star Tycho G in the direction of the remnant of supernova (SN) 1572, based on Keck high-resolution optical spectra. The stellar parameters of this star are found to be those of a G-type subgiant with $T_{\mathrm{eff}} = 5900 \pm 100$ K, \loggl $ = 3.85 \pm 0.30$ dex, and $\mathrm{[Fe/H]} = -0.05 \pm 0.09$. This determination agrees with the stellar parameters derived for the star in a previous survey for the possible companion star of SN 1572 (Ruiz-Lapuente et al. 2004). The chemical abundances follow the Galactic trends, except for Ni, which is overabundant relative to Fe, $[{\rm Ni/Fe}] $ $=$ 0.16 $\pm$ 0.04. Co is slightly overabundant (at a low significance level). These enhancements in Fe-peak elements could have originated from pollution by the supernova ejecta. We find a surprisingly high Li abundance for a star that has evolved away from the main sequence. We discuss these findings in the context of companion stars of supernovae.
We have made multi-epoch VLBI observations of H2O maser emission in the massive star forming region IRAS 06061+2151 with the Japanese VLBI network (JVN) from 2005 May to 2007 October. The detected maser features are distributed within an 1\arcsec$\times$1\arcsec (2000 au$\times$2000 au at the source position) around the ultra-compact H {\small\bf II} region seen in radio continuum emission. Their bipolar morphology and expanding motion traced through their relative proper motions indicate that they are excited by an energetic bipolar outflow. Our three-dimensional model fitting has shown that the maser kinematical structure in IRAS 06061+2151 is able to be explained by a biconical outflow with a large opening angle ($>$ 50\degr). The position angle of the flow major axis coincides very well with that of the large scale jet seen in 2.1$\:\mu\rmn{m}$ hydrogen emission. This maser geometry indicates the existence of dual structures composed of a collimated jet and a less collimated massive molecular flow. We have also detected a large velocity gradient in the southern maser group. This can be explained by a very small (on a scale of several tens of au) and clumpy (the density contrast by an order of magnitude or more) structure of the parental cloud. Such a structure may be formed by strong instability of shock front or splitting of high density core.
We present a measure of the inclination of the velocity ellipsoid at 1 kpc below the Galactic plane using a sample of red clump giants from the RAVE DR2 release. We find that the velocity ellipsoid is tilted towards the Galactic plane with an inclination of 7.3 +/-1.8 degree. We compare this value to computed inclinations for two mass models of the Milky Way. We find that our measurement is consistent with a short scale length of the stellar disc (Rd ~2 kpc) if the dark halo is oblate or with a long scale length (Rd~3 kpc) if the dark halo is prolate. Once combined with independent constraints on the flattening of the halo, our measurement suggests that the scale length is approximately halfway between these two extreme values, with a preferred range [2.5-2.7] kpc for a nearly spherical halo. Nevertheless, no model can be clearly ruled out. With the continuation of the RAVE survey, it will be possible to provide a strong constraint on the mass distribution of the Milky Way using refined measurements of the orientation of the velocity ellipsoid.
Quantum fast-roll initial conditions for the inflaton which are different from the classical fast-roll conditions and from the quantum slow-roll conditions can lead to inflation that last long enough. These quantum fast-roll initial conditions for the inflaton allow for kinetic energies of the same order of the potential energies and nonperturbative inflaton modes with nonzero wavenumbers. Their evolution starts with a transitory epoch where the redshift due to the expansion succeeds to assemble the quantum excited modes of the inflaton in a homogeneous (zero mode) condensate, and the large value of the Hubble parameter succeeds to overdamp the fast-roll of the redshifted inflaton modes. After this transitory stage the effective classical slow-roll epoch is reached. Most of the efolds are produced during the slow-roll epoch and we recover the classical slow-roll results for the scalar and tensor metric perturbations plus corrections. These corrections are important, both for scalar and for tensor perturbations, if scales which are horizon-size today exited the horizon by the end of the transitory stage and as a consequence the lower CMB multipoles get suppressed (fast-roll) or enhanced (precondensate). These two types of corrections can compete and combine in a scale dependent manner. They arise as natural consequences of the quantum nonperturbative inflaton dynamics, and provide a consistent and contrastable model for the origin of the suppression of the quadrupole and for other departures of the low CMB multipoles from the slow-roll inflation-LambdaCMB model which are to be contrasted to the TE and EE multipoles and to the forthcoming and future CMB data.
We present an up to date review of Big Bang Nucleosynthesis (BBN). We discuss the main improvements which have been achieved in the past two decades on the overall theoretical framework, summarize the impact of new experimental results on nuclear reaction rates, and critically re-examine the astrophysical determinations of light nuclei abundances. We report then on how BBN can be used as a powerful test of new physics, constraining a wide range of ideas and theoretical models of fundamental interactions beyond the standard model of strong and electroweak forces and Einstein's general relativity.
The Flamingos-2 Tandem Tunable filter is a tunable, narrow-band filter, consisting of two Fabry-Perot etalons in series, capable of scanning to any wavelength from 0.95 to 1.35 microns with a spectral resolution of R~800. It is an accessory mode instrument for the near-IR Flamingos-2 imaging-spectrograph designed for the Gemini South 8m Observatory and will be fed through the upcoming Multi-Conjugate Adaptive Optics feed. The primary science goal of the F2T2 filter is to perform a ground-based search for the first star forming regions in the universe at redshifts of 7 < z < 11. The construction of the F2T2 filter is complete and it is currently in its calibration and commissioning phases. In this proceeding, we describe the calibration and performance of the instrument.
We model the cosmological co-evolution of galaxies and their central supermassive black holes (BHs) within a semi-analytical framework developed on the outputs of the Millennium Simulation (Croton et al., 2006; De Lucia & Blaizot, 2007). In this work, we analyze the model BH scaling relations, fundamental plane and mass function, and compare them with the most recent observational data. Furthermore, we extend the original code developed by Croton et al. (2006) to follow the evolution of the BH mass accretion and its conversion into radiation, and compare the derived AGN bolometric luminosity function with the observed one. We find, for the most part, a very good agreement between predicted and observed BH properties. Moreover, the model is in good agreement with the observed AGN number density in 0<z<5, provided it is assumed that the cold gas fraction accreted by BHs at high redshifts is larger than at low redshifts (Marulli et al., 2008).
Recent N-body simulations showed that the dynamical decay of the young (~1 Myr) Orion Nebula cluster could be responsible for the loss of at least a half of its initial content of OB stars. This result suggests that other young stellar systems also could lose a significant fraction of their massive stars at the very beginning of their evolution. To check this expectation, we used the Mid-Infrared Galactic Plane Survey (carried out with the Midcourse Space Experiment satellite) to search for bow shocks around a number of young ($\la$ several Myr) clusters and OB associations. We discovered dozens bow shocks generated by OB stars runaway from these stellar systems, supporting the idea of significant dynamical loss of OB stars. In this paper we report the discovery of three bow shocks produced by O-type stars ejected from the open cluster NGC 6611 (M16). One of the bow shocks is associated with the O9.5Iab star HD165319, which was suggested as one of "the best examples for isolated Galactic high-mass star formation". Possible implications of our results for the origin of field OB stars are discussed.
Gamma-Ray Bursts (GRB) are the most energetic events in the Universe, and provide a complementary probe of dark energy by allowing the measurement of cosmic expansion history that extends to redshifts greater than 6. Unlike Type Ia supernovae (SNe Ia), GRBs must be calibrated for each cosmological model considered, because of the lack of a nearby sample of GRBs for model-independent calibration. For a flat Universe with a cosmological constant, we find $\Omega_m=0.25^{+0.12}_{-0.11}$ from 69 GRBs alone. We show that the current GRB data can be summarized by a set of model-independent distance measurements, with negligible loss of information. We constrain a dark energy equation of state linear in the cosmic scale factor using these distance measurements from GRBs, together with the "Union" compilation of SNe Ia, WMAP five year observations, and the SDSS baryon acoustic oscillation scale measurement. We find that a cosmological constant is consistent with current data at 68% confidence level for a flat Universe. Our results provide a simple and robust method to incorporate GRB data in a joint analysis of cosmological data to constrain dark energy.
Mirror matter is a self-collisional dark matter candidate. If exact mirror parity is a conserved symmetry of the nature, there could exist a parallel hidden (mirror) sector of the Universe which has the same kind of particles and the same physical laws of our (visible) sector. The two sectors interact each other only via gravity, therefore mirror matter is naturally "dark". The most promising way to test this dark matter candidate is to look at its astrophysical signatures, as Big Bang nucleosynthesis, primordial structure formation and evolution, cosmic microwave background and large scale structure power spectra.
Quasi-equilibrium models of rapidly rotating triaxially deformed stars are computed in general relativistic gravity, assuming a conformally flat spatial geometry (Isenberg-Wilson-Mathews formulation) and a polytropic equation of state. Highly deformed solutions are calculated on the initial slice covered by spherical coordinate grids, centered at the source, in all angular directions up to a large truncation radius. Constant rest mass sequences are calculated from nearly axisymmetric to maximally deformed triaxial configurations. Selected parameters are to model (proto-) neutron stars; the compactness is M/R = 0.001, 0.1, 0.14, 0.2 for polytropic index n = 0.3 and M/R = 0.001, 0.1, 0.12, 0.14 for n = 0.5. We confirmed that the triaxial solutions exist for these parameters as in the case of Newtonian polytropes. However, it is also found that the triaxial sequences become shorter for higher compactness, and those may disappear at a certain large compactness for the n = 0.5 case. In the scenario of the contraction of proto-neutron stars being subject to strong viscosity and rapid cooling, it is plausible that, once the viscosity driven secular instability sets in during the contraction, the proto-neutron stars are always maximally deformed triaxial configurations, as long as the compactness and the equation of state parameters allow such triaxial sequences. Detection of gravitational waves from such sources may be used as another probe for the nuclear equation of state.
Mirror matter is a promising self-collisional dark matter candidate. Here we study the evolution of thermodynamical quantities in the early Universe for temperatures below ~100 MeV in presence of a hidden mirror sector with unbroken parity symmetry and with gravitational interactions only. This range of temperatures is interesting for primordial nucleosynthesis analyses, therefore we focus on the temporal evolution of number of degrees of freedom in both sectors. Numerically solving the equations, we obtain the interesting prediction that the effective number of extra-neutrino families raises for decreasing temperatures before and after Big Bang nucleosynthesis; this could help solving the discrepancy in this number computed at nucleosynthesis and cosmic microwave background formation epochs.
We consider the prospects for dark matter/energy unification in k-essence type theories. General mappings are established between the k-essence scalar field, the hydrodynamic and braneworld descriptions. We develop an extension of the general relativistic dust model that incorporates the effects of both pressure and the associated acoustic horizon. Applying this to a tachyon model, we show that this inhomogeneous "variable Chaplygin gas" does evolve into a mixed system containing cold dark matter like gravitational condensate in significant quantities. Our methods can be applied to any dark energy model as well as to mixtures of dark energy and traditional dark matter.
We calculate the spin dependent Fermi liquid parameters (FLPs), single particle energies and energy densities of various spin states of polarized quark matter. The expressions for the incompressibility($K$) and sound velocity ($c_1$) in terms of the spin dependent FLPs and polarization parameter $(\xi)$ are derived. Estimated values of $K$ and $c_1$ reveal that the equation of state (EOS) of the polarized matter is stiffer than the unpolarized one. Finally we investigate the possibility of the spin polarization (ferromagnetism) phase transition.
We propose a regular classical field theory realisation of the Dvali-Gabadadze-Porrati mechanism by considering our universe to be the four-dimensional core of a seven dimensional 't Hooft-Polyakov hypermonopole. We show the existence of metastable gravitons trapped in the core. Their mass spectrum is discrete, positive definite, and computed for various values of the field coupling constants: the resulting Newton gravity law is seven-dimensional at small and large distances but can be made four-dimensional on intermediate length scales. There is no need of a cosmological constant in the bulk, the spacetime is asymptotically flat and of infinite volume in the extra-dimensions. Confinement is achieved through the local positive curvature of the extra-dimensions induced by the monopole-forming fields and for natural values of the coupling constants of order unity.
We solve one of the open problems in Einstein-Cartan theory, namely we find a natural matter source whose spin angular momentum tensor is compatible with the cosmological principle. We analyze the resulting evolution equations and find that an epoch of accelerated expansion is an attractor. The torsion field quickly decays in that period. Our results are interpreted in the context of the standard model of cosmology.
In this paper we discuss light neutrino dipole moments, computed in the neutrino-mass extended standard model (SM), as a possible source for neutrino condensates which may cause cosmological constant observed today.
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Naively, one would expect longer papers to have larger impact (i.e., to be cited more). I tested this expectation by selecting all (~30,000) refereed papers from A&A, AJ, ApJ and MNRAS published between 2000 and 2004. These particular years were chosen so papers analyzed would not be too "fresh", but at the same time length of each article could be obtained via ADS. I find that indeed longer papers published in these four major astronomy journals are on average cited more, with a median number of citations increasing from 6 for articles 2-3 pages long to about 50 for articles ~50 pages long. I do however observe a significant "Letters effect", i.e. ApJ and A&A articles 4 pages long are cited more than articles 5-10 pages long. Also, the very few longest (>80 pages) papers are actually cited less than somewhat shorter papers. For individual journals, median citations per paper increase from 11 for ~9,300 A&A papers to 14 for ~5,300 MNRAS papers, 16 for ~2,550 AJ papers, and 20 for ~12,850 ApJ papers (including ApJ Letters and Supplement). I conclude with some semi-humorous career advice, directed especially at first-year graduate students.
We present the first systematic derivation of the one-loop correction to the large scale matter power spectrum in a mixed cold+hot dark matter cosmology with subdominant massive neutrino hot dark matter. Starting with the equations of motion for the density and velocity fields, we derive perturbative solutions to these quantities and construct recursion relations for the interaction kernels, noting and justifying all approximations along the way. We find interaction kernels similar to those for a cold dark matter-only universe, but with additional dependences on the neutrino energy density fraction f_nu and the linear growth functions of the incoming wavevectors. Compared with the f_nu=0 case, the one-loop corrected matter power spectrum for a mixed dark matter cosmology exhibits a decrease in small scale power exceeding the canonical ~8 f_nu suppression predicted by linear theory. For f_nu < 0.1, the suppression factor at z=1 is ~10 f_nu, a result remarkably close to the ~9.8 f_nu decrease seen in multi-component N-body simulations.
We review the ensemble of anticipated gravitational-wave (GW) emission processes in stellar core collapse and postbounce core-collapse supernova evolution. We discuss recent progress in the modeling of these processes and summarize most recent GW signal estimates. In addition, we present new results on the GW emission from postbounce convective overturn and protoneutron star g-mode pulsations based on axisymmetric radiation-hydrodynamic calculations. Galactic core-collapse supernovae are very rare events, but within 3-5 Mpc from Earth, the rate jumps to 1 in ~2 years. Using the set of currently available theoretical gravitational waveforms, we compute upper-limit optimal signal-to-noise ratios based on current and advanced LIGO/GEO600/VIRGO noise curves for the recent SN 2008bk which exploded at ~3.9 Mpc. While initial LIGOs cannot detect GWs emitted by core-collapse events at such a distance, we find that advanced LIGO-class detectors could put significant upper limits on the GW emission strength for such events. We study the potential occurrence of the various GW emission processes in particular supernova explosion scenarios and argue that the GW signatures of neutrino-driven, magneto-rotational, and acoustically-driven core-collapse SNe may be mutually exclusive. We suggest that even initial LIGOs could distinguish these explosion mechanisms based on the detection (or non-detection) of GWs from a galactic core-collapse supernova.
The radio galaxy Fornax A (NGC 1316) is a prominent merger remnant in the outskirts of the Fornax cluster. Its giant radio lobes suggest the presence of a powerful AGN and thus a central supermassive black hole (SMBH). We present high-resolution adaptive optics assisted integral-field data of Fornax A, taken with SINFONI at the Very Large Telescope in the K band. We use axisymmetric orbit models to determine the mass of the SMBH in the centre of Fornax A. The three-dimensional nature of our data provides the possibility to directly test the consistency of the data with axisymmetry by modelling each of the four quadrants separately. According to our dynamical models, consistent SMBH masses and dynamical Ks band mass-to-light ratios are obtained for all quadrants, with <M_BH>=1.3x10^8 M_\odot (rms(M_BH)=0.4x10^8 Msun) and <M/L>=0.68 (rms(M/L)=0.03), confirming the assumption of axisymmetry. For the folded and averaged data we find M_BH=(1.5+0.75-0.8)x10^8 Msun and M/L=(0.65+0.075-0.05) (3-sigma errors). Thus the black-hole mass of Fornax A is consistent within the error with the Tremaine (2002) M-sigma relation, but is a factor ~4 smaller than expected from its bulge mass and the Marconi&Hunt (2003) relation.
A search of the Two Micron All Sky Survey and Sloan Digital Sky Survey reveals 36 previously unknown high proper motion objects with J<17. Their red-optical colors indicate that 27 are M dwarfs, 8 are early-type L dwarfs, and 1 is a late-type T dwarf. The L dwarfs have J-Ks colors near the extrema of known L dwarfs indicating that previous surveys for L dwarfs using color as a selection criterion may be biased. Followup near-infrared spectroscopy of 6 dwarfs confirm they are all late-type with spectral types ranging from M8 to T4. Spectscopy also shows that some of the L dwarfs exhibit peculiar spectral features similar to other peculiar "blue" L dwarfs and one could even be a subdwarf. Photometric distance estimates indicate that 22 of the new M, L and T dwarfs lie within 100 pc of the Sun with the newly discovered T dwarf located at about 25 pc. We also measured the proper motions of known ultracool dwarfs recovered in our survey including, for the first time, SDSS J085834.42+325627.6 (T1), SDSS J125011.65+392553.9 (T4) and 2MASS J15261405+2043414 (L7).
We present an astrometry and photometry catalogue of globular cluster (GC) candidates detected with HST WFPC2 in a sample of 19 early-type galaxies, appropriate for comparison to the low-mass X-ray binary (LMXB) populations observed with Chandra. In a companion paper, we present the Chandra data and investigate the relation between these populations. We demonstrate that, although there is little evidence of a colour-magnitude correlation for the GCs, after estimating mass and metallicity from the photometry, under the assumption of a single age simple stellar population, there is a significant positive correlation between mass and metallicity. We constrained [Z/H] = (-2.1+/-0.2)+(0.25+/-0.04)log M, with a 1-sigma intrinsic scatter of 0.62 dex in metallicity. If GCs are bimodal in metallicity this relation is consistent with recent suggestions of a mass-metallicity relation only for metal-poor clusters. Adopting a new technique to fit the GC luminosity function (GCLF) accounting for incompleteness and the Eddington bias, we compute the V-band local GC specific frequency (Sn) and specific luminosity (Sl) of each galaxy. We show that Sl is the more robust measure of the richness of a GC population where a significant fraction is undetected due to source detection incompleteness. We find that the absolute magnitude of the GCLF turnover exhibits intrinsic scatter from galaxy to galaxy of ~0.3mag (1-sigma), limiting its accuracy as a standard distance measure.
We present a new suite of photometric and spectroscopic data for the faint Bootes II dwarf spheroidal galaxy candidate. Our deep photometry, obtained with the INT/WFC, suggests a distance of 46 kpc and a small half-light radius of 4.0 arcmin (56 pc), consistent with previous estimates. Follow-up spectroscopy obtained with the Gemini/GMOS instrument yielded radial velocities and metallicities. While the majority of our targets covers a broad range in velocities and metallicities, we find five stars which share very similar velocities and metallicities and which are all compatible with the colors and magnitudes of the galaxy's likely red giant branch. We interpret these as a spectroscopic detection of the Bootes II system. These stars have a mean velocity of -117 km/s, a velocity dispersion of (10.5+-7.4) km/s and a mean [Fe/H] of -1.79 dex, with a dispersion of 0.14 dex. At this metallicity, Boo II is not consistent with the stellar-mass-metallicity relation for the more luminous dwarf galaxies. Coupled with our distance estimate, its high negative systemic velocity rules out any physical connection with its projected neighbor, the Bootes I dwarf spheroidal, which has a velocity of ~+100 km/s. The velocity and distance of Bootes II coincide with those of the leading arm of Sagittarius, which passes through this region of the sky, so that it is possible that Bootes II may be a stellar system associated with the Sagittarius stream. Finally, we note that the properties of Bootes II are consistent with being the surviving remnant of a previously larger and more luminous dSph galaxy.
We consider the early stages of cosmic hydrogen or helium reionization, when ionizing sources were still rare. We show that Poisson fluctuations in the galaxy distribution substantially affected the early bubble size distribution, although galaxy clustering was also an essential factor even at the earliest times. We find that even at high redshifts, a significant fraction of the ionized volume resided in bubbles containing multiple sources, regardless of the ionizing efficiency of sources or of the reionization redshift. In particular, for helium reionization by quasars, one-source bubbles last dominated (i.e., contained 90% of the ionized volume) at some redshift above z=7.3, and hydrogen reionization by stars achieved this milestone at z>23. For the early generations of atomic-cooling halos or molecular-hydrogen-cooling halos, one-source ionized regions dominated the ionized volume only at z>31 and z>48, respectively. To arrive at these results we develop a statistical model for the effect of density correlations and discrete sources on reionization and solve it with a Monte Carlo method.
Galaxy Zoo is the first study of nearby galaxies that contains reliable information about the spiral sense of rotation of galaxy arms for a sizeable number of galaxies. We measure the correlation function of spin chirality (the sense in which galaxies appear to be spinning) of face-on spiral galaxies in angular, real and projected spaces. Our results indicate a hint of positive correlation at separations less than ~0.5 Mpc at a statistical significance of 2-3 sigma. This is the first experimental evidence for chiral correlation of spins. Within tidal torque theory it indicates that the inertia tensors of nearby galaxies are correlated. This is complementary to the studies of nearby spin axis correlations that probe the correlations of the tidal field. Theoretical interpretation is made difficult by the small distances at which the correlations are detected, implying that substructure might play a significant role, and our necessary selection of face-on spiral galaxies, rather than a general volume-limited sample.
We report the results of a local stability analysis for a magnetized, gravitationally stratified plasma containing cosmic rays. We account for cosmic-ray diffusion and thermal conduction parallel to the magnetic field and allow beta to take any value, where p is the plasma pressure and B is the magnetic field strength. We take the gravitational acceleration to be in the -z-direction and the equilibrium magnetic field to be in the y-direction, and we derive the dispersion relation for small-amplitude instabilities and waves in the large-|k_x| limit. We use the Routh-Hurwitz criterion to show analytically that the necessary and sufficient criterion for stability in this limit is n k_B dT/dz + dp_cr/dz + (1/8pi)dB^2/dz > 0, where T is the temperature, n is the number density of thermal particles, and p_cr is the cosmic-ray pressure. We present approximate analytical solutions for the normal modes in the low- and high-diffusivity limits, show that they are consistent with the derived stability criterion, and compare them to numerical results obtained from the full, unapproximated, dispersion relation. Our results extend earlier analyses of buoyancy instabilities in galaxy-cluster plasmas to the beta <= 1 regime. Our results also extend earlier analyses of the Parker instability to account for anisotropic thermal conduction, and show that the interstellar medium is more unstable to the Parker instability than was predicted by previous studies in which the thermal plasma was treated as adiabatic.
We investigate the structure of magnetic field amplified by turbulent velocity fluctuations, in the framework of the kinematic Kazantsev-Kraichnan model. We consider Kolmogorov distribution of velocity fluctuations, and assume that both Reynolds number and magnetic Reynolds number are very large. We present the full numerical solution of the model for the spectra and the growth rates of magnetic fluctuations. We consider astrophysically relevant limits of large and small magnetic Prandtl numbers, and address both helical and non-helical cases.
Direct solar coronal magnetic field measurements have become possible since recent development of high-sensitivity infrared detection technology. The SOLARC instrument installed on Mt. Haleakala is such a polarimetric coronagraph that was designed for routinely observing Stokes parameter profiles in near infrared (NIR) wavelengthes. The Fe$^{+12}$ 1075 nm forbidden coronal emission line (CEL) is potential for weak coronal magnetic field detection. As a first step the potential field model has been used to compare with the SOLARC observation in the Fe$^{+12}$ 1075 nm line (Liu and Lin 2008). It's found that the potential fields can be a zeroth-order proxy for approaching the observed coronal field above a simple stable sunspot. In this paper we further discuss several nodi that are hampering the progress for reconstructing the real coronal magnetic field structures. They include the well-known Van Vleck effect in linear polarization signals, ignorance of the information of the NIR emission sources (i.e., inversion problem of coronal magnetic fields), a fat lot of global non-linear force-free field tools available for better modeling coronal magnetic fields, and so on.
Cosmic ray (CR) acceleration at the shock created by the expanding cocoons around active galactic nuclei (AGNs) is studied. It is shown that above the energy $10^{18}$ eV the overall energy spectrum of CRs, produced during the AGN evolution and released in the intergalactic space, has the form $N\propto \epsilon^{-\gamma}$, with $\gamma\approx 2.6$, which extends up to $\epsilon_{max}\sim 10^{20}$ eV. It is concluded that cocoons shocks have to be considered as a main source of extragalactic CRs, which together with Galactic supernova remnants provide the observed CR spectrum.
We analyse the results of recent measurements of nonthermal emission from individual supernova remnants (SNRs) and their correspondence to the nonlinear kinetic theory of cosmic ray (CR) acceleration in SNRs. It is shown that the theory fits these data in a satisfactory way and provides the strong evidences for the efficient CR production in SNRs accompanied by significant magnetic field amplification. Magnetic field amplification leads to considerable increase of CR maximum energy so that the spectrum of CRs accelerated in SNRs is consistent with the requirements for the formation of Galactic CR spectrum up to the energy ~10^17 eV.
A 10.24 days Neptune-mass planet was recently announced to orbit the nearby M2 dwarf Gl 176, based on 28 radial velocities measured with the HRS spectrograph on the Hobby-Heberly Telescope (HET). We obtained 57 radial velocities of Gl 176 with the ESO 3.6m telescope and the HARPS spectrograph, which is known for its sub-m/s stability. The median photon-noise standard error of our measurements is 1.1 m/s, significantly lower than the 4.7 m/s of the HET velocities, and the 4 years period over which they were obtained has much overlap with the epochs of the HET measurements. The HARPS measurements show no evidence for a signal at the period of the putative HET planet, suggesting that its detection was spurious. We do find, on the other hand, strong evidence for a lower mass 8.4 Mearth planet, in a quasi-circular orbit and at the different period of 8.78 days. The host star has moderate magnetic activity and rotates on a 39-days period, which we confirm through modulation of both contemporaneous photometry and chromospheric indices. We detect that period as well in the radial velocities, but it is well removed from the orbital period and no cause for confusion. This new detection of a super-Earth (2 Mearth < M sin(i) < 10 Mearth) around an M dwarf adds to the growing evidence that such planets are common around very low mass stars: a third of the 20 known planets with M sin(i) < 0.1 Mjup and 3 of the 7 known planets with M sin(i) < 10 Mearth orbit an M dwarf, in contrast to just 4 of the ~300 known Jupiter-mass planets.
We have mapped the molecular gas content in the host galaxy of the strongly
lensed high redshift quasar APM 08279+5255 (z=3.911) with the Very Large Array
at 0.3" resolution. The CO(J=1-0) emission is clearly resolved in our maps. The
CO(J=1-0) line luminosity derived from these maps is in good agreement with a
previous single-dish measurement. In contrast to previous interferometer-based
studies, we find that the full molecular gas reservoir is situated in two
compact peaks separated by <~0.4". Our observations reveal, for the first time,
that the emission from cold molecular gas is virtually cospatial with the
optical/near-infrared continuum emission of the central AGN in this source.
This striking similarity in morphology indicates that the molecular gas is
situated in a compact region close to the AGN. Based on the high resolution CO
maps, we present a revised model for the gravitational lensing in this system,
which indicates that the molecular gas emission is magnified by only a factor
of 4 (in contrast to previously suggested factors of 100). This model suggests
that the CO is situated in a circumnuclear disk of ~550 pc radius that is
possibly seen at an inclination of <~25 deg, i.e., relatively close to face-on.
From the CO luminosity, we derive a molecular gas mass of M_gas=1.3x10^11
M_sun for this galaxy. From the CO structure and linewidth, we derive a
dynamical mass of M_dyn(sin i)^2=4.0x10^10 M_sun. Based on a revised mass
estimate for the central black hole of M_BH=2.3x10^10 M_sun and the results of
our molecular line study, we find that the mass of the stellar bulge of APM
08279+5255 falls short of the local M_BH-sigma_bulge relationship of nearby
galaxies by more than an order of magnitude, lending support to recent
suggestions that this relation may evolve with cosmic time and/or change toward
the high mass end.
We have observed cosmic-ray electrons from 10 GeV to 800 GeV by a long duration balloon flight using Polar Patrol Balloon (PPB) in Antarctica. The observation was carried out for 13 days at an average altitude of 35 km in January 2004. The detector is an imaging calorimeter composed of scintillating-fiber belts and plastic scintillators inserted between lead plates with 9 radiation lengths. The performance of the detector has been confirmed by the CERN-SPS beam test and also investigated by Monte-Carlo simulations. New telemetry system using a commercial satellite of Iridium, power supply by solar batteries, and automatic level control using CPU have successfully been developed and operated during the flight. From the long duration balloon observations, we derived the energy spectrum of cosmic-ray electrons in the energy range from 100 GeV to 800 GeV. In addition, for the first time we derived the electron arrival directions above 100 GeV, which is consistent with the isotropic distribution.
Investigations of He II Ly-alpha (304 A rest) absorption toward a half-dozen quasars at z~3-4 have demonstrated the great potential of helium studies of the IGM, but the current critically small sample size of clean sightlines for the He II Gunn-Peterson test limits confidence in cosmological inferences, and a larger sample is required. Although the unobscured quasar sightlines to high redshift are extremely rare, SDSS DR6 provides thousands of z>2.8 quasars. We have cross-correlated these SDSS quasars with GALEX GR2/GR3 to establish a catalog of 200 higher-confidence (~70% secure) cases of quasars at z=2.8-5.1 potentially having surviving far-UV (restframe) flux. We also catalog another 112 likely far-UV-bright quasars from GALEX cross-correlation with other (non-SDSS) quasar compilations. Reconnaissance UV prism observations with HST of 24 of our SDSS/GALEX candidates confirm 12 as detected in the far-UV, with at least 9 having flux extending to very near the He II break; with refinements our success rate is even higher. Our SDSS/GALEX selection approach is thereby confirmed to be an order of magnitude more efficient than previous He II quasar searches, more than doubles the number of spectroscopically confirmed clean sightlines to high redshift, and provides a resource list of hundreds of high-confidence sightlines for upcoming He II and other far-UV studies from HST. Our reconnaissance HST prism spectra suggest some far-UV diversity, confirming the need to obtain a large sample of independent quasar sightlines across a broad redshift range to assess such issues as the epoch(s) of helium reionization, while averaging over individual-object pathology and/or cosmic variance.
We present Hubble Space Telescope imaging and spectroscopic observations of three Brightest Cluster Galaxies, Abell 1836-BCG, Abell 2052-BCG, and Abell 3565-BCG, obtained with the Wide Field and Planetary Camera 2, the Advanced Camera for Surveys and the Space Telescope Imaging Spectrograph. The data provide detailed information on the structure and mass profile of the stellar component, the dust optical depth, and the spatial distribution and kinematics of the ionized gas within the innermost region of each galaxy. Dynamical models, which account for the observed stellar mass profile and include the contribution of a central supermassive black hole (SBH), are constructed to reproduce the kinematics derived from the Halpha and [N II](lambda 6548,6583) emission lines. Secure SBH detection with M_bh=3.61(+0.41,-0.50)x10^9 M_sun and M_bh=1.34(+0.21,-0.19)x10^9 M_sun, respectively, are obtained for Abell 1836-BCG and Abell 3565-BCG, which show regular rotation curves and strong central velocity gradients. In the case of Abell 2052-BCG, the lack of an orderly rotational motion prevents a secure determination, although an upper limit of M_bh < 4.60x10^9 M_sun can be placed on the mass of the central SBH. These measurements represent an important step forward in the characterization of the high-mass end of the SBH mass function.
We report high resolution spectroscopy of the moderately reddened (A$_V$=3)
early type star Cernis 52 located in a region of the Perseus molecular cloud
complex with anomalous microwave emission. In addition to the presence of the
most common diffuse interstellar bands (DIBs) we detect two new interstellar or
circumstellar bands coincident to within 0.01% in wavelength with the two
strongest bands of the naphthalene cation (C$_{10}$H$_{8}^+$) as measured in
gas-phase laboratory spectroscopy at low temperatures and find marginal
evidence for the third strongest band.
Assuming these features are caused by the naphthalene cation, from the
measured intensity and available oscillator strengths we find that 0.008 % of
the carbon in the cloud could be in the form of this molecule. We expect
hydrogen additions to cause hydronaphthalene cations to be abundant in the
cloud and to contribute via electric dipole radiation to the anomalous
microwave emission. The identification of new interstellar features consistent
with transitions of the simplest polycyclic aromatic hydrocarbon adds support
to the hypothesis that this type of molecules are the carriers of both diffuse
interstellar bands and anomalous microwave emission.
Studies of the formation of metal-free Population III stars usually focus primarily on the role played by H2 cooling, on account of its large chemical abundance relative to other possible molecular or ionic coolants. However, while H2 is generally the most important coolant at low gas densities, it is not an effective coolant at high gas densities, owing to the low critical density at which it reaches local thermodynamic equilibrium (LTE) and to the large opacities that develop in its emission lines. It is therefore possible that emission from other chemical species may play an important role in cooling high density primordial gas. A particularly interesting candidate is the H3+ molecular ion. This ion has an LTE cooling rate that is roughly a billion times larger than that of H2, and unlike other primordial molecular ions such as H2+ or HeH+, it is not easily removed from the gas by collisions with H or H2. It is already known to be an important coolant in at least one astrophysical context -- the upper atmospheres of gas giants -- but its role in the cooling of primordial gas has received little previous study. In this paper, we investigate the potential importance of H3+ cooling in primordial gas using a newly-developed H3+ cooling function and the most detailed model of primordial chemistry published to date. We show that although H3+ is, in most circumstances, the third most important coolant in dense primordial gas (after H2 and HD), it is nevertheless unimportant, as it contributes no more than a few percent of the total cooling. We also show that in gas irradiated by a sufficiently strong flux of cosmic rays or X-rays, H3+ can become the dominant coolant in the gas, although the size of the flux required renders this scenario unlikely to occur.
We present a detailed determination of the astrophysical parameters of the chromospherically active binary star EI Eridani. Our new radial velocities allow to improve the set of orbital elements and reveal long-term variations of the barycentric velocity. A possible third-body orbit with a period of approximately 19 years is presented. Absolute parameters are determined in combination with the Hipparcos parallax. EI Eri's inclination angle of the rotational axis is confined to 56.0 plus/minus 4.5 degrees, its luminosity class IV is confirmed by its radius of 2.37 plus/minus 0.12 R_Sun. A comparison to theoretical stellar evolutionary tracks suggests a mass of 1.09 plus/minus 0.05 M_Sun and an age of approximately 6.15 Gyr. The present investigation is the basis of our long-term Doppler imaging study of its stellar surface.
Long-term precise timing of Galactic millisecond pulsars holds great promise for measuring the long-period (months-to-years) astrophysical gravitational waves. Several gravitational-wave observational programs, called Pulsar Timing Arrays (PTA), are being pursued around the world. Here we develop a Bayesian algorithm for measuring the stochastic gravitational-wave background (GWB) from the PTA data. Our algorithm has several strengths: (1) It analyses the data without any loss of information, (2) It trivially removes systematic errors of known functional form, including quadratic pulsar spin-down, annual modulations and zero resets due to a change of equipment, (3) It measures simultaneously both the amplitude and the slope of the GWB spectrum, (4) It can deal with unevenly sampled data and coloured pulsar noise spectra. We sample the likelihood function using 2 methods: (1) Markov Chain Monte Carlo (MCMC) simulations, and (2) multi-parameter Gaussian fitting near the maximum. We find that the former converges robustly only for certain kinds of pulsar noise spectra, while the latter produces reliable estimates for all spectra. We extensively test our approach on mock PTA datasets, and find that the algorithm has significant benefits over currently proposed counterparts. We show that the presence of red component of the pulsar timing noise would significantly hinder detection of the GWB. Lastly, we explore the dependence of the signal-to-noise ratio on the duration of the experiment, number of monitored pulsars, and the magnitude of the pulsar timing noise. These parameter studies will help formulate observing strategies for the PTA experiments.
The plasmoid-induced-reconnection model explaining solar flares based on bursty reconnection produced by an ejecting plasmoid suggests a possible relation between the ejection velocity of a plasmoid and the rate of magnetic reconnection. In this study, we focus on the quantitative description of this relation. We performed magnetohydrodynamic (MHD) simulations of solar flares by changing the values of resistivity and the plasmoid velocity. The plasmoid velocity has been changed by applying an additional force to the plasmoid to see how the plasmoid velocity affects the reconnection rate. An important result is that the reconnection rate has a positive correlation with the plasmoid velocity, which is consistent with the plasmoid-induced-reconnection model for solar flares. We also discuss an observational result supporting this positive correlation.
Most X-ray studies of BALQSOs found significant (N_H~10^{22-24} cm^{-2}) intrinsic column densities of gas absorbing an underlying typical power-law continuum emission, in agreement with expectations from radiatively driven accretion disk wind models. However, direct spectral analysis was performed only on a limited number of bright sources. We investigate the X-ray emission of a large BALQSO sample at medium to high redshift (0.8<z<3.7), drawn from the cross-correlation of SDSS DR5 and 2XMM catalogs. We perform on it moderate-quality X-ray spectral and hardness ratio analysis, and X-ray/optical photometry. No or little intrinsic X-ray neutral absorption is found for one third of the spectroscopically analyzed BALQSO sample (N_H < 4 x 10^{21} cm^{-2} at 90% confidence level), and lower than typical X-ray absorption is found in the remaining sources (<N_H> ~ 5 x 10^{22} cm^{-2}) even including the faintest sources analyzed through hardness ratio analysis. The mean photon index is Gamma~1.9, with no significant evolution with redshift. The alpha_ox are typical of radio-quiet broad line AGN, in contrast with the known (from previous X-ray studies) ``soft X-ray weakness'' of BALQSOs and in agreement with the lack of X-ray absorption. We found the low-Absorption Index (AI) subsample to host the lowest X-ray absorbing column densities of the entire sample. X-ray selected BALQSOs show lower X-ray absorption than purely optically selected ones, and soft X-ray weakness does not hold for any of them. Their outflows may be launched by different mechanisms than classical soft X-ray weak BALQSOs or they may be the tail of the already known population seen along a different line of sight, in both cases expanding the observational parameter space for their search and investigation.
Circumbinary disks are considered to exist in a wide variety of astrophysical objects, e.g., young binary stars, proto-planetary systems, and massive binary black hole systems in active galactic nuclei (AGNs). However, there are no definite evidences for the circumbinary disk except for ones in a few young binary star systems. In this paper, we study possible oscillation modes in circumbinary disks. We find that progarde, non-axisymmetric waves are induced in the inner part of the disk by the time-dependent binary potential. Such waves would cause variabilities in emission line profiles from circumbinary disks. Because of prograde precession of the waves, the distance between each component of the binary and the inner-edge of the circumbinary disk varies with the beat period between the precession period of the wave and the binary orbital period. As a result, the light curves from the circumbinary disks are also expected to vary with the same period. The current study thus provides a new method to detect circumbinary disks in various astrophysical systems.
The problem of a test body in the Schwarzschild geometry is investigated in a Keplerian limit. Beginning with the Schwarzschild metric, a solution to the limited case of approximately elliptical (Keplerian) motion is derived in terms of trigonometric functions. This solution is similar in form to that derived from Newtonian mechanics, and includes first-order corrections describing three effects due to general relativity: precession; reduced radial coordinate; and increased eccentricity. The quantitative prediction of increased eccentricity may provide an additional observational test of general relativity. By analogy with Keplerian orbits, approximate orbital energy parameters are defined in terms of a relativistic eccentricity, providing first-order corrections to Newtonian energies for elliptical orbits. The first-order relativistic equation of orbit is demonstrated to be a limiting case of a very accurate self-consistent solution. This self-consistent solution is supported by exact numerical solutions to the Schwarzschild geometry, displaying remarkable agreement. A more detailed energy parameterization is investigated using the relativistic eccentricity together with the apsides derived from the relativistic effective potential in support of the approximate energy parameters defined using only first-order corrections. The methods and approximations describing this Keplerian limit are applied to more general static spherically-symmetric geometries. Specifically, equations of orbit and energy parameters are also derived in this Keplerian limit for the Reissner-Nordstr\"{o}m and Schwarzschild-de Sitter metrics.
The coefficients defining the mean electromotive force in a Galloway-Proctor flow are determined. This flow shows a two-dimensional pattern and is helical. The pattern wobbles in its plane. Apart from one exception a circular motion of the flow pattern is assumed. This corresponds to one of the cases considered recently by Courvoisier, Hughes and Tobias (2006, Phys. Rev. Lett., 96, 034503). An analytic theory of the alpha effect and related effects in this flow is developed within the second-order correlation approximation and a corresponding fourth-order approximation. In the validity range of these approximations there is an alpha effect but no gamma effect, or pumping effect. Numerical results obtained with the test-field method, which are independent of these approximations, confirm the results for alpha and show that gamma is in general nonzero. Both alpha and gamma show a complex dependency on the magnetic Reynolds number and other parameters that define the flow, that is, amplitude and frequency of the wobbling motion. Some results for the magnetic diffusivity eta_t and a related quantity are given, too. Finally a result for alpha in the case of a randomly varying flow without the aforementioned circular motion is presented. This flow may be a more appropriate model for studying the alpha effect and related effects in flows that are statistical isotropic in a plane.
The past decade has witnessed impressive progress in our understanding of the physical properties of massive stars in the Magellanic Clouds, and how they compare to their cousins in the Galaxy. I summarise new results in this field, including evidence for reduced mass-loss rates and faster stellar rotational velocities in the Clouds, and their present-day compositions. I also discuss the stellar temperature scale, emphasizing its dependence on metallicity across the entire upper-part of the Hertzsprung-Russell diagram.
Despite all advances in multi-dimensional hydrodynamics, investigations of stellar evolution and stellar pulsations still depend on one-dimensional computations. The present work devises an alternative to the mixing length theory or turbulence models usually adopted for the modelling of convective transport in such studies. Assuming that the largest convective patterns generate the majority of convective transport, the convective velocity field is described using two parallel radial columns to represent up- and downstream flows. Horizontal exchange in the form of fluid flow and radiation over their connecting interface couples the two columns and allows a simple circulating motion. The main parameters of this convective description have a straightforward geometrical meaning, namely the diameter of the columns (corresponding to the size of the convective cells) and the ratio of cross section between up- and downdrafts. For this geometrical setup, the time-dependent solution of the equations of radiation hydrodynamics is computed from an implicit scheme which has the advantage of being not affected by the Courant-Friedrichs-Lewy time step limit. In order to demonstrate the approach, results for the example of convection zones in Cepheids are presented.
We present precise optical and near-infrared ground-based photometry of two Globular Clusters (GCs): Omega Cen and 47 Tuc. These photometric catalogs are unbiased in the Red Giant Branch (RGB) region close to the tip. We provide new estimates of the RGB tip (TRGB) magnitudes--m_I(TRGB)=9.84+/-0.05, Omega Cen; m_I(TRGB)=9.46+/-0.06, 47 Tuc--and use these to determine the relative distances of the two GCs. We find that distance ratios based on different calibrations of the TRGB, the RR Lyrae stars and kinematic distances agree with each other within one sigma. Absolute TRGB and RR Lyrae distance moduli agree within 0.10--0.15 mag, while absolute kinematic distance moduli are 0.2--0.3 mag smaller. Absolute distances to 47 Tuc based on the Zero-Age-Horizontal-Branch and on the white dwarf fitting agree within 0.1 mag, but they are 0.1--0.3 mag smaller than TRGB and RR Lyrae distances.
We have performed a detailed systematic search for multiperiodicity in the Population I Cepheids of the Large Magellanic Cloud. In this process we have identified for the first time several new types of Cepheid pulsational behaviour. We have found two triple-mode Cepheids pulsating simultaneously in the first three radial overtones. In 9% of the first overtone Cepheids we have detected weak, but well resolved secondary periodicities. They appear either very close to the primary pulsation frequency or at a much higher frequency with a characteristic period ratio of 0.60-0.64. In either case, the secondary periodicities must correspond to nonradial modes of oscillation. This result presents a major challenge to the theory of stellar pulsations, which predicts that such modes should not be exited in Cepheid variables. Nonradial modes have also been found in three of the fundamental/first overtone double-mode Cepheids, but no such oscillations have been detected in single mode Cepheids pulsating in the fundamental mode. In 19% of double-mode Cepheids pulsating in the first two radial overtones (FO/SO type) we have detected a Blazhko-type periodic modulation of amplitudes and phases. Both modes are modulated with a common period, which is always longer than 700 days. Variations of the two amplitudes are anticorrelated and maximum of one amplitude always coincides with minimum of the other. We have compared observations of modulated FO/SO Cepheids with predictions of theoretical models of the Blazhko effect, showing that currently most popular models cannot account for properties of these stars. We propose that Blazhko effect in FO/SO Cepheids can be explained by a nonstationary resonant interaction of one of the radial modes with another, perhaps nonradial, mode of oscillations.
We develop a method of constraining the cosmic string tension $G\mu$ which uses the Canny edge detection algorithm as a means of searching CMB temperature maps for the signature of the Kaiser-Stebbins effect. We test the potential of this method using high resolution, simulated CMB temperature maps. By modeling the future output from the South Pole Telescope project (including anticipated instrumental noise), we find that cosmic strings with $G\mu > 5.5\times10^{-8}$ could be detected.
Spin parameters of stellar-mass black holes in X-ray binaries are currently being estimated by fitting the X-ray continuum spectra of their accretion disk emission. For this method, it is necessary to know the inclination of the X-ray-producing inner region of the disk. Since the inner disk is expected to be oriented perpendicular to the spin axis of the hole, the usual practice is to assume that the black hole spin is aligned with the orbital angular momentum vector of the binary, and to estimate the inclination of the latter from ellipsoidal modulations in the light curve of the secondary star. We show that the inclination of the disk can be inferred directly if we have both spectral and polarization information on the disk radiation. The predicted degree of polarization varies from 0% to 5% as the disk inclination changes from face-on to edge-on. With current X-ray polarimetric techniques the polarization degree of a typical bright X-ray binary could be measured to an accuracy of 0.1% by observing the source for about 10 days. Such a measurement would constrain the disk inclination to within a degree or two and would significantly improve the reliability of black hole spin estimates. In addition, it would provide new information on the tilt between the black hole spin axis and the orbital rotation axis of the binary, which would constrain any velocity kicks experienced by stellar-mass black holes during their formation.
Low and intermediate frequency quasi-periodic oscillations (QPOs) are thought to be due to oscillations of Comptonizing regions or hot blobs embedded in Keplerian disks. Any movement of these perturbations is expected systematically to change the QPO frequency. Our goal is to find systems where such a systematic drifts have been observed. We also try to find the real cause of such drifts and whether they shed some light on the accretion disk dynamics. Using archival data of the recent outburst of GRO J1655-40, we report the presence of such systematic drifts not only during the rising phase from the 25th of February 2005 to the 12th March 2005, when the QPO frequency monotonically increased from 82mHz to 17.78Hz but also in the decline phase from the 15th September 2005 to the 5th of October 2005, when the QPO frequency decreased from 13.14Hz to 34mHz. We fitted the frequency drifts with the propagatory oscillating shock solution. In the shock-oscillation solution, the frequency is inversely proportional to the infall time scale from the shock location. We obtained the shock location and strength through such a fit. The astonishing smoothness of the variation of the QPO frequency over a period of weeks directly supports the view that it may due to the drift of an oscillating shock rather than the movements of a blob inside a differentially rotating disk.
We present a novel technique to overcome the limitations of the applicability of Principal Component Analysis to typical real-life data sets, especially astronomical spectra. Our new approach addresses the issues of outliers, missing information, large number of dimensions and the vast amount of data by combining elements of robust statistics and recursive algorithms that provide improved eigensystem estimates step-by-step. We develop a generic mechanism for deriving reliable eigenspectra without manual data censoring, while utilising all the information contained in the observations. We demonstrate the power of the methodology on the attractive collection of the VIMOS VLT Deep Survey spectra that manifest most of the challenges today, and highlight the improvements over previous workarounds, as well as the scalability of our approach to collections with sizes of the Sloan Digital Sky Survey and beyond.
We have cross-correlated the SDSS DR3 Schneider et al. (2005) quasar catalog with the XMM-Newton archive. Color and redshift selections (g - r > 0.5 and 0.9 z < 2.1) result in a sample of 17 red, moderate redshift quasars. The redshift selection minimizes possible contamination due to host galaxy emission and Lyalpha forest absorption. Both optical and X-ray information are required to distinguish between the two likely remaining causes of the red colors: 1) dust-reddening and 2) an intrinsically red continuum. We find that 7 of 17 quasars can be classified as probable `intrinsically red' objects. These 7 quasars have unusually broad MgII emission lines (<FWHM>=10,500 km s^{-1}), moderately flat, but unabsorbed X-ray spectra <Gamma>=1.66+/-0.08), and low accretion rates (mdot/mdot_{Edd}} ~ 0.01). We suggest low accretion rates as a possible physical explanation for quasars with intrinsically red optical continua. We find that 8 of 17 quasars can be classified as dust-reddened. Three of these have upper-limits on the absorption column from X-ray spectral fits of N_H = 3-13 x 10^{22} cm^2, while the other five quasars must be absorbed by at least N_H = 10^{23} cm^2 in order to be consistent with a comparably selected alpha_{ox}-l_{uv} distribution. Two objects in the sample are unclassified.
We study reheating in a recently proposed brane "monodromy inflation" model in which the inflaton is the position of a D4 brane on a "twisted torus". Specifically, we study the repeated collisions between the D4 brane and a D6 brane (on which the Standard Model fields are assumed to be localized) at a fixed position along the monodromy direction as the D4 brane rolls down its potential. We find that there is no trapping of the rolling D4 brane until it reaches the bottom of its potential, and that reheating is entirely described by the last brane encounter. Previous collisions have negligible effect on the brane velocity and hence on the reheat temperature. In the context of our setup, reheating is efficient and the reheat temperature is therefore high.
A polarized gamma ray emission spread over a sufficiently wide energy band from a strongly magnetized astrophysical object like gamma ray bursts (GRBs) offers an opportunity to test the hypothesis of axion like particles (ALPs). Based on evidences of polarized gamma ray emission detected in several gamma ray bursts we estimated the level of ALPs induced dichroism, which could take place in the magnetized fireball environment of a GRB. This allows to estimate the sensitivity of polarization measurements of GRBs to the ALP-photon coupling. This sensitivity $\gag\le 2.2\cdot 10^{-11} {\rm GeV^{-1}}$ calculated for the ALP mass $m_a=10^{-3}~{\rm eV}$ and MeV energy spread of gamma ray emission is competitive with the sensitivity of CAST and becomes even stronger for lower ALPs masses.
Non-axisymmetric oscillations of rapidly rotating relativistic stars are studied using the Cowling approximation. The oscillation spectra have been estimated by Fourier transforming the evolution equations describing the perturbations. This is the first study of its kind and provides information on the effect of fast rotation on the oscillation spectra while it offers the possibility in studying the complete problem by including spacetime perturbations. Our study includes both axisymmetric and non-axisymmetric perturbations and provides limits for the onset of the secular bar mode rotational instability. We also present approximate formulae for the dependence of the oscillation spectrum from rotation. The results suggest that it is possible to extract the relativistic star's parameters from the observed gravitational wave spectrum.
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