We present the scientific motivation and observing plan for an upcoming detection survey for debris disks using the James Clerk Maxwell Telescope. The SCUBA-2 Unbiased Nearby Stars (SUNS) Survey will observe 500 nearby main sequence and sub-giant stars (100 of each of the A, F, G, K and M spectral classes) to the 850 micron extragalactic confusion limit to search for evidence of submillimeter excess, an indication of circumstellar material. The survey distance boundaries are 8.6, 16.5, 22, 25 and 45 pc for M, K, G, F and A stars, respectively, and all targets lie between the declinations of -40 deg to 80 deg. In this survey, no star will be rejected based on its inherent properties: binarity, presence of planetary companions, spectral type or age. This will be the first unbiased survey for debris disks since IRAS. We expect to detect ~125 debris disks, including ~50 cold disks not detectable in current shorter wavelength surveys. A substantial amount of complementary data will be required to constrain the temperatures and masses of discovered disks. High resolution studies will likely be required to resolve many of the disks. Therefore, these systems will be the focus of future observational studies using a variety of observatories to characterize their physical properties. For non-detected systems, this survey will set constraints (upper limits) on the amount of circumstellar dust, of typically 200 times the Kuiper Belt mass, but as low as 10 times the Kuiper Belt mass for the nearest stars in the sample (approximately 2 pc).
The primordial abundance of deuterium (D/H) yields a measure of the density of baryons in the universe and is an important complement to determinations from cosmic microwave background (CMB) experiments. Indeed, the current small sample of high redshift D/H measurements from quasar absorption line studies are in excellent agreement with CMB-derived values. Conversely, absorption line measurements of the Galactic D/H ratio in almost 50 stellar sightlines show a puzzlingly large scatter outside the Local Bubble which is difficult to explain simply by astration from the primordial value. Here, we investigate the dust depletion scenario by studying the correlation between D/H and the abundance of titanium, one of the most refractory elements readily observed in the ISM. With a sample 3 times larger than previous work, we confirm a correlation between Ti/H and D/H at the 97% confidence level. However, the magnitude of this dependence is difficult to reconcile with a simple model of dust depletion for two reasons. First, contrary to what is expected from local depletion rates, the gradient of the highly refractory Ti is much shallower than that observed for Fe and Si. Second, we do not observe the established tight, steep correlation between [Ti/H] and the mean volume density of hydrogen. Therefore, whilst dust remains a plausible explanation for the local D/H variations, the abundances of at least some of the refractory elements do not provide unanimous support for this scenario. We also argue that the correlations of [Si/H], [Fe/H], and [Ti/H] with D/H are inconsistent with a simple infall model of low metallicity gas with approximately solar abundances as the dominant cause for D variations.
With this study we aim at the spectroscopic verification of a photometrically selected sample of Low Surface Brightness (LSB) galaxy candidates in a field around the Hubble Deep Field-South (HDF-S). The sample helps to extend the parameter space for LSB galaxies to lower central surface brightnesses and to provide better estimates on the volume densities of these objects. To derive redshifts for the LSB candidates, long-slit spectra were obtained covering a spectral range from 3400{\AA} to 7500{\AA}. The observations have been obtained using the ESO 3.6m telescope, equipped with the EFOSC2 spectrograph. From the measured radial velocities, distances could be estimated. With this distance information, it is possible to differentiate between true LSB galaxies and higher redshift High Surface Brightness (HSB) galaxies which may contaminate the sample. A correction for the surface brightnesses can then be applied, accounting for the cosmological dimming effect (``Tolman Dimming''). We show that ~70% of the LSB candidates, selected based on their location in the color-color space, are real LSB galaxies. Their position in the color-color diagrams, therefore, indicate that the LSB galaxies have a different stellar population mix resulting from a different star formation history compared to HSBs. Our LSB galaxy sample consists only of large disk galaxies with scale-length between 2.5kpc and 7.3kpc. We confirm the flat central surface brightness distribution of previous surveys and extend this distribution down to central surface brightnesses of 27 B mag arcsec^-2.
We have taken K-band spectroscopy of a sample of 13 pre-CVs in order to
examine them for anomalous chemical abundances. In particular, we study the
strength of the 12CO and 13CO absorption bands that have been found diminished
and enhanced, respectively, in similar studies of CVs.
All our systems show CO abundances that are within the range observed for
single stars. The weakest 12CO bands with respect to the spectral type are
found in the pre-CV BPM 71214, although on a much smaller scale than observed
in CVs. Furthermore there is no evidence for enhanced 13CO. Taking into account
that our sample is subject to the present observational bias that favours the
discovery of young pre-CVs with secondary stars of late spectral types, we can
conclude the following: 1) our study provides observational proof that the CO
anomalies discovered in certain CVs are not due to any material acquired during
the common envelope phase, and 2) if the CO anomalies in certain CVs are not
due to accretion of processed material during nova outburst, then the
progenitors of these CVs are of a significantly different type than the
currently known sample of pre-CVs.
The short-period exoplanet HD 147506b (also known as HAT-P-2b) has an eccentric orbit, raising the possibility that it migrated through planet-planet scattering or Kozai oscillations accompanied by tidal dissipation. Either of these scenarios could have significantly tilted the orbit relative to the host star's equatorial plane. Here we present spectroscopy of a transit of HD 147506b, and assess the spin-orbit alignment via the Rossiter-McLaughlin effect. We find the sky projections of the stellar spin axis and orbital axis to be aligned within 14 deg. Thus we find no corroborating evidence for scattering or Kozai migration, although these scenarios cannot be ruled out with the present data.
[ABRIDGED] The distance to the relativistic jet source SS433 and the related supernova remnant W50 is re-examined using new observations of HI in absorption from the VLA, HI in emission from the GBT, and 12CO emission from the FCRAO. The new measurements show HI in absorption against SS433 to a velocity of 75 km/s but not to the velocity of the tangent point, which bounds the kinematic distance at 5.5 < d_k < 6.5 kpc. This is entirely consistent with a 5.5 +/- 0.2 kpc distance determined from light travel-time arguments (Blundell & Bowler 2004). The HI emission map shows evidence of interaction of the lobes of W50 with the interstellar medium near the adopted systemic velocity of V_LSR = 75 km/s. The western lobe sits in a cavity in the HI emission near the Galactic plane, while the eastern lobe terminates at an expanding HI shell. The expanding shell has a radius of 40 pc, contains 8 +/- 3 x 10^3 M_sun of HI and has a measured kinetic energy of 3 +/- 1.5 x 10^{49} ergs. There may also be a static HI ring or shell around the main part of W50 itself at an LSR velocity of 75 km/s, with a radius of 70 pc and a mass in HI of 3.5 - 10 x 10^4 M_sun. We do not find convincing evidence for the interaction of the system with any molecular cloud or with HI at other velocities. The HI emission data suggest that SS433 lies in an interstellar environment substantially denser than average for its distance from the Galactic plane. This Population I system, now about 200 pc below the Galactic plane, most likely originated as a runaway O-star binary ejected from a young cluster in the plane. New astrometric data on SS433 show that the system now has a peculiar velocity of a few tens of km/s in the direction of the Galactic plane. From this peculiar velocity and the symmetry of the W50 remnant we derive a time since the SN of < 10^5 yr.
The nature of ultraluminous X-ray sources in nearby galaxies is one of the major open questions in modern X-ray astrophysics. One possible explanation for these objects is an inhomogeneous, radiation dominated accretion disk around a $\sim 10 M_{\odot}$ black hole -- the so-called ``photon bubble'' model. While previous studies of this model have focused primarily on its radiation-hydrodynamics aspects, in this paper, we provide an analysis of its X-ray spectral (continuum and possible edge and line) characteristics. Compton reflection between high and low density regions in the disk may provide the key to distinguishing this model from others, such as accretion onto an intermediate mass black hole. We couple a Monte Carlo/Fokker-Planck radiation transport code with the XSTAR code for reflection to simulate the photon spectra produced in a photon bubble model for ULXs. We find that reflection components tend to be very weak and in most cases not observable, and make predictions for the shape of the high-energy Comptonizing spectra. In many cases the Comptonization dominates the spectra even down to $\sim$ a few keV. In one simulation, a $\sim 9 \kev$ feature was found, which may be considered a signature of photon bubbles in ULXs; furthermore, we make predictions of high energy power-laws which may be observed by future instruments.
We perform a new estimate of the high energy neutrinos expected from GRBs associated with the first generation of stars in light of new models and constraints on the epoch of reionization and a more detailed evaluation of the neutrino emission yields. We also compare the diffuse high energy neutrino background from Population III stars with the one from "ordinary stars" (Population II), as estimated consistently within the same cosmological and astrophysical assumptions. In disagreement with previous literature, we find that high energy neutrinos from Population III stars will not be observable with current or near future neutrino telescopes, falling below both IceCube sensitivity and atmospheric neutrino background under the most extreme assumptions for the GRB rate. This rules them out as a viable diagnostic tool for these still elusive metal-free stars.
X-ray observations have unveiled the existence of a family of radio-quiet
Isolated Neutron Stars whose X-ray emission is purely thermal, hence dubbed
X-ray Dim Isolated Neutron Stars (XDINSs). While optical observations have
allowed to relate the thermal emission to the neutron star cooling and to build
the neutron star surface thermal map, IR observations are critical to pinpoint
a spectral turnover produced by a so far unseen magnetospheric component, or by
the presence of a fallback disk. The detection of such a turnover can provide
further evidence of a link between this class of isolated neutron stars and the
magnetars, which show a distinctive spectral flattening in the IR.
Here we present the deepest IR observations ever of five XDINSs, which we use
to constrain a spectral turnover in the IR and the presence of a fallback disk.
The data are obtained using the ISAAC instrument at the VLT.
For none of our targets it was possible to identify the IR counterpart down
to limiting magnitudes H = 21.5 - 22.9. Although these limits are the deepest
ever obtained for neutron stars of this class, they are not deep enough to rule
out the existence and the nature of a possible spectral flattening in the IR.
We also derive, by using disk models, the upper limits on the mass inflow rate
in a fallback disk. We find the existence of a putative fallback disk
consistent (although not confirmed) with our observations.
As a continuation of the study of the newly found Delta Scuti star HD 115520, we present a period analysis of recently acquired photometric data covering four nights, as well as some conclusions on the nature of this star.
A large multicolour, wide-field photometric database of the Fornax dwarf spheroidal galaxy has been analysed using three different methods to provide revised distance estimates based on stellar populations in different age intervals. The distance to Fornax was obtained from the Tip of the Red Giant Branch measured by a new method, and using the luminosity of Horizontal Branch stars and Red Clump stars correc ted for stellar population effects. Assuming a reddening $E(B-V)=0.02$, the following distance moduli were derived: $(m-M)_0=20.71 \pm 0.07$ based on the Tip of the Red Giant Branch, $(m-M)_0=20.72 \pm 0.06$ from the level of the Horizontal Branch, and $(m-M)_0=20.73 \pm 0.09$ using the Red Clump method. The weighted mean distance modulus to Fornax is $(m-M)_0=20.72 \pm 0.04$. All these measurements agree within the errors, and are fully consistent with previous determinations and with the distance measurements obtained in a companion paper from near-infrared colour-magnitude diagrams.
We present ~2" resolution submillimeter observations of the submillimeter luminous giant Ly-alpha blob (LAB1) in the SSA 22 protocluster at redshift z=3.1 with the Submillimeter Array (SMA). Although the expected submillimeter flux density is 16 mJy at 880 micron, no emission is detected with the 2".4 x 1".9 (18 x 14 kpc) beam at the 3 sigma level of 4.2 mJy beam^{-1} in the SMA field of view of 35". This is in contrast to the previous lower angular resolution (15") observations where a bright (17 mJy) unresolved submillimeter source was detected at 850 micron toward the LAB1 using the Submillimeter Common-User Bolometer Array on the James Clerk Maxwell Telescope. The SMA non-detection suggests that the spatial extent of the submillimeter emission of LAB1 should be larger than 4" (>30 kpc). The most likely interpretation of the spatially extended submillimeter emission is that starbursts occur throughout the large area in LAB1. Some part of the submillimeter emission may come from spatially extended dust expelled from starburst regions by galactic superwind. The spatial extent of the submillimeter emission of LAB1 is similar to those of high redshift radio galaxies rather than submillimeter galaxies.
We show that pairs of widely separated interferometers are advantageous for measuring the Stokes parameter V of a stochastic background of gravitational waves. This parameter characterizes asymmetry of amplitudes of right- and left-handed waves and generation of the asymmetry is closely related to parity violation in the early universe. The advantageous pairs include LIGO(Livingston)-LCGT and AIGO-Virgo that are relatively insensitive to Omega_GW (the simple intensity of the background). Using at least three detectors, information of the intensity Omega_GW and the degree of asymmetry V can be separately measured.
A new analysis of long-slit CGS4 (UKIRT) spectra of the 3.3 $\mu$m feature of the Red Rectangle and its evolution with offset along the NW whisker of the nebula is presented. The results support a proposed two-component interpretation for the 3.3 $\mu$m feature with peak wavelengths near 3.28 $\mu$m and 3.30 $\mu$m. Both components exhibit a small shift to shorter wavelength with increasing offset from the central star which, by comparison with laboratory studies, is consistent with a decrease in temperature of the carriers with distance from HD 44179. The two-component approach is also applied to 3.3 $\mu$m data for the Red Rectangle, Orion Bar D2 and Orion Bar H2S1 from ISO SWS studies.
(abridged) Deep long-slit optical spectrophotometric observations are
presented for 25 Galactic bulge planetary nebulae (GBPNe) and 6 Galactic disk
planetary nebulae (GDPNe). The spectra, combined with archival ultraviolet
spectra obtained with the International Ultraviolet Explorer (IUE) and infrared
spectra obtained with the Infrared Space Observatory (ISO), have been used to
carry out a detailed plasma diagnostic and element abundance analysis utilizing
both collisional excited lines (CELs) and optical recombination lines (ORLs).
Comparisons of plasma diagnostic and abundance analysis results obtained from
CELs and from ORLs reproduce many of the patterns previously found for GDPNe.
In particular we show that the large discrepancies between electron
temperatures (Te's) derived from CELs and from ORLs appear to be mainly caused
by abnormally low values yielded by recombination lines and/or continua.
Similarly, the large discrepancies between heavy element abundances deduced
from ORLs and from CELs are largely caused by abnormally high values obtained
from ORLs, up to tens of solar in extreme cases. It appears that whatever
mechanisms are causing the ubiquitous dichotomy between CELs and ORLs, their
main effects are to enhance the emission of ORLs, but hardly affect that of
CELs. It seems that heavy element abundances deduced from ORLs may not reflect
the bulk composition of the nebula. Rather, our analysis suggests that ORLs of
heavy element ions mainly originate from a previously unseen component of
plasma of Te's of just a few hundred Kelvin, which is too cool to excite any
optical and UV CELs.
We present a new edition of the catalogue of the low-mass X-ray binaries in the Galaxy and the Magellanic Clouds. The catalogue contains source name(s), coordinates, finding chart, X-ray luminosity, system parameters, and stellar parameters of the components and other characteristic properties of 187 low-mass X-ray binaries, together with a comprehensive selection of the relevant literature. The aim of this catalogue is to provide the reader with some basic information on the X-ray sources and their counterparts in other wavelength ranges ($\gamma$-rays, UV, optical, IR, and radio). Some sources, however, are only tentatively identified as low-mass X-ray binaries on the basis of their X-ray properties similar to the known low-mass X-ray binaries. Further identification in other wavelength bands is needed to finally determine the nature of these sources. In cases where there is some doubt about the low-mass nature of the X-ray binary this is mentioned. Literature published before 1 October 2006 has, as far as possible, been taken into account.
It is shown that collisionless shock waves can be driven in unmagnetized electron-positron plasmas by performing a two-dimensional particle-in-cell simulation. At the shock transition region, strong magnetic fields are generated by a Weibel-like instability. The generated magnetic fields are strong enough to deflect the incoming particles from upstream of the shock at a large angle and provide an effective dissipation mechanism for the shock. The structure of the collisionless shock propagates at an almost constant speed. There is no linear wave corresponding to the shock wave and therefore this can be regarded as a kind of ``instability-driven'' shock wave. The generated magnetic fields rapidly decay in the downstream region. It is also observed that a fraction of the thermalized particles in the downstream region return upstream through the shock transition region. These particles interact with the upstream incoming particles and cause the generation of charge-separated current filaments in the upstream of the shock as well as the electrostatic beam instability. As a result, electric and magnetic fields are generated even upstream of the shock transition region. No efficient acceleration processes of particles were observed in our simulation.
We present a new edition of the catalogue of high-mass X-ray binaries in the Galaxy. The catalogue contains source name(s), coordinates, finding chart, X-ray luminosity, system parameters, and stellar parameters of the components and other characteristic properties of 114 high-mass X-ray binaries, together with a comprehensive selection of the relevant literature. The aim of this catalogue is to provide the reader with some basic information on the X-ray sources and their counterparts in other wavelength ranges ($\gamma$-rays, UV, optical, IR, radio). About 60% of the high-mass X-ray binary candidates are known or suspected Be/X-ray binaries, while 32% are supergiant/X-ray binaries. Some sources, however, are only tentatively identified as high-mass X-ray binaries on the basis of their X-ray properties similar to the known high-mass X-ray binaries. Further identification in other wavelength bands is needed to finally determine the nature of these sources. In cases where there is some doubt about the high-mass nature of the X-ray binary this is mentioned. Literature published before 1 October 2005 has, as far as possible, been taken into account.
Gravitational microlensing surveys target very dense stellar fields in the local group. As a consequence the microlensed source stars are often blended with nearby unresolved stars. The presence of `blending' is a cause of major uncertainty when determining the lensing properties of events towards the Galactic centre. After demonstrating empirical cases of blending we utilize Monte Carlo simulations to probe the effects of blending. We generate artificial microlensing events using an HST luminosity function convolved to typical ground-based seeing, adopting a range of values for the stellar density and seeing. We find that a significant fraction of bright events are blended, contrary to the oft-quoted assumption that bright events should be free from blending. We probe the effect that this erroneous assumption has on both the observed event timescale distribution and the optical depth, using realistic detection criteria relevent to the different surveys. Importantly, under this assumption the latter quantity appears to be reasonably unaffected across our adopted values for seeing and density. The timescale distribution is however biased towards smaller values, even for the least dense fields. The dominant source of blending is from lensing of faint source stars, rather than lensing of bright source stars blended with nearby fainter stars. We also explore other issues, such as the centroid motion of blended events and the phenomena of `negative' blending. Furthermore, we breifly note that blending can affect the determination of the centre of the red clump giant region from an observed luminosity function. This has implications for a variety of studies, e.g. mapping extinction towards the bulge and attempts to constrain the parameters of the Galactic bar through red clump giant number counts. (Abridged)
The next-generation space VLBI mission, VSOP-2, is expected to provide unprecedented spatial resolutions at 8.4, 22, and 43GHz. In this report, phase referencing with VSOP-2 is examined in detail based on a simulation tool called ARIS. The criterion for successful phase referencing was to keep the phase errors below one radian. Simulations with ARIS reveal that phase referencing achieves good performance at 8.4GHz, even under poor tropospheric conditions. At 22 and 43GHz, it is recommended to conduct phase referencing observations under good or typical tropospheric conditions. The satellite is required to have an attitude-switching capability with a one-minute or shorter cycle, and an orbit determination accuracy higher than about 10cm at apogee; the phase referencing calibrators are required to have a signal-to-noise ratio larger than four for a single scan. The probability to find a suitable phase referencing calibrator was estimated by using VLBI surveys. From the viewpoint of calibrator availability, VSOP-2 phase referencing at 8.4GHz is promising. However, the change of finding suitable calibrators at 22 and 43GHz is significantly reduced; it is important to conduct specific investigations for each target at those frequencies.
We present the analysis of the radial gradients of stellar absorption lines in a sample of 32 bulges of edge-on spiral galaxies, spanning nearly the full Hubble sequence (from S0 to Sc types), and a large range of velocity dispersion (from about 60 to 300 km/s). Different diagnostics such as index-index, gradient-gradient diagrams, and simple stellar population models are used to tackle the origin of the variation of the bulge stellar population. We find that the vast majority of bulges show older age, lower metallicity and higher [alpha/Fe] in their outer regions than in their central parts. The radial gradients in [Fe/H] are 2 to 3 times larger than in Log(age). The relation between gradient and bulge velocity dispersion is interpreted as a gradual build up of the gradient mean values and their dispersions from high to low velocity dispersion, rather than a pure correlation. The bulge effective radii and the Hubble type of the parent galaxies seem to play a more minor role in causing the observed spatial distributions. At a given velocity dispersion, bulges and ellipticals share common properties.
This study follows a recent analysis of the galaxy luminosity functions and colour-magnitude red sequences in the Coma cluster (Adami et al. 2007). We analyze here the distribution of very faint galaxies and globular clusters in an east-west strip of $\sim 42 \times 7$ arcmin$^2$ crossing the Coma cluster center (hereafter the CS strip) down to the unprecedented faint absolute magnitude of M$_R \sim -9.5$. This work is based on deep images obtained at the CFHT with the CFH12K camera in the B, R, and I bands. The analysis shows that the observed properties strongly depend on the environment, and thus on the cluster history. When the CS is divided into four regions, the westernmost region appears poorly populated, while the regions around the brightest galaxies NGC 4874 and NGC 4889 (NGC 4874 and NGC 4889 being masked) are dominated by faint blue galaxies. They show a faint luminosity function slope of -2, very significantly different from the field estimates. Results are discussed in the framework of galaxy destruction (which can explain part of the very faint galaxy population) and of structures infalling on to Coma.
Knowledge of the intrinsic shape of galaxy clusters is very important in investigating cosmic structure formation and astrophysical processes. The reconstruction of the 3-dimensional structure usually relies on deprojecting 2-dimensional X-ray, Sunyaev-Zeldovich (SZ) and/or gravitational lensing observations. As known, a joint analysis of these data sets can provide the elongation of the cluster along the line of sight together with its length and width in the plane of the sky. An unbiased measurement of the Hubble constant can be also inferred. Due to some intrinsic degeneracies, the observational constraints obtained from such projected data-sets are not enough to allow an unique inversion. In general, the projected maps can be at the same time compatible with prolate, oblate and with many triaxial configurations. Even a prolate cluster might be interpreted as an oblate system and vice versa. Assuming that the cluster is axially symmetric is likely to overestimate the intrinsic ellipticity, whereas the system always looks rounder performing the inversion under the hypothesis of a triaxial cluster aligned with the line of sight. In general, analysing triaxial clusters under the prolate or oblate assumption may introduce strong biases even when the clusters are actually near to axial symmetry whereas the systematics introduced assuming the cluster to be aligned with the line of sight are more under control.
We report about the status of the PICsIT layer of the imager IBIS. The instrument has been tested in both Spectral Imaging and Spectral Timing Mode. PICsIT Single Events, Multiple and ISGRI data of the Crab are simultaneously fitted to a power law model and fit parameters are compared with the standard values. We present a joint fit of SPI, ISGRI, PICsIT data of the long GRB041219, that was seen by the PICsIT instrument in both Spectral Imaging and Spectral Timing acquisition modes. This allowed us to generate a preliminary version of the instrumental response matrices for the PICsIT Spectral Timing mode.
It has been suggested that magnetic fields play a dynamically-important role in core-collapse explosions of massive stars. In particular, they may be important in the collapsar scenario for gamma-ray bursts (GRB), where the central engine is a hyper-accreting black hole or a millisecond magnetar. The present paper is focussed on the magnetar scenario, with a specific emphasis on the interaction of the magnetar magnetosphere with the infalling stellar envelope. First, the ``Pulsar-in-a-Cavity'' problem is introduced as a paradigm for a magnetar inside a collapsing star. The basic set-up of this fundamental plasma-physics problem is described, outlining its main features, and simple estimates are derived for the evolution of the magnetic field. In the context of a collapsing star, it is proposed that, at first, the ram pressure of the infalling plasma acts to confine the magnetosphere, enabling a gradual build-up of the magnetic pressure. At some point, the growing magnetic pressure overtakes the (decreasing) ram pressure of the gas, resulting in a magnetically-driven explosion. The explosion should be highly anisotropic, as the hoop-stress of the toroidal field, confined by the surrounding stellar matter, collimates the magnetically-dominated outflow into two beamed magnetic-tower jets. This creates a clean narrow channel for the escape of energy from the central engine through the star, as required for GRBs. In addition, the delayed onset of the collimated-explosion phase can explain the production of large quantities of Nickel-56, as suggested by the GRB-Supernova connection. Finally, the prospects for numerical simulations of this scenario are discussed.
We discuss an acceleration mechanism for pulsars out of their supernova remnants based on asymmetric neutrino emission from quark matter in the presence of a strong magnetic field. The polarized electron spin fixes the neutrino emission from the direct quark Urca process in one direction along the magnetic field. We calculate the magnetic field strength which is required to polarize the electron spin as well as the required initial proto-neutron star temperature for a successfull acceleration mechanism. In addition we discuss the neutrino mean free paths in quark as well as in neutron matter which turn out to be very small. Consequently, the high neutrino interaction rates will wash out the asymmetry in neutrino emission. As a possible solution to this problem we take into account effects from colour superconductivity.
This paper explains why planets in binary star systems might have a lower frequency. A transient triple state of the binary causes the dispersal of planets.
We present extensive optical spectroscopy of the early-type magnetic star HD 191612 (O6.5f?pe-O8fp). The Balmer and HeI lines show strongly variable emission which is highly reproducible on a well-determined 538-d period. Metal lines and HeII absorptions (including many selective emission lines but excluding He II 4686A emission) are essentially constant in line strength, but are variable in velocity, establishing a double-lined binary orbit with P(orb) = 1542d, e=0.45. We conduct a model-atmosphere analysis of the primary, and find that the system is consistent with a O8: giant with a B1: main-sequence secondary. Since the periodic 538-d changes are unrelated to orbital motion, rotational modulation of a magnetically constrained plasma is strongly favoured as the most likely underlying `clock'. An upper limit on the equatorial rotation is consistent with this hypothesis, but is too weak to provide a strong constraint.
Aims: To investigate the first high resolution optical spectrum of the B-type
star, LS III +52 24, identified as the optical counterpart of the hot post-AGB
candidate IRAS 22023+5249 (I22023).
Methods: We carried out detailed identifications of the observed absorption
and emission features in the high resolution spectrum (4290 - 9015 A) of I22023
obtained with the Utrecht Echelle Spectrograph on the 4.2m William Herschel
Telescope. Using Kurucz's WIDTH9 program and the spectrum synthesis code,
SYNSPEC, we determined the atmospheric parameters and abundances. The
photospheric abundances were derived under the LTE approximation. The NEBULAR
package under IRAF was used to estimate the electron temperature (T_e) and the
electron density (N_e) from the [N II] and [S II] lines.
Results: We estimated T_eff=24000 K, log g=3.0, xi_t=7 kms^{-1}. The derived
CNO abundances suggest an evolved star with C/O < 1. P-Cygni profiles of
hydrogen and helium indicate ongoing post-AGB mass loss. The presence of [N II]
and [S II] lines and the non-detection of [O III] indicate that photoionisation
has just started. The derived nebular parameters T_e=7000 K, N_e=1.2X10^{4}
cm^{-3} are comparable to those measured in young, compact planetary nebulae
(PNe). The nebular expansion velocity was estimated to be 17.5 kms^{-1}.
Conclusions: The observed spectral features, large heliocentric radial
velocity (-148.31 +/- 0.60 kms^{-1}), atmospheric parameters and chemical
composition indicate that I22023, at a distance of 1.95 kpc, is an evolved
post-AGB star belonging to the old disk population. The nebular parameters
suggest that the central star may be evolving into a compact, young PN, similar
to Hen3-1357.
Around 4% of O-stars are observed in apparent isolation, with no associated
cluster, and no indication of having been ejected from a nearby cluster. We
define an isolated O-star as a star > 17.5 M_\odot in a cluster with total mass
<100 M_\odot which contains no other massive (>10 M_\odot) stars. We show that
the fraction of apparently isolated O-stars is reproduced when stars are
sampled (randomly) from a standard initial mass function and a standard cluster
mass function of the form N(M) \propto M^-2.
This result is difficult to reconcile with the idea that there is a
fundamental relationship between the mass of a cluster and the mass of the most
massive star in that cluster. We suggest that such a relationship is a typical
result of star formation in clusters, and that `isolated O-stars' are low-mass
clusters in which massive stars have been able to form.
(Abridged) The two-dimensional distribution and kinematics of the molecular, ionized, and highly ionized gas in the nuclear regions of Seyfert 1 galaxies have been measured using high spatial resolution (~0''.09) near-infrared spectroscopy from NIRSPEC with adaptive optics on the Keck telescope. Molecular hydrogen, H2, is detected in all nine Seyfert 1 galaxies and, in the majority of galaxies, has a spatially resolved flux distribution. In contrast, the narrow component of the BrG emission has a distribution consistent with that of the K-band continuum. In general, the kinematics of H2 are consistent with thin disk rotation, with a velocity gradient of over 100 km/s measured across the central 0''.5 in three galaxies, and across the central 1''.5 in two galaxies. The kinematics of BrG are in agreement with the H2 rotation, except in all four cases the central 0''.5 is either blue- or redshifted by more than 75 km/s. The highly ionized gas, measured with the [Ca VIII] and [Si VII] coronal lines, is spatially and kinematically consistent with BrG in the central 0''.5. Dynamical models have been fitted to the two-dimensional H2 kinematics, taking into account the stellar mass distribution, the emission line flux distribution, and the point spread function. For NGC 3227 the modeling indicates a black hole mass of Mbh = 2.0{+1.0/-0.4} x 10^7 Msun, and for NGC 4151 Mbh = 3.0{+0.75/-2.2} x 10^7 Msun. In NGC 7469 the best fit model gives Mbh < 5.0 x 10^7 Msun. In all three galaxies, modeling suggests a near face-on disk inclination angle, which is consistent with the unification theory of active galaxies. The direct black hole mass estimates verify that estimates from the indirect technique of reverberation mapping are accurate to within a factor of two with no additional systematic errors.
We investigate how the geometrical and physical properties of soft X-ray flare kernels change with their altitude above the photosphere. We analyze limb flares well observed by {\em Yohkoh}/SXT showing clear geometry with well separated loop-top kernels. Our analysis concerns relations between kernel size, plasma pressure, energy release and the kernel altitude. We define scaling laws describing how the sizes and its physical properties of kernels vary with the altitude above the photosphere. We interpret the observed relations in terms of the general magnetic structure of active regions.
We study the dynamics of Jupiter Trojans in the early phase of the Solar system while the outer planets migrated due to their interaction with the planetesimal disk.
In the framework of the Constrained MSSM we derive the most probable ranges of the diffuse gamma radiation flux from the direction of the Galactic center and of the positron flux from the Galactic halo due to neutralino dark matter annihilation. We find that, for a given halo model, the 95% probability range of the integrated gamma-ray flux spans less than two orders of magnitude, with its detectability by GLAST depending primarily on the cuspiness of the halo profile. The positron flux, on the other hand, appears to be too small to be detectable by PAMELA, unless the boost factor is at least of order ten and/or the halo profile is extremely cuspy.
We present simultaneous high-resolution optical spectroscopy and X-ray data of the X-ray binary system GR Mus (XB1254-690), obtained over a full range of orbital phases. The X-ray observations are used to re-establish the orbital ephemeris for this source. The optical data includes the first spectroscopic detection of the donor star in this system, through the use of the Doppler Tomography technique on the Bowen fluorescence blend (~4630-4650 A). In combination with an estimate for the orbital parameters of the compact object using the wings of the He II 4686 emission line, dynamical mass constraints of 1.20 < M_X/M_{sun} < 2.64 for the neutron star and 0.45 < M_2/M_{sun} < 0.85 for the companion are derived.
We employ the Norris et al. (2005) sample to study the dependence of the pulse temporal properties on energy in long-lag, wide-pulse gamma-ray bursts. Our analysis shows that the pulse peak time, rise time scale and decay time scale are power law functions of energy, which is a preliminary report on the relationships between the three quantities and energy. The power law indexes associated with the pulse width, rise time scale and decay time scale are correlated and the correlation between the indexes associated with the pulse width and the decay time scale is more obvious. In addition, we find that the pulse peak lag is strongly correlated with the CCF lag, but the centroid lag is less correlated with the peak lag and CCF lag. Based on these results and some previous investigations, we tend to believe that all energy-dependent pulse temporal properties may come from the joint contribution of both the hydrodynamic processes of the outflows and the curvature effect, where the energy-dependent spectral lag may be mainly dominated by the dynamic process and the energy-dependent pulse width may be mainly determined by the curvature effect.
Radio activity has been observed in a large variety of stellar objects, including in the last few years, ultra-cool dwarfs. To explore the extent of long-term radio activity in ultra-cool dwarfs, we use data taken over an extended period of 9 hr from the Very Large Array of the source 2MASS J05233822-1403022 in September 2006, plus data taken in 2004. The observation taken in September 2006 failed to detect any radio activity at 8.46 GHz. A closer inspection of earlier data reveals that the source varied from a null detection on 3 May 2004, to $\approx$95 $\mu$Jy on 17 May 2004, to 230 $\mu$Jy on 18 June 2004. The lack of detection in September 2006 suggests at least a factor of ten flux variability at 8.46 GHz. Three short photometric runs did not reveal any optical variability. In addition to the observed pulsing nature of the radio flux from another ultra-cool source, the present observations suggests that ultra-cool dwarfs may not just be pulsing but can also display long-term sporadic variability in their levels of quiescent radio emission. The lack of optical photometric variability suggests an absence of large-scale spots at the time of the latest VLA observations, although small very high latitude spots combined with a low inclination could cause very low amplitude rotational modulation which may not be measurable. We discuss this large variability in the radio emission within the context of both gyrosynchrotron emission and the electron-cyclotron maser, favoring the latter mechanism.
(Abridged) We present a study of the optical spectra of a sample of eight
star-forming nuclear rings and the nuclei of their host galaxies. The spectra
were obtained with the ISIS spectrograph on the William Herschel Telescope and
cover a wide range in wavelength, enabling the measurement of several stellar
absorption features and gas emission lines.
We compared the strength of the absorption lines to a variety of population
synthesis models for the star-formation history in the nuclear rings, including
also the contribution of the older bulge and disc stellar components. We find
that the stars in our sample of nuclear rings have most likely formed over a
prolonged period of time characterised by episodic bursts of star-formation
activity. Constant star formation is firmly ruled out by the data, whereas a
one-off formation event is an unlikely explanation for a common galactic
component such as nuclear rings.
We have used emission-line measurements to constrain the physical conditions
of the ionised gas within the rings. Emission in all nuclear rings originates
from HII-regions with electron densities typical for these kinds of objects,
and that the rings are characterised by values for the gas metallicity ranging
from slightly below to just above solar.
As 20% of nearby spiral galaxies hosts nuclear rings that are currently
forming massive stars, our finding of an episodic star formation history in
nuclear rings implies that a significant population remains to be identified of
young nuclear rings that are not currently in a massive star formation phase.
We use observational primordial abundances of $\De$, $\Het$, $\He$ and $\Li$, recent data from the Cosmic Microwave Background and the 2dFGRS power spectrum, to put limits on the variation of the fine structure constant in the early universe. Furthermore, we use these constraints together with other astronomical and geophysical bounds from the late universe to test Bekenstein's model for the variation of $\alpha$. The model is not able to fit all observational and experimental data.
Aims: The recent outburst of the young eruptive star V1647 Orionis has
produced a spectacular appearance of a new reflection nebula in Orion (McNeil's
nebula). We present an optical/near infrared investigation of McNeil's nebula.
This analysis is aimed at determining the morphology, temporal evolution and
nature of the nebula and its connection to the outburst.
Method: We performed multi epoch B, V, R, I, z, and K imaging of McNeil's
nebula and V1647 Ori as well as K_S imaging polarimetry. The multiband imaging
allows us to reconstruct the extinction map inside the nebula. Through
polarimetric observations we attempt to disentangle the emission from the
nebula from that of the accretion disk around V1647 Ori. We also attempt to
resolve the small spatial scale structure of the illuminating source.
Results: The energy distribution and temporal evolution of McNeil's nebula
mimic that of the illuminating source. The extinction map reveals a region of
higher extinction in the direction of V1647 Ori. Excluding foreground
extionction, the optical extinction due to McNeil's nebula in the direction of
V1647 Ori is A_V ~ 6.5 mag. The polarimetric measurement shows a compact high
polarization emission around V1647 Ori. The percentage of K_S band linear
polarization goes from 10 -- 20 %. The vectors are all well aligned with a
position angle of 90 +/- 9 degree East of North. This may correspond to the
orientation of a possible accretion disk around V1647 Ori. These findings
suggest that the appearance of McNeil's nebula is due to reflection of light by
pre-existing material in the surroundings of V1647 Ori. We also report on the
discovery of a new candidate brown dwarf or protostar in the vicinity of V1647
Ori as well as the presence of clumpy structure within HH 22A.
In this paper we report a refined determination of the orbital parameters and the detection of the Rossiter-McLaughlin effect of the recently discovered transiting exoplanet HAT-P-2b. The large orbital eccentricity and short orbital period of this exoplanet are unexpected and distinguish it from other known transiting exoplanets. We performed high precision radial velocity spectroscopic observations of HD147506 (HAT-P-2) with the new SOPHIE spectrograph, mounted on the 1.93 m telescope at OHP. We obtained 63 new measurements, including 35 on May 14th and 20 on June 11th, at nights that the planet was transiting its star. The RV anomaly observed illustrates that HAT-P-2b orbital motion is set in the same direction as its parent star spin. The sky-projected angle between the normal of the orbital plane and the stellar spin axis, \lambda = 0.0+-9.2 \degr, is consistent with zero. The planetary and stellar radii were re-determined: R_p = 0.952^{+0.020}_{-0.027} R_Jup, R_s = 1.412^{+0.029}_{-0.040} R_Sun. The refined values of HAT-P-2b radius and mass (M_p = 8.64^{+0.29}_{-0.44} M_Jup) indicate a density of 12.41^{+0.42}_{-0.65} g cm^{-3}, suggesting an object in between the known close-in planets with typical density of the order of 1 g cm^{-3}, and the very low-mass stars, with density greater than 50 g cm^{-3}.
Fundamental properties of the extinction curve, like the slope in the rest-frame ultraviolet (UV) and the presence/absence of a broad absorption excess centred at 2175 A (the UV bump), are investigated for a sample of 108 massive, star-forming galaxies at 1 < z < 2.5, selected from the FDF Spectroscopic Survey, the K20 survey, and the GDDS. These characteristics are constrained from a parametric description of the UV spectral energy distribution (SED) of a galaxy, as enforced by combined stellar population and radiative transfer models for different geometries, dust/stars configurations and dust properties. In at least one third of the sample, there is a robust evidence for extinction curves with at least a moderate UV bump. The presence of the carriers of the UV bump is more evident in galaxies with UV SEDs suffering from heavy reddening. We interpret these results as follows. The sample objects possess different mixtures of dust grains and molecules producing extinction curves in between the average ones of the Small and Large Magellanic Cloud, where the UV bump is absent or modest, respectively. Most of the dust embeds the UV-emitting stellar populations or is distributed out of the galaxy mid-plane. Alternatively, even dust with a pronounced UV bump, as for the average Milky-Way extinction curve, can be present and distributed in the galaxy mid-plane. In this case, variations of the continuum scattering albedo with wavelength or an age-dependent extinction are not sufficient to explain the previous trend with reddening. Hence, additional extraplanar dust has to be invoked. The data suggest that the carriers of the UV bump are associated with intermediate-age stellar populations, while they survive in the harshest UV-radiation fields owing to dust self-shielding. [abridged]
We study neutrino emission from direct Urca processes in pion condensed quark matter. In compact stars with high baryon density, the emission is dominated by the gapless modes of the pion condensation which leads to an enhanced emissivity. While for massless quarks the enhancement is not remarkable, the emissivity is significantly larger and the cooling of the condensed matter is considerably faster than that in normal quark matter when the mass difference between $u$- and $d$-quarks is sizable.
Quasinormal ringing of acoustic black holes in Laval nozzles is discussed. The equation for sound waves in transonic flow is written into a Schr\"{o}dinger-type equation with a potential barrier, and the quasinormal frequencies are calculated semianalytically. From the results of numerical simulations, it is shown that the quasinormal modes are actually excited when the background flow in the nozzle is externally perturbed, as well as in the real black hole case. In an actual experiment, however, the purely-outgoing boundary condition will not be satisfied at a late time since the outgoing waves are reflected at the end of the apparatus, and the late-time ringing will be expressed as a superposition of "boxed" quasinormal modes. It is shown that the boxed quasinormal ringing can damp more slowly than the ordinary quasinormal ringing, while its central frequency is not greatly different from that for the ordinary one. Using this fact, an efficient way for detecting the quasinormal ringing of an acoustic black hole is discussed.
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If the early optical data of GRB 060218 up to 1e5 s are interpreted as the black-body flux associated with the supernova shock breakout, we can derive lower limits to the bolometric luminosity and energetics of this black-body component. These limits are more severe for the very early data that imply energetics of order of 1e51 erg. These values, puzzlingly large, are rather independent of the assumed time profile of the emitting surface, provided that the corresponding radius does not increase superluminally. Another concern is the luminosity of the black-body component observed in the X-rays, that is large and appears to be produced by an approximately constant temperature and a surface area increasing only slowly in time. Although it has been suggested that the long X-ray black-body duration is consistent with the supernova shock breakout if anisotropy is assumed, the nearly constant emitting surface requires some fine tuning, allowing and suggesting an alternative interpretation, i.e. emission from late dissipation of the fireball bulk kinetic energy. This in turn requires a small value of the bulk Lorentz factor.
We investigate how the different types of supernovae are relatively affected by the metallicity of their host galaxy. We match the SAI Supernova Catalog to the SDSS-DR4 catalog of star-forming galaxies with measured metallicities. These supernova host galaxies span a range of oxygen abundance from 12 + log(O/H) = 7.9 to 9.3 (~ 0.1 to 2.7 solar) and a range in absolute magnitude from MB = -15.2 to -22.2. To reduce the various observational biases, we select a subsample of well-characterized supernovae in the redshift range from 0.01 to 0.04, which leaves us with 58 SN II, 19 Ib/c, and 38 Ia. We find strong evidence that SN Ib/c are occurring in higher-metallicity host galaxies than SN II, while we see no effect for SN Ia relative to SN II. We note some extreme and interesting supernova-host pairs, including the metal-poor (~ 1/4 solar) host of the recent SN Ia 2007bk, where the supernova was found well outside of this dwarf galaxy. To extend the luminosity range of supernova hosts to even fainter galaxies, we also match all the historical supernovae with z < 0.3 to the SDSS-DR5 sky images, resulting in 1225 matches. This allows us to identify some even more extreme cases, such as the recent SN Ic 2007bg, where the likely host of this hypernova-like event has an absolute magnitude MB ~ -12, making it one of the least-luminous supernova hosts ever observed. This low-luminosity host is certain to be very metal poor (~ 1/20 solar), and therefore this supernova is an excellent candidate for association with an off-axis GRB. The two catalogs that we have constructed are available online and will be updated regularly. Finally, we discuss various implications of our findings for understanding supernova progenitors and their host galaxies.
We study systematically which features in the cosmic microwave background (CMB) and large-scale structure (LSS) probe various inhomogeneous properties of the dark sectors (including neutrinos, dark matter, and dark energy). We stress, and quantify by simple formulas, that the primary CMB anisotropies are very susceptible to the gravitational potentials during horizon entry, less at recombination. The CMB thus allows us to scan \Phi+\Psi and the underlying dark kinetics for all redshifts z~1-10^5. LSS, on the other hand, responds strongest to \Phi at low redshifts. Dark perturbations are often parameterized by the anisotropic stress and effective sound speed (stiffness). We find that the dark anisotropic stress and stiffness influence the visible species at the correspondingly early and late stages of horizon entry, and affect stronger respectively the CMB and LSS. The CMB yet remains essential to probing the stiff perturbations of light neutrinos and dark energy, detectable only during horizon entry. The clustering of dark species and large propagation speed of their inhomogeneities also map to distinctive features in the CMB and LSS. -Any parameterization of the signatures of dark kinetics that assumes general relativity can effectively accommodate any modified gravity (MG) that retains the equivalence principle for the visible sectors. This implies that formally the nonstandard structure growth or \Phi/\Psi ratio, while indicative, are not definitive MG signatures. The definitive signatures of MG may include the strong dependence of the apparent dark dynamics on visible species, its superluminality, and the nonstandard phenomenology of gravitational waves.
We have re-analyzed FUSE data and obtained new Chandra observations of Haro 11, a local (D_L=88 Mpc) UV luminous galaxy. Haro 11 has a similar far-UV luminosity (10^10.3 L_\odot), UV surface brightness (10^9.4 L_\odot kpc^-2), SFR, and metallicity to that observed in Lyman Break Galaxies (LBGs). We show that Haro 11 has extended, soft thermal (kT~0.68 keV) X-ray emission with a luminosity and size which scales with the physical properties (e.g. SFR, stellar mass) of the host galaxy. An enhanced alpha/Fe, ratio of ~4 relative to solar abundance suggests significant supernovae enrichment. These results are consistent with the X-ray emission being produced in a shock between a supernovae driven outflow and the ambient material. The FUV spectra show strong absorption lines similar to those observed in LBG spectra. A blueshifted absorption component is identified as a wind outflowing at ~200-280 km/s. OVI\lambda\lambda1032,1038 emission, the dominant cooling mechanism for coronal gas at T~10^5.5 K is also observed. If associated with the outflow, the luminosity of the OVI emission suggests that <20% of the total mechanical energy from the supernovae and solar winds is being radiated away. This implies that radiative cooling through OVI is not significantly inhibiting the growth of the outflowing gas. In contradiction to the findings of Bergvall et al 2006, we find no convincing evidence of Lyman continuum leakage in Haro 11. We conclude that the wind has not created a `tunnel' allowing the escape of a significant fraction of Lyman continuum photons and place a limit on the escape fraction of f_{esc}<2%. Overall, both Haro 11 and a previously observed LBG analogue VV 114, provide an invaluable insight into the X-ray and FUV properties of high redshift LBGs.
We present a new estimate of the lithium abundance in the atmosphere of the brown dwarf LP 944-20. Our analysis is based on a self-consistent analysis of low, intermediate and high resolution optical and near-infrared spectra. We obtain log N(Li) = 3.25 +/-0.25 using fits of our synthetic spectra to the Li I resonance line doublet profiles observed with VLT/UVES and AAT/SPIRAL. This lithium abundance is over two orders of magnitude larger than previous estimates in the literature. In order to obtain good fits of the resonance lines of K I and Rb I and better fits to the TiO molecular absorption around the Li I resonance line, we invoke a semi-empirical model atmosphere with the dusty clouds located above the photosphere. The lithium abundance, however, is not changed by the effects of the dusty clouds. We discuss the implications of our estimate of the lithium abundance in LP 944-20 for the understanding of the properties of this benchmark brown dwarf.
We study of the effect of turbulence on diffusion processes within magnetized medium. While we exemplify our treatment with heat transfer processes, our results are quite general and are applicable to different processes, e.g. diffusion of heavy elements. Our treatment is also applicable to describing the diffusion of cosmic rays arising from magnetic field wandering. In particular, we find that when the energy injection velocity is smaller than the Alfven speed the heat transfer is partially suppressed, while in the opposite regime the effects of turbulence depend on the intensity of driving. In fact, the scale $l_A$ at which the turbulent velocity is equal the Alfven velocity is a new important parameter. When the electron mean free path $\lambda$ is larger than $l_A$, the stronger the the turbulence, the lower thermal conductivity by electrons is. The turbulent motions, however, induces their own advective transport, that can provide effective diffusivity. For clusters of galaxies, we find that the turbulence is the most important agent for heat transfer. We also show that the domain of applicability of the subdiffusion concept is rather limited.
We compute the probability distribution for the spin of a black hole following a series of minor mergers with isotropically distributed, non-spinning, inspiraling compact objects. By solving the Fokker-Planck equation governing this stochastic process, we obtain accurate analytical fits for the evolution of the mean and standard deviation of the spin distribution in several parameter regimes. We complement these analytical fits with numerical Monte-Carlo simulations in situations when the Fokker-Planck analysis is not applicable. We find that a ~150 solar-mass intermediate-mass black hole that gained half of its mass through minor mergers with neutron stars will have dimensionless spin parameter chi=a/M~0.2 \pm 0.08. We estimate the effect of the spin of the central black hole on the detection range for intermediate-mass-ratio inspiral (IMRI) detections by Advanced LIGO and extreme-mass-ratio inspiral(EMRI) detections by LISA. We find that for realistic black hole spins, the inclination-averaged Advanced-LIGO IMRI detection range may be increased by up to 10% relative to the range for IMRIs into non-spinning intermediate-mass black holes. For LISA, we find that the detection range for EMRIs into 10^5 solar-mass massive black holes (MBHs) is not significantly affected by MBH spin, the range for EMRIs into 10^6 solar-mass MBHs is affected at the ~ 10% level, and EMRIs into maximally spinning 10^7 solar-mass MBHs are detectable to a distance ~25 times greater than EMRIs into non-spinning black holes. The resulting bias in favor of detecting EMRIs into rapidly spinning MBHs will play a role when extracting the MBH spin distribution from EMRI statistics.
The distribution of metals in groups of galaxies holds important information about the chemical enrichment history of the Universe. Here we present radial profiles of temperature and the abundance of iron and silicon of the hot intragroup medium for a sample of 15 nearby groups of galaxies observed by Chandra, selected for their regular X-ray morphology. All but one group display a cool core, the size of which is found to correlate with the mean temperature of the group derived outside this core. When scaled to this mean temperature, the temperature profiles are remarkably similar, being analogous to those of more massive clusters at large radii but significantly flatter inwards of the temperature peak. The Fe abundance generally shows a central excess followed by a radial decline, reaching a typical value of 0.1 solar within r_500, a factor of two lower than corresponding results for clusters. Si shows less systematic radial variation, on average displaying a less pronounced decline than Fe and showing evidence for a flattening at large radii. Off-centre abundance peaks are seen both for Fe and Si in a number of groups with well-resolved cores. Derived abundance ratios indicate that supernovae type Ia are responsible for 80 per cent of the Fe in the group core, but the type II contribution increases with radius and completely dominates at r_500. We present fitting formulae for the radial dependence of temperature and abundances, to facilitate comparison to results of numerical simulations of group formation and evolution. In a companion paper, we discuss the implications of these results for feedback and enrichment in galaxy groups.
Herbig-Haro objects (HHOs) are caused by outflows from young objects. Since the outflow relies on mass accretion from a circumstellar disk, it indicates ongoing growth. Recent results of infrared observations yielded evidence for disks around brown dwarfs. This suggests that at least a certain fraction of brown dwarfs forms like stars. Thus, young sub-stellar objects might cause HHOs as well. We present selected results of a general survey for HHOs based on DSS-II plates and CCD images taken with the Tautenburg Schmidt telescope. Numerous young objects could be identified due to their association with newly detected HHOs. In some cases the luminosity is consistent with very low-mass stars or close to sub-stellar values. This holds for L1415-IRS and a few infrared sources embedded in other dark clouds (e.g., GF9, BHR111). The question on the minimum mass for outflow activity is addressed.
This article describes the theory of cosmological perturbations around a homogeneous and anisotropic universe of the Bianchi I type. Starting from a general parameterisation of the perturbed spacetime a la Bardeen, a complete set of gauge invariant variables is constructed. Three physical degrees of freedom are identified and it is shown that, in the case where matter is described by a scalar field, they generalize the Mukhanov-Sasaki variables. In order to show that they are canonical variables, the action for the cosmological perturbations at second order is derived. Two major physical imprints of the primordial anisotropy are identified: (1) a scalar-tensor ``see-saw'' mechanism arising from the fact that scalar, vector and tensor modes do not decouple and (2) an explicit dependence of the statistical properties of the density perturbations and gravity waves on the wave-vector instead of its norm. This analysis extends, but also sheds some light on, the quantization procedure that was developed under the assumption of a Friedmann-Lemaitre background spacetime, and allows to investigate the robustness of the predictions of the standard inflationary scenario with respect to the hypothesis on the symmetries of the background spacetime. These effects of a primordial anisotropy may be related to some anomalies of the cosmic microwave background anisotropies on large angular scales.
Cold dark matter cosmogony predicts that dark matter halos should be triaxial, whereas observations suggest that halos are rounder. The difference between theory and observation is mostly likely explained by the effect of baryons since their condensation within triaxial dark matter halos is known to lead to rounder halos. This is usually thought to be due to the scattering of box orbits. In order to understand the process by which halos become rounder, we present controlled simulations of disks grown adiabatically inside triaxial dark matter halos. After the disks are grown to full mass we adiabatically evaporate the disks and compare the initial and final shapes of the halos. We find that while the halos are substantially rounder while the disk is at full mass, their final shape after the disk is evaporated is not substantially different from the initial. Thus the condensation of baryons onto the center does not destroy enough of the box/box-like orbits to explain the full intermediate shape change. By following orbits of particles directly, we show that the character of individual orbits is not generally changed by the growing mass unless the disk is very centrally concentrated. Rather than being destroyed, we find that box orbits merely become rounder along with the global potential and that this is sufficient to explain most of the shape change. If chaos is enhanced by the growing baryonic mass then this must still have diffusion timescales of order a Hubble time or longer. We also explored the shape evolution in simulations in which we grew the masses of a small number of satellites, rather than of a central disk. [Abridged]
We present Roche tomograms of the G5-G8 IV/V secondary star in the
long-period cataclysmic variable BV Cen reconstructed from MIKE echelle data
taken on the Magellan Clay 6.5-m telescope. The tomograms show the presence of
a number of large, cool starspots on BV Cen for the first time. In particular,
we find a large high-latitude spot which is deflected from the rotational axis
in the same direction as seen on the K3-K5 IV/V secondary star in the
cataclysmic variable AE Aqr. BV Cen also shows a similar relative paucity of
spots at latitudes between 40-50 degrees when compared with AE Aqr.
Furthermore, we find evidence for an increased spot coverage around longitudes
facing the white dwarf which supports models invoking starspots at the L1 point
to explain the low-states observed in some cataclysmic variables. In total, we
estimate that some 25 per cent of the northern hemisphere of BV Cen is spotted.
We also find evidence for a faint, narrow, transient emission line with
characteristics reminiscent of the peculiar low-velocity emission features
observed in some outbursting dwarf novae. We interpret this feature as a
slingshot prominence from the secondary star and derive a maximum source size
of 75,000 km and a minimum altitude of 160,000 km above the orbital plane for
the prominence.
The entropy landscape technique was applied to determine the system
parameters of BV Cen. We find M_1 = 1.18 (+0.28 -0.16) Msolar, M_2 = 1.05
(+0.23 -0.14) Msolar and an orbital inclination of i = 53 degrees +- 4 degrees
at an optimal systemic velocity of \gamma = -22.3 km s-1. Finally, we also
report on the previously unknown binarity of the G5IV star HD 220492.
We study transverse fast magnetohydrodynamic waves in a system of two coronal loops modeled as smoothed, dense plasma cylinders in a uniform magnetic field. The collective oscillatory properties of the system due to the interaction between the individual loops are investigated from two points of view. Firstly, the frequency and spatial structure of the normal modes are studied. The system supports four trapped normal modes in which the loops move rigidly in the transverse direction. The direction of the motions is either parallel or perpendicular to the plane containing the axes of the loops. Two of these modes correspond to oscillations of the loops in phase, while in the other two they move in antiphase. Thus, these solutions are the generalization of the kink mode of a single cylinder to the double cylinder case. Secondly, we analyze the time-dependent problem of the excitation of the pair of tubes. We find that depending on the shape and location of the initial disturbance, different normal modes can be excited. The frequencies of normal modes are accurately recovered from the numerical simulations. In some cases, because of the simultaneous excitation of several eigenmodes, the system shows beating and the phase lag between the loops is $\pi/2$.
We report on our search for distant clusters of galaxies based on optical and X-ray follow up observations of X-ray candidates from the SHARC survey. Based on the assumption that the absence of bright optical or radio counterparts to possibly extended X-ray sources could be distant clusters. We have obtained deep optical images and redshifts for several of these objects and analyzed archive XMM-Newton or Chandra data where applicable. In our list of candidate clusters, two are probably galaxy structures at redshifts of z$\sim$0.51 and 0.28. Seven other structures are possibly galaxy clusters between z$\sim$0.3 and 1. Three sources are identified with QSOs and are thus likely to be X-ray point sources, and six more also probably fall in this category. One X-ray source is spurious or variable. For 17 other sources, the data are too sparse at this time to put forward any hypothesis on their nature. We also serendipitously detected a cluster at z=0.53 and another galaxy concentration which is probably a structure with a redshift in the [0.15-0.6] range. We discuss these results within the context of future space missions to demonstrate the necessity of a wide field of view telescope optimized for the 0.5-2 keV range.
Exo-planets are preferentially found around high metallicity main sequence stars. We aim at investigating whether evolved stars share this property, and what this tells about planet formation. Statistical tools and the basic concepts of stellar evolution theory are applied to published results as well as our own radial velocity and chemical analyses of evolved stars. We show that the metal distributions of planet-hosting (P-H) dwarfs and giants are different, and that the latter do not favor metal-rich systems. Rather, these stars follow the same age-metallicity relation as the giants without planets in our sample. The straightforward explanation is to attribute the difference between dwarfs and giants to the much larger masses of giants' convective envelopes. If the metal excess on the main sequence is due to pollution, the effects of dilution naturally explains why it is not observed among evolved stars. Although we cannot exclude other explanations, the lack of any preference for metal-rich systems among P-H giants could be a strong indication of the accretion of metal-rich material. We discuss further tests, as well as some predictions and consequences of this hypothesis.
Aims: We explore the lensing properties of asymmetric matter density distributions in Bekenstein's Tensor-Vector-Scalar theory (TeVeS). Methods: Using an iterative Fourier-based solver for the resulting non-linear scalar field equation, we numerically calculate the total gravitational potential and derive the corresponding TeVeS lensing maps. Results: Considering variations on rather small scales, we show that the lensing properties significantly depend on the lens's extent along the line of sight. Furthermore, all simulated TeVeS convergence maps strongly track the dominant baryonic components, non-linear effects, being capable of counteracting this trend, turn out to be very small. Setting up a toy model for the cluster merger 1E0657-558, we infer that TeVeS cannot explain observations without assuming an additional dark mass component in both cluster centers, which is in accordance with previous work.
We have studied the nearby old pulsar PSR B1929+10 and its surrounding medium utilizing the sub-arcsecond angular resolution of Chandra. The Chandra data are found to be fully consistent with the results obtained from deep XMM-Newton observations as far as the pulsar is concerned. The non-thermal emission nature of the pulsar's X-radiation is confirmed. In addition to the X-ray trail seen already in previous observations by ROSAT and XMM-Newton an arc-like nebula intimately surrounding the pulsar is discovered at a signal-to-noise ratio of ~ 5. Using two Chandra observations separated by about six months morphological variability of this arc-like nebula is indicated.
Stellar oscillations are an important tool to probe the interior of a star. Subdwarf B stars are core helium burning objects, but their formation is poorly understood as neither single star nor binary evolution can fully explain their observed properties. Since 1997 an increasing number of sdB stars has been found to pulsate forming two classes of stars (the V361 Hya and V1093 Her stars). We focus on the bright V 361 Hya star PG1605+072 to characterize its frequency spectrum. While most previous studies relied on light variations, we have measured radial velocity variations for as much as 20 modes. In this paper we aim at characterizing the modes from atmospheric parameter and radial velocity variations. Time resolved spectroscopy ($\approx$9000 spectra) has been carried out to detect line profile variations from which variations of the effective temperature and gravity are extracted by means of a quantitative spectral analysis. We measured variations of effective temperatures and gravities for eight modes with semi-amplitudes ranging from $\Delta T_{\rm{eff}}=880$ K to as small as 88 K and $\Delta\log{g}$ of 0.08 dex to as low as 0.008 dex. Gravity and temperature vary almost in phase, whereas phase lags are found between temperature and radial velocity. This profound analysis of a unique data set serves as sound basis for the next step towards an identification of pulsation modes. As rotation may play an important role the modelling of pulsation modes is challenging but feasible.
The two known ``hyper-metal-poor'' (HMP) stars, HE0107-5240 and HE1327-2326, have extremely high enhancements of the light elements C, N, and O relative to Fe and appear to represent a statistically significant excess population relative to the halo metallicity distribution extrapolated from [Fe/H] > -3. This study weighs the available evidence for and against three hypothetical origins for these stars: (1) that they formed from gas enriched by a primordial ``faint supernova'', (2) that they formed from gas enriched by core-collapse supernovae and C-rich gas ejected in rotation-driven winds from massive stars, and (3) that they formed as the low-mass secondaries in binary systems at Z ~ 10^{-5.5} Zsun and acquired their light-element enhancements from an intermediate-mass companion as it passed through an AGB phase. The observations interpreted here, especially the depletion of lithium seen in HE1327-2326, favor the binary mass-transfer hypothesis. If HE0107-5240 and HE1327-2326 formed in binary systems, the statistically significant absence of isolated and/or C-normal stars at similar [Fe/H] implies that low-mass stars could form at that metallicity, but that masses M ~< 1.4 Msun were disfavored in the IMF. This result is also explained if the abundance-derived top-heavy IMF for primordial stars persists to [Fe/H] ~ -5.5. This finding indicates that low-mass star formation was possible at extremely low metallicity, and that the typical stellar mass may have had a complex dependence on metallicity rather than a sharp transition driven solely by gas cooling.
The present paper provides a general overview of the asteroseismic potential of delta Scuti stars in clusters, in particular focusing on convection diagnostics. We give a summarise of the last results obtained by the authors for the Praesepe cluster of which five delta Scuti stars are analysed. In that work, linear analysis is confronted with observations, using refined descriptions for the effects of rotation on the determination of the global stellar parameters and on the adiabatic oscillation frequency computations. A single, complete, and coherent solution for all the selected stars is found, which lead the authors to find important restrictions to the convection description for a certain range of effective temperatures. Furthermore, the method used allowed to give an estimate of the global parameters of the selected stars and constrain the cluster.
In the present work we provide the preliminary results obtained when analysing the rotational Petersen diagrams when including the effects of near degeneracy. We found that near degeneracy affects significantly the fundamental-to-first overtone period ratios, showing wriggles in the Petersen diagrams. Analysis of such wriggles reveals that they are mainly caused by the avoided-crossing phenomenon. The size of wriggles seems to increase with the rotational velocity and could, in certain cases, invalidate any accurate mass and/or metallicity determinations. Nevertheless, deep analysis of near degeneracy effects may allow us to obtain additional information on the mode identification of the radial modes and their corresponding coupled pairs, which would allow us to constrain the modelling.
Recent numerical investigations of wave propagation near coronal magnetic null points (McLaughlin and Hood: Astron. Astrophys. 459, 641,2006) have indicated how a fast MHD wave partially converts into a slow MHD wave as the disturbance passes from a low-beta plasma to a high-beta plasma. This is a complex process and a clear understanding of the conversion mechanism requires the detailed investigation of a simpler model. An investigation of mode conversion in a stratified, isothermal atmosphere, with a uniform, vertical magnetic field is carried out, both numerically and analytically. In contrast to previous investigations of upward-propagating waves (Zhugzhda and Dzhalilov: Astron. Astrophys. 112, 16, 1982a; Cally: Astrophys. J. 548, 473, 2001), this paper studies the downward propagation of waves from a low-beta to high-beta environment. A simple expression for the amplitude of the transmitted wave is compared with the numerical solution.
HESS J1616-508 is one of the brightest emitters in the TeV sky. Recent observations with the IBIS/ISGRI telescope on board the INTEGRAL spacecraft have revealed that a young, nearby and energetic pulsar, PSR J1617-5055, is a powerful emitter of soft gamma-rays in the 20-100 keV domain. In this paper we present an analysis of all available data from the INTEGRAL, Swift, BeppoSAX and XMM-Newton telescopes with a view to assessing the most likely counterpart to the HESS source. We find that the energy source that fuels the X/gamma-ray emissions is derived from the pulsar, both on the basis of the positional morphology, the timing evidence and the energetics of the system. Likewise, the 1.2% of the pulsar's spin down energy loss needed to power the 0.1-10 TeV emission is also fully consistent with other HESS sources known to be associated with pulsars. The relative sizes of the X/gamma-ray and VHE sources are consistent with the expected lifetimes against synchrotron and Compton losses for a single source of parent electrons emitted from the pulsar. We find that no other known object in the vicinity could be reasonably considered as a plausible counterpart to the HESS source. We conclude that there is good evidence to assume that the HESS J1616-508 source is driven by PSR J1617-5055 in which a combination of synchrotron and inverse Compton processes combine to create the observed morphology of a broad-band emitter from keV to TeV energies.
We discuss Spherical Needlets and their properties. Needlets are a form of spherical wavelets which do not rely on any kind of tangent plane approximation and enjoy good localization properties in both pixel and harmonic space; moreover needlets coefficients are asymptotically uncorrelated at any fixed angular distance, which makes their use in statistical procedures very promising. In view of these properties, we believe needlets may turn out to be especially useful in the analysis of Cosmic Microwave Background (CMB) data on the incomplete sky, as well as of other cosmological observations. As a final advantage, we stress that the implementation of needlets is computationally very convenient and may rely completely on standard data analysis packages such as HEALPix.
The hypothesis that the cyanomethyl anion CH2CN- is responsible for the relatively narrow diffuse interstellar band (DIB) at 8037.8 +- 0.15 Angstroms is examined with reference to new observational data. The 0_0^0 absorption band arising from the ^1B_1 - X ^1A' transition from the electronic ground state to the first dipole-bound state of the anion is calculated for a rotational temperature of 2.7 K using literature spectroscopic parameters and results in a rotational contour with a peak wavelength of 8037.78 Angstroms. By comparison with diffuse band and atomic line absorption spectra of eight heavily-reddened Galactic sightlines, CH2CN- is found to be a plausible carrier of the lambda8037 diffuse interstellar band provided the rotational contour is Doppler-broadened with a b parameter between 16 and 33 km/s that depends on the specific sightline. Convolution of the calculated CH2CN- transitions with the optical depth profile of interstellar Ti II results in a good match with the profile of the narrow lambda8037 DIB observed towards HD 183143, HD 168112 and Cyg OB2 8a. The rotational level populations may be influenced by nuclear spin statistics, resulting in the appearance of additional transitions from K_a = 1 of ortho CH2CN- near 8025 and 8050 Angstroms that are not seen in currently available interstellar spectra. For CH2CN- to be the carrier of the lambda8037 diffuse interstellar band, either a) there must be mechanisms that convert CH2CN- from the ortho to the para form, or b) the chemistry that forms CH2CN- must result in a population of K_a'' levels approaching a Boltzmann distribution near 3 K.
Galaxy harassment has been proposed as a physical process that morphologically transforms low surface density disc galaxies into dwarf elliptical galaxies in clusters. It has been used to link the observed very different morphology of distant cluster galaxies (relatively more blue galaxies with 'disturbed' morphologies) with the relatively large numbers of dwarf elliptical galaxies found in nearby clusters. One prediction of the harassment model is that the remnant galaxies should lie on low surface brightness tidal streams or arcs. We demonstrate in this paper that we have an analysis method that is sensitive to the detection of arcs down to a surface brightness of 29 B mag/arcsec^2 and then use this method to search for arcs around 46 Virgo cluster dwarf elliptical galaxies. We find no evidence for tidal streams or arcs and consequently no evidence for galaxy harassment as a viable explanation for the relatively large numbers of dwarf galaxies found in the Virgo cluster.
It is shown that gravitating magnetic fields affect the evolution of curvature perturbations in a way that is reminiscent of a pristine non-adiabatic pressure fluctuation. The gauge-invariant evolution of curvature perturbations is used to constrain the magnetic power spectrum. Depending on the essential features of the thermodynamic history of the Universe, the explicit derivation of the bound is modified. The theoretical uncertainty in the constraints on the magnetic energy spectrum is assessed by comparing the results obtained in the case of the conventional thermal history with the estimates stemming from less conventional (but phenomenologically allowed) post-inflationary evolutions.
Magnetic fields play a crucial role in various astrophysical processes, including star formation, accretion of matter, transport processes (e.g., transport of heat), and cosmic rays. One of the easiest ways to determine the magnetic field direction is via polarization of radiation resulting from extinction on or/and emission by aligned dust grains. Reliability of interpretation of the polarization maps in terms of magnetic fields depends on how well we understand the grain-alignment theory. Currently the grain-alignment theory is a predictive one, and its results nicely match observations. Among its predictions is a subtle phenomenon of radiative torques. after having stayed in oblivion for many years after its discovery, is currently viewed as the most powerful means of alignment. In this article, I shall review the basic physical processes involved in grain alignment, and the currently known mechanisms of alignment. I shall also discuss possible niches for different alignment mechanisms. I shall dwell on the importance of the concept of grain helicity for understanding of many properties of grain alignment, and shall demonstrate that rather arbitrarily shaped grains exhibit helicity when they interact with gaseous flows and radiative fluxes.
In a recent paper, we analyzed the properties of a new kind of spherical wavelets (so-called needlets) for statistical inference procedures on spherical random fields; the results were mainly motivated by applications to cosmological data. In the present work, we exploit the asymptotic uncorrelation of random needlet coefficients at fixed angular distances to construct subsampling statistics evaluated on Voronoi cells on the sphere. We illustrate how such statistics can be used for isotropy tests and for bootstrap estimation of nuisance parameters, even when a single realization of the spherical random field is observed. The asymptotic theory is developed in details, in the high resolution sense.
Small separation between reactants, not exceeding $10^{-8}-10^{-7}cm$, is the necessary condition for various chemical reactions. It is shown that random advection and stretching by turbulence leads to formation of scalar-enriched sheets of {\it strongly fluctuating thickness} $\eta_{c}$. The molecular-level mixing is achieved by diffusion across these sheets (interfaces) separating the reactants. Since diffusion time scale is $\tau_{d}\propto \eta_{c}^{2}$, the knowledge of probability density $Q(\eta_{c},Re)$ is crucial for evaluation of chemical reaction rates. In this paper we derive the probability density $Q(\eta_{c},Re,Sc)$ and predict a transition in the reaction rate behavior from ${\cal R}\propto \sqrt{Re}$ ($Re\leq 10^{4}$) to the high-Re asymptotics ${\cal R}\propto Re^{0}$. The theory leads to an approximate universality of transitional Reynolds number $Re_{tr}\approx 10^{4}$. It is also shown that if chemical reaction involves short-lived reactants, very strong anomalous fluctuations of the length-scale $\eta_{c}$ may lead to non-negligibly small reaction rates.
We describe a kinematic method which is capable of determining the overall mass scale in SUSY-like events at a hadron collider with two missing (dark matter) particles. We focus on the kinematic topology in which a pair of identical particles is produced with each decaying to two leptons and an invisible particle (schematically, $pp\to YY+jets$ followed by each $Y$ decaying via $Y\to \ell X\to \ell\ell'N$ where $N$ is invisible). This topology arises in many SUSY processes such as squark and gluino production and decay, not to mention $t\anti t$ di-lepton decays. In the example where the final state leptons are all muons, our errors on the masses of the particles $Y$, $X$ and $N$ in the decay chain range from 4 GeV for 2000 events after cuts to 13 GeV for 400 events after cuts. Errors for mass differences are much smaller. Our ability to determine masses comes from considering all the kinematic information in the event, including the missing momentum, in conjunction with the quadratic constraints that arise from the $Y$, $X$ and $N$ mass-shell conditions.
We give a rigorous and mathematically well defined presentation of the Covariant and Gauge Invariant theory of scalar perturbations of a Friedmann-Lemaitre-Robertson-Walker universe for Fourth Order Gravity, where the matter is described by a perfect fluid with a barotropic equation of state. The general perturbations equations are applied to a simple background solution of R^n gravity. We obtain exact solutions of the perturbations equations for scales much bigger than the Hubble radius. These solutions have a number of interesting features. In particular, we find that for all values of n there is always a growing mode for the density contrast, even if the universe undergoes an accelerated expansion. Such a behaviour does not occur in standard General Relativity, where as soon as Dark Energy dominates, the density contrast experiences an unrelenting decay. This peculiarity is sufficiently novel to warrant further investigation on fourth order gravity models.
We discuss an inflationary scenario based on Lovelock terms. These higher order curvature terms can lead to inflation when there are more than three spatial dimensions. Inflation will end if the extra dimensions are stabilised, so that at most three dimensions are free to expand. This relates graceful exit to the number of large dimensions.
Based on the asymptotic analysis of ordinary differential equations, we classify all spherically symmetric self-similar solutions to the Einstein equations which are asymptotically Friedmann at large distances and contain a perfect fluid with equation of state $p=(\gamma -1)\mu$ with $0<\gamma<2/3$. This corresponds to a ``dark energy'' fluid and the Friedmann solution is accelerated in this case due to anti-gravity. This extends the previous analysis of spherically symmetric self-similar solutions for fluids with positive pressure ($\gamma>1$). However, in the latter case there is an additional parameter associated with the weak discontinuity at the sonic point and the solutions are only asymptotically ``quasi-Friedmann'', in the sense that they exhibit an angle deficit at large distances. In the $0<\gamma<2/3$ case, there is no sonic point and there exists a one-parameter family of solutions which are {\it genuinely} asymptotically Friedmann at large distances. We find eight classes of asymptotic behavior: Friedmann or quasi-Friedmann or quasi-static or constant-velocity at large distances, quasi-Friedmann or positive-mass singular or negative-mass singular at small distances, or quasi-Kantowski-Sachs at intermediate distances. The self-similar asymptotically quasi-static and quasi-Kantowski-Sachs solutions are analytically extendible and of great cosmological interest. We also investigate their conformal diagram. The results of the present analysis are utilized in an accompanying paper to obtain and physically interpret numerical solutions.
We use a combination of numerical and analytical methods, exploiting the equations derived in an accompanying paper, to classify all spherically symmetric self-similar solutions which are asymptotically Friedmann at large distances and contain a perfect fluid with equation of state $p=(\gamma -1)\mu$ with $0<\gamma<2/3$. The expansion of the Friedmann universe is accelerated in this case. We find a one-parameter family of self-similar solutions representing a black hole embedded in a Friedmann background. This suggests that, in contrast to the positive pressure case, black holes in a universe with dark energy can grow as fast as the Hubble horizon if they are not too large. There are also self-similar solutions which contain a central naked singularity with negative mass. We also find various kinds of self-similar wormhole solutions; these represent a Friedmann universe connected to either another Friedmann universe or some other cosmological model. These wormholes are generally traversable, where we define a wormhole throat as a two-dimensional sphere with minimal area on a spacelike hypersurface.
We consider inhomogeneous preheating in a multi-field trapping model. The curvature perturbation is generated by inhomogeneous preheating which induces multi-field trapping at the enhanced symmetric point (ESP), and results in fluctuation in the number of e-foldings. Instead of considering simple reheating after preheating, we consider a scenario of shoulder inflation induced by the trapping. The fluctuation in the number of e-foldings is generated during this weak inflationary period, when the additional light scalar field is trapped at the local maximum of its potential. The situation may look similar to locked or thermal inflation or even to hybrid inflation, but we will show that the present mechanism of generating the curvature perturbation is very different from these others. Unlike the conventional trapped inflationary scenario, we do not make the assumption that an ESP appears at some unstable point on the inflaton potential. This assumption is crucial in the original scenario, but it is not important in the multi-field model. We also discuss inhomogeneous preheating at late-time oscillation, in which the magnitude of the curvature fluctuation can be enhanced to accommodate low inflationary scale.
In quantum cosmological models, constructed in the Friedmann-Robertson-Walker metrics, a nucleation of Universe with its further extension is described as a tunneling transition (or leaving out) of wave through effective barrier between regions with small and large values of scale factor a at nonzero (or zero) energy. An approach for description of tunneling with leaving outside consists in construction of wave function under choice of needed boundary condition. There are different ways for definition of the boundary condition that leads to different estimations of barrier penetrability and duration of the Universe nucleation. In given paper, with a purpose to describe a process of leaving of the wave from the tunneling region outside accurately as possible, to construct the total wave function on the basis of its two partial solutions unambiguously, the tunneling boundary condition (the total wave function must represent only the wave outgoing outside) is used at point of the wave leaving from the barrier outside, where the following definition for the wave is introduced: the wave is represented by such wave function, module of which is changed minimally under variation of scale factor a. A new method of direct (non-semiclassical) calculation of the total stationary wave function of the Universe is constructed, behavior of this wave function in the tunneling region, near point of leaving from the barrier outside and in the asymptotic region is analyzed, a barrier penetrability is estimated. The following property has been observed: Period of oscillation of the wave function in the above-barrier region decreases uniformly with increasing of a. It has been proposed to use the oscillation period as a characteristics for estimation of dynamics of the Universe extension.
In the context of loop quantum cosmology, we parametrise the lattice refinement by a parameter, $A$, and the matter Hamiltonian by a parameter, $\delta$. We then solve the Hamiltonian constraint for both a self-adjoint, and a non-self-adjoint Hamiltonian operator. Demanding that the solutions for the wave-functions obey certain physical restrictions, we impose constraints on the two-dimensional, $(A,\delta)$, parameter space, thereby restricting the types of matter content that can be supported by a particular lattice refinement model.
Assuming the existence of a 5D purely kinetic scalar field on the class of warped product spaces we investigate the possibility of mimic both an inflationary and a quintessential scenarios on 4D hypersurfaces, by implementing a dynamical foliation on the fifth coordinate instead of a constant one. We obtain that an induced chaotic inflationary scenario with a geometrically induced scalar potential and an induced quasi-vacuum equation of state on 4D dynamical hypersurfaces is possible. While on a constant foliation the universe can be considered as matter dominated today, in a family of 4D dynamical hypersurfaces the universe can be passing for a period of accelerated expansion with a deceleration parameter nearly -1. This effect of the dynamical foliation results negligible at the inflationary epoch allowing for a chaotic scenario and becomes considerable at the present epoch allowing a quintessential scenario.
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