In this paper, we present and analyse optical photometry and spectra of the extremely luminous and slowly evolving Type Ia supernova (SN Ia) 2009dc, and offer evidence that it is a super-Chandrasekhar mass (SC) SN Ia and thus had a SC white dwarf (WD) progenitor. Optical spectra of SN 2007if, a similar object, are also shown. SN 2009dc had one of the most slowly evolving light curves ever observed for a SN Ia, with a rise time of ~23 days and Delta m_15(B) = 0.72 mag. We calculate a lower limit to the peak bolometric luminosity of ~2.1e43 erg/s, though the actual value is likely ~60% larger. Optical spectra of SN 2009dc and SN 2007if obtained near maximum brightness exhibit strong CII features (indicative of a significant amount of unburned material), and the post-maximum spectra are dominated by iron-group elements. All of our spectra of SN 2009dc and SN 2007if also show low expansion velocities. The high luminosity and low expansion velocities of SN 2009dc lead us to derive a possible WD progenitor mass of more than 2 M_sun and a Ni-56 mass of ~1.7 M_sun. We propose that the host galaxy of SN 2009dc underwent a gravitational interaction with a neighboring galaxy in the relatively recent past. This may have led to a sudden burst of star formation which could have produced the SC WD progenitor of SN 2009dc and likely turned the neighboring galaxy into a "post-starburst galaxy." No published model seems to match the extreme values observed in SN 2009dc, but simulations do show that such massive progenitors can exist (likely as a result of the merger of two WDs) and can possibly explode as SC SNe Ia.
We perform numerical calculations of the expected transit timing variations (TTVs) induced on a Hot-Jupiter by an Earth-mass perturber. Motivated by the recent discoveries of retrograde transiting planets, we concentrate on an investigation of the effect of varying relative planetary inclinations, up to and including completely retrograde systems. We find that planets in low order (E.g. 2:1) mean-motion resonances (MMRs) retain approximately constant TTV amplitudes for $0<\,^{\circ}i<170\,^{\circ}$, only reducing in amplitude for $i > 170\,^{\circ}$. Systems in higher order MMRs (E.g. 5:1) increase in TTV amplitude as inclinations increase towards $45\,^{\circ}$, becoming approximately constant for $45 < i < 135$, and then declining for $i > 135\,^{\circ}$. Planets away from resonance slowly decrease in TTV amplitude as inclinations increase from 0 to 180, where-as planets adjacent to resonances can exhibit a huge range of variability in TTV amplitude as a function of both eccentricity and inclination. For highly retrograde systems ($135\,^{\circ} < i \leq 180\,^{\circ}$), TTV signals will be undetectable across almost the entirety of parameter space, with the exceptions occurring when the perturber has high eccentricity or is very close to a MMR. This high inclination decrease in TTV amplitude (on and away from resonance) is important for the analysis of the known retrograde and multi-planet transiting systems, as inclination effects need to be considered if TTVs are to be used to exclude the presence of any putative planetary companions: absence of evidence is not evidence of absence.
We develop an optimized technique to extract density--density and velocity--velocity spectra out of observed spectra in redshift space. The measured spectra of the distribution of halos from redshift distorted mock map are binned into 2--dimensional coordinates in Fourier space so as to be decomposed into both spectra using angular projection dependence. With the threshold limit introduced to minimize nonlinear suppression, the decomposed velocity--velocity spectra are reasonably well measured up to scale k=0.07 h/Mpc, and the measured variances using our method are consistent with errors predicted from a Fisher matrix analysis. The detectability is extendable to k\sim 0.1 h/Mpc with more conservative bounds at the cost of weakened constraint.
We present a suite of full hydrodynamical cosmological simulations that quantitatively address the impact of neutrinos on the (mildly non-linear) spatial distribution of matter and in particular on the neutral hydrogen distribution in the Intergalactic Medium (IGM), which is responsible for the intervening Lyman-alpha absorption in quasar spectra. The free-streaming of neutrinos results in a (non-linear) scale-dependent suppression of power spectrum of the total matter distribution at scales probed by Lyman-alpha forest data which is larger than the linear theory prediction by about 25% and strongly redshift dependent. By extracting a set of realistic mock quasar spectra, we quantify the effect of neutrinos on the flux probability distribution function and flux power spectrum. The differences in the matter power spectra translate into a ~2.5% (5%) difference in the flux power spectrum for neutrino masses with Sigma m_{\nu} = 0.3 eV (0.6 eV). This rather small effect is difficult to detect from present Lyman-alpha forest data and nearly perfectly degenerate with the overall amplitude of the matter power spectrum as characterised by sigma_8. If the results of the numerical simulations are normalized to have the same sigma_8 in the initial conditions, then neutrinos produce a smaller suppression in the flux power of about 3% (5%) for Sigma m_{\nu} = 0.6$ eV (1.2 eV) when compared to a simulation without neutrinos. We present constraints on neutrino masses using the Sloan Digital Sky Survey flux power spectrum alone and find an upper limit of Sigma m_{\nu} < 0.9$ eV (2 sigma C.L.), comparable to constraints obtained from the cosmic microwave background data or other large scale structure probes.
We present and discuss \emph{Spitzer} and near-infrared H$_{2}$ observations of a new bi-polar protostellar outflow in the Rosette Molecular Cloud. The outflow is seen in all four IRAC bands and partially as diffuse emission in the MIPS 24 $\mu$m band. An embedded MIPS 24 $\mu$m source bisects the outflow and appears to be the driving source. This source is coincident with a dark patch seen in absorption in the 8 $\mu$m IRAC image. \emph{Spitzer} IRAC color analysis of the shocked emission was performed from which thermal and column density maps of the outflow were constructed. Narrow-band near-infrared (NIR) images of the flow reveal H$_2$ emission features coincident with the high temperature regions of the outflow. This outflow has now been given the designation MHO 1321 due to the detection of NIR H$_2$ features. We use these data and maps to probe the physical conditions and structure of the flow.
Dark matter axions form a rethermalizing Bose-Einstein condensate. This provides an opportunity to distinguish axions from other forms of dark matter on observational grounds. I show that if the dark matter is axions, tidal torque theory predicts a specific structure for the phase space distribution of the halos of isolated disk galaxies, such as the Milky Way. This phase space structure is precisely that of the caustic ring model, for which observational support had been found earlier. The other dark matter candidates predict a different phase space structure for galactic halos.
Direct imaging of brown dwarfs as companions to solar-type stars can provide a wealth of well-constrained data to "benchmark" the physics of such objects, since quantities like metallicity and age can be determined from their well-studied primaries. We present results from an adaptive optics imaging program on stars drawn from the Anglo-Australian and Keck Planet Search projects, with the aim of directly imaging known cool companions. Simulations have modeled the expected contrast ratios and separations of known companions using estimates of orbital parameters available from current radial-velocity data and then a selection of the best case objects were followed-up with high contrast imaging to attempt to directly image these companions. These simulations suggest that only a very small number of radial-velocity detected exoplanets with consistent velocity fits and age estimates could potentially be directly imaged using the VLT's Simultaneous Differential Imaging system and only under favorable conditions. We also present detectability confidence limits from the radial-velocity data sets and show how these can be used to gain a better understanding of these systems when combined with the imaging data. For HD32778 and HD91204 the detectabilities help little in constraining the companion and hence almost all our knowledge is drawn from the SDI images. Therefore, we can say that these stars do not host cool methane objects, out to on-sky separations of ~2'', with contrasts less than 10-11 magnitudes. However, for HD25874, HD120780 and HD145825, the contrasts and detectabilities can rule out a number of possible solutions, particularly at low angular separations, and for the best case, down to strong methane masses of 40MJ at 1'' separation. The contrast curves constructed for these five stars show 5 sigma contrasts (Delta F1) of ~9.2-11.5 magnitudes at separations of >/=0.6'', which correspond to contrasts of ~9.7-12.0 magnitudes for companions of mid-T spectral type. Such limits allow us to reach down to 40MJ around fairly old field dwarfs that typically constitute high precision radial-velocity programs. Finally, the analysis performed here can serve as a template for future projects that will employ extreme-AO systems to directly image planets already indirectly discovered by the radial-velocity method.
We present observations of newly discovered 24 micron circumstellar structures detected with the Multiband Imaging Photometer for Spitzer (MIPS) around three evolved stars in the Cygnus-X star forming region. One of the objects, BD+43 3710, has a bipolar nebula, possibly due to an outflow or a torus of material. A second, HBHA 4202-22, a Wolf-Rayet candidate, shows a circular shell of 24 micron emission suggestive of either a limb-brightened shell or disk seen face-on. No diffuse emission was detected around either of these two objects in the Spitzer 3.6-8 micron Infrared Array Camera (IRAC) bands. The third object is the luminous blue variable candidate G79.29+0.46. We resolved the previously known inner ring in all four IRAC bands. The 24 micron emission from the inner ring extends ~1.2 arcmin beyond the shorter wavelength emission, well beyond what can be attributed to the difference in resolutions between MIPS and IRAC. Additionally, we have discovered an outer ring of 24 micron emission, possibly due to an earlier episode of mass loss. For the two shell stars, we present the results of radiative transfer models, constraining the stellar and dust shell parameters. The shells are composed of amorphous carbon grains, plus polycyclic aromatic hydrocarbons in the case of G79.29+0.46. Both G79.29+0.46 and HBHA 4202-22 lie behind the main Cygnus-X cloud. Although G79.29+0.46 may simply be on the far side of the cloud, HBHA 4202-22 is unrelated to the Cygnus-X star formation region.
We report on our Chandra Cycle 9 program to observe half of the 60 (unobserved by Chandra) 3C radio sources at z<0.3 for 8 ksec each. Here we give the basic data: the X-ray intensity of the nuclei and any features associated with radio structures such as hot spots and knots in jets. We have measured fluxes in soft, medium and hard bands and are thus able to isolate sources with significant intrinsic column density. For the stronger nuclei, we have applied the standard spectral analysis which provides the best fit values of X-ray spectral index and column density. We find evidence for intrinsic absorption exceeding a column density of 10^{22} cm^{-2} for one third of our sources.
We use the Spitzer Wide-area InfraRed Extragalactic Legacy Survey (SWIRE) to explore the specific star-formation activity of galaxies and their evolution near the peak of the cosmic far-infrared background at 70 and 160\micron. We use a stacking analysis to determine the mean far-infrared properties of well defined subsets of galaxies at flux levels well below the far-infrared catalogue detection limits of SWIRE and other Spitzer surveys. We tabulate the contribution of different subsets of galaxies to the far-infrared background at 70$\micron\ $ and 160$\micron$. These long wavelengths provide a good constraint on the bolometric obscured emission. The large area provides good constraints at low $z$ and in finer redshift bins than previous work. At all redshifts we find that the specific far-infrared luminosity decreases with increasing mass, following a trend $L_{\rm FIR}/M_* \propto M_* ^\beta$ with $\beta =-0.38\pm0.14$. This is a more continuous change than expected from the \cite{Delucia2007} semi-analytic model suggesting modifications to the feedback prescriptions. We see an increase in the specific far-infrared luminosity by about a factor of $\sim100$ from $0<z<2$ and find that the specific far infrared luminosity evolves as $(1+z)^{\alpha}$ with $\alpha=4.4\pm 0.3$ for galaxies with $10.5<\log_{10} M_*/M_\odot\le12$. This is considerably steeper than the \cite{Delucia2007} semi-analytic model ($\alpha\sim2.5$). When separating galaxies into early and late types on the basis of the optical/IR spectral energy distributions we find that the decrease in specific far-infrared luminosity with stellar mass is stronger in early type galaxies ($\beta\sim-0.46$), while late type galaxies exhibit a flatter trend ($\beta\sim-0.15$). The evolution is strong for both classes but stronger for the early type galaxies. The early types show a trend of decreasing strength of evolution as we move from lower to higher masses while the evolution of the late type galaxies has little dependence on stellar mass. We suggest that in late-type galaxies we are seeing a consistently declining specific star-formation rate $\alpha=3.36\pm0.16$ through a common phenomenon e.g. exhaustion of gas supply i.e. not systematically dependent on the local properties of the galaxy.
The Fermi Gamma-Ray Space Telescope has more than doubled the number of Gamma-Ray Bursts (GRBs) detected above 100 MeV within its first year of operation. Thanks to the very wide energy range covered by Fermi's Gamma-ray Burst Monitor (GBM; 8 keV to 40 MeV) and Large Area Telescope (LAT; 25 MeV to >300 GeV) it has measured the prompt GRB emission spectrum over an unprecedentedly large energy range (from ~8 keV to ~30 GeV). Here I briefly outline some highlights from Fermi GRB observations during its first ~1.5 yr of operation, focusing on the prompt emission phase. Interesting new observations are discussed along with some of their possible implications, including: (i) What can we learn from the Fermi-LAT GRB detection rate, (ii) A limit on the variation of the speed of light with photon energy (for the first time beyond the Planck scale for a linear energy dependence from direct time of arrival measurements), (iii) Lower-limits on the bulk Lorentz factor of the GRB outflow (of ~1000 for the brightest Fermi LAT GRBs), (iv) The detection (or in other cases, lack thereof) of a distinct spectral component at high (and sometimes also at low) energies, and possible implications for the prompt GRB emission mechanism, (v) The later onset (and longer duration) of the high-energy emission (>100 MeV), compared to the low-energy (< ~1 MeV) emission, that is seen in most Fermi-LAT GRBs.
Just as big bang nucleosynthesis allows us to probe the expansion rate when the temperature of the universe was around 1 MeV, the measurement of gravity waves from electroweak scale first order phase transitions may allow us to probe the expansion rate when the temperature of the universe was at the electroweak scale. We compute the simple transformation rule for the gravity wave spectrum under the scaling transformation of the Hubble expansion rate. We then apply this directly to the scenario of quintessence kination domination and show how gravity wave spectra would shift relative to LISA and BBO projected sensitivities.
Cygnus OB2 is the nearest example of a massive star forming region, containing over 50 O-type stars and hundreds of B-type stars. We have analysed the properties of young stars in two fields in Cyg OB2 using the recently published deep catalogue of Chandra X-ray point sources with complementary optical and near-IR photometry. Our sample is complete to 1 Msun (excluding A and B-type stars that do not emit X-rays), making this the deepest study of the stellar properties and star formation history in Cyg OB2 to date. From Siess et al. (2000) isochrone fits to the near-IR color-magnitude diagram, we derive ages of 3.5 (+0.75/-1.0) and 5.25 (+1.5/-1.0) Myrs for sources in the two fields, both with considerable spreads around the pre-MS isochrones. The presence of a stellar population somewhat older than the present-day O-type stars, also fits in with the low fraction of sources with inner circumstellar disks (as traced by the K-band excess) that we find to be very low, but appropriate for a population of age ~5 Myrs. We also find that the region lacks a population of highly embedded sources that is often observed in young star forming regions, suggesting star formation in the vicinity has declined. We measure the stellar mass functions in this limit and find a power-law slope of Gamma = -1.09 +/- 0.13, in good agreement with the global mean value estimated by Kroupa (2002). A steepening of the slope at higher masses is observed and suggested as due to the presence of the previous generation of stars that have lost their most massive members. Finally, combining our mass function and an estimate of the radial density profile of the association suggests a total mass of Cyg OB2 of ~3 x 10^4 Msun, similar to that of many of our Galaxy's most massive star forming regions.
We compare the near-infrared (NIR) H band photometric and morphological properties of low-redshift (z<0.3) 3CR radio galaxies with samples of BL Lac object and quasar host galaxies, merger remnants, quiescent elliptical galaxies, and brightest cluster galaxies drawn from the literature. In general the 3CR host galaxies are consistent with luminous (~L*) elliptical galaxies. The vast majority of FR II's (~80%) occupy the most massive ellipticals and form a homogeneous population that is comparable to the population of radio-loud quasar (RLQ) host galaxies in the literature. However, a significant minority (~20%) of the 3CR FR II's appears under-luminous with respect to quasar host galaxies. All FR II objects in this faint tail are either unusually red, or appear to be the brightest objects within a group. We discuss the apparent differences between the radio galaxy and RLQ host galaxy populations. RLQs appear to require >1E11 M_sun host galaxies (and ~1E9 M_sun black holes), whereas radio galaxies and RQQs can exist in galaxies down to 3E10 M_sun. This may be due to biases in the measured quasar host galaxy luminosities or populations studied, or due to a genuine difference in host galaxy. If due to a genuine difference, it would support the idea that radio and optical active galactic nucleii are two separate populations with a significant overlap.
We present an up-to-date, comprehensive summary of the rates for all types of compact binary coalescence sources detectable by the Initial and Advanced versions of the ground-based gravitational-wave detectors LIGO and Virgo. Astrophysical estimates for compact-binary coalescence rates depend on a number of assumptions and unknown model parameters, and are still uncertain. The most confident among these estimates are the rate predictions for coalescing binary neutron stars which are based on extrapolations from observed binary pulsars in our Galaxy. These yield a likely coalescence rate of 100 per Myr per Milky Way Equivalent Galaxy (MWEG), although the rate could plausibly range from 1 per Myr per MWEG to 1000 per Myr per MWEG. We convert coalescence rates into detection rates based on data from the LIGO S5 and Virgo VSR2 science runs and projected sensitivities for our Advanced detectors. Using the detector sensitivities derived from these data, we find a likely detection rate of 0.02 per year for Initial LIGO-Virgo interferometers, with a plausible range between 0.0002 and 0.2 per year. The likely binary neutron-star detection rate for the Advanced LIGO-Virgo network increases to 40 events per year, with a range between 0.4 and 400 per year.
We have modeled the displacement of luminous X-ray binaries from star clusters in star-burst galaxies with an evolutionary population synthesis code developed by Hurley et al. (2000, 2002). In agreement with Kaaret et al. (2004), we find significant spatial offset of X-ray sources from their parent clusters, and the apparent X-ray luminosity vs. displacement correlation can be roughly reconstructed. The correlation is not sensitive to the fundamental properties of the clusters (e.g., initial mass functions of the binary stars) and the kick velocity imparted to the newborn compact stars, except the common envelope parameter. We present the distributions of the main parameters of the current X-ray binaries, which may be used to constrain the models for the formation and evolution of X-ray binaries with future optical observations.
A brief review is given of different methods used to determine the pattern speeds of the Galactic bar and spiral arms. The Galactic bar rotates rapidly, with corotation about halfway between the Galactic center and the Sun, and outer Lindblad resonance not far from the solar orbit, R0. The Galactic spiral arms currently rotate with a distinctly slower pattern speed, such that corotation is just outside R0. Both structures therefore seem dynamically decoupled.
We investigate the contribution of different formation scenarios for type Ia supernovae in elliptical galaxies. The single degenerate scenario (a white dwarf accreting from a late main sequence or red giant companion) is tested against the double degenerate scenario (the spiral-in and merging of two white dwarfs through the emission of gravitational wave radiation). We use a population number synthesis code incorporating the latest physical results in binary evolution, and allowing to differentiate between certain physical scenarios (e.g. description of common envelope evolution) and evolutionary parameters (e.g. mass transfer efficiency during Roche lobe overflow). The obtained theoretical distributions of the delay times of type Ia supernovae are compared to those which are observed, both in morphological shape and absolute number of events. The critical dependency of these distributions on certain parameters is used to constrain the values of the latter. We find that the single degenerate scenario alone cannot explain the morphological shape of the observational delay time distribution, while the double degenerate scenario (or a combination of both) can. Most of these double degenerate type Ia supernovae are created through a normal quasi-conservative Roche lobe overflow followed by a common envelope phase, not through two successive common envelope phases. This may cast doubt on the use in other studies of analytical formalisms to determine delay times. In terms of absolute number, theoretical supernova Ia rates in old elliptical galaxies lie a factor of at least three below the observed ones. We propose a solution involving the effect of rotation on the evolution of intermediate mass binaries.
The radio astronomy community is currently building a number of phased array telescopes. The calibration of these telescopes is hampered by the fact that covariances of signals from closely spaced antennas are sensitive to noise coupling and to variations in sky brightness on large spatial scales. These effects are difficult and computationally expensive to model. We propose to model them phenomenologically using a non-diagonal noise covariance matrix. The parameters can be estimated using a weighted alternating least squares (WALS) algorithm iterating between the calibration parameters and the additive nuisance parameters. We demonstrate the effectiveness of our method using data from the low frequency array (LOFAR) prototype station.
Globular clusters are found usually in galaxies and they are an excellent tracer of dark matter. Long ago it was suggested that there may exist intracluster globular clusters (IGCs) bound to a galaxy cluster rather than to any single galaxy. Here we present a map showing the large scale distribution of globular clusters over the entire Virgo cluster. It shows that IGCs are found out to 5 million light years from the Virgo center, and that they are concentrated in several substructures much larger than galaxies. These objects might have been mostly stripped off from low-mass dwarf galaxies.
Numerous authors have suggested that the ultra-high energy cosmic rays (UHECR) detected by the Pierre Auger Observatory and other cosmic-ray telescopes may be accelerated in the nuclei, jets or lobes of radio galaxies. Here I focus on stochastic acceleration in the lobes. I show that the requirement that they accelerate protons to the highest observed energies places constraints on the observable properties of radio lobes that are satisfied by a relatively small number of objects within the Greisen-Zat'sepin-Kuzmin (GZK) cutoff; if UHECR are protons and are accelerated within radio lobes, their sources are probably already known and catalogued radio galaxies. I show that lobe acceleration also implies a (charge-dependent) upper energy limit on the UHECR that can be produced in this way; if lobes are the dominant accelerators in the local universe and if UHECR are predominantly protons, we are unlikely to see cosmic rays much higher in energy than those we have already observed. I comment on the viability of the stochastic acceleration mechanism and the likely composition of cosmic rays accelerated in this way, based on our current understanding of the contents of the large-scale lobes of radio galaxies, and finally discuss the implications of stochastic lobe acceleration for the future of cosmic ray astronomy.
We report for the first time general geometrical expressions for the angular resolution of an arbitrary network of interferometric gravitational-wave (GW) detectors when the arrival-time of a GW is unknown. We show explicitly elements that decide the angular resolution of a GW detector network. In particular, we show the dependence of the angular resolution on areas formed by projections of pairs of detectors and how they are weighted by sensitivities of individual detectors. Numerical simulations are used to demonstrate the capabilities of the current GW detector network. We confirm that the angular resolution is poor along the plane formed by current LIGO-Virgo detectors. A factor of a few to more than ten fold improvement of the angular resolution can be achieved if the proposed new GW detectors LCGT or AIGO are added to the network. We also discuss the implications of our results for the design of a GW detector network, optimal localization methods for a given network, and electromagnetic follow-up observations.
We have compared far-ultraviolet (FUV), near-ultraviolet (NUV), and Halpha measurements for star forming regions in 21 galaxies, in order to characterise the properties of their discs at radii beyond the main optical radius (R25). In our representative sample of extended and non-extended UV discs we find that half of the extended UV discs also exhibit extended Halpha emission. We find that extended UV discs fall into two categories, those with a sharp truncation in the Halpha disc close to the optical edge (R25), and those with extended emission in Halpha as well as in the ultraviolet. Although most galaxies with strong Halpha truncations near R25 show a significant corresponding falloff in UV emission (factor 10--100), the transition tends to be much smoother than in Halpha, and significant UV emission often extends well beyond this radius, confirming earlier results by Thilker et al. (2007) and others. After correcting for dust attenuation the median fraction of total FUV emission from regions outside of R25 is 1.7%, but it can be as high as 35% in the most extreme cases. The corresponding fractions of Halpha emission are approximately half as large on average. This difference reflects both a slightly lower ratio of Halpha to UV emission in the HII regions in the outer discs, as well as a lower fraction of star clusters showing HII regions. Most HII regions in the extended disc have fluxes consistent with small numbers of ionising O-type stars, and this poor sampling of the upper initial mass function in small clusters can probably account for the differences in the emission properties, consistent with earlier conclusions by Zaritsky & Christlein (2007), without needing to invoke a significant change in the stellar IMF itself. Consistent Ha/FUV ratios and brightest HII region to total Halpha fluxes in the inner and extended discs across our whole galaxy sample demonstrate no evidence for a change in the cluster luminosity function or the IMF in the low gas density outer disc.
The Taiwanese-American Occultation Survey (TAOS) project has collected more than a billion photometric measurements since 2005 January. These sky survey data-covering timescales from a fraction of a second to a few hundred days-are a useful source to study stellar variability. A total of 167 star fields, mostly along the ecliptic plane, have been selected for photometric monitoring with the TAOS telescopes. This paper presents our initial analysis of a search for periodic variable stars from the time-series TAOS data on one particular TAOS field, No. 151 (RA = 17$^{\rm h}30^{\rm m}6\fs$67, Dec = 27\degr17\arcmin 30\arcsec, J2000), which had been observed over 47 epochs in 2005. A total of 81 candidate variables are identified in the 3 square degree field, with magnitudes in the range 8 < R < 16. On the basis of the periodicity and shape of the lightcurves, 29 variables, 15 of which were previously unknown, are classified as RR Lyrae, Cepheid, delta Scuti, SX Phonencis, semi-regular and eclipsing binaries.
The correlation between geomagnetic activity and the sunspot number in the 11-year solar cycle exhibits long-term variations due to the varying time lag between the sunspot-related and non-sunspot related geomagnetic activity, and the varying relative amplitude of the respective geomagnetic activity peaks. As the sunspot-related and non-sunspot related geomagnetic activity are caused by different solar agents, related to the solar toroidal and poloidal fields, respectively, we use their variations to derive the parameters of the solar dynamo transforming the poloidal field into toroidal field and back. We find that in the last 12 cycles the solar surface meridional circulation varied between 5 and 20 m/s (averaged over latitude and over the sunspot cycle), the deep circulation varied between 2.5 and 5.5 m/s, and the diffusivity in the whole of the convection zone was ~10**12 m2/s. In the last 12 cycles solar dynamo has been operating in moderately diffusion dominated regime in the bulk of the convection zone. This means that a part of the poloidal field generated at the surface is advected by the meridional circulation all the way to the poles, down to the tachocline and equatorward to sunspot latitudes, while another part is diffused directly to the tachocline at midlatitudes, "short-circuiting" the meridional circulation. The sunspot maximum is the superposition of the two surges of toroidal field generated by these two parts of the poloidal field, which is the explanation of the double peaks and the Gnevyshev gap in sunspot maximum. Near the tachocline, dynamo has been operating in diffusion dominated regime in which diffusion is more important than advection, so with increasing speed of the deep circulation the time for diffusive decay of the poloidal field decreases, and more toroidal field is generated leading to a higher sunspot maximum. During the Maunder minimum the dynamo was operating in advection dominated regime near the tachocline, with the transition from diffusion dominated to advection dominated regime caused by a sharp drop in the surface meridional circulation which is in general the most important factor modulating the amplitude of the sunspot cycle.
Distances to Bok globules and small dark nebulae are important for a variety of reasons. We provide new distance estimates to several small clouds, some of them known to harbor YSO and molecular outflows, and thus being of particular interest. We use a procedure based on extinctions determined from the (H-K) vs. (J-H) diagram, and stellar distances based on a Hipparcos calibration of the main sequence locus: $M_J[(J-K)_0]$. The cloud confinement on the sky is determined from contours of the average (H-K) color formed in reseaus. Along the sight line stars affected by the clouds extinction may be extracted from the variation of the number density of atomic hydrogen $n_H\sim A_{V,\star}/D_\star$ to provide the cloud distance and its uncertainty. According to our estimates, the group of three globules CB24, CB25 and CB26 is located at 407+/-27 pc, farther than the previous estimates. CB245 and CB246 are found at 272+/-20 pc, suggesting that the current distance to these clouds is underestimated. Toward CB244 we detect a layer at 149+/-16 pc and the cloud at 352+/-18, in good agreement with previous studies. CB52 and CB54, though to be at 1500 pc, are found at 421+/-28 pc and slightly beyond 1000 pc, respectively. It seems that the most distant Bok globule known, CB3, is located at about 1400 pc, also significantly closer than currently accepted.
The origin of the long secondary periods (LSPs) in red variables remains a mystery up to now, although there exist many models. The light curves of some LSPs stars mimic an eclipsing binary with a pulsating red giant component. To test this hypothesis, the observational data of two LSP variable red giants, 77.7795.29 and 77.8031.42, discovered by the MACHO project from the LMC, are collected and analyzed. The probable eclipsing features of the light curves are simulated by the Wilson-Devinney (W-D) method. The simulation yields a contact and a semidetached geometry for the two systems, respectively. In addition, the pulsation constant of the main pulsating component in each binary system is derived. By combining the results of the binary model and the pulsation component, we investigate the feasibility of the pulsating binary model. It is found that the radial velocity curve expected from the binary model has a much larger amplitude than the observed one and a period double the observed one. Furthermore, the masses of the components based on the density derived from the binary orbit solution are too low to be compatible with both the evolutionary stage and the high luminosity. Although the pulsation mode identified by the pulsation constant which is dependent on the density from the binary-model is consistent with the first or second overtone radial pulsation, we conclude that the pulsating binary model is a defective model for the LSP.
We discuss a new one-dimensional non-LTE time-dependent radiative-transfer technique for the simulation of supernova (SN) spectra and light curves. Starting from a hydrodynamical input characterizing the homologously-expanding ejecta at a chosen post-explosion time, we model the evolution of the entire ejecta, including gas and radiation. Non-LTE, which holds in all regions at and above the photosphere, is accounted for. The effects of line blanketing on the radiation field are explicitly included, using complex model atoms and solving for all ion level populations appearing in the statistical-equilibrium equations. Here, we present results for SN1987A, evolving the model "lm18a7Ad" of Woosley from 0.27 to 20.8d. The fastest evolution occurs prior to day 1, with a spectral energy distribution peaking in the range 300-2000A, subject to line blanketing from highly ionized metal and CNO species. After day 1, our synthetic multi-band light curve and spectra reproduce the observations to within 10-20% in flux in the optical, with a greater mismatch for the faint UV flux. We do not encounter any of the former discrepancies associated with the HeI and HI lines in the optical, which can be fitted well with a standard Blue-supergiant-star surface composition and no contribution from radioactive decay. The effects of time dependence on the ionization structure, discussed in Dessart & Hillier, are recovered, and thus nicely integrated in this new scheme. Despite the 1D nature of our approach, its high physical consistency and accuracy will allow reliable inferences to be made on explosion properties and pre-SN star evolution.
Multiple outbursts of type Ia SNe in one galaxy present a unique opportunity to study the homogeneity of these objects. NGC 3147 is only the second known galaxy with three SNe Ia, another one is NGC 1316. We present CCD UBVRI photometry for SN Ia 2008fv and compare the light and color curves of this object with those for SNe Ia discovered earlier in NGC 3147: 1972H and 1997bq. The photometric properties of SNe 1997bq and 2008fv are nearly identical, while SN 1972H exhibits faster declining light curve.
The clustering of X-ray selected AGN appears to be a valuable tool for extracting cosmological information. Using the recent high-precision angular clustering results of ~30000 XMM-Newton soft (0.5-2 keV) X-ray sources (Ebrero et al. 2009), which have a median redshift of $z\sim 1$, and assuming a flat geometry, a constant in comoving coordinates AGN clustering evolution and the AGN bias evolution model of Basilakos et al. (2008), we manage to break the Omega_m-sigma_8 degeneracy. The resulting cosmological constraints are: Omega_m=0.27 (+0.03 -0.05), w=-0.90 (+0.10 -0.16) and sigma_8=0.74 (+0.14 -0.12), while the dark matter host halo mass, in which the X-ray selected AGN are presumed to reside, is M=2.50 (+0.50 -1.50) X 10^13 h^{-1} M(solar). For the constant Lambda model (w=-1) we find Omega_m=0.24 (+- 0.06) and sigma_8=0.83 (+0.11 -0.16), in good agreement with recent studies based on cluster abundances, weak lensing and the CMB, but in disagreement with the recent bulk flow analysis.
{\it GALEX} near ultraviolet (NUV) and far-ultraviolet (FUV) light curves of three extremely low accretion rate polars show distinct modulations in their UV light curves. While these three systems have a range of magnetic fields from 13 to 70 MG, and of late type secondaries (including a likely brown dwarf in SDSSJ121209.31+013627.7), the accretion rates are similar, and the UV observations imply some mechanism is operating to create enhanced emission zones on the white dwarf. The UV variations match in phase to the two magnetic poles viewed in the optical in WX LMi and to the single poles evident in the optical in SDSSJ1212109.31+013627.7 and SDSSJ103100.55+202832.2. Simple spot models of the UV light curves show that if hot spots are responsible for the UV variations, the temperatures are on the order of 10,000-14,000K. For the single pole systems, the size of the FUV spot must be smaller than the NUV and in all cases, the geometry is likely more complicated than a simple circular spot.
Recent studies of outer spiral disks have given rise to an abundance of new results. We discuss the observational and theoretical advances that have spurred the interest in disk outskirts, as well as where we currently stand in terms of our understanding of outer disk structure, ages and metallicities.
We present results of long-slit spectroscopy in several slit positions that cover different morphological structures of the central parts of three bright Galactic HII regions: M8, M17 and NGC7635. We study the spatial distributions of a large number of nebular parameters such as the extinction coefficient, line fluxes, physical conditions and ionic abundances at the maximum spatial resolution attainable with our instrumentation. Particularly, our goal is to study the behaviour of the abundance discrepancy factor of O^{2+}, ADF(O^{2+}), defined as the logarithmic difference of the O^{2+} abundances derived from collisionally excited and recombination lines. We find that the ADF(O^{2+}) remains fairly constant along the slit positions of M8 and M17. In the case of NGC7635, we only detect the OII recombination lines in the integrated spectrum along the whole slit, where the ADF(O^{2+}) reaches a remarkably high value of about 0.59 dex. We compare our results with previous ones obtained for the Orion Nebula. We find several evidences that suggest the presence of a candidate to Herbig-Haro object in M8.
Spectroscopically identified white dwarfs from the SDSS data release 1 are matched against SDSS data release 1 proper motion survey in the search for common proper motion companions
In order to examine the rotational effect around neutron star in tensor-vector-scalar (TeVeS) theory, we consider the slowly rotating relativistic stars with a uniform angular velocity. As a result, we find that similar to the case in general relativity (GR), the angular momentum is proportional to the angular velocity. Additionally, as the value of coupling constant $K$ becomes higher, the frame dragging in TeVeS becomes quite different distribution from that in GR, where we can also see the deviation even in the interior of star. While with smaller value of $K$, although the frame dragging approaches to that expected in GR, the induced vector field due to the rotation does not vanish and still exists. Thus, through the observations associated with relativistic object, one could be possible to distinguish the gravitational theory in strong field regime even in the case that the value of coupling constant $K$ is quite small.
We study the correlations between the VLBA (Very Long Baseline Array) radio emission at 15 GHz, extended emission at 151 MHz, and optical nuclear emission at 5100\,\AA\ for a complete sample of 135 compact jets. We use the partial Kendall's tau correlation analysis to check the link between radio properties of parsec-scale jets and optical luminosities of host active galactic nuclei (AGN). We find a significant positive correlation for 99 quasars between optical nuclear luminosities and total radio (VLBA) luminosities of unresolved cores at 15\,GHz originated at milliarcseconds scales. For 18 BL Lacs, the optical continuum emission correlates with the radio emission of the jet at 15\,GHz. We suggest that the radio and optical emission are beamed and originate in the innermost part of the sub--parsec-scale jet in quasars. Analysis of the relation between the apparent speed of the jet and the optical nuclear luminosity at 5100\,\AA\ supports the relativistic beaming model for the optical emission generated in the jet, and allows the peak values of the intrinsic optical luminosity of the jet and its Lorentz factor to be estimated for the populations of quasars ($2\times10^{20}$W\,Hz$^{-1}$ and $\gamma=52$), BL Lacs ($9\times10^{21}$W\,Hz$^{-1}$ and $\gamma=20$), and radio galaxies ($1.5\times10^{21}$W\,Hz$^{-1}$ and $\gamma=9$). The radio-loudness of quasars (the ratio of 15\,GHz flux density and optical nuclear flux at 5100\,\AA) is found to increase at high redshifts, which can be a result of lower efficiency of the accretion in AGN having higher radio luminosities. A strong positive correlation is found between the intrinsic kinetic power of the jet (measured from the flux density at 151\,MHz) and the apparent luminosities of the total and the unresolved core emission of the jet at 15\,GHz. This correlation is interpreted in terms of intrinsically more luminous parsec-scale jet producing more luminous extended structure which is detectable at low radio frequencies, 151\,MHz. A possibility that the low frequency radio emission is relativistically beamed in superluminal AGN and therefore correlates with radio luminosity of the jet at 15\,GHz can not be ruled out. Monitoring of superluminal AGN in a wide range of frequencies is required to check the contribution of each effect.
V-type asteroids in the inner Main Belt (a < 2.5 AU) and the HED meteorites
are thought to be genetically related to one another as collisional fragments
from the surface of the large basaltic asteroid 4 Vesta. We investigate this
relationship by comparing the near-infrared (0.7-2.5 micron) spectra of 39
V-type asteroids to laboratory spectra of HED meteorites. The central
wavelengths and areas spanned by the 1 and 2 micron pyroxene-olivine absorption
bands that are characteristic of planetary basalts are measured for both the
asteroidal and meteoritic data. The band centers are shown to be well
correlated, however the ratio of areas spanned by the 1 and 2 micron absorption
bands are much larger for the asteroids than for the meteorites. We argue that
this offset in band area ratio is consistent with our currently limited
understanding of the effects of space weathering, however we can not rule out
the possibility that this offset is due to compositional differences. Several
other possible causes of this offset are discussed.
Amongst these inner Main Belt asteroids we do not find evidence for
non-Vestoid mineralogies. Instead, these asteroids seem to represent a
continuum of compositions, consistent with an origin from a single
differentiated parent body. In addition, our analysis shows that V-type
asteroids with low inclinations (i < 6 degrees) tend to have band centers
slightly shifted towards long wavelengths. This may imply that more than one
collision on Vesta's surface was responsible for producing the observed
population of inner belt V-type asteroids. Finally, we offer several
predictions that can be tested when the Dawn spacecraft enters into orbit
around Vesta in the summer of 2011.
Recent analyses show evidence for a thermal emission component that accompanies the non-thermal emission during the prompt phase of GRBs. First, we show the evidence for the existence of this component; Second, we show that this component is naturally explained by considering emission from the photosphere, taking into account high latitude emission from optically thick relativistically expanding plasma. We show that the thermal flux is expected to decay at late times as F_BB ~ t^{-2}, and the observed temperature as T ~ t^{-\alpha}, with \alpha ~ 1/2 - 2/3. These theoretical predictions are in very good agreement with the observations. Finally, we discuss three implications of this interpretation: (a) The relation between thermal emission and high energy, non-thermal spectra observed by Fermi. (b) We show how thermal emission can be used to directly measure the Lorentz factor of the flow and the initial radius of the jet. (c) We show how the lack of detection of the thermal component can be used to constrain the composition of GRB jets.
High-dispersion spectra of 89 potential members of the old, super-metal-rich open cluster, NGC 6253, have been obtained with the HYDRA multi-object spectrograph. Based upon radial-velocity measurements alone, 47 stars at the turnoff of the cluster color-magnitude diagram (CMD) and 18 giants are identified as potential members. Five turnoff stars exhibit evidence of binarity while proper-motion data eliminates two of the dwarfs as members. The mean cluster radial velocity from probable single-star members is -29.4 +/- 1.3 km/sec (sd). A discussion of the current estimates for the cluster reddening, derived independently of potential issues with the BV cluster photometry, lead to an adopted reddening of E(B-V) = 0.22 +/- 0.04. From equivalent width analyses of 38 probable single-star members near the CMD turnoff, the weighted average abundances are found to be [Fe/H] = +0.43 +/- 0.01, [Ni/H] = +0.53 +/- 0.02 and [Si/H] = +0.43 (+0.03,-0.04), where the errors refer to the standard errors of the weighted mean. Weak evidence is found for a possible decline in metallicity with increasing luminosity among stars at the turnoff. We discuss the possibility that our turnoff stars have been affected by microscopic diffusion. For 15 probable single-star members among the giants, spectrum synthesis leads to abundances of +0.46 (+0.02,-0.03) for [Fe/H]. While less than half the age of NGC 6791, NGC 6253 is at least as metal-rich and, within the uncertainties, exhibits the same general abundance pattern as that typified by super-metal-rich dwarfs of the galactic bulge.
This talk presents conclusions for KM3NeT which may be drawn from latest IceCube results and from optimization studies of the IceCube configuration. It discusses possible coordinated efforts between IceCube and KM3NeT (or, for the time being, IceCube and ANTARES). Finally, it lists ideas for formal relations between neutrino telescopes on the cubic kilometer scale.
We present high-resolution 3D smoothed particle hydrodynamics simulations of the formation and evolution of protostellar discs in a turbulent molecular cloud. Using a piecewise polytropic equation of state, we follow the evolution of an isolated and a binary protostellar system in the same environment. In both cases the discs are sufficiently massive to develop gravitational instabilities. The isolated system accretes gas with steadily increasing specific angular momentum until an m = 2 mode develops into material arms that fragment, forming clumps with initial masses of 5.5 Mjup and 7.4 Mjup, and growing to masses of 39 Mjup and 14 Mjup, respectively. The clumps have typical accretion rates of 10^(-5) Msol/yr. While the discs in the binary system are strongly self-gravitating, we find that they are stable against fragmentation due to disc truncation and mass profile steeping by tides, accretion of high specific angular momentum gas by the secondary, and angular momentum being redirected into the binary's orbit.
Spitzer Space Telescope IRAC 3-8 micron and AKARI IRC 2-4 micron photometry are reported for ten white dwarfs with photospheric heavy elements; nine relatively cool stars with photospheric calcium, and one hotter star with a peculiar high carbon abundance. A substantial infrared excess is detected at HE 2221-1630, while modest excess emissions are identified at HE 0106-3253 and HE 0307+0746, implying these latter two stars have relatively narrow (Delta r < 0.1 Rsol) rings of circumstellar dust. A likely 7.9 micron excess is found at PG 1225-079 and may represent, together with G166-58, a sub-class of dust ring with a large inner hole. The existence of attenuated disks at white dwarfs substantiates the connection between their photospheric heavy elements and the accretion of disrupted minor planets, indicating many polluted white dwarfs may harbor orbiting dust, even those lacking an obvious infrared excess.
The effects of noncommutativity on the phase space of a dilatonic cosmological model is investigated. The existence of such noncommutativity results in a deformed Poisson algebra between the minisuperspace variables and their momenta conjugate. For an exponential dilaton potential, the exact solutions in the commutative and noncommutative cases, are presented and compared. We use these solutions to address the late time acceleration issue of cosmic evolution.
The R-matrix method has been used for theoretical calculation of electron collision with atoms and molecules for long years. The method was also formulated to treat photoionization process, however, its application has been mostly limited to photoionization of atoms. In this work, we implement the R-matrix method to treat molecular photoionization problem based on the UK R-matrix codes. This method can be used for diatomic as well as polyatomic molecules, with multi-configurational description for electronic states of both target neutral molecule and product molecular ion. Test calculations were performed for valence electron photoionization of nitrogen (N2) as well as nitric oxide (NO) molecules. Calculated photoionization cross sections and asymmetry parameters agree reasonably well with the available experimental results, suggesting usefulness of the method for molecular photoionization.
Recently Vishik anti-fast dynamo theorem, has been tested against non-stretching flux tubes [Phys Plasmas 15 (2008)]. In this paper, another anti-dynamo theorem, called Cowling's theorem, which states that axisymmetric magnetic fields cannot support dynamo action, is carefully tested against thick tubular and curved Riemannian untwisted flows, as well as thin flux tubes in diffusive and diffusionless media. In the non-diffusive media the Cowling's theorem is not violated in thin Riemann-flat untwisted flux tubes, where the Frenet curvature is negative. Nevertheless the diffusion action in the thin flux tube leads to a a dynamo action driven by poloidal flows as shown by Love and Gubbins (Geophysical Res.) in the context of geodynamos. Actually it is shown that a slow dynamo action is obtained. In this case the Frenet and Riemann curvature still vanishes. In the case of magnetic filaments in diffusive media dynamo action is obtained when the Frenet scalar curvature is negative. Since the Riemann curvature tensor can be expressed in terms of the Frenet curvature of the magnetic flux tube axis, this result can be analogous to a recent result obtained by Chicone, Latushkin and Smith, which states that geodesic curvature in compact Riemannian manifolds can drive dynamo action in the manifold. It is also shown that in absence of diffusion, magnetic energy does not grow but magnetic toroidal magnetic field can be generated by the poloidal field, what is called a plasma dynamo.
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We present observations at 250, 350, and 500 um of the nearby galaxy cluster Abell 3112 (z=0.075) carried out with BLAST, the Balloon-borne Large Aperture Submillimeter Telescope. Five cluster members are individually detected as bright submillimetre sources. Their far-infrared SEDs and optical colours identify them as normal star-forming galaxies of high mass, with globally evolved stellar populations. They all have B-R colours of 1.38+/-0.08, transitional between the blue, active population and the red, evolved galaxies that dominate the cluster core. We stack to determine the mean submillimetre emission from all cluster members, which is determined to be 16.6+/-2.5, 6.1+/-1.9, and 1.5+/-1.3 mJy at 250, 350, and 500 um, respectively. Stacking analyses of the submillimetre emission of cluster members reveal trends in the mean far-infrared luminosity with respect to cluster-centric radius and Ks-band magnitude. We find that a large fraction of submillimetre emission comes from the boundary of the inner, virialized region of the cluster, at cluster-centric distances around R_500. Stacking also shows that the bulk of the submillimetre emission arises in intermediate-mass galaxies (L<L*), with Ks magnitude ~1 mag fainter than the giant ellipticals. The results and constraints obtained in this work will provide a useful reference for the forthcoming surveys to be conducted on galaxy clusters by Herschel.
We present results of an extensive morphological, spectroscopic, and photometric study of the galaxy population of MACS J0025.4$-$1225 (z=0.586), a major cluster merger with clear segregation of dark and luminous matter, to examine the impact of mergers on galaxy evolution. Based on 436 galaxy spectra obtained with Keck DEIMOS, we identified 212 cluster members within 4 Mpc of the cluster centre, and classified them using three spectroscopic types; we find 111 absorption-line, 90 emission-line (including 23 e(a) and 11 e(b)), and 6 E+A galaxies. The fraction of absorption(emission)-line galaxies is a monotonically increasing(decreasing) function of both projected galaxy density and radial distance to the cluster center. More importantly, the 6 observed E+A cluster members are all located between the dark-matter peaks of the cluster and within ~0.3Mpc radius of the X-ray flux peak, unlike the E+A galaxies in other intermediate-redshift clusters which are usually found to avoid the core region. In addition, we use Hubble Space Telescope imaging to classify cluster members according to morphological type. We find the global fraction of spiral and lenticular galaxies in MACS J0025 to be among the highest observed to date in clusters at z>0.5. The observed E+A galaxies are found to be of lenticular type with Sersic indices of ~2, boosting the local fraction of S0 to 70 per cent between the dark-matter peaks. Combing the results of our analysis of the spatial distribution, morphology, and spectroscopic features of the galaxy population, we propose that the starburst phase of these E+A galaxies was both initiated and terminated during the first core-passage about 0.5--1Gyr ago, and that their morphology has already been transformed into S0 due to ram pressure and/or tidal forces near the cluster core. By contrast, ongoing starbursts are observed predominantly in infalling galaxies, and thus appears to be unrelated to the cluster merger.
Identifying the population of young stellar objects (YSOs) in high extinction regions is a prerequisite for studies of star formation. This task is not trivial, as reddened background objects can be indistinguishable from YSOs in near-infrared colour-colour diagrams. Here we combine deep JHK photometry with J- and K-band lightcurves, obtained with UKIRT/WFCAM, to explore the YSO population in the dark cloud IC1396W. We demonstrate that a colour-variability criterion can provide useful constraints on the star forming activity in embedded regions. For IC1396W we find that a near-infrared colour analysis alone vastly overestimates the number of YSOs. In total, the globule probably harbours not more than ten YSOs, among them a system of two young stars embedded in a small (~10000 AU) reflection nebula. This translates into a star forming efficiency SFE of ~1%, which is low compared with nearby more massive star forming regions, but similar to less massive globules. We confirm that IC1396W is likely associated with the IC1396 HII region. One possible explanation for the low SFE is the relatively large distance to the ionizing O-star in the central part of IC1396. Serendipitously, our variability campaign yields two new eclipsing binaries, and eight periodic variables, most of them with the characteristics of contact binaries.
We discuss a novel mechanism of dust acceleration which dominates for particles smaller than $\sim0.1 \mu$m. The acceleration is caused by charge fluctuations occurring on grains during their mutual Coulomb collisions. The energy source for the acceleration are the irreversible plasma fluxes continuously absorbed by grains. In particular, this mechanism of charge-fluctuation-induced acceleration affects the rate of grain coagulation and shattering of the population of small grains.
This contribution summarizes, as of early 2008, the observational and theoretical understanding of the physics, and emission properties of two Double Degenerate Binaries with the shortest orbital period known to date. In particular, the Unipolar Inductor Model and its coupling to GW emission have been introduced to explain a number of puzzling features that these two sources have in common and that are thought difficult to reconcile with models of mass transfer in such systems. Emphasis was put on the relevant new physical features that characterize the model. The role of spin-orbit coupling through the Lorentz torque and the role of GW emission in keeping the electric interaction active at all times has been thoroughly discussed in all their implications. Application of the model to both HM Cnc and V407 Vul accounts in a natural way for their main observational properties. Constraints on physical parameters are derived in order for the model to work, and can be verified by future observations.
Our numerical simulations show that the reconnection of magnetic field becomes fast in the presence of weak turbulence in the way consistent with the Lazarian and Vishniac (1999) model of fast reconnection. We trace particles within our numerical simulations and show that the particles can be efficiently accelerated via the first order Fermi acceleration. We discuss the acceleration arising from reconnection as a possible origin of the anomalous cosmic rays measured by Voyagers.
Observations continue to support the interpretation of the anomalous microwave foreground as electric dipole radiation from spinning dust grains as proposed by Draine and Lazarian (1998ab). In this paper we present a refinement of the original model by improving the treatment of a number of physical effects. First, we consider a disk-like grain rotating with angular velocity at an arbitrary angle with respect to the grain symmetry axis and derive the rotational damping and excitation coefficients arising from infrared emission, plasma-grain interactions and electric dipole emission. The angular velocity distribution and the electric dipole emission spectrum for grains is calculated using the Langevin equation, for cases both with and without fast internal relaxation. Our results show that, the peak emissivity of spinning dust, compared to earlier studies, increases by a factor of ~2 for the Warm Neutral Medium (WNM), the Warm Ionized Medium (WIM), the Cold Neutral Medium (CNM) and the Photodissociation Region (PDR), and by a factor ~4 for Reflection Nebulae (RN). The frequency at the emission peak also increases by factors ~1.4 to ~2 for these media. The increased emission results from the non-sphericity of grain shape and from the anisotropy in damping and excitation along directions parallel and perpendicular to the grain symmetry axis. Second, we provide a detailed numerical study including transient spin-up of grains by single-ion collisions. The impulses broaden the emission spectrum and increase the peak emissivity for the CNM, WNM and WIM. In addition, we present an improved treatment of rotational excitation and damping by infrared emission.
The diffusion of astrophysical magnetic fields in conducting fluids in the presence of turbulence depends on whether magnetic fields can change their topology or reconnect in highly conducting media. Recent progress in understanding fast magnetic reconnection in the presence of turbulence is reassuring that the magnetic field behavior in computer simulations and turbulent astrophysical environments is similar, as far as the magnetic reconnection is concerned. This makes it meaningful to perform MHD simulations of turbulent flows in order to understand the diffusion of magnetic field in astrophysical environments. These simulations support the concept of reconnection diffusion, which describes the ability of magnetic fields to get removed from magnetized clouds and cores in the process of star formation.
We present a joint analysis of the overlapping BLAST 250, 350, 500um, and LABOCA 870um observations (from the LESS survey) of the Extended Chandra Deep Field South. Out to z ~ 3, the BLAST filters sample near the peak wavelength of thermal far-infrared (FIR) emission from galaxies (rest-frame wavelengths ~ 60--200um), primarily produced by dust heated through absorption in star-forming clouds. However, identifying counterparts to individual BLAST sources is very challenging, given the large beams (FWHM 36--60 arcsec). In contrast, the ground-based 870um observations have a significantly smaller 19 arcsec FWHM beam, and are sensitive to higher-redshifts (z ~ 1--5, and potentially beyond) due to the more favourable negative K-correction. In this study we use the LESS data, as well as deep Spitzer and VLA imaging, to identify 125 individual sources that produce significant emission in the BLAST bands. We characterize the temperatures and FIR luminosities for a subset of 73 sources with well-measured submm SEDs and redshift measurements out to z ~ 3. Considering flux-limited sub-samples in each BLAST band, and a dust emissivity index \beta = 2.0, we find a median temperature T = 30K (all bands) as well as median redshifts: z = 1.1 (interquartile range 0.2--1.9) for S_250 > 40 mJy; z = 1.3 (interquartile range 0.6--2.1) for S_350 > 30 mJy; and z = 1.6 (interquartile range 1.2--2.3) for S_500 > 20 mJy. Taking into account the selection effects for our survey (a bias toward detecting lower-temperature galaxies), we find no evidence for evolution in the local FIR-temperature correlation out to z ~ 2.5. Comparing with star-forming galaxy SED templates, about 8% of our sample appears to exhibit significant excesses in the radio and/or mid-IR, consistent with those sources harbouring an AGN. Since our statistical approach differs from most previous studies of submm galaxies, we describe the following techniques in two appendices: our `matched filter' for identifying sources in the presence of point-source confusion; and our approach for identifying counterparts using likelihood ratios. This study is a direct precursor to future joint far-infrared/submm surveys, for which we outline a potential identification and SED measurement strategy.
Magnetic field embedded in a perfectly conducting fluid preserves its topology for all time. Although ionized astrophysical objects, like stars and galactic disks, are almost perfectly conducting, they show indications of changes in topology, `magnetic reconnection', on dynamical time scales. Reconnection can be observed directly in the solar corona, but can also be inferred from the existence of large scale dynamo activity inside stellar interiors. Solar flares and gamma ray busts are usually associated with magnetic reconnection. Previous work has concentrated on showing how reconnection can be rapid in plasmas with very small collision rates. Here we present numerical evidence, based on three dimensional simulations, that reconnection in a turbulent fluid occurs at a speed comparable to the rms velocity of the turbulence, regardless of the value of the resistivity. In particular, this is true for turbulent pressures much weaker than the magnetic field pressure so that the magnetic field lines are only slightly bent by the turbulence. These results are consistent with the proposal by Lazarian and Vishniac (1999) that reconnection is controlled by the stochastic diffusion of magnetic field lines, which produces a broad outflow of plasma from the reconnection zone. This work implies that reconnection in a turbulent fluid typically takes place in approximately a single eddy turnover time, with broad implications for dynamo activity and particle acceleration throughout the universe. In contrast, the reconnection in 2D configurations in the presence of turbulence depends on resistivity, i.e. is slow.
We report the observation of a cloud system on Titan that remained localized near 40S latitude and 60W longitude for at least 34 hours. Ground-based observations obtained with the SINFONI imaging spectrograph at the Very Large Telescope over 4 consecutive nights recorded the lifetime and altitude of the unresolved cloud system. Concomitant measurements made by Cassini/VIMS over 3 hours resolved changes in the altitude and opacity of individual regions within the system during this time. Clouds are measured from 13 to 37 km altitude with optical depths per pixel ranging from $\tau$=0.13 to 7. Short timescale rise times are consistent with previous measurements of the evolution of mid-latitude clouds; however the long timescale localization of the cloud structure is unexplained. We speculate about the role of meso-scale circulation in relation to cloud formation.
The purpose of this paper is to compute the remaining amounts of hydrogen in red giabt donors to see whether the conflict between theory and observations can be overcome. Considering the mass-stripping effect from an optically thick wind and the effect of thermally unstable disk, we systemically carried out binary evolution calculation for WD + MS and WD + RG systems. Here, we focus on the evolution of a WD + RG systems. We found that at the time of the supernova explosion, some donor stars almost maintain only very little hydrogen-rich material on top of the helium core (as low as 0.017 $M_{\odot}$), which is smaller than the upper limit of the amount of the stripped-off material by explosion ejecta derived from observations. Thus, no hydrogen line is expected in the nebular spectra of such SN Ia. We also derive the distributions of the envelope mass and the core mass of the companions from WD + RG channel at the moment of supernova explosion via a binary population synthesis approach. We find that a RG companion with a very low-mass envelope is rare. Furthermore, our models suggest that the remnant from WD + RG channel after the supernova explosion is a single low-mass white dwarf (0.15 $M_{\odot}$ - 0.30 $M_{\odot}$). The fact the no hydrogen line was detected in nebular spectra of SNe Ia is possible evidence to uphold the WD + RG system as the progenitor of SNe Ia.
We consider the problem of self-regulated heating and cooling in galaxy clusters and the implications for cluster magnetic fields and turbulence. Viscous heating of a weakly collisional magnetised plasma is regulated by the pressure anisotropy with respect to the local direction of the magnetic field. The intracluster medium is a high-beta plasma, where pressure anisotropies caused by the turbulent stresses and the consequent local changes in the magnetic field will trigger very fast microscale instabilities. We argue that the net effect of these instabilities will be to pin the pressure anisotropies at a marginal level, controlled by the plasma beta parameter. This gives rise to local heating rates that turn out to be comparable to the radiative cooling rates. Furthermore, we show that a balance between this heating and Bremsstrahlung cooling is thermally stable, unlike the often conjectured balance between cooling and thermal conduction. Given a sufficient (and probably self-regulating) supply of turbulent power, this provides a physical mechanism for mitigating cooling flows and preventing cluster core collapse. For observed density and temperature profiles, the assumed balance of viscous heating and radiative cooling allows us to predict magnetic field strengths, turbulent velocities and turbulent scales as functions of distance from the centre. Specific predictions and comparisons with observations are given for two representative clusters: A1835 (cool-core) and Coma (non-cool-core). Our predictions can be further tested by future observations of cluster magnetic fields and turbulent velocities.
In a previous paper we formulated the problem of the formation and evolution of fragments (or cores) in magnetically-supported, self-gravitating molecular clouds in axisymmetric geometry, accounting for the effects of ambipolar diffusion and Ohmic dissipation, grain chemistry and dynamics, and radiative transfer. Here we present results of star formation simulations that accurately track the evolution of a protostellar fragment over eleven orders of magnitude in density (from 300 cm^-3 to \approx 10^14 cm^-3), i.e., from the early ambipolar-diffusion--initiated fragmentation phase, through the magnetically supercritical, dynamical-contraction phase and the subsequent magnetic decoupling stage, to the formation of a protostellar core in near hydrostatic equilibrium. As found by Fiedler & Mouschovias (1993), gravitationally-driven ambipolar diffusion leads to the formation and subsequent dynamic contraction of a magnetically supercritical core. Moreover, we find that ambipolar diffusion, not Ohmic dissipation, is responsible for decoupling all the species except the electrons from the magnetic field, by a density \approx 3 x 10^12 cm^-3. Magnetic decoupling precedes the formation of a central stellar object and ultimately gives rise to a concentration of magnetic flux (a `magnetic wall') outside the hydrostatic core --- as also found by Tassis & Mouschovias (2005a,b) through a different approach. At approximately the same density at which Ohmic dissipation becomes more important than ambipolar diffusion (\gtrsim 7 x 10^12 cm^-3), the grains carry most of the electric charge as well as the electric current. The prestellar core remains disclike down to radii ~ 10 AU, inside which thermal pressure becomes important. The magnetic flux problem of star formation is resolved for at least strongly magnetic newborn stars by this stage of the evolution, i.e., by a central density \approx 10^14 cm^-3. The hydrostatic core has radius \approx 2 AU, density \approx 10^14 cm^-3, temperature \approx 300 K, magnetic field strength \approx 0.2 G, magnetic flux \approx 5 x 10^18 Wb, luminosity ~ 10^-3 L_\odot, and mass ~ 10^-2 M_\odot.
We report on the investigation of strong radiative shocks generated with the high energy, sub-nanosecond iodine laser at PALS. These shock waves are characterized by a developed radiative precursor and their dynamics is analyzed over long time scales (~50 ns), approaching a quasi-stationary limit. We present the first preliminary results on the rear side XUV spectroscopy. These studies are relevant to the understanding of the spectroscopic signatures of accretion shocks in Classical T Tauri Stars.
We present a study on the clustering of a stellar mass selected sample of 18,482 galaxies with stellar masses M*>10^10M(sun) at redshifts 0.4<z<2.0, taken from the Palomar Observatory Wide-field Infrared Survey. We examine the clustering properties of these stellar mass selected samples as a function of redshift and stellar mass, and discuss the implications of measured clustering strengths in terms of their likely halo masses. We find that galaxies with high stellar masses have a progressively higher clustering strength, and amplitude, than galaxies with lower stellar masses. We also find that galaxies within a fixed stellar mass range have a higher clustering strength at higher redshifts. We furthermore use our measured clustering strengths, combined with models from Mo & White (2002), to determine the average total masses of the dark matter haloes hosting these galaxies. We conclude that for all galaxies in our sample the stellar-mass-to-total-mass ratio is always lower than the universal baryonic mass fraction. Using our results, and a compilation from the literature, we furthermore show that there is a strong correlation between stellar-mass-to-total-mass ratio and derived halo masses for central galaxies, such that more massive haloes contain a lower fraction of their mass in the form of stars over our entire redshift range. For central galaxies in haloes with masses M(halo)>10^13M(sun) we find that this ratio is <0.02, much lower than the universal baryonic mass fraction. We show that the remaining baryonic mass is included partially in stars within satellite galaxies in these haloes, and as diffuse hot and warm gas. We also find that, at a fixed stellar mass, the stellar-to-total-mass ratio increases at lower redshifts. This suggests that galaxies at a fixed stellar mass form later in lower mass dark matter haloes, and earlier in massive haloes. We interpret this as a "halo downsizing" effect, however some of this evolution could be attributed to halo assembly bias.
We observed two secondary eclipses of the exoplanet WASP-12b using the Infrared Array Camera on the Spitzer Space Telescope. The close proximity of WASP-12b to its G-type star results in extreme tidal forces capable of inducing apsidal precession with a period as short as a few decades. This precession would be measurable if the orbit had a significant eccentricity. The ground-based secondary eclipse phase reported by Lopez-Morales et al. (0.510 +/- 0.002) implies eccentricity at the 4.5\sigma level, and the spectroscopic orbit of Hebb et al. has eccentricity 0.049 +/- 0.015, a 3\sigma result, and predicts an eclipse phase of 0.509 +/- 0.007. Our eclipse phases are 0.5012 +/- 0.0006 (3.6 and 5.8 micron) and 0.5007 +/- 0.0007 (4.5 and 8.0 micron). These values are inconsistent with the ground-based data, but marginally consistent with the spectroscopic orbit. Considering the unlikely possibility that precession brought the long axis of the orbit into alignment during our observations, a model considering these points and transit times from professional and amateur observers estimates orbital precession at \omega = 0.02 +/- 0.01 deg/d. This implies a tidal Love number, k2p, of 0.15 +/- 0.08, indicating a very centrally condensed planet. However, if the orbit is actually eccentric, we have observed it at a remarkably special time to find eclipse phases consistent with apsidal alignment. Future observations can decide between these possibilities.
We build on the formulation developed in Sridhar and Singh (arXiv:0910.2141), and present a dynamical theory of the shear dynamo problem that is rigorously valid for small magnetic and fluid Reynolds numbers, but for arbitrary values of the shear parameter. Specializing to the case of a mean magnetic field that is slowly varying in time, explicit expressions for the transport coefficients, $\alpha_{il}$ and $\eta_{iml}$, are derived. We prove that, when the velocity field is non helical, the transport coefficient $\alpha_{il}$ vanishes. We then consider forced, stochastic dynamics for the incompressible velocity field at low Reynolds number. An exact, explicit solution for the velocity field is derived, and the velocity spectrum tensor is calculated in terms of the Galilean-invariant forcing statistics. We consider forcing statistics that is non helical, isotropic and delta-correlated-in-time, and explore the time-correlation properties of the velocity field. Then we specialize to the case when the mean-field is a function only of the spatial coordinate $X_3$ and time $\tau$; this reduction is necessary for comparison with the numerical experiments of Brandenburg et al. (ApJ, 676, 740, 2008). Explicit expressions are derived for all four components of the magnetic diffusivity tensor, $\eta_{ij}(\tau)\,$. Some important properties are: (i) All the $\eta_{ij}$ are zero at $\tau=0$ and saturate at some finite values, $\eta^\infty_{ij}\,$, at late times; (ii) the diagonal components, $\eta_{11}$ and $\eta_{22}$, are positive and behave remarkably alike; (iii) the off-diagonal components, $\eta_{12}$ and $\eta_{21}$, are non zero only when the microscopic resistivity is non zero; (iv) the sign of $\eta_{12}^\infty$ is sensitive to the values of the control parameters, which seems consistent with the different signs reported in the literature; (v) the sign of $\eta_{21}$ is opposite to that of the shear parameter. This implies that the shear-current effect cannot be responsible for dynamo action at small fluid and magnetic Reynolds numbers, but for all values of the shear parameter.
In this paper, we propose a general form of the equation of state (EoS) which is the function of the fractional dark energy density $\Omega_{d}$. At least, five related models, the cosmological constant model, the holographic dark energy model, the agegraphic dark energy model, the modified holographic dark energy model and the Ricci scalar holographic dark energy model are included in this form. Furthermore, if we consider proper interactions, the interactive variants of those models can be included as well. The phase-space analysis shows that the scaling solutions may exist both in the non-interacting and interacting cases. And the stability analysis of the system could give out the attractor solution which could alleviate the coincidence problem.
Effective energy windows (Gamow windows) of astrophysical reaction rates for (p,gamma), (p,n), (p,alpha), (alpha,gamma), (alpha,n), (alpha,p), (n,gamma), (n,p), and (n,alpha) on targets with 10<=Z<=83 from proton- to neutron-dripline are calculated using theoretical cross sections. It is shown that widely used approximation formulas for the relevant energy ranges are not valid for a large number of reactions relevant to hydrostatic and explosive nucleosynthesis. The influence of the energy dependence of the averaged widths on the location of the Gamow windows is discussed and the results presented in tabular form (also at this http URL).
We investigate the extent to which the astrophysical uncertainties associated with the propagation of cosmic rays through the Milky Way impact estimates for the gamma-ray flux from the mid-latitude (10<|b|<20 degrees, 0<l<360 degrees) Galactic region. We firstly consider the standard astrophysical background contribution from the interactions of high energy cosmic rays and interstellar nuclei or radiation fields, fully accounting for contributions from bremsstrahlung, inverse Compton scattering (involving photons from starlight, the far infra-red background and the cosmic microwave background), as well as pi^0-decays. We also take into account contributions from the hundreds of resolved point sources identified by Fermi LAT, as well as estimates from Fermi for residual particle contamination. We deduce that the uncertainties in our predictions for the total gamma-ray flux from the mid-latitude region relating to different choices of propagation parameter values, that are consistent with local B/C and Be10/Be9 data, dominate other sources of uncertainty by at least an order of magnitude within the Fermi LAT energy range (20 MeV < E_gamma < 300 GeV). We tabulate the values of the 12 input parameters associated with our selected propagation parameter configurations producing the best-fits to current experimental data on the local abundance ratios B/C and Be10/Be9, with chi^2 values as low as 1.53 per data point. Comparing these results with the Fermi LAT data from the mid-latitude region, we find that no background configurations with chi^2<20 can fully explain the Fermi LAT data at all energies. We then include an additional contribution from dark matter neutralino within the context of the Minimal Supersymmetric Standard Model. We consider three representative cases of the neutralino and, once again, fully account for bremsstrahlung, inverse Compton and as well as the additional gamma-ray component resulting from the hadronic processes immediately following each annihilation, including pi^0-decay. We find that, without an additional boost factor, all three representative choices of neutralino dark matter provide an insignificant component, some three to four orders of magnitude below the total gamma-ray flux measured by Fermi LAT in the energy range. Minimum boost factors of approximately 15 (50) are needed in order to fit the Fermi LAT measurements when using an Einasto (Burkert) dark matter density profile and propagation parameter configurations yielding chi^2>3.
We recently presented a series of dark energy theorems that place constraints on the equation of state of dark energy ($\wdark$), the ime-variation of Newton's constant ($\dot G$), and the violation of energy conditions in theories with extra dimensions. In this paper, we explore how current and future measurements of $\wdark$ and $\dot G$ can be used to place tight limits on large classes of these theories (including some of the most well-motivated examples) independent of the size of the extra dimensions. As an example, we show that models with conformally Ricci-flat metrics obeying the null energy condition (a common ansatz for Kaluza-Klein and string constructions) are highly constrained by current ata and may be ruled out entirely by future dark energy and pulsar observations.
The measurements of the Doppler shifts of the Fraunhofer lines, scattered by the dust grains in the solar F-corona, provides the insight on the velocity field of the dust and hence on its origin. We report on such measurements obtained during the total eclipse of March 29, 2006. We used a Fabry-P\'erot interferometer with the FOV of 5.9 degrees and the spectral resolution of about 5000 to record Fraunhofer spectral lines scattered by the dust of the F-Corona. The spectral region was centered on the MgI 5172.69 A line. The measured line-on-sight velocities with the amplitude in the range from -10 to 10 km/s show that during our observations the dust grains were on the orbit with a retrograde motion in a plane nearly perpendicular to the ecliptics. This indicates their cometary origin. Indeed, at the end of March, 2006, SOHO recorded several sungrazing comets with the orbital elements close to what was deduced from our measurements. We conclude that the contribution of comets to the dust content in the region close to the Sun can be more important albeit variable in time. We also deduce that the size of the most of the dust grains during our observations was less than 0.1 microns.
We investigate the impact of the existence of a primordial magnetic field on the filter mass, characterizing the minimum baryonic mass that can form in dark matter (DM) haloes. For masses below the filter mass, the baryon content of DM haloes are severely depressed. The filter mass is the mass when the baryon to DM mass ratio in a halo is equal to half the baryon to DM ratio of the Universe. The filter mass has previously been used in semianalytic calculations of galaxy formation, without taking into account the possible existence of a primordial magnetic field. We examine here its effect on the filter mass. For homogeneous comoving primordial magnetic fields of $B_0 \sim 1$ or 2 nG and a reionization epoch that starts at a redshift $z_s=11$ and is completed at $z_r=8$, the filter mass is increased at redshift 8, for example, by factors 4.1 and 19.8, respectively. The dependence of the filter mass on the parameters describing the reionization epoch is investigated. Our results are particularly important for the formation of low mass galaxies in the presence of a homogeneous primordial magnetic field. For example, for $B_0\sim 1\nG$ and a reionization epoch of $z_s\sim 11$ and $z_r\sim7$, our results indicate that galaxies of total mass $M\sim5 \times 10^8\msun$ need to form at redshifts $z_F\gtrsim 2.0$, and galaxies of total mass $M\sim10^8\msun$ at redshifts $z_F\gtrsim 7.7$.
An important aspect of solving the long-standing question as to what triggers various types of Active Galactic Nuclei involves a thorough understanding of the overall properties and formation history of their host galaxies. This is the second in a series of papers that systematically study the large-scale properties of cold neutral hydrogen (HI) gas in nearby radio galaxies. The main goal is to investigate the importance of gas-rich galaxy mergers and interactions among radio-loud AGN. In this paper we present results of a complete sample of classical low-power radio galaxies. We find that extended Fanaroff & Riley type-I radio sources are generally not associated with gas-rich galaxy mergers or ongoing violent interactions, but occur in early-type galaxies without large (> 10^8 M_sun) amounts of extended neutral hydrogen gas. In contrast, enormous discs/rings of HI gas (with sizes up to 190 kpc and masses up to 2 x 10^10 M_sun) are detected around the host galaxies of a significant fraction of the compact radio sources in our sample. This segregation in HI mass with radio source size likely indicates that these compact radio sources are either confined by large amounts of gas in the central region, or that their fuelling is inefficient and different from the fuelling process of classical FR-I radio sources. To first order, the overall HI properties of our complete sample (detection rate, mass and morphology) appear similar to those of radio-quiet early-type galaxies. If confirmed by better statistics, this would imply that low-power radio-AGN activity may be a short and recurrent phase that occurs at some point during the lifetime of many early-type galaxies.
The International X-ray Observatory (IXO) is a joint NASA-ESA-JAXA effort. X-ray observations will resolve pressing astrophysical questions such as: What happens close to a black hole? How do supermassive black holes grow? How does large scale structure form? What is the connection between these processes? To address these questions requires dramatic increases in collection area combined with sensitive new instrumentation. IXO's spectroscopic, timing, and polarimetric capabilities will probe close to the event horizon of super-massive black holes (SMBH) where strong gravity dominates. IXO will determine the evolution and origin of SMBH by measuring their spin to understand their merger history, surveying them to find their luminosity distribution out to high redshift (z~8), and spectroscopically characterizing their outflows during peak activity. IXO will revolutionize our understanding of galaxy clusters by mapping their bulk motions and turbulence. IXO will observe the process of cosmic feedback where black holes inject energy on galactic and intergalactic scales, and characterize the missing baryons in the cosmic web. Meanwhile, surveys of distant clusters will constrain cosmological models. IXO will be available to all astronomers, taking X-ray astrophysics from an era where high-resolution spectra are a rarity to one with vast numbers of spectra from all types of sources. Powerful spectral diagnostics and large collecting areas will reveal unexpected discoveries, with IXO studying new phenomena as they appear-a key feature of great observatories.
We report on the near-infrared selected AGN candidates extracted from 2MASS/ROSAT catalogues and discuss their properties. First, near-infrared counterparts of a X-ray source in ROSAT catalogues (namely, Bright Source Catalogue (BSC) and Faint Source Catalogue (FSC)) were extracted by positional cross-identification of <=30''. Because these counterparts would contain many mis-identifications, we further imposed near-infrared colour selection criteria and extracted reliable AGN candidates (BSC: 5,273, FSC: 10,071). Of 5,273 (10,071) candidates in the BSC (FSC), 2,053 (1,008) are known AGNs. Near-infrared and X-ray properties of candidates show similar properties with known AGNs and are consistent with previous studies. We also searched for counterparts in other wavelengths (that is, optical, near-infrared, and radio), and investigated properties in multiwavelength. No significant difference between known AGNs and unclassified sources could be seen. However, some unclassified sources in the FSC showed slightly different properties compared with known AGNs. Consequently, it is highly probable that we could extract reliable AGN candidates though candidates in the FSC might be spurious.
We investigate the evolution of 5 granular-scale magnetic flux cancellations just outside the moat region of a sunspot by using accurate spectropolarimetric measurements and G-band images with the Solar Optical Telescope aboard Hinode. The opposite polarity magnetic elements approach a junction of the intergranular lanes and then they collide with each other there. The intergranular junction has strong red shifts, darker intensities than the regular intergranular lanes, and surface converging flows. This clearly confirms that the converging and downward convective motions are essential for the approaching process of the opposite-polarity magnetic elements. However, motion of the approaching magnetic elements does not always match with their surrounding surface flow patterns in our observations. This suggests that, in addition to the surface flows, subsurface downward convective motions and subsurface magnetic connectivities are important for understanding the approach and collision of the opposite polarity elements observed in the photosphere. We find that the horizontal magnetic field appears between the canceling opposite polarity elements in only one event. The horizontal fields are observed along the intergranular lanes with Doppler red shifts. This cancellation is most probably a result of the submergence (retraction) of low-lying photospheric magnetic flux. In the other 4 events, the horizontal field is not observed between the opposite polarity elements at any time when they approach and cancel each other. These approaching magnetic elements are more concentrated rather than gradually diffused, and they have nearly vertical fields even while they are in contact each other. We thus infer that the actual flux cancellation is highly time dependent events at scales less than a pixel of Hinode SOT (about 200 km) near the solar surface.
Triton possesses a thin atmosphere, primarily composed of nitrogen, sustained by the sublimation of surface ices. The goal is to determine the composition of Triton's atmosphere and to constrain the nature of surface-atmosphere interactions. We perform high-resolution spectroscopic observations in the 2.32-2.37 $\mu$m range, using CRIRES at the VLT. From this first spectroscopic detection of Triton's atmosphere in the infrared, we report (i) the first observation of gaseous methane since its discovery in the ultraviolet by Voyager in 1989 and (ii) the first ever detection of gaseous CO in the satellite. The CO atmospheric abundance is remarkably similar to its surface abundance, and appears to be controlled by a thin, CO-enriched, surface veneer resulting from seasonal transport and/or atmospheric escape. The CH$_4$ partial pressure is several times larger than inferred from Voyager. This confirms that Triton's atmosphere is seasonally variable and is best interpreted by the warming of CH$_4$-rich icy grains as Triton passed southern summer solstice in 2000. The presence of CO in Triton's atmosphere also affects its temperature, photochemistry and ionospheric composition. An improved upper limit on CO in Pluto's atmosphere is also reported.
A correlative study between the geomagnetic indices and the peak values of various plasma and field parameters during rising, maximum and decay phases as well as during complete solar cycle 23 have been presented. We have also presented the lag/lead analysis between the maximum of Dst and peak values of plasma and field parameters and found that peak values of lag/lead time lies in the +/-10 hr interval. Three geomagnetic storms (GMSs) and associated solar sources observed during these phases of this solar cycle have also been studied and found that GMSs are associated with large flares and halo CMEs.
Mechanisms for the generation of primordial non-Gaussian metric fluctuations in the context of multiple-field inflation are reviewed. As long as kinetic terms remain canonical, it appears that nonlinear couplings inducing non-gaussianities can be split into two types. The extension of the one-field results to multiple degrees of freedom leads to gravity mediated couplings that are ubiquitous but generally modest. Multiple-field inflation offers however the possibility of generating non-gravity mediated coupling in isocurvature directions that can eventually induce large non-Gaussianities in the metric fluctuations. The robustness of the predictions of such models is eventually examined in view of a case study derived from a high-energy physics construction.
CCD BVRcIc photometric observations of the 2010 outburst of the recurrent nova U Scorpii are presented. The light-curve has a smooth development characterized by t2(V)=1.8 and t3(V)=4.1 days, close to the t2(V)=2.2 and t3(V)=4.3 days of 1999 outburst. The plateau phase in 2010 has been brighter, lasting shorter and beginning earlier than in the 1999 outburst. Flickering, with an amplitude twice larger in $I_{\rm C}$ than in $B$ band, was absent on day +4.8 and +15.7, and present on day +11.8, with a time scale of about half an hour.
We combine published optical and near-infrared photometry to identify new
low-mass candidate members in an area of about 0.64 deg^2 in Corona Australis,
using the S-parameter method developed by Comer\'on et al. (2009). Five new
candidate members of the region are selected, with estimated ages between 3 and
15 Myr, and masses between 0.05 and 0.15 M_Sun. Using Spitzer photometry, we
confirm that these objects are not surrounded by optically thick disks.
However, one of them is found to display excess at 24 micron, thus suggesting
it harbours a disk with an inner hole. With an estimated mass of 0.07 M_Sun
according to the SED fitting, this is one of the lowest-mass objects reported
to possess a transitional disk.
Including these new members, the fraction of disks is about 50% among the
total Corona Australis population selected by the same criteria, lower than the
70% fraction reported by Sicilia-Aguilar et al. (2008) for this region. Even
so, we find a ratio of transitional to primordial disks (45%) very similar to
the value derived by these authors. This ratio is higher than for solar-type
stars (5-10%), suggesting that disk evolution is faster in the latter, and/or
that the "transitional disk" stage is not such a short-lived step in the case
of very low-mass objects. However, this impression needs to be confirmed with
better statistics.
We investigate the relationship between R Coronae Borealis (RCB) stars and hydrogen-deficient carbon (HdC) stars by measuring precise 16O/18O ratios for five cool RCB stars. The 16O/18O ratios are derived by spectrum synthesis from high-resolution (R=50,000) K-band spectra. Lower limits to the 16O/17O and 14N/15}N ratios as well as Na and S abundances (when possible) are also given. RCB stars in our sample generally display less 18O than HdC stars - the derived 16O/18O ratios range from 3 to 20. The only exception is the RCB star WX CrA, which seems to be a HdC-like star with 16O/18O=0.3. Our result of a higher 16O/18O ratio for the RCB stars must be accounted for by a theory of the formation and evolution of HdC and RCB stars. We speculate that a late dredge-up of products of He-burning, principally 12C and 16O, may convert a 18O-rich HdC star into a 18O-poor RCB star as the H-deficient star begins its final evolution from a cool supergiant to the top of the white dwarf cooling track.
A high angular resolution, multi-wavelength study of the LINER galaxy NGC1614 has been carried out. OVRO CO 1-0 observations are presented together with extensive multi-frequency radio continuum and HI absorption observations with the VLA and MERLIN. Toward the center of NGC1614, we have detected a ring of radio continuum emission with a radius of 300 pc. This ring is coincident with previous radio and Paschen-alpha observations. The dynamical mass of the ring based on HI absorption is 3.1 x 10E9 Msun. The peak of the integrated CO 1-0 emission is shifted by 1" to the north-west of the ring center and a significant fraction of the CO emission is associated with a crossing dust lane. An upper limit to the molecular gas mass in the ring region is 1.7 x 10E9 Msun. Inside the ring, there is a north to south elongated 1.4GHz radio continuum feature with a nuclear peak. This peak is also seen in the 5GHz radio continuum and in the CO. We suggest that the R=300 pc star forming ring represents the radius of a dynamical resonance - as an alternative to the scenario that the starburst is propagating outwards from the center into a molecular ring. The ring-like appearance probably part of a spiral structure. Substantial amounts of molecular gas have passed the radius of the ring and reached the nuclear region. The nuclear peak seen in 5GHz radio continuum and CO is likely related to previous star formation, where all molecular gas was not consumed. The LINER-like optical spectrum observed in NGC1614 may be due to nuclear starburst activity, and not to an Active Galactic Nucleus (AGN). Although the presence of an AGN cannot be excluded.
We present galaxy counts at 15 microns using the Japanese AKARI satellite's NEP-deep and NEP-wide legacy surveys at the North Ecliptic Pole. The total number of sources detected are approximately 6700 and 10,700 down to limiting fluxes of 117 and 250 microJy (5 sigma) for the NEP-deep and NEP-wide survey respectively. We construct the Euclidean normalized differential source counts for both data sets (assuming 80 percent completeness levels of 200 and 270 microJy respectively) to produce the widest and deepest contiguous survey at 15 microns to date covering the entire flux range from the deepest to shallowest surveys made with the Infrared Space Observatory (ISO) over areas sufficiently significant to overcome cosmic variance, detecting six times as many sources as the largest survey carried out with ISO.We compare the results from AKARI with the previous surveys with ISO at the same wavelength and the Spitzer observations at 16 microns using the peek-up camera on its IRS instrument. The AKARI source counts are consistent with other results to date reproducing the steep evolutionary rise at fluxes less than a milliJansky and super-Euclidean slopes. We find the the AKARI source counts show a slight excess at fluxes fainter than 200 microJanskys which is not predicted by previous source count models at 15 microns. However, we caution that at this level we may be suffering from the effects of source confusion in our data. At brighter fluxes greater than a milliJansky, the NEP-wide survey source counts agree with the Northern ISO-ELAIS field results, resolving the discrepancy of the bright end calibration in the ISO 15 micron source counts.
We suggest a mechanism for the amplification of high-velocity water-vapor maser emission features from the central regions of active galactic nuclei. The model of an emitting accretion disk is considered. The high-velocity emission features originate in the right and left wings of the Keplerian disk. The hyperfine splitting of the signal levels leads to an asymmetry in the spectral profile of the water vapor maser line at a frequency of 22.235 GHz. We show that the gain profile asymmetry must lead to an enhanced brightness of the blueshifted high-velocity emission features compared to the redshifted ones. Such a situation is observed in the source UGC 3789.
We present a multi-epoch and multi-frequency VLBI study of the compact radio source J0650+6001. In VLBI images the source is resolved into three components. The central component shows a flat spectrum, suggesting the presence of the core, while the two outer regions, with a steeper spectral index, display a highly asymmetric flux density. The time baseline of the observations considered to derive the source expansion covers about 15 years. During this time interval, the distance between the two outer components has increased by 0.28+/-0.13 mas, that corresponds to an apparent separation velocity of 0.39c+/-0.18c and a kinematic age of 360+/-170 years. On the other hand, a multi-epoch monitoring of the separation between the central and the southern components points out an apparent contraction of about 0.29+/-0.02 mas, corresponding to an apparent contraction velocity of 0.37c+/-0.02c. Assuming that the radio structure is intrinsically symmetric, the high flux density ratio between the outer components can be explained in terms of Doppler beaming effects where the mildly relativistic jets are separating with an intrinsic velocity of 0.43c+/-0.04c at an angle between 12 and 28 degrees to the line of sight. In this context, the apparent contraction may be interpreted as a knot in the jet that is moving towards the southern component with an intrinsic velocity of 0.66c+/-0.03c, and its flux density is boosted by a Doppler factor of 2.0.
We have derived linear pixel-space filters of E/B decomposition. Using these filter, we may produce rotationally invariant E and B maps. Our method also allows us to diagnose ambiguous pixels in decomposed maps. By diagnosing and excluding ambiguous pixels, we may reduce E/B mixing effectively. We have applied our method to a simulated map blocked by a foreground mask. Our simulation shows that leakage power is smaller than primordial (i.e. unlensed) B mode power spectrum of tensor-to-scalar ratio r ~ 10^{-4} at wide range of multipoles, while allowing us to retain pixels of sky fraction ~ 0.47.
Explosions of sub-Chandrasekhar-mass white dwarfs are one alternative to the standard Chandrasekhar-mass model of Type Ia supernovae. They are interesting since binary systems with sub-Chandrasekhar-mass primary white dwarfs should be common and this scenario would suggest a simple physical parameter which determines the explosion brightness, namely the mass of the exploding white dwarf. Here we perform one-dimensional hydrodynamical simulations, associated post-processing nucleosynthesis and multi-wavelength radiation transport calculations for pure detonations of carbon-oxygen white dwarfs. The light curves and spectra we obtain from these simulations are in good agreement with observed properties of Type Ia supernovae. In particular, for white dwarf masses from 0.97 - 1.15 Msun we obtain 56Ni masses between 0.3 and 0.8 Msun, sufficient to capture almost the complete range of Type Ia supernova brightnesses. Our optical light curve rise times, peak colours and decline timescales display trends which are generally consistent with observed characteristics although the range of B-band decline timescales displayed by our current set of models is somewhat too narrow. In agreement with observations, the maximum light spectra of the models show clear features associated with intermediate mass elements and reproduce the sense of the observed correlation between explosion luminosity and the ratio of the Si II lines at 6355 and 5972 Angstroms. We therefore suggest that sub-Chandrasekhar mass explosions are a viable model for Type Ia supernovae for any binary evolution scenario leading to explosions in which the optical display is dominated by the material produced in a detonation of the primary white dwarf.
Though flux freezing is a good approximation frequently assumed for molecular clouds, ambipolar diffusion (AD) is inevitable at certain scales. The scale at which AD sets in can be a crucial parameter for turbulence and the star formation process. However, both observation and simulation of AD are very challenging and our knowledge of it is very limited. We proposed earlier (Li and Houde 2008) that the difference between ion and neutral velocity spectra is a signature of turbulent AD and can be used to estimate the AD scales and magnetic field strength. Here we present observational evidence showing that this difference between the velocity dispersions from coexistent ions and neutrals is indeed correlated with magnetic field strength.
In a set of 16 drop tower experiments the motion of sub-mm to mm-sized particles under microgravity was observed. Illumination by a halogen lamp induced acceleration of the particles due to photophoresis. Photophoresis on dust-free chondrules, on chondrules, glass spheres and metal spheres covered with SiC dust and on pure SiC dust aggregates was studied. This is the first time that photophoretic motion of mm-sized particles has been studied experimentally. The absolute values for the photophoretic force are consistent with theoretical expectations for spherical particles. The strength of the photophoretic force varies for chondrules, dust covered particles and pure dust from low to strong, respectively. The measurements support the idea that photophoresis in the early Solar System can be efficient to transport solid particles outward.
Our aim is to observationally investigate the cosmic Dark Ages in order to constrain star and structure formation models, as well as the chemical evolution in the early Universe. Spectral lines from atoms and molecules in primordial perturbations at high redshifts can give information about the conditions in the early universe before and during the formation of the first stars in addition to the epoch of reionisation. The lines may arise from moving primordial perturbations before the formation of the first stars (resonant scattering lines), or could be thermal absorption or emission lines at lower redshifts. The difficulties in these searches are that the source redshift and evolutionary state, as well as molecular species and transition are unknown, which implies that an observed line can fall within a wide range of frequencies. The lines are also expected to be very weak. Observations from space have the advantages of stability and the lack of atmospheric features which is important in such observations. We have therefore, as a first step in our searches, used the Odin satellite to perform two sets of spectral line surveys towards several positions. The first survey covered the band 547-578 GHz towards two positions, and the second one covered the bands 542.0-547.5 GHz and 486.5-492.0 GHz towards six positions selected to test different sizes of the primordial clouds. Two deep searches centred at 543.250 and 543.100 GHz with 1 GHz bandwidth were also performed towards one position. The two lowest rotational transitions of H2 will be redshifted to these frequencies from z~20-30, which is the predicted epoch of the first star formation. No lines are detected at an rms level of 14-90 and 5-35 mK for the two surveys, respectively, and 2-7 mK in the deep searches with a channel spacing of 1-16 MHz. The broad bandwidth covered allows a wide range of redshifts to be explored for a number of atomic and molecular species and transitions. From the theoretical side, our sensitivity analysis show that the largest possible amplitudes of the resonant lines are about 1 mK at frequencies <200 GHz, and a few micro K around 500-600 GHz, assuming optically thick lines and no beam-dilution. However, if existing, thermal absorption lines have the potential to be orders of magnitude stronger than the resonant lines. We make a simple estimation of the sizes and masses of the primordial perturbations at their turn-around epochs, which previously has been identified as the most favourable epoch for a detection. This work may be considered as an important pilot study for our forthcoming observations with the Herschel Space Observatory.
As a part of our galaxy-cluster redshift survey, we present a set of 80 new velocities in the 4 clusters Abell 376, Abell 970, Abell 1356, and Abell 2244, obtained at Haute-Provence observatory. This set now completes our previous analysis, especially for the first two clusters. Data on individual galaxies are presented, and we discuss some cluster properties. For A376, we obtained an improved mean redshift <z> = 0.047503$ with a velocity dispersion of \sigma_V = 860 km/s. For A970, we have <z> = 0.058747 with \sigma_V = 881 km/s. We show that the A1356 cluster is not a member of the "Leo-Virgo" supercluster at a mean redshift <z>= 0.112 and should be considered just as a foreground group of galaxies at <z> = 0.0689, as well as A1435 at <z> = 0.062. We obtain <z> = 0.099623 for A2244 with \sigma_V = 965 km/s. The relative proximity of clusters A2244 and A2245 (<z> = 0.0873816, \sigma_V = 992 km/s) suggests that these could be members of a supercluster that would include A2249; however, from X-ray data there is no indication of interaction between A2244 and A2245.
The Antarctic Impulsive Transient Antenna (ANITA) completed its second long-duration balloon flight in January 2009, with 31 days aloft over Antarctica. ANITA searches for impulsive coherent radio Cherenkov emission from 200 to 1200 MHz, arising from the Askaryan charge excess in ultra-high energy neutrino-induced cascades within Antarctic ice. This flight included significant improvements over the first flight in the payload sensitivity, efficiency, and a flight trajectory over deeper ice. Analysis of in-flight calibration pulses from surface and sub-surface locations verifies the expected sensitivity. In a blind analysis, we find 2 surviving events on a background, mostly anthropogenic, of 0.97+-0.39 events. We set the strongest limit to date for 1-1000 EeV cosmic neutrinos, excluding several current cosmogenic neutrino models.
We studied the stellar population in the central 6.6x6.6arcmin,region of the ultra-deep (1Msec) Chandra Galactic field - the "Chandra bulge field" (CBF) approximately 1.5 degrees away from the Galactic Center - using the Hubble Space Telescope ACS/WFC blue (F435W) and red (F625W) images. We mainly focus on the behavior of red clump giants - a distinct stellar population, which is known to have an essentially constant intrinsic luminosity and color. By studying the variation in the position of the red clump giants on a spatially resolved color-magnitude diagram, we confirm the anomalous total-to-selective extinction ratio, as reported in previous work for other Galactic bulge fields. We show that the interstellar extinction in this area is <A_(F625W)>= 4 on average, but varies significantly between ~3-5 on angular scales as small as 1 arcminute. Using the distribution of red clump giants in an extinction-corrected color-magnitude diagram, we constrain the shape of a stellar-mass distribution model in the direction of this ultra-deep Chandra field, which will be used in a future analysis of the population of X-ray sources. We also show that the adopted model for the stellar density distribution predicts an infrared surface brightness in the direction of the "Chandra bulge field" in good agreement (i.e. within ~15%) with the actual measurements derived from the Spitzer/IRAC observations.
A normal outburst of the Be/X-ray binary system A0535+26 has taken place in August 2009. It is the fourth in a series of normal outbursts that have occured around the periastron passage of the source, but is unusual by starting at an earlier orbital phase and by presenting a peculiar double-peaked light curve. A first "flare" (lasting about 9 days from MJD 55043 on) reached a flux of 440 mCrab. The flux then decreased to less than 220 mCrab, and increased again reaching 440 mCrab around the periastron at MJD 55057. Target of Opportunity observations have been performed with INTEGRAL, RXTE and Suzaku. First results of these observations are presented, with special emphasis on the cyclotron lines present in the X-ray spectrum of the source, as well as in the pulse period and energy dependent pulse profiles of the source.
The quiet-Sun X-ray emission is important for deducing coronal heating mechanisms, but it has not been studied in detail since the Orbiting Solar Observatory (OSO) spacecraft era. Bragg crystal spectrometer X-ray observations have generally concentrated on flares and active regions. The high sensitivity of the RESIK (REntgenovsky Spectrometer s Izognutymi Kristalami) instrument on the CORONAS-F solar mission has enabled the X-ray emission from the quiet corona to be studied in a systematic way for the first time. Our aim is to deduce the physical conditions of the non-flaring corona from RESIK line intensities in several spectral ranges using both isothermal and multithermal assumptions. We selected and analyzed spectra in 312 quiet-Sun intervals in January and February 2003, sorting them into 5 groups according to activity level. For each group, the fluxes in selected spectral bands have been used to calculate values parameters for the best-fit that lead to a intensities characteristic of each group. We used both isothermal and multitemperature assumptions, the latter described by differential emission measure (DEM) distributions. RESIK spectra cover the wavelength range (3.3-6.1 A). This includes emission lines of highly ionized Si, S, Cl, Ar, and K, which are suitable for evaluating temperature and emission measure, were used. The RESIK spectra during these intervals of very low solar activity for the first time provide information on the temperature structure of the quiet corona. Although most of the emission seems to arise from plasma with a temperature between 2MK and 3MK, there is also evidence of a hotter plasma (T approx. 10MK) with an emission measure 3 orders smaller than the cooler component. Neither coronal nor photospheric element abundances appear to describe the observed spectra satisfactorily.
We have studied the relationship between the nuclear (high-resolution) radio emission, at 8.4 GHz (3.6 cm) and 1.4 GHz (20 cm), the [O IV] 25.89um, [Ne III] 15.56um and [Ne II] 12.81um emission lines and the black hole mass accretion rate for a sample of Seyfert galaxies. In order to characterize the radio contribution for the Seyfert nuclei we used the 8.4GHz/[O IV] ratio, assuming that [O IV] scales with the luminosity of the AGN. From this we find that Seyfert 1's (i.e., Seyfert 1.0's, 1.2's, and 1.5's) and Seyfert 2's (i.e., Seyfert 1.8's, 1.9's, and 2.0's) have similar radio contributions, relative to the AGN. On the other hand, sources in which the [Ne II] emission is dominated either by the AGN or star formation have statistically different radio contributions, with star formation dominated sources more "radio loud", by a factor of ~2.8 on average, than AGN dominated sources. We show that star formation dominated sources with relatively larger radio contribution have smaller mass accretion rates. Overall, we suggest that 8.4GHz/[O IV], or alternatively, 1.4GHz/[O IV] ratios, can be used to characterize the radio contribution, relative to the AGN, without the limitation of previous methods that rely on optical observables.
We present polarimetric observations in the UBVRI bands of 72 stars located in the direction of the medium age open cluster NGC 5617. Our intention is to use polarimetry as a tool membership identification, by building on previous investigations intended mainly to determine the cluster's general characteristics rather than provide membership suitable for studies such as stellar content and metallicity, as well as study the characteristics of the dust lying between the Sun and the cluster. The obsevations were carried out using the five-channel photopolarimeter of the Torino Astronomical Observatory attached to the 2.15m telescope at the Complejo Astron\'omico El Leoncito (CASLEO; Argentina. We are able to add 32 stars to the list of members of NGC 5617, and review the situation for others listed in the literature. In particular, we find that five blue straggler stars in the region of the cluster are located behind the same dust as the member stars are and we confirm the membership of two red giants. The proposed polarimetric memberships are compared with those derived by photometric and kinematical methods, with excellent results. Among the observed stars, we identify 10 with intrinsic polarization in their light. NGC 5617 can be polarimetrically characterized with $P_{max}= 4.40%$ and $ \theta_{v}= 73^\circ.1$. The spread in polarization values for the stars observed in the direction of the cluster seems to be caused by the uneven distribution of dust in front of the cluster's face. Finally, we find that in the direction of the cluster, the interstellar medium is apparently free of dust, from the Sun's position up to the Carina-Sagittarius arm, where NGC 5617 seems to be located at its farthest border.
We report results of a 14 kgd SIMPLE run with 15 superheated droplet detectors of total active mass 0.209 kg, comprising the first stage of a 30 kgd Phase II measurement. In combination with the results of other, neutron-spin sensitive, experiments, these results yield a limit of |a_p| < 0.32 on the spin-dependent sector of weakly interacting massive particle-nucleus interactions with a 50% reduction in the allowed region of the phase space formerly defined by XENON, KIMS and PICASSO, and a limit of 1.3x10-5 pb in the spin-independent sector at M_W = 35 GeV/c2.
We study cosmological constraints on metric f(R) gravity models that are designed to reproduce the LCDM expansion history with modifications to gravity described by a supplementary cosmological freedom, the Compton wavelength parameter B_0. We conduct a Markov chain Monte Carlo analysis on the parameter space, utilizing the geometrical constraints from supernovae distances, the baryon acoustic oscillations distances, and the Hubble constant, along with all of the cosmic microwave background data, including the largest scales, its correlation with galaxies, and a probe of the relation between weak gravitational lensing and galaxy flows. The strongest constraints, however, are obtained through the inclusion of data from cluster abundance. Using all of the data, we infer a bound of B_0<0.0011 at the 95% C.L.
We analyze the evolution of the perturbations in the inflaton field and metric following the end of inflation. We present accurate analytic approximations for the perturbations, showing that the coherent oscillations of the post-inflationary condensate necessarily break down long before any current phenomenological constraints require the universe to become radiation dominated. Further, the breakdown occurs on length-scales equivalent to the comoving post-inflationary horizon size. This work has implications for both the inflationary "matching" problem, and the possible generation of a stochastic gravitational wave background in the post-inflationary universe.
It is shown that the holographic principle applied to a cosmic causal horizon demands that the cosmological constant is zero. This theory also predicts dynamical dark energy in the form of the holographic dark energy with a parameter $d=1$ and an equation of state $w_0\simeq -0.903$ comparable to current observational data.
In this letter we show that there is a unique non-minimal derivative coupling of the Standard Model Higgs boson to gravity such that: it propagates no more degrees of freedom than General Relativity sourced by a scalar field, reproduces a successful inflating background within the Standard Model Higgs parameters and, finally, does not suffer from dangerous quantum corrections.
We study the motion of neutral test particles along circular orbits in the Reissner-Nordstr\"om spacetime. We use the method of the effective potential with the constants of motion associated to the underlying Killing symmetries. A comparison between the black hole and naked singularity cases is performed. In particular we find that in the naked singularity case for $r<Q^2/M$ no circular orbits can exist, this radius plays a fundamental role in the physics of the naked singularity. For $r>Q^2/M$ and $1<Q/M<\sqrt{9/8}$ there are two stability regions together with a region where all the circular orbits are instable and a zone in which all trajectory are possible but not circular orbits, for $\sqrt{9/8}<Q/M<\sqrt{5}/2$ one stability region and a region where all circular orbits are instable appear, finally for $Q/M>\sqrt{5}/2$ there are all stable circular orbits for $r>Q^2/M$.
The inter-relation of clouds, solar irradiance and surface temperature is complex and subject to different interpretations. Here, we continue our recent work, which related mainly to the period from 1960 to the present, back to 1900 with further, but less detailed, analysis of the last 1000 years. The last 20 years is examined especially. Attention is given to the mean surface temperature, solar irradiance correlation, which appears to be present (with decadal smoothing) with a 22-year period; it is stronger than the 11-year cycle correlation with one year resolution. UV in the solar radiation is a likely cause. Cloud data are taken from synoptic observations back to 1952 and, again, there appears to be a correlation - with opposite phase for high and low clouds - at the 20-30y level. Particular attention is devoted to answering the question, 'what fraction of the observed increase in mean Global temperature (~0.7^oC) can be attributed to solar, as distinct from man-made, effects?' We conclude that a best estimate is 'essentially' all from 1900 to 1956 and <14% from 1956 to the present.
We discuss the non-thermal leptogenesis in the scheme of 5D orbifold SO(10) GUT with the smooth hybrid inflation. With an unambiguously determined Dirac Yukawa couplings and an assumption for the neutrino mixing matrix of the tri-bimaximal from, we analyze baryon asymmetry of the universe via non-thermal leptogenesis in two typical cases for the light neutrino mass spectrum, the normal and inverted hierarchical cases. The resultant baryon asymmetry is obtained as a function of the lightest mass eigenvalue of the light neutrinos, and we find that a suitable amount of baryon asymmetry of the universe can be produced in the normal hierarchical case, while in the inverted hierarchical case the baryon asymmetry is too small to be consistent with the observation.
Neutrino emission in processes of breaking and formation of nucleon Cooper pairs is calculated in the framework of the Larkin-Migdal and the Leggett approaches to the description of superfluid Fermi liquids at finite temperatures. We explain peculiarities of both approaches and explicitly demonstrate that they lead to the same expression for the emissivity in pair breaking and formation processes.
We present a time-dependent and spatially inhomogeneous solution that interpolates the extremal Reissner-Nordstr\"om (RN) black hole and the Friedmann-Lema\^itre-Robertson-Walker (FLRW) universe with arbitrary power-law expansion. It is an exact solution of the $D$-dimensional Einstein-"Maxwell"-dilaton system, where two Abelian gauge fields couple to the dilaton with different coupling constants, and the dilaton field has a Liouville-type exponential potential. It is shown that the system satisfies the weak energy condition. The solution involves two harmonic functions on a $(D-1)$-dimensional Ricci-flat base space. In the case where the harmonics have a single-point source on the Euclidean space, we find that the spacetime describes a spherically symmetric charged black hole in the FLRW universe, which is characterized by three parameters: the steepness parameter of the dilaton potential $n_T$, the U$(1)$ charge $Q$, and the "nonextremality" $\tau $. In contrast with the extremal RN solution, the spacetime admits a nondegenerate Killing horizon unless these parameters are finely tuned. The global spacetime structures are discussed in detail.
Heavy Ion Collisions (HIC) represent a unique tool to probe the in-medium
nuclear interaction in regions away from saturation. In this report we present
a selection of new reaction observables in dissipative collisions particularly
sensitive to the symmetry term of the nuclear Equation of State ($Iso-EoS$). We
will first discuss the Isospin Equilibration Dynamics. At low energies this
manifests via the recently observed Dynamical Dipole Radiation, due to a
collective neutron-proton oscillation with the symmetry term acting as a
restoring force. At higher beam energies Iso-EoS effects will be seen in an
Isospin Diffusion mechanism, via Imbalance Ratio Measurements, in particular
from correlations to the total kinetic energy loss. For fragmentation reactions
in central events we suggest to look at the coupling between isospin
distillation and radial flow. In Neck Fragmentation reactions important Iso-EoS
information can be obtained from fragment isospin content, velocity and
alignement correlations. The high density symmetry term can be probed from
isospin effects on heavy ion reactions at relativistic energies (few AGeV
range), in particular for high transverse momentum selections of the reaction
products. Rather isospin sensitive observables are proposed from
nucleon/cluster emissions, collective flows and meson production. The
possibility to shed light on the controversial neutron/proton effective mass
splitting in asymmetric matter is also suggested.
A large symmetry repulsion at high baryon density will also lead to an
"earlier" hadron-deconfinement transition in n-rich matter. The binodal
transition line of the (T,\rho_B) diagram is lowered to a region accessible
through heavy ion collisions in the energy range of the new planned facilities,
e.g. the FAIR/NICA projects. Some observable effects of the formation of a
Mixed Phase are suggested, in particular a Neutron Trapping mechanism. The
dependence of the results on a suitable treatment of the isovector part of the
interaction in effective QCD Lagrangian approaches is critically discussed. We
stress the interest of this study in nuclear astrophysics, in particular for
supernovae explosions and neutron star structure, where the knowledge of the
Iso-EoS is important at low as well as at high baryon density.
Our Universe is ruled by quantum mechanics and its extension Quantum Field Theory (QFT). However, the explanations for a number of cosmological phenomena such as inflation, dark energy, symmetry breakings, and phase transitions need the presence of classical scalar fields. Although the process of condensation of scalar fields in the lab is fairly well understood, the extension of results to a cosmological context is not trivial. Here we investigate the formation of a condensate - a classical scalar field - after reheating of the Universe. We assume a light quantum scalar field produced by the decay of a heavy particle, which for simplicity is assumed to be another scalar. We show that during radiation domination epoch under certain conditions, the decay of the heavy particle alone is sufficient for the production of a condensate. This process is very similar to preheating - the exponential particle production at the end of inflation. During matter domination epoch when the expansion of the Universe is faster, the decay alone can not keep the growing trend of the field and the amplitude of the condensate decreases rapidly, unless there is a self interaction. This issue is particularly important for dark energy. We show that quantum corrections of the self-interaction play a crucial role in this process. Notably, they induce an effective action which includes inverse power-law terms, and therefore can lead to a tracking behaviour even when the classical self-interaction is a simple power-law of order 3 or 4. This removes the necessity of having nonrenormalisable terms in the Lagrangian. If dark energy is the condensate of a quantum scalar field, these results show that its presence is deeply related to the action of quantum physics at largest observable scales.
In this report, we discuss a candidate mechanism through which one might address the various cosmological constant problems. We first observe that the renormalization of gravitational couplings (induced by integrating out various matter fields) manifests non-local modifications to Einstein's equations as quantum corrected equations of motion. That is, at the loop level, matter sources curvature through a gravitational coupling that is a non-local function of the covariant d'Alembertian. If the functional form of the resulting Newton's `constant' is such that it annihilates very long wavelength sources, but reduces to $1/M^2_{pl}$ ($M_{pl}$ being the 4d Planck mass) for all sources with cosmologically observable wavelengths, we would have a complimentary realization of the degravitation paradigm-- a realization through which its non-linear completion and the corresponding modified Bianchi identities are readily understood. We proceed to consider various theories whose coupling to gravity may a priori induce non-trivial renormalizations of Newton's constant in the IR, and arrive at a class of non-local effective actions which yield a suitably degravitating filter function for Newton's constant upon subsequently being integrated out. We motivate this class of non-local theories through several considerations, discuss open issues, future directions, the inevitable question of scheme dependence in semi-classical gravitational calculations and comment on connections with other meditations in the literature on relaxing of the cosmological constant semi-classically.
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The evolution of the galaxy stellar mass function is especially useful to test the current model of galaxy formation. Observational data have revealed a few inconsistencies with predictions from the $\Lambda {\rm CDM}$ model. For example, most massive galaxies have already been observed at very high redshifts, and they have experienced only mild evolution since then. In conflict with this, semi-analytical models of galaxy formation predict an insufficient number of massive galaxies at high redshift and a rapid evolution between redshift 1 and 0 . In addition, there is a strong correlation between star formation rate and stellar mass for star-forming galaxies, which can be roughly reproduced with the model, but with a normalization that is too low at high redshift. Furthermore, the stellar mass density obtained from the integral of the cosmic star formation history is higher than the measured one by a factor of 2. In this paper, we study these issues using a semi-analytical model that includes: 1) cold gas accretion in massive halos at high redshift; 2) tidal stripping of stellar mass from satellite galaxies; and 3) an evolving stellar initial mass function (bottom-light) with a higher gas recycle fraction. Our results show that the combined effects from 1) and 2) can predict sufficiently massive galaxies at high redshifts and reproduce their mild evolution at low redshift, While the combined effects of 1) and 3) can reproduce the correlation between star formation rate and stellar mass for star-forming galaxies across wide range of redshifts. A bottom-light/top-heavy stellar IMF could partly resolve the conflict between the stellar mass density and cosmic star formation history.
We investigate the local supermassive black hole (SMBH) density function and relative mass accretion rates of all active galactic nuclei (AGNs) identified in a volume-limited sample of infrared (IR) bright galaxies (L_IR > 3 x 10^9 L_sun) to D<15 Mpc (Goulding & Alexander 2009). A database of accurate SMBH mass (M_BH) estimates is compiled from literature sources using physically motivated AGN modeling techniques (reverberation mapping, maser mapping and gas kinematics) and well-established indirect M_BH estimation methods (the M-sigma and M_BH-L_(K,bul) relations). For the three sources without previously published M_BH estimates, we use 2MASS K-band imaging and GALFIT to constrain the bulge luminosities, and hence SMBH masses. In general, we find the AGNs in the sample host SMBHs which are spread over a wide mass range (M_BH ~ (0.1-30) x 10^7 M_sun), but with the majority in the poorly studied M_BH ~ 10^6-10^7 M_sun region. Using sensitive hard X-ray (2-10 keV) and mid-IR constraints we calculate the bolometric luminosities of the AGNs (L_(Bol,AGN)) and use them to estimate relative mass accretion rates. We use these data to calculate the volume-average SMBH growth rate of galaxies in the local Universe and find that the AGNs hosting SMBHs in the mass range M_BH ~ 10^6-10^7 M_sun are dominated by optically unidentified AGNs. These relatively small SMBHs are acquiring a significant proportion of their mass in the present-day, and are amongst the most rapidly growing in the local Universe (SMBH mass doubling times of ~6 Gyrs). Additionally, we find tentative evidence for an increasing volume-weighted AGN fraction with decreasing SMBH mass in the M_BH ~ 10^6-10^8 M_sun range. Overall, we conclude that significant mass accretion onto small SMBHs may be missed in even the most sensitive optical surveys due to absent or weak optical AGN signatures.
A systematic investigation of the relationship between different redshift estimation schemes for more than 91000 quasars in the Sloan Digital Sky Survey (SDSS) Data Release 6 (DR6) is presented. The publicly available SDSS quasar redshifts are shown to possess systematic biases of Dz/(1+z)>=0.002 (600km/s) over both small (dz~0.1) and large (dz~1) redshift intervals. Empirical relationships between redshifts based on i) CaII H & K host galaxy absorption, ii) quasar [OII] 3728, iii) [OIII] 4960,5008 emission, and iv) cross-correlation (with a master quasar template) that includes, at increasing quasar redshift, the prominent MgII 2799, CIII] 1908 and CIV 1549 emission lines, are established as a function of quasar redshift and luminosity. New redshifts in the resulting catalogue possess systematic biases a factor of ~20 lower compared to the SDSS redshift values; systematic effects are reduced to the level of Dz/(1+z)<10^-4 (30km/s) per unit redshift, or <2.5x10^-5 per unit absolute magnitude. Redshift errors, including components due both to internal reproducibility and the intrinsic quasar-to-quasar variation among the population, are available for all quasars in the catalogue. The improved redshifts and their associated errors have wide applicability in areas such as quasar absorption outflows, quasar clustering, quasar-galaxy clustering and proximity-effect determinations.
We report on the discovery of two galaxy clusters, SPT-CL J2332-5358 and SPT-CL J2342-5411, in X-rays. These clusters were also independently detected through their Sunyaev-Zel'dovich effect by the South Pole Telescope, and confirmed in the optical band by the Blanco Cosmology Survey. They are thus the first clusters detected under survey conditions by all major cluster search approaches. The X-ray detection is made within the frame of the XMM-BCS cluster survey utilizing a novel XMM-Newton mosaic mode of observations. The present study makes the first scientific use of this operation mode. We estimate the X-ray spectroscopic temperature of SPT-CL J2332-5358 (at redshift z=0.32) to T = 9.3 (+3.3/-1.9) keV, implying a high mass, M_{500} = 8.8 +/- 3.8 \times 10^{14} M_{sun}. For SPT-CL J2342-5411, at z=1.08, the available X-ray data doesn't allow us to directly estimate the temperature with good confidence. However, using our measured luminosity and scaling relations we estimate that T = 4.5 +/- 1.3 keV and M_{500} = 1.9 +/- 0.8 \times 10^{14} M_{sun}. We find a good agreement between the X-ray masses and those estimated from the Sunyaev-Zel'dovich effect.
We use stripped-down versions of three semi-analytic galaxy formation models to study the influence of different assumptions about gas cooling and galaxy mergers. By running the three models on identical sets of merger trees extracted from high-resolution cosmological N-body simulations, we are able to perform both statistical analyses and halo-by-halo comparisons. Our study demonstrates that there is a good statistical agreement between the three models used here, when operating on the same merger trees, reflecting a general agreement in the underlying framework for semi-analytic models. We also show, however, that various assumptions that are commonly adopted to treat gas cooling and galaxy mergers can lead to significantly different results, at least in some regimes. In particular, we find that the different models adopted for gas cooling lead to similar results for mass scales comparable to that of our own Galaxy. Significant differences, however, arise at larger mass scales. These are largely (but not entirely) due to different treatments of the `rapid cooling' regime, and different assumptions about the hot gas distribution. At this mass regime, the predicted cooling rates can differ up to about one order of magnitude, with important implications on the relative weight that these models give to AGN feedback in order to counter-act excessive gas condensation in relatively massive haloes at low redshift. Different assumptions in the modelling of galaxy mergers can also result in significant differences in the timings of mergers, with important consequences for the formation and evolution of massive galaxies.
This work summarises some of the attempts to explain the phenomenon of dark energy as an effective description of complex gravitational physics and the proper interpretation of observations. Cosmological backreaction has been shown to be relevant for observational (precision) cosmology, nevertheless no convincing explanation of dark energy by means of backreaction has been given so far.
The physical sizes of supernova remnants (SNRs) in a number of nearby galaxies follow an approximately linear cumulative distribution, contrary to what is expected for decelerating shock fronts. This has been attributed to selection effects, or to a majority of SNRs propagating in "free expansion", at constant velocity, into a tenuous ambient medium. We compile a list of 77 known SNRs in the Magellanic Clouds (MCs), and argue that they are a largely complete record of the SNe that have exploded over the last ~20kyr, with most now in the adiabatic, Sedov phase of their expansions. The roughly linear cumulative size distribution (uniform in a differential distribution) can result from the combination of a deceleration during this phase, a transition to a radiation-loss-dominated phase at a radius that depends on the local gas density, and a distribution of ambient densities varying roughly as rho^{-1}. This explanation is supported by the observed -1 power-law distributions of three independent tracers of density: HI column density, Halpha surface brightness, and star formation rate from resolved stellar populations. In this picture, the observed cutoff at r~30 pc in the SNR size distribution is due to a minimum in the mean ambient gas density in the regions where supernovae (SNe) explode. We show that M33 has a SNR size distribution similar to that of the MCs, suggesting these features, and their explanation, may be universal. In a companion paper (Maoz & Badenes 2010), we use our sample of SNRs as an effective "SN survey" to calculate the SN rate and delay time distribution in the MCs. The hypothesis that most SNRs are in free expansion, rather than in the Sedov phase of their evolution, would result in SN rates that are in strong conflict with independent measurements, and with basic stellar evolution theory.
We use the supernova remnants (SNRs) in the two Magellanic Clouds (MCs) as a supernova (SN) survey, "conducted" over tens of kyr, from which we derive the current SN rate, and the SN delay time distribution (DTD), i.e., the SN rate vs. time that would follow a hypothetical brief burst of a star formation. In a companion paper (Badenes, Maoz, & Draine 2010) we have compiled a list of 77 SNRs in the MCS, and argued that it is a largely complete record of the SNRs that are now in the Sedov phase of their expansions. We recover the SN DTD by comparing, on the one hand, the numbers of SNRs observed in small individual "cells" in these galaxies to, on the other hand, the star-formation histories of each cell, as calculated from resolved stellar populations by Harris & Zaritsky. We identify the visibility times of SNRs with the Sedov-phase lifetimes, which depend on the local ambient densities. The local densities are estimated from HI emission, from an inverse Schmidt law based on either Halpha flux or on the star-formation rate from the resolved stellar populations, and from combinations of these tracers. This is the first SN DTD based on resolved stellar populations. In the DTD, we detect "prompt" type-Ia SNe (that explode within 330 Myr of star formation) at >99% confidence level (c.l.). The best fit for the number of prompt SNe-Ia per stellar mass formed is (2.7-11.0) x 10^{-3} /Msun, depending on the density tracer used. The 95% c.l. range for a "delayed" SN Ia component (from 330 Myr to a Hubble time) is < 1.6 x 10^{-13} SN/yr/Msun, consistent with rate measurements in old populations. The current total (core-collapse+Ia) SN rate in the MCs is 2.5-4.6 SNe per millenium (68% c.l.+systematics), or 1.7-3.1 SNuM [SNe/100 yr/10^{10}Msun], in agreement with the historical record and with rates measured in other dwarf irregulars. Conversely, assuming the SNRs are in free expansion, rather than in their Sedov phase, would impose on the SNRs a maximum age of 6 kyr, and would imply a MC SN rate per unit mass that is 5 times higher than in any type of galaxy, and a low-mass limit for core-collapse progenitors in conflict with stellar evolution theory.
The exoplanet host 51 Pegasi has a widely separated red dwarf companion. Two other, far more distant, stars are also co-moving with this star, showing that they are at least of common Galactic orbit due to a common origin.
We present results from the first three-dimensional radiation hydrodynamical calculations to follow the collapse of a molecular cloud core beyond the formation of the stellar core. We find the energy released by the formation of the stellar core, within the optically-thick first hydrostatic core, is comparable to the binding energy of the disc-like first core. This heats the inner regions of the disc, drives a shock wave through the disc, dramatically decreases the accretion rate on to the stellar core, and launches a temporary bipolar outflow perpendicular to the rotation axis that travels in excess of 50 AU into the infalling envelope. This outburst may assist the young protostar in launching a conventional magnetic jet. Furthermore, if these events are cyclic, they may provide a mechanism for intense bursts of accretion separated by long periods of relatively quiescent accretion which can potentially solve both the protostellar luminosity problem and the apparent age spread of stars in young clusters. Such outbursts may also provide a formation mechanism for the chondrules found in meteorites, with the outflow transporting them to large distances in the circumstellar disc.
For the first time, Swift is giving us the opportunity to study supergiant fast X-ray transients (SFXTs) throughout all phases of their life: outbursts, intermediate level, and quiescence. We present our intense monitoring of four SFXTs, observed 2-3 times per week since October 2007. We find that, unexpectedly, SFXTs spend most of their time in an intermediate level of accretion ($L_{X}\sim 10^{33-34} $ erg s$^{-1}$), characterized by rich flaring activity. We present an overview of our investigation on SFXTs with Swift, the key results of our Project. We highlight the unique contribution Swift is giving to this field, both in terms of outburst observations and through a systematic monitoring.
We present a series of three-dimensional hydrodynamical simulations of central AGN driven jets in a dynamic, cosmologically evolved galaxy cluster. Extending previous work, we study jet powers ranging from L_jet = 10^44 erg/s to L_jet = 10^46 erg/s and in duration from 30 Myr to 200 Myr. We find that large-scale motions of cluster gas disrupt the AGN jets, causing energy to be distributed throughout the centre of the cluster, rather than confined to a narrow angle around the jet axis. Disruption of the jet also leads to the appearance of multiple disconnected X-ray bubbles from a long-duration AGN with a constant luminosity. This implies that observations of multiple bubbles in a cluster are not necessarily an expression of the AGN duty cycle. We find that the "sphere of influence" of the AGN, the radial scale within which the cluster is strongly affected by the jet, scales as R ~ L_jet^(1/3). Increasing the duration of AGN activity does not increase the radius affected by the AGN significantly, but does change the magnitude of the AGN's effects. How an AGN delivers energy to a cluster will determine where that energy is deposited: a high luminosity is needed to heat material outside the core of the cluster, while a low-luminosity, long-duration AGN is more efficient at heating the inner few tens of kpc.
On UT 2009 January 16, we observed a white light megaflare on the dM4.5e star YZ CMi as part of a long-term spectroscopic flare-monitoring campaign to constrain the spectral shape of optical flare continuum emission. Simultaneous U-band photometric and 3350A-9260A spectroscopic observations were obtained during 1.3 hours of the flare decay. The event persisted for more than 7 hours and at flare peak, the U-band flux was almost 6 magnitudes brighter than in the quiescent state. The properties of this flare mark it as one of the most energetic and longest-lasting white light flares ever to be observed on an isolated low-mass star. We present the U-band flare energetics and a flare continuum analysis. For the first time, we show convincingly with spectra that the shape of the blue continuum from 3350A to 4800A can be represented as a sum of two components: a Balmer continuum as predicted by the Allred et al radiative hydrodynamic flare models and a T ~ 10,000K blackbody emission component as suggested by many previous studies of the broadband colors and spectral distributions of flares. The areal coverage of the Balmer continuum and blackbody emission regions vary during the flare decay, with the Balmer continuum emitting region always being significantly (~3-16 times) larger. These data will provide critical constraints for understanding the physics underlying the mysterious blue continuum radiation in stellar flares.
We explored the motion of test particles near slowly rotating relativistic star having a uniform luminosity. In order to derive the test particle's equations of motion, we made use of the radiation stress-energy tensor first constructed by Miller and Lamb \cite{ML96}. From the particle's trajectory obtained through the numerical integration of the equations of motion, it is found that for sufficiently high luminosity, "suspension orbit" exists, where the test particle hovers around at uniform angular velocity in the same direction as the star's spin. Interestingly, it turned out that the radial position of the "suspension orbit" was determined by the luminosity and the angular momentum of the star alone and was independent of the initial positions and the specific angular momentum of the particle. Also found is that there exist not only the radiation drag but also "radiation counter-drag" which depends on the stellar radius and the angular momentum and it is this radiation counter-drag that makes the test particle in the "suspension orbit" to hover around at uniform angular velocity which is greater than that induced by the Lense-Thirring effect (i.e., general relativistic dragging of inertial frame).
Aims. We present a diagnostic tool to determine the abundance of the
crystalline silicate forsterite in AGB stars surrounded by a thick shell of
silicate dust. Using six infrared spectra of high mass-loss oxygen rich AGB
stars we obtain the forsterite abundance of their dust shells.
Methods. We use a monte carlo radiative transfer code to calculate infrared
spectra of dust enshrouded AGB stars. We vary the dust composition, mass-loss
rate and outer radius. We focus on the strength of the 11.3 and the 33.6 \mu m
forsterite bands, that probe the most recent (11.3 \mu m) and older (33.6 \mu
m) mass-loss history of the star. Simple diagnostic diagrams are derived,
allowing direct comparison to observed band strengths.
Results. Our analysis shows that the 11.3 \mu m forsterite band is a robust
indicator for the forsterite abundance of the current mass-loss period for AGB
stars with an optically thick dust shell. The 33.6 \mu m band of forsterite is
sensitive to changes in the density and the geometry of the emitting dust
shell, and so a less robust indicator. Applying our method to six high
mass-loss rate AGB stars shows that AGB stars can have forsterite abundances of
12% by mass and higher, which is more than the previously found maximum
abundance of 5%.
We derive the value of the dark matter density at the Sun's location (rho_0) without globally mass-modeling the Galaxy. The proposed method relies on the local equation of centrifugal equilibrium and is independent of i) the shape of the dark matter density profile ii) the knowledge of the rotation curve from the galaxy center out to the virial radius and iii) the uncertainties and the not-uniqueness of the bulge/disk/dark-halo mass decomposition. The result can be obtained in analytic form and explicitly includes the dependence on the relevant observational quantitie, taking into account their uncertainties. Adopting the reference, state-of-the-art values for these we find rho_0=0.43(11)(10) GeV/cm^3, where the quoted uncertainties are due respectively to the uncertainty in the slope of the circular-velocity at the Sun location, and the ratio between that radius and the length scale of the exponential thin stellar disk. The reliable estimate of rho_0 can also take into account future improved measures of the observational quantities it depends on.
Using deep Chandra ACIS observation data for Cygnus A, we report evidence of non-thermal X-ray emission from radio lobes surrounded by a rich intra-cluster medium (ICM). The diffuse X-ray emission, which are associated with the eastern and western radio lobes, were observed in a 0.7--7 keV Chandra$ ACIS image. The lobe spectra are reproduced with not only a single-temperature Mekal model, such as that of the surrounding ICM component, but also an additional power-law (PL) model. The X-ray flux densities of PL components for the eastern and western lobes at 1 keV are derived as 77.7^{+28.9}_{-31.9} nJy and 52.4^{+42.9}_{-42.4} nJy, respectively, and the photon indices are 1.69^{+0.07}_{-0.13} and 1.84^{+2.90}_{-0.12}, respectively. The non-thermal component is considered to be produced via the inverse Compton (IC) process, as is often seen in the X-ray emission from radio lobes. From a re-analysis of radio observation data, the multiwavelength spectra strongly suggest that the seed photon source of the IC X-rays includes both cosmic microwave background radiation and synchrotron radiation from the lobes. The derived parameters indicate significant dominance of the electron energy density over the magnetic field energy density in the Cygnus A lobes under the rich ICM environment.
This is the second paper of a series in which we attempt to put constraints on the flattening of dark halos in disk galaxies. For this purpose, we observe the HI in edge-on galaxies, where it is in principle possible to measure the force field in the halo vertically and radially from gas layer flaring and rotation curve decomposition respectively. To calculate the force fields, we need to analyse the observed XV diagrams to accurately measure all three functions that describe the planar kinematics and distribution of a galaxy: the radial HI surface density, the rotation curve and the HI velocity dispersion. In this paper, we discuss the improvements and limitations of the methods previously used to measure these HI properties. We extend the constant velocity dispersion method to include determination of the HI velocity dispersion as a function of galactocentric radius and perform extensive tests on the quality of the fits. We will apply this 'radial decomposition XV modelling method' to our HI observations of 8 HI-rich, late-type, edge-on galaxies in the third paper of this series.
This is the third paper in a series in which we attempt to put constraints on the flattening of dark halos in disk galaxies. For this purpose we need to analyse the observed XV diagrams in edge-on galaxies to accurately measure the radial HI surface density, the rotation curve and the HI velocity dispersion. We present the results of the modelling of HI observations of 8 HI-rich, late-type, edge-on galaxies. In all of these we find differential rotation. Most systems display HI velocity dispersions of 6.5 to 7.5 km s$^{-1}$ and all except one show radial structure. There is an increase in the mean HI velocity dispersion with maximum rotation velocity, at least up to 120 km s$^{-1}$. Next we analyse the observations to derive the radial variation of the thickness (flaring) of the HI layer. We find that with the exception of the asymmetric IC5052, all of the galaxies in our sample are good candidates for 3D mass modelling to measure the dark halo shape. The flaring profiles are symmetric and have a common shape, increasing linearly inside the stellar disks and exponential outside where the gravitational potential is dominated by the dark halo. In the best example, UGC7321, we find in the inner regions small deviations from the midplane and accompanying increases in thickness of the HI layer that are possibly a result of perturbations by a relatively strong bar.
This is the first paper of a series in which we will attempt to put constraints on the flattening of dark halos in disk galaxies. We observe for this purpose the HI in edge-on galaxies, where it is in principle possible to measure the force field in the halo vertically and radially from gas layer flaring and rotation curve decomposition respectively. In this paper, we define a sample of 8 HI-rich late-type galaxies suitable for this purpose and present the HI observations.
Distant clumpy galaxies are thought to be Jeans-unstable disks, and an important channel for the formation of local galaxies, as suggested by recent spatially-resolved kinematic observations of z~2 galaxies. I study the kinematics of clumpy galaxies at z~0.6, and compare their properties with those of counterparts at higher and lower redshifts. I selected a sample of 11 clumpy galaxies at z~0.6 from the representative sample of emission line, intermediate-mass galaxies IMAGES. Selection was based on rest-frame UV morphology from HST/ACS images, mimicking the selection criteria commonly used at higher redshifts. Their spatially-resolved kinematics were derived in the frame of the IMAGES survey, using the VLT/FLAMES-GIRAFFE multi-integral field spectrograph. For those showing large-scale rotation, I derived the Toomre Q parameter, which characterizes the stability of their gaseous and stellar phases. I find that the fraction of UV-selected clumpy galaxies at z~0.6 is 20+/-12%. Roughly half of them (45+/-30%) have complex kinematics inconsistent with Jeans-unstable disks, while those in the remaining half (55+/-30%) show large-scale rotations. The latter reveal a stable gaseous phase, but the contribution of their stellar phase makes them globally unstable to clump formation. Clumpy galaxies appear to be less unstable at z~0.6 than at z~2, which could explain why the UV clumps tend to vanish in rest-frame optical images of z~0.6 clumpy galaxies, conversely to z~2 clumpy galaxies, in which the stellar phase can substantially fragment. This suggests that the former correspond to patchy star-formation regions superimposed on a smoother mass distribution. A possible and widespread scenario for driving clump formation relies on instabilities by cold streams penetrating the dark matter halos where clumpy galaxies inhabit. While such a gas accretion process is predicted to be significant in massive, z~2 haloes, it is also predicted to be strongly suppressed in similar, z~0.6 haloes, which could explain why lowest-z clumpy galaxies appear to be driven by a different mechanism. Instead, I found that interactions are probably the dominant driver leading to the formation of clumpy galaxies at z<1. I argue that the nature of z>1 clumpy galaxies remains more uncertain. While cold flows could be an important driver at z~2, I also argue that the observed and cumulative merger fraction between z=2 and z=3 is large enough so that every z~2 galaxy might be the result of a merger that occurred within their past 1 Gyr. I conclude that it is premature to rule out mergers as a universal driver for galaxy evolution from z~2 down to z=0.
We have performed mm-wave observations with the IRAM 30m telescope of the 12CO J=2-1 and J=1-0, 13CO J=2-1 and J=1-0, and SiO J=5-4 transitions in the symbiotic stars R Aqr, CH Cyg, and HM Sge. The data were analyzed by means of a simple analytical description of the general properties of molecular emission from the inner shells around the cool star. Numerical calculations of the expected line profiles, taking into account the level population and radiative transfer under such conditions, were also performed. Weak emission of 12CO J=2-1 and J=1-0 was detected in R Aqr and CH Cyg; a good line profile of 12CO J=2-1 in R Aqr was obtained. The intensities and profile shapes of the detected lines are compatible with emission coming from a very small shell around the Mira-type star, with a radius comparable to or slightly smaller than the distance to the hot dwarf companion, 10$^{14}$ - 2 10$^{14}$ cm. We argue that other possible explanations are improbable. This region probably shows properties similar to those characteristic of the inner shells around standard AGB stars: outwards expansion at about 5 - 25 km/s, with a significant acceleration of the gas, temperatures decreasing with radius between about 1000 and 500 K, and densities ~ 10$^9$ - 3 10$^8$ cm$^{-3}$. Our model calculations are able to explain the asymmetric line shape observed in 12CO J=2-1 from R Aqr, in which the relatively weaker red part of the profile would result from selfabsorption by the outer layers (in the presence of a velocity increase and a temperature decrease with radius). The mass-loss rates are somewhat larger than in standard AGB stars, as often happens for symbiotic systems. In R Aqr, we find that the total mass of the CO emitting region is ~ 2 - 3 10$^{-5}$ Mo, corresponding to M' ~ 5 10$^{-6}$ - 10$^{-5}$ Mo/yr, and compatible with results obtained from dust emission. Taking into account other existing data on molecular emission, we suggest that the small extent of the molecule-rich gas in symbiotic systems is mainly due to molecule photodissociation by the radiation of the hot dwarf star.
We investigate the molecular gas properties of the deeply obscured luminous infrared galaxy NGC 4418. We address the excitation of the complex molecule HC3N to determine whether its unusually luminous emission is related to the nature of the buried nuclear source. We use IRAM 30m and JCMT observations of rotational and vibrational lines of HC3N to model the excitation of the molecule by means of rotational diagrams. We report the first confirmed extragalactic detection of vibrational lines of HC3N. We detect 6 different rotational transitions ranging from J=10-9 to J=30-29 in the ground vibrational state and obtain a tentative detection of the J=38-37 line. We also detect 7 rotational transitions of the vibrationally excited states v6 and v7, with angular momenta ranging from J=10-9 to 28-27. The energies of the upper states of the observed transitions range from 20 to 850 K. In the optically thin regime, we find that the rotational transitions of the vibrational ground state can be fitted for two temperatures, 30 K and 260 K, while the vibrationally excited levels can be fitted for a rotational temperature of 90 K and a vibrational temperature of 500 K. In the inner 300 pc of NGC 4418, we estimate a high HC3N abundance, of the order of 10^-7. The excitation of the HC3N molecule responds strongly to the intense radiation field and the presence of warm, dense gas and dust at the center of NGC 4418. The intense HC3N line emission is a result of both high abundances and excitation. The properties of the HC3N emitting gas are similar to those found for hot cores in Sgr B2, which implies that the nucleus (< 300 pc) of NGC 4418 is reminiscent of a hot core. The potential presence of a compact, hot component (T=500 K) is also discussed.
Because energetic particles populate both planetary magnetospheres and interplanetary space in significant quantities, energetic-ion sensors have been flown since the beginning of the space age. Early sensors were solid-state detector (SSD) telescopes, with conical fields of view, often swept through a circle by virtue of the spin motion of the spacecraft (e.g., IMP 7 and 8, ISEE 1 and 2). In the 1980s and 1990s, foil/microchannel plate (MCP) time-of-flight (TOF) measurements were added to the energy measurement provided by the SSD (eg, AMPTE/CCE MEPA, Geotail EPIC/ICS, Galileo EPD). The resulting energy and velocity uniquely identified ion mass. More recently, we have developed a 2-D fan acceptance angle sensor that includes both energy and TOF. When mounted on a spinning spacecraft, this 160^\circ x 12^\circ FOV sweeps out nearly 4\pi steradians in one spin. This sensor, dubbed the "hockey puck" for its shape, is currently in flight on MESSENGER (EPS) and New Horizons Pluto (PEPPSI).Increasingly, energetic-ion sensors fly on 3-axis stabilized spacecraft (e.g., MESSENGER EPS, New Horizons (Pluto) PEPPSI, Cassini MIMI. While 3-axis stabilization serves imaging science well, it hampers the goal of obtaining 4\pi-steradian ion measurements. We are developing an energetic-ion sensor that measures ion energy and composition, and covers 2\pi steradians on a 3-axis-stabilized spacecraft without an articulation mechanism. Based on its shape, we refer to this design as the "mushroom". We describe the internally funded development of the concept and its status at the start of development funding by NASA under the Planetary Instrument Definition and Development Program (PIDDP).
Connecting cosmological simulations to real-world observational programs is often complicated by a mismatch in geometry: while surveys often cover highly irregular cosmological volumes, simulations are customarily performed in a periodic cube. We describe a technique to remap this cube into elongated box-like shapes that are more useful for many applications. The remappings are one-to-one, volume-preserving, keep local structures intact, and involve minimal computational overhead.
Using the 'k-means' cluster analysis algorithm, we carry out an unsupervised classification of all galaxy spectra in the seventh and final Sloan Digital Sky Survey data release (SDSS/DR7). Except for the shift to restframe wavelengths, and the normalization to the g-band flux, no manipulation is applied to the original spectra. The algorithm guarantees that galaxies with similar spectra belong to the same class. We find that 99 % of the galaxies can be assigned to only 17 major classes, with 11 additional minor classes including the remaining 1%. The classification is not unique since many galaxies appear in between classes, however, our rendering of the algorithm overcomes this weakness with a tool to identify borderline galaxies. Each class is characterized by a template spectrum, which is the average of all the spectra of the galaxies in the class. These low noise template spectra vary smoothly and continuously along a sequence labeled from 0 to 27, from the reddest class to the bluest class. Our Automatic Spectroscopic K-means-based (ASK) classification separates galaxies in colors, with classes characteristic of the red sequence, the blue cloud, as well as the green valley. When red sequence galaxies and green valley galaxies present emission lines, they are characteristic of AGN activity. Blue galaxy classes have emission lines corresponding to star formation regions. We find the expected correlation between spectroscopic class and Hubble type, but this relationship exhibits a high intrinsic scatter. Several potential uses of the ASK classification are identified and sketched, including fast determination of physical properties by interpolation, classes as templates in redshift determinations, and target selection in follow-up works (we find classes of Seyfert galaxies, green valley galaxies, as well as a significant number of outliers). The ASK classification is publicly accessible through various websites.
Identified as extinction features against the bright Galactic mid-infrared background, infrared dark clouds (IRDCs) are thought to harbor the very earliest stages of star and cluster formation. In order to better characterize the properties of their embedded cores, we have obtained new 24um, 60-100um, and sub-millimeter continuum data toward a sample of 38 IRDCs. The 24um Spitzer images reveal that while the IRDCs remain dark, many of the cores are associated with bright 24um emission sources, which suggests that they contain one or more embedded protostars. Combining the 24um, 60-100um, and sub-millimeter continuum data, we have constructed broadband spectral energy distributions (SEDs) for 157 of the cores within these IRDCs and, using simple gray-body fits to the SEDs, have estimated their dust temperatures, emissivities, opacities, bolometric luminosities, masses and densities. Based on their Spitzer/IRAC 3-8um colors and the presence of 24um point source emission, we have separated cores that harbor active, high-mass star formation from cores that are quiescent. The active `protostellar' cores typically have warmer dust temperatures and higher bolometric luminosities than the more quiescent, perhaps `pre-protostellar', cores. Because the mass distributions of the populations are similar, however, we speculate that the active and quiescent cores may represent different evolutionary stages of the same underlying population of cores. Although we cannot rule out low-mass star-formation in the quiescent cores, the most massive of them are excellent candidates for the `high-mass starless core' phase, the very earliest in the formation of a high-mass star.
We use the kinematics of satellite galaxies that orbit around the central galaxy in a dark matter halo to infer the scaling relations between halo mass and central galaxy properties. Using galaxies from the Sloan Digital Sky Survey, we investigate the halo mass-luminosity relation (MLR) and the halo mass-stellar mass relation (MSR) of central galaxies. In particular, we focus on the dependence of these scaling relations on the colour of the central galaxy. We find that red central galaxies on average occupy more massive haloes than blue central galaxies of the same luminosity. However, at fixed stellar mass there is no appreciable difference in the average halo mass of red and blue centrals, especially for M* $\lsim$ 10^{10.5} h^{-2} Msun. This indicates that stellar mass is a better indicator of halo mass than luminosity. Nevertheless, we find that the scatter in halo masses at fixed stellar mass is non-negligible for both red and blue centrals. It increases as a function of stellar mass for red centrals but shows a fairly constant behaviour for blue centrals. We compare the scaling relations obtained in this paper with results from other independent studies of satellite kinematics, with results from a SDSS galaxy group catalog, from galaxy-galaxy weak lensing measurements, and from subhalo abundance matching studies. Overall, these different techniques yield MLRs and MSRs in fairly good agreement with each other (typically within a factor of two), indicating that we are converging on an accurate and reliable description of the galaxy-dark matter connection. We briefly discuss some of the remaining discrepancies among the various methods.
We have studied the linear polarization of 86 active galactic nuclei (AGN) in the observed frequency range 80-267 GHz (3.7-1.1mm in wavelength), corresponding to rest-frame frequencies 82-738 GHz, with the IRAM Plateau de Bure Interferometer (PdBI). The large number of measurements, 441, makes our analysis the largest polarimetric AGN survey in this frequency range to date. We extracted polarization parameters via earth rotation polarimetry with unprecedented median precisions of ~0.1% in polarization fractions and ~1.2 degrees in polarization angles. For 73 of 86 sources we detect polarization at least once. The degrees of polarization are as high as ~19%, with the median over all sources being ~4%. Source fluxes and polarizations are typically highly variable, with fractional variabilities up to ~60%. We find that BLLac sources have on average the highest level of polarization. There appears to be no correlation between degree of polarization and redshift, indicating that there has been no substantial change of polarization properties since z~2.4. Our polarization and spectral index distributions are in good agreement with results found from various samples observed at cm/radio wavelengths; thus our frequency range is likely tracing the signature of synchrotron radiation without noticeable contributions from other emission mechanisms. The "millimeter-break" located at frequencies >1 THz appears to be not detectable in the frequency range covered by our survey.
We analyze the quasar two-point correlation function (2pCF) within the redshift interval $0.8<z<2.2$ using a sample of 52303 quasars selected from the recent 7th Data Release of the Sloan Digital Sky Survey. Our approach to 2pCF uses a concept of locally Lorentz (Fermi) frame for determination of the distance between objects and permutation method of the random catalogue generation. Assuming the spatially flat cosmological model with given $\Omega_{\Lambda}=0.726$, we found that the real-space 2pCF is fitted well with the power-low model within the distance range $1<\sigma<35$ $h^{-1}$ Mpc with the correlation length $r_{0}=5.85\pm0.33$ $h^{-1}$ Mpc and the slope $\gamma=1.87\pm0.07$. The redshift-space 2pCF is approximated with $s_{0}=6.43\pm0.63$ $h^{-1}$ Mpc and $\gamma=1.21\pm0.24$ for $1<s<10$ $h^{-1}$ Mpc, and $s_{0}=7.37\pm0.81$ $h^{-1}$ Mpc and $\gamma=1.90\pm0.24$ for $10<s<35$ $h^{-1}$ Mpc. For distances $s>10\,h^{-1}$ Mpc the parameter describing the large-scale infall to density inhomogeneities is $\beta=0.63\pm0.10$ with the linear bias $b=1.44\pm0.22$ that marginally (within 2$\sigma$) agrees with the linear theory of cosmological perturbations. We discuss possibilities to obtain a statistical estimate of the random component of quasars velocities (different from the large-scale infall). We note rather slight dependence of quasars velocity dispersion upon the 2pCF parameters in the region $r<2$ Mpc.
We present high resolution large scale observations of the molecular and atomic gas in the Local Group Galaxy M33. The observations were carried out using the HERA multibeam receiver at the 30m IRAM telescope in the CO(2-1) line achieving a resolution of 12" x 2.6km/s, enabling individual Giant Molecular Clouds (GMCs) to be resolved. The observed region is 650 square arcminutes mainly along the major axis and out to a radius of 8.5 kpc, and covers entirely the 2' x40' radial strip observed with the HIFI and PACS Spectrometers as part of the HERM33ES Herschel key program. The achieved sensitivity in main beam temperature is 20-50mK at 2.6km/s velocity resolution. The CO(2-1) luminosity of the observed region is 1.7+/-0.1x10^7 Kkm/s pc^2 and is estimated to be 2.8+/-0.3x10^7 Kkm/s pc^2 for the entire galaxy, corresponding to H_2 masses of 1.9x10^8 M_sun and 3.3x10^8 M_sun respectively (including He), calculated with a NH2/ICO twice the Galactic value due to the half-solar metallicity of M33. HI 21 cm VLA archive observations were reduced and the mosaic was imaged and cleaned using the multi-scale task in CASA, yielding a series of datacubes with resolutions ranging from 5" to 25". The HI mass within a radius of 8.5 kpc is estimated to be 1.4x10^9 M_sun. The azimuthally averaged CO surface brightness decreases exponentially with a scale length of 1.9+/-0.1kpc whereas the atomic gas surface density is constant at Sigma_HI=6+/-2M_sun pc^2 deprojected to face-on. For a NH2/ICO conversion factor twice that of the Milky Way, the central kiloparsec H_2 surface density is Sigma_H_2=8.5+/-0.2M_sun pc^2 The star formation rate per unit molecular gas (SF Efficiency, the rate of transformation of molecular gas into stars), as traced by the ratio of CO to H_alpha and FIR brightness, is constant with radius. The SFE, with a NH2/ICO factor twice galactic, appears 2-4 times greater that of large spiral galaxies. A morphological comparison of molecular and atomic gas with tracers of star formation is presented showing good agreement between these maps both in terms of peaks and holes. A few exceptions are noted. Several spectra, including those of a molecular cloud situated more than 8 kpc from the galaxy center, are presented.
We analyze the dynamics of a Dirac-Born-Infeld (DBI) field in a cosmological set-up which includes a perfect fluid. Introducing convenient dynamical variables, we show the evolution equations form an autonomous system when the potential and the brane tension of the DBI field are arbitrary power-law or exponential functions of the DBI field. In particular we find scaling solutions can exist when powers of the field in the potential and warp-factor satisfy specific relations. A new class of fixed-point solutions are obtained corresponding to points which initially appear singular in the evolution equations, but on closer inspection are actually well defined. In all cases, we perform a phase-space analysis and obtain the late-time attractor structure of the system. Of particular note is a new fixed-point solution where the Lorentz factor is a finite large constant and the equation of state parameter of the DBI field is $w=-1$. Since in this case the speed of sound $c_s$ becomes constant, the solution can be thought to serve as a good background when considering cosmological perturbations in DBI inflation.
The covariant entropy bound states that the entropy, S, of matter on a light-sheet cannot exceed a quarter of its initial area, A, in Planck units. The gravitational entropy of black holes saturates this inequality. The entropy of matter systems, however, falls short of saturating the bound in known examples. This puzzling gap has led to speculation that a much stronger bound, S< A^{3/4}, may hold true. In this note, we exhibit light-sheets whose entropy exceeds A^{3/4} by arbitrarily large factors. In open FRW universes, such light-sheets contain the entropy visible in the sky; in the limit of early curvature domination, the covariant bound can be saturated but not violated. As a corollary, we find that the maximum observable matter and radiation entropy in universes with positive (negative) cosmological constant is of order Lambda^{-1} (Lambda^{-2}), and not |Lambda|^{-3/4} as had hitherto been believed. Our results strengthen the evidence for the covariant entropy bound, while showing that the stronger bound S< A^{3/4} is not universally valid. We conjecture that the stronger bound does hold for static, weakly gravitating systems.
We show that the power spectrum of a self-interacting scalar field in de Sitter space-time is strongly suppressed on large scales. The cut-off scale depends on the strength of the self-coupling, the number of e-folds of quasi-de Sitter evolution, and its expansion rate. As a consequence, the two-point correlation function of field fluctuations is free from infra-red divergencies.
We study the structure of neutron stars in perturbative f(R) gravity models with realistic equations of state. We obtain the mass-radius relation in gravity models of the form f(R)=R+\alpha R^2 and f(R)=R+\beta R^3. Using the recent observational constraints on the mass-radius relation, we find that |\alpha| \lesssim 10^{10} cm^{2} and |\beta| \lesssim 10^{21} cm^{4}. This implies, for such gravity models, that deviations from Einstein's general relativity in the strong gravity regime should be within a curvature scale of 10^{-10} cm^{-2}.
In a landscape of compactifications with different numbers of macroscopic dimensions, it is possible that our universe has nucleated from a vacuum where some of our four large dimensions were compact while other, now compact, directions were macroscopic. From our perspective, this shapeshifting can be perceived as an anisotropic background spacetime. As an example, we present a model where our universe emerged from a tunneling event which involves the decompactification of two dimensions compactified on the two-sphere. In this case, our universe is of the Kantowski-Sachs (KS) type and therefore homogeneous and anisotropic. We study the deviations from statistical isotropy of the Cosmic Microwave Background (CMB) induced by the RxS2-topology of the KS universe and present a preliminary discussion of their observability if inflation was sufficiently short.
In this paper we consider a unique model of inflation where the universe undergoes rapid asymmetric oscillations, each cycle lasting millions of Planck time. Over many-many cycles the space-time expands to mimic the standard inflationary scenario. Moreover, these rapid oscillations leave a distinctive periodic signature in ln(k) in the primordial power spectrum, where k denotes the comoving scale. The best fit parameters of the cyclic-inflation model provides a very good fit to the 7-year WMAP data.
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We present three-dimensional, adaptive mesh simulations of dwarf galaxy out- flows driven by supersonic turbulence. Here we develop a subgrid model to track not only the thermal and bulk velocities of the gas, but also its turbulent velocities and length scales. This allows us to deposit energy from supernovae directly into supersonic turbulence, which acts on scales much larger than a particle mean free path, but much smaller than resolved large-scale flows. Unlike previous approaches, we are able to simulate a starbursting galaxy modeled after NGC 1569, with realistic radiative cooling throughout the simulation. Pockets of hot, diffuse gas around individual OB associations sweep up thick shells of material that persist for long times due to the cooling instability. The overlapping of high-pressure, rarefied regions leads to a collective central outflow that escapes the galaxy by eating away at the exterior gas through turbulent mixing, rather than gathering it into a thin, unstable shell. Supersonic, turbulent gas naturally avoids dense regions where turbulence decays quickly and cooling times are short, and this further enhances density contrasts throughout the galaxy- leading to a complex, chaotic distribution of bubbles, loops and filaments as observed in NGC 1569 and other outflowing starbursts.
From a deep multi-epoch Chandra observation of the elliptical galaxy NGC 3379
we report the spectral properties of nine luminous LMXBs (LX>1E38 erg/s). We
also present a set of spectral simulations, produced to aid the interpretation
of low-count single-component spectral modeling. These simulations demonstrate
that it is possible to infer the spectral states of X-ray binaries from these
simple models and thereby constrain the properties of the source. Of the nine
LMXBs studied, three reside within globular clusters, and one is a confirmed
field source. Due to the nature of the luminosity cut all sources are either
neutron star binaries emitting at or above the Eddington luminosity or black
hole binaries. The spectra from these sources are well described by
single-component models, with parameters consistent with Galactic LMXB
observations, where hard-state sources have a range in photon index of 1.4-1.9
and thermally dominated sources have inner disc temperatures between ~0.7-1.55
keV.
The large variability observed in the brightest globular cluster source
(LX>4E38 erg/s) suggests the presence of a black hole binary. At its most
luminous this source is observed in a thermally dominated state with kT=1.5
keV, consistent with a black hole mass of 10 Msol. This observation provides
further evidence that globular clusters are able to retain such massive
binaries. We also observed a source transitioning from a bright state (LX~1E39
erg/s), with prominent thermal and non-thermal components, to a less luminous
hard state (LX=4.5E38 erg/s, Gamma=1.85). In its high flux emission this source
exhibits a cool-disc component of ~0.14 keV, similar to spectra observed in
some ultraluminous X-ray sources. Such a similarity indicates a possible link
between `normal' stellar mass black holes in a high accretion state and ULXs.
We present the Smoothed Hessian Major Axis Filament Finder (SHMAFF), an algorithm that uses the eigenvectors of the Hessian matrix of the smoothed galaxy distribution to identify individual filamentary structures. Filaments are traced along the Hessian eigenvector corresponding to the largest eigenvalue, and are stopped when the axis orientation changes more rapidly than a preset threshold. In both N-body simulations and the Sloan Digital Sky Survey (SDSS) main galaxy redshift survey data, the resulting filament length distributions are approximately exponential. In the SDSS galaxy distribution, using smoothing lengths of 10 h^{-1} Mpc and 15 h^{-1} Mpc, we find filament lengths per unit volume of 1.9x10^{-3} h^2 Mpc^{-2} and 7.6x10^{-4} h^2 Mpc^{-2}, respectively. The filament width distributions, which are much more sensitive to non-linear growth, are also consistent between the real and mock galaxy distributions using a standard cosmology. In SDSS, we find mean filament widths of 5.5 h^{-1} Mpc and 8.4 h^{-1} Mpc on 10 h^{-1} Mpc and 15 h^{-1} Mpc smoothing scales, with standard deviations of 1.1 h^{-1} Mpc and 1.4 h^{-1} Mpc, respectively. Finally, the spatial distribution of filamentary structure in simulations is very similar between z=3 and z=0 on smoothing scales as large as 15 h^{-1} Mpc, suggesting that the outline of filamentary structure is already in place at high redshift.
Comparing clustering of differently biased tracers of the dark matter
distribution offers the opportunity to reduce the cosmic variance error in the
measurement of certain cosmological parameters. We develop a formalism that
includes bias non-linearities and stochasticity. Our formalism is general
enough that can be used to optimise survey design and tracers selection and
optimally split (or combine) tracers to minimise the error on the
cosmologically interesting quantities. Our approach generalises the one
presented by McDonald & Seljak (2009) of circumventing sample variance in the
measurement of $f\equiv d \ln D/d\ln a$. We analyse how the bias, the noise,
the non-linearity and stochasticity affect the measurements of $Df$ and explore
in which signal-to-noise regime it is significantly advantageous to split a
galaxy sample in two differently-biased tracers. We use N-body simulations to
find realistic values for the parameters describing the bias properties of dark
matter haloes of different masses and their number density.
We find that, even if dark matter haloes could be used as tracers and
selected in an idealised way, for realistic haloes, the sample variance limit
can be reduced only by up to a factor $\sigma_{2tr}/\sigma_{1tr}\simeq 0.6$.
This would still correspond to the gain from a three times larger survey volume
if the two tracers were not to be split. Before any practical application one
should bear in mind that these findings apply to dark matter haloes as tracers,
while realistic surveys would select galaxies: the galaxy-host halo relation is
likely to introduce extra stochasticity, which may reduce the gain further.
We study filamentary structure in the galaxy distribution at z ~ 0.8 using data from the Deep Extragalactic Evolutionary Probe 2 (DEEP2) Redshift Survey and its evolution to z ~ 0.1 using data from the Sloan Digital Sky Survey (SDSS). We trace individual filaments for both surveys using the Smoothed Hessian Major Axis Filament Finder, an algorithm which employs the Hessian matrix of the galaxy density field to trace the filamentary structures in the distribution of galaxies. We extract 33 subsamples from the SDSS data with a geometry similar to that of DEEP2. We find that the filament length distribution has not significantly changed since z ~ 0.8, as predicted in a previous study using a $\Lamda$CDM cosmological N-body simulation. However, the filament width distribution, which is sensitive to the non-linear growth of structure, broadens and shifts to smaller widths for smoothing length scales of 5-10 Mpc/h from z ~ 0.8 to z ~ 0.1, in accord with N-body simulations.
Keck near-infrared images of Neptune from UT 26 July 2007 show that the cloud feature typically observed within a few degrees of Neptune's south pole had split into a pair of bright spots. A careful determination of disk center places the cloud centers at -89.07 +/- 0 .06 and -87.84 +/- 0.06 degrees planetocentric latitude. If modeled as optically thick, perfectly reflecting layers, we find the pair of features to be constrained to the troposphere, at pressures greater than 0.4 bar. By UT 28 July 2007, images with comparable resolution reveal only a single feature near the south pole. The changing morphology of these circumpolar clouds suggests they may form in a region of strong convection surrounding a Neptunian south polar vortex.
We present the GalMer database, a library of galaxy merger simulations, made available to users through tools compatible with the Virtual Observatory (VO) standards adapted specially for this theoretical database. To investigate the physics of galaxy formation through hierarchical merging, it is necessary to simulate galaxy interactions varying a large number of parameters: morphological types, mass ratios, orbital configurations, etc. On one side, these simulations have to be run in a cosmological context, able to provide a large number of galaxy pairs, with boundary conditions given by the large-scale simulations, on the other side the resolution has to be high enough at galaxy scales, to provide realistic physics. The GalMer database is a library of thousands simulations of galaxy mergers at moderate spatial resolution and it is a compromise between the diversity of initial conditions and the details of underlying physics. We provide all coordinates and data of simulated particles in FITS binary tables. The main advantages of the database are VO access interfaces and value-added services which allow users to compare the results of the simulations directly to observations: stellar population modelling, dust extinction, spectra, images, visualisation using dedicated VO tools. The GalMer value-added services can be used as virtual telescope producing broadband images, 1D spectra, 3D spectral datacubes, thus making our database oriented towards the usage by observers. We present several examples of the GalMer database scientific usage obtained from the analysis of simulations and modelling their stellar population properties, including: (1) studies of the star formation efficiency in interactions; (2) creation of old counter-rotating components; (3) reshaping metallicity profiles in elliptical galaxies; (4) orbital to internal angular momentum transfer; (5) reproducing observed colour bimodality of galaxies.
Atmospheric turbulence is an important limit to high angular resolution in astronomy. Interferometry resolved this issue by filtering the incoming light with single-mode fibers. Thanks to this technique, we obtained with the IOTA interferometer very precise measurements of the spatial frequencies of seven evolved stars. From these measurements, we performed a blind deconvolution to restore an image of the surface of the stars. Six of the them, Betelgeuse, Mu Cep, R leo, Mira, Chi Cyg and CH Cyg, feature very asymmetrical brightness distributions. On the other hand, the Arcturus data are extremely well fitted with a simple limb-darkened photospheric disc. From the observations of $\chi$ Cyg, we show that the star is surrounded by a molecular shell undergoing a ballistic motion. We propose to use the same technique of spatial filtering with single-mode fibers to correct for the effect of turbulence in the pupil of a telescope. Because the pupil is redundant, this technique does require a remapping of the pupil. We developed a dedicated algorithm to show that it was possible to reconstruct images at the diffraction limit of the telescope free of any speckle noise. Our simulations show that a high dynamic range (over 10^6) could be obtained in the visible on an 8 meter telescope. A lab experiment is under construction to validate the concept of this new instrument.
We present new ATCA 21-cm line observations of the neutral hydrogen in the nearby radio galaxy Centaurus A. We image in detail (with a resolution down to 7", ~100pc) the distribution of HI along the dust lane. Our data have better velocity resolution and better sensitivity than previous observations. The HI extends for a total of ~15kpc. The data, combined with a titled-ring model of the disk, allow to conclude that the kinematics of the HI is that of a regularly rotating, highly warped structure down to the nuclear scale. The parameters (in particular the inclination) of our model are somewhat different from some of the previously proposed models but consistent with what was recently derived from stellar light in a central ring. The model nicely describes also the morphology of the dust lane as observed with Spitzer. There are no indications that large-scale anomalies in the kinematics exist that could be related to supplying material for the AGN. Large-scale radial motions do exist, but these are only present at larger radii r>6kpc). This unsettled gas is mainly part of a tail/arm like structure. The relatively regular kinematics of the gas in this structure suggests that it is in the process of settling down into the main disk. The presence of this structure further supports the merger/interaction origin of the HI in Cen A. From the structure and kinematics we estimate a timescale of 1.6-3.2*10^{8}yr since the merging event. No bar structure is needed to describe the kinematics of the HI. The comparison of the timescale derived from the large-scale HI structure and those of the radio structure together with the relative regularity of the HI down to the sub-kpc regions does not suggest a one-to-one correspondence between the merger and the phase of radio activity. Interestingly, the radial motions of the outer regions are such that the projected velocities are redshifted compared to the regular orbits. This means that the blueshifted absorption discovered earlier and discussed in our previous paper cannot be caused by out-moving gas at large radius projected onto the centre. Therefore, the interpretation of the blueshifted absorption, together with at least a fraction of the redshifted nuclear absorption, as evidence for a regular inner disk, still holds. Finally, we also report the discovery of two unresolved clouds detected at 5.2 and 11kpc away (in projection) from the HI disk. They are likely an other example of left-over of the merger that brought the HI gas.
The population of compact massive galaxies observed at z > 1 are hypothesised, both observationally and in simulations, to be merger remnants of gas-rich disc galaxies. To probe such a scenario we analyse a sample of 12 gas-rich and active star forming sub-mm galaxies (SMGs) at 1.8 < z < 3. We present a structural and size measurement analysis for all of these objects using very deep ACS and NICMOS imaging in the GOODS-North field. Our analysis reveals a heterogeneous mix of morphologies and sizes. We find that four galaxies (33% \pm 17%) show clear signs of mergers or interactions, which we classify as early-stage mergers. The remaining galaxies are divided into two categories: five of them (42% \pm 18%) are diffuse and regular disc-like objects, while three (25% \pm 14%) are very compact, spheroidal systems. We argue that these three categories can be accommodated into an evolutionary sequence, showing the transformation from isolated, gas-rich discs with typical sizes of 2-3 kpc, into compact (< 1 kpc) galaxies through violent major merger events, compatible with the scenario depicted by theoretical models. Our findings that some SMGs are already dense and compact provides strong support to the idea that SMGs are the precursors of the compact, massive galaxies found at slightly lower redshift.
The stability of the color flavor locked phase in the presence of a strong magnetic field is investigated within the phenomenological MIT bag model, taking into account the variation of the strange quark mass, the baryon density, the magnetic field, as well as the bag and gap parameters. It is found that the minimum value of the energy per baryon in a color flavor locked state at vanishing pressure is lower than the corresponding one for unpaired magnetized strange quark matter and, as the magnetic field increases, the energy per baryon decreases. This implies that magnetized color flavor locked matter is more stable and could become the ground state inside neutron stars. The mass-radius relation for such stars is also studied.
The observed GeV and TeV emission from M82 and NGC 253 by Fermi, HESS, and VERITAS constrains the physics of cosmic rays (CRs) in these dense star-forming environments. We discuss these constraints in detail, and present an independent analysis of the Fermi data for these starbursts. We argue the gamma-rays are predominantly hadronic in origin; in this case, the measured fluxes imply that both galaxies are consistent with being CR "proton calorimeters:" all of the energy injected in high energy primary CR protons is lost to inelastic proton-proton collisions (pion production) before escape, producing gamma-rays, neutrinos, and secondary electrons and positrons. The case for calorimetry is stronger for M82 than for NGC 253, and the latter may be only marginally calorimetric. We also consider leptonic contributions to the GeV-TeV emission, including the possibility of a "TeV Excess" analogous to that seen in the Galaxy. We show that the GeV-TeV detections of M82 and NGC 253, together with proton calorimetry, imply that (1) starbursts contribute significantly to the diffuse gamma-ray and neutrino backgrounds, (2) a calorimetric FIR--gamma-ray correlation analogous to the FIR-radio correlation should exist for dense starbursts, (3) the CR energy density is dynamically weak compared to gravity in M82 and NGC 253, and (4) relativistic bremsstrahlung and ionization losses compete with synchrotron and Inverse Compton in cooling the CR electron/positron population in starbursts, with important consequences for the physics of the FIR-radio correlation. Finally, as a guide for future studies, we list the brightest star-forming galaxies on the sky and predict their gamma-ray fluxes.
Most theoretical descriptions of the production of solar flare bremsstrahlung radiation assume the collision of dilute accelerated particles with a cold, dense target plasma, neglecting interactions of the fast particles with each other. This is inadequate for situations where collisions with this background plasma are not completely dominant, as may be the case in, for example, low-density coronal sources. We aim to formulate a model of a self-interacting, entirely fast electron population in the absence of a dense background plasma, to investigate its implications for observed bremsstrahlung spectra and the flare energy budget. We derive approximate expressions for the time-dependent distribution function of the fast electrons using a Fokker-Planck approach. We use these expressions to generate synthetic bremsstrahlung X-ray spectra as would be seen from a corresponding coronal source. We find that our model qualitatively reproduces the observed behaviour of some flares. As the flare progresses, the model's initial power-law spectrum is joined by a lower energy, thermal component. The power-law component diminishes, and the growing thermal component proceeds to dominate the total emission over timescales consistent with flare observations. The power-law exhibits progressive spectral hardening, as is seen in some flare coronal sources. We also find that our model requires a factor of 7 - 10 fewer accelerated electrons than the cold, thick target model to generate an equivalent hard X-ray flux. This model forms the basis of a treatment of self-interactions among flare fast electrons, a process which affords a more efficient means to produce bremsstrahlung photons and so may reduce the efficiency requirements placed on the particle acceleration mechanism. It also provides a useful description of the thermalisation of fast electrons in coronal sources.
We present the results of hydrodynamical simulations of the disk photosphere irradiated by strong X-rays produced in the inner most part of the disk. As expected, the irradiation heats the photosphere and drives a thermal wind. To apply our results to the well-studied X-ray transient source GRO J1655-40, we adopted the observed mass of its black hole, and the observed properties of its X-ray radiation. To compare the results with the observations, we also computed transmitted X-ray spectra based on the wind solution. Our main finding is: the density of the fast moving part of the wind is more than one order of magnitude lower than that inferred from the observations. Consequently, the model fails to predict spectra with line absorption as strong and as blueshifted as those observed. However, despite the thermal wind being weak and Compton thin, the ratio between the mass-loss rate and the mass accretion rate is about seven. This high ratio is insensitive to the accretion luminosity, in the limit of lower luminosities. Most of the mass is lost from the disk between 0.07 and 0.2 of the Compton radius. We discovered that beyond this range the wind solution is self-similar. In particular, soon after it leaves the disk, the wind flows at a constant angle with respect to the disk. Overall, the thermal winds generated in our comprehensive simulations do not match the wind spectra observed in GRO J1655-40. This supports the conclusion of Miller et al. and Kallman et al. that the wind in GRO J1655-40, and possibly other X-ray transients, may be driven by magnetic processes. This in turn implies that the disk wind carries even more material than our simulations predict and as such has a very significant impact on the accretion disk structure and dynamics.
We give a pedagogical review of a covariant and fully non-perturbative approach to study nonlinear perturbations in cosmology. In the first part, devoted to cosmological fluids, we define a nonlinear extension of the uniform-density curvature perturbation and derive its evolution equation. In the second part, we focus our attention on multiple scalar fields and present a nonlinear description in terms of adiabatic and entropy perturbations. In both cases, we show how the formalism presented here enables one to easily obtain equations up to second, third and higher orders.
Galaxies are missing most of their baryons, and many models predict these baryons lie in a hot halo around galaxies. We establish observationally motivated constraints on the mass and radii of these haloes using a variety of independent arguments. First, the observed dispersion measure of pulsars in the Large Magellanic Cloud allows us to constrain the hot halo around the Milky Way: if it obeys the standard NFW profile, it must contain less than 4-5% of the missing baryons from the Galaxy. This is similar to other upper limits on the Galactic hot halo, such as the soft X-ray background and the pressure around high velocity clouds. Second, we note that the X-ray surface brightness of hot haloes with NFW profiles around large isolated galaxies is high enough that such emission should be observed, unless their haloes contain less than 10-25% of their missing baryons. Third, we place constraints on the column density of hot haloes using nondetections of OVII absorption along AGN sightlines: in general they must contain less than 70% of the missing baryons or extend to no more than 40 kpc. Flattening the density profile of galactic hot haloes weakens the surface brightness constraint so that a typical L$_*$ galaxy may hold half its missing baryons in its halo, but the OVII constraint remains unchanged, and around the Milky Way a flattened profile may only hold $6-13%$ of the missing baryons from the Galaxy ($2-4 \times 10^{10} M_{\odot}$). We also show that AGN and supernovae at low to moderate redshift - the theoretical sources of winds responsible for driving out the missing baryons - do not produce the expected correlations with the baryonic Tully-Fisher relationship and so are insufficient to explain the missing baryons from galaxies. We conclude that most of missing baryons from galaxies do not lie in hot haloes around the galaxies, and that the missing baryons never fell into the potential wells of protogalaxies in the first place. They may have been expelled from the galaxies as part of the process of galaxy formation.
We study models of late-time cosmic acceleration in terms of scalar-tensor theories generalized to include a certain class of non-linear derivative interaction of the scalar field. The non-linear effect suppress the scalar-mediated force at short distances to pass solar-system tests of gravity. It is found that the expansion history until today is almost indistinguishable from that of the $\Lambda$CDM model or some (phantom) dark energy models, but the fate of the universe depends clearly on the model parameter. The growth index of matter density perturbations is computed to show that its past asymptotic value is given by 9/16, while the value today is as small as 0.4.
We present the results of timing analysis of the low-frequency Quasi-Periodic Oscillation (QPO) in the Rossi X-Ray Timing Explorer data of the black hole binary XTE J1550--564 during its 1998 outburst. The QPO frequency is observed to vary on timescales between $\sim$100 s and days, correlated with the count rate contribution from the optically thick accretion disk: we studied this correlation and discuss its influence on the QPO width. In all observations, the quality factors ($\nu_0$/FWHM) of the fundamental and second harmonic peaks were observed to be consistent, suggesting that the quasi-periodic nature of the oscillation is due to frequency modulation. In addition to the QPO and its harmonic peaks, a new 1.5$\nu$ component was detected in the power spectra. This component is broad, with a quality factor of $\sim$0.6. From this, we argue what the peak observed at half the QPO frequency, usually referred to as "sub-harmonic" could be the fundamental frequency, leading to the sequence 1:2:3:4. We also studied the energy dependence of the timing features and conclude that the two continuum components observed in the power spectrum, although both more intense at high energies, show a different dependence on energy. At low energies, the lowest-frequency component dominates, while at high energies the higher-frequency one has a higher fractional rms. An interplay between these two components was also observed as a function of their characteristic frequency. In this source, the transition between low/hard state and hard-intermediate state appears to be a smooth process.
We study in detail the motions of three planets interacting with each other under the influence of a central star. It is known that the system with more than two planets becomes unstable after remaining quasi-stable for long times, leading to highly eccentric orbital motions or ejections of some of the planets. In this paper, we are concerned with the underlying physics for this quasi-stability as well as the subsequent instability and advocate the so-called "stagnant motion" in the phase space, which has been explored in the field of dynamical system. We employ the Lyapunov exponent, the power spectra of orbital elements and the distribution of the durations of quasi-stable motions to analyze the phase space structure of the three-planet system, the simplest and hopefully representative one that shows the instability. We find from the Lyapunov exponent that the system is almost non-chaotic in the initial quasi-stable state whereas it becomes intermittently chaotic thereafter. The non-chaotic motions produce the horizontal dense band in the action-angle plot whereas the voids correspond to the chaotic motions. We obtain power laws for the power spectra of orbital eccentricities. Power-law distributions are also found for the durations of quasi-stable states. All these results combined together, we may reach the following picture: the phase space consists of the so-called KAM tori surrounded by satellite tori and imbedded in the chaotic sea. The satellite tori have a self-similar distribution and are responsible for the scale-free power-law distributions of the duration times. The system is trapped around one of the KAM torus and the satellites for a long time (the stagnant motion) and moves to another KAM torus with its own satellites from time to time, corresponding to the intermittent chaotic behaviors.
We study the self-consistent, linear response of a galactic disc to non-axisymmetric perturbations in the vertical direction as due to a tidal encounter, and show that the density distribution near the disc mid-plane has a strong impact on the radius beyond which distortions like warps develop. The self-gravity of the disc resists distortion in the inner parts. Applying this approach to a galactic disc with an exponential vertical profile, Saha & Jog showed that warps develop beyond 4-6 disc scalelengths, which could hence be only seen in HI. The real galactic discs, however, have less steep vertical density distributions that lie between a sech and an exponential profile. Here we calculate the disc response for such a general sech^(2/n) density distribution, and show that the warps develop from a smaller radius of 2-4 disc scalelengths. This naturally explains why most galaxies show stellar warps that start within the optical radius. Thus a qualitatively different picture of ubiquitous optical warps emerges for the observed less-steep density profiles. The surprisingly strong dependence on the density profile is due to the fact that the disc self-gravity depends crucially on its mass distribution close to the mid-plane. General results for the radius of onset of warps, obtained as a function of the disc scalelength and the vertical scaleheight, are presented as contour plots which can be applied to any galaxy.
HR\,8799 is a $\lambda$ Bootis, $\gamma$ Doradus star hosting a planetary system and a debris disk with two rings. This makes this system a very interesting target for asteroseismic studies. This work is devoted to the determination of the internal metallicity of this star, linked with its $\lambda$ Bootis nature (i.e., solar surface abundances of light elements, and subsolar surface abundances of heavy elements), taking advantage of its $\gamma$ Doradus pulsations. This is the most accurate way to obtain this information, and this is the first time such a study is performed for a planetary-system-host star. We have used the equilibrium code CESAM and the non-adiabatic pulsational code GraCo. We have applied the Frequency Ratio Method (FRM) and the Time Dependent Convection theory (TDC) to estimate the mode identification, the Brunt-Va\"is\"al\"a frequency integral and the mode instability, making the selection of the possible models. When the non-seismological constraints (i.e its position in the HR diagram) are used, the solar abundance models are discarded. This result contradicts one of the main hypothesis for explaining the $\lambda$ Bootis nature, namely the accretion/diffusion of gas by a star with solar abundance. Therefore, according to these results, a revision of this hypothesis is needed. The inclusion of accurate internal chemical mixing processes seems to be necessary to explain the peculiar abundances observed in the surface of stars with internal subsolar metallicities. The use of the asteroseismological constraints, like those provided by the FRM or the instability analysis, provides a very accurate determination of the physical characteristics of HR 8799. However, a dependence of the results on the inclination angle $i$ still remains. The determination of this angle, more accurate multicolour photometric observations, and high resolution spectroscopy can definitively fix the mass and metallicity of this star.
A wideband analog correlator has been constructed for the Yuan-Tseh Lee Array for Microwave Background Anisotropy. Lag correlators using analog multipliers provide large bandwidth and moderate frequency resolution. Broadband IF distribution, backend signal processing and control are described. Operating conditions for optimum sensitivity and linearity are discussed. From observations, a large effective bandwidth of around 10 GHz has been shown to provide sufficient sensitivity for detecting cosmic microwave background variations.
The Suzaku observation of LMC X-3 gives the best data to date on the shape of the accretion disk spectrum. This is due to the combination of very low absorbing column density along this line of sight which allows the shape of the disk emisison to be constrained at low energies by the CCD's, while the tail can be simultaneously determined up to 30 keV by the high energy detectors. These data clearly demonstrate that the observed disk spectrum is broader than a simple 'sum of blackbodies', and relativistic smearing of the emission is strongly required. However, the intrinsic emission should be more complex than a (color-corrected) sum of blackbodies as it should also contain photo-electric absorption edges from the partially ionised disk photosphere. These are broadened by the relativistic smearing, but the models predict ~ 3-5 per cent deviations for 1/3- 1 solar abundance around the edge energies, significantly stronger than observed. This indicate that the models need to include more physical processes such as self-irradiation, bound-bound (line) absorption, and/or emission from recombination continuua and/or lines. Alternatively, if none of these match the data, it may instead require that the accretion disk density and/or emissivity profile with height is different to that assumed. Thus these data demonstrate the feasibility of observational tests of our fundamental understanding of the vertical structure of accretion disks.
The dimensionless entropy, ${\cal S} \equiv S/k$, of the visible universe, taken as a sphere of radius 50 billion light years with the Earth at its "center", is discussed. An upper limit ($10^{112}$), and a lower limit ($10^{102}$), for ${\cal S}$ are introduced. It is suggested that intermediate-mass black holes (IMBHs) constitute all dark matter, and that they dominate ${\cal S}$.
We constrain the distribution of calcium across the surface of the white dwarf star G29-38 by combining time series spectroscopy from Gemini-North with global time series photometry from the Whole Earth Telescope. G29-38 is actively accreting metals from a known debris disk. Since the metals sink significantly faster than they mix across the surface, any inhomogeneity in the accretion process will appear as an inhomogeneity of the metals on the surface of the star. We measure the flux amplitudes and the calcium equivalent width amplitudes for two large pulsations excited on G29-38 in 2008. The ratio of these amplitudes best fits a model for polar accretion of calcium and rules out equatorial accretion.
The main purpose of this article is to alert spectroscopists, particularly those involved in surveys, to the fact that rapidly pulsating sources induce periodic structures in spectra. This would allow the detection of new classes of objects sending bursts of pulses separated by constant time intervals that are too short to be detected with conventional techniques. The outstanding advantage of the technique is that there is no need for specialized instruments or surveys. One only must incorporate signal-searching algorithms into existing data analyzing software and use it with standard spectroscopic surveys, including existing ones. It is a small effort with a potentially huge pay-off because finding rapidly pulsating objects would be of enormous interest. Even a lack of detection could be used to eliminate exotic theoretical models.
The European Pulsar Timing Array (EPTA) is a multi-institutional, multi-telescope collaboration, with the goal of using high-precision pulsar timing to directly detect gravitational waves. In this article we discuss the EPTA member telescopes, current achieved timing precision, and near-future goals. We report a preliminary upper limit to the amplitude of a gravitational wave background. We also discuss the Large European Array for Pulsars, in which the five major European telescopes involved in pulsar timing will be combined to provide a coherent array that will give similar sensitivity to the Arecibo radio telescope, and larger sky coverage.
According to the no-hair theorem, an astrophysical black hole is uniquely described by only two quantities, the mass and the spin. In this series of papers, we investigate a framework for testing the no-hair theorem with observations of black holes in the electromagnetic spectrum. We formulate our approach in terms of a parametric spacetime which contains a quadrupole moment that is independent of both mass and spin. If the no-hair theorem is correct, then any deviation of the black-hole quadrupole moment from its Kerr value has to be zero. We analyze in detail the properties of this quasi-Kerr spacetime that are critical to interpreting observations of black holes and demonstrate their dependence on the spin and quadrupole moment. In particular, we show that the location of the innermost stable circular orbit and the gravitational lensing experienced by photons are affected significantly at even modest deviations of the quadrupole moment from the value predicted by the no-hair theorem. We argue that observations of black-hole images, of relativistically broadened iron lines, as well as of thermal X-ray spectra from accreting black holes will lead in the near future to an experimental test of the no-hair theorem.
We observed the Galactic black hole candidate H1743-322 with Suzaku for approximately 32 ksec, while the source was in a low/hard state during its 2008 outburst. We collected and analyzed the data with the HXD/PIN, HXD/GSO and XIS cameras spanning the energy range from 0.7-200 keV. Fits to the spectra with simple models fail to detect narrow Fe XXV and Fe XXVI absorption lines, with 90% confidence upper limits of 3.5 eV and 2.5 eV on the equivalent width, respectively. These limits are commensurate with those in the very high state, but are well below the equivalent widths of lines detected in the high/soft state, suggesting that disk winds are partially state-dependent. We discuss these results in the context of previous detections of ionized Fe absorption lines in H1743-322 and connections to winds and jets in accreting systems. Additionally, we report the possible detection of disk reflection features, including an Fe K emission line.
A considerable fraction of the central stars of planetary nebulae (CSPNe) are hydrogen-deficient. As a rule, these CSPNe exhibit a chemical composition of helium, carbon, and oxygen with the majority showing Wolf-Rayet-like emission line spectra. These stars are classified as CSPNe of a spectral type [WC]. We perform a spectral analysis of CSPN PB 8 with the Potsdam Wolf-Rayet (PoWR) models for expanding atmospheres. The source PB 8 displays wind-broadened emission lines from strong mass loss. Most strikingly, we find that its surface composition is hydrogen-deficient, but not carbon-rich. With mass fractions of 55% helium, 40% hydrogen, 1.3% carbon, 2% nitrogen, and 1.3% oxygen, it differs greatly from the 30-50% of carbon which are typically seen in [WC]-type central stars. The atmospheric mixture in PB 8 has an analogy in the WN/WC transition type among the massive Wolf-Rayet stars. Therefore we suggest to introduce a new spectral type [WN/WC] for CSPNe, with PB 8 as its first member. The central star of PB 8 has a relatively low temperature of T=52kK, as expected for central stars in their early evolutionary stages. Its surrounding nebula is less than 3000 years old, i.e. relatively young. Existing calculations for the post-AGB evolution can produce hydrogen-deficient stars of the [WC] type, but do not predict the composition found in PB 8. We discuss various scenarios that might explain the origin of this unique object.
Context: Chemical models of dense cloud cores often utilize the so-called pseudo-time-dependent approximation, in which the physical conditions are held fixed and uniform as the chemistry occurs. In this approximation, the initial abundances chosen, which are totally atomic in nature except for molecular hydrogen, are artificial. A more detailed approach to the chemistry of dense cold cores should include the physical evolution during their early stages of formation. Aims: Our major goal is to investigate the initial synthesis of molecular ices and gas-phase molecules as cold molecular gas begins to form behind a shock in the diffuse interstellar medium. The abundances calculated as the conditions evolve can then be utilized as reasonable initial conditions for a theory of the chemistry of dense cores. Methods: Hydrodynamic shock-wave simulations of the early stages of cold core formation are used to determine the time-dependent physical conditions for a gas-grain chemical network. We follow the cold post-shock molecular evolution of ices and gas-phase molecules for a range of visual extinction up to AV ~ 3, which increases with time. At higher extinction, self-gravity becomes important. Results: As the newly condensed gas enters its cool post-shock phase, a large amount of CO is produced in the gas. As the CO forms, water ice is produced on grains, while accretion of CO produces CO ice. The production of CO2 ice from CO occurs via several surface mechanisms, while the production of CH4 ice is slowed by gas-phase conversion of C into CO.
The Cygnus Loop is interacting with a protrusion of the cavity wall in its eastern edge (the XA region), where the X-ray emission is very bright. The complexity of the environment and the non-linear physical processes of the shock-cloud interaction make the origin of the X-ray emission still not well understood. Our purpose is to understand the physical origin of the X-ray emission in the XA region, addressing, in particular, the role of thermal conduction in the interaction process. We analyzed two XMM-Newton data sets, performing image analysis and spatially resolved spectral analysis on a set of homogeneous regions. We applied a recently developed diagnostic tool to compare spectral analysis results with predictions of theoretical models, and to estimate the efficiency of thermal conduction on the X-ray emitting shocked plasma. We found that the inhomogeneous cavity wall contains both large clumps (the protrusion) and small isolated clumps with different densities. A large indentation bent over to the south is detected. The abundance of the surrounding ISM is ~0.2 times solar value. We confirmed the important role of thermal conduction in the evolution of X-ray emitting plasma during shock-cloud interaction.
The most distant quasars known, at redshifts z=6, generally have properties indistinguishable from those of lower-redshift quasars in the rest-frame ultraviolet/optical and X-ray bands. This puzzling result suggests that these distant quasars are evolved objects even though the Universe was only seven per cent of its current age at these redshifts. Recently one z=6 quasar was shown not to have any detectable emission from hot dust, but it was unclear whether that indicated different hot-dust properties at high redshift or if it is simply an outlier. Here we report the discovery of a second quasar without hot-dust emission in a sample of 21 z=6 quasars. Such apparently hot-dust-free quasars have no counterparts at low redshift. Moreover, we demonstrate that the hot-dust abundance in the 21 quasars builds up in tandem with the growth of the central black hole, whereas at low redshift it is almost independent of the black hole mass. Thus z=6 quasars are indeed at an early evolutionary stage, with rapid mass accretion and dust formation. The two hot-dust-free quasars are likely to be first-generation quasars born in dust-free environments and are too young to have formed a detectable amount of hot dust around them.
Observations indicate that roughly 60% of the baryons may exist in a Warm-Hot Intergalactic Medium (WHIM) at low redshifts. Following up on previous results showing that gas is released through galaxy mergers, we use a semi-analytic technique to estimate the fraction of gas mass lost from haloes solely due to mergers. We find that up to ~25% of the gas in a halo can unbind over the course of galaxy assembly. This process does not act preferentially on smaller mass haloes; bigger haloes \emph{always} release larger amounts of gas in a given volume of the Universe. However, if we include multi-phase gas accretion onto haloes, we find that only a few percent is unbound. We conclude that either non-gravitational processes may be in play to heat up the gas in the galaxies prior to unbinding by mergers or most of the baryons in the WHIM have never fallen into virialised dark matter haloes. We present a budget for stocking the WHIM compiled from recent work.
We compute the growth of the mean square of quantum fluctuations of test fields with small effective mass during a slow changing, nearly de Sitter stage which took place in different inflationary models. We consider a minimally coupled scalar with a small mass, a modulus with an effective mass $ \propto H^2$ (with $H$ as the Hubble parameter) and a massless non-minimally coupled scalar in the test field approximation and compare the growth of the relative mean square with the one of gauge invariant inflaton fluctuations. We find that in most of the single fields inflationary models the mean square gauge invariant inflaton fluctuation grows {\em faster} than any test field with a non-negative effective mass. Hybrid inflationary models can be an exception: the mean square of a test field can dominate over the gauge invariant inflaton fluctuation one on suitably choosing parameters. We also compute the stochastic growth of quantum fluctuation of a second field, relaxing the assumption of its zero homogeneous value, in a generic inflationary model: as a main result, we obtain that the equation of motion of a gauge invariant variable associated, order by order, with a generic quantum scalar fluctuation during inflation can be obtained only if we use the number of e-folds as the time variable in the corresponding Langevin and Fokker-Planck equations for the stochastic approach. We employ this approach to derive some bounds in the case of a model with two massive fields.
We explore the novel possibility that the inflaton responsible for cosmological inflation is a gauge non-singlet in supersymmetric (SUSY) Grand Unified Theories (GUTs). For definiteness we consider SUSY hybrid inflation where we show that the scalar components of gauge non-singlet superfields, together with fields in conjugate representations, may form a D-flat direction suitable for inflation. We apply these ideas to SUSY models with an Abelian gauge group, a Pati-Salam gauge group and finally Grand Unified Theories based on SO(10) where the scalar components of the matter superfields in the $\sixteen$s may combine with a single $\bar {sixteen}$ to form the inflaton, with the right-handed sneutrino direction providing a possible viable trajectory for inflation. Assuming sneutrino inflation, we calculate the one-loop Coleman-Weinberg corrections and the two-loop corrections from gauge interactions giving rise to the "gauge \eta-problem" and show that both corrections do not spoil inflation, and the monopole problem can be resolved. The usual \eta-problem arising from supergravity may also be resolved using a Heisenberg symmetry.
This review addresses the issue of whether there are physically realistic
self-similar solutions in which a primordial black hole is attached to an exact
or asymptotically Friedmann model for an equation of state of the form
$p=(\gamma-1)\rho c^2$. In the positive pressure case ($1 < \gamma < 2$), there
is no such solution when the black hole is attached to an exact Friedmann
background via a sonic point. However, it has been claimed that there is a
one-parameter family of asymptotically Friedmann black hole solutions providing
the ratio of the black hole size to the cosmological horizon size is in a
narrow range above some critical value. There are also "universal" black holes
in which the black hole has an apparent horizon but no event horizon. It turns
out that both these types of solution are only asymptotically {\it
quasi}-Friedmann, because they contain a solid angle deficit at large
distances, but they are not necessarily excluded observationally.
We also consider the possibility of self-similar black hole solutions in a
universe dominated by a scalar field. If the field is massless, the situation
resembles the stiff fluid case, so any black hole solution is again contrived,
although there may still be universal black hole solutions. The situation is
less clear if the scalar field is rolling down a potential and therefore
massive, as in the quintessence scenario. Although no explicit asymptotically
Friedmann black hole solutions of this kind are known, they are not excluded
and comparison with the $0 < \gamma < 2/3$ perfect fluid case suggests that
they should exist if the black hole is not too large. This implies that a black
hole might grow as fast as the cosmological horizon in a quintessence-dominated
universe in some circumstances, supporting the proposal that accretion onto
primordial black holes may have played a role in the production of the
supermassive black holes in galactic nuclei.
We consider the three-body decays of gravitino dark matter in supersymmetric scenarios with bilinear R-parity violation. In particular, gravitino decays into lepton+W^* (lepton f\bar f') and \nu+Z^* (\nu f\bar f) are examined for gravitino masses below Mw. After computing the gravitino decay rates into these three-body final states and studying their dependence on supersymmetric parameters, we find that these new decay modes are often more important than the two-body decay, into a photon and a neutrino, considered in previous works. Consequently, the gravitino lifetime and its branching ratios are substantially modified, with important implications for the indirect detection of gravitino dark matter.
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We report the discovery of HD 156668b, an extrasolar planet with a minimum mass of M_P sin i = 4.15 M_Earth. This planet was discovered through Keplerian modeling of precise radial velocities from Keck-HIRES and is the second super-Earth to emerge from the NASA-UC Eta-Earth Survey. The best-fit orbit is consistent with circular and has a period of P = 4.6455 d. The Doppler semi-amplitude of this planet, K = 1.89 m/s, is among the lowest ever detected, on par with the detection of GJ 581e using HARPS. A longer period (P ~ 2.3 yr), low-amplitude signal of unknown origin was also detected in the radial velocities and was filtered out of the data while fitting the short-period planet. Additional data are required to determine if the long-period signal is due to a second planet, stellar activity, or another source. Photometric observations using the Automated Photometric Telescopes at Fairborn Observatory show that HD 156668 (an old, quiet K3 dwarf) is photometrically constant over the radial velocity period to 0.1 mmag, supporting the existence of the planet. No transits were detected down to a photometric limit of ~3 mmag, ruling out transiting planets dominated by extremely bloated atmospheres, but not precluding a transiting solid/liquid planet with a modest atmosphere.
We report precise Doppler measurements of seven subgiants from Keck Observatory. All seven stars show variability in their radial velocities consistent with planet-mass companions in Keplerian orbits. The host stars have masses ranging from 1.1 < Mstar/Msun < 1.9, radii 3.4 < Rstar/Rsun < 6.1, and metallicities -0.21 < [Fe/H] < +0.26. The planets are all more massive than Jupiter (Msini > 1 Mjup) and have semimajor axes > 1 AU. We present millimagnitude photometry from the T3 0.4m APT at Fairborn observatory for five of the targets. Our monitoring shows these stars to be photometrically stable, further strengthening the interpretation of the observed radial velocity variability. The orbital characteristics of the planets thus far discovered around former A-type stars are very different from the properties of planets around dwarf stars of spectral type F, G and K, and suggests that the formation and migration of planets is a sensitive function of stellar mass. Three of the planetary systems show evidence of long-term, linear trends indicative of additional distant companions. These trends, together with the high planet masses and increased occurrence rate, indicate that A-type stars are very promising targets for direct imaging surveys.
We present HST/WFC3 grism spectroscopy of the brightest galaxy at z>1.5 in the GOODS-South WFC3 Early Release Science grism pointing, covering the wavelength range 0.9-1.7 micron. The spectrum is of remarkable quality and shows the redshifted Balmer lines Hbeta, Hgamma, and Hdelta in absorption at z=1.902, correcting previous erroneous redshift measurements from the rest-frame UV. The average rest-frame equivalent width of the Balmer lines is 8+-1 Angstrom, which can be produced by a post-starburst stellar population with a luminosity-weighted age of ~0.5 Gyr. The M/L ratio inferred from the spectrum implies a stellar mass of ~4x10^11 Msun. We determine the morphology of the galaxy from a deep WFC3 F160W image. Similar to other massive galaxies at z~2 the galaxy is compact, with an effective radius of 2.1+-0.3 kpc. Although most of the light is in a compact core, the galaxy has two red, smooth spiral arms that appear to be tidally-induced. The spatially-resolved spectroscopy demonstrates that the center of the galaxy is quiescent and the surrounding disk is forming stars, as it shows Hbeta in emission. The galaxy is interacting with a companion at a projected distance of 18 kpc, which also shows prominent tidal features. The companion has a slightly redder spectrum than the primary galaxy but is a factor of ~10 fainter and may have a lower metallicity. It is tempting to interpret these observations as "smoking gun" evidence for the growth of compact, quiescent high redshift galaxies through minor mergers, which has been proposed by several recent observational and theoretical studies. Interestingly both objects host luminous AGNs, as indicated by their X-ray luminosities, which implies that these mergers can be accompanied by significant black hole growth. This study illustrates the power of moderate dispersion, low background near-IR spectroscopy at HST resolution, which is now available with the WFC3 grism.
TWA 30 is a remarkable young (7+/-3 Myr), low-mass (0.12+/-0.04 Msun), late-type star (M5+/-1) residing 42+/-2 pc away from the sun in the TW Hydrae Association. It shows strong outflow spectral signatures such as [S II], [O I], [O II], [O III], and Mg I], while exhibiting weak Halpha emission (-6.8+/-1.2 Angstroms). Emission lines of [S II] and [O I] are common to T Tauri stars still residing in their natal molecular clouds, while [O III] and Mg I] emission lines are incredibly rare in this same population; in the case of TWA 30, these latter lines may arise from new outflow material colliding into older outflow fronts. The weak Halpha emission and small radial velocity shifts of line emission relative to the stellar frame of rest (generally <=10 km/s) suggest that the disk is viewed close to edge-on and that the stellar axis may be inclined to the disk, similar to the AA Tau system, based on its temporal changes in emission/absorption line strengths/profiles and variable reddening (A_V=1.5-9.0). The strong Li absorption (0.61+/-0.13 Angstroms) and common kinematics with members of the TWA confirm its age and membership to the association. Given the properties of this system such as its proximity, low mass, remarkable outflow signatures, variability, and edge-on configuration, this system is a unique case study at a critical time in disk evolution and planet-building processes.
Local Group dwarf spheroidal satellite galaxies are the faintest extragalactic stellar systems known. We examine recent data for these objects in the plane of the Baryonic Tully-Fisher Relation (BTFR). While some dwarf spheroidals adhere to the BTFR, others deviate substantially. We examine the residuals from the BTFR and find that they are not random. The residuals correlate with luminosity, size, metallicity, ellipticity, and susceptibility of the dwarfs to tidal disruption. Fainter, more elliptical, and tidally more susceptible dwarfs deviate further from the BTFR. We consider a variety of mechanisms that might lead to this behavior. Reionization does not, by itself, suffice to explain all aspects of the data. Further mechanisms such as supernova feedback or ram pressure stripping may remove gas that would otherwise be present to satisfy the baryonic mass budget. The correlation with ellipticity and tidal susceptibility implies that the usual assumption of spherical systems in stable equilibria may not hold, and suggests an alternate (or additional) mechanism by which baryons are lost through tidal stripping. In this case, we predict the mass of streams that should be associated with each dwarf in order to restore consistency with the BTFR. Finally, we consider an alternative to dark matter, MOND. The mass-to-light ratios of the dwarfs which adhere to the BTFR are reasonable, but those which deviate are not: the mass-to-light ratios of the ultrafaint dwarfs are far too high to be explained by MOND. This would falsify the theory if these objects are stable, bound systems. However, the dwarfs are considerably more susceptible to tidal effects in MOND than with dark matter. The deviation sets in where the observed radii of the dwarfs exceed the MONDian tidal radii. The extent to which the dwarfs are currently being tidally stripped therefore becomes a powerful test of the MOND hypothesis.
We present a detailed analysis of the gas conditions in the H_2 luminous radio galaxy 3C326N at z~0.1, which has a low star formation rate (SFR~0.07 M_sun/yr) in spite of a gas surface density similar to those in starburst galaxies. Its star-formation efficiency is likely a factor ~20-30 lower than those of ordinary star-forming galaxies. Combining new IRAM CO emission-line interferometry with existing Spitzer mid-infrared spectroscopy, we find that the luminosity ratio of CO and pure rotational H_2 line emission is factors 10-100 lower than what is usually found. This may suggest that most of the molecular gas is warm. The Na D absorption-line profile of 3C326N in the optical suggests an outflow with a terminal velocity of ~ -1800 km/s and a mass outflow rate of 30-40 M_sun/yr, which cannot be explained by star formation. The mechanical power implied by the wind, of order 10^43 erg/s, is comparable to the bolometric luminosity of the emission lines of ionized and molecular gas. To explain these observations, we propose a scenario where a small fraction of the mechanical energy of the radio jet is deposited in the the interstellar medium of 3C326N, which powers the outflow, and the line emission through a mass momentum and energy exchange between the different phases in the ISM. Dissipation times are of order 10^7-8 yrs, similar or greater than the typical jet lifetime. Small ratios of CO and PAH surface brightnesses in another 7 H_2 luminous radio galaxies suggest that a similar form of AGN feedback could be lowering star formation efficiencies in these galxies a similar way. The local demographics of radio-loud AGN suggests that secular gas cooling in massive early-type galaxies of >= 10^11 M_sun could be regulated through a fundamentally similar form of 'maintenance-phase' AGN feedback.
We measure the half-light radii of globular clusters (GCs) in 43 galaxies from the ACS Fornax Cluster Survey (ACSFCS). We use these data to extend previous work in which the environmental dependencies of the half-light radii of GCs in early type galaxies in the ACS Virgo Cluster Survey (ACSVCS) were studied, and a corrected mean half-light radius (corrected for the observed environmental trends) was suggested as a reliable distance indicator. This work both increases the sample size for the study of the environmental dependencies, and adds leverage to the study of the corrected half-light radius as a possible distance indicator (since Fornax lies at a larger distance than the Virgo cluster). We study the environmental dependencies of the size of GCs using both a Principal Component Analysis as well as 2D scaling relations. We largely confirm the environmental dependencies shown in Jordan et al. (2005), but find evidence that there is a residual correlation in the mean half-light radius of GC systems with galaxy magnitude, and subtle differences in the other correlations - so there may not be a universal correction for the half-light radii of lower luminosity galaxy GC systems. The main factor determining the size of a GC in an early type galaxy is the GC color. Red GCs have <r_h> = 2.8+/-0.3 pc, while blue GCs have <r_h> = 3.4+/-0.3 pc. We show that for bright early-type galaxies (M_B < -19 mag), the uncorrected mean half-light radius of the GC system is by itself an excellent distance indicator (with error ~11%), having the potential to reach cosmologically interesting distances in the era of high angular resolution adaptive optics on large optical telescopes.
The NRAO VLA Sky Survey (NVSS) is the only dataset that allows an accurate determination of the auto-correlation function (ACF) on angular scales of several degrees for Active Galactic Nuclei (AGNs) at typical redshifts $z \simeq 1$. Surprisingly, the ACF is found to be positive on such large scales while, in the framework of the standard hierarchical clustering scenario with Gaussian primordial perturbations it should be negative for a redshift-independent effective halo mass of order of that found for optically-selected quasars. We show that a small primordial non-Gaussianity can add sufficient power on very large scales to account for the observed NVSS ACF. The best-fit value of the parameter $f_{\rm NL}$, quantifying the amplitude of primordial non-Gaussianity of local type is $f_{\rm NL}=62 \pm 27$ ($1\,\sigma$ error bar) and $25<f_{\rm NL}<117$ ($2\,\sigma$ confidence level), corresponding to a detection of non-Gaussianity significant at the $\sim 3\,\sigma$ confidence level. The minimal halo mass of NVSS sources is found to be $M_{\rm min}=10^{12.47\pm0.26}h^{-1}M_{\odot}$ ($1\,\sigma$) strikingly close to that found for optically selected quasars. We discuss caveats and possible physical and systematic effects that can impact on the results.
We compare the predictions of four different algorithms for the distribution of ionized gas during the Epoch of Reionization. These algorithms are all used to run a 100 Mpc/h simulation of reionization with the same initial conditions. Two of the algorithms are state-of-the-art ray-tracing radiative transfer codes that use disparate methods to calculate the ionization history. The other two algorithms are fast but more approximate schemes based on iterative application of a smoothing filter to the underlying source and density fields. We compare these algorithms' resulting ionization and 21 cm fields using several different statistical measures. The two radiative transfer schemes are in excellent agreement with each other (with the cross-correlation coefficient of the ionization fields >0.8 for k < 10 h/Mpc and in good agreement with the analytic schemes (>0.6 for k < 1 h/Mpc). When used to predict the 21cm power spectrum at different times during reionization, all ionization algorithms agree with one another at the 10s of percent level. This agreement suggests that the different approximations involved in the ray tracing algorithms are sensible and that semi-numerical schemes provide a numerically-inexpensive, yet fairly accurate, description of the reionization process.
The photometry from 2MASS, UCAC3 and SuperCosmos catalogues together with the proper motions from the Tycho-2, XPM and UCAC3 catalogues are used to select the all-sky samples of 34 white dwarfs, 1996 evolved and 7769 unevolved subdwarfs candidates for R from 9 to 17 magnitude. The samples are separated from the main sequence with admixture less than 10% owing to the detailed analysis of the distribution of the stars in the different color index (CI) vs. reduced proper motion (RPM) diagrams for various latitudes with special attention to the estimation of admixtures in the samples and with Monte-Carlo simulation. It is shown that the XPM and UCAC3 have the same level of proper motion accuracy. Most of the selected stars has at least 6-band photometry with accuracy is proved to be better than 0.2. The multi-color photometry allows us to eliminate some admixtures and reveal some binaries. The empirical calibrations of absolute magnitude versus CI and RPM for Hipparcos stars give us photometric distances and 3D distribution for all the stars. Although the selection method and uneven distribution of the XPM and UCAC3 data provide noticeable biases the preliminary conclusions are made. The subdwarfs show some concentration to the galactic centre hemisphere with voids because of extinction in the Gould belt and galactic plane. Some yet unexplained overdensities of the evolved subdwarfs are seen in several parts of the sky. For 183 stars with radial velocities 3D motion and galactic orbits are calculated. For 56 stars with Fe/H collected from various sources we find the relations of the metallicity with CI, asymmetric drift velocity and orbital eccentricity. It is shown that most unevolved subdwarfs belong to the halo with the scale height of $8\pm1$ kpc and local mass density of halo subdwarfs of $2\cdot10^{-5} M\sun pc^{-3}$. Most evolved subdwarfs belong to the thick disk with the scale height of $1.25\pm0.1$ kpc. Main parameters of the selected stars are compiled into new SDWD catalogue for future investigations. Special attention should be paid to spectroscopic observations of these stars because 53% of the selected white dwarfs, 94% of evolved and 98% of unevolved subdwarfs are now classified for the first time whereas the existed spectral classification is wrong in many cases.
We compare the surface brightness-inclination relation for a sample of COSMOS pure disk galaxies at z~0.7 with an artificially redshifted sample of SDSS disks well matched to the COSMOS sample in terms of rest-frame photometry and morphology, as well as their selection and analysis. The offset between the average surface brightness of face-on and edge-on disks in the redshifted SDSS sample matches that predicted by measurements of the optical depth of galactic disks in the nearby universe. In contrast, large disks at z~0.7 have a virtually flat surface brightness-inclination relation, suggesting that they are more opaque than their local counterparts. This could be explained by either an increased amount of optically thick material in disks at higher redshift, or a different spatial distribution of the dust.
We present Rossi X-Ray Timing Explorer and Swift observations made during the final three weeks of the 2006-2007 outburst of the super-Eddington neutron star transient XTE J1701-462, as well as Chandra and XMM-Newton observations covering the first ~800 days of the subsequent quiescent phase. The source transitioned quickly from active accretion to quiescence, with the luminosity dropping by over three orders of magnitude in ~13 days. The spectra obtained during quiescence exhibit both a thermal component, presumed to originate in emission from the neutron star surface, and a non-thermal component of uncertain origin, which has shown large and irregular variability. We interpret the observed decay of the inferred effective surface temperature of the neutron star in quiescence as the cooling of the neutron star crust after having been heated and brought out of thermal equilibrium with the core during the outburst. The interpretation of the data is complicated by an apparent temporary increase in temperature ~220 days into quiescence, possibly due to an additional spurt of accretion. We derive an exponential decay timescale of ~120 (+30/-20) days for the inferred temperature (excluding observations affected by the temporary increase). This short timescale indicates a highly conductive neutron star crust. Further observations are needed to confirm whether the crust is still slowly cooling or has already reached thermal equilibrium with the core at a surface temperature of ~125 eV. The latter would imply a high equilibrium bolometric thermal luminosity of ~5x10^{33} erg/s for an assumed distance of 8.8 kpc.
We present high-sensitivity 2'x4' maps of the J=2-1 rotational lines of SiO, CO, 13CO and C18O, observed toward the filamentary Infrared Dark Cloud (IRDC) G035.39-00.33. Single-pointing spectra of the SiO J=2-1 and J=3-2 lines toward several regions in the filament, are also reported. The SiO images reveal that SiO is widespread along the IRDC (size >2 pc), showing two different components: one bright and compact arising from three condensations (N, E and S), and the other weak and extended along the filament. While the first component shows broad lines (linewidths of ~4-7 kms-1) in both SiO J=2-1 and SiO J=3-2, the second one is only detected in SiO J=2-1 and has narrow lines (~0.8 kms-1). The maps of CO and its isotopologues show that low-density filaments are intersecting the IRDC and appear to merge toward the densest portion of the cloud. This resembles the molecular structures predicted by flow-driven, shock-induced and magnetically-regulated cloud formation models. As in outflows associated with low-mass star formation, the excitation temperatures and fractional abundances of SiO toward N, E and S, increase with velocity from ~6 to 40 K, and from ~1E-10 to >1E-8 respectively, over a velocity range of ~7 kms-1. Since 8 micron sources, 24 micron sources and/or extended 4.5 micron emission are detected in N, E and S, broad SiO is likely produced in outflows associated with high-mass protostars. The excitation temperatures and fractional abundances of the narrow SiO lines, however, are very low (~9 K and ~1E-11, respectively), and consistent with the processing of interstellar grains by the passage of a shock with vs~12 kms-1. This emission could be generated i) by a large-scale shock, perhaps remnant of the IRDC formation process; ii) by decelerated or recently processed gas in large-scale outflows driven by 8 micron and 24 micron sources; or iii) by an undetected and widespread population of lower mass protostars. High-angular resolution observations are needed to disentangle between these three scenarios.
We have used a precision calibrated photodiode as the fundamental metrology reference in order to determine the relative throughput of the PanSTARRS telescope and the Gigapixel imager, from 400 nm to 1050 nm. Our technique uses a tunable laser as a source of illumination on a transmissive flat-field screen. We determine the full-aperture system throughput as a function of wavelength, including (in a single integral measurement) the mirror reflectivity, the transmission functions of the filters and the corrector optics, and the detector quantum efficiency, by comparing the light seen by each pixel in the CCD array to that measured by a precision-calibrated silicon photodiode. This method allows us to determine the relative throughput of the entire system as a function of wavelength, for each pixel in the instrument, without observations of celestial standards. We present promising initial results from this characterization of the PanSTARRS system, and we use synthetic photometry to assess the photometric perturbations due to throughput variation across the field of view.
Primordial black holes (PBHs) are expected to accrete particle dark matter around them to form primordially-laid ultracompact minihalos (PLUMs), if the PBHs themselves are not most of the dark matter. We show that if most dark matter is a thermal relic, then the inner regions of PLUMs around PBHs are highly luminous sources of annihilation products. Flux constraints on gamma rays and neutrinos set strong abundance limits, improving previous limits by orders of magnitude. Assuming enough particle dark matter exists to form PLUMs (if PBHs do not compose all of the dark matter), we find that Omega_PBH <~ 10^-4 (for m_DM c^2 ~ 100 GeV) for a vast range in PBH mass, 10^-18 M_sun to 1000 M_sun.
We report the discovery of four kpc-scale binary AGNs. These objects were originally selected from the Sloan Digital Sky Survey based on double-peaked [O III] 4959,5007 emission lines in their fiber spectra. The double peaks could result from pairing active supermassive black holes (SMBHs) in a galaxy merger, or could be due to bulk motions of narrow-line region gas around a single SMBH. Deep near-infrared (NIR) images and optical slit spectra obtained from the Magellan 6.5 m and the APO 3.5 m telescopes strongly support the binary SMBH scenario for the four objects. In each system, the NIR images reveal tidal features and double stellar bulges with a projected separation of several kpc, while optical slit spectra show two Seyfert 2 nuclei spatially coincident with the stellar bulges, with line-of-sight velocity offsets of a few hundred km/s. These objects were drawn from a sample of only 43 objects, demonstrating the efficiency of this technique to find kpc-scale binary AGNs.
The thermal stability of rotating, stratified, unmagnetized atmospheres is studied by means of linear-perturbation analysis, finding stability, overstability or instability, depending on the properties of the gas distribution, but also on the nature of the perturbations. In the relevant case of distributions with outward-increasing specific entropy and angular momentum, axisymmetric perturbations grow exponentially, unless their wavelength is short enough that they are damped by thermal conduction; non-axisymmetric perturbations typically undergo overstable oscillations in the limit of zero conductivity, but are effectively stabilized by thermal conduction, provided rotation is differential. To the extent that the studied models are representative of the poorly constrained hot atmospheres of disc galaxies, these results imply that blob-like, cool overdensities are unlikely to grow in galactic coronae, suggesting an external origin for the high-velocity clouds of the Milky Way.
Spectroscopic and photometric observations show that many globular clusters host multiple stellar populations, challenging the common paradigm that globular clusters are "simple stellar populations" composed of stars of uniform age and chemical composition. The chemical abundances of second-generation (SG) stars constrain the sources of gas out of which these stars must have formed, indicating that the gas must contain matter processed through the high-temperature CNO cycle. First-generation massive Asymptotic Giant Branch (AGB) stars have been proposed as the source of this gas. In a previous study, by means of hydrodynamical and N-body simulations, we have shown that the AGB ejecta collect in a cooling flow in the cluster core, where the gas reaches high densities, ultimately forming a centrally concentrated subsystem of SG stars. In this Letter we show that the high gas density can also lead to significant accretion onto a pre-existing seed black hole. We show that gas accretion can increase the black hole mass by up to a factor of 100. The details of the gas dynamics are important in determining the actual black hole growth. Assuming a near-universal seed black hole mass and small cluster-to-cluster variations in the duration of the SG formation phase, the outcome of our scenario is one in which the present intermediate-mass black hole (IMBH) mass may have only a weak dependence on the current cluster properties. The scenario presented provides a natural mechanism for the formation of an IMBH at the cluster center during the SG star-formation phase.
Multi-zone chemical evolution models (CEMs), differing in the nucleosynthesis prescriptions (yields) and prescriptions of star formation, have been computed for the Milky Way. All models fit the observed O/H and Fe/H gradients well and reproduce the main characteristics of the gas distribution, but they are also designed to do so. For the C/H gradient the results are inconclusive with regards to yields and star formation. The C/Fe and O/Fe vs. Fe/H, as well as C/O vs. O/H trends predicted by the models for the solar neighbourhood zone were compared with stellar abundances from the literature. For O/Fe vs. Fe/H all models fit the data, but for C/O vs. O/H, only models with increased carbon yields for zero-metallicity stars or an evolving initial mass function provide good fits. Furthermore, a steep star formation threshold in the disc can be ruled out since it predicts a steep fall-off in all abundance gradients beyond a certain galactocentric distance (~ 13 kpc) and cannot explain the possible flattening of the C/H and Fe/H gradients in the outer disc seen in observations. Since in the best-fit models the enrichment scenario is such that carbon is primarily produced in low-mass stars, it is suggested that in every environment where the peak of star formation happened a few Gyr back in time, winds of carbon-stars are responsible for most of the carbon enrichment. However, a significant contribution by zero-metallicity stars, especially at very early stages, and by winds of high-mass stars, which are increasing in strength with metallicity, cannot be ruled out by the CEMs presented here. In the solar neighbourhood, as much as 80%, or as little as 40% of the carbon may have been injected to the interstellar medium by low- and intermediate-mass stars. The stellar origin of carbon remains an open question, although production in low- and intermediate-mass stars appears to be the simplest explanation of observed carbon abundance trends.
We consider the 1.5 years Fermi Large Area Telescope light curves (E > 100 MeV) of the flat spectrum radio quasars 3C 454.3 and PKS 1510-089, which show high activity in this period of time. We characterise the duty cycle of the source by comparing the time spent by the sources at different flux levels. We consider in detail the light curves covering periods of extreme flux. The large number of high-energy photons collected by LAT in these events allows us to find evidence of variability on timescales of few hours. We discuss the implications of significant variability on such short timescales, that challenge the scenario recently advanced in which the bulk of the gamma-ray luminosity is produced in regions of the jet at large distances (tens of parsec) from the black hole.
In the first week of December 2009, the blazar 3C 454.3 became the brightest high energy source in the sky. Its photon flux reached and surpassed the level of 1e-5 ph/cm2/s above 100 MeV. The Swift satellite observed the source several times during the period of high gamma-ray flux, and we can construct really simultaneous spectral energy distributions (SED) before, during, and after the luminosity peak. Our main findings are: i) the optical, X-ray and gamma-ray fluxes correlate; ii) the gamma-ray flux varies quadratically (or even more) with the optical flux; iii) a simple one-zone synchrotron inverse Compton model can account for all the considered SED; iv) in this framework the gamma-ray vs optical flux correlation can be explained if the magnetic field is slightly fainter when the overall jet luminosity is stronger; v) the power that the jet spent to produce the peak gamma-ray luminosity is of the same order, or larger, than the accretion disk luminosity. During the flare, the total jet power surely surpassed the accretion power.
We present an analysis of the far-infrared (FIR) spectral energy distributions (SEDs) of two massive K-selected galaxies at z = 2.122 and z = 2.024 detected at 24um, 70um, 160um by Spitzer, 250um, 350um, 500um by BLAST, and 870um by APEX. The large wavelength range of these observations and the availability of spectroscopic redshifts allow us to unambiguously identify the peak of the redshifted thermal emission from dust at ~ 300um. The SEDs of both galaxies are reasonably well fit by synthetic templates of local galaxies with L_IR ~ 10^{11} L_{sun} -- 10^{12} L_{sun} yet both galaxies have L_{IR} ~ 10^{13} L_{sun}. This suggests that these galaxies are not high redshift analogues of local Hyper-LIRGs/ULIRGs, but are instead "scaled up" versions of local ULIRGs/LIRGs. Several lines of evidence point to both galaxies hosting an AGN; however, the relatively cool best fit templates and the optical emission line ratios suggest the AGN is not the dominant source heating the dust. For both galaxies the star formation rate determined from the best-fit FIR SEDs (SFR(L_{IR})) agrees with the SFR determined from the dust corrected H-alpha luminosity (SFR(H-alpha)) to within a factor of ~ 2; however, when the SFR of these galaxies is estimated using only the observed 24um flux and the standard luminosity-dependent template method (SFR(24um)), it systematically overestimates the SFR by as much as a factor of 6. A larger sample of 24 K-selected galaxies at z ~ 2.3 drawn from the Kriek et al. (2008) GNIRS sample shows the same trend between SFR(24um) and SFR(H-alpha). Using that sample we show that SFR(24um) and SFR(H-alpha) are in better agreement when SFR(24um) is estimated using the log average of local templates rather than selecting a single luminosity-dependent template, because this incorporates lower luminosity templates. The better agreement between SFRs from lower luminosity templates suggests that the FIR SEDs of the BLAST-detected galaxies may be typical for z ~ 2 HLIRGs and ULIRGs, and that the majority are scaled up versions of lower luminosity local galaxies.
Aims. The aim of this work is to study the contribution of the Ly-alpha
emitters to the Star Formation Rate Density (SFRD) of the Universe in the
interval 2 < z < 6.6.
Methods. We have assembled a sample of 217 Ly-a emitters (LAE) from the
Vimos-VLT Deep Survey (VVDS) with secure spectroscopic redshifts in the
redshift range 2 < z < 6.62 and fluxes down to F ~ 1.5x10^-18 erg/s/cm^2. 133
LAE are serendipitous identifications in the 22 arcmin^2 total slit area
surveyed with the VVDS-Deep and the 3.3 arcmin^2 from the VVDS Ultra-Deep
survey; 84 are targeted identifications in the 0.62 deg^2 surveyed with the
VVDS-DEEP and 0.16 deg^2 from the Ultra-Deep survey. We have computed the
luminosity function and derived the star formation density from LAE at these
redshifts.
Results. The VVDS-LAE sample reaches faint line fluxes F(Lya) = 1.5x10^-18
erg/s/cm^2 (corresponding to L(Ly)~10^41 erg/s at z ~ 3) enabling to constrain
the faint end slope of the luminosity function to ~ -1.7 for redshifts 2 to ~
6, significantly steeper than estimated in previous studies, indicating that
sub-L* LAE (L[Lya] < 10^42.5 erg/s) contribute significantly to the SFRD. The
projected number density and volume density of faint LAE in 2 < z < 6.6 with F
> 1.5x10^18 erg/s/cm^2 are 33 galaxies/arcmin2 and ~ 4x10^-2 Mpc^-3,
respectively. We find that the the observed luminosity function of LAE does not
evolve from z=2 to z=6. This implies that, after correction for the redshift
dependant IGM absorption and dust, the intrinsic LF must have evolved
significantly over 3 Gyr. The star formation rate density from LAE is found to
be contributing about 20% of the SFRD at z = 2 -- 3 while the LAE appear to be
the dominant source of star formation producing ionizing photons in the early
universe z > 5 -- 6, becoming equivalent to that of Lyman Break Galaxies.
We present precise Doppler measurements of four stars obtained during the past decade at Keck Observatory by the California Planet Survey (CPS). These stars, namely, HD 34445, HD 126614, HD 13931, and Gl 179, all show evidence for a single planet in Keplerian motion. We also present Doppler measurements from the Hobby-Eberly Telescope (HET) for two of the stars, HD 34445 and Gl 179, that confirm the Keck detections and significantly refine the orbital parameters. These planets add to the statistical properties of giant planets orbiting near or beyond the ice line, and merit follow-up by astrometry, imaging, and space-borne spectroscopy. Their orbital parameters span wide ranges of planetary minimum mass (M sin i = 0.38-1.9 M_Jup), orbital period (P = 2.87-11.5 yr), semi-major axis (a = 2.1-5.2 AU), and eccentricity (e = 0.02-0.41). HD 34445b (P = 2.87 yr, M sin i = 0.79 M_Jup, e = 0.27) is a massive planet orbiting an old, G-type star. We announce a planet, HD 126614Ab, and an M dwarf, HD 126614B, orbiting the metal-rich star HD 126614 (which we now refer to as HD 126614A). The planet, HD 126614Ab, has minimum mass M sin i = 0.38 M_Jup and orbits the stellar primary with period P = 3.41 yr and orbital separation a = 2.3 AU. The faint M dwarf companion, HD 126614B, is separated from the stellar primary by 489 mas (33 AU) and was discovered with direct observations using adaptive optics and the PHARO camera at Palomar Observatory. The stellar primary in this new system, HD 126614 A, has the highest measured metallicity (\feh = +0.56) of any known planet-bearing star. HD 13931b (P = 11.5 yr, M sin i = 1.88 M_Jup, e = 0.02) is a Jupiter analog orbiting a near solar twin. Gl 179b (P = 6.3 yr, M sin i = 0.82 M_Jup, e = 0.21) is a massive planet orbiting a faint M dwarf. The high metallicity of Gl 179 is consistent with the planet-metallicity correlation among M dwarfs, as documented recently by Johnson and Apps.
Observations of intensely bright star-forming galaxies both close by and in the distant Universe at first glance seem to emphasize their similarity. But look a little closer, and differences emerge.
A tight linear correlation is established between the HCN line luminosity and the radio continuum (RC) luminosity for a sample of 65 galaxies (from Gao & Solomon's HCN survey), including normal spiral galaxies and luminous and ultraluminous infrared galaxies (LIRGs/ULIRGs). After analyzing the various correlations among the global far-infrared (FIR), RC, CO, and HCN luminosities and their various ratios, we conclude that the FIR-RC and FIR-HCN correlations appear to be linear and are the tightest among all correlations. The combination of these two correlations could result in the tight RC-HCN correlation we observed. Meanwhile, the non-linear RC-CO correlation shows slightly larger scatter as compared with the RC-HCN correlation, and there is no correlation between ratios of either RC/HCN-CO/HCN or RC/FIR-CO/FIR. In comparison, a meaningful correlation is still observed between ratios of RC/CO-HCN/CO. Nevertheless, the correlation between RC/FIR and HCN/FIR also disappears, reflecting again the two tightest FIR-RC and FIR-HCN correlations as well as suggesting that FIR seems to be the bridge that connects HCN with RC. Interestingly, despite obvious HCN-RC and RC-CO correlations, multi-parameter fits hint that while both RC and HCN contribute significantly (with no contribution from CO) to FIR, yet RC is primarily determined from FIR with a very small contribution from CO and essentially no contribution from HCN. These analyses confirm independently the former conclusions that it is practical to use RC luminosity instead of FIR luminosity, at least globally, as an indicator of star formation rate in galaxies including LIRGs/ULIRGs, and HCN is a much better tracer of star-forming molecular gas and correlates with FIR much better than that of CO.
The Na-O anticorrelation seen in almost all globular clusters ever studied using high-resolution spectroscopy is now generally explained by the primordial pollution from the first generation of the intermediate-mass asymptotic giant branch stars to the proto-stellar clouds of the second generation of stars. However, the primordial pollution scenario may not tell the whole story for the observed Na-O anticorrelations in globular clusters. Using the recent data by Carretta and his collaborators, the different shapes of the Na-O anticorrelations for red giant branch stars brighter than and fainter than the red giant branch bump can be clearly seen. If the elemental abundance measurements by Carretta and his collaborators are not greatly in error, this variation in the Na-O anticorrelation against luminosity indicates an internal deep mixing episode during the ascent of the low-mass red giant branch in globular clusters. Our result implies that the multiple stellar population division scheme solely based on [O/Fe] and [Na/Fe] ratios of a globular cluster, which is becoming popular, is not reliable for stars brighter than the red giant branch bump. Our result also suggests that sodium supplied by the deep mixing may alleviate the sodium under-production problem within the primordial asymptotic giant branch pollution scenario.
Hoyle and Folwler showed that there could be Radiation Pressure Supported Stars (RPSS) even in Newtonian gravity. Much later, Mitra found that one could also conceive of their General Relativistic (GR) version, "Relativistic Radiation Pressure Supported Stars" (RRPSSs). While RPSSs have $z\ll 1$, RRPSSs have $z \gg 1$, where $z$ is the surface gravitational redshift. Here we elaborate on the formation of RRPSSs during continued gravitational collapse by recalling that a contracting massive star must start trapping radiation as it would enter its {\em photon sphere}. It is found that, irrespective of the details of the contraction process, the trapped radiation flux should attain the corresponding Eddington value at sufficiently large $z\gg 1$. This means that continued GR collapse may generate an intermediate RRPSS with $z\gg 1$ before a true BH state with $z=\infty$ is formed asymptotically. An exciting consequence of this is that the stellar mass black hole candidates, at present epoch, should be hot balls of quark gluon plasma, as has been discussed by Royzen in a recent article entitled "{\it QCD against black holes?}".
We develop an analytical model to follow the cosmological evolution of magnetic fields in disk galaxies. Our assumption is that fields are amplified from a small seed field via magnetohydrodynamical (MHD) turbulence. We further assume that this process is fast compared to other relevant timescales, and occurs principally in the cold disk gas. We follow the turbulent energy density using the Shabala & Alexander (2009) galaxy formation and evolution model. Three processes are important to the turbulent energy budget: infall of cool gas onto the disk and supernova feedback increase the turbulence; while star formation removes gas and hence turbulent energy from the cold gas. Finally, we assume that field energy is continuously transferred from the incoherent random field into an ordered field by differential galactic rotation. Model predictions are compared with observations of local late type galaxies by Fitt & Alexander (1993) and Shabala et al. (2008). The model reproduces observed magnetic field strengths and luminosities in low and intermediate-mass galaxies. These quantities are overpredicted in the most massive hosts, suggesting that inclusion of gas ejection by powerful AGNs is necessary in order to quench gas cooling and reconcile the predicted and observed magnetic field strengths.
The continuation of resonant periodic orbits from the restricted to the general three body problem is studied in a systematic way. Starting from the Keplerian unperturbed system we obtain the resonant families of the circular restricted problem. Then we find all the families of the resonant elliptic restricted three body problem which bifurcate from the circular model. All these families are continued to the general three body problem, and in this way we can obtain a global picture of all the families of periodic orbits of a two-planet resonant system. We consider planar motion only. We show that the continuation follows a scheme proposed by Bozis and Hadjidemetriou (1976) for symmetric orbits. Our study includes also asymmetric periodic orbits, which exist in cases of external resonances. The families formed by passing from the restricted to the general problem are continued within the framework of the general problem by varying the planetary mass ratio $\rho$. We obtain bifurcations which are caused either due to collisions of the families in the space of initial conditions or due to the vanishing of bifurcation points. Our study refers to the whole range of planetary mass ratio values ($\rho \in (0,\infty)$) and, therefore we include the passage from external to internal resonances. In the present work, our numerical study includes the case of the 2/1 and 1/2 resonance. The same method can be used to study all other planetary resonances.
An empirical model has been developed to reproduce the drift of the spectrum recorded by EIS on board Hinode using instrumental temperatures and relative motion of the spacecraft. The EIS spectrum shows an artificial drift in wavelength dimension in sync with the revolution of the spacecraft, which is caused by temperature variations inside the spectrometer. The drift amounts to 70 km s$^{-1}$ in Doppler velocity and introduces difficulties in velocity measurements. An artificial neural network is incorporated to establish a relationship between the instrumental temperatures and the spectral drift. This empirical model reproduces observed spectrum shift with an RMS error of 4.4 km s$^{-1}$. This procedure is robust and applicable to any spectrum obtained with EIS, regardless of of the observing field. In addition, spectral curvatures and spatial offset in the North - South direction are determined to compensate for instrumental effects.
Context. NRAO 150 is one of the brightest radio and mm AGN sources on the
northern sky. It has been revealed as an interesting source where to study
extreme relativistic jet phenomena. However, its cosmological distance has not
been reported so far, because of its optical faintness produced by strong
Galactic extinction.
Aims. Aiming at measuring the redshift of NRAO 150, and hence to start making
possible quantitative studies from the source.
Methods. We have conducted spectroscopic and photometric observations of the
source in the near-IR, as well as in the optical.
Results. All such observations have been successful in detecting the source.
The near-IR spectroscopic observations reveal strong H$\alpha$ and H$\beta$
emission lines from which the cosmological redshift of NRAO 150
($z=1.517\pm0.002$) has been determined for the first time. We classify the
source as a flat-spectrum radio-loud quasar, for which we estimate a large
super-massive black-hole mass $\sim5\times 10^{9} \mathrm{M_\odot}$. After
extinction correction, the new near-IR and optical data have revealed a
high-luminosity continuum-emission excess in the optical (peaking at
$\sim2000$\,\AA, rest frame) that we attribute to thermal emission from the
accretion disk for which we estimate a high accretion rate, $\sim30$\,% of the
Eddington limit.
Conclusions. Comparison of these source properties, and its broad-band
spectral-energy distribution, with those of Fermi blazars allow us to predict
that NRAO 150 is among the most powerful blazars, and hence a high luminosity
-although not detected yet- $\gamma$-ray emitter.
It is well known that stars orbited by giant planets have higher abundances of heavy elements when compared with average field dwarfs. A number of studies have also addressed the possibility that light element abundances are different in these stars. In this paper we will review the present status of these studies. The most significant trends will be discussed.
The early evolution of Earth's atmosphere and the origin of life took place at a time when physical conditions at the Earth where radically different from its present state. The radiative input from the Sun was much enhanced in the high-energy spectral domain, and in order to model early planetary atmospheres in detail, a knowledge of the solar radiative input is needed. We present an investigation of the atmospheric parameters, state of evolution and high-energy fluxes of the nearby star kap^1 Cet, previously thought to have properties resembling those of the early Sun. Atmospheric parameters were derived from the excitation/ionization equilibrium of Fe I and Fe II, profile fitting of Halpha and the spectral energy distribution. The UV irradiance was derived from FUSE and HST data, and the absolute chromospheric flux from the Halpha line core. From careful spectral analysis and the comparison of different methods we propose for kap^1 Cet the following atmospheric parameters: Teff = 5665+/-30 K (Halpha profile and energy distribution), log g = 4.49+/-0.05 dex (evolutionary and spectroscopic) and [Fe/H] = +0.10+/-0.05 dex (Fe II lines). The UV radiative properties of kap^1 Cet indicate that its flux is some 35% lower than the current Sun's between 210 and 300 nm, it matches the Sun's at 170 nm and increases to at least 2-7 times higher than the Sun's between 110 and 140 nm. The use of several indicators ascribes an age to kap^1 Cet in the interval ~0.4-0.8 Gyr and the analysis of the theoretical HR diagram suggests a mass ~1.04 Msun. This star is thus a very close analog of the Sun when life arose on Earth and Mars is thought to have lost its surface bodies of liquid water. Photochemical models indicate that the enhanced UV emission leads to a significant increase in photodissociation rates compared with those commonly assumed of the early Earth. Our results show that reliable calculations of the chemical composition of early planetary atmospheres need to account for the stronger solar photodissociating UV irradiation.
We report on a detailed abundance analysis of the strongly r-process enhanced giant star, HE 2327-5642 ([Fe/H] = -2.78, [r/Fe] = +0.99). Determination of stellar parameters and element abundances was based on analysis of high-quality VLT/UVES spectra. The surface gravity was calculated from the NLTE ionization balance between Fe I and Fe II, and Ca I and Ca II. Accurate abundances for a total of 40 elements and for 23 neutron-capture elements beyond Sr and up to Th were determined. The heavy element abundance pattern of HE 2327-5642 is in excellent agreement with those previously derived for other strongly r-process enhanced stars. Elements in the range from Ba to Hf match the scaled Solar r-process pattern very well. No firm conclusion can be drawn with respect to a relationship between the fisrt neutron-capture peak elements, Sr to Pd, in HE 2327-5642 and the Solar r-process, due to the uncertainty of the latter. A clear distinction in Sr/Eu abundance ratios was found between the halo stars with different europium enhancement. The strongly r-process enhanced stars reveal a low Sr/Eu abundance ratio at [Sr/Eu] = -0.92+-0.13, while the stars with 0 < [Eu/Fe] < 1 and [Eu/Fe] < 0 have 0.36 dex and 0.93 dex larger Sr/Eu values, respectively. Radioactive dating for HE 2327-5642 with the observed thorium and rare-earth element abundance pairs results in an average age of 13.3 Gyr, when based on the high-entropy wind calculations, and 5.9 Gyr, when using the Solar r-residuals. HE 2327-5642 is suspected to be radial-velocity variable based on our high-resolution spectra, covering ~4.3 years.
We present a status report on the study of gamma-ray bursts (GRB) in the era of rapid follow-up using the world's largest robotic optical telescopes - the 2-m Liverpool and Faulkes telescopes. Within the context of key unsolved issues in GRB physics, we describe (1) our innovative software that allows real-time automatic analysis and interpretation of GRB light curves, (2) the novel instrumentation that allows unique types of observations (in particular, early time polarisation measurements) and (3) the key science questions and discoveries to which robotic observations are ideally suited, concluding with a summary of current understanding of GRB physics provided by combining rapid optical observations with simultaneous observations at other wavelengths.
The evolution of high order correlation functions of test scalar fields in arbitrary inflationary backgrounds is computed. Taking advantage of the fact that quantum field theory calculations can be mapped, for super-horizon scales, into those of a classical system, we express the expected correlation functions in terms of classical quantities, power spectra, Green functions, that can be easily computed in the long-wavelength limit. Explicit results are presented that extend those already known for a de Sitter background. In particular the expressions of the late time amplitude of bispectrum and trispectrum in terms of the the expansion factor behavior are given. When compared to the case of a de Sitter background, power law inflation and chaotic inflation induced by a massive field are found to induce high order correlation functions the amplitudes of which are amplified by almost one order of magnitude.
Context: The winter seeing at Concordia is essentially bimodal, excellent or quite poor, with relative proportions that depend on altitude above the snow surface. This paper studies the temporal behavior of the good seeing sequences. Aims: An efficient exploitation of extremely good seeing with an adaptive optics system needs long integrations. It is then important to explore the temporal distribution of the fraction of time providing excellent seeing. Methods: Temporal windows of good seeing are created by a simple binary process. Good or bad. Their autocorrelations are corrected for those of the existing data sets, since these are not continuous, being often interrupted by technical problems in addition to the adverse weather gaps. At the end these corrected autocorrelations provide the typical duration of good seeing sequences. This study has to be a little detailed as its results depend on the season, summer or winter. Results: Using a threshold of 0.5 arcsec to define the "good seeing", three characteristic numbers are found to describe the temporal evolution of the good seeing windows. The first number is the mean duration of an uninterrupted good seeing sequence: it is $\tau_0=7.5$ hours at 8 m above the ground (15 hours at 20 m). These sequences are randomly distributed in time, with a negative exponential law of damping time $\tau_1=29$ hours (at elevation 8 m and 20 m). The third number is the mean time between two 29 hours episodes. It is T=10 days at 8 m high (5 days at 20 m).
Globular clusters with their large populations of millisecond pulsars (MSPs) are believed to be potential emitters of high-energy gamma-ray emission. The observation of this emission provides a powerful tool to assess the millisecond pulsar population of a cluster, is essential for understanding the importance of binary systems for the evolution of globular clusters, and provides complementary insights into magnetospheric emission processes. Our goal is to constrain the millisecond pulsar populations in globular clusters from analysis of gamma-ray observations. We use 546 days of continuous sky-survey observations obtained with the Large Area Telescope aboard the Fermi Gamma-ray Space Telescope to study the gamma-ray emission towards 13 globular clusters. Steady point-like high-energy gamma-ray emission has been significantly detected towards 8 globular clusters. Five of them (47 Tucanae, Omega Cen, NGC 6388, Terzan 5, and M 28) show hard spectral power indices $(0.7 < \Gamma <1.4)$ and clear evidence for an exponential cut-off in the range 1.0-2.6 GeV, which is the characteristic signature of magnetospheric emission from MSPs. Three of them (M 62, NGC 6440 and NGC 6652) also show hard spectral indices $(1.0 < \Gamma < 1.7)$, however the presence of an exponential cut-off can not be unambiguously established. Three of them (Omega Cen, NGC 6388, NGC 6652) have no known radio or X-ray MSPs yet still exhibit MSP spectral properties. From the observed gamma-ray luminosities, we estimate the total number of MSPs that is expected to be present in these globular clusters. We show that our estimates of the MSP population correlate with the stellar encounter rate and we estimate 2600-4700 MSPs in Galactic globular clusters, commensurate with previous estimates. The observation of high-energy gamma-ray emission from a globular cluster thus provides a reliable independent method to assess their millisecond pulsar populations that can be used to make constraints on the original neutron star X-ray binary population, essential for understanding the importance of binary systems in slowing the inevitable core collapse of globular clusters.
The B2Vn star HR 7355 is found to be a He-rich magnetic star. Spectropolarimetric data were obtained with FORS1 at UT2 on Paranal observatory to measure the disk-averaged longitudinal magnetic field at various phases of the presumed 0.52 d cycle. A variable magnetic field with strengths between B_z = -2200 and +3200G was found, with confidence limits of 100 to 130G. The field topology is that of an oblique dipole, while the star itself is seen about equator-on. In the intensity spectra the HeI-lines show the typical equivalent width variability of He-strong stars, usually attributed to surface abundance spots. The amplitudes of the equivalent width variability of the HeI lines are extraordinarily strong compared to other cases. These results not only put HR 7355 unambiguously among the early-type magnetic stars, but confirm its outstanding nature: With v sin i = 320 km/s the parameter space in which He-strong stars are known to exist has doubled in terms of rotational velocity.
We investigate the nature and possible evolution of the young Galactic star clusters Collinder 197 (Cr 197) and vdB 92. The colour-magnitude diagrams (CMDs) are basically characterised by a poorly-populated MS and a dominant fraction ($\ga75%$) of PMS stars, and the combined MS and PMS CMD morphology in both clusters consistently constrains the age to within $5\pm4$ Myr, with a $\sim10$ Myr spread in the star formation process. The MS$ + $PMS stellar masses are $\approx660^{+102}_{-59} \ms$ (Cr 197) and $\approx750^{+101}_{-51} \ms$ (vdB 92). Cr 197 and vdB 92 appear to be abnormally large, when compared to clusters within the same age range. They have irregular stellar radial density distributions (RDPs) with a marked excess in the innermost region, a feature that, at less than 10 Myr, is more likely related to the star formation and/or molecular cloud fragmentation than to age-dependent dynamical effects. The velocity dispersion of both clusters, derived from proper motions, is in the range $\sim15 - 22 \kms$. Both clusters appear to be in a super-virial state, with velocity dispersions higher than those expected of nearly-virialised clusters of similar mass and size. A possible interpretation is that Cr 197 and vdB 92 deviate critically from dynamical equilibrium, and may dissolve into the field. We also conclude that early cluster dissolution leaves detectable imprints on RDPs of clusters as massive as several $10^2 \ms$. Cr 197 and vdB 92 may be the link between embedded clusters and young stellar associations.
A survey of young bipolar outflows in regions of low-to-intermediate-mass star formation has been carried out in two class I methanol maser transitions: 7_0-6_1A+ at 44 GHz and 4_{-1}-3_0E at 36 GHz. We detected narrow features towards NGC 1333I2A, NGC 1333I4A, HH25MMS, and L1157 at 44 GHz, and towards NGC 2023 at 36 GHz. Flux densities of the lines detected at 44 GHz are no higher than 11 Jy and the relevant source luminosities are about 10^{22} erg s{-1}, which is much lower than those of strong masers in high-mass star formation regions. No emission was found towards 39 outflows. All masers detected at 44 GHz are located in clouds with methanol column densities of the order of or larger than a few x 10^{14} cm$^{-2}. The upper limits for the non-detections are typically of the order of 3--5 Jy. Observations in 2004, 2006, and 2008 did not reveal any significant variability of the 44 GHz masers in NGC 1333I4A, HH25MMS, and L1157.
Variations in the equivalent width of the neutral potassium line at 7699A are reported, during ingress and into totality of the current eclipse of the enigmatic eclipsing binary epsilon Aurigae. The increase and plateaus of line strength are correlated with new system parameters and interferometric imaging constraints, plus ancillary data being reported contemporaneously. Together, these data reveal structural details of the transiting disc, never before measured. Measured ring and gap placements do not immediately fit any proposed model using simple tidal estimation. However, we predict egress times of interest and urge continued monitoring of this star during the balance of its eclipse, and encourage theoretical treatment of the disc substructure to be pursued.
We report the detection of a strong, organized magnetic field in the helium-variable early B-type star HR 7355 using spectropolarimetric data obtained with ESPaDOnS on the 3.6-m Canada-France-Hawaii Telescope within the context of the Magnetism in Massive Stars (MiMeS) Large Program. HR 7355 is both the most rapidly rotating known main-sequence magnetic star and the most rapidly rotating helium-strong star, with $v \sin i$ = 300 $\pm$ 15 km s$^{-1}$ and a rotational period of 0.5214404 $\pm$ 0.0000006 days. We have modeled our eight longitudinal magnetic field measurements assuming an oblique dipole magnetic field. Constraining the inclination of the rotation axis to be between $38^{\circ}$ and $86^{\circ}$, we find the magnetic obliquity angle to be between $30^{\circ}$ and $85^{\circ}$, and the polar strength of the magnetic field at the stellar surface to be between 13-17 kG. The photometric light curve constructed from HIPPARCOS archival data and new CTIO measurements shows two minima separated by 0.5 in rotational phase and occurring 0.25 cycles before/after the magnetic extrema. This photometric behavior coupled with previously-reported variable emission of the H$\alpha$ line (which we confirm) strongly supports the proposal that HR 7355 harbors a structured magnetosphere similar to that in the prototypical helium-strong star, $\sigma$ Ori E.
We present integral field spectroscopic observations of the central region of the active galaxy NGC 4258 obtained with the fibre IFU system INTEGRAL. We have been able to detect cold neutral gas by means of the interstellar NaD doublet absorption and to trace its distribution and kinematics with respect to the underlying disc. The neutral gas is blue-shifted with projected velocities in the 120--370 km/s range. We have also detected peculiar kinematics in part of the ionized gas in this region by means of a careful kinematic decomposition. The bipolar spatial distribution of the broader component is roughly coincident with the morphology of the X-ray diffuse emission. The kinematics of this gas can be explained in terms of expansion at very high (projected) velocities of up to 300 km/s. The observations also reveal the existence of a strip of neutral gas, parallel to the major kinematic axis, that is nearly coincident with a region of very high [SII]/H$\alpha$ ratio tracing the shocked gas. Our observations are consistent with the jet model presented by \cite{wilsonetal01} in which a cocoon originating from the nuclear jet is shocking the gas in the galaxy disc. Alternatively, our observations are also consistent with the bipolar hypershell model of \cite{Sofue80} and \cite{SofueandVogler01}. On balance, we prefer the latter model as the most likely explanation for the puzzling features of this peculiar object.
We monitored the flaring blazar 3C 454.3 during 2005 June-July with the Spitzer Infrared Spectrograph (IRS: 15 epochs), Infrared Array Camera (IRAC: 12 epochs) and Multiband Imaging Photometer (MIPS: 2 epochs). We also made Spitzer IRS, IRAC, and MIPS observations from 2006 December-2007 January when the source was in a low state, the latter simultaneous with a single Chandra X-ray observation. In addition, we present optical and sub-mm monitoring data. The 2005-2007 period saw 3 major outbursts. We present evidence that the radio-optical SED actually consists of two variable synchrotron peaks, the primary at IR and the secondary at sub-mm wavelengths. The lag between the optical and sub-mm outbursts may indicate that these two peaks arise from two distinct regions along the jet separated by a distance of 0.07-5 pc. The flux at 5-35 microns varied by a factor of 40 and the IR peak varied in frequency from <1E13 Hz to 4E13 Hz between the highest and lowest states in 2005 and 2006, respectively. Variability was well correlated across the mid-IR band, with no measurable lag. Flares that doubled in flux occurred on a time scale of 3 days. The IR SED peak moved to higher frequency as a flare brightened, then returned to lower frequency as it decayed. The fractional variability amplitude increased with frequency, which we attribute to decreasing synchrotron-self absorption optical depth. Mid-IR flares may signal the re-energization of a shock that runs into inhomogeneities along the pre-existing jet or in the external medium. The synchrotron peak frequencies during each major outburst may depend upon both the distance from the jet apex and the physical conditions in the shocks. Variation of the Doppler parameter along a curved or helical jet is another possibility. Frequency variability of the IR synchrotron peak may have important consequences for the interpretation of the blazar sequence, and the presence of a secondary peak may give insight into jet structure.
In the last few years multiwavelength observations have boosted our understanding of Ultraluminous X-ray Sources (ULXs). Yet, the most fundamental questions on ULXs still remain to be definitively answered: do they contain stellar or intermediate mass black holes? How do they form? We investigate the possibility that the black holes hosted in ULXs originate from massive (40-120 $M_\odot$) stars in low metallicity natal environments. Such black holes have a typical mass in the range $\sim 30-90 M_\odot$ and may account for the properties of bright (above $\sim 10^{40}$ erg s$^{-1}$) ULXs. More than $\sim 10^5$ massive black holes might have been generated in this way in the metal poor Cartwheel galaxy during the last $10^7$ years and might power most of the ULXs observed in it. Support to our interpretation comes from NGC 1313 X-2, the first ULX with a tentative identification of the orbital period in the optical band, for which binary evolution calculations show that the system is most likely made by a massive donor dumping matter on a $50-100 M_\odot$ black hole.
Degenerate ignition of helium in low-mass stars at the end of the red giant branch phase leads to dynamic convection in their helium cores. One-dimensional (1D) stellar modeling of this intrinsically multi-dimensional dynamic event is likely to be inadequate. Previous hydrodynamic simulations imply that the single convection zone in the helium core of metal-rich Pop I stars grows during the flash on a dynamic timescale. This may lead to hydrogen injection into the core, and a double convection zone structure as known from one-dimensional core helium flash simulations of low-mass Pop III stars. We perform hydrodynamic simulations of the core helium flash in two and three dimensions to better constrain the nature of these events. To this end we study the hydrodynamics of convection within the helium cores of a 1.25 \Msun metal-rich Pop I star (Z=0.02), and a 0.85 \Msun metal-free Pop III star (Z=0) near the peak of the flash. These models possess single and double convection zones, respectively. We use 1D stellar models of the core helium flash computed with state-of-the-art stellar evolution codes as initial models for our multidimensional hydrodynamic study, and simulate the evolution of these models with the Riemann solver based hydrodynamics code Herakles which integrates the Euler equations coupled with source terms corresponding to gravity and nuclear burning. The hydrodynamic simulation of the Pop I model involving a single convection zone covers 27 hours of stellar evolution, while the first hydrodynamic simulations of a double convection zone, in the Pop III model, span 1.8 hours of stellar life. We find differences between the predictions of mixing length theory and our hydrodynamic simulations. The simulation of the single convection zone in the Pop I model shows a strong growth of the size of the convection zone due to turbulent entrainment. Hence we predict that for the Pop I model a hydrogen injection phase (i.e. hydrogen injection into the helium core) will commence after about 23 days, which should eventually lead to a double convection zone structure known from 1D stellar modeling of low-mass Pop III stars. Our two and three-dimensional hydrodynamic simulations of the double (Pop III) convection zone model show that the velocity field in the convection zones is different from that predicted by stellar evolutionary calculations. The simulations suggest that the double convection zone decays quickly, the flow eventually being dominated by internal gravity waves.
The origin of the extragalactic gamma-ray background is a pressing cosmological mystery. The Fermi Gamma-Ray Space Telescope has recently measured the intensity and spectrum of this background; both are substantially different from previous measurements. This revision demands a re-evaluation of the sources for the cosmic signal. We present a novel calculation of the gamma-ray background from star-forming galaxies like our own. Contrary to longstanding expectations, we find that numerous but individually faint normal galaxies comprise the bulk of the Fermi signal, rather than rare but intrinsically bright active galaxies. The return of star-forming galaxies to dominate the extragalactic gamma-ray sky has wide-ranging implications, including: the possibility to probe cosmic star-formation history with gamma rays; the ability to infer the cosmological evolution of cosmic rays and galactic magnetic fields; and an increased likelihood to identify subdominant components from rare sources (e.g., dark matter clumps) through their large anisotropy.
SNS is a MATLAB-based software library written to aid in the design and analysis of receiver architectures. It uses electrical scattering matrices and noise wave vectors to describe receiver architectures of arbitrary topology and complexity. It differs from existing freely-available software mainly in that the scattering matrices used to describe the receiver and its components are analytic rather than numeric. This allows different types of modeling and analysis of receivers to be performed. Non-ideal behavior of receiver components can be parameterized in their scattering matrices. SNS enables the instrument designer to then derive analytic expressions for the signal and noise at the receiver outputs in terms of parameterized component imperfections, and predict their contribution to receiver systematic errors precisely. This can drive the receiver design process by, for instance, allowing the instrument designer to identify which component imperfections contribute most to receiver systematic errors, and hence place firm specifications on individual components. Using SNS to perform this analysis is preferable to traditional Jones matrix-based analysis as it includes internal reflections and is able to model noise: two effects which Jones matrix analysis is unable to describe. SNS can be used to model any receiver in which the components can be described by scattering matrices. Of particular interest to the sub-mm and terahertz frequency regime is the choice between coherent and direct detection technologies. Steady improvements in mm and sub-mm Low Noise Amplifiers (LNAs) mean that coherent receivers with LNAs as their first active element are becoming increasingly competitive, in terms of sensitivity, with bolometer-based receivers at frequencies above ~100 GHz. As an example of the utility of SNS, we use it to compare two polarimeter architectures commonly used to perform measurements of the polarized Cosmic Microwave Background: differencing polarimeters, an architecture commonly used in polarization sensitive bolometer-based polarimeters; and pseudo-correlation polarimeters, an architecture commonly used in coherent, LNA-based, polarimeters. We parameterize common sources of receiver systematic errors in both architectures and compare them through their Mueller matrices, which encode how well the instruments measure the Stokes parameters of the incident radiation. These analytic Mueller matrices are used to demonstrate the different sources of systematic errors in differencing and correlation polarimeters.
It is not easy to identify and classify low-amplitude variables, but it is important that the classification is done correctly. We use photometry and spectroscopy to classify low-amplitude variables in a 246 deg^2 part of the Akerlof et al. (2002) field. Akerlof and collaborators found that 38% of the RR Lyrae stars in their 2000 deg^2 test field were RR1 (type c). This suggests that these RR Lyrae stars belong to an Oosterhoff Type II population while their period distribution is primarily Oosterhoff Type I. Our observations support their RR0 (type ab) classifications, however 6 of the 7 stars that they classified as RR1 (type c) are eclipsing binaries. Our classifications are supported by spectroscopic metallicities, line-broadening and Galactic rotation measurements. Our 246 deg^2 field contains 16 RR Lyrae stars that are brighter than m_R = 14.5; only four of these are RR1 (type c). This corresponds to an Oosterhoff Type I population in agreement with the period distribution.
We present new B, V and I CCD time-series photometry for 177 variable stars in a 13'X 13' field centered on the globular cluster M54 (lying at the center of the Sagittarius dwarf spheroidal galaxy), 94 of which are newly identified variables. The total sample is composed of 2 anomalous Cepheids, 144 RR Lyrae stars (108 RR0 and 36 RR1), 3 SX Phoenicis, 7 eclipsing binaries (5 W UMA and 2 Algol binaries), 3 variables of uncertain classification and 18 long-period variables. The large majority of the RR Lyrae variables likely belong to M54. Ephemerides are provided for all the observed short-period variables. The pulsational properties of the M54 RR Lyrae variables are close to those of Oosterhoff I clusters, but a significant number of long-period ab type RR Lyrae are present. We use the observed properties of the RR Lyrae to estimate the reddening and the distance modulus of M54, E(B-V)=0.16 +/- 0.02 and (m-M)_0=17.13 +/- 0.11, respectively, in excellent agreement with the most recent estimates. The metallicity has been estimated for a subset of 47 RR Lyrae stars, with especially good quality light curves, from the Fourier parameters of the V light curve. The derived metallicity distribution has a symmetric bell shape, with a mean of <[Fe/H]>=-1.65 and a standard deviation sigma=0.16 dex. Seven stars have been identified as likely belonging to the Sagittarius galaxy, based on their too high or too low metallicity. This evidence, if confirmed, might suggest that old stars in this galaxy span a wide range of metallicities.
We show that for four-dimensional spacetimes with a hypersurface orthogonal Killing vector and for a Chern-Simons (CS) background scalar field, which is constant along the Killing vector, the source-free equations of CS modified gravity decouple into their Einstein and Cotton constituents. Thus, the model supports only general relativity solutions. We also show that, when the cosmological constant vanishes and the gradient of the CS scalar field is parallel to the hypersurface orthogonal Killing vector of constant length, CS modified gravity reduces to topologically massive gravity in three dimensions. Meanwhile, with the cosmological constant such a reduction requires an appropriate source term for CS modified gravity.
Many classical scalar field theories possess remarkable solutions: coherently oscillating, localized clumps, known as oscillons. In many cases, the decay rate of classical small amplitude oscillons is known to be exponentially suppressed and so they are extremely long lived. In this work we compute the decay rate of quantized oscillons. We find it to be a power law in the amplitude and couplings of the theory. Therefore, the quantum decay rate is very different to the classical decay rate and is often dominant. We show that essentially all oscillons eventually decay by producing outgoing radiation. In single field theories the outgoing radiation has typically linear growth, while if the oscillon is coupled to other bosons the outgoing radiation can have exponential growth. The latter is a form of parametric resonance: explosive energy transfer from a localized clump into daughter fields. This may lead to interesting phenomenology in the early universe. Our results are obtained from a perturbative analysis, a non-perturbative Floquet analysis, and numerics.
We compute the transition amplitude between coherent quantum-states of geometry peaked on homogeneous isotropic metrics. We use the holomorphic representations of loop quantum gravity and the Kaminski-Kisielowski-Lewandowski generalization of the new vertex, and work at first order in the vertex expansion, second order in the graph (multipole) expansion, and first order in 1/volume. We show that the resulting amplitude is in the kernel of a differential operator whose classical limit is the canonical hamiltonian of a Friedmann-Robertson-Walker cosmology. This result is an indication that the dynamics of loop quantum gravity defined by the new vertex yields the Friedmann equation in the appropriate limit.
The nonlinear memory effect is a slowly-growing, non-oscillatory contribution to the gravitational-wave amplitude. It originates from gravitational waves that are sourced by the previously emitted waves. In an ideal gravitational-wave interferometer a gravitational-wave with memory causes a permanent displacement of the test masses that persists after the wave has passed. Surprisingly, the nonlinear memory affects the signal amplitude starting at leading (Newtonian-quadrupole) order. Despite this fact, the nonlinear memory is not easily extracted from current numerical relativity simulations. After reviewing the linear and nonlinear memory I summarize some recent work, including: (1) computations of the memory contribution to the inspiral waveform amplitude (thus completing the waveform to third post-Newtonian order); (2) the first calculations of the nonlinear memory that include all phases of binary black hole coalescence (inspiral, merger, ringdown); and (3) realistic estimates of the detectability of the memory with LISA.
K-shell photoabsorption cross sections for the isonuclear C I - C IV ions have been computed using the R-matrix method. Above the K-shell threshold, the present results are in good agreement with the independent-particle results of Reilman & Manson (1979). Below threshold, we also compute the strong 1s -> np absorption resonances with the inclusion of important spectator Auger broadening effects. For the lowest 1s -> 2p, 3p resonances, comparisons to available C II, C III, and C IV experimental results show good agreement in general for the resonance strengths and positions, but unexplained discrepancies exist. Our results also provide detailed information on the C I K-shell photoabsorption cross section including the strong resonance features, since very limited laboratory experimental data exist. The resultant R-matrix cross sections are then used to model the Chandra X-ray absorption spectrum of the blazar Mkn 421.
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