A systematic X-ray survey of the most energetic rotation-powered pulsars known, based on spin-down energy loss rate, $\dot E$ = $I\omega\dot\omega$, shows that all energetic pulsars with $\dot E > \dot E_{c} \approx 3.4 \times\ 10^{36}$ erg s$^{-1}$ are X-ray bright, manifest a distinct pulsar wind nebula (PWN), and are associated with a supernova event, either historically or via a thermal remnant, with over half residing in shell-like supernova remnants. Below $\dot E_c$, the 2-10 keV PWN flux ratio $F_{PWN}/F_{PSR}$ decreases by an order-of-magnitude. This threshold is predicted by the lower limit on the spectral slope $\Gamma_{min} \approx 0.5$ observed for rotation-powered pulsars (Gotthelf 2003). The apparent lack of bright pulsar nebulae below a critical Edot suggests a change in the particle injection spectrum and serves as a constraint on emission models for rotation-powered pulsars. Neither a young age nor a high density environment is found to be a sufficient condition for generating a PWN, as often suggested, instead the spin-down energy loss rate is likely the key parameter in determining the evolution of a rotation-powered pulsar.
The question of whether intelligent life exists elsewhere is one of the fundamental unknowns about our Universe. Over the past decade >200 extra-solar planets have been discovered, providing new urgency for addressing this question in these or other planetary systems. Independently of this perspective, new radio observatories for cosmology are currently being constructed with the goal of detecting 21cm emission from cosmic hydrogen in the redshift range 6<z<15. For example, the Low-Frequency Demonstrator (LFD) of the Mileura Wide-Field Array (MWA), will cover in 8 kHz bins the entire frequency range of 80-300 MHz, which is perfectly matched to the band over which our civilization emits most of its radio power. We show that this and other low-frequency observatories (culminating with the Square Kilometer Array [SKA]) will be able to detect radio broadcast leakage from an Earth-like civilization out to a distance of ~10-500pc, within a spherical volume containing 10^3-10^8 stars. Such a radio signal will show-up as a series of narrow spectral lines that do not coincide with known atomic or molecular lines. The high spectral resolution attainable with the upcoming observatories will allow to monitor the periodic Doppler shift of the broadcasted lines over the planet's orbital period around the parent star. Determination of the parent star mass through observations of its spectrum could then be used to infer the inclination, semi-major axis and eccentricity of the planet's orbit. This, in turn, will alow to estimate the temperature on the planet's surface and to assess whether it can support liquid water or life as we know it.
We report single-dish observations of 12CO, 13CO, C18O, HCN, HNC, HNCO, CS, and HCO+ molecular line emission in the two ultraluminous infra-red galaxies Arp220 and NGC6240. Using this new molecular line inventory in conjunction with existing data in the literature, we have compiled the most extensive molecular line data sets to date of such galaxies. These include rotational transitions of molecules with very different excitation requirements, thus allowing us to probe molecular gas phases with widely different densities and temperatures. In particular, we obtain strong constraints on the properties of the dense gas phase in Arp220 and NGC6240, from which we obtain best estimates of the dense (>10^4 cm^-3) gas mass in these two systems of M_dense = (0.6 - 2.0) x 10^10 Msun and M_dense = (0.8 - 2.4) x 10^10 Msun, respectively. Such large dense gas masses suggest that the bulk of the total gas reservoir in Arp220 and NGC6240 is in the dense phase -- consistent with the notion that most of their IR luminosities are powered by intense star bursts. Our analysis suggest that HCO+/HCN/CS probe progressively denser gas (by factors of ten), consistent with the dense phase residing in a hierarchical structure with denser gas nested inside less dense regions. In particular, we find, contrary to recent claims, that HCN is a better tracer of dense gas than HCO+, which is sub-thermally excited in both systems, thus supporting the notion that HCN can be used to derive reliable dense gas masses and star formation efficiencies. However, whether this is true in IR-luminous, star forming galaxies in general, remains to be seen, and underlines the need for high-J, high-dipole observations of large samples of low- to moderate-z ULIRGs -- a task which we show the HI-FI instrument on board Herschel is ideally suited to do.
There are several lines of evidence which suggest that the relativistic outflows in gamma-ray bursts (GRBs) are collimated into narrow jets. The jet structure has important implications for the true energy release and the event rate of GRBs, and can constrain the mechanism responsible for the acceleration and collimation of the jet. Nevertheless, the jet structure and its dynamics as it sweeps up the external medium and decelerates, are not well understood. In this review I discuss our current understanding of GRB jets, stressing their structure and dynamics.
We present a detailed investigation of the incidence of circumnuclear dust structure in a large, well-matched sample of early-type galaxies with and without Active Galactic Nuclei (AGN). All 34 early-type AGN hosts in our sample have circumnuclear dust, while dust is only observed in 26% (nine) of a pair-matched sample of 34 early-type, inactive galaxies. This result demonstrates a strong correlation between the presence of circumnuclear dust and accretion onto the central, supermassive black hole in elliptical and lenticular galaxies. This correlation is not present at later Hubble types, where a sample of 31 active and 31 inactive galaxies all contain circumnuclear dust. These archival, HST observations reveal a wide range of mostly chaotic dust morphologies. Current estimates suggest the dust settling or destruction time is on order of 10^8 years and therefore the presence of dust in ~ 50% of early-type galaxies requires frequent replenishment and similarly frequent fueling of their central, supermassive black holes. The observed dust could be internally-produced (via stellar winds) or externally-accreted, although there are observational challenges for both of these scenarios. Our analysis also reveals that approximately a third of the early-type galaxies without circumnuclear dust have nuclear stellar disks. These nuclear stellar disks may provide a preferred kinematic axis to externally-accreted material and this material may in turn form new stars in these disks. The observed incidence of nuclear stellar disks and circumnuclear dust suggests that episodic replenishment of nuclear stellar disks occurs and is approximately concurrent with the fueling of the central AGN.
We present a census of the population of deeply embedded young stellar objects (YSOs) in the Perseus molecular cloud complex based on a combination of Spitzer Space Telescope mid-IR data from the c2d legacy team and JCMT/SCUBA submillimeter maps from the COMPLETE team. The mid-IR sources detected at 24 micron and having [3.6]-[4.5] > 1 are located close to the center of the SCUBA cores, typically within 15" of their peaks. The narrowness of the spatial distribution of mid-IR sources around the peaks of the SCUBA cores suggests that no significant dispersal of the newly formed YSOs has occurred. This argues against the suggestion that motions of protostars regulate the time scales over which significant (Bondi-Hoyle) accretion can occur. The most deeply embedded YSOs are found in regions with high extinction, AV > 5, similar to the extinction threshold observed for the SCUBA cores. All the SCUBA cores with high concentrations have embedded YSOs, but not all cores with low concentrations are starless. An unbiased sample of 49 deeply embedded YSOs is constructed. Embedded YSOs are found in 40 of the 72 SCUBA cores with only three cores harboring multiple embedded YSOs within 15". The equal number of SCUBA cores with and without embedded YSOs suggests that the time scale for the evolution through the dense prestellar stages, where the cores are recognized in the submillimeter maps and have central densities of 5e4-1e5 cm^{-3}, is similar to the time scale for the embedded protostellar stages. The current star formation efficiency of cores is estimated to be approximately 10-15%. In contrast, the star formation efficiency averaged over the cloud life time and compared to the total cloud mass is only a few percent, reflecting also the efficiency in assembling cloud material into the dense cores forming stars.
A significant new development in the study of Anomalous X-ray Pulsars (AXPs) has been the recent discovery by INTEGRAL and RXTE of flat, hard X-ray components in three AXPs. These non-thermal spectral components differ dramatically from the steeper quasi-power-law tails seen in the classic X-ray band in these sources. A prime candidate mechanism for generating this new component is resonant, magnetic Compton upscattering. This process is very efficient in the strong magnetic fields present in AXPs. Here an introductory exploration of an inner magnetospheric model for upscattering of surface thermal X-rays in AXPs is offered, preparing the way for an investigation of whether such resonant upscattering can explain the 20-150 keV spectra seen by INTEGRAL. Characteristically flat emission spectra produced by non-thermal electrons injected in the emission region are computed using collision integrals. A relativistic QED scattering cross section is employed so that Klein-Nishina reductions are influential in determining the photon spectra and fluxes. Spectral results depend strongly on the magnetospheric locale of the scattering and the observer's orientation, which couple directly to the angular distributions of photons sampled.
I present results from numerical simulations of gas dynamics outside luminous accretion disks in active galactic nuclei. The gas, gravitationally captured by a super massive black hole, can be driven away by the energy and momentum of the radiation emitted during black hole accretion. Assuming axisymmetry, I study how the mass accretion and outflow rates, and the flow dynamics respond to changes in radiation heating relative to radiation pressure. I find that for a 10^8 MSUN black hole with the accretion luminosity of 0.6 of the Eddington luminosity the flow settles into a steady state and has two components: (1) an equatorial inflow and (2) a bipolar inflow/outflow with the outflow leaving the system along the disk rotational axis. The inflow is a realization of a Bondi-like accretion flow. The second component is an example of a non-radial accretion flow which becomes an outflow once it is pushed close to the rotational axis where thermal expansion and radiation pressure accelerate it outward. The main result of this preliminary work is that although the above two-component solution is robust, its properties are sensitive to the geometry and spectral energy distribution of the radiation field.
We present mid-infrared Spitzer-IRS spectra of the well-known UX Orionis star VV Ser. We combine the Spitzer data with interferometric and spectroscopic data from the literature covering UV to submillimeter wavelengths. The full set of data are modeled by a two-dimensional axisymmetric Monte Carlo radiative transfer code. The model is used to test the prediction of (Dullemond et al. 2003) that disks around UX Orionis stars must have a self-shadowed shape, and that these disks are seen nearly edge-on, looking just over the edge of a puffed-up inner rim, formed roughly at the dust sublimation radius. We find that a single, relatively simple model is consistent with all the available observational constraints spanning 4 orders of magnitude in wavelength and spatial scales, providing strong support for this interpretation of UX Orionis stars. The grains in the upper layers of the puffed-up inner rim must be small (0.01-0.4 micron) to reproduce the colors (R_V ~ 3.6) of the extinction events, while the shape and strength of the mid-infrared silicate emission features indicate that grains in the outer disk (> 1-2 AU) are somewhat larger (0.3-3.0 micron). From the model fit, the location of the puffed-up inner rim is estimated to be at a dust temperature of 1500 K or at 0.7-0.8 AU for small grains. This is almost twice the rim radius estimated from near-infrared interferometry. A best fitting model for the inner rim in which large grains in the disk mid-plane reach to within 0.25 AU of the star, while small grains in the disk surface create a puffed-up inner rim at ~0.7-0.8 AU, is able to reproduce all the data, including the near-infrared visibilities. [Abstract abridged]
We present mid-infrared Spitzer IRAC and MIPS images of the UX Orionis star VV Ser and the surrounding cloud. The 5.6--70 micron images show bright, localized and nebulous emission extended over 4 arcmin centered on VV Ser. We interpret the nebulosity as being due to transiently heated grains excited by UV photons emitted by VV Ser. A companion paper describes how the physical structure of the VV Ser disk has been constrained using a wide range of observational data modeled by an axisymmetric Monte Carlo radiative transfer code. In this paper we employ the model to study the nebulosity surrounding VV Ser using quantum-heated PAH molecules and Very Small Grains (VSGs) consisting of amorphous carbon in the thermal cooling approximation. Imprinted on the nebulosity is a wedge-shaped dark band, centered on the star. We interpret this dark wedge as the shadow cast by the inner regions of a near-edge-on disk in UV light, allowing the PAHs to be excited only outside of this shadow. The presence of a disk shadow strongly constrains the inclination as well as the position angle of the disk. Although depending on the adopted PAH opacity, the abundance of PAHs in the surrounding cloud is constrained to 5+/-2% of the total dust mass, given the opacity. The extent of the nebulosity constrains the density of the gas surrounding the VV Ser disk to 500+/-200 cm-3 for a gas-to-dust ratio of 100. This low density suggests that the quantum heated material is not part of the original envelope of VV Ser and that it is rather a quiescent part of the Serpens molecular cloud that the star has passed into after being formed. [Abstract abridged]
We have used the Hubble Space Telescope's Advanced Camera for Surveys (ACS) to detect and measure ~5300 stars in a single intracluster field in the Virgo Cluster. By performing F606W and F814W photometry on these stars, we have determined their metallicity distribution function, and constrained the types of stars present in this portion of Virgo's intracluster space. Based on the small number of stars detected brighter than the red giant branch (RGB) tip, we suggest that in this region, Virgo's intracluster stars are mostly old (>~10 Gyr). Through analysis of the RGB stars themselves, we determine that the population contains the full range of metallicities probed (-2.3<[M/H]<0.0). We also present evidence that the younger (<10 Gyr) component of the population is more metal-rich, with [M/H]>-0.5. The spatial distribution of the most metal-poor stars in the field shows significantly more structure than that of the metal-rich stars, indicating that the intracluster population is not well-mixed. We discuss the implications these observations have for the production of intracluster stars and the dynamical evolution of the Virgo Cluster.
The Magellanic System harbors >800 expanding shells of neutral hydrogen, providing a unique opportunity for statistical investigations. Most of these shells are surprisingly young, 2--10 Myr old, and correlate poorly with young stellar populations. I summarize what we have learned about shell properties and particularly focus on the puzzling correlation between the shell radius and expansion velocity. In the framework of the standard, adiabatic model for shell evolution this tight correlation suggests a coherent burst of star formation across the whole Magellanic System. However, more than one mechanism for shell formation may be taking place.
We have obtained deep HI observations in the direction of 22 continuum sources without previously detected cold neutral medium (CNM). 18 CNM clouds were detected with the typical HI column density of $3\times10^{18}$ cm$^{-2}$. Our surprisingly high detection rate suggests that clouds with low HI column densities are quite common in the interstellar medium. These clouds appear to represent an extension of the traditional CNM cloud population, yet have sizes in hundreds to thousands of AUs. We present properties of the newly-detected CNM sample, and discuss several theoretical avenues important for understanding the production mechanisms of these clouds.
Three-year data of WMAP implies not only a negative running of the spectral index with large absolute value, but also a large positive running of running of the spectral index with order of the magnitude $10^{-2}$. We calculate the running of running in usual inflation model and noncommutative inflation model. A large tensor-scalar ratio $r\geq 1.23$ is needed in order to fit the WMAP data in the noncommutative inflation model, which roughly saturates the observational upper bound on it.
We show in this article that the metric theory of gravitation proposed by Sobouti (2006) predicts the existence of gravitational waves travelling at the speed of light in vacuum. We also show that an extra additional lensing as compared to the one predicted by standard general relativity is produced. These two points are generally considered to be of crucial importance in the development of relativistic theories of gravity that could describe alternatively what the dark matter paradigm does.
The newly operational X-ray satellite Suzaku observed the southwestern quadrant of the supernova remnant (SNR) RCW 86 in February 2006 to study the nature of the 6.4 keV emission line first detected with the Advanced Satellite for Cosmology and Astronomy (ASCA). The new data confirm the existence of the line, localizing it for the first time; most of the line emission is adjacent and interior to the forward shock and not at the locus of the continuum hard emission. We also report the first detection of a 7.1 keV line that we interpret as the K-beta emission from low-ionization iron. The Fe-K line features are consistent with a non-equilibrium plasma of Fe-rich ejecta with n_{e}t <~ 10^9 cm^-3 s and kT_{e} ~ 5 keV. This combination of low n_{e}t and high kT_{e} suggests collisionless electron heating in an SNR shock. The Fe K-alpha line shows evidence for intrinsic broadening, with a width of 47 (34--59) eV (99% error region). The difference of the spatial distributions of the hard continuum above 3 keV and the Fe-K line emission support a synchrotron origin for the hard continuum.
Star formation in interacting systems may take place in various locations, from the dust--enshrouded core of Ultraluminous Infrared Galaxies to more unusual places such as the debris of colliding galaxies expelled into the intergalactic medium. Determining whether star-formation proceeds in the latter environment, far from the parent galaxies, in a similar way as in spiral disks has motivated the multi--wavelength study presented here. We collected VLA/HI, UV/GALEX, optical Halpha and MIR/Spitzer images of a few nearby interacting systems chosen for their prominent "intergalactic" star formation activity. Preliminary results on the spectacular collisional HI ring around NGC 5291 are presented.
A study of the UHE nu_tau detection performances of a km^3 Neutrino Telescope sitting at the three proposed sites for ANTARES, NEMO and NESTOR in the Mediterranean sea is here performed. In particular, it is analyzed the effect of the underwater surface profile on the total amount of yearly expected tau crossing the fiducial volume in the limit of full detection efficiency and energy resolution.
We present diffraction-limited (FWHM ~ 0.3arcsec) Gemini/T-ReCS mid-infrared (MIR: N-band or narrow-band at 8.7micron) imaging of four Luminous Infrared Galaxies (LIRGs) drawn from a representative local sample. The MIR emission in the central few kpc is strikingly similar to that traced by Pa-alpha, and generally consists of bright nuclear emission and several compact circumnuclear and/or extranuclear HII regions. The central MIR emission is dominated by these powerful HII regions, consistent with the majority of AGN in this local sample of LIRGs contributing a minor part of the MIR emission. The luminous circumnuclear HII regions detected in LIRGs follow the extrapolation of the 8micron vs. Pa-alpha relation found for M51 HII knots. The integrated central 3-7kpc of galaxies, however, present elevated 8micron/Pa-alpha ratios with respect to individual HII regions, similar to the integrated values for star-forming galaxies. Our results show that the diffuse 8micron emission, not directly related to the ionizing stellar population, can be as luminous as that from the resolved HII regions. Therefore, calibrations of the star formation rate for distant galaxies should be based on the integrated 8micron emission of nearby galaxies, not that of the HII regions alone.
In order to fully understand the physical processes in the magnetospheres of the Magnetic Chemically Peculiar stars, we performed multi-frequency radio observations of CU Virginis. The radio emission of this kind of stars arises from the interaction between energetic electrons and magnetic field. The radio data were acquired with the VLA and cover the whole rotational period of CU Virginis. For each observed frequency the radio light curves of the total flux density and fraction of circular polarization were fitted using a three-dimensional MCP magnetospheric model simulating the stellar radio emission as a function of the magnetospheric physical parameters. The observations show a clear correlation between the radio emission and the orientation of the magnetosphere of this oblique rotator. Radio emission is explained as the result of the acceleration of the wind particles in the current sheets just beyond the Alfv\'en radius, that eventually return toward the star following the magnetic field and emitting radiation by gyrosyncrotron mechanism. The accelerated electrons have a hard energetic spectrum ($N(E)\propto E^{-2}$) and the acceleration process has an efficiency of about $10^{-3}$. The Alfv\'en radius we determined is in the range of $12-17 R_\ast$ and, for a dipolar field of 3000 Gauss at the magnetic pole of the star, we determine a mass loss from the star of about $10^{-12}$ M$_{\sun}$ yr$^{-1}$. In the inner magnetosphere a detectable X-ray emission is expected.
We investigate the hydrodynamics of two identical hypersonic stellar winds in a binary system. The interaction of these winds manifests itself in the form of two shocks and a contact surface between them. We neglect the binary rotation and assume that the gas flow ahead of the shocks is spherically symmetrical. In this case the contact surface that separates the gas emanated from the different stars coincides with the midplane of the binary components. In the shock the gas is heated and flows away nearly along the contact surface. We find the shock shape and the hot gas parameters in the shock layer between the shock and the contact surface.
The 5-year project Supernova Legacy Survey (SNLS) delivers $\sim 100$ Type-Ia supernovae (SNe Ia) per year, in the redshift range $0.3 < z < 1.0$, with well-sampled $g'r'i'z'$ lightcurves. The SNLS Collaboration uses the 1 deg$^2$ Megacam imager (36 $2048 \times 4612$ thinned CCDs) mounted on the 3.6-m Canada-France-Hawaii Telescope (CFHT) to observe four fields around the sky, in four filters. The primary goal of the project is to measure the dark energy equation of state with a final statistical precision of $\pm 0.05$. We have shown, using the first year dataset that the calibration uncertainties are currently the dominant contribution to the systematic error budget. The calibration of the SNLS dataset is challenging in several aspects. First, Megacam is a wide-field imager, and only a handful of its 36 CCDs can be directly calibrated using standard star observations. Second, measuring the rest-frame $B$-band luminosity of SNe Ia over the $0.3<z<1.0$ redshift range requires an excellent flux intercalibration of the Megacam bands. Finally, the SN Ia SED differs significantly from that of stars and transfering the stellar calibration to the SNLS data requires a precise knowledge of the SN Ia spectra and the instrument transmissions. We present and discuss the SNLS calibration strategy used to analyze the first year data set. We present the calibration aspects which impact most the cosmological measurements. We also discuss the intercalibration of the SNLS with other surveys, such as the CFHTLS-Wide and the SDSS.
We study brane inflation scenarios in a warped throat geometry and show that there exists a consistency condition between the non-Gaussianity of the curvature perturbation and the amplitude and scale-dependence of the primordial gravitational waves. This condition is independent of the warping of the throat and the form of the inflaton potential. We find that such a relation could be tested by a future CMB polarization experiment if the Planck satellite is able to detect both a gravitational wave background and a non-Gaussian statistic. In models where the observable stage of inflation occurs when the brane is in the tip region of the throat, we derive a further consistency condition involving the scalar spectral index, the tensor-scalar ratio and the curvature perturbation bispectrum. We show that when such a relation is combined with the WMAP3 results, it leads to a model-independent bound on the gravitational wave amplitude given by 0.001 < r < 0.01. This corresponds to the range of sensitivity of the next generation of CMB polarization experiments.
We performed a millimetric survey of a sample of 24 post-AGB stars aimed to search for emission from circumstellar matter, in order to investigate the physical properties of the outer parts of the envelopes. The observations were conducted using the 37-channel Max-Planck Millimeter Bolometer array at the 30-meter IRAM telescope. The continuum emission toward the detected sources was used to quantify the mass of the emitting dust. We combined our observations with data available in literature to construct the spectral energy distribution (SED) of the sources. When the observational data cover a spectral range wide enough, some properties of circumstellar envelopes were derived by comparison with spectra computed using a radiative transfer code. Of the 24 objects in our sample, we detected millimetric continuum emission toward 11 sources. Two other sources were detected at flux level close to 3$\sigma$. The derived circumstellar dust masses range between 0.4 and $24 \times 10^{-4}$ M$_{\odot}$, but these results are affected from the uncertain about the source distances. The parameters derived from the SED fits are consistent with the values characteristic for these kind of object. As confirmed from the flux density extrapolated in the first light channels of the Atacama Large Millimetric Array, such sources would be good targets for future high resolution mapping with the ALMA facility.
In order to find a law characterising the decrease of velocity along a jet, five analytical methods are suggested. The first two simple models examine the variation of velocity in the presence of Newton's or Stoke's resistance. The equation that represents the conservation of the momentum along a pyramidal sector is solved from an analytical point of view (third model). The application of the conservation of the total momentum flux allows us to deduce the velocity of the galaxy as a function of time for classical velocities (fourth model) and relativistic velocities (fifth model). The variation of velocity along the jet combined with an adequate composition of jet precession velocity, rotational velocity of the galaxy, and galaxy dispersion velocity in the cluster allows us to trace the geometrical pattern of the head-tail radio sources. Application of the developed theory/code to the radio galaxies NGC1265,NGC4061,NGC326, and Cygnus A gives the central galaxy's approximate dispersion velocities in the direction perpendicular to the jet. A transition from head--tails to classical double radio galaxies as a function of the increasing jet's mechanical power is introduced.
Context: the observations of young stars with circumstellar disks suggest that the disks are dissipated, starting from the inner region, by the radiation of the central star and eventually by the formation of rocky planetesimals, over a time scale of several million years. It was also shown that strong UV radiation emitted by nearby massive stars can heat a circumstellar disk up to some thousand degrees inducing the photoevaporation of the gas. This process strongly reduces the dissipation time scale. Aims: the aim of this work is to study if there exists a correlation between the spatial distribution of stars with circumstellar disks and the position of massive stars with spectral class earlier than B5, in the open cluster NGC 6611. Methods: for our purpose, we created a multiband catalog of the cluster, down to V~23, using optical data from a WFI observation at 2.2m of ESO in the BVI bands, the 2MASS public point source catalog and an archival X-ray observation made with CHANDRA/ACIS. We selected the stars with infrared excess (due to the emission of a circumstellar disk) using suitable color indices independent from extinction, and studied their spatial distribution. Results: we found that the spatial distribution of the stars with K band excess (due to the presence of a circumstellar disk) is anti correlated with that of the massive stars: the disks are more frequent at large distances from these stars. We argue that this is in agreement with the hypothesis that the circumstellar disks are heated by the UV radiation from the massive stars and photoevaporated.
The scenario of brane inflation without using the conventional slow-roll approximations has been investigated. Based on the mechanism of generating the curvature perturbations at the end of inflation, a new brane inflation paradigm was developed. The conditions for making a sufficiently large enough number of e-foldings and for generating the curvature perturbations without producing dangerous relics were also examined. Benefits of our scenario are subsequently discussed in detail.
We revisit the classification of polarization observables of the cosmic microwave background. There exists a unified approach to the $3 \times 3$ density matrix by which intensity, linear and circular polarization are treated on an equal footing. The representations of the rotation group on the sphere contain certain right-left setup symmetries which have not been taken into account before. Left-right symmetries revise the construction of invariants and certain predictions based on symmetries. There are two true rotational invariants mode by mode in polarization data. Independent of models of cosmological perturbations, we emphasize methods to construct invariant distributions in order to test predictions of isotropy, axial or parity symmetries, and generate covariant and invariant statistics order by order.
DW Carinae is a close but detached early B-type eclipsing binary in the young open cluster Cr 228. We have measured accurate physical properties of its components (masses and radii to 1%) and used these to derive the age, metallicity and distance of Cr 228. The rotational velocities of both components of DW Car are high, so we have investigated the performance of double-Gaussian fitting, one- and two-dimensional cross-correlation and spectral disentangling for measuring radial velocities in the presence of strong line blending. Gaussian and cross-correlation analyses require substantial corrections for the effects of line blending, which are only partially successful for cross-correlation. Disentangling is to be preferred because it does not assume anything about the shapes of spectral lines, and is not significantly affected by blending. Complete Stromgren uvby light curves have been obtained and accurate radii have been measured from them using the Wilson-Devinney program, constrained by an accurate spectroscopic light ratio. The Teffs and reddening have been found from Stromgren photometric calibrations. The masses and radii of DW Car are M_A = 11.34 +/- 0.12 Msun, R_A = 4.558 +/- 0.045 Rsun, M_B = 10.63 +/- 0.14 Msun and R_B = 4.297 +/- 0.055 Rsun. The Teffs are Teff_A = 27900 +/- 1000 K and Teff_B = 26500 +/- 1000 K, and the reddening is E(b-y) = 0.18 +/- 0.02 mag. Using empirical bolometric corrections we find a distance modulus of 12.24 +/- 0.12 mag for DW Car, which is in agreement with, and more accurate than, literature values for Cr 228. A comparison between the properties of DW Car and theoretical predictions is undertaken in the mass--radius and mass--Teff diagrams. Good agreement is found for an age of about 6 Myr and a metal abundance of Z approx 0.01 (abridged).
We present Spitzer observations of the blue compact dwarf galaxy (BCD) Haro 3, with an oxygen abundance of 12+log(O/H)=8.32. These data are part of a larger study of star formation and dust in low-metallicity environments.The IRS spectrum of Haro 3 shows strong narrow Polycyclic Aromatic Hydrocarbon (PAH) emission, with high equivalent widths. Gaseous nebular fine-structure lines are also seen. Despite the absence of optical high-excitation lines, a faint high-ionization [O IV] line at 25.89 micron indicates the presence of radiation as hard as 54.9 eV. A CLOUDY model suggests that the MIR lines originate in two regions: a low-extinction optically-emitting region, and an optically invisible one with much higher extinction. The morphology of Haro 3 changes with wavelength. IRAC 4.5 micron traces extended stellar photospheric emission from the body of the galaxy and hot dust continuum coming mainly from star-forming regions; 8 micron probes extended PAH emission coming mainly from the general ISM; MIPS 24 and 70 micron images map compact small-grain warm dust emission associated with active star formation, and 160 micron reflects cooler extended dust associated with older stellar populations. We have derived the optical-to-radio spectral energy distribution (SED) of the brightest star-forming region A in Haro 3. The best-fit DUSTY model of the SED gives a total luminosity of 2.8e9 Lsun and a mass of 2.8e6 Msun for the ionizing clusters. We infer an extinction A(V)<3, intermediate between the optical A(V)~0.5 and the radio A(V)~8, consistent with the picture that longer wavelength observations probe more deeply into star-forming regions.
The metal-rich bulge globular cluster NGC 6441 shows a well developed blue horizontal branch (Rich et al.), together with a strong slope upward from the red clump to the blue of the RR Lyrae region. Both features, the former corresponding to the well-known second parameter problem, are not explained by conventional evolutionary models. Helium self-enrichment is proposed as a possible solution to both questions, a mechanism already invoked for the interpretation of the peculiarities in NGC 2808 and M13. We make use of horizontal branch simulations, covering a wide range in main sequence helium abundance, to investigate whether the main features of NGC 6441 horizontal branch population, including the RR Lyrae variables period, can be reproduced. To describe the horizontal branch of NGC 6441, the helium content Y in the red clump must reach at least 0.35; values up to Y~0.37 are necessary to populate the RR Lyr region, reproducing also the observed mean long periods; depending on the dispersion in mass loss assumed in the simulations, values up to Y~0.38--0.40 are necessary to populate the blue HB. The total self--enriched population amounts to ~60% of the whole stellar content. Self-enrichment and multiple star formation episodes in the early evolution of globular clusters appear more and more able to account for many of the chemical and population peculiarities observed in these systems. The very large helium abundances (Y>0.35) required for ~14% of the horizontal branch population pose some problem on the enrichment mechanisms.
In this paper, we report the detection of a series of radio recombination lines (RRLs) in absorption near 26 MHz arising from the largest bound carbon atoms detected in space. These atoms, which are more than a million times larger than the ground state atoms are undergoing delta transitions (n~1009, Delta n=4) in the cool tenuous medium located in the Perseus arm in front of the supernova remnant, Cassiopeia A. Theoretical estimates had shown that atoms which recombined in tenuous media are stable up to quantum levels n~1500. Our data indicates that we have detected radiation from atoms in states very close to this theoretical limit. We also report high signal-to-noise detections of alpha, beta and gamma transitions in carbon atoms arising in the same clouds. In these data, we find that the increase in line widths with quantum number (proportional to n^5) due to pressure and radiation broadening of lines is much gentler than expected from existing models which assume a power law background radiation field. This discrepancy had also been noted earlier. The model line widths had been overestimated since the turnover in radiation field of Cassiopeia A at low frequencies had been ignored. In this paper, we show that, once the spectral turnover is included in the modeling, the slower increase in line width with quantum number is naturally explained.
We compare the luminosity function and rate inferred from the BATSE short hard bursts (SHBs) peak flux distribution with the redshift and luminosity distributions of SHBs observed by Swift/HETE II. The Swift/HETE II SHB sample is incompatible with SHB population that follows the star formation rate. However, it is compatible with a distribution of delay times after the SFR. This would be the case if SHBs are associated with the mergers of double neutron star (DNS) systems. DNS may be ``primordial'' or can form dynamically by binary exchange interaction in globular clusters during core collapse. The implied SHB rates that we find range from \sim 8 to \sim 30h_(70)^3 Gpc^(-3)yr^(-1). This rate is a much higher than what was previously estimated and, when beaming is taken into account, it is comparable to the rate of neutron star mergers estimated from statistics of binary pulsars. If GRBs are produced in mergers the implied rate practically guarantees detection by LIGO II and possibly even by LIGO I.
The hard X-ray flux ratio R of the footpoint sources to the loop-top source has been used to investigate non-thermal electron trapping and precipitation in solar flares. Considering the mission-long Yohkoh Hard X-ray Telescope database, from which we selected 117 flares, we investigated a dependence of the ratio R on flare loop parameters like height h and column depth N. We used non-thermal electron beams as a diagnostic tool for magnetic convergence. The ratio R decreases with h which we interpret as an effect of converging field geometry. Two branches seen in the R-h diagram suggest that in the solar corona two kinds of magnetic loops can exist: a more-converged ones that are more frequent (above 80%) and less-converged loops that are less frequent (below 20%). A lack of correlation between the ratio R and N can be due to a more complex configuration of investigated events than seen in soft X-rays. Obtained values of the magnetic mirror ratio are consistent with previous works and suggest a strongly nonpotential configuration. Further investigation including RHESSI data is needed to verify our results.
We investigate the chemical and observational implications of repetitive transient dense core formation in molecular clouds. We allow a transient density fluctuation to form and disperse over a period of 1 Myr, tracing its chemical evolution. We then allow the same gas immediately to undergo further such formation and dispersion cycles. The chemistry of the dense gas in subsequent cycles is similar to that of the first, and a limit cycle is reached quickly (2 - 3 cycles). Enhancement of hydrocarbon abundances during a specific period of evolution is the strongest indicator of previous dynamical history. The molecular content of the diffuse background gas in the molecular cloud is expected to be strongly enhanced by the core formation and dispersion process. Such enhancement may remain for as long as 0.5 Myr. The frequency of repetitive core formation should strongly determine the level of background molecular enhancement. We also convolve the emission from a synthesised dark cloud, comprised of ensembles of transient dense cores. We find that the dynamical history of the gas, and therefore the chemical state of the diffuse inter-core medium, may be determined if a sufficient sample of cores is present in an ensemble. Molecular ratios of key hydrocarbons with SO and SO2 are crucial to this distinction. Only surveys with great enough angular resolution to resolve individual cores, or very small groupings, are expected to show evidence of repetitive dynamical processing. The existence of non-equilibrium chemistry in the diffuse background may have implications for the initial conditions used in chemical models. Observed variations in the chemistries of diffuse and translucent regions may be explained by lines of sight which intersect a number of molecular cloud cores in various stages of evolution.
Young massive star-forming regions are known to produce hot molecular gas cores (HMCs) with a rich chemistry. While this chemistry is interesting in itself, it also allows to investigate important physical parameters. I will present recent results obtained with high-angular-resolution interferometers disentangling the small-scale structure and complexity of various molecular gas components. Early attempts to develop a chemical evolutionary sequence are discussed. Furthermore, I will outline the difficulty to isolate the right molecular lines capable to unambiguously trace potential massive accretion disks.
Abundance observations indicate the presence of rapid-neutron capture (i.e., r-process) elements in old Galactic halo and globular cluster stars. These observations provide insight into the nature of the earliest generations of stars in the Galaxy -- the progenitors of the halo stars -- responsible for neutron-capture synthesis of the heavy elements. The large star-to-star scatter observed in the abundances of neutron-capture element/iron ratios at low metallicities -- which diminishes with increasing metallicity or [Fe/H] -- suggests the formation of these heavy elements (presumably from certain types of supernovae) was rare in the early Galaxy. The stellar abundances also indicate a change from the r-process to the slow neutron capture (i.e., s-) process at higher metallicities in the Galaxy and provide insight into Galactic chemical evolution. Finally, the detection of thorium and uranium in halo and globular cluster stars offers an independent age-dating technique that can put lower limits on the age of the Galaxy, and hence the Universe.
If Wolf-Rayet stars are the progenitors of Gamma-ray bursts (GRBs), they must rotate rapidly to produce the GRB. This rotation may effect their stellar-wind bubbles and possibly explain why so many GRB afterglows occur in a constant density medium.
We present light curves of SDSS J0926+3624, the first eclipsing AM CVn star, observed with the high-speed CCD camera ULTRACAM on the WHT. We find unusually that the accreting white dwarf is only partially eclipsed by its companion. Apart from this, the system shows the classic eclipse morphology displayed by eclipsing dwarf novae, namely the eclipse of a white dwarf and accretion disc followed by that of the bright spot where the mass transfer stream hits the disc. We are able to fit this well to find masses of the accretor and donor to be M1 = 0.84 +/- 0.05 Msun and M2 = 0.029 +/- 0.02 Msun respectively. The mass of the donor is significantly above its zero temperature value and it must possess significant thermal content.
Two-dimensional gas-dynamical modeling of the mass-flow structure is used to study the outburst development in the classical symbiotic star Z And. The stage-by-stage rise of the light during the outburst can be explained in the framework of the colliding winds model. We suggest a scenario for the development of the outburst and study the possible influence of the changes of the flow structure on the light of the system. The model variations of the luminosity due to the formation of a system of shocks are in good agreement with the observed light variations.
We present the results of a spectral analysis of 5 Swift XRT and UVOT observations of the BL Lac object PKS 0548-322 carried out over the period April-June 2005. The X-ray flux of this high energy peaked BL Lac (HBL) source was found to be approximately constant at a level of F(2-10 keV) ~ 4x10^-11 erg cm^-2 s^-1, a factor of 2 brighter than when observed by BeppoSAX in 1999 and close to the maximum intensity reported in the Einstein Slew Survey. The very good statistics obtained in the 0.3-10 keV Swift X-ray spectrum allowed us to detect highly significant deviations from a simple power law spectral distribution. A log-parabolic model describes well the X-ray data and gives a best fit curvature parameter of 0.18 and peak energy in the Spectral Energy Distribution of about 2 keV. The UV spectral data from Swift UVOT join well with a power law extrapolation of the soft X-ray data points suggesting that the same component is responsible for the observed emission in the two bands. The combination of synchrotron peak in the X-ray band and high intensity state confirms PKS 0548-322 as a prime target for TeV observations. X-ray monitoring and coordinated TeV campaigns are highly advisable.
The supernova SN 2006aj associated with GRB 060218 is the second-closest GRB-SN observed to date ($z$=0.033) and is the clearest example of a SN associated with a Swift GRB with the earliest optical spectroscopy. Its optical data showed that this is the fastest evolving and among the least luminous GRB-SNe (70% as luminous as SN1998bw). However, its expansion velocity and a comparison with other stripped-envelope SNe suggest that SN2006aj is an intermediate object between Type Ic GRB-SNe and those not accompained by a GRB. High-resolution optical spectroscopy together with SDSS pre-burst observations revealed that the host galaxy of SN2006aj is a low-luminosity, metal-poor star-forming dwarf galaxy.
We summarize latest PIC simulation results on the radiation from Poynting jets and strongly magnetized collisionless shocks when a Poynting jet runs into cold ambient medium. We find that in all cases the radiative power output is much below that predicted by synchrotron radiation and the critical frequency is also much lower than the synchrotron critical frequency. We discuss the implications for the interpretation of GRB prompt emission data.
We study the production of loops in the cosmic string network in the expanding background. There is an initial regime characterized by production of small loops at the scale of the initial correlation length, but later we see the emergence of a scaling regime of loop production. This qualitatively agrees with earlier expectations derived from the results of flat spacetime simulations. In the final scaling regime the characteristic length of loops scales as $\sim 0.1 t$ in both radiation and matter eras.
We present asteroseismological inferences on RX J2117.1+3412, the hottest known pulsating PG1159 star. Our results are based on full PG1159 evolutionary models recently presented by Miller Bertolami & Althaus (2006). We performed extensive computations of adiabatic g-mode pulsation periods on PG1159 evolutionary models with stellar masses ranging from 0.530 to 0.741 Mo. PG1159 stellar models are extracted from the complete evolution of progenitor stars started from the ZAMS, through the thermally pulsing AGB and born-again phases to the domain of the PG 1159 stars. We constrained the stellar mass of RX J2117.1+3412 by comparing the observed period spacing with the asymptotic period spacing and with the average of the computed period spacings. We also employed the individual observed periods to find a representative seismological model. We derive a stellar mass of 0.56-0.57 Mo from the period spacing data alone. In addition, we found a best-fit model representative for RX J2117.1+3412 with an effective temperature of 163,400 K, a stellar mass of 0.565 Mo, and a surface gravity log g= 6.61. The derived stellar luminosity and radius are log(L/Lo)= 3.36 and log(R/Ro)= -1.23, respectively, and the He-rich envelope thickness is Menv= 0.02 Mo. We derive a seismic distance of 452 pc and a linear size of the planetary nebula of 1.72 pc. These inferences seem to solve the discrepancy between the RX J2117.1+3412 evolutionary timescale and the size of the nebula. All of the seismological tools we use concur to the conclusion that RX J2117.1+3412 must have a stellar mass of 0.565 Mo much in agreement with recent asteroseismology studies and in clear conflict with the predictions of spectroscopy plus evolutionary tracks.
As part of our Spitzer Spirals, Bridges, and Tails project to help understand the effects of galaxy interactions on star formation, we analyze GALEX ultraviolet, SARA optical, and Spitzer infrared images of the interacting galaxy pair Arp 82 (NGC 2535/6) and compare to a numerical simulation of the interaction. We investigate the multiwavelength properties of several individual star forming complexes (clumps). Using optical and UV colors, EW(Halpha), and population synthesis models we constrain the ages of the clumps and find that the median clump age is about 12 Myr. The clumps have masses ranging from a few times 10^6 to 10^9 solar masses. In general, the clumps in the tidal features have similar ages to those in the spiral region, but are less massive. The 8 micron and 24 micron luminosities are used to estimate the far-infrared luminosities and the star formation rates of the clumps. The total clump star formation rate is 2.0+/-0.8 solar masses per year, while the entire Arp 82 system is forming stars at a rate of 4.9+/-2.0 solar masses per year. We find, for the first time, stars in the HI arc to the southeast of the NGC 2535 disk. Population synthesis models indicate that all of the observed populations have young to intermediate ages. We conclude that although the gas disks and some old stars may have formed early-on, the progenitors are late-type or low surface brightness and the evolution of these galaxies was halted until the recent encounter.
It has been suggested that the fuzzy nature of spacetime at the Planck scale may cause lightwaves to lose phase coherence, and if severe enough this could blur images of distant point-like sources sufficiently that they do not form an Airy pattern at the focal plane of a telescope. Blurring this dramatic has already been observationally ruled out by images from Hubble Space Telescope (HST), but I show that the underlying phenomenon could still be stronger than previously considered. It is harder to detect, which may explain why it has gone unseen. A systematic search is made in archival HST images of among the highest known redshift quasars. Planck-scale induced blurring may be evident, but this could be confused with partially resolved sources.
We review the available atomic data used for interpreting and modeling X-ray observations. The applications for these data can be divided into several levels of detail, ranging from compilations which can be used with direct inspection of raw data, such as line finding lists, to synthetic spectra which attempt to fit to an entire observed dataset simultaneously. This review covers cosmic sources driven by both electron ionization and photoionization and touches briefly on planetary surfaces and atmospheres. We review all of this, the applications to X-ray astronomy, the available data, recommendations for astronomical users, and attempt to point out the applications where the shortcomings are greatest
We present our XMM-Newton RGS observations of X Comae, an AGN behind the Coma cluster. We detect absorption by NeIX and OVIII at the redshift of Coma with an equivalent width of 3.3+/-1.8 eV and 1.7+/-1.3 eV, respectively (90% confidence errors or 2.3 sigma and 1.9 sigma confidence detections determined from Monte Carlo simulations). The combined significance of both lines is 3.0 sigma, again determined from Monte Carlo simulations. The same observation yields a high statistics EPIC spectrum of the Coma cluster gas at the position of X Comae. We detect emission by NeIX with a flux of 2.5+/-1.2 x 10^-8 photons cm^-2 s^-1 arcmin^-2 (90% confidence errors or 3.4 sigma confidence detection). These data permit a number of diagnostics to determine the properties of the material causing the absorption and producing the emission. Although a wide range of properties is permitted, values near the midpoint of the range are T = 4 x 10^6 K, n_H = 6 x 10^-6 cm^-3 corresponding to an overdensity with respect to the mean of 32, line of sight path length through it 41 Z/Zsolar^-1 Mpc where Z/Zsolar is the neon metallicity relative to solar. All of these properties are what has been predicted of the warm-hot intergalactic medium (WHIM), so we conclude that we have detected the WHIM associated with the Coma cluster.
We show that the presence of a rho~1/r^{3/2} dark matter overdensity can be robustly predicted at the center of any galaxy old enough to have grown a power-law density cusp in the stars via the Bahcall-Wolf mechanism. Using both Fokker-Planck and direct N-body integrations, we demonstrate collisional generation of these dark matter "crests" (Collisionally REgenerated STtructures) even in the extreme case that the density of both stars and dark matter were previously lowered by slingshot ejection from a binary supermassive black hole. The time scale for collisional growth of the crest is approximately the two-body relaxation time as defined by the stars, which is < 10 Gyr at the centers of stellar spheroids with luminosities comparable to that of the Milky Way bulge or less. The presence of crests can robustly be predicted in such galaxies, unlike the steeper enhancements, called "spikes," produced by the adiabatic growth of black holes. We discuss special cases where the prospects for detecting dark matter annihilations from the centers of galaxy haloes are significantly affected by the formation of crests.
We investigate Arp 295, a pair of interacting spirals at z=0.023. We measure scalelengths 5.24 kpc for Arp 295a and 2.52 kpc for 295b. There is a much smaller Im galaxy associated with the larger spiral. Arp 295b is asymmetric with the disk more extended eastwards but with the brightest star-formation regions on the west side of the nucleus. The spectrum of Arp 295b shows strong emission lines with [OII]3727 prominent We measure the total H-alpha line luminosities of Arp 295b and Arp 295c as 4.58x 10^{41} and 6.76x 10^{40} ergs/s, corresponding to star-formation rates 3.6 and 0.53. To study the kinematics of Arp 295b we observe in H-alpha with the Manchester Echelle Spectrograph, using an E-W spectroscopic slit at a series of 9 positions. We measure the maximum disk rotation velocity as 252.6 km/s. The rotation curve of Arp 295b is very asymmetric. The east (approaching) side has a higher radial velocity than the west with the maximum difference at radius 5 arcsec from the nucleus, where it is 88 km/s. The slowed rotation on the western side of the nucleus may have locally enhanced star-formation.
We perform a comprehensive study of a class of dark energy models - scalar field models where the effective potential can be described by a polynomial series - exploring their dynamical behavior using the method of flow equations that has previously been applied to inflationary models. Using supernova, baryon oscillation, CMB and Hubble constant data, and an implicit theoretical prior imposed by the scalar field dynamics, we find that the LCDM model provides an excellent fit to the data. Constraints on the generic scalar field potential parameters are presented, along with the reconstructed w(z) histories consistent with the data and the theoretical prior. We propose and pursue computationally feasible algorithms to obtain estimates of the principal components of the equation of state, as well as parameters w_0 and w_a. Further, we use the Monte Carlo Markov Chain machinery to simulate future data based on the Joint Dark Energy Mission, Planck and baryon acoustic oscillation surveys and find that the inverse area figure of merit improves nearly by an order of magnitude. Therefore, most scalar field models that are currently consistent with data can be potentially ruled out by future experiments. We also comment on the classification of dark energy models into "thawing'" and "freezing" in light of the more diverse evolution histories allowed by this general class of potentials.
We investigate the formation and evolution of nested bar systems in disk galaxies in a cosmological setting. Development of an isolated dark matter (DM) and baryon density perturbation has been followed. The disks form and grow within the assembling triaxial DM halos. The gas forms stars and the feedback from the stellar evolution is accounted for in terms of supernovae and OB stellar winds. Focusing on a representative model, we show the formation of a nested bars with characteristic sub-kpc and few kpc sizes. The system evolves through successive dynamical couplings and decouplings, forcing the gas inwards, down to the limiting scale of a numerical resolution. It settles in a state of a resonant coupling. The initial bar formation is triggered in response to the tidal torques from the triaxial DM halo which acts as a finite perturbation. An oval disk with strong and varying grand-design arms forms as well. The inflow rate can support a broad range of activity within the central kpc, from quasar- to Seyfert-types, supplemented by a vigorous star formation as a by-product.
We present Arecibo L-band Feed Array 21-cm observations of a sub-complex of HVCs at the tip of the Anti-Center Complex. These observations show morphological details that point to interaction with the ambient halo medium and differential drag within the cloud sub-complex. We develop a new technique for measuring cloud distances, which relies upon these observed morphological and kinematic characteristics, and show that it is consistent with H-alpha distances. These results are consistent with distances to HVCs and halo densities derived from models in which HVCs are formed from cooling halo gas.
We have analyzed the archival XMM-Newton data of the bright Ultra-Luminous X-ray Source (ULX) M82 X-1 with an 105 ksec exposure when the source was in the steady state. Thanks to the high photon statistics from the large effective area and long exposure, we were able to discriminate different X-ray continuum spectral models. Neither the standard accretion disk model (where the radial dependency of the disk effective temperature is T(r) \propto r^-3/4) nor a power-law model gives a satisfactory fit. In fact, observed curvature of the M82 X-1 spectrum was just between those of the two models. When the exponent of the radial dependence (p in T(r) \propto r^-p) of the disk temperature is allowed to be free, we obtained p =0.61^+0.03_-0.02. Such a reduction of p from the standard value 3/4 under extremely high mass accretion rates is predicted from the accretion disk theory as a consequence of the radial energy advection. Thus, the accretion disk in M82 X-1 is considered to be in the Slim disk state, where an optically thick Advection Dominant Accretion Flow (ADAF) is taking place. We have applied a theoretical slim disk spectral model to M82 X-1, and estimated the black hole mass ~ 19-32 M_odot. We propose that M82 X-1 is a relatively massive stellar black hole which has been produced through evolution of an extremely massive star, shining at a super-Eddington luminosity by several times the Eddington limit.
We identify a light echo candidate from Hubble Space Telescope (HST) imaging of NGC 2441, the host galaxy of the Type Ia supernova 1995E. From the echo's angular size and the estimated distance to the host galaxy, we find a distance of 207 +/- 35 pc between the dust and the site of the supernova. If confirmed, this echo brings the total number of observed non-historical Type Ia light echoes to three -- the others being SN 1991T and SN 1998bu -- suggesting they are not uncommon. We compare the properties of the known Type Ia supernova echoes and test models of light echoes developed by Patat et al. (2005). HST photometry of the SN 1991T echo shows a fading which is consistent with scattering by dust distributed in a sphere or shell around the supernova. Light echoes have the potential to answer questions about the progenitors of Type Ia supernovae and more effort should be made for their detection given the importance of Type Ia supernovae to measurements of dark energy.
We study the FeII properties of double-peaked broad low-ionization emission line AGN (dbp emitters) using a sample of 27 dbp emitters from SDSS (DR4), with mean value $\sigma_{H\alpha_{B}}\sim3002\pm139{\rm km\cdot s^{-1}}$. Our first result is that the line spectra in the wavelength range from 4100$\AA$ to 5800$\AA$ can be best fitted by an elliptical accretion disk model, assuming the same double-peaked line profiles for H$\beta$, FeII, H$\gamma$ and HeII$\lambda4686\AA$ as that of double-peaked broad H$\alpha$ for all the 27 dbp emitters, except the object SDSS J2125-0813 which we have discussed in a previous paper. The best fitted results indicate that the optical FeII emission lines of dbp emitters originate from the same region in the accretion disk where the double-peaked Balmer emission lines originate. Some correlations between FeII emission lines and the other broad emission lines for normal AGN can be confirmed for dbp emitters. However, these results should be taken with caution due to the small number of objects and the bias in selecting strong FeII emitters. We show that for dbp emitters, BH masses seems to have more influence on FeII properties than dimensionless accretion rate. We also find that the dbp emitters in the sample are all radio quiet quasars except one dbp emitter with $R_r> 1$ according to the definition by Ivezi$\rm{\acute{c}}$ et al. (2002) and 6 objects undiscovered by FIRST.
The luminosity of the famous red supergiant VY CMa (L ~ 4 - 5 x 10e5 Lsun) is well-determined from its spectral energy distribution and distance, and places it near the empirical upper luminosity limit for cool hypergiants. In contrast, its surface temperature is fundamentally ill-defined. Both contradict a recent paper by Massey, Levesque and Plez (2006). Implications for its location on the HR Diagram and its apparent size are discussed.
We report on a 100 ks Suzaku observation of the bright, nearby (z=0.008486) Seyfert 1.9 galaxy MCG -5-23-16. The broad-band (0.4-100 keV) X-ray spectrum allows us to determine the nature of the high energy emission with little ambiguity. The X-ray continuum consists of a cutoff power-law of photon index $\Gamma=1.9$, absorbed through Compton-thin matter of column density $N_{\rm H}=1.6\times10^{22}$ cm$^{-2}$. A soft excess is observed below 1 keV and is likely a combination of emission from scattered continuum photons and distant photoionized gas. The iron K line profile is complex, showing narrow neutral iron K$\alpha$ and K$\beta$ emission, as well as a broad line which can be modeled by a moderately inclined accretion disk. The line profile shows either the disk is truncated at a few tens of gravitational radii, or the disk emissivity profile is relatively flat. A strong Compton reflection component is detected above 10 keV, which is best modeled by a combination of reflection off distant matter and the accretion disk. The reflection component does not appear to vary. The overall picture is that this Seyfert 1.9 galaxy is viewed at moderate (50 degrees) inclination through Compton-thin matter at the edge of a Compton-thick torus covering $2\pi$ steradians, consistent with unified models.
We present low-resolution ultraviolet spectra of 14 low redshift (z<0.8) quasars observed with HST/STIS as part of a Snap project to understand the relationship between quasar outflows and luminosity. By design, all observations cover the CIV emission line. Nine of the quasars are from the Hamburg-ESO catalog, three are from the Palomar-Green catalog, and one is from the Parkes catalog. The sample contains a few interesting quasars including two broad absorption line (BAL) quasars (HE0143-3535, HE0436-2614), one quasar with a mini-BAL (HE1105-0746), and one quasar with associated narrow absorption (HE0409-5004). These BAL quasars are among the brightest known (though not the most luminous) since they lie at z<0.8. We compare the properties of these BAL quasars to the z<0.5 Palomar-Green and z>1.4 Large Bright Quasar samples. By design, our objects sample luminosities in between these two surveys, and our four absorbed objects are consistent with the v ~ L^0.62 relation derived by Laor & Brandt (2002). Another quasar, HE0441-2826, contains extremely weak emission lines and our spectrum is consistent with a simple power-law continuum. The quasar is radio-loud, but has a steep spectral index and a lobe-dominated morphology, which argues against it being a blazar. The unusual spectrum of this quasar resembles the spectra of the quasars PG1407+265, SDSSJ1136+0242, and PKS1004+13 for which several possible explanations have been entertained.
Initial results on the iron K-shell line and reflection component in several AGN observed as part of the Suzaku Guaranteed time program are reviewed. This paper discusses a small sample of Compton-thin Seyferts observed to date with Suzaku; namely MCG -5-23-16, MCG -6-30-15, NGC 4051, NGC 3516, NGC 2110, 3C 120 and NGC 2992. The broad iron K$\alpha$ emission line appears to be present in all but one of these Seyfert galaxies, while the narrow core of the line from distant matter is ubiquitous in all the observations. The iron line in MCG -6-30-15 shows the most extreme relativistic blurring of all the objects, the red-wing of the line requires the inner accretion disk to extend inwards to within 2.2Rg of the black hole, in agreement with the XMM-Newton observations. Strong excess emission in the Hard X-ray Detector (HXD) above 10 keV is observed in many of these Seyfert galaxies, consistent with the presence of a reflection component from reprocessing in Compton-thick matter (e.g. the accretion disk). Only one Seyfert galaxy (NGC 2110) shows neither a broad iron line nor a reflection component. The spectral variability of MCG -6-30-15, MCG -5-23-16 and NGC 4051 is also discussed. In all 3 cases, the spectra appear harder when the source is fainter, while there is little variability of the iron line or reflection component with source flux. This agrees with a simple two component spectral model, whereby the variable emission is the primary power-law, while the iron line and reflection component remain relatively constant.
We report the results of a high angular resolution near-infrared survey of dusty Wolf-Rayet stars using the Keck-1 Telescope, including new multi-wavelength images of the pinwheel nebulae WR 98a, WR 104, and WR 112. Angular sizes were measured for an additional 8 dusty WR stars using aperture masking interferometry, allowing us to probe characteristics sizes down to ~20 milliarcseconds (~40 AU for typical sources). With angular sizes and specific fluxes, we can directly measure the wavelength-dependent surface brightness and size relations for our sample. We discovered tight correlations of these properties within our sample which could not be explained by simple spherically-symmetric dust shells or even the more realistic ``pinwheel nebula'' (3-D) radiative transfer model, when using optical constants of Zubko. While the tightly-correlated surface brightness relations we uncovered offer compelling indirect evidence of a shared and distinctive dust shell geometry amongst our sample, long-baseline interferometers should target the marginally-resolved objects in our sample in order to conclusively establish the presence or absence of the putative underyling colliding wind binaries thought to produce the dust shells around WC Wolf-Rayets.
We use a large sample of 174 Wolf-Rayet (WR) galaxies drawn from the Sloan Digital Sky Survey to study whether and how the slope of the stellar initial mass function depends on metallicity. We calculate for each object its oxygen abundance according to which we divide our sample into four metallicity subsamples. For each subsample, we then measure three quantities: the equivalent width of \hb emission line, the equivalent width of WR bump around 4650\AA, and the WR bump-to-\hb intensity ratio, and compare to the predictions of the same quantities by evolutionary synthesis models of Schaerer & Vacca. Such comparisons lead to a clear dependence of the slope of initial mass function ($\alpha$) on metallicity in that galaxies at higher metallicities tend to have steeper initial mass functions, with the slope index ranging from $\alpha\sim$1.00 for the lowest metallicity of $Z=0.001$ to $\alpha\sim$3.30 for the highest metallicity $Z=0.02$. We have carefully examined the possible sources of systematic error either in models or in our observational measurements and shown that these sources do not change this result.
We intend to investigate separately the photospheric and circumstellar (CS) magnetic field components in seven Herbig Ae stars. The study is based on low-resolution (R ~ 2000 and 4000) spectropolarimetric data collected from 2003 to 2005 at the Very Large Telescope (ESO, Chile) with the multi-mode instrument FORS1. We show that the spectropolarimetric results strongly depend on the level of CS contribution to the stellar spectra. We have improved the determination accuracy of magnetic fields up to the 7 sigma level in the two Herbig Ae stars HD139614 and HD144432, observed in 2005 when these objects were at a low level state of their CS activity. We have established that at a higher level state of CS activity the polarisation signatures are related mainly to the CS matter. The presence of CS polarisation signatures formed in the stellar wind supports the assumption that the magnetic centrifuge is a principal mechanism of wind acceleration. We conclude that the most effective way to investigate the magnetism of Herbig Ae stars is to monitor their spectropolarimetric behaviour at different states of CS activity. Obviously, higher resolution spectropolarimetric observations would extend the sample of spectral lines to be used for the measurements of magnetic fields at different levels in the stellar atmosphere and CS envelope. Such observations will give a more complete insight into the magnetic topology in Herbig Ae stars.
Outline:
1. Thermal axions
2. Axion field evolution
3. The domain wall problem
4. Cold axions
5. Axion miniclusters
6. Axion isocurvature perturbations
We consider the hypothesis that some active galactic nuclei and other compact astrophysical objects may be current or former entrances to wormholes. A broad mass spectrum for astrophysical wormholes is possible. We consider various new models of the static wormholes including wormholes maintained mainly by an electromagnetic field. We also discuss observational effects of a single entrance to wormhole and a model for a binary astrophysical system formed by the entrances of wormholes with magnetic fields and consider its possible manifestation.
The shape of the UV ionizing background is reconstructed from optically thin metal absorption-line systems identified in spectra of HE2347-4342, Q1157+3143, and HS1700+6416 in the redshift interval 1.8 < z < 2.9. The systems are analyzed by means of the Monte Carlo Inversion method completed with the spectral shape recovering procedure. The UVB spectral shape fluctuates at 2.4 < z < 2.9 mostly due to radiative transfer processes in the clumpy IGM. At z < 1.8, the IGM becomes almost transparent both in the HI and HeII Lyman continua and the variability of the spectral shape comes from diversity of spectral indices describing the QSO/AGN intrinsic radiation. At z > 2.4, the recovered spectral shapes show intensity depression between 3 and 4 Ryd due to HeII Ly-alpha absorption in the IGM clouds (line blanketing) and continuous medium (true Gunn-Petersen effect). The mean HeII Ly-alpha opacity estimated from the depth of this depression corresponds within 1-2sigma to the values directly measured from the HI/HeII Ly-alpha forest towards the quasars studied. The observed scatter in eta = N(HeII)/N(HI) and anti-correlation between N(HI) and eta can be explained by the combined action of variable spectral softness and differences in the mean gas density between the absorbing clouds. Neither of the recovered spectral shapes show features which can be attributed to the putative input of radiation from soft sources like starburst galaxies.
We derive the theoretical red edge of the pulsating GW Vir stars by using full evolutionary calculations that involve mass loss and diffusion. We put the emphasis on the fact that the specific mass loss law used in the evolutionary computations determines the red edge's position. By combining this specific property with the observed location of the red edge in the effective temperature-surface gravity domain, we obtain interesting constraints on possible mass loss laws for PG 1159 stars.
It is widely accepted that the Doppler deboosting effects exist in counter relativistic jets. However, people often neglect another important fact that both Doppler boosting and deboosting effects could happen in forward relativistic jets. Such effects might be used to explain some strange phenomena, such as the invisible gaps between the inner and outer jets of AGNs, and the rapid initial decays and re-brightening bumps in the light curves of GRBs.
We have redetermined kinematic parameters of the Gould Belt using currently available data on the motion of nearby young (log t < 7.91) open clusters, OB associations, and moving stellar groups. Our modeling shows that the residual velocities reach their maximum values of -4 km/s for rotation (in the direction of Galactic rotation) and +4 km/s for expansion at a distance from the kinematic center of about 300 pc. We have taken the following parameters of the Gould Belt center: Ro=150 pc and lo=128 degrees. The whole structure is shown to move relative to the local standard of rest at a velocity of 10.7+-0.7 km/s in the direction l=274+-4degrees and b=-1+-3 degrees. Using the derived rotation velocity, we have estimated the virial mass of the Gould Belt to be 1.5E6 Solar mass.
The nearby, almost face-on, and interacting galaxy M51 offers an excellent opportunity to study the distribution of molecular gas and the mechanisms governing the star formation rate. We have created a complete map of M51 in 12CO 2-1 at a resolution of 11 arcsec corresponding to 450 kpc using HERA at the IRAM-30m telescope. In Schuster et al. (2006) we have combined these data with maps of HI and the radio-continuum to study the star formation efficiency, the local Schmidt law, and Toomre stability of the disk in radial averages out to radii of 12 kpc. Here, we also discuss the distribution of giant molecular associations and its mass spectrum, in comparison with similar studies in the literature.
A GRMHD model of disk outflows with neutrino-driven mass ejection is presented. The model is used to calculate the structure of the outflow in the sub-slow magnetosonic region and the mass loading of the outflow, under conditions anticipated in the central engines of gamma-ray bursts. It is concluded that magnetic launching of ultra-relativistic polar outflows is in principle possible along low inclination field lines (with respect to the symmetry axis), provided the neutrino luminosity is sufficiently low, $L_\nu\simlt10^{52}$ erg s$^{-1}$.
Double neutron star systems lead to strong tests of general relativity. The history of the double pulsar PSR J0737-3039 is also very interesting. There are claims that the younger member of this binary (pulsar B) had a light progenitor. It is possible that such double pulsar systems are double strange stars. We suggest that the collapse of the light progenitor was a phase transition to strange matter and J0737-3039B is a strange star. This would support small baryon loss implied by the small natal kick velocity for the system J0737-3039. Using equation of states for strange quark matter and neutron matter, we have calculated the stellar structure and the baryon content of the progenitor as well as the existing star - to compare with observational predictions. We have also calculated the moment of inertia using both of the equation of states to facilitate comparison with expected future measurements. The baryon number of the progenitor turns out to be ~ 2 X 10^{57} and with small baryon loss the this fits into a strange star of mass 1.25 M_sun. Double neutron stars may be double strange stars. If the moment of inertia of these stars are found in the near future as expected, then our predictions can be further tested.
We report the results of radio and X-ray observations of the high mass X-ray binary 2S 0114+650, made with the Giant Meterwave Radio Telescope and the Rossi X-ray Timing Explorer respectively. No emission was detected at radio wavelengths. The neutral hydrogen column density was found to vary over the orbital period, while no variability over the the super-orbital period was observed. We discuss the causes of the observed relationships and the implications for the underlying mechanisms.
Jeans instability of finite massive bodies at hydrostatic equilibrium is studied. Differential equation governing the evolution of infinitesimal disturbances is derived. We take into account radial inhomogeneity of mass density and other fluid parameters at the equilibrium state. Dispersion relation and a simple analytical formula, generalizing the Jeans criterion of instability, are derived.
The fractional Brownian motion with index $\alpha$ is introduced to construct the fractional excursion set model. A new mass function with single parameter $\alpha$ is derived within the formalism, of which the Press-Schechter mass function (PS) is a special case when $\alpha=1/2$. Although the new mass function is computed assuming spherical collapse, comparison with the Sheth-Tormen fitting function (ST) shows that the new mass function of $\alpha\approx 0.435$ agrees with ST remarkably well in high mass regime, while predicts more small mass halos than the ST but less than the PS. The index $\alpha$ is the Hurst exponent, which exact value in context of structure formation is modulated by properties of the smoothing window function and the shape of power spectrum. It is conjectured that halo merging rate and merging history in the fractional set theory might be imprinted with the interplay between halos at small scales and their large scale environment. And the mass function in high mass regime can be a good tool to detect the non-Gaussianity of the initial density fluctuation.
We consider gamma--ray bursts produced by the merger of a massive white dwarf with a neutron star. We show that these are likely to produce long--duration GRBs, in some cases definitely without an accompanying supernova, as observed recently. This class of burst would have a strong correlation with star formation, and occur close to the host galaxy. However rare members of the class need not be near star--forming regions, and could have any type of host galaxy. Thus a long--duration burst far from any star--forming region would also be a signature of this class. Estimates based on the existence of a known progenitor suggest that our proposed class may be an important contributor to the observed GRB rate.
We discuss CO spectral line data of a volume-limited sample of 23 nearby (z<0.03) low luminosity radio galaxies, selected from the B2 catalogue. We investigate whether the CO properties of our sample are correlated with the properties of the host galaxy, and in particular with the dust component. We find strong evidences for a physical link between the dust disks probed by HST in the galaxy cores and the molecular gas probed by the CO spectral lines, which in two cases display a double-horn shape, consistent with ordered rotation. On the other hand, from a preliminary comparison with other samples of radio sources we find no significant differences in molecular gas properties between FRI and FRII radio sources. In order to confirm the suggestion that the CO is dynamically associated with the core dust disks, the most suitable sources of our sample will be proposed for interferometric imaging at PdBI.
We present three-dimensional, nonrelativistic, hydrodynamic simulations of bow shocks in pulsar wind nebulae. The simulations are performed for a range of initial and boundary conditions to quantify the degree of asymmetry produced by latitudinal variations in the momentum flux of the pulsar wind, radiative cooling in the postshock flow, and density gradients in the interstellar medium (ISM). We find that the bow shock is stable even when travelling through a strong ISM gradient. We demonstrate how the shape of the bow shock changes when the pulsar encounters density variations in the ISM. We show that a density wall can account for the peculiar bow shock shapes of the nebulae around PSR J2124-3358 and PSR B0740-28. A wall produces kinks in the shock, whereas a smooth ISM density gradient tilts the shock. We conclude that the anisotropy of the wind momentum flux alone cannot explain the observed bow shock morphologies but it is instead necessary to take into account external effects. We show that the analytic (single layer, thin shell) solution is a good approximation when the momentum flux is anisotropic, fails for a steep ISM density gradient, and ap- proaches the numerical solution for efficient cooling. We provide analytic expressions for the latitudinal dependence of a vacuum-dipole wind and the associated shock shape, and compare the results to a split-monopole wind. We find that we are unable to distinguish between these two wind models purely from the bow shock morphology.
Analysis of INTEGRAL Core Program and public Open Time observations has recently provided a sample of 60 extragalactic sources selected in the 20-100 keV band above a flux of 1.5 10^-11 erg/cm2/s. As this band probes heavily obscured regions/objects, i.e. those that could be missed in optical, UV, and even X-ray surveys, our sample offers the opportunity to study the extragalactic sky from a different point of view with respect to surveys at lower energies. We present an update of our analysis, including the first sample of AGNs detected above 100 keV. We also discuss the results of follow up observations performed at optical and X-ray frequencies with the aim of classifying our objects and studying the effects of intrinsic absorption in gamma-ray selected AGNs. The average redshift of our sample is 0.134 while the mean 20-100 keV luminosity in Log is 43.84; if blazars are excluded these numbers become 0.022 and 43.48 respectively. Defining an absorbed object as one with NH above 10^22 atoms/cm2, we find that absorption is present in 60% of the objects with at most 14% of the total sample due to Compton thick active galaxies. Almost all Seyfert 2s in our sample are absorbed as are 24% of Seyfert 1s. We also present broad-band spectral information on a sub-sample of the brightest objects: our observations indicate a mean photon index of 1.8 spanning from 30-50 keV to greater than 200 keV. Finally, we discuss the LogN/LogS distribution in the 20-100 and 100-150 keV bands derived from our sample. The present data highlight the capability of INTEGRAL to probe the extragalactic gamma-ray sky, to discover new AGNs and to find absorbed objects.
We present the first high-resolution X-ray spectrum of a prototypical Herbig star (AB Aurigae), measure and interpret various spectral features, and compare our results with model predictions. We use X-ray spectroscopy data from XMM-Newton. The spectra are interpreted using thermal, optically thin emission models with variable element abundances and a photoelectric absorption component. We interpret line flux ratios in He-like triplet of O VII as a function of electron density and the UV radiation field. We use the nearby co-eval classical T Tauri star SU Aur as a comparison. AB Aurigae reveals a soft X-ray spectrum, most plasma being concentrated at 1-6 MK. The He-like triplet reveals no signatures of increased densities and there are no clear indications for strong abundance anomalies. The light curve displays modulated variability, with a period of ~ 42 hr. It is unlikely that a nearby, undetected lower-mass companion is the source of the X-rays. Accretion shocks close to the star should be irradiated by the photosphere, leading to alteration in the He-like triplet fluxes of O VII, which we do not measure. Also, no indications for high densities are found, although the mass accretion rate is presently unknown. Emission from wind shocks is unlikely, given the weak radiation pressure. A possible explanation would be a solar-like magnetic corona. Magnetically confined winds provide a very promising alternative. The X-ray period is indeed close to periods previously measured in optical lines from the wind.
In this paper, the second in a series of two, we justify two important assumptions on which the result is based that in course of a galaxy merger the slingshot ejection of bound stars in the second phase is sufficiently efficient as to allow the black hole binary to merge. The required steep cusp, which is as massive as the binary and surrounds the black holes at the time the binary becomes hard, is formed during the merger from both clusters surrounding each black hole and the matter funneled into the center. We find this profile to be in agreement with observed post-merger distributions after the cusp has been destroyed. The time dependency we derive for the merger predicts that stalled binaries, if they exist at all, will preferably be found at the end of the second phase. To test this prediction we compute the current semimajor axis of 12 candidates of ongoing mergers. We find all of them unambiguously to be already in the last phase where the black holes coalesce due to the emission of gravitational waves. Therefore, in striking contradiction with predictions of a depleted loss-cone, the finding of not a single source in the second phase strongly supports our previous and current results: Binaries merge due to slingshot ejection of stars which have been funneled into the central regions in course of a galaxy collision.
The correction of the influence of phase corrugation in the pupil plane is a fundamental issue in achieving high dynamic range imaging. In this paper, we investigate an instrumental setup which consists in applying interferometric techniques on a single telescope, by filtering and dividing the pupil with an array of single-mode fibers. We developed a new algorithm, which makes use of the fact that we have a redundant interferometric array, to completely disentangle the astronomical object from the atmospheric perturbations (phase and scintillation). This self-calibrating algorithm can also be applied to any - diluted or not - redundant interferometric setup. On an 8 meter telescope observing at a wavelength of 630 nm, our simulations show that a single mode pupil remapping system could achieve, at a few resolution elements from the central star, a raw dynamic range up to 10^6; depending on the brightness of the source. The self calibration algorithm proved to be very efficient, allowing image reconstruction of faint sources (mag = 15) even though the signal-to-noise ratio of individual spatial frequencies are of the order of 0.1. We finally note that the instrument could be more sensitive by combining this setup with an adaptive optics system. The dynamic range would however be limited by the noise of the small, high frequency, displacements of the deformable mirror.
The space mission CoRoT (COnvection, ROtation and planetary Transits) will offer the possibility to detect extrasolar planets by means of the transit method. The satellite will observe about 60000 targets in the range 11.0<V<16.0, located in five fields near the equator. The parts of the preparatory work in which the Italian community has been involved are described, with a particular emphasis on the observations to characterize the fields, on the effects of stellar activity and background stars and on the outreach activities. We performed a quantitative evaluation of instrumental and stellar effects in the planetary transit detection and a more careful evaluation of the stellar content of some specific stellar fields. Also considering the full spectroscopic characterisation of the targets and the precise photometric evaluation of the stellar variability in the CoRoT fields, the Italian researchers provided original and useful inputs to the scientific profile to the mission.
One of the prime goals of future investigations of extrasolar planets is to search for life as we know it. The Earth's biosphere is adapted to current conditions. How would the atmospheric chemistry of the Earth respond if we moved it to different orbital distances or changed its host star? This question is central to astrobiology and aids our understanding of how the atmospheres of terrestrial planets develop. To help address this question, we have performed a sensitivity study using a coupled radiative-convective photochemical column model to calculate changes in atmospheric chemistry on a planet having Earth's atmospheric composition, which we subjected to small changes in orbital position, of the order of 5-10 per cent for a solar-type G2V, F2V, and K2V star. We then applied a chemical source-sink analysis to the biomarkers in order to understand how chemical processes affect biomarker concentrations. We start with the composition of the present Earth, since this is the only example we know for which a spectrum of biomarker molecules has been measured. We then investigate the response of the biomarkers to changes in the input stellar flux. Computing the thermal profile for atmospheres rich in H2 O, CO2 and CH4 is however a major challenge for current radiative schemes, due, among other things, to lacking spectroscopic data. Therefore, as a first step, we employ a more moderate approach, by investigating small shifts in planet-star distance and assuming an earthlike biosphere. To calculate this shift we assumed a criteria for complex life based on the Earth, i.e. the earthlike planetary surface temperature varied between zero to thirty degrees Centigrade which led to a narrow HZ width of (0.94-1.08)
We analyze four XMM-Newton galaxy clusters in order to test whether their soft X-ray excess emission in the 0.2-0.5 keV band as reported by Kaastra et al. (2003) maintains after the application of the current knowledge of the XMM-Newton background and calibration. We show that in the bright central 500 kpc regions the details of the background modeling are insignificant. Thus, the cluster soft excess is not a background artifact, contrary to recent claims by Bregman et al. (2006). We find evidence that the change in PN calibration between years 2002 and 2005 results in significant decrease of the soft excess signal. However, MOS instrument still measures significant amounts of soft excess, or sub-Galactic NH. These inconsistencies indicate that significant calibration problems still exist in PN or MOS instruments, or both. A more thorough cross-calibration is needed to pinpoint the source and the magnitude of the calibration problems, and to derive firm conclusions on the cluster soft X-ray excess emission.
Almost all of the studies devoted to relativistic astrometry are based on the integration of the null geodesic differential equations. However, the gravitational deflection of light rays can be calculated by a different method, based on the determination of the bifunction giving half the squared geodesic distance between two arbitrary points-events, the so-called Synge's world function. We give a brief review of the main results obtained by this method.
The new generation of atomic clocks will reach unprecedented uncertainties in frequency of $10^{-18}$. In order to prepare space missions such as ACES, we compute all relativistic frequency shifts detectable during this mission in the case of a clock aboard the International Space Station.
Microscopic presolar grains extracted from primitive meteorites have extremely anomalous isotopic compositions revealing the stellar origin of these grains. The composition of presolar spinel grain OC2 is different from that of all other presolar spinel grains. Large excesses of the heavy Mg isotopes are present and thus an origin from an intermediate-mass (IM) asymptotic giant branch (AGB) star was previously proposed for this grain. We discuss the isotopic compositions of presolar spinel grain OC2 and compare them to theoretical predictions. We show that the isotopic composition of O, Mg and Al in OC2 could be the signature of an AGB star of IM and metallicity close to solar experiencing hot bottom burning, or of an AGB star of low mass (LM) and low metallicity suffering very efficient cool bottom processing. Large measurement uncertainty in the Fe isotopic composition prevents us from discriminating which model better represents the parent star of OC2. However, the Cr isotopic composition of the grain favors an origin in an IM-AGB star of metallicity close to solar. Our IM-AGB models produce a self-consistent solution to match the composition of OC2 within the uncertainties related to reaction rates. Within this solution we predict that the 16O(p,g)17F and the 17O(p,a)14N reaction rates should be close to their lower and upper limits, respectively. By finding more grains like OC2 and by precisely measuring their Fe and Cr isotopic compositions, it may be possible in the future to derive constraints on massive AGB models from the study of presolar grains.
Aims: An all-sky survey of loop- and arc-like intensity enhancements has been performed in order to investigate the large-scale structure of the diffuse far-infrared emission. Methods: We used maps made of 60 and 100 micrometer processed IRAS data (Sky Survey Atlas and dust infrared emission maps) to identify large-scale structures: loops, arcs or cavities, in the far-infrared emission in the Galaxy. Distances were attributed to a subsample of loops using associated objects. Results: We identified 462 far-infrared loops, analyzed their individual FIR properties and their distribution. This data forms the Catalogue of Far-Infrared Loops in the Galaxy. We obtained observational estimates of f_in~30% and f_out~5% for the hot gas volume filling factor of the inward and outward Galactic neighbourhood of the Solar System. We obtained a slope of the power law size luminosity function {beta}=1.37 for low Galactic latitudes in the outer Milky Way. Conclusions: Deviations in the celestial distribution of far-infrared loops clearly indicate, that violent events frequently overwrite the structure of the interstellar matter in the inner Galaxy. Our objects trace out the spiral arm structure of the Galaxy in the neighbourhood of the Sun and their distribution clearly suggests that there is an efficient process that can generate loop-like features at high Galactic latitudes. Power law indices of size luminosity distributions suggest, that the structure of the ISM is ruled by supernovae and stellar winds at low Galactic latitudes while it is governed by supersonic turbulence above the Galactic plane.
I discuss the role of the sedimentation of helium in galaxy cluster cores on the observed X-ray properties and present a history of the metal accumulation in the ICM, with new calculations with respect to my previous work following the recent evidence of a bi-modal distribution of the delay time in Supernovae Type Ia.
The masses of compact objects like white dwarfs, neutron stars and black holes are fundamental to astrophysics, but very difficult to measure. We present the results of an analysis of subluminous B (sdB) stars in close binary systems with unseen compact companions to derive their masses and clarify their nature. Radial velocity curves were obtained from time resolved spectroscopy. The atmospheric parameters were determined in a quantitative spectral analysis. With high resolution spectra we were able to measure the projected rotational velocity of the stars with high accuracy. The assumption of orbital synchronization made it possible to constrain inclination angle and companion mass of the binaries. Five invisible companions have masses that are compatible with white dwarfs or late type main sequence stars. But four sdBs have very massive companions like heavy white dwarfs, neutron stars or even black holes. Such a high fraction of massive compact companions can not be explained with current models of binary evolution.
The dark matter halos of bright galaxies appear to have densities in their inner parts that are at least an order of magnitude lower than predicted from structure formation simulations. This well-known difficulty for LCDM would be ameliorated if galaxy evolution could drive down the dark matter density in the inner halo. Here I present a study of the halo density reductions that result from torques by an idealized bar. When countervailing compression by baryonic contraction is ignored, I find that moderate strength bars of any size can reduce the mean density of the inner halo by 20% - 30%. Extreme bars, that are long, massive, and skinny, can reduce the mean inner density by a factor ~10, while shorter, but still very strong bars effect a density reduction by a factor of ~2. The largest density reductions are achieved at the expense of removing a sizeable fraction of the angular momentum likely to reside in the baryonic component. I show that these results from simulations with rigid bars are numerically robust.
Near infrared (IR) studies of Cepheid variables in the LMC take advantage of the reduced light curve amplitude and metallicity dependence at these wavelengths. This work presents such photometry for two young clusters known to contain sizeable Cepheid populations: NGC 1866 and NGC 2031. Our goal is to determine light curves and period-luminosity (PL) relations in the near-IR, to assess the similarity between cluster and field pulsators, and to examine the predictive capability of current pulsation models. The light curves are obtained from multiwavelength broadband J,H,Ks photometry of Cepheids in both clusters, with periods previously established from optical photometry. Mean magnitudes for the Cepheids are used to construct PL relations in the near-IR. The properties in the PL planes are compared with the behavior of field Cepheids in the LMC and with the predictions of recent pulsational models, both canonical and overluminous. Cluster and field Cepheids are homogeneous and the inclusion of the cluster Cepheids in the field sample extends nicely the PL relation. The slope of the PL relation is constant over the whole period range and does not show -- at least in the adopted IR bands -- the break in slope at P ~ 10 d reported by some authors. A comparison with the predictions of pulsation models allows an estimate for the distance moduli of NGC 1866 and NGC 2031. The two clusters are found to lie at essentially the same distance. Fitting of theoretical models to the data gives, for the K filter, (m-M)_0 = 18.62+-0.10 if canonical models are used and (m-M)_0 = 18.42+-0.10 if overluminous models are used. On the basis of this result, some considerations on the relationship between the clusters and the internal structure of the LMC are presented.
We report on the possibility of detecting a submillimetre-sized extra dimension by observing gravitational waves (GWs) emitted by pointlike objects orbiting a braneworld black hole. Matter in the `visible' universe can generate a discrete spectrum of high frequency GWs with amplitudes moderately weaker than the predictions of general relativity (GR), while GW signals generated by matter on a `shadow' brane hidden in the bulk are potentially strong enough to be detected using current technology. We know of no other astrophysical phenomena that produces GWs with a similar spectrum, which stresses the need to develop detectors capable of measuring this high-frequency signature of large extra dimensions.
12 Bootis is a double-lined spectroscopic binary whose orbit has been resolved by interferometry. We present a detailed modelling of the system and show that the available observational constraints can be reproduced by models at different evolutionary stages, depending on the details of extra-mixing processes acting in the central regions. In order to discriminate among these theoretical scenarios, additional and independent observational constraints are needed: we show that these could be provided by solar-like oscillations, that are expected to be excited in both system components.
Using the SCUBA bolometer array on the JCMT, we have carried out a
submillimetre survey of Broad Absorption Line quasars (BALQs). The sample has
been chosen to match, in redshift and optical luminosity, an existing benchmark
850um sample of radio-quiet quasars, allowing a direct comparison of the submm
properties of BAL quasars relative to the parent radio-quiet population. We
reach a submm limit 1.5mJy at 850um, allowing a more rigorous measure of the
submm properties of BAL quasars than previous studies. Our submm photometry
complements extensive observations at other wavelengths, in particular X-rays
with Chandra and mid-infrared with Spitzer.
To compare the 850um flux distribution of BALQs with that of the non-BAL
quasar benchmark sample, we employ a suite of statistical methods, including
survival analysis and a novel Bayesian derivation of the underlying flux
distribution. Although there are no strong grounds for rejecting the null
hypothesis that BALQs on the whole have the same submm properties as non-BAL
quasars, we do find tentative evidence (1-4 percent significance from a K-S
test and survival analysis) for a dependence of submm flux on the equivalent
width of the characteristic CIV broad absorption line. If this effect is real -
submm activity is linked to the absorption strength of the outflow - it has
implications either for the evolution of AGN and their connection with star
formation in their host galaxies, or for unification models of AGN.
Due to their low gravitational energies, dwarf galaxies are greatly exposed to energetical influences from internal and external sources. By means of chemodynamical models we show that their star formation is inherently self-regulated, that peculiar abundance ratios can only be achieved assuming different star-formation episodes and that evaporation of interstellar clouds embedded in a hot phase can lead to a fast mixing of the interstellar gas. Metal-enriched hot outflows can accrete onto infalling clouds by means of condensation leading to a large range of timescales for the self-enrichment of the ISM from local scales within a few tens of Myr up to a few Gyr for the large-range circulation. Infall of clouds is also required to explain abundance ratios of metal-poor galaxies at evolved stages because it reduces the metallicity altering only marginally the abundance ratios.
We have studied three-dimensional hydrodynamic interactions of relativistic extragalactic jets with two-phase ambient media. These jets propagate through a denser homogeneous gas and then impact clouds with densities 100 to 1000 times higher than the initial beam density. The deflection angle of the jet is influenced more by the density contrast of the cloud than by the beam Mach number of the jet. A relativistic jet with low relativistic beam Mach number can eventually be slightly bent after it crosses the dense cloud; however, we have not seen permanently bent structures in the interaction of a high relativistic beam Mach number jet with a cloud. The relativistic jet impacts on dense clouds do not necessarily destroy the clouds completely, and much of the cloud body can survive as a coherent blob. This enhancement of cloud durability is partly due to the geometric influence of the off-axis collisions we consider and also arises from the lower rate of cloud fragmentation through the Kelvin-Helmholtz instability for relativistic jets. To compare our simulations with observed extragalactic radio jets, we have computed the approximate surface distributions of synchrotron emission at different viewing angles. These surface intensity maps show relativistic jets interacting with clouds can produce synchrotron emission knots similar to structures observed in many VLBI-scale radio sources. We find that the synchrotron emission increases steeply at the moment of impact and the emission peaks right before the jet passes through the cloud.
In order to help in the identification of INTEGRAL/ISGRI sources, we have developed a software package which allows a rapid and detailed cross-correlation to be performed between various source catalogues. It allows subsets of catalogues to be constructed at a selected level of probability of association, which can then be used to construct multi-waveband correlations.
We present the results of broad band (3-100 keV) observations of several X-ray pulsars with the INTEGRAL and RXTE observatories. We concentrate on the luminosity and energy dependence of the pulse profile and the variations of the cyclotron line energy. In V0332+53 the line energy changes nearly linearly with the source luminosity, while in 4U0115+63 its behavior is more complicated. Strong variations of the pulse profile with the energy and source intensity were found for both of pulsars; in V0332+53 the changes of the pulse profile near the cyclotron line are especially drastic. The preliminary results obtained for Her X-1 and GX 301-2 in a high intensity state show the absence of significant pulse profile changes with the energy. Results and possible emission mechanisms are briefly discussed in terms of theoretical models of accreting pulsars.
It has been recently argued that the HCN J=1--0 line emission may not be an unbiased tracer of dense molecular gas ($\rm n\ga 10^4 cm^{-3}$) in Luminous Infrared Galaxies (LIRGs: $\rm L_{FIR}> 10^{11} L_{\odot}$) and HCO$^+$ J=1--0 may constitute a better tracer instead (Graci\'a-Carpio et al. 2006), casting doubt into earlier claims supporting the former as a good tracer of such gas (Gao & Solomon 2004; Wu et al. 2006). In this paper new sensitive HCN J=4--3 observations of four such galaxies are presented, revealing a surprisingly wide excitation range for their dense gas phase that may render the J=1--0 transition from either species a poor proxy of its mass. Moreover the well-known sensitivity of the HCO$^+$ abundance on the ionization degree of the molecular gas (an important issue omitted from the ongoing discussion about the relative merits of HCN and HCO$^+$ as dense gas tracers) may severely reduce the HCO$^+$ abundance in the star-forming and highly turbulent molecular gas found in LIRGs, while HCN remains abundant. This may result to the decreasing HCO$^+$/HCN J=1--0 line ratio with increasing IR luminosity found in LIRGs, and casts doubts on the HCO$^+$ rather than the HCN as a good dense molecular gas tracer. Multi-transition observations of both molecules are needed to identify the best such tracer, its relation to ongoing star formation, and constrain what may be a considerable range of dense gas properties in such galaxies.
Observations suggest that star clusters often form in binaries or larger bound groups. Therefore, mergers between two clusters are likely to occur. If these clusters both harbor an intermediate-mass black hole (IMBH; 10^{2-4} Msun) in their center, they can become a strong source of gravitational waves when the black holes merge with each other. In order to understand the dynamical processes that operate in such a scenario, one has to study the evolution of the merger of two such young massive star clusters, and more specifically, their respective IMBHs. We employ the direct-summation Nbody4 numerical tool on special-purpose GRAPE6 hardware to simulate a merger of two stellar clusters each containing 63,000 particles and a central IMBH. This allows us to study accurately the orbital evolution of the colliding clusters and the embedded massive black holes. Within ~7 Myr the clusters have merged and the IMBHs constitute a hard binary. The final coalescence happens in ~10^8 yrs. The implication of our analysis is that intermediate-mass black holes merging as the result of coalescence of young dense clusters could provide a source for the Laser Interferometer Space Antenna (LISA) space-based gravitational wave detector mission. We find that interactions with stars increase the eccentricity of the IMBH binary to about 0.8. Although the binary later circularizes by emission of gravitational waves, the residual eccentricity can be detectable through its influence on the phase of the waves if the last few years of inspiral are observed.
HST observations reveal that young massive star clusters form in gas-rich environments like the Antenn{\ae} galaxy which will merge in collisional processes to form larger structures. These clusters amalgamate and if some of these clusters harbour a massive black hole in their centres, they can become a strong source of gravitational waves when they coalesce. In order to understand the dynamical processes that are into play in such a scenario, one has to carefully study the evolution of the merger of two of such young massive star clusters and more specifically their respective massive black holes. This will be a promising source of gravitational waves for both, LISA and the proposed Big Bang Observer (BBO), whose first purpose is to search for an inflation-generated gravitational waves background in the frequency range of $10^{-1}-1$ Hz. We used high-resolution direct summation $N-$body simulations to study the orbital evolution of two colliding globular clusters with different initial conditions. Even if the final eccentricity is almost negligible when entering the bandwidth, it will suffice to provide us with detailed information about these astrophysical events.
We present the results of seven years of K-band monitoring of the low-mass X-ray binary GRS 1915+105. Positive correlations between the infrared flux and the X-ray flux and X-ray hardness are demonstrated. Analysis of the frequency spectrum shows that the orbital period of the system is $P_{orb}= 30.8 \pm 0.2$ days. The phase and amplitude of the orbital modulation suggests that the modulation is due to the heating of the face of the secondary star. We also report another periodic signature between 31.2 and 31.6 days, most likely due to a superhump resonance. From the superhump period we then obtain a range on the mass ratio of the system, $0.05 < q < 0.12$.
Gamma-ray bursts, which are among the most violent events in the universe, are one of the few viable candidates to produce ultra high energy cosmic rays. Recently, observations have revealed that GRBs generally originate from metal-poor galaxies and do not directly trace cosmic star formation, as might have been assumed from their association with core-collapse supernovae. Several implications follow from these findings. The redshift distribution of observed GRBs is expected to peak at higher redshift (compared to cosmic star formation), which is supported by the mean redshift of the Swift GRB sample, <z>~3. If GRBs are, in fact, the source of the observed UHECR, then cosmic-ray production would evolve with redshift in a stronger fashion than has been previously suggested. This necessarily leads, through the GZK process, to an enhancement in the flux of cosmogenic neutrinos, providing a near-term approach for testing the gamma-ray burst-cosmic ray connection with ongoing and proposed UHE neutrino experiments.
Most previous high-angular (<0.1 arcsec) resolution studies of molecular masers in high-mass star forming regions (SFRs) have concentrated mainly on either water or methanol masers. While high-angular resolution observations have clarified that water masers originate from shocks associated with protostellar jets, different environments have been proposed in several sources to explain the origin of methanol masers. Tha aim of the paper is to investigate the nature of the methanol maser birthplace in SFRs and the association between the water and methanol maser emission in the same young stellar object. We have conducted phase-reference Very Long Baseline Interferometry (VLBI) observations of water and methanol masers toward two high-mass SFRs, Sh 2-255 IR and AFGL 5142. In Sh 2-255 IR water masers are aligned along a direction close to the orientation of the molecular outflow observed on angular scales of 1-10 arcsec, tracing possibly the disk-wind emerging from the disk atmosphere. In AFGL 5142 water masers trace expansion at the base of a protostellar jet, whilst methanol masers are more probably tracing infalling than outflowing gas. The results for AFGL 5142 suggest that water and methanol masers trace different kinematic structures in the circumstellar gas.
Shortly after the addition of a 1/R term to the Einstein-Hilbert action was proposed as a solution to the cosmic-acceleration puzzle, Chiba showed that such a theory violates Solar System tests of gravity. A flurry of recent papers have called Chiba's result into question. They argue that the spherically-symmetric vacuum spacetime in this theory is the Schwarzschild-de Sitter solution, making this theory consistent with Solar System tests. We point out that although the Schwarzschild-de Sitter solution exists in this theory, it is not the unique spherically-symmetric vacuum solution, and it is not the solution that describes the spacetime in the Solar System. The solution that correctly matches onto the stellar-interior solution differs from Schwarzschild-de Sitter in a way consistent with Chiba's claims. Thus, 1/R gravity is ruled out by Solar System tests.
[ABRIDGED] We present the rest-frame optical (B, V, and R-band) luminosity
functions (LFs) of galaxies at 2<z<3.5, measured from a K-selected sample
constructed from the deep NIR MUSYC, the ultra-deep FIRES, and the GOODS-CDFS
surveys. This sample is unique for its combination of surveyed area and large
range of luminosities, allowing us to constrain the faint end of the LF, to
probe the bright end with unprecedented statistics, and to properly account for
the effects of field-to-field variations. The measured LF faint-end slopes at
z>2 are consistent with those in the local LFs. The characteristic magnitudes
are significantly brighter than the local values, while the measured values for
Phi_star are a factor of ~5 smaller with respect to the local values. By
integrating the LFs, we estimate the number and luminosity densities. We
present for the first time the LF of Distant Red Galaxies (DRGs; defined here
as z>2 sources with observed J-K>2.3). While DRGs and non-DRGs are
characterized by similar LFs at the bright end, the faint-end slope of the
non-DRG LF is much steeper than that of DRGs. Comparing the rest-frame V-band
LF of non-DRGs to that inferred for Lyman break galaxies by Shapley et al.
(2001), we find a significantly less steep faint-end slope. The contribution of
DRGs to the global densities is 14%-25% in number and 22%-33% in luminosity.
From the rest-frame U-V colors and stellar population synthesis models, we
estimate the mass-to-light ratios (M/L) of the different sub-samples. The M/L
ratios of DRGs are a factor of ~5 (in the rest-frame R- and V-bands) higher
than those of non-DRGs. The global stellar mass density at 2<z<3.5 appears to
be dominated by DRGs. Qualitatively similar results are obtained when the
population is split by rest-frame U-V color instead of observed J-K color.
We report the results of pointed observations of the prototypical ultra-luminous infrared galaxy (ULIRG) Arp 220 at 850 microns using the polarimeter on the SCUBA instrument on the James Clerk Maxwell Telescope. We find a Bayesian 99 per cent confidence upper limit on the polarized emission for Arp 220 of 1.54 per cent, averaged over the 15 arcsec beam-size. Arp 220 can serve as a proxy for other, more distant such galaxies. This upper limit constrains the magnetic field geometry in Arp 220 and also provides evidence that polarized ULIRGs will not be a major contaminant for next-generation cosmic microwave background polarization measurements.
We calculate in this article the CMB and matter power spectra of a class of early $f(R)$ cosmologies, which takes the form of $f(R) = R + \lambda_1 H_0^2\text{exp}[R/(\lambda_2 H_0^2)]$. Unlike the late-time $f(R)$ cosmologies such as $f(R) = R + \alpha(-R)^\beta$ ($\beta<0$), the deviation from $\Lambda\text{CDM}$ of this model occurs at a higher redshift (thus the name \emph{Early $f(R)$ Cosmology}), and this important feature leads to rather different ISW effect and CMB spectrum. The matter power spectrum of this model is, at the same time, again very sensitive to the chosen parameters, and LSS observations such as SDSS should constrain the parameter space stringently. We expect that our results are applicable at least qualitatively to other models that produce $f(R)$ modification to GR at earlier times (\emph{e.g.}, redshifts $\mathcal{O}(10) \lesssim z \lesssim \mathcal{O}(1)$) than when dark energy begins to dominate -- such models are strongly disfavored by data on CMB and matter power spectra.
Disc accretion to a rotating star with a non-dipole magnetic field is investigated for the first time in full three-dimensional (3D) magnetohydrodynamic (MHD) simulations. We investigated the cases of (1) pure dipole, (2) pure quadrupole, and (3) dipole plus quadrupole fields. Simulations have shown that in each case the structure of the funnel streams and associated hot spots on the surface of the star have specific features connected with the magnetic field configuration. In the case (1), matter accretes in two funnel streams which form two arch-like spots near the magnetic poles. In the case (3), most of the matter flows through the quadrupole "belt" forming a ring-shaped hot region on the magnetic equator. In the case (2), magnetic flux in the northern magnetic hemisphere is larger than that in the southern, and the quadrupole belt and the ring are displaced to the south. The stronger the quadrupole, the closer the ring is to the magnetic equator. At sufficiently large misalignment angle $\Theta$, matter also flows to the south pole, forming a hot spot near the pole. The light curves have a variety of different features which makes it difficult to derive the magnetic field configuration from the light curves. There are specific features which are different in cases of dipole and quadrupole dominated magnetic field: (1) Angular momentum flow between the star and disc is more efficient in the case of the dipole field; (2) Hot spots are hotter and brighter in case of the dipole field because the matter accelerates over a longer distance compared with the flow in a quadrupole case.
Supermassive black holes in the centers of giant elliptical galaxies are remarkably faint given their expected accretion rates. This motivates models of radiatively inefficient accretion, due to either thermal decoupling of ions from electrons, the generation of outflows or convective motions that inhibit accretion, or the settling of gas to a gravitationally unstable disk that forms stars in preference to feeding the black hole. A prediction of the latter model is the presence of cold molecular gas in a thin disk around the black hole. Here we report Submillimeter Array observations of the nucleus of the giant elliptical galaxy M87 and the tentative detection of CO(J=2--1) line emission at the position and velocity of the black hole. The implied molecular gas mass is 4.3+-1.2 x 10^6 Msun, in agreement with the predictions of Tan & Blackman (2005). We also detect 1.3mm continuum emission from the nucleus and several knots in the jet, including one that has been undergoing a flare.
The heliosphere serves as a probe of interstellar material (ISM) close to the Sun. Measurements of ISM inside and outside of the heliosphere show that we reside in typical warm partially ionized ISM that can be successfully modeled using equilibrium photoionization models. The heliosphere wake leaves a ~200 X 1000 AU trail in space of low density, n<0.05 /cc, cooling plasma comingled with ISM. The closest ISM flows through the solar vicinity at V_LSR ~20 km/s, with an upwind direction towards the Scorpius-Centaurus Association. Clouds in this flow have thicknesses typically <1 pc. The flow is decelerating, with velocity variations of ~3-4 km/s /pc. The alpha Oph sightline shows evidence of a cold, possibly tiny, cloud.
I review the status of massive star formation theories: accretion from collapsing, massive, turbulent cores; competitive accretion; and stellar collisions. I conclude the observational and theoretical evidence favors the first of these models. I then discuss: the initial conditions of star cluster formation as traced by infrared dark clouds; the cluster formation timescale; and comparison of the initial cluster mass function in different galactic environments.
The star upsilon Andromeda is orbited by three known planets, the innermost of which has an orbital period of 4.617 days and a mass at least 0.69 that of Jupiter. This planet is close enough to its host star that the radiation it absorbs overwhelms its internal heat losses. Here we present the 24 micron light curve of this system, obtained with the Spitzer Space Telescope. It shows a clear variation in phase with the orbital motion of the innermost planet. This is the first demonstration that such planets possess distinct hot substellar (day) and cold antistellar (night) faces.
We investigate the formation of the ten double-lined double white dwarfs that have been observed so far. A detailed stellar evolution code is used to calculate grids of single-star and binary models and we use these to reconstruct possible evolutionary scenarios. We apply various criteria to select the acceptable solutions from these scenarios. We confirm the conclusion of Nelemans et al. (2000) that formation via conservative mass transfer and a common envelope with spiral-in based on energy balance or via two such spiralins cannot explain the formation of all observed systems. We investigate three different prescriptions of envelope ejection due to dynamical mass loss with angular-momentum balance and show that they can explain the observed masses and orbital periods well. Next, we demand that the age difference of our model is comparable to the observed cooling-age difference and show that this puts a strong constraint on the model solutions. However, the scenario in which the primary loses its envelope in an isotropic wind and the secondary transfers its envelope, which is then re-emitted isotropically, can explain the observed age differences as well. One of these solutions explains the DB-nature of the oldest white dwarf in PG1115+116 along the evolutionary scenario proposed by Maxted et al. (2002a), in which the helium core of the primary becomes exposed due to envelope ejection, evolves into a giant phase and loses its hydrogen-rich outer layers.
The distribution of mass on galaxy cluster scales is an important test of structure formation scenarios, providing constraints on the nature of dark matter itself. Several techniques have been used to probe the mass distributions of clusters, sometimes yielding results which are discrepant, or at odds with clusters formed in simulations - for example giving NFW concentration parameters much higher than expected in the standard CDM model. In addition, the velocity fields of some well studied galaxy clusters reveal the presence of several structures close to the line-of-sight, often not dynamically bound to the cluster itself. We investigate what impact such neighbouring but unbound massive structures would have on the determination of cluster profiles using weak gravitational lensing. Depending on its concentration and mass ratio to the primary halo, one secondary halo close to the line-of-sight can cause the estimated NFW concentration parameter to be significantly higher than that of the primary halo, and also cause the estimated mass to be biased high. Although it is difficult to envisage how this mechanism alone could yield concentrations as high as reported for some clusters, multiple haloes close to the line-of-sight, such as in the case of Abell 1689, can substantially increase the concentration parameter estimate. Together with the fact that clusters are triaxial, and that including baryonic physics also leads to an increase in the concentration of a dark matter halo, the tension between observations and the standard CDM model is eased. If the alignment with the secondary structure is imprecise, then the estimated concentration parameter can also be even lower than that of the primary halo, reinforcing the importance of identifying structures in cluster fields.
We discuss images of M87 from 3.6 to 160 um obtained with Spitzer. As found previously, there is an excess in the far infrared over a simple power law interpolation from the radio to the resolved nonthermal features in the mid-infrared and optical. We show that this excess is most likely warm dust in the galaxy itself, and that the properties of this emission component are similar to the far infrared emission of normal giant elliptical galaxies. The new observations let us determine the spectrum of the jet and surrounding lobes of nonthermal emission. We find that even in the lobes the synchrotron break frequency is in the optical, probably requiring in situ particle acceleration not only in the jet but in the lobes as well.
We report on the results of detailed spectral studies of the ultra-luminous X-ray source (ULX), M81 X-9 (Holmberg IX X-1), made with XMM-Newton on 2001 April 22 and with ASCA on 1999 April 6. On both occasions, the source showed an unabsorbed 0.5-10 keV luminosity of ~2E40 erg/s (assuming a distance of 3.4Mpc) and a soft spectrum apparently represented by a multi-color disk model with an innermost disk temperature of 1.3-1.5 keV. Adding a power-law model further improved the fit. However, as previously reported, the high luminosity cannot be reconciled with the high disk temperature within a framework of the standard accretion disk radiating at a sub-Eddington luminosity. Therefore, we modified the multi-color disk model, and allowed the local disk temperature to scale as r^(-p) on the distance r from the black hole, with p being a free parameter. We then found that the XMM-Newton and the ASCA spectra can be both reproduced successfully with p~0.6 and the innermost disk temperature of 1.4-1.8 keV. These flatter temperature profiles suggest deviation from the standard Shakura-Sunyaev disk, and are consistent with predictions of a slim disk model.
We present the results of six Suzaku observations of the recurrent black hole transient 4U1630-472 during its decline from outburst from February 8 to March 23 in 2006. All observations show the typical high/soft state spectral shape in the 2-50keV band, roughly described by an optically thick disk spectrum in the soft energy band plus a weak power-law tail that becomes dominant only above \~20keV. The disk temperature decreases from 1.4keV to 1.2keV as the flux decreases by a factor 2, consistent with a constant radius as expected for disk-dominated spectra. All the observations reveal significant absorption lines from highly ionized (H-like and He-like) iron Ka at 7.0keV and 6.7keV. The brightest datasets also show significant but weaker absorption structures between 7.8keV and 8.2keV, which we identify as a blend of iron Kb and nickel Ka absorption lines. The energies of these absorption lines suggest a blue shift with an outflow velocity of ~1000km/s.. The H-like iron Ka equivalent width remains approximately constant at ~30 eV over all the observations, while that of the He-like Ka line increases from 7 eV to 20 eV. Thus the ionization state of the material decreases, as expected from the decline in flux. We fit the profiles with Voigt functions (curve of growth) to derive absorbing columns, then use these together with detailed photo-ionization calculations to derive physical parameters of the absorbing material. The data then constrain the velocity dispersion of the absorber to 200-2000 km/s, and the size of the plasma as ~1E10 cm assuming a source distance of 10 kpc.
In the Galactic microquasars with double peak kHz quasi-periodic oscillations (QPOs), the ratio of the two frequencies is 3:2. This supports the suggestion that double peak kHz QPOs are due to a non-linear resonance between two modes of accretion disk oscillations. For the microquasars with known mass, we briefly compare the black hole spin estimates based on the orbital resonance model with the recently reported spin predictions obtained by fitting the spectral continua. Results of these two approaches are not in good agreement. We stress that if the spectral fit estimates are accurate and can be taken as referential (which is still questionable), the disagreement between the predicted and referential values would represent a rather generic problem for any relativistic QPO model, as no spin influence would appear in the observed 1/M scaling of the QPO frequencies. The epicyclic frequencies relevant in these models are often considered to be equal to those of a test particle motion. However modifications of the frequencies due to the disc pressure or other non-geodesic effects may play an important role, and the inaccuracy introduced in the spin estimates by the test particle approximation could be crucial.
We investigate the effect of dark energy on the limits on the shear anisotropy in spatially homogeneous Bianchi cosmological models obtained from measurements of the temperature anisotropies in the cosmic microwave background. We shall primarily assume that the dark energy is modelled by a cosmological constant. In general, we find that there are tighter bounds on the shear than in models with no cosmological constant, although the limits are (Bianchi) model dependent. In addition, there are special spatially homogeneous cosmological models whose rate of expansion is highly anisotropic, but whose cosmic microwave background temperature is measured to be exactly isotropic at one instant of time.
The general context of this paper is the study of magnetic fields in the pre-main sequence intermediate mass Herbig Ae/Be stars. Magnetic fields are likely to play an important role in pre-main sequence evolution at these masses, in particular in controlling the gains and losses of stellar angular momentum. The particular aim of this paper is to announce the detection of a structured magnetic field in the Herbig Ae star HD 190073, and to discuss various scenarii for the geometry of the star, its environment and its magnetic field. We have used the ESPaDOnS spectropolarimeter at CFHT in 2005 and 2006 to obtain high-resolution and signal-to-noise circular polarization spectra which demonstrate unambiguously the presence of a magnetic field in the photosphere of this star. Nine circular polarization spectra were obtained, each one showing a clear Zeeman signature. This signature is suggestive of a magnetic field structured on large scales. The signature, which corresponds to a longitudinal magnetic field of 74+- 10 G, does not vary detectably on a one-year timeframe, indicating either an azimuthally symmetric field, a zero inclination angle between the rotation axis and the line of sight, or a very long rotation period. The optical spectrum of HD 190073 exhibits a large number of emission lines. We discuss the formation of these emission lines in the framework of a model involving a turbulent heated region at the base of the stellar wind, possibly powered by magnetic accretion. This magnetic detection brings an important element for our understanding of stellar magnetism at intermediate masses.
We searched for Technetium (Tc) in a sample of bright oxygen-rich asymptotic
giant branch (AGB) stars located in the outer galactic bulge. Tc is an unstable
element synthesised via the s-process in deep layers of AGB stars, thus it is a
reliable indicator of both recent s-process activity and third dredge-up.
We aim to test theoretical predictions on the luminosity limit for the onset
of third dredge-up.
Using high resolution optical spectra obtained with the UVES spectrograph at
ESO's VLT we search for resonance lines of neutral Tc in the blue spectral
region of our sample stars. These measurements allow us to improve the
procedure of classification of stars with respect to their Tc content by using
flux ratios. Synthetic spectra based on MARCS atmospheric models are presented
and compared to the observed spectra around three lines of Tc. Bolometric
magnitudes are calculated based on near infrared photometry of the objects.
Among the sample of 27 long period bulge variables four were found to
definitely contain Tc in their atmospheres.
The luminosity of the Tc rich stars is in agreement with predictions from AGB
evolutionary models on the minimum luminosity at the time when third dredge-up
sets in. However, AGB evolutionary models and a bulge consisting of a single
old population cannot be brought into agreement. This probably means that a
younger population is present in the bulge, as suggested by various authors,
which contains the Tc-rich stars here identified.
{This paper presents detailed analysis and modelisation of the star HD17051 (alias $\iota$ Hor), which appears as a specially interesting case among exoplanet host stars. As most of these stars, $\iota$ Hor presents a metallicity excess which has been measured by various observers who give different results, ranging from [Fe/H] = 0.11 to 0.26, associated with different atmospheric parameters. Meanwhile the luminosity of the star may be determined owing to Hipparcos parallax. Although in the southern hemisphere, this star belongs to the Hyades stream and its external parameters show that it could even be one of the Hyades stars ejected during cluster formation. The aim of this work was to gather and analyse our present knowledge on this star and to prepare seismic tests for future observations with the HARPS spectrometer (planned for November 2006).} {We have computed evolutionary tracks with various metallicities, in the two frameworks of primordial overmetallicity and accretion. We have concentrated on models inside the error boxes given by the various observers in the log g - log T$_{eff}$ diagram. We then computed the adiabatic oscillation frequencies of these models to prepare future observations.} {The detailed analysis of $\iota$ Hor presented in this paper already allowed to constrain its external parameters, mass and age. Some values given in the literature could be rejected as inconsistent with the overall analysis. We found that a model computed with the Hyades parameters (age, metallicity) was clearly acceptable, but other ones were possible too. We are confident that observations with HARPS will allow for a clear conclusion about this star and that it will bring important new light on the physics of exoplanet host stars.}
Studying the internal structure of exoplanets-host stars compared to that of similar stars without detected planets is particularly important for the understanding of planetary formation. The observed overmetallicity of stars with planets may be a hint in that respect. Although it is obviously related to the physical processes which occur during the early phases of planetary formation, the origin of this overmetallicity is unclear. It may be either primordial or related to accretion processes or both. In this framework, asteroseismic studies represent an excellent tool to determine the structural differences between stars with and without detected planets. The two different missions of COROT are linked in this programme: the detection of new planets and the seismic studies of their host stars share the same goal of a better understanding of planetary formation and evolution. The COROT main target HD52265, which is known to host at least one giant planet, will be observed continuously during five months: many interesting results are expected from this long run. Meanwhile, stellar oscillations will be searched for in all stars around which new planets will be discovered.
Studying the internal structure of exoplanets-host stars compared to that of similar stars without detected planets is particularly important for the understanding of planetary formation. The observed overmetallicity of stars around which planets have been detected may be a hint in that respect. In this framework, asteroseismic studies represent an excellent tool to determine the structural differences between stars with and without detected planets. After a general discussion on this subject, I present the special cases of three different stars: $\mu$ Arae which has been observed with the HARPS spectrograph in June 2004, $\iota$ Horologii, that we have studied in detail and will be observed with HARPS in November 2006, and finally HD 52265, one of the main targets of the COROT mission, an exoplanets-host star which will be observed with the COROT satellite during five consecutive months.
We present a study about the possibility to detect neutrino induced extensive air showers at the Pierre Auger Observatory. The Monte Carlo simulations performed take into account the details of the neutrino propagation inside the Earth, the air as well as the surrounding mountains which are modelled by a digital elevation map. Details on the sensitivity with respect to the incoming direction as well as the aperture and the total observable event rates are calculated on the basis of various assumptions of the incoming neutrino flux.
Using archival Chandra data we studied the X-ray emission properties of PSR B2224+65 and its environment. Albeit limited by photon statistics the spectral analysis suggests that the bulk of the emission from PSR B2224+65 is non-thermal. Fitting a power-law to the observed energy spectrum yields a photon index of $\Gamma=1.58^{+0.43}_{-0.33}$. The possible origin of the non-thermal pulsar emission is discussed in the context of the outer-gap model. We did not find any evidence for a compact nebula around PSR B2224+65 though the Chandra data reveal the existence of an extended feature which appears to be associated with PSR B2224+65. It extends from the pulsar position about 2 arcmin to the north-west. Its orientation deviates by $\sim118^{\circ}$ from the pulsar's proper motion direction. Investigating its energy spectrum shows that the emission of this extended feature is much harder than that of the pulsar itself and is non-thermal in nature.
Aims: This is the first paper in a series dedicated to investigating the kinematic properties of nearby associations of young stellar objects. Here we study the Taurus-Auriga association, with the primary objective of deriving kinematic parallaxes for individual members of this low-mass star-forming region. Methods: We took advantage of a recently published catalog of proper motions for pre-main sequence stars, which we supplemented with radial velocities from various sources found in the CDS databases. We searched for stars of the Taurus-Auriga region that share the same space velocity, using a modified convergent point method that we tested with extensive Monte Carlo simulations. Results: Among the sample of 217 Taurus-Auriga stars with known proper motions, we identify 94 pre-main sequence stars that are probable members of the same moving group and several additional candidates whose pre-main sequence evolutionary status needs to be confirmed. We derive individual parallaxes for the 67 moving group members with known radial velocities and give tentative parallaxes for other members based on the average spatial velocity of the group. The Hertzsprung-Russell diagram for the moving group members and a discussion of their masses and ages are presented in a companion paper.
Recently X-ray emission from protostellar jets has been detected with both XMM-Newton and Chandra satellites, but the physical mechanism which can give rise to this emission is still unclear. We performed an extensive exploration of a wide space of the main parameters influencing the jet/ambient interaction. Aims include: 1) to constrain the jet/ambient interaction regimes leading to the X-ray emission observed in Herbig-Haro objects in terms of the emission by a shock forming at the interaction front between a continuous supersonic jet and the surrounding medium; 2) to derive detailed predictions to be compared with optical and X-ray observations of protostellar jets; 3) to get insight into the protostellar jet's physical conditions. We performed a set of bidimensional hydrodynamic numerical simulations, in cylindrical coordinates, modeling supersonic jets ramming a uniform ambient medium. The model takes into account the most relevant physical effects, namely the thermal conduction and the radiative losses. Our model explains the observed X-ray emission from protostellar jets in a natural way. In particular we find that the case of a protostellar jet less dense than the ambient medium reproduces well the observations of the nearest Herbig-Haro object, HH154, and allows us to make detailed predictions of a possible X-ray source proper motion (vsh = 500 km/s), detectable with Chandra. Furthermore our results suggest that the simulated protostellar jets which best reproduce the X-rays observations cannot drive molecular outflows.
We calculate the X-ray emission from both constant and time evolving shocked fast winds blown by the central stars of planetary nebulae (PNs) and compare with observations. Using spherically symmetric numerical simulations with radiative cooling, we calculate the flow structure, and the X-ray temperature and luminosity of the hot bubble formed by the shocked fast wind. We find that a constant fast wind gives results that are very close to those obtained from the self-similar solution. We show that in order for a fast shocked wind to explain the observed X-ray properties of PNs, rapid evolution of the wind is essential. More specifically, the mass loss rate of the fast wind should be high early on when the speed is ~300-700 km/s, and then it needs to drop drastically by the time the PN age reaches ~1000 yr. This implies that the central star has a very short pre-PN (post-AGB) phase.
The detection of gamma-rays from the source HESS J1745-290 in the Galactic Center (GC) region with the H.E.S.S. array of Cherenkov telescopes in 2004 is presented. After subtraction of the diffuse gamma-ray emission from the GC ridge, the source is compatible with a point-source with spatial extent less than 1.2'(stat.) (95% CL). The measured energy spectrum above 160 GeV is compatible with a power-law with photon index of 2.25 +/- 0.04(stat.) +/- 0.10 (syst.) and no significant flux variation is detected. These measurements are discussed in the framework of dark matter annihilation. It is found that the bulk of the VHE emission must have non-dark-matter origin. Loose constraints on the velocity-weighted annihilation cross section <sigma.v> are derived assuming the presence of an astrophysical non-dark-matter gamma-ray contribution.
Stellar photometry of nearby irregular galaxies of the Local Group is used to identify and study the young and old stellar populations of these galaxies. An analysis of the spatial distributions of stars of different ages in face-on galaxies shows that the young stellar populations in irregular galaxies are concentrated toward the center, and form local inhomogeneities in star-forming regions, while the old stellar populations--red giants--form extended structures around the irregular galaxies. The sizes of these structures exceed the visible sizes of the galaxies at the 25m/arcsec^2 isophote by a factor of two to three. The surface density of the red giants decreases exponentially from the center toward the edge, similar to the disk components in spiral galaxies.
In 1925 Sir James Jeans calculated that a star made up of an ideal gas, generating energy as a moderately positive function of temperature and density, could not exist. Such stars would be unstable to oscillations of increasing size. It appears that the flaw in his calculation has never been clearly explained, especially the physical basis for it. I conclude it lies in an almost offhand assumption made about the form of the temperature perturbation. The episode has lessons concerning the structure of stars, the use of perturbation methods (especially in discussing stability), the use of mathematical models and the process by which one theory is chosen over its competitors.
We present a detailed study of the spectral and temporal properties of the X-ray flares emission of several GRBs. We select a sample of GRBs which X-ray light curve exhibits large amplitude variations with several rebrightenings superposed on the underlying three-segment broken powerlaw that is often seen in Swift GRBs. We try to understand the origin of these fluctuations giving some diagnostic in order to discriminate between refreshed shocks and late internal shocks. For some bursts our time-resolved spectral analysis supports the interpretation of a long-lived central engine, with rebrightenings consistent with energy injection in refreshed shocks as slower shells generated in the central engine prompt phase catch up with the afterglow shock at later times.
Stellar photometry obtained using the Hubble Space Telescope is used to study the distributions of the number densities of stars of various ages in 12 irregular and dwarf spiral galaxies viewed edge-on. Two subsystems can be distinguished in all the galaxies: a thin disk comprised of young stars and a thick disk containing a large fraction of the old stars (primarily red giants) in the system. Variations of the stellar number densities in the thin and thick disks in the Z direction perpendicular to the plane of the galaxy follow an exponential law. The size of the thin disk corresponds to the visible size of the galaxy at the mu = 25m/arcsec^2, while the thick disk is a factor of two to three larger. In addition to a thick disk, the massive irregular galaxy M82 also has a more extended stellar halo that is flattened at the galactic poles. The results of our previous study of 12 face-on galaxies are used together with the new results presented here to construct an empirical model for the stellar structure of irregular galaxies.
We study a class of generalized inflation models in which the inflaton is coupled to the Ricci scalar by a general $f(\phi, R)$ term. The scalar power spectrum, the spectral index, the running of the spectral index, the tensor mode spectrum and a new consistency relation of the model are calculated. We discuss in detail the issues of how to diagonize the coupled perturbation equations, how to deal with an entropy-like source, and how to determine the initial condition by quantization. By studying some explicit models, we find that rich phenomena such as a blue scalar power spectrum, a large running of the spectral index, and a blue tensor mode spectrum can be obtained.
Circumstellar disks play an important role in many stages of the evolution of stars. However, it is only possible to directly image circumstellar disks for a few of the nearest stars. For massive stars, the situation is even more difficult, as they are on average further away than the more numerous low mass stars. Here, we discuss spectropolarimetry which is a technique that can reveal the presence of disks on spatial scales of order stellar radii. It is therefore extremely useful in studying disks around young stars, while the method has prospects for quantitative modelling. In this review we will discuss the status on the study of (accretion) disks around intermediate- to high mass pre-main sequence stars and will concentrate on the linear spectropolarimetry aspect. We wil make a brief excursion to observations of massive evolved stars where spectropolarimetry has revealed the clumpy structure of stellar winds, and conclude with a brief outlook.
AIMS: We analyse the photometric properties of the early-type Fornax cluster
dwarf galaxy population, based on a wide field imaging study of the central
cluster area in V and I. We used the instrument/telescope combination
IMACS/Magellan at Las Campanas Observatory, providing much larger light
collecting area and better image resolution than previous surveys.
METHODS: We create a fiducial sample of Fornax cluster dwarf ellipticals
(dEs) in the following three steps: (1) To verify cluster membership, we
measured I-band surface brightness fluctuation (SBF) distances to candidate
dEs; (2) We re-assessed morphological classifications for candidate dEs too
faint for SBF detection; and (3) We searched for new candidate dEs in the
size-luminosity regime close to the resolution limit of previous surveys.
RESULTS: (1) We confirm cluster membership for 28 candidate dEs in the range
-16.6<M_V<-10.1 mag by means of SBF distances. We find no SBF background
galaxy. (2) Of 51 further candidate dEs in the range -13.2<M_V<-8.6 mag, 2/3
are confirmed as probable cluster members by morphological re-assessment, while
1/3 are re-classified as probable background objects. (3) We find 12 new dE
candidates in the range -12.3<M_V<-8.8 mag.
The surface brightness-magnitude relation defined by the resulting fiducial
dE sample shows that Fornax dEs are about 40% larger than Local Group dEs. The
Fornax dE sample furthermore defines a colour-magnitude relation that appears
slightly shallower than that of Local Group dEs. The early-type dwarf galaxy
luminosity function in Fornax has a faint end slope alpha = -1.1 +/- 0.1.
We discuss these findings in the context of structure formation theories.
(ABRIDGED)
We present 3D hydrodynamic simulations aimed at studying the dynamical and chemical evolution of the interstellar medium in dwarf spheroidal galaxies. This evolution is driven by the explosions of Type II and Type Ia supernovae, whose different contribution is explicitly taken into account in our models. We compare our results with avaiable properties of the Draco galaxy. Despite the huge amount of energy released by SNe explosions, in our model the galaxy is able to retain most of the gas allowing a long period ($> 3$ Gyr) of star formation, consistent with the star formation history derived by observations. The stellar [Fe/H] distribution found in our model matches very well the observed one. The chemical properties of the stars derive from the different temporal evolution between Type Ia and Type II supernova rate, and from the different mixing of the metals produced by the two types of supernovae. We reproduce successfully the observed [O/Fe]-[Fe/H] diagram.
Specularly reflected light, or glint, from an ocean surface may provide a useful observational tool for studying extrasolar terrestrial planets. Detection of sea-surface glints would differentiate ocean-bearing terrestrial planets, i.e. those similar to Earth, from other terrestrial extrasolar planets. The brightness and degree of polarization of both sea-surface glints and atmospheric Rayleigh scattering are strong functions of the phase angle of the extrasolar planet. We modify analytic expressions for the bi-directional reflectances previously validated by satellite imagery of the Earth to account for the fractional linear polarization of sea-surface reflections and of Rayleigh scattering in the atmosphere. We compare our models with Earth's total visual light and degree of linear polarization as observed in the ashen light of the Moon, or Earthshine. We predict the spatially-integrated reflected light and its degree of polarization as functions of the diurnal cycle and orbital phase of Earth and Earth-like planets of various imagined types. The difference in polarized reflectances of Earth-like planets may increase greatly the detectability of such planets in the glare of their host star. Finally, sea-surface glints potentially may provide a practical means to map the boundaries between oceans and continents on extrasolar planets.
Exact solutions of the Einstein field equations with cosmic string and space varying cosmological constant, viz., $\Lambda= \Lambda(r)$, in the energy-momentum tensors are presented. Three cases have been studied: where variable cosmological constant (1) has power law dependence, (2) is proportional to the string fluid density, and (3) is purely a constant. Some cases of interesting physical consequences have been found out such that (i) variable cosmological constant can be represented by a power law of the type $\Lambda=3r^{-2}$, (ii) variable cosmological constant and cosmic string density are interdependent to each other according to the relation $\Lambda=-8\pi{\rho}_s$, and (iii) cosmic string density can be scaled by a power law of the type ${\rho}_s=r^{-2}$. It is also shown that several known solutions can be recovered from the general form of the solutions obtained here.
Cosmic voids refer to the large empty regions in the universe with very low number density of galaxies. Because of their low density, voids are likely to be severely disturbed by the tidal effect from the surrounding dark matter. Assuming that the gravitational tidal field deviates the shapes of voids from spherical symmetry, we derive a completely analytic model for the void ellipticity distribution from physical principles. We use the spatial distribution of galaxies in a void as a measure of its shape, tracking the trajectory of the void galaxies under the influence of the tidal field using the Lagrangian perturbation theory. Our model implies that the void ellipticity distribution depends sensitively on the cosmological parameters. Testing our model against the high-resolution Millennium Run simulation, we find excellent quantitative agreements of the analytic predictions with the numerical results. We expect that the void ellipticity distribution will provide a very useful complimentary test of cosmology.
Multi-frequency (X-ray, optical and radio) observations of galaxy clusters indicate that the atmospheres of these cosmic structures consist of a complex structure of thermal (hot and warm) and non-thermal (with different origin and spectra) distribution of electrons (and protons) which is, therefore, far from its modelling as a single, thermal electronic gas. This evidence requires to go beyond the simple, standard lore of the SZ effect. This task is challenging for both the theoretical aspects of their modelling and for the experimental goals to be achieved, but it will return a large amount of physical information by using the SZ effect as a unique tool for astro-particle and cosmology.
The existence of radio pulsars having inferred magnetic elds in the magnetar regime suggests that possible transition objects could be found in the radio pulsar population. The discovery of such an object would contribute greatly to our understanding of neutron star physics. Here we report on unusual X-ray emission detected from the radio pulsar PSR J1119-6127 using XMM-Newton. The pulsar has a characteristic age of 1,700 yrs and inferred surface dipole magnetic eld strength of 4.1x10^13 G. In the 0.5-2.0 keV range, the emission shows a single, narrow pulse with an unusually high pulsed fraction of ~70%. No pulsations are detected in the 2.0-10.0 keV range, where we derive an upper limit at the 99% level for the pulsed fraction of 28%. The pulsed emission is well described by a thermal blackbody model with a high temperature of 2.4x10^6 K. While no unambiguous signature of magnetar-like emission has been found in high-magnetic-eld radio pulsars, the X-ray characteristics of PSR J1119-6127 require alternate models from those of conventional thermal emission from neutron stars. In addition, PSR J1119-6127 is now the radio pulsar with the smallest characteristic age from which thermal X-ray emission has been detected.
We present results from Chandra and XMM-Newton observations pulsar B1046-58. A high-resolution spatial analysis reveals pulsar wind nebula (PWN) ~6"x11" in size. The combined emission pulsar and its PWN is faint, with a best-fit power-law photon index and unabsorbed luminosity of ~10^32 ergs/s in the 0.5-10.0 keV a distance of 2.7 kpc). A spatially resolved imaging analysis presence of softer emission from the pulsar. No pulsations are PSR B1046-58; assuming a worst-case sinusoidal pulse profile, upper limit for the pulsed fraction in the 0.5-10.0 keV range of 53%. PWN emission is seen within 2" of the pulsar; the additional structures asymmetric and extend predominantly to the south-east. We discuss from the PWN as resulting from material downstream of the wind shock, as outflow from the pulsar or as structures confined by a velocity. The first two interpretations imply equipartition fields in structures of & 40-100 uG, while the latter case implies a velocity & 190 n^{-1/2} km/s (where n is the ambient number density in emission from an associated supernova remnant is detected.
We investigate the clustering of galaxy groups and clusters in the SDSS using the Berlind et al. (2006) group sample, which is designed to identify galaxy systems that each occupy a single dark matter halo. We estimate group masses from their abundances, and measure their relative large-scale bias as a function of mass. Our measurements are in agreement with the theoretical halo bias function, given a standard LCDM cosmological model, and they tend to favor a low value of the power spectrum amplitude sigma_8. We search for a residual dependence of clustering on other group properties at fixed mass, and find the strongest signal for central galaxy color in high mass groups. Massive groups with less red central galaxies are more biased on large scales than similar mass groups with redder central galaxies. We show that this effect is unlikely to be caused by errors in our mass estimates, and is most likely observational evidence of recent theoretical findings that halo bias depends on a ``second parameter'' other than mass, such as age or concentration. To compare with the data, we study the bias of massive halos in N-body simulations and quantify the strength of the relation between halo bias and concentration at fixed mass. In addition to confirming a non-trivial prediction of the LCDM cosmological model, these results have important implications for the role that environment plays in shaping galaxy properties.
In order to study the evolution of the relative fraction of obscured Active Galactic Nuclei (AGN) we constructed the largest sample to date of AGN selected in hard X-rays. The full sample contains 2341 X-ray-selected AGN, roughly 4 times the largest previous samples studied in this connection. Of these, 1229 (53%) have optical counterparts for which redshifts are available; these span the redshift range $z$=0-4. The observed fraction of obscured AGN declines only slightly with redshift. Correcting for selection bias, we find that the intrinsic fraction of obscured AGN must actually increase with redshift, as (1+$z$)$^{\alpha}$, with $\alpha$$\simeq0.4\pm$0.1. This evolution is consistent with the integrated X-ray background, which provides the strongest constraints at relatively low redshift, $z\sim$1. Summing over all AGN, we estimate the bolometric AGN light to be 3.8 nW m$^{-2}$ sr$^{-1}$, or $\lesssim$8% of the total extragalactic light. Together with the observed black hole mass density in the local Universe, this implies an accretion efficiency of $\eta \sim$0.1-0.2, consistent with the values typically assumed.
One of the outstanding puzzles about star formation is why it proceeds so slowly. Giant molecular clouds convert only a few percent of their gas into stars per free-fall time, and recent observations show that this low star formation rate is essentially constant over a range of scales from individual cluster-forming molecular clumps in the Milky Way to entire starburst galaxies. This striking result is perhaps the most basic fact that any theory of star formation must explain. I argue that a model in which star formation occurs in virialized structures at a rate regulated by supersonic turbulence can explain this observation. The turbulence in turn is driven by star formation feedback, which injects energy to offset radiation from isothermal shocks and keeps star-forming structures from wandering too far from virial balance. This model is able to reproduce observational results covering a wide range of scales, from the formation times of young clusters to the extragalactic IR-HCN correlation, and makes additional quantitative predictions that will be testable in the next few years.
Aims: We present discovery observations of the new cataclysmic variable star (CV) 1RXS J092737.4-191529, as well as spectra and photometry of SY Vol. The selection technique that turned up these two CVs is described; it should be efficient for finding dwarf novae with high outburst duty cycles. Methods: Two very common observational features of CVs, namely optical variability and X-ray emission, are combined to select targets for follow-up observations. Long-slit spectra were taken to identify CVs in the sample. Results: Two out of three objects selected in this way are CVs. One of these is the known dwarf nova SY Vol, while the second system, 1RXS J092737.4-191529, is a new discovery. We present medium resolution spectra, $UBVRI$ magnitudes, and high-speed photometry for both these CVs. Rapid flickering in the light curve of 1RXS J092737.4-191529 confirms the mass transferring binary nature of this object; it is probably a dwarf nova that was in quiescence during our observations.
Cornell, California Institute of Technology (Caltech), and Jet Propulsion Lab (JPL) have joined together to study development of a 25 meter sub-millimeter telescope (CCAT) on a high peak in the Atacama region of northern Chile, where the atmosphere is so dry as to permit observation at wavelengths as short as 200 micron. The telescope is designed to deliver high efficiency images at that wavelength with a total 1/2 wavefront error of about 10 microns. With a 20 arc min field of view, CCAT will be able to accommodate large format bolometer arrays and will excel at carrying out surveys as well as resolving structures to the 2 arc sec. resolution level. The telescope will be an ideal complement to ALMA. Initial instrumentation will include both a wide field bolometer camera and a medium resolution spectrograph. Studies of the major telescope subsystems have been performed as part of an initial Feasibility Concept Study. Novel aspects of the telescope design include kinematic mounting and active positioning of primary mirror segments, high bandwidth secondary mirror segment motion control for chopping, a Calotte style dome of 50 meter diameter, a mount capable of efficient scanning modes of operation, and some new approaches to panel manufacture. Analysis of telescope performance and of key subsystems will be presented to illustrate the technical feasibility and pragmatic cost of CCAT. Project plans include an Engineering Concept Design phase followed by detailed design and development. First Light is planned for early 2012.
The Amateur Sky Survey (TASS) is a loose confederation of amateur and professional astronomers. We describe the design and construction of our Mark IV systems, a set of wide-field telescopes with CCD cameras which take simultaneous images in the $V$ and $I_C$ passbands. We explain our observational procedures and the pipeline which processes and reduces the images into lists of stellar positions and magnitudes. We have compiled a large database of measurements for stars in the northern celestial hemisphere with $V$-band magnitudes in the range 7 < V < 13. This paper describes data taken over the four-year period starting November, 2001. One of our results is a catalog of repeated measurements on the Johnson-Cousins system for over 4.3 million stars.
We present models that reproduce the observed double-shell structure of the Homunculus Nebula around eta Carinae, including the stratification of infrared H2 and [FeII] emission seen in data obtained with the Phoenix spectrograph on Gemini South, as well as the corresponding stratified grain temperature seen in thermal-infrared data. Tuning the model to match the observed shell thickness allows us to determine the threshold density which permits survival of H2. An average hydrogen density of n_H=(0.5-1)x10^7 cm-3 in the outer zone is required to allow H2 to exist at all latitudes in the nebula, and for Fe+ to recombine. This gives independent confirmation of the very large mass of the Homunculus, indicating a total of roughly 15--35 Msun (although we note reasons why the lower end of this range is favored). At the interface between the atomic and molecular zones, we predict a sharp drop in the dust temperature, in agreement with the bimodal dust color temperatures observed in the two zones. In the outer molecular shell, the dust temperature drops to nearly the blackbody temperature, and becomes independent of grain size because of self-shielding at shorter UV wavelengths and increased heating at longer wavelengths. This relaxes constraints on large grain sizes suggested by near-blackbody color temperatures. Finally, from the strength of infrared [FeII] emission in the inner shell we find that the gas-phase Fe abundance is roughly solar. This is astonishing in such a dusty object, where one normally expects gaseous iron to be depleted by two orders of magnitude.
The massive, luminous Population I Wolf-Rayet stars can be considered as stars with the highest known sustained mass loss rates. Around 10% of WR stars may form carbon-rich dust in their dense and inhomogeneous winds. Though we are yet to find how dust is formed in such an extremely hostile environment, we have made substantial progress over the past decade. Here we discuss the results of recent high-resolution mid-infrared imaging of a sample of the most prodigious WR 'dustars'. This allows one to map rapidly changing dust-forming regions and derive some basic properties of the freshly formed dust.
We study the evolution of linear cosmological perturbations in f(R) models of accelerated expansion in the physical frame where the gravitational dynamics are fourth order and the matter is minimally coupled. These models predict a rich and testable set of linear phenomena. For each expansion history, fixed empirically by cosmological distance measures, there exists two branches of f(R) solutions that are parameterized by B propto d^2f/dR^2. For B<0, which include most of the models previously considered, there is a short-timescale instability that spoils agreement with cosmological observables in the high curvature limit. For the stable B>0 branch, f(R) models can reduce the large-angle CMB anisotropy, alter the shape of the linear matter power spectrum, and qualitatively change the correlations between the CMB and galaxy surveys. All of these phenomena are accessible with current and future data and provide stringent tests of general relativity on cosmological scales.
We review the structural properties of giant extragalactic HII regions and HII galaxies based on two dimensional hydrodynamic calculations, and propose an evolutionary sequence that accounts for their observed detailed structure. The model assumes a massive and young stellar cluster surrounded by a large collection of clouds. These are thus exposed to the most important star-formation feedback mechanisms: photoionization and the cluster wind. The models show how the two feedback mechanisms compete with each other in the disruption of clouds and lead to two different hydrodynamic solutions: The storage of clouds into a long lasting ragged shell that inhibits the expansion of the thermalized wind, and the steady filtering of the shocked wind gas through channels carved within the cloud stratum that results into the creation of large-scale superbubbles. Both solutions are here claimed to be concurrently at work in giant HII regions and HII galaxies, causing their detailed inner structure. A full description of the calculations can be found in The Astrophysical Journal 643, 186. Animated version of the models presented can be found at this http URL}eperez/ssc/ssc.html.
I review the status and perspectives of the research on the diffuse flux of (core collapse) supernova neutrinos (DF). In absence of a positive signal, several upper bounds exist in different detection channels. Of these, the strongest is the limit from SuperKamiokande (SK) of 1.2 electron antineutrinos cm^-2 s^-1 at 90% confidence level above 19.3 MeV of neutrino energy. The predictions of the DF depend on the cosmological rate of supernovae and on the neutrino emission in a individual supernova (spectrum, luminosity,..). Above the SK threshold, they range between 0.05 electron antineutrinos cm^-2 s^-1 up to touching the SK limit. The SK upper bound constrains part of the parameter space of the supernova rate - and indirectly of the star formation rate - only in models with relatively hard neutrino spectra, while predictions with softer spectra would need bounds stronger by about a factor of 4 to be tested. Experimentally, a feasible and very important goal for the future is the improvement of background discrimination and the resulting lowering of the detection threshold. Theory instead will benefit from reducing the uncertainties on the supernova neutrino emission (either with more precise numerical modeling or with data from a galactic supernova) and on the supernova rate. The latter will be provided precisely by next generation supernova surveys up to a normalization factor. Therefore, the detection of the DF is likely to be precious chiefly to constrain such normalization and to study the physics of neutrino emission in supernovae.
A large fraction of barred galaxies host secondary bars that are embedded in their large-scale primary counterparts. These are common also in gas poor early-type barred galaxies. The evolution of such double-barred galaxies is still not well understood, partly because of a lack of realistic $N$-body models with which to study them. Here we report a new mechanism for generating such systems, namely the presence of rotating pseudo-bulges. We demonstate with high mass and force resolution collisionless $N$-body simulations that long-lived secondary bars can form spontaneously without requiring gas, contrary to previous claims. We find that secondary bars rotate faster than primary ones. The rotation is not, however, rigid: the secondary bars pulsate, with their amplitude and pattern speed oscillating as they rotate through the primary bars. This self-consistent study supports previous work based on orbital analysis in the potential of two rigidly rotating bars. The pulsating nature of secondary bars may have important implications for understanding the central region of double-barred galaxies.
Fourier methods are fundamental tools to analyze random fields. Statistical structures of homogeneous Gaussian random fields are completely characterized by the power spectrum. In non-Gaussian random fields, polyspectra, higher-order counterparts of the power spectrum, are usually considered to characterize statistical information contained in the fields. However, it is not trivial how the Fourier modes are distributed in general non-Gaussian fields. In this paper, distribution functions of Fourier modes are directly considered and their explicit relations to the polyspectra are given. Under the condition that any of the polyspectra does not diverge, the distribution function is expanded by dimensionless combinations of polyspectra and a total volume in which the Fourier transforms are performed. The expression up to second order is generally given, and higher-order results are also derived in some cases. A concept of N-point distribution function of Fourier modes are introduced and explicitly calculated. Among them, the one-point distribution function is completely given in a closed form up to arbitrary order. As an application, statistics of Fourier phases are explored in detail. A number of aspects regarding statistical properties of phases are found. It is clarified, for the first time, how phase correlations arise in general non-Gaussian fields. Some of our analytic results are tested against numerical realizations of non-Gaussian fields, showing good agreements.
It is essential for the understanding of stellar structure models of high mass stars to explain why constant stars, non-pulsating chemically peculiar hot Bp stars and pulsating stars co-exist in the slowly pulsating B stars and beta Cephei instability strips. We have conducted a search for magnetic fields in the four Bp stars HD55522, HD105382, HD131120, and HD138769 which previously have been wrongly identified as slowly pulsating B stars. A recent study of these stars using the Doppler Imaging technique revealed that the elements He and Si are inhomogeneously distributed on the stellar surface, causing the periodic variability. Using FORS1 in spectropolarimetric mode at the VLT, we have acquired circular polarisation spectra to test the presence of a magnetic field in these stars. A variable magnetic field is clearly detected in HD55522 and HD105382, but no evidence for the existence of a magnetic field was found in HD131120. The presence of a magnetic field in HD138769 is suggested by one measurement at 3 sigma level. We discuss the occurence of magnetic B stars among the confirmed pulsating B stars and find strong magnetic fields of order kG and oscillations to be mutually exclusive.
We present the first results from the Australia Telescope Large Area Survey (ATLAS), which consist of deep radio observations of a 3.7 square degree field surrounding the Chandra Deep Field South, largely coincident with the infrared Spitzer Wide-Area Extragalactic (SWIRE) Survey. We also list cross-identifications to infrared and optical photometry data from SWIRE, and ground-based optical spectroscopy. A total of 784 radio components are identified, corresponding to 726 distinct radio sources, nearly all of which are identified with SWIRE sources. Of the radio sources with measured redshifts, most lie in the redshift range 0.5-2, and include both star-forming galaxies and active galactic nuclei (AGN). We identify a rare population of infrared-faint radio sources which are bright at radio wavelengths but are not seen in the available optical, infrared, or X-ray data. Such rare classes of sources can only be discovered in wide, deep surveys such as this.
We have analysed ground-based multi-colour Stromgren photometry and single-filter photometry from the star tracker on the WIRE satellite of the delta scuti star Epsilon Cephei. The ground-based data set consists of 16 nights of data collected over 164 days, while the satellite data are nearly continuous coverage of the star during 14 days. The spectral window and noise level of the satellite data are superior to the ground-based data and this data set is used to locate the frequencies. However, we can use the ground-based data to improve the accuracy of the frequencies due to the much longer time baseline. We detect 26 oscillation frequencies in the WIRE data set, but only some of these can be seen clearly in the ground-based data. We have used the multi-colour ground-based photometry to determine amplitude and phase differences in the Stromgren b-y colour and the y filter in an attempt to identify the radial degree of the oscillation frequencies. We conclude that the accuracies of the amplitudes and phases are not sufficient to constrain theoretical models of Epsilon Cephei. We find no evidence for rotational splitting or the large separation among the frequencies detected in the WIRE data set. To be able to identify oscillation frequencies in delta scuti stars with the method we have applied, it is crucial to obtain more complete coverage from multi-site campaigns with a long time baseline and in multiple filters. This is important when planning photometric and spectroscopic ground-based support for future satellite missions like COROT and KEPLER.
We have begun a programme to obtain high-precision photometry of bright detached eclipsing binary (dEB) stars with the Wide field InfraRed Explorer (WIRE) satellite. Due to the small aperture of WIRE only stars brighter than V=6 can be observed. We are collecting data for about a dozen dEB targets and here we present preliminary results for three of them. We have chosen dEBs with primary components of B and early A type. One of our aims is to combine the information from the light curve analyses of the eclipses with asteroseismic information from the analysis of the pulsation of the primary component.
Thanks to the high spatial resolution afforded by 8-10m class telescopes, we are beginning to learn that some sources are extended in their mid-infrared emission because of dusty outflows or heated outflow cavity walls. Therefore one must be extremely careful in interpreting the nature of extended mid-infrared sources (i.e. just because it is extended does not automatically mean it is a disk!).
We present a compilation of redshifts for 686 Compact Groups of galaxies (CG) referenced to the heliocentric reference frame, available from the literature as of 1992. We present an additional list of 157 CGs with published redshifts for one or more member galaxies and 13 apparent CGs with discrepant memberships. The electronic version of the compilation is provided by email request.
The unusual morphology of the Andromeda Spiral (Messier 31, the closest spiral galaxy to the Milky Way) has long been an enigma. Although regarded for decades as showing little evidence of a violent history, M~31 has a well-known outer ring of star formation at a radius of 10 kpc whose center is offset from the galaxy nucleus. In addition, the outer galaxy disk is warped as seen at both optical and radio wavelengths. The halo contains numerous loops and ripples. Here we report the discovery, based on analysis of previously-obtained data, of a second, inner dust ring with projected dimensions 1.5 by 1 kpc and offset by ~0.5kpc from the center of the galaxy. The two rings appear to be density waves propagating in the disk. Numerical simulations offer a completely new interpretation for the morphology of M31: both rings result from a companion galaxy plunging head-on through the center of the disk of M31. The most likely interloper is M32. Head-on collisions between galaxies are rare, but it appears nonetheless that one took place 210 million years ago in our Local Group of galaxies.
Recently, the issue of the role of the Eddington limit in accretion discs became a matter of debate. While the classical (spherical) Eddington limit is certainly an over-simplification, it is not really clear how to treat it in a flattened structure like an accretion disc. We calculate the critical accretion rates and resulting disc luminosities for various disc models corresponding to the classical Eddington limit by equating the attractive and repulsive forces locally. We also discuss the observational appearance of such highly accreting systems by analyzing their spectral energy distributions. Our calculations indicate that the allowed mass accretion rates differ considerably from what one expects by applying the Eddington limit in its classical form, while the luminosities only weakly exceed their classical equivalent. Depending on the orientation of the disc relative to the observer, mild relativistic beaming turns out to have an important influence on the disc spectra. Thus, possible super-Eddington accretion, combined with mild relativistic beaming, supports the idea that ultraluminous X-ray sources host stellar mass black holes and accounts partially for the observed high temperatures of these objects.
The "blazar sequence" posits that the most powerful BL Lacertae objects and flat-spectrum radio quasars should have relatively small synchrotron peak frequencies, nu_peak, and that the least powerful such objects should have the highest nu_peak values. This would have strong implications for our understanding of jet formation and physics and the possible detection of powerful, moderately high-redshift TeV blazars. I review the validity of the blazar sequence by using the results of very recent surveys and compare its detailed predictions against observational data. I find that the blazar sequence in its simplest form is ruled out. However, powerful flat-spectrum radio quasars appear not to reach the nu_peak typical of BL Lacs. This could indeed be related to some sort of sequence, although it cannot be excluded that it is instead due to a selection effect.
We present improved values of the three components of the absolute space velocity of the open cluster NGC6791. One HST ACS/WFC field with two-epoch observations provides astrometric measurements of objects in a field containing the cluster center. Identification of 60 background galaxies with sharp nuclei allows us to determine an absolute reference point, and measure the absolute proper motion of the cluster. We find (mu_alpha cos(delta), mu_delta)_J2000.0 = (-0.57+/-0.13, -2.45+/-0.12)mas/yr, and adopt V_rad = -47.1+/-0.7km/s from the average of the published values. Assuming a Galactic potential, we calculate the Galactic orbit of the cluster for various assumed distances, and briefly discuss the implications on the nature and the origin of this peculiar cluster.
Many planet candidates have been detected by radial velocity variations of the primary star; they are planet candidates, because of the unknown orbit inclination. Detection of the wobble in the two other dimensions, to be measured by astrometry, would yield the inclination and, hence, true mass of the companions. We aim to show that planets can be confirmed or discovered in a close visual stellar binary system by measuring the astrometric wobble of the exoplanet host star as periodic variation of the separation, even from the ground. We test the feasibility with HD 19994, a visual binary with one radial velocity planet candidate. We use the adaptive optics camera NACO at the VLT with its smallest pixel scale (13 mas) for high precision astrometric measurements. The separations measured in single 120 images taken within one night are shown to follow white noise, so that the standard deviation can be devided by the square root of the number of images to obtain the precision. In this paper we present the first results and investigate the achievable precision in relative astrometry with adaptive optics. With a careful data reduction it is possible to achieve a relative astrometric precision as low as 50 micro arc sec for a 0.6 arc sec, binary with VLT/NACO observations in one hour, the best relative astrometric precision ever achieved with a single telescope from the ground. The relative astrometric precision demonstrated here with AO at an 8-m mirror is sufficient to detect the astrometric signal of the planet HD 19994 Ab as periodic variation of the separation between HD 19994 A and B.
We present our chemically consistent GALEV Evolutionary Synthesis models for galaxies and point out differences to previous generations of models and their effects on the interpretation of local and high-redshift galaxy data.
We study possible impact of a softening of the equation of state by a phase transition, or appearance of hyperons, on the spin evolution of of isolated pulsars. Numerical simulations are performed using exact 2-D simulations in general relativity. The equation of state of dense matter at supranuclear densities is poorly known. Therefore, the accent is put on the general correlations between evolution and equation of state, and mathematical strictness. General conjectures referring to the structure of the one-parameter families of stationary configurations are formulated. The interplay of the back bending phenomenon and stability with respect to axisymmetric perturbations is described. Changes of pulsar parameters in a corequake following instability are discussed, for a broad choice of phase transitions predicted by different theories of dense matter. The energy release in a corequake, at a given initial pressure, is shown to be independent of the angular momentum of collapsing configuration. This result holds for various types of phases transition, with and without metastability. We critically review observations of pulsars that could be relevant for the detection of the signatures of the phase transition in neutron star cores.
We present J-band imaging and H+K-band low-resolution spectroscopy of 2MASS1207-3932 AB, obtained with VLT NACO. For the putative planetary mass secondary, we find J = 20.0+/-0.2 mag. The HK spectra of both components imply low gravity, and a dusty atmosphere for the secondary. Comparisons to synthetic spectra yield Teff_A ~ 2550+/-150K, and Teff_B ~ 1600+/-100K, consistent with their late-M and mid-to-late L types. For these Teff, and an age of 5-10 Myrs, evolutionary models imply M_A ~ 24+/-6 M_Jup and M_B ~ 8+/-2 M_Jup. Independent comparisons of these models to the observed colors, spanning ~I to L', also yield the same masses and temperatures. Our primary mass agrees with other recent analyses; however, our secondary mass, while still in the planetary regime, is 2-3 times larger than claimed previously. This discrepancy can be traced to the luminosities: while the absolute photometry and Mbol of the primary agree with theoretical predictions, the secondary is ~ 2.5+/-0.5 mag fainter than expected in all bands from I to L' and in Mbol. This accounts for the much lower secondary mass (and temperature) derived earlier. We argue that this effect is highly unlikely to result from a variety of model-related problems, and is instead real. This conclusion is bolstered by the absence of any luminosity problems in either the primary, or in AB Pic B which we also analyse. We therefore suggest grey extinction in 2M1207B, due to occlusion by an edge-on circum-secondary disk. This is consistent with the observed properties of edge-on disks around T Tauri stars, and with the known presence of a high-inclination evolved disk around the primary. Finally, the system's implied mass ratio of ~0.3 suggests a binary-like formation scenario. (abridged)
We present the results of an all-sky, deep optical survey for faint Local Group dwarf galaxies. Candidate objects were selected from the second Palomar survey (POSS-II) and ESO/SRC survey plates and follow-up observations performed to determine whether they were indeed overlooked members of the Local Group. Only two galaxies (Antlia and Cetus) were discovered this way out of 206 candidates. Based on internal and external comparisons, we estimate that our visual survey is more than 77% complete for objects larger than one arc minute in size and with a surface brightness greater than an extremely faint limit over the 72% of the sky not obstructed by the Milky Way. Our limit of sensitivity cannot be calculated exactly, but is certainly fainter than 25 magnitudes per square arc second in R, probably 25.5 and possibly approaching 26. We conclude that there are at most one or two Local Group dwarf galaxies fitting our observational criteria still undiscovered in the clear part of the sky, and a roughly a dozen hidden behind the Milky Way. Our work places the "missing satellite problem" on a firm quantitative observational basis. We present detailed data on all our candidates, including surface brightness measurements.
Massive BA-type supergiants are among the visually brightest stars in galaxies with active star formation. As such they are versatile tools for studies of stellar and galactochemical evolution. Moreover, they can act as distance indicators for the calibration of the cosmological distance scale. In the present work abundance patterns of the light elements helium, carbon, nitrogen and oxygen are investigated in several Galactic BA-type supergiants in the mass range between 8 and 18 M_sun. Based on high-resolution and high-S/N Echelle spectra obtained with FOCES on the Calar Alto 2.2m telescope, model atmosphere analyses are performed using state-of-the-art non-LTE spectrum synthesis. Stellar parameters and chemical abundances are determined with high accuracy. This gives tight observational constraints on the evolutionary status of the stars. Objects evolving from the main sequence to the red supergiant stage and those on a blue loop can be distinguished by their mixing signature (pure rotational vs. first dredge-up). The most sensitive tracer of nuclear processed matter, the N/C ratio, indicates a higher mixing efficiency than predicted by current evolution models of rotating stars with mass-loss.
LOPES is set up at the location of the KASCADE-Grande extensive air shower experiment in Karlsruhe, Germany and aims to measure and investigate radio pulses from Extensive Air Showers. Data taken during half a year of operation of 10 LOPES antennas (LOPES-10), triggered by showers observed with KASCADE-Grande have been analyzed. We report about results of correlations found of the measured radio signals by LOPES-10 with shower parameters.
When Ultra High Energy Cosmic Rays interact with particles in the Earth's atmosphere, they produce a shower of secondary particles propagating toward the ground. LOPES-30 is an absolutely calibrated array of 30 dipole antennas investigating the radio emission from these showers in detail and clarifying if the technique is useful for largescale applications. LOPES-30 is co-located and measures in coincidence with the air shower experiment KASCADE-Grande. Status of LOPES-30 and first measurements are presented.
Detached, inspiraling and semi-detached, mass-transferring double white dwarf (DWD) binary systems are both expected to be important sources for the proposed space-based gravitational-wave detector, LISA. The mass-radius relationship of individual white dwarf stars in combination with the constraints imposed by Roche geometries permit us to identify population boundaries for DWD systems in LISA's ``absolute'' amplitude-frequency diagram. With five key population boundaries in place, we are able to identify four principal population sub-domains, including one sub-domain that identifies where progenitors of Type Ia supernovae will reside. Given one full year of uninterrupted operation, LISA should be able to measure the rate at which the gravitational-wave frequency $f$ and, hence, the orbital period is changing in the highest frequency subpopulation of our Galaxy's DWD systems. We provide a formula by which the distance to each DWD system in this subpopulation can be determined; in addition, we show how the masses of the individual white dwarf stars in mass-transferring systems may be calculated.
We report on photometric follow-up of the recently discovered transiting planet WASP-1b. We observed two transits with the Wise Observatory 1m telescope, and used a variant of the EBOP code simultaneously with the SysRem detrending code for fitting the light curve. Assuming a stellar mass of 1.15 M_sun we derived a planetary radius of R_p = 1.398 +- 0.076 R_J and mass of M_p = 0.867 +- 0.073 M_J. We also derived an improved ephemeris for the transit: T_c = (2454013.31269 +- 0.00047) + N_tr * (2.519961 +- 0.000018). The new planet is an inflated, low-density planet, similar to HAT-P-1b and HD209458b.
Understanding the origin of stellar masses is a key problem in astrophysics. In the solar neighborhood, the mass distribution of stars follows a seemingly universal pattern. In the centre of the Milky Way, however, there are indications for strong deviations and the same may be true for the nuclei of distant starburst galaxies. Here we present the first numerical hydrodynamical calculations of stars formed in a molecular region with chemical and thermodynamic properties similar to those of warm and dusty circum-nuclear starburst regions. The resulting IMF is top-heavy with a peak at ~ 15 Msun, a sharp turn-down below 7 Msun and a power-law decline at high masses. We find a natural explanation for our results in terms of the temperature dependence of the Jeans mass, with collapse occuring at a temperature of ~ 100 K and an H2 density of a few times 10^5 cm^-3, and discuss possible implications for galaxy formation and evolution.
This paper reviews our knowledge on binary central stars of planetary nebulae and presents some personal opinions regarding their evolution. Three types of interactions are distinguished: type I, where the binary companion induces the mass loss; type II, where it shapes the mass loss but does not enhance it; type III, where a wide orbit causes the centre of mass to move, leading to a spiral embedded in the wind. Surveys for binary central stars are discussed, and the separations are compared to the distribution for binary post-AGB stars. The effect of close binary evolution on nebular morphology is discussed. Post-common-envelope binaries are surrounded by thin, expanding disks, expelled in the orbital plane. Wider binaries give rise to much thicker expanding torii. Type I binary evolution predicts a wide distribution of masses of central stars, skewed towards low masses. Comparison with observed mass distributions suggests that this is unlikely to be the only channel leading to the formation of a planetary nebula. A new sample of compact Bulge nebulae shows about 40% of nebulae with binary-induced morphologies.
Massive protostars evolve from hot cores to ultra-compact HII regions and eventually form classical HII regions; however, details of this evolution are far from understood. A few years ago, a new class of exceptionally small and dense objects, so-called hyper-compact HII regions, was discovered. They are believed to represent a transitional stage in early massive stellar evolution. Thus, their understanding is crucial for the formation of massive stars. In the present study, we investigate the morphology and the evolutionary stage of one of these hyper-compact HII regions, M17-UC1. We investigated the source at infrared and radio wavelengths. M17-UC1 could be resolved into two emission areas separated by a dark lane reminiscent of a circumstellar disk. All observational evidence as well as model calculations suggest that M17-UC1 is surrounded by a disk of cold dust. This first detection of a circumstellar disk around a young hyper-compact HII region is in agreement with the expectations of the disk accretion model for massive star formation.
As part of our program to study stellar photospheric and chromospheric activity, we have examined several young solar type stars with activity levels intermediate between the Sun and the very active RS CVn binaries. We have analysed contemporaneous spectroscopic data obtained at Catania Observatory (Serra La Nave station, Mt. Etna) and photometric data acquired in the Stromgren bands with an automatic photometric telescope (APT) at Fairborn Observatory (Arizona, USA). Surface inhomogeneities have been detected from the rotational modulation of stellar brightness as well as from the modulation of several photospheric line-depth ratios (LDRs). The presence of chromospheric plage-like regions has been inferred from the rotational modulation of the Halpha line equivalent width (EW_Halpha) evaluated with the spectral synthesis method. The most relevant results are the strong correlation between the brightness and temperature curves derived respectively from photometry and the LDRs as well as the striking anti-correlation between brightness and Halpha emission. This suggests a close spatial association of spots and plages, as frequently observed for the largest sunspot groups (e.g., Catalano et al. (1998)) and for some very active RS CVn systems (Catalano et al. 2002). Moreover, a simple spot/plage model applied to the observed flux curves allows a rough reconstruction of photospheric and chromospheric features of young main sequence stars.
We present the first study of bars in the local Universe, based on the Sloan Digitized Sky Survey (SDSS). The large sample of ~5000 local galaxies provides the largest study to date of local bars and minimizes the effect of cosmic variance. The sample galaxies have M_g<=-18.5 mag and cover the redshift range 0.01<=z<0.04. We use a color cut in the color-magnitude diagram and the Sersic index n to identify disk galaxies. We characterize bars and disks using r-band images and the method of iterative ellipse fits and quantitative criteria developed in Jogee at al. (2004, ApJL, 615, L105). After excluding highly inclined (i>60 degrees) systems our results are: (1) the optical (r-band) fraction of barred galaxies among local disk galaxies is 43%, which confirms the ubiquity of local bars, in agreement with other optical studies based on smaller samples (e.g.Eskridge et al. 2000, AJ, 119, 536, Marinova & Jogee 2006, astro-ph/0608039); (2) the optical bar fraction rises for bluer galaxies, suggesting a relation between bars and star formation; (3) preliminary analyzes suggest that the optical bar fraction increases steeply with the galaxy effective radius; (4) the optical bar fraction at z~0 is ~35% for bright disks (M_g<=-19.3 mag) and strong (bar ellipticity >0.4), large-scale (bar semi-major axis >1.5 kpc) bars, which is comparable to the value of 30+/-6% reported earlier (Jogee et al. 2004) for similar disks and bars at z~0.2-1.0.
We present Spitzer mid-infrared imaging of a sample of 35 tidally-distorted pre-merger interacting galaxy pairs selected from the Arp Atlas. We compare their global mid-infrared properties with those of normal galaxies from the SINGS Spitzer Legacy survey, and separate the disk emission from that of the tidal features. The [8.0 micron] - [24 micron], [3.6 micron] - [24 micron], and [5.8 micron] - [8.0 micron] colors of these optically-selected interacting galaxies are redder on average than those of spirals, implying enhancements to the mass-normalized star formation rates (SFRs) of a factor of ~2. Furthermore, the 24 micron emission in the Arp galaxies is more centrally concentrated than that in the spirals, suggesting that gas is being concentrated into the inner regions and fueling central star formation. No significant differences can be discerned in the shorter wavelength Spitzer colors of the Arp galaxies compared to the spirals, thus these quantities are less sensitive to star formation enhancements. No strong trend of Spitzer color with pair separation is visible in our sample; this may be because our sample was selected to be tidally disturbed. The tidal features contribute <10% of the total Spitzer fluxes on average. The SFRs implied for the Arp galaxies by the Spitzer 24 micron luminosities are relatively modest, ~1 M(sun)/yr on average.
Stellar oscillations are excited in non-synchronously rotating stars in binary systems due to the tidal forces. Tangential components of the tides can drive a shear flow which behaves as a differentially forced rotating structure in a stratified outer medium. In this paper we show that our single-layer approximation for the calculation of the forced oscillations yields results that are consistent with the predictions for the synchronization timescales in circular orbits. In addition, calibrating our model results to fit Zahn's relationship between synchronization timescales and orbital separation, we are able to constrain the value of the kinematical viscosity parameter. For the 4Mo+5Mo binary modeled in this paper, the kinematical viscosity is in the range 0.0015 -- 0.0043 Ro^2/d for orbital periods in the range 2.5 -- 25 d. Furthermore, the energy dissipation rate due to the shear flow is found to decrease by ~2 orders of magnitude as synchronization is approached, implying that binary systems may approach synchronization relatively quickly but that it takes a much longer timescale to actually attain this condition. Our model can be used to calculate the energy dissipation rates throughout the orbital cycle for arbitrary values of eccentricity and stellar rotational velocity. We suggest that the asymmetric distribution of energy dissipation over the stellar surface may lead to the appearance of localized regions of enhanced surface activity.
3C 318 is a z=1.574 radio-loud quasar. The small physical size of its radio jets indicate that these jets were triggered relatively recently. In addition to the ultraviolet continuum emission being reddened by dust, detections with IRAS and SCUBA show it to have an exceptionally high far-infrared luminosity. We present CO(2-1) observations of 3C 318 made with the IRAM Plateau de Bure Interferometer. We detect CO(2-1) emission with a FWHM=200 km/s at a signal-to-noise ratio of 5.4. There is evidence for positional (~ 20 kpc) and velocity (~ -400 km/s) offsets between the molecular gas and the quasar which may be due to the quasar experiencing a major merger. The mass of molecular gas inferred from our observations is M_{H_2}=(3.0 +/- 0.6) x 10^{10} M_sun. This molecular gas mass is comparable to that in sub-mm-selected galaxies at similar redshifts. The large molecular gas mass is consistent with the primary source of heating for the cool dust in this quasar to be massive star formation with a star formation rate of 1700 M_sun/yr and a gas depletion timescale of 20 Myr. Our observations support the idea that star formation episodes and jet triggering can be synchronised.
We develop a local model for the exponential growth and saturation of the Reynolds and Maxwell stresses in turbulent flows driven by the magnetorotational instability. We first derive equations that describe the effects of the instability on the growth and pumping of the stresses. We highlight the relevance of a new type of correlations that couples the dynamical evolution of the Reynolds and Maxwell stresses and plays a key role in developing and sustaining the magnetorotational turbulence. We then supplement these equations with a phenomenological description of the triple correlations that lead to a saturated turbulent state. We show that the steady-state limit of the model describes successfully the correlations among stresses found in numerical simulations of shearing boxes.
We present optical measurements of the faint end of the luminosity function in the core of the Coma cluster. Dwarf galaxies are detected down to a limiting magnitude of R approx. 25.75 in images taken with the Hubble Space Telescope. This represents the faintest determination of the Coma luminosity function to date. With the assumption that errors due to cosmic variance are small, evidence is found for a steep faint end slope with alpha < -2. Such a value is expected in theories in which reionization and other feedback processes are dependent on density.
[Abridged] We present the results of a large program conducted with the Very Large Telescope and Keck telescope to search for forming clusters of galaxies near powerful radio galaxies at 2.0 < z < 5.2. We obtained narrow- and broad-band images of nine radio galaxies and their surroundings. The imaging was used to select candidate Lyman alpha emitting galaxies in ~3x3 Mpc^2 areas near the radio galaxies. A total of 337 candidate emitters were found with a rest-frame Lyman alpha equivalent width of EW_0 > 15 A and Sigma = EW_0/Delta EW_0 > 3. Follow-up spectroscopy confirmed 168 Lyman alpha emitters near eight radio galaxies. The success rate of our selection procedure is 91%. At least six of our eight fields are overdense in Lyman alpha emitters by a factor 3-5. Also, the emitters show significant clustering in velocity space. In the overdense fields, the width of the velocity distributions of the emitters is a factor 2-5 smaller than the width of the narrow-band filters. Taken together, we conclude that we have discovered six forming clusters of galaxies (protoclusters). We estimate that roughly 75% of powerful (L_2.7GHz > 10^33 erg/s/Hz/sr) high redshift radio galaxies reside in a protocluster, with a sizes of at least 1.75 Mpc. We estimate that the protoclusters have masses in the range 2-9 x 10^14 Msun and they are likely to be progenitors of present-day (massive) clusters of galaxies. For the first time, we have been able to estimate the velocity dispersion of cluster progenitors from z~5 to ~2. The velocity dispersion of the emitters increases with cosmic time, in agreement with the dark matter velocity dispersion in numerical simulations of forming massive clusters.
In this paper we use the diffuse Galactic synchrotron emission to study the properties of the Galactic magnetic field. We combined data from the low-frequency WENSS survey with single-dish observations carried out by Brouw and Spoelstra to (partially) fill in the central gap in the (u,v) plane that is missing from the interferometer data. The small bandwidth of the WENSS data meant that we could not determine rotation measures (RM) directly. Instead we interpreted the polarization angle gradients that we derived as gradients in RM, and to do this we found a new way to efficiently and reliably fit linear gradients to periodic data. RM are available for the single-dish observations, and we found that we have to rescale these single-dish RM to match the RM gradients that we derive from the combined WENSS/single-dish dataset with the single-dish only RM gradients. We tentatively show that the difference in beamsize between the datasets can be responsible for this. We interpret the scaled-up RM we find in terms of a simple toy model, and by combining our results with those by Haverkorn et al. (2004) we reconstruct the full 3D magnetic field vector along a number of lines-of-sight. For these lines-of-sight we derive the properties of the magnetic field component perpendicular to the Galactic plane.
We investigate the diffuse absolute calibration of the InfraRed Array Camera
on the Spitzer Space Telescope at 8.0microns using a sample of 43 HII regions
with a wide range of morphologies near GLON=312deg. For each region we
carefully measure sky-subtracted,point-source- subtracted, areally-integrated
IRAC 8.0-micron fluxes and compare these with Midcourse Space eXperiment (MSX)
8.3-micron images at two different spatial resolutions, and with radio
continuum maps. We determine an accurate median ratio of IRAC
8.0-micron/MSX\8.3-micron fluxes, of 1.55+/-0.15. From robust spectral energy
distributions of these regions we conclude that the present 8.0-micron diffuse
calibration of the SST is 36% too high compared with the MSX validated
calibration, perhaps due to scattered light inside the camera. This is an
independent confirmation of the result derived for the diffuse calibration of
IRAC by the Spitzer Science Center (SSC).
From regression analyses we find that 843-MHz radio fluxes of HII regions and
mid-infrared (MIR) fluxes are linearly related for MSX at 8.3-microns and
Spitzer at 8.0 microns, confirming the earlier MSX result by Cohen & Green. The
median ratio of MIR/843-MHz diffuse continuum fluxes is 600 times smaller in
nonthermal than thermal regions, making it a sharp discriminant. The ratios are
largely independent of morphology up to a size of ~24 arcsec. We provide
homogeneous radio and MIR morphologies for all sources. MIR morphology is not
uniquely related to radio structure. Compact regions may have MIR filaments
and/or diffuse haloes, perhaps infrared counter- parts to weakly ionized radio
haloes found around compact HII regions. We offer two IRAC colour-colour plots
as quantitative diagnostics of diffuse HII regions.
Swift discovered the high redshift (z=6.29) GRB050904 with the Burst Alert Telescope (BAT) and began observing with its narrow field instruments 161 s after the burst onset. This gamma-ray burst is the most distant cosmic explosion ever observed. Because of its high redshift, the X-ray Telescope (XRT) and BAT simultaneous observations provide 4 orders of magnitude of spectral coverage (0.2-150 keV; 1.4-1090 keV in the source rest frame) at a very early source-frame time (22 s). GRB050904 was a long, multi-peaked, bright GRB with strong variability during its entire evolution. The light curve observed by the XRT is characterized by the presence of a long flaring activity lasting up to 1-2 hours after the burst onset in the burst rest frame, with no evidence of a smooth power-law decay following the prompt emission as seen in other GRBs. However, the BAT tail extrapolated to the XRT band joins the XRT early light curve and the overall behavior resembles that of a very long GRB prompt. The spectral energy distribution softens with time, with the photon index decreasing from -1.2 during the BAT observation to -1.9 at the end of the XRT observation. The dips of the late X-ray flares may be consistent with an underlying X-ray emission arising from the forward shock and with the properties of the optical afterglow reported by Tagliaferri et al. (2005b). We interpret the BAT and XRT data as a single continuous observation of the prompt emission from a very long GRB. The peculiarities observed in GRB050904 could be due to its origin within one of the first star-forming regions in the Universe; very low metallicities of the progenitor at these epochs may provide an explanation.
Gamma-ray bursts at cosmological distances offer a time-varying signal that can be used to search for energy-dependent photon dispersion effects. In particular, we argue that short bursts with narrow pulse structures at high energies will offer the least ambiguous tests for energy-dependent dispersion effects. We discuss an array of quantitative methods to search for such effects in time-tagged photon data. Utilizing observed gamma-ray burst profiles extrapolated to GeV energies, as may expected to be observed by GLAST, we also demonstrate the extent to which these methods can be used as an empirical exploration of quantum gravity formalisms.
We present a study of three Lyman-alpha emitting galaxies (LAEs), selected via a narrow-band survey in the GOODS northern field, and spectroscopically confirmed to have redshifts of z ~ 5.65. Using HST ACS and Spitzer IRAC data, we constrain the rest-frame UV-to-optical spectral energy distributions (SEDs) of the galaxies. Fitting stellar population synthesis models to the observed SEDs, we find best-fit stellar populations with masses between ~ 10^9 - 10^10 M_sun and ages between ~ 5 - 100 Myr, assuming a simple starburst star formation history. However, stellar populations as old as 700 Myr are admissible if a constant star formation rate model is considered. Very deep near-IR observations may help to narrow the range of allowed models by providing extra constraints on the rest-frame UV spectral slope. Our narrow-band selected objects and other IRAC-detected z ~ 6 i'-dropout galaxies have similar 3.6 um magnitudes and z' - [3.6] colors, suggesting that they posses stellar populations of similar masses and ages. This similarity may be the result of a selection bias, since the IRAC-detected LAEs and i'-dropouts probably only sample the bright end of the luminosity function. On the other hand, our LAEs have blue i' - z' colors compared to the i'-dropouts, and would have been missed by the i'-dropout selection criterion. A better understanding of the overlap between the LAE and the i'-dropout populations is necessary in order to constrain the properties of the overall high-redshift galaxy population, such as the total stellar mass density at z ~ 6.
Different hydrodynamic regimes for the gaseous outflows generated by multiple supernovae explosions and stellar winds occurring within compact and massive star clusters are discussed. It is shown that there exists the threshold energy that separates clusters whose outflows evolve in the quasi-adiabatic or radiative regime from those within which catastrophic cooling and a positive feedback star-forming mode sets in. The role of the surrounding ISM and the observational appearance of the star cluster winds evolving in different hydrodynamic regimes are also discussed.
We point out that the Type Ia supernovae in the SNLS dataset are consistent with an early beginning of the cosmic acceleration if dark energy interacts strongly with dark matter. We find that the acceleration could have started at redshift z =3 and higher.
The Triangulum Spiral Galaxy Messier 33 offers unique insights into the building of a galactic disk. We identify spectacular arcs of intermediate age (0.6 Gyr - 2 Gyr) stars in the low-metallicity outer disk. The northern arc spans approx. 120 degrees in azimuth and up to 5 arcmin in width. The arcs are located 2-3 disk scale lengths from the galaxy centre (where 1 disk scale length is equivalent to 0.1 degrees in the V-band) and lie precisely where there is a warp in the HI profile of M33. Warps and infall are inextricably linked (Binney, 1992). We present spectroscopy of candidate stars in the outer northern arc, secured using the Keck I telescope in Hawaii. The target stars have estimated visual magnitudes as faint as V ~ 25m. Absorption bands of CN are seen in all spectra reported in this review talk, confirming their carbon star status. Also presented are PAH emissivity radial profiles generated from IRAC observations of M33 using the Spitzer Space Telescope. A dramatic change of phase in the m=2 Fourier component is detected at the domain of the arcs. M33 serves as an excellent example how the disks of spiral galaxies in our Universe are built: as dynamically open systems, growing from the inward, outward.
Electron degeneracy effects are dominant in ultra-dense plasmas (UDP), such as those found in white dwarfs. These effects can be treated systematically by obtaining an expansion of the screening length in inverse powers of $\hbar^{2}$. The theory exhibits Thomas-Fermi-like screening in an appropriate regime. In general, our theory leads to an ${\cal O}(1)$ effect on the enhancement of fusion rates in white dwarfs. Further, it is shown analytically for these stellar conditions that Bose statistics of nuclei have a negligible effect on the screening length, in consonance with Monte Carlo simulations found in literature.
We observed the clustered star forming complex NGC1333 with the BIMA and FCRAO telescopes in the transitions HCO+(1-0) and N2H+(1-0) over an 11'x11' area with resolution ~10" (0.015pc). The N2H+ emission follows very closely the submillimeter dust continuum emission, while HCO+ emission appears more spatially extended and also traces outflows. We have identified 93 N2H+ cores using the CLUMPFIND algorithm, and we derive N2H+ core masses between 0.05 and 2.5M_sun, with uncertainties of a factor of a few, dominated by the adopted N2H+ abundance. From a comparison with virial masses, we argue that most of these N2H+ cores are likely to be bound, even at the lowest masses, suggesting that the cores do not trace transient structures, and implies the entire mass distribution consists of objects that can potentially form stars. We find that the mass distribution of N2H+ cores resembles the field star IMF, which suggests that the IMF is locked in at the pre-stellar stage of evolution. We find that the N2H+ cores associated with stars identified from Spitzer infrared images have a flat mass distribution. This might be because lower mass cores lose a larger fraction of their mass when forming a star. Even in this clustered environment, we find no evidence for ballistic motions of the cores relative to their lower density surroundings traced by isotopic CO emission, though this conclusion must remain tentative until the surroundings are observed at the same high resolution as the N2H+.
We have observed the cluster RX J0152.7-1357 (z$\sim$0.83) at 24$\mu$m with
the Multiband Imaging Photometer for Spitzer (MIPS). We detected twenty-two
sources associated with spectroscopically confirmed cluster members, while ten
more have photometric redshifts compatible with membership. Two of the 32
likely cluster members contain obvious active nuclei while the others are
associated with dusty star formation. The median IR-determined star formation
rate among the remaining galaxies is estimated at 22 M$_\odot$$ $yr$^{-1}$,
significantly higher than in previous estimates from optical data. Most of the
MIR-emitting galaxies also have optical emission lines, but a few do not and
hence have completely hidden bursts of star formation or AGN activity.
An excess of MIR-emitting galaxies is seen in the cluster in comparison to
the field at the same redshift. The MIR cluster members are more associated
with previously detected infalling late type galaxies rather than triggered by
the ongoing merging of bigger X-ray clumps. Rough estimates also show that ram
pressure may not be capable of stripping the gas away from cluster outskirt
galaxies but it may disturb the gas enough to trigger the star formation
activity. Harassment can also play a role if for example these galaxies belong
to poor galaxy groups. Thus, bursts of star formation occur in the cluster
environment and could also help consume the galaxy gas content in addition to
ram pressure, harassment or galaxy-galaxy strong interactions.
Light echoes are interesting because of the wealth of information they offer about their progenitors and the reflecting dust. Due to their faint surface brightnesses, difference imaging is necessary to separate most light echoes from the sky background. However, difference images reveal only the relative fluxes between two epochs. Obtaining absolute fluxes for individual epochs has traditionally relied on a single template image that is free of light echoes. Since such an observation is normally unavailable, a light echo-free template must be constructed by a complicated and usually subjective process. Here we present an application of the NN2 method of Barris et al. to extract the relative fluxes of light echoes across a range of epochs directly from a series of difference images. This method requires no privileged image and makes maximal use of the observational data. Statistical methods to estimate the zero-flux level and thus the absolute flux are also presented. The efficacy of the technique is demonstrated by an application to the light echoes around SN 1987A. The resulting images reveal new detail and faint light echo structures. This method can be adapted and applied to other extended variable light sources, such as stellar outflows and supernova remnants.
Frequency Selective Bolometers (FSBs) are a new type of detector for millimeter and sub-millimeter wavelengths that are transparent to all but a narrow range of frequencies as set by characteristics of the absorber itself. Therefore, stacks of FSBs tuned to different frequencies provide a low-loss compact method for utilizing a large fraction of the light collected by a telescope. Tests of prototype FSBs, described here, indicate that the absorption spectra are well predicted by models, that peak absolute absorption efficiencies of order 50% are attainable, and that their out-of-band transmission is high.
Gravitational interactions in very young high-density stellar clusters can to some degree change the angular momentum in the circumstellar discs surrounding initially the majority of stars. However, for most stars the cluster environment alters the angular momentum only slightly. For example, in simulations of the Orion Nebula cluster (ONC) encounters reduce the angular momentum of the discs on average at most by 3-5% and in the higher density region of the Trapezium %where encounters are more likely, the disc angular momentum is on average lowered by 15-20% - still a minor loss process. However, in this paper it is demonstrated that the situation is very different if one considers high-mass stars (M* > 10 M(solar) only. Assuming an age of 2 Myr for the ONC, their discs have on average a 50-90% lower angular momentum than primordially. This enormous loss in angular momentum in the disc should result in an equivalent increase in accretion, implying that the cluster environment boosts accretion for high-mass stars, thus %in the cluster center, making them even more massive.
Cool stars are known to produce flares probably as a result of magnetic reconnection in their outer atmospheres. We present simultaneous XMM-Newton optical V band and X-ray observations of the M8 dwarf LP412-31. During the observation a giant flare occurred, with an optical amplitude of 6 mag and total energy of 3 10^(32) erg in each the V band and soft X-rays. Both flare onset and flare decay were completely covered in both wavebands with a temporal resolution of 20 s, allowing for a determination of the flare time scales as well as a study of the temperature evolution of the flaring plasma. The data are consistent with an impulsive energy release followed by radiative cooling without further energy release during the decay phase. Our analysis suggests that the optical flare originates from a small fraction of the surface of LP412-31, while the characteristic scale size of the flaring X-ray plasma is of the order of the stellar radius or larger. The absence of any small-scale variability in the light curve suggests a non-standard flare number energy distribution.
Spectroscopy at 8-13 microns with T-ReCS on Gemini-S is presented for 3 galaxies with substantial silicate absorption features, NGC 3094, NGC 7172 and NGC 5506. In the galaxies with the deepest absorption bands, the silicate profile towards the nuclei is well represented by the emissivity function derived from the circumstellar emission from the red supergiant, mu Cephei which is also representative of the mid-infrared absorption in the diffuse interstellar medium in the Galaxy. There is spectral structure near 11.2 microns in NGC 3094 which may be due to a component of crystalline silicates. In NGC 5506, the depth of the silicate absorption increases from north to south across the nucleus, suggestive of a dusty structure on scales of 10s of parsecs. We discuss the profile of the silicate absorption band towards galaxy nuclei and the relationship between the 9.7 micron silicate and 3.4 micron hydrocarbon absorption bands.
The ratio of the depths of spectral lines is a powerful indicator of the
effective temperature. The method based on this analysis is capable of
discerning small temperature variations of individual stars.
We apply this spectroscopic data analysis to three type of stars, namely an
RS CVn type binary system, a young solar-type star and a Cepheid variable. We
show that individual LDRs converted into temperature through calibration
relations lead to rotational and pulsational modulation of the average surface
temperature with amplitudes of 127 K, 48 K and 1466 K in the three types of
stars, with average estimated errors of some tens Kelvin degrees.
We report on the iron K-alpha line properties of a sample of Seyfert galaxies observed with the XMM-Newton EPIC pn instrument. Using a systematic and uniform analysis, we find that complexity at iron-K is extremely common in the XMM spectra. Once appropriate soft X-ray absorption, narrow 6.4 keV emission and associated Compton reflection are accounted for, ~75 of the sample show an improvement when a further Gaussian component is introduced. The typical properties of the broad emission are both qualitatively and quantitatively consistent with previous results from ASCA. The complexity is in general very well described by relativistic accretion disk models. In most cases the characteristic emission radius is constrained to be within ~50 R_g, where strong gravitational effects become important. We find in about 1/3 of the sample the accretion disk interpretation is strongly favoured over competing models. In a few objects no broad line is apparent. We find evidence for emission within 6 R_g in only two cases, both of which exhibit highly complex absorption. Evidence for black hole spin based on the X-ray spectra therefore remains tentative.
We report the first detection of flux variability in the most luminous X-ray source in the southern ring of the Cartwheel galaxy. XMM--Newton data show that the luminosity has varied over a timescale of six months from L[0.5-10] keV \~1.3 10^{41} erg/s, consistent with the previous Chandra observation, to L[0.5-10] keV < 6.4 x10^{40} erg/s. This fact provides the first evidence that the source is compact in nature and is not a collection of individual fainter sources, such as supernova remnants. The source has been repeatedly observed at the very high luminosity level of L[0.5-10] keV ~1.3 x 10^{41} erg/s, for a period of at least 4 years before dimming at the current level. It represents then the first example of an accreting object revealed in a long lived state of extremely high luminosity.
The Tully-Fisher Relation (TFR) links two fundamental properties of disk galaxies: their luminosity and their rotation velocity (mass). The pioneering work of Vogt et al. in the 1990's showed that it is possible to study the TFR for spiral galaxies at considerable look-back-times, and use it as a powerful probe of their evolution. In recent years, several groups have studied the TFR for galaxies in different environments reaching redshifts beyond one. In this brief review I summarise the main results of some of these studies and their consequences for our understanding of the formation and evolution of disk galaxies. Particular emphasis is placed on the possible environment-driven differences in the behaviour of the TFR for field and cluster galaxies.
We report the first spectropolarimetric observations and modeling of CaH transitions in sunspots. We have detected strong polarization signals in many CaH lines from the A-X system, and we provide the first successful fit to the observed Stokes profiles using the previously developed theory of the Paschen-Back effect in arbitrary electronic states of diatomic molecules and polarized radiative transfer in molecular lines in stellar atmospheres. We analyze the CaH Stokes profiles together with quasi-simultaneous observations in TiO bands and conclude that CaH provides a valuable diagnostic of magnetic fields in sunspots, starspots, cool stars, and brown dwarfs.
We present precise z-band photometric time series spanning times of transit of the two exoplanets recently discovered by the SuperWASP collaboration. We find planetary radii of 1.44 +/- 0.08 R_J and 1.04 +/- 0.06 R_J for WASP-1b and WASP-2b, respectively. These error estimates include both random errors in the photometry and also the uncertainty in the stellar masses. Our results are 5 times more precise than the values derived from the discovery data alone. Our measurement of the radius of WASP-2b agrees with previously published models of hot Jupiters that include both a 20-M_Earth core of solid material and the effects of stellar insolation. In contrast, we find that the models cannot account for the large size of WASP-1b, even if the planet has no core. Thus, we add WASP-1b to the growing list of hot Jupiters that are larger than expected. This suggests that ``inflated'' hot Jupiters are more common than previously thought, and that any purported explanations involving highly unusual circumstances are disfavored.
Consider radar ranging of a distant galaxy in a Friedman-Lemaitre
cosmological model. In this model the comoving coordinate of the galaxy is
constant, hence the equations of null geodesics for photons travelling to the
distant galaxy and back imply the following equation:
\int_{t_e}^{t_r} dt/a(t) = \int_{t_r}^{t_o} dt/a(t).
Here, t_e, t_r and t_o are respectively the times of emission, reflection and
observation of the reflected photons, and a(t) is the scale factor. Since the
universe is expanding, a(t) is a monotonically increasing function, so the
return travel time, t_o - t_r, must be greater than the forward travel time,
t_r - t_e. Clearly, space expands, and on their way back, the photons must
travel a longer distance! The present paper explains why this argument for the
expansion of space is wrong.
We present preliminary results of follow-up optical observations, both photometric and spectroscopic, of stellar X-ray sources, selected from the cross-correlation of ROSAT All-Sky Survey (RASS) and TYCHO catalogues. Spectra were acquired with the Elodie spectrograph at the 193-cm telescope of the Haute Provence Observatory (OHP) and with the REOSC echelle spectrograph at the 91-cm telescope of the Catania Astrophysical Observatory (OAC), while UBV photometry was made at OAC with the same telescope. In this work, we report on the discovery of six late-type binaries, for which we have obtained good radial velocity curves and solved for their orbits. Thanks to the OHP and OAC spectra, we have also made a spectral classification of single-lined binaries and we could give first estimates of the spectral types of the double-lined binaries. Filled-in or pure emission H-alpha profiles, indicative of moderate or high level of chromospheric activity, have been observed. We have also detected, in near all the systems, a photometric modulation ascribable to photospheric surface inhomogeneities which is correlated with the orbital period, suggesting a synchronization between rotational and orbital periods. For some systems has been also detected a variation of H-alpha line intensity, with a possible phase-dependent behavior.
PG1159-035 is the prototype of the PG1159 spectral class which consists of extremely hot hydrogen-deficient (pre-) white dwarfs. It is also the prototype of the GW Vir variables, which are non-radial g-mode pulsators. The study of PG1159 stars reveals insight into stellar evolution and nucleosynthesis during AGB and post-AGB phases. We perform a quantitative spectral analysis of PG1159-035 focusing on the abundance determination of trace elements. We have taken high-resolution ultraviolet spectra of PG1159-035 with the Hubble Space Telescope and the Far Ultraviolet Spectroscopic Explorer. They are analysed with non-LTE line blanketed model atmospheres. We confirm the high effective temperature with high precision (Teff=140,000+/-5000 K) and the surface gravity of logg=7. For the first time we assess the abundances of silicon, phosphorus, sulfur, and iron. Silicon is about solar. For phosphorus we find an upper limit of solar abundance. A surprisingly strong depletion of sulfur (2% solar) is discovered. Iron is not detected, suggesting an upper limit of 30% solar. This coincides with the Fe deficiency found in other PG1159 stars. We redetermine the nitrogen abundance and find it to be lower by one dex compared to previous analyses. The sulfur depletion is in contradiction with current models of AGB star intershell nucleosynthesis. The iron deficiency confirms similar results for other PG1159 stars and is explained by the conversion of iron into heavier elements by n-capture in the s-processing environment of the precursor AGB star. However, the extent of the iron depletion is stronger than predicted by evolutionary models. The relatively low nitrogen abundance compared to other pulsating PG1159 stars weakens the role of nitrogen as a distinctive feature of pulsators and non-pulsators in the GW Vir instability strip.
In these lecture notes I briefly discuss the present day situation and new discoveries in astrophysics of neutron stars focusing on isolated objects. The latter include soft gamma repeaters, anomalous X-ray pulsars, central compact objects in supernova remnants, the Magnificent seven, and rotating radio transients. In the last part of the paper I describe available tests of cooling curves of neutron stars and discuss different additional constraints which can help to confront theoretical calculations of cooling with observational data.
We report here on X-ray and IR observations of the Anomalous X-ray Pulsar 1RXS J170849-400910. First, we report on new XMM-Newton, Swift-XRT and Chandra observations of this AXP, which confirm the intensity-hardness correlation observed in the long term X-ray monitoring of this source by Rea et al. (2005). These new X-ray observations show that the AXP flux is rising again, and the spectrum hardening. If the increase in the source intensity is indeed connected with the glitches and a possible bursting activity, we expect this source to enter in a bursting active phase around 2006-2007. Second, we report on deep IR observations of 1RXS J170849-400910, taken with the VLT-NACO adaptive optics, showing that there are many weak sources consistent with the AXP position. Neither star A or B, previously proposed by different authors, might yet be conclusively recognised as the IR counterpart of 1RXS J170849-400910. Third, using Monte Carlo simulations, we re-address the calculation of the significance of the absorption line found in a phase-resolved spectrum of this source by Rea et al. (2003), and interpreted as a resonant scattering cyclotron feature.
We have detected, for the first time, Cepheid variables in the Sculptor Group
SB(s)m galaxy NGC 55. From wide-field images obtained in the optical V and I
bands during 77 nights in 2002-2003, we have found 143 Cepheids with periods
ranging from 5.6 to 175.9 days. 133 of these objects have periods longer than
10 days, making NGC 55 to-date the galaxy with the largest known number of
long-period Cepheids in the Sculptor Group. We construct period-luminosity
relations from our data and obtain distance moduli corrected for the small
foreground reddening to NGC 55 of 26.79 $\pm$ 0.04 mag (internal error) in V,
26.66 $\pm$ 0.03 mag in I and 26.40 $\pm$ 0.05 mag in the reddening-independent
V-I Wesenheit index. The trend of increasing distance moduli with shorter
wavelength hints at the existence of significant reddening intrinsic to NGC 55
which affects the measured Cepheid magnitudes. From our data, we determine the
intrinsic mean reddening of the Cepheids in NGC 55 as E(B-V) = 0.102 mag which
brings the distance determinations from the different bands into excellent
agreement. Our best distance estimate for NGC 55 from the present optical
Cepheid photometry is 26.40 mag $\pm$ 0.05 mag (internal error) $\pm$ 0.09 mag
(systematic error). This value is tied to an assumed LMC distance of 18.50 mag.
Our quoted systematic error of the present NGC 55 Cepheid distance does not
take into account the current uncertainty on the distance of the fiducial LMC
galaxy itself.
Within the small respective uncertainties, the Sculptor Group galaxies NGC 55
and NGC 300 are at the same distance of 1.9 Mpc, strengthening the case for a
physical association of these galaxies
LOFAR, the Low Frequency Array, is a next-generation radio telescope that is
being built in Northern Europe and expected to be fully operational at the end
of this decade. It will operate at frequencies from 15 to 240 MHz
(corresponding to wavelengths of 20 to 1.2 m). Its superb sensitivity, high
angular resolution, large field of view and flexible spectroscopic capabilities
will represent a dramatic improvement over previous facilities at these
wavelengths. As such, LOFAR will carry out a broad range of fundamental
astrophysical studies.
The design of LOFAR has been driven by four fundamental astrophysical
applications: (i) The Epoch of Reionisation, (ii) Extragalactic Surveys and
their exploitation to study the formation and evolution of clusters, galaxies
and black holes, (iii) Transient Sources and their association with high energy
objects such as gamma ray bursts, and (iv) Cosmic Ray showers and their
exploitation to study the origin of ultra-high energy cosmic rays. In this
conference the foreseen LOFAR work on the epoch of reionisation has been
covered by de Bruyn and on cosmic ray showers by Falcke.
During this contribution we will first present the LOFAR project with an
emphasis on the challenges faced when carrying out sensitive imaging at low
radio frequencies. Subsequently, we will discuss LOFAR's capabilities to survey
the low-frequency radio sky. Main aims for the planned surveys are studies of
z>6 radio galaxies, diffuse emission associated with distant clusters and
starbursting galaxies at z>2.
A range of experimental results point to the existence of a massive neutrino. The recent high precision measurements of the cosmic microwave background and the large scale surveys of galaxies can be used to place an upper bound on this mass. In this letter we perform a thorough analysis of all assumptions that go into obtaining a credible limit on $\sum m_{\nu}$. In particular we explore the impact of a cosmological parameters, the importance of priors, the uncertainties due to biasing in large scale structure and the dependence on choice of initial conditions. We find that the mass constraints are independent of the choice of parameterization as well as the inclusion of spatial curvature. Yet the difference between an upperbound of 2.2 eV, assuming generic initial conditions, and an upper bound of 0.63 eV, assuming adiabaticity and $b=1$, demonstrate the dependence of such a constraint on the assumptions in the analysis.
Barnes-Evans type relations provide an empirical relationship between the surface brightness of stars and their color. They are widely used for measuring the distances to stars of known radii, as the Roche-lobe filling secondaries in cataclysmic variables (CVs). The calibration of the surface brightness of field dwarfs of near-solar metalicity with spectral types A0 to L8 covers all secondary spectral types detectable in CVs and related objects and will aid in the measurement of their distances. The calibrations are based on the radii of field dwarfs measured by the Infrared Flux Method and by interferometry. Published photometry is used and homogenized to the Cousins Rc and Ic and the CIT JHK photometric systems. The narrow band surface brightness at 7500A is based on our own and published spectrophotometry. Care is taken to select the dwarfs for near-solar metalicity, appropriate to CVs, and to avoid errors caused by unrecognized binarity. Relations are provided for the surface brightness in V, Rc, Ic, J, H, K and in a narrow band at 7500A as functions of V-K and of spectral type. The method is tested with selected CVs for which independent information on their distances is available. The observed spread in the radii of early M-dwarfs of given mass or luminosity and its influence on the distance measurements of CVs is discussed. As long as accurate trigonometric parallaxes are not routinely available for a large number of CVs, the surface brightness method remains a reliable means of determining distances to CVs in which a spectral signature of the secondary star can be discerned.
Big Bang Nucleosynthesis (BBN) and the Cosmic Background Radiation (CBR) provide complementary probes of the early evolution of the Universe and of its particle content. Neutrinos play important roles in both cases, influencing the primordial abundances of the nuclides produced by BBN during the first 20 minutes as well as the spectrum of temperature fluctuations imprinted on the CBR when the Universe is some 400 thousand years old. In this talk I review the physical effects of neutrinos at these different epochs in the evolution of the Universe and compare the theoretical predictions with the observational data to explore the consistency of the standard models of cosmology and particle physics and to constrain neutrino physics as well as more general, beyond-the-standard-model physics.