We present the first large-scale effort of creating composite spectra of high-redshift type Ia supernovae (SNe Ia) and comparing them to low-redshift counterparts. Through the ESSENCE project, we have obtained 107 spectra of 88 high-redshift SNe Ia with excellent light-curve information. In addition, we have obtained 397 spectra of low-redshift SNe through a multiple-decade effort at Lick and Keck Observatories, and we have used 45 UV spectra obtained by HST/IUE. The low-redshift spectra act as a control sample when comparing to the ESSENCE spectra. In all instances, the ESSENCE and Lick composite spectra appear very similar. The addition of galaxy light to the Lick composite spectra allows a nearly perfect match of the overall spectral-energy distribution with the ESSENCE composite spectra, indicating that the high-redshift SNe are more contaminated with host-galaxy light than their low-redshift counterparts. This is caused by observing objects at all redshifts with the same slit width, which corresponds to different projected distances. After correcting for the galaxy-light contamination, subtle differences in the spectra remain. We have estimated the systematic errors when using current spectral templates for K-corrections to be ~0.02 mag. The variance in the composite spectra give an estimate of the intrinsic variance in low-redshift maximum-light SN spectra of ~3% in the optical and growing toward the UV. The difference between the maximum light low and high-redshift spectra constrain SN evolution between our samples to be < 10% in the rest-frame optical.
This paper analyses the radio properties of a subsample of optically obscured (R>25.5) galaxies observed at 24um by the Spitzer Space Telescope within the First Look Survey. 96 F[24um]>0.35 mJy objects out of 510 are found to have a radio counterpart at 1.4 GHz, 610 MHz or at both frequencies respectively down to ~40uJy and ~200uJy. IRAC photometry sets the majority of them in the redshift interval z [1-3] and allows for a broad distinction between AGN-dominated galaxies (~47% of the radio-identified sample) and systems powered by intense star-formation (~13%), the remaining objects being impossible to classify. The percentage of radio identifications is a strong function of 24um flux. The radio number counts at both radio frequencies suggest that the physical process(es) responsible for radio activity in these objects have a common origin regardless of whether the source shows mid-IR emission compatible with being an obscured AGN or a star-forming galaxy. We also find that both candidate AGN and star-forming systems follow (although with a large scatter) the relationship between 1.4 GHz and 24um fluxes reported by Appleton et al. (2004) which identifies sources undergoing intense star formation activity. On the other hand, the inferred radio spectral indices alpha indicate that a large fraction of objects in our sample (~60% of all galaxies with estimated alpha) may belong to the population of Ultra Steep Spectrum (USS) Sources, typically 'frustrated' radio-loud AGN. We interpret our findings as a strong indication for concurrent AGN and star-forming activity, whereby the 1.4 GHz flux is of thermal origin, while that at 610 GHz mainly stems from the nuclear source.
It is generally believed that the explosion which gave birth to the Cassiopeia A supernova remmant resulted from core collapse of a hydrogen-deficient star. A progenitor that has lost its hydrogen, and part of its helium, envelope would lead to an explosion with the optical properties of a Type Ic supernova. There is evidence, if not general agreement, that Flamsteed observed the Cas A supernova as a sixth magnitude object in August, 1680. If an explosion with a typical SNIc light curve at the position and distance of Cas A attained maximum luminosity during the winter of 1679-1680, it would at that time have been poorly situated for visual observation, as its upper culmination would have taken place during daylight, while in August, between 170-200 days after peak luminosity, it would have been a sixth magnitude star.
Gamma-ray bursts (GRBs) have been detected up to GeV energies and are predicted by many models to emit in the very high energy (VHE, > 100 GeV) regime too. Detection of such emission would allow us to constrain GRB models. Since its launch, in late 2004, the Swift satellite has been locating GRBs at a rate of approximately 100 per year. The rapid localization and follow-up in many wavelengths has revealed new and unexpected phenomena, such as delayed emission in the form of bright X-ray flares. The Milagro gamma-ray observatory is a wide field of view (2 sr) instrument employing a water Cherenkov detector to continuously ($>$ 90% duty cycle) observe the overhead sky in the 100 GeV to 100 TeV energy range. Over 100 GRBs are known to have been in the field of view of Milagro since January 2000, including 57 since the launch of Swift (through May 2007). We discuss the results of the searches for prompt emission from these bursts, as well as for delayed emission from the X-ray flares observed in some of the Swift bursts.
We use a statistical sample of ~500 rich clusters taken from 72 square degrees of the Red-Sequence Cluster Survey (RCS-1) to study the evolution of ~30,000 red-sequence galaxies in clusters over the redshift range 0.35<z<0.95. We construct red-sequence luminosity functions (RSLFs) for a well-defined, homogeneously selected, richness limited sample. The RSLF at higher redshifts shows a deficit of faint red galaxies (to M_V=> -19.7) with their numbers increasing towards the present epoch. This is consistent with the `down-sizing` picture in which star-formation ended at earlier times for the most massive (luminous) galaxies and more recently for less massive (fainter) galaxies. We observe a richness dependence to the down-sizing effect in the sense that, at a given redshift, the drop-off of faint red galaxies is greater for poorer (less massive) clusters, suggesting that star-formation ended earlier for galaxies in more massive clusters. The decrease in faint red-sequence galaxies is accompanied by an increase in faint blue galaxies, implying that the process responsible for this evolution of faint galaxies is the termination of star-formation, possibly with little or no need for merging. At the bright end, we also see an increase in the number of blue galaxies with increasing redshift, suggesting that termination of star-formation in higher mass galaxies may also be an important formation mechanism for higher mass ellipticals. By comparing with a low-redshift Abell Cluster sample, we find that the down-sizing trend seen within RCS-1 has continued to the local universe.
We evaluate the generation of magnetosonic waves in differentially rotating magnetized plasma. Differential rotation leads to an increase of the azimuthal field by winding up the poloidal field lines into the toroidal field lines. An amplification of weak seed perturbations is considered in this time-dependent background state. It is shown that seed perturbations can be amplified by several orders of magnitude in a differentially rotating flow. The only necessary condition for this amplification is the presence of a non-vanishing component of the magnetic field in the direction of the angular velocity gradient.
The search for habitable planets like Earth around other stars fulfils an ancient imperative to understand our origins and place in the cosmos. The past decade has seen the discovery of hundreds of planets, but nearly all are gas giants like Jupiter and Saturn. Recent advances in instrumentation and new missions are extending searches to planets the size of the Earth, but closer to their host stars. There are several possible ways such planets could form, and future observations will soon test those theories. Many of these planets we discover may be quite unlike Earth in their surface temperature and composition, but their study will nonetheless inform us about the process of planet formation and the frequency of Earth-like planets around other stars.
We present measurements of the neutron-capture elements Rb and Pb for bright giants in the globular clusters M4 and M5. The clusters are of similar metallicity ([Fe/H] = -1.2) but M4 is decidedly s-process enriched relative to M5: [Ba/Fe] = +0.6 for M4 but 0.0 for M5. The Rb and Pb abundances were derived by comparing synthetic spectra with high-resolution, high signal-to-noise ratio spectra obtained with MIKE on the Magellan telescope. Abundances of Y, Zr, La, and Eu were also obtained. In M4, the mean abundances from 12 giants are [Rb/Fe] = 0.39 +/- 0.02 (sigma = 0.07), [Rb/Zr] = 0.17 +/- 0.03 (sigma = 0.08), and [Pb/Fe] = 0.30 +/- 0.02 (sigma = 0.07). In M5, the mean abundances from two giants are [Rb/Fe] = 0.00 +/- 0.05 (sigma = 0.06), [Rb/Zr] = 0.08 +/- 0.08 (sigma = 0.11), and [Pb/Fe] = -0.35 +/- 0.02 (sigma = 0.04). Within the measurement uncertainties, the abundance ratios [Rb/Fe], [Pb/Fe] and [Rb/X] for X = Y, Zr, La are constant from star-to-star in each cluster and none of these ratios are correlated with O or Na abundances. While M4 has a higher Rb abundance than M5, the ratios [Rb/X] are similar in both clusters indicating that the nature of the s-products are very similar for each cluster but the gas from which M4's stars formed had a higher concentration of these products.
We discuss the intriguing possibility that dark energy may change its equation of state in situations where large dark energy fluctuations are present. We show indications of this dynamical mutation in some generic models of dark energy.
We present an investigation of quasar colour-redshift parameter space in order to search for radio-quiet red quasars and to test the ability of a variant of the KX quasar selection method to detect quasars over a full range of colour without bias. This is achieved by combining IRIS2 imaging with the complete Fornax Cluster Spectroscopic Survey to probe parameter space unavailable to other surveys. We construct a new sample of 69 quasars with measured bJ - K colours. We show that the colour distribution of these quasars is significantly different from that of the Large Bright Quasar Survey's quasars at a 99.9% confidence level. We find 11 of our sample of 69 quasars have signifcantly red colours (bJ - K >= 3.5) and from this, we estimate the red quasar fraction of the K <= 18.4 quasar population to be 31%, and robustly constrain it to be at least 22%. We show that the KX method variant used here is more effective than the UVX selection method, and has less colour bias than optical colour-colour selection methods.
We analyze WMAP 3 year data using the one-point distribution functions to probe the non-Gaussianity in the Cosmic Microwave Background (CMB) Anisotropy data. Computer simulations are performed to determine the uncertainties of the results. We report the non-Gaussianity parameter f_NL is constrained to 26<f_NL<82 for Q-band, 12<f_NL<67 for V-band, 7<f_NL<64 for W-band and 23<f_NL<75 for Q+V+W combined data at 95% confidence level (CL).
The dissolution time (t_dis) of clusters in a tidal field does not scale with the ``classical'' expression for the relaxation time. First, the scaling with N, and hence cluster mass, is shallower due to the finite escape time of stars. Secondly, the cluster half-mass radius is of little importance. This is due to a balance between the relative tidal field strength and internal relaxation, which have an opposite effect on t_dis, but of similar magnitude. When external perturbations, such as encounters with giant molecular clouds (GMC) are important, t_dis for an individual cluster depends strongly on radius. The mean dissolution time for a population of clusters, however, scales in the same way with mass as for the tidal field, due to the weak dependence of radius on mass. The environmental parameters that determine t_dis are the tidal field strength and the density of molecular gas. We compare the empirically derived t_dis of clusters in six galaxies to theoretical predictions and argue that encounters with GMCs are the dominant destruction mechanism. Finally, we discuss a number of pitfalls in the derivations of t_dis from observations, such as incompleteness, with the cluster system of the SMC as particular example.
The effect of the initial condition of inflation on the power spectra of scalar and tensor perturbations is estimated assuming a slow-roll inflation model. By defining a more general initial state in inflation particular properties of the power spectrum such as oscillation can be revealed. The behavior of the power spectrum is shown to exhibit a step-like variation with respect to finite inflation length in cases of both radiation- and scalar matter-dominated pre-inflation. The power spectrum is shown to oscillate in the radiation-dominated case. The effects of such a power spectrum on the TT and TE power spectra are examined for three typical slow-roll inflation models; a small-field model, a large field model, and a hybrid model, considering both pre-inflation models. It is found that the discrepancies between WMAP3 data and the Lambda CDM model, such as suppression of the spectrum at l=2, may be explained to a certain extent by the finite length of inflation for inflation of close to 60 e-folds. The small-field inflation model with scalar matter-dominated pre-inflation provides the best fit to the WMAP3 data among the models considered. Relatively large changes in the angular TT power spectrum occur in response to small changes in inflation length in the radiation-dominated pre-inflation models, and half cases do not fit well with the observed data. This behavior is considered to be attributable to the oscillatory behavior of the power spectrum. The scalar matter-dominated case is thus preferred to the radiation-dominated case of pre-inflation, independent of the length of inflation.
Following Paczy\'{n}ski & Zi\'{o}lkowski (1968) and Han et al. (1994), we assume that the envelope of an asymptotic giant branch (AGB) or a first giant branch (FGB) star is lost when the binding energy of the envelope is equal to zero ($\Delta W=0$) and the core mass of the AGB star or the FGB star at the point ($\Delta W=0$) is taken as the final mass. Using this assumption, we calculate the IFMRs for stars of different metallicities.We find that the IFMRs depends strongly on the metallicity, i.e. $Z=0.0001, 0.0003, 0.001, 0.004, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.08$ and 0.1. From $Z=0.04$, the final mass of the stars with a given initial mass increases with increasing or decreasing metallicity. The difference of the final mass due to the metallicity may be up to 0.4 $M_{\odot}$. A linear fit of the initial-final mass relationship in NGC 2099 (M37) shows a potential evidence of the effect of metallicity on the IFMR. The IFMR for stars of $Z=0.02$ obtained in the paper matches well with those inferred observationally in the Galaxy. For $Z\geq 0.02$, helium WDs are obtained from the stars of $M_{\rm i}\leq 1.0 M_{\odot}$ and this result is upheld by the discovery of numerous low-mass WDs in NGC 6791 which is a metal-rich old open cluster. Using the IFMR for stars of $Z=0.02$ obtained in the paper, we have reproduced the mass distribution of DA WDs in Sloan DR4 except for some ultra-massive white dwarfs. The trend that the mean mass of WDs decreases with effective temperature may originate from the increase of the initial metallicities of stars. We predict that metal-rich low-mass stars may become under-massive white dwarfs.
Differential rotation can be detected in single line profiles of stars rotating more rapidly than about $v \sin{i} = 10$ km s$^{-1}$ with the Fourier transform technique. This allows to search for differential rotation in large samples to look for correlations between differential rotation and other stellar parameters. I analyze the fraction of differentially rotating stars as a function of color, rotation, and activity in a large sample of F-type stars. Color and rotation exhibit a correlation with differential rotation in the sense that more stars are rotating differentially in the cooler, less rapidly rotating stars. Effects of rotation and color, however, cannot be disentangled in the underlying sample. No trend with activity is found.
Using the IRAM 30 m telescope, a mapping survey in optically thick and thin lines was performed towards 46 high mass star-forming regions. The sample includes UC H{\sc ii} precursors and UC H{\sc ii} regions. Seventeen sources are found to show "blue profiles", the expected signature of collapsing cores. The excess of sources with blue over red profiles ([$N_{\rm blue}$ -- $N_{\rm red}$]/$N_{\rm total}$) is 29% in the HCO$^+$ $J$=1--0 line, with a probability of 0.6% that this is caused by random fluctuations. UC H{\sc ii} regions show a higher excess (58%) than UC H{\sc ii} precursors (17%), indicating that material is still accreted after the onset of the UC H{\sc ii} phase. Similar differences in the excess of blue profiles as a function of evolutionary state are not observed in low mass star-forming regions. Thus, if confirmed for high mass star-forming sites, this would point at a fundamental difference between low- and high-mass star formation. Possible explanations are inadequate thermalization, stronger influence of outflows in massive early cores, larger gas reserves around massive stellar objects or different trigger mechanisms between low- and high- mass star formation.
Invisible plasma content in blazar jets such as protons and/or thermal electron-positron ($e^{\pm}$) pairs is explored through combined arguments of dynamical and radiative processes. By comparing physical quantities required by the internal shock model with those obtained through the observed broadband spectra for Mrk 421, we obtain that the ratio of the Lorentz factors of a pair of cold shells resides in about $2\sim 20$, which implies that the shocks are at most mildly relativistic. Using the obtained Lorentz factors, the total mass density $\rho$ in the shocked shells is investigated. The upper limit of $\rho$ is obtained from the condition that thermal bremsstrahlung emission should not exceed the observed $\gamma$-ray luminosity, whilst the lower limit is constrained from the condition that the energy density of non-thermal electrons is smaller than that of the total plasma. Then we find $\rho$ is $10^2$-$10^3$ times heavier than that of non-thermal electrons for pure $e^{\pm}$ pairs, while $10^2$-$10^6$ times heavier for pure electron-proton ($e/p$) content, implying the existence of a large amount of invisible plasma. The origin of the continuous blazar sequence is shortly discussed and we speculate that the total mass density and/or the blending ratio of $e^{\pm}$ pairs and $e/p$ plasma could be new key quantities for the origin of the sequence.
It has been argued that the large-angle cosmic microwave background anisotropy has anomalies at 3-sigma level. We review various proposed ideas to explain the origin of the anomalies and discuss how we can constrain the proposed models using future observational data.
We report here on a new VHE source, HESS J1908+063, disovered during the extended H.E.S.S. survey of the Galactic plane and which coincides with the recently reported MILAGRO unidentied source MGRO J1908+06. The position, extension and spectrum measurements of the HESS source are presented and compared to those of MGRO J1908+06. Possible counterparts at other wavelenghts are discussed. For the first time one of the low-lattitude MILAGRO sources is confirmed.
Sgr A* is a source of strongly variable emission in several energy bands. It is generally agreed that this emission comes from the material surrounding the black hole which is either falling in or flowing out. The activity must be driven by accretion but the character of accretion flow in this object is an open question. We suggest that the inflow is dominated by the relatively low angular momentum material originating in one of the nearby group of stars. Such material flows in directly towards the black hole up to the distance of order of ten Schwarzschild radii or less, where it hits the angular momentum barrier which leads naturally to a flow variability. We study both the analytical and the numerical solutions for the flow dynamics, and we analyze the radiation spectra in both cases using the Monte Carlo code to simulate the synchrotron, bremsstrahlung and the Compton scattering. Our model roughly reproduces the broad band spectrum of Sgr A* and its variability if we allow for a small fraction of energy to be converted to non-thermal population of electrons. It is also consistent (for a range of viewing angles) with the strong constraints on the amount of circumnuclear material imposed by the measurements of the Faraday rotation.
A recent analysis of cosmic-ray data from a space borne experiment by the AMS collaboration supports the observation of an excess in the cosmic-ray positron spectrum by previous balloon experiments. The combination of the various experimental data establishes a deviation from the expected background with a significance of more than four standard deviations. The observed change in the spectral index cannot be explained without introducing a new source of positrons. When interpreted within the MSSM a consistent description of the antiproton spectrum, the diffuse gamma-ray flux and the positron fraction is obtained which is compatible with all other experimental data, including recent WMAP data.
We investigate the wave effect in the gravitational lensing by a black hole with very tiny mass less than 10^-19 solar mass, which is called attolensing, motivated by a recent report that the lensing signature might be a possible probe of a modified gravity theory in the braneworld scenario. We focus on the finite source size effect and the effect of the relative motion of the source to the lens, which are influential to the wave effect in the attolensing. Astrophysical condition that the lensed interference signature can be a probe of the modified gravity theory is demonstrated. The interference signature in the microlensing system is also discussed.
The creation of large scale magnetic fields is studied in an inflationary universe where electrodynamics is assumed to be nonlinear. After inflation ends electrodynamics becomes linear and thus the description of reheating and the subsequent radiation dominated stage are unaltered. The nonlinear regime of electrodynamics is described by lagrangians having a power law dependence on one of the invariants of the electromagnetic field. It is found that there is a range of parameters for which primordial magnetic fields of cosmologically interesting strengths can be created.
The luminosities of the optical afterglows of Gamma Ray Bursts, 12 hours (rest frame time) after the trigger, show a surprising clustering, with a minority of events being at a significant smaller luminosity. If real, this dichotomy would be a crucial clue to understand the nature of optically dark afterglows, i.e. bursts that are detected in the X-ray band, but not in the optical. We investigate this issue by studying bursts of the pre-Swift era, both detected and undetected in the optical. The limiting magnitudes of the undetected ones are used to construct the probability that a generic bursts is observed down to a given magnitude limit. Then, by simulating a large number of bursts with pre-assigned characteristics, we can compare the properties of the observed optical luminosity distribution with the simulated one. Our results suggest that the hints of bimodality present in the observed distribution reflects a real bimodality: either the optical luminosity distributions of bursts is intrinsically bimodal, or there exists a population of bursts with a quite significant grey absorption, i.e. wavelength independent extinction. This population of intrinsically weak or grey-absorbed events can be associated to dark bursts.
We report the discovery of a 16-20 Jupiter mass radial velocity companion around the very young (3 Myr) brown dwarf candidate ChaHa8. Based on high-resolution echelle spectra of ChaHa8 taken between 2000 and 2007 with UVES at the VLT, a companion was detected through RV variability with a semi-amplitude of 1.6 km/s. A Kepler fit to the data yields an orbital period of the companion of 1590 days and an eccentricity of e=0.49. A companion minimum mass M2sin i between 16 and 20 Jupiter masses is derived when using model-dependent mass estimates for the primary. The mass ratio M2/M1 might be as small as 0.2 and, with a probability of 87%, it is less than 0.4. ChaHa8 harbors most certainly the lowest mass companion detected so far in a close (~1 AU) orbit around a brown dwarf or very low-mass star. From the uncertainty in the orbit solution, it cannot completely be ruled out that the companion has a mass in the planetary regime. Its discovery is in any case an important step towards RV planet detections around BDs. Further, ChaHa8 is the fourth known spectroscopic brown dwarf or very low-mass binary system with an RV orbit solution and the second known very young one.
It has been well known that in the point of view of a distant observer, all in-falling matter to a black hole (BH) will be eventually stalled and "frozen" just outside the event horizon of the BH, although an in-falling observer will see the matter falling straight through the event horizon. Thus in this "frozen star" scenario, as distant observers, we could never observe matter falling into a BH, neither could we see any "real" BH other than primordial ones, since all other BHs are believed to be formed by matter falling towards singularity. Here we first obtain the exact solution for a pressureless mass shell around a pre-existing BH. The metrics inside and interior to the shell are all different from the Schwarzschild metric of the enclosed mass. The metric interior to the shell can be transformed to the Schwarzschild metric for a slower clock which is dependent of the location and mass of the shell. Another result is that there does not exist a singularity nor event horizon in the shell. Therefore the "frozen star" scenario is incorrect. We also show that for all practical astrophysical settings the in-falling time recorded by an external observer is sufficiently short that future astrophysical instruments may be able to follow the whole process of matter falling into BHs. The distant observer could not distinguish between a "real" BH and a "frozen star", until two such objects merge together. It has been proposed that electromagnetic waves will be produced when two "frozen stars" merge together, but not true when two "real" bare BHs merge together. However gravitational waves will be produced in both cases. Thus our solution is testable by future high sensitivity astronomical observations.
Smooth double crossing of the phantom barrier $w_{\Lambda} = -1$ has been found possible in cosmological model with Gauss-Bonnet-scalar interaction, in the presence of background cold dark matter. Such crossing has been observed to be a sufficiently late time phenomena and independent of the sign of Gauss-Bonnet-scalar interaction. The luminosity distance versus redshift curve shows a perfect fit with the $\Lambda CDM$ model up to $z=3.5$.
Recently the numerical simulations of the process of reionization of the universe at z>6 have made a qualitative leap forward, reaching sufficient sizes and dynamic range to determine the characteristic scales of this process. This allowed making the first realistic predictions for a variety of observational signatures. We discuss recent results from large-scale radiative transfer and structure formation simulations on the observability of high-redshift Ly-alpha sources. We also briefly discuss the dependence of the characteristic scales and topology of the ionized and neutral patches on the reionization parameters.
We present highlights and an overview of 20 FUSE and HST/STIS observations of the bright symbiotic binary EG And. The main motivation behind this work is to obtain spatially-resolved information on an evolved giant star in order to understand the mass-loss processes at work in these objects. The system consists of a low-luminosity white dwarf and a mass-losing, non-dusty M2 giant. The ultraviolet observations follow the white dwarf continuum through periodic gradual occultations by the wind and chromosphere of the giant, providing a unique diagnosis of the circumstellar gas in absorption. Unocculted spectra display high ionization features, such as the OVI resonance doublet which is present as a variable (hourly time-scales), broad wind profile, which diagnose the hot gas close to the dwarf component. Spectra observed at stages of partial occultation display a host of low-ionization, narrow, absorption lines, with transitions observed from lower energy levels up to ~5eV above ground. This absorption is due to chromospheric/wind material, with most lines due to transitions of SiII, PII, NI, FeII and NiII, as well as heavily damped HI Lyman series features. No molecular features are observed in the wind acceleration region despite the sensitivity of FUSE to molecular hydrogen. From analysis of the ultraviolet dataset, as well as optical data, we find that the dwarf radiation does not dominate the wind acceleration region of the giant, and that observed thermal and dynamic wind properties are most likely representative of isolated red giants.
Experimental evidence is reviewed for the existence of superfluid turbulence in a differentially rotating, spherical shell at high Reynolds numbers ($\Rey\gsim 10^3$), such as the outer core of a neutron star. It is shown that torque variability increases with $\Rey$, suggesting that glitch activity in radio pulsars may be a function of $\Rey$ as well. The $\Rey$ distribution of the 67 glitching radio pulsars with characteristic ages $\tau_c \leq 10^6$ {\rm yr} is constructed from radio timing data and cooling curves and compared with the $\Rey$ distribution of all 348 known pulsars with $\tau_c \leq 10^6$ {\rm yr}. The two distributions are different, with a Kolmogorov-Smirnov probability $\geq 1 - 3.9 \times 10^{-3}$. The conclusion holds for (modified) Urca and nonstandard cooling, and for Newtonian and superfluid viscosities.
AMS-02 is a multi-purpose spectrometer with superconducting magnet, and is designed for 3 years of data taking aboard the International Space Station. Its high performance regarding particle identification and energy measurement will allow performing indirect searches for dark matter (DM) in different channels simultaneously: gamma rays, positrons and antiprotons. AMS-02 sensitivity to those signals are presented and --provided the positron excess is due to DM signal-- it is shown that it allows to probe new physics models in detail. Its high sensitivity could even be a unique opportunity to reach the Majorana nature of the DM particle through final state polarization effects.
We present a measure of the hard (2-8 keV) X-ray luminosity function (XLF) of Active Galactic Nuclei up to z~5. At high redshifts, the wide area coverage of the Chandra Multiwavength Project is crucial to detect rare and luminous (Lx > 10^44 erg s^-1) AGN. The inclusion of samples from deeper published surveys, such as the Chandra Deep Fields, allows us to span the lower Lx range of the XLF. Our sample is selected from both the hard (z < 3; f(2-8 keV) > 6.3x10^-16 erg cm^-2 s^-1) and soft (z > 3; f(0.5-2.0 keV) > 1.0x10^-16 erg cm^-2 s^-1) energy band detections. Within our optical magnitude limits (r',i' < 24), we achieve an adequate level of completeness (>50%) regarding X-ray source identification (i.e., redshift). We find that the luminosity function is similar to that found in previous X-ray surveys up to z~3 with an evolution dependent upon both luminosity and redshift. At z > 3, there is a significant decline in the numbers of AGN with an evolution rate similar to that found by studies of optically-selected QSOs. Based on our XLF, we assess the resolved fraction of the Cosmic X-ray Background, the cumulative mass density of Supermassive Black Holes (SMBHs), and the comparison of the mean accretion rate onto SMBHs and the star formation history of galaxies as a function of redshift. A coevolution scenario up to z~2 is plausible though at higher redshifts the accretion rate onto SMBHs drops more rapidly. Finally, we highlight the need for better statistics of high redshift AGN at z > 3, which is achievable with the upcoming Chandra surveys.
We studied the temporal and spectral evolution of the synchrotron emission from the high energy peaked BL Lac object 1E 1207.9+3945. Two recent observations have been performed by the XMM-Newton and Swift satellites; we carried out X-ray spectral analysis for both of them, and photometry in optical-ultraviolet filters for the Swift one. Combining the results thus obtained with archival data we built the long-term X-ray light curve, spanning a time interval of 26 years, and the Spectral Energy Distribution (SED) of this source. The light curve shows a large flux increasing, about a factor of six, in a time interval of a few years. After reaching its maximum in coincidence with the XMM-Newton pointing in December 2000 the flux decreased in later years, as revealed by Swift. The very good statistics available in the 0.5-10 keV XMM-Newton X-ray spectrum points out a highly significant deviation from a single power law. A log-parabolic model with a best fit curvature parameter of 0.25 and a peak energy at ~1 keV describes well the spectral shape of the synchrotron emission. The simultaneous fit of Swift UVOT and XRT data provides a milder curvature (b~0.1) and a peak at higher energies (~15 keV), suggesting a different state of source activity. In both cases UVOT data support the scenario of a single synchrotron emission component extending from the optical/UV to the X-ray band. New X-ray observations are important to monitor the temporal and spectral evolution of the source; new generation gamma-ray telescopes like AGILE and GLAST could for the first time detect its inverse Compton emission.
In order to study the process of cooling in dark-matter (DM) halos and assess how well simple models can represent it, we run a set of radiative SPH hydrodynamical simulations of isolated halos, with gas sitting initially in hydrostatic equilibrium within Navarro-Frenk-White (NFW) potential wells. [...] After having assessed the numerical stability of the simulations, we compare the resulting evolution of the cooled mass with the predictions of the classical cooling model of White & Frenk and of the cooling model proposed in the MORGANA code of galaxy formation. We find that the classical model predicts fractions of cooled mass which, after about two central cooling times, are about one order of magnitude smaller than those found in simulations. Although this difference decreases with time, after 8 central cooling times, when simulations are stopped, the difference still amounts to a factor of 2-3. We ascribe this difference to the lack of validity of the assumption that a mass shell takes one cooling time, as computed on the initial conditions, to cool to very low temperature. [...] The MORGANA model [...] better agrees with the cooled mass fraction found in the simulations, especially at early times, when the density profile of the cooling gas is shallow. With the addition of the simple assumption that the increase of the radius of the cooling region is counteracted by a shrinking at the sound speed, the MORGANA model is also able to reproduce for all simulations the evolution of the cooled mass fraction to within 20-50 per cent, thereby providing a substantial improvement with respect to the classical model. Finally, we provide a very simple fitting function which accurately reproduces the cooling flow for the first ~10 central cooling times. [Abridged]
The giant flares produced by highly magnetized neutron stars, "magnetars," are the brightest sources of high energy radiation outside our solar system. Serendipitous observations with NASA's Rossi X-ray Timing Explorer (RXTE) of the two most recent flares resulted in the discovery of high frequency oscillations in their X-ray fluxes. The frequencies of these oscillations range from about 20 Hz to as high as 1800 Hz, and may represent the first detection of global oscillation modes of neutron stars. Here I will present an observational and theoretical overview of these oscillations and discuss how they might allow us to probe neutron star interiors and dense matter physics.
The stellar populations in the bulges of S0s, together with the galaxies' dynamics, masses and globular clusters, contain very interesting clues about their formation. I present here recent evidence suggesting that S0s are the descendants of fading spirals whose star formation ceased.
We present optical, IR and millimeter observations of the solar-type star 13-277, also known as GM Cep, in the 4 Myr-old cluster Tr 37. GM Cep experiences rapid magnitude variations of more than 2 mag at optical wavelengths. We explore the causes of the variability, which seem to be dominated by strong increases in the accretion, being similar to EX-or episodes. The star shows high, variable accretion rates (up to ~10$^{-6}$ Msun/yr), signs of powerful winds, and it is a very fast rotator (Vsini~43 km/s). Its strong mid-IR excesses reveal a very flared disk and/or a remnant envelope, most likely out of hydrostatic equilibrium. The 1.3 millimeter fluxes suggest a relatively massive disk (Mdisk~0.1 Msun). Nevertheless, the millimeter mass is not enough to sustain increased accretion episodes over large timescales, unless the mass is underestimated due to significant grain growth. We finally explore the possibility of GM Cep having a binary companion, which could trigger disk instabilities producing the enhanced accretion episodes.
The annihilations of WIMPs produce high energy gamma-rays in the final state. These high energy gamma-rays may be detected by IACTs such as the H.E.S.S. array of Imaging Atmospheric Cherenkov telescopes. Besides the popular targets such as the Galactic Center or galaxy clusters such as VIRGO, dwarf spheroidal galaxies are privileged targets for Dark Matter annihilation signal searches. H.E.S.S. observations on the Sagittarius dwarf galaxy are presented. The modelling of the Dark Matter halo profile of Sagittarius dwarf is discussed. Constraints on the velocity-weighted cross section of Dark Matter particles are derived in the framework of Supersymmetric and Kaluza-Klein models. The future of H.E.S.S. will be briefly discussed.
Using the high-level Balmer lines and continuum, we trace the density structure of two magnetospheric disk segments of the prototypical Bp star sigma Ori E (B2p) as these segments occult portions of the star during the rotational cycle. High-resolution spectra of the Balmer lines >H9 and Balmer edge were obtained on seven nights in January-February 2007 at an average sampling of 0.01 cycles. We measured equivalent width variations due to the star occultations by two disk segments 0.4 cycles apart and constructed differential spectra of the migrations of the corresponding absorptions across the Balmer line profiles. We first estimated the rotational and magnetic obliquity angles. We then simulated the observed Balmer jump variation using the model atmosphere codes synspec/circus and evaluated the disk geometry and gas thermodynamics. We find that the two occultations are caused by two disk segments. The first of these transits quickly, indicating that the segment resides in a range of distances, perhaps 2.5-6R_star, from the star. The second consists of a more slowly moving segment situated closer to the surface and causing two semi-resolved absorbing maxima. During its transit this segment brushes across the star's "lower" limb. Judging from the line visibility up to H23-H24 during the occultations, both disk segments have mean densities near 10^{12} cm^{-3} and are opaque in the lines and continuum. They have semiheights less than 1/2 of a stellar radius, and their temperatures are near 10500K and 12000K, respectively. In all, the disks of Bp stars have a much more complicated geometry than has been anticipated, as evidenced by their (sometimes) non-coplanarity, de-centerness, and from star to star, differences in disk height.
In this work we show that 3-3-1 model with right-handed neutrinos has a natural WIMP dark matter candidate. It is a complex scalar with mass of order of some hundreds of GeV which carries two units of lepton number, a scalar bilepton. This makes it a very peculiar WIMP, very distinct from Supersymmetric or Extra-dimension candidates. Besides, although we have to make some reasonable assumptions concerning the several parameters in the model, no fine tunning is required in order to get the correct dark matter abundance. We also analyze the prospects for WIMP direct detection by considering recent and projected sensitivities for WIMP-nucleon elastic cross section from CDMS and XENON Collaborations.
We develop the canonical theory of gravitational collapse in 2+1 dimensions with a negative cosmological constant and obtain exact solutions of the Wheeler--DeWitt equation regularized on a lattice. We employ these solutions to derive the Hawking radiation from black holes formed in all models of dust collapse. We obtain an (approximate) Planck spectrum near the horizon characterized by the Hawking temperature $T_{\mathrm H}=\hbar\sqrt{G\Lambda M}/2\pi$, where $M$ is the mass of a black hole that is presumed to form at the center of the collapsing matter cloud and $-\Lambda$ is the cosmological constant. Our solutions to the Wheeler-DeWitt equation are exact, so we are able to reliably compute the greybody factors that result from going beyond the near horizon region.
We present explicit solutions of the signum-Gordon scalar field equation which have finite energy and are periodic in time. Such oscillons have a strictly finite size. They do not emit radiation.
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We analyze the possibility of delensing CMB polarization maps using foreground weak lensing (WL) information. We build an estimator of the CMB lensing potential out of optimally combined projected potential estimators to different source redshift bins. Our estimator is most sensitive to the redshift depth of the WL survey, less so to the shape noise level. Estimators built using galaxy surveys like LSST and SNAP yield a 30-50% reduction in the lensing B-mode power. We illustrate the potential advantages of a 21-cm survey by considering a fiducial WL survey for which we take the redshift depth zmax and the effective angular concentration of sources n as free parameters. For a noise level of 1 muK arcmin in the polarization map itself, as projected for a CMBPol experiment, and a beam with FWHM=10 arcmin, we find that going to zmax=20 at n=100 gal/sqarcmin yields a delensing performance similar to that of a quadratic lensing potential estimator applied to small-scale CMB maps: the lensing B-mode contamination is reduced by almost an order of magnitude. In this case, there is also a reduction by a factor of ~4 in the detectability threshold of the tensor B-mode power. At this CMB noise level, there is little gain from sources with zmax>20. The delensing gains are lost if the CMB beam exceeds ~20 arcmin. The delensing efficiency and useful zmax depend acutely on the CMB map noise level, but beam sizes below 10 arcmin do not help. Delensing via foreground sources does not require arcminute-resolution CMB observations, a substantial practical advantage over the use of CMB observables for delensing.
Preliminary results are presented from a simple, single-antenna experiment designed to measure the all-sky radio spectrum between 100 and 200 MHz. The system used an internal comparison-switching scheme to reduce non-smooth instrumental contaminants in the measured spectrum to 75 mK. From the observations, we place an initial upper limit of 450 mK on the relative brightness temperature of the redshifted 21 cm contribution to the spectrum due to neutral hydrogen in the intergalactic medium (IGM) during the epoch of reionization, assuming a rapid transition to a fully ionized IGM at a redshift of 8. With refinement, this technique should be able to distinguish between slow and fast reionization scenarios. To constrain the duration of reionization to dz > 2, the systematic residuals in the measured spectrum must be reduced to 3 mK.
INTEGRAL, the European Space Agency's gamma-ray observatory, tripled the number of super-giant high-mass X-ray binaries (sgHMXB) known in the Galaxy by revealing absorbed and fast transient (SFXT) systems. In these sources, quantitative constraints on the wind clumping of the massive stars could be obtained from the study of the hard X-ray variability of the compact accreting object. Hard X-ray flares and quiescent emission of SFXT systems have been characterized and used to derive wind clump parameters. A large fraction of the hard X-ray emission is emitted in the form of flares with a typical duration of 3 ks, frequency of 7 days and luminosity of 1E36 erg/s. Such flares are most probably emitted by the interaction of a compact object orbiting at ~10 R* with wind clumps (1E(22-23) g) representing a large fraction of the stellar mass-loss rate. The density ratio between the clumps and the inter-clump medium is 1E(2-4) in SFXT systems. The parameters of the clumps and of the inter-clump medium, derived from the SFXT flaring behavior, are in good agreement with macro-clumping scenario and line driven instability simulations. SFXT have probably a larger orbital radius than classical sgHMXB.
Transonic accretion flow with self-consistent treatment of random magnetic field is presented.
We expand our Bayesian Monte Carlo method for analyzing the light curves of gravitationally lensed quasars to simultaneously estimate time delays and quasar structure including their mutual uncertainties. We apply the method to HE1104-1805 and QJ0158-4325, two doubly-imaged quasars with microlensing and intrinsic variability on comparable time scales. For HE1104-1805 the resulting time delay of (Delta t_AB) = t_A - t_B = 162.2 -5.9/+6.3 days and accretion disk size estimate of log(r_s/cm) = 15.7 -0.5/+0.4 at 0.2 micron in the rest frame are consistent with earlier estimates but suggest that existing methods for estimating time delays in the presence of microlensing underestimate the uncertainties. We are unable to measure a time delay for QJ0158-4325, but the accretion disk size is log(r_s/cm) = 14.9 +/- 0.3 at 0.3 micron in the rest frame.
We present Hubble Space Telescope (HST) and Spitzer Space Telescope images and photometry of the extremely metal-poor (Z = 0.03 Z_sol) blue dwarf galaxy CGCG 269-049. The HST images reveal a large population of red giant and asymptotic giant branch stars, ruling out the possibility that the galaxy has recently formed. From the magnitude of the tip of the red giant branch, we measure a distance to CGCG 269-049 of only 4.9 +/- 0.4 Mpc. The spectral energy distribution of the galaxy between ~3.6 - 70 microns is also best fitted by emission from predominantly ~10 Gyr old stars, with a component of thermal dust emission having a temperature of 72 +/- 10 K. The HST and Spitzer photometry indicate that more than 60% of CGCG 269-049's stellar mass consists of stars ~10 Gyr old, similar to other local blue dwarf galaxies. Our HST H-alpha image shows no evidence of a supernova-driven outflow that could be removing metals from the galaxy, nor do we find evidence that such outflows occurred in the past. Taken together with CGCG 269-049's large ratio of neutral hydrogen mass to stellar mass (~10), these results are consistent with recent simulations in which the metal deficiency of local dwarf galaxies results mainly from inefficient star formation, rather than youth or the escape of supernova ejecta.
We highlight the importance of gaseous TiO and VO opacity on the highly irradiated close-in giant planets. The atmospheres of these planets naturally fall into two classes that are somewhat analogous to the M- and L-type dwarfs. Those that are warm enough to have appreciable opacity due to TiO and VO gases we term the ``pM Class'' planets, and those that are cooler we term ``pL Class'' planets. We calculate model atmospheres for these planets, including pressure-temperature profiles, spectra, and characteristic radiative time constants. We show that pM Class planets have hot stratospheres $\sim$2000 K and appear ``anomalously'' bright in the mid infrared secondary eclipse, as was recently found for planets HD 149026b and HD 209458b. This class of planets absorbs incident flux and emits thermal flux from high in their atmospheres. Consequently, they will have large day/night temperature contrasts and negligible phase shifts between orbital phase and thermal emission light curves, because radiative timescales are much shorter than possible dynamical timescales. The pL Class planets absorb incident flux deeper in the atmosphere where atmospheric dynamics will more readily redistribute absorbed energy. This will lead to cooler day sides, warmer night sides, and larger phase shifts in thermal emission light curves. Around a Sun-like primary this boundary occurs at $\sim$0.04-0.05 AU. The eccentric transiting planets HD 147506b and HD 17156b alternate between the classes. Thermal emission in the optical from pM Class planets is significant red-ward of 400 nm, making these planets attractive targets for optical detection. The difference in the observed day/night contrast between ups Andromeda b (pM Class) and HD 189733b (pL Class) is naturally explained in this scenario. (Abridged.)
In this study we compile for the first time comprehensive data sets of solar and stellar flare parameters, including flare peak temperatures T_p, flare peak volume emission measures EM_p, and flare durations t_f from both solar and stellar data, as well as flare length scales L from solar data. Key results are that both the solar and stellar data are consistent with a common scaling law of EM_p ~ T_p^4.7, but the stellar flares exhibit ~250 times higher emission measures (at the same flare peak temperature). For solar flares we observe also systematic trends for the flare length scale L(T_p) ~ T_p^0.9 and the flare duration t_F(T_p) ~ T_p^0.9 as a function of the flare peak temperature. Using the theoretical RTV scaling law and the fractal volume scaling observed for solar flares, i.e., V(L) ~ L^2.4, we predict a scaling law of EM_p ~ T_p^4.3, which is consistent with observations, and a scaling law for electron densities in flare loops, n_p ~ T_p^2/L ~ T_p^1.1. The RTV-predicted electron densities were also found to be consistent with densities inferred from total emission measures, n_p=(EM_p/q_V*V)^1/2, using volume filling factors of q_V=0.03-0.08 constrained by fractal dimensions measured in solar flares. Our results affect also the determination of radiative and conductive cooling times, thermal energies, and frequency distributions of solar and stellar flare energies.
This paper is a review of my previous research on gravitational waves from the R^-1 high order theory of gravity. It is shown that a massive scalar mode of gravitational waves from the R^-1 theory generates a longitudinal force in addition of the transverse one which is proper of the massless gravitational waves and the response of an arm of an interferometer to this longitudinal effect in the frame of a local observer is computed. Important conseguences from a theoretical point of view could arise from this approach, because it opens to the possibility of using the signals seen from interferometers to understand which is the correct theory of gravitation.
We consider the propagation of cosmic rays in turbulent magnetic fields. We use the models of magnetohydrodynamic turbulence that were tested in numerical simulations, in which the turbulence is injected on large scale and cascades to small scales. Our attention is focused on the models of the strong turbulence, but we also briefly discuss the effects that the weak turbulence and the slab Alfv\'enic perturbations can have. The latter are likely to emerge as a result of instabilities with in the cosmic ray fluid itself, e.g., beaming and gyroresonance instabilities of cosmic rays. To describe the interaction of cosmic rays with magnetic perturbations we develop a non-linear formalism that extends the ordinary Quasi-Linear Theory (QLT) that is routinely used for the purpose. This allows us to avoid the usual problem of 90 degree scattering and enable our computation of the mean free path of cosmic rays. We apply the formalism to the cosmic ray propagation in the galactic halo and in the Warm Ionized medium (WIM). In addition, we address the issue of the transport of cosmic rays perpendicular to the mean magnetic field and show that the issue of cosmic ray subdiffusion (i.e., propagation with retracing the trajectories backwards, which slows down the diffusion) is only important for restricted cases when the ambient turbulence is far from what numerical simulations suggest to us. As a result, this work provides formalism that can be applied for calculating cosmic ray propagation in a wide variety of circumstances.
We study the three-dimensional and projected shapes of galaxy groups in the Sloan Digital Sky Survey Data Release 4, and examine the alignment between the orientation of the central galaxy and the spatial distribution of satellite galaxies. The projected ellipticity of a group is measured using the moments of the discrete distribution of its member galaxies. We infer the three-dimensional and projected axis ratios of their dark matter haloes by comparing the measured ellipticity distributions with those obtained from Monte Carlo simulations of projected, triaxial dark matter haloes with different axis ratios. We find that the halo shape has a strong dependence on the halo mass. While the haloes of low-mass groups are nearly spherical, those of massive groups tend to be prolate. For groups containing at least four members, the statistical distribution of their measured ellipticities does not have a strong dependence on the colors of their central galaxies. Our analysis further shows that the average three-dimensional axis ratio for haloes with $12<{\rm log}[M/(h^{-1}M_{\odot})]\leq15$ is about $1:0.77:0.61$, resulting in a projected axis ratio of $\sim 0.8$. (abridged)
(Abridged) Lyman-alpha (Lya) is a dominant probe of the galaxy population at
high-z. However, interpretation of data drawn from Lya alone hinges on the Lya
escape fraction which, due to the complex radiative transport, may vary
greatly. Here we map the Lya emission from local starburst Haro 11, a Lya
emitter and the only known candidate for low-z Lyman continuum emission (LyC).
To aid in the interpretation we perform a detailed multi-wavelength analysis
and model the stellar population, dust distribution, ionising photon budget,
and star-cluster population. We use archival X-ray observations to further
constrain properties of the starburst and estimate the HI column density.
The Lya morphology is found to be strongly decoupled from stellar and nebular
(H-alpha) morphologies. General surface photometry finds only very slight
correlation between Lya and H-halpha, E(B-V), and stellar age. Only around the
central Lya-bright cluster do we find the Lya/Ha ratio at values predicted by
recombination theory. The total Lya escape fraction is found to be just 3%. We
compute that ~90% of the Lya photons that escape do so after undergoing
multiple resonance scattering events, masking their point of origin. This leads
to a largely symmetric distribution and, by increasing the distance that
photons must travel to escape, decreases the escape probability significantly.
While dust must ultimately be responsible for the destruction of Lya, it plays
little role in governing the observed morphology, which is regulated more by
ISM kinematics and geometry. We find tentative evidence for local Lya
equivalent width in the immediate vicinity of star-clusters being a function of
cluster age, consistent with hydrodynamic studies. We estimate the ionising
photon production and further constrain the escape fraction at 900 AA to <~9% .
We observed four southern AXPs in 1999 near 1400 MHz with the Parkes 64-m radio telescope to search for periodic radio emission. No Fourier candidates were discovered in the initial analysis, but the recent radio activity observed for the AXP XTE J1810-197 has prompted us to revisit these data to search for single radio pulses and bursts. The data were searched for both persistent and bursting radio emission at a wide range of dispersion measures, but no detections of either kind were made. These results further weaken the proposed link between rotating radio transient sources and magnetars. However, continued radio searches of these and other AXPs at different epochs are warranted given the transient nature of the radio emission seen from XTE J1810-197, which until very recently was the only known radio-emitting AXP.
We focus attention on the Oe/Be stars to test the concept that the disks of
these stars form by magnetic channeling of wind material toward the equator.
Calculations are made of the X-rays expected from the Magnetically Torqued Disk
(MTD) model for Be stars discussed by Cassinelli et al. (2002), by Maheswaran
(2003), and by Brown et al. (2004). The dominant parameters in the model are
the $\beta$ value of the velocity law, the rotation rate of the star, $S_o$,
and the ratio of the magnetic field energy density to the disk gravitational
energy density, $\gamma$.
The model predictions are compared with the $ROSAT$ observations obtained for
an O9.5 star $\zeta$ Oph from \Berghofer et al. (1996) and for 7 Be stars from
Cohen et al. (1997). Extra considerations are also given here to the well
studied Oe star $\zeta$ Oph for which we have $Chandra$ observations of the
X-ray line profiles of the triad of He-like lines from the ion Mg XI.
We have mapped the proto-binary source IRAS 16293-2422 in CO 2-1, 13CO 2-1, and CO 3-2 with the Submillimeter Array (SMA). The maps with resolution of 1".5-5" reveal a single small scale (~3000 AU) bipolar molecular outflow along the east-west direction. We found that the blueshifted emission of this small scale outflow mainly extends to the east and the redshifted emission to the west from the position of IRAS 16293A. A comparison with the morphology of the large scale outflows previously observed by single-dish telescopes at millimeter wavelengths suggests that the small scale outflow may be the inner part of the large scale (~15000 AU) E-W outflow. On the other hand, there is no clear counterpart of the large scale NE-SW outflow in our SMA maps. Comparing analytical models to the data suggests that the morphology and kinematics of the small scale outflow can be explained by a wide-angle wind with an inclination angle of ~30-40 degrees with respect to the plane of the sky. The high resolution CO maps show that there are two compact, bright spots in the blueshifted velocity range. An LVG analysis shows that the one located 1" to the east of source A is extremely dense, n(H_2)~10^7 cm^-3, and warm, T_kin >55 K. The other one located 1" southeast of source B has a higher temperature of T_kin >65 K but slightly lower density of n(H_2)~10^6 cm^-3. It is likely that these bright spots are associated with the hot core-like emission observed toward IRAS 16293. Since both two bright spots are blueshifted from the systemic velocity and are offset from the protostellar positions, they are likely formed by shocks.
In this letter we briefly describe the first results of our numerical study on the possibility of magnetic origin of relativistic jets of long duration gamma ray bursters within the collapsar scenario. We track the collapse of massive rotating stars onto a rotating central black hole using axisymmetric general relativistic magnetohydrodynamic code that utilizes a realistic equation of state of stellar matter, takes into account the cooling associated with emission of neutrinos, and the energy losses due to dissociation of nuclei. The neutrino heating is not included. We describe the solution for one particular model where the progenitor star has magnetic field $B=10^{10}$G. The solution exhibits strong explosion driven by the Poynting-dominated jets whose power exceeds $2\times10^{51} {erg/s}$. The jets originate mainly from the black hole and they are powered via the Blandford-Znajek mechanism. The full details of the simulations together with the results of parameter study will be presented elsewhere. A number of simulation movies can be downloaded from this http URL
The detector material Cadmium Zinc Telluride (CZT), known for its high resolution over a broad energy range, is produced mainly by two methods: the Modified High-Pressure Bridgman (MHB) and the High-Pressure Bridgman (HPB) process. This study is based on MHB CZT substrates from the company Orbotech Medical Solutions Ltd. with a detector size of 2.0x2.0x0.5 cm^3, 8x8 pixels and a pitch of 2.46 mm. Former studies have emphasized only on the cathode material showing that high-work-function improve the energy resolution at lower energies. Therfore, we studied the influence of the anode material while keeping the cathode material constant. We used four different materials: Indium, Titanium, Chromium and Gold with work-functions between 4.1 eV and 5.1 eV. The low work-function materials Indium and Titanium achieved the best performance with energy resolutions: 2.0 keV (at 59 keV) and 1.9 keV (at 122 keV) for Titanium; 2.1 keV (at 59 keV) and 2.9 keV (at 122 keV) for Indium. These detectors are very competitive compared with the more expensive ones based on HPB material if one takes the large pixel pitch of 2.46 mm into account. We present a detailed comparison of our detector response with 3-D simulations, from which we determined the mobility-lifetime-products for electrons and holes. Finally, we evaluated the temperature dependency of the detector performance and mobility-lifetime-products, which is important for many applications. With decreasing temperature down to -30C the breakdown voltage increases and the electron mobility-lifetime-product decreases by about 30% over a range from 20C to -30C. This causes the energy resolution to deteriorate, but the concomitantly increasing breakdown voltage makes it possible to increase the applied bias voltage and restore the full performance.
The reconstruction of images from a small number of projections using the maximum-entropy method (MEM) with the Shannon entropy is considered. MEM provides higher-quality image reconstruction for sources with extended components than the Hogbom CLEAN method, which is also used in low-aspect astrotomography. The quality of image reconstruction for sources with mixed structure containing bright, compact features embedded in a comparatively weak, extended base can be further improved using a difference-mapping method, which requires a generalization of MEM for the reconstruction of sign-variable functions.We draw conclusions based on the results of numerical simulations for a number of model radio sources with various morphologies.
We report the detection of 10 new X-ray filaments using the data from the {\sl Chandra} X-ray satellite for the inner $6^{\prime}$ ($\sim 15$ parsec) around the Galactic center (GC). All these X-ray filaments are characterized by non-thermal energy spectra, and most of them have point-like features at their heads that point inward. Fitted with the simple absorbed power-law model, the measured X-ray flux from an individual filament in the 2-10 keV band is $\sim 2.8\times10^{-14}$ to $10^{-13}$ ergs cm$^{-2}$ s$^{-1}$ and the absorption-corrected X-ray luminosity is $\sim 10^{32}-10^{33}$ ergs s$^{-1}$ at a presumed distance of 8 kpc to the GC. We speculate the origin(s) of these filaments by morphologies and by comparing their X-ray images with the corresponding radio and infrared images. On the basis of combined information available, we suspect that these X-ray filaments might be pulsar wind nebulae (PWNe) associated with pulsars of age $10^3 \sim 3\times 10^5$ yr. The fact that most of the filament tails point outward may further suggest a high velocity wind blowing away form the GC.
We study the dynamics of a twisted tilted disc under the influence of an external radiation field. Assuming the effect of absorption and reemission/scattering is that a pressure is applied to the disc surface where the local optical depth is of order unity, we determine the response of the vertical structure and the influence it has on the possibility of instability to warping. We derive a pair of equations describing the evolution of a small tilt as a function of radius in the small amplitude regime that applies to both the diffusive and bending wave regimes. We also study the non linear vertical response of the disc numerically using an analogous one dimensional slab model. For global warps, we find that in order for the disc vertical structure to respond as a quasi uniform shift or tilt, as has been assumed in previous work, the product of the ratio of the external radiation momentum flux to the local disc mid plane pressure, where it is absorbed, with the disc aspect ratio should be significantly less than unity. Namely, this quantity should be of the order of or smaller than the ratio of the disc gas density corresponding to the layer intercepting radiation to the mid plane density, $\lambda \ll 1$. When this condition is not satisfied the disc surface tends to adjust so that the local normal becomes perpendicular to the radiation propagation direction. In this case dynamical quantities determined by the disc twist and warp tend to oscillate with a large characteristic period $T_{*}\sim \lambda^{-1}T_{K}$, where $T_{K}$ is some 'typical' orbital period of a gas element in the disc. The possibility of warping instability then becomes significantly reduced. In addition, when the vertical response is non uniform, the possible production of shocks may lead to an important dissipation mechanism.
We present new optical, near-IR, and mid-IR observations of the young eruptive variable star V1647 Orionis that went into outburst in late 2004 for approximately two years. Our observations were taken one year after the star had faded to its pre-outburst optical brightness and show that V1647Ori is still actively accreting circumstellar material. We compare and contrast these data with existing observations of the source from both pre-outburst and outburst phases. From near-IR spectroscopy we identify photospheric absorption features for the first time that allow us to constrain the classification of the young star itself. Our best fit spectral type is M0+-2 sub-classes with a visual extinction of 19+-2 magnitudes and a K-band veiling of rK~1.5+-0.2. We estimate that V1647Ori has a quiescent bolometric luminosity of ~9.5Lsun and a mass accretion rate of ~1.10^-6Msun yr^-1. Our derived mass and age, from comparison with evolutionary models, are 0.8+-0.2 Msun and ~0.5Myrs, respectively. The presence towards the star of shock excited optical [S II] and [Fe II] emission as well as near-IR H2 and [Fe II] emission perhaps suggests that a new Herbig-Haro flow is becoming visible close to the star.
Recently, we have developed a method useful for mapping large-scale horizontal velocity fields in the solar photosphere. The method was developed, tuned and calibrated using the synthetic data. Now, we applied the method to the series of Michelson Doppler Imager (MDI) dopplergrams covering almost one solar cycle in order to get the information about the long-term behaviour of surface flows. We have found that our method clearly reproduces the widely accepted properties of mean flow field components, such as torsional oscillations and a pattern of meridional circulation. We also performed a periodic analysis, however due to the data series length and large gaps we did not detect any significant periods. The relation between the magnetic activity influencing the mean zonal motion is studied. We found an evidence that the emergence of compact magnetic regions locally accelerates the rotation of supergranular pattern in their vicinity and that the presence of magnetic fields generally decelerates the rotation in the equatorial region. Our results show that active regions in the equatorial region emerge exhibiting a constant velocity (faster by 60 +/- 9 m/s than Carrington rate) suggesting that they emerge from the base of the surface radial shear at 0.95 R_sun, disconnect from their magnetic roots, and slow down during their evolution.
We studied the clustering properties and multiwavelength spectral energy distributions of a complete sample of 162 Ly Alpha-Emitting (LAE) galaxies at z=3.1 discovered in deep narrow-band MUSYC imaging of the Extended Chandra Deep Field South. LAEs were selected to have observed frame equivalent widths >80A and emission line fluxes >1.5E-17 erg/cm^2/s. Only 1% of our LAE sample appears to host AGN. The LAEs exhibit a moderate spatial correlation length of r_0=3.6+0.8-1.0 Mpc, corresponding to a bias factor b=1.7+0.3-0.4, which implies median dark matter halo masses of log10(M_med) = 10.9+0.5-0.9 M_sun. Comparing the number density of LAEs, (1.5+-0.3)E-3/Mpc^3, with the number density of these halos finds a mean halo occupation ~1-10%. The evolution of galaxy bias with redshift implies that most z=3.1 LAEs evolve into present-day galaxies with L<2.5L*, whereas other z>3 galaxy populations typically evolve into more massive galaxies. Halo merger trees show that z=0 descendants occupy halos with a wide range of masses, with a median descendant mass close to that of L*. Only 30% of LAEs have sufficient stellar mass (>~3E9 M_sun) to yield detections in deep Spitzer-IRAC imaging. A two-population SED fit to the stacked UBVRIzJK+[3.6,4.5,5.6,8.0]micron fluxes of the IRAC-undetected objects finds that the typical LAE has low stellar mass (1.0+0.6-0.4 E9 M_sun), moderate star formation rate (2+-1 M_sun/yr), a young component age of 20+30-10 Myr, and little dust (A_V<0.2). The best fit model has 20% of the mass in the young stellar component, but models without evolved stars are also allowed.
The effect of viscosity and of converging flows on the formation of blobs in the slow solar wind is analysed by means of resistive MHD simulations. The regions above coronal streamers where blobs are formed (Sheeley et al., 1997) are simulated using a model previously proposed by Einaudi et al. (1999). The result of our investigation is twofold. First, we demonstrate a new mechanism for enhanced momentum transfer between a forming blob and the fast solar wind surrounding it. The effect is caused by the longer range of the electric field caused by the tearing instability forming the blob. The electric field reaches into the fast solar wind and interacts with it, causing a viscous drag that is global in nature rather than local across fluid layers as it is the case in normal uncharged fluids (like water). Second, the presence of a magnetic cusp at the tip of a coronal helmet streamer causes a converging of the flows on the two sides of the streamer and a direct push of the forming island by the fast solar wind, resulting in a more efficient momentum exchange.
We present the results of the multi-frequency observations of radio outburst
of the microquasar Cyg X-3 in February and March 2006 with the Nobeyama 45-m
telescope, the Nobeyama Millimeter Array, and the Yamaguchi 32-m telescope.
Since the prediction of a flare by RATAN-600, the source has been monitored
from Jan 27 (UT) with these radio telescopes. At the eighteenth day after the
quench of the activity, successive flares exceeding 1 Jy were observed
successfully. The time scale of the variability in the active phase is
presumably shorter in higher frequency bands.
We also present the result of a follow-up VLBI observation at 8.4 GHz with
the Japanese VLBI Network (JVN) 2.6 days after the first rise. The VLBI image
exhibits a single core with a size of <8 mas (80 AU). The observed image was
almost stable, although the core showed rapid variation in flux density. No jet
structure was seen at a sensitivity of $T_b = 7.5\times 10^5$ K.
We measure the relative evolution of the number of bright and faint (as faint as 0.05 L*) red galaxies in a sample of 28 clusters, of which 16 are at 0.50<= z<=1.27, all observed through a pair of filters bracketing the 4000 Angstrom break rest-frame. The abundance of red galaxies, relative to bright ones, is constant over all the studied redshift range, 0<z<1.3, and rules out a differential evolution between bright and faint red galaxies as large as claimed in some past works. Faint red galaxies are largely assembled and in place at z=1.3 and their deficit does not depend on cluster mass, parametrized by velocity dispersion or X-ray luminosity. Our analysis, with respect to previous one, samples a wider redshift range, minimizes systematics and put a more attention to statistical issues, keeping at the same time a large number of clusters.
We study the cosmological evolution of an induced gravity model with a self-interacting scalar field $\sigma$ and in the presence of matter and radiation. Such model leads to Einstein Gravity plus a cosmological constant as a stable attractor among homogeneous cosmologies and is therefore a viable dark-energy (DE) model for a wide range of scalar field initial conditions and values for its positive $\gamma$ coupling to the Ricci curvature $\gamma \sigma^{2}R$.
The transition from galactic to extragalactic cosmic rays is discussed. One of critical indications for transition is given by the Standard Model of Galactic cosmic rays, according to which the maximum energy of acceleration for iron nuclei is of order of $E_{\rm Fe}^{\rm max} \approx 1\times 10^{17}$ eV. At $E > E_{\rm Fe}^{\rm max}$ the spectrum is predicted to be very steep and thus the Standard Model favours the transition at energy not much higher than $E_{\rm Fe}^{\rm max}$. As observations are concerned there are two signatures of transition: change of energy spectra and elongation rate (depth of shower maximum in the atmosphere $X_{\rm max}$ as function of energy). Three models of transition are discussed: dip-based model, mixed composition model and ankle model. In the latter model the transition occurs at the observed spectral feature, ankle, which starts at $E_a \approx 1\times 10^{19}$ eV and is characterised by change of mass compostion from galactic iron to extragalactic protons. In the dip model the transition occures at the second knee observed at energy $(4 -8)\times 10^{17}$ eV and is characterised by change of mass composition from galactic iron to extragalactic protons. The mixed composition model describes transition at $E \sim 3\times 10^{18}$ eV with mass composition changing from galactic iron to extragactic mixed composition of different nuclei. These models are confronted with observational data on spectra and elongation rates from different experiments, including Auger.
The Tibet air shower array, which has an effective area of 37,000 square meters and is located at 4300 m in altitude, has been observing air showers induced by cosmic rays with energies above a few TeV. We have a plan to add a large muon detector array to it for the purpose of increasing its sensitivity to cosmic gamma rays in the 100 TeV energy region by discriminating them from cosmic-ray hadrons. We have deduced the attainable sensitivity of the muon detector array using our Monte Carlo simulation. We report here on the detailed procedure of our Monte Carlo simulation.
The Tibet air shower array, which has an effective area of 37,000 square meters and is located at 4300 m in altitude, has been observing air showers induced by cosmic rays with energies above a few TeV. We are planning to add a large muon detector array to it for the purpose of increasing its sensitivity to cosmic gamma rays in the 100 TeV (10 - 1000 TeV) energy region by discriminating them from cosmic-ray hadrons. We report on the possibility of detection of gamma rays in the 100 TeV energy region in our field of view, based on the improved sensitivity of our air shower array deduced from the full Monte Carlo simulation.
(Ultra)Luminous Infrared Galaxies [(U)LIRGs] are much more numerous at cosmological distances than locally, and trace one of the preferred ways of galaxy formation. Our goal is to carry out an integral field spectroscopic survey of a representative sample of low redshift (z < 0.26) (U)LIRGs, covering different morphologies from spirals to mergers over the entire infrared luminosity range. The present study is based on optical IFS obtained with the VIMOS instrument on the VLT. The first results of this survey are presented here with the study of two galaxies representative of the two major morphological types observed in (U)LIRGs, interacting pairs and morphologically- regular, weakly-interacting spirals, respectively. We have found that IRAS 06076$-$2139 consists of two low-intermediate mass (0.15 and 0.4 m*) galaxies with relative velocities of ~ 550 km/s and, therefore, it is unlikely that they will merge. The VIMOS IFS has also discovered the presence of a rapidly expanding and rotating ring of gas in the southern galaxy (Gs), likely due to a nearly central head-on passage of an intruder about 140 million years ago. IRASF 12115$-$4656 is a spiral for which we have found a mass of 1.2 m*. The neutral gas (traced by the NaI doublet) and ionized gas components are spatially and kinematically decoupled. The analysis presented here illustrates the full potential of IFS in two important aspects: (i) the study of the kinematics and ionization structure of complex interacting/merging systems, and (2i) the study of the kinematics of the different gas phases, neutral (cool) and ionized (warm), traced by the NaD and Halpha lines, respectively.
(Abridged) The nature of S Ori 70, a faint mid-T type object found towards the direction of the young sigma Orionis cluster, is still under debate. We intend to disentangle whether it is a field brown dwarf or a 3-Myr old planetary-mass member of the cluster. We report on near-infrared JHK_s and mid-infrared [3.6] and [4.5] IRAC/Spitzer photometry recently obtained for S Ori 70. The new near-infrared images (taken 3.82 yr after the discovery data) have allowed us to derive a very small proper motion (11.0 +/- 5.9 mas/yr) for this object, which is consistent with the proper motion of the cluster within 1.5 sigma the astrometric uncertainty. The colors (H-K_s), (J-K_s) and K_s-[3.6] appear discrepant when compared to T4-T7 dwarfs in the field. This behavior could be ascribed to a low-gravity atmosphere or alternatively to an atmosphere with a metallicity significantly different than solar. Taking into account the small proper motion of S Ori 70 and its new near- and mid-infrared colors, a low-gravity atmosphere remains as the most likely explanation to account for our observations. This supports S Ori 70's membership in sigma Orionis, with an estimated mass in the interval 2-7 Mjup, in agreement with our previous derivation.
Period-luminosity (PL) relations of variable red giants in the Large (LMC) and Small Magellanic Clouds (SMC) are presented. The PL diagrams are plotted in three planes: logP-K_S, logP-W_{JK}, and logP-W_I. Fourteen PL sequences are distinguishable, and some of them consist of three closely spaced ridges. Each of the sequences is fitted with a linear or quadratic function. The similarities and differences between the PL relations in both galaxies are discussed for four types of red giant variability: OGLE Small Amplitude Red Giants (OSARGs), Miras and Semiregular Variables (SRVs), Long Secondary Periods (LSPs) and ellipsoidal variables. We propose a new method of separating OSARGs from non-variable stars and SRVs. The method employs the position in the reddening-free PL diagrams and the characteristic period ratios of these multiperiodic variables. The PL relations for the LMC OSARG are compared with the calculated relations for RGB models along isochrones of relevant ages and metallicities. We also compare measured periods and amplitudes of the OSARGs with predictions based on the relations valid for less luminous solar-like pulsators. Miras and SRVs seem to follow PL relation of the same slopes in the LMC and SMC, while for LSP and ellipsoidal variables slopes in both galaxies are different. The PL sequences defined by LSP variables and binary systems overlap in the whole range of analyzed wavebands. We put forward new arguments for the binary star scenario as an explanation of the LSP variability and elaborate on it further. The measured pulsation to orbital period ratio implies nearly constant ratio of the star radius to orbital distance, R/A=0.4, as we find. Combined effect of tidal friction and mass loss enhanced by the low-mass companion may explain why such a value is preferred.
For the 2dFGRS we study the properties of voids and of fainter galaxies within voids that are defined by brighter galaxies. Our results are compared with simulated galaxy catalogues from the Millenium simulation coupled with a semianalytical galaxy formation recipe. We derive the void size distribution and discuss its dependence on the faint magnitude limit of the galaxies defining the voids. While voids among faint galaxies are typically smaller than those among bright galaxies, the ratio of the void sizes to the mean galaxy separation reaches larger values. This is well reproduced in the mock galaxy samples studied. We provide analytic fitting functions for the void size distribution. Furthermore, we study the galaxy population inside voids defined by objects with $B_J -5\log{h}< -20$ and diameter larger than 10 \hMpc. We find a clear bimodality of the void galaxies similar to the average comparison sample. We confirm the enhanced abundance of galaxies in the blue cloud and a depression of the number of red sequence galaxies. There is an indication of a slight blue shift of the blue cloud. Furthermore, we find that galaxies in void centers have higher specific star formation rates as measured by the $\eta$ parameter. We determine the radial distribution of the ratio of early and late type galaxies through the voids. We find and discuss some differences between observations and the Millenium catalogues.
In December 2004, the soft gamma-ray repeater SGR 1806-20 emitted the most powerful giant flare ever observed. This probably involved a large-scale rearrangement of the magnetosphere leading to observable variations in the properties of its X-ray emission. Here we present the results of the first Suzaku observation of SGR 1806-20, together with almost simultaneous observations with XMM-Newton and INTEGRAL. The source seems to have reached a state characterized by a flux close to the pre-flare level and by a relatively soft spectrum. Despite this, SGR 1806-20 remained quite active also after the giant flare, allowing us to study several short bursts observed by Suzaku in the 1-100 keV range. We discuss the broad-band spectral properties of SGR 1806-20, covering both persistent and bursting emission, in the context of the magnetar model, and consider its recent theoretical developments.
SGRs denote ``soft $\gamma$-ray repeaters'', a small class of slowly spinning neutron stars with strong magnetic fields. On 27 December 2004, a giant flare was detected from magnetar SGR 1806-20. The initial spike was followed by a hard-X-ray tail persisting for 380 s with a modulation period of 7.56 s. This event has received considerable attention, particularly in the astrophysics area. Its relevance to the geophysics community lies in the importance of investigating the effects of such an event on the near-earth electromagnetic environment. However, the signature of a magnetar flare on the geomagnetic field has not previously been investigated. Here, by applying wavelet analysis to the high-resolution magnetic data provided by the CHAMP satellite, a modulated signal with a period of 7.5 s over the duration of the giant flare appears in the observed data. Moreover, this event was detected by the energetic ion counters onboard the DEMETER satellite.
We have identified two moderately hot (~18000-22000K) white dwarfs, SDSSJ1228+1040 and SDSSJ1043+0855, which exhibit double-peaked emission lines in the CaII 8600A triplet. These line profiles are unambiguous signatures of gaseous discs with outer radii of ~1Rsun orbiting the two white dwarfs. Both stars accrete from the circumstellar material, resulting in large photospheric Mg abundances. The absence of hydrogen emission from the discs, and helium absorption in the white dwarf photospheres demonstrates that the circumstellar material is depleted in volatile elements, and the most likely origin of these gaseous rings are tidally disrupted rocky asteroids. The relatively high mass of SDSSJ1228+1040 implies that planetary systems can not only form around 4-5Msun stars, but may also survive their post main-sequence evolution.
We observed the Herbig Ae/Be stars UX Ori, HD 34282, HD 100453, HD 101412, HD 104237 and HD 142666, and the T Tauri star HD 319139 and searched for H2 0-0 S(2) emission at 12.278 micron and H2 0-0 S(1) emission at 17.035 micron with VISIR, ESO-VLT's high-resolution MIR spectrograph. None of the sources present evidence for H2 emission. Stringent 3sigma upper limits to the integrated line fluxes and the mass of optically thin warm gas in the disks are derived. The disks contain less than a few tenths of Jupiter mass of optically thin H2 gas at 150 K at most, and less than a few Earth masses of optically thin H2 gas at 300 K and higher temperatures. We compare our results to a Chiang and Goldreich (1997, CG97) two-layer disk model. The upper limits to the disk's optically thin warm gas mass are smaller than the amount of warm gas in the interior layer of the disk, but they are much larger than the amount of molecular gas in the surface layer. We present a calculation of the expected thermal H2 emission from optically thick disks, assuming a CG97 disk structure, a gas-to-dust ratio of 100 and Tgas = Tdust. The expected H2 thermal emission fluxes from typical disks around Herbig Ae/Be stars (10^-16 to 10^-17 erg/s/cm2 at 140 pc) are much lower than the detection limits of our observations (5*10^-15 erg/s/cm2). H2 emission levels are very sensitive to departures from the thermal coupling between the molecular gas and dust. Additional sources of heating of gas in the disk's surface layer could have a major impact on the expected H2 disk emission. In the observed sources the molecular gas and dust in the surface layer have not significantly departed from thermal coupling (Tgas/Tdust< 2) and that the gas-to-dust ratio in the surface layer is very likely lower than 1000.
CO isotopes are able to probe the different components in protostellar clouds. These components, core, envelope and outflow have distinct physical conditions and sometimes more than one component contributes to the observed line profile. In this study we determine how CO isotope abundances are altered by the physical conditions in the different components. We use a 3D molecular line transport code to simulate the emission of four CO isotopomers, 12CO J=2-1, 13CO J=2-1, C18O J=2-1 and C17O J=2-1 from the Class 0/1 object L483, which contains a cold quiescent core, an infalling envelope and a clear outflow. Our models replicate JCMT (James Clerk Maxwell Telescope) line observations with the inclusion of freeze-out, a density profile and infall. Our model profiles of 12CO and 13CO have a large linewidth due to a high velocity jet. These profiles replicate the process of more abundant material being susceptible to a jet. C18O and C17O do not display such a large linewidth as they trace denser quiescent material deep in the cloud.
We present evolutionary tracks of binary systems with high mass companion stars and stellar-through-intermediate mass BHs. Using Eggleton's stellar evolution code, we compute the luminosity produced by accretion from the donor during its entire evolution. We compute also the evolution of the optical spectrum of the binary system taking the disc contribution and irradiation effects into account. The calculations presented here can be used to constrain the properties of the donor stars in Ultraluminous X-ray Sources by comparing their position on the HR or color-magnitude diagrams with the evolutionary tracks of massive BH binaries. This approach may actually provide interesting clues also on the properties of the binary system itself, including the BH mass. We found that, on the basis of their position on the color-magnitude diagram, some of the candidate counterparts considered can be ruled out and more stringent constraints can be applied to the donor masses.
Our aim is to determine the presence and location of the emission from
polycyclic aromatic hydrocarbons (PAHs) towards low and intermediate mass young
stars with disks using large aperture telescopes.
VLT-VISIR N-band spectra and VLT-ISAAC and VLT-NACO L-band spectra of 29
sources are presented, spectrally resolving the 3.3, 8.6, 11.2, and 12.6 micron
PAH features. Spatial-extent profiles of the features and the continuum
emission are derived and used to associate the PAH emission with the disks. The
results are discussed in the context of recent PAH-emission disk models.
The 3.3, 8.6, and 11.2 micron PAH features are detected toward a small
fraction of the T Tauri stars, with typical upper limits between 1E-15 and
5E-17 W/m^2. All 11.2 micron detections from a previous Spitzer survey are
confirmed with (tentative) 3.3 micron detections, and both the 8.6 and the 11.2
micron features are detected in all PAH sources. For 6 detections, the spatial
extent of the PAH features is confined to scales typically smaller than
0.12-0.34'', consistent with the radii of 12-60 AU disks at their distances
(typically 150 pc). For 3 additional sources, WL 16, HD 100546, and TY CrA, one
or more of the PAH features are more extended than the hot dust continuum of
the disk, whereas for Oph IRS 48, the size of the resolved PAH emission is
confirmed as smaller than for the large grains. For HD 100546, the 3.3 micron
emission is confined to a small radial extent of 12 +- 3 AU, most likely
associated with the outer rim of the gap in this disk. Gaps with radii out to
10-30 AU may also affect the observed PAH extent for other sources. For both
Herbig Ae and T Tauri stars, the small measured extents of the 8.6 and 11.2
micron features are consistent with larger (>= 100 carbon atoms) PAHs.
Neutron stars contain persistent, ordered magnetic fields that are the strongest known in the Universe. However, their magnetic fluxes are similar to those in magnetic A and B stars and white dwarfs, suggesting that flux conservation during gravitational collapse may play an important role in establishing the field, although it might also be modified substantially by early convection, differential rotation, and magnetic instabilities. The equilibrium field configuration, established within hours (at most) of the formation of the star, is likely to be roughly axisymmetric, involving both poloidal and toroidal components. The stable stratification of the neutron star matter (due to its radial composition gradient) probably plays a crucial role in holding this magnetic structure inside the star. The field can evolve on long time scales by processes that overcome the stable stratification, such as weak interactions changing the relative abundances and ambipolar diffusion of charged particles with respect to neutrons. These processes become more effective for stronger magnetic fields, thus naturally explaining the magnetic energy dissipation expected in magnetars, at the same time as the longer-lived, weaker fields in classical and millisecond pulsars.
M87 is the first extragalactic source detected in the TeV range that is not a blazar. With the increasing performances of ground-based Cherenkov telescopes, we can now probe the variability in the gamma-ray flux at small timescales, thus putting strong constraints on the size of the emitting zone. A modification of standard emission models of TeV blazars appears necessary to account for the gamma-ray observations despite this misalignment. We explain TeV gamma-ray spectra and fast variability of M87 by invoking an emission zone close to the central supermassive black hole, which is filled with several plasma blobs moving in the large opening angle of the jet formation zone. We develop a new multi-blob synchrotron self-Compton (SSC) model with emitting blobs beyond the Alfven surface in the jet, at a distance of about 100 r_g from the central engine. This model is explicitly adapted to deal with large viewing angles and moderate values of the Lorentz factor inferred from (general relativistic) magnetohydrodynamic models of jet formation. This scenario can account for the recent gamma-ray observations of M87 made by the High Energy Stereoscopic System (H.E.S.S.) telescope array. We find individual blob radii of about 10^{14} cm, which is compatible with the variability on timescales of days recently reported by the H.E.S.S. collaboration and is of the order of the black hole gravitational radius. Predictions of the very high energy emission for three other sources with extended optical or X-ray jet which could be misaligned blazars still with moderate beaming are presented for one Seyfert 2 radiogalaxy, namely Cen A, one peculiar BL Lac, PKS 0521-36, and one quasar, 3C 273.
Context: One of the ways to determine the contribution of the dark halo to the gravitational potential of a galaxy is the study of non-circular (streaming) motions and the associated gas shocks in the bar region. These motions, determined by the potential in the inner parts, can break the disk-halo degeneracy. Here, two main fluid dynamical approaches have been chosen to model the non-circular motions in the bar region; a 2-D Eulerian grid code for an isothermal gas (FS2) and a 3-D smoothed particle hydrodynamic code (N-body/SPH). Aims: The aim of this paper is to compare and quantify the differences of the gas flows in rotating barred potential obtained using two different fluid dynamical approaches. We analyse the effect of using 2-D and a 3-D codes in the calculation of gas flow in barred galaxies and to which extend the results are affected by the code. To do this, we derive the velocity field and density maps for the mass model of NGC 4123 using a 3-D N-body/SPH code and compare the results to the previous 2-D Eulerian grid code results. Methods: Numerical modelling, 3-D N-body/SPH simulations Results: The global velocity field and the gas distribution is very similar in both models. The study shows that the position and strength of the shocks developed in the SPH simulations do not vary significantly compared to the results derived from the 2-D FS2 code. The largest velocity difference across the shock is 20\kms between the 2-D and 3-D fluid dynamical models. Conclusions: The results obtained in the studies deriving the dark matter content of barred galaxies using the bar streaming motions and strength and position of shocks are robust to the fluid dynamical model used. The effect of 2-D and 3-D modelling can be neglected in this type of studies.
GRB 021206 is one of the brightest GRBs ever observed. Its prompt emission, as measured by RHESSI, shows an unexpected spectral feature. The spectrum has a peak energy of about 700 keV and can be described by a Band function up to 4.5 MeV. Above 4.5 MeV, the spectrum hardens again, so that the Band function fails to fit the whole RHESSI energy range up to 17 MeV. Nor does the sum of a blackbody function plus a power law, even though such a function can describe a spectral hardening. The cannonball model on the other hand predicts such a hardening, and we found that it fits the spectrum of GRB 021206 perfectly. We also analysed other strong GRBs observed by RHESSI, namely GRBs 020715, 021008, 030329, 030406, 030519B, 031027, 031111. We found that all their spectra can be fit by the cannonball model as well as by a Band function.
We present results from two high-contrast imaging surveys that exploit a novel technique, L-band angular differential imaging. Our first survey targeted 21 young stars in the Beta Pic and Tuc-Hor moving groups with VLT/NACO reaching typical sensitivities of <1 MJup at r > 20 AU. The statistical analysis of the null result demonstrates that the giant planet population is truncated at 30 AU or less (90% confidence level). Our second, on-going MMT/Clio survey utilizes the unique sensitivity achieved in the L-band for old planets to probe all M-dwarf stars within 6 pc. The proximity of these targets enables direct imaging of planets in orbits like Jupiter for the first time - a key step for directly imaging giant planets.
This contribution intends to give a pedagogical introduction to the topic of dark energy (the mysterious agent supposed to drive the observed late time acceleration of the Universe) and to various observational tests which require only assumptions on the geometry of the Universe. Those tests are the supernovae luminosity, the CMB shift, the direct Hubble data, and the baryon acoustic oscillations test. An historical overview of Cosmology is followed by some generalities on FRW spacetimes (the best large-scale description of the Universe), and then the test themselves are discussed. A convenient section on statistical inference is included as well.
The physical ingredients to describe the epoch of cosmological recombination are amazingly simple and well-understood. This fact allows us to take into account a very large variety of processes, still finding potentially measurable consequences. In this contribution we highlight some of the detailed physics that were recently studied in connection with cosmological hydrogen recombination. The impact of these considerations is two-fold: (i) the associated release of photons during this epoch leads to interesting and unique deviations of the Cosmic Microwave Background (CMB) energy spectrum from a perfect blackbody, which, in particular at decimeter wavelength, may become observable in the near future. Observing these distortions, in principle would provide an additional way to determine some of the key parameters of the Universe (e.g. the specific entropy, the CMB monopole temperature and the pre-stellar abundance of helium), not suffering from limitations set by cosmic variance. Also it permits us to confront our detailed understanding of the recombination process with direct observational evidence. In this contribution we illustrate how the theoretical spectral template for the cosmological recombination spectrum may be utilized for this purpose. (ii) with the advent of high precision CMB data, e.g. as will be available using the Planck Surveyor or Cmbpol, a very accurate theoretical understanding of the ionization history of the Universe becomes necessary for the interpretation of the CMB temperature and polarization anisotropies. (abridged)
We study the initial mass function (IMF) of one of the most massive galactic star-forming regions NGC 3603 to answer a fundamental question in current astrophysics: is the IMF universal, or does it vary? Using our very deep high angular resolution JHKsL' images obtained with the NACO/VLT, we have successfully revealed the low-mass stars down to the subsolar mass range in the core of the starburst cluster. The derived IMF of NGC 3603 is reasonably fitted by a single power-law with index of ~-0.74 within 0.4 - 20 Msun, substantially flatter than the Salpeter-like IMF. A strong radial steepening of the IMF is observed in the inner r < 30" field, indicating mass segregation at the cluster core. We estimate the total mass of NGC 3603 to be about 1.0 - 1.6 x 10^4 Msun. The derived core density is > 6 x 10^4 Msun pc^{-3}, an order of magnitude larger than e.g., the Orion Nebula Cluster. The estimate of the half-mass relaxation time for solar-mass stars is about 10 - 40 Myr, suggesting that the intermediate- and low-mass stars have not yet been affected significantly by the dynamical relaxation in the cluster. The relaxation time for the high-mass stars can be comparable to the age of the cluster. Thus the mass segregation observed through the radial variation of the IMF is likely due to high-mass stars. We estimate that the stars residing outside the observed field can not steepen the IMF significantly, indicating our IMF adequately describes the whole NGC 3603 starburst cluster. Analyzing thoroughly the systematic uncertainties in our IMF determination, we conclude that the power-law index of the IMF of NGC 3603 is -0.74^{+0.62}_{-0.47}. Our result thus supports the hypothesis of a potential top-heavy IMF in massive star-forming clusters and starbursts.
The recently recognized class of "transitional disk" systems consists of young starswith optically-thick outer disks but inner disks which are mostly devoid of small dust. Here we introduce a further class of "pre-transitional disks" with significant near-infrared excesses which indicate the presence of an optically thick inner disk separated from an optically thick outer disk; thus, the spectral energy distributions of pre-transitional disks suggest the incipient development of disk gaps rather than inner holes. In UX Tau A, our analysis of the Spitzer IRS spectrum finds that the near-infrared excess is produced by an inner optically thick disk and a gap of ~56 AU is present. The Spitzer IRS spectrum of LkCa 15 is suggestive of a gap of ~46 AU, confirming previous millimeter imaging. In addition, UX Tau A contains crystalline silicates in its disk at radii >~ 56 AU which poses a challenge to our understanding of the production of this crystalline material. In contrast, LkCa 15's silicates are amorphous and pristine. UX Tau A and LkCa 15 increase our knowledge of the diversity of dust clearing in low-mass star formation.
In the ongoing HATNet survey we have detected a giant planet, with radius 1.33 +/- 0.06 RJup and mass 1.06 +/- 0.12 MJup, transiting the bright (V = 10.5) star GSC 03466-00819. The planet is in a circular orbit with period 3.852985 +/- 0.000005 days and mid-transit epoch 2,454,035.67575 +/- 0.00028 (HJD). The parent star is a late F star with mass 1.29 +/- 0.06 Msun, radius 1.46 +/- 0.06 Rsun, Teff ~ 6570 +/- 80 K, [Fe=H] = -0.13 +/- 0.08 and age ~ 2.3+/-^{0.5}_{0.7}Gy. With this radius and mass, HAT-P-6b has somewhat larger radius than theoretically expected. We describe the observations and their analysis to determine physical properties of the HAT-P-6 system, and briefly discuss some implications of this finding.
We report the detection of HI 21 cm absorption from the $z=2.289$ damped Lyman-$\alpha$ system (DLA) towards TXS 0311+430, with the Green Bank Telescope. The 21 cm absorption has a velocity spread (between nulls) of $\sim 110$ km s$^{-1}$ and an integrated optical depth of $\int \tau {\rm d}V = (0.818 \pm 0.085)$ km s$^{-1}$. We also present new Giant Metrewave Radio Telescope 602 MHz imaging of the radio continuum. TXS 0311+430 is unresolved at this frequency, indicating that the covering factor of the DLA is likely to be high. Combining the integrated optical depth with the DLA HI column density of \nhi = $(2 \pm 0.5) \times 10^{20}$ \cm, yields a spin temperature of $T_s = (138 \pm 36)$ K, assuming a covering factor of unity. This is the first case of a low spin temperature ($< 350$ K) in a $z > 1$ DLA and is among the lowest ever measured in any DLA. Indeed, the $T_s$ measured for this DLA is similar to values measured in the Milky Way and local disk galaxies. We also determine a lower limit (Si/H) $\gtrsim 1/3$ solar for the DLA metallicity, amongst the highest abundances measured in DLAs at any redshift. Based on low redshift correlations, the low $T_s$, large 21 cm absorption width and high metallicity all suggest that the $z \sim 2.289$ DLA is likely to arise in a massive, luminous disk galaxy.
We consider the possibility of cluster membership for 13 planetary nebulae that are located in close proximity to open clusters lying in their lines of sight. The short lifetimes and low sample size of intermediate-mass planetary nebulae with respect to nearby open clusters conspire to reduce the probability of observing a true association. Not surprisingly, line of sight coincidences almost certainly exist for 7 of the 13 cases considered. Additional studies are advocated, however, for 6 planetary nebula/open cluster coincidences in which a physical association is not excluded by the available evidence, namely M 1-80/Berkeley 57, NGC 2438/NGC 2437, NGC 2452/NGC 2453, VBRC 2 & NGC 2899/IC 2488, and HeFa 1/NGC 6067. A number of additional potential associations between planetary nebulae and open clusters is tabulated for reference purposes. It is noteworthy that the strongest cases involve planetary nebulae lying in cluster coronae, a feature also found for short-period cluster Cepheids, which are themselves potential progenitors of planetary nebulae.
Non-linear schr\"{o}dinger-formulation of cosmology is expressed here as a useful method in cosmology. We applied the method to power-law expansion, $a \sim t^q$ with $q =2$ in standard cosmology for a universe in which canonical phantom or non-phantom scalar field and barotropic fluid under arbitrary potential are presented. In the setup with power-law expansion, we obtain scalar field potential as function of time. The potential obtained agrees well with result from standard cosmology method when scalar field is dominant. The method provides an alternative procedure of solving this type of systems.
We present a Markov Chain Monte Carlo global analysis of neutrino parameters using both cosmological and experimental data. Results are presented for the combination of all presently available data from oscillation experiments, cosmology, and neutrinoless double beta decay. In addition we explicitly study the interplay between cosmological, tritium decay and neutrinoless double beta decay data in determining the neutrino mass parameters. We furthermore discuss how the inference of non-neutrino cosmological parameters can benefit from future neutrino mass experiments such as the KATRIN tritium decay experiment or neutrinoless double beta decay experiments.
We model the massive dark object at the center of the Galaxy as a Schwarzschild black hole as well as Janis-Newman-Winicour naked singularities, characterized by the mass and scalar charge parameters, and study gravitational lensing (particularly time delay, magnification centroid, and total magnification) by them. We find that the lensing features are qualitatively similar (though quantitatively different) for the Schwarzschild black holes, weakly naked, and marginally strongly naked singularities. However, the lensing characteristics of strongly naked singularities are qualitatively very different from those due the Schwarzschild black holes. The images produced by Schwarzschild black hole lenses and weakly naked and marginally strongly naked singularity lenses always have positive time delays. On the other hand, the strongly naked singularity lenses can give rise to images with positive, zero, or negative time delays. In particular, for a large angular source position the direct image (the outermost image on the same side as the source) due to strongly naked singularity lensing always has negative time delay. We also found that the scalar field decreases the time delay and increases the magnitude of magnifications of images; this result could have important implications for cosmology. As the Janis-Newman-Winicour metric also describes the exterior gravitational field of a scalar star, naked singularities as well as scalar star lenses, if these exist in nature, will serve as more efficient cosmic telescopes than regular gravitational lenses.
We construct the conserved charges (mass and angular momentum) of the Chern-Simons modified General Relativity in asymptotically flat and Anti-de Sitter (AdS) spacetimes. Our definition is based on background Killing symmetries and reduces to the known expressions in the proper limits.
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We investigate the evolution of angular momentum in simulations of galaxy formation in a cold dark matter universe. We analyse two model galaxies produced in the N-body/hydrodynamic simulations of Okamoto et al. Starting from identical initial conditions, but using different assumptions for the baryonic physics, one of the simulations produced a bulge-dominated galaxy and the other one a disk-dominated galaxy. The main difference is the treatment of star formation and feedback, both of which were designed to be more efficient in the disk-dominated object. We find that the specific angular momentum of the disk-dominated galaxy tracks the evolution of the angular momentum of the dark matter halo very closely: the angular momentum grows as predicted by linear theory until the epoch of maximum expansion and remains constant thereafter. By contrast, the evolution of the angular momentum of the bulge-dominated galaxy resembles that of the central, most bound halo material: it also grows at first according to linear theory, but 90% of it is rapidly lost as pre-galactic fragments, into which gas had cooled efficiently, merge, transferring their orbital angular momentum to the outer halo by tidal effects. The disk-dominated galaxy avoids this fate because the strong feedback reheats the gas which accumulates in an extended hot reservoir and only begins to cool once the merging activity has subsided. Our analysis lends strong support to the classical theory of disk formation whereby tidally torqued gas is accreted into the centre of the halo conserving its angular momentum.
We report on our initial analysis of a deep 510 ks observation of the Galactic oxygen-rich supernova remnant (SNR) G292.0+1.8 with the {\it Chandra X-ray Observatory}. Our new {\it Chandra} ACIS-I observation has a larger field of view and an order of magnitude deeper exposure than the previous {\it Chandra} observation, which allows us to cover the entire SNR and to detect new metal-rich ejecta features. We find a highly non-uniform distribution of thermodynamic conditions of the X-ray emitting hot gas that correlates well with the optical [O {\small III}] emission, suggesting the possibility that the originating supernova explosion of G292.0+1.8 was itself asymmetric. We also reveal spectacular substructures of a torus, a jet, and an extended central compact nebula all associated with the embedded pulsar J1124$-$5916.
We use the kinetic theory of nucleation to explore the properties of dust nucleation in sub-saturated vapors. Due to radiation losses, the sub-critical clusters have a smaller temperature compared to their vapor. This alters the dynamical balance between attachment and detachment of monomers, allowing for stable nucleation of grains in vapors that are sub-saturated for their temperature. We find this effect particularly important at low densities and in the absence of a strong background radiation field. We find new conditions for stable nucleation in the n-T phase diagram. The nucleation in the non-LTE regions is likely to be at much slower rate than in the super-saturated vapors. We evaluate the nucleation rate, warning the reader that it does depend on poorly substantiated properties of the macro-molecules assumed in the computation. On the other hand, the conditions for nucleation depend only on the properties of the large stable grains and are more robust. We finally point out that this mechanism may be relevant in the early universe as an initial dust pollution mechanism, since once the interstellar medium is polluted with dust, mantle growth is likely to be dominant over non-LTE nucleation in the diffuse medium.
Compared to planets around Sun-like stars, relatively little is known about the occurrence rate and orbital properties of planets around stars more massive than 1.3 Msun. The apparent deficit of planets around massive stars is due to a strong selection bias against early-type dwarfs in Doppler-based planet searches. One method to circumvent the difficulties inherent to massive main-sequence stars is to instead observe them after they have evolved onto the subgiant branch. We show how the cooler atmospheres and slower rotation velocities of subgiants make them ideal proxies for F- and A-type stars. We present the early results from our planet search that reveal a paucity of planets orbiting within 1 AU of stars more massive than 1.5 Msun, and evidence of a rising trend in giant planet occurrence with stellar mass.
Hot Jupiters are new laboratories for the physics of giant planet atmospheres. Subject to unusual forcing conditions, the circulation regime on these planets may be unlike anything known in the Solar System. Characterizing the atmospheric circulation of hot Jupiters is necessary for reliable interpretation of the multifaceted data currently being collected on these planets. We discuss several fundamental concepts of atmospheric dynamics that are likely central to obtaining a solid understanding of these fascinating atmospheres. A particular effort is made to compare the various modeling approaches employed so far to address this challenging problem.
We use high-resolution observations of the Sun in Ca II H 3968 A from the Solar Optical Telescope on Hinode to show that there are at least two types of spicules that dominate the structure of the magnetic solar chromosphere. Both types are tied to the relentless magnetoconvective driving in the photosphere, but have very different dynamic properties. ``Type-I'' spicules are driven by shock waves that form when global oscillations and convective flows leak into the upper atmosphere along magnetic field lines on 3-7 minute timescales. ``Type-II'' spicules are much more dynamic: they form rapidly (in ~10s), are very thin (<200km wide), have lifetimes of 10-150s (at any one height) and seem to be rapidly heated to (at least) transition region temperatures, sending material through the chromosphere at speeds of order 50-150 km/s. The properties of Type II spicules suggest a formation process that is a consequence of magnetic reconnection, typically in the vicinity of magnetic flux concentrations in plage and network. Both types of spicules are observed to carry Alfven waves with significant amplitudes of order 20 km/s.
TenTen is a proposed array of Imaging Atmospheric Cherenkov Telescopes (IACT) optimized for the gamma ray energy regime of 10 TeV to 100 TeV, but with a threshold of ~1 to a few TeV. It will offer a collecting area of 10 km2 above energies of 10 TeV. In the initial phase, a cell of 3 to 5 modest-sized telescopes, each with 10-30 m2 mirror area, is suggested for an Australian site. A possible expansion of the array could comprise many such cells. Here we present work on configuration and technical issues from our simulation studies of the array. Working topics include array layout, telescope size and optics, camera field of view, telescope trigger system, electronics, and site surveys.
We report null results on a two year photometric search for outburst predictors in SS Cyg. Observations in Johnson V and Cousins I were obtained almost daily for multiple hours per night for two observing seasons. The accumulated data are put through various statistical and visual analysis techniques but fails to detect any outburst predictors. However, analysis of 102 years of AAVSO archival visual data led to the detection of a correlation between a long term quasi-periodic feature at around 1,000-2,000 days in length and an increase in outburst rate.
Although the occurrence of steady supercritical disk accretion onto a black hole has been speculated about since the 1970s, it has not been accurately verified so far. For the first time, we previously demonstrated it through two-dimensional, long-term radiation-hydrodynamic simulations. To clarify why this accretion is possible, we quantitatively investigate the dynamics of a simulated supercritical accretion flow with a mass accretion rate of ~10^2 L_E/c^2 (with L_E and c being, respectively, the Eddington luminosity and the speed of light). We confirm two important mechanisms underlying supercritical disk accretion flow, as previously claimed, one of which is the radiation anisotropy arising from the anisotropic density distribution of very optically thick material. We qualitatively show that despite a very large radiation energy density, E_0>10^2L_E/(4 pi r^2 c) (with r being the distance from the black hole), the radiative flux F_0 cE_0/tau could be small due to a large optical depth, typically tau 10^3, in the disk. Another mechanism is photon trapping, quantified by vE_0, where v is the flow velocity. With a large |v| and E_0, this term significantly reduces the radiative flux and even makes it negative (inward) at r<70r_S, where r_S is the Schwarzschild radius. Due to the combination of these effects, the radiative force in the direction along the disk plane is largely attenuated so that the gravitational force barely exceeds the sum of the radiative force and the centrifugal force. As a result, matter can slowly fall onto the central black hole mainly along the disk plane with velocity much less than the free-fall velocity, even though the disk luminosity exceeds the Eddington luminosity. Along the disk rotation axis, in contrast, the strong radiative force drives strong gas outflows.
We have compiled the emission-line fluxes of O I 8446, O I 11287, and the near-IR Ca II triplet (8579) observed in 11 quasars. These lines are considered to emerge from the same gas as do the Fe II lines in the low-ionized portion of the broad emission line region (BELR). The compiled quasars are distributed over wide ranges of redshift (0.06 < z < 1.08) and of luminosity (-29.8 < M_B < -22.1), thus representing a useful sample to investigate the line-emitting gas properties in various quasar environments. The measured line strengths and velocities, as functions of the quasar properties, are analyzed using photoionization model calculations. We found that the flux ratio between Ca II and O I 8446 is hardly dependent on the redshift or luminosity, indicating similar gas density in the emission region from quasar to quasar. On the other hand, a scatter of the O I 11287/8446 ratios appears to imply the diversity of the ionization parameter. These facts invoke the picture of the line-emitting gases in quasars that have similar densities and are located at regions exposed to various ionizing radiation fluxes. The observed O I line widths are found to be remarkably similar over more than 3 orders of magnitude in luminosity, which indicates a kinematically-determined location of the emission region and is in clear contrast to the well-studied case of Hb. We also argue about the dust presence in the emission region since the region is suggested to be located near the dust sublimation point at the outer edge of the BELR.
We report on the discovery of three new pulsars in the first blind survey of the north Galactic plane (45 < l < 135 ; |b| < 1) with the Giant Meterwave Radio telescope (GMRT) at an intermediate frequency of 610 MHz. The timing parameters, obtained in follow up observations with the Lovell Telescope at Jodrell Bank Observatory and the GMRT, are presented.
Based on the frequency analysis using the spectral significance as an unbiased statistical quantity, resulting frequencies in the DFT spectra of target and background light curves are comparatively examined. The individual False-Alarm Probabilities are used to deduce conditional probabilities (and conditional spectral significances, correspondingly) for a peak in a target spectrum to be real in spite of a corresponding peak in the background spectrum. An alternative scenario is the search for coincident peaks in the DFTs of compared time series. The question for the joint probability of a frequency to occur in the DFT spectra of several datasets simultaneously leads to the composed spectral significance, which may be applied if measurements of one star are available in different filters, or if several observing runs are examined for corresponding signal components. The composed spectral significance is a measure for the probability that none of the related peaks in the DFT spectra under consideration is due to noise. The method developed in this paper is tested using space photometry. Examples for the composed and the conditional CIndeRelLA mode for different observation setups are presented.
We consider disk accretion resulting purely from the loss of angular momentum due to the outflow of plasma from a magnetized disk. In this limiting case, the dissipation due to the viscosity and finite electrical conductivity of the plasma can be neglected. We have obtained self-consistent, self-similar solutions for dissipationless disk accretion. Such accretion may result in the formation of objects whose bolometric luminosities are lower than the flux of kinetic energy in the ejected material.
Formation of GMCs is one of the most crucial issues in galaxy evolution. I will compare CO and HI in the LMC in 3 dimensional space for the first time aiming at revealing the physical connection between GMCs and associated HI gas at a ~40 pc scale. The present major findings are 1) [total CO intensity] [total HI intensity]0.8 for the 110 GMCs, and 2) the HI intensity tends to increase with the evolution of GMCs. I argue that these findings are consistent with the growth of GMCs via HI accretion over a time scale of a few x 10 Myrs. I will also discuss the role of the background stellar gravity and the dynamical compression by supershells in formation of GMCs.
We study the generation of primeval magnetic fields during inflation era in nonlinear theories of electrodynamics. Although the intensity of the produced fields strongly depends on characteristics of inflation and on the form of electromagnetic Lagrangian, our results do not exclude the possibility that these fields could be astrophysically interesting.
(Abridged)
We study the effects of interstellar clouds on the dynamical and chemical
evolution of gas-rich dwarf galaxies. In particular, we focus on two model
galaxies similar to IZw18 and NGC1569 in comparison to models in which a smooth
initial distribution of gas is assumed. We use a 2-D hydrodynamical code
coupled with a series of routines able to trace the chemical products of SNeII,
SNeIa and intermediate-mass stars. Clouds are simulated by adding overdense
regions in the computational grid, whose locations are chosen randomly and
whose density profiles match observed ones. The clouds are inherently
dynamically coupled to the diffuse gas, and they experience heat conduction
from a hot surrounding gas. Due to dynamical processes and thermal evaporation,
the clouds survive only a few tens of Myr. Due to the additional cooling agent,
the internal energy of cloudy models is typically reduced by 20 - 40% compared
with models of diffuse gas alone. The clouds delay the development of
large-scale outflows by mass loading, therefore helping to retain a larger
amount of gas inside the galaxy. However, their bullet effect can pierce the
expanding supershell and create holes through which the superbubble can vent
freshly produced metals. Moreover, assuming a pristine chemical composition for
the clouds, their interaction with the superbubble dilutes the gas, reducing
the metallicity. The resulting final metallicity is therefore generally lower
(by ~ 0.2 - 0.4 dex) than the one attained by diffuse models.
Recent observations of the Mira AB binary system have revealed a surrounding arc-like structure and a stream of material stretching 2 degrees away in opposition to the arc. The alignment of the proper motion vector and the arc-like structure shows the structures to be a bow shock and accompanying tail. We have successfully hydrodynamically modelled the bow shock and tail as the interaction between the asymptotic giant branch (AGB) wind launched from Mira A and the surrounding interstellar medium. Our simulations show that the wake behind the bow shock is turbulent: this forms periodic density variations in the tail similar to those observed. We investigate the possiblity of mass-loss variations, but find that these have limited effect on the tail structure. The tail is estimated to be approximately 450,000 years old, and is moving with a velocity close to that of Mira itself. We suggest that the duration of the high mass-loss phase on the AGB may have been underestimated. Finally, both the tail curvature and the rebrightening at large distance can be qualitatively understood if Mira recently entered the Local Bubble. This is estimated to have occured 17 pc downstream from its current location.
Three-dimensional large eddy simulations of solar surface convection using realistic model physics are conducted. The thermal structure of convective motions into the upper radiative layers of the photosphere, the range of convection cell sizes, and the penetration depths of convection are investigated. A portion of the solar photosphere and the upper layers of the convection zone, a region extending 60 x 60 Mm horizontally from 0 Mm down to 20 Mm below the visible surface, is considered. We start from a realistic initial model of the Sun with an equation of state and opacities of stellar matter. The equations of fully compressible radiation hydrodynamics with dynamical viscosity and gravity are solved. We use: 1) a high order conservative TVD scheme for the hydrodynamics, 2) the diffusion approximation for the radiative transfer, 3) dynamical viscosity from subgrid scale modeling. The simulations are conducted on a uniform horizontal grid of 600 x 600, with 168 nonuniformly spaced vertical grid points, on 144 processors with distributed memory multiprocessors on supercomputer MVS-15000BM in the Computational Centre of the Russian Academy of Sciences.
We present the results of the timing analysis of five Rossi X-ray Timing Explorer observations of the Black Hole Candidate GRS 1915+105 between 1996 September and 1997 December. The aim was to investigate the possible presence of a type-B quasi-periodic oscillation (QPO). Since in other systems this QPO is found to appear during spectral transitions from Hard to Soft states, we analyzed observations characterized by a fast and strong variability, in order to have a large number of transitions. In GRS 1915+105, transitions occur on very short time scales (~ sec): to single them out we averaged Power Density Spectra following the regular path covered by the source on a 3D Hardness-Hardness-Intensity Diagram. We identified both the type-C and the type-B quasi-periodic oscillations (QPOs): this is the first detection of a type-B QPO in GRS 1915+105. As the spectral transitions have been associated to the emission and collimation of relativistic radio-jets, their presence in the prototypical galactic jet source strengthens this connection.
I present a new census of the stellar population in the Chamaeleon I star-forming region. Using optical and near-IR photometry and followup spectroscopy, I have discovered 50 new members of Chamaeleon I, expanding the census of known members to 226 objects. Fourteen of these new members have spectral types later than M6, which doubles the number of known members that are likely to be substellar. I have estimated extinctions, luminosities, and effective temperatures for the known members, used these data to construct an H-R diagram for the cluster, and inferred individual masses and ages with the theoretical evolutionary models of Baraffe and Chabrier. The distribution of isochronal ages indicates that star formation began 3-4 and 5-6 Myr ago in the southern and northern subclusters, respectively, and has continued to the present time at a declining rate. The IMF in Chamaeleon I reaches a maximum at a mass of 0.1-0.15 M_sun, and thus closely resembles the IMFs in IC 348 and the Orion Nebula Cluster. In logarithmic units where the Salpeter slope is 1.35, the IMF is roughly flat in the substellar regime and shows no indication of reaching a minimum down to a completeness limit of 0.01 M_sun. The low-mass stars are more widely distributed than members at other masses in the northern subcluster, but this is not the case in the southern subcluster. Meanwhile, the brown dwarfs have the same spatial distribution as the stars out to a radius of 3 deg (8.5 pc) from the center of Chamaeleon I.
A perturbative analysis is used to investigate the effect of rotation on the instability of a steady accretion shock (SASI) in a simple toy-model, in view of better understanding supernova explosions in which the collapsing core contains angular momentum. A cylindrical geometry is chosen for the sake of simplicity. Even when the centrifugal force is very small, rotation can have a strong effect on the non-axisymmetric modes of SASI by increasing the growth rate of the spiral modes rotating in the same direction as the steady flow. Counter-rotating spiral modes are significantly damped, while axisymmetric modes are hardly affected by rotation. The growth rates of spiral modes have a nearly linear dependence on the specific angular momentum of the flow. The fundamental one-armed spiral mode (m=1) is favoured for small rotation rates, whereas stronger rotation rates favour the mode m=2. A WKB analysis of higher harmonics indicates that the efficiency of the advective-acoustic cycles associated to spiral modes is strongly affected by rotation in the same manner as low frequency modes, whereas the purely acoustic cycles are stable. These results suggest that the linear phase of SASI in rotating core-collapse supernovae naturally selects a spiral mode rotating in the same direction of the flow, as observed in the 3D numerical simulations of Blondin & Mezzacappa (2007). This emphasizes the need for a 3D approach of core-collapse, before conclusions on the explosion mechanisms and pulsar kicks can be drawn.
We show that future Ultra-High Energy Cosmic Ray samples should be able to distinguish whether the sources of UHECRs are hosted by galaxy clusters or ordinary galaxies, or whether the sources are uncorrelated with the large-scale structure of the universe. Moreover, this is true independently of arrival direction uncertainty due to magnetic deflection or measurement error. The reason for this is the simple property that the strength of large-scale clustering for extragalactic sources depends on their mass, with more massive objects, such as galaxy clusters, clustering more strongly than lower mass objects, such as ordinary galaxies.
We report on the spatial relationship between solar flares and coronal mass ejections (CMEs) observed during 1996-2005 inclusive. We identified 496 flare-CME pairs considering limb flares (distance from central meridian > 45 deg) with soft X-ray flare size > C3 level. The CMEs were detected by the Large Angle and Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric Observatory (SOHO). We investigated the flare positions with respect to the CME span for the events with X-class, M-class, and C-class flares separately. It is found that the most frequent flare site is at the center of the CME span for all the three classes, but that frequency is different for the different classes. Many X-class flares often lie at the center of the associated CME, while C-class flares widely spread to the outside of the CME span. The former is different from previous studies, which concluded that no preferred flare site exists. We compared our result with the previous studies and conclude that the long-term LASCO observation enabled us to obtain the detailed spatial relation between flares and CMEs. Our finding calls for a closer flare-CME relationship and supports eruption models typified by the CSHKP magnetic reconnection model.
We study the relation between high-mass X-ray binary (HMXB) population and recent star formation history (SFH) for the Small Magellanic Cloud (SMC). Using archival optical SMC observations, we have approximated the color-magnitude diagrams of the stellar population by model stellar populations and, in this way, reconstructed the spatially resolved SFH of the galaxy over the past 100 Myr.We analyze the errors and stability of this method for determining the recent SFH and show that uncertainties in the models of massive stars at late evolutionary stages are the main factor that limits its accuracy. By combining the SFH with the spatial distribution of HMXBs obtained from XMM-Newton observations, we have derived the dependence of the HMXB number on the time elapsed since the star formation event. The number of young systems with ages 10 Myr is shown to be smaller than the prediction based on the type-II supernova rate. The HMXB number reaches its maximum ~20-50 Myr after the star formation event. This may be attributable, at least partly, to a low luminosity threshold in the population of X-ray sources studied, Lmin~1e+34 erg/s. Be/X systems make a dominant contribution to this population, while the contribution from HMXBs with black holes is relatively small.
We systematically study the effects of collisions on the overall dynamical evolution of dense star clusters using Monte Carlo simulations over many relaxation times. We derive many observable properties of these clusters, including their core radii and the radial distribution of collision products. We also study different aspects of collisions in a cluster taking into account the shorter lifetimes of more massive stars, which has not been studied in detail before. Depending on the lifetimes of the significantly more massive collision products, observable properties of the cluster can be modified qualitatively; for example, even without binaries, core collapse can sometimes be avoided simply because of stellar collisions.
The high energy neutrino telescope NT200+ is currently in operation in Lake Baikal. We review the status of the Baikal the Baikal Neutrino Telescope, and describe recent progress on key components of the next generation kilometer-cube (km3) Lake Baikal detector, like investigation of new large area phototubes, integrated into the telescope.
We present results on searches for exotic particles (relativistic magnetic monopoles and WIMPs) and for UHE neutrinos, obtained with the Baikal neutrino telescope NT200.
The Parity doublet model containing the SU(2) multiplets including the baryons identified as the chiral partners of the nucleons is applied for neutron star matter. The chiral restoration is analyzed and the maximum mass of the star is calculated.
Ca II triplet spectroscopy has been used to derive stellar metallicities for individual stars in four LMC fields situated at galactocentric distances of 3\arcdeg, 5\arcdeg, 6\arcdeg\@ and 8\arcdeg\@ to the north of the Bar. Observed metallicity distributions show a well defined peak, with a tail toward low metallicities. The mean metallicity remains constant until 6\arcdeg\@ ([Fe/H]$\sim$-0.5 dex), while for the outermost field, at 8\arcdeg, the mean metallicity is substantially lower than in the rest of the disk ([Fe/H]$\sim$-0.8 dex). The combination of spectroscopy with deep CCD photometry has allowed us to break the RGB age--metallicity degeneracy and compute the ages for the objects observed spectroscopically. The obtained age--metallicity relationships for our four fields are statistically indistinguishable. We conclude that the lower mean metallicity in the outermost field is a consequence of it having a lower fraction of intermediate-age stars, which are more metal-rich than the older stars. The disk age--metallicity relationship is similar to that for clusters. However, the lack of objects with ages between 3 and 10 Gyr is not observed in the field population. Finally, we used data from the literature to derive consistently the age--metallicity relationship of the bar. Simple chemical evolution models have been used to reproduce the observed age--metallicity relationships with the purpose of investigating which mechanism has participated in the evolution of the disk and bar. We find that while the disk age--metallicity relationship is well reproduced by close-box models or models with a small degree of outflow, that of the bar is only reproduced by models with combination of infall and outflow.
We present the results of recent observations of phase-dependent variations in brightness designed to characterize the atmospheres of hot Jupiters. In particular, we focus on recent observations of the transiting planet HD 189733b at 8 micron using the Spitzer Space Telescope, which allow us to determine the efficiency of the day-night circulation on this planet and estimate the longitudinal positions of hot and cold regions in the atmosphere. We discuss the implications of these observations in the context of two other successful detections of more sparsely-sampled phase variations for the non-transiting systems upsilon And b and HD 179949b, which imply a potential diversity in the properties of the atmospheres of hot Jupiters. Lastly, we highlight several upcoming Spitzer observations that will extend this sample to additional wavelengths and more transiting systems in the near future.
Short-hard Gamma Ray Bursts (SGRBs) are currently thought to arise from gravitational wave driven coalescences of double neutron star systems forming either in the field or dynamically in globular clusters. For both channels we fit the peak flux distribution of BATSE SGRBs to derive the local burst formation rate and luminosity function. We then compare the resulting redshift distribution with the Swift data, showing that both formation channels are needed in order to reproduce the observations. Double neutron stars forming in globular clusters are found to dominate the distribution at z<0.3, whereas the field population from primordial binaries can account for the high-z SGRBs. This result is not in contradiction with the observed host galaxy type of SGRBs.
The Milky Way is the only galaxy for which we can resolve individual stars at all evolutionary phases, from the Galactic center to the outskirt. The last decade, thanks to the advent of near IR detectors and 8 meter class telescopes, has seen a great progress in the understanding of the Milky Way central region: the bulge. Here we review the most recent results regarding the bulge structure, age, kinematics and chemical composition. These results have profound implications for the formation and evolution of the Milky Way and of galaxies in general. This paper provides a summary on our current understanding of the Milky Way bulge, intended mainly for workers on other fields.
We present HST/WFPC2 Linear Ramp Filter images of high surface brightness emission lines (either [OII], [OIII], or H-alpha+[NII]) in 80 3CR radio sources. We overlay the emission line images on high resolution VLA radio images (eight of which are new reductions of archival data) in order to examine the spatial relationship between the optical and radio emission. We confirm that the radio and optical emission line structures are consistent with weak alignment at low redshift (z < 0.6) except in the Compact Steep Spectrum (CSS) radio galaxies where both the radio source and the emission line nebulae are on galactic scales and strong alignment is seen at all redshifts. There are weak trends for the aligned emission line nebulae to be more luminous, and for the emission line nebula size to increase with redshift and/or radio power. The combination of these results suggests that there is a limited but real capacity for the radio source to influence the properties of the emission line nebulae at these low redshifts (z < 0.6). Our results are consistent with previous suggestions that both mechanical and radiant energy are responsible for generating alignment between the radio source and emission line gas.
Development of the Aarhus adiabatic pulsation code started around 1978. Although the main features have been stable for more than a decade, development of the code is continuing, concerning numerical properties and output. The code has been provided as a generally available package and has seen substantial use at a number of installations. Further development of the package, including bringing the documentation closer to being up to date, is planned as part of the HELAS Coordination Action.
We study CP-violation effects when neutrinos are present in dense matter, such as outside the proto-neutron star formed in a core-collapse supernova. General arguments based on the Standard Model predict that there are no CP-violating effects at the tree level in core-collapse supernovae, justifying the assumption of ignoring the Dirac delta phase made in most of the literature. Physics beyond the Standard Model, especially flavor-changing interactions might induce CP-violating effects. We analyze this possibility.
In April 2006, a 4-channel acoustic antenna has been put in long-term operation on Lake Baikal. The detector was installed at a depth of about 100 m on the instrumentation string of Baikal Neutrino Telescope NT200+. This detector may be regarded as a prototype of a subunit for a future underwater acoustic neutrino telescope. We describe the design of acoustic detector and present first results obtained from data analysis.
The Aarhus code is the result of a long development, starting in 1974, and still ongoing. A novel feature is the integration of the computation of adiabatic oscillations for specified models as part of the code. It offers substantial flexibility in terms of microphysics and has been carefully tested for the computation of solar models. However, considerable development is still required in the treatment of nuclear reactions, diffusion and convective mixing.
We examine the applicability of effective temperature scales of several broad band colours to T Tauri stars (TTS). We take into account different colour systems as well as stellar parameters like metallicity and surface gravity which influence the conversion from colour indices or spectral type to effective temperature. For a large sample of TTS, we derive temperatures from broad band colour indices and check if they are consistent in a statistical sense with temperatures inferred from spectral types. There are some scales (for V-H, V-K, I-J, J-H, and J-K) which indeed predict the same temperatures as the spectral types and therefore can be at least used to confirm effective temperatures. Furthermore, we examine whether TTS with dynamically derived masses can be used for a test of evolutionary models and effective temperature calibrations. We compare the observed parameters of the eclipsing T Tauri binary V1642 Ori A to the predictions of evolutionary models in both the H-R and the Kiel diagram using temperatures derived with several colour index scales. We check whether the evolutionary models and the colour index scales are consistent with coevality and the dynamical masses of the binary components. It turns out that the Kiel diagram offers a stricter test than the H-R diagram. Only the evolutionary models of Baraffe et al. (1998) with mixing length parameter 1.9 and of D'Antona & Mazzitelli (1994, 1997) show consistent results in the Kiel diagram in combination with some conversion scales of Houdashelt et al. (2000) and of Kenyon & Hartmann (1995).
We present a new measurement of the volumetric rate of Type Ia supernova up to a redshift of 1.7, using the Hubble Space Telescope (HST) GOODS data combined with an additional HST dataset covering the North GOODS field collected in 2004. We employ a novel technique that does not require spectroscopic data for identifying Type Ia supernovae (although spectroscopic measurements of redshifts are used for over half the sample); instead we employ a Bayesian approach using only photometric data to calculate the probability that an object is a Type Ia supernova. This Bayesian technique can easily be modified to incorporate improved priors on supernova properties, and it is well-suited for future high-statistics supernovae searches in which spectroscopic follow up of all candidates will be impractical. Here, the method is validated on both ground- and space-based supernova data having some spectroscopic follow up. We combine our volumetric rate measurements with low redshift supernova data, and fit to a number of possible models for the evolution of the Type Ia supernova rate as a function of redshift. The data do not distinguish between a flat rate at redshift > 0.5 and a previously proposed model, in which the Type Ia rate peaks at redshift >1 due to a significant delay from star-formation to the supernova explosion. Except for the highest redshifts, where the signal to noise ratio is generally too low to apply this technique, this approach yields smaller or comparable uncertainties than previous work.
We have examined images from the Precision Solar Photometric Telescope (PSPT) at the Mauna Loa Solar Observatory (MLSO) in search of latitudinal variation in the solar photospheric intensity. Along with the expected brightening of the solar activity belts, we have found a weak enhancement of the mean continuum intensity at polar latitudes (continuum intensity enhancement $\sim0.1 - 0.2%$ corresponding to a brightness temperature enhancement of $\sim2.5{\rm K}$). This appears to be thermal in origin and not due to a polar accumulation of weak magnetic elements, with both the continuum and CaIIK intensity distributions shifted towards higher values with little change in shape from their mid-latitude distributions. Since the enhancement is of low spatial frequency and of very small amplitude it is difficult to separate from systematic instrumental and processing errors. We provide a thorough discussion of these and conclude that the measurement captures real solar latitudinal intensity variations.
Oscillations of magnetic structures in the solar corona have often been interpreted in terms of magnetohydrodynamic waves. We study the adiabatic magnetoacoustic modes of a prominence plasma slab with a uniform longitudinal magnetic field, surrounded by a prominence-corona transition region (PCTR) and a coronal medium. Considering linear small-amplitude oscillations, the dispersion relation for the magnetoacoustic slow and fast modes is deduced assuming evanescent-like perturbations in the coronal medium. In the system without PCTR, a classification of the oscillatory modes according to the polarisation of their eigenfunctions is made in order to distinguish modes with fast-like or slow-like properties. Internal and external slow modes are governed by the prominence and coronal properties respectively, and fast modes are mostly dominated by prominence conditions for the observed wavelengths. In addition, the inclusion of an isothermal PCTR does not substantially influence the mode frequencies, but new solutions (PCTR slow modes) are present.
We have considered precession in accretion disks in which a second moment of inertia relative to an axis perpendicular to the axis of rotation may be very important. This formalism, that takes into account the precession contribution to the angular momentum, is based on the existence of a parameter $\it p$ which determines three characteristic densities resulting from the averaging process and imposes constraints on the actual disk density. It is shown that the precession velocity will lie in a three branch solution, and depends on how large is the disk actual density as compared to the characteristic densities. Besides the large spread on the solution for the precession velocity, depending on the density strength, it may be prograde and retrograde. It is shown that the keplerian thin disk, with very large density values compared to characteristic ones, only precesses very far away from the primary object, which implies very large precession periods. For other models, the disk will thicken, with large deviations from the keplerian approximation. Constraints on the density only will be effective for very large values of the ratio ${{\dot M} \over M_{p}}$, respectively, accretion rate and mass of the primary. Under this condition, the structure of the precessing region is found. Lower bounds on the precession period are found for not so large values of this ratio. Deviations from the mean precessional motion are considered. It is shown that these deviations result in periodic motions as long as the time scales associated to them are comparable to the remaining time scales. Otherwise, they result in misalignment motions, forcing the plane of the disk to become normal to the orbital plane of the secondary.
This paper investigates the clustering properties of a complete sample of 1041 24um-selected sources brighter than F[24um]=400 uJy in the overlapping region between the SWIRE and UKIDSS UDS surveys. We have concentrated on the two (photometric) interval ranges z=[0.6-1.2] (low-z sample) and z>1.6 (high-z sample) as it is in these regions were we expect the mid-IR population to be dominated by intense dust-enshrouded activity such as star formation and black hole accretion. Investigations of the angular correlation function produce a correlation length are r0~15.9 Mpc for the high-z sample and r0~8.5 Mpc for the low-z one. Comparisons with physical models reveal that the high-z sources are exclusively associated with very massive (M>~10^{13} M_sun)haloes, comparable to those which locally host groups-to-clusters of galaxies, and are very common within such (rare) structures. Conversely, lower-z galaxies are found to reside in smaller halos (M_min~10^{12} M_sun) and to be very rare in such systems. While recent studies have determined a strong evolution of the 24um luminosity function between z~2 and z~0, they cannot provide information on the physical nature of such an evolution. Our clustering results instead indicate that this is due to the presence of different populations of objects inhabiting different structures, as active systems at z<~1.5 are found to be exclusively associated with low-mass galaxies, while very massive sources appear to have concluded their active phase before this epoch. Finally, we note that the small-scale clustering data seem to require steep profiles for the distribution of galaxies within their halos. This is suggestive of close encounters and/or mergers which could strongly favour both AGN and star-formation activity.
We present a study of the globular cluster (GC) systems of nearby elliptical and S0 galaxies at a variety of wavelengths from the X-ray to the infrared. Our analysis shows that roughly half of the low mass X-ray binaries (LMXBs), that are the luminous tracers of accreting neutron star or black hole systems, are in clusters. There is a surprisingly strong correlation between the LMXB frequency and the metallicity of the GCs, with metal-rich GCs hosting three times as many LMXBs as metal-poor ones, and no convincing evidence of a correlation with GC age so far. In some of the galaxies the LMXB formation rate varies with GC color even within the red peak of the typical bimodal cluster color distribution, providing some of the strongest evidence to date that there are metallicity variations within the metal-rich GC peak as is expected in a hierarchical galaxy formation scenario. We also note that any analysis of subtler variations in GC color distributions must carefully account for both statistical and systematic errors. We caution that some published GC correlations, such as the apparent 'blue-tilt' or mass-metallicity effect might not have a physical origin and may be caused by systematic observational biases.
In this paper, warm inflationary models on a brane scenario are studied. Here we consider slow-roll inflation and high-dissipation regime in a high-energy scenario. General conditions required for these models to be realizable are derived. We describe scalar and tensor perturbations for these scenarios. Specifically we study power-law potentials considering a dissipation parameter to be a constant on the one hand and $\phi$ dependent on the other hand. We use recent astronomical observations to restrict the parameters appearing in our model.
I discuss the development and resolution of the solar neutrino problem, as well as opportunities now open to us to extend our knowledge of main-sequence stellar evolution and neutrino astrophysics.
We assume the validity of the Standard Model up to an arbitrary high-energy scale and discuss what information on the early stages of the Universe can be extracted from a measurement of the Higgs mass. For Mh < 130 GeV, the Higgs potential can develop an instability at large field values. From the absence of excessive thermal Higgs field fluctuations we derive a bound on the reheat temperature after inflation as a function of the Higgs and top masses. Then we discuss the interplay between the quantum Higgs fluctuations generated during the primordial stage of inflation and the cosmological perturbations, in the context of landscape scenarios in which the inflationary parameters scan. We show that, within the large-field models of inflation, it is highly improbable to obtain the observed cosmological perturbations in a Universe with a light Higgs. Moreover, independently of the inflationary model, the detection of primordial tensor perturbations through the B-mode of CMB polarization and the discovery of a light Higgs can simultaneously occur only with exponentially small probability, unless there is new physics beyond the Standard Model.
We derive the low energy effective theory on a brane in six-dimensional chiral supergravity. The conical 3-brane singularities are resolved by introducing cylindrical codimension one 4-branes whose interiors are capped by a regular spacetime. The effective theory is described by the Brans-Dicke (BD) theory with the BD parameter given by $\omega_{\rm BD}=1/2$. The BD field is originated from a modulus which is associated with the scaling symmetry of the system. If the dilaton potentials on the branes preserve the scaling symmetry, the scalar field has an exponential potential in the Einstein frame. We show that the time dependent solutions driven by the modulus in the four-dimensional effective theory can be lifted up to the six-dimensional exact solutions found in the literature. Based on the effective theory, we discuss a possible way to stabilize the modulus to recover standard cosmology and also study the implication for the cosmological constant problem.
In this paper we use the corrections to the Newton-Einstein secular precessions of the perihelia of some planets (Mercury, Earth, Mars, Jupiter, Saturn) of the Solar System, phenomenologically estimated as solve-for parameters by the Russian astronomer E.V. Pitjeva in a global fit of almost one century of data with the EPM2004 ephemerides, in order to put on the test the expression for the perihelion precession induced by an uniform cosmological constant $\Lambda$ in the Schwarzschild-de Sitter (or Kottler) space-time. We compare such an extra-rate to the estimated corrections to the planetary perihelion precessions by taking their ratio for different pairs of planets instead of using one perihelion at a time for each planet separately, as done so far in literature. The answer is neatly negative, even by further re-scaling by a factor 10 (and even 100 for Saturn) the errors in the estimated extra-precessions of the perihelia released by Pitjeva. However, caution is advised because it would be relevant to repeat the present analysis by using corrections to the precessions of perihelia independently estimated by other teams of astronomers as well.
We introduce a simple prescription for calculating the spectra of thermal fluctuations of temperature-dependent quantities of the form $\hat{\delta T}(t)=\int d^3\vec{r} \delta T(\vec{r},t) q(\vec{r})$. Here $T(\vec{r}, t)$ is the local temperature at location $\vec{r}$ and time $t$, and $q(\vec{r})$ is an arbitrary function. As an example of a possible application, we compute the spectrum of thermo-refractive coating noise in LIGO, and find a complete agreement with the previous calculation of Braginsky, Gorodetsky and Vyatchanin. Our method has computational advantage, especially for non-regular or non-symmetric geometries, and for the cases where $q(\vec{r})$ is non-negligible in a significant fraction of the total volume.
Two-temperature, two-mass quasi-equilibrium plasmas may occur in electron-ion plasmas,nuclear-matter, as well as in electron-hole condensed-matter systems. Dense two-temperature hydrogen plasmas straddle the difficult partially - degenerate regime of electron densities and temperatures which are important in astrophysics, in inertial-confinement fusion research, and other areas of warm dense matter physics. Results from Kohn-Sham calculations and QMC are used to benchmark the procedures used in classical molecular-dynamics simulations, HNC and CHNC methods to derive electron-electron and electron-proton pair - distribution functions. Then, nonequilibrium molecular dynamics for two -temperature, two-mass plasmas are used to obtain the pair distribution. Using these results, the correct HNC and CHNC procedures for the evaluation of pair-distribution functions in two-temperature two-mass two-component charged fluids are established. Results for a mass ratio of 1:5, typical of electron-hole fluids, as well as for compressed hydrogen are presented. PACS Numbers: 52.25.Kn, 52.25Gj, 71.10.-w, 52.27.Gr, 26.30.+k
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We present a spatially resolved comparison of the stellar-mass and total-mass surface distributions of nine early-type galaxies. The galaxies are a subset of the Sloan Lens ACS survey (or SLACS; Bolton et al. 2006). The total-mass distributions are obtained by exploring pixelated mass models that reproduce the lensed images. The stellar-mass distributions are derived from population synthesis models fit to the photometry of the lensing galaxies. Uncertainties - mainly model degeneracies - are also computed. Stars can account for all the mass in the inner regions. A Salpeter IMF actually gives too much stellar mass in the inner regions and hence appears ruled out. Dark matter becomes significant by the half-light radius and becomes increasingly dominant at larger radii. The stellar and dark components are closely aligned, but the actual ellipticities are not correlated. Finally, we attempt to intuitively summarize the results by rendering the density, stellar-vs-dark ratio, and uncertainties as false-colour maps.
The first stars form in dark matter halos of masses ~10^6 M_sun as suggested by an increasing number of numerical simulations. Radiation feedback from these stars expels most of the gas from their shallow potential well of their surrounding dark matter halos. We use cosmological adaptive mesh refinement simulations that include self-consistent Population III star formation and feedback to examine the properties of assembling early dwarf galaxies. Accurate radiative transport is modeled with adaptive ray tracing. We include supernova explosions and follow the metal enrichment of the intergalactic medium. The calculations focus on the formation of several dwarf galaxies and their progenitors. In these halos, baryon fractions in 10^8 solar mass halos decrease by a factor of 2 with stellar feedback and by a factor of 3 with supernova explosions. We find that radiation feedback and supernova explosions increase gaseous spin parameters up to a factor of 4 and vary with time. Stellar feedback, supernova explosions, and H_2 cooling create a complex, multi-phase interstellar medium whose densities and temperatures can span up to 6 orders of magnitude at a given radius. The pair-instability supernovae of Population III stars alone enrich the halos with virial temperatures of 10^4 K to approximately 10^{-3} of solar metallicity. We find that 40% of the heavy elements resides in the intergalactic medium (IGM) at the end of our calculations. The highest metallicity gas exists in supernova remnants and very dilute regions of the IGM.
For a density that is not too sharply peaked towards the center, the local tidal field becomes compressive in all three directions. Available gas can then collapse and form a cluster of stars in the center, including or even being dominated by a central black hole. We show that for a wide range of (deprojected) Sersic profiles in a spherical potential, the tidal forces are compressive within a region which encloses most of the corresponding light of observed nuclear clusters in both late-type and early-type galaxies. In such models, tidal forces become disruptive nearly everywhere for relatively large Sersic indices n >= 3.5. We also show that the mass of a central massive object (CMO) required to remove all radial compressive tidal forces scales linearly with the mass of the host galaxy. If CMOs formed in (progenitor) galaxies with n ~ 1, we predict a mass fraction of ~ 0.1-0.5%, consistent with observations of nuclear clusters and super-massive black holes. While we find that tidal compression possibly drives the formation of CMOs in galaxies, beyond the central regions and on larger scales in clusters disruptive tidal forces might contribute to prevent gas from cooling.
During accretion, a neutron star (NS) is spun up as angular momentum is transported through its liquid surface layers. We study the resulting differentially rotating profile, focusing on the impact this has for type I X-ray bursts. The viscous heating is found to be negligible, but turbulent mixing can be activated. Mixing has the greatest impact when the buoyancy at the compositional discontinuity between accreted matter and ashes is overcome. This occurs preferentially at high accretion rates or low spin frequencies and may depend on the ash composition from the previous burst. We then find two new regimes of burning. The first is ignition in a layer containing a mixture of heavier elements with recurrence times as short as ~5-30 minutes, similar to short recurrence time bursts. When mixing is sufficiently strong, a second regime is found where accreted helium mixes deep enough to burn stably, quenching X-ray bursts altogether. The carbon-rich material produced by stable helium burning would be important for triggering and fueling superbursts.
In the current paradigm, red sequence galaxies are believed to have formed as blue disk galaxies that subsequently had their star formation quenched. Since red-sequence galaxies typically have an early-type morphology, the transition from the blue to the red sequence also involves a morphological transformation. In this paper we study the impact of transformation mechanisms that operate only on satellite galaxies, such as strangulation, ram-pressure stripping and galaxy harassment. Using a large galaxy group catalogue constructed from the SDSS, we compare the colors and concentrations of satellites galaxies to those of central galaxies of the same stellar mass, adopting the hypothesis that the latter are the progenitors of the former. On average, satellites are redder and more concentrated than central galaxies of the same stellar mass. Central-satellite pairs that are matched in both stellar mass and color, however, show no average concentration difference, indicating that the transformation mechanisms affect color more than morphology. The color and concentration differences of matched central-satellite pairs are completely independent of the halo mass of the satellite galaxy, indicating that satellite-specific transformation mechanisms are equally efficient in haloes of all masses. This strongly favors strangulation as the main quenching mechanism for satellite galaxies. Finally, we determine the relative importance of satellite quenching for the build-up of the red sequence. We find that roughly 70 percent of red sequence satellite galaxies with a stellar mass of 10^9 Msun had their star formation quenched as satellites. This drops rapidly to zero with increasing stellar mass, indicating that a significant fraction of red satellites were already quenched before they became a satellite.
Stellar-mass black holes are discovered in X-ray emitting binary systems, where their mass can be determined from the dynamics of their companion stars. Models of stellar evolution have difficulty producing black holes in close binaries with masses >10 solar masses, which is consistent with the fact that the most massive stellar black holes known so all have masses within 1 sigma of 10 solar masses. Here we report a mass of 15.65 +/- 1.45 solar masses for the black hole in the recently discovered system M33 X-7, which is located in the nearby galaxy Messier 33 (M33) and is the only known black hole that is in an eclipsing binary. In order to produce such a massive black hole, the progenitor star must have retained much of its outer envelope until after helium fusion in the core was completed. On the other hand, in order for the black hole to be in its present 3.45 day orbit about its 70.0 +/- 6.9 solar mass companion, there must have been a ``common envelope'' phase of evolution in which a significant amount of mass was lost from the system. We find the common envelope phase could not have occured in M33 X-7 unless the amount of mass lost from the progenitor during its evolution was an order of magnitude less than what is usually assumed in evolutionary models of massive stars.
Despite intense scrutiny, the progenitor system(s) that gives rise to Type Ia supernovae remains unknown. The favored theory invokes a carbon-oxygen white dwarf accreting hydrogen-rich material from a close companion until a thermonuclear runaway ensues that incinerates the white dwarf. However, simulations resulting from this single-degenerate, binary channel demand the presence of low-velocity H-alpha emission in spectra taken during the late nebular phase, since a portion of the companion's envelope becomes entrained in the ejecta. This hydrogen has never been detected, but has only rarely been sought. Here we present results from a campaign to obtain deep, nebular-phase spectroscopy of nearby Type Ia supernovae, and include multi-epoch observations of two events: SN 2005am (slightly subluminous) and SN 2005cf (normally bright). No H-alpha emission is detected in the spectra of either object. An upper limit of 0.01 M_Sun of solar abundance material in the ejecta is established from the models of Mattila et al. which, when coupled with the mass-stripping simulations of Marietta et al. and Meng et al. effectively rules out progenitor systems for these supernovae with secondaries close enough to the white dwarf to be experiencing Roche lobe overflow at the time of explosion. Alternative explanations for the absence of H-alpha emission, along with suggestions for future investigations necessary to confidently exclude them as possibilities, are critically evaluated.
In this brief proceedings article I summarize the review talk I gave at the IAU 246 meeting in Capri, Italy, glossing over the well-known results from the literature, but paying particular attention to new, previously unpublished material. This new material includes a careful comparison of the apparently contradictory results of two independent methods used to simulate the evolution of binary populations in dense stellar systems (the direct N-body method of Hurley, et al. 2007 and the approximate Monte Carlo method of Ivanova, et al. 2005), that shows that the two methods may not actually yield contradictory results, and suggests future work to more directly compare the two methods.
This Supplementary Information provides details about the spectral extraction (crowding issues and the removal of nebular lines), a discussion about the distance to M33, a model for the O-star wind and the measurement of the true photospheric X-ray eclipse width Theta, and details about ellipsoidal modelling. It also contains five related figures, one related table, and additional references.
We present new optical spectroscopy and photometry, 2MASS infrared observations and 24 years of combined AAVSO and AFOEV photometry of the symbiotic star candidate \ae. The long-term light curve is characterized by outbursts lasting several years and having a slow decline of $\sim 2 \times 10^{-4}$ mag/day. The whole range of variability of the star in the $V$ band is about 4 magnitudes. The periodogram of the photometric data reveals strong signals at $\sim$ 342 and 171 days. The presence of the emission feature at $\lambda$ 6830 \AA at minimum and the detection of absorption lines of a $\sim$ K5 type star confirm the symbiotic classification and suggest that AE Cir is a new member of the small group of s-type yellow symbiotic stars. We estimate a distance of 9.4 kpc. Our spectrum taken at the high state shows a much flatter spectral energy distribution, the disappearance of the $\lambda$ 6830 \AA emission feature and the weakness of the He II 4686 emission relative to the Balmer emission lines. Our observations indicate the presence of emission line flickering in time scales of minutes in 2001. The peculiar character of \ae is revealed in the visibility of the secondary star at the high and low state, the light curve resembling a dwarf nova superoutburst and the relatively short low states. The data are hard to reconciliate with standard models for symbiotic star outbursts.
We present a simple and efficient method to set up spherical structure models for N-body simulations with a multi-mass technique. This technique reduces by a substantial factor the computer run time needed in order to resolve a given scale as compared to single-mass models. It therefore allows to resolve smaller scales in N-body simulations for a given computer run time. Here, we present several models with an effective resolution of up to 1.68 x 10^9 particles within their virial radius which are stable over cosmologically relevant time-scales. As an application, we confirm the theoretical prediction by Dehnen (2005) that in mergers of collisonless structures like dark matter haloes always the cusp of the steepest progenitor is preserved. We model each merger progenitor with an effective number of particles of approximately 10^8 particles. We also find that in a core-core merger the central density approximately doubles whereas in the cusp-cusp case the central density only increases by approximately 50%. This may suggest that the central region of flat structures are better protected and get less energy input through the merger process.
We set sensitive upper limits to the X-ray emission of four Type Ia supernovae (SNe Ia) using the Chandra X-ray Observatory. SN 2002bo, a normal, although reddened, nearby SN Ia, was observed 9.3 days after explosion. For an absorbed, high temperature bremsstrahlung model the flux limits are 3.2E-16 ergs/cm^2/s (0.5-2 keV band) and 4.1E-15 ergs/cm^2/s (2-10 keV band). Using conservative model assumptions and a 10 km/s wind speed, we derive a mass loss rate of \dot{M} ~ 2E-5 M_\odot/yr, which is comparable to limits set by the non-detection of Halpha lines from other SNe Ia. Two other objects, SN 2002ic and SN 2005gj, observed 260 and 80 days after explosion, respectively, are the only SNe Ia showing evidence for circumstellar interaction. The SN 2002ic X-ray flux upper limits are ~4 times below predictions of the interaction model currently favored to explain the bright optical emission. To resolve this discrepancy we invoke the mixing of cool dense ejecta fragments into the forward shock region, which produces increased X-ray absorption. A modest amount of mixing allows us to accommodate the Chandra upper limit. SN 2005gj is less well studied at this time. Assuming the same circumstellar environment as for SN 2002i, the X-ray flux upper limits for SN 2005gj are ~4 times below the predictions, suggesting that mixing of cool ejecta into the forward shock has also occurred here. Our reanalysis of Swift and Chandra data on SN 2005ke does not confirm a previously reported X-ray detection. The host galaxies NGC 3190 (SN 2002bo) and NGC 1371 (SN 2005ke) each harbor a low luminosity (L_X ~ 3-4E40 ergs/s) active nucleus in addition to wide-spread diffuse soft X-ray emission.
Over the last decade, the Concentration, Asymmetry and Smoothness (CAS), as well as the M20 and GINI parameters have become popular to automatically classify distant galaxies in images. Ellipticals, spirals and irregular galaxies all appear to occupy different regions of this parameter space. At the same time, the Source Extractor (SE) program has become the mainstay to produce ob ject catalogs from large image surveys. A logical next step would be to incorporate the structural parameters into the Source Extractor software. There are however several problems that arise: 1) the CAS parameters are fits to the images and Source Extractor eschews fits in the interest of speed, 2) the definition of the structural parameters changed over time. Now that there is a clear and agreed-upon definition of the structural parameters, I am incorporating computed versions in the Source Extractor code (v2.5). The fitted CAS parameters are available for the GOODS-N/S fields and I compare the computed structural parameters to those found by the previous fits. My goal is to expand the source structure information in Source Extractor catalogs in order to improve automatic identification of sources, specifically of distant galaxies. The computed parameters perform reasonably close to the fitted versions but noise appears in faint ob jects due to a lack of information. For a subset of objects, the asymmetry signal is outside the SE boundaries and Smoothness still fails to compute for many ob jects. Type classification based on the SE parameters still lacks resolving power.
M85 optical transient 2006-1 (M85 OT 2006-1) is the most luminous member of the small family of V838 Mon-like objects, whose nature is still a mystery. This event took place in the Virgo cluster of galaxies and peaked at an absolute magnitude of I~-13. Here we present Hubble Space Telescope images of M85 OT 2006-1 and its environment, taken before and after the eruption, along with a spectrum of the host galaxy at the transient location. We find that the progenitor of M85 OT 2006-1 was not associated with any star forming region. The g and z-band absolute magnitudes of the progenitor were fainter than about -4 and -6 mag, respectively. Therefore, we can set a lower limit of ~50 Myr on the age of the youngest stars at the location of the progenitor that corresponds to a mass of <7 solar mass. Previously published line indices suggest that M85 has a mean stellar age of 1.6+/-0.3 Gyr. If this mean age is representative of the progenitor of M85 OT 2006-1, then we can further constrain its mass to be less than 2 solar mass. We compare the energetics and mass limit derived for the M85 OT 2006-1 progenitor with those expected from a simple model of violent stellar mergers. Combined with further modeling, these new clues may ultimately reveal the true nature of these puzzling events.
We present spectroscopic observations of the quiescent black hole binary A0620-00 with the the 6.5-m Magellan Clay telescope at Las Campanas Observatory. We measure absorption-line radial velocities of the secondary and make the most precise determination to date (K2 = 435.4 +/- 0.5 km/s). By fitting the rotational broadening of the secondary, we refine the mass ratio to q = 0.060 +/- 0.004; these results, combined with the orbital period, imply a minimum mass for the compact object of 3.10 +/- 0.04 Msun. Although quiescence implies little accretion activity, we find that the disc contributes 56 +/- 7 per cent of the light in B and V, and is subject to significant flickering. Doppler maps of the Balmer lines reveal bright emission from the gas stream-disc impact point and unusual crescent-shaped features. We also find that the disc centre of symmetry does not coincide with the predicted black hole velocity. By comparison with SPH simulations, we identify this source with an eccentric disc. With high S/N, we pursue modulation tomography of H-alpha and find that the aforementioned bright regions are strongly modulated at the orbital period. We interpret this modulation in the context of disc precession, and discuss cases for the accretion disc evolution.
Recent advances have made it possible to obtain two-dimensional line-of-sight magnetic field maps of the solar corona from spectropolarimetric observations of the Fe XIII 1075 nm forbidden coronal emission line. Together with the linear polarization measurements that map the azimuthal direction of the coronal magnetic field, these coronal vector magnetograms now allow for direct observational testing of theoretical coronal magnetic field models. This paper presents a study testing the validity of potential-field coronal magnetic field models. We constructed a theoretical coronal magnetic field model of active region AR 10582 observed by the SOLARC coronagraph in 2004 by a global potential field extrapolation of the synoptic map of Carrington Rotation 2014. Synthesized linear and circular polarization maps from thin layers of the coronal magnetic field model above the active region along the line of sight are compared with the observed maps. We found that reasonable agreement occurs from layers located just above the sunspot of AR 10582, near the plane of the sky. This result provides the first observational evidence that potential field extrapolation can yield a reasonable approximation of the magnetic field configuration of the solar corona for simple and stable active regions.
We report the detection of OH 1667 MHz and wide HI 21cm absorption at $z \sim 0.67$ towards the red quasar 1504+377, with the Green Bank Telescope and the Giant Metrewave Radio Telescope. The HI 21cm absorption extends over a velocity range of $\sim 600$ km/s blueward of the quasar redshift ($z=0.674$), with the new OH 1667 MHz absorption component at $\sim -430$ \kms, nearly coincident with earlier detections of mm-wave absorption at $z \sim 0.6715$. The atomic and molecular absorption appear to arise from a fast gas outflow from the quasar, with a mass outflow rate ${\dot M} \sim 12 M_\odot$ yr$^{-1}$ and a molecular hydrogen fraction $f_{\rm H_2} \equiv (N_{\rm H_2}/N_{\rm HI}) \sim 0.2$. The radio structure of 1504+377 is consistent with the outflow arising due to a jet-cloud interaction, followed by rapid cooling of the cloud material. The observed ratio of HCO$^+$ to OH column densities is $\sim 20$ times higher than typical values in Galactic and high-$z$ absorbers. This could arise due to small-scale structure in the outflowing gas on sub-parsec scales, which would also explain the observed variability in the HI 21cm line.
We report on the discovery of a surprising observed correlation between the slope of the low-mass stellar global mass function (GMF) of globular clusters (GCs) and their central concentration parameter c = log(r_t/r_c), i.e. the logarithmic ratio of tidal and core radii. This result is based on the analysis of a sample of twenty Galactic GCs, with solid GMF measurements from deep HST or VLT data, representative of the entire population of Milky Way GCs. While all high-concentration clusters in the sample have a steep GMF, low-concentration clusters tend to have a flatter GMF implying that they have lost many stars via evaporation or tidal stripping. No GCs are found with a flat GMF and high central concentration. This finding appears counter-intuitive, since the same two-body relaxation mechanism that causes stars to evaporate and the cluster to eventually dissolve should also lead to higher central density and possibly core-collapse. Therefore, severely depleted GCs should be in a post core-collapse state, contrary to what is suggested by their low concentration. Several hypotheses can be put forth to explain the observed trend, none of which however seems completely satisfactory. It is likely that GCs with a flat GMF have a much denser and smaller core than suggested by their surface brightness profile and may well be undergoing collapse at present. It is, therefore, likely that the number of post core-collapse clusters in the Galaxy is much larger than thought so far.
The role of optical Fe III absorption lines in B-type stars as iron abundance diagnostics is considered. To date, ultraviolet Fe lines have been widely used in B-type stars, although line blending can severely hinder their diagnostic power. Using optical spectra, covering a wavelength range ~ 3560 - 9200 A, a sample of Galactic B-type main-sequence and supergiant stars of spectral types B0.5 to B7 are investigated. A comparison of the observed Fe III spectra of supergiants, and those predicted from the model atmosphere codes TLUSTY (plane-parallel, non-LTE), with spectra generated using SYNSPEC (LTE), and CMFGEN (spherical, non-LTE), reveal that non-LTE effects appear small. In addition, a sample of main-sequence and supergiant objects, observed with FEROS, reveal LTE abundance estimates consistent with the Galactic environment and previous optical studies. Based on the present study, we list a number of Fe III transitions which we recommend for estimating the iron abundance from early B-type stellar spectra.
Rydberg Matter (RM) theory is previously shown to give good agreement with the unidentified infrared bands (UIR, UIB) that are observed in emission from many objects in space. From stimulated emission studies in RM, a slightly simpler theoretical model is found that describes the transitions giving the UIR bands better. The general theory for RM was recently shown to be very accurate using rotational spectroscopy to observe several types of RM clusters (Mol. Phys. 105 (2007) 933). Two different large studies of UIR are now interpreted with the improved model. High-resolution UIR observations by Beintema et al. are interpreted as transitions from high levels n = 40 - 80 down to levels n = 5 - 12 in the final state. The upper level quantum numbers for the observed bands agree well with those found in experiments. The stationary UIR bands at 3.3 and 11.3 micrometer are due to deexcitation n = 9 -> 5 and 9 -> 7 of Rydberg species through stimulated emission. The other UIR bands vary considerably in wavelength in different environments and even with time as seen in numerous observational studies. Their great variability is difficult to model by the commonly used PAH model, but is a natural consequence of the varying excitation state of RM.
A multi-dimension, time-dependent Monte Carlo code is used to compute sample gamma-ray spectra to explore whether unambiguous constraints could be obtained from gamma-ray observations of Type Ia supernovae. Both spherical and aspherical geometries are considered and it is shown that moderate departures from sphericity can produce viewing-angle effects that are at least as significant as those caused by the variation of key parameters in one-dimensional models. Thus gamma-ray data could in principle carry some geometrical information, and caution should be applied when discussing the value of gamma-ray data based only on one-dimensional explosion models. In light of the limited sensitivity of current gamma-ray observatories, the computed theoretical spectra are studied to revisit the issue of whether useful constraints could be obtained for moderately nearby objects. The most useful gamma-ray measurements are likely to be of the light curve and time-dependent hardness ratios, but sensitivity higher than currently available, particularly at relatively hard energies (~2-3 MeV), is desirable.
The extremely luminous supernova SN 2006gy challenges the traditional view that the collapse of a stellar core is the only mechanism by which a massive star makes a supernova, because it seems too luminous by more than a factor of ten. Here we report that the brightest supernovae in the modern Universe arise from collisions between shells of matter ejected by massive stars that undergo an interior instability arising from the production of electron-positron pairs. This "pair instability" leads to explosive burning that is insufficient to unbind the star, but ejects many solar masses of the envelope. After the first explosion, the remaining core contracts and searches for a stable burning state. When the next explosion occurs, several solar masses of material are again ejected, which collide with the earlier ejecta. This collision can radiate 1E50 erg of light, about a factor of ten more than an ordinary supernova. Our model is in good agreement with the observed light curve for SN 2006gy and also shows that some massive stars can produce more than one supernova-like outburst.
I provide a short review of the properties of Narrow-line Seyfert 1 (NLS1) galaxies across the electromagnetic spectrum and of the models to explain them. Their continuum and emission-line properties manifest one extreme form of Seyfert activity. As such, NLS1 galaxies may hold important clues to the key parameters that drive nuclear activity. Their high accretion rates close to the Eddington rate provide new insight into accretion physics, their low black hole masses and perhaps young ages allow us to address issues of black hole growth, their strong optical FeII emission places strong constraints on FeII and perhaps metal formation models and physical conditions in these emission-line clouds, and their enhanced radio quiteness permits a fresh look at causes of radio loudness and the radio-loud radio-quiet bimodality in AGN.
We analyze the electromotive force (EMF) terms and basic assumptions of the linear and nonlinear dynamo theories in our three-dimensional (3D) numerical model of the Parker instability with cosmic rays and shear in a galactic disk. We also apply the well known prescriptions of the EMF obtained by the nonlinear dynamo theory (Blackman & Field 2002 and Kleeorin et al. 2003) to check if the EMF reconstructed from their prescriptions corresponds to the EMF obtained directly from our numerical models. We show that our modeled EMF is fully nonlinear and it is not possible to apply any of the considered nonlinear dynamo approximations due to the fact that the conditions for the scale separation are not fulfilled.
The direct detection of gravitational waves will provide valuable astrophysical information about many celestial objects. Also, it will be an important test to general relativity and other theories of gravitation. The gravitational wave detector SCHENBERG has recently undergone its first test run. It is expected to have its first scientific run soon. In this work the data analysis system of this spherical, resonant mass detector is tested through the simulation of the detection of gravitational waves generated during the inspiralling phase of a binary system. It is shown from the simulated data that it is not necessary to have all six transducers operational in order to determine the source's direction and the wave's amplitudes.
We present results of non-linear 2D numerical simulations of magneto-acoustic wave propagation in the photosphere and chromosphere of small-scale flux tubes with internal structure. Waves with realistic periods of 3--5 min are studied, after applying horizontal and vertical oscillatory perturbations to the equilibrium situation. Spurious reflections of shock waves from the upper boundary are minimized thanks to a special boundary condition. This has allowed us to increase the duration of the simulations and to make it long enough to perform a statistical analysis of oscillations. The simulations show that deep horizontal motions of the flux tube generate a slow (magnetic) mode and a surface mode. These modes are efficiently transformed into a slow (acoustic) mode in the Va < Cs atmosphere. The slow (acoustic) mode propagates vertically along the field lines, forms shocks and remains always within the flux tube. It might deposit effectively the energy of the driver into the chromosphere. When the driver oscillates with a high frequency above the cut-off, the non-linear wave propagation occurs with the same dominant driver period at all heights. At low frequencies below the cut-off, the dominant period of oscillations changes with height from 5 minutes in the photosphere to 3 minutes in the chromosphere. Depending on the period and on the type of the driver, different shock patterns are observed.
We report the first determination of a distance bracket for the high-velocity cloud (HVC) complex C. Combined with previous measurements showing that this cloud has a metallicity of 0.15 times solar, these results provide ample evidence that complex C traces the continuing accretion of intergalactic gas falling onto the Milky Way. Accounting for both neutral and ionized hydrogen as well as He, the distance bracket implies a mass of 3-14x10^6 M_sun, and the complex represents a mass inflow of 0.1-0.25 M_sun/yr. We base our distance bracket on the detection of CaII absorption in the spectrum of the blue horizontal branch star SDSS J120404.78+623345.6, in combination with a significant non-detection toward the BHB star BS 16034-0114. These results set a strong distance bracket of 3.7-11.2 kpc on the distance to complex C. A more weakly supported lower limit of 6.7 kpc may be derived from the spectrum of the BHB star BS 16079-0017.
It has been suggested that fossil groups could be the cannibalized remains of compact groups, that lost energy through tidal friction. However, in the nearby universe, compact groups which are close to the merging phase and display a wealth of interacting features (such as HCG 31 and HCG 79) have very low velocity dispersions and poor neighborhoods, unlike the massive, cluster-like fossil groups studied to date. In fact, known z=0 compact groups are very seldom embedded in massive enough structures which may have resembled the intergalactic medium of fossil groups. In this paper we study the dynamical properties of CG6, a massive compact group at z=0.220 that has several properties in common with known fossil groups. We report on new g' and i' imaging and multi-slit spectroscopic performed with GMOS on Gemini South. The system has 20 members, within a radius of 1 h_70^-1 Mpc, a velocity dispersion of 700 km/s and has a mass of 1.8 x 10^14 h_70^-1 Msun, similar to that of the most massive fossil groups known. The merging of the four central galaxies in this group would form a galaxy with magnitude M_r' ~ -23.4, typical for first-ranked galaxies of fossil groups. Although nearby compact groups with similar properties to CG 6 are rare, we speculate that such systems occurred more frequently in the past and they may have been the precursors of fossil groups.
We present the results of Spitzer mid-infrared spectroscopic observations of two highly-obscured massive X-ray binaries: IGR J16318-4848 and GX301-2. Our observations reveal for the first time the extremely rich mid-infrared environments of this type of source, including multiple continuum emission components (a hot component with T > 700 K and a warm component with T ~ 180 K) with apparent silicate absorption features, numerous HI recombination lines, many forbidden ionic lines of low ionization potentials, and pure rotational H2 lines. This indicates that both sources have hot and warm circumstellar dust, ionized stellar winds, extended low-density ionized regions, and photo-dissociated regions. It appears difficult to attribute the total optical extinction of both sources to the hot and warm dust components, which suggests that there could be an otherwise observable colder dust component responsible for the most of the optical extinction and silicate absorption features. The observed mid-infrared spectra are similar to those from Luminous Blue Variables, indicating that the highly-obscured massive X-ray binaries may represent a previously unknown evolutionary phase of X-ray binaries with early-type optical companions. Our results highlight the importance and utility of mid-infrared spectroscopy to investigate highly-obscured X-ray binaries.
Anisotropy in the point spread function (PSF) contributes a systematic error to weak lensing measurements. In this study we use a ray tracer that incorporates all the optical elements of the SNAP telescope to estimate this effect. Misalignments in the optics generates PSF anisotropy, which we characterize by its ellipticity. The effect of three time varying effects: thermal drift, guider jitter, and structural vibration on the PSF are estimated for expected parameters of the SNAP telescope. Multiple realizations of a thousand square degree mock survey are then generated to include the systematic error pattern induced by these effects. We quantify their contribution to the power spectrum of the lensing shear. We find that the dominant effect comes from the thermal drift, which peaks at angular wavenumbers l ~ 10^3, but its amplitude is over one order of magnitude smaller than the size of the expected statistical error. While there are significant uncertainties in our modeling, our study indicates that time-varying PSFs will contribute at a smaller level than statistical errors in SNAP's weak lensing measurements.
The possibility of a mean-field dynamo in nonhelical turbulence with superimposed linear shear is studied numerically in elongated shearing boxes. Exponential growth of magnetic field at scales much larger than the outer scale of the turbulence is found. The charateristic scale of the field is ~ S^{-1/2} and growth rate is gamma ~ S, where S is the shearing rate. This newly discovered form of large-scale dynamo action may have an extremely broad range of applications to astrophysical systems with spatially coherent mean flows.
Very high energy (VHE) gamma-ray observations have proven to be very successful in localizing Galactic acceleration sites of VHE particles. Observations of shell-type supernova remnants have confirmed that particles are accelerated to VHE energies in supernova blast waves; the interpretation of the gamma-ray data in terms of hadronic or leptonic particle components in these objects relies nevertheless strongly on input from X-ray observations. The largest identified Galactic VHE source class consists of pulsar wind nebulae, as detected in X-rays. Many of the remaining VHE sources remain however unidentified until now. With X-ray observations of these enigmatic "dark" objects one hopes to solve the following questions: What is the astrophysical nature of these sources? Are they predominantly electron or hadron accelerators? And what is their contribution to the overall cosmic ray energy budget? The paper aims to provide an overview over the identification status of the Galactic VHE source population.
The focusing of the radiation generated by a polarization current with a superluminally rotating distribution pattern is of a higher order in the plane of rotation than in other directions. Consequently, our previously published asymptotic approximation to the value of this field outside the equatorial plane breaks down as the line of sight approaches a direction normal to the rotation axis, i.e., is nonuniform with respect to the polar angle. Here we employ an alternative asymptotic expansion to show that, though having a rate of decay with frequency (mu) that is by a factor of order mu^(2/3) slower, the equatorial radiation field has the same dependence on distance as the nonspherically decaying component of the generated field in other directions: it, too, diminishes as the inverse square root of the distance from its source. We also briefly discuss the relevance of these results to the giant pulses received from pulsars: the focused, nonspherically decaying pulses that arise from a superluminal polarization current in a highly magnetized plasma have a power-law spectrum (i.e., a flux density proportional to mu^alpha) whose index (alpha) is given by one of the values -2/3, -2, -8/3, or -4.
Using a numerical simulation, we study the effects of ambipolar diffusion and ohmic diffusion on the magnetic field evolution in the interior of an isolated neutron star. We are interested in the behavior of the magnetic field on a long time scale, over which all Alfven and sound waves have been damped. We model the stellar interior as an electrically neutral plasma composed of neutrons, protons and electrons, which can interact with each other through collisions and electromagnetic forces. Weak interactions convert neutrons and charged particles into each other, erasing chemical imbalances. As a first step, we assume that the magnetic field points in one fixed Cartesian direction but can vary along an orthogonal direction. We start with a uniform-density background threaded by a homogeneous magnetic field and study the evolution of a magnetic perturbation as well as the density fluctuations it induces in the particles. We show that the system evolves through different quasi-equilibrium states and estimate the characteristic time scales on which these quasi-equilibria occur.
Simulating the data that a space instrument like COROT will provide might
look presomptuous. Indeed, it is certainly, when comparing to previous
comparable instruments like IPHIR or GOLF. These two examples show that the
nominal behaviour of the instrument is not always reached, but this does not
prevent this instrument to provide very interesting data. However, despite some
technical problems, IPHIR and GOLF yielded a wealth of scientific results.
Thus, what is the interest of simulating COROT data? How close to reality these
simualtions will get? This might not be the most important fact as the
preparation of these simulations will help us to prepare the analysis of real
data and to be ready in case of unexpected technical behaviour of the
instrument perturbating the data, or unexpected physical behaviour of the
targets of the instrument. A consequence of that is that the simulation tool
must include technical and physical aspects, making the task even more
difficult. These aspects cover: photon noise, p modes excitation, granulation
signal, stellar activity signal, orbital perturbations, stellar rotation...
The software presented here is freely available at:
this http URL
We present optical and X-ray data for the first object showing strong evidence for being a black hole in a globular cluster. We show the initial X-ray light curve and X-ray spectrum which led to the discovery that this is an extremely bright, highly variable source, and thus must be a black hole. We present the optical spectrum which unambiguously identifies the optical counterpart as a globular cluster, and which shows a strong, broad [O III] emission line, most likely coming from an outflow driven by the accreting source.
We consider a scenario of cosmological inflation coming from a grand unified theory in higher dimensional orbifold. Flatness of the potential is automatically guaranteed in this orbifold setup thanks to the nonlocality of the Wilson line on higher dimensions and the local quantum gravitational corrections are exponentially suppressed. The spectral index of scalar perturbation (n_s =0.92 - 0.97) and a significant production of gravitational waves are predicted (r= T/S= 0.01 - 0.12) in the perturbative regime of gauge interaction, (1/g_4 = (5-20) X 2 pi R Mpl) where the size of compactification is constrained (R Mpl = 20- 45) by the measurement of scalar power spectrum (Delta_R = 5 X 10^-5).
In this note we present global string solutions which are a generalization of the usual field theory global vortices when the kinetic term is DBI. Such vortices can result from the spontaneous symmetry breaking in the potential felt by a D3-brane. In a previous paper (0706.0485), the DBI instanton solution was constructed which develops a "wrinkle" for stringy heights of the potential. A similar effect is also seen for the DBI vortex solution. The wrinkle develops for stringy heights of the potential. One recovers the usual field theory global string for substringy potentials. As an example of the symmetry breaking, we consider a mobile D3-brane on the warped deformed conifold. Symmetry breaking can occur if the structure of the vacuum manifold of the potential for the D3-brane changes as it moves through the throat region.
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[Abridged] As part of our on-going investigation of magnetic activity in ultracool dwarfs we present simultaneous radio, X-ray, UV, and optical observations of LSR1835+32 (M8.5), and simultaneous X-ray and UV observations of VB10 (M8), both with a duration of about 9 hours. LSR1835+32 exhibits persistent radio emission and H-alpha variability on timescales of ~0.5-2 hr. The detected UV flux is consistent with photospheric emission, and no X-ray emission is detected to a deep limit of L_X/L_bol<10^-5.7. The H-alpha and radio emission are temporally uncorrelated, and the ratio of radio to X-ray luminosity exceeds the correlation seen in F-M6 stars by >2x10^4. Similarly, L_Halpha/L_X>10 is at least 30 times larger than in early M dwarfs, and eliminates coronal emission as the source of chromospheric heating. The lack of radio variability during four rotations of LSR1835+32 requires a uniform stellar-scale field of ~10 G, and indicates that the H-alpha variability is dominated by much smaller scales, <10% of the chromospheric volume. VB10, on the other hand, shows correlated flaring and quiescent X-ray and UV emission, similar to the behavior of early M dwarfs. Delayed and densely-sampled optical spectra exhibit a similar range of variability amplitudes and timescales to those seen in the X-rays and UV, with L_Halpha/L_X~1. Along with our previous observations of the M8.5 dwarf TVLM513-46546 we conclude that late M dwarfs exhibit a mix of activity patterns, which points to a transition in the structure and heating of the outer atmosphere by large-scale magnetic fields. We find that rotation may play a role in generating the fields as evidenced by a tentative correlation between radio activity and rotation velocity. The X-ray emission, however, shows evidence for super-saturation at vsini>25 km/s.
We investigate the stellar populations of a sample of 162 Lyman-alpha emitting galaxies (LAEs) at z = 3.1 in the Extended Chandra Deep Field South, using deep Spitzer IRAC data available from the GOODS and SIMPLE surveys to derive reliable stellar population estimates. We divide the LAEs according to their rest-frame near-IR luminosities into IRAC-detected and IRAC-undetected samples. About 70% of the LAEs are undetected in 3.6 micron down to [3.6] = 25.2 AB. Stacking analysis reveals that the average stellar population of the IRAC-undetected sample has an age of ~ 200 Myr and a mass of ~ 3x10^8 solar masses, consistent with the expectation that LAEs are mostly young and low-mass galaxies. On the other hand, the IRAC-detected LAEs are on average significantly older and more massive, with an average age > 1 Gyr and mass ~ 10^10 solar masses. Comparing the IRAC colors and magnitudes of the LAEs to z ~ 3 Lyman break galaxies (LBGs) shows that the IRAC-detected LAEs lie at the faint blue end of the LBG color-magnitude distribution, suggesting that IRAC-detected LAEs may be the low mass extension of the LBG population. We also present tentative evidence for a small fraction (~ 5%) of obscured AGN within the LAE sample. Our results suggest that LAEs posses a wide range of ages and masses. Additionally, the presence of evolved stellar populations inside LAEs suggests that the Lyman-alpha luminous phase of galaxies may either be a long-lasting or recurring phenomenon.
We analyze systematics in the asteroseismological mass determination methods in pulsating PG 1159 stars. We compare the seismic masses resulting from the comparison of the observed mean period spacings with the usually adopted asymptotic period spacings, and the average of the computed period spacings. Computations are based on full PG1159 evolutionary models with stellar masses ranging from 0.530 to 0.741 Mo that take into account the complete evolution of progenitor stars. We conclude that asteroseismology is a precise and powerful technique that determines the masses to a high internal accuracy, but it depends on the adopted mass determination method. In particular, we find that in the case of pulsating PG 1159 stars characterized by short pulsation periods, like PG 2131+066 and PG 0122+200, the employment of the asymptotic period spacings overestimates the stellar mass by about 0.06 Mo as compared with inferences from the average of the period spacings. In this case, the discrepancy between asteroseismological and spectroscopical masses is markedly reduced when use is made of the mean period spacing instead of the asymptotic period spacing.
We modify a stellar structure code to estimate the effect upon the main sequence of the accretion of weakly interacting dark matter onto stars and its subsequent annihilation. The effect upon the stars depends upon whether the energy generation rate from dark matter annihilation is large enough to shut off the nuclear burning in the star. Main sequence WIMP burners look much like protostars moving on the Hayashi track, although they are in principle completely stable. We make some brief comments about where such stars could be found, how they might be observed and more detailed simulations which are currently in progress. Finally we comment on whether or not it is possible to link the paradoxically young OB stars found at the galactic centre with WIMP burners.
The existence of power law statistics in solar and stellar flares has prompted the suggestion that solar and stellar coronae are in a self-organized critical state, but the physical foundation of this theory is lacking. We present observational evidence from 107 flare events in 37 sun-like stars that solar and stellar coronae self-organize into a critical state set by a bifurcation in the dynamics of magnetic reconnection that initiates coronal eruptions.
We investigate whether the globular clusters (GCs) in the recently published sample of GCs in the Fornax cluster by Bergond and coworkers are indeed intra-cluster objects. We combine the catalogue of radial velocity measurements by Bergond et al. with our CTIO MOSAIC photometry in the Washington system and analyse the relation of metal-poor and metal-rich GCs with their host galaxies. The metal-rich GCs appear to be kinematically associated with their respective host galaxies. The vast majority of the metal-poor GCs found in between the galaxies of the Fornax cluster have velocities which are consistent with them being members of the very extended NGC 1399 GC system. We find that when the sample is restricted to the most accurate velocity measurements, the GC velocity dispersion profile can be described with a mass model derived for the NGC 1399 GC system within 80 kpc. We identify one ``vagrant'' GC whose radial velocity suggests that it is not bound to any galaxy unless its orbit has a very large apogalactic distance.
Observations of collimated outflows in young stellar objects indicate that several features of the jets can be understood by adopting the picture of a two-component outflow, wherein a central stellar component around the jet axis is surrounded by an extended disk-wind. The precise contribution of each component may depend on the intrinsic physical properties of the YSO-disk system as well as its evolutionary stage. In this context, the present article starts a systematic investigation of two-component jet models via time-dependent simulations of two prototypical and complementary analytical solutions, each closely related to the properties of stellar-outflows and disk-winds. These models describe a meridionally and a radially self-similar exact solution of the steady-state, ideal hydromagnetic equations, respectively. By using the PLUTO code to carry out the simulations, the study focuses on the topological stability of each of the two analytical solutions, which are successfully extended to all space by removing their singularities. In addition, their behavior and robustness over several physical and numerical modifications is extensively examined. It is found that radially self-similar solutions (disk-winds) always reach a final steady-state while maintaining all their well-defined properties. The different ways to replace the singular part of the solution around the symmetry axis, being a first approximation towards a two-component outflow, lead to the appearance of a shock at the super-fast domain corresponding to the fast magnetosonic separatrix surface. Conversely, the asymptotic configuration and the stability of meridionally self-similar models (stellar-winds) is related to the heating processes at the base of the wind.
The WIRE satellite was launched in March 1999 and was the first space mission to do asteroseismology from space on a large number of stars. WIRE has produced very high-precision photometry of a few hundred bright stars (V<6) with temporal coverage of several weeks, including K giants, solar-like stars, delta Scuti stars, and beta Cepheids. In the current work we will describe the status of science done on seven detached eclipsing binary systems. Our results emphasize some of the challenges and exciting results expected from coming satellite missions like COROT and Kepler. Unfortunately, on 23 October 2006, communication with WIRE failed after almost eight years in space. Because of this sad news we will give a brief history of WIRE at the end of this paper.
The H.E.S.S. collaboration recently reported the discovery of VHE gamma-ray emission coincident with the young stellar cluster Westerlund 2. This system is known to host a population of hot, massive stars, and, most particularly, the WR binary WR20a. Particle acceleration to TeV energies in Westerlund 2 can be accomplished in several alternative scenarios, therefore we only discuss energetic constraints based on the total available kinetic energy in the system, the actual mass loss rates of respective cluster members, and implied gamma-ray production from processes such as inverse Compton scattering or neutral pion decay. From the inferred gamma-ray luminosity of the order of 10^35 erg/s, implications for the efficiency of converting available kinetic energy into non-thermal radiation associated with stellar winds in the Westerlund 2 cluster are discussed under consideration of either the presence or absence of wind clumping.
We explore a simple model for the high luminosity of SN 2006gy involving photon diffusion of shock-deposited thermal energy. The distinguishing property of the model is that the large ``stellar'' radius of 160 AU required to prevent adiabatic losses is not the true stellar radius, but rather, the radius of an opaque, unbound circumstellar envelope, created when 10 Msun was ejected in the decade before the supernova in an eruption analogous to that of eta Carinae. The supernova light is produced primarily by diffusion of thermal energy following the passage of the blast wave through this shell. This model differs from traditional models of supernova debris interacting with external CSM in that here the shell is optically thick and the escape of radiation is delayed. We show that any model attempting to account for SN2006gy's huge luminosity with radiation emitted by ongoing CSM interaction fails for the following basic reason: the CSM density required to achieve the observed luminosity makes the same circumstellar envelope opaque, forcing a thermal diffusion solution. In our model, the weaker CSM interaction giving rise to SN2006gy's characteristic Type IIn spectrum and soft X-rays is not linked to the power source of the visual continuum; instead, it arises after the blast wave breaks free of the opaque shell into the surrounding wind. While a simple diffusion model can explain the gross properties of the early light curve of SN2006gy, it predicts that the light curve must plummet rapidly at late-times, unless an additional power source is present.
I discuss observational evidence -- independent of the direct spectral diagnostics of stellar winds themselves -- suggesting that mass-loss rates for O stars need to be revised downward by roughly a factor of three or more, in line with recent observed mass-loss rates for clumped winds. These independent constraints include the large observed mass-loss rates in LBV eruptions, the large masses of evolved massive stars like LBVs and WNH stars, WR stars in lower metallicity environments, observed rotation rates of massive stars at different metallicity, supernovae that seem to defy expectations of high mass-loss rates in stellar evolution, and other clues. I pay particular attention to the role of feedback that would result from higher mass-loss rates, driving the star to the Eddington limit too particular attention to the role of feedback that would result from higher mass-loss rates, driving the star to the Eddington limit too soon, and therefore making higher rates appear highly implausible. Some of these arguments by themselves may have more than one interpretation, but together they paint a consistent picture that steady line-driven winds of O-type stars have lower mass-loss rates and are significantly clumped.
SN 2006gy radiated far more energy in visual light than any other supernova so far, and potential explanations for its energy demands have implications for galactic chemical evolution and the deaths of the first stars. It remained bright for over 200 days, longer than any normal supernova, and it radiated more than 1e51 ergs of luminous energy at visual wavelengths. I argue that this Type IIn supernova was probably the explosion of an extremely massive star like Eta Carinae that retained its hydrogen envelope when it exploded, having suffered relatively little mass loss during its lifetime. That this occurred at roughly Solar metallicity challenges current paradigms for mass loss in massive-star evolution. I explore a few potential explanations for SN2006gy's power source, involving either circumstellar interaction, or instead, the decay of 56Ni. If SN 2006gy was powered by the conversion of shock energy into light, then the conditions must be truly extraordinary and traditional interaction models don't work. If SN 2006gy was powered by radioactive decay, then the uncomfortably huge 56Ni mass requires that the star exploded as a pair instability supernova. The mere possibility of this makes SN 2006gy interesting, especially at this meeting, because it is the first good candidate for a genuine pair instability supernova.
The energy losses of a small black hole passing through the Earth are examined. In particular, we investigate the excitations in the frequency range accessible to modern acoustic detectors. The main contribution to the effect is given by the coherent sound radiation of the Cherenkov type.
We performed a timing analysis of the 2003 outburst of the accreting X-ray millisecond pulsar XTE J1807-294 observed by RXTE. Using recently refined orbital parameters we report for the first time a precise estimate of the spin frequency and of the spin frequency derivative. The phase delays of the pulse profile show a strong erratic behavior superposed to what appears as a global spin-up trend. The erratic behavior of the pulse phases is strongly related to rapid variations of the light curve, making it very difficult to fit these phase delays with a simple law. As in previous cases, we have therefore analyzed separately the phase delays of the first harmonic and of the second harmonic of the spin frequency, finding that the phases of the second harmonic are far less affected by the erratic behavior. In the hypothesis that the second harmonic pulse phase delays are a good tracer of the spin frequency evolution we give for the first time a estimation of the spin frequency derivative in this source. The source shows a clear spin-up of $\dot \nu = 2.5^{+1.0}_{-1.1} \times 10^{-14}$ Hz sec$^{-1}$ (90% confidence level). The largest source of uncertainty in the value of the spin-up rate is given by the uncertainties on the source position in the sky. We discuss this systematics on the spin frequency and its derivative.
There are now four low mass X-ray binaries with black holes which show twin resonant-like HFQPOs. Similar QPOs might have been found in Sgr A*. I review the power spectral density distributions of the three X-ray flares and the six NIR flares published for Sgr A* so far, in order to look for more similarities than just the frequencies between the microquasar black holes and Sgr A*. The three X-ray flares of Sgr A* are re-analysed in an identical way and white noise probabilities from their power density distributions are given for the periods reported around 1100 s. Progress of the resonant theory using the anomalous orbital velocity effect is summarized.
We present the results of a deep, wide-field search for transiting `Hot Jupiter (HJ)' planets in the globular cluster omega Centauri. As a result of a 25-night observing run with the ANU 40-inch telescope at Siding Spring Observatory, a total of 109,726 stellar time series composed of 787 independent data points were produced with differential photometry in a 52x52' (0.75 deg^2) field centered on the cluster core, but extending well beyond. Taking into account the size of transit signals as a function of stellar radius, 45,406 stars have suitable photometric accuracy (<=0.045 mag to V=19.5) to search for transits. Of this sample, 31,000 stars are expected to be main sequence cluster members. All stars, both cluster and foreground, were subjected to a rigorous search for transit signatures; none were found. Extensive Monte Carlo simulations based on our actual data set allows us to determine the sensitivity of our survey to planets with radii ~1.5R_Jup, and thus place statistical upper limits on their occurrence frequency 'F'. Smaller planets are undetectable in our data. At 95% confidence, the frequency of Very Hot Jupiters (VHJs) with periods P satisfying 1d<P<3d can be no more than F_VHJ < 1/1040 in omega Cen. For HJ and VHJ distributed uniformly over the orbital period range 1d<P<5d, F_VHJ+HJ < 1/600. Our limits on large, short-period planets are comparable to those recently reported for other Galactic fields, despite being derived with less telescope time.
We use Monte-Carlo simulations, combined with homogeneously determined age and mass distributions based on multi-wavelength photometry, to constrain the cluster formation history and the rate of bound cluster disruption in the Large Magellanic Cloud (LMC) cluster system. We evolve synthetic star cluster systems formed with a power-law initial cluster mass function (ICMF) of spectral index $\alpha =-2$ assuming different cluster disruption time-scales. For each of these disruption time-scales we derive the corresponding cluster formation rate (CFR) required to reproduce the observed cluster age distribution. We then compare, in a Poissonian $\chi^2$ sense, model mass distributions and model two-dimensional distributions in log(mass) vs. log(age) space of the detected surviving clusters to the observations. Because of the bright detection limit ($M_V^{\rm lim} \simeq -4.7$ mag) above which the observed cluster sample is complete, one cannot constrain the characteristic disruption time-scale for a $10^4$ M$_\odot$ cluster, $t_4^{\rm dis}$ (where the disruption time-scale depends on cluster mass as $t_{\rm dis} = t_4^{\rm dis} (M_{\rm cl} / 10^4 {\rm M}_\odot)^0.62$), to better than $t_4^{\rm dis} \ge 1$ Gyr. We conclude that the CFR has increased from 0.3 clusters Myr$^{-1}$ 5 Gyr ago, to a present rate of $(20-30)$ clusters Myr$^{-1}$. For older ages the derived CFR depends sensitively on our assumption of the underlying CMF shape. If we assume a universal Gaussian ICMF, then the CFR has increased steadily over a Hubble time from $\sim 1$ cluster Gyr$^{-1}$ 15 Gyr ago to its present value. If the ICMF has always been a power law with a slope close to $\alpha=-2$, the CFR exhibits a minimum some 5 Gyr ago, which we tentatively identify with the well-known age gap in the LMC's cluster age distribution.
Smooth double crossing of the phantom divide line $w_{\Lambda}=-1$ has been found possible with a single minimally coupled scalar field for a most simple form of generalized k-essence cosmological model, in the presence of background cold dark matter. Such crossing is a sufficiently late time transient phenomena and thus does not have any pathological behaviour.
(Shortened) Ultraviolet observations of the black hole X-ray binary Cygnus X-1 were obtained using the STIS on HSTubble. We detect P Cygni line features show strong, broad absorption components when the X-ray source is behind the companion star and noticeably weaker absorption when the X-ray source is between us and the companion star. We fit the P Cygni profiles using the SEI method applied to a spherically symmetric stellar wind subject to X-ray photoionization from the black hole. The Si IV doublet provides the most reliable estimates of the parameters of the wind and X-ray illumination. The velocity $v$ increases with radius $r$ according to $v=v_\infty(1-r_\star/r)^\beta$, with$\beta\approx0.75$ and $v_\infty\approx1420$ km s$^{-1}$.The microturbulent velocity was $\approx160$ km s$^{-1}$. Our fit implies a ratio of X-ray luminosity to wind mass-loss rate of L$_{X,38}/\dot M_{-6} \approx 0.33$, measured at $\dot M_{-6}$ = 4.8. Our models determine parameters that may be used to estimate the accretion rate onto the black hole and independently predict the X-ray luminosity. Our predicted L$_x$ matches that determined by contemporaneous RXTE ASM remarkably well, but is a factor of 3 lower than the rate according to Bondi-Hoyle-Littleton spherical wind accretion. We suggest that some of the energy of accretion may go into powering a jet.
The dynamics of cosmological gravitating system is governed by the Euler and the Poisson equations. Tiny fluctuations near the big bang singularity are amplified by gravitational instability into the observed structure today. Given the current distribution of galaxies and assuming initial homogeneity, dynamical reconstruction methods have been developed to derive the cosmic density and velocity fields back in time. The reconstruction method described here is based a least action principle formulation of the dynamics of collisionless particle (representing galaxies). Two observational data sets will be considered. The first is the distribution of galaxies which is assumed to be an honest tracer of the mass density field of the dark matter. The second set is measurements of the peculiar velocities (deviations from pure Hubble flow) of galaxies. Given the first data set, the reconstruction method recovers the associated velocity field which can then be compared with the second data set. This comparison constrains the nature of the dark matter and the relation between mass and light in the Universe.
We investigate the manifestation of the spiral structure in the distribution of high-mass X-ray binaries (HMXBs) over the host galaxy. We construct the simple kinematic model. It shows that the HMXBs should be displaced relative to the spiral structure observed in such traditional star formation rate indicators as the Halpha and FIR emissions because of their finite lifetimes. Using Chandra observations of M51, we have studied the distribution of X-ray sources relative to the spiral arms of this galaxy observed in Halpha. Based on K-band data and background source number counts, we have separated the contributions from high-mass and low-mass X-ray binaries and active galactic nuclei. In agreement with model predictions, the distribution of HMXBs is wider than that of bright HII regions concentrated in the region of ongoing star formation. However, the statistical significance of this result is low, as is the significance of the concentration of the total population of X-ray sources to the spiral arms. We also predict the distribution of HMXBs in our Galaxy in Galactic longitude. The distribution depends on the mean HMXB age and can differ significantly from the distributions of such young objects as ultracompact HII regions.
Equations of fully general relativistic radiation hydrodynamics around a rotating black hole are derived by using the Kerr-Schild coordinate where there is no coordinate singularity at the event horizon. Since the radiation interacts with matter moving with relativistic velocities near the event horizon, the interplay between the radiation and the matter should be described fully relativistically. In the formalism used in this study, while the interactions between matter and radiation are introduced in the comoving frame, the equations and the equations and the derivatives for the description of the global evolution of both matter and the radiation are given in the Kerr-Schild frame (KSF) which is a frame fixed to the coordinate describing the central black hole. As a frame fixed to the coordinate, we use the locally non-rotating reference frame (LNRF) representing a radially falling frame when the Kerr-Schild coordinate is used. Around the rotating black hole, both the matter and the radiation are affected by the frame-dragging effects.
Forty years after the discovery of rotation-powered pulsars, we still do not understand many aspects of their pulsed emission. In the last few years there have been some fundamental developments in acceleration and emission models. I will review both the basic physics of the models as well as the latest developments in understanding the high-energy emission of rotation-powered pulsars, with particular emphasis on the polar-cap and slot-gap models. Special and general relativistic effects play important roles in pulsar emission, from inertial frame-dragging near the stellar surface to aberration, time-of-flight and retardation of the magnetic field near the light cylinder. Understanding how these effects determine what we observe at different wavelengths is critical to unraveling the emission physics. I will discuss how current and future X-ray and gamma-ray detectors can test the predictions of these models.
The results from H.E.S.S. observations towards Westerlund 2 are presented. The detection of very-high-energy gamma-ray emission towards the young stellar cluster Westerlund 2 in the HII complex RCW49 by H.E.S.S. provides ample evidence that particle acceleration to extreme energies is associated with this region. A variety of possible emission scenarios is mentioned, ranging from high-energy gamma-ray production in the colliding wind zone of the massive Wolf-Rayet binary WR20a, collective wind scenarios, diffusive shock acceleration at the boundaries of wind-blown bubbles in the stellar cluster, and outbreak phenomena from hot stellar winds into the interstellar medium. These scenarios are briefly compared to the characteristics of the associated new VHE gamma-ray source HESS J1023-575, and conclusions on the validity of the respective emission scenarios for high-energy gamma-ray production in the Westerlund 2 system are drawn.
Observational evidence exists that winds of massive stars are clumped. Many massive star systems are known as non-thermal particle production sites, as indicated by their synchrotron emission in the radio band. As a consequence they are also considered as candidate sites for non-thermal high-energy photon production up to gamma-ray energies. The present work considers the effects of wind clumpiness expected on the emitting relativistic particle spectrum in colliding wind systems, built up from the pool of thermal wind particles through diffusive particle acceleration, and taking into account inverse Compton and synchrotron losses. In comparison to a homogeneous wind, a clumpy wind causes flux variations of the emitting particle spectrum when the clump enters the wind collision region. It is found that the spectral features associated with this variability moves temporally from low to high energy bands with the time shift between any two spectral bands being dependent on clump size, filling factor, and the energy-dependence of particle energy gains and losses.
The High Energy Stereoscopic System (H.E.S.S.), located in the Khomas Highlands of Namibia, is an array of four imaging atmospheric-Cherenkov telescopes designed to detect gamma-rays in the very high energy (VHE; > 100 GeV) domain. Its high sensitivity and large field-of-view (5 deg) make it an ideal instrument to perform a survey within the Galactic plane for new VHE sources. Previous observations in 2004/2005 resulted in numerous detections of VHE gamma-ray emitters in the region l = 330 deg - 30 deg Galactic longitude. Recently the survey was extended, covering the regions l = 280 deg - 330 deg and l = 30 deg - 60 deg, leading to the discovery of several previously unknown sources with high statistical significance. The current status of the survey will be presented.
We present the first measurements of the angular correlation function of galaxies selected in the far (1530 A) and near (2310 A) Ultraviolet from the GALEX survey fields overlapping SDSS DR5 in low galactic extinction regions. The area used covers 120 sqdeg (GALEX - MIS) down to magnitude AB = 22, yielding a total of 100,000 galaxies. The mean correlation length is ~ 3.7 \pm 0.6 Mpc and no significant trend is seen for this value as a function of the limiting apparent magnitude or between the GALEX bands. This estimate is close to that found from samples of blue galaxies in the local universe selected in the visible, and similar to that derived at z ~ 3 for LBGs with similar rest frame selection criteria. This result supports models that predict anti-biasing of star forming galaxies at low redshift, and brings an additional clue to the downsizing of star formation at z<1.
Aims: We investigate the influence of high-energy stellar radiation at close-in orbits on atmospheric mass loss during stellar evolution of a G-type star. Methods: High-energy stellar luminosity varies over a wide range for G field stars. The temporal evolution of the distribution of stellar X-ray luminosity and its influence on the evolution of close-in exoplanets is investigated. X-ray luminosity distributions from the Pleiades, the Hyades and the field are used to derive a scaling law for the evolution of the stellar X-ray luminosity distribution. A modified energy-limited escape approach is used to calculate atmospheric mass loss for a broad range of planetary parameters. Results: We show that the evolution of close-in exoplanets strongly depends on the detailed X-ray luminosity history of their host stars, which varies over several orders-of-magnitude for G stars. Stars located at the high-energy tail of the luminosity distribution can evaporate most of its planets within 0.5 AU, while for a moderate luminosity a significant fraction of planets can survive. We show the change on an initial planetary mass distribution caused by atmospheric escape.
The massive OB-type binary sigma Ori AB is in the centre of the very young sigma Orionis cluster. I have computed the most probable distances and masses of the binary for several ages using a dynamical parallax-like method. It incorporates the BVRIH-band apparent magnitudes of both components, precise orbital parameters, interstellar extinction and a widely used grid of stellar models from the literature, the Kepler's third law and a chi^2 minimisation. The derived distance is 334^(+25)_(-22) pc for an age of 3+/-2 Ma; larger ages and distances are unlikely. The masses of the primary and the secondary lie on the approximate intervals 16-20 and 10-12 Msol, respectively. I also discuss the possibility of sigma Ori AB being a triple system at ~385 pc. These results will help to constrain the properties of young stars and substellar objects in the sigma Orionis cluster.
For some time, the Draco dwarf spheroidal galaxy has garnered interest as a possible source for the indirect detection of dark matter. Its large mass-to-light ratio and relative proximity to the Earth provide favorable conditions for the production of detectable gamma rays from dark matter self-annihilation in its core. The Solar Tower Atmospheric Cherenkov Effect Experiment (STACEE) is an air-shower Cherenkov telescope located in Albuquerque, NM capable of detecting gamma rays at energies above 100 GeV. We present the results of the STACEE observations of Draco during the 2005-2006 observing season totaling 10 hours of livetime after cuts.
We present stellar evolution calculations for Population III stars for both single and binary star evolution. Our models include 10 Msun and 16.5 Msun single stars and a 10 Msun model star that undergoes an episode of accretion resulting in a final mass of 16.1 Msun. For comparison, we present the evolution of a solar heavy element abundance model. We use the structure from late stage evolution models to calculate simulated supernova light curves. Light curve comparisons are made between accretion and non-accretion progenitor models, and models for single star evolution of comparable masses. Where possible, we make comparisons to previous works. Similar investigations have been carried out, but primarily for solar or near solar heavy metal abundance stars and not including both the evolution and supernovae explosions in one work.
Luminous red galaxies (LRGs) are much rarer and more massive than L* galaxies. Coupled with their extreme colours, LRGs therefore provide a demanding testing ground for the physics of massive galaxy formation. We present the first self-consistent predictions for the abundance and properties of LRGs in hierarchical structure formation models. We test two published models which use quite different mechanisms to suppress the formation of massive galaxies: the Bower et al. (2006) model, which invokes ``AGN-feedback'' to prevent gas from cooling in massive haloes, and the Baugh et al. (2005) model which relies upon a ``superwind'' to eject gas before it is turned into stars. Without adjusting any parameters, these models predict abundances of LRGs which bracket the observations. In the models, LRGs are typically bulge dominated systems with stellar masses of ~ 2 x 10^11 h^{-1}M_sun and velocity dispersions of ~ 250 km s^{-1}. Around half of the stellar mass in the model LRGs is already formed by z ~ 2.2 and is assembled into one main progenitor by z ~ 1.5; on average, only 25% of the mass of the main progenitor is added after z ~ 1. LRGs are predicted to be found in a wide range of halo masses, a conclusion which relies on properly taking into account the scatter in the formation histories of haloes. Remarkably, we find that the correlation function of LRGs is predicted to be a power law down to small pair separations, in excellent agreement with observational estimates. The ``AGN-feedback'' model provides the best match to the abundance of LRGs; however, several of the properties predicted by the ``superwind'' model are in better agreement with observations. Neither model is able to reproduce the radii of LRGs.
We investigate the dynamics of magnetic fields in spiral galaxies by performing 3D MHD simulations of galactic discs subject to a spiral potential. Recent hydrodynamic simulations have demonstrated the formation of inter-arm spurs as well as spiral arm molecular clouds provided the ISM model includes a cold HI phase. We find that the main effect of adding a magnetic field to these calculations is to inhibit the formation of structure in the disc. However, provided a cold phase is included, spurs and spiral arm clumps are still present if $\beta \gtrsim 0.1$ in the cold gas. A caveat to two phase calculations though is that by assuming a uniform initial distribution, $\beta \gtrsim 10$ in the warm gas, emphasizing that models with more consistent initial conditions and thermodynamics are required. Our simulations with only warm gas do not show such structure, irrespective of the magnetic field strength. Furthermore, we find that the introduction of a cold HI phase naturally produces the observed degree of disorder in the magnetic field, which is again absent from simulations using only warm gas. Whilst the global magnetic field follows the large scale gas flow, the magnetic field also contains a substantial random component that is produced by the velocity dispersion induced in the cold gas during the passage through a spiral shock. Without any cold gas, the magnetic field in the warm phase remains relatively well ordered apart from becoming compressed in the spiral shocks. Our results provide a natural explanation for the observed high proportions of disordered magnetic field in spiral galaxies and we thus predict that the relative strengths of the random and ordered components of the magnetic field observed in spiral galaxies will depend on the dynamics of spiral shocks.
Using STIS and VLT UVES observations we have examined the ionization, abundances, and differential dust depletion of metals, the kinematic structure, and the physical conditions in the molecular hydrogen-bearing sub-damped Ly alpha system toward HE 0515-4414 at z = 1.15. The velocity interval of associated metal lines extends for 700 km/s. In addition, saturated H I absorption is detected in the blue damping wing of the main component. The column density ratios of associated Al II, Al III, and Fe II lines indicate that the absorbing material is ionized. 19 of in total 31 detected metal line components are formed within peripheral H II regions, while only 12 components are associated with the predominantly neutral main absorber. For the main absorber the observed abundance ratios of refractory elements to Zn range from Galactic warm disk [Si/Zn] = - 0.40, [Fe/Zn] = -1.10 to halo-like and essentially undepleted patterns. The dust-corrected metal abundances indicate a nucleosynthetic odd-even effect and might imply an anomalous depletion of Si relative to Fe for two components, but otherwise do correspond to solar ratios. The intrinsic average metallicity is almost solar [Fe/H] = -0.08, whereas the uncorrected average is [Zn/H] = -0.38. The ion abundances in the periphery conform with solar element composition. The detection of H II as well as the large variation in dust depletion for this sight line raises the question whether in future studies of damped Ly alpha systems ionization and depletion effects have to be considered in further detail. Ionization effects, for instance, may pretend an enrichment of alpha elements. An empirical recipe for detecting H II regions is provided.
We study the evolution of simple cosmic string loop solutions in an inflationary universe. We show, for the particular case of circular loops, that periodic solutions do exist in a de Sitter universe, below a critical loop radius $R_c H=1/2$. On the other hand, larger loops freeze in comoving coordinates, and we explicitly show that they can survive more $e$-foldings of inflation than point-like objects. We discuss the implications of these findings for the survival of realistic cosmic string loops during inflation, and for the general characteristics of post-inflationary cosmic string networks. We also consider the analogous solutions for domain walls, in which case the critical radius is $R_c H=2/3$.
We construct the holographic dual theory of unparticles. The Randall-Sundrum type hard wall model is shown to produce deconstructing particles, whose spectrum has a finite mass gap proportional to the inverse of the fifth direction segment. The introduction of new scale corresponds to setting a brane in ${\rm AdS}_5$. The broken conformal symmetry due to this brane is restored when it is moved to infinity. Unparticles then emerge as an infinite tower of massless particles.
In this paper a neutron star with an inner core which undergoes a phase transition, which is characterized by conformal degrees of freedom on the phase boundary, is considered. Typical cases of such a phase transition are e.g. quantum hall effect, superconductivity and superfluidity. The stability of such a core is studied considering the general relativistic effects of these boundary degrees of freedom (predicted by QFT). This nontrivial stress tensor enters in the Einstein field equations through Israel's junction conditions. By solving the junction conditions it is found the range of physical parameters which can guarantee a stable equilibrium of the core of the neutron star. The relevant parameters turn out to be not only the density difference but also on the difference of the slope of the density profiles of the two phases. The values of the parameters which guarantee the stability turn out to be in a phenomenologically reasonable range. For the parameter values where the inner core is generically unstable possible astrophysical consequences related, for instance, to sudden changes of the moment of inertia of the star are shortly discussed. The possibility of exact pulsation modes is briefly considered.
We study the modified theory of gravity in Friedmann Robertson Walker universe composed of several perfect fluids. We consider the power law inflation and determine the parameters of the modified gravity's Lagrangian in terms of equation of state parameters and the equilibrium temperature. We also discuss the gravitational baryogenesis in this model.
In this paper we study the possibility of testing \emph{CPT} symmetry with Cosmic Microwave Background (CMB) measurements. Working with an effective lagrangian of the photon with \emph{CPT} violation ${\cal L} \sim p_{\mu}A_{\nu}\tilde F^{\mu\nu}$ which causes the polarization vectors of the propagating CMB photons rotated, we determine the rotation angle $\Delta\alpha$ using the BOOMERanG 2003 and the WMAP3 angular power spectra. In this analysis we have included the newly released $TC$ and $GC$ ($l<450$) information of WMAP3 and found $\Delta\alpha=-6.2\pm3.8$ deg at $1\sigma$ confidence level. This result increases slightly the significance for the \emph{CPT} violation obtained in our previous paper (Feng \emph{et al.}, 2006) $\Delta\alpha=-6.0 \pm 4.0$ deg (1$\sigma$). Furthermore we examine the constraint on the rotation angle with the simulated Planck data. Our results show that the Planck will be sensitive to $\Delta \alpha$ at the level of 0.057 deg and able to test the \emph{CPT} symmetry with a higher precision.
Determining the final spin of a black-hole binary is a question of key importance in astrophysics, and it has attracted a renewed interest since numerical-relativity simulations have allowed the first quantitative measures. Modelling this quantity in general is made difficult by the fact that it depends on the 7-dimensional space of parameters characterizing the two initial black holes. However, in special cases, when symmetries can be exploited, the description can become considerably simpler. For black-hole binaries with unequal masses but with equal spins which are aligned with the orbital angular momentum, we show that the use of recent numerical-relativity simulations and basic but exact constraints inspired from the extreme mass-ratio limit allow to model this quantity with a simple analytic expression. Despite the simple dependence, the fitting expression models very accurately all of the available estimates, with errors of a couple of percent at most. We also discuss how to use the fitting function to predict when a Schwarzschild black hole is produced by the merger of two spinning black holes, when the spin of the spacetime ``flips'' sign, or under what conditions the final black hole is ``spun-up'' by the merger. Last but not least, we show that the fit obtained here can be trivially extended to consider unequal-spin binaries, thus providing a complete description of the final spin from the coalescence of generic black-hole binaries with spins aligned to the orbital angular momentum.
This is the first part of a survey whose ultimate purpose is to clarify the significance of the famous coincidence between the Hubble age of the universe and a certain combination of microphysical parameters. In this part the way is prepared by a discussion of the manner in which familiar local phenomena depend qualitatively, and in order of magnitude, quantitatively on the fundamental parameters of microphysics. In order to keep the account concise while remaining self contained, only the barest essentials of the standard nuclear physical and astrophysical calculations involved are given. Only six of the fundamental parameters play a dominant part, namely the coupling constants of the strong, electromagnetic, and gravitational forces, and the mass ratios of the proton, neutron, electron and pi-meson. Attention is drawn to the important consequences of three coincidental relationships between these parameters. It is shown that most of the principle limiting masses of astrophysics arise (in fundamental units) simply as the reciprocal of the gravitational fine structure constant, with relatively small adjustment factors. The dividing point between red dwarf and blue giant stars turns out to be an exception: this division occurs within the range of the main sequence stars only as a consequence of the rather exotic coincidence that the ninth power of the electromagnetic fine structure constant is roughly equal to the square root of the gravitational fine structure constant.
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