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rss_1.0 Recursos de colección

Caltech Authors (119,780 recursos)
Repository of works by Caltech published authors.

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Mostrando recursos 1 - 20 de 52,562

1. Role of thermalizing and nonthermalizing walls in phonon heat conduction along thin films - Ravichandran, Navaneetha K.; Minnich, Austin J.
Phonon boundary scattering is typically treated using the Fuchs-Sondheimer theory, which assumes that phonons are thermalized to the local temperature at the boundary. However, whether such a thermalization process actually occurs and its effect on thermal transport remains unclear. Here we examine thermal transport along thin films with both thermalizing and nonthermalizing walls by solving the spectral Boltzmann transport equation for steady state and transient transport. We find that in steady state, the thermal transport is governed by the Fuchs-Sondheimer theory and is insensitive to whether the boundaries are thermalizing or not. In contrast, under transient conditions, the thermal decay...

2. Physical properties of the planetary systems WASP-45 and WASP-46 from simultaneous multiband photometry - Ciceri, S.; Calchi Novati, S.; Elyiv, A.; Surdej, J.; Wertz, O.
Accurate measurements of the physical characteristics of a large number of exoplanets are useful to strongly constrain theoretical models of planet formation and evolution, which lead to the large variety of exoplanets and planetary-system configurations that have been observed. We present a study of the planetary systems WASP-45 and WASP-46, both composed of a main-sequence star and a close-in hot Jupiter, based on 29 new high-quality light curves of transits events. In particular, one transit of WASP-45 b and four of WASP-46 b were simultaneously observed in four optical filters, while one transit of WASP-46 b was observed with the...

3. Larger and faster: revised properties and a shorter orbital period for the WASP-57 planetary system from a pro-am collaboration - Southworth, John; Calchi Novati, S.
Transits in the WASP-57 planetary system have been found to occur half an hour earlier than expected. We present 10 transit light curves from amateur telescopes, on which this discovery was based, 13 transit light curves from professional facilities which confirm and refine this finding, and high-resolution imaging which show no evidence for nearby companions. We use these data to determine a new and precise orbital ephemeris, and measure the physical properties of the system. Our revised orbital period is 4.5 s shorter than found from the discovery data alone, which explains the early occurrence of the transits. We also...

4. European Pulsar Timing Array limits on continuous gravitational waves from individual supermassive black hole binaries - Babak, S.; Mingarelli, C. M. F.; van Haasteren, R.
We have searched for continuous gravitational wave (CGW) signals produced by individually resolvable, circular supermassive black hole binaries (SMBHBs) in the latest European Pulsar Timing Array (EPTA) data set, which consists of ultraprecise timing data on 41-ms pulsars. We develop frequentist and Bayesian detection algorithms to search both for monochromatic and frequency-evolving systems. None of the adopted algorithms show evidence for the presence of such a CGW signal, indicating that the data are best described by pulsar and radiometer noise only. Depending on the adopted detection algorithm, the 95 per cent upper limit on the sky-averaged strain amplitude lies in...

5. A free-form prediction for the reappearance of supernova Refsdal in the Hubble Frontier Fields cluster MACSJ1149.5+2223 - Diego, Jose M.; Broadhurst, Tom; Chen, Cuncheng; Lim, Jeremy; Zitrin, Adi; Chang, Brian; Coe, Dan; Ford, Holland C.; Lam, Daniel; Zheng, Wei
The massive cluster MACSJ1149.5+2223(z = 0.544) displays five very large lensed images of a well-resolved spiral galaxy at z_(spect) = 1.491. It is within one of these images that the first example of a multiply lensed supernova (SN) has been detected recently as part of the Grism Lens-Amplified Survey from Space. The depth of this data also reveals many H ii regions within the lensed spiral galaxy which we identify between the five counter-images. Here, we expand the capability of our free-form method to incorporate these H ii regions locally, with other reliable lensed galaxies added for a global solution....

6. Non-linearity and environmental dependence of the star-forming galaxies main sequence - Erfanianfar, G.; Fadda, D.
Using data from four deep fields (COSMOS, AEGIS, ECDFS, and CDFN), we study the correlation between the position of galaxies in the star formation rate (SFR) versus stellar mass plane and local environment at z < 1.1. To accurately estimate the galaxy SFR, we use the deepest available Spitzer/MIPS 24 and Herschel/PACS data sets. We distinguish group environments (M_(halo) ∼ 10^(12.5–14.2) M_⊙) based on the available deep X-ray data and lower halo mass environments based on the local galaxy density. We confirm that the main sequence (MS) of star-forming galaxies is not a linear relation and there is a flattening towards...

7. The RedGOLD cluster detection algorithm and its cluster candidate catalogue for the CFHT-LS W1 - Licitra, Rossella; Mei, Simona; Raichoor, Anand; Erben, Thomas; Hildebrandt, Hendrik
We present RedGOLD (Red-sequence Galaxy Overdensity cLuster Detector), a new optical/NIR galaxy cluster detection algorithm, and apply it to the CFHT-LS W1 field. RedGOLD searches for red-sequence galaxy overdensities while minimizing contamination from dusty star-forming galaxies. It imposes an Navarro–Frenk–White profile and calculates cluster detection significance and richness. We optimize these latter two parameters using both simulations and X-ray-detected cluster catalogues, and obtain a catalogue ∼80 per cent pure up to z ∼ 1, and ∼100 per cent (∼70 per cent) complete at z ≤ 0.6 (z ≲ 1) for galaxy clusters with M ≳ 10^(14) M_⊙ at the CFHT-LS Wide depth. In the CFHT-LS W1, we...

8. Versatile directional searches for gravitational waves with Pulsar Timing Arrays - Madison, D. R.; Ravi, V.
By regularly monitoring the most stable millisecond pulsars over many years, pulsar timing arrays (PTAs) are positioned to detect and study correlations in the timing behaviour of those pulsars. Gravitational waves (GWs) from supermassive black hole binaries (SMBHBs) are an exciting potentially detectable source of such correlations. We describe a straightforward technique by which a PTA can be ‘phased-up’ to form time series of the two polarization modes of GWs coming from a particular direction of the sky. Our technique requires no assumptions regarding the time-domain behaviour of a GW signal. This method has already been used to place stringent...

9. Galaxy morphology and star formation in the Illustris Simulation at z = 0 - Snyder, Gregory F.; Torrey, Paul; Lotz, Jennifer M.; Genel, Shy; McBride, Cameron K.; Vogelsberger, Mark; Pillepich, Annalisa; Nelson, Dylan; Sales, Laura V.; Sijacki, Debora; Hernquist, Lars; Springel, Volker
We study how optical galaxy morphology depends on mass and star formation rate (SFR) in the Illustris Simulation. To do so, we measure automated galaxy structures in 10 808 simulated galaxies at z = 0 with stellar masses 10^(9.7) < M_*/M_⊙ < 10^(12.3). We add observational realism to idealized synthetic images and measure non-parametric statistics in rest-frame optical and near-IR images from four directions. We find that Illustris creates a morphologically diverse galaxy population, occupying the observed bulge strength locus and reproducing median morphology trends versus stellar mass, SFR, and compactness. Morphology correlates realistically with rotation, following classification schemes put forth...

10. High-energy properties of the high-redshift flat spectrum radio quasar PKS 2149−306 - D'Ammando, F.; Orienti, M.
We investigate the γ-ray and X-ray properties of the flat spectrum radio quasar PKS 2149−306 at redshift z = 2.345. A strong γ-ray flare from this source was detected by the Large Area Telescope on board the Fermi Gamma-ray Space Telescope satellite in 2013 January, reaching on January 20 a daily peak flux of (301 ± 36) × 10^(−8) ph cm^(−2) s^(−1) in the 0.1–100 GeV energy range. This flux corresponds to an apparent isotropic luminosity of (1.5 ± 0.2) × 10^(50) erg s^(−1), comparable to the highest values observed by a blazar so far. During the flare the increase...

11. X-ray fluorescent lines from the Compton-thick AGN in M51 - Xu, Weiwei; Liu, Zhu; Gou, Lijun; Liu, Jiren
The cold disc/torus gas surrounding active galactic nuclei (AGN) emits fluorescent lines when irradiated by hard X-ray photons. The fluorescent lines of elements other than Fe and Ni are rarely detected due to their relative faintness. We report the detection of Kα lines of neutral Si, S, Ar, Ca, Cr, and Mn, along with the prominent Fe Kα, Fe Kβ, and Ni Kα lines, from the deep Chandra observation of the low-luminosity Compton-thick AGN in M51. The Si Kα line at 1.74 keV is detected at ∼3σ, the other fluorescent lines have a significance between 2 and 2.5 σ, while...

12. Hard X-ray emission of the luminous infrared galaxy NGC 6240 as observed by NuSTAR - Puccetti, S.; Comastri, A.; Bauer, F. E.; Brandt, W. N.; Fiore, F.; Harrison, F. A.; Luo, B.; Stern, D.; Urry, C. M.; Alexander, D. M.; Annuar, A.; Arévalo, P.; Baloković, M.; Boggs, S. E.; Brightman, M.; Christensen, F. E.; Craig, W. W.; Gandhi, P.; Hailey, C. J.; Koss, M. J.; La Massa, S.; Marinucci, A.; Ricci, C.; Walton, D. J.; Zappacosta, L.; Zhang, W. W.
We present a broadband (~0.3−70 keV) spectral and temporal analysis of NuSTAR observations of the luminous infrared galaxy NGC 6240 combined with archival Chandra, XMM-Newton, and BeppoSAX data. NGC 6240 is a galaxy in a relatively early merger state with two distinct nuclei separated by ~1.̋5. Previous Chandra observations resolved the two nuclei and showed that they are both active and obscured by Compton-thick material. Although they cannot be resolved by NuSTAR, we were able to clearly detect, for the first time, both the primary and the reflection continuum components thanks to the unprecedented quality of the NuSTAR data at...

13. Probing star formation in the dense environments of z ~ 1 lensing haloes aligned with dusty star-forming galaxies detected with the South Pole Telescope - Welikala, N.; Doré, O.; Murphy, E. J.; Vieira, J. D.
We probe star formation in the environments of massive (∼10^(13) M_⊙) dark matter haloes at redshifts of z ∼ 1. This star formation is linked to a submillimetre clustering signal which we detect in maps of the Planck High Frequency Instrument that are stacked at the positions of a sample of high redshift (z > 2) strongly lensed dusty star-forming galaxies (DSFGs) selected from the South Pole Telescope (SPT) 2500 deg^2 survey. The clustering signal has submillimetre colours which are consistent with the mean redshift of the foreground lensing haloes (z ∼ 1). We report a mean excess of star formation...

14. The diverse evolutionary paths of simulated high-z massive, compact galaxies to z= 0 - Wellons, Sarah; Torrey, Paul; Ma, Chung-Pei; Rodriguez-Gomez, Vicente; Pillepich, Annalisa; Nelson, Dylan; Genel, Shy; Vogelsberger, Mark; Hernquist, Lars
Massive quiescent galaxies have much smaller physical sizes at high redshift than today. The strong evolution of galaxy size may be caused by progenitor bias, major and minor mergers, adiabatic expansion, and/or renewed star formation, but it is difficult to test these theories observationally. Herein, we select a sample of 35 massive, compact galaxies (M_* = 1–3 × 10^(11) M_⊙, M_*/R^(1.5) > 10^(10.5) M_⊙/kpc^(1.5)) at z = 2 in the cosmological hydrodynamical simulation Illustris and trace them forwards to z = 0 to uncover their evolution and identify their descendants. By z = 0, the original factor of 3 difference...

15. An empirically derived three-dimensional Laplace resonance in the Gliese 876 planetary system - Nelson, Benjamin E.; Robertson, Paul M.; Payne, Matthew J.; Pritchard, Seth M.; Deck, Katherine M.; Ford, Eric B.; Wright, Jason T.; Isaacson, Howard T.
We report constraints on the three-dimensional orbital architecture for all four planets known to orbit the nearby M dwarf Gliese 876 based solely on Doppler measurements and demanding long-term orbital stability. Our data set incorporates publicly available radial velocities taken with the ELODIE and CORALIE spectrographs, High Accuracy Radial velocity Planet Searcher (HARPS), and Keck HIgh Resolution Echelle Spectrometer (HIRES) as well as previously unpublished HIRES velocities. We first quantitatively assess the validity of the planets thought to orbit GJ 876 by computing the Bayes factors for a variety of different coplanar models using an importance sampling algorithm. We find...

16. Parabolized stability analysis of jets from serrated nozzles - Sinha, Aniruddha; Gudmundsson, Kristján; Xia, Hao; Colonius, Tim
We study the viscous spatial linear stability characteristics of the time-averaged flow in turbulent subsonic jets issuing from serrated (chevroned) nozzles, and compare them to analogous round jet results. Linear parabolized stability equations (PSE) are used in the calculations to account for the non-parallel base flow. By exploiting the symmetries of the mean flow due to the regular arrangement of serrations, we obtain a series of coupled two-dimensional PSE problems from the original three-dimensional problem. This reduces the solution cost and manifests the symmetries of the stability modes. In the parallel-flow linear stability theory (LST) calculations that are performed near...

17. Resolved Millimeter-wavelength Observations of Debris Disks around Solar-type Stars - Steele, Amy; Hughes, A. Meredith; Carpenter, John; Ricarte, Angelo; Andrews, Sean M.; Wilner, David J.; Chiang, Eugene
The presence of debris disks around young main-sequence stars hints at the existence and structure of planetary systems. Millimeter-wavelength observations probe large grains that trace the location of planetesimal belts. The Formation and Evolution of Planetary Systems Spitzer Legacy survey of nearby young solar analogues yielded a sample of five debris disk-hosting stars with millimeter flux suitable for interferometric follow-up. We present observations with the Submillimeter Array (SMA) and the Combined Array for Research in Millimeter-wave Astronomy at ~2'' resolution that spatially resolve the debris disks around these nearby (d ~ 50 pc) stars. Two of the five disks (HD...

18. Extreme stiffness tunability through the excitation of nonlinear defect modes - Serra-Garcia, M.; Lydon, J.; Daraio, C.
The incremental stiffness characterizes the variation of a material's force response to a small deformation change. In lattices with noninteracting vibrational modes, the excitation of localized states does not have any effect on material properties, such as the incremental stiffness. We report that, in nonlinear lattices, driving a defect mode introduces changes in the static force-displacement relation of the material. By varying the defect excitation frequency and amplitude, the incremental stiffness can be tuned continuously to arbitrarily large positive or negative values. Furthermore, the defect excitation parameters also determine the displacement region at which the force-displacement relation is being tuned....

19. Differential rotation of the unstable nonlinear r-modes - Friedman, John L.; Lindblom, Lee; Lockitch, Keith H.
At second order in perturbation theory, the r-modes of uniformly rotating stars include an axisymmetric part that can be identified with differential rotation of the background star. If one does not include radiation reaction, the differential rotation is constant in time and has been computed by Sá. It has a gauge dependence associated with the family of time-independent perturbations that add differential rotation to the unperturbed equilibrium star: For stars with a barotropic equation of state, one can add to the time-independent second-order solution arbitrary differential rotation that is stratified on cylinders (that is a function of distance ϖ to...

20. Erratic Flaring of BL Lac in 2012-2013: Multiwavelength Observations - Wehrle, Ann E.; Grupe, Dirk; Jorstad, Svetlana G.; Marscher, Alan P.; Gurwell, Mark; Baloković, Mislav; Hovatta, Talvikki; Madejski, Grzegorz M.; Harrison, Fiona H.; Stern, Daniel
BL Lac, the eponymous blazar, flared to historically high levels at millimeter, infrared, X-ray, and gamma-ray wavelengths in 2012. We present observations made with Herschel, Swift, NuSTAR, Fermi, the Submillimeter Array, CARMA, and the VLBA in 2012–2013, including three months with nearly daily sampling at several wavebands. We have also conducted an intensive campaign of 30 hr with every-orbit observations by Swift and NuSTAR, accompanied by Herschel, and Fermi observations. The source was highly variable at all bands. Time lags, correlations between bands, and the changing shapes of the spectral energy distributions can be explained by synchrotron radiation and inverse...

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