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Caltech Authors (144.724 recursos)

Repository of works by Caltech published authors.

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Mostrando recursos 1 - 20 de 773

  1. Propagation of Thermonuclear Flames on Rapidly Rotating Neutron Stars: Extreme Weather during Type I X-Ray Bursts

    Spitkovsky, Anatoly; Levin, Yuri; Ushomirsky, Greg
    We analyze the global hydrodynamic flow in the ocean of an accreting, rapidly rotating, nonmagnetic neutron star in a low-mass X-ray binary during a type I X-ray burst. We use both analytical arguments and numerical simulations of simplified models for ocean burning. Our analysis extends previous work by taking into account the rapid rotation of the star and the lift-up of the burning ocean during the burst. We find a new regime for the spreading of a nuclear burning front, where the flame is carried along a coherent shear flow across the front. If turbulent viscosity is weak, the speed...

  2. A Parametric Study of the Acoustic Mechanism for Core-collapse Supernovae

    Harada, A.; Nagakura, H.; Iwakami, W.; Yamada, S.
    We investigate the criterion for the acoustic mechanism to work successfully in core-collapse supernovae. The acoustic mechanism is an alternative to the neutrino-heating mechanism. It was proposed by Burrows et al., who claimed that acoustic waves emitted by g-mode oscillations in proto-neutron stars (PNS) energize a stalled shock wave and eventually induce an explosion. Previous works mainly studied to which extent the g-modes are excited in the PNS. In this paper, on the other hand, we investigate how strong the acoustic wave needs to be if it were to revive a stalled shock wave. By adding the acoustic power as...

  3. Beating the Standard Sensitivity-Bandwidth Limit of Cavity-Enhanced Interferometers with Internal Squeezed-Light Generation

    Korobko, M.; Kleybolte, L.; Ast, S.; Miao, H.; Chen, Y.; Schnabel, R.
    The shot-noise limited peak sensitivity of cavity-enhanced interferometric measurement devices, such as gravitational-wave detectors, can be improved by increasing the cavity finesse, even when comparing fixed intracavity light powers. For a fixed light power inside the detector, this comes at the price of a proportional reduction in the detection bandwidth. High sensitivity over a large span of signal frequencies, however, is essential for astronomical observations. It is possible to overcome this standard sensitivity-bandwidth limit using nonclassical correlations in the light field. Here, we investigate the internal squeezing approach, where the parametric amplification process creates a nonclassical correlation directly inside the...

  4. Directional Limits on Persistent Gravitational Waves from Advanced LIGO’s First Observing Run

    Abbott, B. P.; Abbott, R.; Adhikari, R. X.; Ananyeva, A.; Anderson, S. B.; Appert, S.; Arai, K.; Araya, M. C.; Barayoga, J. C.; Barish, B. C.; Berger, B. K.; Billingsley, G.; Biscans, S; Blackburn, J. K.; Bork, R.; Brooks, A. F.; Brunett, S.; Cahillane, C.; Callister, T.; Cepeda, C. B.; Couvares, P.; Coyne, D. C.; Drever, R. W. P.; Ehrens, P.; Eichholz, J.; Etzel, T.; Fries, E. M.; Gossan, S. E.; Gushwa, K. E.; Gustafson, E. K.; Hall, E. D.; Heptonstall, A. W.; Isi, M.; Kanner, J. B.; Kondrashov, V.; Korth, W. Z.; Kozak, D. B.; Lazzarini, A.; Maros, E.; Massinger, T. J.; Matichard, F.; McIntyre, G.; McIver, J.; Meshkov, S.; Pedraza, M.; Perreca, A.; Quintero, E. A.; Reitze, D. H.; Robertson, N. A.; Rollins, J. G.; Sachdev, S.; Sanchez, E. J.; Schmidt, P.; Singer, A.; Smith, R. J. E.; Taylor, R.; Torrie, C. I.; Tso, R.; Urban, A. L.; Vajente, G.; Vass, S.; Venugopalan, G.; Wade, A. R.; Wallace, L.; Weinstein, A. J.; Williams, R. D.; Wipf, C. C.; Yamamoto, H.; Zhang, L.; Zucker, M. E.; Zweizig, J.; Blackman, J.; Chen, Y.; Ma, Y.; Varma, V.
    We employ gravitational-wave radiometry to map the stochastic gravitational wave background expected from a variety of contributing mechanisms and test the assumption of isotropy using data from the Advanced Laser Interferometer Gravitational Wave Observatory’s (aLIGO) first observing run. We also search for persistent gravitational waves from point sources with only minimal assumptions over the 20–1726 Hz frequency band. Finding no evidence of gravitational waves from either point sources or a stochastic background, we set limits at 90% confidence. For broadband point sources, we report upper limits on the gravitational wave energy flux per unit frequency in the range F_(α,Θ)(f)<(0.1–56)×10^(-8) erg cm^(-2) s^(-1) Hz^(-1)(f/25  Hz)^(α-1) depending...

  5. Unifying Type II Supernova Light Curves with Dense Circumstellar Material

    Morozova, Viktoriya; Piro, Anthony L.; Valenti, Stefano
    A longstanding problem in the study of supernovae (SNe) has been the relationship between the Type IIP and Type IIL subclasses. Whether they come from distinct progenitors or they are from similar stars with some property that smoothly transitions from one class to another has been the subject of much debate. Here, using one-dimensional radiation-hydrodynamic SN models, we show that the multi-band light curves of SNe IIL are well fit by ordinary red supergiants surrounded by dense circumstellar material (CSM). The inferred extent of this material, coupled with a typical wind velocity of ~10-100 km s^(-1), suggests enhanced activity by...

  6. The impact of stellar feedback on hot gas in galaxy haloes: the Sunyaev–Zel'dovich effect and soft X-ray emission

    van de Voort, Freeke; Quataert, Eliot; Hopkins, Philip F.; Faucher-Giguère, Claude-André; Feldmann, Robert; Kereš, Dušan; Chan, T. K.; Hafen, Zachary
    The thermal Sunyaev–Zel'dovich (SZ) effect and soft X-ray emission are routinely observed around massive galaxies and in galaxy groups and clusters. We study these observational diagnostics of galaxy haloes for a suite of cosmological ‘zoom-in’ simulations from the ‘Feedback In Realistic Environments’ project, which spans a large range in halo mass (10^(10–13) M_⊙). We explore the effect of stellar feedback on the hot gas observables. The properties of our simulated groups, such as baryon fractions, SZ flux, and X-ray luminosities (LX), are broadly consistent with existing observations, even though feedback from active galactic nuclei is not included. We make predictions for...

  7. On the equal-mass limit of precessing black-hole binaries

    Gerosa, Davide; Sperhake, Ulrich; Vošmera, Jakub
    We analyze the inspiral dynamics of equal-mass precessing black-hole binaries using multi-timescale techniques. The orbit-averaged post-Newtonian evolutionary equations admit two constants of motion in the equal-mass limit, namely the magnitude of the total spin S and the effective spin ξ. This feature makes the entire dynamics qualitatively different compared to the generic unequal-mass case, where only ξ is constant while the variable S parametrizes the precession dynamics. For fixed individual masses and spin magnitudes, an equal-mass black-hole inspiral is uniquely characterized by the two parameters (S, ξ): these two numbers completely determine the entire evolution under the effect of radiation...

  8. Probing Sagittarius A* accretion with ALMA

    Murchikova, Elena
    The submm Hydrogen recombination line technique can be used as a probe of the Galactic Center. We present the results of our H30α observations of ionized gas from within 0.015 pc around SgrA*. The observations were obtained on ALMA in cycle 3. The line was not detected, but we were able to set a limit on the mass of the cool gas (T~ 10^4 K) at 2 × 10^(-3)M⊙. This is the unique probe of gas cooler than T ~10^6 K traced by X-ray emission. The total amount of gas near SgrA* gives us clues to understanding the accretion rate...

  9. Near Infrared Imaging of the Hubble Deep Field with the Keck Telescope

    Hogg, David W.; Neugebauer, G.; Armus, Lee; Matthews, K.; Pahre, Michael A.; Soifer, B. T.; Weinberger, A. J.
    Two deep K-band (2.2 ¡im) images, with point-source detection limits of K=25.2 mag (one sigma), taken with the Keck Telescope in subfields of the Hubble Deep Field, are presented and analyzed. A sample of objects to K=24 mag is constructed and V_(606)—I_(814) and I_(814)-K colors are measured. By stacking visually selected objects, mean I_(814)—K colors can be measured to very faint levels; the mean I_(814)—K color is constant with apparent magnitude down to V_(606) = 28 mag.

  10. Planet-induced Stellar Pulsations in HAT-P-2's Eccentric System

    De Wit, Julien; Lewis, Nikole K.; Knutson, Heather A.; Fuller, Jim; Antoci, Victoria; Fulton, Benjamin J.; Laughlin, Gregory; Deming, Drake; Shporer, Avi; Batygin, Konstantin; Cowan, Nicolas B.; Agol, Eric; Burrows, Adam S.; Fortney, Jonathan J.; Langton, Jonathan; Showman, Adam P.
    Extrasolar planets on eccentric short-period orbits provide a laboratory in which to study radiative and tidal interactions between a planet and its host star under extreme forcing conditions. Studying such systems probes how the planet's atmosphere redistributes the time-varying heat flux from its host and how the host star responds to transient tidal distortion. Here, we report the insights into the planet–star interactions in HAT-P-2's eccentric planetary system gained from the analysis of ~350 hr of 4.5 μm observations with the Spitzer Space Telescope. The observations show no sign of orbit-to-orbit variability nor of orbital evolution of the eccentric planetary...

  11. An architecture for efficient multimodal gravitational wave parameter estimation with linear surrogate models

    O'Shaughnessy, Richard; Blackman, Jonathan; Field, Scott E.
    The recent direct detection of gravitational waves has further emphasized the need for fast, low-cost, and accurate methods to infer the parameters of gravitational wave sources. The performance of these calculations is limited by the cost of evaluating the likelihood function, due to expense in data handling and waveform generation. Building on recently developed surrogate models and a novel parameter estimation pipeline, we show how to quickly generate the likelihood function as a simple, analytic closed-form expression. Using a simple variant of a production-scale parameter estimation code, we demonstrate our method using surrogate models of effective-one-body and numerical relativity waveforms. Our study is the first time these models have...

  12. Equation of State Effects on Gravitational Waves from Rotating Core Collapse

    Richers, Sherwood; Ott, Christian D.; Abdikamalov, Ernazar; O'Connor, Evan; Sullivan, Chris
    Gravitational waves (GWs) generated by axisymmetric rotating collapse, bounce, and early postbounce phases of a galactic core-collapse supernova are detectable by current-generation gravitational wave observatories. Since these GWs are emitted from the quadrupole-deformed nuclear-density core, they may encode information on the uncertain nuclear equation of state (EOS). We examine the effects of the nuclear EOS on GWs from rotating core collapse and carry out 1824 axisymmetric general-relativistic hydrodynamic simulations that cover a parameter space of 98 different rotation profiles and 18 different EOS. We show that the bounce GW signal is largely independent of the EOS and sensitive primarily to...

  13. Are the Formation and Abundances of Metal-poor Stars the Result of Dust Dynamics?

    Hopkins, Philip F.; Conroy, Charlie
    Large dust grains can fluctuate dramatically in their local density, relative to the gas, in neutral turbulent disks. Small, high-redshift galaxies (before reionization) represent ideal environments for this process. We show via simple arguments and simulations that order-of-magnitude fluctuations are expected in local abundances of large grains (>100 Å) under these conditions. This can have important consequences for star formation and stellar metal abundances in extremely metal-poor stars. Low-mass stars can form in dust-enhanced regions almost immediately after some dust forms even if the galaxy-average metallicity is too low for fragmentation to occur. We argue that the metal abundances of...

  14. Dynamical ejecta from precessing neutron star-black hole mergers with a hot, nuclear-theory based equation of state

    Foucart, F.; Desai, D.; Brege, W.; Duez, M. D.; Kasen, D.; Hemberger, D. A.; Kidder, L. E.; Pfeiffer, H. P.; Scheel, M. A.
    Neutron star-black hole binaries are among the strongest sources of gravitational waves detectable by current observatories. They can also power bright electromagnetic signals (gamma-ray bursts, kilonovae), and may be a significant source of production of r-process nuclei. A misalignment of the black hole spin with respect to the orbital angular momentum leads to precession of that spin and of the orbital plane, and has a significant effect on the properties of the post-merger remnant and of the material ejected by the merger. We present a first set of simulations of precessing neutron star-black hole mergers using a hot, composition dependent,...

  15. Extraction of gravitational-wave energy in higher dimensional numerical relativity using the Weyl tensor

    Cook, William G.; Sperhake, Ulrich
    Gravitational waves are one of the most important diagnostic tools in the analysis of strong-gravity dynamics and have been turned into an observational channel with LIGO's detection of GW150914. Aside from their importance in astrophysics, black holes and compact matter distributions have also assumed a central role in many other branches of physics. These applications often involve spacetimes with D  >  4 dimensions where the calculation of gravitational waves is more involved than in the four dimensional case, but has now become possible thanks to substantial progress in the theoretical study of general relativity in D  >  4. Here, we develop a numerical implementation...

  16. Tidally Induced Pulsations in Kepler Eclipsing Binary KIC 3230227

    Guo, Zhao; Gies, Douglas R.; Fuller, Jim
    KIC 3230227 is a short period (P ≈ 7.0 days) eclipsing binary with a very eccentric orbit (e = 0.6). From combined analysis of radial velocities and Kepler light curves, this system is found to be composed of two A-type stars, with masses of M_1 = 1.84 ± 0.18 M_⊙, M_2 = 1.73 ± 0.17 M_⊙ and radii of R_1 = 2.01 ± 0.09 R_⊙, R_2 = 1.68 ± 0.08 R_⊙ for the primary and secondary, respectively. In addition to an eclipse, the binary light curve shows a brightening and dimming near periastron, making this a somewhat rare eclipsing heartbeat...

  17. Post-outburst Radio Observations of the High Magnetic Field Pulsar PSR J1119-6127

    Majid, Walid A.; Pearlman, Aaron B.; Dobreva, Tatyana; Horiuchi, Shinji; Kocz, Jonathon; Lippuner, Jonas; Prince, Thomas A.
    We have carried out high-frequency radio observations of the high magnetic field pulsar PSR J1119-6127 following its recent X-ray outburst. While initial observations showed no evidence of significant radio emission, subsequent observations detected pulsed emission across a large frequency band. In this Letter, we report on the initial disappearance of the pulsed emission and its prompt reactivation and dramatic evolution over several months of observation. The periodic pulse profile at S-band (2.3 GHz) after reactivation exhibits a multi-component emission structure, while the simultaneous X-band (8.4 GHz) profile shows a single emission peak. Single pulses were also detected at S-band near...

  18. Under pressure: quenching star formation in low-mass satellite galaxies via stripping

    Fillingham, Sean P.; Cooper, Michael C.; Pace, Andrew B.; Boylan-Kolchin, Michael; Bullock, James S.; Garrison-Kimmel, Shea; Wheeler, Coral
    Recent studies of galaxies in the local Universe, including those in the Local Group, find that the efficiency of environmental (or satellite) quenching increases dramatically at satellite stellar masses below ∼10^8 M⊙. This suggest a physical scale where quenching transitions from a slow ‘starvation’ mode to a rapid ‘stripping’ mode at low masses. We investigate the plausibility of this scenario using observed H I surface density profiles for a sample of 66 nearby galaxies as inputs to analytic calculations of ram-pressure and turbulent viscous stripping. Across a broad range of host properties, we find that stripping becomes increasingly effective at M* ≲...

  19. Feedback first: the surprisingly weak effects of magnetic fields, viscosity, conduction, and metal diffusion on galaxy formation

    Su, Kung-Yi; Hopkins, Philip F.; Hayward, Christopher C.; Faucher-Giguère, Claude-André; Kereš, Dušan; Ma, Xiangcheng; Robles, Victor H.
    Using high-resolution simulations with explicit treatment of stellar feedback physics based on the FIRE (Feedback in Realistic Environments) project, we study how galaxy formation and the interstellar medium (ISM) are affected by magnetic fields, anisotropic Spitzer-Braginskii conduction and viscosity, and sub-grid turbulent metal diffusion. We consider controlled simulations of isolated (non-cosmological) galaxies but also a limited set of cosmological "zoom-in" simulations. Although simulations have shown significant effects from these physics with weak or absent stellar feedback, the effects are much weaker than those of stellar feedback when the latter is modeled explicitly. The additional physics have no systematic effect on...

  20. ALMA Resolves the Nuclear Disks of Arp 220

    Scoville, Nick; Murchikova, Lena; Walter, Fabian; Vlahakis, Catherine; Koda, Jin; Vanden Bout, Paul; Barnes, Joshua; Henrquist, Lars; Sheth, Kartik; Yun, Min; Sanders, David; Armus, Lee; Cox, Pierre; Thompson, Todd; Robertson, Brant; Zschaechner, Laura; Tacconi, Linda; Torrey, Paul; Hayward, Christopher C.; Genzel, Reinhard; Hopkins, Phil; van der Werf, Paul; Decarli, Roberto
    We present 90 mas (37 pc) resolution ALMA imaging of Arp 220 in the CO (1-0) line and continuum at λ = 2.6 mm. The internal gas distribution and kinematics of both galactic nuclei are well resolved for the first time. In the west nucleus, the major gas and dust emission extends out to 0.”2 radius (74 pc); the central resolution element shows a strong peak in the dust emission but a factor of 3 dip in the CO line emission. In this nucleus, the dust is apparently optically thick (τ_(2.6 mm) ~ 1) at λ = 2.6 mm with...

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