569 research outputs found

    Status and Prospects of Planetary Transit Searches: Hot Jupiters Galore

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    The first transiting extrasolar planet, orbiting HD209458, was a Doppler wobble planet before its transits were discovered with a 10 cm CCD camera. Wide-angle CCD cameras, by monitoring in parallel the light curves of tens of thousands of stars, should find hot Jupiter transits much faster than the Doppler wobble method. The discovery rate could easily rise by a factor 10. The sky holds perhaps 1000 hot Jupiters transiting stars brighter than V=13. These are bright enough for follow-up radial velocity studies to measure planet masses to go along with the radii from the transit light curves. I derive scaling laws for the discovery potential of ground-based transit searches, and use these to assess over two dozen planetary transit surveys currently underway. The main challenge lies in calibrating small systematic errors that limit the accuracy of CCD photometry at milli-magnitude levels. Promising transit candidates have been reported by several groups, and many more are sure to follow.Comment: To appear in: Scientific Frontiers in Research on Extrasolar Planets, 18-21 Jun 2002, Washington D.C., ASP Conference Series Vol ???, 2003, D.Deming and S.Seager, eds v2: update notes ogle-tr-56b discover

    Kepler-like Multi-Plexing for Mass Production of Microlens Parallaxes

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    We show that a wide-field Kepler-like satellite in Solar orbit could obtain microlens parallaxes for several thousand events per year that are identified from the ground, yielding masses and distances for several dozen planetary events. This is roughly an order of magnitude larger than previously-considered narrow-angle designs. Such a satellite would, in addition, roughly double the number of planet detections (and mass/distance determinations). It would also yield a trove of brown-dwarf binaries with masses, and distances and (frequently) full orbits, enable new probes of the stellar mass function, identify isolated black-hole candidates. We show that the actual Kepler satellite, even with degraded pointing, can demonstrate these capabilities and make substantial initial inroads into the science potential. We discuss several "Deltas" to the Kepler satellite aimed at optimizing microlens parallax capabilities. Most of these would reduce costs. The wide-angle approach advocated here has only recently become superior to the old narrow-angle approach, due to the much larger number of ground-based microlensing events now being discovered.Comment: ApJ Letters, in press, 12 pages, 4 figure

    Photoionized HBeta Emission in NGC 5548: It Breathes!

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    Emission-line regions in active galactic nuclei and other photoionized nebulae should become larger in size when the ionizing luminosity increases. This 'breathing' effect is observed for the Hbeta emission in NGC 5548 by using Hbeta and optical continuum lightcurves from the 13-year 1989-2001 AGN Watch monitoring campaign. To model the breathing, we use two methods to fit the observed lightcurves in detail: (i) parameterized models and, (ii) the MEMECHO reverberation mapping code. Our models assume that optical continuum variations track the ionizing radiation, and that the Hbeta variations respond with time delays due to light travel time. By fitting the data using a delay map that is allowed to change with continuum flux, we find that the strength of the Hbeta response decreases and the time delay increases with ionizing luminosity. The parameterized breathing models allow the time delay and the Hbeta flux to depend on the continuum flux so that, the time delay is proportional to the continuum flux to the power beta, and the Hbeta flux is proportional to the continuum flux to the power alpha. Our fits give 0.1 < beta < 0.46 and 0.57 < alpha < 0.66. alpha is consistent with previous work by Gilbert and Peterson (2003) and Goad, Korista and Knigge (2004). Although we find beta to be flatter than previously determined by Peterson et al. (2002) using cross-correlation methods, it is closer to the predicted values from recent theoretical work by Korista and Goad (2004).Comment: 13 pages, 13 figures. Accepted for publication in MNRA

    How fast do Jupiters grow? Signatures of the snowline and growth rate in the distribution of gas giant planets

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    We present here observational evidence that the snowline plays a significant role in the formation and evolution of gas giant planets. When considering the population of observed exoplanets, we find a boundary in mass-semimajor axis space that suggests planets are preferentially found beyond the snowline prior to undergoing gap-opening inward migration and associated gas accretion. This is consistent with theoretical models suggesting that sudden changes in opacity -- as would occur at the snowline -- can influence core migration. Furthermore, population synthesis modelling suggests that this boundary implies that gas giant planets accrete ~ 70 % of the inward flowing gas, allowing ~ 30$ % through to the inner disc. This is qualitatively consistent with observations of transition discs suggesting the presence of inner holes, despite there being ongoing gas accretion.Comment: 7 pages, 6 figures, accepted for publication in Monthly Notices of the Royal Astronomical Societ

    Quasar Tomography: Unification of Echo Mapping and Photoionisation Models

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    Reverberation mapping uses time-delayed variations in photoionised emission lines to map the geometry and kinematics of emission-line gas in active galactic nuclei. In previous work, the light travel time delay tau=R(1+cos(theta))/c and Doppler shift v give a 2-d map Psi(tau,v) for each emission line. Here we combine the velocity-delay information with photoionisation physics in a maximum entropy fit to the full reverberating spectrum F_lam(lam,t) to recover a 5-d map of the differential covering fraction f(R,theta,n,N,v), with n and N the density and column density of the gas clouds. We test the method for a variety of geometries (shells, rings, disks, clouds, jets) by recovering a 3-d map f(R,theta,n) from reverberations in 7 uv emission lines. The best test recovers a hollow shell geometry, defining R to 0.15 dex, n to 0.3 dex, and ionisation parameter U ~ 1/(n R^2) to 0.1 dex. The results are sensitive to the adopted distance and luminosity, suggesting that these parameters may be measurable as well.Comment: Accepted 4 Sep 2002 for publication in MNRA

    Conformal gravity rotation curves with a conformal Higgs halo

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    We discuss the effect of a conformally coupled Higgs field on Conformal Gravity (CG) predictions for the rotation curves of galaxies. The Mannheim-Kazanas (MK) metric is a valid vacuum solution of CG's 4-th order Poisson equation if and only if the Higgs field has a particular radial profile, S(r) = S0 a/(r + a), decreasing from S0 at r = 0 with radial scale length a. Since particle rest masses scale with S(r)/S0, their world lines do not follow time-like geodesics of the MK metric gμν, as previously assumed, but rather those of the Higgs-frame MK metric ḡμν = Ω2 gμν, with the conformal factor Ω(r) = S(r)/S0. We show that the required stretching of the MK metric exactly cancels the linear potential that has been invoked to fit galaxy rotation curves without dark matter. We also formulate, for spherical structures with a Higgs halo S(r), the CG equations that must be solved for viable astrophysical tests of CG using galaxy and cluster dynamics and lensing.Publisher PDFPeer reviewe

    Testing Bekenstein's Relativistic MOND gravity with Lensing Data

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    We propose to use multiple-imaged gravitational lenses to set limits on gravity theories without dark matter, specificly TeVeS (Bekenstein 2004), a theory which is consistent with fundamental relativistic principles and the phenomenology of MOdified Newtonian Dynamics (MOND) theory. After setting the framework for lensing and cosmology, we derive analytically the deflection angle for the point lens and the Hernquist galaxy profile, and fit galaxy-quasar lenses in the CASTLES sample. We do this with three methods, fitting the observed Einstein ring sizes, the image positions, or the flux ratios. In all cases we consistently find that stars in galaxies in MOND/TeVeS provide adequate lensing. Bekenstein's toy μ\mu function provides more efficient lensing than the standard MOND μ\mu function. But for a handful of lenses [indicated in Table 2,3, fig 16] a good fit would require a lens mass orders of magnitude larger/smaller than the stellar mass derived from luminosity unless the modification function μ\mu and modification scale a0a_0 for the universal gravity were allowed to be very different from what spiral galaxy rotation curves normally imply. We discuss the limitation of present data and summarize constraints on the MOND μ\mu function. We also show that the simplest TeVeS "minimal-matter" cosmology, a baryonic universe with a cosmological constant, can fit the distance-redshift relation from the supernova data, but underpredicts the sound horizon size at the last scattering. We conclude that lensing is a promising approach to differentiate laws of gravity (see also astro-ph/0512425).Comment: reduced to 17p, 16 figs, discussed cosmology and constraints on mu-function, MNRAS accepte
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