Samuel J. George, Ian R. Stevens
We present results from new low frequency observations of two extrasolar planetary systems (Epsilon Eridani and HD128311) taken at 150 MHz with the Giant Metrewave Radio Telescope (GMRT). We do not detect either system, but are able to place tight upper limits on their low frequency radio emission.
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The search for radio emission from extra-solar planets has so far been unsuccessful. Much of the effort in modelling the predicted emission has been based on the analogy with the well-known emission from Jupiter. Unlike Jupiter, however, many of the targets of these radio searches are so close to their parent stars that they may well lie inside the stellar magnetosphere. For these close-in planets we determine which physical processes dominate the radio emission and compare our results to those for large-orbit planets that are immersed in the stellar wind. We have modelled the reconnection of …
The extraordinary astrometric accuracy of radio interferometry creates an important and unique opportunity for the discovery and characterization of exo-planets. Currently, the Very Long Baseline Array can routinely achieve better than 100 microarcsecond accuracy, and can approach 10 microarcsecond with careful calibration. We describe here RIPL, the Radio Interferometric PLanet search, a new program with the VLBA and the Green Bank 100 m telescope that will survey 29 low-mass, active stars over 3 years with sub-Jovian planet mass sensitivity at 1 AU. An upgrade of the VLBA bandwidth will incr…
Context. Close-in giant extrasolar planets (''Hot Jupiters'') are believed to be strong emitters in the decametric radio range. Aims. We present the expected characteristics of the low-frequency magnetospheric radio emission of all currently known extrasolar planets, including the maximum emission frequency and the expected radio flux. We also discuss the escape of exoplanetary radio emission from the vicinity of its source, which imposes additional constraints on detectability. Methods. We compare the different predictions obtained with all four existing analytical models for all currently kn…
We present Spitzer Space Telescope time series photometry of the exoplanet system HD 189733 spanning two times of secondary eclipse, when the planet passes out of view behind the parent star. We estimate the relative eclipse depth in 5 distinct bands and find the planet-to-star flux ratio to be 0.256 +/- 0.014% (3.6 microns), 0.214 +/- 0.020% (4.5 microns), 0.310 +/- 0.034% (5.8 microns), 0.391 +/- 0.022% (8.0 microns), and 0.598 +/- 0.038% (24 microns). For consistency, we re-analyze a previously published time series to deduce a contrast ratio in an additional band, 0.519 +/- 0.020% (16 micr…
We estimate flux ratios of the extrasolar planet XO-1b to its host star XO-1 at 3.6, 4.5, 5.8 and 8.0 microns with the IRAC on the Spitzer Space Telescope to be 0.00086 +/- 0.00007, 0.00122 +/- 0.00009, 0.00261 +/- 0.00031 and 0.00210 +/- 0.00029, respectively. The fluxes are inconsistent with a canonical cloudless model for the thermal emission from a planet and suggest an atmosphere with a thermal inversion layer and a possible stratospheric absorber. A newly emerging correlation between the presence of a thermal inversion layer in the planetary atmosphere and stellar insolation of the plane…
Eclipsing planetary systems give us an important window on extrasolar planet atmospheres. By measuring the depth of the secondary eclipse, when the planet moves behind the star, we can estimate the strength of the thermal emission from the day side of the planet. Attaining a ground-based detection of one of these eclipses has proven to be a significant challenge, as time-dependent variations in instrument throughput and atmospheric seeing and absorption overwhelm the small signal of the eclipse at infrared wavelengths. We gathered a series of simultaneous L grism spectra of the transiting plan…
The condition of radio emission is proposed, on the base of which the theory of themal radio emission for gaseous disk is developed. This theory explains the radio emission spectra of known types of extended radio sources, located beyond the Solar planetary system. Besides, the thermal radio emission spectra of Venus and Jupiter are explained.
The motivation to build spaceborne interferometric arrays for low-frequency radio astronomy is widely recognised because frequencies below the ionospheric cutoff are inaccessible for ground-based radio telescopes. We discuss the theoretical possibilities to use low-frequency spacecraft arrays to detect signals from magnetized extrasolar planets, including earthlike ones. A major uncertainty that prohibits us from knowing if it is possible to detect exoplanet cyclotron maser signals is the incomplete knowledge of the properties of the interstellar plasma. We also present some ideas of how to co…
The synchrotron interpretation of radio emission from various astrophysical objects encounters the essential difficulties . These difficulties may be overcome in a new theory of thermal radio emission of non-uniform gas which is based on a stimulated character of thermal radio emission following from the relations between Einstein?s coefficients for spontaneous and induced emission of radiation .
The relations between Einstein's coefficients for spontaneous and induced emission of radiation with account for the natural linewidth are obtained . It is shown that thermal radio emission is stimulated one . Thermal radio emission of non-uniform gas is considered .
Radio emission is a good indicator of the jet power of radio-loud quasars, while the emission in broad-line can well represent the accretion disc radiation in quasars. We compile a sample of all sources of which the broad-line fluxes are available from 1 Jy, S4 and S5 radio source catalogues. A correlation between radio and broad-line emission for this sample of radio-loud quasars is presented, which is in favour of a close link between the accretion processes and the relativistic jets. The BL Lac objects seem to follow the statistical behaviour of the quasars, but with fainter broad-line emis…
We explore the relationship between the extended radio and line emission for a radio-loud quasar sample including both core-dominated and lobe-dominated quasars. A strong correlation is present between the extended radio and broad-line emission. The core emission is also correlated with the broad-line emission for core-dominated quasars in the sample. The statistic behaviour on the core emission of lobe-dominated quasars is rather different from that of core-dominated quasars. The extended radio luminosity is a good tracer for jet power, while the core luminosity can only be a jet power tracer…
We report the spectroscopic detection of mid-infrared emission from the transiting exoplanet HD 209458b. Using archive data taken with the Spitzer/IRS instrument, we have determined the spectrum of HD 209458b between 7.46 and 15.25 microns. We have used two independent methods to determine the planet spectrum, one differential in wavelength and one absolute, and find the results are in good agreement. Over much of this spectral range, the planet spectrum is consistent with featureless thermal emission. Between 7.5 and 8.5 microns, we find evidence for an unidentified spectral feature. If this …
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