Spherical Atmospheres

Sobolev, V.V.

doi:10.1016/b978-0-08-017934-6.50017-6

Cited by 73 publications

(19 citation statements)

References 3 publications

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“…Furthermore, if the planet's reflectivity is assumed to be Lambertian (i.e., the planetary surface reflects isotropically in all directions), it has been shown that the planetary albedo will have at most a value of two thirds (Sobolev 1975). Higher values imply that the planetary surface or atmosphere would be strongly backscattering.…”

Section: Discussionmentioning

confidence: 99%

Evidence for a spectroscopic direct detection of reflected light from 51 Pegasi b

Martins

Santos

Figueira

et al. 2015

A&A

133

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Context. The detection of reflected light from an exoplanet is a difficult technical challenge at optical wavelengths. Even though this signal is expected to replicate the stellar signal, not only is it several orders of magnitude fainter, but it is also hidden among the stellar noise. Aims. We apply a variant of the cross-correlation technique to HARPS observations of 51 Peg to detect the reflected signal from planet 51 Peg b. Methods. Our method makes use of the cross-correlation function (CCF) of a binary mask with high-resolution spectra to amplify the minute planetary signal that is present in the spectra by a factor proportional to the number of spectral lines when performing the cross correlation. The resulting cross-correlation functions are then normalized by a stellar template to remove the stellar signal. Carefully selected sections of the resulting normalized CCFs are stacked to increase the planetary signal further. The recovered signal allows probing several of the planetary properties, including its real mass and albedo. Results. We detect evidence for the reflected signal from planet 51 Peg b at a significance of 3σ noise . The detection of the signal permits us to infer a real mass of 0.46 +0.06 −0.01 M Jup (assuming a stellar mass of 1.04 M Sun ) for the planet and an orbital inclination of 80 +10 −19 degrees. The analysis of the data also allows us to infer a tentative value for the (radius-dependent) geometric albedo of the planet. The results suggest that 51Peg b may be an inflated hot Jupiter with a high albedo (e.g., an albedo of 0.5 yields a radius of 1.9 ± 0.3 R Jup for a signal amplitude of 6.0 ± 0.4 × 10 −5 ). Conclusions. We confirm that the method we perfected can be used to retrieve an exoplanet's reflected signal, even with current observing facilities. The advent of next generation of instruments (e.g. VLT-ESO/ESPRESSO) and observing facilities (e.g. a new generation of ELT telescopes) will yield new opportunities for this type of technique to probe deeper into exoplanets and their atmospheres.

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Section: Discussionmentioning

confidence: 99%

Evidence for a spectroscopic direct detection of reflected light from 51 Pegasi b

Martins

Santos

Figueira

et al. 2015

A&A

133

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“…Because we know from our earlier, exact calculations (see NKK) that the temperature of this layer is always sufficiently low so that the gas is weakly ionized, we can simply use the albedo of the neutral matter, given, for example, by Magdziarz & Zdziarski (1995). The reÑected X-ray Ñux at an energy E is then given by equation (8.100) of Sobolev (1975, with his x 1 \ 0 because we assume that the scattering is isotropic), with the albedo as given by Magdziarz & Zdziarski A \ A c (E) (1995), and the notation changed appropriately to ours (e.g., etc.). Clearly, this approach is not accurate for q 0 4 q s , sharp spectral features, such as the Fe Ka line, or for high photon energies, i.e., keV or so, but it is nonetheless E Z 50 adequate for our purposes (see°3).…”

Section: Approximate Radiation T Ransfermentioning

confidence: 99%

“…We can then follow the methods described in Sobolev (1975), developed for the treatment of radiation transfer in the atmospheres of planets. In this approach, Compton scattering is assumed to be monochromatic (justiÐable here since the photon energies we consider are much smaller than and the skin temperature is m e c2 only roughly a few keV).…”

Section: Approximate Radiation T Ransfermentioning

confidence: 99%

“…Strictly speaking, this assumption is appropriate only when where f is the cosine of q s /f > 1, the incident angle for the X-rays. Instead of this, we now use the following iterative procedure : (1) Assume an initial value for the Thomson depth of the skin and calculate the radiation Ðeld within the skin with the approximate methods discussed in Sobolev (1975) and described in some detail in°2.2. (2) Find the gas pressure at the bottom of the skin (the point at which see Nayakshin & P gas \ P c ; Kallman 2001).…”

Section: Disk X-ray Illumination and Albedomentioning

confidence: 99%

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Modeling the X‐Ray–Optical Correlations in NGC 3516

Kazanas

Nayakshin

2001

ApJ

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We test the "" reprocessing paradigm ÏÏ of opticalÈUV active galactic nucleus (AGN) variability, according to which the variations in this wavelength range are driven by a variable X-ray component, by detailed modeling of the correlated X-rayÈoptical (3590 and 5510 variability of the recent multi-A ) wavelength campaign of NGC 3516. To this end we produce model optical light curves by convolving the observed X-ray Ñux with the response function of an inÐnite, thin accretion disk, illuminated by a pointlike X-ray source located at a given height above the compact object (the lamppost model). We h X also produce the ionized X-ray reÑection and Fe Ka line spectra that result from the reprocessing of the same X-rays on the disk surface. Then we compare the properties of the model light curves (amplitude, morphology, lags) as well as those of the Fe Ka line proÐles to those observed. Our calculations improve on those of similar past treatments by including the e †ects of an X-rayÈheated ionized layer in hydrostatic equilibrium on its surface, which greatly a †ects its X-ray timing and spectral properties. The results of our calculations do not provide a clear-cut picture that would either support or refute the reprocessing paradigm : despite the large (^50%) amplitude excursions of the X-ray Ñux, the model optical light curves exhibit variability amplitudes of only 3%È4% and vary in synchrony in the two bands, in agreement with observations. However, the model light curves, when viewed in detail, do not have a direct correspondence to those observed. Futhermore, while the observed intraband synchrony generally points toward smaller values for the black hole mass (M \ 107 the X-ray Fe Ka line, X-ray reÑection, and M _ ), opticalÈUV spectra seem to favor larger mass values (M \ 108Generally, no combination of the M _ ). model parameters seems to produce agreement with the ensemble of the constraints imposed by optical/ UV/X-ray spectral and timing observations ; we are thus led to believe that the simplest version of the lamppost model geometry is inconsistent with the NGC 3516 observations.

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“…Due to the circular symmetry of the surface of stars, the net polarization signal is zero (Chandrasekhar 1960;Sobolev 1975). In various types of stars, different physical scattering mechanisms can produce a non-vanishing local polarization signal (see e.g.…”

Section: Introductionmentioning

confidence: 99%

Polarimetry Microlensing of Close-in Planetary Systems

Sajadian

Hundertmark

2017

ApJ

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A close-in giant planetary (CGP) system has a net polarization signal whose value varies depending on the orbital phase of the planet. This polarization signal is either caused by the stellar occultation or by reflected starlight from the surface of the orbiting planet. When the CGP system is located in the Galactic bulge, its polarization signal becomes too weak to be measured directly. One method for detecting and characterizing these weak polarization signatures due to distant CGP systems is gravitational microlensing. In this work, we focus on potential polarimetric observations of highlymagnified microlensing events of CGP systems. When the lens is passing directly in front of the source star with its planetary companion, the polarimetric signature caused by the transiting planet is magnified. As a result some distinct features in the polarimetry and light curves are produced. In the same way microlensing amplifies the reflection-induced polarization signal. While the planetinduced perturbations are magnified, whenever these polarimetric or photometric deviations vanish for a moment the corresponding magnification factor or the polarization component(s) is equal to the related one due to the planet itself. Finding these exact times in the planet-induced perturbations helps us to characterize the planet. In order to evaluate the observability of such systems through polarimetric or photometric observations of high-magnification microlensing events, we simulate these events by considering confirmed CGP systems as their source stars and conclude that the efficiency for detecting the planet-induced signal with the state-of-the-art polarimetric instrument (FORS2/VLT) is less than 0.1%. Consequently, these planet-induced polarimetry perturbations can likely be detected under favorable conditions by high-resolution and short-cadence polarimeters of the next generation.

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Spherical Atmospheres

Cited by 73 publications

References 3 publications

Evidence for a spectroscopic direct detection of reflected light from 51 Pegasi b

Evidence for a spectroscopic direct detection of reflected light from 51 Pegasi b

Modeling the X‐Ray–Optical Correlations in NGC 3516

Polarimetry Microlensing of Close-in Planetary Systems

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