Raman and Rayleigh Scattering of Lyman   by Molecular Hydrogen

Dalgarno, A.; Williams, D. A.; Bates, D. R.

doi:10.1093/mnras/124.4.313

Cited by 29 publications

(12 citation statements)

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“…The features described so far are also visible in Figures 3 and 4, which show light curve plots of I/I Q averaged over several channels together with models discussed in the next section. The wavelength dependence of I/I Q is consistent with Rayleigh scattering, which has a A" 4 dependence at visual and near-ultraviolet wavelengths but steepens shortward of about 2000 A for many media (e.g., N 2 gas [Dalgarno et al, 1967] or H 2 gas [ Dalgarno and Williams, 1962]). The possible atmospheric constituents that could plausibly produce significant extinction by this mechanism appear to be N 2 gas or a very fine haze with diameter <0.03 /xm (throughout this paper, particle sizes will be given as diameters).…”

Section: _ J^o O T X F X R I (X^ax)dxmentioning

confidence: 54%

CH₄ and haze in Triton's lower atmosphere

Herbert¹,

Sandel²

1991

J. Geophys. Res.

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Voyager 2 ultraviolet spectrometer occultation observations at Triton have revealed two constituents of the troposphere: CH4 and another absorber visible between 1400 and 1600 Å below about 20 km altitude. The CH4appears to be saturated at the surface at both entrance and exit occultation sites. The density scale height and wavelength dependence of the long‐wavelength absorber are consistent with Rayleigh scattering in N2. However, the inferred N2 column abundance is inconsistent with the Voyager radio science (RSS) occultation measurement, and so the N2hypothesis is discarded. The most attractive alternative hypothesis for the identity of the long‐wavelength opacity is Rayleigh scattering by an aerosol haze, because the optical depth is noticeably wavelength dependent, both within the EUV range of measurement and over the range between the EUV and visual wavelengths. EUV Rayleigh scattering requires that the haze particles be very small (≤ 0.03 μm) and abundant. These characteristics suggest formation as photochemical smog or condensing N2 with a great abundance of nucleation centers. Condensation onto ions allows rapid formation of very small particles, so possibly ions created by penetrating magnetospheric charged particles (0.1 to several MeV) are nucleating the haze. Small particle size also promotes long residence times against settling, essential for accumulation to significant abundance and suggesting that eddy transport dominates settling. If this is the case, the haze scale height likely approximates the gas scale height, and the implied temperature is around 38 K. This is lower than the 50 K estimated by the RSS and is also too low for the dust devil hypothesis for the visible atmospheric plumes.

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Section: _ J^o O T X F X R I (X^ax)dxmentioning

confidence: 54%

CH₄ and haze in Triton's lower atmosphere

Herbert¹,

Sandel²

1991

J. Geophys. Res.

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“…An upper limit to Rayleigh scattering by H 2 can be set independently by the nondetection of the Raman-shifted feature at 1280 A. We derive an upper limit to the flux in a 8-A FWHM line at 1280 A of 30 Rayleighs from the spectrum to be discussed in section 6 (see also Figure 5), which corresponds to an upper limit to H Ly a emission of roughly 100 Rayleighs [Brandt, 1963;Dalgarno and Williams, 1962]. An upper limit to the contribution from resonant scattering by H can be set independently from the minimum observed brightness to date, assuming that the Uranus atmospheric H Ly a albedo and solar flux both change slowly compared to the variability of the bulk of the observed emission from Uranus, and recognizing that some of this emission may be due to charged particle excitation.…”

Section: This In Turn Limits the Contributions From Resonant Andmentioning

confidence: 99%

Continued observations of the H Ly α emission from Uranus

Clarke¹,

Durrance²,

Atreya³

et al. 1986

J. Geophys. Res.

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We present four years of observations of the disk‐averaged H Ly α emission from Uranus performed with the IUE Observatory. A detailed analysis of the uncertainties of these measurements is discussed, based both on known calibration uncertainties and on a new analysis of the uncertainty in our customized extraction procedure. On the basis of roughly 30 observations we derive an average brightness of 1400 Rayleighs. The larger data base now available has allowed us to perform a more detailed analysis of the character of this emission and its functional relationship with other parameters. The observed extent and time scales of the variability of the emission are presented, and no evidence for correlation with the solar H Ly α variations is found, implying a largely self‐excited emission. Limits are derived from the minimum observed brightness and from a modeling of the atmosphere of Uranus for the possible contribution by reflected solar H Ly α emission, which we estimate to be roughly 200 Rayleighs. We therefore interpret the remaining self‐excited emission as being produced by charged particle excitation, i.e., an aurora. Studies of possible correlations between the self‐excited component of the H Ly α emission and the density and velocity of the local solar wind are presented, based on comparisons with solar wind measurements performed in the vicinity of Uranus from the Voyager 2 and Pioneer 11 spacecraft. No evidence is found for any correlation between the solar wind density and the H Ly α brightness. We estimate an upper limit to the energy of the precipitating particles based on the lack of observed H2 band emission (which sets a lower limit to the ratio H Ly α/H2) and by analogy to the auroral precipitation on Jupiter. Finally, an estimate of the total power in the precipitating particles is on the order of 1012 watts (comparable to the aurora on Saturn), and the disturbance of the upper atmosphere by the deposited energy is discussed.

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“…Late stellar types (such as our K7V case or later), although more numerous at close distance from the Sun, are intrinsically very faint at the wavelengths at which the most notable Raman peaks appear, thus making the observations of Raman features very challenging. In order to compute CO 2 cross sections for Rayleigh scattering and the rotational Raman scattering, we use the approximate formulae from Dalgarno & Williams (1962). Because CO 2 has a relatively complicated structure of vibrational transitions, we consider only rotational Raman transitions in this work and assume all molecules are in the ground electronic and vibrational state.…”

Section: Discussionmentioning

confidence: 99%

How Does the Shape of the Stellar Spectrum Affect the Raman Scattering Features in the Albedo of Exoplanets?

Oklopčić

Hirata

Heng

2017

ApJ

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The diagnostic potential of the spectral signatures of Raman scattering, imprinted in planetary albedo spectra at short optical wavelengths, has been demonstrated in research on planets in the solar system, and has recently been proposed as a probe of exoplanet atmospheres, complementary to albedo studies at longer wavelengths. Spectral features caused by Raman scattering offer insight into the properties of planetary atmospheres, such as the atmospheric depth, composition, and temperature, as well as the possibility of detecting and spectroscopically identifying spectrally inactive species, such as H 2 and N 2 , in the visible wavelength range. Raman albedo features, however, depend on both the properties of the atmosphere and the shape of the incident stellar spectrum. Identical planetary atmospheres can produce very different albedo spectra depending on the spectral properties of the host star. Here we present a set of geometric albedo spectra calculated for atmospheres with H 2 /He, N 2 , and CO 2 composition, irradiated by different stellar types ranging from late A to late K stars. Prominent albedo features caused by Raman scattering appear at different wavelengths for different types of host stars. We investigate how absorption due to the alkali elements sodium and potassium may affect the intensity of Raman features, and we discuss the preferred strategies for detecting Raman features in future observations.

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Raman and Rayleigh Scattering of Lyman by Molecular Hydrogen

Cited by 29 publications

References 0 publications

CH₄ and haze in Triton's lower atmosphere

CH₄ and haze in Triton's lower atmosphere

Continued observations of the H Ly α emission from Uranus

How Does the Shape of the Stellar Spectrum Affect the Raman Scattering Features in the Albedo of Exoplanets?

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Raman and Rayleigh Scattering of Lyman by Molecular Hydrogen

Cited by 29 publications

References 0 publications

CH4 and haze in Triton's lower atmosphere

CH4 and haze in Triton's lower atmosphere

Continued observations of the H Ly α emission from Uranus

How Does the Shape of the Stellar Spectrum Affect the Raman Scattering Features in the Albedo of Exoplanets?

Contact Info

Product

Resources

About

CH₄ and haze in Triton's lower atmosphere

CH₄ and haze in Triton's lower atmosphere