936 research outputs found
Planetary Fabry-Perot spectroscopy
Application of high spectral resolution, Earth-based Fabry-Perot spectroscopy to the study of planetary atmospheres, for which current topics are outer planet HD and H2 spectra (atmospheric structure, D/H ratio), Mars CO2, CO, O2, and H2O spectra (atomspheric photochemistry), Venus H2O and HDO, associated laboratory spectroscopy (especially H2 overtone bands, HDO) was accomplished. Monochromatic charge coupled device (CCD) imaging photometry of the Jovian nebula, with images taken in rapid sequence among the diagnostic spectral lines of ionized sulfur species, provided self-supporting snapshots of the Jupiter/Io plasma conditions (spatially resolved electron and ion densities and temperatures), covering the post-Voyager period from 1981 and leading up to the Galileo tour in the early 1990s. High spectral resolution Fabry-Perot/charge coupled device (CCD) imaging of comets (OI, CI, and H2O(+) velocity maps and spatial distriubtions), and Io's charge exchanged neutral jet was studied
The HD/H2 ratio in the atmosphere of Uranus
High resolution spectra of HD and H2 were brought together to derive the D/H ratio for Uranus. The deuterium concentration in the dominant molecular hydrogen phase is least susceptible to the effects of isotope fractionation in the planetary atmosphere, and the determination of relative abundances of HD and H2 is unambiguous due to nearness and relative weakness of the chosen spectral lines. The HD 5-0 R(0) and R(1) dipole lines and the H2 4-0 S(0), S(1), and S(2) quadrupole lines were obtained with a PEPSIOS instrument at the Palomar 5-meter telescope. The H2 spectra, which resolve the asymmetric line profiles resulting from pressure shifts in the deep stratified Uranus atmosphere, unambiguously define the line-of-sight hydrogen abundance for comparison with the HD spectra. The 5-0 band of HD was chosen to minimize interference from blended CH4 lines. However, weak interfering lines were found in the 5-0 bands from Uranus as well, and some uncertainties remain regarding the intrinsic line strengths in molecular hydrogen, complicating the analysis of the HD/H2 data. Nevertheless, it is established that the D/H ratio in the atmosphere of Uranus is smaller than the Jovian value, and is significantly smaller than recent theoretical predictions for Uranus based on estimates of isotope fractionation in the pre-planetary solar nebulae
Phase Functions and Light Curves of Wide Separation Extrasolar Giant Planets
We calculate self-consistent extrasolar giant planet (EGP) phase functions
and light curves for orbital distances ranging from 0.2 AU to 15 AU. We explore
the dependence on wavelength, cloud condensation, and Keplerian orbital
elements. We find that the light curves of EGPs depend strongly on wavelength,
the presence of clouds, and cloud particle sizes. Furthermore, the optical and
infrared colors of most EGPs are phase-dependent, tending to be reddest at
crescent phases in and . Assuming circular orbits, we find that at
optical wavelengths most EGPs are 3 to 4 times brighter near full phase than
near greatest elongation for highly-inclined (i.e., close to edge-on) orbits.
Furthermore, we show that the planet/star flux ratios depend strongly on the
Keplerian elements of the orbit, particularly inclination and eccentricity.
Given a sufficiently eccentric orbit, an EGP's atmosphere may make periodic
transitions from cloudy to cloud-free, an effect that may be reflected in the
shape and magnitude of the planet's light curve. Such elliptical orbits also
introduce an offset between the time of the planet's light curve maximum and
the time of full planetary phase, and for some sets of orbital parameters, this
light curve maximum can be a steeply increasing function of eccentricity. We
investigate the detectability of EGPs by proposed space-based direct-imaging
instruments.Comment: submitted to Astrophysical Journa
A study of the Jovian [S II] nebula at high spectral resolution
Observations of forbidden line S II λλ6716-6731 A emissions from the Jovian magnetosphere have been carried out with a PEPSIOS spectrometer at the Hale 5 m telescope. Spectral resolving power was sufficient to resolve the forbidden line S II line widths. From measured λλ6716-6731 A doublet ratios and spectral line widths a thermal plasma is found characterized by temperatures about 2 x 10^4 K and electron densities about ~2 x 10^3 cm^(-3). The source of forbidden line S II emissions was centered within a toroidal region of radius 5 Jupiter radii (inside the orbit of Io), with tight latitudinal confinement near the equilibrium equator for ions in the tilted corotating Jovian magnetic field, and significant long-lived longitudinal structure
The evaluation of a shuttle borne lidar experiment to measure the global distribution of aerosols and their effect on the atmospheric heat budget
A shuttle-borne lidar system is described, which will provide basic data about aerosol distributions for developing climatological models. Topics discussed include: (1) present knowledge of the physical characteristics of desert aerosols and the absorption characteristics of atmospheric gas, (2) radiative heating computations, and (3) general circulation models. The characteristics of a shuttle-borne radar are presented along with some laboratory studies which identify schemes that permit the implementation of a high spectral resolution lidar system
Theoretical Spectra and Atmospheres of Extrasolar Giant Planets
We present a comprehensive theory of the spectra and atmospheres of
irradiated extrasolar giant planets. We explore the dependences on stellar
type, orbital distance, cloud characteristics, planet mass, and surface
gravity. Phase-averaged spectra for specific known extrasolar giant planets
that span a wide range of the relevant parameters are calculated, plotted, and
discussed. The connection between atmospheric composition and emergent spectrum
is explored in detail. Furthermore, we calculate the effect of stellar
insolation on brown dwarfs. We review a variety of representative observational
techniques and programs for their potential for direct detection, in light of
our theoretical expectations, and we calculate planet-to-star flux ratios as a
function of wavelength. Our results suggest which spectral features are most
diagnostic of giant planet atmospheres and reveal the best bands in which to
image planets of whatever physical or orbital characteristics.Comment: 47 pages, plus 36 postscript figures; with minor revisions, accepted
to the Astrophysical Journal, May 10, 2003 issu
The structure of Io's thermal corona and implications for atmospheric escape
We investigate the escape of species from Io's atmosphere using a steady-state model of Io's exospheric
corona and its interaction with the Io plasma torus. The corona is assumed to be spherically symmetric with
the radial density and compositional structure determined by the gas kinetic temperature, critical level radius,
and mixing ratios of the component species. Thermal and nonthermal escape rates are calculated and the
results compared with previously estimated torus and neutral cloud supply rates for O, S, Na, and K. Both
oxygen- and sulfur-dominated exospheres are considered. Atmospheric sputtering is found to be the major
escape mechanism for models in which the plasma flow reaches the critical level. However, such models
produce total mass-loading rates an order of magnitude larger than inferred values suggesting that either (1)
the structure of the thermal corona is significantly modified by the nonthermal interaction, or (2) substantial
plasma flow modification and deflection occurs in the corona at or above the critical level. Assuming that the
thermal model is a correct description of the corona, a comparison of these results with the observed near-Io
distribution of neutral Na and estimated source rates for the neutral Na "jets" suggests an extended Na
coronal component. Assuming that this component is part of the thermal exosphere, we find that the observations
are consistent with an O-dominated corona, an exospheric temperature ~1000 K, a 0.001 critical level
mixing ratio of Na, and a critical level radius ~1.5 R_(Io)
Stellar Populations at the Center of IC 1613
We have observed the center of the Local Group dwarf irregular galaxy IC 1613
with WFPC2 aboard the Hubble Space Telescope in the F439W, F555W, and F814W
filters. We find a dominant old stellar population (aged ~7 Gyr), identifiable
by the strong red giant branch (RGB) and red clump populations. From the (V-I)
color of the RGB, we estimate a mean metallicity of the intermediate-age
stellar population [Fe/H] = -1.38 +/- 0.31. We confirm a distance of 715 +/- 40
kpc using the I-magnitude of the RGB tip. The main-sequence luminosity function
down to I ~25 provides evidence for a roughly constant SFR of approximately
0.00035 solar masses per year across the WFPC2 field of view (0.22 square kpc)
during the past 250-350 Myr. Structure in the blue loop luminosity function
implies that the SFR was ~50% higher 400-900 Myr ago than today. The mean heavy
element abundance of these young stars is 1/10th solar. The best explanation
for a red spur on the main-sequence at I = 24.7 is the blue horizontal branch
component of a very old stellar population at the center of IC 1613. We have
also imaged a broader area of IC 1613 using the 3.5-meter WIYN telescope under
excellent seeing conditions. The AGB-star luminosity function is consistent
with a period of continuous star formation over at least the age range 2-10
Gyr. We present an approximate age-metallicity relation for IC 1613, which
appears similar to that of the Small Magellanic Cloud. We compare the Hess
diagram of IC 1613 to similar data for three other Local Group dwarf galaxies,
and find that it most closely resembles the nearby, transition-type dwarf
galaxy Pegasus (DDO 216).Comment: To appear in the September 1999 Astronomical Journal. LaTeX, uses
AASTeX v4.0, emulateapj style file, 19 pages, 12 postscript figures, 2
tables. 5 of the figures available separately via the WW
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