111 research outputs found
Archival Study of Energetic Processes in the Upper Atmosphere of the Outer Planets
We compare International Ultraviolet Explorer (IUE) spectral observations of Jupiter's UltraViolet (UV) aurora in H-Lyman alpha (H-Lya) and H2 emissions with images of the UV aurora with HST to make more realistic interpretations of the IUE dataset. Use the limited spatial information in the IUE line-by-line spectra of the bright H-Lya line emission in the form of pseudo-monochromatic images at the IUE 3.5 arcsec resolution (Lya pseudo-images), to derive information on the emissions. Analysing of H2 spectra of Saturn's UV aurora to infer atmospheric level of auroral excitation from the methane absorption (color ratios). Analysing of a Uranus IUE dataset to determine periodicity in the emissions attributable to auroral emission fixed in magnetic longitude. Reviewing of the results from IUE observations of the major planets, upper atmospheres and interactions with the planets magnetospheres. Analysing of IUE spectra of the UV emissions from Io to identify excitation processes and infer properties of the Io-torus-Jupiter system
Temperature-Pressure Profile of the hot Jupiter HD 189733b from HST Sodium Observations: Detection of Upper Atmospheric Heating
We present transmission spectra of the hot Jupiter HD 189733b taken with the
Space Telescope Imaging Spectrograph aboard HST. The spectra cover the
wavelength range 5808-6380 Ang with a resolving power of R=5000. We detect
absorption from the NaI doublet within the exoplanet's atmosphere at the 9
sigma confidence level within a 5 Ang band (absorption depth 0.09 +/- 0.01%)
and use the data to measure the doublet's spectral absorption profile. We
detect only the narrow cores of the doublet. The narrowness of the feature
could be due to an obscuring high-altitude haze of an unknown composition or a
significantly sub-solar NaI abundance hiding the line wings beneath a H2
Rayleigh signature. We compare the spectral absorption profile over 5.5 scale
heights with model spectral absorption profiles and constrain the temperature
at different atmospheric regions, allowing us to construct a vertical
temperature profile. We identify two temperature regimes; a 1280 +/- 240 K
region derived from the NaI doublet line wings corresponding to altitudes below
~ 500 km, and a 2800 +/- 400 K region derived from the NaI doublet line cores
corresponding to altitudes from ~ 500-4000 km. The zero altitude is defined by
the white-light radius of Rp/Rstar=0.15628 +/- 0.00009. The temperature rises
with altitude, which is likely evidence of a thermosphere. The absolute
pressure scale depends on the species responsible for the Rayleigh signature
and its abundance. We discuss a plausible scenario for this species, a
high-altitude silicate haze, and the atmospheric temperature-pressure profile
that results. In this case, the high altitude temperature rise for HD 189733b
occurs at pressures of 10^-5 to 10^-8 bar
Optical to near-infrared transmission spectrum of the warm sub-Saturn HAT-P-12b
We present the transmission spectrum of HAT-P-12b through a joint analysis of
data obtained from the Hubble Space Telescope Space Telescope Imaging
Spectrograph (STIS) and Wide Field Camera 3 (WFC3) and Spitzer, covering the
wavelength range 0.3-5.0 m. We detect a muted water vapor absorption
feature at 1.4 m attenuated by clouds, as well as a Rayleigh scattering
slope in the optical indicative of small particles. We interpret the
transmission spectrum using both the state-of-the-art atmospheric retrieval
code SCARLET and the aerosol microphysics model CARMA. These models indicate
that the atmosphere of HAT-P-12b is consistent with a broad range of
metallicities between several tens to a few hundred times solar, a roughly
solar C/O ratio, and moderately efficient vertical mixing. Cloud models that
include condensate clouds do not readily generate the sub-micron particles
necessary to reproduce the observed Rayleigh scattering slope, while models
that incorporate photochemical hazes composed of soot or tholins are able to
match the full transmission spectrum. From a complementary analysis of
secondary eclipses by Spitzer, we obtain measured depths of
and at 3.6 and 4.5 m, respectively, which are
consistent with a blackbody temperature of K and indicate
efficient day-night heat recirculation. HAT-P-12b joins the growing number of
well-characterized warm planets that underscore the importance of clouds and
hazes in our understanding of exoplanet atmospheres.Comment: 25 pages, 19 figures, accepted for publication in AJ, updated with
proof correction
Hubble Space Telescope Imaging of the Circumstellar Nebulosity of T Tauri
Short-exposure Planetary Camera images of T Tauri have been obtained using broadband filters spanning the wavelength range 0.55-0.80 μm. The optically visible star lies very close to an arc of reflection nebulosity. The arc's northern arm extends approximately 5" from the star, while its southwestern arm appears brighter and extends only 2". The arc shows an approximate symmetry along an axis toward the west-northwest, the direction of Hind's Nebula and the blueshifted molecular outflow. The morphology of the reflected light is similar to models of scattered light within an illuminated, axisymmetric outflow cavity in a circumbinary envelope, viewed ≈ 45° from the outflow axis. However, our model images do not successfully account for the amount of limb brightening that is seen. No optical counterpart to the infrared companion is seen to a limiting magnitude of V = 19.6, which suggests A_V > 7 mag toward this source. There is no evidence for an optical tertiary, to a limiting ΔV = 5.1 mag fainter than the primary, at the position where such an object has been previously reported
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
Hubble Space Telescope Observations of the Draco Dwarf Spheroidal
We present an F606W-F814W color-magnitude diagram for the Draco dwarf
spheroidal galaxy based on Hubble Space Telescope WFPC2 images. The luminosity
function is well-sampled to 3 magnitudes below the turn-off. We see no evidence
for multiple turnoffs and conclude that, at least over the field of the view of
the WFPC2, star formation was primarily single-epoch. If the observed number of
blue stragglers is due to extended star formation, then roughly 6% (upper
limit) of the stars could be half as old as the bulk of the galaxy. The color
difference between the red giant branch and the turnoff is consistent with an
old population and is very similar to that observed in the old, metal-poor
Galactic globular clusters M68 and M92. Despite its red horizontal branch,
Draco appears to be older than M68 and M92 by 1.6 +/- 2.5 Gyrs, lending support
to the argument that the ``second parameter'' which governs horizontal branch
morphology must be something other than age. Draco's observed luminosity
function is very similar to that of M68, and the derived initial mass function
is consistent with that of the solar neighborhood.Comment: 16 pages, AASTeX, 9 postscript figures, figures 1 and 2 available at
ftp://bb3.jpl.nasa.gov/pub/draco/. Accepted for publication in the
Astronomical Journa
Lyman‐α imaging of the SO 2 distribution on Io
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94916/1/grl12620.pd
Stellar Populations in Three Outer Fields of the LMC
We present HST photometry for three fields in the outer disk of the LMC
extending approximately four magnitudes below the faintest main sequence
turnoff. We cannot detect any strongly significant differences in the stellar
populations of the three fields based on the morphologies of the
color-magnitude diagrams, the luminosity functions, and the relative numbers of
stars in different evolutionary stages. Our observations therefore suggest
similar star formation histories in these regions, although some variations are
certainly allowed. The fields are located in two regions of the LMC: one is in
the north-east field and two are located in the north-west. Under the
assumption of a common star formation history, we combine the three fields with
ground-based data at the same location as one of the fields to improve
statistics for the brightest stars. We compare this stellar population with
those predicted from several simple star formation histories suggested in the
literature, using a combination of the R-method of Bertelli et al (1992) and
comparisons with the observed luminosity function. The only model which we
consider that is not rejected by the observations is one in which the star
formation rate is roughly constant for most of the LMC's history and then
increases by a factor of three about 2 Gyr ago. Such a model has roughly equal
numbers of stars older and younger than 4 Gyr, and thus is not dominated by
young stars. This star formation history, combined with a closed box chemical
evolution model, is consistent with observations that the metallicity of the
LMC has doubled in the past 2 Gyr.Comment: 30 pages, includes 10 postscript figures. Figure 1 avaiable at
ftp://charon.nmsu.edu/pub/mgeha/LMC. Accepted for publication in Astronomical
Journa
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