25 research outputs found
Seeing Double at Neptune's South Pole
Keck near-infrared images of Neptune from UT 26 July 2007 show that the cloud
feature typically observed within a few degrees of Neptune's south pole had
split into a pair of bright spots. A careful determination of disk center
places the cloud centers at -89.07 +/- 0 .06 and -87.84 +/- 0.06 degrees
planetocentric latitude. If modeled as optically thick, perfectly reflecting
layers, we find the pair of features to be constrained to the troposphere, at
pressures greater than 0.4 bar. By UT 28 July 2007, images with comparable
resolution reveal only a single feature near the south pole. The changing
morphology of these circumpolar clouds suggests they may form in a region of
strong convection surrounding a Neptunian south polar vortex.Comment: 10 pages, 7 figures; accepted to Icaru
Retrieving Neptune's aerosol properties from Keck OSIRIS observations. I. Dark regions
We present and analyze three-dimensional data cubes of Neptune from the
OSIRIS integral-field spectrograph on the 10-m Keck telescope, from July 2009.
These data have a spatial resolution of 0.035"/pixel and spectral resolution of
R~3800 in the H and K broad bands. We focus our analysis on regions of
Neptune's atmosphere that are near-infrared dark- that is, free of discrete
bright cloud features. We use a forward model coupled to a Markov chain Monte
Carlo algorithm to retrieve properties of Neptune's aerosol structure and
methane profile above ~4 bar in these near-infrared dark regions.
Using a set of high signal-to-noise spectra in a cloud-free band from 2-12N,
we find that Neptune's cloud opacity is dominated by a compact, optically thick
cloud layer with a base near 3 bar and composed of low albedo, forward
scattering particles, with an assumed characteristic size of ~1m. Above
this cloud, we require a vertically extended haze of smaller (~0.1 m)
particles, which reaches from the upper troposphere (~0.6 bar) into the
stratosphere. The particles in this haze are brighter and more isotropically
scattering than those in the deep cloud. When we extend our analysis to 18
cloud-free locations from 20N to 87S, we observe that the optical depth in
aerosols above 0.5 bar decreases by a factor of 2-3 or more at mid- and
high-southern latitudes relative to low latitudes.
We also consider Neptune's methane (CH) profile, and find that our
retrievals indicate a strong preference for a low methane relative humidity at
pressures where methane is expected to condense. Our preferred solution at most
locations is for a methane relative humidity below 10% near the tropopause in
addition to methane depletion down to 2.0-2.5 bar. We tentatively identify a
trend of lower CH columns above 2.5 bar at mid- and high-southern latitudes
over low latitudes.Comment: Published in Icarus: 15 September 201
Jupiter's Deep Cloud Structure Revealed Using Keck Observations of Spectrally Resolved Line Shapes
Technique: We present a method to determine the pressure at which significant cloud opacity is present between 2 and 6 bars on Jupiter. We use: a) the strength of a Fraunhofer absorption line in a zone to determine the ratio of reflected sunlight to thermal emission, and b) pressure- broadened line profiles of deuterated methane (CH3D) at 4.66 meters to determine the location of clouds. We use radiative transfer models to constrain the altitude region of both the solar and thermal components of Jupiter's 5-meter spectrum. Results: For nearly all latitudes on Jupiter the thermal component is large enough to constrain the deep cloud structure even when upper clouds are present. We find that Hot Spots, belts, and high latitudes have broader line profiles than do zones. Radiative transfer models show that Hot Spots in the North and South Equatorial Belts (NEB, SEB) typically do not have opaque clouds at pressures greater than 2 bars. The South Tropical Zone (STZ) at 32 degrees South has an opaque cloud top between 4 and 5 bars. From thermochemical models this must be a water cloud. We measured the variation of the equivalent width of CH3D with latitude for comparison with Jupiter's belt-zone structure. We also constrained the vertical profile of H2O in an SEB Hot Spot and in the STZ. The Hot Spot is very dry for a probability less than 4.5 bars and then follows the H2O profile observed by the Galileo Probe. The STZ has a saturated H2O profile above its cloud top between 4 and 5 bars
The InfraRed Imaging Spectrograph (IRIS) for TMT: latest science cases and simulations
The Thirty Meter Telescope (TMT) first light instrument IRIS (Infrared
Imaging Spectrograph) will complete its preliminary design phase in 2016. The
IRIS instrument design includes a near-infrared (0.85 - 2.4 micron) integral
field spectrograph (IFS) and imager that are able to conduct simultaneous
diffraction-limited observations behind the advanced adaptive optics system
NFIRAOS. The IRIS science cases have continued to be developed and new science
studies have been investigated to aid in technical performance and design
requirements. In this development phase, the IRIS science team has paid
particular attention to the selection of filters, gratings, sensitivities of
the entire system, and science cases that will benefit from the parallel mode
of the IFS and imaging camera. We present new science cases for IRIS using the
latest end-to-end data simulator on the following topics: Solar System bodies,
the Galactic center, active galactic nuclei (AGN), and distant
gravitationally-lensed galaxies. We then briefly discuss the necessity of an
advanced data management system and data reduction pipeline.Comment: 15 pages, 7 figures, SPIE (2016) 9909-0
Dust, Ice and Gas in Time (DIGIT) Herschel program first results: A full PACS-SED scan of the gas line emission in protostar DK Cha
DK Cha is an intermediate-mass star in transition from an embedded
configuration to a star plus disk stage. We aim to study the composition and
energetics of the circumstellar material during this pivotal stage. Using the
Range Scan mode of PACS on the Herschel Space Observatory, we obtained a
spectrum of DK Cha from 55 to 210 micron as part of the DIGIT Key Program.
Almost 50 molecular and atomic lines were detected, many more than the 7 lines
detected in ISO-LWS. Nearly the entire ladder of CO from J=14-13 to 38-37
(E_u/k = 4080 K), water from levels as excited as E_u/k = 843 K, and OH lines
up to E_u/k = 290 K were detected. The continuum emission in our PACS SED scan
matches the flux expected from a model consisting of a star, a surrounding disk
of 0.03 Solar mass, and an envelope of a similar mass, supporting the
suggestion that the object is emerging from its main accretion stage.
Molecular, atomic, and ionic emission lines in the far-infrared reveal the
outflow's influence on the envelope. The inferred hot gas can be photon-heated,
but some emission could be due to C-shocks in the walls of the outflow cavity.Comment: 4 Page letter, To appear in A&A special issue on Hersche
The InfraRed Imaging Spectrograph (IRIS) for TMT: Overview of innovative science programs
IRIS (InfraRed Imaging Spectrograph) is a first light near-infrared
diffraction limited imager and integral field spectrograph being designed for
the future Thirty Meter Telescope (TMT). IRIS is optimized to perform
astronomical studies across a significant fraction of cosmic time, from our
Solar System to distant newly formed galaxies (Barton et al. [1]). We present a
selection of the innovative science cases that are unique to IRIS in the era of
upcoming space and ground-based telescopes. We focus on integral field
spectroscopy of directly imaged exoplanet atmospheres, probing fundamental
physics in the Galactic Center, measuring 10^4 to 10^10 Msun supermassive black
hole masses, resolved spectroscopy of young star-forming galaxies (1 < z < 5)
and first light galaxies (6 < z < 12), and resolved spectroscopy of strong
gravitational lensed sources to measure dark matter substructure. For each of
these science cases we use the IRIS simulator (Wright et al. [2], Do et al.
[3]) to explore IRIS capabilities. To highlight the unique IRIS capabilities,
we also update the point and resolved source sensitivities for the integral
field spectrograph (IFS) in all five broadband filters (Z, Y, J, H, K) for the
finest spatial scale of 0.004" per spaxel. We briefly discuss future
development plans for the data reduction pipeline and quicklook software for
the IRIS instrument suite.Comment: Proceedings of the SPIE, 9147-36
AVIATR - Aerial Vehicle for In-situ and Airborne Titan Reconnaissance A Titan Airplane Mission Concept
We describe a mission concept for a stand-alone Titan airplane mission: Aerial Vehicle for In-situ and Airborne Titan Reconnaissance (AVIATR). With independent delivery and direct-to-Earth communications, AVIATR could contribute to Titan science either alone or as part of a sustained Titan Exploration Program. As a focused mission, AVIATR as we have envisioned it would concentrate on the science that an airplane can do best: exploration of Titan's global diversity. We focus on surface geology/hydrology and lower-atmospheric structure and dynamics. With a carefully chosen set of seven instruments-2 near-IR cameras, 1 near-IR spectrometer, a RADAR altimeter, an atmospheric structure suite, a haze sensor, and a raindrop detector-AVIATR could accomplish a significant subset of the scientific objectives of the aerial element of flagship studies. The AVIATR spacecraft stack is composed of a Space Vehicle (SV) for cruise, an Entry Vehicle (EV) for entry and descent, and the Air Vehicle (AV) to fly in Titan's atmosphere. Using an Earth-Jupiter gravity assist trajectory delivers the spacecraft to Titan in 7.5 years, after which the AVIATR AV would operate for a 1-Earth-year nominal mission. We propose a novel 'gravity battery' climb-then-glide strategy to store energy for optimal use during telecommunications sessions. We would optimize our science by using the flexibility of the airplane platform, generating context data and stereo pairs by flying and banking the AV instead of using gimbaled cameras. AVIATR would climb up to 14 km altitude and descend down to 3.5 km altitude once per Earth day, allowing for repeated atmospheric structure and wind measurements all over the globe. An initial Team-X run at JPL priced the AVIATR mission at FY10 $715M based on the rules stipulated in the recent Discovery announcement of opportunity. Hence we find that a standalone Titan airplane mission can achieve important science building on Cassini's discoveries and can likely do so within a New Frontiers budget
A SEARCH FOR C AND C IN THE (MOLECULAR) CARBON-RICH SIGHTLINE TOWARD HD 204827
{ S. P. Souza \& B. L. Lutz, {\em Astrophys. J.{ J. P. Maier, N. M. Lakin, G. A. H. Walker, \& D. A. Bohlender, {\em Astrophys. J.{ T. Oka, J. A. Thorburn, B. J. McCall, S. D. Friedman, L. M. Hobbs, P. Sonnentrucker, D. E. Welty, \& D. G. York, {\em Astrophys. J.{ M. Adamkovics, G. A. Blake, \& B. J. McCall, {\em Astrophys. J.{ J. P. Maier, G. A. H. Walker, \& D. A. Bohlender, {\em Astrophys. J.Author Institution: Astronomy Department, 601 Campbell Hall, University of California,; Berkeley, CA 94720; Division of Chemistry and Chemical Engineering, California; Institute of Technology, Pasadena, CA 91125; Departments of Chemistry and Astronomy, University of Illinois at; Urbana-Champaign, 601 S. Mathews Ave., Urbana, IL 61801\hspace{0.2in} The simplest carbon-chain molecule C was discovered in the interstellar medium in 1977} {\bf 213}, L129 (1977)}. Fourteen years later, J. P. Maier and others reported the first detection of C in three diffuse cloud sightlines} {\bf 553}, 267 (2001)}. A followup survey at lower resolution} {\bf 582}, 823 (2003)} detected C in 15 lines of sight with E ranging from 0.33 to 1.12 and noted that the sightline toward HD 204827 showed particularly high C and C column densities. This result was confirmed by a survey at higher resolution} {\bf 595}, 235 (2003)}. \hspace{0.2in} The next-longest carbon chains, C and C, have not yet been detected in the interstellar medium. A low resolution search was performed by Oka et al., and a more sensitive high resolution search has been reported} {\bf 602}, 286 (2004)} towards Ophiuchi using the 3789 \AA\ band of C and the 5109 \AA\ band of C. While Ophiuchi is a very bright star (=2.56), its C column density ( cm) is considerably lower than that towards HD 204827 ( cm). Consequently, we decided to attempt a sensitive search for C and C in this carbon-rich sightline. The relative faintness (=7.94) of the source was overcome by the large aperture (10-m) of the Keck telescope and a long (two nights) integration. Unfortunately, this work has not yielded a detection. A detailed interpretation of this non-detection in terms of carbon chain chemistry in diffuse clouds is hampered both by uncertainties in the oscillator strengths of the transitions as well as by the comparatively immature state of chemical models of diffuse cloud chemistry (relative to models of dense cloud chemistry). We encourage further theoretical and modelling efforts along these lines
EXCITATION PROFILES IN DIFFUSE INTERSTELLAR CLOUDS
Department of Astronomy, University of California, Berkeley, CA 94720.Author Institution: Department of Chemistry, University of California; Division of Geological and Planetary Sciences 150-21, California Institute of Technology; Department of Chemistry, University of CaliforniaThe very high-resolution , very high signal-to-noise , optical (4051 {\AA}) spectrum of the carbon-chain molecule is reported for 10 diffuse interstellar clouds, demonstrating the possibility for detailed study of polyatomic molecules in the diffuse interstellar medium (ISM). Thus far, is the largest identified molecular species to be observed in absorption in the diffuse ISM. The first detection of toward three stars (Maier et al., 2001) contained a single spectrum of sufficient quality to show a non-thermal equilibrium rotational excitation profile. This data was adequately modeled with a two-temperature thermal distribution. Rotationally resolved was then measured in one additional source, and a detailed radiative balance model was used to analyze the data (Roueff et al., 2002). A low resolution survey (Oka et al., 2002) has measured the column densities of in roughly 30 targets, laying the groundwork for high resolution observations. We present rotationally resolved and very high signal-to-noise spectra taken with the HIRES spectrometer on the 10-m Keck telescope and with the Hamilton echelle spectrometer on the Shane 3-m Lick Observatory telescope. The measurements allow for a detailed analysis of the molecular excitation in a variety of diffuse interstellar environments. The observed excitation profiles are modeled using 1) thermal distributions incorporating either one or two kinetic temperatures and 2) a new technique involving a least squares fit of the entire spectrum using the population in each rotational level as a fit parameter. We discuss how these observations constrain our understanding of the various environments in these sightlines, correlation between and , and the prospects for the study of larger polyatomic molecules in the diffuse ISM