Sona Hosseini

ON THE EXISTENCE OF ENERGETIC ATOMS IN THE UPPER ATMOSPHERE OF EXOPLANET HD209458b

Stellar irradiation and particle forcing strongly affect the immediate environment of extrasolar giant planets orbiting near their parent stars. However, it is not clear how the energy is deposited over the planetary atmosphere, nor how the momentum and energy spaces of the different species that populate the system are modified. Here, we use far-ultraviolet emission spectra from HD209458 in the wavelength range (1180-1710) A to bring new insight to the composition and energetic processes in play in the gas nebula around the transiting planetary companion. In that frame, we consider up-to-date atmospheric models of the giant exoplanet where we implement non-thermal line broadening to simulate the impact on the transit absorption of superthermal atoms (H I, O I, and C II) populating the upper layers of the nebula. Our sensitivity study shows that for all existing models, a significant line broadening is required for O I and probably for C II lines in order to fit the observed transit absorptions. In that frame, we show that O I and C II are preferentially heated compared to the background gas with effective temperatures as large as T O I /TB ~ 10 for O I and T C II /TB ~ 5 for C II. By contrast, the situation is much less clear for H I because several models could fit the Lyα observations including either thermal H I in an atmosphere that has a dayside vertical column [H I] ~ 1.05 × 1021 cm–2, or a less extended thermal atmosphere but with hot H I atoms populating the upper layers of the nebula. If the energetic H I atoms are either of stellar origin or populations lost from the planet and energized in the outer layers of the nebula, our finding is that most models should converge toward one hot population that has an H I vertical column in the range [H I]hot ~ (2-4) × 1013 cm–2 and an effective temperature in the range T H I ~ (1-1.3) × 106 K, but with a bulk velocity that should be rather slow.

Khayyam: a tunable spatial heterodyne spectrometer for observing diffuse emission line targets

We describe first results from a new instrument-telescope configuration that combines all of the capabilities necessary to obtain high resolving power visible band spectra of diffuse targets from small aperture telescopes where significant observing time can be obtained. This instrument –Khayyam- is a tunable all-reflective spatial heterodyne spectrometer (SHS) that is mounted to a fixed focal plane shared by the 0.6m Coude auxiliary telescope and the 3m Shane telescope on Mt. Hamilton. Khayyam has an up to 78 arcmin input field of view, resolving power up to 176000, and a tunable bandpass from 350-700 nm. It is being field tested for initial use to study spatially extended solar system targets where high resolving power is necessary to separate multimodal signals, crowded molecular bands, and to sample low velocities (<10 km/s) and rapid temporal cadence is necessary to track physical evolution. Two of the best comet targets during next year is comet C/2011 L4 (PanSTARRS), and C/2011 F1 (LINEAR). Our goal is to sequentially measure isotopic ratios of 14N:15N and 12C:13C in CN, along with the production rate and the production rate ratios of varies daughter species, particularly C2, C3, NH2, OI, and CN, as a function of heliocentric distance and time.

Tunable spatial heterodyne spectroscopy (TSHS): a new technique for broadband visible interferometry

In the study of faint, extended sources at high resolving power, interferometry offers significant etendue advantages relative to conventional dispersive grating spectrometers. A Spatial Heterodyne Spectrometer (SHS) is a compact format two-beam interferometer that produces wavenumber dependent 2-D Fizeau fringe pattern from which an input spectrum can be obtained via a Fourier transform. The sampled bandpass of SHS is limited by the highest spatial frequency that can be sampled by the detector, which is typically less than 10 nm. This limitation has made these instruments useful primarily for studies of single emission line features or molecular bands. To date there have been few broadband implementations. We describe here continuing progress toward development of a broadband tunable SHS (TSHS) that is based on an all-reflective format where a single grating operates simultaneously as a beam-splitter, dispersive element, and beam combiner. The narrow spectral coverage of the TSHS is moved to different tuning wavenumbers by adjusting the angle of the pilot mirrors that guide the interfering beams through the optical path, thus slewing the acceptance band over a much broader spectral range. Our present effort involves a breadboard laboratory prototype of a secondgeneration TSHS in which we address several technical limitations of an earlier version. In particular the new design reduces wavefront distortions on the pilot mirrors, solves problems with magnification and focus of the fringe localization plane onto the detector, and addresses the variability in sensitivity and resolving power limitations of using a single grating over a large bandpass.

Concept study for a compact planetary homodyne interferometer (PHI) for temporal global observation of methane on Mars in IR

We present a concept study to develop a new instrument to sequentially and over a long time measure methane abundance on Mars and find out its global seasonal variations, if any. The Planetary Homodyne Interferometer (PHI) can offer integrated spectra over a wide field-of-view (FOV) in high spectral resolution (R~105) in a compact design using no (or a small < 1m) primary mirror. PHI is best suited to studies of sources where temporally tracing specific spectral features sensitivity, and spectral resolution is of higher significance than spatial fidelity.

Concept study for a compact homodyne astrophysics spectrometer for exoplanets (CHASE)

In this concept study, we are targeting to build a new instrument to sequentially observe exoplanet atmospheres and their parent’s stellar spectra over a significant time in NUV and FUV. The Compact Homodyne Astrophysics Spectrometer for Exoplanets (CHASE) offers integrated spectra over a wide field-of-view (FOV~40arcsec) in high spectral resolution (R>105) in a miniaturized architecture using no (or a small < 1m) primary mirror. CHASE’s wide FOV is compatible with the relaxed pointing requirements of current CubeSats and SmallSats which makes it readily qualifiable for space in a compact format and have the potential to enable major scientific breakthroughs.

Khayyam: progress and prospects of coupling a spatial heterodyne spectrometer (SHS) to a Cassegrain telescope for optical interferometry

In the temporal study of faint, extended sources at high resolving power, Spatial Heterodyne Spectrometer (SHS) can offer significant advantages about conventional dispersive grating spectrometers. We describe here a four-year continuous progress in Mt. Hamilton, Lick Observatory, toward development of a prototype reflective Spacial Heterodyne Spectrometer, Khayyam, instrument-telescope configuration to combine all of the capabilities necessary to obtain high resolving power visible band spectra of diffuse targets from small aperture on-axis telescopes where significant observing time can be obtained. We will discuss the design considerations going into this new system, installation, testing of the interferometer-telescope combination, the technical challenges and procedures moving forward.

Design of a low cost mission to the Neptunian system

Visited only by Voyager 2 in 1989, Neptune and its moon Triton hold important clues to the formation and evolution of the solar system and exoplanetary systems. Neptune-sized planets are the most commonly discovered exoplanets to date. Neptune, an ice giant, is theorized to have migrated from its formation location in the early solar system. This migration affects the expected interior structure, composition, and dynamical evolution of the planet. Triton is conjectured to be a heavily-processed, captured Kuiper Belt Object (KBO), a remnant from the early solar nebula and unique in our solar system. Triton may possess a subsurface aqueous ocean, making it an important astrobiological target. The 2013-2022 Planetary Science Decadal Survey [1] identified a number of high priority science goals for the Neptunian system, including understanding the structure, composition, and dynamics of Neptunes atmosphere and magnetosphere, as well as surveying the surface of Triton. Following these guidelines, we present a low cost flyby mission concept to Neptune and Triton: TRIDENT (Taking Remote and In-situ Data to Explore Neptune and Triton). TRIDENT would carry six instruments and a government furnished atmospheric probe and would provide significant improvements over the scientific measurements undertaken by Voyager 2. In this paper, we first provide a detailed overview of the science questions pertaining to Neptune and Triton and of the science investigations necessary to elucidate them. We then present the design of TRIDENTs instrument suite, the trajectory and the spacecraft, as well as the motivation behind each of our choices. In particular, we demonstrate that, for a mission launched on an Atlas V 551, a Neptune orbiter mission would be infeasible with current technology levels without the use of aerocapture. We therefore present a flyby mission concept with a cost lower than FY2015

First calibration and visible wavelength observations of Khayyam, a tunable spatial heterodyne spectroscopy (SHS)

1.5B. We also show that the proposed mission has low risk and significant margin and that several de-scope options are available in the event of cost overruns. This study was prepared in conjunction with the NASA 2013 Planetary Science Summer School. The work presented is a hypothetical mission proposal, for planning and discussion purposes only. It does not represent NASAs interests in any way.

Khayyam: a second generation tunable spatial heterodyne spectrometer for broadband observation of diffuse emission line targets

We describe results from a new instrument-telescope configuration that combines all of the capabilities necessary to obtain high resolving power visible band spectra of diffuse targets from small aperture on-axis telescopes where significant observing time can be obtained. This instrument, Khayyam, is a tunable all-reflective spatial heterodyne spectrometer (TSHS) that is mounted to a fixed focal plane shared by the 0.6m Coude auxiliary telescope on Mt. Hamilton, CA. Khayyam has up to 55 arcsec input field of view, resolving power up to 176000, and a tunable bandpass covering (triangle)λB < 100nm. Khayyam is being field tested to study spatially extended astronomical targets where high resolving power is necessary to separate multimodal signals, crowded molecular bands, and to sample low (<10 km/s) velocities at rapid temporal cadence. Here we will discuss the design considerations going into this new system, its installation, testing of the interferometer-telescope combination, the first science target observations and future plans.

A Second Generation Tunable Spatial Heterodyne Spectrometer for Ground-Based Observations of Diffuse Emission Line Targets

We report on progress toward development of a second-generation tunable spatial heterodyne spectrometer (TSHS) at the fixed focus of the Coudé Auxiliary Telescope (CAT) in the Shane observatory at Lick Observatory (Khayyam). SHS instruments are a class of interferometric sensor capable of providing a combination of large étendue, high resolving power (R=λ/dλ~ 105) and wide field of view (FOV~0.5 degree) at Optical and NUV wavelengths in a compact format. The TSHS implementation addresses the bandpass limitation of the basic SHS through controlled rotation of pilot mirrors in the interferometer. The use of a single grating as both a dispersing and beam-splitting element in the all-reflective SHS greatly relaxes the precision required in the alignment of the other optical elements relative to a more typical scanning Fourier Transform Spectrometer and allows the TSHS implementation to be accomplished with low-cost commercial rotation stages. The new design builds on a previous design originally tested in 2007, and will address several issues identified with the input beam, output imaging, and grating efficiency (Dawson and Harris, 2009). Here we will discuss the design considerations going into this new system and the initial results of the installation and testing of the TSHS and the future plans.