30 research outputs found
Titan's topography and shape at the end of the Cassini mission
No full textWith the conclusion of the Cassini mission, we present an updated topographic map of Titan, including all the available altimetry, SARtopo, and stereophotogrammetry topographic data sets available from the mission. We use radial basis functions to interpolate the sparse data set, which covers only ∼9% of Titan's global area. The most notable updates to the topography include higher coverage of the poles of Titan, improved fits to the global shape, and a finer resolution of the global interpolation. We also present a statistical analysis of the error in the derived products and perform a global minimization on a profile-by-profile basis to account for observed biases in the input data set. We find a greater flattening of Titan than measured, additional topographic rises in Titan's southern hemisphere and better constrain the possible locations of past and present liquids on Titan's surface
Reproductive Biology and Leaf Structure of Abronia Macrocarpa Galloway (Nyctaginaceae), an Endangered East Texas Endemic
No full textAbronia macrocarpa, large fruited sand verbena, is classified as an endangered species. Distribution is restricted to three counties in eastern Texas. The species grows as a perennial throughout its range. Established plants and seedlings develop a basal rosette in the Fall and over-winter. Anthesis typically begins in March or April and is completed by May. Anthesis occasionally occurs in the Fall following periods of high precipitation. The flowers exhibit characteristics of a moth pollinated species. Since fruits did not develop in the greenhouse unless flowers were hand pollinated, there is probably no self pollination. Average pollen viability is 91.6%. Average fruit set is 62%, and seed viability is low (27%). Leaves are ovate to elliptic with entire margins. The epidermis is covered with glandular trichomes and anomocytic stomata. There are more stomata within the upper epidermal layer than the lower epidermal layer. The mesophyll is differentiated with an abundance of substomatal chambers in the palisade layer. Bundles of raphide crystals occur within idioblastic cells distributed throughout the blade and petiole.Biolog
The UV multi-object slit-spectrograph FIREBall-2 simulator
No full textInternational audienceno abstrac
Topographic Constraints on the Evolution and Connectivity of Titan's Lacustrine Basins
No full textThe topography provided by altimetry, synthetic aperture radar-topography, and stereo radargrammetry has opened new doors for Titan research by allowing for quantitative analysis of morphologic form. Using altimetry measurements, we show that Titan's Maria are consistent with an equipotential surface but that several filled lakes are found to be hundreds of meters above this sea level, suggesting that they exist in isolated or perched basins. Within a given drainage basin, empty lake floors are typically higher than the liquid elevation of nearby lakes/seas, suggesting local subsurface connectivity. The majority of Titan's lakes reside in topographically closed, sharp-edged depressions whose planform curvature suggests lateral expansion through uniform scarp retreat. Many, but not all, empty lake basins exhibit flat floors and hectometer-scale raised rims that present a challenge to formation models. We conclude that dissolution erosion can best match the observed constraints but that challenges remain in the interpretation of formation processes and materials
THE ATACAMA COSMOLOGY TELESCOPE: The POLARIZATION-SENSITIVE ACTPol INSTRUMENT
No full textThe Atacama Cosmology Telescope (ACT) makes high angular resolution measurements of anisotropies in the Cosmic Microwave Background (CMB) at millimeter wavelengths. We describe ACTPol, an upgraded receiver for ACT, which uses feedhorn-coupled, polarization-sensitive detector arrays, a 3° field of view, 100 mK cryogenics with continuous cooling, and meta material antireflection coatings. ACTPol comprises three arrays with separate cryogenic optics: two arrays at a central frequency of 148 GHz and one array operating simultaneously at both 97 GHz and 148 GHz. The combined instrument sensitivity, angular resolution, and sky coverage are optimized for measuring angular power spectra, clusters via the thermal Sunyaev–Zel'dovich (SZ) and kinetic SZ signals, and CMB lensing due to large-scale structure. The receiver was commissioned with its first 148 GHz array in 2013, observed with both 148 GHz arrays in 2014, and has recently completed its first full season of operations with the full suite of three arrays. This paper provides an overview of the design and initial performance of the receiver and related systems
Figuring Out Gas & Galaxies in Enzo (FOGGIE). XI. Circumgalactic O VI Emission Traces Clumpy Inflowing Recycled Gas
No full textThe circumgalactic medium (CGM) is host to gas flows into and out of galaxies and regulates galaxy growth, but the multiphase, diffuse gas in this region is challenging to observe. We investigate the properties of gas giving rise to O vi emission from the CGM that upcoming missions, such as the Aspera smallsat, will be able to map in local galaxies. We use the FOGGIE simulations to predict the O vi emission from edge-on galaxies across the redshift range z = 1 → 0. O vi emission is brightest surrounding small, clumpy structures near the galaxy where the gas density is high. Most of the O vi surface brightness originates from collisionally ionized, T ∼ 10 ^5.5 K, inflowing gas and is not preferentially aligned with the major or minor axis of the galaxy disk. Simulated galaxies with higher halo masses, higher median CGM gas density, and higher star formation rates produce brighter and more widespread O vi emission in their CGM. We show that while O vi emission primarily originates in inflowing gas, turning off outflows in a simulation without star formation feedback eliminates most of the O vi emission. Enrichment from feedback is necessary to mix with the inflowing gas and allow it to glow in O vi . Collectively, our findings point toward a picture where O vi emission traces warm, ionized envelopes of cooler clouds that are accreting onto the galaxy in a metal-enriched galactic fountain. Finally, we show that the detection limit of Aspera is sufficient to detect O vi emission tens of kiloparsecs from the galaxy center for ∼ L ^⋆ galaxies
A Precision Photometric Comparison between SDSS-II and CSP Type Ia Supernova Data
No full textConsistency between Carnegie Supernova Project (CSP) and SDSS-II Supernova Survey ugri measurements has been evaluated by comparing Sloan Digital Sky Survey (SDSS) and CSP photometry for nine spectroscopically confirmed Type Ia supernova observed contemporaneously by both programs. The CSP data were transformed into the SDSS photometric system. Sources of systematic uncertainty have been identified, quantified, and shown to be at or below the 0.023 mag level in all bands. When all photometry for a given band is combined, we find average magnitude differences of equal to or less than 0.011 mag in ugri, with rms scatter ranging from 0.043 to 0.077 mag. The u-band agreement is promising, with the caveat that only four of the nine supernovae are well observed in u and these four exhibit an 0.038 mag supernova-to-supernova scatter in this filter.</p
Radiometric Calibration Targets for the Mastcam-Z Camera on the Mars 2020 Rover Mission
No full textThe Mastcam-Z Camera is a stereoscopic, multispectral camera with zoom capability on NASA's Mars-2020 Perseverance rover. The Mastcam-Z relies on a set of two deck-mounted radiometric calibration targets to validate camera performance and to provide an instantaneous estimate of local irradiance and allow conversion of image data to units of reflectance (R* or I/F) on a tactical timescale. Here, we describe the heritage, design, and optical characterization of these targets and discuss their use during rover operations. The Mastcam-Z primary calibration target inherits features of camera calibration targets on the Mars Exploration Rovers, Phoenix and Mars Science Laboratory missions. This target will be regularly imaged during flight to accompany multispectral observations of the martian surface. The primary target consists of a gold-plated aluminum base, eight strong hollow-cylinder Sm2Co17 alloy permanent magnets mounted in the base, eight ceramic color and grayscale patches mounted over the magnets, four concentric, ceramic grayscale rings and a central aluminum shadow post (gnomon) painted with an IR-black paint. The magnets are expected to keep the central area of each patch relatively free of Martian aeolian dust. The Mastcam-Z secondary calibration target is a simple angled aluminum shelf carrying seven vertically mounted ceramic color and grayscale chips and seven identical, but horizontally mounted ceramic chips. The secondary target is intended to augment and validate the calibration-related information derived from the primary target. The Mastcam-Z radiometric calibration targets are critically important to achieving Mastcam-Z science objectives for spectroscopy and photometric properties.</p
Towards Equitable, Diverse, and Inclusive science collaborations: The Multimessenger Diversity Network
No full textThe Multimessenger Diversity Network (MDN), formed in 2018, extends the basic principle of multimessenger astronomy – that working collaboratively with different approaches enhances understanding and enables previously impossible discoveries – to equity, diversity, and inclusion (EDI) in science research collaborations. With support from the National Science Foundation INCLUDES program, the MDN focuses on increasing EDI by sharing knowledge, experiences, training, and resources among representatives from multimessenger science collaborations. Representatives to the MDN become engagement leads in their collaboration, extending the reach of the community of practice. An overview of the MDN structure, lessons learned, and how to join are presented
