Extensive observations were made of six FU Orionis objects (RNO 1B/1C, V1057 Cygni, Elias 1-12, V1515 Cygni and FU Orionis) and one pre-outburst candidate (V1331 Cygni) using the Owens Valley millimeter-wave array and the Caltech Submillimeter Observatory (CSO). Aperture synthesis maps of CO (1\u21920), \u00b9\u00b3CO (1\u21920), \u00b9\u00b3CO (2\u21921), \u00b9\u2078CO (1\u21920), and \u00b3CO (2\u21921) molecular lines and associated dust continuum emission trace the masses, kinematics and morphology of FU Orionis disks, envelopes, and outflows. Maps from the CSO delineate outflowing gas at larger spatial scales while line strengths, when input into radiative transfer models, yield column densities and fractional chemical abundances.
\r\n\r\nUnresolved 1.3 mm continuum emission from Vl331 Cygni and V1057 Cygni reveal massive circumstellar disks of 0.5 and 0.09 M\u2609, respectively. Maps of the 2.6 and 3.1 mm continuum emission reveal that RNO 1C is surrounded by a flattened dusty envelope, 5000 AU in size, with mass \u2a7e 1.1 M\u2609. No evidence is seen for multiple systems with orbital periods \u2273 4 x 10\u2074 years years.\r\n\r\nAll sources, with the exception of RNO 1B/1C are surrounded by large molecular gas envelopes between 2000-7500 AU in size, with masses ranging from 2 x 10\u207b\u00b3 to 0.36 M\u2609. Aperture synthesis maps suggest the envelopes are asymmetrically distributed. Gas kinematics around V1057 Cygni and Elias 1-12 suggest, but do not demand, that this material is rotating and possibly infalling.
\r\n\r\nOf the seven sources observed, all but FU Orionis show signs of outflowing molecular gas. No high velocity clumps or \"bullets\" are seen towards any of the sources. V1331 Cygni, V1057 Cygni, and V1515 Cygni possess arc or ring-like outflow morphologies, while emission from RNO 1B/1C and Elias 1-12 delineates filled outflow shells. All emission patterns are consistent with outflow shells being viewed at different angles. Although based on the statistics of small numbers, observations suggest shells are seen more frequently around FUors than T Tauri stars. Shell formation may therefore be caused by time-dependent events in the outflow. Cross-cutting arcs within the shell structure, seen towards RNO 1B/1C and Elias 1-12, are probably ridges of gas swept-up by the most recent outbursts, confirming the repetitive nature of FUor outbursts. Estimates of the dynamical ages of the arcs suggest that the interval between outbursts is ~5 x 10\u00b3 and 1.3 x 10\u2074 years for RNO 1B/1C and Elias 1-12 respectively, consistent with previous estimates of FUor cycling times.
\r\n\r\nComparable envelopes and shell-like outflow structure are seen towards embedded sources while envelopes surrounding T Tauri stars are smaller and less massive. This suggests FU Orionis objects are transition sources between deeply embedded and optically visible stars. The strength of the molecular outflow emission is correlated with the mass of the extended envelope; the outflow has evacuated molecular gas leaving less to be swept-up by subsequent outbursts, while envelope masses are smaller since less material is available for accretion.
\r\n\r\nChemically, fractional abundances of SiO and methanol are enhanced towards RNO 1B/1C by over an order of magnitude. Methanol is enhanced relative to HCN and H2CO towards Elias 1-12. Such large changes in fractional abundances must be caused by chemical processing. The SiO enrichments may be produced by sputtering or evaporation of dust grains in regions of directly shocked material or by chemical reactions of SiH4 after sublimation from grain surfaces. Methanol enrichments are difficult to produce in strong shocks, and may be caused by low velocity grain-grain collisions. For RNO 1B/1C, evaporation of the entire methanol rich grain mantles seems to be required; while for Elias 1-12 mantle phase changes from an amorphous ice to a clathrate hydrate can be invoked, expelling the methanol, with smaller molecules remaining trapped in the clathrate. Such low velocity collisions probably occur in the turbulent shear zones surrounding the outflowing gas.
", "doi": "10.7907/14NE-ZW09", "publication_date": "1995", "thesis_type": "phd", "thesis_year": "1995" }, { "id": "thesis:7397", "collection": "thesis", "collection_id": "7397", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01142013-104747074", "primary_object_url": { "basename": "Rowan_lr_1993.pdf", "content": "final", "filesize": 38194629, "license": "other", "mime_type": "application/pdf", "url": "/7397/1/Rowan_lr_1993.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Equation of state of molten mid-ocean ridge basalt. Structure of Kilauea volcano.", "author": [ { "family_name": "Rowan", "given_name": "Linda Rose", "clpid": "Rowan-L-R" } ], "thesis_advisor": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Stolper", "given_name": "Edward M.", "clpid": "Stolper-E-M" }, { "family_name": "Clayton", "given_name": "Robert W.", "clpid": "Clayton-R-W" } ], "thesis_committee": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Stolper", "given_name": "Edward M.", "clpid": "Stolper-E-M" }, { "family_name": "Clayton", "given_name": "Robert W.", "clpid": "Clayton-R-W" }, { "family_name": "Rossman", "given_name": "George Robert", "clpid": "Rossman-G-R" }, { "family_name": "Westphal", "given_name": "James A.", "clpid": "Westphal-J-A" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Basalts are the most ubiquitous rocks erupting at the earth's surface at the present\r\ntime and they provide an important probe of the subsurface processes occurring\r\nwithin planetary interiors. Recent advances in both mineral physics and seismic\r\nanalysis have allowed me to undertake two independent studies related to the genesis\r\nand eruption of basaltic magmas. Chapters 1 and 2 are part of an experimental study\r\nconducted in the shock wave laboratory on the equation of state of molten mid-ocean\r\nridge basalt and the chemical interactions of the shocked liquid with its Mo container.\r\nMy advisors for this project were Thomas Ahrens and Edward Stolper. Chapter 3 is a\r\ntravel time tomography study of the three-dimensional structure of Kilauea Volcano,\r\nHawaii in collaboration with Robert Clayton. Chapter 3 is currently in press in the\r\nJournal of Geophysical Research.
\r\n\r\nThe EOS of molten MORB to 20 GPa was accomplished using the innovative silicate\r\nliquid shock wave measurement technique on the 40 mm propellant gun developed\r\nby Rigden [1986] and Miller [1990). This technique has been used to determine\r\nthe EOS for four synthetic melts and this thesis applies the technique to a natural\r\nmelt, a MORB dredged from the Juan de Fuca ridge. The resulting EOS indicates\r\nthat the MORB liquid is very compressible and therefore has a low bulk modulus of\r\n11.7 GPa. These results are consistent with low pressure static compression experiments\r\non similar basalts, but are not consistent with the results of ultrasonic interferometry.\r\nThe compressible nature of the MORB liquid is related to its composition\r\nand this may be expressed best by comparing the MORB Hugoniot to the Hugoniot\r\ndetermined for An_(36)Di_(64) and komatiite. The MORB and An_(36)Di_(64) Hugoniots show\r\nsignificant increase in density at low pressure followed by a stiffening at high pressures\r\nwhere the liquid Hugoniot approaches its respective dense oxide high pressure\r\ncomposition. This may be related to gradual coordination changes from four-fold to\r\nsix-fold for the Si^(+4) and Al^(+3) which are essentially complete at the high pressure\r\nwhere the curve stiffens. The MORB is much more compressible than the komatiite\r\nand overtakes the komatiite in density at a low pressure of 2.5 GPa. This is a\r\ncompositional effect caused by the enrichment of the MORB in Al_2O_3 and SiO_2 and\r\ndepletion in MgO compared to komatiite. The compressible nature of the MORB\r\nallows it to become denser than the surrounding mantle near the base of the low\r\nvelocity zone and therefore it is unlikely that MORB can be derived from very deep\r\nin the earth's upper mantle.
\r\n\r\nFor most shock wave experiments, the sample is not recovered and nothing can\r\nbe determined about its structure or composition due to the passage of the shock\r\nwave. In a few of my EOS experiments on molten MORB, however, the shocked sample\r\nwas recovered and could be studied in detail. Observations of impact-induced\r\ninteractions between the silicate liquid and its Mo container provide insight into\r\nplanetary impact and differentiation processes involving metal-silicate partitioning.\r\nThe shocked liquids showed extreme reduction and with increasing pressure the FeO\r\ncontent of the initial melt was reduced to almost nothing by reaction with the Mo.\r\nThese reactions produced metallic particles enriched in Mo, Fe and Si. These particles\r\nshow a similar texture as those found at impact sites on the earth and moon\r\nand provide clues to the impact origin of metallic particles.
\r\n\r\nA travel time tomography study of local P wave data from Kilauea Volcano,\r\nHawaii, was undertaken to determine the lateral heterogeneities produced by its intricate\r\nmagmatic and tectonic environment. The technique proved to be a powerful\r\nprobe of the volcano's intrusive plumbing because the presence of a dense seismic\r\narray and many local earthquakes allowed for excellent coverage of complex subsurface\r\nfeatures. Analysis and interpretation of the tomographic images leads to the\r\nfollowing inferrred model. The main shallow magma reservoir is delineated by a\r\nslow anomaly centered 2 km southeast of Halemaumau caldera. There is a distinct\r\nhigh velocity region centered northwest of the summit from 0 to 2 km depth that\r\nmay represent a dense wall and/or cap of intrusive rock that acts as a barrier or\r\ncontainment structure for the northern part of the reservoir. We suggest that the\r\nshallow reservoir is a narrow, compartmentalized region of sills and dikes because of\r\nthe closely spaced high and low velocity anomalies near the summit. The rift zones\r\nof Kilauea are imaged as major, high velocity entities, widening to the south with\r\ndepth until 6 km. These fast anomalies may be related to the sheeted dike complexes\r\nalong the rifts. On a finer scale, magma pockets centered at 0-2 km depth have been\r\ninferred beneath Makaopuhi, Mauna Ulu and Puu Oo, along the east rift zone. The\r\nHilina and Kaoiki fault zones, are imaged as slow features at shallow depths (less than 6\r\nkm), related to their tensional structures that produce the open fractures and cracks\r\nin the basaltic edifice. The Koae fault system is imaged as a slightly fast shallow\r\nstructure (less than 6 km) possibly related to intrusive diking from the adjacent rift zones.\r\nContinued inversions with the immense amount of seismic data collected for Hawaiian\r\nevents will allow the detailed development of a three-dimensional velocity model\r\nfor Kilauea. Such a model will be extremely useful to seismologists and petrologists\r\nalike for understanding the tectonic growth and magmatic evolution of this dynamic\r\nshield volcano.
\r\n\r\n", "doi": "10.7907/J6D0-GV56", "publication_date": "1993", "thesis_type": "phd", "thesis_year": "1993" }, { "id": "thesis:2993", "collection": "thesis", "collection_id": "2993", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-08012006-093137", "type": "thesis", "title": "I. Phase Transformations and the Spectral Reflectance of Solid Sulfur: Possible Metastable Sulfur Allotropes on Io's Surface. II. Photochemistry and Aerosol Formation in Neptune's Atmosphere", "author": [ { "family_name": "Moses", "given_name": "Julianne Ives", "orcid": "0000-0002-8837-0035", "clpid": "Moses-Julianne-Ives" } ], "thesis_advisor": [ { "family_name": "Yung", "given_name": "Yuk L.", "clpid": "Yung-Y-L" }, { "family_name": "Westphal", "given_name": "James A.", "clpid": "Westphal-J-A" } ], "thesis_committee": [ { "family_name": "Westphal", "given_name": "James A.", "clpid": "Westphal-J-A" }, { "family_name": "Yung", "given_name": "Yuk L.", "clpid": "Yung-Y-L" }, { "family_name": "Blake", "given_name": "Geoffrey A.", "clpid": "Blake-G-A" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "clpid": "Ingersoll-A-P" }, { "family_name": "Burnett", "given_name": "Donald S.", "clpid": "Burnett-D-S" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "This thesis consists of two independent papers:
\r\n\r\nPAPER I:
\r\n\r\nThe spectral reflectance of elemental sulfur is examined in a set of laboratory experiments to determine the factors that affect the transformation rate of monoclinic (\u03b2) sulfur and various other sulfur allotropes into orthorhombic (\u03b1) sulfur. The laboratory data have implications for the spectral variation and physical behavior of freshly solidified sulfur, if any exists, on Jupiter's satellite Io. Depending on its thermal history, molten sulfur on Io would initially solidify into a glassy solid or a monoclinic crystalline lattice; these forms might contain polymeric sulfur molecules as well as the more abundant S8 molecules. If freshly frozen sulfur on Io could lose heat rapidly and approach ambient dayside Io temperatures within several hours, then some of the metastable sulfur allotropes could be maintained on Io virtually indefinitely. Small droplets of sulfur ejected during plume eruptions might cool quickly enough to preserve these allotropes, but sulfur in large volcanic flows or lakes would probably remain warm long enough for phase transformations to proceed at a visible rate.
\r\n\r\nPAPER II:
\r\n\r\nPhotodissociation of methane at high levels in Neptune's atmosphere leads to the production of more complex hydrocarbon species such as ethane, acetylene, methylacetylene, propane, diacetylene, ethylacetylene, and butane. These gases diffuse to the lower stratosphere where temperatures are low enough to allow all seven of the aforementioned species to condense. Particle formation may not occur readily, however, as the vapor species become supersaturated. We present a theoretical analysis of particle formation mechanisms at conditions relevant to Neptune's troposphere and stratosphere and show that hydrocarbon nucleation is very inefficient under Neptunian conditions: saturation ratios much greater than unity are required for aerosol formation by either heterogeneous, ion-induced, or homogeneous nucleation. Thus, stratospheric hazes may form far below their saturation levels. We compare nucleation models with detailed atmospheric photochemical models in order to place realistic constraints on the altitude levels at which we expect hydrocarbon hazes or clouds to form on Neptune.
\r\n", "doi": "10.7907/S8F2-V423", "publication_date": "1991", "thesis_type": "phd", "thesis_year": "1991" }, { "id": "thesis:7994", "collection": "thesis", "collection_id": "7994", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10172013-085025235", "primary_object_url": { "basename": "Polanskey_ca_1989.pdf", "content": "final", "filesize": 19873642, "license": "other", "mime_type": "application/pdf", "url": "/7994/1/Polanskey_ca_1989.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "I. Impact Spallation Experiments: Fracture Patterns and Spall Velocities. II. Craters in Carbonate Rocks: An Electron Paramagnetic Resonance Analysis of Shock Damage", "author": [ { "family_name": "Polanskey", "given_name": "Carol Ann", "clpid": "Polanskey-Carol-Ann" } ], "thesis_advisor": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Burnett", "given_name": "Donald S.", "orcid": "0000-0001-9521-8675", "clpid": "Burnett-D-S" } ], "thesis_committee": [ { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Burnett", "given_name": "Donald S.", "orcid": "0000-0001-9521-8675", "clpid": "Burnett-D-S" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Westphal", "given_name": "James A.", "clpid": "Westphal-J-A" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "This work is divided into two independent papers.
\r\n\r\nPAPER 1.
\r\n\r\nSpall velocities were measured for nine experimental impacts into San Marcos gabbro targets. Impact velocities ranged from 1 to 6.5 km/sec. Projectiles were iron, aluminum, lead, and basalt of varying sizes. The projectile masses ranged from a 4 g lead bullet to a 0.04 g aluminum sphere. The velocities of fragments were measured from high-speed films taken of the events. The maximum spall velocity observed was 30 m/sec, or 0.56 percent of the 5.4 km/sec impact velocity. The measured velocities were compared to the spall velocities predicted by the spallation model of Melosh (1984). The compatibility between the spallation model for large planetary impacts and the results of these small scale experiments are considered in detail.
\r\n\r\nThe targets were also bisected to observe the pattern of internal fractures. A series of fractures were observed, whose location coincided with the boundary between rock subjected to the peak shock compression and a theoretical \"near surface zone\" predicted by the spallation model. Thus, between this boundary and the free surface, the target material should receive reduced levels of compressive stress as compared to the more highly shocked region below.
\r\n\r\nPAPER 2.
\r\n\r\nCarbonate samples from the nuclear explosion crater, OAK, and a terrestrial impact crater, Meteor Crater, were analyzed for shock damage using electron paramagnetic resonance, EPR. The first series of samples for OAK Crater were obtained from six boreholes within the crater, and the second series were ejecta samples recovered from the crater floor. The degree of shock damage in the carbonate material was assessed by comparing the sample spectra to spectra of Solenhofen limestone, which had been shocked to known pressures.
\r\n\r\nThe results of the OAK borehole analysis have identified a thin zone of highly shocked carbonate material underneath the crater floor. This zone has a maximum depth of approximately 200 ft below sea floor at the ground zero borehole and decreases in depth towards the crater rim. A layer of highly shocked material is also found on the surface in the vicinity of the reference bolehole, located outside the crater. This material could represent a fallout layer. The ejecta samples have experienced a range of shock pressures.
\r\n\r\nIt was also demonstrated that the EPR technique is feasible for the study of terrestrial impact craters formed in carbonate bedrock. The results for the Meteor Crater analysis suggest a slight degree of shock damage present in the \u03b2 member of the Kaibab Formation exposed in the crater walls.
", "doi": "10.7907/3rgr-f070", "publication_date": "1989", "thesis_type": "phd", "thesis_year": "1989" }, { "id": "thesis:2512", "collection": "thesis", "collection_id": "2512", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-06072007-141923", "type": "thesis", "title": "Quantitative Studies of the Martian South Polar Region Using Spacecraft Images", "author": [ { "family_name": "Herkenhoff", "given_name": "Kenneth Edward", "clpid": "Herkenhoff-Kenneth-Edward" } ], "thesis_advisor": [ { "family_name": "Albee", "given_name": "Arden Leroy", "clpid": "Albee-A-L" }, { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" } ], "thesis_committee": [ { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" }, { "family_name": "Albee", "given_name": "Arden Leroy", "clpid": "Albee-A-L" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Murray", "given_name": "Bruce C.", "clpid": "Murray-B-C" }, { "family_name": "Westphal", "given_name": "James A.", "clpid": "Westphal-J-A" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Spacecraft observations must be calibrated absolutely in order to investigate the photometric properties of the Martian surface and atmosphere. The accuracy of the Mariner 9 and Viking Orbiter television system calibration was evaluated by comparing the two data sets with each other and with Earth-based spectrophotometry of Mars and Phobos. The Viking imaging data are consistent with published estimates of the geometric albedo of Phobos, which is uncertain by about 20%. Mariner 9 data are calibrated to within about \u00b120% by comparing Phobos images with Viking data. Better photometric observations of Phobos are necessary to improve the calibration of the Viking Orbiter and Mariner 9 television systems. Similarly, inflight Phobos observations should be used to calibrate imaging systems on future Mars missions.
\r\n\r\nMariner 9 images were processed for comparison with nearly simultaneous infrared spectra of the south polar cap of Mars recorded in 1971-72. Combined analysis of these observations indicates that the southern residual cap was covered by carbon dioxide frost throughout the summer, in agreement with Viking Orbiter measurements made three Mars years later. Thermal modeling of the spectra shows that areas of intermediate albedo are cooled to the sublimation temperature of CO2, suggesting that frost is present but not visible. Topographic roughness may shade the CO2 from the sun and produce the variegated appearance of the residual cap.
\r\n\r\nFive color/albedo units, including polar frost, have been recognized and mapped in the southern layered deposits on Mars. Atmospheric dust scattering was measured in shadows and modeled in order to remove the component of brightness due to the atmosphere and quantify the albedo and color of the surface. The layered deposits appear to be mantled by red dust, except where eolian stripping has exposed the underlying bedrock. Frost and bare ground are mixed below the resolution of the images in many areas adjacent to the polar cap, some of which appear to be younger than the surrounding layered terrain. Dark material has been deposited in topographic depressions in much of the south polar region, including the layered deposits. The available observational data suggest that the layered deposits are composed of bright dust, ice, and a small amount of dark material. If the dark material is sand, a periodic change in polar winds seems required in order to transport the sand poleward into the layered terrain. In any case, the observations are not consistent with the layered deposits being composed only of bright dust and ice.
\r\n\r\nMaximum slopes of 10-20 degrees occur on an exposure of layered deposits within the south polar residual cap of Mars. A new photoclinometric technique is used to produce profiles of slope and albedo using high resolution Mariner 9 images. Stereophotogrammetry is also used to constrain the photoclinometric solutions, which resolve layer thicknesses of 100-300 meters. The results are limited by the ~200 meter resolution of the images, and thinner (unresolved) layers are likely. The ~25% maximum albedo variations are correlated with slope, indicating that frost is present on level areas. There is evidence for temporal changes in frost distribution in the 7 days (4\u00b0 of Ls) between the two images used in this study, demonstrating that future photoclinometric studies of the polar regions must be attempted carefully. The magnitude of the slopes derived here suggest that the layers are competent, perhaps due to the presence of a weathering rind.
\r\n\r\nWeathering of the layered deposits by sublimation of water ice can account for the data presented here and previous observations of the north polar deposits. The non-volatile component of the layered deposits appears to consist mainly of bright red dust, with small amounts of dark dust or sand. Deposition of sand in the layered deposits is problematical, so inclusion of dark dust is preferred. The dark dust may be similar to the magnetic material found at the Viking Lander sites, and may therefore preferentially form ~ 100\u00b5 filamentary residue particles upon weathering. Once eroded from the layered deposits, these particles may then saltate to form the dark sand dunes found in both polar regions. Eventual destruction of the particles could allow recycling of the dark dust into the layered deposits via atmospheric suspension.
", "doi": "10.7907/bty4-vk56", "publication_date": "1989", "thesis_type": "phd", "thesis_year": "1989" }, { "id": "thesis:16217", "collection": "thesis", "collection_id": "16217", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10292023-222051513", "type": "thesis", "title": "Investigations of Earthquakes and Other Seismic Sources in Regions of Volcanism", "author": [ { "family_name": "Eissler", "given_name": "Holly Kathleen", "clpid": "Eissler-Holly-Kathleen" } ], "thesis_advisor": [ { "family_name": "Anderson", "given_name": "Donald L.", "clpid": "Anderson-D-L" } ], "thesis_committee": [ { "family_name": "Anderson", "given_name": "Donald L.", "clpid": "Anderson-D-L" }, { "family_name": "Kanamori", "given_name": "Hiroo", "orcid": "0000-0001-8219-9428", "clpid": "Kanamori-H" }, { "family_name": "Harkrider", "given_name": "David G.", "clpid": "Harkrider-D-G" }, { "family_name": "Tanimoto", "given_name": "Toshiro", "clpid": "Tanimoto-T" }, { "family_name": "Westphal", "given_name": "James A.", "clpid": "Westphal-J-A" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Source properties of earthquakes in Hawaii and seismological aspects of explosive volcanic eruptions are examined in three chapters. In Chapter 1, source depths are estimated for all earthquakes larger than magnitude 6 on the island of Hawaii since 1940 by comparing relative amplitudes of short-period surface waves to body waves. Rayleigh wave excitation functions are calculated versus source depth, and the calculation is compared with observed data and calibrated using known depths of recent earthquakes. In general, results show that large earthquakes near the volcanic flanks and fault systems are shallow (\u2264 20 km), but those near active volcanic centers can\r\nbe deeper (~ 50 km). Two earthquakes with the largest depth estimates (40-55 km and 35-50 km) occurred under the active volcanoes Mauna Loa and Kilauea, preceding eruptions by three days and 14 months respectively. As a check on the data set, which consisted of Pasadena seismograms alone, M_s values assigned from many global amplitude readings were compared with those from Pasadena amplitudes for worldwide earthquakes. Global M_s values on the average are 0.05 magnitude units larger than M_s values from Pasadena amplitudes.
\r\n\r\nIn Chapter 2, the horizontal single-force source used to model seismic radiation from the Mt. St. Helens landslide is investigated as the source of the M_s = 7.1 Kalapana, Hawaii earthquake. The azimuthal radiation pattern of 100 s Love waves is two-lobed, consistent with a horizontal single-force source. The observed surface deformation is also more consistent with the single force than the conventional double-couple shear dislocation source. The single force is a crude representation of\r\nmotion of a large slide mass that is partially decoupled from the Earth. The interpretation is that the bulk of seismic radiation from the Kalapana earthquake was produced by large-scale slumping of the south flank of Kilauea volcano. The peak amplitude f\u2080 of the force time function is estimated at 1 x 10\u00b2\u2070 dyne from Love and Rayleigh surface waves. The peak acceleration inferred from the seismic force is 10 - 100 cm s\u207b\u00b2, comparable to that of gravity on a gently inclined plane.
\r\n\r\nIn Chapter 3, far-field seismograms were searched for signals associated with recent large volcanic eruptions to examine whether models of the volcano as a seismic source derived for Mt. St. Helens are applicable to other explosive volcanoes. The 1982 eruption of El Chich6n in Mexico produced Rayleigh waves and body waves that were marginally recorded at IDA and SRO stations less than 40\u00b0 away; still, several characteristics of the eruption can be inferred from the seismic waves. Near-field seismograms of smaller eruptions at Mt. Asama, Japan, were found to be comparable in size to smaller secondary eruptions of Mt. St. Helens, and appear to have a more complicated source. Atmospheric pressure waves recorded on barographic instruments from several large explosive eruptions are compared and show differences in signal duration, amplitude, and characteristic period that are indicative of the overall size of the eruption.
", "doi": "10.7907/wmxt-sv17", "publication_date": "1986", "thesis_type": "phd", "thesis_year": "1986" }, { "id": "thesis:4069", "collection": "thesis", "collection_id": "4069", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-10132005-145503", "primary_object_url": { "basename": "Jewitt_d_1983.pdf", "content": "final", "filesize": 12757025, "license": "other", "mime_type": "application/pdf", "url": "/4069/1/Jewitt_d_1983.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "I. Physical Studies of Distant Comets. II. Morphologies of Planetary Nebulae", "author": [ { "family_name": "Jewitt", "given_name": "David Clifford", "orcid": "0000-0003-0262-8160", "clpid": "Jewitt-David-Clifford" } ], "thesis_advisor": [ { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" } ], "thesis_committee": [ { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Westphal", "given_name": "James A.", "clpid": "Westphal-J-A" }, { "family_name": "Searle", "given_name": "Leonard", "clpid": "Searle-Leonard" }, { "family_name": "Soifer", "given_name": "B. Thomas", "clpid": "Soifer-B-T" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Part 1:
\r\n\r\nBroadband observations of comets P/Stephan-Oterma (1980g), Bowell (1980b) and Panther (1980u) in the visual (0.5 \u227e \u03bb(\u00b5m) \u227e 0.9) and infrared (1.2 \u227e \u03bb(\u00b5m) \u227e 20) wavelength regions are reported together with measurements in the 1.5 to 2.4 \u00b5m wavelength range having 5% spectral resolution. The visual data indicate the existence of solid grains in extended halos around the nuclei of the three comets. The visual photometric profiles of comets P/Stephan-Oterma and Panther are interpreted as evidence that grains around Panther and those close to the nucleus of P/Stephan-Oterma are sublimating. Broadband near infrared and thermal infrared measurements of comet Panther suggest the presence of 2 to 4 \u00b5m radius particles in the coma. The particles within a 5.8 x 106 diameter region centered on the comet have a total cross section of 108m2 and a near infrared geometric albedo of about 14%. Comet Bowell presents a total cross section of 3 x 108m2 within a 1.2 x 107m region centered on the comet and its coma grains also have an albedo of 14%.
\r\n\r\nThe near infrared spectrum of P/Stephan-Oterma is a featureless solar-reflection continuum. The near infrared spectra of Bowell and Panther exhibit features which are similar in the two comets. The spectral features are not due to H2O, CH4 or CO2 ices nor to emissions from gases released from the nuclei nor to reflection from mineral grains of known composition in the comae. The spectrum of solid ammonia provides the best match to the near infrared; it is nevertheless significantly different from the comet spectra.
\r\n\r\nThe synthesis of the visual data with the infrared data is attempted in terms of a model involving a mantle of volatile material on the nuclei of Bowell and Panther, but not on P/Stephan-Oterma. The composition of the mantle cannot be exactly specified from the existing data but a complex molecule incorporating the N-H bond may be present.
\r\n\r\nPart 2:
\r\n\r\nAn extensive series of observations of comet Bowell at optical and infrared wavelengths is summarized and interpreted in terms of a model of the outgassing of the nucleus. The observations indicate that the optical coma consists of large grains. The outer edge of the coma is expanding from the nucleus at 0.9 \u00b1 0.2 ms-1: extrapolation of the expansion suggests that the coma was ejected from the nucleus when the comet was at a heliocentric distance R ~ 10 AU. At this distance, water ice sublimation would be negligible. Models of the brightness of the comet as a function of R are compared with the measured brightness variation. Between R = 5.3 and 3.4 AU, the apparent cometary brightness changed by a factor of less than 20. Models which account for the equilibrium sublimation of volatiles from the nucleus predict much larger brightness variations. In particular, the models confirm that the sublimation of water ice does not control the activity of comet Bowell. The observations are consistent with the presence of an inert nucleus surrounded by a dissipating grain coma ejected impulsively at R ~ 10 AU. Strong OH production observed near R = 3.4 AU could be a result of the photodissociation of water molecules released from the coma grains by sublimation. However, near infrared spectra of the grains show no evidence for the presence of OH. Instead, several absorptions similar to the overtones of NH bond vibrations are observed. It is noted that the outgassing properties of the comet are similar to those of proton-bombarded laboratory ice specimens. Both the impulsive coma ejection and the peculiar near infrared spectrum may result from the presence of unstable compounds produced in the nucleus by cosmic ray bombardment. The activity of comet Bowell is quite unlike that exhibited by comets at small R, but may be representative of the properties of the distant comets.
\r\n\r\nPart 3:
\r\n\r\nThe spatial distribution of [CI] 9823, 9850 \u00c5 emission in NGC 6720 is reported. Like [01], the [CI] radiation appears enhanced in the region of the bright filaments. A few percent of the carbon atoms in the filaments are neutral. This neutral fraction is consistent with ionization equilibrium calculations made under the assumption of complete shielding of direct stellar radiation by hydrogen. The observed carbon lines are excited by photoelectrons produced from hydrogen by the nebular diffuse radiation field. The [CI] observations confirm that the filaments in NGC 6720 are regions of locally enhanced shielding.
\r\n\r\nPart 4:
\r\n\r\nThe preliminary results of a CCD survey designed to detect and investigate faint halos around planetary nebulae are described. A TI 800 x 800 pixel CCD was used to take deep exposures of 44 planetary nebulae. The exposures were mostly obtained through an Ha filter at the Cassegrainian focus of the Palomar 1.5 m telescope. Spatial resolutions of 1 to 2 arcsecond were obtained across 400 arcsecond wide fields. The images, which are in many cases considerably deeper than any previously taken, reveal numerous planetary nebula halos. About 2/3 of the studied nebulae possess extensive outer halos. In some nebulae the mass in the halo is comparable to the mass contained in the primary HII region. We have used the data to place constraints on the mode of origin of the halos. It is likely that the halos originate either by dynamical separation of a single ejected shell of gas, or by the ejection of two or more such shells from the central star. It is less likely that the halos are caused by excitation of the pre-planetary stellar wind and highly improbable that the halos represent reflection nebulae.
", "doi": "10.7907/f9ge-m194", "publication_date": "1983", "thesis_type": "phd", "thesis_year": "1983" } ]