explanation blue bibcodes open ADS page with paths to full text
Author name code: wittmann
ADS astronomy entries on 2022-09-14
author:"Wittmann, Axel"
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Title: Tissintite-II and Other High Pressure High Temperature Minerals
in Lunar Meteorite Northwest Africa 13967
Authors: Kroemer, C. R.; Wittmann, A.; Wadhwa, M.; Sharp, T. G.
2022LPICo2678.1316K Altcode:
Minerals that form under high pressure including tissintite, corundum,
silica, and olivine were examined to study the history of lunar
meteorite NWA 13967.
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Title: The Drill Core Diary: Unravelling the Rapid Emplacement of
Suevite and Impact Melt Phases Within the Chicxulub Impact Structure
Authors: Kaskes, P.; de Graaff, S. J.; Feignon, J. -G.; Déhais,
T.; Goderis, S.; Ferrière, L.; Koeberl, C.; Smit, J.; Wittmann, A.;
Gulick, S. P. S.; Debaille, V.; Mattielli, N.; Claeys, Ph.
2022LPICo2678.2656K Altcode:
A reconstruction of the emplacement of crater suevite and impact melt
in the first moments after the Chicxulub impact event using a recent
IODP-ICDP drill core.
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Title: Shock impedance amplified impact deformation of zircon in
granitic rocks from the Chicxulub impact crater
Authors: Wittmann, Axel; Cavosie, Aaron J.; Timms, Nicholas E.;
Ferrière, Ludovic; Rae, Auriol; Rasmussen, Cornelia; Ross, Catherine;
Stockli, Daniel; Schmieder, Martin; Kring, David A.; Zhao, Jiawei;
Xiao, Long; Morgan, Joanna V.; Gulick, Sean P. S.; IODP-ICDP Expedition
364 Scientists
2021E&PSL.57517201W Altcode:
Zircon is a precise chronometer and prominent recorder of impact
deformation. However, many impact-induced features in zircon are poorly
calibrated, sometimes due to contradicting experimental data, in other
instances due to the lack of systematic studies of impact-deformed
zircon. To resolve issues with the shock petrographic use of zircon,
we classified impact deformation features in 429 zircon grains in a
continuous drill core of uplifted, granitic bedrock in the peak ring
of the 200-km-diameter K-Pg Chicxulub impact structure. Following
initial identification in backscattered electron (BSE) images,
Raman spectroscopy and electron backscatter diffraction confirmed one
reidite-bearing zircon grain. Quartz-based shock barometry indicates
the host rock of this zircon-reidite grain experienced an average shock
pressure of 17.5 GPa. A survey of BSE images of 429 ZrSiO<SUB>4</SUB>
grains found brittle deformation features are ubiquitous, with
planar fractures in one to five sets occurring in 23% of all zircon
grains. Our survey also reveals a statistically significant correlation
of the occurrence of planar fractures in zircon with the types of host
materials. Compared to zircon enclosed in mafic, higher density mineral
hosts, felsic, low-density minerals show a much higher incidence of
zircon with planar fractures. This finding suggests amplification
of pressure due to shock impedance contrasts between zircon and its
mineral hosts. Using the impedance matching method, we modeled the
shock impedance pressure amplification effect for zircon inclusions
in Chicxulub granitic hosts. Our modeling indicates shock impedance
could have amplified the average 17.5 GPa shock pressure in a zircon
inclusion in quartz or feldspar in the Chicxulub granitic rocks to 24
± 1 GPa, suggesting that reidite in these rocks formed between 17.5
and 25 GPa. In essence, our study of impedance-induced shock pressure
amplification in zircon assemblages, including the onset of reidite
formation, details how shock impedance in mineral associations can be
quantified to refine shock pressure estimates.
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Title: Permeability of Chicxulub Peak Ring Rocks and Implications
for the Post-Impact Hydrothermal System
Authors: McCall, Naoma; Gulick, Sean; Bhandari, Athma; Tikoo, Sonia;
Vanorio, Tiziana; Rasmussen, Cornelia; Kring, David; Wittmann, Axel;
Ketcham, Richard; Hesse, Marc
2021AGUFM.P54A..08M Altcode:
We present the first-ever permeability measurements on samples
from the Chicxulub peak ring obtained from International Ocean
Discovery Program/International Continental Scientific Drilling
Program Expedition 364, Site M0077. We measured steady-state liquid
permeability using deionized water on 1-inch (25.4 mm) core plugs
from the Chicxulub core under multiple confining stress conditions
(10 to 26 MPa) in four loading-unloading cycles while maintaining
pore pressure constant at ~7 MPa. We performed tests on five core
plugs from three different lithologies in the core: a suevite sample
with macroscopic red hydrothermal alteration (Unit 2a, 658.3 mbsf),
a suevite sample without this evidence of alteration (Unit 2a, 659.3
mbsf), a melt rock sample (Unit 3b, 738.2 mbsf), a macroscopically
intact granitoid sample (Unit 4, 1143.3 mbsf), and a cataclastically
fractured granitoid sample (Unit 4, 963.7mbsf). Permeability values are
in the millidarcy range (1.10.87 mD or 1.1 10-15 8.6 10-16 m2) for the
granitoid samples (porosity = 168 %) to the microdarcy range (44-0.66
D or 4.4 10-17 6.5 10-19 m2) for the suevite and melt rock samples
(porosity = 2919 %). All samples were micro-CT scanned at 20 m voxel
resolution before and after permeability testing. A comparison study
at Stanford University will be done using helium gas and the pressure
pulse-decay method to measure Klinkenberg-corrected gas permeability
on parallel samples from the same sections of the Chicxulub core. The
measured permeability values will constrain core-scale modeling of the
post-impact hydrothermal system. We explore the implications of the
three-orders of magnitude contrast in permeability between the granite
and the suevite and melt rock have for the lifespan of the post-impact
hydrothermal system. The low permeability values of the suevite and
melt rock may suggest a prolonged hydrothermal system due to low flux
between the permeable peak ring granitoids and the overlying ocean.
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Title: Carletonmooreite, Ni3Si, a new silicide from the Norton County
aubrite meteorite
Authors: Garvie, Laurence A. J.; Ma, Chi; Ray, Soumya; Domanik,
Kenneth; Wittmann, Axel; Wadhwa, Meenakshi
2021AmMin.106.1828G Altcode:
No abstract at ADS
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Title: Location and Speciation of Germanium in the Butler and
Northwest Africa 859 Ungrouped Iron Meteorites
Authors: Garvie, L. A. J.; Ma, C.; Wittmann, A.
2021LPI....52.2398G Altcode:
Germanium, in the Butler and NWA 859 ungrouped iron meteorites,
partitions with tetrataenite (to 0.6 wt%) and to 10 wt% in a new and
common Ni-Ge-P sub-micron-sized precipitate.
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Title: Carl Friedrich Gauss and the Gauss Society: a brief overview
Authors: Wittmann, Axel D.
2020HGSS...11..199W Altcode:
Carl Friedrich Gauss (1777-1855) was one of the most eminent scientists
of all time. He was born in Brunswick, studied in Göttingen, passed
his doctoral examination in Helmstedt, and from 1807 until his death,
was the director of the Göttingen Astronomical Observatory. As
a professor of astronomy, he worked in the fields of astronomy,
mathematics, geodesy, and physics, where he made world-famous and
lasting contributions. In his honour, and to preserve his memory,
the Gauss Society was founded in Göttingen in 1962. The present
paper aims to give nonspecialists a brief introduction into the life
of Gauss and an introduction into the Gauss Society and its history.
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Title: Shocked titanite records Chicxulub hydrothermal alteration
and impact age
Authors: Timms, Nicholas E.; Kirkland, Christopher L.; Cavosie, Aaron
J.; Rae, Auriol S. P.; Rickard, William D. A.; Evans, Noreen J.;
Erickson, Timmons M.; Wittmann, Axel; Ferrière, Ludovic; Collins,
Gareth S.; Gulick, Sean P. S.
2020GeCoA.281...12T Altcode:
Hydrothermal activity is a common phenomenon in the wake of impact
events, yet identifying and dating impact hydrothermal systems can be
challenging. This study provides the first detailed assessment of the
effects of shock microstructures and impact-related alteration on the
U-Pb systematics and trace elements of titanite (CaTiSiO<SUB>5</SUB>),
focusing on shocked granite target rocks from the peak ring of the
Chicxulub impact structure, Mexico. A > 1 mm long, shock-twinned
titanite grain preserves a dense network of irregular microcracks, some
of which exploit shock twin interfaces. Secondary microcrystalline
anatase and pyrite are heterogeneously distributed along some
microcracks. In situ laser ablation multi-collector inductively-coupled
plasma mass spectrometry (LA-MC-ICPMS) analysis reveals a mixture of
three end-member Pb components. The Pb components are: 1) common Pb,
consistent with the Pb isotopic signature of adjacent alkali feldspar;
2) radiogenic Pb accumulated since magmatic crystallization; and 3)
a secondary, younger Pb signature due to impact-related complete
radiogenic Pb loss. The youngest derived ages define a regression
from common Pb that intersects Concordia at 67 ± 4 Ma, in agreement
with the established age of 66.04 ± 0.05 Ma for the Chicxulub impact
event. Contour maps of LA-MC-ICPMS data reveal that the young ages are
spatially restricted to microstructurally-complex domains that correlate
with significant depletion in trace elements (REE-Y-Zr-Nb-Mo-Sn-Th) and
reduction in magnitude of the Eu/Eu* anomaly. Mapping by time-of-flight
secondary ion mass spectrometry (ToF-SIMS) show that patterns of
localised element depletion in titanite are spatially related to
microcracks, which are enriched in Al. The spatial correlation of ages
and trace element abundance is consistent with localised removal of Pb
and other trace elements from a pervasive network of fast fluid pathways
in fractured domains via a fluid-mediated element transport process
associated with the impact event. Here we interpret the 67 ± 4 Ma U-Pb
age to represent hydrothermal Pb-loss in the Chicxulub peak ring in the
wake of the impact event. These results highlight the potential of our
analytical approach using titanite geochronology and geochemistry for
dating post-impact hydrothermal activity in impact structures elsewhere.
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Title: Volatiles in Magnesian Glasses Occurring in Lunar Feldspathic
Breccia Northwest Africa 10404
Authors: Hahn, T.; Jin, Z.; Wittmann, A.; Bose, M.; Irving, A.
2020LPI....51.2627H Altcode:
We report hydrogen isotope analyses of Mg-rich glasses and the vitric
matrix in NWA 10404, which may originate from a water-ice deposit near
the lunar poles.
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Title: Petrology and Ejection History of Lunar Pink Spinel-Bearing
Impact Melt Rock Northwest Africa 10228
Authors: Wittmann, A.; Irving, A. J.; Nishiizumi, K.; Caffee, M. W.;
Jull, A. J. T.
2020LPI....51.2176W Altcode:
A new lunar rock that retains a record of deep-seated equilibration and
cosmogenic nuclides chronicling its ejection and pairing relationships.
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Title: Component Analysis of Sorted Suevite in the Chicxulub Impact
Crater
Authors: Wittmann, A.; Expedition 364 Scientists
2020LPI....51.2211W Altcode:
Chicxulub sorted suevite records clues to its formation and emplacement
that challenge interpretations and models.
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Title: Petrogenesis of lunar impact melt rock meteorite Oued
Awlitis 001
Authors: Wittmann, Axel; Korotev, Randy L.; Jolliff, Bradley L.;
Nishiizumi, Kunihiko; Jull, A. J. Timothy; Caffee, Marc W.; Zanetti,
Michael; Irving, Anthony J.
2019M&PS...54.2167W Altcode:
Oued Awlitis 001 is a highly feldspathic, moderately equilibrated,
clast-rich, poikilitic impact melt rock lunar meteorite that was
recovered in 2014. Its poikilitic texture formed due to moderately
slow cooling, which judging from textures of rocks in melt sheets of
terrestrial impact structures, is observed in impact melt volumes
at least 100 m thick. Such coherent impact melt volumes occur
in lunar craters larger than 50 km in diameter. The composition
of Oued Awlitis 001 points toward a crustal origin distant from
incompatible-element-rich regions. Comparison of the bulk composition
of Oued Awlitis 001 with Lunar Prospector 5° γ-ray spectrometer data
indicates a limited region of matches on the lunar farside. After its
initial formation in an impact crater larger than 50 km in diameter,
Oued Awlitis 001 was excavated from a depth greater than 50 m. The
cosmogenic nuclide inventory of Oued Awlitis 001 records ejection from
the Moon 0.3 Ma ago from a depth of at least 4 m and little mass loss
due to ablation during its passage through Earth's atmosphere. The
terrestrial residence time must have been very short, probably less
than a few hundred years; its exact determination was precluded by a
high concentration of solar cosmic ray-produced <SUP>14</SUP>C. If
the impact that excavated Oued Awlitis 001 also launched it, this
event likely produced an impact crater >10 km in diameter. Using
petrologic constraints and Lunar Reconnaissance Orbiter Camera and
Diviner data, we test Giordano Bruno and Pierazzo as possible launch
craters for Oued Awlitis 001.
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Title: Zircon U-Pb Geochronology and Trace Elements of the Chicxulub
Impact Structure Basement
Authors: Ross, C. H.; Stockli, D. F.; Rasmussen, C.; Gulick, S. P. S.;
de Graaff, S. J.; Claeys, Ph.; Zhao, J.; Xiao, L.; Pickersgill,
A. E.; Schmieder, M.; Kring, D. A.; Wittmann, A.; Morgan, J. V.;
IODP 364 Science Party
2019LPICo2136.5120R Altcode:
One of Yucatán basement ages is preserved within the Chicxulub
peak ring and is 300 - 350 Ma, which helps constrain the collision
of Gondwana and Laurentia as well as understand distal K-Pg ejecta
processes.
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Title: Six Million Years of Hydrothermal Activity at Chicxulub?
Authors: Pickersgill, A. E.; Christou, E.; Mark, D. F.; Lee, M. R.;
Tremblay, M. M.; Rasmussen, C.; Morgan, J. V.; Gulick, S. P. S.;
Schmieder, M.; Bach, W.; Osinski, G. R.; Simpson, S.; Kring, D. A.;
Cockell, C.; Collins, G. S.; Christeson, G.; Tikoo, S.; Stockli, D.;
Ross, C.; Wittmann, A.; Swindle, T.; Expedition 364 Scientists
2019LPICo2136.5082P Altcode:
Could hydrothermal activity have lasted 6 million years around the
peak ring of Chicxulub? Yes.
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Title: The first day of the Cenozoic
Authors: Gulick, Sean P. S.; Bralower, Timothy J.; Ormö, Jens; Hall,
Brendon; Grice, Kliti; Schaefer, Bettina; Lyons, Shelby; Freeman,
Katherine H.; Morgan, Joanna V.; Artemieva, Natalia; Kaskes, Pim;
de Graaff, Sietze J.; Whalen, Michael T.; Collins, Gareth S.; Tikoo,
Sonia M.; Verhagen, Christina; Christeson, Gail L.; Claeys, Philippe;
Coolen, Marco J. L.; Goderis, Steven; Goto, Kazuhisa; Grieve, Richard
A. F.; McCall, Naoma; Osinski, Gordon R.; Rae, Auriol S. P.; Riller,
Ulrich; Smit, Jan; Vajda, Vivi; Wittmann, Axel
2019PNAS..11619342G Altcode:
Highly expanded Cretaceous-Paleogene (K-Pg) boundary section from the
Chicxulub peak ring, recovered by International Ocean Discovery Program
(IODP)-International Continental Scientific Drilling Program (ICDP)
Expedition 364, provides an unprecedented window into the immediate
aftermath of the impact. Site M0077 includes ∼130 m of impact melt
rock and suevite deposited the first day of the Cenozoic covered by
<1 m of micrite-rich carbonate deposited over subsequent weeks to
years. We present an interpreted series of events based on analyses of
these drill cores. Within minutes of the impact, centrally uplifted
basement rock collapsed outward to form a peak ring capped in melt
rock. Within tens of minutes, the peak ring was covered in ∼40 m
of brecciated impact melt rock and coarse-grained suevite, including
clasts possibly generated by melt-water interactions during ocean
resurge. Within an hour, resurge crested the peak ring, depositing
a 10-m-thick layer of suevite with increased particle roundness and
sorting. Within hours, the full resurge deposit formed through settling
and seiches, resulting in an 80-m-thick fining-upward, sorted suevite
in the flooded crater. Within a day, the reflected rim-wave tsunami
reached the crater, depositing a cross-bedded sand-to-fine gravel
layer enriched in polycyclic aromatic hydrocarbons overlain by charcoal
fragments. Generation of a deep crater open to the ocean allowed rapid
flooding and sediment accumulation rates among the highest known in
the geologic record. The high-resolution section provides insight into
the impact environmental effects, including charcoal as evidence for
impact-induced wildfires and a paucity of sulfur-rich evaporites from
the target supporting rapid global cooling and darkness as extinction
mechanisms.
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Title: The Final Settling of Meteoritic Matter on the Peak-Ring of the
Chicxulub Impact Structure at Site M0077A of IODP-ICDP Expedition 364
Authors: Goderis, S.; Sato, H.; Ferrière, L.; Schmitz, B.; Burney,
D.; Bralower, T. J.; de Graaff, S. J.; Déhais, T.; de Winter, N. J.;
Elfman, M.; Feignon, J. -G.; Gulick, S. P. S.; Ishikawa, A.; Kaskes,
P.; Koeberl, C.; Kristiansson, P.; Lowery, C. M.; Morgan, J.; Neal,
C. R.; Owens, J. D.; Schulz, T.; Sinnesael, M.; Smit, J.; Vellekoop,
J.; Whalen, M. T.; Wittmann, A.; Vanhaecke, F.; Van Malderen, S.;
Claeys, Ph.
2019LPICo2136.5068G Altcode:
This abstract focuses on the distribution of siderophile elements in
the IODP-ICDP Expedition 364 core in the peak-ring of the Chicxulub
impact structure to better constrain the final phases of impact crater
formation and the fate of the impactor.
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Title: Electron Microprobe Analysis of Cohenite and Haxonite
Precipitates in the Canyon Diablo (IAB-MG) and Colonia Obrera (IIIE)
Iron Meteorites and Qeqertarsuaq (Disko Island), Greenland, Rocks
Authors: Wittmann, A.; Garvie, L. A. J.
2019LPI....50.2510W Altcode:
Carbides are widespread in planetary materials, but quantitative data
for them are rare; this is a recipe for measuring carbides with the
electron microprobe.
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Title: The Rochechouart 2017-Cores Rescaled: Major Features
Authors: Lambert, P.; Alwmark, C.; Baratoux, D.; Bouley, S.; Brack,
A.; Bruneton, A.; Buchner, E.; Claeys, P.; Courtin Nomade, A.; Dence,
M. R.; Duhamel Achin, I.; Floc'h, J. P.; French, B. M.; Fudge, C.;
Gattacceca, J.; Gibson, R. L.; Goderis, S.; Grieve, R. A. F.; Hauser,
N.; Hodges, K. V.; Horz, F.; Humayun, M.; Jourdan, F.; Kelley, S.;
Kenkmann, T.; Kring, D. A.; Langenhorst, F.; Lebreton, J. P.; Lee,
M. R.; Lindgren, P.; Lofi, J.; Lorand, J. P.; Luais, B.; Masaitis,
V.; Meunier, A.; Moore, C. B.; Ormo, J.; Osinski, G. R.; Petit.,
D.; Pezard, P.; Poelchau, M.; Pohl, J.; Quesnel, Y.; Ramboz, C.;
Reeves, H.; Reimold, W. U.; Rochette, P.; Sapers, H. M.; Schmieder,
M.; Schultz, P. H.; Schwenzer, S. P.; Sharp, T.; Shoemaker, C. S.;
Simpson, S. L.; Stöffler, D.; Sturkell, E.; Trumel, H.; Walton, E.;
Westall, F.; Wittmann, A.; Wuennemann, K.
2019LPI....50.2005L Altcode:
Presenting and discussing the rescaled and correlated core/borehole
wall observations for the cumulated 544 m cores recovered in the
Rochechouart impact structure.
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Title: Spinel assemblages in lunar meteorites Graves Nunataks 06157
and Dhofar 1528: Implications for impact melting and equilibration
in the Moon's upper mantle
Authors: Wittmann, Axel; Korotev, Randy L.; Jolliff, Bradley L.;
Carpenter, Paul K.
2019M&PS...54..379W Altcode:
Magnesium-rich spinel assemblages occur in the two lunar vitric
breccia meteorites—Dhofar (Dho) 1528 and Graves Nunataks (GRA)
06157. Dho 1528 contains up to 0.7 mm cumulate Mg-rich spinel crystals
associated with Mg-rich olivine, Mg- and Al-rich pyroxene, plagioclase,
and rare cordierite. Using thermodynamic calculations of these mineral
assemblages, we constrain equilibration depths and discuss an origin of
these lithologies in the upper mantle of the Moon. In contrast, small,
10 to 20 μm spinel phenocryst assemblages in glassy melt rock clasts
in Dho 1528 and GRA 06157 formed from the impact melting of Mg-rich
rocks. Some of these spinel phenocrysts match compositional constraints
for spinel associated with "pink spinel anorthosites" inferred from
remote sensing data. However, such spinel phenocrysts in meteorites
and Apollo samples are typically associated with significant amounts
of olivine ± pyroxene that exceed the compositional constraints
for pink spinel anorthosites. We conclude that the remotely sensed
"pink spinel anorthosites" have not been observed in the collections
of lunar rocks. Moreover, we discuss impact-excavation scenarios for
the spinel-bearing assemblages in Dhofar 1528 and compare the bulk
rock composition of Dho 1528 to strikingly similar compositions of
Luna 20 samples that contain ejecta from the Crisium impact basin.
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Title: Extraordinary rocks from the peak ring of the Chicxulub
impact crater: P-wave velocity, density, and porosity measurements
from IODP/ICDP Expedition 364
Authors: Christeson, G. L.; Gulick, S. P. S.; Morgan, J. V.; Gebhardt,
C.; Kring, D. A.; Le Ber, E.; Lofi, J.; Nixon, C.; Poelchau, M.; Rae,
A. S. P.; Rebolledo-Vieyra, M.; Riller, U.; Schmitt, D. R.; Wittmann,
A.; Bralower, T. J.; Chenot, E.; Claeys, P.; Cockell, C. S.; Coolen,
M. J. L.; Ferrière, L.; Green, S.; Goto, K.; Jones, H.; Lowery,
C. M.; Mellett, C.; Ocampo-Torres, R.; Perez-Cruz, L.; Pickersgill,
A. E.; Rasmussen, C.; Sato, H.; Smit, J.; Tikoo, S. M.; Tomioka, N.;
Urrutia-Fucugauchi, J.; Whalen, M. T.; Xiao, L.; Yamaguchi, K. E.
2018E&PSL.495....1C Altcode:
Joint International Ocean Discovery Program and International
Continental Scientific Drilling Program Expedition 364 drilled into the
peak ring of the Chicxulub impact crater. We present P-wave velocity,
density, and porosity measurements from Hole M0077A that reveal
unusual physical properties of the peak-ring rocks. Across the boundary
between post-impact sedimentary rock and suevite (impact melt-bearing
breccia) we measure a sharp decrease in velocity and density, and an
increase in porosity. Velocity, density, and porosity values for the
suevite are 2900-3700 m/s, 2.06-2.37 g/cm<SUP>3</SUP>, and 20-35%,
respectively. The thin (25 m) impact melt rock unit below the suevite
has velocity measurements of 3650-4350 m/s, density measurements of
2.26-2.37 g/cm<SUP>3</SUP>, and porosity measurements of 19-22%. We
associate the low velocity, low density, and high porosity of suevite
and impact melt rock with rapid emplacement, hydrothermal alteration
products, and observations of pore space, vugs, and vesicles. The
uplifted granitic peak ring materials have values of 4000-4200 m/s,
2.39-2.44 g/cm<SUP>3</SUP>, and 8-13% for velocity, density, and
porosity, respectively; these values differ significantly from typical
unaltered granite which has higher velocity and density, and lower
porosity. The majority of Hole M0077A peak-ring velocity, density,
and porosity measurements indicate considerable rock damage, and are
consistent with numerical model predictions for peak-ring formation
where the lithologies present within the peak ring represent some of
the most shocked and damaged rocks in an impact basin. We integrate
our results with previous seismic datasets to map the suevite near
the borehole. We map suevite below the Paleogene sedimentary rock
in the annular trough, on the peak ring, and in the central basin,
implying that, post impact, suevite covered the entire floor of the
impact basin. Suevite thickness is 100-165 m on the top of the peak
ring but 200 m in the central basin, suggesting that suevite flowed
downslope from the collapsing central uplift during and after peak-ring
formation, accumulating preferentially within the central basin.
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Title: Shergottite Northwest Africa 6963: A Pyroxene-Cumulate
Martian Gabbro
Authors: Filiberto, Justin; Gross, Juliane; Udry, Arya; Trela, Jarek;
Wittmann, Axel; Cannon, Kevin M.; Penniston-Dorland, Sarah; Ash,
Richard; Hamilton, Victoria E.; Meado, Andrea L.; Carpenter, Paul;
Jolliff, Brad; Ferré, Eric C.
2018JGRE..123.1823F Altcode:
Northwest Africa (NWA) 6963 was found in Guelmim-Es-Semara, Morocco, and
based on its bulk chemistry and oxygen isotopes, it was classified as a
Martian meteorite. On the basis of a preliminary study of the textures
and crystal sizes, it was resubclassified as a gabbroic shergottite
because of the similarity with terrestrial and lunar gabbros. However,
the previous work was not a quantitative investigation of NWA 6963; to
supplement the original resubclassification and enable full comparison
between this and other Martian samples; here we investigate the
mineralogy, petrology, geochemistry, quantitative textural analyses,
and spectral properties of gabbroic shergottite NWA 6963 to constrain
its petrogenesis, including the depth of emplacement (i.e., base of
a flow versus crustal intrusion). NWA 6963 is an enriched shergottite
with similar mineralogy to the basaltic shergottites but importantly
does not contain any fine-grained mesostasis. Consistent with the
mineralogy, the reflectance (visible/near-infrared and thermal infrared)
spectrum of powdered NWA 6963 is similar to other shergottites because
they are all dominated by pyroxene, but its reflectance is distinct in
terms of albedo and spectral contrast due to its gabbroic texture. NWA
6963 represents a partial cumulate gabbro that is associated with the
basaltic shergottites. Therefore, NWA 6963 could represent a hypabyssal
intrusive feeder dike system for the basaltic shergottites that erupted
on the surface.
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Title: Petrology and Radioisotopic Ages of Allanite in the Peak Ring
of the Chicxulub Impact Crater
Authors: Wittmann, A.; van Soest, M.; Hodges, K. V.; Darling, J. R.;
Morgan, J. V.; Gulick, S. P. S.; Stockli, D.; Rasmussen, C.; Kring,
D. A.; Schmieder, M.
2018LPICo2067.6286W Altcode:
We report Th-Pb ages for REE-rich allanite in Chicxulub's peak ring that
chronicle alteration events, possibly including hydrothermal/metasomatic
alteration triggered by the impact.
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Title: Chicxulub Zircon (and Apatite!)
Authors: Wittmann, A.
2018LPICo2067.6295W Altcode:
I surveyed the zircon and apatite inventory in Chicxulub's peak ring:
planar fractures in apatite indicates shock pressures <20 GPa based
on constraints from quartz; zircon may also show planar elements below
their canonical onset at 20 GPa.
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Title: Characterization of a New High-Pressure Assemblage After
Anorthitic Plagioclase in Polymict Eucrite Northwest Africa 10658
Authors: Fudge, C.; Sharp, T. G.; Hu, J.; Ma, C.; Tschauner, O.;
Wittmann, A.
2018LPI....49.2417F Altcode:
We summarize structural and textural results on a new, garnet-bearing
high-pressure assemblage after plagioclase in polymict eucrite Northwest
Africa 10658.
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Title: Scrutinizing Six Silicide-Bearing Samples of Metal from the
Norton County Aubrite
Authors: Garvie, L. A. J.; Ray, S.; Wadhwa, M.; Wittmann, A.;
Domanik, K.
2018LPI....49.2104G Altcode:
The correct empirical formula for perryite is based on a cation:anion
ratio of 31:12. Norton County aubrite contains a new silicide — Ni3Si.
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Title: Rochechouart 2017-Drilling Campaign: First Results
Authors: Lambert, P.; Alwmark, C.; Baratoux, D.; Bouley, S.; Brack,
A.; Bruneton, P.; Buchner, E.; Claeys, P.; Dence, M. R.; Courtin
Nomade, A.; Duhamel Achin, I.; Floch, J. P.; French, B. M.; Fudge,
C.; Gattacceca, J.; Gibson, R. L.; Goderis, S.; Grieve, R. A. F.;
Hodges, K. W.; Hörz, F.; Humayun, M.; Jourdan, F.; Kelley, S. P.;
Kenkmann, T.; Kring, D. A.; Langenhorst, F.; Lee, M. R.; Lindgren,
P.; Lofi, J.; Lorand, J. P.; Luais, B.; Masaitis, V.; Meunier, A.;
Moore, C. B.; Ormö, J.; Osinski, G. R.; Petit, S.; Oezard, P. A.;
Poelchau, M.; Pohl, J.; Quesnel, Y.; Ramboz, C.; Reeves, H.; Rochette,
P.; Sapers, H. M.; Schmieder, M.; Schultz, P. H.; Schwenzer, S. P.;
Sharp, T.; Shoemaker, C. S.; Simpson, S. L.; Stöffler, D.; Sturkell,
E.; Trumel, H.; Walton, E.; Westall, F.; Wittmann, A.; Wünnemann, K.
2018LPI....49.1954L Altcode:
Characteristics and initial description of the 18 holes and 515m of
cores recovered (cumulative length) at Rochechouart.
---------------------------------------------------------
Title: Shergottite Northwest Africa (NWA) 6963 a Pyroxene-Cumulate
Martian Gabbro: Constraints on the Mineralogy, Petrology, and Physical
Properties of the Martian Crust at Depth
Authors: Filiberto, J.; Gross, J.; Udry, A.; Trela, J.; Wittmann, A.;
Cannon, K. M.; Penniston-Dorland, S.; Ash, R. D.; Hamilton, V. E.;
Meado, A. L.; Carpenter, P.; Jolliff, B.; Ferre, E. C.
2018LPI....49.2107F Altcode:
Pyroxenes whisper / Born deep, trapped inside, and froze. / Martian
volcano.
---------------------------------------------------------
Title: Constraints for Emplacement Conditions of the Chicxulub
Impact Crater's Upper Peak Ring Section (747−617 mbsf) in IODP-ICDP
Expedition 364 Drill Cores
Authors: Wittmann, A.
2018LPI....49.2994W Altcode:
Petrography and zirconology of suevites and impact melt rocks from
Chicxulub.
---------------------------------------------------------
Title: Cubic zirconia in >2370 °C impact melt records Earth's
hottest crust
Authors: Timms, Nicholas E.; Erickson, Timmons M.; Zanetti, Michael R.;
Pearce, Mark A.; Cayron, Cyril; Cavosie, Aaron J.; Reddy, Steven M.;
Wittmann, Axel; Carpenter, Paul K.
2017E&PSL.477...52T Altcode:
Bolide impacts influence primordial evolution of planetary bodies
because they can cause instantaneous melting and vaporization of
both crust and impactors. Temperatures reached by impact-generated
silicate melts are unknown because meteorite impacts are ephemeral,
and established mineral and rock thermometers have limited temperature
ranges. Consequently, impact melt temperatures in global bombardment
models of the early Earth and Moon are poorly constrained, and may not
accurately predict the survival, stabilization, geochemical evolution
and cooling of early crustal materials. Here we show geological
evidence for the transformation of zircon to cubic zirconia plus
silica in impact melt from the 28 km diameter Mistastin Lake crater,
Canada, which requires super-heating in excess of 2370 °C. This new
temperature determination is the highest recorded from any crustal
rock. Our phase heritage approach extends the thermometry range for
impact melts by several hundred degrees, more closely bridging the
gap between nature and theory. Profusion of >2370 °C superheated
impact melt during high intensity bombardment of Hadean Earth likely
facilitated consumption of early-formed crustal rocks and minerals,
widespread volatilization of various species, including hydrates,
and formation of dry, rigid, refractory crust.
---------------------------------------------------------
Title: Secondary Sulfides in Hydrothermally Altered Impactites and
Basement Rocks of the Chicxulub Peak Ring — A Preliminary Survey
Authors: Schmieder, M.; Kring, D. A.; Goderis, S.; Claeys, Ph.;
Coolen, M. J. L.; Wittmann, A.; Expedition 364 Science Party
2017LPICo1987.6139S Altcode:
Hydrothermally altered impactites from the Chicxulub peak ring
(Core M0077A) contain a variety of sulfides, including Co-Ni-Cu-rich
Fe-sulfide and framboidal pyrite.
---------------------------------------------------------
Title: Elemental and Structural Diversity in Norton County Metal
Nodules
Authors: Garvie, L. A. J.; Wittmann, A.; Ray, S.; Wadhwa, M.
2017LPICo1987.6384G Altcode:
Here, we present structural and elemental data from six Norton County
"nodules", with the view of revealing metal structures that correlate
with specific formation histories.
---------------------------------------------------------
Title: Northwest Africa 10658, a Uniquely Shocked Eucrite with a
Range of Deformation, Transformation and Recrystallization Effects
Authors: Fudge, C.; Sharp, T. G.; Ma, C.; Hu, J.; Wittmann, A.;
Tschauner, O.
2017LPICo1987.6297F Altcode:
We report a range of shock effects and high pressure minerals preserved
in NWA 10658, and discuss a previously undescribed transformation of
plagioclase to garnet.
---------------------------------------------------------
Title: Sphene and TiO2 Assemblages in the Chicxulub Peak Ring: U-Pb
Systematics and Implications for Shock Pressures, Temperatures,
and Crater Cooling
Authors: Schmieder, M.; Kring, D. A.; Lapen, T. J.; Gulick, S. P. S.;
Stockli, D. F.; Rasmussen, C.; Rae, A. S. P.; Ferrière, L.; Poelchau,
M.; Xiao, L.; Wittmann, A.; Expedition 364 Science Party
2017LPICo1987.6134S Altcode:
The discovery of TiO2-II, a high-pressure polymorph of TiO2 associated
with altered sphene in shocked granite from the Chicxulub peak ring,
places new constraints on shock pressure, post-shock temperatures,
and crater cooling.
---------------------------------------------------------
Title: Shock Metamorphic Effects of the Peak Ring Granites within
the Chicxulub Crater
Authors: Zhao, J. W.; Xiao, L.; Liu, H. S.; Xiao, Z. Y.; Morgan,
J.; Gulick, S.; Kring, D.; Claeys, P.; Riller, U.; Wittmann, A.;
Ferriere, L.
2017LPI....48.1421Z Altcode:
We conduct shock metamorphic effects study of the peak ring granites
of the Chicxulub Crater and find no remarkable shock pressure variation
from top to bottom.
---------------------------------------------------------
Title: Who Launched Lunar Meteorite Oued Awlitis 001?
Authors: Wittmann, A.; Korotev, R. L.; Jolliff, B. L.; Zanetti, M.;
Nishiizumi, K.; Jull, A. J. T.; Caffee, M. W.; Irving, A. J.
2017LPI....48.2482W Altcode:
We discuss the launch of lunar meteorite Oued Awlitis 001 in a recent
impact that produced a crater >10 km in diameter, possibly Giordano
Bruno or Goddard A.
---------------------------------------------------------
Title: Paleocene-Eocene Climatic Events in the IODP-ICDP Expedition
364, Chicxulub Impact Crater: Geochemical Preliminary Results
Authors: Perez-Cruz, L.; Keller, A.; Kirtland Turner, S.; Choumiline,
K.; Chenot, E.; Coolen, M. J. L.; Ocampo-Torres, R.; Pickersgill,
A.; Sato, H.; Wittmann, A.; Yamaguchi, K. E.; Expedition 364 Scientists
2017LPI....48.2575P Altcode:
Preliminary low-resolution geochemical data revealed short warm events
in the post-impact rocks.
---------------------------------------------------------
Title: Preliminary Chemical Data for IODP-ICDP Expedition 364 Drill
Cores of the Chicxulub Impact Structure's Peak Ring
Authors: Wittmann, A.; Claeys, P. F.; Chenot, E.; Coolen, M. J. L.;
Ocampo-Torres, R.; Perez-Cruz, L. L.; Pickersgill, A. E.; Sato, H.;
Yamaguchi, K. E.
2017LPI....48.2075W Altcode:
IODP-ICDP recovered a continuous section of impact rocks from
Chicxulub’s peak ring that includes a continuous siderophile element
enriched K-Pg section.
---------------------------------------------------------
Title: Shock Induced Feldspar and Silica Transformation in Polymict
Eucrite Northwest Africa 10658
Authors: Fudge, C.; Hu, J.; Ma, C.; Wittmann, A.; Sharp, T. G.
2017LPI....48.2525F Altcode:
We report on shock metamorphic features and high pressure minerals
preserved in NWA 10658. These features will be used to constrain P-T
impact conditions.
---------------------------------------------------------
Title: CIRIR Programs: Drilling and Research Opportunities at the
Rochechouart Impact Structure
Authors: Lambert, P.; Alwmark, C.; Baratoux, D.; Brack, A.; Bruneton,
P.; Buchner, E.; Chevremont, P.; Claeys, P.; Dence, M. R.; Floch,
J. P.; French, B. M.; Gattacceca, J.; Gibson, R. L.; Goderis, S.;
Grieve, R. A. F.; Hodges, K. V.; Hörz, F.; Jourdan, F.; Kelley, S. P.;
Kenkmann, T.; Kring, D. A.; Langenhorst, F.; Lee, M. R.; Lindgren,
P.; Lofi, J.; Lorand, J. P.; Luais, B.; Masaitis, V.; Meunier, A.;
Moore, C. B.; Ormö, J.; Osinski, G. R.; Petit, S.; Pohl, J.; Quesnel,
Y.; Reeves, H.; Rochette, P.; Sapers, H. M.; Schmieder, M.; Schultz,
P. H.; Schwenzer, S. P.; Shoemaker, C. S.; Stöffler, D.; Trumel,
H.; Westall, F.; Wittmann, A.; Wünnemann, K.
2017LPI....48.1936L Altcode:
Presenting the CIRIR, its scientific programs including the Rochechouart
2017 drilling campaign, and the related research opportunities.
---------------------------------------------------------
Title: The K/Pg Transition on the Peak-Ring of the Chicxulub Impact
Structure in Core M0077 of IODP-ICDP Expedition 364
Authors: Claeys, Ph.; Goderis, S.; de Winter, N. J.; Wittmann, A.;
Whalen, M.; IODP-ICDP Expedition 364 Science Party
2017LPI....48.1520C Altcode:
This abstract describes the K/Pg interval sampled by IODP-ICDP core
drilled in the Chicxulub Crater, Yucatán.
---------------------------------------------------------
Title: A pressure-temperature phase diagram for zircon at extreme
conditions
Authors: Timms, Nicholas E.; Erickson, Timmons M.; Pearce, Mark A.;
Cavosie, Aaron J.; Schmieder, Martin; Tohver, Eric; Reddy, Steven M.;
Zanetti, Michael R.; Nemchin, Alexander A.; Wittmann, Axel
2017ESRv..165..185T Altcode:
Hypervelocity impact processes are uniquely capable of generating
shock metamorphism, which causes mineralogical transformations and
deformation that register pressure (P) and temperature (T) conditions
far beyond even the most extreme conditions created by terrestrial
tectonics. The mineral zircon (ZrSiO<SUB>4</SUB>) responds to shock
deformation in various ways, including crystal-plasticity, twinning,
polymorphism (e.g., transformation to the isochemical mineral reidite),
formation of granular texture, and dissociation to ZrO<SUB>2</SUB>
+ SiO<SUB>2</SUB>, which provide robust thermobarometers that record
different extreme conditions. The importance of understanding these
material processes is two-fold. First, these processes can mobilize
and redistribute trace elements, and thus be accompanied by variable
degrees of resetting of the U-Pb system, which is significant for the
use of zircon as a geochronometer. Second, some features described
herein form exclusively during shock events and are diagnostic
criteria that can be used to confirm the hypervelocity origin of
suspected impact structures. We present new P-T diagrams showing
the phase relations of ZrSiO<SUB>4</SUB> polymorphs and associated
dissociation products under extreme conditions using available empirical
and theoretical constraints. We present case studies to illustrate
zircon microstructures formed in extreme environments, and present
electron backscatter diffraction data for grains from three impact
structures (Mistastin Lake of Canada, Ries of Germany, and Acraman
of Australia) that preserve different minerals and microstructures
associated with different shock conditions. For each locality, we
demonstrate how systematic crystallographic orientation relationships
within and between minerals can be used in conjunction with the new
phase diagrams to constrain the P-T history. We outline a conceptual
framework for a zircon-based approach to 'extreme thermobarometry' that
incorporates both direct observation of high-P and high-T phases, as
well as inferences for the former existence of phases from orientation
relationships in recrystallised products, a concept we refer to
here as 'phase heritage'. This new approach can be used to unravel
the pressure-temperature history of zircon-bearing samples that have
experienced extreme conditions, such as rocks that originated in the
Earth's mantle, and those shocked during impact events on Earth and
other planetary bodies.
---------------------------------------------------------
Title: IODP/ICDP Expedition 364-Drilling the Cretaceous-Paleogene
Chicxulub impact crater: Insights into large craters formation and
their effect on life.
Authors: Gulick, S. P. S.; Morgan, J. V.; Fucugauchi, J. U.; Bralower,
T. J.; Chenot, É.; Christeson, G. L.; Claeys, P.; Cockell, C. S.;
Collins, G. S.; Coolen, M.; Gebhardt, C.; Goto, K.; Kring, D. A.;
Xiao, L.; Lowery, C.; Mellett, C.; Ocampo-Torres, R.; Osinski, G. R.;
Perez-Cruz, L. L.; Pickersgill, A.; Poelchau, M.; Rae, A.; Rasmussen,
C.; Rebolledo-Vieyra, M.; Riller, U. P.; Sato, H.; Schmitt, D. R.;
Smit, J.; Tikoo, S.; Tomioka, N.; Whalen, M. T.; Zylberman, W.; Jones,
H.; Gareth, C.; Wittmann, A.; Lofi, J.; Yamaguchi, K. E.; Ferrière, L.
2016AGUFM.P31E..05G Altcode:
An international project to drill the Chicxulub impact crater was
conducted in April and May, 2016 as Expedition 364 of the International
Ocean Discovery Program (IODP) and International Continental Scientific
Drilling Project (ICDP). Site M0077 is located offshore Yucatan in
the southern Gulf of Mexico. The target was to core the only pristine
terrestrial peak ring and to measure physical properties of the entire
borehole. Specific questions included: What rocks comprise a topographic
peak ring? How are peak rings formed? How are rocks weakened during
large impacts to allow them to collapse and form relatively wide,
flat craters? What insights arise from biologic recovery in the
Paleogene within a potentially "toxic" ocean basin? Are impact craters
(including peak rings) habitats for life? Coring occurred from 503 -
1334.7 mbsf with nearly 100% recovery. Wireline logs were collected
from ultra slimline tools to total depth including gamma ray, magnetic
susceptibility, sonic, borehole fluid temperature and conductivity,
resistivity data, borehole images, and a finely spaced vertical
seismic profile. Stratigraphy cored included 110 m of Eocene and
Paleocene carbonates, 130 m of allochthonous impactites, and 590
m of crustal basement with dikes. All cores were measured using a
shipboard core logger (density, gamma ray, magnetic susceptibility
and resistivity) and shorebased dual energy, 0.3 mm resolution CT
scanner. These data allow us to: 1) refine numerical models of the
formation of the Chicxulub impact structure; 2) place constraints
on environmental perturbations that led to the K-Pg mass extinction;
3) improve simulations of impact craters on other planetary bodies;
4) examine deformation mechanisms for insights into how rocks weaken
during impacts; 5) study impact generated hydrothermal systems and 6)
understand the effects of impacts on the deep biosphere including as
a habitat for microbial life with implications for evolution on Earth
and astrobiology. Key results are that the Chicxulub peak ring is formed
from fractured basement rocks that may host a subsurface biosphere. The
impactite layer overlying the peak ring in turn provides insight into
resurge and tsunami processes, while the Paleogene sediments contain
the record of the recovery of life after the mass extinction event.
---------------------------------------------------------
Title: Impact-Related Deformation of Zircon
Authors: Timms, N. E.; Erickson, T. M.; Cavosie, A. J.; Pearce, M. A.;
Reddy, S. M.; Zanetti, M.; Tohver, E.; Schmieder, M.; Nemchin, A. A.;
Wittmann, A.
2016LPICo1921.6304T Altcode:
In this presentation, impact-related deformation microstructures in
zircon will be examined in detail, especially techniques to reliably
identify them, and how relationships among them can be interpreted in
terms of processes.
---------------------------------------------------------
Title: Shock Effects and High Pressure Polymorphs in Polymict Eucrite
Northwest Africa 10658
Authors: Fudge, C.; Wittmann, A.; Garvie, L. A. J.; Sharp, T. G.
2016LPICo1921.6480F Altcode:
We report the presence of coesite in polymict eucrite NWA 10658. High
pressure silica phases have previously been described to coexist
with silica glass in the Béréba eucrite. We will present data from
transmission electron microscope investigations.
---------------------------------------------------------
Title: Lunar Mantle Rocks in Dhofar 1528
Authors: Wittmann, A.; Korotev, R. L.
2016LPICo1921.6019W Altcode:
Lunar meteorite Dhofar 1528 contains assemblages of Mg-rich spinel,
Al-rich orthopyroxene, forsterite, and cordierite. Thermodynamic
modeling indicates these assemblages equilibrated ≥37 km deep in
the Moon, below the on average 34 km thick crust.
---------------------------------------------------------
Title: Shock Condition Forensics and Cryptic Phase Transformations
from Crystallographic Orientation Relationships in Zircon
Authors: Timms, N. E.; Erickson, T. M.; Cavosie, A. J.; Pearce, M. A.;
Reddy, S. M.; Zanetti, M.; Tohver, E.; Schmieder, M.; Nemchin, A. A.;
Wittmann, A.
2016LPICo1921.6302T Altcode:
We present an approach to constrain pressure and temperature conditions
during impact events involving identification of cryptic histories of
phase transformations from orientation relationships in shocked zircon,
linked to new P-T phase diagrams.
---------------------------------------------------------
Title: Preparing the 2017 Drilling Campaign at Rochechouart Impact
Structure
Authors: Lambert, P.; Goderis, S.; Hodges, K. V.; Kelley, S.; Lee,
M. R.; Jourdan, G. R.; Osinski, G. R.; Sapers, H. M.; Schmieder, M.;
Schwenzer, S.; Trumel, H.; Wittmann, A.
2016LPICo1921.6471L Altcode:
Presenting the programme and objective of 2017 drilling campaign towards
a better understanding of 1- Rochechouart, and 2- large impacts and
collateral effects (habitability of early Earth and planets/emergence
and evolution of life).
---------------------------------------------------------
Title: The Origin and Processing of Magnesian Glass in Lunar Meteorite
Northwest Africa 10404
Authors: Wittmann, A.; Korotev, R. L.; Kuehner, S. M.; Irving, A. J.
2016LPICo1921.6025W Altcode:
Magnesian glass clasts in lunar meteorite NWA 10404 record fusion of
Mg-rich lunar rocks or an achondrite impactor with feldspathic crust;
the meteorite's launch caused vitrification and vesiculation of its
groundmass and reheated the glass clasts.
---------------------------------------------------------
Title: The Electron Microprobe Laboratory at Arizona State University
Authors: Wittmann, A.; Convey, D.; Sharp, T.; Wadhwa, M.; Buseck,
P.; Hodges, K.
2016LPI....47.3018W Altcode:
ASU's Electron Microprobe Laboratory offers state-of-the-art
microchemical analytical capacities for the study of planetary
materials.
---------------------------------------------------------
Title: Petrologic, Chemical and Physical Characterization of Unique
Lunar Vitric Regolith Breccia Northwest Africa 10404
Authors: Kuehner, S. M.; Wittmann, A.; Korotev, R. L.; Carpenter,
P.; Macke, R. J.; Britt, D. T.; Irving, A. J.; Pitt, D.
2016LPI....47.2246K Altcode:
We describe a unique lunar feldspathic meteorite containing partly
devitrified glass clasts. Could this be evidence for impacts into
ice-bearing regolith?
---------------------------------------------------------
Title: Petrogenesis of Lunar Poikilitic Impact Melt Meteorite Oued
Awlitis 001
Authors: Wittmann, A.; Korotev, R. L.; Jolliff, B. L.; Irving, A. J.
2015LPI....46.1141W Altcode: 2015LPICo1832.1141W
Did an impact excavating a ≥500 m-Ø crater in the melt sheet of a
≥50 km-Ø impact crater in the Moon’s highlands launch poikilitic
melt rock Oued Awlitis 001?
---------------------------------------------------------
Title: Lunar Mantle Spinel in Dhofar 1528?
Authors: Wittmann, A.; Korotev, R. L.; Jolliff, B. L.
2015LPI....46.1460W Altcode: 2015LPICo1832.1460W
Dhofar 1528 contains mineral assemblages that could have originally
crystallized as cumulates in the mantle of the Moon.
---------------------------------------------------------
Title: Petrology and Composition of Lunar Mare Basalt Meteorite
Northwest Africa 8632 from Chwichiya, Morocco
Authors: Korotev, R. L.; Irving, A. J.; Wittmann, A.; Kuehner, S. M.;
Chennaoui-Aoudjehane, H.; Labenne, L.
2015LPI....46.1195K Altcode: 2015LPICo1832.1195K
New mare basalt from the Moon to Morocco for us to delight.
---------------------------------------------------------
Title: Petrography and composition of Martian regolith breccia
meteorite Northwest Africa 7475
Authors: Wittmann, Axel; Korotev, Randy L.; Jolliff, Bradley L.;
Irving, Anthony J.; Moser, Desmond E.; Barker, Ivan; Rumble, Douglas
2015M&PS...50..326W Altcode:
The Northwest Africa (NWA) 7475 meteorite is one of the several
stones of paired regolith breccias from Mars based on petrography,
oxygen isotope, mineral compositions, and bulk rock compositions. Its
inventory of lithic clasts is dominated by vitrophyre impact melts
that were emplaced while they were still molten. Other clast types
include crystallized impact melt rocks, evolved plutonic rocks, possible
basalts, contact metamorphosed rocks, and siltstones. Impact spherules
and vitrophyre shards record airborne transport, and accreted dust
rims were sintered on most clasts, presumably during residence in
an ejecta plume. The clast assemblage records at least three impact
events, one that formed an impact melt sheet on Mars ≤4.4 Ga ago,
a second that assembled NWA 7475 from impactites associated with the
impact melt sheet at 1.7-1.4 Ga, and a third that launched NWA 7475
from Mars ~5 Ma ago. Mildly shocked pyroxene and plagioclase constrain
shock metamorphic conditions during launch to >5 and <15 GPa. The
mild postshock-heating that resulted from these shock pressures would
have been insufficient to sterilize this water-bearing lithology
during launch. Magnetite, maghemite, and pyrite are likely products
of secondary alteration on Mars. Textural relationships suggest that
calcium-carbonate and goethite are probably of terrestrial origin,
yet trace element chemistry indicates relatively low terrestrial
alteration. Comparison of Mars Odyssey gamma-ray spectrometer data
with the Fe and Th abundances of NWA 7475 points to a provenance in
the ancient southern highlands of Mars. Gratteri crater, with an age
of ~5 Ma and an apparent diameter of 6.9 km, marks one possible launch
site of NWA 7475.
---------------------------------------------------------
Title: Gabbroic Shergottite NorthWest Africa 6963
Authors: Filiberto, J.; Gross, J.; Trela, J.; Cannon, K. M.;
Penniston-Dorland, S.; Wittmann, A.; Jolliff, B.; Carpenter, P.;
Ferré, E. C.; Mustard, J.
2014LPICo1800.5064F Altcode:
Here, we investigate the mineralogy, petrology, geochemistry (major
and trace elements, and Li isotopes), shape preferred orientation of
pyroxene, and spectral properties of gabbroic shergottite NWA 6963 to
constrain its petrogenetic history.
---------------------------------------------------------
Title: Decomposition of Zircon in Mistastin Lake Impact Melt Glass:
An Integrated SIMS, Hyperspectral-CL, Raman, and EPMA Study
Authors: Zanetti, M.; Wittmann, A.; Nemchin, A.; Carpenter, P.;
Vicenzi, E.; Jolliff, B.
2014LPICo1800.5371Z Altcode:
Multiple analytical techniques are used to examine two exceptionally
well-preserved zircon grains entrained in glassy impact melt in order
to study impact induced decomposition of zircon and determine the
impact age from the dissolution reaction rim.
---------------------------------------------------------
Title: Petrology and Chemistry of a Lunar Feldspathic Impact Melt
Rock Meteorite from Oued Awlitis, Morocco
Authors: Wittmann, A.; Korotev, R. L.; Jolliff, B. L.;
Chennaoui-Aoudjehane, H.; Irving, A. J.
2014LPICo1800.5352W Altcode:
Oued Awlitis 001 is a new lunar meteorite from Morocco. Using chemical
data and petrographic observations we explore the petrogenesis of this
moderately slow cooled, clast-rich, feldspathic impact melt rock.
---------------------------------------------------------
Title: What Heated H/L Chondrite LaPaz Icefield 031047 ~0.5 Million
Years Ago?
Authors: Welten, K. C.; Huber, L.; Caffee, M. W.; Wittmann, A.; Kring,
D. A.; Wieler, R.; Nishiizumi, K.
2014LPICo1800.5422W Altcode:
Based on the unusual cosmic-ray exposure and thermal history of H/L
chondrite LAP 031047, we conclude that this meteorite was not heated
by impact on the parent body, but was heated to >700°C during
close passage to the Sun ~0.5 Myr ago .
---------------------------------------------------------
Title: Third of a Kind — Impact Melted Lunar Granulitic Breccia
Meteorite Dhofar 1766
Authors: Wittmann, A.; Korotev, R. L.; Jolliff, B. L.
2014LPI....45.1182W Altcode:
Dho 1766 is an impact melted variety of granulite Dho 733. Is their
composition evidence for unknown lunar lithologies or impact melt
origins for granulites?
---------------------------------------------------------
Title: Trace Element Composition of Impact Melts in Lunar Meteorite
Shişr 161
Authors: Wittmann, A.; Korotev, R. L.; Jolliff, B. L.; Lapen, T. J.
2013M&PSA..76.5262W Altcode:
LA-ICP-MS data for components in lunar meteorite Shişr 161 indicate
a common petrogenesis of impact melt clasts and admixture of exotic
spherules. Does this material represent fragments of the upper part
of a basin melt sheet?
---------------------------------------------------------
Title: Petrology of Impact Melt Rich Martian Regolith Breccia
Northwest Africa 7475
Authors: Wittmann, A.; Korotev, R. L.; Jolliff, B. L.; Kuehner, S. M.;
Irving, A. J.
2013M&PSA..76.5272W Altcode:
The petrography of “basaltic breccia” NWA 7475 indicates a
suevite-like regolith breccia. Spherules, crystallized and vitric
impact melts, siltstone, accretionary lapilli, and diverse basaltic
and plutonic rock and mineral clasts constitute martian soil.
---------------------------------------------------------
Title: Miller Range 05029: Evidence for a Large Impact on the L
Chondrite Parent Body >4.5 Ga
Authors: Weirich, J. R.; Wittmann, A.; Isachsen, C. E.; Rumble, D.;
Swindle, T. D.; Kring, D. A.
2013LPICo1737.3062W Altcode:
MIL 05029 is a slowly cooled, clast-free L impact melt rock with an
^40Ar-^39Ar age of ~4.52 Ga. Slow cooling implies deep burial and a
crater diameter of 25-60 km. This impact may have shattered the parent
body and disrupted the onion shell structure.
---------------------------------------------------------
Title: Petrology of impactites from El'gygytgyn crater: Breccias in
ICDP-drill core 1C, glassy impact melt rocks and spherules
Authors: Wittmann, Axel; Goderis, Steven; Claeys, Philippe; Vanhaecke,
Frank; Deutsch, Alexander; Adolph, Leonie
2013M&PS...48.1199W Altcode:
<title type="main">AbstractEl'gygytgyn is a 18 km diameter,
3.6 Ma old impact crater in NE Siberia. International Continental
Scientific Drilling Program—El'gygytgyn hole 1C was drilled on the
frozen crater lake, 2.3 km from the crater center to a final depth
of 517 m below the lake floor. Petrographic and geochemical analyses
of 26 drill core samples, three impact melt rocks from the surface,
and seven glass spherules from surface deposits outside the crater
are used to characterize the impactite inventory at El'gygytgyn. The
bottom 98 m of hole 1C intersected monomict brecciated, unshocked,
rhyolitic ignimbrite with minor intercalations of polymict breccia and
mafic inclusions. These lithologies are overlain by 89 m of polymict
breccia whose components occasionally exhibit scarce, low-degree shock
metamorphic features. This unit is succeeded by 10 m of suevite that
contains about 1 vol% glassy impact melt shards <1 cm in size and
a low amount of shock metamorphosed lithic clasts. The suevite is
capped by a reworked fallout deposit that constitutes a transition
over 4 m into lacustrine sedimentation. A higher abundance of shock
metamorphosed lithic clasts, and glass spherules, some with Ni-rich
spinel and admixture of an ultramafic component, characterize this
unit. We tentatively interpret this impactite section as allochthonous
breccia in the vicinity of El'gygytgyn's central ring uplift. The
geochemical compositions of seven glass spherules from terrace deposits
2 km outside the crater and eight spherules from the reworked fallout
deposit in hole 1C show far greater variability than the composition
of impact melt shards and impact melt rocks. Some of these spherules
also show strong enrichments in siderophile elements.
---------------------------------------------------------
Title: Testing the ureilite projectile hypothesis for the El'gygytgyn
impact: Determination of siderophile element abundances and Os
isotope ratios in ICDP drill core samples and melt rocks
Authors: Goderis, S.; Wittmann, A.; Zaiss, J.; Elburg, M.; Ravizza,
G.; Vanhaecke, F.; Deutsch, A.; Claeys, P.
2013M&PS...48.1296G Altcode: 2013M&PS..tmp..358G
The geochemical nature of the impactites from International Continental
Scientific Drilling Project—El'gygytgyn lake drill core 1C is
compared with that of impact melt rock fragments collected near the
western rim of the structure and literature data. Concentrations of
major and trace elements, with special focus on siderophile metals Cr,
Co, Ni, and the platinum group elements, and isotope ratios of osmium
(Os), were determined to test the hypothesis of an ureilite impactor
at El'gygytgyn. Least squares mixing calculations suggest that the
upper volcanic succession of rhyolites, dacites, and andesites were
the main contributors to the polymict impact breccias. Additions of
2-13.5 vol% of basaltic inclusions recovered from drill core intervals
between 391.6 and 423.0 mblf can almost entirely account for the
compositional differences observed for the bottom of a reworked
fallout deposit at 318.9 mblf, a polymict impact breccia at 471.4
mblf, and three impact melt rock fragments. However, the measured
Os isotope ratios and slightly elevated PGE content (up to 0.262
ng g<SUP>-1</SUP> Ir) of certain impactite samples, for which the
CI-normalized logarithmic PGE signature displays a relatively flat
(i.e., chondritic) pattern, can only be explained by the incorporation
of a small meteoritic contribution. This component is also required
to explain the exceptionally high siderophile element contents and
corresponding Ni/Cr, Ni/Co, and Cr/Co ratios of impact glass spherules
and spherule fragments that were recovered from the reworked fallout
deposits and from terrace outcrops of the Enmyvaam River approximately
10 km southeast of the crater center. Mixing calculations support the
presence of approximately 0.05 wt% and 0.50-18 wt% of ordinary chondrite
(possibly type-LL) in several impactites and in the glassy spherules,
respectively. The heterogeneous distribution of the meteoritic
component provides clues for emplacement mechanisms of the various
impactite units.
---------------------------------------------------------
Title: Iron-Nickel(-Cobalt) Metal in Lunar Rocks Revisited
Authors: Wittmann, A.; Korotev, R. L.
2013LPI....44.3035W Altcode: 2013LPICo1719.3035W
Occurrences of metal particles with high Ni and Co concentrations in
lunar rocks are compared with those in lunar meteorite Shişr 161.
---------------------------------------------------------
Title: Feldspathic Granulite Clasts in Lunar Meteorite Shişr 161
— Cumulates from a Differentiated Basin Melt Sheet?
Authors: Wittmann, A.; Korotev, R. L.; Jolliff, B. L.
2013LPI....44.2061W Altcode: 2013LPICo1719.2061W
Poikilitic granulites could be cumulate rocks that formed from
fractional crystallization in lunar basin impact melt sheets.
---------------------------------------------------------
Title: A retrospective of the GREGOR solar telescope in scientific
literature
Authors: Denker, C.; von der Lühe, O.; Feller, A.; Arlt, K.;
Balthasar, H.; Bauer, S. -M.; Bello González, N.; Berkefeld, Th.;
Caligari, P.; Collados, M.; Fischer, A.; Granzer, T.; Hahn, T.;
Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Kentischer, T.; Klva{ňa,
M.; Kneer, F.; Lagg, A.; Nicklas, H.; Popow, E.; Puschmann, K. G.;
Rendtel, J.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Solanki, S. K.;
Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; Waldmann,
T.; Wiehr, E.; Wittmann, A. D.; Woche, M.
2012AN....333..810D Altcode: 2012arXiv1210.3167D
In this review, we look back upon the literature, which had the
GREGOR solar telescope project as its subject including science cases,
telescope subsystems, and post-focus instruments. The articles date
back to the year 2000, when the initial concepts for a new solar
telescope on Tenerife were first presented at scientific meetings. This
comprehensive bibliography contains literature until the year 2012,
i.e., the final stages of commissioning and science verification. Taking
stock of the various publications in peer-reviewed journals and
conference proceedings also provides the “historical” context
for the reference articles in this special issue of Astronomische
Nachrichten/Astronomical Notes.
---------------------------------------------------------
Title: The GREGOR Fabry-Pérot Interferometer
Authors: Puschmann, K. G.; Denker, C.; Kneer, F.; Al Erdogan, N.;
Balthasar, H.; Bauer, S. M.; Beck, C.; Bello González, N.; Collados,
M.; Hahn, T.; Hirzberger, J.; Hofmann, A.; Louis, R. E.; Nicklas, H.;
Okunev, O.; Martínez Pillet, V.; Popow, E.; Seelemann, T.; Volkmer,
R.; Wittmann, A. D.; Woche, M.
2012AN....333..880P Altcode: 2012arXiv1210.2921P
The GREGOR Fabry-Pérot Interferometer (GFPI) is one of three
first-light instruments of the German 1.5-meter GREGOR solar telescope
at the Observatorio del Teide, Tenerife, Spain. The GFPI uses two
tunable etalons in collimated mounting. Thanks to its large-format,
high-cadence CCD detectors with sophisticated computer hard- and
software it is capable of scanning spectral lines with a cadence
that is sufficient to capture the dynamic evolution of the solar
atmosphere. The field-of-view (FOV) of 50 arcsec × 38 arcsec is well
suited for quiet Sun and sunspot observations. However, in the vector
spectropolarimetric mode the FOV reduces to 25 arcsec × 38 arcsec. The
spectral coverage in the spectroscopic mode extends from 530-860 nm
with a theoretical spectral resolution of R ≈ 250,000, whereas in
the vector spectropolarimetric mode the wavelength range is at present
limited to 580-660 nm. The combination of fast narrow-band imaging and
post-factum image restoration has the potential for discovery science
concerning the dynamic Sun and its magnetic field at spatial scales
down to ∼50 km on the solar surface.
---------------------------------------------------------
Title: Gale Crater: Formation and post-impact hydrous environments
Authors: Schwenzer, S. P.; Abramov, O.; Allen, C. C.; Bridges, J. C.;
Clifford, S. M.; Filiberto, J.; Kring, D. A.; Lasue, J.; McGovern,
P. J.; Newsom, H. E.; Treiman, A. H.; Vaniman, D. T.; Wiens, R. C.;
Wittmann, A.
2012P&SS...70...84S Altcode:
Gale Crater, the landing site of the 2011 Mars Science Laboratory
mission, formed in the Late Noachian. It is a 150 km diameter complex
impact structure with a central mound (Mount Sharp), the original
features of which may be transitional between a central peak and
peak ring impact structure. The impact might have melted portions of
the substrate to a maximum depth of ∼17 km and produced a minimum
of 3600 km<SUP>3</SUP> of impact melt, half of which likely remained
within the crater. The bulk of this impact melt would have pooled in an
annular depression surrounding the central uplift, creating an impact
melt pool as thick as 0.5-1 km. The ejecta blanket surrounding Gale
may have been as thick as ∼600 m, which has implications for the
amount of erosion that has occurred since Gale Crater formed. After
the impact, a hydrothermal system may have been active for several
hundred thousand years and a crater lake with associated sediments is
likely to have formed. The hydrothermal system, and associated lakes
and springs, likely caused mineral alteration and precipitation. In
the presence of S-rich host rocks, the alteration phases are modelled
to contain sheet silicates, quartz, sulphates, and sulphides. Modelled
alteration assemblages may be more complex if groundwater interaction
persisted after initial alteration. The warm-water environment might
have provided conditions supportive of life. Deep fractures would have
allowed for hydraulic connectivity into the deep subsurface, where
biotic chemistry (and possibly other evidence of life) may be preserved.
---------------------------------------------------------
Title: Spherules and Glasses in Lunaite Shişr 161 Record Reworked
Regolith and a Magnesian Component of the Feldspathic Highlands
Terrane
Authors: Wittmann, A.; Korotev, R. L.; Jolliff, B. L.; Irving, A. J.
2012LPICo1677...63W Altcode:
Feldspathic breccia Shişr 161 contains metamorphosed spherules that
likely formed fallback debris into a large lunar impact crater. Together
with glass shards, they record broad variations among precursor rocks
that generated a magnesian character.
---------------------------------------------------------
Title: Depositional Record of Pristine Impactites and Traces of the
Projectile in El'gygytgyn Crater
Authors: Wittmann, A.; Goderis, S.; Claeys, P.; Elburg, M.; Vanhaecke,
F.; Zaiss, J.; Ravizza, G.; Deutsch, A.
2012LPI....43.1999W Altcode:
Formation and emplacement constraints for a continuous section of
impactites and traces of the impacting projectile from trace-element
data (platinum-group elements and Os-isotopes) in drill core samples
from El’gygytgyn crater.
---------------------------------------------------------
Title: H/L chondrite LaPaz Icefield 031047 - A feather of Icarus?
Authors: Wittmann, Axel; Friedrich, Jon M.; Troiano, Julianne; Macke,
Robert J.; Britt, Daniel T.; Swindle, Timothy D.; Weirich, John R.;
Rumble, Douglas; Lasue, Jeremie; Kring, David A.
2011GeCoA..75.6140W Altcode:
Antarctic meteorite LAP 031047 is an ordinary chondrite composed
of loosely consolidated chondritic fragments. Its petrography,
oxygen isotopic composition and geochemical inventory are
ambiguous and indicate an intermediate character between H and L
chondrites. Petrographic indicators suggest LAP 031047 suffered a
shock metamorphic overprint below ∼10 GPa, which did not destroy its
unusually high porosity of ∼27 vol%. Metallographic textures in LAP
031047 indicate heating above ∼700 °C and subsequent cooling, which
caused massive transformation of taenite to kamacite. The depletion
of thermally labile trace elements, the crystallization of chondritic
glass to microcrystalline plagioclase of unusual composition, and the
occurrence of coarsely crystallized chondrule fragments is further
evidence for post-metamorphic heating to ∼700-750 °C. However,
this heating event had a transient character because olivine and low-Ca
pyroxene did not equilibrate. Nearly complete degassing up to very high
temperatures is indicated by the thorough resetting of LAP 031047's
Ar-Ar reservoir ∼100 ± 55 Ma ago. A noble gas cosmic-ray exposure
age indicates it was reduced to a meter-size fragment at <0.5 Ma. In
light of the fact that shock heating cannot account for the thermal
history of LAP 031047 in its entirety, we test the hypothesis that this
meteorite belonged to the near-surface of an Aten or Apollo asteroid
that underwent heating during orbital passages close to the Sun.
---------------------------------------------------------
Title: El'gygytgyn Impact Crater's Fireball Layer: Spherules, Impact
Melts, Meteoritic Component
Authors: Goderis, S.; Elburg, M.; Vanhaecke, F.; Claeys, Ph.;
Wittmann, A.
2011M&PSA..74.5338G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: 40Ar-39Ar Dating of Larkman Nunatak 06299: Comparison to
Paired Sample LAR 06298 and to Other LL Chondrites
Authors: Swindle, T. D.; Weirich, J. R.; Isachsen, C. E.; Wittmann,
A.; Kring, D. A.
2011M&PSA..74.5497S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Fold Hinge in Overturned Coconino Sandstone and its Structural
Displacement During the Formation of Barringer Meteorite Crater
(a.k.a Meteor Crater)
Authors: Kring, D. A.; Balcerski, J.; Blair, D. M.; Chojnacki, M.;
Donohue, P. H.; Drummond, S. A.; Garber, J. M.; Hopkins, M.; Huber,
M. S.; Jaret, S. J.; Losiak, A.; Maier, A.; Mitchell, J.; Ong, L.;
Ostrach, L. R.; O'Sullivan, K. M.; Potter, R. W. K.; Robbins, S.;
Shankar, B.; Shea, E. K.; Singer, K. N.; Sori, M.; Sturm, S.; Willmes,
M.; Zanetti, M.; Wittmann, A.
2011LPI....42.1740K Altcode:
New details are uncovered about the overturning and emplacement of
impact ejecta at the classic impact site: Meteor Crater.
---------------------------------------------------------
Title: Petrography and Provenance of Impact Melt and Granulite
Particles from the Ancient Regolith Breccias 60016, 61135, and 66035
Authors: Wittmann, A.; Lapen, T.; Swindle, T. D.; Kring, D. A.
2011LPI....42.2289W Altcode:
Granulite and melt particles in ancient regolith breccias 60016,
61135, and 66035 formed in variably energetic impacts, and record
their provenance from feldspathic, noritic, and KREEP-rich precursor
rocks during the basin forming epoch on the Moon.
---------------------------------------------------------
Title: Provenance of Impact Melt and Granulite Clasts in Lunar
Meteorite PCA 02007
Authors: Vaughan, W. M.; Wittmann, A.; Joy, K. H.; Lapen, T. J.;
Kring, D. A.
2011LPI....42.1247V Altcode:
EMP and LA ICP-MS analyses of impact melt and granulite clasts in
the lunar meteorite PCA 02007 reveal clues to their provenance in
KREEP-poor regions of the Moon dominated by feldspathic lithologies.
---------------------------------------------------------
Title: Preliminary Petrography of Impactites from El'gygytgyn Crater,
NE Siberia, Including Cores from ICDP-Lake Drilling Hole D1
Authors: Wittmann, A.; Goderis, S.; Claeys, P.
2011LPI....42.2792W Altcode:
Comparison of glassy melt bombs near the crater rim with impactites
from a drilling near the central uplift of El'gygytgyn crater indicate
a melt deficiency in this impact structure.
---------------------------------------------------------
Title: Eucrite Impact Melt NWA 5218 — Evidence for a Large Crater
on Vesta
Authors: Wittmann, A.; Hiroi, T.; Ross, D. K.; Herrin, J. S.; Rumble,
D.; Kring, D. A.
2011LPI....42.1984W Altcode:
NWA 5218 is a clast-rich eucrite impact melt rock, which may have
resulted from an impact that affected the mid-to lower crust of Vesta;
its reflectance spectra may be useful for DAWN to identify melt outcrops
on Vesta.
---------------------------------------------------------
Title: Asymmetrical Distribution of Impact Ejected Lithologies at
Barringer Meteorite Crater (a.k.a Meteor Crater)
Authors: Kring, D. A.; Balcerski, J.; Blair, D. M.; Chojnacki, M.;
Donohue, P. H.; Drummond, S. A.; Garber, J. M.; Hopkins, M.; Huber,
M. S.; Jaret, S. J.; Losiak, A.; Maier, A.; Mitchell, J.; Ong, L.;
Ostrach, L. R.; O'Sullivan, K. M.; Potter, R. W. K.; Robbins, S.;
Shankar, B.; Shea, E. K.; Singer, K. N.; Sori, M.; Sturm, S.; Willmes,
M.; Zanetti, M.; Wittmann, A.
2011LPI....42.1746K Altcode:
Eighty meters of ejected material was sheared from the rim of Meteor
Crater and deposited at greater distances, which explains the asymmetry
of ejecta around the crater.
---------------------------------------------------------
Title: Geological Context of Ordinary Chondrite Impact Melt NWA 4150
Authors: Wittmann, A.; Swindle, T. D.; Greshake, A.; Rumble, D.;
Kring, D. A.
2011LPI....42.1419W Altcode:
NWA 4150 is a clast-rich impact melt rock whose metallographic
characteristics suggest it formed in a ≥5-km-diameter crater on the
L-chondrite asteroid.
---------------------------------------------------------
Title: The Ar-Ar age and petrology of Miller Range 05029: Evidence
for a large impact in the very early solar system
Authors: Weirich, J. R.; Wittmann, A.; Isachsen, C. E.; Rumble, D.;
Swindle, T. D.; Kring, D. A.
2010M&PS...45.1868W Altcode: 2010M&PS..tmp..105W
Miller Range (MIL) 05029 is a slowly cooled melt rock with metal/sulfide
depletion and an Ar-Ar age of 4517 ± 11 Ma. Oxygen isotopes and
mineral composition indicate that it is an L chondrite impact melt, and
a well-equilibrated igneous rock texture with a lack of clasts favors
a melt pool over a melt dike as its probable depositional setting. A
metallographic cooling rate of approximately 14 °C Ma<SUP>-1</SUP>
indicates that the impact occurred at least approximately 20 Ma before
the Ar-Ar closure age of 4517 Ma, possibly even shortly after accretion
of its parent body. A metal grain with a Widmanstätten-like pattern
further substantiates slow cooling. The formation age of MIL 05029
is at least as old as the Ar-Ar age of unshocked L and H chondrites,
indicating that endogenous metamorphism on the parent asteroid was
still ongoing at the time of impact. Its metallographic cooling rate of
approximately 14 °C Ma<SUP>-1</SUP> is similar to that typical for L6
chondrites, suggesting a collisional event on the L chondrite asteroid
that produced impact melt at a minimum depth of 5-12 km. The inferred
minimum crater diameter of 25-60 km may have shattered the 100-200 km
diameter L chondrite asteroid. Therefore, MIL 05029 could record the
timing and petrogenetic setting for the observed lack of correlation
of cooling rates with metamorphic grades in many L chondrites.
---------------------------------------------------------
Title: Impact Melts and Granulites in the Lunar Meteorite PCA 02007
Authors: Vaughan, W. M.; Wittmann, A.; Joy, K. H.; Kring, D. A.
2010lpii.conf...25V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Impact cratering on the H chondrite parent asteroid
Authors: Wittmann, Axel; Swindle, Timothy D.; Cheek, Leah C.; Frank,
Elizabeth A.; Kring, David A.
2010JGRE..115.7009W Altcode:
This paper reports petrological data for LaPaz Icefield 02240,
03922, 031125, 031173, 031308, 04462, and 04751, which are meteoritic
samples of clast-rich impact melt rocks from the H chondrite parent
asteroid. The size distribution and metallographic characteristics
of Fe-Ni metal in the melts indicate very rapid 1 to 40°C/s cooling
in the temperature range between >1500 and ∼950°C when the
clast-melt mixtures were thermally equilibrating. Cooling slowed
to values between 10<SUP>-3</SUP> and 10<SUP>-2</SUP>°C/s in the
temperature range between 700 and 400°C when the melt rocks were
cooling to their surroundings. These data suggest that the rocks cooled
near the surface of the H chondrite asteroid within suevitic impact
deposits. Integrating these data with the petrologic characteristics
of other H chondrite melt rocks and their radioisotopic ages indicates
that the H chondrite asteroid suffered at least one large impact event
while still cooling from endogenous metamorphism at ∼4500 Ma; this
impact must have degraded the asteroid's integrity but did not cause
shattering. Impact events in the era between ∼4100 and ∼3600 Ma
produced melt volumes large enough to allow segregation of metal and
troilite from silicate melts, possibly within continuous impact melt
sheets contained in craters. The impact record after 3600 Ma does not
display such assemblages, which suggests a decrease in the rate of
large impact events or a catastrophic size reduction of the H chondrite
parent asteroid at around this time.
---------------------------------------------------------
Title: The Ries Crater and the Interpretation of Ejecta Deposits at
Impact Craters on Mars
Authors: Kenkmann, T.; Wittmann, A.
2010LPICo1559...16K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Exploring Martian Impact Craters: Why They are Important for
the Search for Life
Authors: Schwenzer, S. P.; Abramov, O.; Allen, C. C.; Clifford, S.;
Filiberto, J.; Kring, D. A.; Lasue, J.; McGovern, P. J.; Newsom,
H. E.; Treiman, A. H.; Vaniman, D. T.; Wiens, R. C.; Wittmann, A.
2010LPICo1538.5527S Altcode:
We make a case for exploring impact craters as potential windows
into habitable environments. This includes studying lake deposits,
hydrothermal alteration, and excavated material from a potentially
habitable region beneath the martian cryosphere.
---------------------------------------------------------
Title: Zircon-Reidite Relations in Breccias from the Chesapeake Bay
Impact Structure
Authors: Malone, L.; Boonsue, S.; Spray, J.; Wittmann, A.
2010LPI....41.2286M Altcode:
The natural high pressure polymorph of ZrSiO4 exhibits distinct
zonations in shock stage III (45-60 GPa, 900°-1500°C) materials. A
decomposition front at the rim still contains reidite, which raises
questions about the durability of reidite-zircon.
---------------------------------------------------------
Title: Highly Porous and Compositionally Intermediate Ordinary
Chondrite LAP 031047
Authors: Wittmann, A.; Kring, D. A.; Friedrich, J. M.; Troiano, J.;
Macke, R. J.; Britt, D. T.; Swindle, T. D.; Weirich, J. R.; Rumble, D.
2010LPI....41.1848W Altcode:
LAP 031047 is a highly porous ordinary chondrite with a very young Ar-Ar
age, and oxygen isotopic, and bulk and silicate mineral composition
intermediate between H- and L-chondrites: Shock-lithified debris of
a distinct ordinary chondrite asteroid?
---------------------------------------------------------
Title: Exploring Martian Impact Craters: What They Can Reveal About
the Subsurface and Why They are Important in the Search for Life
Authors: Schwenzer, S. P.; Abramov, O.; Allen, C. C.; Clifford, S.;
Filiberto, J.; Kring, D. A.; Lasue, J.; McGovern, P. J.; Newsom,
H. E.; Treiman, A.; Vaniman, D. T.; Wiens, R. C.; Wittmann, A.
2010LPI....41.1589S Altcode:
On Noachian Mars, impact craters were frequent, could have
penetrated an existing cryosphere and potentially hosted hydrothermal
systems. Therefore, they are important targets to explore the subsurface
and potential habitats on Noachian terrain.
---------------------------------------------------------
Title: Clast-rich H-Chondrite Impact Melts
Authors: Wittmann, A.; Swindle, T. D.; Kring, D. A.
2009M&PSA..72.5403W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Fluidization of the Ries Crater's Ejecta Blanket
Authors: Wittmann, A.; Kenkmann, T.
2009M&PSA..72.5392W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Shock-Petrographic Study of Impactites from the Chesapeake
Bay Crater
Authors: Malone, L.; Wittmann, A.; Kring, D. A.
2009lpii.conf...19M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Carbonate-rich Phases of Meteor Crater Impact Melt Particles
Authors: Anders, D.; Wittmann, A.; Kring, D. A.
2009lpii.conf....4A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Petrography of MIL05029, the First Accretional Impact Melt
from the L-Chondrite Parent Body
Authors: Wittmann, A.; Weirich, J. R.; Swindle, T. D.; Rumble, D.;
Kring, D. A.
2009LPI....40.1426W Altcode:
Petrographic characteristics, radioisotopic age, and the thermal
history of MIL05029, an igneous rock with L-chondritic affinity,
suggest formation as an impact melt in a 15-60 km diameter crater
during accretion of the L-chondrite parent body.
---------------------------------------------------------
Title: Petrographic and Geochemical Analysis of Feldspathic Lunar
Meteorite Shişr 161
Authors: Foreman, A. B.; Korotev, R. L.; Zeigler, R. A.; Wittmann,
A.; Kring, D. A.; Irving, A. J.; Kuehner, S. M.
2009LPI....40.2304F Altcode:
We present petrographic and geochemical analyses of the lunar meteorite
Shişr 161 - a feldspathic regolith breccia compositionally similar
to the NWA 3163/4483/4881 granulites.
---------------------------------------------------------
Title: Petrography and Metallographic Cooling Rate of H-Chondrite
Impact Melt Breccia LAP 04751
Authors: Frank, E. A.; Wittmann, A.; Kring, D. A.
2009LPI....40.2034F Altcode:
An impact event melted a portion of the H-chondrite parent body, mixing
with surviving clastic material. The melt-rich breccia was deposited
as a thin unit at a depth <10 m, implying an ejecta blanket or the
uppermost fraction of a breccia lens.
---------------------------------------------------------
Title: MIL05029, an (Impact?) Melt Rock From the Early Solar System
Authors: Weirich, J. R.; Wittmann, A.; Swindle, T. D.; Kring, D. A.
2008AGUFM.V53B2155W Altcode:
Impact cratering is the dominant geologic process affecting the surfaces
of small asteroids and, due to the relative ease of resetting the
39Ar-40Ar (Ar-Ar) system, heavily shocked and/or melted meteorites
can be used to reconstruct the impact history of the asteroid
belt. MIL05029 is an L-chondrite melt rock with an Ar-Ar age greater
than 4.4 Ga, making it the third such meteorite known (the other two
being Shaw and PAT91501). Moreover, while Shaw and PAT91501 have Ar-Ar
ages between 4.4-4.5 Ga, three whole-rock samples of MIL05029 give
well-defined plateau ages of 4.53±0.02 Ga, the oldest ever measured
in an L-chondrite melt rock. As a result of this older age, the event
that created MIL05029 could have occurred while metamorphism was still
occurring on the parent body. Both Shaw and PAT91501 contain shocked
relic material, indicating impact as the heat source. However, MIL05029
is a complete melt without this tell-tale signature, making definitive
identification of the melt-forming event more complicated. MIL05029
is depleted in metal and sulfide relative to unshocked L-chondrites
(<2% vs. ~14%), indicating a loss of denser phases after melting
of the asteroid. Because the canonical L-chondrite parent body was
not sufficiently hot for differentiation, the metal depletion in
MIL05029 is either the product of shock-melting on that body (the
more probable solution), or indicates MIL05069 formed on a previously
unknown parent body where endogenous melting occurred. Petrologically,
all three meteorites are grossly similar. For example, all three
contain large pyroxene grains that poikilitically enclose olivine,
but melt in both Shaw and PAT9150 contains vesicles, which is not
true for MIL05029. The Ar-Ar data reveals two main sources of 39Ar
(a proxy for K), both with similar activation energies, but with grain
sizes different by about a factor of 5. Microprobe data also reveal two
sources of K, melt inclusions and albitic feldspar, whose K mass balance
and grain size match well with that determined from the Ar-Ar data. A
small amount of 39Ar (~5%) released at high temperature (>1100°C)
is unaccounted for, but is most likely due to recoil or melted feldspar.
---------------------------------------------------------
Title: Petrography of the Suevite-like Depth Interval (1397-1550 m)
in Drill Core Eyreville-B, Chesapeake Bay Impact Structure, USA
Authors: Wittmann, A.; Reimold, W. U.; Hansen, B.; Kenkmann, T.
2008LPI....39.2435W Altcode:
A sub-division of suevite-like deposits in a drill core through the
Chesapeake Bay impact structure based on component-size distribution
and petrography suggests a gradation from groundsurge to fallback
within the first ~6 minutes after impact.
---------------------------------------------------------
Title: Petrography, Geochemistry, and Radiometric Dating of Impact
Melts from the Chesapeake Bay Impact Structure, USA
Authors: Fernandes, V. A.; Wittmann, A.; Schmitt, R. -T.; Reimold,
W. U.; Hecht, L.; Povenmire, H.
2008LPI....39.2383F Altcode:
Various impact melts from a USGS-ICDP drill core in the Chesapeake Bay
crater are used for a petrologic comparison of melt particles from
resurge and ejecta plume deposits with impact melt rocks that allow
a first direct radiometric dating.
---------------------------------------------------------
Title: The Volume of Impact Melt in the Chesapeake Bay Crater
Authors: Wittmann, A.; Reimold, W. U.
2008LPICo1423.3039W Altcode:
Quantitative analyses of a drill core through the Chesapeake Bay
Crater confirm a max. amount of ~10 km3 of melt inside the crater. This
suggests dispersal of 95 % of potentially produced melt due to release
of volatiles from the marine target.
---------------------------------------------------------
Title: A Model for the Formation of the Chesapeake Bay Impact Crater
as Revealed by Drilling and Numerical Simulation
Authors: Collins, G. S.; Kenkmann, T.; Wünnemann, K.; Wittmann, A.;
Reimold, W. U.; Melosh, H. J.
2008LPICo1423.3059C Altcode:
The combination of numerical simulation results and petrographic
analysis of drill core from the recent ICDP-USGS drilling project
provides new insight into the formation of the Chesapeake Bay impact
crater.
---------------------------------------------------------
Title: Preliminary Age of Impact Melts from the Chesapeake Bay
Impact Structure
Authors: Wittmann, A.; Fernandes, V. A.; Renne, P. R.; Schmitt, R. T.;
Reimold, W. U.; Hecht, L.; Povenmire, H.
2008LPICo1423.3093W Altcode:
First preliminary Ar-Ar ages for melt rocks of the Chesapeake Bay
impact structures are between 44.8 and 48.1 Ma. The difference to
the ages of ~35-36 Ma that were based on ejecta and biostratigraphic
correlations may be due to inherited Ar.
---------------------------------------------------------
Title: Geologic Column for the ICDP-USGS Eyreville-B Core, Chesapeake
Bay Impact Structure: Impactites and Crystalline Rocks, 1,095-1,766 m
Authors: Horton, J. W.; Gibson, R. L.; Reimold, W. U.; Wittmann, A.;
Gohn, G. S.; Edwards, L. E.
2008LPICo1423.3091H Altcode:
The ICDP-USGS Eyreville drill cores in the Chesapeake Bay impact
structure provide one of the most complete geologic sections ever
obtained from an impact structure. Geologic columns are presented for
the deepest sections.
---------------------------------------------------------
Title: Modern Solar Facilities - Advanced Solar Science
Authors: Kneer, Franz; Puschmann, Klaus G.; Wittmann, Axel D.
2007msfa.conf.....K Altcode:
An international workshop entitled: Modern Solar Facilities - Advanced
Solar Science was held in Göttingen Sept. 27-29, 2006. The workshop,
which was attended by 88 participants from 24 different countries, gave
a broad overview of the current state of solar research, with emphasis
on telescopes and instrumentation, high-resolution and high-precision
observations, and theory and interpretation. The book collects written
versions of 71 papers presented at the conference.
---------------------------------------------------------
Title: GREGOR: the New German Solar Telescope
Authors: Balthasar, H.; von der Lühe, O.; Kneer, F.; Staude, J.;
Volkmer, R.; Berkefeld, T.; Caligari, P.; Collados, M.; Halbgewachs,
C.; Heidecke, F.; Hofmann, A.; Klvaňa, M.; Nicklas, H.; Popow, E.;
Puschmann, K.; Schmidt, W.; Sobotka, M.; Soltau, D.; Strassmeier,
K.; Wittmann, A.
2007ASPC..368..605B Altcode: 2007arXiv0704.2693B
GREGOR is a new open solar telescope with an aperture of 1.5 m. It
replaces the former 45-cm Gregory Coudé telescope on the Canary island
Tenerife. The optical concept is that of a double Gregory system. The
main and the elliptical mirrors are made from a silicon-carbide material
with high thermal conductivity. This is important to keep the mirrors
on the ambient temperature avoiding local turbulence. GREGOR will be
equipped with an adaptive optics system. The new telescope will be ready
for operation in 2008. Post-focus instruments in the first stage will be
a spectrograph for polarimetry in the near infrared and a 2-dimensional
spectrometer based on Fabry-Pérot interferometers for the visible.
---------------------------------------------------------
Title: Reconstruction of the Chicxulub Ejecta Plume's Depositional
History at Drill Core Yaxcopoil-1
Authors: Wittmann, A.; Kenkmann, T.; Hecht, L.; Stöffler, D.
2007LPI....38.1705W Altcode:
Formation conditions of suevite-like impactites from a drill core
in the Chicxulub crater were reconstructed by petrological and image
analytical methods. This spans the temporal evolution of the cratering
process from the initial stage of excavation to t
---------------------------------------------------------
Title: From the "Göttingen" Fabry-Perot Interferometer to the
GREGOR FPI
Authors: Puschmann, K. G.; Kneer, F.; Nicklas, H.; Wittmann, A. D.
2007msfa.conf...45P Altcode:
Fabry-Perot Interferometers (FPIs) have advantages over slit
spectrographs, allowing fast two-dimensional, narrowband imaging
and post factum image reconstruction of the spectropolarimetric data
obtained. The resulting intensity, velocity and magnetic field maps
are a fundamental base for the understanding of the dynamics of
the solar atmosphere and its magnetic fields at smallest spatial
scales. Efforts are undertaken to provide, with the Göttingen
Fabry-Perot interferometer, an up-todate post-focus instrument for
the German 1.5 m GREGOR solar telescope. Therefore a renewal of the
spectrometer has been achieved during the first half of 2005. First
observations at the German Vacuum Tower Telescope (VTT) reveal new
scientific aspects and a very promising outlook for the future at
GREGOR. In this contribution a general description of the upgraded
spectrometer is given. Its final optical design at GREGOR is described
and an optical analysis of the GREGOR FPI is outlined. Latest results
with the new instrument obtained at the VTT are presented.
---------------------------------------------------------
Title: New high resolution solar telescope GREGOR
Authors: Volkmer, R.; von der Lühe, O.; Kneer, F.; Staude, J.;
Balthasar, H.; Berkefeld, T.; Caligari, P.; Collados, M.; Halbgewachs,
C.; Heidecke, F.; Hofmann, A.; Klvaña, M.; Sobotka, M.; Nicklas, H.;
Popow, E.; Puschmann, K. G.; Schmidt, W.; Soltau, D.; Strassmeier,
K.; Wittmann, A. D.
2007msfa.conf...39V Altcode:
The 1.5m solar telescope GREGOR is being constructed at Tenerife,
Spain. Its purpose is to observe with high spatial and spectral
resolution small-scale dynamic magnetic features on the Sun. The
telescope is completely open with retractable dome and actively cooled
primary mirror made of silicon carbide to minimize thermal effects
on the image quality. After completion it will be one of the most
powerful solar telescopes. This paper presents a general overview of
the telescope characteristics and the current status.
---------------------------------------------------------
Title: Modern solar facilities - advanced solar science
Authors: Kneer, Franz; Puschmann, Klaus G.; Wittmann, Axel D.
2007msfa.conf....0K Altcode:
An international workshop entitled: Modern Solar Facilities - Advanced
Solar Science was held in Göttingen Sept. 27-29, 2006. The workshop,
which was attended by 88 participants from 24 different countries, gave
a broad overview of the current state of solar research, with emphasis
on telescopes and instrumentation, high-resolution and high-precision
observations, and theory and interpretation. The book collects written
versions of 71 papers presented at the conference.
---------------------------------------------------------
Title: Indications for Fluidization of the Ries Crater's Ejecta
Blanket
Authors: Wittmann, A.; Kenkmann, T.
2007bget.conf..129W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: BOOK REVIEW: Development of Solar Research - Entwicklung
der Sonnenforschung
Authors: Sterken, C.; Wittmann, A. D.; Wolfschmidt, G.; Duerbeck, H. W.
2006JAD....12....5S Altcode:
This publication contains the Proceedings of a Colloquium on the
development of solar research, supplemented with a number of papers
which were written especially for this book. The volume contains 14
papers dealing with archeo-astronomy related to the Sun, solar cults,
and (mainly) solar research. Ten papers are written in English, the
remaining four are in German, but all papers have a quite extensive
Abstract in both languages. The volume closes with a comprehensive
Name Index. I found this book most pleasant to read with many useful
illustrations (more than 120 photographs and reproductions of which
about 100 cover truly historic material, quite often from authors'
private archives). <P />The first three papers (by A. Haenel,
W. Schlosser and R. Hansen) deal with very ancient information:
megalithic tombs as solar observatories, the Nebra sky-disk (showing
Sun, Moon, Pleiades and other stars), and solar cults. These papers
(adding up to about 90 pages) are not only descriptive, but also
contain an analysis based on quantitative facts. <P />One paper deals
with letters exchanged by astronomers serving as data sources for the
counting of sunspots during the Maunder minimum. More specifically,
several hundreds of letters by Gottfried Kirch (1639-1710) are being
edited and analysed by Klaus-Dieter Herbst. <P />Medieval solar-eclipse
maps with totality paths are reproduced in an interesting paper by
Robert van Gent, who presents eclipse cartography of as early as 1699
- at least 15 years prior to the generally accepted first such map
by Edmond Halley. <P />R. Schielicke's paper on the 1851 Koenigsberg
daguerrotype photograph of the solar corona gives interesting details
on the history of daguerrotype photography, and has a number of very
useful basic references, including OCR-based transcripts of a 1851-dated
document describing an early corona daguerrotype (in German). <P
/>Three consecutive papers (one by H.W. Duerbeck, followed by papers
by G. Wolfschmidt and M.P. Seiler) not only reveal scientific history,
but also crucial information on how governmental sponsorship, from
the 1860s till the end of WW II, modulated the development of solar
research. This paper reveals lots of cross-references on scientists
and government agents, and also offers insight on the interplay between
political actors and scientific researchers. The last paper covers very
dense time lines, and also vividly illustrates the military value of
basic fundamental research - that is, the forecast of radio propagation
disturbances caused by solar flares. This element is also dealt with
in the subsequent paper by Hubertus Wohl, on the spectroheliogram
archives of the Fraunhofer (now Kiepenheuer) Institute. <P />Accounts
of pioneering episodes are given in Axel Wittmann's paper on site
testing at La Palma in the early seventies, as well as in the subsequent
paper on solar research with stratospheric balloons (by Manuel Vazquez
and Axel Wittmann). These authors sketch a very concise but detailed
history of civil ballooning, and illustrate this with several images
from private archives. <P />Alltogether, this book is well-edited,
and offers lots of historical facts for the money.
---------------------------------------------------------
Title: Implications for the Chicxulub Fireball Derived from a
Systematic Analysis of Its Deposits
Authors: Wittmann, A.; Stöffler, D.; Hecht, L.; Kenkmann, T.
2006M&PSA..41.5078W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The new 1.5m solar telescope GREGOR: first light and start
of commissioning
Authors: Volkmer, Reiner; von der Lühe, Oskar; Kneer, Franz; Staude,
Jürgen; Berkefeld, Thomas; Caligari, Peter; Halbgewachs, Clemens;
Heidecke, Frank; Schmidt, Wolfgang; Soltau, Dirk; Nicklas, Harald;
Wittmann, Axel; Balthasar, Horst; Hofmann, Axel; Strassmeier, Klaus;
Sobotka, Michal; Klvana, Miroslav; Collados, Manuel
2006SPIE.6267E..0WV Altcode: 2006SPIE.6267E..29V
The integration of the three main silicon carbide mirrors into the new
1.5 m solar telescope GREGOR at Izana on Tenerife, Spain is planned
during 2006. We expect first light at the end of 2006. A progress
report about integration of the optics and mechanics and planning of
the commissioning phase of the telescope and post focus instruments
will be presented at the meeting. The GREGOR telescope is build by a
consortium of the Kiepenheuer Institut fur Sonnenphysik in Freiburg,
the Astrophysikalische Institut Potsdam, the Institut fur Astronomie
Gottingen and additional national and international Partners.
---------------------------------------------------------
Title: The new Göttingen Fabry-Pérot spectrometer for
two-dimensional observations of the Sun
Authors: Puschmann, K. G.; Kneer, F.; Seelemann, T.; Wittmann, A. D.
2006A&A...451.1151P Altcode:
Studies of small-scale dynamics and magnetic fields in the solar
atmosphere require spectroscopy and polarimetry with high spatial
resolution. For this purpose, spectrometers based on Fabry-Pérot
interferometers (FPIs) have advantages over slit spectrographs. They
possess a high throughput and allow fast two-dimensional,
narrow-band imaging and image reconstruction of the data. In the
present contribution we describe an upgrade, essentially renewal,
of the Göttingen FPI spectrometer achieved during the first half of
2005. A new etalon from IC Optical Systems Ltd. (formerly Queensgate),
England, with 70 mm free aperture for high spectral resolution has
been mounted. New CCD detectors from LaVision GmbH (Göttingen) with
powerful computer hard- and software were implemented. We consider the
product of signal-to-noise ratio, frame rate, and field of view as a
measure of the efficiency. At low light levels, e.g. in narrow-band
speckle applications, this product has increased by a factor ~60
compared to the old system. In addition, several spectral regions can
now be scanned quasi-simultaneously. We present first results obtained
with the upgraded spectrometer. The efforts are undertaken to provide
an up-to-date post-focus instrument for the new German 1.5 m GREGOR
solar telescope presently under construction at the Observatorio del
Teide on Tenerife.
---------------------------------------------------------
Title: Shock-metamorphosed zircon in terrestrial impact craters
Authors: Wittmann, A.; Kenkmann, T.; Schmitt, R. T.; StöFfler, D.
2006M&PS...41..433W Altcode:
To ascertain the progressive stages of shock metamorphism of zircon,
samples from three well-studied impact craters were analyzed by
optical microscopy, scanning electron microscopy (SEM), and Raman
spectroscopy in thin section and grain separates. These samples are
comprised of well-preserved, rapidly quenched impactites from the Ries
crater, Germany, strongly annealed impactites from the Popigai crater,
Siberia, and altered, variably quenched impactites from the Chicxulub
crater, Mexico. The natural samples were compared with samples of
experimentally shock-metamorphosed zircon. Below 20 GPa, zircon exhibits
no distinct shock features. Above 20 GPa, optically resolvable planar
microstructures occur together with the high-pressure polymorph reidite,
which was only retained in the Ries samples. Decomposition of zircon to
ZrO<SUB>2</SUB> only occurs in shock stage IV melt fragments that were
rapidly quenched. This is not only a result of post-shock temperatures
in excess of ∼1700 °C but could also be shock pressure-induced,
which is indicated by possible relics of a high-pressure polymorph
of ZrO<SUB>2</SUB>. However, ZrO<SUB>2</SUB> was found to revert
to zircon with a granular texture during devitrification of impact
melts. Other granular textures represent recrystallized amorphous
ZrSiO<SUB>4</SUB> and reidite that reverted to zircon. This requires
annealing temperatures >1100 °C. A systematic study of zircons from
a continuous impactite sequence of the Chicxulub impact structure yields
implications for the post-shock temperature history of suevite-like
rocks until cooling below ∼600 °C.
---------------------------------------------------------
Title: Composition and Characteristics of the Chicxulub Ejecta Plume
Authors: Wittmann, A.; Kenkmann, T.; Hecht, L.; Stöffler, D.
2006LPI....37.1590W Altcode:
Quantitative analyses of ejecta components at Chicxulub yield
implications for oxidizing conditions in the ejecta plume and the
depositional sequence of the continuous suevite-like deposits.
---------------------------------------------------------
Title: Hans-Heinrich Voigt's Wirken in der Astronomie und der
Gauß-Gesellschaft
Authors: Wittmann, Axel
2006MitGG..43...57W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Magnetic Structures on the Sun: Osbervations with the New
"GÖTTINGEN" Two-Dimensional Spectrometer on Tenerife
Authors: Kneer, F.; Puschmann, K. G.; Blanco Rodríguez, J.;
Sánchez-Andrade Nuño, B.; Wittmann, A. D.
2005ESASP.596E..71K Altcode: 2005ccmf.confE..71K
No abstract at ADS
---------------------------------------------------------
Title: The new 1.5 solar telescope GREGOR: progress report and
results of performance tests
Authors: Volkmer, Reiner; von der Lühe, Oskar; Kneer, Franz; Staude,
Jürgen; Berkefeld, Thomas; Caligari, Peter; Halbgewachs, Clemens;
Schmidt, Wolfgang; Soltau, Dirk; Nicklas, Harald; Wittmann, Axel;
Balthasar, Horst; Hofmann, Axel; Strassmeier, Klaus; Sobotka, Michal;
Klvana, Miroslav; Collados, Manuel
2005SPIE.5901...75V Altcode:
The telescope structure including control system and the complete
retractable dome of the new 1.5 m solar telescope GREGOR were
assembled during 2004 at Izana on Tenerife, Spain. The GREGOR
telescope is build by a consortium of the Kiepenheuer Institut fuer
Sonnenphysik, the Astrophysikalische Institut Potsdam, the Institut
fuer Astrophysik Goettingen and additional national and international
Partners. Pointing, tracking and thermal tests were made to verify
the proposed performance. The results of these tests and a progress
report of the project will be presented.
---------------------------------------------------------
Title: Development of Solar Research -- Entwicklung der
Sonnenforschung
Authors: Wittmann, Axel D.; Wolfschmidt, Gundrun; Duerbeck, Hilmar W.
2005dsr..conf.....W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar research with stratospheric balloons
Authors: Vázquez, Manuel; Wittmann, Axel D.
2005dsr..conf..262V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The June 1973 site testing expedition at the Roque de los
Muchachos La Palma
Authors: Wittmann, Axel D.
2005dsr..conf..251W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Development of Solar Research
Authors: Wittmann, Axel D.; Wolfschmidt, Gudrun; Duerbeck, Hilmar W.
2005AcHA...25.....W Altcode:
Originally based on a workshop on “Development of Solar Research”,
held in Freiburg/Breisgau, this book contains articles on megalithic
structures, the Nebra sky-disk, ancient sun cults, the observation
of sunspots, the photography of the sun during eclipses, eclipse
maps and expeditions, solar telescopes, solar physics during the
Nazi era, archives of solar observations, scientific ballooning for
solar research, site-testing on the Canary Islands, as well as on
international cooperation.
---------------------------------------------------------
Title: On the Berkowski daguerreotype (Königsberg, 1851 July 28):
the first correctly-exposed photograph of the solar corona
Authors: Schielicke, Reinhard; Wittmann, Axel D.
2005AcHA...25..128S Altcode:
The first correctly-exposed photograph of the solar corona was
made during the total phase of the solar eclipse of 28 July 1851
at Königsberg (now Kaliningrad) by a local daguerreotypist named
Berkowski. Berkowski observed at the Royal Observatory following a
proposal by its director A. Busch. A small refracting telescope (D =
6.1 cm, f = 81.2 cm) was attached to the hour drive of the 15.8-cm
Fraunhofer heliometer, and a 84-s exposure was taken shortly after the
beginning of totality. After the eclipse, Busch (who did not observe
the eclipse at Königsberg but at Rixhöft), published some details
about the daguerreotype (without mentioning Berkowski's first name) and
ordered a local artist (R. Trossin) to make an enlarged steel engraving
from the daguerreotype plate. On the original plate the moon's diameter
is 7.85 mm, and at least 5 prominences are well visible on the limb of
the sun. Later Berkowski himself made some daguerreotype reproductions
from his original plate. One of these is still preserved at Jena
University Observatory, it has a moon diameter of 8.69 mm. In 1891 the
Königsberg Astronomer C.F.W. Peters ordered photographic reproductions
of the original daguerreotype (which then still existed) to be made,
some of which have been published in astronomical textbooks. We have
calculated the local circumstances, in particular the contact times,
of the Königsberg eclipse and compared them with observations. We
describe the Berkowski daguerreotype and some of its copies, and we
report about the Jena copy of this famous daguerreotype.
---------------------------------------------------------
Title: On the Berkowski daguerreotype (Königsberg, 1851 July 28):
the first correctly-exposed photograph of the solar corona
Authors: Schielicke, Reinhard E.; Wittmann, Axel D.
2005dsr..conf..128S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar research with stratospheric balloons
Authors: Vázquez, Manuel; Wittmann, Axel D.
2005AcHA...25..262V Altcode:
Balloons, driven by hot air or some gas lighter than air, were the
first artificial machines able to lift payloads (including humans)
from the ground. After some pioneering flights the study of the
physical properties of the terrestrial atmosphere constituted the
first scientific target. A bit later astronomers realized that the
turbulence of the atmospheric layers above their ground-based telescopes
deteriorated the image quality, and that balloons were an appropriate
means to overcome, total or partially, this problem. Some of the most
highly-resolved photographs and spectrograms of the sun during the
20th century were actually obtained by balloon-borne telescopes from
the stratosphere. Some more recent projects of solar balloon astronomy
will also be described.
---------------------------------------------------------
Title: The June 1973 site testing expedition at Roque de los
Muchachos, La Palma
Authors: Wittmann, Axel D.
2005AcHA...25..251W Altcode:
After site tests in the Mediterranean had not given very promising
results the international organization JOSO in 1972 started a series
of site tests in the Canary Islands under the direction of Karl-Otto
Kiepenheuer. These included aircraft campaigns for measuring air
temperature fluctuations at various altitudes, which were supported
from the ground. The second JOSO expedition to the Roque de los
Muchachos, the highest peak of the island of La Palma - the first
expedition during which a large telescope was used to take solar
photographs from the ground - was carried out from 13 June until 3
July 1973. Participants were the author and Hartmut S. Schneider,
both from the University Observatory Göttingen. This paper reports
about our expedition and about some of the more personal impressions
gained by the author during the course of this event.
---------------------------------------------------------
Title: Progress report of the 1.5 m solar telescope GREGOR
Authors: Volkmer, Reiner; von der Lühe, Oskar F.; Kneer, Franz;
Staude, Jürgen; Berkefeld, Thomas; Caligari, Peter; Schmidt,
Wolfgang; Soltau, Dirk; Nicklas, Harald; Wiehr, Eberhardt; Wittmann,
Axel; Balthasar, Horst; Hofmann, Axel; Strassmeier, Klaus; Sobotka,
Michal; Klvana, Miroslav; Collados, Manuel
2004SPIE.5489..693V Altcode:
GREGOR is the new 1.5 m solar telescope assembled on Tenerife, Spain, by
the German consortium of the Kiepenheuer Institut fur Sonnenphysik, the
Astronomischen Institut Potsdam, the Universitats-Sternwarte Gottingen
and other national and international Partners. The refurbishment of
the building is almost finished. The manufacturing of the telescope
structure and the optics is still in progress. After the integration of
the new complete retractable dome in July 2004 the telescope structure,
optic and post focus instruments will be assembled during the rest of
the year. First light is planned during May 2005.
---------------------------------------------------------
Title: Composition of impact melt particles and the effects of
post-impact alteration in suevitic rocks at the Yaxcopoil-1 drill
core, Chicxulub crater, Mexico
Authors: Hecht, Lutz; Wittmann, Axel; Schmitt, Ralf-Thomas; Stöffler,
Dieter
2004M&PS...39.1169H Altcode:
Petrographical and chemical analysis of melt particles and alteration
minerals of the about 100 m-thick suevitic sequence at the Chicxulub
Yax-1 drill core was performed. The aim of this study is to determine
the composition of the impact melt, the variation between different
types of melt particles, and the effects of post-impact hydrothermal
alteration. We demonstrate that the compositional variation between
melt particles of the suevitic rocks is the result of both incomplete
homogenization of the target lithologies during impact and subsequent
post-impact hydrothermal alteration. Most melt particles are andesitic
in composition. Clinopyroxene-rich melt particles possess lower SiO2
and higher CaO contents. These are interpreted by mixing of melts
from the silicate basement with overlying carbonate rocks. Multi-stage
post-impact hydrothermal alteration involved significant mass transfer
of most major elements and caused further compositional heterogeneity
between melt particles. Following backwash of seawater into the crater,
palagonitization of glassy melt particles likely caused depletion of
SiO2, Al2O3, CaO, Na2O, and enrichment of K2O and FeOtot during an
early alteration stage. Since glass is very susceptible to fluid-rock
interaction, the state of primary crystallization of the melt particles
had a significant influence on the intensity of the post impact
hydrothermal mass transfer and was more pronounced in glassy melt
particles than in well crystallized particles. In contrast to other
occurrences of Chicxulub impactites, the Yax-1 suevitic rocks show
strong potassium metasomatism with hydrothermal K-feldspar formation and
whole rock K2O enrichment, especially in the lower unit of the suevitic
sequence. A late stage of hydrothermal alteration is characterized by
precipitation of silica, analcime, and Na-bearing Mg-rich smectite,
among other minerals. This indicates a general evolution from a
silica-undersaturated fluid at relatively high potassium activities
at an early stage toward a silica-oversaturated fluid at relatively
high sodium activities at later stages in the course of fluid rock
interaction.
---------------------------------------------------------
Title: Origin and emplacement of the impact formations at Chicxulub,
Mexico, as revealed by the ICDP deep drilling at Yaxcopoil-1 and by
numerical modeling
Authors: Stöffler, Dieter; Artemieva, Natalya A.; Ivanov, Boris A.;
Hecht, Lutz; Kenkmann, Thomas; Schmitt, Ralf Thomas; Tagle, Roald
Alberto; Wittmann, Axel
2004M&PS...39.1035S Altcode:
We present and interpret results of petrographic, mineralogical,
and chemical analyses of the 1511 m deep ICDP Yaxcopoil-1 (Yax-1)
drill core, with special emphasis on the impactite units. Using
numerical model calculations of the formation, excavation, and dynamic
modification of the Chicxulub crater, constrained by laboratory data,
a model of the origin and emplacement of the impact formations of
Yax-1 and of the impact structure as a whole is derived. The lower
part of Yax-1 is formed by displaced Cretaceous target rocks (610 m
thick), while the upper part comprises six suevite-type allochthonous
breccia units (100 m thick). From the texture and composition of
these lithological units and from numerical model calculations, we
were able to link the seven distinct impact-induced units of Yax-1
to the corresponding successive phases of the crater formation and
modification, which are as follows: 1) transient cavity formation
including displacement and deposition of Cretaceous "megablocks;" 2)
ground surging and mixing of impact melt and lithic clasts at the base
of the ejecta curtain and deposition of the lower suevite right after
the formation of the transient cavity; 3) deposition of a thin veneer of
melt on top of the lower suevite and lateral transport and brecciation
of this melt toward the end of the collapse of the transient cavity
(brecciated impact melt rock); 4) collapse of the ejecta plume and
deposition of fall-back material from the lower part of the ejecta
plume to form the middle suevite near the end of the dynamic crater
modification; 5) continued collapse of the ejecta plume and deposition
of the upper suevite; 6) late phase of the collapse and deposition of
the lower sorted suevite after interaction with the inward flowing
atmosphere; 7) final phase of fall-back from the highest part of
the ejecta plume and settling of melt and solid particles through the
reestablished atmosphere to form the upper sorted suevite; and 8) return
of the ocean into the crater after some time and minor reworking of the
uppermost suevite under aquatic conditions. Our results are compatible
with: a) 180 km and 100 km for the diameters of the final crater and the
transient cavity of Chicxulub, respectively, as previously proposed by
several authors, and b) the interpretation of Chicxulub as a peak-ring
impact basin that is at the transition to a multi-ring basin.
---------------------------------------------------------
Title: Structure and impact indicators of the Cretaceous sequence
of the ICDP drill core Yaxcopoil-1, Chicxulub impact crater, Mexico
Authors: Kenkmann, T.; Wittmann, A.; Scherler, D.
2004M&PS...39.1069K Altcode:
As part of the ICDP Chicxulub Scientific Drilling Project, the
Yaxcopoil-1 (Yax-1) bore hole was drilled 60 km south-southwest of
the center of the 180 km-diameter Chicxulub impact structure down to a
depth of 1511 m. A sequence of 615 m of deformed Cretaceous carbonates
and sulfates was recovered below a 100 m-thick unit of suevitic
breccias and 795 m of post-impact Tertiary rocks. The Cretaceous
rocks are investigated with respect to deformation features and shock
metamorphism to better constrain the deformational overprint and the
kinematics of the cratering process. The sequence displays variable
degrees of impact-induced brittle damage and post-impact brittle
deformation. The degree of tilting and faulting of the Cretaceous
sequence was analyzed using 360°-core scans and dip-meter log data. In
accordance with lithological information, these data suggest that the
sedimentary sequence represents a number of structural units that are
tilted and moved with respect to each other. Three main units and nine
sub-units were discriminated. Brittle deformation is most intense
at the top of the sequence and at 1300-1400 m. Within these zones,
suevitic dikes, polymict clastic dikes, and impact melt rock dikes
occur and may locally act as decoupling horizons. The degree of brittle
deformation depends on lithology; massive dolomites are affected by
penetrative faulting, while stratified calcarenites and bituminous
limestones display localized faulting. The deformation pattern is
consistent with a collapse scenario of the Chicxulub transient crater
cavity. It is believed that the Cretaceous sequence was originally
located outside the transient crater cavity and eventually moved
downward and toward the center to its present position between the
peak ring and the crater rim, thereby separating into blocks. Whether
or not the stack of deformed Cretaceous blocks was already displaced
during the excavation process remains an open question. The analysis
of the deformation microstructure indicates that a shock metamorphic
overprint is restricted to dike injections with an exception of the
so called "paraconglomerate." Abundant organic matter in the Yax-1
core was present before the impact and was mobilized by impact-induced
heating and suggests that >12 km3 of organic material was excavated
during the cratering process.
---------------------------------------------------------
Title: Geochemistry of drill core samples from Yaxcopoil-1 Chicxulub
impact crater, Mexico
Authors: Schmitt, Ralf T.; Wittmann, Axel; Stöffler, Dieter
2004M&PS...39..979S Altcode:
The chemical composition of suevites, displaced Cretaceous target rocks,
and impactgenerated dikes within these rocks from the Yaxcopoil-1
(Yax-1) drill core, Chicxulub impact crater, Mexico, is reported and
compared with the data from the Yucatán 6 (Y6) samples. Within the
six suevite subunits of Yax-1, four units with different chemical
compositions can be distinguished: a) upper/lower sorted and upper
suevite (depth of 795-846 m); b) middle suevite (depth of 846-861 m); c)
brecciated impact melt rock (depth of 861-885 m); and d) lower suevite
(depth of 885-895 m). The suevite sequence (a), (b), and (d) display
an increase of the CaO content and a decrease of the silicate basement
component from top to bottom. In contrast, the suevite of Y6 shows an
inverse trend. The different distances of the Yax-1 and Y6 drilling
sites from the crater center (~60, and ~47 km, respectively) lead to
different suevite sequences. Within the Cretaceous rocks of Yax-1, a
suevitic dike (depth of ~916 m) does not display chemical differences
when compared with the suevite, while an impact melt rock dike (depth
of ~1348 m) is significantly enriched in immobile elements. A clastic
breccia dike (depth of ~1316 m) is dominated by material derived locally
from the host rock, while the silicate-rich component is similar to
that found in the suevite. Significant enrichments of the K2O content
were observed in the Yax-1 suevite and the impact-generated dikes. All
impactites of Yax-1 and Y6 are mixtures of a crystalline basement
and a carbonate component from the sedimentary cover. An anhydrite
component in the impactites is missing (Yax-1) or negligible (Y6).
---------------------------------------------------------
Title: Impact-related dike breccia lithologies in the ICDP drill
core Yaxcopoil-1, Chicxulub impact structure, Mexico
Authors: Wittmann, A.; Kenkamnn, T.; Schmitt, R. T.; Hecht, L.;
Stöffler, D.
2004M&PS...39..931W Altcode:
Petrographic descriptions of three dike breccia lithologies from
drill core Yaxcopoil-1 (Yax-1) are presented. They occur within
allochthonous units of displaced sedimentary megablocks of the
Chicxulub impact structure. The suevitic dike breccias are the
uppermost dike lithology. They contain melt rock particles and melt
injections into the dike groundmass. Shock features occur ubiquitously
and indicate a strong thermal annealing. Flow textures suggest a highly
energetic emplacement process, possibly during the excavation stage as a
ground-surge related deposit. The impact melt rock dikes are present in
a strongly brecciated megablock interval as flow textured, anastomozing
veinlets of impact melt rock that were altered to clay minerals. The
melt impregnated a dolomitic host rock, indicating a low viscosity
and, thus, high initial temperatures. Brecciation of the impact melt
rock dikes occurred while they were still below the glass transition
temperature, suggesting that dynamic conditions prevailed shortly after
the emplacement process. Major element data indicates that the impact
melt rock dikes differ in composition from the homogenized impact
melt rock of Chicxulub. This could point to an emplacement during the
late compression or early excavation stages of cratering. The clastic
polymict dike breccias are coeval with pervasive brittle fracturing of
the host rocks. They bear clasts including some crystalline basement
and possible melt rock particles in a fine-grained dolomite matrix
with turbulent flow textures. Fabric and texture indicate a granular
flow at ambient pressures. Such conditions could be envisaged for the
excavation phase while the transient cavity grew and fractures opened.
---------------------------------------------------------
Title: Zircon as a Shock Indicator in Impactites of Drill Core
Yaxcopoil-1, Chicxulub Impact Structure, Mexico
Authors: Wittmann, A.; Stöffler, D.; Schmitt, R. T.; Tagle, R.;
Kenkmann, T.; Hecht, L.
2004LPI....35.1742W Altcode:
Zircons in impactites of drillcore Yax-1 (Chicxulub) show decorated and
undecorated PDF, shock mosaicism, recrystallized grains, dissociation
to baddeleyite, but no reidite, inferring shock pressures of <5
~100 GPa and thermal annealing of >1500°C.
---------------------------------------------------------
Title: The Fluidized Chicxulub Ejecta Blanket, Mexico: Implications
for Mars
Authors: Schönian, F.; Stöffler, D.; Kenkmann, T.; Wittmann, A.
2004LPI....35.1848S Altcode:
The presence of water and the incorporation of local clays and not
atmospheric processes account for the deposition of the Albion Fm. and
for its large runout. This emphasizes the role of volatiles in the
formation of Martian ejecta blankets.
---------------------------------------------------------
Title: The Cretaceous Sequence of the Chicxulub YAX-1 Drillcore:
What is Impact-derived?
Authors: Kenkmann, T.; Wittmann, A.; Scherler, D.; Stöffler, D.
2003lmim.conf.4075K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Origin and Emplacement of the Impact Formations at Chicxulub,
Mexico, with Special Emphasis on the Yax-1 Deep Drilling
Authors: Stöffler, D.; Ivanov, B. A.; Hecht, L.; Kenkmann, T.;
Schmitt, R. T.; Salge, T.; Schönian, F.; Tagle, R.; Weseler, S.;
Wittmann, A.
2003lmim.conf.4092S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The ICDP Drill Core Yaxcopoil-1, Chicxulub Impact Crater,
Mexico: Shock Metamorphism of the Impactite Units (794 894 m)
Authors: Schmitt, R. T.; Wittmann, A.; Stöffler, D.
2003lmim.conf.4061S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Impact Melt Rocks in the “Cretaceous Megablock Sequence”
of Drill Core Yaxcopoil-1, Chicxulub Crater, Yucatan, Mexico
Authors: Wittmann, A.; Kenkmann, T.; Schmitt, R. T.; Hecht, L.;
Stöffler, D.
2003lmim.conf.4125W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Characteristics of the Multi-Ring Impact Basin of Chicxulub,
Mexico, as Derived from Drill Core Data and Numerical Modeling
Authors: Stöffler, D.; Hecht, L.; Ivanov, B. A.; Kenkmann, T.; Salge,
T.; Schmitt, R. T.; Schönian, F.; Tagle, R.; Wittmann, A.
2003M&PSA..38.5241S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Petrography, Composition, Shock Metamorphism, and Geology
of the Impact Formations of the ICDP Drill Core YAX-1, Chicxulub
Crater, Mexico
Authors: Hecht, L.; Kenkmann, T.; Schmitt, R. T.; Stöffler, D.;
Tagle, R.; Wittmann, A.
2003M&PSA..38.5180H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Berkowski Daguerreotype (Konigsberg, 1851 July 28):
The First Correctly Exposed Eclipse Photograph of the Solar Corona
Authors: Schielicke, Reinhard E.; Wittmann, Axel D.
2003ANS...324...91S Altcode: 2003ANS...324..K05S
No abstract at ADS
---------------------------------------------------------
Title: Properties, Classification, and Genetic Interpretation of the
Allochthonous Impact Formations of the ICDP Chicxulub Drill Core YAX-1
Authors: Stöffler, D.; Hecht, L.; Kenkmann, T.; Schmitt, R. T.;
Wittmann, A.
2003LPI....34.1553S Altcode:
The Chicxulub drill core exposes 100 m of suevite-type breccias
consisting of 6 layered units. The upper four layers are interpreted
as ballistic "fall out" suevite and the lower two units may represent
ground surged and laterally transported polymict, melt-rich clastic
material.
---------------------------------------------------------
Title: Shock Metamorphism of Impactite Lithologies of the ICDP
Chicxulub Drill Core YAX-1
Authors: Schmitt, R. T.; Stöffler, D.; Wittmann, A.
2003LPI....34.1327S Altcode:
The ICDP Chicxulub drillcore YAX-1 exposes about 100 m of allochthonus
polymict impact breccias in a depth of 794.63 to 894.94 m. In this
preliminary study we focus on the shock effects and shock metamorphism
of these impactites.
---------------------------------------------------------
Title: Hydrocarbons and Aqueous Fluids in Cretaceous Sediments of
the ICDP-Chicxulub Drill Core Yax-1
Authors: Lüders, V.; Horsfield, B.; Kenkmann, T.; Mingram, B.;
Wittmann, A.
2003LPI....34.1378L Altcode:
Fluid inclusion studies in quartz from fissures of the Chicxulub drill
core reveal evidence for high-temperature fluid and hydrocarbon
migration. Hydrocarbons formed from organic matter in the
megablock. Mobilization is likely caused by the impact.
---------------------------------------------------------
Title: Clastic Polymict Dikes in the "Megablock" Sequence of the
ICDP-Chicxulub Drill Core Yax-1
Authors: Wittmann, A.; Kenkmann, T.; Schmitt, R. T.; Stöffler, D.
2003LPI....34.1386W Altcode:
Clastic, polymict dikes in the megablock units of Chicxulub-YAX-1
drill core were studied. Petrographic and structural relationships
are used to interprete ductile and brittle deformation stages linked
to the cratering process.
---------------------------------------------------------
Title: Hydrothermal Alteration of the Impactites at the ICDP Drill
Site Yax-1 (Chicxulub Crater)
Authors: Hecht, L.; Schmitt, R. T.; Wittmann, A.
2003LPI....34.1583H Altcode:
Post-impact hydrothermal alteration including alkali metasomatism and
devitrification of impact melt glass has significantly modified the
mineralogy and chemistry of the impact breccia lithologies.
---------------------------------------------------------
Title: Deformation Features of the Cretaceous Units of the
ICDP-Chicxulub Drill Core Yax-1
Authors: Kenkmann, T.; Wittmann, A.; Scherler, D.; Schmitt, R. T.
2003LPI....34.1368K Altcode:
The Chicxulub Yax-1 drill core penetrated through 600 m of sediments
below the impactites. These rocks are predominantly carbonates and
sulfates. Layers enriched in organic matter are frequent. The degree
of deformation depends on the lithology.
---------------------------------------------------------
Title: GREGOR: the new 1.5m solar telescope on Tenerife
Authors: Volkmer, Reiner; von der Luehe, Oskar; Kneer, Franz; Staude,
Juergen; Hofmann, Axel; Schmidt, Wolfgang; Sobotka, Michal; Soltau,
Dirk; Wiehr, Eberhardt; Wittmann, Axel; Berkefeld, Thomas
2003SPIE.4853..360V Altcode:
The new 1.5 m high resolution telescope will be build up on the reused
solar tower of the German 45 cm Gregory Coudé Telescope at the Teide
Observatory, Izaña, Tenerife. The new telescope is a Gregory type
with open telescope structure, alt-azimuth mount, complete retractable
dome, and a pool of well established and new developed post focus
instruments. An adaptive optics system provides the capability for
diffraction limited observations at visible wavelengths and the
polarimetry device in the secondary focus reduces the perturbation
due to instrumental polarization in an efficient way. We describe the
main optical characteristics and the focal plane instrumentation with
respect to the latest status of the project.
---------------------------------------------------------
Title: Visual and photoelectric measurements of the solar diameter
(1972-2002): Methods and results
Authors: Wittmann, A. D.
2003AN....324..378W Altcode:
Measurements of the solar diameter using both visual and photoelectric
drift scan techniques have been made since 1972 using two almost
identical 45-cm Gregory-Coudé telescopes at Locarno/Switzerland and
Izaña/Tenerife. The method, in which a time measurement substitutes
an angular measurement, is especially suited to obtain about 30
measurements of the absolute solar semidiameter per day. During the
years 1972-2002 a total of 10996 visual timing measurements have
been made on 320 observing days, an additional 1373 photoelectric
recordings have been obtained on 117 observing days. The data were used
to study the long-term behaviour of the solar semidiameter R at unit
distance and its possible variations. No fluctuations dR in excess of
about +/-0.05" have been found, neither long-term nor short-term. The
photoelectric semidiameter, which refers to the continuum at lambda ~
585 nm, is Rphot = (959.89 +/- 0.12)". The visual semidiameter, which
refers to the footpoint of the limb intensity profile at lambda ~
550 nm, is Rvis = (960.62 +/- 0.02)".
---------------------------------------------------------
Title: From the Gregory-Coudé Telescope to GREGOR: a development
from past to future. Summary of workshop held in Göttingen, July
24-26, 2002
Authors: Kneer, F.; Wiehr, E.; Wittmann, A. D.
2003AN....324..283K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: GREGOR, a 1.5 m Gregory-type telescope for solar observation
Authors: Kneer, F.; Hofmann, A.; von der Lühe, O.; Soltau, W. Schmidt
D.; Staude, J.; Wiehr, E.; Wittmann, A. D.
2002NCimC..25..689K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book Review: The Role of Visual Representations in Astronomy
(eds. K. Hentschel, A.D. Wittmann)
Authors: Sterken, C.; Hentschel, K.; Wittmann, A. D.
2001JAD.....7...10S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Post-focus instrumentation for GREGOR
Authors: Kneer, F.; Hofmann, A.; von der Lühe, O.; Schmidt, W.;
Soltau, D.; Staude, J.; Wiehr, E.; Wittmann, A. D.
2001AN....322..361K Altcode:
GREGOR is a high-resolution solar telescope with an aperture of 1.5
m. It will be equipped with an Adaptive Optics system and is designed
for high-precision measurements of magnetic fields and plasma motions
in the solar photosphere and chromosphere with a resolution of 70
km on the Sun. GREGOR will replace the Gregory Coudé Telescope at
the Observatorio del Teide on Tenerife. In concert with the other
solar telescopes at Teide Observatory it will be useful for studying
the dynamics of the solar atmosphere and the underlying physical
processes. GREGOR will also serve as a test bed for next generation
solar telescopes. We discuss briefly the postfocus instrumentation
of GREGOR.
---------------------------------------------------------
Title: GREGOR, a 1.5 m Gregory-type Telescope for Solar Observation
Authors: Kneer, F.; Hofmann, A.; von der Lühe, O.; Schmidt, W.;
Soltau, D.; Staude, J.; Wiehr, E.; Wittmann, A. D.
2001AGM....18.P223K Altcode:
GREGOR is a high-resolution solar telescope with an aperture of 1.5
m. It will be equipped with an Adaptive Optics system and is designed
for high-precision measurements of magnetic fields and plasma motions
in the solar atmosphere and chromosphere with a resolution of 70 km
on the Sun. GREGOR will replace the Gregory Coudé Teleskope at the
Observatorio del Teide on Tenerife. We describe the optical design
and the focal plane instrumentation. In concert with the other solar
telescopes at Teide Observatory it will be useful for studying the
dynamics of the solar atmosphere and the underlying processes. GREGOR
will also serve as a test bed for next generation solar telescopes.
---------------------------------------------------------
Title: Center-to-Limb Variation of Solar Granulation from Partial
Eclipse Observations
Authors: Sánchez Cuberes, M.; Bonet, J. A.; Vázquez, M.; Wittmann,
A. D.
2000ApJ...538..940S Altcode:
We have measured the center-to-limb variation (CLV) of parameters
describing geometric and photometric statistical properties of the
solar granulation at 6708 Å. This work is based on an excellent
series of white-light images obtained with the Swedish Vacuum Solar
Telescope at Roque de los Muchachos Observatory, La Palma, during the
partial solar eclipse of 1994 May 10. The lunar limb profile, which is
visible in each frame, was used as a calibration tool for estimating
the point-spread function of the combined optical system formed by the
atmosphere and the telescope. Before restoration, noise was removed
from the images by a novel application of the so-called optimum filter
for two-dimensional objects. The latter was optimized in terms of
rms error and was constructed from very precise smoothed models of the
specific power spectrum of the granulation at each position on the solar
disk. The determination of the positions on the solar disk was achieved
with high accuracy by matching the position of the Moon's limb in our
images to a numerical simulation of the eclipse geometry. The CLV curve
of the ΔI<SUB>rms</SUB> granular contrast shows one of the steepest
gradients among those reported in the literature and quite a high value
(9.6%) at the disk center considering that our working wavelength is
in the far-red range of the solar spectrum. The elliptical shape of
the restored power spectra with ellipticities equal to those expected
just from foreshortening proves that radiative transfer effects do not
alter the isotropy of the horizontal intensity pattern of the solar
granulation, at least up to μ=0.4. The mean wavenumber, k, derived
from the two-dimensional power spectra azimuthally integrated along
the ellipses amounts to a value of 6.15 Mm<SUP>-1</SUP> at the center
of the solar disk and then shows a decrease toward the limb. Apart
from the power spectra analysis, a direct statistical study of the
granulation size and brightness, based on the image segmentation for
defining granular contours, has also been performed. A general increase
in both granular and intergranular areas is found as we move toward the
solar limb. The mean granular cell area varies from 1.36 Mm<SUP>2</SUP>
at μ=1 up to 2.06 Mm<SUP>2</SUP> at μ=0.6, and in parallel, the
granular filling factor (the percentage of area of the image covered
by granules) decreases from 44.2% to 42.8%. In the small area range,
the granular brightness increases linearly with the granular cell size
and is preserved constant, on average, for granular cells larger than
~2.0". No slope variation is found for the intergranular intensities
versus granular cell areas. Observations close to the solar limb detect
granular structures as small as 0.53" or even smaller up to a distance
of at least ~0.5" from the limb, showing that the ΔT associated
with the granulation persist at least until z~200 km. However, this
penetration could be different for small and large granules because we
find several hints indicating the progressive disappearance of small
structures toward the limb.
---------------------------------------------------------
Title: Drift-Time Measurements of the Solar Diameter 1990-2000:
New Limits on Constancy
Authors: Wittmann, A. D.; Bianda, M.
2000ESASP.463..113W Altcode: 2000sctc.proc..113W
No abstract at ADS
---------------------------------------------------------
Title: The Role of Visual Representations in Astronomy: History and
Research Practice. Contributions to a Colloquium held at Göttingen
in 1999
Authors: Hentschel, Klaus; Wittmann, Axel D.
2000AcHA....9.....H Altcode:
Astronomy would not exist without nonverbal representations: With the
majority of celestial objects perceptible to us only by the light
or radiations they emit, images of all kinds have always played a
central role in the history of astronomy. From prehistoric sketches
of the moon with a supernova or bright planet, star-charts in temples
and tombs of the Ancients, celestial and lunar maps from the Middle
Ages to modern photographs and spectrograms of sun, moon, and planets,
two-dimensional images and three-dimensional models have always been
an integral element of astronomy. Added to these are a variety of more
technical charts and graphs, like the Hertzsprung-Russell diagram,
the Maunder-type solar activity diagrams, the light curves of variable
stars, the spectral atlases of the sun and the brightest stars, and so
forth; and more recently, of course, there are the spectacular images
obtained from large ground-based telescopes, satellite observatories,
and deep space probes. This intimate relationship between science and
image is not as straightforward, however, as it might at first seem. How
direct is this graphic conversion of the subject of observation or
registration by man or machine? What problems emerge in the translation
process? Does this endless quest for ever better representational
forms and ever better resolution have repercussions on the research
practice? What is the impact of technological developments? How do
astronomers and astrophysicists interact with their illustrators,
engravers, lithographers, photographers and other graphic arts
specialists? And how can these visual records from the past best be
preserved? This collection of papers, which - with one exception - were
presented during a one-day international conference at the Göttingen
University Observatory on 20 September 1999, offers answers to some
of these questions. This volume is intended for those interested in
the development of visual representations or the history of astronomy.
---------------------------------------------------------
Title: Did Struve observe the nucleus of Halley's comet in 1835?
Authors: Wittmann, Axel D.
2000AcHA....9...79W Altcode:
During its apparition in 1835 Halley's comet reached its minimum
distance from the earth (0.187 au) on 13 October in the constellation
of Ursa Major. Telescopic visual observations were made, e.g., by
F.W. Bessel at Königsberg and by F.G.W. Struve at Dorpat (Tartu). In
particular a drawing made by Struve on 8 October of what he calls the
`nucleus' and describes as a small, slightly yellowish glowing piece
of coal of elongated shape bears such a striking resemblance to the
images of Halley's nucleus obtained in 1986 by the Giotto spacecraft
that it merits further examination: Could Struve, who had been using
a 24.4 cm refractor at 254-fold magnification, possibly have observed
the real nucleus? Closer examination shows that neither Struve's
maximum possible resolution (0.13 arc seconds or 23 km at the comet),
nor his measured size of the nucleus (160 x 400 km), nor his verbal
description of the nucleus (as a bright object) support this idea:
It rather seems that the term `nucleus' was used at the time for
the brightest, innermost part of the coma. It is concluded that,
nevertheless, Struve quite correctly envisaged the structure of the
innermost coma, and to a considerable degree of accuracy anticipated
the correct shape and structure of the nucleus (elongated, 1:2) and
its localized sources of outstreaming gas.
---------------------------------------------------------
Title: Finsternisse und Sonnendurchmesser.
Authors: Wittmann, A. D.
1999A&R....36....4W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Implementation of a Filter for the Restoration of Solar
Granulation Images
Authors: Sánchez Cuberes, M.; Bonet, J.; Vázquez, M.; Wittmann, A.
1999ASPC..183..515S Altcode: 1999hrsp.conf..515S
No abstract at ADS
---------------------------------------------------------
Title: Did Struve in 1835 observe the nucleus of Halley's comet?
Authors: Wittmann, Axel D.
1999AGAb...15...82W Altcode: 1999AGAb...15...82A; 1999AGM....15..K07W
During its apparition in 1835 comet Halley reached its minimum distance
from the Earth (0.187 au) on 13 October in the constellation of Ursa
Major. Telescopic visual observations were made, e.g., by F.W. Bessel
at Königsberg and by F.G.W. Struve at Dorpat (Tartu/Estonia). In
particular a drawing made by Struve on 8 October of what he calls the
'nucleus' and describes as a small, slightly yellowish glowing piece
of coal of elongated shape bears such a striking resemblance with the
images of Halley's nucleus obtained in 1986 by the HMC camera aboard
the Giotto spacecraft that it merits further examination: Could Struve,
who had been using a 24.4 cm refractor at 254-fold magnification,
possibly have observed the real nucleus? Closer examination shows
that neither Struve's maximum possible resolution (0.13” or 23 km at
the comet), nor his measured size of the nucleus (163x 407 km), nor
his verbal description of the nucleus (a bright object) support this
idea: It rather seems that the term `nucleus' at the time was used for
the brightest, innermost part of the coma, and it is concluded that,
nevertheless, Struve quite correctly envisaged the structure of the
innermost coma, and to a considerable degree of accuracy anticipated
the correct shape and structure of the nucleus (elongated, 1:2) and its
localized sources of outstreaming gas. Struve's observations will be
described, and examples of his drawings and of Giotto's CCD closeups
of the true nucleus (size 8x 15 km) will be shown.
---------------------------------------------------------
Title: Image processing and analysis of CCD time seriesof the solar
granulation
Authors: Bovelet, B.; Wittmann, A. D.
1999AGAb...15...93B Altcode: 1999AGM....15..P12B
Using a fast CCD camera and and a frame grabber at the
Gregory-Coudé-Telescope (Izaña/Tenerife), seven time series of
the solar granulation at the disk centre have been obtained in
1996 (at 486 nm) and in 1998 (at 583 nm). From several thousand
frames of size 92” x 92” (512 x 512 pixels) we have selected 865
frames of highest intensity-rms. The images were two-dimensionally
deconvolved, derotated and shift-aligned by cross-correlation methods
and represent seven ordered time series, which typically cover areas of
60” x 60” and time intervals between 31 and 52 minutes. Our series
comprise approximately 2300 individual granules per frame. To obtain
statistically independent samples we furthermore selected the best
frames from the seven series. Using sophisticated algorithms (IDL)
of granule-finding and shape-tracking developed by one of us (B.B.),
we have studied morphological characteristics and dynamical aspects
of the evolving granulation pattern and of individual granules as
well. Particularly we have analyzed our samples with respect to:
Correlation lifetime of the entire granulation pattern Surface number
density and mean size of granules Histogram of effective diameter and
area contribution Analysis of the fractal dimension of granular shapes
Definition and distribution of individual granule lifetimes
---------------------------------------------------------
Title: Centre-To-Limb Variation of the Solar Granulation
Authors: Sánchez Cuberes, M.; Bonet, J. A.; Vázquez, M.; Wittmann,
A. D.
1998Ap&SS.263..343S Altcode: 1999Ap&SS.263..343S
An excellent series of images of solar granulation was taken during
the partial solar eclipse of 1994 May 10 at the Swedish Vacuum Solar
Telescope at Roque de los Muchachos Observatory. Making use of the
lunar limb profile, images at different heliocentric positions were
corrected for instrumental and atmospheric effects. The centre-to-limb
variation of the granulation contrast was calculated and compared with
previous determinations.
---------------------------------------------------------
Title: The solar diameter derived from Tobias Mayer's observations
1756-1761
Authors: Wittmann, Axel D.
1998AcHA....3...49W Altcode:
Tobias Mayer (1726-1762), one of the leading astronomers of the 18th
century, was particularly famous for the precision of his positional
observations. In 1751 Mayer became director of Göttingen University
Observatory, where he worked until his untimely death in 1762. Mayer's
observations were made with a 6-ft. mural quadrant (D=5.0 cm, f=1.86
m, 96 partes = 90 degrees) manufactured by John Bird/London. This
instrument is one of the most accurate mural quadrants ever made and
is still preserved in our institute. Among Mayer's observations is a
series of meridian transit times of the Sun which were observed across
a 5-wire fiducial grid in the focal plane of the telescope (at about
30-fold magnification) and were timed using a precision pendulum clock
designed by Franz Kampe. Although these observations have been analyzed
several times before (Mayer, 1762 [published 1767]; Wittmann, 1980;
Toulmonde, 1995) they still merit revisiting with regard to possible
long-term variations of the solar diameter. From a recent analysis,
using improved reduction techniques and as many as possible of Mayer's
observations, the author has obtained the following results (where R
is the angular solar semidiameter at 1 au): 1. The absolute time of
meridian passage (transit of disk centre) was measured with an accuracy
of typically +/- 0.7 or 11 arc seconds (note that in case of the Sun
this must be inferred from the transit time of opposite limbs and
that this also depends on the absolute accuracy of the clock). 2. The
observations split into two distinctly different groups (with a gap in
between). The first group (N=120, 1756-1758) is much more homogeneous
and considerably more accurate than the second group (N=13, 1760-1761),
and it may, therefore, be justified to completely disregard the second
group: 1st group: R = (960.46 +/- 0.11) arc seconds [N=120] 2nd group:
R = (959.85 +/- 0.72) arc seconds [N=13] Both: R = (960.40 +/- 0.12) arc
seconds [N=133] 3. If, with due allowance for the accuracies involved,
this is compared to recent drift timing results obtained during a joint
project by A.D. Wittmann at Tenerife in 1981/1990-1997 (1st group) and
by M. Bianda at Locarno in 1990-1997 (2nd group), viz. 1st group: R =
(960.59 +/- 0.03) arc seconds [N=7627] 2nd group: R = (960.59 +/- 0.05)
arc seconds [N=2244] Both: R = (960.59 +/- 0.02) arc seconds [N=9871]
we can conclude that there has been no significant secular change in
the size of the Sun during the last 250 years, or that such a trend,
if it exists, would not have exceeded +0.00086 arc second/yr.
---------------------------------------------------------
Title: Tobias Mayers Transitmessungen der Sonne (1756 - 1761):
Eine Neudiskussion und ein Vergleich mit Transitmessungen von Gauß
(1819 - 1820).
Authors: Wittmann, A. D.
1998GGMit..35...53W Altcode:
Während manche Beobachtungen Tobias Mayers (1723 - 1762) nur noch
historisch interessant sind, sind andere Messungen auch heute noch von
aktuellem Interesse. Dazu zählen unter anderem die Sonnenbeobachtungen,
da diese zeitlich weit genug zurückliegen und dabei trotzdem noch
genau genug sind, um für moderne Fragestellungen Verwendung zu
finden, wie zum Beispiel die nach eventuellen Schwankungen oder
gar langfristigen Veränderungen des Sonnendurchmessers. Im Rahmen
der gegebenen Unsicherheiten und Fehlergrenzen stimmen die gefundenen
Werte recht gut mit den heutigen Sonnenradien überein. Es ist daher die
Schlußfolgerung gerechtfertigt, daß sich aus dem Vergleich über einen
Zeitraum von rund 250 Jahren kein Anhaltspunkt für eine langfristig
sehr wesentliche Schrumpfung oder Ausdehnung der Sonne ergibt.
---------------------------------------------------------
Title: Astronomical refraction
Authors: Wittmann, A. D.
1997AN....318..305W Altcode:
In real-time applications fast and accurate algorithms for calculating
astronomical refraction are required. Some of the most widely-used
expressions are fast, but numerically unstable, and can not be applied
where the correction is largest, i.e. close to the horizon. In the
present paper a new formula for refraction, which is both fast and
numerically stable, is given and compared with previously published
refraction formulas. The approximate calculation of refraction 'below
the horizon', and of the finite distance correction near the horizon,
are also discussed.
---------------------------------------------------------
Title: Ccd-Drift Scan Measurements of the Solar Diameter: Method
and First Results
Authors: Wittmann, Axel D.
1997SoPh..171..231W Altcode:
A new method of measuring the solar diameter, combining the advantages
of both photoelectric and visual drift-timing techniques, has been
put into operation at Observatorio del Teide/Tenerife: a CCD camera is
placed in the focus of the Gregory-Coudé Telescope, and a number of
two-dimensional pictures are quickly read out during the passage of
each of the two opposite limbs of the Sun across the CCD. Accurate
time marks are stored in each frame, and image motion due to the
Earth's atmosphere is compensated by fitting the limb positions in each
series of frames with respect to time and by reducing them to a common
reference position. The first results are described and compared with
those of visual measurements.
---------------------------------------------------------
Title: On the Relation between the Synodic and Sidereal Rotation
Period of the Sun
Authors: Wittmann, Axel D.
1996SoPh..168..211W Altcode:
It is pointed out that by taking Kepler's second law into account, the
`sidereal correction', i.e., the correction to be added to the observed
synodic rotation rate of the Sun in order to get the sidereal rate,
can be calculated more directly than described in a recent paper by
Roša et al. (1995).
---------------------------------------------------------
Title: CCD-Doppler Measurements of Solar Differential Rotation
Authors: Wittmann, Axel D.
1996SoPh..167..441W Altcode:
Using the AT1 CCD camera at the Echelle spectrograph of the GCT at
Tenerife, solar Doppler rotation measurements in the photospheric
lines Fe I 6301.5 Å and 6302.5 Å and in the chromospheric line
Na-D<SUB>2</SUB> 5890.0 Å have been made. The line shifts measured
at different heliographic latitudes around the limb were corrected
for observer motion and converted into sidereal rotation rates. At
the equator the observed chromospheric rotation rate is about 8 %
larger than the photospheric rate, and the average observed Doppler
rotation rate is not very much different from the mean rotation rates
deduced from `all' published tracer works and `all' published Doppler
works. Near the poles (where tracer methods rely on extrapolation)
both the chromospheric and the photospheric rotation rate are slightly
smaller than the `all' Doppler rate and are considerably smaller than
the extrapolated `all' tracer rate. If `all' previous measurements
of solar rotation are taken into account, a surface rotation law with
lower error bounds than previously possible can be derived.
---------------------------------------------------------
Title: On the Relation between the Sun's (Geocentric) Angular Diameter
and the Observed (Topocentric) `Drift Time'
Authors: Wittmann, Axel D.; Neckel, Heinz
1996SoPh..163....1W Altcode:
It is pointed out that the relation between the Sun's geocentric
diameter and the so-called drift time observed on the Earth's surface
does not depend on topocentric data (distance, declination, parallax,
refraction), but only on the geocentric values of distance, declination,
and variation of right ascension.
---------------------------------------------------------
Title: Realistic computerized human phantoms
Authors: Zankl, M.; Veit, R.; Petoussi, N.; Mannweiler, E.; Wittmann,
A.; Drexler, G.
1994AdSpR..14j.423Z Altcode: 1994AdSpR..14..423Z
To estimate the risk resulting from exposures to ionizing radiation,
the organ and tissue doses should be assessed. A convenient method
is the calculation of these doses using representations of the
human body, called models or phantoms, together with computer codes
simulating the transport of radiation in the body. Most commonly used
are mathematical phantoms whose external and internal volumes are
defined by simple geometric bodies. More recently, phantoms constructed
from computed tomographic data of real persons were introduced as an
improvement. These phantoms present advantages concerning the location
and shape of the organs, in particular the hard bone and bone marrow,
whose distribution can be assessed with high resolution. So far,
three of these phantoms were constructed at the GSF, a fourth is under
process. The construction technique is described, and some calculational
results of organ doses due to external photon irradiation are presented.
---------------------------------------------------------
Title: Spectral lines unaffected by instrumental
polarization. II. Selected lines of astrophysical interest
Authors: Vela Villahoz, E.; Sanchez Almeida, J.; Wittmann, A. D.
1994A&AS..103..293V Altcode:
Lines with no linear polarization induced by Zeeman effect
are unaffected by instrumental polarization. We compile 86 such
electric dipole lines with differing temperature and magnetic field
sensitivities. In addition, we list 420 spectral lines which produce
negligible linear polarization. In most cases, this second set can
also be regarded as lines unaffected by instrumental polarization.
---------------------------------------------------------
Title: Spectroscopy of spot Mt. Wilson No. 27549 (24 Jul - 5 Aug 1992)
Authors: Wittmann, A. D.
1994smf..conf..210W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Contribution to the Round Table Discussion Concerning Solar
Databases at Catania, May 12, 1993
Authors: Wittmann, A. D.
1994emsp.conf..219W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: VizieR Online Data Catalog: Lines unaffected by polarization
(Vela Villahoz+ 1994)
Authors: Vela Villahoz, E.; Sanchez Almeida, J.; Wittmann, A. D.
1993yCat..41030293V Altcode:
Not Available (2 data files).
---------------------------------------------------------
Title: Detection of a Significant Change in the Solar Diameter
Authors: Wittmann, Axel D.; Alge, Edoardo; Bianda, Michele
1993SoPh..145..205W Altcode:
Drift-time measurements of the solar diameter made at Izaña and
Locarno in 1990-1992 show a significant increase of the observed angular
semidiameter when compared to results obtained at the same two sites
in 1981. The observed increase of ≈0.4″ is not due to a systematic
(or long-term) variation, but seems to reflect a more complicated
behaviour with time: As both series of measurements were made around a
maximum of the 11-year cycle, it seems that a variation in phase with
solar activity (in the sense of the Secchi-Rosa law) can be ruled out.
---------------------------------------------------------
Title: Recent results on the solar diameter
Authors: Wittmann, A. D.; Alge, E.; Bianda, M.
1991SoPh..135..243W Altcode:
Using optically identical telescopes at different sites, we have
measured the solar diameter with a drift-scan technique. In order
to investigate the cause of the observed fluctuations, we not only
compare observations made simultaneously by different observers at
the same telescope, but also observations made simultaneously at
two different sites. Our main results are: (a) The mean error of a
single drift time measurement is ±0.08s(or ± 1.1″) at Izaña and
±0.11 s (or ± 1.7″) at Locarno; this closely corresponds to the
angular resolution at those two sites under normal seeing conditions,
(b) We find no correlation between observations at different sites;
a significant correlation exists, however, between observations made
simultaneously by different observers at the same site: This indicates
that most of the observed fluctuations are due to atmospheric effects
(`image motion') rather than personality effects, (c) The mean solar
semi-diameter derived from a total of 1122 observations made in 1990
(472 at Izaña, 650 at Locarno) is R = (960.56 ± 0.03)″ (Izaña:
960.51″, Locarno: 960.59″); this may be compared with R = (960.32
± 0.02)″ which is obtained from a re-analysis of 1773 observations
made in 1981 (Izaña: 960.16″, Locarno: 960.38″). Although a
small residual increase of the solar diameter during the last ten
years seems to be indicated, we conclude that most - if not all -
of the observed variations are due to variable seeing conditions,
and that there is still no conclusive evidence for a genuine solar
variation with amplitudes in excess of about ±0.3″.
---------------------------------------------------------
Title: The instrumental polarization of a Gregory-Coudé telescope
Authors: Sanchez Almeida, J.; Martinez Pillet, V.; Wittmann, A. D.
1991SoPh..134....1A Altcode:
We calculate a theoretical model of the polarization properties of
a Gregory-Coudé telescope to predict the behaviour of the German
Gregory-Coudé Telescope installed at the Observatorio del Teide
(Spain). Measurements of the real effects produced by this telescope
acting upon light of known polarization are compared with the model. We
estimate an uncertainty in its predictions of about 10%, which is
produced by the uncertainties of the (complex) refractive index of the
metallic layers covering the mirrors. The paper concludes by briefly
considering the way in which the plain telescope changes the Stokes'
profiles.
---------------------------------------------------------
Title: Solar Spectroscopy with a 100 X 100 Diode Array.
Authors: Wittmann, A. D.
1991RvMA....4...61W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The GRECOS operating system of the GCT
Authors: Wittmann, Axel D.; Kroll, Reinhold
1990Ap&SS.171..357W Altcode:
The computer operating system of the Gregory Coudé Telescope (GCT)
at Observatorio del Teide is described. The GRECOS command language
provides the user with a flexible means of operating both telescope
and spectrograph, to execute complex measuring sequences, and to handle
and display his observational data.
---------------------------------------------------------
Title: Der Sonnendurchmesser und seine Variabilität.
Authors: Wittmann, Axel D.; Debarbat, Suzanne
1990S&W....29..420W Altcode:
Methods of measuring the solar diameter and its variability are
described. The historical development of these methods is reviewed,
and the causes of inaccuracy are examined, including annual effects,
solar effects, and special effects. The results of routine measurements
of the solar diameter made over the past 200 years are reviewed.
---------------------------------------------------------
Title: Observations of Line Asymmetries with a 2-D Diode Array
Authors: Hanslmeier, A.; Wittmann, A. D.; Mattig, W.
1990Ap&SS.170...47H Altcode:
From two-dimensional Reticon spectra obtained at the Gregory Coudé
Telescope (Tenerife) two Fei lines were studied. It is shown that
the resultant line bisectors could be separated according to their
origination in granular-intergranular regions and that the resolved
bisectors no longer had a C-shape form.
---------------------------------------------------------
Title: Comparison of heliographic sunspot coordinates observed with
seven different solar telescopes.
Authors: von Alvensleben, A.; Casas, R.; Csepura, G.; Lustig, G.;
Otruba, W.; Schroll, A.; Vazquez, M.; Wittmann, A. D.; Wöhl, H.
1990AGAb....5...43V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Influence of Blurring on Granular Doppler Shifts
Authors: Wittmann, A. D.
1989AGAb....3...14W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Über die astronomischen Koordinaten der Göttinger Sternwarte.
Authors: Wittmann, A.; Tamke, G.
1989GGMit..26R....W Altcode:
By combining all measurements of latitude and longitude of Göttingen
University Observatory published during 1816 - 1974, its astronomical
coordinates were found as follows: φ = +51°31'48″08±0″55, λ =
+09°56'33″2±3″1 (altitude 158.6 m). The location of the former
Göttingen Observatory (Tobias Mayer's Observatory, operated 1750
- 1818) has been reconstructed from old maps, and its astronomical
coordinates were derived as follows: φ = 51°31'54″13±0″56, λ =
+09°56'04″8±3″2 (altitude 159.4 m).
---------------------------------------------------------
Title: High Resolution Granulation Spectroscopy with a 100x100 RETICON
Authors: Hanslmeier, A.; Wittmann, A.
1989AGAb....3...11H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Gregory-Coudé-Telescope in the Observatorio del Teide,
Izaña.
Authors: Kneer, F.; Wiehr, E.; Wittmann, A. D.
1988AGAb....1...46K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The behaviour of solar activity as inferred from sunspot
observations165 BC to 1986.
Authors: Wittmann, A. D.; Xu, Z. T.
1988ssgv.conf..131W Altcode:
The authors have studied the behaviour of solar activity on the basis
of a catalogue of non-telescopic sunspot observations covering the
period 165 BC to 1684, to which a catalogue of naked-eye sunspots of
the period 1764 to 1986 has recently been appended. While both the
"modern" and the "reliable" ancient spots show a bimodal distribution
of O-C values with a distinct concentration around zero, the residuals
for the whole sample of ancient spots show only weak indications of
a maximum and are almost evenly distributed.
---------------------------------------------------------
Title: A catalogue of sunspot observations from 165 BC to AD 1684
Authors: Wittmann, A. D.; Xu, Zhentao
1988VA.....31..127W Altcode:
We have compiled a new catalogue of sunspot observations covering the
period 165 BC to AD 1684 by updating and merging previously published
catalogues and by adding a substantial amount of new data. The
catalogue is in machine-readable form, the total number of entries
being 235. Epoch analyses of the data have been made with regard to
(a) the usefulness of naked-eye observable sunspots as tracers of
the maximum epochs, and (b) the long-term phase behaviour of the
sunspot cycle. The average period of the sunspot cycle 11.116+0.007
years, with individual periods ranging from 7.5 to 14.5 years (70%
are between 9.9 and 12.3 years). Gaps(or scarcities of observations)
are obvious between AD 600 AD 800 (Medieval Minimum) and AD 1400-1500
(Spörer Minimum), but not during 1640-1715 (Maunder Minimum). A useful
numerical approximation for the maximum epochs is: Year (Max.)=4.0 +
11.116N, where N is an arbitrary cycle number (n=178 for the maximum
of 1980/81). <P />For details of this paper see Wittmann and Xu (1987).
---------------------------------------------------------
Title: A catalogue of sunspot observations from 165 BC to AD 1684
Authors: Wittmann, A. D.; Xu, Z. T.
1987A&AS...70...83W Altcode:
We have compiled a new catalogue of sunspot observations covering the
period 165 BC to AD 1684 by updating and merging previously published
catalogues and by adding a substantial amount of new data. The
catalogue is in machine-readable form, the total number of entries
being 235. Epoch analyses of the data have been made with regard to
(a) the usefulness of naked-eye observable sunspots as tracers of the
maximum epochs, and (b) the long-term phase behaviour of the sunspot
cycle. The average period of the sunspot cycle is 11.116 ± 0.007
years, with individual periods ranging from 7.5 to 14.5 years (70% are
between 9.9 and 12.3 years). Gaps (or scarcities of observations) are
obvious between AD 600 and AD 800 (Medieval Minimum) and AD 1400-1500
(Sporer Minimum), but not during 1640-1715 (Maunder Minimum). A useful
numerical approximation for the maximum epochs is: Year (Max.) = 4.0 +
11.116 N, where N is an arbitrary cycle number (N = 178 for the maximum
of 1980/81).
---------------------------------------------------------
Title: A catalogue of non-telescopic sunspot observations from 165
BC to AD 1684.
Authors: Wittmann, A. D.; Xu, Z. T.
1987PPMtO...6..233W Altcode:
The authors have compiled a new catalogue of non-telescopic sunspot
observations covering the period 165 BC to AD 1684 by updating and
merging previously published catalogues and by adding a substantial
amount of new data. The catalogue is in machine-readable form, the total
number of entries being 235. Epoch analyses of the data have been made.
---------------------------------------------------------
Title: Construction of the German Solar Telescopes at Observatorio
del Teide/Tenerife: The Gregory-Coude Telescope
Authors: Kneer, F.; Schmidt, W.; Wiehr, E.; Wittmann, A. D.
1987MitAG..68..181K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: An Enlarged Catalogue of Pre-telescopic Sunspots
Authors: Wittmann, A. D.; Xu, Z. T.
1986MitAG..67..287W Altcode:
The authors compiled a new catalogue of non-telescopic sunspot
observations covering the period 165 BC to AD 1684. The catalugue
is in machine-readable form. A detailed report is in preparation for
Astron. Astrophys., Suppl. Ser.
---------------------------------------------------------
Title: Die Schiefe der Ekliptik und ihre zeitliche Variation.
Authors: Wittmann, A. D.
1985S&W....24...24W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Variation of the Obliquity of the Ecliptic
Authors: Wittmann, A. D.
1984MitAG..62..201W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Multi-band Spectral Photometry of Sunspots
Authors: Wittmann, A. D.
1983MitAG..60..280W Altcode:
Results are given from fast computer-controlled photoelectric scans
across sunspots, granulation, pores and the solar limb. The scans were
obtained during periods of excellent seeing conditions in August, 1978,
at the Locarno solar station of Goettingen University Observatory,
using the 45-cm Gregory-Coude vacuum telescope. Several hundred
digitized scans have been individually corrected for the effects of
seeing (as determined from limb intensitiy profiles) and scattered
light (as determined from aureole scans). Fine structures such as
granules, penumbral filaments, and umbral dots are well resolved,
and the corrected relative intensities I(min), I(mean), and I(max)
of photosphere (granulation), penumbra (filaments), umbra (dots),
and pores (dots) have been derived as a function of wavelength and -
in some cases distance from the limb.
---------------------------------------------------------
Title: Deceleration of the Earth's Rotation from Old Solar
Observations
Authors: Wittmann, A. D.
1982tfer.conf...51W Altcode:
Contents: Analysis of solar tables. The length of the year (Motion
comparison).
---------------------------------------------------------
Title: Balloon-borne imagery of the solar granulation. III - Digital
analysis of a white-light time series
Authors: Wittmann, A.
1981A&A....99...90W Altcode:
An analysis is presented of a time series of 17 high-resolution,
computer processed solar granulation pictures, obtained during the
'Spektro-Stratoskop' project from an altitude of 28 km. On each
negative, a rectangle of 29.7 x 44.6 arcsec (where 1 arcsec corresponds
to 733.3 km on the sun) was scanned with a microphotometer, and the
digitized intensities (200 x 300/frame) were corrected for instrumental
blurring by means of a two-dimensional deconvolution. Numerical
data were used to generate power spectra, correlation coefficients,
brightness histograms, and contour plots, and a simplified morphological
model was used to interpret the data. Major conclusions include
the following: (1) granular rms brightness fluctuation at 500 nm
equals 9.9%; (2) mean granular contrast at 500 nm equals 21.9%; (3)
fractional area of granules equals 47.1%; and (4) the peak at 3.4/Mm
exhibited by previous power spectra is resolved into three components
with wavenumbers 2.0/Mm, 4.4/Mm, and 7.4/Mm.
---------------------------------------------------------
Title: Digitale Bildverarbeitung und photometrische Analyse einer
Zeitserie von Ballonaufnahmen der Sonnengranulation
Authors: Wittmann, A.
1981MitAG..52..165W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the variability of the solar diameter
Authors: Wittmann, A. D.; Bonet Navarro, J. A.; Woehl, H.
1981phss.conf..424W Altcode:
In an attempt to elucidate the daily fluctuations seen in the 1980
drift time data (August 30-September 13) and to monitor the solar
diameter for an interval as long as possible, visual drift timing
observations were made on 46 consecutive days, from May 16 to June 30,
1981. A total of 2091 visual drift times (including 11 doubtful ones)
was obtained. From the observations, R(vis) is found to be 960.2 +
or - 0.1 arcsec, that is, the standard value of 961.18 arcsec derived
from Greenwich transits is much too large. With due weight assigned
to the photoelectric observations, it is concluded that the correct
value of R is 960.0 + or - 0.1 arcsec.
---------------------------------------------------------
Title: Solar observations at the Göttingen University Observatory
Authors: Wiehr, E.; Wittmann, A.; Wöhl, H.
1980SoPh...68..207W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Gradual Shrinkage of the Sun
Authors: Wittmann, A.
1980S&T....60..190W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Mayer, Tobias Observations of the Sun - Evidence against a
Secular Decrease of the Solar Diameter
Authors: Wittmann, A.
1980SoPh...66..223W Altcode:
Evidence for a significant secular decrease of the solar diameter has
recently been presented by Eddy and Boornazian (1979). With regard
to the enhanced interest in periodic or non-periodic variations of
figure and size of the Sun, a very reliable series of 129 transit
observations made by Tobias Mayer in 1756-1760 has been analyzed. The
necessity for applying adequate corrections to measurements of this
kind is stressed again. Mayer's observations yield R<SUB>⊙</SUB> =
(960.16±0.13)″. This is in excellent agreement with more recent
photoelectric transit observations and lends no support whatsoever to
the assumption of a secular decrease.
---------------------------------------------------------
Title: The influence of spatial resolution on the Ca/+/K line width
and shift in a quiescent prominence
Authors: Engvold, O.; Wiehr, E.; Wittmann, A.
1980A&A....85..326E Altcode:
A series of 17 spectrograms of the Ca<SUP>+</SUP> K line in a large
quiescent prominence are investigated for the effects of spatial
smearing due to seeing. It is found that the full width at half- maximum
(FWHM) decreases from 0.190 Å to 0.125 Å when the spatial resolution
increases from 15" to about 2". High spatial resolution also facilitates
the detection of large line shifts Δλ. The narrowest line profiles -
which are detected in the case of high spatial resolution and large
shift - yield FWHM<SUB>min</SUB> ≍ 0.090 Å, which exceeds the
pure thermal broadening width by a factor of 2-3. The most probable
value of the resolved macroscopic velocity is found to be 23 km
s<SUP>-1</SUP>. This velocity corresponds to an equipartition magnetic
field strength of about 3.8 G.
---------------------------------------------------------
Title: The solar limb darkening function at 5012 A and its possible
variations
Authors: Wittmann, A.
1980A&A....83..312W Altcode:
New photoelectric measurements of the solar center-to-limb variation
(CLV) in the continuum at 5011.5 A have been performed to verify the
brightness asymmetry reported by Wittman (1978). The N-S asymmetry
found in the 1976 data also appears in the 1977 data. In addition,
an E-W asymmetry of about the same magnitude is observed whose
existence with time implies a low probability for a solar origin of
both asymmetries. From a total of 2304 CLV scans, the average CLV,
including the limb intensity profile, has been determined with
considerable accuracy.
---------------------------------------------------------
Title: Mayer, Tobias Meridional Observations of the Sun and the
Question of the Variability of Solar Measurements
Authors: Wittmann, A.
1980MitAG..48...25W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Sonnenforschung auf La Palma.
Authors: Wittmann, A.
1980Umsch..80...92W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The obliquity of the ecliptic.
Authors: Wittmann, A.
1979A&A....73..129W Altcode:
In view of the discrepancy between observed and calculated secular
rates of change in the mean apparent obliquity of the ecliptic,
a reassessment of observed values of the obliquity of the ecliptic
is made. Least-squares adjusted values of the obliquity are derived
for a number of epochs (1000 B.C. to A.D. 2000). A simple numerical
expression for the obliquity is given which supersedes the standard
expression and amply approximates the expected cyclic behavior for a
time span of at least 1 million years.
---------------------------------------------------------
Title: Observations of solar granulation - a review.
Authors: Wittmann, A.
1979ssms.conf...29W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Wie beeinflußt die Lichtablenkung im Schwerefeld den
beobachteten Sonnendurchmesser?
Authors: Wittmann, A.
1979Umsch..79..579W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Sunspot Cycle before the Maunder Minimum
Authors: Wittmann, A.
1978A&A....66...93W Altcode:
Summary. Several hundred observations of giant sunspots have been
recorded during the pre-telescopic era, especially in ancient China. The
clustering of observations reveals approximately 50 activity maxima
during this era, which-in combination with the modern record of sunspot
be used to trace the phase of the 11-year sunspot cycle back to the 5th
century B.C. Although long-term modulations exist, it is highly likely
that the sunspot cycle persisted without interruption throughout this
time span. The mean period is equal to 11.135 yr. Key words: solar
activity - sunspot periodicity - pretelescopic sunspot observations -
solar-terrestrial relations.
---------------------------------------------------------
Title: A north-south asymmetry in the solar brightness.
Authors: Wittmann, A.
1978A&A....64...91W Altcode:
Photoelectric measurements in July 1976 of the continuum center-to-limb
variation of the quiet sun along polar and equatorial diameters have
detected a north-south asymmetry in solar brightness. The cause and
duration of the asymmetry are unknown. The south polar region was 19 K
warmer (at an optical depth of 0.15) and the north polar region was 19
K cooler than average, although the equatorial brightness distribution
did not depart significantly from the average. The observed intensities
were corrected for scattered light, image blurring, and differential
extinction, and radiative transfer calculations were used to interpret
the measurements. The measurements were more in accord with the HSRA
temperature distribution than with the Holweger-Mueller model.
---------------------------------------------------------
Title: R. W. Wilson received the Nobel Prize for Physics.
Authors: Wittmann, A.
1978Umsch..78R.766W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Zur Frage der Sonnenaktivität vor dem Maunder-Minimum
Authors: Wittmann, A.
1978MitAG..43..142W Altcode:
The characteristics of solar activity are partly determined by long-term
variations with time scales in the range from 100 to 500 years. These
long-term variations are superimposed on the 11-year cycles. The last
minimum, which is known as the Maunder minimum, occurred during the
time from 1645 to 1715. It is in this connection of interest to find
out whether the 11-year cycle existed during the centuries before the
Maunder minimum. The power spectrum of the relative number of sunspots
for the time from 1701 to 1976 shows clearly the dominance and the
long-term phase stability of the 11-year cycle during the considered
period. A study of the solar conditions for the time before the Maunder
minimum shows that the 11-year cycle can be traced back to approximately
500 B.C.
---------------------------------------------------------
Title: A. A. Penzias received the Nobel Prize for Physics.
Authors: Wittmann, A.
1978Umsch..78Q.766W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Die Erforschung der Sonne mit Ballonteleskopen.
Authors: Wittmann, A.
1978S&W....17....8W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Die Periodizität der Sonnenflecken in alter Zeit.
Authors: Wittmann, A.
1978S&W....17..412W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The diameter of the sun.
Authors: Wittmann, A.
1977A&A....61..225W Altcode:
Measurements of the solar semidiameter made between 1836 and 1975 are
discussed. The currently adopted irradiation constant of -1.55 arcsec,
which is based on a true semidiameter of 959.63 arcsec, is checked by a
direct comparison of simultaneous transit observations and photoelectric
drift scans. A constant of -0.96 arcsec is obtained, supporting the
conclusion that the irradiation correction will not always be as
large as 1.55 arcsec. The mean semidiameters at unit distance, as
derived from the heliometer/drift-scan and transit observations since
1836, are 959.87 arcsec and 961.32 arcsec, respectively. The transit
semidiameter becomes 960.07 arcsec with a correction of -1.25 + or -
0.30 arcsec. By combining all measurements, the mean semidiameter
finally becomes 960.00 + or - 0.09 arcsec or 696,265 + or - 65 km.
---------------------------------------------------------
Title: Balloon-borne imagery of the solar granulation. I. Digital
image enhancement and photometric properties.
Authors: Wittmann, A.; Mehltretter, J. P.
1977A&A....61...75W Altcode:
Summary. Digital image processing and restoration techniques have been
applied to high-resolution photographs of the solar granulation that
were obtained with a balloon-borne telescope. The final resolution that
has been achieved is 0.3" or 220 km on the sun. From the digitized and
computer-processed images we have determined photometric properties
of the solar granulation at the disc centre: The true rms amplitude
ofthe granular intensity fluctuation is found to be 8.7 %, which for a
simplified model of bright and dark elements corresponds to a contrast
of 19.0 %. At 5560 A this is equivalent to a blackbody temperature
difference of 254 K. The fractional area occupied by elements darker
than average is 52.4 %. Key words: solar granulation image processing
---------------------------------------------------------
Title: Computer-Processed Granulation Pictures of Project
"Spectro-Stratoscope"
Authors: Wittmann, A.; Mehltretter, J. P.
1977MitAG..42..114W Altcode:
The pictures which were processed had been obtained on May 17, 1975,
when a balloon-borne solar telescope performed a 10-hour flight at 27
km altitude. During the flight 400 spectrograms and 1000 high-quality
white light pictures were obtained of the solar granulation. Digital
image enhancement and restoration techniques were afterwards applied
to the digitized, two-dimensional intensity distribution. The employed
deconvolution method, which is known as van Cittert's method, has been
described by van Wittmann (1971). The final resolution achieved is
approximately 110 km on the solar surface. According to the obtained
results the granules are approximately 1.19 times as bright as the
intergranular background.
---------------------------------------------------------
Title: Spectral synthesis in a magnetic field.
Authors: Wittmann, A.
1977A&A....54..175W Altcode:
A numerical technique is described which performs LTE spectral synthesis
for arbitrary stellar atmospheres with magnetic fields, macroscopic
velocity fields, and any number of contributing atomic transitions
with arbitrary Zeeman splitting. With the technique, a section of the
solar spectrum (5249.3 A-5252.5 A) has been synthesized for both the
photosphere (nonmagnetic case) and a sunspot umbra (magnetic-field
case). The computed spectra are compared with observed spectra. Some
questionable line identifications are discussed, and new identifications
are given for 12 spectral lines. The behavior of the magnetograph line
Fe I 5250.21 A as well as magnetooptical effects in the synthesized
umbral spectrum are also investigated.
---------------------------------------------------------
Title: Neue Großteleskope für die Radioastronomie.
Authors: Wittmann, A.
1977Umsch..77..384W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Zusammenstoß im Weltall. Begegnet eine interstellare Wolke
dem Sonnensystem?
Authors: Wittmann, A.
1977Umsch..77..608W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Emission heights and centre-to-limb variation of some
chromospheric lines.
Authors: Wittmann, A.
1976A&A....48..121W Altcode:
A modified photoelectric-drift scan technique has been used to measure
emission heights as well as the center-to-limb variation of some of
the strongest lines in the quiet chromosphere (Ca(+) K, Mg b(1), Na
D, H-alpha). The true center-to-limb variations as derived from the
measurements are compared with previous results and with predictions
from very recent non-LTE calculations. With few exceptions, the
agreement is very satisfactory. A high-resolution computerized version
of Mohler's (1960) method has been used to determine mean emission
heights at the limb. The measured heights are compared with previous
empirical results.
---------------------------------------------------------
Title: High-Resolution Multichannel Drift Scans of the Sun
Authors: Wittmann, A.
1976MitAG..38..137W Altcode:
Advantages of a use of photoelectric drift scans are related to an
avoidance of detrimental effects produced by the motion of optical
components, the employment of a highly constant and very accurately
known scanning rate, and the relatively high value of the scanning
rate. A description is given of the results of a number of observational
programs in which techniques employing photoelectric drift scans
were used. The results are related to the tangential height of line
emission, the center-to-limb variation of central line intensity,
and the solar diameter.
---------------------------------------------------------
Title: Sonnenforschung mit Stratosphärenballons.
Authors: Wittmann, A.
1976Umsch..76..293W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Line Formation with Magnetic Field: Review and Practical
Applications
Authors: Hardorp, J.; Shore, S. N.; Wittmann, A.
1976paps.coll..419H Altcode: 1976IAUCo..32..419H
No abstract at ADS
---------------------------------------------------------
Title: Scattered Light - A Comparison between Theory and Experiments
during the 1973 Transit of Mercury
Authors: Wittmann, A.; Woehl, H.
1975SoPh...44..231W Altcode:
We check the formalism used to derive stray light corrections from
measured aureole intensities and correct an error in the pertinent
literature. We solve the alledged problem of appropriately normalizing
the spread function by treating blurring and scattering separately. We
test the method by comparing stray light corrections derived from both
the aureole and from intensity profiles across Mercury's disc obtained
during the transit of November 10, 1973.
---------------------------------------------------------
Title: Zur Streulichtbehandlung solarer Intensitätsmessungen
Authors: Wittmann, A.; Wöhl, H.
1975MitAG..36..138W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Alles beim alten? Neues aus der relativistischen Astrophysik.
Authors: Wittmann, A.
1975S&W....14..125W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Préparation Automatisée de Perles pour l'Analyse par la
Fluorescence de Rayons X
Authors: Wittmann, A.; Chmeleff, J.; Herrmann, H.
1974XRS.....3..137W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Computation and Observation of Zeeman Multiplet Polarization
in Fraunhofer Lines. III: Magnetic Field Structure of Spot Mt. Wilson
18488
Authors: Wittmann, A.
1974SoPh...36...29W Altcode:
From an analysis of Stokes parameter profiles measured in a unipolar
sunspot, properties of its large-scale magnetic field structure have
been derived. With due allowance for our present knowledge about the
Wilson effect and the height of line formation, an expression for the
field strength distribution H(r, z) has been obtained. The corresponding
field strength gradient equals ∂H/∂z = - 1.5 G km<SUP>−1</SUP> at
a height z = 300 km, it increases with decreasing z and vice versa. The
inclination of the magnetic vector increases from ψ = 0 ° at r =
0 to ψ = 90 ° at the penumbra-photosphere border, its variation
across the spot is not consistent with a purely radial (poloidal)
field. The field azimuth has been determined across a sunspot diameter
on several days with due allowance for the Macaluso-Corbino effect,
and significant azimuthal components H<SUB>χ</SUB> have been found
especially in the umbra.
---------------------------------------------------------
Title: Photoelectric Drift Scans. II: Time Pulse Evaluation, Limb
Profiles and the Solar Diameter
Authors: Wittmann, A.
1974SoPh...36...65W Altcode:
The method of computer controlled photoelectric drift scans has been
improved by virtue of a new timing technique, allowing for an accuracy
of 4 ms or equivalently 50 km on the Sun. With this technique, our
previous result for the solar semidiameter has been confirmed: R =
960.277″. The extreme solar limb intensity profile at 5012 Å has
been derived from drift scans. A comparison with the computed profile
has been made, and parameters for the base of the chromosphere have
been derived.
---------------------------------------------------------
Title: Numerical Simulation of the Mercury Transit Black Drop
Phenomenon
Authors: Wittmann, A.
1974A&A....31..239W Altcode:
Summary. A numerical investigation into the cause of the Mercury
transit black drop phenomenon has been made. Computations of the
degraded two-dimensional intensity distribution of the planetary disc
in the vicinity of the solar limb, made with high spatial resolution,
are presented in the form of graphical displays which clearly
reveal the observed effect and its strengthening with increasingly
deteriorating atmospheric blurring. It is thus demonstrated that
blurring in the Earth's atmosphere is mainly responsible for the
black drop phenomenon. Key words: Mercury - transit - black drop -
solar seeing - stray light
---------------------------------------------------------
Title: Computation and Observation of Zeeman Multiplet Polarization
in Fraunhofer Lines. II: Computation of Stokes Parameter Profiles
Authors: Wittmann, A.
1974SoPh...35...11W Altcode:
A self-contained summary of the generalized Unno theory of LTE line
formation in solar magnetic fields and its application to the numerical
computation of Stokes parameter profiles is given. Within this context,
computational details of general interest are described and numerical
results for sunspot fields are given. Finally, a new method of computing
the height of line formation is presented.
---------------------------------------------------------
Title: Der Merkurdurchgang vom 10. November 1973.
Authors: Wittmann, A.; Wöhl, H.
1974S&W....13...41W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: FG Sagittae - Testobjekt der Sternentwicklung.
Authors: Wittmann, A.
1974S&W....13..269W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Computation and Observation of Zeeman Multiplet Polarization
in Fraunhofer Lines. I: Photographic Measurement of Stokes Parameters
Authors: Wittmann, A.
1973SoPh...33..107W Altcode:
A brief introduction to the concept of Stokes parameters and their
application to solar magnetic field measurements is followed by
the description of a new photographic polarimeter which is capable
of measuring profiles of all Stokes parameters simultaneously. Its
performance characteristics and the method of measuring and correcting
instrumental polarization are discussed.
---------------------------------------------------------
Title: The Solar Diameter at 5000 Åand Hα from Photo-electric
Drift Scans
Authors: Wittmann, A.
1973SoPh...29..333W Altcode:
An improved method is described for the measurement of both the
solar radius and the height of the chromosphere in any desired
wavelength. Possible sources of uncertainty are discussed and a
comparison with other methods is made. The first results from the 1972
observing period are given: R = (960.24 ±0.16)″ for the continuum
at 5011.5 Å and R = (966.9 ±0.4)″ for Hα ± 0.5 Å. This yields
a mean height of Ha emission of (4900 ± 400) km.
---------------------------------------------------------
Title: The line dispersion function for enhanced damping
Authors: Wittmann, A.
1973A&AS....9..209W Altcode:
In analogy to the Taylor series expansion of the line dispersion
function F(a, v) for small damping parameter a (similar to that of
the related Voigt function), an approximation of F(a, v) for large
a is provided in order to facilitate frequent computations of that
function. Key words: Zeeman line formation - anomalous dispersion
---------------------------------------------------------
Title: Photographische Messung solarer Magnetfelder
Authors: Wittmann, A.
1973MitAG..32..163W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Transit of Mercury.
Authors: Wittmann, A.; Woehl, H.
1973IAUC.2598....1W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Berechnung und Messung der Stokesparameter in solaren
Zeeman-Multipletts.
Authors: Wittmann, A.
1973PhDT.......103W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Site testing auf La Palma.
Authors: Wittmann, A.
1973S&W....12..361W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Detection of Blends in the Vicinity of Zeeman Lines
Authors: Wittmann, A.
1972SoPh...23..294W Altcode:
High resolution spectrograms taken in polarized light have revealed the
presence of significant blending within the profiles of some important
Zeeman multiplets of a large umbra. Wavelength and equivalent width of
each depictable blend have been derived from the corrected spectrograms
and some preliminary identifications have been made.
---------------------------------------------------------
Title: Magnetooptische Effekte in Fraunhoferlinien mit
Zeeman-Aufspaltung
Authors: Wittmann, A.
1972MitAG..31..150W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Elimination of Seeing Effects from Solar Intensity
Measurements
Authors: Wittmann, A.
1971SoPh...21..237W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On Magneto-Optical Effects in Sunspots
Authors: Wittmann, A.
1971SoPh...20..365W Altcode:
Magneto-optical effects on the circular polarization within the line
FEI λ 6302.5 are investigated. Quantitative results on the V-reversal
near the line centre are given for homogeneous magnetic fields.
---------------------------------------------------------
Title: Prominent Zeeman Lines in Sunspot Spectra and Their Temperature
Sensitivity
Authors: Wittmann, A.
1971SoPh...20...78W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A complete photoelectric sunspot spectrum: An atlas from 3900
8000 Å
Authors: Wöhl, H.; Wittmann, A.; Schröter, E. H.
1970SoPh...13..104W Altcode:
Complete photoelectric spectra of the photosphere as well as of both
umbra and penumbra of a typical sunspot, ranging from 3900-8000 Å, have
been obtained at the Locarno observatory. An automatic scanning device,
a high precision electronic divider and an on-line Oscillomink penless
recorder enabled us to eliminate the noise produced by image distortion
and to scan the entire visible spectrum within just 5 h. The recordings
have a linear dispersion of about 50 mm/Å and a spectral resolution of
40 mÅ or better. Simultaneously with these observations the momentary
continuous spot intensity and its fast variation with time due to seeing
variations have been recorded with a frequency resolution up to 100
Hz. In order to provide as much data as possible for the correction
of the umbral spectrum for parasitic light, we also measured the limb
profile and the aureola intensity at several wavelengths.
---------------------------------------------------------
Title: The Intensity, Velocity and Magnetic Structure of a Sunspot
Region. V: On the Gradients of Temperature and Pressure in Sunspots
Authors: Wittmann, A.; Schröter, E. H.
1969SoPh...10..357W Altcode:
High resolution sunspot photographs in the blue, red and
infrared continuum exposed on various days were used to derive the
center-to-limb variation of the intensity ratio φ = I<SUB>sp</SUB> /
I<SUB>ph</SUB>. Special care was taken to correct for image blurring,
scattered light and the influence of line absorption.
---------------------------------------------------------
Title: Some Properties of Umbral Flashes
Authors: Wittmann, A.
1969SoPh....7..366W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Temperaturschichtung und Wilson-Effekt in symmetrischen
Einzelflecken
Authors: Wittmann, A.; Schröter, E. H.
1968MitAG..25..191W Altcode:
No abstract at ADS
