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Dive into the research topics where Gunter Wiedemann is active.

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Featured researches published by Gunter Wiedemann.


Applied Optics | 1993

Immersion grating for infrared astronomy

Gunter Wiedemann; Donald E. Jennings

An immersion grating with high refractive index n increases spectral resolution n-fold over that of a surface reflection grating of equal length.


The Astrophysical Journal | 1994

Observations of 13.5 micron rotation-vibration lines of SiS in IRC +10216

Robert J. Boyle; John J. Keady; D. E. Jennings; K. L. Hirsch; Gunter Wiedemann

We report the first observations of the 13.5 micron fundamental band of SiS in the spectrum of the heavily obscured carbon star IRC +10216. The lines are formed in the inner region of the circumstellar envelope where the gas is accerlerating and where the temperature ranges from 800-500 K. We have carried out a detailed model of the observed line profiles. Our observations are best fit by a gradient in the abundance of SiS. We derive an abundance relative to molecular hydrogen of x(SiS) = 4.3 x 10(exp -6) at a distance of twelve stellar radii from the central star rising to x(SiS) = 4.3 x 10(exp -5) at a few stellar radii from the surface of the star.


The Astrophysical Journal | 1988

Solar magnetic field studies using the 12 micron emission lines. I - Quiet sun time series and sunspot slices

Drake Deming; Robert J. Boyle; Donald E. Jennings; Gunter Wiedemann

The use of the extremely Zeeman-sensitive IR emission line Mg I, at 12.32 microns, to study solar magnetic fields. Time series observations of the line in the quiet sun were obtained in order to determine the response time of the line to the five-minute oscillations. Based upon the velocity amplitude and average period measured in the line, it is concluded that it is formed in the temperature minimum region. The magnetic structure of sunspots is investigated by stepping a small field of view in linear slices through the spots. The region of penumbral line formation does not show the Evershed outflow common in photospheric lines. The line intensity is a factor of two greater in sunspot penumbrae than in the photosphere, and at the limb the penumbral emission begins to depart from optical thinness, the line source function increasing with height. For a spot near disk center, the radial decrease in absolute magnetic field strength is steeper than the generally accepted dependence. 66 references.


Astrophysical Journal Supplement Series | 1993

Solar magnetic field studies using the 12 micron emission lines. II - Stokes profiles and vector field samples in sunspots

Tilak Hewagama; Drake Deming; Donald E. Jennings; Vladimir A. Osherovich; Gunter Wiedemann; D. Zipoy; Donald L. Mickey; Howard A. Garcia

This paper reports a polarimetric study of the extremely Zeeman-sensitive 12.32 μm neutral magnesium (Mg I) emission line from sunspots. A single blocked impurity band (BIB) detector in a cryogenic grating postdisperser was used to limit the McMath Fourier transform spectrometer (FTS) bandpass and obtain high signal/noise spectra at 0.005 cm −1 spectral resolution with 4″.5 spatial resolution. A polarization analyzer preceded the FTS and consisted of an antireflection coated CdS 1/4 waveplate, a thin film Ge linear polarizer, and a second 1/4 waveplate. The instrument polarization introduced by the McMath telescope is shown to be negligible for the purpose of 12 μm polarimetry. Stokes I, Q, U, V profiles were generated, with a time resolution of 12 minutes, by subtracting successive interferograms


The Astrophysical Journal | 1986

Detection of 12 micron Mg I and OH lines in stellar spectra

D. E. Jennings; Drake Deming; Gunter Wiedemann; John J. Keady

Infrared lines of Mg I and OH have been detected in stellar spectra near 12.3 microns. The Mg I 7i-6h transition was seen in Alpha Ori and Alpha Tau, and the R2e(23.5) and R1f(24.5) transitions of OH were seen in Alpha Ori. All lines appear in absorption, in contrast to the solar spectrum where the Mg I line shows a prominent emission core. The lack of emission in these low surface gravity stars is due to a greatly reduced volume recombination rate for the high-n states of Mg I, which is not fully compensated by the increased chromospheric scale height. The OH equivalent widths are sensitive to the temperature structure of the upper photosphere of Alpha Ori, and they indicate that the photosphere near tau 5000 of about 10 to the -5th is approximately 100 K hotter than is given by flux constant models. The OH measurements agree more closely with the 1981 semiemprical model of Basri, Linsky, and Eriksson (1981), which is based on Ca II and Mg II ultraviolet features.


The Astrophysical Journal | 1992

Limb observations of the 12.32 micron solar emission line during the 1991 July total eclipse

Drake Deming; Donald E. Jennings; George H. McCabe; Robert W. Noyes; Gunter Wiedemann; F. Espenak

The limb profile of the Mg I 12.32-micron emission line is determined by occultation in the July 11, 1991 total solar eclipse over Mauna Kea. It is shown that the emission peaks are very close to the 12-micron continuum limb, as predicted by recent theory for this line as a non-LTE photospheric emission. The increase in optical depth for this extreme limb-viewing situation indicates that most of the observed emission arises from above the chromospheric temperature minimum, and it is found that this emission is extended to heights well in excess of the model predictions. The line emission can be observed as high as 2000 km above the 12-micron continuum limb, whereas theory predicts it to remain observable no higher than about 500 km above the continuum limb. The substantial limb extension observed in this line is quantitatively consistent with limb extensions seen in the far-IR continuum, and it is concluded that it is indicative of departures from gravitational hydrostatic equilibrium, or spatial inhomogeneities, in the upper solar atmosphere.


The Astrophysical Journal | 1993

High-resolution mid-infrared spectra of Co II, Ni I, and Fe II in SN 1987A

D. E. Jennings; Robert J. Boyle; Gunter Wiedemann; S. H. Moseley

Ground-based infrared observations of SN 1987A on day 612 after the explosion have yielded resolved line profiles of Co II, Ni I, Fe II at 10.52, 11.31, and 17.94 micron, respectively. The spectra were taken at a resolving power of about 1000 with an array grating spectrometer on the 4 m telescope of Cerro Tololo Inter-American Observatory. Based on the observed line intensities we have estimated the minimum mass of each ion: M(Co II) = (6.0 +/- 1.8) x 10 exp -5 solar mass; M(Ni I) = (1.1 +/- 0.1) x 10 exp -3 solar mass; and M(Fe II) = (8.0 +/- 1.5) x 10 exp -3 solar mass. From these we infer total masses for cobalt, nickel, and iron in the ejecta. The nickel and iron line profiles are markedly asymmetric. We interpret these as arising from two components, one centered on the stellar rest velocity with an approximately 3250 km/s full width, and the second at about +1200 km/s with an approximately 1100 km/s full width. The asymmetry may represent a large-scale fracturing of the ejecta by Rayleigh-Taylor instabilities.


The Astrophysical Journal | 1990

Observations of the 12.3 micron Mg I emission line during a major solar flare

Drake Deming; Donald E. Jennings; Vladimir A. Osherovich; Gunter Wiedemann; Tilak Hewagama

The extremely Zeeman-sensitive 12.32 micron Mg I solar emission line was observed during a 3B/X5.7 solar flare on October 24, 1989. When compared to postflare values, Mg I emission-line intensity in the penumbral flare ribbon was 20 percent greater at the peak of the flare in soft X-rays, and the 12 micron continuum intensity was 7 percent greater. The flare also excited the emission line in the umbra where it is normally absent. The umbral flare emission exhibits a Zeeman splitting 200 G less than the adjacent penumbra, suggesting that it is excited at higher altitude. The absolute penumbral magnetic field strength did not change by more than 100 G between the flare peak and postflare period. However, a change in the inclination of the field lines, probably related to the formation and development of the flare loop system, was seen.


Symposium - International Astronomical Union | 2004

Infrared spectroscopic search for short-period giant extrasolar planets

Gunter Wiedemann; L. Drake Deming; Gordon L. Bjoraker; Cedric Goukenleuque

IR spectroscopy with a resolution ⋋/△⋋ ≳ 10, 000 is a powerful technique for the investigation of short-periodic giant extra-solar planets. For an unambiguous direct detection attempt one exploits the large-amplitude Doppler modulation of the planets IR spectrum. A successful measurement of the planets radial velocity amplitude would yield directly the planet-star mass ratio. Spectral information can be extracted if high per-pixel S/N levels are achieved.


Proceedings of The International Astronomical Union | 1994

12-µm Observations at the 1991 Eclipse

D. E. Jennings; Drake Deming; G. McCabe; Robert W. Noyes; Gunter Wiedemann; F. Espenak

The 11 July 1991 total solar eclipse over Mauna Kea was a unique opportunity to study the limb profile of the 12.32 µm MgI emission line. Our observations used the NASA 3-meter Infrared Telescope Facility,1 and a new Goddard large cryogenic grating spectrometer. Spectra of the line were taken in the slitless mode at second contact. The results show that the emission peaks within ~ 300 km of the 12-µm continuum limb. This agrees with recent theoretical predictions for this line as a NLTE upper photospheric emission feature. However, the increase in optical depth for this extreme limb-viewing situation means that most of the observed emission arises from aboveT min,and we find that this emission is extended to altitudes well in excess of the model predictions. The line emission can be traced to altitudes as high as 2000 km above the 12-µm continuum limb, whereas theory predicts it to remain observable no higher than 500 km above the continuum limb. The substantial limb-extension observed in this line is qualitatively consistent with limb-extensions seen by other observers in the far-IR continuum, and may be indicative of departures from gravitational hydrostatic equilibrium in the upper solar atmosphere, and/or may result from temperature and density inhomogeneities. The extended altitude of formation of this line enhances its value as a Zeeman probe of magnetic fields.

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D. E. Jennings

Goddard Space Flight Center

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Donald E. Jennings

Goddard Space Flight Center

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F. Espenak

Goddard Space Flight Center

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George H. McCabe

The Catholic University of America

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Gordon L. Bjoraker

Goddard Space Flight Center

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John J. Keady

Goddard Space Flight Center

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