ABSTRACT We have obtained contemporaneous optical interferometry and spectropolarimetry of seven ... more ABSTRACT We have obtained contemporaneous optical interferometry and spectropolarimetry of seven Be stars. The interferometry was done using both continuum and narrow H α line filters to observe the circumstellar envelope emission. The envelopes of all seven stars were resolved interferometrically in H α. Of these seven stars, the envelopes of four were not circularly symmetric and showed clear evidence of elongation.
Astron. Astrophys. 312, 160-166 (1996) ASTRONOMY AND ASTROPHYSICS Angular diameter and limb darke... more Astron. Astrophys. 312, 160-166 (1996) ASTRONOMY AND ASTROPHYSICS Angular diameter and limb darkening of Arcturus A. Quirrenbach1'2'3, D.
ABSTRACT We use a numerical simulation to investigate the effectiveness of pinhole spatial filter... more ABSTRACT We use a numerical simulation to investigate the effectiveness of pinhole spatial filters for optical/IR interferometers and to compare them with single-mode optical fibre spatial filters and interferometers without spatial filters. We show that fringe visibility measurements in interferometers containing spatial filters are much less affected by changing seeing conditions than equivalent measurements without spatial filters.
ABSTRACT Group delay fringe tracking using spectrally dispersed fringes is suitable for stabilizi... more ABSTRACT Group delay fringe tracking using spectrally dispersed fringes is suitable for stabilizing the optical path difference in ground-based astronomical optical interferometers in low light level situations.
abstract The VLTI Spectro Imager project aims to perform imaging with a temporal resolution of 1 ... more abstract The VLTI Spectro Imager project aims to perform imaging with a temporal resolution of 1 night and with a maximum angular resolution of 1 milliarcsecond, making best use of the Very Large Telescope Interferometer capabilities. To fulfill the scientific goals (see Garcia et. al.), the system requirements are: a) combining 4 to 6 beams; b) working in spectral bands J, H and K; c) spectral resolution from R= 100 to 12000; and d) internal fringe tracking on-axis, or off-axis when associated to the PRIMA dual-beam facility.
Abstract: The VLTI Spectro Imager (VSI) was proposed as a second-generation instrument of the Ver... more Abstract: The VLTI Spectro Imager (VSI) was proposed as a second-generation instrument of the Very Large Telescope Interferometer providing the ESO community with spectrally-resolved, near-infrared images at angular resolutions down to 1.1 milliarcsecond and spectral resolutions up to R= 12000. Targets as faint as K= 13 will be imaged without requiring a brighter nearby reference object.
Abstract: Fringe tracking in interferometers is typically analyzed with the implicit assumption t... more Abstract: Fringe tracking in interferometers is typically analyzed with the implicit assumption that there is a single phase associated with each telescope in the array. If the telescopes have apertures significantly larger than r0 and only partial adaptive optics correction, then the phase measured by a fringe sensor may differ significantly from the" piston" component of the aperture phase. In some cases, speckle noise will cause" branch points" in the measured phase as a function of time, causing large and sudden jumps in the phase.
Abstract Context. Long-baseline optical interferometry uses the power spectrum and bispectrum con... more Abstract Context. Long-baseline optical interferometry uses the power spectrum and bispectrum constructs as fundamental observables. Noise arising in the detection of the fringe pattern results in both variance and biases in the power spectrum and bispectrum. Previous work on correcting the biases and estimating the variances for these quantities typically includes restrictive assumptions about the sampling of the interferogram and/or about the relative importance of Poisson and Gaussian noise sources.
Nowadays, compact sources relatively warm like surfaces of nearby stars, circumstellar environmen... more Nowadays, compact sources relatively warm like surfaces of nearby stars, circumstellar environments of stars from early stages to the most evolved ones and surroundings of active galactic nuclei can be investigated at milli-arcsecond scales only with the VLT in its interferometric mode. We propose a spectro-imager, named VSI (VLTI spectro-imager), which is capable to probe these sources both over spatial and spectral scales in the near-infrared domain.
abstract Conventional adaptive optics systems using a single wavefront corrector suffer from a li... more abstract Conventional adaptive optics systems using a single wavefront corrector suffer from a limited field of view. Multi-conjugate adaptive optics use two or more corrector to improve off-axis correction. We describe an experimental system which simulates dual-layer turbulence, and present results using a single corrector showing anisoplanatic effects. Future experiments using a second corrector are also discussed.
Astron. Astrophys. 286, 1019-1027 (1994) ASTRONOMY AND ASTROPHYSICS Phase-referenced visibility a... more Astron. Astrophys. 286, 1019-1027 (1994) ASTRONOMY AND ASTROPHYSICS Phase-referenced visibility averaging in optical long-baseline interferometry A. Quirrenbach1'2'3, D.
Mon. Not. R. astr. Soc. (1990) 245, Short Communication, 7p-1 1~ 1 INTRODUCTION The M-supergiant ... more Mon. Not. R. astr. Soc. (1990) 245, Short Communication, 7p-1 1~ 1 INTRODUCTION The M-supergiant star Betelgeuse ( a Orionis) shows irregular photometric, polarimetric and spectroscopic vanability, suggesting the occurrence of complex activity on the star's surface and in its extended atmosphere.
ABSTRACT We have obtained contemporaneous optical interferometry and spectropolarimetry of seven ... more ABSTRACT We have obtained contemporaneous optical interferometry and spectropolarimetry of seven Be stars. The interferometry was done using both continuum and narrow H α line filters to observe the circumstellar envelope emission. The envelopes of all seven stars were resolved interferometrically in H α. Of these seven stars, the envelopes of four were not circularly symmetric and showed clear evidence of elongation.
Astron. Astrophys. 312, 160-166 (1996) ASTRONOMY AND ASTROPHYSICS Angular diameter and limb darke... more Astron. Astrophys. 312, 160-166 (1996) ASTRONOMY AND ASTROPHYSICS Angular diameter and limb darkening of Arcturus A. Quirrenbach1'2'3, D.
ABSTRACT We use a numerical simulation to investigate the effectiveness of pinhole spatial filter... more ABSTRACT We use a numerical simulation to investigate the effectiveness of pinhole spatial filters for optical/IR interferometers and to compare them with single-mode optical fibre spatial filters and interferometers without spatial filters. We show that fringe visibility measurements in interferometers containing spatial filters are much less affected by changing seeing conditions than equivalent measurements without spatial filters.
ABSTRACT Group delay fringe tracking using spectrally dispersed fringes is suitable for stabilizi... more ABSTRACT Group delay fringe tracking using spectrally dispersed fringes is suitable for stabilizing the optical path difference in ground-based astronomical optical interferometers in low light level situations.
abstract The VLTI Spectro Imager project aims to perform imaging with a temporal resolution of 1 ... more abstract The VLTI Spectro Imager project aims to perform imaging with a temporal resolution of 1 night and with a maximum angular resolution of 1 milliarcsecond, making best use of the Very Large Telescope Interferometer capabilities. To fulfill the scientific goals (see Garcia et. al.), the system requirements are: a) combining 4 to 6 beams; b) working in spectral bands J, H and K; c) spectral resolution from R= 100 to 12000; and d) internal fringe tracking on-axis, or off-axis when associated to the PRIMA dual-beam facility.
Abstract: The VLTI Spectro Imager (VSI) was proposed as a second-generation instrument of the Ver... more Abstract: The VLTI Spectro Imager (VSI) was proposed as a second-generation instrument of the Very Large Telescope Interferometer providing the ESO community with spectrally-resolved, near-infrared images at angular resolutions down to 1.1 milliarcsecond and spectral resolutions up to R= 12000. Targets as faint as K= 13 will be imaged without requiring a brighter nearby reference object.
Abstract: Fringe tracking in interferometers is typically analyzed with the implicit assumption t... more Abstract: Fringe tracking in interferometers is typically analyzed with the implicit assumption that there is a single phase associated with each telescope in the array. If the telescopes have apertures significantly larger than r0 and only partial adaptive optics correction, then the phase measured by a fringe sensor may differ significantly from the" piston" component of the aperture phase. In some cases, speckle noise will cause" branch points" in the measured phase as a function of time, causing large and sudden jumps in the phase.
Abstract Context. Long-baseline optical interferometry uses the power spectrum and bispectrum con... more Abstract Context. Long-baseline optical interferometry uses the power spectrum and bispectrum constructs as fundamental observables. Noise arising in the detection of the fringe pattern results in both variance and biases in the power spectrum and bispectrum. Previous work on correcting the biases and estimating the variances for these quantities typically includes restrictive assumptions about the sampling of the interferogram and/or about the relative importance of Poisson and Gaussian noise sources.
Nowadays, compact sources relatively warm like surfaces of nearby stars, circumstellar environmen... more Nowadays, compact sources relatively warm like surfaces of nearby stars, circumstellar environments of stars from early stages to the most evolved ones and surroundings of active galactic nuclei can be investigated at milli-arcsecond scales only with the VLT in its interferometric mode. We propose a spectro-imager, named VSI (VLTI spectro-imager), which is capable to probe these sources both over spatial and spectral scales in the near-infrared domain.
abstract Conventional adaptive optics systems using a single wavefront corrector suffer from a li... more abstract Conventional adaptive optics systems using a single wavefront corrector suffer from a limited field of view. Multi-conjugate adaptive optics use two or more corrector to improve off-axis correction. We describe an experimental system which simulates dual-layer turbulence, and present results using a single corrector showing anisoplanatic effects. Future experiments using a second corrector are also discussed.
Astron. Astrophys. 286, 1019-1027 (1994) ASTRONOMY AND ASTROPHYSICS Phase-referenced visibility a... more Astron. Astrophys. 286, 1019-1027 (1994) ASTRONOMY AND ASTROPHYSICS Phase-referenced visibility averaging in optical long-baseline interferometry A. Quirrenbach1'2'3, D.
Mon. Not. R. astr. Soc. (1990) 245, Short Communication, 7p-1 1~ 1 INTRODUCTION The M-supergiant ... more Mon. Not. R. astr. Soc. (1990) 245, Short Communication, 7p-1 1~ 1 INTRODUCTION The M-supergiant star Betelgeuse ( a Orionis) shows irregular photometric, polarimetric and spectroscopic vanability, suggesting the occurrence of complex activity on the star's surface and in its extended atmosphere.
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Papers by David Buscher