Dispersion affecting the VLTI and 10 micron interferometry using MIDI

Jeffrey A. Meisner; Rudolf S. Le Poole

doi:10.1117/12.459072

21 February 2003 Dispersion affecting the VLTI and 10-micron interferometry using MIDI

Jeffrey A. Meisner, Rudolf S. Le Poole

Proceedings Volume 4838, Interferometry for Optical Astronomy II; (2003) https://doi.org/10.1117/12.459072
Event: Astronomical Telescopes and Instrumentation, 2002, Waikoloa, Hawai'i, United States

Abstract

A wideband interferometer is sensitive to the effects of longitudinal dispersion which affect the interfering light beams unequally. At shorter wavelengths the major effect of dispersion is from dry air itself, while at mid infrared wavelengths the effect of water vapor is dominant. MIDI, the future 10 micron instrument of the VLTI, will experience significant effects from the imbalances in the water vapor content affecting the paths of the two interfering beams. This imbalance will include terms due to the unbalanced air paths in the delay line, random atmospheric humidity fluctuations in the lines-of-sight to the star, and random humidity variations inside of the VLTI delay line tunnels. Large amounts of dispersion, if not monitored, can reduce the accuracy of measured visibility amplitudes. Measurements of the visibility phase as a function of wavelength will be highly sensitive to dispersion. This will then become a source of noise in results dependent on the phase of interference, such as imaging of non-symmetric objects, or detection of faint companions. In addition to dispersion over the 7 - 14 micron region detected by MIDI, observations using phase tracking with detection in the near IR, could be catastrophically affected by differential phase delays between the 2 micron and 10 micron bands. Dispersion measurements from VINCI observing in the K band, both due to dry air and to water vapor, are presented. Combining VINCI results with published data from millimeter wave measurements leads us to expect atmospheric differential water vapor fluctuations to exceed 1 mole/m² rms over typical baselines. Specific effects from such a level of unmonitored dispersion variations are presented, which demand corrective action. Various solutions to monitor water vapor dispersion in realtime are considered.

Citation Download Citation

Jeffrey A. Meisner and Rudolf S. Le Poole "Dispersion affecting the VLTI and 10-micron interferometry using MIDI", Proc. SPIE 4838, Interferometry for Optical Astronomy II, (21 February 2003); https://doi.org/10.1117/12.459072

ACCESS THE FULL ARTICLE

INSTITUTIONAL
Select your institution to access the SPIE Digital Library.

SELECT YOUR INSTITUTION

PERSONAL
Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.

PERSONAL SIGN IN

No SPIE Account? Create one

PURCHASE THIS CONTENT

SUBSCRIBE TO DIGITAL LIBRARY

50 downloads per 1-year subscription

Members: $195

Non-members: $335 ADD TO CART

25 downloads per 1 - year subscription

Members: $145

Non-members: $250 ADD TO CART

PURCHASE SINGLE ARTICLE

Includes PDF, HTML & Video, when available