| Name: Abhirami S Raghu |
| Affiliation: Indian Institute of Technology, Kanpur |
| Conference ID: ASI2026_46 |
| Title: Mid-IR Water-Vapor Seeing: Implications for METIS High-Contrast Imaging from VLTI Data |
| Abstract Type: Poster |
| Abstract Category: Facilities, Technologies and Data science |
| Author(s) and Co-Author(s) with Affiliation: Abhirami S Raghu(Indian Institute of Technology Kanpur, 208016, India), Prashant Pathak(Indian Institute of Technology Kanpur, 208016, India), Olivier Absil(STAR Institute, Université de Liège, Allée du Six Août 19c, B-4000 Liège, Belgium) |
| Abstract: Mid-infrared (mid-IR) observations from ground-based telescopes are significantly affected by spatial and temporal fluctuations in atmospheric water vapour (WV), which introduce chromatic phase errors that are not corrected by near-infrared adaptive optics. This poses a major challenge for high-contrast imaging (HCI) instruments such as the Mid-infrared Extremely Large Telescope Imager and Spectrograph (METIS), which aims to directly detect thermal emission from exoplanets in the N-band (8–13 𝜇m).
We analyze K-band fringe tracker data from the GRAVITY instrument at the Very Large Telescope Interferometer (VLTI) and derive the optical path difference (OPD) between the group delay and phase delay measurements to quantify wavefront errors induced by WV fluctuations. This OPD is directly linked to the differential WV column density (𝛴) above the various telescopes of the interferometric array. In this study, we explored the variability of the 𝛴 and studied its correlation with various atmospheric parameters such as precipitable water vapor (PWV), seeing, wind speed, AH, RH and airmass. The analysis showed that 𝛴 is strongly correlated with PWV, supporting PWV as a robust metric for WV-induced fluctuations. We further explore whether this correlation depends on the vertical profile of PWV across the atmosphere. We then quantify how increasing PWV modulates 𝛴 variability using power-spectral-density analysis. Together, these results provide a quantitative basis for improving the operational capabilities of next-generation mid-IR HCI instruments such as METIS.
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