The VLT/ERIS grating vector Apodizing Phase Plate coronagraph

Authors: M. A. Kenworthy, F. A. Dannert, J. Hayoz, D. Doelman, B. J. Sutlieff, P. L. Liu, F. Snik, M. J. Bonse, S. P. Quanz, C. U. Keller, O. Absil, G. Orban de Xivry, R. J. De Rosa, C. Ginski, X. T. Chen, A. Zurlo, B. A. Biller, J. L. Birkby, A. Baruffolo, Y. Dalliliar, R. Davies, M. Dolci, H. Feuchtgruber, A. Glauser, P. Grani, K. Kravchenko, M. MacIntosh, A. Puglisi, C. Rau, A. Riccardi, E. Sturm, W. Taylor Date: 2026-03-25 Paper ID: openalex:2603.24469

Summary

This paper details the design, laboratory fabrication, and on-sky validation of the grating vector apodizing phase plate (gvAPP) coronagraph implemented on the Very Large Telescope’s ERIS instrument. While the device achieved its target raw contrast of $1 \times 10^{-5}$ in the lab across K to L bands, on-sky testing revealed that electronic detector noise artifacts limited the achievable post-processed contrast. The authors recommend its use for characterizing known substellar companions placed within the coronagraphic dark holes, and note the leakage term can serve as a photometric reference. This work serves as a crucial pathfinder for future Extremely Large Telescope instruments featuring improved gvAPP designs.

Key Contributions

• Successfully manufactured and tested the grating vector apodizing phase plate (gvAPP) coronagraph for the ERIS instrument on the VLT.
• Achieved the design specification for optic transmission (90% in K bands, 60% in L band) and raw contrast performance ($1 \times 10^{-5}$) in laboratory settings.
• Identified electronic detector noise (cross-talk from Airy core PSF) as the limiting factor preventing achievement of post-processed contrast specifications in on-sky observations.
• Recommended the gvAPP as a viable tool for characterizing substellar companions by placing them in coronagraphic dark holes, despite on-sky contrast limitations.

Limitations

The post-processed contrast performance ($5 \times 10^{-5}$) was not reached in on-sky observations due to electronic detector noise causing cross-talk artifacts. Contrast performance may limit time-series photometry to only the brightest targets.

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