First result with AMBER+FINITO on the VLTI: The high-precision angular diameter of V3879 Sgr

TL;DR

This paper demonstrates high-precision stellar diameter measurements using the AMBER instrument with VLTI and FINITO fringe tracking, achieving 25 micro-arcsecond accuracy on V3879 Sgr, showcasing the setup's potential for advanced stellar studies.

Contribution

First demonstration of AMBER+FINITO on VLTI achieving micro-arcsecond precision in stellar diameter measurements, enabling new stellar astrophysics applications.

Findings

Achieved 25 micro-arcsecond accuracy in diameter measurement

Confirmed the round photosphere of V3879 Sgr at sub-percent level

Demonstrated technique independence from absolute calibration

Abstract

Our goal is to demonstrate the potential of the interferometric AMBER instrument linked with the Very Large Telescope Interferometer (VLTI) fringe-tracking facility FINITO to derive high-precision stellar diameters. We use commissioning data obtained on the bright single star V3879 Sgr. Locking the interferometric fringes with FINITO allows us to record very low contrast fringes on the AMBER camera. By fitting the amplitude of these fringes, we measure the diameter of the target in three directions simultaneously with an accuracy of 25 micro-arcseconds. We showed that V3879 Sgr has a round photosphere down to a sub-percent level. We quickly reached this level of accuracy because the technique used is independent from absolute calibration (at least for baselines that fully span the visibility null). We briefly discuss the potential biases found at this level of precision. The proposed AMBER+FINITO instrumental setup opens several perspectives for the VLTI in the field of stellar astrophysics, like measuring with high accuracy the oblateness of fast rotating stars or detecting atmospheric starspots.