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The European Organisation for Astronomical Research in the Southern Hemisphere, commonly referred to as the European Southern Observatory (ESO), is an intergovernmental research organisation made up of 16 member states for ground-based astronomy. Created in 1962, ESO has provided astronomers with state-of-the-art research facilities and access to the southern sky. The organisation employs over 750 staff members and receives annual member state contributions of approximately €162 million. Its observatories are located in northern Chile. ESO has built and operated some of the largest and most technologically advanced telescopes. These include the 3.6 m New Technology Telescope, an early pioneer in the use of active optics, and the Very Large Telescope (VLT), which consists of four individual 8.2 m telescopes and four smaller auxiliary telescopes which can all work together or separately. The Atacama Large Millimeter Array observes the universe in the millimetre and submillimetre

High resolution differential laser interferometry for the VLTI (Very Large Telescope Interferometer)

Olivier Boris Scherler

One method for locating extrasolar planets is to observe the lateral movement of a star in the sky caused by a planet in orbit around it. In order to detect this displacement, the angular position of the star has to be measured with high accuracy. This technique is called astrometry. The Very Large Telescope Interferometer (VLTI) is operated by the European Southern Observatory and located at the Paranal Observatory in Chile. The purpose of the PRIMA instrument (Phase Referenced Imaging and Micro-arcsecond Astrometry) of the VLTI is to perform high-resolution astrometric measurements and high-resolution imaging of faint stars using white light interferometry, by combining the light collected by two telescopes. In order to allow the detection of extrasolar planets, the astrometric measurement has to be performed with micro-arcsecond accuracy. In astrometric mode the PRIMA instrument observes two targets at the same time: the object of scientific interest, and a bright reference star. The angular position of the science object relative to the reference star is obtained by monitoring the differential optical path travelled by the light of each object in two separate white-light interferometers. The aim of this work was to develop a high-resolution laser metrology based on superheterodyne interferometry, with an accuracy of 5 nm over a differential optical path of 100 mm. Moreover the laser source had to be stabilised on an absolute frequency reference, in order to ensure the long-term stability and calibration required to achieve the target performance. Superheterodyne interferometry allowed the direct measurement of the differential optical path using two heterodyne interferometers working with two different frequency shifts. The differential phase measurement between the two interferometers was obtained by electronic mixing of the two heterodyne signals, leading to the differential optical path needed for the astrometric measurement

Institut de Microtechnique, Université de Neuchâtel2006

TDCOSMO II. Six new time delays in lensed quasars from high-cadence monitoring at the MPIA 2.2m telescope

Vivien François Bonvin, Hung-Hsu Chan, Frédéric Courbin, Sun Hee Kim, Cameron Alexander Campbell Lemon, Martin Raoul Robert Millon, Eric Gérard Guy Paic, Karina Alexandra Rojas Olate

We present six new time-delay measurements obtained from Rc-band monitoring data acquired at the Max Planck Institute for Astrophysics (MPIA) 2.2m telescope at La Silla observatory between October 2016 and February 2020. The lensed quasars HE0047 1756, WG0214 2105, DES 0407 5006, 2M1134 2103, PSJ 1606 2333, and DES 2325 5229 were observed almost daily at high signal-to-noise ratio to obtain highquality light curves where we can record fast and small-amplitude variations of the quasars. We measured time delays between all pairs of multiple images with only one or two seasons of monitoring with the exception of the time delays relative to image D of PSJ 1606 2333. The most precise estimate was obtained for the delay between image A and image B of DES 0407 5006, where tau AB = 128:4+(3:5) (3:8) d (2.8% precision) including systematics due to extrinsic variability in the light curves. For HE0047 1756, we combined our high-cadence data with measurements from decade-long light curves from previous COSMOGRAIL campaigns, and reach a precision of 0.9 d on the final measurement. The present work demonstrates the feasibility of measuring time delays in lensed quasars in only one or two seasons, provided high signal-to-noise ratio data are obtained at a cadence close to daily.

EDP SCIENCES S A2020

COSMOGRAIL XVII. Time delays for the quadruply imaged quasar PG 1115+080

Vivien François Bonvin, Hung-Hsu Chan, Frédéric Courbin, Sun Hee Kim, Georges Meylan, Martin Raoul Robert Millon, Eric Gérard Guy Paic, Karina Alexandra Rojas Olate, Malte Tewes

We present time-delay estimates for the quadruply imaged quasar PG 1115+080. Our results are based on almost daily observations for seven months at the ESO MPIA 2.2m telescope at La Silla Observatory, reaching a signal-to-noise ratio of about 1000 per quasar image. In addition, we re-analyze existing light curves from the literature that we complete with an additional three seasons of monitoring with the Mercator telescope at La Palma Observatory. When exploring the possible source of bias we considered the so-called microlensing time delay, a potential source of systematic error so far never directly accounted for in previous time-delay publications. In 15 yr of data on PG 1115+080, we find no strong evidence of microlensing time delay. Therefore not accounting for this effect, our time-delay estimates on the individual data sets are in good agreement with each other and with the literature. Combining the data sets, we obtain the most precise time-delay estimates to date on PG 1115+080, with Delta t(AB) = 8.3(-1.6)(+1.5) days (18.7% precision), Delta t(AC) = 9.9(-1.1)(+1.1) days (11.1%) and Delta t(BC) = 18.8(-1.6)(+1.6) days (8.5%). Turning these time delays into cosmological constraints is done in a companion paper that makes use of ground-based Adaptive Optics (AO) with the Keck telescope.

EDP SCIENCES S A2018

High resolution differential laser interferometry for the VLTI (Very Large Telescope Interferometer)

Olivier Boris Scherler

Institut de Microtechnique, Université de Neuchâtel2006