TROIA adaptive optics system for DAG Telescope

ABSTRACT

This paper presents the specifications of TROIA - TuRkish adaptive Optics system for Infrared Astronomy system, the science rationale for these specifications, and description of the site technical and environmental conditions to be taken into account in the adaptive optics (AO) system design for the Eastern Anatolia Observatory - DAG telescope. With it’s 468 actuators, EMCCD camera, and the pyramid wavefront sensor configuration; TROIA is able to adapt the degree of correction to a given guide star (GS) brightness during observations. The high actuator density of TROIA AO system will allow DAG to perform astronomical observations at ExAO performances.

1. INTRODUCTION

TROIA, already built and delivered to Ataturk University Astrophysics research and Application Center (ATASAM), is the first Turkish AO system. The objective is double and ambitious: Allowing high resolution astronomy: seeing limited angular resolution is about 1”, but 20 times better with a 4 m telescope with adaptive optics correction. The potential science gain is enormous. Adaptive optics development: developing AO knowledge in universities in Turkey in order to offer this capabilities to the national astronomical community. At first light, DAG will be equipped with an AO system using natural guide stars (NGS). While laser guide stars (LGS) are highly desirable to maximize the sky coverage, AO laser technology is at a level of complexity that would be too difficult to handle on a first AO project. This shall be kept for a future upgrade of the system. TROIA is based on a flexible concept, where the number of corrected modes (aberrations) is systematically adapted to the atmospheric conditions and NGS brightness. This is possible thanks to the use of a 468 actuators deformable mirror (DM) and a pyramid based wavefront sensor (PWFS). In good conditions, Strehl ratio (image contrast) in the range 80 % to 90 % in the near infrared (NIR) will be achievable, while a decent Strehl ratio, allowing science data acquisition, will be accessible in moderate to bad seeing conditions. In this report, the specifications of TROIA system, the science rationale for these specifications, and description of the site technical and environmental conditions to be taken into account in the AO system design are presented.

Science Rationale

DAG first generation instruments

DAG first generation instruments will consist in a 30" FoV near-infrared (NIR) diffraction limited camera and a stellar coronagraph. An AO infrared imager on a 4 m telescope can support a broad range of scientific interests needing high-definition NIR imaging: from low-mass star and exoplanet search and characterization to studies of star-formation in the Milky Way and nearby galaxies, as well as analyses of intermediate and high redshift galaxies, including imaging of electromagnetic counterparts to gravitational wave detections. An AO based stellar coronagraph is the most suitable instrument to study nearby stars circum-stellar environment (protoplanetary discs, hot Jupiters etc.) DAG coronagraph will use a novel concept of star light suppression, using a programmable spatial light modulator (SLM) which can adapt to the structure of the star system, i.e it can suppress light from a multiple star system in one run, opening a completely new way of exploring stars’ immediate environment.