RSAA Colloquia / Seminars / Feast-of-Facts: Monday, 19 March 2018, 11:00-12:00; Duffield Lecture Theatre

Bingqiu Chen, Zhengyang Li, and Yang Huang

"Multi-channel Photometric Survey Telescope - Mephisto (Bingqiu Chen & Zhengyang Li; 35min) / Galactic disk chemistry and kinematics from LAMOST (Yang Huang; 25min)"

[Multi-channel Photometric Survey Telescope - Mephisto] - Large-scale astronomical surveys play a key in modern astrophysical studies, leading to new discoveries and revolutionizing our understanding of the origin and evolution of the universe. The fast technological advances are changing the ways we view the sky, from snapshot taking in surveys such as SDSS and XSTPS-GAC, to movie shooting by observing the same sky thousands of times in surveys such as ZTF, Skymapper, WFST and LSST. The developments open up the possibility to probe the universe in multi-dimensions, in particular in time domain. Build upon the experiences of those surveys and to make a step forward, we plan to build a wide-field multi-channel survey telescope - the Multi-channel Photometric Survey Telescope (Mephisto), the first of this type in the world. Mephisto has a 1.6m primary and is equipped with three CCD cameras of a field-of-view 3.14 deg^2, capable of simultaneously imaging the same patch of sky in three bands (ugi or vrz). The three cameras boast a total of 1.4 Giga pixels. Mephisto will yield real-time colours of astronomical objects with unprecedented accuracies, and deliver for the first time a coloured documentary of our evolving universe. The development of Mephisto is expected to take four years (2018-2021), and is expected to be operational in 2022. The Mephisto surveys will have two components: the Mephisto-W covering the whole northern sky of ~26,000 deg^2 and the Mephisto-D, Mephisto-H and Mephisto-M covering sky areas of respectively thousands, hundreds and tens of square degrees with a corresponding cadence of days, hours and minutes, targeting specifically fast variables and transients. The unique capability of recording high-precision real-time colours, thus allowing quick and robust classification of fast transients, makes Mephisto particularly powerful in time domain astrophysics. Celestial objects and forefront problems that Mephisto will target and tackle include, for example, astrophysical transients and the underlying physics, galaxies and cosmology, extreme metal-poor stars and Galactic archeology, stars and planetary systems including the Solar System. Mephisto data products will be publicly available to the domestic and international communities. / [Optical design for Mephisto] - Multiple channel Photometric Survey Telescope (Mephisto) is an ambitious project aimed at efficient survey the northern sky with three multiple band simultaneously. Mephisto, with 1.6meter aperture 2 degrees FOV, was design as Ritchey-Chretien type, similar with SKYMAPPER. Equipped with a field corrector, the optics can delivered an ideal image quality of 0.3arcsec (80% encircled energy circle diameter), an observation image quality of 0.6arcsec without ADC. The optical splitting system was tricky. For avoiding the astigmatism introduced by the dichroic mirrors, 300mm beam splitting prisms were used for splitting the convergent beam to 0.31-0.41, 0.41-0.70, and 0.70-1 micrometer. Preliminary results show that the splitter is feasible and qualified. / [Galactic disk chemistry and kinematics from LAMOST] - One of the fundamental tasks of modern astrophysics is to understand how galaxies form and evolve. Generally, the quest can be pursed in two ways: statistical analyses of large samples of distant galaxies (deep-field cosmology) and detailed studies of large samples of member stars in the Local Group of galaxies including our own, the Milky Way (near-field cosmology). Initiated and aimed to make a major contribution to this latter, ’near-field cosmology’ quest for understanding the galaxy formation and evolution, the LAMOST Galactic Spectroscopic Surveys have hitherto collected quality spectra of over 7M Galactic stars, and this number is still increasing at a rate of 1M per annum. Combining with data from other available photometric, astrometric and spectroscopic surveys (e.g. Gaia, APOGEE, GALAH), the Surveys have yielded a unique dataset to help us draw an exquisite picture of unprecedented detail of our Galaxy, in particular of the Galactic disk. In this talk, I will present the scope and motivation, data reduction and release, as well as scientific results of the surveys.