Wide Field Optical Spectrograph (WFOS) is the first light instrument of Thirty Meter Telescope (TMT), which will be one of the wide field spectrographs for optical spectroscopy and can probe the faintest limits. In order to reach the faintest limits provided by the aperture of TMT, WFOS is designed to have multi-object slit-based spectrograph. WFOS can observe about ~60 objects in a given exposure and cover the full wavelength range in low resolution (R~1500) observing mode. Slitless spectroscopy has been popular in space based instruments, however it is not pursued in ground based observatories due to the background contamination. Considering large plate scale of TMT and oversampling of seeing disk we will be able to extract the individual spectra from WFOS slitless observing mode. Here we present the feasibility of slitless mode of TMT-WFOS and the sensitivity limit for various field densities focusing on MilkyWay satellite galaxies. We study the background contamination due to the bright targets and the density distribution of the satellite galaxy fields.
We present a conceptual design for a fiber positioning system for multi-object high-resolution spectroscopy, designed to be compatible with the upcoming large telescopes with a wide field of view. The design incorporates multiple Atmospheric Dispersion Correctors (ADCs) and tip-tilt mirrors that receive non-telecentric input from individual targets and direct it to the ADCs. Here, we introduce a mechanical design for the fiber positioner that accommodates the optics and operates in a curved focal plane with a Radius of Curvature (R) of 3m. This mechanical design provides four degrees of freedom to access the focal volume, enhancing targeting efficiency. The proposed design and an efficient target allocation algorithm ensure a targeting efficiency of approximately 80-100% for a primary observation session. We also present a methodology for target assignment, positioning, and quantification based on sequential and Monte Carlo (MC) algorithms. This method has been tested on realistic fields with varying target densities to validate its performance.
Highly multiplexed spectroscopic surveys have changed the astronomy landscape in recent years. However, these surveys are limited to low and medium spectral resolution. High spectral resolution spectroscopy is often photon starved and will benefit from a large telescope aperture. Multiplexed high-resolution surveys require a wide field of view and a large aperture for a suitable large number of bright targets. This requirement introduces several practical difficulties, especially for large telescopes, such as the future ELTs. Some of the challenges are the need for a wide field atmospheric dispersion corrector and to deal with the curved non-telecentric focal plane. Here we present a concept of Multi-Object Spectroscopy (MOS) mode for TMT High-Resolution Optical Spectrograph (HROS), where we have designed an atmospheric dispersion corrector for individual objects that fit inside a fiber positioner. We present the ZEMAX design and the performance of the atmospheric dispersion corrector for all elevations accessible by TMT.
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