Design for Enabling Echelle and OMR Spectrograph Observations for Point and Extended Sources on the Same Night at VBT

TL;DR

This paper presents a novel optical setup enabling simultaneous use of high-resolution echelle and OMR spectrographs on the VBT, allowing observations of point and extended sources in a single night.

Contribution

The paper introduces a new fiber and optics configuration that allows VBT to operate both spectrographs simultaneously, overcoming previous mode-switching limitations.

Findings

Optimized fiber and lenslet setup is undergoing lab testing.

Enables seamless switching between spectrographs during observations.

Enhances VBT's observational flexibility for diverse astronomical sources.

Abstract

The 2.34m Vainu Bappu Telescope (VBT) is a reflecting telescope that operates in two modes, prime focus and cassegrain focus, and is equipped with two instruments. In prime focus mode, the telescope has the F-number of f/3.25, and the High-Resolution Echelle Spectrograph (HRES) is employed through optical fiber. On the other hand, in cassegrain focus mode, the F-number is f/13, and the OMR Spectrograph (OMRS) is mounted for low and medium-resolution spectroscopy. Currently, the VBT faces a limitation: either the OMRS or the HRES can be used due to the switch in the heavy secondary mirror. To overcome this, we present a novel method enabling the OMRS to operate from prime mode alongside the HRES. The fiber setup for OMRS is optimized with a 25-lenslet + fiber-based Integral Field Unit (IFU) capable of observing both point and extended sources. The optimized lenslet, fiber, and fore optics design is undergoing lab testing. Our approach allows seamless operation of both spectrographs on the same night, enhancing the observational capabilities of astronomical studies with VBT.