# Stability analysis of VBT Echelle spectrograph for precise radial velocity measurements

## TL;DR

This paper analyzes the stability of the VBT Echelle spectrograph for precise radial velocity measurements, focusing on instrumental stability issues and calibration improvements to enhance Doppler precision.

## Contribution

It introduces a methodology for stability analysis of the spectrograph and discusses potential upgrades and error mitigation strategies.

## Key findings

- Measured spectrograph stability using ThAr calibration frames
- Identified temperature and pressure fluctuations as stability sources
- Proposed calibration and upgrade strategies for improved precision

## Abstract

A fiber-fed Echelle spectrograph at 2.3 m Vainu Bappu Telescope (VBT), Kavalur, has been in operation since 2005. Owing to various technological advancements in precision spectroscopy in recent years, several research avenues have been opened in observational astronomy. These developments have created a demand to improve the Doppler precision of our spectrograph. Currently, the stability of the instrument is compromised by the temperature and pressure fluctuations inside the Echelle room. Further, a better wavelength calibration approach is needed to carefully track and disentangle the instrumental effects from stellar spectra. While planning a possible upgrade with an Iodine absorption gas cell, we measured the raw stability of the spectrograph using a series of calibration frames taken with the ThAr gas discharge lamp. The time series data were analysed with cross-correlation method and the shift in ThAr emission lines was accurately measured across different Echelle orders. In this paper, we present our stability analysis methodology and results for the Kavalur spectrograph. We also identify possible sources of error and discuss our strategy to mitigate them.