Stability analysis of VBT Echelle spectrograph for precise radial velocity measurements

摘要

A fiber-fed Echelle spectrograph at 2.3 m Vainu Bappu Telescope (VBT),Kavalur, has been in operation since 2005. Owing to various technologicaladvancements in precision spectroscopy in recent years, several researchavenues have been opened in observational astronomy. These developments havecreated a demand to improve the Doppler precision of our spectrograph.Currently, the stability of the instrument is compromised by the temperatureand pressure fluctuations inside the Echelle room. Further, a better wavelengthcalibration approach is needed to carefully track and disentangle theinstrumental effects from stellar spectra. While planning a possible upgradewith an Iodine absorption gas cell, we measured the raw stability of thespectrograph using a series of calibration frames taken with the ThAr gasdischarge lamp. The time series data were analysed with cross-correlationmethod and the shift in ThAr emission lines was accurately measured acrossdifferent Echelle orders. In this paper, we present our stability analysismethodology and results for the Kavalur spectrograph. We also identify possiblesources of error and discuss our strategy to mitigate them.