Design and development of Fabry-Perot based wavelength calibration system for PARAS-2 spectrograph
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| Format: | Preprint |
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2026
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| author | Das, Shubhendra Nath Bharadwaj, Kapil Kumar Chakraborty, Abhijit Lad, Kevikumar A. Neelam, Jajaendra Siva Seshu Vera Prasad Sharma, Rishikesh Jithendran, Nikitha Joshi, Vishal |
| author_facet | Das, Shubhendra Nath Bharadwaj, Kapil Kumar Chakraborty, Abhijit Lad, Kevikumar A. Neelam, Jajaendra Siva Seshu Vera Prasad Sharma, Rishikesh Jithendran, Nikitha Joshi, Vishal |
| contents | Precise wavelength calibration is essential for high-precision radial velocity (RV) spectrographs, necessitating a stable calibrator that provides a dense grid of uniformly spaced lines to accurately determine stellar line positions and monitor instrumental drifts. In this work, we present the development of a cost-effective Fabry-Perot (FP) etalon-based wavelength calibrator designed to overcome the limitations of conventional sources such as hollow cathode lamps (HCLs) and iodine cells. This FP calibrator, combined with a Xenon (Xe) arc lamp assembly, has been integrated with the PARAS-2 spectrograph on the PRL 2.5m telescope at Mount Abu Observatory. Operated under controlled temperature and pressure conditions, the system generates a dense, comb-like spectrum covering 62 echelle orders with more than 10,000 well-defined and stable spectral lines, enabling precise measurement of instrumental drift. Initial results show that the free spectral range (FSR) varies from 0.16 Å~near 4000 Å~to 0.49 Å~ near 7000 Å, with a value of 0.3 Å~around the central wavelength of 5500 Å~. The estimated finesse ranges from 9 near 4000 Å~to 19 near 6900 Å, with an approximate value of 17 at 5500 Å. The temperature and pressure stability tests demonstrate RMS variations of $0.002 ^\circ\mathrm{C}$ and $5\times10^{-4}$ mbar, respectively. Based on these values, the theoretical stability of the FP wavelength calibrator is estimated to be within 10 cm/s, establishing it as a reliable alternative to Laser Frequency Combs (LFCs) for high-resolution spectroscopic calibration. We present an initial assessment of the RV stability of the FP calibrator, yielding 40-70 cm/s of relative drifts, which are up for further investigations. The observed excess over the theoretically estimated limit is likely attributable to instabilities arising from arc wandering in the xenon arc lamp. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2606_01769 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Design and development of Fabry-Perot based wavelength calibration system for PARAS-2 spectrograph Das, Shubhendra Nath Bharadwaj, Kapil Kumar Chakraborty, Abhijit Lad, Kevikumar A. Neelam, Jajaendra Siva Seshu Vera Prasad Sharma, Rishikesh Jithendran, Nikitha Joshi, Vishal Instrumentation and Methods for Astrophysics Earth and Planetary Astrophysics Precise wavelength calibration is essential for high-precision radial velocity (RV) spectrographs, necessitating a stable calibrator that provides a dense grid of uniformly spaced lines to accurately determine stellar line positions and monitor instrumental drifts. In this work, we present the development of a cost-effective Fabry-Perot (FP) etalon-based wavelength calibrator designed to overcome the limitations of conventional sources such as hollow cathode lamps (HCLs) and iodine cells. This FP calibrator, combined with a Xenon (Xe) arc lamp assembly, has been integrated with the PARAS-2 spectrograph on the PRL 2.5m telescope at Mount Abu Observatory. Operated under controlled temperature and pressure conditions, the system generates a dense, comb-like spectrum covering 62 echelle orders with more than 10,000 well-defined and stable spectral lines, enabling precise measurement of instrumental drift. Initial results show that the free spectral range (FSR) varies from 0.16 Å~near 4000 Å~to 0.49 Å~ near 7000 Å, with a value of 0.3 Å~around the central wavelength of 5500 Å~. The estimated finesse ranges from 9 near 4000 Å~to 19 near 6900 Å, with an approximate value of 17 at 5500 Å. The temperature and pressure stability tests demonstrate RMS variations of $0.002 ^\circ\mathrm{C}$ and $5\times10^{-4}$ mbar, respectively. Based on these values, the theoretical stability of the FP wavelength calibrator is estimated to be within 10 cm/s, establishing it as a reliable alternative to Laser Frequency Combs (LFCs) for high-resolution spectroscopic calibration. We present an initial assessment of the RV stability of the FP calibrator, yielding 40-70 cm/s of relative drifts, which are up for further investigations. The observed excess over the theoretically estimated limit is likely attributable to instabilities arising from arc wandering in the xenon arc lamp. |
| title | Design and development of Fabry-Perot based wavelength calibration system for PARAS-2 spectrograph |
| topic | Instrumentation and Methods for Astrophysics Earth and Planetary Astrophysics |
| url | https://arxiv.org/abs/2606.01769 |