Exoplanets, -moons, -comets

An Initial Assessment Of The Hanle Echelle Spectrograph For Exoplanet Atmosphere Studies

By Keith Cowing

Status Report

astro-ph.EP

September 24, 2025

Filed under astro-ph.EP, atmosphee, exoplanet, Hanle Echelle Spectrograph, HD 209458b, Himalayan Chandra Telescope, hot jupiter, Hubble, JWST

An Initial Assessment Of The Hanle Echelle Spectrograph For Exoplanet Atmosphere Studies — Observed spectra after dividing by the out-of-transit spectrum (residuals), shown in the stellar rest frame. Vertical orange and green dotted lines indicate the positions of the Na D2 and D1 lines, respectively. The region between the two horizontal dotted lines corresponds to in-transit observations, while regions outside represent out-of-transit data. The tilted red lines at the positions of Na D2 and D1 indicate the expected shift of the planetary absorption signal. — astro-ph.EP

Transmission spectroscopy is an effective technique for probing exoplanetary atmospheres.

While most observations have relied on space facilities such as HST and JWST, ground-based high-resolution transmission spectroscopy (HRTS) has also provided valuable insights by resolving individual atomic features.

In this work, we present an initial performance assessment and feasibility test of the Hanle Echelle Spectrograph (HESP) on the 2 m Himalayan Chandra Telescope (HCT) for HRTS. As a benchmark, we observed the hot Jupiter HD 209458b during a single transit at a resolution of R = 30,000. We developed a Python-based, semi-automated data reduction and analysis pipeline that includes corrections for telluric contamination and stellar radial velocity shifts.

The final achieved signal-to-noise ratio and spectral stability allow us to probe for features at the 0.1% level. This work establishes a methodology and demonstrates the operational capability of the HESP-HCT for obtaining high-resolution transmission spectra.

Manjunath Bestha, Athira Unni, T. Sivarani, Shivangi Menon, Parvathy M, Arun Surya, Pallavi Saraf, Devika Divakar, Lokesh Manickavasaham

Comments: Published in the SPIE Proceedings
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2509.17142 [astro-ph.EP] (or arXiv:2509.17142v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2509.17142
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Related DOI:
https://doi.org/10.1117/12.3064331
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Submission history
From: Manjunath Bestha
[v1] Sun, 21 Sep 2025 16:14:02 UTC (483 KB)
https://arxiv.org/abs/2509.17142
Astrobiology,

Keith Cowing

Biologist, Explorers Club Fellow, ex-NASA Space Biologist and Payload integrator, Editor of NASAWatch.com and Astrobiology.com, Lapsed climber, Explorer, Synaesthete, Former Challenger Center board member 🖖🏻

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