PARAS (PRL Advanced Radial velocity Abu Sky Search)
The PRL optical fiber-fed high-resolution cross-dispersed echelle spectrograph (Prl Advanced Radial-velocity Abu-sky Search), which was commissioned
at the Mount Abu 1.2 m telescope in India in 2012. Data obtained as part of the post commissioning tests with PARAS show velocity precision better
than 2 m/s over a period of several months to years on bright RV standard stars.
For observations of σ Dra, a 1.7 m/s precision for a period of 2 years, and 3.5m/s on HD55567 have been demonstrated. PARAS is capable of
single-shot spectral coverage of 3800–9500 Å at a resolution of ∼67000. The RV results were obtained between 3800 Å and 6900 Å using simultaneous
wavelength calibration with a thorium-argon (ThAr) hollow cathode lamp or UAr (Uranium hollow cathode lamps).
The spectrograph is maintained under stable conditions of temperature with a precision of 0.01–0.02° C (rms) at 25.55° C and is enclosed in a vacuum
vessel at pressure of 0.1 _ 0.03 mbar. The blaze peak efficiency of the spectrograph between 5000 and 6500 Å, including the detector, is ∼30%; it is
∼25% with the fiber transmission. The total efficiency, including spectrograph, fiber transmission, focal ratio degradation (FRD), and telescope
(with 81% reflectivity) is ∼7% in the same wavelength region on a clear night with good seeing conditions. The stable point-spread function (PSF),
environmental control, existence of a simultaneous calibration fiber, and availability of observing time make PARAS attractive for a variety of
exoplanetary and stellar astrophysics projects.
Light is injected to the spectrograph using combinations of octagonal and circular optical fibers A and B which carries star light and spectral
light from spectral lamps for calibration respectively and simultaneously.
Above image shows the PARAS in the vacuum chamber. Top left: The CCD dewar aligned inside the vacuum chamber. Top right: The vacuum vessel being
installed inside the inner room. Bottom left: Some of the optical components seen in the chamber, where M1 and M2 are the off-axis parabolic mirrors
and FM is the fold mirror, Bottom right: The optical fiber interface with the vacuum chamber and part of the camera lens system.
Below image shows Portion of raw image for ThAr-ThAr exposure (left panel) and stellar exposure with simultaneous ThAr calibration (right panel).
Important exoplanet or brown-dwarf discoveries from PARAS:
-
“Discovery of an inflated hot Jupiter around a slightly evolved
star TOI-1789” 2021arXiv210608660K Submitted to
MNRAS.
The Astronomical Journal, arXiv:2106.08660 Bibcode: 2022MNRAS.509.3339K doi: 10.1093/mnras/stab2970 -
“TOI-503: The First Known Brown-dwarf Am-star Binary from the TESS Mission”.
The Astronomical Journal, arXiv:1909.07984 Bibcode: 2020AJ....159..151S doi: 10.3847/1538-3881/ab7245 -
"Evidence of a Sub-Saturn around Epic 211945201". The Astronomical Journal.
The Astronomical Journal, arXiv:1805.03466. Bibcode: Bibcode:2018AJ....156....3C. doi: doi:10.3847/1538-3881/aac436
-
Precision wavelength calibration for Radial Velocity measurements using Uranium lines between 3800-6900 Å.
The Astronomical Journal, arXiv:2105.12942 Bibcode: 2021JATIS...7c8005S doi: 10.1117/1.JATIS.7.3.038005 - “Masses and Radii of Four Very Low-mass Stars in F+M Eclipsing Binary Systems”. The Astronomical Journal, 2018AJ....156...27C
- Review Article: State of the Field: Extreme Precision Radial Velocities PASP, 2016PASP..128f6001F
- “Determination of mass and orbital parameters of a low-mass star HD 213597B” 2014MNRAS.442.3737C
- “The PRL Stabilized High-Resolution Echelle Fiber-fed Spectrograph: Instrument Description and First Radial Velocity Results” 2014PASP..126..133C
In view of the upcoming of the PRL 2.5m telescope, which will have an advanced version of PARAS called PARAS-2, original PARAS has been renamed as PARAS-1. PARAS-2 will operate at R~100,000 between 3800 and 6900A and is designed similar to HARPS-N spectrograph. It is expected to have sub-1m/s RV precision.