The PRL Stabilized High-Resolution Echelle Fiber-fed Spectrograph: Instrument Description and First Radial Velocity Results

Abstract

ABSTRACT. We present spectrograph design details and initial radial velocity results from the PRL optical fiberfed high-resolution cross-dispersed echelle spectrograph (PARAS), which has recently been commissioned at the Mount Abu 1.2 m telescope in India. Data obtained as part of the postcommissioning tests with PARAS show velocity precision better than 2 m s À1 over a period of several months on bright RV standard stars. For observations of σ Dra, we report 1:7 m s À1 precision for a period of 7 months, and for HD 9407, we report 2:1 m s À1 over a period of 2 months. PARAS is capable of single-shot spectral coverage of 3800-9500 Å at a resolution of ∼67; 000. The RV results were obtained between 3800 and 6900 Å using simultaneous wavelength calibration with a thorium-argon (ThAr) hollow cathode lamp. 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 AE 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. Future plans include testing of octagonal fibers for further scrambling of light and extensive calibration over the entire wavelength range up to 9500 Å using thorium-neon (ThNe) or uranium-neon (UNe) spectral lamps. Thus, we demonstrate how such highly stabilized instruments, even on small aperture telescopes, can contribute significantly to the ongoing radial velocity searches for low-mass planets around bright stars.

State of the Field: Extreme Precision Radial Velocities

“…An e2v deep depletion 4kx4k CCD is used for imaging the spectra along with the ARC Inc., Leach Controller 60 Presentation by Abhijit Chakraborty for CCD electronics and interface with Computer. Simultaneous ThAr exposure along with a ThAr exposure immediately after the observation is used to correct for instrument drifts with an rms error of 90 cm s −1 or better (Chakraborty et al 2014). The blaze peak efficiency of the spectrograph between 5000Å and 6500Å, including the detector, is about 30%; and about 25% including the fiber transmission.…”

“…Typically, two to three RV points are used to calculate the nightly mean velocity. Chakraborty et al (2014) demonstrate a mean nightly rms scatter of 1.2 m s Figure 10 shows the estimated measurement precision of PARAS for 27 bright stars since the beginning of observations in 2012. These sources have at least 10 epochs of observations spanning more than 30 days.…”

Solar Contamination in Extreme-precision Radial-velocity Measurements: Deleterious Effects and Prospects for Mitigation

“…The simulated science and sky fiber spectra are passed through our RV analysis code, which has been extensively vetted at the <1 m s −1 level on both PARAS and HARPS data (Roy et al 2016). Cross-correlation functions (CCFs) are calculated using a standard stellar mask-based technique (Baranne et al 1996;Pepe et al 2002;Chakraborty et al 2014) for each order, then summed to form an aggregate CCF. Effective velocity offsets are measured by fitting a Gaussian to the peak of the aggregate CCF.…”

A Versatile Technique to Enable Sub-Milli-Kelvin Instrument Stability for Precise Radial Velocity Measurements: Tests With the Habitable-Zone Planet Finder*

“…HPF uses the simultaneous reference technique, and has three fibers, which record science, calibration and sky spectra simultaneously. HPF draws rich design heritage from the Penn State Pathfinder NIR prototype (Ramsey et al 2010;Ycas et al 2012), the APOGEE instrument (Blank et al 2010;Wilson et al 2010), and the PRL Stabilized High Resolution Echelle fiber-fed Spectrograph (PARAS) (Chakraborty et al 2014), and is in turn a significant source of heritage for the NN-EXPLORE NEID spectrometer being designed for the 3.5 m WIYN telescope.…”