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Register a new userThe Pathfinder Testbed: Exploring Techniques for Achieving Precision Radial Velocities in the Near-Infrared
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The Penn State Pathfinder is a prototype warm fiber-fed Echelle spectrograph with a Hawaii-1 NIR detector that has already demonstrated 7-10 m/s radial velocity precision on integrated sunlight. The Pathfinder testbed was initially setup for the Gemini PRVS design study to enable a systematic exploration of the challenges of achieving high radial velocity precision in the near-infrared, as well as to test possible solutions to these calibration challenges. The current version of the Pathfinder has an R3 echelle grating, and delivers a resolution of R~50,000 in the Y, J or H bands of the spectrum. We will discuss the on sky-performance of the Pathfinder during an engineering test run at the Hobby Eberly Telescope as well the results of velocity observations of M dwarfs. We will also discuss the unique calibration techniques we have explored, like Uranium-Neon hollow cathode lamps, notch filter, and modal noise mitigation to enable high precision radial velocity observation in the NIR. The Pathfinder is a prototype testbed precursor of a cooled high-resolution NIR spectrograph capable of high radial velocity precision and of finding low mass planets around mid-late M dwarfs.
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Precision radial velocity (RV) measurements in the near-infrared are a powerful tool to detect and characterize exoplanets around low-mass stars or young stars with higher magnetic activity. However, the presence of strong telluric absorption lines and emission lines in the near infrared that significantly vary in time can prevent extraction of RV information from these spectra by classical techniques, which ignore or mask the telluric lines. We present a methodology and pipeline to derive precision RVs from near-infrared spectra using a forward-modeling technique. We applied this to spectra with a wide wavelength coverage (Y, J, and H bands, simultaneously), taken by the InfraRed Doppler (IRD) spectrograph on the Subaru 8.2-m telescope. Our pipeline extracts the instantaneous instrumental profile of the spectrograph for each spectral segment, based on a reference spectrum of the laser-frequency comb that is injected into the spectrograph simultaneously with the stellar light. These profiles are used to derive the intrinsic stellar template spectrum, which is free from instrumental broadening and telluric features, as well as model and fit individual observed spectra in the RV analysis. Implementing a series of numerical simulations using theoretical spectra that mimic IRD data, we test the pipeline and show that IRD can achieve $<2$ m s$^{-1}$ precision for slowly rotating mid-to-late M dwarfs with a signal-to-noise ratio $> 100$ per pixel at 1000 nm. Dependences of RV precision on various stellar parameters (e.g., $T_{rm eff}$, $vsin i$, [Fe/H]) and the impact of telluric-line blendings on the RV accuracy are discussed through the mock spectra analyses. We also apply the RV-analysis pipeline to the observed spectra of GJ 699 and TRAPPIST-1, demonstrating that the spectrograph and the pipeline are capable of an RV accuracy of $<3$ m s$^{-1}$ at least on a time scale of a few months.
Radial velocity identification of extrasolar planets has historically been dominated by optical surveys. Interest in expanding exoplanet searches to M dwarfs and young stars, however, has motivated a push to improve the precision of near infrared radial velocity techniques. We present our methodology for achieving 58 m/s precision in the K band on the M0 dwarf GJ 281 using the CSHELL spectrograph at the 3-meter NASA IRTF. We also demonstrate our ability to recover the known 4 Mjup exoplanet Gl 86 b and discuss the implications for success in detecting planets around 1-3 Myr old T Tauri stars.
SPIRou is a near-infrared (nIR) spectropolarimeter at the CFHT, covering the YJHK nIR spectral bands ($980-2350,mathrm{nm}$). We describe the development and current status of the SPIRou wavelength calibration in order to obtain precise radial velocities (RVs) in the nIR. We make use of a UNe hollow-cathode lamp and a Fabry-Perot etalon to calibrate the pixel-wavelength correspondence for SPIRou. Different methods are developed for identifying the hollow-cathode lines, for calibrating the wavelength dependence of the Fabry-Perot cavity width, and for combining the two calibrators. The hollow-cathode spectra alone do not provide a sufficiently accurate wavelength solution to meet the design requirements of an internal error of $mathrm{<0.45,m,s^{-1}}$, for an overall RV precision of $mathrm{1,m,s^{-1}}$. However, the combination with the Fabry-Perot spectra allows for significant improvements, leading to an internal error of $mathrm{sim 0.15,m,s^{-1}}$. We examine the inter-night stability, intra-night stability, and impact on the stellar RVs of the wavelength solution.
With the advent of high-resolution infrared spectrographs, Radial Velocity (RV) searches enter into a new domain. As of today, the most important technical question to address is which wavelength reference is the most suitable for high-precision RV measurements. In this work we explore the usage of atmospheric absorption features. We make use of CRIRES data on two programs and three different targets. We re-analyze the data of the TW Hya campaign, reaching a dispersion of about 6 m/s on the RV standard in a time scale of roughly 1 week. We confirm the presence of a low-amplitude RV signal on TW Hya itself, roughly 3 times smaller than the one reported at visible wavelengths. We present RV measurements of Gl 86 as well, showing that our approach is capable of detecting the signal induced by a planet and correctly quantifying it. Our data show that CRIRES is capable of reaching a RV precision of less than 10 m/s in a time-scale of one week. The limitations of this particular approach are discussed, and the limiting factors on RV precision in the IR in a general way. The implications of this work on the design of future dedicated IR spectrographs are addressed as well.
Aims: We evaluate the radial velocity (RV) information content and achievable precision on M0-M9 spectra covering the ZYJHK bands. We do so while considering both a perfect atmospheric transmission correction and discarding areas polluted by deep telluric features, as done in previous works. Methods: To simulate the M-dwarf spectra, PHOENIX-ACES model spectra were employed; they were convolved with rotational kernels and instrumental profiles to reproduce stars with a $v.sin{i}$ of 1.0, 5.0, and 10.0 km/s when observed at resolutions of 60 000, 80 000, and 100 000. We considered the RV precision as calculated on the whole spectra, after discarding strongly polluted areas, and after applying a perfect telluric correction. In our simulations we paid particular attention to the details of the convolution and sampling of the spectra, and we discuss their impact on the final spectra. Results: Our simulations show that the most important parameter ruling the difference in attainable precision between the considered bands is the spectral type. For M0-M3 stars, the bands that deliver the most precise RV measurements are the Z, Y, and H band, with relative merits depending on the parameters of the simulation. For M6-M9 stars, the bands show a difference in precision that is within a factor of $sim$2 and does not clearly depend on the band; this difference is reduced to a factor smaller than $sim$1.5 if we consider a non-rotating star seen at high resolution. We also show that an M6-M9 spectrum will deliver a precision about two times better as an M0-M3 spectra with the same signal-to-noise ratio. Finally, we note that the details of modelling the Earth atmosphere and interpreting the results have a significant impact on which wavelength regions are discarded when setting a limit threshold at 2-3%. (abridged)
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