The first part of this review will be devoted to the different stellar processes leading to spurious radial velocities. They are due to magnetic activity (spots, plages, and flares to a lesser extent) and to flows at various scales (from granulation to meridional circulation), or a combination of both (inhibition of the convective blueshift in plages). The second part of the talk will review ...
Understanding the effect of stellar activity on the measured radial velocity (RV) is essential for the reliable detection of exoplanets around stars. It becomes even more vital when we are searching for low-mass planets around M-dwarfs, which are known to be particularly affected by active regions. Photospheric activity features in M-dwarfs stem from the depth of the convective layers and...
Distinguishing between a signal induced by stellar activity or a planet is the main challenge in radial velocity (RV) searches for low-mass exoplanets these days. Even when the presence of a transiting planet and hence its period are known, stellar activity is often the main barrier in nailing down the correct amplitude of the planetary signal. Observing the Sun-as-a-star provides a unique...
It is quite common to find periodic signals in time series of precise radial velocities that cannot unambiguously be attributed either to a planetary companion or to intrinsic variability of the star. In such cases, plausibility criteria (e.g., fit quality, expected “typical” RV jitter, dynamical stability) and different types of additional information (e.g., stability of line profiles or line...
Stellar spectra are polluted with the absorption lines produced by the Earth's atmosphere. Earlier modeling work showed that a perfect telluric correction increases the radial velocity precision compared to masking the regions affected by telluric absorption. But what is the case for real observations? With CARMENES near-infrared spectra, I will show the impact of the telluric correction on...
We performed simulations using the Kurucz solar spectrum and TAPAS generated telluric spectra across a year with varying atmospheric conditions to quantify the effects of telluric contamination in PRVs. We chose the wavelength range from 350nm to 2.5 micron and assumed a spectral resolution of R=120,000 with no photon noise. We assumed perfectly known spectral PSF, wavelength solution, and...
Emission and absorption from the Earth’s atmosphere at infrared and optical wavelengths introduces a significant source of contamination for ground based precision RV spectroscopy. These telluric features not only add statistical noise and remove flux from our spectra, but introduce additional uncertainty because some of the telluric line strengths themselves are highly variable and not known...
Laser frequency combs (LFCs) comprising thousands of evenly spaced laser lines with absolutely and precisely known optical frequencies can meet the calibration requirements for extreme precision in radial velocity measurements.
We present a LFC for accurate and precise spectrograph calibration in the near-infrared. The LFC is based on electro-optic modulation of a continuous-wave laser and...
Precise wavelength calibration is a persistent problem for highest precision Doppler spectroscopy. The ideal calibrator provides an extremely stable spectrum of equidistant, narrow lines over a wide bandwidth, is reliable over timescales of years, and simple to operate. Unlike traditional hollow cathode lamps, etalons provide an engineered spectrum with adjustable line distance and width, and...
Estimating precise radial velocities due to orbiting exoplanets in the presence of stellar activity is a challenging statistical problem. As instrumentation continues to improve, allowing for the detection of sub meter-per-second shifts, the effect of stellar activity becomes more problematic because the stellar activity can cause distortions in the spectra that mimic the RV of an orbiting...
Since the discovery of the first extra-solar planet in 1995, Doppler spectroscopy proved to be one of the most successful methods in the search of exoplanets. With new high precision instruments like ESPRESSO and new data analysis methods, it will be possible to detect Earth-like planets on Sun-like stars with similar orbital parameters of Earth. Unfortunately, the search for exoplanets comes...
The eccentricity of a planet is a key information on its present dynamics and puts constraints on formation scenarios. However, eccentricity estimates are known to be subject to caution, for instance it has been shown that low eccentricities are on average overestimated. In this talk, we present a comprehensive study of the eccentricity estimation from radial velocity data and give conditions...
With new missions and surveys such as TESS and SPECULOUS, the discovery of the first transiting, potentially earth-like planets is just around the corner. Once discovered, those planets will immediately become the focus of observations in search of atmospheric biomarkers such as H2O, CH4, O3, and O2. Recent studies suggest the latter will be best detected from the ground. Here we present a...
NASA's Transiting Exoplanet Survey Satellite (TESS) will identify
thousands of planets orbiting nearby bright stars in a two-year survey
beginning in the Southern sky. MINERVA-Australis at USQ's Mount Kent
Observatory is the only southern hemisphere precise radial velocity
facility wholly dedicated to follow-up of TESS planets. Mass
measurements of these planets are critically necessary...
Veloce is a new precision Doppler spectrograph for the 3.9m Anglo-Australian Telescope sited on Siding Spring Observatory in Australia. Cost considerations for an instrument with a total budget of A$5.4m mean that Veloce's design philosophy is one of "just enough" stabilisation (i.e. stabilising the spectrograph in pressure and temperature so that changes over time will be small and...
We present recent results from the latest addition to the spectrograph zoo: PEPSI, the new bench-mounted fiber-fed and stabilized “Potsdam Echelle Polarimetric and Spectroscopic Instrument” for the 11.8m Large Binocular Telescope (LBT). Besides the LBT the instrument is also fiber linked to a disk-integration solar telescope and the Vatican Observatory's 1.8m VATT. I will introduce PEPSI and...
The CARMENES high-precision spectrometer started operations in January 1, 2016 at the 3.5-m telescope of the Calar Alto Observatory. Since then, the CARMENES consortium is carrying out a 750-night survey searching for exoplanets around M dwarf stars, preferably in their habitable zones, using the radial velocity technique. CARMENES has the unique capability of providing continuous...
The Infrared Doppler (IRD) instrument is a fiber-fed high-resolution near-infrared spectrometer for the Subaru 8.2-m telescope covering the Y-, J-, and H-bands simultaneously with a spectral resolution of ~70,000. It aims at achieving measurement precision of 1-2 m/s in radial velocity (RV) with a very stable spectrograph and an original laser frequency comb. The most effective...
iLocater is a next-generation precision radial velocity spectrograph under development for the Large Binocular Telescope (LBT). The instrument has three major subsystems which are currently undergoing simultaneous development: a single-mode fiber fed high-resolution (R~150,000-240,000) NIR echelle spectrograph, an adaptive optics fed fiber-injection system, and a fabry-perot etalon based...
We present our radial-velocities (RVs) with the iSHELL spectrograph at the NASA Infrared Telescope facility. Replacing the 25 year old CSHELL instrument, iSHELL offers improvements in spectral grasp (~40x), resolution (70,000 versus 46,000), throughput, optics, and detector characteristics. Our primary goal with iSHELL is to characterize the precise radial-velocity performance of the methane...
The GMT-Consortium Large Earth Finder (G-CLEF), is currently scheduled to be the first PRV-capable instrument on an ELT. G-CLEF embraces many design paradigms of earlier PRV instruments, especially the HARPSs. However, the G-CLEF design team is exploiting several novel technologies to deliver an exceptionally stable and calibratable spectrograph. In this talk, we provide an overview of the...
Significant progress has been made in recent years in measuring the sky-projected obliquity distribution of early-type planet hosting systems via precise Rossiter-McLaughlin (RM) effect observations. However, currently only two M-dwarf systems, GJ 436 and Kepler-45, have published obliquities—and interestingly GJ 436 is observed to be misaligned. With such a sparse sample, key questions remain...
As the number of known super-Earths and Neptune-like planets keeps growing, the properties and frequency of such systems start to be revealed. Planet formation models suggest that these low-mass planets, unlike giant planets, should be frequent around stars with low metallicities. But this theoretical prediction still needs to be observationally confirmed.
I will present the analysis of a...
The precision radial velocity community is pushing spectrometer hardware to new and ever more exciting stability levels that support a velocity precision of ~1 m/s in the near-infrared, and sub 50 cm/s in the visible. These developments must be backed by increasingly sophisticated software algorithms and data reduction pipelines that can realize the potential of the new instruments. I will...
An iodine cell placed in the light path of a high-resolution spectrograph can
act as a simultaneous wavelength and point-spread-function fiducial which
enables precise radial velocities to be extracted from un-stabilized or
slit-fed spectrographs. This technique enabled the detection and
characterization of many of the first known exoplanets and played a significant
role in establishing the...
Thanks to a number of technical developments, the precision of RV surveys has been steadily improving. While the spectrographs of fifty years ago yielded RVs with errors in excess of 1 km/s, today's state-of-the-art stabilised spectrographs boast 10 cm/s precisions. Yet very little has changed in the way individual RVs are actually extracted from observed spectra: i.e., cross correlating...
...
Abstract: In order to measure stellar radial velocities at high precision, an accurate wavelength solution is of paramount importance. To achieve such a solution, hollow-cathode (HC) lamps have frequently been used (e.g. on HARPS, SOPHIE). By identifying and cross-matching their spectral lines with very precise catalogues, a pixel-wavelength correlation can be generated. However, these...
CARMENES is a large RV-survey for low-mass planets of M-stars. In contrast to other M-star surveys its main focus are M3-M4V stars.
One of its aims is to determine the frequency of planets with periods of less than 50 days. Although the survey is still on-going, we have started to develop a method to determine the detection limits for each star. The basic idea is to simulate the RV-signal of...
To deliver a radial velocity instrument capable of extreme precision requires careful design with attention to the interplay of optical, mechanical and thermal design choices. Ideally, an instrument starts with a spectrograph of sufficient resolution and an intrinsic stability that leads to optimal precision over months or years. For a demonstrator instrument developed at Macquarie University,...
We present the science case for a 1.45 meter space telescope to survey the closest, brightest FGKM main sequence stars to search for Habitable Zone (HZ) Earth analogs using the precise radial velocity (PRV) technique at a precision of 1-10 cm/s. Our baseline instrument concept uses three diffraction-limited spectrographs operating in the 0.3-0.4, 0.4-0.9, and 0.9-2.4 microns spectral regions...
We present the software package Echelle++, an open-source C++ code to simulate realistic raw spectra based on the Zemax model of any spectrograph, with a particular emphasis on cross-dispersed Échelle spectrographs.
Echelle++ generates realistic spectra of astronomical and calibration sources, with accurate representation of optical aberrations, the shape of the point-spread function,...
We have analyzed four years of Automated Planet Finder (APF) data to understand the error sources in the measured radial velocities. Our approach combines two data sets, long term measurements on a few standard stars and an intense campaign observing simultaneously observing two stars with both the APF and the PFS on Magellan. We find that, despite the strong similarities between the APF's...
KPF is a fiber-fed, high-resolution, high-stability spectrometer in development for the W.M. Keck Observatory. The instrument is designed to characterize exoplanets via Doppler spectroscopy with a single measurement precision of 0.5 m/s or better, however its resolution and stability will enable a wide variety of other astrophysical observations. KPF will have a resolving power of > 80,000,...
Astronomical laser frequency combs (LFCs) have become invaluable tools for precision astronomical spectroscopy. By serving as extremely stable wavelength references, they are ideal for searching Earth-like extrasolar planets using the radial-velocity method. LFCs generate a regular pattern of sharp emission lines, whose optical frequencies are referenced to an atomic clock. The relative...
MINiature Exoplanet Radial Velocity Array (MINERVA) - Australis is a new telescope array and spectrograph at Mt Kent observatory in Australia. It is run by a consortium of US, Australian and Chinese universities and has been operational since 2018 Nov 10. It is made up of five 0.7m CDK 700 telescopes from Planewave (three currently installed and operating) and a high-resolution (R>80000)...
The discoveries of the Earth-sized exoplanets orbiting Proxima Centauri and Trappist-1 lend further support to the theory that terrestrial planets may be common around low-mass stars. Since low-mass stars are intrinsically faint at optical wavelengths, obtaining the meter-per-second Doppler precision necessary to detect their Earth-sized planetary companions remain a challenge for instruments...
We describe the laser frequency comb that is now installed and operating as the primary wavelength calibrator for the Habitable Zone Planet Finder (HPF) spectrograph at the 10 m Hobby-Eberly Telescope. The laser frequency comb, with 30 GHz mode spacing, is built around a combination of electro-optic and integrated-photonic technologies to address the challenges of bandwidth, mode spacing, and...
NEID and HPF both were conceived to deliver ground-breaking precision in their wavelength regime. HPF has now been commissioned at the Hobby Eberly Telescope, while NEID is fully integrated and set to be deployed at WIYN in Summer 2019. The instruments both use 2x1 mosaic of the same RGL master grating at R4, with nearly 200mm beam diameter, in a white pupil configuration. The cross dispersion...
NEID is a high resolution (R~100,000) fiber - fed Radial Velocity (RV) spectrograph, that will be commissioned at the 3.5 m WIYN telescope at Kitt Peak, USA. In this presentation, I will discuss the details of the NEID fiber feed, which contains octagonal and circular fibers. I shall discuss and share techniques we used to polish these fibers in custom fused silica pucks, FRD, scrambling and...
For nearly 20 years, the California Planet Search (CPS) has simultaneously monitored precise radial velocities and chromospheric activity levels of stars from Keck observatory to search for exoplanets. This sample provides a useful set of stars to assess the dependence of RV jitter on various astrophysical processes. We measure astrophysical jitter for ~650 stars in the CPS covering a wide...
Reliable, high precision wavelength calibration is a bottleneck for commissioning a number of the next generation of Doppler spectrographs. We have developed a method to reference a wide bandwidth Etalon to a Rubidium transition to enable long-term stability and precision in the range below 10 cm/s. A key part of the whole instrument is the Etalon assembly itself. We strive to reach maximum...
Spectroscopic information content and stellar brightness define the fundamental limits for radial velocity (RV) measurements. We summarize the available theoretical and empirical information about RV precision limits and compare the performance between various VIS and NIR instrument designs.
We show how to use the Python package RadVel to characterize Keplerian orbits of planetary systems with radial velocity (RV) data. RadVel can model multi-planet, multi-instrument datasets, while incorporating constraints such as transit ephemerides and secondary eclipse times. It includes several built-in Gaussian process kernels for the treatment of stellar activity, and employs MCMC and...
We screened the most suitable G, K and M nearby stars for the detection of Earth-class exoplanets with ESPRESSO. For most of these stars, we investigate the existence of stellar binaries. We derived the activity level using chromospheric activity indexes log(R'HK) and Ha, as well as the projected rotational velocity v sin i. For cases where planet companions are already known we also accessed...
Future direct imaging missions such as WFIRST, HabEx, and LUVOIR aim to catalog and characterize Earth-analogs around nearby stars. The observing strategy and science yield are strongly dependent on the frequency of Earth-like planets, and precursor knowledge of which stars specifically host suitable planetary systems. Ground- or space-based radial velocity surveys can potentially identify...
When the noise affecting time series is colored (i.e. frequency dependent) with unknown statistics, a difficulty for the detection of periodic signals is to control the true significance level of the test outcome.
Recent hydrodynamic simulations, performed in 3 dimensions, are able to generate reliable time series of convection, which is a stochastic colored noise for exoplanet detection. The...
Detecting Earth-mass exoplanets using the Doppler method places
stringent requirements on detector stability. NEID is a new Doppler
spectrometer in development for the WIYN 3.5-m telescope at Kitt Peak
National Observatory as part of the NN-Explore partnership. The wide
spectral grasp of NEID (380-930 nm) requires a monolithic CCD detector
with a large area, small pixels, and excellent quantum...
NIRSPEC is a high-resolution (R=𝝀/𝛥𝜆~25,000), cross-dispersed, echelle spectrograph operating from 1-5 um on the Keck II telescope. In Fall 2018, we upgraded the instrument to increase its sensitivity and ensure its continued longevity. We have also used the NIRSPEC instrument as a testbed for developing new technologies, such as laser frequency combs, to improve instrumental stability for...
