We are developing a “dual-aperture fiber nuller” (DAFN) as a technology to bridge the gap in observation of exoplanets with orbital separations between 1-10s of AU. Such an instrument interferometrically achieves an on-axis (starlight) null while off-axis light (planet light) is transmitted to a high-resolution spectrograph. The performance of the DAFN is competitive among only a few existing technologies such as the vortex fiber nuller. Furthermore, it has the cost-effective advantage of improving angular resolution by expanding the interferometric baseline rather than increasing aperture size. We present a monochromatic demonstration of this technology’s angular resolution (< 1 λ/D) and sensitivity to starlight suppression in the lab. The DAFN technology can potentially be deployed to preexisting interferometric frameworks such as the Large Binocular Telescope Interferometer or the Very Large Telescope Interferometer. It can also benefit prospective space-based exoplanet direct imaging missions, e.g. LIFE, as well as ground-based ELT searches for terrestrial planets in the habitable zone.
The Keck Planet Imager and Characterizer (KPIC), a series of upgrades to the Keck II Adaptive Optics System and Instrument Suite, aims to demonstrate high-resolution spectroscopy of faint exoplanets that are spatially resolved from their host stars. In this paper, we measure KPIC’s sensitivity to companions as a function of separation (i.e., the contrast curve) using on-sky data collected over four years of operation. We show that KPIC is able to reach contrasts of 1.3 × 10−4 at 90 mas and 9.2 × 10−6 at 420 mas separation from the star, and that KPIC can reach planet-level sensitivities at angular separations within the inner working angle of coronagraphic instruments such as GPI and SPHERE. KPIC is also able to achieve more extreme contrasts than other medium-/high-resolution spectrographs that are not as optimized for high-contrast performance. We decompose the KPIC performance budget into individual noise terms and discuss limiting factors. The fringing that results from combining a high-contrast imaging system with a high-resolution spectrograph is identified as an important source of systematic noise. After mitigation and correction, KPIC is able to reach within a factor of 2 of the photon noise limit at separations < 200 mas. At large separations, KPIC is limited by the background noise performance of NIRSPEC.
The Keck Planet Imager and Characterizer (KPIC) combines high contrast imaging with high resolution spectroscopy (R∼35,000 in K band) to study directly imaged exoplanets and brown dwarfs in unprecedented detail. KPIC aims to spectrally characterize substellar companions through measurements of planetary radial velocities, spins, and atmospheric composition. Currently, the dominant source of systematic noise for KPIC is fringing, or oscillations in the spectrum as a function of wavelength. The fringing signal can dominate residuals by up to 10% of the continuum for high S/N exposures, preventing accurate wavelength calibration, retrieval of atmospheric parameters, and detection of planets with flux ratios less than 1% of the host star. To combat contamination from fringing, we first identify its three unique sources and adopt a physically informed model of Fabry-Pérot cavities to apply to post-processed data. We find this strategy can effectively model the fringing in observations of bright stars, reducing the residual systematics caused by fringing by a factor of 2. Next, we wedge two of the transmissive optics internal to KPIC to eliminate two sources of fringing and confirm the third source as the entrance window to the spectrograph. Finally, we apply our previous model of the Fabry-Pérot cavity to new data taken with the wedged optics to reduce the amplitude of the residuals by a factor of 10.
HISPEC is a new, high-resolution near-infrared spectrograph being designed for the W.M. Keck II telescope. By offering single-shot, R 100,000 spectroscopy between 0.98 – 2.5 μm, HISPEC will enable spectroscopy of transiting and non-transiting exoplanets in close orbits, direct high-contrast detection and spectroscopy of spatially separated substellar companions, and exoplanet dynamical mass and orbit measurements using precision radial velocity monitoring calibrated with a suite of state-of-the-art absolute and relative wavelength references. MODHIS is the counterpart to HISPEC for the Thirty Meter Telescope and is being developed in parallel with similar scientific goals. In this proceeding, we provide a brief overview of the current design of both instruments, and the requirements for the two spectrographs as guided by the scientific goals for each. We then outline the current science case for HISPEC and MODHIS, with focuses on the science enabled for exoplanet discovery and characterization. We also provide updated sensitivity curves for both instruments, in terms of both signal-to-noise ratio and predicted radial velocity precision.
Vortex fiber nulling (VFN) is a single-aperture interferometric technique for detecting and characterizing exoplanets separated from their host star by less than a diffracted beam width. VFN uses a vortex mask and single-mode fiber to selectively reject starlight while coupling off-axis planet light with a simple optical design that can be readily implemented on existing direct imaging instruments that can feed light to an optical fiber. With its axially symmetric coupling region peaking within the inner working angle of conventional coronagraphs, VFN is more efficient at detecting new companions at small separations than conventional direct imaging, thereby increasing the yield of on-going exoplanet search campaigns. We deployed a VFN mode operating in K band (2.0 to 2.5 μm) on the Keck Planet Imager and Characterizer (KPIC) instrument at the Keck II Telescope. We present the instrument design of this first on-sky demonstration of VFN and the results from on-sky commissioning, including planet and star throughput measurements and predicted flux-ratio detection limits for close-in companions. The instrument performance is shown to be sufficient for detecting a companion 103 times fainter than a fifth magnitude host star in 1 h at a separation of 50 mas (1.1 λ / D). This makes the instrument capable of efficiently detecting substellar companions around young stars. We also discuss several routes for improvement that will reduce the required integration time for a detection by a factor >3.
The Planetary Systems Imager (PSI), a proposed instrument suite for the Thirty Meter Telescope (TMT), enables a broad range of extreme-AO, high-contrast observations. PSI is specifically optimized for high contrast exoplanet science from 0.5 to 13 μm and to that end includes a core near-IR AO system that feeds multiple AO+science instrument subsystems. In this paper, we present a preliminary optical design for the full PSI-AO system, feeding the PSI-Red (2—5 μm), PSI-Blue (0.5-–1.8 μm), and PSI-10 (8—13 μm) subsystems. We discuss an initial concept of testing and operations for the system that feeds into the conceptual design. We build on our preliminary end-to-end PSI-Red AO simulation to estimate the raw planet-to-star contrast ratios associated with PSI-Red and extrapolate these results to represent the effects of a PSI-Blue deformable mirror.
HISPEC (High-resolution Infrared Spectrograph for Exoplanet Characterization) is an infrared (0.95 to 2.46 microns) cross-dispersed, R=100,000 single-mode fiber-fed diffraction-limited echellette spectrograph for the Keck II telescope’s adaptive optics (AO) system. MODHIS (Multi-Objective Diffraction-limited High-resolution Infrared Spectrograph) shares similar specifications as HISPEC while being optimized for TMT’s first-light AO system NFIRAOS. Keck-HISPEC (2025) then TMT-MODHIS will provide increasingly compelling science capabilities from exoplanet atmosphere characterization through both transit and direct high-contrast spectroscopy, to detection and mass measurements through infrared precision radial velocity (RV). The science cases include the precise RV measurements of stars orbiting the Galactic Center, Solar System studies, and the chemodynamical history of nearby dwarf galaxies and the galactic halo.
The Keck Planet Imager and Characterizer (KPIC) is a series of upgrades for the Keck II Adaptive Optics system and the NIRSPEC spectrograph to enable diffraction-limited, high-resolution (R>30,000) spectroscopy in the K and L bands. KPIC’s use of single-mode fibers provides a substantial reduction in sky background as well as an extremely stable line-spread function. In this paper we present the results of extensive system-level laboratory testing and characterization of Phase II of the instrument and each of its modes. We also show early on-sky results from the first few months of commissioning with these upgrades along with the next steps for the instrument.
KPIC (Keck Planet Imager and Characterizer) is a series of upgrades to Keck II adaptive optics and the NIR-SPEC spectrograph enabling K-band diffraction-limited high-resolution spectroscopy. KPIC’s single-mode fibers provide a substantial reduction in sky background as well as an extremely stable line-spread function. In this paper we present the on-sky performance of KPIC phase I and lessons learned from calibration and operation of the system, including procedures for maximizing throughput and assessments of long-term line-spread and calibration stability. During phase I, KPIC successfully detected 23 exoplanets and brown dwarfs, with separations from 200 to 3600 mas and K-band magnitudes up to 17.
The Planetary Systems Imager (PSI) is a proposed instrument for the Thirty Meter Telescope (TMT) that provides an extreme adaptive optics (AO) correction to a multi-wavelength instrument suite optimized for high contrast science. PSI's broad range of capabilities, spanning imaging, polarimetry, integral field spectroscopy, and high resolution spectroscopy from 0.6–5 μm, with a potential channel at 10 μm, will enable breakthrough science in the areas of exoplanet formation and evolution. Here, we present a preliminary optical design and performance analysis of the 2–5 μm component of the PSI AO system, which must deliver the wavefront quality necessary to support infrared high contrast science cases.
The Keck Planet Imager and Characterizer (KPIC) is an upgrade to the Keck II adaptive optics system enabling high contrast imaging and high-resolution spectroscopic characterization of giant exoplanets in the mid-infrared (2-5 microns). The KPIC instrument will be developed in phases. Phase I entails the installation of an infrared pyramid wavefront sensor (PyWFS) based on a fast, low-noise SAPHIRA IR-APD array. The ultra-sensitive infrared PyWFS will enable high contrast studies of infant exoplanets around cool, red, and/or obscured targets in star forming regions. In addition, the light downstream of the PyWFS will be coupled into an array of single-mode fibers with the aid of an active fiber injection unit (FIU). In turn, these fibers route light to Keck's high-resolution infrared spectrograph NIRSPEC, so that high dispersion coronagraphy (HDC) can be implemented for the first time. HDC optimally pairs high contrast imaging and high-resolution spectroscopy allowing detailed characterization of exoplanet atmospheres, including molecular composition, spin measurements, and Doppler imaging.
We will provide an overview of the instrument, its science scope, and report on recent results from on-sky commissioning of Phase I. We will discuss plans for optimizing the instrument to seed designs for similar modes on extremely large telescopes.
One of the major goals of the exoplanet community in the coming decades is to detect Earth-like exoplanets (exoEarths) and look for biomarkers in their atmospheres. High-dispersion coronagraphy (HDC) may allow detection and characterization to be done simultaneously, as well as relax the starlight suppression requirements of the telescope and coronagraph. However, similar to other direct imaging techniques, HDC faces challenging thermal and/or exozodiacal background levels. In this paper, we present simulations of coronagraphic observations using a variety of space telescope apertures ranging in diameter from 1 to 15 m, specifically incorporating thermal and exozodiacal background. We investigate the effects of instrument temperature and aperture on the maximum usable wavelength, as well as the effects of exozodiacal disk inclination and thickness on observational SNR. We then identify the spectral resolutions which maximize observational SNR subject to detector noise and the required starlight suppression levels for the detection of various potential biomarker molecules (H2O, O2, CO2, and CH4).
More than half of the stars in the solar neighborhood reside in binary/multiple stellar systems, and recent studies suggest that gas giant planets may be more abundant around binaries than single stars. Yet, these multiple systems are usually overlooked or discarded in most direct imaging surveys, as they prove difficult to image at high-contrast using coronographs. This is particularly the case for compact binaries (less than 1’’ angular separation) with similar stellar magnitudes, where no existing coronagraph can provide high-contrast regime. Here we present preliminary results of an on-going Palomar pilot survey searching for low-mass companions around ~15 young “challenging” binary systems, with angular separation as close as 0’’3 and near-equal K-band magnitudes. We use the Stellar Double Coronagraph (SDC) instrument on the 200-inch Telescope in a modified optical configuration, making it possible to align any targeted binary system behind two vector vortex coronagraphs in cascade. This approach is uniquely possible at Palomar, thanks to the absence of sky rotation combined with the availability of an extreme AO system, and the number of intermediate focalplanes provided by the SDC instrument. Finally, we expose our current data reduction strategy, and we attempt to quantify the exact contrast gain parameter space of our approach, based on our latest observing runs.
We summarize the red channel (2-5 micron) of the Planetary Systems Imager (PSI), a proposed second-generation instrument for the TMT. Cold exoplanets emit the majority of their light in the thermal infrared, which means these exoplanets can be detected at a more modest contrast than at other wavelengths. PSI-Red will be able to detect and characterize a wide variety of exoplanets, including radial-velocity planets on wide orbits, accreting protoplanets in nearby star-forming regions, and reflected-light planets around the nearest stars. PSI-Red will feature an imager, a low-resolution lenslet integral field spectrograph, a medium-resolution lenslet+slicer integral field spectrograph, and a fiber-fed high-resolution spectrograph.
Spectroscopy of exoplanets can potentially detect biomarkers in habitable planets around other stars. The high dispersion coronagraphy (HDC) technique provides a pathway to search for biomarkers in planets around M dwarfs with next-generation ground-based extremely large telescopes (ELTs). The HDC consists of a coronagraph operating behind an extreme adaptive optics (AO) system, a single-mode fiber injection unit, and a high resolution spectrometer (HRS). The coronagraph spatially filters out starlight while the HRS spectrally discriminates starlight from planet light, reaching a starlight suppression level that enables biomarker detection. I will simulating ELT HDC instrument performance as a function of wavelength, spectral resolution, starlight suppression, and planet types, considering realistic noise budget that includes speckle noise, thermal and sky background and exozodical background.
The High Contrast spectroscopy testbed for Segmented Telescopes (HCST) is being developed at Caltech. It aims at addressing the technology gap for future exoplanet imagers and providing the U.S. community with an academic facility to test components and techniques for high contrast imaging, focusing on segmented apertures proposed for future ground-based (TMT, ELT) and space-based telescopes (HabEx, LUVOIR). We present an overview of the design of the instrument and a detailed look at the testbed build and initial alignment. We offer insights into stumbling blocks encountered along the path and show that the testbed is now operational and open for business. We aim to use the testbed in the future for testing of high contrast imaging techniques and technologies with amongst with thing, a TMT-like pupil.
A milestone in understanding life in the universe is the detection of biosignature gases in the atmospheres of habitable exoplanets. Future mission concepts under study by the 2020 decadal survey, e.g., Habitable Exoplanet Imaging Mission (HabEx) and the Large UV/Optical/IR Surveyor (LUVOIR), have the potential of achieving this goal. We investigate the baseline requirements for detecting four molecular species, H2O, O2, CH4, and CO2, assuming concentrations of these species equal to that of modern Earth. These molecules are highly relevant to habitability and life on Earth and other planets. Through numerical simulations, we find the minimum requirements of spectral resolution, starlight suppression, and exposure time for detecting biosignature and habitability marker gases. The results are highly dependent on cloud conditions. A low-cloud case is more favorable because of deeper and denser lines whereas a no-cloud case is the pessimistic case for its low albedo. The minimum exposure time for detecting a certain molecule species can vary by a large factor (∼10) between the low-cloud case and the no-cloud case. For all cases, we provide baseline requirements for HabEx and LUVOIR. The impact of exozodiacal contamination and thermal background is also discussed and will be included in future studies.
The High Contrast Spectroscopy Testbed for Segmented Telescopes (HCST) at Caltech is aimed at filling gaps in technology for future exoplanet imagers and providing the U.S. community with an academic facility to test components and techniques for high contrast imaging with future segmented ground-based telescope (TMT, E-ELT) and space-based telescopes (HabEx, LUVOIR). The HCST will be able to simulate segmented telescope geometries up to 1021 hexagonal segments and time-varying external wavefront disturbances. It also contains a wavefront corrector module based on two deformable mirrors followed by a classical 3-plane single-stage corona- graph (entrance apodizer, focal-plane mask, Lyot stop) and a science instrument. The back-end instrument will consist of an imaging detector and a high-resolution spectrograph, which is a unique feature of the HCST. The spectrograph instrument will utilize spectral information to characterize simulated planets at the photon-noise limit, measure the chromaticity of new optimized coronagraph and wavefront control concepts, and test the overall scientific functions of high-resolution spectrographs on future segmented telescopes.
In preparation for the Astro 2020 Decadal Survey NASA has commissioned the study four flagship missions spanning to a wide range of observable wavelengths: the Origins Space Telescope (OST, formerly the Far-Infrared Surveyor), Lynx (formerly the X-ray Surveyor), the Large UV/Optical/Infrared Surveyor (LUVOIR) and the Habitable Exoplanet Imager (HabEx). One of the key scientific objectives of the latter two is the detection and characterization of the earth-like planets around nearby stars using the direct imaging technique (along with a broad range of investigations regarding the architecture of and atmospheric composition exoplanetary systems using this technique). As a consequence dedicated exoplanet instruments are being studied for these mission concepts. This paper discusses the design of the coronagraph instrument for the architecture “A” (15 meters aperture) of LUVOIR. The material presented in this paper is aimed at providing an overview of the LUVOIR coronagraph instrument. It is the result of four months of discussions with various community stakeholders (scientists and technologists) regarding the instrument’s basic parameters followed by meticulous design work by the the GSFC Instrument Design Laboratory team. In the first section we review the main science drivers, presents the overall parameters of the instrument (general architecture and backend instrument) and delve into the details of the currently envisioned coronagraph masks along with a description of the wavefront control architecture. Throughout the manuscript we describe the trades we made during the design process. Because the vocation of this study is to provide a baseline design for the most ambitious earth-like finding instrument that could be possibly launched into the 2030’s, we have designed an complex system privileged that meets the ambitious science goals out team was chartered by the LUVOIR STDT exoplanet Working Group. However in an effort to minimize technological risk we tried to maximize the number of technologies that will be matured by the WFIRST coronagraph instruments.
Coupling a high-contrast imaging instrument to a high-resolution spectrograph has the potential to enable the most detailed characterization of exoplanet atmospheres, including spin measurements and Doppler mapping. The high-contrast imaging system serves as a spatial filter to separate the light from the star and the planet while the high-resolution spectrograph acts as a spectral filter, which differentiates between features in the stellar and planetary spectra. The Keck Planet Imager and Characterizer (KPIC) located downstream from the current W. M. Keck II adaptive optics (AO) system will contain a fiber injection unit (FIU) combining a high-contrast imaging system and a fiber feed to Keck’s high resolution infrared spectrograph NIRSPEC. Resolved thermal emission from known young giant exoplanets will be injected into a single-mode fiber linked to NIRSPEC, thereby allowing the spectral characterization of their atmospheres. Moreover, the resolution of NIRSPEC (R = 37,500) is high enough to enable spin measurements and Doppler imaging of atmospheric weather phenomenon. The module will be integrated and tested at Caltech before being transferred to Keck in 2018.
A milestone in understanding life in the universe is the detection of biosignature gases in the atmospheres of habitable exoplanets. Future mission concepts under study by the 2020 decadal survey, e.g., HabEx and LUVOIR, have the potential of achieving this goal. We investigate the baseline requirements for detecting four molecular species, H2O, O2, CH4, and CO2. These molecules are highly relevant to habitability and life activity on Earth and other planets. Through numerical simulations, we find the minimum requirement for spectral resolution (R) and starlight suppression level (C) for a given exposure time. We consider scenarios in which different molecules are detected. For example, R = 6400 (400) and C = 5 × 10−10 (2 × 10−9 ) are required for HabEx (LUVOIR) to detect O2 and H2O for an exposure time of 400 hours for an Earth analog around a solar-type star at a distance of 5 pc. The full results are given in Table 2. The impact of exo-zodiacal contamination and thermal background is also discussed
Despite recent advances in high-contrast imaging techniques, high resolution spectroscopy for characterization of exoplanet atmospheres is still limited by our ability to suppress residual starlight speckles at the planet’s location. We have demonstrated a new concept for speckle nulling by injecting directly imaged planet light into a single-mode fiber, linking a high-contrast adaptively-corrected coronagraph to a high-resolution spectrograph (diffraction-limited or not). The restrictions on the incident electric field that will couple into the single-mode fiber give the adaptive optics system additional degrees of freedom to suppress the speckle noise on top of destructive interference. We are able to achieve a starlight suppression gains that are an order of magnitude better than conventional techniques in broadband light with minimal planet throughput losses.
Detection and characterization of exoplanets faces challenges of smaller angular separation and high contrast between exoplanets and their host stars. High contrast imaging (HCI) instruments equipped with coronagraphs are built to meet these challenges, providing a way of spatially suppressing and separating stellar flux from that of a planet. Another way of separating stellar flux can be achieved by high-resolution spectroscopy (HRS), exploiting the fact that spectral features are different between a star and a planet. Observing exoplanets with HCI+HRS will achieve a higher contrast than the spatial or the spectroscopic method alone, improving the sensitivity to planet detection and enabling the study of the physical and chemical processes. Here, we simulate the performance of a HCI+HRS instrument (i.e., the upgrade Keck NIRSPEC and the fiber injection unit) to study its potential in detecting and characterizing currently known directly imaged planets. The simulation considers the spectral information content of an exoplanet, telescope and instrument specifications and realistic noise sources. The result of the simulation helps to set system requirement and informs designs at system-level. We also perform a trade study for a HCI+HRS instrument for a space mission to study an Earth-like planet orbiting a Sun-like star at 10 pc.
The Keck Planet Imager and Characterizer (KPIC) is a cost-effective upgrade path to the W.M. Keck observatory (WMKO) adaptive optics (AO) system, building on the lessons learned from first and second-generation extreme AO (ExAO) coronagraphs. KPIC will explore new scientific niches in exoplanet science, while maturing critical technologies and systems for future ground-based (TMT, EELT, GMT) and space-based planet imagers (HabEx, LUVOIR). The advent of fast low-noise IR cameras (IR-APD, MKIDS, electron injectors), the rapid maturing of efficient wavefront sensing (WFS) techniques (Pyramid, Zernike), small inner working angle (IWA) coronagraphs (e.g., vortex) and associated low-order wavefront sensors (LOWFS), as well as recent breakthroughs in high contrast high resolution spectroscopy, open new direct exoplanet exploration avenues that are complementary to planet imagers such as VLT-SPHERE and the Gemini Planet Imager (GPI). For instance, the search and detailed characterization of planetary systems on solar-system scales around late-type stars, mostly beyond SPHERE and GPI's reaches, can be initiated now at WMKO.
Jian Ge, Bo Zhao, Scott Powell, Ji Wang, Adam Fletcher, Liang Chang, John Groot, Xiaoke Wan, Hali Jakeman, Derek Myers, Elliot Grafer, Jian Liu, Frank Varosi, Sidney Schofield, Alexandria Moore, Maria-Ines van Olphen, Jordan Katz, Rory Barnes
This paper is to report the design and performance of a very high Doppler precision cross-dispersed
echelle spectrograph, EXtremely high Precision ExtrasolaR planet Tracker III (EXPERT-III), as part of a
global Exoplanet Tracker (ET) network. The ET network is designed to hunt low mass planets, especially
habitable rocky planets, around GKM dwarfs. It has an extremely high spectral resolution (EHR) mode of
R=110,000 and a high resolution (HR) mode of R=56,000 and can simultaneously cover 0.38-0.9 μm
with a 4kx4k back-illuminated Fairchild CCD detector with a single exposure. EXPERT-III is optimized
for high throughput by using two-prisms cross-disperser and a large core diameter fiber (2 arcsec on sky,
or 80 μm at f/4) to collect photons from the Kitt Peak National Observatory (KPNO) 2.1m telescope. The
average overall detection efficiency is ~6% from above the atmosphere to the detector for the EHR Mode
and about 11% for the HR mode. The extremely high spectral resolution in a compact design (the
spectrograph dimension, 1.34x0.8x0.48 m) is realized by coupling the single input 80 μm telescope fiber
into four 40 μm fibers and re-arranging the four small core diameter fibers into a linear fiber slit array (a
one-to-four fiber image slicer). EXPERT-III is operated in a vacuum chamber with temperature controlled
to ~2 milli-Kelvin rms for an extended period of time. The radial velocity (RV) drift is controlled to
within 10 meters/second (m/s) over a month. EXPERT-III can reach a photon noise limited RV
measurement precision of ~0.3 m/s for a V=8 mag GKM type dwarf with small rotation (vsini =2 km/s) in
a 15 min exposure. EXPERT-III’s RV measurement uncertainties for bright stars are primarily limited by
the Thorium-Argon (ThAr) calibration source (~0.5 m/s). EXPERT-III will serve as an excellent public
accessible high resolution optical spectroscope facility at the KPNO 2.1m telescope.
We report the system design and predicted performance of the Florida IR Silicon immersion grating
spectromeTer (FIRST). This new generation cryogenic IR spectrograph offers broad-band high resolution
IR spectroscopy with R=72,000 at 1.4-1.8 μm and R=60,000 at 0.8-1.35 μm in a single exposure with a
2kx2k H2RG IR array. It is enabled by a compact design using an extremely high dispersion silicon
immersion grating (SIG) and an R4 echelle with a 50 mm diameter pupil in combination with an Image
Slicer. This instrument is operated in vacuum with temperature precisely controlled to reach long term
stability for high precision radial velocity (RV) measurements of nearby stars, especially M dwarfs and
young stars. The primary technical goal is to reach better than 4 m/s long term RV precision with J<9 M
dwarfs within 30 min exposures. This instrument is scheduled to be commissioned at the Tennessee State
University (TSU) 2-m Automatic Spectroscopic Telescope (AST) at Fairborn Observatory in spring 2013.
FIRST can also be used for observing transiting planets, young stellar objects (YSOs), magnetic fields,
binaries, brown dwarfs (BDs), ISM and stars.
We plan to launch the FIRST NIR M dwarf planet survey in 2014 after FIRST is commissioned at the
AST. This NIR M dwarf survey is the first large-scale NIR high precision Doppler survey dedicated to
detecting and characterizing planets around 215 nearby M dwarfs with J< 10. Our primary science goal is
to look for habitable Super-Earths around the late M dwarfs and also to identify transiting systems for
follow-up observations with JWST to measure the planetary atmospheric compositions and study their
habitability. Our secondary science goal is to detect and characterize a large number of planets around M
dwarfs to understand the statistics of planet populations around these low mass stars and constrain planet
formation and evolution models. Our survey baseline is expected to detect ~30 exoplanets, including 10
Super Earths, within 100 day periods. About half of the Super-Earths are in their habitable zones and one
of them may be a transiting planet. The AST, with its robotic control and ease of switching between
instruments (in seconds), enables great flexibility and efficiency, and enables an optimal strategy, in terms
of schedule and cadence, for this NIR M dwarf planet survey.
We present a fixed delay interferometer to be installed in IR-ET (Infra-Red Exoplanets Tracker). We introduce
the design, fabrication and testing processes. In particular, we present a new methodology of computing the
fundamental limit of radial velocity (RV) measurement given by photon noise for DFDI (Dispersed Fixed Delay
Interferometer) method as opposed to conventional echelle method. The new method is later used to determine
the optical path difference (OPD) of the IR-ET interferometer. In addition, we introduce a novel method
of monitoring the stability of the interferometer for IR-ET in broad-band using fourier-transform white-light
scanning interferometry technique. The new method can be potentially expanded and applied to thermo-optic
effect measurement if temperature control system is introduced into the experiment. The thermal response of
the optical system is 3500 m/s/°C. We find that the RV calibration precision of 'Bracketing' method is 1.74
m/s without temperature control.
Doppler searches are extending to the near infrared to detect and characterize habitable planets around low mass stars.
We present an optical design and performance of a near-IR Doppler instrument. This instrument has two operating
modes covering 0.8-1.8 microns. One mode is called IRET, which consists of a fix-delay interferometer and a crossdispersed
echelle spectrograph to simultaneously cover 0.8-1.35 microns with a spectral resolution of R=22000 on a 2k x
2k H2RG IR array. The other mode is called FIRST, which uses a silicon immersion grating as the main disperser to
simultaneously cover 1.4-1.8 microns with a spectral resolution of R=55000 on the same detector as IRET. The triplepass
parabola white pupil design is used to restrain background scatter radiation with stable configuration for precision
radial velocity measurements. We used high index standard glasses for camera optics and VPH gratings as crossdispersers
in both modes. The FIRST mode can be switched in and out conveniently while the IRET mode is kept
without moving parts to increase its stability. This instrument is designed to deliver up to 1 m/s Doppler precision RV
measurements of nearby bright M dwarfs at the Apache Point Observatory 3.5 meter telescope. The instrument is
expected to be operational in the spring 2011.
Jian Ge, Bo Zhao, John Groot, Liang Chang, Frank Varosi, Xiaoke Wan, Scott Powell, Peng Jiang, Kevin Hanna, Ji Wang, Rohan Pais, Jian Liu, Liming Dou, Sidney Schofield, Shaun McDowell, Erin Costello, Adriana Delgado-Navarro, Scott Fleming, Brian Lee, Sandeep Bollampally, Troy Bosman, Hali Jakeman, Adam Fletcher, Gabriel Marquez
We report design, performance and early results from two of the Extremely High Precision Extrasolar
Planet Tracker Instruments (EXPERT) as part of a global network for hunting for low mass planets in the
next decade. EXPERT is a combination of a thermally compensated monolithic Michelson interferometer
and a cross-dispersed echelle spectrograph for extremely high precision Doppler measurements for nearby
bright stars (e.g., 1m/s for a V=8 solar type star in 15 min exposure). It has R=18,000 with a 72 micron
slit and a simultaneous coverage of 390-694 nm. The commissioning results show that the instrument has
already produced a Doppler precision of about 1 m/s for a solar type star with S/N~100 per pixel. The
instrument has reached ~4 mK (P-V) temperature stability, ~1 mpsi pressure stability over a week and a
total instrument throughput of ~30% at 550 nm from the fiber input to the detector. EXPERT also has a
direct cross-dispersed echelle spectroscopy mode fed with 50 micron fibers. It has spectral resolution of
R=27,000 and a simultaneous wavelength coverage of 390-1000 nm.
In high precision radial velocity (RV) measurements for extrasolar
planets searching and studies, a stable wide field Michelson
interferometer is very critical in Exoplanet Tracker (ET) instruments.
Adopting a new design, monolithic interferometers are homogenous and
continuous in thermal expansion, and field compensation and thermal
compensation are both satisfied. Interferometer design and fabrication are decrypted in details. In performance evaluations, field angle is typically 22° and thermal sensitivity is typically -1.7 x 10-6/°C, which corresponds to ~500 m/s /°C in RV scale. In interferometer stability monitoring using a wavelength stabilized laser source, phase shift data was continuously recorded for nearly seven days. Appling a frequent calibration every 30 minutes as in typical star observations, the interferometer instability contributes less than 1.4 m/s in RV error, in a conservative estimation.
We report performance of a new generation multi-object Doppler instrument for the on-going
Multi-object APO Radial-velocity Exoplanet Large-area Survey (MARVELS) of the Sloan
Digital Sky Survey III (SDSS-III) program. This instrument is based on dispersed fixed-delay
interferomtry design. It consists of a multi-object fiber-feed, a thermally compensated monolithic
fixed-delay interferometer, a high throughput spectrograph and a 4kx4k CCD camera. The
spectrograph resolving power is R=11,000 and the wavelength coverage is 500-570 nm. The
instrument is capable of measuring 60 stars in a single exposure for high to moderate precision
radial velocity (3-20 m/s) measurements depending on the star magnitudes (V=7.6-12). The
instrument was commissioned at the SDSS telescope in September 2008 and used to collect
science data starting in October 2008. Observations of reference stars show that the measured
photon noise limiting errors are consistent with the prediction for most of the measurements.
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