Scott Powell

Design, performance, and early results from extremely high Doppler precision instruments in a global network

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.

High resolution Florida IR silicon immersion grating spectrometer and an M dwarf planet survey

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.

Wide-field tracking of moving objects with a compact multi-object dispersed fixed-delay interferometer

We present a new concept for a Doppler imaging remote sensing instrument to track moving objects within a wide field of view using a compact multi-object Dispersed Fixed-Delay Interferometer (DFDI). The instrument is a combination of a Michelson type interferometer with a fixed optical delay and a medium resolution spectrograph. This takes advantage of the strength of the DFDI approach over the traditional cross-dispersed echelle spectrograph approach for high radial velocity (RV) precision measurements: multi-object capability, high throughput and a compact design. The combination of a fiber integral field unit (IFU) with a DFDI instrument allows simultaneous sampling of all of the objects within the observing field of view (FOV) to provide differential RV measurements of moving objects over background objects. Due to the three dimensional nature of the IFU spectroscopy the object location and spectral features can be simultaneously acquired. With the addition of RV signals to the measurements, this approach allows precise extraction of trajectories and spectral properties of moving objects (such as space debris and near Earth Objects (NEOs)) through sequential monitoring of moving objects. Measurement results from moving objects in a lab as well as moving cars in a field using this innovative approach are reported.

Design and Performance of a New Generation, Compact, Low Cost, Very High Doppler Precision and Resolution Optical Spectrograph

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.

Silicon immersion gratings and their spectroscopic applications

Silicon immersion gratings (SIGs) offer several advantages over the commercial echelle gratings for high resolution infrared (IR) spectroscopy: 3.4 times the gain in dispersion or ~10 times the reduction in the instrument volume, a multiplex gain for a large continuous wavelength coverage and low cost. We present results from lab characterization of a large format SIG of astronomical observation quality. This SIG, with a 54.74 degree blaze angle (R1.4), 16.1 l/mm groove density, and 50x86 mm2 grating area, was developed for high resolution IR spectroscopy (R~70,000) in the near IR (1.1-2.5 μm). Its entrance surface was coated with a single layer of silicon nitride antireflection (AR) coating and its grating surface was coated with a thin layer of gold to increase its throughput at 1.1-2.5 m. The lab measurements have shown that the SIG delivered a spectral resolution of R=114,000 at 1.55 m with a lab testing spectrograph with a 20 mm diameter pupil. The measured peak grating efficiency is 72% at 1.55 m, which is consistent with the measurements in the optical wavelengths from the grating surface at the air side. This SIG is being implemented in a new generation cryogenic IR spectrograph, called the Florida IR Silicon immersion grating spectrometer (FIRST), to offer broad-band high resolution IR spectroscopy with R=72,000 at 1.4-1.8 um under a typical seeing condition in a single exposure with a 2kx2k H2RG IR array at the robotically controlled Tennessee State University 2-meter Automatic Spectroscopic Telescope (AST) at Fairborn Observatory in Arizona. FIRST is designed to provide high precision Doppler measurements (~4 m/s) for the identification and characterization of extrasolar planets, especially rocky planets in habitable zones, orbiting low mass M dwarf stars. It will also be used for other high resolution IR spectroscopic observations of such as young stars, brown dwarfs, magnetic fields, star formation and interstellar mediums. An optimally designed SIG of the similar size can be used in the Silicon Immersion Grating Spectrometer (SIGS) to fill the need for high resolution spectroscopy at mid IR to far IR (~25-300 μm) for the NASA SOFIA airborne mission in the future.

The first super-Earth detection from the high cadence and high radial velocity precision Dharma Planet Survey

The Dharma Planet Survey (DPS) aims to monitor about 150 nearby very bright FGKM dwarfs (within 50 pc) during 2016

On-sky Doppler performance of TOU optical very high-resolution spectrograph for detecting low-mass planets

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A robotic, compact, and extremely high resolution optical spectrograph for a close-in super-Earth survey

2020 for low-mass planet detection and characterization using the TOU very high resolution optical spectrograph (R

On-sky calibration performance of a monolithic Michelson interferometer filtered source

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On-sky performance of a high resolution silicon immersion grating spectrometer

100,000, 380-900nm). TOU was initially mounted to the 2-m Automatic Spectroscopic Telescope at Fairborn Observatory in 2013-2015 to conduct a pilot survey, then moved to the dedicated 50-inch automatic telescope on Mt. Lemmon in 2016 to launch the survey. Here we report the first planet detection from DPS, a super-Earth candidate orbiting a bright K dwarf star, HD 26965. It is the second brightest star (