NEID is a radial velocity (RV) instrument including an ultra-stabilized fiber-fed spectrograph, installed in 2019 at the 3.5m WIYN telescope at Kitt Peak National Observatory. Accompanying it is a solar feed system built to supply the spectrograph with disk-integrated sunlight. Observing the Sun “as a star” is essential for developing and validating mitigation strategies for RV variations due to stellar activity and instrument systematics, thus enabling more-effective detections of lower-mass exoplanets. In this paper, we will detail the design of the NEID solar feed system and showcase early results addressing NEID systematics and solar RV variability.
Modern precise radial velocity spectrometers are designed to infer the existence of planets orbiting other stars by measuring few-nm shifts in the positions of stellar spectral lines recorded at high spectral resolution on a large-area digital detector. While the spectrometer may be highly stabilized in terms of temperature, the detector itself may undergo changes in temperature during readout that are an order of magnitude or more larger than the other optomechanical components within the instrument. These variations in detector temperature can translate directly into systematic measurement errors. We explore a technique for reducing the amplitude of CCD temperature variations by shuffling charge within a pixel in the parallel direction during integration. We find that this “dither clocking” mode greatly reduces temperature variations in the CCDs being tested for the NEID spectrometer. We investigate several potential negative effects this clocking scheme could have on the underlying spectral data.
Teledyne’s H2RG detector images suffer from crosshatch like patterns, which arise from subpixel quantum efficiency (QE) variation. We present our measurements of this subpixel QE variation in the Habitable-Zone Planet Finder’s H2RG detector. We present a simple model to estimate the impact of subpixel QE variations on the radial velocity and how a first-order correction can be implemented to correct for the artifact in the spectrum. We also present how the HPF’s future upgraded laser frequency comb will enable us to implement this correction.
Two key areas of emphasis in contemporary experimental exoplanet science are the detailed characterization of transiting terrestrial planets and the search for Earth analog planets to be targeted by future imaging missions. Both of these pursuits are dependent on an order-of-magnitude improvement in the measurement of stellar radial velocities (RV), setting a requirement on single-measurement instrumental uncertainty of order 10 cm / s. Achieving such extraordinary precision on a high-resolution spectrometer requires thermomechanically stabilizing the instrument to unprecedented levels. We describe the environment control system (ECS) of the NEID spectrometer, which will be commissioned on the 3.5-m WIYN Telescope at Kitt Peak National Observatory in 2019, and has a performance specification of on-sky RV precision <50 cm / s. Because NEID’s optical table and mounts are made from aluminum, which has a high coefficient of thermal expansion, sub-milliKelvin temperature control is especially critical. NEID inherits its ECS from that of the Habitable-Zone Planet Finder (HPF), but with modifications for improved performance and operation near room temperature. Our full-system stability test shows the NEID system exceeds the already impressive performance of HPF, maintaining vacuum pressures below 10 − 6 Torr and a root mean square (RMS) temperature stability better than 0.4 mK over 30 days. Our ECS design is fully open-source; the design of our temperature-controlled vacuum chamber has already been made public, and here we release the electrical schematics for our custom temperature monitoring and control system.
The Habitable-zone Planet Finder (HPF) is a highly stabilized fiber fed precision radial velocity (RV) spec- trograph working in the Near Infrared (NIR): 810 – 1280 nm. In this paper we present an overview of the preparation of the optical fibers for HPF. The entire fiber train from the telescope focus down to the cryostat is detailed. We also discuss the fiber polishing, splicing and its integration into the instrument using a fused silica puck. HPF was designed to be able to operate in two modes, High Resolution (HR- the only mode mode currently commissioned) and High Efficiency (HE). We discuss these fiber heads and the procedure we adopted to attach the slit on to the HR fibers.
NEID is a new extreme precision Doppler spectrometer for the WIYN telescope. It is fiber fed and employs a classical white pupil Echelle configuration. NEID has a fiber aperture of only 0.92” on sky in high-resolution mode, and its tight radial velocity error budget resulted in very stringent stability requirements for the input illumination of the spectrograph optics. Consequently, the demands on the fiber injection are challenging. In this paper, we describe the layout and optical design of the injection module, including a broadband, high image quality relay and a high-performance atmospheric dispersion corrector (ADC) across the bandwidth of 380 – 930 nm.
The Habitable-Zone Planet Finder (HPF) is a stabilized, fiber-fed, NIR spectrometer recently commissioned at the 10m Hobby-Eberly telescope (HET). HPF has been designed and built from the ground up to be capable of discovering low mass planets around mid-late M dwarfs using the Doppler radial velocity technique. Novel apects of the instrument design include mili-kelvin temperature control, careful attending to fiber scrambling, and optics, mounting and detector readout schemes designed to minimize drifts and maximize the radial velocity precision. The optical design of the HPF is an asymmetric white pupil spectrograph layout in a vacuum cryostat cooled to 180 K. The spectrograph uses gold-coated mirrors, a mosaic echelle grating, and a single Teledyne Hawaii-2RG (H2RG) NIR detector with a 1.7-micron cutoff covering parts of the information-rich z, Y and J NIR bands at a spectral resolution of R~55,000. The use of 1.7 micron H2RG enables HPF to operate warmer than most other cryogenic instruments- with the instrument operating at 180K (allowing normal glasses to be used in the camera) and the detector at 120K. We summarize the engineering and commissioning tests on the telescope and the current radial velocity performance of HPF. With data in hand we revisit some of the design trades that went into the instrument design to explore the remaining tall poles in precision RV measurements in the near-infrared. HPF seeks to extend the precision radial velocity technique from the optical to the near-infrared, and in this presentation, we seek to share with the community our experience in this relatively new regime.
Proc. SPIE. 9908, Ground-based and Airborne Instrumentation for Astronomy VI
KEYWORDS: Spectrographs, Control systems, Doppler effect, Precision optics, Velocimetry, Control systems design, Optical benches, Exoplanets, Temperature metrology, Electronics
We present preliminary results for the environmental control system from NEID, our instrument concept for NASA's Extreme Precision Doppler Spectrograph, which is now in development. Exquisite temperature control is a requirement for Doppler spectrographs, as small temperature shifts induce systematic Doppler shifts far exceeding the instrumental specifications. Our system is adapted from that of the Habitable Zone Planet Finder instrument, which operates at a temperature of 180K.We discuss system modifications for operation at T ~ 300K, and show data demonstrating sub-mK stability over two weeks from a full-scale system test.
We present recent long-term stability test results of the cryogenic Environmental Control System (ECS) for the Habitable zone Planet Finder (HPF), a near infrared ultra-stable spectrograph operating at 180 Kelvin. Exquisite temperature and pressure stability is required for high precision radial velocity (< 1m=s) instruments, as temperature and pressure variations can easily induce instrumental drifts of several tens-to-hundreds of meters per second. Here we present the results from long-term stability tests performed at the 180K operating temperature of HPF, demonstrating that the HPF ECS is stable at the 0:6mK level over 15-days, and <10-7 Torr over months.
We describe the Instrument Control Software (ICS) package that we have built for The Habitable-Zone Planet Finder (HPF) spectrometer. The ICS controls and monitors instrument subsystems, facilitates communication with the Hobby-Eberly Telescope facility, and provides user interfaces for observers and telescope operators. The backend is built around the asynchronous network software stack provided by the Python Twisted engine, and is linked to a suite of custom hardware communication protocols. This backend is accessed through Python-based command-line and PyQt graphical frontends. In this paper we describe several of the customized subsystem communication protocols that provide access to and help maintain the hardware systems that comprise HPF, and show how asynchronous communication benefits the numerous hardware components. We also discuss our Detector Control Subsystem, built as a set of custom Python wrappers around a C-library that provides native Linux access to the SIDECAR ASIC and Hawaii-2RG detector system used by HPF. HPF will be one of the first astronomical instruments on sky to utilize this native Linux capability through the SIDECAR Acquisition Module (SAM) electronics. The ICS we have created is very flexible, and we are adapting it for NEID, NASA's Extreme Precision Doppler Spectrometer for the WIYN telescope; we will describe this adaptation, and describe the potential for use in other astronomical instruments.
Proc. SPIE. 9915, High Energy, Optical, and Infrared Detectors for Astronomy VII
KEYWORDS: Near infrared, Sensors, Mercury cadmium telluride, Detector arrays, Sensors, Near infrared, Contamination, Quantum efficiency, Temperature metrology, Signal detection, Absorption, Black bodies
Infrared detectors with cutoff wavelengths of ~ 1.7 μm have much lower sensitivity to thermal background contamination than those with longer cutoff wavelengths. This low sensitivity offers the attractive possibility of reducing the need for fully cryogenic systems for YJH-band work, offering the potential for “warm-pupil" instrumentation that nonetheless reduces detected thermal background to the level of dark current. However, residual sensitivity beyond the cutoff wavelength is not well characterized, and may preclude the implementation of such warm-pupil instruments. We describe an experiment to evaluate the long-wavelength sensitivity tail of a 1.7 µm-cutoff HAWAII-2RG array using a thermal blocking filter. Our results suggest the possibility of measurable red sensitivity beyond ~ 2 μm. Ongoing improvements will confirm and refine this measurement. The thermal blocking filter offers the prospect of warm-pupil NIR instrument operation, which is particularly valuable for cost-effective and efficient testing systems: it has facilitated NIR detector characterization and will enable crucial laboratory tests of laser frequency comb calibration systems and other NIR calibration sources.
We present the design concept of the wavelength calibration system for the Habitable-zone Planet Finder instrument (HPF), a precision radial velocity (RV) spectrograph designed to detect terrestrial-mass planets around M-dwarfs. HPF is a stabilized, fiber-fed, R~50,000 spectrograph operating in the near-infrared (NIR) z/Y/J bands from 0.84 to 1.3 microns. For HPF to achieve 1 m s-1 or better measurement precision, a unique calibration system, stable to several times better precision, will be needed to accurately remove instrumental effects at an unprecedented level in the NIR. The primary wavelength calibration source is a laser frequency comb (LFC), currently in development at NIST Boulder, discussed separately in these proceedings. The LFC will be supplemented by a stabilized single-mode fiber Fabry-Perot interferometer reference source and Uranium-Neon lamp. The HPF calibration system will combine several other new technologies developed by the Penn State Optical-Infrared instrumentation group to improve RV measurement precision including a dynamic optical coupling system that significantly reduces modal noise effects. Each component has been thoroughly tested in the laboratory and has demonstrated significant performance gains over previous NIR calibration systems.
HPF is an ultra-stable, precision radial velocity near infrared spectrograph with a unique environmental
control scheme. The spectrograph will operate at a mid-range temperature of 180K, approximately half
way between room temperature and liquid nitrogen temperature; it will be stable to sub -milli-Kelvin(mK)
levels over a calibration cycle and a few mK over months to years. HPF‟s sensor is a 1.7 micron H2RG
device by Teledyne. The environmental control boundary is a 9 m2 thermal enclosure that completely
surrounds the optical train and produces a near blackbody cavity for all components. A large, pressure -
stabilized liquid nitrogen tank provides the heat sink for the system via thermal straps while a multichannel
resistive heater control system provides the stabilizing heat source. High efficiency multi-layer
insulation blanketing provides the outermost boundary of the thermal enclosure to largely isolate the
environmental system from ambient conditions. The cryostat, a stainless steel shell derived from the
APOGEE design, surrounds the thermal enclosure and provides a stable, high quality vacuum environment.
The full instrument will be housed in a passive „meat -locker‟ enclosure to add a degree of additional
thermal stability and as well as protect the instrument. Effectiveness of this approach is being empirically
demonstrated via long duration scale model testing. The full scale cryostat and environmental control
system are being constructed for a 2016 delivery of the instrument to the Hobby-Eberly Telescope. This
report describes the configuration of the hardware and the scale-model test results as well as projections for
performance of the full system.
The Habitable-Zone Planet Finder is a stabilized, fiber-fed, NIR spectrograph being built for the 10m Hobby- Eberly telescope (HET) that will be capable of discovering low mass planets around M dwarfs. The optical design of the HPF is a white pupil spectrograph layout in a vacuum cryostat cooled to 180 K. The spectrograph uses gold-coated mirrors, a mosaic echelle grating, and a single Teledyne Hawaii-2RG (H2RG) NIR detector with a 1.7-micron cutoff covering parts of the information rich z, Y and J NIR bands at a spectral resolution of R∼50,000. The unique design of the HET requires attention to both near and far-field fiber scrambling, which we accomplish with double scramblers and octagonal fibers. In this paper we discuss and summarize the main requirements and challenges of precision RV measurements in the NIR with HPF and how we are overcoming these issues with technology, hardware and algorithm developments to achieve high RV precision and address stellar activity.
We present developments in simulations and software for the Habitable Zone Planet Finder (HPF), an R~50,000 near-infrared cross-dispersed radial velocity spectrograph that will be used to search for planets around M dwarfs. HPF is fiber-fed, operates in the zYJ bands, and uses a 1.7μm cutoff HAWAII-2RG (H2RG) NIR detector. We have constructed an end-to-end simulator that accepts as input a range of stellar models contaminated with telluric features and processes these through a simulated detector. This simulator accounts for the characteristics of the H2RG, including interpixel capacitance, persistence, nonlinearities, read noise, and other detector characteristics, as measured from our engineering-grade H2RG. It also implements realistic order curvature. We describe applications of this simulator including optimization of the fiber configuration at the spectrograph slit and selection of properties for a laser frequency comb calibration source. The simulator has also provided test images for development of the HPF survey extraction and RV analysis pipeline and we describe progress on this pipeline itself, which will implement optimal extraction, laser frequency comb and emission lamp wavelength calibration, and cross-correlation based RV measurement.
We describe the development of a software simulator to support development of the Habitable Zone Planet Finder
Spectrograph (HPF), currently being designed to search for planets around M dwarf stars. HPF is a near infrared
R 50,000 cross-dispersed radial velocity spectrograph using a HAWAII-2 RG (H2RG) NIR array, is cooled to
200K, is fiber-fed, and operates in the Y and J bands. This instrument is funded and is in the design phase,
and will be commissioned on the 10m Hobby-Eberly Telescope in 2015. Our simulations process high-resolution
stellar spectra through models of the instrument, detector, and a simple extraction pipeline. Our objective is to
create a a fully functional simulation of the entire HPF system, which can be used to guide spectrograph design
and to aid in observation planning. We describe the fundamental design of these simulations and the tests we
have performed, which verify that the simulator code is stable with inclusion of simple detector effects, and is
ready for expansion to account for more complex factors such as order curvature.
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