We perform a calculation of the vectorial field distribution in the focal plane of a multi-axial beam combiner and show the fundamental limitations with respect to the longitudinal component of the polarization of such a combiner for nulling interferometry.
We present a description of a new instrument development, HARPS3, planned to be installed on an upgraded and roboticized Isaac Newton Telescope by end-2018. HARPS3 will be a high resolution (R≃115,000) echelle spectrograph with a wavelength range from 380-690 nm. It is being built as part of the Terra Hunting Experiment - a future 10- year radial velocity measurement programme to discover Earth-like exoplanets. The instrument design is based on the successful HARPS spectrograph on the 3.6m ESO telescope and HARPS-N on the TNG telescope. The main changes to the design in HARPS3 will be: a customised fibre adapter at the Cassegrain focus providing a stabilised beam feed and on-sky fibre diameter ≈1:4 arcsec, the implementation of a new continuous ow cryostat to keep the CCD temperature very stable, detailed characterisation of the HARPS3 CCD to map the effective pixel positions and thus provide an improved accuracy wavelength solution, an optimised integrated polarimeter and the instrument integrated into a robotic operation. The robotic operation will optimise our programme which requires our target stars to be measured on a nightly basis. We present an overview of the entire project, including a description of our anticipated robotic operation.
MASCARA, the Multi-site All-Sky CAmeRA, is a project aimed at finding exoplanets transiting the brightest stars, in the V = 4 to 8 magnitude range, currently probed neither by space nor by ground based surveys. The target population for MASCARA consists mostly of hot Jupiters, for which the average transit depth is around 1%, and hot Neptunes. In order to achieve consistently a signal-to-noise ratio of better than 100 per hour at magnitude 8, MASCARA is based on three main concepts; simplicity stability and calibration.
MASCARA was designed with a minimum number of moving components. Five fixed, shutter-less, Peltier-cooled cameras, fitted with standard Canon 24 mm f/1.4 lenses are operating in a temperature controlled environment. Each camera constantly stares at the same patch of the sky. The exposure time is set to 6.4 seconds, keeping trailing of stars and saturation to a minimum while allowing for continuous exposures. Each camera is connected to its own control and data processing computer, allowing for fully independent operation of each of the cameras. Each camera takes between 4,000 and 7,000 exposures per night, which are reduced locally to produce un-calibrated light curves for the up to ~40,000 pre-selected stars, as well as image stacks of 50 images. For each set of 50 images, astrometry of the solution is verified to monitor drifts in the station. Currently both reduced data as well as raw data (~500 GB/night) are transferred to a central data repository, but for stations with less bandwidth, potentially only the reduced data could be transferred. MASCARA currently only permanently stores the reduced light curves and binned image stacks, deleting the raw images after one month.
After transfer, the raw light curves are self-calibrated in batches of 2-4 weeks, removing the spatially varying transmission of the camera, the impact of crowding and spatially variable PSF, and the time variable transmission of the atmosphere. Using a combination of SysRem and flagging of data points that are impacted by known artifacts (moon, sun, clouds, etc.), we have demonstrated a photometric stability of MASCARA down to 0.3% at magnitude V=7.7 within 5.3 minutes.
The detection of Earth twins with the radial velocity (RV) method requires extreme Doppler precision and long term stability. One of the limiting factors in RV precision is the variation of the instrumental response due primarily to guiding errors, changes in focus or seeing. In order to provide extreme stability, we propose to use single-mode fibers to couple small amateur telescopes to a compact and ultra-stable high-resolution spectrograph. Here, we present a concept study for DREAMS, a Dedicated Robotic EArths-finding single-Mode Spectrograph, which should allow unprecedented RV precision on very bright stars.
MASCARA, the Multi-site All-Sky CAmeRA, consists of several fully-automated stations. Its goal is to find exoplanets transiting the brightest stars, in the mV = 4 to 8 magnitude range. Each station contains five wide- angle cameras monitoring the near-entire sky at each location. The five cameras are located in a temperature- controlled enclosure and look at the sky through five windows. A housing with a moving roof protects MASCARA from the environment. Here, we present the opto-mechanical design of the first MASCARA station.
MASCARA, the Multi-site All-Sky CAmeRA, will consist of several fully-automated stations distributed across the globe. Its goal is to find exoplanets transiting the brightest stars, in the mV = 4 to 8 magnitude range, currently probed neither by space- nor by ground-based surveys. The nearby transiting planet systems that MASCARA is expected to discover will be key targets for future detailed planet atmosphere observations. The target population for MASCARA consists mostly of hot Jupiters. The main requirement set on MASCARA to detect these planets around stars down to magnitude 8 is to reach a minimum Signal-to-Noise Ratio of 100 within one hour of observation.
Each MASCARA station consists of five low-noise off-the-shelf full-frame CCD cameras, fitted with standard Canon 24 mm , f/1.4 lenses, monitoring the near-entire sky down to magnitude 8 at that location. Measurements have demonstrated that the required Signal-to-Noise Ratio of 100, can be achieved in less than thirty minutes. MASCARA aims at deploying several stations world-wide to provide a nearly continuous coverage of the dark sky, at sub-minute cadence.
While at the faint end MASCARA is limited mainly by photon noise, at the bright end scintillation and red noise become the limiting factors. Instrumental noise sources are reduced by placing the cameras in a fixed orientation and in a temperature controlled environment. By defocusing and allowing stars to drift over the detector, the impact of pixel-to-pixel variations on the photometry are minimized, while taking exposures at fixed sidereal times allows accurate cross-calibration of consecutive nights. The exposure time of 6.4 seconds gives rise to a high data acquisition rate of a MASCARA station, around 500GB per night. In order to minimize data transport and data storage requirements, the raw images are reduced to produce accurate light curves in nearly real time.
The first MASCARA station will be integrated on La Palma during the summer of 2014. MASCARA test
data were taken in July 2013 with one camera targeting the transiting exoplanet HD 189733b. Its brightness of mV = 7:7 is close to the faint end of the MASCARA magnitude range. The 5 - σ detection of the 2.8% deep transit with a 5-minute binning of the data confirms that we will be able to detect 1% transit at the faint end within one hour.
MASCARA, the Multi-site All-Sky CAmeRA, consists of several fully-automated stations distributed across the globe. Its goal is to find exoplanets transiting the brightest stars, in the V = 4 to 8 magnitude range, currently probed neither by space- nor by ground-based surveys. The nearby transiting planet systems that MASCARA is expected to discover will be key targets for future detailed planet atmosphere observations. Each station contains five wide-angle cameras monitoring the near-entire sky at each location. Once fully deployed, MASCARA will provide a nearly continuous coverage of the dark sky, down to magnitude 8, at sub-minute cadence. Effectively taking an image of the full sky every 6.4 seconds, MASCARA will produce approximately 500 GB of raw data per night, per station. This data needs to be processed in order to produce calibrated light curves, for up to ~40,000 stars down to magnitude 8 and with a signal-to-noise-ratio of better than 100. The aim of the data reduction pipeline is to process the data locally and in real time, both to immediately have quality control, as well as to prevent a data back-log. Although the cameras are fixed and the stars are therefore drifting over the CCDs, MASCARA is a targeted mission. Data processing consists of three main steps: 1. Compute a complete astrometric solution to sub-pixel level for each exposure and extracting postage stamps for each of the stars in the field of view. 2. Perform accurate photometry on each of the postage stamps, including back-ground subtraction and identification of errors in the photometry due to bad pixels, satellites, air planes or Laser Guide Stars. 3. Remove fluctuations on time scales typical for transits, i.e., several hours, caused by for example the camera and atmospheric transmission, color variations in stars and pixel-to-pixel gain fluctuations. Photometry on short time scales already shows noise levels close to the photon noise limit, and using a combination of calibration and relative photometry the red-noise component can be reduced to close to this photon noise limit, allowing for semi-automated identification of exo-planet transits. This paper discusses the data handling, processing and calibration and shows the first results of the pipeline.
The detection of Earth analogs with radial velocity requires long-term precision of 10 cm/s. One of the factors
limiting precision is variation in instrumental profile from observation to observation due to changes in the
illumination of the slit and spectrograph optics. Fiber optics are naturally efficient scramblers. Our research is
focused on understanding the scrambling properties of fibers with different geometries. We have characterized
circular and octagonal fibers in terms of focal ratio degradation, near-field and far-field distributions. We have
characterized these fibers using a bench-mounted high-resolution spectrograph: the Yale Doppler Diagnostics
The detection of Earth analogs with radial velocity requires extreme Doppler precision and long term stability.
Variations in the illumination of the slit and of the spectrograph optics occur on time scales of seconds and
minutes, primarily because of guiding, seeing and focusing. These variations yield differences in the instrumental
profile (IP). In order to stabilize the IP, we designed a fiber feed for the Hamilton spectrograph at Lick and for
HIRES at Keck. Here, we report all results obtained with these fiber scramblers. We also present the design of
a new double scrambler/pupil slicer for HIRES at Keck.
CHIRON is a fiber-fed Echelle spectrograph with observing modes for resolutions from 28,000 to 120,000, built
primarily for measuring precise radial velocities (RVs). We present the instrument performance as determined during
integration and commissioning. We discuss the PSF, the effect of glass inhomogeneity on the cross-dispersion prism,
temperature stabilization, stability of the spectrum on the CCD, and detector characteristics. The RV precision is
characterized, with an iodine cell or a ThAr lamp as the wavelength reference. Including all losses from the sky to the
detector, the overall efficiency is about 6%; the dominant limitation is coupling losses into the fiber due to poor guiding.
The detection of earth-like exoplanets with the Doppler technique requires extreme precision spectrographs stable over
timescales of years. The precision requirement of 10 cm/s is equivalent to a relative uncertainty of 3x10-10, and, with the typical dispersion of the Echelle spectrographs used for this purpose, translates to a shift of a few nanometers of the spectrum on the detector. Consequently, the instrument must be well understood and optimized in every component and detail. We describe the Yale Doppler diagnostic facility (YDDF), a dedicated bench mounted Echelle spectrograph in
our lab at Yale University, which will be used to systematically study the influence of different components at this
precision level. The spectrograph bench allows for a flexible optical configuration, high resolution and sampling, and
wide spectral coverage. Further, we incorporated a turbulence and guiding simulator to realistically reproduce the
situation at the telescope, enabling end-to-end tests of important parameters.
Exoplanets can be detected from a time series of stellar spectra by looking for small, periodic shifts in the absorption
features that are consistent with Doppler shifts caused by the presence of an exoplanet, or multiple exoplanets, in the
system. While hundreds of large exoplanets have already been discovered with the Doppler technique (also called radial
velocity), our goal is to improve the measurement precision so that many Earth-like planets can be detected. The smaller
mass and longer period of true Earth analogues require the ability to detect a reflex velocity of ~10 cm/s over long time
periods. Currently, typical astronomical spectrographs calibrate using either Iodine absorptive cells or Thorium Argon
lamps and achieve ~10 m/s precision, with the most stable spectrographs pushing down to ~2 m/s. High velocity
precision is currently achieved at HARPS by controlling the thermal and pressure environment of the spectrograph.
These environmental controls increase the cost of the spectrograph, and it is not feasible to simply retrofit existing
spectrometers. We propose a fiber-fed high precision spectrograph design that combines the existing ~5000-6000 A
Iodine calibration system with a high-precision Laser Frequency Comb (LFC) system from ~6000-7000 A that just
meets the redward side of the Iodine lines. The scientific motivation for such a system includes: a 1000 A span in the red
is currently achievable with LFC systems, combining the two calibration methods increases the wavelength range by a
factor of two, and moving redward decreases the "noise" from starspots. The proposed LFC system design employs a
fiber laser, tunable serial Fabry-Perot cavity filters to match the resolution of the LFC system to that of standard
astronomical spectrographs, and terminal ultrasonic vibration of the multimode fiber for a stable point spread function.
Small telescopes coupled to high resolution spectrometers are powerful tools for Doppler planet searches. They allow for
high cadence observations and flexible scheduling; yet there are few such facilities. We present an innovative and
inexpensive design for CHIRON, a high resolution (R~80.000) Echelle spectrometer for the 1.5m telescope at CTIO.
Performance and throughput are very good, over the whole spectral range from 410 to 870nm, with a peak efficiency of
15% in the iodine absorption region. The spectrograph will be fibre-fed, and use an iodine cell for wavelength
calibration. An image slicer permits a moderate beam size. We use commercially available, high performance optical
components, which is key for quick and efficient implementation. We discuss the optical design, opto-mechanical
tolerances and resulting image quality.
The detection of Earth analogues requires extreme Doppler precision and long term stability in order to measure tiny reflex velocities in the host star. The PSF from the spectrometer should be slowly varying with temperature and pressure changes. However, variations in the illumination of the slit and of the spectrograph optics occur on time scales of seconds, primarily because of guiding errors, but also on timescales of minutes, because of changes in the focus or seeing. These variations yield differences in the PSF from observation to observation, which are currently limiting the Doppler precision. Here, we present the design of a low cost fiber optic feed, FINDS, used to stabilize the PSF of the Hamilton spectrograph of Lick observatory along with the first measurements that show dramatic improvement in stability.
We present simulations and experimental results on encoding information both in the longitudinal and transverse
directions of an optical beam reflected from an asymmetric pit. The method does not require interferometric
detection but is based on intensity measurements using a simple quadrant detector. In addition, we also discuss
the implementation of this scheme in an optical recording setup and make an analysis of the crosstalk between
The optical properties of materials are wavelength-dependent. This property, called dispersion, affects the
performance of a wide-band nulling interferometer by inducing wavelength-dependent phase differences between
the arms of the interferometer. In this paper, we analyze the influence of dispersion in nulling interferometers
for exoplanet detection.
We present the design of a new testbed experiment to demonstrate nulling interferometry using polarization properties.
This three-beam set-up is perfectly symmetric with respect to the number of reflections and transmissions
and should therefore allow a high rejection ratio in a wide spectral band.
We show the theoretical limitations of a multi-axial nulling interferometer with respect to longitudinal polarization.
We furthermore analyze the filtering capabilities of a single-mode fiber in this case.
We discuss the previously-reported measurements of a three-beam nulling interferometer without achromatic
phase-shifters, using delay lines only. The theoretical rejection ratio of a few thousand has not been achieved
experimentally. In order to explain the obtained results, some direct spectral and polarization measurements have
been performed. We present here the latest results and discuss some asymmetries in the interference patterns.
We present a new type of nulling interferometer that makes use of polarization properties to have on-axis destructive interference. The proposed design, which only involves commercial components and no achromatic device, is also suitable for internal modulation. This type of interferometer should enable a high rejection ratio in a theoretically unlimited spectral band. We implemented that concept on a two-beam white-light interferometer and we present here the first experimental results.