The latter is a specific working example of the Integral Field Spectrograph (IFS) planned for the next Planet Finder instrument on the Very Large Telescope (SPHERE) facility. The work presented in this dissertation is entirely devoted to high-contrast diffraction-limited integral-field spectroscopy.
Properties of the observed circumstellar disks 58
Dynamical perturbation of the star 70
Direct detection of extrasolar planets 83
Planet features useful for Simultaneous Differential Imaging 97
Characterization of the telescope PSF with AO-compensation 101
Integral Field Spectroscopy at the diffraction limit: S-SDI 112
Coherent and Incoherent CrossTalks 149
Format of the final spectra on the IFS Detector plane 152
TIGER and BIGRE Integral Field Units vs. SPHERE/IFS TLRs 155
The BIGRE Integral Field Unit for SPHERE/IFS 158
The science milestone: rocky planets 195
Top Level Requirements for the EPICS/Instruments 199
Note the increase (Maxwell-Bolzmann plasma), maximum and decrease (Fermi-Dirac plasma) of the core temperature for brown dwarfs. 175 Figure 6-8: SPHERE/IFS/Camera dot plots from on-axis configuration to.
The realm of sub-stellar objects
- Proper characteristics of brown dwarfs and giant planets evolution
- Model atmospheres for brown dwarfs
- Insight on the brown dwarfs formation mechanisms
- Brown dwarfs statistics
This process involves the formation of a circumstellar disk due to the conservation of angular momentum. The mass function of the brown dwarf population as a whole is another observable link to the possible formation processes.
Theories of planetary system formation
The Capture formation scenario
On the contrary, the Capture formation scenario should be foreseen. a decrease in the planet's mass function towards the low-mass region. Much further, the physical processes leading to the formation of the planets in the Disk Instability mechanism depend only on the gravitational instability of the gas contained in the protoplanetary disk, independent of the growth of dust grains, which in turn leads to the formation of Planetesimals.
Insight on the present-day theoretical approaches to planetary system formation These planetary formation scenarios presented above succeed to explain some characteristics
On the other hand, direct radial migration is expected due to inward torques between the planet and the disc or outward torques between the planet and the star, or finally to outward torques due to Roche lobe overflow and consequent mass loss of the planet (Trilling et al. 1998). . Currently, all the new theoretical topics (in situ formation, migration, circularization, etc.) are matters of debate between two main formation scenarios, which in turn represent the thoughtful update of the old solar nebula and capture (see Sections 1.2.1 and 1.2).2 for details): the Core Accretion and Disk Instability mechanisms.
Model atmospheres for extrasolar giant planets
This classification was improved in Sudarsky et al. 2003), which obtains the spectral profile of the total energy (i.e. the sum of the reflected and internal - blackbody - radiations) emitted by the atmospheres of irradiated extrasolar giant planets. The specifications of the Sudarsky's spectral classification of extrasonic giant planets are properly described in Sudarsky et al.
Earth’s atmosphere and models for extrasolar terrestrial planets
In the Earth's spectrum, this pattern is detected as a strong increase in spectral albedo beyond 0.7 [micron] (see Figure 1-17) and is then called the Red Edge. The interferometric pattern in the center right of the figure is the CCD edge with which the instrumental spectrum produced by the detector is divided.
Statistical properties of the observed planetary systems
Properties of the observed exoplanets
Currently, the avoidance zone observed in the diagram correlating orbital eccentricity and semi-major orbital axis (see Figure 1-22) is interpreted as a manifestation of the gravitational tidal circularization of the orbits induced by the host star. Within the framework of the Core Accretion scenario, this statistical trend could be interpreted as the evidence that planetary migration depends on the metallicity of the star and then on the metallicity of the protoplanetary disk.
Properties of the observed circumstellar disks
Protoplanetary disks
Dusty disks
Similar structures in the dusty Solar System are associated with the presence of planets; for this reason, the observed structures in extrasolar dust disks have given rise to the idea that they could also be the result of as yet undiscovered distant exoplanets in these systems (cf. In addition, such disks can contain comparable amounts of dynamically coupled gas and dust and - in the case of embedded planets - this the feature could enable the direct detection of dynamic interactions between the planet and the disc, which could shed light on the migration processes of the planets (cfr. Artymowicz 1999).
Bibliography
Hayashi, C., Fundamental Problems in the Theory of Stellar Evolution; Proceedings of the symposium, Kyoto, Japan, July. These works should be considered the first pioneering attempts to collect the light of a planet separately from that of its parent star.
Dynamical perturbation of the star
The Radial Velocity technique
The radial velocity Vs of the star, measured along the line of sight (from the upper right side of the diagram), depends on the sine of the orbital inclination angle. Shaking of a star is due to various causes, including convective motions in the stellar photospheres, activity, etc.
The Astrometric Perturbation technique
A strategy that takes into account multiple measurements of radial velocities in a suitable time frame could significantly lower the threshold for detecting extrasolar planets using the radial velocity technique. On this subject, the remarkable observations of Benedict et al. 2002), in which they took advantage of the HST Fine Guiding System for astrometric measurements in combination with measurements obtained using the radial velocity technique for a planet orbiting Gliese 876.
The Timing Delay technique
It will contribute to the large-scale systematic detection of Jupiter-like planets up to 150-200 pc from Earth. The scientific goals of SIM are focused on a list of target stars, with the aim of finding planets down to the mass of the Earth (Extra-Solar Planet Interferometric Survey).
The Transit technique
In the transit technique, the photometric accuracy determines the accuracy of the estimate of the planet's radius. In the general description of the Transit technique, it is necessary to mention the problem of false alarms.
The Gravitational Microlensing
This is probably due to a planet obscuring a starspot on the surface of the star (cfr, Charbonneau et al. 2006). Gravitational microlensing is a very rare phenomenon that requires very close alignment of the lens and the magnified object; therefore, the background field must be very rich in potential targets.
Direct detection of extrasolar planets
Key scientific requirements for direct detection
11 In the following, background noise is defined as the Poisson noise of the target star whose signal is parallel to the optical axis of any direct detection instrument. 12 In the following, sky noise is defined as Poisson noise due to the transmitted spectral distribution of Earth energy.
Interferometry
Null interferometry is difficult to perform with ground-based telescopes due to the influence of atmospheric turbulence. Calibration of the residual (usually incoherent) stellar halo, including residual atmospheric and instrumental effects.
Bibliography
Lenzen, Rainer; Close, Laird; Brandner, Wolfgang; Hartung, Markus; Biller, Beth, Science with Adaptive Optics, Proceedings of an ESO workshop held in Garching, Germany, 16-19 September 2003. Coronagraphy represents the first remedy for this noise by reducing the coherent diffraction pattern on the PSF axis.
Planet features useful for Simultaneous Differential Imaging
Curves are calculated in different wavelength band below the K-band limit with realistic SR levels for the AO compensation of the signal coming from this model star (courtesy of the CHEOPS team). Curves are calculated in different wavelength windows below the K band with realistic SR levels for the AO compensation of the signal coming from this model star (courtesy of the CHEOPS team).
Characterization of the telescope PSF with AO-compensation
- Computation of the telescope PSF before AO-compensation
- Computation of the telescope PSF after AO-compensation
- Definition of the Speckle pattern field
- Computation of the PSF beyond the AO Control Radius
Calculating the telescope PSF before AO compensation requires introducing the phase statistics (Φ) of the EF across the entrance pupil. In both cases the term IC represents the central intensity of the EF reaching the Focal Plane of the telescope.
Speckle Noise
Note that the simulations considered in the preparation of Figure 3-11 assume only a Spike pattern field due to atmospheric turbulence. Note that the simulations considered in the preparation of this figure assume a Spike pattern field due only to atmospheric turbulence.
SDI at the diffraction limit
The main difference between SDI and Spectroscopic-SDI (or S-SDI) lies in the determination of the wavelength λ1 and λ2. The last point is more critical due to the fact that the chromaticity of the Speckle pattern always causes a certain amount of phase errors depending on the difference between the center wavelength of the narrowband filters: δλij.
Integral Field Spectroscopy at the diffraction limit: S-SDI
- Requirement and Options
- Speckle Chromatism in the specific case of 3D-Spectroscopy
- S-SDI as powerful improvement of standard SDI
- First high contrast imaging with an Integral Field Spectrograph
This capability is essentially based on the spatial sampling of the central RVP via the NIm parameter. The plane of the IFS entrance slit becomes a matrix of micropupils corresponding to different parts of the original field of view.
Bibliography
This section38 describes the scientific objectives of the instrument and derives its high-level requirements. Instead, a detailed description of the IFS subsystem is a separate argument of Sections 5 and 6.
Science case
The instrument uses an XAO37 turbulence compensation system (SAXO), Focal Plane Tip-Tilt correction and interference coronagraphs. Expected performances are presented in terms of a semi-analytical performance estimation tool for sensitivity analysis at the level of the single subsystems.
Observational modes
A larger comprehensive survey of another ~300 targets will finally lead to a statistically relevant sample of planets with masses between a few tenths up to about 10 MJUPIT, in the distance bin between 1 and 20 AU in a sample of more than 400 nearby stars.
System architecture
- Global overview
- Common Path optics
- The XAO system SAXO
- ZIMPOL
- IRDIS
The optical design of the Common Path is based on the use of three toroidal mirrors produced by spherical polishing of pre-sheltered substrates. 4QPMC was recently demonstrated at VISible (see Figure 4-4 and Figure 4-5), where the main difficulties of precision edge polishing and assembly of HWPs were addressed and excellent performance was demonstrated (cf.
Performance analysis
The module “focus level 2” represents the performance simulator code implemented for ZIMPOL, IRDIS and IFS respectively.
Bibliography
This surface lies in the focal plane of the re-imaging telescope and samples a portion of the telescope PSF, according to the Nyquist criterion. The TIGER spaxel concept, optimized for Nyquist spatial sampling of the telescope's re-imaged Focal Plane, is shown in Figure 5-4.
Optical quality of the single IFS Slit
Speckle Chromatism on the single final spectrum
In a 3D cube, speckle chromaticism appears as the slope of the final spectra (see Figure 5-13). R is the spectral resolution and λC is the central wavelength of the region covered by the 3D spectrograph49.
Coherent and Incoherent CrossTalks
Incoherent CrossTalk: the formalism
Let Ii(λ) be the incoherent intensity characteristic of the ith monochromatic IFS slot on the plane of the IFS detector. Once this spectral alignment is found, an estimate of the incoherent crosstalk can be given by measuring the incoherent intensity of a single monochromatic IFS slot at a distance equal to the transverse separation between adjacent spectra.
Format of the final spectra on the IFS Detector plane
Length of the single spectrum on the Detector plane Defining the Spectral Purity (SP) of the IFS as
TIGER and BIGRE Integral Field Units vs. SPHERE/IFS TLRs
R together with the geometric configuration adopted for the spectral alignment, the Detector pixel size (dpixel=18 [micron]), the IFS optical zoom, the lens pitch and the total number of spaxels, set the maximum detector pixel fill factor. Through Equation 5-13, the Detector pixel size, IFS optical magnification, and minimum wavelength determine the minimum value of the spaxel output focal ratio.
The BIGRE Integral Field Unit for SPHERE/IFS
The controls at the bottom (colored green) take into account any limitations imposed by the SPHERE/IFS TLRs and the technical limitations within the SPHERE main module. Note that the spreadsheet contains - as output - the basic specifications of the SPHERE/IFS optical design.
SPHERE/IFU prototype
CrossTalk measures
An experiment was set up to measure the incoherent crosstalk on the IFS slit plane and the intensity peaks of the interference signal generated by two adjacent spaxels (see Figure 5-29). Faint hexagonal structures are visible in the images obtained with Setup-A, due to the Coherent Cross Talk of the grid.
Bibliography
The basic optical feature of SPHERE/IFS is to image the array of slits, generated by the BIGRE IFU and chromatically separated by an appropriate scattering device, in the plane of the IFS detector. -1: Scheme of the main SPHERE/IFS subsystems: a) BIGRE IFU subsystem; b) IFS Collimator subsystem;.
Description of the ongoing IFS optical layout
Input Focal Ratio on BIGRE Subsystem FIN 316 Output Focal Ratio of BIGRE Subsystem FOUT 8.13 Focal Ratio of IFS Subsystem Collimator Fcoll 8.13 Camera Vs.
FTM16
- Optimization of the IFS Collimator
- Tolerance analysis for the IFS Collimator
- Optimization of the IFS Camera
- Tolerance analysis for the IFS Camera
- Optimization of the IFS Disperser
The optical quality of the optimized collimator is within the diffraction limit, as Figure 6-5 shows. The optical quality of the optimized Camera is within the diffraction limit, as Figure 6-8 shows.
Transmission of the IFS optics
The mask deposited on the BIGRE lens array (see Figure 6-16) circularly reproduces the shape of the first surface of each lens in the array. The adopted mask hole is fixed to be 95% of the lens height; it allows to remove the stray light generated by the edges, the lens shape of the BIGRE IFU adopted for SPHERE/IFS, which is hexagonal, and to adapt each spaxel to a circular shape with good transmission level: 0.819 for a mask hole equal to 0.95⋅DL , contained in a hexagonal lens with pitch equal to DL.
- Thermal and Pressure analyses
- Dithering analysis
- Ghost analysis
- Bibliography
- The science milestone: rocky planets
Different considerations should be made for the optical elements that are on the collimated part of the beam (Disperser, High-Pass Chromatic Filter and Neutral Density Filter). The worst ghosting is due to reflection back from the detector surface and then back onto the fist surface of the IFU.
Space 0.01 mmag 0.1 mmag
To further consider the imaging of rocky planets with OWL/EPICS in a general context, we consider in Table 7-1 the detection of rocky planets in the Habitable Zone, that is, planets similar to our Earth, with different techniques. In the last column we list the main sources of disturbance in the various observational techniques.
Space 10 10
- Instrument concept
- Adaptive Optics
- Coronagraphy
- Top Level Requirements for the EPICS/Instruments
For EPICS, the AO system has been optimized, in the NIR, to provide a high starlight halo rejection efficiency for angular separations from 30 [mas] to 200 [mas], corresponding to the expected locations of rocky planets in the habitable zone around stars of the three defined spectral types. This results in a net gain of more than a factor of 10 in integration time for detecting rocky planets in the habitable zone with respect to the single step only.