108 research outputs found
Search for extra-solar planets with high precision radial velocity curves
No full textThis Ph.D. Thesis has as general subject the study of extrasolar planets using the radial velocity technique from both, instrumental and observative, points of view. Two main parts compose the work: the upgrade of the spectrograph FOCES, a high resolution spectrograph that will be installed next year at the Wendelstein Observatory, and the
search of giant planets around stars in the open cluster Messier-67 (M67).Die vorliegende Dissertation behandelt die Suche von extra-solaren Planeten mit der Radialgeschwindigkeits Methode und zwar sowohl in Bezug auf die dafür notwendige Instrumentierung
als auch auf die Beobachtung. Die Arbeit ist in zwei Teile gegliedert. Im ersten Teil
werden die vorgenommenen Verbesserungen
des hochauflösenden Spektrographen FOCES
beschrieben, der im kommenden Jahr
am Wendelstein Observatorium installiert werden
wird. Der zweite Teil handelt von der Suche nach Gasplaneten im offenen Sternhaufen M67
Optimization of the Ariel primary mirror
No full textThe primary mirror of the Ariel space telescope (an ESA M class mission aimed at the study of exoplanets, scheduled for launch in 2029) is an elliptical off-axis paraboloid. Like the entire telescope, it is built of aluminum. As a massive part of the payload, as well as one of the most delicate components of the telescope, this mirror has to be accurately designed, in order to minimize its mass while not degrading its optical performances. This paper discusses the optimization study of the primary mirror of Ariel. Starting from its optical and geometrical specifications, we have run an iterative process based on FEA dynamic analyses, in order to compute the first ”free-free” eigenfrequencies while varying the three fundamental parameters of the honeycomb structure of the mirror - the thickness of the ribs, the outer edge, and the reflecting surface. Later, the optimization routine has been improved by adding the honeycomb geometry as a variable parameter. As a result, the best configurations is identified as the ones giving the higher ratios of the first relevant eigenfrequency divided by the mass
Search for giant planets in M 67 V: A warm Jupiter orbiting the turn-off star S1429
No full textContext. Planets orbiting members of open or globular clusters offer a great opportunity to study exoplanet populations systematically, as stars within clusters provide a mostly homogeneous sample, at least in chemical composition and stellar age. However, even though there have been coordinated efforts to search for exoplanets in stellar clusters, only a small number of planets have been detected. One successful example is the seven-year radial velocity (RV) survey ‘Search for giant planets in M 67’ of 88 stars in the open cluster M 67, which led to the discovery of five giant planets, including three close-in ( P < 10 days) hot-Jupiters. Aims. In this work, we continue and extend the observation of stars in M 67, with the aim being to search for additional planets. Methods. We conducted spectroscopic observations with the Habitable Planet Finder (HPF), HARPS, HARPS-North, and SOPHIE spectrographs of 11 stars in M 67. Six of our targets showed a variation or long-term trends in their RV during the original survey, while the other five were not observed in the original sample, bringing the total number of stars to 93. Results. An analysis of the RVs reveals one additional planet around the turn-off point star S1429 and provides solutions for the orbits of stellar companions around S2207 and YBP2018. S1429 b is a warm-Jupiter on a likely circular orbit with a period of \[\77.48_{-0.19}^{+0.18}\] days and a minimum mass of M sin i = 1.80 ± 0.2 M J . We update the hot-Jupiter occurrence rate in M 67 to include the five new stars, deriving \[\4.2_{-2.3}^{+4.1} \%\] when considering all stars, and \[\5.4_{-3.0}^{+5.1} \%\] if binary star systems are removed
Preliminary analysis of ground-to-flight mechanical tolerances of the Ariel mission telescope
No full textAriel (Atmospheric Remote-Sensing Infrared Exoplanet Large Survey) is the adopted M4 mission of ESA “Cosmic
Vision” program. Its purpose is to conduct a survey of the atmospheres of known exoplanets through transit
spectroscopy. Launch is scheduled for 2029. Ariel scientific payload consists of an off-axis, unobscured Cassegrain
telescope feeding a set of photometers and spectrometers in the waveband between 0.5 and 7.8 μm, and operating
at cryogenic temperatures.
The Ariel Telescope consists of a primary parabolic mirror with an elliptical aperture of 1.1 m of major axis,
followed by a hyperbolic secondary, a parabolic recollimating tertiary and a flat folding mirror directing the
output beam parallel to the optical bench. The secondary mirror is mounted on a roto-translating stage for
adjustments during the mission.
Proper operation of the instruments prescribes a set of tolerances on the position and orientation of the
telescope output beam: this needs to be verified against possible telescope misalignments as part of the ongoing
Structural, Thermal, Optical and Performance Analysis.
A specific part of this analysis concerns the mechanical misalignments, in terms of rigid body movements of
the mirrors, that may arise after ground alignment, and how they can be compensated in flight. The purpose is to derive the mechanical constraints that can be used for the design of the opto-mechanical mounting systems
of the mirrors.
This paper describes the methodology and preliminary results of this analysis, and discusses future steps
Toward ARIEL’s primary mirror
No full textAriel (Atmospheric Remote-Sensing Infrared Exoplanet Large Survey) is the adopted M4 mission of ESA “Cosmic
Vision” program. Its purpose is to conduct a survey of the atmospheres of known exoplanets through transit
spectroscopy. Launch is scheduled for 2029.
Ariel scientific payload consists of an off-axis, unobscured Cassegrain telescope feeding a set of photometers and
spectrometers in the waveband between 0.5 and 7.8 µm, and operating at cryogenic temperatures.
The Ariel Telescope consists of a primary parabolic mirror (M1) with an elliptical aperture of 1.1 m of major axis and
0.7 m of minor axis, followed by a hyperbolic secondary (M2) , a parabolic recollimating tertiary (M3) and a flat folding
mirror (M4).
The Primary mirror is a very innovative device made of lightened aluminum. Aluminum mirrors for cryogenic
instruments and for space application are already in use, but never before now it has been attempted the creation of such
a large mirror made entirely of aluminum: this means that the production process must be completely revised and finetuned, finding new solutions, studying the thermal processes and paying a great care to the quality check. By the way, the advantages are many: thermal stabilization is simpler than with mirrors made of other materials based on
glass or composite materials, the cost of the material is negligeable, the shape may be free and the possibility of making
all parts of the telescope, from optical surfaces to the structural parts, of the same material guarantees a perfect alignment
at whichever temperature.
This paper describes the methodology and preliminary results of this manufacturing process and discusses future steps
A new generation of spectral extraction and analysis package for Fiber Optics Cassegrain Echelle Spectrograph (FOCES)
No full textExperimental characterization of modal noise in multimode fibers for astronomical spectrometers
No full textContext. High resolution spectroscopy at high signal-to-noise ratios (S/Ns) is one the key techniques of the quantitative study of the atmospheres of extrasolar planets. Observations at near-infrared wavelengths with fiber-fed spectrographs coupled to extremely large telescopes are particularly important to tackle the ultimate goal of detecting biosignatures in rocky planets.
Aims. To achieve high S/Ns in fiber-fed spectrogrpahs, the systematic noise effects introduced by the fibers must be properly understood and mitigated. In this paper we concentrate on the effects of modal noise in multimode fibers.
Methods. Starting from our puzzling on-sky experience with the GIANO-TNG spectrometer we set up an infrared high resolution spectrometer in our laboratory and used this instrument to characterize the modal noise generated in fibers of different types (circular and octagonal) and sizes. Our experiment includes two conventional scrambling systems for fibers: a mechanical agitator and an optical double scrambler.
Results. We find that the strength of the modal noise primarily depends on how the fiber is illuminated. It dramatically increases when the fiber is under-illuminated, either in the near field or in the far field. The modal noise is similar in circular and octagonal fibers. The Fourier spectrum of the noise decreases exponentially with frequency; i.e., the modal noise is not white but favors broad spectral features. Using the optical double scrambler has no effect on modal noise. The mechanical agitator has effects that vary between different types of fibers and input illuminations. In some cases this agitator has virtually no effect. In other cases, it mitigates the modal noise, but flattens the noise spectrum in Fourier space; i.e., the mechanical agitator preferentially filters the broad spectral features.
Conclusions. Our results show that modal noise is frustratingly insensitive to the use of octagonal fibers and optical double scramblers; i.e., the conventional systems used to improve the performances of spectrographs fed via unevenly illuminated fibers. Fiber agitation may help in some cases, but its effect has to be verified on a case-by-case basis. More generally, our results indicate that the design of the fiber link feeding a spectrograph should be coupled with laboratory measurements that reproduce, as closely as possible, the conditions expected at the telescope
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