The method of stellar velocity variations measurement has recently shown its capability by discovering tens of extra-solar planets. Accuracies achieved today are in the range of 3 to 10 m/s. The spectrograph EMILIE coupled to the Absolute Astronomical Accelerometer (AAA) system and established at the 1.52 m telescope of the Observatoire de Haute Provence is an instrument which aims at reaching an accuracy better than 1 m/s, long term. Results on some typical stars are presented.

The spectrograph EMILIE (Bouchy et al., 1999; Bouchy, 1999; Bouchy et al., 2000) coupled to the Absolute Astronomical Accelerometer (AAA, Connes, 1985; Schmitt, 1997) and implemented at the 152-cm Coudé telescope of the Observatoire de Haute Provence is dedicated to high-precision Doppler measurements. The AAA method uses a sliding reference spectrum constrained to track the stellar lines and to use the spectrograph as a null-checking device. The goal of AAA is to eliminate the calibration of the spectrograph as well as the displacement of the spectra across the CCD pixels due to the earth motion (and suspected to introduce a systematic error in the RV measurement). Here we report seismological results obtained with AAA on the Sun and the bright stars Procyon and ζ Her A that are expected to present solar-like oscillations.

. We have observed Procyon with the fiber-fed echelle spec trograph ELODIE coupled with a Fabry-Perot etalon at the 193-cm of the Observatoire de Haute Provence (France) over 5 nights during 1997 December - 1998 January. Here, we present the results of a search for solar-like oscillations on this star and the performance of this instrumen tation for asteroseismology. The power spectra show an excess of signal between 0.42 mHz and 1.46 mHz, which could be due to stellar oscilla tions.

Precise Doppler measurements of the star Procyon (alpha CMi, HR 2943) have been obtained with the ELODIE fiber-fed cross-dispersed echelle spectrograph on the 1.93 m telescope at Observatoin de Haute Provence. Here, we present the analysis of data from 10 days observing run carried out in November 1998. We detect significant excess in the power between 0.5-1.5 mHz in the periodograms of the time series of mean Doppler shifts. Observations of eta Cas made with the same instrument during the same time interval and in almost identical night conditions show a flat spectrum in this frequency range, indicating that the excess of Doppler signal seen on Procyon is of stellar origin. When data from the whole run are jointly analyzed, a period analysis places an upper limit of 0.500.60 ms(-1) for the amplitude of oscillations, while the frequency cutoff is around 1.5 mHz. The power evidently drops near 0.55 and 1.5 mHz on the average of unfiltered power spectra of individual nights, which is consistent with the expected p-mode oscillation properties for Procyon. Several equispaced peaks in frequency are recurrent in the power spectra of two independent segments of 4 and 3 contiguous nights; the most probable frequency spacing seems to be 55 mu Hz. In conclusion, we now have an instrument set-up which is sufficiently stable and fast to be used for a multi-site campaign involving instruments with comparable velocity precisions, to detect the oscillation modes of sun-like stars.

The fiber-fed echelle spectrograph EMILIE designed for the measurement of stellar radial-velocity changes is presently being laboratory-tested. Using a 204 x 408 mm grating and a 1k x 1k CCD detector, it samples about 50% of the 410-620 nm wavelength range with spectral resolution R similar to 150 000 This spectrograph is coupled to the telescope via a single 50-mu m fiber, which accepts 2.7 arcsec from the shy. An automatic guiding system stabilizes the image at the entrance of the fiber. The fiber transmits alternately to the spectrograph the stellar beam and the reference beam. The same pixels of the CCD detector are used alternately far the two spectra, which requires an excellent short term stability. Hence, later on, the spectrograph will be located within a vacuum tank, with active thermal control. The instrument will be set up at the focus of the 1.52-m coude telescope at the Observatoire de Haute-Provence (OHP) and will undertake programs of asteroseismology and detection of extrasolar-planets.

The absolute accelerometry technique has been developed by P. Connes (1985) to detect small radial-velocity changes. In order to estimate the performance of the Absolute Astronomical Accelerometer (AAA) for asteroseismology, Ne conducted specific observations, i.e. long continuous observing runs, with a preliminary version of the AAA coupled with the spectrograph Elodie at the T193 (ORP). The present accuracy shows that the AAA is a very promising instrument for the search for solar-like oscillations.

The method of stellar radial velocity variations has recently shown its capability by the first discovery of several extra-solar planets. Accuracies achieved today are in the range 3-10 m/s. The AAA (absolute astronomical accelerometer) is an instrument which aims to reach the photon noise limit for the measurement of velocity changes, with systematic errors of about 1 m/s, long term. The principle is to use a servo-controlled CCD spectrograph as a null detector, and to register always the lines of the star on the same CCD pixels. Thus, systematic errors linked to the Earth-induced large variations are cancelled. A tunable Fabry-Perot channelled spectrum is also following the star spectrum, while the FP thickness is measured by heterodyne detection of the beats between a tunable laser diode and a stabilized laser diode. A complete prototype of the instrument is operating with laboratory sources and the first results are presented. It is planned to use this system with a new spectrograph, to be coupled to the 152 cm telescope at Observatoire de Haute Provence.

We have measured apparent fluctuations in stellar radial velocities with the ELODIE fiber-fed crossed-dispersion spectrograph and the 193-cm telescope of Observatoire de Haute-Provence. Within one given night, the fluctuations consist of two terms which may be sorted out. The first comes from imperfect scrambling of the stellar beam; the second arises from photon noise and agrees closely with our published calculations. So far, scrambler noise dominates for bright stars, but a perfect scrambler could be built by combining adatative optics and a single-mode fiber. The photon-noise results confirm that extrasolar planetary searching by the radial-velocity technique may be implemented with relatively small telescopes for a large number of stars. Consequences for the detection of ‘astrophysical noise” are discussed.

An historical account of the development of high-resolution astronomical and laboratory Fourier transform spectrometry at Laboratoire Aimé Cotton under the leadership of P. Jacquinot, over the years 1964–1974.

Absolute accelerometry is a technique for detecting small radial velocity changes involving lasers. The final output is a beat frequency similar to that from a Doppler radar. A progress report is presented on the development which began three years ago. While a suitable stellar échelle spectrograph is being built at Observatoire de Haute Provence, a demonstration of the main features on laboratory sources and the Sun is attempted at Verrières. Partial results are presented.

This review is of current and projected applications of optical fibers to observational astronomy. The intent is to provide astronomers with a broad perspective on the subject, with the hope of encouraging productive use of optical fibers in the design of new instrumentation. The unique characteristics of fibers have been (or soon will be) exploited to advantage in several areas of astronomical instrumentation, including multiplexers for muti-object spectrographs, remote optical feeds for spectrographs and photometers, coherent beam recombiners for optical interferomety, and many miscellaneous applications. We discuss the most important such applications in detail, with reference to operational instruments wherever possible, and with emphasis on the optical properties of fibers and the engineering considerations encountered in their application to observational astronomy.

Historical account of the early development of Fourier Transform Spectrometry at Laboratoire Aime Cotton under Pierre Jacquinot's leadership, over the years 1954-1963.

The SUN experiment is a UV and visible Space Interferometer aimed at ultra-high resolution in the solar atmosphere. It has been proposed to ESA as part of the SIMURIS Mission Proposal which has recently been accepted for an Assessment Study in the framework of the Space Station. The 4 × 20 cm telescopes of the SUN linear array are non-redundantly placed to cover a 2 m baseline, and the instrument makes full use of stabilized interferometry potential, the 4 telescopes being co-aligned and co-phased on a reference field on the sun. After a brief outline of the scientific objectives, the concept of the instrument is described, and its image reconstruction potential is illustrated.

SIMURIS is an interferometric investigation of the very fine structure of the solar atmosphere from the photosphere to the corona. It was proposed to ESA /1/, November 30 1989, for the Next Medium Size Mission — M2, and accepted in February 1990 for an Assessment Study in the context of the Space Station. The main scientific objectives will be outlined, and the ambitious model payload featuring the Solar Ultraviolet Network (SUN), a 2 m long monolithic array of 4 telescopes of Ø20 cm, and the Imaging Fourier Transform Spectrometer (IFTS), an UV and Visible Imaging Fourier Transform Spectrometer coupled to a Ø40 cm Gregory, described.

Present Solar telescope projects, on ground or in Space (like the Orbiting Solar Laboratory) are limited in their ambitions to visible wavelengths and to spatial resolutions not better than a tenth of an arcsec. The Solar Ultraviolet Network (SUN) proposal presented in this paper, is an interferometric concept capable of observations with a spatial resolution better than 0.013" (10 km) on the Sun, in the UV range. Based on Stabilized Interferometry principles it consists in 4 telescopes of 20 cm diameter aligned non-redundantly on a 2 m baseline. Despite its size (2.1 x 1.0 x 0.7 m) and its intrinsic complexity, SUN would be perfectly suited for use on the Space Station, when implemented on a pointing platform of performances comparable with the Instrument Pointing System (flown on Spacelab2). The remarkable capabilities of the SUN instrument, resulting from its "compact" non-redundant configuration of telescopes, allow high resolution imaging on a 2 x 2 arcsec2 field (and with a dynamic on the reconstructed images superior to 100 for phase stabilities ≥ λ/10), on the Solar disk (granulation, flares and micro-flares, prominences and filaments), or at the limb and above, across coronal loops.

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text Pierre Connes, Michael Smyth, Armand Hadni, and Xavier Gerbaux, "Heinrich Rubens, Herbert Hollnagel, and Fourier transform spectroscopy," Optics News 14(3), 6-14 (1988) Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

Perfecting instruments is all in the day's work; introducing truly novel experiments remains a rarer achievement. Still, we have seen over the last thirty years the growth of three highly similar and yet independent Fourier spectroscopies. Who feels ready to stick the fourth feather in Fourier's cap?

Gabriel Lippmann's interference colour photography is totally discussed today, but his ideas and technique were to prove essential for holography. The author describes first the aborted Newtonian attempts at explaining substantial colours through interference effects analogous to those actually at work in Lippmann's plates. Second, he shows how the standing-waves concept passed from acoustics to optics. Third, he follows across the 19th century what appears now a sideline in the development of colour photography: the discoveries of Seebeck, Herschel and Becquerel. While these are no longer of any practical importance, their little known story is more complex and perhaps more instructive than that of three-colour photography. As to the final 1891 Lippmann demonstration, it was both widely acclaimed and disputed at the time, in part for chauvinistic reasons.

The invention of the multiple-beam interferometer may be understood as having proceeded from the fortunate convergence of two independent developments. On the one hand, during two centuries of near-misses, the multiple-beam interference phenomenon was consistently observed (and even computed by Poisson and Airy) but its specific and pregnant feature, the fringe sharpening was not understood before the 1892 Thesis of Charles Fabry. Throughout, the motivation had been purely intellectual search. On the other hand, a long succession of technicians, most of them unknown, strove to produce better mirrors for wholly commercial purposes; the end result was the semi-transparent silver film, essential for multiple-beam interferometry. The corresponding fringes, first observed by Boulouch, were immediately put to good use by Fabry and Perot in 1896. Through a remarkable coincidence, essentially the same phenomena were simultaneously discovered in the Hertz laboratory with Hertzian waves. One more convergence, with Einsteinian stimulated emission, has since given us coherent light.

Absolute astronomical accelerometry is a new proposed technique specifically optimized to detect small radial velocity changes (i.e. accelerations) of either the Sun or a star; it is intended for the two problems of stellar seismology and the search for extrasolar planetary systems. In both cases the computed performance is such that positive results should be obtainable in a large number of cases with a moderate size telescope. Essentially the method involves two separate and simultaneous servo loops. In the first a variable path-difference Fabry-Perot interferometer is adjusted so that its bandpasses track the fluctuations of the lines in the stellar spectrum. Then a tunable laser tracks the fluctuations of the FP and one has only to measure the beat frequency from a stabilized laser. The result is absolute i.e. obtained solely in terms of frequencies and the speed of light. All instrumental or spectral characteristics drop out; no calibration is required. Furthermore the method can be demonstrated to approach closely a so far never computed photon noise limit for radial velocities.