排序方式： 共有5条查询结果，搜索用时 203 毫秒
1
1.
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. 相似文献
2.
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. 相似文献
3.
Pierre Connes 《Astrophysics and Space Science》1994,212(1-2):357-367
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.Paper presented at the Conference onPlanetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A. 相似文献
4.
Summary 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. 相似文献
5.
Pierre Connes 《Astrophysics and Space Science》1985,110(2):211-255
Two distinct but fully compatible novel concepts are proposed here for solar/stellar velocity measurements. The first is that of absolute accelerometry proper. This involves two simultaneously, operating servo-control loops First, a variable path-difference Fabry-Perot interferometer is adjusted so that its bandpasses track the fluctuations of either a single spectral line (in the solar case, leading to the solar accelerometer), or of all lines simultaneously (stellar accelerometer). The second loop involves a tunable laser tracking one of the FP bandpasses. The net overall result is that a laser line tracks the stellar/solar ones: the problem of measuring Doppler-shift changes has been transferred from the incoherent to the coherent optics domain. One then measures the beat frequency generated by mixing the tunable laser beam with that of stabilized laser. Only velocity changes are accessible; the devices are true accelerometers, but absolute ones. All instrumental or spectral characteristics drop out; no calibration of any kind is required; hence, one may hope for an unusually low level of systematic errors. The second concept is that of optimum measurement of Doppler shifts as far as photon count limitations are concerned. A simple but so far never performed calculation leads to the fundamental RMS velocity error corresponding to a given spectral profile and photon count. One next shows that a dispersive spectrometer with an image detector may closely approach that limit provided direct access to a computer is available, and the signal is treated by a specific algorithm. This treatment being precisely the one used in the stellar accelerometer, our device is seen as the first proposed one approaching fundamental limits in this field; however, standard radial velocity measurements (not involving accelerometry) should also benefit from our proposal. A full calculation shows that a velocity error reduction of the order of 30 is within reach relative to the most efficient so far available device, i.e., CORAVEL. For faint objects, detector noise must be added, but the treatment remains demonstrably optimum. The two principal fields of application for absolute accelerometry are celestial seismology (a seismometer is nothing but an accelerometer), and the search for extra-solar planetary systems. In both cases a large number of objects will be accessible with a small telescope. One may also look for solar system accelerations (relative to some system of reference stars) due to any cause whatsoever: for instance a faint solar companion, or even gravitational waves. 相似文献
1