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1.
Arnaud M. Aubourg E. Bareyre P. Br';ehin S. Caridroit R. de Kat J. Dispau G. Djidi K. Gros M. Lachièze-Rey M. Laigneau Y. Laurent B. Lesquoy E. Lavocat Ph. Magneville C. Mazeau B. Milsztajn A. Moscoso L. Pasquaud J. Paul B. Perrin P. Petibon J. Piret Y. Queinnec F. Rich J. Spiro M. de Trogoff J. Vigroux L. Zylberajch S. Ansari R. Cavalier F. Moniez M. Beaulieu J. P. Ferlet R. Grison Ph. Vidal-Madjar A. Adrianzyk G. Berger J. P. Burnage R. Delclite J. C. Kohler D. Magnan R. Richaud A. Guibert J. Moreau O. Tajahmady F. Baranne A. Maurice E. Prévôt L. Gry C. 《Experimental Astronomy》1994,4(3-4):265-278
A 20cm
2
CCD mosaic camera has been especially built to search for dark galactic halo objects by the gravitational microlensing effect. The sensitive area is made of 16 edge-buttable CCDs developped by Thomson-CTS, with 23×23 µm
2
pixels. The 35 kg camera housing and mechanical equipment is presented. The associated electronics and data acquisition system are described in a separate paper. The camera resides at the focal plane of a 40 cm, f/10, Ferson reflector. The instrument has been in operation since December 1991 at the La Silla Observatory (ESO). 相似文献
2.
R. Ferlet A. Lecavelier Des Etangs G. Perrin A. Vidal-Madjar F. Sèvre F. Colas J. E. Arlot C. Buil H. Beust A. M. Lagrange-Henri J. Lecacheux M. Deleuil C. Gry 《Astrophysics and Space Science》1994,212(1-2):173-180
The inner regions of the circumstellar disk around Pictoris might be dust-free due to a possible planet which may have cleared up dust particles. We present a new observational technique based on the use of an anti-blooming CCD in order to directly image this zone. The structure of the disk is revealed down to 2 arcsec from the star (30 AU). We show that the Pic disk brightness is neutral inV, R, andI
C
, but drops down when going inward inB, possibly related to a change in the dust composition. Also, a slight disk asymmetry is present but inverted from the outer to the inner zones.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
3.
Arnaud M. Aubourg E. Bareyre P. Br';ehin S. Caridroit R. de Kat J. Dispau G. Djidi K. Gros M. Lachièze-Rey M. Laigneau Y. Laurent B. Lesquoy E. Lavocat Ph. Magneville C. Mazeau B. Milsztajn A. Moscoso L. Pasquaud J. Paul B. Perrin P. Petibon J. Piret Y. Queinnec F. Rich J. Spiro M. de Trogoff J. Vigroux L. Zylberajch S. Ansari R. Cavalier F. Moniez M. Beaulieu J. P. Ferlet R. Grison Ph. Vidal-Madjar A. Adrianzyk G. Berger J. P. Burnage R. Delclite J. C. Kohler D. Magnan R. Richaud A. Guibert J. Moreau O. Tajahmady F. Baranne A. Maurice E. Prévôt L. Gry C. 《Experimental Astronomy》1994,4(3-4):279-296
Conclusion To summarize, the readout and the control system of the CCD mosaic camera are running since December 1991 at the La Silla Observatory (ESO). The overall performance of the camera has been good. About 12000 pictures (data and flat-fields) have been successfully registered up to now. We will report in the near future preliminary scientific results of the EROS experiment. 相似文献
4.
Current theoretical models do not satisfactorily explain observed variations of the global exospheric atomic hydrogen density distribution. Differences between the mesospheric upward flux and the Jeans escape mechanism indicate that other escape fluxes affect hydrogen density. Observations of latitudinal depletions and an early morning trough in the exosphere can be attributed to the influence of additional escape mechanisms. These variations of the exospheric hydrogen density distribution seem to be correlated with other observed variations in the atmosphere; however, no straightforward explanation has been proposed to date. 相似文献
5.
Several satellite experiments have measured the solar Lyman-α line, either in scattering from upper atmospheric atomic hydrogen (the Lyman-α airglow) or directly at line center (which determines the hydrogen column density along the line of sight). Recent analyses of data from the above experiments consistently reveal the presence of an atomic hydrogen depletion at high latitudes. In situ determinations of hydrogen at lower altitude show no evidence of such behaviour. This has led us to postulate two mechanisms which may be more effective in reducing the high-latitude density at the high altitudes of the exospheric measurements (500–2000 km). The first is the polar wind loss of protons, which depletes atomic hydrogen through a charge exchange reaction. The second is a high-latitude magnetospheric heating of protons, followed by charge exchange. Opposing the above loss mechanisms are the influences of ballistic lateral flow and mean meriodional winds. We have shown by means of a three-dimensional exospheric transport model that none of the above mechanisms can reconcile the disparate results in the two altitude regimes, nor can they provide the large outward hydrogen fluxes and the correct seasonal variations observed at high latitudes. 相似文献
6.
7.
After being turned off in 1972 the OSO-5 satellite was reactivated during the summer of 1974 for one year. The University of Paris experiment designed to monitor the solar L flux operated almost perfectly during that period which occurred near a minimum in solar activity. This new set of data is presented here, showing that neither the total L flux nor the flux emitted at the center of the line correlate with the solar activity indices in the same manner as previously found at higher levels of activity.These new observations confirm that the solar L flux varies approximately by a factor of two from solar maximum to solar minimum.Furthermore, the lower boundary of the transition region seems to be strongly perturbated near solar minimum, since the flux variations observed at the center of the L line are drastically different from all those previously reported. This seems to be related to the presence of large coronal holes over the Sun. 相似文献
8.
A. Vidal-Madjar 《Solar physics》1975,40(1):69-86
Four consecutive years of a quasi-continuous survey of the solar Lα line are presented. Absolute calibration and aging correction are evaluated producing higher quality measurements which are: -the total Lα flux, -the central Lα flux, -the blue wing flux at 0.33 Å from the center, -the slope of the blue wing at the same location. Empirical laws are deduced from this large amount of data giving a relation between these different parameters and the flux integrated over the whole line. Furthermore, other empirical laws are obtained between the total Lα flux and two solar activity indices. These relations give a possibility of evaluating the solar Lα flux even when no observation is available and, as previously found by Prinz (1974), show that to a first approximation the solar Lα flux is composed of a quiet and of an active component. The active component changes with the 27 days period; the quiet one with the 11 yr solar cycle. 相似文献
9.
In this study, we try to refine the relation existing between the exobase temperature and density distributions of atomic hydrogen around the Earth (assuming that the zero net ballistic flux condition is satisfied all over the critical level). We find essentially that neither local heating in high latitude regions, nor the addition of proton fluxes around the Earth, induce large perturbations in the equatorial density distribution (less than 10 per cent). On the other hand, certain local heating can give large perturbations in the global density distribution (more than 50 per cent).The effect of the Earth's rotation is also studied. We find that at the exobase the density distribution of atomic hydrogen lags about one hour behind the temperature distribution. At higher altitudes this time lag increases, reaching 5–6 hr at 20 Earth radii.We show also that, due to a density inversion which takes place at 2 Earth radii, if the minimum of density at the exobase is on the dayside, above 2 Earth radii, a maximum of density is then on the dayside when going higher, due to the rotational effect, that density maximum shifts towards the evening, reaching early parts of the night at 20 Earth radii. 相似文献
10.
Laurent Koechlin Denis Serre Paul Deba Roser Pelló Christelle Peillon Paul Duchon Ana Ines Gomez de Castro Margarita Karovska Jean-Michel Désert David Ehrenreich Guillaume Hebrard Alain Lecavelier des Etangs Roger Ferlet David Sing Alfred Vidal-Madjar 《Experimental Astronomy》2009,23(1):379-402
The Fresnel Interferometric Imager has been proposed to the European Space Agency (ESA) Cosmic Vision plan as a class L mission.
This mission addresses several themes of the CV Plan: Exoplanet study, Matter in extreme conditions, and The Universe taking shape. This paper is an abridged version of the original ESA proposal. We have removed most of the technical and financial issues,
to concentrate on the instrumental design and astrophysical missions. The instrument proposed is an ultra-lightweight telescope,
featuring a novel optical concept based on diffraction focussing. It yields high dynamic range images, while releasing constraints
on positioning and manufacturing of the main optical elements. This concept should open the way to very large apertures in
space. In this two spacecraft formation-flying instrument, one spacecraft holds the focussing element: the Fresnel interferometric
array; the other spacecraft holds the field optics, focal instrumentation, and detectors. The Fresnel array proposed here
is a 3.6 ×3.6 m square opaque foil punched with 105 to 106 void “subapertures”. Focusing is achieved with no other optical element: the shape and positioning of the subapertures (holes
in the foil) is responsible for beam combining by diffraction, and 5% to 10% of the total incident light ends up into a sharp
focus. The consequence of this high number of subapertures is high dynamic range images. In addition, as it uses only a combination
of vacuum and opaque material, this focussing method is potentially efficient over a very broad wavelength domain. The focal
length of such diffractive focussing devices is wavelength dependent. However, this can be corrected. We have tested optically
the efficiency of the chromatism correction on artificial sources (500 < λ < 750 nm): the images are diffraction limited, and the dynamic range measured on an artificial double source reaches 6.2
10 − 6. We have also validated numerical simulation algorithms for larger Fresnel interferometric arrays. These simulations yield
a dynamic range (rejection factor) close to 10 − 8 for arrays such as the 3.6 m one we propose. A dynamic range of 10 − 8 allows detection of objects at contrasts as high as than 10 − 9 in most of the field. The astrophysical applications cover many objects in the IR, visible an UV domains. Examples are presented,
taking advantage of the high angular resolution and dynamic range capabilities of this concept. 相似文献