共查询到20条相似文献,搜索用时 625 毫秒
1.
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
2.
In Situ Biological Contamination Studies of the Moon: Implications for Planetary Protection and Life Detection Missions 总被引:1,自引:0,他引:1
Daniel P. Glavin Jason P. Dworkin Mark Lupisella David R. Williams Gerhard Kminek John D. Rummel 《Earth, Moon, and Planets》2010,107(1):87-93
NASA and ESA have outlined visions for solar system exploration that will include a series of lunar robotic precursor missions
to prepare for, and support a human return to the Moon, and future human exploration of Mars and other destinations, including
possibly asteroids. One of the guiding principles for exploration is to pursue compelling scientific questions about the origin
and evolution of life. The search for life on objects such as Mars will require careful operations, and that all systems be
sufficiently cleaned and sterilized prior to launch to ensure that the scientific integrity of extraterrestrial samples is
not jeopardized by terrestrial organic contamination. Under the Committee on Space Research’s (COSPAR’s) current planetary
protection policy for the Moon, no sterilization procedures are required for outbound lunar spacecraft, nor is there a different
planetary protection category for human missions, although preliminary COSPAR policy guidelines for human missions to Mars
have been developed. Future in situ investigations of a variety of locations on the Moon by highly sensitive instruments designed
to search for biologically derived organic compounds would help assess the contamination of the Moon by lunar spacecraft.
These studies could also provide valuable “ground truth” data for Mars sample return missions and help define planetary protection
requirements for future Mars bound spacecraft carrying life detection experiments. In addition, studies of the impact of terrestrial
contamination of the lunar surface by the Apollo astronauts could provide valuable data to help refine future Mars surface exploration plans for a human mission to Mars. 相似文献
3.
We present new radio observations of molecular lines in the region of high mass star formation, namely G122.0-7.1. A large-scale
map of the emission observed in the 12CO (J = 1−0) and 13CO (J = 1−0) lines covers the area of 15′ × 9′, revealing two dense regions. The molecular bipolar outflows have been resolved
in ASO1 region. It is associated with the known candidate YSO nearby IRAS 0042 + 5530. Also, a new dense region has been discovered
in the North-Western part of the G122.0-7.1 at a distance of 5′ from IRAS 0042 + 5530. Its position is close to the peak of
4850 MHz emission.
The text was submitted by the authors in English. 相似文献
4.
In this empirical study, we compare high-resolution observations obtained with the 65-cm vacuum reflector at Big Bear Solar
Observatory (BBSO) in 2005 and with the Dunn Solar Telescope (DST) at the National Solar Observatory/Sacramento Peak (NSO/SP)
in 2006. We measure the correction of the high-order adaptive optics (AO) systems across the field of view (FOV) using the
spectral ratio technique, which is commonly employed in speckle masking imaging, and differential image motion measurements.
The AO correction is typically much larger (10′′ to 25′′) than the isoplanatic angle and can be described by a radially symmetric function with a central core and extended wings.
The full-width at half-maximum (FWHM) of the core represents a measure of the AO correction. The average FWHM values for BBSO
and NSO/SP are 23.5′′ and 18.2′′, respectively. The extended wings of the function show that the AO systems still contribute to an improved speckle reconstruction
at the periphery of the 80′′×80′′ FOV. The major differences in the level of AO correction between BBSO and NSO/SP can be explained by different contributions
of ground-layer- and free-atmosphere-dominated seeing, as well as different FOVs of the wavefront sensors. In addition, we
find an anisotropic spectral ratio in sunspot penumbrae caused by the quasi-one-dimensional nature of penumbral filaments,
which introduces a significant error in the estimation of the Fourier amplitudes during the image restoration process. 相似文献
5.
Jagadish Singh 《Astrophysics and Space Science》2009,321(2):127-135
The effect of small perturbations ε and ε
′ in the Coriolis and the centrifugal forces, respectively on the nonlinear stability of the triangular points in the restricted
three-body problem with variable mass has been studied. It is found that, in the nonlinear sense, the triangular points are
stable for all mass ratios in the range of linear stability except for three mass ratios, which depend upon ε, ε
′ and β, the constant due to the variation in mass governed by Jeans’ law. 相似文献
6.
Glenn S. Orton 《Earth, Moon, and Planets》2009,105(2-4):143-152
This report presents both a retrospective of ground-based support for spacecraft missions to the outer solar system and a perspective of support for future missions. Past support is reviewed in a series of case studies involving the author. The most basic support is essential, providing the mission with information without which the planned science would not have been accomplished. Another is critical, without which science would have been returned, but missing a key element in its understanding. Some observations are enabling by accomplishing one aspect of an experiment which would otherwise not have been possible. Other observations provide a perspective of the planet as a whole which is not available to instruments with narrow fields of view and limited spatial coverage, sometimes motivating a re-prioritizing of experiment objectives. Ground-based support is also capable of providing spectral coverage not present in the complement of spacecraft instruments. Earth-based observations also have the capability of filling in gaps of spacecraft coverage of atmospheric phenomena, as well as providing surveillance of longer-term behavior than the coverage available to the mission. Future missions benefiting from ground-based support would include the Juno mission to Jupiter in the next decade, a flagship-class mission to the Jupiter or to the Saturn systems currently under consideration, and possible intermediate-class missions which might be proposed in NASA’s New Frontiers category. One of the principal benefits of future 30 m-class giant telescopes would be to improve the spatial resolution of maps of temperature and composition which are derived from observations of thermal emission at mid-infrared and longer wavelengths. In many situations, this spatial resolution is competitive with those of the relevant instruments on the spacecraft themselves. 相似文献
7.
Chuan Peng Zhang Jarken Esimbek Jian Jun Zhou Gang Wu Zhi Mao Du 《Astrophysics and Space Science》2012,337(1):283-302
There are relatively few H2CO mappings of large-area giant molecular cloud (GMCs). H2CO absorption lines are good tracers for low-temperature molecular clouds towards star formation regions. Thus, the aim of
the study was to identify H2CO distributions in ambient molecular clouds. We investigated morphologic relations among 6-cm continuum brightness temperature
(CBT) data and H2CO (111−110; Nanshan 25-m radio telescope), 12CO (1–0; 1.2-m CfA telescope) and midcourse space experiment (MSX) data, and considered the impact of background components
on foreground clouds. We report simultaneous 6-cm H2CO absorption lines and H110α radio recombination line observations and give several large-area mappings at 4.8 GHz toward W49 (50′×50′), W3 (70′×90′),
DR21/W75 (60′×90′) and NGC2024/NGC2023 (50′×100′) GMCs. By superimposing H2CO and 12CO contours onto the MSX color map, we can compare correlations. The resolution for H2CO, 12CO and MSX data was ∼10′, ∼8′ and ∼18.3″, respectively. Comparison of H2CO and 12CO contours, 8.28-μm MSX colorscale and CBT data revealed great morphological correlation in the large area, although there
are some discrepancies between 12CO and H2CO peaks in small areas. The NGC2024/NGC2023 GMC is a large area of HII regions with a high CBT, but a H2CO cloud to the north is possible against the cosmic microwave background. A statistical diagram shows that 85.21% of H2CO absorption lines are distributed in the intensity range from −1.0 to 0 Jy and the ΔV range from 1.206 to 5 km s−1. 相似文献
8.
S. García-Burillo F. Combes J. Graciá-Carpio A. Usero M. Guélin 《Astrophysics and Space Science》2008,313(1-3):261-265
High-resolution CO maps are an essential tool to search for observational evidence of AGN fueling in galaxy nuclei. While
their capabilities will be surpassed by ALMA, current mm-interferometers can already provide relevant information on scales
which are critical for the process of angular momentum transfer in fueling the AGN. In this context we present the latest
results issued from the NUclei of GAlaxies (NUGA) project, a high-resolution (0.5′′–1′′) CO survey of low luminosity AGNs conducted with the IRAM Plateau de Bure interferometer (PdBI). The use of more specific
molecular tracers of dense gas can probe the feedback influence of activity on the chemistry and energy balance in the interstellar
medium of nearby galaxies, a prerequisite to understanding how feedback operate at higher redshift galaxies. We discuss the
results obtained in an ongoing study devoted to probe the feedback of activity from nearby Seyferts to high-redshift QSO. 相似文献
9.
V. N. Frolov Yu. K. Ananjevskaja D. L. Gorshanov E. V. Polyakov 《Astronomy Letters》2010,36(5):338-348
We present the results of our comprehensive study of the Galactic open star cluster NGC 6866. The positions of stars in the
investigated region have been obtained with the “Fantasy” automatic measuring machine from 10 plates of the normal astrograph
at the Pulkovo Astronomical Observatory. The size of the investigated field is 40′ × 40′, the limiting magnitude is B ∼ 16·
m
6, and the maximum epoch difference is 79 yr. For 1202 field stars, we have determined the relative proper motions with an
rms error of 2.5 mas yr−1. Out of them, 423 stars may be considered cluster members with a probability P > 70% according to the astrometric criterion. Photometric diagrams have been used as an additional criterion. We have performed
two-color BV CCD photometry of stars with the Pulkovo ZA-320M mirror astrograph. The U magnitudes from the literature have also been used to construct the two-color diagrams. A total of 267 stars have turned
out to be members of NGC 6866 according to the two criteria. We present refined physical parameters of the cluster and its
age estimate (5.6 × 108 yr). The cluster membership of red and blue giants, variable, double, and multiple stars is considered. We have found an
almost complete coincidence of the positions of one of the stars in the region (a cluster nonmember) and a soft X-ray source
in the ROSAT catalog. The “Fantasy” automatic measuring machine is described in the Appendix. 相似文献
10.
Mahesh Anand 《Earth, Moon, and Planets》2010,107(1):65-73
One of the most exciting recent developments in the field of lunar science has been the unambiguous detection of water (either
as OH or H2O) or water ice on the Moon through instruments flown on a number of orbiting spacecraft missions. At the same time, continued
laboratory-based investigations of returned lunar samples by Apollo missions using high-precision, low-detection, analytical
instruments have for the first time, provided the absolute abundance of water (present mostly as structurally bound OH− in mineral phases) in lunar samples. These new results suggest that the Moon is not an anhydrous body, questioning conventional
wisdom, and indicating the possibility of a wet lunar interior and the presence of distinct reservoirs of water on the lunar
surface. However, not all recent results point to a wet Moon and it appears that the distribution of water on the Moon may
be highly heterogeneous. Additionally, a number of sources are likely to have contributed to the water inventory of the Moon
ranging from primordial water to meteorite-derived water ice through to the water formed during the reaction of solar-wind
hydrogen with the lunar soil. Water on the Moon has implications for future astrobiological investigations as well as for
generating resources in situ during future exploration of the Moon and other airless bodies in the Solar System. 相似文献
11.
Magnetic clouds (MCs) are a subset of interplanetary coronal mass ejections (ICMEs) which exhibit signatures consistent with
a magnetic flux rope structure. Techniques for reconstructing flux rope orientation from single-point in situ observations typically assume the flux rope is locally cylindrical, e.g., minimum variance analysis (MVA) and force-free flux rope (FFFR) fitting. In this study, we outline a non-cylindrical magnetic
flux rope model, in which the flux rope radius and axial curvature can both vary along the length of the axis. This model
is not necessarily intended to represent the global structure of MCs, but it can be used to quantify the error in MC reconstruction
resulting from the cylindrical approximation. When the local flux rope axis is approximately perpendicular to the heliocentric
radial direction, which is also the effective spacecraft trajectory through a magnetic cloud, the error in using cylindrical
reconstruction methods is relatively small (≈ 10∘). However, as the local axis orientation becomes increasingly aligned with the radial direction, the spacecraft trajectory
may pass close to the axis at two separate locations. This results in a magnetic field time series which deviates significantly
from encounters with a force-free flux rope, and consequently the error in the axis orientation derived from cylindrical reconstructions
can be as much as 90∘. Such two-axis encounters can result in an apparent ‘double flux rope’ signature in the magnetic field time series, sometimes
observed in spacecraft data. Analysing each axis encounter independently produces reasonably accurate axis orientations with
MVA, but larger errors with FFFR fitting. 相似文献
12.
An empirical model has been developed to reproduce the drift of the spectrum recorded by the EIS on Hinode using instrumental temperatures and relative motion of the spacecraft. The EIS spectrum shows an artificial drift in wavelength
dimension in sync with the revolution of the spacecraft, which is caused by temperature variations inside the spectrometer.
The drift amounts to 70 km s−1 in Doppler velocity and introduces difficulties in velocity measurements. An artificial neural network is incorporated to
establish a relationship between the instrumental temperatures and the spectral drift. This empirical model reproduces observed
spectrum shift with an rms error of 4.4 km s−1. This procedure is robust and applicable to any spectrum obtained with EIS, regardless of the observing field. In addition,
spectral curvatures and spatial offset in the north – south direction are determined to compensate for instrumental effects. 相似文献
13.
Emmanuel Hinglais 《Experimental Astronomy》2011,30(2-3):85-110
In 2009, the Centre National d??Etudes Spatiales (CNES) carried out an assessment study on a ??Fresnel telescope?? concept based on a two-spacecraftformation flying configuration. This concept uses a binary Fresnel zone plate, and the principle of diffraction focusing, which allows high resolution optical imaging for astrophysics. In addition to CNES, the Laboratoire d??Astrophysique de Toulouse Tarbes (LATT) was deeply involved at two levels: through Research & Technology (R&T) studies to simulate and validate on a test bench the Fresnel concept performance, and through active participation in the CNES team for the optical aspects and to define the astrophysical fields of Fresnel-based space missions. The study was conducted within the technical limitations that resulted from a compromise between the R&T state of the art and the potential scientific domains of interest. The main technical limitations are linked to the size of the primary Fresnel array and to its usable spectral bandwidth. In this framework, the study covers ambitious architectures, correlating the technology readiness of the main critical components with the time-scale and programmatic horizons. The possible scientific topics arise from this range of missions. In this paper, I present a mission launched by a Soyuz, dedicated to astrophysics in the Ultra Violet (UV) band: 120 to 300 nm using a 4-m Fresnel array. It could be competitive in the next fifteen years, whereas a 10-m aperture mission in different bands; UV, visible or Infra Red (IR) (up to 6 ??m) could be achievable in the future. Larger missions, using a primary array larger than 20 m, request technologies not yet available but that will probably be based on new inflatable structures with membranes, as already tested in the USA for other ends. 相似文献
14.
We present the results of our studies of the cosmic-ray fluctuations in the frequency range 10−4−1.67 × 10−3 Hz based on energetic particle flux measurements on spacecraft in the solar wind, in the magnetosphere, and at Earth in the
11-year solar cycle. The cosmic-ray fluctuation spectrum is shown to have an 11-year modulation related to the solar cycle.
A different behavior of the level of energetic particle fluctuations measured in different regions of space is observed for
cosmic rays of different origins. We conclude that the new, previously unknown phenomenon of 11-year modulation of the cosmic-ray
fluctuation spectrum has been established. A possible explanation of this phenomenon is given. 相似文献
15.
B. Karthikeyan V. Raja N. Rajamanickam S. P. Bagare 《Astrophysics and Space Science》2006,306(4):231-234
For molecular identification in astrophysical sources, an astrophysicist needs some spectroscopic parameters such as dissociation
energy, vibrational or rotational temperature of the source, band or line wavelengths, transition probability parameters,
etc. The Franck-Condon(FC) factors are proportional to the transition probabilities. In this study, the FC factors and r-centroids for the vibronic (vibration-electronic) transitions C
1 Σ + → X
1 Σ + of aluminium hydride (AlH), b
3 Σ ( −) → a
3 Π, C
1 Σ + → A
1 Π & C
′1 Δ → Δ 1 Π of boron hydride (BH) have been evaluated and the results are presented in tables which include band origin/head wavelengths.
The physical & astrophysical significances of our evaluated FC factors & r-centroids have been discussed and the possible presence of AlH in sunspot umbral spectra is also predicted.
PACS: 33 · 70 · Ca 相似文献
16.
Robert L. Forward 《Earth, Moon, and Planets》1980,22(4):419-433
Future missions to the Moon should include a detailed high-resolution global gravity survey from a low (15–30 km) polar orbiting spacecraft. The use of gravity gradiometer instruments on board the spacecraft will give higher-resolution data at lower total mission cost that the present Doppler tracking technique. Simulations show that although a three axis gradiometer system is preferred, and can even be used to estimate spacecraft attitude and altitude variation, a properly oriented single rotating gravity gradiometer can be used to resolve closely spaced mascons in both the along-track and cross-track directions.Paper presented at theFuture Lunar Exploration session of the Tenth Lunar and Planetary Science. Conference, Johnson Space Center, Houston, Texas, 19–23 March 1979. 相似文献
17.
The twin Solar Terrestrial Relations Observatory (STEREO) spacecraft reached a separation angle of 180° on 6 February 2011. This provided a unique opportunity to test the
intercalibration between the Sun–Earth Connection Coronal and Heliospheric Investigation (SECCHI) telescopes on both spacecraft
for areas above the limb. So long as the corona is optically thin, at 180° separation each spacecraft sees the same corona
from opposite directions. Thus, the data should appear as mirror images of each other. We report here on the results of the
comparison of the images taken by the inner coronagraph (COR1) on the STEREO-Ahead and -Behind spacecraft in the hours when the separation was close to 180°. We find that the intensity values seen by the two telescopes
agree with each other to a high degree of accuracy. This validates both the radiometric intercalibration between the COR1
telescopes, and the method used to remove instrumental background from the images. The relative error between COR1-A and COR1-B
is found to be less than 10−9
B/B
⊙ over most of the field-of-view, growing to a few ×10−9
B/B
⊙ for the brighter pixels near the edge of the occulter. The primary source of error is the background determination. We also
report on the analysis of star observations which show that the absolute radiometric calibration of either COR1 telescope
has not changed significantly since launch. 相似文献
18.
John Enright Ilija Jovanovic Laila Kazemi Harry Zhang Tom Dzamba 《Celestial Mechanics and Dynamical Astronomy》2018,130(2):13
This paper examines the effectiveness of small star trackers for orbital estimation. Autonomous optical navigation has been used for some time to provide local estimates of orbital parameters during close approach to celestial bodies. These techniques have been used extensively on spacecraft dating back to the Voyager missions, but often rely on long exposures and large instrument apertures. Using a hyperbolic Mars approach as a reference mission, we present an EKF-based navigation filter suitable for nanosatellite missions. Observations of Mars and its moons allow the estimator to correct initial errors in both position and velocity. Our results show that nanosatellite-class star trackers can produce good quality navigation solutions with low position (\(<300\,\text {m}\)) and velocity (\(<0.15\,\text {m/s}\)) errors as the spacecraft approaches periapse. 相似文献
19.
P. Janardhan 《Journal of Astrophysics and Astronomy》2006,27(2-3):201-207
At the Sun-Earth distance of one astronomical unit (1 AU), the solar wind is known to be strongly supersonic and super Alfvenic
with Mach and Alfven numbers being on average 12 and 9 respectively. Also, solar wind densities (average ∼10cm-3) and velocities (average ∼450kms-1) at 1AU, are known to be inversely correlated with low velocities having higher than average densities andvice versa. However, on May 11 and 12 1999 the Earth was engulfed by an unusually low density (< 0.1cm-3) and low velocity (< 350km s-1) solar wind with an Alfven Mach number significantly less than 1. This was a unique low-velocity, low-density, sub-Alfvénic
solar wind flow which spacecraft observations have shown lasted more than 24 hours. One consequence of this extremely tenuous
solar wind was a spectacular expansion of the Earth’s magnetosphere and bow shock. The expanding bow shock was observed by
several spacecraft and reached record upstream distances of nearly 60 Earth radii, the lunar orbit. The event was so dramatic
that it has come to be known asthe solar wind disappearance event. Though extensive studies of this event were made by many authors in the past, it has only been recently shown that the unusual
solar wind flows characterizing this event originated from a small coronal hole in the vicinity of a large active region on
the Sun. These recent results have put to rest speculation that such events are associated with global phenomenon like the
periodic solar polar field reversal that occurs at the maximum of each solar cycle. In this paper we revisit the 11 May 1999
event, look at other disappearance events that have ocurred in the past, examine the reasons why speculations about the association
of such events with global phenomena like solar polar field reversals were made and also examine the role of transient coronal
holes as a possible solar source for such events. 相似文献
20.
We calculate the expression forΔ
-s in terms of true anomalies and classical orbital elements, referring to a common fixed plane and working up to power four
of eccentricities and tangents of inclinations. We obtained two final results: the first wheny
′>y, the second wheny>y
′. 相似文献