首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 796 毫秒
1.
Emission from the Herschel telescope is the dominant source of radiation for the majority of SPIRE Fourier transform spectrometer (FTS) observations, despite the exceptionally low emissivity of the primary and secondary mirrors. Accurate modelling and removal of the telescope contribution is, therefore, an important and challenging aspect of FTS calibration and data reduction pipeline. A dust-contaminated telescope model with time invariant mirror emissivity was adopted before the Herschel launch. However, measured FTS spectra show a clear evolution of the telescope contribution over the mission and strong need for a correction to the standard telescope model in order to reduce residual background (of up to 7 Jy) in the final data products. Systematic changes in observations of dark sky, taken over the course of the mission, provide a measure of the evolution between observed telescope emission and the telescope model. These dark sky observations have been used to derive a time dependent correction to the telescope emissivity that reduces the systematic error in the continuum of the final FTS spectra to ～0.35 Jy.  相似文献   

2.
The Herschel SPIRE Fourier transform spectrometer (FTS) performs spectral imaging in the 447–1546 GHz band. It can observe in three spatial sampling modes: sparse mode, with a single pointing on sky, or intermediate or full modes with 1 and 1/2 beam spacing, respectively. In this paper, we investigate the uncertainty and repeatability for fully sampled FTS mapping observations. The repeatability is characterised using nine observations of the Orion Bar. Metrics are derived based on the ratio of the measured intensity in each observation compared to that in the combined spectral cube from all observations. The mean relative deviation is determined to be within 2 %, and the pixel-by-pixel scatter is ～ 7 %. The scatter increases towards the edges of the maps. The uncertainty in the frequency scale is also studied, and the spread in the line centre velocity across the maps is found to be ～ 15 km s ? 1. Other causes of uncertainty are also discussed including the effect of pointing and the additive uncertainty in the continuum.  相似文献   

3.
Herschel/SPIRE Fourier transform spectrometer (FTS) observations contain emission from both the Herschel Telescope and the SPIRE Instrument itself, both of which are typically orders of magnitude greater than the emission from the astronomical source, and must be removed in order to recover the source spectrum. The effects of the Herschel Telescope and the SPIRE Instrument are removed during data reduction using relative spectral response calibration curves and emission models. We present the evolution of the methods used to derive the relative spectral response calibration curves for the SPIRE FTS. The relationship between the calibration curves and the ultimate sensitivity of calibrated SPIRE FTS data is discussed and the results from the derivation methods are compared. These comparisons show that the latest derivation methods result in calibration curves that impart a factor of between 2 and 100 less noise to the overall error budget, which results in calibrated spectra for individual observations whose noise is reduced by a factor of 2–3, with a gain in the overall spectral sensitivity of 23 % and 21 % for the two detector bands, respectively.  相似文献   

4.
New broadband observations in several passbands between 30 and 500 μm of Mercury, Venus, Mars, Jupiter, Saturn, and Uranus are presented. The best agreement between the data and various thermal models of Mars, Jupiter, and Uranus is obtained with a slightly cooler absolute temperature scale than that previously adopted by Armstrong et al. (1972). The effective temperature of Uranus is 58 ± 2°K, which is in agreement with its solar equilibrium temperature. The existence of an internal energy source of Saturn has been reconfirmed and must lie within the range of 0.9 to 3.2 times the absorbed solar flux. A depression exists in the spectra of Jupiter, Saturn, and Uranus between 80 and 300 μm, which may be a result of NH3 opacity.  相似文献   

5.
Multicolor photometric observations of the optical afterglow from GRB 060526 with the Russian-Turkish 1.5-m RTT-150 telescope (Mount Bakyrlytepe, Turkey) are presented. The afterglow light curve was measured in detail starting from about 5 h after the GRB and over five ensuing nights. In addition, upper limits were obtained on the rapid variability of the afterglow on the first night of observations and the history of afterglow color variations was measured in detail. In the time interval from 6 to 16 h after the burst, the flux gradually decreased approximately as a power law with a slope of ?1.14 ± 0.02. Subsequently, variability was observed on a time scale δt < t and the afterglow began to decay much faster. The afterglow color was approximately constant (V?R ≈ 0.5) throughout the observations, despite the flux variability. Variability time scales up to δt/t ≈ 0.0055 were observed at ΔF ν/F ν ≈ 0.3, which violates many constraints on the variability of the observed emission from an ultrarelativistic jet obtained by Ioka et al. (2005). We suggest explaining this variability by the fact that the shell motion is no longer ultrarelativistic at this time.  相似文献   

6.
D. Goorvitch  C. Chackerian 《Icarus》1977,32(3):348-361
With the advent of high-resolution instruments and their use high above most of the telluric water vapor, we can expect to observe the hydrogen pure rotational quadrupole lines at 28, 17, and 12 μm from the atmospheres of the outer planets. We have calculated the best values for the line strengths, pressure-broadening coefficients, diffusion constants, and pressure shifts for these rotational transitions. We have used the collisionally narrowed Galatry profile to calculate brightness temperature line profiles for these H2 transitions for the outer planets Jupiter and Uranus. We have also included the effect of the H2 rotational-translational continuum and the NH3ν2 band.  相似文献   

7.
The different algorithms appropriate for point source photometry on data from the SPIRE instrument on-board the Herschel Space Observatory, within the Herschel Interactive Processing Environment (HIPE) are compared. Point source photometry of a large ensemble of standard calibration stars and dark sky observations is carried out using the 4 major methods within HIPE: SUSSEXtractor, DAOphot, the SPIRE Timeline Fitter and simple Aperture Photometry. Colour corrections and effective beam areas as a function of the assumed source spectral index are also included to produce a large number of photometric measurements per individual target, in each of the 3 SPIRE bands (250, 350, 500μm), to examine both the accuracy and repeatability of each of the 4 algorithms. It is concluded that for flux densities down to the level of 30mJy that the SPIRE Timeline Fitter is the method of choice. However, at least in the 250 and 350μm bands, all 4 methods provide photometric repeatability better than a few percent down to at approximately 100mJy. The DAOphot method appears in many cases to have a systematic offset of ～8 % in all SPIRE bands which may be indicative of a sub-optimal aperture correction. In general, aperture photometry is the least reliable method, i.e. largest scatter between observations, especially in the longest wavelength band. At the faintest fluxes, <30mJy, SUSSEXtractor or DAOphot provide a better alternative to the Timeline Fitter.  相似文献   

8.
We studied the relationship between the power-law exponent γ on the rigidity R of the spectrum of galactic cosmic-ray (GCR) intensity variation (δD(R)/D(R)∝R ?γ ) and the exponents ν y and ν z of the power spectral density (PSD) of the B y and B z components of the interplanetary magnetic field (IMF) turbulence (PSD～f ?ν , where f is the frequency). We used the data from neutron monitors and IMF for the period of 1968?–?2002. The exponents ν y and ν z were calculated in the frequency interval Δf=f 2?f 1=3×10?6 Hz of the resonant frequencies (f 1=1×10?6 Hz, f 2=4×10?6 Hz) that are responsible for the scattering of GCR particles with the rigidity range detected by neutron monitors. We found clear inverse correlations between γ and ν y or ν z when the time variations of the resonant frequencies were derived from in situ measurements of the solar wind velocity U sw and IMF strength B during 1968?–?2002. We argue that these inverse relations are a fundamental feature in the GCR modulation that is not restricted to the analyzed years of 1968?–?2002.  相似文献   

9.
The Fourier Transform Spectrometer (FTS) of the Spectral and Photometric Imaging REceiver (SPIRE) on board the ESA Herschel Space Observatory has two detector setting modes: (a) a nominal mode, which is optimized for observing moderately bright to faint astronomical targets, and (b) a bright-source mode recommended for sources significantly brighter than 500 Jy, within the SPIRE FTS bandwidth of 446.7–1544 GHz (or 194–671 microns in wavelength), which employs a reduced detector responsivity and out-of-phase analog signal amplifier/demodulator. We address in detail the calibration issues unique to the bright-source mode, describe the integration of the bright-mode data processing into the existing pipeline for the nominal mode, and show that the flux calibration accuracy of the bright-source mode is generally within 2 % of that of the nominal mode, and that the bright-source mode is 3 to 4 times less sensitive than the nominal mode.  相似文献   

10.
M. Podolak  R.T. Reynolds 《Icarus》1984,57(1):102-111
The planetary ratios of ice to rock (IR) abundances expected in Uranus and Neptune are derived on the basis of several cosmogonic theories. For both Uranus and Neptune the value of IR lies between about 1.0 and 3.6. This value is difficult to reconcile with a scenario in which N and C are accreted primarily in the form of N2 and CO. It is consistent with some versions of both giant protoplanet theories and equilibrium accretion theories.  相似文献   

11.
F.H. Briggs  B.H. Andrew 《Icarus》1980,41(2):269-277
We present high-resolution interferometry of Uranus at 6 cm wavelength and single-dish observations of the disk-averaged brightness temperature, TB, at 2.8 and 4.8 cm wavelength. The 1978 measurements of TB of 228 ± 2,243 ± 9, and 259 ± 4 K at 2.8, 4.8, and 6 cm, respectively, support the finding of M. J. Klein and J. A. Turegano (1978, Astrophy. J.224, L31–L34) that the brightness temperature of Uranus has been rising. There is no evidence for radio emission from outside the visible disk at 6 cm. Radiation from a synchrotron radiation belt or from the Uranian rings is certainly less than 10% of the total radio flux. The interferometry shows a possible 55 ± 20 K difference in brightness temperature between the equator and the currently exposed pole. The pole appears to be ～275 K while the equator is ～220 K. However, a permanent gradient of this magnitude is insufficient to account for the rise in disk-averaged brightness by simple reorientation of Uranus' globe relative to our line of sight. The changing insolation probably triggers a redistribution of the trace constituent NH3 which is responsible for the radio opacity. The NH3 may be interacting strongly with H2S on Uranus.  相似文献   

12.
《Planetary and Space Science》1999,47(10-11):1225-1242
Infrared spectra of Jupiter and Saturn have been recorded with the two spectrometers of the Infrared Space Observatory (ISO) in 1995–1998, in the 2.3–180 μm range. Both the grating modes (R=150–2000) and the Fabry-Pérot modes (R=8000–30,000) of the two instruments were used. The main results of these observations are (1) the detection of water vapour in the deep troposphere of Saturn; (2) the detection of new hydrocarbons (CH3C2H, C4H2, C6H6, CH3) in Saturn’s stratosphere; (3) the detection of water vapour and carbon dioxide in the stratospheres of Jupiter and Saturn; (4) a new determination of the D/H ratio from the detection of HD rotational lines. The origin of the external oxygen source on Jupiter and Saturn (also found in the other giant planets and Titan in comparable amounts) may be either interplanetary (micrometeoritic flux) or local (rings and/or satellites). The D/H determination in Jupiter, comparable to Saturn’s result, is in agreement with the recent measurement by the Galileo probe (Mahaffy, P.R., Donahue, T.M., Atreya, S.K., Owen, T.C., Niemann, H.B., 1998. Galileo probe measurements of D/H and 3He/4He in Jupiters atmosphere. Space Science Rev. 84 251–263); the D/H values on Uranus and Neptune are significantly higher, as expected from current models of planetary formation.  相似文献   

13.
Energetic electron injection events result in the arrival of loss-cone distributions of electrons at energies of a few keV close to the plasmapause at local midnight. These distributions favour the growth of strong electrostatic waves with some conversion to electromagnetic nonthermal continuum emissions near to the geomagnetic equator.GEOS2 located at the geostationary orbit (L = 6.6, 3.3° South) has observed these continuum emissions for a number of electron injection events. Their unique frequency structure provides a measurement of the geomagnetic field strength at the source and hence its radial position, while direction finding measurements at GEOS2 complete the source location determination.Measurements of source locations as a function of time after the start of an electron injection event, yield typical inwards motions of 1REh?1. In this way the emissions provide a remote sensing of the plasmapause location from the geostationary orbit.  相似文献   

14.
We report on spectro-imaging infrared observations of Jupiter's auroral zones, acquired in October 1999 and October 2000 with the FTS/BEAR instrument at the Canada-France-Hawaii Telescope. The use of narrow-band filters at 2.09 and 2.12 μm, combined with high spectral resolution (0.2 cm−1), allowed us to map emission from the H2S1(1) quadrupole line and from several H3+ lines. The H2 and H3+ emission appears to be morphologically different, especially in the north, where the latter notably exhibits a “hot spot” near 150°-170° System III longitude. This hot spot coincides in position with the region of increased and variable hydrocarbon, FUV and X-ray emission, but is not seen in the more uniform H2S1(1) emission. We also present the first images of the H2 emission in the southern polar region. The spectra include a total of 14 H3+ lines, including two hot lines from the 3ν2-ν2 band, detected on Jupiter for the first time. They can be used to determine H3+ column densities, rotational (Trot) and vibrational (Tvib) temperatures. We find the mean Tvib of the v2=3 state to be lower (960±50 K) than the mean Trot in v2=2 (1170±75 K), indicating an underpopulation of the v2=3 level with respect to local thermodynamical equilibrium. Rotational temperatures and associated column densities are generally higher and lower, respectively, than inferred previously from ν2 observations. This is a likely consequence of a large positive temperature gradient in the sub-microbar auroral atmosphere. While the signal-to-noise is not sufficient to take full advantage of the 2-D capabilities of the observations, the search for correlations between line intensities, Tvib and column densities, indicates that variations in line intensities are mostly due to correlated variations in the H3+ column densities. The thermostatic role played by H3+ at ionospheric levels may provide an explanation. The exception is the northern “hot spot,” which exhibits a Tvib about 250 K higher than other regions. A partial explanation might invoke a homopause elevation in this region, but a fully consistent scenario is not yet available. The different distributions of the H2 and H3+ emission are equally difficult to explain.  相似文献   

15.
The line intensity of the green coronal line and the continuum intensity are derived from the filter and white light photographs of the solar corona obtained during the 1980 total solar eclipse. Ratio of the line to continuum intensity is plotted against the radial distancer(=R/R0,R 0 is the solar radius), in various position angles. A simple model assuming an electron density dependence of the line and continuum intensities suggests a dominant collisional mechanism for the excitation of the line in the innermost regions (～ 1.4R 0). The measured line to continuum ratio tends to a constant value at different radial distances in different position angles. The constancy of the measured line to continuum ratio indicates significant radiative excitation beyond 1.4 R0, in some of the position angles.  相似文献   

16.
New laboratory spectra of crystalline and amorphous diacetylene ice have been recorded in the range of 7000-500 cm−1 (1.4-20 μm) to aid in the identification of solid diacetylene on Saturn's moon Titan. We have established that amorphous diacetylene ice is stable only at temperatures less than 70±1 K. With respect to observations on Titan, the best approach would be to utilize future space-based telescopes to search for the ν4 (3277/3271 cm−1) in absorption against the reflected light from the sun and the slightly weaker ν8 absorption bands (676/661 cm−1) in absorption against the continuum emission.  相似文献   

17.
Out-of-field stray-light spots of the Herschel telescope optics relative to the PACS and SPIRE instrument apertures were modeled by ray tracing simulations with the Advanced Systems Analysis Program (ASAP, by Breault Research Organization) prior to launch. The predicted stray-light behaviour was verified by dedicated stray-light calibration observations in-flight. This resulted in a special feature of the Herschel Science Mission Planning Software, marking the sky positions of stray-light spots by the very bright infrared planetary sources Venus, Mars, Jupiter, and Saturn, as well as the Moon, thus avoiding contamination of scientific photometric observations by out-of-field stray-light of these sources.  相似文献   

18.
We report on mid-resolution (R∼2000) spectroscopic observations of Titan, acquired in November 2000 with the Very Large Telescope and covering the range 4.75-5.07 μm. These observations provide a detailed characterization of the CO (1-0) vibrational band, clearly separating for the first time individual CO lines (P10 to P19 lines of 13CO). They indicate that the CO/N2 mixing ratio in Titan’s troposphere is 32±10 ppm. Comparison with photochemical models indicates that CO is not in a steady state in Titan’s atmosphere. The observations confirm that Titan’s 5-μm continuum geometric albedo is ∼0.06, and further indicates a ∼20% albedo decrease over 4.98-5.07 μm. Nonzero flux is detected at the 0.01 geometric albedo level in the saturated core of the 12CO (1-0) band, at 4.75-4.85 μm, providing evidence for backscattering on the stratospheric haze. Finally, emission lines are detected at 4.75-4.835 μm, coinciding in position with lines from the CO(1-0) and/or CO(2-1) bands. Matching them by thermal emission would require Titan’s stratosphere to be much warmer (by ∼ 25 K at 0.1 mbar) than indicated by the methane 7.7-μm emission and the Voyager radio-occultation. We show instead that a nonthermal mechanism, namely solar-excited fluorescence, is a more plausible source for these emissions. Improved observations and laboratory measurements on the vibrational-translational relaxation of CO are needed for further interpretation of these emissions in terms of a CO stratospheric mixing ratio.  相似文献   

19.
We have constructed Locally Rotationally Symmetric Bianchi type I (LRSBI) cosmological models in the f(R,T) theory of gravity when the source of gravitation is the bulk viscous fluid. The models are constructed for f(R,T)=R+2f(T) and f(R,T)=f 1(R)+f 2(T). We found that in the first case the model degenerates into effective stiff fluid model of the universe. In the second case we obtained degenerate effective stiff fluid model as well as general bulk viscous models of the universe. Some physical and kinematical properties of the models are also discussed.  相似文献   

20.
D.Chris Benner  Uwe Fink 《Icarus》1980,42(3):343-353
Laboratory band-model absorption coefficients of CH4 are used to calculate the Uranus spectrum from 5400 to 10,400 Å. A good fit of both strong and weak bands for the Uranus spectrum over the entire wavelength interval is achieved for the first time. Three different atmospheric models are employed: a reflecting layer model, a homogeneous scattering layer model, and a clear atmosphere sandwiched between two scattering layers. The spectrum for the reflecting layer model exhibits serious discrepancies but shows that large amounts of CH4 (5–10 km-am) are necessary to reproduce the Uranus spectrum. Both scattering models give reasonably good fits. The homogeneous model requires a particle scattering albedo (g?wp) ? 0.998 and an abundance per scattering mean free path (a?) ofa?1 km-am. The parameters derived from the sandwich layer model are: forsb the upper scattering layer a continuum single scattering albedo (g?w0) of 0.995 and a scattering optical depth variable with wavelength consistent with Rayleigh scattering; for the clear layer they are a CH4 abundance (a) of 2.2 km-am and an effective pressure (p) ? 0.1 atm; for the lower cloud deck a Lambert reflectivity (L) of 0.9 resulted. A severe depletion of CH4 in the upper scattering layer is required. An enrichment of CH4/H2 over the solar ratio by a factor of 4–14 in the lower atmosphere is, however, indicated.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号