数字边带分离校准研究

边带分离(Sideband-separating, 2SB)接收可实现上边带(Upper Sideband, USB)和下边带(Lower Sideband, LSB)信号同时观测,观测效率高且上、下两边带不会出现混叠.因此在射电天文观测应用中越来越受到重视.由于全模拟边带分离接收机存在难以克服的幅度和相位误差,导致了边带抑制率较低,影响了系统的性能.数字边带分离接收机可通过数字信号处理方法,有效改善系统边带抑制率.在3–18 GHz频段构建数字边带分离接收机原理实验,并基于边带分离理论和数字校准方法,实现实验系统的边带不平衡度校准,大大改善了系统的边带抑制率.     

In-flight calibration of the HIFI diplexers

HIFI is a heterodyne spectrometer aboard the Herschel Space Observatory, providing high-spectral-resolution capabilities. Of its seven frequency bands, four (bands 3, 4, 6, and 7) employ Martin-Puplett diplexers to combine sky signal and local oscillator at the two linear polarizations H and V, prior to feeding them into the mixers (receivers). The optical path difference in each of these 8 diplexers must be tuned to the observed frequency. The required actuator currents were determined in flight before the start of routine science observations. We here report on regular (roughly quarterly) engineering test observations to validate the repeatability of the HIFI diplexers during the routine phase of Herschel operations. We find the optical path difference to be stable to within 0.4 % of the relevant wavelength, typically at the sub-micron level. We conclude that the repeatability and precision of the diplexer tuning mechanism are so high that science data are in no way negatively affected. With the diplexer calibration established and validated, this line of reasoning can be reversed, and the diplexers can be used as relative spectrometers to measure the local-oscillator frequency, i.e., to check the spectral purity of the local oscillator across the diplexer bands. This was done from before launch out to the last months of cryogenic operations in space.     

Kinematics and Mass Modelling of NGC 1068

We present the kinematics of the ionized gas over the inner 140″ (10 kpc) from observations with the HIFI Fabry-Perot interferometer. There is clear evidence for density wave streaming and bar-driven streaming across the field, with bi-symmetric arms that penetrate to within 200 pc of the nucleus. CO maps show linear structures along (although slightly offset from) the bar consistent with a strong shock. Along the spiral arms which encircle the bar, the H II regions lie downstream of the CO gas in the rest frame of the bar, as do the dust lanes, only if the gas outruns the stellar bar. As a first step towards understanding the details of the gas kinematics, and attempting to determine the mass inflow rate towards the nucleus, we build a mass model for the central disk constrained by near-infrared images. We plan to use this model as gravitational background potential for hydrodynamical simulations of the gas response to the bar. Comparing these with the data presented should enable us to constrain various quantities such as pattern speed, stellar mass-to-light ratio, central mass concentration, and gas fueling rate. This revised version was published online in July 2006 with corrections to the Cover Date.     

Water in star‐forming regions with Herschel

The Herschel Space Observatory is well suited to address several important questions in star‐ and planet formation, as is evident from its first year of operation. This paper focuses on observations of water, a key molecule in the physics and chemistry of star‐formation. In the WISH Key Program, a comprehensive set of water lines is being obtained with the HIFI and PACS instruments toward a large sample of well‐characterized protostars, covering a wide range of luminosities and evolutionary stages. Lines of H₂O, CO and their isotopologues, as well as chemically related hydrides, [O I] and [C II] are observed. Together, the data determine the abundance of water in cold and warm gas, reveal the entire CO ladder up to 4000 K above ground, elucidate the physical processes responsible for the warm gas (passive heating, UV or X‐ray‐heating, shocks), quantify the main cooling agents, and probe dynamical processes associated with forming stars and planets (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Recovery of the mean Jovian temperature structure from inversion of spectrally resolved thermal radiance data

The mean thermal structure of the Jovian atmosphere near the temperature minimum (0.1 bar) is recovered by inversion of thermal radiance data. Improvements over previous studies of this type are made in two respects. (1) Care is taken to select data sources which are on a consistent calibration scale and from a frequency region which minimizes the variance in the recovered temperature. (2) The accuracy in the temperature recovery vs the vertical resolution capability is studied quantitatively. The contributions of various sources of systematic error, which generate significant uncertainty in the recovered thermal structure, are assessed. Sources of systematic error include assumptions about the stratospheric NLTE source function, the extent of cloud cover, the methane mixing ratio, and the calibration scale. Future investigations are outlined which would reduce such uncertainties and provide consistency with a wider range of data on the Jovian upper atmosphere.     

Herschel celestial calibration sources

Celestial standards play a major role in observational astrophysics. They are needed to characterise the performance of instruments and are paramount for photometric calibration. During the Herschel Calibration Asteroid Preparatory Programme approximately 50 asteroids have been established as far-IR/sub-mm/mm calibrators for Herschel. The selected asteroids fill the flux gap between the sub-mm/mm calibrators Mars, Uranus and Neptune, and the mid-IR bright calibration stars. All three Herschel instruments observed asteroids for various calibration purposes, including pointing tests, absolute flux calibration, relative spectral response function, observing mode validation, and cross-calibration aspects. Here we present newly established models for the four large and well characterized main-belt asteroids (1) Ceres, (2) Pallas, (4) Vesta, and (21) Lutetia which can be considered as new prime flux calibrators. The relevant object-specific properties (size, shape, spin-properties, albedo, thermal properties) are well established. The seasonal (distance to Sun, distance to observer, phase angle, aspect angle) and daily variations (rotation) are included in a new thermophysical model setup for these targets. The thermophysical model predictions agree within 5 % with the available (and independently calibrated) Herschel measurements. The four objects cover the flux regime from just below 1,000 Jy (Ceres at mid-IR N-/Q-band) down to fluxes below 0.1 Jy (Lutetia at the longest wavelengths). Based on the comparison with PACS, SPIRE and HIFI measurements and pre-Herschel experience, the validity of these new prime calibrators ranges from mid-infrared to about 700 μm, connecting nicely the absolute stellar reference system in the mid-IR with the planet-based calibration at sub-mm/mm wavelengths.     

The opacity of spiral galaxy disks: IX. Dust and gas surface densities

Our aim is to explore the relation between gas, atomic and molecular, and dust in spiral galaxies. Gas surface densities are from atomic hydrogen and CO line emission maps. To estimate the dust content, we use the disk opacity as inferred from the number of distant galaxies identified in twelve HST/WFPC2 fields of ten nearby spiral galaxies. The observed number of distant galaxies is calibrated for source confusion and crowding with artificial galaxy counts and here we verify our results with sub‐mm surface brightnesses from archival Herschel ‐SPIRE data. We find that the opacity of the spiral disk does not correlate well with the surface density of atomic (H I) or molecular hydrogen (H₂) alone implying that dust is not only associated with the molecular clouds but also the diffuse atomic disk in these galaxies. Our result is a typical dust‐to‐gas ratio of 0.04, with some evidence that this ratio declines with galactocentric radius, consistent with recent Herschel results. We discuss the possible causes of this high dust‐to‐gas ratio; an over‐estimate of the dust surface‐density, an under‐estimate of the molecular hydrogen density from CO maps or a combination of both. We note that while our value of the mean dust‐to‐gas ratio is high, it is consistent with the metallicity at the measured radii if one assumes the Pilyugin & Thuan (2005) calibration of gas metallicity. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Far‐Infrared Emission of Galaxies

C01 Study of local infrared bright galaxies with HERSHCEL‐PACS C02 PDR modeling of the COBE Far‐Infrared data of the Milky Way C03 MAMBO observations of BzK‐selected vigorous starburst galaxies at z ∼ 2 C04 Starburst galaxies in the far‐infrared. Modelling the line, PAH and dust continuum emission C05 The SED from isothermal clouds C06 PDRs in M83 and M51: The road to HIFI/Herschel and SOFIA C07 Large Scale Mapping of Molecular Gas in the Vicinity of 30 Doradus in the Large Magellanic Cloud C08 Modelling far‐infrared emission from dust in gas‐rich galaxies C09 [CII]/CO(1‐0) Line Ratio at low Metallicities C10 Gas, Stars and Dust in the Spiral Arms of M51 C11 The ISOPHOT 170 micron Serendipity Survey (ISOSS) catalog of optically identified galaxies C12 Spitzer Images of M33: A Probe to Radio‐FIR Correlation C13 Observations of far‐infrared emission from dust in gas‐rich galaxies C14 Dust and Gas in Nearby Galaxies: First Results from SINGS and THINGS C15 Sequential Starburst in Arp220?     

Sidebands to the lower kilohertz quasi-periodic oscillation in 4U 1636–53

In this paper we report on further observations of the third and fourth kilohertz quasi-periodic oscillations (QPOs) in the power spectrum of the low-mass X-ray binary (LMXB) 4U 1636−53. These kilohertz QPOs are sidebands to the lower kilohertz QPO. The upper sideband has a frequency  55.5 ± 1.7 Hz  larger than that of the contemporaneously measured lower kilohertz QPO. Such a sideband has now been measured at a significance  >6σ  in the power spectra of three neutron-star LMXBs (4U 1636−53, 1728−34 and 1608−52). We also confirm the presence of a sideband at a frequency ∼55 Hz less than the frequency of the lower kilohertz QPO. The lower sideband is detected at a 3.5σ level only when the lower kilohertz QPO frequency is between 800 and 850 Hz. In that frequency interval, the sidebands are consistent with being symmetric around the lower kilohertz QPO frequency. The upper limit to the rms amplitude of the lower sideband is significantly lower than that of the upper sideband for lower kilohertz QPO frequencies >850 Hz. Symmetric sidebands are unique to 4U 1636−53. This might be explained by the fact that lower kilohertz QPO frequencies as high as 800–850 Hz are rare for 4U 1728−34 and 1608−52. Finally, we also measured a low-frequency QPO at a frequency of ∼43 Hz when the lower kilohertz QPO frequency is between 700 and 850 Hz. A similar low-frequency QPO is present in the power spectra of the other two systems for which a sideband has been observed. We briefly discuss the possibility that the sideband is caused by Lense–Thirring precession.     

Performance results of HESP physical model

As a continuation to the published work on model based calibration technique with HESP(Hanle Echelle Spectrograph) as a case study, in this paper we present the performance results of the technique. We also describe how the open parameters were chosen in the model for optimization, the glass data accuracy and handling the discrepancies. It is observed through simulations that the discrepancies in glass data can be identified but not quantifiable. So having an accurate glass data is important which is possible to obtain from the glass manufacturers. The model’s performance in various aspects is presented using the ThAr calibration frames from HESP during its pre-shipment tests. Accuracy of model predictions and its wave length calibration comparison with conventional empirical fitting, the behaviour of open parameters in optimization, model’s ability to track instrumental drifts in the spectrum and the double fibres performance were discussed. It is observed that the optimized model is able to predict to a high accuracy the drifts in the spectrum from environmental fluctuations. It is also observed that the pattern in the spectral drifts across the 2D spectrum which vary from image to image is predictable with the optimized model. We will also discuss the possible science cases where the model can contribute.     

Elemental composition of 433 Eros: New calibration of the NEAR-Shoemaker XRS data

We present a new calibration of the elemental-abundance data for Asteroid 433 Eros taken by the X-ray spectrometer (XRS) aboard the NEAR-Shoemaker spacecraft. (NEAR is an acronym for “Near-Earth Asteroid Rendezvous.”) Quantification of the asteroid surface elemental abundance ratios depends critically on accurate knowledge of the incident solar X-ray spectrum, which was monitored simultaneously with asteroid observations. Previously published results suffered from incompletely characterized systematic uncertainties due to an imperfect ground calibration of the NEAR gas solar monitor. The solar monitor response function and associated uncertainties have now been characterized by cross-calibration of a large sample of NEAR solar monitor flight data against contemporary broadband solar X-ray data from the Earth-orbiting GOES-8 (Geostationary Operational Environmental Satellite). The results have been used to analyze XRS spectra acquired from Eros during eight major solar flares (including three that have not previously been reported). The end product of this analysis is a revised set of Eros surface elemental abundance ratios with new error estimates that more accurately reflect the remaining uncertainties in the solar flare spectra: Mg/Si=0.753+0.078/−0.055, Al/Si=0.069±0.055, S/Si=0.005±0.008, Ca/Si=0.060+0.023/−0.024, and Fe/Si=1.678+0.338/−0.320. These revised abundance ratios are consistent within cited uncertainties with the results of Nittler et al. [Nittler, L.R., and 14 colleagues, 2001. Meteorit. Planet. Sci. 36, 1673-1695] and thus support the prior conclusions that 433 Eros has a major-element composition similar to ordinary chondrites with the exception of a strong depletion in sulfur, most likely caused by space weathering.     

相位校准电路原理分析及测试

该文详细地介绍了相位校准单元的电路和数学原理以及测试结果。在电路原理部分主要介绍相位校准单元的工作原理、各个关键点的波形以及用隧道二极管产生梳状谱的典型电路。数学原理主要阐述了测量梳状谱的数学依据。最后给出了该相位校准单元的测试要求和测试结果。     

QPOs in microquasars and Sgr A.: measuring the black hole spin

In all four microquasars which show double peak kHz QPOs, the ratio of the two frequencies is 3:2. This strongly supports the suggestion that twin peak kHz QPOs are due to a resonance between some modes of accretion disk oscillations. Here, we stress that fits to observations of the hypothetical resonances between vertical and radial epicyclic frequencies (particularly of the parametric resonance) give an accurate estimate of the spin for the three microquasars with known mass. Measurement of double peak QPOs frequencies in the Galaxy centre seems also to be consistent with the 3:2 ratio established by previous observations in microquasars, however the SgrA* data are rather difficult for the same exact analysis. If confirmed, the 3:2 ratio of double peak QPOs in SgrA* would be of a fundamental importance for the black hole accretion theory and the precise measurement could help to solve the question of QPOs nature. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Density and Temperature Measurements on Laser Generated Radiative Shocks

This paper presents some recent measurements on radiative shocks generated in a xenon gas cell using high power laser. We show new results on temperature and electronic density, and on radial expansion of the shock at various initial conditions (laser energy and gas pressure). The data obtained are compared with one-dimensional and two-dimensional hydro simulations.     

Parametric Decay of a Circularly Polarized Electromagnetic Wave in an Electron-Positron Magnetized Plasma

We study the parametric decays of an electromagnetic wave propagating along an external magnetic field in an electron-positron plasma. We include weakly relativistic effects on the particle motions in the wave field, and the nonlinear ponderomotive force. We find resonant and nonresonant wave couplings. These include, ordinary decay instabilities, in which the pump wave decays into an electro-acoustic mode and a sideband wave. There are also nonresonant couplings involving two sideband waves, and a nonresonant modulational instability in which the pump wave decays into two sideband modes. Depending on the parameters involved, there is a resonant modulational instability involving a forward propagating electro-acoustic mode and a sideband daughter wave.     

Detectability of minor constituents in the martian atmosphere by infrared and submillimeter spectroscopy

Spectroscopic remote sensing in the infrared and (sub)millimeter range is a powerful technique that is well suited for detecting minor species in planetary atmospheres (Planet Space Sci. 43(1995) 1485). Yet, only a handful of molecules in the Mars atmosphere (CO₂, CO and H₂O along with their isotopic species, O_3, and more recently H₂O₂ and CH₄) have been detected so far by this method. New high performance spectroscopic instruments will become available in the future in the infrared and (sub)millimeter range, for observations from the ground (infrared spectrometers on 8 m class telescopes, large millimeter and submillimeter interferometers) and from space, in particular the Planetary Fourier Spectrometer (PFS) aboard Mars Express (MEx), and the Heterodyne Instrument for the Far-Infrared (HIFI) aboard the Herschel Space Observatory (HSO). In this paper we will present results of a study that determines detectability of minor species in the atmosphere of Mars, taking into account the expected performance of the above spectroscopic instruments. In the near future, a new determination of the D/H value is expected with the PFS, especially during times of maximum H₂O abundance in the martian atmosphere. PFS is also expected to place constraints on the abundance of several minor species (H₂O₂,CH₄,CH₂O, SO₂, H₂S, OCS, HCl) above any local outgassing sources, the hot spots. It will be possible to obtain complementary information on some minor species (O₃,H₂O₂, CH₄) from ground-based infrared spectrometers on large telescopes. In the more distant future, HIFI will be ideally suited for measuring the isotopic ratios with unprecedented accuracy. Moreover, it should be able to observe O₂, which has not yet been detected spectroscopically in the IR/submm range, as well as H₂O₂. HIFI should also provide upper limits for several species that have not yet been detected (HCl, NH₃, PH₃) in the atmosphere of Mars. Some species (SO, SO₂,H₂S, OCS, CH₂O) that may be observable from the ground could be searched for with present single-dish antennae and arrays, and in the future with the Atacama Large Millimeter Array (ALMA) submillimeter interferometer.     

EUV Full-Sun Imaging and Pointing Calibration of the SOHO Coronal Diagnostic Spectrometer

Although the field of view of the Normal Incidence Spectrometer (NIS) of the Coronal Diagnostic Spectrometer (CDS) is 4×4 arc min, it is possible to observe the full solar disk by forming a mosaic of images taken in succession. This paper describes just such a study which has been used to collect images of the Sun simultaneously in six wavelengths between 304 Ú and 630 Ú, and with a temperature coverage between 5×10⁴ K and 2.5×10⁶ K. A representative sample of the resulting images is presented. These data can be used to explore the origin of solar EUV variability, and examine large-scale solar features. Another use of these data is to calibrate the pointing of the CDS Offset Pointing System (OPS), by comparing them against the SOHO Extreme ultraviolet Imaging Telescope (EIT) full-disk images taken at the same time. Many joint observations are made with CDS and other SOHO instruments, and calibration of the pointing is crucial to the co-pointing of the instruments, and to the analyses of these data. Coalignment is done by fitting to a cross-correlation function, using an IDL procedure which can be applied to any CDS/NIS data set. The accuracy of an individual coalignment can be demonstrated to be in the range 1–2 arc sec. The overall accuracy of the OPS calibration is ±5 arc sec, mainly attributable to measurement error in the actuator positions. An onboard Spartan Intermediate Sun Sensor of the Lockheed design, which was intended to provide greater pointing accuracy, exhibits a time-varying calibration, possibly due to a gradual loss of sensitivity.     

A Cross-Comparison of Cotemporal Magnetograms Obtained with MDI/SOHO and SP/<Emphasis Type="Italic">Hinode</Emphasis>

We compared a set of cotemporal magnetograms of active regions obtained with the Michelson Doppler Imager (MDI) aboard SOHO and the Spectro-Polarimeter (SP) of the Solar Optical Telescope (SOT) on board Hinode. The comparison shows that even with the recent calibration of level-1.8 data, the magnetic flux density derived from the MDI data is still lower than that obtained with SP. The average ratio between current version 2008 MDI level-1.8 data and SP magnetograms is 0.71, and is 0.82 for version 2007 MDI level-1.8 data. The comparison also shows that the most recent version 2008 calibration of MDI level-1.8 data has successfully removed the center-to-limb variation, while version 2007 level-1.8 data did not, as estimated by Ulrich et al. (Solar Phys. 255, 53, 2009).     

天文图象数据无失真实时数据压缩方法

本文介绍一种用于天文观测图象数据无信息丢失的现场实时数据压缩方法。在对原始图象数据可压缩性统计分析之后，介绍了一种适合天文观测数据现场实时数据压缩的方法＂基础比特＋溢出比特＂编码方法。讨论了为提高压缩比而采取的各种措施。以ＤＥＮＩＳ项目中现场观测原始数据压缩为例，说明了信息保存型实时数据压缩的实现过程，最后给出了该方法的实验结果，实验表明，本文介绍的数据压缩方法在无任何信息丢失的情况下，可获得接近理论值的数据压缩比。     

The UKIRT wide field camera ZYJHK photometric system: calibration from 2MASS

In this paper, we describe the photometric calibration of data taken with the near-infrared Wide Field Camera (WFCAM) on the United Kingdom Infrared Telescope (UKIRT). The broad-band ZYJHK data are directly calibrated from Two-Micron All-Sky Survey (2MASS) point sources which are abundant in every WFCAM pointing. We perform an analysis of spatial systematics in the photometric calibration, both inter- and intradetector show that these are present at up to the ∼5 per cent level in WFCAM. Although the causes of these systematics are not yet fully understood, a method for their removal is developed and tested. Following the application of the correction procedure, the photometric calibration of WFCAM is found to be accurate to ≃1.5 per cent for the JHK bands and 2 per cent for the ZY bands, meeting the survey requirements. We investigate the transformations between the 2MASS and WFCAM systems and find that the Z and Y calibrations are sensitive to the effects of interstellar reddening for large values of   E ( B − V )'  , but that the JHK filters remain largely unaffected. We measure a small correction to the WFCAM Y -band photometry required to place WFCAM on a Vega system, and investigate WFCAM measurements of published standard stars from the list of UKIRT faint standards. Finally, we present empirically determined throughput measurements for WFCAM.