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1.
Optical Characteristics of the Soft X-Ray Telescope Aboard <Emphasis Type="Italic">Yohkoh</Emphasis>
We have studied the point spread function (PSF) of the Yohkoh Soft X-ray Telescope (SXT) using the pre-launch calibration data. It is revealed from our study that both a careful consideration
on the undersampling effect and a proper choice of statistics are indispensable for determining the best fit analytical function
for the SXT PSF. We present the results of numerical simulations supporting our approach toward proper handling of the undersampled
PSF. Examples of the derived SXT PSF using a limited number of pre-launch calibration data are shown as a case study. 相似文献
2.
N. Crouzet T. Guillot F. Fressin A. Blazit the A STEP team 《Astronomische Nachrichten》2007,328(8):805-808
Exoplanetary transit and stellar oscillation surveys require a very high precision photometry. The instrumental noise has therefore to be minimized. First, we perform a semi‐analytical model of different noise sources. We show that the noise due the CCD electrodes can be overcome using a Gaussian PSF (Point Spread Function) of full width half maximum larger than 1.6 pixels. We also find that for a PSF size of a few pixels, the photometric aperture has to be at least 2.5 times larger than the PSF full width half maximum. Then, we compare a front‐ with a back‐illuminated CCD through a Monte‐Carlo simulation. Both cameras give the same results for a PSF full width half maximum larger than 1.5 pixels. All these simulations are applied to the A STEP (Antarctica Search for Transiting Extrasolar Planets) project. As a result, we choose a front‐illuminated camera for A STEP because of its better resolution and lower price, and we will use a PSF larger than 1.6 pixels. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
3.
We present a photometric calibration of the SOHO/LASCO-C2 coronagraph appropriate to Solar System objects based on the extensive analysis of all stars down to magnitude V=8 which transited its field-of-view during the past nine years of operation (1996-2004). An automatic procedure was developed to analyze some 143,000 images, and to detect, locate and measure those stars. Aperture photometry was performed using three different aperture sizes and the zero points of the photometric transformations between the LASCO-C2 magnitudes for its three filters (orange, blue and red) and the standard V magnitudes were determined after introducing a correction for the color of the stars. The calibration coefficients for the surface photometry of extended sources were then derived from the zero points. An analysis of their temporal evolution indicates a slight decrease of the sensitivity of LASCO-C2 at a rate of ∼0.7% per year. 相似文献
4.
The LASCO-C3 coronagraph on SOHO, launched in December 1995, has been collecting images of the corona and background star
fields in a regular manner since 1996. This instrument contains a number of broadband filters with various passbands in the
range between 400 and 1100 nm. The filter used most often has been the Clear filter (400–900 nm) but there are four other
filters with about 100 nm passbands that are also used periodically. Preliminary calibration of the C3 optical system was
done before flight and a number of techniques that use star intensities or magnitudes and position have been applied during
flight. In order to understand the long-term behavior of the C3 instrument, we have recently performed an analysis of LASCO
data that examines the observed intensities of a set of moderately bright stars whose spectra is known from 13 color photometry.
Using these star spectra and the observed count rates we have derived the photometric calibration factors of the C3 coronagraph
for all five color filters with an absolute precision of about ± 7%. Observations with the Clear filter have been used to
look for long-term trends in the instrument sensitivity. The observations indicate a very slight decrease in the instrument
sensitivity of about 3.5% over the 8 years studied here. 相似文献
5.
S. T. Hodgkin M. J. Irwin P. C. Hewett S. J. Warren 《Monthly notices of the Royal Astronomical Society》2009,394(2):675-692
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. 相似文献
6.
Kenneth J. Mighell 《Monthly notices of the Royal Astronomical Society》2005,361(3):861-878
The key features of the matphot algorithm for precise and accurate stellar photometry and astrometry using discrete point spread functions (PSFs) are described. A discrete PSF is a sampled version of a continuous PSF, which describes the two-dimensional probability distribution of photons from a point source (star) just above the detector. The shape information about the photon scattering pattern of a discrete PSF is typically encoded using a numerical table (matrix) or an FITS (Flexible Image Transport System) image file. Discrete PSFs are shifted within an observational model using a 21-pixel-wide damped sinc function, and position-partial derivatives are computed using a five-point numerical differentiation formula. Precise and accurate stellar photometry and astrometry are achieved with undersampled CCD (charge-coupled device) observations by using supersampled discrete PSFs that are sampled two, three or more times more finely than the observational data. The precision and accuracy of the matphot algorithm is demonstrated by using the c -language mpd code to analyse simulated CCD stellar observations; measured performance is compared with a theoretical performance model. Detailed analysis of simulated Next Generation Space Telescope observations demonstrate that millipixel relative astrometry and mmag photometric precision is achievable with complicated space-based discrete PSFs. 相似文献
7.
We present an analysis of the results of photometric investigations of two distant comets, C/2002 VQ94 (LINEAR) and 29P/Schwassmann-Wachmann-1,
obtained with the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. The comets under
study demonstrate sufficient activity out of the zone of water ice sublimation (at heliocentric distances longer than 5 AU).
In the spectra of the investigated comets, we found the CO+ and N2+ emission. The presence of this emission may say that the comets were formed in the outer parts of the Solar System, in a
protoplanetary cloud at a temperature ≤25 K. We found that the photometric maximum of the ionosphere (in the CO+ filter) of the comet C/2002 VQ94 (LINEAR) is shifted relative to the photometric center of the dust coma by 1.4″ (7.44 ×
103 km) in the direction deflected by 63° from the direction to the Sun. Using special filters to process the images, we picked
out active structures (jets) in the dust coma of the 29P/Schwassmann-Wachmann-1 comet. 相似文献
8.
S. Dye A. N. Taylor E. M. Thommes K. Meisenheimer C. Wolf J. A. Peacock 《Monthly notices of the Royal Astronomical Society》2001,321(4):685-698
Gravitational lensing magnifies the observed flux of galaxies behind the lens. We use this effect to constrain the total mass in the cluster Abell 1689 by comparing the lensed luminosities of background galaxies with the luminosity function of an undistorted field. Under the assumption that these galaxies are a random sample of luminosity space, this method is not limited by clustering noise. We use photometric redshift information to estimate galaxy distance and intrinsic luminosity. Knowing the redshift distribution of the background population allows us to lift the mass/background degeneracy common to lensing analysis. In this paper we use nine filters observed over 12 h with the Calar Alto 3.5-m telescope to determine the redshifts of 1000 galaxies in the field of Abell 1689. Using a complete sample of 146 background galaxies we measure the cluster mass profile. We find that the total projected mass interior to 0.25 h −1 Mpc is M 2D (<0.25 h −1 Mpc)=(0.48±0.16)×1015 h −1 M⊙ , where our error budget includes uncertainties from the photometric redshift determination, the uncertainty in the offset calibration and finite sampling. This result is in good agreement with that found by number-count and shear-based methods and provides a new and independent method to determine cluster masses. 相似文献
9.
J. S. Morrill C. M. Korendyke G. E. Brueckner F. Giovane R. A. Howard M. Koomen D. Moses S. P. Plunkett A. Vourlidas E. Esfandiari N. Rich D. Wang A. F. Thernisien P. Lamy A. Llebaria D. Biesecker D. Michels Q. Gong M. Andrews 《Solar physics》2006,233(2):331-372
We present a detailed review of the calibration of the LASCO C3 coronagraph on the SOHO satellite. Most of the calibration
has been in place since early in the mission and has been utilized to varying degrees as required by specific analysis efforts.
However, using observational data from the nearly decade-long database of LASCO images, we have re-evaluated and improved
many aspects of the calibration. This includes the photometric calibration, vignetting function, geometric distortion, stray
light, and exposure and observation times. Using this comprehensive set of corrections we have generated and made available
a set of calibrated coronal images along with a set of periodic background images to ease the accessibility and use of the
LASCO database.
Deceased 相似文献
10.
R. Wachter J. Schou M. C. Rabello-Soares J. W. Miles T. L. Duvall Jr. R. I. Bush 《Solar physics》2012,275(1-2):261-284
We describe the imaging quality of the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) as measured during the ground calibration of the instrument. We describe the calibration techniques and report our results for the final configuration of HMI. We present the distortion, modulation transfer function, stray light, image shifts introduced by moving parts of the instrument, best focus, field curvature, and the relative alignment of the two cameras. We investigate the gain and linearity of the cameras, and present the measured flat field. 相似文献
11.
The Heliospheric Imagers (HI) on the Solar TErrestrial RElations Observatory (STEREO) observe the solar wind and disturbances therein as it propagates from close to the Sun to 1 AU and beyond. In this article we use stellar photometry over much of the mission to date to make a determination of the long-term evolution of the photometric response of the inner (HI-1) cameras. We find very slow degradation rates of the order of 0.1 % per year, similar to those found for HI-2 by Tappin, Eyles and Davies (Solar Phys. 290, 2143, 2015) and significantly slower than rates found for other comparable instruments. We also find that it is necessary to make a small (\({\approx}\,1~\%\)) revision to the photometric calibration parameters used to convert instrument units into physical units. Finally, we briefly discuss the effects of pointing instabilities on the measurement of stellar count rates. 相似文献
12.
Thomas E. Thorpe 《Icarus》1976,27(2):229-239
Although photometry of Mars is not listed as a major mission objective, the Viking Project has provided the Orbiter Imaging Team with cameras exhibiting significant improvement in photometric measurement as compared with past Mariners. Sample calibration data are described, together with predicted performance capabilities. 相似文献
13.
A. A. Hakobyan A. R. Petrosian G. A. Mamon B. McLean D. Kunth M. Turatto E. Cappelaro F. Mannucci R. J. Allen N. Panagia M. Della Valle 《Astrophysics》2009,52(1):40-53
The determination of the supernova (SN) rate is based not only on the number of detected events, but also on the properties
of the parent galaxy population. This is the first paper of a series aimed at obtaining new, refined, SN rates from a set
of five SN surveys, by making use of a joint analysis of near-infrared (NIR) data. We describe the properties of the 3838
galaxies that were monitored for SNe events, including newly determined morphologies and their DENIS, and POSS-II/UKST I,
2MASS and DENIS J and Ks and 2MASS H magnitudes. We have compared 2MASS, DENIS and POSS-II/UKST IJK magnitudes in order to find possible systematic
photometric shifts in the measurements. The DENIS and POSS-II/UKST I band magnitudes show large discrepancies (mean absolute
difference of 0.4 mag.), mostly due to different spectral responses of the two instruments, with an important contribution
(0.33 mag rms) from the large uncertainties in the photometric calibration of the POSS-II and UKST photographic plates. In
the other wavebands, the limiting near infrared magnitude, morphology, and inclination of the galaxies are the most influential
factors which affect the determination of photometry of the galaxies. Nevertheless, no significant systematic differences
have been found between any pair of NIR magnitude measurements, except for a few percent of galaxies showing large discrepancies.
This allows us to combine DENIS and 2MASS data for the J and Ks filters.
Published in Astrofizika, Vol. 52, No. 1, pp. 47–62 (Februay 2009). 相似文献
14.
Pavel Spurný Hans Betlem Jaap van't Leven Peter Jenniskens 《Meteoritics & planetary science》2000,35(2):243-249
Abstract— Precise atmospheric trajectories including dynamic and photometric data on thirteen of the brightest Leonid fireballs have been determined from the double‐station photographic observations of Leonid meteors during the ground‐based expedition to China in 1998 November. the expedition was organized as a collaboration between the dutch and chinese academy of sciences and was supported by the leonid multi‐instrument aircraft campaign (mac) program (jenniskens and butow, 1999). All data presented here were taken at Xinglong Observatory and at a remote station, Lin Ting Kou near Beijing, on the night of 1998 November 16/17. At the Xinglong station, photographic cameras were accompanied by an all‐sky television camera equipped with an image intensifier and 15 mm fish‐eye objective in order to obtain precise timings for all observed meteors up to magnitude +2. Whereas beginning heights of photographed meteors are all lower than 130 km, those observed by the all‐sky television system are at ~160 km, and for three brightest events, even > 180 km. Such high beginnings for meteors have never before been observed. We also obtained a precise dynamic single‐body solution for the Leonid meteor 98003, including the ablation coefficient, which is an important material and structural quantity (0.16 s2 km?2). From this and from known photometry, we derived a density of this meteoroid of 0.7 g/cm3. Also, all PE coefficients indicate that these Leonid meteors belonged to the fireball group IIIB, which is typical for the most fragile and weak interplanetary bodies. From a photometric study of the meteor lightcurves, we found two typical shapes of light curves for these Leonid meteors. 相似文献
15.
G. Krämer H. J. Einighammer G. Elwert H. Bräuninger H. H. Fink J. Trümper 《Solar physics》1978,57(2):345-367
Soft X-ray photographs of the Sun taken at O vii 21.6 Å and in a spectral band ranging from 13.2 to 22.1 Å have been analysed in order to establish spatially resolved maps of temperature and emission measure for several active regions in the corona. The photographs were taken on 11 March, 1971, and on 2 March, 1972, with Fresnel zone plate cameras which were flown on ESRO and NRL sounding rockets.In Part I of this paper we first deal with those aspects of the instrumentation which are important for setting up a suitable image analysis procedure. We discuss the characteristics of the wavelength dependent image formation by zone plates combined with absorption filters. Results of the calibration of the X-ray film are given. Then we describe a specific iterative data reduction procedure and finally present the resulting maps of temperature and emission measure for a selected active region. In Part II corresponding results for further active regions will be given and discussed. 相似文献
16.
《New Astronomy》2017
We present a new set of CCD photometric observations for the short period eclipsing binary 1SWASP J1743 (= V1067 Her). We have determined the available times of light minima and two new linear and quadratic ephemerides have been obtained. The photometric solutions for the system have been performed using Wilson and Devinney Code. The 3D and fill out configuration revealed that V1067 Her is an over contact W UMa binary with relatively low fill-out factor of about 16%.We investigated the period variation for the system. It showed a strong evidence of period changes by using the (O-C) residual diagram method and we have concluded long-term orbital period decrease rate dP/dt= −3.0 × 10−7 d/yr, corresponding to a time scale 8.6 × 105 yr. Such period decrease in the A-type W UMa systems is usually interpreted to be due to mass transfer from the more to the less massive component. 相似文献
17.
Bao-An Yao Chun-Sheng Zhang Qing LinShanghai Astronomical Observatory Chinese Academy of Sciences Shanghai Purple Mountain Observatory Chinese Academy of Sciences Nanjing 《中国天文和天体物理学报》2004,4(4):397-410
A performance study of several CCD cameras of the Chinese Joint Laboratory of Optical Astronomy (CJLOA) is presented. The main results are: 1) We propose a modified classical method to analyse the linearity of CCD cameras. This method is more sensitive and accurate as well as more intuitive, especially in measuring around the 0.1%-0.2% range of nonlinearity. 2) To illustrate the advantage of the method, the linearity performance of the CCD cameras at CJLOA has been measured and analysed. 3) For the CCD systems tested, there is no unique formula to represent the correlation over the entire CCD frame between the deviation from linearity and the pixel value, i.e., different pixel has different correction even though their pixel values are the same. 4) For the BFOSC (BAO Faint Object Spectrograph Camera) Loral CCD camera and the Tek CCD camera at the 1.56-m reflector, blooming (bleeding) happens long before saturation, and we suspect whether it could have resulted from the charge transfer efficiency (CTE) n 相似文献
18.
J.W. Keen D_f. Buscher P.J. Warner 《Monthly notices of the Royal Astronomical Society》2001,326(4):1381-1386
We use a numerical simulation to investigate the effectiveness of pinhole spatial filters for optical/IR interferometers and to compare them with single-mode optical fibre spatial filters and interferometers without spatial filters. We show that fringe visibility measurements in interferometers containing spatial filters are much less affected by changing seeing conditions than equivalent measurements without spatial filters. This reduces visibility calibration uncertainties, and hence can reduce the need for frequent observations of separate astronomical sources for calibration of visibility measurements. We also show that spatial filters can increase the signal-to-noise ratios (SNRs) of visibility measurements and that pinhole filters give SNRs within 17 per cent of the values obtained with single-mode fibres for aperture diameters up to 3 r 0 . Given the simplicity of the use of pinhole filters we suggest that it represents a competitive, if not optimal, technique for spatial filtering in many current and next generation interferometers. 相似文献
19.
Zoltan Balog Thomas Müller Markus Nielbock Bruno Altieri Ulrich Klaas Joris Blommaert Hendrik Linz Dieter Lutz Attila Moór Nicolas Billot Marc Sauvage Koryo Okumura 《Experimental Astronomy》2014,37(2):129-160
This paper provides an overview of the PACS photometer flux calibration concept, in particular for the principal observation mode, the scan map. The absolute flux calibration is tied to the photospheric models of five fiducial stellar standards (α Boo, α Cet, α Tau, β And, γ Dra). The data processing steps to arrive at a consistent and homogeneous calibration are outlined. In the current state the relative photometric accuracy is ~2 % in all bands. Starting from the present calibration status, the characterization and correction for instrumental effects affecting the relative calibration accuracy is described and an outlook for the final achievable calibration numbers is given. After including all the correction for the instrumental effects, the relative photometric calibration accuracy (repeatability) will be as good as 0.5 % in the blue and green band and 2 % in the red band. This excellent calibration starts to reveal possible inconsistencies between the models of the K-type and the M-type stellar calibrators. The absolute calibration accuracy is therefore mainly limited by the 5 % uncertainty of the celestial standard models in all three bands. The PACS bolometer response was extremely stable over the entire Herschel mission and a single, time-independent response calibration file is sufficient for the processing and calibration of the science observations. The dedicated measurements of the internal calibration sources were needed only to characterize secondary effects. No aging effects of the bolometer or the filters have been found. Also, we found no signs of filter leaks. The PACS photometric system is very well characterized with a constant energy spectrum νF ν = λF λ = const as a reference. Colour corrections for a wide range of sources SEDs are determined and tabulated. 相似文献
20.
A. V. Devyatkin D. L. Gorshanov V. V. Kouprianov I. A. Verestchagina 《Solar System Research》2010,44(1):68-80
We describe in detail the Apex I and Apex II software packages created for astrometric and photometric reductions of astronomical
observations with CCD cameras. The Apex I software package has been created for the semiautomatic reduction of astronomical
observations and has a convenient user interface. The Apex II software package allows for the completely automatic reduction
of astrometric and photometric observations to be performed. 相似文献