共查询到20条相似文献，搜索用时 31 毫秒
1.
S. C. Joshi J. B. Srivastava T. D. Padalia C. D. Kandpal 《Earth, Moon, and Planets》1988,40(2):217-218
Positions of comet Wilson have been measured from the photographic plates taken at the Cas-segrain focus of the 104-cm reflector of Uttar Pradesh State Observatory, Naini Tal. 相似文献
2.
Manoranjan Rao 《Planetary and Space Science》1975,23(6):923-927
On certain occasions, whistler rate occurrences at Gulmarg (24°N geomagnetic) and Naini Tal (19°N geomagnetic) are found to exhibit some periodicity. Power spectrum analyses of the occurrence rates yield a dominant period of about 1 hr. It is suggested that this period is an indication of the duct-life times at low L-values. Dispersion analyses of the whistlers have qualitatively confirmed the existence of separate ducts during the period of observation. It is pointed out that power spectrum analyses may not be applicable to whistler data corresponding to high L-values. 相似文献
3.
Ram Sagar 《Astrophysics and Space Science》1985,113(1):171-180
Existing methods for age estimation of open clusters are discussed. Most of the observed open clusters (except extremely young and old) contain 50–90% unevolved Main-Sequence stars. Possible difficulties encountered in estimating the actual age of an unevolved Main-Sequence star are discussed. For a relatively reliable cluster age estimation only a small percentage of cluster members are suitable. The effect of unevolved Main-Sequence stars on open cluster age estimates using the modified method of isochromes is analyzed.On leave of absence from the Department of Physics, Kumaon University, Naini Tal, India. 相似文献
4.
We designed a prime focus CCD photometer, Argos, optimized for high speed time-series measurements of blue variables (Nather
& Mukadam 2004) for the 2.1 m telescope at McDonald Observatory. Lack of any intervening optics between the primary mirror
and the CCD makes the instrument highly efficient. We measure an improvement in sensitivity by a factor of nine over the 3-channel
PMT photometers used on the same telescope and for the same exposure time. The CCD frame transfer operation triggered by GPS
synchronized pulses serves as an electronic shutter for the photometer. This minimizes the dead time between exposures, but
more importantly, allows a precise control of the start and duration of the exposure. We expect the uncertainty in our timing
to be less than 100μs.
Hubble Fellow 相似文献
5.
Steady state level density of 20 levels of boron-like ions, Mg viii and Si x, have been computed as a function of electron density and temperature. We have accounted for collisional and spontaneous radiative processes. Photo-excitation between the two levels of the ground term has also been considered. Using the computed level density, line intensities have been obtained as a function of electron density and temperature. In case of Mg viii, line intensity ratio I(430.47)/I(436.62) is found to be electron density sensitive. Likewise other pairs of lines namely, I(75.03)/I(74.86), I(315.02)/I(430.47), and I(315.02)/I(335.23) are also found to be density sensitive. Similar density sensitive line intensity ratios have been found for Si x. Absolute line fluxes from these ions at earth distance have been computed and are found to be comparable with values obtained, using various satellite and rocket measurements.Paper presented at the 5th Astronomical Society of India Meeting, held at Uttar Pradesh State Observatory, Naini Tal, India, 5–9 November, 1979. 相似文献
6.
An investigation of the spatial extent of aurorae was undertaken from College, Alaska, by the ground based Lockheed two channel (5577 and 4278 Å) image intensifier TV system and with a multichannel boresighted tilting filter photometer. The measurements indicate that even on clear nights the extinction due to scattering in the 4278 Å is significant unless the measurements are taken at small zenith angles. To confirm the results and to avoid the low altitude scattering problem, measurements were made on a quite arc with the Lockheed 6 channel tilting filter zenith photometer during the NASA CV 990 expedition. These results show that in the cases observed there was no significant difference between the latitude profiles of O(5577) and N2+(4278) emissions. 相似文献
7.
对北京天文台新近改造成的三通道高速光度计的结构和性能进行介绍,并给出了在兴隆站85公分望远镜的一些实测结果. 相似文献
8.
本文介绍了北京天文台新研制的光电光度计。本光度计是带有微计算机星天交替式的。可通过计算机控制实现星天和滤光片自动转换。可以很方便地进行随机采集和连续采集,可以实时显示数据和处理观测结果。已经正规观测两年多,取得了一批观测成果,精度可达±0.003~m,能很好地归化到国际系统。 相似文献
9.
Peschke S. B. Grün E. Böhnhardt H. Campins H. Osip D. J. Hanner M. S. Heinrichsen I. Knacke R. F. Leinert Ch. Lemke D. Stickel M. Lisse C. M. Sykes M. Zarnecki J. 《Earth, Moon, and Planets》1997,78(1-3):299-304
Comet Hale-Bopp has been observed five times with ISOPHOT, the photometer on board the Infrared Space Observatory (ISO), four
times before its perihelion passage at heliocentric distances of 4.92, 4.58, 2.93 and 2.81 AU, and at 3.91 AU postperihelion.
Each time, multi-filter photometry covering the range between 3.6–175 μm with eight to ten filters was performed to sample
the spectral energy distribution of the comet. These measurements were used to determine dust temperatures for the cometary
coma. The evolution of the strength of the silicate feature can be followed in the data as well as the flux deficit at longer
wavelengths.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
11.
A collaborative programme searching for mmag pulsations in chemically peculiar stars in the northern hemisphere was initiated
in 1997 between Nainital, India, and Cape Town, South Africa. It was therefore named as theNainital-Cape Survey programme. The detection limits imposed by the observing conditions (including atmospheric noise and telescope size) at both
Manora Peak and Devasthal sites are described. The scintillation noise on the best photometric nights is≈ 0.1 to 0.2 mmag for these sites. Both places allow one to detect few mmag variation in bright stars(B ≤ 12 mag), and are therefore particularly well-suited for carrying out the proposed survey work. The main characteristics of
the three-channel photometer developed at ARIES for carrying out the observations are also presented. This excellent instrument
has been used extensively since 1999 at the f/13 Cassegrain focus of ARIES’ 104 cm telescope. In particular, it allowed the
survey to result in the discovery of δ Scuti like pulsations in four Am stars, in one rapidly oscillating Ap star, and in
a number of probable variables so far. The future prospects are then presented, which regard the acquisition of a high speed
time series CCD photometer, a project to build a 3-metre class telescope at Devasthal, and collaborative observations with
Indian and foreign astronomical sites. 相似文献
12.
N. I. Lebedev V. D. Kuznetsov Yu. D. Zhugzhda S. I. Boldyrev 《Solar System Research》2011,45(3):200-205
The helioseismological experiment onboard the CORONAS-PHOTON satellite is intended for the study of characteristics and the
internal structure of the Sun using the solar eigenmodes spectrum obtained by the measurement of fluctuations of the solar
radiation intensity. This experiment is the continuation of investigations of solar global oscillations started onboard artificial
satellites CORONAS-I and CORONAS-F. Measurements of fluctuations of the solar radiation intensity in seven optical ranges—from
the near ultraviolet to infrared spectral regions—are carried out by the solar photometer SOKOL (SOlnechnye KOLebaniya (Solar
Oscillations)) developed at IZMIRAN. Over an instrument operation period of more than 9 months, a large volume of the scientific
information (more than 500 MB) has been obtained. The primary processing of obtained data was performed, and spectra of fluctuations
of the solar radiation intensity were constructed. On the basis of part of the processed information obtained by the photometer
SOKOL, and data of the experiment DIFOS (Differential Oscillations of the Sun) onboard the artificial satellite CORONAS-F,
the dependence of the relative amplitude of oscillations on the wavelength of the observation was determined. 相似文献
13.
A few methods of estimating Fried's parameter (r
0) from specklegrams of solar features are described. Some of these methods were used to estimate r
0 for the speckle data obtained from Kodaikanal Observatory (KO), Uttar Pradesh State Observatory (UPSO) and Udaipur Solar Observatory (USO). The average value of r
0 was found to be 3 cm at USO and UPSO during our observations. At KO, values of r
0 ranging from 6 to 10 cm were estimated. 相似文献
14.
R. Poggiani 《Experimental Astronomy》2004,18(1-3):109-132
The domain of high speed optical astrophysics is still quite unexplored. The availability of 10 meter diameter telescopes
offers the unique possibility to investigate variability of faint objects at submillisecond time scales. In this paper I describe
the concepts of a photometer and a spectrometer for high speed astronomical observations. The instruments are based on a photon
counting detector developed for high energy physics, the Visible Light Photon Counter (VLPC). The detector has a quantum efficiency
in the visible as high as 88% and performs photon counting with sub microsecond time resolution. The photometer is built using
VLPC arrays. Adding a grating a VLPC array can be used in a time resolved spectrograph with medium resolution. This paper
develops, starting from experimental data, the concept of the two VLPC based instruments and their application to time resolved
photometry and spectroscopy of compact objects (pulsars, cataclysmic variables, low mass X-ray binary systems etc) and optical
counterparts of Gamma Ray Bursts. The high speed optical observations are the ideal complement to X/γ rays and gravitational
wave studies. The application of the instruments to the optical photometry of pulsars, the spectrophotometry of the prompt
optical flash from Gamma Ray Bursts and the study of binary systems are discussed in detail: in the last two applications
the instruments offer better opportunities than existing instruments. 相似文献
15.
L. Pizzo P. Andreani G. Dall'Oglio R. Lemke N. Whyborn A. Otàrola 《Experimental Astronomy》1995,6(3):249-256
A double channel (1.2 and 2 mm) photometer has been installed at the focus of the 15m SEST antenna in Chile to perform measurements of the Sunyaev-Zeldovich effect towards X-ray ROSAT clusters. This paper describes the instrument and the characteristics of the system: its sensitivity, field of view, noise and the performed calibrations. 相似文献
16.
The note shows how to estimate accurately the optimum measuring time in the measurement of a periodical optical source by
means of a synchronous photometer affected by phase-tracking error.
The procedure used can be easily generalized to sources or signal patterns not considered here.
The optimum number of scans to be averaged results to be typicallyN
opt≈0.5r/ɛ for an optical source of Lorentzian signal pattern, wherer is the duty cycle of the pulsed component and ɛ the relative truncation error of the local sync to the source period.
Work supported by Consiglio Nazionale delle Ricerche, Gruppo Nazionale di Astronomia, Settore Tecnologie Astronomiche. Trieste
Observatory — Instruments and Data Processing Group (4/76). 相似文献
17.
This paper describes a real-time spectrum analyser with on-line definition of the confidence levels built at Trieste Observatory
for a research program on periodical components of unknown period in optical sources. The system is realized by a photon counting
photometer on-line to a computer that elaborates in real-time the data from the photometer and displays the spectrum of the
source measured. The spectrum is normalized to unity mean value and the display is calibrated by the confidence levels relative
to the
distribution of the spectrum displayed. Some experimental data show the performance of the machine that operates in real-time
at full efficiency up to 160 Hz.
Work supported by Consiglio Nazionale delle Ricerche, Gruppo Nazionale di Astronomia, Settore Tecnologie Astronomiche. Trieste
Observatory — Instruments and Data Processing Group (1/76). 相似文献
18.
High speed photometry during the lunar occultation of a stellar system provides an effective means of achieving high angular
resolution in one dimension at the sub arc second level which is well suited for resolving close binary projected separations
in the range of 10–100 milliarc seconds. An optical fast photometer designed for such a purpose is described and some results
from the initial observations taken with the system including the resolution of a projected separation of 55 milli arcsecond
in one binary system are detailed. 相似文献
19.
M. G. Revnivtsev R. A. Burenin A. Yu. Tkachenko I. M. Khamitov T. Ak A. Merloni M. N. Pavlinsky R. A. Sunyaev 《Astronomy Letters》2012,38(4):238-248
We present the results of our studies of the aperiodic optical flux variability for SS Cyg, an accreting binary systemwith
a white dwarf. The main set of observational data presented here was obtained with the ANDOR/iXon DU-888 photometer mounted
on the RTT-150 telescope, which allowed a record (for CCD photometers) time resolution up to 8 ms to be achieved. The power
spectra of the source’s flux variability have revealed that the aperiodic variability contains information about the inner
boundary of the optically thick flow in the binary system. We show that the inner boundary of the optically thick accretion
disk comes close to the white dwarf surface at the maximum of the source’s bolometric light curve, i.e., at the peak of the
instantaneous accretion rate onto the white dwarf, while the optically thick accretion disk is truncated at distances 8.5
× 109 cm ∼10R
WD in the low state. We suggest that the location of the inner boundary of the accretion disk in the binary can be traced by
studying the parameters of the power spectra for accreting white dwarfs. In particular, this allows the mass of the accreting
object to be estimated. 相似文献
20.
A. Kontogeorgos P. Tsitsipis C. Caroubalos X. Moussas P. Preka-Papadema A. Hilaris V. Petoussis C. Bouratzis J.-L. Bougeret C. E. Alissandrakis G. Dumas 《Experimental Astronomy》2006,21(1):41-55
We present the improved solar radio spectrograph of the University of Athens operating at the Thermopylae Satellite Telecommunication
Station. Observations now cover the frequency range from 20 to 650 MHz. The spectrograph has a 7-meter moving parabola fed
by a log-periodic antenna for 100–650 MHz and a stationary inverted V fat dipole antenna for the 20–100 MHz range. Two receivers
are operating in parallel, one swept frequency for the whole range (10 spectrums/sec, 630 channels/spectrum) and one acousto-optical
receiver for the range 270 to 450 MHz (100 spectrums/sec, 128 channels/spectrum). The data acquisition system consists of
two PCs (equipped with 12 bit, 225 ksamples/sec ADC, one for each receiver). Sensitivity is about 3 SFU and 30 SFU in the
20–100 MHz and 100–650 MHz range respectively. The daily operation is fully automated: receiving universal time from a GPS,
pointing the antenna to the sun, system calibration, starting and stopping the observations at preset times, data acquisition,
and archiving on DVD. We can also control the whole system through modem or Internet. The instrument can be used either by
itself or in conjunction with other instruments to study the onset and evolution of solar radio bursts and associated interplanetary
phenomena. 相似文献