共查询到20条相似文献，搜索用时 31 毫秒
1.
M. R. Kundu 《Solar physics》1970,13(2):348-356
Some properties of solar active regions at 9, 3.5 and 1.2 mm wavelengths are discussed. The regions have excess brightness temperatures of up to 1000, 700 and 150 K at 9, 3.5 and 1.2 mm wavelengths. The background radiation at 3.5 mm is often seen to be absorbed in regions closely coincident with H dark filaments on the disk. Interpretation of this absorption as due to the large optical thickness of the overlying filamentary material leads to an estimate of electron density in the filaments. The 9 and 3.5 mm- regions show almost one-to-one correspondence with the Ca-plage regions as well as with the regions on magnetograms. The latter relationship suggests the possibility of measuring chromospheric magnetic fields from the measurement of polarization at millimeter wavelengths. 相似文献
2.
Maria A. Loukitcheva Sami K. Solanki Stephen White 《Astrophysics and Space Science》2008,313(1-3):197-200
The very nature of the solar chromosphere, its structuring and dynamics, remains far from being properly understood, in spite
of intensive research. Here we point out the potential of chromospheric observations at millimeter wavelengths to resolve
this long-standing problem. Computations carried out with a sophisticated dynamic model of the solar chromosphere due to Carlsson
and Stein demonstrate that millimeter emission is extremely sensitive to dynamic processes in the chromosphere and the appropriate
wavelengths to look for dynamic signatures are in the range 0.8–5.0 mm. The model also suggests that high resolution observations
at mm wavelengths, as will be provided by ALMA, will have the unique property of reacting to both the hot and the cool gas,
and thus will have the potential of distinguishing between rival models of the solar atmosphere. Thus, initial results obtained
from the observations of the quiet Sun at 3.5 mm with the BIMA array (resolution of 12″) reveal significant oscillations with
amplitudes of 50–150 K and frequencies of 1.5–8 mHz with a tendency toward short-period oscillations in internetwork and longer
periods in network regions. However higher spatial resolution, such as that provided by ALMA, is required for a clean separation
between the features within the solar atmosphere and for an adequate comparison with the output of the comprehensive dynamic
simulations. 相似文献
3.
Donald F. Neidig Jr. 《Solar physics》1973,33(1):63-67
The brightness temperature curve of the quiet Sun at millimeter wavelengths suggests a possible inversion in the mid-millimeter range. Interpreting this as a result of an actual inversion in the chromospheric temperature structure, and example of a model chromoshere is presented whose calculated temperature curve exhibits such an inversion. This model is then tested for radial brightness distribution at millimeter wavelengths. Comparing the calculated distributions at 3.2 mm and 6 mm with eclipse measurements made with parabolic cylinders at 3.2 mm and 8.6 mm shows qualitative agreement, allowing for instrumental smoothing. It is conluded that a chromospheric temperature inversion, either actual or effective, could account for the inversion suggested by millimeter data and also the complex brightness distributions measured during eclipses with parabolic cylinders. 相似文献
4.
Until recently, most of the information on particle acceleration processes in solar flares has been obtained from hard X-ray and cm-microwave observations. As a rule they provide information on electrons with energies below 300 keV. During recent years it became possible to measure the gamma-ray and millimeter radio emission with improved sensitivities. These spectral ranges carry information on much higher energy electrons. We studied the temporal and spectral behaviour of the radio burst emission at centimeter-millimeter wavelengths (8–50 GHz) by using the data from the patrol instruments of IAP (Bern University). We have analyzed more than 20 impulsive and long duration radio bursts (of 10 s to several 100 s duration).The main finding of the data analysis is the presence of spectral flattening throughout the bursts, which occurs always during the decay phase of flux peaks, at frequencies well above the spectral peak frequency and independently of burst duration. Furthermore, for some of the bursts, the flux maxima at higher frequencies are delayed. These findings can serve as evidence of the hardening of the electron spectrum at energies above some hundreds of keV during the decay phase of cm–mm flux peaks. As a most likely reason for such a hardening we consider Coulomb collisions of energetic electrons continuously injected and trapped in a flaring loop. 相似文献
5.
The onset of most flares at the meter wavelengths consists of type III bursts and their variants. These bursts usually occur during the explosive phase of flare events and in close association with similar impulsive bursts at other wavelengths. Pre-burst brightenings, corresponding to the preexplosive-phase heating observed at microwave and shorter wavelengths, have so far not been reported from observations with the Culgoora meterwave heliograph. At the same time, if substantial pre-heating occurred in the coronal source regions of meterwave radiation, then, on theoretical grounds, significant, but not spectacular, pre-burst brightenings would be expected at short meter wavelengths. A search for such pre-burst brightenings will become possible when the Culgoora heliograph begins to operate in a new mode which will allow all incoming data (rather than selected segments, as at present) to be kept for further analysis.On leave from the CSIRO-Division of Radiophysics, Sydney, Australia.Visiting Scientist, High Altitude Observatory, national Center for Atmospheric Research. The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
6.
Based on the results of calibrator observations at 13.5-mm and 8.2-mm wavelengths in 1985 and 2005, the dependence of the
effective area of the RT-22 CrAO RI antenna on ambient temperature and elevation was determined. The obtained results confirm
a high quality of the RT-22 antenna at millimeter wavelengths. A high accuracy of the reflector surface makes it possible
to observe at millimeter wavelengths right to 2 mm. At 8.2-mm wavelength, the effective area changes by no more than 5% when
the antenna is reinstalled from the zenith to 15° elevation angle. Large antennas, intended to operate at maximum frequencies,
should be built either taking into account the climatic conditions of the antenna sites or taking measures to provide thermal
stability of the antenna. 相似文献
7.
F. I. Shimabukuro 《Solar physics》1968,5(4):498-506
Radio bursts observed at a wavelength of 3.3 mm are always associated with flares. The enhancement in the millimeter emission is strongly correlated with some optical event that is associated with the flare. Emissions in the bursts observed thus far, with the possible exception of those associated with proton flares, have not been large increases over quiescent readings and can be explained by a thermal mechanism.This work was supported by the U.S. Air Force under Contract No. F04695-67-C-0158. 相似文献
8.
In this lecture, we review the properties of protoplanetary disks as derived from high angular resolution observations at millimeter wavelengths. We discuss how the combination of several different high angular resolution techniques allow us to probe different regions of the disk around young stellar objects and to derive the properties of the dust when combined with sophisticated disk models. The picture that emerges is that the dust in circumstellar disks surrounding pre-main sequence stars is in many cases significantly evolved compared to the dust in molecular clouds and the interstellar medium. It is however still difficult to derive a consistent picture and timeline for dust evolution in disks as the observations are still limited to small samples of objects.We also review the evidence for and properties of disks around high-mass young stellar objects and the implications on their formation mechanisms. The study of massive YSOs is complicated by their short lifetimes and larger average distances. In most cases high angular resolution data at millimeter wavelengths are the only method to probe the structure of disks in these objects.We provide a summary of the characteristics of available high angular resolution millimeter and submillimeter observatories. We also describe the characteristics of the ALMA observatory being constructed in the Chilean Andes. ALMA is going to be the world leading observatory at millimeter wavelengths in the coming decades, the project is now in its main construction phase with early science activities envisaged for 2010 and full science operations for 2012. 相似文献
9.
Eugene E. Epstein Bryan H. Andrew Frank H. Briggs Bruce M. Jakosky Frank D. Palluconi 《Icarus》1983,56(3):465-475
Measurements at 3.5 mm of the disk-average brightness temperature of Mars during the 1978 opposition can be represented by (The errors cited are from the internal scatter; the estimated absolute calibration uncertainty is 3%.) This longitudinal variation must be taken into account if Mars is to be used as a calibration source at millimeter wavelengths. The total range of the 3.5-mm variation is three to four times larger than both the 2.8-cm and 20-μm variations. This unexpected result can possibly be explained by subsurface scattering from rocks ?1.5-cm radius. 相似文献
10.
M. Simon 《Solar physics》1971,21(2):297-304
High resolution observations of the Sun at 3.3 mm, 3.5 mm, 1.35 cm, and 1.95 cm which were obtained by tracking narrow beam width antennas on the lunar limb as it occulted the Sun are described. The observations indicate that: (1) the region emitting at these wavelengths is very irregular with typical length scales smaller than one half minute of arc, (2) the number of roughness elements responsible for the irregular structure is small within an area of one half minute of arc square, and (3) the roughness elements observed at wavelengths greater than 1 cm extend to 109 cm beyond the optical limb. 相似文献
11.
I. M. Chertok V. V. Fomichev R. V. Gorgutsa J. Hildebrandt A. Krüger A. Magun V. V. Zaitsev 《Solar physics》1995,160(1):181-198
An analysis of solar radio burst spectra in the range 3–80 GHz is carried out using measurements of the observatories at Bern and Nobeyama supplemented by data from worldwide network stations. Special interest was focused on strong events at frequencies above 30 GHz. It is found that there exists an extended group of events with a flattening of the spectra at millimeter wavelengths. In particular, two types of flattening are observed: (i) a high-frequency flattening either following a monotonic spectral flux increase at cm-waves or forming a flat broad-band spectrum at mm-wavelengths ; (ii) a millimetric flattening as a decrease of the slope (i.e., a hardening) of the descending branch of the spectrum having a peak in the microwave range. Besides this, in complicated bursts a strong temporal evolution of millimeter spectra may occur resulting in either type of the flattening. Some factors capable of producing the millimeter flattening are considered: (1) superposition of multiple source regions of gyrosynchrotron radiation, (2) gyromagnetic radiation from a two-component energy spectrum of the accelerated electrons at high energies, or by a temporal hardening of the electron spectrum during extended flares, and (3) optically thin bremsstrahlung of evaporated plasma.Presented at the CESRA Workshop on Coronal Magnetic Energy Release at Caputh near Potsdam in May 1994. 相似文献
12.
B.L. Ulich 《Icarus》1974,21(3):254-261
Absolute measurements of the brightness temperatures of the Sun, new Moon, Venus, Mars, Jupiter, Saturn, and Uranus, and of the flux density of DR21 at 2.1-mm wavelength are reported. Relative measurements at 3.5-mm wavelength are also presented which resolve the absolute calibration discrepancy between The University of Texas 16-ft radio telescope and the Aerospace Corporation 15-ft antenna. The use of the bright planets and DR21 as absolute calibration sources at millimeter wavelengths is discussed in the light of recent observations. 相似文献
13.
Lei Zhu Yue-Fang Wu Yue Wei Department of Astronomy Peking University Beijing 《中国天文和天体物理学报》2006,6(1)
We report on a study of the molecular cloud S64 with observations at millimeter wavelengths of multiple molecular lines of CO isotopes.A weak outflow is found,and its physical parameters are estimated.The departure of the core of S64 from the S64 HII region indicates that there are still other star formation activities in that region. 相似文献
14.
E. E. Reber 《Solar physics》1971,16(1):75-86
Absolute brightness temperatures and brightness temperature ratios of a quiet region near the center of the solar disk and the central region of the new moon were measured simultaneously at the 6 mm wavelength. The measured quiet sun/new moon brightness temperature ratios and reported central brightness temperatures of the new moon confirm the measured brightness temperature of the quiet sun at the 6 mm wavelength.Reported central brightness temperatures of the new moon are tabulated and graphed as a function of frequency and wavelength. The equation of a linear regression line for the reported measurements is given for estimating the brightness temperature of the new moon at any millimeter wavelength. Estimated brightness temperatures of the new moon and measured quiet sun/new moon ratios are used to estimate solar brightness temperatures at several millimeter wavelengths. The solar brightness temperatures, the regression line, and the Van de Hulst theoretical model are presented graphically as a function of frequency and wavelength. The regression line equation is given for estimating solar brightness temperatures at any wavelength in the 6 to 1 mm wavelength interval and is solved for the wavelength of the measured ratios.Reported solar brightness temperatures in the millimeter wavelength region are tabulated. The measured temperatures in the 6 to 1 mm wavelength interval and a linear regression line are presented graphically as a function of frequency and wavelength. The regression line equation is given and solved for the solar brightness temperatures at the 6 mm wavelength.This work supported by the U.S. Air Force under Contract No. F04701-69-C-0066. 相似文献
15.
Various observations indicate that coronal holes generally appear as low brightness temperature regions (LTRs) in the centimeter and millimeter wavelength ranges. However, within their borders local enhancements of radiation, that is, high brightness temperature regions (HTRs), often occur. The theory behind the described behavior is not fully understood and therefore we analyze full-disk solar images obtained at a wavelength of 8 mm at Metsähovi Radio Observatory and compare them with data simultaneously taken in other wavelength ranges. The observational finding that the average brightness temperature of coronal holes is not much different from the quiet-Sun level (with localized deviations toward higher and lower intensities on the order of a few percent) is compared with theoretical models of the thermal bremsstrahlung radiation originating in the solar chromosphere, transition region, and corona. Special attention is devoted to the interpretation of the localized enhancements of radiation observed inside coronal holes at millimeter wavelengths. The main conclusion is that the most important contribution to the brightness temperature comes from an increased density in the transition region and low corona (i.e., at the heights where the temperature is below 106 K). This can explain both the LTRs and HTRs associated with coronal holes. 相似文献
16.
New measurements of the Sun, Moon, Mercury, Venus, Mars, Jupiter, and Saturn at 3.1 and 8.6 mm wavelengths are given. The temperatures reported for the planets at 3.1 mm wavelength are higher than previous measurements in this wavelength range and change the interpretation of some planetary spectra. For Mercury, it is found that the mean brightness temperature is independent of wavelength and that a temperature dependent thermal conductivity is not required to match the observations. In the case of Mars, the spectrum is shown to rise in the millimeter region as simple models predict. For Jupiter, the need to recalculate the spectrum with recent models is demonstrated. The flux density scale proposed by Dent (1972) has been revised according to a more accurate determination of the millimeter brightness temperature of Jupiter. 相似文献
17.
Rapid developments in the techniques of interferometry at millimeter wavelengths now permit the use of telescope arrays similar to the Very Large Array at microwave wavelengths. These new arrays represent improvements of orders of magnitude in the spatial resolution and sensitivity of millimeter observations of the Sun, and will allow us to map the solar chromosphere at high spatial resolution and to study solar radio burst sources at millimeter wavelengths with high spatial and temporal resolution. Here we discuss the emission mechanisms at millimeter wavelengths and the phenomena which we expect will be the focus of such studies. We show that the flare observations study the most energetic electrons produced in solar flares, and can be used to constrain models for electron acceleration. We discuss the advantages and disadvantages of millimeter interferometry, and in particular focus on the use of and techniques for arrays of small numbers of telescopes.Paper presented at the 4th CESRA Workshop in Ouranopolis (Greece) 1991. 相似文献
18.
Observations of the quiet sun at wavelengths from 3 Å to 75 cm show (with two exceptions: the Ovi line at 1032 Å and possibly the continuum at 1.2 mm) either no limb brightening or less than had been supposed. On the other hand, the brightness temperature is observed to increase with wavelength in the millimeter and centimeter range. If this increase is due to greater visibility of hot overlying material, that material ought to be evident at the limb at shorter wavelengths, resulting in limb brightening. The only possible explanation for the absence of limb brightening at almost all wavelengths is that the emitting surface is rough at all wavelengths, with a scale of roughness approximately equal to the scale height at each temperature. Contradictions with existing models, along with the additional observations required for an improved model are discussed. 相似文献
19.
对云南天文台“四波段太阳射电高时间分辨率同步观测系统”自１９８９年１２月—１９９４年１月期间观测到的１００个射电爆发和与其共生的２９个快速精细结构在日球和日面的经度分布做了统计,并做了初步的分析和讨论。 相似文献
20.
A. Sillanpää 《Astrophysics and Space Science》1995,226(1):47-49
One of the most amazing phenomena in astronomy, during the last twenty years, have been cosmic gamma-ray bursts (GRBs). The duration of these events vary from a few milliseconds to hundreds of seconds. We have never been able to identify the source of these bursts in other wavelengths. These objects have also never been seen in-rays after the initial bursts although there is some very weak statistical evidence that some of the bursts will repeat (Quashnock and Lamb 1993). The standard explanation for these bursts has been that they are somehow related to neutron stars in our own Galaxy. The latest results from the Burst and Transient Source Experiment aboard the Compton Gamma-Ray Observatory (Fishmanet al. 1994) show clearly that there is no excess concentration of these events (743 bursts) in the Galactic plane. After this, a more promising explanation is that the bursts are related to the Galactic halo or that the origin is extragalactic. In this letter we show that it is very probable that the origin of these events is the QSOs and that the radiation comes from the same synchrotron source as in the other observed wavelengths. 相似文献