共查询到20条相似文献，搜索用时 15 毫秒
1.
In this paper we estimated the temperatures and brightnesses of the Monoceros radio loop at 1420, 820 and 408 MHz. The linear spectrum is estimated for mean temperatures versus frequency between 1420, 820 and 408 MHz. The spectral index of Monoceros loop is also obtained. The brightness temperatures and surface brightnesses of the loop are computed using data taken from radio‐continuum surveys at the three frequencies. The spectral index of the loop is also obtained from T‐T plots between 1420–820, 1420–408, and 820–408 MHz. The obtained results confirm non‐thermal origin of the Monoceros radio loop (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
2.
J. Meaburn 《Astrophysics and Space Science》1968,1(2):230-238
The Rosette Nebula was photographed through filters isolating the H,OII andOIII nebular emission lines. Isophotes were constructed at these wavelengths. Measurements of the radial velocity differences across the Rosette were obtained from an interferogram. These were compared to some conflicting measurements made by previous authors. Some small regions in the Rosette and Barnard's Arc were shown to be emitting lines wider than the bulk of the matter. 相似文献
3.
The profiles obtained from radial-velocity observations of the Rosette Nebula with a Fabry-Pérot (F.P.) interferometer (Meaburn andSmith, 1968) had to be corrected, for the spreading action of the instrumental function, and for motion of the observer. Two current methods are compared and a method devised for fitting a sum of Gaussians to a noisy output profile. 相似文献
4.
The Monoceros ring, a circular optical nebulosity 3°.5 in diameter and centred at R.A.=6h37m, Dec.=6°30 (l
ii
=205°.5,b
ii
=0°.2) is in good structural agreement with radio observations. A neutral hydrogen shell is also accurately projected on the ring. These observations are consistent with the Monoceros ring being a supernova remnant 90–100 pc in diameter expanding at about 45 km s–1 and having an age of the order of a million years. Bright Hii regions containing early-type stars (e.g., galactic cluster NGC 2244 in the Rosette nebula) and extremely young stars of the OB association Mon OB2 lie at the edges of the ring. The positional and temporal coincidence of the Mon OB2 association with a supernova remnant suggests that probably the star formation in this region is induced or speeded up by the passage of a supernova shock wave through the clumpy interstellar medium. 相似文献
5.
Malcolm G. Smith 《Astrophysics and Space Science》1968,1(1):68-73
The results of observations of the Rosette Nebula using the equipment described byMeaburn andSmith (1968) and the reduction procedures outlined inSmith andWalker (1968) are reported. The results and conclusions differ markedly from an earlier report (Flynn, 1965), of detailed radial-velocity observations of this nebula. The peak positions of the H-line profiles have now been shown not to vary greatly. The mean of 37 measurements at different points gives, for the heliocentric velocity of the Rosette nebula, +35±5 km sec–1. The widths of the lines are consistent with a model of randomly directed streaming motions of order 15 to 25 km sec–1. 相似文献
6.
We present optical photometric and spectroscopic studies of ROSAT X-ray stellar sources in the Rosette Nebula star-forming region. The brightest X-ray sources are either massive stars or active T Tauri stars associated with the open cluster NGC 2244, or are foreground stars. Some of the spectra of the young stars newly identified in the region are presented. 相似文献
7.
A. D. Fokker 《Solar physics》1967,2(3):316-326
The concept of homology, introduced by Ellison, Mc
Kenna, and Rceid (1960) for optical flares, can be extended to flare-associated radio events. Successive flares within the same centre of activity sometimes produce radio events that are remarkably similar. The similarity amounts to the fact that they extend over about the same range(s) in frequency, producing at each frequency responses of comparable intensity and duration. On some occasions the intensity curves at individual frequencies show even detailed resemblance. The occurrence of homologous radio events is commonly restricted to periods of less than 48 hours.Without being homologous, radio events that occur in the same centre of activity may present a common characteristic that is typical for that centre. Two such characteristics are (1) the production of radio responses at centimetric, decimetric and metric frequencies, and (2) the impulsiveness of microwave outbursts. The distribution of time intervals during which such bursts occur is compared with the same distribution for homologous events (Figure 3). 相似文献
8.
In the preceding paper by Vengeret al. (1984) the results of observations of neutral gas in the vicinity of some galacticHii regions were considered; and it was demonstrated that 17 of the regions observed are surrounded by expandingHi envelopes. This paper describes a model of interaction between theHii regions and the surrounding interstellar medium constructed on the basis of the said results. It is assumed that the main dynamic factor in the envelope formation mechanism is the total stellar wind from the stars which ionze theHii regions. The employment of the observations of the line at =21 cm, of the radio continuum and IR dust continuum made it possible to determine the differential mass spectra of the stars exciting theHii zones and calculate some characteristics of the stellar population. The mass spectrum index of the objects considered turned out to be much higher than that for the mass spectra of background stars and scattered clusters of stars. 相似文献
9.
N. N. Kalinichenko 《Astrophysics and Space Science》2009,319(2-4):131-138
Interplanetary scintillation observations of eleven supernova remnants and the pulsar J1939+2134, around which the existence of a supernova remnant remains obscure, were carried out with the largest in the world decameter radio telescope UTR-2 at 20, 25 and 30 MHz to determine if any of them contain compact radio sources with the angular size θ<5″. The sample included the young Galactic remnants and the other powerful SNRs. The interplanetary scintillations of the compact radio source in the Crab Nebula associated with the well-known pulsar J0534+2200 and the pulsar J1939+2134 were observed. Apart from the Crab Nebula, we have not detected a compact radio source in supernova remnants with the angular size θ<5″ and the flux density more than 10 Jy. The observations do not confirm the existence of the low frequency compact source in Cassiopeia A that has remained controversial. 相似文献
10.
V. L. Afanasiev S. N. Dodonov A. V. Moiseev V. Chavushyan R. Mujica Y. Juarez A. G. Gorshkov V. K. Konnikova M. G. Mingaliev 《Astronomy Letters》2003,29(9):579-586
We present the classification of optical identifications and radio spectra of six radio sources from a complete (in flux density) sample in the declination range 10° to 12°30′ (J2000.0). The observations were carried out with the 6-m Special Astrophysical Observatory telescope (Russia) in the wavelength range 3600–10000 Å, the 2.1-m GHAO telescope (Mexico) in the range 4200–9000 Å, and the RATAN-600 radio telescope in the frequency range 0.97–21.7 GHz. Three of the six objects under study are classified as quasars, one is a BL Lac object, one is an absorption-line radio galaxy, and one is an emission-line radio galaxy. Five objects have flat radio spectra, and one object has a power-law radio spectrum. All of the radio sources identified as quasars or BL Lac objects show variable radio flux densities. The spectra of three objects were separated into extended and compact components. 相似文献
11.
The Monoceros nebula is seen in the optical and in radio as a 3°.5 degree diameter ring. It is believed to be an old supernova remnant. Here is reported the detection of X-rays from the Monoceros nebula, confirming its supernova remnant nature.Einstein imaging proportional counter observations of 0.2 to 5 keV X-rays were analyzed to produce a surface brightness map. Preliminary modeling of the Monoceros supernova remnant yields an age of 50 000 years. A large age is expected for such a large remnant. However, the remnant is found to still be in the adiabatic blast wave stage of evolution.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984. 相似文献
12.
We have attempted to detect linear polarization in carbon and hydrogen 76 radio recombination lines from the Hii region NGC 2024. The upper limits set by these measurements are briefly discussed.On leave of absence from Cornell University, Ithaca, N.Y., U.S.A. 相似文献
13.
D. Onić 《Astrophysics and Space Science》2013,346(1):3-13
A considerable fraction of Galactic supernova remnants (SNRs) characterize flat spectral indices (α<0.5). There are several explanations of the flat radio spectra of SNRs in the present literature. The most of models involve a significant contribution of the second-order Fermi mechanism but some of them also discuss high compressions (>4), contribution of secondary electrons left over from the decay of charged pions, as well as the possibility of thermal contamination. In the case of expansion in high density environment, intrinsic thermal bremsstrahlung could theoretically shape the radio spectrum of an SNR and also account for observable curved—“concave up” radio spectra of some Galactic SNRs. This model could also shed a light on the question of flat spectral indices determined in some Galactic SNRs. On the other hand, present knowledge of the radio continuum spectra (integrated flux densities at different frequencies) of SNRs prevent definite conclusions about the significance of proposed models so the question on flat spectral indices still remains open. New observations, especially at high radio continuum frequencies, are expected to solve these questions in the near future. Finally, as there is a significant connection between the majority of Galactic SNRs with flat integrated radio spectrum and their detection in γ-rays as well as detection of radiative recombination continua in their X-ray spectra, the analysis of high energy properties of these SNRs is very important. 相似文献
14.
Based on the half-century-long history of radio observations of the Crab Nebula, we investigate the evolution of its radio luminosity. We found a secular decrease in the radio luminosity; it has decreased by 9% since the discovery of the radio source in 1948. Apart from the secular decrease in the luminosity of the Crab Nebula, we identified two time intervals, 1981–1987 and 1992–1998, when radio bursts with energy release ～1041 erg took place. In these years, the spectral indices of the instantaneous spectra decreased significantly due to the increase in the flux densities at short (centimeter and millimeter) wavelengths. These events were preceded by sudden increases in the pulsar’s rotation rates, the largest of which, with an amplitude of ΔΩ/Ω = 3 × 10?8, occurred in 1975 and 1989. We show that the magnetospheric instability mechanism that accompanies strong glitches can provide the energetics of the excess luminosity of the Nebula through the ejection of relativistic electrons with a total energy higher than 6 × 1042 erg from the pulsar’s magnetosphere. 相似文献
15.
Jin-Zeng LiNational Astronomical Observatories Chinese Academy of Sciences Beijing 《中国天文和天体物理学报》2003,3(6):495-498
We report on the discovery of an optical jet-Rosette HH2-in the Rosette Nebula. The jet system bears unique features for residing at the center of a giant HII region, and its energy source is visible with apparently very low extinction along the line of sight. Unlike most other Herbig-Haro jets, this jet indicates a high-excitation origin, and its extended portion shows a seemingly intact structure, instead of normally a shocked working surface, which is attributed to photoablation. 相似文献
16.
David McConnell 《Solar physics》1983,84(1-2):361-369
Some interpretations of solar S burst spectra are presented. It is shown that the spectra provide evidence for small (～ 500 km) radio sources in the corona which radiate at the fundamental plasma frequency. The possibility of S burst fringes corresponding to coronal MHD waves of wavelength λ ～- 103 km is discussed. 相似文献
17.
C. Goudis 《Astrophysics and Space Science》1975,38(1):13-18
The radio spectra of particular radio sources (mainly Hii regions) are plotted on the same graph for comparison. Various physical parameters of these objects are obtained from the radio data through a model. Predictions about the number and the nature of the exciting stars of six Hii regions are made. A comparison with the so far identified exciting stars is also presented. 相似文献
18.
The analysis of discrete radio sources spectra in the range 10–5000 MHz reveals that deviations from a power law in the low-frequency region may be due to distortion of differential energy spectra of relativistic electrons at low energies. An empirical expression for an energy-spectrum law was found to be in a good agreement with most of the radio spectra measured. The main physical parameters of 92 sources are evaluated. It is concluded that a low-energy electron excess exists with respect to the lawE
– in most of the discrete sources which radiate non-linear low-frequency spectra.The forms of radio and energy spectra are further considered in a logarithmic scale. 相似文献
19.
Peak flux spectra of solar radio bursts in a wide frequency band have been statistically determined for different morphological types of bursts, for various ranges of magnetic field of the burst-associated sunspots and also for the bursts occurring in the central and limb region of the solar disk. Important results obtained are: (i) The generalised spectra have two peaks, one near to meter-wave and the other in the centimeter-wave region, the former peak being more pronounced than the latter; (ii) identical spectral shape is observed for the great and impulsive types and also for GRF and PBI types of bursts; (iii) the radio emission intensity is relatively higher in the central part than that in the limb part of the solar disk for frequencies 1–10 GHz, while the reverse is true for frequencies 0.245–1 GHz and 10–35 GHz; (iv) the optical depth of the absorbing layer above the source of a burst is found to be the same for meter to centimeter-wavelength bursts, implying that the radio sources in this wide band have uniform characteristics with respect to optical thickness; (v) in case of simultaneous emission in the dekameter to X-ray band, most of the decimetric bursts are seen to be very prompt and coincident with the associated flare's starting time. The interpretations of the obtained spectra give an insight into the possible generation mechanisms, pointing to the location of the source region in the solar atmosphere. 相似文献
20.
We have compared the radio continuum emission of three samples of bright (B
t
o
<13) galaxies with LINER,HII region-like, and Seyfert nuclei. Basically, we have found that the objects of the first class are the weakest total and central radio emitters (for total and central unit light, respectively), whereas the Seyfert galaxies contain the most powerful central radio sources. 相似文献