共查询到20条相似文献,搜索用时 15 毫秒
1.
The behaviour of pulsars at low radio-frequencies (below ≈ 50 MHz) remains poorly understood mainly due to very limited observational
data on pulsars at these frequencies. We report here our measurements of pulse profiles at 34.5 MHz of 8 pulsars using the
Gauribidanur Radio Telescope. None of the 8 pulsars show any significant interpulse emission at this frequency which conflicts
with an earlier claim from 25 MHz observations. With the exception of one pulsar (PSR 0943 + 10) all the observed pulsars
show turnovers at frequencies above 35 MHz in their spectra. We also report our attempts to study the short and long term
variations in the pulsar signals at this low frequency. 相似文献
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P. G. Tsybulev N. A. Nizhelskii M. V. Dugin A. N. Borisov D. V. Kratov R. Yu. Udovitskii 《Astrophysical Bulletin》2018,73(4):494-500
We describe the development of the tools and methods of 4.7-GHz band observations on RATAN-600 radio telescope and present a new design solution—a radiometric unit, and the development of an uncooled tuned receiver based on this unit and meant for operating in the “total power” radiometer mode.We discuss the design of the radio unit and the specificities of the radiometer design.We demonstrate the possibility of conducting observations in the total power radiometer mode at the theoretical sensitivity on time scales up to 10 seconds. The sensitivity of such a radiometer remains higher than that of a Dicke radiometer on time scales up to 100 seconds. 相似文献
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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
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The MRT survey will be by far one of the most extensive survey at low frequencies. This survey will provide a moderately deep
radio catalog reaching a source density of about 2 × 104 sr-1over the southern sky with an angular resolution of 4' × 4' and a limiting flux density of 70 mJy (1 σ) at 151 MHz. The availability
of zero spacing and short baselines in the MRT array will make it sensitive to the background temperature and to large scale
features in the sky. In addition to this feature, the low frequency operation makes a study of continuum emission from large
radio sources by MRT to have several interesting and important implications in the study of radio galaxies. This paper discusses
the parameter space of radio galaxies which can be explored using the MRT. Images of a few extended radio galaxies are also
presented.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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V. N. Melnik A. I. Brazhenko A. A. Konovalenko H. O. Rucker A. V. Frantsuzenko V. V. Dorovskyy M. Panchenko A. A. Stanislavskyy 《Solar physics》2014,289(1):263-278
An unusual solar burst was observed simultaneously by two decameter radio telescopes UTR-2 (Kharkov, Ukraine) and URAN-2 (Poltava, Ukraine) on 3 June 2011 in the frequency range of 16?–?28 MHz. The observed radio burst had some unusual properties, which are not typical for the other types of solar radio bursts. Its frequency drift rate was positive (about 500 kHz?s?1) at frequencies higher than 22 MHz and negative (100 kHz?s?1) at lower frequencies. The full duration of this event varied from 50 s up to 80 s, depending on the frequency. The maximum radio flux of the unusual burst reached ≈103 s.f.u. and its polarization did not exceed 10 %. This burst had a fine frequency-time structure of unusual appearance. It consisted of stripes with the frequency bandwidth 300?–?400 kHz. We consider that several accompanied radio and optical events observed by SOHO and STEREO spacecraft were possibly associated with the reported radio burst. A model that may interpret the observed unusual solar radio burst is proposed. 相似文献
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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
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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
8.
New observations show that dark elephant trunks in the Rosette nebula are often built up by thin filaments. In several of
the trunks the filaments seem to form a twisted pattern. This pattern is hard to reconcile with current theory. We propose
a new model for the formation of twisted elephant trunks in which electromagnetic forces play an important role. The model
considers the behaviour of a twisted magnetic filament in a molecular cloud, where a cluster of hot stars has been recently
born. As a result of stellar winds, and radiation pressure, electromagnetic forces, and inertia forces part of the filament
can develop into a double helix pointing towards the stars. The double helix represents the twisted elephant trunk. A simple
analogy experiment visualizes and supports the trunk model.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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K. R. Subramanian R. Ramesh M. S. Sundara Rajan Ch. V. Sastry 《Astrophysics and Space Science》1996,243(1):259-262
Observations of the Sun at two frequencies (51 and 77 MHz) using the East-West arm of the Gauribidanur Radio heliograph are presented. 相似文献
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V. V. Krymkin 《Astrophysics and Space Science》1978,54(1):187-197
The results of observations of the Rosette emission nebula NGC 2237 with the radio telescope UTR-2 at frequencies 12.6, 14.7, 16.7, 20.0 and 25.0 MHz are given in the shape of contours of constant brightness temperature. The half-power beamwidth of the telescope to zenith at 25.0 MHz was 28×38. Density weighted mean values for the non-thermal radio emissivity between the Sun and the source (7.9×10–41 W m–3 Hz–1 ster–1 at 25.0 MHz) and the ratio of the intensity of emissivity generated before the area and the intensity of galactic radio emissivity appearing beyond the area equal to 1.3 have been obtained. The electron temperatureT
e=3600 K, the optical depth (about ten at 25 MHz), the measure of emission (ME=3500 cm–6 pc), the electron densityN
e=8 cm–3 and the nebular mass 16.6×10+3
M
have been determined. A comparison with other observation results has been made. 相似文献
14.
Jin-Zeng Li 《中国天文和天体物理学报》2009,9(5)
Photoionized jets immersed in HII regions display special properties, which made them a distinctive category of Herbig-Haro (HH) flows. Detailed studies of such jet systems became one of the key issues in our understanding of jet production and evolution. HH 890, initially called the Rosette HH2 jet, is the second photoionized jet discovered in the spectacular HII region of the Rosette Nebula. Contrary to conventional impres-sions of a jet, its discrete components are found to be unexpectedly broad and spatially detached from the proposed energy source. The jet displays additional unusual features which point to the disputable nature of the system. Here, we investigate the kinematics of the jet through high-quality echelle spectrograms. It is distinctively resolved into a fast component with a mean approaching velocity of-39 km s-1 with respect to the systemic rest frame and a slow component with radial velocity centered at -9 km s-1. The slow component indicates an apparently larger dispersion in radial velocity in various emission lines and is likely dissolving at roughly the speed of sound, which favors a photoevap-orated origin. The [SII] doublet ratios indicate an electron density of~1.1×103 cm-3in the collimated jet and ~9×102cm-3 in the HII region. This, along with the diffuse appearance of the extensive part of the jet, leads to a dissipation of the jet in the fully ionized medium of Rosette. In addition, time series of photometric observations provide evidence for remarkable light variations of the energy source. Its amplitudes of variation amount to1 mag in both R and I, which is commensurate with the young evolutionary status of the source as indicated by a red, late type optical spectrum. 相似文献
15.
Lei Qian Zhichen Pan Hongfei Liu Hengqian Gan Jinglong Yu Lei Zhao Jiguang Lu Cun Sun Jingye Yan Peng Jiang 《天文和天体物理学研究(英文版)》2023,(1):3-5
We present the estimation of solar observation with the Five-hundred-meter Aperture Spherical radio Telescope(FAST). For both the quiet Sun and the Sun with radio bursts, when pointing directly to the Sun, the total power received by FAST would be out of the safe operational range of the signal chain, even resulting in damage to the receiver. As a conclusion, the Sun should be kept at least ~2° away from the main beam during observations at~1.25 GHz. The separation for lower frequency should be ... 相似文献
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The 1.6 m clear aperture solar telescope in Big Bear is operational and with its adaptive optics (AO) system it provides diffraction limited solar imaging and polarimetry in the near-infrared (NIR). While the AO system is being upgraded to provide diffraction limited imaging at bluer wavelengths, the instrumentation and observations are concentrated in the NIR. The New Solar Telescope (NST) operates in campaigns, making it the ideal ground-based telescope to provide complementary/supplementary data to SDO and Hinode. The NST makes photometric observations in Hα (656.3 nm) and TiO (705.6 nm) among other lines. As well, the NST collects vector magnetograms in the 1565 nm lines and is beginning such observations in 1083.0 nm. Here we discuss the relevant NST instruments, including AO, and present some results that are germane to NASA solar missions. 相似文献