共查询到20条相似文献，搜索用时 133 毫秒
1.
Dainis Dravins Stephan LeBohec Hannes Jensen Paul D. Nuñez 《New Astronomy Reviews》2012,56(5):143-167
Using kilometric arrays of air Cherenkov telescopes at short wavelengths, intensity interferometry may increase the spatial resolution achieved in optical astronomy by an order of magnitude, enabling images of rapidly rotating hot stars with structures in their circumstellar disks and winds, or mapping out patterns of nonradial pulsations across stellar surfaces. Intensity interferometry (once pioneered by Hanbury Brown and Twiss) connects telescopes only electronically, and is practically insensitive to atmospheric turbulence and optical imperfections, permitting observations over long baselines and through large airmasses, also at short optical wavelengths. The required large telescopes (～10 m) with very fast detectors (～ns) are becoming available as the arrays primarily erected to measure Cherenkov light emitted in air by particle cascades initiated by energetic gamma rays. Planned facilities (e.g., CTA, Cherenkov Telescope Array) envision many tens of telescopes distributed over a few square km. Digital signal handling enables very many baselines (from tens of meters to over a kilometer) to be simultaneously synthesized between many pairs of telescopes, while stars may be tracked across the sky with electronic time delays, in effect synthesizing an optical interferometer in software. Simulated observations indicate limiting magnitudes around mV = 8, reaching angular resolutions ～30 μarcsec in the violet. The signal-to-noise ratio favors high-temperature sources and emission-line structures, and is independent of the optical passband, be it a single spectral line or the broad spectral continuum. Intensity interferometry directly provides the modulus (but not phase) of any spatial frequency component of the source image; for this reason a full image reconstruction requires phase retrieval techniques. This is feasible if sufficient coverage of the interferometric (u, v)-plane is available, as was verified through numerical simulations. Laboratory and field experiments are in progress; test telescopes have been erected, intensity interferometry has been achieved in the laboratory, and first full-scale tests of connecting large Cherenkov telescopes have been carried out. This paper reviews this interferometric method in view of the new possibilities offered by arrays of air Cherenkov telescopes, and outlines observational programs that should become realistic already in the rather near future. 相似文献
2.
Michael Shao 《Astrophysics and Space Science》1996,241(1):105-110
This paper summarizes the limits of ground-based interferometry for differential astrometry as well as ground-based interferometry for direct detection of exo-planets and exo-zodi dust levels. For direct detection, ground-based interferometry at near IR wavelengths using large telescopes with adaptive optics offers a significant advantage over single telescopes with adaptive optics. Ground-based differential astrometry for exo-planet detection is extremely accurate with sufficient accuracy to detect Neptune mass planets around 400–600 nearby stars. Ground-based interferometry using large (>6m) telescopes is also capable of detecting the 10 m emission of the zodiacal light around nearby stars with zodi levels similar to our solar system 相似文献
3.
Webster Cash 《Experimental Astronomy》2003,16(2):91-136
For the astronomer, X-ray interferometry is the theory and practice of building dilute aperture telescopes for studying celestial X-ray sources. The short wavelengths and high surface brightness of X-ray sources will make the eventual scientific payoff very high, with direct imaging of the event horizons of black holes as the centerpiece. In this article, we review the history of X-ray interferometry and discuss the recent technical developments toward astronomical applications. We present several mission concepts and show they are achievable with todays technology. 相似文献
4.
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
5.
J.-P. Berger F. Malbet F. Baron A. Chiavassa G. Duvert M. Elitzur B. Freytag F. Gueth S. H?nig J. Hron H. Jang-Condell J.-B. Le Bouquin J.-L. Monin J. D. Monnier G. Perrin B. Plez T. Ratzka S. Renard S. Stefl E. Thiébaut K. R. W. Tristram T. Verhoelst S. Wolf J. Young 《Astronomy and Astrophysics Review》2012,20(1):1-55
The number of publications of aperture-synthesis images based on optical long-baseline interferometry measurements has recently increased due to easier access to visible and infrared interferometers. The interferometry technique has now reached a technical maturity level that opens new avenues for numerous astrophysical topics requiring milli-arcsecond model-independent imaging. In writing this paper our motivation was twofold: (1) review and publicize emblematic excerpts of the impressive corpus accumulated in the field of optical interferometry image reconstruction; (2) discuss future prospects for this technique by selecting four representative astrophysical science cases in order to review the potential benefits of using optical long-baseline interferometers. For this second goal we have simulated interferometric data from those selected astrophysical environments and used state-of-the-art codes to provide the reconstructed images that are reachable with current or soon-to-be facilities. The image-reconstruction process was ??blind?? in the sense that reconstructors had no knowledge of the input brightness distributions. We discuss the impact of optical interferometry in those four astrophysical fields. We show that image-reconstruction software successfully provides accurate morphological information on a variety of astrophysical topics and review the current strengths and weaknesses of such reconstructions. We investigate how to improve image reconstruction and the quality of the image possibly by upgrading the current facilities. We finally argue that optical interferometers and their corresponding instrumentation, existing or to come, with six to ten telescopes, should be well suited to provide images of complex sceneries. 相似文献
6.
The European Very Large Telescope program has been approved in 1987. It aims to consists of an array of four 8 m telescopes, plus two additional 2 m class auxiliary telescopes, the latter being fully dedicated to optical (infrared and visible) interferometry, with possible combination of some and, in the long term, all large telescopes. We discuss the implementation of this program in the next ten years.Paper presented at the Symposium on the JNLT and Related Engineering Developments, Tokyo, November 29–December 2, 1988. 相似文献
7.
Martin Nekola René Hudec Martin Jelínek Matůš Kocka Petr Kubánek Filip Münz Cyril Polášek Vojtěch Šimon Jan Štrobl 《Experimental Astronomy》2010,28(1):79-85
We report on two small aperture robotic telescopes called BART and D50 operated in Ondřejov. Both telescopes are capable of
automatic observation of gamma ray burst (GRB) optical afterglows. Coordinates of GRBs are taken from alerts distributed via
Internet. Telescopes observe other interesting high energy sources when there is not any alert. The smaller telescope BART
has aperture D = 254 mm. The bigger telescope D50 has a primary mirror of diameter D = 500 mm. Both telescopes are controlled
by free software package RTS2 and are accessible through Internet. We describe the two telescopes and related software and
show some results such as our first observed optical counterpart of GRB. 相似文献
8.
Optical long-baseline interferometry is a unique and powerful technique for astronomical research. Since the 1980’s (with I2T, GI2T, Mark I to III, SUSI, ...), optical interferometers have produced an increasing number of scientific papers covering various fields of astrophysics. As current interferometric facilities are reaching their maturity, we take the opportunity in this paper to summarize the conclusions of a few key meetings, workshops, and conferences dedicated to interferometry. We present the most persistent recommendations related to science cases and discuss some key technological developments required to address them. In the era of extremely large telescopes, optical long-baseline interferometers will remain crucial to probe the smallest spatial scales and make breakthrough discoveries. 相似文献
9.
Intensity interferometry removes the stringent requirements on mechanical precision and atmospheric corrections that plague all amplitude interferometry techniques at the cost of severely limited sensitivity. A new idea we recently introduced, very high redundancy, alleviates this problem. It enables the relatively simple construction (∼1 cm mechanical precision) of a ground-based astronomical facility able to transform a two-dimensional field of point-like sources to a three-dimensional distribution of microarcsec resolved systems, each imaged in several optical bands. Each system will also have its high-resolution residual timing, high-quality (inside each band) spectra and light curve, emergent flux, effective temperature, polarization effects and perhaps some thermodynamic properties, all directly measured. All the above attributes can be measured in a single observation run of such a dedicated facility. We conclude that after three decades of abandonment, optical intensity interferometry deserves another review, also as a ground-based alternative to the science goals of space interferometers. 相似文献
10.
M. Ishiguro 《Astrophysics and Space Science》1989,160(1-2):377-384
The technical feasibility of submillimeter interferometry at Mauna Kea, Hawaii, by connecting existing and planned optical/IR telescopes as well as submillimeter telescopes is discussed.Paper presented at the Symposium on the JNLT and Related Engineering Developments, Tokyo, November 19–December 2, 1988.Nobeyama Radio Observatory is a branch of the National Astronomical Observatory, the Ministry of Education, Science and Culture of Japan. 相似文献
11.
C. H. Townes 《Journal of Astrophysics and Astronomy》1984,5(2):111-130
The potential of high-resolution spatial interferometry for detailed mapping and precision astrometry in the mid-infrared
region, somewhat analogous to interferometry now done in the microwave region, is discussed from an instrumental point of
view. Some results from a prototype system and from tests of atmospheric properties are given. The design of a more advanced
two-telescope system now under construction is outlined. This involves movable telescopes of 1.65 m aperture and of high precision,
using heterodyne detection of infrared in the 10 Μm atmospheric window. 相似文献
12.
A novel method is presented which will enhance the sensitivity of neutrino telescopes to identify transient sources such as Gamma-Ray Bursts (GRBs) and core-collapse Supernovae (SNe). Triggered by the detection of high energy neutrino events from IceCube or other large scale neutrino telescopes, an optical follow-up program will allow the identification of the transient neutrino source. We show that once the follow-up program is implemented, the achievable sensitivity of IceCube to neutrinos from SNe and GRBs would increase by a factor of 2–3. The program can be realized with a small network of automated 1–2 m telescopes and has rather modest observing time requirements. 相似文献
13.
We present the results of our study of 19 novae in the galaxy M31 on photographs taken with wide-field telescopes in 1999–2005. Two of the six novae discovered in our program (ShA 65 and ShA 67) have been identified with supersoft X-ray sources, the discovery of one nova (ShA 69) was reported in IAU Circulars, and the other three novae (ShA 66, ShA 68, and ShA 70) are reported for the first time. 相似文献
14.
Most of the known pulsars are sources of highly linearly polarized radiation. Faraday rotation in the intervening medium rotates
the plane of the linear polarization as the signals propagate through the medium. The Rotation Measure (RM), which quantifies
the amount of such rotation as a function of wavelength, is useful in studying the properties of the medium and in recovering
the intrinsic polarization characteristics of the pulsar signal. Conventional methods for polarization measurements use telescopes
equipped with dual orthogonally polarized feeds that allow estimation of all 4 Stokes parameters. Some telescopes (such as
the Ooty Radio Telescope) that offer high sensitivity for pulsar observations may however be receptive to only a single linear
polarization. In such a case, the apparent spectral intensity modulation, resulting from differential Faraday rotation of
the linearly polarized signal component within the observing bandwidth, can be exploited to estimate the RM as well as to
study the linear polarization properties of the source. In this paper, we present two improved procedures by which these observables
can be estimated reliably from the intensity modulation over large bandwidths, particularly at low radio frequencies. We also
highlight some other applications where such measurements and procedures would be useful. 相似文献
15.
Fermi卫星对GeV能段的河外伽马射线背景(Extragalactic Gamma-ray Background, EGB)进行了较为精确的测量, 极大提高了对高能伽马射线背景的认识, 但是在TeV能段, 使用空间探测器进行观测非常困难, 只能依赖地面伽马射线探测器, 如成像大气切伦科夫望远镜. 目前, 对于TeV能段的河外伽马射线背景的认识还不完善. 使用有低活跃状态能谱的61个TeV源(包含2个星暴星系、6个射电星系以及53个耀变体)的累计流量给出河外TeV伽马射线背景的下限. 结果显示, 低能段(0.5--4.5TeV)流量由两个临近的耀变体Mrk 421和Mrk 501主导, 贡献了大约58%的累计背景流量; 而大于4.5TeV的能段, 由3个已观测到10TeV以上能段流量的极端耀变体H 1426+428、1ES 1959+650以及1ES 0229+200主导. 最后分别探究了星暴星系、射电星系以及耀变体对河外TeV伽马射线背景的贡献, 不同耀变体子类对河外TeV伽马射线背景的贡献以及不同红移区间TeV源对河外伽马射线背景的贡献. 相似文献
16.
We consider the production of high energy neutrinos and cosmic rays in radio-quiet active galactic nuclei (AGN) or in the central regions of radio-loud AGN. We use a model in which acceleration of protons takes place at a shock in an accretion flow onto a supermassive black hole, and follow the cascade that results from interactions of the accelerated protons in the AGN environment. We use our results to estimate the diffuse high energy neutrino intensity and cosmic ray intensity due to AGN. We discuss our results in the context of high energy neutrino telescopes under construction, and measurements of the cosmic ray composition in the region of the “knee” in the energy spectrum at 107 GeV. 相似文献
17.
V. R. Amirkhanyan V. L. Afanas'ev S. N. Dodonov A. V. Moiseev V. P. Mikhailov 《Astronomy Letters》2004,30(12):834-842
We performed spectroscopic observations of 22 radio sources from the Zelenchuk survey (Sternberg Astronomical Institute) using the 6-m and 1-m Special Astrophysical Observatory telescopes. For 18 objects, we determined the redshifts. Ten, seven, and one of these objects were identified with quasars, elliptical galaxies, and a Seyfert galaxy, respectively. Four radio sources have a continuum spectrum, and three of them are BL Lac objects. We failed to classify one object. 相似文献
18.
Andreas Quirrenbach 《Experimental Astronomy》2009,26(1-3):49-63
Astronomical interferometry was pioneered by Fizeau and Michelson in the 19th century. In the 1920s, the first stellar diameters were measured. The development of radio interferometry began in the 1950s, and led to the construction of powerful synthesis arrays operating at cm, mm, and sub-mm wavelengths. Modern computer and control technology has enabled the interferometric combination of light from separate telescopes also in the visible and infrared regimes. Imaging with milliarcsecond resolution and astrometry with microarcsecond precision have thus become reality. 相似文献
19.
We discuss recent results from near-infrared bispectrum speckle interferometry observations of the young outflow sources in the S140 and Mon R2 star forming regions. With spatial resolutions down to 0.075'', our data represent the highest resolution images obtained so far for these objects and exhibit previously unseen complex structures in the immediate vicinity of the young stellar objects. We discuss the relation of these structures to the jets and outflows. 相似文献
20.
D. C. Gabuzda P. YU. Kochenov R. I. Kollgaard T. V. Cawthorne 《Monthly notices of the Royal Astronomical Society》2000,315(2):229-240
Total intensity and polarization λ =6 cm Very Large Array (VLA) and global very long baseline interferometry (VLBI) images of the quasar 0917+624 and the BL Lacertae object 0954+658 (both at epoch 1991.43) are analysed. Integrated measurements using the VLA during the VLBI observations indicated that, although there were no substantial total intensity variations, there were significant polarization variations for both sources during the 24-h VLBI experiment. The VLBI data were divided into 2–3 h segments in order to try to identify corresponding rapid variability in the VLBI structure. This analysis revealed intraday variability (IDV) in the VLBI core of 0917+624: both the polarized flux and the polarization position angle varied substantially on time-scales of ∼5–10 h. There is evidence that the VLA polarization variations for 0954+658 occurred in an inner VLBI jet component, where the polarized flux varied by ∼30–40 per cent on time-scales of ∼2 h. 0917+624 and 0954+658 were observed together with 0716+714, an object that also displayed IDV in the polarized flux density measured during our experiment (analysed in a separate paper). These three sources were targeted for the VLBI observations since they had been previously identified as intraday variables, but we had no way of knowing whether they would vary during our observations. The fact that all three exhibited IDV in polarization (but not in total intensity) during our experiment suggests that polarization IDV occurs frequently in at least some IDV sources. 相似文献