共查询到20条相似文献,搜索用时 31 毫秒
1.
Ana I. Gómez?de?Castro Jesús Maíz Pablo Rodriguez Maite Gómez Juan A. Larruquert José A. Méndez Tomas Belenguer Victor Rodrigo-Gudiel Fátima López-Martínez Paola Sestito 《Astrophysics and Space Science》2011,335(1):283-289
ISSIS is the Imaging and Slitless Spectroscopy Instrument for the World Space Observatory-Ultraviolet (WSO-UV) mission. ISSIS
is a multipurpose instrument designed to carry out high resolution (<0.1 arcsec) imaging in the far UV with fields of view
≥2×2 arcmin2. ISSIS has two acquisition channels: the High Sensitivity Channel (HSC) and the Channel for Surveys (CfS). The HSC is equipped
with an MCP-type detector to guarantee high sensitivity in the 1150–1750 ? range and high rejection of lower energy radiation.
The CfS is equipped with a large CCD detector (4k×4k) to obtain images from the far UV to the red (1150–8500 ?); the CfS is
implemented to allow observing UV bright sources such as reflection nebulae or nearby massive star forming regions. The design
drivers and the current status of the instrument are described in this contribution. 相似文献
2.
E.E. Becklin M. Silverstone R. Chary J. Hare B. Zuckerman C. Spangler A. Sargent 《Astrophysics and Space Science》1997,255(1-2):113-118
The DEBRIS project is a search for infrared excess around Sun-like main sequence stars, and other types of stellar targets,
using the Infrared Space Observatory. Some results, calibration issues, and changes to our original program are presented.
Future platforms for advancing this project after the conclusion of the ISO mission are indicated.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
3.
J. R. Martirosian 《Astrophysics》2007,50(3):301-310
This is a statistical study of galaxies with a UV excess. A sample of 702 Kazarian galaxies (KG) is used. The KGs are identified
with objects from the MAPS, IRAS FSC, IRAS PSC, and NVSS catalogs. The O and E magnitudes are known for more than 92% of the
KGs. It is shown that the KG sample is complete up to 16m.0 in the blue and to 16m.5 in the red. More than 36% of the KGs
are identified with infrared (IR) sources at wavelengths of 12, 25, 60, and 100 m. Calculations of the far IR (FIR) luminosities
show that 4% of the KGs are strong FIR emitters (LFIR ≥ 1011 L⊙). More than 32% of the KGs have been identified as radio sources at a frequency of 1.4 GHz. A determination of the radio
luminosities shows that the sample of KGs with known radial velocities include one powerful, LR ≥ 1025 W/Hz, radio object (Kaz 273) which is a BL Lac object. A close correlation (r=0.93) is bound between the FIR and radio luminosities
for galaxies with a UV excess. An examination of the relationship between the FIR and radio luminosities for galaxies in different
spectral classes shows that the correlation coefficient is higher (r=0.99) and the slope of the fit curve is larger (a=1.18)
for Seyfert galaxies. Calculations of the logarithm of the ratio of the FIR and radio fluxes indicate that the sample includes
4 KGs with a radio excess, while there are none with an IR excess.
__________
Translated from Astrofizika, Vol. 50, No. 3, pp. 369–379 (August 2007). 相似文献
4.
The results of a statistical investigation of bright galaxies with a UV excess are given. The data obtained for them are compared
with those for normal galaxies. A list of bright galaxies (mpg ≤14m.5 ) with a UV excess has been compiled, numbering 461. Their absolute stellar magnitudes and average geometrical linear diameters
were determined. The relationships between Mpg and log D are given for galaxies with a UV excess and normal galaxies. The graphs of the relationships are expressed by second-degree
equations. It is shown that the UV evolutionary stage of the galaxies has no influence on the relationship between Mpg and log D.
Translated from Astrofizika, Vol. 43, No. 1, pp. 21-32, January–March, 2000. 相似文献
5.
K. A. Wills C. N. Tadhunter T. G. Robinson R. Morganti 《Monthly notices of the Royal Astronomical Society》2002,333(1):211-221
We present William Herschel Telescope spectropolarimetry observations of a complete RA-limited sample of nine low-redshift (0.05< z <0.2) 3CR radio sources in order to investigate the nature of the ultraviolet (UV) excess in nearby powerful radio galaxies. Of the nine galaxies studied in detail from this sample, we find that four show a measurable UV excess following nebular continuum subtraction, but none of the sources shows significant polarization in the UV. One of the radio galaxies with a UV excess – 3C 184.1 – shows evidence for broad permitted lines and hence direct active galactic nucleus (AGN) light. In the remaining three galaxies we argue that the most likely contributor to the UV excess is a young stellar component. For these three galaxies we find that the best-fitting model for the optical/UV continuum consists of a combination of an old stellar population (10–15 Gyr old elliptical galaxy) plus a reddened young stellar population (0.05–2 Gyr) . The reddened young stellar component typically accounts for half of the total flux at 4780 Å, following nebular continuum subtraction, and E ( B - V ) values of between 0.2 and 0.7 mag are required. However, for the majority of sources in our sample (six out of nine), continuum modelling provides no evidence for a significant young stellar component in the nuclear regions of the host galaxies. Our results are discussed in the context of far-infrared evidence for star formation activity. 相似文献
6.
H. McNamara J. Jones B. Kauffman R. Suggs W. Cooke S. Smith 《Earth, Moon, and Planets》2004,95(1-4):123-139
In an attempt to overcome some of the deficiencies of existing meteoroid models, NASA’s Space Environments and Effects (SEE)
Program sponsored a 3 year research effort at the University of Western Ontario. The resulting understanding of the sporadic
meteoroid environment – particularly the nature and distribution of the sporadic sources – were then incorporated into a new
Meteoroid Engineering Model (MEM) by members of the Space Environments Team at NASA’s Marshall Space Flight Center. This paper
discusses some of the revolutionary aspects of MEM which include (a) identification of the sporadic radiants with real sources
of meteoroids, such as comets, (b) a physics-based approach which yields accurate fluxes and directionality for interplanetary
spacecraft anywhere from 0.2 to 2.0 astronomical units (AU), and (c) velocity distributions obtained from theory and validated
against observation. Use of the model, which gives penetrating fluxes and average impact speeds on the surfaces of a cube-like
structure, is also described along with its current limitations and plans for future improvements. 相似文献
7.
M. A. Kazarian 《Astrophysics》1997,40(3):296-307
A list of galaxies with a UV excess in which at least one supernova (SN) has exploded is compiled. Distributions of the linear
distances of SN in synthetic galaxies are obtained, constructed for galaxies with a UV excess and normal galaxies. It is shown
that SN activity is the same in galaxies with a UV excess and in normal galaxies.
Translated from Astrofizika, Vol. 40, No. 3, pp. 457–472, August, 1997. 相似文献
8.
E. Pian P. Romano D. Maoz A. Cucchiara C. Pagani V. La Parola 《Monthly notices of the Royal Astronomical Society》2010,401(1):677-686
We have observed four low-luminosity active galactic nuclei (AGNs) classified as type 1 Low-Ionization Nuclear Emission-Line Regions (LINERs) with the X-Ray Telescope (XRT) and the Ultraviolet–Optical Telescope (UVOT) onboard Swift , in an attempt to clarify the main powering mechanism of this class of nearby sources. Among our targets, we detect X-ray variability in NGC 3998 for the first time. The light curves of this object reveal variations of up to 30 per cent amplitude in half a day, with no significant spectral variability on this time-scale. We also observe a decrease of ∼30 per cent over 9 d, with significant spectral softening. Moreover, the X-ray flux is ∼40 per cent lower than observed in previous years. Variability is detected in M81 as well, at levels comparable to those reported previously: a flux increase in the hard X-rays (1–10 keV) of 30 per cent in ∼3 h and variations by up to a factor of 2 within a few years. This X-ray behaviour is similar to that of higher luminosity, Seyfert-type objects. Using previous high-angular-resolution imaging data from the Hubble Space Telescope ( HST ), we evaluate the diffuse UV emission due to the host galaxy and isolate the nuclear flux in our UVOT observations. All sources are detected in the UV band, at levels similar to those of the previous observations with HST . The XRT (0.2–10 keV) spectra are well described by single power laws and the UV-to-X-ray flux ratios are again consistent with those of Seyferts and radio-loud AGNs of higher luminosity. The similarity in X-ray variability and broad-band energy distributions suggests the presence of similar accretion and radiation processes in low- and high-luminosity AGNs. 相似文献
9.
Hao Tong Ren-Xin Xu Li-Ming Song Institute of High Energy Physics Chinese Academy of Sciences Beijing China School of Physics State Key Laboratory of Nuclear Physics Technology Peking University Beijing 《中国天文和天体物理学报》2011,(12)
X-ray dim isolated neutron stars are peculiar pulsar-like objects,characterized by their Planck-like spectrum.In studying their spectral energy distributions,optical/ultraviolet(UV) excess is a long standing problem.Recently Kaplan et al.measured the optical/UV excess for all seven sources,which is understandable in the resonant cyclotron scattering(RCS) model previously addressed.The RCS model calculations show that the RCS process can account for the observed optical/UV excess for most sources.The ?at spe... 相似文献
10.
The Transition Region and Coronal Explorer (TRACE) instrument includes a “white light” imaging capability with novel characteristics.
Many flares with such white-light emission have been detected, and this paper provides an introductory overview of these data.
These observations have 0.5″ pixel size and use the full broad-band response of the CCD sensor; the images are not compromised
by ground-based seeing and have excellent pointing stability as well as high time resolution. The spectral response of the
TRACE white-light passband extends into the UV, so these data capture, for the first time in images, the main radiative energy
of a flare. This initial survey is based on a sample of flares observed at high time resolution for which the Reuven Ramaty
High-Energy Solar Spectroscopic Imager (RHESSI) had complete data coverage, a total of 11 events up to the end of 2004. We
characterize these events in terms of source morphology and contrast against the photosphere. We confirm the strong association
of the TRACE white-light emissions - which include UV as well as visual wavelengths – with hard X-ray sources observed by
RHESSI. The images show fine structure at the TRACE resolution limit, and often show this fine structure to be extended over
large areas rather than just in simple footpoint sources. The white-light emission shows strong intermittency both in space
and in time and commonly contains features unresolved at the TRACE resolution. We detect white-light continuum emission in
flares as weak as GOES C1.6. limited by photon statistics and background solar fluctuations, and support the conclusion of
Neidig (1989) that white-light continuum occurs in essentially all flares. 相似文献
11.
L. Fossati D. Bisikalo H. Lammer B. Shustov M. Sachkov 《Astrophysics and Space Science》2014,354(1):9-19
The success of the International Ultraviolet Explorer (IUE) first and then of the STIS and COS spectrographs on-board the Hubble Space Telescope (HST) demonstrate the impact that observations at UV wavelengths had and are having on modern astronomy. Several discoveries in the exoplanet field have been done at UV wavelengths. Nevertheless, the amount of data collected in this band is still limited both in terms of observed targets and time spent on each of them. For the next decade, the post-HST era, the only large (2-m class) space telescope capable of UV observations will be the World Space Observatory–UltraViolet (WSO–UV). In its characteristics, the WSO–UV mission is similar to that of HST, but all observing time will be dedicated to UV astronomy. In this work, we briefly outline the major prospects of the WSO–UV mission in terms of exoplanet studies. To the limits of the data and tools currently available, here we also compare the quality of key exoplanet data obtained in the far-UV and near-UV with HST (STIS and COS) to that expected to obtain with WSO–UV. 相似文献
12.
13.
Roger J. Sylvester Vincent Mannings 《Monthly notices of the Royal Astronomical Society》2000,313(1):73-86
Photometric observations at optical and near-infrared wavelengths are presented for members of a new sample of candidate Vega-like systems, or main sequence stars with excess infrared emission due to circumstellar dust. The observations are combined with IRAS fluxes to define the spectral energy distributions of the sources. Most of the sources show only photospheric emission at near-IR wavelengths, indicating a lack of hot (∼1000 K) dust. Mid-infrared spectra are presented for four sources from the sample. One of them, HD 150193, shows strong silicate emission, while another, HD 176363, was not detected. The spectra of two stars from our previous sample of Vega-like sources both show UIR-band emission, attributed to hydrocarbon materials. Detailed comparisons of the optical and IRAS positions suggest that in some cases the IRAS source is not physically associated with the visible star. Alternative associations are suggested for several of these sources. Fractional excess luminosities are derived from the observed spectral energy distributions. The values found are comparable to those measured previously for other Vega-like sources. 相似文献
14.
D. S. Wiebe 《Solar System Research》2017,51(7):587-591
In this contribution, I consider those aspects of the modern star formation theory, which can be substantiated with observations in the UV band, paying special attention to early stages of molecular cloud formation and initial conditions for the chemical evolution of starless cores. I describe the main results of available diffuse cloud observations in the UV band, as well as prospective directions for future studies with the instrumentation of the World Space Observatory project. 相似文献
15.
Andrew Fittingoff J. Xavier Prochaska Jasonjot S. Kalirai Jay Strader † Puragra Guhathakurta Kyle F. Kaplan 《Monthly notices of the Royal Astronomical Society》2009,399(2):728-736
We have performed a wide-area ultraviolet (UV) imaging survey using the GALaxy Evolution eXplorer to search for bright, point-like UV sources behind M31's extended halo. Our survey consisted of 46 pointings covering an effective area of ≈50 deg2 , in both the far-UV and near-UV channels. We combined these data with optical R -band observations acquired with the WIYN Mosaic-1 imager on the Kitt Peak National Observatory 0.9-m WIYN telescope. An analysis of the brightness and colours of sources matched between our photometric catalogues yielded ≈100 UV-bright quasar candidates. We have obtained discovery spectra for 76 of these targets with the Kast spectrometer on the Lick 3-m telescope and confirmed 30 active galactic nuclei and quasars, 29 galaxies at z > 0.02 including several early-type systems, 16 Galactic stars (hot main-sequence stars) and one featureless source previously identified as a BL Lac object. Future UV spectroscopy of the brightest targets with the Cosmic Origins Spectrograph on the Hubble Space Telescope will enable a systematic search for diffuse gas in the extended halo of M31. 相似文献
16.
Laurent Koechlin Denis Serre Paul Deba Roser Pelló Christelle Peillon Paul Duchon Ana Ines Gomez de Castro Margarita Karovska Jean-Michel Désert David Ehrenreich Guillaume Hebrard Alain Lecavelier des Etangs Roger Ferlet David Sing Alfred Vidal-Madjar 《Experimental Astronomy》2009,23(1):379-402
The Fresnel Interferometric Imager has been proposed to the European Space Agency (ESA) Cosmic Vision plan as a class L mission.
This mission addresses several themes of the CV Plan: Exoplanet study, Matter in extreme conditions, and The Universe taking shape. This paper is an abridged version of the original ESA proposal. We have removed most of the technical and financial issues,
to concentrate on the instrumental design and astrophysical missions. The instrument proposed is an ultra-lightweight telescope,
featuring a novel optical concept based on diffraction focussing. It yields high dynamic range images, while releasing constraints
on positioning and manufacturing of the main optical elements. This concept should open the way to very large apertures in
space. In this two spacecraft formation-flying instrument, one spacecraft holds the focussing element: the Fresnel interferometric
array; the other spacecraft holds the field optics, focal instrumentation, and detectors. The Fresnel array proposed here
is a 3.6 ×3.6 m square opaque foil punched with 105 to 106 void “subapertures”. Focusing is achieved with no other optical element: the shape and positioning of the subapertures (holes
in the foil) is responsible for beam combining by diffraction, and 5% to 10% of the total incident light ends up into a sharp
focus. The consequence of this high number of subapertures is high dynamic range images. In addition, as it uses only a combination
of vacuum and opaque material, this focussing method is potentially efficient over a very broad wavelength domain. The focal
length of such diffractive focussing devices is wavelength dependent. However, this can be corrected. We have tested optically
the efficiency of the chromatism correction on artificial sources (500 < λ < 750 nm): the images are diffraction limited, and the dynamic range measured on an artificial double source reaches 6.2
10 − 6. We have also validated numerical simulation algorithms for larger Fresnel interferometric arrays. These simulations yield
a dynamic range (rejection factor) close to 10 − 8 for arrays such as the 3.6 m one we propose. A dynamic range of 10 − 8 allows detection of objects at contrasts as high as than 10 − 9 in most of the field. The astrophysical applications cover many objects in the IR, visible an UV domains. Examples are presented,
taking advantage of the high angular resolution and dynamic range capabilities of this concept. 相似文献
17.
The second part of the First Byurakan Survey is aimed at detecting all bright (B < 16.5) UV-excess starlike objects in a large
area of the sky. By comparison with other major surveys such as the ROSA T All Sky Survey, the ROSAT WGACAT catalogue of point
sources, the IRAS survey, the 6cm Green Bank, the 1.4GHz NRAO VLA, and the 92cm Westerbork Northern sky surveys and with the
catalogue of mean UBVdata on stars, we estimate the number of AGNs present in the FBS survey and its completeness. We have made spectroscopic observations
of nine of the most promising FBS candidates. We have found six new QSOs, bringing the total number of known QSOs in this
survey to 42. By comparison with the Bright Quasar Survey, we found that the completeness of this last survey is of the order
of 70% rather than 30–50% as suggested by several authors.
Based party on observations collected at the Observatorie de Haute-Provence (CNRS, France). The APS databases are supported
by the National Foundation, the National Aeronautics and Space Administration, and the University of Minnesota, and are available
at hup:// aps.umn.edu. The Digitized Sky Survey was produced at the Space Telescope Science Institute (STScI) under U.S. Government
Grant NAG W-2166.
Published in Astrofizika, Vol. 42, No. 1, pp. 5–22, January–March, 1999. 相似文献
18.
M. A. Hassan B. A. Korany R. Misra I. A. M. Issa M. K. Ahmed F. A. Abdel-Salam 《Astrophysics and Space Science》2012,339(2):355-364
We undertake a spectral study of a sample of bright X-ray sources taken from six XMM-Newton fields at high galactic latitudes,
where AGN are the most populous class. These six fields were chosen such that the observation had an exposure time more than
60 ksec, had data from the EPIC-pn detector in the full-Frame mode and lying at high galactic latitude |b|>25∘. The analysis started by fitting the spectra of all sources with an absorbed power-law model, and then we fitted all the
spectra with an absorbed power-law with a low energy black-body component model.The sources for which we added a black body
gave an F-test probability of 0.01 or less (i.e. at 99% confidence level), were recognized as sources that display soft excess. We
perform a comparative analysis of soft excess spectral parameters with respect to the underlying power-law one for sources
that satisfy this criterion. Those sources, that do not show evidence for a soft excess, based on the F-test probability at a 99% confidence level, were also fitted with the absorbed power-law with a low energy black-body component
model with the black-body temperature fixed at 0.1 and 0.2 keV. We establish upper limits on the soft excess flux for those
sources at these two temperatures. Finally we have made use of Aladdin interactive sky atlas and matching with NASA/IPAC Extragalactic
Database (NED) to identify the X-ray sources in our sample. For those sources which are identified in the NED catalogue, we
make a comparative study of the soft excess phenomenon for different types of systems. 相似文献
19.
Luciana Bianchi Alexander de la Vega Bernard Shiao Ralph Bohlin 《Astrophysics and Space Science》2018,363(3):56
We present a new, expanded and improved catalog of Ultraviolet (UV) sources from the GALEX All-Sky Imaging survey: GUVcat_AIS (Bianchi et al. in Astrophys. J. Suppl. Ser. 230:24, 2017). The catalog includes 83 million unique sources (duplicate measurements and rim artifacts are removed) measured in far-UV and near-UV. With respect to previous versions (Bianchi et al. in Mon. Not. R. Astron. Soc. 411:2770 2011a, Adv. Space Res. 53:900–991, 2014), GUVcat_AIS covers a slightly larger area, 24,790 square degrees, and includes critical corrections and improvements, as well as new tags, in particular to identify sources in the footprint of extended objects, where pipeline source detection may fail and custom-photometry may be necessary. The UV unique-source catalog facilitates studies of density of sources, and matching of the UV samples with databases at other wavelengths.We also present first results from two ongoing projects, addressing respectively UV variability searches on time scales from seconds to years by mining the GALEX photon archive, and the construction of a database of ~120,000 GALEX UV spectra (range ~1300–3000 Å), including quality and calibration assessment and classification of the grism, hence serendipitous, spectral sources. 相似文献