Using the Urumqi 25 m radio telescope, sources from the first three months of the Fermi-large area telescope detected active galactic nuclei (AGN) catalog with a declination of 〉 0° were observed in 2009 at 4....Using the Urumqi 25 m radio telescope, sources from the first three months of the Fermi-large area telescope detected active galactic nuclei (AGN) catalog with a declination of 〉 0° were observed in 2009 at 4.8 GHz. The radio flux density ap- peared to correlate with the γ-ray intensity. Intra-day variability (IDV) observations were performed in March, April and May 2009 for 42 selected γ-ray bright blazars, and ~60% of them showed evidence of flux variability at 4.8 GHz during the IDV observations. The IDV detection rate was higher than that in previous flat-spectrum AGN samples. IDV appeared more often in the very long baseline interferometry-core dominant blazars, and the non-IDV blazars showed relatively "steeper" spectral in- dices than the IDV blazars. Pronounced inter-month variability was also found in two BL Lac objects: J0112+2244 and J0238+1636.展开更多
An NUV-optical diagram composed from sources from the second Galaxy Evolution Explorer(GALEX) Ultraviolet Variability(GUVV-2) Catalog provides us with a method to tentatively classify the unknown GUVV-2 sources by...An NUV-optical diagram composed from sources from the second Galaxy Evolution Explorer(GALEX) Ultraviolet Variability(GUVV-2) Catalog provides us with a method to tentatively classify the unknown GUVV-2 sources by their NUV-optical magnitudes.For the purpose of testing the correctness and generality of the method,we carry out a program on the spectroscopic observations of the unidentified GUVV-2 sources.The spectroscopic identification of these 37 sources are 19 type-A to-F stars,10 type-G to-K stars and 7 M dwarf stars together with an AGN.We also present the light curves in the R-band for two RR Lyrae star candidates selected from the NUV-optical diagram,both of which undergo cyclic variations.Combining their light curves and colors,we classify them as RR Lyrae stars.To confirm the re-sults,we show a color-color diagram for the 37 newly identified spectroscopic objects compared with previously identified ones,which are consistent with our previous re-sults,indicating that the ultraviolet variable sources can initially be classified by their NUV/optical color-color diagram.展开更多
We discovered three large HⅡ regions: G148.8+2.3, G149.5+0.0 and G169.9+2.0 in the Sino-German A6 cm polarization survey of the Galactic plane. They have been identified based on the flat spectral indexes and the...We discovered three large HⅡ regions: G148.8+2.3, G149.5+0.0 and G169.9+2.0 in the Sino-German A6 cm polarization survey of the Galactic plane. They have been identified based on the flat spectral indexes and the strong infrared emission properties.展开更多
Observational astronomy has shown significant growth over the last decade and has made important contributions to cosmology. A major paradigm shift in cosmology was brought about by observations of Type Ia supernovae....Observational astronomy has shown significant growth over the last decade and has made important contributions to cosmology. A major paradigm shift in cosmology was brought about by observations of Type Ia supernovae. The notion that the universe is accelerating has led to several theoretical challenges. Unfortunately, although high-quality supernovae data-sets are being produced, their statistical anal- ysis leaves much to be desired. Instead of using the data to directly test the model, several studies seem to concentrate on assuming the model to be correct and limiting themselves to estimating model parameters and internal errors. As shown here, the important purpose of testing a cosmological theory is thereby vitiated.展开更多
We present a large sample which includes 82 BL Lac objects with red- shifts below 0.2 from recent literature. We find strong correlations in both flux and luminosity between the radio (5 GHz) and optical bands (5500 A...We present a large sample which includes 82 BL Lac objects with red- shifts below 0.2 from recent literature. We find strong correlations in both flux and luminosity between the radio (5 GHz) and optical bands (5500 A). The correlations in other bands are very weak. Five TeV BL Lacs and two suspect sources are found to have similar properties as high- frequency- peaked BL Lacs (HBLs). Our results suggest that both the radio and optical emissions are from the same radiation mech- anism in the SSC model. The TeV BL Lac candidates should be HBLs or HBL-like objects with small redshifts.展开更多
We propose a consistency test for some recent X-ray gas mass fraction (fgas) measurements in galaxy clusters, using the cosmic distance-duality relation, Ttneory = DL(1 + Z)-2/DA, with luminosity distance (DL) ...We propose a consistency test for some recent X-ray gas mass fraction (fgas) measurements in galaxy clusters, using the cosmic distance-duality relation, Ttneory = DL(1 + Z)-2/DA, with luminosity distance (DL) data from the Union2 compilation of type Ia supernovae. We set Z/theory = 1, instead of assigning any red- shift parameterizations to it, and constrain the cosmological information preferred by fga8 data along with supernova observations. We adopt a new binning method in the reduction of the Union2 data, in order to minimize the statistical errors. Four data sets of X-ray gas mass fraction, which are reported by Allen et al. (two samples), LaRoque et al. and Ettori et al., are analyzed in detail in the context of two theoretical models of fgas. The results from the analysis of Alien et al.'s samples demonstrate the feasibility of our method. It is found that the preferred cosmology by LaRoque et al.'s sample is consistent with its reference cosmology within the 1σ confidence level. However, for Ettori et al.'s fgas sample, the inconsistency can reach more than a 3σ confidence level and this dataset shows special preference to an ΩA = 0 cosmology.展开更多
Supernovae of type Ia (SNe Ia) are confirmed to be the best distance indicators to derive the cosmic expansion rate. The dispersion of their peak luminosity at optical bands (BVI) is approximate to 0.13 mag, after ta...Supernovae of type Ia (SNe Ia) are confirmed to be the best distance indicators to derive the cosmic expansion rate. The dispersion of their peak luminosity at optical bands (BVI) is approximate to 0.13 mag, after taking into account the effects of the second parameters (i.e., the Antial decline rate m15(B) and (B - V) color at maximum light). The local calibrations from HST indicate an absolute magnitude of 19.48 ± 0.08mag (in V band) for SNe Ia in spiral galaxies. The current expansion rate, Ho, is found to be 63.6 ± 1.8 (random) ±5.7 (systematic) kms-1 Mpc-1. This Value will decrease by 3% when the metallicity effect on the cepheid distances is considered. In addition, a marginal local outward flow of 4.0 ± 4.5% within the velocity-distance of 7000 km s-1 can be inferred from SNe Ia for the Einstein-de Sitter universe; however, this outward flow is only 2.2 ± 4.4% for an accelerating expansion universe (which is supported by high-z SNe Ia).展开更多
This paper is dedicated to the expansion of the framework of general interpolant observables introduced by Azouani,Olson,and Titi for continuous data assimilation of nonlinear partial differential equations.The main f...This paper is dedicated to the expansion of the framework of general interpolant observables introduced by Azouani,Olson,and Titi for continuous data assimilation of nonlinear partial differential equations.The main feature of this expanded framework is its mesh-free aspect,which allows the observational data itself to dictate the subdivision of the domain via partition of unity in the spirit of the so-called Partition of Unity Method by Babuska and Melenk.As an application of this framework,we consider a nudging-based scheme for data assimilation applied to the context of the two-dimensional Navier-Stokes equations as a paradigmatic example and establish convergence to the reference solution in all higher-order Sobolev topologies in a periodic,mean-free setting.The convergence analysis also makes use of absorbing ball bounds in higherorder Sobolev norms,for which explicit bounds appear to be available in the literature only up to H^(2);such bounds are additionally proved for all integer levels of Sobolev regularity above H^(2).展开更多
基金supported by the National Natural Science Foundation of China (Grant No. 11073036)the NationalBasic Research Program of China (973 Program 2009CB824800)
文摘Using the Urumqi 25 m radio telescope, sources from the first three months of the Fermi-large area telescope detected active galactic nuclei (AGN) catalog with a declination of 〉 0° were observed in 2009 at 4.8 GHz. The radio flux density ap- peared to correlate with the γ-ray intensity. Intra-day variability (IDV) observations were performed in March, April and May 2009 for 42 selected γ-ray bright blazars, and ~60% of them showed evidence of flux variability at 4.8 GHz during the IDV observations. The IDV detection rate was higher than that in previous flat-spectrum AGN samples. IDV appeared more often in the very long baseline interferometry-core dominant blazars, and the non-IDV blazars showed relatively "steeper" spectral in- dices than the IDV blazars. Pronounced inter-month variability was also found in two BL Lac objects: J0112+2244 and J0238+1636.
基金Supported by the National Natural Science Foundation of China(Grant No.10803008)supported by the National Basic Research Program of China (Grant 2009CB824800)supported by the Open Project Program of the Key Laboratory of Optical Astronomy,NAOC,CAS
文摘An NUV-optical diagram composed from sources from the second Galaxy Evolution Explorer(GALEX) Ultraviolet Variability(GUVV-2) Catalog provides us with a method to tentatively classify the unknown GUVV-2 sources by their NUV-optical magnitudes.For the purpose of testing the correctness and generality of the method,we carry out a program on the spectroscopic observations of the unidentified GUVV-2 sources.The spectroscopic identification of these 37 sources are 19 type-A to-F stars,10 type-G to-K stars and 7 M dwarf stars together with an AGN.We also present the light curves in the R-band for two RR Lyrae star candidates selected from the NUV-optical diagram,both of which undergo cyclic variations.Combining their light curves and colors,we classify them as RR Lyrae stars.To confirm the re-sults,we show a color-color diagram for the 37 newly identified spectroscopic objects compared with previously identified ones,which are consistent with our previous re-sults,indicating that the ultraviolet variable sources can initially be classified by their NUV/optical color-color diagram.
基金the National Natural Science Foundation of China
文摘We discovered three large HⅡ regions: G148.8+2.3, G149.5+0.0 and G169.9+2.0 in the Sino-German A6 cm polarization survey of the Galactic plane. They have been identified based on the flat spectral indexes and the strong infrared emission properties.
文摘Observational astronomy has shown significant growth over the last decade and has made important contributions to cosmology. A major paradigm shift in cosmology was brought about by observations of Type Ia supernovae. The notion that the universe is accelerating has led to several theoretical challenges. Unfortunately, although high-quality supernovae data-sets are being produced, their statistical anal- ysis leaves much to be desired. Instead of using the data to directly test the model, several studies seem to concentrate on assuming the model to be correct and limiting themselves to estimating model parameters and internal errors. As shown here, the important purpose of testing a cosmological theory is thereby vitiated.
基金the NationalNatural Science FOundation of China and NaturaI Science Foundation of Yunnan Province(2000A004M).
文摘We present a large sample which includes 82 BL Lac objects with red- shifts below 0.2 from recent literature. We find strong correlations in both flux and luminosity between the radio (5 GHz) and optical bands (5500 A). The correlations in other bands are very weak. Five TeV BL Lacs and two suspect sources are found to have similar properties as high- frequency- peaked BL Lacs (HBLs). Our results suggest that both the radio and optical emissions are from the same radiation mech- anism in the SSC model. The TeV BL Lac candidates should be HBLs or HBL-like objects with small redshifts.
基金supported by the National Basic Research Program of China (973 program Grant Nos. 2009CB824800 and 2012CB821804)+1 种基金the National Natural Science Foundation of China (Grant Nos. 11033002 and 11173006)the Fundamental Research Funds for the Central Universities
文摘We propose a consistency test for some recent X-ray gas mass fraction (fgas) measurements in galaxy clusters, using the cosmic distance-duality relation, Ttneory = DL(1 + Z)-2/DA, with luminosity distance (DL) data from the Union2 compilation of type Ia supernovae. We set Z/theory = 1, instead of assigning any red- shift parameterizations to it, and constrain the cosmological information preferred by fga8 data along with supernova observations. We adopt a new binning method in the reduction of the Union2 data, in order to minimize the statistical errors. Four data sets of X-ray gas mass fraction, which are reported by Allen et al. (two samples), LaRoque et al. and Ettori et al., are analyzed in detail in the context of two theoretical models of fgas. The results from the analysis of Alien et al.'s samples demonstrate the feasibility of our method. It is found that the preferred cosmology by LaRoque et al.'s sample is consistent with its reference cosmology within the 1σ confidence level. However, for Ettori et al.'s fgas sample, the inconsistency can reach more than a 3σ confidence level and this dataset shows special preference to an ΩA = 0 cosmology.
基金the National Natural Science Foundation of China(19733002) Project of“973”(G19990750401)
文摘Supernovae of type Ia (SNe Ia) are confirmed to be the best distance indicators to derive the cosmic expansion rate. The dispersion of their peak luminosity at optical bands (BVI) is approximate to 0.13 mag, after taking into account the effects of the second parameters (i.e., the Antial decline rate m15(B) and (B - V) color at maximum light). The local calibrations from HST indicate an absolute magnitude of 19.48 ± 0.08mag (in V band) for SNe Ia in spiral galaxies. The current expansion rate, Ho, is found to be 63.6 ± 1.8 (random) ±5.7 (systematic) kms-1 Mpc-1. This Value will decrease by 3% when the metallicity effect on the cepheid distances is considered. In addition, a marginal local outward flow of 4.0 ± 4.5% within the velocity-distance of 7000 km s-1 can be inferred from SNe Ia for the Einstein-de Sitter universe; however, this outward flow is only 2.2 ± 4.4% for an accelerating expansion universe (which is supported by high-z SNe Ia).
基金partially supported by the award PSC-CUNY64335-0052,jointly funded by The Professional Staff Congress and The City University of New York。
文摘This paper is dedicated to the expansion of the framework of general interpolant observables introduced by Azouani,Olson,and Titi for continuous data assimilation of nonlinear partial differential equations.The main feature of this expanded framework is its mesh-free aspect,which allows the observational data itself to dictate the subdivision of the domain via partition of unity in the spirit of the so-called Partition of Unity Method by Babuska and Melenk.As an application of this framework,we consider a nudging-based scheme for data assimilation applied to the context of the two-dimensional Navier-Stokes equations as a paradigmatic example and establish convergence to the reference solution in all higher-order Sobolev topologies in a periodic,mean-free setting.The convergence analysis also makes use of absorbing ball bounds in higherorder Sobolev norms,for which explicit bounds appear to be available in the literature only up to H^(2);such bounds are additionally proved for all integer levels of Sobolev regularity above H^(2).