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61.
S. G. Kleinmann M. G. Lysaght W. L. Pughe S. E. Schneider M. F. Skrutskie M. D. Weinberg S. D. Price K. Y. Matthews B. T. Soifer J. P. Huchra C. A. Beichman T. J. Chester T. Jarrett G. L. Kopan C. J. Lonsdale J. Elias J. W. Liebert P. Seitzer 《Experimental Astronomy》1994,3(1-4):65-72
This paper describes the design, expectations, and prototyping of a new allsky survey, called 2MASS (Two Micron All Sky Survey) to be carried out with the new generation of infrared array detectors. 相似文献
62.
本文在文[3]的基础上,考虑背景电磁波色散方程的弱磁化修正,在1<ωpe/Ωe<10的范围内(主委适用于太阳高日冕、行星际空间及星系射电喷流等),计算了由束流不稳定性直接放大正常模和反常模的增长率。增长率随着频率、ωpe/Ωe、电磁波传播角以及非热电子入射角等参数的变化规律,和忽略磁场时的结果与文[3]大体相同,但是反常模的增长,则随着ωpe/Ωe的增大而受到明显的抑制,因而在本文参数范围内,束流不稳定性所放大的电磁波以正常模为主,可以解释太阳III型爆发和星系射电喷流的偏振性质。 相似文献
63.
FITSIO软件包的简介及应用举例 总被引:1,自引:0,他引:1
简单介绍了用于读写FITS格式文件的FITSIO软件包的主要功能和特点。利用该软件包对 SDSS(Sloan Digital Sky Survey)数据中椭圆星系NGC4044和漩涡星系NGC5227的g,r,i三个波段的 FITS图像文件进行了重新读写,使这三个波段的FITS文件中天体的坐标完全对应。并以此合成了“真彩图”和“颜色分布图”,可以清楚地看出这些星系不同位置处颜色的变化。 相似文献
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68.
In an earlier paper, we quantified the mean merger rate of dark matter haloes as a function of redshift z , descendant halo mass M 0 , and progenitor halo mass ratio ξ using the Millennium simulation of the Λ cold dark matter cosmology. Here, we broaden that study and investigate the dependence of the merger rate of haloes on their surrounding environment. A number of local mass overdensity variables, both including and excluding the halo mass itself, are tested as measures of a halo's environment. The simple functional dependence on z , M 0 , and ξ of the merger rate found in our earlier work, is largely preserved in different environments, but we find that the overall amplitude of the merger rate has a strong positive correlation with the environmental densities. For galaxy-mass haloes, we find mergers to occur ∼2.5 times more frequently in the densest regions than in voids at both z = 0 and higher redshifts. Higher mass haloes show similar trends. We present a fitting form for this environmental dependence that is a function of both mass and local density and valid out to z = 2 . The amplitude of the progenitor (or conditional) mass function shows a similar correlation with local overdensity, suggesting that the extended Press–Schechter model for halo growth needs to be modified to incorporate environmental effects. 相似文献
69.
Andrés E. Piatti Juan J. Clariá Andrea V. Ahumada 《Monthly notices of the Royal Astronomical Society》2009,397(2):1073-1083
We present CCD photometry in the Johnson U , B and V and Kron–Cousins I passbands for the open cluster NGC 2587. The sample consists of 4406 stars reaching down to V ∼ 21.0 . We developed a new method to clean statistically the colour–magnitude diagrams. NGC 2587 appears to be a sparse, relatively bright open cluster, with a few tens of members projected on to a populous star field. The comparatively bright F7/8 II type star HD 70927, located close to the cluster centre, seems not to be a member. Our analysis suggests that NGC 2587 is slightly younger than the Hyades and probably of solar metallicity. A cluster radius of roughly 8 arcmin was estimated from the radial stellar density profile. From 18 probable cluster members with measured proper motions, we derive the following mean values for NGC 2587: μα =−4.3 ± 3.6 mas yr−1 and μδ =−2.5 ± 3.4 mas yr−1 . Adopting the theoretical metal content Z = 0.02 , which provides the best global fit, we derive a cluster age of 500+60 −50 . Simultaneously, colour excesses E ( B − V ) = 0.10 and E ( V − I ) = 0.15 and an apparent distance modulus of V − MV = 12.50 are obtained. The interstellar extinction in the cluster direction is found to follow the normal law. NGC 2587 is located at a distance of (2.70 ± 0.70) kpc from the Sun and ∼9.8 kpc from the Galactic centre. 相似文献
70.
O. Laurent I.F. Mirabel P. Gallais M. Sauvage L. Vigroux C. Cesarsky V. Charmandaris 《Astrophysics and Space Science》1999,266(1-2):175-180
We present a new diagnostic diagram based on ISOCAMspectra (5-16 m) to distinguish the emission inducedby the active galactic nucleus (AGN) from that associated with thestar formation activity. This diagnostic based on the mid-IRcontinuum and the Unidentified Infrared Band (UIB) intensity allowsus to estimate the relative importance of the three components (HIIregions, diffuse/photo-dissociation regions (PDRs), and AGN) contained ingalaxy mid-infrared emission. In AGN spectra, we confirm the absenceof UIBs presumably photodissociated by the X-UV radiation field. Inaddition, a non-negligible continuum below 9 m commonlyassociated with emission from hot dust is present in AGNs. Adiagnostic diagram derived from these two results can be used fordetecting obscured AGNs embedded in a large concentration of dust. 相似文献