The large quasar reference frame (LQRF) - An optical representation of the ICRS
The large quasar reference frame (LQRF) - An optical representation of the ICRS
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DOI：
10.1051/0004-6361/200912041
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发表时间：
2009-07
影响因子：
6.5
通讯作者：
A. Andrei;J. Souchay;N. Zacharias;R. Smart;R. V. Martins;D. D. S. Neto-D.;J. Camargo;M. Assafin;C. Barache;S. Bouquillon;J. Penna;F. Taris
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文献类型：
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作者：
A. Andrei;J. Souchay;N. Zacharias;R. Smart;R. V. Martins;D. D. S. Neto-D.;J. Camargo;M. Assafin;C. Barache;S. Bouquillon;J. Penna;F. Taris
上下文。来自不同调查的大量类星体和全天分布，以及它们在大型深天体测量目录中的存在，使我们能够按照国际天文参考系的定义原则建立一个光学物化系统。即：它相对于遥远的河外天体是运动学上不旋转的；与J2000的平均赤道和动力分点对齐；并通过采用的河外源坐标列表来实现。目标。大型类星体参考框架的建立注意到避免其组成类星体的不正确匹配，使收集组成类星体的不同星表和列表的天体测量均一化，并实现与国际天文参考框架的毫角秒全球对准，以及高于100毫角秒�的典型单源位置精度。方法：研究方法。从最新的可能是完整的大类星体天体测量星表(LQAC)开始，这些类星体的初始光学位置可以在USNO B1.0和GSC2.3星表中找到，也可以从SDSS Data Release 5中找到。初始位置接下来被放置到基于UCAC2的参照系中，随后是与ICRF的对准，当存在可靠的光学对应物时，在其中添加了来自VLBA校准器列表和VLA校准器列表的最精确的来源。最后，通过球谐函数检查LQRF轴，以定义右升、赤纬和震级项。结果。LQRF包含100,165个类星体，它们很好地横跨天空，从−83.5到+88.5◦的赤纬，是相邻元素之间平均距离的10弧度。与ICRF的全球对准为1.5 mA，单个位置的精度由泊松分布表示，该分布在赤经139 mA和赤纬130 mA处达到峰值。作为副产品，所有使用的星表(SDSS DR5除外)都有显著的赤道改正，可以讨论GSC2.3中间和微弱区域的经验震级改正，2MASS和初步最北端的UCAC2位置的天体测量结果与UCAC2主星表一致，而且调和项总是很小。结论。LQRF包含J2000参考赤道坐标，并由LQAC提供的红移和测光信息补充。它被设计成一个天体测量框架，但它也是GAIA任务初始类星体列表的基础，可以作为类星体空间分布和光度函数研究的试验台。LQRF将在实现新的类星体识别和使用的天体测量框架的更新版本时进行更新。在后一种情况下，它本身可以用来检查这些帧之间的关系。
Context. The large number and all-sky distribution of quasars from different surveys, along with their presence in large, deep astrometric catalogs, enables us to build of an optical materialization of the International Celestial Reference System (ICRS) following its defining principles. Namely: that it is kinematically non-rotating with respect to the ensemble of distant extragalactic objects; aligned with the mean equator and dynamical equinox of J2000; and realized by a list of adopted coordinates of extragalatic sources. Aims. The Large Quasar Reference Frame (LQRF) was built with the care of avoiding incorrect matches of its constituents quasars, homogenizing the astrometry from the different catalogs and lists in which the constituent quasars are gathered, and attaining a milli-arcsec global alignment with the International Celestial Reference Frame (ICRF), as well as typical individual source position accuracies higher than 100 milli-arcsec � . Methods. Starting from the updated and presumably complete Large Quasar Astrometric Catalog (LQAC) list of QSOs, the initial optical positions of those quasars are found in the USNO B1.0 and GSC2.3 catalogs, and from the SDSS Data Release 5. The initial positions are next placed onto UCAC2-based reference frames, This is followed by an alignment with the ICRF, to which were added the most precise sources from the VLBA calibrator list and the VLA calibrator list – when reliable optical counterparts exist. Finally, the LQRF axes are inspected through spherical harmonics, to define right ascension, declination and magnitude terms. Results. The LQRF contains 100,165 quasars, well represented accross the sky, from −83.5 to +88.5 ◦ in declination, being 10 arcmin the average distance between adjacent elements. The global alignment with the ICRF is 1.5 mas, and the individual position accuracies are represented by a Poisson distribution that peaks at 139 mas in right ascension and 130 mas in declination. As a by-product, significant equatorial corrections are found for all the catalogs used (apart from the SDSS DR5), an empirical magnitude correction can be discussed for the GSC2.3 intermediate and faint regimes, both the 2MASS and the preliminary northernmost UCAC2 positions are shown of astrometry consistent with the UCAC2 main catalog, and the harmonic terms are found to be always small. Conclusions. The LQRF contains J2000 referred equatorial coordinates, and is complemented by redshift and photometry information from the LQAC. It is designed to be an astrometric frame, but it is also the basis for the GAIA mission initial quasars’ list, and can be used as a test bench for quasars’ space distribution and luminosity function studies. The LQRF is meant to be updated when new quasar identifications and newer versions of the astrometric frames used are realized. In the later case, it can itself be used to examine the relations between those frames.