The Gaia spacecraft of the European Space Agency (ESA) has been securing
observations of solar system objects (SSOs) since the beginning of its
operations. Gaia Data Release 2 (DR2) contains the observations of a selected
sample of 14,099 SSOs. These asteroids have been already identified and have
been numbered by the Minor Planet Center. Positions are provided for each Gaia
observation at CCD level. As additional information, the apparent brightness of
SSOs in the unfiltered G band is also provided for selected observations. We
explain the processing of SSO data, and describe the criteria we used to select
the sample published in Gaia DR2. We then explore the data set to assess its
quality. To exploit the epoch astrometry of asteroids in Gaia DR2 it is
necessary to take into account the unusual properties of the uncertainty, as
the position information is nearly one-dimensional. When this aspect is handled
appropriately, an orbit fit can be obtained with post-fit residuals that are
overall consistent with the a-priori error model that was used to define
individual values of the astrometric uncertainty. The distribution of residuals
allowed us to identify possible contaminants in the data set. Photometry in the
G band was compared to computed values from reference asteroid shapes and to
the flux registered at the corresponding epochs by the red and blue photometers
(RP and BP). The overall astrometric performance is close to the expectations,
with an optimal range of brightness G~12-17. In this range, the typical
transit-level accuracy is well below 1 mas. For fainter asteroids, the growing
photon noise deteriorates the performance. Asteroids brighter than G~12 are
affected by a lower performance of the processing of their signals. The
dramatic improvement brought by Gaia DR2 astrometry of SSOs is demonstrated by
preliminary tests on the detection of subtle non-gravitational effects.

该文介绍了欧洲空间局的 Gaia 航天器及其 Data Release 2 (DR2) 数据，其中包含了 14,099 个太阳系物体的观测数据。论文着重讨论了关于这些数据的处理与精度评估，以及利用它们探测细微非引力效应的可行性。

盖亚数据第二次发布：太阳系物体的观测

Gaia Data Release 2: Observations of solar system objects

This paper describes the Seventh Data Release of the Sloan Digital Sky Survey
(SDSS), marking the completion of the original goals of the SDSS and the end of
the phase known as SDSS-II. It includes 11663 deg^2 of imaging data, with most
of the roughly 2000 deg^2 increment over the previous data release lying in
regions of low Galactic latitude. The catalog contains five-band photometry for
357 million distinct objects. The survey also includes repeat photometry over
250 deg^2 along the Celestial Equator in the Southern Galactic Cap. A
coaddition of these data goes roughly two magnitudes fainter than the main
survey. The spectroscopy is now complete over a contiguous area of 7500 deg^2
in the Northern Galactic Cap, closing the gap that was present in previous data
releases. There are over 1.6 million spectra in total, including 930,000
galaxies, 120,000 quasars, and 460,000 stars. The data release includes
improved stellar photometry at low Galactic latitude. The astrometry has all
been recalibrated with the second version of the USNO CCD Astrograph Catalog
(UCAC-2), reducing the rms statistical errors at the bright end to 45
milli-arcseconds per coordinate. A systematic error in bright galaxy photometr
is less severe than previously reported for the majority of galaxies. Finally,
we describe a series of improvements to the spectroscopic reductions, including
better flat-fielding and improved wavelength calibration at the blue end,
better processing of objects with extremely strong narrow emission lines, and
an improved determination of stellar metallicities. (Abridged)

本文简要介绍了斯隆数字天空巡天 (SDSS) 的第七次数据发现，主要涵盖了光度学、光谱学、测角学等方面，包含了多个方面的观测数据和探测记录，其中数据质量得到大幅提升。

Sloan 数字化天空勘测第七批数据发布

The Seventh Data Release of the Sloan Digital Sky Survey

The Sloan Digital Sky Survey (SDSS) will provide the data to support detailed
investigations of the distribution of luminous and non- luminous matter in the
Universe: a photometrically and astrometrically calibrated digital imaging
survey of pi steradians above about Galactic latitude 30 degrees in five broad
optical bands to a depth of g' about 23 magnitudes, and a spectroscopic survey
of the approximately one million brightest galaxies and 10^5 brightest quasars
found in the photometric object catalog produced by the imaging survey. This
paper summarizes the observational parameters and data products of the SDSS,
and serves as an introduction to extensive technical on-line documentation.

Sloan 数字天文巡天（SDSS）提供支持研究宇宙中光亮和非光亮物质分布的数据，该巡天使用光度和天文度量学校准的数字成像调查，在五个光学波段上提供了约 pi steradians，深度为 g' 约 23 个星等的数据，并在由成像调查生成的光学目标目录中进行了约一百万个最亮星系和 10^5 个最亮类星体的光谱巡视。本文概述了 SDSS 的观测参数和数据产品，并作为广泛在线技术文档的简介。