Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties (1609.04172v1)

Abstract: At about 1000 days after the launch of Gaia we present the first Gaia data release, Gaia DR1, consisting of astrometry and photometry for over 1 billion sources brighter than magnitude 20.7. We summarize Gaia DR1 and provide illustrations of the scientific quality of the data, followed by a discussion of the limitations due to the preliminary nature of this release. Gaia DR1 consists of: a primary astrometric data set which contains the positions, parallaxes, and mean proper motions for about 2 million of the brightest stars in common with the Hipparcos and Tycho-2 catalogues and a secondary astrometric data set containing the positions for an additional 1.1 billion sources. The second component is the photometric data set,consisting of mean G-band magnitudes for all sources. The G-band light curves and the characteristics of ~3000 Cepheid and RR Lyrae stars, observed at high cadence around the south ecliptic pole, form the third component. For the primary astrometric data set the typical uncertainty is about 0.3 mas for the positions and parallaxes, and about 1 mas/yr for the proper motions. A systematic component of ~0.3 mas should be added to the parallax uncertainties. For the subset of ~94000 Hipparcos stars in the primary data set, the proper motions are much more precise at about 0.06 mas/yr. For the secondary astrometric data set, the typical uncertainty of the positions is ~10 mas. The median uncertainties on the mean G-band magnitudes range from the mmag level to ~0.03 mag over the magnitude range 5 to 20.7. Gaia DR1 represents a major advance in the mapping of the heavens and the availability of basic stellar data that underpin observational astrophysics. Nevertheless, the very preliminary nature of this first Gaia data release does lead to a number of important limitations to the data quality which should be carefully considered before drawing conclusions from the data.

• The paper presents a groundbreaking release of Gaia astrometric data, merging Hipparcos and Tycho catalogs for precise star measurements.
• It details robust photometric observations in the G-band and time-series data for variable stars to enhance calibration and modeling.
• The findings significantly improve cosmic distance scales and stellar mapping while noting systematic limitations for future data refinements.

Overview of Gaia Data Release 1

The document in question provides a comprehensive summary of Gaia Data Release 1 (DR1), which delivers astrometric and photometric data for over a billion celestial sources. This release represents a milestone in the Gaia mission, offering essential information that significantly enhances our understanding of stellar and galactic structures through unprecedented accuracy and scope in astrometric and photometric observations.

Core Components and Methodology

Gaia DR1 is composed of three main data components:

1. Astrometric Data Set:
   • Primary Astrometric Data: Contains positions, parallaxes, and proper motions for approximately 2 million stars. Notably, it merges Gaia data with legacy Hipparcos and Tycho catalogues, forming the Tycho-Gaia Astrometric Solution (TGAS).
   • Secondary Astrometric Data: Provides positional information for an additional 1.1 billion sources.
2. Photometric Data Set: This includes mean G-band magnitudes for all sources, where the Gaia G-band is a white-light photometric band, covering a broad range (330–1050 nm).
3. Variable Star Data Set: Photometric time-series data for about 3,000 variable stars, including Cepheid and RR Lyrae stars, highlighting high-cadence observations around the south ecliptic pole.

Results and Limitations

Gaia DR1 offers unparalleled precision, with typical uncertainties for the positions and parallaxes of primary stars around 0.3 mas and proper motions around 1 mas/yr. The secondary data set provides positional uncertainties of approximately 10 mas. These measurements are critical for many astronomical applications, including calibrating cosmic distance scales and refining models of stellar evolution.

Nevertheless, the release also includes limitations due to its preliminary nature. The data processing strategy employed for this release was not fully iterative and relied on a restricted calibration model. Thus, the astrometric data is subject to systematic errors, particularly color-dependent and spatially correlated systematics, potentially reaching up to 0.3 mas. The completeness of the star catalog is likewise affected by the constraints of initial data collection protocols and processing models, which will be addressed in future data releases.

Implications and Future Developments

Gaia DR1 represents a foundational advance in astrometry and photometry, paving the way for a transformative understanding of the cosmos. By offering high-precision parallax and motion data on a massive scale, this release sets the stage for advancements in a broad array of fields, from mapping the Milky Way to exoplanet discovery and beyond. Moreover, the release is expected to stimulate the astronomical community's scrutiny and refinement of results, ultimately leading to improved data processing techniques and insights in subsequent releases.

Anticipation surrounds the subsequent data releases, particularly Gaia DR2, which will include radial velocities and factor in the drawbacks of DR1 through enhanced calibration and data processing methodologies. Ultimately, Gaia's mission completion is expected to revolutionize our comprehension of fundamental astronomical questions, transforming astrological catalogs into more accurate celestial cartographies for broader scientific applications.