Gaia DR1

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Accumulation of objects in the firmament.
Color coding: none / extremely little! ! ! ! ! ! ! many objects per square degree

Gaia DR1 is a star catalog of approximately 1.1 billion objects, which is mainly based on the observations of the Gaia space probe , taking into account some of the data from the Hipparcos mission . Gaia DR1 is an abbreviation for Gaia Data Release1 , the first major release of data on September 14, 2016 as part of several publications up to the final data catalog of the Gaia mission.

Data basis

The DR1 data is based on Gaia's observations from July 25, 2014 to September 16, 2015. Before publication, the objects had to meet certain criteria, in particular the data had to have a certain minimum number of observations and be below a statistical uncertainty, so that in certain areas clear gaps can be found especially along the ecliptic. The Initial Gaia Source List was used to identify the objects, which is compiled from a series of catalogs that roughly represent the level of knowledge at the beginning of the mission.

An observation time of a little more than a year is too short to be able to reliably distinguish the proper movement or angular velocity from the parallax and movements around a barycentre in the presence of massive exoplanets. Thus, Gaia DR1 mainly contains position data and Gaia magnitudes .

Tycho-Gaia Astrometric Solution (TGAS)

Position, parallax (distance), and angular velocity for more than 2 million stars were determined using Tycho-Gaia Astrometric Solution (TGAS). Only the position data from the Hipparcos and Tycho-2 catalogs were included and used together with the positions of Gaia to calculate the angular velocities and parallaxes. There is a period of about 25 years between the data from Hipparcos or Tycho-2 and those from Gaia. This enabled the calculation of the proper movement with an uncertainty of a few milli-arcseconds per year. The proper movements and parallaxes calculated in the previous catalogs were not used for TGAS. The typical uncertainty of the stars of TGAS is ± 0.3 milli-arcsecond (mas) for positions and parallaxes and 1 mas per year for proper motions.

In the run-up to TGAS there was the Hundred Thousand Proper Motions ( HTPM ) project. Together with the first Gaia data for the hundred thousand stars in the Hipparcos catalog, the project should achieve an accuracy in right ascension of 65 μas / year and in declination of 48 μas / year for proper motion. For stars with a known radial speed of up to 1–2 km / s, the accuracy should be 10 μas / year. The results should then be used to update the Hipparcos catalog. With TGAS the project was obsolete.

Result

On September 14, 2016, the first larger, as yet incomplete data sets for 1.1 billion objects were published (Gaia DR1). 400 million of them were not cataloged before. There is a lack of information about very bright objects with a magnitude of G Insbesondere 7. Particularly in very densely populated regions, there is a lack of data on less light objects, while in less populated regions even faint objects with a magnitude of G ≥ 20 were recorded. Faint objects in close proximity to bright objects are sometimes missing. Objects with a large apparent movement are missing, as are very red or very blue objects. Double stars with a distance of less than 4 aa are not yet resolved with optimal results.

Gaia DR 1 contains measurements of over 2000 quasars from the International Celestial Reference Frame , the positions of which have already been measured to 40 micro-arcseconds (μas) and which can serve as the Gaia Celestial Reference Frame 1 ( GCRF1 ) as a reference frame. Most quasars are extremely far away, so that their proper motion and parallax are negligibly small.

All data from DR1 can be accessed via the Internet in the Gaia archive.

The result of DR1
Type of objects number available data
Total number of objects (two parameters) 1,142,679,769 Position (α, δ), G-band magnitude (G)
TGAS objects (five parameters)
  • Of which: Hipparcos
  • Of which: Tycho-2 without Hipparcos
 2,057,050
93,635
1,963,415 		Position (α, δ), G-band magnitude (G), parallax , angular velocity (μ α , µ δ )
Objects with intensity curves 3,194
2,595
599 		Position, intensity curves
ICRF quasars or

Gaia Celestial Reference Frame 1

2.152 Position, G-band magnitude

Deviations:
G <17: ~ 0.25 mas
G = 20: some mas
<1 mas for 44% and <10 mas for 94% of the objects

In the neighboring galaxy M33 , 2.4 million light-years away , Gaia recorded approximately 40,000 of the brightest of the galaxy's estimated 40 billion stars.

New discoveries

Not only were many faint objects re-cataloged as expected, but unexpected discoveries were also made. One of the bigger surprises is the discovery of a large star cluster that had previously escaped observation. With a simple counting of the objects already used by Wilhelm and Caroline Herschel in relation to certain units of area, Sergey E. Koposov found a significant accumulation of objects in the area of Sirius . The discovery initially looked like artifacts, i.e. apparent objects that are created by the intense overexposure to Sirius, but the high number of objects found did not correspond to the amount of artifacts that Sirius expected. The new star cluster is named Gaia 1, another newly found star cluster was named Gaia 2.

more publishments

  • The second Gaia catalog ( Gaia DR2 ) was published on April 25, 2018. It contains almost 1.7 billion objects, of which 1.3 billion have their own movements and parallaxes.
  • The Gaia DR3 catalog should come out in early 2021. According to the new plan, DR3 is to be published in two parts. The first part under the name Gaia EDR3 with around 1.8 billion is planned for the end of 2020 and should contain improved astrometry and photometry such as B. star locations, parallaxes, proper motion, three-band photometry as well as quasars and extensive objects.
  • The second part of Gaia DR3 with the remaining more complex data is expected to come out in the second half of 2021. In addition to the data from EDR3, DR3 should also include the spectroscopic and photometric object classifications for easily evaluable objects, RVS spectra and information on the stellar atmosphere, radial velocities, classifications for variable stars with photometric curves, catalogs of objects of the solar system with preliminary orbital data and individual data about their observations contain.
  • Gaia DR4: The publication for the data obtained during the official mission period (until July 15, 2019) was originally expected towards the end of 2022. The provisional publication date has been withdrawn and a new date has not yet been published. This includes all astrometric and photometric data, all variable stars, all double and multiple star systems, classifications and various astrometric data for stars, unresolved double stars, galaxies and quasars, a list of exoplanets, all epochs and transit dates for all objects.Template: future / in 2 years
  • Gaia DR5: Due to the official mission extension, further publications will follow. The last publications are expected two to three years after the end of the probe operation at the earliest.

Hot Stuff for One Year (HSOY)

The previously known data together with the results of Gaia DR1 allowed a further development of the data situation in order to bridge the time between the publication of DR1 and DR2. The Hot Stuff for One Year (HSOY) data was calculated from Gaia DR1 data and terrestrial astrometry from the PPMXL catalog in the same way as the PPMXL catalog was calculated. In this way, the proper motion could be calculated for 583 million stars and the values ​​achieved the high precision in the position of Gaia and proper motions with a precision of significantly less than 1 to 5 mas / year, depending on the brightness and sky position. The catalog does not contain parallaxes, so the catalog has four parameters.

literature

  • Gaia Collaboration: Gaia Data Release 1; Documentation release 1.2 . Ed .: European Space Agency and Gaia Data Processing and Analysis Consortium. December 18, 2017 ( esa.int [PDF]).

Individual evidence

  1. ^ A b Daniel Michalik, Lennart Lindegren, David Hobbs: The Tycho-Gaia astrometric solution; How to get 2.5 million parallaxes with less than one year of Gaia data . December 24, 2014, doi : 10.1051 / 0004-6361 / 201425310 ( aanda.org [PDF]).
  2. ↑ Lennart Lindegren, U. Lammers, U. Bastian et al .: Gaia Data Release 1 - Astrometry: one billion positions, two million proper motions and parallaxes . November 2016, doi : 10.1051 / 0004-6361 / 201628714 ( aanda.org [PDF]).
  3. ^ F. Mignard: The Hundred Thousand Proper Motions Project . GAIA-C3-TN-OCA-FM-040-01. Ed .: DPAC. October 21, 2009 ( esa.int ).
  4. ↑ Detailed map shows Milky Way is bigger than we thought. September 14, 2016, accessed September 16, 2016 .
  5. ↑ a b Gaia DR1 - Cosmos. Retrieved August 6, 2017 (UK English).
  6. ↑ Gaia's billion-star map hints at treasures to come. ESA press release, September 13, 2016.
  7. ↑ F. Mignard, S. Klioner, L. Lindegren et al .: Gaia Data Release 1; Reference frame and optical properties of ICRF sources . November 2016, p. 2 , doi : 10.1051 / 0004-6361 / 201629534 ( aanda.org [PDF]).
  8. ↑ Gaia Archives. Retrieved August 6, 2017 .
  9. ↑ Gaia Collaboration: Gaia Data Release 1; Summary of the astrometric, photometric, and survey properties . Astronomy & Astrophysics, August 31, 2016, p. 4 , doi : 10.1051 / 0004-6361 / 201629512 ( aanda.org [PDF]).
  10. ↑ F. Mignard, p Klioner, L. Lindegren, U. Bastian, A. Bombrun: Gaia Data Release 1: Reference frame and optical properties of ICRF sources . In: Astronomy & Astrophysics . tape 595 , November 2016, ISSN  0004-6361 , p. A5 , doi : 10.1051 / 0004-6361 / 201629534 ( aanda.org [accessed August 24, 2020]).
  11. ↑ An extragalactic star-forming region. Retrieved August 5, 2017 (UK English).
  12. ↑ How do you find a star cluster? Easy, simply count the stars. Retrieved November 21, 2017 (UK English).
  13. ↑ a b Data Release scenario. ESA, 2017, accessed September 4, 2017 .
  14. ^ M. Altmann, S. Roeser, M. Demleitner, U. Bastian, E. Schilbach: Hot Stuff for One Year (HSOY); A 583 million star proper motion catalog derived from Gaia DR1 and PPMXL . Ed .: A&A. January 4, 2017, doi : 10.1051 / 0004-6361 / 201730393 .

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