FAQ - Gaia Users
Frequently Asked Questions
Gaia Archive and Gaia data
Planned maintenance to the Gaia Archive is announced through Gaia Cosmos and/or through a pop-up warning at the Gaia Archive. If you cannot access the Gaia Archive, and the unavailability of the Gaia Archive is not announced there, please contact us through the Gaia Helpdesk.
The first aid solution to most issues with the Gaia Archive GUI (from seemingly disappeared tables or strange behaviour after a query or problems signing in or out), is to close your browser, clear your cache and then retry. In most cases, this will solve things and you will be able to continue working in no time.
A second solution might be to switch browsers. Some browsers show more hickups than others in combination with the use of the Gaia Archive GUI.
Assumed is that you entered the Gaia Archive with a registered account. A registered account has the benefits of a dedicated user space with more space and larger quota. If you get an error message that you have exceeded your file quota, but you did not according to the information in your account, first check if you have jobs that failed to complete. You could see whether deleting the jobs that failed. solves the issue. Even though they seem to take up no space (0 bytes), sometimes they do and deleting them will free up space.
Another quick test to try and see if you can solve the exceeded file quota yourself, is to clear your cache (so close your browser and start a new private window) and then check again.
The Gaia Archive team is continuously working towards making the Gaia Archive more efficient and easy to use. New releases of the Gaia Archive come out at regular intervals. Service interruptions are announced beforehand in the GUI (one-time pop-ups). On the Gaia Archive "New Releases" page you can find information on the current and previous releases.
This table provides a link between the HEALPix identifier (level 6, so Nside = 2^6 = 64) and equatorial, Galactic, and ecliptic coordinates. The text file has four header lines and 49152 lines, each with seven columns separated by commas:
- HEALPix identifier [nest scheme, Gaia default]
- Right ascension [deg]
- Declination [deg]
- Galactic Longitude [deg]
- Galactic Latitude [deg]
- Ecliptic Longitude [deg]
- Ecliptic Latitude [deg]
- HEALPix identifier [ring scheme]
The conversion from Gaia source_id to HEALPix number with nest pixel ordering is described here. The built-in Archive function GAIA_HEALPIX_INDEX(order, source_id) can be used to do the transformation within ADQL queries, more details at the Archive Help - ADQL syntax (part 3). Additional functions available. Read here about ring and nested HEALPix ordering.
This is the unavoidable consequence of using the Initial Gaia Source List (IGSL) for bootstrapping the cross-match procedures for Gaia Data Release 1. The IGSL is a collection of multiple, incomplete pre-Gaia catalogues, known to contain spurious and duplicate sources. To avoid dropping Hipparcos stars in the IGSL, those entries not matched were added as a "fake" Tycho-2 star with Tycho-2 identifier idTYCHO = 9999999000000+idHIP. Because of a bug in the matching procedures, approximately 12000 Hipparcos stars have been entered twice. These can be identified as objects with auxHIP = 1 and idTYCHO > 9999999000000 and should not be used.
The Gaia Archive data model (column description, units, etc.) along with the extensive documentation of the data and its processing can be found here, with the opportunity to download the full data release documentation.
There are limits on how much data can be retrieved via ADQL (TAP) and how long a query can last. They are different for anonymous and registered (authenticated) users.
Anonymous access (as documented here):
- Synchronous query time-out: 30 s
- Maximum number of rows if execution time <30s: 3,000,000
- Maximum number of rows if execution time >=30s: 2,000
- Asynchronous query time-out: 90 min
- Maximum number of rows: 3,000,000
Authenticated users (after login):
- Synchronous query time-out: 60 s
- Maximum number of rows if execution time <60s: unlimited
- Maximum number of rows if execution time >=60s: 2,000
- Asynchronous query time-out: 120 min
- Maximum number of rows: unlimited
- User space:
- Jobs (ADQL query output): 20 GB
- User tables: 1 GB
The DataLink maximum number of sources that can be retrieved is equal for registered and anonymous users: 5,000 per query.
Anybody can self-register for a Gaia ESA Archive user account through this page and then "SIGN IN" using the button in the top-right corner of the Gaia Archive, after which the reported user quota apply. In exceptional cases, upon demonstrated need, users can request (temporary) changes to their quota by sending a motivated request to the Gaia Helpdesk.
These stars might be too bright for Gaia. They saturate the sensitive CCD detectors on-board of Gaia. The brightest object included in Gaia DR2 has a G magnitude (phot_g_mean_mag) of 1.71 but incompleteness is large until G ≈ 3. So practically, no star visible to the naked eye made it into Gaia DR1. More information on this topic can be found in the Gaia Data Release documentation or more specifically here.
A five-parameter astrometric solution, including proper motions and parallaxes, has been computed for a sub-sample of about 1,3 billion sources of the total of 1,7 billion sources in Gaia Data Release 2; and has been computed for the TGAS sub-sample comprising circa 2 million sources in Gaia Data Release 1. More information can be found here.
Negative parallaxes are caused by errors in the observations. Even if a negative distance has no physical meaning, there are a certain number of stars expected to have negative parallaxes just from an error propagation perspective. The negative parallax tail is a very useful diagnostic on the quality of the astrometric solution. Further details can be found here and here.
There are two ways to do this:
- Basic tab: create a list of RA DEC coordinates (no header, one entry per line, separated by spaces) and upload them to the Archive as explained in this tutorial.
- Advanced (ADQL): follow the White Dwarfs Exploration tutorial here.
The file to be uploaded to the
basic tab of the Gaia Archive online search tool requires a specific format. The description of the format can be found by hoovering the mouse over the "Select a file with Target Names" and clicking once the question mark appears.
The input file has no header and one entry per line. Three different name resolvers are tried: Simbad, NED and Vizier. An intermediate job with the retrieved source properties (name, coordinates, parallax and proper motion, if available) is created and cross-matched against the Gaia Archive. A mixture of object names and positions in the sky (see previous FAQ) is allowed.
This problem most likely originates from the way Python is installed. Native Python distributions (e.g. those downloaded from python.org) include an “Install Certificate” script that install a set of SSL certificates. However, this is not the case if the user is running the Python distribution that comes along with the Conda package. A workaround is to execute the following command in a terminal:
The simplest way to do this is to manually select all the jobs that are listed in the Archive and then press the "Delete selected jobs" button on the bottom right corner of the Archive webpage. An alternative to this potentially tedious task is to use the Astroquery.Gaia Python module (link).
The steps to do this are detailed below:
from astroquery.gaia import Gaia Gaia.login() jobs = [job for job in Gaia.list_async_jobs()] # To print all the jobs owned by the user: for job in jobs: print(job.jobid) # To remove all the jobs at once: job_ids = [job.jobid for job in jobs] Gaia.remove_jobs(job_ids)
A dedicated website for the scientific community using Gaia data is in place: Gaia Cosmos. Gaia data release information is available from this website, as well as information on upcoming data releases. A set of frequently asked questions on the Gaia Mission and Gaia Data Releases can be found here.
First check out the internet and perform a search with your question. You probably find that the answer to your question is already around on one of the Gaia information pages. There might be an answer available already from the Gaia FAQ (answering questions on the Gaia Mission and Data Releases).
Please also have a look at the Gaia Archive help pages which contains lots of helpful information and tutorials or perform a search through the Gaia Data Release Documentation and the Gaia Data Release papers (Gaia DR1, Gaia DR2). The question might be hidden in the information on some other Gaia Cosmos page or Gaia pages of our DPAC partners. When not sure what information is around for a certain data release, check out the overview pages for each release: Gaia Data Release 1, Gaia Data Release 2 and Gaia Early Data Release 3.
If the internet search is not providing you with answers to your question, feel free to contact the Gaia Helpdesk. The Gaia Helpdesk helps out with questions on the Gaia Archive, use of the Gaia Archive, content of the Gaia Archive and more.
Many of the catalogues hosted by the Gaia Archive (including the entire Gaia DR1, DR2, and eDR3 source catalogues) are available for bulk download in plain text (comma separated value, csv) format via the "Download" button visible in the landing page of the Archive. Because of the large volume of the data, the catalogue content is split in multiple files. To download all these files at once, it is suggested to use the "wget" command from a terminal. For example, the entire Gaia eDR3 source catalogue can be downloaded to the user local machine by typing the command:
wget --recursive --no-parent 'http://cdn.gea.esac.esa.int/Gaia/gedr3/gaia_source/'
The Astroquery.Gaia Python module (included in Astroquery, an Astropy affiliated package) is under continuous development. When a new Astroquery version is released it can happen that, during a few weeks, the Astroquery.Gaia documentation is updated although its associated Python module remains the same when trying to install it via e.g.
$ pip install astroquery
In order to install the most up-to-date version of Astroquery you can type:
$ pip install --pre astroquery
If Astroquery is already installed in your machine, then make sure to include the --upgrade install option:
$ pip install --pre --upgrade astroquery
The ADQL language is case-insensitive (unless double quotes are used; see Sects. 2 and 2.1.7 of the ADQL 2.1 recommendation standard). Because of this, if a table uploaded by a user contains column names with uppercase letters, the Gaia ESA Archive will automatically convert them to lowercase letters. To learn how to upload a table to the Archive please take a look at this tutorial.
Duplicate sources are produced when the Gaia on-board detection software receives multiple triggers from one object. Although most multiple detections are successfully filtered out on ground, it can happen that the same celestial object has more than one source_id. The on-board detections originating from the same source are divided between the two sources, typically in such a way that one source has reliable astrometry with many transits whereas the other has suspect astrometry and a limited number of transits. Any duplicates with projected separation below 0.18” have been filtered out in Gaia EDR3, and for each duplicate only the source with the best astrometric solution has been kept in the catalogue. Although unlikely, it is possible that sources having a projected separation above 0.18” and nearly identical astrometry and photometry are duplicates. Would that be the case, we recommend to use quality indicators (like those indicated in Sect. 3.1 of the Gaia EDR3 summary article) to asses which one of the solutions contains the best astrometry.
The binary_masses table is described in Gaia Data Release 3: Stellar multiplicity, a teaser for the hidden treasure (Gaia Collaboration, Arenou et al. 2022). Indeed, a few thousand entries in this table have fluxratio <= 0 and 2996 actually also have fluxratio_upper <= 0. Most of such cases are a natural outcome of the estimation process for fluxratio that has been used, analogous to the presence of negative parallaxes.
Symbolically speaking, with R denoting the flux ratio F2/F1, the (linear) semi-major axis of the astrometric photocentre equals a0= a (M2/(M1+M2) - F2/(F1+F2)) = a1 – a R / (1+R), where a denotes the relative semi-major axis. As a result, R is estimated using 1 / R = a / (a1-a0) – 1.
In the processing for Gaia DR3, R has been estimated using a0 from the astrometric processing of non-single stars, a1 = a1 sini / sini from the spectroscopic and astrometric processing, a from the period, M1 from the Hertzsprung-Russell diagram, and M2 from the spectroscopic mass function. Clearly, R is an estimated quantity with uncertainties (fluxratio_lower and fluxratio_upper). Although the true R is physically positive, estimates of it can be negative within the quoted uncertainties. Extreme cases, meaning when the flux ratio and its uncertainties are very unlikely compatible with being positive, point at special systems (for instance ternary systems) and/or inconsistencies in the astrometric and spectroscopic Gaia DR3 data processing of the object (for instance, when a0 >> a1, R would be negative, and in such cases, the spectra of the two components would not necessarily be resolved so that the “spectrocentre” variations could be measured instead). Such cases should obviously be treated with care.
The nss_two_body_orbit table is described in Gaia Data Release 3: Stellar multiplicity, a teaser for the hidden treasure (Gaia Collaboration, Arenou et al. 2022). Indeed, in this table, the inclination is provided explicitly only for eclipsing binaries. However, for astrometric and combined astrometric-spectroscopic orbits, the Thiele-Innes orbital elements (A, B, F, G) rather than the Campbell elements (a0, i, Ω, ⍵) are provided. In these cases, the inclination (plus the two other angles as well as the semi-major axis of the photocentre) can be computed using the Python (or R) code provided on https://www.cosmos.esa.int/web/gaia/dr3-nss-tools.