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SIMBAD Reference

Free reference guide: SIMBAD Reference

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About SIMBAD Reference

The SIMBAD Database Reference is a comprehensive guide for astronomers and astrophysicists working with SIMBAD (Set of Identifications, Measurements and Bibliography for Astronomical Data), the CDS astronomical object database containing over 14 million objects. It covers basic search modes including identifier queries (Messier, NGC, HD, 2MASS designations), coordinate-based cone searches in ICRS/FK5/Galactic frames, reference (bibcode) searches, and criteria-based catalog queries with filters on object type, spectral type, parallax, and radial velocity.

The scripting and API section details SIMBAD TAP (Table Access Protocol) services for SQL-based queries against the database tables. It covers the basic table (main_id, ra, dec, plx_value, rvz_radvel, sp_type, otype), the ident table for cross-identification queries to find all aliases for an object, and the flux table for multi-band photometric data. The SIMBAD script language for batch queries with custom output formatting is also documented.

Python access through astroquery.simbad is covered extensively with working code examples: query_object() for single object lookup, query_region() with SkyCoord and radius for area searches, query_objectids() to retrieve all identifiers, add_votable_fields() to customize return columns (spectral type, V magnitude, parallax), query_bibobj() for paper-based object retrieval, query_catalog() for entire catalog enumeration, and VizieR cross-matching integration. The reference also documents the SIMBAD object type classification system including stellar types (V*, EB*, Ce*, WD*, NS*), galaxy types (SyG, SBG, QSO, AGN), and photometric filter codes (Johnson-Cousins, SDSS, 2MASS, Gaia, WISE).

Key Features

  • Identifier search with support for Messier, NGC, HD, 2MASS, and hundreds of other catalog designations
  • Coordinate cone search in ICRS, FK5, Galactic frames with HMS/DMS, decimal degree, and galactic coordinate input
  • TAP SQL queries against basic, ident, and flux tables with JOIN syntax and object type filtering
  • Python astroquery.simbad code examples: query_object, query_region with SkyCoord, add_votable_fields
  • Complete object type code reference: stellar (V*, EB*, WD*, NS*), extragalactic (G, QSO, AGN, BLL)
  • Spectral type classification system (OBAFGKM) with luminosity class suffixes (I through V)
  • Cross-identification: query_objectids for all aliases, ident table SQL, and VizieR catalog cross-matching
  • Bibcode format reference and query_bibobj/query_catalog for literature-based and catalog-based searches

Frequently Asked Questions

What is SIMBAD and how many objects does it contain?

SIMBAD (Set of Identifications, Measurements and Bibliography for Astronomical Data) is maintained by CDS in Strasbourg, France. It contains over 14 million astronomical objects with their identifiers, coordinates, photometric data, spectral types, and bibliographic references. It provides cross-identification, linking the same object across hundreds of catalogs.

How do I search SIMBAD by coordinates?

Use coordinate cone search with RA and Dec in multiple formats: HMS/DMS (10:45:03.5 -59:41:04), decimal degrees (10.684 -59.684), or galactic coordinates (l=121.17 b=-21.57). Specify a search radius in arcminutes and the coordinate frame (ICRS, FK5, Galactic). SIMBAD returns all objects within the cone sorted by distance from the center.

How do I use TAP SQL to query SIMBAD?

SIMBAD provides a TAP service for SQL queries. The main tables are: basic (main_id, ra, dec, otype, sp_type, plx_value), ident (cross-identification aliases), and flux (photometric magnitudes by filter). Example: SELECT main_id, ra, dec, otype FROM basic WHERE otype = 'QSO' AND dec BETWEEN -30 AND 30 ORDER BY ra. TAP endpoints support ADQL (Astronomical Data Query Language).

How do I access SIMBAD from Python?

Use the astroquery.simbad module: from astroquery.simbad import Simbad. Query a single object with Simbad.query_object("M 31"). Search by region with Simbad.query_region(SkyCoord, radius). Add extra fields with Simbad.add_votable_fields("sptype", "flux(V)", "plx"). Results are returned as astropy Table objects.

What do the SIMBAD object type codes mean?

Object type codes classify astronomical objects: Star (general star), V* (variable star), EB* (eclipsing binary), Ce* (Cepheid), WD* (white dwarf), NS* (neutron star), BH* (black hole candidate), G (galaxy), SyG (Seyfert galaxy), QSO (quasar), AGN (active galactic nucleus), PN (planetary nebula), SNR (supernova remnant), HII (HII region), GClstr (galaxy cluster).

How does cross-identification work in SIMBAD?

SIMBAD links the same physical object across hundreds of catalogs. Use query_objectids("M 31") to get all identifiers: NGC 224, LEDA 2557, UGC 454, 2MASS J00424433+4116074, etc. In TAP SQL, query the ident table by joining on oidref to find all catalog entries for a given object. This is one of SIMBAD's most valuable features for multi-wavelength astronomy.

How do I interpret spectral types in SIMBAD?

Spectral types follow the OBAFGKM sequence from hottest to coolest. The letter is followed by a subtype digit (0-9) and luminosity class: V (main sequence), IV (subgiant), III (giant), II (bright giant), I (supergiant). Examples: O5V (hot main sequence), G2V (Sun-like), M2V (red dwarf), K5III (K-type giant). SIMBAD stores these in the sp_type field.

Can I integrate SIMBAD with VizieR and other tools?

Yes. Use astroquery.vizier to cross-match SIMBAD results with VizieR catalogs (e.g., 2MASS catalog II/246) using the same SkyCoord and radius. SIMBAD supports SAMP protocol for interoperability with DS9 (image viewer), Aladin (sky atlas), and TOPCAT (table analysis). Bibcode queries link directly to ADS (Astrophysics Data System) for full paper access.