SIMBAD: Query objects from criteria


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Sampling is done by writing a combination of constraints pretty much like the \itf where part of a SQL statement, but without having to know anything about the structure of the database.

The available criteria are presented on the web page, with the allowed operators for each criteria.

This page contains detailed information on particular topics.

Constraints

A single constraint has always the syntax:

criterion_name operator value

The criterion name must be taken from the large list displayed on the web page.

The operator must be one of the operators available for the criterion. They are described below.

The value can be a numeric one (i.e. 12.35), a string enclosed in single quotes (i.e. 'star') or a list of items enclosed in parenthesis, associated with the 'IN' operator (i.e. ('hip','ppm'). If the items contain no spaces, the quotes can be ommited for strings (i.e. (hip,ppm))

An exception to this syntax is made by the region criterion (see below) which represents a constraint by itself, without operator, nor value.

Complex constraints can be build by combining single criterions with and ('&') and or ('|') operators and parenthesis to group sub-expressions.

Examples:

Operators

Each criterion – except the region criterion – can use one or several operators Depending on a given criterion, These operators are:

operator   description   example
=   equality   otype = '*'
!=   not equal   otype != 'galaxy'
<   less than   ubv.v < 5.5
<=   less or equal than   sptype <= 'G5'
>   greater than   pm > 10
>=   greater or equal than   redshift >= 1.0
  contains the wildcard expression   author ∼ 'egret*'
!∼  does not contain the wildcard expression  
in   contains at least one value among the list   cat in ('hd','hip','ppm')

Particular cases

Coordinate regions

This criterion defines a region in the sky. It can be combined with any other criteria. Unlike others, it doesn't need an operator, nor a comparison value.

The region criterion has two syntaxes, and accepts many default values, simplifying its writing:

The different options are:

Regions can also be combined using and (&) and or (|) operators and combined with other criteria:

(region(rotatedbox, gal, 120.10 -10.10, 5d 30m, 45)
| region(rotatedbox, gal, 120.10 -10.10, 5d 30m, -45))
& Vmag > 5.0

Proper motion

The pm criterion is done on the euclidian norm of pmra,pmdec.
pm = sqrt(pmra2+pmdec2)

Spectral types

A spectral types represent a complex data piece, and has therefore several criteria:

All details concerning spectral type writing can be found here.

Object types

Object types build a hierarchy defined here.

Each astronomical object has a main type defined, and several other types generally infered from its identifiers.

Therefore, there are four different object type criterions:

Example:
otype = 'Pu*' retrieves all objects having exactly the generic type 'Pulsating variable star'. otypes = 'Pu*' retrieves all objects having this type or any more specific type like Mira Cet, RR Lyr, Cepheid, and so on..

Author names

Author names always contain the last name followed by the first name letters. Queries are case insensitive.
One must be careful in the usage of the operators:


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2017.11.20-13:00:55

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