# 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:

• dec > 85 & (cat = 'hip' | cat = 'ppm') & radvel > 10
Get all objects having a declination over 85 deg, a radial velocity over 10 km/sec and being in either the hipparcos or the ppm catalog.

• region(GAL,180 0,2d) & otype = 'G' & (nbref >= 10|bibyear >= 2000)
Find all galaxies in a 2 deg radius circle around the anti galactic center and having not less than 10 bibliographic references or references earlier then 2000.

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:

• region(shape, frame, epoch, equinox, coordinates, dimension, angle)
for querying by coordinates in any frame
• region(shape, identifier, dimension, angle)
for querying around a given identifier

The different options are:

• shape It defines the kind of region. The following shapes are available:

• CIRCLE : A circle defined by the coordinates of the center and the radius as dimension parameter. It is the default region type, and may be omitted.
Example: region(circle, gal, 123.5 -17.8, 0.5d)

• ELLIPSE : An ellipse defined by the coordinates of the center and the major and minor axes as the dimension parameter. The ellipse angle is the last parameter.
Example: region(ellipse,12 30 +10 10,1d 0.5d,45)

• ZONE : A zone is defined by two small circles (declination = constant) and two great circles (right ascension = constant). The coordinates parameter defines the center, and dimension defines the size in r.a. and decl.
Example : region(zone,10 30 +60 10, 3d 10m)

• BOX : A box is defined by great circles in right ascension and declination. The coordinates parameter defines the center, and dimension defines the size in r.a. and decl.
Example : region(box,10 30 +60 10, 3d 10m)

• ROTATEDBOX : Like a box. The rotation angle is a extra parameter after the dimension parameter.
Example: region(rotatedbox,10 30 +60 10, 3d 10m,45)

• POLYGON : A polygon defined by the coordinates of every node. No dimension parameter is needed.
Example : region(polygon gal,123 -10,124 -9,127 -12)

• frame The coordinate frame is expressed by one of the following keywords:
ICRS,FK5,FK4,GAL,SGAL,ECL. The default is ICRS

• epoch The coordinate epoch. If present, this parameter must be prefixed by B or J. Epoch can be a decimal number (i.e. B1950.5, J2007.43). The default is J2000.

• equinox An equinox, needed for some frames (FK4). It is a decimal number. The default is 2000.

• coordinates They always contain a longitude and a latitude. The latitude must be preceeded by a sign. They can be either given as decimal numbers, which are always degrees or sexagesimal values, which represent by default hours for the right ascension. For defining a POLYGON, coordinates are made of a comma separated list of node coordinates, each of them contaiing a longitude and a latitude.

• dimension Dimension are defined by one value for a circle, two values for an ellipse, a zone, a box and a rotatedbox. By default the unit is arcmin. Arcsec, arcmin or degrees can be explicitely specified by suffixing the radius by the letters 's', 'm' or 'd'. The default radius is 10m.
Example: 300s, 5m, 0.08333d

• angle an ellipse and a rotatedbox require an angle parameter. It must be expressed in degrees.
Example: 30, -45, 10.5

• identifier a valid simbad identifier of an object having coordinates. Its coordinates will be used as the center of the region. Frame, epoch and equinox used are those of Simbad: ICRS,J2000,2000. This region definition cannot be used with a polygon. An identifier must be surrounded with single quotes if it contains commas, otherwise the quotes are optional.

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:

• sptype which is used to retrieve the objects having exactly the requested type.
I.e. sptype = 'K0' will return only objects having 'K0' alone as spectral type.
• sptypes which should be used to retrive all objects having a spectral type containing the one specified.
I.e. sptypes = 'K0' will return all objects having 'K0' as a spectral type, but also 'K0III' or 'K0IIIp', ...).
• splum can be used to retrieve objects having a given luminosity class.
I.e. splum = 'III', splum >= 'IV'.
Equality operator does not include luminosity with uncertainty (':' suffix). To include those in the query, it is needed to query
splum = 'II' | splum = 'II:' or
splum in ('II', 'II:').
• sppec allows queries only by spectral type peculiarities.
I.e. sppec in ('cn','m').

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:

• maintype and otype looks for objects having exactly the requested type, either as the main type or any type.

• maintypes and otypes retrieves all objects having the given type or any type underneath the given one in its hierarchy sub-tree.

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:

• '=' (equal) means that the name you type must be exactly the one in the database:
author = 'egret d.' for instance will work, but not author = 'egret'.
• (tilde) means that the name you are searching will be appended by a '*' as wildcard, if you don't write your own wildcards:
author ∼ 'jaschek' will return all objects having a reference with JASCHEK C., JASCHEK M., JASCHEK-CORVALAN M. or JASCHEK C.O.

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