Querator Help

Optional Constraints

The only optional constraint currently available is the exclusion of non-scientific exposures. When this option is selected, non-scientific data (e.g. calibration exposures) will be excluded from returned results. The actual condition to exclude these data depends on the selected instrument/archive and its selection is trasparent to the user.

Target Name

The target name which, resolved by SIMBAD, will translate into a pair of coordinates. These, together with the Search Radius, will determine the region of interest on the sky (e.g. NGC 474). If not empty, this field overrides the RA/DEC and Galactic Coordinates fields.

RA/DEC

RA [hours] and DEC [deg] of the object of interest (J2000). These, together with the Search Radius, will determine the region of interest on the sky. If not empty, these fields override the l/b fields. Values can be in decimal or in sexagesimal format. For sexagesimal format, both spaces and colons are valid separators.

Galactic Coord. (l,b)

Galactic Coordinates of the object of interest. These, together with the Search Radius, will determine the region of interest on the sky.

RA Min

The minimum value of the right ascension (in hours) of the region of the sky of interest. This value can be expressed both in decimal hours (e.g. 8.2) and in sexagesimal hours. In the latter case, hours minutes and seconds need to be either blank (e.g., 8 12 00) or colon separated (e.g., 8:12:00).

RA Max

The maximum value of the right ascension (in hours) of the region of the sky of interest. This value can be expressed both in decimal hours (e.g. 8.2) and in sexagesimal hours. In the latter case, hours minutes and seconds need to be either blank (e.g., 8 12 00) or colon separated (e.g., 8:12:00).

DEC Min

The minimum value of the declination (in degrees) of the region of the sky of interest. This value can be expressed both in decimal degrees (e.g. 8.2) and in sexagesimal degrees. In the latter case, degrees arcminutes and arcseconds need to be either blank (e.g., 8 12 00) or colon separated (e.g., 8:12:00).

DEC Max

The minimum value of the declination (in degrees) of the region of the sky of interest. This value can be expressed both in decimal degrees (e.g. 8.2) and in sexagesimal degrees. In the latter case, degrees arcminutes and arcseconds need to be either blank (e.g., 8 12 00) or colon separated (e.g., 8:12:00).

Input File

The Input File field offers users the possibility to upload lists of coordinates or target names (to be resolved by SIMBAD).

The file needs to be in ASCII format. The information in it has to be properly formatted for Querator to be able to correctly parse it. The actual format is specified via the Format popup menu (see below).

Format

This popup menu defines the format of the Input File.

At present, two formats are supported: coordinate lists or target name lists. In the first case, the Input File contains values in three, TAB separated columns: RA (in hours), DEC (in degrees) and an identifier (any text label). Coordinates are expected to be in J2000. Another option is using Galactic coordinates (L,B) in degrees. Alternatively, the Input File can consist of a single columns. In this case, Querator expects it to list target names, which will be resolved by SIMBAD.

Querator will point out, if necessary, the lines of the Input File whose syntax was not correct.

External Server

An external server can be queried to build a sample of astronomical objects according to some physical criteria. The returned list is then internally used by Querator to query the supported archives. Given the fact that NASA has discontinued the Astronomical Data Center services, the only External Server currently available is Hyperleda.

Physical Constraints

Users can write in this field queries to be sent to the External Server. It's important to follow the query syntax (SQL-like for Hyperleda) of the chosen external server. In the case of Hyperleda, only the part of the query following the WHERE clause needs to be written. Some simple query examples for Hyperleda:

query	meaning
objname = 'NGC4486'	Retrieve the object listed under name NGC4486. Hyperleda valid identifiers include: NGC - IC - UGC - ESO - HD - BD - PGC - Others. Note: Messier is not a recognised Hyperleda identifier (e.g., M87 is not known, NGC4486 is). Work is in progress on this problem and a solution will be shortly provided.
abs(de2000) > 80.5	Retrieve all objects which declination is greater than 80.5 degrees or less than -80.5 degrees
abs(b2)>70 and ubt<0 and mup is not null	Retrieve all objects having a known modulus distance (mup), a negative U-B colour (ubt), and a absolute galactic latitude (b2) > 70 degrees.

See the list of Hyperleda parameters. Note that values for all character fields must be enclosed in single quotes. Other query examples can be found here.

Output Param.

Space or comma separated list of parameters, from the selected external server, to be visualized in the output. The al2000 and ra2000 parameters (Ra and DEC) are automatically added as first two output fields because they are needed for Querator processing of obtained output.

Clustering Radius

The clustering radius (in arcseconds) defines groups of images in the region of interest.

That of clustering radius is an important concept. When users define a region of interest on the sky (using, for instance, the RA Min, RA Max, DEC Min and DEC Max fields), Querator needs a way of grouping images. This is essential to apply the colour constraints and is done via the clustering radius. At first Querator retrieves, on a per instrument basis, the list of available datasets. These datasets need to satisfy all users constraints but the ones on filters.

After that, Querator builds all possible groups of datasets based on the coordinates of their pointing and on the value of the clustering radius. To each dataset are, therefore, associated all the images closer to it then a clustering radius.

In a subsequent step, Querator discards all groups (clusters) of images that are proper subsets of, at least, another cluster. After that, the resulting groups are checked against constraints on colours and filters. The final clusters are presented to the user.

Search Radius

The search radius (in arcseconds), together with a Target Name (or a list of coordinates/target names), defines the region(s) of interest on the sky.

In essence, every image closer to the object(s) of interest then a search radius is considered in the search process. In order to apply the colour constraints, a clustering algorithm is applied to the selected images (see the discussion about the clustering radius).

Instrument

The instrument name(s). Users choose the instrument(s) they are interested in from the supplied list. At least one instrument has to be selected.

Min Exposure Time

The minimum exposure time (in seconds) for a dataset to be examined by the search engine.

Start Time

This field constraints the exposure date of the observations to be examined.
To specify a minimum value, use the syntax '>=dd/mm/yyyy' (without quotes). Similarly for upper limits. For a range of dates, separate the extremes by two dots: 'dd/mm/yyyy..dd/mm/yyyy' (without quotes). Examples include: '>=31/03/1972' (without quotes) to select observation performed after March, the 31th 1972 or '31/03/1972..31/03/2002' (without quotes) to select images observed between March, the 31th 1972 and March, the 31th 2002.
Leave the field empty if you do not want to put constraints on the Exposure Date.

Disable filters' constraints

Tick this checkbox to disable constraints on filters' number, wavelength range and filter type on the query to retrieve data.

Wavelengths

The wavelengths (in nm) of interest.
Users can list exact values and/or ranges of values using blanks as separators (e.g. lambda1 lambda2 lambda3..lambda4 lambda5). A range is defined by its extremes separated by two dots (e.g. min..max). Only filters covering the specified wavelengths will be selected.

Min Filter Number

The minimum number of distinct filters users are interested in (see the discussion about the clustering radius).

Filter Type

The type of filters users are interested in (e.g. broad band / narrow band).

Total Exposure Time

This field, if not left empty, constraints the minimum value of the total exposure time per filter of every association of images.

FoV Check

This, if checked, tells users whether or not the object(s) of interest fall(s) into the Field of View of selected instrument(s), on a per image basis. During Sky box search Fov check is disabled. Supported instruments are: NICMOS, WFPC2.

Max Seeing

This, if checked, restricts the search to images whose seeing is less than the given value.
For space based observations 'seeing' refers to the theoretical stellar PSF FWHM. Supported instruments are: ACS, FOC, NICMOS, WFPC2, WFI, FORS1, FORS2, ISAAC.