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MAST/SKYMAP SKY2000 Version 3 Correlation Help

This page explains how to use the MAST/SKY2000 cross-correlator.

Version 3 of the SKY2000 master catalog contains nearly 300,000 star entries with visual magnitudes between -1.4 and 12.92, all of which have coordinates accurate to less than or equal to 1.5 arcsec. More than 99% of the entries have Johnson V magnitudes, however note that not all the included fields have values for every star entry.

To use the SKY2000 form, simply indicate the V or B magnitude, B-V color, coordinates, Parallax (mas), and/or Spectral Type that define the subset of the catalog that you're interested in, and which missions you want to cross correlate this subset with. The page is initially displayed to search all MAST missions except FGS and HSP. To search on individual missions, first click the "unmark all" button and then select the specific missions desired. (Selecting fewer missions will speed up the search.) You can also specify a search radius for each mission different from the default given in the page.

The MAST cross-correlator will extract the subset of the SKY2000 catalog that meets your qualifications, and will begin polling the selected mission databases to see which missions have observed these stars. (Note that queries returning a large subset of the SKY2000 catalog can take a long time to complete.) The results will be presented in a simple tabular form, with links to the MAST search pages for individual missions:

  • The name of the catalog or mission will be linked to that mission's search form, with the RA and Dec for the catalog target as defaults.
  • The target name will be linked to a preview image or spectrum, if one is available.
  • The name of the exposure (the Dataset Name for HST data, the Entry ID for IUE data, etc) will be linked to a page of information about that specific observation. (This is still under development for non-HST data.)

The MAST project wishes to thank Wayne H. Warren Jr. (Raytheon Technical Services Company) and Christopher B. Sande (Computer Sciences Corporation) for their assistance in obtaining the SKY2000 master catalog and documentation.

V Magnitude
Apparent magnitude in the Johnson V band. 
Qualification  Meaning
-------------- ---------------------------------------
   > 18        V greater (dimmer) than 18
   < 22        V less (brighter) than 22
 18.5 .. 22.5  V between 18.5 and 22.5
   18.0        V of exactly 18
The range of values of this field in the SKY2000 version 3 catalog is -1.44 to 12.92. (This does not mean that the SKY2000 catalog is complete to 12.92.)

B Magnitude
Apparent magnitude in the Johnson B band. The range of values for this field is -1.43 to 16.66.

B-V Color
Johnson B-V color, expressed as a magnitude difference. Values range from -0.6 to 5.9.

Parallax
Trigonometric parallax, in milliarcseconds (mas). Values range from 742 to -343 although negative values have no physical meaning.

Spectral Type
A 30 character field containing spectral class, luminosity class, and peculiarity type. This field is case-sensitive, so that searches using it will go faster. (The database engine wouldn't be able to use the index otherwise.)

Right ascension range
Right ascension range (J2000). Use this to limit the catalog extraction to a specific area of the sky. This field should be used to specify a range of right ascensions. While a single RA would be recognized, in general such a specification would not be useful, since the cross-correlator will try to match the RA exactly- an operation that would be subject to the whims of floating-point computer arithmetic.

Here's how to specify a range of right ascensions. 

	12 00 00 .. 14 00 00
	12 00 .. 14 00
	12h00m00s .. 14h00m00s
	12h 00m 00s .. 14h 00m 00s
	12h 00' 00" .. 14h 00' 00"
	180 .. 210
Note that if the right ascension is given as a single floating-point number, as in the last line in the above set of examples, it will be interpreted as degrees, not hours.

You can also use < and >: 

	< 5 00 00
	> 14 00 00
	< 2, > 20
The last line means "less than 2 OR greater than 20". A comma may be to OR two RA qualifications.

Declination range
Declination range (J2000). Use this to limit the catalog extraction to a specific area of the sky. This field should be used to specify a range of declinations. While a single Dec would be recognized, in general such a specification would not be useful, since the cross-correlator will try to match the Dec exactly- an operation that would be subject to the whims of floating-point computer arithmetic.

Here's how to specify a range of declinations: 

	20 30 00 .. 21 00 00
	20 30 .. 21 00
	20h30m00s .. 21h00m00s
	20h 30m 00s .. 21h 00m 00s
	20h 30' 00" .. 21h 00' 00"
	20.5 .. 21.0
You can also use < and >: 
	< 20
	> -20
	< -20, > 20
The last line means "south of -20 OR north of +20".

Missions
Select one or more missions with which to cross-correlate the selected catalog. (For HST, each instrument is treated as a separate mission.) You can use the Show catalog entries that match any/all of the selected missions selector (see below) to control whether any or all missions have to match a catalog entry in order for that catalog entry's results to be displayed.

Radius (arcmin)
The radius in arcminutes on which to cross-correlate the mission with the object catalog catalog. Each mission has its own independent radius. For each mission, a default radius has been chosen that is more or less appropriate for that mission.

Show catalog entries that match any/all of the selected missions
When you select multiple missions, you can use this selector to control how an catalog row's results will be displayed: Set it to any to show results if the catalog entry cross-correlates with at least one of the selected missions, or set it to all to show only those catalog entries that cross-correlate with every selected mission. For example, you might set this selector to all if you are looking for catalog entries that have been observed with both HST and IUE, or to any to find catalog entries observed with either HST or IUE.

Display n rows per mission
Use this selector to determine how many rows from each mission will be displayed. When ALL is selected, every row found for the mission will be displayed. Optionally, you may use this selector to reduce the number of rows from each mission reported, reducing the length of the results page. The total number of rows for each mission will always be reported.