spacer link to MAST page spacer logo image spacer
link to STScI page

Tips of the trade for running Spectral Classes forms


Users should note that all MAST interface pages, like Gaul, are divided into three parts. Since the top (target search) and bottom (output format) sections are functionally the same, only the middle part shows function-specific changes. However, the lower section will list output columns specific to the interface. This means that creative use of the "User specified field" menu (middle section) and addition of Output Columns (lower section) can be used to filter on and/or display additional fields, say, like V-magnitude.

Users should likewise be aware of the use of the file upload form, which allows queries for many objects/coordinates at once. Both interfaces can also be used with alternate output page formats, e.g. csv, Excel, etc.

Two other useages that can be handy upon occasion are the (1) Show Query and the (2) Make Rows Distinct options. Clicking on Show Query displays the SQL command interpreted by your query and may help users interpret their search results. Clicking the Distinct button eliminates duplicate output rows and is therefore useful for separating unneeded "chaff" from needed "wheat." This is particularly useful when only a few output columns are specified.

To use the "Classification String" form elements, users should know that MAST ignores all spaces in the users input, and has deleted all spaces in the original catalog classification strings. Also, be sure to read the help (Field Description) page for such syntactical tips as use of wild cards (*) and sequences (,). Notice how wild carding (e.g. B9*, for all kinds of B9 stars), and how multiple searches (e.g. O9*, B0*) can be done with * and , characters. Also, input strings are case insensitive.

As for all MAST interface forms, users can sort results based on values from specific fields. Three levels of sorting are allowed so if several rows have the same value for the first level sort, those rows are further sorted using the 2nd level sort field, and so on for the 3rd level. Users can change the default sort fields (i.e. ang sep, RA, & Dec in that order) which are geared toward cone searches on target name or coordinates. If these defaults are used however, multiple entries for a particular target will not be ordered in a predictable way.

"Spectral Classes of Like Stars" page:

  • Providing a List of "unique" star names: (e.g., "give me all A5V stars").
    As this title implies, often a user initially wants just a unique list of star names with the same spectral type, luminosity class or ranges thereof. Although the MAST spectral database is not designed to provide this capability, a judicious use of the "Make Rows Distinct" button can get users there, with perhaps just a little more pruning of the retrieval page table. For example, clicking this button and removing the Data ID and Instr Config columns can help remove duplicate observations on stars. Even this expedient can be inadequate for like stars. For example, a query on "RR Tel" will result in several rows for "RR Tel" and "RR-Tel". These are extra entries resulting from possibly different spellings the original mission Guest Observers gave for a given target. To get unique target names it can help to remove fields that can vary between observations (e.g. "data ID", "Instr Config", "Bibcode", "Mission", coordinates, etc.) The idea here is to remove fields whose values may differ for the same object while still retaining those that may be of interest to the user.

  • Most reliable matching to an intended star among the catalogs. Sort on "Catalog selection flag." This flag has no analog on other MAST mission or tool interface pages. The lower number in this heading is the most reliable match. GO and/or authors quoted in the classification catalogs do not use uniform names or positions, and of course proper motions in close visual binaries also complicate the matching. Please note the non-default output column Xmatch_comment. This is a brief description of the method used to Xmatch with the input target name or coordinates. You can find a description of the Catalog Selection Flag and Xmatch_comment fields on the Field descriptions page.

  • Multiple values can be specified for the Sp. Types, Subtypes, Lum Class, and Peculiarities form elements in 2 ways. Consecutive values can be selected by clicking on the first entry and shift-clicking the last entry. Alternatively, individual entries can be selected using a command-click. Note that the P3 and P4 peculiarities however will be displayed for the earliest spectral type selected although the encoded values selected will apply to all types.

  • Use the "Clear form" button if previous selections are not desired in new queries.

"Skiff Spectral Catalog" page:

  • The TT,tt,LL,P1P2P3P4 form elements can be treated as numerical fields allowing numerical operators to be included. For example, to find O,B, and A stars, set TT = 10..12. Use the Spectral Classification Tables to see how values are assigned.

  • The Skiff catalog includes all the published spectral classiifcations for a given star going back as far as 1866 (the "Spectral Classes of Like Stars" table only includes the spectral classification from the latest paper for each cross-matched target). Sorting on bibcode in "reverse" order will display the latest papers first. It is interesting to see how classifications changed with time.

  • The suggestions for listing unique star names also applies to searching the Skiff catalog.

  • Searches on special fields can be useful (e.g. bibcode, magnitude, etc.):