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
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.
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.):