Introduction to the Hipparcos Catalog
The Hipparcos Catalog provides a comprehensive database for nearby stars.
A copy of the catalog is available on our local computer systems in the
directory /home/data/hipparcos/.
Click for a larger view
For your use
we have extracted data and created a subset of the original catalog that
includes only stars for which parallaxes are greater than 0.5
milliarcseconds, and of those, only the ones that also have both B-V and
V-I magnitudes. This revised catalog has approximately 110,000 stars
closer than 2 KPc. The original catalog is called hip_main.dat. The revised
catalog is hipparcos.dat. Follow this procedure to allow easy access
from your account using a softlink to the database:
- cd
- mkdir hipparcos
- cd hipparcos
- ln -s /home/data/hippparcos/hipparcos.dat hipparcos.dat
This creates a subdirectory in your account and places a softlink in that
directory which points to the catalog. You will not be able to write
to this file, put you can read it.
In order to load the catalog into a Grace (xmgr) database, follow this
procedure:
- cd hipparcos (if not there already)
- xmgr
- Then while running Grace (aka xmgr) --
- Data -> Import -> Ascii
- Click on hipparcos.dat in the Files listing
- Load as NXY then press OK
- Close the Read Sets menu by pressing Cancel
- File -> Save as
- Name the new file something like hipparcos.agr
You now have a Grace database that has entries for all the stars. The .agr
extension is the usual one to use with Grace files. You can start from
this point at any time by typing xmgr hipparcos.agr
on the command line.
The data within grace will
appear as different data "sets", each made of an (x,y) pair for
each star in the catalog. The hipparcos.agr database you have made
will always have x equal to the index number of the star in the Hipparcos
catalog, and y equal to a quantity of interest. Thus each set provides
something unique about the star:
- s0 - Right Ascension in degrees (like phi in spherical coordinates)
- s1 - Declination in degrees (like theta in spherical coordinates)
- s2 - Distance in parsecs
- s3 - Apparent magnitude V
- s4 - Absolute magnitude M
- s5 - Color B-V
- s6 - Color V-I
Note that the sets are numbered from 0, rather than from 1, and that there
are seven of them. You can work with them through the functions
that are available in the Grace menus, particularly
Data -> Transformations. Here is how to create a plot
of absolute magnitude versus B-V -- a color-magnitude or
Hertzsprung-Russell diagram:
- xmgr hipparcos.agr (starts with the database you created above)
- Data -> Transformations -> Evaluate expressions
- The two columns are the "source" and the "target" for creating a new set.
Left click on the source column's G0.S4 to select the absolute magnitude,
but do not select a set in the destination column.
This means the destination will be a new set. Now in
the "Formula" box type:
x=s5.y
and press "Apply" This expression tells Grace to create a new set with
x-values that are the y-values of set 5. By default, Grace will replace
only the x, and the current y-values of the selected set remain unchanged.
- You'll now see a set G0.S7 that was just created. x-values in the new
set will be B-V (from set 5), and y-values will be M (from set 4).
- The plot you see is not useful because all of the data
are being displayed, which makes no sense.
Right click on each set in the Source list and select "Hide", except for the
new set S7 that you just created. (A shortcut is to left click on the
first one, and hold the shift key down while you left click on S6 to select
the entire block, then right click and hide them all in one step.)
- Press the "AS" for autoscale button and the plot will appear. It is not yet
in a useful form, but it displays only the data from the set you just
created.
- Close the Evaluate Expression menu, and open Plot->Set Appearance.
Select S7, and under Line Properties pick "None" instead of "Straight".
Under Symbol Properties select "Circle" and adjust the slide bar for
a size to make the circles small (say "2"). Press Apply and
you should see a plot with each star separately indicated. You can change
the color, and select a fill option that will make solid dots instead of
drawn circles if you prefer.
- This plot has positive M at the top of the y-axis, but the standard
color-magnitude diagram reverses this with negative M (brighter stars)
at the top. To change the axes use Plot -> Axis properties. Select
the y-axis and look for the small button that says "Invert axis" Press it,
and "Apply". You can change the tick marks and label axes under this
menu as well.
- The finished work may be saved as a new file under the File -> Save as
menu. For simplicity and to reduce the file size, you
could delete or "kill" unwanted sets by using the Data -> Transformations ->
Expressions menu. Right click in the "Source" file list and "Kill"
a data set to make it go away forever.
- Print the plot with File -> Print. Note that File -> Print Setup
also provides for creating a jpg file or saving the print version as a
PostScript or an Encapsulated PostScript file.
This is useful for including the graph in other applications.
Questions
- Make a B-V color magnitude diagram as described above and print the graph
that you obtain.
- Repeat again but this time for V-I. How do the two color magnitude
diagrams differ?
- Identify the main sequence and find the difference in absolute
magnitude between the brightest and faintest main sequence stars. What is the
ratio of the luminosity of these stars?
- Identify the group of white dwarf stars around B-V=0 . How much smaller in
radius are they than the main sequence stars of the same temperature?
- Identify the group of red giant stars around B-V=1.5 . How much
larger in
radius are they than the main sequence stars of the same temperature?
Reference Material
Navigate
Last update: September 26, 2005
kielkopf@louisville.edu
