The Lick/IDS system.
This page is useful for observers interested in transforming their data to
the Lick/IDS system to take advantage of all the scrutiny and
modeling that has been done with it.
It is vital to do well at this, since the interesting
science is at the level where systematics are very important.
- The single most important ingredient needed is: repeat
observations of Lick/IDS stars. To facilitate this, here is a list of
bright field stars with coordinates and
magnitudes, compiled a long time ago by Jesús
González. There are plenty of stars reachable from the southern
hemisphere, including some standard stars.
- Once you have
observed the stars you will need to know the correct amount to broaden
your spectra by to approximate the 8-11 Angstroms FWHM of the IDS
data. This is probably best done by cross-correlating with the actual
IDS spectra. You can download FITS spectra
here. Or, you can read the helpful appendix to
Worthey & Ottaviani 1997 (572-KB PostScript),
which gives resolution as a function of wavelength and a couple of
examples of new data-to-Lick/IDS transformations.
- Make sure you use the most up-to-date
wavelength definitions for
the indices (wavelength accuracy has improved since the early papers).
A prettier table is in the document file from the updated
index catalog available from this page.
And if you need to test out your index-measuring routine,
indextest.tar.Z is a compressed tarfile
containing a collection of 8 spectra with
accompanying index values, where the wavelength scales from the headers are
used. The latest index definition table is there as well.
Finally, a list of all 25 index measurements for 460 stars can
be found in a document file and
a data file
(from Worthey & Ottaviani 1997 and Worthey et al. 1994). And a similar
file for 370 galaxies can be found here
(from Trager et al. 1998 and Lee & Worthey 2005). The format is:
galaxy name, goodness parameter, N_observations, then 25 (index,
error) pairs, and the last column is the velocity dispersion. These
data are corrected to velocity dispersion zero.
- Let me know if these resources are helpful to you!
to Worthey main page.