README file to accompany Worthey (1994) CD_ROM package. The package
as described here should be regarded as copyright 1996 by Guy
Worthey. Permission is given for free copying and alteration of the
files here provided the intent is for scientific investigation.

This collection of model grids is meant to allow users to explore
the consequences to integrated light indices (colors, line strengths,
M/L ratios, SFB magnitudes) as stellar population parameters (age mix,
metal mix, IMF, helium abundance) are varied. Programs are provided
that interpolate in the model grid and combine populations together.
They are intended as a starting place for users.



----------------------------------
1. CHANGES FROM WORTHEY (1994)

For this CD-ROM, only two changes have been made to the original
Worthey (1994, =W94) models.  First, for metal-poor populations, the
morphology of the horizontal branch now follows the behavior of the
Galactic globulars, becoming extended toward the blue. M3 and M92 were
used as models for this behavior as in Aaronson et al. (1978), the M3
horizontal branch extending to log Te=4, and the M92 horizontal
branch extending from log Te=3.9 to log Te=4.1. The switch to M3
morphology happens below [Fe/H] = -0.95; the switch to M92 morphology
happens below [Fe/H] = -1.55. This scheme is discussed in Worthey (1993).

Second, the $M/L$ ratios have been put on a less arbitrary scale.  The
lower mass-cutoff of the power-law IMFs was varied to make the models
match a globular cluster M/L_V = 2.5.  The upper mass cutoff was
assumed to be 10 Mo. It is also assumed that there are no stellar
remnants above this mass. Below 10 Mo the Weidemann (1987)
initial-to-final mass relation was assumed. 

Here are the lower mass-cutoffs as a function of power-law IMF slope:

Power-law slope    lower mass cutoff
1.35               0.33  Mo
1.85               0.18
2.35 (Salpeter)    0.21
2.85               0.28
3.35               0.33

The normalization of the mass follows W94: the INITIAL mass of the
system, obtained by integrating under the IMF, is normalized to be a
million Mo. The mass of the population changes somewhat as stars are
converted into remnants, and it is this reduced mass which is used to
calculate the M/L ratios. There is a paper in preparation which
focusses on the M/L issue.

These two changes were wrought because of their obvious utility (for
instance, the M/L ratios may now have some physical meaning!). The
temptation to change underlying isochrones or fluxes was resisted in
order to have all of the details in W94 apply to this CD-ROM
distribution. 

One last detail: the new definitions for H gamma and H delta are
included in the model output. There is some risk that these model
predictions will change a little bit in the future because the paper
which describes the stellar data and fitting functions is not yet
refereed (Worthey & Ottaviani 1996).



----------------------------------
2. THE WEB

If you are only an occasional consumer of population models, the web
page 

http://astro.sau.edu/~worthey/dial/dial_a_model.html

may be all you need: it is a working version of the software on this
CD-ROM connected to the display mechanism of HTML browsers.



----------------------------------
3. THE DIRECTORY TREE AND WHAT IS THERE

The directory on the CDROM that this README file is in I am calling
the "root directory." It contains a few fortran modules, a makefile,
and 11 subdirectories. One subdirectory contains William Pence's
FITSIO routines. The rest contain collections of FITS format files,
each of which has data for a population model of one age and one
metallicity. The file names are formed from the age and Z.  The FITS
files are composed of several batches of header information, a binary
array of model fluxes, and 3 ascii table extensions with index data,
color/SBF data, and the underlying color-magnitude diagram. THERE IS
MORE INFORMATION IN THE FITS FILES THAN IS EXPLICITLY READ BY THE
FORTRAN PROGRAMS. Users are encouraged to browse through a FITS file
and modify the programs as they see fit.
	The fortran programs for interpolation should be set up as
described below.
	The Wo_FITSIO directory has its own README, fortran routines,
and a makefile geared for unix users. A branch directory "Pe_FITSIO"
contains the original FITSIO distribution, the user manual,
VMS-specific code, and slick makefiles by Steve Allen.

	We have:

Root directory:
Wo_-README	| this README file
Wo_ask.f	| driver program
Wo_getmodel.f	| fortran module
Wo_locate.f	| fortran module
Wo_rfits.f	| fortran module
Wo_makefile	| makefile for unix systems
	Wo_FITSIO/   	dir	FITSIO modules, makefile, Pe_FITSIO subdir
	Wo__vanilla/	dir	Zero models. Salpeter IMF, dY/dZ = 2.7
	Wo_MillerSc/	dir     Miller-Scalo (1979) IMF
	Wo_Salp+0.5/	dir     IMF slope up 0.5. slope = 2.85
	Wo_Salp+1.0/	dir     IMF slope up 1.0. slope = 3.35
	Wo_Salp-0.5/	dir 	IMF slope down 0.5. slope = 1.85
	Wo_Salp-1.0/	dir	IMF slope down 1.0. slope = 1.35
	Wo_Ymaximum/	dir	High helium content.
	Wo_Yminimum/	dir	Low helium.
	Wo_Yshallow/	dir	dY/dZ=6 at low Z, dY/dZ=0 at high Z.
	Wo_NoLateSt/	dir	No horizontal branch or later stages
	Wo_original/	dir	W94 exactly as tabulated



----------------------------------
4. EXPLANATION OF MODEL FLAVORS

(a) Wo__vanilla, Wo_original
    These two directories differ from each other as described above:
    "original" has no provision for stellar remnants, its IMF is
    integrated from 0.1 to 2.0 solar masses, and all of this mass is
    assumed to contribute to the M/L ratios. The horizontal branch is
    assumed to lie in a clump at all metallicities in the "original."
    "Vanilla" has a Salpeter IMF integrated from 0.21 to 10.0 solar
    masses, stellar remnants, and a horizontal branch that varies as a
    function of metallicity.

(b) Wo_Salp+0.5, Wo_Salp+1.0, Wo_Salp-0.5, Wo_Salp-1.0, Wo_MillerSc
    These directories have variations of IMF. The lower mass cutoff is
    0.1 Mo for the Miller & Scalo (1979) IMF, otherwise is given by
    the table in section 1. The upper mass cutoff is 10 Mo.

(c) Wo_Yminimum, Wo_Ymaximum, Wo_Yshallow
    Helium abundance is a free parameter in the W94 models. It is
    allowed to affect stellar lifetimes and temperatures through
    the helium flash. It affects later stage lifetimes through
    modulation of the helium core mass, but any temperature
    effects are neglected for later stages.
       The Y_minimum and Y_maximum flavors are set by the helium
    abundances chosen by VandenBerg in the input evolutionary 
    isochrones. He chose Y=0.20 and Y=0.30 below Z=0.008, and
    Y=0.25 and Y=0.35 above that value. (In the near-solar-Z regime
    some interpolation was needed. See W94.)
       The Y_shallow scheme is that Y = 0.228 + 6*Z below Z=0.0077
    and Y = 0.274 above that value. The Z=0.0077 corresponds to 
    [Fe/H] = -0.34. (VandenBerg solar Z = 0.0169. See W94.) The
    default scheme in "vanilla" is Y = 0.228 + 2.7*Z at all Z.

(d) Wo_NoLateSt
    All stages of stellar evolution beyond the helium flash are truncated.



----------------------------------
5. INTERPOLATION SOFTWARE

The fortran programs driven by Wo_ask.f will interpolate a model of
any [Fe/H] and age from any of the available model flavors.  The
program is interactive and will walk the user through the
process. Users may discard the "ask" driver and use the rest of the
subroutines directly if they so desire. The makefiles were designed
for unix platforms, but the fortran is standard, and should run on any
platform. (Now that I think of it, there is one exception: a routine
in Wo_ask.f called ctime is unix-specific, and maybe even
Sun-specific, but all it does is return the time and date, so it can
easily be deleted or replaced.)

	To get the interpolation programs working:

	1. Copy all *.f programs, the Wo_makefile file, and the
entire Wo_FITSIO directory to your own disk space. These instructions
assume that you have left the directory structure and file names 
intact.
	2. rename "Wo_makefile" to "makefile." If you have a VMS
machine, the makefile will not work - you are on your own. (I have
little experience with VMS. The programs were debugged and tested on
Sun workstations running SUNOS and SOLARIS.)
	3. rename "Wo_FITSIO/Wo_Makefile" to "Makefile." Type "make."
This should make an object library called "libfitsio.a." The code for
VMS users is in the next directory: "Pe_FITSIO."
	4. IMPORTANT: Edit Wo_ask.f, and change the data for the 
variable "rootdir" to reflect the absolute pathname of the directory
where the Wo_ask.f file sits on the cdrom. Also edit the variable
"nchar" that keeps track of the number of characters in the "rootdir"
string. 
	5. Do the final compile with a "make" in the Wo_ask.f 
directory. Invoke the program with "Wo_ask."



------------------------------
6. ACKNOWLEDGEMENTS

I would like to thank Claus Leitherer, Uta Fritze-von Alvensleben, and
John Huchra, first for a good conference, and second for providing the
impetus for me to provide these grids, a task which I always meant to
do, but never made a first priority. Thanks also to Philip Hughes, and,
historically, to Steve Allen. They both provided me with needed files
and stellar technical advice.



------------------------------
7. REFERENCES

Aaronson, M., Cohen, J. G., Mould, J. R., Malkan, M. 1978, ApJ, 223, 824
Miller, G. E., & Scalo J. M. 1979, ApJS, 41, 573
Worthey, G. 1993, ApJL, 415, L91
Worthey, G. 1994, ApJS, 95, 107; W94



------------------------------
8. SECTION FROM THE LEITHERER ET AL. PASP PAPER

Worthey (1994, ApJS, 95, 107) models 

The Worthey (1994) evolutionary population models give integrated
UBVR$_C$I$_C$JHKLL$'$M colors and magnitudes, SBF magnitudes, spectral
energy distributions, and Lick/IDS spectral index strengths for
populations of arbitrary age, and (assumed scaled-solar) abundance
[Fe/H]. The ages range from 1 to 18 Gyr, and abundances from -2.0 to
+0.5 dex. Helium abundance $Y$ is a free parameter. The underlying
stellar evolution is that of VandenBerg (VandenBerg 1985, VandenBerg
\& Bell 1985, VandenBerg \& Laskarides 1987).  The stellar fluxes used
to compute integrated flux are mostly theoretical (Kurucz 1992,
Bessell et al. 1989, 1991), and explicitly include the effects of
metallicity on the spectral shape and colors. Please see Worthey
(1994) for details.

The distribution on the CD-ROM includes several ``flavors'' of model
grid: (1) Five power-law IMFs plus Miller \& Scalo (1979) are
provided. For the power-law IMFs the lower mass cutoff was chosen so
that $M/L_V=2.5$ for globular cluster-like populations (with a
reasonable accounting of stellar remnants; Worthey 1996, in
preparation), so output $M/L$ values differ from the tabulation in
Worthey (1994) by a constant factor plus a small perturbation caused
by the fact that a small amount of low-mass starlight is missing.  (2)
Also included are four schemes for how helium abundance tracks overall
abundance. (3) One model grid without helium-burning and later stages
of stellar evolution is included for those interested in adding HB-,
AGB-, EAGB-, PAGB-stages, or other stages of evolution by
themselves. (4) The models as tabulated in Worthey (1994) are also
included unaltered.

Each model (at one age and [Fe/H]) is stored in a FITS file with ascii
table extensions. One ``flavor'' is made of a grid of FITS files
covering the range of age and [Fe/H]. A fortran program is provided
that reads the data using William Pence's FITSIO routines (also
included), interpolates in the model grid to arbitrary age and
metallicity, and combines populations in any combination the user
specifies.  Multicolor color-magnitude diagrams are also available in
the FITS file ascii extensions.

If the reader is but an occasional consumer of population models, he
or she would probably best be served by the web page
http://www.astro.lsa.umich.edu/users/worthey/getmodels/dial_a_model.html
which contains a form-driven version of the interpolation/addition
program on this CD-ROM.


Bessell, M. S., Brett, J. M., Scholz, M., \& Wood, P. R. 1989, A&AS, 77, 1
Bessell, M. S., Brett, J. M., Scholz, M., \& Wood, P. R. 1991, A&AS, 89, 335
Kurucz, R. L. 1992, private communication
Miller, G. E., \& Scalo J. M. 1979, ApJS, 41, 573
VandenBerg, D. A. 1985, ApJS, 58, 561
VandenBerg, D. A., \& Bell, R. A. 1985, ApJS, 58, 561
VandenBerg, D. A., \& Laskarides, P. G. 1987, ApJS, 64, 103
Worthey, G. 1994, ApJS, 95, 107
