Dear Readers,

Welcome to the second edition of the MIPS/IRAC GTO newsletter.  This 
episode features three new white papers!  Michael Pahre describes an 
IRAC program to study the spectral energy distributions and evolution 
of normal galaxies out to Z=1, George Rieke discusses a MIPS program 
to study the evolution of galaxies in clusters, and Charles Lada and 
Erick Young discuss the great discoveries that are possible with SIRTF 
by doing surveys of circumstellar disks.  This latter white paper 
includes two figures, which are available in the web version of the 
newsletter at:       http://mips/MIPS/Science_f.html  
In addition, there is a brief editorial by me explaining the purpose 
of the newsletter and a note from Steve Willner describing the structure 
of the IRAC GTO science team. 

If you have comments on any of the papers in this newsletter, you can
send them to me and they will be included in the next newsletter.  The 
deadline for submissions to the next newsletter is Friday, October 2.


Doug Kelly, editor (dkelly@as.arizona.edu)


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************		    LETTERS    		      ************
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Title: What is this newsletter about anyway?

Submitted by:   Doug Kelly, editor

I first heard about the GTO newsletter about a month ago, a week before 
the rest of you.  I agreed to serve as editor and to write a letter 
of announcement.  Like many of you, I thought the newsletter sounded like 
a great idea.  But what would the newsletter be about?  I asked George 
Rieke that question.  He said that since IRAC and MIPS had agreed to 
coordinate science programs and time was running fast, the newsletter 
should serve as a forum for the rapid exchange of ideas to help define 
those programs.  It could also serve as a forum for the introduction
and discussion of new ideas for possible GTO science.  Now that the
newsletter is started, it is up to you, the members of the IRAC and
MIPS science teams, to make this effort a success.  As can be seen in
this issue, we are off to a good start.  I encourage all of you to 
participate in the discussion and to make sure that your favorite GTO 
program gets some airtime.  In that way, you can be sure that the 
newsletter evolves to serve the needs of you and your science team.


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Title:	A Note About the IRAC GTO Science Team

Submitted by:	Steve Willner 

This is an administrative note about how IRAC is planning for GTO
observations.  We have organized into three teams covering broad
areas of research:
  Star Formation and Brown Dwarfs (John Stauffer)
  Early Universe (Giovanni Fazio)
  Galaxies (Steve Willner)

Other GTO's -- MIPS, IRS, general -- who are interested in
collaborating in these areas are invited to contact the appropriate
IRAC team leader.  Mike Pahre, in this newsletter, describes one
project that the Galaxy team is considering.


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************		NEW WHITE PAPERS	      ************
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Title:   The SEDs of Normal Galaxies and Their Evolution at 0<z<1
Submitted by:	Michael Pahre / IRAC (CfA)
Instruments:	IRAC.  (MIPS under discussion [see below].)
Total Time:	25 hours (IRAC)

The deep, Distant Galaxies GTO programs for IRAC and MIPS [see newsletter 
#1 agreement by G. Rieke] will produce dramatic images of galaxies at z>2 
undergoing their formation stages.  While such images will be impressive 
and exciting, it will be important to place the global properties of such
galaxies in the context of the "normal" galaxy population at more modest
redshifts.  Without such a "comparison" galaxy sample, it will be difficult 
to assess the changes in the comoving number density of luminous and 
sub-luminous galaxies, the evolution of the global star formation rate, 
and the weak (or passive) evolutionary history of the oldest stellar 
populations.  It will also be important to study the evolution of the 
SEDs of nearby galaxies in order to develop IR photometric redshift 
techniques---especially those based on the 1.6um "bump" in the 
rest-frame SED.

For such a comparison to be worthwhile it is necessary that:  (1) the
nearby galaxies be observed, selected, and analyzed in a manner that 
is similar to the distant galaxies (in the respective rest frames); 
(2) the redshifts of the nearby galaxies be known; and (3) the redshift 
distribution of the nearby galaxies be broad enough that the redshifts 
1.6um feature moves through several imaging filters (i.e., 0<z<1).

Imaging with IRAC of "pencil beam" redshift survey fields---already 
studied by other researchers, and documented in the literature---will 
provide large galaxy samples which satisfy these requirements.  Fields 
include those from the CFRS (Lilly et al. 1995), the Hawaii survey 
(Songaila et al. 1994), the Caltech survey (Cohen et al. 1996a, 1998), 
the CNOC2 survey (Carlberg et al.  1998), and the HDF Flanking Fields 
(Cohen et al. 1996b).  In ~25 hours, these fields can be imaged with 
IRAC to moderate depths sufficient to detect passively-evolved galaxies 
two magnitudes fainter than L* at z=1, thus providing the SEDs of normal 
galaxies throughout the LF at 0<z<1.

Construction of flux-limited galaxy samples at 3.5<lambda<8.0um, along 
with a follow-up redshift survey to "fill-in" the remaining unidentified 
galaxies in such surveys, will allow the LF and its evolution to be 
measured during the last half of a Hubble time.  Hierarchical galaxy 
formation models make specific predictions about the evolutionary history 
of the IR LF even at these modest redshifts (e.g., Kauffmann & Charlot 
1998).  Measurement of the IR LF and its possible evolution therefore 
constrain cosmological and galaxy formation models.  Adding far-IR 
observations will allow for the calculation of the lower-redshift, global 
star formation rate per unit comoving volume.

It will also be crucial to the understanding of the far-IR background---
both in discrete sources and a DC background flux---to have a complete 
inventory of the far-IR properties of nearby, normal galaxies.  The 
detection of an optical background light (Bernstein 1997) and the sum 
of the flux detected in galaxies at 2.2um with the Keck Telescope 
(Djorgovski et al. 1995; Moustakas et al.  1997; Bershady et al. 1998) 
suggests that two to three times more flux has been detected from normal 
galaxies than may have been included in the simple models used for 
comparison with the detection of the far-IR background (Dwek et al. 
1998); the full accounting of normal galaxies is therefore crucial for 
the interpretation of a possible population of high redshift, dusty 
protogalaxies as a source of the far-IR background.

While no MIPS observations have been considered yet, they would provide 
important information on the global SEDs of "normal" galaxies that is a 
context for the Distant Galaxies, IR Ultraluminous Galaxies, and IR 
Background observing programs.  It is the interest of the IRAC GTO panel 
to assess the possible interest of the MIPS GTO panel in developing a 
cooperative research program on normal galaxies at 0<z<1 which would 
benefit other GTO programs of both panels, in addition to providing 
exciting results by itself.


Bershady, M., Lowenthal, J. D., & Koo, D. C.  1998, ApJ, 505, 50
Carlberg, R., et al.  1998, in Large Scale Structure in the Universe, in press
Cohen, J. G., Hogg, D. W., Pahre, M. A., & Blandford, R.  1996a, ApJ, 462, L9
Cohen, J. G., Cowie, L. L., Hogg, D. W., Songaila, A., Blandford, R., Hu, E. 
  M., & Shopbell, P.  1996b, ApJ, 471, L5
Cohen, J. G., Hogg, D. W., Pahre, M. A., Blandford, R., Shopbell, P., & 
  Richberg, K.  1998, ApJS, in press
Djorgovski, S., et al.  1995, ApJ, 438, L13
Dwek, E., et al.  1998, ApJ, in press
Kauffmann, G., & Charlot, S.  1998, MNRAS, 297, L23
Lilly, S. J., Tresse, L., Hammer, F., Le Fevre, O., & Crampton, D.  1995, 
  ApJ, 455, 108
Moustakas, L. A., Davis, M., Graham, J. R., Silk, J., Peterson, B. A., &
  Yoshii, Y.  1997, ApJ, 475, 445
Songaila, A., Cowie, L. L., Hu, E. M., & Gardner, J. P.  1994, ApJS, 94, 461


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Title: SIRTF/MIPS Observations of Rich Galaxy Clusters

Submitted by:	G. H. Rieke, 9/18/98

A variety of science objectives could be addressed by a SIRTF program 
on galaxy clusters. For example, what is the nature of the 
intergalactic medium in clusters? Does it contain dust? What are its 
energetics? How do galaxies in clusters undergo cosmic evolution? Does 
the cluster environment noticeably change the time evolution of galaxy 
luminosity and if so, how? In particular, the increased potential for 
galaxy interactions and the possibility of stripping of interstellar 
gas by the intracluster medium both suggest that galaxy evolution may 
be strongly modified. This hypothesis appears to be supported by the 
relatively high incidence of S0 galaxies and of peculiar dwarfs in rich 
clusters, but further insights can be achieved by looking at far 
infrared luminosities, particularly for distant clusters where detailed 
morphologies become difficult to obtain, even with HST. 

These questions are subject of active interest. Dwek et al. (1990) 
developed a model of the Coma cluster to explain observations of a 
modest level of extinction toward background galaxies, presumably due 
to intracluster dust. To accompany the perported extinction, they 
predicted relatively strong far infrared fluxes through heating of dust 
by the hot gas between galaxies; to avoid exceeding the IRAS detection 
limits, they had to place this dust in a previously undetected large 
halo around the visible cluster. If this model is correct, it would 
imply a previously undetected large mass of gas in the outer regions of 
the cluster, as they point out. Hu (1992) found that clusters with 
cooling flow galaxies were detectable in the IRAS data and concluded 
that the fluxes originated from the intracluster medium. Wise et al. 
(1993) tried to detect 56 clusters in the IRAS data, succeeded with 
only 4-5, and concluded that two of the detections were at levels above 
those expected from individual galaxies and hence could be due to an 
intracluster medium. Recently Stickel et al. (1998) have reported a 
detection of a surface brightness in the Coma cluster of 0.1 MJy/sr at 
120microns, within about a factor of two of the prediction by Dwek et 
al. (1990). Stickel et al. assume that the theoretical prediction is 
confirmed by these ISOPHOT measurements. Thus, the possibility of large 
amounts of gas associated with the cluster appears to be confirmed.

However, we have just finished a paper (Quillen et al. 1998) which re-
examines the far infrared emission by the member galaxies of the Coma 
cluster. We combine IRAS and new ISOCAM data with H alpha imaging and 
radio data from the literature. The infrared, H alpha, and radio 
estimates for the Coma galaxies give very consistent estimates of the 
overall star formation rate. Through standard ratios of H alpha and/or 
radio to far infrared, we have generated independent estimates of the 
integrated infrared luminosity of the cluster galaxies that agree to 
within a factor of two or better with the estimate from the infrared 
observations. The estimated far infrared surface brightness of the 
cluster due to its member galaxies we find to be more than half, and 
perhaps all, of the surface brightness measured by Stickel et al. with 
ISOPHOT. Thus, the emission of the diffuse intergalactic medium must be 
at least four times smaller than the theoretical prediction of Dwek et 
al.(1990). Their model could probably be adjusted to produce lower 
fluxes (with further increase in the previously unseen body of gas), so 
it is still unclear whether Coma has diffuse emission at an interesting 
level. Quillen et al. show that most other clusters may also have a 
significant contribution from their member galaxies, so to probe them 
we need observations of greater sensitivity and resolution than 
available from IRAS - and it does not appear that ISO will supply 
them.

This situation can easily be clarified by SIRTF measurements. The 
combination of high sensitivity and reasonably good angular resolution, 
plus the ability to map rich clusters efficiently at 24, 70, and 160 
microns are the keys. MIPS scans over these clusters will unambiguously 
detect the individual emitting galaxies. The resolution of ~ 6" at 24 
microns will identify which galaxies are emitting significantly, while 
the longer bands will constrain their spectral energy distributions. 
The good dc stability that should be achieved by MIPS, plus the high 
sensitivity, will allow detection of any diffuse intragalactic emission 
to low levels. For example, 0.1 mJy/sr corresponds to 2.5 mJy in a MIPS 
160 micron beam and to 0.7 mJy  in a 70 micron beam. Although these 
values are near the confusion limit at the latter wavelength, they will 
be strongly detected above photon noise in both bands (1 sigma in about 
1 minute) and by cleaning the scans of discrete galaxies and smoothing, 
a diffuse component should become easily visible.

Another view of the far infrared emission of rich clusters was taken by 
Kelly & Rieke (1990). They assumed that the cluster far infrared 
emission was entirely due to the sum of the outputs of the member 
galaxies. By summing the IRAS data on ~70 optically selected high 
redshift clusters, they achieved a high weight detection of a "typical" 
rich cluster at an average z = 0.4. They compared this detection with 
nearby clusters and hence estimated the integrated evolution of the 
cluster far infrared outputs. For the nearby clusters, they estimated a 
luminosity function from sources then available. For each cluster with 
high sensitivity IRAS data, they normalized the luminosity function to 
the IRAS detections of the brightest galaxies, then integrated down to 
low luminosities to get the total for the cluster. The result was an 
average luminosity for nearby clusters that was similar to the average 
for the clusters at z = 0.4, and hence contrary to expectations of 
possibly faster-than-"normal" evolution for cluster galaxies due to 
accelerated rates of interactions and mergers, for example. In Quillen 
et al. (1998), we show that the low end of the cluster galaxy 
luminosity function is probably incorrectly estimated in the references 
used by Kelly & Rieke, and hence that they overestimated the 
luminosities of the nearby clusters by a factor of ~ 3. Using a 
luminosity function with slope similar to the field galaxy function, 
and also to the optical luminosity function in rich clusters, it is 
shown that the nearby clusters are likely to be significantly fainter 
than the ones at z = 0.4. The nominal luminosity evolution over this 
range of z is (1+z)^(~3.9), but large uncertainties remain in 
determining the nearby cluster luminosities and hence in this rate of 
evolution.

It is ironic that we seem to know more about the luminosity of clusters 
at z = 0.4 than we do about ones at z < 0.05. The problem with the 
nearby clusters is that IRAS had too limited angular resolution and 
sensitivity to make a good census of their member galaxies. In terms of 
integrated cluster measurements, the clusters are so large on the sky 
that the IRAS confusion noise overwhelms the cluster signal. This 
situation is made clear by the multi-aperture extractions of Wise et 
al. (1993), who found that the cluster detectability decreased rapidly 
with increasing aperture size, even where the aperture was still within 
the Abell diameter. 

The same MIPS scans that would be used to search for diffuse cluster 
emission would be well suited to making a nearly full census of the 
infrared emission from the member galaxies also. For example, the 
detection limits discussed above for Coma would reach to galaxy 
luminosities of about 10^8 L_o, well below L* and hence capable of 
defining the luminosity function well and constraining the galaxian 
luminosity from the cluster accurately. Assuming that there are no 
serious complications from emission by an intracluster medium at a 
higher level than the sum of the galaxy contributions, these 
measurements would allow determination of overall cluster luminosity 
evolution from z = 0.4, just by comparing with IRAS. Additional 
measurements of clusters at higher redshift could extend evolutionary 
studies back to earlier epochs, to an era where strong evolution is 
apparent in field galaxies and hence a meaningful comparison can be 
made with the cluster evolution. The cluster-averaged flux at z = 0.4 
is about 30 mJy at 60 microns, so the MIPS sensitivity would easily 
allow extension of cluster studies to much greater redshifts. 

In summary, a relatively modest MIPS program on nearby and distant 
galaxy clusters could provide unique information both on the presence 
of a substantial intracluster medium, and on the possibly different 
pattern of galaxy evolution compared with the field. 


Dwek, E., Rephaeli, Y., & Mathur, J. 1990, ApJ, 475, 565
Hu, E. M. 1992, ApJ, 391, 608
Kelly, D. M., & Rieke, G. H. 1990, ApJ, 361, 354
Quillen, A., Rieke, G. H., Rieke, M. J., Caldwell, N., & Elgelbracht, 
C. 1998, submitted to ApJ.
Stickel, M., Lemke, D., Mattila, K., Haikala, L.~K., & Hass, M. 1998,
A&A, 329, 55
Wise, M. W., O'Connell, R.W., Bregman, J.N., & Roberts, M.S. 1993,
ApJ, 405, 94


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Title:	The Evolution and Lifetimes of Protoplanetary Disks

Submitted by:	Charles Lada & Erick Young  -- MIPS Team


Introduction and Background:

Understanding the origin of the solar system has long been one of the 
fundamental objectives of astrophysical research.  In the last few years 
two major breakthroughs have convinced many researchers that significant 
progress toward the realization of this goal is now possible.  First, 
extrasolar planets have been indirectly detected toward a number of
nearby stellar systems including 51 Pegasi, 70 Virginis, and 47 Ursa 
Majoris (Mayor & Queloz 1995, Marcy and Butler 1996, etc.).  This has 
provided truly compelling evidence that the sun is not unique in having 
planetary companions.  How often planetary systems accompany stars in the 
galaxy is difficult to ascertain with present knowledge.  However, by 
analogy with the solar system, it is thought that such planets would 
likely have formed from a spatially thin circumstellar disk of material.  
Theoretical considerations suggest such disks should accompany a star 
during its formation as a result of angular momentum conservation in 
collapsing gas (e.g., Adams, Lada and Shu 1987).  The second major
breakthrough in this area of research, the discovery of circumstellar 
disks around numerous newly formed and forming stars, has suggested 
that the physical circumstances that lead to planet formation may be 
a common occurrence and, indeed, a natural consequence of the star 
formation process (e.g., Beall 1987, Rucinski 1987, Beckwith et al. 
1990, Lada and Adams 1992).

Circumstellar disks can have many observational manifestations, both 
direct and indirect, the most compelling being resolved images of 
disks.  Such images are extremely rare but have been obtained at 
submillimeter-wavelengths through VLBI techniques and at optical
wavelengths in the one region, the Orion Nebula, where the HST is 
sensitive enough to image such objects in silhouette against the 
bright background of the HII region (McCaughrean & O'Dell 1996). 
Despite the fact that it is currently very difficult to resolve
them, circumstellar disks can nonetheless be quite easily detected. 
Because they contain substantial amounts of dust they readily emit 
and reflect light at infrared through millimeter wavelengths.  
Consider that if the earth were to be crushed into particles the
sizes and masses of interstellar grains, the surface area of the 
material would increase by 14 orders of magnitude.  Thus, a 
protoplanetary disk is much easier to detect than the planetary 
system that ultimately forms from it.  Current detectors are 
sensitive to very small amounts of dust, and circumstellar disks 
with total masses comparable to the minimum mass needed to produce 
all the planets of the solar system can be detected at infrared 
and millimeter wavelengths around stars in the closest star forming 
regions.  Consequently, infrared surveys are the best tool for 
determining the frequency of circumstellar disks and ascertaining 
how common are the conditions for planet formation.

Figure 1 shows the energy distributions expected for a three solar 
luminosity K5 pre-main sequence star at the distance of Taurus (or 
Ophiuchus) with and without an optically thick circumstellar disk. 
For wavelengths longer than about 1 micron the source energy
distribution of the star with the disk exceeds that of the naked star. 
In this model almost all the excess infrared emission is starlight 
absorbed and reprocessed by the disk.  The infrared excess systematically 
increases with wavelength, along with the ability to recognize the 
signature of disk emission around the star.  For example, as is 
illustrated in the diagram, the excess emission produced by the disk 
at a wavelength of 30 microns is more than 10x that produced at 
2 microns.  Whereas such factors as disk orientation, stellar surface 
temperature, and inner disk holes make detection of the disk excess 
emission difficult at wavelengths shorter than about 3 microns, at 
longer wavelengths the presence of disk excess is essentially 
unambiguous.  Indeed, ground-based observations have shown that only 
about 1/2 the stars with circumstellar disks produce a significant 
enough infrared excess to be detected at 2.2 microns.  Moreover, 
around the youngest stars, starlight scattered by residual protostellar 
envelopes can also produce infrared excess at wavelengths shorter 
than 2 microns, making the association of near-infrared excess with
the presence of a circumstellar disk more ambiguous.  An accurate census 
of circumstellar disks in star forming regions requires sensitive 
observations at mid and far infrared wavelengths.  Such observations 
are difficult to obtain from the ground.

SIRTF offers an unparalleled capability to detect circumstellar disks 
in star forming regions.  For example, Figure 1 displays the SIRTF 
sensitivity at 8 and 30 microns.  The two horizontal lines represent 
the 50 sigma detection limits at these two wavelengths.  Equivalently, 
SIRTF is capable of detecting the naked photosphere of a 3 million year
old, pre-main sequence star in Taurus which has a mass near that 
corresponding to the hydrogen burning limit.  In fact, SIRTF is capable 
of detecting the photospheres of such young stars across the entire 
spectrum of stellar mass in star forming regions which are as distant 
as 1 kpc from the sun!  Clearly then, SIRTF can detect both optically 
thin as well as optically thick disks around young stars over a 
relatively large volume of space.


Proposed Scientific Program:

We propose to use SIRTF to obtain an extensive census of protoplanetary 
disks in young star clusters and selected star forming regions.  The goal 
of this survey will be to determine the frequency distributions of these 
disks as functions of age, stellar mass and content in young stellar 
clusters and to use this information to determine the lifetimes of
circumstellar disks and thus directly constrain the duration of planet 
building activity and the likelihood of planet formation around young stars.

As an illustration of how we will use such observations to constrain 
disk lifetimes and evolution, we show in Figure 2 some related results 
obtained from ground-based 2.2 micron surveys of a few nearby clusters. 
Here we plot the fraction of near-infrared excess sources in the cluster 
vs the cluster age.  One immediately observes that the likelihood of
finding infrared excess sources in a cluster is dependent on the cluster 
age.  At about 6 million years it appears that stars with near-infrared 
excess are no longer present in young clusters.  This appears to place a 
global limit on the lifetimes of the inner disks for stars formed in 
young clusters and thus places a direct constraint on the timescale 
allowed for planet building in the inner regions of circumstellar disks.

However, this constraint is strictly an upper limit because of the fact 
that the duration of star formation is likely comparable to the ages of 
these clusters.  For example, if the duration of star formation is 5 
million years in each cluster and stars form at the same rate over this 
period, the results in Figure 2 would also be consistent with a disk 
(or more accurately infrared-excess) lifetime of only 1-2 million years. 
Because the duration and history of star formation may vary from one 
cluster to another and the duration of the disk phase may vary between 
individual stars within a cluster, a more detailed analysis of such
data is required to derive any more meaningful constraints on the 
evolution of protoplanetary disks.  However, because of the ambiguities 
in using 2.2 micron data to trace disk emission, existing data like that 
in Figure 2 cannot be used for this purpose.  It is first necessary to 
obtain observations of clusters at  longer wavelengths which can more
accurately and completely trace their disk populations.

We propose to use SIRTF to image ~ 20 young clusters spanning ages 
between 1-70 million years to determine the lifetimes and investigate 
the evolution of protoplanetary disks.  SIRTF will provide us with such 
complete inventories of circumstellar disk populations in clusters that 
we will be able to explore aspects of disk evolution not possible with 
any other type of observation.  For example, we will be able to determine 
how disk lifetime varies with stellar mass.  Do lower mass stars have 
longer lived disks than higher mass stars?  If so what are the corresponding 
implications for the production of planets as a function of stellar mass 
(e.g., is it more difficult to form planets around higher mass stars?).  
With such sensitive observations of a large sample of clusters we will 
also be able to explore the effect of stellar environment on disk 
lifetimes.  For example, does the presence of O stars in a cluster 
significantly abbreviate disk lifetimes due to photoevaporation, as 
observations of the Trapezium cluster now seem to suggest?  Because good 
color-magnitude diagrams exist for many of the clusters we plan to observe
(e.g., NGC 2362, NGC 2264, IC348, etc) we can combine these with 
pre-main sequence tracks to investigate the evolution of disks as a 
function of both age and mass within individual clusters as well as 
across clusters of differing age.  Moreover, because of the great increase 
in sensitivity afforded by SIRTF we anticipate being able to follow the 
evolution of disks to much later ages than shown in Figure 2.  Evidently 
after only a few million years (or less) disks evolve to the point where 
they become too optically thin to be detected at near-IR wavelengths from 
the ground.  But these optically thin disks may remain detectable by SIRTF 
for long periods of time, perhaps up to 50-100 million years or more. 
We may be able to follow the evolution of disks into a new regieme, that 
of post planet formation when the disk begins its evolution toward a 
Beta Pic like object. Thus, we anticipate that SIRTF will fundamentally 
alter our understanding of the evolution of circumstellar disks and in 
doing so place strong constraints on the question of the ubiquity of 
planetary systems in the galaxy.

It is important for us to obtain multi-wavelength images of the clusters 
we select for study in order to define the SEDs of the candidate disks. 
This will be particularly important for measuring the infrared excess 
produced by evolved, optically thin disks and more distant sources.  So 
we expect to utilize both MIPS and IRAC for this project.  In particular,
observations with IRAC will be necessary for some cluster cores where 
crowding may cause confusion even at 30 microns.  We will typically need 
to survey a region about 1/2 degree square toward each cluster.  
Observations of control fields will be needed in some cases as well. 
Our sample of clusters will include all the nearby, well studied young
clusters as well as a few more distant clusters selected on the basis of 
age, stellar content, and richness.

In preparation for our proposed SIRTF program we plan to obtain 
observations at 10 and 20 microns with the WIRE satellite.  Erick Young 
and Charles Lada are co-investigators on an approved WIRE AI program 
(PI: Elizabeth Lada, University of Florida) to perform large scale 
surveys of nearby GMCs and young clusters.  Our WIRE program was
allocated a significant amount of priority 1 orbit segments.  We will 
take advantage of the wide-field capability of WIRE to obtain complete 
inventories of circumstellar disks and young stellar objects within 
the large extended regions of nearby GMCs, something that would be too 
time consuming for SIRTF to do.  This, in combination with our proposed
SIRTF observations will enable a comparison of disk properties for stars 
formed in and out of clusters.  In addition, WIRE observations will be 
obtained for as many young clusters as possible.  The WIRE data will 
thus be used to help select the clusters for inclusion in our SIRTF 
survey.  For the most part the WIRE observations of clusters will be 
severly limited by source confusion due to the instrument's relatively 
poor angular resolution.  Nonetheless, the WIRE observations we obtain 
for embedded clusters will play a critical role in our detailed planning 
of the SIRTF survey.


References:

Adams, F. C., Lada, C. J. & Shu F. H.  1987 ApJ, 321, 788.
Beal J. H. 1987 ApJ, 316, 227.
Beckwith S. et al. 1990 AJ, 99, 924.
Lada, C. J.  & Adams, F. C. 1992 ApJ, 393, 278.
McCaughrean, M. J. & O'Dell C. R. 1996, AJ, 111, 1979
Rucinski, S. M. 1985 AJ, 90, 2321.

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