SPITZER OBSDRVATIONS OF GAS IN CIRCUMSTELLAR DISKS: UPPER LIMITS TO GAS MASSES
IN HD 105 AND ....

Author list to be determined:  this paper will be led by U. Gorti and D. Hollenbach

We will start this paper assuming only HD105 data will be analyzed, although
we may add HD 134319 once we have MIPS data and a good dust model.  Mostly,
the paper is to show our technique of using the Gorti and Hollenbach thermo/chemical
model to set upper limits or values on gas masses.  Future papers can then
refer to the methods we spell out in detail in this paper. 

Paper draft outline (comments welcome, this is subject to revision!)

  1.INTRODUCTION: (2 pages) 

	Evolution of gas in disks, importance of detecting gas, implications 
	for core accretion theories of planet formation, how small masses of 
	gas can affect terrestrial planet dynamics.  Note that inner holes
        can be created by gas mixed with dust, and do not necessarily
        imply planets.

	Previous observations of gas in disks, difficulties in detecting gas,
	summary of present understanding based on available information (e.g., 
	CO and H2, rapid dispersal, photoevaporation etc).
	
 	FEPS H2 program to detect gas in disks, description of project and 
	goals of the study. Describe how targets were chosen, ages, X-ray
	luminosities etc.  A few words on the sources discussed in this
        paper: HD 105 and (maybe) HD 134319 (but leave most for section 2). 

        Outline of paper and following section topics.

  2. SOURCE INFORMATION AND BACKGROUND (HD 105 and HD 134319?): (1 page)

	List all known properties of source(s?) such as spectral type, age, 
	distance, luminosity, X-rays, UV, dust measurements or infrared 
	excesses and any other observations of relevance.

  3. OBSERVATIONAL ANALYSIS: (1-2 pages)
        (To be written by a volunteer from the H2 data reduction team)

 	Details of observations, photometric and spectroscopic data obtained,
	data reduction procedures, and figures and tables of the data. 

  4. DATA MODELING: (2-3 pages)

      A. Dust models: Brief description of dust models used, with reference 
	 to our published  paper on the first look results. Procedure used for 
         arriving at the best fits, and best fit parameters and fits to observed SEDs. 
 
      B. Gas models: Brief description of model with reference to Gorti and
         Hollenbach (2004) paper, and 
	 procedure used for modeling gas, i.e., use above dust model, stellar
	 parameters, and change mass and spatial distribution of gas to obtain
	 upper limits for gas mass.  Possible need to try a few different dust
         models, since our limited dust data do not uniquely specify the dust.
         Also need to consider not having a constant dust to gas ratio as a
         function of position within a given disk model. 

  5. RESULTS AND DISCUSSION: (2-3 pages)

	Show the possible configurations for gas and dust, and plots of how
	line fluxes vary with gas mass in each case. Discuss figures, and
	arrive at numbers for the upper limits to gas mass. Discussion of which
	lines are more sensitive and the underlying physics (gas heating mechanisms,
	density and chemistry, etc).     

	Implications of the above result on planet formation. For example, there
	is too little gas to form gas giants, planet building epoch must be over
	in HD 105. Presence or absence of gas in terrestrial planet zone, how small
	amounts of inner gas can shield outer gas (preventing us from detecting
        rather large amounts of outer gas, while not seeing the shielding inner
        gas either because of beam dilution effects, and small amount of shielding
        mass required. 

	
  6. SUMMARY AND CONCLUSIONS: (1/2-1 page)

        Summarize paper, state upper limits obtained for gas in  HD 105, the 
	implications of the results obtained, future data and questions to be 
        answered by the FEPS H2 project. 'Proof of concept' nature of this paper.