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date	2004.11.30.15.27.18;	author PaoloPadovani;	state Exp;
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date	2004.11.30.14.50.24;	author PaoloPadovani;	state Exp;
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@IMF within 1 kpc: from planetary to stellar masses
==================================================

by Timo Prusti (ESA)

Introduction
------------

The initial mass function (IMF) is a fundamental astrophysical quantity
linking galactic and extragalactic astronomy together. As an outcome of
the star formation process, the IMF constrains different scenarios: no
theory of star formation is valid without being able to explain the IMF.
On the other hand, the IMF is a key input parameter for our
understanding of the chemical evolution of the universe.

Deducing the IMF spanning from planetary to high stellar masses is not
easy. Typically scientific articles proposing an IMF over a wide mass
range are compilations of several pieces of work published in
astronomical literature. Although "The Initial Mass Function" sounds
like an appealing title for the science reference mission (SRM) of the
European Virtual Observatory (VO), it is not suitable as such. The
elements needed for the compilation of the IMF, however, are suited for
VO work. This proposal will concentrate on deducing the IMF at the
lowest masses, as indicated in the project title. Whether the SRM should
also contain the requirements for deducing the IMF at the high mass end,
is left open at this stage.

Science aspects
---------------

- The lowest masses can be reached in the youngest regions because sources
are more luminous at their youth.
- Going to younger regions means more dust in the surroundings leading to
the necessity of extinction correction.
- Close by regions contain typically few hundreds to few thousands members
which means that all members need to be found and distinguished from field
stars for statistical studies.
- Starting point has to be a deep survey data set in optical, NIR and/or
MIR wavelengths.
- Known (bright) members have to be identified by using X-ray, H_alpha
emission line, variability, proper motion, IR excess etc. criteria.
- By using the known members one tries to characterise the properties
of members in the deep survey data and use these characteristics to
find the faint members.
- Construct a sample of members with known completeness levels as a
function of some observable
- Calculation of individual luminosities of sources with a possibility
to make extinction corrections
- Binning luminosities into an observed luminosity function
- Construction of model luminosity function with input parameters such as
pre-main sequence tracks, star forming history, binary fraction, and,
above all, a model IMF
- Comparison of observed luminosity function with the modelled one to find
the most probable IMF for the sample

VO aspects
----------

Data:

The best starting point would be to look deep Spitzer data of close by
star forming regions. After finding a suitable set which is not anymore
proprietary, one should look for the availability of optical and NIR data
of the region. The X-ray, H_alpha emission line, etc. data would need
to be searched from the literature (i.e. VizieR).

Tools:

- Point source extractor for images
- Cross matching tool to combine data from different wavelengths to each
individual source
- Table manipulation/plotting tool to examine the properties of members
- Method/tool to record observationally covered areas including possible
sensitivity changes over the field (needed for statistics to handle
the observational fact that not the same area is covered in all wavelength
regimes and even within covered regions sensitivities may change across
the area)
- SED analysis tool with possibility to display data, overlay models,
correct for extinction, and calculate luminosities

VO need
-------

The gain of VO in this IMF work is mainly in efficiency. It is
foreseeable that work for a region like Chamaeleon I could be done
'manually' by using available tools, but VO would provide large benefit
when the same has to be repeated to other regions and especially when
the other region is Orion with an order of magnitude more members.
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