Up: Have Observations Revealed a Variable Upper End of the Initial Mass Function?

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               SECOND ANNOUNCEMENT

"Up: Have Observations Revealed a Variable Upper

      End of the Initial Mass Function?"

        to be held June 20-25, 2010,

           in Sedona, Arizona, USA

      http://up2010.obs.carnegiescience.edu

      DEADLINE FOR ABSTRACT SUBMISSION IS

           MONDAY, FEBRUARY 15, 2010

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               MEETING ABSTRACT

   The stellar initial mass function (IMF) is a

fundamental parameter that not only encodes the

complex gas phase astrophysics of star formation,

but is also crucial for interpreting the vast

majority of observations made in extragalactic

astronomy today.  Therefore, it is imperative to

constrain its functional form, and the manner in

which it may vary between different environments.

   Since the idea of the "original" mass function

was introduced by Salpeter in 1955, considerable

effort has been made to verify its form, and

previous observations have led many to assume that

it is invariant. In recent years, however, work

challenging this assumption has been accumulating.

In particular, some observations and models suggest

a deficiency of high mass stars in low-density

regions, such as those found in star-forming dwarf

galaxies and the outer disks of spiral galaxies.

Other observations suggest an excess of high mass

stars in some regions, including starbursts and high

redshift galaxies. High mass stars dominate the

luminous and chemical output of galaxies, and

are the basis of most star formation indicators. If

such variations are proven real, they would have

broad consequences for studies of the star

formation histories and chemical evolution

of galaxies, and theoretical work on star

formation.

   A general commonality of recent work providing

possible evidence for IMF variations is that they

are based on the light integrated over galaxies

or regions of galaxies. Such observations only provide

indirect constraints, since IMF variations will be

degenerate with population age and star formation

history. A range of other confounding parameters

must also be considered given that stars are not

being measured individually. On the other hand,

there is some evidence for consistency between

observations and semi-analytic models which assume

systematic deficiencies or excesses in high mass stars.

   The presence of observations both for and against

the universality of the IMF suggest that this is an

appropriate time for a critical re-evaluation of the

ensemble of accumulated observational evidence

constraining the upper end of the IMF, and for

garnering new insights into the physical parameters

controlling high mass star and cluster formation.

The goal of this meeting will be to synthesize a

coherent picture of the IMF slope and characteristic

mass within individual galaxies and across the galaxy

population. Further implications and observational

tests of potential IMF variations must also

be formulated, particularly in the context of the

new capabilities enabled by the recent refurbishment

of HST, the next generation of extremely large

telescopes, or capabilities not yet planned that

must be developed to finally provide unambiguous

constraints on this fundamental astrophysical issue.

SOC: Daniela Calzetti, Edvige Corbelli, Julianne Dalcanton,

Bruce Elmegreen, Janice Lee (chair), Mark Krumholz,

Pavel Kroupa, Barry Madore, Francesca Matteucci,

Chris Martin, Naveen Reddy, David Schiminovich,

Mark Seibert, David Thilker