A 3-day workshop at STScI on "pearls", "feathers", and "spurs" in spiral galaxies. The workshop will bring observers together with theorists and modelers, and focus primarily on substructure in and between spiral arms and what it can (and can not) tell us about spiral structure and the processes of massive star formation in disk galaxies.

Attendance is limited to about 30 participants, by invitation.

Issues to be addressed concern the apparently disparate approaches taken and the different assumptions made by theorists and modelers of star formation in spiral arms, and the fundamental question of what exactly is it that observers measure. The intention is to provide a forum for debate on the theoretical issues, to become aware of the state of the observations, and to consider the observational consequences of theory.

Specific issues of interest in and near spiral arms include:

• Morphology and kinematics of "feathers" and "spurs".
• Gradients in stellar populations.
• Regularity/periodicity in the incidence of OB associations along arms.
• Appearance and excitation of atomic and molecular tracers.
• Physics and modeling of gas flow.
• Organization and triggering of star formation.

The aim is to move on from the general qualitative principles of spiral structure and star formation formulated about 40 years ago towards a quantitative picture of what happens to the ISM when it passes through a spiral arm, and how we can interpret observations of the various tracers involved. To this end the workshop aims to draw together detailed observations on flow fields and locations of gas and star formation tracers (CO, HI, dust, IR, UV, radio continuum) in several nearby grand-design galaxies, combine this with physical models of what controls the motion of the ISM and what excites the tracers observed, take stock of recent computational modeling efforts, and consider the next steps both for observations and theory.

The workshop will take place in the John Bahcall Auditorium at STScI from about coffee-time Tuesday, 29 September through to the end of the afternoon on Thursday, 01 October with a break to attend the STScI Colloquium on Wednesday after tea.

The oral presentations are intended to serve as (mini-)reviews of the subject.

Poster papers on details and recent new results are greatly encouraged. A "poster session" will provide the junior author of each poster with an opportunity (2 minutes + 2 slides) to advertise.

For further information contact Ron Allen, rjallen@stsci.edu.