Introduction

All research papers have as the first element to the body of the paper a section called 'Introduction'. This piece describes the particular issue or issues that your paper will address, why these issues are important, and provides the reader with a mini history lesson to the topic. No research is conducted in a vacuum. No matter what you elect to investigate, there is likely to be some paper out there, already published, that has some relevance to your topic. It is your responsibility to find all of the relevant articles and cite those that impact your work.

As a research scientist, you already know off the top of your head the significant papers in your area. You may have to do a bit of library research to uncover additional papers that have been published. Usually, all of this work is done BEFORE you start your investigation. You might, for instance, be reading someone's paper on infrared observations of the Orion Nebula, and decide to study the infrared emission from the Lagoon Nebula. Have these already been made? If not, you are free to do them yourself if you have the resources. But make sure that you tell the reader why such observations are needed by citing similar studies done by others and their conclusions.

Introductions have to be kept simple, and should probably not constitute more that 10 percent of your paper. Again, I cannot stress enough that you make certain you include citations to all related work that has been published, but keep this list brief. No one wants to see 50 citations, but the top 5 or 10 may be a good minimum.

Interstellar clouds with a cometary or filamentary appearance present a unique opportunity to study the interaction between these clouds and their ambient medium. Heretofore, the number of examples have been rather limited so that only qualitative statements could be made about the nature of this interaction. Within the last 5 years, however, a variety of surveys have begun to shed new light on this subject.

Studies of star formation in low-mass Bok globules near the Gum Nebula ( Hawarden and Brand, 1976; Sandqvist, 1976 and Reipurth, 1983) have identified 36 globules with comet-like shapes, whose tails are pointed away from the central region of the nebula containing an OB association. The clouds have masses from 2 - 70 times the sun's, sizes of about 0.3 pc, and in at least one case, Bernes 135, a pre-main sequence star is associated with the head of the cloud. According to extensive CO mapping by Bally et al(1987) of the Orion Molecular cloud, it also has a cometary appearance though at a scale of 13 pc and masses of about 50,000 times the sun's. In addition to these objects, it is now known that clouds with a filamentary shape are a major component of the local interstellar medium.

The Infrared Astronomical Satellite (IRAS) detected a large- scale 'cirrus' component (Low et al, 1984) that dominates the infrared sky at 100 microns. Weiland et al(1986) have demonstrated that the brightest cirrus features are also coincident with some of the high- latitude CO clouds discovered by Blitz, Magnani and Mundy (1984:hereafter BMM) and Magnani, Blitz and Mundy (1984 : hereafter MBM). These CO clouds are believed to be within ~100 pc of the sun, have sizes ~ 1 pc and are probably not gravitationally bound.

The possibility that magnetic fields may also be involved in shaping at least some filamentary clouds has been raised by McCutcheon et al(1986) in a study of L204 from the list of 23 'globular filament' clouds identified by Schneider and Elmegreen(1979). Optical polarization studies of L204 imply a magnetic field with B ~ 50 micro Gauss aligned perpendicular to the major axis of the filament. This appears to be a classic case of gravitational collapse, impeded perpendicular to the field axis, where magnetic pressure can help to support the cloud against collapse.

The study of the Draco molecular cloud (Plate 1(k)) by Odenwald and Rickard(1987) suggests that the appearance of this 'hybrid', comet / filamentary cloud may be the result of the ablative shedding of mass at low Reynolds number as the cloud passes through the ISM. Using the 100 micron data in the IRAS survey, a total of 15 objects was discovered with comet-like or filamentary appearances that also show evidence for hydrodynamic processes at work. In this study, the far- IR and optical properties of these objects are described. Their morphologies are also used to place constraints on cloud dynamics and the properties of the interstellar medium.

RETURN to the Paper topic index.