RANDY L. PHELPS

This is the Palomar-Las Campanas Observatory-NOAO (PLCON) Open Cluster Survey Homepage.

Star clusters are unique laboratories for investigating a wide range of astrophysical problems relating to star formation, stellar evolution, the formation and structure of the Milky Way (henceforth, also the "Galaxy"), and the age and distance scale of the Universe.  This unique role can be attributed to the fact that distances and ages can be determined for clusters, whereas these fundamental parameters are difficult to determine for isolated, or "field", stars. Consequently a large number of cluster studies were undertaken in the 1950s and 1960s. The majority of the effort since then, however, has been concentrated on the globular clusters, whose spatial distribution defines the spherical halo of the Milky Way, and which are the oldest, and most massive of the Galaxy's clusters. Despite the recognized importance of less massive, typically young open star clusters (spatially found in the disk) for investigating a wide range of astrophysical problems, only some 200-300 of the more than 1200 known clusters (Lynga 1987) have received more than superficial attention.

The advent of solid-state charge-coupled devices (CCDs) in the 1980s revolutionized astronomy, allowing research on to be undertaken on small telescopes that once was achievable only with the largest ones. The advantages of CCD detectors over those used previously are enormous; they are linear detectors and they can be used to measure reliably positions and brightnesses (a technique called "point-spread function (PSF) photometry") for thousands/tens of thousands of stars on a single image, whereas previously only dozens or hundreds of stars were able to be measured (and not always precisely). CCDs are also much more sensitive than earlier detectors, allowing small telescopes to reach faint stars. The fields of view available with CCDs match the apparent angular sizes of most open clusters quite well, making them prime targets for smaller telescopes and CCDs.

Surprisingly, however, only about 100 open clusters have been observed with CCDs, and most of them were already the subjects of previous photographic and/or photoelectric studies. There remains, therefore, an untapped wealth of knowledge to be found within the nearly 900-1000 open clusters that have been the subject of few, if any, studies. The clusters that have been observed to-date are typically the largest, closest, more massive ones that are, not surprisingly, the easiest to observe. Without a more complete, homogeneous survey, the biases inherent in our current understanding of the open cluster population will seriously compromise our understanding of star formation history within the Galactic disk, the characteristic sizes, masses, and integrated luminosities and colors of Galactic open clusters (and hence our interpretations of integrated properties of clusters in other galaxies), the internal dynamical evolution and subsequent break-up of open clusters (leading to many of the stars we see in the field), the age of the Galactic disk, the chemical enrichment history within the disk, and a host of other timely astrophysical problems.

For the first time, it is possible technologically to observe the majority of the known population of open clusters, thereby improving our understanding of a large number of astrophysical problems.

As a step toward this goal, I have been undertaking a program to obtain and/or reduce and analyze CCD data for ~500 open clusters for which little or no information is currently available. This will bring the total number of open clusters with available CCD data to ~600, or fully 50% of the known open cluster population. The "Palomar-Las Campanas Observatory-NOAO (PLCON) Open Cluster Survey" will significantly enhance our knowledge of the Galaxy's population of open clusters, and provide meaningful, self-consistent cluster parameters (e.g, ages and distances) that will form the basis for numerous follow-up studies in a wide range of astrophysical disciplines.

Click here to see PLCON papers (in press and/or published)

Click here to see PLCON presentations at recent meetings/conferences

Click here to access the PLCON database homepage

Click here to see PLCON-related student research activities