The Discovery of λ Bootis Stars: The Southern Survey I

The lambda Boo stars are a class of chemically peculiar Population I A-type stars characterized by under-abundances of the refractory elements, but near-solar abundances of carbon, nitrogen, oxygen, and sulfur. There is some evidence that lambda Boo stars have higher frequencies of "bright" debris disks than normal A-type stars. The discovery of four exoplanets orbiting HR 8799, a lambda Boo star with a resolved debris disk, suggests that the lambda Boo phenomenon may be related to the presence of a dynamic debris disk, perhaps perturbed by migrating planets. However, only 64 lambda Boo stars are known, and those stars were discovered with different techniques, making it problematic to use that sample for statistical purposes, including determining the frequency of debris disks. The purpose of this paper is to derive a new sample of lambda Boo stars using a technique that does not lead to biases with respect to the presence of infrared excesses. Through spectroscopic observations in the southern hemisphere, we have discovered 33 lambda Boo stars and have confirmed 12 others. As a step toward determining the proportion of lambda Boo stars with infrared excesses, we have used WISE data to examine the infrared properties of this sample out to 22 mu m. On this basis, we cannot conclude that lambda Boo stars have a greater tendency than normal A-type stars to show infrared excesses. However, observing this sample at longer wavelengths may change that conclusion, as many lambda Boo debris disks are cool and do not radiate strongly at 22 mu m.