Observation and Global Campaigns of the DSN

The Delta Scuti Network (DSN) is a collaboration of astronomers from all around the globe who observe and study short period variable stars. It was founded by Michel Breger at the University of Texas (McDonald Observatory) and at the University of Vienna (Institute of Astronomy) in 1983 with the goal to improve the frequency solutions of multiperiodic Delta Scuti stars.

The purpose of multisite campaigns is to avoid regular observing gaps, caused by day light or bad weather, by utilizing different telescopes spaced all around the globe. These gaps would seriously affect the detection of the pulsation frequencies. Meanwhile, after 20 years and 23 campaigns, the field of studied variables has been expanded, now also including Gamma Doradus stars as well as central stars of young planetary nebulae.

The three Delta Scuti stars receiving most attention at the moment are FG Virginis, 44 Tau and 4 CVn. We are preparing campaigns, consisting of simultaneous photometric and high resolution spectroscopic measurements for all three objects, which will enable us to detect pulsation frequencies down to 0.2 mmag amplitude and perform mode identifications in order to compute and improve stellar pulsation models.

For low radial order p-mode pulsators such as Delta Scuti stars every new frequency provides additional and independent information for the models to be computed. This is the motivation for large campaigns such as the 2002/03 FG Vir campaign, during which more than 1000 hours of photometric data were aquired. The noise level in the power spectrum was lowered to approx. 0.05 mmag, making the detection of frequencies with amplitudes as low as 0.2 mmag possible. From the phase difference in different Strömgren filters, the degree l can be determined.

In addition, high resolution time series spectroscopy can yield the degree l and the azimuthal order m of many detected modes. We are able to perform the mode identification from spectroscopy by applying direct line profile fitting and the moment method.