Introduction

This chapter attempts to provide a summary of the course I gave during the XXII Canary Island Winter School of Astrophysics. In no way should this chapter be perceived as the final answer to a problem. I hope that this chapter can serve as a basis for students and fellow scientists to go beyond what is written here. As in many approaches that I have pursued, this work is a snapshot of where I am and hopefully a possible starting point from which one can expand to other paths not yet ventured.

This chapter starts with a short historical introduction on signal processing and statistics or how our forefathers started doing data analysis more than 200 years ago. The second part is related to the sampling and acquisition of continuous physical signals for subsequent analysis in a digital world.

Introduction

The four lectures that I presented at the XXII Winter School of Astrophysics were an eclectic mix of topics loosely bound under the title of this chapter: an observer's views and tools. The presentations given by all of the lecturers at the Winter School are available at the time of this writing on the IAC Web site (see “about the school” and “lecturers and topics” on that web site). This chapter can be read in conjunction with the lecture presentations on that web site, but that is not required. This chapter does not completely follow the order of the presentations.

Chemically peculiar and pulsating stars of the upper main sequence

On and near the main sequence for Teff > 6, 600 K, there is a plethora of spectrally peculiar stars and photometric variable stars with a bewildering confusion of names. There are Ap, Bp, CP, and Am stars; there are classical Am stars, marginal Am stars, and hot Am stars; there are roAp stars and noAp stars; there are magnetic peculiar stars and nonmagnetic peculiar stars; He-strong stars, He-weak stars; Si stars, SrTi stars, SrEuCr stars, HgMn stars, PGa stars; λ Boo stars; stars with strong metals, stars with weak metals; pulsating peculiar stars, nonpulsating peculiar stars; pulsating normal stars; nonpulsating normal stars; δ Sct stars, δ Del stars, and ρ Pup stars; γ Dor stars, SPB stars, β Cep stars; γ Cas stars, λ Eri stars, α Cyg stars; sharp-lined and broad-lined stars, some of which are peculiar and some of which are not.

Introduction

Asteroseismology, and hence the study of stellar properties, is being revolutionized by the extremely accurate and extensive data from the CoRoT (Baglin et al., 2009) and Kepler (Borucki et al., 2009) space missions. Analysis of time series of unprecedented extent, continuity, and sensitivity has allowed the study of a broad range of stellar variability, including oscillations of a variety of pulsating stars (see, e.g., Gilliland et al., 2010; Christensen-Dalsgaard and Thompson, 2011, for reviews), and leading to comparative asteroseismology (or synasteroseismology) for main-sequence stars showing solar-like oscillation (Chaplin et al., 2011). Also, early analyses of Kepler data have demonstrated the power of asteroseismology in characterizing the central stars in planetary systems (Christensen-Dalsgaard et al., 2010; Batalha et al., 2011), and such investigations will undoubtedly play a major role in the continuing Kepler exploration of extrasolar planetary systems.

However, perhaps the most striking results of space asteroseismology have come from the investigation of red giants. Given the extensive outer convection zones of red giants, solar-like oscillations were predicted quite early (Christensen-Dalsgaard and Frandsen, 1983). Ground-based observations have been carried out in a few cases (e.g., Frandsen et al., 2002; De Ridder et al., 2006) but, owing to the very long periods of these huge stars, such observations are extremely demanding in terms of observing and observer's time. Space observations, on the other hand, allow nearly continuous observations over very extended periods, as demonstrated by early observations by the WIRE (Retter et al., 2003) and MOST (Barban et al., 2007) satellites.