The CNRS astrophysics schools gather professional astronomers several times per year to discuss hot scientific topics. Since 2003 and every 3 years, at Oléron and then at La Rochelle, a CNRS astrophysics school welcomes, for the first time, amateur astronomers. That is how about 15 professionals and 35 amateurs, with already a good practice of astronomy, meet to exchange on topics and methods of observations. The goal is to have the passion for astronomy of amateurs converge with useful objectives for the scientific community.

This chapter focuses on the fundamental origin of lines observed in astrophysical spectra. Some properties of the atomic world are qualitatively explained as an introduction to spectroscopy. General laws and rules are exposed and applied to celestial bodies. Please note: it is possible to read this chapter quickly concentrating only on the sentences in bold type.

This paper reviews the overall principles of astronomical spectrographs and the design rules that cover low, medium, and high spectral resolution instruments. Several examples of spectrograph designs are described that are easy to build and are optimised for amateur telescopes. Results are given for each of these instruments. Despite the modest size of amateur telescopes, we show that high performance spectrographs in the hands of amateur astronomers provide access to some specialised areas where the amateur could contribute to useful astrophysical work.

Spectral data reduction is a crucial step, as so important as the acquisition process. Rigor shall be as well applied at this stage to not degrade the quality of the data acquired. It is the last step before the computation of the astrophysical quantities. It is thus necessary to understand what is involved in each processing steps and the underlying limitations. Thus limitations or limit conditions are usually embedded and then hidden in a specific software command that everyone use without completely mastering what is really at stake. In this chapter we will introduced the different type of processing and spectral analysis which can dispose an amateur in several software packages. The first processing will treat about basic images correction which are linked to the CCD acquisition and the processes pipeline. We will then describe the different strategy to calibrate the spectral profile in wavelength and the few corrections driven by the earth environment to increase the accuracy of the future measurements. We will end with the description of few tools on quantitative spectral analysis and their limitations. The practice of spectral acquisition and processing is just at its beginning in amateur world. We hope that this section will demystify the essential step of spectral processing and will motivate the amateur to go beyond the contemplative watching of sky wonders.

The Sun is our nearest star. Its thorough study permits to extend results to other stars for which one does not think at once to encounter features first discovered on the Sun: spots, differential rotation, oblateness, radial surface displacements, etc. The Sun is thus an irreplaceable laboratory, as much as physical conditions prevailing there are often hardly reproducible on Earth. In this chapter, we do not intend to give an exhaustive survey of what we know about our Sun. We want only to give an original lighting on topical questions related to the subject of this book, based on stellar spectroscopy, and we will focus on what we call the solar code. What can we learn from the solar spectrum? More generally, what are we learning from solar oscillations and from the activity cycle? This chapter is divided into three parts, bearing in mind that results obtained on the Sun are transferable to other stars.

In a first part, we will show that the electromagnetic light code permits to access to different atmospheric solar layers. In a second part, we will show that the sound code is a fantastic tool for investigating the internal structure and the dynamics of the Sun. Thus tackled, the Sun is “peeled” as an onion, each successive shells giving an indication on the physical conditions acting in the studied layer, starting from the external atmosphere, crossing the free surface, to progressively go deeper inside, down to the core. In the third part, we will emphasize the “shape” concept, as departures to sphericity are essential in such an approach. This also allows us to study some global astrophysical properties, such as the angular momentum, the gravitational moments and the effect of distortion induced on the visible surface. We will conclude by extending such ideas to other stars, and especially by mentioning new results obtained on the oblateness of Altair and Achernar, including gravity darkening and geometrical distortion.

We intentionally replaced this whole matter in an instrumental context, by highlighting the observations, to the detriment of mathematical formulations, often tempting, but difficult: the reader will be able to find them, thanks to the many bibliographical references given.

This chapter describes non supergiant B-type stars that show emission lines, called Be stars. The emission is caused by the presence of a circumstellar decretion disk. Many physical phenomena are thought to be involved in these stars, such as rapid rotation, pulsations and magnetic fields, and give rise to variations. Spectroscopy is used as a diagnostic tool to study Be stars, by professional astronomers as well as by amateurs.

Cometary spectroscopy from the ultraviolet to the radio wavelength domain provides us with insights on the composition of the gases that are released by the cometary nuclei. While infrared to millimeter spectroscopy give access to the parent molecules that are released directly from the nucleus, visible spectroscopy enables observation of daughter species. Those “radicals” observable in the visible domain have more complex spectroscopic band-like structures and are mainly CN, C2, C3, NH2. Their spectroscopic signatures are easily accessible to amateur astronomers class equipment. Provided that carefully calibrated data are acquired, some simple calculation can readily be done to convert the line intensities into comet molecular outgassing rates and thus provide interesting physical data on comets. In addition to broadband dust measurements, the interested amateur can produce valuable scientific data on comets that will always be welcome from the professional community and certainly useful as the monitoring of comets activity is always essential.

Nebular emission lines are easy to observe, and their spectrum contains a lot of information. We explain the mechanisms of production of the emissions, and the relation between the intensity of the recombination and forbidden lines, and the physical parameters of the objects. A gallery of emission lines spectra is presented, and a rough analysis will clarify their differences. The case of Planetary Nebulae will be developed, in order to determine the extinction constant, the plasma parameters (electron density and temperature), the chemical abundances, and also the properties of the central star (temperature, mass, stellar wind velocity, age).