Areas of Specialization
- optical properties
Ph.D. in Astronomy; University College London
B.S. in Astrophysics; Queen Mary University of London
Dr. Speck studies many aspects of material ejected by dying stars. Early in the history of the Universe, all matter was in the form of hydrogen and helium; elements more massive than helium form via nuclear fusion in stars. Newly-formed elements are ejected from stars either explosively in the case of supernovae, or gently over a few hundred thousand years for lower mass stars like the Sun. These new elements become part of the interstellar medium (ISM), from which new stars and their planets form. Life also needs these new elements to form. Indeed, only 10% of the mass of the human body is made of primordial elements hydrogen and helium. All heavier elements, including carbon, nitrogen and oxygen that dominate living things form inside stars and get ejected as these stars die. Hence we are all star stuff.
While massive stars tend to explode and eject newly-formed elements violently, lower mass stars, like the sun end their lives more gently via approximately a million years of mass loss. This intensive mass loss characterizes the phase of a stars life known as the Asymptotic Giant Branch (AGB) phase and produces a circumstellar shell of dust, molecules and neutral gas. At the end of the AGB, mass loss stops (or at least decreases dramatically) and the circumstellar shell begins to drift away from the star. At the same time the central star begins to shrink and heat up from about 3000K until it is hot enough to ionize the surrounding gas, at which point the object becomes a planetary nebula (PN). Between the end of the AGB phase and the onset of ionization indicative of the PN phase is the post-AGB or proto-planetary nebula (PPN) phase.
In order to understand the nature of the material that goes on to enrich the ISM, we need to understand dust and molecule formation and processing during the lifetime of a star, i.e. during the AGB, proto-planetary nebula (PPN) and PN phases. Our group investigates the nature of the circumstellar material around AGB stars PPNe and PNe from a variety of perspectives, including dust shell morphologies, relative locations of different molecular, ionized and dust species and the mineralogy of the dust.
Click here for a list of publications.