By Elena Mora
“Probably, this is the first study aimed at understanding how much stellar dust is produced”
“Stardust is important for understanding the universe as a whole. For example, in our Milky Way and in other galaxies, it is basic for our understanding of their formation and evolution”
“Within this project we have laid the foundations of another study aimed at understanding the evolution of globular clusters”
Paolo Ventura, Professor of Stellar Astrophysics at the University of Rome "Roma Tre" and researcher at the Astronomical Observatory of Rome (INAF-OAR), became interested in Astrophysics during time at university, when the research groups working on these objects were the most active in the world and had a well- recognized tradition.
Today, he belongs to the Stellar Group at the Observatory of Rome, and his line of research is Stellar Physics, specifically the structure and evolution of stars, stellar nucleosynthesis processes and chemical abundances in the interstellar medium.
The idea of working on AGB stars arose when his team started to realize the importance of these stars in the evolution of globular clusters and complex star systems, which have been used as laboratories for the development of stellar evolution theories. Motivated by this, Paolo Ventura has spent a month working with the group coordinated by Aníbal García-Hernández, a researcher at the Instituto de Astrofísica de Canarias (IAC), in the framework of the Severo Ochoa short-term Visitors Program.
Question: Your research deals with the evolutionary and structural properties of the stars. Could you explain in more detail what it is?
Answer: Well, this is clearly a very general field of research, but my particular collaboration at the IAC with the group led by Anibal Garcia-Hernández is on a project we started a few years ago which studies the dust which is produced by stars. We collaborate with Anibal because he has long experience in observations of the class of stars expected to produce the largest quantity of dust, which are the stars evolving along the so called asymptotic giant branch (AGB). There are many stages in the evolution of stars but this is probably the first study which is devoted to understanding the amount of dust produced by stars.
Q: What are AGB stars? What happens during that phase of stellar evolution?
A: It is a phase which almost all stars pass through, that is to say all those which do not explode as supernovae. All those which have initial masses less than 8-10 solar masses go through this phase in their evolution, which is very short, and so is not easy to detect. However, it is especially important, because it is when the outer layers of the star- its mantle- is expelled, and contaminates the surrounding interstellar medium with the dust produced. It is just during this phase that a star produces the majority of its dust.
Q: So it should be very important to study this process, shouldn’t it?
A: Very important indeed. That’s why we started to research it because stellar dust is important for the universe as a whole. For example in the Milky Way and in other galaxies it is basic to our understanding of their formation and evolution. The birth of new stars is completely determined by the quantity of dust produced by previous generations of stars, so understanding how to do this is important for many reasons, not only for stellar physics, but in the whole of astrophysics. That’s why we are working hard on this project.
Q: How do you study this process, this interstellar dust? What instruments do you need?
A:That’s a good question. I think that this study is going to be very important, in a way it already is, and it will have a big impact on the scientific literature because we have performed our research combining a theoretical approach, which we have developed over the past 10 years, and the observational experience of Anibal’s group.
As for the instruments, there is a great deal of data obtained with satellites such as ISO (Infrared Space Observatory) and Spitzerfor sources within our Galaxy. However, we are working with the data obtained by Anibal’s group. Now we have started to use further data from Spitzer on galaxies outside the Milky Way, and soon we are sure to be using the James Webb Space Telescope which will be launched in a few years.
Q: What are your next challenges?
A: In the future we will have challenges both inside and outside the Galaxy. Outside the Galaxy the James Webb Space Telescope will allow us to extend our research to all the galaxies in the Local Group –the group of galaxies to which the Milky Way belongs- in contrast to the present situation where we can only reach the Magellanic Clouds –two nearby dwarf galaxies within the Local Group- using data from Spitzer. From within the Galaxy, the Gaia satellite will be providing us with very accurate distances, and characterization of many AGB stars in the Milky Way, which will greatly enhance the sample we have now.
Q: In which projects have you worked during your stay of one month at the IAC? Would you recommend this experience to your colleagues?
A: First, I would like to say that in the present project we have laid the foundations for another study using data from APOGEE –the Apache Point Observatory Galactic Evolution Experiment within the Sloan (SDSS) collaboration-, in which IAC staff members are working, to understand the evolution of globular clusters are involved.
As for my experience here, I would say that it is highly recommendable, even fascinating. From the professional point of view, it has been an excellent opportunity for personal growth. I am happy with my own scientific contribution here, so that I would recommend people to spend at least a month here. Sometime family commitments do not allow people to be away from home for long periods, but I would recommend any astronomer to spend a month here, if they can, because the research atmosphere is very stimulating.
