As a "theoretical scientist", Yakiv Pavlenko develops models to interpret and explain qualitatively and quantitatively observed phenomenahea. Physics graduated from the University of Kiev (Ukraine) in 1976 and Doctors in Astrophysics from the Institute of Astrophysics and Atmospheric Physics of Estonia in 1982, Pavlenko devotes most of his time to theoretical modeling and interpretation of stellar spectra. He is an expert in radiative transfer and the physics of the formation of atomic and molecular lines in the stellar atmospheres. Since 1989, he has been collaborating with the research group on Exoplanets and Astrobiology of the Instituto de Astrofísica de Canarias (IAC) and has recently been part of the Visitor Program of the Juan Serra Foundation, an initiative of the IAC that seeks to increase collaboration between its staff and prestigious researchers from other leading scientific institutions.
By Marian Moreno (IAC)
“I use definition of molecular astrophysics to describe complex of tools and procedures used to determine the spectroscopic properties of molecules.”
“We cannot get any reliable results of late type stars, brown dwarfs and exoplanets’ spectra without account of molecular opacities.”
"The study of very high quality molecular lines requires the development of large international projects to calculate perfect molecular data such as HITRAN and EXOMOL."
Question: In 2013, you were at the IAC collaborating with the research group of Exoplanets an Astrobiology. During your stay, you worked in spectral models of young dwarfs in open clusters. Today, you are developing your research in Planetary Systems and Solar System in this center again. What do you think about the research environment that IAC offers?
Answer: I have collaborated with the IAC group from 1989, visited the IAC many times and can compare the capacity and scientific quality of the IAC group with other leading researcher teams in the world. I should note that the IAC group works at the frontiers of modern science. Respectively, it means that research environment of the IAC is on the respectively high level.
Q: Your research focuses, among others, on studies and spectroscopic analysis of brown dwarfs, ultra-cool dwarfs and evolved stars. What models are used to study them? What are the most significant differences that have been determined in these stars once analyzed their spectra?
A: I prefer to use model spectra computed in the framework of classical approach by my own programs. It allows us to control all steps of the process of the numerical simulations: input data, opacities, chemical equilibrium, abundances. However, I compute the synthetic spectra and spectral energy distributions using model atmospheres of other authors, mainly NEXTGEN/Phoenix group. In general, using the hires spectra we should see natural dispersion of abundances and other physical parameters among different populations of Galaxies. For example, looking at halo dwarfs we enhancement of abundances of alpha-elements. In general, in some cases only abundances can provide a proper clue to determine the status of observed object. Lithium test is used to identify population of brown dwarfs, deuterium test can be used to assess population of exoplanets.
Q: Your colleagues from the Exoplanet and Astrobiology group observed the spectra of 20 new isolated planets, cool dwarfs, in the sigma Orionis cluster during your previous stay at the IAC. What was your role in that collaboration?
A: My colleagues from Chile, the Centro de Astrobiología (CAB) and the group of Exoplanets and Astrobiology of the IAC, among them Victor J. S Béjar, devoted themselves to analyzing the spectra of these objects, observed with the OSIRIS instrument, installed on the Gran Telescopio CANARIAS (GTC), and with the Isaac Newton Telescope (INT), both located at the Roque de los Muchachos Observatory, in Garafía (La Palma). Their spectra, type L (temperatures between 2,000 K and 1,800 K), showed similar characteristics to those ones expected in hot Jupiters and young exoplanets.
Now, the main objective of my research is to interpret and explain qualitatively and quantitatively these observed phenomena and, soon, I will work on the theoretical interpretation of those objects.
Q: In your opinion, what advantages does OSIRIS offers for the study of exoplanets? Does this instrument help the scientists to find possible biological traces on exoplanets?
A: We use OSIRIS to obtain spectral data and analyze objects as interesting as the VHS binary system J125601.92-125723.9, and also to study the spectral distribution of very faint objects. To me, it is very useful instrument for the investigation of low mass late-type hosting stars. These investigations are of importance due to weakness of exoplanet which cannot be observed directly.
Q: What is molecular astrophysics? What kind of astronomical observation and instrumentation requires this field of astrophysics?
A: I use definition of molecular astrophysics to describe complex of tools and procedures used to determine the spectroscopic properties of molecules. In most cases, spectra of late type stars, brown dwarfs and exoplanets are governed completely by molecular absorption. We cannot get any reliable results without account of molecular opacities. On the other hand, realization of lithium and deuterium tests which were developed in the IAC requires the use of molecular lists of very high quality. By the way, it triggers appearance of big international projects aimed to compute perfect molecular data, like EXOMOL and HITRAN.
