The remarkable progress, achieved in studies of solar physics lately, is connected first of all with the rapid development of space observation facilities. Nevertheless, quite many fundamental questions in the field still remain open. The prizewinner of the 2011 Contest of Governmental Program of Science Research Support for Young Russian Scholars, leading researcher of Lebedev Physics Institute, RAS (FIAN), Sergei Bogachev, Dr. Sc. (Phys. & Math.), told Vasily Yanchilin, a correspondent of the Poisk newspaper, about issues that are in the focus of astrophysicists' attention.

He emphasized that issues, related to the corona "activity" (outer solar atmosphere), present a real interest for scientists. As it is known, the temperature on the Sun's surface is about 6,000 °C, and in the thin, in solar scales, so-called transition region, where plasma density decreases considerably, reaches 1.5 min °C. So the energy is transmitted from a relatively cold body to a hot one. According to Bogachev, it is caused by the activity of some specific mechanisms. Due to space study devices, enabling to obtain unique detailed data on the object, we are capable to disclose and explore the causes of the given phenomenon.

Today scientists are already aware that none of the known solar activity manifestations has anything to do with heating. Such a conclusion was drawn from recent experiments. In 2008-2009, when this heavenly body underwent one of the most thorough observations of minimums of its "vital activity" for the last 260 years, no sunspots, no flashes, no strong magnetic fields were registered by the scientists. Nevertheless, the corona did not get cold at that time, its size and density did not decrease. This fact testifies that the hot solar atmosphere forms due to invisible uninterrupted microprocesses. Modern methods allow to determine where precisely they occur: 10,000 km thick area is registered directly over the Sun's surface, and the temperature at its lowest border makes up about 4,500 °C, while at the highest border it is about a million. It is quite obvious that it's not so important what kind of mechanisms are "involved" in the corona heating, they do work in this very area, concluded Bogachev.

To understand the essence of the phenomena, the accuracy of the conducted observations should be considerably increased. Nowadays the outer star atmosphere studies are carried out with a spatial resolution ~1-2 angular seconds. The TES IS complex of space telescopes, which had such characteristics, was designed in early 2000s at the Laboratory of X-ray Astronomy of the Sun (FIAN), where they observed stars from the Russian Koronas-Photon satellite, launched on January 30, 2009 from the Plesetsk Cosmodrome (the town of Mirny, Arkhangelsk Region). This is a rather good indicator, stated Bogachev, but it's not enough for finding the answer to the fundamental questions of the corona structure and dynamics.

The same is true of time resolution. Today space telescopes allow to obtain images in several tens of seconds (it is the time spent on the exposure and processing of the film in outer space), whereas the processes, that cause a rise of temperatures in the outer solar atmosphere last no more than 1 to 10 seconds. According to astrophysicists, to solve the problem of heating of solar or other star atmospheres, it is necessary to increase linear and time resolution of the equipment 10 times minimum. Proceeding from the contemporary level of instrument-making, both of the tasks may be accomplished in 5 years. If everything goes as planned, Bogachev empha-

sized, in 2015 we will get the first detailed images of the area under consideration from the orbit.

In the course of the TESIS experiment, going on till December 1, 2009, before the failure of Meteor-3M space platform with special scientific instruments, specialists registered, using high-quality X-ray optics, a unique time resolution--up to 4 s--against typical for this range 30-60. Some facts for comparison: after the work of our devices was over, the US National Aerospace Agency (NASA) put into orbit the newest Solar Observatory (SDO), the telescopes of which managed to reach maximum of time resolution. Nevertheless, Americans failed to surpass the results of Russian scientists.

This is what Bogachev told about the future plans: we are going to study in detail all rapid processes of the corona heating area, using TESIS complex data (it's about 20,000 exposures), to find out if there are microflashes there, if any vibrations are observed, what kind of energy is contained in it and how fast it transfers into heat. It is only a part of a large program, its ultimate goal is to put into orbit a specialized small scientific satellite for studies of small scale processes in the corona. For this purpose a new generation telescopes with a resolution of 0.15 angular seconds were offered, which will allow to see structures with a linear size of 100 km. It was developed by two groups of specialists from FIAN and NASA. European scientific groups are also participating in the project.

According to Bogachev, today we witness a real boom in solar physics: perspective directions are available in

abundance, each of them has a broad range of tasks. The only bad thing is a lack of a large national satellite, working in a wide range of modes. The scientist is sure that no "foreign" data can replace our own active experiments, when one can formulate tasks and choose objects for research independently. In 2009, we conducted research from the TESIS Observatory, but it is no longer in orbit, so FIAN authorities are seeking a full substitute for the lost satellite. By the way, Russian scientists have already worked out a project identified as "Solaris", which will involve ten Russian scientific organizations. Now much effort is made to include it into space program.

Its main aim, said Bogachev, is to prolong the course of studies, which started at the Kownas-Photon. At that time we got significant results in the course of solar macrospicules--rather quick and numerous incandescent ionized gas splashes lasting 5-10 min, registered at the edge of the solar disk. It was for the first time in the world history when the telescope measured plasma acceleration inside flows and testified that it is different from gravitational acceleration and therefore is managed by some unknown force. These data bring us to two fundamental problems: one is connected with solar heating, the other concerns acceleration of the solar wind, arising at the same altitudes.

In 2001-2005, the most enigmatic phenomenon, the so-called hot spots on the sun, were discovered during FIAN observations with the help of Koronas-F, which was designed by Russian and Ukrainian scientists. The satellite was launched on July 31, 2001 and ceased its existence in the course of natural evolution of the orbit on December 6, 2005. In the corona, says Bogachev, there emerge unreasonably compact objects, of the size of about 10,000 km, and the temperature over 10 min °C, and during some splashes--up to 30. For example, in March-April 2009, during minimal solar activity, the instruments registered about 20 "fires" on the quiet solar disk. There are still no explanations to these phenomena. The major problem constitutes the issue of sources of heating. The project "Solaris" will possibly help us unthread the mystery, allowing to significantly enlarge our knowledge of solar physics.

V. Yanchilin, "The Corona with Heating", "Poisk" newspaper, April 8, 2011

Illustrations from the TESIS site of the Laboratory of X-ray Astronomy of the Sun (FIAN)