M. E. Sachkov

“Spektr-UF” project

The “Spektr-UF” project is intended for the design and development of a large space observatory operating in the ultraviolet (UV) band of the spectrum inaccessible for survey from the surface of the Earth. The main observatory instrument is a space telescope T-170M with a primary mirror 1.7 m in diameter; it will be equipped with high and low resolution spectrographs and cameras for high-quality UV imaging. In respect of capabilities, the project is similar to the American Hubble Space Telescope (HST), and exceeds the latter in some parameters. The project is included in the Russian Federal Space Program for the period 2006–2015. The launch is planned for 2016. The project is under development by the Lavochkin Association in cooperation with the Institute of Astronomy, Russian Academy of Sciences.

Two period-radius relations for classical Cepheids: Determining the pulsation mode and the distance scale

Based on our radial-velocity measurements and on published photometric observations, we calculated the radii of 64 classical Cepheids that were previously assumed to be fundamental-mode pulsators. Our detailed analysis of the period-radius diagram shows that the sample of Cepheids with pulsation periods shorter than 9 days probably contains a significant fraction (up to 30%) of stars pulsating in the first overtone. This fact leads to incorrect luminosity estimates for Cepheids and may be partly responsible for the discrepancy between the short and long distance scales.

Spectral studies of comets in the ultraviolet range and prospects of the WSO-UV project in these studies

Many problems of determining the chemical composition of comets and studying the physical processes in cometary nuclei can only be solved by using observational data in the UV range of the electromagnetic spectrum (115–300 nm). Cometary observations have a number of features in comparison with such studies of other astronomical objects. The World Space Observatory — Ultraviolet mission, planned for launch in 2021, will overcome most of the challenges in these studies and will be able to become an essential tool of cometary UV research in the following decade.

Abundance Analysis and Searching for Nonradial Pulsations in the Atmosphere of the Chemically Peculiar Star HD 115708

We present the results of our abundance analysis for the magnetic chemically peculiar star HD 115708 based on high-resolution spectra. The atmospheric chemical composition of HD 115708 (Teff = 7550 K) is shown to be typical of cool Ap stars with a significant ionization disequilibrium for the first and second rare earth ions, which is commonly observed in the atmospheres of pulsating Ap (roAp) stars. Our study of the vertical distribution of elements has shown that Mg, Ca, Cr, and Fe concentrate in deeper atmospheric layers, with their abundances decreasing sharply in the upper layers. The jumps in abundance are 1.5–3 orders of magnitude. Silicon is distributed in depth almost uniformly in the atmosphere of HD 115708. The derived empirical Cr and Fe distributions agree qualitatively with the results of diffusion calculations. Since the atmospheric chemical peculiarities in HD 115708 correspond to roAp stars, we have performed a spectroscopic monitoring to find nonradial pulsations. We have been able to determine only an upper limit for the amplitude of the possible radial velocity pulsations, ∼100 m s−1, due to the insufficient temporal resolution and instability of the main stellar spectrograph (MSS) of the 6-m telescope.

Science issues of the “Spektr-UF” project

The “Spektr-UF” project (“World Space Observatory-Ultraviolet” (WSO-UV)) will be the largest space observatory for observations in the UV band. In this paper we briefly outline the key science issues that the WSO-UV will address during its lifetime with the help of its instrumentation: spectrographs and a field camera unit. Of special interest are early Universe physics (reionization and search for baryonic matter), star formation, chemical evolution of galaxies, astrophysical accretion processes, stellar atmosphere physics, and planetary atmosphere studies.

Ultraviolet observatories of the future

The ultraviolet spectral region is extremely important for studying astrophysical objects in a wide temperature range of 3000 to 300000 K. Over the past three decades, several tens of space experiments were conducted and space observatories were injected into orbit for observing objects in the ultra violet (UV) spectral region. Works on next-generation UV missions are now in progress in Europe, the United States, and Russia. A summary of requirements for these missions and a brief description of the main projects are presented.

Galactic Astronomy in the Ultraviolet

We propose a number of prospective observational programs for the ultraviolet space observatory WSO-UV, which seem to be of great importance to modern galactic astronomy. The programs include the search for binary Cepheids; the search and detailed photometric study and the analysis of radial distribution of UV-bright stars in globular clusters (“blue stragglers”, blue horizontal-branch stars, RR Lyrae variables, white dwarfs, and stars with UV excesses); the investigation of stellar content and kinematics of young open clusters and associations; the study of spectral energy distribution in hot stars, including calculation of the extinction curves in the UV, optical and NIR; and accurate definition of the relations between the UV-colors and effective temperature. The high angular resolution of the observatory allows accurate astrometric measurements of stellar proper motions and their kinematic analysis.

Experimental Spectroscopy in the Ultraviolet Range of the Electromagnetic Spectrum

The main parameters of spectroscopic experiments in the UV range of the electromagnetic spectrum are estimated. Different spectral devices are compared in terms of their potential quality. Some technical details of current UV experiments and prospects of spectrographs of the WSO-UV project are discussed.

Web-Resources for Astronomical Data in the Ultraviolet

In this paper we describe databases of space projects that are operating or have operated in the ultraviolet spectral region. We give brief descriptions and links to major sources for UV data on the web: archives, space mission sites, databases, catalogues. We pay special attention to the World Space Observatory—Ultraviolet mission that will be launched in 2021.

Doppler methods of search and monitoring of exoplanets

The main stages of the development of Doppler methods of search and study of extrasolar planetary systems (exoplanets) are described. The main instrumental and methodological effects that influence the measurement accuracy of spectral line positions in the study of exoplanets are considered. The development of the domestic spectrograph for spectroscopic monitoring with high-precision determination of radial velocities is reported. Directions for further development of high-resolution spectroscopy are discussed.