SCORPIO-2 guiding and calibration system in the prime focus of the 6-m telescope

We describe a device (adapter) for off-axis guiding and photometric calibration of wide-angle spectrographs operating in the prime focus of the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. To compensate coma in off-axis star images an achromatic lens corrector is used, which ensures maintaining image quality (FWHM) at a level of about 1″ within 15′ from the optical axis. The device has two 54″-diameter movable guiding fields, which can move in 10′ × 4.′5 rectangular areas. The device can perform automatic search for guiding stars, use them to control the variations of atmospheric transmittance, and focus the telescope during exposure. The limiting magnitude of potential guiding stars is m _R ~ 17^m. The calibration path whose optical arrangement meets the telecentrism condition allows the spectrograph to be illuminated both by a source of line spectrum (a He–Ne–Ar filled lamp) and by a source of continuum spectrum. The latter is usually represented either by a halogen lamp or a set of light-emitting diodes, which provide illumination of approximately uniform intensity over the wavelength interval from 350 to 900 nm. The adapter is used for observations with SCORPIO-2 multimode focal reducer.     

ADAM low- and medium-resolution spectrograph for 1.6-m AZT-33IK telescope

We describe the design of a suspended low- and medium-resolution spectrograph (R ≈ 300–1300) designed and made at the Special Astrophysical Observatory of the Russian Academy of Sciences for the 1.6-m AZT-33IK telescope of Sayan Observatory of the Institute of Solar-Terrestrial Physics of the Siberian Branch of the Russian Academy of Sciences. We report the results of laboratory measurements of the parameters of the instrument and tests performed on the 1-m Zeiss-1000 telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. We measured the total quantum efficiency of the “spectrograph + telescope + detector” system on AZT-33IK telescope, which at its maximum reaches 56%. Such a hight transparency of the spectrograph allows it to be used with the 1.6-m telescope to determine the types and redshifts of objects with integrated magnitudes m_AB ≈ 20–21, and this result was confirmed by actual observations.     

Camera lens for the 6-m Russian telescope fiber-optic magnetometer

We have designed and produced a speed camera lens for fiber-optic magnetometer of the prime focus of the 6-m Russian telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. Resolution of the developed lens obtained during test observations corresponds to the calculated value. The transmission of the lens was measured at three wavelength ranges. It is equal to 78% at a wavelength of 6328 Å, 80% at λ 5320 Å, and 19% at λ 4050 Å. A transmission cutoff for wavelengths shorter than 430 nm is outside the operational range of the spectrograph of the fiber-optic magnetometer which is 430–690 nm.     

Investigation of galaxies in the second byurakan sky survey. I. Spectroscopic observations in a field at 15h30m, +59°

The results of spectroscopic observations of 30 galaxies from the Second Byurakan Spectral Sky Survey in a field of 16 square degrees centered at coordinates a = 15^h30^m, δ = + 53°are presented. The spectra were obtained on the 6-m telescope of the Special Astrophysical Observatory, Russian Academy of Sciences, in the wavelength range of 4000–7400 Å with 15 Å resolution. Emission lines are present in the spectra of most of the galaxies. Redshifts and absolute stellar magnitudes were determined for all the galaxies.     

Spectral classification of stars in the second Byurakan Sky Survey. II

The results of the spectra/classification of 310 stars and objects having a continuous spectrum, selected in the course of the Second Byurakan Spectral Sky Survey, are given. Slit spectra were used in the work, which were obtained from 1978 to 1994, mainly on the 6-m telescope of the Special Astrophysical Observatory, Russian Academy of Sciences; some of the spectra were obtained on the 2.6-m telescope of the Byurakan Astrophysical Observatory, National Academy of Sciences of Armenia, and the 4.5-m Multiple-Mirror Telescope (USA), with 5–15 Å resolution. The sample contains objects in the range of stellar magnitudes 11.0 ≤ m(pg) ≤ 19.5. We found 93 DA, 2 DO, 12 DB, and 1 DC white dwarfs, 83 sdB and 20 sdO subdwarfs, 34 NHB variables, 2 cataclysmic variables, 48 stars of late spectral types, 8 spectroscopic binary systems, and 7 objects having a continuous spectrum. Several recordings are given for each of these spectral types.     

Radial velocity measurements with stellar spectrographs of the 6-m telescope

Solutions are considered that allow the accuracy of stellar radial velocity measurements with the spectroscopic instruments of the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences to be improved. The factors that limit the accuracy of spectroscopic V _r measurements are analyzed both in general and for the particular design of the telescope and its housing.     

Spectroscopy of stars in ground-based ultraviolet. II: Atmospheres

Some of the tasks of spectroscopic studies of stellar atmospheres in the ground-based ultraviolet are reviewed in historical perspective. Examples used include fragments of spectra that we obtained with the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences     

Astroclimate of Northern Caucasus—Myths and reality

We list the principal stages of astroclimatic studies concerned with choosing the sites for astrophysical observatories in Caucasus and Crimea. We chow that the sites for three observatories in Northern Caucasus (Kislovodsk Mountain Astronomical Station of Pulkovo Main Astronomical Observatory of the Russian Academy of Sciences, Special Astrophysical Observatory of the Russian Academy of Sciences, Terskol Observatory) were chosen without obtaining representative statistical data in terms of the number of clear night hours and seeing. We report the data on the number of clear night hours and seeing for the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences based on results of long-term observations. We discuss the possible causes of the discrepancies between experimental and forecast data and conclude that currently none of the three observatories in the North Caucasus can be preferred because of the great variety of the methods employed and limited statistics in terms of astroclimatic and meteorological parameters for some sites.     

Stellar spectroscopy in ground-based ultraviolet. III: Chromospheres and envelopes of cool stars

In historical perspective we discuss selected tasks in the studies of stellar chromospheres and circumstellar envelopes using spectroscopic methods in the ground-based ultraviolet. We illustrate our discussion by fragments of spectra that we took with the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences.     

Investigation of galaxies of the second byurakan sky survey. II. Spectroscopic observations in the 08h00m, +59° field

The results of spectroscopic observations of 25 objects of the Second Byurakan Spectroscopic Sky Survey in a field with central coordinates a = 08^h00^m, δ = +59° are given. The spectra were obtained on the 2.6- m telescope of the Byurakan Astrophysical Observatory, National Academy of Sciences of the Republic of Armenia, and the 6- m telescope of the Special Astrophysical Observatory, Russian Academy of Sciences, in 1997– 1998 with a spectral resolution of from 5 to 15Å. The redshifts and absolute stellar magnitudes of all the galaxies were determined and they were classified. A histogram of the redshift distribution of the complete sample of galaxies in this field of the survey is given.     

Radial velocity measurements using an absorption cell

The potential of an algorithm of semiempirical modeling of stellar spectra recorded via an iodine absorption cell is analyzed. This algorithm, when used with the NES quartz echelle spectrograph of the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences, is shown to be able to achieve a Doppler shift measurement accuracy of 20 m/s with an internal accuracy of 2 m/s.     

One-meter Schmidt telescope of the Byurakan Astrophysical Observatory: New capabilities

In 2013–2015 the Laboratory of spectroscopy and photometry of extragalactic objects (LS-PEO) of the Special Astrophysical Observatory together with Armenian specialists upgraded the 1-m Schmidt telescope of the Byurakan Astrophysical Observatory of the National Academy of Sciences of Armenia. We completely redesigned the control system of the telescope: we replaced the actuating mechanisms, developed telescope control software, and made the guiding system. We reworked and prepared a 4k × 4k Apogee (USA) liquid-cooled CCD with RON ~ 11.1 e^?, a pixel size of 0.″868, and field of view of about 1□°, and in October 2015 mounted it in the focus of the telescope. The detector is equipped with a turret bearing 20 intermediate-band filters (FWHM = 250 Å) uniformly covering the 4000–9000 Å wavelength range, five broadband filters (u, g, r, i, z SDSS), and three narrow-band filters (5000 Å, 6560 Å and 6760 Å, FWHM = 100 Å). During the first year of test operation of the 1-m telescope we performed pilot observations within the framework of three programs: search for young stellar objects, AGNevolution, and stellar composition of galaxy disks.We confirmed the possibility of efficiently selecting of young objects using observations performed in narrow-band Hα and [SII] filters and the intermediate-band 7500 Å filter. Three-hours long exposures with SDSS g-, r-, and i-band filters allow us to reach the surface brightness level of 28^m/□″ when investigating the stellar content of galaxy disks for a sample of nine galaxies. We used observations performed with the 1-m telescope in five broadband (SDSS u, g, r, i, and z) and 15 intermediate-band filters (4000–7500 Å) to construct a sample of quasar candidates with 0.5 < z < 5 (330 objects) in about one-sq. degree SA68 field complete down to R_AB = 23^m. Spectroscopic observations of 29 objects (19.^m5 < R < 22^m) carried out at the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences confirmed the quasar nature of 28 objects.     

A globular cluster in the dwarf galaxy Sextans B

We present spectroscopic observations of a massive globular cluster in the dwarf irregular galaxy Sextans B, discovered by us on the Hubble Space Telescope Wide Field and Planetary Camera 2 (HST WFPC2) images. Long-slit spectra were obtained with the SCORPIO spectrograph on the 6-m telescope at the Special Astrophysical Observatory of the Russian Academy of Sciences. We determine the age, metallicity and alpha-element abundance ratio for the globular cluster to be 2 ± 1 Gyr, ?1.35 ±0.25 dex, and 0.1 ± 0.1 dex, respectively. Main photometric and structural parameters of it were determined using our surface photometry on the HST images. The mass (～10⁵ M⊙), luminosity and structural parameters appear to be typical of the globular clusters in our own Galaxy. Our findings shed new light on the evolutionary history of Sextans B.     

Dichroic circular polarization analyzer for the Main Stellar Spectrograph of the 6-m telescope

We describe a dichroic circular polarization analyzer with a double image slicer providing seven slices for each polarization developed for the Main Stellar Spectrograph of the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. The analyzer is designed for measuring stellar magnetic fields using the Zeeman effect and represents an upgraded version compared to earlier used polarization analyzers. We report the parameters of the analyzer and estimate the accuracy of measurements performed with it.     

Investigation of atmosphere nonstationarity in the supergiant 55Cyg. I. Temporal line profile variability

The CCD spectra taken with echelle spectrographs of the 2-m telescope of the Shemakha Astrophysical Observatory of the National Academy of Sciences of Azerbaijan and the 1-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences are used to study the line profile variations in the spectrum of the hot supergiant 55Cyg. The variability of the radial velocity and profiles of the lines of heavy elements is shown to be due to radial pulsation type motions. The corresponding variations for He I lines are due to nonradial pulsations. In the case of the H _β and H _α lines the pattern and behavior of variations differ for different observing periods. The variability of these lines is mostly due to the photometric and positional variability of the absorption and emission components of their profiles. The profiles of these lines show additional emission components, which move from the blue toward the red line wing. Such a behavior is indicative of the clumpy structure of the stellar envelope.     

Fiber-optic magnetometer for prime focus of 6-m BTA telescope based on suspended echelle spectrograph

We have developed and manufactured a fiber-optic magnetometer for the prime focus of the 6-m BTA telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences based on a suspended echelle spectrograph. The magnetometer is designed to improve the spectrum stability and eliminate the effect of instrumental polarization of the diagonal mirror on the results of magnetic field measurements. The magnetometer is to be used for measurements of stellar magnetic fields in stars and to study their chemical composition. The instrument operates in the 5000–6800 Å wavelength interval with mean reciprocal dispersion of 0.15 Å/pixel. According to the estimates for 9 ^m .5 stars, the standard error of magnetic field measurements based on 400 spectral lines would be 100 G for a half-hour exposure.     

Investigation of Galaxies of the Second Byurakan Sky Survey. III. Spectroscopic Observations in the Fields of 09h47m, +51° and 09h50m, +55°

The results of observations of 49 objects from the second Byurakan spectroscopic sky survey are given; they complete the recent spectroscopy of galactic samples in the fields centered on the coordinates = 09^h47^m, = +51° and = 09^h50^m, = +55°. The spectra were obtained on the 2.6-m telescope of the Byurakan Astrophysical Observatory, National Academy of Sciences of the Republic of Armenia, and the 6-m telescope of the Special Astrophysical Observatory, Russian Academy of Sciences, during 1998-2000. Redshifts and absolute stellar magnitudes were determined for all the galaxies.     

Study of the quality of the Zeiss-1000 telescope optical system using the Shack–Hartmann wavefront sensor

The results of studies of the optics of the 1-m Zeiss-1000 telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS) by the Shack–Hartmann (SH) method are presented. Using a Shack–Hartmann wavefront sensor (SH WFS) we have adjusted the telescope optical system by means of shifts and tilts of the secondary mirror. The procedure has significantly reduced the aberrations that appeared during the long-term instrument operation. A new method to investigate the surface quality of the mirrors of the Zeiss-1000 being applied, characteristics close to the diffraction limit are achieved. In general, the entire opto-mechanical telescope system provides an image quality of about 0.5″ at 80%energy level.     

Measuring stellar line-of-sight velocities with the SCORPIO instrument

We analyze factors that affect the accuracy of stellar line-of-sight velocities measured from the spectra obtained with the SCORPIO instrument attached to the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. We show that nonuniform illumination of the spectrograph slit combined with the effect of differential atmospheric refractionmay result in substantial systematic errors in the inferred line-of-sight velocities, and formulate recommendations concerning the methodology of observations, which allow the errors of line-of-sight velocity measurements to be minimized.