Structural Investigations in the Central Part of the Coma Cluster on the Base of Equidensity Diagrams. I.

On the base of a photographic plate in system V, which was taken with the 134/200/400 cm Schmidt camera of the Karl-Schwarzschild-Observatorium Tautenburg maximal diameters of galaxies in the centre of the Coma cluster are determined by photographic equidensitometry. An other system of diameters is determined for medium densities of the objects. The results are compared with ROOD and BAUM'S who derived the diameters by visual measurements on plates taken with the 5-metre telescope of the Hale Observatories. Both statistics contain galaxies up to 19^m. They are complete up to 17^m.5. It is pointed out that the Tautenburg diameters are in the mean 3 times larger than those derived by ROOD and BAUM. Diameter-magnitude diagrams and ellipticities of the objects are derived, further photometric corrections for tilted objects. For describing the general structure of the cluster diameter functions are derived instead of magnitude functions. The accuracy of a brightness determination by the equidensity method from the diameter-magnitude diagrams is nearly twice better than according to ROOD and BAUM.     

The equidensitometric determination of angular diameters of compact galaxies

On Tautenburg Schmidt plates in system V taken at seeings of about 2″ the determination of real angular diameters of compact galaxies down to 4″ is possible. Diameter-magnitude diagrams of objects in four fields around the globular cluster M₃ show the possibility for getting homogeneous material concerning both the uniformity of the equidensitometric copying process and the measuring process with the iris photometer in order to determine the integral brightness of single galaxies from their limiting equidensities.     

Dwarf Galaxies in the M 81/82 Group. New Photometric Data

We present a list of 39 dwarf galaxies of the M 81/82 group. Three different methods are applied to determine their apparent integral magnitude: digital processing, equidensitometry, and calculation according to the formulae of FISHER and TULLY . The plates used were obtained with the Tautenburg Schmidt telescope. For a distance of the group of 3.5 Mpc the absolute magnitudes of the dwarf galaxies investigated are -15^m < M < -9^m.     

Three new remarkable pairs of spherical compact galaxies

On plates taken with the 152 cm Ritchey-Chrétien telescope of the Figl Observatory for Astrophysics three very close pairs of spherical compact galaxies were found. The separations of their components are so narrow that they must touch or even penetrate each other with their outer parts. On plates of the Tautenburg 134/200/400 cm Schmidt camera magnitudes in U, B, V, colour indices and the position in the two colour diagram could be determined. Distances, absolute magnitudes of the pairs and diameters and surface magnitudes for the single components were determined, too.     

Structural investigations in the central part of the coma cluster on the base of equidensity diagrams. II

On the base of Tautenburg UBV-Schmidt plates equidensitometric diameters of galaxies of ROOD and BAUM 's list are given and the ellipticities in the three colours are determined. It was found that there is no difference in the ellipticities depending on the colours, on the average. The percentage of spherical objects (ε = 0.00) was found to 21.5 per cent. The surface brightness for 213 objects in the system V is given. The mean surface brightness is 22.75 mag/□′ with a dispersion of 2.5 mag/□′. It shows only a very slight dependence on the integrated magnitude.     

Search for Optical Identifications in the 5C3-Radio Survey III. Spectroscopic Results

52 possible optical identifications (V ≲ 19.5) of 43 radio sources of the ₅C₃ area have been spectroscopically examined by use of objective prism plates from KARL SCHWARZSCHILD Observatory Tautenburg. The aim was to select objects of special interest for further slit spectrographic investigation. Besides 42 probably ordinary stars and 3 galaxies, five quasar spectra have been found, but only one redshift could be determined. Two further objects probably have unusual spectra.     

Investigations of clusters of galaxies near the North Galactic Pole

The number-density distribution of several clusters of galaxies was derived by counting galaxies on B and R plates of the 2-m Schmidt telescope of the Karl-Schwarzschild-Observatory Tautenburg.     

Photometry of groups of galaxies. II. The NGC 972 group

A nearby group of galaxies, centered at the spiral galaxy NGC 972 and conspicuously rich in faint dwarf spheroidal galaxies, has been investigated photometrically on the B and V plates, obtained with the Tautenburg 2m Schmidt telescope. For ten certain and probable group members the equivalent B and V brightness profiles have been extracted. Integrated magnitudes and mean colours of faint group members have been estimated. Typically, the dwarfs show a “subexponential” (i.e. a convex curvature over the linear radius) surface brightness profile and often a central excess. Their equivalent profiles are reasonably well fitted by modified isothermal (King) models.     

A study of the photometric system of the Kiev network telescope

We performed a series of CCD observations in BVRI bands of a celestial region in cluster M67 (NGC 2682) to study the photometric system of the Kyiv network telescope. The signal recording system consists of a CGE-1400 telescope, Celestron #94175 focal reducer, an automatic turret with a set of UBVRI filters, and a Rolera Mgi CCD camera. The operating field of the system is 10.62′ × 10.62′. CCD images are processed in the MIDAS/ROMAFOT package. The reduction coefficients of the instrumental photometric system relative to Johnson’s BVRI system are determined. The resulted value of the module of distance to cluster M67 V ? M _V = 9.63 ^m does not contradict the results of other researchers. The mean square errors for one determination of stellar magnitude for different bands are 0.02–0.12 ^m . The errors in determining equatorial coordinates in the TYCHO-2 catalog system are ± 1″.     

Schmidt plate survey in the galactic centre direction. 1. Investigation of open clusters in the Sagittarius-Carina spiral arm

A study of four open clusters on Tautenburg Schmidt plates in the direction to the Galactic Centre (l = 17.0°, b = +0.8°) is presented. In a field of 8.95 square degrees proper motions and B, V magnitudes were determined for about 36 500 stars up to the limiting magnitudes B = 17^m.9, V = 16^m.8. For stars brighter than B = 16^m an accuracy of about 3 mas/year has been estimated for proper motions. The rms errors of stellar magnitudes and (B—V) colours is about 0.1 mag. There are two open clusters already known in this sky area: Trumpler 32 (C 1814-133) and NGC 6611 (C 1816-138). By the inspection of the plates two additional anonymous clusters were identified near the double star ADS 11285 or BD −14°5014 (C 1819-146) and near the star BD −14°5016 (C 1820-146). The cluster membership determination was carried out using information on spatial and proper motion distributions of stars in the field. The colour-magnitude diagrams up to the limiting stellar magnitude were constructed. For each cluster interstellar extinction A_V, diameters of the core and corona, ages and spatial velocity components (V, W) relative to the LSR in the Y, Z-galactic directions were derived. The distances to the clusters were obtained to 1720 pc, 2260 pc, 2130 pc and 2130 pc for Trumpler 32, NGC 6611, C 1819-146 and C 1820-146, respectively. All clusters are situated in the Sagittarius-Carina spiral arm. Their spatial location confirms the assumption that galactic spiral arms are close to logarithmic spirals with a characteristic angle of about 20 degrees.     

SN2015bh in NGC 2770: LBV core collapse in merging of binary system components

We present spectroscopy and multicolor photometry for the optical transient PSN J09093496+3307204 in the galaxy NGC2770, which has afterwards been transferred into the supernova phase and got the name SN2015bh. Medium-resolution spectral observations were carried out between February 2015 to May 2016 using the focal reducer SCORPIO at the 6-m Russian telescope BTA. They were followed by by photometric observations at the BTA and six other telescopes with 0.5–1m apertures. Both at the phase of the SN impostor (2015a) and at the supernova phase (2015b), besides Balmer emissions, the strong Fe II emissions are seen in the spectrum; so, these spectra resemble those of Williams Fe II type classical novae. Taking into account circumstellar, interstellar and galactic absorption, A_V = 1.^m 14 ±0.^m 15), we determined maximum absolute magnitudes of the object to be M_V =–15.^m 0 ±0.^m 3 at the 2015a phase and of M^V =–18.^m 14 ±0.^m 30 at the 2015b phase. The light curve at the 2015b phase is similar to those of SN IIL. The supernova progenitor is a luminous blue variable (LBV) star with the powerful Hα emission. We consider several hypotheses of supernovae explosions following optical transients related with LBV. The hypothesis of core collapse of an evolved massive star interrupting the process of its merging with massive companion in a binary system (a failed luminous red nova) was chosen as the preferable one for this event.     

Schmidt plate survey towards the Galactic centre. 2. Stellar statistics in the direction of the Sagittarius-Carina arm

A study of the structure and kinematics of the Galaxy from Tautenburg Schmidt plates taken towards the Galactic centre (l = 17.0°, b = +0.8°) is presented. Proper motions and B, V magnitudes were determined for about 36 500 stars up to the limiting magnitude V = 16^m.8 in a field of 8.95 square degrees. Proper motion accuracy of about 3 mas/year has been obtained for stars brighter than V = 15^m. The rms errors of stellar magnitudes and (B–V) colours is about 0.1 mag. The majority of field stars in the survey are main sequence stars and red giants of the disk. They belong to the Local or Sagittarius-Carina arms, or they are located between these spiral arms. Comparing the modelled and observed distributions of magnitudes and colours, we specified the interstellar extinction determined in the preceding study of open clusters in this field. The luminosity function towards the Galactic centre was determined for stars with absolute magnitudes from -4^m.35 to +9^m. Kinematical and spatial distribution parameters up to 4 kpc from the Sun were obtained as a function of galactocentric distance.     

Polarization effects in RATAN-600 solar observations in the “Southern sector with a flat reflector” mode

We report the results of numerical simulations of the instrumental signal in the Stokes V channel of circular polarization as observed by RATAN-600 radio telescope operating in the “Southern sector with a flat reflector” mode. Our simulations are based on an improved algorithm of the beam pattern computation that takes into account diffraction in the space between the telescope mirrors. The computations cover a wide range of wavelengths in the case of a focused antenna and in the presence of aberrations. We analyze the structure and properties of the element M ₄₁ of the Mueller matrix and of the parasite signal from the solar disk in various cases of the antenna irradiation. We estimate the differences between the left- and right-polarization power-beam patterns of the telescope. We report the computed M ₁₁ and M ₄₁ elements for the case of observation of the right- and left-polarized radiation at different points of the focal line of the secondary mirror, and analyze their variations as a function of a number of parameters, including, in particular, the shift applied to correct the displacement of scans.     

Faint Blue Galaxies in the Virgo Cluster Region

Finding charts, coordinates, B magnitudes, and U – B color estimates are given for 110 faint blue galaxies located near the centre of the Virgo cluster of galaxies. The galaxies have been found by blinking on plates taken with the Tautenburg 52 inch SCHMIDT telescope.     

New probable dwarf galaxies in northern groups of the Local Supercluster

We have searched for nearby dwarf galaxies in 27 northern groups with characteristic distances 8–15 Mpc based on the Second Palomar Sky Survey prints. In a total area of about 2000 square degrees, we have found 90 low-surface-brightness objects, more than 60% of which are absent from known catalogs and lists. We have classified most of these objects (～80%) as irregular dwarf systems. The first 21-cm line observations of the new objects with the 100-m Effelsberg radio telescope showed that the typical linear diameters (1–2 kpc), internal motions (～30 km s^?1), and hydrogen masses (～2 × 10⁷ M _⊙) of the new galaxies correspond to those expected for the dwarf population of nearby groups.     

STEREO SECCHI COR1-A/B Intercalibration at 180° Separation

The twin Solar Terrestrial Relations Observatory (STEREO) spacecraft reached a separation angle of 180° on 6 February 2011. This provided a unique opportunity to test the intercalibration between the Sun–Earth Connection Coronal and Heliospheric Investigation (SECCHI) telescopes on both spacecraft for areas above the limb. So long as the corona is optically thin, at 180° separation each spacecraft sees the same corona from opposite directions. Thus, the data should appear as mirror images of each other. We report here on the results of the comparison of the images taken by the inner coronagraph (COR1) on the STEREO-Ahead and -Behind spacecraft in the hours when the separation was close to 180°. We find that the intensity values seen by the two telescopes agree with each other to a high degree of accuracy. This validates both the radiometric intercalibration between the COR1 telescopes, and the method used to remove instrumental background from the images. The relative error between COR1-A and COR1-B is found to be less than 10⁻⁹ B/B _⊙ over most of the field-of-view, growing to a few ×10⁻⁹ B/B _⊙ for the brighter pixels near the edge of the occulter. The primary source of error is the background determination. We also report on the analysis of star observations which show that the absolute radiometric calibration of either COR1 telescope has not changed significantly since launch.     

Search for Optical Identifications in the 5C3-Radio Survey II. Statistical Treatment and Results

On plates of the large Schmidt-telescope of Karl-Schwarzschild-Observatory Tautenburg, taken by F. BÖRNGEN, 139 radio sources of the ₅C₃ area were inspected for possible identifications with optical objects. The results are published in paper I and in the appendix of the present paper II. A detailed analysis of these objects showed a relatively large number of about 65 real identifications up to the utmost plate limit B ≈ 21^m.7, which corresponds to an identification rate of about 47%. The individual reliability of each possible optical identification is estimated (table 6). Apparently the identified objects (see tables 4 and 6) are galaxies, “blue” and “neutral” quasars, and one H II-region of the Andromeda nebula. It is of great cosmological interest that no “red” quasars could be found.     

Beobachtungen Kleiner Planeten. VI.

A summary is given about the Minor Planet survey performed in 1985 on Tautenburg Schmidt plates. There were discovered 95 asteroids and calculated 168 positions for them. These are 20 numbered objects and 75 asteroids with provisional designations, two of them have no new designation. Tautenburg observations could give a tribute to twelve planets numbered in the period of this report. Two asteroids discovered in Tautenburg have received numbers and names: (3245) Jensch = 1973 UL5 and (3338) Richter = 1973 UX5.     

The Cepheid impostor HD 18391 and its anonymous parent cluster

New and existing photometry for the G0 Ia supergiant HD 18391 is analyzed in order to confirm the nature of the variability previously detected in the star, which lies off the hot edge of the Cepheid instability strip. Small‐amplitude variability at a level of δV = 0.016 ± 0.002 is indicated, with a period of P = 123^d.04 ± 0^d.06. A weaker second signal may be present at P = 177^d.84 ± 0^d.18 with δV = 0.007 ± 0.002, likely corresponding to fundamental mode pulsation if the primary signal represents overtone pulsation (123.04/177.84 = 0.69). The star, with a spectroscopic reddening of E_B–V = 1.02 ± 0.003, is associated with heavily‐reddened B‐type stars in its immediate vicinity that appear to be outlying members of an anonymous young cluster centered ∼10′ to the west and 1661 ± 73 pc distant. The cluster has nuclear and coronal radii of r_n = 3.5′ and R_c = 14′, respectively, while the parameters for HD 18391 derived from membership in the cluster with its outlying B stars are consistent with those implied by its Cepheid‐like pulsation, provided that it follows the semi‐period‐luminosity relation expected of such objects. Its inferred luminosity as a cluster member is M_V = –7.76 ± 0.10, its age (9 ± 1) × 10⁶ years, and its evolutionary mass ∼19 M_⊙. HD 18391 is not a classical Cepheid, yet it follows the Cepheid period‐luminosity relation closely, much like another Cepheid impostor, V810 Cen (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Weitere OB-Assoziationen in den äußersten Randzonen von M 31

In comparing a U- and a B-plate of the Tautenburg 2 m Schmidt telescope 7 scattered groupings of blue objects have been discovered in the outer regions of the large Andromeda nebula. A closer investigation showed these objects to be apparently so far not known OB associations, well fitting to a spiral structure. With distances from the centre of the Andromeda nebula between R = 22.8 kpc and R = 27.9 kpc the objects still surpass the most distant association OB 188 of VAN den BERGH (R = 25.0 kpc).