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.     

The Diameter of (106) Dione

The mean diameter D = 147 ± 3 km of (106) Dione is derived from visual observations in Denmark, Germany and the Netherlands of the occultation of AGK₃ + 25°0989 on 1983 January 19. Photoelectric magnitudes are: B(1, 2°.4) = 8^m.51 ± 0^m.06 and B – V = 0^m.65 ± 0^m.07. The visual albedo is pv = .064. Constraints on the axis of rotation are derived from the observed elliptical contour.     

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.     

BV observations of the eclipsing binary WX Eridani

Photoelectric observations of WX Eridani inB andV filters have been discussed. The maximum magnitudes of the system areB=9 ^m .70 andV=9 ^m .46. TheB-V colours of the components are 0 ^m .16 and 0 ^m .80 for the primary and the secondary, respectively, while their spectral types are A5+K0. The period has been found to be constant and its revised value is 0^d.823 270 76.     

Astrometric catalogue of stars in the KMAC3 equatorial zone

The catalogue of positions and stellar V magnitudes of up to 17 ^m stars in the declination zone from 2° to 5.5° has been compiled. The catalogue includes 2.05 × 10⁶ stars and is based on the observations performed in 2010–2015 on the meridian axial circle (MAC) of GAO NAN Ukraine and the Astronomical Observatory of Taras Shevchenko National University. The errors of the positions and photometry for stars of 11–14 magnitude are 0.06″–0.08″ and 0.04 ^m –0.08 ^m , respectively.     

Investigation of the kinematics and structure of the Galaxy in the vicinity of the North galactic pole

In the framework of the programme of studying the meridional section of the Galaxy (MEGA) the absolute proper motions of more than 11000 stars with respect to 3000 galaxies and their stellar magnitudes in the B, V Johnson system are determined in two sky regions near the North Galactic Pole (NGP) by means of Tautenburg Schmidt plates. The limiting and completing apparent stellar magnitudes are B = 20.4 and 18.3 mag, the overall and the investigated sky areas are 16.4 and 14.6 square degrees, respectively. Distances have been determined using the stellar magnitudes, colours, proper motions and reduced proper motions. Stellar kinematics, eccentricities of Galactic orbits, spatial distribution and changes of these characteristics with Z-distance from the Galactic plane are obtained up to 15 kpc. Four subsystems distinguished in the NGP direction, respectively with semithicknesses of 0.25, 0.38, 0.67, 1.48 kpc and density ellipsoid axial ratios of 0.09, 0.20, 0.28, 0.49 show mean velocities in the Galactic rotation direction relative to the LSR of 5.6 ± 0.6, − 11.0 ± 0.6, − 62.5 ± 1.2, − 181.6 ± 4.4 km/s, and ages of 0.1, 0.4, 0.9, 1 of the Galaxy age.     

<Emphasis Type="Italic">BVRI</Emphasis> CCD-photometry of comparison stars in the neighborhoods of galaxies with active nuclei. III

Observations with a matrix photometer are reported. The stellar magnitudes in the BVRcIc bands are estimated for 80 comparison stars in the neighborhoods of 10 galaxies with active nuclei: 2 Seyfert galaxies, 4 quasars, and 4 BL Lac objects. The stellar magnitudes of the observed stars range from 11 to 19^m.5. For stars with magnitudes of 14–15^m the typical photometric errors are 0^m.011, 0^m.008, 0^m.006, and 0^m.007 in the B, V, R, and I bands, respectively. The BVRI magnitudes for most of these stars were not known previously. 14′ × 14′ finding charts for these stars are included. These results can be used for differential BVRI photometry of active galactic nuclei. __________ Translated from Astrofizika, Vol. 50, No. 1, pp. 57–72 (February 2007).     

CF octantis,an RS CVn-type variable with a prominent activity cycle

Photoelectric photometry has been obtained for CF Octantis on 39 nights. The object is a member of the RS CVn class and has a highly active chromosphere. A 20.15 ±0.06 d period has been found from theB andV magnitudes, which is interpreted as the rotational modulation of the light from a non-uniformly spotted star. The amplitude of this spot wave is observed to vary slowly between ΔV about 0^m.l and 0^m.3, which may be evidence for an activity cycle of 9 ±3 years.     

Investigation of PPM catalogue accuracy

The PPM catalogue contains the most complete and accurate information concerning positions, proper motions and some astrophysical data for practically all stars (about 379000) down to 10^m-11^m over the whole sky. The systems and rms errors of the PPm positions, proper motions, stellar magnitudes and spectral classification are studied by comparison with catalogues of stellar characteristics and on the basis of the PPM data itself. The residual errors of stellar data in the PPM catalogue are small and/or they can be determined and eliminated.     

Kinematics of Hot Subdwarfs from the Gaia DR2 Catalogue

We have studied the kinematic properties of the candidates for hot subdwarfs (HSDs) selected by Geier et al. from theGaiaDR2 catalogue. We have used a total of 12 515 stars with relative trigonometric parallax errors less than 30%. The HSDs are shown to have different kinematics, depending on their positions on the celestial sphere. For example, the sample of low-latitude (|b| < 20°) HSDs rotates around the Galactic center with a linear velocity V0 = 221 ± 5 km s^?1. This suggests that they belong to the Galactic thin disk. At the same time, they lag behind the local standard of rest by ΔV_☉ ~ 16 km s^?1 due to the asymmetric drift. The high-latitude (|b| ≥ 20°) HSDs rotate with a considerably lower velocity, V_☉ = 168 ^± 6 km s^?1. Their lagging behind the local standard of rest is already ΔV_☉ ～ 40 km s^?1. Based on the entire sample of 12 515 HSDs, we have found a positive rotation around the x axis significantly differing from zero with an angular velocity ω₁ = 1.36±0.24 km s^?1 kpc^?1. We have studied the samples of HSDs that are complete within r < 1.5 kpc. Based on them, we have traced the evolution of the parameters of the residual velocity ellipsoid as a function of both latitude |b| and coordinate |z|. The following vertical disk scale heights have been found: h = 180 ± 6 and 290 ± 10 pc from the low- and high-latitude HSDs, respectively. A new estimate of the local stellar density Σ_out = 53 ± 4 M☉ kpc^?2 has been obtained for z_out = 0.56 kpc from the high-latitude HSDs.

     

Photoelectric observations in a wide-field area around the Praesepe cluster

The PPM catalogue numbers, photoelectric magnitudes V, color-indexes U – B, B – V, V – R and rms errors of their determinations for 51 stars of the secondary wide-angle photoelectric standard are published. The catalogue accuracy of quantities mentioned above is 0.007, 0.015, 0.006, 0.006 mag, respectively. A list of ten stars which are probably variable is published.     

New absolute magnitude calibrations for detached binaries

Lutz‐Kelker bias corrected absolute magnitude calibrations for the detached binary systems with main‐sequence components are presented. The absolute magnitudes of the calibrator stars were derived at intrinsic colours of Johnson‐Cousins and 2MASS (Two Micron All Sky Survey) photometric systems. As for the calibrator stars, 44 detached binaries were selected from the Hipparcos catalogue, which have relative observed parallax errors smaller than 15% (σ_π/π ≤ 0.15). The calibration equations which provide the corrected absolute magnitude for optical and near‐infrared pass bands are valid for wide ranges of colours and absolute magnitudes: –0.18 < (B – V)₀ < 0.91, –1.6 < M_V < 5.5 and –0.15 < (J – H)₀ < 0.50, –0.02 < (H – K_s)₀ < 0.13, 0 < M_J < 4, respectively. The distances computed using the luminosity‐colours (LCs) relation with optical (BV) and near‐infrared (JHK_s) observations were compared to the distances found from various other methods. The results show that new absolute magnitude calibrations of this study can be used as a convenient statistical tool to estimate the true distances of detached binaries out of Hipparcos' distance limit. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Total-to-selective extinction ratio in nearby and distant objects

In an area of nearly 23.1 square degrees centered at α(1950) = 23^h57^m and δ(1950) = + 59δ48' magnitudes, colors, and spectral classes were determined for 1419 stars brighter than m_pg = 13^m.00. Star counts were made in this area for all objects brighter than m_pg = m_pv = 15^m.5. Altogether 50585 stars were included in the pv counts. The original photographic data have been transformed to the B, V system. From star counts the ratio of total-to-selective extinction was derived to be R ≉ 4.0 ± 0.2. It depends on the distance to the stars under consideration as well as on the surface density of the objects inside the considered region. In einem Gebiet von annähernd 23.1 Quadratgrad mit den Mittelpunktskoordinaten α(1950) = 23^h57^m und δ(1950) = 59°48' werden für 1419 Sterne heller als m_pg = 13^m.00 Helligkeiten, Farben und Spektraltypen bestimmt. Sternzählungen in Helligkeitsintervallen m_pg und m_pv wurden für alle Objekte heller als m_pg = m_pv = 15^m.5 durchgeführt. Für diese 50585 Sterne wurden die gemessenen photographischen und photovisuellen Helligkeiten in das B, V-System transformiert. Im Ergebnis dieser Sternzählungen wurde ein Wert von R ≉ 4.0 ± 0.2 abgeleitet. Er hängt sowohl von der Entfernung der betrachteten Objektgruppen als auch von der Flächendichte der Sterne innerhalb der Region ab.     

Homogenized Hertzsprung‐Russell diagram for the open cluster NGC 188

We considered some selected published stellar catalogues with B – V and V values for the open cluster NGC 188 and estimated the errors from data comparisons. The results are used to homogenize the data by averaging with weights inversely proportional to the errors squared. A recent calibration by Casagrande et al. (2010) of B – V versus effective temperatures for F, G, and K dwarfs and subgiants is used to produce the homogenized effective temperatures for the cluster stars. A homogenized Hertzsprung‐Russell diagram (relationship between the effective temperatures and the absolute magnitudes) is presented and analysed. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical identification of IRAS point sources based on low-dispersion spectra from the First Byurakan Survey. V

Part five of optically identified point sources from the IRAS Point Source Catalog (PSC) contains data on 19 late-type stars. The identifications were based on the Digitized Sky Survey (DSS), the First Byurakan Survey (FBS), blue and red maps of the Palomar survey (POSS), and infrared fluxes at 12, 25, 60, and 100 mm in the region of +61° ≤ δ ≤ +65° and 05 ^h 30 ^m ≤ α ≤ 18 ^h 35 ^m with an area of 357 sq. deg. Of the 76 objects given in the IRAS PSC as unidentified sources of infrared radiation, 51 are associated with known stars in existing catalogs, 6 are objects from the FBS of late-type stars, and 19 sources remained unknown in the optical range. For the identified stars we determined the optical coordinates, their departures from the IR coordinates, the Vstellar magnitudes, the color indices CI,and the preliminary spectral subtypes. The objects have optical magnitudes in the range of 8 ^m −16 ^m .Gas-dust shells are assumed to exist around four of the sources. Finder charts from the DSS are given for 19 of the objects. Translated from Astrofizika, Vol. 42, No. 1, pp. 53–59, January–March, 1999.     

UBV observations of the eclipsing binary FW Monocerotis

Photoelectric observations of FW Monocerotis inU,B, andV filters have been discussed. The depths of the primary minimum inU BV colours are 2 _. ^m 63, 2 _. ^m 17 and 1 _. ^m 76, respectively. No variation in the period has been found and its revised value is 3 _. ^d 8735868.     

A near‐infrared/optical/X‐ray survey in the centre of σ Orionis

Because of the intense brightness of the OB‐type multiple star system σ Ori, the low‐mass stellar and substellar populations close to the centre of the very young σ Orionis cluster is poorly know. I present an IJHK_s survey in the cluster centre, able to detect from the massive early‐type stars down to cluster members below the deuterium burning mass limit. The near‐infrared and optical data have been complemented with X‐ray imaging. Ten objects have been found for the first time to display high‐energy emission. Previously known stars with clear spectroscopic youth indicators and/or X‐ray emission define a clear sequence in the I vs. I – K_s diagram. I have found six new candidate cluster members that follow this sequence. One of them, in the magnitude interval of the brown dwarfs in the cluster, displays X‐ray emission and a very red J – K_s colour, indicative of a disc. Other three low‐mass stars have excesses in the K_s band as well. The frequency of X‐ray emitters in the area is 80±20 %. The spatial density of stars is very high, of up to 1.6±0.1 arcmin^–2. There is no indication of lower abundance of substellar objects in the cluster centre. Finally, I also report two cluster stars with X‐ray emission located at only 8000–11000 AU to σ Ori AB, two sources with peculiar colours and an object with X‐ray emission and near‐infrared magnitudes similar to those of previously‐known substellar objects in the cluster. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photovisual magnitude differences of double stars

Differences in magnitudes between the components of 874 double stars have been derived from visual estimates on several series of multi-exposure photographic plates. The plates were obtained with long focus refractors primarily for the purpose of determining the relative positions of double stars according to the well-known Hertzsprung method. Except for binaries with magnitude differences less than half a magnitude, plates were taken with objective gratings limiting the effective magnitude differences between the components to half a magnitude. Similar to what has been done in variable star work, it was found possible to estimate the magnitude difference to the nearest tenth from this material by visual inspection, using a seven power eyepiece. The internal mean error of a single estimate of a magnitude is ±0 ^m .064, while the external mean error of a single value in the catalogue based upon an average of three independent determinations is ±0 ^m .054. Comparisons with other photometric series of this type have been made. In particular the photoelectric series by Eggen (1963, 1966) and by Johnson (1953) show close agreements, with no systematic differences. The results will appear inPubl. U.S. Naval Obs., 2nd Series,18, Pt. V.     

Difference between the optical flickering colours of cataclysmic variables and symbiotic recurrent novae

We performed simultaneous observations in 3 bands (U BV) of the flickering variability of the recurrent novae RS Oph and T CrB at quiescence. Using new and published data, we compare the colours of the flickering in cataclysmic variables and symbiotic recurrent novae. We find a difference between the colours of the flickering source in these two types of accreting white dwarfs. The detected difference is highly significant with p ‐values ≈2 x 10^–6 for the distributions of (U – B)₀ colour and p ≈ 3 x 10^–5 on an (U – B) versus (B – V) diagram. The possible physical reasons are briefly discussed. The data are available upon request from the authors. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Very short-term behaviour of the flare star EV Lac

Sinusoidal variations in Johnson'sB-band of the flare star EV Lac have been confirmed at its quiet state luminosity. The cycle lengths are more than one hour and less than two hours with amplitudes varying from 0 _. ^m 105 to 0 _. ^m 306. These registered cycles have agreed with cycles detected by Mavridis and Varvoglis (1990) and Mavridis (1990). In the same time, the cycles have confirmed the light variation detection in Johnson'sV-band in the same flare star by Pettersen (1980) with a cyclic period equals about 4 _. ^d 378 and an amplitude of about 0 _. ^m 07. Our net results confirm, to some extent, the presence of active region(s) as an origin of stellar flare phenomenon of UV Ceti type flare stars. We can cautiously say that the solar and stellar flare phenomenon have a similar origin.