Galactic rotation parameters from data on open star clusters

Currently available data on the field of velocities V _r , V _l , V _b for open star clusters are used to perform a kinematic analysis of various samples that differ by heliocentric distance, age, and membership in individual structures (the Orion, Carina-Sagittarius, and Perseus arms). Based on 375 clusters located within 5 kpc of the Sun with ages up to 1 Gyr, we have determined the Galactic rotation parameters ω ₀ = ?26.0 ± 0.3 km s^?1 kpc^?1, ω′₀ = 4.18 ± 0.17 km s^?1 kpc^?2, ω″₀ = ?0.45 ± 0.06 km s^?1 kpc^?3, the system contraction parameter K = ?2.4 ± 0.1 km s^?1 kpc^?1, and the parameters of the kinematic center R ₀ = 7.4 ± 0.3 kpc and l ₀ = 0° ± 1°. The Galactocentric distance R ₀ in the model used has been found to depend significantly on the sample age. Thus, for example, it is 9.5 ± 0.7 and 5.6 ± 0.3 kpc for the samples of young (≤50 Myr) and old (>50 Myr) clusters, respectively. Our study of the kinematics of young open star clusters in various spiral arms has shown that the kinematic parameters are similar to the parameters obtained from the entire sample for the Carina-Sagittarius and Perseus arms and differ significantly from them for the Orion arm. The contraction effect is shown to be typical of star clusters with various ages. It is most pronounced for clusters with a mean age of ≈100 Myr, with the contraction velocity being Kr = ?4.3 ± 1.0 km s^?1.     

CCD BVI Photometry of the Southern Open Clusters Pismis 23 and BH 222

CCD BVI Johnson–Cousins photometry of the open cluster candidates Pismis 23 and BH 222 is presented. Both the analysis of the colour-magnitude diagrams and star counts performed in the regions of these two objects support their physical reality. For Pismis 23 we derive E(B?V) = 2.0 ± 0.1, E(V?I) = 2.6 ± 0.1, a distance from the Sun d= (2.6 ± 0.6) kpc and an age of (300 ± 100) Myr, while for BH 222 we obtain E(V?I) = 2. 4 ± 0.2, d= (6.0 ± 2.7) kpc and (60 ± 30) Myr. Both objects, located beyond the Sagittarius arm, are among the most reddened and distant open clusters known in the direction towards the Galactic centre.     

The structure and dynamics of young star clusters: King 16, NGC 1931, NGC 637 and NGC 189

In this paper, using 2MASS photometry, we study the structural and dynamical properties of four young star clusters viz. King 16, NGC 1931, NGC 637 and NGC 189. For the clusters King 16, NGC 1931, NGC 637 and NGC 189, we obtain the limiting radii of 7′, 12′, 6′ and 5′ which correspond to linear radii of 3.6 pc, 8.85 pc, 3.96 pc and 2.8 pc respectively. The reddening values E(B?V) obtained for the clusters are 0.85, 0.65–0.85, 0.6 and 0.53 and their true distances are 1786 pc, 3062 pc, 2270 pc and 912 pc respectively. Ages of the clusters are 6 Myr, 4 Myr, 4 Myr and 10 Myr respectively. We compare their structures, luminosity functions and mass functions (φ(M)=dN/dM ∝ M ^?(1+χ)) to the parameter τ=t _age /t _relax to study the star formation process and the dynamical evolution of these clusters. We find that, for our sample, mass seggregation is observed in clusters or their cores only when the ages of the clusters are comparable to their relaxation times (τ≥1). These results suggest mass seggregation due to dynamical effects. The values of χ, which characterize the overall mass functions for the clusters are 0.96±0.11, 1.16±0.18, 0.55±0.14 and 0.66±0.31 respectively. The change in χ as a function of radius is a good indicator of the dynamical state of clusters.     

Evolutionary studies of the young star clusters: NGC 1960, NGC 2453 and NGC 2384

We report the analysis of the young star clusters NGC 1960, NGC 2453 and NGC 2384 observed in the J (1.12 μm), H (1.65 μm) and K′ (2.2 μm) bands. Estimates of reddening, distance and age as E(B?V)=0.25, d=1380 pc and t=31.6 to 125 Myr for NGC 1960, E(B?V)=0.47, d=3311 pc and t=40 to 200 Myr for NGC 2453 and E(B?V)=0.25, d=3162 pc and t=55 to 125 Myr for NGC 2384 have been obtained. Also, we have extended the color–magnitude diagrams of these clusters to the fainter end and thus extended the luminosity functions to fainter magnitudes. The evolution of the main sequence and luminosity functions of these clusters have been compared with themselves as well as Lyngå 2 and NGC 1582.     

A photometric investigation of the asteroid (89) Julia

New photometric data of the light curve of the minor planet (89) Julia were obtained on nine nights during the 1972 opposition using the 60cm telescope at OHP. A synodic period of 11^h23^m14^s ± 7^s and an amplitude of 0.25mag were derived from the measurements. The light curve is rather unsymmetric and no plausible explanation for this has been offered so far. The measurements have been carried out in instrumental V′; the data obtained in B′ and U′ supplement all conclusions from V′ data concerning the rotation of Julia.     

Open clusters IC 4665 and Cr 359 and a probable birthplace of the pulsar PSR B1929+10

Based on the epicyclic approximation, we have simulated the motion of the young open star clusters IC 4665 and Collinder 359. The separation between the cluster centers is shown to have been minimal 7 Myr ago, 36 pc. We have established a close evolutionary connection between IC 4665 and the Scorpius-Centaurus association — the separation between the centers of these structures was ≈200 pc 15 Myr ago. In addition, the center of IC 4665 at this time was near two well-known regions of coronal gas: the Local Bubble and the North Polar Spur. The star HIP 86768 is shown to be one of the candidates for a binary (in the past) with the pulsar PSR B1929+10. At the model radial velocity of the pulsar V _r = 2 ± 50 km s^?1, a close encounter of this pair occurs in the vicinity of IC 4665 at a time of ?1.1 Myr. At the same time, using currently available data for the pulsar B1929+10 at its model radial velocity V _r = 200 ± 50 km s^?1, we show that the hypothesis of Hoogerwerf et al. (2001) about the breakup of the ζ Oph-B1929+10 binary in the vicinity of Upper Scorpius (US) about 0.9 Myr ago is more plausible.     

Photometric properties of the Martian satellites

New photoelectric observations yield V(1, α) = 12.95 + 0.036 α ± 0.05, BV = 0.65 ± 0.03, and UB = 0.18 ± 0.03 for Deimos and V(1, 0) = 11.9 ± 0.2 for Phobos. The derived geometric albedos of both satellites are near 0.065. Combined photometric and polarimetric results lead to the conclusion that the satellites have dusty surfaces and are possibly basaltic but more likely carbonaceous in composition.     

Galactic kinematics from data on open star clusters from the MWSC catalogue

Open star clusters from the MWSC (Milky Way Star Clusters) catalogue have been used to determine the Galactic rotation parameters. The circular rotation velocity of the solar neighborhood around the Galactic center has been found from data on more than 2000 clusters of various ages to be V ₀ = 236 ± 6 km s^?1 for the adopted Galactocentric distance of the Sun R ₀ = 8.3 ± 0.2 kpc. The derived angular velocity parameters are Ω ₀ = 28.48 ± 0.36 km s^?1 kpc^?1, Ω’₀ = ?3.50 ± 0.08 km s^?1 kpc_?2, and Ω″₀ = 0.331 ± 0.037 km s^?1 kpc^?3. The influence of the spiral density wave has been detected only in the sample of clusters younger than 50 Myr. For these clusters the amplitudes of the tangential and radial velocity perturbations are f ^θ = 5.6 ± 1.6 km s^?1 and f _R = 7.7 ± 1.4 km s^?1, respectively; the perturbation wavelengths are λ _θ = 2.6 ± 0.5 kpc (i _θ = ^?11? ± 2?) and λ _R = 2.1 ± 0.5 kpc (i _R = ?9? ± 2?) for the adopted four-armed model (m = 4). The Sun’s phase in the spiral density wave is (χ_⊙)_θ = ?62? ± 9? and (χ_⊙)_R = ?85? ± 10? from the residual tangential and radial velocities, respectively.     

Kinematics of Stars from the TGAS (Gaia DR1) Catalogue

Based on the stellar proper motions of the TGAS (Gaia DR1) catalogue, we have analyzed the velocity field of main-sequence stars and red giants from the TGAS catalogue with heliocentric distances up to 1.5 kpc. We have obtained four variants of kinematic parameters corresponding to different methods of calculating the distances from the parallaxes of stars measured with large relative errors. We have established that within the Ogorodnikov–Milne model changing the variant of distances affects significantly only the solar velocity components relative to the chosen centroid of stars, provided that the solution is obtained in narrow ranges of distances (0.1 kpc). The estimates of all the remaining kinematic parameters change little. This allows the Oort coefficients and related Galactic rotation parameters as well as all the remaining Ogorodnikov–Milne model parameters (except for the solar terms) to be reliably estimated irrespective of the parallax measurement accuracy. The main results obtained from main-sequence stars in the range of distances from 0.1 to 1.5 kpc are: A = 16.29 ± 0.06 km s^?1 kpc^?1, B = ?11.90 ± 0.05 km s^?1 kpc^?1, C = ?2.99 ± 0.06 km s^?1 kpc^?1, K = ?4.04 ± 0.16 km s^?1 kpc^?1, and the Galactic rotation period P = 217.41 ± 0.60 Myr. The analogous results obtained from red giants in the range from 0.2 to 1.6 kpc are: the Oort constants A = 13.32 ± 0.09 km s^?1 kpc^?1, B = ?12.71 ± 0.06 km s^?1 kpc^?1, C = ?2.04 ± 0.08 km s^?1 kpc^?1, K = ?2.72 ± 0.19 km s^?1 kpc^?1, and the Galactic rotation period P = 236.03 ± 0.98 Myr. The Galactic rotation velocity gradient along the radius vector (the slope of the Galactic rotation curve) is ?4.32 ± 0.08 km s^?1 kpc^?1 for main-sequence stars and ?0.61 ± 0.11 km s^?1 kpc^?1 for red giants. This suggests that the Galactic rotation velocity determined from main-sequence stars decreases with increasing distance from the Galactic center faster than it does for red giants.     

Photometry of the unlit face of Saturn's rings

From our telescopic observations of Saturn's rings in 1966, 1979, and 1980, the luminance of the unlit face at λ = 0.58 μm is derived as a function of the height B′ of the Sun above the lit face. A maximum is reached at B′ = 1.9° and a decrease is observed for larger values of B′. Ring B is 1.8 time less bright than ring A and Cassini division. The unlit/lit luminances ratios for the two rings merged together is 8% at B′ = 1.0° and 3% at B′ = 2.8°. The larger value at more grazing incidence is related to the photometric “opposition effect” which reflects more of the incident light backward into the ring plane when the height of the sun is small; the light so reflected is again reflected and scattered and a certain flux reaches the unlit face to escape toward the observer. The unlit face luminances for blue and for yellow light indicate a contribution by micron size particles. The Saturn globe produces a ring illumination which, observed from the Earth, amounts to 1.8 × 10^?3 of the disk center reflectance. The rings observed exactly edge-on do not disappear but a faint lineament remains, which produces a flux of (0.30 ± 0.15) 10^?3 times the brightness of a segment of 1 arcsec width at Saturn disk center; illuminations of rings' borders or particles outside the exact ring plane are indicated.     

Results of Complex Observations of Asteroid (596) Scheila at the Sanglokh International Astronomical Observatory

Results of astrometric and BVRI photometric observations of the active asteroid (596) Scheila are presented. The observations were carried out at the Zeiss-1000 telescope of the Sanglokh International Astronomical Observatory of the Institute of Astrophysics of the Academy of Sciences of the Republic of Tajikistan on June 16?17 and from July 30 to August 1, 2017. The coordinates of the object and its orbit were determined; and the apparent brightness in four filters, the absolute brightness in the V and R filters, and the color indices were obtained. The light curves suggest that no substantial changes in the asteroid’s brightness occurred during the observations. The absolute brightness of the asteroid in the V and R filters was (9.1 ± 0.05)^m and (8.8 ± 0.03)^m, respectively. The mean value of the asteroid diameter was (119 ± 2) km. The mean values of the color indices (B?V = (0.72 ± 0.05)^m, V?R = (0.29 ± 0.03)^m, and R?I = (0.31 ± 0.03)^m) agree well with the values for asteroids of the P- and D-types and its averages. The rotation period of the asteroid estimated from photometric observations was 16.1 ± 0.2 h. The analysis of the data has shown that the asteroid continues to exhibit the same values of absolute brightness and other characteristics as those before the collision with a small body in December 2010, though the latter resulted in the outburst event and cometary activity of the asteroid. Most likely, the collision of asteroid (596) Scheila with a small body did not lead to catastrophic changes in the surface of the asteroid or to its compete break-up.     

BV photometry of a possible open star cluster pair NGC 7031/NGC 7086

We present a CCD BV photometry of the possible binary open star cluster NGC 7031/NGC 7086. The aim is to confirm or disprove their common nature on the grounds of their age and distance. An age of 224 ± 25 Myr and a distance of 831 ± 72 pc was determined for NGC 7031, and 178 ± 25 Myr, 955 ± 84 pc for NGC 7086, respectively. Based on these differences in age and distance we conclude that the two clusters are most likely not formed together from one and the same giant molecular cloud and thus do not form a true binary cluster. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A search for variable stars in the open clusters NGC7209, NGC1582 and Dolidze 18

CCD time-series photometric observations are presented for the stars in the fields of the open clusters NGC7209, NGC1582 and Dolidze 18 in Johnson V, together with some photometric observations in R, and B. The results reveal 14 variable stars in the three clusters in total, among which 13 are newly-discovered variables. With color–magnitude diagrams and color–color diagram, memberships of the variable stars are estimated. With the derived light curves, scales of time and amplitude of variability of these variable stars are obtained. Together with the spectral types due to the estimation of color temperatures, possible types of the variable stars are preliminarily discussed.     

Photometry of the poorly studied galactic open star clusters King 13, King 18, King 19, King 20, NGC 136, and NGC 7245

We present the results of our BV R _c I _c CCD photometry for six Galactic open star clusters toward the Perseus spiral armperformed at the Special Astrophysical Observatory of the Russian Academy of Sciences. Based on these data and using JHK _s photometry from the 2MASS catalog, we have determined the ages, distances, and color excesses for the clusters: 710 Myr, 2960₋₃₄₀⁺⁴⁰⁰ pc, 0_· ^m 56 ± 0_· ^m 04 (King 13); 130 Myr, 3010₋₂₈₀⁺³⁰⁰ pc, 0_· ^m 69 ± 0_· ^m 04 (King 18); 560 Myr, 2630₋₂₇₀⁺³¹⁰ pc, 0_· ^m 69 ± 0_· ^m 08 (King 19); 160 Myr, 1750₋₇₀⁺⁸⁰ pc, 0_· ^m 77 ± 0_· ^m 05 (King 20); 250 Myr, 5220₋₃₂₀⁺³⁵⁰ pc, 0_· ^m 70 ± 0_· ^m 09 (NGC 136); 320 Myr, 3390₋₂₀₀⁺²¹⁰ pc, 0_· ^m 43 ± 0_· ^m 03 (NGC 7245).     

Corrections for the Lutz-Kelker bias for Galactic masers

Based on published data, we have collected information about Galactic maser sources with measured distances. In particular, 44 Galactic maser sources located in star-forming regions have trigonometric parallaxes, proper motions, and radial velocities. In addition, ten more radio sources with incomplete information are known, but their parallaxes have been measured with a high accuracy. For all 54 sources, we have calculated the corrections for the well-known Lutz-Kelker bias. Based on a sample of 44 sources, we have refined the parameters of the Galactic rotation curve. Thus, at R ₀ = 8kpc, the peculiar velocity components for the Sun are (U _⊙, V _⊙, W _⊙) = (7.5, 17.6, 8.4) ± (1.2, 1.2, 1.2) km s^?1 and the angular velocity components are ω ₀ = ?28.7 ± 0.5 km s^?1 kpc^?1, ω ₀′ = +4.17 ± 0.10 km s^?1 kpc^?2, and ω₀″ = ?0.87 ± 0.06 km s^?1 kpc^?3. The corresponding Oort constants are A = 16.7 ± 0.6 km s^?1 kpc^?1 and B = ?12.0 ± 1.0 km s^?1 kpc^?1; the circular rotation velocity of the solar neighborhood around the Galactic center is V ₀ = 230 ± 16 km s^?1. We have found that the corrections for the Lutz-Kelker bias affect the determination of the angular velocity ω ₀ most strongly; their effect on the remaining parameters is statistically insignificant. Within themodel of a two-armed spiral pattern, we have determined the pattern pitch angle $i = - 6_.^ \circ 5$ and the phase of the Sun in the spiral wave χ ₀ = 150°.     

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″.     

Photometric survey near the Main Galactic Meridian: 1. Photoelectric stellar magnitudes and colours in the UBVR system

A catalogue of photoelectric stellar magnitudes and colours in the UBVR Johnson system in 47 sky areas with galaxies near the Main Galactic Meridian is presented. The catalogue includes 1141 stars within the V magnitude interval 4^m.5–15^m.5. The rms errors are ±0.014, ±0.026, ±0.012, ±0.016 mag for stellar magnitudes V and colours (U – B),(B – V),(V – R), respectively. The catalogue contains accurate equatorial coordinates (α, δ)1950.0, too.     

Absolute magnitudes and kinematic parameters of the subsystem of RR Lyrae variables

The statistical parallax technique is applied to a sample of 262 RRab Lyrae variables with published photoelectric photometry, metallicities, and radial velocities and with measured absolute proper motions. Hipparcos, PPM, NPM, and the Four-Million Star Catalog (Volchkov et al. 1992) were used as the sources of proper motions; the proper motions from the last three catalogs were reduced to the Hipparcos system. We determine parameters of the velocity distribution for halo [(U ₀, V ₀, W ₀) = (?9±12, ?214 ±10, ? 10, ?16±7) km s ^?1 and (σ _U , σ _V , σ _W ) = (164±11, 105±7, 95±7) km s ^?1] and thick-disk [(U ₀, V ₀, W ₀) = (?16±8, ?41±7, ?18±5) km s ^?1], and [(σ _U , σ _V , σ _W ) = (53±9, 42±8, 26±5) km s ^?1] RR Lyrae, as well as the intensity-averaged absolute magnitude for RR Lyrae of these populations: 〈M _V 〉 = 0.77 ± 0.10 and 〈M _V 〉 = +1.11 ± 0.25 for the halo and thickdisk objects, respectively. The metallicity dependence of the absolute magnitude of RR Lyrae is analyzed (〈M _V 〉 = (0.76 ± 0.12) + (0.26 ± 0.26) · ([Fe/H]+1.6)=1.17+0.26 · [Fe/H]). Our results are in satisfactory agreement with the ?M _V ?(RR)?[Fe/H]relation from Carney et al. (1992) (〈M _V 〉(RR)=1.01+0.15·[Fe/H]) obtained by Baade-Wesselink's method. They provide evidence for a short distance scale: the LMC distance modulus and the distance to the Galactic center are 18.22±0.11 and 7.4±0.5 kpc, respectively. The zero point of the distance scale and the kinematic parameters of the RR Lyrae populations are shown to be virtually independent of the source of absolute proper motions used and of whether they are reduced to the Hipparcos system or not.     

Lightcurves and phase relation of asteroid 324 Bamberga

A worldwide photometric investigation of the asteroid 324 Bamberga was conducted during the period September–November 1978. The full-cycle lightcurve shows two maxima and two minima with a maximum amplitude of 0.075 mag; the rotation period was found to be P_syn = 29.^h42 ± 0.^h01. A linear least-squares solution of the phase relation gives β_y = (0.334 ± 0.001) mag/degree and V₀ (1, 0) = (7.17 ± 0.01) mag. The color indices measured are B-V = 0.69, U-B=0.36, in agreement with the C taxonomic type given for 324 Bamberga. The very long period indicates 324 Bamberga is an unusual object among asteroids with diameters greater than 200 km.     

Frequency splitting in stria bursts: Possible roles of low-frequency waves

The kinematics of the process L ± F→ L′ are explored where L represents a parallel Langmuir wave, F represents a low frequency fluctuation and L′ represents a secondary Langmuir wave, and the results are used to discuss (a) a possible interpretation of the frequency splitting in stria bursts in terms of the processes L ± F → L′, L′ ± F′ → t, where t represents a transverse wave, and (b) second harmonic emission due to the processes L ± s→ L′, L + L′ → t, where s represents an ion sound wave. The following results are obtained:

1. The processes L ± s → L′ are allowed only for k _s < 2k _L ± k ₀, respectively, with k ₀ = ω _p /65 V _e .
2. The inclusion of a magnetic field does not alter the result (1) and adds further kinematic restrictions related to angles of propagation; the kinematic restriction T _e > 5 × 10⁵ K for second harmonic emission through process (b) above is also unchanged by inclusion of the magnetic field. The effect of a spread in the wavevectors of the Langmuir waves on this restriction is discussed in the Appendix.
3. For parallel Langmuir waves the process L - F → L′ is forbidden for lower hybrid waves and for nearly perpendicular resonant whistlers, and the process L + F → L′ is allowed only for resonant whistlers at ω _F ? 1/2ω _p (Ω _e /ω _p )².
4. The sequential three wave processes L ± s → L′, L′ ± s → t and L + F → L′, L′ ± F′ → t encounter difficulties when applied to the interpretation of the splitting in split pair and triple bursts.
5. The four-wave process L ± F ± F′ → t is kinematically allowed and provides a favourable qualitative interpretation of the splitting when F denotes a resonant whistler near the frequency mentioned in (3) above. The four wave processes should saturate under conditions which are not extreme and produce fundamental plasma emission with brightness temperature T _t equal to the effective temperature T _L of the Langmuir waves.