A large number (~2 million) of VLBI observations have been reduced in order to re ne the measured coordinates of the observed radio sources. The data reduction was carried out in the OCCAM package using the least squares colocation method. Corrections to the coordinates of 642 objects were derived. The accuracy of the catalog is no worse than 0.2 milliseconds of arc for stable sources.
We report on the first wide-field, very long baseline interferometry (VLBI) survey at 90cm. The survey area consists of two overlapping 28deg^2^ fields centered on the quasar J0226+3421 and the gravitational lens B0218+357. A total of 618 sources were targeted in these fields, based on identifications from Westerbork Northern Sky Survey (WENSS) data. Of these sources, 272 had flux densities that, if unresolved, would fall above the sensitivity limit of the VLBI observations. A total of 27 sources were detected as far as 2{deg} from the phase center. The results of the survey suggest that at least 10% of moderately faint (S~100mJy) sources found at 90 cm contain compact components smaller than ~0.1"-0.3" and stronger than 10% of their total flux densities.
A CCD V light curve for the eclipsing binary star AzV 73 is presented. This new photometric observations are analysed together with previously published CCD I photometry from Udalski et al. (1998AcA....48..563U) and spectrographic data from Niemela & Bassino (1994ApJ...437..332N), by means of the Wilson-Devinney code. It is found that this system is semi-detached, with an orbital inclination of roughly 86{deg} and a separation of 42R_{sun}_. The sizes and masses are R_1_=11.53 +/-0.5R_{sun}_, M_1_=25.26+/-0.7M_{sun}_, and R_2_=15.46+/-0.4R_{sun}_, M_2_=21.96+/-0.8M_{sun}_ for the primary and secondary components, respectively.
Sequences of spectra of the nova-like cataclysmic variable (CV) BZ Cam were acquired on nine nights in 2005-2006 in order to study the time development of episodes of wind activity known to occur frequently in this star. We confirm the results of Ringwald & Naylor that the P-Cygni absorption components of the lines mostly evolve from higher expansion velocity to lower velocity as an episode progresses. We also commonly find blueshifted emission components in the H{alpha} line profile, whose velocities and durations strongly suggest that they are also due to the wind. Curiously, Ringwald & Naylor reported common occurrences of redshifted H{alpha} emission components in their BZ Cam spectra. We have attributed these emission components in H{alpha} to occasions when gas concentrations in the bipolar wind (both front side and back side) become manifested as emission lines as they move beyond the disk's outer edge. We also suggest, based on changes in the P-Cygni profiles during an episode, that the progression from larger to smaller expansion velocities is due to the higher velocity portions of a wind concentration moving beyond the edge of the continuum light of the disk first, leaving a net redward shift of the remaining absorption profile. We derive a new orbital ephemeris for BZ Cam, using the radial velocity of the core of the HeI{lambda}5876 line, finding P=0.15353(4). Using this period, the wind episodes in BZ Cam are found to be concentrated near the inferior conjunction of the emission line source. This result helps confirm that the winds in nova-like CVs are often phase dependent, in spite of the puzzling implication that such winds lack axisymmetry. We argue that the radiation-driven wind in BZ Cam receives an initial boost by acting on gas that has been lifted above the disk by the interaction of the accretion stream with the disk, thereby imposing flickering timescales onto the wind events, as well as leading to an orbital modulation of the wind due to the non-axisymmetric nature of the stream/disk interaction. Simultaneous photometry and spectroscopy were acquired on three nights in order to test the possible connection between flickering continuum light and the strength of the front-side wind. We found strong agreement on one night, some agreement on another, and no agreement on the third. We suggest that some flickering events lead to only back-side winds which will not have associated P-Cygni profiles.
RW Aur A is a classical T Tauri star, believed to have undergone a reconfiguration of its circumstellar environment as a consequence of a recent flyby of its stellar companion, RW Aur B. This interaction stripped away part of the circumstellar disk of RW Aur A, leaving a tidally disrupted "arm" and a short truncated circumstellar disk. We present photometric observations of the RW Aur system from the Kilodegree Extremely Little Telescope survey showing a long and deep dimming that occurred from 2010 September until 2011 March. The dimming has a depth of ~2mag, a duration of ~180 days, and was confirmed by archival observations from American Association of Variable Star Observers. We suggest that this event is the result of a portion of the tidally disrupted disk occulting RW Aur A, specifically a fragment of the tidally disrupted arm. The calculated transverse linear velocity of the occulter is in excellent agreement with the measured relative radial velocity of the tidally disrupted arm. Using simple kinematic and geometric arguments, we show that the occulter cannot be a feature of the RW Aur A circumstellar disk, and we consider and discount other hypotheses. We also place constraints on the thickness and semimajor axis of the portion of the arm that occulted the star.
We observed a new cataclysmic variable (CV) SDSS J080434.20+510349.2 to study the origin of long-term variability found in its light curve. Multi-longitude, time-resolved, photometric observations were acquired to analyze this uncommon behavior, which has been found in two newly discovered CVs. This study of SDSS J080434.20+510349.2 concerns primarily the understanding of the nature of the observed, double-humped, light curve and its relation to a cyclic brightening that occurs during quiescence. The observations were obtained early in 2007, when the object was at about V~17.1, about 0.4mag brighter than the pre-outburst magnitude. The light curve shows a sinusoidal variability with an amplitude of about 0.07mag and a periodicity of 42.48min, which is half of the orbital period of the system. We observed in addition two "mini-outbursts" of the system of up to 0.6mag, which have a duration of about 4days each. The "mini-outburst" has a symmetric profile and is repeated in approximately every 32days. Subsequent monitoring of the system shows a cyclical behavior of such "mini-outbursts" with a similar recurrence period. The origin of the double-humped light curve and the periodic brightening is discussed in the light of the evolutionary state of SDSS J080434.20+510349.2.
We present differential CCD photometry for the high-amplitude delta Scuti star V567 Ophiuchi obtained in the Johnson V-band. It was observed on 15 nights in two consecutive years in order to resolve the long-standing ambiguity related to its secondary period. A frequency analysis of almost 5000 individual single-filtered measurements resulted in two independent frequencies (f_1_=6.6879c/d and f_2_=11.8266c/d) with a ratio of f_1_/f_2_=0.565. The presented photometric data are differential magnitudes relative to the comparison star C_1_ (GSC 00417-01714) from Powell et al. (1990PASP..102.1131P)
What is the origin of the large-amplitude variability in Wolf-Rayet WN8 stars in general and WR123 in particular? A dedicated spectroscopic campaign targets the ten-hour period previously found in the high-precision photometric data obtained by the MOST satellite. In June-August 2003 we obtained a series of high signal-to-noise, mid-resolution spectra from several sites in the {lambda}{lambda}4000-6940{AA} domain. We also followed the star with occasional broadband (Johnson V) photometry. The acquired spectroscopy allowed a detailed study of spectral variability on timescales from ~5 minutes to months.
WR 29 is a known WN7h+O double-lined binary system with a rather short period (3.164-days). We search for light variations to determine the inclination of the system and thus the absolute masses of both components. We observed photometrically the field of WR 29 between December, 2002 and February, 2006. We find that the V light of WR 29 varies in phase with the spectroscopic period of 3.16412-days, presenting two minima corresponding to the conjunctions of the binary components. Numerical models fitted to the light curve indicate an orbital inclination of about 44{deg}, and masses of 53M_{sun}_ and 42M_{sun}_ for the O- and WN-type components, respectively.
We report an analysis of photometric behaviour of DI UMa, an extremely active dwarf nova. The observational campaign (completed in 2007) covers five superoutbursts and four normal outbursts. We examined principal parameters of the system to understand peculiarities of DI UMa, and other active cataclysmic variables. Based on precise photometric measurements, temporal light curve behaviour, O-C analysis, and power spectrum analysis, we investigated physical parameters of the system. We found that the period of the supercycle now equals 31.45+/-0.3days. Observations during superoutbursts infer that the period of superhumps equals P_sh_=0.055318(11)days (79.66+/-0.02min). During quiescence, the light curve reveals a modulation of period P_orb_=0.054579(6)days (78.59+/-0.01min), which we interpret as the orbital period of the binary system. The values obtained allowed us to determine a fractional period excess of 1.35+/-0.02%, which is surprisingly small compared to the usual value for dwarf novae (2%-5%). A detailed O-C analysis was performed for two superoutbursts with the most comprehensive coverage. In both cases, we detected an increase in the superhump period with a mean rate of (dP/dt)/P_sh_=4.4(1.0)x10^-5^. Based on these measurements, we confirm that DI UMa is probably a period bouncer, an old system that reached its period minimum a long time ago, has a secondary that became a degenerate brown dwarf, the entire system evolving now toward longer periods. DI UMa is an extremely interesting object because we know only one more active ER UMa star with similar characteristics (IX Dra).
