Period investigation of two RS CVn-type binary stars: RU Cancri and AW Herculis

Orbital period variations of two RS CVn-type binaries, RU Cnc and AW Her, are presented based on the analysis of all available times of light minima. It is discovered that the orbital period of RU Cnc shows two possible period oscillations with periods of 13.38(±0.23) and 37.6(±3.4) years. The corresponding amplitudes of the oscillations are about 0.0098(±0.0023) and 0.0119(±0.0017) days. For AW Her, it is found that the period shows a cyclic variation with a period of 12.79(±0.34) years and an amplitude of about 0.0327(±0.0063) days. Since RU Cnc and AW Her are two RS CVn-type systems, the cyclic period oscillations are more likely to be caused by the magnetic activity cycles.     

Rotational Quasi-Periodicities and the Sun – Heliosphere Connection

Mutual quasi-periodicities near the solar-rotation period appear in time series based on the Earth’s magnetic field, the interplanetary magnetic field, and signed solar-magnetic fields. Dominant among these is one at 27.03±0.02 days that has been highlighted by Neugebauer et al. (J. Geophys. Res. 105, 2315, 2000). Extension of their study in time and to different data reveals decadal epochs during which the ≈ 27.0 days, or a ≈ 28.3 days, or other quasi-periods dominate the signal. Space-time eigenvalue analyses of time series in 30 solar latitude bands, based on synoptic maps of unsigned photospheric fields, lead to two maximally independent modes that account for almost 30% of the data variance. One mode spans 45° of latitude in the northern hemisphere and the other one in the southern. The modes rotate around the Sun rigidly, not differentially, suggesting connection with the subsurface dynamo. Spectral analyses yield familiar dominant quasi-periods 27.04±0.03 days in the North and at 28.24±0.03 days in the South. These are replaced during cycle 23 by one at 26.45±0.03 days in the North. The modes show no tendency for preferred longitudes separated by ≈ 180°.     

The Rotation Of Comet C/1995 O1 Hale–Bopp From Inner Coma Photometry

We present a further investigation of the periodogram resulting from the photometric data by Rodríguez et al. (1997) for comet C/1995 O1 Hale–Bopp and interpret that the main period in the data is 11.23 ± 0.01 h, but not 7.19 days. The latter is now attributed to an alias of the 11.23-h period. Assuming that the periodicity observed in the photometry is the solar day, the 11.23-h period is consistent with estimates of the sidereal rotation period by Farnham et al. (1998), and Jorda et al. (1997–1999) provided that the obliquity of the comet‘s equatorial plane to its orbital plane is larger than 75° and 80°, respectively. This result is in agreement with estimates of the obliquity by Sekanina (1997–1999) and Jorda et al. (1998). A weaker periodic signal in the light curve could be 5.48 ± 0.01 h, but we suggest that this is an alias of a 3.25 ± 0.01 h period of unknown origin. This revised version was published online in July 2006 with corrections to the Cover Date.     

Magnetic field structure and accretion regimes of the asynchronous polar by Cam

Series of photometric CCD observations of the asynchronous polar BY Cam in a low accretion state (R = 14^m–16^m) were made on the K-380 telescope at the Crimean Astrophysical Observatory (CrAO) over 100 hours in the course of 31 nights during 2004–2005. A period of P ₁ = 0.137120±0.000002 days was found for the variations in the brightness, along with less significant periods of P ₂ = 0.139759±0.000003 and P₃ = 0.138428±0.000002 days, where P₂ and P₃ are obviously the orbital and rotation periods, while the dominant period P₁ is the sideband period. A modulation in the brightness and an amplitude of 0.137 days in the oscillations at the orbital-rotational beat period (synodic cycle) of 14.568±0.003 day are found for the first time. The profile of the modulation period is four humped. This indicates that the magnetic field has a quadrupole component, which shows up well during the low brightness state. Accretion takes place simultaneously into two or three accretion zones, but at different rates. The times of the times of maxima for the main accretion zone vary with the phase of the beat period. Three types of variation of this sort are distinguished: linear, discontinuous, and chaotic, which indicate changes in the accretion regimes. At synodic phases 0.25 and 0.78 the bulk of the stream switches by 180°, and at phase 0.55, by ∼75°. At phases of 0.25–0.55 and 0.55–0.78, the O-C shift with a period of 0.1384 days, which can be explained by a retrograde shift of the main accretion zone relative to the magnetic pole and/or a change in the angle between the field lines and the surface of the white dwarf owing to the asynchronous rotation. For phases of 0.78–1.25 the motion of the accretion zone is quite chaotic. It is found that synchronization of the components occurs at a rate of less than dP_rot/P_rot∼10⁻⁹ day/day. __________ Translated from Astrofizika, Vol. 49, No. 1, pp. 121–137 (February 2006).     

Periodicity of flare index revisited using the Hilbert–Huang transform method

Using the Hilbert–Huang Transform (HHT) method, we investigate the periodicity in the monthly mean flare indices from 1966 to 2007 (corresponding to almost four complete solar cycles), calculated by T. Atac and A. Ozguc. The results show as following. (1) The periods of 9.37 ± 2.53, 11.8 ± 0.172 and 23.6 ± 0.316 years are found to be statistically significant in the flare index. The most eminent period is 9.37 ± 2.53 years. (2) Other periods of 0.237 ± 0.196 years (86.6 ± 71.6 days), 0.525 ± 0.0508 years (191 ± 18.5 days), 1.05 ± 0.478 years (383 ± 174 days) and 2.37 ± 0.395 years are below the 99% confidence level line, suggesting they are due to stochastic random noise.     

Stardust-NExT,Deep Impact,and the accelerating spin of 9P/Tempel 1

The evolution of the spin rate of Comet 9P/Tempel 1 through two perihelion passages (in 2000 and 2005) is determined from 1922 Earth-based observations taken over a period of 13 year as part of a World-Wide observing campaign and from 2888 observations taken over a period of 50 days from the Deep Impact spacecraft. We determine the following sidereal spin rates (periods): 209.023 ± 0.025°/dy (41.335 ± 0.005 h) prior to the 2000 perihelion passage, 210.448 ± 0.016°/dy (41.055 ± 0.003 h) for the interval between the 2000 and 2005 perihelion passages, 211.856 ± 0.030°/dy (40.783 ± 0.006 h) from Deep Impact photometry just prior to the 2005 perihelion passage, and 211.625 ± 0.012°/dy (40.827 ± 0.002 h) in the interval 2006–2010 following the 2005 perihelion passage. The period decreased by 16.8 ± 0.3 min during the 2000 passage and by 13.7 ± 0.2 min during the 2005 passage suggesting a secular decrease in the net torque. The change in spin rate is asymmetric with respect to perihelion with the maximum net torque being applied on approach to perihelion. The Deep Impact data alone show that the spin rate was increasing at a rate of 0.024 ± 0.003°/dy/dy at JD2453530.60510 (i.e., 25.134 dy before impact), which provides independent confirmation of the change seen in the Earth-based observations.The rotational phase of the nucleus at times before and after each perihelion and at the Deep Impact encounter is estimated based on the Thomas et al. (Thomas et al. [2007]. Icarus 187, 4–15) pole and longitude system. The possibility of a 180° error in the rotational phase is assessed and found to be significant. Analytical and physical modeling of the behavior of the spin rate through of each perihelion is presented and used as a basis to predict the rotational state of the nucleus at the time of the nominal (i.e., prior to February 2010) Stardust-NExT encounter on 2011 February 14 at 20:42.We find that a net torque in the range of 0.3–2.5 × 10⁷ kg m² s^?2 acts on the nucleus during perihelion passage. The spin rate initially slows down on approach to perihelion and then passes through a minimum. It then accelerates rapidly as it passes through perihelion eventually reaching a maximum post-perihelion. It then decreases to a stable value as the nucleus moves away from the Sun. We find that the pole direction is unlikely to precess by more than ～1° per perihelion passage. The trend of the period with time and the fact that the modeled peak torque occurs before perihelion are in agreement with published accounts of trends in water production rate and suggests that widespread H₂O out-gassing from the surface is largely responsible for the observed spin-up.     

Records of the Moon‐forming impact and the 470 Ma disruption of the L chondrite parent body in the asteroid belt from U‐Pb apatite ages of Novato (L6)

Novato, a newly observed fall in the San Francisco Bay area, is a shocked and brecciated L6 ordinary chondrite containing dark and light lithologies. We have investigated the U‐Pb isotope systematics of coarse Cl‐apatite grains of metamorphic origin in Novato with a large geometry ion microprobe. The U‐Pb systematics of Novato apatite reveals an upper intercept age of 4472 ± 31 Ma and lower intercept age of 473 ± 38 Ma. The upper intercept age is within error identical to the U‐Pb apatite age of 4452 ± 21 Ma measured in the Chelyabinsk LL5 chondrite. This age is interpreted to reflect a massive collisional resetting event due to a large impact associated with the peak arrival time at the primordial asteroid belt of ejecta debris from the Moon‐forming giant impact on Earth. The lower intercept age is consistent with the most precisely dated Ar‐Ar ages of 470 ± 6 Ma of shocked L chondrites, and the fossil meteorites and extraterrestrial chromite relicts found in Ordovician limestones with an age of 467.3 ± 1.6 Ma in Sweden and China. The lower intercept age reflects a major disturbance related to the catastrophic disruption of the L chondrite parent body most likely associated with the Gefion asteroid family, which produced an initially intense meteorite bombardment of the Earth in Ordovician period and reset and degassed at least approximately 35% of the L chondrite falls today. We predict that the 470 Ma impact event is likely to be found on the Moon and Mars, if not Mercury.     

Lead and Mg isotopic age constraints on the evolution of the HED parent body

The large collection of howardite‐eucrite‐diogenite (HED) meteorites allows us to study the initial magmatic differentiation of a planetesimal. We report Pb‐Pb ages of the unequilibrated North West Africa (NWA) 4215 and Dhofar 700 diogenite meteorites and their mass‐independent ²⁶Mg isotope compositions (²⁶Mg*) to better understand the timing of differentiation and crystallization of their source reservoir(s). NWA 4215 defines a Pb‐Pb age of 4484.5 ± 7.9 Myr and has a ²⁶Mg* excess of +2.3 ± 1.6 ppm whereas Dhofar 700 has a Pb‐Pb age of 4546.4 ± 4.7 Myr and a ²⁶Mg* excess of +25.5 ± 1.9 ppm. We interpret the young age of NWA 4215 as a thermal overprint, but the age of Dhofar 700 is interpreted to represent a primary crystallization age. Combining our new data with published Mg isotope and trace element data suggests that approximately half of the diogenites for which such data are available crystallized within the first 1–2 Myr of our solar system, consistent with a short‐lived, early‐formed magma ocean undergoing convective cooling. The other half of the diogenites, including both NWA 4215 and Dhofar 700, are best explained by their crystallization in slowly cooled isolated magma chambers lasting over at least ~20 Myr.     

Extensive photometry of the WZ Sge-type dwarf nova V455 And (HS2331+3905): Detection of negative superhumps and coherence features of the short-period oscillations

We report the results of photometry of the WZ Sge-type dwarf nova V455 And. Observations were obtained over 19 nights in 2013 and 2014. The total duration of the observations was 96 h. We clearly detected three coherent oscillations with periods of 80.376 ± 0.003 min, 40.5431 ± 0.0004 min and 67.619685 ± 0.000040 s. The 67.619685-s period can be the spin period of the white dwarf. The 40.5431-minute period is the first harmonic of the orbital period. The 80.376-minute oscillation can be a negative superhump because its period is 0.9% less than the orbital period. This oscillation was evident both in the data of 2013 and in the data of 2014. These results make V455 And a permanent superhump system which shows negative superhumps. This is also the first detection of persistent negative superhumps in a WZ Sge-type dwarf nova. In addition, the analysis of our data revealed incoherent oscillations with periods in the range 5–6 min, which were observed earlier and accounted for by non-radial pulsations of the white dwarf. Moreover, we clearly detected an oscillation with a period of 67.28 ± 0.03 s, which was of a low degree of coherence. This oscillation conforms to the beat between the spin period of the white dwarf and the 3.5-h spectroscopic period, which was discovered earlier and accounted for by the free precession of the white dwarf. Because the 67.28-s period is shorter than the spin period and because the free precession of the white dwarf is retrograde, we account for the 67.28-s oscillation by the free precession of the white dwarf.     

New estimates of retrograde free core nutation parameters

Based on the available celestial intermediate pole (CIP) coordinate determinations from VLBI observations over the last 25 years, we have constructed a new highly accurate combined series of CIP coordinates. An amplitude-phase analysis of this series has allowed us to improve the previously estimated retrograde free core nutation (RFCN) parameters as functions of time. During this interval, the RFCN period changed several times. It was −418.1 ± 0.2 days before 1992.1 and then −431.6 ± 0.2 days until 1999.0. In 1999, the CIP oscillations damped out almost completely and the processwas restructured. Since 2000, the amplitude of these oscillations has increased and their period has become 450.7± 0.1 days.     

Complete hydrothermal re‐equilibration of zircon in the Maniitsoq structure,West Greenland: A 3001 Ma minimum age of impact?

Zircon in five samples of variably comminuted, melted, and hydrothermally altered orthogneiss from the Maniitsoq structure of southern West Greenland yield a weighted mean ²⁰⁷Pb/²⁰⁶Pb age of 3000.9 ± 1.9 Ma (ion probe data, n = 37). The age data constitute a rare example of pervasive and nearly complete isotopic resetting of zircon during a regional hydrothermal event. Many zircon grains are homogeneous or display weak flame‐like patterns in backscattered electron images. Other grains show complex internal textures, where homogeneous, high‐U fronts commonly cut across relict igneous‐type oscillatory zonation. Inclusions of quartz, plagioclase, mica, and other Al ± Na ± Ca ± Fe‐bearing silicates are very common. In two samples, selective replacement of zircon with baddeleyite occurs along concentric zones with relict igneous zonation, and as specks a few microns large within recrystallized, high‐U areas. We interpret the 3000.9 ± 1.9 Ma date as the minimum age of the recently proposed impact structure at Maniitsoq. The great geographical extent and intensity of the hydrothermal event suggest massive invasion of water into the currently exposed crust, implying that the age of the hydrothermal alteration would closely approximate the age of the proposed impact at Maniitsoq. At the western margin of the Taserssuaq tonalite complex, which postdates the Maniitsoq event, a ²⁰⁷Pb/²⁰⁶Pb mean age of 2994.6 ± 3.4 Ma obtained from zircon has mostly retained igneous‐type oscillatory zonation. A subsequent thermal event at approximately 2975 Ma is recorded in several samples by zircon with baddeleyite replacement textures.     

Searching for superhump period of cataclysmic variable AY Psc

The results obtained from unfiltered photometric CCD observations of AY Psc made during 17, 20 and 12 nights, respectively, in 2003, 2004 and 2005 are presented. A period of 0.21732 ± 0.00001 d was detected in the data. This period is consistent with the previously proposed orbital period of P_orb = 0.2173209 d ((Diaz and Steiner, 1990)). Since this period was present in the light curves taken in all three years, with no apparent change in its value or amplitude, it is interpreted as the orbital period of this binary system. In addition, quasi-periodicities of 0.2057 ± 0.0001 d, 0.2063 ± 0.0001 d, 0.2072 ± 0.0001 d for the years 2003, 2004 and 2005, respectively, were also discovered. These periods were interpreted as negative superhump periods and it was seen that they changes from year to year. Therefore AY Psc is then classified as a negative superhump system.     

Rotation period of Venus estimated from Venus Express VIRTIS images and Magellan altimetry

The 1.02 μm wavelength thermal emission of the nightside of Venus is strongly anti-correlated to the elevation of the surface. The VIRTIS instrument on Venus Express has mapped this emission and therefore gives evidence for the orientation of Venus between 2006 and 2008. The Magellan mission provided a global altimetry data set recorded between 1990 and 1992. Comparison of these two data sets reveals a deviation in longitude indicating that the rotation of the planet is not fully described by the orientation model recommended by the IAU. This deviation is sufficiently large to affect estimates of surface emissivity from infrared imaging. A revised period of rotation of Venus of 243.023 ± 0.002 d aligns the two data sets. This period of rotation agrees with pre-Magellan estimates but is significantly different from the commonly accepted value of 243.0185 ± 0.0001 d estimated from Magellan radar images. It is possible that this discrepancy stems from a length of day variation with the value of 243.023 ± 0.002 d representing the average of the rotation period over 16 years.     

Sunspot Time Series – Relations Inferred from the Location of the Longest Spotless Segments

Spotless days (i.e., days when no sunspots are observed on the Sun) occur during the interval between the declining phase of the old sunspot cycle and the rising phase of the new sunspot cycle, being greatest in number and of longest continuous length near a new cycle minimum. In this paper, we introduce the concept of the longest spotless segment (LSS) and examine its statistical relation to selected characteristic points in the sunspot time series (STS), such as the occurrences of first spotless day and sunspot maximum. The analysis has revealed statistically significant relations that appear to be of predictive value. For example, for Cycle 24 the last spotless day during its rising phase should be about August 2012 (± 9.1 months), the daily maximum sunspot number should be about 227 (± 50; occurring about January 2014±9.5 months), and the maximum Gaussian smoothed sunspot number should be about 87 (± 25; occurring about July 2014). Using the Gaussian-filtered values, slightly earlier dates of August 2011 and March 2013 are indicated for the last spotless day and sunspot maximum for Cycle 24, respectively.     

UU CNC and VZ PSC,contact systems before the common envelope phase?

We have analyzed the existing photoelectric light curves of twoK-type binary systems: UU Cnc, with a period of about 100 days, and VZ Psc, with a period of about 6 hours. Both show a large overcontact (38% for UU Cnc, 56% for VZ Psc) and a large temperature difference between components (T1500 K and 1100 K, respectively). In the case of VZ Psc, the variability is due only to the non-spherical shape, i.e., no eclipse occurs, but the determination of the photometric solution is made possible by the existence of a spectroscopic mass ratio. We find that UU Cnc is now probably undergoing Case C mass transfer in a dynamical time-scale, with the mass ratio reversal having already occurred; the system is in contact, and is likely to evolve to a 100% filling factor, that is the so-called pre-common envelope phase, a unique case never observed before. The situation for VZ Psc is more uncertain, but a similar, although not identical, possibility exists.Associated with the Istituto Nazionale Fisica Nucleare, Italy.On leave from N. Copernicus Astronomical Center, Polish Academy of Sciences, Warsaw, Poland.     

The period variation of the double mode high amplitude δ Scuti variable VZ Cnc

VZ Cnc is a population I double mode high amplitude δ Scuti variable. We observed the star and collected the data from January 2007 to January 2009 to determine 14 times of maximum light. We also searched its times of maximum light from other papers and from IBVS and got 57 values. We collected a total of 194 times of maximum light and used them to perform an (O-C) analysis and concluded that there may be no tendency of binary orbital light time effect. But by parabola tendency, it shows a continuous period increasing at the rate of 1.4×10⁻⁸ per year; this is compatible with the stellar evolution model calculation both in direction and size.     

On the rotation period of Capella

We present differential Hα and Hβ photometry of the very bright RS CVn‐binary α Aurigae (Capella)obtained with theVienna automatic photoelectric telescope in the years 1996 through 2000. Low‐level photometric variations of up to 0^m_.04 are detected in Hα. A multifrequency analysis suggests two real periods of 106 ± 3 days and 8.64 ± 0.09 days, that we interpret to be the rotation periods of the cool and the hot component of the Capella binary, respectively. These periods confirm that the hotter component of Capella rotates asynchronously, while the cooler component appears to be synchronized with the binary motion. The combined Hα data possibly contains an additional period of 80.4 days that we, however, believe is either spurious and was introduced due to seasonal amplitude variations or stems from a time‐variable circumbinary mass flow. The rotational periods result in stellar radii of 14.3 ± 4.6 R_⊙ and 8.5 ± 0.5 R_⊙ for the cool and hot component, respectively, and are in good agreement with previously published radii based on radiometric and interferometric techniques. The long‐period eclipsing binary Aurigae served as our check star, and we detected complex light variations outside of eclipse of up to 0^m_.15 in H α and 0^m_.20 in Hβ. Our frequency analysis suggests the existence of at least three significant periods of 132, 89, and 73 days. One of our comparison stars (HD 33167, F5V) was discovered to be a very‐low amplitude variable with a period of 2.6360 ± 0.0055 days.     

Comparisons of Supergranule Characteristics During the Solar Minima of Cycles 22/23 and 23/24

Supergranulation is a component of solar convection that manifests itself on the photosphere as a cellular network of around 35 Mm across, with a turnover lifetime of 1 – 2 days. It is strongly linked to the structure of the magnetic field. The horizontal, divergent flows within supergranule cells carry local field lines to the cell boundaries, while the rotational properties of supergranule upflows may contribute to the restoration of the poloidal field as part of the dynamo mechanism, which controls the solar cycle. The solar minimum at the transition from cycle 23 to 24 was notable for its low level of activity and its extended length. It is of interest to study whether the convective phenomena that influence the solar magnetic field during this time differed in character from periods of previous minima. This study investigates three characteristics (velocity components, sizes and lifetimes) of solar supergranulation. Comparisons of these characteristics are made between the minima of cycles 22/23 and 23/24 using MDI Doppler data from 1996 and 2008, respectively. It is found that whereas the lifetimes are equal during both epochs (around 18 h), the sizes are larger in 1996 (35.9 ± 0.3 Mm) than in 2008 (35.0 ± 0.3 Mm), while the dominant horizontal velocity flows are weaker (139 ± 1 m s⁻¹ in 1996; 141 ± 1 m s⁻¹ in 2008). Although numerical differences are seen, they are not conclusive proof of the most recent minimum being inherently unusual.     

CCD Photometry of the W UMa type star QX Andromeda

We present new B- and V-band photometry of the W UMa-type binary system QX And, which is a member of the open cluster NGC 752. Revised orbital period and new ephemerides were given for the binary system based on the data of times of light minima. The result of a period analysis reveals that the system is undergoing a continuous orbital period increase during the past decades. The rate of period increasing turns out to be about 2.7 × 10^?7 d yr^?1. With the Wilson–Devinney code, a photometric solution is computed. It yields a contact configuration for the system with a filling factor of 0.361. Combining the results from the photometric solution along with that from the radial-velocity observations, we have determined the absolute parameters for the two components of the system. The masses, radii and luminosity of the primary and secondary stars are calculated as 1.43 ± 0.04 M_⊙, 1.45 ± 0.09 R_⊙, 2.87 ± 0.40 L_⊙ and 0.44 ± 0.02 M_⊙, 0.87 ± 0.05 R_⊙, 0.99 ± 0.13 L_⊙, respectively. The evolutionary status and physical nature of the contact binary system were discussed compared with the theoretical models.     

Observations of the Deeply Eclipsing Dwarf Nova Gy Cnc

We present photometric measurements of the eclipsing dwarf nova and X-ray source GY Cnc. The observations were collected during outbursts and in quiescence. The investigation of plates from the Sonneberg archive showed that the mean outburst interval is about 210–270 days, that the outburst is very fast, and lasts for about 5 days.