Rotation Periods of Nine ROSAT Selected Solar-Type Stars

We monitored 16 X-ray selected young solar-type stars for light variation and found appreciable periodic light variability with amplitudes of a few hundredths of a magni-tude in nine of the objects. Using the method of Phase Dispersion Minimization (PDM) and Fourier analysis (software PERIOD04), the rotation periods of these stars were determined from the photometric data. The rotation periods of all nine stars are shorter than about 3days. It is suggested that, as with the Pleiades cluster, small amplitude light variations are quite common among young solar-type stars with rotation periods around 3 days or less. This gives further evidence for the spin up of solar-type stars predicted by models of angular momentum evolution of pre-main sequence stars.     

A photometric and spectroscopic study of the hottest pulsating extreme helium star, V2076 Oph (HD 160641)

We present results from a three-site photometric and high-resolution spectroscopic campaign on the hottest known extreme helium star V2076 Oph (HD 160641). A core programme of intensive observations covered two weeks and a much lower sampling rate extended over another two months. Despite the fact that the data seem to indicate periodicity near half a day (though the light curves are clearly not formed by a single periodicity), conventional Fourier analysis of the data fails to reveal coherent frequencies. Furthermore, we are unable to recover frequencies which were apparently clear in an earlier campaign on the star. Evidence of monotonic pulsation amplitude changes is seen at the higher frequencies from a wavelet analysis, but more data are needed before this study can be extended to lower frequencies. The application of linear stochastic differential equation (LSDE) methods indicates that the observed light variations could be a result of random variations giving the appearance of intermittent periodicity. High-resolution spectroscopic observations were obtained during the campaign and additional observations were made three years later. Complex line profile variations were observed. It is proposed that the different behaviour of the emission line studied may indicate it is associated with a stellar wind or resident circumstellar material. The frequencies that are extracted from the velocity data do not conform to those identified in the current or previous photometric campaigns.     

A Two—Temperature Supernova Fallback Disk Model for Anomalous X—ray Pulsars

We present a case study of the relevance of the radially pulsational instability of a two-temperature accretion disk around a neutron star to anomalous X-ray pulsars (AXPs). Our estimates are based on the approximation that such a neutron star disk with mass in the range of 10^-6-10^-5M⊙ is formed by supernova fallback. We derive several peculiar properties of the accretion disk instability: a narrow interval of X-ray pulse periods; lower X-ray luminosities; a period derivative and an evolution time scale. All these results are in good agreement with the observations of the AXPs.     

The period–luminosity relation for type II Cepheids in globular clusters

We report the result of our near-infrared observations ( JHK _s) for type II Cepheids (including possible RV Tau stars) in galactic globular clusters. We detected variations of 46 variables in 26 clusters (10 new discoveries in seven clusters) and present their light curves. Their periods range from 1.2 d to over 80 d. They show a well-defined period–luminosity relation at each wavelength. Two type II Cepheids in NGC 6441 also obey the relation if we assume the horizontal branch stars in NGC 6441 are as bright as those in metal-poor globular clusters in spite of the high metallicity of the cluster. This result supports the high luminosity which has been suggested for the RR Lyr variables in this cluster. The period–luminosity relation can be reproduced using the pulsation equation     assuming that all the stars have the same mass. Cluster RR Lyr variables were found to lie on an extrapolation of the period–luminosity relation. These results provide important constraints on the parameters of the variable stars.
Using Two Micron All-Sky Survey (2MASS) data, we show that the type II Cepheids in the Large Magellanic Cloud (LMC) fit our period–luminosity relation within the expected scatter at the shorter periods. However, at long periods (   P > 40  d, i.e. in the RV Tau star range) the LMC field variables are brighter by about one magnitude than those of similar periods in galactic globular clusters. The long-period cluster stars also differ from both these LMC stars and galactic field RV Tau stars in a colour–colour diagram. The reasons for these differences are discussed.     

One of the first members of RS CVn‐type systems: MM Herculis

We present the long‐term multi‐colour photometry of MM Her which is one of the first members of the RS CVn‐type of eclipsing binary systems. We took advantage of its photometry‐spanning 33 years to evaluate its long‐term variation, which is caused by the evolution of the activity structures located on the surface of the cooler component. In this study we found that the long‐term variation in the brightness, colour, and amplitude of seasonal light curves over the years could be represented by two periods: one of which is of around 22.5 years, and is similar to all in this regard, but the other is a period value of about 9.5 years for the brightness variation, and of about 7.5 years for the variation in colour and amplitude. The analysis of the spot minimum phases gives a migration period of approximately 7.8 years. We also presented a new light curve analysis solution, and improved its light elements in this study. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Evidence for pole switching in the magnetic cataclysmic variable BY Camelopardalis

An analysis of X-ray and optical light curves of the magnetic cataclysmic variable (MCV) BY Cam is presented. This system is one of three MCVs in which the spin period of the white dwarf and the binary orbital period differ by ∼1 per cent. As such these 'BY Cam' stars are important objects with which to probe the field structure of the magnetic white dwarf and ultimately the nature of synchronization of AM Her binaries. We confirm asynchronous rotation of the magnetic white dwarf with respect to the binary. We find evidence that the accretion stream accretes directly on to the white dwarf as in AM Her systems, but further, the stream impacts on to different magnetic poles over the course of the beat period. We present evidence that the optical and hard X-ray light curves modulate in phase, but together they are out of phase with the soft X-ray light curve. We confirm the spin down of the white dwarf which is expected to lead to the synchronization of the spin and orbital periods of BY Cam.     

The Blazhko behavior of RV UMa

RV UMa is one of the most extensively studied RR Lyrae stars showing Blazhko modulation. Its photometric observations cover more than 90 years. The published photoelectric observations of RV UMa obtained at the Konkoly Observatory (Kanyó 1976) were re‐considered and completed with previously unpublished data. During the time interval of the observations the periods of both the pulsation and the modulation varied within the ranges of 0.000007 and 0.9 days, respectively. We have found a definite but not strict inverse relation between the pulsation and modulation periods of RV UMa. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the moving subfeatures in the Be star ζ Oph

We analyse a series of line profile observations of the He  i 6678 line in ζ Oph. A period analysis on these data using the mode and moments of the line profile confirms the two previously known periods. We describe a new method of mode identification for pulsating stars in which the calculated profiles are directly fitted to observed profiles. The method yields the full set of pulsational parameters including the spherical harmonic degree, ℓ, and azimuthal number, m . Application of the method to these data confirms the mode identifications previously suggested for the two periodicities. We find that the derived pulsational parameters are physically realistic and conclude that non-radial pulsation is the most likely explanation for the travelling subfeatures. However, a unique mode identification is still not possible – several non-sectorial modes fit the data as well as the usually adopted sectorial identifications. The predicted photometric amplitudes are in good accord with upper limits derived from photometric observations. We conclude that ζ Oph is a star in the β Cep instability strip in which two modes of high degree (probably ℓ=4 and ℓ=8) are excited. We present an interpretation of these findings in which the cause of the low-order line profile and light variations in periodic Be stars is corotating photospheric clouds, while the travelling subfeatures are incidental to the Be phenomenon and are a result of non-radial pulsation.     

The pulsating hydrogen-deficient star LSS 3184 (BX Cir)

We present extensive photometry and spectroscopy of the extremely hydrogen-deficient star, LSS 3184, recently discovered to be a rapid variable (period ∼0.1066 d) strikingly similar to V652 Her. Over 95 h of photometry confirms the reported variability, which is of rather low amplitude (Δ V ∼0.03 mag), defines the light curve with greater precision and establishes a much more accurate ephemeris (period ∼0.106 578 4 d) to form a basis for detecting period change. Attention is drawn to the usefulness of a period-finding technique that fits harmonic components to the photometric observations. Spectroscopy shows a peak-to-peak variation in radial velocity of about 30 km s⁻¹, which, when combined with the photometric observations, confirms the pulsational nature of the variability and strongly indicates that the pulsations are radial in nature.     

Short-period line profile and light variations in the Be star λ Eridani

We present three seasons of photometric observations and one season of intensive high-dispersion spectroscopic observations of the Be star λ Eridani. We show that only one period,   P =0.70173 d  , is present in the photometry, although there are large light amplitude variations from season to season. We confirm a suspicion that light outbursts repeat at intervals of about 475 d. A total of 348 echelle spectra of the star were obtained over a 2-week observing run. We show that the periodic variations are present in the emission wings of the helium lines, in the emission wings of the H α line and in the absorption cores of H β and H γ . Together with the fact that the periodic variations appear outside the projected rotational velocity limit, this indicates that they are associated with circumstellar material immediately above the photosphere and supports the idea of corotating gas clouds. We present evidence in support of a true rotational period of  2 P =1.40346 d  and suggest that the mass loss in Be stars is caused by centrifugal magnetic acceleration.     

INTEGRAL and XMM–Newton observations of the X-ray pulsar IGR J16320−4751/AX J1631.9−4752

We report on observations of the X-ray pulsar IGR J16320−4751 (also known as AX J1631.9−4752) performed simultaneously with International Gamma-Ray Astrophysics Laboratory ( INTEGRAL ) and XMM–Newton . We refine the source position and identify the most likely infrared counterpart. Our simultaneous coverage allows us to confirm the presence of X-ray pulsations at ∼1300 s, that we detect above 20 keV with INTEGRAL for the first time. The pulse fraction is consistent with being constant with energy, which is compatible with a model of polar accretion by a pulsar. We study the spectral properties of IGR J16320−4751 during two major periods occurring during the simultaneous coverage with both satellites, namely a flare and a non-flare period. We detect the presence of a narrow 6.4 keV iron line in both periods. The presence of such a feature is typical of supergiant wind accretors such as Vela X-1 or GX 301−2. We inspect the spectral variations with respect to the pulse phase during the non-flare period, and show that the pulse is solely due to variations of the X-ray flux emitted by the source and not due to variations of the spectral parameters. Our results are therefore compatible with the source being a pulsar in a High Mass X-ray Binary. We detect a soft excess appearing in the spectra as a blackbody with a temperature of ∼0.07 keV. We discuss the origin of the X-ray emission in IGR J16320−4751: while the hard X-rays are likely the result of Compton emission produced in the close vicinity of the pulsar, based on energy argument we suggest that the soft excess is likely the emission by a collisionally energized cloud in which the compact object is embedded.     

Resolving the pulsations of subdwarf B stars: PG 0154+182, HS 1824+5745 and HS 2151+0857

We continue our programme of extended single-site observations of pulsating subdwarf B (sdB) stars and present the results of extensive time-series photometry to resolve the pulsation spectra for use in asteroseismological analyses. PG 0154+182, HS 1824+5745 and HS2151+0857 were observed at the MDM Observatory during 2004 and 2005. Our observations are sufficient to resolve the pulsations of all three target stars. We extend the number of known frequencies for PG 0154+182 from one to six, confirm that HS 1824+5745 is a monoperiodic pulsator and extend the number of known frequencies to five for HS 2151+0857. We perform standard tests to search for multiplet structure, measure amplitude variations as pertains to stochastic excitation and examine the mode density to constrain the mode degree ℓ.     

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.     

The complete set of ASCA X-ray observations of non-magnetic cataclysmic variables

We present the complete set of 34 ASCA observations of non-magnetic cataclysmic variables. Timing analysis reveals large X-ray flux variations in dwarf novae in outburst (Z Cam, SS Cyg and SU UMa) and orbital modulation in high inclination systems (including OY Car, HT Cas, U Gem, T Leo). We also found episodes of unusually low accretion rate during quiescence (VW Hyi and SS Cyg). Spectral analysis reveals broad temperature distributions in individual systems, with emission weighted to lower temperatures in dwarf novae in outburst. Absorption in excess of interstellar values is required in dwarf novae in outburst, but not in quiescence. We also find evidence for subsolar abundances and X-ray reflection in the brightest systems.
LS Peg, V426 Oph and EI UMa have X-ray spectra that are distinct from the rest of the sample and all three exhibit candidate X-ray periodicities. We argue that they should be reclassified as intermediate polars.
In the case of V345 Pav we found that the X-ray source had been previously misidentified.     

Ultraviolet variability of HD 62001 – The central star of the missing nebula V-V 1-7

IUE observations of HD 62001 do not confirm the ultraviolet variability of 0.15 mag seen from the ANS observations. These intriguing variations in ANS observations seem to be caused by a nearby (∼ 70 arcsec away) B star getting in and out of the field of view of the telescope, which had a jitter of 20 arcsec. There seems to be no evidence for the presence of a hot companion, either from the energy distribution or from UV variability. However, visual light variations are present. This, coupled with the radial velocity variations, indicates a binary nature probably of Algol type. Based on observations obtained with IUE satellite at the Villafranca Satellite Tracking Station of the European Space Agency.     

The unique frequency spectrum of the Blazhko RRc Star LS Her

The Blazhko effect in RR Lyrae stars is still poorly understood theoretically. Stars with multiple Blazhko periods or in which the Blazhko effect itself varies are particularly challenging. This study investigates the Blazhko effect in the RRc star LS Her. Detailed CCD photometry in the   V , R _C  and I _C band has been performed on 63 nights during six months. LS Her is confirmed to have a Blazhko period of  12.75 ± 0.02  d. However, where normally the side frequencies of the Blazhko triplet are expected, an equidistant group of three frequencies is found on both sides of the main pulsation frequency. As a consequence, the period and amplitude of the Blazhko effect itself vary in a cycle of  109 ± 4  d. LS Her is a unique object turning out to be very important in the verification of the theories for the Blazhko effect.     

Photometric and spectrophotometric observations of the classical symbiotic star YY Her during its return to quiescence

We present new photometric UBVRI and spectroscopic observations of the symbiotic star YY Her during its return to quiescence after a strong outburst in 1993. High-resolution spectra of YY Her at similar phases at outburst maximum ?=0.48) and in quiescence ?=0.37) are presented for the first time. The ephemeris of YY Her has been refined P=586^d). The last two observed minima (in 1999 and 2000) differed radically in shape from the 1997 minimum described previously. Both were sharp and deep $(\Delta U \sim 1\mathop .\limits^m 6, \Delta V \sim 0\mathop .\limits^m 9)$ . To explain this shape of the V light curve, which is only slightly affected by nebular emission, it should be assumed that the cool component of YY Her fills much of its Roche lobe and has a hot spot on the hemisphere facing the hot component. The emission spectrum rich in Fe II lines, which is characteristic of symbiotic stars, was observed during the outburst, but high-ionization lines (He II λ4686) were also observed. The He I λλ5876, 7065 lines exhibit distinct P Cyg profiles; the centers of the absorption components are shifted from the emission ones by V _r≈100 km s^?1, suggesting moderate outflow velocities.     

A photometric study of the southern Blazhko star SS For: unambiguous detection of quintuplet components

We present our analysis of photometric data in the Johnson B and V filter of the southern Blazhko star SS For. In parallel, we analysed the V observations obtained with the All Sky Automated Survey-3 photometry of the star gathered between 2000 and 2008. In the frequency spectra resulting from a Fourier analysis of our data, the triplet structure is detectable up to high order, both in the B and V data. Moreover, we find evidence for quintuplet components. We confirm from our data that the modulation components decrease less steeply than the harmonics of the main frequency. We derived the variations of the Fourier parameters quantifying the light-curve shape over the Blazhko cycle. There is good agreement between the spectroscopic abundance and the metallicity determined from the Fourier parameters of the average light curve. SS For is peculiar as a Blazhko star because of its strong variations around minimum light.     

恒星射电耀发6cm波段偏振观测试验

利用新疆天文台南山基地25m射电望远镜在6cm波段对恒星V772 Her和βPer进行了偏振观测试验.通过数据处理和校准得到恒星的射电光变曲线.探测到V772 Her的射电耀发现象,耀发时的线偏振度约达30%,偏振位置角约4°;探测到βPer的缓变成份及叠加其上的快速耀发,βPer耀发时线偏振很弱.     

Fibonacci Sequences and the Multiperiodicity of the Variable Star UW Herculis

We present an application of the methods recently developed for the study of quasicrystal structures to the analysis of multiperiodicity of semiregular variables. A light curve analysis of UW Her shows frequencies that can be included within the general scheme characterizing the Fourier spectra of Fibonacci quasiperiodic sequences. The analysed data come from the BAA Variable Star Section computerised archive.