XY UMa Research Articles

An X-Ray Study of Coronally Connected Active Eclipsing Binaries

We present a detailed X-ray analysis and imaging of stellar coronae of five coronally connected eclipsing binaries, namely, 44 Boo, DV Psc, ER Vul, XY UMa, and TX Cnc. Both components of these binaries are found to be active. The X-ray light curves of detached and semidetached type systems show eclipsed-like features, whereas no evidence for coronal eclipsing is shown by the contact type systems. The X-ray light curve of DV Psc shows the O’Connell-like effect where the first maximum is found to be brighter than that of the second. Results of the coronal imaging using three-dimensional deconvolution of X-ray light curves show the coronae of all these binaries are either in the contact or over-contact configuration, with the primary being 1.7–4 times X-ray brighter than its companion. In the current sample, a minimum of 30%–50% of total UV emission is found to originate from the photosphere and positively correlated with the X-ray emission. X-ray spectra of these systems are well explained by two-temperature plasma models. The temperature corresponding to cool and hot components of plasma are found to be in the ranges of 0.25–0.64 and 0.9–1.1 keV, respectively. For the majority of binaries in the sample, the phase-resolved X-ray spectral analysis shows the orbital modulation in X-ray luminosity and emission measure corresponding to the hot component. A total of seven flaring events are also detected in the four systems with the flare energy in the range of (1.95–27.0) × 1033 erg and loop length of the order of 109–11 cm.

Three X-ray flares near primary eclipse of the RS CVn binary XY UMa

We report on an archival X-ray observation of the eclipsing RS CVn binary XY UMa (Porb ≈ 0.48 d). In two Chandra ACIS observations spanning 200 ks and almost five orbital periods, three flares occurred. We find no evidence for eclipses in the X-ray flux. The flares took place around times of primary eclipse, with one flare occurring shortly (< 0.125 Porb) after a primary eclipse, and the other two happening shortly (< 0.05 Porb) before a primary eclipse. Two flares occurred within roughly one orbital period (Δα ≈ 1.024 Porb) of each other. We analyze the light curve and spectra of the system, and investigate coronal length scales during both quiescence and flares, as well as the timing of the flares. We explore the possibility that the flares are orbit-induced by introducing a small orbital eccentricity, which is quite challenging for this close binary.

PERIOD VARIATION AND ASYMMETRY LIGHT CURVES OF XY URSAE MAJORIS

New CCD photometric observations of the chromospherically active binary XY Ursae Majoris (XY UMa) were obtained every year since 2006. The light curves obtained in the late Spring of 2006 show obvious variations on a short timescale, while the light curves obtained in 2008 December do not. But both sets of light curves are markedly asymmetric, and were analyzed using the 2003 version of the Wilson–Devinney code with spot model. New absolute physical parameters are obtained. It is found that the total spotted area on the more massive component covers 7% of the photospheric surface in 2008 December. Fitting all available light minimum times including the newly obtained ones with a sinusoidal ephemeris and a four-part linear ephemeris reveals that the orbital period undergoes quasi-periodic oscillation rather than sinusoidal variations. Between the two mechanisms of magnetic activity and a third body around the eclipsing pair, the former one is more plausible.

Radial Velocity Studies of Close Binary Stars. XII.

Radial velocity measurements and sine-curve fits to the orbital radial velocity variations are presented for 10 close binary systems: OO Aql, CC Com, V345 Gem, XY Leo, AM Leo, V1010 Oph, V2612 Oph, XX Sex, W UMa, and XY UMa. Most of these binaries have been observed spectroscopically before, but our data are of higher quality and consistency than in the previous studies. While most of the studied eclipsing pairs are contact binaries, V1010 Oph is probably a detached or semidetached double-lined binary, and XY UMa is a detached, chromospherically active system whose broadening functions clearly show well-defined and localized dark spots on the primary component. A particularly interesting case is XY Leo, which is a member of visually unresolved quadruple system composed of a contact binary and a detached, noneclipsing, active binary with an 0.805 day orbital period. V345 Gem and AM Leo are known members of visual binaries. We found faint visual companions at about 2''-3'' from XX Sex and XY UMa.

Short-period Active Binaries – Retrospect and Prospects

The most important characteristics and multi-frequency behaviour of the active RS CVn binaries are reviewed. New long-term photometric and spectroscopic observations of several short-period active RS CVn binaries are presented. The results for RT And, XY UMa and preliminary analysis of SV Cam and ER Vul are given. New prospects for research in the field are outlined.

Period Changes in Four Short-Period Spotted Binaries: UV Piscium, YY Geminorum, CG Cygni, and XY Ursae Majoris

Recently acquired times of minimum for three RS CVn systems and one BY Draconis binary, all with periods under a day, are presented. Times of minimum for UV Psc, YY Gem, CG Cyg, and XY UMa have been measured for decades. These observations have been collected, and the O-C curves for each system have been examined for period changes. The O-C curves for UV Psc and YY Gem showed a linear deviation, and improved periods have been computed. CG Cyg and XY UMa, though, appear to have experienced true changes in their periods. An additional 11.0 yr periodic variation has been found in the O-C data of XY UMa. The mechanism for the period variations remains uncertain.

Starspot distributions on XY UMa during 1997-2000 from eclipse mapping

We present narrow-band red light curves and surface maps of the short-period RS CVn binary system XY UMa, obtained between 1997 January and 2000 March. The light-curve morphology of this system is known to vary on time-scales of a few days. We have used eclipse-mapping techniques to map the distribution of cool starspots on the surface of the primary star. The resulting maps show the continued evolution of spot features on time-scales of a few days to a week. By comparison with the images of Collier Cameron & Hilditch, we also find evidence for longer term trends, including a decline to an activity minimum during 1997 and a rise in activity during 1998–2000. We also find marginal evidence from the O–C ephemeris curves for a periodicity and a peak corresponding to the time of activity minimum.

Starspot distributions on XY UMa during 1997-2000 from eclipse mapping

We present narrow-band red light curves and surface maps of the short-period RS CVn binary system XY UMa, obtained between 1997 January and 2000 March. The light-curve morphology of this system is known to vary on time-scales of a few days. We have used eclipse-mapping techniques to map the distribution of cool starspots on the surface of the primary star. The resulting maps show the continued evolution of spot features on time-scales of a few days to a week. By comparison with the images of Collier Cameron & Hilditch, we also find evidence for longer term trends, including a decline to an activity minimum during 1997 and a rise in activity during 1998–2000. We also find marginal evidence from the O–C ephemeris curves for a periodicity and a peak corresponding to the time of activity minimum.

An active binary XY UMa revisited

New extensive multicolour photoelectric photometry, performed since 1994, is presented. 17 more- or-less complete light curves were obtained and analyzed. The Wilson-Devinney code applied to the BVRI light curves without the maculation eect together with published spectroscopic mass ratio and semi-major axis yielded new absolute parameters of the eclipsing pair: m1 =1 :10 M, m2 =0 :66 M, R1 =1 :16 R, R2 =0 :63 R, a =3 :107 R and the orbital inclination i =8 0:9. The observed orbital period changes are conclusively explained by the mutual action of the third body in the system (P3 = 30 years) and the maculation eects. Simultaneous analysis of the period changes and the visual brightness excludes the possibility of their explanation by Applegate's mechanism. The dierences in the maxima heights caused by the maculation exhibit variations with the period of 70910 days. The distance to the system d =8 65 pc determined from the absolute dimensions and luminosities of the components is larger than the Hipparcos astrometric value d =6 6 6p c.

Time-resolved Spectroscopy of RS Canum Venaticorum Short-Period Systems. II. RT Andromedae, WY Cancri, and XY Ursae Majoris

We present the second part of the results of our spectroscopic study of orbital phase resolution of short-period active binaries. In this paper we present the observations of the binaries RT And, WY Cnc, and XY UMa, for which we obtained simultaneous low-resolution spectra in the Hα, Hβ, and Ca II infrared triplet (IRT; 8498 and 8542 A) lines, and higher resolution spectra in Hα for WY Cnc and XY UMa. Hα and Hβ emission excess was found in all the observed orbital phases of WY Cnc and XY UMa, while RT And showed Hα emission only during some orbital phases. We measure a clear Ca II (IRT) excess in all the spectra of the three binaries. The ratio of the flux excesses derived for these binaries, EHα/EHβ 1–3 and E8542/E8498 1–3, give low values typical of solar plage structures. In the higher resolution Hα spectra, we found emissions that can be associated with both stellar components of XY UMa and WY Cnc, indicating that the faint secondary stars in both binaries are active late-type dwarfs. Some Hα emission components, which could originate in extended structures between the stars, were detected in both systems.

A ROSAT observation of the eclipsing binary system XY UMa

A ROSAT observation of the eclipsing binary system XY UMa

The orbital period study and photometric analysis of XY Ursae Majoris

Photoelectric observations of the eclipsing binary XY UMa have been carried out in B and V colours at the Ege University Observatory. Combining these newly obtained data with the previous ones available in the literature, the problem pertaining to the orbital period of the system has been investigated through a detailed description of the diagram. The sinusoidal and secular changes have been found. Such variations of the orbital period have been examined in terms of three plausible mechanisms, namely (i) a light-time effect due to a third body, (ii) the orbital period modulation due to magnetic activity cycle of a component star, and (iii) a mass loss case in which the ejected material escapes out from the binary system. A combination of a magnetic activity cycle mechanism and a mass loss case is found to reproduce satisfactorily the period changes. Further, the observed photoelectric light curves of the system have been analyzed with the Wilson-Devinney approach. This analysis shows that the asymmetries of the light curves of XY UMa can be interpreted in terms of cool star-spot covering 7% of the stellar photosphere of the primary component of this binary. The system is found to be a Lyrae type detached binary. The absolute elements of the system are also deduced.

Spectroscopy and eclipse-mapping of the mass-exchanging binary star V361 Lyr

We present the first spectroscopic investigation of the short-period (P = 0.309614 d) mass-exchanging binary system V361 Lyr. From observations over two complete orbits, we show that the system is double-lined, with the stars having minimum masses of m1 sin3i = 1.25 ± 0.03 M⊙ and m2 sin3i = 0.87 ± 0.03 M⊙. The mass ratio m2/m1 = 0.69 ± 0.02 and the projected semimajor axis of the relative orbit is a sin i = 2.47 ± 0.05 R⊙. The spectral type of the primary component is estimated to be F8-G0. The H± line profile clearly shows two absorption components when the system is at its brightest and bluest stage, around orbital phases 0.35–0.45. The published V and I light curves are analysed with light2 to show that the primary component (T = 6200 K) fills its Roche lobe, whilst the secondary (T = 4500 K) is detached and fills ≈ 57 per cent of the available Roche volume. Eclipse maps of both stellar surfaces are derived via dots from light curves obtained in 1988, 1989 and 1992. These show that the secondary has a persistent elongated hot structure on its equator with an estimated temperature of 10000 K that is consistent with the expectations of a theoretical mass transfer stream leaving the primary at its inner Lagrangian point and falling on to the secondary. The accretion luminosity of ≈ 0.5 L⊙ from that impacting stream, as estimated from the observed decrease in orbital period and the derived stellar masses, is about twice the luminosity of the structure inferred from the light curves and the surface-image reconstructions. The eclipse maps for the primary illustrate small changes in the cool spot structures that are typical of magnetic activity observed in other rapidly-rotating solar-type stars that are single or are members of binary systems (e.g. AB Dor, XY UMa). This model for V361 Lyr predicts successfully the phase-dependent variations observed in the Hα line. The properties of this mass-exchanging semidetached binary are compared with the near-contact and the contact systems of the W UMa type for the purpose of establishing whether or not it represents the short-lived phase of evolution into contact for the first time, or the broken-contact stage of a thermal-relaxation oscillation. The derived locations of both components on the zero-age main sequence would favour the former interpretation. V361 Lyr is reddened by E(B − V) = 0.43 and lies at a distance of 520 α 40 pc.

Eclipse mapping of starspots on XY UMa in 1992 and 1995

We present and analyse V-band light curves of the detached eclipsing binary system XY UMa, obtained in 1992 October, 1995 March and November, and 1996 February. The light-curve morphology of this system is known to vary on time-scales of a few days. We have used eclipse mapping techniques to search for evidence that cool starspots are the agents responsible for the variability of the light curve. We derive a new set of geometric system parameters, which we find to be very similar to those derived by Hilditch & Bell. The image derived from the 1992 light curve shows an amorphous band of unresolved spots with a low filling factor, extending over much of the inward-facing hemisphere of the primary. This result is consistent with the extent of the dark-zone model proposed by Hilditch & Bell in their earlier analysis of this same light curve. Irregularities in the primary eclipse profile observed in 1995 and early 1996 are consistent with the eclipse of a dark spot or spots on the inner face of the primary. The major spot in this region appears to be resolved on our 9° surface grid, indicating that the spot consists of an unbroken umbral region some 15° in radius.

Are there prominences around binary systems?

I examine the possibility that large, cool prominences can be formed in close binary systems, when coronal structures grow beyond the point where centrifugal force balances gravitational attraction. X-ray light curves of the eclipsing binary XY UMa indicate that an extended corona is probably present and this is likely to reach heights &gt; 1.5 R⊙, where centrifugal compression may render plasma in the coronal loop apexes unstable to thermal perturbations. Cool condensations could form, explaining features such as the dips in the X-ray light curves of V471 Tau, and the circumstellar material deduced to be present in several close binary systems.

Photometric evidence for widespread spot activity on the primary component of the short-period RS CVn binary XY UMa

Photometric evidence for widespread spot activity on the primary component of the short-period RS CVn binary XY UMa

High-precision photometry of the RS CVn binary system XY UMa and a dark-zone photometric model

CCD V-band photometry is presented of the short-period RS CVn-type binary system XY UMa, providing a complete light curve defined by 1189 observations with a precision of 0.004 mag. The data were all obtained during 1992 October contemporaneously with ROSAT pointed-phase observations, and demonstrate that the primary star showed substantial star-spot activity at that time, predominantly on the hemisphere of the primary component that faces the cooler companion. Combining these accurate data with previously published spectroscopy, we obtain a good geometric description of the system, and are able to represent the distribution of surface brightness over the primary star by a dark-zone model centred on the equator, ±15° in latitude, and encircling the star

Time-Resolved Spectroscopy of Short Period RS CVn Systems

AbstractWe have initiated a programme of spectroscopic observations of RS CVn short-period group, with orbital phase resolution. The systems of this group are all eclipsing binaries with both components at the Main Sequence, and most of them have similar spectral type components. The high rotational velocities and their short orbital periods (less than 1 day) hinder the spectroscopic study of these stars. We presents the first results yielded by Hα line observations of the systems XY UMa and WY Cnc. Both systems were observed during 1991 with reasonably wide orbital phase coverage. The analysis of the spectra is made by comparison with a binary model, constructed from the observed spectra of normal stars of the same spectral type as the RS CVn system components. The model accounts for the partial contribution of each component at any orbital phase within eclipses.

Spectroscopic observations of the RS CVn-type binary systems SV Cam and XY UMa⋆

Radial velocities of the primary components of the two RS CVn-type binary systems SV Cam and XY UMa are presented. Neither secondary component could be detected. A change of 5.0 ± 1.3 km/s in the systemic velocity of SV Cam is found over 40 years which lends some support to the current model of SV Cam being a triple system.

Starspot Activity on Short-period RS CVn Stars

We have yet to understand the magnetic activity cycles of cool close binary systems of sunlike stars. Mutual tidal interactions, as well as magnetic ones, may result from a regime of dynamo models not yet tested, because these have been developed for single stars. To arrive at the basic physics, though, requires that we first examine the phenomenology of magnetic activity for binary systems. In particular, we would like to discover if such activity has a clearly-defined cycle, such as the sun exibits.Among the proxy indicators of magnetic activity are the Ca II H and K lines. Strassmeier et al. (1988) used the strength of these lines as the primary criterion for the inclusion of systems in The Catalog of Chromospherically Binary Stars. Of the RS CVn stars in the catalog, 12 have orbital periods of one day or shorter; 9 are eclipsing systems. As part of a decade-long program, we have focussed our observations and models on eight of the short-period group (Hall, 1976): XY UMa, UV Psc, SV Cam, RT And, CG Cyg, ER Vul, BH Vir, and WY Cnc. These close systems are tidally-locked in synchronous rotation and tidally-distorted into Roche lobe configurations.