Photometric and spectroscopic observations of three rapidly rotating late‐type stars: EY Dra,V374 Peg,and GSC 02038‐00293

Here, BV (RI)_C broad band photometry and intermediate resolution spectroscopy in H_α region are presented for two rapidly rotating late‐type stars: EY Dra and V374 Peg. For a third rapid rotator, GSC 02038‐00293, intermediate resolution H_α spectroscopy and low resolution spectroscopy are used for spectral classification and stellar parameter investigation of this poorly known object. The low resolution spectrum of GSC 02038‐00293 clearly indicates that it is a K‐type star. Its intermediate resolution spectrum can be best fitted with a model with T_eff = 4750 K and v sin i = 90 km s^–1, indicating a very rapidly rotating mid‐K star. The H_α line strength is variable, indicating changing chromospheric emission on GSC 02038‐00293. In the case of EY Dra and V374 Peg, the stellar activity in the photosphere is investigated from the photometric observations, and in the chromosphere from the H_α line. The enhanced chromospheric emission in EY Dra correlates well with the location of the photospheric active regions, indicating that these features are spatially collocated. Hints of this behaviour are also seen in V374 Peg, but it cannot be confirmed from the current data. The photospheric activity patterns in EY Dra are stable during one observing run lasting several nights, whereas in V374 Peg large night‐tonight variations are seen. Two large flares, one in the H_α observations and one from the broadband photometry, and twelve smaller ones were detected in V374 Peg during the observations spanning nine nights. The energy of the photometrically detected largest flare is estimated to be 4.25 × 10³¹– 4.3 × 10³² erg, depending on the waveband. Comparing the activity patterns in these two stars, which are just below and above the mass limit of full convection, is crucial for understanding dynamo operation in stars with different internal structures (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A Photometric Study of EB-type eclipsing binary GO CYG

Two colour (B and V) photoelectric observations of EB-type eclipsing binary GO Cyg were carried out for 15 nights during October and December 1996. Three new times of minimum lights have been derived. With these and previously published times of minimum lights, a continuous period increase of dP/dt = 1.51 × 10^-7 d yr^-1 was estimated from the quadratic light element. B and V light curves have been analyzed by the method of the Wilson and Devinney Differential Correction. GO Cyg is confirmed to belong to the group of near contact systems based on light curve analysis and its absolute dimensions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Orbital Period Changes of Two Very Short-Period W UMa Stars CC Com and V523 Cas: A Possible Evidence for TRO Plus AML Model

Orbital period changes of the two very short-period contactbinaries, CC Com and V523 Cas, are presented. It is shownthat the period of CC Com varies in secular decrease withrate of dP/dt = –4.39 ×10^-8 days/year, while theperiod of V523 Cas is increasing at rate of dP/dt =+9.09 ×10^-8 days/year. The physical parameters of the twoW UMa stars are nearly equal which indicates that the physicalproperties of the two contact binaries are almost the same.The different types of period changes in the two systemsmay strongly suggest that, although they are undergoingsecular angular momentum loss (AML), the oscillatory characterpredicted by thermal relaxation oscilation (TRO) theory stillexist and they are on the different TRO stages, i.e., CC Comis on the shrinking TRO stage, but V523 Cas is on the expendingTRO stage. The present period changes of the two systems can beexplained by the combination of the TRO and the AML theories.     

Photometric and polarimetric studies of three W UMa-type binaries: FZ Ori,V407 Peg and LP UMa

We present analyses of new optical photometric observations of three W UMa-type contact binaries FZ Ori, V407 Peg and LP UMa. Results from the first polarimetric observations of the FZ Ori and V407 Peg are also presented. The periods of FZ Ori, V407 Peg and LP UMa are derived to be 0.399986, 0.636884 and 0.309898 d, respectively. The O?C analyses indicate that the orbital periods of FZ Ori and LP UMa have increased with the rate of 2.28×10^?8 and 1.25×10^?6 d?yr^?1, respectively and which is explained by transfer of mass between the components. In addition to the secularly increasing rate of orbital period, it was found that the period of FZ Ori has varied in sinusoidal way with oscillation period of ～30.1 yr. The period of oscillations are most likely to be explained by the light-time effect due to the presence of a tertiary companion. Small asymmetries have been seen around the primary and secondary maxima of light curves of all three systems, which is probably due to the presence of cool/hot spots on the components. The light curves of all three systems are analysed by using Wilson-Devinney code (WD) and the fundamental parameters of these systems have been derived. The present analyses show that FZ Ori is a W-subtype, and V407 Peg and LP UMa are A-subtype of the W UMa-type contact binary systems. The polarimetric observations in B, V, R and I bands, yield average values of polarization to be 0.26±0.03, 0.22±0.02, 0.22±0.03 and 0.22±0.05 per cent for FZ Ori and 0.21±0.02, 0.29±0.03, 0.31±0.01 and 0.31±0.04 per cent for V407 Peg, respectively.     

Diagnostics of a flare on EQ Peg B from optical pulsations

Based on the methods of coronal seismology, we have investigated the ten-second quasi-periodic pulsations of the optical flare emission from the active red dwarf EQ Peg B detected with the William Herschel Telescope on La Palma. We propose and analyze a model in which they could be produced by sausage oscillations of a coronal flare loop. The amplitude and phase relations between the displacement components of the radial oscillations and the conditions for their excitation in loops with footpoints frozen into the photosphere are considered. The temperature (≈6 × 10⁷ K), plasma density (≈2.7 × 10¹¹ cm⁻³), and magnetic field strength (≈540 G) in the region of energy release have been determined. Our estimate of the flare loop length (≈0.4R _⋆) provides evidence for the existence of extended coronae on red dwarf stars.     

Four years of photometry of DK draconis=HR 4665

Differential BV photometry of the K0III+K0III long-period RS CVn-type binary DK Dra=HR 4665 in 1977, 1978, 1979, and 1980 at eight different observatories is presented. A least squares fit to times of maximum and minimum light yields the ephemeris JD=2 443 219.5+63 _. ^d 75E for times of minimum. This photometric period is 1% shorter than the spectroscopically determined orbital period 64 _. ^d 44. The light curve was symmetrical and roughly sinusoidal in 1979 and 1980 but was asymmetrical in 1977 and 1978, with a faster rise to maximum. During these four years DK Dra varied between V=6 _. ^m 07 and 6 _. ^m 35.Of the AAVSO.Amateur Astronomers, Inc.     

Period Change of CU Pegasi

On the basis of the published times of minima and our own observations, we analysed the period change of the Algol-type eclipsing binary CU Pegasi. Over almost seventy years of observations, the parabolic period change has been clearly seen as dP/dt = 1.38 × 10⁻⁶ d/year. The estimated mass transfer in the system is about 1 × 10⁻⁷ M_M⊙/year.     

Isotopic abundances of silicon in four red giants

High-resolution spectra near 4 m of the four red giants— Peg,o ¹ Ori, 10 Dra, and HR 1105—have been analysed to obtain estimates of the²⁸Si/²⁹Si and²⁸Si/³⁰Si abundance ratios. For Peg and the S star HR 1105, the²⁸Si/²⁹Si ratio is close to the solar ratio (²⁸Si/²⁹Si=20).²⁹Si appears to be underabundant in the MS staro ¹ Ori (²⁸Si/²⁹Si=40) and the M star 10 Dra (²⁸Si/²⁹Si53). The³⁰Si isotope appears to be underabundant by, perhaps, about a factor of 2 in all four stars.     

Long‐term photometry of the ultra‐fast rotator LO Peg

LO Peg is a young main‐sequence star of spectral type K3. With its equatorial rotation velocity of 65 km s^–1 it is amongst the ultra‐fast rotators. Its high equatorial rotation velocity and rapidly changing surface activity features make it an important object in terms of both stellar activity and the evolution of stellar rotation and angular momentum. Since its discovery as a variable star, it has mostly been subject to spectral surface mapping studies such as Doppler Imaging, while there have been very few photometric studies on it. This paper aims to present the first long‐term photometric observations and its results covering the years between 2003 and 2009. The UBVR Johnson wide band photometric data showed that the surface activity structures of LO Peg vary in timescales changing between days and months, and parallel to this, the mean, maximum and minimum brightness and amplitudes change dramatically between years and sometimes even within the same observation season. Long‐term changes in system brightness and colours, both characteristic features of active stars, were also seen in this ultra‐fast young star. The active longitudes, which has a life time of ∼1.3 years and an activity cycle period of ∼4.8 years for LO Peg were estimated (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Classical and relativistic node precessional effects in WASP-33b and perspectives for detecting them

WASP-33 is a fast rotating, main sequence star which hosts a hot Jupiter moving along a retrograde and almost polar orbit with semi-major axis a=0.02 au and eccentricity provisionally set to e=0. The quadrupole mass moment J₂^*J_{2}^{\star} and the proper angular momentum S _⋆ of the star are 1900 and 400 times, respectively, larger than those of the Sun. Thus, huge classical and general relativistic non-Keplerian orbital effects should take place in such a system. In particular, the large inclination Ψ_⋆ of the orbit of WASP-33b to the star’s equator allows to consider the node precession [(W)\dot]\dot{\Omega} and the related time variation dt _d /dt of the transit duration t _d . The WASP-33b node rate due to J₂^*J_{2}^{\star} is 9×10⁹ times larger than the same effect for Mercury induced by the Sun’s oblateness, while the general relativistic gravitomagnetic node precession is 3×10⁵ times larger than the Lense-Thirring effect for Mercury due to the Sun’s rotation. We also consider the effect of the centrifugal oblateness of the planet itself and of a putative distant third body X. The magnitudes of the induced time change in the transit duration are of the order of 3×10⁻⁶,2×10⁻⁷,8×10⁻⁹ for J₂^*J_{2}^{\star}, the planet’s rotational oblateness and general relativity, respectively. A yet undiscovered planet X with the mass of Jupiter orbiting at more than 1 au would induce a transit duration variation of less than 4×10⁻⁹. A conservative evaluation of the accuracy in measuring dt _d /dt over 10 yr points towards ≈10⁻⁸. The analysis presented here will be applicable also to other exoplanets with similar features if and when they will ne discovered.     

Search for evolutionary changes in Cepheid periods using the Harvard plate collection: ASAS 101538-5933.1

In the plate collection of the Harvard College Observatory, we have obtained 528 photographic magnitude estimates for the recently discovered long-period classical Cepheid ASAS 101538-5933.1 (P = 51.4 days). Together with the published photoelectric and CCD observations, our data have allowed us to construct an O-C diagram spanning a time interval of 120 years. The O-C diagram has the shape of a parabola, which has made it possible to determine for the first time the quadratic light elements and to calculate the rate of evolutionary increase in the period, dP/dt = 51.8 (±4.8) s yr⁻¹ or $ \dot P $ \dot P /P = 7.3 (±0.7) s, in agreement with the results of theoretical calculations for the third crossing of the instability strip. The available data reduced by the method of Eddington and Plakidis reveal small random period fluctuations that do not distort the evolutionary trend in the O-C residuals.     

AV Hydrae: A Near-Contact Semi-Detached Binary with Possible Massand Angular Momentum Loss

The photoelectric observations of the neglected binary AV Hya published by Srivastava and Kandpal (1980) have been re-analyzed using Wilson-Devinney's synthetic light-curve program. The binary turns out to be a near-contact semi-detached system. The primary, more massive, more luminous and greater component, eclipsed at primary minimum, is detached from its Roche lobe (85%). The secondary fills its Roche lobe and has a temperature difference of T=,-3414 K. As with other semi-detached binaries, the secondary is more evolved than that of the primary. Thetimes of light minima of the eclipsing have been analyzed,showing that the orbital period of AV Hya undergoes acontinuous decrease with a rate of dP/dE=-8.26×10^-8 day/year. The mass transfer between the twocomponents can not explain the present orbital period variationsince the secondary component is filling the Roche lobe. Theorbital period change demonstrates that the system may undergoa secular mass and angular momentum loss and the system mayevolve from the present short-period near-contact system intoan A-type contact binary.     

Search for evolutionary changes in the periods of Cepheids: U Sgr

For the classical Cepheid U Sgr, we have constructed an O - C diagram spanning a time interval of 144 years. The O - C diagram has the shape of a parabola, which has made it possible to determine for the first time the quadratic light elements and to calculate the rate of evolutionary increase in the period, dP/dt = 0.39 (±0.10) s yr^?1, in agreement with the results of theoretical calculations for the third crossing of the instability strip. The available data reduced by the Eddington-Plakidis method reveal small random period fluctuations that do not distort the evolutionary trend in the O - C residuals.     

Absolute dimensions of the close binary systems V453 Monocerotis and V523 Cassiopeiae

We present multi-colour CCD observations of the low-temperature contact binaries, V453 Mon and V523 Cas. Their light curves are modelled to determine a new set of stellar and orbital parameters. Analysis of mid-eclipse times yields a new linear ephemeris for both systems. A period decrease (dP/dt=2.3×10⁻⁷ days/yr) in V453 Mon is discovered. V523 Cas, however, is detected to show a period increase (dP/dt=9.8×10⁻⁸ days/yr) because of the mass transfer of a rate of 1.1×10⁻⁷ M_⊙ yr⁻¹, from a less massive donor. Using these findings we can determine the physical parameters of the components of V523 Cas to be M ₁=0.76 (3)M _⊙, M ₂=0.39 (2)M _⊙, R ₁=0.74 (2)R _⊙, R ₂=0.55 (2)R _⊙, L ₁=0.19 (3)L _⊙, L ₂=0.14 (3)L _⊙, and the distance of system as 46(9) pc.     

On the period variations of several low declination high amplitude delta Scuti variables

A 16-inch Schmidt-Cassegrain telescope on the campus of Naresuan University of Thailand and several similar-size telescopes in China equipped with CCD cameras were used to observe 14 high amplitude delta Scuti stars: GP And, CY Aqr, BS Aqr, YZ Boo, AD CMi, VZ Cnc, EH Lib, DY Her, V927 Her, KZ Hya, BE Lyn, V1162 Ori, DY Peg, and CW Ser, between the years 1999 and 2010. Data were also collected from scientific journals and sources on the Internet for these variable stars. Times of light maximum of these delta Scuti stars were then either determined from the observations or obtained from the literature to analyze the pulsation period variations. For the 14 delta Scuti stars we concluded that 7 stars (BS Aqr, CY Aqr, AD CMi, EH Lib, KZ Hya, BE Lyn and DY Peg) are binary or multiple systems. 10 delta Scuti stars are found with periods increasing with rates between 5.86×10⁻⁹ and 2.34×10⁻⁶ per year and the other 4 stars (BS Aqr, DY Her, BE Lyn and DY Peg) show periods decreasing with rates of about 10⁻⁹ to 10⁻⁸ per year.     

Detailed photospheric abundances of 28 Peg and HD 202240

The atmospheric parameters and chemical abundances of two neglected A-type stars, 28 Peg and HD 202240, were derived using high resolution spectra obtained at the TÜBİTAK National Observatory. We determined the photospheric abundances of 11 elements for 28 Peg and 20 for HD 202240, using equivalent-width measurement and spectral synthesis methods. Their abundance patterns are in good agreement with those of chemically normal A-type stars having similar atmospheric parameters. We pinpoint the position of these stars on the H-R diagram and estimate their masses and ages as; 2.60 ± 0.10 M_⊙ and 650 ± 50 Myr for 28 Peg and 4.50 ± 0.09 M_⊙ and 150 ± 10 Myr for HD 202240. To compare our abundance determinations with those of stars having similar ages and atmospheric parameters, we select members of open clusters. We notice that our target stars exhibit similar abundance patterns with these members.     

Long‐term orbital period behaviors of the neglected Algol type binaries: CC Herculis and XZ Aquilae

Orbital period variations of two neglected Algol type binaries, CC Her and XZ Aql, are studied based on all available times of minima. In the case of CC Her, it is found that the O –C curve displays a tilted sinusoidal variation with an eccentricity of 0.54 ± 0.03 and a period of 52.4 ± 0.4 yr, which can be explained by the light‐time effect due to the presence of an unseen component. The course of the orbital period change in XZ Aql appears less reliable but its O –C curve can be represented by a periodic variation with a period of 36.7 ± 0.6 yr superimposed on an upward parabola. The parabolic variation indicates a secular period increase with a rate of dP /dt = 7.1 s per century. The corresponding conservative mass transfer from less massive component to the more massive one is about 3.26 × 10^–7 M_⊙ yr^–1. It is interesting to see that the O –C variation of CC Her displays no evidence (as upward parabola) on the mass transfer characteristic for Algols. The periodic change of the orbital period of XZ Aql, like CC Her, may be caused by the presence of the thirdbody. The lower limits of the masses of the hypothetical unseen components for CC Her and XZ Aql are found to be 2.69 M_⊙ and 0.47 M_⊙, respectively. The third body of CC Her should be detectable not only spectroscopically but also photoelectrically, if it exists. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

B,V photometry of the active RS CVn system II Peg

In this work,B andV photometry of the RS CVn-type binary II Peg is presented. The light curves obtained in 1983 and 1984 display two unequal maxima. The light curves of the system have different amplitudes. The amplitude seems to vary with three different periods. 10, 6, and 4 years of periods may be attributed to those variations.     

Photometric modelling of close binary star CN And

The results of two color photometry of active close binary CN And are presented and analyzed. The light curves of the system are obviously asymmetric, with the primary maximum brighter than the secondary maximum, which is known as the O’Conell effect. The most plausible explanation of the asymmetry is expected to be due to spot activity of the primary component. For the determination of physical and geometrical parameters, the most new version of W-D code was used, but the presence of asymmetry prevented the convergence of the method when the whole light curves were used. The solutions were obtained by applying mode 3 of W-D code to the first half of the light curves, assuming synchronous rotation and zero eccentricity. Absolute parameters of the system were obtained from combining the photometric solution with spectroscopic data obtained from radial velocity curve analysis. The results indicate the poor thermal contact of the components and transit primary minimum. Finally the O-C diagram was analyzed. It was found that the orbital period of the system is changing with a rate ofd P/dt = − 2.2(6) × 10⁻¹⁰ which corresponds to mass transfer from more massive component to less massive with the rate ofd M/dt ∼4.82 × 10⁻⁸ M _sun/year.     

On the change of period of Dy Pegasi

In the course of testing a 3-channel photon-counting, high-speed photometer, we observed DY Peg on three nights, 1980 September 18, 19, and November 15, and obtained 7 light maxima. Combining with results observed over the past 30 years, we re-calculated the formula for the maximum epoch to be

$\text{T}{}_{\max }\text{=}\text{H.J.D.}\text{2432751.96182 + 0.072926362}\text{E}\text{? 2.28 × 10}{}^{\mathrm{?13}}\text{E}{}^2\text{± 0.00008 ± 0.000000001 ± 0.09}$

and the period decay rate to be (3.1± 0.1) × 10^?8yr^?1.