UBVRI Photometric Analysis of the Solar-Type Eclipsing Binary TYC 3034-299-1

TYC 3034-0299-1 (CVn) is a magnetically active, contact binary, ROTSE variable. UBVRcIc light curves are presented along with a period study and a simultaneous UBVRI light curve solution. Our light curves show eclipse amplitudes of 0.72 and 0.62 mags (V) in the primary and secondary eclipses. Modeled results include a dark spot region, found at longitude 51°, a 24% Roche lobe fill-out, and a mass ratio of 0.48. A total eclipse is found to occur in the secondary eclipse making TYC 3034-0299-1 a W-type (less massive star is hotter) W UMa variable.

GU Monocerotis: A high-mass eclipsing overcontact binary in the young open cluster Dolidze 25

Context. The eclipsing binary GU Mon is located in the star-forming cluster Dolidze 25, which has the lowest metallicity measured in a Milky Way young cluster. Aims. GU Mon has been identified as a short-period eclipsing binary with two early B-type components. We set out to derive its orbital and stellar parameters. Methods. We present a comprehensive analysis, including B and V light curves and 11 high-resolution spectra, to verify the orbital period and determine parameters. We used the stellar atmosphere code FASTWIND to obtain stellar parameters and create templates for cross-correlation. We obtained a model to fit the light and radial-velocity curves using the Wilson-Devinney code iteratively and simultaneously. Results. The two components of GU Mon are identical stars of spectral type B1 V with the same mass and temperature. The light curves are typical of an EW-type binary. The spectroscopic and photometric analyses agree on a period of 0.896640 ± 0.000007 d. We determine a mass of 9.0 ± 0.6 M⊙ for each component and for temperatures of 28 000 ± 2000 K. Both values are consistent with the spectral type. The two stars are overfilling their respective Roche lobes, sharing a common envelope and, therefore the orbit is synchronised and circularised. Conclusions. The GU Mon system has a fill-out factor above 0.8, containing two dwarf B-type stars on the main sequence. The two stars are in a very advanced stage of interaction, with their extreme physical similarity likely due to the common envelope. The expected evolution of such a system very probably leads to a merger while still on the main sequence.

Transiting exoplanets from the CoRoT space mission VIII. CoRoT-7b: the first super-Earth with measured radius

Aims. We report the discovery of very shallow (Delta F/F approximate to 3.4 x 10(-4)), periodic dips in the light curve of an active V = 11.7 G9V star observed by the CoRoT satellite, which we interpret as caused by a transiting companion. We describe the 3-colour CoRoT data and complementary ground-based observations that support the planetary nature of the companion. Methods. We used CoRoT colours information, good angular resolution ground-based photometric observations in- and out- of transit, adaptive optics imaging, near-infrared spectroscopy, and preliminary results from radial velocity measurements, to test the diluted eclipsing binary scenarios. The parameters of the host star were derived from optical spectra, which were then combined with the CoRoT light curve to derive parameters of the companion. Results. We examined all conceivable cases of false positives carefully, and all the tests support the planetary hypothesis. Blends with separation >0.40 '' or triple systems are almost excluded with a 8 x 10(-4) risk left. We conclude that, inasmuch we have been exhaustive, we have discovered a planetary companion, named CoRoT-7b, for which we derive a period of 0.853 59 +/- 3 x 10(-5) day and a radius of R(p) = 1.68 +/- 0.09 R(Earth). Analysis of preliminary radial velocity data yields an upper limit of 21 M(Earth) for the companion mass, supporting the finding. Conclusions. CoRoT-7b is very likely the first Super-Earth with a measured radius. This object illustrates what will probably become a common situation with missions such as Kepler, namely the need to establish the planetary origin of transits in the absence of a firm radial velocity detection and mass measurement. The composition of CoRoT-7b remains loosely constrained without a precise mass. A very high surface temperature on its irradiated face, approximate to 1800-2600 K at the substellar point, and a very low one, approximate to 50 K, on its dark face assuming no atmosphere, have been derived.

Study on period search methods of variable stars: Application to ASAS and CRTS databases

Study on variable stars is an important topic of modern astrophysics. After the invention of powerful telescopes and high resolving powered CCD’s, the variable star data is accumulating in the order of peta-bytes. The huge amount of data need lot of automated methods as well as human experts. This thesis is devoted to the data analysis on variable star’s astronomical time series data and hence belong to the inter-disciplinary topic, Astrostatistics. For an observer on earth, stars that have a change in apparent brightness over time are called variable stars. The variation in brightness may be regular (periodic), quasi periodic (semi-periodic) or irregular manner (aperiodic) and are caused by various reasons. In some cases, the variation is due to some internal thermo-nuclear processes, which are generally known as intrinsic vari- ables and in some other cases, it is due to some external processes, like eclipse or rotation, which are known as extrinsic variables. Intrinsic variables can be further grouped into pulsating variables, eruptive variables and flare stars. Extrinsic variables are grouped into eclipsing binary stars and chromospheri- cal stars. Pulsating variables can again classified into Cepheid, RR Lyrae, RV Tauri, Delta Scuti, Mira etc. The eruptive or cataclysmic variables are novae, supernovae, etc., which rarely occurs and are not periodic phenomena. Most of the other variations are periodic in nature. Variable stars can be observed through many ways such as photometry, spectrophotometry and spectroscopy. The sequence of photometric observa- xiv tions on variable stars produces time series data, which contains time, magni- tude and error. The plot between variable star’s apparent magnitude and time are known as light curve. If the time series data is folded on a period, the plot between apparent magnitude and phase is known as phased light curve. The unique shape of phased light curve is a characteristic of each type of variable star. One way to identify the type of variable star and to classify them is by visually looking at the phased light curve by an expert. For last several years, automated algorithms are used to classify a group of variable stars, with the help of computers. Research on variable stars can be divided into different stages like observa- tion, data reduction, data analysis, modeling and classification. The modeling on variable stars helps to determine the short-term and long-term behaviour and to construct theoretical models (for eg:- Wilson-Devinney model for eclips- ing binaries) and to derive stellar properties like mass, radius, luminosity, tem- perature, internal and external structure, chemical composition and evolution. The classification requires the determination of the basic parameters like pe- riod, amplitude and phase and also some other derived parameters. Out of these, period is the most important parameter since the wrong periods can lead to sparse light curves and misleading information. Time series analysis is a method of applying mathematical and statistical tests to data, to quantify the variation, understand the nature of time-varying phenomena, to gain physical understanding of the system and to predict future behavior of the system. Astronomical time series usually suffer from unevenly spaced time instants, varying error conditions and possibility of big gaps. This is due to daily varying daylight and the weather conditions for ground based observations and observations from space may suffer from the impact of cosmic ray particles. Many large scale astronomical surveys such as MACHO, OGLE, EROS, xv ROTSE, PLANET, Hipparcos, MISAO, NSVS, ASAS, Pan-STARRS, Ke- pler,ESA, Gaia, LSST, CRTS provide variable star’s time series data, even though their primary intention is not variable star observation. Center for Astrostatistics, Pennsylvania State University is established to help the astro- nomical community with the aid of statistical tools for harvesting and analysing archival data. Most of these surveys releases the data to the public for further analysis. There exist many period search algorithms through astronomical time se- ries analysis, which can be classified into parametric (assume some underlying distribution for data) and non-parametric (do not assume any statistical model like Gaussian etc.,) methods. Many of the parametric methods are based on variations of discrete Fourier transforms like Generalised Lomb-Scargle peri- odogram (GLSP) by Zechmeister(2009), Significant Spectrum (SigSpec) by Reegen(2007) etc. Non-parametric methods include Phase Dispersion Minimi- sation (PDM) by Stellingwerf(1978) and Cubic spline method by Akerlof(1994) etc. Even though most of the methods can be brought under automation, any of the method stated above could not fully recover the true periods. The wrong detection of period can be due to several reasons such as power leakage to other frequencies which is due to finite total interval, finite sampling interval and finite amount of data. Another problem is aliasing, which is due to the influence of regular sampling. Also spurious periods appear due to long gaps and power flow to harmonic frequencies is an inherent problem of Fourier methods. Hence obtaining the exact period of variable star from it’s time series data is still a difficult problem, in case of huge databases, when subjected to automation. As Matthew Templeton, AAVSO, states “Variable star data analysis is not always straightforward; large-scale, automated analysis design is non-trivial”. Derekas et al. 2007, Deb et.al. 2010 states “The processing of xvi huge amount of data in these databases is quite challenging, even when looking at seemingly small issues such as period determination and classification”. It will be beneficial for the variable star astronomical community, if basic parameters, such as period, amplitude and phase are obtained more accurately, when huge time series databases are subjected to automation. In the present thesis work, the theories of four popular period search methods are studied, the strength and weakness of these methods are evaluated by applying it on two survey databases and finally a modified form of cubic spline method is intro- duced to confirm the exact period of variable star. For the classification of new variable stars discovered and entering them in the “General Catalogue of Vari- able Stars” or other databases like “Variable Star Index“, the characteristics of the variability has to be quantified in term of variable star parameters.

Determinacão do período orbital de sistemas binários clipsantes

In this work is presented a new method for the determination of the orbital period (Porb) of eclipsing binary systems based on the wavelet technique. This method is applied on 18 eclipsing binary systems detected by the CoRoT (Convection Rotation and planetary transits) satellite. The periods obtained by wavelet were compared with those obtained by the conventional methods: box Fitting (EEBLS) for detached and semi-detached eclipsing binaries; and polynomial methods (ANOVA) for contact binary systems. Comparing the phase diagrams obtained by the different techniques the wavelet method determine better Porb compared with EEBLS. In the case of contact binary systems the wavelet method shows most of the times better results than the ANOVA method but when the number of data per orbital cicle is small ANOVA gives more accurate results. Thus, the wavelet technique seems to be a great tool for the analysis of data with the quality and precision given by CoRoT and the incoming photometric missions.

Sistemas binários eclipsantes na missão CoRot

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

MY Camelopardalis, a very massive merger progenitor

Context. The early-type binary MY Cam belongs to the young open cluster Alicante 1, embedded in Cam OB3. Aims. MY Cam consists of two early-O type main-sequence stars and shows a photometric modulation suggesting an orbital period slightly above one day. We intend to confirm this orbital period and derive orbital and stellar parameters. Methods. Timing analysis of a very exhaustive (4607 points) light curve indicates a period of 1.1754514 ± 0.0000015 d. High-resolution spectra and the cross-correlation technique implemented in the todcor program were used to derive radial velocities and obtain the corresponding radial velocity curves for MY Cam. Modelling with the stellar atmosphere code fastwind was used to obtain stellar parameters and create templates for cross-correlation. Stellar and orbital parameters were derived using the Wilson-Devinney code, such that a complete solution to the binary system could be described. Results. The determined masses of the primary and secondary stars in MY Cam are 37.7 ± 1.6 and 31.6 ± 1.4M⊙, respectively. The corresponding temperatures, derived from the model atmosphere fit, are 42 000 and 39 000 K, with the more massive component being hotter. Both stars are overfilling their Roche lobes, sharing a common envelope. Conclusions. MY Cam contains the most massive dwarf O-type stars found so far in an eclipsing binary. Both components are still on the main sequence, and probably not far from the zero-age main sequence. The system is a likely merger progenitor, owing to its very short period.

Análise wavelet em curvas de luz estelares de sistemas binários da missão espacial CoRoT

Binary systems are key environments to study the fundamental properties of stars. In this work, we analyze 99 binary systems identified by the CoRoT space mission. From the study of the phase diagrams of these systems, our sample is divided into three groups: those whose systems are characterized by the variability relative to the binary eclipses; those presenting strong modulations probably due to the presence of stellar spots on the surface of star; and those whose systems have variability associated with the expansion and contraction of the surface layers. For eclipsing binary stars, phase diagrams are used to estimate the classification in regard to their morphology, based on the study of equipotential surfaces. In this context, to determine the rotation period, and to identify the presence of active regions, and to investigate if the star exhibits or not differential rotation and study stellar pulsation, we apply the wavelet procedure. The wavelet transform has been used as a powerful tool in the treatment of a large number of problems in astrophysics. Through the wavelet transform, one can perform an analysis in time-frequency light curves rich in details that contribute significantly to the study of phenomena associated with the rotation, the magnetic activity and stellar pulsations. In this work, we apply Morlet wavelet (6th order), which offers high time and frequency resolution and obtain local (energy distribution of the signal) and global (time integration of local map) wavelet power spectra. Using the wavelet analysis, we identify thirteen systems with periodicities related to the rotational modulation, besides the beating pattern signature in the local wavelet map of five pulsating stars over the entire time span.

Análise wavelet em curvas de luz estelares de sistemas binários da missão espacial CoRoT

Binary systems are key environments to study the fundamental properties of stars. In this work, we analyze 99 binary systems identified by the CoRoT space mission. From the study of the phase diagrams of these systems, our sample is divided into three groups: those whose systems are characterized by the variability relative to the binary eclipses; those presenting strong modulations probably due to the presence of stellar spots on the surface of star; and those whose systems have variability associated with the expansion and contraction of the surface layers. For eclipsing binary stars, phase diagrams are used to estimate the classification in regard to their morphology, based on the study of equipotential surfaces. In this context, to determine the rotation period, and to identify the presence of active regions, and to investigate if the star exhibits or not differential rotation and study stellar pulsation, we apply the wavelet procedure. The wavelet transform has been used as a powerful tool in the treatment of a large number of problems in astrophysics. Through the wavelet transform, one can perform an analysis in time-frequency light curves rich in details that contribute significantly to the study of phenomena associated with the rotation, the magnetic activity and stellar pulsations. In this work, we apply Morlet wavelet (6th order), which offers high time and frequency resolution and obtain local (energy distribution of the signal) and global (time integration of local map) wavelet power spectra. Using the wavelet analysis, we identify thirteen systems with periodicities related to the rotational modulation, besides the beating pattern signature in the local wavelet map of five pulsating stars over the entire time span.

A cyclic bipolar wind in the interacting binary V 393 Scorpii

V393 Scorpii is a double periodic variable characterized by a relatively stable non-orbital photometric cycle of 253 d. Mennickent et al. argue for the presence of a massive optically thick disc around the more massive B-type component and describe the evolutionary stage of the system. In this paper, we analyse the behaviour of the main spectroscopic optical lines during the long non-orbital photometric cycle. We study the radial velocity of the donor determining its orbital elements and find a small but significant orbital eccentricity (e = 0.04). The donor spectral features are modelled and removed from the spectrum at every observing epoch using the light-curve model given by Mennickent et al. We find that the line emission is larger during eclipses and mostly comes from a bipolar wind. We also find that the long cycle is explained in terms of a modulation of the wind strength; the wind has a larger line and continuum emissivity at the high state. We report the discovery of highly variable chromospheric emission in the donor, as revealed by the Doppler maps of the emission lines Mg II 4481 and C I 6588. We discuss notable and some novel spectroscopic features like discrete absorption components, especially visible at blue depressed O I 7773 absorption wings during the second half-cycle, Balmer double emission with V/R curves showing 'Z-type' and 'S-type' excursions around secondary and main eclipses, respectively, and H beta emission wings extending up to +/- 2000 km s(-1). We also discuss possible causes for these phenomena and for their modulations with the long cycle.

The masses of the neutron and donor star in the high-mass X-ray binary IGR J18027-2016

Aims. We report near-infrared observations of the supergiant donor to the eclipsing high mass X-ray binary pulsar IGR J18027-2016. We aim to determine its spectral type and measure its radial velocity curve and hence determine the stellar masses of the components. Methods. ESO/VLT observations of the donor utilising the NIR spectrograph ISAAC were obtained in the H and K bands. The multi-epoch H band spectra were cross-correlated with RV templates in order to determine a radial solution for the system. Results. The spectral type of the donor was confirmed as B0-1 I. The radial velocity curve constructed has a semi-amplitude of 23.8 ± 3.1 km s-1. Combined with other measured system parameters, a dynamically determined neutron star mass of 1.4  ±  0.2–1.6  ±  0.3 M⊙ is found. The mass range of the B0-B1 I donor was 18.6  ±  0.8–21.8  ±  2.4 M⊙. These lower and upper limits were obtained under the assumption that the system is viewed edge-on (i = 90° with β = 0.89) for the lower limit and the donor fills its Roche lobe (β = 1 with i = 73.1°) for the upper limit respectively.

The evolution and masses of the neutron star and donor star in the high mass X-ray binary OAO 1657−415

We report near-infrared radial velocity (RV) measurements of the recently identified donor star in the high mass X-ray binary (HMXB) system OAO 1657−415 obtained in the H band using ISAAC on the Very Large Telescope. Cross-correlation methods were employed to construct a RV curve with a semi-amplitude of 22.1 ± 3.5 km s−1. Combined with other measured parameters of this system it provides a dynamically determined neutron star (NS) mass of 1.42 ± 0.26 M⊙ and a mass of 14.3 ± 0.8 M⊙ for the Ofpe/WN9 highly evolved donor star. OAO 1657−415 is an eclipsing HMXB pulsar with the largest eccentricity and orbital period of any within its class. Of the 10 known eclipsing X-ray binary pulsars OAO 1657−415 becomes the ninth with a dynamically determined NS mass solution and only the second in an eccentric system. Furthermore, the donor star in OAO 1657−415 is much more highly evolved than the majority of the supergiant donors in other HMXBs, joining a small but growing list of HMXBs donors with extensive hydrogen depleted atmospheres. Considering the evolutionary development of OAO 1657−415, we have estimated the binding energy of the envelope of the mass donor and find that there is insufficient energy for the removal of the donor’s envelope via spiral-in, ruling out a common envelope evolutionary scenario. With its non-zero eccentricity and relatively large orbital period the identification of a definitive evolutionary pathway for OAO 1657−415 remains problematic, we conclude by proposing two scenarios which may account for OAO 1657−415 current orbital configuration.

The crowded magnetosphere of the post-common-envelope binary QS Virginis

We present high-speed photometry and high-resolution spectroscopy of the eclipsing post-common-envelope binary QS Virginis (QS Vir). Our Ultraviolet and Visual Echelle Spectrograph (UVES) spectra span multiple orbits over more than a year and reveal the presence of several large prominences passing in front of both the M star and its white dwarf companion, allowing us to triangulate their positions. Despite showing small variations on a time-scale of days, they persist for more than a year and may last decades. One large prominence extends almost three stellar radii from the M star. Roche tomography reveals that the M star is heavily spotted and that these spots are long-lived and in relatively fixed locations, preferentially found on the hemisphere facing the white dwarf. We also determine precise binary and physical parameters for the system. We find that the 14 220 ± 350 K white dwarf is relatively massive, 0.782 ± 0.013 M⊙, and has a radius of 0.010 68 ± 0.000 07 R⊙, consistent with evolutionary models. The tidally distorted M star has a mass of 0.382 ± 0.006 M⊙ and a radius of 0.381 ± 0.003 R⊙, also consistent with evolutionary models. We find that the magnesium absorption line from the white dwarf is broader than expected. This could be due to rotation (implying a spin period of only ˜700 s), or due to a weak (˜100 kG) magnetic field, we favour the latter interpretation. Since the M star's radius is still within its Roche lobe and there is no evidence that it is overinflated, we conclude that QS Vir is most likely a pre-cataclysmic binary just about to become semidetached.

Pulsar binary systems in a nonsymmetric theory of gravitation II. Dipole radiation

This paper deals with the emission of gravitational radiation in the context of a previously studied metric nonsymmetric theory of gravitation. The part coming from the symmetric part of the metric coincides with the mass quadrupole moment result of general relativity. The one associated to the antisymmetric part of the metric involves the dipole moment of the fermionic charge of the system. The results are applied to binary star systems and the decrease of the period of the elliptical motion is calculated.