CCD Washington photometry of three highly field star contaminated open clusters in the third Galactic quadrant

We present CCD photometry in the Washington system C and T₁ passbands down to T₁ ～ 19.5 magnitudes in the fields of Czernik 26, Czernik 30, and Haffner 11, three poorly studied open clusters located in the third Galactic quadrant. We measured T₁ magnitudes and C ? T₁ colors for a total of 6472 stars distributed throughout cluster areas of 13.6′ × 13.6′ each. Cluster radii were estimated from star counts in appropriate-sized boxes distributed throughout the entire observed fields. Based on the best fits of isochrones computed by the Padova group to the (C ? T₁, T₁) color-magnitude diagrams (CMDs), we derived color excesses, heliocentric distances and ages for the three clusters. These are characterized by a relatively small angular size and by a high field star contamination. We performed a firm analysis of the field star contamination of the CMDs and examined different relationships between the position in the Galaxy of known open clusters located within 1 kpc around the three studied ones, their age and their interstellar visual absorption. We confirm previous results in the sense that the closer the cluster birthplace to the Galactic plane, the higher the interstellar visual absorption. We also found that the space velocity dispersion perpendicular to the Galactic plane diminishes as the clusters are younger. The positions, interstellar visual absorptions, ages, and metallicities of the three studied clusters favor the hypothesis that they were not born in the recently discovered Canis major (CMa) dwarf galaxy before it was accreted by the Milky Way.     

Robust limits on Lorentz violation from gamma-ray bursts

We constrain the possibility of a non-trivial refractive index in free space corresponding to an energy-dependent velocity of light: c(E) ≃ c₀(1 − E/M), where M is a mass scale that might represent effect of quantum-gravitational space-time foam, using the arrival times of sharp features observed in the intensities of radiation with different energies from a large sample of gamma-ray bursters (GRBs) with known redshifts. We use wavelet techniques to identify genuine features, which we confirm in simulations with artificial added noise. Using the weighted averages of the time-lags calculated using correlated features in all the GRB light curves, we find a systematic tendency for more energetic photons to arrive earlier. However, there is a very strong correlation between the parameters characterizing an intrinsic time-lag at the source and a distance-dependent propagation effect. Moreover, the significance of the earlier arrival times is less evident for a subsample of more robust spectral structures. Allowing for intrinsic stochastic time-lags in these features, we establish a statistically robust lower limit: M > 0.9 × 10¹⁶ GeV on the scale of violation of Lorentz invariance.     

Gamma–hadron separation methods for the VERITAS array of four imaging atmospheric Cherenkov telescopes

Ground-based arrays of imaging atmospheric Cherenkov telescopes have emerged as the most sensitive γ-ray detectors in the energy range of about 100 GeV and above. The strengths of these arrays are a very large effective collection area on the order of 10⁵ m², combined with excellent single photon angular and energy resolutions. The sensitivity of such detectors is limited by statistical fluctuations in the number of Cosmic-ray initiated air showers that resemble γ-ray air showers in many ways. In this paper, we study the performance of simple event reconstruction methods when applied to simulated data of the Very Energetic Radiation Imaging Telescope Array System (VERITAS) experiment. We review methods for reconstructing the arrival direction and the energy of the primary photons, and examine means to improve on their performance. For a software threshold energy of 300 GeV (100 GeV), the methods achieve point source angular and energy resolutions of σ_63% = 0.1° (0.2°) and σ_68% = 15% (22%), respectively. The main emphasis of the paper is the discussion of γ–hadron separation methods for the VERITAS experiment. We find that the information from several methods can be combined based on a likelihood ratio approach and the resulting algorithm achieves a γ–hadron suppression with a quality factor that is substantially higher than that achieved with the standard methods used so far.     

Spatial correlation of OH Meinel and O2 infrared atmospheric nightglow emissions observed with VIRTIS-M on board Venus Express

We present the two-dimensional distribution of the O₂ a¹Δ–X³Σ (0–0) band at 1.27 μm and the OH Δv = 1 Meinel airglow measured simultaneously with the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on board Venus Express. We show that the two emissions present very similar spatial structures. A cross-correlation analysis indicates that the highest level of correlation is reached with only very small relative shifts of the pairs of images. In spite of the strong spatial correlation between the morphology of the bright spots in the two emissions, we also show that their relative intensity is not constant, in agreement with earlier statistical studies of their limb profiles. We conclude that the two emissions have a common precursor that controls the production of both excited species. We argue that atomic oxygen, which produces O₂ (¹Δ) molecules by three-body recombination and is the precursor of ozone formation, also governs to a large extent the OH airglow morphology through the H + O₃ → OH^* + O₂ reaction.     

Accretion of dust by chondrules in a MHD-turbulent solar nebula

Numerical magnetohydrodynamic (MHD) simulations of a turbulent solar nebula are used to study the growth of dust mantles swept up by chondrules. A small neighborhood of the solar nebula is represented by an orbiting patch of gas at a radius of 3 AU, and includes vertical stratification of the gas density. The differential rotation of the nebular gas is replaced by a shear flow. Turbulence is driven by destabilization of the flow as a result of the magnetorotational instability (MRI), whereby magnetic field lines anchored to the gas are continuously stretched by the shearing motion. A passive contaminant mimics small dust grains that are aerodynamically well coupled to the gas, and chondrules are modeled by Lagrangian particles that interact with the gas through drag. Whenever a chondrule enters a region permeated by dust, its radius grows at a rate that depends on the local dust density and the relative velocity between itself and the dust. The local dust abundance decreases accordingly. Compaction and fragmentation of dust aggregates are not included. Different chondrule volume densities ρ_c lead to varying depletion and rimmed-chondrule size growth times. Most of the dust sweep-up occurs within ～1 gas scale-height of the nebula midplane. Chondrules can reach their asymptotic radius in 10–800 years, although short growth times due to very high ρ_c may not be altogether realistic. If the sticking efficiency Q of dust to chondrules depends on their relative speed δv, such that Q < 10^?2 whenever δv > v_stick ≈ 34 cm/s (with v_stick a critical sticking velocity), then longer growth times result due to the prevalence of high MRI-turbulent relative velocities. The vertical variation of nebula turbulent intensity results in a moderate dependence of mean rimmed-chondrule size with nebula height, and in a ～20% dispersion in radius values at every height bin. The technique used here could be combined with Monte Carlo (MC) methods that include the physics of dust compaction, in a self-consistent MHD-MC model of dust rim growth around chondrules in the solar nebula.     

A Study of Potential Earth-like Planets in the GJ 876 Planetary System

We perform numerical simulations to investigate potential Earth-like planets in the GJ 876 planetary system. We show that the secular resonances ν₁ and ν₂ (resulting respectively from the inner and outer giant planets) can excite the eccentricities of Earth-like planets with orbits 0.21 AU ≤ a < 0.50 AU and cause them to be ejected out of the system in a short time. However, in the dynamical sense, Earth-like planets potentially exist in the region 0.50 AU ≤ a ≤ 1.00 AU, in stable low-eccentricity orbits which may last up to 10⁵ yr.     

The outcome of the protoplanetary disk of very massive stars

We suggest that planets, brown dwarfs, and even low mass stars can be formed by fragmentation of protoplanetary disks around very massive stars (M ? 100 M_⊙). We discuss how fragmentation conditions make the formation of very massive planetary systems around very massive stars favorable. Such planetary systems are likely to be composed of brown dwarfs and low mass stars of ～0.1–0.3 M_⊙, at orbital separations of ～ few × 100–10⁴ AU. In particular, scaling from solar-like stars suggests that hundreds of Mercury-like planets might orbit very massive stars at ～10³ AU where conditions might favor liquid water. Such fragmentation objects can be excellent targets for the James Webb Space Telescope and other large telescopes working in the IR bands. We predict that deep observations of very massive stars would reveal these fragmentation objects, orbiting in the same orbital plane in cases where there are more than one object.     

The detached eclipsing binary TX Her revisited

This paper presents new CCD Bessell BVRI light curves and photometric analysis of the Algol-type binary star TX Her. The CCD observations were carried out at Çanakkale Onsekiz Mart University Observatory in 2010. New BVRI light curves from this study and radial velocity curves from Popper (1970) were solved simultaneously using modern light and radial velocity curves synthesis methods. The general results show that TX Her is a well-detached eclipsing binary, however, both component stars fill at least half of their Roche lobes. A significant third light contribution to the total light of the system could not be determined. Using O–C residuals formed by the updated minima times, an orbital period study of the system was performed. It was confirmed that the tilted sinusoidal O–C variation corresponds to an apparent period variation caused by the light travel time effect due to an unseen third body. The following absolute parameters of the components were derived: M₁ = 1.62 ± 0.04 M_⊙, M₂ = 1.45 ± 0.03 M_⊙, R₁ = 1.69 ± 0.03 R_⊙, R₂ = 1.43 ± 0.03 R_⊙, L₁ = 8.21 ± 0.90 L_⊙ and L₂ = 3.64 ± 0.60 L_⊙. The distance to TX Her was calculated as 155 ± 10 pc, taking into account interstellar extinction. The position of the components of TX Her in the HR diagram are also discussed. The components are young stars with an age of ～500 Myr.     

Galactic longitude dependent galactic model parameters

We present the Galactic model parameters for thin disc estimated by Sloan Digital Sky Survey (SDSS) data of 14 940 stars with apparent magnitudes 16 < g₀ ⩽ 21 in six intermediate latitude fields in the first Galactic quadrant. Star/galaxy separation was performed by using the SDSS photometric pipeline and the isodensity contours in the (g − r)₀ − (r − i)₀ two colour diagram. The separation of thin disc stars is carried out by the bimodal distribution of stars in the (g − r)₀ histogram, and the absolute magnitudes were evaluated by a procedure presented in the literature (Bilir, S., Karaali, S., Tunçel, S. 2005. AN 326, 321). Exponential density law fits better to the derived density functions for the absolute magnitude intervals 8 < M(g) ⩽ 9 and 11 < M(g) ⩽ 12, whereas sech/sech² laws are more appropriate for absolute magnitude intervals 9 < M(g) ⩽ 10 and 10 < M(g) ⩽ 11. We showed that the scaleheight and scalelength are Galactic longitude dependent. The average values and ranges of the scaleheight and the scalelength are 〈H〉 = 220 pc (196 ⩽ H ⩽ 234 pc) and 〈H〉 = 1900 pc (1561 ⩽ h ⩽ 2280 pc) respectively. This result would be useful to explain different numerical values claimed for those parameters obtained by different authors for the fields in different directions of the Galaxy.     

Spectroscopic and photometric study of the contact binary BO CVn

We present the results of the study of the contact binary system BO CVn. We have obtained physical parameters of the components based on combined analysis of new, multi-color light curves and spectroscopic mass ratio. This is the first time the latter has been determined for this object. We derived the contact configuration for the system with a very high filling factor of about 88%. We were able to reproduce the observed light curve, namely the flat bottom of the secondary minimum, only if a third light has been added into the list of free parameters. The resulting third light contribution is significant, about 20–24%, while the absolute parameters of components are: M₁ = 1.16, M₂ = 0.39, R₁ = 1.62 and R₂ = 1.00 (in solar units).The O-C diagram shows an upward parabola which, under the conservative mass transfer assumption, would correspond to a mass transfer rate of dM/dt = 6.3 × 10^?8M_⊙/yr, matter being transferred from the less massive component to the more massive one. No cyclic, short-period variations have been found in the O-C diagram (but longer-term variations remain a possibility).     

The eclipsing binary star V380 Gem: First V and Rc light curve analysis and estimation of its absolute elements

We obtained complete V and R_c light curves of the eclipsing binary V380 Gem in 2012. With our data we were able to determine six new times of minimum light and refine the orbital period of the system to 0.3366088 days. The 2003 version of the Wilson–Devinney code was used to analyze the light curves in the V and R_c bands simultaneously. It is shown that V380 Gem may be classified as an W-type W Ursae Majoris system with a high mass ratio q = 1.45, a degree of contact f = 10.6% the same temperature for both the components (ΔT = 10 K) and an orbital inclination of i  = 81.5°. Our observations show symmetric light curves in all passbands with brightness in both maxima at the same level. The absolute dimensions of V380 Gem are estimated and its dynamical evolution is inferred.     

Cyclic period changes and the light-time effect in eclipsing binaries: A low-mass companion around the system VV Ursae Majoris

In this article, a period analysis of the late-type eclipsing binary VV UMa is presented. This work is based on the periodic variation of eclipse timings of the VV UMa binary. We determined the orbital properties and mass of a third orbiting body in the system by analyzing the light-travel time effect. The O−C diagram constructed for all available minima times of VV UMa exhibits a cyclic character superimposed on a linear variation. This variation includes three maxima and two minima within approximately 28,240 orbital periods of the system, which can be explained as the light-travel time effect (LITE) because of an unseen third body in a triple system that causes variations of the eclipse arrival times. New parameter values of the light-time travel effect because of the third body were computed with a period of 23.22 ± 0.17 years in the system. The cyclic-variation analysis produces a value of 0.0139 day as the semi-amplitude of the light-travel time effect and 0.35 as the orbital eccentricity of the third body. The mass of the third body that orbits the eclipsing binary stars is 0.787 ± 0.02 M_⊙, and the semi-major axis of its orbit is 10.75 AU.     

Orbital period investigations of two short-period early-type overcontact binaries BH Cen and V701 Sco in two extremely young galactic clusters IC 2944 and NGC 6383

Both V701 Sco and BH Cen are two early-type short-period overcontact systems (P = 0.^d762 and P = 0.^d792, respectively). V701 Sco is a member of the young galactic cluster NGC 6383, while BH Cen is a component of a younger galactic cluster IC 2944 where star formation is in process. They provide good opportunity to understand the formation and evolution of binary stars. In the present paper, orbital period changes of the two binaries are investigated. It is discovered that the orbital period of BH Cen shows a long-term increase with a rate of dP/dt = +1.70(±0.39) × 10⁻⁷ days/year while it undergoes a cyclic oscillation with a period of 44.6 years and an amplitude of A₃ = 0.^d0216. For V701 Sco, its O-C curve reveals a periodic change with a period of 41.2 years and amplitude of A₃ = 0.^d0158. The mass ratio of BH Cen is 0.84, but V701 Sco contains twin B1-1.5V type stars with a mass ratio of unit. The continuous period increase of BH Cen is caused by the mass transfer from the less massive component to the more massive one at a rate of dM₂/dt = 3.5 × 10⁻⁶ days/year.The cyclic period changes of both systems can be plausibly explained as the results of light-travel time effects suggesting that they are triple systems. The astrophysical parameters of the unseen tertiary components in the two systems have been determined. We think that the invisible tertiary components in both binaries played an important role in the formations and evolutions of the overcontact configurations by bringing angular momentum out from the central systems. For BH Cen, this process created the initial short period and will support its evolution into an overcontact configuration via a Case A mass transfer within the life time of the extremely young cluster IC 2944. For V701 Sco, two identical zero-age main-sequence components in an overcontact configuration suggest that it may have been formed by fission, possibly by the fission of the third body. The fact that no long-term continuous period variations were found for V701 Sco may suggest that an overcontact binary with the mass ratio of unity can be in an equilibrium revealing that the original configuration of the binary was overcontact as is its present state. It has been reported that faint stars in the two extremely young clusters are relatively scare. From the present study, it is shown that faint stars in young clusters are usually formed as companions of OB stars (including binaries). It is very difficult to detect them because of their low luminosity when compared with the more luminous OB stars.     

Revealing the parameters of the open cluster Ruprecht 58

We present results of a study that combines UBVI photometry, MK spectral classification and proper motions in the area of the, up to now unknown, open cluster Ruprecht 58 at the Puppis region. Star counts from the 2MASS data catalog together with the analysis of CCD UBVI photometry demonstrate that it is a real open cluster with 9′ size approximately. The cluster is placed at a distance of 3.9 kpc and is about 250 Myr old with mean reddening E_(B−V) = 0.33 mag. Proper motions confirm Ruprecht 58 is a real cluster with mean absolute proper motions μ_αcosδ = −2.77 ± 0.45 mas/yr and μ_δ = 4.54 ± 0.45 mas/yr in the magnitude range 13.5 < V < 14.5 and μ_αcosδ = −2.70 ± 0.32 mas/yr and μ_δ = 3.19 ± 0.32 mas/yr in the range 14.5 < V < 16.0. The computation of the cluster mass spectrum slope yielded x = 1.8 in the mass range from ≈1.4 to ≈4m_⊙.     

Search for relativistic magnetic monopoles with the Baikal neutrino telescope

We present results of a search for relativistic magnetic monopoles with the Baikal neutrino telescope NT200, using data taken between April 1998 and February 2003. No monopole candidates have been found. We set an upper limit 4.6 × 10⁻¹⁷ cm⁻² s⁻¹ sr⁻¹ for the flux of monopoles with β_m = 1. This is a factor of 20 below the Chudakov–Parker bound which is inferred from the very existence of large-scale galactic magnetic fields.     

A Kinematical Study of the Galaxy Based on the Revised Hipparcos Astrometric Data

On the basis of the revised Hipparcos data recently released, the zero-point of the period-luminosity relation for classical cepheids is reexamined. Fitting the proper motion and radial velocity data via an axisymmetric model, the Oort constants and circular rotation velocity of the LSR are calculated to obtain the Galactocentric distance of the Sun, R₀ = 8.0 ± 0.8 kpc. From the rotation curve in solar neighborhood, the existence of weak ellipticity of the Galactic potential is found. Adopting a simple asymmetric model, we have obtained the ellipticity ∈(R₀) = 0.067 ± 0.036 at the Sun, while the minor axis points to φ_b = 32° ± 15°.     

A new absolute magnitude calibration with 2MASS for cataclysmic variables

Using reliable trigonometric measurements, we find that the absolute magnitude of cataclysmic variables depends on the orbital period and de-reddened (J − H)₀ and (H − K _s)₀ colours of 2MASS (Two Micron All Sky Survey) photometric system. The calibration equation covers the ranges 0.032^d < P_orb ⩽ 0.454^d, −0.08 < (J − H)₀ ⩽ 1.54, −0.03 < (H − K_s)₀ ⩽ 0.56 and 2.0 < M_J < 11.7; It is based on trigonometric parallaxes with relative errors of (σ_π/π) ⩽ 0.4. By using the period-luminosity-colours (PLCs) relation, we estimated the distances of cataclysmic variables with orbital periods and 2MASS observations and compared them with distances found from other methods. We suggest that the PLCs relation can be a useful statistical tool to estimate the distances of cataclysmic variables.     

Absolute and geometric parameters of W UMa type contact binary TYC 1174-344-1

We present the results of our investigation on the geometrical and physical parameters of W UMa-type binary TYC1174-344-1 from analyzed CCD (BVRI) light curves and radial velocity data. The photometric data were obtained in 2009 at Ankara University Observatory (AUO) and the spectroscopic observations were made in 2008 at Astrophysical Observatory of Asiago (Italy). Light and radial velocity observations were analyzed simultaneously by using the well-known Wilson–Devinney (2007 revision) code to obtain absolute and geometrical parameters. According to our solutions, the system is found to be a low mass-ratio A-type W UMa system. Combining our photometric solution with the spectroscopic data, we derived mass and radii of the eclipsing system as M₁ = 1.381 M_⊙, M₂ = 0.258 M_⊙, R₁ = 1.449 R_⊙ and R₂ = 0.714 R_⊙. We finally discussed the evolutionary condition of the system.     

Absolute properties of the overcontact binary HH Boo

We obtained multi-colour light curves of the overcontact binary system HH Boo and analysed the orbital period variation of the system. Our analysis tentatively indicates either mass transfer from the secondary to the primary or mass loss from the system at a rate of -5.04 × 10⁻⁷ M_⊙ per year. Through a combined analysis of the published radial velocity curve and light curves, we determined an inclination (i) of 69°.71 ± 0°.16 and a semi-major axis (a) of 2.246 ± 0.064 R_⊙ for HH Boo. The masses of the primary and secondary components were found to be 0.92 ± 0.08 M_⊙ and 0.58 ± 0.06 M_⊙, respectively. The radius determined for the primary was 0.98 ± 0.03 R_⊙, while that determined for the secondary was 0.80 ± 0.02 R_⊙. We demonstrated that HH Boo is most likely a member of the A-type subclass of W UMa binaries.     

CCD photometric analysis of the W UMa-type binary V376 Andromeda

This study presents the absolute parameters of the contact binary system V376 And. CCD photometric observations were made at the Çanakkale Onsekiz Mart University Observatory in 2004. The instrumental magnitudes of all observed stars were converted into standard magnitudes. New BV light curves of the system were analysed using the Wilson–Devinney method supplemented with a Monte Carlo type algorithm. Since there are large asymmetries between maxima (i.e., O’Connell effect) in these light curves, two different models (one with a cool spot and one with a hot spot) were applied to the photometric data. The best fit, which was obtained with a large hot spot on the secondary component, gives V376 And as an A sub-type contact binary in poor thermal contact and a small value of the filling factor (f ≈ 0.07). Combining the solutions of our light curves and Rucinski et al. (2001)’s radial velocity curves, the following absolute parameters of the components were determined: M₁ = 2.44 ± 0.04 M_⊙, M₂ = 0.74 ± 0.03 M_⊙, R₁ = 2.60 ± 0.03 R_⊙, R₂ = 1.51 ± 0.02 R_⊙, L₁ = 40 ± 4 L_⊙ and L₂ = 5 ± 1 L_⊙. We also discuss the evolution of the system, which appears to have an age of 1.6 Gyr. The distance to V376 And was calculated as 230 ± 20 pc from this analysis, taking into account interstellar extinction.