Neglected reverse Algol system: WZ Hor

This paper presents the first analysis of spectroscopic and photometric observations of the eclipsing binary star WZ Hor. Observations of the system were made at the Mt. John University Observatory in 2007. Since the light contribution of the secondary component was merely 2-3% of the total light of the system in the optical wavelengths, the radial velocity of the primary component could only be determined using the cross-correlation method. A single-lined spectroscopic orbital solution of WZ Hor was obtained, and the BVRI light curves of the system and radial velocity curve of the primary component were analysed simultaneously using the Wilson-Devinney method. The results describe WZ Hor as a reverse Algol-like binary star with a detached configuration. The following absolute parameters of the components were also derived: M₁ = 1.51 ± 0.03 M_⊙, M₂ = 0.66 ± 0.01 M_⊙, R₁ = 1.62 ± 0.02 R_⊙, R₂ = 0.66 ± 0.01 R_⊙, L₁ = 4.93 ± 0.64 L_⊙ and L₂ = 0.09 ± 0.02 L_⊙. The distance to WZ Hor was calculated as 95 ± 8 pc using distance modulus with correction for interstellar extinction, in agreement with the HIPPARCOS value.     

Stellar contents and star formation in the young cluster Stock 18

We have carried out deep (V ∼ 21 mag) UBVRI photometric study of the star cluster Stock 18. These along with archival Infrared data have been used to derive the basic cluster parameters and also to study the star formation processes in and around the cluster region. The distance to the cluster is derived as 2.8 ± 0.2 kpc while its age is estimated as 6.0 ± 2.0 Myr. Present study indicates that interstellar reddening is normal in the direction of the cluster. The mass function slope is found to be −1.37 ± 0.27 for the mass range 1 < M/M_⊙ < 11.9. There is no evidence found for the effect of mass segregation in main-sequence stars of the cluster. A young stellar population with age between 1-2 Myr have been found in and around the cluster region. The presence of IRAS and AKARI sources with MSX intensity map also show the youth of the Sh2-170 region.     

A spectroscopic study of DD UMa: Ursa Major group member and candidate for BRITE

The Ursa Major group is a nearby stellar supercluster which, while not gravitationally bound, is defined by co-moving members. DD UMa is a δ Scuti star whose membership in the Ursa Major group is unclear.The objective of this study is to confirm the membership of DD UMa in the Ursa Major group, as well as perform a detailed spectral analysis of the star. Since DD UMa is a low-amplitude δ Scuti star, we performed a frequency analysis. We determined fundamental parameters, chemical abundances, and derive a mass and age for the star.For this study we observed DD UMa at the Okayama Astrophysical Observatory with the high-resolution spectrograph HIDES, between the 27th of February and the 4th March, 2009. Additional observations were extracted from the ELODIE archive in order to expand our abundance analysis. Group membership of DD UMa was assessed by examining the velocity of the star in Galactic coordinates. Pulsational frequencies were determined by examining line profile variability in the HIDES spectra. Stellar fundamental parameters and chemical abundances were derived by fitting synthetic spectra to both the HIDES and ELODIE observations.DD UMa is found to be a member of the extended stream of the Ursa Major group, based on the space motion of the star. This is supported by the chemical abundances of the star being consistent with those of Ursa Major group members. The star is found to be chemically solar, with T_eff = 7450 ± 150 K and logg = 3.98 ± 0.2. We found pulsational frequencies of 9.4 and 15.0 c/d. While these frequencies are insufficient to perform an asteroseismic study, DD UMa is a good bright star candidate for future study by the BRITE-constellation.     

Close binary system GO Cyg

In this study, we present long term photometric variations of the close binary system GO Cyg. Modelling of the system shows that the primary is filling Roche lobe and the secondary of the system is almost filling its Roche lobe. The physical parameters of the system are M₁ = 3.0 ± 0.2M_⊙, M₂ = 1.3 ± 0.1M_⊙, R₁ = 2.50 ± 0.12R_⊙, R₂ = 1.75 ± 0.09R_⊙, L₁ = 64 ± 9L_⊙, L₂ = 4.9 ± 0.7L_⊙, and a = 5.5 ± 0.3R_⊙. Our results show that GO Cyg is the most massive system near contact binary (NCB). Analysis of times of the minima shows a sinusoidal variation with a period of 92.3 ± 0.5 yr due to a third body whose mass is less than 2.3M_⊙. Finally a period variation rate of −1.4 × 10⁻⁹ d/yr has been determined using all available light curves.     

The photometric periods of the nova-like cataclysmic variable LQ Pegasi (PG 2133+115)

We present a time-resolved differential photometric study and time series analysis of the nova-like cataclysmic variable star LQ Peg. We discover three periodicities in the photometry, one with a period of 3.42 ± 0.03 h, and another with a period of 56.8 ± 0.01 h. We interpret these to be the apsidal superhump and precessional periods of the accretion disk, respectively, and predict that the orbital period of LQ Peg is 3.22 ± 0.03 h. The third periodicity, with a period of 41.3 ± 0.01 h, we interpret to be the nodal precessional period of the accretion disk. We also report a flare that lasted four minutes and had an energy in visible light of (1.2 ± 0.3) × 10³⁶ ergs, or 10^4-5 times more energetic than the largest solar flares, comparable to the most energetic visible-light stellar flares known. We calculate the absolute magnitude of LQ Peg to be M_J = 4.78 ± 0.54, and its distance to be 800 ± 200 pc.     

Early-type W UMa contact binary system: New data on V535 Ara

This paper presents the results of spectroscopic and photometric observations of the early-type W UMa system V535 Ara. New high-resolution spectra were taken at the Mt. John University Observatory in 2007. Radial velocities and spectroscopic orbital elements of the system were determined by applying KOREL spectral disentangling. The resulting orbital elements were: a₁sini = 0.0047 ± 0.0001 AU, a₂sini = 0.0146 ± 0.0001 AU, M₁sin³i = 1.85 ± 0.01 M_⊙, and M₂sin³i = 0.59 ± 0.01 M_⊙. The components were found to be in synchronous rotation following examination of their disentangled Hγ line profiles. Four photometric data-sets (1966 BV, 1967 BV, HIPPARCOS and ASAS) were modeled using the Wilson-Devinney method. The model describes V535 Ara as an A sub-type W UMa type eclipsing binary which has a fill out factor of 0.22 in marginal contact configuration. The simultaneous solution of light and radial velocity curves gave the following absolute parameters: M₁ = 1.94 ± 0.04 M_⊙, M₂ = 0.59 ± 0.02 M_⊙, R₁ = 2.09 ± 0.03 R_⊙, R₂ = 1.23 ± 0.02R_⊙, L₁ = 18 ± 3 L_⊙ and L₂ = 6 ± 1 L_⊙. The distance to V535 Ara was calculated as 123 ± 20 pc using distance modulus with correction for interstellar extinction.     

The extreme physical properties of the CoRoT-7b super-Earth

The search for rocky exoplanets plays an important role in our quest for extra-terrestrial life. Here, we discuss the extreme physical properties possible for the first characterised rocky super-Earth, CoRoT-7b (R_pl = 1.58 ± 0.10 R_Earth, M_pl = 6.9 ± 1.2 M_Earth). It is extremely close to its star (a = 0.0171 AU = 4.48 R_st), with its spin and orbital rotation likely synchronised. The comparison of its location in the (M_pl, R_pl) plane with the predictions of planetary models for different compositions points to an Earth-like composition, even if the error bars of the measured quantities and the partial degeneracy of the models prevent a definitive conclusion. The proximity to its star provides an additional constraint on the model. It implies a high extreme-UV flux and particle wind, and the corresponding efficient erosion of the planetary atmosphere especially for volatile species including water. Consequently, we make the working hypothesis that the planet is rocky with no volatiles in its atmosphere, and derive the physical properties that result. As a consequence, the atmosphere is made of rocky vapours with a very low pressure (P ? 1.5 Pa), no cloud can be sustained, and no thermalisation of the planet is expected. The dayside is very hot (2474 ± 71 K at the sub-stellar point) while the nightside is very cold (50-75 K). The sub-stellar point is as hot as the tungsten filament of an incandescent bulb, resulting in the melting and distillation of silicate rocks and the formation of a lava ocean. These possible features of CoRoT-7b could be common to many small and hot planets, including the recently discovered Kepler-10b. They define a new class of objects that we propose to name “Lava-ocean planets”.     

Absolute properties of the neglected eclipsing B-type binary HD 194495

We present the results of the high-resolution spectroscopic observations of the neglected binary system HD 194495 (B3 IV-V+B4 V). A combined analysis of three different photometric data set (Tycho B_T and V_T photometry, H_p-band data of Hipparcos and V-band data of ASAS3 photometry) and radial velocities indicates that the system has an orbital period of 4.90494 ± 0.00005 days and an inclination of 69 ± 1 degrees. This solution yields masses and radii of M₁ = 7.57 ± 0.08 M_⊙ and R₁ = 5.82 ± 0.03 R_⊙ for the primary and M₂ = 5.46 ± 0.09 M_⊙ and R₂ = 3.14 ± 0.08 R_⊙ for the secondary. Based on the position of the two stars plotted on a theoretical H-R diagram, we find that the age of the system is ?28 Myr, according to stellar evolutionary models. The spectroscopic and photometric results are in agreement with those obtained using theoretical predictions.     

Kinematics of stellar populations with RAVE data

We study the kinematics of the Galactic thin and thick disk populations using stars from the RAVE survey’s second data release together with distance estimates from Breddels et al. (2010). The velocity distribution exhibits the expected moving groups present in the solar neighborhood. We separate thick and thin disk stars by applying the X (stellar-population) criterion of Schuster et al. (1993), which takes into account both kinematic and metallicity information. For 1906 thin disk and 110 thick disk stars classified in this way, we find a vertical velocity dispersion, mean rotational velocity and mean orbital eccentricity of (σ_W, 〈V_Φ〉, 〈e〉)_thin = (18 ± 0.3 km s⁻¹, 223 ± 0.4 km s⁻¹, 0.07 ± 0.07) and (σ_W, 〈V_Φ〉, 〈e〉)_thick = (35 ± 2 km s⁻¹, 163 ± 3 km s⁻¹, 0.31 ± 0.16), respectively. From the radial Jeans equation, we derive a thick disk scale length in the range 1.5-2.2 kpc, whose greatest uncertainty lies in the adopted form of the underlying potential. The shape of the orbital eccentricity distribution indicates that the thick disk stars in our sample most likely formed in situ with minor gas-rich mergers and/or radial migration being the most likely cause for their orbits. We further obtain mean metal abundances of 〈[M/H]〉_thin = +0.03 ± 0.17, and 〈[M/H]〉_thick = −0.51 ± 0.23, in good agreement with previous estimates. We estimate a radial metallicity gradient in the thin disk of −0.07 dex kpc⁻¹, which is larger than predicted by chemical evolution models where the disk grows inside-out from infalling gas. It is, however, consistent with models where significant migration of stars shapes the chemical signature of the disk, implying that radial migration might play at least part of a role in the thick disk’s formation.     

A comprehensive photometric study of the marginal-contact binary BE Cephei

New photometry for the eclipsing binary BE Cephei was performed from 2008 to 2011. The light-curve synthesis indicates that it is a marginal-contact binary with a mass ratio of q = 2.340(±0.009) and a degree of contact of f = 6.9%(±2.3%). From the O − C curve, it is discovered that the orbital period changes show a sinusoidal curve superimposed on a downward parabola. The period and semi-amplitude of the cyclic variation are P_mod = 59.26(±0.52) yr and A = 0.^d0067(±0.^d0010), which may be possibly attributed to light-time effect via the presence of an unseen third body. The long-term period decreases at a rate of dP/dt = −4.84(±0.31) × 10⁻⁸ d yr⁻¹, which may result from mass transfer from the more massive component to the less massive one, accompanied by angular momentum loss. With the period decreasing, the degree of contact will increase. Finally, the marginal-contact binary BE Cep may be evolving into a deep-contact configuration.     

Archival HST study of novae. I. The Seyfert galaxy NGC 3627

A V-band nova search was carried out in NGC 3627 with archival Hubble Space Telescope WFPC2 data which was obtained in the period between November 1997 and January 1998. A total of four novae candidates were discovered which corresponds to a global nova rate of R = 83.65 ± 7.58 yr⁻¹. Taking into account the K-band luminosity obtained from 2MASS (Jarrett et al., 2003) yielded a luminosity specific nova rate (LSNR) of ν_K = 9.60 ± 1.64 novae per year per 10¹⁰L_⊙,K. Excluding one of the candidates which may be a long-period variable leads to a LSNR of ν_K = 7.20 ± 1.23 novae per year per 10¹⁰L_⊙,K. These values are higher than other known nova rates for external galaxies except the Magellanic Clouds.     

Photometric observations and orbital period variations of HS 0705 + 6700 and NY Vir

We present photometric observations of two post-common-envelope stars, NY Vir (=PG 1336-018) and HS 0705 + 6700. The V band CCD observation of NY Vir was performed by a 40 cm telescope at Ege University Observatory and the R band observations of HS 0705 + 6700 were performed by 100 cm telescope at TÜB?TAK National Observatory. The new light curves were analyzed by the WD code and the physical parameters of stars were determined. We obtained new mid-eclipse timings for HS 0705 + 6700 and combined them with those previously published data. The analysis of the O-C residuals yields a period of about 8.06 ± 0.28 yr and an amplitude of 98.5 s for the system HS 0705 + 6700, which is attributed to the third star physically bounded to the evolved eclipsing pair. A mass function of 1.2 × 10⁻⁴ M_⊙ for the third star is obtained. The existence of a third star is also confirmed by the light curve analysis, indicating light contribution of about 0.043 at phase 0.25 in R-bandpass of the eclipsing pair. Using mass-luminosity relationship of the low mass stars we estimate a mass of 0.12 M_⊙ with an orbital inclination of about 20°. The O-C residuals obtained for the system NY Vir were represented by a downward parabola which indicates orbital period decrease in the system. Using the coefficient of quadratic term we calculate a rate of orbital period decrease of about dP/dt = −4.09 × 10⁻⁸days yr⁻¹. The period decrease we have measured in NY Vir may be explained by angular momentum loss from the binary system.     

The orbital period and negative superhumps of the nova-like cataclysmic variable V378 Pegasi

A radial velocity study is presented of the cataclysmic variable V378 Pegasi (PG 2337 + 300). It is found to have an orbital period of 0.13858 ± 0.00004 d (3.32592 ± 0.00096 h). Its spectrum and long-term light curve suggest that V378 Peg is a nova-like variable, with no outbursts. We use the approximate distance and position in the Galaxy of V378 Peg to estimate E(B − V) = 0.095, and use near-infrared magnitudes to calculate a distance of 680 ± 90 pc and M_V = 4.68 ± 0.70, consistent with V378 Peg being a nova-like. Time-resolved photometry taken between 2001 and 2009 reveals a period of 0.1346 ± 0.0004 d (3.23 ± 0.01 h). We identify this photometric variability to be negative superhumps, from a precessing, tilted accretion disk. Our repeated measurements of the photometric period of V378 Peg are consistent with this period having been stable between 2001 and 2009, with its negative superhumps showing coherence over as many as hundreds or even thousands of cycles.     

A possible YORP effect on C and S Main Belt Asteroids

A rotating frequency analysis in a previous paper, showed that two samples of C and S-type asteroids belonging to the Main Belt, but not to any families, present two different values for the transition diameter to a Maxwellian distribution of the rotation frequency, respectively 48 and 33 km. In this paper, after a more detailed statistical analysis, aiming to verify that the result is physically relevant, we found a better estimate for the transition diameter, respectively D_C = 44 ± 2 km and D_S = 30 ± 1 km. The ratio between these estimated transition diameters, D_C/D_S = 1.5 ± 0.1, can be supported with the help of the YORP (Yarkovsky-O’Keefe-Radzievskii-Paddack) effect, although other physical causes cannot be completely ruled out.In this paper we have derived a simple scaling law for YORP which, taking into account the different average heliocentric distance, the bulk density, the albedo and the asteroid “asymmetry surface factor”, has enabled us to reasonably justify the ratio between the diameters transition of C-type and S-type asteroids. The same scaling law can be used to estimate a new ratio between the bulk densities of S and C asteroids samples (giving ρ_S/ρ_C ≈ 2.9 ± 0.3), and can explain why the asteroids near the transition diameter have about the same absolute magnitude. For C-type asteroids, using the found density ratio and other estimates of S-type density, it is also possible to estimate an average bulk density equal to 0.9 ± 0.1 g cm⁻³, a value compatible with icy composition. The suggested explanation for the difference of the transition diameters is a plausible hypothesis, consistent with the data, but it needs to be studied more in depth with further observations.     

The thermal and physical characteristics of the Gao-Guenie (H5) meteorite

Measurements of the bulk density, grain density, porosity, and magnetic susceptibility of 19 Gao-Guenie H5 chondrite meteorite samples are presented. We find average values of bulk density 〈ρ_bulk〉=3.46±0.07 g/cm³, grain density 〈ρ_grain〉=3.53±0.08 g/cm³, porosity 〈P(%)〉=2.46±1.39, and bulk mass magnetic susceptibility 〈log χ〉=5.23±0.11. Measurements of the specific heat capacity for a 3.01-g Gao-Guenie sample, a 61.37-g Gao-Guenie sample, a 62.35-g Jilin H5 chondrite meteorite sample, and a 51.37-g Sikhote-Alin IIAB Iron meteorite sample are also presented. Temperature interpolation formula are further provided for the specific heat capacity, thermal conductivity, and thermal diffusivity of the 3.01-g Gao-Guenie sample in the temperature range 300<T (K)<800. We briefly review the possible effects of the newly deduced specific heat and thermal conductivity values on the ablation of meteoroids within the Earth's atmosphere, the modeling of asteroid interiors and the orbital evolution of meteoroids through the Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect.     

Differences between the two types Seyfert 2 galaxies - With and without polarized broad lines

Based on spectropolarimetric observations Seyfert 2 (Sy2) galaxies are generally divided into two populations. Some Sy2s show polarized broad emission lines (PBLs) which is an evidence for the hypothesis of the Unified model while others do not. In order to determine the properties of these two apparently different populations we compiled a sample of 66 Sy2 objects with and without detected PBLs. We used a (J − H) − (H − K_s) diagram based on 2MASS J, H, K_s magnitudes in 14 arcsec aperture, the F_[OIII] emission line flux and the infrared emission flux F_Ks using the K_s filter. From the (J − H) − (H − K_s) diagram we determined that one third of the Sy2 objects with PBLs have a power-law infrared component which could be a result of both a non-thermal AGN component scattered by free electrons (or dust) and emission from hot dust near its sublimation temperature. The rest of the objects (with PBLs) are significantly dominated by a dust thermal re-emission. The Sy2s without PBLs show infrared emission dominated by a host galaxy stellar component and also by thermal dust re-emission. The Sy2s with PBLs tend to have a few times larger L_[OIII] luminosities than those without. Following the median values of F_[OIII]/F_Ks, it seems that this ratio is sensitive enough to separate our sample of Sy2 galaxies into two types - with and without PBLs. There are no Sy2s with PBLs having Eddington ratio below 10⁻³ which confirms the results of Nicastro et al. (2003).     

Micrometer-sized ice particles for planetary-science experiments - I. Preparation, critical rolling friction force, and specific surface energy

Coagulation models assume a higher sticking threshold for micrometer-sized ice particles than for micrometer-sized silicate particles. However, in contrast to silicates, laboratory investigations of the collision properties of micrometer-sized ice particles (in particular, of the most abundant H₂O-ice) have not been conducted yet. Thus, we used two different experimental methods to produce micrometer-sized H₂O-ice particles, i.e. by spraying H₂O droplets into liquid nitrogen and by spraying H₂O droplets into a cold nitrogen atmosphere. The mean particle radii of the ice particles produced with these experimental methods are (1.49 ± 0.79) μm and (1.45 ± 0.65) μm. Ice aggregates composed of the micrometer-sized ice particles are highly porous (volume filling factor: ? = 0.11 ± 0.01) or rather compact (volume filling factor: ? = 0.72 ± 0.04), depending on the method of production. Furthermore, the critical rolling friction force of F_Roll,ice = (114.8 ± 23.8) × 10⁻¹⁰ N was measured for micrometer-sized ice particles, which exceeds the critical rolling friction force of micrometer-sized SiO₂ particles . This result implies that the adhesive bonding between micrometer-sized ice particles is stronger than the bonding strength between SiO₂ particles. An estimation of the specific surface energy of micrometer-sized ice particles, derived from the measured critical rolling friction forces and the surface energy of micrometer-sized SiO₂ particles, results in γ_ice = 0.190 J m⁻².     

Using the youngest asteroid clusters to constrain the space weathering and gardening rate on S-complex asteroids

We have extended our earlier work on space weathering of the youngest S-complex asteroid families to include results from asteroid clusters with ages <10⁶ years and to newly identified asteroid pairs with ages <5 × 10⁵ years. We have identified three S-complex asteroid clusters amongst the set of clusters with ages in the range 10^5-6 years—(1270) Datura, (21509) Lucascavin and (16598) 1992 YC2. The average color of the objects in these clusters agrees with the color predicted by the space weathering model of Willman et al. (Willman, M., Jedicke, R., Nesvorný, D., Moskovitz, N., Ivezi?, Z., Fevig, R. [2008]. Icarus 195, 663-673). SDSS five-filter photometry of the members of the very young asteroid pairs with ages <10⁵ years was used to determine their taxonomic classification. Their types are consistent with the background population near each object. The average color of the S-complex pairs is PC₁ = 0.49 ± 0.03, over 5σ redder than predicted by Willman et al. (Willman, M., Jedicke, R., Nesvorný, D., Moskovitz, N., Ivezi?, Z., Fevig, R. [2008]. Icarus 195, 663-673). This may indicate that the most likely pair formation mechanism is a gentle separation due to YORP spin-up leaving much of the aged and reddened surface undisturbed. If this is the case then our color measurement allows us to set an upper limit of ∼64% on the amount of surface disturbed in the separation process. Using pre-existing color data and our new results for the youngest S-complex asteroid clusters we have extended our space weather model to explicitly include the effects of regolith gardening and fit separate weathering and gardening characteristic time scales of τ_w = 960 ± 160 Myr and τ_g = 2000 ± 290 Myr respectively. The first principal component color for fresh S-complex material is PC₁ = 0.37 ± 0.01 while the maximum amount of local reddening is ΔPC₁ = 0.33 ± 0.06. Our first-ever determination of the gardening time is in stark contrast to our calculated gardening time of τ_g ∼ 270 Myr based on main belt impact rates and reasonable assumptions about crater and ejecta blanket sizes. A possible resolution for the discrepancy is through a ‘honeycomb’ mechanism in which the surface regolith structure absorbs small impactors without producing significant ejecta. This mechanism could also account for the paucity of small craters on (433) Eros.     

The cool surfaces of binary near-Earth asteroids

Here we show results from thermal-infrared observations of km-sized binary near-Earth asteroids (NEAs). We combine previously published thermal properties for NEAs with newly derived values for three binary NEAs. The η value derived from the near-Earth asteroid thermal model (NEATM) for each object is then used to estimate an average thermal inertia for the population of binary NEAs and compared against similar estimates for the population of non-binaries. We find that these objects have, in general, surface temperatures cooler than the average values for non-binary NEAs as suggested by elevated η values. We discuss how this may be evidence of higher-than-average surface thermal inertia. This latter physical parameter is a sensitive indicator of the presence or absence of regolith: bodies covered with fine regolith, such as the Earth’s moon, have low thermal inertia, whereas a surface with little or no regolith displays high thermal inertia. Our results are suggestive of a binary formation mechanism capable of altering surface properties, possibly removing regolith: an obvious candidate is the YORP effect.We present also newly determined sizes and geometric visible albedos derived from thermal-infrared observations of three binary NEAs: (5381) Sekhmet, (153591) 2001 SN₂₆₃, and (164121) 2003 YT₁. The diameters of these asteroids are 1.41 ± 0.21 km, 1.56 ± 0.31 km, and 2.63 ± 0.40 km, respectively. Their albedos are 0.23 ± 0.13, 0.24 ± 0.16, and 0.048 ± 0.015, respectively.