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This paper discusses the B?ohm-Vitense gap, a gap in the colours of stars that occurs when the atmosphere changes from radiative to convective in deep layers. We are using different algorithms for detecting gaps in colour-magnitude diagrams (CMDs), including the k-nearest neighbours (k-NN) and UniDip algorithms. We propose using a combination of the k-NN algorithm and the UniDip algorithm and manual verification to identify gaps unlikely to be of a statistical origin. Using the Gaia photometric system, i.e. BP - RP, we took the data of 130 star clusters and searched for gaps in the ranges of 0.40 to 0.47mag, and 0.56 to 0.60mag, respectively. We analysed all data statistically and identified the gaps in the individual clusters. Finally, we applied the kernel density estimator to see how the gaps are distributed. [ABSTRACT FROM AUTHOR]

Focuses on color change of stars. Factors which determines how stars appear to space travelers; Power spectrum of light emitted by stars; Effect of the Doppler shift on the spectrum; How humans perceived the color of various spectra; Relativistic doppler shift; Employing color matching technique in determining the visual appearance of star color.

Parallaxes with an accuracy better than 10% and proper motions from the Gaia DR1 TGAS catalogue, radial velocities from the Pulkovo Compilation of Radial Velocities (PCRV), accurate Tycho-2 photometry, theoretical PARSEC, MIST, YaPSI, BaSTI isochrones, and the most accurate reddening and interstellar extinction estimates have been used to analyze the kinematics of 9543 thin-disk B-F stars as a function of their dereddened color. The stars under consideration are located on the Hertzsprung-Russell diagram relative to the isochrones with an accuracy of a few hundredths of a magnitude, i.e., at the level of uncertainty in the parallax, photometry, reddening, extinction, and the isochrones themselves. This has allowed us to choose the most plausible reddening and extinction estimates and to conclude that the reddening and extinction were significantly underestimated in some kinematic studies of other authors. Owing to the higher accuracy of TGAS parallaxes than that of Hipparcos ones, the median accuracy of the velocity components U, V, W in this study has improved to 1.7 km s−1, although outside the range −0.1m < (BT − VT)0 < 0.5m the kinematic characteristics are noticeably biased due to the incompleteness of the sample. We have confirmed the variations in the mean velocity of stars relative to the Sun and the stellar velocity dispersion as a function of their dereddened color known from the Hipparcos data. Given the age estimates for the stars under consideration from the TRILEGAL model and the Geneva-Copenhagen survey, these variations may be considered as variations as a function of the stellar age. A comparison of our results with the results of other studies of the stellar kinematics near the Sun has shown that selection and reddening underestimation explain almost completely the discrepancies between the results. The dispersions and mean velocities from the results of reliable studies fit into a ±2 km s−1 corridor, while the ratios σV/σU and σW/σU fit into ±0.05. Based on all reliable studies in the range −0.1m < (BT − VT)0 < 0.5m, i.e., for an age from 0.23 to 2.4 Gyr, we have found: W⊙ = 7.15 km s−1, σU=16.0e1.29(BT−VT)ο, σV=10.9e1.11(BT−VT)ο, σW=6.8e1.46(BT−VT)ο, the stellar velocity dispersions in km s−1 are proportional to the age in Gyr raised to the power βU = 0.33, βV = 0.285, and βW = 0.37. [ABSTRACT FROM AUTHOR]

We present mock optical images, broad-band and Hα fluxes, and D4000 spectral indices for 30 145 galaxies from the EAGLE hydrodynamical simulation at redshift z = 0.1, modelling dust with the SKIRT Monte Carlo radiative transfer code. The modelling includes a subgrid prescription for dusty star-forming regions, with both the subgrid obscuration of these regions and the fraction of metals in diffuse interstellar dust calibrated against far-infrared fluxes of local galaxies. The predicted optical colours as a function of stellar mass agree well with observation, with the SKIRT model showing marked improvement over a simple dust-screen model. The orientation dependence of attenuation is weaker than observed because EAGLE galaxies are generally puffier than real galaxies, due to the pressure floor imposed on the interstellar medium (ISM). The mock Hα luminosity function agrees reasonably well with the data, and we quantify the extent to which dust obscuration affects observed Hα fluxes. The distribution of D4000 break values is bimodal, as observed. In the simulation, 20 per cent of galaxies deemed 'passive' for the SKIRT model, i.e. exhibiting D4000 >1.8, are classified 'active' when ISM dust attenuation is not included. The fraction of galaxies with stellar mass greater than 1010 M⊙ that are deemed passive is slightly smaller than observed, which is due to low levels of residual star formation in these simulated galaxies. Colour images, fluxes and spectra of EAGLE galaxies are to be made available through the public EAGLE data base. [ABSTRACT FROM AUTHOR]

Context: Mode identification has remained a major obstacle in the interpretation of pulsation spectra in rapidly rotating stars. This has motivated recent work on calculating realistic multi-colour mode visibilities in this type of star. Aims: We would like to test mode identification methods and seismic diagnostics in rapidly rotating stars, using oscillation spectra that are based on these new theoretical predictions. Methods: We investigate the auto-correlation function and Fourier transform of theoretically calculated frequency spectra, in which modes are selected according to their visibilities. Given that intrinsic mode amplitudes are determined by non-linear saturation and cannot currently be theoretically predicted, we experimented with various ad-hoc prescriptions for setting the mode amplitudes, including using random values. Furthermore, we analyse the ratios between mode amplitudes observed in different photometric bands to see up to what extent they can identify modes. Results: When non-random intrinsic mode amplitudes are used, our results show that it is possible to extract a mean value for the large frequency separation or half its value and, sometimes, twice the rotation rate, from the auto-correlation of the frequency spectra. Furthermore, the Fourier transforms are mostly sensitive to the large frequency separation or half its value. The combination of the two methods may therefore measure and distinguish the two types of separations. When the intrinsic mode amplitudes include random factors, which seems more representative of real stars, the results are far less favourable. It is only when the large separation or half its value coincides with twice the rotation rate, that it might be possible to detect the signature of a frequency regularity. We also find that amplitude ratios are a good way of grouping together modes with similar characteristics. By analysing the frequencies of these groups, it is possible to constrain mode identification, as well as determine the large frequency separation and the rotation rate. [ABSTRACT FROM AUTHOR]

We present the effective temperatures (Teff), metallicities, and colours in Sloan Digital Sky Survey (SDSS), Two Micron All Sky Survey, andWide-field Infrared Survey Explorer filters, of a sample of 3834 late-K and early-M dwarfs selected from the SDSS Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectroscopic survey ASPCAP (APOGEE Stellar Parameters and Chemical Abundances Pipeline) catalogue. We confirm that ASPCAP Teff values between 3550 < Teff < 4200 K are accurate to ~100 K compared to interferometric Teff values. In that same Teff range, ASPCAP metallicities are accurate to 0.18 dex between -1.0 <[M/H]<0.2. For these cool dwarfs, nearly every colour is sensitive to both Teff and metallicity. Notably, we find that g - r is not a good indicator of metallicity for near-solar metallicity early-M dwarfs. We confirm that J - KS colour is strongly dependent on metallicity, and find that W1 - W2 colour is a promising metallicity indicator. Comparison of the late-K and early-M dwarf colours, metallicities, and Teff to those from three different model grids shows reasonable agreement in r - z and J - KS colours, but poor agreement in u - g, g - r, and W1 - W2. Comparison of the metallicities of the KM dwarf sample to those from previous colour-metallicity relations reveals a lack of consensus in photometric metallicity indicators for late-K and early-M dwarfs. We also present empirical relations for Teff as a function of r - z colour combined with either [M/H] or W1 - W2 colour, and for [M/H] as a function of r - z and W1 - W2 colour. These relations yield Teff to ~100 K and [M/H] to ~0.18 dex precision with colours alone, for Teff in the range of 3550-4200 K and [M/H] in the range of -0.5-0.2. [ABSTRACT FROM AUTHOR]

We revisit the subject of Be candidate stars towards the Magellanic Clouds, previously studied by the authors using SPM4 proper motions. We obtain Gaia DR2 parallaxes and proper motions for 2357 and 994 LMC and SMC Be candidates, respectively. Parallaxes and proper motions versus colour V − I easily reveal the presence of the redder galactic contaminant foreground, as concluded in our previous work, but this time we do find a few red Be candidates consistent with being true Magellanic objects. A membership assessment to each Magellanic Cloud is done for each Be candidate, based on the distribution of their parallaxes and proper motions. From a compilation of published catalogues of spectroscopically confirmed emission line stars,we find that 41 (LMC) and 56 (SMC) of the Be candidates have shown the H α line in emission. Near-infrared IRSF JHKs magnitudes are obtained for about 70 per cent of the Be candidates with Gaia DR2 astrometric data. Mid-infrared SAGE IRAC 3.6, 4.5, 5.8, and 8.0 |$\mu$| m magnitudes are obtained for about 85 per cent as well. After discarding possible Herbig Ae/Be stars, one LMC and three SMC B emission line confirmed stars show significantly redder optical, near- and mid-infrared colours than what has been typically measured for Classical Be stars – they are called red Be stars. Taking into account that classical Be stars do not show these red colours, further studies about these four stars are needed in order to establish their true nature and explain the observed red excess. [ABSTRACT FROM AUTHOR]

A star coloring of a graph G is a proper vertex coloring in which every path on four vertices in G is not bicolored. The star chromatic number Xs (G) of G is the least number of colors needed to star color G. In this paper, we determine the star chromatic number of lexicographic product of complete graph with complete graph Km[Kn], complete graph with wheel graph Km[Wn], complete graph with path Km[Pn] and path with path Pm[Pn]. [ABSTRACT FROM AUTHOR]

An acyclic coloring of a graph G is a proper vertex coloring such that G contains no bicolored cycles. The more restricted notion of star coloring of G is an acyclic coloring in which each path of length 3 is not bicolored. In this paper, we mainly study on the acyclic and star coloring of P 4 -reducible and P 4 -sparse graphs. Moreover, we list polynomial-time algorithms for giving an optimal acyclic or star coloring of a P 4 -reducible or P 4 -sparse graph. [ABSTRACT FROM AUTHOR]

Mass-to-light versus colour relations (MLCRs), derived from stellar population synthesis models, are widely used to estimate galaxy stellar masses (M*), yet a detailed investigation of their inherent biases and limitations is still lacking. We quantify several potential sources of uncertainty, using optical and near-infrared (NIR) photometry for a representative sample of nearby galaxies from the Virgo cluster. Our method for combining multiband photometry with MLCRs yields robust stellar masses, while errors in M* decrease as more bands are simultaneously considered. The prior assumptions in one's stellar population modelling dominate the error budget, creating a colour-dependent bias of up to 0.6 dex if NIR fluxes are used (0.3 dex otherwise). This matches the systematic errors associated with the method of spectral energy distribution (SED) fitting, indicating that MLCRs do not suffer from much additional bias. Moreover, MLCRs and SED fitting yield similar degrees of random error (~0.1-0.14 dex) when applied to mock galaxies and, on average, equivalent masses for real galaxies with M* ~ 108-11 M⊙. The use of integrated photometry introduces additional uncertainty in M* measurements, at the level of 0.05-0.07 dex. We argue that using MLCRs, instead of time-consuming SED fits, is justified in cases with complex model parameter spaces (involving, for instance, multiparameter star formation histories) and/or for large data sets. Spatially resolved methods for measuring M* should be applied for small sample sizes and/or when accuracies less than 0.1 dex are required. An appendix provides our MLCR transformations for 10 colour permutations of the grizH filter set. [ABSTRACT FROM AUTHOR]

As a major component of the LAMOST Galactic surveys, the LAMOST Spectroscopic Survey of the Galactic Anticentre (LSS-GAC) aims to survey a significant volume of the Galactic thin/thick discs and halo for a contiguous sky area of over 3400 deg2 centred on the Galactic anticentre (|b| ≤ 30°, 150 ≤ l ≤ 210°), and obtain λλ3700–9000 low-resolution (R ∼ 1800) spectra for a statistically complete sample of ∼3 M stars of all colours down to a limiting magnitude of r ∼ 17.8 mag (to 18.5 mag for limited fields). Together with Gaia, the LSS-GAC will yield a unique data set to advance our understanding of the structure and assemblage history of the Galaxy, in particular its disc(s). In addition to the main survey, the LSS-GAC will also target hundreds of thousands objects in the vicinity fields of M 31 and M 33 and survey a significant fraction (over a million) of randomly selected very bright stars (r ≤ 14 mag) in the Northern hemisphere. During the Pilot and the first year Regular Surveys of LAMOST, a total of 1042 586 [750 867] spectra of a signal-to-noise ratio S/N(7450 Å) ≥ 10 [S/N(4650 Å) ≥ 10] have been collected. In this paper, we present a detailed description of the target selection algorithm, survey design, observations and the first data release of value-added catalogues (including radial velocities, effective temperatures, surface gravities, metallicities, values of interstellar extinction, distances, proper motions and orbital parameters) of the LSS-GAC. [ABSTRACT FROM PUBLISHER]

Binks & Jeffries and Malo et al. have recently reported Li depletion boundary (LDB) ages for the β Pictoris moving group (BPMG) which are twice as old as the oft-cited kinematic age of ∼12 Myr. In this study, we present (1) a new evaluation of the internal kinematics of the BPMG using the revised Hipparcos astrometry and best available published radial velocities, and assess whether a useful kinematic age can be derived, and (2) derive an isochronal age based on the placement of the A-, F-, and G-type stars in the colour–magnitude diagram (CMD). We explore the kinematics of the BPMG looking at velocity trends along Galactic axes, and conducting traceback analyses assuming linear trajectories, epicyclic orbit approximation, and orbit integration using a realistic gravitational potential. None of the methodologies yield a kinematic age with small uncertainties using modern velocity data. Expansion in the Galactic X and Y directions is significant only at the 1.7σ and 2.7σ levels, and together yields an overall kinematic age with a wide range (13–58 Myr; 95 per cent CL). The A-type members are all on the zero-age main sequence, suggestive of an age of >20 Myr, and the loci of the CMD positions for the late-F- and G-type pre-main-sequence BPMG members have a median isochronal age of 22 Myr (± 3 Myr statistical, ±1 Myr systematic) when considering four sets of modern theoretical isochrones. The results from recent LDB and isochronal age analyses are now in agreement with a median BPMG age of 23 ± 3 Myr (overall 1σ uncertainty, including ±2 Myr statistical and ±2 Myr systematic uncertainties). [ABSTRACT FROM AUTHOR]

We analyse Galactic, Large Magellanic Cloud and Small Magellanic Cloud Cepheids and RR Lyrae variables in terms of period–colour (PC) and amplitude–colour (AC) diagrams at the phases of maximum and minimum light. We compiled Galactic Cepheids V- and I-band data from the literature. We make use of optical bands light-curve data from OGLE-III survey for Cepheids and RR Lyrae variables in the Magellanic Clouds. We apply the F-statistical test to check the significance of any variation in the slope of PC and AC relations for Cepheid variables. The PC relation at maximum light for Galactic Cepheids with periods longer than about 7 d is shallow and the corresponding AC relation is flat for the entire period range. For the fundamental mode Cepheids in the Magellanic Clouds, we find significant breaks in the PC and AC relations at both maximum and minimum light for periods around 10 d. The PC relation at maximum light for the Magellanic Clouds is flat for Cepheids with periods greater than 10 d. First overtone Cepheids with periods less than 2.5 d have a shallow PC relation at minimum light. For fundamental mode RR Lyraes, we confirm earlier work supporting a flat PC relation at minimum light and a significant relation between amplitude and colour at maximum light. We find that no such relations exist for first overtone RR Lyrae stars. These findings are in agreement with stellar photosphere/hydrogen ionization front interaction considerations. These non-linearities can provide strong constraints for models of stellar pulsation and evolution. [ABSTRACT FROM AUTHOR]

We present 17 high-precision light curves of five transits of the planet Qatar-2 b, obtained from four defocused 2 m-class telescopes. Three of the transits were observed simultaneously in the Sloan g′r′i′z′ passbands using the seven-beam Gamma Ray Burst Optical and Near-Infrared Detector imager on the MPG/ESO 2.2-m telescope. A fourth was observed simultaneously in Gunn grz using the Centro Astronómico Hispano Alemán 2.2-m telescope with Bonn University Simultaneous Camera, and in r using the Cassini 1.52-m telescope. Every light curve shows small anomalies due to the passage of the planetary shadow over a cool spot on the surface of the host star. We fit the light curves with the prism+gemc model to obtain the photometric parameters of the system and the position, size and contrast of each spot. We use these photometric parameters and published spectroscopic measurements to obtain the physical properties of the system to high precision, finding a larger radius and lower density for both star and planet than previously thought. By tracking the change in position of one star-spot between two transit observations, we measure the orbital obliquity of Qatar-2 b to be λ = 4 $_{.}^{\circ}$3 ± 4 $_{.}^{\circ}$5, strongly indicating an alignment of the stellar spin with the orbit of the planet. We calculate the rotation period and velocity of the cool host star to be 11.5 ± 0.2 d and 3.28 ± 0.04 km s−1 at a colatitude of 74°. We assemble the planet's transmission spectrum over the 386–976 nm wavelength range and search for variations of the measured radius of Qatar-2 b as a function of wavelength. Our analysis highlights a possible H2/He Rayleigh scattering in the blue. [ABSTRACT FROM PUBLISHER]

We investigate the effect of color superconductivity on the non-radial oscillations of pure self-bound quark stars using an equation of state in the framework of the MIT bag model. The equations of non-radial oscillations are integrated within the Cowling approximation in order to determine the frequency of the fundamental mode and of the first and second pressure modes. We employ several parametrizations of the equation of state that result in a maximum mass larger than the mass of the recently observed PSR J1614-2230 and PSR J0348-0432 with M ≈ 2 M⊙. The pulsation frequencies are compared with the corresponding modes of quark stars without pairing. For the fundamental mode, the oscillation frequency is typically 2-3 kHz. Parametrizations of the equations of state with larger values of the pairing gap Δ tend to give smaller values of the frequency. For the first and second pressure modes, the frequencies lie in the range 5-10 kHz for stars with masses above 1.5 M⊙ and diverge as the mass of the star tends to zero. From the numerical results we obtain parabolic fittings of the frequency of the fundamental mode as a function of the gravitational redshift at the surface of the star. For the p1 and p2 modes we find power law fittings that are rather independent of the parametrization of the equations of state. The here obtained results can be used to extract details about the internal composition of compact stars from observed modes of pulsation. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Changes in the brightness and color of stars obscured by gas-dust protoplanets are studied using Equation (1). In a quite general case, assuming only that τ(x, y)∈[0, τ ] , it is shown that the ratio $ {{{\left( {\Delta m_2^{\min }-\Delta m_1^{\min }} \right)}} \left/ {{\Delta m_1^{\min }}} \right.} $ decreases with increasing $ \Delta m_1^{\min } $ at the brightness minima. The region where points from the set {E; E} can lie on an E vs E diagram is localized within a rather narrow parallelogram with a long diagonal given by Eq. (10). If $ \uptau \left( {x,y} \right)={\uptau^{\max }}\sqrt{{1-{{{\left( {{x^2}+{y^2}} \right)}} \left/ {{{R^2}}} \right.}}} $, then the unknown E as a function of E is essentially given by Eq. (10). Calculated 'brightness-color' curves are fundamentally different from the interstellar absorption law. If it is held that the color indices increase linearly in Ae/Be Herbig stars with falling brightness, i.e., $ {{{\left( {\Delta {m_2}-\Delta {m_1}} \right)}} \left/ {{\Delta {m_1}=\mathrm{const}}} \right.} $, and that this ratio is independent of the depth of eclipsing, then it appears that the Algol-like variation in the brightness of Ae/Be Herbig stars cannot be explained in terms of a model of occultation by a protoplanet. [ABSTRACT FROM AUTHOR]

MAIA, an acronym for Mercator Advanced Imager for Asteroseismology, is a three-channel instrument that targets fast-cadence threecolour photometry, installed at the 1.2-m Mercator telescope at the Roque de los Muchachos at La Palma (Canary Islands, Spain). This instrument observes a 9:4 × 14.1 arcmin2 field-of-view simultaneously in three wavelength bands on three large frame-transfer CCDs. These detectors were developed for ESA's cancelled Eddington space mission and were o ered on permanent loan to the Institute of Astronomy (KU Leuven, Belgium). MAIA uses its own ugr photometric system that is a crude approximation of the SDSS system. The instrument is designed to perform multi-colour observations for asteroseismology, with specific emphasis on subdwarf and white dwarf single and binary stars. We describe the design of the instrument, discuss key components, and report on its performance and first results. [ABSTRACT FROM AUTHOR]

Highlights: [•] Photometric characterization of (101955) Bennu, target of the OSIRIS-REx mission, was conducted between the years 2005–2012. [•] The rotation period, ECAS colors, BVRI colors and phase function were determined. [•] Color photometry is consistent with being a primitive B-type carbonaceous asteroid. [•] A linear phase slope of 0.040±0.003 magnitudes per degree of phase angle is consistent with an albedo of 0.03–0.04. [ABSTRACT FROM AUTHOR]

Aims. With the aim of characterizing the flux and color variations of the multiple components of the gravitationally lensed quasar UM673 as a function of time, we have performed multiepoch and multiband photometric observations with the Danish 1.54 m telescope at the La Silla Observatory. Methods. The observations were carried out in the VRi spectral bands during four seasons (2008-2011). We reduced the data using the point spread function photometric technique as well as aperture photometry. Results. Our results show for the brightest lensed component some significant decrease in flux between the first two seasons (+0.09/+0.11/+0.05 mag) and a subsequent increase during the following ones (-0.11/-0.11/-0.10 mag) in the V/R/i spectral bands, respectively. Comparing our results with previous studies, we find smaller color variations between these seasons as compared with previous ones. We also separate the contribution of the lensing galaxy from that of the fainter and close lensed component. [ABSTRACT FROM AUTHOR]

Photometry in I, or contemporaneously in I and R, of the known variable ultracool dwarfs Kelu-1 and 2MASS J11553952−3727350 is presented. The nature of the variability of Kelu-1 appears to evolve on time-scales of a day or less. Both the period and amplitude of the variability of 2MASS J11553952−3727350 have changed substantially since publication of earlier observations of the object. DENIS 1454−6604 is a new variable ultracool dwarf, with persistent and prominent brightness modulations at a period of 2.6 h. [ABSTRACT FROM AUTHOR]

We introduce a method for constructing end-to-end mock galaxy catalogues using a semi-analytical model of galaxy formation, applied to the halo merger trees extracted from a cosmological N-body simulation. The mocks that we construct are lightcone catalogues, in which a galaxy is placed according to the epoch at which it first enters the past lightcone of the observer, and incorporate the evolution of galaxy properties with cosmic time. We determine the position between the snapshot outputs at which a galaxy enters the observer's lightcone by interpolation. As an application, we consider the effectiveness of the BzK colour selection technique, which was designed to isolate galaxies in the redshift interval 1.4 < z < 2.5. The mock catalogue is in reasonable agreement with the observed number counts of all BzK galaxies, as well as with the observed counts of the subsample of BzKs that are star-forming galaxies. We predict that over 75 per cent of the model galaxies with KAB ≤ 23, and 1.4 < z < 2.5, are selected by the BzK technique. Interloper galaxies, outside the intended redshift range, are predicted to dominate bright samples of BzK galaxies (i.e. with KAB ≤ 21). Fainter K-band cuts are necessary to reduce the predicted interloper fraction. We also show that shallow B-band photometry can lead to confusion in classifying BzK galaxies as being star forming or passively evolving. Overall, we conclude that the BzK colour selection technique is capable of providing a sample of galaxies that is representative of the 1.4 < z < 2.5 galaxy population. [ABSTRACT FROM AUTHOR]

The diverse behaviours displayed by X-ray binaries make it difficult to determine the nature of the underlying compact objects. In particular, identification of systems containing black holes is currently considered robust only if a dynamical mass is obtained. We explore a model-independent means of identifying the central bodies – neutron stars or black holes – of accreting binary systems. We find that four categories of object (classic black holes, GRS 1915-like black holes, pulsars and non-pulsing neutron stars) occupy distinct regions in a 3D colour–colour–intensity (CCI) diagram. Assuming that this clustering effect is due to intrinsic properties of the sources (such as mass-accretion rate, binary separation, mass ratio, magnetic field strength, etc.), we suggest possible physical effects that drive each object to its specific location in the CCI phase space. We also suggest a surface in this space which separates systems that produce jets from those which do not, and demonstrate the use of CCI for identifying X-ray pulsars where a period has not been established. This method can also be used to study subclustering within a category and may prove useful for other classes of objects, such as cataclysmic variables and active galactic nuclei. [ABSTRACT FROM AUTHOR]

We investigate the shape of the extinction law in two 1° square fields of the Perseus molecular cloud complex. We combine deep red-optical (r, i and z band) observations obtained using Megacam on the MMT with UKIRT (United Kingdom Infrared Telescope) Infrared Deep Sky Survey near-infrared (J, H and K band) data to measure the colours of background stars. We develop a new hierarchical Bayesian statistical model, including measurement error, intrinsic colour variation, spectral type and dust reddening, to simultaneously infer parameters for individual stars and characteristics of the population. We implement an efficient Markov chain Monte Carlo algorithm utilizing generalized Gibbs sampling to compute coherent probabilistic inferences. We find a strong correlation between the extinction (AV) and the slope of the extinction law (parametrized by RV). Because the majority of the extinction towards our stars comes from the Perseus molecular cloud, we interpret this correlation as evidence of grain growth at moderate optical depths. The extinction law changes from the ‘diffuse’ value of RV ∼ 3 to the ‘dense cloud’ value of RV ∼ 5 as the column density rises from AV = 2 to 10 mag. This relationship is similar for the two regions in our study, despite their different physical conditions, suggesting that dust grain growth is a fairly universal process. [ABSTRACT FROM PUBLISHER]

We have examined the relationship between the morphological types and the u-r, g-i, and r-z color indices of 365 pairs of galaxies with radial velocities 3000

Amethod for determining the most probable spectral types, color excesses E, and distances of stars from multicolor photometry is described. The main idea of the method is modeling the photometric data using various models for the stellar spectra and the interstellar extinction law, and applying the maximum likelihood method. The reliability of the method is estimated using stars with known spectral types and WBVR photometry, based on the empirical library of stellar spectra of Pickles and the model for the interstellar extinction law developed by Fluks et al. [ABSTRACT FROM AUTHOR]

Results from three-color photoelectric observations of the early-spectral type eclipsing-binary system V729 Cyg at the Abastumani Astrophysical Observatory are presented. These observations, the first for this star, covered the secondary maximum quite well and revealed a displacement of Max II to a phase of 0.80. There is reason to suspect that this phase shift reflects increasing activity of a mass flux in a common envelope. The light curves of V729 Cyg are unstable and asymmetric, and thereby create a maximum after the second minimum that is brighter than the first maximum. The spread in these points exceeds the measurement error. The observed fluctuations in the brightness are caused by the physical conditions in this system. There is no doubt that mass transfer has played an important role in the evolution of this system. [ABSTRACT FROM AUTHOR]

Context. The interpretation that bimodal colour distributions of globular clusters (GCs) reflect bimodal metallicity distributions has been challenged. Non-linearities in the colour to metallicity conversions caused for example by the horizontal branch (HB) stars may be responsible for transforming a unimodal metallicity distribution into a bimodal (optical) colour distribution. Aims. We study optical/near-infrared (NIR) colour distributions of the GC systems in 14 E/S0 galaxies. Methods. We test whether the bimodal feature, generally present in optical colour distributions, remains in the optical/NIR ones. The latter colour combination is a better metallicity proxy than the former. We use KMM and GMM tests to quantify the probability that different colour distributions are better described by a bimodal, as opposed to a unimodal distribution. Results. We find that double-peaked colour distributions are more commonly seen in optical than in optical/NIR colours. For some of the galaxies where the optical (g - z) distribution is clearly bimodal, a bimodal distribution is not preferred over a unimodal one at a statistically significant level for the (g- K) and (z- K) distributions. The two most cluster-rich galaxies in our sample, NGC4486 and NGC4649, show some interesting differences. The (g - K) distribution of NGC4649 is better described by a bimodal distribution, while this is true for the (g - K) distribution of NGC4486 GCs only if restricted to a brighter sub-sample with small K-band errors (<0.05 mag). Formally, the K-band photometric errors cannot be responsible for blurring bimodal metallicity distributions to unimodal (g - K) colour distributions. However, simulations including the extra scatter in the colour-colour diagrams (not fully accounted for in the photometric errors) show that such scatter may contribute to the disappearance of bimodality in (g - K) for the full NGC4486 sample. For the less cluster-rich galaxies results are inconclusive due to poorer statistics. Conclusions. A bimodal optical colour distribution is not necessarily an indication of an underlying bimodal metallicity distribution. Horizontal branch morphology may play an important role in shaping some of the optical GC colour distributions. However, we find tentative evidence that the (g - K) colour distributions remain bimodal in the two cluster-rich galaxies in our sample (NGC4486 and NGC4649) when restricted to clusters with small K-band photometric errors. This bimodality becomes less pronounced when including objects with larger errors, or for the (z - K) colour distributions. Deeper observations of large numbers of GCs will be required to reach more secure conclusions. [ABSTRACT FROM AUTHOR]

ABSTRACT In this work we present an atlas of composite spectra of galaxies based on the data of the Sloan Digital Sky Survey Data Release 7 (SDSS DR7). Galaxies are classified by colour, nuclear activity and star formation activity to calculate average spectra of high signal-to-noise ratio (S/N) and resolution ( at Δλ= 1 Å), using an algorithm that is robust against outliers. Besides composite spectra, we also compute the first five principal components of the distributions in each galaxy class to characterize the nature of variations of individual spectra around the averages. The continua of the composite spectra are fitted with BC03 stellar population synthesis models to extend the wavelength coverage beyond the coverage of the SDSS spectrographs. Common derived parameters of the composites are also calculated: integrated colours in the most popular filter systems, line-strength measurements and continuum absorption indices (including Lick indices). These derived parameters are compared with the distributions of parameters of individual galaxies, and it is shown on many examples that the composites of the atlas cover much of the parameter space spanned by SDSS galaxies. By co-adding thousands of spectra, a total integration time of several months can be reached, which results in extremely low noise composites. The variations in redshift not only allow for extending the spectral coverage bluewards to the original wavelength limit of the SDSS spectrographs, but also make higher spectral resolution achievable. The composite spectrum atlas is available online at . [ABSTRACT FROM AUTHOR]