Intrinsic colour indices of Be stars obtained from 2MASS photometry

This paper is based on 2MASS photometry (J H K_s magnitudes) of 1172 Be stars. The observed mean intrinsic colours have been derived with aid of two‐colour diagrams for Be stars of luminosity classes Ie‐IIe, IIIe and IVe‐Ve. The obtained results are the first determinations of their intrinsic colours in the astronomical literature. The smoothed infrared colours are compared with those obtained for “normal” B stars. Several two‐colour diagrams and plots of observed and smoothed intrinsic colour versus spectral type of luminosity classes Ie‐IIe, IIIe and IVe‐Ve are presented. Generally the determined infrared intrinsic colours of Be stars (V – J)₀, (V – H)₀, and (V – K_s)_o differ substantially from those of “normal” B stars. It is found that the intrinsic colours of B stars are generally bluer than Be stars of corresponding spectral type and luminosity class. The mean absolute visual magnitude M_v of 528 Be stars for luminosity classes Iae, Ibe‐Iabe, IIe, IIIe and IVe‐Ve is derived from HIPPARCOS parallaxes. The M_v calibration is compared with the existing ones. The Be stars are generally brighter than “normal” B stars of corresponding spectral types. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Eddingtons Zahlen,Einsteins Kriterium und Rydbergs rationelles Dimensionssystem

The discussions about the meaning of the “hierarchy of interactions” and in connection with this about the role of Eddington's “cosmological number” imply the question of the “big numbers” in physics. According to Einstein's and Bridgman's criteria such “big numbers” are hints at unsolved problems in the foundations of physics. Eddington gives a theory of the big number like cosmological quantities. – A new point of view on this question may be to remember Rydberg's suggestion on independigly physical dimensions of lengths L, surfaces S, and volumina V, and to remember Dällenbach's suggestion to introduce a new universal constant α which describes the operational connections between the quardrate of lengths L² and the surface S in microphysics. Coulomb's and Nwton's laws have the same structure. But, the electrical forces are depending on L^-2 and the gravitational forces are depending on S^-1 ∼ (1/α) L^-2 because “gravitation is geometry”. In Planck's elementary units h, c and f Dällenbach's “surface-constant of the vacuum” α is a pure number α ≈ hc/fm², th. i. Eddington's cosmological number ω ∼ 10⁴⁰. However, Rydberg's physical dimensions in geometry and Dällenbach's constant suggest new formulations of the question of “geometrization of physics” and “physicallization of geometry” and the connections between cosmology and microphysics.     

A retrospective of the GREGOR solar telescope in scientific literature

In this review, we look back upon the literature, which had the GREGOR solar telescope project as its subject including science cases, telescope subsystems, and post‐focus instruments. The articles date back to the year 2000, when the initial concepts for a new solar telescope on Tenerife were first presented at scientific meetings. This comprehensive bibliography contains literature until the year 2012, i.e., the final stages of commissioning and science verification. Taking stock of the various publications in peer‐reviewed journals and conference proceedings also provides the “historical” context for the reference articles in this special issue of Astronomische Nachrichten/Astronomical Notes (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Singularitäten in der Allgemeinen Relativitätstheorie

“Regular solutions of EINSTEIN 's equations” mean very different things. In the case of the empty-space equations, R_ik = 0, such solutions must be metrics g_ik(x^l) without additionaly singular “field sources” (EINSTEIN 's “Particle problem”). – However the “phenomenological matter” is defined by the EINSTEIN equations R_ik – 1/2g_ikR =–xT_ik itselves. Therefore if 10 regular functions g_ik(x^l) are given (which the inequalities of LORENTZ -signature fulfil) then these g_ik define 10 functions T_ik(x^l) without singularities. But, the matter-tensor T_ik must fulfil the two inequalities T ≥ 0, T ≥ 1/2 T only and therefore the EINSTEIN -equations with “phenomenological matter” mean the two inequalities R ≥ 0, R ≤ 0 which are incompatible with a permanently regular metric with LORENTZ -signature, generally.     

Sun,Solar System,Stars, Interstellar Matter,Galaxy, Extragalactic Systems,Instruments, History of Astronomy

P01 Calibrations on DSS‐II Plates P02 High‐Resolution Near‐Infrared Speckle Interferometry and Radiative Transfer Modeling of the OH/IR star OH 26.5 + 0.6 P03 Mid‐infrared long‐baseline interferometry of the symbiotic Mira star RX Pup with the VLTI/MIDI instrument P04 N₂D⁺ abundance in high mass star forming regions P05Causal Viscosity in Accretion Disc Boundary layers P06 Planetesimals in protoplanetary disks P07 Star Clusters in the Large Magellanic Cloud P08 Is there a universal mass function? P09 On CO cooling in dense molecular clouds P10 An unbiased search for molecular clumpuscules P11 Vertical structure of accretion disks P12 A New Data Acquisition System and User Control Program for CCD Cameras at “Hoher List” Observatory P13 Tracing the Photon Dominated Region around DR21 with CO, CI, CII, and OI emission P14 Time resolved spectroscopy of CI Aql P15 Empirical Color Transformations between SDSS Photometry and Other Photometric Systems P16 V4332 Sgr P17 Low rotation velocities of white dwarfs from the CaII K line P18 E‐Learning in Astronomy P19 RR Lyrae stars: Kinematics, orbits and z‐distribution P20 New developments on the field of chemically peculiar stars in the milky way and the LMC P21 Large‐scale CO Mapping of the CEPHEUS Giant Molecular Cloud using KOSMA P22 HoLiCS II – The “Hoher List Control System” II P23 88 GHz “Holotransmitter” for the Nanten2 Telescope P24 Comet Astrometry – Tracing the last witnesses of the solar system's childhood P25 Considerations on the spectral appearance of M‐type brown dwarfs P26 Photon Dominated Region Modelling of Barnard 68 P27 A New Versatile Multichannel CCD‐Controller for BUSCA P28 High Precision “Bonn Shutters” for the largest CCD Mosaic Cameras P29 High‐Resolution Near‐Infrared Speckle Interferometry and Radiative Transfer Modeling of the OH/IR star OH 104.9 + 2.4 P30 A new Doppler image of the weak‐line T Tauri star V410 Tauri P31 Improving our knowledge on open cluster radial velocities P32 The Distribution of MSX Infrared Dark Clouds in the inner Milky Way P33 Was the Early Earth shielded from UV by Ozone produced from the Smog Mechanism? P34 Structure Analysis of the CO data in the Perseus clouds P35 Evidence for Turbulence in the Velocity Fields of Perseus Cores P36 Dust‐driven Winds and Their Resulting Mass Loss at Subsolar Metallicity P37 Two adjacent gigantic (∼9°) IRAS filaments of bipolar morphology: An almost invisible pair P38 A new optical filament of the Monogem Ring P39 The Far Ultraviolet Spectroscopic Explorer Survey of OVI Emission in the Milky Way     

Turbulent dynamo near tachocline and reconstruction of azimuthal magnetic field in the solar convection zone

In order to extend the abilities of the αΩ dynamo model to explain the observed regularities and anomalies of the solar magnetic activity, the negative buoyancy phenomenon and the magnetic quenching of the α effect were included in the model, as well as newest helioseismically determined inner rotation of the Sun were used. Magnetic buoyancy constrains the magnitude of toroidal field produced by the Ω effect near the bottom of the solar convection zone (SCZ). Therefore, we examined two “antibuoyancy” effects: i) macroscopic turbulent diamagnetism and ii) magnetic advection caused by vertical inhomogeneity of fluid density in the SCZ, which we call the ∇ρ effect. The Sun's rotation substantially modifies the ∇ρ effect. The reconstruction of the toroidal field was examined assuming the balance between mean‐field magnetic buoyancy, turbulent diamagnetism and the rotationally modified ∇ρ effect. It is shown that at high latitudes antibuoyancy effects block the magnetic fields in the deep layers of the SCZ, and so the most likely these deep‐rooted fields could not become apparent at the surface as sunspots. In the near‐equatorial region, however, the upward ∇ρ effect can facilitate magnetic fields of about 3000 – 4000 G to emerge through the surface at the sunspot belt. Allowance for the radial inhomogeneity of turbulent velocity in derivations of the helicity parameter resulted in a change of sign of the α effect from positive to negative in the northern hemisphere near the bottom of the SCZ. The change of sign is very important for direction of the Parker's dynamo‐waves propagation and for parity of excited magnetic fields. The period of the dynamo‐wave calculated with allowance for the magnetic quenching is about seven years, that agrees by order of magnitude with the observed mean duration of the sunspot cycles. Using the modern helioseismology data to define dynamo‐parameters, we conclude that north‐south asymmetry should exist in the meridional field. At low latitudes in deep layers of the SCZ, the αΩ dynamo excites most efficiency the dipolar mode of the meridional field. Meanwhile, in high‐latitude regions a quadrupolar mode dominates in the meridional field. The obtained configuration of the net meridional field is likely to explain the magnetic anomaly of polar fields (the apparent magnetic “monopole”) observed near the maxima of solar cycles. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Integrated colours of Milky Way globular clusters and horizontal branch morphology

Broadband colours are often used as metallicity proxies in the study of extragalactic globular clusters. A common concern is the effect of variations in horizontal branch (HB) morphology – the second‐parameter effect – on such colours. We have used UBVI, Washington, and DDO photometry for a compilation of over 80 Milky Way globular clusters to address this question. Our method is to fit linear relations between colour and [Fe/H], and study the correlations between the residuals about these fits and two quantitative measures of HB morphology. While there is a significant HB effect seen in U – B, for the commonly used colours B – V, V – I, and C – T₁, the deviations from the baseline colour‐[Fe/H] relations are less strongly related to HB morphology. There may be weak signatures in B –V and C –T₁, but these are at the limit of observational uncertainties. The results may favour the use of B –I in studies of extragalactic globular clusters, especially when its high [Fe/H]‐sensitivity is considered. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Absolute magnitudes for late‐type dwarf stars for Sloan photometry

We present a new formula for absolute magnitude determination for late‐type dwarf stars as a function of (g – r) and (r – i) for Sloan photometry. The absolute magnitudes estimated by this approach are brighter than those estimated by colour‐magnitude diagrams, and they reduce the luminosity function rather close to the luminosity function of Hipparcos. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Die Asymmetrie der kosmischen Zeit und RIEMANNS Gravitationstheorie1)

RIEMANN himself has considered his formulation of the differential geometry of curved spaces as a first step to a unified geometrical theory of “one ether of gravity, electricity and magnetism”. RIEMANN has pointed out that a fundamental point in such a theory of gravitation has to be the asymmetry of its sources: only positive masses exist. – According to RIEMANN this asymmetry of sources to be coupled with an asymmetry of gravitation field equation against the time-reversion t → - t. Therefore, the gravitation field equation is of the type of a continuity-equation of a velocity field v_i˜g^ikθ _k Φ. RIEMANN 's ether is incompressible in empty space-domains: θ _k (g^1/2v^k) = o. But, in domains with a massdensity σ > o it is θg^1/2/θt = −2 kcσ = − 2 kcg^1/2σ₀ (with a universal constant kc). The matter-density defines depressions of the ether. In a general-relativistic approach RIEMANN 's ansatz means that in empty space-time domains the world-geometry is the purely metrical “RIEMANN ian” geometry. However, in domains with a non-vanishing matter-tensor T_μ^v ≠ o the geometry becomes “non-RIEMANN ian” affine connecting and is of the type of WEYL 's geometry or of the “EINSTEIN -CARTAN theories of gravitation”. Especially, RIEMANN 's field equation for the empty space θ _k ((g^1/2g^ikθ _k Φ) = o. is the EINSTEIN equation (-|g_μv|)^1/2 R₀⁰ = o with g₀₀ = - Φ²c^-4.     

Das Korrespondenzprinzip in der Kosmologie. II. Klassische und relativistische Darstellungen der Weltmodelle

According to the equivalence between the FRIEDMANN equation of relativistic cosmology and the condition for the time-independence H = o of the HAMILTON ian H of an isotropic particle-system in the NEWTON ian mechanics (which equivalence is proved in the part I of our paper) we construct the corresponding classical HAMILTON ians to the relativistic world-models. Each cosmological model which is resulting from a physically meaningful gravitation theory must give a FRIEDMANN equation as the cosmological formulation of the time-independence condition of the energy H for the corresponding NEWTON ian N-particle system. In general relativity, EINSTEIN's field equations are including EINSTEIN's strong principle of equivalence and are giving the constance f = o and M = o of the gravitation-number f and of the mass M of the universe additional to FRIEDMANN's equation. – In special relativity, we have fM = o and this MILNE -universe is possessing a NEWTON ian and a general relativistic interpretation, too. – However, if the postulate together with the “cosmological principle” other principles about the world structure, too (p. e. MACH'S or DIRAC'S principle or the “perfect cosmological principle” by the steady-state cosmology), then EINSTEIN'S weak principle of equivalence can be fulfilled, only. In these world models the gravity-mass fM becomes a function of the cosmic time t [d/dt(fM) ± o] and this variability of fM is compatible with the constance H = o of the energy H of the NEWTON ian particle-system. For flat three-dimensional cosmological spaces (with H = Ḣ = o) a creation of rest-mass (M > o) is possible. This creation is the pecularity of the steady-state cosmos (with M > o, f = o) and of JORDAN'S cosmos (with M > o, f < o). The MACH -EINSTEIN -doctrine about the perfect determination of the inertia and of the space-time-metric by the cosmic gravitation is founded on the substitution of the NEWTON ian HAMILTON ian by a GAUSS -RIEMANN ian gravitation potential U^*(r_AB' v_AB) (TREDER 1972). Therefore, the FRIEDMANN equation for a universe with MACH'S principle is resulting from the analytical expression of the time-independence of this RIEMANNian potential U* = 0. In the case of such MACH-EINSTEIN's-Universes EINSTEIN'S condition 3fM = c8r between the mass A4 and the radius Y of the universe is valid additional to FRIEDMANN'S equation. For these universes, the EINSTEIN condition determinates the instantaneous value of the gravitation-number f. - The explicite form of the conditions H = o or h' = o gives the equation of motion for the cosmic fundamental particles with attraction and repulsion forces, generally.     

The young open cluster Trumpler 3

We present a photometric and spectroscopic study of the poorly investigated open cluster Trumpler 3. Basic parameters such as the age of 70 ± 10 Myr, the color excess E (B – V) = 0.30 ± 0.02 mag, the distance of 0.69 ± 0.03 kpc and the limiting radius of 12′ were redetermined and compared with previous preliminary studies. The distance of 0.65 ± 0.09 kpc was determined independently by spectral parallaxes. Simultaneously, our analysis allowed us to estimate a total number of members to be N_tot = 570 ± 90 and a total mass of the cluster to be M_tot = 270 ± 40 M_⊙. We also determined a state of cluster's dynamical evolution. We conclude that Trumpler 3 is a young low‐massive stellar ensemble with a typical mass function slope, located near to the outer edge of the Galaxy's Orion Spur. As a result of a wide‐field search for short period variable stars, 24 variables were discovered in the cluster's area. Only one of them – a variable of the γ ‐Dor type – was found to be a likely cluster member (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Gravitation und weitreichende schwache Wechselwirkungen bei Neutrino-Feldern Gedanken zu einer Theorie der solaren Neutrinos

The strange non-evidence of the solar-neutrino current by the experiments of DAVIS et al. postulates a fundamental revision of the theory of weak interactions and of its relations to gravitation theory. (We assume that the astrophysical stellar models are not completely wrong.) – Our paper is based on PAULI 's grand hypothesis about the connection between weak and gravitational interactions. According to PAULI and BLACKETT the (dimensionless) gravitation constant is the square of the (dimensionless) FERMI -interaction constant and according to the hypotheses of PAULI, DE BROGLIE , and JORDAN the RIEMANN -EINSTEIN gravitational metric g_ik is fusioned by the four independent WEYL ian neutrino fields (β-neutrinos and β-antineutrinos, μ-neutrinos and μ-antineutrinos). This fusion gives four reference tetrads h_i^A(x^l) as neutrino-current vectors, firstly. Then, the metric g_ik is defined by the equation g_ik = η_AB h_i^Ah_η^B according to EINSTEIN 's theory of tele-parallelism in RIEMANN ian space-times. The relation of the gravitation field theory to FERMI 's theory of weak interactions becomes evident in our reference-tetrads theory of gravitation (TREDER 1967, 1971). – According to this theory the coupling of the gravitation potential h_i^A with the matter T_ιⁱ is given by a potential-like (FERMI -like) interaction term. In this interaction term two WEYL spinor-fields are operating on the matter-tensor, simultanously. Therefore, the gravitation coupling constant is PAULI 's square of the FERMI -constant. Besides of the fusion of the RIEMANN -EINSTEIN metric g_ik by four WEYL spinors we are able to construct a conformal flat metric ĝ_ik = ϕ²η_ik by fusion from each two WEYL spinors. (This hypothesis is in connection with our interpretation of EINSTEIN 's hermitian field theory as a unified field-theory of the gravitational metric g_ik and a WEYL spinor field [TREDER 1972].) Moreover, from the reference-tetrads theory is resulting that the WEYL spinors in the “new metric” ĝ_ik are interacting with the DIRAC matter current by a FERMI -like interaction term and that these WEYL spinors fulfil a wave equation in the vacuum. Therefore, we have a long-range interaction with the radiced gravitational constant \documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt {\frac{{tm^2 }}{{hc}}} $\end{document} as a coupling constant. That means, we have a long-range interaction which is 10¹⁸ times stronger than the gravitation interaction. – However, according to the algebraic structure of the conform-flat this long-range interaction is effective for the neutrino currents, only. And for these neutrinos the interaction is giving an EINSTEIN -like redshift of its frequences. The characteristic quantity of this “EINSTEIN shift” is a second gravitation radius â of each body: N = number of baryons, m = mass of a baryon.) This radius â is 10¹⁸ times larger than the EINSTEIN -SCHWARZSCHILD gravitation radius a = fM/c²: But, this big “weak radius” â has a meaning for the neutrinos, only.–The determination of the exterior and of the interior “metrics” ĝ_ik is given by an “ansatz” which is analogous to the ansatz for determination of strong gravitational fields in our tetrads theory. That is by an ansatz which includes the “self-absorption” of the field by the matter. For all celestial bodies the “weak radius” â is much greater than its geometrical dimension. Therefore, a total EINSTEIN redshift of the neutrino frequences v is resulting according to the geometrical meaning of our long-range weak interaction potential ĝ_ik = ϕ²η_ik. That means, the cosmic neutrino radiation becomes very weak and unable for nuclear reactions. Theoretically, our hypothesis means an ansatz for unitary theory of gravitation and of weak interaction. This unitary field theory is firstly based on EINSTEIN 's hermitian field theory and secondly based on our reference-tetrads theory of gravitation.     

Cyclic light and period variations of the UV Leonis system

Solutions of the new standard V‐light curves for the EA type binary UV Leo are obtained using the PHOEBE code (0.31a version). Absolute parameters of the stellar components were then determined, enabling them to be positioned on the absolute magnitude‐color (l.e. M_V vs. B – V) isochrones diagram, based on which the age of the system is estimated to be >4×10⁹ yr. Also times of minima data (“O – C curve”) have been analyzed. Apart from an almost sinusoidal variation with a period of 29.63 yr, which modulates the orbital period, and was attributed to a third body orbiting around the system, other cyclic variation in the orbital period and also brightness, with time scales of 24.25 and 22.77 yr were found, respectively. We associate this with a magnetic activity cycle newly reported here for UV Leo (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The value of the superstring tension and dark matter

The last line of the abstract should read “about μ = 10^–5c ²/G. This corresponds to 1.2 · 10³⁹ Newton”. The main text remains unchanged. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Meteorite and meteoroid: New comprehensive definitions

Abstract– Meteorites have traditionally been defined as solid objects that have fallen to Earth from space. This definition, however, is no longer adequate. In recent decades, man‐made objects have fallen to Earth from space, meteorites have been identified on the Moon and Mars, and small interplanetary objects have impacted orbiting spacecraft. Taking these facts and other potential complications into consideration, we offer new comprehensive definitions of the terms “meteorite,”“meteoroid,” and their smaller counterparts: A meteoroid is a 10‐μm to 1‐m‐size natural solid object moving in interplanetary space. A micrometeoroid is a meteoroid 10 μm to 2 mm in size. A meteorite is a natural, solid object larger than 10 μm in size, derived from a celestial body, that was transported by natural means from the body on which it formed to a region outside the dominant gravitational influence of that body and that later collided with a natural or artificial body larger than itself (even if it is the same body from which it was launched). Weathering and other secondary processes do not affect an object’s status as a meteorite as long as something recognizable remains of its original minerals or structure. An object loses its status as a meteorite if it is incorporated into a larger rock that becomes a meteorite itself. A micrometeorite is a meteorite between 10 μm and 2 mm in size. Meteorite– “a solid substance or body falling from the high regions of the atmosphere” ( Craig 1849 ); “[a] mass of stone and iron that ha[s] been directly observed to have fallen down to the Earth’s surface” (translated from Cohen 1894 ); “[a] solid bod[y] which came to the earth from space” ( Farrington 1915 ); “A mass of solid matter, too small to be considered an asteroid; either traveling through space as an unattached unit, or having landed on the earth and still retaining its identity” ( Nininger 1933 ); “[a meteoroid] which has reached the surface of the Earth without being vaporized” (1958 International Astronomical Union (IAU) definition, quoted by Millman 1961 ); “a solid body which has arrived on the Earth from outer space” ( Mason 1962 ); “[a] solid bod[y] which reach[es] the Earth (or the Moon, Mars, etc.) from interplanetary space and [is] large enough to survive passage through the Earth’s (or Mars’, etc.) atmosphere” ( Gomes and Keil 1980 ); “[a meteoroid] that survive[s] passage through the atmosphere and fall[s] to earth” ( Burke 1986 ); “a recovered fragment of a meteoroid that has survived transit through the earth’s atmosphere” ( McSween 1987 ); “[a] solid bod[y] of extraterrestrial material that penetrate[s] the atmosphere and reach[es] the Earth’s surface” ( Krot et al. 2003 ).     

Vesta,Vestoids, and the howardite,eucrite, diogenite group: Relationships and the origin of spectral differences

Abstract— Spectra of asteroid 4 Vesta and 21 small (estimated diameters less than 10 km) asteroids with Vesta‐like spectral properties (Vestoids) were measured at visible and near‐infrared wavelengths (～0.44 to ～1.65 μm). All of the measured small asteroids (except for 2579 Spartacus) have reflectance spectra consistent with surface compositions similar to eucrites and howardites and consistent with all being derived from Vesta. None of the observed asteroids have spectra similar to diogenites. We find no spectral distinction between the 15 objects tabulated as members of the Vesta dynamical family and 6 of the 7 sampled “non‐family” members that reside just outside the semi‐major axis (a), eccentricity (e), and inclination (i) region of the family. The spectral consistency and close orbital (a‐e‐i) match of these “non‐family” objects to Vesta and the Vesta family imply that the true bounds of the family extend beyond the subjective cut‐off for membership. Asteroid 2579 Spartacus has a spectrum consistent with a mixture of eucritic material and olivine. Spartacus could contain olivine‐rich material from Vesta's mantle or may be unrelated to Vesta altogether. Laboratory measurements of the spectra of eucrites show that samples having nearly identical compositions can display a wide range of spectral slopes. Finer particle sizes lead to an increase in the slope, which is usually referred to as reddening. This range of spectral variation for the best‐known meteoritic analogs to the Vestoids, regardless of whether they are actually related to each other, suggests that the extremely red spectral slopes for some Vestoids can be explained by very fine‐grained eucritic material on their surfaces.     

A revisit to agglomerates of early‐type Hipparcos stars

We study the spatial structure and sub‐structure of regions rich in Hipparcos stars with blue B_T – V_T colours. These regions, which comprise large stellar complexes, OB associations, and young open clusters, are tracers of on‐going star formation in the Galaxy. The DBSCAN (Density‐Based Spatial Clustering of Applications with Noise) data clustering algorithm is used to look for spatial overdensities of early‐type stars. Once an overdensity, “agglomerate”, is identified, we carry out a data and bibliographic compilation of their star member candidates. The actual membership in agglomerate of each early‐type star is studied based on its heliocentric distance, proper motion, and previous spectro‐photometric information. We identify 35 agglomerates of early‐type Hipparcos stars. Most of them are associated to previously known clusters and OB associations. The previously unknown P Puppis agglomerate is subject of a dedicated study with Virtual Observatory tools. It is actually a new, nearby, young open cluster (d ∼ 470 pc, age ∼ 20 Ma) with a clear radial density gradient.We list P Puppis and other six agglomerates (including NGC 2451 A, vdBH 23, and Trumpler 10) as new sites for substellar searches because of their youth, closeness, and spatial density. We investigate in detail the sub‐structure in the Orion, CMa‐Pup and Pup‐Vel OB complexes (“super‐agglomerates”). We confirm or discover some stellar overdensities in the Orion complex, like the 25 Ori group, the Horsehead region (including the σ Orionis cluster), and the η Orionis agglomerate. Finally, we derive accurate parallactic distances to the Pleiades, NGC 2451 A, and IC 2391, describe several field early‐type stars at d < 200 pc, and discuss the incompleteness of our search. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the UV-excesses of cepheid variables

On the basis of the intrinsic (U – B)₀ colours of the cepheid variables, found by the authors, the UV-excesses in the maximum and minimum light δ(U – B)^max and δ(U – B)^min are defined. It is found out that the UV-excesses in the maximum light δ(U – B)^min increase with the period P (Fig. 2), but there is no correlation between δ(U – B)^min and log P. A correlation between δ(U – B)^max and the “amplitude defects” f_B is also determined. These results in connection with some other considerations, as well as the possible causes of the UV-excesses, are discussed.     

L and T brown dwarfs in the Ursa Major moving group

We have applied the “moving cluster” method to an archive of L and T brown dwarf stars to identify those stars which are members of the Ursa Major moving group.We show that five stars have proper motion directions which agree with the direction of motion expected for a cluster member, and which have proper motion distances in agreement with distances determined by trigonometrical parallax observations. We then use 2MASS data to produce an M _K versus J ‐ K _S colour magnitude diagram. The group members define an empirical 400 Myr isochrone, which is compared to theoretical models. This is the first cluster/group to have a known T dwarf member. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)