Single Be stars as binary ejecta?

Among the mechanisms suggested for the creation of discs around Be stars is interaction with binary companions. This idea has largely been dismissed, because the majority of Be stars have no observed companion. This difficulty can be circumvented if single Be stars are actually ejected from binary systems (owing, for instance, to the supernova of the companion). Using Hipparcos data, we show that this explanation is not likely, by comparing the velocity distributions of Be stars with those of normal B stars. We find that the distributions are consistent to within 1 σ uncertainties, and thus do not support the formation of single Be stars through binary breakup.     

Coalescing neutron stars as gamma ray bursters?

We investigate the dynamics and evolution of coalescing neutron stars. The three-dimensional Newtonian equations of hydrodynamics are integrated by the Piecewise Parabolic Method on an equidistant Cartesian grid. The code is purely Newtonian, but does include the emission of gravitational waves and their back-reaction. The properties of neutron star matter are described by the equation of state of Lattimer and Swesty (1991). Energy loss by all types of neutrinos and changes of the electron fraction due to the emission of electron neutrinos and antineutrinos are taken into account by an elaborate neutrino leakage scheme. We simulate the coalescence of two identical, cool neutron stars with a baryonic mass of 1.6M and a radius of 15 km and with an initial center-to-center distance of 42 km. The initial distributions of density and electron concentration are given from a model of a cold neutron star in hydrostatic equilibrium. We investigate three cases which differ by the initial velocity distribution in the neutron stars. The orbit decays due to gravitational-wave emission and after one revolution the stars are so close that dynamical instability sets in. Within 1 ms the neutron stars merge into a rapidly spinning (P 1 ms), high-density body ( 10¹⁴ g/cm³) with a surrounding thick disk of material with densities 10¹⁰ – 10¹² g/cm³ and orbital velocities of 0.3-0.5 c. The peak emission of gravitational waves has a maximum luminosity of a few times 10⁵⁵ erg/s and is reached for about 1 ms. The amplitudes of the gravitational waves are close to 3 10^–23 at a distance of 1 Gpc and the typical frequency is near the dynamical value of the orbital motion of the merging neutron stars of 2 KHz. In a post-processing step, the rate of neutrino-antineutrino annihilation is calculated from the neutrino luminosities generated during the hydrodynamical simulations. We find the integral annihilation rate to be a few 10⁵⁰ erg/s during the phase of strongest neutrino emission, which is too small to generate the observed bursts considering the fact that the merged object of about 3M will most likely collapse to a black hole within milliseconds.     

Measurement of Hubble constant: were differences in secondary distance indicators apparent as early as the HST Key Project?

Different measurements of the Hubble constant(H₀)are not consistent,and a tension between the CMB based methods and cosmic distance ladder based methods has been observed.Measurements from various distance based methods are also inconsistent.To aggravate the problem,the same cosmological probe(TypeⅠa SNe for instance)calibrated through different methods also provides different values of H₀.We compare various distance ladder based methods through the already available unique data obtained from the Hubble Space Telescope(HST).Our analysis is based on parametric(t-test)as well as non-parametric statistical methods such as the Mann-Whitney U test and Kolmogorov-Smirnov test.Our results show that different methods provide different values of H₀ and the differences are statistically significant.The biases in the calibration would not account for these differences as the data have been taken from a single telescope with a common calibration scheme.The unknown physical effects or issues with the empirical relations of distance measurement from different probes could give rise to these differences.     

The CMF as provenance of the stellar IMF?

In the present work we examined the hypothesis that, a core mass function (CMF), such as the one deduced for cores in the Orion molecular cloud (OMC), could possibly be the primogenitor of the stellar initial mass function (IMF). Using the rate of accretion of a protostar from its natal core as a free parameter, we demonstrate its quintessential role in determining the shape of the IMF. By varying the rate of accretion, we show that a stellar mass distribution similar to the universal IMF could possibly be generated starting from either a typical CMF such as the one for the OMC, or a uniform distribution of prestellar core masses which leads us to suggest, the apparent similarity in shapes of the CMF and the IMF is perhaps, only incidental. The apodosis of the argument being, complex physical processes leading to stellar birth are crucial in determining the final stellar masses, and consequently, the shape of stellar mass distribution. This work entails partial Monte-Carlo treatment of the problem, and starting with a randomly picked sample of cores, and on the basis of classical arguments which include protostellar feedback and cooling due to emission from warm dust, a theoretical distribution of stellar masses is derived for five realisations of the problem; the magnetic field, though, has been left out of this exercise.     

Unusual comets (?) as observed from the Hubble Space Telescope

In separate projects, the Hubble Space Telescope has been used to assess the nature of 3 unusual objects: Chiron, Pholus and P/Shoemaker-Levy 9. This paper will compare these objects and discuss how the unique capabilities of the HST may be used to address the issue of cometary activity in each. Chiron, which has exhibited obvious cometary characteristics for several years, might have a bound dust coma that is unresolvable from the ground. In an attempt to directly observe this bound coma, we have obtained a series of images of Chiron with the HST Planetary Camera. Inner coma structure out to 0.2 has been detected. From these observations we infer a low bulk nucleus density for Chiron. Both HST and ground-based images of 5145 Pholus have been obtained to search for evidence of activity. The ground-based data give the most sensitive limits; however, it is shown that the WFPC-2 on HST can give limits 2–3 orders of magnitude more sensitive than conventional ground-based limits. Finally, as part of a collaborative effort, we have been obtaining HST observations of SL9 in order to determine the fragment sizes and to assess their nature (i.e., cometary vs. asteroid). Both ground-based observations from the UH 2.2m telescope on Mauna Kea and HST observations show that the near-nucleus dust is redder than the sun. While FOS spectra did not detect OH emission, the WFPC-2 HST data show that the inner coma remained very circular from July 1993 up until 2 weeks prior to impact, implying continued production of dust.     

Particle beams as a source of noise storm depression?

The February 5, 1986 flare-related radio continuum depression is studied, compared with other noise storm depression events and discussed in the framework of current type I storm models. The influence of flare plasma flow or shocks and of superthermal electrons on noise storm radiation is considered. The presence of fast drifting emission features just before and during the decrease of the intensity, the association between the depression onset and the microwave burst maximum, the simultaneous appearance of the intensity minimum over a broad spectral range as well as preflare evidence of an interconnection of the flare site and the noise storm source are arguments for a preference of the role of beams of superthermal electrons. We distinguish abrupt and slow depressions (Figure 5). The abrupt depressions are in agreement with Melrose's (1980) predictions. Slow depressions can only be understood by invoking the diffusion of super-thermal electrons through the magnetic field carrying the storm source.     

Does the region of flare-energy release work as a vacuum-cleaner?

We aim to explore the unusual flare event which took place in the solar atmosphere on September 22, 2011 and propose its theoretical interpretation. We analyze the process of energy release in the twisted magnetic flux-rope associated with the event, assuming the excitation of anomalous resistivity of turbulent plasma in the rope, and solve numerically nonlinear two-dimensional (2D) magnetohydrodynamic (MHD) equations. The analytical approach to the problem of flare-energy release show that the conditions of excitation of anomalous resistivity can be satisfied in the twisted magnetic flux-rope whose parameters fits well the SDO observational findings. One of the most remarkable properties of the flare phenomenon under the present consideration was the permanent sucking of the coronal/chromospheric gas from the very remote points to the flare filament, i.e. into the low-lying hot region of the flare energy release. This unusual phenomenon has been simulated by numerical methods in terms of ideal MHD. The numerical results reveal that siphon back-flow exhibits characteristic spatial signatures which mimic the observational findings. The flare-energy release region, as a part of strongly twisted magnetic flux-rope, is able to work as a vacuum-cleaner.     

Mean-Motion Resonances as a Source for Infalling Comets toward β Pictoris

Repeated time-variable redshifted absorption features in the spectrum of β Pictoris (β Pic) have been attributed to comet-like bodies falling toward the star, when evaporating in its immediate vicinity. This model explains now a large number of observational characteristics, but the exact mechanism that could generate these numerous star-grazers is still controversial, even if planetary perturbations are thought to be the basic process. The different models proposed up to now are here reviewed, and we discuss in particular a recent one, involving the effect of secular resonances in the β Pic system. We stress that it seems highly improbable that such a mechanism could apply to the β Pic case, because the extremely strong power of secular resonances is connected to the very specific structure of the Solar System. Therefore, the secular resonance mechanism is highly non-generic. Conversely, we propose a model involving the eccentricity-pumping effect of mean-motion resonances with a massive planet on a moderately eccentric orbit. We show in particular that the 4:1 mean-motion resonance is a very active source of star-grazers as soon as the eccentricity of the perturbing planet is ?0.05, while the 3:1 mean-motion resonance is less efficient. We stress that this mechanism is very generic. These theoretical predictions are confirmed by numerical integrations using the Extended Schubart Integrator. The time-scale of the process is discussed, and we show that if the eccentricity of the perturbing planet fluctuates, due to secular perturbations, this time-scale is compatible with the age of β Pic's system.     

Supernova SN2006gy as a first ever Quark Nova?

The most luminous Supernova SN2006gy (more than 100 times brighter than a typical supernova) has been a challenge to explain by standard models. For example, pair-instability supernovae which are luminous enough seem to have too slow a rise, and core-collapse supernovae do not seem to be luminous enough. We present an alternative scenario involving a Quark Nova (an explosive transition of the newly born neutron star to a quark star) in which a second explosion (delayed) occurs inside the ejecta of a normal supernova. The reheated supernova ejecta can radiate at higher levels for longer periods of time primarily due to reduced adiabatic-expansion losses, unlike the standard supernova case. We find an encouraging match between the resulting light curve and that observed in the case of SN2006gy suggesting that we might have at hand the first ever signature of a Quark Nova. Successful application of our model to SN2005gj and SN2005ap is also presented.     

Resonant Absorption as Mode Conversion? II. Temporal Ray Bundle

A fast-wave pulse in a simple, cold, inhomogeneous MHD model plasma is constructed by Fourier superposition over frequency of harmonic waves that are singular at their respective Alfvén resonances. The pulse partially reflects before reaching the resonance layer, but also partially tunnels through to it to convert to an Alfvén wave. The exact absorption/conversion coefficient for the pulse is shown to be given precisely by a function of transverse wavenumber tabulated in Paper I of this sequence, and to be independent of frequency and pulse width.     

Properties of the solar chromosphere Hα spicules as observed spectrally

Time succession of 25 H spicules has been studied. The spectra are obtained at a height of 6 arc sec during 21 min (38 pictures) with the 53 cm Lyot coronagraph. Total intensities W, widths and radial velocities V _r are determined (about 650 H line profiles). For 14 spicules the sign of V _r varies, for the rest the sign variation is absent or it is doubtful. Characterized period of V _r variation is 3–7 min with a mean amplitude of ± 4km s^–1. W and also vary with a similar period and mean amplitudes equal to 50% and 30% respectively. dependence of W (Figure 1) points to the existence of two spicules groups: group I (70%) characterized by relatively small W and (mean values are 0.08 Å and 1.3 Å respectively); group II comprising brighter (W 0.13 Å) spicules with wider profiles ( 1.6 Å). Group II may consist of the unresolved, superimposed group I spicules. We believe, that H spicules involve formations consisting of separate elements having the temperature of 6000 K and non-thermal velocities of 25 km s^–1.     

The mass budget necessary to explain ‘Oumuamua as a nitrogen iceberg

Recently, a nitrogen iceberg was proposed as a possible origin for the first interstellar object, 1I/2017 U1, also known as ‘Oumuamua. Here, we show that the mass budget in exo-Pluto planets necessary to explain the detection of ‘Oumuamua as a nitrogen iceberg chipped off from a planetary surface requires a mass of heavy elements exceeding the total quantity locked in stars with 95% confidence, making the scenario untenable because only a small fraction of the mass in stars ends in exo-Plutos.     

Did the moon form as a result of a thermonuclear explosion?

The proposed model explains the Moon formation as a result of a thermo-nuclear explosion due to which a big land mass was torn off from the Earth. Within the model framework, on the one hand, the data on the Moon’s physical and chemical parameters are in good agreement. On the other hand, this model corresponds to modern ideas about the dynamism of the Earth’s geological structure which presupposes the presence of a powerful energy source in the Earth’s core, which might have thermonuclear origin.     

Short Gamma Ray Bursts as electromagnetic counterpart of coalescing binary systems

Coalescing binary systems, consisting of two collapsed objects, are among the most promising sources of high frequency gravitational waves signals detectable, in principle, by ground-based interferometers. Binary systems of Neutron Star or Black Hole/Neutron Star mergers should also give rise to short Gamma Ray Bursts, a subclass of Gamma Ray Bursts. Short-hard-Gamma Ray Bursts might thus provide a powerful way to infer the merger rate of two-collapsed object binaries. Under the hypothesis that most short Gamma Ray Bursts originate from binaries of Neutron Star or Black Hole/Neutron Star mergers, we outline here the possibility to associate short Gamma Ray Bursts as electromagnetic counterpart of coalescing binary systems.     

The occultation of ϵ Gem by Mars as observed from Agassiz Station

Observations of the April 8, 1976 occultation of ? Gem by Mars made at the Agassiz Station of the Harvard College Observatory have been analyzed to yield temperature profiles of the Martian atmosphere for number densities between 10¹³ and 10¹⁵ cm^?3. Pronounced wavelike structure is evident in both immersion and emersion profiles, with a peak-tto-peak variation of up to 50°K and a vertical scale of 20 km.     

A Study on the Paul-Baker System as an Instrument for Multi-object Spectrum Observation

Paul-Baker systems with 4°flat field and 5°flat field are studied. Their light obstructions under different f/ratios of the primary mirror are analyzed. Due to the strong f/ratio of the system, a focal length extender is designed in order to match the following fiber instrumentation, and two kinds of dispersion prism correctors are designed for correcting the atmospheric dispersion. We compare the designed Paul-Baker system with LAMOST, the national major scientific project now under construction.     

New Variable Stars Discovered as By-product of the Beijing Astronomical Observatory Supernova Survey

The Beijing Astronomical Observatory (BAO) 0.6 m telescope has been used for nearby supernova survey in more than 3000 fields, covering a total area of 235 deg2. More than 260000 CCD images have been collected since April 1996, with 45 supernovae discovered. We searched for variables in about 90000 images taken during 1996-1998. For the fields in which long period variables (LPVs) were discovered, we reduced further images taken from 1999 to 2000, for the period estimation. Among the 280000 stars selected from the survey fields, i.e., brighter than 18 mag, we discovered seven new LPVs and reconfirmed three known LPVs. Additionally, we found 146 variable star candidates, and reconfirmed about 20 previously known or suspected objects.     

On the Large-Scale Structure of the Universe as given by the Voronoi Diagrams

The size distributions of 2D and 3D Voronoi cells and of cells of Vp(2,3),-2D cut of 3D Voronoi diagram-are explored, with the single-parameter (re-scaled) gamma distribution playing a central role in the analytical fitting. Observational evidence for a cellular universe is briefly reviewed. A simulated Vp(2,3) map with galaxies lying on the cell boundaries is constructed to compare, as regards general appearance, with the observed CfA map of galaxies and voids, the parameters of the simulation being so chosen as to reproduce the largest observed void size.