The search for brown dwarfs with infrared surveys

I compute the maximum number of observable brown dwarfs for various infrared surveys by combining the maximum possible Oort limit (0.1 missing Mpc^–3 with all possible brown dwarf mass and age distributions. This approach shows what limits will be placed on the contribution of brown dwarfs to any possible missing mass if no brown dwarfs are observed. I consider brown dwarfs with masses of 0.01—0.08 M and ages of 10⁹—10¹⁰ years.The full range of predicted numbers of brown dwarfs above 6 times the noise of each of the below surveys is: IRAS Point Source Catalog 0.02—6 IRAS Faint Source Catalog |b| > 10° 0.05—16 ISO (2 week 12µm survey) 0.15—80 SIRTF (2 week 12µm survey) 2.50—1600 WIRE (4 month 12µm survey) 21.80—6000 DENIS (half sky) |b| > 10° 0.00—2000 2MASS (full sky) |b| > 10° 0.00—8000A failure to find brown dwarfs in the IRAS FSC would just barely rule out about half of the mass—age range for Oort limit total masses. A failure to find brown dwarfs in 2MASS/DENIS would rule out roughly the same mass—age range, but would set a limit of 0.1—0.01 times the Oort mass in that mass—age region. No limits would be set for the other half of the mass—age range since both IRAS and 2MASS/DENIS have insufficient sensitivity for brown dwarfs with T < 750 K.A failure to find brown dwarfs with ISO would rule out almost all of the mass—age range for Oort limit total masses, but would not set a significantly lower limit to the brown dwarf mass limit. A failure to find brown dwarfs with SIRTF or WIRE would rule out the entire mass—age range for Oort limit total masses and set an upper limit of 0.1—0.001 times the Oort mass.To date, about 18% of the IRAS FSC has been searched down to 6, and no brown dwarfs have been found. This sets a 95% upper limit of 3 in 18% of the sky, or 13 in the entire FSC for |b| > 10°. To begin to set useful limits from 2MASS or DENIS, approximately 400 square degrees needs to be analyzed. To date, only a few square degrees of results from the 2MASS prototype camera have been examined, with no brown dwarfs found so far.     

The three-dimensional structure of ‘loop-like’ coronal mass ejections

We have measured the brightness and latitudinal extent of the depleted (cavity) region behind the leading edge of three coronal mass ejection (CME) events from the Skylab epoch. The events chosen are among those believed to be typical of non-impulsive, loop-like CMEs (Sime, MacQueen, and Hundhausen, 1984). The pre-event coronal brightness has been matched by a model corona, assuming both a background contribution and a contribution from a range of hypothetical streamer models, distinguished by differing longitudinal extent. Then, assuming that the cavities are voided regions in which the local electron density is negligible, we estimate their minimum line-of-sight extent and find them to be comparable to, or greater than, their measured latitudinal extent. As a result, we suggest this unambiguously demonstrates the three-dimensional nature of these — and likely, this class of — events.     

Gas—Dust Shells around Some Early-Type Stars with an IR Excess (of Emission)

The results of an investigation of IR (IRAS) observations of 58 O—B—A—F stars of different luminosity classes, which are mainly members of various associations, are presented. The color indices of these stars are determined and two-color diagrams are constructed. The emission excesses at 12 and 25 mm (E ₁₂ and E ₂₅) are also compared with the absorption A₁₆₄₀ of UV radiation. It is concluded that 24 stars (of the 58 investigated) are disk systems of the Vega type, to which Vega = N 53 also belongs. Eight known stars of the Vega type are also given in the figures for comparison. The remaining 34 stars may have gas—dust shells and/or shell—disks. The IR emission excesses of the 34 investigated stars and 11 comparison stars (eight of them are Be-Ae stars) are evidently due both to thermal emission from grains and to the emission from free—free transitions of electrons in the gas—dust shells of these stars.     

On the Dynamics of Weak Stability Boundary Lunar Transfers

Recent studies demonstrate that lunar and solar gravitational assists can offer a good reduction of total variation of velocity Vneeded in lunar transfer trajectories. In particular the spacecraft, crossing regions of unstable equilibrium in the Earth—Moon—Sun system, can be guided by the Sun towards the lunar orbit with the energy needed to be captured ballistically by the Moon. The dynamics of these transfers, called weak stability boundary (WSB) transfers, will be studied here in some detail. The crucial Earth—Moon—Sun configurations allowing such transfers will be defined. The Sun's gravitational effect and lunar gravitational capture will be analyzed in terms of variations of the Jacobi constants in the Earth—Sun and Earth—Moon systems. Many examples will be presented, supporting the understanding of the dynamical mechanism of WSB transfers and analytical formulas will be obtained in the case of quasi ballistic captures.This revised version was published online in October 2005 with corrections to the Cover Date.     

Polarimetric Studies of Stars with an Infrared Emission Excess

The results of polarimetric and IR (IRAS) observations of 24 B-A-F stars are given. Intrinsic polarization of the light from 11 of the 24 stars is observed. The degree of polarization for the other 13 stars is within the measurement errors. Two-color diagrams are also constructed. From a comparison of the degree of polarization with the color index on the two-color diagrams it is seen that 8 of these 13 stars probably are of the Vega type, while 5 are stars with gas—dust shells and/or disk—shells. It is shown that 6 of the aforementioned 11 stars with intrinsic polarization evidently are stars with gas—dust shells and/or disk—shells, while 5 of them (also including No. 24) are of the Vega type. It is also shown that the IR emission from 10 of the stars corresponds to a power-law distribution F . This fact may be explained both by free—free transitions of electrons and by thermal emission from dust grains in circumstellar gas—dust shells (disks).     

Evolution of massive close binaries and formation of neutron stars and black holes

Main results of computations of evolution for massive close binaries (10M +9.4M , 16M +15M , 32M +30M , 64M +60M ) up to oxygen exhaustion in the core are described. Mass exchange starting in core hydrogen, shell hydrogen and core helium burning stages was studied. Computations were performed assuming both the Ledoux and Schwarzschild stability criteria for semiconvection. The influence of UFI-neutrino emission on evolution of close binaries was investigated. The results obtained allow to outline the following evolutionary chain: two detached Main-Sequence stars — mass exchange — Wolf-Rayet star or blue supergiant plus main sequence star — explosion of the initially more massive star appearing as a supernova event — collapsed or neutron star plus Main-Sequence star, that may be observed as a runaway star — mass exchange leading to X-rays emission — collapsed or neutron star plus WR-star or blue supergiant — second explosion of supernova that preferentially disrupts the system and gives birth to two single high spatial velocity pulsars.Numerical estimates concerning the number and properties of WR-stars, pulsars and X-ray sources are presented. The results are in favour of the existence of UFI-neutrino and of the Ledoux criterion for describing semiconvection. Properties of several well-known X-ray sources and the binary pulsar are discussed on base of evolutionary chain of close binaries.     

A technique for predicting the amplitude of the solar cycle

Predictions of the amplitude of the last three solar cycles have demonstrated the value and accuracy of the group of prediction methods known as the precursor techniques. These are based on a correlation between cycle amplitude and phenomena observed on the Sun, or originating from the Sun, during the declining phase of the cycle or at solar minimum. In many cases, precursor predictions make use of the long record of geomagnetic disturbance indices, assuming that these indices are indicative of solar phenomena such as the occurrence of coronal holes.This paper describes a precursor technique for predicting the amplitude of the solar cycle using geomagnetic indices. The technique is accurate — it would have predicted each of the last 11 cycles with a typical error of less than 20 in sunspot number. It has also advantage that a prediction of the lower limit of the amplitude can be made throughout the declining phase, this limit building to a final value at the onset of the new cycle.     

Contributions to the kinematics of type I tails of comets

Observed irregular oscillations of the ion tail axis in comets have by some authors been brought in connection with changes in the flow conditions in the solar wind. We are defending in this paper — by arguments resting on well known observations — the conception that these oscillations are caused by slight variations in the emission conditions for the ions at their source which has always its place close to the cometary nucleus. A complete renovation of the innermost tail part up to a length of a few million km (called by Hoffmeister the primary tail) and defining the tail axis can take place within a few to several hours. Shifts of this axis are becoming visible when the new tail rays finish their closure along another direction than the earlier ones.The not so rarely observed jumps in the direction of the primary tail lead in connection with the large time scale — of about 24h — for a complete closure of a ray system from an individual ion out-break to the conclusion that we should expect occasionally the existence of two (or even more) different axis to which tail rays make their closure. Some photographs of Comet Bennett 1969i seem to show such double axis.     

Upper limits to the rotation measure and magnetism of the Great Attractor supercluster

A substantial concentration of galaxies towardl ⁱⁱ =320°,b ⁱⁱ =+7°, with a mean radial velocity of 4000 km s^–1, has earlier been nicknamed the Great Attractor — it is a nearby supercluster of galaxies. Here, an attempt is made to detect an excess Faraday rotation measure that could be attributed to the magnetic field and thermal gas in the space between the galaxies inside the Great Attractor supercluster. Only an upper limit to the rotation measure, of at most 8 rad m^–2, could be placed on the Great Attractor supercluster, implying in turn an upper limit on the supercluster magnetic field, of at most 0.1 microgauss (ordered component only).     

MHD simulations of solar and interplanetary phenomena

Workers in the field of magnetohydrodynamics (MHD) have been interested in the hypothesis that observed solar activities can be utilized in a deterministic way to predict the bulk flow consequences of these activities in the three-dimensional heliosphere. Exploration of this hypothesis, using the conventional/classic initial boundary value approach, will be reviewed against the background of basic, ideal (except for shocks) one-fluid approximations. This work has been divided into two parts: near-Sun simulations in two dimensions of coronal mass ejections (CMEs) as well as interplanetary simulations in 2D and 3D of propagating shocks. In the latter case, the flows behind the shocks should be thought of as interplanetary ICMEs, i.e., the interplanetary, evolutionary consequences of the near-Sun simulations.Initialization of these simulations has been based on observations (optical, soft X-ray, radio) from both ground-and space-based instruments. Simulation outputs have been compared within situ plasma and field observations and interplanetary scintillations (IPS). Improvements in the initialization procedures — spatial/temporal variations of solar plasma and field parameters at the coronal base — are expected from YOHKOH, SOHO, CORONAS-I, and TRACE experiments. Ground truth observations from WIND, SOHO, ACE, and INTERBALL experiments should then be compared with three-dimensional MHD outputs in tests of the fluid hypothesis noted above.     

Soliton solutions to the Einstein gravitational field equations in the presence of a spherically-symmetric static background field

Using a differential geometry approach, we have found two sets of new solutions to Einstein's equation of gravity in the presence of a spherically-symmetrical gravitational background, like the Earth. The transverse and longitudinal components of the metric tensor representing the gravity waves are all soliton solutions, propagating towards the origin of the Earth. If we consider the situation where the static background field is absent, the solutions still remain soliton-like in nature. The difference between our result and Einstein's is attributed to the two approximations taken previously — weak field and harmonic condition.On study leave of absence from Zhong Shan University, China     

Spectrophotometric observations and evolutionary status of ten Be stars

The continuum energy distribution data of ten Be stars — namely, HR 1761, HR 1786, HR 1820, Ori, Ori, OT Gem, Lyr, HR 7983, Cyg, and 59 Cyg — have been presented in the wavelength range 3200–8000 Å. The observed energy distribution curve shows near infrared excess for majority of Be stars and a double Balmer jump for HR 8047 and HR 8146. Empirical effective temperatures of these stars have been estimated by comparing the observed continuum energy distributions with that of computed theoretical models given by Kurucz (1979).On the basis of an HR diagram with evolutionary tracks for different solar masses the masses of these Be stars have been estimated. Position of these studied stars on the HR diagram suggests that these Be stars may be in the stage of core contraction after exhausting hydrogen at the centre and have undergone hydrogen exhaustion in the thick shell.     

A new word on the spectral classification of stars

With the deepening of our knowledge on the stellar Universe, the problem is set forth concerning a further development of the spectral classification of stars —the actual means for investigation of the realm of stars.A new word on the spectral classification of stars — the idea of the MK Process — has been coined by Morgan; it marks a new stage in the study of our Universe.     

Cosmic rotation and the inertial system

A second order aberration term is employed for a determination of cosmic rotation from extremely precise relative positions of pairs of quasars. The value derived ( o/Ho<10^–5) corresponds with values derived from fluctuations of cosmic background radiation.     

Tidal evolution in close binary systems

The aim of the present paper will be to give a mathematical outline of the theory of tidal evolution in close binary systems of secularly constant total momentum — an evolution activated by viscous friction of dynamical tides raised by the two components on each other. The first section contains a general outline of the problem; and in Section 2 we shall establish the basic expressions for the energy and momenta of close binaries consisting of components of arbitrary internal structure. In Section 3 we shall investigate the maximum and minimum values of the energy (kinetic and potential) which such systems can attain for given amount of total momentum; while in Section 4 we shall compare these results with the actual facts encountered in binaries with components whose internal structure (and, therefore, rotational momenta) are known to us from evidence furnished by the observed rates of apsidal advance.The results show that all such systems — be these of detached or semi-detached type — disclose that more than 99% of their total momenta are stored in the orbital momentum. The sum of the rotational momenta of the constituent components amounts to less than a percent of the total — a situation characteristic of a state close to the minimum energy for given total momentum. This appears, moreover, to be true not only of the systems with both components on the Main Sequence, but also of those possessing evolved components in contact with their Roche limits.Under such conditions, a synchronism between rotation and revolution (characteristic of both extreme states of maximum and minimum energy) is not only possible, but appears to have been actually approached — if not attained — in the majority of cases. In other words, it would appear that — in at least a large majority of known cases — the existing close binaries have already attained orbits of maximum distension consistent with their momenta; and tidal evolution alone can no longer increase the present separations of the components to any appreciable extent.The virtual absence, in the sky, of binary systems intermediate between the stages of maximum and minimum energy for given momentum leads us to conjecture that the process of dynamical evolution activated by viscous tides may enroll on a time-scale which is relatively short in comparison with their total age — even for systems like Y Cygni or AG Persei, whose total age can scarcely exceed 10⁷ yr. A secular increase of the semi-major axes of relative orbits is dynamically coupled with a corresponding variation in the velocity of axial rotation of both components through the tidal lag arising from the viscosity of stellar material. The differential equations of so coupled a system are given in Section 5; but their solution still constitutes a task for the future.The Lunar Science Institute Contribution No. 90. The Lunar Science Institute is operated by the Universities Space Research Association under Contract No. NSR 09-051-001 with the National Aeronautics and Space Administration.     

Fourier analysis of the light curves of eclipsing variables,IX

The aim of the present paper will be to detail the procedure outlined in our previous investigations (Kopal, 1975; Kopalet al., 1976) for a solution of the elements of distorted eclipsing systems by a Fourier analysis of their light changes. This procedure—which constitutes an equivalent, in the frequency-domain, of rectification hitherto practised in the time-domain — should enable us to free the observed momentsA _2m of the light curves from all photometric effects of distortion (between minima as well as within eclipses) — a feat impossible in the time-domain except under very restricted conditions — and thus to make it possible to obtain the geometrical elements of the eclipses which should be free from any obvious source of systematic errors.     

Statistical masses of Abell clusters

The analysis of a homogeneous sample of 108 Abell clusters has led to an average peculiar velocity for the center of mass motion of these clusters of 610±750 km s^–1. From this result, an upper limit for the average mass of the Abell clusters of (1.6±2.4)×10¹⁵ M was obtained under the assumption that the peculiar motion is due to the excess of neighbours with respect to an uniform background. A lower limit of (2.42.9) x 10¹⁴ h ^-10.4 M was derived if one assumes that the peculiar velocity results from the mutual acceleration with the nearest neighbour.     

Note on Cid's radial intermediary and the method of averaging

In the main problem of artificial satellite theory, the difference between the Hamiltonian and Cid's radial intermediary is a function of the argument of latitude whose average over the mean anomaly is zero.Así debe ser—dijo cl Cura—; y en lo de casarsc vuestro amo, yo haré en ello todos mis poderíos. —MIGUEL de CERVANTES SAAVEDRA, El ingenioso hidalgo don Quijote de la Mancha.     

IUE observations of HL CMa and the winds of cataclysmic variables

As evidenced by the P Cygni profiles of their ultraviolet resonance lines, cataclysmic variables—like early-type stars—are known to have extensive, high velocity winds. Assisted by AAVSO visual data andIUE ultraviolet spectra, we present an observational and theoretical study of the P Cygni profiles of the dwarf nova HL CMa. As these profiles are dependent upon the ionization structure of the wind, we describe a model of a radiatively-driven shocked wind for cataclysmic variables, and present results for the temperature and ionization structure of the outflowing gas.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F.R.G., 16–19 June, 1986.     

Two X-ray sources model of Cyg X-3

A model of Cyg X-3, as a binary cocooned star system with two sources of X-rays, one above the polar caps of the neutron star — the usual pulsar radiation — and the other around the equatorial plane of the magneto-bounding surface formed due to the interaction of the infalling plasma and the magnetic field of the neutron star, is made. The X-ray, -ray, and IR radiation light curves are considered from the shadow effect. An upper limit on the mass of the neutron star is estimated from the consideration of periodic derivative purely due to mass loss. A comparison is made with the results of Elsneret al. (1980) and Ghoshet al. (1981), which they derived from the consideration of period derivative purely from apsidal motion.