13106340
The Prospects for Finding Brown Dwarfs in Eclipsing Binary Systems and Measuring Brown Dwarf Properties
We present the results of a simulation to investigate the prospects of measuring mass, age, radius, metallicity, and luminosity data for brown dwarfs in fully eclipsing binary systems around dwarf spectral types from late K to early M that could be identified by ultra-wide-field transit surveys such as SuperWASP. These surveys will monitor approximately a million K and M dwarfs with (where blending of sources is not FbF 1 20 a significant problem) at a level sufficient to detect transits of low-luminosity companions. We look at the current observational evidence for such systems and suggest that ∼1% of late K and early-to-mid M dwarfs could have a very close (∼0.02 AU) brown dwarf companion. With this assumption, and using SuperWASP as an example, our simulation predicts that ∼400 brown dwarfs in fully eclipsing binary systems could be discovered. All of these eclipsing binaries could yield accurate brown dwarf mass and radius measurements from radial velocity and follow-up light curve measurements. By inferring the brown dwarf effective temperature distribution, assuming a uniform age spread and an companion brown dwarf mass function, the simulation estimates that brown a p 0.5 dwarf brightness could also be measurable (at the 10% level) for ∼60 of these binary systems from near-infrared follow-up light curves of the secondary eclipse. We consider irradiation of these brown dwarfs by their primary stars and conclude that it would be below the 10% level for ∼70% of them. This means that in these cases, the measured brown dwarf brightnesses should essentially be the same as those of free-floating counterparts. The predicted age distribution of the primaries is dominated by young systems, and ∼20 binaries could be younger than 1 Gyr. Irradiation will be below the 10% level for ∼80% of these. We suggest that many of these young binary systems will be members of "kinematic moving groups," allowing their ages to be accurately constrained.
7248338
Selection functions in doppler planet searches
We present a preliminary analysis of the sensitivity of Anglo-Australian Planet Search data to the orbital parameters of extrasolar planets. To do so, we have developed new tools for the automatic analysis of large-scale simulations of Doppler velocity planet search data. One of these tools is the two-dimensional Keplerian Lomb-Scargle (LS) periodogram that enables the straightforward detection of exoplanets with high eccentricities (something the standard LS periodogram routinely fails to do). We used this technique to redetermine the orbital parameters of HD20782b, with one of the highest known exoplanet eccentricities (e = 0.97 +/- 0.01). We also derive a set of detection criteria that do not depend on the distribution functions of fitted Keplerian orbital parameters (which we show are non-Gaussian with pronounced, extended wings). Using these tools, we examine the selection functions in orbital period, eccentricity and planet mass of Anglo-Australian Planet Search data for three planets with large-scale Monte Carlo like simulations. We find that the detectability of exoplanets declines at high eccentricities. However, we also find that exoplanet detectability is a strong function of epoch-to-epoch data quality, number of observations and period sampling. This strongly suggests that simple parametrizations of the detectability of exoplanets based on `whole-of-survey' metrics may not be accurate. We have derived empirical relationships between the uncertainty estimates for orbital parameters that are derived from least-squares Keplerian fits to our simulations and the true 99 per cent limits for the errors in those parameters, which are larger than equivalent Gaussian limits by the factors of 5-10. We quantify the rate at which false positives are made by our detection criteria, and find that they do not significantly affect our final conclusions. And finally, we find that there is a bias against measuring near-zero eccentricities, which becomes more significant in
13406335
A search for southern ultracool dwarfs and wide binary systems in young moving groups
We associate 135 low-mass ultracool dwarfs in the southern hemisphere as candidate members of five moving groups using photometric and astrometric selection techniques. Of these objects, three candidates possess published radial velocities allowing a galactic space motion to be calculated, and the kinematic membership of the moving groups to be assessed. One object is a possible member of the IC2391 or Hyades moving groups. We also re-identify a previously known member of the Castor moving group. Also identified is a possible member of the Pleiades moving group, although the large uncertainties associated with the space motion of this object mean that it remains unconfirmed kinematically. Possible membership of moving groups has allowed possible ages and metallicities to be constrained for these objects and evolutionary models have been used to estimate their mass. In addition, the SuperCOSMOS and Hipparcos catalogues were searched for common proper motion binary companions to the 135 candidate moving group members. Three potential binary systems have been found. Further investigation is required to determine if one of these is the widest double brown dwarf binary system known, and another may consist of a low-mass star and a dwarf carbon star. We estimate that up to ∼75 of our candidate moving group members should be genuine, and discuss future work that will confirm and exploit this major new sample.
14166441
The Liverpool-Edinburgh high proper motion survey
We present a catalogue of 6206 stars which have proper motions exceeding 0.18 �� yr −1 with an R-band faint magni- tude limit of 19.5 mag. This catalogue has been produced using SuperCOSMOS digitized R-band ESO and UK Schmidt Plates in 131 Schmidt fields covering more than 3000 square degrees (>7.5% of the whole sky) at the South Galactic Cap. The survey is ≥90% complete within the nominal limits of the Luyten Two Tenths Catalogue of mR ≤ 18.5 mag and 0.2 ≤ µ ≤ 2.5 �� yr −1 , and is ≥80% complete for mR ≤ 19.5 mag and µ ≤ 2.5 �� yr −1 .
15353935
Two T dwarfs from the UKIDSS early data release
Context: We report on the first ultracool dwarf discoveries from the UKIRT Infrared Deep Sky Survey (UKIDSS) Large Area Survey Early Data Release (LAS EDR), in particular the discovery of T dwarfs which are fainter and more distant than those found using the 2MASS and SDSS surveys. Aims: We aim to show that our methodologies for searching the ~27 deg 2 of the LAS EDR are successful for finding both L and T dwarfs via cross-correlation with the Sloan Digital Sky Survey (SDSS) DR4 release. While the area searched so far is small, the numbers of objects found shows great promise for near-future releases of the LAS and great potential for finding large numbers of such dwarfs. Methods: Ultracool dwarfs are selected by combinations of their YJH ( K )$ UKIDSS colours and SDSS DR4 z - J and i - z colours, or, lower limits on these red optical/infrared colours in the case of DR4 dropouts. After passing visual inspection tests, candidates have been followed up by methane imaging and spectroscopy at 4 m and 8 m-class facilities. Results: Our main result is the discovery following CH 4 imaging and spectroscopy of a T4.5 dwarf, ULAS J 1452+0655, lying ~80 pc distant. A further T dwarf candidate, ULAS J 1301+0023, has very similar CH4 colours but has not yet been confirmed spectroscopically. We also report on the identification of a brighter L0 dwarf, and on the selection of a list of LAS objects designed to probe for T-like dwarfs to the survey J -band limit. Conclusions: Our findings indicate that the combination of the UKIDSS LAS and SDSS surveys provide an excellent tool for identifying L and T dwarfs down to much fainter limits than previously possible. Our discovery of one confirmed and one probable T dwarf in the EDR is consistent with expectations from the previously measured T dwarf density on the sky.
18728713
Effective temperatures, rotational velocities, microturbulent velocities and abundances in the atmospheres of the Sun, HD 1835 and HD 10700★
We describe our procedure to determine effective temperatures, rotational velocities, microturbulent velocities, and chemical abundances in the atmospheres of Sun-like stars. We use independent determinations of iron abundances using the fits to the observed Fe I and Fe II atomic absorption lines. We choose the best solution from the fits to these spectral features for the model atmosphere that provides the best confidence in the determined log N(Fe), Vt , and v sin i .Computations were done in the framework of LTE. Blending effects were accounted for explicitly. First, we compute the abundance of iron for a set of adopted microturbulent velocities. In some cases, a few points of log N(Fe I) = log N(Fe II) can be found. To determine the most selfconsistent effective temperature and microturbulent velocity in any star’s atmosphere, we used an additional constraint where we minimise the dependence of the derived abundances of Fe I and Fe II on the excitation potential of the corresponding lines. Using this procedure we analyse the spectra of the Sun and two well known solar type stars, HD1835 and HD10700 to determine their abundances, microturbulent velocity and rotational velocity. Our approach allows us to determine self-consistent values for the effective temperatures, abundances, Vt and v sin i . For the Sun we obtain the best agreement for a model atmosphere of Teff /log g/[Fe/H] = 5777/4.44/0.0, iron abundances and microturbulent velocities of log N(Fe) =4.44, Vt = 0.75 km/s, for the Fe I lines, and log N(Fe) = -4.47, Vt = 1.5 km/s for the Fe II lines. Furthermore, abundances of other elements obtained from the fits of their absorption features agree well enough (± 0.1 dex) with the known values for the Sun. We determined a rotational velocity of v sin i = 1.6 ± 0.3 km/s for the spectrum of the Sun as a star. For HD1835 the self-consistent solution for Fe I and Fe II lines log N(Fe)=+0.2 was obtained with a model atmosphere of 5807/4.47/+0.2 and microturbulent velocity Vt = 0.75 km/s, and leads to v sin i = 7.2 ± 0.5 km/s. For HD10700 the self-consistent solution log N(Fe) = -4.93 was obtained using a model atmosphere of 5383/4.59/-0.6 and microturbulent velocity Vt = 0.5 km/s. The Fe I and Fe II lines give rise to a v sin i = 2.4 ± 0.4 km/s. Using the Teff found from the ionisation equilibrium parameters for all three stars, we found abundances of a number of other elements: Ti, Ni, Ca, Si, Cr. We show that uncertainties in the adopted values of Teff of 100 K and Vt of 0.5 km/s change the abundances of elements up to 0.1 and 0.2 dex respectively. Galactic abundances variations can generally be larger than this measurement precision and therefore we can study abundance variations throughout the Galaxy.
18922676
On the phase structure of the 3D SU(2)-Higgs model and the electroweak phase transition
Abstract The phase structure of the 3D SU (2)-Higgs model, the dimensionally reduced effective theory for the electroweak model at finite temperature, is analysed on the lattice using a variant of the linear δ-expansion. We develop a systematic variational cumulant expansion for general application to the study of gauge-invariant operators in 3D gauge-Higgs models, with emphasis on the symmetric phase. In particular, the technique is not restricted to finite lattice volumes, and application to the fundamental 3D SU (2)-Higgs model allows the discontinuity of certain observables across the first-order transition to be observed directly for small 4I) Higgs masses. The resulting phase structure agrees well with Monte Carlo simulations for small Higgs masses, but, at least to the order calculated, the technique is less sensitive to the expected evolution of the transition to a crossover for Higgs masses above 80 GeV.
119134006
Dual PT-symmetric quantum field theories
Abstract Some quantum field theories described by non-Hermitian Hamiltonians are investigated. It is shown that for the case of a free fermion field theory with a γ 5 mass term the Hamiltonian is PT -symmetric. Depending on the mass parameter this symmetry may be either broken or unbroken. When the PT symmetry is unbroken, the spectrum of the quantum field theory is real. For the PT -symmetric version of the massive Thirring model in two-dimensional space–time, which is dual to the PT -symmetric scalar sine-Gordon model, an exact construction of the C operator is given. It is shown that the PT -symmetric massive Thirring and sine-Gordon models are equivalent to the conventional Hermitian massive Thirring and sine-Gordon models with appropriately shifted masses.
121385013
Perturbative QCD and the exclusive decay of heavy quarkonium into a photon and two mesons
We consider the radiative decays of the 3S1 ground state QQ into a real photon and two light pseudoscalar or vector mesons. For sufficiently large mass of the heavy quark Q, the decay, e.g. ϒ → γππ, can be calculated in perturbative QCD, provided that the photon does not carry away a predominant fraction of the available energy. We present differential and integrated Dalitz plot distributions and, for quarkonium states produced with transverse polarization in e+e− annihilation, angular distributions of the orientation of the decay triangle relative to the beam direction.
2335337
CONFORMAL MAPPING, POWER CORRECTIONS, AND THE QCD BOUND STATE SPECTRUM
We analyze the heavy quark bound state spectrum using an order-dependent conformal mapping to re-sum the peturbative expansion for current correlators. The procedure consists of two main steps. Firstly, the Borel plane structure of the truncated perturbative expression is modified to ensure consistency with the operator product expansion. This is analogous to a resummation of infrared renormalon chains. Secondly, this perturbative expansion is conformally mapped to a new series with improved convergence properties. This approach may be shown to induce power corrections consistent with existing condensates, and the resulting expansion may be ordered in powers of an infrared-analytic effective coupling. The technique is then applied to and sum rules without any explicit introduction of vacuum condensate parameters. Ground state masses for the vector, axial–vector and A′ channels are well reproduced, while results for the scalar–pseudoscalar mass splitting are less impressive.
121175185
Gluon effects and nonet mixing in the current quark picture
Abstract The effects on the meson mass spectrum of gluon interactions, and in particular of quark annihilation diagrams, are investigated in the current quark framework. The resulting mixing scheme leads to mixing angles θ p ≅ −13° and θ V ≅ − 52° for the pseudoscalar and vector nonets respectively, in moderate agreement with present data on radiative decays. For virtual electromagnetic processes additional gluon diagrams play a role. In η → 3 π the net effect is to almost double the current algebra prediction, while in ω → 2 π the ω → ϱ 0 transition amplitude is correctly predicted in both sign and magnitude. The relation between the Hamiltonian approach and the U(1) problem, as formulated in terms of axial divergences, is briefly discussed.