67841979
Carbon monoxide in low-mass dwarf stars
We compare high resolution infrared observations of the CO 3-1 bands in the 2.297– 2.310 µm region of M dwarfs and one L dwarf with theoretical expectations. We find a good match between the observational and synthetic spectra throughout the 20003500K temperature regime investigated. Nonetheless, for the 2500-3500 K temperature range the temperatures that we derive from synthetic spectral fits are higher than expected from more empirical methods by several hundred K. In order to reconcile our findings with the empirical temperature scale it is necessary to invoke warming of the model atmosphere used to construct the synthetic spectra. We consider that the most likely reason for the back-warming is missing high temperature opacity due to water vapour. We compare the water vapour opacity of the Partridge & Schwenke (1997) line list used for the model atmosphere with the output from a preliminary calculation by Barber & Tennyson (2004). While the Partridge & Schwenke line list is a reasonable spectroscopic match for the new line list at 2000 K, by 4000 K it is missing around 25% of the water vapour opacity. We thus consider that the offset between empirical and synthetic temperature scales is explained by the lack of hot water vapour used for computation of the synthetic spectra. For our coolest objects with temperatures below 2500 K we find best fits when using synthetic spectra which include dust emission. Our spectra also allow us to constrain the rotational velocities of our sources, and these velocities are consistent with the broad trend of rotational velocities increasing from M to L.
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
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.
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.
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 .
120377044
Electroproduction of isolated protons at high energy as a probe of the proton wave function in QCD
AbstractWe investigate the feasibility of using the process
$$eq \to ep\bar q\bar q$$
 as a means of determining the proton wave function which governs all exclusive processes involving protons. The calculation is performed in the limitŴ2≪Q2, whereŴ is the CM energy of the subprocess. The resulting expressions simplify considerably when an additional constraint is imposed excluding any hadrons accompanying the proton from a cone around it of half-angle θ≪1. However, a direct determination is still only possible in the case of a symmetric wave-function. A numerical exploration of the sensitivity of the cross-section to the parameters of an ansatz for the wave function shows a strong dependence on components which are not totally symmetric.
120327115
Comment on a proposed three-dimensional wave equation for mesons
A proposed equation for bound states of confined quarks is shown to be invalid. Possible modifications are discussed.
121068756
Phenomenological approach to chiral - symmetry breaking
It is shown that all meson-baryon and meson-meson $\ensuremath{\sigma}$ terms which can be extracted from experiment can be reconciled with the (3, \ifmmode\bar\else\textasciimacron\fi{}3) chiral-symmetry-breaking scheme, ${H}^{\ensuremath{'}}={u}_{0}+{\mathrm{cu}}_{8}$, provided that $c$ assumes the value $c\ensuremath{\sim}\ensuremath{-}1.0$.
15241449
Scattering from localized non-Hermitian potentials
We highlight the conceptual issues that arise when one applies the quasi-Hermitian framework to analyze scattering from localized non-Hermitian potentials, in particular complex square wells or delta functions. When treated in the framework of conventional quantum mechanics, these potentials are generally considered as effective theories, in which probability is not conserved because of processes that have been ignored. However, if they are treated as fundamental theories, the Hilbert-space metric must be changed. In order for the newly defined probability to be conserved, it must differ from the standard one, even at asymptotically large distances from the scattering center, and the mechanism for this is the nonlocality of the new metric, as we show in detail in the model of a single complex delta function. However, properties of distant bound-state systems, which do not interact physically with the non-Hermitian scattering potential, should not be affected. We analyze a model Hamiltonian that supports this contention.
119087895
Semiclassical calculation of the C operator in PT-symmetric quantum mechanics
Abstract To determine the Hilbert space and inner product for a quantum theory defined by a non-Hermitian PT -symmetric Hamiltonian H , it is necessary to construct a new time-independent observable operator called C . It has recently been shown that for the cubic PT -symmetric Hamiltonian H = p 2 + x 2 + iϵx 3 one can obtain C as a perturbation expansion in powers of ϵ . This Letter considers the more difficult case of noncubic Hamiltonians of the form H = p 2 + x 2 ( ix ) δ ( δ ⩾0). For these Hamiltonians it is shown how to calculate C by using nonperturbative semiclassical methods.