7184822
PARALLAXES OF SOUTHERN EXTREMELY COOL OBJECTS. I. TARGETS, PROPER MOTIONS, AND FIRST RESULTS
We present results from the PARallaxes of Southern Extremely Cool objects (PARSEC) program, an observational program begun in 2007 April to determine parallaxes for 122 L and 28 T southern hemisphere dwarfs using the Wide Field Imager on the ESO 2.2 m telescope. The results presented here include parallaxes of 10 targets from observations over 18 months and a first version proper motion catalog. The proper motions were obtained by combining PARSEC observations astrometrically reduced with respect to the Second US Naval Observatory CCD Astrograph Catalog, and the Two Micron All Sky Survey Point Source Catalog. The resulting median proper motion precision is 5 mas yr–1 for 195,700 sources. The 140 0.3 deg2 fields sample the southern hemisphere in an unbiased fashion with the exception of the galactic plane due to the small number of targets in that region. The proper motion distributions are shown to be statistically well behaved. External comparisons are also fully consistent. We will continue to update this catalog until the end of the program, and we plan to improve it including also observations from the GSC2.3 database. We present preliminary parallaxes with a 4.2 mas median precision for 10 brown dwarfs, two of which are within 10 pc. These increase the present number of L dwarfs by 20% with published parallaxes. Of the 10 targets, seven have been previously discussed in the literature: two were thought to be binary, but the PARSEC observations show them to be single; one has been confirmed as a binary companion and another has been found to be part of a binary system, both of which will make good benchmark systems. These results confirm that the foreseen precision of PARSEC can be achieved and that the large field of view will allow us to identify wide binary systems. Observations for the PARSEC program will end in early 2011 providing three to four years of coverage for all targets. The main expected outputs are: more than a 100% increase in the number of L dwarfs with parallaxes, increment in the number of objects per spectral subclass up to L9—in conjunction with published results—to at least 10, and to put sensible limits on the general binary fraction of brown dwarfs. We aim to contribute significantly to the understanding of the faint end of the H-R diagram and of the L/T transition region.
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
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.
16852132
The discovery of an M4+T8.5 binary system
The original article can be found at: http://www3.interscience.wiley.com Copyright Blackwell Publishing / Royal Astronomical Society. DOI: 10.1111/j.1365-2966.2009.14620.x
16341718
A Neptune-mass Planet Orbiting the Nearby G Dwarf HD 16417
Original article can be found at: http://www.iop.org/EJ/journal/1538-3881 Copyright IOP Publishing / American Astronomical Society. DOI: 10.1088/0004-637X/697/2/1263 [Full text of this article is not available in the UHRA]
119127602
WKB Analysis of PT-Symmetric Sturm-Liouville problems. II
In a previous paper it was shown that a one-turning-point WKB approximation gives an accurate picture of the spectrum of certain non-Hermitian PT -symmetric Hamiltonians on a finite interval with Dirichlet boundary conditions. Potentials to which this analysis applies include the linear potential V = igx and the sinusoidal potential V = ig sin(αx). However, the one-turning-point analysis fails to give the full structure of the spectrum for the cubic potential V = igx, and in particular it fails to reproduce the critical points at which two real eigenvalues merge and become a complex-conjugate pair. The present paper extends the method to cases where the WKB path goes through a pair of turning points. The extended method gives an extremely accurate approximation to the spectrum of V = igx, and more generally it works for potentials of the form V = igx2N+1. When applied to potentials with half-integral powers of x, the method again works well for one sign of the coupling, namely that for which the turning points lie on the first sheet in the lower-half plane.
119410428
Soft gluon resummation formulae for hard parton processes in QCD
Abstract We briefly review the treatment of leading logarithmic behaviour of the parton distributions in QCD within the Bethe-Salpeter framework by analysing directly parton hadron Green functions in the limit of parton four-momentum k 2 → − ∞ in a special light-like gauge involving a spectator vector. This technique allows us to derive the factorization of parton probabilities in leading logarithmic order in QCD in the various inclusive processes involving a single short-distance scale. The proof requires us to show that the use of planar gauges η = p A + p B + ⋯, where p A , p B ⋯ are the observed hadron momenta, reduces to choosing the appropriate light-like gauge for each hadron-parton BS channel, after demonstrating a Bloch-Nordsieck cancellation of the real and virtual soft left-over gluons. In the case where two large momentum scales appear, by restricting the transverse phase space into which the gluons are radiated, we derive the double logarithmic eikonal renormalization of the hard scattering formula of the type proposed recently by Parisi and Petronzio.
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.
46321890
Complex square well - a new exactly solvable quantum mechanical model
Recently, a class ofPT -invariant quantum mechanical models described by the non- Hermitian HamiltonianHDp2 +x2.ix/ was studied. It was found that the energy levels for this theory are real for all > 0. Here, the limit as !1is examined. It is shown that in this limit, the theory becomes exactly solvable. A generalization of this Hamiltonian, H D p 2 +x 2M.ix/ (MD 1;2;3;:::) is also studied, and thisPT -symmetric Hamiltonian becomes exactly solvable in the large- limit as well. In effect, what is obtained in each case is a complex analogue of the Hamiltonian for the square-well potential. Expansions about the large- limit are obtained.
119309345
Analytic results for a PT-symmetric optical structure
Propagation of light through a medium with a complex refractive index in which gain and loss are engineered to be PT symmetric has many remarkable features. In particular the usual unitarity relations are not satisfied, so that the reflection coefficients can be greater than 1, and in general are not the same for left or right incidence. Within the class of optical potentials of the form v(x) = v1cos (2βx) + iv2sin (2βx) the case v2 = v1 is of particular interest, as it lies on the boundary of PT-symmetry breaking. It has been shown in a recent paper by Lin et al that in this case one has the property of ‘unidirectional invisibility’, while for propagation in the other direction there is a greatly enhanced reflection coefficient proportional to L2, where L is the length of the medium in the direction of propagation. For this potential we show how analytic expressions can be obtained for the various transmission and reflection coefficients, which are expressed in a very succinct form in terms of modified Bessel functions. While our numerical results agree very well with those of Lin et al we find that the invisibility is not quite exact, in amplitude or phase. As a test of our formulas we show that they identically satisfy a modified version of unitarity appropriate for PT-symmetric potentials. We also examine how the enhanced transmission comes about for a wave packet, as opposed to a plane wave, finding that the enhancement now arises through an increase, of O(L), in the pulse length, rather than the amplitude.