11498709
A H13CN/HN13C linelist, model atmospheres and synthetic spectra for carbon stars
‘The definitive version is available at www.blackwell-synergy.com’. Copyright Blackwell Publishing DOI: 10.1111/j.1365-2966.2008.13642.x
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.
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]
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
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
120722437
Dynamics versus selection rules in diffraction dissociation
Abstract In a diffraction model arising from duality, and in related models, the Morrison and other selection rules for diffraction dissociation are shown not to hold. An examination of experimental data also indicates a failure of these rules. The consequences of the model for the helicity structure of A 1 πϱ couplings are explored.
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.
123586127
Variational approach to the SU(2) mass gap on the lattice
A brief introduction is given to the basic idea of the linear delta expansion, which is illustrated in the case of a simple integral. The method is then applied to the calculation of the scalar glueball mass in lattice SU(2).
118106812
Groups, Representations and Physics
General properties of groups and mappings group representations properties of irreducible representations physical applications continuous groups SO(N) further applications the SU(N) groups and particle physics representations of the Poincare group gauge groups.
14770938
Interface between Hermitian and non-Hermitian Hamiltonians in a model calculation
We consider the interaction between the Hermitian world, represented by a real delta-function potential -{alpha}{delta}(x), and the non-Hermitian world, represented by a PT-symmetric pair of delta functions with imaginary coefficients i{beta}({delta}(x-L)-{delta}(x+L)). In the context of standard quantum mechanics, the effect of the introduction of the imaginary delta functions on the bound-state energy of the real delta function and its associated wave function is small for L large. However, scattering from the combined potentials does not conserve probability as conventionally defined. Both these problems can be studied instead in the context of quasi-Hermiticity, whereby quantum mechanics is endowed with a new metric {eta}, and consequently a new wave function {psi}(x), defined in terms of the original wave function {psi}(x) by means of {eta}. In this picture, working perturbatively in {beta}, the bound-state wave function is actually unchanged from its unperturbed form for |x| >L, is changed in a significant manner. In particular, there are incoming and outgoing waves on both sides of the potential. One can then no longer talk in terms of reflection and transmission coefficients, but the total right-moving flux is now conserved.