Signal-to-noise ratio of the bispectral analysis of speckle interferometry

Monte Carlo simulations of an atmospheric phase screen, based on a Kolmogorov spectrum of phase fluctuations, were performed. Speckle patterns produced from the phase screens were used to derive statistical properties of power spectra and bispectra of speckle interferograms. We present the bispectral modulation transfer function and its signal-to-noise ratio at high light levels. The results confirm the validity of a heuristic treatment based on an interferometric picture of speckle pattern formation in deriving the attenuation factor and the signal-to-noise ratio of the bispectral modulation transfer function in the mid-spatial-frequency range. The derived modulation transfer function is also interpreted in terms of the signal-to-noise ratio at low light levels. A general expression of the signal-to-noise ratio of the bispectrum is derived as a function of the transfer functions of the telescope, the number of speckles, and the mean photon counts in the mid-spatial-frequency range

Near Infrared Spectroscopy of M Dwarfs. I. CO Molecule as an Abundance Indicator of Carbon

Based on the near infrared spectra of 42 M dwarfs, carbon abundances are determined from the ro-vibrational lines of CO 2-0 band. We use Teff values based on the angular diameters if available or apply a logTeff - M3.4 (the absolute magnitude at 3.4 micron based on the WISE W1 flux and the Hipparcos parallax) relation to estimate Teff values of objects for which angular diameters are unknown. Also, we discuss briefly the HR diagram of low mass stars. On the observed spectrum of M dwarf, the continuum is depressed by the numerous weak lines of H2O and only the depressed continuum or the pseudo- continuum can be seen. On the theoretical spectrum of M dwarfs, we find that the pseudo-continuum can be evaluated accurately thanks to the recent H2O line database. Then quantitative analysis of the spectrum of M dwarf can be done by referring to the pseudo-continua both on the observed and theoretical spectra. Since the basic principle of the spectroscopic analysis should be the same whether the true- or pseudo-continuum is referred to, the difficulty related to the continuum in cool stars can in principle be overcome. Then, the numerous CO lines can be excellent abundance indicators of carbon, since almost all the carbon atoms are in stable CO molecules whose abundance remains almost unchanged for the changes of physical condition in the photosphere and, somewhat unexpectedly, carbon abundances in late-type stars can best be determined in M dwarfs rather than in solar type stars. The resulting C/Fe ratios for most M dwarfs are nearly constant at about the solar value based on the classical high carbon abundance rather than on the recently revised lower value. This result implies that the solar carbon abundance is atypical for its metallicity among the stellar objects in the solar neighborhood if the downward revised solar carbon abundance is correct.Comment: 33 pages, 17 figures, 13 tables + 1 table for electronic version only, minor changes in abstract, errors corrected in Tables 5, 8, and 10, corrected typos, accepted by PAS

An Interpretation of Flat Density Cores of Clusters of Galaxies by Degeneracy Pressure of Fermionic Dark Matter: A Case Study of Abell 1689

Flat density cores have been obtained for a limited number of clusters of galaxies by strong gravitational lensing. This paper explores the possibility that the degeneracy pressure of fermionic dark matter accounts for the flat top density profiles. This is a case study of A1689 for which the density profile has been obtained from the inner region out to 1Mpc by the combination of strong and weak lensing. In the case that the dark matter consists of the mixture of degenerate relic neutrinos and collisionless cold dark matter particles, the acceptable mass range for relic neutrinos is between 1 and 2 eV, if the ratio of the two kinds of dark matter particles is fixed to its cosmic value.Comment: Accepted for Publication in ApJ. Companion paper to astro-ph/060709

Noise in optical synthesis images. II. Sensitivity of an ^nC_2 interferometer with bispectrum imaging

We study the imaging sensitivity of a ground-based optical array of n apertures in which the beams are combined pairwise, as in radio-interferometric arrays, onto n(n - 1)/2 detectors, the so-called ^nC_2 interferometer. Groundbased operation forces the use of the fringe power and the bispectrum phasor as the primary observables rather than the simpler and superior observable, the Michelson fringe phasor. At high photon rates we find that bispectral imaging suffers no loss of sensitivity compared with an ideal array (space based) that directly uses the Michelson fringe phasor. In the opposite limit, when the number of photons per spatial coherence area per coherence time drops below unity, the sensitivity of the array drops rapidly relative to an ideal array. In this regime the sensitivity is independent of n, and hence it may be efficient to have many smaller arrays, each operating separately and simultaneously