K Band (k + band)

Distribution by Scientific Domains


Selected Abstracts


MMIC medium-power amplifier in K band with matching and power-divider/combiner networks implemented with the use of lumped elements

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 6 2002
L. Álvarez
Abstract The design and measurements of a monolithic K-band medium-power amplifier are reported. The matching, biasing, and power-splitter networks have been implemented with the use of lumped elements, reducing the chip size. The model predictions of passive circuitry have been tested through electromagnetic simulations. The amplifier has shown interesting performance in K band. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 33: 397,400, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10334 [source]


IRAC photometric analysis and the mid-IR photometric properties of Lyman-break galaxies

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008
G. E. Magdis
ABSTRACT We present photometric analysis of deep mid-infrared (mid-IR) observations obtained by Spitzer/IRAC covering the fields Q1422+2309, Q2233+1341, DSF2237a,b, HDFN, SSA22a,b and B20902+34, giving the number counts and the depths for each field. In a sample of 751 Lyman-break galaxies (LBGs) lying in those fields, 443, 448, 137 and 152 are identified at 3.6-, 4.5-, 5.8-, 8.0-,m IRAC bands, respectively, expanding their spectral energy distribution to rest-near-IR and revealing that LBGs display a variety of colours. Their rest-near-IR properties are rather inhomogeneous, ranging from those that are bright in IRAC bands and exhibit [R],[3.6] > 1.5 colours to those that are faint or not detected at all in IRAC bands with [R],[3.6] < 1.5 colours and these two groups of LBGs are investigated. We compare the mid-IR colours of the LBGs with the colours of star-forming galaxies and we find that LBGs have colours consistent with star-forming galaxies at z, 3. The properties of the LBGs detected in the 8-,m IRAC band (rest-frame K band) are examined separately, showing that they exhibit redder [R],[3.6] colours than the rest of the population and that although in general, a multiwavelength study is needed to reach more secure results, IRAC 8-,m band can be used as a diagnostic tool, to separate high z, luminous AGN-dominated objects from normal star-forming galaxies at z, 3. [source]


Imaging and spectroscopy of ultrasteep spectrum radio sources,

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2007
Carlos G. Bornancini
ABSTRACT We present a sample of 40 ultrasteep spectrum (USS; ,,, 1.3, S,,,,) radio sources selected from the Westerbork in the Southern Hemisphere (WISH) catalogue. The USS sources have been imaged in K band at the Cerro Tololo Inter-American Observatory (CTIO) and with the Very Large Telescope (VLT) at Cerro Paranal. We also present VLT, Keck and William Herschel Telescope (WHT) optical spectroscopy of 14 targets selection from four different USS samples. For 12 sources, we have been able to determine the redshifts, including four new radio galaxies at z > 3. We find that most of our USS sources have predominantly small (<6 arcsec) radio sizes and faint magnitudes (K, 18). The mean K -band counterpart magnitude is . The expected redshift distribution estimated using the Hubble K,z diagram has a mean of , which is higher than the predicted redshift obtained for the Sydney University Molonglo Sky Survey,NRAO VLA Sky Survey (SUMSS,NVSS) sample and the expected redshift obtained in the 6C** survey. The compact USS sample analysed here may contain a higher fraction of galaxies which are high redshift and/or are heavily obscured by dust. Using the 74, 352 and 1400 MHz flux densities of a subsample, we construct a radio colour,colour diagram. We find that all but one of our USS sources have a strong tendency to flatten below 352 MHz. We also find that the highest redshift source from this paper (at z= 3.84) does not show evidence for spectral flattening down to 151 MHz. This suggests that very low frequency selected USS samples will likely be more efficient to find high redshift galaxies. [source]


Cosmic microwave background signal in Wilkinson Microwave Anisotropy Probe three-year data with fastica

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007
D. Maino
ABSTRACT We present an application of the fast Independent Component Analysis (fastica) to the Wilkinson Microwave Anisotropy Probe (WMAP) three-year data with the goal of extracting the cosmic microwave background (CMB) signal. We evaluate the confidence of our results by means of Monte Carlo simulations including the CMB, foreground contaminations and instrumental noise specific to each WMAP frequency band. We perform a complete analysis involving all or a subset of the WMAP channels in order to select the optimal combination for CMB extraction, using the frequency scaling of the reconstructed component as a figure of merit. We find that the combination KQVW provides the best CMB frequency scaling, indicating that the low-frequency foreground contamination in Q, V and W bands is better traced by the emission in the K band. The CMB angular power spectrum is recovered up to the degree scale; it is consistent within errors for all WMAP channel combinations considered, and in close agreement with the WMAP three-year results. A power spectrum analysis is made of the sky map divided into two hemispheres that have been previously reported as showing evidence of an asymmetric ratio of power on large angular scales. We then confirm the findings of several previous works with independent techniques. [source]


Keck infrared observations of GRO J0422+32 in quiescence

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2007
Mark T. Reynolds
ABSTRACT We present Keck K -band photometry and low-resolution H - and K -band spectroscopy of the X-ray nova GRO J0422+32 obtained while the system was in the quiescent state. No clear ellipsoidal modulation is present in the light curve, which is instead dominated by a strong flickering component. In the K band, we observe strong Br, emission, with an equivalent width of 38 ± 5 Ĺ. From this, we conclude that the accretion disc is the most likely source of the observed photometric contamination, and that previous infrared-based attempts to constrain the mass of the putative black hole in this system are prone to considerable uncertainty. We finally proceed to show how it is possible to place meaningful constraints on some of the binary parameters of this system, even in the presence of a relatively high level of contamination from the disc. [source]


Gas and stellar dynamics in NGC 1068: probing the galactic gravitational potential

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2006
Eric Emsellem
ABSTRACT We present SAURON integral field spectrography of the central 1.5 kpc of the nearby Seyfert 2 galaxy NGC 1068, encompassing the well-known near-infrared (NIR) inner bar observed in the K band. We have successively disentangled the respective contributions of the ionized gas and stars, thus deriving their two-dimensional distribution and kinematics. The [O iii] and H, emission lines exhibit a very different spatial distribution and kinematics, the latter following inner spiral arms with clumps associated with star formation. Strong inward streaming motions are observed in both the H, and [O iii] kinematics. The stellar kinematics also exhibit clear signatures of a non-axisymmetric tumbling potential, with a twist in both the velocity and Gauss,Hermite h3 fields. We re-examined the long-slit data of Shapiro, Gerssen & van der Marel using a pPXF: a strong decoupling of the Gauss,Hermite term h3 is revealed, and the central decrease of Gauss,Hermite term h4 hinted in the SAURON data is confirmed. These data also suggest that NGC 1068 is a good candidate for a so-called , drop. We confirm the possible presence of two separate pattern speeds applying the Tremaine,Weinberg method to the Fabry,Perot H, map. We also examine the stellar kinematics of bars formed in N -body + smoothed particle hydrodynamics (SPH) simulations built from axisymmetric initial conditions approximating the luminosity distribution of NGC 1068. The resulting velocity, dispersion and higher order Gauss,Hermite moments successfully reproduce a number of properties observed in the two-dimensional kinematics of NGC 1068 and the long-slit data, showing that the kinematic signature of the NIR bar is imprinted in the stellar kinematics. The remaining differences between the models and the observed properties are likely mostly due to the exclusion of star formation and the lack of the primary large-scale oval/bar in the simulations. These models nevertheless suggest that the inner bar could drive a significant amount of gas down to a scale of , 300 pc. This would be consistent with the interpretation of the , drop in NGC 1068 being the result of central gas accretion followed by an episode of star formation. [source]


The correlation of metallicity gradient with galaxy mass

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2005
Duncan A. Forbes
ABSTRACT A number of previous studies have searched for a correlation between radial metallicity gradients and early-type galaxy mass , no convincing trends have been found. Here we re-examine this issue with several key enhancements: using total metallicity from studies that have broken the age,metallicity degeneracy, excluding galaxies with young stellar ages (i.e. those that have experienced a recent central starburst) and using the K band to derive galaxy luminosities. We find that Coma cluster galaxies have metallicity gradients that correlate with galaxy mass. Furthermore, gradients have values similar to those of monolithic collapse models. The combination of dissipative formation and energy injection from supernovae provides a mechanism for the trends with galaxy mass; however, other explanations are possible. Additional high-quality observational data are needed to constrain further the gas physics involved in galaxy formation. [source]


Optical absorption, paramagnetic resonance and depolarisation currents in MgAl2O4 spinel

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2007
Roberto Paiva
Abstract Optical Absorption (OA), Electron Paramagnetic Resonance (EPR) and Thermally Stimulated Depolarisation Currents (TSDC) techniques were applied to study the effects of irradiation and thermal treatments in the formation, aggregation and destruction processes of dipole defects in MgAl2O4 spinel. Irradiated MgAl2O4 crystals present two OA bands centred at 3.4 eV and 5.1 eV. The 3.4 eV band increases with the irradiation-dose, stabilizes its maximum height for doses near 10 kGy and is completely destroyed for thermal treatments above 500 K. This same band decays when the sample is maintained at room temperature reaching a constant value after a few weeks. The EPR spectrum is composed by two superimposed bands at g = 2.011. The gamma dose dependence, the thermal treatments between 370 K and 500 K and the thermal decay of the two bands at room temperature, show that each band behaves in a different way thus indicating that they are associated with two different defects. Gamma dose of 10 kGy produces a TSDC band at 245 K. When the sample is maintained at room temperature, after the gamma irradiation, for several weeks, a displacement in the peak position to 290 K, is observed. Thermal treatments above 500 K destroy the 290 K band. This band is associated to at least two V-type centres. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]