Laser frequency combs for astronomical observations

A direct measurement of the universe's expansion history could be made by observing in real time the evolution of the cosmological redshift of distant objects. However, this would require measurements of Doppler velocity drifts of about 1 centimeter per second per year, and astronomical spectrographs have not yet been calibrated to this tolerance. We demonstrate the first use of a laser frequency comb for wavelength calibration of an astronomical telescope. Even with a simple analysis, absolute calibration is achieved with an equivalent Doppler precision of approximately 9 meters per second at about 1.5 micrometers - beyond state-of-the-art accuracy. We show that tracking complex, time-varying systematic effects in the spectrograph and detector system is a particular advantage of laser frequency comb calibration. This technique promises an effective means for modeling and removal of such systematic effects to the accuracy required by future experiments to see direct evidence of the universe's putative acceleration.Comment: Science, 5th September 2008. 18 pages, 7 figures (7 JPG files), including Supporting Online Material. Version with higher resolution figures available at http://astronomy.swin.edu.au/~mmurphy/pub.htm

Pregnancy experiences of Western Australian women attending a specialist childbirth and mental illness antenatal clinic

Our purpose was to explore the pregnancy experiences of Australian women attending a specialized Childbirth and Mental Illness (CAMI) antenatal clinic. A qualitative exploratory design was selected to give voice to women with a severe mental illness receiving antenatal care. Telephone interviews with 41 women, 24 primiparous and 17 multiparous, were analysed using thematic analysis. Three themes emerged: ‘Building relationships’, ‘Acknowledged me as a person with special needs’ and ‘Respect and understanding without stigma’. Findings offer insight into care experiences possible within a multidisciplinary model developed to addresses psychiatric and obstetric needs of pregnant women with severe mental illness

Manipulating the Phenolic Acid Content and Digestibility of Forage Grasses by Targeted Expression of Fungal Cell Wall Degrading Enzymes

Grass cell walls constitute 30-80% of forage dry matter, representing a major source of energy for ruminants. Ferulic acid (4-hydroxy-3-methoxy-cinnamic acid) and other hydroxycinnamic acids are ester linked to arabinosyl residues in arabinoxylans of grass cell walls and undergo oxidative coupling reactions resulting in the formation of a variety of dehydrodiferulate dimers which cross-link cell wall polymers. Although such cross-links have a number of important roles in the cell wall, they also hinder the rate and extent of cell wall degradation by ruminant microbial and fungal enzymes. We have shown previously the expression of a ferulic acid esterase gene from Aspergillus niger in Festuca arundinacea and the potential of the expressed FAE to break phenolic cross-links and release monomeric and dimeric ferulic acids on cell death in vacuole targeted FAE plants. This was enhanced several fold by the addition of exogenous recombinant xylanase (Buanafina et al., 2002). We propose to decrease the level of phenolic cross-linking of cell wall carbohydrate by inducible expression of FAE to the apoplast, ER and golgi and by co-expressing FAE and endo-ß-1,4-xylanase from Trichoderma reesei to the apoplast and vacuole

Rashba spin-orbit coupling in the square lattice Hubbard model: A truncated-unity functional renormalization group study

The Rashba-Hubbard model on the square lattice is the paradigmatic case for studying the effect of spin-orbit coupling, which breaks spin and inversion symmetry, in a correlated electron system. We employ a truncated-unity variant of the functional renormalization group which allows us to analyze magnetic and superconducting instabilities on equal footing. We derive phase diagrams depending on the strengths of Rasbha spin-orbit coupling, real second-neighbor hopping and electron filling. We find commensurate and incommensurate magnetic phases which compete with d-wave superconductivity. Due to the breaking of inversion symmetry, singlet and triplet components mix; we quantify the mixing of d-wave singlet pairing with f-wave triplet pairing

Projected Rotational Velocities and Stellar Characterization of 350 B Stars in the Nearby Galactic Disk

Projected rotational velocities (vsini) are presented for a sample of 350 early B-type main sequence stars in the nearby Galactic disk. The stars are located within ~1.5 kpc from the Sun, and the great majority within 700 pc. The analysis is based on high-resolution spectra obtained with the MIKE spectrograph on the Magellan Clay 6.5-m telescope at the Las Campanas Observatory in Chile.Spectral types were estimated based on relative intensities of some key line absorption ratios and comparisons to synthetic spectra. Effective temperatures were estimated from the reddening-free Q index, and projected rotational velocities were then determined via interpolation on a published grid that correlates the synthetic full width at half maximum of the He I lines at 4026, 4388 and 4471 A with vsini. As the sample has been selected solely on the basis of spectral types it contains an selection of B stars in the field, in clusters, and in OB associations. The vsini distribution obtained for the entire sample is found to be essentially flat for vsini values between 0-150 km/s, with only a modest peak at low projected rotational velocities. Considering subsamples of stars, there appears to be a gradation in the vsini distribution with the field stars presenting a larger fraction of the slow rotators and the cluster stars distribution showing an excess of stars with vsini between 70 and 130 km/s. Furthermore, for a subsample of potential runaway stars we find that the vsini distribution resembles the distribution seen in denser environments, which could suggest that these runaway stars have been subject to dynamical ejection mechanisms.Comment: 38 pages, 11 figures. Complete sample table. AJ accepte

HD 178892 - a cool Ap star with extremely strong magnetic field

We report a discovery of the Zeeman resolved spectral lines, corresponding to the extremely large magnetic field modulus =17.5 kG, in the cool Ap star HD 178892. The mean longitudinal field of this star reaches 7.5 kG, and its rotational modulation implies the strength of the dipolar magnetic component Bp>=23 kG. We have revised rotation period of the star using the All Sky Automated Survey photometry and determined P=8.2478 d. Rotation phases of the magnetic and photometric maxima of the star coincide with each other. We obtained Geneva photometric observation of HD 178892 and estimated Teff=7700+/-250 K using photometry and the hydrogen Balmer lines. Preliminary abundance analysis reveals abundance pattern typical of rapidly oscillating Ap stars.Comment: Accepted by Astronomy & Astrophysics; 4 pages, 4 figure

Mesoscale features create hotspots of carbon uptake in the Antarctic Circumpolar Current

The influence of eddy structures on the seasonal depletion of dissolved inorganic carbon (DIC) and carbon dioxide (CO2) disequilibrium was investigated during a trans-Atlantic crossing of the Antarctic Circumpolar Current (ACC) in austral summer 2012. The Georgia Basin, downstream of the island of South Georgia (54-55°S, 36-38°W) is a highly dynamic region due to the mesoscale activity associated with the flow of the Subantarctic Front (SAF) and Polar Front (PF). Satellite sea-surface height and chlorophyll-a anomalies revealed a cyclonic cold core that dominated the northern Georgia Basin that was formed from a large meander of the PF. Warmer waters influenced by the SAF formed a smaller anticyclonic structure to the east of the basin. Both the cold core and warm core eddy structures were hotspots of carbon uptake relative to the rest of the ACC section during austral summer. This was most amplified in the cold core where greatest CO2 undersaturation (-78 µatm) and substantial surface ocean DIC deficit (5.1 mol m-2) occurred. In the presence of high wind speeds, the cold core eddy acted as a strong sink for atmospheric CO2 of 25.5 mmol m-2 day-1. Waters of the warm core displayed characteristics of the Polar Frontal Zone (PFZ), with warmer upper ocean waters and enhanced CO2 undersaturation (-59 µatm) and depletion of DIC (4.9mol m-2). A proposed mechanism for the enhanced carbon uptake across both eddy structures is based on the Ekman eddy pumping theory: (i) the cold core is seeded with productive (high chlorophyll-a) waters from the Antarctic Zone and sustained biological productivity through upwelled nutrient supply that counteracts DIC inputs from deep waters; (ii) horizontal entrainment of low-DIC surface waters (biological uptake) from the PFZ downwell within the warm core and cause relative DIC-depletion in the upper water column. The observations suggest that the formation and northward propagation of cold core eddies in the region of the PF could project low-DIC waters towards the site of Antarctic Intermediate Water formation and enhance CO2 drawdown into the deep ocean

High-precision wavelength calibration of astronomical spectrographs with laser frequency combs

We describe a possible new technique for precise wavelength calibration of high-resolution astronomical spectrographs using femtosecond-pulsed mode-locked lasers controlled by stable oscillators such as atomic clocks. Such `frequency combs' provide a series of narrow modes which are uniformly spaced according to the laser's pulse repetition rate and whose absolute frequencies are known a priori with relative precision better than 10^{-12}. Simulations of frequency comb spectra show that the photon-limited wavelength calibration precision achievable with existing echelle spectrographs should be ~1 cm/s when integrated over a 4000A range. Moreover, comb spectra may be used to accurately characterise distortions of the wavelength scale introduced by the spectrograph and detector system. The simulations show that frequency combs with pulse repetition rates of 5-30GHz are required, given the typical resolving power of existing and possible future echelle spectrographs. Achieving such high repetition rates, together with the desire to produce all comb modes with uniform intensity over the entire optical range, represent the only significant challenges in the design of a practical system. Frequency comb systems may remove wavelength calibration uncertainties from all practical spectroscopic experiments, even those combining data from different telescopes over many decades.Comment: 10 pages, 6 figures, 1 table. Accepted by MNRAS. v2: Fig. 3 augmented and minor changes to text (including extended title