Position and Mode Dependent Optical Detection Back-Action in Cantilever Beam Resonators

Optical detection back-action in cantilever resonant or static detection presents a challenge when striving for state-of-the-art performance. The origin and possible routes for minimizing optical back-action have received little attention in literature. Here, we investigate the position and mode dependent optical back-action on cantilever beam resonators. A high power heating laser (100 {\mu}W) is scanned across a silicon nitride cantilever while its effect on the first three resonance modes is detected via a low-power readout laser (1 {\mu}W) positioned at the cantilever tip. We find that the measured effect of back-action is not only dependent on position but also the shape of the resonance mode. Relevant silicon nitride material parameters are extracted by fitting the temperature-dependent frequency response of the first three modes to finite element (FE) simulations. In a second round of simulations, using the extracted parameters, we successfully fit the FEM results with the measured mode and position dependent back-action. Finally, different routes for minimizing the effect of this optical detection back-action are described, allowing further improvements of cantilever-based sensing in general

The wind speed profile at offshore wind farm sites

Using Monin-Obukhov theory the vertical wind speed profile can be predicted from the wind speed at one height, when the two parameters Monin-Obukhov length and sea surface roughness are known. The applicability of this theory for wind power prediction at offshore sites is investigated using data from the measurement program Rdsand in the Danish Baltic Sea. Different methods to estimate the two parameters are discussed and compared. Significant deviations to the theory are found for near-neutral and stable conditions, where the measured wind shear is larger than predicted. A simple correction method to account for this effect has been developed and tested. As

A G1-like globular cluster in NGC 1023

The structure of a very bright (MV = -10.9) globular cluster in NGC 1023 is analyzed on two sets of images taken with the Hubble Space Telescope. From careful modeling of King profile fits to the cluster image, a core radius of 0.55+/-0.1 pc, effective radius 3.7+/-0.3 pc and a central V-band surface brightness of 12.9+/-0.5 mag / square arcsec are derived. This makes the cluster much more compact than Omega Cen, but very similar to the brightest globular cluster in M31, G1 = Mayall II. The cluster in NGC 1023 appears to be very highly flattened with an ellipticity of about 0.37, even higher than for Omega Cen and G1, and similar to the most flattened clusters in the Large Magellanic Cloud.Comment: 14 pages, 3 figures, 1 table. Accepted for AJ, Oct 200

Sizes and Shapes of Young Star Cluster Light Profiles in M83

We measure the radii and two-dimensional light profiles of a large sample of young, massive star clusters in M83 using archival HST/WFC3 imaging of seven adjacent fields. We use GALFIT to fit the two-dimensional light profiles of the clusters, from which we find effective (half-light) radii, core radii, and slopes of the power-law (EFF) profile ($\eta$). We find lognormal distributions of effective radius and core radius, with medians of $\approx$2.5 pc and $\approx$1.3 pc, respectively. Our results provide strong evidence for a characteristic size of young, massive clusters. The average effective radius and core radius increase somewhat with cluster age. Little to no change in effective radius is observed with increasing galactocentric distance, except perhaps for clusters younger than 100 Myr. We find a shallow correlation between effective radius and mass for the full cluster sample, but a stronger correlation is present for clusters 200-300 Myr in age. Finally, the majority of the clusters are best fit by an EFF model with index $\eta\leq3.0$. There is no strong evidence for change in $\eta$ with cluster age, mass, or galactocentric distance. Our results suggest that clusters emerge from early evolution with similar radii and are not strongly affected by the tidal field of M83. Mass loss due to stellar evolution and/or GMC interactions appear to dominate cluster expansion in the age range we study.Comment: 34 pages, 11 figures, 3 tables, accepted by MNRAS. Machine-readable table attached (full version of Table 3). To obtain, download the source file from the "Other formats" link abov

2FGL J0846.0+2820: A new neutron star binary with a giant secondary and variable γ\gamma-ray emission

We present optical photometric and spectroscopic observations of the likely stellar counterpart to the unassociated \emph{Fermi}-Large Area Telescope (LAT) $\gamma$-ray source 2FGL J0846.0+2820, selected for study based on positional coincidences of optical variables with unassociated LAT sources. Using optical spectroscopy from the SOAR telescope, we have identified a late-G giant in an eccentric ($e$ = 0.06) 8.133 day orbit with an invisible primary. Modeling the spectroscopy and photometry together lead us to infer a heavy neutron star primary of $\sim 2 M_{\odot}$ and a partially stripped giant secondary of $\sim 0.8 M_{\odot}$. H$\alpha$ emission is observed in some of the spectra, perhaps consistent with the presence of a faint accretion disk. We find the $\gamma$-ray flux of 2FGL J0846.0+2820 dropped substantially in mid-2009, accompanied by an increased variation in the optical brightness, and since then it has not been detected by \emph{Fermi}. The long period and giant secondary are reminiscent of the $\gamma$-ray bright binary 1FGL J1417.7--4407, which hosts a millisecond pulsar apparently in the final stages of the pulsar recycling process. The discovery of 2FGL J0846.0+2820 suggests the identification of a new subclass of millisecond pulsar binaries that are the likely progenitors of typical field millisecond pulsars.Comment: 12 pages, 8 figures, 3 tables. Accepted for publication in Ap