The Purple Haze of Eta Carinae: Binary-Induced Variability?

Asymmetric variability in ultraviolet images of the Homunculus obtained with the Advanced Camera for Surveys/High Resolution Camera on the Hubble Space Telescope suggests that Eta Carinae is indeed a binary system. Images obtained before, during, and after the recent ``spectroscopic event'' in 2003.5 show alternating patterns of bright spots and shadows on opposite sides of the star before and after the event, providing a strong geometric argument for an azimuthally-evolving, asymmetric UV radiation field as one might predict in some binary models. The simplest interpretation of these UV images, where excess UV escapes from the secondary star in the direction away from the primary, places the major axis of the eccentric orbit roughly perpendicular to our line of sight, sharing the same equatorial plane as the Homunculus, and with apastron for the hot secondary star oriented toward the southwest of the primary. However, other orbital orientations may be allowed with more complicated geometries. Selective UV illumination of the wind and ejecta may be partly responsible for line profile variations seen in spectra. The brightness asymmetries cannot be explained plausibly with delays due to light travel time alone, so a single-star model would require a seriously asymmetric shell ejection.Comment: 8 pages, fig 1 in color, accepted by ApJ Letter

Emission Line Galaxies in the STIS Parallel Survey II: Star Formation Density

We present the luminosity function of [OII]-emitting galaxies at a median redshift of z=0.9, as measured in the deep spectroscopic data in the STIS Parallel Survey (SPS). The luminosity function shows strong evolution from the local value, as expected. By using random lines of sight, the SPS measurement complements previous deep single field studies. We calculate the density of inferred star formation at this redshift by converting from [OII] to H-alpha line flux as a function of absolute magnitude and find rho_dot=0.043 +/- 0.014 Msun/yr/Mpc^3 at a median redshift z~0.9 within the range 0.46<z<1.415 (H_0 = 70 km/s/Mpc, Omega_M=0.3, Omega_Lambda=0.7. This density is consistent with a (1+z)^4 evolution in global star formation since z~1. To reconcile the density with similar measurements made by surveys targeting H-alpha may require substantial extinction correction.Comment: 16 preprint pages including 5 figures; accepted for publication in Ap

Measurements of the Diffuse Ultraviolet Background and the Terrestrial Airglow with the Space Telescope Imaging Spectrograph

Far-UV observations in and near the Hubble Deep Fields demonstrate that the Space Telescope Imaging Spectrograph (STIS) can potentially obtain unique and precise measurements of the diffuse far-ultraviolet background. Although STIS is not the ideal instrument for such measurements, high-resolution images allow Galactic and extragalactic objects to be masked to very faint magnitudes, thus ensuring a measurement of the truly diffuse UV signal. The programs we have analyzed were not designed for this scientific purpose, but would be sufficient to obtain a very sensitive measurement if it were not for a weak but larger-than-expected signal from airglow in the STIS 1450-1900 A bandpass. Our analysis shows that STIS far-UV crystal quartz observations taken near the limb during orbital day can detect a faint airglow signal, most likely from NI\1493, that is comparable to the dark rate and inseparable from the far-UV background. Discarding all but the night data from these datasets gives a diffuse far-ultraviolet background measurement of 501 +/- 103 ph/cm2/sec/ster/A, along a line of sight with very low Galactic neutral hydrogen column (N_HI = 1.5E20 cm-2) and extinction (E(B-V)=0.01 mag). This result is in good agreement with earlier measurements of the far-UV background, and should not include any significant contribution from airglow. We present our findings as a warning to other groups who may use the STIS far-UV camera to observe faint extended targets, and to demonstrate how this measurement may be properly obtained with STIS.Comment: 7 pages, Latex. 4 figures. Uses corrected version of emulateapj.sty and apjfonts.sty (included). Accepted for publication in A

Clinical observation of diminished bone quality and quantity through longitudinal HR-pQCT-derived remodeling and mechanoregulation.

High resolution peripheral quantitative computed tomography (HR-pQCT) provides methods for quantifying volumetric bone mineral density and microarchitecture necessary for early diagnosis of bone disease. When combined with a longitudinal imaging protocol and finite element analysis, HR-pQCT can be used to assess bone formation and resorption (i.e., remodeling) and the relationship between this remodeling and mechanical loading (i.e., mechanoregulation) at the tissue level. Herein, 25 patients with a contralateral distal radius fracture were imaged with HR-pQCT at baseline and 9-12 months follow-up: 16 patients were prescribed vitamin D3 with/without calcium supplement based on a blood biomarker measures of bone metabolism and dual-energy X-ray absorptiometry image-based measures of normative bone quantity which indicated diminishing (n = 9) or poor (n = 7) bone quantity and 9 were not. To evaluate the sensitivity of this imaging protocol to microstructural changes, HR-pQCT images were registered for quantification of bone remodeling and image-based micro-finite element analysis was then used to predict local bone strains and derive rules for mechanoregulation. Remodeling volume fractions were predicted by both average values of trabecular and cortical thickness and bone mineral density (R2 > 0.8), whereas mechanoregulation was affected by dominance of the arm and group classification (p < 0.05). Overall, longitudinal, extended HR-pQCT analysis enabled the identification of changes in bone quantity and quality too subtle for traditional measures

Emission Line Galaxies in the STIS Parallel Survey I: Observations and Data Analysis

In the first three years of operation STIS obtained slitless spectra of approximately 2500 fields in parallel to prime HST observations as part of the STIS Parallel Survey (SPS). The archive contains almost 300 fields at high galactic latitude (|b|>30) with spectroscopic exposure times greater than 3000 seconds. This sample contains 220 fields (excluding special regions and requiring a consistent grating angle) observed between 6 June 1997 and 21 September 2000, with a total survey area of about 160 square arcminutes. At this depth, the SPS detects an average of one emission line galaxy per three fields. We present the analysis of these data, and the identification of 131 low to intermediate redshift galaxies detected by optical emission lines. The sample contains 78 objects with emission lines that we infer to be redshifted [OII]3727 emission at 0.43<z<1.7. The comoving number density of these objects is comparable to that of H-alpha emitting galaxies in the NICMOS parallel observations. One quasar and three probable Seyfert galaxies are detected. Many of the emission-line objects show morphologies suggestive of mergers or interactions. The reduced data are available upon request from the authors.Comment: 58 preprint pages, including 26 figures; accepted for publication in ApJ

Measurement of Cosmic Shear with the Space Telescope Imaging Spectrograph

Weak lensing by large-scale structure allows a direct measure of the dark matter distribution. We have used parallel images taken with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope to measure weak lensing, or cosmic shear. We measure the shapes of 26036 galaxies in 1292 STIS fields and measure the shear variance at a scale of 0.51 arcminutes. The charge transfer efficiency (CTE) of STIS has degraded over time and introduces a spurious ellipticity into galaxy shapes during the readout process. We correct for this effect as a function of signal to noise and CCD position. We further show that the detected cosmic shear signal is nearly constant in time over the approximately four years of observation. We detect cosmic shear at the 5.1 sigma level, and our measurement of the shear variance is consistent with theoretical predictions in a LambdaCDM universe. This provides a measure of the normalization of the mass power spectrum sigma_8=(1.02 +- 0.16) (0.3/Omega_m)^{0.46} (0.21/Gamma)^{0.18}$. The one-sigma error includes noise, cosmic variance, systematics and the redshift uncertainty of the source galaxies. This is consistent with previous cosmic shear measurements, but tends to favor those with a high value of sigma_8. It is also consistent with the recent determination of sigma_8 from the Wilkinson Microwave Anisotropy Probe (WMAP) experiment.Comment: 9 pages, 5 figure, 1 table, Accepted to Ap

Geotechnical Observations of the November 3, 2002 M7.9 Denali Fault Earthquake

The M 7.9 earthquake of November 3, 2002 event ruptured more than 340 kilometers on three fault, causing widespread liquefaction in the fluvial deposits of steep alpine valleys of the Alaska Range and eastern lowlands of the Tanana River. The event occurred in a remote and largely undeveloped portion of the rugged Alaskan central range, with few seismometer recordings. The areas affected by liquefaction are largely confined to native Holocene river deposits, areas bounded by stiffer ground moraine, Pleistocene uplands, and bedrock. Liquefaction affected areas of alluvial river valleys draining mountainous and glacier-proximal rivers. The most noteworthy observations are that liquefaction damage was focused towards the eastern end of the rupture area. In the western portion of the rupture zone, localized liquefaction developed in recent deposits of the Susitna and Delta rivers in the immediate vicinity of the surface rupture of the fault. More abundant and severe liquefaction occurred on the eastern Robertson, Slana, Tok, Chisana and, especially, Nabesna Rivers. In the Tanana lowland, liquefaction features were sparse on the western bars of the Tanana River in the vicinity of Fairbanks to west of Delta, but became pervasive throughout the eastern region from Delta to Northway. Though liquefaction observations were abundant, there was a dearth of instrumental recordings useful to relate damage effects to measured intensity. To characterize soil properties and stiffness of liquefaction evaluation sites, we used a portable spectral analysis of surface waves (SASW) apparatus to profile the shear wave velocity of the ground. On the Nabesna and Delta rivers that cross the fault, we only observe liquefaction features in soil deposits where normalized shear wave velocities fall below 230 m/s. Severity of sand boils, fissuring and lateral displacement of liquefied ground dramatically increase in soils of lower shear wave velocity, especially below 170 m/s. Some of the most pronounced ground failures are far from the fault zone (60-100 km) in extremely loose, low velocity (~120 m/s) fine sands of the bars of the Tanana River. Strong motion instrumentation was sparse within 150 kilometers of the fault rupture and the seismometers of Alyeska pump stations PS9 (PGA=0.09), PS10 (PGA=0.36g), and PS11 (PGA=0.09) serve as the principal strong motion recordings. Insufficient strong motion instrumentation is available to identify areas of amplified ground motio