Robert F. Loewenstein

Atmospheric turbulence at the South Pole and its implications for astronomy

To investigate the low-atmosphere turbulence at the South Pole, we have measured, using a SODAR, the temperature fluctuation constant (C 2 ) during winter, as a function of altitude up to 890 m. We found that the turbulence was on average concentrated inside a boundary layer sitting below 270 m. While at the peak of winter the turbulence was stable and clearly bounded, during other seasons there was a more complex turbulence profile which extended to higher altitudes. We found that this behaviour could be explained by the horizontal wind speed conditions whose altitude profile closely matched the turbulence profile. We also observed the presence of a vertical wind velocity change of direction at an altitude range corresponding to the turbulent region. The turbulence gives rise to an average seeing of 1:73 00 , which compares poorly with the best astronomy sites. The location of the turbulence, however, means that the seeing quickly decreases above the boundary layer (dropping to 0:37 00 above 300 m). We also have recorded the largest isoplanatic angle (AO= 3:3 00 ) and the longest coherence time (AO= 2: 9m s)

First Results from the Submillimeter Polarimeter for Antarctic Remote Observations: Evidence of Large-Scale Toroidal Magnetic Fields in the Galactic Center

We have observed the linear polarization of 450 μm continuum emission from the Galactic center, using a new polarimetric detector system that is operated on a 2 m telescope at the South Pole. The resulting polarization map extends ~170 pc along the Galactic plane and ~30 pc in Galactic latitude, and thus covers a significant fraction of the central molecular zone. Our map shows that this region is permeated by large-scale toroidal magnetic fields. We consider our results together with radio observations that show evidence of poloidal fields in the Galactic center and with Faraday rotation observations. We compare all of these observations with the predictions of a magnetodynamic model for the Galactic center that was proposed in order to explain the Galactic Center Radio Lobe as a magnetically driven gas outflow. We conclude that the observations are fundamentally consistent with the model.We have observed the linear polarization of 450 µm continuum emission from the Galactic center, using a new polarimetric detector system that is operated on a 2 m telescope at the South Pole. The resulting polarization map extends � 170 pc along the Galactic plane and � 30 pc in Galactic latitude, and thus covers a significant fraction of the central molecular zone. Our map shows that this region is permeated by large-scale toroidal magnetic fields. We consider our results together with radio observations that show evidence for poloidal fields in the Galactic center, and with Faraday rotation observations. We compare all of these observations with the predictions of a magnetodynamic model for the Galactic center that was proposed in order to explain the Galactic Center Radio Lobe as a magnetically driven gas outflow. We conclude that the observations are basically consistent with the model.

The star formation histories of low surface brightness galaxies

We have performed deep imaging of a diverse sample of 26 low surface brightness galaxies (LSBGs) in the optical and the near-infrared. Using stellar population synthesis models, we find that it is possible to place constraints on the ratio of young to old stars (which we parametrize in terms of the average age of the galaxy), as well as the metallicity of the galaxy, using optical and near-infrared colours. LSBGs have a wide range of morphologies and stellar populations, ranging from older, high-metallicity earlier types to much younger and lower-metallicity late-type galaxies. Despite this wide range of star formation histories, we find that colour gradients are common in LSBGs. These are most naturally interpreted as gradients in mean stellar age, with the outer regions of LSBGs having lower ages than their inner regions. In an attempt to understand what drives the differences in LSBG stellar populations, we compare LSBG average ages and metallicities with their physical parameters. Strong correlations are seen between an LSBG’s star formation history and its K-band surface brightness, K-band absolute magnitude and gas fraction. These correlations are consistent with a scenario in which the star formation history of an LSBG primarily correlates with its surface density and its metallicity correlates with both its mass and its surface density.

Dust and gas contributions to the energy output of SN 1987A on day 1153

16-30 μm spectra of SN 1987A taken with the Kuiper Airborne Observatory on 1990 April 20 and 22, days 1152 and 1154 after core collapse ar presented. The spectrum is characterized by a flat continuum of 0.62 ± 0.65 Jy, and a strong line at ∼26 μm which is attributed to the [Fe II] 25.98 μm transition. The observations are used to derive the mass of radiating Fe II in the ejecta, the mass and temperature of the dust that gives rise to the continuum emission, and combined with optical and near infrared observations, the total bolometric luminosity of the supernova

HIGH-RESOLUTION IMAGING OF PHOTODISSOCIATION REGIONS IN NGC 6334

We have used the SPIREX telescope to conduct a wide-—eld thermal infrared imaging study of the star formation complex NGC 6334 in the southern Galactic plane. We imaged a 30@ region along the main star-forming ridge of NGC 6334 with pixel scale through broadband —lters for L (3.5 km) and 0A.6 M (4.8 km) and through narrowband —lters for the v \ 1¨0 Q-branch (2.42 km), polycyclic aromatic H 2 hydrocarbon (PAH) (3.3 km), and Bra (4.05 km) lines. The images reveal the spectacular, complex struc- ture of the photodissociation regions (PDRs) that pervade the region, with enhanced line emission around each of the seven sites of massive star formation along the ridge. Bubbles and loops of PAH emission, typically 1¨1.5 pc across, have been carved out of the parent molecular cloud by the intense UV radiation from the massive stars and surround H II regions (seen in Bra) typically 0.2¨0.3 pc across. The PAH emission regions coincide with both (C II) 158 km line emission, indicating that the PAHs are excited in PDR gas, and extensive emission, which therefore must be —uorescent. However, the tex- H 2 tures of the emission regions in PAH and are diUerent. This is attributable to variations in the physi- H 2 cal environment in which the gas is excited. Several compact reddened objects are observed; these are likely to be massive protostars. Subject headings: infrared: generalinfrared: ISM: lines and bandsISM: molecules ¨ ISM: structurestars: formationtelescopes

The effective temperature of Neptune

The brightness temperature of Neptune has been measured in two broad passbands with flux-weighted mean wavelengths of 45 and 93 microns, permitting a direct determination of its effective temperature. The derived value of 55.5 plus or minus 2.3 K implies that Neptune radiates twice as much power as it receives from the sun.

HAWC: a far-infrared camera for SOFIA

When SOFIA enters operation, it will be the largest far- infrared telescope available, so it will have the best intrinsic angular resolution. HAWC (High-resolution Airborne Wideband Camera) is a far-infrared camera designed to cover the 40 - 300 micron spectral range at the highest possible angular resolution. Its purpose is to provide a sensitive, versatile, and reliable facility-imaging capability for SOFIAs user community during its first operational use.

A Hartmann Differential Image Motion Monitor (H-DIMM) for Atmospheric Turbulence Characterisation

We describe the use of a multi-aperture Hartmann mask coupled to a slightly out-of-focus focal plane array imager to monitor atmospheric turbulence (‘seeing’) produced by refractive index fluctuations. The imager (a CCD) is located inside or outside the focal surface of the imaging system so that each sub-aperture of the Hartmann mask produces an image well separated from all of the other images produced by the mask. Since the depth of focus of the sub-apertures is an order of magnitude larger than that of the parent optical system, the individual images are still diffraction-limited. We obtain short (10 to 100 msec) exposures and monitor the position fluctuations of the images. Analysis of the position and intensity fluctuations of the images can be used to determine the atmospheric parameter r 0 , the wind direction and velocity, and, under some circumstances, the distance of the turbulent layer from the observing site.

Automated Shack-Hartmann seeing measurements at the South Pole

The statistics and dynamics of the atmospheric seeing at the South Pole have been studied over a period of 101 days in winter. These measurements have been made with the first fully autonomous dierential image motion monitor, the A-DIMM. The analysis shows an average seeing of 1:9 00 with a standard deviation of 0:6 00 . The extensive set of data has allowed the study of the seeing time variations, showing that the seeing varies by a factor of two within a characteristic time of 2 hours.

Airborne spectrophotometry of P/Halley from 16 to 30 microns

We report on the first medium resolution spectrophotometric observations of a comet ever obtained in the 16- to 30-μm region. Comet P/Halley was observed using the Cornell University 7-channel spectrometer (Δλ/λ ~ 0.02 on board the Kuiper Airborne Observatory on 1985 December 14.2. Measurements were made centered on the nuclear condensation. These observations show a complex spectrum which could not be fit with simple models. The 20 μm silicate feature, if present, is very weak; and a relatively narrow (Δλ ~ 0.5 μm), strong feature centered at approximately 28.4 μm is observed and attributed to dust emission.