Astronomical instrumentation

Abstract:

A system to measure image size and motion has been designed, constructed and put into operation at the 4-meter Mayall telescope at Kitt Peak National Observatory (KPNO). The present system configuration consists of three elements. A 128 multiplied by 128 pixel CID camera is mounted at the south port of the Cassegrain instrument rotator. The CID camera is fed, under software control, by a movable mirror in the instrument rotator. Focusing is achieved by determining the point of zero-image motion when the f/8 beam is cut by a rotating Newall mask. Focal plane images are digitized and stored on digital disk for later determination of image size and motion as a function of time. The second element is a two-dimensional position sensor which records image motion induced along an air path located between the primary and secondary mirrors of the telescope. The third element monitors temperature of the telescope and air throughout the telescope structure. The system is described and preliminary results are presented.

Abstract:

A new megamaser galaxy has been discovered as part of an OH survey of selected IRAS galaxies. This increases the number of known megamaser galaxies to seven, and extends the range of their infrared luminosity and colour temperature. The new megamaser differs from the others in that it appears optically as a spiral galaxy with a bright core, although the megamaser emission itself indicates that this core must contain an active nucleus. Both the infrared luminosity and the 60/100 K colour temperature are below those of any other OH megamaser galaxies, but the OH/infrared luminosity ratio is close to the median value, lending support to the suggested relationship between OH and infrared luminosities.

Abstract:

Spectra between 8-13 microns of 15 planetary nebulae are presented. Those planetaries with strong continuum emission are classified according to their dust emission spectra as oxygen or carbon rich. The spectrum of NGC 6302 shows a very strong emission line at 7.65 microns, confirming the reality of the feature seen by the low-resolution spectrometer on IRAS. The data presented here bring the number of available 8-13-micron spectra to 49. The far-infrared properties of planetary nebulae are found to reflect the differences in the dust chemistry found from the 8-13-micron spectra. This dependence is clearly seen in color-color plots constructed from the IRAS data, so that the different grain materials seen in the 8-13 micron spectra also show differences in the dust emissivity at longer wavelengths.

Abstract:

Spectra are presented with a resolving power λ/Δλ \ap 1100 of the dusty Wolf-Rayet star Ve 2-45 and the southern H II region G333.6-0.2. An upper limit on the equivalent width of any features in the range 11.0 to 13.0 μm is determined to be 0.0022 μm towards Ve 2-45. This figure is compared with the predicted strength of the unobserved narrow feature at 11.52 μm which has been proposed to be associated with small graphite grains (Draine).