The performance of a new liquid Nitrogen cooled Fabry-Perot etalon for imaging at 3-5µm is described. Capacitance sensors monitor the etalon mirror spacing and parallelism, and error signals produced as a consequence of changes in these parameters are used in a feedback loop with piezoelectric actuators for active cavity control. These new cryogenic etalons are designed to be compatible with the Queensgate Instruments Ltd CS100/ET servo-stabilized Fabry-Perot system.

The cryogenic etalon has a clear aperture of 50mm and a nominal mirror spacing of between 5 and 60µm. It is coated for the 3 - 5µm spectral region, although coatings are also available for the 2 - 2.5µm and 8 - 13µm regions. Under servo-control at operating temperature the etalon has a response time of 30 msec and a minimum cavity tuning range of ±3µm about the nominal cavity length, corresponding to approximately 3 orders of interference at the midrange wavelength of 4µm.

We report observations of the v = 1-0 S(1) line of molecular hydrogen in the high excitation Planetary Nebula NGC 2440. The emission is particularly strong at the positions of the two bright condensations which lie well within the H II region and close to the position of the very hot T = 350,000 K central star. The emission is consistent with an excited molecular hydrogen mass of 2–4 × 10−5 M⊙ in the condensations, and we estimate the total mass of excited molecular hydrogen associated with the H II region to be 6 × 10−3 M⊙. We show that the radiation pressure from the central star is insufficient to excite the S(1) line emission. We also show that a stellar wind driven shock would imply a mass loss rate of 3 × 10−7 M⊙ yr−1 if we adopt a wind velocity of 2000 km s−1.

We have detected the central star of NGC 7027 by imaging the nebula through a narrow band ‘continuum’ filter onto the IPCS detector at the 2.5m Isaac Newton Telscope. We obtain an apparent visual magnitude for the central star of mv = 17.7 ± 0.5 mags.

Assuming that the central star radiates approximately as a blackbody, which is reasonable for the case of a hot star, then Zanstra temperatures for the central star can be calculated. We find TZ(H) = 3.9 × 105K and Tz(HeII) = 2.6 × 105K. Using the correction due to Stasinska & Tylenda (1986) we estimate the central star of NGC 7027 to have a temperature, Teff = 3.1 × 105K.

The luminosity and radii are found assuming a distance of d=1.2 kpc., giving L = 12,600 L⊙ and R = 0.039 R⊙. Placing the central star on the Log L - Log T diagram and comparing with evolutionary tracks for central stars with various masses from Wood & Faulkner (1986), indicates that the central star of NGC 7027 must have a mass, M ≥ 0.8 M⊙.

Radio observations of NGC 7027 have been taken using the Westerbork Radio Synthesis Telesocpe at 21cm. Self calibration techniques have been employed to give a radio continuum map of high dynamic range. These observations are being compared with a deep optical Hβ map to study the nature of the faint halo seen around NGC 7027 (Atherton et al. 1979)

The application of monochromatic images and internal kinematic data to the construction of 3-dimensional models for the HII regions of planetary nebulae is discussed, and the role of models in investigating envelope evolution is commented upon.

A description is given of a rocket payload designed to record high resolution ultraviolet stellar spectra using the star-stabilised ‘Skylark’ rocket vehicle. The system consists of a 35 cm aperture f/12 Cassegrain telescope and a spectrometer in which the high spectral dispersion of an echelle grating is crossed with that of a plane grating to separate the echelle orders. The spectrum is focussed onto an electrostatic image intensifier tube, the fibre optic faceplate of which is coated with sodium salicylate to give ultraviolet sensitivity. Photographic film is used to record the two dimensional spectrum array with a resolving power λ/dλ ≃ 104 between 1200 Å and 3000 Å. Efficiency measurements of components indicate that the photometric efficiency of the entire system will allow spectra to be recorded for early-type stars which are brighter than mr ≃ 5.

The echelle diffraction grating can be used to provide high spectral resolution in compact instrumentation which is very suitable for space astronomy applications. Spectrographs in which the high dispersion of the echelle is crossed with that of a concave grating have been flown in ‘Skylark’ sounding rockets to record the solar spectrum in the wavelength range 1200 Å–2200 Å, and further instrumentation is in preparation for observation of stellar spectra. Efficiency measurements have been made on some echelle replicas used in the instruments, and are correlated with surface conditions on the reflecting facets of the rulings. Results are also presented to demonstrate a spectral resolving power of λ/Δλ ≈ 105 over the wavelength range.