MAX at UKIRT: Highlights

S. Ligori
Max-Planck-Institut für Astronomie
Heidelberg, Germany

The nebula detected with MAX shows a clear bipolar nature with a complex structure: in addition to the outer, more prominent ring, an inner ring is observed along the equatorial plane. From the data shown here, and using previously available spectrophotometric data, we were able to revise the old estimate of the distance from 2.2 kpc to 1.2 kpc, with clear implications on the determination of the evolutionary status of the star. With a simple geometrical model it was possible to estimate the dust mass, while the spectral energy distribution enabled us to constrain the properties of the dust grains.

T Tauri stars and IR Companions

Thanks to the excellent sky conditions which are usually present on top of Mauna Kea and to the good optical quality of both UKIRT and MAX, we can routinely obtain diffraction-limited images at 10 µm. This allows us to obtain resolved spectrophotometry of close binary systems. This capability has been used, for instance, in the study of the T Tauri system, characterized by the presence of an optically invisible companion with a separation of 0".69. Herbst et al. (1997) presented resolved photometry in the Mid- and Near-IR obtained at UKIRT (See Fig. 2). Thanks to the silicate filter set, it is possible to evaluate separately the silicate feature of the two compo-

MAX (Mid-IR Array eXpandable) is the thermal infrared instrument of the Max-Planck-Institut für Astronomie, Heidelberg (Germany). The MAX project started to provide groundbased data to complement the information coming from the ISO mission, and in particular from the ISOPHOT instrument. The optical layout, based entirely on reflective elements, was designed to allow the instrument to be operated both at UKIRT and at the 3.5m telescope in Calar Alto. MAX is equipped with a Rockwell 128x128 Si:As BIB detector, but an upgrade to a larger format device (like the 256x256 currently available from Boeing) is possible with only minor modifications to the hardware. With this detector, the pixel scale at UKIRT is 0.27", and the resulting field of view is about 34" X 34".
Two filter wheels provide a large filter set with broad and narrow-band filters, including a sequence around the 9.7 µm silicate feature.

Max has been visiting UKIRT on a regular basis for a number of years, as part of the MPIA’s twice-yearly allocation of telescope time (which was in payment for the provision of UKIRT’s tip-tilt system and a new secondary mirror).
The firstlight run for MAX at UKIRT, which took place in November, 1995, was a complete success: the first stellar image obtained straight away showed several diffraction rings! Since then, MAX has been used exclusively at UKIRT. Now, after 5 successful years this guaranteed time is over, so it is the right moment for a summary of the main results

obtained.

Over the last years the MPIA team has used, thanks to the collaboration of the entire UKIRT staff, all the instruments available at UKIRT: in fact, the combination of mid-IR imaging with the near-IR imaging and spectroscopic capabilities provided by UKIRT, the excellent average seeing conditions and the good optical quality of UKIRT make this telescope almost unique for a number of studies. In the following, though, we mainly review the results obtained by MAX alone.

Fig. 1: Three-colour composite image of HD168625. The blue is associated to the 4.7 µm image, the green to the 10.1 µm image, and the red to the 19.9 µm image

Warm dust around blue hypergiants

A good example of how the combination of high spatial resolution and wide spectral coverage in the thermal IR can contribute to the