UKIRT HIGHLIGHTS

IRCAM Then and Now : New Images of M87 after 9 years

Tom Geballe

Head of UKIRT Operations

It has been claimed that from 1970 to the present, the sensitivity of astronomical instruments at infrared wavelengths has increased by a factor of two per year on average. The advent of infrared arrays is a big reason for this, but as these K band images of M87 and its famous jet testify (see the images below), the above improvement has continued since their arrival.

The first image (on the left) was obtained in 1987, shortly after the commissioning of IRCAM1 (the world's first common-user infrared camera) with its 58x62 detector array, and required 3 hours of observing time. The pixel size of 0.6'' oversampled the ~1.5-2'' image quality.

The second image (in the middle), obtained late in 1996, is a portion of a sky-subtracted frame obtained using IRCAM3 with its 256x256 array of 0.3'' pixels, with source and sky each exposed for 30 seconds, and with tip/tilt stabilisation turned on. Image quality was not good on this night, so the resultant resolution obtained by tip/tilt was only about 0.6''.

The improvements in signal-to-noise and in image quality over the 1987 data are dramatic. The final image (on the right), also from late 1996, is the result of a five-point mosaic requiring a total integration time of 5 minutes for object plus sky. In it many details of the jet are seen; in addition some of M87's globular clusters are discernible.

These images and similar ones obtained recently at J and H are being analysed by Tim Cawthorne and Ian Robson.

Imaging Polarimetry with IRCAM3

Antonio Chrysostomou

UKIRT Support Scientist

Since IRPOL was redesigned with a new and reliable polarimetry module, and the IRCAM furnished with a Wollaston prism, in August 1995, dual-beam imaging polarimetry has been available at UKIRT. Already there have been some published results from that initial commissioning period.

However, it was not until November 1996, that the UKIRT community has had the opportunity to take advantage of image stabilisation which the tip-tilt and fast guider system provides.

Imaging Polarimetry of the core region of Mon R2 IRS3. The offsets are measured from the nearby source IRS2. Note the structure in the distribution of polarisation vectors at the source.

The image above, obtained in February 1997, shows the first imaging polarimetry conducted with full image stabilisation. The full IRS2 and IRS3 field, in the Monoceros R2 star forming region, was observed in the K band and the figure above shows a close up of just the central core region of IRS3. The whole field was obtained in approximately 5 minutes integration (ignoring necessary overheads).

The image is startling in that it exhibits exceptional detail in the core region of the source. Such data provide empirical evidence that circumstellar environments are not as uniform as once believed.

These data are being analysed by researchers at the University of Hertfordshire and Observatoire de Grenoble.

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