Astronomical Images from CIRSI on the 2.5m Isaac Newon Telescope and the 4.2m William Herschel Telescope

# CIRSI Astronomical Images

Note: many of the images are displayed as small gifs to speed up display: click on these images to see the full size image

Caption: Mosiac of two adacent H band(1.6microns) images of a region of sky containing the massive X-ray luminous cluster Abell 2219. The image shown has dimsensions 5arcmins by 20arcmins.

### The Gravitational Lens: Abell 2219

The rich cluster of galaxies Abell 2219(z=0.228) is a massive gravitational lens. This picture is 3 colour image of the galaxy cluster is based on a 2.5hr H band exposure obtained with CIRSI combined with B and I band opticcal CCD images. The CIRSI was obtained on the 4.2m William Herschel Telescope in June 1998. This image reveals evidence for lensed features. The observation are being used to trace the dark matter distribution within the cluster The field of view is 4.8 arcmin x 4.8 arcmin and the measured seeing in H band image is 0.7 arc seconds.

### Contiguous mosaic of four adjacent CIRSI pointings

A contiguous mosaic based on four adjacent pointings obtained with CIRSI at the 2.5m INT. The final merged image is 4000x4000pixels at 0.46''/pixel. The field of view is 29 arc minutes on each side. The exposure time per pointing is 13minutes. The 5$\sigma$ limit of the image within an aperture of diameter 2 arcsecs is H=18.5$\pm$0.5. At this limit there are $\sim$1000 galaxies some of which should lie at a redshift of z$\sim$1, and $\sim$150 galactic stars.

### A cluster of galaxies with a redshift of 0.81

INT H band image of the luminous x=0.81, X-ray galaxy cluster RX J 1716.6+6708 which is at z=0.81 The observations were obtained in June 1998 and this is the first 23 minutes out of a 90minute observing sequence. The image is from a quarter of chip 2, and the field of view is approximately 4' x 4'.

Below are set of images that show our on sky progress with cirsi. Many of the images have only undergone basic 'at telescope' data reduction. Some image show various artifacts that will be removed by further data processing such as better dark subraction and linear pattern noise filtering and geometric rectification.

## CIRSI image of the Galactic Centre

On the left is 10 minute exposure with CIRSI on the 2.5m Isaac Newton Telescope, in the H(1.65micron) waveband of a the region of sky in the direction of the centre of the Milky Way, the so called Galactic Centre. Each white dot is an star like the Sun. The clump of objects just bottom left of centre is a densely packed cluster of of millions stars believed to be located at the centre of the Milky Way. Bottom right of centre is a another cluster of stars near the galactic centre. These two clusters are about 30 light years apart. The seeing on this image is 0.9".

On the right is an optical image of the same region of sky. The optical image is quite different from the Infra-Red. The main difference is that the Infra-red image has about 100 times more detected stars.

## Dark matter and low mass stars

Stars like the Sun are not the commonest type of star in the Universe. In fact most of the mass in the Universe is believed to be contained in low mass stars that are much cooler than the Sun. These cool stars are very faint in the optical but are much brighter in the infra-red. However, one cannot measure the mass of a star by observing how bright it is. One project that we are tackling with CIRSI is a program to directly determine the masses of low mass stars by searching for stars that are eclipsing binaries. The figure below shows two images of the star cluster NGC6633. These images were obtained on the nights of June 15th 1998 and June 17th 1998. The aim is to compare the two images and look for stars that have changed in brightness between the dates.

CIRSI images of the star cluster NGC6633. One image was taken on the night of June 15th 1998 and the other was taken on the night of June 17th 1998. The aim is to use this data to seach for star that have changed in brightness, due the passage of an unseen companion like a planet or very low mass star, in front of the stellar disk. By determining the orbital period and radial velocities of these binary stars we can make a direct measurement of their masses using Newtons' laws of gravitation.

## Messier 16

Images of Messier 16 in the optical and Infrared. Messier 16 is a cloud of gas and dust like Orion, within which stars are currently forming. Messier 16 lies at a distance of around 7,000 light years from the Earth. In astronomical terms Messier 16 is quite young, with an age of a mere 5.5 Million years. In the optical we can only see a few of the stars that lie in this young stellar nursery. Using CIRSI can see right inside this dusty cloud.

# CIRSI H band image of Gamma Ray Burst GRB980613 BeppoSAX error box

### The Spiral Galaxy M51

• M51 contiguous mosaic with quadrant scaling artifact This image exhibits poor sky subtracted due to biasing of the sky estimator by the presence of M51. Note this is just the central quarter of the full dataset ie 15'x15'. The full raw image is 30'x30'. Chip 4 which is on the bottom right shows some structure which is under investigation.

## WHT June 98 run

Pointing pattern for WHT image of M13. In this example M13 was placed on each of the 4 independent chips to allow a detailed analysis of the geometric distortion in order to test our geometric rectification software. The tangential pattern is probably caused by the fact the the individual fpa's are not perfectly aligned in the XY plane.

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• core of Messier 13 [false colour ] [ grey scale ] This is a single 9 point dither of M13 with an on sky exposure time of 10mins. The image quality was 0.7"(fwhm)

• core of Messier 13 [ greyscale ] [ false colour ] This image is an coadd from 4 independent chips. There is an arc-like swirl pattern which may be due to the alignment of the chips or geometric optical distortions. It will be a good test of our analysis pipeline to ensure that this is image is coadded properly.

### The Gravitational Lens: Abell 2219

The rich cluster of galaxies Abell 2219(z=0.228) is a massive gravitational lens. This short exposure (27minutes) was obtained with CIRSI on the 4.2m William Herschel Telescope on June 2th 1998. This image already reveals evidence for lensed features. The total exposure, of 2.5hrs at each of two positions, will trace the dark matter distribution over unprecedented cosmic scales.
• Massive, X-ray luminous cluster of galaxies Abell 1689
• Massive, X-ray luminous cluster of galaxies Abell 2219
• More results from the WHT

### INT May 98 run

• Our first large mosaic! 30' x 30' image of the ELAIS N2 region

• Images of the globular cluster Messier 13

### First light images from WHT Jan 98

• Coma Cluster(from the Jan. '98 WHT run)
• ### First light images from INT Dec 97

• Saturn image
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Richard McMahon, rgm@ast.cam.ac.uk