Supernova sn2005cs in M51 8th Aug 2005

A third spectrum of this supernova captured 42 days after discovery at mag +14.5. This exposure is 180x 30sec taken around midnight UT in dark skies. The image was taken at prime focus, using the Star Analyser diffraction grating without a slit.

The graph of the spectrum has been overlaid on the results from 4th July.

The previously clear H lines are almost lost in the noise. It is not certain if this represents a real change or if it is due to increased background interference because of the lack of slit.

Eyepiece projection with slit - Supernova sn2005cs in M51 4th July 2005

A second spectrum of this supernova captured 7 days after discovery. This exposure is 150x 30sec taken around midnight UT when the skies were darkest but still in twilight.

See the image from 1st July below for more details of the technique used

The spectrum image after subtraction of the background

At less than mag 14, this is the faintest spectrum I have been able to record to date. Since this was also recorded in twilight skies, It appears the slit aperture technique has enabled the magnitude range to be extended.

The spectrum of the supernova.

There are now signs of P Cygni type Hydrogen Balmer lines - a combination of emission lines from hot gas from the explosion and blue shifted absorption lines from the cooler gas thrown out in our direction.

The blue shift is approximately 2.7% corresponding to a velocity for the expanding gas of about 8000 km/second.

The core of the galaxy was sufficiently condensed in the image to allow some features to be seen in the spectrum. A Hydrogen alpha emission line is tentatively identified.

Eyepiece projection with slit - Supernova sn2005cs in M51 1st July 2005

The SC3 "PIPCAM" modified webcam was used with the VC200L and the prototype 1.25 inch filter cell 100 l/mm grating.

Eyepiece projection allowed a slit aperture to be used. This reduced the interfering glow from the twilight sky.

This image was produced with the slit wide open and no diffraction grating. Magnitude is estimated at 14.5 CCD referenced to Vmag

The upper spectrum image was taken with the slit narrowed. The spectrum of the background produced by the slit was subtracted to produce the lower spectrum image. The resulting spectrum shows no obvious features. It is too noisy to be worth plotting. Since this is supernova is reported as type II, it is expected that an H alpha absorption and emmision line feature will evolve in the comming weeks

Eyepiece projection with slit - Mizar a & b 1st July 2005

To calibrate the spectrograph, a spectrum of the double star Mizar was recorded. (Vesta SC3 "pipcam" modified webc amused in normal exposure mode) The strange star shapes in the zero order image are due to misalignment in the spectrograph optics. Despite this, some Balmer absorption lines can be seen.

The spectra of the two components were graphed and calibrated using Visual Spec. A linear fit to the H Balmer absorption lines was used. (The values given by the fit are slightly different to the true values but all are within better than +-10A/0.5pixels). Mizar a is spectral type A2V and component b appears to be very similar