BAA VSS SPECTROSCOPY WORKSHOP AT THE
NORMAN LOCKYER OBSERVATORY.
The attendance of fifty participants at the BAA Spectroscopy Workshop, held at the
Norman Lockyer Observatory (NLO) on October 10th 2015, was a testament to the
increasing interest about this fascinating aspect of astronomy. People had come from far
and wide to attend the meeting. One of our speakers, Olivier Thizy, had travelled from
south west France, and another speaker, Robin Leadbeater, had come from Cumbria.
Olivier Thizy is a director of Shelyak Instruments and is passionate about spectroscopy.
He launched the proceedings with his subject of “Why we do Spectroscopy”. He
showed us the construction of his Alpy slit spectrograph, and demonstrated the
contrasting line profiles obtained from the blue and golden components of the double
star Albireo. He went on to demonstrate how to obtain a Planck curve from the data, and
hence how we can work out the temperatures of these two stars. Olivier then covered the
subject of the bright emission line stars such as Gamma Cas and Beta Lyrae which had
been discovered in 1866 by Father Angelo Secchi. He explained that this emission, seen
as bright lines, was caused by re-emitted energy expelled from a disc of matter surrounding
each of these stars.
A rather more challenging project for the spectroscopist would be to demonstrate the
Doppler-Fizeau effect, obtained from red-shifted galaxy spectra, which shows the expansion
of the universe. He also showed us the capabilities of the LHIRES III high resolution
spectrograph, which was able to detect Saturn’s rotational speed, and analyse spectroscopic binaries. Olivier’s talk demonstrated that off-the-shelf equipment and software was now well within the reach of the amateur spectroscopist.
Robin Leadbeater is one of the UK’s leading amateur spectroscopists and was next, to
talk about “How we do Spectroscopy: preparation, acquisition and data reduction”.
Robin started his presentation by explaining about the different types of spectrographs
currently available, ranging from:
- the entry level diffraction grating: Star Analyser (SA) 100 (£100)
- to the medium resolution Alpy(£1000)
- to the high resolution LISA (£2300) and e-Shel spectrograph (£10K).
He showed that slit spectroscopy, compared with an SA100 grating, gave greater spectral
resolution but with the sacrifice of less light transmission. In addition, spectrographic
performance is affected by telescope aperture and the focal ratio. Mirror slit guiding is currently the universally adopted solution for focussing and guiding. Robin went through the basics of using the spectral analysis software ISIS, and showed how to produce an instrument response curve and a rectified spectrum. Some projects he highlighted included high cadence differential spectroscopy of the fast transient T Tauri star DN Tau, which had been imaged every 15 minutes. In this case data was obtained using a low resolution slitless spectrograph. He also showed how to use an Alpy 200 for supernovae type identification.
Andy Wilson’s talk was titled “My First steps in Spectroscopy”, and considering that he
had started just 12 months before, the quality of his spectra showed that he had already
mastered the subject. His equipment included a Littrow spectrograph L200, and a LHIRES
III in conjunction with a SXVR-H694 CCD. Andy described the process of focussing and
positioning the star on the slit, and processing the spectrum, including correcting for tilt
and slant. He showed examples of some of his interesting targets, including Kappa Cyg,
Rho Persei, Chi Cyg, AG Peg, M42 and Comet Lovejoy.
David Boyd’s talk was titled “Observing with a LISA Spectrograph”. David is another of
our leading UK spectroscopists, regularly submitting his data to the professionals. His
equipment includes a LISA spectrograph in conjunction with a C11 and an SXVR-H694
CCD. David showed us how he flux calibrates his data with a view to monitoring changes
in the energy output of a star over time, or to detect changes in the energy distribution
across the spectrum. He also showed how to correct for interstellar extinction and reddening.
Some examples he showed included an outburst of SS Cyg, and the peculiar eclipsing binary V Sagittae. The last part of his talk demonstrated that it is possible to measure radial velocities of stars with a LISA spectrograph.
This intensive workshop ran from 11.00am – 6.00pm, however with a one hour break for
lunch there was a chance to have a look at some of the historic prismatic cameras and
equipment at the NLO, that was used by Norman Lockyer and his colleagues some 100
Our thanks must be extended to Roger Pickard and the BAA for organising this event
and to our excellent speakers who have willingly shared their knowledge and made all
their talks available for download from Olivier’s website: