Western looks to the Galaxy

by Mitchell Zimmer

In spite of the fact that over 20 different Universities throughout Canada offer a Ph.D. in Astronomy, only seven optical telescopes in excess of one meter in diameter exist in Canada. Western is one of the fortunate few, with a 1.2-meter reflector telescope located near Elginfield, just 25 kilometers north of campus.

The Cassegrain focus, at the rear of the telescope tube itself, is where instruments such as a spectrograph, polarimeter, and a two-star photometer can be used. The coude focus takes light reflected from the secondary mirror and channels it through a set of flat mirrors down through the floor of the dome where it is then diverted through more mirrors to a spectrograph. This instrument has can resolve starlight about 100,000 times, that is powerful enough to analyze spectral lines in most stars.

The facility was built in 1969. The Natural Sciences and Engineering Research Council of Canada and the province of Ontario provided the 1.5 million dollars to build the telescope, the observatory building plus some additional equipment. If an equivalent telescope were built today, it would cost in the neighbourhood of 10-15 million dollars. However, the style of the telescope would be somewhat different, since there is more advanced technology available now to make lighter mirrors to deal with problems of expansion.

In some ways these factors make Elginfield a modest observatory today, but that has its advantages. Many students contribute in the operation of the facility. They take part in everything from cleaning apparatus, designing experiments to the most delicate process of resilvering the primary mirror. This hands-on approach is unlikely to be found in larger observatories.

"Elginfield has a lot of advantages," says Mike Debruyne, the technician responsible for the day to day operations of the telescope. "It's not very far, so the observers can drive there in twenty-five minutes." The close proximity helps in the development of new instruments that are constructed at Western and then tested at Elginfield before researchers take them to other larger telescopes elsewhere in the world.

Research on the site, although varied, is primarily in spectroscopy. The work Prof. David Gray of the Physics and Astronomy Department provides an example. "We're spreading the light out into its colours and we're seeing the relative brightness in different colours," says Gray. "If the light is spread out a great deal, then you see all kinds of absorption features called spectral lines. Every one of these lines comes from some chemical... by looking at the lines in the first instance you can tell which chemicals are present."

"It turns out that every one of those spectral lines, if you look at it in great detail, has a precise shape. That shape is formed by a number of processes all mixed together: the rotation rate of the star, the velocity fields and storm activity in the atmosphere of the star, the convection as it appears on the surface of the star, surface features and magnetic fields." Dr. Gray's research concentrates on teasing out these various individual factors from the information contained in the spectra. The results of his work challenges current theory on the amount of convection occurring on some stars. Even though these phenomena are light years away, this work is important in understanding the physics of hydrodynamics. "People do very elaborate non-linear computations on the biggest computers you can get to try and simulate the flow of the gasses under these situations. ...Now from the practical point of view, these kinds of calculations are relevant to understanding the weather, ocean flows, and atmospheric flows generally. "

Another facet of Prof. Gray's work is in the study of the magnetic cycles of sun-like stars outside of the Solar system. "Magnetic cycles are not well understood, so it's interesting to figure out how our Sun compares to other stars.... Of course, one of the big issues of the day is global warming. I do not mean to downplay the problems of pollution, these are very serious problems and they must be addressed. Global warming is influenced by the amount of carbon dioxide and other greenhouse gases we produce... At the same time it's important to view the picture comprehensively and it's becoming increasingly clear that the Sun plays a significant role in climate change on the Earth."

Gray is following up on the observation that if a graph of the Earth's temperature change since the mid 1850's until now is superimposed over a plot of the length of the Solar magnetic cycle over the same time period there is a striking similarity. "Now we don't understand the mechanism, the power variation that's observed for the Sun over the last cycle or two of magnetic activity is only about one part per thousand, it's about a tenth of a per cent. That's generally considered to be too small to do much for climate on the Earth." The magnetic cycle and energy output link has been demonstrated in the past.

Between 1650 and 1710 the Sun didn't have a magnetic cycle, this period is called the Maunder minimum. During that time the 'little ice age' developed where glaciers advanced and growing seasons were shortened. To properly study the Sun today, research would have to be carried out over centuries. Gray has opted for a strategy to compensate for this, "There are lots of stars in the sky that are like the Sun, let's take a look at them let's see what they're doing. Do they show magnetic cycles? You bet they do, most of them do. Some don't.... Now we need to unravel, why are they not active? Are they in a Maunder minimum type or are they non-magnetics for other reasons. For those stars that are magnetic, how many of them really show cycles like the Sun does. Now that's measured from the power variations and measured spectroscopically. In fact spectroscopically, it's the techniques that I've developed here for measuring precise temperatures for these other stars that we've applied to the Sun that gave us the determination."

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