October 2001 Meeting Report

rasc.ca
  • No tags were found...

Dec - The Royal Astronomical Society of Canada, Halifax Centre

the annual meeting would be after therefreshment break, would have enough timeto reconfigure several computers and theirconnections to the data projector, as well aspower to the overhead projector, etc. It remindedme of a scene from one of the early episodesof Star Trek: The Next Generation, whereData had to put all of the isolinear chipsfrom the warp drive computer back in thecorrect sequence! David (Lane) presentedthe financial report, which you will findelsewhere in this issue. I am not sure if itis a good sign, but Ian Anderson, this year’sauditor, was making notes to himself throughoutDave’s entire presentation!Lastly, we had an introduction to the membersof next year’s centre executive. David (Tindall)pointed out that some people were beingreused, some were being recycled, and thatwe actually had some new faces as well,which is always good news.This scribe did the handbook talk on thesubject of the nearest stars. I did have somepeople fooled when I started by putting up atransparency of the handbook’s index, notto do talk on the index, but to show whereit was in this year’s issue. Munchies time!After the refreshment break, David Tindallintroduced the main speaker for the evening.Dr. Bob Garrison is currently the nationalpresident of the RASC, and so far during histerm has visited 20 of the society’s 26 centres.His visit to our centre was part of atour of the four Atlantic centres.Dr Garrison is now professor emeritus at theDepartment of Astronomy and Astrophysicsat the University of Toronto, having retiredthis summer. During his career he publishedover 150 papers and two books. He taughtthe first Life in the Universe course in NorthAmerica (over 25 years ago) and always hada full class of 200 students plus many on awaiting list! He always enjoyed his work, andsaw spectroscopy as a method to learn aboutthe ‘personalities’ of individual stars. Usingthis tool, he also was able to discover quitea number of ‘peculiar’ stars. He said that itwas not that hard to find weird stars whenthere are millions of stars to observe. Thebest way to start was with a survey of aparticular type of star. The survey could beall of the stars at a single declination; all starswithin a certain distance of the Sun; all starswith a certain surface temperature; as longas you looked at lots of stars.Over his career he has discovered manystars that definitely qualify as weird. In1973 he discovered a ‘helium’ star. Itsspectrum showed lots of helium lines, butno sign of any hydrogen. He announced theresults at a conference in India, and was beinginterviewed by a particularly keen reporterwho understood the concept of hydrogendeficientstars, but asked Dr. Garrison what hewas going to do about the lack of hydrogenin this particular star!Another discovery made by Dr. Garrison was,as he liked to call it, the People’s CV. Mostcataclysmic variable (CV) stars reach a maximumvisual magnitude that rarely exceeds14. His reached a brightness of 9.4, puttingit well into the reach of amateur astronomers.He also found aluminum oxide in the spectrumof Mira-type variable. (He described Mira-typevariables as sinks for astronomers becausethey get into the field because of the strangeproperties of these objects, spend a lot of timestudying them, but never learn much in theend.) He has also found stars with very strongbarium lines, and Population II stars (the onesthat are only supposed to have hydrogen andhelium) with carbon lines.He then showed some pictures of the varioustelescopes that he has used over the years.He has made many trips to Chile and over a26 year period has obtained over 30,000spectra of more than 10,000 stars. He hasalso used the David Dunlap Observatory. Henoted that the surrounding municipalities havelight pollution abatement ordinances whichhas resulted in no increase in the light pollutionat the DDO. The telescope is still usedevery clear night, and the new operator isactually a RASC member who believes thatshe has died and gone to heaven!Spectroscopy can also be used to determinethe distance to a star that is too far away tohave its distance measured by parallax. Thetechnique is quite straightforward. First, youfind a star whose distance can be found byparallax. By knowing its visual magnitude anddistance, you can then calculate its absolutemagnitude (the visual magnitude it wouldhave at a distance of 10 parsecs). If you nowfind a distant star that has the same spectrum,you know that it must have the same properties,including absolute magnitude. Byknowing its absolute magnitude and observingits visual magnitude, you can now calculateits distance. Refinements have been madeto this method as the parallax data from theHipparcos satellite now allows us to calibratethe spectra of stars out to a distance of 100parsecs.At this point, Dr. Garrison reviewed the classificationsystem that is used to categorizestars, the MK process. A star is classified bycomparing its spectrum to those of standardspectral types. One advantage of this system, isthat it takes advantage of the human brain’stremendous ability to recognize patterns.(Think of how little data the brain needs torecognize the face of a friend – or an enemy– at great distances.) In fact, someone whohas no idea what they are looking at can stillclassify stellar spectra!He showed some examples of how the patternschange. These included all of the subtypeswithin the O-type stars (O5, O6, etc.) andone A-star subtype, going from luminosityclass I (supergiant) down to luminosity classV (main sequence). He also shown a seriesof spectra of the L-class stars, ranging fromL0 to L8. Oh, you have never heard of anL-class star before? That makes two of us!These stars are on the main sequence, butare cooler than M-type stars, with surfacetemperatures measured in hundreds ofdegrees. The reason they had not been seenbefore is because they are faint, very faint,26th magnitude faint. To see them you needsomething like the Keck Telescope.Dr. Garrison concluded his talk by statingthat a large number of automated telescopeswill soon be used to obtain the spectra of stars,and that these systems will produce a lot ofdata, which will also require a lot of patternrecognizingbrains to classify the results.After a number of questions from the audience,the official meeting concluded. Thosewho stayed were treated to a travelogue ofDr. Garrison’s trips to Chile. There were somespectacular pictures of the scenery, andinstruments. There was limited wildlife buthe had a picture of a fox that would alwaysmanage to spot him whenever he returned froma 2-km walk to the American residence. Shewould follow several metres behind him andwhen he reached the Canadian residence, shewould be rewarded with an egg which shewould pick up in her mouth and carry backto her den. We also saw a close-up pictureof a condor. These birds have wingspans offive metres, and the number visible wasactually used during the day to gauge theseeing for the coming night! The rating wentfrom one condor (a prediction of very goodseeing as there were very few thermals) toten condor (poor seeing, many thermals).Two great talks from one person! Whatmore can you ask for? ✯10

More magazines by this user
Similar magazines