Mississauga Centre RASC

103rd Meeting

                                                         Speakers’ Night           

           

 

Day:                Friday April 11, 2008

 

Chair:               Ian McGregor

 

Speaker:          Doug Welch

 

     

Giving Up the Ghost – Searching for Light Echoes from Historical Supernovas in the Milky Way

 

 

Dr. Doug Welch is a professor of physics and astronomy at McMaster University.   He was on the Board of Directors of the Gemini Project and he credited the people who did the hard work namely Armin Rest, Marcel Bergmann, and graduate students Lindsay Oaster and Brandon Sinnott. 

 

Light echoes from supernovas (SN) first became evident as a result of the MACHO project which looked for dark mater in various places in the form of particles that rarely interacted but changed the light level of background stars.  The project saw microlensing events until the telescope on Mt. Stromlo in Australia was destroyed in a bush fire.  Follow-up then continued with the SUPERMACHO project at Cerro Tololo using the 4 meter telescope and a factor of 10 more powerful with a f 2.9 system.  From 2001 to 2005, 150 half-nights were used to gather data.  Subtraction of images showed a huge list of variable objects in the LMC.  Follow-up was conducted with an 8 meter telescope. 

 

In the course of this project, light echoes were seen from SN 1987A.  Dr. Welch described the echo ellipsoid and the rings of light at different times in the form of a movie.  The multiobject spectrograph on the Gemini telescope (GMOS) is capable of taking many spectra at the same time.  The echo spectrum looks different showing that SN 1987A was asymmetric.  On year 3 of the light echo subtraction, a line was found gradually moving away; calculations showed that this was from light echoes of other supernovas in the LMC ¼ to ½ millennium old.  The spectrum of this second SN matches the spectrum of a recent known SN enabling one to find out what kind of Type 1A supernova it is.   One unassociated echo from an unknown source was also found. 

 

Next, Dr. Welch looked at the Milky Way.  However this is harder because it is much larger, with a 20 degree width.   Cassiopeia A in the northern sky was probably a SN in the late 17th century but was not noticed at the time.  The Spitzer team has seen motion in infrared light, but this is not as useful because dust is not reflecting the light but re-radiating it.  Observations in October and December 2006 shower “first light” for Cas A and discovered as well the Tycho SN light echoes. 5% of the fields show light echoes. Amateurs can image the brightest ones; they move 20 to 40” per year.  Some of the dust sheets image light echoes of both supernovas and allow calculations of the absolute distance between them.  Information on the light echo project can be found at http://arxiv.org/abs/0801.4762

 

 

RASC business

 

Ian McGregor asked for volunteers for the GA of the RASC.

Terry Hardman spoke about Astronomy Day Sat. May 10. 

 

Ian discussed the business meeting of the National Society of March 30.  A major issue arose from the federal guidelines for charitable status.  Toronto is a charitable organization but Mississauga is not.  As a result, the National society is outside of federal guidelines if it transfers funds to Mississauga or other non-charitable centres.  Debate was held and a motion was passed to disclose the situation to the CCRA.  Scott Young has retired as president during his term and Dave Lane will take over.  At the GA there will be a vote for a national fee increase by $16. 

Finally, Vic Cooper spoke about payment methods, fees and donations.  He recommended that we give donations directly to the centre.

 

 

 Submitted by Chris Malicki, Secretary  Chris Malicki, Secretary                               back to Miss Centre. meeting reports page
Mississauga Centre RASC