VARIABLE OF THE MONTH - MYRA AND HER SISTERS

Brian Fraser reports that when Omicron Ceti (Mira to you) was last at naked eye brightness, he had the following exchange with a Johannesburg Centre member:

Brian: Have you seen Mira?
Member: Myra who?

Over the years, a few Mira variables featured in the "Variable" column but I have not been as persuasive about the value of long period variable star observations as Lee Anne Willson, a much respected professional and president of the AASO. Below is a letter from her. If this motivates you to do Miras, then Brian and I will be glad to get you started.

Danie Overbeek

President's message:

The meeting in Huntsville last April was tremendously exciting - one of the best meetings I've been to in the last several years. There are certainly a lot of new and exciting opportunities for professional/amateur collaboration, even in areas that until recently were very much limited to a few professionals with access to the right spacecraft. Given these new opportunities, what is the importance, if any, of the AAVSO's traditional specialties?

The AAVSO archives contain nearly 10 million observations, and roughly 60% of those are observations of long period variables extending to the early 20th Century or late 19th in many cases and longer in a few. Only fairly recently have these data become widely accessible, both in the "Quick-look" files for very up-to-date light-curves and by instant-request for verified data. Given the extensive archives and the long time-line, do we have "enough" data on long-period variables? Should we be concentrating on new sources reachable only by CCDs or 24" telescopes??

With all the news flashes, alert notices, and other special notifications that AAVSO sends out, it is easy to get the impression that the AAVSO no longer cares about long period variables. On the web site, as well, other classes of variables get most of the attention, at least until one digs a little.

Are long period red variables passe? I would argue that the Miras and their close relations are still, and justifiably, the most important variables in the AAVSO's data base. Let me tell you why, and speculate a little about what would be required if we were to try to replace the AAVSO observers by some mechanical device(s). Note that if one looks at the activities of headquarters, rather than just the web and electronic publications, then one finds a somewhat different picture. Most of the requests for data are for Miras. Several recent research papers from headquarters deal with these stars, and the newest professional staff member is an astronomer who specializes in these objects.

1. Miras are fundamentally important objects for understanding the fates of stars and planets.

Most stars, including our Sun, will go through a Mira stage of evolution during which they will shed most of their mass. What is left will be a white dwarf star with a final mass around 60% of the Sun's present mass. The size that the Sun achieves during this stage determines the fate of the Earth - to be incinerated or merely singed. Perhaps, by observing Miras, we will be able to pick up some signs of planets plunging to their final fates!

2. Miras are many and thus require many observers.

There are many more of Miras known than there are professional astronomers in the world, by at least an order of magnitude, and only a small fraction of professional astronomers are studying stars individually. The only way that professional observers could hope to keep track of this many stars would be through continuing, all-sky monitoring with a lot of data-analysis (to pick out the Miras) and processing. Even assuming such equipment comes "on-line" during the 21st century, it will be costly (many millions of dollars is an estimate based on the costs of proposed all-sky monitoring projects), and it will require nearly a hundred years to catch up with the timeline of the data base at the AAVSO.

3. Miras show a host of not-well-explained phenomena that happen on timescales up to centuries or longer.

This summer, I've had a group of talented undergraduates working with me to understand more about the properties of Miras as these can be deduced from their light-curves. One comment that these teens and 20-somethings have made several times is "we need a bunch more data on this one!" Again, for any other method of observing these stars, at least a century is needed to build up to the level of AAVSO data. Plus, if other methods can be made compatible, existing and continuing AAVSO data will be essential to provide cross-calibration and extend the timeline back through the 20th century.

4. Mira periods are long (~1 year) so the glimpse that is obtainable during a single observing run on most
     professional telescopes is too short to reveal what is going on.

Perhaps it is a strange habit to be thrilled by a string of numbers. But, whenever I am immersed in the analysis of the light curve of a Mira variable or puzzling over the excursions of an SR, I feel both excited and fortunate to be the beneficiary of the dedication of so many observers over so many years.

Forwarded by

Danie Overbeek.