Old news is that a workshop on Delta Scuti and Related Stars will be held in Vienna in
the week before the solar eclipse. Certainly not old news will be the contents of the
talks and discussions. The field of Delta Scuti and now also Gamma Doradus stars has
really grown and developed in the last decade. I have great hopes that at the meeting the
assembled group of experts will highlight the many great developments and also focus on
the scientific problems that need to be solved. Since the conference proceedings/handbook
on Delta Scuti stars will be published the Conference series of the Astronomical Society
of the Pacific (thank you, Harold!), you can judge for yourself whether or not our aims
were reached. In this newsletter, we have again assembled a number of different
discoveries and interpretations. The paper by Mike Montgomery and Darragh O'Donoghue on
the errors of least-squares fitting to time series data has an interesting background.
Recently, we submitted the 4 CVn paper (34 frequencies determined from the
DSN 15 campaign) to A&A. This paper contains the formulae and their application
of the uncertainties of the amplitude and phase determined by least-squares sine-curve
fits to observational data. The referee asked us to send him the derivation of these
formulae. This made us aware that these formulae are not really known to everybody. In
fact, in discussions of amplitude variability or phase differences between the light
curves measured in different colors an estimate of the uncertainties may be crucial. Which
brings me to the question of statistics. My brother-in-law is a high-ranking official in
the Austrian Ministry of Economics. His favorite joke is, 'do not use any statistics you
have not falsified yourself.' In reality, things are probably not that bad, neither in
government nor in astronomy. Still, statistics cannot replace experience. And in our
business of extracting multiple periods from astronomical data experience really helps. My
personal philosophy is not to believe results which are not statistically significant, and
not to believe most significant results either. This is why after many photometric
campaigns of the Delta Scuti Network we still accept only new peaks with
amplitude signal/noise > 4.0, although a lower limit could well be statistically
significant. In fact, Peter Reegen and I were crazy enough to try a numerical experiment
with the times of real data randomly shuffled 1000 different ways. The peaks in the
resulting power spectra were examined. Peter finds only 0.0016 erroneous peaks/shuffle for
our adopted S/N ratio and the chosen frequency range. That is comforting. Of course,
observational noise is not randomly distributed. On the other hand, stars are measured in
more than one campaign: one of the best statistics is still finding a mode in two or more
independent data sets. The upshot of all of this: experience still counts.
Michel Breger
Editor
How to reach us
To submit a news item (or an abstract of your latest paper, or an article for the next
newsletter), you have several possibilities:
Please keep in mind that TEX or LATEX files are our preferred source for publication.
If you have special software which you want to share with the Delta Scuti community, again
use an anonymous FTP (see point 2) to dsn.astro.univie.ac.at. Go to the directory
/incoming and deposit your program. We will move it to the appropriate directory and
publish a news item. To see what public software is available, please check out our
software page at http://dsn.astro.univie.ac.at/dsn/DSSNSoftware.html.
Erratum
The reference given on the cover of DSSN 12 was incorrect. The correct reference is :
Tomkin, J., 1998 April, Sky & Telescope, p.59.