Sky and Telescope - January 2017 - 84

FOCAL POINT by Franz-Josef Hambsch

The First Pulsing White Dwarf
How amateurs helped professional astronomers make a major discovery

I'VE BEEN INTERESTED in astronomy

◗ The original version of this
article appeared as a community
news blog on skyandtelescope.
com on August 15, 2016.

84

Artist's impression of AR Scorpii,
newly identified as a double star

that became operational in 2011. The
weather in the Atacama Desert is marvelous, and I examined AR Sco over the
course of several weeks.
I performed these observations with
an Orion Optics 16-inch f/6.8 Optimized Dall Kirkham telescope and an
FLI ML16803 CCD camera binned 3×3.
I began a series of 60-second exposures
through an Astrodon photometric V
filter, as I thought I'd need a long exposure for a star of magnitude 14.5 to 16.5.
While the results show a rather scattered
light curve (see https://is.gd/r6L08J,
third image), they confirmed the period
of the brightness variations known since
the 1970s.
But the light curve's shape ruled out a
Delta Scuti classification.
Additional observations didn't bring
us any closer to explaining the nature of
this star, so we decided to seek the help
of professional astronomers. My astrobuddies in Germany had already worked
with the pros on previous projects, and
they put us in touch with Boris Gänsicke
at the University of Warwick in the UK.

J A N U A R Y 2 0 1 7 * SK Y & TELESCOPE

Gänsicke found the object so fascinating that he convinced colleagues
who had observing time at the Very
Large Telescope to take a spectrum
of AR Sco. With the VLT spectrum in
hand, as well as a run of high-speed
photometry from the William Herschel Telescope, the ball started rolling.
More professional astronomers became
involved, looking at AR Sco in all available passbands.
The exciting result of all this pro-am
work appeared in the September 15th
Nature. AR Sco, it turns out, is not one
star but two, one of which is a white
dwarf that's pulsing - the first known
of its kind (see page 11).
We amateurs were delighted to contribute to work published in one of the
world's premier scientific journals.
■ FRANZ-JOSEF "JOSCH" HAMBSCH is
a nuclear physicist at the Joint Research
Centre in Geel, Belgium. A list of recent
astronomy papers in which Hambsch is
a coauthor may be seen at https://is.gd/
dsXpmd.

M. G A RLICK / UNIV ERSIT Y OF WA RWICK / ESO

since childhood, and I began observing with a 4.25-inch Newtonian when
I was 18. About a quarter century later,
I started using a CCD camera to shoot
pretty pictures, some of which even
became Astronomy Pictures of the Day
(e.g., https://is.gd/ZLkWgw).
But after a few years of imaging
experience, and maybe because I make
a living as a scientist, I switched to
observing variable stars. Nowadays, you
can contribute to scientific research
using digital cameras. So I joined three
amateur groups in Europe that focus
on variable stars: VVS (Belgium), GEOS
(France), and BAV (Germany).
Among the projects I undertook
when I began observing variable stars
was to monitor high-amplitude Delta
Scuti variables. These are short-pulsating stars for which one can observe
several maxima in a single night. My
contributions to this topic have resulted
in several publications.
Since weather conditions in central
Europe are often unfavorable, many
amateurs turn to armchair astronomy.
It was such a group of amateurs mining databases of automatic surveys that
approached me to observe AR Scorpii, a
star varying by 2 magnitudes in brightness and classified at the time as a Delta
Scuti variable. The changes in brightness
and the star's classification didn't match,
however, and new scrutiny was needed.
The star's southern declination
made it difficult to observe from central Europe. Fortunately, I had built a
remote personal observatory in Chile


https://www.is.gd/ZLkWgw https://www.is.gd/r6L08J https://www.is.gd/dsXpmd https://www.is.gd/dsXpmd

Sky and Telescope - January 2017

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