Sky & Telescope - June 2019 - 84

FOCAL POINT by Robert Vanderbei

Blink and You'll See It

The author's serendipitous rediscovery of a Mira variable recalls the decidedly
singular way the star was originally found.

as Messier 27 and NGC 6853, is one of
my favorite nebulae, and over the years
I've taken many pictures of it. I like to
joke to my friends that it's named after
me - the dumbbell.
Last October, I invited my freshman seminar astronomy class to my
home to show them how to do some
astrophotography. Eight students came.
We snapped images of stars and other
objects before I suggested we take a
sequence of pictures of M27. They
agreed, and over the next few hours
my telescope and camera did just that
while my students and I enjoyed tea and
brownies inside and talked astronomy.
The resulting photo came out pretty
nicely - almost as nicely as one I'd
taken two years earlier with the same
telescope and camera. Seeing the
similarity between the two, I thought
it'd be fun to combine the pair, thereby
achieving a better picture. So I loaded
both photos into a stacking program
and set about aligning the images.
As I ﬂipped back and forth between
the two photos, I noticed that a fairly
prominent star in the 2016 image was
entirely missing from the 2018 one.
This caught me completely by surprise.
84

J U N E 2 019 * SK Y & TELESCOPE

p Messier 27, aka the Dumbbell Nebula, with
the Goldilocks Variable visible in 2016 (left, see
arrow) and invisible in 2018 (right)

I'd never before seen a star totally disappear like that.
I uploaded the earlier photo showing the star to astrometry.net to get
an astrometrically annotated version
of the picture in FITS, the widely used
digital ﬁle format. I loaded that into my
planetarium program and determined
the mysterious star's right ascension
and declination. Finally, I entered these
coordinates into the SIMBAD website.
The database revealed that the star is a
known Mira-type variable star.
Although a thrill for me, my accidental rediscovery pales in interest next to
the unusual manner of the original identiﬁcation, which occurred as recently
as 1990. While creating a map of M27,
Czech amateur astronomer Leos Ondra
consulted the covers of that year's May
issue of Astronomy and Autumn issue
of Deep Sky, both of which, by chance,
featured photos of the Dumbbell Nebula.
To his astonishment, Ondra noticed a
red star on the Astronomy cover that was
altogether missing from the Deep Sky
image. After the star was conﬁrmed as a

newly identiﬁed Mira star, he dubbed it
the Goldilocks Variable.
Prior to my own "discovery," I was
unfamiliar with Mira stars, though I've
long had an interest in RR Lyrae variables and the globular clusters in which
they lie. Noticeably blue, RR Lyrae stars
have a period that's typically shorter
than a day, and they vary in brightness
by only a modest amount. Mira variables, on the other hand, are red giants
with long periods - on the order of a
year - and dramatic dips in brightness.
It is this last property that astonished
me the most after my ﬁnd. It means
that, as my two pictures above show,
a Mira star can seemingly disappear
and then return, phoenix-like, from
the sidereal ashes. A few days after my
revelation, I blinked the two pictures
for my class, and they were as dumbfounded as I'd been.
¢ ROBERT VANDERBEI is a professor at
Princeton University affiliated with several departments, including Astrophysics. He coauthored, with J. Richard Gott,
Sizing Up the Universe: The Cosmos in
Perspective (National Geographic). A
mathematician by training, he's interested in variables of all sorts.

ROBERT VA NDERBEI (2)

THE DUMBBELL NEBULA, also known

http://www.astrometry.net

Sky & Telescope - June 2019

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