Sky & Telescope - May 2023 - 57

Pro-Am Conjunction
by Diana Hannikainen
Surveying
the Neutral
Hydrogen
Sky
Researchers dip into S&T
editors' survey data.
T
he fascination of Sky & Telescope's
very own Dennis di Cicco with the
hydrogen-alpha (Hα) sky dates to the
1960s, when he was still in high school.
Back then, he'd shoot images of nebulae
using photographic emulsions - lightsensitive
materials, for those of you too
young to remember. After Associate
Editor Sean Walker joined the S&T staff
in 2000, the pair - having discovered
a mutual interest - experimented with
imaging in Hα from Dennis's backyard
observatory. Things really took off when
they started dabbling in wide-angle
imaging with camera lenses.
For an early project, Dennis and
Sean tackled the huge, faint western
edge of the Orion-Eridanus Superbubble.
Night after night they acquired
data, probing the limits of what they
could image in Hα. Sean then assembled
the results into a mosaic, which
they published in the April 2009 issue
of the magazine. The final image covered
more than 4,000 square degrees
(that's almost 10% of the whole sky
visible from Earth!). The file size was a
whopping 100 MB.
The survey begins. Shortly after
that, the S&T duo joined forces with
David Mittelman (1954−2017). Passionate
about astronomy since college, he
operated a couple of telescopes remotely
in New Mexico. The three of them
would meet regularly and talk all things
astronomy - and process the data
coming out of New Mexico. During
these sessions, chats about Dennis and
Sean's Hα work planted a seed in their
collective minds: Could they possibly
map the whole sky in Hα? One evening
in late 2015, over dinner and wine,
they decided they could . . . and thus
the MDW Hydrogen-Alpha Sky Survey
blossomed into being. (MDW stands for
the first initial of the three gentlemen's
surnames; the Survey is now part of the
Mittelman Family Foundation.)
The trio had the talents and the abilities
to fulfill this plan. Says Sean, " You
don't have to be a visionary to think
up a survey - it's just that we had the
interests and resources to actually do it. "
And do it they did. They started building
and testing the telescopes and, following
the commissioning phase, officially
launched the survey in May 2016.
Dennis and Sean expect to complete
the northern campaign this year, which
will cover the entire sky from declination
-32° to +90°. This will consist of
3,179 fields; they already have 3,009.
" When we finish the northern portion
of the survey, we'll have covered 77% of
the whole sky, " says Dennis. They're currently
in the process of shutting down
and shipping one of the New Mexico
scopes to Chile (the other is expected to
follow within a year) so as to complete
coverage of Southern Hemisphere skies,
which will require some 900 fields and
around three years of work.
Pros dip in. In 2017, the renowned
website Astronomy Picture of the Day
showcased an image from the Survey
(https://is.gd/mdw_apod), which
The Hα data highlight the
swirls and whorls in the
Orion-Eridanus Superbubble.
piqued the curiosity of researchers.
Among the professional astronomers to
get in touch with the trio was Robert
Fesen (professor emeritus at Dartmouth
College). Fesen, who's research focuses
on galactic supernova remnants, used
MDW data in several papers that he
published in academic journals. He
included Dennis, Sean, and Dave as
coauthors.
But the MDW Survey isn't limited to
observing in Hα. Recently, Fesen - as a
member of a collaboration of amateurs
and professionals - contacted Sean and
Dennis and requested observations in
O III. With these data, they confirmed
the presence of a long filamentary
feature near M31. The team presented
this result in a recently published paper
(https://is.gd/M31_filament).
Fesen, for one, encourages other
researchers to explore the data coming
out of the MDW Survey. And, if you're
an amateur, why not consider borrowing
a page from the team's playbook? " Amateurs
taking dozens of images using
narrow filters on telescope-and-camera
systems can detect emission-line nebulae
that can be hard to detect with much
larger professional telescopes, " he says.
¢ Observing Editor DIANA HANNIKAINEN
loves to lose herself in the swirls of the
MDW Survey images.
ON THE SURVEY: Learn more about the
project at mdwskysurvey.org and in
S&T: Oct. 2019, p. 20.
sk yand tele scope .o r g * MAY 2023 57
MDW HYDROGEN-ALPHA SKY SURVEY
https://www.is.gd/M31_filament https://www.mdwskysurvey.org/ https://www.is.gd/mdw_apod https://skyandtelescope.org/
Sky & Telescope - May 2023

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