http://www.skyandtelescope.com.au 49by Alan Plummer VARIABLE STARSOutburst on the way
Make sure you’re watching when V442 Centauri blows its top.
M
ost of the targets I’ve written
about in this column have been
long-period variables. Often
bright, easy to find, and slow changing
with large amplitudes, these are the
‘bread and butter’ of visual variable
star observers. Yet there is another
class at which visual observers excel
— cataclysmic variables. Meet one of
them, the dwarf nova V442 Centauri.
Dwarf novae are binary star systems
that comprise a white dwarf drawing
mass from its lower-mass, less-evolved
companion star via an accretion
disk. Think of water circling down a
plughole, moving though a spinning
disc-like structure. Dwarf novae
outbursts originate in the disk, and are
entirely different to classical novae and
supernovae (although the same systems
can produce these different events).
In a classical nova the accreted shell
on the white dwarf explodes, while a
supernova is the explosion of the entire
white dwarf.
The February 1978 issue of the USW V442 Cen is located at 11h 24m 51.91s,
–35° 54' 36.7" (epoch J2000). This chart
(courtesy of the AAVSO) has visual
magnitudes shown with decimal points
omitted to avoid confusion with faint stars
— so 124 denotes a magnitude 12.4 star.
The two bright stars are half a degree apart.edition of this magazine published an
early (misinterpreted) light curve of
V442 Cen, from the work of the Royal
Astronomical Society of New Zealand.
This star has outbursts of short duration
every few weeks, and interpreting the
data is very difficult. I’ve studied the
extensive data set, and it’s easier to see
the scheduling habits of the observers
than to tell much about the long term
nature of the star itself. So we need
more observers please!
V442 Cen is reasonably easy to
find and observe. You’ll need an atlas
to find the two 5th-magnitude stars
shown on the chart above — half a
degree apart, they’ll be easily visible
through a finder. The rest is easy. If you
can see 12th magnitude, you won’t have
to wait too long before glimpsing V442
Cen in outburst.■ ALAN PLUMMER observes from the
Blue Mountains west of Sydney, and
can be contacted at alan.plummer@
variablestarssouth.orgSPOTTED IN CARINA
A bright (magnitude 5.7 at red
wavelengths) transient object —
possibly a classical nova — was
spotted near the galactic plane in
Carina on March 23. The discovery
was made by the All Sky Automated
Survey for SuperNovae (ASAS-SN).
The before image (top) is from a
POSS2/UK Schmidt Telescope Unit
red photographic plate taken in 1991;
the after image was taken by Ernesto
Guido using the 43-cm f/6.8 astrograph
plus CCD camera at the iTelescope
Observatory at Siding Spring.
At the time of writing, there was
still some doubt as to whether this
was a classical nova or some other
kind of exotic outburst, with more
spectrographic studies needed.
■ JONATHAN NALLY