Recording Epsilon Aurigae at minimum angular separation from the Sun 7th June 2009
Every 27 years Epsilon Aurigae is eclipsed by a strange extended
object, the exact nature of which is poorly understood.
The eclipse 2009-2011
will be
closely studied by amateurs
and
professionals alike. In
particular it will be the
first
time that amateurs
equipped
with
high
resolution
spectrographs
will be able to
contribute. I will be posting some of the
spectra
I record
during the
campaign on
this
page. If you fancy trying spectroscopy for the first time click
here for a simple way to record a low resolution
spectrum of Epsilon Aurigae
using a
digital SLR camera Follow
these
links
for
further
information on Eps
Aur and the
2009-2011
eclipse
campaign
AAVSO
Variable Star of the
Month Jan
2008 This page contains the most recent
observations. Earlier observations are archived here ---------------------------------------------------------------------------------------------------- Update 14th February 2010 - Analysis of
variations in radial velocity in the K I 7699 line
profile The profile of the KI 7699 line during eclipse contains
information about the line of sight velocity in
different parts of the
eclipsing
disc
. Analysing the
way the
profile changes during
eclipse could
potentially provide
information
about the
structure and
dynamics of the
eclipsing object. To track these
profile
changes, the line
has been divided into
a series of 0.3A
wide
zones
(11.5km/s Radial V
elocity)
and
the Equivalent Widths in
each zone
calculated for
each
spectrum.
The pre
eclipse contribution was
subtracted
and the
resulting changes in EW with
time have
been plotted
for
each RV
zone. (The
total EW for the
line,
less the pre
eclipse
component is also
plotted) Update 16th January 2010 - Second
Contact Potassium 7699A
line Photometrically the light curve has flattened
off, indicating that the densest part of the
eclipsing
object now
stretches
across
the F
star and the second
contact
point of the eclipse has
been
reached.
The more
tenuous outer
regions of the
eclipsing
object however (as tracked for example
by the
additional absorption
in the K I 7699
line)
have
been
spread across the
width of
the
eclipsed star for some
months
now. As
a result, the
changes
in
the K I
7699
line have
become more subtle
since
November
2009.
Although
the
Equivalent
W
idth
has
continued
to
increase
overall,
the
changes
have
been more at the edges
of the
line profile
with
little increase in
the
maximum
absorption.
This may
be
explained if
the eclipsing
object
is
a
rotating disc in Keplerian motion.
a) As the eclipse progresses, an increasing proportion of the
rotating disc in front of the star is moving almost
transversely
relative to our line
of
sight and so
shows little doppler
shift due to the
rotation.
This produces
an
increase in
absorption
around
the
KI
rest
wavelength,
currently at the
blue edge of
the
absorption line
profile.
b)
The
inner
regions of
the
leading
half
of the disc are now
moving in
front
of the star.
These are
rotating
faster
than
the
outer
regions
now moving off
the
far
edge of
the
star
and the net
result is an
increased radial velocity
red shift.
Citizen Sky Project
Jeff
Hopkin's Campaign
page
Rob Stencel's
Campaign
page
BAA Variable Star Section
page
The intensity of the additional absorption in the KI 7699 line has now reached 400 mAngstrom equivalent width, similar to the value seen at this stage by Lambert and Sawyer during the previous eclipse.
KI 7699 EW data and line profiles from Three Hills Observatory were included in this poster paper presented at the 110th AAS meeting Washington DC January 2010.
The EW results were also included in this poster paper presented at the 25th New Mexico Symposium January 2010 as part of a collaboration with Apache Point Observatory.
The THO results are in good agreement with those obtained using the 3.5m ARC telescope and ARCES spectrograph at APO as shown in fig 7 of the paper.
Hydrogen alpha 6563A line
Identifying changes in the Hydrogen alpha line due to the eclipse is complicated by variations seen in this line outside eclipse (both in the absorption core and in the red and blue emission wings).
The emergence of an additional absorption component during ingress to the red of the out of eclipse absorption core is clear however.
H gamma and metal lines 4270-4370A
The "shell spectrum" of narrow metal lines, extracted by dividing the in eclipse spectra by the mean pre eclipse, was identified by Ferluga during the last eclipse and was first seen in THO spectra during this eclipse in August 2009
During ingress the H gamma line in the shell spectrum has increased significantly in intensity, the other features less so. Note also the absence in the shell spectrum of some lines present in the pre eclipe spectrum. The Ti II line at 4331A is a good example.
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Earlier observations are archived here