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SPACE
TELESCOPESCIENCE
INSTITUTE
TIPS
Meeting
20
June
1996
R.
Jedrzejewski
Summary
of
FOC
Activities
for
the
period
23
May
-
19
June
1996
Operations .
The
F/96
relay
has
been
operating
nominally.
.
The
F/48
relay
was
not
used
in
this
period.
Proposals
Executed
.
There
were
5
GTO/GO
proposals
and
1
CAL
proposal
executed
using
the
FOC:
6309
Determining
the
SED
of
an
Ultraviolet
Flare
at
the
Center
of
the
Elliptical
Galaxy
NGC
4552
(DD)
6349
Snap
Shot
Search
for
High
Redshift
QSOs
with
Far­UV
Flux
(SNAP)
6306
Supernova
Light
Echoes
(GTO)
6891
Imaging
and
Polarization
Studies
of
Radio
Galaxies
and
Jets
(GT
O)
6689
Determination
of
the
Distances
and
Masses
of
2
Galactic
Cepheids
(GO)
6160
FOC
Cycle
5
UV
Throughput
Monitoring
(CAL)

SPACE
TELESCOPESCIENCE
INSTITUTE
TIPS
Meeting
20
June
1996
R.
Jedrzejewski
Summary
of
FOC
Activities
for
the
period
23
May
-
19
June
1996
New
ISRs FOC­093
FOC
Cycle
4
Calibration
Program:
Observations
and
Results
FOC­094
FOC
Neutral
Density
Filter
Throughputs
(internal
review)
Activities FOC
PDB
update
submitted
to
give
an
improved
F/48
aperture
location
based
on
the
results
of
last
month's
F/48
aperture
location
test.
The
position
was
only
approximately
1
arcsecond
from
the
pre­existing
value,
which
had
been
derived
before
COSTAR
was
inserted.

SPACE
TELESCOPESCIENCE
INSTITUTE
TIPS
Meeting
20
June
1996
R.
Jedrzejewski
Special
Topic:
FOC
Absolute
Sensitivity
The
absolute
sensitivity
of
the
FOC
is
determined
by
taking
images
of
a
spectrophotomet­
ric
standard
star,
and
comparing
the
measured
count
rate
(observed)
with
what
would
be
expected
by
folding
the
star's
spectrum
through
the
optical
system
(OTA+COS­
TAR+FOC+filters). E.g.
for
Cycle
4,
using
the
standard
stars
HZ4
(V=14.52)
and
BPM16274
(V=14.20),
it
w
as
found
that
the
(Observed/Expected)
ratio
was
an
approximately
linear
function
of
wave­
length:

SPACE
TELESCOPESCIENCE
INSTITUTE
TIPS
Meeting
20
June
1996
R.
Jedrzejewski
Special
Topic:
FOC
Absolute
Sensitivity
This
linear
function
was
applied
to
the
existing
FOC
DQE
curve
in
CDBS
(foc_96_dqe_003)
to
give
a
new
version
(foc_96_dqe_004).
When
this
curve
was
used
to
predict
the
count
rates
for
the
star/filter
combination,
the
results
were
better:
The
linear
relation
was
ascribed
to
an
aperture
effect
when
compared
to
pre­COST
AR
measurements
that
had
used
a
larger
aperture;
more
flux
falls
in
that
aperture
but
outside
the
new
aperture
in
the
UV
than
in
the
visib
le.

SPACE
TELESCOPESCIENCE
INSTITUTE
TIPS
Meeting
20
June
1996
R.
Jedrzejewski
Special
Topic:
FOC
Absolute
Sensitivity
Assumptions
made:
The
standard
stars
are
known
perfectly
The
FOC
filters
behave
exactly
as
measured
on
the
ground
>15
years
ago
Other
components
(OTA,
COSTAR,
FOC
format­dependent
sensitivity)
are
known
perfectly
and
are
not
time­dependent
For
the
Cycle
5
DQE
calibration
program,
HZ4
was
used
for
some
filter
combinations,
some
of
which
duplicate
Cycle
4
observations,
and
LB227
was
used
to
verify
indepen­
dence
against
standard
star.
In
the
meantime,
the
standard
star
fluxes
``changed''
slightly ,
partly
due
to
a
renormaliza­
tion
of
the
visible
spectra
(OKE
DBSP).
The
Cycle
5
data
were
analyzed
using
the
same
algorithms
as
for
the
Cycle
4
data
(same
aperture
radii,
same
region
used
for
sky
determination).

SPACE
TELESCOPESCIENCE
INSTITUTE
TIPS
Meeting
20
June
1996
R.
Jedrzejewski
Special
Topic:
FOC
Absolute
Sensitivity
Result: Cycle
5
HZ4
observations
agree
reasonably
well
with
the
Cycle
4
HZ4
data.
Cycle
5
LB227
observations
do
not
agree
with
the
Cycle
4
HZ4
data,
at
the
10%
le
vel.

SPACE
TELESCOPESCIENCE
INSTITUTE
TIPS
Meeting
20
June
1996
R.
Jedrzejewski
Special
Topic:
FOC
Absolute
Sensitivity
Possible
Explanations:
1)
the
faintest
spectrophotometric
standard
star
calibrations
are
only
good
to
10%
or
so
2)
the
FOC
absolute
sensitivity
can
v
ary
from
turn­on
to
turn­on.
The
first
explanation
is
plausible
in
the
UV
(these
are
the
f
aintest
standards),
especially
in
the
2000­2400å
r
ange
where
the
spectra
are
very
noisy.
But
in
the
visible,
the
spectropho­
tometry
is
known
to
be
consistent
with
the
B
and
V
magnitudes
to
+/­
0.02
mag.
The
second
explanation
is
unlikely
since
we
have
seen
from
the
UV
throughput
monitoring
program
that
photometry
with
the
FOC
is
repeatable
at
the
2­3%
level
for
a
single
observa­
tion,
and
there
is
no
evidence
for
any
significant
fall
in
UV
sensitivity
over
the
2
years
since
COSTAR
was
inserted
(except
for
a
possible
small
drop
at
1200å).

SPACE
TELESCOPESCIENCE
INSTITUTE
TIPS
Meeting
20
June
1996
R.
Jedrzejewski
Special
Topic:
FOC
Absolute
Sensitivity
What
next?
The
Cycle
5
DQE
program
will
be
repeated
because
the
OTA
was
somewhat
out
of
focus
for
the
exposures
already
taken;
since
they
were
designed
to
serve
as
PSFs,
it
is
essential
that
they
have
a
focus
setting
close
to
that
used
for
science
observations.
This
will
give
a
check
on
the
repeatability
of
the
FOC
observations.
This
focus
error
did
not
affect
the
flux
measurement
since
a
large
(1''
radius)
aperture
was
used.
The
Cycle
6
DQE
program
uses
a
PRIMARY
standard;
there's
no
cross­matching
to
IUE,
OKE,
FOS
spectrophotometry
(apart
from
their
use
in
determining
the
white
dwarf
mod­
els).
This
will
test
whether
the
f
aint
standards
could
be
less
accurate
than
specified.