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CORONAL
METALLICITIES
OF
ACTIVE
BINARIES
Vinay
Kashyap,
Jeremy
Drake,
Deron
Pease
Harvard­Smithsonian
Center
for
Astrophysics
J¨
urgen
Schmitt
Max
Planck
Institut
f¨ ur
Extraterrestriche
Physik
SUMMARY
We
analyze
EUV
and
X­ray
data
on
a
sample
of
X­ray
active
binary
stars
(HR
1099,
–
And,
UX
Ari,
VY
Ari,
¸
UMa,
44i
Boo,
and
YY
Gem)
to
determine
coronal
abundances.
EUVE
spectrometer
data
are
used
to
obtain
line
fluxes,
which
are
then
used
to
determine
Differential
Emission
Measures
(DEMs).
The
continuum
emission
predicted
for
these
DEMs
(constrained
at
high
temperatures
by
measurements
in
the
X­ray
regime
where
available)
are
then
compared
with
EUVE/DS
counts
to
derive
coronal
metallicities.
These
measurements
indicate
whether
the
coronae
on
these
stars
are
metal
deficient
(the
``MAD
Syndrome'')
or
subject
to
the
FIP­effect
(low
First
Ionization
Potential
elements
have
enhanced
abundances
relative
to
the
photospheres).
0
Presented
at
the
192
nd
meeting
of
the
AAS,
San
Diego,
CA,
Jun
7­11,
1998

EUV
DATA
Table
1:
EUVE
Observations
Star
Instrument
Exposure
count
rate
[ks]
[ct
ks
\Gamma1
]
HR
1099
DS
318
660
\Sigma
1.49
SW
306
80
\Sigma
0.90
–
And
DS
81
187
\Sigma
1.56
SW
81
43
\Sigma
1.52
UX
Ari
DS
194
388
\Sigma
1.44
SW
189
47
\Sigma
1.01
VY
Ari
DS
140
155
\Sigma
1.10
SW
147
40
\Sigma
1.11
¸
UMa
DS
249
293
\Sigma
1.20
SW
169
27
\Sigma
1.00
44i
Boo
DS
227
278
\Sigma
1.22
SW
178
31
\Sigma
1.00
YY
Gem
DS
256
228
\Sigma
26
SW
316
16
\Sigma
0.6

METALLICITIES
(METHOD)
We
derive
stellar
coronal
metallicities
by
comparing
the
flux
predicted
from
a
Differential
Emission
Measure
(DEM)
distribution
at
various
metallicities
with
observed
broad­band
fluxes:­
1.
Measure
fluxes
for
lines
detected
in
the
EUVE
spectrometers.
2.
Identify
these
lines
and
compute
emissivities
using,
e.g.,
the
CHIANTI
database
(Dere
et
al.
1997,
A&AS,
125,
173)
of
atomic
data
and
the
ion­balances
of
Arnaud
&
Raymond
(1992,
ApJ
398,
39).
3.
Derive
a
DEM
as
a
function
of
temperature
using
the
measured
line
fluxes
and
computed
line
emissivities
(e.g.,
Kashyap
&
Drake
1998,
Aug
10).
The
DEM
thus
derived
is
inversely
dependent
on
the
adopted
metallicity .
4.
Use
the
DEM
derived
above
to
predict
continuum
as
well
as
line
emission
in
the
EUVE/DS
or
the
long
wavelength
part
of
the
EUVE/SW.
5.
The
predicted
fluxes
will
scale
inversely
as
the
adopted
metallicity,
and
will
thus
enable
us
to
measure
coronal
metallicities
by
matching
the
predicted
and
observed
fluxes.

METALLICITIES
(RESULTS)
Table
2:
DERIVED
METALLICITIES
Star
[Fe/H]
HR
1099
(­0.8,
­0.4)
[1]
–
And
?
­1.0
UX
Ari
(­0.8,
­0.4)
[2]
VY
Ari
?
­1.0
¸
UMa
­0.5
\Sigma
0.2
­0.65
\Sigma
0.05
[3]
44i
Boo
(­1.0,
­0.6)
YY
Gem
¸
­1
[4]
NOTES:­
1.
Consistent
with
photospheric
metallicity
2.
ASCA
estimate
is
[Fe/H]
­0.7
--
­0.3
(White
1996,
Cool
Stars
9,
193)
3.
From
VMEKAL
fit
to
ASCA
spectrum
4.
``MAD''
star
ffl
Derived
coronal
[Fe/H]
are
similar
to
photospheric
[Fe/H]
for
HR1099
(Randich
et
al.
1994,
A&A,
283,
893).
ffl
YY
Gem
appears
to
be
strongly
metal
depleted;
indeed,
we
are
unable
to
place
a
proper
lower
bound
on
its
metallicity .
ffl
Contributions
from
lines
that
form
at
temperatures
beyond
those
constrained
during
the
derivation
of
the
DEM
will
increase
the
predicted
flux
and
consequently
result
in
higher
values
of
the
metallicity .
The
derived
[Fe/H]
are
therefore
lower
bounds.

FIGURE
CAPTIONS
HR
1099
EUVE/SW
Spectrum:
The
short­wavelength
spectrum
of
HR
1099
obtained
from
concatenated
EUVE
ob­
servations
of
?
300
ksec.
Flare
events
are
excluded
from
this
spectrum,
which
consequently
represents
the
quiescent
corona
of
HR
1099.
Strong
lines
in
the
spectrum
which
were
used
to
construct
the
Differential
Emission
Measure
(DEM)
distribution
are
labeled.
The
thin
solid
line
denotes
the
location
of
the
continuum
computed
using
this
DEM
for
a
metallicity
[Fe/H]=
\Gamma0:7
.
¸
UMa
ASCA
Spectrum:
The
best­fit
three­temperature
models
to
the
ASCA
flare
and
quiescent
spectra
of
¸
UMa
B
(G0
V).
In
the
fitting
process,
the
abundances
of
elements
with
first
ionization
potentials
above
and
below
10
eV
were
treated
as
two
independent
variables
in
order
to
test
whether
or
not
a
solar­like
``FIP
Effect''
---
a
relative
enhancement
of
low
FIP
element
abundances
to
high
FIP
element
abundances
---
is
present
in
the
corona
of
¸
UMa
B.
Fitting
using
the
Cash
''C''
statistic
indicated
aproximately
equal
high
and
low
FIP
abundances
during
both
flare
and
quiescent
states,
with
a
value
[Fe/H]
ú
­0.6
\Sigma
0.05.
We
estimate
the
true
uncertainty
to
be
much
larger
at
ú
50%.
The
photospheric
metallicity
of
¸
UMa
is
[Fe/H]=
\Gamma0:34
\Sigma
0:1.
Metallicity
measurement:
The
metallicity
of
¸
UMa
B
measured
by
comparing
the
line
and
continuum
fluxes.
The
curved
line
is
the
of
the
predicted
flux
as
seen
in
the
EUVE/DS
(upper
panel)
and
the
long
wavelength
end
of
the
EUVE/SW
(lower
panel)
obtained
by
scaling
the
DEM
(calculated
using
strong
lines
identified
in
the
EUVE/SW,
MW,
and
LW
spectrometers)
with
the
metallicity .
A
10%
error
on
line
fluxes
and
atomic
data
are
assumed,
and
are
denoted
by
the
flanking
dotted
lines.
The
thick
horizontal
line
represents
the
observed
integrated
flux
in
the
band.
The
horizontal
dotted
lines
represent
1
oe
errors
on
the
observed
flux.