1997AJ
113.
.
713D
THE
ASTRONOMICAL
JOURNAL
VOLUME
113,
NUMBER
2
FEBRUARY
1997
CCD
STRÖMGREN
PHOTOMETRY
OF
YOUNG
REDDENED
CLUSTERS
An onio
J.
Delgado,
1
and
Emilio
J.
Al a o
1
Ins i u o
de
As o ísica
de
Andalucía,
CSIC.
P.O.
Box
3004,
E-18080,
G anada,
Spain
Elec onic
mail:[email p o ec ed],
[email p o ec ed]
Jesús
Cab e a-Caño
Facul ad
de
Física,
Uni e sidad
de
Se illa,
P.O.
Box
1045,
E-41080,
Se illa,
Spain
Elec onic
mail:
[email p o ec ed]
Recei ed
1996
Augus
15;
e ised
1996
Oc obe
31
abs ac
The
capabili ies
o
CCD
u by
pho ome y
o
he
s udy
o
eddened
young
clus e s
a e
in es iga ed.
Obse a ions
o
ou
ields
in
he
di ec ion
o
he
clus e s
Basel
1,
Be keley
86,
NGC
6704,
and
NGC
6756,
wi h
a
o al
o
1665
s a s
measu ed
in
a
leas
he
y
and
b
bands,
p oduce
new
es ima es
o
he
clus e s
pa ame e s.
The
esul s
a e
compa ed
o
hose
om
p e iously
published
s udies
in
di e en
pho ome ic
sys ems
showing
good
ag eemen
in
he
alues
o
colo
excess
and
dis ance
modulus,
wi h
he
excep ion
o
NGC
6756,
o
which
an
essen ially
la ge
dis ance
is
ound.
Fu he mo e,
he
ages
es ima ed
o
his
clus e ,
Basel
1,
and
NGC
6704
a e
ound
o
be
highe
han
p e iously
assumed,
in
pa icula
o
he
las
one.
The
p esence
o
ed
gian s
as
clus e
membe s
is
sugges ed
in
Basel
1,
NGC
6704,
and
NGC
6756.
©
1997
Ame ican
As onomical
Socie y.
[80004-6256(97)01702-0]
1.
INTRODUCTION
A
p ojec
on
CCD
u by
pho ome y
o
eddened
young
clus e s
has
been
unning
du ing
he
pas
h ee
yea s,
wi h
he
aims
o
gaining
u he
insigh
in
he
peculia i ies
o
eddened
u by
colo s
o
OB- ype
s a s.
P e ious
wo k
(Man oid
&
S e ken
1987;
Delgado
&
Al a o
1989;
Al a o
&
Delgado
1991;
Delgado
e
al
1992)
has
e ealed
and
dis-
cussed
he
exis ence
o
sys ema ic
e o s
in
he
in insic
u by
colo s,
possibly
dependen
on
spec al
ype,
and/o
colo
excess.
The
u by
obse a ion
o
young
eddened
clus e s
wi h
a
CCD
o e s
some
ad an ages
in
his
con ex .
Wi h
elescopes
o
mode a e
size,
and
easonable
in eg a ion
imes,
i
is
pos-
sible
o
secu e
measu emen s
o
s a s
in
a
wide
ange
o
spec al
ypes,
om
he
mos
luminous
OB- ype
clus e
membe s,
down
o
F-,
and
e en
ea ly
G- ype
main
sequence
s a s.
This
allows
a
mo e
eliable
de e mina ion
o
he
clus e
pa ame e s,
and
in
pa icula ,
he
analysis
o
he
eddening
a ec ing
he
clus e .
When
complemen ed
wi h
measu e-
men s
in
he
Hyß
sys em,
indi idual
de e mina ions
o
he
colo
excess
a e
possible
o
he
whole
spec al
ype
ange
co e ed,
allowing
in
u n
a
measu emen
o
he
clus e
me-
allici y.
Finally,
hese
obse a ions
help
in
e ining
he
knowledge
o
he
quan i y
and
quali y
o
he
in e s ella
ed-
dening
in
he
di ec ion
o
he
clus e .
In
pa icula ,
he
spe-
ci ic
ea u es
o
he
ex inc ion
due
o
in aclus e
ma e ,
as
di e enced
om
he
di use
in e s ella
ex inc ion
(Tu ne
1994,
and
e e ences
he ein),
can
be
in es iga ed.
A
selec ion
o
no he n
objec s
om
he
ca alog
o
Lyngà,
Visi ing
As onome ,
Ge man-Spanish
As onomical
Cen e ,
Cala
Al o,
ope a ed
by
he
Max
Planck
Ins i u e
ü
As onomie,
Heidelbe g,
join ly
wi h
he
Spanish
Comisión
Nacional
de
As onomía.
713
As on.
J.
113
(2),
Feb ua y
1997
wi h
a
colo
excess
E(B
—
V)
la ge
han
0.5,
and
ages
equal
o
less
han
10
8
yea s,
p o ides
a
sample
o
abou
50
clus-
e s.
The
amoun
o
published
da a
o
he
clus e s
in
his
sample
is
inhomogeneous.
Only
a
ew
ha e
published
mea-
su emen s
in
he
S ömg en
sys em,
and
o
many
o
hem
he
ca alogued
alues
s em
om
old
pho ome ic
s udies
in
he
RGU
pho og aphic
sys em.
In
his
pape ,
we
p esen
he
esul s
o
he
i s
CCD
obse ing
campaigns,
o
he
clus e s
Basel
1,
Be keley
86,
NGC
6704,
and
NGC
6756.
S ömg en
pho ome y
is
usually
complemen ed
wi h
measu emen s
in
he
C aw o d
Hß-sys em.
In
ac ,
o
s a s
o
spec al
ype
la e
han
A,
he
Hß
index
is
commonly
used
as
he
inde-
penden
empe a u e
pa ame e ,
and
mos
calib a ions,
in-
cluding
hose
o
me allici y,
[Fe/H],
in
e ms
o
Smi,
make
use
o
i .
Addi ional
wo k
is
unde
way,
o
comple e
he
p esen
da a
wi h
measu emen s
o
he
Hß
index,
which,
ob iously
enough,
a e
mo e
ime
consuming
by
an
impo an
ac o ,
i
one
wan s
o
achie e
measu emen s
wi h
p ecision
compa able
o
he
one
in
u by
bands,
o
he
s a s
in
he
lowe
main
sequence.
In
he
nex
sec ion
we
desc ibe
he
educ ion
p ocedu e
and
he
ans o ma ion
o
he
s anda d
sys em.
Sec ion
3
con-
ains
he
analysis
o
he
pho ome ic
diag ams,
calcula ion
o
he
es ima es
o
he
di e en
clus e s
pa ame e s,
and
a
compa ison
wi h
esul s
p e iously
published.
The
las
sec-
ion
esumes
he
main
conclusions
o
ou
s udy.
2.
OBSERVAHONS
AND
DATA
REDUCTION
The
obse a ions
we e
ob ained
a
he
1.5
m,
and
1.23
m
elescopes
in
he
Cala
Al o
Obse a o y,
in
1993
June.
Fig-
u es
1(a)-1(d),
show
plo s
o
he
obse ed
ields,
wi h
he
s a s
measu ed
in
a
leas
y
and
b
bands.
The
do
sizes
a e
indica i e
o
he
ela i e
ins umen al
y
magni ude
in
each
©
1997
Am.
As on.
Soc.
713
0004-6256/97/113
(2)/713/9/$
10.00
©
Ame ican
As onomical
Socie y
•
P o ided
by
he
NASA
As ophysics
Da a
Sys em
1997AJ
113.
.
713D
714
DELGADO
ET
AL.
:
YOUNG
REDDENED
CLUSTERS
714
Basel
1
Be keley
86
NGC
6704
NGC
6756
Fig.
1.
(a)-(d).
Schema ic
maps
o
he
ou
clus e
ields
obse ed.
Only
s a s
measu ed
in
a
leas
y
and
b
a e
plo ed.
The
size
o
he
do s
ep esen s
ela i e
b igh ness
o
s a s
in
he
ield.
No h
is
up
and
Eas
le
in
all
ields,
wi h
he
excep ion
o
he
ield
in
Basel
1,
whe e
he
No h-Sou h
axis
is
clockwise
o a ed
abou
30
deg ees.
ame.
The
da es,
and
de ec o s
used
in
each
elescope
a e,
1.5
m
elescope:
1993
June
14-19,
de ec o
THX
1024
X
1024,
wi h
19 jilpx,
and
0.33%*.
1.23
m
elescope:
1993
June
13-17,
de ec o
Tex4
520X520,
wi h
lljjilpx,
and
0.57%*.
In
Table
1
we
include
he
schedule
o
he
obse a-
ions
in
bo h
ins umen s,
along
wi h
in eg a ion
imes,
ai -
mass
a
he
middle
o
obse a ion,
and
ull
wid h
a
hal
maximum
in
each
ame.
The
s anda d
s a s
we e
selec ed
om
h ee
sou ces,
y-
ing
o
co e
he
la ges
possible
ange
in
{b
—
y)
alues.
P ima y
s anda ds
we e
selec ed
om
he
ca alog
by
Olsen
(1983).
Some
s a s
we e
also
aken
om
he
measu emen s
o
B- ype
s a s
by
Knude
(1992)
and
om
he
compila ion
o
Schus e
&
Nissen
(1988).
Howe e ,
he
ans o ma ion
o
s anda d
colo s
equi es
ex apola ion
o
he
calib a ion
ela-
ions.
In
he
absence
o
signi ican ly
eddened
B- ype
s an-
da ds,
he
e ec s
o
his
ex apola ion
can
be
diminished
by
including
la e
ype
s a s
in
he
s anda d
sample.
This
can
howe e
in oduce
new
unce ain ies,
since
he
a ia ions
o
colo
indices
due
o
eddening
migh
di e
om
hose
due
o
di e ences
in
spec al
ype
(Delgado
&
Al a o
1989).
Table
©
Ame ican
As onomical
Socie y
•
P o ided
by
he
NASA
As ophysics
Da a
Sys em
1997AJ
113.
.
713D
715
DELGADO
ET
AL.
:
YOUNG
REDDENED
CLUSTERS
715
Table
1.
Schedule
o
he
obse a ions.
Table
3.
Numbe s
o
measu ed
s a s.
Clus e
(da e,
Tl.)
Band
T
in
(s)
Ai mass
FWHM
(px)
Basel
1
16.6.93,
1.5
300
800
1200
3000
1.373
1.401
1.441
1.558
5.1
7.0
5.7
6.6
Be keley
86
17.6.93,
1.5
20
300
50
500
1200
120
3000
1.191
1.157
1.150
1.132
1.083
1.062
1.030
3.5
4.4
4.0
5.3
5.3
3.8
5.0
NGC
6704
14.6.93,
1.23
620
1180
1500
3600
1.356
1.360
1.383
1.484
3.2
3.4
4.4
4.5
15.6.93,
1.23
NGC
6756
16.6.93,
1.23
960
1360
1500
3600
1080
2000
3000
3600
1.425
1.361
1.355
1.400
1.345
1.226
1.191
1.209
3.5
3.5
3.8
4.0
4.0
4.9
4.6
5.5
2
lis s
he
s anda d
s a s
measu ed
in
bo h
elescopes,
wi h
numbe
o
measu emen s
and
e e ences.
The
educ ion
o
all
ames
was
done
wi h
he
IRAF
ou-
ines
o
he
bias,
da k
and
la - ield
co ec ions,
and
he
eg-
is e ing
and
combina ion
o
ames.
The
ames
lis ed
in
Table
1
a e
hose
ac ually
used
o
pho ome y.
The
in eg a-
ion
imes
in
his
able
a e
in
some
cases
(Basel
1,
y;
NGC
6704,
NGC
6756
all
bands)
he
esul
o
adding
se e al
con-
secu i e
ames,
a e
p e ious
egis e ing
o
all
ames
o
Table
2.
S anda d
s a s
obse ed.
HD
b-y
Sp
1.23
1.50
Re
133769
134248
135200
135262
161848
165503
166179
166600
166710
166928
164760
165343
160233
170783
171491
175544
177549
180126
8.541
8.372
8.122
8.563
8.911
7.844
8.328
8.639
8.353
8.532
7.959
8.490
9.102
7.717
7.952
7.395
9.257
8.012
0.181
0.402
0.271
0.457
0.489
0.160
0.188
0.277
0.497
0.255
0.163
0.151
0.025
0.187
0.541
0.144
0.300
0.207
0.270
0.205
0.143
0.199
0.340
0.220
0.168
0.185
0.246
0.121
0.038
0.048
0.032
0.016
-0.056
0.002
-0.092
-0.029
0.778
0.343
0.616
0.434
0.283
0.749
0.693
0.748
0.428
1.100
0.958
0.648
0.071
0.593
0.201
0.171
0.325
0.361
F0
GO
F0
GO
K0
F0
F0
GO
GO
A5
B9
B8
B5
B5
B5
B3
B3
B3
2
5
6
4
0
7
0
4
3
11
3
3
0
1
0
1
0
0
Re :
1.
Olsen
1983,
2.
Knude
1992,
3.
Schus e
&
Nissen
1989.
Bands
Bas
1
Be
86
NGC
6704
NGC
6756
To al
y,b
604
160
533
368
1665
u, ,b,y
121
59
a
165
139
484
a
The
5
b igh es
s a s
in
Be
86
a e
sa u a ed
in
he
«- ame.
he
same
ield
wi h
espec
o
he
b igh es
ame
in
he
y
band.
The
sho
and
long
ames
o
Be keley
86
we e
e-
duced
sepa a ely,
and
he
inal
ins umen al
magni udes
in
each
band
we e
ob ained
om
weigh ed
a e ages
o
bo h
ames.
The
IRAF/DAOPHOT
package
(upda e
1994
Janua y)
was
used
o
ob ain
ape u e
pho ome y,
and
PSF
i ing
and
ap-
e u e
co ec ions
o
he
p oblem
s a s.
The
e o s
o
he
ape u e
co ec ion,
de ined
as
he
ms
de ia ion
o
he
co -
ec ions
o
abou
10
s a s
pe
ame,
a e
be ween
0.01
and
0.02
o
he
1.5
m
elescope
ames,
and
0.05
o
he
1.23
elescope
ames.
In
Table
3
we
p esen
he
numbe
o
s a s
measu ed
in
a
leas
wo
bands
(y,b)
and
in
he
ou
u by
bands,
in
he
espec i e
clus e
ields.
A mosphe ic
ex inc ion
co ec ions
we e
pe o med
ol-
lowing
a
mul inigh
me hod
(see
Young
1974),
whe eby
ex-
inc ion
coe icien s
a e
calcula ed
e e y
nigh ,
as
he
mean
o
he
coe icien s
o
all
he
s anda d
s a s
measu ed.
The
e o s
o
he
coe icien s
( ms
de ia ion)
amoun
o
0.01,
whe eas
hose
o
he
ex inc ion
co ec ed
magni udes
a e
mos
equen ly
below
0.01.
Wi h
he
ex inc ion
co ec ed
magni udes,
he
ollowing
se
o
ans o ma ions
a e
ob-
ained
o
each
elescope:
1.5
m
elescope:
y¿
=
4.175+1.036
V-0.074
(b~y)
0.03
—y)
¿
=
0.138
+
1001
{b-y)
0.02
-0.458+1.018^-0.185
{b-y)
0.05
{u
¿
—
0.569+
1.024
{u
—
¿7)
+
0.171
{b-y)
0.03
1.23
m
elescope:
y¿=
6.100+
1.027V—0.108
{b-y)
0.04
(¿>
—
y)-
=
0.180+
1.107
{b-y)
0.01
q
¿=
—0.473
+
0.577C!
—
0.316
{b-y)
0.02
(w
b)}
—
0.084+
0.814
(m-¿7)
+
0.259
{b-y)
0.06
m
{
=
[{u
—
b)
-
2
(¿7
—y)-cJ/2,
whe e
he
subindex
i
s ands
o
ins umen al
magni udes.
The
co esponding
s anda d
e o s,
de ined
as
he
ms
de ia-
ion
o
he
esiduals,
a e
also
quo ed.
Conce ning
he
V
ans o ma ion,
i
has
been
poin ed
ou
ha
a
coe icien
o
he
y
magni ude
sligh ly
bu
signi ican ly
smalle
han
1
migh
be
a
ea u e
o
ins umen al
sys ems
wi h
a
CCD
(Jónch-Só ensen
&
Knude
1990;
Jónch-
Só ensen
1993).
This
possibili y
is
es ed
o
ou
bo h
ins u-
men al
sys ems.
As
o
he
m!
index,
i
is
compu ed
om
he
ans o med
{b-y),Ci,
and
{u
—
b)
indices.
This
p ocedu e
is
ad isable
o
diminish
as
much
as
possible
he
sys ema ic
e o s
in
he
s anda d
alues
caused
by
he
una oidable
ex-
apola ion
o
he
ans o ma ions
(Delgado
&
Al a o
1989).
©
Ame ican
As onomical
Socie y
•
P o ided
by
he
NASA
As ophysics
Da a
Sys em
1997AJ
113.
.
713D
716
DELGADO
ETAL:
YOUNG
REDDENED
CLUSTERS
10
V
15
10
V
15
Fig.
2.
To al
es ima ed
c ’s
o
he
s anda d
V,{b
~y),c
x
,(u
—
b)
plo ed
s
V.
C osses,
1.23
m
elescope;
ci cles,
1.5
m
elescope.
Only
s a s
selec ed
as
membe s
om
hei
loca ions
in
a
leas
wo
CM
diag ams
a e
plo ed
(Sec.
3.1).
An
es ima e
o
he
o al
unce ain y
a ec ing
ou
s anda d
indices
can
be
gained
om
Fig.
2,
whe e
he
o al
<x’s
(squa e
oo
o
he
added
squa ed
e o s
men ioned
abo e:
PSF- i ing,
ape u e
co ec ion,
ex inc ion,
and
ans o ma-
ion)
a e
plo ed
e sus
V,
o
V,(b
—
y),c
l
,
(
u
—
b).
These
plo s
show
only
hose
s a s
conside ed
clus e
membe s
om
he
loca ion
o
hei
ep esen a i e
poin s
in
a
leas
wo
colo -magni ude
(CM)
diag ams
(see
Sec.
3.1
below).
Fo
he
selec ed
B- ype
membe s,
which
a e
he
ones
used
o
compu e
he
colo
excess
(see
also
Sec.
3),
he
la ges
e o s
in
y,(&
—y),^
,(w
—Z?)
amoun
o
0.06,
0.08,
0.12,
0.11,
and
0.03,
0.04,
0.07,
0.05
o
he
1.23
and
1.5
obse a ions
e-
spec i ely.
A
able
wi h
he
comple e
pho ome y
o
he
1665
s a s
measu ed
a
leas
in
y
and
b
bands,
oge he
wi h
coo dina es
X,Y
in
he
ields
ske ched
in
Fig.
1,
can
be
ob-
ained
om
he
au ho s
on
eques .
3.
PHOTOMETRIC
DIAGRAMS
3.1
Membe
S a s
and
Reddening
Slopes
The
i s
s ep
in
he
analysis
is
he
es ima e
o
membe -
ship
o
he
s a s
measu ed
in
each
ield.
This
can
be
done
wi h
he
use
o
se e al
CM
diag ams,
and
he
equi emen
ha
he
s a s
lie
close
o
he
main
sequence
concen a ion
in
all
hem.
He e
we
use
he
h ee
CM
diag ams
V—(b
—
y),
V—(u
—
b),
and
V—( —y).
S a s
selec ed
as
membe s
ha e
o
lie
a
dis ances
no
la ge
han
0.2
om
eye-es ima ed
lines
along
he
main
sequence
concen a ion
in
each
diag am.
In
Fig.
3
we
show
as
example
he
CM
diag ams
V—(b
—y)
o
he
ou
clus e s,
wi h
hese
lines
d awn.
The
dis ance
chosen
o
selec ion
akes
in o
accoun
no
only
he
e o s
in
V
and
he
di e en
colo
indices,
bu
also
he
ex-
pec ed
p esence
o
a ia ions
in
colo
excess,
which
can
each
se e al
en hs
o
a
magni ude.
In
addi ion,
we
selec
as
membe s
he
s a s
lying
in
simila
posi ions
in
he
gian
e-
gion
in
all
diag ams.
Ob iously,
he
only
c i e ion
a ailable
he e
o
decide
he
membe ship
o
gian
s a s
o
he
clus e s
is
based
on
hei
pho ome ic
colo s.
The
loca ion
o
hese
s a s
in
he
diag ams
o
he
h ee
olde
clus e s
is
howe e
a
716
(b-y)
(b-y)
Fig.
3.
V-(b-y)
diag am
o
he
ou
clus e s.
The
hues
used
o
membe
selec ion
a e
plo ed
as
example.
Fo
commen s
on
he
wo
ci cled
do s
in
Be keley
86
(Sec.
3.1)
s ong
indica ion
in
a o
o
hei
membe ship.
As
we
shall
see
la e ,
he
h ee
clus e s
Basel
1,
NGC
6704,
and
NGC
6756
ha e
ages
simila
o
he
Hyades,
and
he
p esence
o
gian
membe s
should
be
expec ed.
The
i s
membe s
selec ion
om
his
p ocedu e,
is
now
e ined
wi h
he
use
o
he
diag ams
Ci
—
(b
—
y),
(u
—
b)
—
(b
—
y),
and
Ci
—
(u
—
b).
These
diag ams
help
also
in
es ablishing
an
spec al
classi ica ion
be ween
s a s
ea lie
and
la e
han
spec al
ype
A0,
and
es ima ing
o
mean
ed-
dening
slopes,
app op ia ed
o
he
pa icula
egion.
Fo
hese
es ima es,
we
use
he
e e ence
lines
o
un eddened
s a s
gi en
by
C aw o d
(1978,
1979,
and
1975,
o
B-,
A-,
and
F-
ype
s a s,
espec i ely).
The
e e ence
line
o
in e -
media e
A- ype
s a s
by
Hildi ch
e
al.
(1983),
linking
he
B
and
A
anges
o
he
C aw o d’s
ines
is
also
used.
Figu e
4
shows
as
example
he
men ioned
wo
colo
dia-
g ams
o
he
clus e
Basel
1,
wi h
e e ence
ines
shi ed
acco ding
o
he
quo ed
alues
o
colo
excess,
and
edden-
ing
slopes.
Ci cled
do s
indica e
he
s a s
selec ed
as
B- ype
membe s,
acco ding
o
hei
loca ions
in
all
h ee
diag ams.
The
eddening
slopes
E(ci)/E(b
—
y),E(u
—
b)/E(b—y)
es-
ima ed
wi h
his
p ocedu e
a e
0.20,1.60;0.20,1.40;0.30,
1.50
o
Basel
1,
NGC
6704,
and
NGC
6756.
Fo
Be keley
86
he
a ailable
A-
and
F-
ype
s a s
a e
e y
sca ce.
He e
we
a e
helped
by
published
spec al
ypes
o
some
clus e
membe s
(Fo bes
e
al.
1992,
he ea e
F92).
Un o una ely,
he
i e
b igh es
s a s
in
ou
ield
a e
sa u a ed
in
he
u
ame.
Only
o
s a
No.
6
in
he
pho ome y
o
F92
we
ha e
©
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As onomical
Socie y
•
P o ided
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he
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As ophysics
Da a
Sys em
1997AJ
113.
.
713D
717
DELGADO
ET
AL.
:
YOUNG
REDDENED
CLUSTERS
Fig.
4.
Two
colo
diag ams
o
Basel
1.
The
e e ence
lines
a e
shi ed
wi h
he
alues:
E(¿>
—y)
=
0.33,E(c])/£(£
—;y)
=
0.20,E(w
—
¿?)/E(¿>
—
;y)
=
1.60.
The
ci cled
do s
a e
he
selec ed
B- ype
membe s.
spec al
ype
(B2
V)
and
measu ed
(u
—
b)
and
Cj
indices.
The
slopes
used,
0.18,1.52,
ha e
been
compu ed
o
his
s a ,
using
he
calib a ion
o
in insic
colo s
in
e ms
o
spec al
ype
gi en
by
Wa en
(1976).
Fu he mo e,
wo
o
he
s a s
gi en
as
membe s
by
F92
(Nos.
24,
26),
i s
excluded
by
ou
c i e ion,
ha e
also
been
included
as
B- ype
membe s
in
Be -
keley
86.
They
a e
indica ed
wi h
ci cled
do s
in
Fig.
3.
In
all
cases,
he
slope
o
he
m
1
index
is
compu ed
as
E(mi)/
E(b
—
y)
=
[E(u
—
b)/E(b
—
y)
—
2
—
E(ci)/E(b
—
y)]/2.
A
quan i a i e
es ima e
o
he
unce ain ies
o
hese
slopes
is
di icul
o
ob ain,
since
hey
a e
based
on
isual
i s.
How-
e e ,
hey
will
be
ob iously
a ec ed
by
a
leas
he
same
e o s
han
hose
o
he
co esponding
pho ome ic
indices
o
he
selec ed
B- ype
membe s
(see
Sec.
2).
In
iew
o
hese
e o s,
he
di e ences
o
he
slopes
used
he e
wi h
hose
ob ained
by
C aw o d
&
Mandwewala
(1976:
E(ci)/
E(b-y)
=
0.20,E(u-b)/E(b-y)
=
l.54)
canno
be
consid-
e ed
signi ican .
3.2
Pho ome ic
Pa ame e s
3.2.1
Reddening
and
me allici y
Once
he
eddening
slopes
a e
es ima ed,
we
p oceed
o
de e mine
he
in insic
colo s
o
indi idual
s a s.
We
can
do
his
only
o
s a s
ea lie
han
A0,
as
he
calib a ion
o
(£
—y)o
o
la e
s a s
depends
on
he
H/3
index.
The
s a s
selec ed
as
B- ype
membe s
a e
de eddened
wi h
he
o mu-
las
gi en
by
Shobb ook
(1984).
Fo
he
emaining
s a s
se-
lec ed
as
membe s,
he
colo
excess
is
compu ed
as
he
mean
o
he
alues
ob ained
o
indi idual
B- ype
membe s.
The
alues
o
colo
excess
ob ained
amoun
o
717
0.33±0.04,0.71
±0.10,0.54±0.03,0.73±0.04
o
Basel
1,
Be keley
86,
NGC
6704,
and
NGC
6756,
espec i ely.
O h-
e wise,
he
in insic
la ges
e o
o
he
colo
excess
o
one
s a
can
be
es ima ed
om
he
pho ome ic
e o s
gi en
in
Sec.
2
(see
Phelps
&
Janes
1994,
o
an
explana ion
o
he
quan i a i e
es ima es).
They
a e
0.07
and
0.13
o
he
1.5
(Basel
1,
Be keley
86)
and
1.23
(NGC
6704,
NGC
6756)
measu emen s,
espec i ely,
which
a e
o
be
compa ed
wi h
he
ms
de ia ions
o
he
mean,
gi en
abo e.
The e o e,
no
signs
o
di e en ial
o
a iable
eddening
abo e
he
pho o-
me ic
e o s
can
be
guessed
om
ou
da a,
wi h
he
excep-
ion
o
Be keley
86.
An
es ima e
o
he
me allici y
could
be
a emp ed,
a
leas
o
Basel
1
and
NGC
6704,
whe e
we
ha e
a
la ge
numbe
o
obse ed
F- ype
s a s.
The
compu a ion
wi h
he
a ailable
calib a ions
o
[Fe/H]
in
e ms
o
£ a
0
(
Z
?
—y)
=
a
0
/
/
ne
—
m
0
^
(C aw o d
1975;
C aw o d
&
Pe y
1976),
p oduces
he
mean
[Fe/H]
alues
—0.3±0.7,
0.6±
1.3
o
Basel
1
and
NGC
6704,
espec i ely.
The
la ge
unce ain ies
e lec
he
la ge
e o s
o
ou
pho ome ic
indices
o
he
weakes
mem-
be s.
Measu emen s
o
H/3,
and
longe
in eg a ion
imes
also
in
he
and
u
bands,
should
imp o e
his
de e mina ion
h ough
a
de e mina ion
o
indi idual
eddening
o
AF
s a s,
use
o
Sm
0
(
ß
)
,
mo e
p ecise
membe ship
de e mina ion,
and,
ob iously,
mo e
p ecise
alues
o
he
magni udes
in
he
di e en
bands.
3.2.2
Dis ances
and
ages
As
has
been
also
exempli ied
by
Tu ne
(1994),
local
a ia ions
o
he
eddening
slopes
a e
in
some
cases
associ-
a ed
wi h
a ia ions
o
R,
he
a io
o
abso p ion
in
V
o
colo
excess
E(B
—
V).
How
hese
a ia ions
migh
beha e
in
he
S ömg en
sys em
is
unknown.
On
he
o he
hand,
he
eddening
slopes
used
he e
a e
no
signi ican ly
di e en
om
he
a e age
alues
commonly
used
(C aw o d
&
Mand-
wewala
1976).
We
assume
R
=
3,
and
compu e
he
abso p-
ion
coe icien
o
each
clus e
wi h
he
ela ion
be ween
E(B—V)
and
E(b~y)
gi en
by
Penp ase
(1992).
Dis ance
moduli
a e
hen
ob ained
by
shi ing
he
obse a ional
main
sequence
o
i
he
de eddened
CM
diag am
V
0
-
(
b
-
y
)
0
.
The
esul s
a e
11.0±0.3,11.1±0.3,11.3±0.4,12.6±0.4
o
Basel
1,
Be keley
86,
NGC
6704,
and
NGC
6756,
espec-
i ely.
The
unce ain ies
o
hese
alues
ha e
been
es ima ed
om
he
pho ome ic
e o s,
ollowing
he
easoning
by
Phelps
&
Janes
(1994).
To
es ima e
he
ages
we
dispose
o
ecen
model
isoch-
ones,
p o ided
o
speci ic
ages
by
Cla e
(1996,
p i a e).
All
he
isoch ones
used
he e
a e
o
sola
chemical
compo-
si ion
(Z=
0.02,A=0.7).
The
models
include
he
conside -
a ion
o
newes
opaci ies
and
ene gy
gene a ion
a es.
A
mode a e
amoun
o
o e shoo ing
om
he
con ec i e
co e
is
pa ame ically
included
in
he
compu a ions
(see
Cla e
1995,
and
F.
Pé ez-Hemández
e
al.
1995,
o
a
desc ip ion
o
he
models,
and
he
calib a ions
used
o
empe a u e
and
bolome ic
co ec ion
in
e ms
oí
UBV
colo s).
The
isoch-
ones
a e
ansla ed
o
he
S ömg en
colo -magni ude
dia-
g ams,
F
0
-
(
¿
?-y)
0
,
and
V
0
-
(
w
-
Z
?)
0
,
wi h
he
well
cali-
b a ed
o mulas
gi en
by
Penp ase
(1992)
o
( -y)o
and
Tu ne
(1990)
o
(«-¿>)
0
.
In
Fig.
5
we
show
he
in insic
©
Ame ican
As onomical
Socie y
•
P o ided
by
he
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As ophysics
Da a
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718
DELGADO
ET
AL
:
YOUNG
REDDENED
CLUSTERS
718
Fig.
5.
(a)-(d).
Isoch one
i s
o
he
de eddened
V-(b-y)
0
,
and
V—(u
—
b)
0
diag ams:
(a)
Basel
1,
(b)
Be keley
86,
(c)
NGC
6704,
(d)
NGC
6756.
The
co esponding
ages
and
dis ance
moduli
a e
lis ed
in
Table
4.
Empi ical
ZAMS
lines
a e
plo ed
as
hicke
lines.
La ge
do s
indica e
membe s
in
all
h ee
CM
diag ams,
acco ding
o
ou
c i e ion
(Sec.
3.1).
colo
magni ude
diag ams
o
he
ou
clus e s,
wi h
he
bes
isoch one
i s
supe imposed.
The
e o s
o
hese
age-
es ima es
can
only
be
guessed
quali a i ely,
on
he
basis
o
he
e o s
o
he
pho ome ic
poin s,
and
he
a ia ions
o
he
i
quali y
wi h
a ying
age
o
he
isoch one,
in
bo h
CM
diag ams
simul aneously.
We
es ima e
ages
o
2.3
+
0.3X10
8
y ,8±5X
10
6
y ,2.0±0.6X
10
8
y ,1.3±0.6
X
10
8
y ,
o
Basel
1,
Be keley
86,
NGC
6704,
NGC
6756,
espec i ely.
The
bes
guesses,
based
on
hese
i s,
a e
in-
cluded
in
Table
4,
oge he
wi h
ou
es ima es
o
he
dis-
ance
moduli
and
colo
excess,
compa ed
o
alues
gi en
in
he
li e a u e.
We
wish
o
s ess
he e
he
adequacy
o
his
isoch one
calib a ion,
ia
colo
ans o ma ion,
ha
can
be
app ecia ed
in
he
good
ag eemen
be ween
he
ans o med
isoch ones,
and
he
obse a ional
u by
main
sequence
lines,
also
plo ed
in
Fig.
5
as
hicke
con inuous
ines.
Fu he mo e,
we
con-
side
ou
age
es ima es
as
eliable,
in
iew
o
he
sa is ac o y
simul aneous
i s
o
heo e ical
in insic
colo s,
om
wo
in-
dependen
calib a ions,
o
ou
wo
CM
diag ams,
in
a
ela-
i ely
la ge
ange
o
spec al
ypes
along
he
main
sequence.
3.3
Compa ison
wi h
P e ious
S udies
Pho ome ic
s udies
ha e
been
published
o
he
ou
clus-
e s
in
he
p esen
epo .
The
amoun
o
in o ma ion
is
a i-
able,
bu
all
hem
ha e
a
leas
one
de e mina ion
o
he
basic
pho ome ic
pa ame e s,
colo
excess,
age,
and
dis ance.
O h-
e wise,
none
o
hem
has
published
u by
pho ome y,
and
only
some
s a s
in
Be keley
86
ha e
published
spec al
ypes
(Me milliod,
Ga ison:
p i a e).
The
h ee
clus e s
Basel
1,
NGC
6704,
and
NGC
6756
we e
measu ed
in
he
pho o-
g aphic
RGU
sys em
some
decades
ago
(Fenka
1965;
G ubbisich
1965;
Slo opoulos
1965).
Excep
o
NGC
6704,
©
Ame ican
As onomical
Socie y
•
P o ided
by
he
NASA
As ophysics
Da a
Sys em
1997AJ
113.
.
713D
719
DELGADO
ET
AL.
:
YOUNG
REDDENED
CLUSTERS
719
Table
4.
Clus e s
pa ame e s
compa ed
o
published
es ima es.
Clus e
E(b-y)
Log
Age
(yea s)
DM,
E(B-V)
Bas
1
0.33
8.35
7.76(0)
11.00
10.67
(0)
11.00
(1)
10.62
(2)
11.02
(3)
0.43
0.57(0)
Be
86
0.71
6.94
6.78(0)
6.75(4)
6.78(5)
6.40(6)
6.70(7)
11.10
10.23
(0)
11.18
(5)
11.39
(6)
11.01
(7)
0.89
0.99(0)
0.96(5)
0.80(6)
1.01(7)
NGC
6704
0.54
8.30
7.30(0)
11.30
11.44
(0)
11.29
(2)
11.40
(8)
0.69
0.72(0)
0.71(8)
NGC
6756
0.73
8.12
7.67(0)
8.48(9)
12.60
10.89
(0)
11.09(10)
0.91
1.18(0)
REFERENCES.—(0)
Lyngá,
Open
Clus e s
Ca alog.
(1)
Becke
&
Fenka
1970.
(2)
G ubissich
1965.
(3)
Fenka
1965.
(4)Smi h
e
al.
1988.
(5)
Fo bes
1981.
(6)
Massey
e
al.
1995.
(7)
Fo bes
e
al.
1992.
(8)
Fo bes
&
DuPuy
1978.
(9)
San os
e
al.
1993.
(10)
Slo opoulos
1965.
o
which
U
BV
pho ome y
has
been
published
mo e
e-
cen ly
(Fo bes
&
DuPuy
1978,
he ea e
e e ed
o
as
F78),
hese
RGU
wo ks
con ain
he
only
a ailable
es ima es
o
he
clus e
pa ame e s.
Fo
Be keley
86,
UBV
pho ome y
has
been
published
by
Fo bes
(1981),
F92,
and
Massey
e
al.
(1995).
3.3.1
Compa ison
o
indi idual
s a s
The
compa ison
wi h
p e iously
published
pho ome ic
indices
can
be
pe o med
o
he
clus e s
Be keley
86
and
NGC
6704,
a e
ans o ma ion
o
ou
u by
indices
(b
—
y)
and
(u
—
b)
wi h
o mulas
gi en
by
Tu ne
(1990).
The
a e age
di e ences
o
he
s a s
in
common
wi h
he
UBV
pho ome ic
s udy
by
F92,
in
he
sense
F92-ou s,
a e
AV=0.10±0.15,A(5-y)
=
0.01±0.03,A(U-5)=-0.00
±0.07.
The
ag eemen
is
qui e
sa is ac o y,
bu
a
sys ema ic
di -
e ence
appea s
in
he
V
alues,
whe eas
he
di e ences
in
(B
—
V)
and
(U-B)
a e
smalle
and
no
sys ema ic.
The
di e ence
in
V
is
signi ican ly
dec eased
using
he
classical
ans o ma ion
o
ob ain
he
V
s anda d
magni udes
(C aw-
o d
&
Ba nes
1970;
see
Sec.
2
abo e):
y
i
-
V
=
4
A
T8-0.11T(b-y)
S .e o
=
0.03
which
gi es
a
di e ence
A
—0.06±0.13.
Figu e
6
shows
he
wo
se s
o
magni udes
compa ed
o
hose
in
F92.
Two
o
he
s a s
in
common,
(s a s
3,
4
in
F92),
deno ed
wi h
squa es
in
he
igu e,
s ill
show
la ge
di e ences
wi h
ou
alues.
On
he
o he
hand,
he
mean
di e ence
wi h
he
CCD
alues
ob ained
by
Massey
e
al.
(1995)
o
h ee
s a s
in
common
(1,
2,
and
4
in
F92)
a e
much
smalle ,
AV=—
0.009±0.009
in
he
sense
Massey-ou s.
We
no e
ha
Fig.
6.
Di e ences
be ween
ou
V
magni udes
and
hose
in
F92,
o
he
s a s
in
common
in
Be keley
86.
The
esul s
o
wo
ans o ma ions
o
he
s an-
da d
sys em
a e
shown.
Ci cles:
V
ans o ma ion
wi h
a iable
y
coe i-
cien .
Do s:
V
ans o ma ion
wi h
y
coe icien
equal
o
1.
Fo
commen s
on
he
wo
squa ed
do s
(Sec.
3.3.1).
s a s
F92-3
and
F92-4
a e
double,
and
p obably
e y
ha dly
sepa able
in
pho oelec ic
pho ome y.
Rejec ing
hem,
he
a e age
di e ence
F92-ou s
educes
o
AV=-0.02±0.07.
On
he
basis
o
he
good
ag eemen
wi h
he
pho oelec ic
alues
in
F92,
and
hose
o
Massey
e
al.
as
well,
we
use
he
ans o ma ion
equa ion
wi h
he
y-coe icien
equal
o
1
o
he
measu emen s
in
he
1.5
m
elescope
ins umen al
sys-
em.
Fo
NGC
6704,
we
compa e
wi h
he
esul s
in
F78,
he
only
UBV
pho ome ic
s udy
known
o
us.
The
in o ma ion
con ained
in
he
ables
o
F78
is
somewha
con using,
mak-
ing
unce ain
he
compa ison
wi h
hei
pho og aphic
alues.
O
he
41
s a s
in
common
wi h
us,
5
ha e
pho oelec ic
measu emen s
in
F78
(s a s
A,
B,
F,
H,
J,
whe eas
A,
F,
and
H,
also
ha e
pho og aphic
measu emen s).
Res ic ing
he
compa ison
o
hese
5
s a s,
we
ob ain
mean
alues,
A
-0.01
±0.07,
A(B-V)=-
0.01
±
0.27,
A(U-B)
=
0.07±0.27.
The
di e ences
a e
no
e y
big,
bu
he
dis-
pe sions
a e
oo
high,
well
abo e
he
e o s
o
ei he
ou
pho ome y,
o
he
one
in
F78.
We
canno
hink
o
a
eason-
able
explana ion
o
ha .
We
jus
no e
ha
he
mean
di e -
ences
in
F78,
be ween
hei
own
pho og aphic
and
pho o-
elec ic
alues
o
he
h ee
s a s
wi h
bo h
kind
o
measu emen s,
a e
al eady
e y
high,
A
V=
0.04±0.11,
A(B-V)
=
0.10±0.07,
A(U-B)
=
0.28±0.17.
3.3.2
Membe ship
Membe ship
assignmen s
a e
gi en
in
he
pho ome ic
s udies
ci ed
abo e
o
all
ou
clus e s,
using
he
loca ion
o
he
ep esen a i e
poin s
in
he
espec i e
pho ome ic
dia-
g ams.
Some
di e ences
wi h
ou
assignmen s
a e
p esen ,
mainly
o
s a s
o
spec al
ypes
a ound
BA,
and
la e .
In
gene al
we
keep
ou
es ima es,
conside ing
hem
mo e
con-
iden
on
he
basis
o
he
wide
ange
o
spec al
ypes
mea-
su ed,
and
he
disposal
o
3
independen
colo
magni ude
diag ams.
We
jus
commen
on
wo
di e ences
he e.
Fi s ,
s a s
24,
26,
in
Be keley
86
(F92
numbe s),
we e
i s
ejec ed
by
us
because
o
hei
{b
—
y)
alues,
al hough
hei
loca ions
in
he
o he
CM
diag ams
we e
inside
he
dis ance
chosen
o
selec ion.
The
s a s
a e
conside ed
membe s
by
F92,
based
on
hei
pho oelec ic
colo s,
and
we
ha e
indeed
included
©
Ame ican
As onomical
Socie y
•
P o ided
by
he
NASA
As ophysics
Da a
Sys em
1997AJ
113.
.
713D
720
DELGADO
ET
AL
:
YOUNG
REDDENED
CLUSTERS
720
400
x
200
0
400
7/9
x
^
200
0
400
7/9
x
200
0
400
200
0
X(pxs)
e o s
es ima ed
o
ou
pho ome y.
We
conside
ou
alues
mo e
ealis ic,
in
iew
o
he
accep able
i s
o
bo h
obse a-
ional
e e ence
lines,
and
isoch ones,
o
a
wide
ange
along
he
main
sequence.
The
h ee
clus e s
seem
in
ac
o
be
he
same
objec ,
jus
obse ed
a
di e en
dis ances.
In
pa icu-
la ,
we
poin
ou
he
imp o emen
o
he
age
es ima e
o
NGC
6704,
which
u ns
ou
o
be
signi ican ly
olde
han
p e iously
es ima ed.
Be keley
86
is
a
much
younge
objec .
The
age
ob ained
he e
is
in
good
ag eemen
wi h
p e iously
published
alues,
bu
ou
absolu e
dis ance
modulus
is
smalle
han
o he
e-
cen
de e mina ions
by
0.1
o
0.3.
We
ha e
seen
in
he
p e-
ious
subsec ion
ha
he
ag eemen
wi h
he
alues
o
ed-
dening,
and
o
colo
indices
o
he
s a s
in
common,
in
pa icula
in
V,
is
accep able.
On
he
o he
hand,
he
alue
o
dis ance
modulus
ob ained
by
Massey
e
al.
(1995)
is
la ge
han
ou s
by
0.3,
and
is
based
on
spec al
ypes.
This
di e -
ence
is
mos
p obably
due
o
he
egion
co e ed
by
he
ob-
se a ions
o
Massey
e
al,
o
abou
hal
a
deg ee,
while
ou
obse a ions
a e
es ic ed
o
he
mo e
eddened
clus e
co e.
In
ac ,
hey
ob ain
a
lowe
colo
excess,
E(£
—V)
=
0.8,
compa ed
o
ou
alue
E(Z?-y)
=
0.71
which
esul s
in
E(5
—
V)
=
0.89
wi h
he
ela ion
by
Penp ase
(1992).
Wi h
a
alue
o
he
abso p ion
coe icien
R
=
3,
also
used
in
hei
wo k,
his
causes
a
di e ence
in
dis ance
modulus
o
0.3,
which
accoun s
o
he
disc epancy.
Fig.
7.
Densi y
con ou s
o
membe
s a s
in
he
ield
o
NGC
6756
shown
in
Fig.
1(d).
(a)
All
membe s,
(b)
F^18.
(c)F^16.5.
hem
as
B- ype
membe s
in
he
compu a ion
o
he
colo
excess
o
he
clus e .
Second,
in
none
o
he
published
s ud-
ies
on
he
clus e s
Basel
1,
NGC
6704,
and
NGC
6706
is
he e
a
men ion
o
he
membe ship
o
gian
s a s.
In
hese
h ee
clus e s,
we
sugges
some
gian
s a s
as
membe s,
on
he
basis
o
hei
loca ion
in
all
CM
diag ams.
In
Fig.
5,
showing
he
de eddened
CM
diag ams,
we
obse e
he
ac-
cep able
loca ion
o
hese
s a s,
in
spi e
o
he
ough
es i-
ma es
o
hei
colo
excesses.
As
has
been
commen ed
abo e,
wi h
he
ages
ob ained
o
hese
clus e s,
hey
a e
expec ed
o
ha e
an
incipien
ed
gian
b anch.
The
spa ial
dis ibu ion
o
membe s
has
been
only
ana-
lyzed
o
NGC
6756,
he
a hes
clus e
in
ou
sample,
whe e
he
obse ed
ield
is
expec ed
o
comp ise
mo e
com-
ple ely
he
clus e
dimensions.
Some
signs
o
mass
seg ega-
ion
can
be
obse ed
in
ha
case.
In
Fig.
7
we
show
densi y
con ou s,
o
membe
s a s
in
h ee
V
magni ude
anges:
All
s a s,
U^18,
and
U^16.5.
This
plo s
e eal
s onge
con-
cen a ion
o
b igh e
membe s.
3.3.3
Compa ison
wi h
published
ages
and
dis ances
In
Table
4
we
ha e
also
included
he
a ailable
published
alues
o
he
clus e
pa ame e s.
As
can
be
seen,
ou
es i-
ma es
o
he
ages
a e
e y
simila ,
and
la ge
han
10
8
yea s
o
all
h ee
clus e s
Basel
1,
NGC
6704,
and
NGC
6756.
In
he
ca alog
o
Lyngà
( e e ence
0
in
Table
4),
hese
objec s
ha e
quo ed
ages
sensibly
below
his
igu e,
and
in
pa icula
o
NGC
6756,
he
exis ing
es ima es
o
dis ance
a e
sensi-
bly
di e en
om
ou
esul s,
he
di e ence
being
abo e
he
4.
SUMMARY
AND
CONCLUSIONS
We
ha e
ob ained
imp o ed
measu emen s
o
colo
ex-
cess,
dis ance
and
age
o
ou
galac ic
clus e s.
The
new
es ima es
di e
om
p e iously
published
alues
in
some
issues.
We
poin
ou
he
ages
ob ained
o
he
h ee
clus e s
Basel
1,
NGC
6704,
and
NGC
6756,
which
u n
ou
o
be
olde
han
p e iously
assumed,
in
pa icula
o
he
wo
i s
ones.
As
o
NGC
6756,
i s
dis ance
is
dis inc ly
la ge
han
he
alues
es ima ed
by
o he
au ho s.
We
indeed
conside
ou
esul s
as
an
imp o emen ,
as
hey
a e
based
on
i s
o
bo h
e e ence
lines,
and
upda ed
model
isoch ones
on
a
wide
ange
o
spec al
ypes
om
B
o
F.
The
membe ship
o
gian
s a s
is
sugges ed
in
he
h ee
clus e s
Basel
1,
NGC
6704,
and
NGC
6756,
om
hei
lo-
ca ions
in
h ee
colo
magni ude
diag ams.
In
his
las
clus-
e ,
signs
o
mass
seg ega ion
a e
de ec ed,
in
he
sense
o
he
mos
massi e
membe s
being
mo e
concen a ed
owa ds
he
clus e
co e.
We
a e
g a e ul
o
Eloy
Rod iguez,
o
allowing
us
he
use
o
he
obse ing
ime
g an ed
o
him
in
he
1.23
m
ele-
scope
a
he
CAHA.
P i a e
communica ions
by
R.
F.
Ga -
ison,
on
spec al
ypes,
and
J.
C.
Me milliod,
who
p o ided
us
wi h
his
Open
Clus e s
Da a
Base,
a e
acknowledged.
This
wo k
has
been
inancially
suppo ed
by
he
Spanish
DGICYT,
h ough
g an s
numbe s
PB91-0053,
PB94-0007,
and
by
he
Resea ch
and
Educa ion
Council
o
he
Au ono-
mous
Go e nmen
o
Andalucía
(Spain).
The
obse a ions
ha e
been
aken
a
he
Ge man-Spanish
Obse a o y
o
Cala
Al o
(Spain).
©
Ame ican
As onomical
Socie y
•
P o ided
by
he
NASA
As ophysics
Da a
Sys em
721
DELGADO
ETAL:
YOUNG
REDDENED
CLUSTERS
721
REFERENCES
Al a o,
E.
L,
&
Delgado,
A.
J.
1991,
A&A,
241,
69
Becke ,
W.,
&
Fenka ,
R.
1971,
A&AS,
4,
241
Cla e ,
A.
1995,
A&AS,
109,
441
C aw o d,
D.
L.
1975,
AJ,
80,
955
C aw o d,
D.
L.
1978,
AJ,
83,
48
C aw o d,
D.
L.
1979,
AJ,
84,
1858
C aw o d,
D.
L.,
&
Ba nes,
J.
V.
1970,
AJ,
75,
978
C aw o d,
D.
L„
&
Mandwewala,
N.
1976,
PASP,
88,
917
C aw o d,
D.
L.,
&
Pe y,
1976,
PASP,
88,
454
Delgado,
A.
J.,
&
Al a o,
E.
J.
1989,
A&A,
219,
121
Delgado,
A.
J.,
Al a o,
E.
J.,
Ga cia
Pelayo,
J.
M.,
&
Ga ido,
R.
1992,
AJ,
103,
891
Fenka ,
R.
P.
1965,
Z A,
62,
90
Fo bes,
D.
1981,
PASP,
93,
441
Fo bes,
D.,
&
DuPuy,
D.
L.
1978,
AJ,
83,
266
(F78)
Fo bes,
D.,
English,
D.,
DeRobe is,
M.
M.,
&
Dawson,
P.
C.
1992,
AJ,
103,
916
(F92)
G ubissich,
Cl.
1965,
Z A,
60,
249
Hildi ch,
R.
W„
Hill,
G.,
&
Ba nes,
J.
V.
1983,
MNRAS,
204,
241
Jónch-Só ensen,
H.
1993,
A&A,
267,
54
J iinch-Só ensen,
H.,
&
Knude,
J.
1990,
A&A,
238,
75
Knude,
J.
1992,
A&AS,
92,
841
Lyngá,
G.
1987,
Ca alogue
o
Open
Clus e
Da a
(Lund
Obse a o y)
Man oid,
J.,
&
S e ken,
C.
1987,
A&AS,
71,
539
Massey,
P.,
Johnson,
K.
E.,
&
DeGioia-Eas wood,
K.
1995,
ApJ,
454,
151
Olsen,
E.
H.
1983,
A&AS,
54,
55
Penp ase,
B.
E.
1992,
ApJS,
83,
273
Pé ez-Hemández,
F.,
Cla e ,
A.,
&
Belmon e,
J.
A.
1995,
A&A,
295,
113
Phelps,
R.
L,
&
Janes,
K.
A.
1994,
ApJS,
90,
31
San os,
J.
F.
C,
&
Bica,
E.
1993,
MNRAS,
260,
915
Schus e ,
W.
J.,
&
Nissen,
P.
E.
1988,
A&AS,
73,
225
Shobb ook,
R.
R.
1984,
MNRAS,
211,
659
Slo opoulos,
S
1965,
Z A,
61,
105
Smi h,
L.
F.,
Meyne ,
G.,
&
Me milliod,
J.
C.
1988,
A&A,
287,
835
Tu ne ,
D.
G.
1990,
PASP,
102,
1331
Tu ne ,
D.
G.
1994,
RMxA&A,
29,
163
Wa en,
W.
H.
1976,
MNRAS,
174,
111
Young,
A.
T.
1974,
Me hods
Exp.
Phys.,
12A,
123
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