Two high luminosity population II blue stars of high galactic latitude, BD+33 deg 2642 and HD 137569 were observed at high resolution. The stellar spectra show the effect of mass loss in BD+33 deg 2642 and abnormally weak metallic lines in HD 137569. The interstellar lines in the direction of BD+33 deg 2642, which lies at a height z greater than or equal to 6.2 kpc from the galactic plane, are split into two components. No high ionization stages are found at the low velocity component; nor can they be detected in the higher velocity clouds because of mixing with the corresponding stellar/circumstellar lines

Franco, M. L.

Hack, M.

Stalio, R.

English

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IUE OBSERVATIONS OF BLUE HALO HIGH LUMINOSITY STARS m
Margherita Hack, Margarita L. Franco and Roberto Stalio
Astronomical Observatory, Trieste, Italy
ABSTRACT
Two high luminosity population II blue stars of high galac-
tic latitude, BD+33°2642 and HD 187569 have been observed at high
resolution. The stellar spectra show the effect of mass loss in
BD+33o2642 and abnormally weak metallic lines in HD 137569. The
interstellar lines in the direction of BD+33°2642, which lies at
a height z_ 6.2 kpc from the galactic plane, are split into two
components. No high ionization stages are found at the low ve-
locity component; nor carl they be detected in the higher velocity
clouds, because of mixing with the corresponding stellar/circum-
stellar lines.
INTRODUCTION
Various classes and subclasses of blue halo stars of popu-
lation II and old disk population have recently been described
and discussed (ref.s 1 and 2). Three large groups, which include
all subclasses, are generally recognized to be important: the
horizontal branch (HB) stars, the subdwarfs, the high luminosity
(HL) population II-B stars. This last group is formed of stars
which lie several magnitudes above the HB stars. Bernard 29, in
the globular cluster M 13, BD+33°2642 and HD 137569 are commonly
thought to belong to the HL-population II-B-star group.
Here we report on the high resolution IUE observations of
BD+33°2642 and HD 137569. The spectrum of BD+33°2642 (only SWP
observations, exposure time 4.7 hours) will be discussed more ex-
tensively since it presents the effects of mass-loss in the high-
Based on observations by the International Ultraviolet Explor-
er (IUE) collected at the Villafranca Satellite Tracking Station
Of the European SPace'Agency. This work was partly supported by
a CNR-Italy contract.
193
https://ntrs.nasa.gov/search.jsp?R=19810017381 2020-03-21T12:27:24+00:00Z
ly ionized resonance lines of C IV, Si III and Si IV, and in-
trlguing evidence for the presence of high ionization stages in
the interstellar lines. The basic data for the two stars are
presented in Table 1.
THE STELLAR SPECTRA
The main results emerging from a study of BD+33°2642 made
by Stalio and Franco (ref. 6) are:
i) the effective temperature, on the basis of the spectral ener-
gy distribution, is found to be about 18000 K, lower than the
temperature determined from the line spectrum (ref. 4) Dy about
5000 K. Discrepancies between temperatures determined from the
continuum and line spectrum are also found in population I early'
type supergiants (see e.g. ref. 7) but seem not to be so great.
They are generally ascribed to the different depths of formation
of _he two spectra,
2) the carbon spectrum appears less ionized than in _ Sco, whose
UV spectrum has been used for comparison. This result is proba_
bly due to combined effects of a lower effective temperature and
lower carbon abundance,
3) the photospheric turbulence is small: it has been calculated
to be 2.3 km s from a curve of growth of Fe Ill lines. This
value is in agreement with the visual data, but in conflic9 with
the observations of population I stars having similar effective
temperature and gravity (ref. 8),
4) the star has a stellar wind revealed by the displaced lines of
C IV, Si III and Si IVl(figure i). The terminal velocity is esti-
mated to be -520 km s from the steep blue edge of the Si III
resonance prof_e. A _wer limit for the mass-loss is calculated
to be 4.7 x i0 - M yr .
e
HD 137569, on the contrary, does not show clear evidence for
mass flux: the most prominent features in the UV, the resonance
lines of C II, have large symmetrical wings. The remaining spec-
trum consists of abnormally weak metallic lines of Mg II, Si III
and Fe III, multiplet 34. The ultraviolet flux distribution is
that of a B3 supergiant with no reddening. The anomalous B-V
colour index, and the vat{able radial velocities reported in ref.
5, support the idea that the star is part of a binary system.
194
THE INTERSTELLAR SPECTRA
If we consider both stars as having low mass (ref. 2) typi-
cal of population II objects, their height from the galactic pla-
ne is 6.2 kpe for BD+33°2642 and 0.8 kpc for HD 187569. By vir-
tue of its distance, BD+33°2642 can provide information on the
high ionization galactic halo gas. The interstellar spectrum is
split into two components at about -35 and -105 km s-1. All mea-
surable lines are presented in table 2. Hig1_ ionization stages,
C IV and Si IV, seem to be present (figure i) at the stellar ve-
locity, thus suggesting that they might come from gas formed
around the star.
The interstellar spectrum is very well measurable in HD
137569 due to the weakness of stellar lines. All usually obser-
ved interstellar lines are present at about zero velocity. T_re
might be evidence of weak Si IV components at 0 and -iO0 km s .
CONCLUSIONS
We have studied two stars of the group of HL-population II-
B objects, whose cinematical and evolutionary situation is rath-
er controversial. BD+33°2642 is likely to be a population II ob_
ject, similar to the globular cluster giant Bernard 29; it has a
large amount of mass loss for its low mass, and, besides abun-
dances, presents differences with population I stars of the same
spectral class in the size of the photospheric turbulent motions,
which are smaller, and in the _nonnt 6f aiscrepancies between the
effective temperature determined from the continuum and line spec-
trum. HD 137569 has a simpler UV spectrum than BD+33°2642: it
shows abnormally weak metallic lines and no evidences of hitch
ionization sta_es and mass flux, unlike all known early type
stars of low gravity.
For both stars the reddening, as deduced from the interstel-
lar bump at 2175 _, is low. The radial velocities of the _nter-
stellar g_ in the line of sight of BD+33°2642 are at -35 and
-105 km s ; no high ionization stages are found in the low ve-
locity cloud; nor can they be detected in the higher velocity
cloud, because of mixing with the corresponding stellar/circum-
stellar lines.
195
REFERENCES
i. Newell,E.B.:lS73, Astrophys. J. Suppl. _, 7
2. Greenstein,J.L., Sargent,A.I.:1974, Astrophys. J.Suppl. 2__88, 157
3. Blanco,V.M.,Demars,S.,Douglass,G.G,Fitzgerald,M.p.- Publ.of
the United States Naval Observatory, 2naseries,Voli21
4. Traving,G.:1962, Astrophys. J. 13__5,439
5. Danziger,I.J.,Jura,M.A.:1970, Astrophys. J. 16___!, 997
6. Stalio,R.,Franco,M.L.:1980, Astron.Astrophys., in press
7. Stalio,R.,Selvelli,P.L.,Crivellari,L.: 1977, Astron.Astrophy_.
60, 109
8. Lamers,H.J.G.L.i,{.,DeLoore,C.:1975, in Physique:de$_:Mouvements
dans les Atmospheres Stellaires, Ed. R.Cayrel and M. Steinber_,
CNRS France,P.453
9. Rogerson,J.B.Jr.,Upson,W.L.:1977, Astrophys. J.Suppl. 3__5,37
196
TABLE 1 : The Basic Data.
BD+33°2642 HD 137569
Spectral Type B2 B5
l
V i0.8 7.86 ( ref. 3
B-V -0.14 0.24 }
i
i" 520 21 o
b" +510 +520
-i -1
Radial Velocity -95 km s variable; -30 km s
in our spectrum
22900 °K_ 120OO' °K )Tef f
io_ g 2.3 _ref.4 2.3
ref. 5
M -3.9 -2,6 based on masses
v of 0.66 M
®
197
TABLE _, : Radial velocities of _he interstellar lines on the wavelength scale
of the star rest frame,BD+33o2642.
Vel Vel Ion k (A) Vell Veil
Ion I (A) (km s -1) (km s -1) (km s- ) (km s- )
C I 1656.928 - -103 Si II 1260.418 -42 -I01
1657.380 - -113 1264.730 - -103
1657.907 - -118 1265.023 - -102
1328.833 -20 -110 1304.369 -40 - 98
1277.240 -29 - 1526.719 -33 - 72
C II 1334.530 -20 -110 1533.445 - -112
1335.700 -23 -102 Si Ill 1206.510 - - 90
C IV 1548.202 - - 87 Si IV 1393.755 - - 90
w ,
1550.774 - - 81 1402.769 - - 85
N I -1199.549 -15;-55 - S II 1250.586 -35 -106
1200.224 -34 - 1253.-812 -29 -100
1200.7ti -5;-43 - 1259.520 -30 -102
L
0 1 {302.170 -36 - 98 Fe II 1608.456 -28 - 84
Mg I 2026.405 - - 82 Ni II 17_1.560 -31 -117:
A III 1670.786 U41 - 95 175!.920 522
A! III 1854.726 - -106" !Z7! 960 -42 -
w
1862.795 -" -102 Zn II 20_6.097 -27 -105
Si II i193.784, -36 - 87 \
. . .I194_497- - " 90 _Iso photospheric
contributions
BD+33 ° 2642 TAU SCO
Q5
>-
,.,o 1544 1546 1548 1550 1552 ,1544 1546 154-8 1550 1552
z
LI.I
LuQC I I I ,_ I I I I
1_200 1202 1204 1206 1208 1200 1202 1204 1206 1208
1.0
0.0 i i ,, I i I I I I I I I
1389 1391 1393 1395 1397 1389 1391 1393 1395 1397
WAV E L E N GT H (,_,)
Fi.!.:. 1. i_<-sona.nce line prof'iles oi" the C IV doublet (toip), of
Si Ill 1206.52 (middle) and el" Si IV 1898.73 (bottom)
coim_arcd with tile same iii"_es obse:_ved in See (:'ef. o).


IUE observations of blue halo high luminosity stars

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