Recent IUE observations of two Tc-deficient S-type peculiar red giants that are also spectroscopic binaries, HR 363 and HR 1105 are reported. A 675 min SWP exposure of HR 363 shows emission lines of O I 1304 and Si II 1812 and a trace of continuum. Compared to the M giants, the far UV flux may be relatively larger, indicating a possible contribution from a white dwarf companion, but no high temperature emission lines are seen to indicate that this is an interacting system where mass-transfer recently occurred. However, HR 1105 appears to have a highly variable UV companion. In 1982, no UV flux was discerned for this system, but by 1986 C IV was strong, increasing by a factor of 3 in 1987 with prominent lines of Si III, C III, O III, Si IV, and N V. Using orbital parameters, these observations are consistent with high activity occuring when the side of the S-star primary illuminated by the companion faces the Earth, but since the IUE data were taken over 3 orbits, a secular change in the UV component cannot be excluded

Ake, Thomas B., III

Johnson, Hollis R.

Perry, Benjamin F., Jr.

English

NASA Technical Reports Server

PR_EDING PAGE BLANg NOT F1-LMFA)
t
/
245
N89-10729 ,
COMPANIONS TO PECULIAR RED GIANTS: IIR 363 AND HR 1105
Thomas B. Ake, IIl Hollis R. Johnson Benjamin F. Peery, Jr.
Astronomy Programs
Computer Sciences Corporation
Space Telescope Science Institute
Astronomy Department
Indiana University
Dept. of Physics and Astronomy
Howard University
ABSTRACT
We report recent IUE observations of two Tc-deficient S-type
peculiar red giants that are also spectroscopic binaries, II1/. 303
and HR 1105. A 675 min SWP exposure of IIR 363 shows
emission lines of O I 1304 and Si II 1812 and a trace of
continuum. Compared to the M giants, the far UV flux may be
relatively larger, indicating a possible contribution from a
white dwarf companion, but no high temperature emission
lines are seen to indicate that this is an interacting system
where mass-transfer has recently occurred. HR 1105, on the
other hand, appears to have a highly variable UV companion.
In 1982, no UV flux was discerned for this system, but by 1986
C IV was strong, increasing by a factor of 3 in 1987 with
prominent lines of Si IIl], C IIl], O III], Si IV and N V. Using
orbital parameters, these observations are consistent with high
activity occuring when the side of the S-star primary
illuminated by the companion faces the Earth, but since the
IUE data were taken over 3 orbits, a secular change in the UV
component cannot be ruled out.
1. INTRODUCTION
It is becoming increasingly apparent that the peculiar
abundance red giants (PRGs) of type MS, S, SC and C are a
heterogeneous group of objects with different evolutionary
histories. One group of these, the stars of considerable
s-process element overabundances but without Tc, appear to
be more closely related to Ba II stars than to K-M giants and
thus may have been mass-transfer binaries in the past (Ref. 1).
Under this scenario, the current primary did not evolve into a
PRG, but was polluted by material from a companion that
once went through this phase. Since the primary itself is not in
a thermally pulsating state, its composition reflects that of the
PRG phase of the companion, except that elements such as Tc
should have decayed away. This compaation should now be a
white dwarf (WD) star.
The latest list of PRGs that have been searched for Tc is by
Little et al (Ref. 2). ff the above scenario is correct, the
Tc-deficient stars should be binaries with WD secondaries.
Two surveys for WD companions of the MS and S stars have
been published (refs. 3-4) and companions to a few stars have
been discovered serendipitously (refs. 5-6). These observations
were undertaken without regard to Tc abundance or
indications of binary nature, but have resulted in the discovery
of three stars with hot secondaries: HD 35155, HR 1105 and o 1
Ori. The first two show no Tc but have strong emission lines in
the UV, while the third has Tc but no high temperature lines.
liD 35155 also has been noted to be higtdy variable in the UV,
both in the continuum and the lines. Thus HD 35155 and HR
1105 may be interacting mass-transfer binaries while o I Ori is
not, and the expected correlation with Tc holds. We report
here observations on another Tc-poor S star, IIR 363, and
demonstrate that HR 1105 is also a UV variable as HD 35155
has been found to be.
2. HR 363
HR 363 (S3-1-/2-) was noted in the General Catalogue of
Stellar Radial Velocities as being a spectroscopic binary, based
presumably on its velocity variations, but no orbit or period
was established. Ake and Johnson (Ref. 4) determined an
upper limit on the luminosity of a degenerate secondary based
on a quick SWP survey, but due to the importance of this
object on the binary hypothesis, we have reobserved it with a
longer exposure. Figure 1 shows the resultant spectrum after
removing extraneous hits and reprocessing with a Gaussian
extraction routine. A low level continuum and emission fines of
S I + O I 1300 and S I + Si II 1815 are prominent as is typical
in deep exposures of M giant stars (Ref. 7). The feature at
1815 uni'ortunately is affected by a cosmic-ray hit that
probably has only been partially removed by our re-extraction
technique since the normal Si H 1808/1817 splitting is not
apparent. Compared to other red giants, other chromospheric
emission is suggestive but not obvious. In Figure 1 we show in
comparison an M giant of similar temperature, 7 Cru (M3 III).
The stronger emission lines are as noted from high dispersion
observations by Carpenter et al (Ref. 8). While there are
corresponding excursions in the HR 363 data at some of the
these points, in general the spectrum is too noisy for positive
confirmation. Since HR 363 has a composition dissimilar from
the M giants and may have undergone convective mixing, the
existence of a chromosphere similar to the M giants should not
be automatically assumed.
Since we are looking for a hot companion to HR 363, we are
A Decade of UV Astronomy wtth IUE, Proc Celebratory Symposium, GSFC, Greenbelt, USA, 12-15 April 1988, ESA SP-281, Vol. 1 (June 1988)
https://ntrs.nasa.gov/search.jsp?R=19890001358 2020-03-20T06:08:53+00:00Z
246 T B AKE, H R JOHNSON & B F PEERY
_ 1 r 1 T i" 1 r 1
- IIIII
E
_ 2
_ 0 -
3 0 i
_" Cru
E cl + s i +
X 2 S I C I 0 I Fe II Si II
co? 17 I II J_ s, -
._x 0 _
1 100 1200 1300 1400 1500 1600 1700 1800 1900 2000
Wovelength (A)
Figure 1. SWP spectra of the PRG HR 363 and the M3 III star 7 Cru. Chromospheric lines in 7 Cru are identified.
Corresponding positions are showr, for HR 363, where the reality of the weaker lines is unclear.
interested in whether there is additional continuum flux
compared to other stars. While there has been much work
done on the emission line spectra of cool giants, little has been
said about the general underlying continuum, perhaps because
of concerns about scattered light in the SWP. Prom rough
estimates of the contamination, Stickland and Sanner (Ref. 7)
argue that the continuum in this region for M giants is not due
to grating scatter, but arises from the lower chromospheres in
these stars. Since their paper, Basri et al (Ref. 9) have derived
an improved scattering model for the SWP. We have calculated
the scattered light contribution as prescribed in the revision by
Basri (Ref. 10) and find that it cannot contribute more than
25% of the flux at 1900 A, and likely is below 5%. Thus the far
UV continuum in single M giants is real and one must exercise
some caution in interpreting the data as evidence for
companions.
By the flatness of the-spectrum for HR 363, a WD with
Tell > 15000K is not present. In Ref. 4 we describe a method
for determining the upper limit to the luminosity of a hot
secondary by measuring the average flux in the region 1250 to
1950 A, converting it to a magnitude scale by computing
rex600 = -2.5 log(f18oo) - 21.1, and using the resultant
Table 1. Average Fluxes at 1600 A for Red Giants
Star HR 363 7 Cru p Per g Her
Spectral Type $3+/2 M3 III M4 II-III M6 III
V 6.43 1.62 3.2 5.05
E(B - V) 0.05 0.00 0.03 0.0O
SWP Number 32472 5891 32553 1387
F,xp Time (rain) 675 90 249 154
Observer Ake Sarmer Ake Wing
(m16oo- V)o 9.63 10.24 10.05 10.00
m16o0 -- V color with similar determinations for field white
dwarfs and the absolute magnitude of the primary to compute
the upper limit. In Table 1 we present the mlB00 - V colors for
HR 363 as well as for 3 late-type M giants. The data is
corrected for the tabulated reddening values, which we
obtained for the M giants by comparing published UBVRI
observations with mean colors for their spectral type, and for
HR 363 from Eggen (Ref. 11). Note that the color for HR 363
is about 0.5 mag bluer than the M stars indicating there is
added flux in the SWP region. If the entire continuum in HR
363 is due to a companion, we derive Mv=ll.2, but the flux
for a WD of this magnitude should curve upwards at the
shortest wavelengths (see Ref. 4). If we assume that HI{ 363
has a chromospheric spectrum comparable to the M giants, we
find that the added flux yields Mv=ll.7 for the companion,
which would then have a flatter energy distribution.
3. HR 1105
HR 11o5 ($3.5/2) is a 596 day spectroscopic binary (ReL 12)
whose secondary was first reported by Peery (Ref. 6). He had
obtained 2 SWP exposures of 20 min. and 87 rain. duration on
the same day, the longer one taken after C IV emission was
fotmd in the first image. Interestingly a 20 rain. exposure was
obtained by O'Brien and Johnson in 1982 and no emission was
seen. We have obtained 2 other observations and can confirm
the variability of this object. In Figure 2 we show plots of the
spectra with the stronger emission lines identified, and in Table
2 we present the integrated line fluxes and a continuum flux
centered in the relatively line free region at 1460/_. Orbital
phases from Griffm's determination are also indicated.
The recent observations have caught the system in a higher
state than previously seen, with a subsequent decline from
December 1987 to March 1988 in both the continuum and
COMPANIONSTOPECULIARREDGIANTSHR363& HR1105 247
oD
E
¢9
x
X
Z3
2O
15
10
m
5 _ [
f
o I
11Q0 1200
N V
I
O I
Sl IV C IV
O III 1
SWP 32552
Sl III]
Si II
h,t ?
SWP 33059
SWP 27678
1 300 1400 1 :500 1 600 1 700 1800 1900
Wavelength (A)
20Q0
Figure 2. Temporal variation of the PRG HR 1105 in the SWP region. Successive plots are offset by
5 x 10 -14 ergs/cm2/sec/A each. Prominent emission features are labelled and continuum slopes are indicated.
emission lines. In general, the lines and continuum scale
together, with little change in the relative line strengths and
the continuum slope, although the continuum is slightly bluer
in December 1987. The density sensitive Si III]/C III] ratio is
essentially unchanged, as are ratios of lines of different
excitation. These observations argue that the decline was not
associated with a change in the energetics of the system, but
rather the total luminosity was reduced by a decrease in the
apparent size of the emitting region. Compared to the
observation in 1986, however, some variations in the lines are
seen, although the exposure is somewhat weak. The continuum
flux at 1460 A is nearly the same in the Feb 1986 and March
1988 observations, but in 1986 N V is weaker and the
Si III]/C III] ratio is < 1. Thus on a longer time scale, the
physical conditions of tiffs system appear to be variable.
4. DISCUSSION
While both HR 363 and HR 1105 are Tc-deficient
spectroscopic binary PRGs, their characteristics in the far UV
are quite different and the evidence for the mass-transfer
hypothesis for the origin of their current abundance
peculiarities is mixed. Based on comparison with the M giants,
a WD companion to HR 363 can only be inferred. Further
analysis of the chromospheres of other red giants is required to
confirm that appropriate comparison objects were chosen.
From the Stickland and Sanner data, we find that the
(miss0 - V) color for K and earlier type M giants is even
redder, so using other standards would opt for a brighter
companion. Finally we note that if excess UV flux is from a
WD companion, the absence of high temperature emission
lines such as C IV indicates that tiffs is not currently an
interacting system like HD 35155 and HR 1105.
For Hit 1105, clearly a hot companion is present, but as with
the symbiotics, the source of the UV radiation is not clear.
The variability and brightness of the continuum indicate that
the photosphere of a WD companion is not directly observed.
Possible locations of the radiation for systems such as these are
an accretion disk around the secondary, a stream between the
components, or a hot outer atmosphere of the primary heated
by the companion. In the last two cases, the observed changes
should be correlated with orbital phase. In Figure 3 we show
the points at which the observations have been made. There is
Date SWP No.
1982 Aug 31 17816
1986 Feb 7 27678
1987 Dec 17 32552
1988Mar 6 33059
Overexposed
Table 2. IUE Observations of HR 1105
Flux (x 10 -13 ergs/cm2/s)
Phase NV OI SiIV CIV SilII] CIIII
4.057
6.163 1.38 1.71 2.34 9.27 0.18 0.49
7.302 7.60 3.02 6.17 > 27 a 2.03 1.78
7.436 3.80 2.69 1.75 11.7 1.12 0.92
f1460
(ergs/cm2/s/_)
8.6a(-15)
1.60(-14)
3.01(-14)
1.63(-14)
248 T B AKE, H R JOHNSON & B F PEERY
__ 27678
17816
=0
Figure 3. Motion of the HR 1105 S-type primary about the
system center of mass. Phases at which SWP spectra have
been taken are marked.
a general relationship in that the highest state occurred when
the hemisphere of the primary illuminated by the companion
was nearly face on, while the lowest phase (i.e., no emission
seen in 1982) occurred when the primary was in front of the
plane of the sky. But except for the observations made in the
past year, the data was collected at different orbital cycles: so
the correspondences are somewhat suspect since secular
variations cannot be ruled out. Further observations are
required to confirm if the changes are actually periodic.
6. ACKNOWLEDGEMENTS
We gratefully acknowledge the assistance of the IUE staff in
obtaining these observations and the GSFC RDAF in the
specialized extraction routines. The work by T. B. A. is
supported by NASA grant NAS 5-28749.
5. REFERENCES
1. Smith V E & Lambert D L 1988, preprint.
2. Little S J, Little-Marenin I R & Bauer W H 1987,
Astron J, 94, 981.
3. Smith V E & Lambert D L 1987, Astron J, 94, 977.
4. Ake T B & Johnson H R 1988, Astrophys J, _27, 214.
5. Johnson H R & Ake T B 1983, in Cool Stars, Stellar
Systems, and the Sun, eds. S L Ballunas & L Hartmann,
(New York: Springer-Verlag), p. 362.
6. Peery B F Jr 1986, in New Insights in Astrophysics:
8 Years of UV Observations with IUE, ed. E l%olfe,
ESA SP-263, p. 117.
7. Stickland D J & Sanner F 1981, Mon Not Roy Astr Soc,
197, 791.
8. Carpenter K G, Pease J E, Stencel R E, Brown A,
Johansson S & Wing R F 1988, Astrophys J, submitted.
9. Basri G, Clarke J T & Haisch B M 1985, Astron Astrophys,
144, 161.
10. Basri G 1985, NASA IUE Newsletter, No. 28, p. 58.
11. Eggen O J 1972, Astrophys J, 177, 479.
12. Griffin R F 1984, Observatory, 104, 224.


Companions to peculiar red giants: HR 363 and HR 1105

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server