Observations and analysis of the Aug. 1987 outburst of the recurrent nova V394 CrA are presented. This nova is extremely fast and its outburst characteristics closely resemble those of the recurrent nova U Sco. Hydrodynamic simulations of the outbursts of recurrent novae were performed. Results as applied to the outbursts of V394 CrA and U Sco are summarized

Ferland, Gary

Gehrz, Robert D.

Heathcote, S.

Kenyon, Scott

Ney, Edward P.

Shaviv, G.

Sonneborn, G.

Sparks, Warren M.

Starrfield, S.

Williams, R. E.

English

NASA Technical Reports Server

IYA J/J 5
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N89-10710
167
OBSERVATIONS AND SIMULATIONS OF RECURRENT NOVAE: U SCO AND V394 CRA
S. Starrfieid
Department of Physics, Arizona State University and
Theoretical Division, Los Alamos National Laboratory
G. Sonneborn //
IUE Observatory, Goddard Space Flight Center
Warren M. Sparks
Applied Theoretical Physics Division
Los Alamos National Laboratory
G. Shaviv
Department of Physics, The Technion
R. E. Williams and S. Heathcote
Cerro Toiolo Interamerican Observatory
Gary Ferland
Department of Astronomy, Ohio State University
Robert D. Gehrz and Edward P. Ney
Department of Astronomy, University of Minnesota
Scott Kenyon
Center for Astrophysics, Harvard University
James W. Truran
Department of Astronomy, University of Illinois
C.- C. Wu
Space Telescope Science Institute
ABSTRACT
We present observations and analysis of the August 1987
outburst of the recurrent nova V394 CrA. This nova was
extremely fast and its outburst characteristics closely
resembled those of the Recurrent Nova U Sco. In addi-
tion to the observations, we have performed hydro-
dynamic simulations of the outbursts of recurrent novae
and present a summary of these results as applied to the
outbursts of V394 CrA and U Sco.
I. INTRODUCTION
The IUE Satellite has observed four recurrent novae
during its 10 year lifetime. These are WZ Sge, U Sco,
RS Oph and V394 CrA. The ultraviolet data showed that
WZ Sge was a long period dwarf nova and, therefore, its
outburst is not relevant to this work which is concerned
only with recurrent classical novae. The 1979 outburst
of U Sco was well studied both in the ultraviolet, with
the IUE Satellite, and in the optical (Williams et al.
1981). The May 1987 outburst was well studied in the
optical (Sekiguchi etal. 1987) but the nova was too close
to the sun to be studied with the IUE Satellite. Recent-
ly, some of us have published simulations of its 1979
outburst (Starrfield, Sparks, and Truran 1985).
RS Oph is more of a puzzle and its outburst resembles
that of a nova exploding into a stellar wind. In addition,
there is some controversy about what caused its outburst.
A summary of its behavior can be found in the proceed-
ings of a symposium held specifically to discuss its
outburst and that of other recurrent novae (Bode 1986).
V 394 CrA exploded in August 1987 and we were able to
obtain both optical and ultraviolet data. A previously
recorded outburst occurred in 1949 (Duerbeck 1987).
These data are now being analyzed and this nova appears
to have had an outburst similar to that of U Sco. The
data from this outburst will be presented and discussed
in this paper. In a companion study, we have done new
simulations for the outbursts of both U SCo and V 394
CrA. We assumed a 1.35M®, hot white dwarf accreting
at high rates. Given mass accretion rates as high as
10-6M®yr -I, it is possible to achieve a runaway in less
than 3 years from the beginning of accretion. These
calculations have been done with new boundary condi-
tions that include the effects of the accretion energy on
the thermonuclear runaway. They also include the
effects of radiation pressure driven mass loss.
2. The 1987 Outburst of V394 CrA
V394 Coronae Austrinae was reported to be in outburst
by Liller (IAU Circular 4428) who also noted that spectra
taken on August 3.021, 1987 showed intense Ha emission
blended with [NII] plus a weak continuum. McNaught
(IAU Circular 4429) noted the coincidence in position of
V394 CrA with a star of mag-18 on a UK Schmidt J
Plate at a position of a - 17 n 56 m 58.18 s, 6 = -39 °
00'29.3". Some of us began obtaining spectra with the
CTIO l-meter telescope on August 4, 1987 and reported
that the nova (IAU Circular 4430) showed broad emission
from the Balmer lines, He l, and He II 4686A. In
addition these spectra also showed strong recombination
lines from NII at 5005A, 5679A, and 5178A). A spectrum
obtained on August 4, 1987 is shown in Figure la and a
spectrum obtained on August 19, 1987 is given in Figure
lb. Note the rapid evolution and decay of the emission
lines over the two week interval. Exactly the same
behavior was found for U SCo (Barlow et al. 1981).
Note also that at all times HeII 4686A is stronger than
HE. This inversion of line strengths is unusual but also
seen in U SCo and some of the other old novae.
However, we also note that VI500 Cygni 1975, which also
shows HeII 4686A stronger than H beta has been found
to be an AM Her variable (Schmidt, Stockman, and Lamb
1988, preprint).
Unfortunately, we were unable to obtain an IUE spectrum
A Decade of UV Astronomy with 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=19890001339 2020-03-20T06:08:43+00:00Z
168 S STARRFIELD ET AL
1.75E-12
1.50E-12
1.25E-12
1.00E-12
7.50E-13
5.00E-13
2.50E-13
I I I I
4000
I
5000 6000 7000
lambda (angstroms)
Figure la. The optical spectrum of V394 CrA obtained on August 4, 1987. The line
identifications for the strongest lines can be found in Table 1. Note the strength of
Hell 4686A as compared to H/L The structure in Ha is certainly real and characteristic
of novae ejecta.
I I 1 I
8.00E-14 -
6.00E-14 -
4.00E-14 - t_
2.00E-14_I _/_¢_dv_'_ ' _ J
4000 5000 6000
lambda (angstromsl
7000
Figure lb. The optical spectrum on August 19, 1987. The nova declined very rapidly
over the two week period. This behavior is analogous to that of U Sco. However, the
4640A complex was much stronger in U Sco than in this nova.
OBSERVATIONS& SIMULATIONSFRECURRENTNOVAEUSCO&V394CRA 169
until August 23, 1987 and by then the nova had faded
considerably. We show this spectrum as Figure 2a and
2b. We give the entire usable spectrum in Figure 2a in
order to demonstrate the excellent match to a spectrum
that we obtained of the Recurrent Nova U SCo on June
30, 1979 (Williams et al. 1981). In Figure 2b. we show
only the region from 1300A to 1950A in order to show
the profiles of' CIV 1550A and NIII] 1750A in more detail.
Note that the same blend at 1750A appears in the June
30, 1979 spectrum of U Sco. We do not have an
identification for the line at -1735A. The most
important features to notice about this spectrum is the
great strength of the nitrogen lines. Their strength
strongly supports the suggestion of Heathcote, Gomez,
and Williams (IAU Announcement Card #:4430) that
nitrogen is enhanced in this nova.
3. Discussion
The strong resemblance of both the optical and ultra-
violet spectra of V394 CrA to those obtained of U Sco
during its 1979 and 1987 outbursts (Barlow et al. 1981;
Williams et al. 1981; Sekiguchi et al. 1987) strongly
suggests that these objects are closely related. A high
priority of future optical observations should be a study
of both recurrent novae at minimum in order to
determine the parameters of the binary systems.
The current hydrodynamic modeling of recurrent novae
(see Starrfield, Sparks, and Shaviv 1988, and references
therein) implies that we are witnessing the effects of
thermonuclear runaways on very massive white dwarfs.
This conjecture can be tested by radial velocity studies
of these two systems at minimum. In fact, their
outbursts are so rapid that they have already returned to
minimum but are not too faint to be studied with large
telescopes in the southern hemisphere.
The theoretical studies of these systems also show that
it is possible to obtain a thermonuclear runaway and
mass ejection even if the secondary is transferring
material with no CNO enhancement. The luminosity of
the shell source is sufficient to drive mass from off of
the white dwarf purely by radiation pressure. However,
only a small fraction of the accreted mass is ejected
during the outburst; most of it is burnt to helium during
the runaway and acts purely to increase the mass of the
white dwarf towards the Chandrasekhar limit. Therefore,
we predict that these two systems, U Sco and V 394
CrA, are evolving to a point where the white dwarf will
exceed a mass of 1.4M® and become a neutron star.
These systems will then become low mass X-ray binaries.
An argument in favor of this suggestion is that the low
mass X-ray binaries seem to be transferring material rich
in helium (Williams 1988, in preparation).
Acknowledgements
This study would not have been possible without the
rapid response of the IUE Observatory to the request for
Target-of-Opportunity observations of V394 CrA. We are
grateful for their continued support of nova observations.
The data were reduced with the facilities of the RDAF at
the University of Colorado which are supported by NASA
Grant NAS5-28731 and we are grateful for the excellent
assistance from T. Armitage of that facility. We also
acknowledge partial support for this research from NASA,
NSF, and the DOE through grants to our various institu-
tions.
References
Barlow, M.J., Brodie, J.l:*, Brunt, C.C., Hanes, D.A., Hill,
P.W., Mayo, S.K., Pringle, J.E., Ward, M.J., Watson,
M.G., Whelan, J.A.J., and Willis, A. J. 1981, M.N.R.A_,
195, 61.
Bode, M. F. 1986, RS O0h(198_) and the Recurrent NOva
Phenomenon (Utrecht: VNU Science Press).
Duerbeck, H. 1987, A Reference Catalogue and Atlas of
Galactic Novae, (Dordrecht: Reidel).
Schmidt, G., Stockman, H.S., and Lamb, D. Q. 1988,
preprint.
Sekiguchi, K, Feast, M. W., Whitelock, P. A., Overbeek,
M.D., Wargau, W. and Spencer Jones, J. 1988,
M.N.R.A.S., in press.
Starrfield, S., Sparks, W.M., and Shaviv, G. 1988, Ao. J,
Lett, 325, L35.
Starrfield, S., Sparks, W.M., and Truran, J.W. 1985, AD.
J., 291, 136.
Williams, R.E., Sparks, W.M., Gallagher, J.S., Ney, E.P.,
Starrfield, S., and Truran, J.W. 1981, Ao. J., 251, 221.
TABLE 1
Identification Wavelength (A)
Lya 1216A
NV 1240A
N1V] 1486A
CIV 1549A
Hell 1640A
OIlI] 1663A
NIl1] 1750A
H6 4101A
Hq, 4340A
He II 4686A
HE 4861A
NIl 5005A
NIl 5178A
HelI 5411A
NII 5679A
Hel 5876A
Ha 6563A
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170 S STARRFIELD ET AL
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Figure 2a and b. The IUE spectrum of V394 CrA obtained on August 23, 1987. The
upper plot shows the entire usable spectrum while the lower plot emphasizes the strong
lines and shows the peculiar profile around NIII] 1750A. This spectrum closely
resembles that of U Sco obtained on June 30, 1979.
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Observations and simulations of recurrent novae: U Sco and V394 CrA

Observations and simulations of recurrent novae: U Sco and V394 CrA

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