arXiv:astro-ph/0310037v1 1 Oct 2003
Mon. Not. R. Astron. Soc. 000, 1–13 (2003)Printed 2 February 2008(MN LATEX style file v2.2)
Photometric study of southern SU UMa-type dwarf novae
and candidates – III: NSV 10934, MM Sco, AB Nor,
Taichi Kato1, Peter Nelson2, Chris Stockdale3, Berto Monard4,
Tom Richards5, Rod Stubbings6, Hitoshi Yamaoka7, Bernard Heathcote8,
1Department of Astronomy, Faculty of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502 Japan
2RMB 2493, Ellinbank 3820, Australia
3Hazelwood Observatory, RMB 4036 Matta Drive, Hazelwood South, Victoria 3840, Australia
4Bronberg Observatory, PO Box 11426, Tiegerpoort 0056, South Africa
5Woodridge Observatory, 8 Diosma Rd, Eltham, Vic 3095, Australia
619 Greenland Drive, Drouin 3818, Victoria, Australia
7Faculty of Science, Kyushu University, Fukuoka 810-8560, Japan
8Tardis Astronomical Observatory, Mia Mia, Victoria, Australia
9Southern Stars Observatory, Po Box 60972, 98702 FAAA TAHITI, French Polynesia
Accepted. Received; in original form
We photometrically observed four southern dwarf novae in outburst (NSV 10934,
MM Sco, AB Nor and CAL 86). NSV 10934 was confirmed to be an SU UMa-type
dwarf nova with a mean superhump period of 0.07478(1) d. This star also showed
transient appearance of quasi-periodic oscillations (QPOs) during the final growing
stage of the superhumps. Combined with the recent theoretical interpretation and with
the rather unusual rapid terminal fading of normal outbursts, NSV 10934 may be a
candidate intermediate polar showing SU UMa-type properties. The mean superhump
periods of MM Sco and AB Nor were determined to be 0.06136(4) d and 0.08438(2)
d, respectively. We suggest that AB Nor belongs to a rather rare class of long-period
SU UMa-type dwarf novae with low mass-transfer rates. We also observed an outburst
of the suspected SU UMa-type dwarf nova CAL 86. We identified this outburst as a
normal outburst and determined the mean decline rate of 1.1 mag d−1.
Key words: accretion: accretion disks — stars: cataclysmic — stars: dwarf novae —
stars: individual (NSV 10934, MM Sco, AB Nor, CAL 86)
Cataclysmic variables (CVs) are close binary systems con-
sisting of a white dwarf and a red-dwarf secondary transfer-
ring matter via Roche-lobe overflow. SU UMa-type dwarf
novae comprise an important subgroup of CVs, which is
characterized by the presence of superoutbursts and super-
humps. The superhumps and superoutbursts are now widely
believed to be a result of the combination of two types
of disk-instabilities (thermal and tidal instabilities), which
have provided a laboratory to understand the basic astro-
physical processes, such as the origin of viscosity and reso-
nant actions on a fluid disk in close binaries (see a review
by Osaki (1996); see also Ogilvie 2002 for recent theoretical
development). We, the VSNET Collaboration (Kato et al.
2003d),1have been studying the properties of (mostly new)
southern SU UMa-type dwarf novae, candidates, and related
systems with a perspective described in Kato et al. (2003c).
In this paper, we report on the detection of superhumps in
three systems, and also report on photometric observations
of an SU UMa-type candidate which underwent a likely nor-
2 T. Kato et al.
Table 1. Observers and Equipment.
aSCT = Schmidt-Cassegrain telescope.
bUsed for NSV 10934.
2 CCD OBSERVATION
The observers, equipment and reduction software are sum-
marized in Table 1. All observers performed aperture pho-
tometry, and the magnitudes were determined relative to
a nearby comparison star, which was confirmed to be con-
stant during the observation by a comparison with a check
star. The observations used unfiltered CCD systems having
a response close to Kron-Cousins Rc band for outbursting
dwarf novae. The errors of single measurements are typically
less than 0.01–0.03 mag unless otherwise specified. The ob-
servers abbreviations will be used in “Obs” field in the later
Barycentric corrections to the observed times were ap-
plied before the following analysis.
NSV 10934 was originally discovered as a large-amplitude
suspected variable star of unknown classification. Kato et al.
(2002a) noticed the identification with a bright ROSAT
source (1RXS J184050.3−834305), and suggested that the
object is a cataclysmic variable. Kato et al. (2002a) indeed
detected multiple outbursts. These outbursts generally bore
resemblance to dwarf nova outbursts, but are unusual in the
rapid decline during the terminal stages of these outbursts.
From these findings, Kato et al. (2002a) suggested that NSV
10934 may be an analogous object to the intermediate polar
(IP), HT Cam, which shows brief dwarf nova-like outbursts
(Ishioka et al. 2002; Kemp et al. 2002). Kato et al. (2002a)
also predicted that the orbital period of NSV 10934 would
be slightly longer than that of HT Cam (86 min), if NSV
10934 indeed turns out to be an HT Cam-like object.
Since then, NSV 10934 has been monitored by one of
the authors (Rod Stubbings), and it has been established,
by the end of 2002, that the object shows short outbursts,
as described in Kato et al. (2002a), at rather regular inter-
vals of 40–60 d. Following a call for observing campaign in
2002 December (vsnet-campaign-dn 31412), the object went
into a superoutburst, which will be described in the next
subsection. A recent long-term visual light curve is shown
in Figure 1.
JD - 2452000
Figure 1. Long-term visual light curve of NSV 10934. In addition
to short, normal outbursts recurring with time-scales of 40–60 d,
there is a long, bright superoutburst around JD 2452643. The
enlarged CCD light curve of this superoutburst is shown in Figure
3.22003 January Outburst
The outburst was first detected on 2003 January 2.480 UT at
a visual magnitude of 15.0 by Rod Stubbings. On January
2.767 UT, the object was observed to further brighten to
11.9 mag (vsnet-alert 76013). A time-resolved CCD photo-
metric campaign started on the next night of this detection.
The object was still rising in brightness. As described later,
this outburst was confirmed to be a superoutburst by the
detection of secure superhumps. The log of observation is
summarized in Table 2.
Figure 2 shows the entire light curve of this superout-
burst drawn from CCD observations. The CCD magnitudes
(system close to Rc) are given relative to GSC 9523.351
(Rc ∼11.8). The zero point is adjusted to the most com-
prehensive Peter Nelson’s observations.
Figure 3 shows nightly light curves of NSV 10934 during the
2003 January superoutburst. The light curve on January 3
showed almost no feature of superhumps. On January 4,
superhumps started to grow. The amplitudes of the super-
humps reached a maximum at around January 5–6. We first
determined the mean superhump period using Phase Disper-
sion Minimization (PDM: Stellingwerf 1978), after removing
the linear decline trend during the plateau stage (January
5–13) of the superoutburst. The result is shown in Figure 4.
The strongest signal at a frequency of 13.373(1) d−1corre-
sponds to the best superhump period of 0.07478(1) d. The
selection of the correct alias has been confirmed by indepen-
dent analyses of continuous nightly observations.
Figure 5 shows the mean superhump profile (of the
plateau phase of the superoutburst), phase-averaged with
the period of 0.07478 d. The rapid rise and slower decline
are characteristic of SU UMa-type superhumps (Vogt 1980;
Southern SU UMa-Type Dwarf Novae3
Table 2. Journal of the 2003 CCD photometry of NSV 10934.
2003 Date Start–Enda
BJD - 2452600
NSV 10934 (2003 January superoutburst)
Figure 2. The 2003 January superoutburst of NSV 10934. The
CCD magnitudes (close to Rc) are given relative to GSC 9523.351
3.4Superhump period change
We extracted the maximum times of superhumps from the
light curve by eye. The averaged times of a few to several
points close to the maxima were used as representatives of
the maximum times. Thanks to the high-precision data, the
errors of the maximum times are usually less than ∼0.001
d. The resultant superhump maxima are given in Table 3.
The values are given to 0.0001 d in order to avoid the loss
of significant digits in a later analysis. The cycle count (E)
is defined as the cycle number since BJD 2452643.9874. A
linear regression to the observed superhump times gives the
following ephemeris (the errors correspond to 1σ errors at
E = 48):
BJD(maximum) = 2452644.0033(16) + 0.074851(38)E.(1)
Fraction of BJD
Figure 3. Nightly light curves of NSV 10934 during the 2003 Jan-
uary superoutburst. The light curve on January 3 showed almost
no feature of superhumps. On January 4, superhumps started to
grow. The amplitudes of the superhumps reached a maximum
around January 5–6.
Figure 6 shows the (O − C)’s against the mean super-
hump period (0.074851 d) from a linear regression (equa-
tion 1). The diagram clearly shows the decrease in the su-
perhump period throughout the superoutburst plateau. The
superhump maxima during the plateau phase (13≤ E ≤110)
is well expressed by a quadratic term corresponding to a pe-
riod derivative of ˙P/P = −10.2±1.0 × 10−5. The earlier
stage (E <13) shows a large deviation from this quadratic
fit, which is probably a result of the rapid evolution of su-
perhumps at this stage. The observed decrease of the super-
hump period is one of the largest among known SU UMa-
type dwarf novae (cf. Kato et al. 2003c).
On January 4 (just after the initial growth time of the su-
perhumps), there was an indication of quasi-periodic oscilla-
tions (QPOs) superimposed on superhumps (Figure 7). The
lower panel of Figure 7 is to better illustrate the QPO sig-
nal, by subtracting the mean superhump profile by using a
Fourier decomposition of the superhump profile from these
data up to the fourth harmonics. Figure 8 shows the power
spectrum of the QPOs. The strongest signal was found at
a frequency of 65 d−1, corresponding to a period of 0.015
d. No comparable QPOs were observed on preceding and
following nights. This transient appearance of the QPO sig-
4T. Kato et al.
101112 13 141516
Figure 4. Period analysis of NSV 10934 (plateau stage: 2003
January 5–13). The strongest signal at a frequency of 13.373(1)
d−1corresponds to the best superhump period of 0.07478(1) d.
-.4-.20 .2 .4.6.811.21.4
NSV 10934 (P=0.07478 d)
Figure 5. Mean superhump profile of NSV 10934.
nal is very reminiscent of “super-QPOs” in some SU UMa-
type dwarf novae, which only appear during the early stage
of the superhump evolution (Kato et al. 1992; Kato 2002).
Warner & Woudt (2002) suggested that these super-QPOs
would be a result of interaction between the weak mag-
netism of the white dwarf and some kind of wave in the
inner accretion disk. If this interpretation could apply to
NSV 10934, the possible intermediate polar-type interpreta-
tion of this object (Kato et al. 2002a) would be consistent
with the present finding.
3.6NSV 10934 as an SU UMa-Type Dwarf Nova
Although the supercycle length of NSV 10934 has not yet
been established, the intervals between normal outbursts
(40–60 d) are typical values for an SU UMa-type dwarf nova
in the intermediate activity class (Vogt 1993). The appar-
ent lack of terminal brightening during the superoutburst
plateau also fits the general properties of SU UMa-type
dwarf nova with this superhump period (Kato et al. 2003b).
However, the presence of terminal rapid declines during nor-
Table 3. Times of superhump maxima of NSV 10934.
O − Cb
aCycle count since BJD 2452643.9874.
bO − C calculated against equation 1.
Cycle count (E)
Figure 6. O − C diagram of superhump maxima of NSV 10934.
The error bars correspond to the upper limits of the errors except
for E = 83, which has a larger error 0.002 d. The parabolic fit for
13≤ E ≤110 is shown with a dotted line.
mal outbursts (Kato et al. 2002a) is rather unusual, because
the contribution from quiescent luminosity usually works
to slow down the decline rate near the terminal stage of
such outbursts (e.g. van Paradijs et al. 1994). It may be that
the inner accretion disk is truncated by the weak magnetic
field of the white dwarf to produce such rapid terminal de-
clines (e.g. Ishioka et al. 2002), while the field strength is not
strong enough to moderate dwarf nova-type outburst prop-
erties (e.g. Angelini & Verbunt 1989). As stated in section
3.5, the supposed presence of a weak magnetic field would
naturally explain the appearance of super-QPOs at the same
time. A search for a coherent signal in X-ray, ultraviolet, and
optical wavelengths is encouraged. The only other SU UMa-
type dwarf nova which was proposed to be an IP is VZ Pyx
(Remillard et al. 1994; Alvarez et al. 1995; Kato & Nogami
Southern SU UMa-Type Dwarf Novae5
Raw light curve
43.96 43.98 44 44.02 44.04 44.06 44.0844.144.1244.14
BJD - 2452600
Figure 7. Enlarged light curve NSV 10934 on 2003 January 4.
(Upper:) Raw data (the dotted line represents the best-fit super-
hump signal). (Lower:) Residual light curve subtracted for the
best-fit mean superhump light curve. Quasi-periodic oscillations
with periods ∼0.015 d are present.
0 100 200300 400500
Figure 8. Power spectrum of the QPOs on 2003 January 4. The
strongest signal is at a frequency of 65 d−1, corresponding to a
period of 0.015 d.
1997; Kiyota 1999). Although this object was originally pro-
posed to be an IP, the modern observational evidence is
rather against this classification (cf. Kato & Nogami 1997;
Warner et al. 2003).4
4The well-known SU UMa-type dwarf nova SW UMa is also
suspected to be an IP (Shafter et al. 1986; Robinson et al. 1987;
Szkody et al. 1988; Rosen et al. 1994), although the outburst pa-
rameters of SW UMa are rather unusual among SU UMa-type
dwarf novae (Shafter et al. 1987; Howell et al. 1995a,b). It is pos-
sible that this possible IP nature may be responsible for the most
striking appearance of super-QPOs (Kato et al. 1992).
Table 4. Journal of the 2002 CCD photometry of MM Sco.
MM Sco was discovered as a dwarf nova on Harvard plates
(cf. Glasby 1970; Walker & Olmsted 1958). Petit (1956) sug-
gested, from the apparently long outburst interval (≥500
d), that MM Sco may a similar object to UV Per, which
is currently known as an SU UMa-type dwarf nova with
long supercycles (Udalski & Pych 1992; Kato 1990; see also
Kato et al. 2001b for a discussion on the relation to WZ
Sge-type dwarf novae). This cycle length was adopted in
Kukarkin et al. (1969). However, F. M. Bateson suggested
that the mean outburst cycle length (∼28 d) is much
shorter than what has been believed, and observed max-
ima were fainter than the originally reported magnitude
(see the description in Vogt (1983); this period was adopted
in Kholopov et al. (1985); for a more recent reference, see
Bateson et al. 1997). The reported outburst characteristics
of MM Sco was thus rather controversial.5
4.22002 September Outburst
MM Sco has been monitored by the VSNET members since
the outburst in 1997 (cf. vsnet-alert 9466) because of its ap-
parently low frequency of outbursts, which is a rather com-
monly met signature of SU UMa-type dwarf novae.
The 2002 September outburst was detected by Rod
Stubbings on 2002 September 5.428 UT at a visual mag-
nitude of 14.0 (vsnet-outburst 44857). The object further
brightened to a magnitude of 13.4 next night, indicating
that the present outburst may be a long, bright outburst.
We carried out time-resolved CCD photometry upon this
information. The log of observation is summarized in Table
Figure 9 shows the nightly light curves of MM Sco. Su-
perhumps were clearly visible on all nights; this confirms
the SU UMa-type nature of MM Sco. Figure 10 shows the
result of a period analysis using PDM applied to the entire
data set after removing the nightly linear decline trends.
The strongest signal at a frequency of 16.298(11) d−1corre-
sponds to the best superhump period of 0.06136(4) d.
Figure 11 shows the mean superhump profile phase-
averaged with the period of 0.06136 d. The rapid rise and
slower decline are characteristic of SU UMa-type super-
humps. We did not attempt to determine a period derivative
5In a most recent publication, Mason & Howell (2003) listed
MM Sco as a candidate SU UMa-type dwarf nova, though they
reported that no superhumps have yet been observed.
6T. Kato et al.
.7.75 .8.85 .9.95
Fraction of BJD
Sept. 10 (+0.5 d)
Sept. 11 (+0.5 d)
Figure 9. Nightly light curves of MM Sco. Superhumps were
clearly visible on all nights.
12131415 1617 18 1920
P = 0.06136 d
Figure 10. Period analysis of MM Sco. The strongest signal at a
frequency of 16.298(11) d−1corresponds to the best superhump
period of 0.06136(4) d.
(e.g. Kato et al. 2003c,a) because of the short baseline of the
observation. The less sharp appearance of the superhump
maximum, compared to other fully grown superhumps of SU
UMa-type dwarf novae (e.g. Harvey & Patterson (1995)),
was probably because the observation started ∼5 d after
the start of the superoutburst. The superhumps may have
entered its decaying phase at the time of our observation.
Further detailed observations of the full evolutionary course
MM Sco (P = 0.06136 d)
Figure 11. Mean superhump profile of MM Sco.
of the superhumps, as well as determination of the orbital
period, are strongly encouraged to fully understand the be-
havior of superhumps in this system.
4.3Astrometry and Quiescent Counterpart
We measured the position of the outbursting object with
respect to the UCAC1 reference frame and yielded R. A. =
17h30m45s.254, Decl. = −42◦11′42′′.69 (J2000.0) (Fig.
12). Vogt & Bateson (1982) exactly points the object at
this position. On the other hand, the DSS 2 images of this
region show an only faint object, implying that MM Sco
was accidentally caught in a slightly brightened state in
Vogt & Bateson (1982). The DSS 2 star apparently moved
in the west-southwest direction between two plates (I-band,
epch 1980.478 and R-band, epoch 1997.249). This star is
likely the object marked on Downes’ online atlas.8There is
a possibility that MM Sco in true quiescence is fainter than
the limit of the DSS 2 images and that the apparently mov-
ing object is an unrelated star. If it is the case, the outburst
amplitude could exceed 6 mag. Definite quiescent identifica-
tion and precise amplitude measurement should await deep
direct imaging with higher spatial resolution.
4.4MM Sco as an SU UMa-Type Dwarf Nova
Figure 13 shows the long-term visual light curve of MM
Sco. Table 5 lists the observed outbursts. Six well-defined
superoutbursts (JD 2450712, 2451010, 2451385, 2451729,
2452025, and 2452523) with durations longer than 8 d are
unambiguously identified. The supercycle lengths are thus
in the range of 298–497 d. There does not seem to be a fixed
supercycle length as recorded in KK Tel (Kato et al. 2003c).
In spite of the relatively bright superoutburst magni-
tudes (usually 13.3–13.8), very few normal outbursts have
been detected, which could have easily reached detectable
magnitudes. Although the small number of observations
makes it difficult to draw a firm conclusion on the type of
Southern SU UMa-Type Dwarf Novae7
Figure 12. Identification of MM Sco. Up is north, left is east, 5
minutes square. (Upper) In quiescence, reproduced from the DSS
2 red image. (Lower) In outburst, taken on 2002 Sept. 10.77 UT
by B. Monard. V = MM Sco.
outburst, the outburst on JD 2450596 was the only candi-
date normal outburst since 1997. Such a low number ra-
tio normal outbursts over superoutbursts is exceptional (cf.
Warner 1995; Nogami et al. 1997). In combination with the
relatively short superhump period (0.06146 d), the initially
proposed analogy (Petit 1956) with UV Per (PSH = 0.06641
d) looks likes to be more strengthened. The shortest inter-
vals (28 d) of outbursts may have corresponded to a pre-
cursor outburst or a rebrightening phenomenon, both of
which are relatively commonly observed in SU UMa-type
dwarf novae with short superhump periods and less fre-
quent normal outbursts (Lemm et al. 1993; Patterson et al.
Table 5. List of Outbursts of MM Sco.
1993; Howell et al. 1995b; Kato 1997; Nogami et al. 1998;
Baba et al. 2000; Kato et al. 2001a; Ishioka et al. 2001).
This finding makes a contrast to what was originally
suggested by F. M. Bateson (Vogt 1983). It may be either
possible that the finding by F. M. Bateson did not correctly
describe the outburst behavior of this object due to the lack
of appropriate information at that time, or that the out-
burst characteristics exhibited a long-term variation. Since
some SU UMa-type dwarf novae are known to show dra-
matic long-term variation, particularly in the number of nor-
mal outbursts (e.g. V503 Cyg: Kato et al. (2002b); DM Lyr:
Nogami et al. (2003a); MN Dra = Var73 Dra: Nogami et al.
(2003b)), this possibility in MM Sco needs to be carefully
checked by future observations.
AB Nor was discovered by Swope & Caldwell (1930) during
the photographic survey of the southern Milky Way. Only
little had been studied until very recent years. Petit (1960)
simply provided a “long?” recurrence period in the table of
dwarf nova candidates. Vogt & Bateson (1982) proposed a
quiescent counterpart based on its blue color, but the direct
attempt to identify the object by recording an outburst was
not successful. The first outburst reported to VSNET was in
1997 (section 5.4); the object has been regularly monitored
An outburst in 2000 April, detected by the Rod Stub-
bings, was most unusual. Five days after the initial bright-
ness peak decayed, the object sudden underwent a rebright-
ening (vsnet-alert 45749). Since such an early-stage rebright-
ening is usually associated with a superoutburst triggered
by an immediately preceding precursor (Marino & Walker
1979; Warner 1985; Kato 1997; see also the PU CMa case
in Kato et al. (2003c)) in SU UMa-type dwarf novae, AB
Nor was thereby strongly suspected to be an SU UMa-type
dwarf nova. Upon this alert in VSNET, W. S. G. Walker
reported on the possible presence of a 0.4 mag superhump
(vsnet-alert 458910). Walker reported an approximate su-
perhump period of 0.078–0.079 d, based on the second-night
observation (vsnet-alert 459711). Although the suggested SU
UMa-type nature of AB Nor was almost confirmed by this
8 T. Kato et al.
JD - 2450000
Figure 13. Long-term visual light curve of MM Sco. Large and small dot represent positive detections and upper limit observations,
respectively. Outbursts other than on JD 2450596 are superoutbursts.
Table 6. Journal of the 2002 CCD photometry of AB Nor.
observation, the lack of long-baseline, time-resolved observa-
tion at this moment required us another opportunity for in-
dependent confirmation of superhumps, as well as precisely
determining their period and evolution.
5.22002 August–September Outburst
The next chance arrived two years later. The 2002 August–
September Outburst was detected by Rod Stubbings on Au-
gust 31.437 UT at a visual magnitude of 14.0 (vsnet-alert
745712). We conducted a CCD time-series photometry cam-
paign during this outburst.
The log of observation is summarized in Table 6.
The initial observation was performed only one day later
than the initial detection. The observation during this night
clearly caught the evolutionary stage of the superhumps
Figure 15 shows the nightly light curves of AB Nor.
Unavoidable gaps are present between observations, mainly
because of the wide gap in longitudinal distribution of the
two observers. The superhumps had grown on September
2. The September 12 observation was performed just before
the object started fading rapidly from the superoutburst
BJD - 2452500
AB Nor (2002 Septermber 1)
Figure 14. Light variation of AB Nor on 2003 September 1 (1
d after the detection of the outburst). The amplitudes of the
superhumps were rapidly growing.
As is naturally expected from the early epoch obser-
vation coincident with the rapid evolutionary stage of the
superhumps, and partly owing to the gap in observation, we
have not been able to uniquely determine the superhump
period common to the entire observing period. We thereby
divided the data into three segments (1) early evolutionary
stage: September 1, (2) fully developed stage: September 2–
4, and (3) late stage: September 11–12, and first determined
the superhump periods within respective segments. A pe-
riod analysis of the early evolutionary stage yielded a signal
around a frequency of 12.1(1) d−1, corresponding to a period
of 0.0829(9) d. The significance of this periodicity is 93%.
This periodicity did not appear in the later segments, and it
likely reflected the stage of a rapid change in the superhump
period. During the latter two segments, a common frequency
around 11.87(3) d−1, corresponding to a period of 0.0842(3)
d, was present. The selection of the alias was based on the
proximity to the period derived from the segment 1 and the
common presence in segment 2 (significance >99.9%) and
Southern SU UMa-Type Dwarf Novae9
Fraction of BJD
Figure 15. Nightly light curves of AB Nor. Unavoidable gaps are
present between observations, mainly because of the wide gap in
longitudinal distribution of the two observers.
11.211.4 11.6 11.81212.212.4
AB Nor (2002 September 2-12)
Figure 16. Period analysis of AB Nor from the September 2–12
segment 3 (significance 87%). From the combination of seg-
ment 2 and 3, we obtained a period of 0.08438(2) d (Figure
16). We consider that this period is the representative su-
perhump period of AB Nor, although a better coverage of
a future superoutburst is desired to decisively identify the
superhump period and its evolution.
-.4-.188.8.131.52 .81 1.21.4
AB Nor (P=0.08438 d)
Figure 17. Mean superhump profile of AB Nor.
Table 7. List of Outbursts of AB Nor.
MaxDuration (d) Type
5.3Astrometry and Quiescent Counterpart
We measured the position of AB Nor with the outburst im-
age taken by P. Nelson on 2002 Sept. 1.438 UT. The derived
position with respect to UCAC1 reference stars is R. A. =
15h49m15s.475, Decl. = −43◦04′48′′.49 (J2000.0), with
a fitting error of about 0′′.2 for each coordinate (Fig. 18).
This result is almost identical with the value derived by A.
Henden using 2000 April outburst images taken by Walker
(B. Sumner, vsnet-chat 280013). The quiescent counterpart
is clearly seen in every DSS images at mag about 20. No
proper motion of this object was detected by the examina-
tion of available archived images.
5.4AB Nor as an SU UMa-Type Dwarf Nova
Figure 19 shows the long-term visual light curve of AB Nor.
Table 7 lists the observed outbursts. Two well-defined super-
outbursts (JD 2451636 and 2452517) with durations longer
than 12 d are unambiguously identified. The outburst on JD
2450746 is also likely a superoutburst based on its bright-
ness. The outburst on JD 2451320 is probably a normal
outburst based on its faintness. Although there are observa-
tional gaps, there seems to be little chance of many missed
outbursts. The supercycle of AB Nor is thereby estimated
to be ∼880/N d, where N is either 1 or 2. We suggest that
AB Nor belongs to SU UMa-type dwarf novae with long
The derived superhump period of 0.08438 d is the one
10T. Kato et al.
JD - 2450000
Figure 19. Long-term visual light curve of AB Nor. Large and small dot represent positive detections and upper limit observations,
of the longest periods among SU UMa-type dwarf novae be-
low the period gap. The other long-period systems include
TY PsA (P=0.08765 d: Barwig et al. 1982; Warner et al.
1989), BF Ara (P=0.08797 d: Kato et al. 2003a) and YZ
Cnc (P=0.09204 d: Patterson 1979; van Paradijs et al. 1994;
Kato 2001a), which show frequent outbursts and super-
outbursts. Among SU UMa-type dwarf novae with simi-
lar superhump periods, EF Peg (P=0.08705 d: Kato 2002),
V725 Aql (P=0.09909 d: Uemura et al. 2001) and DV UMa
(P=0.08869 d: Nogami et al. 2001) have a low frequency of
outbursts comparable to that of AB Nor. Both EF Peg and
V725 Aql are considered to be unusual in its outburst fre-
quency and behavior (Uemura et al. 2001; Kato 2002), and
may have low mass-transfer rate comparable to WZ Sge-type
dwarf novae (Kato et al. 2001b). Being easily observable at
minimum (compared to EF Peg and V725 Aql), further de-
tailed observation of AB Nor in quiescence will be helpful
identifying the nature of these long-period SU UMa-type
dwarf novae with supposed low mass-transfer rates.
6 CAL 86
J054613.6−683523 is a cataclysmic variable in the di-
rection of the Large Megellanic Cloud (LMC). This
star was originally selected as an Einstein X-ray source.
Schmidtke et al. (2002) reported the detection of its short
(0.066 d) orbital period and at least five outbursts from
the MACHO observations. Some of the outbursts reached
V = 14 (amplitude 5 mag). This orbital period, together
with the presence of large-amplitude outbursts, makes CAL
86 a good SU UMa-type candidate. Upon this information
we undertook a monitoring campaign (vsnet-campaign-dn
256114) since 2002 December. Only one outburst was
observed (in 2003 February) up to 2003 August.
86= 1RXP J054610−6835.1=1RXS
Table 8. Journal of the 2003 CCD photometry of CAL 86.
2003 Date Start–Enda
6.22003 February Outburst
The 2003 February outburst was detected at a visual mag-
nitude of 13.2 on February 23.454 UT by Rod Stubbings
(vsnet-alert 764515). The outburst very quickly faded after
the outburst detection (Figure 20). The mean fading rate of
the initial 2.5 d was 1.1 mag d−1, which is a typical value for
a normal outburst of an SU UMa-type dwarf nova (Bailey
1975; Kato et al. 2002c).
The log of observation is summarized in Table 8.
Figure 21 shows the light curve drawn from the time-
resolved CCD observations. The object was rapidly and
smoothly fading during this observing period. A period anal-
ysis of the data did not reveal any superhump-type variation
with an amplitude larger than 0.05 mag. Figure 22 shows an
“orbital” light curve phase-averaged at the reported orbital
period of 0.066 d, after removing the trend of steady decline
from Figure 21. Only a marginal (0.02 mag) modulation was
detected, which is not inconsistent with the general lack of
orbital signatures in outbursting non-eclipsing dwarf novae
(see also Kato 2001b).
6.3Astrometry and Quiescent Counterpart
Since CAL 86 is located in the LMC field with a huge num-
ber of faint stars, we tried to make independent astrometry
and identification using the outburst CCD images. The po-
sition with respect to UCAC1 frame was derived to be R. A.
= 05h46m14s.973, Decl. = −68◦35′23′′.76 (J2000.0), with
Southern SU UMa-Type Dwarf Novae11
Figure 18. Identification of AB Nor. Up is north, left is east, 5
minutes square. (Upper) In quiescence, reproduced from the DSS
2 red image. (Lower) In outburst, taken on 2002 Sept. 1.438 UT
by P. Nelson. V = AB Nor.
a fitting error less than 0′′.1 for each coordinate (Fig. 23).
This star is identical to the one labeled as “Star No. 2” in the
chart of Schmidtke et al. (1994), and to a USNO-B1.0 star
having position end figures of 14s.98, 24′′.1 (r2 mag 18.77).
The examination of archived images revealed no detectable
proper motion of this object, which was accidentally caught
in outburst on an image taken on 1987 Jan. 24 as noted in
Downes et al.’s online catalog. The USNO-B1.0 entry also
shows no proper motion.
JD - 2452000
Figure 20. The 2003 February outburst of CAL 86. The filled
squares and downward arrows represent positive detections and
upper limit observations, respectively. The open circles represent
Monard’s snapshot unfiltered CCD photometry.
184.108.40.206 5.86 6.2
BJD - 2452690
Figure 21. The 2003 February outburst of CAL 86 drawn from
the time-resolved CCD observations. The magnitudes are given
relative to GSC 9163.607 (approximate Rc magnitude 12.4). A
rapid, smooth decline is apparent.
We photometrically observed four southern dwarf novae in
outburst (NSV 10934, MM Sco, AB Nor and CAL 86). We
succeeded in measuring the superhump periods of the first
three systems, and clarified the long-term outburst charac-
teristics from long-term visual observations.
(1) NSV 10934 was confirmed to be an SU UMa-type
dwarf nova with a mean superhump period of 0.07478(1) d.
The star also showed transient appearance of quasi-periodic
oscillations (QPOs) during the final growing stage of the
superhumps. Combined with the recent theoretical interpre-
tation and with the rather unusual rapid terminal fading of
normal outbursts, NSV 10934 may be a candidate interme-
diate polar showing SU UMa-type properties.
(2) We determined the mean mean superhump periods
of the newly identified SU UMa-type dwarf nova MM Sco
to be 0.06136(4) d. The combination of a short superhump
12 T. Kato et al.
-.4-.20 .2.4 .6.811.21.4
Figure 22. “Orbital” light curve phase-averaged at the reported
orbital period of 0.066 d. Only a marginal (0.02 mag) modulation
period and a low frequency of outbursts suggests that MM
Sco belongs to a class of infrequently outbursting SU UMa-
type dwarf novae resembling UV Per. The true quiescence
of MM Sco may be fainter than has been believed.
(3) We determined the mean superhump period of AB
Nor, whose SU UMa-type nature is established by this study,
to be 0.08438(2) d. We suggest that AB Nor belongs to a
rather rare class of long-period SU UMa-type dwarf novae
with low mass-transfer rates.
(4) We also observed an outburst of the suspected SU
UMa-type dwarf nova CAL 86. We identified this outburst
as a normal outburst and determined the mean decline rate
of 1.1 mag d−1.
This work is partly supported by a grant-in-aid [13640239,
15037205 (TK), 14740131 (HY)] from the Japanese Ministry
of Education, Culture, Sports, Science and Technology. The
CCD operation of the Bronberg Observatory is partly spon-
sored by the Center for Backyard Astrophysics. The CCD
operation by Peter Nelson is on loan from the AAVSO,
funded by the Curry Foundation. This research has made
use of the Digitized Sky Survey producted by STScI, the
ESO Skycat tool, the VizieR catalogue access tool.
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