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Acta Polytechnica CTU Proceedings 2(1): 238–241, 2015

238

doi: 10.14311/APP.2015.02.0238

Spectroscopic Monitoring Observations of Nova V1724 Aql in 2012

T. Kajikawa1, M. Nagashima1, H. Kawakita1, A. Arai1,2, Y. Ikeda1,3, M. Isogai1,4, M. Fujii5,
K. Ayani6

1Kyoto Sangyo Univearsity / Koyama Astronomical Observatory
2University of Hyogo / Nishi-Harima Astronomical Observatory
3Photocoding
4National Astronomical Observatory of Japan
5Fujii-Kurosaki Observatory
6Bisei Astronomical Observatory

Corresponding author: kawakthd@cc.kyoto-su.ac.jp

Abstract

Spectroscopic and photometric monitoring observations of nova Apl 2012 (V1724 Apl) were conducted at Koyama Astro-

nomical Observatory, Fujii-Kurosaki Observatory and Bisei Astronomical Observatory. The nova was initially considered

as an outbursting pre-main-sequence young stellar object. Our monitoring observations have revealed the nova to be a Fe

II type classical nova. The temporal evolution of spectra and light curves of the nova were similar to those of a slow nova

(e.g., V1280 Sco and V5558 Sgr). We observed no evidence of molecule formation in V1724 Aql in contrast with V2676

Oph in which dust formation occurred after the molecular formation in the nova outflow.

Keywords: cataclysmic variables - classical novae - optical - spectroscopy - photometry - individual: V1724 Aql.

1 Introduction

Nova Aql 2012 (later named as V1724 Aql) was
discovered on 2012 October 20.4 UT (Nishiyama &
Kabashima 2012). The brightness of the nova during
the discovery was reported as 12.6 mag. Just after the
discovery, we conducted our spectroscopic monitoring
observations at the Koyama Astronomical Observatory
(KAO), Fujii-Kurosaki Observatory (FKO) and Bisei
Astronomical Observatory (BAO) in Japan.

The first optical spectrum taken on October 21.4
UT was reported by Fujii (2012) at FKO. The object
showed a sharp Hα emission ( probably with a P Cygni
profile) on a very red continuum. This object was
considered a classical nova affected by a severe inter-
stellar extinction (strong absorption of the Na D line
was observed). Munari (2012) also reported that the
spectrum of this object on October 21.8 UT showed
a weak and sharp Hα emission on a very red contin-
uum, with strong Na I and Ba II absorption lines. This
spectrum was basically consistent with that reported
by Fujii (2012). However, it was considered that the
spectrum is more similar to that of an outbursting pre-
main-sequence young stellar object than that of a nova
before maximum brightness. On 2012 October 23.5 UT,
Ayani (2012) also reported the optical spectrum of this

object taken at BAO, with Fe II emission and O I emis-
sion with a P Cygni profile. This object was finally
identified as a Fe II type classical nova according to the
classification by Williams (1992).

Here we report the spectroscopic and photometric
observations of V1724 Aql performed in a collaboration
among three observatories (KAO, FKO and BAO) in
Japan.

2 Spectroscopic and Photometric
Observations

The observations conducted in our collaboration were
follows. Spectroscopic observations were performed at
three sites:

1. A 0.4-m telescope with a low-dispersion spectro-
graph (λ = 4500 — 9000 Å with R ∼ 500) at
Fujii-Kurosaki Observatory,

2. A 1.01-m telescope with a low- and moderate-
dispersion spectrograph (λ = 3600 — 9000 Å
with R ∼ 1500 for a low-resolution mode) at Bisei
Astronomical Observatory, and

3. A 1.3-m Araki telescope with a low-dispersion

238

http://dx.doi.org/10.14311/APP.2015.02.0238


Spectroscopic Monitoring Observations of Nova V1724 Aql in 2012

spectrograph LOSA/F2 (λ = 3800 — 8000 Å with
R ∼ 600; Shinnaka et al. 2013) at Koyama As-
tronomical Observatory.

In addition to the spectroscopic observations, pho-
tometric observations were performed at KAO by the
imaging camera ADLER (Araki DuaL-band imagER;
Nakagawa et al. 2013) with intermediate and broad-
band filters (y-, i′-, and z′-band filters).

Figure 1 shows the spectral evolution of V1724 Aql.
Figure 2 shows the light curves (with the multi-band
light curves taken from AAVSO database). We also
show the close-up views for Hα and O I emission lines
to make clear the evolution of their line shapes. Clearly,
the line widths increased for later epochs in the case of
Hα while the temporal change in the P Cygni profile
of O I emission indicated faster expansion velocities at
later dates.

 0

 5

 10

 15

 20

 25

 4000  5000  6000  7000  8000  9000
Wavelength [A]

+35d:K
+26d:K

+25d:F
+24d:F
+22d:F
+22d:K
+17d:K
+16d:F
+16d:K
+10d:K
+8d:K
+5d:F
+4d:K
+4d:B

+4d:F
+3d:F
+2d:F
+2d:B
+1d:K

+0d:F

H
β

F
e

 I
I 

(7
4

)
F

e
 I

I 
(7

4
)

F
e

 I
I 

(7
4

)

O
I 

(7
7

7
4

)

N
a

 I
(5

8
8

9
)

M
g

II
+

O
I

O
I(

8
4

4
6

)

F
e

 I
I 

(4
2

)

H
α[O

I]
 (

6
3

0
0

)

C
a

 I
I

K: KAO
F: FKO
B: BAO

lo
g

  
 (

F
lu

x)
 +

 c
o

n
st

.
1
0

Figure 1: Low-dispersion spectra of V1724 Aql obtained at three sites from 2012 Oct 21 to Nov 25 UT. All
spectra are shifted by different offsets for readability. Emission lines were on the highly red continuum. The line
width of Hα emission became broader and stronger compared with the nearby continuum, and the Ca II triplet
emission lines bacame stronger later. Note that the bluish continuum might overlap with the spectra of the nova
in the shorter wavelength region (λ < 4500 Å ), probably due to a forground (or background) star.

239



T. Kajikawa et al.

3 Discussion and Conclusion

From the viewpoint of the spectral evolution, the spec-
tra of V1724 Aql slowly changed during the period of
our observations. Emission lines (Hα, Hβ, Fe II, Na
I, O I and Ca II) were on the reddened continuum.
We estimated E(B − V ) based on the measurements
of Balmer decrement by the method described in Hel-
ton et al. (2010), E(B − V )∼3.1, which indicated se-
vere interstellar extinction for the nova. This value is
slightly higher than that reported by Rudy et al. (2012)
but both values indicate severe interstellar reddening.
Note that the spectra of the nova showed enhancement
in a shorter wavelength region (λ < 4500Å ) that ap-
peared similar to a bluish continuum component but
was noisier. The nova may be overlapped with another
foreground (or background) stellar object that had a
high temperature. Although one may consider that we
should estimate E(B − V ) based on the (B − V ) of the
nova around the optical brightness maximum, we had to
be careful of the contamination with the B-band bright-
ness of the nova.

 8
 9

 10
 11
 12
 13
 14
 15
 16
 17
 18
 19

 0  5  10  15  20  25  30  35  40  45

M
a

g
n

itu
d

e
s

Days from 2012 Oct 20 UT

V
R
I
B
y
i’
z’

Figure 2: Optical light curves of V1724 Aql obtained
at KAO with the multi-band light curves of the nova
taken from AAVSO database. The vertical tick-marks
at the top of panel indicate the dates of our spectro-
scopic observations.

The line width of Hα emission had clearly increased
and became stronger compared with the nearby contin-
uum, and O I and Ca II triplet emission lines grew at
later dates. The ejection velocity was ∼400 km/s based
on the P Cygni profile of Hα at t=1d after the outburst
(Figure 3). It then increased; 630 km/s (t=2d), 640 and
750 km/s (t=5d), and 1150 km/s (t=9d) based on the
P Cygni profiles of O I as shown in Figure 4. Finally,
the ejection velocity reached ∼2000 km/s based on the
FWZI of Hα (Figure 3) after the brightness maximum
at t=17d. The ejection velocities were slower during
the earlier phase, and faster during later phase. Such
temporal changes in ejection velocity in V1724 Aql was

similar to those of slow novae, e.g., V1280 Sco (Naito et
al. 2012) and V5558 Sgr (Tanaka et al. 2011). V1724
Aql was similar to a slow nova from the viewpoint of
spectral evolution.

 0

 0.2

 0.4

 0.6

 0.8

 1

-4000 -2000  0  2000  4000

R
e
la

tiv
e
 f
lu

x

Velocity [km/s]

+10d:K
+8d:K
+5d:F
+4d:K
+3d:F
+2d:F
+1d:K

0d:F

 0

 0.2

 0.4

 0.6

 0.8

 1.0

-4000 -2000  0  2000  4000

R
e
la

tiv
e
 f
lu

x

Velocity [km/s]

+35d:K
+26d:K
+25d:F
+24d:F
+22d:K
+17d:K
+16d:K
+10d:K

Figure 3: Temporal change of Hα emission line before
and after the brightness maximum at t=17d after the
outburst (upper and lower panels, respectively). The
line widths became broader at later dates. The black
arrow in the lower panel shows the change in blue-shift
component that could have been caused by the change
in the velocity structure of the ejected materials.

Based on the light curves shown in Figure 2, nova
V1724 Aql showed very slow evolution in brightness af-
ter the outburst until its brightness maximum in the V -
band (t=17d, V =13.6±0.2 mag). The visual brightness
was almost unchanged (but oscillating with small ampli-
tude) until the brightness maximum since the outburst
(14.4±0.4 mag in V -band). The evolution in bright-
ness was slow for V1724 Aql in earlier phase. However,
after the brightness maximum (t=17d), its brightness
in V -band become fainter with a decline rate of +0.14
mag/day (t2 was 14.3 days). Although this decline rate
was indicative of a fast nova rather than a slow nova
(Payne-Gaposchkin 1957), the light curves after the
brightness maximum might be affected by dust forma-
tion as suggested by the molecular formation observed
by Rudy et al. (2012).

240



Spectroscopic Monitoring Observations of Nova V1724 Aql in 2012

-1

-0.5

 0

 0.5

 1

-4000 -3000 -2000 -1000  0  1000  2000  3000  4000

R
e

la
tiv

e
 f

lu
x

Velocity [km/s]

+10d:K
+8d:K
+4d:K
+1d:K

Figure 4: Temporal change of the P Cygni profile for
O I (7774 Å at rest) emission line before the brightness
maximum. The measured ejection velocites based on
the P Cygni profiles were 630 km/s (at t=2d), 640 and
750 km/s (at t=5d), and 1150 km/s (at t=9d).

Rudy et al. (2012) reported the detection of CO
molecular emission in the near-infrared spectra taken
on 2012 Oct 27 and 28 UT (before the brightness max-
imum), indicating that molecule formation was ongo-
ing, with dust formation likely to follow. Nova V1724
Aql was probably a slow nova that showed CO emis-
sion during the pre-maximum halt (at least, before the
maximum). However, there were no hints for C2 and
CN absorption bands in optical spectra of the nova (c.f.
V2676 Oph, Nagashima et al. 2014). Those molec-
ular absorption bands were expected to appear dur-
ing several days (as in the cases of V2676 Oph and
DQ Her). Our spectroscopic observations were per-
formed frequently enough to detect them if a consid-
erable amount of molecules formed in the outflow of
the nova. We propose the hypothesis that the ejecta
of V1724 Aql was oxygen-rich and the atomic carbon
might not be over-abundant with respect to the atomic
oxygen (C < O) in the ejecta. As demonstrated by the
model calculations (Pontefract & Rawlings 2004), for-
mation of C2 (and also CN) is more difficult than CO
in an oxygen-rich atmosphere. V1724 Aql might have
oxygen-rich ejecta. The spectroscopic observations of
V1724 Aql in the nebular phase (if reported in the fu-
ture) will be helpful to test this hypothesis.

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	Introduction
	Spectroscopic and Photometric Observations
	Discussion and Conclusion