A spectroscopic study of Nova Oph 1994

1997 Chin. Astron. Astrophys. Vol. 21, No. 3, pp. 313-318. of Acra Astrophys. Sin. Vol. 17, No. 2, pp. 175-181. 1997 0 1997 Elsevier Science B.V. All rights reserved Printed in Great Bmain 0275-1062/97 $32.00 + 0 00

A translation

Pergamon

PII: SO2751062(97)00041-6

A spectroscopic

study of Nova Oph 1994 t JIANG

HU Jing-yao Beijing Joint

Astronomical

Laboratory

Abstract attached

We observed to the 2.16m

Observatory. it belongs rather

Observatory,

Chinese

for Optical Astronomy,

The

Nova Oph reflector

strong

Academy

Chinese

of Sciences,

Academy

Beijing

of Sciences,

Fe11 emission

Station,

Beijing

The spectral

spectrograph indicate

of the emission

characteristics

100080

Astronomical

lines in the early spectra structure

100080

Beijing

1994 with a Zeiss universal

at the Xinglong

to Fe11 novae, but the multi-peaked

rare for this subtype.

Xiao-jun

that

lines is

and their evolution

are

discussed. Key

words:

nova-Nova

Oph 1994-spectra

1. INTRODUCTION Nova Oph

1994 (R.A.=17h35m44.62”,

graphically magnitude

by Japanese

amateur

astronomer

34.0”

Akihiko

(2000.0))

to be available

Nova explosion the general

and the gas overflowing

involved.

attention.

There

Chandrasekhar

different

binaries

and it is only through For this reason,

is a certain limit,

Although

1.4 M,,

at present

state white dwarf accretes

the Roche lobe impinges

because

vary one from another cal process

phenomenon.

that a degenerate

hence the explosion,

and spectroscopic

photo-

He estimated

a

observational

2 days later.

is a transient

scenario

was discovered

Tago on 1994-06-01.

at the time of MpB = 7.0. A series of photometric

data began

indicators,

Dee=-19’19’

on its surface,

have different observations

observational

link between

causing

parameters,

interest

on

from its companion nuclear reactions

and

the nova explosions

that we can understand

the physi-

study of novae has been given increasing

explosions

of novae and Type-I

is the dividing line), and these objects

hence our continued

there is consensus

matter

even after some preliminary

supernovae

can be used understanding

a9

(the

distancrb has been

gained. In this paper in time.

we discuss

A quantitative

the spectral

analysis

based

features

of Nova Oph 1994 and their cvolutiou

on the observed

spectra

will be given in a separate

paper.

f Supported Received

by National 190&O!&30;

Natwd revised

Science version

Foundation lW6-IO-23

313

and

Nationa\

Scaling-the-Heigllts

i?ogrrtm

314

HU Jing-yao & JIANG Xiao-jun

2. OBSERVATIONS We carried out systematic observations of Nova Oph 1994 at Beijing Observatory Xinglong Observing Station in the period 1994-06-10 to 1995-05-29. The instrument used is the Zeiss Universal spectrograph attached to the Cassegrain focus of the 2.16 m telescope. The detector used in 1994 was a TEK512 CCD, pixel size 27,umx27pm, the spectrograph used a lens camera

and the spectral

range was 4400-9300A.

In 1995 we changed

to a TEK 1024CCD,

Image: June 17

Image: June 10

lOOF”“““““““““““’ 80 : I

b----AJb; , , , , , , , ( , , , , , , , , ( , , , , , ,, L 8000 9000 5000 6000 7000

0, 5000

6000

7000

8000

9000

Image: July 2

Image: July 1

100 80

60 40 20 0 5000

6000

7000

5000

9000

8000

6000

7000

8000

9000

Image: Aug. 7

Image: July 16 100

100

80

80

60

60

40

40

20

20 0

0 5ooo

6000

7000

8000

5000

9000

6000

7000

8000

9000

7000

8000

9000

Image: Aug. 24

Image: Aug. 18 100

100 80

a0

60

60

40

40

20

20 0

0 5000

6000

7000

8000

5000

9000

Wavelength (A)

Fig. 1

Wavelength (A)

Low-dispersion and

1994

6000

August

spectra taken between 1994 June 24 (resolution

5.3A/pixel)

10

Nova

pixel size 24 +x extended

24 pm, and the camera

Oph

315

1994

was changed

to a Schmidt-Cassegrain

system,

which

the usable short wave range down to 3700 AI’]. In 1994 when the nova was bright,

we used two gratings, (dispersion

325 line pairs/mm

50 AA/mm)

and the corresponding

we only used the first grating, We obtained

a total

(dispersion

195 AA/mm)

resolutions

and 1200 line pairs/mm

were 5.3 and 1.4 A/pixel.

and with the smaller pixel size, gave a resolution

of 9 nights

of low dispersion

data and 2 nights

In 1995

of 4.7 A/pixel.

of medium

dispersion

data. We used a Fe-Ne lamp for wavelength calibration medium

of the spectral21 and ESO’s dispersion

and 08-19.

observations

calibration,

MIDAS

were centered

In Figs. 1-3, we give the spectra

the Oke standards

for relative

flux

software package for the data treatment.

The

on the Ha line and were made on 1994-07-18

of the nova after calibration

of the relative

flux.

Image: H, look”“““““““““““““‘? r

80:

iz

60:

4

40

2

20: o-“““““““‘““““““~’ 6450 6500

Wavelength (;\)

Fig.2

6550

6600

6650

6700

Wavelength (A)

Intermediate-dispersion

spectra

(centered

on H,,

taken

on 1994 July

resolution

18 and

1994

August

19

1.4A/pixel)

Image: 1995 May 29 100

OF,,,,,,,,,,,,,,,, 4000

,,,I 5000

6000

7000

Wavelength (A)

Fig. 3

Low-dispersion

3.

The most commonly

V magnitudes Internet.

CLASSIFICATION

used classification

of decline as measured ta, to characterize

spectrum taken on 1995 May 29 (resolution

NOVAE

of novae is based on the light curve, using the speed

by the times taken to fall 2 or 3 magnitudes

the object

as fast, intermediate

of the nova provided

Unfortunately

OF

4.7A/pixel)

by Kyoto

from the maximum,

or ~10~1~1. Fig. 4 reproduces University

we do not have photometric

Astronomy

Department

data at the maximum.

t2 or

the visual and through

The spectrum

316

HU Jing-yao & JIANG Xiao-jun

at maximum is related to the velocity of expansion. According to the medium dispersion spectra of 1994-07-18 and 08-19, the FWHM expansion velocity of Ho is V& > 1100 km/s, so the spectrum should be earlier than B5131, and its B - V = -0.17. The photographic magnitude at discovery (06-Ol), mpg N 7.0, can be taken to be near the maximum, so we take V,, = 7.0. From Fig.4 we then find t3,V = 15d, so it belongs to the class of fast novae, which also accords with its high expansion velocity.

-Y 9-

-

$ =

+ 0

+

nl” v

ln 2 IO.r: 6 r”

-

0

%

* +o + ++ l++* 0 + =%I0

+ 0

11 -

0

D

0 :+

+ ++

++

+

l

+

12 -

+

0

+

+

0 ++

I~~~‘l~~~~l~~.~l,,,~I,~~~I,,,,I,,,,I,,, 0

10

20

30

40

50

60

IO

80

Days after Discovery

Fig. 4

Light curve of Nova Oph 1994

With the replacement of the photographic plate by digitized detectors like CCD in the last 20 years, we can now study the emission lines (unsaturated) in the early spectra of novae instead of only the absorption lines. R. E. Williams used the spectral features in the few days after the maximum to classify novae into two types, Fe II and He/Nl*l. Nova Oph 1994 possessed almost all the features which Williams found from a combined analysis of the strongest non-Balmer a series of Fe11 type novae: 1) A few days after the maximum, lines were 42 multiplets of Fe II. 2) The emission lines are narrow, with HWZI< 2500 km/s (for Nova Oph 1994, 2300 km/s). 3) The spectrum varies slowly. 4) The earliest appearing forbidden lines are aurora1 lines of N and 0, such as [0 I] 6300 A. 5) There are lowly ionized However, Nova Oph 1994 differs from fluorescence lines in the red part of the spectrum. usual Fe11 type novae in that its emission lines has a rectangular shape with a flat top and has a multiple peak structure (see the Ha profile of 1994-07-18 of Fig.2). We think that the line is produced in winds of low-excitation lines of Fe11 and others, and that here, the wind density is low, so a flat-topped, multipeak structure similar to the lines in gas shells is produced.

4. EVOLUTION

OF SPECTRUM

As stated above, we take the nova maximum to be on June 1, and our observations began on June 10. The course of evolution of the emission lines is shown in Table 1. The spectrum

317

Nova Oph 1994

Table

The Principal

1 June

[NeIII] 3669 [NeIIIj 3968 H6 [OIII] 4363/H, NH1 4641

10

June

17

Emission

Lines in the Spectra

July

1 July

2 July

Aug.

7

Aug.

18

Aug.

24

May

29(1995) M

I I I I

I I I I

I I I I

I I I I

I I I I

I I I I

I I / I

I l I I

M

M

S

S

S

S

S

S

S

W

M

M

M

M

S

S

S

S

S

S

S

S

S

HeII 4686 S

HP

16

of Nova Oph 1994

S

S

S

[OIII] 4959/5007

W M S

S M

[FeVII]5159

M

[FeVI]5176 NII 5180

M

M

M

M

M

W

W

[FeIII] 5270

M

HeII 5412

W

Fe (42) Fe (49) NII 5679,

5686

M

W

M

M

W

M

M

M

M

M

M

S

S

S

S

S

S

S

W

W

S

S

S

S

W

W

M

M

M

M

M

M

M

M

M

M

S

S

S

S

S

S

S

M

M

M

M

W

M M

[NII] 5755 HeI 5876

M

M

S

[FeVII] 6087 [Ol] 630016364 [FeX] 6375 S

H,

S

[NII] 6584

M

He1 6687

W

HeI 7065

I

CII 7111 [ArIV]

W

W

7236

[OII] 7330 017773 MgII 7877

S

S

W

W

N18216

M

S

MgII 8232

M

M

018446

S

S

NI 8686

S

S

S=strong, “outside

W

M=medium, observing

W=weak.

I I I / / I I I I A blank

M

M

M

M

M

W

S

I I I I I I I I I I

I I I I I I I I I I

/

W

I

M

I I I I I I I I

W

M M

M

M

S

M

W S

M

M

M

S

S

S

M

means

“not

seen in the spectnnu”.

S

I I / I I I A slash

means

window”

of June 10 comprises, apart from the strongest Bahner lines, mainly low-excitation Fe11 and 0 I lines, and in the red part, multiplets of heavy elements such as Mg II, generated by fluorescence resonance by Lyp. In the spectrum of June 17, the 0 I lines increased in strength relative to HP, and [N II] 5755 became more pronounced. Of course, Fe II remained still the more prominent feature. In the spectra of July 1 and 2, the most obvious changes are the clear strengthening of [N II] 5755, [0 I] 6300/6364, while 0 IS446 remained as the strong&

318

HU Jing-yao & JIANG Xiao-jun

line next to Ho and [0 II] 7330 b e g an to strengthen. On July 16, [0 III] 4959/5007 began to be prominent, and by now the Fe II lines had greatly weakened. Also, high-excitation He I and N III lines got stronger and the 0 I lines, weaker. These trends continued on Aug 7, and [0 III] 5007 neared H/3 in strength, showing the beginning of the nebular stage. It should be pointed out that at this point, the [01] 6300 line is actually weaker than the 6364 line, possibly because the latter has been contaminated by [Fe X] 6375. Some 300 days after the maximum, on 1995 May 29, we observed the nova again (Fig. 3). Now, the spectrum is typical nebular spectrum, and [0 III] 4363, 4959, 5007 and [N II] 6548+6584 are the strongest lines, stronger than the Balmer lines, and there appear also highly ionized Fe forbidden lines and high excitation He lines. These features should all be taken to have been produced in the cloud formed from matter ejected by the nova. The spectral evolution reflects changes in the physical conditions of the central body and the ejected matter, especially changes in the temperature of the former and the density of the latter. R. E. Williams et a1.151divide the lines in nova spectra into permitted lines P, aurora1 lines A, nebular

line N and coronal

line C. Accordingly,

the spectral

evolution

of

Nova Oph 1994 is P”~,-An,o-No.

5. Ho PROFILE As Fig. 1 shows, nearly all the emission lines in 1994 showed a structure of peaks. As stated above we think the emission lines in the early spectrum were formed inside stellar winds, it then follows that the peaked structure should help us understand the structure of the winds at the time of the explosion. On July 18 and Aug 19, 1994, we obtained the medium dispersion spectra of Ho (resolution 1.4 A/pixel), s h own in Fig. 2. It shows four peaks which were stable on time scales of months. The four peaks are almost symmetrical to the rest wavelength of Ha, so we can regard them as produced in lump-like the ejected material. Because the four large clumps were inclined at different line of sight, different shifts with respect to the rest wavelength are produced.

with respect structures in angles to the

6. CONCLUSION Nova Oph 1994 is an interesting object. According to its early spectrum we can classify it as an Fe11 type nova, but its emission lines also have the multiple peak structure of the He/N type. We think the multi-peak structure probably originated in lumps of matter ejected in the explosion, and hope to confirm this guess with direct imaging observation of the later nebula.

References

[l]

Hu Jing-yao,

[2]

Oke J. B., ApJS,

[3]

Hack M. et al., Cataclysmic

[4]

Williams

R. E., AJ, 1992, 104, 725

[ 51

Williams

R. E. et al., ApJ, 1991, 376, 721

Joint Laboratory

Optical

Laboratory

Xinglong

and Related

Objects,

Base Handbook,

1995

1974, 27, 21 Variables

NASA

SP-507,

1993, 261