.4atronomical and Astrophysical Transactaonr, 1998, Vol. 15, pp. 101-115 Reprints available directly from the publisher Photocopying permitted by license only

a 1 9 9 8 OPA (Overdeu Publidhers Association) Amalerdam B.V. Publiahed under license

in The Netherlands under the Gordon and Breach Science Publishers imprint.

Printed in India.

THE INVESTIGATION OF CONTEMPORARY CLASSICAL NOVAE

V. P. GORANSKIJ', E. A. KARITSKAYA2, A. V. KUSAKIN3, N. V. METLOVA', T. M. POGROSHEVA3, and S. Yu. SHUGAROV'

Stersberg State Astronomical Institute, 19 Universitetskiy Prospect Moscow 11 9899, Russia

'Institute of Astronomy, Russian Academy of Science, 48 Pyatnitskaya St., Moscow 10901 7, Russia

Tien-Shan High Altitude Observatory, Working Group of Sternberg State Astronomical Institute

(Received July 12, 1996)

The investigation of five classid novae: N Cyg 1992 = V1974 Cyg, N Ad 1993 = V1419 Aql, N Cas 1993 = V705 Cas, N Aql 1995 and N Cas 1995 is reported in this paper. The identifications of these novae with faint stars in the Palomar Sky Survey were checked. N Aqll993 was identified with a star of 21 mag on the POSS 0 plate. The light curves and the colour index variation curves were obtained using original observations by the authors and other published data. The behaviour of several type classical novae and X-ray novae in the twa-colour diagrams is found to be considerably different. The appearance of two light periodicities in N Cas 1992 in the late stages of outburst is confirmed, but the observations can not be fitted by any linear elements in a time interval of more than 200 d.

KEY WORDS two-colour disgluns, periods of novae

Novae, X-ray novae, identifications, photometric observations, light curve, colou~s,

Five classical novae: N Cyg 1992 = V1974 Cyg, N Aqll993 = V1419 Aql, N Cas 1993 = V705 Cas, N Aql 1995 and N Cas 1995 are investigated. For all the objects astrometric measurements were carried out to identify them with faint stars from the PaloInar Observatory Sky Survey (POSS). The novae fields taken from the blue POSS 0 glass copies are reproduced i n Figure 1. POSS glass copies were scanned and digitized with an autoniatical microdensitometer (AMD). These densitograms were reproduced on a PC screen with the help of our special computer program. The contrast has been sharpened with a numerical method. The crosses denoting novae positions have been plotted by astrometrical methods relative to reference stars from GSC and PPM catalogues (see Figure 1).

N Aql 1993 is identified with a faint star of 21 mag on the POSS 0 plate (see Figure 1). The star is absent on the red POSS E plate. The identifications of N Cas 4993 (Munari et d., 1994) and N Cas 1995 (Williams, 1995) are confirmed. Pre-

101

102 V. P. GOKANSIiIJ et al.

N Cyg 1992 = V1974 c y g N Aql 1993 = V1419 Aql

N Aql 1995

N Cas 1995

Figure 1 Reproductions of the novae fields Irolll the blue I’OSS glass copies. North is at the top. Fig.ld dimensions are 4 arcmill x 4 arcmin. The calculated aqtrometric positions are denoted by crosses.

= 5.0 0

3 6.0 7.0

8.0

9.0

10.0

- ." r

CONTEMPORARY CLASSICAL NOVAE 103

I N Cy9 1992 x- Cl-Lut +- VdMl *- W w n .- ahw

12.0 lLO t

48800 49000 49200 13400 19600 49800 SOOW J.O. 2400000~

Figure 2 The light curves of five novae in V. The original observations by the authors of tlus paper and by other observeis have been used. The different symbols correspond t.o original observations by the authors and other sources using different photometers: Cr-Lut, the photometer of V. M. Lutyi in the Crimea; Cr (or Moscow)-ShV, the photometer constructed by S. Yu. Shugarov and I. M. Vokov used in the Crimea (or in Moscow); AA-Korn, the photometer constructed by V. G. Kornilov used in Tien-Shan (Alma-Ata); AA-Nadir, WBVR standard plant construct.ed photometer; AA-unfilt, observations without filters but with dichroic plate dividem in Tien-Shan. The small dots correspond to published observations of other authors. The systematic differences of observations using different equipment have not been taken into account.

nova Cns 1993 is seen as a northern 17.0 B companion merged with the southern one in the 2 arcsec pair. N Cas 1995 is reliably identified with a star of magnitude 19.0 f 0.2 B and 17.5 f 0.5 R before the outburst. (see Figure 1). The recent N Cyg 1992 position is situated on the edge of a 19 niag star image (see Figure l) , the centre of which is displaced by 2 arcsec according to the nova's position. It. may be that the pre-nova image blends with the star's image. In the case of N Aql 1995 a faint, 20 mag star is situated too far (by 2.5 arcsec) to the south-east from the recent nova position (see Figure 1). So we assume that this star is not a pre-nova.

Since 1992 we have monitored these five novae in the UBV and WBVR pho- tometric systems. The light curves (Figure 2) and colour index curves (Figure 3) obtained in the study allowed us to investigate both the distinctions between classi- cal novae of various types and those between clksical and X-ray novae. N Cyg 1992 is a 0-Ne-Mg nova and has unusual variations of colour indices. For example, it has power UV excess up to A(W - B) = -4.0 mag (see Figure 3). N A l l 1993 and

104

= B.0

.: 9.0 co = 10.0

E -0

11.0

12.0

L3.0

14.0

15.0

16.0

V. P. CORANSKIJ et al.

I N Aql 1993 -5 X- 0 - L U < M X I *a&> *- cr-w

0- M-Korn 0- M-un~lll. 0 - other

x

1 - . : *( -

a - - +

L P' ;t. &r: 0

- .r=" 0 . X 8 X 88 a . - 0

- t I I I 1 . 1 1 ,

11.0

12.0

13.0

14.0

49200 49300 49400 49500 49600 49700 49800 49900 500GG 3.0. 2400000+

- - - -

3 6.0

4 7.0 2 .- 5 8.0 S

9.0

10.0

N Cas 1993 I!

. ...+P $ 6 * r w : * s * .

x- mscarsw e- M a n *- W d l r 9- othw

16.0 15-0 t --a I 1 I I I I I I I

49400 49500 49600 49700 49800 49900 50000 50100 2.0. 2400000+

Figure 2 Continued.

CONTEMPORARY CLASSICAL NOVAE 105

3 8.0

E 0

c .- & 9.0 n S

10.0

11.0

12.0

13.0

11.0

N A q l 1995 0- ~OrcOcrLMI

-- othmr -. *- Iu-mrn - - *. - .* .

9 . .. - .*

%. . .. - - *' 0 :/

* * a -

1 , I I 49760 49800 49840 49880 49920 49960 50000 50040 50080 50120

J.O. 2400000+

7.0

7.5 3

b; '0

.L 2 8.0 P $ 8.5

9.0

9.5

10.0

10.5

11.0

11.5

12.0

- 0

N Cas 1995 0- noscorrBMI x- Cr-LUc .- * n *- w i -- othmr

I I I I 1 I 1 I

49940 49960 49980 50000 50020 50040 50060 50080 50100 50120 50140 J.D. 2400000+

Figure 2 Continued.

1 Of3 V. P. GORANSKIJ e t 01.

a -1.0

3

k

m

a -0.5 0

0.0

-

-

-

0.5

1.0

-4.a

F 5 -3.5

b

m

'' -3.0 =I

- u

-2.5

-2.0

-1.5

-i.Q

-0.5

. x x .. . -.. . X .. : t;: .. *.I :. p

z

N Cyq 1992 x - C r - L I i *- cr-M *- M-Korn 9 - o t h u

.

8

48800 49000 49200 49400 49600 49000 50000 J.O. 2100000+

X . I.. x

. N Cyq 1992

W

4saoo 49000 49200 49400 49600 49aoo 50000 J.0. 2400000+

Figure 3 The colour index variation curves. Symbols are the same BP in Figure 2.

7 m

0.0 L 0 0 0

c

0.5

1.0

a A 0.5 b - 0

1 .o

1.5

2.0

CONTEMPORARY CLASSICAL NOVAE I07

I X

JF I . . x+ = 2:.

I 0

U U

. . . . . . . I 0 .

X

* * . 0. * . a r: .

. .

49200 49300 49400 49500 49600 49700 49800 49900 50000 J.0. 240M00+

3' J t

i T i 0

0

. . .

N Aql 1993 x- 0-Lut c-1 *.&> *- (ZaMI 0- M o r n 0- M-Milt. .- other

. 0

49200 49300 49400 49500 49600 49700 49800 49900 50000 J.O. 2$00000+

Figure 3 Continued.

108 V. P. GORANSKIJ et 01.

3 m .. L 0 - s

0.5

t.0

8 3 7 -1.0 3

b d 0

-0.5

0.0

0.5

a a

I a

i +

a

a . 49400 49500 49600 49700 49800 49900 SO000 50100

J.D. 2100000+

t

t

N Cas 1993 x- lbKarSNl . M-Korn

t - m-mr a- other

b

a .

):I . I . . . a 9 I .

49400 49500 19600 49700 19800 I9900 50000 J.O. 2400000t

Figure 3 Continued.

CONTEMPORARY CLASSICAL NOVAE 109

-* 0.2 L 0.3 2 0.4

0.5 0.6 0.7 0.8 0.9 i .0 1.1 1.2 1.3 1.4 1.5 1.6

8

0.3 3 m

I) 0.4 L

8

0.5

0.6

0.7

0.8

-

- - - - - - - - - - - - -

d 0

0

e e a e ..

0

0

0

O

N Aql 1995 0- MacoL9-shu 0- M-Worn -- 0 t h

0

0

0

m m m e

I I I 1 I I

49840 19880 49920 49960 50000 50010 J.D. 2400000+

-0.4 - -0.3 - *

2 -0.1

il 0.1 - m 0.0 -

O O 0

0 0

0

0

iJ Aql 1995 0- w .- M-Yorn. =- other \

0 0

e m

19810 19880 49920 19960 50oMl . 50040 J.D. 2400000t

Figure 3 Continued.

110

-0.8 -0.7 -0.6

m 2 -0.5 .- -0.4

-0.3 -0.2 -0.1

0.0

0.1

0.2

0.3 0.4

0.5

0.6

b u

? (D

- - - - 8

- - - - - - - - - -

k 0.4 c

0

0.5-

0.6

0.7

V. P. GORANSKIJ et al.

e 3?

0 0

8

N Cas 1995 0- n D a o v s M l I- criurrp .- -Idlo* *- nvvi * - 0tk.c

I

JE: 0

e 0 0

0

0

0

X X

P 0

o e 0 0

0 0 0

49980 50000 50020. 50010 50060 50080 50100 50120 5011C J.O. 2100000+

0.7 1 N Cas 1995 0- nolwu-swI a- Cr-LUl 0- M-Korn *- w i .- 0th.r

0

0

0

49900 50000 50020 50040 50060 50080 50100 50120 50140 LO. 2400000t

Figure 3 Continued.

CONTEMPORARY CLASSICAL NOVAE 111

m I

3

- 2

- 1

0 .

+ 1 -

a

/ I / N cyg 1992

/

- 1 0 + l B - v

F igure 4 The clrifts of five novae under research in two-colour diagrams (V - B)-(B - V ) , (W - B)-(B - V ) and (I? - V)-(V - R).

N Cas 1993 are dust novae of DQ Her type. Their light curves show the typical dips connected with dust envelope formation. The disappearance of UV excess which is connected with UV light absorption by large particles of dust is a typical feature of these 0bject.s. Also, the significant red excess is observed in episodcv of dust envelope formation. Dust IR radiation has been revealed in the case of N Aql 1995 but we did not observe the characteristic light curve dip of DQ Her type in this object. Nevertheless the significant R excess was observed in N Aql 1995.

N Cas 1995 shows unusual behaviour. Its oulburst demonstrates very slow de- velopment and low velocity of envelope expansion (Figure 1). During seven months the star had a normal photosphere. In December 1995 a mini-outburst was observed with an amplitude of 1.5 mag, and bright Balmer Ha emission and UV excess were detected photometrically. These light and colour changes in December, 1995 sugg-

112

m

L

- 3

I

- 2

- 1

0

+l

V. P. GORANSKIJ et 01.

i d t i B - v + 2 Figure 4 Continued.

est the formation of a dense atmosphere. It is interesting that the shape. of the light curve of N Cas 1995 is.very similar to that of slow Nova RR Pic. The last one had maxima due to three short-living mini-outbursts over the flat prolonged maximum finished with a slow fading. Upto until April, 1996 N Cas 1995 had three mini-outbursts, too. An assumption that this object is not a symbiotic nova but rather a classical nova is confirmed by spectroscopic observations (Iijima and Rosino, 1996).

- 1

P I

>

0

t i

+ 2

CONTEMPORARY CLASSICAL NOVAE 113

C

N Cyg 1992

- * I I

- 1 0 + 1 B - Y + 2

Figure 4 Continued.

For all the classical novae under research there are systematic deviations of ob- servations obtained with different photometers. These deviations are changing with time and strongly increase in the later stages of the outbursts. Note, that they reach 0.6-1.0 mag in the V band in spite of the equality of colour equation coefficients to zero in all devices if the coefficients were derived using normal stars. The devia- tions may be due to sinall device-to-device and temperature changes in photometric bands which cannot be controlled with convenient methods of photometry. When the bright emissions are situated near the edge of a photometric band the systematic deviation may increase up to 1.0 mag. Having variations of power emission lines in the spectra one may expect these deviations to change. So one may observe only the major tendencies of star shifts in two-colour diagrams (Figure 4). Such behaviour of the studied novae differs considerably from the behaviour of X-ray novae which

114

a 13.22 - '0 a a * a

a

a 3 c 0 '$13.27 - .I

Il a I a a a

8 I Dm .D

13.32 - a . .. W a

13.37 - I a ~n

m W

13.42 - 4 I

V. P. GORANSKIJ et 01.

0 U 3 13.50 ." t 0

13.60

13.70

13.80

13.90

- W W

8 b * * . .. a . . a - 8

a a a

. W a D : s a a

a m . . a n , a a

a .*

-1 I W ' a* . # -

- . 0-0.08 '13 3 L .PI

i -0 .05 L

-0.02

0.01

0.01

1 0.0 0.5 1.0 Phase 1.5

a C

-

I. r.

a

a #

a

a

- a

-

- 8 , I 8

Figure 5 The folded light curves for N Cyg 1992 accodng to ephemerides determined in this paper for three time intervale - a. JD 2449202: T=HJD 2449202356 + 0.081985 d*E; b, JD 2449265369 T=HJD 2449369.085 + 0.0819853 d*E c, JD 244952CL560: T=HJD 2449533.210 + 0.0851306 d*E.

CONTEMPORARY CLASSICAL NOVAE 115

have spectra similar to high-temperature blackbody or accretion discs (Bochkarev ei al., 1991; Goranskij ei ol., 1996) in all the stages of outburst. X-ray novae are situated along the line of interstellar reddening. They do not change their positions in two-colour diagrams with time (Goranskij et ol., 1996).

Our observations confirm the appearance of two light-curve periodicities in the late stages of N Cyg 1992 outburst. For time interval JD 2449200-365 we revealed the period P = 0.081985 d (Figure 5). This period differs from P = 0.81263 d, which had been derived earlier by De Young and Schmidt (1994). In time interval JD 2449531-549 we revealed the period P = 0.085 d which is in agreement with the period found by Semeniuk ef al. (1994) and attributed to superhumps similar to SU UMa. The amplitude of variation in V light is equal to 0.12-0.18 mag and increases with wavelength. Over a time interval of 200 d these oscillations are not coherent and can not be fitted by any linear elements.

Acknowledgements

This research was supported by Ministry of Science of the Russian Federation Grant No. 3-201 of the programme Astronomy, and also by the scientific budgetary item project The Optical Monitoring of Unique Astrophysical Objects.

References

Bochkarev, N. G., Karitskaya, E. A., Shakura, N. I., and Zhekov, S. A. (1991) Astror. .isfropAjs.

De Young, J. A. and Schmidt, R. E. (1994) Astrophys. J. 431, L43. Goranslrij, V. P., Karitskaya, E. A., KurodrLin, N. E., and 'hnkovaky, E. M. (1996) Rrsr. A s f w n .

Iijima, T. and Rosino, L. (1996) IAU Circ. No. 6365. Munari, U., Tomov, T. V., Hric, L., and Hazucha, P. (1994) I f . Bull. Variable Sfars No. 3977. Semeniuk, I., Pych, W., Olech, A., and R u b w r k i , M. (1994) Acts Aitron. 44, No. 3,277. Williams, G. V. (1995) IAU Circ. No. 6213.

Trans. 2 , 41.

Left. 22, 371.