Outburst profiles in V1329 Cyg: 1990-2003
G. Poyner
February 2004
When symbiotic stars are discussed, we generally think of an object which might spend long periods in quiescence, interrupted by the odd occasion when something might be seen to happen, only for this activity to cease and normality is resumed. Then every once in while, the star will undergo a sudden brightening or 'outburst', spend several months in this highly active state before returning to minimum. One need look no further than Z And, CI Cyg & YY Her for examples of this behaviour. There are exceptions to the rule of course, with V1329 Cyg being a perfect example of this. Discovered in 1969 by Kohoutek (as HBV 475) through it's peculiar emission spectrum, a search of plate archives revealed the star had undergone a Nova like outburst in 1964, and was still at maximum brightness at the time of discovery - leading to it (and a few others, including AG Peg) to be termed a Symbiotic Nova.
Various plate searches revealed that the outburst detected in 1969 actually began in 1956, as the photographic magnitude rose from 15.5 to 14.2 in seven years. Then followed the dramatic rise to mpg 12.5 in 1964, followed by a gradual fading [1]. Close monitoring of the star revealed a one magnitude periodic oscillation, with this period showing to be 950-960 days. This was interpreted as an eclipse of the outbursting star by it's M type companion.
Only one spectrum was available before the 1964 outburst. This revealed an M type star with no emission lines present [2]. However spectra obtained after 1964 display strong H I and weak He I emission. The line profiles in the spectra are extremely complex, and may be caused by an expanding gas cloud, or perhaps dust shells as observed in classical novae [3]
Figure. 1 shows the visual light curve of V1329 Cyg plotted from 728 observations made between 1990 & 2003 (the plot extends past 2003) using 22cm, 40cm & 44cm Newtonian reflectors, and a 35cm SCT. It's plain to see that the star is very active, with 6 'outbursts' detected within this relatively short period. The eclipses mentioned above are also evident in the plot, and fall in line with the 950-960 day orbital period. From this light curve, it can be determined that the outburst interval had been increasing from 1991 through to the 2001 outburst - 1991-93 350d, 1993-95/6 448d, 1996-98 625d, 1998-01 777d. However the 2003 outburst came 558 days after V1329 Cyg had returned to quiescence in 2001 (here quiescence is regarded as visual magnitude 13.7). Can we expect this trend to continue in the future?
Fig 1. Visual light curve 1990-2003: Poyner
A comparative look at the profiles of the outbursts recorded from 1990 to 2003 is an interesting exercise. Figures 2-7 below show the outbursts as observed visually by the author. The 1990 outburst appeared as 'double peaked', and lasted some 356 days. The 1993 outburst lasted 195d and was followed by another 'double' outburst of some 349 days duration in 1995/6. The 1998 outburst lasted for 180 days. In 2001 the outburst period was 156 days, but peaked slightly fainter at magnitude 12.7. This was followed in 2003 by an outburst lasting 133 days, and peaking at magnitude 12.5 - around one magnitude above minimum. One obvious conclusion which can be derived from these figures, is that the duration of the outburst (time spent above magnitude 13.7) has been decreasing since 1990, yet the intensity of the outburst has been increasing with brighter magnitudes being reached! Is this also a repeating trend? Only further observations will determine these interesting points.
Fig. 2 'Double' outburst of 1990
Fig 3. The 1993 outburst
Fig 4. Double outburst of 1995/6
Fig. 5 1998 outburst
Fig. 6 2001 outburst
Fig. 7 2003 outburst
One of the least observed but more interesting of symbiotic stars observable through amateur telescopes, V1329 Cygni is a prime target for further study by visual observers. Telescopes of 20-25cm aperture will reveal the star at minimum, whilst a 15cm will show it when it's bright. Continued observation of the stars behaviour will reveal the interesting features of the outbursts described above, and help to determine whether these trends are real. How can you not observe it?
G. Poyner
References:
1: Kohoutek L & Bossen H. 1970, Astrophys lett. 6, 157
2: Steinon, F. M., Chartrand M. R. & Shao C. Y, 1974 AJ, 79, 47
3: Tamura, S 1977 Astrophys lett. 19, 57
Here for a monthly updated light curve for V1329 Cyg