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(updated July 3rd 2010)
V1413 Aql (AS 338 & Hen 1737) is an eclipsing symbiotic system located at 19h 03m 46.8s +16d 26' 19" (2000.0). The maximum and minimum magnitudes are listed as 10.6-15.1V, and the eclipse period is 434.1 days.
The eclipsing and outbursting nature of this object was first noted by M. Wakuda , and reported in VSOLJ bulletin 5, 17, 1988 (1). He gave the following eclipse ephemeris …
Min = JD 2445784 + 434 E
Further analysis by U.Munari (2) gave the following revised eclipse ephemeris…
Min = JD 2446650 + 434.1 E
+/-15 +/-0.2
Munari concluded from Optical and UV Spectroscopy and Photometry that V1413 Aql was composed of an M5 star and a very hot compact star, resulting in a symbiotic nova type thermonuclear runaway, without a detectable mass ejection (2).
I began to monitor V1413 Aql following John Bortle's outburst announcement in 1995, and have kept it under observation ever since. Eclipses which occur during the first half of the year are near impossible for me to observe because of local obstructions, even in the pre-dawn sky.
The light curve for V1413 Aql also reveals intrinsic variation in the symbiotic system itself, fading from 11.0 in 1994 to a mean magnitude of 13.5 by 2005. V1413 Aql then began to rise slowly in brightness, reaching it's 1994 level by 2010.
The eclipses themselves are interesting to follow. Figure 1 shows the 1999 eclipse in some detail. According to my visual observations, the eclipse lasted a total of 71 days. Eclipse ingress took 22 days, and the egress 28 days - 21 days were spent in eclipse. The depth of the eclipse is just over 2 magnitudes deep. However the intrinsic brightness of V1413 Aql dictates how easy the eclipses are to follow. The 1997 eclipse for example dropped from magnitude 12.3-14.4, and was fairly easy to observe even with a 22cm telescope. The 1999 eclipse however faded from 13.0-15.2, and needed a larger telescope to confidently follow the whole eclipse event. To make matters worse, there is a close field star near to V1413 Aql at magnitude 13.1. The closeness of this star can cause problems when estimating the brightness of V1413 Aql with small telescopes around the 12.5-13.5 magnitude range.
Fig. 1: The 1999 eclipse.
Following Munari's ephemeris, the following dates for mid eclipse for future events are as follows...
July 23rd 2011
Sept. 29th 2012
December 7th 2013
February 14th 2015
If simply the eclipse is to be observed, then it is recommended that monitoring begins at least one month before the above dates!
V1413 Aql offers a rare chance to observe an eclipse in a symbiotic system over a reasonable period of time. The intrinsic variations of the system are also extremely interesting to follow, and as with all symbiotic systems, are unpredictable in their nature.
G. Poyner
1: Kato. T. vsnet-alert Apr 11, 1997
2: Astronomy & Astrophysics. 257, 163, 1992)