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(updated July 17th 2005)
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. Several outbursts have been recorded, most notably by Munari & Yudin (IAUC 5884 1993, Oct 28) in that the magnitude of V1413 Aql had risen from 13.0V in 1990 to 11.2 in 1993, and the most recent by John Bortle who reported an increase in brightness from magnitude 13.0v in Dec 1994, to 11.2v in February 1995.
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 Bortle's outburst announcement in 1995. Unfortunately for me the next eclipse occurred during February 1996, when the field is extremely difficult for me to observe because of local obstructions. Eclipses were observed however in 1997, 1998, 1999, 2000 & 2004 (see light curve). What is also apparent from the light curve is that V1413 Aql has been showing a very slow intrinsic fade since the 1995 outburst - some three magnitudes over a ten year period, with a very brief outburst to magnitude 11.2 in the Summer of 1996.
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. Future eclipses will become increasingly difficult if the system continues the slow fading trend it has displayed over the past ten years. To make matters worse, there is a close field star near to V1413 Aql at magnitude 13.2. 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.
Looking at the dates for minima in previous eclipses, and taking the period as 434.1 days, the dates for mid eclipse for the next five eclipses are...
Aug 23rd 2005 (JD 2453605)
Oct 31st 2006 (JD 2454039)
Jan 8th 2008 (JD 2454473)
March 17th 2009 (JD 2454907)
May 25th 2010 (JD 2455341)
If simply the eclipse is to be monitored, then it is recommended that monitoring begins at least one month before the above dates!
There now exists a V sequence by Arne Henden and chart created by Mike Simonsen. Go here for the chart.
V1413 Aql offers a rare chance to observe an eclipse in a symbiotic system, and over a fairly long period in time. The fading of the system over recent years also offers the observer the opportunity to monitor the long-term intrinsic magnitude variations. All in all a most interesting star to add to one's observing programme.
G. Poyner
1: Kato. T. vsnet-alert Apr 11, 1997
2: Astronomy & Astrophysics. 257, 163, 1992)
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