Science Projects

Epsilon Aurigae with the University of Portsmouth

University of Portsmouth

Epsilon Aurigae

A University of Portsmouth project in association with HAG to monitor and record the eclipse of Epsilon Aurigae.

Epsilon Aurigae is a pulsating Supergiant F0 class variable star of magnitude +3 (varying by magnitude ~0.2) that is eclipsed once every 27.1 years. The eclipse lasts for between 640 and 721 days, and during the eclipse the brightness of the star will dim by 48%. The distance Epsilon Aurigae is from earth is approximately 2'000 light years, and is about 15 solar mass.

The observations made in 1821 by Johann Fritsch suggest he was the first to notice that this was a variable star. The system wasn't sufficiently observed until German mathematician Eduard Heis and Prussian astronomer Friedrich Wilhelm Argelander began observing it once every few years, from 1842 to 1848 The star was observed to dim significantly in 1847.

Hans Ludendorff, who had also been observing Epsilon Aurigae, was the first to conduct a detailed study of the star.  He published a paper in 1904 suggesting it was an Algol type star.

In 1937 the ‘three greats’ Kuiper. Struve. Stromgren., suggest that Epsilon Aurigae is being eclipsed by a large opaque star.

S. S. Huang (1965) suggested an edge on thick disk to replace Kuiper/Struve/Stromgren’s opaque supermassive star model.

Robert Wilson (1971) suggested Edge on thin tilted disk with central opening.

Huang (1975) Concentrates on the thin disk with central opening as a best fit with observations.

The most recently accepted theory put forward by Carroll et al. (1991) suggest….

  • The primary is an F01 supergiant, possibly well over 10 solar masses, and is itself pulsating
  • The secondary is a cool, thin disk of varying opacity, probably with a hole in the centre, and tilted or warped with respect to its orbit about the F star
  • At the centre of the disk, there is a hot object -- most likely a massive close binary system B5-type stars rather than a black hole, and
  • The combined mass of the disk and central object of the secondary is nearly the same as that of the primary.

Bennett et al. (2005) suggests that it is now likely that there is an early-type binary system with components having spectral class B5 or earlier at the centre of the disk, based upon the ultraviolet spectrum obtained with Far Ultraviolet Spectroscopic Explorer (FUSE).

During the 1982-84 eclipse the central brightening was the brightest ever.  The duration of minimum was the longest, and the fading and brightening happened fastest. From 1901 to 1983 the time of minimum has increased from 313 to 445 days.  The overall eclipse duration has declined from 727 to 640 days.


Where to find the star

Epsilon Aurigae shown next to Capella


Some of the major questions that may be answered with close observations

  • What is the mass of the system and the evolutionary state of the star(s)?
  • What is at the centre of the disk -- one or more stars or something else?
  • What is the geometry of the system, and in particular, is the centre of the disk empty or not?
  • Will the shape of the light curve in different wavelengths change relative to the 1984-85 eclipse, indicating precession or other physical changes in the inner region of the eclipsing disk?


Next Eclipse - JD 2,455,050 (6th August 2009)

  • 1st Contact - JD 2,455,050 - 6 Aug 09
  • 2nd Contact - JD 2,455,187 - 21 Dec 09
  • Mid-Eclipse - JD 2455410 - 01 Aug 10
  • 3rd Contact - JD 2,454,633 - 12 Mar 11
  • 4th Contact - JD 2,456,697 - 15 May 11

Note: All Dates are Approximate !!


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