Eclipsing Ring System J1407

1SWASP J140747.93-394542.6 (ASAS 140748-3945.7, 2MASS J14074792-3945427, GSC 0780700004).

(artwork by Mike Osadciw)

1SWASP J140747.93-394542.6 ("J1407") is a recently discovered young variable star that had an extraordinarily deep, long, and complex eclipse in early 2007. The eclipses took place over a ~52 day period, with the deepest portion being ~3.3 magnitudes fainter than the out-of-eclipse mean brightness (V ~ 12.3 mag).

In Mamajek et al. (2012), we propose that the eclipse sequence in 2007 appears to be due to the presense of a low-mass object (probably substellar object - likely a brown dwarf or giant planet) with a series of discrete rings orbiting it. If it is a giant planet, this may be the first instance of a "protoexosatellite disk" - i.e. a circumplanetary disk where moon formation is taking place (small bodies are likely present to dynamically sculpt the ring system). If it is a brown dwarf, then we are similarly seeing the dust signatures of the formation of a miniature planetary system. Either way, this is an interesting and, so far, unique system.

The period of the eclipses is currently unknown, but definitely >850 days. We are requesting regular observations of the V-band brightness of J1407 to identify the next period so that we can constrain the period of the eclipsing body. This will help determine the absolute scale of the ring system and help constrain the mass of the companion to J1407 and the masses of the companion's companions! Thus far we estimate that the ring system is likely to have a maximum radius of ~0.1-0.4 AU.

An analysis of SuperWASP light curves over 2006-2009 and ASAS light curves over 2001-2009 showed evidence for only one deep eclipse - in April/May 2007. In both datasets, a modest-amplitude periodicity of 3.211 days is present, which is likely due to stellar rotation (starspots).

Figures and numbers are taken from Mamajek et al. (2012).

RA, Dec 14:07:47.93 -39:45:42.7 (J2000)
Vmag 12.31  (average, out of eclipse)
~16 (eclipse minima)
amplitude ~0.1 mag (due to starspots, period = 3.211 days)
First eclipse epoch HJD 2454220
Distance 128+-13 parsecs (417+-42 light years)
Mass ~90% solar mass
Age ~16 million years


Photometry from SuperWASP and ASAS around the time of the Apr/May 2007 eclipse.

Plot of nightly average photometry from SuperWASP and ASAS for J1407 during April/May 2007. Note the depth and lopsidedness of the central eclipse, and the symmetry of the smaller eclipses in the days before and after the main eclipse.

Photometry from SuperWASP (filled points) and ASAS (open triangles) in the days before the 2007 minimum (out-of-eclipse magnitude is V = 12.3).

Photometry from SuperWASP (filled points) and ASAS (open triangles) in the days during and after the 2007 minimum (out-of-eclipse magnitude is V = 12.3).

Toy model of what we think is responsible for the eclipses: a disk + multi-ring system orbiting a low-mass companion to J1407 (the star itself is shown to scale as the filled circle on the right, with real diameter of ~1 million km). The vertical optical depth (at V-band) of the thick inner ring is ~0.5, and the optical depths of the three major outer rings are less (~0.05-0.2 each). The optical depths during the eclipses are higher as it appears that the system is tilted, hence more starlight from J1407 is extinguished or scattered. The mass of J1407B (the companion) is unknown, but likely substellar.

Note that J1407 itself does not appear to have a significant amount of circumstellar material around it.  Its spectral energy distribution is very normal  -- it is consistent that of a lightly reddened K-type pre-main sequence star, but there is no evidence for infrared excess consistent with circumstellar material. So the material orbiting J1407B must be fairly small and cold.

(DSS2 finder chart; 10' field of view).
(AAVSO finder chart, 30' field of view).

Any help with supporting observations to search for the next eclipse would be appreciated!

Eric Mamajek (CTIO, Univ. of Rochester)
Erin Scott (Univ. of Rochester)
Matthew Kenworthy (Univ. of Leiden)