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Alert Notice 462: Monitoring of J1407 for next extrasolar ring system transit

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June 25, 2012: Dr. Eric Mamajek (Cerro Tololo Interamerican Observatory and University of Rochester) has requested AAVSO observers' assistance in monitoring the young star 1SWASP J140747.93-394542.6 to help determine the eclipse behavior related to a transiting ringed substellar companion.

This observing campaign begins now and continues until further notice. Dr. Mamajek writes:

"The young star 1SWASP J140747.93-394542.6 ("J1407"; V=12.3 mag) underwent a series of symmetric, deep eclipsing events in April/May 2007, consistent with a transiting substellar companion surrounded by a complex ring system moving in front of the star. The series of eclipses were of depth ~0.5-3 magnitudes and occurred over a 52-day period. Unfortunately only a single eclipse sequence was seen, and the period of the ringed companion (likely to be a brown dwarf or giant planet) and the exact scale of the ring system remain unknown. We are gathering observations to test whether this may constitute a moon-forming "protoexosatellite disk". The unusual nature of this star was discovered by E. Mamajek & M. Pecaut in December 2010, and details of the eclipses and characterization of the eclipsed star are described in Mamajek et al. 2012, Astronomical Journal, Vol. 143, 72 (

"We are asking for nightly photometry in one or more visible photometric bands (preferably V) to search for the start of the next eclipse. This star is no longer being monitored by the surveys that led to the initial discovery of this object.

"A brightness dip of more than ~0.15 magnitude in V will indicate the transit of the outermost ring, with additional deeper transits leading up to the central transit approximately 3 weeks later, where an eclipse depth has been measured of at least 3 magnitudes in V band.

"As soon as the first eclipses are confirmed, we will conduct a large multiple observatory monitoring campaign to capture in detail the structure and composition of this ring system based on the monitoring photometry from the AAVSO."

Coordinates: RA 14 07 47.925 Dec -39 45 42.72 (J2000.0)

More information may be found at

Charts for 1SWASP J140747.93-394542.6 may be created using the AAVSO Variable Star Plotter (VSP) at

Please submit observations to the AAVSO International Database using the name 1SWASP J140747.93-394542.6 or J1407. This campaign is being followed on the AAVSO Observing Campaigns page.

This campaign offers the chance to contribute fundamental knowledge on an intriguing stellar system - if you can participate, please do!

This AAVSO Alert Notice was compiled by Elizabeth O. Waagen.


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