White Dwarf WD-1145+17 "Zombie Star" Consumes Asteroid
Abstract
It has long been suspected that white dwarfs accrete asteroid debris as evidenced by heavy metals in many white dwarf spectra. WD1145 was initially detected in Kepler data as an exoplanet candidate with a repeating 1.3% dip over the course of the Jul-Sep 2014 observing season. Follow-up ground based observations were conducted with professional telescopes during March through May of 2015, and these showed that the Kepler dip must likely consist of deeper and shorter dips which come and go with an uncertain pattern. It was hypothesized that the observations were due to an asteroid in a 4.5 hour orbit. In anticipation of its return to nighttime visibility, major observatories scheduled time starting in 2016 Feb. A pro/am collaboration was formed in late 2015 for amateur observations prior to the 2016 Feb professional observations in order to determine an ephemeris for fade activity for the purpose of scheduling relatively short observations with professional telescopes. The amateur observations began in 2015 Nov, sooner than requested, and they showed that the fade activity level had exploded, becoming 20 times the level measured by Kepler. As many as 13 different fades per 4.5-hour orbit were measured, and these varied in depth from night to night. The amateur project turned into a full assault on the star with as many as 4 amateur telescopes observing on the same night. Continuous monitoring mysteriously showed that the clouds drifted in phase with respect to the dominant period i.e., they have a shorter period than measured by Kepler; this would imply that the orbiting dust clouds were located inside the orbit of the parent planetesimal. The best model indicated that the parent planetesimal was releasing fragments from inside its Hill sphere at the L1 Lagrange point, causing them to fall into an inner orbit. New astrophysics was described for the first time when the team used the diameter of the planetesimal orbit, and the diameter of the drift fragment orbit, to calculate the diameter of the Hill sphere from which the mass of the still unseen planetesimal could be inferred. Additionally, retroactive plotting of the drifting fade events backward in time hinted at a convergence date sometime in 2015 Aug, suggesting that this is when fragments broke away from the planetesimal's L1 end and began the dramatic rise in fade activity; this tentative scenario requires more observational confirmation. Since 2015 Dec the fade activity subsided to 5 times the level Kepler observed, occurring just before the scheduled professional observations. These amateur observations remain the most comprehensive to date.
- Publication:
-
Society for Astronomical Sciences Annual Symposium
- Pub Date:
- May 2016
- Bibcode:
- 2016SASS...35..127K