A disintegrating minor planet transiting a white dwarf

Abstract

Most stars become white dwarfs after they have exhausted their nuclear fuel (the Sun will be one such). Between one-quarter and one-half of white dwarfs have elements heavier than helium in their atmospheres, even though these elements ought to sink rapidly into the stellar interiors (unless they are occasionally replenished). The abundance ratios of heavy elements in the atmospheres of white dwarfs are similar to the ratios in rocky bodies in the Solar System. This fact, together with the existence of warm, dusty debris disks surrounding about four per cent of white dwarfs, suggests that rocky debris from the planetary systems of white-dwarf progenitors occasionally pollutes the atmospheres of the stars. The total accreted mass of this debris is sometimes comparable to the mass of large asteroids in the Solar System. However, rocky, disintegrating bodies around a white dwarf have not yet been observed. Here we report observations of a white dwarf--WD 1145+017--being transited by at least one, and probably several, disintegrating planetesimals, with periods ranging from 4.5 hours to 4.9 hours. The strongest transit signals occur every 4.5 hours and exhibit varying depths (blocking up to 40 per cent of the star's brightness) and asymmetric profiles, indicative of a small object with a cometary tail of dusty effluent material. The star has a dusty debris disk, and the star's spectrum shows prominent lines from heavy elements such as magnesium, aluminium, silicon, calcium, iron, and nickel. This system provides further evidence that the pollution of white dwarfs by heavy elements might originate from disrupted rocky bodies such as asteroids and minor planets.

High-Speed Photometry of the Disintegrating Planetesimals at Wd1145+017: Evidence for Rapid Dynamical Evolution

“…Here we report the first high-speed photometry of the transits at WD 1145+017, which show a dramatic evolution of the system in the seven months since the observations of Vanderburg et al (2015) and Croll et al (2015) and suggest a rapid evolution of the planetesimals and their debris.…”

“…As WD 1145+017 9 also exhibits both a large infrared excess, as well as strong photospheric metal pollution, Vanderburg et al (2015) interpreted the transit events as the signature of debris clouds from a disintegrating planetesimal occulting the white dwarf. Given the detection of multiple periodicities in the K2 light curve, Vanderburg et al (2015) argued for the presence of several, possibly six individual planetesimals.…”

“…As WD 1145+017 9 also exhibits both a large infrared excess, as well as strong photospheric metal pollution, Vanderburg et al (2015) interpreted the transit events as the signature of debris clouds from a disintegrating planetesimal occulting the white dwarf. Given the detection of multiple periodicities in the K2 light curve, Vanderburg et al (2015) argued for the presence of several, possibly six individual planetesimals. Following up WD 1145+017 with ground-based photometry, Vanderburg et al (2015) and Croll et al (2015) detected several relatively short (;10 minutes) and deep (;40%) transit events that did, however, only occasionally repeat at the same phase during subsequent observations.…”

“…Given the detection of multiple periodicities in the K2 light curve, Vanderburg et al (2015) argued for the presence of several, possibly six individual planetesimals. Following up WD 1145+017 with ground-based photometry, Vanderburg et al (2015) and Croll et al (2015) detected several relatively short (;10 minutes) and deep (;40%) transit events that did, however, only occasionally repeat at the same phase during subsequent observations. These optical transits were compatible with the ;4.5 hr period identified in the K2 data.…”

“…Recently, Vanderburg et al (2015) announced the discovery of transits in the K2 light curve of the white dwarf WD 1145+017, recurring every ;4.5 hr, i.e., near the Roche-limit for a strengthless rubble pile. As WD 1145+017 9 also exhibits both a large infrared excess, as well as strong photospheric metal pollution, Vanderburg et al (2015) interpreted the transit events as the signature of debris clouds from a disintegrating planetesimal occulting the white dwarf.…”