Fast spectrophotometry of WD1145+017


Change log
Abstract

WD1145+017 is currently the only white dwarf known to exhibit periodic transits of planetary debris as well as absorption lines from circumstellar gas. We present the first simultaneous fast optical spectrophotometry and broad-band photometry of the system, obtained with the Gran Telescopio Canarias (GTC) and the Liverpool Telescope, respectively. The observations spanned 5.5 h, somewhat longer than the 4.5-h orbital period of the debris. Dividing the GTC spectrophotometry into five wavelength bands reveals no significant colour differences, confirming grey transits in the optical.We argue that absorption by an optically thick structure is a plausible alternative explanation for the achromatic nature of the transits that can allow the presence of small-sized (~μm) particles. The longest (87 min) and deepest (50 per cent attenuation) transit recorded in our data exhibits a complex structure around minimum light that can be well modelled by multiple overlapping dust clouds. The strongest circumstellar absorption line, Fe II λ5169, significantly weakens during this transit, with its equivalent width reducing from a mean out-of-transit value of 2 to 1Å in-transit, supporting spatial correlation between the circumstellar gas and dust. Finally, we made use of the Gaia Data Release 2 and archival photometry to determine the white dwarf parameters. Adopting a helium-dominated atmosphere containing traces of hydrogen and metals, and a reddening E(B - V) = 0.01 we find Teff = 15 020 ± 520 K, log g = 8.07 ± 0.07, corresponding to MWD = 0.63 ± 0.05M⊙ and a cooling age of 224 ± 30 Myr.

Description
Keywords
5109 Space Sciences, 5107 Particle and High Energy Physics, 5101 Astronomical Sciences, 51 Physical Sciences
Journal Title
Monthly Notices of the Royal Astronomical Society
Conference Name
Journal ISSN
1365-2966
1365-2966
Volume Title
481
Publisher
Oxford University Press
Sponsorship
Science and Technology Facilities Council (ST/N000927/1)
Science and Technology Facilities Council (ST/J003344/2)
Science and Technology Facilities Council (ST/K003453/1)