Abstract
Many white dwarf stars show signs of having accreted smaller bodies, implying that they may host planetary systems. A small number of these systems contain gaseous debris discs, visible through emission lines. We report a stable 123.4-minute periodic variation in the strength and shape of the Ca ii emission line profiles originating from the debris disc around the white dwarf SDSS J122859.93+104032.9. We interpret this short-period signal as the signature of a solid-body planetesimal held together by its internal strength.
Highlights
25 Gemini Observatory, Northern Operations Center, 670 N
We report a stable 123.4 min periodic variation in the strength and shape of the Ca II emission line profiles originating from the debris disc around the white dwarf SDSS J122859.93+104032.9
Our observations were conducted with the 10.4 m Gran Telescopio Canarias (GTC, on La Palma) with the goal of searching for additional variability on the Keplerian orbital time-scales within the disc, which are of the order of hours [21]
Summary
SDSS J1228+1040 was observed at the 10.4 m GTC in 2017 April 20 & 21 and 2018 March 19, April 10, and May 2 using the OSIRIS spectrograph [38], with the volume-phased holographic R2500I grating, and the data were obtained using 2×2 pixel binning and a readout speed of 200 kHz. The nightly average EW measurements of the 2018 profiles in Fig. S2 (see Table S2) change more than can be explained by variations in the continuum normalisation, revealing variability in the strength of the Ca II triplet on a time-scale of weeks to months. The amplitude of these variations is larger than that of the two-hour signal we discuss in the main text, and cause artifacts in both the phase-folded trailed spectrogram, and the phase-folded EW and blue-to-red ratio curves. We scale the strength of the 2018 EW profiles when producing Fig. 1 & 2 to that of the average strength of the 2018 March 19 data
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