Browsing by Author "Gansicke, B. T."

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    A DUSTY COMPONENT TO THE GASEOUS DEBRIS DISK AROUND THE WHITE DWARF SDSS J1228+1040
    (2009) Brinkworth, C. S.; Gansicke, B. T.; Marsh, T. R.; Hoard, D. W.; Tappert, C.
    We present Infrared Spectrometer And Array Camera (ISAAC) spectroscopy and ISAAC, UKIDSS, and Spitzer Space Telescope broadband photometry of SDSS J1228+1040-a white dwarf for which evidence of a gaseous metal-rich circumstellar disk has previously been found from optical emission lines. The data show a clear excess in the near- and mid-infrared (IR), providing compelling evidence for the presence of dust in addition to the previously identified gaseous debris disk around the star. The IR excess can be modeled in terms of an optically thick but geometrically thin disk. We find that the inner disk temperatures must be relatively high (similar to 1700 K) in order to fit the spectral energy distribution in the near- IR. These data provide the first evidence for the coexistence of both gas and dust in a disk around a white dwarf, and show that their presence is possible even around moderately hot (similar to 22,000 K) stars.
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    The White Dwarf Binary Pathways Survey -III. Contamination from hierarchical triples containing a white dwarf
    (2020) Lagos, F.; Schreiber, M. R.; Parsons, S. G.; Zurlo, A.; Mesa, D.; Gansicke, B. T.; Brahm, R.; Caceres, C.; Canovas, H.; Hernandez, M-S; Jordan, A.; Koester, D.; Schmidtobreick, L.; Tappert, C.; Zorotovic, M.
    The White Dwarf Binary Pathways Survey aims at increasing the number of known detached A, F, G, and K main-sequence stars in close orbits with white dwarf companions (WD+AFGK binaries) to refine our understanding about compact binary evolution and the nature of Supernova Ia progenitors. These close WD+AFGK binary stars are expected to form through common envelope evolution, in which tidal forces tend to circularize the orbit. However, some of the identified WD+AFGK binary candidates show eccentric orbits, indicating that these systems are either formed through a different mechanism or perhaps they are not close WD+AFGK binaries. We observed one of these eccentric WD+AFGK binaries with SPHERE and find that the system TYC 7218-934-1 is in fact a triple system where the WD is a distant companion. The inner binary likely consists of the G-type star plus an unseen low-mass companion in an eccentric orbit. Based on this finding, we estimate the fraction of triple systems that could contaminate the WD+AFGK sample. We find that less than 15 per cent of our targets with orbital periods shorter than 100 d might be hierarchical triples.
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    WD 1856 b: a close giant planet around a white dwarf that could have survived a common envelope phase
    (2021) Lagos, F.; Schreiber, M. R.; Zorotovic, M.; Gansicke, B. T.; Ronco, M. P.; Hamers, Adrian S.
    The discovery of a giant planet candidate orbiting the white dwarf WD 1856+534 with an orbital period of 1.4 d poses the questions of how the planet reached its current position. We here reconstruct the evolutionary history of the system assuming common envelope evolution as the main mechanism that brought the planet to its current position. We find that common envelope evolution can explain the present configuration if it was initiated when the host star was on the asymptotic giant branch, the separation of the planet at the onset of mass transfer was in the range 1.69-2.35 au, and if in addition to the orbital energy of the surviving planet either recombination energy stored in the envelope or another source of additional energy contributed to expelling the envelope. We also discuss the evolution of the planet prior to and following common envelope evolution. Finally, we find that if the system formed through common envelope evolution, its total age is in agreement with its membership to the Galactic thin disc. We therefore conclude that common envelope evolution is at least as likely as alternative formation scenarios previously suggested such as planet-planet scattering or Kozai-Lidov oscillations.