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LSPM J0207+3331
LSPM J0207+3331 is a cold and old white dwarf that hosts a circumstellar disk, located 145 light-years from Earth. It was discovered in October 2018 by a volunteer participating in the Backyard Worlds citizen science project.[1][2] Until 2021 it was the oldest and coldest white dwarf known to host a disk. The white dwarf WD 2317+1830 with a detected disk is at least twice as old and around 2,000 K colder.[3][4] The white dwarf has a radius of 0.011 R☉, which is about 1.2 times the radius of the earth. Because white dwarfs are such dense objects, LSPM J0207 has a mass of about 0.69 M☉. The presence of the Paschen Beta-Line in a near-infrared spectrum from the Keck telescope helped to determine that the atmosphere of LSPM J0207 is dominated by hydrogen (spectral type DA). Due to the inner disk around the white dwarf, it should be expected that the atmosphere has a lot of other elements and that it is a metal-polluted white dwarf. To confirm this hypothesis, it is required to take an optical spectrum of the white dwarf.[5] Debris diskThe star has a circumstellar disk despite being 3 billion years old. The infrared excess in the spectrum is consistent with two rings at different temperatures: an outer colder ring with a temperature of 480 K and an inner ring with a temperature between 550–1400 K. It may be a debris disk created from asteroids broken apart by the star's gravity.[5] The inner disk is optically thick with an inner radius of 0.047 R☉ and an outer radius of 0.21 R☉. The outer disk is optically thin. It is located near the Roche radius at around 0.94 R☉ and has a mass of a small asteroid or comet. This suggests that the outer disk formed relative recently from a tidal disruption of such a small body. If this outer disk is confirmed, it would be the first known dusty white dwarf with a two-component ring system.[5] Alternatively the gap in the disk could be explained by a dense exoplanet orbiting inside the disk and clearing a gap, or a planet orbiting outside the disk and opening a gap via resonant dynamics.[6] Due to the inner edge of the inner disk being located near the sublimation radius of fayalite and iron, it is suggested that the inner disk is composed of these materials. It is however not excluded that forsterite is a component of the inner disk.[6] Models predict only a low rate of asteroids to be disrupted by an old white dwarf. The 1 Gyr simulations by Debes et al. found that only one asteroid per simulation was disrupted 200 Myrs after the white dwarf has formed.[7] The presence of a disk around a 3 Gyr white dwarf sets new demands for models that seek to explain dust around white dwarfs.[5] A survey of 249 white dwarfs to be observed with JWST MIRI at 10 and 15 μm includes LSPM J0207+3331. This might detect the infrared excess coming from the disk in the mid-infrared. The status information in July 2024 showed that it was withdrawn from being observed.[8] See alsoOther old and cold white dwarfs with planetary debris:
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