LSPM J0207+3331

LSPM J0207+3331 is, as of 2019, the oldest and coldest known white dwarf star to host 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]

LSPM J0207+3331

Artist's impression
Credit: NASA’s Goddard Space Flight Center/Scott Wiessinger
Observation data
Epoch J2000      Equinox J2000
Constellation Triangulum
Right ascension 02h 07m 33.8059837915s
Declination +33 31 29.534350702
Characteristics
Evolutionary stage white dwarf
Spectral type DA
Apparent magnitude (g) 17.86 ± 0.02
Apparent magnitude (r) 17.49 ± 0.02
Apparent magnitude (i) 17.34 ± 0.02
Apparent magnitude (J) 16.6±0.1
Astrometry
Parallax (π)22.44 ± 0.20 mas
Distance145 ± 1 ly
(44.6 ± 0.4 pc)
Details
Mass0.69+0.01
−0.02 M☉
Radius0.011 R☉
Surface gravity (log g)8.16±0.03 cgs
Temperature6120+48
−57 K
Age3±0.2 Gyr
Other designations
2MASS J02073383+3331296, Gaia DR2 325899163483416704
Database references
SIMBADdata

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 the white dwarf is a metal-polluted white dwarf. To confirm this hypothesis, it is required to take an optical spectrum of the white dwarf.[3]

Debris Disk

The 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.[3]

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.[3] 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.[4]

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.[4]

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.[5] The presence of a disk around a 3 Gyr white dwarf sets new demands for models that seek to explain dust around white dwarfs.[3]

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.[6]

References
  1. "Volunteer Discovers Record-Setting White Dwarf Star". NASA.gov. 19 February 2019. Retrieved 22 February 2019.
  2. "Citizen Scientists Invited to Join Quest for New Worlds". NOAO. Retrieved 22 February 2019.
  3. Debes, John H.; Thevenot, Melina; Kuchner, Marc; Burgasser, Adam; Schneider, Adam; Meisner, Aaron; Gagne, Jonathan; Faherty, Jaqueline K.; Rees, Jon M.; Allen, Michaela; Caselden, Dan; Cushing, Michael; Wisniewski, John; Allers, Katelyn; The Backyard Worlds: Planet 9 Collaboration; The Disk Detective Collaboration (2019). "A 3 Gyr White Dwarf with Warm Dust Discovered via the Backyard Worlds: Planet 9 Citizen Science Project". The Astrophysical Journal. 872 (2): L25. arXiv:1902.07073. Bibcode:2019ApJ...872L..25D. doi:10.3847/2041-8213/ab0426. S2CID 119359995.
  4. Steckloff, Jordan K.; Debes, John; Steele, Amy; Johnson, Brandon; Adams, Elisabeth R.; Jacobson, Seth A.; Springmann, Alessondra (2021-04-28). "How Sublimation Delays the Onset of Dusty Debris Disk Formation around White Dwarf Stars". The Astrophysical Journal Letters. 913 (2): L31. arXiv:2104.14035. Bibcode:2021ApJ...913L..31S. doi:10.3847/2041-8213/abfd39. PMC 8740607. PMID 35003618.
  5. Debes, John H.; Walsh, Kevin J.; Stark, Christopher (2012-03-01). "The Link between Planetary Systems, Dusty White Dwarfs, and Metal-polluted White Dwarfs". The Astrophysical Journal. 747 (2): 148. arXiv:1201.0756. Bibcode:2012ApJ...747..148D. doi:10.1088/0004-637X/747/2/148. ISSN 0004-637X. S2CID 118688656.
  6. "Program Information - SURVEY 3964". STScI. Retrieved 2023-08-28.
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