WD J2147–4035

WD J2147–4035

Optical+infrared image of WD J2147–4035 (orange star in the center) Credit: Legacy Surveys / D. Lang (Perimeter Institute)
Observation data Epoch J2000      Equinox J2000
Constellation	Grus
Right ascension	21^h 47^m 56.59^s
Declination	−40° 35′ 27.79″
Characteristics
Evolutionary stage	white dwarf
Spectral type	DZQH[1]
Apparent magnitude (G)	19.96[1]
Variable type	rotational variable[1]
Astrometry
Radial velocity (Rv)	80.6 ±17.1[1] km/s
Proper motion (μ)	RA: -84.113 ±0.418 mas/yr[2] Dec.: -112.391 ±0.423 mas/yr[2]
Parallax (π)	35.7904 ± 0.4921 mas[2]
Distance	91 ± 1 ly (27.9 ± 0.4 pc)
Details[1]
Mass	0.69 ±0.02 M☉
Radius	0.01100 ±0.00032 R☉
Surface gravity (log g)	8.195 ±0.042 cgs
Temperature	3048 ±35 K
Rotation	13 hours
Age	10.7 ±0.3 Gyr
Other designations
DES J214756.46-403529.3, WISE J214756.50-403529.2, EQ J2147-4035, Gaia DR2 6584418167391671808
Database references
SIMBAD	data

WD J2147–4035 (DES J214756.46-403529.3) is a very cold white dwarf with a temperature of about 3,050 Kelvin (2780 °C; 5030 °F). It also shows signs of pollution with planetary debris.^[1]

A light curve for WD J2147-4035, adapted from Elms et al. (2022)^[1]

WD J2147–4035 was first identified from Gaia data as a white dwarf candidate in 2019.^[3] In 2021 it was pointed out as an unusual faint white dwarf in the solar neighbourhood. The researchers found it could be extremely old (about 10 Gyrs).^[4] In 2022 results from observations with X-shooter on the Very Large Telescope were published. The object was identified as a white dwarf, likely with a helium-dominated atmosphere. The researchers also detected metal pollution in the form of sodium, lithium, potassium and possibly carbon. The lithium line shows Zeeman splitting, which indicates that WD J2147–4035 is a magnetic white dwarf. The researchers measure a magnetic field strength of 0.55 ±0.03 Megagauss. The magnetism can lead to inhomogeneous brightness distribution and the TESS light curve shows that the white dwarf has a rotation period of around 13 hours. The nature of the accreted parent body is unclear as of September 2024.^[1]

WD J2147–4035 was once a main-sequence star with a mass of 2.47 ±0.22 M_☉, which had a lifetime of about 500 Myrs. Once the star became an AGB star, it lost mass and became a white dwarf with a mass of 0.69 ±0.02 M_☉. The white dwarf existed for 10.21 ±0.22 Gyrs, meaning the total age is 10.7 ±0.3 Gyrs.^[1]

Cold white dwarfs are often strongly affected by collision induced absorption (CIA) of hydrogen. This can lead to faint optical red and infrared brightness. These white dwarfs are also called IR-faint white dwarfs. WD J2147–4035 is however very red (r-z=2.29 mag) which is seen as evidence that it only has a low hydrogen to helium ratio, resulting in very mild CIA and therefore giving it the distinct orange color.^[1]

See also

• List of exoplanets and planetary debris around white dwarfs
• ESO 439-26 is a cold white dwarf, once thought to be the faintest

Other cool metal-polluted white dwarfs:

• WD J2356−209
• WD 2317+1830

References

1. Elms, Abbigail K.; Tremblay, Pier-Emmanuel; Gänsicke, Boris T.; Koester, Detlev; Hollands, Mark A.; Gentile Fusillo, Nicola Pietro; Cunningham, Tim; Apps, Kevin (2022-12-01). "Spectral analysis of ultra-cool white dwarfs polluted by planetary debris". Monthly Notices of the Royal Astronomical Society. 517 (3): 4557–4574. arXiv:2206.05258. Bibcode:2022MNRAS.517.4557E. doi:10.1093/mnras/stac2908. ISSN 0035-8711.
2. Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
3. Torres, S.; Cantero, C.; Rebassa-Mansergas, A.; Skorobogatov, G.; Jiménez-Esteban, F. M.; Solano, E. (2019-06-01). "Random Forest identification of the thin disc, thick disc, and halo Gaia-DR2 white dwarf population". Monthly Notices of the Royal Astronomical Society. 485 (4): 5573–5589. arXiv:1903.07362. Bibcode:2019MNRAS.485.5573T. doi:10.1093/mnras/stz814. ISSN 0035-8711.
4. Apps, Kevin; Smart, R. L.; Silvotti, Roberto (2021-10-01). "Discovery of a Uniquely Cool and Compact Source at 28 pc from the Sun". Research Notes of the American Astronomical Society. 5 (10): 229. arXiv:2109.12707. Bibcode:2021RNAAS...5..229A. doi:10.3847/2515-5172/ac2df2. ISSN 2515-5172.