LP 40-365
Star in the constellation Ursa Minor
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LP 40-365 is a low-mass white dwarf star in the constellation Ursa Minor. It travels at high speed through the Milky Way and has a very unusual elemental composition, lacking hydrogen, helium or carbon. It may have been produced in a subluminous Type Iax supernova that failed to destroy its host star totally.[2][7][8] The "LP" name is derived from the Luyten-Palomar proper motion catalogue in which it appeared in the 1960s.[9] Another catalog name for this star is "GD 492".[6] The star was cataloged as a Giclas object with the designation "GD 492" being assigned by Henry Giclas in 1970.[10]
Tangential movement of LP 40-365 between 1955 and 1995. The field of view is 8 × 8 arcminutes. Credit: Digitized Sky Survey | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Ursa Minor |
| Right ascension | 14h 06m 35.45s[1] |
| Declination | +74° 18′ 58.0″[1] |
| Apparent magnitude (V) | 15.51 ± 0.09[2] |
| Characteristics | |
| Spectral type | D[2] |
| Astrometry | |
| Radial velocity (Rv) | 498[2] km/s |
| Total velocity | ~546[2] km/s |
| Proper motion (μ) | RA: −49.569±0.029 mas/yr[3] Dec.: 148.642±0.029 mas/yr[3] |
| Parallax (π) | 1.6375±0.0257 mas[3] |
| Distance | 1,990 ± 30 ly (611 ± 10 pc) |
| Absolute magnitude (MV) | 8.14+0.60 −0.90[2] |
| Details[4] | |
| Mass | 0.28+0.28 −0.14 M☉ |
| Radius | 0.16±0.01 R☉ |
| Surface gravity (log g) | 5.50±0.30 cgs |
| Temperature | 9800±300 K |
| Rotation | 8.914122 ± 0.000020 hours[5] |
| Rotational velocity (v sin i) | 30.5 ± 2.0[2] km/s |
| Other designations | |
| 2MASS J14063545+7418579[6] | |
| Database references | |
| SIMBAD | data |
The abundance analysis of LP 40-365 did show that the atmosphere is dominated by oxygen and neon, with substantial traces of intermediate-mass elements such as aluminium and silicon. The white dwarf core on the other hand is likely composed of a mix of carbon, oxygen and neon.[2] Additional observations did suggest the atmosphere is dominated by helium. This is in contrast to the previous analysis.[11] Later helium was excluded with high quality spectra for other similar stars and therefore a oxygen-neon dominated atmosphere is favoured for LP 40-365. Neon has the highest mass fraction of below 60%, oxygen has a mass fraction of around 30%, followed by around 8% of magnesium.[nb 1] 11 other elements are detected in the atmosphere, but they make up 1–2% of the mass. The atmospheric composition is a strong indicator of partial carbon-, oxygen- and silicon-burning, likely connected to a thermonuclear explosion that did not entirely disrupt the progenitor. The origin could be either a peculiar Type Iax or electron-capture supernova. In the future LP 40-365 and similar objects are predicted to evolve into oxygen-rich white dwarfs.[4]
The new parallax with Gaia helped to refine the radius to 18% of the radius of the Sun. This is 15 times larger than other white dwarfs. The new kinematic analysis showed that LP 40-365 is leaving the Milky Way with 1.5 times the escape velocity of the solar neighbourhood. The object crossed the galactic disk 5.3±0.5 Ma ago in the direction of Carina, likely coming from beneath the plane. The team estimated that it was ejected with a speed of 600 km/s from its progenitor binary. This speed suggests a close binary consisting of a white dwarf and a helium-star donor. This donor-star had a mass of 0.8 to 1.32 M☉ and the binary had an orbital period of 30 to 60 minutes. Today LP 40-365 has a rest-frame velocity of 852±10 km/s.[12] Variability was detected with the help of TESS, Hubble and WISE. TESS in the optical showed an amplitude of 1.0%, Hubble in the ultraviolet showed an amplitude of 5.8% and WISE in the infrared shows an amplitude of around 2.2%. The rotation period was measured at 8.914 hours. The researchers suggest the variations are caused by an inhomogeneity on the surface, rotating in and out of view.[5]
Additional stars with similar characteristics are called LP 40-365 stars, making LP 40-365 the prototype of chemically peculiar runaway stars that are the survivors of thermonuclear explosions.[4]
Notes
- These values are measured from figure 13 and are therefore less accurate. General values for LP 40-365-like stars are given in section 5.1.2: Ne (59–65%), O (29–31%), Mg (3–9%).
