CWISE J1249+3621

CWISE J1249+362 is a low-mass hypervelocity star.
CWISE J1249+3621

UKIRT Hemisphere Survey image, showing the motion of CWISE J1249+362
Observation data
Epoch J2000      Equinox J2000
Constellation Canes Venatici
Right ascension 12h 49m 09.08s[1]
Declination +36° 21′ 16″[1]
Characteristics
Evolutionary stage subdwarf
Spectral type sdL1[1]
Apparent magnitude (i) 21.48±0.15[1]
Apparent magnitude (z) 20.01±0.06[1]
Apparent magnitude (y) 19.13±0.05[1]
Astrometry
Radial velocity (Rv)−103±10[1] km/s
Total velocity456±27[1] km/s
Proper motion (μ) RA: 344±5 mas/yr[1]
Dec.: −814±5 mas/yr[1]
Distance408±26 ly
(125±8 pc)[1]
Details[1]
Mass0.082+0.002
−0.003 M☉
Surface gravity (log g)4.4 to 5.1 cgs
Temperature1715 to 2320 K
Metallicity−1.4 to −0.5
Age≥5 Gyr
Other designations
WISEA J124908.94+362121.8, CWISE J124909.08+362116.0

CWISE J1249+362 (CWISE J124909.08+362116.0) is a low-mass hypervelocity star about 408 light-years distant in the constellation Canes Venatici. It has an L spectral type and is either a low-mass red dwarf or a high-mass brown dwarf. It has a speed of 456±27 km/s in the galactic rest frame, near the local escape velocity of the Milky Way.[1]

Discovery

CWISE J1249+362 was first identified in the Backyard Worlds project by the citizen scientists Tom Bickle, Martin Kabatnik, and Austin Rothermich (now astronomer). The astronomers of the project observed the object because its motion and distance suggested a high velocity. The astronomers used NIRES on the Keck Observatory to take a spectrum of the object. The researchers also identify the esdL1 dwarf ULAS J231949.36+044559.5 as an additional candidate hypervelocity star (vtan≈513 km/s) with a low mass.[1]

Physical properties and origin

The object has a distance of 125±8 parsec from the sun and its spectrum is sdL1, with sd noting that it is a cool subdwarf. The star has a high tangential velocity of 524±33 km/s and a high radial velocity of −103±10 km/s. In the galactic rest frame this translates into a speed of 456±27 km/s. It has an estimated mass between 83 and 88 MJ, which would make it a low-mass star near the hydrogen-burning limit. The researchers say that the object does have a 10% probability to be a high-mass brown dwarf because the evolutionary model does not account for potential systematic biases for old low-temperature sources.[1]

The researchers explore different scenarios which could have caused the high velocity of CWISE J1249+362. One possibility is that it originates from the galactic center. The object is currently moving towards the galactic center, so it could be on its return pass. This is however only possible if it is bound to the Milky Way. Another possibility is that it was ejected during a type Ia supernova. In this scenario CWISE J1249+362 would have been in a tight binary with a massive white dwarf, which would have involved mass transfer in a cataclysmic variable star. The predicted ejection speed for this scenario agrees with the speed of CWISE J1249+362. Two other possibilities are that it originates from a dynamical ejection from a globular cluster or ejection from a nearby dwarf galaxy. There are however no globular clusters in the past position of this object. It is unlikely that CWISE J1249+362 is an extragalactic star, because its motion is confined within the galactic plane, which makes an origin within the Milky Way more likely.[1]

More research that involves a direct measurement of its parallax and additional optical and infrared spectra are needed to narrow down its origin. If it originated in a type Ia supernova, its atmosphere could for example be enriched in heavy elements, particularly in nickel.[1]

References

  1. ^ a b c d e f g h i j k l m n o p Burgasser, Adam J.; Gerasimov, Roman; Kremer, Kyle; Brooks, Hunter; Alvarado, Efrain; Schneider, Adam C.; Meisner, Aaron M.; Theissen, Christopher A.; Softich, Emma; Karpoor, Preethi; Bickle, Thomas P.; Kabatnik, Martin; Rothermich, Austin; Caselden, Dan; Kirkpatrick, J. Davy; Faherty, Jacqueline K; Casewell, Sarah L.; Kuchner, Marc J.; Backyard Worlds: Planet 9 Collaboration (2024-08-01). "Discovery of a Hypervelocity L Subdwarf at the Star/Brown Dwarf Mass Limit". The Astrophysical Journal. 971 (1): L25. arXiv:2407.08578. Bibcode:2024ApJ...971L..25B. doi:10.3847/2041-8213/ad6607. ISSN 0004-637X.{{cite journal}}: CS1 maint: numeric names: authors list (link)
  • press-release by NASA
  • press-release by UC San Diego
  • press-release by the W.M. Keck Observatory
  • Artist's simulation of the ejection of CWISE J1249+362 in a type Ia supernova on youtube
  • Artist's simulation of the ejection of CWISE J1249+362 during a close encounter with a binary black hole on vimeo
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