Fr.: objet stellaire
Fr.: objet sous-stellaire
Thorne-Zytkow object (TŻO)
Fr.: objet Thorne-Żytkow
A theoretical class of → stellar objects in which a → neutron star core is surrounded by a large and diffuse envelope. TŻOs are expected to form as a result of the evolution of two → massive stars in a → close binary, with the neutron star forming when the more massive star explodes as a → supernova. During subsequent evolution of the system, the expanding envelope of the companion may lead to a common envelope state and the spiral-in of the neutron star into the core of its companion. Alternately, a TŻO may be produced when a newly-formed neutron star receives a supernova "kick" velocity in the direction of its companion and becomes embedded. Supergiant TŻOs are predicted to be almost identical in appearance to → red supergiants (RSGs). The best features that can be used at present to distinguish TŻOs from the general RSG population are the unusually strong → heavy element and → lithium lines present in their spectra, products of the star's fully → convective envelope linking the → photosphere with the extraordinarily hot burning region in the vicinity of the neutron star core. These objects are thought to be extremely rare, with as few as 20-200 of them predicted to exist in the Galaxy at present, though some authors have doubted whether such an object could survive the merger with the envelope intact. A candidate is HV 2112 (Levesque et al., 2014, MNRAS, arXiv:1406.0001; Beasor et al., 2018, MNRAS, arXiv:1806.07399).
Thorne K. S., Żytkow A., 1975, ApJ 199, L19.
trans-Neptunian object (TNO)
Fr.: objet trans-neptunien
A member of a class of objects in orbit around the Sun at a larger distance than the distance between Neptune and the Sun. This includes several → dwarf planets, such as → Eris, → Pluto, and many small solar system bodies.
unidentified flying object (UFO)
barâxt-e parande-ye nâ-idânidé, padide-ye havâ-fazâyi-ye nâ-idânidé
Fr.: Objet Volant Non Identifié (OVNI)
Any flying object or phenomenon that cannot be identified by the observer.
young stellar object (YSO)
barâxt-e setâreyi-ye javân
Fr.: objet stellaire jeune
Any star that has evolved past the → protostar stage, but has not yet arrived on the → main sequence. There is a variety of YSOs depending on their age, mass, and environment, including → Herbig stars, → T Tauri stars, and, in general, compact infrared sources embedded in molecular clouds.
→ young; → stellar; → object.