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Type Ia supernova
abar-now-axtar-e gune-ye Ia
Fr.: supernova de type Ia
A → Type I supernova that presents a singly-ionized silicon (Si II) absorption feature at 6150 Å near peak brightness. Type Ia SNe are believed to result from mass → accretion to a carbon-oxygen → white dwarf in a → close binary system. When the white dwarf mass exceeds the → Chandrasekhar limit, the → degenerate electron pressure can no longer support the accumulated mass and the star collapses in a thermonuclear explosion producing a supernova. The → peak luminosity of SNe Ia is set by the radioactive decay chain 56Ni → 56Co → 56Fe, and the observed photometric correlation between the peak luminosity and the time-scale over which the → light curve decays from its maximum is understood physically as having both the luminosity and → opacity being set by the mass of 56Ni synthesized in the explosion. Type Ia supernovae occur in all types of galaxies. Type Ia SNe are used as → standard candles in determining cosmological distances, after normalizing their light curves with the → Phillips relation.
Type Ib supernova
abar-now-axtar-e gune-ye Ib
Fr.: supernova de type Ia
A → Type I supernova that has neutral helium line (He I) at 5876 Å, and no strong silicon (Si II) absorption feature at 6150 Å. Type Ib supernovae are believed to result from the evolution of → massive stars.
Type Ic supernova
abar-now-axtar-e gune-ye Ic
Fr.: supernova de type Ia
Type II burst
belk-e gune-ye II
Fr.: sursaut de type II
A burst of → X-rays observed toward → low-mass X-ray binary (LMXB)s and characterized by quick succession of bursts with recurrence intervals as short as ~ 7 s. Type II X-ray bursts look similar to → Type I bursts, but they are thought to be related with spasmodic episodes of → accretion.
Type II error
irang-e gune-ye II
Fr.: erreur de type II
Type II migration
kuc-e gune-ye II
Fr.: migration de type II
The → orbital migration of forming → planets that → accrete enough disk material to exceed the critical mass. This type migrates in a gap created in the → protoplanetary disk. Compare with → Type I migration.
Type II supernova
abar-now-axtar-e gune-ye II
Fr.: supernova de type II
A supernova type whose spectrum contains hydrogen lines. Compared with → Type I supernovae, its → light curve has a broader peak at maximum and dies away more rapidly. The magnitudes are smaller, ranging from MV = -12 to -13.5, and the ejecta have lower velocities (about 5,000 km/sec). These supernovae, which result from the final evolution of → massive stars, have three main divisions: → Type II-P, → Type II-L, and → Type II-n.
Type II tail
dom-e gune-ye II
Fr.: queue de type II
Type II-L supernova (SN II-L)
abar-now-axtar-e gune-ye II-L
Fr.: supernova de type II-L
Type II-n supernova (SN II-n)
abar-now-axtar-e gune-ye II-n
Fr.: supernova de type II-n
Type II-P supernova (SN II-P)
abar-now-axtar-e gune-ye II-P
Fr.: supernova de type II-P
A → Type II supernova which reaches a plateau in its → light curve. The vast majority of Type II SNe are characterized by a fast (few days) rise to a flat light curve, most pronounced in the reddest optical bands, with a duration of 80-100 days. This plateau phase is interpreted as the recession of the photosphere as the ejecta expand and cool. The spectra of SNe II-P are typically dominated by strong → P Cygni profiles of hydrogen lines, as well as iron absorption features (for a review, e.g., see Filippenko 1997, ARA&A 35, 309).
Having all or most of the characteristics shared by others of the same kind and therefore suitable as an example of it.
From M.L. typicalis "symbolic," from L.L. typicus "of or pertaining to a type," from Gk. typikos, from typos "impression," from typ(os) + -ikos, → -ic.
Gune-vâr, from guné, → type, + -vâr a suffix meaning "resembling, like" (Mid.Pers. -wâr, Av. -vara, -var, cf. Skt. -vara).
Fr.: U Antliae
A → carbon star of the → asymptotic giant branch type located in the constellation of → Antlia. Its other designations are HIP 51821 (→ Hipparcos Star Catalogue), HD 91793, and HR 4153. U Antliae is an → irregular variable that changes its → visual magnitude between 5.27 and 6.04. About 850 → light-years from Earth, it shines with a → luminosity approximately 8,000 times that of the → solar luminosity and has a → surface temperature 2,800 K. It is surrounded by a complex structure of dust shells. Around 2,700 years ago, U Antliae went through a short period of rapid → mass loss. During this period of only a few hundred years, the material making up the shell seen in the → Atacama Large Millimeter Array (ALMA) data was ejected at high speed (Kerschbaum et al., 2017, A&A 605, A116, arXiv:1708.02915).
Fr.: U Gémeaux
The prototypical and first discovered → cataclysmic variable. It is a → dwarf nova system with a relatively long → orbital period of 4 hr 17 minutes. U Gem undergoes → outbursts on time-scales between 30 and 250 days and shows → grazing occultations. The → accretion disk is partially eclipsed, but the → white dwarf remains visible during mideclipse. The mass of the white dwarf → primary is estimated to be 1.24 Msun, about two times higher than the mass of the → secondary; the → angle of inclination is 69°.7 (P. J. Groot 2001, ApJ 551, L89).
visp-bâšandé, visp-bâš, visp-bâšâ
Existing or being everywhere, especially at the same time; omnipresent.
From L. ubiquitarius, from ubique "everywhere," from ubi "where" + que "any, also, ever."
visp-bâšandegi, visp-bâši, visp-bâšâyi
Fr.: ubiquité, omniprésence
The state or capacity of being everywhere, especially at the same time; omnipresence.
Noun from visp-bâšandé, visp-bâš, visp-bâšâyi, → ubiquitous.
Fr.: système photométrique UBV
A → photometric system which consists of measuring an object's → apparent magnitude through three broad-band filters: the ultraviolet (U) at 3650 Å, the blue (B) at 4400 Å, and the visual (V) in the green-yellow spectral region at 5500 Å. The filter bandwidths are 680, 980, and 890 Å respectively. The system is defined so that for A0 stars B - V = U - B = 0. The system was devised by Harold Johnson (1921-1980) and William Morgan (1906-1994) at Yerkes Observatory. It was extended to the R and I bands centered at 7000 and 9000 Å respectively and later to other infrared bands.
U, B, and V referring to "ultraviolet," "blue," and "visible" respectively; → system.
Short for → unidentified flying object.
Fr.: vision d'OVNI
The act or occasion of catching sight of a UFO.
→ UFO; sighting, from sight, M.E. from O.E. sihth; cf. Dan. sigte, Swed. sigt, Du. zicht, O.H.G. siht, Ger. Sicht, Gesicht, related to see.
Didâr "sight, vision," verbal noun from didan "to see" (Mid.Pers. ditan "to see, regard, catch sight of, contemplate, experience;" O.Pers. dī- "to see;" Av. dā(y)- "to see," didāti "sees;" cf. Skt. dhī- "to perceive, think, ponder; thought, reflection, meditation," dādhye; Gk. dedorka "have seen").
Fr.: ufologie, ovnilogie
A term that describes the collective efforts of those who study → unidentified flying object (UFO) reports.