An Etymological Dictionary of Astronomy and Astrophysics
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Of a number, not divisible by two.
A function such as f(x) with the property that f(-x) = - f(x) for any value of x; e.g. sin(x).

From M.E. odde, from O.N. oddi "odd (number)."

Tâq, related to tak "single, alone", from Mid.Pers. tak, tâg "single, alone," maybe related to tâi, tâ "unit, piece."

Nucleus which contains an odd number of protons and an even number of neutrons.

→ odd; → even; → nucleus.

Nucleus which contains an odd number of both protons and neutrons.

→ odd; → nucleus.

The science of → wines. Same as enology.

From Gk. oeno-, from oinos cognate with → wine.

Bâdešenâsi, from bâdé, bâda "wine," from Mid.Pers. bâtak "wine," + -šenâsi, → -logy.

The unit of magnitude of magnetic field strength or magnetic intensity in c.g.s. units, i.e. the force in dynes which a unit magnetic pole would experience at any point in a magnetic field.

In honor of Hans Christian Ørsted (1777-1851), the Danish physicist and philosopher, who was the first to notice the interaction of electric current and the magnetic needle (1819) thereby initiating the study of electromagnetism.

An → O star whose spectrum displays strong N III 4634-4640-4642 emission and strong He II 4686 emission. The N III lines are always much stronger than C III 4647-4650-4651 when the latter are present. Historically, Of stars were considered to belong to the peculiar category, hence the f notation (see below). In his thesis work, Walborn (1971, ApJS 23, 257) removed them from that category and established them as the normal O-type → supergiants. He also used the notation ((f)), (f), and f to describe the progression from strong He II 4686 absorption, through weakened/absent, to emission, respectively, correlated with increasing N III emission strength, subsequently showing that it is a luminosity sequence -- the first such for stars earlier than O9.

The reason for the Of designation is that the letters Oa-Oe were used in the original Harvard classification to denote various types of → Wolf-Rayet and OB spectra. Therefore Of was the next available when Plaskett and Pearce (1931, Pub. Dominion Ap. Obs 5, 99) wished to distinguish O-type spectra with selective emission in N III 4634-4640-4642 and He II 4686 ("selective" because other lines from the same ions appear in absorption); → star.

A → massive star spectrum whose principal defining characteristics is the presence of C III 4647, 4650, 4651 emission lines with strength comparable to that of N III 4634, 4640, 4642. This category was introduced by Walborn (1972) to describe two well-known peculiar stars, HD 108 and HD 148937. → Of star

→ Of star; the question mark was intended to denote doubt that these stars are normal Of supergiants; p for "peculiar."

(adverb & preposition) From a place or position; at a distance in space or time. So as to be separated from support.

M.E., from O.E. of "away, away from;" cf. Du. af "off, down," Ger. ab "off, from, down;" PIE *apo- "off, away," → apo-.

Away from a place.

→ off; cognate with Av. and O.Pers. apā "away from, from," as below.

Ap-, from apâ-, from Av. and O.Pers. apā "away from, from;" cf. Skt. apa "away, off;" L. ab- "from, away;" Hittite appa; Gothic af-; Ger. ab-; E. of, as above; PIE base *apo- "off, away"

An → optical system in which the → optical axis of the → aperture is not coincident with the mechanical center of the aperture.

→ off; → axis; → optical; → system.

Of computers, operating independently of, or disconnected from, an associated computer.

→ off; → line.

An observation when the telescope is pointed away from the source in order to measure the sky background contribution.

→ off-; → source; → observation.

1) Cause to feel upset, annoyed, or resentful.
2) Commit an illegal act; break a commonly accepted rule or principle (OxfordDictionaries.com).

M.E. offenden, from O.Fr. ofendre "transgress, antagonize," and directly from L. offendere "to hit, strike against," figuratively "to stumble, commit a fault, displease," from assimilated form of ob "in front of against" + -fendere "to strike, push," from PIE root *g^when- "to strike, kill;" cf. Av. -γna- "slaying," → murder.

Âfandidan, from âfand "strife, war," probably from Proto-Iranian *â-fanda-, from prefix *â- + *fanda-, from *fan- "to move;" cf. Yazghulami fin-/fud "to descend, come down," fəndan- "to bring down;" Roshani sifan-, Bartangi sifân- "to rise;" Skt. phan- "to jump" (Cheung 2007).

A person who commits an illegal act; a person or thing that does something wrong or causes problems (OxfordDictionaries.com).

→ offend; → -er.

1) A breach of a law or rule; an illegal act.
2) Annoyance or resentment brought about by a perceived insult to or disregard for oneself.
3) The action of attacking someone or something (OxfordDictionaries.com).

M.E. offence, offense, from O.Fr. ofense and directly from L. offensa "an offense, affront, crime," literally "a striking against," noun use of fem. p.p. of offendere, → offend.

1) Causing resentful displeasure; highly irritating, angering, or annoying.
2) The position or attitude of aggression or attack (Dictionary.com).

→ offense; → -ive.

1) A shift in the pointing position of a telescope with respect to a reference position.
2) Another term for the → bias in → CCD detectors.
3) Surveying: A short distance measured perpendicularly from a main survey line.

→ off- + → set.

Ap-, → off-; + neh present stem of nehâdan "to place, put; to set" Mid.Pers. nihâtan; Av. ni- "down; below; into," → ni-, + dā- "to put; to establish; to give," dadāiti "he gives;" cf. Skt. dadāti "he gives;" Gk. didomi "I give;" L. do "I give;" PIE base *do- "to give."

Guiding an astronomical exposure on a star, when the object of interest is nearby, but invisible.

→ offset; → guiding.

A small class of evolved → massive stars showing spectral properties intermediate between those of → Of star and → WN Wolf-Rayet stars. Several of them have been found to possess non-spherical nitrogen-rich circumstellar nebulae. Ofpe/WN9 stars are considered to be transition objects between Of and W-R stars. This type of stars was first identified by Walborn (1982), who introduced the classification Ofpe/WN9, indicating that the stars could not be classified solely as Of stars, nor as WNL stars. Ofpe/WN9 stars have been found in the → Milky Way, the → Large Magellanic Cloud, → M31, and M33. Currently 10 Ofpe/WN9 stars are known in the LMC. Observational evidence suggests a close relationship between the class of → LBVs and the Ofpe/WN9 stars. A notable example is the prototype Ofpe/WN9 star R127 in the LMC that became an LBV on a time-scale of the order of a year. The possibility of such a relationship has been explored by Smith et al. (1994), who proposed that some LBVs show spectral morphologies that make them appear as an extension of the WN sequence toward later spectral types. Hence, they reclassified Ofpe/WN9 stars as WN10-11.

Ofpe, from → Of star; p for "peculiar;" e refers to the presence of other emission lines in addition to the Of ones, mainly H and He I, although also Si III. This peculiar class in the LMC was first described by Walborn (1977, ApJ 215, 53), where he called them "O Iafpe extr" based on the most similar Galactic objects known at that time. Subsequently Walborn (1983, ApJ 256, 452) and Bohannan & Walborn (1989, PASP 101, 520) suggested an extension of the WN sequence and/or transition between Of and WN. This nomenclature Ofpe/WN9 has been rather widely adopted. Later on, Smith et al. (1994) broke the Ofpe/WN9 and related Galactic types into WN10-11 subtypes to include this group of emission line stars.

Many times; frequently; in many cases.

M.E. oftin, from O.E. oft "often, frequently," akin to cognates: O.Frisian ofta, Danish ofte, O.H.G. ofto, Ger. oft, of unknown origin.

Basvân, from bas "many, much," → frequency, + -vân on the model of farâvân, → abundance.