An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

Once more; a second time; in return.

M.E., from O.E. ongean "toward, opposite, against," from on "on" + -gegn "against, toward."

Dobâré, from do, → two, + bâr "time, fold," → twice.

In opposition to; contrary to; adverse or hostile to.

M.E. agens, ageynes, from ageyn, ongean "again," from on + gegn "against, toward," → gegenschein.

Patâr from Mid.Pers. paitiyârak, "every thing that counteracts and checks the good powers: adversaries of the evil powers;" Av. paiti-ār- "to advance against," paiti-ārəna- "adversary," from paiti- "against," → counter-, + ar- "to move," → access; cf. Mod.Pers. patyâré "affliction, misery, misfortune; anything ugly, terrific;" Mid.Pers. padirag, patirak "against, counter-," Sogd. patrêt "against, opposite, toward."

A measure of the directivity of a radio telescope. It is the ratio of the amount of power received in the direction the dish is pointing to the smaller amount of power from other directions in the sidelobes.

→ antenna; → gain.

A → post-AGB star that undergoes a last → thermal pulse when it is already on the → white dwarf  → cooling track. The thermal pulse will expand the hot central star, whereby hydrogen will be ingested into the → helium burning shell. This will temporarily return the star to the → AGB phase it has previously left.

→ born; → again; → asymptotic giant branch; → star.

A → planetary nebula which is thought to have experienced a → very late thermal pulse (VLTP) when the central star (→ CSPN) was on the → white dwarf cooling track. The VLTP event occurs when the thermonuclear → hydrogen shell burning has built up a → shell of helium with the critical mass to ignite its → fusion into carbon and oxygen (→ helium shell burning). Since the → white dwarf envelope is shallow, the increase of pressure from this last helium shell flash leads to the ejection of newly processed material inside the old planetary nebula, leaving the stellar core intact. As the stellar envelope expands, its → effective temperature decreases and the star goes back to the → asymptotic giant branch (AGB) region in the → H-R diagram. The subsequent stellar evolution is fast and will return the star back to the → Post-AGB track in the H-R diagram: the envelope of the star contracts, its effective temperature and ionizing photon flux increase, and a new fast stellar wind develops (see, e.g. J. A. Toalá et al. 2015, ApJ 799, 67).

→ born; → again; → planetary; → nebula.

In a → CCD detector, the ratio of the initial number of electrons in a → pixel to the final number of → analog-to-digital units (or counts) reported by camera software. For example, a gain of 1.8 e-/count means that the camera produces 1 count for every 1.8 recorded electrons.

→ charge-coupled device (CCD); → gain.

1) A measure of the → amplification of an electronic device, usually expressed as the ratio of → output power to → input power.
2) → antenna gain.

From M.Fr. gain, from O.Fr. gaaigne, from guaaignier "to obtain," from Germanic *waidanjan "to hunt, plunder," also "to graze, pasture," from P.Gmc. *wartho "hunting ground" (cf. Ger. weide "pasture, pasturage"); PIE base *weiə- "to go after something, strive after."

Bahré, from bahr "part, portion, share, lot;" Av. baxəδra- "portion," from bag- "to attribute, allot," → division.