An Etymological Dictionary of Astronomy and Astrophysics

A peculiar → Mira variable with a → pulsation period of 387 days surrounded by an extended → emission nebula. R Aqr is a → symbiotic  → binary star with a mass-losing, pulsating → red giant and an accreting hot companion with a jet → outflow which ionizes an emission nebula. The orbital period of the R Aqr binary is about 44 years as inferred from periodic phases of reduced brightness observed around 1890, 1933, and 1977. These phases are interpreted as partial obscurations of the mira by the companion with its → accretion disk and the associated gas and dust flows. The inferred orbital period is supported by → radial velocity measurements (Schmid et al., 2018, A&A 602, A53 and references therein).

See also: R, → Beyer designation; → Aquarius.

A peculiar → Mira variable with a → pulsation period of 387 days surrounded by an extended → emission nebula. R Aqr is a → symbiotic  → binary star with a mass-losing, pulsating → red giant and an accreting hot companion with a jet → outflow which ionizes an emission nebula. The orbital period of the R Aqr binary is about 44 years as inferred from periodic phases of reduced brightness observed around 1890, 1933, and 1977. These phases are interpreted as partial obscurations of the mira by the companion with its → accretion disk and the associated gas and dust flows. The inferred orbital period is supported by → radial velocity measurements (Schmid et al., 2018, A&A 602, A53 and references therein).

See also: R, → Beyer designation; → Aquarius.

A → stellar association containing a number of → reflection nebulae. The stars are of low or intermediate mass and young, less than a million years old. They are
still surrounded by patches of dust that reflect and absorb light from the interstellar cloud in which they formed. This type of association was first suggested by Sidney van den Bergh (1966, AJ 71, 900).

See also: R, from → reflection; → association.

A → stellar association containing a number of → reflection nebulae. The stars are of low or intermediate mass and young, less than a million years old. They are
still surrounded by patches of dust that reflect and absorb light from the interstellar cloud in which they formed. This type of association was first suggested by Sidney van den Bergh (1966, AJ 71, 900).

See also: R, from → reflection; → association.

A → nucleosynthesis process in which
→ chemical elements heavier than → zinc are created through the intense bombardment of other elements by → neutrons in rapid succession. The essential feature of the r-process is the release of great numbers of neutrons in a very short time (less than 100 seconds). The r-process is a “rapid” version of the → s-process, occurring in supernova → core collapse and possibly when a → neutron star merges with a → black hole in a → binary star.

See also: r stands for rapid, since the process entails a succession of rapid neutron captures on iron seed nuclei; → process.

A → nucleosynthesis process in which
→ chemical elements heavier than → zinc are created through the intense bombardment of other elements by → neutrons in rapid succession. The essential feature of the r-process is the release of great numbers of neutrons in a very short time (less than 100 seconds). The r-process is a “rapid” version of the → s-process, occurring in supernova → core collapse and possibly when a → neutron star merges with a → black hole in a → binary star.

See also: r stands for rapid, since the process entails a succession of rapid neutron captures on iron seed nuclei; → process.

A spherical → ionization front of → H II regions that moves radially outward from the → exciting star at a velocity much higher than → sound speed in the surrounding cold neutral gas of uniform density (ahead of the front). R-type ionization fronts corresponds to early evolution of H II regions, and will eventually transform into → D-type ionization fronts. If the motion of the front is supersonic relative to the gas behind as well as ahead of the front, the front is referred to as weak R. The strong R front correspond to a large density increase across the front.

See also: R referring to a rarefied gas; → type; → ionization; → front.

A spherical → ionization front of → H II regions that moves radially outward from the → exciting star at a velocity much higher than → sound speed in the surrounding cold neutral gas of uniform density (ahead of the front). R-type ionization fronts corresponds to early evolution of H II regions, and will eventually transform into → D-type ionization fronts. If the motion of the front is supersonic relative to the gas behind as well as ahead of the front, the front is referred to as weak R. The strong R front correspond to a large density increase across the front.

See also: R referring to a rarefied gas; → type; → ionization; → front.

The central object of the → 30 Doradus nebula in the → Large Magellanic Cloud. Also known as HD 38268, it was thought to be a single star of several thousands → solar masses until → speckle interferometry techniques resolved it into a rich and compact star cluster. Recent high-resolution studies have shown that R136 contains 39 known O3 stars, which is more than known to be contained in the rest of the → Milky Way, → LMC,
and → SMC combined. R136 is a prototype “super star cluster,” with an estimated mass of 10⁵ solar masses. Its most massive stars are less than 1-2 million yeas old, while its lower-mass stars formed 4-5 millions years ago.

See also: The Radcliffe serial number 136 (Feast et al. 1960, MNRAS 121, 25).

The central object of the → 30 Doradus nebula in the → Large Magellanic Cloud. Also known as HD 38268, it was thought to be a single star of several thousands → solar masses until → speckle interferometry techniques resolved it into a rich and compact star cluster. Recent high-resolution studies have shown that R136 contains 39 known O3 stars, which is more than known to be contained in the rest of the → Milky Way, → LMC,
and → SMC combined. R136 is a prototype “super star cluster,” with an estimated mass of 10⁵ solar masses. Its most massive stars are less than 1-2 million yeas old, while its lower-mass stars formed 4-5 millions years ago.

See also: The Radcliffe serial number 136 (Feast et al. 1960, MNRAS 121, 25).