An Etymological Dictionary of Astronomy and Astrophysics
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→ preplanetary nebula.

→ proto-; → planetary; → nebula.

The fluid substance within the living cell that consists of two major divisions, the cytoplasm and the nucleoplasm (cell nucleus). It is composed mainly of nucleic acids, proteins, lipids, carbohydrates, and inorganic salts.

→ proto- + -plasm, → plasma.

Describing the conditions prior to the formation of the → solar system, or pertaining to the → protostar that became the → Sun.

→ proto- + → solar.

The abundance of a chemical element pertaining to the proto-→ solar nebula from which the → solar system was formed. → CI chondrite; → CAI meteorite.

→ protosolar; → abundance.

A stage in the process of → star formation, after the → gravitational collapse of the dense → pre-stellar core and before the initiation of → nuclear fusion in the central object which will eventually become a star. Protostars are classified into four groups: → Class 0, → Class I, → Class II, and → Class III.

→ proto- + → star.

Of or pertaining to → protostars.

→ proto-; → stellar.

A → gravitational collapse leading to the formation of a → protostar.

→ protostellar; → collapse.

A disk of gas and dust surrounding a → protostar. These structures are rotating → accretion disks through which matter is transferred to protostars.

→ protostellar; → disk.

A high-velocity and highly → collimated jet associated with the earliest phase of → star formation that propagating along the polar axis of the → protostar-→ accretion disk system. Protostellar jets are usually detected in the [S II], [O I], and Hα lines and are therefore referred to as optical jets. They may have more than a parsec in length. Their formation is related to the → magnetohydrodynamics (MHD) of accretion disks. These jets are detected in protostellar sources over a wide range of masses, from the very early stages of formation (sources associated with infalling envelopes whose mass exceeds that of the growing star) all the way to the → classical T Tauri stars, whose envelopes have already dispersed. This phenomenon is thought to play a key role in regulating the star formation process by removing the excess → angular momentum of disk material and enabling matter to flow toward the center. Protostellar winds also provide an important → feedback mechanism between the forming star and the surrounding medium, to which they return mass and energy. Protostellar jets are at the origin of → bipolar outflows. The et sweeps up ambient → molecular cloud material into two thin shells, which manifest themselves as the observed bipolar lobes of → carbon monoxide (CO) emission. Once the molecular cloud material has been swept away (on a timescale of 10⁵ years), the bipolar outflow disappears, leaving the protostellar jet to erratically fire away for a further 10⁶-10⁷ years.

→ protostellar; → jet.

The Sun at its protostellar formation stage, before becoming a main sequence star, nearly 5 billion years ago. The protosun was more luminous than today and larger, with a radius comparable to that of the orbits of the inner planets

→ proto- + → sun.

The original or model on which something is based or formed.
Something that serves to illustrate the typical qualities of a class.

→ proto-; → type.