Eltanin (Gamma Draconis)
The brightest star in the constellation → Draco, with a visual magnitude of V = 2.23 and color B - V +1.52. It is a cool (4000 K) → giant star of spectral Type K5 III, lying 148 → light-years. Gamma Draconis has a luminosity 600 times that of the Sun and a diameter 50 times that of the Sun. It crosses the sky near the zenith point for England, a nd this was the reason why James Bradley (1693-1762) observed γ Draconis when he was trying to detect parallax and so calculate the distance. He found that the star undergoes a yearly shift of a form quite different from that expected from parallax. In a 1728 paper, Bradley announced his discovery and explained the effect as due to the → aberration of starlight . Variant names: Etamin, Etanin; Ettanin, other designations: HR 6705, HD 164058.
From Ar. At-Tinnin (
Fermi Gamma-ray Space Telescope
Durbin-e fazâyi-ye partowhâ-ye gâmâ Fermi
Fr.: Télescope spatial à rayons gamma Fermi
A space observatory, formerly named GLAST, devoted to the study of → gamma rays emitted from astrophysical objects. Developed by NASA in collaboration with the U.S. Department of Energy, along with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden, and the United States, Fermi was launched on June 11, 2008. The main instrument, the Large Area Telescope (LAT), is an imaging → camera covering the energy range from about 20 → MeV to more than 300 → GeV. Such gamma rays are emitted only in the most extreme conditions, by particles moving very nearly at the → speed of light. The LAT's → field of view covers about 20% of the sky at any time, and it scans continuously, covering the whole sky every three hours. Another instrument, the Gamma-ray Burst Monitor (GBM) has a field of view several times larger than the LAT and provides → spectral coverage of → gamma-ray burst that extends from the lower limit of the LAT down to 10 → keV.
1) The third letter of the Greek alphabet (γ, Γ).
The third letter of the Gk. alphabet, from Gk. gamma, from Phoenician gimel.
Fr.: γ Cephei
A bright, third → magnitude (3.22) → giant star of → spectral type K1, also called → Errai, HR 8974, HIP 116727, and HD 222404. γCephei has a → surface temperature of 4920 K a mass of 1.40 Msun, a → luminosity 10.6 solar, and a radius 4.8 solar. Its distance is estimated to be 45 → light-years. γ Cephei will become the → Pole Star in about 2,000 years. γ Cephei has a low mass → companion (B), a main → main sequence star of spectral type M4 V with a mass of 0.4 Msun. It orbits the → primary star every 67.5 years. An → extrasolar planet. (γ Cephe b) has been discovered orbiting the main star.
Fr.: γ Cygni
The star → Sadr.
tabâhi-ye gâmâ (#)
Fr.: désintégration gamma
Fr.: mécanisme γ
A process which reinforces the → kappa mechanism in a → partial ionization zone. Because the temperature in the partial ionization zone is lower than in the adjacent stellar layers, heat tends to flow into the zone during compression, prompting further ionization.
partowhâ-ye gâmmâ (#)
Fr.: rayons gamma
axtaršenâsi-ye partowhâ-ye gâmmâ (#)
Fr.: astronomie en rayons gamma
gamma-ray burst (GRB)
belk-e partowhâ-ye gâmmâ
Fr.: sursaut de rayons gamma
An intense discharge of → gamma rays, which range in duration from tenth of a second to tens of seconds and occur from sources widely distributed over the sky. The radio wave → afterglow from the → burst can last more than a year, making long-term observations of the sources possible. The favored hypothesis is that they are produced by a relativistic jet created by the merger of two → compact objects (specifically two → neutron stars or a neutron star and a → black hole). Mergers of this kind are also expected to create significant quantities of neutron-rich radioactive species, whose decay should result in a faint → transient, known as a → kilonova, in the days following the burst. Indeed, it is speculated that this mechanism may be the predominant source of stable → r-process elements in the Universe. Recent calculations suggest that much of the kilonova energy should appear in the → near-infrared spectral range, because of the high optical opacity created by these heavy r-process elements (Tanvir et al., 2017, Nature 500, 547).
belkvar-e partow-e gâmmâ
Fr.: source à sursaut gamma
xan-e partowhâ-ye gâmma
Fr.: source de rayons gamma
1) An astronomical object that emits → gamma rays.
Fr.: γ2 Velorum
The closest → Wolf-Rayet star, located at 336 → parsecs. Also known as HR 3207, HD 68273, and WR 111. γ2 Velorum is composed of a → WC8 component in a → close binary system with an → O star in a 78.5 day orbit (see, e.g., Lamberts et al., 2017, arXiv: 1701.01124).
GCN: The Gamma-ray Coordinates Network
turbast-e hamârâhâ-ye partowhâ-ye gâmâ
Fr.: Le réseau des coordonnées des rayons gamma
A follow-up community network concerned with → gamma-ray burst (GRB)s. It deals with: 1) locations of GRBs and other → transients detected by spacecraft (most in real-time while the GRB is still bursting), and 2) reports of follow-up observations (the Circulars) made by ground-based and space-based optical, radio, X-ray, TeV, and other observers. The GCN Circulars allow the GRB follow-up community to make optimum use of its limited resources (labor and telescope time) by communicating what has already been done or will soon be done.
soft gamma repeater (SGR)
bâzgaršgar-e gâmmâ-ye narm
Fr.: répéteur gamma mou
A member of a small class of objects which emit intense bursts of → gamma rays and → X-rays (> 100 keV) at irregular intervals. The bursts last for some 100 milli-seconds. It is conjectured that they are → magnetars. See also → starquake.
soft gamma-ray repeater (SGR)
bâzgaršgar-e partowhâ-ye gâmmâ-ye narm
Fr.: répéteur des rayons gamma mous
Same as → soft gamma repeater (SGR).