Hamal

Hamal or Hemal (Alpha Arietis / α Ari / 13 Arietis / HD 12929) is the brightest star in the constellation Aries, with apparent magnitude +2.00.

Name

Hamal (حمال) is an Arabic name meaning "ram", used in this culture to designate the entire constellation. Due to this confusion between star and constellation, it can be found referred to as راس حمل, rās al-ħamal, "the ram's head".

Features

Hamal is an orange giant of spectral type K2III or K2IIICa (where “Ca” indicates the presence of calcium lines in its emission spectrum). Including the infrared radiation it emits, it shines with a luminosity 90 times greater than that of the Sun, with a surface temperature of 4590 K. Its metallicity is only 60% of the solar value, and its mass is approximately twice that of the Sun.

Its diameter, as befits a giant star, is 14.7 times bigger than the solar one; this value is obtained from the precise measurement of its angular diameter, 0.00680 seconds of arc. Due to its large size and relative closeness, it is one of the few stars for which the effect of limb dimming has been observed. It appears to be slightly variable, with oscillations in its brightness of 0.05 magnitudes. It is located 66 light years from the Solar System.

Planetary system

In 2011 the discovery of an extrasolar planet, called Alpha Arietis b, around Hamal was announced. It has a minimum mass equivalent to 1.8 times the mass of Jupiter and the semi-major axis of its orbit is 1.2 AU.