Delta² Lyrae (δ² Lyr) is a 4th

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

star in the constellation

Lyra , from ; pronounced: ) is a small constellation. It is one of the 48 listed by the 2nd century astronomer Ptolemy, and is one of the modern 88 constellations recognized by the International Astronomical Union. Lyra was often represented on star ...

, approximately 770

light year A light-year, alternatively spelled light year (ly or lyr), is a unit of length used to express astronomical distance, astronomical distances and is equal to exactly , which is approximately 9.46 trillion km or 5.88 trillion mi. As defined by t ...

s away from

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

. It is visible to the

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. It is one of the M4II spectral standard stars.

Characteristics

It began life as a hot blue main sequence star, but now is a large cool

asymptotic giant branch The asymptotic giant branch (AGB) is a region of the Hertzsprung–Russell diagram populated by evolved cool luminous stars. This is a period of stellar evolution undertaken by all low- to intermediate-mass stars (about 0.5 to 8 solar masses) lat ...

star with a degenerate carbon-oxygen core. It is a semi-regular

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes systematically with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are ...

that has its brightness change by 0.2 magnitudes over an ill-defined period. Delta² Lyrae was a star when still in the

main sequence In astronomy, the main sequence is a classification of stars which appear on plots of stellar color index, color versus absolute magnitude, brightness as a continuous and distinctive band. Stars on this band are known as main-sequence stars or d ...

, but due to

stellar mass loss Stellar mass loss is a phenomenon observed in stars by which stars lose some mass over their lives. Mass loss can be caused by triggering events that cause the sudden ejection of a large portion of the star's mass. It can also occur when a star g ...

it has lost 0.5 solar masses. The star's

photosphere The photosphere is a star's outer shell from which light is radiated. It extends into a star's surface until the plasma becomes opaque, equivalent to an optical depth of approximately , or equivalently, a depth from which 50% of light will esc ...

has expanded to 290 times the size of the Sun, and is now radiating 10,200 times the

luminosity of the Sun The solar luminosity () is a unit of radiant flux ( power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars, galaxies and other celestial objects in terms of the output of the Sun. One nominal s ...

. It has cooled to , giving Delta² Lyrae a reddish hue typical of

M-type star In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

It is the brightest member of the scattered

open cluster An open cluster is a type of star cluster made of tens to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way galaxy, and ...

Stephenson 1 The Delta Lyrae cluster or Stephenson 1 is a sparse open cluster of stars located about 1,220 light years away in the northern constellation of Lyra. Centered on the bright star Delta2 Lyrae for which it is named but not a member like Delt ...

, also known as the δ Lyrae Cluster. Other known members include δ¹ Lyrae, a handful of 8th-9th magnitudes stars, and at least thirty other stars down to 14th magnitude.

Variability

δ² Lyrae is a

, probably a

semiregular variable In astronomy, a semiregular variable star, a type of variable star, is a Red giant, giant or supergiant of intermediate and late (cooler) spectral type. It shows considerable periodicity in its light changes, accompanied or sometimes interrupted b ...

. It has a magnitude range of 4.22 to 4.33.

Companion stars

Multiple star catalogues list several companions to δ² Lyrae, with designations such as

ADS" \n\nads.txt (Authorized Digital Sellers) is an initiative from IAB Technology Laboratory. It specifies a text file that companies can host on their web servers, listing the other companies authorized to sell their products or services. This is des ...

11825. Two of them are a close pair of 10th magnitude stars about 87" from δ², designated components B and C. The spectral type of the pair suggests that they are at the same distance as Delta² Lyrae, which could mean that the three stars form a

triple Triple is used in several contexts to mean "threefold" or a " treble": Sports * Triple (baseball), a three-base hit * A basketball three-point field goal * A figure skating jump with three rotations * In bowling terms, three strikes in a row * I ...

star system. In this case, the ADS 11825BC pair would be 24,000 AU away from δ² Lyrae, and it would take 24,000 years for it to make an orbit. The two stars in the BC system take at least 10,500 years to make an orbit and are separated by 600 AU. Delta² Lyrae was once thought to form a

visual binary A visual binary is a gravitationally bound binary star system that can be resolved into two stars. These stars are estimated, via Kepler's third law, to have periods ranging from a few years to thousands of years. A visual binary consists of two st ...

with the star Delta¹ Lyrae, but it does not, only appearing to do so if seen from Earth's direction.

Notes

References

{{Stars of Lyra Lyra Lyrae, Delta Lyrae, 12 7139 175588 BD+36 3319 092791 M-type bright giants Asymptotic-giant-branch stars Semiregular variable stars