Vega

From Wikipedia, the free encyclopedia

(Redirected from Vega (astronomy))

Jump to: navigation, search
This article is about the star. For other uses, see Vega (disambiguation).
Vega

Location of Vega in the constellation Lyra.

Observation data
Epoch J2000.0 Equinox J2000.0

Constellation
Lyra
(pronunciation)

Right ascension 18h 36m 56.3364s[1]

Declination +38° 47' 01.291"[1]

Apparent magnitude (V) 0.03[1]

Characteristics

Spectral type A0V[1]

U-B color index −0.01[1]

B-V color index +0.00[1]

Variable type Suspected Delta Scuti[2]

 Astrometry

Radial velocity (Rv) −13.9[1] km/s

Proper motion (μ) RA: 201.03[1] mas/yr

Dec.: 287.47[1] mas/yr

Parallax (π) 128.93 ± 0.55[1] mas

Distance 25.3 ± 0.1 ly

(7.76 ± 0.03 pc)

Absolute magnitude (MV) 0.58[3]

Details

Mass 2.11[4] M☉

Radius 2.26 × 2.78[5] R☉

Surface gravity (log g) 4.1 ± 0.1[5]

Luminosity 37 ± 3[5] L☉

Temperature 9602 ± 180[6] K

Metallicity [M/H] = −0.5[6]

Rotation 12.5 h

Age 3.86–5.72×108[4] years

Other designations

Wega,[7] Lucida Lyrae,[8] Alpha Lyrae, α Lyrae, 3 Lyr, GJ 721, HR 7001, BD +38°3238, HD
172167, GCTP 4293.00, LTT 15486, SAO 67174, HIP 91262.[1]
Vega (α Lyr / α Lyrae / Alpha Lyrae) (IPA: /viːɡə/) or (IPA: /veɪɡə/) is the
brightest star in the constellation Lyra, the fifth brightest star in the
night sky and the second brightest star in the northern celestial
hemisphere, after Arcturus. It is a relatively nearby star at only
25.3 light-years (7.8 pc) from Earth, and, together with Arcturus and
Sirius, one of the most luminous stars in the Sun's neighborhood.
Vega has been extensively studied by astronomers, leading it to be
termed, "arguably the next most important star in the sky after the
Sun".[9] Historically, Vega served as the northern pole star at about
12,000 BCE and will do so again at around 14,000 CE. Vega was the first
star, other than the Sun, to have its photograph taken and the first to
have its spectrum photographed. It was also one of the first stars to
have its distance estimated through parallax measurements. Vega has
served as the baseline for calibrating the photometric brightness scale,
and was one of the stars used to define the mean values for the UBV
photometric system.
This star is relatively young when compared to the Sun. It has an
unusually low abundance of the elements with a higher atomic number
than that of helium.[6] Vega is also a suspected variable star that may
vary slightly in magnitude in a periodic manner. [10] It is rotating rapidly
with a velocity of 274 km/s at the equator. This is causing the equator to
bulge outward because of centrifugal effects, and, as a result, there is a
variation of temperature across the star's photosphere that reaches a
maximum at the poles. From the Earth, Vega is being observed from the
direction of one of these poles.[4]
Based upon an excess emission of infrared radiation, Vega has a
circumstellar disk of dust. This dust is likely the result of collisions
between objects in an orbiting debris disk, which is analogous to the
Kuiper belt in the Solar System.[11] Stars that display an infrared excess
because of dust emission are termed Vega-like stars. [12] Irregularities in
Vega's disk also suggest the presence of at least one planet, likely to be
about the size of Jupiter,[13] in orbit around Vega.[14]
Contents
[hide]
 1 Observation history
 2 Visibility
 3 Physical properties
o 3.1 Rotation
o 3.2 Element abundance
o 3.3 Kinematics
 4 Planetary system
o 4.1 Infrared excess
o 4.2 Debris disk
o 4.3 Possible planets
  5 Etymology and cultural significance
 6 See also
 7 Notes and references

 8 External links

[edit] Observation history

Astrophotography, the photography of celestial objects, began in 1840
when John William Draper took an image of the Moon using the
daguerreotype process. On July 17, 1850, Vega became the first star
(other than the Sun) to be photographed, when it was imaged at the
Harvard College Observatory, also with a daguerreotype.[15][16][7] Draper
took the first photograph of a star's spectrum in August 1872 when he
took an image of Vega, and he also became the first person to show
absorption lines in the spectrum of a star.[17] (Similar lines had already
been identified in the spectrum of the Sun.) [18] In 1879, William Huggins
used photographs of the spectra of Vega and similar stars to identify a
set of twelve "very strong lines" that were common to this stellar
category. These were later identified as lines from the Hydrogen Balmer
series.[19]
The distance to Vega can be determined by measuring its parallax shift
against the background stars as the Earth orbits the Sun. The first
person to publish a star's parallax was Friedrich G. W. von Struve, when
he announced a value of 0.125 arcseconds (0.125″) for Vega.[20] But
Friedrich Bessel was skeptical about Struve's data, and, when Bessel
published a parallax of 0.314″ for the star system 61 Cygni, Struve
revised his value for Vega's parallax to nearly double the original
estimate. This change cast further doubt on Struve's data. Thus most
astronomers at the time, including Struve, credited Bessel with the first
published parallax result. However, Struve's initial result was actually
surprisingly close to the currently-accepted value of 0.129″. [21][22]
The brightness of a star, as seen from Earth, is measured with a
standardized, logarithmic scale. This apparent magnitude is a numerical
value that decreases in value with increasing brightness of the star. The
faintest stars visible with the unaided eye are sixth magnitude, while the
brightest, Sirius, has magnitude −1.47. To standardize the magnitude
scale, astronomers chose Vega to represent magnitude zero at all
wavelengths. Thus, for many years, Vega was used as a baseline for the
calibration of absolute photometric brightness scales.[23] However, this is
no longer the case as the apparent magnitude zero point is now
commonly defined in terms of a particular numerically-specified flux.
This approach is more convenient for astronomers as Vega is not always
available for calibration.[24]
The UBV photometric system measures the magnitude of stars through
ultraviolet, blue and yellow filters, producing U, B and V values,
respectively. Vega is one of six A0V stars that were used to set the initial
mean values for this photometric system when it was introduced in the
1950s. The mean magnitudes for these six stars were defined as: U - B =
B - V = 0. In effect, the magnitude of these stars is the same in the
yellow, blue and ultraviolet parts of the electromagnetic spectrum.[25]
Thus, Vega has a relatively flat electromagnetic spectrum in the visual
region—wavelength range 350-850 nanometers, most of which can be
seen with the human eye—so the flux densities are roughly equal; 2000-
4000 Jy.[26] However, the flux density of Vega drops rapidly in the
infrared, and is near 100 Jy at 5 micrometers.[27]
Photometric measurements of Vega during the 1930s appeared to show
that the star had a low-magnitude variability on the order of ±0.03
magnitudes. This range of variability was near the limits of observational
capability for that time and so the subject of Vega's variability has been
controversial. The magnitude of Vega was measured again in 1981 at
the David Dunlap Observatory and showed some slight variability. Thus
it was suggested that Vega showed occasional low-amplitude pulsations
associated with a Delta Scuti variable.[28] This is a category of stars that
oscillate in a coherent manner, resulting in periodic pulsations in the
star's luminosity.[29] Although Vega fits the physical profile for this type
of variable, other observers have found no such variation. Thus the
variability may be the result of systematic errors in measurement. [10][30]
In 1983, Vega became the first star found to have a disk of dust. The
Infrared Astronomical Satellite (IRAS) discovered an excess of infrared
radiation coming from the star, and this was attributed to energy
emitted by the orbiting dust as it was heated by the star. [31]

[edit] Visibility
Vega can often be seen near the zenith in the mid-northern latitudes
during the evening in the Northern Hemisphere summer.[32] From mid-
southern latitudes it can be seen low above the northern horizon during
the Southern Hemisphere winter. With a declination of +38.78°, Vega
can only be viewed at latitudes north of 51° S. At latitudes to the north
of +51° N Vega remains continually above the horizon as a circumpolar
star. On about July 1, Vega reaches midnight culmination when it crosses
the meridian at that time.[33]
The summer triangle.
This star lies at a vertex of a widely-spaced asterism called the Summer
Triangle, which consists of the zero-magnitude stars Vega in the
constellation Lyra and Altair in Aquila, plus the first magnitude star
Deneb in Cygnus.[32] This formation is the approximate shape of a right
triangle, with Vega located at its right angle. The Summer Triangle is
recognizable in the northern skies for there are few other bright stars in
its vicinity.[34]
The Lyrids are a strong meteor shower that peak each year during April
21–22. When a small meteor enters the Earth's atmosphere at a high
velocity it produces a streak of light as the object is vaporized. During a
shower, a multitude of meteors arrive from the same direction, and,
from the perspective of an observer, their glowing trails appear to
radiate from a single point in space. In the case of the Lyrids, the meteor
trails radiate from the direction of Lyra, and hence are sometimes called
the Alpha Lyrids. However, they actually originated from debris emitted
by the comet C/1861 G1 Thatcher and have nothing to do with the star.
[35]

[edit] Physical properties

Vega's spectral class is A0V, making it a blue-tinged white main
sequence star that is fusing hydrogen to helium in its core. Since more
massive stars use their fusion fuel more quickly than smaller ones,
Vega's main sequence lifetime is only one billion years, a tenth of our
Sun's.[36] The current age of this star is between 386 and 511 million
years, or up to about half its expected total main sequence life span.
After leaving the main sequence, Vega will become a class-M red giant
and shed much of its mass, finally becoming a white dwarf. At present
Vega has more than twice the mass[4] of the Sun and its full luminosity is
about 37 times the Sun's value. If Vega is variable, then it may be a
Delta Scuti type with a period of about 0.107 days.[2]
Most of the energy produced at Vega's core is generated by the carbon-
nitrogen-oxygen cycle (CNO cycle), a nuclear fusion process that
combines protons to form helium nuclei through intermediary nuclei of
carbon, nitrogen and oxygen. This process requires a temperature of
16 million K, which is higher than the core temperature of the Sun, but is
more efficient than the Sun's proton-proton chain reaction fusion
reaction. The CNO cycle is highly temperature sensitive, which results in
a convection zone about the core[37] that evenly distributes the 'ash'
from the fusion reaction within the core region. The overlying
atmosphere is in radiative equilibrium. This is in contrast to the Sun,
which has a radiation zone centered on the core with an overlying
convection zone.[38][39]
The energy flux from Vega has been precisely measured against
standard light sources. At 5480 Å, the flux is 3,650 Jy with an error
margin of 2%.[40] The visual spectrum of Vega is dominated by
absorption lines of hydrogen; specifically by the hydrogen Balmer series
with the electron at the n=2 principal quantum number.[41][42] The lines of
other elements are relatively weak, with the strongest being ionized
magnesium, iron and chromium.[43] The X-ray emission from Vega is very
low, demonstrating that the corona for this star must be very weak or
non-existent.[44]

[edit] Rotation

When the radius of Vega was measured to high accuracy with an

interferometer, it resulted in an unexpectedly large estimated value of
2.73 ± 0.01 times the radius of the Sun. This is 60% larger than the
radius of the star Sirius, while stellar models indicated it should only be
about 12% larger. However, this discrepancy can be explained if Vega is
a rapidly-rotating star that is being viewed from the direction of its pole
of rotation. Observations by the CHARA array in 2005–06 confirmed this
deduction.[5]

Size comparison of Vega (left) to the Sun (right).

The pole of Vega—its axis of rotation—is inclined no more than five
degrees from the line-of-sight to the Earth. The equator of Vega has a
rotation velocity of 274 km/s (for a rotation period of about 12.5 hours),
[4]
which is 93% of the speed that would cause the star to start breaking
up from centrifugal effects. This rapid rotation of Vega produces a
pronounced equatorial bulge, so the radius of the equator is 23% larger
than the polar radius. (The estimated polar radius of this star is
2.26 ± 0.02 solar radii, while the equatorial radius is 2.78 ± 0.02 solar
radii.[5]) From the Earth, this bulge is being viewed from the direction of
its pole, producing the overly large radius estimate.
The local gravitational acceleration at the poles is greater than at the
equator, so, by the Von Zeipel theorem, the local luminosity is also
higher at the poles. This is seen as a variation in effective temperature
over the star: the polar temperature is near 10,000 K, while the
equatorial temperature is 7,600 K.[4] As a result, if Vega were viewed
along the plane of its equator, then the luminosity would be about half
the apparent luminosity as viewed from the pole. [9][45] This large
temperature difference between the poles and the equator produces a
strong 'gravity darkening' effect. As viewed from the poles, this results in
a darker (lower intensity) limb than would normally be expected for a
spherically-symmetric star. The temperature gradient may also mean
Vega has a convection zone around the equator,[5][46] while the
remainder of the atmosphere is likely to be in almost pure radiative
equilibrium.[47]
If Vega was actually a slowly rotating, spherically-symmetric star and it
was radiating the same energy as viewed from the Earth, then the
apparent luminosity of Vega would be 57 times the luminosity of the
Sun. This value is much larger than the luminosity of a typical slowly
rotating star with the same mass as Vega. Thus the discovery of fast
rotation of Vega resolved this discrepancy. The true full luminosity of
Vega is about 37 times the luminosity of the Sun. [5]
As Vega had long been used as a standard star for calibrating
telescopes, the discovery that it is rapidly rotating may challenge some
of the underlying assumptions that were based on it being spherically
symmetric. With the viewing angle and rotation rate of Vega now better
known, this will allow for improved instrument calibrations. [48]

[edit] Element abundance

Astronomers term "metals" those elements with higher atomic numbers

than helium. The metallicity of Vega’s photosphere is only about 32% of
the abundance of heavy elements in the Sun’s atmosphere. [49] (Compare
this, for example, to a three-fold metallicity abundance in the similar star
Sirius as compared to the Sun.) For comparison, the Sun has an
abundance of elements heavier than helium of about
ZSol = 0.0172 ± 0.002.[50] Thus, in terms of abundances, only about
0.54% of Vega consists of elements heavier than Helium.
The unusually low metallicity of Vega makes it a weak Lambda Boötis-
type star.[51][52] However, the reason for the existence of such chemically-
peculiar, spectral class A0-F0 stars remains unclear. One possibility is
that the chemical peculiarity may be the result of diffusion or mass loss,
although stellar models show that this would normally only occur near
the end of a star's hydrogen-burning lifespan. Another possibility is that
the star formed from an interstellar medium of gas and dust that was
unusually metal-poor.[53]
The observed helium to hydrogen ratio in Vega is 0.030 ± 0.005, which
is about 40% lower than for the Sun. This may be caused by the
disappearance of a helium convection zone near the surface. Energy
transfer is instead performed by the radiative process, which may be
causing an abundance anomaly through diffusion. [54]

[edit] Kinematics

The radial velocity of Vega is the component of this star's motion along
the line-of-sight to the Earth. Movement away from the Earth will cause
the light from Vega to shift to a lower frequency (toward the red), or to a
higher frequency (toward the blue) if the motion is toward the Earth.
Thus the velocity can be measured from the amount of redshift (or
blueshift) of the star's spectrum. Precise measurements of this redshift
give a value of −13.9 ± 0.9 km/s.[55] The minus sign indicates a relative
motion toward the Earth.
Motion transverse to the line of sight causes the position of Vega to shift
with respect to the more distant background stars. Careful measurement
of the star's position allows this angular movement, known as proper
motion, to be calculated. Vega's proper motion is 202.03 ± 0.63 milli-
arcseconds (mas) per year in Right Ascension—the celestial equivalent
of longitude—and 287.47 ± 0.54 mas/y in Declination, which is
equivalent to a change in latitude.[56] The net proper motion of Vega is
327.78 mas/y,[57] which results in angular movement of a degree every
11,000 years.
In the Galactic coordinate system, the space velocity components of
Vega are U = −13.9 ± 0.9, V = −6.3 ± 0.8 and W = −7.7 ± 0.3, for a net
space velocity of 17 km/s.[58] The radial component of this velocity—in
the direction of the Sun—is −13.9 km/s, while the transverse velocity is
9.9 km/s. Although Vega is at present only the fifth-brightest star in the
sky, the star is slowly brightening as proper motion causes it to
approach the Sun.[59] Vega will eventually become the brightest star in
the sky in around 210,000 years, will attain a peak brightness of
magnitude –0.81 in about 290,000 years and will be the brightest star in
the sky for about 270,000 years.[60]
Based on this star's kinematic properties, it appears to belong to a
stellar association called the Castor Moving Group. This group contains
about 16 stars, including Alpha Librae, Alpha Cephei, Castor, Fomalhaut
and Vega. All members of the group are moving in near parallel with
similar space velocities. Membership in a moving group implies a
common origin for these stars in a open cluster that has since become
gravitationally unbound.[61] The estimated age of this moving group is
200 ± 100 million years, and they have an average space velocity of
16.5 km/s.[62][58]

[edit] Planetary system

[edit] Infrared excess

A mid-infrared image of the debris disk around Vega.

One of the early results from the Infrared Astronomy Satellite (IRAS) was
the discovery of excess infrared flux coming from Vega; beyond what
would be expected from the star alone. This excess was measured at
wavelengths of 25, 60 and 100 μm, and came from within an angular
radius of 10 arcseconds (10″) centered on the star. At the measured
distance of Vega, this corresponded to an actual radius of
80 astronomical units (AU), where an AU is the average radius of the
Earth's orbit around the Sun. It was proposed that this radiation came
from a field of orbiting particles with a dimension on the order of a
millimeter, as anything smaller would eventually be removed from the
system by radiation pressure or drawn into the star by means of
Poynting-Robertson drag.[63] The latter is the result of radiation pressure
creating an effective force that opposes the orbital motion of a dust
particle, causing it to spiral inward. This effect is most pronounced for
tiny particles that are closer to the star.[64]
Subsequent measurements of Vega at 193 μm showed a lower than
expected flux for the hypothesized particles, suggesting that they must
instead be on the order of 100 μm or less. To maintain this amount of
dust in orbit around Vega, a continual source of replenishment would be
required. A proposed mechanism for maintaining the dust was a disk of
coalesced bodies that were in the process of collapsing to form a planet.
[63]
Models fitted to the dust distribution around Vega indicate that it is a
120 AU-radius circular disk viewed from nearly pole-on. In addition, there
is a hole in the center of the disk with a radius of no less than 80 AU.[65]
Following the discovery of an infrared excess around Vega, other stars
have been found that display a similar anomaly that is attributable to
dust emission. As of 2002, about 400 of these stars have been found,
and they have come to be termed "Vega-like" or "Vega-excess" stars. It
is believed that these may provide clues to the origin of the Solar
System.[12]

[edit] Debris disk

By 2005, the Spitzer Space Telescope had produced high resolution

infrared images of the dust around Vega. It was shown to extend out to
43″ (330 AU) at a wavelength of 24 μm, 70″ (543 AU) at 70 μm and 105″
(815 AU) at 160 μm. These much wider disks were found to be circular
and free of clumps, with dust particles ranging from 1–50 μm in size. The
estimated total mass of this dust is 3×10-3 times the mass of the Earth.
Production of the dust would require collisions between asteroids in a
population corresponding to the Kuiper Belt around the Sun. Thus the
dust is more likely created by a debris disk around Vega, rather than
from a protoplanetary disk as was earlier thought.[11]

Artist concept illustrates how a massive collision of objects may have smashed together to
create the dust ring around the star Vega.
The inner boundary of the debris disk was estimated at 11″ ± 2″, or 70–
102 AU. The disk of dust is produced as radiation pressure from Vega
pushes debris from collisions of larger objects outward. However,
continuous production of the amount of dust observed over the course of
Vega's lifetime would require an enormous starting mass—estimated as
hundreds of times the mass of Jupiter. Hence it is more likely to have
been produced as the result of a relatively recent breakup of a
moderate-sized (or larger) comet or asteroid, which then further
fragmented as the result of collisions between the smaller components
and other bodies. This dusty disk would be relatively young on the time
scale of the star's age, and it will eventually be removed unless other
collision events supply more dust.[11]
Observations with the CHARA array at Mt. Wilson in 2006 revealed
evidence for an inner dust band around Vega. Originating within 8 AU of
the star, this dust may be evidence of dynamical perturbations within
the system.[66] This may be caused by an intense bombardment of
comets or meteors, and may be evidence for the existence of a
planetary system.[67]

[edit] Possible planets

Observations from the James Clerk Maxwell Telescope in 1997 revealed

an "elongated bright central region" that peaked at 9″ (70 AU) to the
northeast of Vega. This was hypothesized as either a perturbation of the
dust disk by a planet or else an orbiting object that was surrounded by
dust. However, images by the Keck telescope had ruled out a companion
down to magnitude 16, which would correspond to a body with more
than 12 times the mass of Jupiter.[68] Astronomers at the Joint Astronomy
Centre in Hawaii and at UCLA suggested that the image may indicate a
planetary system still undergoing formation.[69]
Determining the nature of the planet has not been straightforward; a
2002 paper hypothesizes that the lumps are caused by a roughly Jupiter-
mass planet on an eccentric orbit. Dust would collect in orbits that have
mean-motion resonances with this planet—where their orbital periods
form integer fractions with the period of the planet—producing the
resulting clumpiness.[13]
In 2003 it was hypothesized that these lumps could be caused by a
roughly Neptune-mass planet having migrated from 40 to 65 AU over
56 million years,[14] an orbit large enough to allow the formation of
smaller rocky planets closer to Vega. The migration of this planet would
likely require gravitational interaction with a second, higher mass planet
in a smaller orbit.[70]
Using a coronagraph on the Subaru telescope in Hawaii in 2005,
astronomers were able to further constrain the size of a planet orbiting
Vega to no more than 5–10 times the mass of Jupiter. [71] Although a
planet has yet to be directly observed around Vega, the presence of a
planetary system can not yet be precluded. Thus there could be smaller,
terrestrial planets orbiting closer to the star. The inclination of planetary
orbits around Vega is likely to be closely aligned to the equatorial plane
of this star.[72] From the perspective of an observer on a hypothetical
planet around Vega, the Sun would appear as a faint 4.3 magnitude star
in the Columba constellation.[73]

[edit] Etymology and cultural significance

Each night the positions of the stars appear to change as the Earth
rotates. However, when a star is located along the Earth's axis of
rotation, it will remain in the same position and thus is called a pole star.
The direction of the Earth's axis of rotation gradually changes over time
in a process known as the precession of the equinoxes. A complete
precession cycle requires 25,770 years,[74] during which time the pole of
the Earth's rotation follows a circular path across the celestial sphere
that passes near several prominent stars. At present the pole star is
Polaris, but around 12,000 BCE the pole was pointed only five degrees
away from Vega. Through precession, the pole will again pass near Vega
around 14,000 CE.[75] It is the brightest of the successive northern pole
stars.[7]
In Inuit astronomy, Vega is known as the Old Woman.[citation needed] Among
the northern polynesian people, Vega was known as whetu o te tau, the
year star. For a period of history it marked the start of their new year
when the ground would be prepared for planting. Eventually this
function became denoted by the Pleiades.[76]
The Assyrians named this pole star Dayan-same, the "Judge of Heaven",
while in Akkadian it was Tir-anna, "Life of Heaven". In Babylonian
astronomy, Vega may have been one of the stars named Dilgan, "the
Messenger of Light". To the ancient Greeks, the constellation Lyra was
formed from the harp of Orpheus, with Vega as its handle.[8] For the
Roman Empire, the start of autumn was based upon the hour at which
Vega set below the horizon.[7]
In Chinese mythology, there is a love story of Qi Xi 七夕 in which Niu Lang
牛郎 (Altair) and his two children (β and γ Aquilae) are separated from
their mother Zhi Nü 織女 (Vega) who is on the far side of the river, the
Milky Way 銀河.[77] However, one day per year on the seventh day of the
seventh month of the Chinese lunisolar calendar, magpies make a
bridge so that Niu Lang and Zhi Nü can be together again for a brief
encounter. This is apparently a reference to the Perseids.[1] The Japanese
Tanabata festival is also based on this legend. [78] In Zoroastrianism, Vega
was sometimes associated with, Vanant, a minor divinity whose name
means "conqueror".[79]
The name Wega[7] (later Vega) comes from a loose transliteration of the
Arabic word waqi meaning "falling", via the phrase ‫ النسر الواقع‬an-nasr
al-wāqi‘, which sources translate as "the falling eagle" [80] or "the
swooping vulture",[81] as this constellation was represented as a vulture
in ancient Egypt,[82] and as an eagle or vulture in ancient India.[83][84] The
Arabic name then appeared in the western world in the Alfonsine Tables,
[7]
which were drawn up between 1215–70 by order of Alfonso X.[85]
Medieval astrologers counted Vega as one of the Behenian stars[86] and
related it to chrysolite and winter savory. Cornelius Agrippa listed its
kabbalistic sign under Vultur cadens, a literal Latin translation of the
Arabic name. [87]
Medieval star charts also listed the alternate names
Waghi, Vagieh and Veka for this star.[33]
Vega became the first star to have a car named after it when Chevrolet
launched the Vega in 1971.[88] Other vehicles named after Vega include
the ESA's Vega launch system[89] and the Lockheed Vega aircraft.[90]

[edit] See also

 Vega in fiction

[edit] Notes and references

1. ^ a b c d e f g h i j k Staff (October 30, 2007). "SIMBAD query result: V* alf Lyr -- Variable
Star". Centre de Données astronomiques de Strasbourg. Retrieved on 2007-10-30.—use the
"display all measurements" option to show additional parameters.
2. ^ a b Fernie, J. D. (1981). "On the variability of VEGA". Astronomical Society of the Pacific
93 (2): 333–337. doi:10.1086/130834. Retrieved on 2007-10-30.
3. ^ For apparent magnitude m and parallax π, the absolute magnitude Mv is given by:

See: Tayler, Roger John (1994). The Stars: Their Structure and Evolution. Cambridge
University Press, 16. ISBN 0521458854.

4. ^ a b c d e f Peterson, D. M.; Hummel, C. A.; Pauls, T. A.; Armstrong, J. T.; Benson, J. A.;
Gilbreath, G. C.; Hindsley, R. B.; Hutter, D. J.; Johnston, K. J.; Mozurkewich, D.; Schmitt,
H. R. (1999). "Vega is a rapidly rotating star". Nature 440 (7086): 896–899.
doi:10.1038/nature04661. Retrieved on 2007-10-29.
5. ^ a b c d e f g Aufdenberg, J.P.; Ridgway, S.T. et al (2006). "First results from the CHARA
Array: VII. Long-Baseline Interferometric Measurements of Vega Consistent with a Pole-
On, Rapidly Rotating Star?" (PDF). Astrophysical Journal 645: 664–675.
doi:10.1086/504149. Retrieved on 2007-11-09.
6. ^ a b c Kinman, T.; Castelli, F. (2002). "The determination of Teff for metal-poor A-type stars
using V and 2MASS J, H and K magnitudes". Astronomy and Astrophysics 391: 1039–
1052. doi:10.1051/0004-6361:20020806. Retrieved on 2007-10-30.
7. ^ a b c d e f Allen, Richard Hinckley (1963). Star Names: Their Lore and Meaning. Courier
Dover Publications. ISBN 0486210790.
8. ^ a b Kendall, E. Otis (1845). Uranography: Or, A Description of the Heavens; Designed for
Academics and Schools; Accompanied by an Atlas of the Heavens. Philadelphia: Oxford
University Press.
9. ^ a b Gulliver, Hill, Austin F.; Graham; Adelman, Saul J. (1994). "Vega: A rapidly rotating
pole-on star". The Astrophysical Journal 429 (2): L81–L84. doi:10.1086/187418. Retrieved
on 2007-10-29.
10. ^ a b I.A., Vasil'yev; Merezhin, V. P.; Nalimov, V. N.; Novosyolov, V. A. (March 17, 1989).
"On the Variability of Vega". Commission 27 of the I.A.U.. Retrieved on 2007-10-30.
11. ^ a b c K. Y. L. Su et al (2005). "The Vega Debris Disk: A Surprise from Spitzer". The
Astrophysical Journal 628 (1): 487–500. doi:10.1086/430819. Retrieved on 2007-11-02.
12. ^ a b Song, Inseok; Weinberger, A. J.; Becklin, E. E.; Zuckerman, B.; Chen, C. (2002). "M-
Type Vega-like Stars". The Astronomical Journal 124 (1): 514–518. doi:10.1086/341164.
Retrieved on 2007-11-10.
13. ^ a b Wilner, D.; Holman, M.; Kuchner, M.; Ho, P.T.P. (2002). "Structure in the Dusty
Debris around Vega". The Astrophysical Journal 569: L115–L119. doi:10.1086/340691.
Retrieved on 2007-10-30.
14. ^ a b Wyatt, M. (2002). "Resonant Trapping of Planetesimals by Planet Migration: Debris
Disk Clumps and Vega's Similarity to the Solar System". The Astrophysical Journal 598:
1321–1340. doi:10.1086/379064. Retrieved on 2007-10-30.
15. ^ Barger, M. Susan; White, William B. (2000). The Daguerreotype: Nineteenth-Century
Technology and Modern Science. JHU Press. ISBN 0801864585.
16. ^ Holden, Edward S.; Campbell, W. W. (1890). "Photographs of Venus, Mercury and
Alpha Lyræ in Daylight.". Publications of the Astronomical Society of the Pacific 2 (10):
249–250. doi:10.1086/120156. Retrieved on 2007-11-18.
17. ^ Barker, George F. (1887). "On the Henry Draper Memorial Photographs of Stellar
Spectra". Proceedings of the American Philosophical Society 24: 166–172.
18. ^ "Spectroscopy and the Birth of Astrophysics". American Institute of Physics. Retrieved
on 2007-11-15.
19. ^ Hentschel, Klaus (2002). Mapping the Spectrum: Techniques of Visual Representation in
Research and Teaching. Oxford University Press. ISBN 0198509537.
20. ^ Berry, Arthur (1899). A Short History of Astronomy. New York: Charles Scribner's Sons.
21. ^ Débarbat, Suzanne (1988). "The First Successful Attempts to Determine Stellar
Parallaxes in the Light of the Bessel/Struve Correspondances", Mapping the Sky: Past
Heritage and Future Directions. Springer. ISBN 9027728100.
22. ^ Anonymous (June 28, 2007). "The First Parallax Measurements". Astroprof. Retrieved on
2007-11-12.
23. ^ Garfinkle, Robert A. (1997). Star-Hopping: Your Visa to Viewing the Universe.
Cambridge University Press. ISBN 0521598893.
24. ^ Cochran, A. L. (1981). "Spectrophotometry with a self-scanned silicon photodiode array.
II - Secondary standard stars". Astrophysical Journal Supplement Series 45: 83–96.
doi:10.1086/190708. Retrieved on 2007-11-12.
25. ^ Johnson, H. L.; Morgan, W. W. (1953). "Fundamental stellar photometry for standards of
spectral type on the revised system of the Yerkes spectral atlas". Astrophysical Journal 117:
313–352. doi:10.1086/145697. Retrieved on 2007-11-05.
26. ^ Walsh, J. (March 6, 2002). "Alpha Lyrae (HR7001)". Optical and UV
Spectrophotometric Standard Stars. ESO. Retrieved on 2007-11-15.—flux versus
wavelength for Vega.
27. ^ McMahon, Richard G. (November 23, 2005). "Notes on Vega and magnitudes" (Text).
University of Cambridge. Retrieved on 2007-11-07.
28. ^ Fernie, J. D. (1999). "On the variability of VEGA". Astronomical Society of the Pacific
93: 333–337. doi:10.1086/130834. Retrieved on 2007-11-11.
29. ^ A. Gautschy, H. Saio (1995). "Stellar Pulsations Across The HR Diagram: Part 1".
Annual Review of Astronomy and Astrophysics 33: 75–114.
doi:10.1146/annurev.aa.33.090195.000451. Retrieved on 2007-05-14.
30. ^ Hayes, D. S. (May 24-29, 1984). "Stellar absolute fluxes and energy distributions from
0.32 to 4.0 microns". Proceedings of the Symposium, Calibration of fundamental stellar
quantities: pp. 225–252, Como, Italy: Dordrecht, D. Reidel Publishing Co.. Retrieved on
2007-11-12.
31. ^ Harvey, Paul E.; Wilking, Bruce A.; Joy, Marshall (1984). "On the far-infrared excess of
Vega". Nature 307: 441–442. doi:10.1038/307441a0. Retrieved on 2007-11-12.
32. ^ a b Pasachoff, Jay M. (2000). A Field Guide to Stars and Planets, Fourth edition,
Houghton Mifflin Field Guides. ISBN 0395934311.
33. ^ a b Burnham, Robert J. R. (1978). Burnham's Celestial Handbook: An Observer's Guide to
the Guide to the Universe Beyond the Solar System, vol. 2. Courier Dover Publications.
ISBN 0486235688.
34. ^ Upgren, Arthur R. (1998). Night Has a Thousand Eyes: A Naked-Eye Guide to the Sky,
Its Science, and Lore. Basic Books. ISBN 0306457903.
35. ^ Arter, T. R.; Williams, I. P. (1997). "The mean orbit of the April Lyrids". Monthly
Notices of the Royal Astronomical Society 289 (3): 721–728. Retrieved on 2007-11-02.
36. ^ Mengel, J. G.; Demarque, P.; Sweigart, A. V.; Gross, P. G. (1979). "Stellar evolution
from the zero-age main sequence". Astrophysical Journal Supplement Series 40: 733–791.
doi:10.1086/190603. Retrieved on 2007-11-05.—From pages 769–778: for stars in the
range 1.75<M<2.2, 0.2<Y<0.3 and 0.004<Z<0.01, stellar models give an age range of
0.43–1.64×109 years between a star joining the main sequence and turning off to the red
giant branch. With a mass closer to 2.2, however, the interpolated age for Vega is less than
a billion.
37. ^ Browning, Matthew; Brun, Allan Sacha; Toomre, Juri (2004). "Simulations of core
convection in rotating A-type stars: Differential rotation and overshooting". Astrophysical
Journal 601: 512–529. doi:10.1086/380198. Retrieved on 2007-12-09.
38. ^ Padmanabhan, Thanu (2002). Theoretical Astrophysics. Cambridge University Press.
ISBN 0521562414.
39. ^ Cheng, Kwong-Sang; Chau, Hoi-Fung; Lee, Kai-Ming (2007). "Chapter 14: Birth of
Stars". Nature of the Universe. Honk Kong Space Museum. Retrieved on 2007-11-26.
40. ^ Oke, J. B.; Schild, R. E. (1970). "The Absolute Spectral Energy Distribution of Alpha
Lyrae". Astrophysical Journal 161: 1015–1023. doi:10.1086/150603. Retrieved on 2007-
11-15.
41. ^ Richmond, Michael. "The Boltzmann Equation". Rochester Institute of Technology.
Retrieved on 2007-11-15.
42. ^ Clayton, Donald D. (1983). Principles of Stellar Evolution and Nucleosynthesis.
University of Chicago Press. ISBN 0226109534.
43. ^ Michelson, E. (1981). "The near ultraviolet stellar spectra of alpha Lyrae and beta
Orionis". Monthly Notices of the Royal Astronomical Society 197: 57–74. Retrieved on
2007-11-15.
44. ^ Schmitt, J. H. M. M. (1999). "Coronae on solar-like stars.". Astronomy and Astrophysics
318: 215–230. Retrieved on 2007-11-15.
45. ^ From the poles, the star presents a circular profile, while from the equator the star appears
as an ellipse. The cross-sectional area of the star's elliptical profile is only about 81% of the
cross-sectional area of the star's polar profile, so less energy is received along the plane of
the equator. Any additional difference in luminosity is accounted for by the temperature
distribution. From the Stefan–Boltzmann law, the energy flux from Vega's equator will be
about:

or 33% of the flux from the pole.

46. ^ Staff (January 10, 2006). "Rapidly Spinning Star Vega has Cool Dark Equator", National
Optical Astronomy Observatory. Retrieved on 2007-11-18.
47. ^ Adelman, Saul J. (July 8-13, 2004). "The physical properties of normal A stars" (PDF).
The A-Star Puzzle: pp. 1-11, Poprad, Slovakia: Cambridge University Press. Retrieved on
2007-11-22.
48. ^ Quirrenbach, Andreas (2007). "Seeing the Surfaces of Stars". Science 317 (5836): 325–
326. doi:10.1126/science.1145599. PMID 17641185. Retrieved on 2007-11-19.
49. ^ For a metallicity of −0.5, the proportion of metals relative to the Sun is given by:

.
50. ^ Antia, H. M.; Basu, Sarbani (2006). "Determining Solar Abundances Using
Helioseismology". The Astrophysical Journal 644 (2): 1292–1298. doi:10.1086/503707.
Retrieved on 2007-11-05.
51. ^ Renson, P.; Faraggiana, R.; Boehm, C. (1990). "Catalogue of Lambda Bootis
Candidates". Bulletin d'Information Centre Donnees Stellaires 38: 137–149. Retrieved on
2007-11-07.—Entry for HD 172167 on p. 144.
52. ^ Qiu, H. M.; Zhao, G.; Chen, Y. Q.; Li, Z. W. (2001). "The Abundance Patterns of Sirius
and Vega". The Astrophysical Journal 548 (2): 77–115. doi:10.1086/319000. Retrieved on
2007-10-30.
53. ^ Martinez, Peter; Koen, C.; Handler, G.; Paunzen, E. (1998). "The pulsating lambda
Bootis star HD 105759". Monthly Notices of the Royal Astronomical Society 301 (4): 1099–
1103. doi:10.1046/j.1365-8711.1998.02070.x. Retrieved on 2007-11-05.
54. ^ Adelman, Saul J. (1990). "An elemental abundance analysis of the superficially normal A
star VEGA". Astrophysical Journal, Part 1 348: 712–717. doi:10.1086/168279. Retrieved
on 2007-11-07.
55. ^ Evans, D. S. (June 20-24, 1966). "The Revision of the General Catalogue of Radial
Velocities". Proceedings from IAU Symposium no. 30: 57, London, England: Academic
Press. Retrieved on 2007-11-09.
56. ^ M. A. Perryman et al (1997). "The Hipparcos Catalogue.". Astronomy and Astrophysics
323: L49–L52. Retrieved on 2007-11-09.
57. ^ Majewski, Steven R. (2006). "Stellar Motions". University of Virginia. Retrieved on
2007-09-27.—The net proper motion is given by:

where μα and μδ are the components of proper motion in the R.A. and Declination,
respectively, and δ is the Declination.

58. ^ a b Barrado y Navascues, D. (1998). "The Castor moving group. The age of Fomalhaut and
VEGA". Astronomy and Astrophysics 339: 831–839. Retrieved on 2007-10-31.
59. ^ Moulton, Forest Ray (1906). An Introduction to Astronomy. The Macmillan company, p.
502.
60. ^ Tomkin, Jocelyn (April 1998). "Once And Future Celestial Kings". Sky and Telescope 95
(4): 59–63.
61. ^ Inglis, Mike (2003). Observer's Guide to Stellar Evolution: The Birth, Life, and Death of
Stars. Springer. ISBN 1852334657.
62. ^ U = −10.7 ± 3.5, V = −8.0 ± 2.4, W = −9.7 ± 3.0 km/s. The net velocity is:

63. ^ a b Harper, D. A.; Loewenstein, R. F.; Davidson, J. A. (1984). "On the nature of the
material surrounding VEGA". Astrophysical Journal, Part 1 285: 808–812.
doi:10.1086/162559. Retrieved on 2007-11-02.
64. ^ Robertson, H. P. (April 1937). "Dynamical effects of radiation in the solar system".
Monthly Notices of the Royal Astronomical Society 97: 423–438. Royal Astronomical
Society. Retrieved on 2007-11-02.
65. ^ Dent, W. R. F.; Walker, H. J.; Holland, W. S.; Greaves, J. S. (2000). "Models of the dust
structures around Vega-excess stars". Monthly Notices of the Royal Astronomical Society
314 (4): 702–712. doi:10.1046/j.1365-8711.2000.03331.x. Retrieved on 2007-11-07.
66. ^ Absil, O. et al (2006). "Circumstellar material in the Vega inner system revealed by
CHARA/FLUOR". Astronomy and Astrophysics 452 (1): 237–244. doi:10.1051/0004-
6361:20054522. Retrieved on 2007-11-19.
67. ^ Girault-Rime, Marion (Summer 2006). "Vega's Stardust". CNRS International Magazine.
Retrieved on 2007-11-19.
68. ^ Holland, Wayne S.; Greaves, Jane S.; Zuckerman, B.; Webb, R. A.; McCarthy, Chris;
Coulson, Iain M.; Walther, D. M.; Dent, William R. F.; Gear, Walter K.; Robson, Ian
(1998). "Submillimetre images of dusty debris around nearby stars". Nature 392 (6678):
788–791. doi:10.1038/33874. Retrieved on 2007-11-10.
69. ^ Staff (April 21, 1998). "Astronomers discover possible new Solar Systems in formation
around the nearby stars Vega and Fomalhaut", Joint Astronomy Centre. Retrieved on 2007-
10-29.
70. ^ Gilchrist, E.; Wyatt, M.; Holland, W.; Maddock, J.; Price, D. P. (December 1, 2003).
"New evidence for Solar-like planetary system around nearby star", Royal Observatory,
Edinburgh. Retrieved on 2007-10-30.
71. ^ Itoh, Yoichi (2006). "Coronagraphic Search for Extrasolar Planets around ε Eri and
Vega". The Astrophysical Journal 652 (2): 1729–1733. doi:10.1086/508420. Retrieved on
2007-11-10.
72. ^ Campbell, B.; Garrison, R. F. (1985). "On the inclination of extra-solar planetary orbits".
Publications of the Astronomical Society of the Pacific 97: 180–182. doi:10.1086/131516.
Retrieved on 2007-11-16.
73. ^ The Sun would appear at the diametrically opposite coordinates from Vega at
α=6h 36m 56.3364s, δ=−38° 47' 01.291", which is in the western part of Columba. The visual
magnitude is given by
74. ^ Chaikin, Andrew L. (1990). The New Solar System, 4th edition, Cambridge, England:
Cambridge University Press. ISBN 0521645875.
75. ^ Roy, Archie E.; Clarke, David (2003). Astronomy: Principles and Practice. CRC Press.
ISBN 0750309172.
76. ^ Smith, S. Percy (1919). "The Fatherland of the Polynesians – Aryan and Polynesian
Points of Contact". The Journal of the Polynesian Society 28: 18–20. Retrieved on 2008-08-
08.
77. ^ Wei, Liming; Yue, L.; Lang Tao, L. (2005). Chinese Festivals. Chinese Intercontinental
Press. ISBN 750850836X.
78. ^ Kippax, John Robert (1919). The Call of the Stars: A Popular Introduction to a
Knowledge of the Starry Skies with their Romance and Legend. G. P. Putnam's Sons.
79. ^ Boyce, Mary (1996). A History of Zoroastrianism, volume one: The Early Period. New
York: E. J. Brill. ISBN 9004088474.
80. ^ Glasse, Cyril (2001). The New Encyclopedia of Islam. Rowman Altamira. ISBN
0759101906.—"astronomy" entry.
81. ^ Harper, Douglas (November 2001). "Vega". Online Etymology Dictionary. Retrieved on
2007-11-01.
82. ^ Massey, Gerald (2001). Ancient Egypt: the Light of the World. Adamant Media
Corporation. ISBN 140217442X.
83. ^ Olcott, William Tyler (1911). Star Lore of All Ages: A Collection of Myths, Legends, and
Facts Concerning the Constellations of the Northern Hemisphere. G.P. Putnam's sons.
84. ^ Houlding, Deborah (December 2005). "Lyra: The Lyre". Sktscript. Retrieved on 2007-11-
04.
 85. ^ Houtsma, M. Th.; Wensinck, A. J.; Gibb, H. A. R.; Heffening, W.; Lévi-Provençal
(1987). E.J. Brill's First Encyclopaedia of Islam, 1913-1936 VII. E.J. Brill, p. 292.
86. ^ Tyson, Donald; Freake, James (1993). Three Books of Occult Philosophy. Llewellyn
Worldwide. ISBN 0875428320.
87. ^ Agrippa, Heinrich Cornelius (1533). De Occulta Philosophia.
88. ^ Frommert, Hartmut. "Vega, Alpha Lyrae". SEDS. Retrieved on 2007-11-02.
89. ^ Staff (May 20, 2005). "Launch vehicles - Vega". European Space Agency. Retrieved on
2007-11-12.
90. ^ Rumerman, Judy (2003). "The Lockheed Vega and Its Pilots". U.S. Centennial of Flight
Commission. Retrieved on 2007-11-12.

[edit] External links

 "Vega". SolStation. Retrieved on 2005-11-09.
 Gilchrist, Eleanor; Wyatt, Mark; Holland, Wayne; Price, Douglas Pierce; Maddock,
Julia (December 1, 2003). "New evidence for Solar-like planetary system around
nearby star", Joint Astronomy Centre. Retrieved on 2007-11-10.
 Gay Yee Hill and Dolores Beasley (January 10, 2005). "Spitzer Sees Dusty
Aftermath of Pluto-Sized Collision", NASA/Spitzer Space Telescope. Retrieved on
2007-11-02.
 Sir Harry Kroto, NL presents 8 Astrophysical Lectures including discussion of
Vega Freeview videos provided by the Vega Science Trust.