Vega

Coordinates: Sky map 18h 36m 56.3364s, +38° 47′ 01.291″
Source: Wikipedia, the free encyclopedia.
"Star Vega" redirects here. For the psychologist, see Star Vega (psychologist). For other uses, see Vega (disambiguation).

Vega
Location of Vega (circled)
Observation data
J2000.0
Constellation Lyra
Pronunciation
 /ˈviːɡə/[1][2][3] or /ˈveɪɡə/[2]
Right ascension 18h 36m 56.33635s[4]
Declination +38° 47′ 01.2802″[4]
Apparent magnitude (V) +0.026[5] (−0.02 – +0.07)[6]
Characteristics
Evolutionary stage Main sequence
Spectral type A0Va[7]
U−B color index 0.00[8]
B−V color index 0.00[8]
Variable type Delta Scuti[6]
Distance
25.04 ± 0.07 ly
(7.68 ± 0.02 pc)
Absolute magnitude (MV)+0.582[10]
Details
Myr
LTT 15486[17]
Database references
SIMBADdata

Vega is the brightest

Sun's neighborhood. It is the fifth-brightest star in the night sky, and the second-brightest star in the northern celestial hemisphere, after Arcturus
.

Vega has been extensively studied by astronomers, leading it to be termed "arguably the next most important star in the sky after the Sun".

zero point for the UBV photometric system
.

Vega is only about a tenth of the age of the Sun, but since it is 2.1 times as massive, its expected lifetime is also one tenth of that of the Sun; both stars are at present approaching the midpoint of their main sequence lifetimes. Compared with the Sun, Vega has a lower abundance of elements heavier than helium.[13] Vega is also a variable star—that is, a star whose brightness fluctuates. It is rotating rapidly with a speed of 236 km/s at the equator. This causes the equator to bulge outward due to 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 Earth, Vega is observed from the direction of one of these poles.[22]

Based on observations of more

ultra-hot Neptune on a 2.43-day orbit around Vega was discovered with the radial velocity method, additionally, another possible Saturn-mass signal with a period of about 200 days.[25]

Nomenclature

Vega is the brightest star in the constellation of Lyra.

Working Group on Star Names (WGSN)[27] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[28] included a table of the first two batches of names approved by the WGSN; which included Vega for this star. It is now so entered in the IAU Catalog of Star Names.[29]

Observation

The Summer Triangle

Vega can often be seen near the zenith in the mid-northern latitudes during the evening in the Northern Hemisphere summer.[30] 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. Therefore, it does not rise at all anywhere in Antarctica or in the southernmost part of South America, including Punta Arenas, Chile (53° S). At latitudes to the north of 51° N, Vega remains continuously above the horizon as a circumpolar star. Around July 1, Vega reaches midnight culmination when it crosses the meridian at that time.[31]

Small white disks representing the northern stars on a black background, overlaid by a circle showing the position of the north pole over time
The path of the north celestial pole among the stars due to the precession. Vega is the bright star near the bottom.

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

precession of the equinoxes. A complete precession cycle requires 25,770 years,[32] 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.[33] Vega is the brightest of the successive northern pole stars.[15] In 210,000 years, Vega will become the brightest star in the night sky,[34] and will peak in brightness in 290,000 years with an apparent magnitude of –0.81.[34]

This star lies at a vertex of a widely spaced asterism called the Summer Triangle, which consists of Vega plus the two first-magnitude stars Altair, in Aquila, and Deneb in Cygnus.[30] 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.[35]

Observational history

Astrophoto of Vega
"On the night of July 16–17, 1850, Whipple and Bond made the first daguerreotype of a star (Vega)"

spectrum of this star has served as one of the stable anchor points by which other stars are classified.[39]

The distance to Vega can be determined by measuring its parallax shift against the background stars as the Earth orbits the Sun. Giuseppe Calandrelli noted stellar parallax in 1805-6 and came up with a 4-second value for the star which was a gross overestimate.[40] The first person to publish a star's parallax was Friedrich G. W. von Struve, when he announced a value of 0.125 arcsecond (0.125″) for Vega.[41] 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 close to the currently accepted value of 0.129″,[42][43] as determined by the Hipparcos astrometry satellite.[4][44][45]

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 to the unaided eye are sixth magnitude, while the brightest in the night sky, Sirius, is of magnitude −1.46. To standardize the magnitude scale, astronomers chose Vega and several similar stars and averaged their brightness 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.[46] 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, since Vega is not always available for calibration and varies in brightness.[47]

The

micrometers.[50]

Photometric measurements of Vega during the 1930s appeared to show that the star had a low-magnitude variability on the order of ±0.03 magnitude (around ±2.8%[note 2] luminosity). 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.[51] This is a category of stars that oscillate in a coherent manner, resulting in periodic pulsations in the star's luminosity.[52] Although Vega fits the physical profile for this type of variable, other observers have found no such variation. Thus the variability was thought to possibly be the result of systematic errors in measurement.[53][54] However, a 2007 article surveyed these and other results, and concluded that "A conservative analysis of the foregoing results suggests that Vega is quite likely variable in the 1–2% range, with possible occasional excursions to as much as 4% from the mean".[55] Also, a 2011 article affirms that "The long-term (year-to-year) variability of Vega was confirmed".[56]

Vega became the first solitary

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.[58]

Physical characteristics

Vega's

bolometric luminosity is about 40 times the Sun's. Because it is rotating rapidly, approximately once every 16.5 hours,[14] and seen nearly pole-on, its apparent luminosity, calculated assuming it was the same brightness all over, is about 57 times the Sun's.[12] If Vega is variable, then it may be a Delta Scuti type with a period of about 0.107 day.[51]

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 becomes dominant at a temperature of about 17 million K,[60] which is slightly higher than the core temperature of the Sun, but is less efficient than the Sun's proton–proton chain fusion reaction. The CNO cycle is highly temperature sensitive, which results in a convection zone about the core[61] 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.[62]

The energy flux from Vega has been precisely measured against standard light sources. At 5,480 Å, the flux density is 3,650 Jy with an error margin of 2%.

absorption lines of hydrogen; specifically by the hydrogen Balmer series with the electron at the n=2 principal quantum number.[64][65] The lines of other elements are relatively weak, with the strongest being ionized magnesium, iron and chromium.[66] The X-ray emission from Vega is very low, demonstrating that the corona for this star must be very weak or non-existent.[67] However, as the pole of Vega is facing Earth and a polar coronal hole may be present,[57][68] confirmation of a corona as the likely source of the X-rays detected from Vega (or the region very close to Vega) may be difficult as most of any coronal X-rays would not be emitted along the line of sight.[68][69]

Using

rotational modulation with a period of 0.68 day.[72]

Rotation

Vega has a rotation period of 12.5 hours,

oblate
like those two planets.

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

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.[12]

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. At the high end of estimates for the

projected) rotational velocity because Vega is seen almost pole-on. This is 88% of the speed that would cause the star to start breaking up from centrifugal effects.[11] This rapid rotation of Vega produces a pronounced equatorial bulge, so the radius of the equator is 19% larger than the polar radius, compared to just under 11% for Saturn, the most oblate of the Solar System's planets. (The estimated polar radius of this star is 2.362±0.012 solar radii, while the equatorial radius is 2.818±0.013 solar radii.[11]
) From the Earth, this bulge is being viewed from the direction of its pole, producing the overly large radius estimate.

The local surface gravity at the poles is greater than at the equator, which produces a variation in effective temperature over the star: the polar temperature is near 10,000 K, while the equatorial temperature is about 8,152 K.[11] 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 that Vega has a convection zone around the equator,[12][73] while the remainder of the atmosphere is likely to be in almost pure radiative equilibrium.[74] By the Von Zeipel theorem, the local luminosity is higher at the poles. As a result, if Vega were viewed along the plane of its equator instead of almost pole-on, then its overall brightness would be lower.

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 improved instrument calibrations.[75]

Element abundance

In astronomy, those elements with higher atomic numbers than helium are termed "metals". The metallicity of Vega's photosphere is only about 32% of the abundance of heavy elements in the Sun's atmosphere.[note 3] (Compare this, for example, to a threefold 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.[76] Thus, in terms of abundances, only about 0.54% of Vega consists of elements heavier than helium. Nitrogen is slightly more abundant, oxygen is only marginally less abundant and sulfur abundance is about 50% of solar. On the other hand, Vega has only 10% to 30% of the solar abundance for most other major elements with barium and scandium below 10%.[11]

The unusually low metallicity of Vega makes it a weak

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.[79]

The observed helium to hydrogen ratio in Vega is 0.030±0.005, which is about 40% lower than 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.[80]

Kinematics

The

blueshift give a value of −13.9±0.9 km/s.[9]
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

milliarcseconds (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. The net proper motion of Vega is 327.78 mas/y,[81]
which results in angular movement of a degree every 11,000 years.

In the

perihelion distance of 13.2 ly (4.04 pc).[84]

Based on this star's kinematic properties, it appears to belong to a stellar association called the

space velocities. Membership in a moving group implies a common origin for these stars in an open cluster that has since become gravitationally unbound.[85] The estimated age of this moving group is 200±100 million years, and they have an average space velocity of 16.5 km/s.[note 4][82]

Possible planetary system

The Vega planetary system[25]
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(days) 		Eccentricity Inclination Radius
b (unconfirmed) ≥21.9±5.1 M⊕ 0.04555±0.00053 2.42977±0.00016 0.25±0.15 — —
Debris disk 86–815 AU 6.2?° —
A mid-infrared (24 μm) image of the debris disk around Vega

Infrared excess

One of the early results from the

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 millimetre, as anything smaller would eventually be removed from the system by radiation pressure or drawn into the star by means of Poynting–Robertson drag.[86] 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.[87]

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.[86] Models fitted to the dust distribution around Vega indicate that it is a 120-astronomical-unit-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.[88]

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.[24]

Debris disks

By 2005, 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.[23]

Artist's concept of a recent massive collision of dwarf planet-sized objects that may have contributed to the dust ring around Vega

The inner boundary of the debris disk was estimated at 11″±2″, or 70–100 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.[23]

Observations, first with the

meteors, and may be evidence for the existence of a planetary system.[92]

Possible planets

Observations from the

UCLA suggested that the image may indicate a planetary system still undergoing formation.[94]

Determining the nature of the planet has not been straightforward; a 2002 paper hypothesizes that the clumps 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.[95]

Artist's impression of a planet around Vega

In 2003, it was hypothesized that these clumps could be caused by a roughly

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.[97]

Using a

Herschel Space Telescope.[101]

Although a planet has yet to be directly observed around Vega, the presence of a planetary system cannot yet be ruled out. Thus there could be smaller,

inclination of planetary orbits around Vega is likely to be closely aligned to the equatorial plane of this star.[102]

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.[note 5]

In 2021, a paper analyzing 10 years of spectra of Vega detected a candidate 2.43-day signal around Vega, statistically estimated to have only a 1% chance of being a false positive.[25] Considering the amplitude of the signal, the authors estimated a minimum mass of 21.9±5.1 Earth masses, but considering the very oblique rotation of Vega itself of only 6.2° from Earth's perspective, the planet may be aligned to this plane as well, giving it an actual mass of 203±47 Earth masses.[25] The researchers also detected a faint 196.4+1.6
−1.9-day signal which could translate to a 80±21 Earth masses (740±190 at 6.2° inclination) but is too faint to claim as a real signal with available data.[25]

Etymology and cultural significance

See also:
Vega in fiction

The name is believed to be derived from the

King Alfonso X.[108] Medieval astrolabes of England and Western Europe used the names Wega and Alvaca, and depicted it and Altair as birds.[109]

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.[110]

The

ancient Greeks, the constellation Lyra was formed from the harp of Orpheus, with Vega as its handle.[16] For the Roman Empire, the start of autumn was based upon the hour at which Vega set below the horizon.[15]

In

γ Aquilae) are separated from their mother Zhinü (織女, lit. "weaver girl", Vega) who is on the far side of the river, the Milky Way.[113] However, one day per year on the seventh day of the seventh month of the Chinese lunisolar calendar, magpies make a bridge so that Niulang and Zhinü can be together again for a brief encounter. The Japanese Tanabata festival, in which Vega is known as Orihime (織姫), is also based on this legend.[114]

In Zoroastrianism, Vega was sometimes associated with Vanant, a minor divinity whose name means "conqueror".[115]

The indigenous

Boorong people of north-western Victoria, Australia, named it Neilloan,[116] "the flying loan".[117]

In the

Srimad Bhagavatam, Shri Krishna tells Arjuna, that among the Nakshatras he is Abhijit, which remark indicates the auspiciousness of this Nakshatra.[118]

kabbalistic sign under Vultur cadens, a literal Latin translation of the Arabic name.[120] Medieval star charts also listed the alternate names Waghi, Vagieh and Veka for this star.[31]

W. H. Auden's 1933 poem "A Summer Night (to Geoffrey Hoyland)"[121] famously opens with the couplet, "Out on the lawn I lie in bed,/Vega conspicuous overhead".

Vega became the first star to have a car named after it with the French

ESA's Vega launch system[123] and the Lockheed Vega aircraft.[124]

Notes

  1. ^ The polar temperature is around 2,000 K higher than at the equator due to the rapid rotation of Vega
  2. ISBN 978-0-387-98746-0
    .:
    Mbol = −2.5 log L/L☉ + 4.74,
    where Mbol is the
    bolometric magnitude, L is the star's luminosity, and L☉ is the solar luminosity
    . A Mbol variation of ±0.03 gives
    Mbol2 − Mbol1 = 0.03 = 2.5 log L1/L2
    for
    L1/L2 = 100.03/2.5 ≈ 1.028,
    or a ±2.8% luminosity variation.
  3. ^ For a metallicity of −0.5, the proportion of metals relative to the Sun is given by
    .
    See: Matteucci, Francesca (2001). The Chemical Evolution of the Galaxy. Astrophysics and Space Science Library. Vol. 253. Springer Science & Business Media. p. 7.
    ISBN 978-0792365525
    .
  4. ^ The space velocity components in the Galactic coordinate system are: U = −10.7±3.5, V = −8.0±2.4, W = −9.7±3.0 km/s. UVW is a Cartesian coordinate system, so the Euclidean distance formula applies. Hence, the net velocity is
    See: Bruce, Peter C. (2015). Introductory Statistics and Analytics: A Resampling Perspective. John Wiley & Sons. p. 20.
    ISBN 978-1118881330
    .
  5. ^ 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  π
    See: Hughes, David W. (2006). "The Introduction of Absolute Magnitude (1902–1922)". Journal of Astronomical History and Heritage. 9 (2): 173–179.
    S2CID 115611984
    .
  6. ^ That is, a vulture on the ground with its wings folded (Edward William Lane, Arabic-English Lexicon).

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