Wikipedia

Vega

"Star Vega" redirects here. For the psychologist, seeStar Vega (psychologist).For other uses, seeVega (disambiguation).

Vegais the brighteststarin the northernconstellationofLyra.It has theBayer designationα Lyrae,which isLatinisedtoAlpha Lyraeand abbreviatedAlpha Lyrorα Lyr.This star isrelatively closeat only 25light-years(7.7parsecs) from theSun,and one of the most luminous stars in theSun's neighborhood.It is thefifth-brightest starin thenight sky,and the second-brightest star in thenorthern celestial hemisphere,afterArcturus.

Vega
Location of Vega (circled)
Observation data
EpochJ2000.0EquinoxJ2000.0
Constellation Lyra
Pronunciation /ˈviːɡə/[1][2][3]or/ˈveɪɡə/[2]
Right ascension 18h36m56.33635s[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−Bcolor index 0.00[8]
B−Vcolor index 0.00[8]
Variable type Delta Scuti[6]
Astrometry
Radial velocity(Rv)−13.9±0.9[9]km/s
Proper motion(μ)RA:200.94[4]mas/yr
Dec.:286.23[4]mas/yr
Parallax(π)130.23 ± 0.36mas[4]
Distance25.04 ± 0.07ly
(7.68 ± 0.02pc)
Absolute magnitude(MV)+0.582[10]
Details
Mass2.15+0.10
−0.15[11]M☉
Radius2.726±0.006(equatorial),2.418±0.008(polar)[11]R☉
Luminosity47.2±0.2[11]L☉
Surface gravity(logg)4.1±0.1[12]cgs
Temperature10,070±90(polar),8,910±130(equatorial)[11]K
Metallicity[Fe/H]−0.5[13]dex
Rotation16.3h[14]
Rotational velocity(vsini)21.3±0.2[11]km/s
Age700+150
−75[11]Myr
Other designations
Wega[15],Lucida Lyrae[16],Alpha Lyrae, α Lyrae,3 Lyrae,BD+38°3238,GJ721,HD172167,HIP91262,HR7001,SAO67174,LTT15486[17]
Database references
SIMBADdata

Vega has been extensively studied by astronomers, leading it to be termed "arguably the next most important star in the sky after the Sun".[18]Vega was the northernpole stararound 12,000 BCE and will be so again around the year 13,727, when itsdeclinationwill be +86° 14′.[19]Vega was the first star other than the Sun to have its image andspectrumphotographed.[20][21]It was one of the first stars whose distance was estimated throughparallaxmeasurements. Vega has functioned as the baseline for calibrating thephotometricbrightness scale and was one of the stars used to define thezero pointfor theUBV 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 theirmain sequencelifetimes. Compared with the Sun, Vega has a lower abundance ofelements heavier than helium.[13]Vega is also avariable star—that is, a star whose brightness fluctuates. It isrotatingrapidly with a speed of236 km/sat the equator. This causes the equator to bulge outward due tocentrifugaleffects, and, as a result, there is a variation of temperature across the star'sphotospherethat reaches a maximum at the poles. From Earth, Vega is observed from the direction of one of these poles.[22]

Based on observations of moreinfraredradiation than expected, Vega appears to have acircumstellar diskofdust.This dust is likely to be the result of collisions between objects in an orbitingdebris disk,which is analogous to theKuiper beltin theSolar System.[23]Stars that display an infrared excess due to dust emission are termed Vega-like stars.[24]In 2021, a candidateultra-hot Neptuneon a 2.43-day orbit around Vega was discovered with theradial velocitymethod, additionally, another possible Saturn-mass signal with a period of about 200 days.[25]

Nomenclature

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Vega is the brightest star in the constellation of Lyra.

αLyrae(LatinisedtoAlpha Lyrae) is the star'sBayer designation.The traditional nameVega(earlierWega[15]) comes from a loose transliteration of theArabicwordwāqi'(Arabic:واقع) meaning "falling" or "landing", via the phrasean-nasr al-wāqi'(Arabic:النّسر الْواقع), "the falling eagle".[26]In 2016, theInternational Astronomical Union(IAU) organized aWorking 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 includedVegafor this star. It is now so entered in theIAU Catalog of Star Names.[29]

Observation

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TheSummer Triangle

Vega can often be seen near thezenithin the mid-northernlatitudesduring the evening in theNorthern Hemispheresummer.[30]From mid-southern latitudes, it can be seen low above the northern horizon during theSouthern Hemispherewinter. With adeclinationof +38.78°, Vega can only be viewed at latitudes north of51° S.Therefore, it does not rise at all anywhere inAntarcticaor in the southernmost part of South America, includingPunta Arenas,Chile(53° S). At latitudes to the north of51° N,Vega remains continuously above the horizon as acircumpolar star.Around July 1, Vega reaches midnightculminationwhen it crosses themeridianat that time.[31]Complementarily, Vega swoops down and kisses the horizon at true North at midnight on Dec 31/Jan 1, as seen from 51° N.

Path of Vega at winter solstice, as seen from 51°N
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 apole star.The direction of the Earth's axis of rotation gradually changes over time in a process known as theprecession 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 thecelestial spherethat passes near several prominent stars. At present the pole star isPolaris,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 becomethe brightest starin 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 avertexof a widely spacedasterismcalled theSummer Triangle,which consists of Vega plus the two first-magnitude starsAltair,inAquila,andDenebinCygnus.[30]This formation is the approximate shape of aright triangle,with Vega located at itsright angle.The Summer Triangle is recognizable in the northern skies for there are few other bright stars in its vicinity.[35]

Observational history

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Astrophoto of Vega
"On the night of July 16–17, 1850,WhippleandBondmade the firstdaguerreotypeof a star (Vega) "

Astrophotography,thephotographyof celestial objects, began in 1840 whenJohn William Drapertook an image of theMoonusing thedaguerreotypeprocess. On 17 July 1850, Vega became the first star (other than the Sun) to be photographed, when it was imaged byWilliam BondandJohn Adams Whippleat theHarvard College Observatory,also with a daguerreotype.[15][20][36]In August 1872,Henry Drapertook a photograph of Vega'sspectrum,the first photograph of a star's spectrum showing absorption lines.[21]Similar lines had already been identified in the spectrum of the Sun.[37]In 1879,William Hugginsused 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 HydrogenBalmer series.[38]Since 1943, thespectrumof 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 theEarthorbits the Sun.Giuseppe Calandrellinoted 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 wasFriedrich G. W. von Struve,when he announced a value of 0.125 arcsecond (0.125″) for Vega.[41]Friedrich Besselwas skeptical about Struve's data, and, when Bessel published a parallax of 0.314″ for the star system61 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 theHipparcosastrometrysatellite.[4][44][45]

The brightness of a star, as seen from Earth, is measured with a standardized,logarithmic scale.Thisapparent magnitudeis 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 absolutephotometricbrightness 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 specifiedflux.This approach is more convenient for astronomers, since Vega is not always available for calibration and varies in brightness.[47]

TheUBV photometric systemmeasures the magnitude of stars throughultraviolet,blue and yellow filters, producingU,BandVvalues, respectively. Vega is one of sixA0V starsthat 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 scale has been calibrated so that the magnitude of these stars is the same in the yellow, blue and ultraviolet parts of theelectromagnetic spectrum.[48]Thus, Vega has a relatively flat electromagnetic spectrum in the visual region—wavelength range 350–850nanometers,most of which can be seen with the human eye—so the flux densities are roughly equal; 2,000–4,000Jy.[49]However, the flux density of Vega drops rapidly in theinfrared,and is near100 Jyat5micrometers.[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 1]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 theDavid Dunlap Observatoryand showed some slight variability. Thus it was suggested that Vega showed occasional low-amplitude pulsations associated with aDelta 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 solitarymain-sequence starbeyond the Sun known to be an X-ray emitter when in 1979 it was observed from an imaging X-ray telescope launched on anAerobee350 from theWhite Sands Missile Range.[57]In 1983, Vega became the first star found to have a disk of dust. TheInfrared 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

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Vega'sspectral classis A0V, making it a blue-tinged whitemain-sequence starthat isfusinghydrogentoheliumin its core. Since more massive stars use their fusion fuel more quickly than smaller ones, Vega's main-sequence lifetime is roughly one billion years, a tenth of the Sun's.[59]The current age of this star is about 455 million years,[60]or up to about half its expected total main-sequence lifespan. After leaving the main sequence, Vega will become a class-Mred giantand shed much of its mass, finally becoming awhite dwarf.At present, Vega has more than twice the mass[22]of the Sun and itsbolometric luminosityis 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 aDelta Scuti typewith 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), anuclear fusionprocess that combinesprotonsto form helium nuclei through intermediary nuclei of carbon, nitrogen and oxygen. This process becomes dominant at a temperature of about 17 million K,[61]which is slightly higher than the core temperature of the Sun, but is less efficient than the Sun'sproton–proton chainfusion reaction. The CNO cycle is highly temperature sensitive, which results in aconvection zoneabout the core[62]that evenly distributes the 'ash' from the fusion reaction within the core region. The overlying atmosphere is inradiative equilibrium.This is in contrast to the Sun, which has aradiation zonecentered on the core with an overlying convection zone.[63]

The energy flux from Vega has been precisely measured against standard light sources. At5,480 Å,the flux density is3,650 Jywith an error margin of 2%.[64]The visual spectrum of Vega is dominated byabsorption linesof hydrogen; specifically by the hydrogenBalmer serieswith theelectronat the n=2principal quantum number.[65][66]The lines of other elements are relatively weak, with the strongest being ionizedmagnesium,ironandchromium.[67]TheX-rayemission from Vega is very low, demonstrating that thecoronafor this star must be very weak or non-existent.[68]However, as the pole of Vega is facing Earth and a polarcoronal holemay be present,[57][69]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.[69][70]

Usingspectropolarimetry,amagnetic fieldhas been detected on the surface of Vega by a team of astronomers at theObservatoire du Pic du Midi.This is the first such detection of a magnetic field on a spectral class A star that is not anApchemically peculiar star.The average line of sight component of this field has a strength of−0.6±0.3gauss (G).[71]This is comparable to the mean magnetic field on the Sun.[72]Magnetic fields of roughly 30 G have been reported for Vega, compared to about 1 G for the Sun.[57]In 2015, brightstarspotswere detected on the star's surface—the first such detection for a normalA-type star,and these features show evidence ofrotational modulationwith a period of 0.68 day.[73]

Rotation

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Vega has a rotation period of 16.3 hours,[14]much faster than the Sun's rotational period but similar to, and slightly slower than, those ofJupiterandSaturn.Because of that, Vega is significantlyoblatelike those two planets.

When the radius of Vega was measured to high accuracy with aninterferometer,it resulted in an unexpectedly large estimated value of2.73±0.01times theradius 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 theCHARA arrayin 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 therotationvelocity for Vega is236.2±3.7 km/s[60]along the equator, much higher than the observed (i.e.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 fromcentrifugaleffects.[60]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 is2.362±0.012solar radii,while the equatorial radius is2.818±0.013solar radii.[60]) From the Earth, this bulge is being viewed from the direction of its pole, producing the overly large radius estimate.

The localsurface gravityat the poles is greater than at the equator, which produces a variation ineffective temperatureover the star: the polar temperature is near10,000K,while the equatorial temperature is about8,152 K.[60]This large temperature difference between the poles and the equator produces a stronggravity darkeningeffect. 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][74]while the remainder of the atmosphere is likely to be in almost pureradiative equilibrium.[75]By theVon Zeipel theorem,the local luminosity is higher at the poles. As a result, if Vega were viewed along the plane of itsequatorinstead of almost pole-on, then its overall brightness would be lower.

As Vega had long been used as astandard 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.[76]

Element abundance

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In astronomy, those elements with higheratomic numbersthan helium are termed "metals". Themetallicityof Vega'sphotosphereis only about 32% of the abundance of heavy elements in the Sun's atmosphere.[note 2](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.[77]Thus, in terms of abundances, only about 0.54% of Vega consists of elements heavier than helium.Nitrogenis slightlymoreabundant,oxygenis only marginally less abundant andsulfurabundance is about 50% of solar. On the other hand, Vega has only 10% to 30% of the solar abundance for most other major elements withbariumandscandiumbelow 10%.[60]

The unusually low metallicity of Vega makes it a weakLambda Boötis star.[78][79]However, the reason for the existence of such chemically peculiar,spectral classA0–F0 stars remains unclear. One possibility is that the chemical peculiarity may be the result ofdiffusionor 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 aninterstellar mediumof gas and dust that was unusually metal-poor.[80]

The observed helium to hydrogen ratio in Vega is0.030±0.005,which is about 40% lower than the Sun. This may be caused by the disappearance of a heliumconvection zonenear the surface. Energy transfer is instead performed by theradiative process,which may be causing an abundance anomaly through diffusion.[81]

Kinematics

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Theradial velocityof 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 lowerfrequency(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 shift of the star's spectrum. Precise measurements of thisblueshiftgive 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 asproper motion,to be calculated. Vega's proper motion is202.03±0.63milliarcseconds(mas) per year inright ascension—the celestial equivalent oflongitude—and287.47±0.54 mas/yindeclination,which is equivalent to a change inlatitude.The net proper motion of Vega is327.78 mas/y,[82]which results in angular movement of a degree every11,000 years.

In thegalactic coordinate system,thespace velocitycomponents of Vega are (U, V, W) =(−16.1±0.3,−6.3±0.8,−7.7±0.3) km/s,for a net space velocity of19 km/s.[83]The radial component of this velocity—in the direction of the Sun—is−13.9 km/s,while the transverse velocity is12.9 km/s.[citation needed]Although Vega is at present only the fifth-brightest star in the night sky, the star is slowly brightening as proper motion causes it to approach the Sun.[84]Vega will make its closest approach in an estimated 264,000 years at aperiheliondistance of 13.2 ly (4.04 pc).[85]

Based on this star's kinematic properties, it appears to belong to a stellar association called theCastor Moving Group.However, Vega may be much older than this group, so the membership remains uncertain.[60]This group contains about 16 stars, includingAlpha Librae,Alpha Cephei,Castor,Fomalhautand Vega. All members of the group are moving in nearly the same direction with similarspace velocities.Membership in a moving group implies a common origin for these stars in anopen clusterthat has since become gravitationally unbound.[86]The estimated age of this moving group is200±100 million years,and they have an average space velocity of16.5 km/s.[note 3][83]

Possible planetary system

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The Vega planetary system[25][87]
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(days) 		Eccentricity Inclination Radius
b(unconfirmed) ≥21.9±5.1M🜨 0.04555±0.00053 2.42977±0.00016 0.25±0.15 — —
(unconfirmed) 20M🜨 ~2–5 — — — —
Hot dust ≤0.2AU — —
Inner Disk (3-5)–78AU 7-8° —
Kuiper-Belt Analogue 78–170AU 9-11° —
Halo <250AU — —
The debris disk around Vega with JWSTMIRI(all images) and ALMA (contours lower right image). Image published by Su et al.[87]

Infrared excess

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One of the early results from theInfrared Astronomy Satellite(IRAS) was the discovery ofexcess infrared fluxcoming from Vega, beyond what would be expected from the star alone. This excess was measured atwavelengthsof 25, 60 and100μm,and came from within an angular radius of10 arcseconds(10″) centered on the star. At the measured distance of Vega, this corresponded to an actual radius of80astronomical 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 ofPoynting–Robertson drag.[88]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.[89]

Subsequent measurements of Vega at193 μmshowed a lower than expected flux for the hypothesized particles, suggesting that they must instead be on the order of100 μmor 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.[88]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 than80 AU.[90]

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 theSolar System.[24]

Debris disks

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By 2005, theSpitzer Space Telescopehad produced high-resolution infrared images of the dust around Vega. It was shown to extend out to 43″ (330 AU) at a wavelength of24 μm,70″ (543 AU) at70 μmand105″(815 AU) at160 μm.These much wider disks were found to be circular and free of clumps, with dust particles ranging from 1–50 μmin size. The estimated total mass of this dust is 3×10−3times themass of the Earth(around 7.5 times more massive than theasteroid belt). Production of the dust would require collisions between asteroids in a population corresponding to theKuiper Beltaround the Sun. Thus the dust is more likely created by adebris diskaround Vega, rather than from aprotoplanetary diskas was earlier thought.[23]

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

The inner boundary of the debris disk was estimated at11″±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 themass 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 thePalomar Testbed InterferometerbyDavid CiardiandGerard van Bellein 2001[91]and then later confirmed with theCHARA arrayat Mt. Wilson in 2006 and theInfrared Optical Telescope Arrayat Mt. Hopkins in 2011,[92]revealed evidence for an inner dust band around Vega. Originating within8 AUof the star, thisexozodiacal dustmay be evidence of dynamical perturbations within the system.[93]This may be caused by an intense bombardment ofcometsormeteors,and may be evidence for the existence of a planetary system.[94]

The disk was also observed withALMAin 2020[95],theLMTin 2022[96]and withHubbleSTIS[97]andJWSTMIRI in 2024.[87]The ALMA image did resolve the outer disk for the first time.[95]The Hubble observation is the first image of the disk in scattered light and found an outer halo made up of small dust grains.[97]JWST observations also detected the Halo, the outer disk and for the first time the inner disk. The infrared observations also showed a gap at 60 AU for the first time. The dust interior of the outer disk is consistent with dust being dragged by thePoynting-Robertson effect.The inner edge of the inner disk is hidden behind thecoronagraph,but it was inferred to be 3-5 AU from photometry. The star is also surrounded by hot infrared excess, located at the sub-AU region, leaving a second gap between the inner disk and the hot dust around the star. This hot infrared excess lies within about 0.2 AU or closer and is made up of small grains, likegraphiteandironandmanganeseoxides, which was previously verified.[87]

Possible planets

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Observations from theJames Clerk Maxwell Telescopein 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 aplanetor else an orbiting object that was surrounded by dust. However, images by theKeck telescopehad ruled out a companion down to magnitude 16, which would correspond to a body with more than 12 times the mass of Jupiter.[98]Astronomers at theJoint Astronomy Centrein Hawaii and atUCLAsuggested that the image may indicate a planetary system still undergoing formation.[99]

Determining the nature of the planet has not been straightforward; a 2002 paper hypothesizes that the clumps are caused by a roughlyJupiter-mass planet on an eccentric orbit.Dust would collect in orbits that havemean-motion resonanceswith this planet—where their orbital periods form integer fractions with the period of the planet—producing the resulting clumpiness.[100]

Artist's impression of a planet around Vega

In 2003, it was hypothesized that these clumps could be caused by a roughlyNeptune-mass planet havingmigratedfrom 40 to65AUover 56 million years,[101]an orbit large enough to allow the formation of smallerrocky planetscloser to Vega. The migration of this planet would likely require gravitational interaction with a second, higher-mass planet in a smaller orbit.[102]

Using acoronagraphon theSubaru Telescopein 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.[103]The issue of possible clumps in the debris disc was revisited in 2007 using newer, more sensitive instrumentation on thePlateau de Bure Interferometer.The observations showed that the debris ring is smooth and symmetric. No evidence was found of the blobs reported earlier, casting doubts on the hypothesized giant planet.[104]The smooth structure has been confirmed in follow-up observations by Hughes et al. (2012)[105]and theHerschel Space Telescope.[106]

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,terrestrial planetsorbiting closer to the star. Theinclinationof planetary orbits around Vega is likely to be closely aligned to theequatorialplane of this star.[107]

From the perspective of an observer on a hypothetical planet around Vega, the Sun would appear as a faint 4.3-magnitude star in theColumbaconstellation.[note 4]

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 of21.9±5.1Earth 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 of203±47Earth masses.[25]The researchers also detected a faint196.4+1.6
−1.9-day signal which could translate to80±21Earth masses (740±190at 6.2° inclination) but is too faint to claim as a real signal with available data.[25]

Observations of the disk with JWST MIRI did find a very circular face-on disk. The morphology indicate that there is no planet more massive thanSaturnbeyond 10 AU. The disk has a gap at around 60 AU. Gap-opening planets are inferred for disks around other stars and the team tests this idea for Vega by running simulations. The simulations have shown that a planet with ≥6MEat 65 AU would introduce interior asymetric structures that are not seen in the disk of Vega. Any gap-opening planet would need to be less massive. Additionally the inner edge of the inner disk was inferred to be 3-5 AU. Vega shows also evidence for hot infrared excess at the sub-AU region. The inner boundary of the warm debris might indicate that there is aNeptune-mass planet inside,shepherdingit.[87]

Etymology and cultural significance

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See also:Summer TriangleandStars in astrology § Vega

The name is believed to be derived from theArabictermAl Nesr al Wakiالنسر الواقعwhich appeared in theAl Achsasi al Mouakketstar catalogue and was translated intoLatinasVultur Cadens,"the falling eagle/vulture".[108][note 5]The constellation was represented as a vulture inancient Egypt,[109]and as an eagle or vulture inancient India.[110][111]The Arabic name then appeared in thewestern worldin theAlfonsine tables,[112]which were drawn up between 1215 and 1270 by order ofKing Alfonso X.[113]MedievalastrolabesofEnglandandWestern Europeused the names Wega and Alvaca, and depicted it andAltairas birds.[114]

Among the northernPolynesianpeople, Vega was known aswhetu 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 thePleiades.[115]

TheAssyriansnamed this pole star Dayan-same, the "Judge of Heaven", while inAkkadianit was Tir-anna, "Life of Heaven". InBabylonian astronomy,Vega may have been one of the stars named Dilgan, "the Messenger of Light". To theancient Greeks,the constellation Lyra was formed from the harp ofOrpheus,with Vega as its handle.[16]For theRoman Empire,the start of autumn was based upon the hour at which Vega set below the horizon.[15]

InChinese,Chức nữ(Zhī Nǚ), meaningWeaving Girl(asterism),refers to anasterismconsisting of Vega,ε Lyraeandζ1Lyrae.[116]Consequently, theChinese namefor Vega isChức nữ nhất(Zhī Nǚ yī,English:the First Star of Weaving Girl).[117]InChinese mythology,there is a love story ofQixi(Thất tịch) in which Niulang (Ngưu lang,Altair) and his two children (β Aquilaeandγ Aquilae) are separated from their mother Zhinü (Chức nữ,lit. "weaver girl", Vega) who is on the far side of the river, theMilky Way.[118]However, one day per year on the seventh day of the seventh month of theChinese lunisolar calendar,magpiesmake a bridge so that Niulang and Zhinü can be together again for a brief encounter. The JapaneseTanabatafestival, in which Vega is known asOrihime( chức cơ ), is also based on this legend.[119]

InZoroastrianism,Vega was sometimes associated with Vanant, a minor divinity whose name means "conqueror".[120]

The indigenousBoorongpeople of north-westernVictoria,Australia, named itNeilloan,[121]"the flyingloan".[122]

In theSrimad Bhagavatam,Shri KrishnatellsArjuna,that among the Nakshatras he is Abhijit, which remark indicates the auspiciousness of this Nakshatra.[123]

Medievalastrologerscounted Vega as one of theBehenian stars[124]and related it tochrysoliteandwinter savory.Cornelius Agrippalisted itskabbalisticsignunderVultur cadens,a literal Latin translation of the Arabic name.[125]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)"[126]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 FrenchFacel Vegaline of cars from 1954 onwards, and later on, in America,Chevroletlaunched theVegain 1971.[127]Other vehicles named after Vega include theESA'sVegalaunch system[128]and theLockheed Vegaaircraft.[129]

Notes

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  1. ^FromCox, Arthur N., ed. (1999).Allen's Astrophysical Qualities(4th ed.). New York: Springer-Verlag. p. 382.ISBN978-0-387-98746-0.:
    Mbol= −2.5 logL/L☉+ 4.74,
    whereMbolis thebolometric magnitude,Lis the star's luminosity, andL☉is thesolar luminosity.AMbolvariation of ±0.03 gives
    Mbol2−Mbol1= 0.03 = 2.5 logL1/L2
    for
    L1/L2= 100.03/2.5≈ 1.028,
    or a ±2.8% luminosity variation.
  2. ^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.ISBN978-0792365525.
  3. ^The space velocity components in theGalactic coordinate systemare: U =−10.7±3.5,V =−8.0±2.4,W =−9.7±3.0 km/s.UVW is aCartesian coordinate system,so theEuclidean distanceformula applies. Hence, the net velocity is
    See:Bruce, Peter C. (2015).Introductory Statistics and Analytics: A Resampling Perspective.John Wiley & Sons. p. 20.ISBN978-1118881330.
  4. ^The Sun would appear at the diametrically opposite coordinates from Vega at α =6h36m56.3364s,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.Bibcode:2006JAHH....9..173H.doi:10.3724/SP.J.1440-2807.2006.02.06.S2CID115611984.
  5. ^That is, a vulture on the ground with its wings folded (Edward William Lane,Arabic-English Lexicon).

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