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Beta Lyrae
Location of β Lyrae (circled in red)
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Lyra
Right ascension 18h 50m 04.79525s[1]
Declination +33° 21′ 45.6100″[1]
Apparent magnitude (V) 3.52[2] (3.25 – 4.36[3])
Characteristics
Spectral type B6-8II[4][5] + B[2]
U−B color index −0.56[6]
B−V color index +0.00[6]
Variable type β Lyr[3]
Astrometry
A
Radial velocity (Rv)−19.2[7] km/s
Proper motion (μ) RA: 1.90[1] mas/yr
Dec.: −3.53[1] mas/yr
Parallax (π)3.39±0.17 mas[1]
Distance960 ± 50 ly
(290 ± 10 pc)
Absolute magnitude (MV)−3.82[8]
B
Radial velocity (Rv)−14±5[9] km/s
Proper motion (μ) RA: 4.373±0.087[10] mas/yr
Dec.: −0.982±0.098[10] mas/yr
Parallax (π)3.0065±0.0542 mas[10]
Distance1,080 ± 20 ly
(333 ± 6 pc)
Orbit[2]
PrimaryAa1
CompanionBeta Lyrae Aa2
Period (P)12.9414 days
Semi-major axis (a)0.865±0.048 mas
Eccentricity (e)0
Inclination (i)92.25 ± 0.82°
Longitude of the node (Ω)254.39 ± 0.83°
Details[11]
β Lyr Aa1
Mass2.97 ± 0.2 M☉
Radius15.2 ± 0.2 R☉
Luminosity6,500 L☉
Surface gravity (log g)2.5 ± 0.1 cgs
Temperature13,300 K
Age23 Myr
β Lyr Aa2
Mass13.16 ± 0.3 M☉
Radius6.0 ± 0.2 R☉
Luminosity26,300 L☉
Surface gravity (log g)4.0 ± 0.1 cgs
Temperature30,000 ± 2,000 K
Other designations
Sheliak, Shelyak, Shiliak, WDS 18501+3322[12]
β Lyrae A: 10 Lyrae, AAVSO 1846+33, BD+33 3223, FK5 705, HD 174638, HIP 92420, HR 7106, SAO 67451/2
β Lyrae B: HD 174664, BD+33 3224, SAO 67453
Database references
SIMBADβ Lyrae
B

Beta Lyrae (β Lyrae, abbreviated Beta Lyr, β Lyr) officially named Sheliak (Arabic: الشلياق, Romanization: ash-Shiliyāq) (IPA: /ˈʃiːliæk/), the traditional name of the system, is a multiple star system in the constellation of Lyra. Based on parallax measurements obtained during the Hipparcos mission, it is approximately 960 light-years (290 parsecs) distant from the Sun.

Although it appears as a single point of light to the naked eye, it actually consists of six components of apparent magnitude 14.3 or brighter. The brightest component, designated Beta Lyrae A, is itself a triple star system, consisting of an eclipsing binary pair (Aa) and a single star (Ab). The binary pair's two components are designated Beta Lyrae Aa1 and Aa2. The additional five components, designated Beta Lyrae B, C, D, E, and F, are currently considered to be single stars.[12][13][14][15][16][17]

Nomenclature

[edit]

β Lyrae (Latinised to Beta Lyrae) is the system's Bayer designation, established by Johann Bayer in his Uranometria of 1603, and denotes that it is the second brightest star in the Lyra constellation. WDS J18501+3322 is a designation in the Washington Double Star Catalog. The designations of the constituents as Beta Lyrae A, B and C, or alternatively WDS J18501+3322A, B and C, and additionally WDS J18501+3322D, E and F, and those of A's components - Aa1, Aa2 and Ab - derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[18]

Beta Lyrae bore the traditional name Sheliak (occasionally Shelyak or Shiliak), derived from the Arabic الشلياق šiliyāq or Al Shilyāk, one of the names of the constellation of Lyra in Islamic astronomy.[19] Notably, in Arabic sources the Lyra constellation is primarily referred to as سِلْيَاق (Romanization: Siliyāq),[20][21] whereas شلياق (Šiliyāq) primarily is used to refer to Beta Lyrae in what might be a form of linguistic reborrowing.[22][23] Persian sources on the other hand, do refer to the Lyra constellation as شلياق (Šiliyāq), which may be the source of this confusion.[24][25]

In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[26] to catalogue and standardize proper names for stars. The WGSN decided to attribute proper names to individual stars rather than entire multiple systems.[27] It approved the name Sheliak for the component Beta Lyrae Aa1 on 21 August 2016 and it is now so included in the List of IAU-approved Star Names.[28]

In Chinese astronomy, Tsan Tae (漸台 (Jiāntāi), meaning Clepsydra Terrace, refers to an asterism consisting of this star, Delta² Lyrae, Gamma Lyrae and Iota Lyrae.[29] Consequently, the Chinese name for Beta Lyrae itself is 漸台二 (Jiāntāièr, English: the Second Star of Clepsydra Terrace.)

Properties

[edit]

Beta Lyrae Aa is a semidetached binary system made up of a stellar class B6-8 primary star and a secondary that is probably also a B-type star. The fainter, less massive star in the system was once the more massive member of the pair, which caused it to evolve away from the main sequence first and become a giant star. Because the pair are in a close orbit, as this star expanded into a giant it filled its Roche lobe and transferred most of its mass over to its companion.

The secondary, now more massive star is surrounded by an accretion disk from this mass transfer, with bipolar, jet-like features projecting perpendicular to the disk.[2] This accretion disk blocks humans' view of the secondary star, lowering its apparent luminosity and making it difficult for astronomers to pinpoint what its stellar type is. The amount of mass being transferred between the two stars is about 2 × 10−5 solar masses per year, or the equivalent of the Sun's mass every 50,000 years, which results in an increase in orbital period of about 19 seconds each year. The spectrum of Beta Lyrae shows emission lines produced by the accretion disc. The disc produces around 20% of the brightness of the system.[2]

In 2006, an adaptive optics survey detected a possible third companion, Beta Lyrae Ab. It was detected at 0.54" angular separation with a differential magnitude of +4.53. The difference in magnitudes suggests its spectral class is in the range B2-B5 V. This companion would make Beta Lyrae A a hierarchical triple system.[30]

Variability

[edit]
A light curve for Beta Lyrae, plotted from TESS data[31]

The variable luminosity of this system was discovered in 1784 by the British amateur astronomer John Goodricke.[32] In 1894, Aristarkh Belopolsky identified Beta Lyrae as an eclipsing spectroscopic binary.[33] The orbital plane of this system is nearly aligned with the line of sight from the Earth, so the two stars periodically eclipse each other. This causes Beta Lyrae to regularly change its apparent magnitude from +3.2 to +4.4 over an orbital period of 12.9414 days. It forms the prototype of a class of ellipsoidal "contact" eclipsing binaries.[3]

The two components are so close together that they cannot be resolved with optical telescopes, forming a spectroscopic binary. In 2008, the primary star and the accretion disk of the secondary star were resolved and imaged using the CHARA Array interferometer[34] and the Michigan InfraRed Combiner (MIRC)[35] in the near infrared H band (see video below), allowing the orbital elements to be computed for the first time.[2]

In addition to the regular eclipses, the system shows smaller and slower variations in brightness. These are thought to be caused by changes in the accretion disc and are accompanied by variation in the profile and strength of spectral lines, particularly the emission lines. The variations are not regular but have been characterised with a period of 282 days.[36]

The date of a primary minimum can be calculated according the following formula:

Primary_Minimum = 2436793.48 + 12.93095*n + 0.00000386*n*n

whereby n is a natural number. The calculated date is given in Julian days.

Companions

[edit]

In addition to Beta Lyrae A, several other companions have been catalogued. β Lyr B, at an angular separation of 45.7", is of spectral type B7V, has an apparent magnitude of +7.2, and can easily be seen with binoculars. It is about 80 times as luminous as the Sun. In 1962 it was identified as spectroscopic binary with a period of 4.348 days,[37] but the 2004 release of the SB9 catalog of Spectroscopic Binary Orbits omitted it, so it is now considered a single star.[13]

The next two brightest components are E and F. β Lyr E is magnitude 10.1v, separation 67", and β Lyr F is magnitude 10.6v, separation 86". Both are chemically peculiar stars;[38] both are catalogued as Ap stars, although component F is sometimes thought to be an Am star.[39]

The Washington Double Star Catalog lists two fainter companions, C and D, at 47" and 64" separation, respectively.[40] Component C has been observed to vary in brightness by over a magnitude, but the type of variability is not known.[41]

Components A, B, and F are thought to be members of a group of stars around β Lyrae, at approximately the same distance and moving together. The others just happen to be in the same line of sight.[39] Analysis of Gaia Data Release 2 astrometry reveals a group of about 100 stars around β Lyrae which share its space motion and are at the same distance. This cluster has been named Gaia 8. The cluster members are all main sequence stars and the lack of a main sequence turnoff means that a precise age cannot be calculated, but the cluster age is estimated at 30 to 100 million years. The average Gaia DR2 parallax for the member stars is 3.4 mas.[4]

The Gaia spacecraft has provided these data for the stars listed in the WDS:

Component[42] Spectral Class Magnitude (G) Proper Motion Radial Velocity (km/s) Parallax (mas) Simbad
RA (mas/yr) δ (mas/yr)
A[43][a] 3.25 – 4.36 2.045 ± 0.18 -3.685 ± 0.2069 2.20 ± 0.7 3.5982 ± 0.1836 [12]
B[10] B7V 7.19 2.174 ± 0.09 -1.272 ± 0.1039 -14 ± 5 3.5125 ± 0.0898 [13]
C[44] B2 13.07 -1.936 ± 0.01 -1.934 ± 0.0129 ? 0.2884 ± 0.0104 [14]
D[45] K3V 14.96 0.024 ± 0.034 -17.781 ± 0.0409 ? 0.845 ± 0.0333 [15]
E[46] G5 9.77 1.841 ± 0.015 0.536 ± 0.0159 1.4 1.5737 ± 0.0155 [16]
F[47] G5 10.10 1.416 ± 0.013 -3.963 ± 0.0149 -16.83 ± 1.41 3.4897 ± 0.0133 [17]
  1. ^ Gaia DR2 astrometric quality considered to be "terrible" for β Lyr A[4]

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Beta Lyrae

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Beta Lyrae, also known as Sheliak, is a prominent eclipsing system in the constellation , serving as the prototype for the class of Beta Lyrae variables, characterized by semi-detached components with ongoing mass transfer from the cooler primary to the hotter secondary via a thick . The system exhibits continuous photometric variability due to tidal distortions and eclipses, with an apparent visual magnitude ranging from 3.25 to 4.36 and an of 12.9414 days that is gradually increasing at a rate of about 19 seconds per year. Located approximately 960 light years from Earth, it was first recognized as a by John Goodricke in 1784. The primary component, Beta Lyrae Aa1, is a B7–B8 with a surface of about 12,000–14,500 , a of 15.2 solar radii, a of about 3 solar masses, and a of around 6,500–8,300 times that of the Sun; it fills its and transfers to the companion. The secondary, Beta Lyrae Aa2, is a hotter B0.5–B-type (around 30,000 ) with a of about 13 solar masses, a of 6 solar radii, and a of about 26,000–28,000 solar luminosities, partially obscured by the that contributes up to 20% of the system's total brightness. This phase, known as rapid phase , results in ellipsoidal shapes for both stars and evidence of bipolar outflows perpendicular to the orbital plane, making Beta Lyrae a key system for studying close binary . Beyond the close binary pair, Beta Lyrae is part of a multiple star system with at least five additional components, including a B7 V star (Beta Lyrae B, magnitude 7.19) and a G5 star (Beta Lyrae F, magnitude 10.10), forming a hierarchical structure; in 2019, it was identified as a member of the young star cluster Gaia 8, with an estimated age of 30–100 million years. Observations across wavelengths reveal unique traits, such as a flat ultraviolet light curve below 1,200 Å contrasting with the optical variability, and strong emission lines indicative of the active circumstellar environment. As one of the brightest and most studied eclipsing binaries, Beta Lyrae continues to provide insights into stellar interactions, with its light curve showing broad minima and rounded maxima that allow visual monitoring of both primary and secondary eclipses.

Nomenclature

Traditional Names

Beta Lyrae was assigned its , β Lyrae, by the German astronomer in his 1603 star atlas Uranometria, which systematically labeled stars in each constellation using Greek letters in order of apparent brightness. The star's primary traditional name, Sheliak (sometimes spelled Shelyak or Shiliak), derives from the term al-shilyāk (or similar transliterations), one of the names for the constellation as a whole in medieval astronomy; it is translated as "the tortoise" in some sources (likely alluding to the mythological tortoise whose shell Hermes used to fashion the ) and "the harp" in others, reflecting the constellation's lyre shape. In , the star was known as Šiliak, a direct adaptation of the . In ancient , Beta Lyrae formed part of the asterism Jiāntāi (漸台, "Clepsydra Terrace"), specifically designated as Jiāntāièr (漸台二, "Second Star of Clepsydra Terrace"), within the larger celestial palace enclosure. The (IAU) formally approved Sheliak as the proper name for the system's primary component, Beta Lyrae Aa1, on August 21, 2016, through its Working Group on Star Names. Historically, the name Sheliak has been used for the integrated system comprising multiple components.

Astronomical Designations

Beta Lyrae is formally designated HD 174638 in the Henry Draper Catalogue, a comprehensive survey of stellar spectra and magnitudes conducted in the early 20th century. In the Hipparcos Catalogue, which provided precise astrometric data from the 1990s satellite mission, it is listed as HIP 92420. The Gaia Data Release 3, from the European Space Agency's astrometry mission, assigns the primary component the identifier Gaia DR3 2090687795056051328, enabling high-precision position, parallax, and proper motion measurements. The multiple-star system follows a hierarchical , with the brightest member labeled Beta Lyrae A, comprising the close eclipsing binary pair Aa and the nearby third star Ab. Surrounding this core are fainter outer companions designated B through F, resolved as visual multiples. In the Washington Double Star Catalog (WDS), maintained by the U.S. Naval Observatory, the system is cataloged as WDS J18501+3322, compiling historical and modern measurements of double and multiple stars. The primary visual pair AB, discovered by F. G. W. Struve and designated STFA 39, has a typical separation of about 45.7 arcseconds, while other pairs like BC and CD exhibit separations ranging from 40 to 100 arcseconds based on epoch-dependent observations. For cross-referencing across databases, the astronomical database at the Centre de Données astronomiques de Strasbourg (CDS) uses the primary identifier * bet Lyr, linking to numerous catalogs including HD, HIP, , and WDS entries. The CDS's service provides further identifiers and metadata for comprehensive queries on the system's components. The traditional name Sheliak serves as a common alias in these references.

Observational History

Early Discoveries

Beta Lyrae, a prominent star in the constellation , was cataloged in as part of the lyre-shaped figure associated with the musician . It appears in Ptolemy's (2nd century CE), the foundational Greek star catalog, where includes 16 stars, with Beta Lyrae noted as the second-brightest after Alpha Lyrae (). Arabic astronomers, building on Ptolemaic traditions during the , referred to the star as Sheliak, derived from al-Shilyāk, a term evoking a tortoise shell or harp-like form linked to the constellation's musical theme; this name reflects observations in catalogs like those of Al-Sufi (10th century). In ancient , Beta Lyrae was known as Tsan Tae within the Tianfu asterism, part of broader stellar records dating back to the (circa 2nd century BCE), emphasizing its role in seasonal and calendrical systems. The star's variability was first recognized in 1784 by English amateur astronomer Edward Pigott, who observed irregular brightness changes during systematic sky surveys from his York observatory. Pigott's discovery was soon confirmed by his collaborator John Goodricke, a young deaf who meticulously tracked the over several months, estimating an initial period of about 13 days (precisely 12 days 21 hours 41 minutes in his 1785 report). Goodricke hypothesized that the variations resulted from eclipses or occultations by a companion body, marking an early insight into dynamics, though the exact mechanism remained debated. Advancing into the 19th century, spectroscopic observations by Italian astronomer Angelo Secchi in 1866 revealed Beta Lyrae's spectrum as belonging to his Class III (now recognized as B-type stars), characterized by strong Balmer hydrogen emission lines superimposed on absorption features—a pioneering identification of what would later be termed Be stars. Secchi's work at the , using a simple slit spectroscope, highlighted the star's hot, blue-white nature and unusual spectral variability tied to its light changes. In the 1880s, Harvard astronomer Edward C. Pickering advanced the binary hypothesis through detailed spectral analysis, noting cyclic shifts in emission lines that suggested orbital motion between two massive components, challenging earlier single-star pulsation models. The eclipsing binary nature of Beta Lyrae received formal recognition in 1907 by German astronomer Hans Ludendorff, who analyzed light curves and data to confirm mutual eclipses as the cause of the observed variations, establishing it as a for binary systems. Beta Lyrae thus became the namesake for the Beta Lyrae variable class, characterized by continuous light modulation from close-contact eclipses.

Recent Interferometric and Spectroscopic Studies

In the mid-20th century, observations played a pivotal role in elucidating the dynamics of Beta Lyrae. Studies by Sahade and collaborators in the , including detailed spectroscopic analysis of emission and absorption lines, provided evidence for ongoing between the binary components, marking one of the earliest confirmations of this process in close binaries. These measurements revealed asymmetric velocity curves indicative of material flow from the donor to the accretor, with semi-amplitudes supporting a consistent with evolution. Ultraviolet spectroscopy advanced this understanding during the 1970s and 1980s through observations with the International Ultraviolet Explorer (IUE) satellite. IUE spectra captured strong emission lines and continuum flux variations, attributed to hot spots where the mass-transfer stream impacts the , heating regions to temperatures exceeding 10,000 . These data highlighted phase-dependent emissions, particularly during non-eclipse phases, revealing the disk's opaque nature and the presence of extended gaseous structures illuminated by the central stars. Post-2000 interferometric efforts have resolved fine-scale structures in the system. Observations with the CHARA Array in 2018 resolved the radius of the secondary gainer component at approximately 6 solar radii and mapped the extent of the optically thick , spanning up to 30 solar radii, through near-infrared combining and instruments. This work confirmed the disk's flattened geometry and its dominance in the system's visibility function, providing constraints on the mass-transfer rate. Space-based and photometry have further refined systemic parameters. The Data Release 3 (2022) measurement of 3.01 ± 0.05 mas yields a distance of approximately 1080 light years (332 parsecs), refining prior estimates and aiding in absolute luminosity determinations. Meanwhile, (TESS) photometry since 2018 has delivered high-cadence light curves spanning multiple orbits, confirming the orbital period's stability at 12.9414 days with no significant deviations over short baselines. Recent analyses (as of 2023) of archival light curves have further confirmed the orbital period's long-term stability at 12.9414 days, supporting models of steady . The star cluster Gaia 8, centered on Beta Lyrae with ~100 members, was discovered in 2019 using DR2 and further confirmed by DR3 (2022) data, providing evidence of co-moving companions. Additionally, there is an ongoing need for with the to probe the cooler outer components (B–F) and disentangle their contributions from the inner system's glare.

Physical Properties

Position and Distance

Beta Lyrae is located in the constellation , positioned near the bright star . Its equatorial coordinates for the epoch J2000.0 are 18h 50m 04.63s and +33° 21′ 45.8″. The system has a of +1.90 mas/yr in and -3.53 mas/yr in , as determined from Data Release 3 observations. The distance to Beta Lyrae is 960 ± 50 light-years (290 ± 10 pc), derived from the DR3 parallax measurement of 3.40 ± 0.17 mas; this value revises earlier estimates from the mission, which suggested a similar distance. The systemic radial velocity of the Beta Lyrae system is -18.1 ± 0.5 km/s. The system is visible from most locations in the northern hemisphere, reaching a maximum apparent magnitude of 3.4.

Integrated System Characteristics

The Beta Lyrae system exhibits a mean apparent visual magnitude of 3.52 in the V band, varying between 3.4 and 4.3 due to its eclipsing nature. Its absolute visual magnitude is approximately -3.0, reflecting the combined luminosity of the dominant inner components at a distance of about 290 pc as measured by Gaia. The integrated spectral type of the system is classified as B8Ib, arising predominantly from the spectral contributions of the A subsystem's evolved and its companion. The age of the Beta Lyrae system is estimated at 30–100 million years, consistent with evolutionary models of its massive binary components and supported by its membership in the young Gaia 8, which shares similar proper motions, , and . The system's is solar-like, with overall chemical abundances approximating those of the Sun, though evidence from spectroscopic analysis indicates past enrichment due to , including significant overabundance (up to 6 times solar) in the atmosphere of the primary component.

Variability

Eclipsing Binary Behavior

Beta Lyrae serves as the prototype for the Beta Lyrae variable class of eclipsing binaries, featuring short-period photometric variations driven by mutual eclipses in its inner Aa subsystem. The of this subsystem is precisely measured at 12.94129 ± 0.00007 days, reflecting the close interaction between the components. This period governs the timing of the eclipses, with the equation for the orbital cycle given by P=12.94129P = 12.94129 days. Interferometric measurements have further constrained the semi-major axis of the relative orbit to approximately 58 R_⊙\odot, highlighting the compact nature of the system. The displays continuous variability outside of phases, arising from tidal distortion of the stellar envelopes and active from the donor to the gainer star. These effects produce a smoothly undulating profile, with the stars' ellipsoidal shapes contributing to the overall flux modulation. The eclipses feature broad minima without flat bottoms, resulting from the extended sizes of the stars, the , and high near 90 degrees. The primary eclipse occurs when the cooler primary component (Aa1) is occulted by the hotter secondary (Aa2), reaching a depth of about 1.0 magnitude in visual bands and lasting roughly 1.5 days due to the extended duration of the alignment. In contrast, the secondary eclipse, where Aa2 is occulted by Aa1, is significantly shallower at 0.1 magnitude, primarily because of the asymmetric distribution of the optically thick that partially obscures the cooler star and alters the effective eclipsing geometry. This asymmetry in eclipse depths underscores the role of the disk in shaping the observed photometry, distinguishing Beta Lyrae from simpler detached eclipsing systems.

Long-Term Photometric Variations

The of Beta Lyrae is increasing at a rate of about 19 seconds per year, attributed to ongoing from the primary to the secondary, which lengthens the orbit over time. This secular change is monitored through timing of eclipses and contributes to the system's long-term . Beta Lyrae displays long-term photometric variations superimposed on its short-term eclipsing behavior, characterized by a prominent 282-day cycle identified through extensive V-band monitoring. This periodicity was established from 2852 homogenized observations spanning 36 years, revealing a cyclic modulation in brightness that affects the overall shape. The cycle has an amplitude of approximately Δm ≈ 0.15 mag over the ~282 days, influencing eclipse depths and out-of-eclipse brightness levels. The origin of the 282-day period remains debated but has been attributed to of the or orbital apsidal motion in the inner . Early models suggested disk could modulate the disk's orientation and visibility, leading to periodic changes, while apsidal motion might alter the geometry of . However, detailed analyses indicate that neither mechanism fully explains the observed stability and amplitude, with alternative explanations involving variable rates that thicken or thin the disk over super-orbital timescales. Beyond this cycle, Beta Lyrae exhibits irregular photometric fluctuations of 0.1–0.2 mag occurring over several years, indicative of instabilities in the structure. These variations arise from episodic changes in or disk , causing non-periodic brightenings and fadings that disrupt the regularity of the 282-day modulation. Ground-based surveys, including data from the All-Sky Automated Survey for Supernovae (ASAS-SN) collected throughout the , document these fluctuations without evidence of strict periodicity, highlighting the dynamic nature of the disk. Recent space-based observations, such as those from the (TESS) after 2020, provide high-cadence photometry but lack comprehensive analysis of cycle stability for these long-term variations. This gap limits current understanding of whether the 282-day period remains consistent or evolves amid the irregular fluctuations.

Stellar Components

The Inner Triple System (Beta Lyrae A)

The inner triple system of Beta Lyrae A consists of a close eclipsing binary (Aa1 and Aa2) and a more distant companion (Ab), forming a hierarchical configuration with ongoing in the inner pair. The donor star Aa1 is a semi-detached B6-8II giant undergoing Roche lobe overflow, transferring material to the accretor Aa2 via an opaque . This has reversed the initial , placing the system in a post-main-sequence evolutionary stage where the donor has expanded beyond its , leading to a current mass ratio q ≈ 0.23 (defined as MAa1 / MAa2). The geometry is highly distorted due to the close orbit and rapid rotation of Aa1, with the donor filling approximately 100% of its volume. The donor Aa1 has a mass of 2.97 ± 0.06 M⊙, a of 15.2 ± 0.2 R⊙, and an Teff = 13,300 K, consistent with its spectral classification and photometric properties during non-eclipsing phases. The accretor Aa2 is a B-type embedded in an opaque , with a mass of 13.16 ± 0.08 M⊙ (yielding a total binary mass of 16.13 M⊙), an Teff ≈ 30,000 K for the central , and a disk of ~20 R⊙. The disk is optically thick, contributing significantly to the system's and the observed variability from Aa eclipses, where the disk partially occults the donor during secondary eclipse. The rate is estimated at ~10−5 M⊙ yr−1, sustaining the disk structure and jet-like outflows observed in high-resolution imaging. The third component Ab is a B2-B5 V main-sequence star with an estimated mass of ~3–5 M⊙, orbiting the inner binary at an angular separation of 0.25″ (corresponding to ~85 AU at the system's distance of ~340 pc) with an orbital period of ~200 years. Ab was detected via adaptive optics imaging in 2006–2008, revealing its bound orbit and contribution to the system's dynamics without significant interaction with the inner mass transfer. The triple system's stability is maintained by the wide separation of Ab, which has minimal influence on the inner binary's evolution but may affect long-term photometric variations through gravitational perturbations.

Outer Companions (Beta Lyrae B–F)

The Beta Lyrae system features several fainter outer companions designated B through F, located at angular separations ranging from tens to hundreds of arcseconds from the dominant inner triple system (Beta Lyrae A), which accounts for the vast majority of the system's integrated brightness. These companions were first cataloged as part of the visual multiple ADS 11745 in early astrometric surveys, with subsequent spectroscopic and photometric studies aiming to assess their physical association through proper motions, radial velocities, and distances. While Beta Lyrae A lies at a distance of approximately 340 pc based on DR3 measurements, the binding status of the outer stars remains debated, with some showing consistent kinematics and others appearing unbound; potential membership in the 8 (discovered 2019, ~100 members centered on Beta Lyrae) supports association for kinematically matched components like B and F. No resolved orbital parameters for these wide companions have been determined since 2019, limiting insights into their long-term dynamics. Beta Lyrae B is the brightest outer companion, classified as a with an apparent visual magnitude of 7.2. It is separated by about 46 arcseconds from Beta Lyrae A and exhibits a of -18.3 km/s, closely matching that of the inner system (-17.5 to -19.5 km/s), supporting potential physical association and possible 8 membership. However, pre- estimates placed it at around 1,080 light-years, suggesting it could be a foreground interloper, though recent DR3 data yield a corresponding to roughly 350 pc, indicating similar distance and likely membership in the 8 cluster. At a separation of 47 arcseconds, Beta Lyrae C is a B2 spectral type star with an of 13.07 and evidence of photometric variability, though its type remains unspecified. It shows possible common with the inner system in older measures, but DR3 reveals a significantly larger of over 3,400 pc and differing proper motions (pmRA = -1.859 mas/yr, pmDEC = -1.934 mas/yr compared to the inner system's +2.045 mas/yr, -3.685 mas/yr), implying it is unbound and likely a chance alignment. Its membership in the 8 cluster centered on Beta Lyrae remains unclear due to these discrepancies. Beta Lyrae D, a faint K3 V with an apparent magnitude of 14.96, orbits at 86 arcseconds from the primary. Limited spectroscopic data confirm its late-type nature, and photometric analysis suggests it is a background object not physically linked to Beta Lyrae, with no evidence of shared motion or cluster association. The companions E and F form a close pair at separations of 45 and 47 arcseconds from Beta Lyrae A, respectively, with magnitudes of 10.1 and 10.6. Both are classified as G5 stars with chemical peculiarities suggestive of Am-type metallic-line anomalies, though E's classification carries uncertainty (possibly Am). measurements for E (+10.9 km/s) disagree with the inner system's values, indicating it is probably unbound, while F's kinematics are more consistent, hinting at possible association and 8 membership. Like C and D, their membership in the 8 cluster is unresolved, with no post-2019 orbital resolutions available.
ComponentSpectral TypeApparent Magnitude (V)Separation (arcsec)Key Notes
BB7 V7.2~46Possible bound member; radial velocity match; likely Gaia 8.
CB213.0747Variable; likely unbound (distant per ).
DK3 V14.9686Faint ; background object.
EG5 (Am?)10.145Chemically peculiar; likely unbound.
FG5/Am10.647Chemically peculiar; paired with E, possible bound, 8.

References

  1. http://stars.astro.illinois.edu/sow/sheliak.html
  2. https://www.aavso.org/vsots_betalyr
  3. https://www.star-facts.com/sheliak-beta-lyrae/
  4. https://arxiv.org/abs/1303.5812
  5. https://www.aanda.org/articles/aa/abs/1996/42/aap0693/aap0693.html
  6. https://www.aanda.org/articles/aa/abs/2019/10/aa36595-19/aa36595-19.html
  7. https://www.lindahall.org/about/news/scientist-of-the-day/johann-bayer/
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