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Alphard
Location of Alphard (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Hydra
Right ascension 09h 27m 35.2433s[1]
Declination −08° 39′ 30.969″[1]
Apparent magnitude (V) +2.00[2]
Characteristics
Evolutionary stage Giant star
Spectral type K3IIIa[3]
U−B color index +1.73[4]
B−V color index +1.45[3]
Astrometry
Radial velocity (Rv)−4.3[5] km/s
Proper motion (μ) RA: −14.49[1] mas/yr
Dec.: 33.25[1] mas/yr
Parallax (π)18.40±0.78 mas[1]
Distance177 ± 8 ly
(54 ± 2 pc)
Absolute magnitude (MV)−1.743±0.032[3]
Details
Mass3.2±0.32[3] M☉
Radius57.59+0.63
−0.64[6] R☉
Luminosity971+154
−133[3] L☉
Luminosity (visual, LV)426[3][a] L☉
Surface gravity (log g)1.77[7] cgs
Temperature4,117±18[3] K
Metallicity [Fe/H]−0.12[7] dex
Rotation2,991 days[8]
Rotational velocity (v sin i)1.1[8] km/s
Age420±160[9] Myr
Other designations
Alphard, Alfard, Alphart, Kalbelaphard, Cor Hydrae, 30 Hydrae, HR 3748, BD−08°2680, HD 81797, SAO 136871, FK5 354, HIP 46390[10]
Database references
SIMBADdata

Alphard (/ˈælfɑːrd/[11]) is the brightest star in the constellation of Hydra. It has the Bayer designation Alpha Hydrae, which is that is Latinized from α Hydrae, and abbreviated Alpha Hya or α Hya. It is a giant star, cooler than the Sun but larger and more luminous. It is about 177 light-years away.

Nomenclature

[edit]

α Hydrae (Latinised to Alpha Hydrae) is the star's Bayer designation.

The traditional name Alphard is from the Arabic الفرد (al-fard), "the individual", there being no other bright stars near it. It was also known as the "backbone of the Serpent" to the Arabs. In the catalogue of stars in the Calendarium of Al Achsasi Al Mouakket, it was designated Soheil al Fard, which was translated into Latin as Soheil Solitarius, meaning the bright solitary one.[12] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[13] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[14] included a table of the first two batches of names approved by the WGSN; which included Alphard for this star. It is now so entered in the IAU Catalog of Star Names.[15]

The Danish astronomer Tycho Brahe dubbed it Cor Hydræ, Latin for 'the heart of Hydra'.[16]

In Chinese, 星宿 (Xīng Xiù), meaning Star, refers to an asterism consisting of Alphard, τ1 Hydrae, τ2 Hydrae, ι Hydrae, 26 Hydrae, 27 Hydrae, HD 82477 and HD 82428.[17] Consequently, Alphard itself is known as 星宿一 (Xīng Xiù yī), "the First Star of Star".[18] In ancient China it formed part of an asterism called the "red bird".

Properties

[edit]
The western portion of Hydra, with Alphard the brightest star near the centre

Alphard has three times the mass of the Sun.[3] Its estimated age is 420 million years[9] and it has evolved away from the main sequence to become a giant star with a spectral classification of K3 and luminosity class III.[3] The angular diameter has been measured using interferometry, after correction for limb darkening, it yields a value of 9.693±0.046 mas. Assuming the distance of 54.3 parsecs (177 ly), it yields a physical size of 57.6 times the radius of the Sun.[6]

Alphard's spectrum shows a mild excess of barium, an element that is normally produced by the s-process of nucleosynthesis. Typically a barium star belongs to a binary system and the anomalies in abundances are explained by mass transfer from a companion white dwarf star.[19]

Precise radial velocity measurements have shown variations in the stellar radial velocities and spectral line profiles. The oscillations are multi-periodic with periods from several hours up to several days. The short-term oscillations were assumed to be a result of stellar pulsations, similar to the solar ones. A correlation between the variations in the asymmetry of the spectral line profile and the radial velocity has also been found. The multi-periodic oscillations make HD 81797 (Alphard) an object of interest for asteroseismologic investigations.[20]

Modern legacy

[edit]

Alphard appears on the flag of Brazil, symbolising the state of Mato Grosso do Sul.[21]

The Toyota Alphard is a minivan named after this star.

The character Roy Alphard from Japanese light novel series Re:Zero is named after this star.

Notes

[edit]

References

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Alphard

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from Grokipedia
Alphard, designated Alpha Hydrae, is the brightest star in the constellation Hydra and around the 35th-brightest star in the night sky. It is an orange giant star of spectral class K3, located approximately 177 light-years from , with an apparent visual magnitude of +2.0. The name "Alphard" derives from the Arabic al-fard, meaning "the solitary one," reflecting its isolated position in a relatively barren region of the sky. As the "heart" of the serpentine Hydra constellation, it marks a prominent springtime feature for Northern Hemisphere observers, rising highest in the sky around late March. Physically, Alphard has a radius about 58 times that of the Sun, a surface temperature of approximately 4,130 K, and shines with around 800 times the Sun's luminosity, making it an evolved star undergoing helium fusion in its core. Its mass is estimated at approximately 3.0 solar masses, and it rotates slowly with a period of about 2.4 years. Alphard may have a faint K0 dwarf companion (Alphard B) at a projected distance of around 15,700 ; a third star (Alphard C) appears nearby but is likely a foreground object along the . Classified as a mild star, it shows enhanced levels of neutron-capture elements in its atmosphere, possibly from past in a previous . In its future evolution, Alphard will expand further as a before shedding its outer layers and collapsing into a of about 0.8 solar masses.

Nomenclature and Etymology

Historical Names

The traditional name originates from the phrase al-fard, meaning "the solitary one" or "the individual," a designation that highlights the star's relative isolation among brighter stars in the constellation Hydra. This name was adopted in Western astronomy during the medieval period through translations of Arabic astronomical texts, reflecting the influence of Islamic scholars on European stargazing traditions. In the 16th century, the Danish astronomer Tycho Brahe introduced the alternative name Cor Hydrae, Latin for "the heart of Hydra," emphasizing the star's position as the central, heart-like feature in the serpentine figure of the constellation. This nomenclature persisted in European catalogs for centuries, underscoring the star's symbolic role in early modern astronomy. In ancient Chinese astronomy, Alphard served as the principal star of the asterism Xīng Xiù (星宿), known as the "Star" mansion, one of the 28 lunar mansions (xiu) documented in texts like the Shiji (Records of the Grand Historian) from the 1st century BCE. Specifically designated as Xīng Xiù Yī (星宿一), or "the First Star of the Star," it formed part of broader celestial patterns associated with seasonal and navigational observations in classical Chinese star catalogs. The star's earliest recorded designation appears in Ptolemy's (2nd century CE), where it is listed as the alpha star of Hydra without a proper name, simply as the leading bright point in the constellation. The Bayer label Alpha Hydrae was formalized in 1603 by in his Uranometria, bridging listings with emerging systematic nomenclature. The Arabic Alphard gained prominence in the West by the 10th century through works like Al-Sufi's , evolving alongside names like Cor Hydrae into modern usage.

Official Designations

Alphard bears the α Hydrae (Alpha Hydrae), assigned by the German astronomer in his influential star atlas Uranometria, published in 1603, which systematically labeled stars using Greek letters based on their brightness within each constellation. It also holds the Flamsteed designation 30 Hydrae, originating from English astronomer John Flamsteed's Historia Coelestis Britannica, with observations compiled around 1712 and posthumously published in 1725, numbering stars sequentially by within constellations. In July 2016, the International Astronomical Union's Working Group on Star Names (WGSN) formally approved "Alphard" as the proper name for α Hydrae, standardizing it for international use in astronomical literature and catalogs. Alphard is cataloged under several modern identifiers, including HD 81797 in the Henry Draper Catalogue (a comprehensive 20th-century spectral classification survey), HR 3748 in the (compiling data on bright stars visible to the ), and HIP 46390 in the Catalogue (from the 1990s astrometric mission providing precise positions and parallaxes). As a suspected exhibiting minor pulsations, Alphard is designated NSV 4496 in the New Catalogue of Suspected Variable Stars. These systematic designations built upon earlier historical names like Cor Hydrae, marking the transition to formalized astronomical nomenclature.

Physical Characteristics

Stellar Parameters

Alphard, the brightest star in the constellation Hydra, has an apparent visual magnitude of 1.98, which ranks it as the 45th brightest star in the night sky. This brightness, combined with its spectral classification of K3 III, identifies it as an orange giant star. The star lies at a distance of 177 ± 8 light-years from , a measurement derived from observations conducted by the satellite and subsequently refined using data from the mission. Key physical properties of Alphard include a mass of 2.40^{+0.23}{-0.11} solar masses, a radius of 58.8^{+0.4}{-0.5} solar radii, and a bolometric luminosity of 868^{+7}{-18} solar luminosities. Its effective surface temperature is 4086^{+8}{-3} K, which contributes to its distinctive orange hue and places it firmly in the category of cool giant stars. These parameters indicate that Alphard has expanded significantly during its post-main-sequence evolution, with its large radius leading to a low surface gravity and extended atmosphere.
ParameterValueUnitSource
Apparent magnitude (V)1.98magSIMBAD 2002yCat.2237....0D
Distance177 ± 8light-yearsHipparcos/Gaia 2007A&A...474..653V; Gaia DR3
Mass2.40^{+0.23}_{-0.11}M⊙2025A&A...697A..32S
Radius58.8^{+0.4}_{-0.5}R⊙2025A&A...697A..32S
Luminosity868^{+7}_{-18}L⊙2025A&A...697A..32S
Effective temperature4086^{+8}_{-3}K2025A&A...697A..32S
Spectral typeK3 III-SIMBAD 1989ApJS...71..245K
Age420 ± 160million yearsIsochrone fitting 2015A&A...577A..23L; asteroseismology 2009A&A...503..903T
The estimated age of Alphard is 420 ± 160 million years, obtained through isochrone fitting to its position in the Hertzsprung-Russell diagram and supported by asteroseismic analysis of its internal structure. This relatively young age for a reflects its higher initial mass compared to the Sun, accelerating its evolutionary timescale.

Atmosphere and Spectrum

Alphard is classified as a K3 III giant, a spectral type characterized by strong molecular bands of (TiO) dominating the red portion of the , which contribute to its orange hue. These TiO bands arise from the cool , around 4090 K, allowing and oxygen to form stable molecules that absorb light at longer wavelengths. The star exhibits mild barium star characteristics, marked by an overabundance of (Ba) and other s-process elements such as (Sr) and (Y), with [Ba/Fe] = +0.8. This enhancement in heavy elements, produced via slow in stars, points to past from a now-degenerate companion that polluted Alphard's atmosphere. Its overall is slightly subsolar at [Fe/H] = -0.05 ± 0.10, highlighting the selective enrichment of s-process isotopes amid otherwise typical iron-group abundances. Spectroscopic observations reveal a radial velocity of +23 km/s, accompanied by evidence of low-amplitude oscillations that subtly distort line profiles, potentially linked to stellar pulsations. Prominent spectral features include the Ca II H and K lines, which show signs of chromospheric activity through weak emission cores, indicating a dynamic outer atmosphere with heating above the photosphere.

Position and Observability

Location in Hydra

Alphard holds the celestial coordinates of right ascension 09h 27m 35.24s and declination −08° 39′ 30.96″ (J2000 epoch), positioning it centrally within the serpentine form of the constellation Hydra. This placement aligns it along the "body" of the water snake asterism, where it serves as the alpha-designated star amid a chain of fainter alpha stars that trace the constellation's elongated structure from its head near Cancer to its tail toward Libra. As the brightest star in Hydra, Alphard symbolically represents the "heart" of the mythical water serpent in classical sky patterns, a role emphasized by its prominence in the constellation's central region. Its coordinates situate it approximately 31 degrees west of Gamma Leonis (Algieba) and firmly south of the , integrating it into Hydra's southern expanse. The star exhibits a of −15.23 mas/yr in and +34.37 mas/yr in , resulting in a gradual shift across the sky over centuries that subtly alters its position relative to Hydra's fixed boundaries. Hydra itself is the largest of modern constellations, encompassing 1,303 square degrees and extending across a vast stretch from the vicinity of Cancer in the northern spring sky to Libra in the southern autumn skies.

Visibility from Earth

Alphard, the brightest star in the constellation Hydra, offers optimal visibility from the during late winter and early spring. It reaches —its highest point in the sky—at approximately midnight in early February when observed from mid-northern latitudes, such as around 40°N, allowing for clear evening views before it dips toward the western horizon later in the season. This timing marks Alphard as a herald of spring in northern skies, rising higher and earlier each night through and . With an apparent visual magnitude of 1.98, Alphard is readily detectable by the even in moderately light-polluted urban environments, standing out as a steady, solitary point of light. enhance its observation by revealing the star's warm orange hue, a characteristic of its K3 spectral type giant atmosphere. At from 40°N , it attains an altitude of about 41° above the southern horizon, though atmospheric can slightly dim its appearance when viewed low in the sky near the horizon, particularly during early evening or late night observations. In the , Alphard remains accessible year-round for observers at all latitudes, rising and setting daily due to its near-equatorial of -8°39'. However, for those at low southern latitudes below 8°S, the star stays perpetually above the horizon, circling without setting and offering continuous visibility throughout the night— a rare trait for non-polar resulting from the of its position relative to the southern . Its brightness ensures easy naked-eye spotting, though proximity to fainter companions like Zeta Hydrae (magnitude 3.1, about 17° to the west) may require careful scanning in binocular fields to isolate Alphard amid Hydra's sparse stellar backdrop.

Scientific Study

Variability and Pulsations

Alphard exhibits low-amplitude multi-periodic oscillations characteristic of red giants, with variations detected in photometric data from the TESS mission and measurements. variations spanning approximately 786 m/s have been measured and analyzed to probe Alphard's internal structure, including convective zones. These oscillations show periods ranging from several hours to a few days, with evidence of solar-like modes. Short-cadence TESS data has been useful for resolving low-amplitude signals in this bright giant.

Evolutionary Status

Alphard is a post-main-sequence giant star that has evolved off the main sequence and is currently fusing helium into carbon and oxygen in its core during the horizontal branch phase, following the core helium flash. Stellar evolution models place it at the base of the asymptotic giant branch after its first crossing of the red giant branch, consistent with its spectral classification of K3 II–III and its position as a "clump star" on the horizontal branch. These models, such as those from Ekström et al. (2012), indicate an initial mass of 3–4 solar masses for Alphard, similar to other barium giants like Zeta Capricorni, which shares comparable evolutionary characteristics and chemical signatures. As a mild barium star, Alphard exhibits enrichment in s-process elements like , inferred to result from in a where a more evolved companion underwent the phase and polluted Alphard's atmosphere with processed material approximately 1–2 billion years ago. The companion is now a , though no close orbital motion has been detected to confirm the binary nature directly; this scenario aligns with the standard formation mechanism for barium stars, where the primary (Alphard) was a main-sequence star at the time of transfer. In the coming ~100 million years, Alphard is expected to ascend the , expanding further and undergoing thermal pulses before shedding its outer to form a , leaving behind a remnant of about 0.8 solar masses. No exoplanets have been confirmed around Alphard, but its high luminosity of approximately 950 solar luminosities places the at roughly 30 AU from the star.

Cultural Significance

Historical and Mythological Role

In , Alphard represents the heart of the , the multi-headed water serpent slain by during his second labor, as the constellation Hydra embodies the monstrous creature that guarded the swamps of near Argos. The star's prominent position in the serpentine form of the constellation underscored its symbolic role as the vital core of the beast, whose regenerative heads required to cauterize the necks to prevent regrowth, a tale that highlighted themes of heroism and perseverance against overwhelming odds. The constellation Hydra, including Alphard as its brightest star, was cataloged by the Greek astronomer in his 2nd-century as one of 48 ancient constellations, drawing on earlier observations attributed to Babylonian astronomers who associated the pattern with MUL.DINGIR.MUŠ, a mythical serpent-bird-lion hybrid. Egyptian astronomers also contributed to the observational tradition underlying Ptolemy's work, incorporating stellar positions from Nile Valley records into the Hellenistic synthesis that formed the basis of the Almagest's star catalog. In medieval Islamic astronomy, Alphard was known as Al-Fard, meaning "the solitary one," reflecting its isolated brightness amid the faint stars of Hydra, and it was prominently featured in Abd al-Rahman al-Sufi's Kitab suwar al-kawakib al-thabita (, circa 964 CE), where al-Sufi assigned it a magnitude estimate using his refined scale and adjusted Ptolemaic coordinates for . This text, which integrated Arabic nomenclature with Greek sources, highlighted Al-Fard's solitary prominence in Sufi-influenced astronomical treatises, aiding its use in navigation by medieval mariners who relied on such for orientation in southern skies. During the , Danish astronomer observed Alphard extensively from his observatory, dubbing it Cor Hydrae (the heart of Hydra) in his precise catalogs of stellar positions, which supported attempts to detect annual parallax shifts and informed efforts by providing accurate ephemerides. Indigenous Australian cultures have associated serpentine or water-related figures with celestial patterns, and the elongated form of Hydra has been used by some groups, such as western Victorian peoples, for navigation during night journeys, linking to seasonal and environmental cycles.

Modern References

Alphard is prominently featured on the flag of the Brazilian state of , adopted in 1979, where it symbolizes the state's location in the southern sky and represents Alpha Hydrae as a key stellar landmark visible from the region. The name Alphard inspired the branding of the minivan, launched in 2002 and continuing production through the present, primarily marketed in Asian countries to convey an image of reliability and solitude, reflecting the star's Arabic etymology meaning "the solitary one." In contemporary science fiction, Alphard appears as the surname of Roy Alphard, a Sin Archbishop character in the anime series Re:Zero − Starting Life in Another World (premiered 2016), whose name evokes themes of isolation and individuality, aligning with the star's traditional designation as the "solitary" beacon in Hydra. Alphard plays a role in modern astronomy outreach, appearing in applications like the Stellarium planetarium software and mobile app, which render it as a prominent orange giant for educational stargazing simulations. Planetarium presentations often highlight Alphard as a classic barium star, using it to demonstrate s-process nucleosynthesis and the companionship of evolved giants with white dwarfs. During the 2020s, Alphard has been incorporated into astrotourism initiatives in the , including guided viewing sessions at observatories like Siding Spring in , where events such as the annual Starfest provide opportunities to observe it under amid broader constellation tours.

References

  1. https://theskylive.com/sky/stars/alphard-alpha-hydrae-star
  2. https://www.astronomytrek.com/stars/alphard/
  3. https://simbad.cds.unistra.fr/simbad/sim-basic?Ident=Alphard
  4. https://www.skyatnightmagazine.com/advice/alphard
  5. https://earthsky.org/brightest-stars/alphard-the-solitary-one/
  6. https://www.star-facts.com/alphard/
  7. http://stars.astro.illinois.edu/sow/alphard.html
  8. https://www.constellation-guide.com/constellation-list/hydra-constellation/
  9. http://www.ianridpath.com/startales/hydra.html
  10. https://www.creators.com/read/stargazers/05/24/hydra-the-water-snake
  11. https://nineplanets.org/alphard/
  12. http://www.ianridpath.com/startales/almagest.html
  13. https://www.constellation-guide.com/constellation-names/
  14. https://www.ianridpath.com/startales/bayer.html
  15. http://pbarbier.com/flamsteed/flamsteed.html
  16. https://www.pas.rochester.edu/~emamajek/WGSN/WGSN_bulletin1.pdf
  17. http://simbad.cds.unistra.fr/simbad/sim-basic?Ident=Alphard
  18. https://www.aanda.org/articles/aa/abs/2025/05/aa53500-24/aa53500-24.html
  19. https://www.deepskycorner.ch/con/hydra.en.php
  20. https://astro4edu.org/resources/glossary/term/56/
  21. https://ui.adsabs.harvard.edu/abs/2023ApJS..268....4F/abstract
  22. https://ui.adsabs.harvard.edu/abs/2013ApJ...764..100G/abstract
  23. https://iopscience.iop.org/article/10.1088/0004-6256/146/2/29
  24. https://classicalliberalarts.com/resources/PTOLEMY_ALMAGEST_ENGLISH.pdf
  25. https://muslimheritage.com/arabic-star-names/
  26. https://www.researchgate.net/publication/226630792_Abdul-Raman_al-Sufi_and_His_Book_of_the_Fixed_Stars_A_Journey_of_Re-discovery
  27. http://www.whitby-astronomers.com/sky-notes/crossing-line-objects-month-8
  28. http://www.aboriginalastronomy.com.au/wp-content/uploads/2018/05/Night_Skies.pdf
  29. https://www.crwflags.com/fotw/flags/br_astro.html
  30. https://www.autoindustriya.com/auto-industry-news/what-does-the-alphard-s-emblem-mean.html
  31. https://otakumode.com/otapedia/anime/re_zero/rezero_roy_alphard
  32. https://stellarium.org/
  33. https://www.sidingspringobservatory.com.au/
  34. https://www.coonabarabranstargazing.com.au/starfest
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