Lambda Boötis star

A Lambda Boötis star is a type of peculiar star which has an unusually low abundance of iron peak elements in its surface layers. One possible explanation for this is that it is the result of accretion of metal-poor gas from a circumstellar disc, and a second possibility is the accretion of material from a hot Jupiter suffering from mass loss. The prototype is Lambda Boötis.[1]

References

  1. ^ Jura, M. (2015). "Lambda Boo Abundance Patterns: Accretion from Orbiting Sources". The Astronomical Journal. 150 (6). 166. arXiv:1509.04672. Bibcode:2015AJ....150..166J. doi:10.1088/0004-6256/150/6/166.
14 Comae Berenices

14 Comae Berenices is a single star in the northern constellation of Coma Berenices, and is the second brightest member of the Coma Star Cluster. It is a faint star but visible to the naked eye with an apparent visual magnitude of 4.95. Parallax measurements place the star at a distance of about 266 light years.The spectrum of this star is peculiar and it has been assigned a number of different stellar classifications: A5, F0p, F0 III Sr, F0 vp, F1 IV: np Sr shell, A9 IV np Sr II, F1 IV, and A9 V + shell. Abt & Morrell (1995) designated this a Lambda Boötis star but this was later refuted. No surface magnetic field has been detected on 14 Comae Bernices.14 Comae Berenices is a well-known shell star with a high rate of spin, showing a projected rotational velocity of 226 km/s. This is giving the star an oblate shape with an equatorial bulge that is 12% larger than the polar radius. It is radiating 76 times the Sun's luminosity from its photosphere at an effective temperature of 7,300 K.

15 Andromedae

15 Andromedae, abbreviated 15 And, is a single, variable star in the northern constellation of Andromeda. 15 Andromedae is the Flamsteed designation, while its variable star designation is V340 And. Its apparent visual magnitude is 5.55, which indicates it is faintly visible to the naked eye. Its estimated distance from the Earth is 252 light years, and it is moving further away with a heliocentric radial velocity of 13 km/s.Depending on the source, this star has been classified as a giant star with a stellar classification of A1 III, an A-type main-sequence star with a class of A1 Va, or a Lambda Boötis star with a class of kA1hA3mA0.5 Va+. It is a Delta Scuti variable that changes in brightness by 0.03 magnitude. Two variability cycles, with periods 0.0403 and 0.0449 days, have been observed, a common feature for Lambda Boötis stars. The star is around 130 million years old and has a high rotation rate, showing a projected rotational velocity of 105 km/s. It has 2.7 times the mass of the Sun and is radiating 27 times the Sun's luminosity from its photosphere at an effective temperature of 9,225 K.This system has an excess emission of infrared radiation that suggests the presence of an orbiting disk of dust at a distance of around 50 AU from the host star.

16 Camelopardalis

16 Camelopardalis is a single star in the northern circumpolar constellation Camelopardalis, located 348 light years away from the Sun as determined from parallax measurements. It is visible to the naked eye as a faint, white-hued star with an apparent visual magnitude of 5.28. This object is moving further from the Earth with a heliocentric radial velocity of around 12 km/s.This is an A-type main-sequence star with a stellar classification of A0 Vn, where the 'n' notation indicates "nebulous" lines due to rapid rotation. In the past it was misidentified as a Lambda Boötis star. It is around 400 million years old and is spinning with a projected rotational velocity of 217 km/s. The star has 2.8 times the mass of the Sun and 3.3 times the Sun's radius. It is radiating 97 times the Sun's luminosity from its photosphere at an effective temperature of 9,748 K.An infrared excess indicates it has a dusty debris disk with a mean temperature of 120 K orbiting at a distance of 52 AU from the star. This disk has a combined mass equal to 2.1% the mass of the Earth.

2 Andromedae

2 Andromedae, abbreviated 2 And, is a binary star system in the northern constellation of Andromeda. 2 Andromedae is the Flamsteed designation. It is a faint star system but visible to the naked eye with a combined apparent visual magnitude of 5.09. Based upon an annual parallax shift of 7.7 mas, it is located 420 light years away. The binary nature of the star was discovered by American astronomer Sherburne Wesley Burnham at Lick Observatory in 1889. The pair orbit each other over a period of 74 years with a high eccentricity of 0.8.The magnitude 5.26 primary, designated component A, is an A-type main-sequence star based on a stellar classification of A1V or A2V, although it may have already left the main sequence. It was identified as a candidate Lambda Boötis star, but this was ruled out by Paunzen et al. (2003) as it doesn't match the typical characteristics of these objects. Although 2 And does not display a significant infrared excess, it is a shell star that displays varying absorption features due to circumstellar dust grains. This may indicate it has an orbiting debris disk containing gas that is being viewed edge-on. The star is about 100 million years old and is spinning rapidly with a projected rotational velocity of 212 km/s.The magnitude 7.43 secondary companion, component B, is a suspected variable star and may be a Delta Scuti variable. Alternatively, it may be an ellipsoidal variable with a brown dwarf companion. It is an F-type main-sequence star with a class of F1V/F4.

36 Serpentis

36 Serpentis, also known as b Serpentis, is a star in the constellation Serpens. It is a binary with the primary component being a Lambda Boötis star, meaning that it has solar-like amounts of carbon, nitrogen, and oxygen, while containing very low amounts of iron peak elements.

50 Cancri

50 Cancri is a single star in the zodiac constellation of Cancer, located 183 light years away from the Sun. It has the Bayer designation A2 Cancri; 50 Cancri is the Flamsteed designation. It is faintly visible to the naked eye as a white-hued star with an apparent visual magnitude of 5.89. The star is moving away from the Earth with a heliocentric radial velocity of 23 km/s, having come to within 118 light-years some 1.2 million years ago.This is a chemically peculiar A-type main-sequence star with a stellar classification of A1 Vp. It is a Lambda Boötis star displaying strongly-depleted iron peak and alpha process elements, but otherwise relatively normal solar abundances. The star shows no variability down to a detection limit of 1.6 millimagnitudes. It is 264 million years old with a relatively low projected rotational velocity of 18 km/s. 50 Cancri has 2.1 times the mass of the Sun and is radiating 11 times the Sun's luminosity from its photosphere at an effective temperature of 8,340 K.50 Cancri has an infrared excess, which most likely indicates a debris disk in orbit around the host star. A blackbody model of the emission shows a two component fit, with the warm section having a temperature of 246±91 K at a radius of 4±3 AU from the star, and a cool component at 108±21 K with a separation of 22±8 AU.

97 Aquarii

97 Aquarii (abbreviated 97 Aqr) is a binary star system in the equatorial constellation of Aquarius. 97 Aquarii is the Flamsteed designation. The combined apparent visual magnitude of the system is 5.20; the brighter star is magnitude 5.59 while the companion is magnitude 6.72. Based upon an annual parallax shift of 15.30 milliarcseconds, this system is at a distance of around 210 light-years (64 parsecs) from Earth.

The two stars in this system orbit each other over a period of 64.62 years at an eccentricity of 0.14. Both are A-type main sequence stars; the primary has a stellar classification of A2 V while its companion is A7 V. Their composite spectrum shows the properties of a Lambda Boötis star, which means it displays peculiar abundances of certain elements.

Epsilon Herculis

Epsilon Herculis, Latinized from ε Herculis, is a fourth-magnitude multiple star system in the northern constellation of Hercules. The combined apparent visual magnitude of 3.9111 is bright enough to make this system visible to the naked eye. Based upon an annual parallax shift of 21.04 mas as seen from Earth, it is located 155 light years from the Sun. The system is moving closer to the Sun with a radial velocity of −25 km/s.There is disagreement over the properties of this system. Petrie (1939) classified two components as class A0 and A2 with a visual magnitude difference of 1.5. Batten et al. (1989) catalogued it as a double-lined spectroscopic binary system with an orbital period of four days and an eccentricity of 0.02. However, Hipparcos was not able to detect the duplicity. Tokovinin (1997) and Faraggiana et al. (2001) catalogued it as a triple star system. Cowley et al. (1969) gave it a combined stellar classification of A0 V, whereas Gray & Garrison (1987) classified it as an A0 IV+. Wolff & Preston (1978) listed a magnesium overabundance. Since 1995 it has been classified as a Lambda Boötis star, although this has been brought into question.In Chinese, 天紀 (Tiān Jì), meaning Celestial Discipline, refers to an asterism consisting of ε Herculis, ξ Coronae Borealis, ζ Herculis, 59 Herculis, 61 Herculis, 68 Herculis, HD 160054 and θ Herculis. Consequently, the Chinese name for ε Herculis itself is 天紀三 (Tiān Jì sān, English: the Third Star of Celestial Discipline.)

HD 179791

HD 179791 is suspected variable star in the equatorial constellation of Aquila. It is a challenge to see with the naked eye even under good viewing conditions, having an apparent visual magnitude of 6.48. The distance to HD 179791 can be estimated from its annual parallax shift of 5.3 mas, which yields a value of 616 light years. It is moving further from the Earth with a heliocentric radial velocity of +16 km/s. Astrometric measurements of the star show changes in motion that may indicate it is a member of a close binary system.This is an A-type main-sequence star with a stellar classification of A3 V. It is a suspected chemically peculiar star and formerly a candidate Lambda Boötis star. The status as a Lambda Boötis star was reviewed and changed to non-member in 2015. It is spinning rapidly with a projected rotational velocity of 196 km/s. The star has 2.55 times the mass of the Sun and about 2.5 times the Sun's radius. It is radiating 66 times the Sun's luminosity from its photosphere at an effective temperature of 8,912 K.

HD 225218

HD 225218 is a quadruple star system in the northern constellation of Andromeda. The primary component, HD 225218 A, is a giant star with a stellar classification of B9III, an apparent magnitude of 6.16, and is a candidate Lambda Boötis star. It has a fainter, magnitude 9.65 companion, HD 225218 B, at an angular separation of 5.2″ along a position angle of 171°. The primary itself has been identified as a binary star system through interferometry, with the two components separated by 0.165″. The pair, HD 225218 Aa and Ab, orbit each other with a period of about 70 years and an eccentricity of 0.515. Component B is likewise a spectroscopic binary.

HD 56405

HD 56405 (also known as HIP 35180) is a main sequence star in the Canis Major constellation. On the eastern side of HD 56405 is the open cluster NGC 2360 also known as Caroline's Cluster. It was classed as a Lambda Boötis star, but more recently this classification has been rejected by astronomers due to the star having an inconsistent UV flux and RV variability and being a high vsin i A2 Va standard star.

HD 5789/5788

HD 5789 and HD 5788 is a pair of stars comprising a binary star system in the northern constellation of Andromeda. Located approximately 151 parsecs (490 ly) away, the primary is a hot, massive blue star with an apparent magnitude of 6.06 while the secondary is slightly smaller and cooler, with an apparent magnitude of 6.76. Both stars are main-sequence stars, meaning that they are currently fusing hydrogen into helium in their cores. As of 2016, the pair had an angular separation of 7.90″ along a position angle of 195°. While both have a similar proper motion and parallax, there's still no proof that the pair is gravitationally bound.

The primary component is HD 5789, a B-type main-sequence star with a stellar classification of B9.5Vnn (λ Boo), where the 'n' indicates "nebulous" lines due to rapid rotation. Abt and Morrell (1995) listed it as a Lambda Boötis star, although this is disputed. It has 2.7 times the mass of the Sun and is spinning rapidly with a projected rotational velocity of 249 km/s. The star is radiating 86 times the Sun's luminosity from its photosphere at an effective temperature of 9,977 K.The fainter secondary component is an A-type main-sequence star with a class of A2 Vn. It shows a projected rotational velocity of 270 km/s and has 2.7 times the Sun's mass. The star shines with 73 times the Sun's luminosity at an effective temperature of 9,840 K.

HR 8799 c

HR 8799 c is an extrasolar planet located approximately 129 light-years away in the constellation of Pegasus, orbiting the 6th magnitude Lambda Boötis star HR 8799. This planet has a mass between 5 and 10 Jupiter masses and a radius from 20 to 30% larger than Jupiter's. It orbits at 38 AU from HR 8799 with an unknown eccentricity and a period of 190 years; it is the 2nd planet discovered in the HR 8799 system. Along with two other planets orbiting HR 8799, this planet was discovered on November 13, 2008 by Marois et al., using the Keck and the Gemini observatories in Hawaii. These planets were discovered using the direct imaging technique. In January 2010, HR 8799 c became the 3rd exoplanet to have a portion of its spectrum directly observed (following 2M1207b and 1RXS J1609b), confirming the feasibility of direct spectrographic studies of exoplanets.

HR 8799 d

HR 8799 d is an extrasolar planet located approximately 129 light-years away in the constellation of Pegasus, orbiting the 6th magnitude Lambda Boötis star HR 8799. It has a mass between 5 and 10 Jupiter masses and a radius from 20 to 30% larger than Jupiter's. The planet orbits at 24 AU from HR 8799 with an eccentricity greater than 0.04 and a period of 100 years. Upon initial discovery, it was the innermost known planet in the HR 8799 system, but e, discovered later, is now known to be closer to their parent star. Along with two other planets orbiting HR 8799, this planet was discovered on November 13, 2008 by Marois et al., using the Keck and Gemini observatories in Hawaii. These planets were discovered using the direct imaging technique.Near infrared spectroscopy from 995 to 1769 nanometers made with the Palomar Observatory show evidence of Acetylene, Methane, and Carbon Dioxide, but Ammonia is not definitively detected.

Pi1 Orionis

Pi1 Orionis (π1 Ori, π1 Orionis) is a star in the equatorial constellation of Orion. It is faintly visible to the naked eye with an apparent visual magnitude of 4.74. Based upon an annual parallax shift of 28.04 mas, it is located about 116 light years from the Sun.

This is an A-type main sequence star with a stellar classification of A3 Va. It is a Lambda Boötis star, which means the spectrum shows lower than expected abundances for heavier elements. Pi1 Orionis is a relatively young star, just 100 million years old, and is spinning fairly rapidly with a projected rotational velocity of 120 km/s. It has nearly double the mass of the sun and 167% of the Sun's radius. The star radiates 16.6 times the solar luminosity from its outer atmosphere at an effective temperature of 8,611 K.An infrared excess indicates there is a debris disk with a temperature of 80 K orbiting 49 AU from the star. The dust has a combined mass 2.2% that of the Earth.

Rho Virginis

Rho Virginis (ρ Vir, ρ Virginis) is the Bayer designation for a star in the constellation Virgo. It has an apparent visual magnitude of +4.9, making it a challenge to view with the naked eye from an urban area (according to the Bortle Dark-Sky Scale). The distance to this star has been measured directly using the parallax method, which places it 118.3 light-years (36.3 parsecs) away with a margin of error of about a light year.Rho Virginis is an A-type main sequence star with a stellar classification of A0 V. It is larger than the Sun with a radius 60% larger and about twice the mass. As such it is generating energy at a higher rate than the Sun, with a luminosity 14 times greater. The outer atmosphere has an effective temperature of 8,930 K, which is what gives it the white-hued glow of an A-type star. It is classified as a Delta Scuti type variable star and its brightness varies by 0.02 magnitudes over periods of 0.5 to 2.4 hours.

This star has been established as a Lambda Boötis star that displays low abundances of iron peak elements. It displays an excess of infrared emission, but it is unclear whether this is being caused by a circumstellar debris disk or from the star passing through and heating up a diffuse interstellar dust cloud. Most likely it is the former, in which case the dusty disk has a radius of around 37 AU and a mean temperature of 90 K.

Tau2 Serpentis

Tau2 Serpentis, Latinized from τ2 Serpentis, is a B-type main sequence star in the constellation of Serpens, approximately 430 light-years from Earth. It has an apparent visual magnitude of approximately 6.218. This is a Lambda Boötis star.

Theta Hydrae

Theta Hydrae, Latinized from θ Hydrae, is a binary star system in the constellation Hydra. It is visible to the naked eye with an apparent visual magnitude of 3.9. The star system has a high proper motion with an annual parallax shift of 28.74 mas, indicating a distance of about 113 light years. Theta Hydrae forms a double with a magnitude 9.9 star located at an angular separation of 29 arcseconds.The primary component of this system is a B-type main sequence star with a stellar classification of B9.5 V. It is a candidate Lambda Boötis star, indicating it displays an underabundance of iron peak elements. However, it is also underabundant in oxygen, a characteristic not shared by other Lambda Boötis stars. Instead, it may be a peculiar B star.An orbiting white dwarf companion was discovered in 1998 from its X-ray emission. This degenerate star must have evolved from a progenitor that was once more massive than the current primary. Burleigh and Barstow (1999) gave a mass estimate of 0.68 times the mass of the Sun, whereas Holberg et al. (2013) put it as high as 1.21 times the Sun's mass. The latter would put it beyond the theoretical upper limit for white dwarf remnants of typical single stars that did not undergo a merger or mass loss.

Xi Aurigae

Xi Aurigae, Latinized from ξ Aurigae, is the Bayer designation for a single, white-hued star in the northern constellation of Auriga. This star was once considered part of the constellation of Camelopardalis and held the Flamsteed designation 32 Camelopardalis. It is visible to the naked eye with an apparent visual magnitude of +5.0. The measured annual parallax shift of this star is 13.69 ± 0.28 mas, which corresponds to a physical distance of 238 light-years (73 parsecs) with a 5 light-year margin of error. At that distance, the visual magnitude of the star is diminished by an extinction of 0.108 due to interstellar dust.This is an A-type main sequence star with a stellar classification of A2 Va. Although it was one of the first stars to be cataloged as a Lambda Boötis star, Murphy et al. (2015) don't consider it to be a member of this population. The star has nearly twice the mass of the Sun and about 1.1 times the Sun's radius. It is an estimated 174 million years old and is spinning with a projected rotational velocity of 62 km/s. Xi Aurigae is radiating 49.5 times the Sun's luminosity from its photosphere at an effective temperature of around 9,152 K.

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