Helium-weak star

Helium-weak stars are chemically peculiar stars which have a weak helium lines for their spectral type.[1][2] Their helium lines place them in a later (ie. cooler) spectral type then their hydrogen lines.[3]

List of helium-weak stars

This is a non-extensive list of helium-weak stars.[4][5]

  • HR 939
  • HR 1100
  • HR 1121
  • HR 1441
  • HR 2509
  • HR 3448
  • HR 4801
  • HR 8137
  • Theta Hydri
  • HD 34797
  • HD 35456

See also

References

  1. ^ Landstreet, J. D.; Bohlender, David A. (1988). "Abundance and Magnetic Field Geometries of Helium-Strong and Helium-Weak Stars". Symposium - International Astronomical Union. 132: 309–312. doi:10.1017/S0074180900035191. ISSN 0074-1809.
  2. ^ Preston, George W. (1974). "The Chemically Peculiar Stars of the Upper Main Sequence". Annual Review of Astronomy and Astrophysics. 12 (1): 257–277. doi:10.1146/annurev.aa.12.090174.001353.
  3. ^ "A Digital Spectral Classification Atlas - R. O. Gray". ned.ipac.caltech.edu. Retrieved 2019-05-31.
  4. ^ Jaschek, Mercedes; Jaschek, Carlos; Arnal, Marcelo (October 1969). "Helium-Weak Stars". Helium-Weak Stars: 651. Bibcode:1969PASP...81..650J. doi:10.1086/128832 – via NASA/ADS.
  5. ^ Alonso, M. S.; López-García, Z.; Malaroda, S.; Leone, F. (April 2003). "Elemental abundance studies of CP stars. The helium-weak stars HD 19400, HD 34797 and HD 35456*" – via NASA/ADS.
12 Canis Majoris

12 Canis Majoris is a variable star located 184 light years away from the Sun in the southern constellation of Canis Major. It has the variable star designation HK Canis Majoris; 12 Canis Majoris is the Flamsteed designation. This body is just barely visible to the naked eye as a dim, blue-white hued star with a baseline apparent visual magnitude of +6.07. It is moving away from the Earth with a heliocentric radial velocity of +16 km/s. This is the brightest star in the vicinity of the open cluster NGC 2287, although it is probably not a member based on its proper motion.This star has a stellar classification of B7 II/III, matching a B-type giant/bright giant hybrid. (Cidale et al. (2007) show a class of B5 V, which would indicate it is instead a B-type main-sequence star.) It is a magnetic Bp star of the helium–weak variety (CP4), with the spectrum displaying evidence for vertical stratification of helium in the atmosphere. Samus et al. (2017) classify it as an SX Arietis variable with a brightness varies from magnitude +6.00 down to +6.05 over a period of 2.18045 days. It has 1.25 times the mass of the Sun and 2.73 times the Sun's radius. The star is radiating 498 times the Sun's luminosity from its photosphere at an effective temperature of 6,500 K.

15 Camelopardalis

15 Camelopardalis is a triple star system in the northern circumpolar constellation of Camelopardalis. It has the variable star designation DV Camelopardalis; 15 Camelopardalis is the Flamsteed designation. This is just visible to the naked eye as a dim, blue-white hued star with a baseline apparent visual magnitude of 6.13. It is a probable (99%) member of the Cas-Tau OB association.This system includes a double-lined spectroscopic binary with an orbital period of 6.7 days and a large eccentricity of around 0.48, plus a third component in a wider orbit. The close pair consist of a very slowly rotating helium-weak star plus an ordinary mid-B-type star with a more rapid rotation rate. Together they form an Algol-type eclipsing binary with a depth of about 0.2 magnitude. The third component is a slowly pulsating B-type star.

36 Lyncis

36 Lyncis is a solitary variable star located around 570 light years away from the Sun in the northern constellation of Lynx. It has the variable star designation of EI Lyncis, while 36 Lyncis is the Flamsteed designation. This object is visible to the naked eye as a dim, blue-white hued star with an apparent visual magnitude of 5.30. It is moving further away from the Earth with a heliocentric radial velocity of 21 km/s.This is a magnetic, helium-weak Bp star with a stellar classification of B8 IIImnp. It is sometimes classified as a mercury-manganese star. It is also an 'sn' star, displaying a spectrum with generally sharp lines for most elements in combination with broad, diffuse lines of helium. 36 Lyncis has been classified as an SX Arietis variable with an amplitude of 0.03 in visual magnitude and a rotationally-modulated period of 3.834 days. The star is spinning with a projected rotational velocity of 49 km/s and a rotation rate of 3.83476 days. It has 4.21 times the Sun's radius and is radiating 443 times the luminosity of the Sun from its photosphere at an effective temperature of 13,700 K.

3 Centauri

3 Centauri is a triple star system in the southern constellation of Centaurus, located approximately 300 light years from the Sun. It is visible to the naked eye as a faint, blue-white hued star with a combined apparent visual magnitude of 4.32. As of 2017, the two visible components had an angular separation of 7.851″ along a position angle of 106°. The system has the Bayer designation k Centauri; 3 Centauri is the Flamsteed designation. It is a suspected eclipsing binary with a variable star designation V983 Centauri.The brighter member, designated component A, is a magnitude 4.52 chemically peculiar star of the helium-weak (CP4) variety, and has a stellar classification of B5 III-IVp. The spectrum of the star displays overabundances of elements such as nitrogen, phosphorus, manganese, iron, and nickel, while carbon, oxygen, magnesium, aluminium, sulfur, and chlorine appear underabundant relative to the Sun. Weak emission line features are also visible.The magnitude 5.97 secondary, component B, is a single-lined spectroscopic binary star system with an orbital period of 17.4 days and an eccentricity of 0.21. The pair have an angular separation of 2.485 mas. The visible component is a B-type main-sequence star with a class of B8 V.

4 Cygni

4 Cygni is a binary star system in the northern constellation of Cygnus. It is a faintly visible to the naked eye with an apparent visual magnitude of 5.17. The distance to 4 Cygni, as determined from its annual parallax shift of 5.8 mas, is about 560 light years.

This is single-lined spectroscopic binary with an orbital period of 35 days and an eccentricity of 0.45. The visible component is a B-type star with a stellar classification of B8p Si (Fe II), where the suffix notation indicates this is type of chemically peculiar star known as a silicon star. It displays an overabundance of iron in the visual spectrum, while the star appears helium-weak in the ultraviolet.4 Cygni A is a Alpha2 Canum Venaticorum variable that varies by 0.02 magnitude over a period of 0.68674 days. The average quadratic field strength of the magnetic field is (254.7±57.2)×10−4 T. With an age of 145 million years, it has four times the mass of the Sun and five times the Sun's radius. It radiates around 501 times the Sun's luminosity from its photosphere at an effective temperature of 12,190 K.

HD 105382

HD 105382 (also known as V863 Centauri) is a star in the constellation Centaurus. Its apparent magnitude is 4.47. From parallax measurements, it is located 130 parsecs (440 light years) from the sun.

HD 105382 is a variable star whose apparent magnitude varies with an amplitude of 0.012 over a period of 1.295 days. It has been previously classified as a Be star, which would explain the variability as stellar pulsations, but this classification was probably due to accidental observation of the nearby Be star δ Centauri. A 2004 study showed that the 1.295 day period is actually the rotation period of the star, and that the variability is caused by non-homogeneous distribution of elements in the stellar surface. In particular, HD 105382 is a helium-weak chemically peculiar star with a helium abundance varying between 0.5% and 15% of the solar abundance, and a silicon abundance varying between 0.00044% and 0.0069% the solar value. Regions with more helium appear to coincide with the regions with less silicon, and vice versa. This peculiar abundance pattern is probably related to HD 105382's magnetic field, which has a polar strength of 2.3 kG.From astrometric measurements by the Hipparcos spacecraft, HD 105382 is identified as a probable astrometric binary. It is only 267" away from δ Centauri, and both stars appear to be at the same distance from Earth and have the same motion through space, so they may be related. In total, this may be a five star system. It is a member of the Lower Centaurus-Crux (LCC) subgroup of the Scorpius–Centaurus Association.

HD 142250

HD 142250 (HR 5910, HIP 77900) is a star in the constellation Scorpius. It has a visual apparent magnitude of 6.10, being visible to the naked eye only in excellent seeing conditions. From parallax measurements, it is located about 500 light-years (155 parsecs) away from Earth. This distance, together with the star's proper motion, indicate that HIP 77900 is a member of the Upper Scorpius subgroup of the Scorpius–Centaurus Association, the nearest OB association to the Sun. This subgroup is the youngest of the three of the association, with an estimated age of 11 million years.This is a B-type main-sequence star with a spectral type of B6Vp and a mass estimated at 3.7 times the solar mass. HIP 77900 is a helium-weak chemically peculiar star, and has a magnetic field and a slow rate of rotation, with a projected rotational velocity (v sin i) of 34 km/s. Its photosphere is radiating light with a luminosity 220 times greater the Sun's at an effective temperature of 13,600 K.Stars in young stellar associations are frequent targets for direct imaging searches for sub-stellar objects, because these objects lose luminosity with time. A 2013 article, using data from the Pan-STARRS and UKIDSS surveys and follow up observations with the IRTF telescope, presented the discovery of an object of spectral type M9 and effective temperature of 2400 ± 150 K separated from HIP 77900 by 21.8 arcseconds, or more than 3200 ± 300 AU at the system's distance. Its mass, estimated from evolutionary models and assuming an age of 10 million years, is 20+7−3 Jupiter masses, so the object is probably a low mass brown dwarf. The physical association between the two bodies has not been confirmed through common proper motion observation, but is considered likely given the proximity of the two objects in the sky and that the probable brown dwarf shows signs of youth.

HD 143699

HD 143699 is a single star in the southern constellation of Lupus. It is a dim star but visible to the naked eye with an apparent visual magnitude of 4.90. Based upon an annual parallax shift of 9.2 mas, it is located around 350 light years away. It is most likely (90% chance) a member of the Upper Centaurus-Lupus subgroup of the Sco OB2 moving group.

This star has a stellar classification of B5/7 III/IV, suggesting it is an evolving star that is entering the giant stage. However, according to Zorec and Royer (2012) it is only 56% of the way through its main sequence lifespan. It is a chemically peculiar magnetic B star, showing an averaged quadratic field strength of (167.2±140.4)×10−3 T. Helium-weak, it displays an underabundance of helium in its spectrum. Radio emissions have been detected from this source.HD 143699 has 4.3 times the mass of the Sun and 4.4 times the Sun's radius. It has a high rate of spin with a projected rotational velocity of 123 km/s. The star is radiating 438 times the Sun's luminosity from its photosphere at an effective temperature of 14,521 K.

KK Andromedae

KK Andromedae, also known as HD 9531, is a variable star in the northern constellation of Andromeda. It has an apparent visual magnitude of 5.90, which places it near the lower limit of visibility to the naked eye even under good viewing conditions. An Alpha2 Canum Venaticorum variable, it varies in brightness by 0.012 magnitude every 0.66 days. Based upon an annual parallax shift of 7.5 mas as seen from Earth, it is located around 437 light years from the Sun. At that distance, the brightness of the star is diminished by an extinction of 0.26 magnitude due to interstellar dust.Cowley et al. (1969) assigned this star a stellar classification of B9 IV, which would indicate it is a B-type star in the subgiant stage that has exhausted the hydrogen supply at its core and is expanding. It is a catalogued as an Ap star that displays an abnormal silicon abundance, but has been reported to actually be a helium-weak chemically peculiar star. The star has just over three times the mass of the Sun and about 2.7 times the Sun's radius. It is spinning rapidly with a projected rotational velocity of 163 km/s and a rotation period of 16 hours. KK And is radiating 91 times the Sun's luminosity from its photosphere at an effective temperature of 11,729 K.

KT Lupi

KT Lupi is a visual binary star system in the constellation Lupus. It is visible to the naked eye with a combined apparent visual magnitude of 4.55. As of 1983, the pair had an angular separation of 2.19″±0.03″. Based upon an annual parallax shift of 7.6 mas as seen from Earth's orbit, it is located 430 light years from the Sun. The system is moving further from the Earth with a heliocentric radial velocity of +6.5 km/s. It is a member of the Lower Centaurus Crux sub-group of the Scorpius–Centaurus Association.The primary, component A, is a variable Be star, with the variation being modulated by rotation. It is visual magnitude 4.66 with a stellar classification of B3 V, matching a B-type main-sequence star. Hiltner et al. (1969) gave a class of B3 IVp, which is still used in some studies. It is a helium-weak chemically peculiar star showing an enhanced silicon patch near the equator and a silicon-weak region close to the pole. The star is about 21 million years old with nearly six times the mass of the Sun and three times the Sun's radius. It is radiating roughly 794 times the Sun's luminosity from its photosphere at an effective temperature of 18,400 K.The secondary companion, component B, is of magnitude 6.62 with a class of B6 V. It has 2.79 times the Sun's mass.

K Puppis

k Puppis (k Pup, k Puppis) is a Bayer designation given to an optical double star in the constellation Puppis, the two components being k1 Puppis and k2 Puppis.

Lambda Librae

λ Librae (Latinised as Lambda Librae) is the Bayer designation for a binary star system in the zodiac constellation of Libra. It can be faintly seen with the naked eye on a dark night, having an apparent visual magnitude of 5.03. With an annual parallax shift of 10.54 mas, it is located roughly 310 light years from the Sun. At that distance, the visual magnitude of this system is diminished by an extinction factor of 0.22 due to interstellar dust.This is a single-lined spectroscopic binary star system with an orbital period of 14.48 days and an eccentricity of 0.27. The visible component is a B-type main sequence star with a stellar classification of B3 V. It is a helium-weak chemically peculiar star and a rotating ellipsoidal variable. The star has an estimated 3.9 times the radius of the Sun and five times the Sun's mass. This is a candidate Vega-like star, meaning that it shows an infrared excess characteristic of a circumstellar debris disk. The system is a source of X-ray emission.

Omega Cassiopeiae

Omega Cassiopeiae (ω Cassiopeiae) is a binary star system in the northern constellation of Cassiopeia. It has a combined apparent visual magnitude of +4.99, which means it is a faint star but visible to the naked eye. Based upon an annual parallax shift of 4.65 mas as seen from Earth, this system is located roughly 700 light years from the Sun. At that distance, the visual magnitude is diminished by an extinction of 0.16 due to interstellar dust.This is a single-lined spectroscopic binary star system with an orbital period of 69.92 days and an eccentricity of 0.30. The visible component has the spectrum of an evolved, B-type giant star with a stellar classification of B8 III. It is a helium-weak star, a type of chemically peculiar star that displays abnormally weak absorption lines of helium for a star of its temperature. Omega Cassiopeiae has an estimated 4.7 times the mass of the Sun and is radiating 488 times the Sun's luminosity from its photosphere at an effective temperature of around 12,737 K.

Theta Hydri

Theta Hydri, Latinized from θ Hydri, is the Bayer designation for a blue-white hued star in the southern constellation of Hydrus. It is faintly visible to the naked eye with an apparent visual magnitude of +5.53. Based upon an annual parallax shift of 6.34 mas as seen from Earth, is located roughly 510 light years from the Sun. At that distance, the visual magnitude of the star is diminished by an extinction of 0.10 due to interstellar dust. It is moving away from the Sun with a radial velocity of +12.3 km/s.A stellar classification of B8 III/IV suggests it is an evolving B-type star showing mixed traits of a subgiant or giant star. It is a PGa star – a higher temperature variety of the class of chemically peculiar stars known as mercury-manganese stars (HgMn stars). That is, it displays a rich spectra of singly-ionized phosphorus and gallium, in addition to ionized mercury and manganese. As such, Theta Hydri forms a typical example of this type. The absorption lines for these ionized elements are found to vary, most likely as the result of uneven surface distribution combined with the star's rotation. It is a helium-weak star, having helium lines that are anomalously weak for its spectral type. A weak and variable longitudinal magnetic field has been detected.There is a nearby companion star of class A0 IV located at an angular separation of 0.1 arc seconds along a position angle of 179°, as of 2002. Schöller et al. (2010) consider this to be a visual companion, although Eggleton and Tokovinin (2008) listed the pair as a probable binary star system.

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