Rapidly oscillating Ap stars (roAp stars) are a subtype of the Ap star class that exhibit short-timescale rapid photometric or radial velocity variations. The known periods range between 5 and 23 minutes. They lie in the δ Scuti instability strip on the main sequence.
The first roAp star to be discovered was HD 101065 (Przybylski's Star). The oscillations were discovered by Donald Kurtz using the 20-inch (510 mm) telescope at the South African Astronomical Observatory, who saw 10–20-millimagnitude variations in the light curve of the star with a period of 12.15 minutes.
The roAp stars are sometimes referred to as rapidly oscillating α2 Canum Venaticorum variables. Both the roAp stars and some α2 CVn variables lie on the δ Scuti instability strip and are magnetic chemically peculiar stars, but the roAp stars have very short periods less than an hour.
The roAp stars oscillate in high-overtone, low-degree, non-radial pressure modes. The usual model that is used to explain the behavior of these pulsations is the oblique pulsator model. In this model the axis of pulsation is aligned with the magnetic axis, which can lead to modulation of the amplitude of the pulsation, depending on the orientation of the axis to the line of sight, as it varies with rotation. The apparent link between the magnetic axis and the pulsation axis gives clues to the nature of the driving mechanism of the pulsations. As the roAp stars seem to occupy the main sequence end of the δ Scuti instability strip, it has been suggested that the driving mechanism may be similar, i.e. the opacity mechanism operating in the hydrogen ionization zone. No standard pulsation model can be made to excite oscillations of the roAp type using the opacity mechanism. As the magnetic field appears to be important, research has taken this into account in deriving non-standard pulsation models. It has been suggested that the modes are driven by the suppression of convection by the strong magnetic field near the magnetic poles of these stars, which would account for the alignment of the pulsation axis with the magnetic axis. An instability strip for the roAp stars has been calculated, which agreed with the positions on the Hertzsprung–Russell diagram of the roAp stars discovered up to that point, but predicted the existence of longer-period pulsators among the more evolved roAp stars. Such a pulsator was discovered in HD 177765, which has the longest pulsation period of any roAp star at 23.6 minutes.
Most roAp stars have been discovered using small telescopes to observe the small changes in amplitude caused by the pulsation of the star. However, it is also possible to observe such pulsations by measuring the variations in radial velocity of sensitive lines, such as neodymium or praseodymium. Some lines are not seen to pulsate, such as iron. It is thought that the pulsations are of highest amplitude high in the atmospheres of these stars, where the density is lower. As a result, the spectral lines that are formed by elements that are radiatively levitated high in the atmosphere are likely to be most sensitive to measuring the pulsation, whereas the lines of elements such as iron, which gravitationally settle, are not expected to exhibit radial velocity variations.
|Star name||V magnitude||Spectral type||Period (minutes)|
|AP Scl, HD 6532||8.45||Ap SrEuCr||7.1|
|BW Cet, HD 9289||9.38||Ap SrCr||10.5|
|BN Cet, HD 12098||8.07||F0||7.61|
|HD 12932||10.25||Ap SrEuCr||11.6|
|BT Hyi, HD 19918||9.34||Ap SrEuCr||14.5|
|DO Eri, HD 24712||6.00||Ap SrEu(Cr)||6.2|
|UV Lep, HD 42659||6.77||Ap SrCrEu||9.7|
|HD 60435||8.89||Ap Sr(Eu)||9.7|
|LX Hya, HD 80316||7.78||Ap Sr(Eu)||11.4–23.5|
|IM Vel, HD 83368||6.17||Ap SrEuCr||11.6|
|AI Ant, HD 84041||9.33||Ap SrEuCr||15.0|
|HD 86181||9.32||Ap Sr||6.2|
|Przybylski's star, HD 101065||7.99||controversial||12.1|
|LZ Hya, HD 119027||10.02||Ap SrEu(Cr)||8.7|
|PP Vir, HD 122970||8.31||unknown||11.1|
|α Cir, HD 128898||3.20||Ap SrEu(Cr)||6.8|
|HI Lib, HD 134214||7.46||Ap SrEu(Cr)||5.6|
|β CrB, HD 137909||3.68||F0p||16.2|
|GZ Lib, HD 137949||6.67||Ap SrEuCr||8.3|
|HD 150562||9.82||A/F(p Eu)||10.8|
|HD 161459||10.33||Ap EuSrCr||12.0|
|HD 166473||7.92||Ap SrEuCr||8.8|
|HD 176232||5.89||F0p SrEu||11.6|
|HD 185256||9.94||Ap Sr(EuCr)||10.2|
|CK Oct, HD 190290||9.91||Ap EuSr||7.3|
|QR Tel, HD 193756||9.20||Ap SrCrEu||13.0|
|AW Cap, HD 196470||9.72||Ap SrEu(Cr)||10.8|
|γ Eql, HD 201601||4.68||F0p||12.4|
|BI Mic, HD 203932||8.82||Ap SrEu||5.9|
|MM Aqr, HD 213637||9.61||A(p EuSrCr)||11.5|
|BP Gru, HD 217522||7.53||Ap (Si)Cr||13.9|
|CN Tuc, HD 218495||9.36||Ap EuSr||7.4|
10 Aquilae (abbreviated 10 Aql) is a star in the equatorial constellation of Aquila. 10 Aquilae is the Flamsteed designation. It has an apparent visual magnitude of 5.9 and thus is a faint star that is just visible to the naked eye in dark skies. The brightness of this star is diminished by 0.17 in visual magnitude from extinction caused by interstellar gas and dust. Based on an annual parallax shift of 13.45 mas, the distance to this star is around 240 light-years (74 parsecs).
The outer envelope of this star has an effective temperature of 7,550 K, giving it the yellow-white hued glow of an F-type star. It is a type of chemically peculiar star known as an Ap star, as indicated by the 'p' in the stellar classification.
10 Aql was described as a variable star in 1973 and a period of six days was suggested. Its small amplitude, period, chemical peculiarity, and position in the H–R diagram indicated that it may be an α2 CVn variable and it was given this classification in the General Catalogue of Variable Stars, along with the variable star designation V1286 Aquilae. Later studies showed that the period was spurious and several very short pulsation periods were found: 11.6, 12.0, and 13.4 minutes. This indicated that 10 Aql was a member of the new rapidly oscillating Ap star class.78 Virginis
78 Virginis is a variable star in the zodiac constellation of Virgo, located 175 light years from the Sun. It has the variable star designation CW Virginis and the Bayer designation o Virginis; 78 Virginis is the Flamsteed designation. This object is visible to the naked eye as a faint, white-hued star with an apparent visual magnitude of 4.92. It is moving closer to the Earth with a heliocentric radial velocity of −10 km/s.This is an Ap star with a stellar classification of ApEuCrSr, displaying strong lines of strontium, chromium, and other iron peak elements. It is classified as a Alpha2 Canum Venaticorum variable, ranging in magnitude from 4.91 down to 4.99 with a period of 3.722 days. 78 Virginis is the first star other than the Sun to have a magnetic field detected; it displays a dipole structure with a surface intensity of around 3.3 kG. It is a candidate rapidly oscillating Ap (roAp) star. This star is 435 million years old with 2.16 times the mass of the Sun and 2.11 times the Sun's radius. It is radiating 27 times the Sun's luminosity from its photosphere at an effective temperature of 9,100 K.Beta Coronae Borealis
Beta Coronae Borealis (β Coronae Borealis, abbreviated Beta CrB, β CrB) is a binary star in the constellation of Corona Borealis. It appears to the naked eye to be a single star and is the second-brightest star in its constellation with an apparent visual magnitude varying between 3.65 and 3.72. Based on parallax measurements taken during the Hipparcos mission, it is approximately 112 light-years from the Sun.
The two components are designated Beta Coronae Borealis A (officially named Nusakan , the traditional name of the system) and BCircinus
Circinus is a small, faint constellation in the southern sky, first defined in 1756 by the French astronomer Nicolas-Louis de Lacaille. Its name is Latin for compass, referring to the drafting tool used for drawing circles (it should not be confused with Pyxis, a constellation that represents a mariner's compass which points north). Its brightest star is Alpha Circini, with an apparent magnitude of 3.19. Slightly variable, it is the brightest rapidly oscillating Ap star in the night sky. AX Circini is a Cepheid variable visible with the unaided eye, and BX Circini is a faint star thought to have been formed from the merger of two white dwarfs. Two sun-like stars have planetary systems: HD 134060 has two small planets, and HD 129445 has a Jupiter-like planet. Supernova SN 185 appeared in Circinus in 185 AD and was recorded by Chinese observers. Two novae have been observed more recently, in the 20th century.
The Milky Way runs through the constellation, featuring prominent objects such as the open cluster NGC 5823 and the planetary nebula NGC 5315. Circinus hosts a spiral galaxy, the Circinus Galaxy, which was discovered in 1977 and is the closest Seyfert galaxy to the Milky Way. The Alpha Circinids (ACI), a meteor shower also discovered in 1977, radiate from this constellation.List of stars in Circinus
This is the list of notable stars in the constellation Circinus, sorted by decreasing brightness.List of stars in Corona Australis
This is the list of notable stars in the constellation Corona Australis, sorted by decreasing brightness.List of stars in Crater
This is the list of notable stars in the constellation Crater, sorted by decreasing brightness.List of stars in Equuleus
This is the list of notable stars in the constellation Equuleus, sorted by decreasing brightness.List of stars in Grus
This is the list of notable stars in the constellation Grus, sorted by decreasing brightness.List of stars in Hydrus
This is the list of notable stars in the constellation Hydrus, sorted by decreasing brightness.List of stars in Lepus
This is the list of notable stars in the constellation Lepus, sorted by decreasing brightness.List of stars in Libra
This is the list of notable stars in the constellation Libra, sorted by decreasing brightness.List of stars in Microscopium
This is the list of notable stars in the constellation Microscopium, sorted by decreasing brightness.List of stars in Octans
This is the list of notable stars in the constellation Octans, sorted by decreasing brightness.List of stars in Sculptor
This is the list of notable stars in the constellation Sculptor, sorted by decreasing brightness.List of stars in Vela
This is the list of notable stars in the constellation Vela, sorted by decreasing brightness.
This constellation's Bayer designations (Greek-letter star names) were given while it was still considered part of the constellation of Argo Navis. After Argo Navis was broken up into Carina, Vela, and Puppis, these Greek-letter designations were kept, so that Vela does not have a full complement of Greek-letter designations. For example, since Argo Navis's alpha star went to Carina, there is no Alpha Velorum.Outline of astronomy
The following outline is provided as an overview of and topical guide to astronomy:
Astronomy – studies the universe beyond Earth, including its formation and development, and the evolution, physics, chemistry, meteorology, and motion of celestial objects (such as galaxies, planets, etc.) and phenomena that originate outside the atmosphere of Earth (such as the cosmic background radiation).Przybylski's Star
Przybylski's Star (pronounced or ), or HD 101065, is a rapidly oscillating Ap star at roughly 355 light-years (109 parsecs) from the Sun in the southern constellation of Centaurus.ROAP
ROAP can mean:
Rights Object Acquisition Protocol
RTCWeb Offer/Answer Protocol
Rapidly oscillating Ap star (roAp star).
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