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'''Rapidly Oscillating [[Ap star]]s (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 21 min. They lie in the [[delta Scuti]] instability strip on the [[main sequence]].
'''Rapidly oscillating Ap stars (roAp stars)''' are a subtype of the [[Ap star|Ap star class]] that exhibit short-timescale rapid [[Photometry (astronomy)|photometric]] or [[radial velocity]] variations. The known periods range between 5 and 23 minutes. They lie in the [[Delta Scuti variable|δ Scuti]] [[instability strip]] on the [[main sequence]].


==Discovery==
==Discovery==
The first roAp star to be discovered was HD 101065 ([[Przybylski's star]])<ref>Kurtz, D.W. Information Bulletin on Variable Stars, vol 1436, 1978[http://www.konkoly.hu/cgi-bin/IBVS?1436]</ref>. The oscillations were discovered by [[Donald Kurtz]] using the 20 inch telescope at the [[South African Astronomical Observatory]], who saw 10-20 millimagnitude variations in the lightcurve of the star with a period of 12.15 min.
The first roAp star to be discovered was HD 101065 ([[Przybylski's Star]]) in 1961.<ref>{{cite journal |bibcode=1978IBVS.1436....1K |title=12.15 Minute Light Variations in Przybylski's Star, HD 101065 |last1=Kurtz |first1=D. W. |journal=Information Bulletin on Variable Stars |year=1978 |volume=1436 |page=1 }}</ref> The oscillations were discovered by [[Donald Kurtz]] using the {{convert|20|inch|adj=on}} 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.

==Classification==
The roAp stars are sometimes referred to as rapidly oscillating α<sup>2</sup> Canum Venaticorum variables.<ref name=gcvs>{{cite journal|bibcode=2009yCat....102025S|title=VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)|journal=VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S|volume=1|display-authors=etal|last1=Samus|first1=N. N.|last2=Durlevich|first2=O. V.|year=2009}}</ref> Both the roAp stars and some [[Alpha2 Canum Venaticorum variable|α<sup>2</sup> CVn variables]] lie on the δ Scuti instability strip and are magnetic [[chemically peculiar star]]s, but the roAp stars have very short periods less than an hour.


==Oscillations==
==Oscillations==
The roAp stars oscillate in high-overtone, low-degree, non-radial pressure modes. The usual model that is used to explain the behaviour of these pulsations is the oblique pulsator model<ref>Kurtz, D.W. Monthly Notices of the Royal Astronomical Society, vol 200, p 807, 1982[http://articles.adsabs.harvard.edu/full/1982MNRAS.200..807K]</ref><ref>Shibahashi, H. & Takata, M. Publication of the Astronomical Society of Japan, vol 45, p 617, 1993[http://articles.adsabs.harvard.edu/full/1993PASJ...45..617S]</ref><ref>Bigot, L. & Dziembowski, W. Astronomy & Astrophysics, vol 391, p 235, 2002[http://www.aanda.org/index.php?option=article&access=bibcode&bibcode=2002A%2526A...391..235BFUL]</ref>. 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 [[delta 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<ref>Balmforth, N. et al. Monthly Notices of the Royal Astronomical Society, vol 323, p 362, 2001[http://articles.adsabs.harvard.edu/full/2001MNRAS.323..362B]</ref> which would account for the alignment of the pulsation axis with the magnetic axis. An instability strip for the roAp stars has been calculated<ref>Cunha, M.S. Monthly Notices of the Royal Astronomical Society, vol 333, p 47, 2002[http://articles.adsabs.harvard.edu/full/2002MNRAS.333...47C]</ref> 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 amongst the more evolved roAp stars. Such a pulsator was discovered in HD 116114<ref>Elkin, V.G. et al. Monthly Notices of the Royal Astronomical Society, vol 358, p 665[http://articles.adsabs.harvard.edu/full/2005MNRAS.358..665E]</ref> which has the longest pulsation period of any roAp star at 21 min.
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.<ref>{{cite journal |bibcode=1982MNRAS.200..807K |title=Rapidly oscillating AP stars |last1=Kurtz |first1=D. W. |journal=Monthly Notices of the Royal Astronomical Society |year=1982 |volume=200 |issue=3 |page=807 |doi=10.1093/mnras/200.3.807 |doi-access=free }}</ref><ref>{{cite journal |bibcode=1993PASJ...45..617S |title=Theory for the Distorted Dipole Modes of the Rapidly Oscillating AP Stars: A Refinement of the Oblique Pulsator Model |last1=Shibahashi |first1=Hiromoto |last2=Takata |first2=Masao |journal=Publications of the Astronomical Society of Japan |year=1993 |volume=45 |page=617 }}</ref><ref>{{cite journal |bibcode=2002A&A...391..235B |title=The oblique pulsator model revisited |last1=Bigot |first1=L. |last2=Dziembowski |first2=W. A. |journal=Astronomy and Astrophysics |year=2002 |volume=391 |page=235 |doi=10.1051/0004-6361:20020824 |doi-access=free }}</ref> 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 [[delta Scuti|δ Scuti]] [[instability strip]], it has been suggested that the driving mechanism may be similar, i.e. the [[opacity (optics)|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,<ref>{{cite journal |bibcode=2001MNRAS.323..362B |title=On the excitation mechanism in roAp stars |last1=Balmforth |first1=N. J. |last2=Cunha |first2=M. S. |last3=Dolez |first3=N. |last4=Gough |first4=D. O. |last5=Vauclair |first5=S. |journal=Monthly Notices of the Royal Astronomical Society |year=2001 |volume=323 |issue=2 |page=362 |doi=10.1046/j.1365-8711.2001.04182.x |doi-access=free }}</ref> which would account for the alignment of the pulsation axis with the magnetic axis. An instability strip for the roAp stars has been calculated,<ref>{{cite journal |bibcode=2002MNRAS.333...47C |title=A theoretical instability strip for rapidly oscillating Ap stars |last1=Cunha |first1=Margarida S. |journal=Monthly Notices of the Royal Astronomical Society |year=2002 |volume=333 |issue=1 |page=47 |doi=10.1046/j.1365-8711.2002.05377.x |doi-access=free }}</ref> 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]],<ref>{{cite journal |doi=10.1111/j.1745-3933.2011.01211.x |title=Discovery of the longest period rapidly oscillating Ap star HD 177765★ |year=2012 |last1=Alentiev |first1=D. |last2=Kochukhov |first2=O. |last3=Ryabchikova |first3=T. |last4=Cunha |first4=M. |last5=Tsymbal |first5=V. |last6=Weiss |first6=W. |journal=Monthly Notices of the Royal Astronomical Society: Letters |volume=421 |issue=1 |pages=L82–L86 |doi-access=free |arxiv=1112.4473 |s2cid=117092062 |bibcode=2012MNRAS.421L..82A }}</ref> 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 [[Chemical element|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.
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 [[Chemical element|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.


==Identified roAp stars==
==List of identified roAp stars==
{| class="wikitable sortable" border="1"
{| class="wikitable sortable"
|+ roAp stars<ref name=tess>{{cite journal |bibcode=2022MNRAS.510.5743B |title=Rapidly oscillating TESS A-F main-sequence stars: Are the roAp stars a distinct class? |last1=Balona |first1=L. A. |journal=Monthly Notices of the Royal Astronomical Society |year=2022 |volume=510 |issue=4 |page=5743 |doi=10.1093/mnras/stac011 |doi-access=free |arxiv=2109.02246 }}</ref>
|-
|-
! Star Name
! Star name
! ''V'' magnitude
! ''V'' magnitude
! Spectral Type
! Spectral type
! Period (min)
! Period (minutes)
|-
|-
| AP Scl, HD 6532
| AP Scl, HD 6532
Line 22: Line 26:
| 7.1
| 7.1
|-
|-
| BW Cet, HD 9289
| BW Cet, [[HD 9289]]
| 9.38
| 9.38
| Ap SrCr
| Ap SrCr
| 10.5
| 10.5
|-
|-
| BN Cet, HD 12098
| V988 Cas, HD 12098
| 8.07
| 8.07
| F0
| F0
| 7.61
| 7.61
|-
|-
| HD 12932
| BN Cet, HD 12932
| 10.25
| 10.25
| Ap SrEuCr
| Ap SrEuCr
Line 42: Line 46:
| 14.5
| 14.5
|-
|-
| DO Eri, HD 24712
| [[HR 1217|DO Eri]], HD 24712
| 6.00
| 6.00
| Ap SrEu(Cr)
| Ap SrEu(Cr)
Line 60: Line 64:
| 7.78
| 7.78
| Ap Sr(Eu)
| Ap Sr(Eu)
| 11.4-23.5
| 11.4–23.5
|-
|-
| IM Vel, HD 83368
| IM Vel, [[HR 3831|HD 83368]]
| 6.17
| 6.17
| Ap SrEuCr
| Ap SrEuCr
Line 82: Line 86:
| 10.7
| 10.7
|-
|-
| [[Przybylski's star]], HD 101065
| [[Przybylski's Star]], HD 101065
| 7.99
| 7.99
| controversial
| controversial
Line 117: Line 121:
| 16.2
| 16.2
|-
|-
| GZ Lib, HD 137949
| [[Zeta2 Librae|GZ Lib]], HD 137949
| 6.67
| 6.67
| Ap SrEuCr
| Ap SrEuCr
Line 137: Line 141:
| 12.0
| 12.0
|-
|-
| HD 166473
| V694 CrA, [[HD 166473]]
| 7.92
| 7.92
| Ap SrEuCr
| Ap SrEuCr
| 8.8
| 8.8
|-
|-
| HD 176232
| [[10 Aquilae|10 Aql]], HD 176232
| 5.89
| 5.89
| F0p SrEu
| F0p SrEu
| 11.6
| 11.6
|-
| [[HD 177765]]
| 9.1
| Ap
| 23.6
|-
|-
| HD 185256
| HD 185256
Line 167: Line 176:
| 10.8
| 10.8
|-
|-
| γ Eql, HD 201601
| [[Gamma Equulei|γ Equ]], HD 201601
| 4.68
| 4.68
| F0p
| F0p
Line 194: Line 203:


==References==
==References==
{{reflist}}
<references/>


{{Variable star topics|state=collapsed}}
⚫
[[Category:Star types]]


[[Category:Rapidly oscillating Ap stars|*]]
[[ru:RoAp-звезда]]
⚫
[[Category:A-type stars|*Ap]]

Latest revision as of 07:27, 27 November 2024

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.

Discovery

[edit]

The first roAp star to be discovered was HD 101065 (Przybylski's Star) in 1961.[1] 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.

Classification

[edit]

The roAp stars are sometimes referred to as rapidly oscillating α2 Canum Venaticorum variables.[2] 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.

Oscillations

[edit]

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.[3][4][5] 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,[6] which would account for the alignment of the pulsation axis with the magnetic axis. An instability strip for the roAp stars has been calculated,[7] 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,[8] 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.

List of identified roAp stars

[edit]
roAp stars[9]
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
V988 Cas, HD 12098 8.07 F0 7.61
BN Cet, 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
HD 99563 8.16 F0 10.7
Przybylski's Star, HD 101065 7.99 controversial 12.1
HD 116114 7.02 Ap 21.3
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 154708 8.76 Ap 8.0
HD 161459 10.33 Ap EuSrCr 12.0
V694 CrA, HD 166473 7.92 Ap SrEuCr 8.8
10 Aql, HD 176232 5.89 F0p SrEu 11.6
HD 177765 9.1 Ap 23.6
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 Equ, 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

References

[edit]
  1. ^ Kurtz, D. W. (1978). "12.15 Minute Light Variations in Przybylski's Star, HD 101065". Information Bulletin on Variable Stars. 1436: 1. Bibcode:1978IBVS.1436....1K.
  2. ^ Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
  3. ^ Kurtz, D. W. (1982). "Rapidly oscillating AP stars". Monthly Notices of the Royal Astronomical Society. 200 (3): 807. Bibcode:1982MNRAS.200..807K. doi:10.1093/mnras/200.3.807.
  4. ^ Shibahashi, Hiromoto; Takata, Masao (1993). "Theory for the Distorted Dipole Modes of the Rapidly Oscillating AP Stars: A Refinement of the Oblique Pulsator Model". Publications of the Astronomical Society of Japan. 45: 617. Bibcode:1993PASJ...45..617S.
  5. ^ Bigot, L.; Dziembowski, W. A. (2002). "The oblique pulsator model revisited". Astronomy and Astrophysics. 391: 235. Bibcode:2002A&A...391..235B. doi:10.1051/0004-6361:20020824.
  6. ^ Balmforth, N. J.; Cunha, M. S.; Dolez, N.; Gough, D. O.; Vauclair, S. (2001). "On the excitation mechanism in roAp stars". Monthly Notices of the Royal Astronomical Society. 323 (2): 362. Bibcode:2001MNRAS.323..362B. doi:10.1046/j.1365-8711.2001.04182.x.
  7. ^ Cunha, Margarida S. (2002). "A theoretical instability strip for rapidly oscillating Ap stars". Monthly Notices of the Royal Astronomical Society. 333 (1): 47. Bibcode:2002MNRAS.333...47C. doi:10.1046/j.1365-8711.2002.05377.x.
  8. ^ Alentiev, D.; Kochukhov, O.; Ryabchikova, T.; Cunha, M.; Tsymbal, V.; Weiss, W. (2012). "Discovery of the longest period rapidly oscillating Ap star HD 177765★". Monthly Notices of the Royal Astronomical Society: Letters. 421 (1): L82–L86. arXiv:1112.4473. Bibcode:2012MNRAS.421L..82A. doi:10.1111/j.1745-3933.2011.01211.x. S2CID 117092062.
  9. ^ Balona, L. A. (2022). "Rapidly oscillating TESS A-F main-sequence stars: Are the roAp stars a distinct class?". Monthly Notices of the Royal Astronomical Society. 510 (4): 5743. arXiv:2109.02246. Bibcode:2022MNRAS.510.5743B. doi:10.1093/mnras/stac011.
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