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Zeta Cassiopeiae

A magnificent hot (21,000 Kelvin) blue class B (B2) subgiant (but see below), it well deserves a place beside the others. Set within the Milky Way at a distance of 600 light years, the star is far enough to be dimmed some by interstellar dust. If space were clear, Zeta would shine 0.13 magnitude brighter and almost make third magnitude. Taking that and the severe ultraviolet light that comes with high temperature into account leads to a luminosity 6400 times that of the Sun, a radius 6.1 times solar, and a high mass of 9 times solar, which puts Zeta Cas at or near the limit at which stars develop iron cores and explode as supernovae. If below the limit, Zeta Cas will instead become a massive white dwarf, perhaps one made of neon and oxygen rather than carbon and oxygen. Rather than being a subgiant (which suggests the star is near the end of its life), Zeta Cas really seems to be a hydrogen-fusing dwarf, albeit one that is some three-quarters of the way through its 25 million year dwarf lifetime. Tiny variations of under 0.005 magnitudes with a period of 1.56 days reveal Zeta to be member of the "Slowly Pulsating B" (SPB) stars whose prototype is 53 Persei and that are just slightly dimmer and cooler than the better known Beta Cephei pulsators. Zeta Cas stands out as the first of its tribe to be found with a magnetic field (odd for hot stars). Variations in the outflowing wind that is modulated by the field leads to a rotation period of 5.37 days and a rotation speed of 56 kilometers per second, rather low for the class. The observed projected value of 14 km/s shows the star to be spinning with its rotation axis rather pointing toward Earth. The effect of the slow pulsations on the spectrum once fooled us into thinking that the star had a companion. None, however, is seen or even suggested, Zeta Cas heading toward its final state -- whether supernova or white dwarf -- quite alone.

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Photometric and spectroscopic observations of the 53 Persei type stars: Zeta Cassiopeiae     1994A&A...287..509S

Abstract

We present the results of photometric and spectroscopic observations of the star zeta Cas. The luminosity fluctuations are inside 0.004 magnitude in the u, v, and b Stroemgren's filters. For a given night the radial velocity measurements vary inside 1 km/s. We suppose that the observed night to night radial velocity variations are due to a close binarity. The orbital period could be 11.53 days with a 2K amplitude equal 3.6 km/s. The full width at half maximum (FWHM) measurements of the 4552 A SiIII are variable from night to night inside 0.08 A. After detrending for this variation, a peak appears in the power spectrum at 0.27 day with a half amplitude of 0.01 A possibly due to a non radial g mode. We do not detect the 0.9 d. period determined by Smith (1980). So the only short time variable parameter is the shape of the line profile. This is the main characteristic of a 53 Per type star.










2007A&A...466..675S - Astron. Astrophys., 466, 675-682 (2007) - 10.05.07 02.08.07 May(I) 2007

Variations of the ultraviolet resonance lines of the B2IV-V star ζ Cassiopeiae.

SMITH M.A.; BOHLENDER D.A.

Abstract (from CDS): Recently Neiner et al. reported that the B2IV-V star ζCas contains a weak magnetic field which varies on the same 5.37-day period found from the modulations of its NV, CIV, and SiIV UV resonance lines. We have studied the time variable properties of the same resonance lines in greater detail to determine the physical characteristics of the magnetospheric structure responsible for them. In our formulation this structure takes the form of an axisymmetric ``disk'' similar to those around magnetic He-strong Bp stars. This structure corotates with the star, covering greater or lesser amounts of its area during its transit. ζCas offers a special case because we observe it from a low inclination and yet its magnetic axis is substantially inclined to the rotation axis. The equivalent width-phase curves show a flat maximum for half the cycle, indicating that the disk is extended out of the plane, extends to the star's surface in the magnetic plane, or both. Synthetic spectra of the line profiles during the maximum and minimum occultation phases can be best reconciled with a disk geometry in which the resonance lines are formed at a closed outer edge and along a thin outer layer. We speculate that observed weak redshifted emission is formed in ``auroral caps'' located near the magnetic poles of the star. We argue that this results from shocks of stagnated wind material returning to the star and shocking against the outflowing wind.

Key words: stars: individual: $\zeta$ Cassiopeiae -- magnetic fields -- stars: circumstellar matter -- stars: winds, outflows -- stars: early-type -- ultraviolet: stars




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Title
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1  2007A&A...466..675S
1.000 05/2007 A      E  F          X          D          R          S              U      

Smith, M. A.; Bohlender, D. A.
Variations of the ultraviolet resonance lines of the B2 IV-V star ζ Cassiopeiae
2  2003A&A...406.1019N
1.000 08/2003 A      E  F                      D          R  C      S              U      

Neiner, C.; Geers, V. C.; Henrichs, H. F.; Floquet, M.; Frémat, Y.; Hubert, A.-M.; Preuss, O.; Wiersema, K.
Discovery of a magnetic field in the Slowly Pulsating B star zeta Cassiopeiae
3  2003EAS.....9..265G
1.000 00/2003 A      E                              T                                      

Geers, V. C.; Henrichs, H. F.; Neiner, C.
Discovery of a magnetic field in the B2 IV star zeta Cassiopeia
4  2001ESASP.464..431M
1.000 01/2001 A          F  G                      T      R  C                      U      

Martić, M.; Lebrun, J. C.; Schmitt, J.; Appourchaux, T.; Bertaux, J. L.
Observing solar-like oscillations: α CMi, η Cas A and ζ Her A
5  2000AAS...196.0503B
1.000 05/2000 A                                                                          U      

Bjorkman, K. S.; Miroshnichenko, A. S.; Krugov, V. D.
Long-term High-Resolution Spectroscopy of γ Cas, ζ Tau, and π Aqr
6  1994A&A...287..509S
1.000 07/1994 A          F  G                              R  C      S                  

Sadsaoud, H.; Le Contel, J. M.; Chapellier, E.; Le Contel, D.; Gonzalez-Bedolla, S.
Photometric and spectroscopic observations of the 53 Persei type stars: Zeta Cassiopeiae
7  1994IAUS..162...39S
1.000 00/1994             F  G                      T      R                              

Sadsaoud, H.; Le Contel, D.; Chapellier, E.; Gonzalez-Bedolla, S.; Le Contel, J. M.
Photometric and spectroscopic observations of the 53 Per star: Zeta CAS
8  1987BCrAO..72...57G
1.000 00/1987                                                                                     

Galkina, T. S.
Changes in emission in the Hα and Hβ lines for some Be stars:γ Cas, ζ Tau, and 66 Oph.
9  1985IzKry..72...72G
1.000 00/1985 A                                                          S                  

Galkina, T. S.
Emission variations in H-alpha and H-beta lines in the spectra of some Be stars - Gamma Cas, Zeta Tau, and 66 OPH
10  1985BCrAO..72...57G
1.000 00/1985                                                     C                          

Galkina, T. S.
Changes in emission in the Hα and Hβ lines for some Be stars: γ Cas, ζ Tau, and 66 Oph
11  1984BIEBe..10...29G
1.000 00/1984

Galkina, T. S.
On the behaviour of the Hα and Hβ emission in the spectra of three Be stars: γ Cas, ζ Tau and 66 Oph.
12  1983HvaOB...7..167N
1.000 00/1983 A          F  G                                  C                          

Ninkov, Z.; Yang, S.; Walker, G.
Rapid spectroscopic variations in Gamma CAS and Zeta OPH
13  1982VarCo...3...12N
1.000 00/1982                                                                             U      

Neven, S.
Observations of Eight Variable Stars / Delta-Cephei Zeta-Gemini Gamma-Aquilae Beta-Persei Beta-Lyrae Tau-Cassiopeiae Rho-Cassiopeiae
14  1977ApJ...211...91V
1.000 01/1977 A          F  G                              R  C      S          O  U      

Vidal-Madjar, A.; Laurent, C.; Bonnet, R. M.; York, D. G.
The ratio of deuterium to hydrogen in interstellar space. III - The lines of sight to Zeta Puppis and Gamma Cassiopeiae
15  1976BAAS....8..523M
1.000 09/1976             F  G                                                              

Morgan, T. H.; Kondo, Y.; Modisette, J. L.
Spectrophotometry of the Mg II Resonance Doublet Near 2800A of γ Cas ζ Tau and κ Dra.
16  1969A&A.....1..452S
1.000 04/1969             F  G                              R  C      S              U      

Snijders, M. A. J.
The abundance of iron in the B2 stars zeta Cassioppeiae and gamma Pegasi.
17  1969VilOB..26...23S
1.000 00/1969             F  G                                                              

Sudzius, J.
Photometry of classical cepheids eta Aql, SU Cas and zeta Gem in the system UPXYZVS
18  1955MmSAI..26..499H
1.000 00/1955                                                     C                      U      

Hack, M.
Ricerche sulle stelle a righe metalliche: ζ Lyrae A e confronto con le stelle normali δ Cassiopeiae, β Cassiopeiae e 41 Cygni
19  1950MNRAS.110...84J
1.000 00/1950 A          F  G                                          S              U      

Johnson, Martin
Adjustments within shells and asymmetric ejecta from Z Andr, ζ Auri, β Lyra, ρ Cass and γ Cass
20  1940Obs....63..108W
1.000 04/1940             F  G                                                              

Walraven, T.; Koelbloed, D.
Observations of zeta Aurigae and gamma Cassiopeiae