Variety, equity and efficiency‐product variety in an industrial society

Kaufer, Erich

doi:10.1002/mde.4090020409

Cited by 3 publications

(5 citation statements)

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“…These pulsations were present for a few cycles and then vanished. Kaufer et al (1997) did not find radial pulsations for Deneb, although their data may have suggested such variability. Simultaneous photometry of the star is necessary for finding the radial pulsations because the atmosphere is also unstable to many non-radial modes simultaneously.…”

Section: Discussionmentioning

confidence: 81%

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A FIVE-YEAR SPECTROSCOPIC AND PHOTOMETRIC CAMPAIGN ON THE PROTOTYPICAL Α CYGNI VARIABLE AND a-Type SUPERGIANT STAR DENEB

Richardson

Morrison

Kryukova

et al. 2010

The Astronomical Journal

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Deneb is often considered the prototypical A-type supergiant, and is one of the visually most luminous stars in the Galaxy. A-type supergiants are potential extragalactic distance indicators, but the variability of these stars needs to be better characterized before this technique can be considered reliable. We analyzed 339 high resolution echelle spectra of Deneb obtained over the five-year span of 1997 through 2001 as well as 370 Strömgren photometric measurements obtained during the same time frame. Our spectroscopic analysis included dynamical spectra of the Hα profile, Hα equivalent widths, and radial velocities measured from Si II λλ 6347, 6371. Time-series analysis reveals no obvious cyclic behavior that proceeds through multiple observing seasons, although we found a suspected 40 day period in two, non-consecutive observing seasons. Some correlations are found between photometric and radial velocity data sets, and suggest radial pulsations at two epochs. No correlation is found between the variability of the Hα profiles and that of the radial velocities or the photometry. Lucy (1976) found evidence that Deneb was a long period single-lined spectroscopic binary star, but our data set shows no evidence for radial velocity variations caused by a binary companion.

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Section: Discussionmentioning

confidence: 81%

“…Lefever et al 2007). Kaufer et al (1996Kaufer et al ( , 1997 examined the radial velocity variations and the Hα profile variations of Deneb and five other supergiants. They found that the radial velocities were multiperiodic and showed different periods in different observing seasons.…”

Section: Introductionmentioning

confidence: 99%

A FIVE-YEAR SPECTROSCOPIC AND PHOTOMETRIC CAMPAIGN ON THE PROTOTYPICAL Α CYGNI VARIABLE AND a-Type SUPERGIANT STAR DENEB

Richardson

Morrison

Kryukova

et al. 2010

The Astronomical Journal

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“…We associate the changes at H α as arising in the wind, which is in accord with the observed changes in the profile shape and equivalent width of H α along with the polarimetric variability. For the continuum polarization, we explore a spiral shaped wind density enhancement in the equatorial plane of the star, in keeping with the suggestion of Kaufer et al (1997). Variable polarization signatures across H α are too complex to be explained by this simple model and will require a more intensive polarimetric follow-up study to interpret properly.…”

mentioning

confidence: 79%

“…We have presented relatively medium resolution spectropolarimetric data of the highly variable A supergiant HD 92207. It has been suggested by Kaufer et al (1997) that the observed photometric and H α line variations are the result of a corotating structure in the wind, which they consider to be in the star's equato-rial plane. To explore that possibility, we begin with a consideration of the variable continuum polarization.…”

Section: Discussionmentioning

confidence: 99%

Spectropolarimetric Variability and Corotating Structure in Hd 92207

Ignace

Hubrig

Schöller

2009

The Astronomical Journal

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We report on low resolution (R ≈ 3000) spectropolarimetry of the A0 supergiant star HD 92207. This star is well-known for significant spectral variability. The source was observed on seven different nights spanning approximately 3 months in time. With a rotation period of approximately 1 year, our data covers approximately a quarter of the star's rotational phase. Variability in the continuum polarization level is observed over this period of time. The polarization across the H α line on any given night is typically different from the degree and position angle of the polarization in the continuum. Interestingly, Hβ is not in emission and does not show polarimetric variability. We associate the changes at H α as arising in the wind, which is in accord with the observed changes in the profile shape and equivalent width of H α along with the polarimetric variability. For the continuum polarization, we explore a spiral shaped wind density enhancement in the equatorial plane of the star, in keeping with the suggestion of Kaufer et al. (1997). Variable polarization signatures across H α are too complex to be explained by this simple model and will require a more intensive polarimetric follow-up study to interpret properly.

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“…After the core hydrogen depletion, massive stars (M 15M ⊙ ) enter the BA supergiant phase of stellar evolution. During this epoch of evolution, they exhibit periodic and/or quasi-periodic low amplitude flux microvariability in addition to variations in radial velocity and equivalent width of spectral lines (Waelkens et al 1998;Kaufer et al 1996Kaufer et al , 1997Bresolin et al 2004). Spectroscopic analysis of Lefever et al (2007) clarified that blue supergiants (BSGs) pulsate in the gravity mode.…”

Section: Introductionmentioning

confidence: 99%

ASTEROSEISMOLOGY OF THE NEARBY SN II PROGENITOR RIGEL. II. Ε-Mechanism TRIGGERING GRAVITY-MODE PULSATIONS?

Moravveji

Moya

Guinan

2012

ApJ

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The cores of luminous B and A-type (BA) supergiant stars are the seeds of later core collapse supernovae. Thus, constraining the near-core conditions in this class of stars can place tighter constraints on the size, mass and chemical composition of supernova remnants. Asteroseismology of these massive stars is one possible approach into such investigations. Recently, Moravveji et al. (2012, hereafter Paper I) extracted 19 significant frequencies from a 6-year radial velocity monitoring or Rigel (β Ori, B8 Ia). The periods they determined broadly range from 1.22 to 74.74 days. Based on our differentially rotating stellar structure and evolution model, Rigel, at its current evolutionary state, is undergoing core He burning and shell H burning. Linear fully non-adiabatic non-radial stability analyses result in the excitation of a dense spectrum of non-radial gravity-dominated mixed modes. The fundamental radial mode (ℓ = 0) and its overtones are all stable. When the hydrogen burning shell is located even partially in the radiative zone, a favorable condition for destabilization of g-modes through the so-called ǫ-mechanism becomes viable. Only those g-modes that have high relative amplitudes in the hydrogen burning (radiative) zone can survive the strong radiative damping. From the entire observed range of variability periods of Rigel (found in Paper I), and based on our model, only those modes with periods ranging between 21 to 127 days can be theoretically explained by the ǫ-mechanism. The origin of the short-period variations (found in Paper I) still remain unexplained. Because Rigel is similar to other massive BA supergiants, we believe that the ǫ-mechanism may be able to explain the long-period variations in α Cygni class of pulsating stars.

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Variety, equity and efficiency‐product variety in an industrial society

Cited by 3 publications

References 0 publications

A FIVE-YEAR SPECTROSCOPIC AND PHOTOMETRIC CAMPAIGN ON THE PROTOTYPICAL Α CYGNI VARIABLE AND a-Type SUPERGIANT STAR DENEB

A FIVE-YEAR SPECTROSCOPIC AND PHOTOMETRIC CAMPAIGN ON THE PROTOTYPICAL Α CYGNI VARIABLE AND a-Type SUPERGIANT STAR DENEB

Spectropolarimetric Variability and Corotating Structure in Hd 92207

ASTEROSEISMOLOGY OF THE NEARBY SN II PROGENITOR RIGEL. II. Ε-Mechanism TRIGGERING GRAVITY-MODE PULSATIONS?

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