Radio Rhythm Club: Race, Authenticity, and the British Swing Boom

Baade, Christina

doi:10.1093/acprof:oso/9780195372014.003.0006

Cited by 7 publications

(10 citation statements)

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“…Baade (1982) determined the nearest neighboring stellar frequency at 0.73 c/d. Maintz et al (2003) derived f rot = 0.9 c/d and f Kepler = 1.1 c/d.…”

Section: Relation To Rotation and Revolutionmentioning

confidence: 99%

“…Since the first discoveries (Baade 1982;Bolton 1982) of nonradial pulsations (NRPs) in Be stars, it has been hoped that they might provide the missing angular momentum and energy to lift stellar matter into circumstellar orbits. The variability of the emission-line strength, which may drop to zero, suggesting the complete dispersal of the disk (e.g., Wisniewski et al 2010;Carciofi et al 2012), and observations of discrete mass loss events in light curves (Huat et al 2009), spectra (Peters 1986;Baade et al 1988), and polarization ) have led to the notion that much, if not all, of the star-to-disk mass-transfer process is episodic.…”

Section: Introductionmentioning

confidence: 99%

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Short-term variability and mass loss in Be stars

Baade

Rivinius

Pigulski

et al. 2016

A&A

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Context. Empirical evidence for the involvement of nonradial pulsations (NRPs) in the mass loss from Be stars ranges from (i) a singular case (μ Cen) of repetitive mass ejections triggered by multi-mode beating to (ii) several photometric reports about enormous numbers of pulsation modes that suddenly appear during outbursts and on to (iii) effective single-mode pulsators. Aims. The purpose of this study is to develop a more detailed empirical description of the star-to-disk mass transfer and to check the hypothesis that spates of transient nonradial pulsation modes accompany and even drive mass-loss episodes. Methods. The BRITE Constellation of nanosatellites was used to obtain mmag photometry of the Be stars η and μ Cen. Results. In the low-inclination star μ Cen, light pollution by variable amounts of near-stellar matter prevented any new insights into the variability and other properties of the central star. In the equator-on star η Cen, BRITE photometry and Heros echelle spectroscopy from the 1990s reveal an intricate clockwork of star-disk interactions. The mass transfer is modulated with the frequency difference of two NRP modes and an amplitude three times as large as the amplitude sum of the two NRP modes. This process feeds a highamplitude circumstellar activity running with the incoherent and slightly lower so-called Štefl frequency. The mass-loss-modulation cycles are tightly coupled to variations in the value of the Štefl frequency and in its amplitude, albeit with strongly drifting phase differences. Conclusions. The observations are well described by the decomposition of the mass loss into a pulsation-related engine in the star and a viscosity-dominated engine in the circumstellar disk. Arguments are developed that large-scale gas-circulation flows occur at the interface. The propagation rates of these eddies manifest themselves as Štefl frequencies. Bursts in power spectra during mass-loss events can be understood as the noise inherent to these gas flows.

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“…Baade (1982) determined the nearest neighboring stellar frequency at 0.73 c/d. Maintz et al (2003) derived f rot = 0.9 c/d and f Kepler = 1.1 c/d.…”

Section: Relation To Rotation and Revolutionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Short-term variability and mass loss in Be stars

Baade

Rivinius

Pigulski

et al. 2016

A&A

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“…are rather common among early-type Be stars (Baade 1982(Baade , 1984Porri & Stalio 1988;Floquet et al 1992;Neiner et al 2002). The observed line profile variability (LPV) is characterized by moving bumps traveling from blue to red across the line profile on timescales ranging from minutes to a few days.…”

Section: Introductionmentioning

confidence: 99%

“…Non-radial pulsations (NRP) have been proposed as an explanation of the LPV observed in hot stars (e.g. Smith 1977;Baade 1982;Vogt & Penrod 1983). NRP produce LPV thanks to the combination of the Doppler displacement of stellar surface elements with their associated temperature variations due to the compression/expansion caused by the passage of waves through the photosphere.…”

Section: Introductionmentioning

confidence: 99%

Photometric variability of the Be star CoRoT-ID 102761769

Emílio

Andrade

Janot-Pacheco

et al. 2010

A&A

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Context. Classical Be stars are rapid rotators of spectral type late O to early A and luminosity class V-III, which exhibit Balmer emission lines and often a near infrared excess originating in an equatorially concentrated circumstellar envelope, both produced by sporadic mass ejection episodes. The causes of the abnormal mass loss (the so-called Be phenomenon) are as yet unknown. Aims. For the first time, we can now study in detail Be stars outside the Earth's atmosphere with sufficient temporal resolution. We investigate the variability of the Be Star CoRoT-ID 102761769 observed with the CoRoT satellite in the exoplanet field during the initial run. Methods. One low-resolution spectrum of the star was obtained with the INT telescope at the Observatorio del Roque de los Muchachos. A time series analysis was performed using both cleanest and singular spectrum analysis algorithms to the CoRoT light curve. To identify the pulsation modes of the observed frequencies, we computed a set of models representative of CoRoT-ID 102761769 by varying its main physical parameters inside the uncertainties discussed. Results. We found two close frequencies related to the star. They are 2.465 c d −1 (28.5 μHz) and 2.441 c d −1 (28.2 μHz). The precision to which those frequencies were found is 0.018 c d −1 (0.2 μHz). The projected stellar rotation was estimated to be 120 km s −1 from the Fourier transform of spectral lines. If CoRoT-ID 102761769 is a typical Galactic Be star it rotates near the critical velocity. The critical rotation frequency of a typical B5-6 star is about 3.5 c d −1 (40.5 μHz), which implies that the above frequencies are really caused by stellar pulsations rather than star's rotation.

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“…Cuypers et al (1989); Balona et al (1992) confirmed this trend. The short-periodic line variation is considered to be due to nonradial pulsation in Baade's work (Baade, 1982). While Balona (1990Balona ( , 1995 attributed the variation to stellar spots and coratating clouds.…”

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confidence: 99%

Irregular changes in Hα emission line of V423 Aur observed by LAMOST Medium-Resolution Spectrographs

Hsia

et al. 2020

Res. Astron. Astrophys.

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We obtained 7 spectra of the Be star V423 Aur on Dec. 5th, 2017 using the LAMOST Medium-Resolution Spectrograph with exposures from 600 to 1200 seconds.These spectra show the irregular Hα emission line profile variations (LPVs). In the seven spectra, from the 4th to 7th, the left part of Hα profile even show excess. However, no variation can be seen from the follow-up observation of photometry by 1.26-m telescope and High-Resolution spectra by 2.16-m telescope. According to the High-Resolution spectra, we conclude that it is a B7V type star with E(B-V)= 0.709±0.036 and its vsini is ∼ 221.8km/s. The short-term Hα LPVs could be explained as a result of the transient ejection of matter from rotating disk or shell around V423 Aur.

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Radio Rhythm Club: Race, Authenticity, and the British Swing Boom

Cited by 7 publications

References 0 publications

Short-term variability and mass loss in Be stars

Short-term variability and mass loss in Be stars

Photometric variability of the Be star CoRoT-ID 102761769

Irregular changes in Hα emission line of V423 Aur observed by LAMOST Medium-Resolution Spectrographs

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