scholarly journals Mass-ejection events in Be stars triggered by coupled nonradial pulsation modes

2016 ◽  
Vol 12 (S329) ◽  
pp. 384-384
Author(s):  
D. Baade ◽  
Th. Rivinius ◽  
A. Pigulski ◽  
A. Carciofi ◽  
Keyword(s):  
Power Spectra ◽  
Unknown Origin ◽  
Circumstellar Matter ◽  
List Type ◽  
Be Stars ◽  
Aspect Angle ◽  
Stellar Pulsation ◽  
Mass Ejection ◽  
Nonradial Pulsation ◽  
High Cadence

AbstractBe stars (for an in-depth review see Rivinius, Carciofi & Martayan 2013) rotate at ⩾80% of the critical velocity and are multi-mode nonradial pulsators. Magnetic dipole fields are not detected, and binaries with periods less than 30 days are rare. The name-giving emission lines form in a Keplerian decretion disk, which is viscously re-accreted and also radiatively ablated unless replenished by outburts of unknown origin.Months-long, high-cadence space photometry with the BRITE-Constellation nanosatellites (Pablo et al. 2016) of about 10 early-type Be stars reveals the following (cf. Baade et al. 2016a, Baade et al. 2016b): ○Many Be stars exhibit 1 or 2 so-called Δ frequencies, which are differences between two nonradial-pulsation (NRP) frequencies and much lower (mostly less than 0.1 c/d) than the parent frequencies. The associated light curves are roughly sinusoidal. The amplitudes can exceed that of the sum of the parent amplitudes.○Conventional beat patterns also occur.○Amplitudes of both Δ and beat frequencies can temporarily be enhanced. Around phases of maximal amplitude the mean brightness is in- or decreased, and the scatter can be enhanced.○During high-activity phases (outbursts), broad and dense groups of numerous spikes arise in the power spectra. The two strongest groups often have a frequency ratio near 2. The phase coherence seems to be low.○Time coverage (less than half a year) is not yet sufficient to infer whether two Δ or beat frequencies can combine to cause long-lasting (years) superoutbursts (cf. Carciofi et al. 2012).From these observations it is concluded: •The variable mean brightness and the increased Δ-frequency amplitude and scatter trace the amount of near-circumstellar matter.•Increase or decrease of mean brightness is aspect-angle dependent (pole-on vs. equator-on).•Increased amounts of near-circumstellar matter are due to rotation-assisted mass ejections caused by coupled NRP modes.•Observations do not constrain the location of the coupling (atmosphere or stellar interior).•Broad frequency groups do not represent stellar pulsation modes but circumstellar variability.•Be stars later than B5 are less active and may in some cases even behave differently.

scholarly journals Pulsations of Be stars: time series analysis of He I λ4921

1994 ◽  
Vol 162 ◽  
pp. 100-101
Author(s):  
M. E. Hahula ◽  
D. R. Gies
Keyword(s):  
Time Series ◽  
Time Series Analysis ◽  
Mass Loss ◽  
Power Spectra ◽  
Phase Content ◽  
Be Stars ◽  
Optical Photometry ◽  
Multi Wavelength ◽  
Spectroscopy Optical ◽  
Nonradial Pulsation

We present the results of time series observations of He I λ4921 in the spectra of 10 Be stars. The spectra were obtained during multi-wavelength campaigns of IUE spectroscopy, optical photometry and polarimetry, and spectroscopy undertaken to study the connection (if any) between nonradial pulsation (NRP) and mass loss in Be stars. Power spectra have been calculated for the time series of intensity variations within the profiles. These were used to determine periodic variability and phase content to analyze the variations in the context of the NRP model. The observations were made at three observatories (Table 1). All the spectra record at least Hβ and He I λ4921 with a S/N > 200 per pixel and a resolution of ≈ 0.2 Å. We have concentrated the analysis on He I λ4921 as a probe of photospheric variability. This line is generally free of emission (unlike He I λ6678), but in some cases an Fe II λ4924 shell component appears in the red wing.

scholarly journals Study of a sample of faint Be stars in the exofield of CoRoT

2018 ◽  
Vol 613 ◽  
pp. A70 ◽  
Author(s):  
T. Semaan ◽  
A. M. Hubert ◽  
J. Zorec ◽  
J. Gutiérrez-Soto ◽  
Y. Frémat ◽  
...  
Keyword(s):  
Power Spectrum ◽  
Main Sequence ◽  
Power Spectra ◽  
Circumstellar Disks ◽  
Light Curves ◽  
Radial Pulsation ◽  
Be Stars ◽  
Time Frequency ◽  
Mass Ejection ◽  
Low Amplitude

Context. The class of Be stars are the epitome of rapid rotators in the main sequence. These stars are privileged candidates for studying the incidence of rotation on the stellar internal structure and on non-radial pulsations. Pulsations are considered possible mechanisms to trigger mass-ejection phenomena required to build up the circumstellar disks of Be stars. Aims. Time series analyses of the light curves of 15 faint Be stars observed with the CoRoT satellite were performed to obtain the distribution of non-radial pulsation (NRP) frequencies in their power spectra at epochs with and without light outbursts and to discriminate pulsations from rotation-related photometric variations. Methods. Standard Fourier techniques were employed to analyze the CoRoT light curves. Fundamental parameters corrected for rapid-rotation effects were used to study the power spectrum as a function of the stellar location in the instability domains of the Hertzsprung–Russell (H-R) diagram. Results. Frequencies are concentrated in separate groups as predicted for g-modes in rapid B-type rotators, except for the two stars that are outside the H-R instability domain. In five objects the variations in the power spectrum are correlated with the time-dependent outbursts characteristics. Time-frequency analysis showed that during the outbursts the amplitudes of stable main frequencies within 0.03 c d−1 intervals strongly change, while transients and/or frequencies of low amplitude appear separated or not separated from the stellar frequencies. The frequency patterns and activities depend on evolution phases: (i) the average separations between groups of frequencies are larger in the zero-age main sequence (ZAMS) than in the terminal age main sequence (TAMS) and are the largest in the middle of the MS phase; (ii) a poor frequency spectrum with f ≲ 1 cd−1 of low amplitude characterizes the stars beyond the TAMS; and (iii) outbursts are seen in stars hotter than B4 spectral type and in the second half of the MS. Conclusions. The two main frequency groups are separated by δf = (1.24 ± 0.28) × frot in agreement with models of prograde sectoral g-modes (m = −1, −2) of intermediate-mass rapid rotators. The changes of amplitudes of individual frequencies and the presence of transients correlated with the outburst events deserve further studies of physical conditions in the subatmospheric layers to establish the relationship between pulsations and sporadic mass-ejection events.

scholarly journals Short-term variability and mass loss in Be stars

2018 ◽  
Vol 610 ◽  
pp. A70 ◽  
Author(s):  
D. Baade ◽  
A. Pigulski ◽  
Th. Rivinius ◽  
A. C. Carciofi ◽  
D. Panoglou ◽  
...  
Keyword(s):  
Mass Loss ◽  
Circumstellar Matter ◽  
Radial Pulsation ◽  
Be Stars ◽  
Solar Mass ◽  
Solar Mass Ejection Imager ◽  
Feeder Mechanism ◽  
The Difference ◽  
Mass Ejection

Context. Be stars are important reference laboratories for the investigation of viscous Keplerian discs. In some cases, the disc feeder mechanism involves a combination of non-radial pulsation (NRP) modes. Aims. We seek to understand whether high-cadence photometry can shed further light on the role of NRP modes in facilitating rotation-supported mass loss. Methods. The BRITE-Constellation of nanosatellites obtained mmag photometry of 28 Cygni for 11 months in 2014–2016. We added observations with the Solar Mass Ejection Imager (SMEI) in 2003–2010 and 118 Hα line profiles, half of which were from 2016. Results. For decades, 28 Cyg has exhibited four large-amplitude frequencies: two closely spaced frequencies of spectroscopically confirmed g modes near 1.5 c/d, one slightly lower exophotospheric (Štefl) frequency, and at 0.05 c/d the difference (Δ) frequency between the two g modes. This top-level framework is indistinguishable from η Cen (Paper I), which is also very similar in spectral type, rotation rate, and viewing angle. The circumstellar (Štefl) frequency alone does not seem to be affected by the Δ frequency. The amplitude of the Δ frequency undergoes large variations; around maximum the amount of near-circumstellar matter is increased and the amplitude of the Štefl frequency grows by a factor of a few. During such brightenings dozens of transient spikes appear in the frequency spectrum; these spikes are concentrated into three groups. Only 11 frequencies were common to all years of BRITE observations. Conclusions. Be stars seem to be controlled by several coupled clocks, most of which are not very regular on timescales of weeks to months but function for decades. The combination of g modes to the slow Δ variability and/or the atmospheric response to it appears significantly non-linear. As in η Cen, the Δ variability seems to be mainly responsible for the modulation of the star-to-disc mass transfer in 28 Cyg. A hierarchical set of Δ frequencies may reach the longest known timescales of the Be phenomenon.

scholarly journals Adrenal insufficiency in a woman secondary to standard-dose inhaled fluticasone propionate therapy

2014 ◽  
Vol 2014 ◽  
Author(s):  
Casey M Hay ◽  
Daniel I Spratt
Keyword(s):  
Fluticasone Propionate ◽  
Adrenal Insufficiency ◽  
Cortisol Level ◽  
Standard Dose ◽  
Clinical Signs ◽  
Unknown Origin ◽  
Adrenal Crisis ◽  
List Type ◽  
Morning Cortisol ◽  
Low Serum

Summary A 55-year-old woman with asthma presented with adrenal insufficiency of unknown origin. She was referred to our Division of Reproductive Endocrinology to further evaluate an undetectable morning cortisol level discovered during the evaluation of a low serum DHEA-S level. She was asymptomatic other than having mild fatigue and weight gain. Her medication list included 220 μg of inhaled fluticasone propionate twice daily for asthma, which she was taking as prescribed. On presentation, the undetectable morning cortisol level was confirmed. A urinary measurement of fluticasone propionate 17β-carboxylic acid was markedly elevated. Fluticasone therapy was discontinued and salmeterol therapy initiated with supplemental hydrocortisone. Hydrocortisone therapy was discontinued after 2 months. A repeat urinary fluticasone measurement 4 months after the discontinuation of fluticasone therapy was undetectably low and morning cortisol level was normal at 18.0 μg/dl. Inhaled fluticasone is generally considered to be minimally systemically absorbed. This patient's only clinical evidence suggesting adrenal insufficiency was fatigue accompanying a low serum DHEA-S level. This case demonstrates that adrenal insufficiency can be caused by a routine dose of inhaled fluticasone. Missing this diagnosis could potentially result in adrenal crisis upon discontinuation of fluticasone therapy. Learning points Standard-dose inhaled fluticasone can cause adrenal insufficiency. Adrenal insufficiency should be considered in patients taking, or who have recently discontinued, inhaled fluticasone therapy and present with new onset of nonspecific symptoms such as fatigue, weakness, depression, myalgia, arthralgia, unexplained weight loss, and nausea that are suggestive of adrenal insufficiency. Adrenal insufficiency should be considered in postoperative patients who exhibit signs of hypoadrenalism after fluticasone therapy has been withheld in the perioperative setting. Routine screening for hypoadrenalism in patients without clinical signs or symptoms of adrenal insufficiency after the discontinuation of inhaled fluticasone therapy is not indicated due to the apparently low incidence of adrenal insufficiency caused by fluticasone.

scholarly journals Pulsations of Ob-Stars: New Observations

1998 ◽  
Vol 185 ◽  
pp. 347-354 ◽  
Author(s):  
Dietrich Baade
Keyword(s):  
Main Sequence ◽  
Physical Parameters ◽  
Be Stars ◽  
Instability Strip ◽  
Ob Stars ◽  
Analysis Strategies ◽  
The Galaxy ◽  
Order Line ◽  
Nonradial Pulsation ◽  
Radial Pulsations

Improved observing and data analysis strategies have initiated a considerable expansion of the empirical knowledge about the pulsations of OB stars. Possible correlations between physical parameters and associated pulsation characteristics are becoming more clearly perceivable. This starts to include the asteroseismologically fundamental areas of g-modes and rapid rotation. The β Cephei instability strip continues to be the only locus where radial pulsations occur (but apparently not in all stars located in that strip). Except for spectral types B8/B9 near the main sequence, where pulsations are hardly detected even at low amplitudes, any major group of stars in the Galaxy that are obviously not candidate pulsators still remains to be identified. However, the incidence and amplitudes of OB star pulsations decrease steeply with metallicity. The behaviour of high-luminosity stars is less often dominated by very few modes. In broad-lined stars the moving-bump phenomenon is more common than low-order line-profile variability. But its relation to nonradial pulsation is not clear. The beating of low-ℓ nonradial pulsation modes that have identical angular mode indices may be the clockwork of the outbursts of at least some Be stars. The physics of this episodic mass loss process remains to be identified.

scholarly journals Formation and Dissipation of Viscous Disks around Be Stars

2004 ◽  
Vol 215 ◽  
pp. 529-534
Author(s):  
A. T. Okazaki
Keyword(s):  
Smoothed Particle Hydrodynamics ◽  
Rotation Axis ◽  
Be Stars ◽  
Disk Model ◽  
Innermost Part ◽  
Outer Disk ◽  
Particle Hydrodynamics ◽  
Smoothed Particle ◽  
Be Star ◽  
Mass Ejection

Based on the viscous decretion disk model for Be Stars, we study the effect of the torque from the star on the Be star disk, using a 3-D smoothed particle hydrodynamics code and turning on and off the mass ejection from the star. We find that, after the mass ejection is shut off, the innermost part of the disk begins to accrete and the accreting part gradually propagates outward. We also find that the Be disk in misaligned binaries precesses in a retrograde sense when no mass is supplied from the star. If the mass supply is resumed for such a disk, an inner disk is formed with its rotation axis misaligned with that of the outer disk. By the interaction between the inner and outer disks, the outer disk rapidly changes its direction to that of the inner disk.

scholarly journals The circumstellar discs of Be stars

2010 ◽  
Vol 6 (S272) ◽  
pp. 325-336 ◽  
Author(s):  
Alex C. Carciofi
Keyword(s):  
Angular Resolution ◽  
Central Star ◽  
High Angular Resolution ◽  
Be Stars ◽  
Keplerian Orbit ◽  
Physical Processes ◽  
Simple Description ◽  
Model Predictions ◽  
Mass Ejection ◽  
Very High

AbstractCircumstellar discs of Be stars are thought to be formed from material ejected from a fast-spinning central star. This material possesses large amounts of angular momentum and settles in a quasi-Keplerian orbit around the star. This simple description outlines the basic issues that a successful disc theory must address: 1) What is the mechanism responsible for the mass ejection? 2) What is the final configuration of the material? 3) How the disc grows? With the very high angular resolution that can be achieved with modern interferometers operating in the optical and infrared we can now resolve the photosphere and immediate vicinity of nearby Be stars. Those observations are able to provide very stringent tests for our ideas about the physical processes operating in those objects. This paper discusses the basic hydrodynamics of viscous decretion discs around Be stars. The model predictions are quantitatively compared to observations, demonstrating that the viscous decretion scenario is currently the most viable theory to explain the discs around Be stars.

scholarly journals Short-term variability and mass loss in Be stars

2018 ◽  
Vol 620 ◽  
pp. A145 ◽  
Author(s):  
D. Baade ◽  
A. Pigulski ◽  
Th. Rivinius ◽  
L. Wang ◽  
Ch. Martayan ◽  
...  
Keyword(s):  
Be Stars ◽  
Frequency Pattern ◽  
Similar Frequency ◽  
Good Target ◽  
Variability Pattern ◽  
Be Star ◽  
Shell Star ◽  
Mass Ejection ◽  
Combination Frequencies

Context. In early-type Be stars, groups of nonradial pulsation (NRP) modes with numerically related frequencies may be instrumental for the release of excess angular momentum through mass-ejection events. Difference and sum/harmonic frequencies often form additional groups. Aims. The purpose of this study is to find out whether a similar frequency pattern occurs in the cooler third-magnitude B7-8 IIIe shell star ν Pup. Methods. Time-series analyses were performed of space photometry with BRITE-Constellation (2015, 2016/17, and 2017/18), SMEI (2003–2011), and HIPPARCOS (1989–1993). Two IUE SWP and 27 optical echelle spectra spanning 20 years were retrieved from various archives. Results. The optical spectra exhibit no anomalies or well-defined variabilities. A magnetic field was not detected. All three photometry satellites recorded variability near 0.656 c/d which is resolved into three features separated by ∼0.0021 c/d. Their first harmonics and two combination frequencies form a second group, whose features are similarly spaced by 0.0021 c/d. The frequency spacing is very nearly but not exactly equidistant. Variability near 0.0021 c/d was not detected. The long-term frequency stability could be used to derive meaningful constraints on the properties of a putative companion star. The IUE spectra do not reveal the presence of a hot subluminous secondary. Conclusions. ν Pup is another Be star exhibiting an NRP variability pattern with long-term constancy and underlining the importance of combination frequencies and frequency groups. This star is a good target for efforts to identify an effectively single Be star.

scholarly journals Models for the Circumstellar Envelopes of Be Stars: (Review Paper)

1976 ◽  
Vol 70 ◽  
pp. 335-370 ◽  
Author(s):  
J. M. Marlborough
Keyword(s):  
Ad Hoc ◽  
Review Paper ◽  
Circumstellar Matter ◽  
Be Stars ◽  
Circumstellar Envelopes ◽  
Structure And Dynamics ◽  
Restricted Problems ◽  
Be Star ◽  
Physical Phenomena

A survey is presented of the theoretical attempts to determine the structure of the circumstellar matter around Be stars. The general equations describing the structure and dynamics of Be star envelopes are given. The complications introduced by various physical phenomena are briefly discussed and initial attempts to solve restricted problems are considered. The various ad hoc models proposed for Be stars are discussed and comparisons of the observations with predictions of these models are illustrated. The strengths and weaknesses of these models are evaluated and areas where progress is being or should be made are considered.

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