The circumstellar discs of Be stars

Carciofi, A. C.

doi:10.1017/s1743921311010738

Cited by 29 publications

(29 citation statements)

References 24 publications

(43 reference statements)

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“…Non-radial pulsation and turbulence due to small-scale magnetic fields remain the most likely mechanisms, along with rapid rotation, responsible for the creation of the disks (Rivinius et al 2013b). When the disks are present, they appear to undergo Keplerian rotation (Meilland et al 2007;Wheelwright et al 2012), and many of the observational signatures are consistent with those predicted by the viscous decretion disk model (Lee et al 1991;Carciofi et al 2009;Carciofi 2011).…”

Section: Introductionmentioning

confidence: 84%

HIGH-RESOLUTION H-BAND SPECTROSCOPY OF Be STARS WITH SDSS-III/APOGEE. I. NEW Be STARS, LINE IDENTIFICATIONS, AND LINE PROFILES

Chojnowski

Whelan

Wisniewski

et al. 2014

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The Apache Point Galactic Evolution Experiment (APOGEE) has amassed the largest ever collection of multi-epoch, high-resolution (R ∼ 22, 500), H-band spectra for B-type emission line (Be) stars. These stars were targeted by APOGEE as telluric standard stars and subsequently identified via visual inspection as Be stars based on H i Brackett series emission or shell absorption in addition to otherwise smooth continua and occasionally non-hydrogen emission features. The 128/238 APOGEE Be stars for which emission had never previously been reported serve to increase the total number of known Be stars by ∼ 6%. Because the H-band is relatively unexplored compared to other wavelength regimes, we focus here on identification of the H-band lines and analysis of the emission peak velocity separations (∆v p ) and emission peak intensity ratios (V/R) of the usually double-peaked H i and non-hydrogen emission lines. H i Br11 emission is found to preferentially form in the circumstellar disks at an average distance of ∼2.2 stellar radii. Increasing ∆v p toward the weaker Br12-Br20 lines suggests these lines are formed interior to Br11. By contrast, the observed IR Fe ii emission lines present evidence of having significantly larger formation radii; distinctive phase lags between IR Fe ii and H i Brackett emission lines further supports that these species arise from different radii in Be disks. Several emission lines have been identified for the first time including C i 16895, a prominent feature in the spectra for almost a fifth of the sample and, as inferred from relatively large ∆v p compared to the Br11-Br20, a tracer of the inner regions of Be disks. Emission lines at 15760Å and 16781Å remain unidentified, but usually appear along with and always have similar line profile morphology to Fe ii 16878. Unlike the typical metallic lines observed for Be stars in the optical, the H-band metallic lines, such as Fe ii 16878, never exhibit any evidence of shell absorption, even when the H i lines are clearly shell-dominated. The first known example of a quasi-triple-peaked Br11 line profile is reported for HD 253659, one of several stars exhibiting intra-and/or extra-species V/R and radial velocity variation within individual spectra. Br11 profiles are presented for all discussed stars, as are full APOGEE spectra for a portion of the sample.

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Section: Introductionmentioning

confidence: 84%

HIGH-RESOLUTION H-BAND SPECTROSCOPY OF Be STARS WITH SDSS-III/APOGEE. I. NEW Be STARS, LINE IDENTIFICATIONS, AND LINE PROFILES

Chojnowski

Whelan

Wisniewski

et al. 2014

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“…This is a consequence of the fact that the dynamical solutions reach a near steady-state very quickly in the vicinity of the injection radius ). Furthermore, provided that mass is injected not too far from the stellar photosphere (i.e., assumingR inj 1), the domain 1 ≤R ≤R inj is much narrower than the region where the continuum visual flux of Be stars is generated (Carciofi 2011), which means that the emission from this region can be ignored. Consequently, we conclude that Σ 0 (τ) (with the assumption thatR inj 1) is a much better parameter for describing the mass injection history of the disc than the pair of parameters M inj (τ) andR inj .…”

Section: Dynamical Disc Parametersmentioning

confidence: 99%

The life cycles of Be viscous decretion discs: fundamental disc parameters of 54 SMC Be stars

Rímulo

Carciofi

Vieira

et al. 2018

Monthly Notices of the Royal Astronomical Society

105

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Be stars are main-sequence massive stars with emission features in their spectrum, which originates in circumstellar gaseous discs. Even though the viscous decretion disc (VDD) model can satisfactorily explain most observations, two important physical ingredients, namely the magnitude of the viscosity (α) and the disk mass injection rate, remain poorly constrained. The light curves of Be stars that undergo events of disc formation and dissipation offer an opportunity to constrain these quantities. A pipeline was developed to model these events that uses a grid of synthetic light curves, computed from coupled hydrodynamic and radiative transfer calculations. A sample of 54 Be stars from the OGLE survey of the Small Magellanic Cloud (SMC) was selected for this study. Because of the way our sample was selected (bright stars with clear disc events), it likely represents the densest discs in the SMC. Like their siblings in the Galaxy, the mass of the disc in the SMC increases with the stellar mass. The typical mass and angular momentum loss rates associated with the disk events are of the order of ∼10 −10 M yr −1 and ∼5 × 10 36 g cm 2 s −2 , respectively. The values of α found in this work are typically of a few tenths, consistent with recent results in the literature and with the ones found in dwarf novae, but larger than current theory predicts. Considering the sample as a whole, the viscosity parameter is roughly two times larger at build-up ( α bu = 0.63) than at dissipation ( α d = 0.26). Further work is necessary to verify whether this trend is real or a result of some of the model assumptions.

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“…Decretion disks around Classical Be stars are generally modeled with a single power law for the density structure, as mentioned in Section 4 and Sigut & Jones (2007). When hydrodynamic models are used, a more complex density structure is predicted (Carciofi 2011). As shown by the cur-rent work, HAeBe stars do not seem to follow a single power law for their disk structure, perhaps as expected.…”

Section: Discussionmentioning

confidence: 95%

Photoionization Models of the Inner Gaseous Disk of the Herbig Be Star Bd+65 1637

Patel

Sigut

Landstreet

2016

ApJ

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We attempt to constrain the physical properties of the inner, gaseous disk of the Herbig Be star BD+65 1637 using non-LTE, circumstellar disk codes and observed spectra (3700 to 10,500Å) from the ESPaDOnS instrument on CFHT. The photoionizing radiation of the central star is assumed to be the sole source of input energy for the disk. We model optical and near-infrared emission lines that are thought to form in this region using standard techniques that have been successful in modeling the spectra of Classical Be stars. By comparing synthetic line profiles of hydrogen, helium, iron and calcium with the observed line profiles, we try to constrain the geometry, density structure, and kinematics of the gaseous disk. Reasonable matches have been found for all line profiles individually; however, no disk density model based on a single powerlaw for the equatorial density was able to simultaneously fit all of the observed emission lines. Amongst the emission lines, the metal lines, especially the Ca ii IR triplet, seem to require higher disk densities than the other lines. Excluding the Ca ii lines, a model in which the equatorial disk density falls as 10 −10 (R * /R) 3 g cm −3 seen at an inclination of 45 • for a 50 R * disk provides reasonable matches to the overall line shapes and strengths. The Ca ii lines seem to require a shallower drop off as 10 −10 (R * /R) 2 g cm −3 to match their strength. More complex disk density models are likely required to refine the match to the BD+65 1637 spectrum.

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The circumstellar discs of Be stars

Cited by 29 publications

References 24 publications

HIGH-RESOLUTION H-BAND SPECTROSCOPY OF Be STARS WITH SDSS-III/APOGEE. I. NEW Be STARS, LINE IDENTIFICATIONS, AND LINE PROFILES

HIGH-RESOLUTION H-BAND SPECTROSCOPY OF Be STARS WITH SDSS-III/APOGEE. I. NEW Be STARS, LINE IDENTIFICATIONS, AND LINE PROFILES

The life cycles of Be viscous decretion discs: fundamental disc parameters of 54 SMC Be stars

Photoionization Models of the Inner Gaseous Disk of the Herbig Be Star Bd+65 1637

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