A SYSTEMATIC STUDY OF Hα PROFILES OF Be STARS

Silaj, J.; Jones, C. E.; Tycner, C.; Sigut, T. A. A.; Smith, A. D.

doi:10.1088/0067-0049/187/1/228

Cited by 95 publications

(143 citation statements)

References 32 publications

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“…Thus, the Be disk and orbital plane might indeed be misaligned in XTE J1946+274. Özbey Arabacı et al (2014) recently analyzed optical spectra of the system and noted, however, that deriving the Be-disk inclination from the Hα line profile is highly uncertain based on theoretical investigations by Silaj et al (2010). Assuming that the orbital plane and the Be disk are aligned (i disk =i), Özbey Arabacı et al (2014) derived the rotational velocity of the Be star.…”

Section: Smmentioning

confidence: 99%

The Transient Accreting X-Ray Pulsar Xte J1946+274: Stability of X-Ray Properties at Low Flux and Updated Orbital Solution

Marcu-Cheatham

Pottschmidt

Kühnel³

et al. 2015

ApJ

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We present a timing and spectral analysis of the X-ray pulsar XTE J1946+274 observed with Suzaku during an outburst decline in 2010 October and compare with previous results. XTE J1946+274 is a transient X-ray binary consisting of a Be-type star and a neutron star with a 15.75 s pulse period in a 172 days orbit with 2-3 outbursts per orbit during phases of activity. We improve the orbital solution using data from multiple instruments. The X-ray spectrum can be described by an absorbed Fermi-Dirac cut-off power-law model along with a narrow Fe Kα line at 6.4 keV and a weak Cyclotron Resonance Scattering Feature (CRSF) at ∼35 keV. The Suzaku data are consistent with the previously observed continuum flux versus iron line flux correlation expected from fluorescence emission along the line of sight. However, the observed iron line flux is slightly higher, indicating the possibility of a higher iron abundance or the presence of non-uniform material. We argue that the source most likely has only been observed in the subcritical (non-radiation dominated) state since its pulse profile is stable over all observed luminosities and the energy of the CRSF is approximately the same at the highest (∼5×10 37 erg s −1 ) and lowest (∼5×10 36 erg s −1 ) observed 3-60 keV luminosities.

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Section: Smmentioning

confidence: 99%

The Transient Accreting X-Ray Pulsar Xte J1946+274: Stability of X-Ray Properties at Low Flux and Updated Orbital Solution

Marcu-Cheatham

Pottschmidt

Kühnel³

et al. 2015

ApJ

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“…Another possibility could be that since disks are denser at low metallicity (for a given mass and age), they could be more easily detected at low metallicity. According to Silaj et al (2010), the minimum density for a disk to produce Hα emission is 5 × 10 −13 g cm −3 . Finally, the analysis of Cranmer (2005), which sets a minimum velocity for becoming a Be-type star that varies as a function of the effective temperature was performed at solar metallicity.…”

Section: Possible Link Between Very Rapid Rotationmentioning

confidence: 99%

“…Interestingly enough, Silaj et al (2010) modelled Hα emission line profiles of Be stars with their non-LTE radiative transfer code BEDISK by fitting disk parameters: their Table 3 shows that disks around B0 type stars are more massive than disks around B8 type stars. Our models predict extensions for the disk's outer radius of some thousands of solar radii.…”

Section: Comparison Of the Disk Mass Extension And Diffusion Timementioning

confidence: 99%

Populations of rotating stars

Granada

Ekström

Georgy

et al. 2013

A&A

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Context. Even though it is broadly accepted that single Be stars are rapidly rotating stars surrounded by a flat rotating circumstellar disk, there is still a debate about how fast these stars rotate and also about the mechanisms involved in the angular-momentum and mass input in the disk. Aims. We study the properties of stars that rotate near their critical-rotation rate and investigate the properties of the disks formed by equatorial mass ejections. Methods. We used the most recent Geneva stellar evolutionary tracks for rapidly rotating stars that reach the critical limit and used a simple model for the disk structure. Results. We obtain that for a 9 M star at solar metallicity, the minimum average velocity during the main-sequence (MS) phase to reach the critical velocity is around 330 km s −1 , whereas it would be 390 km s −1 at the metallicity of the Small Magellanic Cloud (SMC). Red giants or supergiants originating from very rapid rotators rotate six times faster and show N/C ratios three times higher than those originating from slowly rotating stars. This difference becomes stronger at lower metallicity. It might therefore be very interesting to study the red giants in clusters that show a large number of Be stars on the MS band. On the basis of our single-star models, we show that the observed Be-star fraction with cluster age is compatible with the existence of a temperature-dependent lower limit in the velocity rate required for a star to become a Be star. The mass, extension, and diffusion time of the disks produced when the star is losing mass at the critical velocity, obtained from simple parametrized expressions, are estimated to be between 9.4 × 10 −12 and 1.4 × 10 −7 M (3 × 10 −6 to 4.7 × 10 −2 times the mass of the Earth), 2000 and 6500 R , and 10 and 30 yr. These values are not too far from those estimated for disks around Be-type stars. At a given metallicity, the mass and the extension of the disk increase with the initial mass and with age on the MS phase. Denser disks are expected in low-metallicity regions.

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“…Furthermore, rapid changes in line profile types are explained as the result of dynamical effects due to the misalignment of the disc orbital plane and the stellar equator (see Porter & Rivinius 2003). Recent studies propose that density changes in the disc thermal structure may be the origin as well (Silaj et al 2010, and references therein).…”

Section: Long-term Be-disc/neutron Star Interactionmentioning

confidence: 99%

Recent activity of the Be/X-ray binary system SAX J2103.5+4545

Camero

Zurita

Gutiérrez‐Soto

et al. 2014

A&A

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Aims. We present a multiwavelength study of the Be/X-ray binary system SAX J2103.5+4545 with the goal of better characterizing the transient behaviour of this source. Methods. SAX J2103.5+4545 was observed by Swift/XRT four times in 2007 from April 25 to May 5, and during quiescence in 2012 August 31. In addition, this source has been monitored from the ground-based astronomical observatories of El Teide (Tenerife, Spain), Roque de los Muchachos (La Palma, Spain), and Sierra Nevada (Granada, Spain) since 2011 August, and from the TÜBİTAK National Observatory (Antalya, Turkey) since 2009 June. We performed spectral and photometric temporal analyses to investigate the different states exhibited by SAX J2103.5+4545. Results. In X-rays, an absorbed power-law model provided the best fit for all the XRT spectra. An iron-line feature at ∼6.42 keV was present in all the observations except for that taken during quiescence in 2012. The photon indexes are consistent with previous studies of SAX J2103.5+4545 in high/low-luminosity states. Pulsations were found in all the XRT data from 2007 (2.839(2) mHz; MJD 54 222.02), but not during quiescence. The two optical outbursts in 2010 and 2012 lasted for about eight or nine months (as the one in 2007 probably did and the current one in 2014 might do) and were most probably caused by mass-ejection events from the Be star that eventually fed the circumstellar disc. All of these outbursts started about three months before the triggering of the X-ray activity, and at about the same period before the maximum of the Hα line equivalent width (in emission) was reached at only ∼-5 Å. The global correlation between the BV variability and the X-ray intensity was also observed at longer wavelengths in the IR domain.

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A SYSTEMATIC STUDY OF Hα PROFILES OF Be STARS

Cited by 95 publications

References 32 publications

The Transient Accreting X-Ray Pulsar Xte J1946+274: Stability of X-Ray Properties at Low Flux and Updated Orbital Solution

The Transient Accreting X-Ray Pulsar Xte J1946+274: Stability of X-Ray Properties at Low Flux and Updated Orbital Solution

Populations of rotating stars

Recent activity of the Be/X-ray binary system SAX J2103.5+4545

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