Properties and nature of Be stars

Ruždjak, Domagoj; Božić, H.; Harmanec, P.; Fiřt, Roman; Chadima, P.; Bjorkman, K. S.; Gies, Douglas R.; Kaye, A. B.; Koubský, P.; McDavid, D.; Richardson, Noel D.; Sudar, D.; Šlechta, M.; Wolf, M.; Yang, S.

doi:10.1051/0004-6361/200810526

Cited by 36 publications

(38 citation statements)

References 48 publications

(70 reference statements)

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“…Similar direct ultraviolet detections of hot subdwarf companions have been accomplished for FY CMa (Peters et al 2008), 59 Cyg (Peters et al 2013), HR 2142 (Peters et al 2016), and o Pup (Rivinius et al 2012, Koubský et al 2012) all with small mass functions in the range of 2 × 10 −3 − 1.3 × 10 −2 M ⊙ . Other Be binaries that have not had direct detections of the companion stars such as γ Cas (Smith et al 2012) or ζ Tau (Ruždjak et al 2009) also show similar mass functions (f (M ) = 1 × 10 −3 and f (M ) = 6 × 10 −3 respectively) that indicate low-mass companions. The mass function of the single-lined orbit we derived for β CMi (f (M ) = 2.0 × 10 −3 M ⊙ ) is indicative of a very low mass companion, similar to the aforementioned Be binaries with ultraviolet detections of the companions.…”

Section: Discussionmentioning

confidence: 96%

A Spectroscopic Orbit for the Late-type Be Star β CMi

Richardson

Gerhartz

Bjorkman

et al. 2017

ApJ

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The late-type Be star β CMi is remarkably stable compared to other Be stars that have been studied. This has led to a realistic model of the outflowing Be disk by Klement et al. These results showed that the disk is likely truncated at a finite radius from the star, which Klement et al. suggest is evidence for an unseen binary companion in orbit. Here we report on an analysis of the Ritter Observatory spectroscopic archive of β CMi to search for evidence of the elusive companion. We detect periodic Doppler shifts in the wings of the Hα line with a period of 170 d and an amplitude of 2.25 km s −1 , consistent with a low-mass binary companion (M ≈ 0.42M ⊙ ). We then compared the small changes in the violet-to-red peak height changes (V /R) with the orbital motion. We find weak evidence that it does follow the orbital motion, as suggested by recent Be binary models by Panoglou et al. Our results, which are similar to those for several other Be stars, suggest that β CMi may be a product of binary evolution where Roche lobe overflow has spun up the current Be star, likely leaving a hot subdwarf or white dwarf in orbit around the star. Unfortunately, no direct sign of this companion star is found in the very limited archive of International Ultraviolet Explorer spectra.

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Section: Discussionmentioning

confidence: 96%

A Spectroscopic Orbit for the Late-type Be Star β CMi

Richardson

Gerhartz

Bjorkman

et al. 2017

ApJ

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“…unsaturated profiles. The reasons the emission wings should provide a good estimate of the true orbital motion of the Be primary around the common centre of gravity with the secondary were recently summarized in detail by Ruždjak et al (2009). To them, we can add that Poeckert & Marlborough (1978) modelled the Hα emission of γ Cas, and their model showed that the Hα emission wings originate in regions that are much closer to the star than the radiation that is forming the upper part of the line.…”

Section: Long-term and Periodic Rv Changes And The New Orbital Solutionsmentioning

confidence: 97%

Properties and nature of Be stars

Nemravová

Harmanec

Koubský

et al. 2012

A&A

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A detailed analysis of more than 800 electronic high-resolution spectra of gamma Cas, which were obtained during a time interval of over 6000 days (16.84 yr) at several observatories, documents the smooth variations in the density and/or extent of its circumstellar envelope. We found a clear anticorrelation between the peak intensity and FWHM of the Hα emission, which seems to agree with recent models of such emission lines. The main result of this study is a confirmation of the binary nature of the object, determination of a reliable linear ephemeris T min.RV = HJD (2 452 081.9±0.6)+(203. d 52±0. d 08)× E, and a rather definitive set of orbital elements. We clearly demonstrated that the orbit is circular within the limits of accuracy of our measurements and has a semi-amplitude of radialvelocity curve of 4.30 ± 0.09 km s −1 . No trace of the low-mass secondary was found. The time distribution of our spectra does not allow a reliable investigation of rapid spectral variations, which are undoubtedly present in the spectra. We postpone this investigation for a future study, based on series of dedicated whole-night spectral observations.

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“…2. For binary Be stars with strong Hα emission, this is the best measure of the true orbital motion of the Be component -see Božić et al (1995), Ruždjak et al (2009) and Peters et al (2013). This is not so for BR CMi, since its Hα emission rises to only 20% above the continuum level, and the measured RV curve of the Hα emission wings is poorly defined and has a phase shift with respect to expected orbital motion of component 1.…”

Section: Finding Reliable Orbital Elementsmentioning

confidence: 99%

Properties and nature of Be stars

Harmanec

Koubský

Nemravová

et al. 2015

A&A

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Reliable determination of the basic physical properties of hot emission-line binaries with Roche-lobe filling secondaries is important for developing the theory of mass exchange in binaries. It is a very hard task, however, which is complicated by the presence of circumstellar matter in these systems. So far, only a small number of systems with accurate values of component masses, radii, and other properties are known. Here, we report the first detailed study of a new representative of this class of binaries, BR CMi, based on the analysis of radial velocities and multichannel photometry from several observatories, and compare its physical properties with those for other well-studied systems. BR CMi is an ellipsoidal variable seen under an intermediate orbital inclination of ∼51• , and it has an orbital period of 12.d 919059(15) and a circular orbit. We used the disentangled component spectra to estimate the effective temperatures 9500(200) K and 4655(50) K by comparing them with model spectra. They correspond to spectral types B9.5e and G8III. We also used the disentangled spectra of both binary components as templates for the 2D cross-correlation to obtain accurate radial velocities and a reliable orbital solution. Some evidence of a secular period increase at a rate of (1.1 ± 0.5) s per year was found. This, together with a very low mass ratio of 0.06 and a normal mass and radius of the mass gaining component, indicates that BR CMi is in a slow phase of the mass exchange after the mass-ratio reversal. It thus belongs to a still poorly populated subgroup of Be stars for which the origin of Balmer emission lines is safely explained as a consequence of mass transfer between the binary components.

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Properties and nature of Be stars

Cited by 36 publications

References 48 publications

A Spectroscopic Orbit for the Late-type Be Star β CMi

A Spectroscopic Orbit for the Late-type Be Star β CMi

Properties and nature of Be stars

Properties and nature of Be stars

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