FAR-ULTRAVIOLET DETECTION OF THE SUSPECTED SUBDWARF COMPANION TO THE Be STAR 59 CYGNI

Peters, Geraldine J.; Pewett, Tiffany; Gies, Douglas R.; Touhami, Y.; Grundstrom, Erika D.

doi:10.1088/0004-637x/765/1/2

Cited by 86 publications

(94 citation statements)

References 26 publications

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“…This star becomes the dominant light source and a Be star with a small, 1.5M ⊙ companion with a long orbital period of 126 d. This situation appears to be common for a wide variety of Be stars. 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.…”

Section: Discussionsupporting

confidence: 62%

“…The largest difficulty is obtaining high precision velocities with the rapid rotation, but this has been accomplished for the rapid rotator Regulus . Follow-up spectroscopy in the ultraviolet could easily show the spectroscopic signs of the companion, as evidenced by the results of Matson et al (2015), Peters et al (2008Peters et al ( , 2013Peters et al ( , 2016, or Gies et al (1998). Lastly, emission lines that form at very large radii should be investigated to look for further structure caused in the presence of a companion star.…”

Section: Discussionmentioning

confidence: 87%

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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: Discussionsupporting

confidence: 62%

Section: Discussionmentioning

confidence: 87%

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

Richardson

Gerhartz

Bjorkman

et al. 2017

ApJ

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“…The uncertainties associated with these velocities are probably larger than reported in the table. Indeed, since they are too faint, the interstellar lines in the spectrum of ϕ Persei cannot be used to correct for zeropoint shifts of the star position with respect to the slit in the large-aperture observations (Peters et al 2013). Notes.…”

Section: Spectroscopic Orbital Determination From Radial Velocity Meamentioning

confidence: 99%

“…In this case, the companion would lose most of its envelope and would appear as a hot, stripped-down He-star remnant. The Be binary star ϕ Persei represents the first detection of a Be star with a hot, faint companion (Poeckert 1981;Thaller et al 1995;Gies et al 1998), and it is one of three such systems known at present (Peters et al 2013). Clearly it is important to study such Be binaries to determine the physical properties of the stars at the conclusion of their transformative interaction.…”

Section: Introductionmentioning

confidence: 99%

Spectral and spatial imaging of the Be+sdO binaryϕPersei

Mourard

Monnier

Meilland

et al. 2015

A&A

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Aims. The rapidly rotating Be star ϕ Persei was spun up by mass and angular momentum transfer from a now stripped-down, hot subdwarf companion. Here we present the first high angular resolution images of ϕ Persei made possible by new capabilities in longbaseline interferometry at near-IR and visible wavelengths. We analyzed these images to search for the companion, to determine the binary orbit, stellar masses, and fluxes, and to examine the geometrical and kinematical properties of the outflowing disk surrounding the Be star. Methods. We observed ϕ Persei with the MIRC and VEGA instruments of the CHARA Array. MIRC was operated in six-telescope mode, whereas VEGA was configured in four-telescope mode with a change of quadruplets of telescopes during two nights to improve the (u, v) plane coverage. Additional MIRC-only observations were performed to track the orbital motion of the companion, and these were fit together with new and existing radial velocity measurements of both stars to derive the complete orbital elements and distance. We also used the MIRC data to reconstruct an image of the Be disk in the near-IR H-band. VEGA visible broadband and spectro-interferometric Hα observations were fit with analytical models for the Be star and disk, and image reconstruction was performed on the spectrally resolved Hα emission line data. Results. The hot subdwarf companion is clearly detected in the near-IR data at each epoch of observation with a flux contribution of 1.5% in the H band, and restricted fits indicate that its flux contribution rises to 3.3% in the visible. A new binary orbital solution is determined by combining the astrometric and radial velocity measurements. The derived stellar masses are 9.6 ± 0.3 M and 1.2 ± 0.2 M for the Be primary and subdwarf secondary, respectively. The inferred distance (186 ± 3 pc), kinematical properties, and evolutionary state are consistent with membership of ϕ Persei in the α Per cluster. From the cluster age we deduce significant constraints on the initial masses and evolutionary mass transfer processes that transformed the ϕ Persei binary system. The interferometric data place strong constraints on the Be disk elongation, orientation, and kinematics, and the disk angular momentum vector is coaligned with and has the same sense of rotation as the orbital angular momentum vector. The VEGA visible continuum data indicate an elongated shape for the Be star itself, due to the combined effects of rapid rotation, partial obscuration of the photosphere by the circumstellar disk, and flux from the bright inner disk.

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“…Božić et al 1995;Koubský et al 2010;Nemravová et al 2012;Peters et al 2013). The basic reasons for the RV curve of the strong Hα emission wings giving the most reliable estimate of the true orbital motion of the Be primary can be found in Ruždjak et al (2009) or Harmanec et al (2002).…”

Section: Spectroscopic Observations and Their Reductionsmentioning

confidence: 99%

HD 161306: a radiatively interacting Be binary?

Koubský

Kotková

Kraus

et al. 2014

A&A

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The spectrum of the Be star HD 161306 is shown to vary periodically with a period of ∼100 days. The radial velocity of the He i 6678 Å emission peak varying in antiphase to the radial velocity of the Hα emission wings component suggests that the star is a binary similar to φ Per, 59 Cyg, or FY CMa, i.e. a radiatively interacting Be binary -a rare case among Be stars. This type of object is also called a φ Per-type binary or Be + sdO binaries. The range of radial-velocity variations of the strong emission peak in the helium line observed in HD 161306 is about 180 km s −1 , similar to what is observed for these systems. We therefore conclude that HD 161306 may represent another case of a Be star with a hot subdwarf companion.

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FAR-ULTRAVIOLET DETECTION OF THE SUSPECTED SUBDWARF COMPANION TO THE Be STAR 59 CYGNI

Cited by 86 publications

References 26 publications

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

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

Spectral and spatial imaging of the Be+sdO binaryϕPersei

HD 161306: a radiatively interacting Be binary?

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