A Study of π Aquarii during a Quasi‐normal Star Phase: Refined Fundamental Parameters and Evidence for Binarity

Bjorkman, K. S.; Мирошниченко, А. С.; McDavid, D.; Pogrosheva, T.

doi:10.1086/340751

Cited by 63 publications

(139 citation statements)

References 41 publications

(75 reference statements)

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“…5). π Aqr: The star had a very strong emission spectrum before 1995/96 (Bjorkman et al 2002). No short-term periodic behavior is known for π Aqr, but recently Bjorkman et al (2002) reported it to be a binary with a period of 84.1 d. Our data, obtained during the low emission phase after 1996 confirms such a timescale in the Balmer emission lines.…”

Section: Individual Objectssupporting

confidence: 64%

“…π Aqr: The star had a very strong emission spectrum before 1995/96 (Bjorkman et al 2002). No short-term periodic behavior is known for π Aqr, but recently Bjorkman et al (2002) reported it to be a binary with a period of 84.1 d. Our data, obtained during the low emission phase after 1996 confirms such a timescale in the Balmer emission lines. Three spectra in October 2001 show a relatively strong Hα emission filling up the absorption and a peak height of about 1.1 of the continuum, but by 2002 the emission had weakened again to the previous value, with peak heights of about 0.9 of the ambient continuum.…”

Section: Individual Objectssupporting

confidence: 64%

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Non-radially pulsating Be stars

Rivinius

Baade

Štefl

2003

A&A

147

192

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Abstract. Based on more than 3000 high-resolution echelle spectra of 27 early-type Be stars, taken over six years, it is shown that the short-term periodic line profile variability of these objects is due to non-radial pulsation. The appearance of the line profile variability depends mostly on the projected rotational velocity v sin i and thus, since all Be stars rotate rapidly, on the inclination i. The observed variability of the investigated stars is described, and for some of them line profile variability periods are given for the first time. For two of the investigated stars the line profile variability was successfully modeled as non-radial pulsation with = m = +2 already in previous works. Since Be stars with similarly low v sin i share the same variability properties, these are in general explainable under the same model assumptions. The line profile variability of stars with higher v sin i is different from the one observed in low v sin i stars, but can be reproduced by the same model, if only the model inclination is modified to more equatorial values. Only for a few stars with periodic line profile variability the = m = 2 non-radial pulsation mode is not able to provide a satisfying explanation. These objects might pulsate in different modes (e.g. tesseral ones, |m|). Almost all stars in the sample show traces of outburst-like variability, pointing to an ephemeral nature of the mass-loss phenomenon responsible for the formation of the circumstellar disk of early-type Be stars, rather than a steady star-to-disk mass transfer. In addition to the variability due to non-radial pulsation present in most stars, several objects were found to show other periods residing in the immediate circumstellar environment. The presence of these secondary periods is enhanced in the outburst phases. Short-lived aperiodic phenomena were clearly seen in two stars. But, given the unfavourable sampling of our database to follow rapid variability of transient nature, they might be more common. Only in two out of 27 stars short-term spectroscopic variability was not detected at all.

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Section: Individual Objectssupporting

confidence: 64%

Section: Individual Objectssupporting

confidence: 64%

Non-radially pulsating Be stars

Rivinius

Baade

Štefl

2003

A&A

147

192

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“…The time evolution of the Hα EW of π Aqr (Figure 2) also provides clear evidence of a disk-loss event, at a higher sampling frequency than available in previous publications (Bjorkman et al 2002). Our data indicate that it took at least ∼2440 days for π Aqr's disk to transform from its strongest state observed during our time coverage (1989 October 26; EW = −24.6 Å; Table 2) to the likely start of its minimum state of pure absorption (1996 July 4; EW = 4.1 Å; Table 2).…”

Section: π Aqrsupporting

confidence: 60%

“…π Aqr (HD 212571) is a B1 III-IVe classical Be star (Slettebak 1982). As discussed in Bjorkman et al (2002) and references therein, π Aqr's most recent disk likely developed in the early 1950s and persisted until 1996. Analysis of spectroscopic data obtained after 1996, when the star was in a diskless "normal B star" phase, revealed the star has a close binary companion with an orbital period of 84.1 days (Bjorkman et al 2002), which might be engaged in variable mass transfer with the primary.…”

Section: Disk-loss and Disk-renewal Phases In Classical Be Stars I mentioning

confidence: 99%

DISK-LOSS AND DISK-RENEWAL PHASES IN CLASSICAL Be STARS. I. ANALYSIS OF LONG-TERM SPECTROPOLARIMETRIC DATA

Wisniewski

Draper

Bjorkman

et al. 2010

ApJ

Self Cite

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Classical Be stars are known to occasionally transition from having a gaseous circumstellar disk ("Be phase") to a state in which all observational evidence for the presence of these disks disappears ("normal B-star phase"). We present one of the most comprehensive spectropolarimetric views to date of such a transition for two Be stars, π Aquarii and 60 Cygni.The disk-loss episode of 60 Cyg was characterized by a generally monotonic decrease in emission strength over a timescale of ∼1000 days from the maximum V-band polarization to the minimum Hα equivalent width, consistent with the viscous timescale of the disk, assuming α ∼0.14. π Aqr's disk loss was episodic in nature and occurred over a timescale of ∼2440 days. An observed time lag between the behavior of the polarization and Hα in both stars indicates the disk clearing proceeded in an "inside-out" manner. We determine the position angle of the intrinsic polarization to be 166.• 7 ± 0.• 1 for π Aqr and 107.• 7 ± 0.• 4 for 60 Cyg, and model the wavelength dependence of the observed polarization during the quiescent diskless phase of each star to determine the interstellar polarization along the line of sight. Minor outbursts observed during the quiescent phase of each star shared similar lifetimes as those previously reported for μ Cen, suggesting that the outbursts represent the injection and subsequent viscous dissipation of individual blobs of material into the inner circumstellar environments of these stars. We also observe deviations from the mean intrinsic polarization position angle during polarization outbursts in each star, indicating deviations from axisymmetry. We propose that these deviations might be indicative of the injection (and subsequent circularization) of new blobs into the inner disk, either in the plane of the bulk of the disk material or in a slightly inclined (non-coplanar) orbit.

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“…13, dust-free models corresponding to the lowest F W4 /F W1 value (close to the stellar locus), followed by low-dust models at an intermediate F W4 /F W1 value, and finally the high-dust model "C_hd_0.71_inter" falling above the limit of the figure. Zasche (2009); (2) Zasche (2011); (3) Budding et al (2004) and references therein; (4) Linnell et al (1988); (5) Blind et al (2011);(6) Kreiner (2004); (7) Linnell et al (1988); (8) Kreiner (2004); (9) Walborn (1982); (10) Grundstrom et al (2007); (11) Plavec (1989); (12) Hegedus (1988); (13) Zoła & Ogłoza (2001); (14) Hummel & Štefl (2001); (15) Bjorkman et al (2002); (16) Waters et al (1991); (17) Berdyugin & Piirola (2002).…”

Section: Wise Datamentioning

confidence: 99%

Non-conservative evolution in Algols: where is the matter?

Deschamps

Braun

Jorissen

et al. 2015

A&A

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Context. There is indirect evidence of non-conservative evolutions in Algols. However, the systemic mass-loss rate is poorly constrained by observations and generally set as a free parameter in binary-star evolution simulations. Moreover, systemic mass loss may lead to observational signatures that still need to be found. Aims. Within the "hotspot" ejection mechanism, some of the material that is initially transferred from the companion star via an accretion stream is expelled from the system due to the radiative energy released on the gainer's surface by the impacting material. The objective of this paper is to retrieve observable quantities from this process and to compare them with observations. Methods. We investigate the impact of the outflowing gas and the possible presence of dust grains on the spectral energy distribution (SED). We used the 1D plasma code Cloudy and compared the results with the 3D Monte-Carlo radiative transfer code Skirt for dusty simulations. The circumbinary mass-distribution and binary parameters were computed with state-of-the-art binary calculations done with the Binstar evolution code. Results. The outflowing material reduces the continuum flux level of the stellar SED in the optical and UV. Because of the timedependence of this effect, it may help to distinguish between different ejection mechanisms. If present, dust leads to observable infrared excesses, even with low dust-to-gas ratios, and traces the cold material at large distances from the star. By searching for this dust emission in the WISE catalogue, we found a small number of Algols showing infrared excesses, among which the two rather surprising objects SX Aur and CZ Vel. We find that some binary B[e] stars show the same strong Balmer continuum as we predict with our models. However, direct evidence of systemic mass loss is probably not observable in genuine Algols, since these systems no longer eject mass through the hotspot mechanism. Furthermore, owing to its high velocity, the outflowing material dissipates in a few hundred years. If hot enough, the hotspot may produce highly ionised species, such as Si iv, and observable characteristics that are typical of W Ser systems. Conclusions. If present, systemic mass loss leads to clear observational imprints. These signatures are not to be found in genuine Algols but in the closely related β Lyraes, W Serpentis stars, double periodic variables, symbiotic Algols, and binary B[e] stars. We emphasise the need for further observations of such objects where systemic mass loss is most likely to occur.

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A Study of π Aquarii during a Quasi‐normal Star Phase: Refined Fundamental Parameters and Evidence for Binarity

Cited by 63 publications

References 41 publications

Non-radially pulsating Be stars

Non-radially pulsating Be stars

DISK-LOSS AND DISK-RENEWAL PHASES IN CLASSICAL Be STARS. I. ANALYSIS OF LONG-TERM SPECTROPOLARIMETRIC DATA

Non-conservative evolution in Algols: where is the matter?

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