A search for luminous Be stars

Negueruela, I.

doi:10.1002/asna.200410245

Cited by 32 publications

(47 citation statements)

References 41 publications

(72 reference statements)

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“…Quoted as belonging to NGC 6913 (Humphreys 1978), HD 229234 was classified as an O 9If star by Massey et al (1995) whilst Negueruela (2004) reported an O 9II classification and Morgan et al (1955) reported this star as O 9.5III. Previous investigations of Liu et al (1989) and Boeche et al (2004) proposed this star to be a binary system with an orbital period of 3.5105 days.…”

Section: Hd 229234mentioning

confidence: 99%

A spectroscopic investigation of the O-type star population in four Cygnus OB associations

Mahy

Rauw

Becker

et al. 2013

A&A

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Context. Establishing the multiplicity of O-type stars is the first step towards accurately determining their stellar parameters. Moreover, the distribution of the orbital parameters provides observational clues to the way that O-type stars form and to the interactions during their evolution. Aims. Our objective is to constrain the multiplicity of a sample of O-type stars belonging to poorly investigated OB associations in the Cygnus complex and for the first time to provide orbital parameters for binaries identified in our sample. Such information is relevant to addressing the issue of the binarity in the context of O-type star formation scenarios. Methods. We performed a long-term spectroscopic survey of nineteen O-type stars. We searched for radial velocity variations to unveil binaries on timescales from a few days up to a few years, on the basis of a large set of optical spectra. Results. We confirm the binarity for four objects: HD 193443, HD 228989, HD 229234, and HD 194649. We derive for the first time the orbital solutions of three systems, and we confirm the values of the fourth, showing that these four systems all have orbital periods shorter than 10 days. Besides these results, we also detect several objects that show non-periodic line profile variations in some of their spectral lines. These variations mainly occur in the spectral lines that are generally affected by the stellar wind and are not likely to be related to binarity. Conclusions. The minimal binary fraction in our sample is estimated to be 21%, but it varies from one OB association to the next. Indeed, 3 O stars of our sample out of 9 (33%) belonging to Cyg OB1 are binary systems, 0% (0 out of 4) in Cyg OB3, 0% (0 out of 3) in Cyg OB8, and 33% (1 out of 3) in Cyg OB9. Our spectroscopic investigation also stresses the absence of long-period systems among the stars in our sample. This result contrasts with the case of the O-type stellar population in NGC 2244 among which no object showed radial velocity variations on short timescales. However, we show that it is probably an effect of the sample and that this difference does not a priori suggest a somewhat different star forming process in these two environments.

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Section: Hd 229234mentioning

confidence: 99%

A spectroscopic investigation of the O-type star population in four Cygnus OB associations

Mahy

Rauw

Becker

et al. 2013

A&A

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“…This is Full Tables 1 and 4 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/595/A132 in contrast to early-type supergiants in which emission in the Balmer lines is a "passive" consequence of their extended atmosphere. Even when some classic Be stars are believed to survive as such in the bright giant phase (Negueruela 2004), this definition excludes the heterogeneous group of objects presenting the B[e] phenomenon, which likely manifests at different states of stellar evolution (Lamers et al 1998). Be stars have long been known as rapid rotators (Struve 1931) and, accordingly, these stars are assumed to create their circumstellar disk or envelope thanks mainly to this rapid rotation.…”

Section: Introductionmentioning

confidence: 99%

Critical study of the distribution of rotational velocities of Be stars

Zorec

Frémat

Souza

et al. 2016

A&A

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Context. Among intermediate-mass and massive stars, Be stars are the fastest rotators in the main sequence (MS) and, as such, these stars are a cornerstone to validate models of structure and evolution of rotating stars. Several phenomena, however, induce under-or overestimations either of their apparent Vsin i, or true velocity V. Aims. In the present contribution we aim at obtaining distributions of true rotational velocities corrected for systematic effects induced by the rapid rotation itself, macroturbulent velocities, and binarity. Methods. We study a set of 233 Be stars by assuming they have inclination angles distributed at random. We critically discuss the methods of Cranmer and Lucy-Richardson, which enable us to transform a distribution of projected velocities into another distribution of true rotational velocities, where the gravitational darkening effect on the Vsin i parameter is considered in different ways. We conclude that iterative algorithm by Lucy-Richardson responds at best to the purposes of the present work, but it requires a thorough determination of the stellar fundamental parameters. Results. We conclude that once the mode of ratios of the true velocities of Be stars attains the value V/V c 0.77 in the main-sequence (MS) evolutionary phase, it remains unchanged up to the end of the MS lifespan. The statistical corrections found on the distribution of ratios V/V c for overestimations of Vsin i, due to macroturbulent motions and binarity, produce a shift of this distribution toward lower values of V/V c when Be stars in all MS evolutionary stages are considered together. The mode of the final distribution obtained is at V/V c 0.65. This distribution has a nearly symmetric distribution and shows that the Be phenomenon is characterized by a wide range of true velocity ratios 0.3 V/V c 0.95. It thus suggests that the probability that Be stars are critical rotators is extremely low. Conclusions. The corrections attempted in the present work represent an initial step to infer indications about the nature of the Be-star surface rotation that will be studied in the second paper of this series.

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“…A first run was made in 2003 with the 1.5 m telescope of the Observatorio Astronómico Nacional (OAN) in Calar Alto, Almería, Spain. A sample of emission-line stars from the catalogs by Kohoutek & Wehmeyer (1999, 2003, 2004 and Robertson & Jordan (1989) was observed. The targets were selected on the base of spectral types determined considering their position in the reddening-free [m 1 ] − [c 1 ] photometric diagram (Moon 1986).…”

Section: The Setting Up Of the Faint Be-star Samplementioning

confidence: 99%

“…Their Be phenomenon could be thought of as favored by the rotational acceleration they acquire during the secondary contraction phase. According to Negueruela (2004) some of them could even be interacting binaries. This figure also shows the evolutionary tracks of rotating stars whose initial equatorial rotational velocities in the ZAMS are V ini /V c = 0.4 (Ekström et al 2012).…”

Section: The Apparent and True Hr Diagram Of The Programmentioning

confidence: 99%

“…It will then be quite important to see whether their Be characteristic is due to pulsation or other phenomena. It may happen that their circumstellar disk is only a remnant from the period of the secondary contraction, produced by a noticeable increase in the surface rotation velocity that could favor the critical rotation (Negueruela 2004). …”

Section: Corot Id Nmentioning

confidence: 99%

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Study of a sample of faint Be stars in the exofield of CoRoT

Semaan

Hubert

Zorec

et al. 2013

A&A

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Context. Be stars are probably the most rapid rotators among stars in the main sequence (MS) and, as such, are excellent candidates to study the incidence of the rotation on the characteristics of their non-radial pulsations, as well as on their internal structure. Pulsations are also thought to be possible mechanisms that help the mass ejection needed to build up the circumstellar disks of Be stars. Aims. The purpose of this paper is to identify a number of faint Be stars observed with the CoRoT satellite and to determine their fundamental parameters, which will enable us to study their pulsation properties as a function of the location in the HR diagram and to search for correlations with the light outbursts, which are possibly produced by discrete mass ejections. Methods. We identified those objects in the exofields of CoRoT presenting the Be phenomenon using Hα surveys, as well as automated methods based on pulsation properties that we finally confirmed with FLAMES/GIRAFFE and X-shooter spectroscopic observations at VLT/ESO, and with near-IR photometry. The spectra were 1) corrected for the veiling effect, 2) treated with the GIRFIT code to determine apparent fundamental parameters, and 3) corrected with the FASTROT code for effects induced by the rapid rotation. Results. A list of 41 Be star candidates were found from photometric and spectroscopic criteria. The spectral coverage useful for determining the fundamental parameters was obtained for only about half of them. We then spectroscopically identified 21 Be stars, two probable Be stars, and two B stars contaminated by the Sh 2-284 nebulosity. A short description of the spectral characteristics of each star is given. The fundamental parameters and, in particular, the rotation frequency ν r (cycles per day) were all corrected for rotational effects at rotation rates ranging from Ω/Ω c = 0.8 to 1.0. We have determined the positions of Be stars in the HR diagram and find two of them located beyond the MS phase. Conclusions. The well-determined fundamental parameters presented in this paper for a statistically reliable sample of Be stars will enable us in forthcoming papers to compare the properties of stars as pulsators either according to their location in different regions of the HR diagram or with those predicted from theory.

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A search for luminous Be stars

Cited by 32 publications

References 41 publications

A spectroscopic investigation of the O-type star population in four Cygnus OB associations

A spectroscopic investigation of the O-type star population in four Cygnus OB associations

Critical study of the distribution of rotational velocities of Be stars

Study of a sample of faint Be stars in the exofield of CoRoT

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