The on Stars: A Wider Spectroscopic Definition

Bisiacchi, G. F.; López, J. M.; Firmani, C.

doi:10.1007/978-94-009-7910-9_52

Cited by 12 publications

(18 citation statements)

References 3 publications

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“…Previously estimated to be about 95 km s −1 (Conti & Ebbets 1977), we measured, for four lines (He ii λ 4686, O iii λ 5592, C iv λ 5801, and He i λ 5876), a mean value of about v sin i = 110 ± 18 km s −1 . The spectral type was previously quoted as O7.5 V ((f)) (Conti & Leep 1974), O7 V (Bisiacchi et al 1982), or O7 III ((f)) (Walborn 1971). In our data, the He i λ 4471 to He ii λ 4542 ratio implies an O7.5 type, while the EW ratio between Si iv λ 4088 and He i λ 4143 favors a main-sequence (MS) luminosity class.…”

Section: Hd 46 573supporting

confidence: 47%

“…We measured a mean projected rotational velocity of about v sin i = 100 ± 17 km s −1 , while the literature reports a value of v sin i = 103 km s −1 (Penny 1996). HD 46 223 was previously classified as O5 (Hiltner 1956;Johnson 1962;Bisiacchi et al 1982), O4 (Morgan et al 1965), O5 ((f)) (Conti & Leep 1974), an O4 V ((f + )) spectral type. We also detected weak emission in the Hα line probably due to the nebular material surrounding the star as we already mentioned for HD 46 056.…”

Section: Hd 46 223mentioning

confidence: 95%

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Early-type stars in the young open cluster NGC 2244 and in the Monoceros OB2 association

Mahy¹,

Nazé²,

Rauw³

et al. 2009

A&A

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Aims. We present the results obtained from a long-term spectroscopic campaign to study the multiplicity of O-type stars in both the young open cluster NGC 2244 and the Mon OB2 association. Methods. Our spectroscopic monitoring was performed over several years, allowing us to investigate different timescales. For each star, several spectral diagnostic tools were applied to search for line shifts and profile variations. We also measured the projected rotational velocity and revisited the spectral classification. Results. Several stars in our sample have been previously considered to be spectroscopic binaries, although only a few scattered observations were available. Our results now have identified a more complex situation for two new spectroscopic binaries (HD 46 149 in NGC 2244 and HD 46 573 in Mon OB2). The first object is a long-period double-lined spectroscopic binary, although the exact value of its period remains uncertain and the second object is classified as an SB1 system with a period of about 10.67 days but the time series of our observations do not enable us to derive a unique orbital solution for this system. We also find another star to be variable in radial velocity (HD 46 150) and detect line profile variations in two rapid rotators (HD 46 056 and HD 46 485). Conclusions. This spectroscopic investigation places a firm lower limit (17%) on the binary fraction of O-stars in NGC 2244 and reveals the lack of short-period O+OB systems in this cluster. In addition, a comparison of these new results with two other wellstudied clusters (NGC 6231 and IC 1805) puts forward possible hints of a relation between stellar density and binarity, which could provide constraints on the theories of the formation and early evolution of hot stars.

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Section: Hd 46 573supporting

confidence: 47%

Section: Hd 46 223mentioning

confidence: 95%

Early-type stars in the young open cluster NGC 2244 and in the Monoceros OB2 association

Mahy¹,

Nazé²,

Rauw³

et al. 2009

A&A

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“…One of the targets is HD 46223, the hottest member of NGC 2244. Situated at about 1.4-1.7 kpc (Hensberge et al 2000), this star was previously A&A 533, A4 (2011) quoted in the literature as having a spectral type O5 V (Hiltner 1956;Bisiacchi et al 1982), O5 ((f)) (Conti & Leep 1974), O4 ((f)) (Massey et al 1995) and O4 V((f + )) (Mahy et al 2009). The nine-year spectroscopic campaign by Mahy et al to investigate multiplicity did not reveal any significant variation of the radial velocity related to the presence of a companion.…”

Section: Introductionmentioning

confidence: 71%

Variability in the CoRoT photometry of three hot O-type stars

Blomme

Mahy

Catala

et al. 2011

A&A

108

121

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Context. The detection of pulsational frequencies in stellar photometry is required as input for asteroseismological modelling. The second short run (SRa02) of the CoRoT mission has provided photometric data of unprecedented quality and time-coverage for a number of O-type stars. Aims. We analyse the CoRoT data corresponding to three hot O-type stars, describing the properties of their light curves and search for pulsational frequencies, which we then compare to theoretical model predictions. Methods. We determine the amplitude spectrum of the data, using the Lomb-Scargle and a multifrequency HMM-like technique. Frequencies are extracted by prewhitening, and their significance is evaluated under the assumption that the light curve is dominated by red noise. We search for harmonics, linear combinations, and regular spacings among these frequencies. We use simulations with the same time sampling as the data as a powerful tool to judge the significance of our results. From the theoretical point of view, we use the MAD non-adiabatic pulsation code to determine the expected frequencies of excited modes. Results. A substantial number of frequencies is listed, but none can be convincingly identified as being connected to pulsations. The amplitude spectrum is dominated by red noise. Theoretical modelling shows that all three O-type stars can have excited modes, but the relation between the theoretical frequencies and the observed spectrum is not obvious. Conclusions. The dominant red noise component in the hot O-type stars studied here clearly points to a different origin than the pulsations seen in cooler O stars. The physical cause of this red noise is unclear, but we speculate on the possibility of sub-surface convection, granulation, or stellar wind inhomogeneities being responsible.

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“…Let δ = b l /b u − 1, with non-LTE departure coefficients b l and b u for the lower and upper level of the considered transition. By expansion, we then find for the IR line source function (in units of the Planck-function) Mathys (1988Mathys ( , 1989, Conti & Alschuler (1971), Conti & Frost (1977), Bisiacchi et al (1982) are plotted with crosses for dwarfs, circles for giants and squares for supergiants. Typical errors in the observations are 5 to 10%.…”

Section: Near-infrared Line Trendsmentioning

confidence: 99%

Modeling the near-infrared lines of O-type stars

Lenorzer

Mokiem

Koter

et al. 2004

A&A

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Abstract. We use a grid of 30 line-blanketed unified stellar photosphere and wind models for O-type stars; computed with the code  in order to evaluate its potential in the near-infrared spectral domain. The grid includes dwarfs, giants and supergiants. We analyse the equivalent width behaviour of the 20 strongest lines of hydrogen and helium in spectral windows that can be observed using ground-based instrumentation and compare the results with observations. Our main findings are that: i) He /He  line ratios in the J, H and K bands correlate well with the optical ratio employed in spectral classification, and can therefore be used to determine the spectral type; ii) in supergiant stars the transition from the stellar photosphere to the wind follows a shallower density gradient than the standard approach followed in our models, which can be mimicked by adopting a lower gravity in our prescription of the density stratification; iii) the Brγ line poses a number of peculiar problems which might partly be related to wind clumping; and iv) the Brα line is an excellent mass-loss indicator. For the first and last item we provide quantitative calibrations.

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The on Stars: A Wider Spectroscopic Definition

Cited by 12 publications

References 3 publications

Early-type stars in the young open cluster NGC 2244 and in the Monoceros OB2 association

Early-type stars in the young open cluster NGC 2244 and in the Monoceros OB2 association

Variability in the CoRoT photometry of three hot O-type stars

Modeling the near-infrared lines of O-type stars

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