The heterogeneous class of<i>λ</i>Bootis stars

Gerbaldi, M.; Faraggiana, R.; Lai, Olivier

doi:10.1051/0004-6361:20031472

Cited by 34 publications

(97 citation statements)

References 51 publications

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“…The selective-accretion theory of Venn & Lambert (1990) is currently the most widely supported model. In the recent literature, Faraggiana & Bonifacio (1999); Gerbaldi et al (2003) and Faraggiana et al (2004) mention that binarity can play an underestimated role. The composite spectrum might mimic the spectrum of a truly underabundant single star.…”

Section: Discussionmentioning

confidence: 99%

Chemical analysis of 24 dusty (pre-)main-sequence stars

Acke¹,

Waelkens²

2004

A&A

106

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Abstract. We have analysed the chemical photospheric composition of 24 Herbig Ae/Be and Vega-type stars in search for the λ Bootis phenomenon. We present the results of the elemental abundances of the sample stars. Some of the stars were never before studied spectroscopically at optical wavelengths. We have determined the projected rotational velocities of our sample stars. Furthermore, we discuss stars that depict a (selective) depletion pattern in detail. HD 4881 and HD 139614 seem to display an overall deficiency. AB Aur and possibly HD 126367 have subsolar values for the iron abundance, but are almost solar in silicon. HD 100546 is the only clear λ Bootis star in our sample.

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Section: Discussionmentioning

confidence: 99%

Chemical analysis of 24 dusty (pre-)main-sequence stars

Acke¹,

Waelkens²

2004

A&A

106

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“…Large inconsistencies between the atmospheric parameters derived from the calibration of visual photometric colour indices and the UV flux distribution, discussed by Gerbaldi et al (2003) for the stars observed by TD1, are also signs that the star is not a classical λ Boo.…”

Section: Duplicity Detection From Spectroscopic and Photometric Datamentioning

confidence: 99%

“…Binary systems detected by imaging are discussed in detail by Gerbaldi et al (2003). The measure of separation and magnitude difference made it possible to recognize that 12 objects, corresponding to 9% of the total, classified as λ Boo, are in reality binaries that cannot be resolved at the spectrograph entrance.…”

Section: Binary Stars Producing Composite Spectramentioning

confidence: 99%

“…The target stars are extracted from the list of λ Boo stars compiled by Gerbaldi et al (2003); this list contains all the stars that have been classified as members of this class and for each of them the reference to the classifier(s) is given.…”

Section: Detected Composite Spectramentioning

confidence: 99%

“…

Abstract.We examine the large sample of λ Boo candidates collected in Table 1 of Gerbaldi et al (2003) to see how many of them show composite spectra. Of the 132 λ Boo candidates we identify 22 which definitely show composite spectra and 15 more for which there are good reasons to suspect a composite spectrum.

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confidence: 99%

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$\mathsf{\lambda}$ Bootis stars with composite spectra

Faraggiana

Bonifacio

Caffau

et al. 2004

A&A

Self Cite

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Abstract.We examine the large sample of λ Boo candidates collected in Table 1 of Gerbaldi et al. (2003) to see how many of them show composite spectra. Of the 132 λ Boo candidates we identify 22 which definitely show composite spectra and 15 more for which there are good reasons to suspect a composite spectrum. The percentage of λ Boo candidates with composite spectra is therefore >17% and possibly considerably higher. For such stars the λ Boo classification should be reconsidered taking into account the fact that their spectra are composite. We argue that some of the underabundances reported in the literature may simply be the result of the failure to consider the composite nature of the spectra. This leads to the legitimate suspicion that some, if not all, the λ Boo candidates are not chemically peculiar at all. A thorough analysis of even a single one of the λ Boo candidates with composite spectra, in which the composite nature of the spectrum is duly considered, which would demonstrate that the chemical peculiarities persist, would clear the doubt we presently have that the stars with composite spectra may not be λ Boo stars at all.

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Investigating the A-Type Stars Using Kepler Data

Murphy

2015

Springer Theses

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Rotation is a key physical process operating in the A stars. We present a method by which rotation periods might be measured with Fourier transforms of Kepler data, potentially removing the requirement of spectroscopic observations to acquire similar information. Angular rotational velocities reach their maximum at about A5, but slowly rotating A stars are also seen and these tend to be chemically peculiar. For Ap stars, rotational braking is understood, but too few progenitors are observed. A review of a rare class of stars, the 'sn' stars, leads us to suggest these may contribute to the 'missing' Ap progenitors. For Am stars, we find the tidal braking mechanisms proposed in the literature induce mixing that is incompatible with observed abundance anomalies. At the other end of the scale are the λ Boo stars, whose rotation velocities are above average. The two main theories for the origin of their metal underabundances are discussed and it is suggested that both of them imply the λ Boo stars contain a high fraction of pulsators -a suggestion that is backed up by observations in the literature. Many λ Boo stars also have circumstellar material, suggesting they are potential planet hosts. This, and the use of asteroseismology to study their interiors, are two excellent reasons to adopt them as prime targets for detailed investigation with Kepler.Pulsation is a common phenomenon in A stars. The δ Sct stars receive wide attention but the fraction of stars that pulsate at the 50 µmag level is shown to be only 56 per cent. The non-δ Sct stars in the δ Sct instability strip receive far less attention. Some of these stars, without appreciable granulation or stellar winds, ii are probably the least variable objects on the HR diagram. It is shown that they have the potential to be among the most peculiar Am stars. Their investigation has led to two important conclusions: (1) the presence of γ Dor pulsation in non-δ Sct stars in the δ Sct instability strip may inhibit the development of the expected Am peculiarities; and (2) chemically normal, non-δ Sct stars in the δ Sct instability strip do exist at the µmag level.Fourier transforms are invaluable tools in the field of stellar pulsation. TheKepler Space Telescope is providing data of exquisite precision, and thus more detail is seen in the Fourier transform than ever before. Truly understanding the properties of the data is fundamental to their successful utilisation. Through statistical analysis of noise levels in over 20 000 stars, granulation is concluded to be visible in Fourier transforms of stars cooler than 7500 K. Another property investigated is the Nyquist frequency. We found that periodically modulated sampling on board Kepler allows distinction between real pulsation frequencies and Nyquist aliases, even when those real frequencies exceed the Nyquist frequency of the data. This discovery opens up study of many hundreds of stars previously thought to have insurmountable Nyquist ambiguities in their data.iii ContentsAbstract ii In Don Kurtz, I have h...

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The heterogeneous class ofλBootis stars

Cited by 34 publications

References 51 publications

Chemical analysis of 24 dusty (pre-)main-sequence stars

Chemical analysis of 24 dusty (pre-)main-sequence stars

$\mathsf{\lambda}$ Bootis stars with composite spectra

Investigating the A-Type Stars Using Kepler Data

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