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

Faraggiana, R.; Bonifacio, P.; Caffau, E.; Gerbaldi, M.; Nonino, M.

doi:10.1051/0004-6361:20040216

Cited by 18 publications

(42 citation statements)

References 45 publications

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“…have been expressed most strongly by Faraggiana & Bonifacio (1999), Gerbaldi et al (2003, Faraggiana et al (2004, and in earlier papers by that group and quoted by them. The main focus of their suggestions was the possibility that λ Boo stars are unrecognised binaries consisting of two fairly similar stars, so the apparently single spectrum which is observed is in reality composite, the continuum flux of one component weakening the absorption lines of its companion.…”

Section: Introductionmentioning

confidence: 82%

The composite-spectrum binary hypothesis does not explain theλBootis stars

Griffin

Gray

Corbally³

2012

A&A

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The existence of the λ Boo type as a class of chemically-peculiar stars in its own right has taxed numerous researchers, and has challenged spectroscopists to produce a model which is plausible, comprehensive and predictive. Stars which are recognized as members of the λ Boo class have late-B to early-F spectral types, and exhibit (often substantially) low abundances of Fe-peak elements although elements such as C, N, O and S may have more nearly solar abundances. Since less than 2% of objects within the relevant spectral-type domain appear to be λ Boo stars their existence has demanded rather special conditions, and has triggered opinion that this group may not in fact exist but that each case can be explained as an unrecognized binary. In this paper we examine those claims by monitoring 10 stars, listed in the literature as possible λ Boo stars but said to be "likely candidates" for composite-spectrum binaries, by employing high-dispersion spectroscopy in an intermittent observing programme designed to reveal the sort of line-profile changes that should be detectable if each object were really a pair of similar stars in an SB2 system. We also monitor two other stars: HR 7903, said to be a binary (but is more like an Ap star), and λ Boo itself. The sample includes 1 possible, 1 marginal and 4 definite λ Boo classifications. In addition, we derive the physical properties of the 12 stars by photometric and spectroscopic synthesis, and measure their radial velocities. Three of the sample show small line-profile variations, but not of the sort that can be attributed to the presence of a companion star; they are the suspected Ap star HR 7903, HR 6878 (which exhibits spectrum peculiarities very similar to those of HR 7903 but has not previously been classified as Bp or Ap), and λ Aql, whose rapid spectrum variations resemble those observed in spotted or CP stars. None of the stars shows any evidence to suggest that it could be a composite-spectrum binary.

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Section: Introductionmentioning

confidence: 82%

The composite-spectrum binary hypothesis does not explain theλBootis stars

Griffin

Gray

Corbally³

2012

A&A

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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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“…* HD 290492 AB is a close binary with ρ = 0.739 ± 0.005 arcsec, θ = 63.9 ± 1.9 deg (Δb = 0.6 ± 0.2 magRossiter 1955; Marchetti et al 2001). It is a non-variable, mild λ Boo star candidate (Paunzen & Gray 1997;Paunzen et al 2002-but see Gerbaldi et al 2003and Faraggiana et al 2004). Paunzen (2001) derived a photometric distance of d = 279 ± 20 pc, but he erroneously assumed no contamination by the secondary in the spectrum of the primary.…”

Section: Notes To Table A4mentioning

confidence: 98%

Young stars and brown dwarfs surrounding Alnilam (ϵ Orionis) and Mintaka (δ Orionis)

Caballero

Solano

2008

A&A

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Aims. We look for new regions to search for substellar objects. Methods. Two circular areas, 45 arcmin-radius each, centred on the young massive star systems Alnilam and Mintaka in the Orion Belt, were explored. The regions are very young (less than 10 Ma), have low extinction, and are neighbours to σ Orionis (∼3 Ma), a young open cluster very rich in brown dwarfs and planetary-mass objects. We used Virtual Observatory tools, the astro-photometric Tycho-2, DENIS and 2MASS catalogues, 10 control fields at similar galactic latitudes, as well as X-ray, mid-infrared, and spectroscopic data from the literature. Results. We compiled exhaustive lists of known young stars and new candidate members in the Ori OB1b association and of foreand background sources. A total of 136 stars display features of extreme youth, like early spectral types, lithium in absorption, or mid-infrared flux excess. Other two young brown dwarf and 289 star candidates have been identified from an optical/near-infrared colour-magnitude diagram. We list another 74 known objects that might belong to the association. This catalogue can serve as input for characterising the stellar and high-mass substellar populations in the Orion Belt. Finally, we investigated the surface densities and radial distributions of young objects surrounding Alnilam and Mintaka and compared them with those in the σ Orionis cluster. We report on a new open cluster centred on Mintaka. Conclusions. Both regions can be analogues to the σ Orionis cluster, but more massive, more extended, slightly older, and less radially concentrated.

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

Cited by 18 publications

References 45 publications

The composite-spectrum binary hypothesis does not explain theλBootis stars

The composite-spectrum binary hypothesis does not explain theλBootis stars

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

Young stars and brown dwarfs surrounding Alnilam (ϵ Orionis) and Mintaka (δ Orionis)

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