2012A&A...547A...8G

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 Query : 2012A&A...547A...8G

2012A&A...547A...8G - Astronomy and Astrophysics, volume 547A, 8-8 (2012/11-1)

The composite-spectrum binary hypothesis does not explain the λ Bootis stars.

GRIFFIN R.E., GRAY R.O. and CORBALLY C.J.

Abstract (from CDS):

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.

Journal keyword(s): stars: early-type - binaries: spectroscopic - stars: chemically peculiar - stars: individual: λ Bootis

Full paper

 Number of rows : 13
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
#notes
1 * 21 LMi dS* 10 07 25.7629578 +35 14 40.896470 4.74 4.67 4.49 4.31 4.24 A7V(n) 220 0
2 V* DT CVn dS* 12 50 10.7400521424 +37 31 00.979591260   6.025 5.872     A5Vp_lB 93 0
3 * lam Boo dS* 14 16 23.0187965 +46 05 17.900526 4.31 4.26 4.18 4.16 4.13 A0Va_lB 339 0
4 HD 125489 ** 14 19 40.9504184928 +00 23 03.603726852   6.377 6.179     A7Vn 50 0
5 * tau02 Ser * 15 32 09.6750062424 +16 03 22.209057684   6.184 6.216     B9V 58 0
6 HD 169009 * 18 23 02.1094394400 -10 13 08.238885060   6.443 6.313     B9III 51 0
7 * lam Aql PM* 19 06 14.9386542192 -04 52 57.225885348 3.07 3.34 3.43 3.46 3.55 B8.5V 216 0
8 HD 179791 V* 19 13 44.0319885648 +05 30 56.198549232 6.69 6.58 6.49     A3V 51 0
9 * c Aql dS* 19 29 00.9869402808 +01 57 01.616825124   5.865 5.783     A0IVp 174 0
10 HD 196821 V* 20 39 10.6488328200 +21 49 02.792407836   6.027 6.075     A0III 55 0
11 HD 218407 EB* 23 07 17.9993119296 +46 04 05.327603220 5.93 6.585 6.654     B2V 87 0
12 * tau Peg dS* 23 20 38.2462291728 +23 44 25.278232056   4.745 4.580     A5Vp_lB 179 0
13 * 15 And dS* 23 34 37.5368337288 +40 14 11.182658856   5.652 5.563 6.91   A1Va 129 0

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2022.09.24-19:01:31