The spectroscopic binaries 21 Her andγGem

Abstract

Abstract. In the framework of a search campaign for short-term oscillations of early-type stars we analysed recently obtained spectroscopic and photometric observations of the early A-type spectroscopic binaries 21 Her and γ Gem. From the radial velocities of 21 Her we derived an improved orbital period and a distinctly smaller eccentricity in comparison with the values known up to now. Moreover, fairly convincing evidence exists for an increase of the orbital period with time. In addition to the orbital motion we find further periods in the orbital residuals. The longest period of 57.d 7 is most likely due to a third body which has the mass of a brown dwarf, whereas the period of 1.d 48 could be related to the half rotational period of the star. For the spectral types we deduced A1 III for the primary and M for the secondary. Two further periods of 0.d 21 and 0. d 22 give hint to the existence of short-term pulsations in 21 Her. Their period difference is of the order of the expected rotational period so that one possible explanation could be rotational splitting of nonradial pulsation modes. Because of the very strong aliasing of the data this finding has to be confirmed by observations having a more suitable time sampling, however. The analysis of photometric series and the Hipparcos photometry give no certain evidence for periodic light variations. For γ Gem, besides the orbital RV variation, no variations with amplitudes larger than about 100 m s −1 could be detected. The orbital elements of γ Gem are only slightly changed compared to the previously known orbital solution by including our new radial velocities, but their accuracy is improved. For some chemical elements we determined their abundances, NLTE values of C, O, and Na as well as LTE values of Mg, Sc, Fe, Cr, and Ti. We find the abundances to be rather close to the solar values, only carbon shows a little underabundance.

Magnetic geometry and surface differential rotation of the bright Am star Alhena A

“…Each of the 40 echelle orders of each of the 43 spectra were normalized using the continuum task of IRAF 1 . Lehmann et al (2002). The red circles correspond to the measurements by Adelman et al (2015) shifted by −1.4 km s −1 .…”

“…In Fig. 1 we compare the orbital solution derived by Lehmann et al (2002) with the recent radial velocity measurements. The data from Adelman et al (2015) had to be shifted by −1.4 km s −1 to bring it into agreement with the published spectroscopic orbit.…”

“…Scholz et al (1997) analyzed several hundred radial velocity measurements covering a time span of over 100 yr, establishing an orbital period of 4614.51 d (12.6 yr). Their orbital solution has been updated by Lehmann et al (2002), who derived K1 = 11.9 km s −1 and e = 0.893. Sixteen new radial velocity measurements were reported by Adelman et al (2015) and 25 data points are provided by our study (Table 1).…”

Ap stars with resolved magnetically split lines: Magnetic field determinations from StokesIandVspectra

“…The orbital period of HD 134759, 23.42 y (Heintz 1982), is much longer than 1000 d. It appears doubtful that HD 147869 and HD 196133 are actually Ap stars. Although HD 147869 is listed as an A1p Sr star by Renson & Manfroid (2009), it had been classified as A1 III by Abt & Morrell (1995); Lehmann et al (2002) also regard it as an evolved star rather than a (chemically peculiar) main-sequence star. Renson & Manfroid (2009) note that HD 196133 is perhaps an Am star rather than an Ap star, while Bertaud & Floquet (1967) explicitly state that it is an A2 star without any noticeable peculiarity.…”

Lithium, Sodium, and Potassium Abundances in Sharp-Lined A-Type Stars

“…In this connection, Burkhart and Coupry (1991a) stated (based on their study of late A-type stars) that "occurrence of Li-deficient stars is not exceptional without any clearcut division between normal and Am stars." Yet, as far as early A-type stars are concerned, the fact that Li tends to remain almost unaffected in nearnormal stars such as γ Gem (believed to have almost the solar abundances; e.g., Adelman & Philip 1996, Lehmann et al 2002 and π Dra (which were previously considered as normal even though later found to have only weak Am anomaly; cf. Sadakane & Okyudo 1990) might suggest the existence of some connection between the conspicuous Li deficit of α CMa or o Peg and their Am phenomenon.…”