Did globular clusters reionize the Universe?     

Massimo Ricotti 《Monthly notices of the Royal Astronomical Society》2002,336(2):L33-L37

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Spectroscopic binaries near the north Galactic pole paper 24: HD 106104, 109281, 109463 and 110743     

R. F. Griffin 《Journal of Astrophysics and Astronomy》2001,22(2-3):187-211

The four stars treated in this paper have been under observation with photoelectric radial-velocity spectrometers for many years. They have proved to be binaries with periods of 30, 1828, 1514 and 822 days respectively; the orbits are of modest eccentricity apart from that of HD 110743 which is indistinguishable from a circle. The mass functions are small, and no companion has been observed for any of the stars. HD 110743, a K dwarf, is much the nearest of the four, and its orbit is of short enough period for the photocentric motion to have been recognized byHipparcos. An eleventh-magnitude star rather more than 1≈ away from HD 106104 is shown to be a genuine physical companion, with practically identical radial velocity, proper motion and distance modulus, although the projected separation is about 13,000 AU.  相似文献   

The spectral variations of the O-type runaway supergiant HD 188209     

G. Israelian  A. Herrero  F. Musaev  A. Kaufer  A. Galeev  G. Galazutdinov  E. Santolaya-Rey 《Monthly notices of the Royal Astronomical Society》2000,316(2):407-417

We report spectral time series of the late O-type runaway supergiant HD 188209. Radial velocity variations of photospheric absorption lines with a possible quasi-period of ∼6.4 d have been detected in high-resolution echelle spectra. Night-to-night variations in the position and strength of the central emission reversal of the H α profile occurring over ill-defined time-scales have been observed. The fundamental parameters of the star are derived using state-of-the-art plane-parallel and unified non-LTE model atmospheres, the latter including the mass-loss rate. The derived helium abundance is moderately enhanced with respect to solar, and the stellar masses are lower than those predicted by the evolutionary models. The binary nature of this star is not suggested either from Hipparcos photometry or from radial velocity curves.  相似文献   

Comparisons of images derived from independent Zeeman Doppler imaging codes     

G. A. J. Hussain  J.-F. Donati  A. Collier Cameron  J. R. Barnes 《Monthly notices of the Royal Astronomical Society》2000,318(4):961-973

We compare surface brightness and magnetic field surface maps for the K0 dwarf AB Doradus, obtained using two independently developed Zeeman Doppler imaging codes. We find that even the fine structure in the two sets of images shows excellent agreement. Magnetic field maps appear to be less sensitive to line-modelling effects than brightness maps. We argue that these results point to the consistency and reliability of Doppler imaging techniques even when using poorly sampled data sets, provided that the spectra used are of sufficiently high signal-to-noise ratio.  相似文献   

Magnetic cycle of LQ Hydrae: observational indications and dynamo model     

L. L. Kitchatinov  M. Jardine  J.-F. Donati 《Monthly notices of the Royal Astronomical Society》2000,318(4):1171-1176

We present a model for the differential rotation and dynamo activity of the young rapidly rotating K0 dwarf LQ Hya ( P _rot=1.6 d). As might be expected from observations of the similar rapid rotator AB Dor, the predicted differential rotation is small (≃0.8 per cent) but extremely efficient in generating magnetic fields. The dynamo, which is of a distributed type, produces a globally axisymmetric field with radial and azimuthal components that are of the same magnitude and display a phase-lag in their evolution of about π/2. This is consistent with the long-term Zeeman–Doppler imaging study by Donati. The latitudinal distribution of flux is, however, a little different from that observed and the cycle period of 3.2 yr is somewhat shorter than suggested by the observations.  相似文献   

Contribution to the search for binaries among Am stars – IV. HD 100054B and 187258     

N. Ginestet  J.-L. Prieur  J.-M. Carquillat  R. F. Griffin 《Monthly notices of the Royal Astronomical Society》2003,342(1):61-68

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1988–1991 photometry of the chromospherically active double-lined binary system HD 163621 = V835 Herculis     

Douglas S. Hall  Gregory W. Henry 《Journal of Astrophysics and Astronomy》1994,15(3):321-328

Photometry inV andB with a 16inch automatic telescope from 1988 to 1991 confirms the synchronous rotation suspected earlier and reveals variability up to 0^M.10 in theB bandpass at one epoch. Five spots formed with lifetimes ranging from 0.15 to 0.77 years. As with other rapid rotators, the differential rotation coefficient (k = 0.03) is significantly smaller than that of the Sun (k = 0.19).  相似文献   

A peculiar metal-rich star, HD 135485     

C. Trundle  P.L. Dufton  W.R.J. Rolleston  R.S.I. Ryans  D.J. Lennon  N. Lehner 《Monthly notices of the Royal Astronomical Society》2001,328(1):291-300

Local thermodynamic equilibrium (LTE) absolute and differential abundances are presented for a peculiar metal-rich B-type star, HD 135485. These suggest that HD 135485 has a general enrichment of ∼0.5 dex in all the metals observed (C, N, O, Ne, Mg, Al, Si, P, S, Cl, Ar, Sc, Ti, Cr, Mn, Fe and Sr), except for nickel. The helium enhancement and hence hydrogen deficiency can account for ≤ 0.2 dex of this enhancement of metals, with the additional enhancement probably being representative of the progenitor gas. However, some of the metals appear to have greater enhancements, which may have occurred during the star's evolution. The significantly larger nitrogen abundance coupled with a modest helium enhancement observed in HD 135485 indicates that carbon–nitrogen (CN) processed material has possibly contaminated the stellar surface. Neon and carbon enhancements may indicate that helium core flashes have also occurred in HD 135485. Some of the iron-group elements (viz. Mn and Ni) appear to have similar abundance patterns to that of silicon Ap stars, but it is uncertain how these abundance patterns formed if they were not present in the progenitor gas. From a kinematical investigation it is unclear whether this star formed in a metal-rich region as implied by its chemical composition. From its position in the Hertzsprung–Russell diagram, HD 135485 would appear to be an evolved star lying close to or on the horizontal branch.  相似文献   

Pulsation in the pre-main-sequence Herbig Ae star HD 142666     

D.W. Kurtz  M. Müller 《Monthly notices of the Royal Astronomical Society》2001,325(4):1341-1345

Asteroseismology of pre-main-sequence δ Scuti stars has the potential not only to provide unprecedented constraints on models of these stars, but also to allow for the possibility of detecting evolutionary period changes, thus providing a direct measure of the pre-main-sequence evolutionary time-scale. In the last two years, the published number of such stars known has doubled from four to eight. Searches are now being conducted amongst the Herbig Ae stars, which are considered to be excellent candidates. We announce the discovery of δ Scuti pulsation in one Herbig Ae star, HD 142666, which lies within Marconi & Palla's theoretically predicted instability strip for pre-main-sequence stars, making this the ninth known pre-main-sequence δ Scuti star. We also demonstrate a lack of δ Scuti pulsation in another such star, HD 142527.  相似文献   

Optical spectroscopy of X-Mega targets – II. The massive double-lined O-type binary HD 93205     

N.I. Morrell †  R.H. Barbá †  V.S. Niemela ‡  M.A. Corti §  J.F. Albacete Colombo  G. Rauw ¶  M. Corcoran  T. Morel  J.-F. Bertrand  A.F.J. Moffat  N. St-Louis 《Monthly notices of the Royal Astronomical Society》2001,326(1):85-94

A new high-quality set of orbital parameters for the O-type spectroscopic binary HD 93205 has been obtained combining échelle and coudé CCD observations. The radial velocity orbits derived from the He  ii λ 4686 Å (primary component) and He  i λ 4471 Å (secondary component) absorption lines yield semi-amplitudes of 133±2 and 314±2 km s⁻¹ for each binary component, resulting in minimum masses of 31 and 13 M_⊙ ( q =0.42) . We also confirm for the binary components the spectral classification of O3 V+ O8 V previously assigned. Assuming for the O8 V component a 'normal' mass of 22–25 M_⊙ we would derive for the primary O3 V a mass of 'only' 52–60 M_⊙ and an inclination of about 55° for the orbital plane. We have also determined for the first time a period of apsidal motion for this system, namely 185±16 yr using all available radial velocity data sets of HD 93205 (from 1975 to 1999). Phase-locked variations of the X-ray emission of HD 93205 consisting of a rise of the observed X-ray flux near periastron passage are also discussed.  相似文献