An investigation of galactic structure made from the study of the northern-hemisphere early type stars at intermediate galactic latitudes

Photometric and spectroscopic observations have been made of northern hemisphere early type stars at intermediate galactic latitudes. Stellar distances, the corresponding distances from the galactic plane and the interstellar reddening along the lines of sight have been derived. The available published data was used to support the observational results. The HI spiral features seem to have corresponding optical counterparts, and the agreement between the two patterns is remarkably good. The neutral hydrogen kinematic distances depart from the stellar distances. This can be explained in terms of the density wave theory, with a small modification which may be the result of a non-zero distance from the galactic plane. The Local Arm extends to about 500pc above the galactic plane and the Perseus Arm to 1 kpc. Thus it seems that the interpretation of intermediate latitude high and intermediate velocity features, as vertical extensions to the spiral arms in the galactic plane, may be correct. Stellar and interstellar calcium radial velocities suggest that these intermediate latitude spiral features adhere closely to differential galactic rotation, and that the small departures from this motion exhibit a significant correlation with the predictions of the density wave theory. Published proper motions are used together with the stellar radial velocities to derive the components of the stellar space motions with respect to their local standards of rest. In cases where the component normal to the galactic plane was significantly different from zero, the dynamical lifetime was calculated on the assumption that the star was formed in the galactic plane. These were found to be compatible with the evolutionary lifetimes for only half of the stars considered, suggesting that about 50% of intermediate latitude OB stars were formed in or near the galactic plane and subsequently ejected from it. The remainder seem to have been formed at considerable distances from the galactic plane, and a scheme for explaining this is proposed. This scheme also explains the apparent asymmetry between the northern and southern galactic hemispheres. A few interesting high velocity stars and OB star associations are also considered

Orbital Characteristics of the Subdwarf-B and F V Star Binary EC~20117-4014(=V4640 Sgr)

Among the competing evolution theories for subdwarf-B (sdB) stars is the binary evolution scenario. EC~20117-4014 (=V4640~Sgr) is a spectroscopic binary system consisting of a pulsating sdB star and a late F main-sequence companion (O'Donoghue et al. 1997), however the period and the orbit semi-major axes have not been precisely determined. This paper presents orbital characteristics of the EC 20117-4014 binary system using 20 years of photometric data. Periodic Observed minus Calculated (O-C) variations were detected in the two highest amplitude pulsations identified in the EC 20117-4014 power spectrum, indicating the binary system's precise orbital period (P = 792.3 days) and the light-travel time amplitude (A = 468.9 s). This binary shows no significant orbital eccentricity and the upper limit of the eccentricity is 0.025 (using 3 $\sigma$ as an upper limit). This upper limit of the eccentricity is the lowest among all wide sdB binaries with known orbital parameters. This analysis indicated that the sdB is likely to have lost its hydrogen envelope through stable Roche lobe overflow, thus supporting hypotheses for the origin of sdB stars. In addition to those results, the underlying pulsation period change obtained from the photometric data was $\dot{P}$ = 5.4 ($\pm$0.7) $\times$ $10^{-14}$ d d$^{-1}$, which shows that the sdB is just before the end of the core helium-burning phase

Detection of Photometric Variations in the sdBV Star JL 166

We report the discovery of oscillations in the hot subdwarf B star JL 166 from time-series photometry using the Goodman Spectrograph on the 4.1-m Southern Astrophysical Research Telescope. Previous spectroscopic and photometric observations place the star near the hot end of the empirical sdB instability strip and imply the presence of a cool companion. Amplitude spectra of the stellar light curve reveal at least 10 independent pulsation modes with periods ranging from 97 to 178 s and amplitudes from 0.9 to 4 mma. We adopt atmospheric parameters of T_eff = 34350 K and log g = 5.75 from a model atmosphere analysis of our time-averaged, medium-resolution spectrum.Comment: 18 pages, 6 figures, accepted for publication in the Astronomical Journa

Investigating the properties of granulation in the red giants observed by Kepler

More than 1000 red giants have been observed by NASA/Kepler mission during a nearly continuous period of ~ 13 months. The resulting high-frequency resolution (< 0.03 muHz) allows us to study the granulation parameters of these stars. The granulation pattern results from the convection motions leading to upward flows of hot plasma and downward flows of cooler plasma. We fitted Harvey-like functions to the power spectra, to retrieve the timescale and amplitude of granulation. We show that there is an anti-correlation between both of these parameters and the position of maximum power of acoustic modes, while we also find a correlation with the radius, which agrees with the theory. We finally compare our results with 3D models of the convection.Comment: 4 pages, 1 figure. To appear in the ASP proceedings of "The 61st Fujihara seminar: Progress in solar/stellar physics with helio- and asteroseismology", 13th-17th March 2011, Hakone, Japa

A new ab initio ground-state dipole moment surface for the water molecule

A valence-only (V) dipole moment surface (DMS) has been computed for water at the internally contracted multireference configuration interaction level using the extended atom-centered correlation-consistent Gaussian basis set aug-cc-pV6Z. Small corrections to these dipole values, resulting from core correlation (C) and relativistic (R) effects, have also been computed and added to the V surface. The resulting DMS surface is hence called CVR. Interestingly, the C and R corrections cancel out each other almost completely over the whole grid of points investigated. The ground-state CVR dipole of H(2) (16)O is 1.8676 D. This value compares well with the best ab initio one determined in this study, 1.8539+/-0.0013 D, which in turn agrees well with the measured ground-state dipole moment of water, 1.8546(6) D. Line intensities computed with the help of the CVR DMS shows that the present DMS is highly similar to though slightly more accurate than the best previous DMS of water determined by Schwenke and Partridge [J. Chem. Phys. 113, 16 (2000)]. The influence of the precision of the rovibrational wave functions computed using different potential energy surfaces (PESs) has been investigated and proved to be small, due mostly to the small discrepancies between the best ab initio and empirical PESs of water. Several different measures to test the DMS of water are advanced. The seemingly most sensitive measure is the comparison between the ab initio line intensities and those measured by ultralong pathlength methods which are sensitive to very weak transitions

The rapidly pulsating sdO star, SDSS J160043.6+074802.9

A spectroscopic analysis of SDSS J160043.6+074802.9, a binary system containing a pulsating subdwarf-O (sdO) star with a late-type companion, yields Teff = 70 000 +/- 5000 K and log g = 5.25 +/- 0.30, together with a most likely type of K3V for the secondary star. We compare our results with atmospheric parameters derived by Fontaine et al. (2008) and in the context of existing evolution models for sdO stars. New and more extensive photometry is also presented which recovers most, but not all, frequencies found in an earlier paper. It therefore seems probable that some pulsation modes have variable amplitudes. A non-adiabatic pulsation analysis of uniform metallicity sdO models show those having log g > 5.3 to be more likely to be unstable and capable of driving pulsation in the observed frequency range.Comment: 14 pages, 12 figures, accepted for publication in MNRAS, 2009 September