Ve Sin Research Articles

Oxygen and Nitrogen Abundances in Hyades F Type Dwarfs

The abundances of oxygen and nitrogen were investigated for eleven Hyades F type main-sequence stars, based on the line-profile of O I (+Fe I) 8446 and the equivalent-widths of N I 8629/8683, in order to examine whether any conspicuous abundance deficiency exists for O and N at Teff ∼ 6700 K similar to that observed for Li, since its possibility was suggested by the diffusion interpretation of this “Li-chasm”. It turned out, however, that the abundances appear to be nearly independent of Teff (and ve sin i) for both O and N, without showing any apparent dip larger than ∼ 0.2 dex (for O) or ∼ 0.3 dex (for N), being consistent with the results of García-López et al.'s (1993, AAA 58.114.068) study for oxygen. This may indicate that the diffusion process alone is probably not responsible for the origin of the Li-gap. Regarding the averaged O and N abundances in these Hyades F stars, a moderate N-excess by ∼ 0.3 dex relative to the Sun was suggested (though not definite), with oxygen being nearly normal.

Oxygen λ7771–5 Triplet in Hyades A-Type Stars: A Quest for the Key to the Am Phenomenon

An extensive profile-fitting analysis of the OI 7771–5 triplet (along with the nearby FeI line) was carried out for thirty-one A-type stars, eighteen of them belonging to the Hyades group, in order to clarify the key factor which plays the decisive role in the appearance of abundance anomalies of metallic-line stars (Am), by examining whether any meaningful relation exists between the microturbulence (ξ), the oxygen abundance (log ∊O), the iron abundance (log ∊Fe), the projected rotational velocity (ve sin i), and the stellar atmospheric parameters. It was clearly found based on the Hyades results that the abundance of O/Fe, both being good indicators of the Am phenomenon, because of the negative/positive correlation with the metallicity estimated from colors, progressively increases/decreases (i.e., toward the direction of disappearance of anomaly) with an increase in ve sin i as well as with a decrease in log g. It was thus concluded that the most important driver of the Am phenomenon, producing a significant deficiency/excess of O/Fe, is the rotational velocity which appears to be responsible for not only the triggering, but also the extent of the peculiarity. Meanwhile, the observed log g-dependence of the abundance e anomalies is considered to be nothing but superficial, which may be interpreted as being due to the correlation between log g and ve sin i, i.e., rotation-induced lowering of the effective gravity.

HD 195636: A Metal-Poor Rotator Near the HB/AGB Transition

view Abstract Citations (8) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS HD 195636: A Metal-Poor Rotator Near the HB/AGB Transition Preston, George W. Abstract The color temperature and Balmer jump inferred from UBV and Strömgren photometric indices, the low gravity and low metallicity derived from spectrum analysis, and weakness of all CH molecular lines combine to suggest that HD 195636 is in an evolutionary state near the transition between the horizontal branch and asymptotic giant branch. The projected equatorial rotational velocity of HD 195636 is Ve sin i=25 km/s, a value at least 2.5 times greater than that expected if known blue horizontal branch axial rotators in globular clusters conserve envelope angular momentum during horizontal branch evolution. Constancy of the radial velocity on time scales of 3, 10, and 90 days indicates that the axial rotation is not due to co-rotation in a short-period binary. Therefore, it seems most plausible that transfer of angular momentum from core to envelope occurred during HB evolution. The Balmer line profiles are peculiar. Hα is abnormally shallow, as if the core were filled by emission, and higher members of the Balmer series are significantly broader than those of HD 200564, a slightly cooler giant star of similar metallicity. The space velocity of HD 195636 calculated for an assumed RHB/AGB luminosity, Mv=-0.5, is 470 km/s retrograde, a high but not extraordinary value. Publication: The Astronomical Journal Pub Date: May 1997 DOI: 10.1086/118397 Bibcode: 1997AJ....113.1860P Keywords: STARS: HORIZONTAL-BRANCH; STARS: AGB; STARS: INDIVIDUAL: HD 195636 full text sources ADS | data products SIMBAD (3)

Line-Profile Analysis of KI 7699 in the Sun and in Procyon

The profiles of the resonance line of potassium (KI 7698.98) in the flux spectrum of the Sun and Procyon were studied in detail using the multi-parameter fitting method, in order to extract information regarding the fundamental atomic parameters responsible for the formation of this line as well as to diagnose the nature of the velocity fields in their atmospheres. It was concluded from an analysis of the solar KI 7699 profile that neutral-hydrogen collisions are practically negligible compared to electron collisions in the rate equation of statistical equilibrium, and that an empirical correction to the Unsöld's standard (van der Waals effect) damping constant is Δ log C6 ≃ + 1.0 with the most consistent microturbulent velocity of ξ ≃ 0.8 km s−1 . Based upon these results, the atmospheric-velocity parameters of Procyon were determined to be ξ ≃ 1.4 km s−1, ζRT≃ 6.7 km s−1 (the radial-tangential macroturbulence), and ve sin i ≃ 3.3 km s−1 (the projected rotational velocity). The potassium abundances of the Sun and Procyon derived from this resonance line, which are significantly affected by the non-LTE effect amounting to ∼ 0.4 dex (Sun) and ∼ 0.7 dex (Procyon), turned out to be nearly the same and log εK ≃ 5.1. It also appears that the microturbulence tends to decrease with an increase in the atmospheric height of the Sun as well as of Procyon.

The He-strong star HD 96446: oblique rotator or pulsating magnetic variable?

HD 96446 is a B2p He-strong star, in which a large-scale organized magnetic field is present. From spectra recorded in both circular polarizations, various moments of this magnetic field have been repeatedly determined, among which the mean longitudinal magnetic field and the crossover. The mean longitudinal magnetic field 〈Hz〉 is the line-intensity weighted average over the visible stellar hemisphere of the line-of-sight component of the magnetic vector. The crossover, ve sin i 〈x Hz〉,is the product of the projected equatorial velocity, ve sini, and of the mean asymmetry of the longitudinal magnetic field, 〈x Hz〉. The latter is the line-intensity weighted first-order moment about the plane defined by the line of sight and the stellar rotation axis of the component of the magnetic field along the line of sight.

Observations of Stellar Rotation and Line Strengths for Ob Stars

For 121 southern stars of spectral types between 05 and A3, including 35 supergiants, equivalent widths and values of ve sini have been measured for absorption lines on direct-intensity tracings of coudé spectrograms from Mount Stromlo, with original dispersion 150 microns per angstrom. For stars of a particular temperature and luminosity class, the strength of the hydrogen lines is weaker and the triplet helium lines stronger in fast rotators than in sharp-lined objects which are rotating more slowly. Full details are in print (Monthly Notices Roy. Astron. Soc. 144 (1969), 1): subsequent papers in press present detailed profiles of the Balmer lines for 23 slowly rotating stars and details of emission features shown by several fast rotators.The investigation is being continued with spectrograms of northern B stars secured at the Dominion Astrophysical Observatory, supported in part by grant GP-13544 from the National Science Foundation.

Altitude of Stabilization for Slowly Tumbling Re-Entry Vehicles

Abstract : An analysis is made to identify the parameters which determine the altitude of stabilization defined as the altitude at which the angle of attack rate first vanishes for slowly tumbling re-entry vehicles. The analysis is limited to small tumble rates and angles of attack which allow the assumptions of Cm = Cm and Cm = constant respectively. An expression is derived which implicitly relates the altitude of stabilization to (1) the initial descent velocity, VE sin , (2) the atmospheric scale height, (3) a vehicle stability parameter, Cm Al/I, and (4) the quantity ( o/ o). The important result is the fact that the initial angle of attack and initial tumble rate, i.e., o and o respectively, appear only as a ratio, o/ o, the remaining parametric quantities being properties of the vehicle, the atmosphere, and the trajectory.