Dynamics of Line‐driven Winds from Disks in Cataclysmic Variables. II. Mass‐Loss Rates and Velocity Laws
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We analyze the dynamics of two-dimensional stationary, line-driven winds from accretion disks in cataclysmic variable (CV) stars by generalizing the formalism of Castor, Abbott, and Klein (CAK) for O stars. In Paper I, we solved the wind Euler equation, derived its two eigenvalues, and addressed the solution topology and wind geometry. Here, we focus on mass-loss rates and velocity laws of the wind. We find that disk winds, even in luminous nova-like variables, have low optical depth, even in the strongest driving lines. This suggests that thick-to-thin transitions in these lines occur in the wind. For disks with a realistic radial temperature law, the mass loss is dominated by gas emanating from the inner decade in radius. The total mass-loss rate associated with the wind from a disk of luminosity 10 L☉ is ~10-12 M☉ yr-1, or 10-4 of the mass accretion rate. This is 1 order of magnitude below the lower limit obtained from fitting P Cygni line profiles using kinematical wind models when the Lyman continuum is suppressed. The difficulties associated with such small mass-loss rates for line-driven winds from disks in CVs are principal and confirm our previous work on this subject. We conjecture that this issue may be resolved by detailed non-LTE calculations of the CAK line force within the context of CV disk winds and/or by better accounting for the disk energy distribution and wind ionization structure. We find that the wind velocity profile is well approximated by the empirical law used in kinematical modeling. The acceleration length scale is given by the footpoint radius of the wind streamline in the disk. This suggests an upper limit of ~10rwd to the acceleration scale, which is smaller by factor of a few as compared with values derived from line fitting.Keywords:
Polar wind
We present an analysis of 402 F, G, and K solar neighborhood stars, with accurate estimates of [Fe/H] in the range -1.0 to +0.5 dex, aimed at the detection of α-enhanced stars and at the investigation of their kinematical properties. The analysis is based on the comparison of 571 sets of spectral indices in the Lick/IDS system, coming from four different observational data sets, with synthetic indices computed with solar-scaled abundances and with α-element enhancement. We use selected combinations of indices to single out α-enhanced stars without requiring previous knowledge of their main atmospheric parameters. By applying this approach to the total data set, we obtain a list of 60 bona fide α-enhanced stars and of 146 stars with solar-scaled abundances. The properties of the detected α-enhanced and solar-scaled abundance stars with respect to their [Fe/H] values and kinematics are presented. A clear kinematic distinction between solar-scaled and α-enhanced stars was found, although a one-to-one correspondence to "thin disk" and "thick disk" components cannot be supported with the present data.
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Abstract The Pristine survey uses narrow-band photometry on the region of the Ca II H & K absorption lines to find extremely metal-poor stars. With a spectroscopic follow-up sample of 205 stars in the magnitude range 14 < V < 18, we compute the success rates for finding extremely metal-poor stars and modify the selection criteria used to select stars for follow-up. This reduces the sample to 149 stars, and from these we report success rates of 22% for recovering stars with [Fe/H] < −3.0 and 70% for [Fe/H] < −2.5. When compared to previous works that search for extremely metal-poor stars, the success rates of Pristine show an improvement in efficiency by a factor of ~4 − 5.
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A large sample of Be stars has been studied spectrophotometrically in the visible region. The continuum energy distribution data for 23 Be stars included in the list of Harmanecet al. (1983) are presented and discussed in the wavelength range λλ3200 A–8000 A. For 15 Be stars the observations reported in the present work are new. By comparing the observed continua with models, the effective temperatures of these stars have been estimated. It is found that, in general, Be stars have lower effective temperature than the corresponding normal B stars. The present study shows that the early-Be stars (B0–B5) possess near-ultraviolet and near-infrared excess emissions more frequently than the late-Be stars (B5–B9). The seven new Be stars are detected to show pole-on characteristics.
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The sn stars present sharp Balmer lines, sharp metallic lines and broad coreless He I lines. Initially Abt & Levato proposed a shell-like nature to explain the sn stars, although this scenario was subsequently questioned. We aim to derive abundances for a sample of 9 stars, including sn and non-sn stars, to determine the possible relation between sn and CP stars. We analysed the photospheric chemical composition of sn stars and show that approximately 40% of them display chemical peculiarities (such as He-weak and HgMn stars) within a range of temperature of 10300 - 14500 K. We have studied the possible contribution of different processes to the broad He I lines present in the sn stars. Although NLTE effects could not be completely ruled out, it seems that NLTE is not directly related to the broad He I profiles observed in the sn stars. The broad-line He I 4026 is the clearest example of the sn characteristics in our sample. We succesfully fit this line in 4 out of 7 sn stars by using the appropriate Stark broadening tables, while small differences appear in the other 3 stars. Studying the plots of abundance vs depth for the He I lines resulted in some sn stars probably being stratified in He. However, a further study of variability in the He I lines would help for determining whether a possible non-uniform He superficial distribution could also play a role in these sn stars. We conclude that the broad He I lines that characterize the sn class could be modelled (at least in some of these stars) by the usual radiative transfer process with Stark broadening, without needing another broadening mechanism. The observed line broadening in sn stars seems to be related to the normal He line formation that originates in these atmospheres. (abridged)
Balmer series
Line (geometry)
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Abstract The present paper concentrates on several seemingly nonstandard cases of variability related to CP stars. Variability of magnetic CP stars with time scales different from rotational period, variability among the HgMn stars, variability of normal stars with variations similar to CP stars, and a relation between Be and CP stars are shortly discussed.
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Abstract A limited list of new results of the searches for the new magnetic stars among late B and early A stars is in this work. Continual observations with spectroscopic devices of the 6m Russian telescope BTA led to successful detection of about 10 new magnetic stars that occupy different parts of evolutional tracks for the stars of 2–3 solar masses. Measurements of the longitudinal magnetic field show weak and medium strength magnetic field in all program stars.
Longitudinal field
Solar mass
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Abstract Recently, the line profile variability (lpv) of two low- v sin i Be stars, μ Cen and ω (28) CMa was successfully modelled as nonradial pulsation (nrp) of rapidly rotating stars seen pole-on. In this work, it is shown that the lpv of low- v sin i early-type Be stars in general closely resembles these two cases, and is therefore explainable by the same mechanism. The lpv of intermediate to high- v sin i Be stars can be explained by the same model if the inclination angle of the model alone is increased. Consequently, early-type Be stars form a distinct, fairly homogeneous class of non-radial low-order g -mode pulsators.
Mode (computer interface)
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To understand the origin of WR-rings it is of interest to consider nebulae associated with the precursors of WR stars and with stars at later stages of evolution. The former are represented by numerous Of stars and the latter by only four WO stars which, according to Barlow and Hummer (1982), are the most extreme WR stars near the end of their lives.
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Abstract Quantitative analyses of the Ga abundances in 27 Hg-Mn stars, 11 Si (magnetic) stars, 8 He-weak stars, and 7 normal stars are made with the resonance lines of Ga II at 1414 Å and Ga III at 1495 Å in IUE spectra. The Ga overabundances are confirmed as a genuine anomaly in many peculiar stars. Only upper limits of the Ga abundance can be obtained for some stars. However these upper limits are much lower than those inferred from visual spectra. Among the 27 Hg-Mn stars, 17 stars are distributed in the range of 2.0 – 3.8 dex of overabundances of Ga. Ten other stars show upper limits less than 2.1 dex. Fifteen stars of 20 hotter Hg-Mn stars with T eff > 11000 K show high overabundances in a narrow range of 2.6 – 3.8 dex, while, among 7 cooler Hg-Mn stars, the only star HR 7775 shows the same overabundance as in these 15 stars. Of 11 Si stars, 9 stars have Ga overabundances ranging from 1.9 to 3.2 dex. Gallium is overabundant in 5 out of 8 He-weak stars in the range of 1.7 – 3.2 dex, while in the three other stars the upper limits are less than 1.3 dex. The Ga abundances in normal stars are all upper limits which roughly correspond to the solar value.
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