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[MATH] =0.3067 [MATH] 0.0005. Physical parameters and dynamical age Given the spectroscopic redshift, we can determine observational parameters that characterize the GRG reported; i.e., the linear size, [MATH] , and the volume of the cocoon, [MATH] , via the axial ratio AR, and radio luminosity, [MATH] . Other physical... |
[MATH] , and the radio spectrum ( [MATH] ), which usually provides [MATH] at a number of observing frequencies [MATH] … The values of other free parameters of the model have to be assumed. |
4.1 Linear size, volume, and luminosity The high symmetry of the radio structure and the weak strength of the core suggests that an inclination angle of the jet axis towards the observer’s line of sight is large, possibly close to 90°. Thus, the linear size of J1420 [MATH] 0545 is [MATH] =4690 kpc; i.e. it is larger th... |
[MATH] [MATH] . Following Leahy & Williams ( 1984 we measure the axial ratio AR as the ratio between the angular size of the total structure and the average of the full width ( [MATH] ) of its two lobes. The latter is determined as the largest deconvolved width of the transversal cross section through the lobes measure... |
[MATH] ; however, this latter value is likely an upper limit for the axial ratio, because the cocoon’s width further down towards the core can be larger than the width of the detected lobes. The dependence of age and other physical parameters of J1420 [MATH] 0545 on the value of AR is considered in the next subsection.... |
W Hz -1 sr -1 and [MATH] W Hz -1 sr -1 respectively. Because of the limited radio data, the model parameters derived in the next subsection are fitted using the above two luminosity values only. |
4.2 Age and other parameters The model requires the density distribution of the ambient medium (which is invariant with redshift) to be modeled by a power law, [MATH] [MATH] , where [MATH] |
is the core radius and the exponent [MATH] describes the density profile. With this assumption, the age of a radio structure of linear size [MATH] is |
[EQUATION] the pressure within the cocoon is [EQUATION] and the energy density and the corresponding equipartition magnetic field strength are |
[EQUATION] where [MATH] is the adiabatic index of the lobes’ (cocoon) material. If we take the same values of the model’s free parameters as in Machalski et al. ( 2007a , in particular |
[MATH] = 10 kpc, [MATH] = 1.5, and [MATH] = 5/3, the values of [MATH] [MATH] , and [MATH] are determined by the fit to the observed luminosities and volume of the source (cf. KDA). But that fit depends on [MATH] . In the KDA model this also has to be assumed; however, the DYNAGE algorithm allows us to find its value th... |
[MATH] and different hypothetical ages of J1420 [MATH] 0545 are shown in the log [MATH] –log [MATH] diagram in Figure [MATH] . The two pairs of curves (solid and dashed) give the fits for two different values of AR; the one determined from the width of the observed lobes (cf. §4.1), and the same, but decreased by a fac... |
compared with that for AR=12, while the values of the age [MATH] and [MATH] remain comparable. The dependence of the resulting model solutions of [MATH] [MATH] |
[MATH] , and [MATH] on [MATH] for AR=12 is shown in Figure [MATH] . The vertical line and the arrow indicate the value of [MATH] that corresponds to the minimum value of the product |
[MATH] . The minimum of this product, which gives the kinetic energy delivered to the cocoon by the jet, corresponds to a minimum of the energy density in the cocoon, [MATH] , as is expected from the KDA model assumption of energy equipartition between magnetic fields and particles. The parameter values resulting from ... |
and [MATH] is equivalent to either [MATH] , log( [MATH] ), or log( [MATH] (cf. Figure [MATH] ). These uncertainties were determined during the fitting procedure of a set of pairs ( [MATH] [MATH] ) with the above forms. Therefore, the errors given in Table 2 do not account for uncertainties of the model’s free parameter... |
[MATH] [MATH] , etc., as well as that of the observational parameter AR. A possible influence of uncertainties of the above parameters on the DYNAGE predictions has been discussed in Machalski et al. ( 2007a Because of limited radio spectral data for J1420 [MATH] 0545, we suppose that the quoted errors for this radio g... |
4.3 Discussion of the results The DYNAGE model solution for J1420 [MATH] 0545 strongly suggests that this radio galaxy is at least twice as young as other GRGs at redshifts of about 0.1, and that it evolved in an exceptionally low-density environment. The fitted value of [MATH] is a factor of 100 lower than the central... |
found for J1420 [MATH] 0545 is about 20 times lower than that for 3C236 (cf. Table 2). Enlarging the cocoon’s width, i.e. assuming that AR=8, causes a further decrease of the fitted value of [MATH] by a factor of 3.4. On the other hand, the above enlargement does not change significantly the model solutions for the val... |
value of around 0.48, and the age estimate is around 45 Myr. Such a relatively young age seems to be confirmed by evident hot spots that were clearly visible in both of the lobes of the source when it was mapped using the FIRST survey. |
Having modeled the values of age and jet power with DYNAGE, we can estimate the value of the IGM (ambient) density at the jet heads, [MATH] . Balancing the ram pressure of the IGM and the thrust of the jet, Begelman & Cioffi ( 1989 derived the equation for the age of a FR type II source (their eq. ), |
[EQUATION] where [MATH] and [MATH] are the cross-sectional areas of the bow shock at the head of the jet and of the cocoon, respectively. Thus, if we assume that the jet speed is close to the speed of light and take into account that the areas |
[MATH] and [MATH] can be derived from the radio maps, a value of [MATH] can be calculated from the above equation. Usually [MATH] is identified with the cross-sectional area of hot spots. The deconvolved lateral angular sizes of the hot spots in the lobes of J1420 [MATH] 0545 are 3.8 [MATH] and 4.1 [MATH] . Averaging t... |
[MATH] [MATH] for AR=12. Substituting these values of [MATH] and [MATH] , as well as the values of [MATH] and [MATH] from Table 2, into the above equation, we find that [MATH] [MATH] |
kg m -3 . If the cocoon were (1.5) times fatter (i.e. if AR=8), the resulting ambient density would be lower by a factor of about 37 and would reach an unacceptably low value of about [MATH] kg m -3 Such a low value of AR is also very unlikely because the ambient density of |
[MATH] kg m -3 would correspond to that calculated from the density profile [MATH] [MATH] at a radius of [MATH] Mpc! A power-law density distribution at such a very large distance from the host galaxy is absolutely improbable. On the other hand, the value of [MATH] kg m -3 seems to be reasonable as it corresponds to a ... |
There is also the possibility that the gaseous halo of the host galaxy is much smaller, and although the halo’s density profile in the case of J1420 [MATH] 0545 is not known, its jets may propagate through the (nearly) uniform IGM for a considerable fraction of the entire source lifetime. Therefore, while assuming that... |
[MATH] =0, leads to an unphysical picture that the density at the head of jets, 2.2 Mpc away from the host galaxy, would be equal to its central density, it may be worthwhile to check how the fitted parameters of the source, i.e., the density in the front of the jets, [MATH] , the jets’ power, and the source age, would... |
As a result, we find that [MATH] would be almost twice as strong as its value in Table 2, and the ambient density [MATH] would be lower by a factor of 4 than [MATH] kg m -3 . Moreover, the source would be also younger than 47 Myr, which, in turn, would imply some even higher average expansion velocity of the source alo... |
There are two possible explanations that could account for lowering the true age of the source and enhancing its expansion speed: |
1. Large errors in the flux densities used to calculate the radio luminosity of the lobes (cocoon) at the two observing frequencies. If the radio spectrum determined from these flux densities is flatter than the actual one, the source will appear younger in the modelling procedure; |
2. Not all the kinetic energy in the jet flow had been transferred to the magnetic field and the relativistic electrons in the lobes. Such a situation is actually foreseen in the KDA model, in which the ratio ( [MATH] ) of the energy densities of thermal particles to that of electrons when they are spread into the coco... |
In order to provide a quantitative check of the possible influence of the uncertain radio spectrum, we generated a fiducial spectrum steeper than that derived from the observations available to date and ran the fitting procedure for the frequency range 150–4800 MHz. We found that the age of J1420 [MATH] 0545 could poss... |
Following Kaiser et al. ( 1997 , up to this point we have neglected any influence of the thermal particles in the lobes of J1420 [MATH] 0545; i.e. [MATH] =0 was assumed. However, in order to check how the thermal plasma can modify the model parameters derived from the fit, we performed comparison calculations in which ... |
[MATH] , while, on the other hand, an increase of [MATH] causes a decrease of the advance speed of the lobes. We note that the age [MATH] increases in a much slower manner than do the other parameters. Thus, a very high value of [MATH] (k= [MATH] [MATH] 10) would be necessary to reduce the advance speed of the galaxy t... |
are not ruled out on the basis of the observed asymmetries of sources (Scheuer, 1995 Also, the jets may not keep expanding with a constant opening angle and it is not at all clear that the velocities will keep systematically decreasing. The hot spot size seems to increase with the overall source size untill about 10–20... |
To summarize, we argue that the fitted parameters for J1420 [MATH] 0545 as given in Table 2 seem to be quite realistic ones, and the current uncertainty of its radio spectrum and the unknown influence of thermal plasma are not likely to significantly change the values derived in this paper. The very low ambient density... |
4.4 Comparison to other radio galaxies of different linear size In order to compare the derived parameters of J1420 [MATH] 0545 with the corresponding parameters of other FR type II radio galaxies we use the sample of 30 GRGs and 120 normal-sized galaxies (NSGs) analyzed by Machalski & Jamrozy ( 2006 for which dynamica... |
[MATH] , as well as the corresponding pressure, [MATH] , are extremely low (Figure [MATH] ). The value of [MATH] (in Table 2) is a factor of 2.5 lower than that for 3C236, although the redshifts of J1420 [MATH] 0545 and 3C236 differ by a factor of 3. This confirms that J1420 [MATH] 0545 actually traces very low density... |
[MATH] cm -3 Furthermore, Figure [MATH] shows that GRGs are characterized by much lower radio luminosities than are NSGs of the same jet power. This is what one expects using the KDA model. The model predicts that the luminosity in the inverse-Compton–dominated regime decreases as |
[MATH] or [MATH] , where [MATH] is the adiabatic index of a magnetic ”fluid” and is equal to 4/3. Thus, for the assumed value of [MATH] =1.5 and [MATH] =5/3, one finds that |
[MATH] or [MATH] . Figure [MATH] shows that J1420 [MATH] 0545 is less luminous than NSGs with a comparable jet power by a factor of about 100. Applying the predicted luminosity evolution with size [MATH] , one would expect J1420 [MATH] 0545 to have had the same luminosity as those NSGs when its linear size was about 38... |
[MATH] kg m -3 and only three with [MATH] kg m -3 . Therefore, although the largest radio galaxies can likely have evolved from younger and smaller sources, J1420 [MATH] 0545 is evidently a nontypical GRG due to its exceptionally low-density (a void?) environment as found by the fit. |
The authors thank the Service Programme staff for the WHT observations, Alex Kraus for his help with the Effelsberg observations, and Michal Siwak for the Mount Suhora observations, as well as the Centre Director of the NCRA, TIFR, for the allocation of discretionary observing time and Chiranjib Konar for his assistanc... |
# Source: arxiv 0808.3026 # Title: Difference in Narrow Emission Line Spectra of Seyfert 1 and 2 galaxies # Sections: all # Downloaded: 2026-03-02T07:58:26.037692+00:00 |
Difference in Narrow Emission Line Spectra of Seyfert 1 and 2 galaxies Abstract In the unification scheme of Seyfert galaxies, a dusty torus blocks the continuum source and broad line region in Seyfert 2 galaxies. However it is not clear whether or not and to what extent the torus affects the narrow line spectra. In th... |
galaxies: active–galaxies:Seyfert–(galaxies:) quasars: emission lines Introduction The unification scheme of Seyfert galaxies has been widely accepted to explain the dichotomy of Seyfert 1 (hereafter Sy1) and Seyfert 2 galaxies (hereafter Sy2) (e.g. Antonucci 1993). The basic idea is that the differences between Sy1s a... |
While it is general agreed that dusty tori obscure BLR and continuum source, and even the central narrow line region (NLR) of Sy2s (e.g., Rhee & Larkin 2005; Haas et al. 2005), it is still unclear to what extent they obscure the NLR, and how the obscuration depends on the orientation (i.e., the difference in NLR obscur... |
It is well known that NLR is stratified, at least for AGNs of some sort (e.g.,Veilleux et al. 1991, Robinson et al. 1994). Emission lines of higher critical density or ionization potential are produced averagely closer to the active nucleus than those of lower critical density or ionization. This fact can be used to ch... |
In this paper, we study the location of Sy1s and Sy2s on the BPT diagrams, short for Baldwin-Phillips-Terlevich diagrams (Baldwin et al 1981), which are often used for classification of narrow emission line galaxies. With the large spectroscopic sample of both Sy1s and Sy2s available from the Sloan Digital Sky Survey (... |
Sample and Data Analysis 2.1 Seyfert 1 and 2 galaxy samples The Seyfert 2 galaxies sample is selected from the galaxy catalog of SDSS Data Release 4 (DR4). For our purpose, a redshift cut of [MATH] 0.3 is used to ensure that the emission lines of interest, [MATH] , H [MATH] , [O III] and [N II], [S II], fall in the spe... |
Seyfert 1 galaxies were drawn from quasar and galaxy catalogues of SDSS DR4 at redshift [MATH] . For nucleus dominated sources where Fe II multiplets and other broad emission lines are highly blended, we fit simultaneously the nuclear continuum, the Fe II multiplets and emission lines (see Dong et al. 2008 for details)... |
absorption line or high order Balmer lines or Na I [MATH] , a starlight model is also included using the 6 IC templates as described in the above. The decomposition of host-galaxy starlight, nuclear continuum and FeII emission were carried out following the procedure as described in detail in Zhou et al. (2006). We fit... |
Based on the fitted emission-line parameters, we construct the sample of Sy1s according to the criteria as follows. (1) Adding a broad gaussian component of H [MATH] to the model can improve the fit significantly with a chance probability less than 0.05 according to F-test; (2) The broad component is detected with S/N ... |
2.2 Emission Line Fitting For Sy2s, after removing the starlight, we fit the emission-line spectra using the code described in detail in Dong et al. (2005). Briefly, every line is fitted with one or more Gaussians as is statistically justified (mostly with 1–2 Gaussians); the line parameters are achieved by minimizing ... |
For Sy1s, once the nuclear continuum and the Fe II emission are subtracted, we perform a refined fit of the emission-line spectra. The narrow lines are modeled as for Sy2s. The broad lines are modeled with multi-gaussians, as many as is statistically justified. One concern is the reliability of the decomposition of nar... |
Results 3.1 A Comparison between Seyfert 1 and 2 galaxies Dong et al.(2008) found that the distribution of broad-line Balmer decrement for blue AGNs is a gaussian in the logarithmic space, with a peak at 0.486 (H [MATH] /H [MATH] =3.1) and an intrinsic standard deviation only [MATH] 0.03. The reddening interpretation o... |
[MATH] . Extinction to narrow lines is also estimated using the Balmer decrement and assuming an intrinsic narrow-line Balmer decrement of 3.1. Using the |
[MATH] and extinction curve, the intrinsic luminosities of [MATH] , H [MATH] broad lines, as well as H [MATH] [MATH] , [O III] [N II], [S II] narrow lines can be calculated. |
We plot the 5544 Sy2 and 2768 Sy1 sources on the BPT diagram in Figure 1. The intermediate broad line [MATH] group are not plotted for clarity. One can easily see that Sy1s and Sy2s apparently occupy different regions on BPT diagram. We defined a line (S12 line for short) such that Sy2s rarely appear on the left side: |
[EQUATION] Only 409 (7.3%) Sy2s lie on the left side of S12 line while 913 (33.0%) Sy1s on the left side. The overall trend is very clear that Sy1s lie to the left of Sy2s on the diagram. On average, [N II]/H [MATH] ratio is 0.11 dex higher in Sy2s than in Sy1s. |
3.2 Seyfert 1 galaxies of different extinction If we regard Sy2s as Seyfert galaxies with extremely high [MATH] in broad lines, the trend of different types of Seyfert galaxies should also be traced for Sy1s of different broad line extinction [MATH] . In the right panel of Fig 1, we split the source according to their ... |
are plotted for clarity. It is evident that as the [MATH] increases, the distribution moves to right. This is in accordance with our hypothesis. One can see that a small fraction (23.8%) of objects in the [MATH] group lie on the left side of S12 line while the fraction for the low extinction group is (43.3%). |
3.3 On the narrow and broad line correlation From the broad line sample, an empirical relationship between uncorrected [O III] luminosity and broad H [MATH] line luminosity can be obtained. The broad H [MATH] is corrected from the extinction to the broad line region as in last section. |
[EQUATION] In Fig 2, we split the sample by their [MATH] and plot them on the [O III] vs H [MATH] diagram. The purple crosses are with low [MATH] while green triangle symbols with high |
[MATH] . The average ratios (in logarithmic value) of luminosities of [O III] and H [MATH] for these two groups are [MATH] and [MATH] . Thus the [O III] luminosities of the low [MATH] group are on average two times (0.334 dex) larger than that of high [MATH] group at a given broad line luminosity. The mean values of th... |
according to the Student’s t-test. One concern is that this may be introduced by the biases that the measurement error in the [MATH] will lead to a shift in the relation for different [MATH] . However, Monte-Carlo simulation shows that it causes a deviation of only 0.06 dex for a typical H [MATH] luminosity, much small... |
Discussion and conclusion We find that Seyfert 1 galaxies have significantly smaller [N II]/H [MATH] ratios than Seyfert 2 galaxies. A similar trend has also been observed in Sy1s with different BLR reddening: unreddened Seyfert 1 galaxies have smaller ratios than reddened ones. We also show that reddened Seyfert 1 gal... |
Before discussing the implication of these findings, we would like to rule out the possibility that they are introduced by systematic bias in our spectral modeling and sample selection. First, as a sanity check, we fit all the above-mentioned narrow lines assuming that they have the same profile; it does not change our... |
[MATH] group and 44.6% for Sy1s in the [MATH] group. These values are almost the same as those presented in §3. Let’s consider the fact that there are substantial Sy1s with very low [N II]/H [MATH] first. Low [N II]/H [MATH] can be produced with very metal poor gas (Groves et al. 2006), or presence of gas with a densit... |
The different distribution of Sy1s and Sy2s on BPT diagram does not suggest the failure of AGN unification because reddened Sy1s show a distribution in between. Rather it can be interpreted as partial obscuration to the NLR in Sy2s. It is well established that the NLR is stratified with high density and high ionization... |
The obscuring material can be the extended part of the torus or a dusty lane in the host galaxy. The inner edge of dusty torus is known to be order of parsecs from the central engine (Rhee et al. 2006), but the extent and height of the torus are not well constrained. Schmitt et al. (2003) showed that all Sy1s have a re... |
We thank Guinevere Kauffmann and Xue-Guang Zhang, as well as the anonymous referee for critical comments. We also thank Ting Xiao and Shaohua Zhang for useful discussion. This work is supported by Chinese NSF grants NSF-10533050 and NSF-10573015, the Knowledge Innovation Program (Grant No. KJCX2-YW-T05). Funding for th... |
# Source: arxiv 0808.3045 # Title: A seismic approach to testing different formation channels of subdwarf B stars # Sections: all # Downloaded: 2026-03-02T07:58:27.211172+00:00 |
A seismic approach to testing different formation channels of subdwarf B stars (Received 21 May 2008 / Accepted 22 July 2008 ) Abstract |
Context. There are many unknowns in the formation of subdwarf B stars. Different formation channels are considered to be possible and to lead to a variety of helium-burning subdwarfs. All seismic models to date, however, assume that a subdwarf B star is a post-helium-flash-core surrounded by a thin inert layer of hydro... |
Aims. We examine an alternative formation channel, in which the subdwarf B star originates from a massive ( [MATH] [MATH] 2 M ) red giant with a non-degenerate helium-core. Although these subdwarfs may evolve through the same region of the [MATH] diagram as the canonical post-flash subdwarfs, their interior structure i... |
Methods. Using detailed stellar evolution calculations we construct subdwarf B models from both formation channels. The iron accumulation in the driving region due to diffusion, which causes the excitation of the modes, is approximated by a Gaussian function. The pulsation modes and frequencies are calculated with a no... |
Results. A detailed comparison of two subdwarf B models from different channels, but with the same [MATH] and [MATH] , shows that their mode excitation is different. The excited frequencies are lower for the post-flash than for the post-non-degenerate subdwarf B star. This is mainly due to the differing chemical compos... |
determinations, allows us to distinguish between the two formation channels. Key Words.: subdwarfs – stars: evolution – stars: oscillation – methods: numerical |
Introduction Commonly, subdwarf B (sdB) stars are identified as extreme horizontal branch (EHB) stars, and they are believed to be post-He-core-flash products with core masses [MATH] 0.5 M surrounded by a very thin inert H-envelope (Heber 1986 ; Saffer et al. 1994 . From a single stellar evolution point of view, this c... |
[MATH] ) progenitors that ignite helium quiescently, where the latter can be a subchannel of either the CEE channel or the stable RLOF channel. Binary population synthesis shows that the massive progenitors do not contribute significantly to the sdB population (Han et al. 2003 . But one should keep in mind that it is a... |
(Hu et al. 2007 . We therefore want to explore the possibility of this neglected class of progenitors in a different manner, by using the seismic properties that have been observed in some sdB stars. |
Although the post-flash and the post-non-degenerate sdB stars can appear in the same [MATH] region, their interior structure is quite different. In particular, the chemical composition profiles differ greatly depending on whether helium ignited in a flash or quiescently. For example, the canonical post-He-flash sdB sta... |
The sdB pulsators consist of two classes, the short-period variable EC 14026 stars (Kilkenny et al. 1997 , and the long-period variable PG 1716 stars |
(Green et al. 2003 . The rapid oscillations in EC 14026 stars are interpreted in terms of low-order [MATH] -modes (Charpinet et al. 1996 , driven by the |
[MATH] -mechanism operating in the iron opacity bump. The same mechanism has been shown to excite long-period, high-order [MATH] -modes in the cooler models |
(Fontaine et al. 2003 . The local iron enhancement necessary in the driving region around [MATH] is due to the competing diffusion processes of radiative levitation and gravitational settling. It is well-known that the opacities play an important role in the study of the pulsations. Seaton & Badnell ( 2004 showed that ... |
(Seaton et al. 1994 ; Badnell & Seaton 2003 compared with OPAL opacities (Iglesias & Rogers 1996 Jeffery & Saio ( 2006 found that, using OP opacities and nickel enhancement in addition to iron, the theoretical instability strip of [MATH] -mode sdB oscillators is more consistent with observations. For our purposes it is... |
The details of the computations are given in § . The results are presented in § . In § 3.3 , we compare the detailed physical characteristics of two reference models with different formation histories. In § 3.4 we compare the frequency characteristics globally between two grids of models. The results and conclusions ar... |
Computations 2.1 The evolution calculations We constructed sdB structure models with the stellar evolution code developed by Eggleton ( 1971 1972 1973 Eggleton et al. ( 1973 , and updated by |
Han et al. ( 1994 and Pols et al. ( 1995 1998 The updated version of the code uses an equation of state that includes pressure ionization and Coulomb interaction, nuclear reaction rates from Caughlan et al. ( 1985 and Caughlan & Fowler ( 1988 , and neutrino loss rates from Itoh et al. ( 1989 1992 . Both convective and ... |
[EQUATION] where [MATH] is the ratio of radiation pressure to gas pressure and [MATH] is the overshooting parameter. Schröder et al. ( 1997 showed that [MATH] gives the best fit to observations of [MATH] |
Aurigae binaries, which corresponds to an overshooting length of [MATH] [MATH] . For our comparative study, it suffices to adopt [MATH] but keep in mind that core overshooting can in fact also be probed by asteroseismology, e.g. Aerts et al. ( 2003 |
We evolved stars assuming a chemical composition of [MATH] and [MATH] . We used a mixing-length parameter (the ratio of the mixing-length to the local pressure scaleheight) of [MATH] . If not mentioned otherwise, the opacity tables were constructed by combining the OPAL opacities |
(Iglesias & Rogers 1996 with the conductive opacities (Hubbard & Lampe 1969 ; Canuto 1970 ; Iben 1975 , as implemented in the Eggleton code by |
Eldridge & Tout ( 2004 We started by evolving zero-age main-sequence (ZAMS) models in the range [MATH] to the tip of the RGB, adopting a Reimer’s mass loss rate (Reimers 1975 |
[EQUATION] with an efficiency of [MATH] (Iben & Renzini 1983 ; Carraro et al. 1996 . For simplicity, we did not include mass-loss on the EHB. Unglaub & Bues ( 2001 showed that, if the observed chemical abundances are the result of the combined effects of diffusion and mass loss, the sdB mass-loss rate should be in the ... |
At the RGB tip, we removed the envelope, while keeping the chemical compositions fixed. Thus, we assume that the mass transfer happens on a much shorter timescale than the nuclear timescale. This is a reasonable assumption for sdB stars in short-period binaries formed by CE ejection, which is the majority of the observ... |
On the EHB, we used for temperatures [MATH] the same opacities as mentioned above. In the outer layers of the star, [MATH] , where the pulsation driving region is located, the opacities were calculated by interpolating between several OPAL tables computed with iron abundance enhanced by factors of [MATH] , 2, 5 , and 1... |
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