Core Burning Research Articles

The case for Case C mass transfer in the galactic evolution of black hole binaries

Earlier works, which we review, have shown that if the Fe core in a presupernova star is to be sufficiently massive to collapse into a black hole, earlier in the evolution of the star the He core must be covered (clothed) by a hydrogen envelope during He core burning and removed only following this, in, e.g., common envelope evolution. This is classified as Case C mass transfer. These previous arguments were based chiefly on stellar evolution, especially depending on the way in which 12C burned. In this work we argue for Case C mass transfer on the basis of binary evolution. The giant progenitor of the black hole will have a large radius ∼1000 R ⊙ at the end of its supergiant stage. Its lifetime at that point will be short, ∼1000 years, so it will not expand much further. Thus, the initial giant radius for Case C mass transfer will be constrained to a narrow band about ∼1000 R ⊙. This has the consequence that the final separation a f following common envelope evolution will depend nearly linearly on the mass of the companion m d which becomes the donor after the He core of the giant has collapsed into the black hole. The separation at which this collapse takes place is essentially a f, because of the rapid evolution of the giant. (In at least two binaries the black hole donor separation has been substantially increased because of mass loss in the black hole formation. These can be reconstructed from the amount of mass deposited on the donor in this mass loss.) We show that the reconstructed preexplosion separations of the black hole binaries fit well the linear relationship.

The Capella Giants and Coronal Evolution across the Hertzsprung Gap

We present an analysis of the coronal line Fe XXI λ1354 observed in medium-resolution Hubble Space Telescope/Space Telescope Imaging Spectrograph echelle spectra of Capella obtained on 1999 September 12. These data were collected in support of a multiwavelength spectroscopic campaign designed to provide detailed temperature and density diagnostics over a wide range of temperatures, and they are accompanied by simultaneous Chandra, Extreme Ultraviolet Explorer, BeppoSAX, and Very Large Array observations. The line Fe XXI λ1354 formed at 107 K is crucial to the interpretation of these data sets since it allows the deconvolution of the coronal flux of the two binary components. While earlier observations implied comparable coronal emission from both stars, our data indicate that nearly all the Fe XXI flux in the C I/Fe XXI blend at 1354 A arises from the rapidly rotating G1 III secondary. This suggests a significant decline in the hottest part of the corona of the G8 III primary over the past 5 years. For the first time, we can assign the variability of the high-temperature X-rays to the cooler He core burning star in the system. This result suggests that nascent coronae in the early Hertzsprung gap phase apparently do not vary and that cyclic activity and strong variability are seen only in later evolutionary stages when dynamos are more developed in deeper convective envelopes.

The evolution of naked helium stars with a neutron star companion in close binary systems

The evolution of helium stars with masses of 1.5 – 6.7 M⊙ in binary systems with a 1.4 M⊙ neutron-star companion is presented. Such systems are assumed to be the remnants of Be/X-ray binaries with B-star masses in the range of 8 – 20 M⊙ which underwent a case B or case C mass transfer and survived the common-envelope and spiral-in process. The orbital period is chosen such that the helium star fills its Roche lobe before the ignition of carbon in the centre. We distinguish case BA (in which mass transfer is initiated during helium core burning) from case BB (onset of Rochelobe overflow occurs after helium core burning is terminated, but before the ignition of carbon). We found that the remnants of case BA mass transfer from 1.5 – 2.9 M⊙ helium stars are heavy CO white dwarfs. This implies that a star initially as massive as 12 M⊙ is able to become a white dwarf. CO white dwarfs are also produced from case BB mass transfer from 1.5 – 1.8 M⊙ helium stars, while ONe white dwarfs are formed from 2.1 – 2.5 M⊙helium stars. Case BB mass transfer from more-massive helium stars with a neutron-star companion will produce a double neutron-star binary. We are able to distinguish the progenitors of type Ib supernovae (as the high-mass helium stars or systems in wide orbits) from those of type Ic supernovae (as the lower-mass helium stars or systems in close orbits). Finally, we derive a ”zone of avoidance” in the helium star mass vs. initial orbital period diagram for producing neutron stars from helium stars.

Formation of high mass X-ray black hole binaries

The discrepancy in the past years of many more black-hole soft X-ray transients (SXTs), of which a dozen have now been identified, had challenged accepted wisdom in black hole evolution. Reconstruction in the literature of high-mass X-ray binaries has required stars of up to ∼40 M ⊙ to evolve into low-mass compact objects, setting this mass as the limit often used for black hole formation in population syntheses. On the other hand, the sheer number of inferred SXTs requires that many, if not most, stars of ZAMS masses 20–35 M ⊙ end up as black holes ( Portegies Zwart et al., 1997; Ergma and van den Heuvel, 1998). In this paper we show that this can be understood by challenging the accepted wisdom that the result of helium core burning in a massive star is independent of whether the core is covered by a hydrogen envelope, or ‘naked’ while it burns. The latter case occurs in binaries when the envelope of the more massive star is transferred to the companion by Roche Lobe overflow while in either main sequence or red giant stage. For solar metallicity, whereas the helium cores which burn while naked essentially never go into high-mass black holes, those that burn while clothed do so, beginning at ZAMS mass ∼20 M ⊙ , the precise mass depending on the 12C( α, γ) 16O rate as we outline. In this way the SXTs can be evolved, provided that the H envelope of the massive star is removed only following the He core burning. Whereas this scenario was already outlined in 1998 by Brown et al. [NewA 4 (1999) 313], their work was based on evolutionary calculations of Woosley et al. [ApJ 448 (1995) 315] which employed wind loss rates which were too high. In this article we collect results for lower, more correct wind loss rates, finding that these change the results only little. We go into the details of carbon burning in order to reconstruct why the low Fe core masses from naked He stars are relatively insensitive to wind loss rate. The main reason is that without the helium produced by burning the hydrogen envelope, which is convected to the carbon in a clothed star, a central 12C abundance of ∼1/3 remains unburned in a naked star following He core burning. The later convective burning through 12C+ 12C reactions occurs at a temperature T∼80 keV. Finally, we show that in order to evolve a black hole of mass ≳10 M ⊙ such as observed in Cyg X-1, even employing extremely massive progenitors of ZAMS mass ≳60 M ⊙ for the black hole, the core must be covered by hydrogen during a substantial fraction of the core burning. In other words, the progenitor must be a WNL star. We evolve Cyg X-1 in an analogous way to which the SXTs are evolved, the difference being that the companion in Cyg X-1 is more massive than those in the SXTs, so that Cyg X-1 shines continuously.

Formation and evolution of black hole X-ray transient systems

We study the formation of low-mass black hole X-ray binaries with main sequence companions that have formed through case C mass transfer (mass transfer following the helium core burning phase of the black hole progenitor). We identify these objects with the observed soft X-ray transients. Although this scenario requires a set of fine tuned conditions, we are able to produce a current Galactic population of ∼2000 objects, in agreement with estimates based on observations. The narrow interval in initial separations leading to case C mass transfer, combined with the allowed narrow range of separations after the common envelope evolution, constrains the common envelope efficiency in this scenario: λα ce≈0.2−0.5.

Reprocessing theHipparcosdata for evolved giant stars II. Absolute magnitudes for the R-type carbon stars

The Hipparcos Intermediate Astrometric Data for carbon stars have been reprocessed using an algorithm which provides an objective criterion for rejecting anomalous data points and constrains the parallax to be positive. New parallax solutions have been derived for 317 cool carbon stars, mostly of types R and N. In this paper we discuss the results for the R stars. The most important result is that the early R stars (i.e., R0 { R3) have absolute magnitudes and V K colors locating them among red clump giants in the Hertzsprung-Russell diagram. The average absolute magnitude MK for early R-type stars (with V K< 4) has been derived from a Monte-Carlo simulation implicitly incorporating all possible biases. It appears that the simulated magnitude distribution for a population with a true Gaussian distribution of mean MK = 2:0 and intrinsic standard deviation 1.0 mag provides a satisfactory match to the observed distribution. These values are consistent with the average absolute magnitudeMK = 1:6 for clump red giants in the solar neighborhood (Alves 2000). Further, early R-type stars are non-variable, and their infrared photometric properties show that they are not undergoing mass loss, properties similar to those of the red clump giants. Stars with subtypes R4 { R9 tend to be cooler and have similar luminosity to the N-type carbon stars, as conrmed by their position in the (J H;H K) color-color diagram. The sample of early R-type stars selected from the Hipparcos Catalogue appears to be approximately complete to magnitude K0 7, translating into a completeness distance of 600 pc if all R stars had MK = 2 (400 pc if MK = 1). With about 30 early R-type stars in that volume, they comprise about 0.04% (0.14% for MK = 1) of the red clump stars in the solar neighborhood. Identication with the red clump locates these stars at the helium core burning stage of stellar evolution, while the N stars are on the asymptotic giant branch, where helium shell burning occurs. The present analysis suggests that for a small fraction of the helium core burning stars (far lower than the fraction of helium shell-burning stars), carbon produced in the interior is mixed to the atmosphere in sucient quantities to form a carbon star.

The formation of high-mass black holes in low-mass X-ray binaries

We suggest that high-mass black holes; i.e., black holes of several solar masses, can be formed in binaries with low-mass main-sequence companions, provided that the hydrogen envelope of the massive star is removed in common envelope evolution which begins only after the massive star has finished He core burning.

The Origin of Extreme Horizontal Branch Stars

Strong mass loss on the red giant branch (RGB) can result in the formation of extreme horizontal branch (EHB) stars. The EHB stars spend most of their He core and shell burning phase at high temperatures and produce copious ultraviolet flux. They have very small hydrogen envelopes and occupy a small range in mass. We have computed evolutionary RGB models with mass loss for stars with a range of metallicities at initial masses < 1.1 Msun corresponding to populations ages between 12.5 and 14.5 Gyr. We used the Reimers formula to characterize mass loss, but investigated a larger range of the mass loss efficiency parameter, eta, than is common. To understand how the number of EHB stars varies with metallicity in a stellar population we considered how the zero-age horizontal branch (ZAHB) is populated. The range in eta producing EHB stars is comparable to that producing `mid-HB' stars. Somewhat surprisingly, neither the range nor magnitude of eta producing EHB stars varies much metallicity. In contrast, the range of eta producing mid-HB stars decreases with increasing metallicity. Hence the HB of populations with solar metallicity and higher, such as expected in elliptical galaxies and spiral bulges, will be bimodal if the distribution covers a sufficiently large range in eta.

Foxfire: Confessions of a Girl Gang

The time is the 1950s. The place is a blue-collar town in upstate New York, where five high school girls are joined in a gang dedicated to pride, power, and vengeance on a world they never made - a world that seems made to denigrate and destroy them. Foxfire is Joyce Carol Oates' strongest and most unsparing novel yet...an often engrossing, often shocking evocation of female rage, gallantry, and grit. Here, then, are the Foxfire chronicles - the secret history of a sisterhood of blood, a haven from a world of lechers and oppressors, marked by a liberating fury that burns too hot to last. It is the story of Maddy Monkey, who writes it...of Goldie, whose womanly body masks a fierce, explosive temper...of Lana, with her Marilyn Monroe hair and packs of Chesterfields...of timid Rita, whose humiliation leads to the first act of Foxfire revenge. Above all, it is the story of Legs Sadovsky, with her lean, on-the-edge, icy beauty, whose nerve, muscle, hate, and hurt make her the spark of Foxfire, its guiding spirit, its burning core. At once brutal and lyrical, this is a careening joyride of a novel - charged with outlaw energy and lit by intense emotion. The story moves over the years from the first eruption of adolescent anger at sexual abuse to a shared life financed by luring predatory men into traps baited with sex. But then the gang's very success leads to disaster - as Foxfire makes a last tragic stand against a society intent on swallowing it up. Yet amid scenes of violence, sexual abuse, exploitation, and vengeance lies this novel's greatest power: the exquisite, astonishing rendering of the bonds that link the girls of Foxfire together - especially that between Maddy, the teller ofthe tale, and Legs, whose quintessential strength and bedrock bravery make her one of the most vivid and vital heroines in modern fiction.

Mid-IR (8?13 ?m) images of the 21 ?m, carbon rich proto-planetary nebulae

We present 9.7 and 11.8 μm narrow band (Δλ/λ=10%) images of three carbon (C-) rich proto-planetary nebulae with an unusual 21 μm feature: IRAS 07134+ 1005, IRAS 22272+5435, and IRAS 04296+3429. The images were taken at UKIRT using the Berkeley/IGPP/LEA mid-IR camera. All three objects have a bipolar shape adding to the existing evidence that C-rich PPNe are by nature bipolar. Furthermore, we find the same bipolar morphology in a previous study of the C-rich, young planetary nebula, IRAS 21282+5050. We believe these four objects form an evolutionary sequence which links the C-rich asymptotic giant branch (AGB) stars with the C-rich planetary nebulae (PNe). From this evolutionary sequence, we conclude that bipolarity in C-rich PNe begins on the AGB and that the dynamical ages of these PPNe are in fair agreement with theoretical ages for a 0.6 M⊙ hydrogen burning core star.

The intermediate age open cluster NGC 7044

We present the photometric analysis for the open cluster NGC 7044, based on Johnson-Cousins UBVR CCD observations of 896 stars in a region of 4′20″×2′40″ in the cluster field. Reddening and metallicity are estimated by means of the location of selected samples of members in the (U-B) vs (B-V) diagram, with respect to the lines of the Hyades ZAMS and giants. This selection is performed by considering the location of the representative points in both the V vs (B-V) and V vs (U-B) diagrams simultaneously. The final estimates are found to be very dependent on whether, and to what extent, reddening slopes and absorption coefficients are considered to vary with spectral type. Global considerations, based on the photometric information together with the results of the comparison with theoretical model isochrones, lead to the following set of values: E(B-V)=0.57, [Fe/H]=0.0, (m-M)0= 12.4, and log age(y)=9.4. We discuss to some extent the influence that varying absorption coefficients, published in the literature, would have on these estimates. Our color-magnitude (CM) diagram is compared with selected sets of isochrones, based on evolutionary models computed with and without considering convective overshooting from the stellar core during the phases of H and He core burning. Better general agreement is found when using the overshooting models, between predicted and observed features of the CM diagram, particularly in what concerns the properties of the so-called Red Giant Clump (RGC). With the adopted solution, NGC 7044 turns out to be one of the oldest intermediate-age clusters, very close to, or even beyond the limiting age separating the regimes of He flash and quiet onset of He burning in the red giant phase. The location of the RGC in absolute magnitude, together with the resulting (B-V)0 at the turnoff, leads us to suggest that the efficiency of convective core overshooting in stars of masses around and below 1.5 script M sign⊙ should be slightly higher than that of the models used. An analysis of the spatial distribution of the stars suggest that a mass segregation mechanism is acting in the cluster, in the sense that the most massive members are concentrated in the center. Luminosity and mass functions have been computed; a classical power law fitted to the latter results in a slope of x=-1.66±0.06.

Comparison between the masses of Delta Scuti-variables

Estimates of the pulsation massesMQ and of massesMg=gR2/G (g is the surface gravity;R, the mean stellar radius; andG, the gravitational constant) of 89 Delta Scuti-variables have been obtained. An intercomparison of three kinds of masses —Me, Mg, andMQ — is performed; the evolutionary massesMe of the same variables were estimated in a previous paper (Tsvetkov, 1986). It is pointed out that within the limits of the accuracy of determination, the three kinds of masses agree for the majority of the stars under study. For several varaibles, however, there is a considerable discrepancy between the estimates of the pulsation massesMQ and the estimates of the massesMe andMg. Arguments are represented, which may alleviate or even remove this mass discrepancy for some of these stars. It is shown that the results from the comparison between the three kinds of masses of the considered Delta Scuti-stars are not very sensitive to the choice of the system of evolutionary tracks and the adopted chemical composition as well as to the evolutionary phases of the variables (core or shell hydrogen burning). The variations of the chemical composition in most of the stars under study are probably not very large.

Combustion kinetics of high-ash coals in fluidized beds

Burnout times of high-ash coals in a fluidized bed were determined for coal particle sizes ranging from 0.125 to 4 mm, over a temperature range of 973–1173 K and fluidization velocities varying from 3.7 U mf to 6.2 U mf. The results show that the mode with which anthracite particles burn resembles that of a shrinking core of unchanged initial particle diameter. With these anthracites it was observed that diffusion through an ash layer becomes more important as the burning core diameter decreases with time. It can also be concluded that the combustion of the anthracites appears to be most influenced by the bed temperature and particle size. The combustion of particles at 1173 K is primarily controlled by diffusion of oxygen to the surface of the particles and through the ash layer. The influence of chemical kinetics on the combustion process increases considerably with decreasing bed temperature and is the dominant resistance below 1073 K for all the particle sizes tested.

The pulsational stability of Wolf-Rayet stars

Representative radial and nonradial pulsational modes of five WR star models are calculated. In agreement with Maeder (1984), a hydrogen-free 50-solar-mass model, evolved from an original main-sequence 120-solar-mass model, has a pulsationally unstable radial fundamental mode. All radial overtones are stable in this model, as is typical of massive He stars pulsationally driven by the epsilon effect at their centers. For the other four models, all with some residual surface hydrogen, no radial modes are unstable. Further, no unstable g-type nonradial modes are found for any of the five models. The nonradial modes have large amplitudes outside of the convective core, where they might be expected to be driven by the epsilon mechanism in their hydrogen-burning shells. However, their stability suggests that nonradial pulsations do not contribute to the extreme mass-loss rates observed for WR stars. Radial pulsations can occur for the hot He core burning (WNE, WC, and WO) WR stars, and could possibly cause mass loss, but only very late in their evolution. 22 references.

Evolution of massive stars in very young clusters and associations

Statistics concerning the stellar content of young galactic clusters and associations which show well defined main sequence turnups have been analyzed in order to derive information about stellar evolution in high-mass galaxies. The analytical approach is semiempirical and uses natural spectroscopic groups of stars on the H-R diagram together with the stars' apparent magnitudes. The new approach does not depend on absolute luminosities and requires only the most basic elements of stellar evolution theory. The following conclusions are offered on the basis of the statistical analysis: (1) O-tupe main-sequence stars evolve to a spectral type of B1 during core hydrogen burning; (2) most O-type blue stragglers are newly formed massive stars burning core hydrogen; (3) supergiants lying redward of the main-sequence turnup are burning core helium; and most Wolf-Rayet stars are burning core helium and originally had masses greater than 30-40 solar mass. The statistics of the natural spectroscopic stars in young galactic clusters and associations are given in a table.

Yellow giants in young clusters. II - A comparison of observation with theory

view Abstract Citations (16) References (34) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Yellow giants in young clusters. II. A comparison of observation withtheory. Schmidt, E. G. Abstract Luminosities and effective temperatures are calculated for 17 nonvariable yellow giants and supergiants and nine Cepheids which were previously identified as members of open clusters. These stars are identified as being in the helium core burning stage of evolution. A comparison with the predictions of pulsation theory does not show any disagreement. On the other hand, several comparisons with the theory of stellar evolution produce discrepancies which suggest that effects neglected in the calculations may play an important role in the evolution of these stars. Publication: The Astrophysical Journal Pub Date: December 1984 DOI: 10.1086/162685 Bibcode: 1984ApJ...287..261S Keywords: Cepheid Variables; Giant Stars; Star Clusters; Supergiant Stars; Helium; Hertzsprung-Russell Diagram; Stellar Cores; Stellar Evolution; Stellar Luminosity; Stellar Temperature; Astrophysics full text sources ADS | data products SIMBAD (21) Related Materials (1) Part 1: 1984ApJS...55..455S

Comparisons between observational color-magnitude diagrams and synthetic cluster diagrams for young star clusters in the Magellanic Clouds

Young star clusters (&lt;3 × 108 yr) in the Maqellanic Clouds (MC) can be used to test the current status of the theory of stellar evolution as applied to intermediate and massive stars. The color-magnitude diagram of many young clusters in the MC shows, unlike the case of clusters in our Galaxy, large numbers of stars in both the main sequence and post main sequence evolutionary phases. Usina a arid of stellar evolution models, synthetic cluster H-R diagrams are constructed and compared to observed color-magnitude diagrams to determine the age, age spread, and composition for any given cluster. In addition, for those cases where the data is of high quality, detailed comparisons between theory and observation can provide a diagnostic of the accuracy of the stellar evolution models. Initial indications of these comparisons suggest that the theoretical models should be altered to include: a larger value for the mixing length parameter (α), a larger rate of mass loss during the asymptotic giant branch (AGB) phase, and possibly convective overshoot during the core burning phases.

Astrophysical properties of red giants in three open clusters older than the hyades

Results from CMT1T2 1T2 broad-band and DDO intermediate-band photometry are presented for G and K giants in the old open clusters NGC. 2482, NGC 3680, and IC 4651. Two independent photometric criteria have been used to separate red field stars from the physical members of the clusters. Recent calibrations of the DDO and CMT1T2 systems have been used to derive reddening, distance moduli, metallicities, effective tempe- ratures, and surface gravities. Rough estimates of masses have also been made. The giants of NGC 2482 and IC 4651 have CN strengths nearly identical to the Hyades giants, while those of NGC 3680 are slightly richer in CN than the nearby K giants. CMT1T2 abundance analysis in NGC 2482 and NGC 3680 yield (Fe/H)MT = - 0.1 ± 0.1 as derived from the iron lines, while abundances derived from the CNO - contaminated (C - M) index are 0.4 dex higher. Both CMT1T2 and DDO data support the conclusion that 1C 4651, with (Fe/H) = + 0.2 ± 0.1, is on the metal- rich side of the distribution of intermediate and old open clusters. Finally, the mass results suggest that the clump stars in NGC 3680 and. IC 4651 could have undergone mass loss before reaching their helium core burning phase of evolution.

Effect of oscillating flow on combustion rate of coal particles

The burning times of captive coal particles (1–3 mm in diameter) in oscillating flow of controlled velocity amplitude and frequency have been measured. This study was undertaken to explain the high values of combustion intensities reported in experiments with pulsating combustors. The experimental data, presented herein, indicate that higher values of the ratio of the air displacement amplitude to the initial radius of the coal particle result in greater reduction in the burning time. The experiments also revealed the existence of two-stage combustion for the residue: shell burning, for which the combustion rate is controlled by the rate of oxygen transport in the gas phase; and core burning, for which the combustion rate is controlled by the rate of diffusion of oxygen through the porous ash layer formed during combustion. A theoretical model is discussed which explains the effect of the ash layer on the combustion rate of the particle. This model shows that the reduction in burning time of a particle of ash-forming coal (for which the ash does not flake off) caused by the enhanced rate of oxygen transport in the gas phase may be significantly less than the corresponding reduction in burning time of a coal particle for which the ash layer is absent.

Theoretical studies of massive stars. II - Evolution of a 15 solar-mass star from carbon shell burning to iron core collapse

The evolution of a Population I star of 15 solar masses is described from the carbon shell burning stage to the formation and collapse of an iron core. An unusual aspect of the evolution is that neon ignition occurs off-center and neon burning propagates inward by a series of shell flashes. The extent of the core burning is generally smaller than the Chandrasekhar mass, so that most of the nuclear energy generation occurs in shell sources. Because of degeneracy and the influence of rapid convective mixing, these shell sources are unstable and the core goes through large excursions in temperature and density. The small core also causes the shell sources to converge into a narrow mass region slightly above the Chandrasekhar mass. Thus, the final nucleosynthesis yields are generally small, with silicon being most strongly enhanced with respect to solar system abundances.