Mass Of Heavy Elements Research Articles

DETERMINATION OF THE MINIMUM MASSES OF HEAVY ELEMENTS IN THE ENVELOPES OF JUPITER AND SATURN

We calculate the minimum mass of heavy elements required in the envelopes of Jupiter and Saturn to match the observed oversolar abundances of volatiles. Because the clathration efficiency remains unknown in the solar nebula, we have considered a set of sequences of ice formation in which the fraction of water available for clathration is varied between 0 and 100 %. In all the cases considered, we assume that the water abundance remains homogeneous whatever the heliocentric distance in the nebula and directly derives from a gas phase of solar composition. Planetesimals then form in the feeding zones of Jupiter and Saturn from the agglomeration of clathrates and pure condensates in proportions fixed by the clathration efficiency. A fraction of Kr and Xe may have been sequestrated by the H3+ ion in the form of stable XeH3+ and KrH3+ complexes in the solar nebula gas phase, thus implying the formation of at least partly Xe- and Kr-impoverished planetesimals in the feeding zones of Jupiter and Saturn. These planetesimals were subsequently accreted and vaporized into the hydrogen envelopes of Jupiter and Saturn, thus engendering volatiles enrichments in their atmospheres, with respect to hydrogen. Taking into account both refractory and volatile components, and assuming plausible molecular mixing ratios in the gas phase of the outer solar nebula, we show that it is possible to match the observed enrichments in Jupiter and Saturn, whatever the clathration efficiency. Our calculations predict that the O/H enrichment decreases from 6.7 to 5.6 times solar (O/H) in the envelope of Jupiter and from 18.1 to 15.4 times solar (O/H) in the envelope of Saturn with the growing clathration efficiency in the solar nebula.

Empirical models of pressure and density in Saturn's interior: Implications for the helium concentration, its depth dependence, and Saturn's precession rate

We present ‘empirical’ models (pressure vs. density) of Saturn's interior constrained by the gravitational coefficients J 2 , J 4 , and J 6 for different assumed rotation rates of the planet. The empirical pressure–density profile is interpreted in terms of a hydrogen and helium physical equation of state to deduce the hydrogen to helium ratio in Saturn and to constrain the depth dependence of helium and heavy element abundances. The planet's internal structure (pressure vs. density) and composition are found to be insensitive to the assumed rotation rate for periods between 10h:32m:35s and 10h:41m:35s. We find that helium is depleted in the upper envelope, while in the high pressure region ( P ≳ 1 Mbar ) either the helium abundance or the concentration of heavier elements is significantly enhanced. Taking the ratio of hydrogen to helium in Saturn to be solar, we find that the maximum mass of heavy elements in Saturn's interior ranges from ∼6 to 20 M ⊕ . The empirical models of Saturn's interior yield a moment of inertia factor varying from 0.22271 to 0.22599 for rotation periods between 10h:32m:35s and 10h:41m:35s, respectively. A long-term precession rate of about 0.754 ″ yr −1 is found to be consistent with the derived moment of inertia values and assumed rotation rates over the entire range of investigated rotation rates. This suggests that the long-term precession period of Saturn is somewhat shorter than the generally assumed value of 1.77 × 10 6 years inferred from modeling and observations.

Main-sequence instability strip for different opacities and heavy element abundances: a comparison with observations

Updated theoretical instability domains are presented for β Cephei and SPB star models. Calculations were performed using new OP opacities for old (GN93) and new (A04) solar heavy element mixtures. The position of observed β Cephei and SPB variables in the HR and related diagrams is compared with theoretical domains for three heavy element mass fractions: Z = 0.020, 0.015 and 0.010.

Dust masses and abundances in planetary nebulae: likely strong elemental depletion in low-abundance sources

An analysis is undertaken of the relation between dust/gas mass ratios and elemental abundances within planetary nebulae (PNe). It is found that MDUST/MGAS is broadly invariant with abundance, and similar to the values observed in asymptotic giant branch (AGB)-type stars. However, it is noted that the masses of dust observed in low-abundance PNe are similar to the masses of heavy elements observed in the gas phase. This is taken to imply that levels of elemental depletion must be particularly severe, and extend to many more species than have been identified so far. In particular, given that levels of C and O depletion are likely to be large, then this probably implies that species such as Fe, S, Si and Mg are depleted as well. There is already evidence for depletion of Fe, Si and Mg in individual PNe. It follows that whilst quoted abundances may accurately reflect gas-phase conditions, they are likely to be at variance with intrinsic abundances in low ZN nebulae. Finally, we note that there appears to be a variation in dust/gas mass ratios with galactocentric distance, with gradient similar to that observed for several elemental abundances. This may represent direct evidence for a correlation between dust/gas mass ratios and nebular abundances.

Stellar Population Models and Individual Element Abundances. I. Sensitivity of Stellar Evolution Models

Integrated light from distant galaxies is often compared to stellar population models via the equivalent widths of spectral features—spectral indices—whose strengths rely on the abundances of one or more elements. Such comparisons hinge not only on the overall metal abundance, but also on relative abundances. Studies have examined the influence of individual elements on synthetic spectra but little has been done to address similar issues in the stellar evolution models that underlie most stellar population models. Stellar evolution models will primarily be influenced by changes in opacities. In order to explore this issue in detail, 12 sets of stellar evolution tracks and isochrones have been created at constant heavy element mass fraction Z that self-consistently account for varying heavy element mixtures. These sets include scaled-solar, α-enhanced, and individual cases where the elements C, N, O, Ne, Mg, Si, S, Ca, Ti, and Fe have been enhanced above their scaled-solar values. The variations that arise between scaled-solar and the other cases are examined with respect to the H-R diagram and main-sequence lifetimes.

On the Origin of HD 149026b

The high density of the recently discovered close-in extrasolar planet HD 149026b suggests the presence of a huge core in its interior, which challenges planet formation theory. We first derive constraints on the total mass of heavy elements in the planet and find its preferred value is 50-80 M? . We then explore the possibility of the formation of HD 149026b through subcritical core accretion as envisioned for Uranus and Neptune, and find the subcritical accretion scenario is very unlikely in the case of HD 149026b for at least two reasons: (1) subcritical planets are such that the ratio of their core mass to their total mass is above ~0.7, in contradiction with constraints for all but the most extreme interior models of HD 149026b and (2) high accretion rates and large isolation mass required for the formation of a subcritical >50 M? core are possible only at specific orbital distances in a disk with a surface density of dust equal to at least 30 times that of the minimum-mass solar nebula. These facts point toward two main routes for the formation of HD 149026b: (i) gas accretion limited by a slow viscous inflow in an evaporating disk or (ii) a significant modification of the planetary composition after gas accretion ended. Illustrating the second route, we show that collision between two gas giants leads to a substantial loss of the gas component and thus may make the planet highly enriched in heavy elements. Alternatively, the planet may be supplied with heavy elements by planetesimals through secular perturbations. In both the giant impact and the secular perturbation scenarios, we expect an outer giant planet to be present. Observational studies by imaging, astrometry, and long-term interferometry of this system are needed to better narrow down the ensemble of possibilities.

A correlation between the heavy element content of transiting extrasolar planets and the metallicity of their parent stars

Nine extrasolar planets with masses between 110 and 430M are known to transit their star. The knowledge of their masses and radii allows an estimate of their composition, but uncertainties on equations of state, opacities and possible missing energy sources imply that only inaccurate constraints can be derived when considering each planet separately. Aims: We seek to better understand the composition of transiting extrasolar planets by considering them as an ensemble, and by comparing the obtained planetary properties to that of the parent stars. Methods: We use evolution models and constraints on the stellar ages to derive the mass of heavy elements present in the planets. Possible additional energy sources like tidal dissipation due to an inclined orbit or to downward kinetic energy transport are considered. Results: We show that the nine transiting planets discovered so far belong to a quite homogeneous ensemble that is characterized by a mass of heavy elements that is a relatively steep function of the stellar metallicity, from less than 20 earth masses of heavy elements around solar composition stars, to up to 100M for three times the solar metallicity (the precise values being model-dependant). The correlation is still to be ascertained however. Statistical tests imply a worst-case 1/3 probability of a false positive. Conclusions: Together with the observed lack of giant planets in close orbits around metal-poor stars, these results appear to imply that heavy elements play a key role in the formation of close-in giant planets. The large masses of heavy elements inferred for planets orbiting metal rich stars was not anticipated by planet formation models and shows the need for alternative theories including migration and subsequent collection of planetesimals.

Atmosphere, Interior, and Evolution of the Metal‐rich Transiting Planet HD 149026b

We investigate the atmosphere and interior of the new transiting planet HD 149026b, which appears to be very rich in heavy elements. We first compute model atmospheres at metallicities ranging from solar to 10 times solar and show how for cases with high metallicity or inefficient redistribution of energy from the dayside, the planet may develop a hot stratosphere due to absorption of stellar flux by TiO and VO. The spectra predicted by these models are very different than cooler atmosphere models without stratospheres. The spectral effects are potentially detectable with the Spitzer Space Telescope. In addition, the models with hot stratospheres lead to a large limb brightening, rather than darkening. We compare the atmosphere of HD 149026b to other well-known transiting planets, including the recently discovered HD 189733b, which we show has a planet-to-star flux ratio twice that of HD 209458 and TrES-1. The methane abundance in the atmosphere of HD 189733b is a sensitive indicator of atmospheric temperature and metallicity and can be constrained with Spitzer IRAC observations. We then turn to interior studies of HD 149026b and use a grid of self-consistent model atmospheres and high-pressure equations of state for all components to compute thermal evolution models of the planet. We estimate that the mass of heavy elements within the planet is in the range of 60-93 M⊕. Finally, we discuss trends in the radii of transiting planets with metallicity in light of this new member of the class.

α‐Enhanced Integrated Lick/IDS Spectral Indices and Milky Way and M31 Globular Clusters and Early‐Type Galaxies

All 25 Lick/IDS spectral indices have been computed for the integrated light of simple stellar populations over broad ranges of age and metallicity and with effects from horizontal-branch stars fully implemented. Our models employ α-enhanced isochrones at the sub-solar metallicity regime, but solar-scaled ones at solar and super-solar metallicity. We have also employed the updated response functions of Houdashelt et al. at the solar and super-solar metallicity regime, so that we could assess the light-element enhancement phenomena seen from metal-rich early-type galaxies. For Balmer indices a significant response was noted for Hγ and Hδ when α-elements are enhanced, but Hβ is rather α-insensitive. We also find that our 5 and 12 Gyr models of Hγ and Hδ overlap in the metal-poor regime because of changing populations of blue horizontal-branch stars. Furthermore, for populations younger than 1 Gyr, Balmer lines become weaker in the metal-poor regime because the main-sequence turnoff is hotter than 10,000 K. We present models at fixed [Fe/H] (rather than fixed heavy element mass fraction Z) and compare to Milky Way globular clusters that have independently estimated mean [Fe/H] and [α/Fe]. Comparison of our models with observations of Milky Way and M31 globular clusters in index-index space are favorable, tracing the observations at a model age of 12 Gyr without any zero-point shifts that are needed by some other models. The metallicity range of M31 globular clusters is similar to that of their Galactic counterparts. We also verify Beasley et al.'s recent hypothesis of the existence of young and intermediate-age star clusters in M31. Contrary to the literature values, the Milky Way globular cluster NGC 6553 appears more metal-rich than NGC 6528 from metal indices. We present Hδ and Hγ Lick/IDS indices for the Lick/IDS sample of galaxies. We confirm the well-known enhancement of Mg and Na relative to Fe and Ca among early-type galaxies, and its increase with increasing velocity dispersion. There are distinct differences between globular clusters and galaxies in diagrams involving CN1 and CN2, hinting that the globular cluster environment may be a special one in terms of the amount of N incorporated into stars.

How Accurately Can We Calculate the Depth of the Solar Convective Zone?

We evaluate the logarithmic derivative of the depth of the solar convective zone (CZ) with respect to the logarithm of the radiative opacity, ∂ ln RCZ/∂ ln κ. We use this expression to show that the radiative opacity near the base of the solar CZ must be known to an accuracy of ±1% in order to calculate the CZ depth to the accuracy of the helioseismological measurement, RCZ = 0.713 ± 0.001 R☉. The radiative opacity near the base of the CZ that is obtained from OPAL tables must be increased by ~21% in the 2004 Bahcall-Pinsonneault solar model if one wants to invoke opacity errors in order to reconcile recent solar heavy abundance determinations with the helioseismological measurement of RCZ. We show that the radiative opacity near the base of the CZ depends sensitively on the assumed heavy-element mass fraction, Z. The uncertainty in the measured value of Z is currently the limiting factor in our ability to calculate the depth of the CZ. Different state-of-the-art interpolation schemes using the existing OPAL tables yield opacity values that differ by ~4%. We describe the finer grid spacings that are necessary to interpolate the radiative opacity to ±1%. Uncertainties due to the equation of state do not significantly affect the calculated depth of the CZ.

Image-Subtraction Photometry of the Globular Cluster M3: Identification of New Double-Mode RR Lyrae Stars

We have applied the image subtraction method of Alard and Lupton to the extensive M3 data set previously analyzed by Corwin and Carney using DAOPHOT and ALLSTAR. This new analysis has produced light curves and periods for 15 variables not found in the previous study but already known to be variables, and it has also resulted in improved periods for several other variables. The additional variables recovered with the image subtraction analysis are in the very central region of M3, where crowding is severe and the photometry was not of sufficient quality that it could be put on the standard system. The present study brings to 222 the total number of RR Lyrae variables in Corwin and Carney's M3 data set for which light curves and periods are available. Among them we have identified three new candidate double-mode pulsating variables (V13, V200, and V251), reported here for the first time. This brings to eight the total number of double-mode RR Lyrae (RRd's) identified in M3. Of the newly discovered RRd's V13 is unusual in that it has the fundamental as the dominant pulsation mode. M3 is unique among the globular clusters in having RRd variables with a dominant fundamental mode. Two of the new candidate RRd's (V13 and V200) have period ratios as low as 0.738–0.739. They lie well separated from all previously known double-mode variable stars in the Petersen diagram in positions implying a large spread in mass and/or, less likely, in heavy element mass fraction, among the M3 horizontal-branch (HB) stars. We explore mass transfer and helium enhancement as possible explanations for the apparent spread in HB masses. We also note that the masses derived from the double-mode analyses now favor little mass loss on the red giant branch. We find that V200 has changed its dominant pulsation mode from fundamental to first overtone, while V251 has changed its dominant mode from first overtone to fundamental in the interval 1992 to 1993. Together with M3-V166 this is the first time that double-mode variables are observed to switch their dominant pulsation modes while remaining RRd's. The phenomenon is found to occur in a 1 yr time span, thus suggesting that these stars are undergoing a rapid evolutionary phase and that both redward and blueward evolution may take place among the HB stars in the Oosterhoff type I cluster M3. The unusual behavior of the M3 RRd's is discussed in detail and compared with that of the double-mode RR Lyrae identified so far in globular clusters and in the field of our and other Local Group galaxies. We find a lack of correlation between the presence of RRd variables and any of the cluster structural parameters.

Peculiar Chemical Abundances in the Starburst Galaxy M82 and Hypernova Nucleosynthesis

X-ray observations have shown that the chemical abundance in the starburst galaxy M82 is quite rich in Si and S compared with oxygen. Such an abundance pattern cannot be explained with any combination of conventional Type I and II supernova yields. Also the energy to heavy element mass ratio of the observed hot plasma is much higher than the value resulted from normal supernovae. We calculate explosive nucleosynthesis in core-collapse hypernovae and show that the abundance pattern and the large ratio between the energy and the heavy element mass can be explained with the hypernova nucleosynthesis. Such hypernova explosions are expected to occur for stars more massive than >~ 20-25 Msun, and likely dominating the starburst, because the age after the starburst in M82 is estimated to be as short as ~ 10^6 - 10^7 yr. We also investigate pair-instability supernovae (~ 150-300 Msun) and conclude that the energy to heavy element mass ratio in these supernovae is too small to explain the observation.

An elementary model for the dust cycle in galaxies

We give an elementary model for the evolution of dust in galaxies, based on abundance arguments. The model takes account of grain core production in both supernovae and giant stars, and includes mantle growth in the interstellar medium. Destruction of grain cores does not appear to be a dominant effect. We show that a self-consistent picture can be made in which the interstellar dust mass is an approximately constant fraction of the heavy element mass in the interstellar medium. This result is demonstrated to be essentially independent of outflow or inflow of interstellar material

A Spectroscopic Study of a Large Sample Of Wolf‐Rayet Galaxies

We analyze long-slit spectral observations of 39 Wolf-Rayet (WR) galaxies with heavy element mass fraction ranging over 2 orders of magnitude, from Z☉/50 to 2Z☉. Nearly all galaxies in our sample show broad WR emission in the blue region of the spectrum (the blue bump) consisting of an unresolved blend of N III λ4640, C III λ4650, C IV λ4658, and He II λ4686 emission lines. Broad C IV λ5808 emission (the red bump) is detected in 30 galaxies. Additionally, weaker WR emission lines are identified, most often the N III λ4512 and Si III λ4565 lines, which have very rarely or never been seen and discussed before in WR galaxies. These emission features are characteristic of WN7-WN8 and WN9-WN11 stars, respectively. We derive the numbers of early WC (WCE) and late WN (WNL) stars from the luminosities of the red and blue bumps, and the number of O stars from the luminosity of the Hβ emission line. Additionally, we propose a new technique for deriving the numbers of WNL stars from the N III λ4512 and Si III λ4565 emission lines. This technique is potentially more precise than the blue-bump method because it does not suffer from contamination of WCE and early WN (WNE) stars and nebular gaseous emission. It is found that the relative number of WR stars N(WR)/N(O+WR) decreases with decreasing metallicity, in agreement with predictions of evolutionary synthesis models. The relative number ratios N(WC)/N(WN) and the equivalent widths of the blue bump EW(λ4650) and of the red bump EW(λ5808) derived from observations are also in satisfactory agreement with theoretical predictions, except for the most metal-deficient WR galaxies. A possible source of disagreement is too low a line emission luminosity adopted for a single WCE star in low-metallicity models. We assemble a sample of 30 H II regions with detected He II λ4686 nebular emission to analyze the possible connection of this emission with the hard UV radiation of the WR stars. The theoretical predictions satisfactorily reproduce the observed intensities and equivalent widths of the He II λ4686 nebular emission line. However, galaxies with nebular He II λ4686 emission do not always show WR emission. Therefore, in addition to the ionization of He+ in the H II region by WR stars, other mechanisms for the origin of He II λ4686 such as radiative shocks probably need to be invoked.

The Metal Contents of Milky Way Globular Clusters

ABSTRACTGlobular clusters in the Milky Way contain total masses of heavy elements ranging from a few solar masses to as great as 104 M⊙. Given that a massive star of greater than 40 M⊙ can produce in excess of 12 M⊙ of heavy elements, it is possible that at least some globular clusters contain the metals from only a very small number of supernovae, although many clusters contain a sufficiently large mass of metals that the contribution from 10 to 200 or more supernovae is required. More than one supernova event would be needed within an initially metal‐free cloud to raise the heavy‐element abundance to a level greater than [A/H] = -1.8 dex. Many halo field stars have metallicities much lower than this. It is possible that such stars formed from cold primeval clouds with masses in excess of 2 × 106M⊙ that were self‐enriched by only one or two supernovae.The metallicity distribution of Milky Way globular clusters shows some features that may vary with cluster mass. By binning clusters into integrated‐magnitude groups of MV,t less than −8.0, −8.0 to −6.5, and greater than −6.5, it is shown that the percentage of clusters with metallicities [A/H] > -1.0 increases with decreasing cluster mass. In addition to this trend, the occurrence of intermediate metallicities with [A/H] = -1.0 ± 0.2 is mainly restricted to globular clusters fainter than MV,t = -8.0. It is possible that some of these intermediate‐metallicity clusters formed during an era in the Galactic halo that favored the production of lower mass systems.

A comparison of the interiors of Jupiter and Saturn

Interior models of Jupiter and Saturn are calculated and compared in the framework of the three-layer assumption, which rely on the perception that both planets consist of three globally homogeneous regions: a dense core, a metallic hydrogen envelope, and a molecular hydrogen envelope. Within this framework, constraints on the core mass and abundance of heavy elements (i.e. elements other than hydrogen and helium) are given by accounting for uncertainties on the measured gravitational moments, surface temperature, surface helium abundance, and on the inferred protosolar helium abundance, equations of state, temperature profile and solid/differential interior rotation. Results obtained solely from static models matching the measured gravitational fields indicate that the mass of Jupiter’s dense core is less than 14 M ⊕ (Earth masses), but that models with no core are possible given the current uncertainties on the hydrogen–helium equation of state. Similarly, Saturn’s core mass is less than 22 M ⊕ but no lower limit can be inferred. The total mass of heavy elements (including that in the core) is constrained to lie between 11 and 42 M ⊕ in Jupiter, and between 19 and 31 M ⊕ in Saturn. The enrichment in heavy elements of their molecular envelopes is 1–6.5, and 0.5–12 times the solar value, respectively. Additional constraints from evolution models accounting for the progressive differentiation of helium (Hubbard WB, Guillot T, Marley MS, Burrows A, Lunine JI, Saumon D, 1999. Comparative evolution of Jupiter and Saturn. Planet. Space Sci. 47, 1175–1182) are used to obtain tighter, albeit less robust, constraints. The resulting core masses are then expected to be in the range 0–10 M ⊕, and 6–17 M ⊕ for Jupiter and Saturn, respectively. Furthermore, it is shown that Saturn’s atmospheric helium mass mixing ratio, as derived from Voyager, Y=0.06±0.05, is probably too low. Static and evolution models favor a value of Y=0.11−0.25. Using, Y=0.16±0.05, Saturn’s molecular region is found to be enriched in heavy elements by 3.5 to 10 times the solar value, in relatively good agreement with the measured methane abundance. Finally, in all cases, the gravitational moment J 6 of models matching all the constraints are found to lie between 0.35 and 0.38×10 −4 for Jupiter, and between 0.90 and 0.98×10 −4 for Saturn, assuming solid rotation. For comparison, the uncertainties on the measured J 6 are about 10 times larger. More accurate measurements of J 6 (as expected from the Cassini orbiter for Saturn) will therefore permit to test the validity of interior models calculations and the magnitude of differential rotation in the planetary interior.

The Baryonic Content of Galaxies and Clusters

Optical and X-ray observations of early-type galaxies, groups, and clusters of galaxies show that a greater fraction of the gravitating mass is in rich clusters than in individual galaxies. In elliptical galaxies, only a few percent of the gravitating mass is observed in stars or gas, while in rich clusters, approximately 30% of the mass is contained in hot gas and galaxies. In this Letter, we show that if the recent estimate of the MACHO abundance in our Galaxy is representative of all galaxies, then the observable content of galaxies, groups, and rich clusters (in the form of MACHOs, stars, and gas) is nearly constant at 50% of the total mass. We also explore the consequences for the gaseous content of groups and clusters if MACHOs are the stellar remnants of an early population of stars. Previous studies have shown that the hot gas in clusters cannot be supplied by the present population of stars in clusters, which implies that the gas is primordial. However, based on the MACHO detection rate in our Galaxy, we find that the stellar progenitors of MACHOs could produce the observed gas mass and abundance of heavy elements in rich clusters. The observed trend of increasing gas mass fraction between groups and clusters then can be explained within the context of hierarchical clustering scenarios.

Classical nova models with accretion heating at accretion rates of 10 exp -9 and 10 exp - 10 solar masses per year

view Abstract Citations (22) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Classical Nova Models with Accretion Heating at Accretion Rates of 10 -9 and 10 -10 Msun per Year Prialnik, Dina ; Kovetz, Attay Abstract Two evolutionary sequences of accretion on to a 1.25 solar mass C-O white dwarf are computed for constant accretion rates of 10 exp -10 and 10 exp -9 solar mass/yr and are carried through the thermonuclear runaway and the dynamical phases of mass loss, followed by contraction of the remnant and decline. Improved algorithms are used for diffusion during the accretion phase and for the computation of mass loss. Accretional heating is taken into account. It is concluded that outbursts typical of classical novae may be achieved for the adopted rather high accretion rates that are compatible with observations. The heavy element mass fractions in the ejecta are found to be 0.31 and 0.19, the maximal velocities reached are 2300 and 1600 km/s, and mass loss lasts for 12 and 25 days, respectively, for the two models. The effect of diffusion and its dependence on the accretion rate are discussed. Publication: The Astrophysical Journal Pub Date: February 1992 DOI: 10.1086/170972 Bibcode: 1992ApJ...385..665P Keywords: Accretion Disks; Cataclysmic Variables; Novae; Stellar Evolution; Stellar Mass Ejection; Stellar Models; Mass Transfer; Thermonuclear Reactions; White Dwarf Stars; Astrophysics; ACCRETION; ACCRETION DISKS; STARS: ABUNDANCES; STARS: EVOLUTION; STARS: MASS LOSS; STARS: NOVAE; CATACLYSMIC VARIABLES full text sources ADS |

Formation of a planet orbiting pulsar 1829–10 from the debris of a supernova explosion

THE 10-Earth-mass planet1 in a nearly circular 0.7-AU orbit around PSR1829–10 is unlikely to have survived the supernova, or especially the pre-supernova evolution of the star that became the pulsar. Here we describe how the planet might have been created inside the young supernova remnant1–3. The principal difficulty lies not in providing enough mass or conducive thermo-dynamic conditions for planet formation, but in explaining the large angular momentum (∼3 x 1048 erg s) and small eccentricity (<0.1) of the orbit. We propose that the planet formed from a rotationally supported disk of ∼0.02 solar mass of heavy elements that fell back from the supernova explosion to an initial radius of about 1,000 km. Viscous evolution of the disk then concentrated most of its angular momentum into a small amount of material at the disk's outer extremity: 10 Earth masses at 1013 cm. Here, dust grains that had condensed and precipitated towards the mid-plane grew through cohesive collisions and gravitational instabilities into 100-km planetesimals, which coagulated into the planet on a million-year timescale. We find the presence of a second planet, more massive and more distant, unlikely, although residual planetesimals may provide the fuel for γ-ray bursts.

Molecular gas in luminous infrared galaxies

view Abstract Citations (456) References (43) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Molecular Gas in Luminous Infrared Galaxies Sanders, D. B. ; Scoville, N. Z. ; Soifer, B. T. Abstract CO (1 -> 0) emission profiles are presented for 60 infrared luminous, [L-ir_(8-1000 microns) = 5 x 10^10^-3 x 10^12^ L_sun_, H_0_ = 75 km s^-1^ Mpc^-1^], bright (F_60 micron_ > 5.24 Jy), IRAS galaxies at redshifts 1500-25,000 km s^-1^ Most of these galaxies are sufficiently distant that a single 55" beam measures the total CO luminosity and hence the total molecular gas content. The data for these galaxies are analyzed together with that for a sample of 29 closer IRAS bright galaxies with L_ir_ down to 2 x 10^10^ L_sun_ mapped by Tinney et al. (1990). All of the IRAS bright galaxies are extremely rich in molecular gas with M(H_2_) = 1 x 10^9^-6 x 10^10^ M_sun_, corresponding to 0.5-30 times the mass of H_2_ gas in the Milky Way. The dust masses are evaluated from the IRAS data and the mean ratio of H_2_ gas to "warm dust" is 540 +/- 290. Including the mass of heavy elements and the contribution from H I implies a mean gas-to-dust ratio in the range 900-1100. The discrepancy between this value and the standard Galactic gas-to-dust ratio of ~ 150 could be due to the presence of large quantities of cold dust to which IRAS is insensitive, and/or errors in the assumed dust mass absorption coefficient. The infrared luminosity-to-H_2_ mass ratios, L_ir_/M(H_2_), range from 2-220 L_sun_ M^-1^_sun_, up to a factor of 55 times the mean ratio for molecular clouds in the Galaxy. The ratio L_ir_/M(H_2_) increases with increasing L_ir_, but shows no systematic dependence on M(H_2_). The higher values of L_ir_/M(H_2_) obtained in the most luminous galaxies suggests either an increased star formation efficiency and/or an additional source of luminosity. The kinetic energy of colliding galaxies is ruled out as a significant source of the luminosity in view of the independence of the L_ir_/M(H_2_) ratios on the galactic velocity dispersions and the merging time scales which are too long. If the excess luminosity is supplied by star formation, the implied lifetime of the interstellar medium is <= 3 x 10^8^ yr. However, a significant number of the galaxies with the highest L_ir_/M(H_2_) ratios exhibit non-thermal optical emission lines characteristic of an active galactic nucleus (AGN), and an AGN appears to be an important energy source for these galaxies. Publication: The Astrophysical Journal Pub Date: March 1991 DOI: 10.1086/169800 Bibcode: 1991ApJ...370..158S Keywords: Galactic Structure; Infrared Sources (Astronomy); Luminosity; Molecular Gases; Active Galactic Nuclei; Emission Spectra; Infrared Astronomy Satellite; Interstellar Matter; Line Spectra; Red Shift; Astrophysics; GALAXIES: INTERSTELLAR MATTER; INFRARED: SOURCES full text sources ADS | data products SIMBAD (63) NED (60)