Solar abundances of lithium,beryllium and boron

New solar abundances have been derived for Li, Be and B. They are mainly based on high-resolution spectra obtained at the Jungfraujoch Scientific Station (Switzerland). For Li, the abundance results from a discussion of the photospheric and sunspot spectra. Our results, log N _Li = 0.42, log N _Be = 1.17 and log N _B < 2.80 (in the log N _H = 12.00 scale), are lower than the previously admitted abundances for these elements. The far UV spectrum ( < 3000 Å) has also been considered in each case. The meaning of our results is discussed from the point of view of the destruction of these elements during the evolution of the sun.This work has been sponsored in part by the Air Force Cambridge Research Laboratories, OAR, through the European Office of Aerospace Research, U.S.A.F., under Contract AF 61 (052)-955, and by the Comité National Belge de la Coopération Géophysique Internationale (C.N.B.C.G.I.).     

Distribution of lithium,beryllium, and boron in meteoritic chondrules

Abstract— The distribution of Li, Be, and B was studied by ion microprobe mass spectrometry in 36 chondrules from the Semarkona, Bishunpur, Allende, Clovis #1, and Hedjaz meteorites. Within a single chondrule, Li-Be-B concentrations can vary up to one order of magnitude. For example, in a chondrule from Hedjaz, concentrations range from 0.3 to 2.4 ppm for Li, from <0.001 to 0.17 ppm for Be, and from 0.4 to 5.5 ppm for B. Among chondrules from Semarkona and Bishunpur, clear crystal-mesostasis partitioning was observed in nine chondrules for Li, in nine chondrules for Be, and in three chondrules for B. The heterogeneities in the distribution of Li, Be, and B in chondrules from Semarkona and Bishunpur appear to be primary features that were inherited from the chondrules' precursors and not totally obscured during the chondrules' formation. A redistribution of B was nevertheless observed at the whole-rock scale for Allende (B-Al₂O₃ correlation) and Hedjaz (B–SiO₂ correlation). At the scale of bulk chondrules, a robust correlation is observed for all studied meteorites between the B/Be and the B/Li ratios, which indicates that Li and Be are much less heterogeneously distributed in chondrites than B. Mean Li, Be, and B concentrations of chondrules ([Li] ? 0.83^+0.86 ppm; [Be] ? 0.043^0.027 ppm; [B] ? 0.89^+3.71_-0.72 ppm) are consistent with those of Orgueil ([Li] ? 1.49 ppm; [Be] ? 0.0249 ppm; [B] ? 0.87 ppm), but the mean Li/Be ratio of chondrules (24.5^+6.5_-9.1) is a factor of ～4 depleted relative to Orgueil (Li/Be ratio of ～78). Such a depletion is puzzling because no correlation between Li and Na or B has been found as would be expected to result from volatilization processes during chondrule melting and cooling. As a consequence, the exact abundance of solar system Li remains an open question.     

Propagation of H and He cosmic ray isotopes in the Galaxy: astrophysical and nuclear uncertainties

Observations of light isotopes in cosmic rays provide valuable information on their origin and propagation in the Galaxy. Using the data collected by the AMS-01 experiment in the range ∼0.2–1.5 GeV nucleon⁻¹, we compare the measurements on ¹ H, ² H, ³ He, and ⁴ He with calculations for interstellar propagation and solar modulation. These data are described well by a diffusive-reacceleration model with parameters that match the B/C ratio data, indicating that He and heavier nuclei such as C–N–O experience similar propagation histories. Close comparisons are made within the astrophysical constraints provided by the B/C ratio data and within the nuclear uncertainties arising from errors in the production cross section data. The astrophysical uncertainties are expected to be dramatically reduced by the data upcoming from AMS-02, so that the nuclear uncertainties will likely represent the most serious limitation on the reliability of the model predictions. On the other hand, we find that secondary-to-secondary ratios such as ² H/³ He, ⁶ Li/⁷ Li or ¹⁰ B/¹¹ B are barely sensitive to the key propagation parameters and can represent a useful diagnostic test for the consistency of the calculations.     

Gas,dust and molecules in the Galaxy

The relative abundances of cool neutral hydrogen, carbon monoxide and formaldehyde are studied using all the available observational data in the literature. The obtained mean valuesN _{H 1}/ ,N _{H 1}/N _CO,N _CO/ are approximately constant in the dark clouds of the solar neighbourhood and in the distant molecular clouds.The observed correlationsN _CO,A _v and ,A _v show that formaldehyde can also be used as an indicator of molecular hydrogen. The ratioN H₁/A _v depends on densities and decays considerably in the ranges of visual absorptions in which the molecules become detectable (A _v 2 mg); an average of /N _{H 1}10 is calculated for the dense dark clouds.Indications of systematic temperature gradiens T/A _v are found for formaldehyde and neutral hydrogen inside the dark clouds, and qualitative comparisons are made with theoretical quantum mechanics calculations.The observed carbon monoxide and formaldehyde abundances, the free electron layer in the Galaxy, the distribution of neutral hydrogen in different states are only compatible if an ionization rate of 10^–16 is accepted, provided presumably by 2 MeV protons of cosmic radiation.Three main states for neutral hydrogen and dust are identified from different kinds of observational data (21 cm line in emission, absorption in galactic radio sources and self-absorption in the hot gas background): (1) a homogeneous intercloud stratum of tenuous gas and dust with a galactic halfwidth of 350 pc and mean parametersn _H=0.2 atom cm^–3, spin temperatureT _s 10000 K andn _d 0.3 mg kpc^–1; (2) cool gas and dust concentrated in spiral features with a galactic half-width of less than 100 pc, probably forming clouds with diffuse and indefinite limits, with mean parametersn _H2 atom cm^–3,T _s <1100 K (probable average,T _s =135 K) andn _d 3 mg kpc^–1; (3) dense gas and dust clouds with a mean diameter of 7 pc and mean parametersn _H700 atom cm^–3 (90% in a molecular state),T _s 63 K andn _d 1 mg pc^–1 on which molecules as CO and H₂CO are formed.The application of the Jeans criteria for gravitational instability shows that the dense clouds are gravitationally bound while the gas in the intermediate state (2) can be protected against collapse by the total internal energy in the medium increasing due to cosmic rays and the magnetic field in the Galaxy.The observed velocity halfwidths and galacticZ-halfwidths in states (1) and (2) are compatible with a total mass density in the galactic layer of 90M pc^–2 (gas plus stars) according to the barometric equation.The relative abundancesN _{H 1}/N _CO, calculated from C¹²O and C¹³O data and comparisons with studies in the 21 cm emission line, show that the antenna temperatureT _A ⁺ in the 2.6 mm line of C¹²O is a good indicator of the cool gas densities in the Galaxy. The possible application of this for studies in galactic structure is discussed and hypothetical distributions of carbon monoxide in the zones outside the galactic planeB=0° are presented.From a synthesis based on the results obtained, a cycle is postulated for the neutral hydrogen in the Galaxy: condensation and cooling of gas molecular formation gravitational collapse and star formation gas dissipation and heating by cosmic rays and UV radiation.     

Cross sections from 5 to 35 MeV for the reactions natMg(3He,x)26Al, 27Al(3He,x)26Al,natCa(3He,x)41Ca,and natCa(3He,x)36Cl: Implications for early irradiation in the solar system

Abstract– Cross sections were measured for the nuclear reactions ^natMg(³He,x)²⁶Al, ²⁷Al(³He,x)²⁶Al, ^natCa(³He,x)⁴¹Ca, and ^natCa(³He,x)³⁶Cl in the energy region from approximately 5–35 MeV. The rates of these reactions are important for studies of early solar system irradiation scenarios. The ²⁶Al, ³⁶Cl, and ⁴¹Ca were separated chemically, and the numbers of atoms produced in each reaction channel were measured using accelerator mass spectrometry (AMS). From these results, 26 cross sections were determined and compared with predictions of the TALYS code. Agreement is within 40% for most cross sections. Our measurements were used to model the production of ⁷Be, ¹⁰Be, ²⁶Al, and ⁴¹Ca in the early solar system. For projectiles ¹H, ³He, and ⁴He, we assumed energy spectra of the general form E^?α. For a wide range of parameterizations, the modeled ratios of ⁷Be/Be and ¹⁰Be/Be on the one hand and of ²⁶Al/²⁷Al and ⁴¹Ca/Ca on the other are coupled because the excitation functions for the relevant nuclear reactions have similar shapes. Modeling of a closed system with the constraint that ¹⁰Be/⁹Be = 0.001 fails to reproduce simultaneously the range of ⁷Be/⁹Be, ²⁶Al/²⁷Al, and ⁴¹Ca/Ca ratios inferred for the early solar system from studies of meteorites.     

The hydrocarbon ring C3H2 is ubiquitous in the Galaxy

We report the discovery of a strong microwave (lambda 1.6 cm) spectral line, the carrier of which is common and widespread throughout the Galaxy. A survey of a large number of sources shows that the line appears in emission in cold dust clouds, in absorption in the direction of the Galactic center, and exhibits complex profiles toward H II regions. Toward Cas A and distant H II regions, intervening "spiral arm" clouds produce absorption. For almost all cases, the absorption features show a striking 1 : 1 radial velocity correspondence with those seen, e.g., in H2CO spectra of the same objects. The data indicate that the line arises between low-lying energy states of rather polar molecule. Recent work by Thaddeus, Vrtilek, and Gottlieb, reported in 1985 incorporating the present data, shows that the line in question is the 1(10)-1(01) transition of the small hydrocarbon ring C3H2.     

Annihilation of positrons in the Galaxy

Observations of electron-positron annihilation radiation from the Galactic Center region with the SPI instrument aboard INTEGRAL are summarized. The measured width of the 511 keV line and inferred fraction of positrons annihilating through positronium formation are consistent with the annihilation taking place in the warm ISM phase, although combinations of several ISM phases are also allowed by the data. The spatial distribution of 511 keV emission suggests that positron sources are concentrated toward the Galactic bulge and avoid the Galactic disk.     

Cosmic-ray tracks and cobalt-60 in near-surface samples of the Jilin chondrite

Abstract— Cosmic-ray track densities (CRTDs) have been measured on several spot samples from two Jilin specimens from the strewn field (VI-21-057 and VI-42-04), along with ⁶⁰Co activity in three and four sections, respectively, of the same specimens. The observed CRTD gradient agrees remarkably well with that predicted by Bhattacharya et al.'s calculations (1973) of CRTD variation as a function of shielding depth, which indicates a negligible contribution from the first 2π-irradiation stage. The shortest distance of each specimen to the preatmospheric surface is 3.6 cm and 6.8 cm, respectively. The distance scale deduced from these measurements allows the determination of the variation of ⁶⁰Co activity with shielding depth, at low depth values, which is found to be much less steep than model predictions. Two slightly different ⁶⁰Co profiles are proposed that correspond to the two specimens studied. The mean preatmospheric radius of the Jilin chondrite is 85 ± 8 cm, the uncertainty reflecting in part the meteoroid surface roughness.     

187Re,recyclingR-process elements through stars,and the age of the Galaxy

The enhanced -decay rate of ionized¹⁸⁷Re in stars has been studied within the context of a detailed numerical model of the production ofr-process elements and their recycling through stars during the course of galactic evolution. It is concluded that the enhanced decay rate does not significantly reduce the Re-Os chronometer age for the Galaxy. Consequently, the¹⁸⁷Re -decay half-life and the neutron cross-section ratio (¹⁸⁶Os)/(¹⁸⁷Os) remain as the significant uncertainties in this chronology. Unlike the uncertainties in other chronologies, both are amenable to laboratory measurements.     

The ultraluminous and hyperluminous infrared galaxies in the Sloan Digital Sky Survey, 2dF Galaxy Redshift Survey and 6dF Galaxy Survey

We present a result of cross-correlating the Infrared Astronomical Satellite Faint Source Catalogue with the spectroscopic catalogues of galaxies in the Fourth Data Release of the Sloan Digital Sky Survey, the Final Data Release of the 2dF Galaxy Redshift Survey (2dFGRS) and the Second Data Release of the 6dF Galaxy Survey. We have identified 324 ultraluminous infrared galaxies (ULIRGs) including 190 newly discovered ULIRGs, and two hyperluminous infrared galaxies. Adding these new ULIRGs, we increase the number of known ULIRGs by about 30 per cent. The reliability of the cross-correlation is estimated using the likelihood ratio method. The incompleteness of our sample introduced by the identification procedure in this study is estimated to be about 5 per cent. Our sample covers the redshift range of   z = 0.037–0.517  with a median redshift of     , which is larger than that     of the sample of previously known ULIRGs.     

Evidence for lithium and boron from star‐forming regions implanted in presolar SiC grains

Abstract— We report the first measurements of lithium and boron isotope ratios and abundances measured in “gently separated” presolar SiC grains. Almost all analyses of presolar SiC grains since their first isolation in 1987 have been obtained from grains that were separated from their host meteorite by harsh acid dissolution. We recently reported a new method of “gently” separating the grains from meteorites by using freeze‐thaw disaggregation, size, and density separation to retain any nonrefractory coatings or alteration to the surfaces of the grains that have been acquired in interstellar space. Nonrefractory coats or amorphized surfaces will almost certainly be removed or altered by the traditional acid separation procedure. High Li/Si and B/Si ratios of up to ～10^?2 were found implanted in the outer 0.5 μm of the grains dropping to ～10^?5 in the core of the grains. ⁷Li/⁶Li and ¹¹B/¹⁰B ratios indistinguishable from solar system average values were found. Analyses obtained from SiC grains from the acid dissolution technique showed isotope ratios that were the same as those of gently separated grains, but depth profiles that were different. These results are interpreted as evidence of implantation of high velocity (1200–1800 km s^?1) Li and B ions into the grains by shock waves as the grains traveled through star‐forming regions some time after their condensation in the outflow of an AGB star that was their progenitor. The results are in line with spectroscopic measurements of Li and B isotope ratios in star‐forming regions and may be used to infer abundances and isotopic sources in these regions.     

Distribution of hydroxyl clouds in the Galaxy

Principal Astronomical Observatory, Ukrainian Academy of Sciences. Translated from Astrofizika, Vol. 28, No. 2, pp. 391–404, March–April, 1988.     

Galaxy candidates in the Zone of Avoidance

Motivated by recent discoveries of nearby galaxies in the Zone of Avoidance (ZOA), we conducted a pilot study of galaxy candidates at low galactic latitude, near galactic longitude l  ∼ 135°, where the Supergalactic plane is crossed by the Galactic plane. We observed with the 1-m Wise Observatory in the l band 17 of the 'promising' candidates identified by visual examination of Palomar red plates by Hau et al. A few candidates were also observed in R or B bands, or had spectroscopic observations performed at the Isaac Newton Telescope and at the Wise Observatory. Our study suggests that there are probably 10 galaxies in this sample. We also identify a probable planetary nebula. The final confirmation of the nature of these sources must await the availability of full spectroscopic information. The success rate of ∼ 50 per cent in identifying galaxies at galactic latitude | b | < 5° indicates that the ZOA is a promising region to discover new galaxies.     

Interpretation of3He abundance variations in the solar wind

The ion composition instrument (ICI) on ISEE-3 has observed the isotopes of helium of mass 3 and 4 in the solar wind almost continuously between August 1978 and July 1982. This period included the increase towards the maximum of solar activity cycle 21, the maximum period, and the beginning of the descent towards solar minimum. Observations were made when the solar wind speed was between 300 and 620 km s^–1. For part of the period evidence for regular interplanetary magnetic sector structure was clear and a number of³He flares occurred during this time.The long-term average⁴He⁺⁺/³He⁺⁺ flux ratio R, was 2050 ± 200, a agreement with a previously reported result obtained using part of this data set, and in very good agreement with the previous measurements made over much shorter periods of time with the foil technique. The R values for 6-month intervals show statistically significant differences. The highest of these values is 2300 and coincides with the solar maximum of cycle 21 indicating that at solar maximum there may be changes in the character and rate of occurrence of short-term variations in R. We also find that R drops under conditions of low proton flux in the solar wind, and that it is high when solar wind speeds are lowest.At solar wind speeds above 400 km s^–1 R is nearby constant at about 2000; at lower speeds it is larger and more variable, in agreement with the idea that the sources of high and low speed wind are different. At times of sector boundary current sheet crossings, identified with coronal streamers, there is a characteristic rise in the value of R indicating an encounter with a plasma with reduced³He⁺⁺ abundance. Autocorrelations have been computed for⁴He⁺⁺ and³He⁺⁺ and indicate correlation times of about 14 and 20 hr, respectively. Periods of duration of about one day whenR is less than 1000 tend to coincide with the observation of compound streams.The possibility of detectable increases in³He⁺⁺ flux in plasma which left the Sun at the time of³He flares has been investigated, but no significant increase was seen.     

Investigation of the Environmental Dependence of Galaxy Age in the CMASS Galaxy Sample of SDSS DR12

Astrophysics - In this study, I investigate the environmental dependence of galaxy age in the CMASS sample of the Sloan Digital Sky Survey Data Release 12 (SDSS DR12). It is found that galaxy age...