Velocity Of He Research Articles

ESPRESSO observations of HE 0107−5240 and other CEMP-no stars with [Fe/H] ≤ –4.5

Context. HE 0107−5240 is a hyper metal-poor star with [Fe/H] = −5.39, one of the lowest-metallicity stars known. Its stellar atmosphere is enhanced in carbon, with [C/Fe] = +4.0, without a detectable presence of neutron-capture elements. Therefore, it belongs to the carbon-enhanced metal-poor (CEMP−no) group, along with the majority of the most metal-poor stars known to date. Recent studies have revealed variations in the line-of-sight velocity of HE 0107−5240, suggesting it belongs to a binary system. CEMP-no stars are the closest descendants of the very first Pop III stars, and binarity holds important clues for the poorly known mechanism that leads to their formation. Aims. We performed high-resolution observations with the ESPRESSO spectrograph at the VLT to constrain the kinematical properties of the binary system HE 0107−5240 and to probe the binarity of the sample of the eight most metal-poor stars with [Fe/H] ≤ −4.5. Methods. Radial velocities are obtained by using a cross-correlation function in the interval 4200−4315 Å , which contains the relatively strong CH band, against a template that could be either a synthetic spectrum or a combined observed spectrum in an iterative process. A Bayesian method is applied to calculate the orbit using the ESPRESSO measurements and others from the literature. Chemical analysis has also been performed for HE 0107−5240, employing spectral synthesis with the SYNTHE and ATLAS codes. Results. Observations of HE 0107−5240 spanning more than 3 years show a monotonic decreasing trend in radial velocity at a rate of approximately 0.5 m s−1 d−1. A maximum vrad was reached between March 13, 2012, and December 8, 2014. The period is constrained at Porb = 13009−1370+1496 d. New, more stringent upper limits have been found for several elements: (a) [Sr/Fe] and [Ba/Fe] are lower than −0.76 and +0.2, respectively, confirming the star is a CEMP-no; (b) A(Li) < 0.5 is well below the plateau at A(Li) = 1.1 found in the lower red giant branch stars, suggesting Li was originally depleted; and (c) the isotopic ratio 12C/13C is 87 ± 6, showing very low 13C in contrast to what is expected from a ‘spinstar’ progenitor. Conclusions. We confirm that HE 0107−5240 is a binary star with a long period of about 13 000 d (∼36 yr). The carbon isotopic ratio excludes the possibility that the companion has gone through the asymptotic giant branch phase and transferred mass to the currently observed star. The binarity of HE 0107−5240 implies that some of the first generations of low-mass stars formed in multiple systems and indicates that the low metallicity does not preclude the formation of binaries. Finally, a solid indication of vrad variation has also been found in SMSS 1605−1443.

ESPRESSO highlights the binary nature of the ultra-metal-poor giant HE 0107−5240

Context. The vast majority of the known stars of ultra low metallicity ([Fe/H] < −4.5) are known to be enhanced in carbon, and belong to the “low-carbon band” (A(C) = log(C/H)+12 ≤ 7.6). It is generally, although not universally, accepted that this peculiar chemical composition reflects the chemical composition of the gas cloud out of which these stars were formed. The first ultra-metal-poor star discovered, HE 0107−5240, is also enhanced in carbon and belongs to the “low-carbon band”. It has recently been claimed to be a long-period binary, based on radial velocity measurements. It has also been claimed that this binarity may explain its peculiar composition as being due to mass transfer from a former AGB companion. Theoretically, low-mass ratios in binary systems are much more favoured amongst Pop III stars than they are amongst solar-metallicity stars. Any constraint on the mass ratio of a system of such low metallicity would shed light on the star formation mechanisms in this metallicity regime. Aims. We acquired one high precision spectrum with ESPRESSO in order to check the reality of the radial velocity variations. In addition we analysed all the spectra of this star in the ESO archive obtained with UVES to have a set of homogenously measured radial velocities. Methods. The radial velocities were measured using cross correlation against a synthetic spectrum template. Due to the weakness of metallic lines in this star, the signal comes only from the CH molecular lines of the G-band. Results. The measurement obtained in 2018 from an ESPRESSO spectrum demonstrates unambiguously that the radial velocity of HE 0107−5240 has increased from 2001 to 2018. Closer inspection of the measurements based on UVES spectra in the interval 2001–2006 show that there is a 96% probability that the radial velocity correlates with time, hence the radial velocity variations can already be suspected from the UVES spectra alone. Conclusions. We confirm the earlier claims of radial velocity variations in HE 0107−5240. The simplest explanation of such variations is that the star is indeed in a binary system with a long period. The nature of the companion is unconstrained and we consider it is equally probable that it is an unevolved companion or a white dwarf. Continued monitoring of the radial velocities of this star is strongly encouraged.

Charge Transfer, Complexes Formation and Furan Fragmentation Induced by Collisions with Low-Energy Helium Cations.

The present work focuses on unraveling the collisional processes leading to the fragmentation of the gas-phase furan molecules under the He+ and He2+ cations impact in the energy range 5–2000 eV. The presence of different mechanisms was identified by the analysis of the optical fragmentation spectra measured using the collision-induced emission spectroscopy (CIES) in conjunction with the ab initio calculations. The measurements of the fragmentation spectra of furan were performed at the different kinetic energies of both cations. In consequence, several excited products were identified by their luminescence. Among them, the emission of helium atoms excited to the 1s4d 1D2, 3D1,2,3 states was recorded. The structure of the furan molecule lacks an He atom. Therefore, observation of its emission lines is spectroscopic evidence of an impact reaction occurring via relocation of the electronic charge between interacting entities. Moreover, the recorded spectra revealed significant variations of relative band intensities of the products along with the change of the projectile charge and its velocity. In particular, at lower velocities of He+, the relative cross-sections of dissociation products have prominent resonance-like maxima. In order to elucidate the experimental results, the calculations have been performed by using a high level of quantum chemistry methods. The calculations showed that in both impact systems two collisional processes preceded fragmentation. The first one is an electron transfer from furan molecules to cations that leads to the neutralization and further excitation of the cations. The second mechanism starts from the formation of the He−C4H4O+/2+ temporary clusters before decomposition, and it is responsible for the appearance of the narrow resonances in the relative cross-section curves.

Determination of Anisotropic Ion Velocity Distribution Function in Intrinsic Gas Plasma. Theory.

The first seven coefficients of the expansion of the energy and angular distribution functions in Legendre polynomials for Hg+ ions in Hg vapor plasma with the parameter E/P ≈ 400 V/(cm Torr) are measured for the first time using a planar one-sided probe. The analytic solution to the Boltzmann kinetic equation for ions in the plasma of their parent gas is obtained in the conditions when the resonant charge exchange is the predominant process, and ions acquire on their mean free path a velocity much higher than the characteristic velocity of thermal motion of atoms. The presence of an ambipolar field of an arbitrary strength is taken into account. It is shown that the ion velocity distribution function is determined by two parameters and differs substantially from the Maxwellian distribution. Comparison of the results of calculation of the drift velocity of He+ ions in He, Ar+ in Ar, and Hg+ in Hg with the available experimental data shows their conformity. The results of the calculation of the ion distribution function correctly describe the experimental data obtained from its measurement. Analysis of the result shows that in spite of the presence of the strong field, the ion velocity distribution functions are isotropic for ion velocities lower than the average thermal velocity of atoms. With increasing ion velocity, the distribution becomes more and more extended in the direction of the electric field.

Experimental and theoretical determination of the strongly anisotropic velocity distribution functions of ions in the intrinsic gas plasma in strong fields

The first seven coefficient of expansion of the energy and angular distribution functions in the Legendre polynomials for Hg+ ions in the Hg vapor plasma with parameter E/P ≈ 400 V/(cm Torr) are measured for the first time using a planar one-sided probe. The analytic solution to the Boltzmann kinetic equation for ions in the plasma of their parent gas is obtained in the conditions when the resonant charge exchange is the predominant process, and an ion acquires on its mean free path a velocity much higher than the characteristic velocity of thermal motion of atoms. The presence of an ambipolar field of an arbitrary strength is taken into account. It is shown that the ion velocity distribution function is determined by two parameters and differs substantially from the Maxwellian distribution. Comparison of the results of calculation of the drift velocity of He+ ions in He, Ar+ in Ar, and Hg+ in Hg with the available experimental data shows their conformity. The results of calculation of the ion distribution function correctly describe the experimental data on its measurement. Analysis of the result shows that in spite of the presence of the strong field, the ion velocity distribution functions are isotropic for ion velocities lower than the average thermal velocity of atoms. With increasing ion velocity, the distribution becomes more and more extended in the direction of the electric field.

Electron drift velocities in He and water mixtures: measurements and an assessment of the water vapour cross-section sets.

The drift velocity of electrons in mixtures of gaseous water and helium is measured over the range of reduced electric fields 0.1-300 Td using a pulsed-Townsend technique. Admixtures of 1% and 2% water to helium are found to produce negative differential conductivity (NDC), despite NDC being absent from the pure gases. The measured drift velocities are used as a further discriminative assessment on the accuracy and completeness of a recently proposed set of electron-water vapour cross-sections [K. F. Ness, R. E. Robson, M. J. Brunger, and R. D. White, J. Chem. Phys. 136, 024318 (2012)]. A refinement of the momentum transfer cross-section for electron-water vapour scattering is presented, which ensures self-consistency with the measured drift velocities in mixtures with helium to within approximately 5% over the range of reduced fields considered.

The Influence of Acoustic Emission on the Onset of Turbulent Flow in He II

An experimental study is carried out on the influence of acoustic emission on the development of turbulent flow in He II at temperature 370 mK and at various pressures, from the saturated vapor pressure to that of 4He crystallization. The experimental technique of oscillating quartz tuning fork was applied for simultaneously exciting both superfluid flow, near the oscillating tuning fork prongs, and the acoustic wave emission. The flow rate of He II and the amplitude of the radiated acoustic waves were driven by the fork prongs, excited by voltage oscillations. Furthermore, the power of an acoustic wave depends on the density and sound velocity in He II as ρ/c5, which in turn depends on the pressure. This allowed to measure the influence of the amplitude of acoustic emission on the flow in He II. It has been shown that the occurrence of acoustic radiation by tuning fork leads to an increased flow velocity for the beginning of nonlinear flow regime.

A LUMINOUS AND FAST-EXPANDING TYPE Ib SUPERNOVA SN 2012au

We present a set of photometric and spectroscopic observations of a bright Type Ib supernova SN 2012au from -6d until ~+150d after maximum. The shape of its early R-band light curve is similar to that of an average Type Ib/c supernova. The peak absolute magnitude is M_R=-18.7+-0.2 mag, which suggests that this supernova belongs to a very luminous group among Type Ib supernovae. The line velocity of He I {\lambda}5876 is about 15,000 km/s around maximum, which is much faster than that in a typical Type Ib supernova. From the quasi-bolometric peak luminosity of (6.7+-1.3)x10^(42) erg/s, we estimate the \Ni mass produced during the explosion as ~0.30 Msun. We also give a rough constraint to the ejecta mass 5-7 Msun and the kinetic energy (7-18)x10^(51) erg. We find a weak correlation between the peak absolute magnitude and He I velocity among Type Ib SNe. The similarities to SN 1998bw in the density structure inferred from the light curve model as well as the large peak bolometric luminosity suggest that SN 2012au had properties similar to energetic Type Ic supernovae.

Detecting the Eight Kinds of Organic Solvent Residue in Paper by HS-GC/MS

A method is established to determine eight kinds of residual solvents in paper package by HS-GC/MS, such as benzene, toluene etc. Response surface method is used to optimize pretreatment temperature and time, the terminal pre-temperature is 100 °C, with time 40min. The result reveals that the pretreatment-temperature has a significant impact on peak area and pretreatment-time has no significant influence. The residual solvents in sample was separated using HP-5MS chromatographic column; Flow velocity of He:1ml/min; Inlet temperature:250°C; programmed temperature: keep 2 min at initial temperature of 35 °C, then rise to 100 °C at a rate of 10 °C/min and keep 3min; the total time is 14.5min. The eight kinds of residual solvents can be effectively separated by this method. The linear range was 0.330~7.956mg/m2 and the correlation coefficient was between 0.995~0.999.The Recovery rate was 99%~114.8% and the relative standard deviation (n=5) was 0.916%~1.333%.

Production and Growth Mechanisms of Pd Nanoclusters

Size-selected palladium nanoclusters have been produced by dc sputtering and inert gas condensation technique using mixtures of argon and helium gases. By controlling the source parameters, it was possible to produce Pd nanoclusters with size in the range of 2-10 nm. Transmission electron microscopy (TEM) images were used to confirm the produced sizes of nanocluster. It was found that increas- ing the percentage of helium to argon have two main effects: i) decreases the nanocluster size as a result of the high drift velocity of he- lium, and ii) decreases the number of measured nanoclusters due to the low sputtering yield of helium. Since He gas is primarily respon- sible for the cluster-condensation process, its partial pressure can be used to control the nanoclusters growth. The source parameters and their effects on the size and number of nanoclusters are of great importance in understanding the Pd nanoclusters growth mechanism.

A hypervelocity star from the Large Magellanic Cloud

Abstract We study the acceleration of the star HE 0437−5439 to hypervelocity and discuss its possible origin in the Large Magellanic Cloud (LMC). The star has a radial velocity of 723 km s−1 and is located at a distance of 61 kpc from the Sun. With a mass of about 8 M⊙, the traveltime from the Galactic Centre is about 100 Myr, much longer than its main-sequence lifetime. Given the relatively small distance to the LMC (18 kpc), we consider it likely that HE 0437−5439 originated in the Cloud rather than in the Galactic Centre like the other hypervelocity stars. The minimum ejection velocity required to travel from the LMC to its current location within its lifetime is about 500 km s−1. Such a high velocity can only be obtained in a dynamical encounter with a massive black hole. We perform three-body scattering simulations in which a stellar binary encounters a massive black hole, and find that a black hole more massive than 103 M⊙ is necessary to explain the high velocity of HE 0437−5439. We look for possible parent clusters for HE 0437−5439, and find that NGC 2100 and 2004 are young enough to host stars coeval to HE 0437−5439 and dense enough to produce an intermediate-mass black hole able to eject an 8-M⊙ star with hypervelocity.

The Herbig B0e star HD 53367: circumstellar activity and evidence of binarity

Aims. We investigate the spectroscopic behaviour of the young B0e star HD 53367 within a cooperative observing programme conducted from 1994 to 2005. Methods. The data include more than 100 high-resolution spectra collected at the Crimean Astronomical Observatory (CrAO) near Ha, Hβ, He I A 5876, 6678 A, DNa I, and O II λ 6641 A lines. Two spectra obtained at the Observatorio do Pico dos Dias (LNA), in the spectral bands λλ 4575-725 A and 5625-5775 A, were used for spectral classification of HD 53367. The temporal behaviour of the circumstellar lines Ha and Hβ as well as the photospheric lines O II λ 6641 A and He I λ 6678 A were investigated during different stages of the photometric activity of this object. Results. We confirm that the long-term photometric variability of HD 53367 is related to the alternation of two states of this object when the gaseous circumstellar envelope disappears and rises again. Both these processes start near the star and spread to the outlying parts of the envelope. We find that the radial velocities of He I and O II photospheric lines demonstrate a cyclic variability with a period of P = 183.7 days and semi-amplitude K = 19 km s -1 . The radial velocity change is interpreted in the framework of a model in which the star is a component of an eccentric binary system. An orbital solution is derived and the system's parameters estimated. We find that the orbital eccentricity is e = 0.28, and the mean companion separation is 1.7 AU. Conclusions. Based on the estimated parameters, we conclude that the system consists of a massive (∼20 M Θ ) main sequence primary BOe star, and a secondary which is most likely a 5 solar mass pre-main sequence object. We found evidence that the main part of the circumstellar gas in this system is concentrated near the secondary companion. Although the young age of HD 53367, its evolved primary BOe star seems to have already became a classical Be star exhibiting a specific alternation of the B-Be stages.

A New Interpretation of the Low Radial Velocity Determined from the HeII Emission Line in the Galactic Supersoft X-Ray Source RX J0019.8+2156

We propose a new interpretation for the low radial velocity of He II emission line in the Galactic supersoft X-ray source RX J0019.8+2156 based on a 2-D numerical simulation of dynamical mass transfer in binary systems. A more massive main-sequence (MS) companion of ~ 2.0 M⊙ is derived for a ~ 0.6 M⊙ white dwarf (WD) primary.The Galactic supersoft X-ray source RX J0019.8+2156 (hereafter, RX J0019) with a 12.2 mag optical counterpart was discovered by ROSAT. The source is a binary with the period of 0.66 days and its X-ray luminosity is fairly constant, at least, for 7 yrs. Therefore RX J0019 seems to be a typical luminous supersoft X-ray source (SSS) with steady hydrogen shell-burning on a mass-accreting white dwarf (WD).

―超高圧流体反応―高密度気体（流体）の超音波速度測定による相分離と凝固

Ultrasound velocities of He and Ne were measured up to 3.0 and 3.7 GPa, respectively, at 295 K. Ultrasound velocities of Ar, Kr and Xe were measured up to solidification pressures at room temperature. The phenomena of phase separation and solidification in the systems of He-Kr, He-Ar, Ne-Ar and He-CO2 were investigated by sound velocities and optical methods. Phase diagrams of He-Kr and He-CO2 were represented by those methods. Solidification curves of He-Ar and Ne-Ar were obtained at 295 K.

Very low temperature drift tube mass spectrometer

A new selected ion drift tube mass spectrometer, which has been developed for ion swarm experiments at very low temperature, is presented. Gas temperature of 2 K in the drift tube as the lowest one for this apparatus is achieved by liquid helium cooling. Details of techniques in the low temperature experiment, which are concerned in the development of this apparatus, is discussed. Preliminary experiments have been carried out in measurements of drift velocity of He+ ions in He gas at 4.3 and 2 K.

Ions and the landau critical velocity in He II

Investigations of the motion of conventional negative ions (electron bubbles) in He II under pressures above 11 bar have provided the only means of measuring the Landau critical velocity for roton creation,vL, and for studying supercritical dissipation at higher velocities. Earlier work on roton creation is reviewed and it is pointed out that there is still no generally agreed explanation of the fact that the rotons seem to be emitted from the moving ionin pairs; nor is it known why the matrix element characterising the pair emission process should decrease rapidly with pressure. The possibility of studying these phenomena through use either of the “fast ion” (whose nature remains unknown), or of selected ions from the large variety of species that can be injected into He II by the recently developed technique of laser ablation, is discussed.

Transition to superfluid turbulence in two-fluid flow of He II.

We have extended our previous measurements of the transition to superfluid turbulence in flows where the superfluid and normal-fluid velocities can be varied independently. The results indicate that the critical line in the V/sub n/-V/sub s/ plane which forms the boundary between laminar flow and superfluid turbulence is a closed curve about the origin. The existence of this critical line suggests that most theories of the critical velocity in He II are incomplete.

レーザードップラー流速計（ＬＤＶ）のＨｅ ＩＩ流れへの応用 Ｈｅ ＩＩ軸対称ジェットの研究

The application of a laser Doppler velocimeter (LDV) is successfully attempted to He II jet, which is produced by pushing bellows, by employing neutral buoyant H2-D2 solid particles as scattering tracers. The LDV measurement gives detail information of the normal fluid velocity in He II with high temporal and spatial resolution. It was found that the normal fluid velocity in circular He II jet could be measured at least up to 15cm/s by the LDV without any appreciable degradation. The fluiddynamic behaivor of He II jet was found as the result of the present measurement to be similar to those of the turbulent jets of usual viscous fluids.

EXPERIMENTAL STUDIES OF EXCITED STATES IN COLLISIONS BETWEEN He+ AND Ar

One electron capture process and direct exciting process both occured in collision between-He+ and Ar in energy range 70-150 keV. From the comparison of experimental results between He++Ar and He++Ne collision systems, we see that the emission cross sections of the triplet Hel of the former are much larger than those of the latter, when the velocity of incident ion He+ is small. The latter become larger than the former, when the velocity of He+ is greater than 1.0 a.u (2.2×108 cm/s). Therefore, the potential energy defect and the velocity of projectile are very important factors in the electron capture process and there is a competition between them-in collisions.

The influence of neutral winds on He + distributions in the equatorial ionosphere

The effects of F-region neutral winds on the distribution of He + in the equatorial ionosphere have been examined using a theoretical model and an observational data set. It is shown by the model that components of neutral wind in the magnetic meridian up to only 50 m s − can produce He + gradients in the northern and southern sectors of a flux tube that differ by more than 80%. This is associated with interhemisphere transport velocities of He + as large as 15 m s −1 at 800 km. A substantial latitude gradient in the He + distribution across the dip equator also results from the redistribution of He + The changes in the He + concentration at the dip equator and the latitude distribution of He + in response to different neutral wind components is determined from the model and used to construct longitude distributions of He + to compare with observations made at equinox. Good agreement between the calculations and observations is obtained both at the geographic and geomagnetic equators using the relationship between neutral winds, interhemispheric transport velocity and He + concentration derived from the model. If these relationships can be extrapolated to accommodate the different conditions expected during solstice, we can also discuss the He + distributions expected during this season.