Helium Abundance Research Articles

New Determinations of the Surface Abundances of HD 1280

New abundances for several chemical elements are measured for HD 1280 using updated atomic data and spectrum synthesis. The abundances of calcium and scandium are solar whereas strontium is mildly overabundant. The abundances of helium, magnesium, titanium, chromium, manganese, iron and barium are in good agreement with a former abundance analysis. This reinforces the status of HD 1280 as a normal rapidly rotating A star with essentially normal abundances of elements lighter than iron and mild overabundances of heavier elements which may actually have been present in the environment where the star was born.

The Influence of Disk Composition on the Evolution of Stars in the Disks of Active Galactic Nuclei

Disks of gas accreting onto supermassive black holes, powering active galactic nuclei (AGN), can capture stars from nuclear star clusters or form stars in situ via gravitational instability. The density and thermal conditions of these disks can result in rapid accretion onto embedded stars, dramatically altering their evolution in comparison to stars in the interstellar medium. Theoretical models predict that, when subjected to sufficiently rapid accretion, fresh gas replenishes hydrogen in the cores of these stars as quickly as it is burned into helium, reaching a quasi-steady state. Such massive, long-lived (“immortal”) stars may be capable of dramatically enriching AGN disks with helium, and would increase the helium abundance in AGN broad-line regions relative to that in the corresponding narrow-line regions and hosts. We investigate how the helium abundance of AGN disks alters the evolution of stars embedded therein. We find, in agreement with analytical arguments, that stars at a given mass are more luminous at higher helium mass fractions, and so undergo more radiation-driven mass loss. We further find that embedded stars tend to be less massive in disks with higher helium mass fractions, and that immortal stars are less common in such disks. Thus, disk composition can alter the rates of electromagnetic and gravitational wave transients as well as further chemical enrichment by embedded stars.

On the Question of the Primordial Helium Abundance by the RRL Observations in Orion A

Radio recombination lines comprise a powerful tool for studying the interstellar medium. One of the important tasks is to measure the primordial abundance of helium formed during the primordial nucleosynthesis of the Universe, which, in turn, allows us to verify the conclusions of the Standard Cosmological Model. The Orion A nebula is an interesting object for studying this problem. Previously, we found that, in this HII region, the region of ionized helium is smaller than the region of ionized hydrogen. Therefore, the actual helium abundance, n(He)/n(H), is not less than the maximum measured value of y+ = n(He+)/n(H+). This makes it possible to obtain restrictions on the primordial helium abundance. This article presents new observations of radio recombination lines in Orion A at a wavelength of 13 mm. It was found that the maximum value of y+ is in the range 10.03–11.55%. Therefore, it can be expected that the primordial helium abundance (Yp, He/H mass ratio) can be not less than ≈24.93–29.40%, which allows deviations from the conclusions of the Standard Model; for instance, it allows the presence of unknown light particles during primordial nucleosynthesis. Observations of doubly ionized helium in Orion A and the planetary nebula NGC 7027 were also made. It was found that the contribution of doubly ionized helium, y++ = n(He++)/n(H+), is 7 × 10–4 in Orion A and 2.7(±1.3)% for NGC 7027. Estimates of the electron temperature are also made. In particular, for NGC7027, it was found that Тe ≈ 11 900–12 300 K, which is higher than for the HII regions.

On the Question of the Primordial Helium Abundance by the RRL Observations in Orion A

On the Question of the Primordial Helium Abundance by the RRL Observations in Orion A

Mirror dark sector solution of the Hubble tension with time-varying fine-structure constant

We explore a model introduced by Cyr-Racine, Ge, and Knox (arXiv:2107.13000(2)) that resolves the Hubble tension by invoking a ``mirror world" dark sector with energy density a fixed fraction of the ``ordinary" sector of Lambda-CDM. Although it reconciles cosmic microwave background and large-scale structure observations with local measurements of the Hubble constant, the model requires a value of the primordial Helium mass fraction that is discrepant with observations and with the predictions of Big Bang Nucleosynthesis (BBN). We consider a variant of the model with standard Helium mass fraction but with the value of the electromagnetic fine-structure constant slightly different during photon decoupling from its present value. If $\alpha$ at that epoch is lower than its current value by $\Delta \alpha \simeq -2\times 10^{-5}$, then we can achieve the same Hubble tension resolution as in Cyr-Racine, et al. but with consistent Helium abundance. As an example of such time-evolution, we consider a toy model of an ultra-light scalar field, with mass $m <4\times 10^{-29}$ eV, coupled to electromagnetism, which evolves after photon decoupling and that appears to be consistent with late-time constraints on $\alpha$ variation and the weak equivalence principle.

Primordial lepton asymmetries in the precision cosmology era: Current status and future sensitivities from BBN and the CMB

Using a new sample of extremely metal poor systems, the EMPRESS survey has recently reported a primordial helium abundance that is $3\sigma$ smaller than the prediction from the standard big bang nucleosynthesis (BBN) scenario. This measurement could be interpreted as a hint for a primordial lepton asymmetry in the electron neutrino flavor. Motivated by the EMPRESS results, we present a comprehensive analysis of the lepton asymmetry using measurements of the abundances of primordial elements, along with cosmic microwave background (CMB) data from Planck. Assuming that there is no dark radiation in our Universe, we find an electron neutrino chemical potential $\xi_{\nu_e} = 0.043 \pm 0.015$, which deviates from zero by $2.9\sigma$. If no assumption is made on the abundance of dark radiation in the Universe, the chemical potential is $\xi_{\nu_e} = 0.046 \pm 0.021$, which deviates from zero by $2.2\sigma$. We also find that this result is rather insensitive to the choice of nuclear reaction rates. If the true helium abundance corresponds to the EMPRESS central value, future CMB observations from the Simons Observatory and CMB-S4 will increase the significance for a nonzero lepton asymmetry to $4\sigma$ and $5\sigma$ respectively, assuming no dark radiation, or to $3\sigma$ when no assumption is made on the abundance of dark radiation.

New Determinations of the Surface Abundances of HD 1909: Paper I: The Light Elements (from Helium to Sulfur)

New abundances for the elements helium to sulfur are derived for the brightest member of the spectroscopic binary HD 1909 using updated atomic data and spectrum synthesis. The majority of these elements are underabundant, the depletion factors appear in parenthesis: helium (0.02 times the solar helium abundance), carbon and oxygen (0.40 ⊙), neon (0.15 ⊙), magnesium (0.45 ⊙), aluminum (0.02 ⊙). silicon (0.50 ⊙) and sulfur (0.35 ⊙). In contrast, phosphorus is overabundant by a factor of 12.5 ⊙ and the silicon–phosphorus–sulfur triad is inverted. The lines of the companion are redshifted by about +122.5 km s−1 with respect to the B9 Hg star in the spectrum analyzed here.

The Deep Atmospheric Composition of Jupiter from Thermochemical Calculations Based on Galileo and Juno Data

The deep atmosphere of Jupiter is obscured beneath thick clouds. This causes direct observations to be difficult, and thermochemical equilibrium models fill in the observational gaps. This research uses Galileo and Juno data together with the Gibbs free energy minimization code GGchem to update the gas phase and condensation equilibrium chemistry of the deep atmosphere of Jupiter down to 1000 bars. Specifically, the Galileo data provides helium abundances and, with the incorporated Juno data, we use new enrichment values for oxygen, nitrogen, carbon and sulphur. The temperature profile in Jupiter’s deep atmosphere is obtained following recent interior model calculations that fit the gravitational harmonics measured by Juno. Following this approach, we produced pressure–mixing ratio plots for H, He, C, N, O, Na, Mg, Si, P, S and K that give a complete chemical model of all species occurring to abundances down to a 10−20 mixing ratio. The influence of the increased elemental abundances can be directly seen in the concentration of the dominant carriers for each element: the mixing ratio of NH3 increased by a factor of 1.55 as compared with the previous literature, N2 by 5.89, H2O by 1.78, CH4 by 2.82 and H2S by 2.69. We investigate the influence of water enrichment values observed by Juno on these models and find that no liquid water clouds form at the oxygen enrichment measured by Galileo, EH2O = 0.47, while they do form at higher water abundance as measured by Juno. We update the mixing ratios of important gas phase species, such as NH3, H2O, CO, CH4 and H2S, and find that new gas phase species, such as CN−, (NaCN)2, S2O and K+, and new condensates, namely H3PO4 (s), LiCl (s), KCl (s), NaCl (s), NaF (s), MgO (s), Fe (s) and MnS (s), form in the atmosphere.

Photochemical Hazes Can Trace the C/O Ratio in Exoplanet Atmospheres

Photochemical hazes are suspected to obscure molecular features, such as water, from detection in the transmission spectra of exoplanets with atmospheric temperatures <800 K. The opacities of laboratory produced organic compounds (tholins) from Khare et al. have become a standard for modeling haze in exoplanet atmospheres. However, these tholins were grown in an oxygen-free, Titan-like environment that is very different from typical assumptions for exoplanets, where C/O ∼ 0.5. This work presents the 0.13–10 μm complex refractive indices derived from laboratory transmission measurements of tholins grown in environments with different oxygen abundances. With the increasing uptake of oxygen, absorption increases across the entire wavelength range, and a scattering feature around 6 μm shifts toward shorter wavelengths and becomes more peaked around 5.8 μm, due to a C = O stretch resonance. Using GJ 1214 b as a test case, we examine the transmission spectra of a sub-Neptune planet with C/O ratios of solar, 1, and 1000 to evaluate the effective differences between our opacities and those of Khare. For an atmosphere with solar hydrogen and helium abundances, we find a difference of 200–1500 ppm, but for high-metallicity (Z = 1000) environments, the difference may only be 20 ppm. The 1–2 μm transmission data for GJ 1214 b rule out the Titan-like haze model, and are more consistent with C/O = 1 and C/O = solar haze models. This work demonstrates that using haze opacities that are more consistent with underlying assumptions about bulk atmospheric composition are important for building self-consistent models that appropriately constrain the atmospheric C/O ratio, even when molecular features are obscured.

The Abundances of Helium, Magnesium and Phosphorus in the Atmosphere of HD144844

Abundances of helium and magnesium are derived in LTE for the B9 Mn P Ga star HD 144844 using the group of He i lines near 4470.40 Å and the Mg ii triplet at 4481.22 Å. Both elements are found to be very underabundant, about 2% of the solar helium and magnesium abundances. The profile of the Mg ii line at 4481.22 Å clearly shows two components and confirms that this star is a double-lined spectroscopic binary. The synthesis of three P ii lines at 6024.18, 6034.04 and 6043.88 Å yields phosphorus abundances from 150 up to 200 times the solar phosphorus abundance. A NLTE synthesis is necessary to derive more accurate abundances.

Investigation of Unusual Activities of the Universe Concerning Solar and Terrestrial Context

A controlled thermonuclear fusion reaction of the Sun appears to be a remarkable evidence of the existence of a planet in the outer space. A microwave background of radiation of a planet in the outer space subjected to white dwarf plasma becomes relevant to the case of a temperature at 0⁰c. Since singularity collapse concerning a Hot Big Bang, the edge of space- time fails. Irregular change of galaxies deals with a vacuum to exhibit spiral radio galaxies permeated by magnetic pressure. The expansion of universe can be extended rigorously to raise its temperature with the growing of a magnetic field as the singularity collapses at the point at infinity and the universe will become fall into ice as the temperature becomes true. Indeed, the configuration of the Sun leads to supernova explosion concerning the abundance of helium to become a neutron star.

Effects of rotation on the spectroscopic observables of massive stars

Context. Rotation is ubiquitous among massive stars and with rotation comes a deformation to the surface geometry. This, in turn leads to alterations in the distribution of parameters across the surface including surface gravity, temperature, and ionization balance of the surface elements. These 3D effects are often neglected when analyzing the spectra of rapidly rotating massive stars. Aims. We aim to determine whether neglecting the 3D deformations resulting from rapid rotation has an impact on the final spectroscopic observables, and if so to what degree. Methods. Using the SPAMMS code, we generated a grid of synthetic spectra that account for the 3D geometry of rapidly rotating stars and compared them to synthetic spectra generated assuming spherical geometry. Using equivalent width (EW) and full width half maximum (FWHM) measurements as proxies, we determined how the measured temperature, helium abundance, and projected rotation rates of individual lines in different ionization states vary with rotation rates and inclinations. Results. We find that the 3D geometry can have a significant impact on the measured parameters. We show that the temperature is highly dependent on both the rotation rate and the inclination, and that the same system viewed at different inclinations can have measured temperatures that differ by as much as 10%. We also find that the helium abundance can be underestimated by as much as 60% and that lines in different ionization states can have measurable differences in rotation rates. We demonstrate that these differences in rotation rates can be seen in observed data and show that this could allow for an inclination-independent measurement of the rotational velocity. Conclusions. Our results indicate that neglecting the 3D effects of rotation can cause significant biases in the measured spectroscopic parameters and that in many cases, the measured values are more than 3σ away from the true values.

The Solar Cycle Dependence of In Situ Properties of Two Types of Interplanetary CMEs during 1999–2020

Generally, in situ parameters of interplanetary coronal mass ejections (ICMEs) are analyzed as a whole, or ICMEs are classified by speed or whether they are with and without magnetic clouds. Zhai and colleagues found that ICMEs with and without flares can be extracted only by the average charge states of iron (Q Fe). In the present study, the ICMEs are categorized into two types, flare CMEs (FCs) and nonflare CMEs (NFCs) by the Q Fe. We find that the occurrence rates of FCs and NFCs are both decreased from solar maximum to minimum. The occurrence rates and proportions of FCs are both higher in solar cycle 23 than in solar cycle 24. In contrast, the occurrence rates of NFCs are almost the same during the two solar cycles. The durations of FCs are longer than those of NFCs. The fractions of FCs and NFCs that are associated with magnetic clouds (MCs) or magnetic field direction rotation evidence are 73% and 69%, respectively. The speed, Q Fe, O7+/O6+, helium abundance (A He), and first ionization potential bias are all higher for FCs than for NFCs. The above parameters inside NFCs and solar wind are almost the same. The solar cycle dependence of the parameters inside NFCs is more clear than that inside FCs. The statistical results demonstrate that the material sources of FCs are not completely the same as those of NFCs. Part of the material inside FCs should come from the lower atmosphere where the A He is higher. The statistical results indicate that all CMEs are associated with flux ropes on the Sun.

Multiple Stellar Populations of Globular Clusters from Homogeneous Ca–CN–CH–NH Photometry. VII. Metal-poor Populations in 47 Tucanae (NGC 104)* * Based on observations made with the Cerro Tololo Inter-American Observatory (CTIO) 1 m telescope, which is operated by the SMARTS consortium. † †This work presents results from the European Space Agency space mission Gaia. Gaia data are being processed by the

We present new large field-of-view (∼1°×1°) Ca-CN photometry of the prototypical metal-rich globular cluster 47 Tucanae (NGC 104). Our results are the following. (1) The populational number ratios of the red giant branch (RGB) and red horizontal branch (RHB) are in excellent agreement: n(CN-w):n(CN-s) = 30:70 (±1–2), where the CN-w and CN-s stand for the CN-weak and CN-strong populations, respectively. Both the CN-s RGB and RHB populations are more centrally concentrated than those of CN-w populations are. (2) Our photometric metallicities of individual RGB stars in each population can be well described by bimodal distributions with two metallicity peaks, [Fe/H] ∼−0.72 and −0.92 dex, where the metal-poor components occupy ∼13% of the total RGB stars. The metal-poor populations are more significantly centrally concentrated than the metal-rich populations, showing a similar result that we found in M3. (3) The RGB bump V magnitudes of individual populations indicate that there is no difference in the helium abundance between the two metal-poor populations, while the helium enhancement of ΔY ∼0.02–0.03 is required between the the two metal-rich populations. (4) The RHB morphology of 47 Tuc appears to support our idea of the bimodal metallicity distribution of the cluster. We suggest that 47 Tuc could be another example of merger remnants of two globular clusters, similar to M3 and M22.

Isochrone fitting of Galactic globular clusters – IV. NGC 6362 and NGC 6723

Abstract We present new isochrone fits to the colour–magnitude diagrams of the Galactic globular clusters NGC 6362 and NGC 6723. We utilize 22 and 26 photometric filters for NGC 6362 and NGC 6723, respectively, from the ultraviolet to mid-infrared using data sets from Hubble Space Telescope, Gaia, unWISE, and other photometric sources. We use models and isochrones from the Dartmouth Stellar Evolution Database (DSED) and Bag of Stellar Tracks and Isochrones (BaSTI) for α-enhanced [α/Fe] = +0.4 and different helium abundances. The metallicities [Fe/H] = −1.04 ± 0.07 and −1.09 ± 0.06 are derived from the red giant branch slopes in our fitting for NGC 6362 and NGC 6723, respectively. They agree with spectroscopic estimates from the literature. We find a differential reddening up to ΔE(B − V) = 0.13 mag in the NGC 6723 field due to the adjacent Corona Australis cloud complex. We derive the following for NGC 6362 and NGC 6723, respectively: distances 7.75 ± 0.03 ± 0.15 (statistic and systematic error) and 8.15 ± 0.04 ± 0.15 kpc; ages 12.0 ± 0.1 ± 0.8 and 12.4 ± 0.1 ± 0.8 Gyr; extinctions AV = 0.19 ± 0.04 ± 0.06 and 0.24 ± 0.03 ± 0.06 mag; reddenings E(B − V) = 0.056 ± 0.01 ± 0.02 and 0.068 ± 0.01 ± 0.02 mag. DSED provides systematically lower [Fe/H] and higher reddenings than BaSTI. However, the models agree in their relative estimates: NGC 6723 is 0.44 ± 0.04 kpc further, 0.5 ± 0.1 Gyr older, ΔE(B − V) = 0.007 ± 0.002 more reddened, and with 0.05 ± 0.01 dex lower [Fe/H] than NGC 6362. The lower metallicity and greater age of NGC 6723 with respect to NGC 6362 explain their horizontal branch morphology difference. This confirms age as the second parameter for these clusters. We provide lists of the cluster members from the Gaia Data Release 3.

Models for metal-poor stars with different initial abundances of C, N, O, Mg, and Si − III. Grids of isochrones for −2.5 ≤ [Fe/H] ≤ −0.5 and helium abundances Y = 0.25 and 0.29 at each metallicity

ABSTRACT Stellar evolutionary tracks for $0.12 \le {\cal M}/{\cal M_{\odot }}\le 1.0$ have been computed for each of several variations in the abundances of C, N, and O, assuming mass-fraction helium abundances Y = 0.25 and 0.29, and 11 metallicities in the range −2.5 ≤ [Fe/H] ≤ −0.5, in 0.2-dex increments. Such computations are provided for mixtures with [O/Fe] between +0.4 and +0.8, for different C:N:O ratios at a fixed value of [CNO/Fe] and for enhanced C. Computer codes are provided to interpolate within these grids to produce isochrones for ages ${\gtrsim}7$ Gyr and to generate magnitudes and colours for many broad-band filters using bolometric corrections based on MARCS model atmospheres and synthetic spectra. The models are compared with (i) similar computations produced by other workers, (ii) observed UV, optical, and IR colour-magnitude diagrams (CMDs), (iii) the effective temperatures, (V − IC)0 and (V − KS)0 colours of Pop. II stars in the solar neighbourhood, and (iv) empirical data for the absolute magnitude of the tip of the red-giant branch (TRGB). The isochrones are especially successful in reproducing the observed morphologies of optical CMDs and in satisfying the TRGB constraints. They also fare quite well in explaining the IR colours of low-mass stars in globular clusters, indicating that they have [O/Fe] ≈ +0.6, though some challenges remain.

Rotating Solar Models in Agreement with Helioseismic Results and Updated Neutrino Fluxes

Standard solar models (SSMs) constructed in accordance with old solar abundances are in reasonable agreement with seismically inferred results, but SSMs with new low-metal abundances disagree with the seismically inferred results. The constraints of neutrino fluxes on solar models exist in parallel with those of helioseismic results. The solar neutrino fluxes were updated by the Borexino Collaboration. We constructed rotating solar models with new low-metal abundances where the effects of enhanced diffusion and convection overshoot were included. A rotating model using OPAL opacities and the Caffau abundance scale has better sound-speed and density profiles than the SSM with the old solar abundances and reproduces the observed p-mode frequency ratios r 02 and r 13. The depth and helium abundance of the convection zone of the model agree with the seismically inferred ones at the level of 1σ. The updated neutrino fluxes are also reproduced by the model at the level of 1σ. The effects of rotation and enhanced diffusion not only improve the model’s sound-speed and density profiles but also bring the neutrino fluxes predicted by the model into agreement with the detected ones. Moreover, the calculations show that OP may underestimate opacities for the regions of the Sun with T ≳ 5 × 106 K by around 1.5%, while OPAL may underestimate opacities for the regions of the Sun with 2 × 106 K ≲ T ≲ 5 × 106 K by about 1%–2%.

Dynamo Simulations of Jupiter's Magnetic Field: The Role of Stable Stratification and a Dilute Core

AbstractUnderstanding Jupiter's present‐day interior structure and dynamics is key to constraining planetary accretion models. In particular, the extent of stable stratification (i.e., non‐convective regions) in the planet strongly influences long‐term cooling processes, and may record primordial heavy element gradients from early in a planet's formation. Because the Galileo entry probe measured a subsolar helium abundance, Jupiter interior models often invoke an outer stably stratified region due to helium rain. Additionally, Juno gravity data suggest a deeper, potentially stratified dilute core extending halfway through the planet. However, fits to Jupiter's gravitational data are non‐unique, and outstanding uncertainty over the equations of state for hydrogen and helium remain. Here, we use high‐resolution numerical magnetohydrodynamic simulations of Jupiter's magnetic field to place constraints on the extent of stable stratification within the planet. We find that compared to traditional interior models, an upper stably stratified layer between 0.9 and 0.95 Jupiter radii (RJ) helps to explain both Jupiter's dipolar magnetic field and zonal winds. In contrast, an extended dilute core that is entirely stably stratified (no convective layers) yields significantly worse fits to both. However, our models with extended deep stratification still generate dipolar magnetic fields if an upper stratified region is also present. Overall, we find that a planet with a dilute core i.e., strongly stably stratified is increasingly challenging to reconcile with Jupiter's magnetic field and winds. Thus if a dilute core is present, alternative modalities such as a fully convective dilute core, a complex multilayered interior structure, or double diffusive convection may be required.

Helium Abundance Decrease in ICMEs in 23–24 Solar Cycles

Based on the OMNI database, the influence of the solar activity decrease in solar cycles (SCs) 23–24 on the behavior of the relative helium ions abundance Nα/Np inside interplanetary coronal mass ejections (ICMEs) is investigated. The dependences of the helium abundance on the plasma and interplanetary magnetic field parameters in the epoch of high solar activity (SCs 21–22) and the epoch of low activity (SCs 23–24) are compared. It is shown that Nα/Np significantly decreased in SCs 23–24 compared to SCs 21–22. The general trends of the dependences have not changed with the change of epoch, but the helium abundance dependences on some parameters (for example, the magnitude of the interplanetary magnetic field) have become weaker in the epoch of low activity than they were in the epoch of high activity. In addition, the dependence of the helium abundance on the distance from spacecraft to the ICME axis was revealed; the clearest dependence is observed in magnetic clouds. The Nα/Np maximum is measured at the minimum distance, which confirms the hypothesis of the existence of a helium-enriched electric current inside an ICME.

Dynamics of He++ Ions at Interplanetary and Earth’s Bow Shocks

Experimental investigations of the fine plasma structure of interplanetary shocks are extremely difficult to conduct due to their small thickness and high speed relative to the spacecraft. We studied the variations in the parameters of twice-ionized helium ions (4He++ ions or α-particles) in the solar wind plasma during the passage of interplanetary shocks and Earth’s bow shock. We used data with high time resolution gathered by the BMSW (Bright Monitor of Solar Wind) instrument installed on the SPEKTR-R satellite, which operated between August 2011 and 2019. The MHD parameters of He++ ions (the bulk velocity Vα, temperature Tα, absolute density Nα, and helium abundance Nα/Np) are analyzed for 20 interplanetary shocks and compared with similar parameters for 25 Earth bow shock crossings. Measurements from the WIND, Cluster, and THEMIS satellites were also analyzed. The correlations in the changes in helium abundance Nα/Np with the parameters βi, θBn, and MMS were investigated. The following correlation between Nα/Np and the angle θBn was found: the lower the value of θBn, the greater the drop in helium abundance (Nα/Np) falls behind the IP shock front. For Earth’s bow shock crossings, we found a significant increase in the helium abundance (Nα/Np) in quasi-perpendicular events.