Determining the He/H ratio in cool stars presents a fundamental astrophysical challenge. While this ratio is established for hot O and B stars, its extrapolation to cool stars remains uncertain due to the absence of helium lines in their observed spectra. We address this knowledge gap by focusing on the Sun as a representative cool star. We conduct spectroscopic analyses of the observed solar photospheric lines by utilizing a combination of MgH molecular lines and neutral Mg atomic lines including yet another combination of CH and C_2 molecular lines with neutral C atomic lines. Our spectroscopic analyses were further exploited by adopting solar model atmospheres constructed for distinct He/H ratios to determine the solar photospheric helium abundance. The helium abundance is determined by enforcing the fact that for an adopted model atmosphere with an appropriate He/H ratio, the derived Mg abundance from the neutral Mg atomic lines and that from the MgH molecular lines must be the same. Ditto holds for the C abundance derived from neutral C atomic lines and that from CH lines of the CH molecular band and C_2 lines from the C_2 Swan band. The estimated He/H ratio for the Sun is discussed based on the one-dimensional local thermodynamic equilibrium (1D LTE) model atmosphere. The helium abundance (He/H = 0.091(+0.019/+0.014)) obtained for the Sun serves as a critical reference point to characterize the He/H ratio of cool stars across the range in their effective temperature. Using this derived He/H ratio, the solar mass fractions are determined to be X_sun=0.7232(+0.0305/-0.0377), Y_sun=0.2633(+0.0384/-0.0311), and Z_sun=0.0135(+0.0006/-0.0007).
Helioseismic data for solar cycles 23 and 24 have shown unequivocally that solar dynamics changes with solar activity. Changes in solar structure have been more difficult to detect. Basu & Mandel (2004) had claimed that the then available data revealed changes in the HeII ionization zone of the Sun. The amount of change, however, indicated the need for larger than expected changes in the magnetic fields. Now that helioseismic data spanning two solar cycles are available, we have redone the analysis using improved fitting techniques. We find that there is indeed a change in the region around th…
BPS CS 22940-0009 is a helium-rich B-star that shares characteristics with both helium-rich B subdwarfs and extreme helium stars. The optical spectrum of BPS CS 22940-0009 has been analysed from SALT observations. The atmospheric parameters were found to be $T_{\rm eff} = 34970 \pm 370$ K, $\log g/{\rm cm \, s^{-2}} = 4.79 \pm 0.17$, $n_{\rm H}/n_{\rm He} \simeq 0.007$, $n_{\rm C}/n_{\rm He} \simeq 0.007$, $n_{\rm N}/n_{\rm He} \simeq 0.002$, although further improvement to the helium line fits would be desirable. This places the star as a link between the He-sdB and EHe populations in $g$-$T$…
In this paper, we present corrections to the spectroscopic parameters of DB and DBA white dwarfs with -10.0 < log(H/He) < -2.0, 7.5 < log(g) < 9.0 and 12000 K < T_eff < 34000 K, based on 282 3D atmospheric models calculated with the CO5BOLD radiation-hydrodynamics code. These corrections arise due to a better physical treatment of convective energy transport in 3D models when compared to the previously available 1D model atmospheres. By applying the corrections to an existing SDSS sample of DB and DBA white dwarfs, we find significant corrections both for the effective temperature and surface …
Two main models have been developed to explain the mechanisms of release, heating and acceleration of the nascent solar wind, the wave-turbulence-driven (WTD) models and reconnection-loop-opening (RLO) models, in which the plasma release processes are fundamentally different. Given that the statistical observational properties of helium ions produced in magnetically diverse solar regions could provide valuable information for the solar wind modelling, we examine the statistical properties of the helium abundance (A_He) and the speed difference between helium ions and protons (v_alpha,p) for co…
We report the discovery of a new eclipsing EL CVn-type binary, consisting of a $δ$ Sct-type pulsator and a thermally bloated low-mass pre-He white dwarf (WD). Spectroscopy and time-series $BV$ photometry of V1224 Cas were carried out. The spectroscopy reveals a spectral type of A3 for the star. Light-curve modelling indicate that V1224 Cas is a short-period detached system containing a possible low-mass WD with an effective temperature of about 9516 K. Based on the effective temperature and the surface gravity of the A-type primary star from the spectroscopic results, the absolute parameters o…
Toward a Spectroscopic Census of White Dwarfs Within 40 parsecs of the Sun
我们目前的初步调查结果，旨在显着增加光谱确认的白矮星的本地普查的范围和完整性。目前对附近白矮星的普查只完成了大约20秒差距的太阳，一个包括大约130个白矮星的体积，样本太小，无法进行详细的统计分析。这次普查主要是基于对具有非常大自行的恒星的后续调查。我们在这里描述的基础上的一种方法，将导致一个目录的白矮星在40秒差距的太阳和天球赤道以北，从而增加了8倍的北部天空普查的范围。白矮星候选人确定从SUPERBLINK自行数据库，使我们能够调查恒星自行限制mu>40 mas yr-1，同时尽量减少附近物体的运动学偏差。选择标准和距离估计是基于颜色幅度和减少自行图的组合。我们的后续光谱观测活动迄今已发现了193颗新的白矮星，其中我们确认了127颗DA星（包括9颗DA+dM星和4颗磁性星）、1颗DB星、56颗DC星、3颗DQ星和6颗DZ星。我们进行光谱分析的子样本的84个DA，并提供其大气参数。特别是，我们确定了11个新的白矮星的光谱距离在25 pc的太阳，包括5个候选人的D<20 pc的子集。
Several B-type main-sequence stars show chemical peculiarities. A particularly striking class are the $^3$He stars, which exhibit a remarkable enrichment of $^3$He with respect to $^4$He. This isotopic anomaly has also been found in blue horizontal branch (BHB) and subdwarf B (sdB) stars, which are helium-core burning stars of the extreme horizontal branch. Using a hybrid local/non-local thermodynamic equilibrium (LTE/NLTE) approach for B-type stars, we analyzed high-quality spectra of two known $^3$He BHBs and nine known $^3$He sdBs to determine their isotopic helium abundances and $^4$He/$^3…
We present an analysis of all single white dwarf stars known to exhibit spectroscopic signatures of neutral helium line splitting due to the presence of a strong magnetic field. Using state-of-the-art models taking into account the effects of magnetic fields on the synthetic spectra, we determine effective temperatures, surface gravities and masses for the stars in our sample. Our analysis uses data from the second and third Gaia (early) data release, photometric data from diverse surveys such as the Sloan Digital Sky Survey and Pan-STARRS, and archived spectroscopic data. We are able to succe…
A data-driven estimate of the protosolar helium mass fraction
STAR Institute, Université de Liège（列日大学STAR研究所）；Department of Physics, Kurume University（久留米大学物理系）；Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange（蔚蓝海岸大学、蔚蓝海岸天文台、法国国家科学研究中心拉格朗日实验室）；Centre Spatial de Liège, Université de Liège（列日大学空间中心）
Abundance Calculations of Neon Isotopes in the Predicted Lifetime of the Sun
University of Sharjah（沙迦大学）；Sharjah Academy for Astronomy, Space Sciences and Technology（沙迦天文学、空间科学与技术学院）；Arab Union for Astronomy and Space Sciences（阿拉伯天文学与空间科学联盟）；The University of Jordan（约旦大学）
Full velocities and propagation directions of coronal mass ejections inferred from simultaneous full-disk imaging and Sun-as-a-star spectroscopic observations
The study of the elemental composition of stars and galaxies is a key topic for understanding their origin and evolution. In this study, we present the results of the calculation of solar abundances of the isotopes $^{1}$H, $^{4}$He, $^{12}$C, $^{14}$N, $^{15}$O, $^{16}$O, $^{17}$O, and $^{18}$O during the four phases of the solar life; Hydrogen burning, Onset of rapid growth and red giant, Helium burning and Helium exhaustion. The open source package nucnet-tools from the Webnucleo Group in Clemson University, SC, USA was used for this purpose. The results for all isotopes are listed in table…
Atmospheres of RR Lyrae Stars: Hypersonic Shock waves, Helium line detection and Magnetic fields. A few spectra for George Preston on the occasion of his birthday
Role of input atomic data in spectroscopic analyses of the Sun and metal-poor stars
高分辨率恒星光谱的分析在很大程度上依赖于原子数据。这些包括粒子和光子之间各种类型的相互作用的能级、波长、横截面，例如光致电离和碰撞诱导跃迁。量子力学计算提供了这些数据的大部分。在本文中，我描述了在局部热力学平衡（LTE）假设和更一般的非LTE情况下计算晚型恒星的模型大气和谱线形成所需的原子数据。我将重点讨论21 < Z < 29的过渡金属，并讨论是否（以及在哪里）需要更完整和/或准确的原子数据。
The relative abundance of alpha particles with respect to proton, usually expressed as $A_{He}$ = ($n_α/n_p$)*100, is known to respond to solar activity although changes in its behaviour in the last four solar cycles are not known. In this letter, by systematically analysing inter-calibrated $A_{He}$ data obtained from the first Lagrangian point of the Sun-Earth system, we show that $A_{He}$ variations are distinctively different in solar cycle 24 as compared to the last three cycles. The frequency of $A_{He}$ = 2-3% events is significantly higher in slow/intermediate solar winds in cycle 24 a…
White dwarf photospheric parameters are usually obtained by means of spectroscopic or photometric analysis. These results are not always consistent with each other, with the published values often including just the statistical uncertainties. The differences are more dramatic for white dwarfs with helium-dominated photospheres, so to obtain realistic uncertainties we have analysed a sample of 13 of these white dwarfs, applying both techniques to up to three different spectroscopic and photometric data sets for each star. We found mean standard deviations of < $σT_{\mathrm{eff}}$ > = 524 K, < $…
The presence of extreme horizontal branch (EHB) and blue hook stars in some Galactic globular clusters (GGCs) constitutes one of the remaining mysteries of stellar evolution. In this paper, we focus on $ω$ Cen, a peculiar, massive GGC that hosts multiple stellar populations. We use non-LTE model atmospheres to derive atmospheric parameters (Teff, log g and N(He)/N(H)) and spectroscopic masses for 152 EHB stars in the cluster. This constitutes the largest spectroscopic sample of EHB stars ever analyzed in a GGC and represents ~20% of the EHB population of $ω$ Cen. We also search for close binar…
内容：虽然经典模型成功地再现了许多过渡区谱线的强度，但它们预测氦EUV谱线强度比观测值低大约一个数量级。目标：确定氦EUV共振线的相关形成机制，能够解释安静太阳条件下的高强度。方法：利用三维辐射-磁流体动力学模拟模型合成出射光谱并进行研究。数值模拟中自洽地包含了日冕照明以及氢和氦的非平衡电离的影响。结果如下：辐射转移计算导致氦EUV线强度比在经典假设下计算的强度大一个数量级。He I 584的增强强度主要由He II复合级联引起。He II 304和He II 256的增强强度主要由非平衡氦电离引起。结论：分析表明，长期存在的问题，高氦EUV线强度消失时，考虑到光学厚辐射转移和非平衡电离效应。
Statistics of Solar Filament Mass based on CHASE Sun-as-a-star Spectroscopic Observations
Nanjing University（南京大学）；Key Laboratory of Modern Astronomy and Astrophysics, Ministry of Education（现代天文学与天体物理学教育部重点实验室）；Department of Astronomy, Graduate School of Science, Kyoto University（京都大学理学研究科天文学系）；Leibniz Institute for Astrophysics（莱布尼茨天体物理研究所）
The spectroscopic evolution of the symbiotic star AG Draconis. I.The O VI Raman, Balmer, and helium emission line variations during the outburst of 2006-2008
AG Dra是一小群低金属量的S-型共生双星之一，它们与K-型巨星共生，偶尔会发生不明原因的短期爆发。我们的目的是利用红巨星风中的光学拉曼谱线和其他辐射特征来研究白矮星在爆发过程中的行为。我们的目标是确定在一个重大的爆发事件，并研究在一个重大的爆发过程中的紫外线和光学之间的耦合在这个系统中的增益的包络线和风的变化。利用中、高分辨率的地基光谱，并与档案资料中的$FUSE$和$HST/STIS$光谱进行对比，研究了2006年9月以来爆发期间OVI特征和Balmer、He I、He II谱线的演化。到2007年5月，并包括最近的观测（2009年），以研究源的后续演变。的O VI拉曼功能完全消失在高峰期的主要爆发和随后的变化与前十年的报告有很大不同。He I和He II线以及巴耳末线的相位随拉曼特征而变化，但在2006-2008年期间，He I 6678，7065相对于O VI拉曼6825的变化存在双重值，这在以前没有报道过。通过爆发间隔的拉曼特征比的变化是一致的O VI FUV共振风线从白矮星和周围的O $^{+5}$电离区域内的红巨星风引起的膨胀和冷却的白矮星光球的消失。
Solar analogues are important stars to study for understanding the properties of the Sun. Evolutionary modeling, combined with seismic and spectroscopic analysis, becomes a powerful method to characterize stellar intrinsic parameters, such as mass, radius, metallicity and age.However, these characteristics, relevant for other aspects of astrophysics or exoplanetary system physics for example, are difficult to obtain with a high precision and/or accuracy. The goal of this study is to characterize the two solar analogues HD42618 and HD43587, observed by CoRoT. In particular, we aim to infer prec…
Identifying the source of the material within coronal mass ejections (CMEs) and understanding CME onset mechanisms are fundamental issues in solar and space physics. Parameters relating to plasma composition, such as charge states and He abundance (\ahe), may be different for plasmas originating from differing processes or regions on the Sun. Thus, it is crucial to examine the relationship between in-situ measurements of CME composition and activity on the Sun. We study the CME that erupted on 2014 September 10, in association with an X1.6 flare, by analyzing AIA imaging and IRIS spectroscopic…
Direct sampling of interstellar neutral (ISN) atoms close to the Sun enables studies of the very local interstellar medium (VLISM) around the heliosphere. The primary population of ISN helium atoms has, until now, been assumed to reflect the pristine VLISM conditions at the heliopause. Consequently, the atoms observed at 1 au by the Interstellar Boundary Explorer (IBEX) were used to determine the VLISM temperature and velocity relative to the Sun, without accounting for elastic collisions with other species outside the heliopause. Here, we evaluate the effect of these collisions on the primary…
A medium- and high-resolution spectroscopic survey of helium-rich hot subdwarfs is being carried out using the Southern African Large Telescope (SALT). Objectives include the discovery of exotic hot subdwarfs and of sequences connecting chemically-peculiar subdwarfs of different types. The first phase consists of medium-resolution spectroscopy of over 100 stars selected from low-resolution surveys. This paper describes the selection criteria, and the observing, classification and analysis methods. It presents 107 spectral classifications on the MK-like Drilling system and 106 coarse analyses (…
In the present paper, we use Si IV 1393.755 Å spectral line observed by the Interface Region Imaging Spectrograph (IRIS) in the quiet-Sun to determine physical nature of the solar transition region (TR) oscillations. We analyze the properties of these oscillations using wavelet tools (e.g., power, cross-power, coherence, and phase difference) along with the stringent noise model (i.e., power-law + constant). We estimate the period of the intensity and Doppler velocity oscillations at each chosen location in the quiet-Sun (QS) and quantify the distribution of the statistically significant power…
Despite the fact that the initial helium abundance is an essential ingredient in modelling solar-type stars, its abundance in these stars remains a poorly constrained observational property. This is because the effective temperature in these stars is not high enough to allow helium ionization, not allowing any conclusions on its abundance when spectroscopic techniques are employed. To this end, stellar modellers resort to estimating the initial helium abundance via a semi-empirical helium-to-heavy element ratio, anchored to the the standard Big Bang nucleosynthesis value. Depending on the choi…
Ultracompact accreting binary systems each consist of a stellar remnant accreting helium-enriched material from a compact donor star. Such binaries include two related sub-classes, AM CVn-type binaries and helium cataclysmic variables, in both of which the central star is a white dwarf. We present a spectroscopic and photometric study of six accreting binaries with orbital periods in the range of 40--70 min, including phase-resolved VLT spectroscopy and high-speed ULTRACAM photometry. Four of these are AM CVn systems and two are helium cataclysmic variables. For four of these binaries we are a…
Orbital decay mechanisms argue that double white dwarf mergers are inevitable, but extremely rare. Whilst some mergers result in explosions, the survivors re-ignite helium and burn brightly for tens of thousands or millions of years. Candidate survivors include extreme helium stars, R CrB variables and various classes of helium-rich subluminous star. Nuclear waste on the survivors' surfaces provides evidence of the stars' nuclear history prior to and their nucleosynthesis during the merger. Extensive and deep spectroscopic surveys offer rich prospects for future discoveries.
