Mira stars are popular with amateur astronomers because they are generally bright and their pulsations produce large changes in brightness. This also means they are eminently suitable to study using spectroscopy. We report here on spectroscopic observations of five Mira stars: RY Cep, SU Cam, T Cep, V667 Cas and OR Cep. We describe the lifecycle of a Mira star and explain how the carbon-oxygen balance in its atmosphere determines its spectral classification. Atmospheric pulsations in these stars produce shocks which generate Balmer emission. We present graphically their different spectral behaviours and development of emission lines.
Miras are fascinating stars. A kappa-mechanism in their atmosphere drives pulsations which produce changes in their photometric brightness, apparent spectral type and effective temperature. These pulsations also drive the formation of Balmer emission lines in the spectrum. This behaviour can be observed and investigated with small telescopes. We report on a three-year project combining spectroscopy and photometry to analyse the behaviour of Mira stars SU Cam and RY Cep, and describe how their brightness, colour, spectral type, effective temperature and Balmer emission vary over four pulsation …
The spectroscopic evolution of the symbiotic-like recurrent nova V407 Cygni during its 2010 outburst. II. The circumstellar environment and the aftermath
Asymptotic Giant Branch (AGB) stars are major contributors of cosmic dust to the universe. Typically, dust around AGB stars is investigated via radiative transfer (RT) modeling, or via simple deconstruction of observed spectra. However, methodologies applied vary. Using archival spectroscopic, photometric, and temporal data for the archetypal dusty star, Mira, we identify its circumstellar silicate dust grains. This is achieved by matching the positions and widths of observed spectral features with laboratory data. To do this comparison properly, it is necessary to account for the continuum em…
Mira Variable Stars From LAMOST DR4 Data: Emission Features, Temperature Types, and Candidate Selection
基于广泛的光谱研究的光度确认样本的Mira变量，我们发现之间的关系相对巴耳末发射线强度和光谱温度富O的Mira星。当恒星从M0冷却到M10时，$F_{\rm Hδ}/F_{\rm Hγ}$的通量比从小于1增加到5，这可能是由于在最深的冲击波发射区域上方增加TiO吸收。我们还讨论了我们的Mira样本星的Balmer发射线的等效宽度和光度光度相位之间的关系。利用我们的291个Mira光谱作为参考模板，从LAMOST DR 4星表中新识别出191个Mira候选者。我们总结的标准，通过选择米拉候选人的发射线指数和分子吸收带的基础上。这种放大的光谱样本的Mira变量有可能大大有助于我们的知识的Mira恒星的光学性质，并将促进这些晚型，长周期变量的进一步研究。
We analyzed the light curves of 165 AGB variables, mostly Miras, in the sky area centered between M16 and M17 (l=16, b=0), using the OGLE GVS database in the I_C band. Comparison with the published light curves, derived about 50 years earlier by P.~Maffei using Kodak I-N photographic plates, allowed us to find no significant period changes in any star. Remarkably, a few stars of the sample appear to have substantially changed their average luminosity, the most striking case being KZ Ser. We provide a better identification for three stars: IX Ser, NSV 10522, and NSV 10326, all of them being Mir…
In a shallow near-infrared survey of the dwarf Irregular galaxy, NGC 3109, near the periphery of the Local Group, we have found eight Mira variables, seven of which appear to be oxygen-rich (O-Miras). The periods range from about 430 days to almost 1500 days. Because of our relatively bright limiting magnitude, only 45 of the more than 400 known carbon stars were measured, but none was found to be a large amplitude variable. One of the Miras may be an unrecognised C star. Five of the O-Miras are probably hot-bottom burning stars considering that they are brighter than expected from the period-…
An observational study of dust nucleation in Mira ($o$ Ceti): I. Variable features of AlO and other Al-bearing species
尘埃是由冷巨星有效地产生的，但无机尘埃的凝结却知之甚少。目的：确定并描述Mira（鲸鱼座$o$）星周气体中含铝物质的特征，以阐明它们在Al $_2$ O $_3$尘埃产生中的作用。研究方法：在（亚）毫米、远红外和光学波长下的多历元谱线观测，包括：用ALMA探测恒星附近~30 mas处的气体分布的地图; 2013-2015年用ALMA、APEX和Herschel进行的观测，用于研究含铝分子旋转线的周期和周期间变化;光学记录早在1965年，以检查电子跃迁的变化，随着时间的推移，从几天到几十年;和速度测量和激发分析的光谱特征，约束的物理参数的气体。结果如下：三个双原子分子AlO，AlOH和AlH，和原子Al I是Mira中主要的可观察到的铝物种，尽管铝的重要部分可能存在于尚未确定的其他物种中。AlO（可能是Al $_2$ O $_3$的直接前体）的（亚）毫米和光学特征的强烈不规则变化表明激发条件发生了重大变化，或者可能与恒星中的冲击有关的丰度变化。AlO的不均匀分布可能影响沙尘产生的时空特征。结论：我们无法从气体中定量追踪铝的消耗，但丰富的观测材料限制了随时间变化的化学网络。未来的改进应包括更高的铝氧化物的光谱特性，协调观测的灰尘和气体物种在不同的可变阶段，以及工具，以获得丰富的冲击激发气体。
We present a detailed analysis of five bright spectroscopic binary systems (HD 18665, HD 27131, HD 171852, HD 215550, HD 217427) that have orbital periods of P < 500 days. We determined the complete set of orbital parameters using the toolkit RadVel by analyzing the observed radial velocity curves. To study the properties of the five systems, we also analyzed the intermediate resolution spectra (R = 20,000) observed with the TIGRE telescope and determined the stellar parameters of the primary stars using the toolkit iSpec. With Gaia Early Data Release 3 parallaxes, a correction for interstella…
The spectroscopic and photometric analysis of sample Am stars are carried out to determine the stellar characteristics of each studied star. The CCD photometric analysis of HD 98851 and HD 207561 show clear evidence of pulsation variability of 1.55 hr and 5.8 min respectively. Similarly, a clear evidence of the photometric variability is also found for an Am star HD 73045 which is likely to be pulsating in nature with a period of about 36-min. We are also found dissimilar behaviour of elemental abundances of various ions for HD 113878 and HD 118660. The basic stellar parameters (mass, luminosi…
The photometric analysis of sample Am stars is carried out to determine the stellar characteristics and to constrain the stellar dynamics. The spectroscopic analysis of the studied Am stars confirms their general characteristics of Am stars. The available data on elemental abundances for HD 113878 and HD 118660 have shown different characteristics during different epochs of observations. The basic stellar parameters (mass, luminosity, radius, life time, distance, proper-motion, etc.) are also determined to identify the stellar habitat zones for earth like exoplanet. Such information is importa…
A Five-year Spectroscopic and Photometric Campaign on the Prototypical alpha Cygni Variable and A-type Supergiant Star Deneb
天津四通常被认为是典型的A型超巨星，是银河系中视觉上最明亮的恒星之一。A型超巨星是潜在的河外距离指示器，但在这种技术被认为可靠之前，这些恒星的变化需要更好地表征。我们分析了在1997年至2001年的五年跨度中获得的天津四的339个高分辨率阶梯光谱，以及在同一时间范围内获得的370个Stromgren光度测量。我们的光谱分析包括动态光谱的H-α轮廓，H-α等效宽度，和径向速度从Si II 6347，6371测量。时间序列分析表明，没有明显的周期性行为，通过多个观测季节进行，虽然我们发现了一个可疑的40天的时间在两个，非连续的观测季节。光度和径向速度数据集之间的一些相关性，并建议径向脉动在两个时代。没有相关性之间的变化的H-α配置文件和径向速度或光度。Lucy（1976）发现天津四是一颗长周期单线光谱双星的证据，但我们的数据集没有证据表明双星伴星会导致径向速度变化。
New infrared spectra of 33 Galactic carbon stars from FORCAST on SOFIA reveal strong connections between stellar pulsations and the dust and molecular chemistry in their circumstellar shells. A sharp boundary in overall dust content, which predominantly measures the amount of amorphous carbon, separates the semi-regular and Mira variables, with the semi-regulars showing little dust in their spectra and the Miras showing more. In semi-regulars, the contribution from SiC dust increases rapidly as the overall dust content grows, but in Miras, the SiC dust feature grows weaker as more dust is adde…
A photometric and spectroscopic investigation is performed on five W Ursae Majoris eclipsing binaries (EWs) J015818.6+260247 (hereinafter as J0158b), J073248.4+405538 (hereinafter as J0732), J101330.8+494846 (hereinafter as J1013), J132439.8+130747 (hereinafter as J1324) and J152450.7+245943 (hereinafter as J1524). The photometric data are collected with the help of the 1.3\,m Devasthal Fast Optical Telescope (DFOT), the 1.04\,m Sampurnanand Telescope (ST) and the TESS space mission. The low-resolution spectra of the 4\,m Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) are u…
In a well-aimed search based on the recently published Gaia~DR2 radial velocity data and performed with the robotic TIGRE telescope, we have discovered 19 bright ($m_V<7.66$~mag) spectroscopic binary stars. We present the radial velocity curves of five of these stars (HD~20656, HD~27259, HD~98812, HD~150600, HD~193082) with periods of $P<365$~days. We determined their orbital parameters using the toolkit RadVel. The complete set of basic stellar parameters (effective temperature, surface gravity, metallicity, mass and age) of the primary stars are determined using the observed intermediate res…
We present results from long-term optical photometric and spectroscopic observations of 5 pre-main sequence stars, located in the vicinity of the bight nebula NGC 7129. We obtained UBVRI photometric observations in the field centered on the star V391 Cep, north-west of the bright nebula NGC 7129. Our multicolor CCD observations spanned the period from February 1998 to November 2016. At the time of our photometric monitoring, a total of thirteen medium-resolution optical spectra of the stars were obtained. The results from our photometric study show that all stars exhibit strong variability in …
LAMOST J202629.80+423652.0 has been recently classified as a new symbiotic star containing a long-period Mira, surrounded by dust (D-type) and displaying in the optical spectra high ionization emission lines, including the Raman-scattered OVI at 6825 Ang. We have observed LAMOST J202629.80+423652.0 photometrically in the BVRI bands and spectroscopically over the 3500-8000 Ang range. We have found it to be a normal G8IV sub-giant star, deprived of any emission line in its spectrum, and reddened by E(B-V)=0.35 mag. Combining our photometry with data from all-sky patrol surveys, we find LAMOST J2…
In this paper we present a spectroscopic study of six double-lined binaries, five of which were recently discovered in a high-resolution spectroscopic survey of optical counterparts of stellar X-ray sources. Thanks to high-resolution spectra acquired with CAOS spectropolarimeter during seven years, we were able to measure the radial velocities of their components and determine their orbital elements. We have applied our code COMPO2 to determine the spectral types and atmospheric parameters of the components of these spectroscopic binaries and found that two of these systems are composed of mai…
美国航天局的开普勒太空望远镜提供了前所未有的时间序列观测，彻底改变了星震学领域，即利用恒星振荡探测恒星内部。开普勒数据包括对疏散星团中恒星的观测，这对星震学特别有意义。开普勒观测到的星系团之一是NGC 6811，这是本文的目标。然而，除了高精度的时间序列观测外，通过星震学探测疏散星团中恒星的内部还需要准确和精确的大气参数以及单个恒星的星团成员指标。我们使用中等分辨率（R~ 25，000）的光谱观测，和三个独立的分析方法，推导出有效的温度，表面重力，金属丰度，投影旋转速度和径向速度，在疏散星团NGC 6811领域的15颗恒星。我们发现了两个双线和三个单线光谱双星。其中8颗恒星被归类为确定或非常可能的星团成员，3颗恒星被归类为非成员。对于四颗恒星，无法评估星团成员资格。其中五颗被观测到的恒星是G-型巨星，它们位于星团红团区域的色星等图上。其中两颗恒星是首次被确认为红丛星。对于这五颗恒星，我们提供了31种元素的化学丰度。NGC 6811的平均径向速度为+6.68 $\pm$ 0.08 km s $^{-1}$，其平均金属丰度和总体丰度模式与太阳非常接近，但Ba的丰度过高。
We report the validation of a recently proposed infrared selection criterion for symbiotic stars (SySts). Spectroscopic data were obtained for seven candidates, selected from the SySt candidates of Akras et al. (2019, MNRAS, 483, 5077) by employing the new supplementary infrared selection criterion for SySts in the VST/OmegaCAM Photometric H-Alpha Survey (VPHAS+). Five of them turned out to be genuine SySts after the detection of H$α$, He II and [O III] emission lines as well as TiO molecular bands. The characteristic O VI Raman-scattered line is also detected in one of these SySts. According …
Low-resolution spectroscopic characterisation of five poorly known Galactic stellar clusters
University of Groningen（格罗宁根大学）；Università di Bologna（博洛尼亚大学）；INAF - Osservatorio di Astrofisica e Scienza dello Spazio di Bologna（意大利国家天体物理研究所博洛尼亚天文与空间科学观测站）；INAF - Osservatorio Astronomico di Padova（意大利国家天体物理研究所帕多瓦天文台）；Durham University（杜伦大学）
We used high-resolution near-infrared spectroscopy from the NIRSPEC instrument on the Keck II telescope, taken over multiple epochs spanning five years, to examine two young binary T Tauri star systems, S Corona Australis and VV Corona Australis. The stars in these 1-2" separation systems have optically thick circumstellar disks and high extinctions at optical and near-infrared wavelengths. Using a combination of new and archival data, we have determined the spectral types of all the stars in these two systems for the first time, examined the variable NIR veiling, measured the emission line eq…
Elemental Abundances of Cool Stars: A Spectroscopic Framework Applied to Five Planet-Host Stars
McMaster University（麦克马斯特大学）；Université de Montréal（蒙特利尔大学）；Institut Trottier de recherche sur les exoplanètes, Département de Physique, Université de Montréal（蒙特利尔大学物理系特鲁蒂埃系外行星研究所）；Observatoire de Genève, Département d’Astronomie, Université de Genève（日内瓦大学天文学系日内瓦天文台）
We have developed a new method for spectral analysis of binaries. Our method successfully identifies SB2 candidates from high-resolution Gaia-ESO spectra. Compared to the commonly used cross-correlation function analysis, it works for binaries with rapidly rotating components. We test our method on synthetic and observational spectra of BAFG-stars in the open cluster M 11. We confirm five previously detected SB2 candidates and find 19 new ones. For three SB2 candidates we find circular orbits and obtain dynamical mass ratios.
Employing a new machine learning method, named hierarchical extreme learning machine (HELM) algorithm, we identified 56 hot subdwarf stars in the first data release (DR1) of the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST) survey. The atmospheric parameters of the stars are obtained by fitting the profiles of hydrogen (H) Balmer lines and helium (He) lines with synthetic spectra calculated from non-Local Thermodynamic Equilibrium (NLTE) model atmospheres. Five He-rich hot subdwarf stars were found in our sample with their log(nHe/nH) > -1 , while 51 stars are He-poor sdB,…
We report the results of optical spectroscopic monitoring observations of a T Tauri star, V409 Tau. A previous photometric study indicated that this star experienced dimming events due to the obscuration of light from the central star with a distorted circumstellar disk. We conducted medium-resolution (R ~10,000) spectroscopic observations with 2-m Nayuta telescope at Nishi-Harima Astronomical Observatory. Spectra were obtained in 18 nights between November 2015 and March 2016. Several absorption lines such as Ca I and Li, and the H alpha emission line were confirmed in the spectra. The Ic-ban…
In a dynamically relaxed cluster around a massive black hole a dense stellar cusp of old stars is expected to form. Previous observations showed a relative paucity of red giant stars within the central 0.5 pc in the Galactic Center. By co-adding spectroscopic observations taken over a decade, we identify new late-type stars, including the first five warm giants (G2-G8III), within the central 1 arcsec 2 (0.04 {\times} 0.04 pc^2) of the Galaxy. Our findings increase the number of late-type stars to 21, of which we present deep spectra for 16. The updated star count, based on individual spectral …
The advent of large-scale stellar spectroscopic surveys naturally leads to the implementation of machine learning techniques to isolate, for example, small sub-samples of potentially interesting stars from the full data set. A recent example is the application of the t-SNE statistical method to $\sim$600,000 stellar spectra from the GALAH survey in order to identify a sample of candidate extremely metal-poor (EMP, [Fe/H] $\leq$ -3) stars. We report the outcome of low-resolution spectroscopic follow-up of 83 GALAH EMP candidates that lack any previous metallicity estimates. Overall, the statist…
