We analysed 337 multi-epoch optical spectra of 38 Herbig Ae/Be (HAeBe) stars to gain insights into the variability behaviour of the circumstellar (CS) atomic gas. Equivalent widths (EWs) and line fluxes of the Halpha, [OI]6300, HeI5876 and NaID lines were obtained for each spectrum; the Halpha line width at 10% of peak intensity (W10) and profile shapes were also measured and classified. The mean line strengths and relative variabilities were quantified for each star. Simultaneous optical photometry was used to estimate the line fluxes.
We present a homogeneous spectroscopic database of HAeBe stars. The lines are variable in practically all stars and timescales, although 30 % of the objects show a constant EW in [OI]6300, which is also the only line that shows no variability on timescales of hours. The HeI5876 and NaID EW relative variabilities are typically the largest, followed by those in [OI]6300 and Halpha. The EW changes can be larger than one order of magnitude for the HeI5876 line, and up to a factor 4 for Halpha. The [OI]6300 and Halpha EW relative variabilities are correlated for most stars in the sample. The Halpha mean EW and W10 are uncorrelated, as are their relative variabilities. The Halpha profile changes in 70 % of the objects. The massive stars in the sample usually show more stable Halpha profiles with blueshifted self-absorptions and less variable 10% widths.
Our data suggest multiple causes for the different line variations, but the [OI]6300 and Halpha variability must share a similar origin in many objects. The physical mechanism responsible for the Halpha line broadening does not depend on the amount of emission; unlike in lower-mass stars, physical properties based on the Halpha luminosity and W10 would significantly differ. Our results provide additional support to previous works that reported different physical mechanisms in Herbig Ae and Herbig Be stars.
Models of magnetically driven accretion and outflows reproduce many observational properties of T Tauri stars. For the more massive Herbig Ae/Be stars, the corresponding picture is not well established. Nonetheless, it is expected that accretion flows in pre-main-sequence stars are guided from the circumstellar disk to stellar regions of high latitude along the magnetic field lines inside a magnetosphere. Using near-infrared multi-epoch spectroscopic data obtained with ISAAC, CRIRES, and X-shooter on the VLT, we examined magnetospheric accretion in the two Herbig Ae stars HD101412 and HD104237…
Exploring the long-term temporal variability in polarization through multi-epoch optical spectro-polarimetry - Part I: A sample of Herbig Ae/Be and classical Be stars
Physical Research Laboratory（物理研究实验室）；Indian Institute of Technology Gandhinagar（甘地纳加尔印度理工学院）
HD 163296 is a Herbig Ae star that underwent a dramatic $\sim$0.8 magnitude drop in brightness in the V photometric band in 2001 and a brightening in the near-IR in 2002. Because the star possesses Herbig-Haro objects travelling in outflowing bipolar jets, it was suggested that the drop in brightness was due to a clump of dust entrained in a disk wind, blocking the line-on-sight toward the star. In order to quantify this hypothesis, we investigated the brightness drop at visible wavelengths and the brightening at near-IR wavelengths of HD 163296 using the Monte Carlo Radiative Transfer Code, H…
We use Gaia Data Release 2 (DR2) to place 252 Herbig Ae/Be stars in the HR diagram and investigate their characteristics and properties. For all known Herbig Ae/Be stars with parallaxes in Gaia DR2, we collected their atmospheric parameters and photometric and extinction values from the literature. To these data we added near- and mid-infrared photometry, collected H$α$ equivalent widths and line profiles, and their binarity status. In addition, we developed a photometric variability indicator from Gaia's DR2 information. We provide masses, ages, luminosities, distances, variabilities and infr…
We report the detection of weak mean longitudinal magnetic fields in the Herbig Ae double-lined spectroscopic binary AK Sco and in the presumed spectroscopic Herbig Ae binary HD95881 using observations with the High Accuracy Radial velocity Planet Searcher polarimeter (HARPSpol) attached to the European Southern Observatory's (ESO's) 3.6m telescope. Employing a multi-line singular value decomposition (SVD) method, we detect a mean longitudinal magnetic field <B_z>=-83+-31G in the secondary component of AK Sco on one occasion. For HD95881, we measure <B_z>=-93+-25G and <B_z>=105+-29G at two dif…
We present optical spectroscopy observations of 145 high-mass pre-main sequence candidates from the catalogue of Vioque et al. (2020). From these, we provide evidence for the Herbig nature of 128 sources. This increases the number of known objects of the class by $\sim50\%$. We determine the stellar parameters of these sources using the spectra and Gaia EDR3 data. The new sources are well distributed in mass and age, with 23 sources between $4$-$8$ M$_{\odot}$ and 32 sources above $8$ M$_{\odot}$. Accretion rates are inferred from H$α$ and H$β$ luminosities for 104 of the new Herbigs. These ac…
Models of magnetically driven accretion reproduce many observational properties of T Tauri stars. For the more massive Herbig Ae/Be stars, the corresponding picture has been questioned lately, in part driven by the fact that their magnetic fields are typically one order of magnitude weaker. Indeed, the search for magnetic fields in Herbig Ae/Be stars has been quite time consuming, with a detection rate of about 7%, also limited by the current potential to detect weak magnetic fields. Over the last two decades, magnetic fields were found in about twenty objects and for only two Herbig Ae/Be sta…
Batabat Astrophysical Observatory of Nakhchivan State University（纳希切万州立大学巴塔巴特天文台）；Shamakhy Astrophysical Observatory named after N.Tusi（以N.图西命名的沙马基天文台）；Akdeniz University（安塔利亚大学）
研究聚焦暗弱 HAeBe 恒星 AS 442A，结合存档测光与光谱观测，统计约 3500 次测量探究其光谱和光度变异性，发现周期性食可解释其类似御夫座 UX 型变星的亮度下降，揭示伴星轨道特性与恒星变异性的关系。
The dynamics of magnetic flux tubes (MFTs) in the accretion disk of typical Herbig Ae/Be star with fossil large-scale magnetic field is modeled taking into account the buoyant and drag forces, radiative heat exchange with the surrounding gas, and the magnetic field of the disk. The structure of the disk is simulated using our magnetohydrodynamic (MHD) model, taking into account the heating of the surface layers of the disk with the stellar radiation. The simulations show that MFTs periodically rise from the innermost region of the disk with speeds up to $10-12$ km s$^{-1}$. MFTs experience dec…
The VLT-FLAMES Tarantula Survey. XV. VFTS 822: a candidate Herbig B[e] star at low metallicity
Armagh Observatory（阿马天文台）；Department of Physcis & Astronomy, Queen’s University Belfast（贝尔法斯特女王大学物理与天文学系）；UK Astronomy Technology Centre, Royal Observatory, Edinburgh（爱丁堡皇家天文台英国天文学技术中心）；ESA/STScI（欧洲空间局/太空望远镜科学研究所）；Department of Physics and Astronomy, The Open University（开放大学物理与天文学系）；Astronomical Institute Anton Pannekoek, Amsterdam University（阿姆斯特丹大学安东·潘内库克天文研究所）；Institue voor Sterrenkunde, KU Leuven（鲁汶大学天体物理研究所）；European Space Astronomy Centre（欧洲空间天文中心）
We have been monitoring, at high cadence, the photometric and spectroscopic evolution of VES 263 following the discovery in 2018 of a brightening labeled as event Gaia-18azl. VES 263 is so far a neglected emission-line object discovered in the 1960s on objective prism plates, tentatively classified as a semi-regular AGB cool giant by automated analysis of ASASSN lightcurves. We have discovered that VES 263 is a bonafide massive pre-Main Sequence object (~12 Msun), of the Herbig AeBe type. It is located at 1.68+/-0.07 kpc distance, within the Cyg OB2 star-forming region, and it is highly redden…
The Herbig Ae star HD 169142 is known to have a gaseous disk with a large inner hole, and also a photometrically variable inner dust component in the sub-au region. Following up our previous analysis, we further studied the temporal evolution of inner dust around HD 169142, which may provide information on the evolution from late-stage protoplanetary disks to debris disks. We used near-infrared interferometric observations obtained with VLTI/PIONIER to constrain the dust distribution at three epochs spanning six years. We also studied the photometric variability of HD 169142 using our optical-…
We present two new epochs of Hubble Space Telescope/Space Telescope Imaging Spectrograph coronagraphic imaging, along with multi-epoch optical, near-IR, and radio monitoring, of the HD 163296 system. We find ansae features identified in earlier epoch HST imagery are a 4th ring, that resides at a semi-major axis distance of 3.25" (330 au). We determine the scale height of the dust is 64 au at a radial distance of 330 au. We observe surface brightness variations in the 4th ring on <3 month timescales, including large-scale, azimuthally asymmetric changes. This variability resembles earlier studi…
Time-variable Scattered Light in Herbig Disks Observed with Subaru/SCExAO
University of Victoria（维多利亚大学）；The University of Arizona（亚利桑那大学）；Peking University（北京大学）；Kavli Institute for Astronomy and Astrophysics, Peking University（北京大学科维理天文与天体物理研究所）；Academia Sinica Institute of Astronomy & Astrophysics (ASIAA)（中央研究院天文及天文物理研究所）；National Institutes of Natural Sciences（国立自然科学研究所）；Max-Planck-Institut für Astronomie（马克斯·普朗克天文学研究所）；NRC Herzberg Astronomy and Astrophysics（加拿大国家研究委员会赫茨伯格天文学和天体物理学研究所）；University of Maryland, Baltimore County（马里兰大学巴尔的摩县分校）；NASA-GSFC（美国国家航空航天局戈达德太空飞行中心）
R~CrA is the brightest member of the Coronet star forming region and it is the closest Herbig AeBe star with a spectrum dominated by emission lines. Its luminosity has been monitored since the end of the 19th century, but the origin of its variability, which shows a stable period of $65.767\pm 0.007$~days, is still unknown. We studied photometric and spectroscopic data for this star to investigate the nature of the variability of R~CrA. We exploited the fact that near infrared luminosity of the Herbig AeBe stars is roughly proportional to the total luminosity of the stars to derive the absorpt…
W 601 (NGC 6611 601) is one of the handful of known magnetic Herbig Ae/Be stars. We report the analysis of a large dataset of high-resolution spectropolarimetry. The star is a previously unreported spectroscopic binary, consisting of 2 B2 stars with a mass ratio of 1.8, masses of 12 M$_\odot$ and 6.2 $M_\odot$, in an eccentric 110-day orbit. The magnetic field belongs to the secondary, W 601 B. The H$α$ emission is consistent with an origin in W 601 B's centrifugal magnetosphere; the star is therefore not a classical Herbig Be star in the sense that its emission is not formed in an accretion d…
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…
Short-term spectroscopic variability of Plaskett's star
上下文普拉斯凯特的恒星（HD 47129）是一颗质量非常大的O型双星，处于后罗奇瓣溢出阶段。该系统的CoRoT观测揭示了光度的变化与一些频率。目标。本文的目的是表征光谱的变化，并调查其起源。方法.为了对HD 47129的短期变异性进行采样，在两次光谱活动中对它进行了密集监测，每次六个晚上。光谱被解开和傅立叶分析进行，以确定可能的周期性和研究的相位常数和振幅的周期性的波长依赖性。结果观察到复杂的线轮廓变化。在He i 4471、He ii 4542和N iii 4510-4518谱线中始终检测到接近1.65、0.82和0.37 d^-1的频率。这些频率与测光中检测到的最强信号的频率一致。这些变化源于脉动，最近检测到的磁场或潮汐相互作用的可能性进行了讨论。结论.虽然所有三种情况都有其优势，但目前没有一种情况可以解释所有观测到的线路轮廓变化特性。
Accretion plays an important role in protoplanetary disk evolution, and it is thought that the accretion mechanism changes between low- and high-mass stars. Here, we characterize accretion in intermediate-mass, pre-main-sequence Herbig Ae/Be (HAeBe) stars to search for correlations between accretion and system properties. We present new high-resolution, near-infrared spectra from the Immersion GRating INfrared Spectrograph for 102 HAeBes and analyze the accretion-tracing Br$γ$ line at 2.166 $μ$m. We also include the samples of Fairlamb et al. and Donehew & Brittain, for a total of 155 targets.…
