Variability is a characteristic feature of young stellar objects (YSOs) and could contribute to the large scatter observed in HR diagrams for star forming regions. For typical YSOs, however, the long-term effects of variability are poorly constrained. Here I use archived near-infrared photometry from 2MASS, UKIDSS, and DENIS to investigate the long-term variability of high-confidence members of the four star forming regions Rho-Oph, ONC, IC348, and NGC1333. The total sample comprises more than 600 objects, from which ~320 are considered to have a disk. The dataset covers timescales up to 8 yr. About half of the YSOs are variable on a 2sigma level, with median amplitudes of 5-20%. The fraction of highly variable objects with amplitudes >0.5 mag in at least two near-infrared bands is very low - 2% for the entire sample and 3% for objects with disks. These sources with strong variability are mostly objects with disks and are prime targets for follow-up studies. The variability amplitudes are largest in NGC1333, presumably because it is the youngest sample of YSOs. The frequency of highly variable objects also increases with the time window of the observations (from weeks to years). These results have three implications: 1) When deriving luminosities for YSOs from near-infrared magnitudes, the typical error introduced by variability is in the range of 5-20% percent and depends on disk fraction and possibly age. 2) Variability is a negligible contribution to the scatter in HR diagrams of star forming regions (except for a small number of extreme objects), if luminosities are derived from near-infrared magnitudes. 3) Accretion outbursts with an increase in mass accretion rate by several order of magnitudes, as required in scenarios for episodic accretion, occur with a duty cycle of >2000-2500 yr in the Class II phase. (abridged)
T Tauri has long been the prototypical young pre-main-sequence star. However, it has now been decomposed into a triple system with a complex disk and outflow geometry. We aim to measure the brightness of all three components of the T Tauri system (T Tau N, T Tau Sa, T Tau Sb) in the mid-infrared in order to obtain photometry around the $\sim 9.7~μm$ silicate feature. This allows us to study their variability and to investigate the distribution of dust and the geometry of circumstellar and circumbinary disks in this complex system. We observe T Tauri with the VLT/VISIR-NEAR instrument. With ker…
We present a detailed study based on infrared photometry of all Galactic RV Tauri stars from the General Catalogue of Variable Stars (GCVS). RV Tauri stars are the brightest among the population II Cepheids. They are thought to evolve away from the asymptotic giant branch (AGB) towards the white dwarf domain. IRAS detected several RV Tauri stars because of their large IR excesses and it was found that they occupy a specific region in the [12] - [25], [25] - [60] IRAS two-colour diagram. We used the all sky survey of WISE to extend these studies and compare the infrared properties of all RV Tau…
Accretion is one of the defining characteristics of classical T Tauri stars, fueled by the presence of a circumstellar disk comprised of dust and gas. Accretion produces a UV and optical excess, while re-radiated emission at the inner edge of the dust component of the disk produces a near-infrared (NIR) excess. The interplay between stars and their disks helps regulate protoplanetary disk evolution and dispersal, which is key to a full understanding of planet formation. To investigate the relations between NIR excess and optical excess in both single and binary stars, we used an archival sampl…
This paper presents optical ($ugri$H$α$)-infrared ($JHK$s,3.6--8.0$μ$m) photometry, and $Gaia$ astrometry of 55 Classical T-Tauri stars (CTTS) in the star-forming region Sh 2-012, and it's central cluster NGC 6383. The sample was identified based on photometric H$α$ emission line widths, and has a median age of 2.8$\pm$1.6 Myr, with a mass range between 0.3-1 $M_{\odot}$. 94% of CTTS with near-infrared cross-matches fall on the near-infrared T-Tauri locus, with all stars having mid-infrared photometry exhibiting evidence for accreting circumstellar discs. CTTS are found concentrated around the…
Understanding Balmer Decrements in T Tauri stars in terms of Multiflow Magnetospheric Accretion
Institute for Astrophysical Research, Department of Astronomy, Boston University（波士顿大学天体物理研究所）；Department of Astronomy, University of Michigan（密歇根大学天文学系）；Centro de Investigaciones de Astronomía (CIDA)（天文学研究中心）；Department of Physics, Faculty of Science, Chulalongkorn University（朱拉隆功大学理学院物理学系）
Context. RV Tauri-type variables are pulsating post-AGB stars that evolve rapidly through the instability strip after leaving the Asymptotic Giant Branch. Their light variability is dominated by radial pulsations. Members of the RVb subclass show an additional variability in form of a long-term modulation of the mean brightness, for which the most popular theories all assume binarity and some kind of circumstellar dust. Here we address if the amplitude modulations are consistent with the dust obscuration model. Aims. We measure and interpret the overall changes of the mean amplitude of the pul…
Context : The properties of the inner disks of bright Herbig AeBe stars have been studied with near infrared (NIR) interferometry and high resolution spectroscopy. The continuum and a few molecular gas species have been studied close to the central star; however, sensitivity problems limit direct information about the inner disks of the fainter T Tauri stars. Aims : Our aim is to measure some of the properties of the inner regions of disks surrounding southern T Tauri stars. Methods : We performed a survey with the PIONIER recombiner instrument at H-band of 21 T Tauri stars. The baselines used…
Far-ultraviolet (FUV) radiation plays an important role in determining chemical abundances in protoplanetary disks. HI Lyman alpha is suspected to be the dominant component of the FUV emission from Classical T Tauri Stars (CTTSs), but is difficult to measure directly due to circumstellar and interstellar HI absorption. To better characterize the intrinsic Lyman alpha radiation, we present FUV spectra of 14 CTTSs taken with the Hubble Space Telescope COS and STIS instruments. H2 fluorescence, commonly seen in the spectra of CTTSs, is excited by Lyman alpha photons, providing an indirect measure…
Mid-infrared molecular line emission detected with the Spitzer Space Telescope is often interpreted using slab models. However, we need to understand the mid-infrared line emission in 2D disk models, such that we gain information about from where the lines are being emitted and under which conditions, such that we gain information about number densities, temperatures, and optical depths in both the radial and vertical directions. In this paper, we introduce a series of 2D thermochemical models of a prototypical T Tauri protoplanetary disk, in order to examine how sensitive the line-emitting re…
Spatially resolved mid-infrared observations of the triple system T Tauri
为了提高我们的知识的特点和分布的拱星尘埃与年轻的层次三重系统T头的各个组成部分，在N-波段的观测与VLTI进行。我们的研究是基于干涉和分光光度测量，并辅以新的视觉和红外光度。此外，相位进行了研究，以确定在近南双星中占主导地位的中红外光源。这些数据是在一个复杂的物理磁盘模型的帮助下拟合的。该模型利用基于蒙特卡罗方法的辐射转移代码MC 3D。在系统的所有三个组件周围都发现了扩展的中红外发射。同时配合测光和干涉测量数据证实了一个几乎面对拱盘周围的T头N的图片。朝向这颗恒星，在发射中可以看到硅酸盐带。这个发射特征被用来模拟星周盘的尘埃含量。在T Tau S附近，在吸收中可以看到硅酸盐带。这种吸收对红外伴星T Tau Sa非常明显，这可以从两个南部分量的第一个单独的N带光谱中看出。我们的配合支持以前的建议，一个几乎边缘上的光盘是目前围绕T头萨。因此，这个圆盘相对于T Tau N周围的拱星圆盘没有对准。干涉测量数据表明，磁盘T头萨周围是面向南北方向，这有利于这个源作为发射场的东西射流。我们进一步确定从干涉数据的相对位置的组件的南方二进制。
Edge-on disk around the T Tauri star [MR81] Halpha 17 NE in CrA
科勒和他的合作者们使用位于3.5米ESO NTT的斑点照相机SHARP，在南冕座（CrA）恒星形成区的金牛座T星[MR 81] Ha 17东北仅1.3”处发现了一个暗约3.5等的物体，它可能是一颗褐矮星或一颗边缘盘的金牛座T星。我们试图详细研究这个微弱的物体。我们在三个时期获得了深VLT NACO近红外图像，以确定[MR 81] Ha 17和附近的微弱物体是否共同移动，并测量两个物体的红外颜色。我们获得了光学和红外光谱的两个对象与VLT使用FORS和ISAAC，分别确定光谱类型和温度以及年龄和质量。金牛座T星[MR 81] Ha 17和附近的暗天体的投影距离为1369.58质量，即178天文单位，130秒差距。它们共享相同的自行（~5 sigma），因此它们肯定会形成一个束缚双星对。明显较暗的成分[MR 81] Ha 17 NE的光谱类型为M2 e，而明显较亮的成分[MR 81] Ha 17 SW，即先前已知的金牛座T星，光谱类型为M4-5e。我们可以通过目视检查在[MR 81] Ha 17 NE周围识别出一个近边缘的圆盘，其直径至少为30至50 AU。我们能够在[MR 81] Ha 17 NE中检测到强烈的发射线，这几乎可以肯定是由于正在进行的吸积。NE天体只能通过它的散射光来探测。如果这两个天体是同时代的（2- 300万年），并且位于相同的距离（约为CrA的130 pc），那么…
We aim to characterise the surface magnetic fields of a sample of 8 T Tauri stars from high-resolution near-IR spectroscopy. Some stars in our sample are known to be magnetic from previous spectroscopic or spectropolarimetric studies. Our goals are 1) to apply Zeeman broadening modelling to T Tauri stars with high-resolution data, 2) to expand the sample of stars with measured surface magnetic field strengths, 3) to investigate possible rotational or long-term magnetic variability by comparing spectral time series of given targets, and 4) to compare the magnetic field modulus <B> tracing small…
A high angular resolution near-infrared polarized-intensity image of the GG Tau A binary system was obtained with the Subaru Telescope. The image shows the circumbinary disk scattering the light from the central binary. The azimuthal profile of the polarized intensity of the circumbinary disk is roughly reproduced by a simple disk model with the Henyey-Greenstein function and the Rayleigh function, indicating small dust grains at the surface of the disk. Combined with a previous observation of the circumbinary disk, our image indicates that the gap structure in the circumbinary disk orbits ant…
A multiwavelength observing campaign of the T Tauri star (TTS) GM Aur was undertaken in 2019 December that obtained Swift X-ray and NUV fluxes, HST NUV spectra, LCOGT ugri and TESS photometry, CHIRON Halpha spectra, ALMA 13CO and C18O line fluxes, and VLA 3 cm continuum fluxes taken contemporaneously over one month. The X-ray to optical observations were presented previously. Here we present the ALMA and VLA data and make comparisons to GM Aur's accretion and X-ray properties. We report no variability in the observed millimeter CO emission. Using disk chemistry models, we show that the magnitu…
Aims. In this paper, we aim to measure the strength of the surface magnetic fields for a sample of five intermediate mass T Tauri stars and one low mass T Tauri star from late-F to mid-K spectral types. While magnetic fields of T Tauri stars at the low mass range have been extensively characterized, our work complements previous studies towards the intermediate mass range; this complementary study is key to evaluate how magnetic fields evolve during the transition from a convective to a radiative core. Methods. We studied the Zeeman broadening of magnetically sensitive spectral lines in the H-…
Radiative transfer modelling offers a powerful tool for understanding the enigmatic hydrogen emission lines from T Tauri stars. This work compares optical and near-IR spectroscopy of 29 T Tauri stars with our grid of synthetic line profiles. The archival spectra, obtained with VLT's X-Shooter, provide simultaneous coverage of many optical and infrared hydrogen lines. The observations exhibit similar morphologies of line profiles seen in other studies. We used the radiative transfer code TORUS to create synthetic H$α$, Pa$β$, Pa$γ$, and Br$γ$ emission lines for a fiducial T Tauri model that inc…
Context. The prototypical low-mass young stellar object, T Tauri, is a well-studied multiple system with at least three components. Aims. We aim to explore the T Tau system with the highest spatial resolution, study the time evolution of the known components, and re-determine the orbital parameters of the stars. Methods. Near-infrared classical imaging and integral field spectrograph observations were obtained during the Science Verification of SPHERE, the new high-contrast imaging facility at the VLT. The obtained FWHM of the primary star varies between 0.050" and 0.059", making these the hig…
Equivalent widths and line widths of Ca II infrared triplet emission lines were measured in high-resolution optical spectra of 39 young stellar objects.We found that the equivalent widths of the emission lines decrease with stellar evolution. It has been often claimed that strong chromospheric activity is generated by a dynamo process caused by fast rotation of the photosphere. However, we found no clear correlation between the strength of the Ca II lines and the stellar rotation velocity. Instead, we found that the objects with high mass accretion rates had stronger Ca II emission lines. This…
We investigate which properties of protoplanetary disks around T Tauri stars affect the physics and chemistry in the regions where mid- and far-IR water lines originate and their respective line fluxes. We search for diagnostics for future observations. With the code ProDiMo, we build a series of models exploring a large parameter space, computing rotational and rovibrational transitions of water in nonlocal thermodynamic equilibrium (non-LTE). We select a sample of transitions in the mid- IR regime and the fundamental ortho and para water transitions in the far-IR. We investigate the chemistr…
Brown dwarf disks are excellent laboratories to test our understanding of disk physics in an extreme parameter regime. In this paper we investigate a sample of 29 well-characterized brown dwarfs and very low mass stars, for which Herschel far-infrared fluxes as well as (sub)-mm fluxes are available. We have measured new Herschel PACS fluxes for 11 objects and complement these with (sub)-mm data and Herschel fluxes from the literature. We analyze their spectral energy distributions in comparison with results from radiative transfer modeling. Fluxes in the far-infrared are strongly affected by t…
Classical T Tauri stars are young low-mass systems still accreting material from their disks. These systems are dynamic on timescales of hours to years. The observed variability can help us infer the physical processes that occur in the circumstellar environment. We aim at understanding the dynamics of the magnetic interaction between the star and the inner accretion disk in young stellar objects. We present the case of the young stellar system V2129 Oph, which is a well-known T Tauri star. We performed a time series analysis of this star using high-resolution spectroscopic data at optical and…
We present a blind comparison of two methods to measure the mean surface magnetic field strength of the classical T Tauri star CI Tau based on Zeeman broadening of sensitive spectral lines. Our approach takes advantage of the greater Zeeman broadening at near-infrared compared to optical wavelengths. We analyze a high signal-to-noise, high spectral resolution spectrum from 1.5-2.5um observed with IGRINS (Immersion GRating INfrared Spectrometer) on the Discovery Channel Telescope. Both stellar parameterization with MoogStokes (which assumes an uniform magnetic field) and modeling with SYNTHMAG …
Variations of the 10 um Silicate Features in the Actively Accreting T Tauri Stars: DG Tau and XZ Tau
利用斯皮策太空望远镜上的红外光谱仪，我们观测到附近金牛座-御夫座恒星形成区中11颗活跃吸积的金牛座T星的多个时期。在第2和第3周期的1.5年中，共收集了88个低分辨率中红外光谱。这个多时期的调查结果表明，10微米的硅酸盐复杂的光谱中的两个源- DG Tau和XZ Tau -经历了显着的变化与硅酸盐的功能越来越弱和强，超过一个月和一年的时间尺度。较短的时间尺度变化的一天到一周的时间尺度内没有检测到测量通量的错误。该数据集的时间分辨率覆盖范围不足以确定变化是否是周期性的。纯发射组成模型的硅酸盐复合物在每个时代的DG头和XZ头光谱提供不良的拟合所观察到的硅酸盐功能。这些结果与以前的小组，试图只适合这些来源的单历元观测结果。简单的两个温度，两个板坯模型具有相似的成分成功地再现了所观察到的硅酸盐特征的变化。这些模型暗示了硅酸盐复合物减少的自吸收起源，而不是排放尘埃颗粒的人口组成变化。我们讨论了几种情况下产生这种变化，包括磁盘阴影，垂直混合，磁盘加热的变化，和磁盘风事件与吸积爆发。
We introduce a new modelling framework called FLiTs to simulate infrared line emission spectra from protoplanetary discs. This paper focuses on the mid-IR spectral region between 9.7 um to 40 um for T Tauri stars. The generated spectra contain several tens of thousands of molecular emission lines of H2O, OH, CO, CO2, HCN, C2H2, H2 and a few other molecules, as well as the forbidden atomic emission lines of SI, SII, SIII, SiII, FeII, NeII, NeIII, ArII and ArIII. In contrast to previously published works, we do not treat the abundances of the molecules nor the temperature in the disc as free par…
The star S CrA is a tight visual binary consisting of two classical T Tauri stars, both with outstanding spectral characteristics and brightness variations. High-resolution spectra were collected at ESO and photometric observations with the SMARTS telescope. Both stars undergo large variation in brightness caused mainly by variable foreground extinction. From the stellar parameters we conclude that the two stars are remarkably similar, and that S CrA can be regarded as a T Tauri twin. Rotational periods and inclinations are also similar. The stars differ, however, in terms of degree of veiling…
We investigate the properties of X-ray emission from accretion shocks in classical T Tauri stars (CTTSs), generated where the infalling material impacts the stellar surface. Both observations and models of the accretion process reveal several aspects that are still unclear: the observed X-ray luminosity in accretion shocks is below the predicted value, and the density versus temperature structure of the shocked plasma, with increasing densities at higher temperature, deduced from the observations, is at odds with that proposed in the current picture of accretion shocks. To address these open i…
T Tauri remains an enigmatic triple star for which neither the evolutionary state of the stars themselves, nor the geometry of the complex outflow system is completely understood. Eight-meter class telescopes equipped with state-of-the-art adaptive optics provide the spatial resolution necessary to trace tangential motion of features over a timescale of a few years, and they help to associate them with the different outflows. We used J-, H-, and K-band high-contrast coronagraphic imaging with VLT-SPHERE recorded between 2016 and 2018 to map reflection nebulosities and obtain high precision nea…
In the framework of the GIARPS@TNG High-resolution Observations of T Tauri stars (GHOsT) project, we study the accretion properties of 37 Classical T Tauri Stars of the Taurus-Auriga star forming region (SFR) with the aim of characterizing their relation with the properties of the central star, of jets and disk winds, and of the global disk structure, in synergy with complementary ALMA millimiter observations. We derive stellar parameters, optical veiling, accretion luminosity ($\rm L_{acc}$) and mass accretion rate ($\rm \dot M_{acc}$) in a homogeneous and self-consistent way using high-resol…
At early stages of stellar evolution young stars show powerful jets and/or outflows that interact with protoplanetary discs and their surroundings. Despite the scarce knowledge about the interaction of jets and/or outflows with discs, spectroscopic studies based on Herschel and ISO data suggests that gas shocked by jets and/or outflows can be traced by far-IR (FIR) emission in certain sources. We want to provide a consistent catalogue of selected atomic ([OI] and [CII]) and molecular (CO, OH, and H$_{2}$O) line fluxes observed in the FIR, separate and characterize the contribution from the jet…
Infrared and (sub-)mm observations of disks around T Tauri and Herbig Ae/Be stars point to a chemical differentiation between both types of disks, with a lower detection rate of molecules in disks around hotter stars. To investigate the potential underlying causes we perform a comparative study of the chemistry of T Tauri and Herbig Ae/Be disks, using a model that pays special attention to photochemistry. The warmer disk temperatures and higher ultraviolet flux of Herbig stars compared to T Tauri stars induce some differences in the disk chemistry. In the hot inner regions, H2O, and simple org…
Detection of Strong Millimeter Emission from the Circumstellar Dust Disk Around V1094 Sco: Cold and Massive Disk around a T Tauri Star in a Quiescent Accretion Phase?
我们目前的发现，一个冷的大规模尘埃盘周围的金牛座T星V1094斯科在狼疮分子云从1.1毫米连续观测与阿兹TEC的ASTE。一个紧凑的（$r\lesssim$ 320 AU）连续发射符合恒星的位置具有272毫焦耳的通量密度，这是最大的金牛座T星在狼。我们还介绍了在$^{12}$ CO J=3- 2和$^{13}$ CO J=3- 2的五点观测中发现的与恒星有关的分子气体。由于我们对$^{12}$ CO和$^{13}$ CO的观测没有显示出任何大规模外流或大质量包层的迹象，致密的尘埃排放很可能来自恒星周围的盘。观测到的V1094 Sco的SED没有显示出从近红外到毫米波长的明显转换，这可以很好地用尘埃成分的扁平盘来描述，并且在10 $\micron$附近没有明显的倾角特征，表明盘中没有内孔。我们适合一个简单的幂律磁盘模型所观察到的SED。估计的盘质量范围从0.03到$\gtrsim$ 0.12 $M_\sun$，这是一个或两个数量级以上的中位数盘质量的金牛座金牛座T星。
