scholarly journals The wind and the magnetospheric accretion onto the T Tauri star S Coronae Australis at sub-au resolution

2017 ◽  
Vol 608 ◽  
pp. A78 ◽  
Author(s):  
◽  
R. Garcia Lopez ◽  
K. Perraut ◽  
A. Caratti o Garatti ◽  
B. Lazareff ◽  
...  
Keyword(s):  
Binary System ◽  
Spectral Resolution ◽  
Near Infrared ◽  
Line Emission ◽  
High Spectral Resolution ◽  
Simultaneous Presence ◽  
Field Mode ◽  
T Tauri ◽  
Magnetospheric Accretion ◽  
The Continuum

Aims. To investigate the inner regions of protoplanetary discs, we performed near-infrared interferometric observations of the classical T Tauri binary system S CrA. Methods. We present the first VLTI-GRAVITY high spectral resolution (R ~ 4000) observations of a classical T Tauri binary, S CrA (composed of S CrA N and S CrA S and separated by ~1.̋4), combining the four 8m telescopes in dual-field mode. Results. Our observations in the near-infrared K-band continuum reveal a disc around each binary component, with similar half-flux radii of about 0.1 au at d ~ 130 pc, inclinations (i = 28 ± 3° and i = 22 ± 6°), and position angles (PA = 0°± 6° and PA = –2°± 12°), suggesting that they formed from the fragmentation of a common disc. The S CrA N spectrum shows bright He i and Brγ line emission exhibiting inverse P Cygni profiles, typically associated with infalling gas. The continuum-compensated Brγ line visibilities of S CrA N show the presence of a compact Brγ emitting region whose radius is about ~0.06 au, which is twice as big as the truncation radius. This component is mostly tracing a wind. Moreover, a slight radius change between the blue- and red-shifted Brγ line components is marginally detected. Conclusions. The presence of an inverse P Cygni profile in the He i and Brγ lines, along with the tentative detection of a slightly larger size of the blue-shifted Brγ line component, hint at the simultaneous presence of a wind and magnetospheric accretion in S CrA N.

Spectrum Filter Performance Analysis on Near-Infrared High-Spectral-Resolution Lidar

2016 ◽  
Vol 43 (4) ◽  
pp. 0414004
Author(s):  
张与鹏 Zhang Yupeng ◽  
刘东 Liu Dong ◽  
杨甬英 Yang Yongying ◽  
罗敬 Luo Jing ◽  
成中涛 Cheng Zhongtao ◽  
...  
Keyword(s):  
Performance Analysis ◽  
Spectral Resolution ◽  
Near Infrared ◽  
High Spectral Resolution ◽  
Filter Performance ◽  
High Spectral Resolution Lidar

Magnetic Accretion Funnels in Young Stellar Objects: Thermal Structure and Emission Signatures

1997 ◽  
Vol 163 ◽  
pp. 760-760
Author(s):  
Steven C. Martin ◽  
Arieh Königl
Keyword(s):  
Magnetic Field ◽  
Near Infrared ◽  
Thermal Structure ◽  
Line Emission ◽  
Young Stellar Objects ◽  
Rate Equations ◽  
Gas Temperature ◽  
Ionization State ◽  
Object A ◽  
T Tauri

AbstractA self-consistent procedure is outlined for determining the thermal structure of gas inflowing along magnetic field lines of a young stellar object. A young pre-main-sequence star (e.g., a classical T Tauri star) is assumed to possess a dipole magnetic field that disrupts a geometrically thin accretion disk and channels the incoming gas toward the stellar surface, leading to the formation of a pair of accretion funnels that terminate in shocks at high stellar latitudes. The heat equation is solved together with the rate equations for hydrogen, and the main physical processes that heat and cool the gas are identified. In particular, in the case of T Tauri stars, it is found that adiabatic compression is the principal heat source and that the Ca II and Mg II ions act as a powerful thermostat that regulates the gas temperature. The ionization state of the gas in the radiation field of the stellar photosphere and of the accretion shocks is found in this case to be controlled by Balmer continuum photons. The implications of these calculations to the observational signatures of accreting YSOs (e.g., their near-infrared hydrogen and CO overtone line emission) are discussed.

scholarly journals Global monitoring of terrestrial chlorophyll fluorescence from moderate spectral resolution near-infrared satellite measurements: methodology, simulations, and application to GOME-2

2013 ◽  
Vol 6 (2) ◽  
pp. 3883-3930 ◽  
Author(s):  
J. Joiner ◽  
L. Guanter ◽  
R. Lindstrot ◽  
M. Voigt ◽  
A. P. Vasilkov ◽  
...  
Keyword(s):  
Chlorophyll Fluorescence ◽  
Spectral Resolution ◽  
Near Infrared ◽  
High Spectral Resolution ◽  
High Signal ◽  
Good Precision ◽  
Atmospheric Absorption ◽  
Red Fluorescence ◽  
Fluorescence Measurements ◽  
Global Mapping

Abstract. Globally mapped terrestrial chlorophyll fluorescence retrievals are of high interest because they can provide information on the functional status of vegetation including light-use efficiency and global primary productivity that can be used for global carbon cycle modeling and agricultural applications. In addition, fluorescence can contaminate photon path estimates from the O2 A-band that has become an integral part of missions to accurately measure greenhouse gas concentrations. Global mapping of far-red (~ 755–770 nm) terrestrial vegetation solar-induced fluorescence from space has been accomplished using the high spectral resolution (ν/Δ ν > 35 000) interferometer on the Japanese Greenhouse gases Observing SATellite (GOSAT). These satellite retrievals of fluorescence rely solely upon the filling-in of solar Fraunhofer lines that are not significantly affected by atmospheric absorption. Although these measurements provide near global coverage on a monthly basis, they suffer from relatively low precision and sparse spatial sampling. Here, we describe a new methodology to retrieve global far-red fluorescence information; we use hyperspectral data to disentangle the spectral signatures of three basic components in and surrounding the O2 A-band: atmospheric absorption, surface reflectance, and fluorescence radiance. Through detailed simulations, we demonstrate the feasibility of the approach and show that moderate spectral resolution measurements with a relatively high signal-to-noise ratio within and outside the O2 A-band can be used to retrieve far-red fluorescence information with good precision and accuracy. The method is then applied to data from the Global Ozone Monitoring Instrument 2 (GOME-2). The GOME-2 fluorescence retrievals display similar spatial structure as compared with GOSAT. GOME-2 enables global mapping of far-red fluorescence with higher precision over smaller spatial and temporal scales than is possible with GOSAT. It should be noted that both GOME-2 and GOSAT were designed to make atmospheric trace gas measurements and were not optimized for fluorescence measurements. Our approach can be applied to other existing and future space-based instruments that provide moderate spectral resolution observations in the near-infrared region.

scholarly journals AMBER/VLTI Snapshot Survey on Circumstellar Environments

2014 ◽  
Vol 9 (S307) ◽  
pp. 297-300 ◽  
Author(s):  
Th. Rivinius ◽  
W.J. de Wit ◽  
Z. Demers ◽  
A. Quirrenbach ◽  
Keyword(s):  
Spatial Resolution ◽  
Spectral Resolution ◽  
Spatial Scales ◽  
Line Emission ◽  
High Spectral Resolution ◽  
Unique Combination ◽  
Hot Stars ◽  
Circumstellar Environments ◽  
Colour Terms ◽  
Neutral Colour

AbstractOHANA is an interferometric snapshot survey of the gaseous circumstellar environments of hot stars, carried out by the VLTI group at the Paranal observatory. It aims to characterize the mass-loss dynamics (winds/disks) at unexplored spatial scales for many stars. The survey employs the unique combination of AMBER's high spectral resolution with the unmatched spatial resolution provided by the VLTI. Because of the spatially unresolved central OBA-type star, with roughly neutral colour terms, their gaseous environments are among the easiest objects to be observed with AMBER, yet the extent and kinematics of the line emission regions are of high astrophysical interest.

scholarly journals Near-Infrared Coronagraphic Observations of the T Tauri Binary System UY Aur

2007 ◽  
Vol 134 (2) ◽  
pp. 880-885 ◽  
Author(s):  
Tomonori Hioki ◽  
Yoichi Itoh ◽  
Yumiko Oasa ◽  
Misato Fukagawa ◽  
Tomoyuki Kudo ◽  
...  
Keyword(s):  
Binary System ◽  
Near Infrared ◽  
T Tauri

scholarly journals Development of a high spectral resolution surface albedo product for the ARM Southern Great Plains central facility

2011 ◽  
Vol 4 (3) ◽  
pp. 3097-3145
Author(s):  
S. A. McFarlane ◽  
K. L. Gaustad ◽  
E. J. Mlawer ◽  
C. N. Long ◽  
J. Delamere
Keyword(s):  
Great Plains ◽  
Spectral Resolution ◽  
Surface Albedo ◽  
Vegetation Index ◽  
Near Infrared ◽  
High Spectral Resolution ◽  
Surface Type ◽  
Southern Great Plains ◽  
Green Vegetation ◽  
Visible Wavelengths

Abstract. We present a method for identifying dominant surface type and estimating high spectral resolution surface albedo at the Atmospheric Radiation Measurement (ARM) facility at the Southern Great Plains (SGP) site in Oklahoma for use in radiative transfer calculations. Given a set of 6-channel narrowband visible and near-infrared irradiance measurements from upward and downward looking multi-filter radiometers (MFRs), four different surface types (snow-covered, green vegetation, partial vegetation, non-vegetated) can be identified. A normalized difference vegetation index (NDVI) is used to distinguish between vegetated and non-vegetated surfaces, and a scaled NDVI index is used to estimate the percentage of green vegetation in partially vegetated surfaces. Based on libraries of spectral albedo measurements, a piecewise continuous function is developed to estimate the high spectral resolution surface albedo for each surface type given the MFR albedo values as input. For partially vegetated surfaces, the albedo is estimated as a linear combination of the green vegetation and non-vegetated surface albedo values. The estimated albedo values are evaluated through comparison to high spectral resolution albedo measurements taken during several Intensive Observational Periods (IOPs) and through comparison of the integrated spectral albedo values to observed broadband albedo measurements. The estimated spectral albedo values agree well with observations for the visible wavelengths constrained by the MFR measurements, but have larger biases and variability at longer wavelengths. Additional MFR channels at 1100 nm and/or 1600 nm would help constrain the high resolution spectral albedo in the near infrared region.

scholarly journals Probing the magnetospheric accretion region of the young pre-transitional disk system DoAr 44 using VLTI/GRAVITY

2020 ◽  
Vol 636 ◽  
pp. A108 ◽  
Author(s):  
J. Bouvier ◽  
K. Perraut ◽  
J.-B. Le Bouquin ◽  
G. Duvert ◽  
C. Dougados ◽  
...  
Keyword(s):  
Geometric Model ◽  
Stellar System ◽  
Line Emission ◽  
Position Angle ◽  
Young Stellar Objects ◽  
Continuum Emission ◽  
Disk System ◽  
Compact Region ◽  
Magnetospheric Accretion ◽  
The Continuum

Context. Young stellar objects are thought to accrete material from their circumstellar disks through their strong stellar magnetospheres. Aims. We aim to directly probe the magnetospheric accretion region on a scale of a few 0.01 au in a young stellar system using long-baseline optical interferometry. Methods. We observed the pre-transitional disk system DoAr 44 with VLTI/GRAVITY on two consecutive nights in the K-band. We computed interferometric visibilities and phases in the continuum and in the Brγ line in order to constrain the extent and geometry of the emitting regions. Results. We resolve the continuum emission of the inner dusty disk and measure a half-flux radius of 0.14 au. We derive the inclination and position angle of the inner disk, which provides direct evidence that the inner and outer disks are misaligned in this pre-transitional system. This may account for the shadows previously detected in the outer disk. We show that Brγ emission arises from an even more compact region than the inner disk, with an upper limit of 0.047 au (~5 R⋆). Differential phase measurements between the Brγ line and the continuum allow us to measure the astrometric displacement of the Brγ line-emitting region relative to the continuum on a scale of a few tens of microarcsec, corresponding to a fraction of the stellar radius. Conclusions. Our results can be accounted for by a simple geometric model where the Brγ line emission arises from a compact region interior to the inner disk edge, on a scale of a few stellar radii, fully consistent with the concept of magnetospheric accretion process in low-mass young stellar systems.

scholarly journals Measuring the physical conditions of accreting gas in T Tauri systems

2007 ◽  
Vol 3 (S243) ◽  
pp. 95-102
Author(s):  
Jeffrey S. Bary ◽  
Sean P. Matt
Keyword(s):  
Near Infrared ◽  
Young Star ◽  
Emission Lines ◽  
Line Flux ◽  
Star Forming ◽  
Physical Conditions ◽  
T Tauri ◽  
Hydrogen Emission Lines ◽  
Line Theory ◽  
Magnetospheric Accretion

AbstractHydrogen emission lines observed from T Tauri stars (TTS) are associated with the accretion/outflow of gas in these young star forming systems. Magnetospheric accretion models have been moderately successful at reproducing the shapes of several Hi emission line profiles, suggesting that the emission arises in the accretion funnels. Despite considerable effort to model and observe these emission features, the physical conditions of the gas confined to the funnel flows remain poorly constrained by observation. We conducted a mutli-epoch near-infrared spectroscopic survey of 16 actively accreting classical TTS in the Taurus-Auriga star forming region. We present an analysis of these simultaneously acquired line flux ratios of many Paschen and Brackett series emission lines, in which we compare the observed ratios to those predicted by the Case B approximation of hydrogen recombination line theory. We find that the line flux ratios for the Paschen and Brackett decrements as well as a comparison between Brγ and Paschen transitions agree well with the Case B models with T < 5000 K and ne ≈ 1010 cm−3.

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