scholarly journals Thermal Structure of Magnetic Funnel Flows

1997 ◽  
Vol 182 ◽  
pp. 455-463
Author(s):  
Steven C. Martin
Keyword(s):  
Near Infrared ◽  
Thermal Structure ◽  
Line Emission ◽  
Rate Equations ◽  
Bremsstrahlung Radiation ◽  
Ionization Degree ◽  
Thermodynamic Structure ◽  
Accretion Rates ◽  
Funnel Flow ◽  
Stellar Magnetic Fields

The thermodynamic structure of gas that is channeled by stellar magnetic fields onto a young (pre–main-sequence) star is presented. In this model, the star possesses a dipole magnetic field which disrupts the inner regions of a geometrically thin accretion disk and channels the inflowing gas onto the stellar surface, thereby forming an accretion funnel. The temperature and ionization degree of the inflowing gas is calculated by solving the heat equation coupled to statistical rate equations for hydrogen. It is found that for typical accretion rates of ∼ 10–7M⊘yr–1, temperatures of ∼ 7000 K and hydrogen ionization fractions (nH+/nH) of ∼ 10–2 can be attained in the funnel flow. The principal heat source is found to be adiabatic compression, and coolants include bremsstrahlung radiation as well as line emission from the Ca II and Mg II ions. The relatively hot and ionized funnel flow lead to observational signatures such as inverse P Cygni line profiles seen in upper Balmer and near-infrared lines. In addition, carbon monoxide bandhead emission may be an important tracer of the outer portions of the funnel flow.

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 Flybys in protoplanetary discs – II. Observational signatures

2019 ◽  
Vol 491 (1) ◽  
pp. 504-514 ◽  
Author(s):  
Nicolás Cuello ◽  
Fabien Louvet ◽  
Daniel Mentiplay ◽  
Christophe Pinte ◽  
Daniel J Price ◽  
...  
Keyword(s):  
Radiative Transfer ◽  
Near Infrared ◽  
Scattered Light ◽  
Line Emission ◽  
Star Clusters ◽  
Post Process ◽  
Accretion Rates ◽  
Fu Ori ◽  
Hydrodynamical Simulations ◽  
Multiwavelength Observations

ABSTRACT Tidal encounters in star clusters perturb discs around young protostars. In Cuello et al., we detailed the dynamical signatures of a stellar flyby in both gas and dust. Flybys produce warped discs, spirals with evolving pitch angles, increasing accretion rates, and disc truncation. Here, we present the corresponding observational signatures of these features in optical/near-infrared scattered light and (sub) millimetre continuum and CO line emission. Using representative prograde and retrograde encounters for direct comparison, we post-process hydrodynamical simulations with radiative transfer methods to generate a catalogue of multiwavelength observations. This provides a reference to identify flybys in recent near-infrared and submillimetre observations (e.g. RW Aur, AS 205, HV Tau and DO Tau, FU Ori, V2775 Ori, and Z CMa).

scholarly journals On the Coronal and Prominence Structures Observed at the Total Solar Eclipse of 11 July 1991

1994 ◽  
Vol 154 ◽  
pp. 205-210
Author(s):  
Y. Suematsu ◽  
H. Fukushima ◽  
Y. Nishino
Keyword(s):  
Solar Eclipse ◽  
Near Infrared ◽  
Thermal Structure ◽  
Wavelength Region ◽  
Total Solar Eclipse ◽  
Preliminary Results ◽  
Spectroscopic Observations ◽  
Physical Conditions ◽  
Made In

Coronal images were taken in the light of the He I 10830 Å line, the 10000 Å continuum, and the Fe XIV 5303 Å line, with the aim of studying the thermal structure of the corona. In addition, spectroscopic observations were made in the violet wavelength region (3760-4060 Å) and near-infrared (10745-10835 Å), to obtain details of physical conditions of the corona, especially of its cool part. The data obtained do not show any distinct cool structures other than ordinary prominences. Some preliminary results concerning the corona and prominence structures are given.

scholarly journals Evidence of a significant rotational non-LTE effect in the CO<sub>2</sub> 4.3 µm PFS-MEX limb spectra

2017 ◽  
Vol 10 (1) ◽  
pp. 265-271 ◽  
Author(s):  
Alexander A. Kutepov ◽  
Ladislav Rezac ◽  
Artem G. Feofilov
Keyword(s):  
Near Infrared ◽  
Thermal Structure ◽  
Radiative Lifetime ◽  
Martian Atmosphere ◽  
Vibrational States ◽  
Rotational States ◽  
First Results ◽  
Rotational Distribution ◽  
Multi Level ◽  
Excited Molecules

Abstract. Since January 2004, the planetary Fourier spectrometer (PFS) on board the Mars Express satellite has been recording near-infrared limb spectra of high quality up to the tangent altitudes ≈ 150 km, with potential information on density and thermal structure of the upper Martian atmosphere. We present first results of our modeling of the PFS short wavelength channel (SWC) daytime limb spectra for the altitude region above 90 km. We applied a ro-vibrational non-LTE model based on the stellar astrophysics technique of accelerated lambda iteration (ALI) to solve the multi-species and multi-level CO2 problem in the Martian atmosphere. We show that the long-standing discrepancy between observed and calculated spectra in the cores and wings of 4.3 µm region is explained by the non-thermal rotational distribution of molecules in the upper vibrational states 10011 and 10012 of the CO2 main isotope second hot (SH) bands above 90 km altitude. The redistribution of SH band intensities from band branch cores into their wings is caused (a) by intensive production of the CO2 molecules in rotational states with j > 30 due to the absorption of solar radiation in optically thin wings of 2.7 µm bands and (b) by a short radiative lifetime of excited molecules, which is insufficient at altitudes above 90 km for collisions to maintain rotation of excited molecules thermalized. Implications for developing operational algorithms for massive processing of PFS and other instrument limb observations are discussed.

scholarly journals Red Giant Winds as Emission Line Clouds (Broad or Narrow) in Active Galactic Nuclei

1989 ◽  
Vol 134 ◽  
pp. 310-311
Author(s):  
Demosthenes Kazanas
Keyword(s):  
Standard Model ◽  
Emission Line ◽  
Line Emission ◽  
Cloud Formation ◽  
Uniform Density ◽  
Dynamical Mechanism ◽  
The Standard Model ◽  
Accretion Rates ◽  
Red Giant ◽  
Self Gravity

It is proposed that the clouds thought responsible for the line emission in AGN are not of uniform density but stratified. Such a stratification may be a result either of their self-gravity or of gas dynamics associated with each cloud (e.g. winds). To fix ideas we assume the latter possibility, we examine the consequences and compare with the observations and the phenomenology of emission line clouds.(For the general properties of these clouds see review by Netzer in this volume). Given the successes of the standard model the reader may wonder why is there any need for revisions. The reasons are given in detail elsewhere (see also Scoville and Norman this volume). In brief these are the drag of clouds though the confining medium, the excessive accretion rates implied by the standard model, the response of the line radiation to changes in the continuum, and the lack of a dynamical mechanism for cloud formation. Finally, in the “standard” picture the narrow line clouds are a distinct population with separate dynamics and origin.

scholarly journals Hot Accretion Disks with Magnetic Field and Thermal Cyclo-Synchrotron Radiation

1994 ◽  
Vol 159 ◽  
pp. 485-485
Author(s):  
Masaaki Kusunose ◽  
Andrzej A. Zdziarski
Keyword(s):  
Magnetic Field ◽  
Synchrotron Radiation ◽  
Spectral Index ◽  
Accretion Disks ◽  
Qualitative Properties ◽  
Bremsstrahlung Radiation ◽  
X Ray ◽  
Accretion Rates ◽  
Galactic Black Hole ◽  
Two Temperature

We study the structure of hot, two-temperature accretion disks around black holes, including the effects of thermal cyclo-synchrotron radiation and magnetic viscosity. This work is an extension of previous work by Björnsson & Svensson (1991a, b, 1992) and Kusunose & Mineshige (1992), which did not include those effects. Magnetic field, B, is assumed to be randomly oriented and determined by prescribing the ratio α = Pmag/Pgas or α = Pmag/(Pgas + Prad), where Pmag, Pgas, and Prad are the pressures of magnetic field, gas, and radiation, respectively. We find those effects do not change the qualitative properties of the disks, i.e., there are two critical accretion rates related to production of e± pairs, ṀcrU and ṀcrL that affect the number of local and global disk solutions, as recently found for the case with B = 0 (Björnsson & Svensson 1991a, b, 1992). However, a critical value of the α-viscosity parameter above which those critical accretion rates disappear becomes smaller than αcr = 1 found in the case of B = 0, for Pmag = α(Pgas + Prad). If Pmag = αPgas, on the other hand, αcr is still about unity. Moreover, when Comptonized cyclo-synchrotron radiation dominates Comptonized bremsstrahlung, radiation from the disk obeys a power law with the energy spectral index of ∼ 0.5, in a qualitative agreement with X-ray observations of AGNs and Galactic black hole candidates. The spectral index is weakly dependent on the mass accretion rate.

scholarly journals Properties of LBGs with [OIII] detection at z ∼ 3.5

2019 ◽  
Vol 631 ◽  
pp. A123 ◽  
Author(s):  
Fang-Ting Yuan ◽  
Denis Burgarella ◽  
David Corre ◽  
Veronique Buat ◽  
Médéric Boquien ◽  
...  
Keyword(s):  
Physical Properties ◽  
Emission Line ◽  
Near Infrared ◽  
Spectral Energy Distribution ◽  
Formation Rate ◽  
Line Emission ◽  
Stellar Mass ◽  
Spectral Energy ◽  
Emission Data ◽  
The Impact

Context. Nebular emission lines are critical to measure physical properties in the ionized gas (e.g., metallicity, the star formation rate, or dust attenuation). They also account for a significant fraction of broadband fluxes, in particular at the highest redshifts, and therefore can strongly affect the determination of other physical properties, such as the stellar mass, which are crucial in shaping our understanding of galaxy formation and evolution. Aims. We investigate a sample of 51 Lyman break galaxies at 3.0 <  zspec <  3.8 with detected [OIII] line emissions and estimated the physical properties of these galaxies to examine the impact of including nebular emission data in the Spectral energy distribution (SED) fitting. Methods. We used the Code Investigating GALaxy Emission (CIGALE) to fit the rest-frame ultraviolet-to-near-infrared SEDs of these galaxies and their emission line data simultaneously. We ran CIGALE with and without the nebular model or the emission line data, and compare the results to show the importance of including the nebular emission line data in the SED fitting. Results. We find that without the nebular model, the SED fitting overestimates the stellar mass due to the strong [OIII] lines that are redshifted to the Ks-band, which is consistent with previous results. The emission line data are necessary to constrain the nebular model in the SED fitting. We examine the Ks-band excess, which is mostly used to estimate the emissions of the [OIII]+Hβ lines when there is no spectral data, and we find that the estimation and observation are statistically consistent. However, the difference can reach up to more than 1 dex in some catastrophic cases, which shows the importance of obtaining spectroscopic measurements for these lines. We also estimate the equivalent width of the Hβ absorption and find it negligible compared to the Hβ emission. Conclusions. Line emission is important to constrain the nebular models and to obtain reliable estimates of the physical properties of galaxies. These data should be taken into account in the SED fitting.

Tunable dual emission in visible and near-infrared spectra using Co2+-doped PbSe nanocrystals embedded in a chalcogenide glass matrix

2016 ◽  
Vol 18 (33) ◽  
pp. 23036-23043 ◽  
Author(s):  
Sidney A. Lourenço ◽  
Ricardo S. Silva ◽  
Noelio O. Dantas
Keyword(s):  
Excited State ◽  
Infrared Spectra ◽  
Glass Matrix ◽  
Near Infrared ◽  
Line Emission ◽  
Energy Transition ◽  
Narrow Line ◽  
Dual Emission ◽  
Broadband Emission ◽  
Near Infrared Spectra

Emission of Co2+-doped PbSe nanocrystals (NCs) present a excited-state crossover from 4T1(P) → 4A2(F) broadband emission to 2E(G) → 4A2(F) narrow-line emission, and its localized energy transition (4A2(F) → 4T1(4F)) can be tunable from band-gap to the conduction-band by change NC size.

A single-double pass Sisam spectrometer for the near infrared

1977 ◽  
Vol 353 (1674) ◽  
pp. 421-430 ◽  
Keyword(s):  
High Resolution ◽  
Near Infrared ◽  
Line Emission ◽  
Signal Strength ◽  
Emission Sources ◽  
Double Pass ◽  
Single Pass ◽  
Modulation Technique ◽  
Infra Red ◽  
Coherent Modulation

A double-pass Sisam spectrometer of high resolution and sensitivity, previously described, has been modified for single-pass operation. For discrete line emission sources, this modification provides a gain of a factor of 6 in sensitivity at the expense of a loss of a factor of 2 in resolution in the near infra red region. As is demonstrated, the modified instrument is particularly suitable for the study of weak spectral sources. A coherent modulation system has also been incorporated which eliminates the periodic variations in signal strength arising from the non-coherent modulation technique previously employed.

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