Infrared Hydrogen Lines Research Articles

Hydrogen emission from accretion and outflow in T Tauri stars

ABSTRACT 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/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 included axisymmetric magnetospheric accretion and a polar stellar wind. The distribution of Reipurth types and line widths for the synthetic H α lines is similar to the observed results. However, the modelled infrared lines are narrower than the observations by ${\approx}80\,{~\rm km\,s}^{-1}$, and our models predict a significantly higher proportion (≈90 per cent) of inverse P-Cygni profiles. Furthermore, our radiative transfer models suggest that the frequency of P-Cygni profiles depends on the ratio of the mass-loss to mass accretion rates and blue-shifted sub-continuum absorption was predicted for mass-loss rates as low as 10−12 M⊙ yr−1. We explore the effect of rotation, turbulence, and the contributions from red-shifted absorption in an attempt to explain the discrepancy in widths. Our findings show that, singularly, none of these effects is sufficient to explain the observed disparity. However, a combination of rotation, turbulence, and non-axisymmetric accretion may improve the fit of the models to the observed data.

Bolometric luminosity estimators using infrared hydrogen lines for dust obscured active galactic nuclei

ABSTRACT Bolometric luminosity is an important quantity that tells us the radiative energy output of an active galactic nucleus (AGN). A common way to estimate bolometric luminosity is to use ultraviolet (UV) or optical luminosities as its proxies, but the UV- or optical-based-bolometric luminosity estimators can be easily affected by dust extinction. In this study, we present new methods for estimating bolometric luminosities using infrared (IR) hydrogen Paschen and Brackett line luminosities to alleviate the dust extinction effects. We show that there exist tight correlations between the bolometric luminosities and the IR hydrogen line luminosities, and present the IR hydrogen line-based-bolometric luminosity estimators. As an example, we apply the relation to dust obscured red AGNs, confirming previous results that red AGNs have higher Eddington rations than unobscured AGNs. The new bolometric luminosity estimator will be useful for studying obscured AGNs (e.g. red AGNs, Compton thick AGNs, and Type 2 AGNs), during the coming era of sensitive near-infrared (NIR) and mid-infrared (MIR) missions, such as the James Webb Space Telescope.

Accretion in $\mathsf{\rho}$ Ophiuchus brown dwarfs: infrared hydrogen line ratios

Context. Mass accretion rate determinations are fundamental for an understanding of the evolution of pre-main sequence star circumstellar disks. Aims. Magnetospheric accretion models are used to derive values of the mass accretion rates in objects of very different properties, from brown dwarfs to intermediate-mass stars; we test the validity of these models in the brown dwarf regime, where the stellar mass and luminosity, as well as the mass accretion rate, are much lower than in T Tauri stars. Methods. We have measured nearly simultaneously two infrared hydrogen lines, Pa β and Br$_\gamma$, in a sample of 16 objects in the star-forming region ρ -Oph. The sample includes 7 very low mass objects and brown dwarfs and 9 T Tauri stars. Results. Brown dwarfs where both lines are detected have a ratio Pa β /Br$_\gamma$of ~2. Larger values, $\ga$3.5, are only found among the T Tauri stars. The low line ratios in brown dwarfs indicate that the lines cannot originate in the column of gas accreting from the disk onto the star along the magnetic field lines, and we suggest that they form instead in the shocked photosphere, heated to temperatures of ~3500 K. If so, in analogy to veiling estimates in T Tauri stars, the hydrogen infrared line fluxes may provide a reliable measure of the accretion rate in brown dwarfs.

Near infrared hydrogen lines as diagnostic of accretion and winds in T Tauri stars

From a sample of 50 T Tauri stars, mostly from the Taurus-Auriga complex, Pa$\mathrm{\beta}$ line profiles were obtained for 49 of the stars and Br$\mathrm{\gamma}$ profiles for 37 of the stars. Emission at Pa$\mathrm{\beta}$ was observed for 42 stars and emission at Br$\mathrm{\gamma}$ was found for 30 stars. The most conspicuous features in the line profiles is the almost complete absence of blueshifted absorption components and the relatively high frequency of inverse P Cygni profiles (IPC). At Pa$\mathrm{\beta}$, 34% of the profiles are IPC while at Br$\mathrm{\gamma}$ 20% are IPC. The redshifted absorption features indicate infall at velocities of about $200 s}^{-1}$, compatible with free fall from a few radii out. In general, line profiles are broad centrally peaked with slightly blueshifted line peaks. Existing wind and accretion models fail, in quantitative terms, to explain the shape of the observed profiles. Magnetospheric accretion models, being the currently preferred ones, produce lines too narrow (by ∼ $100 \mathrm{km s}^{-1}$ FWHM ), wings extending to velocities too low (by at least ∼ $100 s}^{-1}$) and with maximum normalized intensities too high by factors of a few. A qualitative agreement between some of the accretion model predicted profiles and some observations hint that emission in these lines might, at least partially, arise from infalling material. Definite claims regarding the origin of the emission in these lines cannot be made until models match observations much better than they currently do.

Hydrogen Emission from Low Column Density Gas: Case C

ABSTRACTWith modern detectors it is now possible to image dilute gas near powerful sources of ionizing radiation. This note concerns hydrogen emission expected from such gas. Hydrogen recombination lines are usually said to be formed under either Case A or Case B conditions. Case B occurs when the neutral hydrogen column density is large enough for Lyman lines to be optically thick. They undergo multiple scatterings and are eventually degraded into a Balmer line and Lyα or two‐photon emission. Case A occurs when the neutral hydrogen column density is small enough for Lyman lines to be optically thin and so freely escape the cloud. Optical and infrared hydrogen lines are weaker in Case A than Case B since a significant fraction of the energy escapes as Lyman lines.Numerical simulations presented here show that when a photoionized cloud is optically thin in the Lyman lines its optical and infrared emission is not described by Case A. These lines will always be enhanced by continuum pumping unless the continuum source contains strong Lyman absorption lines. Continuum fluorescence in the Lyman lines will usually be competitive with recombination since the integrated continuous oscillator strength of the Lyman continuum is of order that of the Lyman lines. The line spectrum produced by a low column density cloud is mainly determined by the spectrum of the incident radiation field and the Lyman line optical depth. This situation was defined in the original literature as “Case C.” It was not developed because the central stars of nebulae might have strong Lyman absorption lines, and so little pumping occurs in the interstellar case. This effect will be generally important for lower column density clouds in extragalactic sources, where Lyman lines are seldom in absorption. The purpose of this note is to draw attention to Case C and to motivate more precise calculations of emission in this limit.

Properties of infrared hydrogen lines of YSOs: Hou Jin-liang, Fu cheng-qi & Jiang Dongrong Shanghai Observatory, Chinese Academy of Sciences, Shanghai 200030

Properties of infrared hydrogen lines of YSOs: Hou Jin-liang, Fu cheng-qi & Jiang Dongrong Shanghai Observatory, Chinese Academy of Sciences, Shanghai 200030

Modeling the Infrared Magnesium and Hydrogen Lines from Quiet and Active Solar Regions

The emission lines of Mg I at 7.4, 12.2, and 12.3 μm are now known to be formed in the upper photosphere; the line emission is due to collisional coupling of higher levels with the continuum together with radiative depopulation of lower levels. These combined effects cause the line source functions of high-lying transitions to exceed the corresponding Planck functions. However, there are uncertainties in a) the relevant atomic data, particularly the collisional rates and ultraviolet photoionization rates, and b) the sensitivity of the calculated results to changes in atmospheric temperature and density. These uncertainties are examined by comparing twelve calculated Mg I line profiles in the range 2.1-12.3 μm with ATMOS satellite observations. We show results based on different rates, and using different atmospheric models representing a range of dark and bright spatial features. The calculated Mg profiles are found to be relatively insensitive to atmospheric model changes, and to depend critically on the choice of collisional and photoionization rates. We find better agreement with the observations using collision rates from van Regemorter (1962) rather than from Seaton (1962). We also compare twelve calculated hydrogen profiles in the range 2.2-12.4 μm with ATMOS observations. The available rates and cross sections for hydrogen seem adequate to account for the observed profiles, while the calculated lines are highly sensitive to atmospheric model changes. These lines are perhaps the best available diagnostics of the temperature and density structure of the photosphere and low chromosphere. Further calculations based on these infrared hydrogen lines should lead to greatly improved models of the solar atmosphere.

Computation of Infrared Hydrogen Lines

We compare infrared hydrogen lines observed with ATMOS with computations for two models of the solar atmosphere, one without and one with a chromosphere. The weaker H I lines are formed in the photosphere. Proper evaluation of Stark broadening is required to reproduce their profiles; the heavy ion contribution is most important. The cores of the stronger lines are sensitive to the structure of the chromosphere, but detailed NLTE modeling is needed for diagnostic applications.

Pa-beta measurements and reddening in Seyfert 1.8 and 1.9 galaxies

view Abstract Citations (41) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS PA beta Measurements and Reddening in Seyfert 1.8 and 1.9 Galaxies Goodrich, Robert W. Abstract The class of active galactic nuclei known as Seyfert 1.8 and Seyfert 1.9 galaxies exhibit weak broad-Balmer emission lines and large Balmer decrements. One theory proposed to explain these characteristics is that the broad-line regions (BLRs) are reddened by dust along our line-of-sight. An alternative theory points out that BLR clouds with low-optical depths and low-ionization parameters can reproduce the observed line ratios. These two theories predict very different fluxes of the infrared hydrogen lines. In order to test the theories this paper presents measurements of the Paβ emission lines of 10 intermediate Seyferts. Three objects known to have exhibited extreme spectral variability, NGC 2622, NGC 7603, and Mrk 1018, now all in Seyfert 1 states, are consistent with the reddening theory, as is IRAS 1958-183. Two other objects, Mrk 609 (a Seyfert 1.5) and UGC 7064, are more consistent with the optical depth/ionization parameter theory. Hence the Seyfert 1.8/1.9 class is evidently a heterogeneous one. Publication: The Astrophysical Journal Pub Date: May 1990 DOI: 10.1086/168743 Bibcode: 1990ApJ...355...88G Keywords: Astronomical Models; Balmer Series; Paschen Series; Seyfert Galaxies; Active Galactic Nuclei; Infrared Spectroscopy; Interstellar Extinction; Optical Thickness; Astrophysics; GALAXIES: NUCLEI; GALAXIES: SEYFERT; INFRARED: SPECTRA full text sources ADS | data products SIMBAD (14) NED (10) MAST (1)

The Spectra of Helium and Hydrogen

WITH regard to Mr. Evans's communication to NATURE, September 4, p. 5, I should like to remark that while I have for some time recognised that the experimental evidence, on the whole, seems to be in favour of helium as the origin of the new lines 4686, c these bands are of very feeble intensity at the low pressures necessary for their approximate isolation in the spectrum of the pure gas, but I have seen them greatly intensified when carbonic oxide was present as an impurity in helium. Also, the Ritz series of infra-red hydrogen lines was found by Paschen to be brighter in a mixture of hydrogen and helium than in hydrogen alone. Apart from this, I find it difficult to believe that the close agreement of one set of lines with the principal series calculated for hydrogen by Rydberg is merely accidental.

The Spectra of Helium and Hydrogen

WITH regard to Mr. Evans's communication to NATURE, September 4, p. 5, I should like to remark that while I have for some time recognised that the experimental evidence, on the whole, seems to be in favour of helium as the origin of the new lines 4686, c these bands are of very feeble intensity at the low pressures necessary for their approximate isolation in the spectrum of the pure gas, but I have seen them greatly intensified when carbonic oxide was present as an impurity in helium. Also, the Ritz series of infra-red hydrogen lines was found by Paschen to be brighter in a mixture of hydrogen and helium than in hydrogen alone. Apart from this, I find it difficult to believe that the close agreement of one set of lines with the principal series calculated for hydrogen by Rydberg is merely accidental.