scholarly journals Near-IR Fluorescent Molecular Hydrogen Emission from NGC 2023

1998 ◽  
Vol 15 (2) ◽  
pp. 194-201 ◽  
Author(s):  
Michael G. Burton ◽  
J. E. Howe ◽  
T. R. Geballe ◽  
P. W. J. L. Brand
Keyword(s):  
Energy Range ◽  
Spectral Resolution ◽  
Ground State ◽  
Molecular Hydrogen ◽  
Line Emission ◽  
Hydrogen Line ◽  
Atmospheric Transmission ◽  
Hydrogen Emission ◽  
Near Ir ◽  
Photodissociation Regions

AbstractSpectra from 1 to 2·5 μm, at 230–430 spectral resolution, are presented of the fluorescent molecular hydrogen line emission from two locations in the reflection nebula NGC 2023. Over 100 H2 lines can be identified in the spectra, although blending and poor atmospheric transmission mean that reliable level column densities can only be obtained from 35 lines. This latter group includes lines from v = 1–8 and v = 10, spanning an energy range from 6000 to 45,000 K above the ground state. These data may be used to constrain models of photodissociation regions and of fluorescent excitation for molecular hydrogen.

scholarly journals Excitation of H2 and HD in Shocks and PDRs

2000 ◽  
Vol 197 ◽  
pp. 191-201 ◽  
Author(s):  
F. Bertoldi ◽  
B. T. Draine ◽  
D. Rosenthal ◽  
R. Timmermann ◽  
S. K. Ramsay Howat ◽  
...  
Keyword(s):  
Emission Line ◽  
High Velocity ◽  
Molecular Hydrogen ◽  
Line Emission ◽  
High Excitation ◽  
Vibrationally Excited ◽  
Photodissociation Regions ◽  
Very High

Photodissociation regions (PDRs) and shocks give rise to conspicuous emission from rotationally and vibrationally excited molecular hydrogen. This line emission has now been studied with ISO and from the ground in great detail. A remarkable discovery has been that toward the Orion outflow and other shock-excited regions, the H2 level populations show a very high excitation component. We suggest that these high-excitation populations may arise from non-thermal pumping processes, such as H2 formation and high-velocity ion-molecule collision in partially dissociative shocks. In PDRs such as NGC 7023 however, formation pumping is always less important than fluorescent pumping.We furthermore present two HD emission line detections toward Orion Peak 1. This enables the first comparison of the H2 and the HD excitation, which surprisingly turn out to be identical.

scholarly journals Spectropolarimetry of the molecular hydrogen line emission from OMC-1

1988 ◽  
Vol 235 (1) ◽  
pp. 161-174 ◽  
Author(s):  
M. G. Burton ◽  
J. H. Hough ◽  
D. J. Axon ◽  
T. Hasegawa ◽  
M. Tamura ◽  
...  
Keyword(s):  
Molecular Hydrogen ◽  
Line Emission ◽  
Hydrogen Line

Infrared Surveys from Antarctica

1996 ◽  
Vol 13 (1) ◽  
pp. 7-9 ◽  
Author(s):  
Jeremy Bailey
Keyword(s):  
Galaxy Evolution ◽  
Molecular Hydrogen ◽  
High Redshift ◽  
Brown Dwarfs ◽  
Emission Lines ◽  
Star Forming ◽  
Hydrogen Emission ◽  
Near Ir ◽  
Infrared Surveys ◽  
Galactic Sources

AbstractThe very low background observed from Antarctica in a window from about 2·25 to 2·45 μm can be exploited as a way of making deep near-IR surveys over wide areas of sky. Imaging surveys using the entire window can cover large areas of sky to limits of around K = 20, and can be used to study galaxy evolution and to search for high-redshift quasars, dust-obscured quasars and brown dwarfs. It is also possible to make spectroscopic surveys in this window. The window includes molecular hydrogen emission and CO absorption in galactic sources, and can also be used to search for emission lines such as Hα in high-redshift star-forming galaxies.

scholarly journals The spatial distribution and velocity field of the molecular hydrogen line emission from the centre of the Galaxy

1986 ◽  
Vol 222 (2) ◽  
pp. 299-306 ◽  
Author(s):  
Ian Gatley ◽  
Terry J. Jones ◽  
A. R. Hyland ◽  
Richard Wade ◽  
T. R. Geballe ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Velocity Field ◽  
Molecular Hydrogen ◽  
Line Emission ◽  
Hydrogen Line ◽  
The Galaxy

scholarly journals Molecular Hydrogen Emission from Cold Condensations in NGC 2440

1989 ◽  
Vol 131 ◽  
pp. 207-207
Author(s):  
N. K. Reay ◽  
N. A. Walton ◽  
P. D. Atherton
Keyword(s):  
Planetary Nebula ◽  
Molecular Hydrogen ◽  
Total Mass ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Line Emission ◽  
Central Star ◽  
Hydrogen Emission ◽  
H Ii Region ◽  
Hydrogen Mass

We report observations of the v = 1-0 S(1) line of molecular hydrogen in the high excitation Planetary Nebula NGC 2440. The emission is particularly strong at the positions of the two bright condensations which lie well within the H II region and close to the position of the very hot T = 350,000 K central star. The emission is consistent with an excited molecular hydrogen mass of 2–4 × 10−5 M⊙ in the condensations, and we estimate the total mass of excited molecular hydrogen associated with the H II region to be 6 × 10−3 M⊙. We show that the radiation pressure from the central star is insufficient to excite the S(1) line emission. We also show that a stellar wind driven shock would imply a mass loss rate of 3 × 10−7 M⊙ yr−1 if we adopt a wind velocity of 2000 km s−1.

scholarly journals Evidence of chromospheric molecular hydrogen emission in a solar flare observed by the IRIS satellite

2021 ◽  
Author(s):  
Sargam M Mulay ◽  
Lyndsay Fletcher
Keyword(s):  
Molecular Hydrogen ◽  
Line Emission ◽  
Temporal Correlation ◽  
Impulsive Phase ◽  
Turbulent Plasma ◽  
Temperature Minimum ◽  
Line Broadening ◽  
Comprehensive Investigation ◽  
Hydrogen Emission ◽  
Gradual Decay

Abstract We have carried out the first comprehensive investigation of enhanced line emission from molecular hydrogen, H2 at 1333.79 Å, observed at flare ribbons in SOL2014-04-18T13:03. The cool H2 emission is known to be fluorescently excited by Si iv 1402.77 Å UV radiation and provides a unique view of the temperature minimum region (TMR). Strong H2 emission was observed when the Si iv 1402.77 Å emission was bright during the flare impulsive phase and gradual decay phase, but it dimmed during the GOES peak. H2 line broadening showed non-thermal speeds in the range 7-18 $\rm {km~s}^{-1}$, possibly corresponding to turbulent plasma flows. Small red (blue) shifts, up to 1.8 (4.9) $\rm {km~s}^{-1}$ were measured. The intensity ratio of Si iv 1393.76 Å and Si iv 1402.77 Å confirmed that plasma was optically thin to Si iv (where the ratio = 2) during the impulsive phase of the flare in locations where strong H2 emission was observed. In contrast, the ratio differs from optically thin value of 2 in parts of ribbons, indicating a role for opacity effects. A strong spatial and temporal correlation between H2 and Si iv emission was evident supporting the notion that fluorescent excitation is responsible.

scholarly journals Fluorescent Line Emission of Molecular Hydrogen

1987 ◽  
Vol 115 ◽  
pp. 139-141 ◽  
Author(s):  
John H. Black ◽  
Ewine F. van Dishoeck
Keyword(s):  
High Temperature ◽  
Ground State ◽  
Molecular Hydrogen ◽  
Line Emission ◽  
Electric Quadrupole ◽  
Thermal Excitation ◽  
Hot Stars ◽  
Interstellar Clouds ◽  
Vibration Rotation ◽  
Electronic Ground

The electric quadrupole vibration-rotation transitions of molecular hydrogen can be excited either by thermal collisions in regions of high temperature or by ultraviolet absorption and fluorescence that leaves the molecules in excited levels, v>0, of the electronic ground state in interstellar clouds located very close to hot stars. Predictions of this fluorescent emission (Gould and Harwit 1963, Black and Dalgarno 1976) have only recently been confirmed by observations in Orion (Hayashi et al. 1985) and toward the reflection nebula NGC 2023 (Gatley and Kaifu 1987). Most previous observations of the 2 μm H2 lines have been consistent with thermal excitation in shocked regions.

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