Observations of the Hydrogen Recombination Line 158α in Galactic H II Regions

1967 ◽  
Vol 150 ◽  
pp. 435 ◽  
Author(s):  
Nannielou H. Dieter
Keyword(s):  
H Ii Regions ◽  
Recombination Line ◽  
Hydrogen Recombination

scholarly journals An nl-model with radiative transfer for hydrogen recombination line masers

2019 ◽  
Author(s):  
Andri Prozesky ◽  
Derck P Smits
Keyword(s):  
Radiative Transfer ◽  
Atomic Hydrogen ◽  
H Ii Regions ◽  
Recombination Line ◽  
Escape Probability ◽  
General Behaviour ◽  
Hydrogen Recombination ◽  
Theoretical Predictions ◽  
Good Agreement ◽  
Atomic Populations

Abstract Atomic hydrogen masers occur in recombination plasmas in sufficiently dense H ii regions. These hydrogen recombination line (HRL) masers have been observed in a handful of objects to date and the analysis of the atomic physics involved has been rudimentary. In this work a new model of HRL masers is presented which uses an nl-model to describe the atomic populations interacting with free-free radiation from the plasma, and an escape probability framework to deal with radiative transfer effects. The importance of including the collisions between angular momentum quantum states and the free-free emission in models of HRL masers is demonstrated. The model is used to describe the general behaviour of radiative transfer of HRLs and to investigate the conditions under which HRL masers form. The model results show good agreement with observations collected over a broad range of frequencies. Theoretical predictions are made regarding the ratio of recombination lines from the same upper quantum level for these objects.

scholarly journals Probing Sagittarius A* accretion with ALMA

2016 ◽  
Vol 11 (S322) ◽  
pp. 21-24
Author(s):  
Elena Murchikova
Keyword(s):  
Galactic Center ◽  
Accretion Rate ◽  
Recombination Line ◽  
Ionized Gas ◽  
X Ray ◽  
Sagittarius A ◽  
Hydrogen Recombination ◽  
Unique Probe ◽  
Cool Gas

AbstractThe submm Hydrogen recombination line technique can be used as a probe of the Galactic Center. We present the results of our H30α observations of ionized gas from within 0.015 pc around SgrA*. The observations were obtained on ALMA in cycle 3. The line was not detected, but we were able to set a limit on the mass of the cool gas (T~ 104 K) at 2 × 10−3M⊙. This is the unique probe of gas cooler than T ~106 K traced by X-ray emission. The total amount of gas near SgrA* gives us clues to understanding the accretion rate of SgrA*.

Recombination-line and continuum observations of compact H II regions at 10.5 GHz

1976 ◽  
Vol 81 ◽  
pp. 512 ◽  
Author(s):  
M. R. Viner ◽  
J. N. Clarke ◽  
V. A. Hughes
Keyword(s):  
H Ii Regions ◽  
Recombination Line

Compact H II regions - Hydrogen recombination and OH maser lines

1985 ◽  
Vol 289 ◽  
pp. 681 ◽  
Author(s):  
G. Garay ◽  
M. J. Reid ◽  
J. M. Moran
Keyword(s):  
H Ii Regions ◽  
Hydrogen Recombination

scholarly journals A Survey of Recombination-line Abundances in Planetary Nebulae and H II Regions

2003 ◽  
Vol 209 ◽  
pp. 383-384 ◽  
Author(s):  
Y. G. Tsamis ◽  
M. J. Barlow ◽  
X.-W. Liu ◽  
I. J. Danziger
Keyword(s):  
Planetary Nebulae ◽  
Magellanic Cloud ◽  
H Ii Regions ◽  
Recombination Line ◽  
Large Aperture

We have derived C, N and O abundances, relative to H, using optical recombination lines (ORLs), for a number of galactic planetary nebulae and for three Magellanic Cloud PNe (LMC N66, N141, SMC N87) and compared them with the corresponding abundances derived from collisionally-excited lines (CELs). Our goal was to investigate the fact that PNe ORL abundances are in most cases larger than those obtained from CELs. Our scanning, long-slit observations were combined with large-aperture IUE, IRAS and ISO data to yield integrated abundances for more than half of our target objects.

scholarly journals ALMA observations of the submillimetre hydrogen recombination line from the type 2 active nucleus of NGC 1068

2016 ◽  
Vol 459 (4) ◽  
pp. 3629-3634 ◽  
Author(s):  
Takuma Izumi ◽  
Kouichiro Nakanishi ◽  
Masatoshi Imanishi ◽  
Kotaro Kohno
Keyword(s):  
Recombination Line ◽  
Active Nucleus ◽  
Hydrogen Recombination ◽  
Ngc 1068

scholarly journals Observations of 23 Planetary Nebulae at 408 MHz

1969 ◽  
Vol 22 (4) ◽  
pp. 545 ◽  
Author(s):  
AE Le Marne
Keyword(s):  
Planetary Nebulae ◽  
Radio Flux ◽  
Recombination Line ◽  
Hydrogen Recombination

Various observers (e.g. Slee and Orchiston 1965; Davies et al. 1967; Hughes 1967; Thompson and Colvin 1967; Thompson, Colvin, and Stanley 1967; Kaftan-Kassim 1968) have so far detected nearly 100 planetary nebulae a.t high radiofrequencies (~3 GHz). In this range, the nebulae have been shown to be optically thin, their spectra being almost flat. Wherever possible, the radio flux densities have been compared with hydrogen recombination line observations.

scholarly journals Recombination Line Survey of Galactic H II Regions.

1967 ◽  
Vol 72 ◽  
pp. 824
Author(s):  
E. C., III Reifenstein ◽  
T. L. Wilson ◽  
B. F. Burke ◽  
P. G. Gomez
Keyword(s):  
H Ii Regions ◽  
Recombination Line ◽  
Line Survey

scholarly journals In-depth study of the hypercompact H II region G24.78+0.08 A1

2019 ◽  
Vol 624 ◽  
pp. A100 ◽  
Author(s):  
R. Cesaroni ◽  
M. T. Beltrán ◽  
L. Moscadelli ◽  
Á. Sánchez-Monge ◽  
R. Neri
Keyword(s):  
Massive Star ◽  
Physical Structure ◽  
Continuum Emission ◽  
Expansion Velocity ◽  
Recombination Line ◽  
Hydrogen Recombination ◽  
Lyman Continuum ◽  
Depth Study ◽  
Region Size ◽  
The Continuum

Context. The earliest phases of the evolution of a massive star are closely related to the developement of an H II region. Hypercompact H II regions are the most interesting in this respect because they are very young, and hence best suited to study the beginning of the expansion of the ionised gas inside the parental core. Aims. We have analysed the geometrical and physical structure of the hypercompact H II region G24.78+0.08 A1, making use of new continuum and hydrogen recombination line data (H41α, H63α, H66α, H68α) and data from the literature (H30α, H35α). Methods. We fit the continuum spectrum with a homogenous, isothermal shell of ionised gas at 104 K and derive the size of the H II region and the Lyman continuum luminosity of the ionising star. We also fit the recombination line spectra emitted from the same shell with a model taking into account expansion at constant speed. Results. The best fits to the continuum and line spectra allow the derivation of the Lyman continuum luminosity of the ionising star, H II region size, geometrical thickness of the shell, and expansion velocity. Comparison between the 5 cm and 7 mm brightness temperature distributions demonstrates that a thin layer of ionised gas of a few 1000 K at the surface of the H II region is necessary to reproduce the morphology of the continuum emission at both wavelengths. Conclusions. We confirm that the G24 A1 hypercompact H II region consists of a thin shell ionised by an O9.5 star. The shell is expanding at a speed comparable to the sound speed in the ionised gas. The radius of the H II region exceeds the critical value needed to trap the ionised gas by the gravitational field of the star, consistent with the observed expansion.

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