scholarly journals Hydrogen Content of Young Stellar Clusters. II. Clusters NGC2175, 2264, 2353, and 2362

1973 ◽  
Vol 26 (6) ◽  
pp. 837 ◽  
Author(s):  
HM Tovmassian ◽  
ET Shahbazian
Keyword(s):  
Electron Density ◽  
Hydrogen Content ◽  
Neutral Hydrogen ◽  
Gaseous Hydrogen ◽  
Stellar Clusters

Measurements of the total amount of gaseous hydrogen associated with the O-type stellar clusters NGC 2175, 2264, 2353, and 2362 are reported. For the nebula in which NGC2175 is embedded, a mean electron density of 20cm- 3 and a mass of ionized hydrogen of 1400Mo were obtained. For the nebula in which NGC2264 is embedded, a mean electron density of 10 cm - 3 and a mass of ionized hydrogen of 60Mo (with a possible, though unlikely, additional 40Mo of neutral hydrogen) were obtained. No hydrogen in association with NGC 2353 or 2362 was detected.

scholarly journals Hydrogen Content of Young Stellar Clusters. I. Methods of Observation and Reduction

1973 ◽  
Vol 26 (6) ◽  
pp. 829 ◽  
Author(s):  
HM Tovmassian
Keyword(s):  
Radio Telescope ◽  
Hydrogen Content ◽  
Data Reduction ◽  
Neutral Hydrogen ◽  
Hydrogen Gas ◽  
Continuum Emission ◽  
Stellar Clusters ◽  
Hydrogen Line ◽  
Galactic Clusters

Observations of 16 open galactic clusters in their continuum emission and at the neutral hydrogen line have been made with the Parkes 64 m radio telescope in an attempt to determine the total amount of hydrogen gas associated with them. In this, the first of a series of five papers, the observing procedure and the method of data reduction are described.

scholarly journals Hydrogen Content of Young Stellar Clusters. V. Clusters NGC6604, 6611, and 6823

1973 ◽  
Vol 26 (6) ◽  
pp. 861 ◽  
Author(s):  
HM Tovmassian ◽  
SE Nersessian
Keyword(s):  
Hydrogen Content ◽  
Total Mass ◽  
Neutral Hydrogen ◽  
Hydrogen Gas ◽  
Stellar Clusters

Measurements of the total amount of hydrogen gas associated with the O-type clusters NGC 6604, 6611, and 6823 are reported. Only a small part of the large visible nebula in which NGC 6604 appears to be embedded is associated with the cluster. The small ionized nebula associated with NGC6604 has a mass of ~600Mo and is part of a larger neutral cloud. The mass of the ionized nebula associated with NGC 6611 is ~ 5000 M 0, while a neutral hydrogen shell with a total mass of ~ 105 M 0 probably surrounds the ionized nebula. The cluster NGC 6823 is embedded in a bright nebula of mass ~ 1800 Mo. A neutral hydrogen shell of mass ~ 2000 M 0 surrounds the ionized nebula, so that the total mass of hydrogen associated with NGC 6823 is ~ 4000 Mo.

scholarly journals Hydrogen Content of Young Stellar Clusters. IV.Clusters NGC6231, 6383, 6514, and 6531

1973 ◽  
Vol 26 (6) ◽  
pp. 853 ◽  
Author(s):  
HM Tovmassian ◽  
SE Nersessian ◽  
ET Shahbazian
Keyword(s):  
Hydrogen Content ◽  
Total Mass ◽  
Line Emission ◽  
Neutral Hydrogen ◽  
Type Star ◽  
Stellar Clusters ◽  
Hydrogen Line ◽  
Hydrogen Atoms ◽  
The Continuum

The total amount of hydrogen associated with the young stellar clusters NGC6231, 6383, 6514, and 6531 has been obtained from observations in the continuum at 1410 MHz and in the hydrogen-line emission. NGC6231 contains in its southern part a cloud of neutral hydrogen atoms of density 6 cm- 3 and total mass l00M0 and in its northern part a small ionized cloud of the same density and a mass of ~ 50 M 0. NGC 6383 is embedded in a large neutral hydrogen complex, of which a small part of mass ~450M0 is ionized. The Trifid nebula is ionized by a single 07-type star at nearly twice the accepted distance of NGC6514 and the existence of NGC6514 as a physical cluster appears to be doubtful. The mass of the ionization-bounded Trifid nebula is nearly 5000M0 ? Neither neutral nor ionized hydrogen was found in association with NGC6531.

scholarly journals Hydrogen Content of Young Stellar Clusters. III. Clusters NGC3293, 6167, 6193, 6200, and 6204

1973 ◽  
Vol 26 (6) ◽  
pp. 843 ◽  
Author(s):  
HM Tovmassian ◽  
ET Shahbazian ◽  
SE Nersessian
Keyword(s):  
Hydrogen Content ◽  
Neutral Hydrogen ◽  
Type Star ◽  
Stellar Clusters

The total amount of hydrogen associated with the O-type clusters NGC 3293, 6193, and 6204 and the suspected clusters NGC6167 and 6200 has been measured. Neither neutral nor ionized hydrogen was found to be associated with NGC 3293 and the visible nebula in this region is most likely associated with a single 07-type star, which does not appear to belong to the cluster, while an irregular expanding shell of neutral hydrogen probably surrounds the ionized nebula. The mass of hydrogen associated with NGC6193 does not exceed 500MQ? Neither neutral nor ionized hydrogen was detected at the position ofNGC 6204. The features detected by hydrogenline observations at the positions of suspected clusters NGC6167 and 6200 provide evidence that both visual groupings may be real clusters. The amount of neutral hydrogen probably connected with NGC6167 is ~ 1000 M Q ?

scholarly journals Pulsar Astrometry

1984 ◽  
Vol 110 ◽  
pp. 347-353
Author(s):  
Joseph H. Taylor ◽  
Carl R. Gwinn ◽  
Joel M. Weisberg ◽  
Lloyd A. Rawley
Keyword(s):  
Electron Density ◽  
Reference Frames ◽  
Neutral Hydrogen ◽  
Space Velocity ◽  
Solar Neighborhood ◽  
Dispersion Measure ◽  
Direct Measurements ◽  
Pulse Timing ◽  
Local Space ◽  
Dispersion Measures

High precision measurements of the celestial coordinates of pulsars are desirable for a number of reasons. If carried out at several epochs, the measurements can yield angular proper motions; together with distance estimates based on dispersion measure, the proper motion of a pulsar reveals two of three components of its space velocity, and consequently provides important kinematic information on pulsar ages (see, for example, Manchester, Taylor and Van 1974; Lyne, Anderson and Salter 1982; and references therein). Direct measurements of annual parallaxes are also possible in principle, and are marginally feasible with present techniques for a few of the closest pulsars. Model independent distances obtained from parallax measurements, together with observed pulsar dispersion measures, yield the electron density along the line of sight to the pulsar. Knowledge of the interstellar electron density in the solar neighborhood provides a calibration of the dispersion-based distance scale that is complementary to the calibration derived from neutral hydrogen absorption measurements of more distant pulsars (Weisberg et al. 1980), and permits appropriate statistical analyses to be made of the local space density of pulsars and their birthrate (e.g. Taylor and Manchester 1977). Finally, pulsar astrometry can be expected to yield important information on the relative orientations of fundamental reference frames. In particular, pulse timing observations yield positions in a reference frame based on motions of the planets, while interferometric position measurements are based on an Earth-equatorial system. At present the relative orientation of these two coordinate systems is known to only accuracy, though the potential precision of both types of measurements is much higher.

The neutral hydrogen content of early type disk galaxies

1991 ◽  
Vol 102 ◽  
pp. 572 ◽  
Author(s):  
J. Eder ◽  
R. Giovanelli ◽  
M. P. Haynes
Keyword(s):  
Hydrogen Content ◽  
Neutral Hydrogen ◽  
Disk Galaxies ◽  
Early Type

scholarly journals Pressure Broadening of UV Lines

1971 ◽  
Vol 2 ◽  
pp. 561-565
Author(s):  
H. van Regemorter
Keyword(s):  
Electron Density ◽  
Neutral Hydrogen ◽  
Uv Spectra ◽  
Line Broadening ◽  
Pressure Broadening ◽  
Static Approximation ◽  
Impact Approximation ◽  
Typical Time ◽  
Static Regime ◽  
The Impact

Most of the lines in the UV spectra are lines of ions which are formed in high temperature regions where the pressure broadening is caused by electrons and protons. This is the case in O and B type stars for which the theoretical calculation of the width of all the strong UV lines is important in determining both the blanketing effect and the abundances of the elements.The cores of these strong lines are formed in non-LTE layers near the surface where the electron density is very low. The wings of some of the lines are more easy to interpret, being formed in deeper layers of the star, where one can assume LTE and where the electron density - or in the Sun, the neutral hydrogen density - is such that the pressure broadening is much more important than the natural width.Two opposite approximations have been applied to the line broadening problem; the impact approximation is generally valid for electrons when the perturbations are so rapid that the collision timeτcis very small compared to the typical time, Δω-1, of importance in computing the profile at the frequencyΔω = ω – ω0measured from the line centre. On the contrary, whenτc≫Δω−1the quasi static approximation may be assumed. Both of these approximations have been considerably improved and efforts have been made recently to develop a unified theory valid from the impact regime to the static regime.

scholarly journals Inevitable imprints of patchy reionization on the cosmic microwave background anisotropy

2020 ◽  
Vol 500 (1) ◽  
pp. 232-246 ◽  
Author(s):  
Sourabh Paul ◽  
Suvodip Mukherjee ◽  
Tirthankar Roy Choudhury
Keyword(s):  
Cosmic Microwave Background ◽  
Electron Density ◽  
Neutral Hydrogen ◽  
Density Fluctuations ◽  
Microwave Background ◽  
Free Electron Density ◽  
Polarization Signal ◽  
External Data ◽  
Spatial Fluctuations ◽  
Electron Density Fluctuations

ABSTRACT Reionization of the cosmic neutral hydrogen by the first stars in the Universe is an inhomogeneous process, which produces spatial fluctuations in free electron density. These fluctuations lead to observable signatures in cosmological probes like the cosmic microwave background (CMB). We explore the effect of the electron density fluctuations on CMB using photon-conserving seminumerical simulations of reionization named SCRIPT. We show that the amplitude of the kinematic Sunyaev–Zeldovich (kSZ) and the B-mode polarization signal depends on the patchiness in the spatial distribution of electrons along with the dependence on mid-point and extent of the reionization history. Motivated by this finding, we provide new scaling relations for the amplitude of kSZ and the B-mode polarization signal which can capture the effects arising from the mean optical depth, width of reionization, and spatial fluctuations in the electron density arising from patchy reionization. We show that the amplitude of the kSZ and the B-mode polarization signal exhibits different dependency on the width of reionization and the patchiness of reionization, and hence a joint study of these CMB probes will be able to break the degeneracy. By combining external data sets from 21-cm measurements, the degeneracy can be further lifted by directly exploring the sizes of the ionized regions.

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