A discussion on infared astronomy - Expected infrared spectra of gaseous nebulae

1969 ◽  
Vol 264 (1150) ◽  
pp. 241-247 ◽  
Keyword(s):  
Infrared Spectra ◽  
Galactic Plane ◽  
Interstellar Extinction ◽  
Mount Everest ◽  
Gaseous Nebulae ◽  
The Galaxy ◽  
The Mean ◽  
Spiral Arm

If we are asked why we want to use the infrared to observe gaseous nebulae, we might reply with George Mallory, who was asked why he wanted to climb Mount Everest, ‘Because its there’. More specifically, one reason is the very great space penetration possible in the infrared. Diffuse nebulae characteristically are close to the galactic plane, and interstellar extinction therefore prevents the observation of distant objects. At MATHS FORMULA the mean range to which diffuse nebulae can easily be observed is about 1500 parsecs (pc), while many of these nebulae are so reddened as to be nearly unobservable at Hβ. It is for this reason that at present the observation of diffuse nebulae is almost entirely limited to our own spiral arm and its immediate neighbours. However, because of the decrease of interstellar extinction to longer wavelengths, at 1 μm the range of observation would be about 3000 pc; at 2 μm about 10 000 pc, comparable with the distance to the centre of the Galaxy; and at 10μm, about 100 000 pc, far larger than the diameter of the Galaxy. (The form of the interstellar reddening curve is from Whitford 1958.)

scholarly journals Analysis of Interstellar Extinction towards the Hypergiant Cyg OB2 No. 12

2016 ◽  
Vol 25 (1) ◽  
Author(s):  
O. V. Maryeva ◽  
E. L. Chentsov ◽  
V. P. Goranskij ◽  
S. V. Karpov
Keyword(s):  
Interstellar Extinction ◽  
Stellar Association ◽  
The Galaxy ◽  
The Mean

AbstractThe Cyg OB2 stellar association hosts an entire zoo of unique objects, and among them – an enigmatic star Cyg OB2 No. 12 (Schulte 12, MT 304). MT 304 is enigmatic not only due to its highest luminosity (according to various estimates, it is one of the brightest stars in the Galaxy), but also because its reddening is anomalously large, greater than the mean reddening in the association. To explain the nature of anomalous reddening (

scholarly journals An Interpretation of the Distribution of Metre Wavelength Radio Emission

1968 ◽  
Vol 21 (2) ◽  
pp. 167 ◽  
Author(s):  
KW Yates
Keyword(s):  
High Latitude ◽  
Large Scale ◽  
Galactic Halo ◽  
Galactic Plane ◽  
Absolute Calibration ◽  
Fundamental Difficulty ◽  
The Galaxy ◽  
Calibration Accuracy ◽  
Limit Estimate ◽  
Spiral Arm

A recent 85 MHz survey of the southern sky had an absolute calibration accuracy and resolution comparable with a number of surveys made for the northern skies. By combining the results of these surveys in both hemispheres a complete sky map has been produced, and in this paper an analysis is made of the distribution of the medium and high latitude emission. A fundamental difficulty encountered is the identification and isolation of the spurs of emission projecting from the galactic plane. Two hypotheses are proposed. The first attributes the spurs to a large-scale feature associated with the galactic core and the remaining emission to a galactic halo. The second postulates the origin of the spurs within the local spiral arm, which is itself considered to contribute significantly to the high latitude background. An upper-limit estimate of the emissivity of the local arm is made from currently available independent data. Using this result a model local arm is proposed, which, together with an isotropic component from beyond the Galaxy and a small additional galactic component, explains the observed distribution.

scholarly journals Giant Molecular Clouds in the Galaxy: The Massachusetts-Stony Brook CO Galactic Plane Survey

1987 ◽  
Vol 115 ◽  
pp. 499-499 ◽  
Author(s):  
P. M. Solomon
Keyword(s):  
Molecular Clouds ◽  
Galactic Plane ◽  
Far Infrared ◽  
Formation Mechanisms ◽  
H Ii Regions ◽  
Giant Molecular Clouds ◽  
Star Forming ◽  
The Galaxy ◽  
Two Populations ◽  
Spiral Arm

The CO Galactic Plane Survey consists of 40,572 spectral line observations in the region between 1 = 8° to 90° and b = −1°.05 to +1°.05 spaced every 3 arc minutes, carried out with the FCRAO 14-m antenna. The velocity coverage from −100 to +200 km/s includes emission from all galactic radii. This high resolution survey was designed to observe and identify essentially all molecular clouds or cloud components larger than 10 parsecs in the inner galaxy. There are two populations of molecular clouds which separate according to temperature. The warm clouds are closely associated with H II regions, exhibit a non-axisymmetric galactic distribution and are a spiral arm population. The cold clouds are a disk population, are not confined to any patterns in longitude-velocity space and must be widespread in the galaxy both in and out of spiral arms. The correlation between far infrared luminosities from IRAS, and molecular masses from CO is utilized to determine a luminosity to mass ratio for the clouds. A face-on picture of the galaxy locating the warm population is presented, showing ring like or spiral arm features at R ∼ 5, 7.5 and 9 kpc. The cloud size and mass spectrum will be discussed and evidence presented showing the presence of clusters of giant molecular clouds with masses of 106 to 107 M⊙. The two populations of clouds probably have different star forming luminosity functions. The implication of the two populations for star formation mechanisms will be discussed.

scholarly journals Graphite Grains and Graphite-Core-Ice-Mantle Grains

1965 ◽  
Vol 7 ◽  
pp. 167-184
Author(s):  
N. C. Wickramasinghe
Keyword(s):  
Ad Hoc ◽  
Narrow Range ◽  
Interstellar Extinction ◽  
Characteristic Size ◽  
Size Parameter ◽  
Grain Sizes ◽  
Desirable Feature ◽  
The Galaxy ◽  
The Mean ◽  
Grain Model

Among the First Requirements for a Grain Model is that it should explain the observed interstellar extinction law or laws as they are now understood; a desirable feature of such a model is that as few ad hoc assumptions be made as possible.A criticism of the classical ice grain theory is that a very narrow range of grain sizes (or a size distribution with a size parameter specified to within a few percent) must be postulated in order to obtain a fit with the mean extinction law. (See refs. 1 and 2.) While it is true that regional variations in the extinction law have recently been detected (refs. 3 and 4), the best available evidence indicates that the extinction law is quite uniform when averaged over individual large regions which are widely distributed in the galaxy. (See ref. 5 and paper by Nandy in the present compilation.) The restriction of particle size to a radius within a few percent of an arbitrarily specified value (r ≈ 3 X 10-5 cm) demanded on the basis of pure ice absorption is therefore considered quite unsatis-factory, particularly in view of the fact that no characteristic size parameter emerges from the Oort-van de Hulst theory for the formation and destruction of grains. (See ref. 6.)

scholarly journals Optical Observations of Galactic and Extragalactic Light: Implications for Galactic Structure

1990 ◽  
Vol 139 ◽  
pp. 21-34
Author(s):  
Gary N. Toller
Keyword(s):  
Galactic Plane ◽  
Historical Review ◽  
Interstellar Extinction ◽  
Galactic Structure ◽  
Optical Observations ◽  
The Sun ◽  
Color Distribution ◽  
Background Light ◽  
Dominant Component ◽  
Spiral Arm

A historical review of integrated starlight, diffuse galactic light, and extragalactic light studies is presented. Together, these components compose the “background light.” Methods ranging from star counts to space-based photometric surveys have succeeded in quantifying the contribution of each component of the background. Integrated starlight is the dominant component. The contribution of diffuse galactic light in the general interstellar medium peaks slightly off the galactic plane and declines toward higher latitudes. The extragalactic light has been determined from both galaxy counts and photometric methods. The blue and red intensity and B–R color distribution of background light have been mapped. The relation between galactic structure and background light measurements is established. The distribution of interstellar extinction is the primary regulator of the brightness. However, spiral arm and stellar distribution effects are discerned in Carina and Sagittarius. The sun lies 13 pc north of the galactic plane as defined by brightness and dust distributions.

scholarly journals The Problem of the UV Interstellar Absorption Band at 2200A

1977 ◽  
Vol 43 ◽  
pp. 26-26
Author(s):  
D.J. Carnochan ◽  
K. Nandy ◽  
A.J. Willis ◽  
R. Wilson
Keyword(s):  
Galactic Plane ◽  
Interstellar Extinction ◽  
Extinction Curve ◽  
Absorption Feature ◽  
The Sun ◽  
The Galaxy ◽  
Satellite Experiment ◽  
Using Data ◽  
Broad Scale ◽  
Pronounced Peak

The ultraviolet interstellar extinction curve from 2740Å to 1350Å has been obtained using data from the S2/68 satellite experiment. The extinction increases into the ultraviolet and shows a pronounced peak at 2200Å. This is interpreted as a general scattering continuum with a strong absorption feature superposed on it at 2200Å. The profile of the feature appears to be symmetrical and has a half-width of 360Å. There is a strong correlation between the strength of the feature and the scattering part of the curve in both the ultraviolet and the visible. On a broad scale the shape of the extinction curve is constant showing no variation with distance from the sun, direction around the galaxy, and height above the galactic plane.

scholarly journals The stellar metallicity distribution of the Galaxy from the BATC survey

2013 ◽  
Vol 9 (S298) ◽  
pp. 432-432
Author(s):  
Xiyan Peng ◽  
Cuihua Du ◽  
Zhenyu Wu ◽  
Jun Ma ◽  
Xu Zhou
Keyword(s):  
Effective Temperature ◽  
Main Sequence ◽  
Galactic Plane ◽  
Calibration Method ◽  
Thick Disk ◽  
Atmospheric Parameters ◽  
Photometric Calibration ◽  
The Galaxy ◽  
The Mean ◽  
Metallicity Distribution

AbstractUsing ~2200 BATC main sequence (MS) stars which include SDSS stellar atmospheric parameters, we develop the polynomial photometric calibration method to evaluate the stellar effective temperature and metallicity for BATC data. This calibration method has been applied to about 160 000 MS stars. The mean stellar metallicity smoothly decreases from −0.65 to −0.78 dex in the interval 0.5 < |Z| ≤ 2 kpc. Metallicity distributions in the halo and the thick disk seem invariant with the distance from the Galactic plane.

scholarly journals Vertical Force Law Kz and Chemical Gradient in the Galaxy

1977 ◽  
Vol 45 ◽  
pp. 289-291
Author(s):  
L. Martinet ◽  
M. Grenon
Keyword(s):  
Galactic Plane ◽  
Vertical Force ◽  
Chemical Gradient ◽  
The Galaxy ◽  
Metal Abundance ◽  
Lower Variation ◽  
The Mean ◽  
K Giants

At Tbilissi, Prof. Blaauw (1975) reported on results of uvby photometry of F-type stars and showed a relation between the quantity Δm and the distance z to the galactic plane. This relationship could be interesting if Δm1is a non ambiguous indicator of metallicity. It was found that the mean relative metal abundance decreases by a factor of about one third between 0 and 700 pc. The same type of relationship was obtained by M. Grenon (1976) for K giants and shows a lower variation of the metallicity with z.

scholarly journals A new near-IR window of low extinction in the Galactic plane

2018 ◽  
Vol 616 ◽  
pp. A26 ◽  
Author(s):  
Dante Minniti ◽  
Roberto K. Saito ◽  
Oscar A. Gonzalez ◽  
Javier Alonso-García ◽  
Marina Rejkuba ◽  
...  
Keyword(s):  
Near Infrared ◽  
Milky Way ◽  
Galactic Plane ◽  
Structural Constraints ◽  
Magnitude Distribution ◽  
Near Ir ◽  
Disk Structure ◽  
The Galaxy ◽  
The Mean ◽  
Red Clump

Aims. The windows of low extinction in the Milky Way (MW) plane are rare but important because they enable us to place structural constraints on the opposite side of the Galaxy, which has hither to been done rarely. Methods. We use the near-infrared (near-IR) images of the VISTA Variables in the Vía Láctea (VVV) Survey to build extinction maps and to identify low extinction windows towards the Southern Galactic plane. Here we report the discovery of VVV WIN 1713−3939, a very interesting window with relatively uniform and low extinction conveniently placed very close to the Galactic plane. Results. The new window of roughly 30 arcmin diameter is located at Galactic coordinates (l, b) = (347.4, −0.4) deg. We analyse the VVV near-IR colour-magnitude diagrams in this window. The mean total near-IR extinction and reddening values measured for this window are AKs = 0.46 and E(J − Ks) = 0.95. The red clump giants within the window show a bimodal magnitude distribution in the Ks band, with peaks at Ks = 14.1 and 14.8 mag, corresponding to mean distances of D = 11.0 ± 2.4 and 14.8 ± 3.6 kpc, respectively. We discuss the origin of these red clump overdensities within the context of the MW disk structure.

scholarly journals Extended Carbon Emission in the Galaxy: Dark Gas along the G328 Sightline

2015 ◽  
Vol 11 (S315) ◽  
Author(s):  
M. Burton ◽  
M. Ashley ◽  
C. Braiding ◽  
M. Freeman ◽  
C. Kulesa ◽  
...  
Keyword(s):  
Galactic Plane ◽  
Line Emission ◽  
Precipitable Water ◽  
High Elevation ◽  
Precipitable Water Vapour ◽  
The Galaxy ◽  
Photodissociation Regions ◽  
Low Levels ◽  
The Antarctic ◽  
Spiral Arm

AbstractWe present spectral data cubes of the [CI] 809 GHz, 12CO 115 GHz, 13CO 110 GHz and HI 1.4 GHz line emission from a ~1° region along the l = 328° (G328) sightline in the Galactic Plane. The [CI] data comes from the High Elevation Antarctic Terahertz telescope at Ridge A on the summit of the Antarctic plateau, where the extremely low levels of precipitable water vapour open atmospheric windows for THz observations. The CO data comes from the Southern Galactic Plane Survey being conducted with the Mopra telescope. Emission arises principally from gas in three spiral arm crossings along the sight line. The distribution of the emission in the CO and [CI] lines is found to be similar, with the [CI] slightly more extended, and both are enveloped in extensive HI. Spectral line ratios are similar across the entire extent of the Galaxy. However, towards the edges of the molecular clouds the [CI]/13CO and 12CO/13CO line ratios rise by ~ 50%, and the [CI]/Hi ratio falls by ~ 10%. We attribute this to sightlines passing predominantly through the surfaces of photodissociation regions (PDRs), where the carbon is found mainly as C or C+ rather than CO, while the gas is mostly molecular. This is the signature of dark molecular gas.

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