Reflection nebula

For the dichroic photolysis mechanism to be successful, amino acids must be synthesised and destroyed in an intense circularly polarised radiation field. Daylight shows little or no excess but recent observations at 2.2 /rm of the Orion reflection nebula OMC-1 shows polarisations in excess of 17 per cent, although... 

The gaseous nebulas are divided up into dark nebulas, reflection nebulas, Hll regions (see below), planetary nebulas and supernova remnants. 

Reflection nebulas are visually much more beautiful. These are clouds of gas and dust that shine by light borrowed from nearby stars, just as the planets shine by the reflected light of the Sun. Starlight is scattered by dust grains floating... 

Zellner, B., 1973. Dust grains in reflection nebulae, in Interstellar Dust and Related Topics, IAU Symposium No. 52, J. M. Greenberg and H. C. van de Hulst (Eds.), D. Reidel, Dordrecht, Holland, pp. 109-113. 

Fig. 2. The infrared emission spectrum from the reflection nebula HD 44179, the Red Rectangle (a from Ref. [44], b from Ref. [15].)...

Fig. 8. Emission spectra of several compact PAHs calculated from their absorption spectra measured in the laboratory at room temperature compared to the observed spectrum of the reflection nebula NGC 2023 (dots) (Figure reproduced from Ref [50])...

For this reason, dust particles that are not dense enough to cause extinction may, instead, produce a reflection nebula, regions of space that have a bluish appearance to observers on Earth because of the light reflected from them off dust particles. 

In contrast to these red stars, reflection nebulae have been found near several AFCRL sources (Cohen et al. 1975 Kleinmann and Lebofsky, 1975 Ney al. 1975 Westbrook et al. 1975), and high resolution spectra of a few of these indicate that the stars illuminating them have spectral types ranging from B to late F. 

A large tenuous cloud surrounds the object and is seen as a reflection nebula illuminated by the starlight that escapes above and below the ring of dust. The discovery of this object has provided dramatic evidence supporting earlier hypotheses that circum-stellar envelopes of infrared stars must be flattened. The large optical depth of the toroid produces a featureless, mid-infrared spectrum (Forrest eit 1976) but the chemical nature of the cloud has been deduced from optical spectroscopy of the reflection nebula (Crampton, Cowley and Humphreys, 1975) and by detection of a molecular cloud association with the source (Lo and Bechis, 1976 and Zuckermann ad 1976). These observations show that the 0.1 M cloud is carbon-rich, and, in fact has led to the suggestion that the source may be the progenitor of a planetary nebula. 

Another object associated with multiple reflection nebulae is CRL 437. The reflection nebula was found by Kleinmann and Lebofsky (1975) in their search for optical counterparts for new AFCRL sources by means of near-infrared photography with image tube cameras at KPNO. Direct observation of the brightest part of the complex nebula on the KPNO 1.3-m indicated at first, that the source was ten times fainter than reported in the AFCRL Catalogue. This cast doubt on the identification of the reflection nebula with... 

Figure 8 The 10-15 )im spectrum of the outflow from a star known as the Red Rectangle because of the rectangular appearance of its associated reflection nebula on red plates. Bands in this spectral region are largely due to the C-H out-of-plane bending mode whose exact peak position is sensitive to the number of adjacent H atoms involved. The boxes underneath the spectra give the ranges where PAHs with the indicated number of adjacent H atoms emit. The arrow labelled 6 indicates the position for benzene. These spectra were obtained with the Short-Wave-length Spectrometer on board the Infrared Space Observatory at a spectral resolution ranging from 250 to 2000.

Dust radiates in the infrared. By Kirchhoff s law, solid material in thermal equilibrium radiates like a blackbody. Most of the incident energy falling on the grain is scattered, hence the blueness of reflection nebulae and the reddening of starlight. The absorbed photons are reradiated at a rate approximated by = where k, ... 

Observations of the reflection spectrum of interstellar dust have also yielded some insights concerning the properties of interstellar dust particles in particular, it has been found that, at least in some reflection nebulae, the particles are very efficient scatterers of far-UV radiation. Except in the vicinity of the 220-nm extinction peak, it appears that most of the interstellar extinction is due to scattering rather than pure absorption. 

The water maser emission associated with the infrared centers IRS 1 and IRS 3 of the NGC 207 HR star-forming region was studied by Seth, Greenhill, and Holder, 2002 [305]. They used water masers as tracers for protostellar disks. NGC 2027 is a reflection nebula in the constellation of Orion. 

Solomon et al. (1993b) detect 3.29 pm feature emission along a bright ridge (at K) in the reflection nebula NGC 7023. Interestingly, the ridge exhibits a cooler color temperature than the rest of the reflection nebula. These data (see Fig. 2) were recently acquired with the Rodiester 256 X 256... 

Key wordst Molecular clouds - Reflection nebulae - Surface brightness... 

We obtained a polarization image at K (2.18 on) of BN/EL region in an area of 16.6 X 4.6 arc minuets, and found extended 4.6 X 4.6 ar-cmin) polarized nebulosity (Fig. 2). Polarization vectors of the nebula show centro-symmetric pattern centered near BN/KL, suggesting it is a reflection nebula. It has clear relations with the distribution of the 1 - 0 S(l) molec-ular hydrogen emission as well as radio molecular line emission such as CS and HC3N, giving us the information about the mass distribution around BN/KL cluster. 

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