Next Contents Previous


The literature was searched for determinations of dust scattering properties in objects possessing Milky Way interstellar dust. Astrophysical objects which satisfy this constraint are reflection nebulae, dark clouds, and the DGL.

For inclusion in this review, each study had to satisfy four criteria. These criteria are:

  1. Determine albedo & g: This requires that specific values be quoted for the two quantities. Studies which were only sensitive to one of the two quantities were included as long as a realistic range of the other quantity was probed. Usually, the albedo (a) was the quantity determined with calculations performed for g values between zero and one. While this criteria means that the large number of early studies which only put limits on a and/or g are neglected, their limits are usually consistent with the values determined from later studies.
  2. Determine uncertainties: The importance of this criteria cannot be understated. The uncertainties presented here are either the uncertainties quoted in the original paper or reflect the range of a & g values allowed by models presented in each study. This can mean that multiple models (with different assumptions) have been combined into a single measurement with larger uncertainties than a single model.
  3. Refereed Publication: This ensures that the full details of the work have be presented. In addition to the usual journals (eg., ApJ, AJ, A&A, PASP, MNRAS, etc.), theses were counted as refereed publications.
  4. Not be superseded by other work: A number of studies are superseded by newer work which usually used better radiative transfer models (especially the case for DGL studies). This usually results in significantly different determinations of a & g.

The studies satisfying the first three criteria are listed in Table 1, separated by astrophysical object studied. These tables give the study reference, a brief description, a model code, and whether the study satisfied the fourth criteria and, as such, was included in Figs. 1 - 4. Each model code is explained in Table 2 where the method of calculation, sources, and dust geometry are summarized. Ideally, the model used to interpret the observations of a specific object would include realistic illuminators (location and spectrum), a realistic dust distribution, and calculate the full multiple scattering of photons. This ideal is unlikely to be fully met by any specific model, but models which come closest have the best chance of producing good dust scattering properties. The original study reference should be consulted for the full details of each study.

Table 1: Literature Dust Scattering Studies

Reference Description Model Inc.

Reflection Nebulae

Witt et al. 1982 NGC 7023; IUE 1200-3000 Å RN1 Yes1
  & ground-based 3470-5515 Å    
Witt et al. 1992 NGC 7023; UIT 1400 & 2800 Å RN1 Yes
Witt et al. 1993 NGC 7023; RN1 Yes
  Vogager 2 1000-1300 Å    
Gordon et al. 1994 Sco OB2; 1365 & 1769 Å RN2 Yes
Calzetti et al. 1995 IC 435; IUE 1200-3100 Å & RN1 Yes
  ground-based B & V    
Burgh et al. 2002 NGC 2023; FOT 900-1400 Å RN1 Yes
Gibson et al. 2003 Pleiades; WISP 1650 & 2200 Å RN3 Yes

Dark Clouds

Matilla 1970 Coalsack and Libra dark DC1 Yes
  cloud; UBV    
Fitzgerald et al. 1976 Thumbprint Nebula; B DC1 Yes
Laureijs et al. 1987 L1642; 3500-5500 Å DC1 Yes2
Witt et al. 1990 Bok globule; 4690-8560 Å DC1 Yes
Hurwitz 1994 Taurus molecular cloud; DC2 Yes
  Berkeley UVX 1600 Å    
Haikala et al. 1995 G251.2+73.3 cirrus cloud; DC1 Yes
  FAUST 1400-1800 Å    
Lehtinen & Mattila 1996 Thumbprint Nebula; JHK DC1 Yes2

Diffuse Galactic Light

Witt 1968 ground-based 3600, 4350, DGL1 No3
  & 6100 Å    
Mathis 1973 ground-based 3600 & DGL2 Yes2
  4350 Å    
Witt & Lillie 1973 OAO-2 1500-4200 Å DGL3 No4
Lillie & Witt 1976 OAO-2 1500-4200 Å DGL2 Yes
Morgan et al. 1976 TD-1 2350 & 2740 Å DGL3 Yes2
Toller 1981 Pioneer 10 4400 Å DGL4 Yes
Hurwitz et al. 1991 Berkeley UVX 1625 Å DGL5 No5
Murthy et al. 1993 Voyager 2 1050 Å DGL6 Yes2
Murthy & Henry 1995 Berkley UVX & others DGL6 Yes2
Sasseen & Deharveng 1996 FAUST 1565 Å DGL7 No6
Petersohn 1997 DE 1 1565 Å DGL8 Yes
Witt et al. 1997 FAUST 1564 Å DGL8 Yes
Schiminovich et al. 2001 NUVIEWS 1740 Å DGL9 Yes

1UV g determinations not included, not enough radial data for unique g solution
2No g determination possible
3Superseded by Mathis 1973
4Superseded by Lillie & Witt 1976
5Superseded by Murthy & Henry 1995
6Superseded by Witt et al. 1997

The a and g values for the studies which satisfy all four criteria are plotted separate in Figs. 1 - 3 for reflection nebulae, dark clouds, and the DGL. In addition, predictions for different dust grain models are included in these figures (see Section 3.1. for model details). The results have been divided between object classes to highlight their differences. It would not be surprising to find real differences in the a and g values between object classes. For example, reflection nebulae and dark clouds possess, on average, larger dust grains than the DGL. This is seen from the different RV values measured for these objects as RV is a rough measure of the average grain size. Examining the results separately also allows for the impact of the different strengths and weaknesses of each object on the derived scattering parameters to be examined. The final reason to separate the results is to check if the assumptions in the modeling based on object type significantly affect the resulting scattering values. All of the a and g values have been plotted together in Fig. 4 to check the consistency of determinations between the three astrophysical object types.

Table 2: Radiative Transfer Models

Name Method Sources Dust Geometry

RN1 Monte Carlo single star homogeneous sphere
RN2 Monte Carlo multiple stars homogeneous sphere
RN3 analytic multiple stars approximated
  single scattering   clumpy slab
DC1 Monte Carlo MW ISRF & homogeneous sphere
    specific stars  
DC2 numerical int. MW ISRF 2D distribution
DGL1 analytic Galaxy model homogeneous slab
DGL2 numerical int. MW ISRF infinite cylinder
  n=8 scatterings boundary condition  
DGL3 analytic constant infinite slab
DGL4 numerical int. star counts non-homogeneous
  n=2 scatterings    
DGL5 numerical int. TD-1 star catalog clumped dust
DGL6 numerical int. SKYMAP catalog dust based on
      HI survey
DGL7 Monte Carlo star catalogs dust based on
      HI survey
DGL8 Monte Carlo TD-1 star catalog dust cloud spectrum
      based on HI survey
DGL9 Monte Carlo 3D TD-1 star catalog dust cloud spectrum
      based on HI survey

Figure 1

Figure 1. Determinations of the albedo and g in reflection nebulae are plotted versus wavelength. In addition, predictions from dust grain models are plotted for comparison.

Figure 2

Figure 2. Determinations of the albedo and g in dark clouds are plotted versus wavelength. In addition, predictions from dust grain models are plotted for comparison.

Figure 3

Figure 3. Determinations of the albedo and g in the DGL are plotted versus wavelength. In addition, predictions from dust grain models are plotted for comparison.

Figure 4

Figure 4. The combined determinations of the albedo and g in reflection nebulae, dark clouds, and the DGL are plotted versus wavelength. The plot symbols are not identified and do not correspond to legends in previous figures, see Figs. 1 - 3 for information about specific studies. In addition, predictions from dust grain models are plotted for comparison.

Next Contents Previous