Interstellar Extinction in the Galaxy

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Responsible: Prof. Dr. Eduardo Brescansin de Amôres

Permanent position at:

Universidade Estadual de Feira de Santana (Departamento de Física and Observatório Antares)
Av. Transnordestina, S/N, Novo Horizonte, Feira de Santana, BA, 
Brazil, CEP:  44036-900
contact: ebamores (--at--)


Models for interstellar extinction in the Galaxy (Amôres & Lépine, 2005, AJ, 130, 679)


We present two models for the interstellar extinction in the Galaxy, that are based on the hypothesis that the interstellar dust is well mixed with the gas, with a constant ratio (except for a small dependence of metallicity on the galactic radius), and therefore, the extinction is proportional to the column density of the gas. In a first model, we assume that the Galaxy is axis-symmetric; the gas density in the disk is a function of the galactic radius and of the distance perpendicular to the galactic plane, and the extinction is proportional to the column density of the gas. In the second model, we take into account the spiral structure of the Galaxy. In this case, instead of increasing almost linearly with distance, the extinction increases by steps each time a spiral arm is crossed, but only increases slowly in the inter-arms regions. The gas density distribution is obtained from the Berkeley and Parkes HI surveys, and from the Columbia University CO survey. The IRAS 100 microns brightness distribution is  also used as a tracer of the interstellar dust column density. The predictions of the models are compared with data taken from a number of catalogs that present color excess and distances for large samples of stars. Our models are useful to estimate distances of objects, color corrections for objects for which the distance can be estimated by some other method, and for star-counts and brightness models of the Galaxy, among other applications.

Download the paper (Published in AJ, 130, 679 - PDF version)

Download the paper (Published  in AJ, 133, 1519-1527 - PDF version)

In the case of questions or suggestions,  please write an email to:

Eduardo Am
ôres (        

Modifications log :

-  August, 1st 2005: Version 1.0: (IDL prompt line programs) as published in the paper AJ, 130, 679
-  April, 20th 2006:  Version 1.1: IDL Virtual machine (executable programs)
-  March, 26th 2007: Version 1.2: Fortran Version Model (A, A2) + IDL version Model A2 (as published in AJ, 133, 1519)


The simulations as well as the programs modifications did by the users are made by your own risks. We are not responsible for inadequately applications or modifications of our models. In the case of questions, please contact us.

Useful comments:
  1. At the moment our models need the galactic coordinates (in degrees) to calculate the extinction. But if you have the coordinates of your object(s) in equatorial coordinates you can use either the IDL program ( or calculate it from the NED web page.
  2. If you want to convert the Av predictions of our models to another filter, we suggest to use the relations proposed by Schlegel et al. (1998).

In order to use our models, you have two options:
i-) run the executable version of the models (you do not need an IDL License to do this!)

ii-) download the source code to run the programs in IDL prompt line + Fotran version of the Model A and A2

Are you want to know more about IDL ? (IDL is a trademark of Research Systems)

i-) Using the executable version (At the moment, available only for the Linux users)

ii-) Download the IDL + Fortran programs of the Models published in the paper

                                  Some interesting and useful links related to the interstellar extinction:

Others extinction models:

- Arenou et al. (1992):
A tridimensional model of the galactic interstellar extinction

-Hakilla et al. (1997):
A Computerized Model of Large-Scale Visual Interstellar Extinction
- Mendez & van Altena (1998):
A new optical reddening model for the solar neighborhood. Galactic structure through low-latitude
starcounts from the Guide Star Catalogue
- Drimmel et al. (2003):
A three-dimensional Galactic extinction model

Catalogs: Catalogs with the estimative for the interstellar extinction for a large sample of stars.

- Catalog of Extinction Data (Neckel & Klare, 1980) 
- UV Interstellar Extinction Excesses for 1415 Stars (Savage et al. 1985)
- Guarinos (1992)
- Diplas & Savage (1994)
- Reddening in open and globular clusters (Dutra & Bica, 2000)

Extinction Maps:

- Reddening Maps derived from HI and Galaxy Counts (Burstein & Heiles, 1982)
- Maps of Dust IR Emission/Reddening (J/ApJ/500/525 Schlegel+ 1998)

Extinction at the galactic center:

- Interstellar extinction  (Schultheis et al., 1999)
- K extinction near the Galactic Centre (Dutra et al. 2003)

The gas survey data:

HI surveys:
Berkeley Low-Latitude H I Survey (Weaver, Williams 1973)
H I Survey of the Galactic Center Region (Burton, 1983)
Fully Sampled HI Survey of Southern Milky Way (Kerr, 1986)

CO surveys:
- Composite CO Survey of the Milky Way (Dame, 1987)