Our tentative plan for the atlas is as follows:

1. Review of Morphological Classification of Galaxies
2. The de Vaucouleurs Revised Hubble Classification System
3. Physical galaxy morphology
4. The Atlas and interpretations
5. Appendices covering other aspects of morphology, such as:
- outer ring subclassifications; resonance rings
- inner and outer lenses
- luminosity classifications
- arm character classifications
- secondary bars
- I0s
- low surface brightness galaxies
- dust-penetrated galaxy classification
- computer classification - isophotal classifications of elliptical galaxies
- etc

The first section on review of galaxy classification systems is essential to place the work into context. It will not duplicate what is presented in van den Bergh (1998), which highlights most of the important issues in galaxy classification and morphology. We will, however, build on some of the issues that van den Bergh raises, and expound on other issues he did not cover well. For a similar but brief review, see Buta (1992).

The second section will describe the de Vaucouleurs classification system explicitly with great attention to its actual application, based on the experience of the authors. This will be done using the cross-sectional approach, where galaxies at each stage along the revised Hubble classification volume are illustrated by family and variety. An example of one such cross section is shown in section 3. This shows 9 galaxies in a cut through the classification volume in the Sa-Sb range of types.

The third section will summarize what physical factors may underlie the de Vaucouleurs types in particular and galaxy morphology in general. It will build around concepts such as those listed in Table 1, section 4. which is an updated version of a table given by Buta (1989). Under Atlas Samples, we give some interpretations of features seen in NGC 1433 and NGC 2835 as examples of how we will use physical morphology. The philosophy here is that galaxy morphology is not so mysterious that we cannot say anything about the physical meaning of observed features. Enough has been learned since de Vaucouleurs published his views that we can interpret many features that we see. This physical approach will also highlight what is least understood about morphology at the time the book is published.

The fourth section will be the atlas of images itself. This section will, of course, be the ``meat'' of the book. It will be based exclusively on digital images from charge-coupled devices (CCDs). The main illustrations will be based on logarithmic, sky-subtracted B-band images. These will be reproduced in black and white. Since the atlas will prefer bright, well-known galaxies, we will in most cases be able to derive a zero point for each image, so that the units of all images will be mag arcsec^-2. This will add a degree of homogeneity to the project and will insure that the bright central areas and faint outer regions are adequately illustrated.

Although the atlas will be in black and white, we plan to include multicolor information by using both non-B-band images as well as color index maps. Galaxies are rarely imaged in only one filter these days, and our image sources will include filters other than the B-band. Where possible and where relevant, we plan to show images in other bandpasses that highlight how features such as bars, rings, and spirals change in appearance with wavelength. Under Atlas Samples, we show B and H images of NGC 1433. The B-band samples the light at 0.44m and emphasizes the Population I component while the H-band samples the light at 1.6m and emphasizes the old disk and population II components. The de Vaucouleurs classification for this galaxy is (R)SB(r)ab, although the ring is made of tightly wrapped spiral structure. The images show that the family and variety of this galaxy are nearly invariant from B to H. The main differences are that the inner ring looks more like a pseudoring at H, and the stage appears to be Sa rather than Sab.

On the other hand, for some galaxies, morphology will change greatly from blue light to the near-IR. We will highlight cases like M51 and NGC 5195 where the family changes from nonbarred to barred as the wavelength changes from B to H. In blue light, M51 has the de Vaucouleurs type SA(s)bc while NGC 5195 has the type I0. In the near-IR, M51 is clearly a barred spiral while NGC 5195 is type SB0 (Block et al. 1994a).

Photographs under Atlas Samples also show how we will use both deprojected images and color index maps to highlight de Vaucouleurs classification features. For example, a deprojected image of NGC 1433 shows how the inner ring is an oval aligned with the bar axis. De Vaucouleurs first pointed out this characteristic many years ago, and it has been shown to be generally true (Buta 1995) but it was not recognized in either the Hubble Atlas or the Carnegie Atlas. A B-I color index map shows how recent star formation in NGC 1433 follows the rings and pseudorings, as well as the linear bar dust lanes. Thus, deprojected images and color index maps can provide much additional information on a galaxy like NGC 1433. Color index maps will help to highlight what kinds of stars are contributing the features that define the de Vaucouleurs classification. The inclusion of color information in this manner would distinguish the de Vaucouleurs atlas from the Carnegie Atlas, and would enhance its value for extragalactic research.

We will draw on as many sources as possible for the illustrations, including our own image databases, public databases such as the images of Frei et al. (1998), the HST archives, the National Extragalactic Database (NED) image archive, and other sources we can locate. For example, we asked for, and received, permission to use several private image databases We will seek to acquire new images ONLY if there are types under-represented in the pre-existing databases, or if the available image databases do not include images of a particular type of high enough quality. The initial sample of galaxies we will focus on for the atlas is the list provided in Table 15 of Buta et al. (1994). At each stage along the revised Hubble sequence, Buta et al. listed a small number of galaxies representative of the type, covering a range of familes and varieties. This list has about 175 galaxies, and will be supplemented in order to cover special aspects of morphology and any type not fully included in the list. We anticipate that the final atlas will involve about 250 galaxies. At 2-4 galaxies per page with text and appendices, we anticipate that the final book will be around 100-150 pages long.

Finally, the appendices will focus briefly on other aspects of morphology that have come to the forefront since de Vaucouleurs published his ideas on galaxy morphology. For example, Buta (1985, 1995) and Buta and Crocker (1991) built within the de Vaucouleurs framework a subclassification of outer rings and pseudorings based on subtle differences of morphology that connect the features to the outer Lindblad resonance. Figure 1 below shows a schematic of these ``OLR subclasses,'' while Figure 2 shows blue light images of several especially good examples.

Figure 1: The OLR subclasses of outer rings and pseudorings, where subscripts appended to de Vaucouleurs' ring notation is being used.
Figure 2: Deprojected images of four galaxies showing classic de Vaucouleurs outer pseudorings (denoted R'). The subtle morphological differences between the two galaxies in the upper panels and the two in the lower panels are highlighted with the notation in Figure 1. Upper left: NGC 2665. Upper right: UGC 12646. Lower left: ESO 577-3. Lower right: ESO 325-28.
Kormendy (1979) brought attention to features known as inner and outer lenses, occasionally misclassified as inner and outer rings, and recommended notations with the framework of de Vaucouleurs classifications (Figure 3). A lens is a region with only a very shallow luminosity gradient, almost a plateau in a luminosity profile. A ring may be a subtle enhancement at the edge of a lens. Both Kormendy's lens notations and the OLR subclasses were used in classifications provided in the Catalogue of Southern Ringed Galaxies (Buta 1995).
Figure 3: Examples of Kormendy lenses. NGC 4909 (left) has an inner lens in the place where an inner ring would normally be found. NGC 2983 (right) has an outer lens in the place where an outer ring would normally be found. Kormendy (1979) proposed using (l) for inner lens and (L) for outer lens in the framework of de Vaucouleurs' system.

Buta and Crocker (1993) built nuclear rings into the de Vaucouleurs system using notation such as nr for closed nuclear rings and nrfor nuclear pseudorings. In this appendix, we will illustrate the relation between de Vaucouleurs varieties and nuclear rings, and how a ``nuclear variety'' can defined in much the same way as a regular variety. Figure 4 shows how nuclear rings, inner rings, and outer rings compare among different galaxies, and also illustrates how the three ring types may coexist in the same galaxy.

Figure 4: Illustrations of different ring types, including nuclear rings which are not generally recognized in de Vaucouleurs' system. Upper left: ESO 565-11, with bright, knotty nuclear ring. Upper right: IC 5240, strong SB(r)-type spiral. Lower left: NGC 1543, with bright outer ring. Lower right: NGC 6782, an early-type which includes all three ring types.

De Vaucouleurs was keenly interested in van den Bergh luminosity classifications, and spent considerable effort in evaluating systematic effects in such classifications for use in distance scale research. Odewahn and de Vaucouleurs (1992) have carried out the most extensive analysis of luminosity classifications, and we will draw on their results to illustrate the luminosity classification system with CCD images. Van den Bergh (1998) has commented that luminosity effects along the main axis of the revised Hubble sequence is a problem for the de Vaucouleurs system, as it was also for the Hubble revision. A full de Vaucouleurs type would be specified as something SB(s)c II-III with the luminosity classification appended. De Vaucouleurs also instituted the numerical type T and luminosity class L indices (see Table 2). He used these indices to develop a distance-independent index of absolute magnitude known as the luminosity index, . Thus, de Vaucouleurs recognized that at least in the revised Hubble system, both type and luminosity class are needed to account for luminosity effects in the system. Figures 5 and 6 show examples of different luminosity classes.

Figure 5: Illustrations of different luminosity class spirals, where class I is the most luminosity and class V is the least luminous. Those in this figure are all high luminosity according to Sandage and Tammann (1987). Upper left: NGC 5985 (I). Upper right: NGC 5850 (I-II). Lower left: NGC 5457 (I). Lower right: NGC 7479 (I-II).
Figure 6: Illustrations of different luminosity class spirals, where class I is the most luminosity and class V is the least luminous. Those in this figure are all lower luminosity according to Sandage and Tammann (1987). Upper left: NGC 45 (III). Upper right: NGC 2500 (III). Lower left: NGC 4618 (II). Lower right: NGC 2366 (IV-V).

De Vaucouleurs was also interested in the multiplicity of spiral structure (number of arms) as well as arm character (``massive'' versus ``filamentary''). In Atlas Samples, Maffei 2 is an example of a "2+2" mulitplicity spiral, with two main arms and two secondary arms. NGC 1433 is similar. We will also highlight in this Appendix the Elmegreen Arm Classes (AC, Elmegreen and Elmegreen 1987). In this system, AC 9 refers to strong "grand design" spiral patterns while AC 1 refers to "flocculent" or very filamentary patterns. Galaxies later known as ``flocculent'' spirals by Elmegreen and Elmegreen (1987) were denoted high multiplicity, filamentary spirals by de Vaucouleurs (1956). All of the objects in Figure 5 are AC 8-9 while NGC 45 and 2500 in Figure 6 are AC 1 examples.

In 1974, de Vaucouleurs described at a conference two galaxies having secondary bars lying within a primary bar. De Vaucouleurs was very interested in these unusual structures, and in 1975 published an excellent paper on NGC 1291, a barred S0/a having a secondary bar misaligned with the primary bar by about 30. NGC 1291 is also one of the nearest examples of an outer-ringed galaxy. In this appendix, we will illustrate and discuss secondary bars and what is currently known about them. Figure 7 shows an example of a double-barred galaxy. Triple-barred galaxies are also known to exist and will be illustrated in this section (Wozniak et al. 1995; Erwin and Sparke 1999).

Figure 7: I-band image of NGC 6782 a galaxy showing both secondary and primary bars, each crossing a prominent ring in blue light.

Other topics to be covered and illustrated include low surface brightness galaxies (Bothun et al. 1987; Schombert et al. 1995), dust-penetrated galaxy classification (Block and Puerari 1999), I0 galaxies (e.g., Steiman-Cameron, Kormendy, and Durisen 1992; Block et al. 1994a), computer classification (Odewahn, Cohen, and Windhorst 2000; Kriessler et al. 1998), and disky versus boxy elliptical classifications (Kormendy and Bender 1996). These issues will be highlighted in this web page when images become available to us.