Chapter 1: Introduction
Fig. 1.1. -- Photograph of the Pleiades cluster by
E. E. Barnard (1927),
courtesy of the Carnegie Institution of Washington. Flamsteed
numbers are shown.
Fig. 1.2. -- Pleiades optical nebulosity on photo negative prints from the
National Geographic Society - Palomar Observatory Sky Survey. Top left:
central cluster in red (POSS E) filter. Top right: central cluster in
blue (POSS O) filter. Bottom: outer nebulosity in blue light. The
vertical line left of center is a plate boundary.
Fig. 1.3. -- Interstellar reddening toward 89 cluster members, from Breger (1986). Stars on the east side of the
cluster generally exhibit E(B-V) ~ 0.03. Those on the west show around twice
as much, while the region of the CO cloud southwest of 23 Tau is eight times
more reddened. These results correlate well with White's (1984) measurements of CH+. His
15 stars are marked with Flamsteed and Henry Draper numbers. Single
underscores represent lower column densities of N(CH+) ~
5x1012 cm-2. Double underscores represent higher column
densities of N(CH+) ~ 2.5x1013cm-2.
Plain labels indicate nondetections, which typically have upper limits
consistent with the lower column density detections. However HD 23512's limit
of N(CH+) <~ 1.7x1013 cm-2 is not
small enough to preclude membership in the higher column density category.
Fig. 1.4. -- Fields and pointings of thesis observations:
The WISP field is indicated by the 5° x 1.7° diagonal box.
Schmidt fields are 1.1° dotted circles; for simplicity, each pointing-pair
is shown here as a single field.
The Green Bank mosaic is the large 19° x 11° irregular box.
The VLA mosaic is the small 2° x 2° square.
Filled circles indicate major Pleiads.
Coudé feed sightlines are marked with open star symbols.
Fig. 1.5. -- Larger context of the observed fields. The Pleiades reside in the
northwest corner of Taurus, which is bordered by (clockwise from top) Perseus,
Andromeda, Triangulum, Aries, Pisces, Cepheus, Eridanus, Orion, Gemini, and
Auriga. The cluster lies near enough the celestial equator (dotted
line) to be easily visible from both hemispheres of the Earth. Its
position some 22° south of the galactic plane (dashed-dotted) puts
it in the middle of Gould's belt, a ring of bright stars around the sky thought
to be a relic of a past star formation episode in this part of the galaxy.
Finally, close proximity to the plane of the ecliptic (dashed) allows
Pleiads to be studied via lunar occultation, but unfortunately also complicates
observation of the cluster in mid-infrared bands by maximizing background
emission from solar zodiacal dust. Stars in this plot are taken from the
Bright Star Catalog (Hoffleit & Warren
1991) and are limited to ~7th magnitude.