VR, thanks for your reply on my request for comments on my AIG article
about Hugh. While you agree with Hugh on many issues, you disagree with him
more than I thought that you did. Many of the things that you said require no
response; I'll respond to a few things as I find the time. Let me address the
MACHO/Keck/LMC question in this post.
In my article I stated that the Keck telescopes would have been unsuitable
for this work for two reasons: the objects studied were far too bright to
require the large aperature of the Kecks, and such large telescopes are rarely
dedicated to such long-term projects that consume large amounts of time (the one
exception might be the 200 inch (5m) Hale telescope, but that stems from its
unique governance). Another reason that the Kecks were not used is that they
are too far north. The latitude at Mauna Kea is a little less than 20 N
degrees. That means that from that location one can see down to about -70
degrees declination. The center of the LMC is at about -69 degrees declination,
meaning that the center doesn't get more than a degree or two above the horizon
at the Kecks. Part of the LMC wouldn't rise at all, even with refraction
lifting them about ½ degree. As one gets lower in the sky, the amount of
atmosphere one is looking through increases rapidly. The rule of thumb in
photometry (the kind of work here) is that you rarely, if ever, go below 30
degrees altitude. In my experience the photometry completely falls apart about
that altitude, so any photometry much below that is impossible from the ground,
even at a great sight such as Mauna Kea. Therefore, the involvement of the
Kecks was impossible.
I've given careful thought to your suggestion that Hugh meant that the
MACHOS were in the LMC in the same sense that we say that a planet, asteroid,
comet, meteor, nova, supernova, variable stars, and even extra-galatic objects
are in a costellation. I can't think of a single instance where I've heard
terminology (of a foreground object seen in the same direction of a galaxy) used
this way, so this would be very novel. The constellation method of location is
used for a couple of reasons. One is that it stems from ancient times (we
astronomers can be so conservative - we're still using magnitudes after two
millenia). The other is that the entire celestial sphere is divided into 88
constellations with definite boundaries (or at least since about 1930), so that
every part of the sky is in some constellation. For instance, it would have
been correct to state that the MACHOS were in Dorado. The LMC is a very
work-horse object that has been used to discover many important things in
astronomy, such as the Cepheid variable period-luminosity relation. Hence,
there probably have been thousands of papers published on objects in the LMC.
In every one, "in the LMC" means just that. Given this, I can only conclude
that any astronomer means "in the LMC" when he says "in the LMC."
As for your suggestion that the LMC is so close to the Milky Way that
objects in the halo are close enough to be in the LMC, I ran a few numbers. The
LMC has a galactic latitude of about -34 degrees. Using the near distance of
160,000 light years (many think that the distance is closer to 180,000 light
years, I get a distance projected in the galactic plane of about 133,000 light
years. The LMC has a galactic longitude of about 280 degrees, which means it
makes an angle of 80 degrees with the galactic center as viewed from our
location. Assuming that we are 25,000 light years from the galactic center, I
get a distance of the LMC from the galactic center projected onto the galactic
plane at about 130,000 light years. Taking a large diameter for the MW at
120,000 light years, I find that this distance is over twice the radius from the
center as the MW radius. Therefore, the LMC is far outside the halo. One might
argue that the outer halo could extend about as far as the LMC, particularly for
objects tidally lifted out, but I doubt that there is much mass that far out.
In short, the MACHOS described in the articles Hugh cited are far closer to us
than the LMC, and they cannot be in the LMC, as that term is universally used.
Therefore, I stand behind my criticism of Hugh on this. As I've tried to
emphasize before, one or two things such as this are excusable, but I see a
pattern of these sorts of things.
Danny

Danny R. Faulkner
a stellar astronomer
faulkner@...