In praise of twelfth magnitude

[Stupendous Man <richmond@a188-l009.rit.edu>]

  Tom said:

>  If we don't go as deep as we can, then we run the risk of 
>  only measuring previously well studied objects.

  Arne wrote:

> ... So you have to look at what is unique about the Mark IV and
> make the uniqueness work for you.
> In my mind (and I've told Tom this before), the unique aspects
> are the simultaneous V&I exposures and better angular resolution. ...

  <soapbox>

  I agree 100% with Arne: the Mark IV _can_ do "real science"
even at mag 12, or mag 10.  Yes, (almost) every object which is
mag 12 has been seen and recorded before by someone --- BUT 
so what?  In (almost) every case, the recorded and catalogued
measurements are 
 
          a) years old
          b) a very few epochs 
          c) taken only in the V-band, or the "photographic" passband

  What we _don't_ have is a set of accurate and precise photometric
measurements, at the 3-5 percent level, of thousands of stars in
the V-band and the I-band.  Nor do we have knowledge of the variability
of all these stars.  And, and, in just a FEW cases (say, 1 in 10 million),
we don't even have accurate positions, because the stars are moving 
_so_ fast that they move an arcsecond every year, and matching up
such extremely fast-moving stars on different plates taken years
apart is really hard (Arne knows a lot more about this particular
item than I do, of course, and I hope he'll correct me if I'm way
off here.   But I do think that is the possibility to catch the
one-in-10-million or 1-in-100-million shot here).

  Anyway, I second Arne's claim that repeated observations of 
even bright stars -- with proper photometric calibration -- is something
rare in astronomy.  Most astronomers don't have five years to make
a proper study of such things: they have to produce a result in
six months, in time to write the next grant proposal.  TASS members
can beat (most of) the pros at this game, no problem.

  Arne mentions ROTSE, for example.  The ROTSE team use a robotic
telescope with a scad of CCDs to measure stars in a huge field,
16-degrees on a side.  Their primary goal is to find optical
counterparts to gamma-ray bursts, and they have done so for 
exactly one GRB.  They also measure stars, on the side, as it were.
You can read their first paper describing their stellar measurements
in ApJ, April 2000, vol 119, p. 1901, or at

 http://www.journals.uchicago.edu/AJ/journal/issues/v119n4/990545/990545.html

  Now, they present an impressive number of observations in this
paper.  Note the following sentence:

        "... Photometric calibration is somewhat more complex. 
         The Tycho catalog includes only B and V photometry, 
         and ROTSE-I images are obtained with unfiltered CCDs ..."

  Yes, they do find a lot of variable stars.  That is good, and in now
way do I wish to demean their work.  But, if one wants to know more
about any particular system, one may be stuck: there is no measurement
in a standard passband (such as B, V or I), and there is also no
indication of stellar color (and hence temperature).  

  Should we throw up our hands and say, "Gosh, what's the point, 
ROTSE has already seen all the variable stars"?  I reply, "No."

  Oh, in addition, you might note that they have published the analysis
for stars in only 9 of their 160 patrol fields across the sky.  

  Anyway, please don't give up hope that "we can't do any good science
without pushing the limits."  Other people are going to beat us 
to any particular limit --- but few will be able to stay the course
in the long term.  I look at TASS as a marathon runner: not as fast
as a sprinter, but longer lasting.  

  </soapbox>
                                                  Michael Richmond