Proper motion candidates

[Tass Mailing List <tass@mail.alembic.net>]

Date: Wed, 11 Oct 2006 11:07:50 -0400
From: Michael Richmond <richmond@stupendous.cis.rit.edu>
To: tass@tass-survey.org
Cc: mwrsps@rit.edu
Subject: Proper motion candidates


  Tom asked:

> What became of the proper motion studies?  Is anyone going to collect
> all the results and see if it has enough content for a paper?  Seems
> worthwhile to me.

  Ah.  Right.  I guess I'd better tell my tale of woe.

  Last month, I collected the lists that many people (especially
Michael Sallman) made of the promising objects from the big
list of 1027 candidates at

       http://spiff.rit.edu/tass/proper_motion/group_cand_index.html

  There were a total of 105 "promising objects".  As I was running
through this list, it seemed to me that we were more sensitive to
motion in Dec than in RA.  The very smallest proper motion that
we could detect was _something_ like 0.1 arcsec per year in Dec,
but that was only for bright, isolated stars.


  I compared these promising objects to stars in existing proper motion
catalogs.  For example, the LHS (Revised Luyten Half-Second Catalog),
which can be found in SIMBAD:

       http://cdsweb.u-strasbg.fr/viz-bin/Cat?I/279

In the area covered by the Mark IV survey (-5 < Dec < 88.2),
I asked how many stars in LHS had proper motions of over 1.0
arcseconds per year.  I found

          263 stars with PM > 1 arcsec/yr   and  R  < 15
          213 stars with PM > 1 arcsec/yr   and  R  < 14
          174 stars with PM > 1 arcsec/yr   and  R  < 13
          123 stars with PM > 1 arcsec/yr   and  R  < 12

  These counts suggest that our Mark IV list of candidates
is not complete: that is, our list of moving objects has
apparently missed a significant fraction of all the known
stars with high proper motions.

  I then took our list of 105 promising candidates and
searched the LHS catalog within a 120-arcsec radius of
each candidate.  There were 52 matches.  Almost all the
remainder of our promising candidates appeared in other
proper motion catalogs: Luyten Two-Tenths, or Giclas,
or New Luyten Two-Tenths.

  There were only 2 promising candidates in our list
which didn't appear in the set of proper motion catalogs
I first checked.  I did a bit more work on them:

  candidate 21599
     http://spiff.rit.edu/tass/proper_motion/cand_21599/measure_21599.html

        has PM measured in Tycho-2
        its reduced proper motion (a combination of apparent magnitude
               and proper motion, see Salim and Gould, ApJ 582, 1011, 2003)
               suggests it is a main sequence star

  candidate 61383
     http://spiff.rit.edu/tass/proper_motion/cand_61383/measure_61383.html

        has PM measured by Tycho-2 and USNOB1.0
        its reduced proper motion also suggests a nearby main-sequence star


  However, when I checked a very recent, very large catalog of
stars with high proper motion, the LSPM-North

      http://cdsweb.u-strasbg.fr/viz-bin/Cat?I/298

I found that it included both of these objects.

  So, the bottom line, to my mind, is

          a) the Mark IV survey does detect _some_ stars with
                 high proper motion, but not all of them

          b) there aren't any obvious new interesting candidates
                 that are unknown to science in our list of candidates


  Maybe the most interesting facet of this study is the weak
limit we can place on stars with _VERY_ high proper motions -- say,
10 arcseconds per year.  Most proper motion studies are good at finding
stars which move within a certain range of speeds: not too slow
(because then there's no apparent motion between pictures), but also
not too fast (because then the star moves so far that it doesn't
appear in both pictures, or can't be matched up easily).
In some parts of the sky, the Mark IV measured positions 10 or 20
times within a span of 3 months, and _would_ easily detect
and match up at least a subset of the observations of a hypothetical
star with proper motion 10 or 12 or 15 arcseconds per year.
We detect no such stars, though we did detect Barnard's star,
which moves about 11 arcsec per year -- see

  http://spiff.rit.edu/tass/proper_motion/cand_8125432/measure_8125432.html


  Anyway, after coming to these conclusions, I just closed my
notebook and moved onto the next topic ...

                         Michael