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Special AAVSO Photoelectric Photometry Alert Notice

             THE AMERICAN ASSOCIATION OF VARIABLE STAR OBSERVERS
                   25 Birch Street, Cambridge, MA 02138 USA
                          INTERNET:  aavso@aavso.org
                   Tel. 617-354-0484       Fax 617-354-0665

    SPECIAL AAVSO PHOTOELECTRIC PHOTOMETRY ALERT NOTICE (September 20, 2001)

REQUEST TO MONITOR 2248+16 IM PEGASI IN SUPPORT OF GRAVITY PROBE B SATELLITE

Gravity Probe B (GP-B) will test two predictions of general relativity by
measuring the precessions of gyroscopes in an earth-orbiting spacecraft with
respect to an external frame of reference.  That frame will be defined by the
guide star IM Peg = HR 8703.  GP-B needs a guide star whose proper motion can
be measured with better than 0.15 milliarcsecond/year accuracy with respect to
an extragalactic frame which is defined by pointlike sources called quasars.
These are radio sources whose positions are stable to the necessary accuracy.
The guide star must also be a nearly pointlike radio source whose position can
be measured to milliarcsecond accuracy.  For more information about GP-B, see
the web site:

                          http://einstein.stanford.edu/

The radio results may be found at:

              http://aries.phys.yorku.ca/~bartel/GPBresults.html

IM Peg = HR 8703 is an RS CVn star, a K2 giant star which shows a high level
of "activity".  This activity includes compact radio emission, whose position
can be compared, using radio interferometers, with the extragalactic reference
frame.  IM Peg is a 24.65-day spectroscopic binary.  Radio interferometers can
actually detect the motion of the radio star in its orbit!  The most recent
optical study of IM Peg is by Berdyugina et al. Astron. Astrophys., 360, 272
(2000), which presents surface images of the star.  The period of spot rotation
is 24.73 days.

IM Peg varies in brightness because of the rotation of spotted regions into
and out of our line of sight.  This changing brightness, relative to the
non-variable binary companion or other stars or nebulosity within the 140"
diameter field of view of the spacecraft's guide telescope, could possibly
bias the "average" proper motion of the star.  In addition, the observation of
any relatively rare (perhaps once per year), short-lived, bright flares on the
active giant, as have been seen on other RS CVn binaries, would also be quite
interesting.

Astronomers at the Harvard-Smithsonian Center for Astrophysics have requested
our assistance in providing close monitoring of IM Peg.  What is needed from
our photoelectric photometry observers is monitoring of IM Peg regularly.
GP-B is not planned for launch until 2002, but the monitoring should begin as
soon as possible to test the procedure.  The star will also be monitored with
a robotic telescope, but this is in operation for only part of the year.
Usually no robotic observations are made from late January until early May, or
from early July until mid-September of each year.  Observations during these
intervals would be especially valuable.

The variable, comparison, and check stars to be used are:

Variable  =  IM Peg: HR 8703: HD 216489: HIP 112997: Range = 5.60-5.85 V (GCVS),
                     SpT =  K1-2II-III
 		RA 22h 53m 02.2s (2000), Dec +16 degrees 50' 28" (2000)

Comp  =  HD 216635: HIP 113105: V = 6.60, B-V = +1.001, SpT = G8III
 		RA 22h 54m 18s (2000), Dec +17 degrees 47' 42" (2000)

Check  =  HR 8788: HD 218235: HIP 114081: V = 6.16, B-V = +0.482, SpT = F6V
 		RA 23h 06m 18s (2000), Dec +18 degrees 31' 03" (2000)

IM Peg should be observed once or twice each night, with a V filter, and
standard procedures used for our other PEP program stars should be followed.
Please report your observations both to Howard Landis (Lndvarstars@aol.com),
the present chair, and to Phil Manker (pmanker@qwest.net), the
future chair of the AAVSO Photoelectric Photometry Committee.

Accompanying is an AAVSO Photoelectric Photometry chart for IM Peg prepared by
C. Scovil.  Please use this chart to make your V observations.  (The chart may
also be downloaded from our website (http://www.aavso.org) or from our FTP site
(209.192.236.2) ftp://ftp.aavso.org/alerts/alertpep).

Our colleagues have also requested that IM Peg be observed with B, R, and I
filters.  Please let us know if you have any of these filters and would be able
to observe IM Peg with them.  If you do not have B, R, or I filters and would
like to make multicolor observations, we may be able to obtain financial
support so that we can purchase and distribute these filters on longterm loan
from the AAVSO.

If you are interested in participating in this very important project, whether
observing in V, or BVRI, please fill out the form below and return it to AAVSO
Headquarters.

Please note that this Special PEP Alert Notice was distributed via postal mail
only (not via email), but has been posted on the AAVSO website
(http://www.aavso.org, under Alert Notices).

We look forward to hearing from you and to your participation in this exciting
project.

Good Observing!

Howard Landis     Phil Manker    John Percy        Janet Mattei
Current PEP       Future PEP     PEP Newsletter    Director
Chair             Chair          Editor

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               THE AMERICAN ASSOCIATION OF VARIABLE STAR OBSERVERS
                    25 Birch Street, Cambridge, MA 02138 USA
                          INTERNET:  aavso@aavso.org
                    Tel. 617-354-0484       Fax 617-354-0665

       PHOTOELECTRIC PHOTOMETRY INFORMATION FORM FOR IM PEGASI PROJECT

Yes, I am interested in participating in the IM Peg project.

Name:  _______________________________________________________________________

Address:  ____________________________________________________________________
          ____________________________________________________________________

Phone:  __________________________       Fax:  _______________________________

E-mail:  _________________________________________________


1. Location of my observatory is:  ____________________________________________
_______________________________________________________________________________


2. Latitude and Longitude:  ___________________________________________________


3. I have the following filters:  _____________________________________________


4. The brand name and thickness of each are ( V, Schott GG-495 3mm, etc.):
_______________________________________________________________________________
_______________________________________________________________________________


5. I am interested in having B, R, and I filters on loan from the AAVSO for
this project:
                         Yes _____         No_____

6. I have determined my V transformation constant, and it is:
_______________________________________________________________________________


7. I have not determined my V transformation constant and would like
information as to how to do so:

                         Yes _____        No_____





                                                                      9/19/2001

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