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AAVSO Special Notice #151

Monitoring of the neutron star binary SDSS J102347.68+003841.2
April 3, 2009

Anne Archibald (McGill University) and collaborators request long-term
monitoring of the transient source SDSS J102347.68+003841.2 (== FIRST
J102347.6+003841).  This object is a known ellipsoidal variable (V ~
17.3-17.8) consisting of a neutron star primary and a 0.2 solar mass
secondary, with a binary period of 0.198 days.  While the known
ellipsoidal variation is understood to be a combination of tidal
deformation of the secondary and heating of the side closer to the
primary, the system was also observed to go into optical outburst in
2001, increasing in optical flux by a factor of 4 (~1.5 magnitudes),
suggesting that a mass transfer episode occurred.  The neutron star is a
known pulsar, and the system is described as a "radio-selected
cataclysmic variable"; the intermittent accretion may indicate that this
is a very evolved low-mass X-ray binary.  Currently (as of 2009 April)
the system does not appear to be active, and no sign of an accretion
disk is seen.  Long-term monitoring of this faint star for future
outbursts of a similar nature is requested.  Future outbursts will
trigger X-ray and radio observations of this source to better understand
the evolution of neutron star binary systems.

This is primarily a monitoring program, and so time-series are not
required while the object is in quiescence.  Those with larger aperture
telescopes may be able to detect the orbital modulation if integration
times are substantially shorter than the orbital period of 0.198 days. 
The maximum brightness resulting from the orbital variations is around
V=17.3; any observations significantly brighter than this may indicate
an outburst, and observers are asked to submit observations as quickly
as possible.  If the system does enter outburst, please obtain
time-series coverage with the highest signal to noise feasible during
the bright phase and decline.

SDSS J102347.68+003841.2 is located at the following J2000 coordinates:

RA: 10 23 47.68 , Dec: +00 38 41.2

Charts for this object may be plotted using VSP:


(Note that because the target is faint, crosshairs will not appear on
E-scale and larger charts made with VSP default settings.)

Please submit observations to the AAVSO using the name "SDSS
J102347.68+003841.2" (AUID 000-BJN-598).  The alias "FIRST J1023" may
also be used to submit observations.

This AAVSO Special Notice was prepared by M. Templeton.


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