Skip to main content

Special Notice #151: Monitoring of the neutron star binary SDSS J102347.68+003841.2 [AY Sex]

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 [AY Sex]).  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.


Information on submitting observations to the AAVSO may be found at:


A Special Notice archive is available at the following URL:

Subscribing and Unsubscribing may be done at the following URL:


AAVSO 49 Bay State Rd. Cambridge, MA 02138 617-354-0484