This call for observations is excerpted from Alert Notice 348 of the American Association of Variable Star Observers (AAVSO), issued April 6, 2007.

Dr. Gordon Sarty, University of Saskatchewan, Canada, has requested assistance in obtaining BVRI photometry (or any subset thereof) of four (4) high-mass X-ray binaries (HMXBs) for the months of April and May 2007. Dr. Sarty will be acquiring spectroscopy of the four HMXBs, for the purpose of measuring their radial velocities, with the Dominion Astrophysical Observatory (DAO) 1.85-meter Plaskett telescope in Victoria, BC, Canada, from April 24th to May 2nd. The object is to determine the orbital periods of the HMXBs. Optical photometry will also reveal other periods and variations due to mass transfer, pulsations, and other effects. The availability of photometry will be very valuable for interpreting the spectroscopic data.

HMXBs consist of an exotic neutron star or black hole in orbit around a more massive ordinary (O- or B-type) star. Mass is transferred from the ordinary star to the exotic star through a variety of mechanisms, including accretion disks (to the exotic star), deaccretion disks (from a rapidly spinning ordinary star), and high stellar winds. These mass-transfer processes cause many HMXBs to be variable stars. The true distribution of HMXB orbital periods is not yet known because many such periods are years in length. Thus amateur observations of HMXBs will be very valuable for finding the true distribution. More information about HMXBs will be published in an article in an upcoming issue of the JAAVSO. A preprint of that article may be found here:

The table below lists the four target HMXBs for this observing campaign:

Desig.   AAVSO Name  Name          R.A.(2000)  Dec.(2000)   Mag  LPH
1930+53  1936+541    1936+541      19:32:52.3  +53:52:45.5  9.8  115
2027+47  J2030.5+47  J2030.5+4751  20:30:30.9  +47:51:50.7  9.3  123
2157+49  2202+501    2202+501      22:01:38.2  +50:10:04.6  8.8  127
2204+54  2206+543    2206+543      22:07:57.1  +54:31:05.8  9.9  128

Note that 2204+54 2206+543 was formerly in the AAVSO validation file as 2204+53 2204+54CEP; the designation and name have been changed as shown in the above list.

The LPH number is a cross-reference to the HMXB listing in the JAAVSO paper and the HMXB chart Web page, which may be found here:

Please follow the observing instructions given on the chart Web page and on the charts and submit your results to the AAVSO International Database or, if differential photometry only is possible, directly to Dr. Sarty at [email protected] (please also send any questions you may have as well). Contributors of useful data will be offered authorship on any publications we get out of this observing campaign.

Request to Monitor AR UMa for Spitzer Space Telescope Observations

Dr. Steve Howell (National Optical Astronomy Observatory) and Dr. Donald Hoard (Spitzer Science Center) have requested time-series observations of the AM Herculis-type cataclysmic variable AR Ursae Majoris (11:15:44.68 +42:58:22.5 [J2000]) to coincide with upcoming Spitzer Space Telescope observations.

Both B- and V-band CCD time-series observations are requested leading up to and during the Spitzer observations scheduled for 2007 May 9–10, and continuing through May 13–14. Time-series observations during the May 9–10 observing window are most critically needed, while time-series observations before and after will help to establish the range of behavior of this object. The star varies between V=14.5 and V=16.5; please use exposure times that yield a signal-to-noise ratio of 50 per measurement.

AAVSO charts are available here:

A Henden-Sumner sequence file is available here:

Reporting Your Observations

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

If you cannot access this URL, please contact the AAVSO for submission details. You may also call the AAVSO's toll-free phone number (888-802-STAR = 888-802-7827) or send a fax (+1 617-354-0665) to report your observations.

Please check the online version of this AstroAlert on Sky & Telescope's website for possible minor updates:

Any major updates will be announced via subsequent AstroAlert messages. Many thanks for your efforts and your astronomical contributions. Good observing!

Dr. Matthew Templeton
Staff Astronomer

Elizabeth O. Waagen
Senior Technical Assistant


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