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Alert Notice 348: Observe HMXBs; monitor AR UMa; update on Alert Notice 345

April 6, 2007

SUBJECTS:

  1. REQUEST TO OBSERVE HMXBs IN SUPPORT OF RADIAL VELOCITY OBSERVATIONS

  2. REQUEST TO MONITOR AR UMA FOR SPITZER SPACE TELESCOPE OBSERVATIONS

  3. UPDATE ON ALERT NOTICE 345 (REQUEST TO MONITOR CVs)

1. REQUEST TO OBSERVE HMXBs IN SUPPORT OF RADIAL VELOCITY OBSERVATIONS

Dr. Gordon Sarty, University of Saskatchewan, Canada, has requested our 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 acquiring spectroscopy of the four HMXBs, for the purpose of measuring their radial velocities, with the Dominion Astrophysical Observatory (DAO) 1.85-m Plaskett telescope, in Victoria, BC, Canada, from April 24 to May 2. The object is to determine the orbital periods of the HMXBs. Optical photometry will also reveal other periods and variation 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 the orbital periods of many 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 by Sarty et al. in an upcoming issue of the JAAVSO. A preprint of that article may be found at

http://arxiv.org/abs/astro-ph/0702248

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

Desig.     AAVSO Name   Name          R.A.(2000)  Dec.(2000)   Mag  LPH no.
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 at:

http://homepage.usask.ca/~ges125/AAVSO_HMXB_Charts.html

"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 gordon.sarty@usask.ca (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."

2. 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 UMa (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 at:

http://www.aavso.org/vsp

A Henden-Sumner sequence file is available at: ftp://ftp.aavso.org/public/calib/sumner/aruma.seq

3. UPDATE ON ALERT NOTICE 345 (REQUEST TO MONITOR CVs FOR RADIO OBSERVATIONS)

Further to AAVSO Alert Notice 345, the AAVSO requests continued observations of the bright dwarf novae 0749+22 U Gem (07:55:05.2 +22:00:05 (2000.0)) and 2138+43 SS Cyg (21:42:42.8 +43:35:10 2000.0)) in support of radio observations of these objects by Dr. Christian Knigge, University of Southampton, UK. Dr. Knigge and collaborators will use the Very Large Array (New Mexico, USA) and MERLIN (Jodrell Bank, UK) radio telescopes to detect the brief spike in radio emission coincident with the onset of a dwarf nova outburst.

AAVSO visual and CCD observers are requested to submit all observations - including positive observations during quiescence, transition, and outburst, as well as "fainter-than" observations - to the AAVSO via WebObs as rapidly as possible. Radio observations will only be made if they can be initiated within six hours of the onset of an outburst. Because of this constraint, we must know both that the star was in quiescence and that it is rising to outburst within the past six hours. If possible, please submit observations as they are made or immediately following your observing session.

AAVSO charts for SS Cyg and U Gem may be found at the following URL:

http://www.aavso.org/vsp

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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