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Special Notice #146: Request to monitor the candidate high-mass X-ray binary BG Gem

AAVSO Special Notice #146

Request to monitor the candidate high-mass X-ray binary BG Gem
February 4, 2009

Dr. Mark Reynolds (U. Michigan) has requested photometric monitoring of the candidate high-mass X-ray binary BG Geminorum to coincide with a 3-month monitoring campaign by the MDM 1.3-meter telescope at Kitt Peak, Arizona.  BG Geminorum is one star of a close double (separated by 6 arcseconds).  It was originally classified as an RV Tauri star, but observational evidence now indicates it is an eclipsing binary with a massive primary; it is uncertain whether the primary is a black hole with an accretion disk or a B star. 

Observations are requested beginning immediately (2009 February 4, JD 2454867.0) to continue through 2009 May 1 (JD 2454953.0).  Dr. Reynolds' aim is to better constrain the ephemeris of this system, and use the improved orbital parameters to better constrain the properties of the primary star.  He is requesting nightly V, Rc, and Ic monitoring of this star during the observing window.  Time series are not required, so please obtain the best S/N observations that you can in reasonable time; the average magnitude of BG Gem is about V=13.4. 

Because the pair to which BG Gem belongs is very close, it will be difficult to separate the two with aperture photometry.  Furthermore, BG Gem lies in a crowded field, and so any photometry will be challenging. If you have software capable of performing PSF-fitting and have a telescope, camera, and seeing conditions allowing you to split the two, please perform PSF photometry.  If you do not, please combine both stars in a single aperture and photometer the pair; regardless of which method you use, please indicate in the comments field whether your magnitude includes both stars.  We also request that you save your CCD frames so that the PI has the opportunity to perform PSF photometry in the future, if this is desired.  Photometry in V, Rc, and Ic bands is desirable, but Rc is the priority if time or other constraints permit the use of only one filter.

The AAVSO currently has a small amount of data for this star; there is an ASAS-3 (Pojmanski 2002) light curve available at the following URL: http://www.astrouw.edu.pl/asas/?psect=acvs&page=details&id=060331+2741.9

BG Geminorum (AUID 000-BCV-935) is located at the following (J2000 coordinates (from 2MASS):

RA: 06 03 30.81 , Dec: +27 41 50.7

Charts for BG Gem may be plotted using VSP: http://www.aavso.org/observing/charts/vsp/index.html?pickname=BG%20Gem

Please submit data to the AAVSO as "BG Gem".

This AAVSO Special Notice was prepared by Dr. Matthew Templeton.

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