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Special Notice #350: 1RXS J105010.3-140431 and SDSS J153817.35+512338.0 next HST/COS targets

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April 30, 2013:  Further to AAVSO Alert Notice 471 (, HST/COS is scheduled to observe the eclipsing WZ Sge-type cataclysmic variable 1RXS J105010.3-140431:

1RXS J105010.3-140431  2013 May 10 07:51:01 through 12:01:57 UT

The HST team will be making a final decision on observing 1RXS J105010.3-140431 based on the observations of May 8/9, and observations from the following night will also be essential. Close monitoring of 1RXS J105010.3-140431 through May 11 is requested to be sure it is below the threshold brightness and to have a good magnitude value for correlation with the HST observations. 1RXS J105010.3-140431 is V=17 at minimum; its magnitude at maximum is unknown.

After 1RXS J105010.3-140431, the next target will be the dwarf nova SDSS J153817.35+512338.0:

SDSS J153817.35+512338.0   2013 May 13 UT (time to be announced later)

Giving 1RXS J105010.3-140431 highest priority, please begin covering SDSS J153817.35+512338.0 now; close monitoring through May 14 is essential. SDSS J153817.35+512338.0 is V=18.6 at minimum and its magnitude at maximum is unknown.

As instructed in AAVSO Alert Notice 471, for CCD observers, simultaneous photometry [shortly before, during, and after the HST observations] would be ideal. For the magnitude estimates, a nightly V measurement from now through the HST observations and a day beyond would be best. If positive visual observations are possible, they are welcome, as are visual fainter-than observations fainter than magnitude 15.0.

Coordinates (2000.0)
1RXS J105010.3-140431        R.A. 10 50 10.803  Dec. -14 04 36.64
SDSS J153817.35+512338.0  R.A. 15 38 17.31   Dec. +51 23 38.0

Charts may be created using the AAVSO Variable Star Plotter (

Please report observations as soon as possible to the AAVSO International Database using the names 1RXS J105010.3-140431 and SDSS J153817.35+512338.0, respectively. If an outburst is detected, please report observations immediately.  Many thanks!

This AAVSO Special Notice was compiled by Elizabeth O. Waagen.



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