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Special Notice #353: SDSS J153817.35+512338.0 obs crucial now and DT Oct is next

May 13, 2013:  Further to AAVSO Alert Notice 471 (http://www.aavso.org/aavso-alert-notice-471) and AAVSO Special Notice #351 (http://www.aavso.org/aavso-special-notice-351), HST/COS is scheduled to observe the dwarf nova SDSS J153817.35+512338.0:

SDSS J153817.35+512338.0 2013 May 16 22:44:06 through May 17 02:14:05 UT

The HST team will be making a final decision on observing SDSS J153817.35+512338.0 based on the observations of May 13/14 and 14/15, and observations from the following two nights will also be essential. Close monitoring of 1RXS J105010.3-140431 through May 18 is requested. SDSS J153817.35+512338.0 is V=18.6 at minimum and its magnitude at maximum is unknown.

After SDSS J153817.35+512338.0, the next target will be the SU UMa-type dwarf nova DT Oct:

DT Oct  2013 May 23 23:31:07 through May 24 02:05:03 UT

This date is revised from the preliminary date given in AAVSO Special Notice #351. Giving SDSS J153817.35+512338.0 highest priority, please also monitor DT Oct; close monitoring May 17 through 25 is essential. DT Oct is V=16.5 at minimum and V=11.8 at maximum.

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)
SDSS J153817.35+512338.0  R.A. 15 38 17.31   Dec. +51 23 38.0
DT Oct                                  R.A. 18 40 52.31   Dec.  -83 43 10.0

Charts may be created using the AAVSO Variable Star Plotter (http://www.aavso.org/vsp).

Please report observations as soon as possible to the AAVSO International Database using the names SDSS J153817.35+512338.0 and DT Oct, 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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