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Special Notice #376: HST observations of U Gem scheduled for December 6

December 2, 2013: Further to AAVSO Special Notice #318 (M. Templeton) and AAVSO Alert Notice 475 (E. Waagen), Dr. Michael Shara (American Museum of Natural History) informs us that HST/COS observations of the dwarf nova U Gem have been scheduled for 2013 December 6 UT (one day earlier than originally indicated in the December 2 posting to the AAVSO forums). The observations will take place:

            2013 December 6  09:54:08 through 11:59:59 UT

It is thanks to the extensive and careful coverage of U Gem you have provided these past weeks and months that this HST scheduling could take place. Dr. Shara needs to observe following closely on an outburst, and without knowing the outburst state of U Gem (and the fact that an outburst had just concluded), the satellite could not have been appropriately or safely scheduled.

Dr. Shara has worked with the AAVSO before and truly appreciates your efforts and your valuable observations. In addition to determining the outburst state of U Gem, they are to be used for correlation with and interpretation of spectra obtained by HST/COS in an effort to determine the dominant energy source in dwarf novae (and thus the physical mechanism of dwarf novae outbursts), fundamental information still not known about this class of objects (current theories do not explain all of the observational evidence).

According to Dr. Shara, "intensive monitoring in UBVRI (or ugriz) would be ideal. Starting immediately through December 8, twice hourly coverage would be wonderful. On December 6, coverage every ~5 minutes would be excellent." Visual observations, particularly positive ones, are also encouraged.

Dr. Shara adds that if any AAVSO "observers have visible and/or near-IR spectrographic capabilities, spectra on December 6 would be wonderful."

U Gem is nearly back to minimum following an outburst that began on 2013 November 9. As of 2013 December 02.67071 UT (JD 2456629.17071), it was 14.406 V +/-0.012 (MGW, Gordon Myers, Hillsborough, CA, USA) and fading. By December 6 it should be fully back to minimum at around V=14.8-15.0.

Please observe U Gem as indicated above and report your observations to the AAVSO International Database using the name U GEM. Since U Gem has just had an outburst, it should not be bright, but if you do see U Gem brightening again, please report your observations at once. Many thanks!

Coordinates: R.A. 07 55 05.21   Dec. +22 00 04.8  (2000.0)

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

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

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