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AAVSO Alert Notice 417

Request for observations of GW Lib and V842 Cen in support of HST observations
March 3, 2010

Dr. Paula Szkody (U. Washington) has requested the help of AAVSO observers 
to provide monitoring of two cataclysmic variables, GW Lib and V842 Cen, 
in support of Hubble Space Telescope observations in March 2010. 
Observations of both objects are requested beginning immediately, with 
intensive observations requested beginning 48 hours prior to the scheduled 
HST visit.  The first observation of GW Lib has now been scheduled for 
2010 March 11 03:45 UT (JD 2455266.6563); intensive observations by the 
AAVSO community are requested beginning 2010 March 9 UT (JD 2455264.5).  
Observations of V842 Cen are expected to be scheduled during the dates of 
2010 March 18-22.
GW Lib and V842 Cen are dwarf novae/novae that have undergone outbursts in 
the past.  Observations of both sources are requested to guarantee to 
ground controllers at STScI that they are below V~14.0 which is considered 
the safe limit for the Cosmic Origins Spectrograph.  Positive observations 
are preferred if at all possible,however any fainter-than below V=14 is 

Details about the V842 Cen observations will be issued via Alert Notice 
when they are finalized.

The GW Lib observations are tentatively scheduled for 2010 March 11 03:45 
UT pending confirmation that the star remains in quiescence. Please 
promptly report all observations of this star to the AAVSO via WebObs.  
The use of WebObs will ensure the fastest delivery of your data to Dr. 
Szkody and STScI.  We recommend using at least the "143" (AUID 
000-BBW-012) and "147" (000-BBW-026) comparisons for fainter-than 
estimates.  We note that GW Lib is an infrequent outburster, and it is 
highly unlikely that it will rise above its current brightness around 
V=17.0 on March 11.  However, STScI will still require confirmation of 
this to ensure the safety of the Hubble Space Telescope and thus your 
observations may be key to triggering these observations.

GW Lib is located at the following (J2000) coordinates:

        RA: 15 19 55.45 , Dec: -25 00 25.30

Charts for GW Lib may be plotted using AAVSO VSP:


Please report all observations of GW Lib to the AAVSO using the name "GW

This AAVSO Alert Notice was prepared by Matthew Templeton.


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