[vsnet-alert 6228] Observations requested of AM Her and VY Scl stars, for Keck campaign

[Frederick Ringwald <fringwal@csufresno.edu>]

Dear VSnet and CBA observers,

Please don't forget, our Keck run is coming up this weekend:

If you have any time for brief nightly observations of other targets
during the WZ Sge campaign, please get V-band photometry of your favorite
AM Her stars and VY Scl stars, and report the observations to VSnet.

Many cataclysmic variables, especially AM Her and VY Scl stars, have
erratic and poorly understood low states.  We have an observing run
scheduled on the Keck I telescope from August 12-14, to find out why.  It
has long been suspected that these low states may be due to starspots on
the mass-losing star that form or move over L1 and choke off the flow.
This idea is not without problems, however, but then that's why we want to
get our spectra.

Spectra aren't accurate photometric measurements, though.  Nightly
observations by you on the nights leading up to, and during, our run would
help a lot, because these low states are unpredictable.  We don't know
which objects are going to be in their low states, so we need to have
ready a list of many targets, and decide which to observe in detail only
when the Keck observations have started.  It would help even more to have
long-term light curves, which VSnet and CBA particularly excel at: we
would know whether we observed a low state or (more desirable) a very low
state, in which the mass transfer in some systems apparently turns
completely off.

Specific targets to monitor include:

		RA(2000)	DEC(2000)	Vmax	Vmin	Type
MV Lyrae	19 07 16.4  	+44 01 07   	12.1	17.7	VY
AM Her		18 16 13.4	+49 52 03	12.0	15.2	AM
EF Eri		03 14 13.1	-22 35 42	13.7	16.5	AM dips
V442 Oph 	17 32 15.2 	-16 15 23	12.6	15.5	VY
TT Ari		02 06 53.0	+15 17 42	 9.5	15.5	VY
V751 Cyg      	20 52 12.6	+44 19 26 	13.2	16.	VY

Secondary (fainter) targets:

V794 Aql      	20 17 34.2  	-03 39 50 	13.7	20.2	VY
HU Aqr        	21 07 58.2  	-05 17 39	15.3	20.  	AM ecl
V425 Cas      	23 03 46.5  	+53 17 15	14.5	18	VY
VY Scl        	23 29 00.5  	-29 46 47 	12.9	18.5	VY

Tertiary targets (not observed by VSnet):

V2301 Oph     	18 00 35.6  	+08 10 12 	16.1	21.	AM ecl
VZ Scl        	23 50 09.2  	-26 22 53      	15.6   >18. 	VY ecl

Thank you,

======================================================================
Fred Ringwald                   ... to further the progress of science,
Department of Physics               to guide to an understanding
California State University, Fresno      of the majesty of the heavens,
2345 E. San Ramon Ave., M/S MH37    to emphasize that
Fresno, CA 93740-8031              under the great celestial firmament,
 Phone: 559-278-8426        there is order, interdependence, and unity.
   Fax: 559-278-7741                     -- Adler Planetarium, Chicago
E-mail: fringwal@csufresno.edu   http://zimmer.csufresno.edu/~fringwal/

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