[vsnet-alert 15806] OR And entering a low state - a possible HST target

Boris Gaensicke Boris.Gaensicke at warwick.ac.uk
Thu Jun 6 10:44:51 JST 2013


Dear All,

as part of our HST program we plan to observe two VY Scl
stars during a low state - in this class of CVs, the white dwarf
can only be detected once accretion switches off. We did
BB Dor in February with mixed success: the star crept out
if the low state just when HST observed it.

It looks like we may get another opportunity: OR And has
entered a low state, fading from V~15 to V~18.5. The historic
light curve (1990IBVS.3432....1W<http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990IBVS.3432....1W&db_key=AST&link_type=ABSTRACT&high=510ed9928c14824>)
did reveal several low states,
but failed to detect the star in its faint state.

We will obtain within the next ~week a short observation with
the Swift satellite to  determine the brightness of OR And in
the ultraviolet, and then proceed with planning the HST
observations.

As usual, we will need your help to make this work. Please
monitor OR And over the next few weeks. One measurement
per night will be sufficient. Given how faint OR And is now,
it will probably need stacking of several images,  and possibly
going for unfiltered photometry rather than V-band.

A chart for OR And is available from the AAVSO's VSP<http://www.aavso.org/vsp>.


Best wishes,

Boris

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For more information on this HST program, see

http://deneb.astro.warwick.ac.uk/phsdaj/public_html/12870/
http://deneb.astro.warwick.ac.uk/phsdaj/public_html/12870/Targets.html


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