(cba:news) POLARS... intermediate and full-fledged

Joe Patterson jop at astro.columbia.edu
Wed Aug 1 11:49:18 EDT 2018

Hi CBAers,

Something new!

We are preparing a proposal to observe a bunch of polars (AM Her stars) 
in hard X-rays (10-60 keV).  These energies are comparable to the 
free-fall energy onto a white dwarf.  And since the conventional model 
for polars invokes accreting gas falling directly to the surface, this 
observation can reveal the white-dwarf masses (more massive WDs are much 
smaller, and thus should produce much higher infall energies).

This experiment has been done successfully for a few of the celebrity 
polars.  We'd like to try it for some of the rank and file.  Here are 
the stars: VV Pup, UZ For, EP Dra, V834 Cen, V2301 Oph, HU Aqr, ST LMi. 
All these stars are known or at least likely to have high and low 
states, and it's important to know how bright they are now.  Probably 
the X-ray observation will only succeed if the star is in a high state. 
So at a minimum, is the star *currently* in a high state?

1. This will probably require a 2-hour observation, since the stars vary 
strongly over an orbital cycle (generally 1.5-2.2 hours).

2. Someone will need to estimate how long the star is likely to stay 
bright.  JUst a guess, of course... and I suppose that's my job (by 
consulting literature), but if anyone feels like doing that search of 
previous papers, I'd be grateful.

3. Most of these stars are around 16-17 mag, and for that we always 
recommend unfiltered light.  But consider also a V filter.  Time 
resolution is of no great importance here, and unfiltered brings some 
problem, since these stars typically have very crazy colors (because of 
cyclotron radiation.  This is mitigated by V, which has a much narrower 
poassband and is the reference standard of most previously published 

Try to get as many as you can.  Not much need to do a *second* 2-hour 
light curve of a particular star.

Being faint and rapid large-amplitude flickerers, these stars tend to 
persuade the rookie observer that the data are no good.  But on a good 
night, it's likely the data are quite good.

We hope to submit this proposal, or part of it, soon... so see what you 
can do with this!

Re the intermediate polars, and the Star of the Year ASASSN-18ey, I'll 
write tomorrow.

joe p

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