(cba:news) (cba:chat) Keeping watch on the DQ Hers

Joe Patterson jop at astro.columbia.edu
Tue Mar 26 13:18:58 EDT 2013

Hi Bill et al.,

Here's the bible on intermediate polars (DQ Her stars):


A great listing, also with some critical discussion of scientific 
issues, and discussions of *candidate* members.  This particular link 
has down-time episodes, so keep trying it if it fails (it's usually up).

In the sky now, the ones I recommend are EI UMa, EX Hya, and HZ Pup (I 
wish!).  And, for a few more weeks, V418 Gem = RX0704+26.

And I attach a plain-text commentary on other more-or-less-current targets.


On 3/26/2013 11:44 AM, Bill Goff wrote:
> Hi Joe or Enrique,
> I seem to remember Joe put out a table of these objects sometime ago and I can't seem to find a copy.  Is that information still around and could I get a copy?
> Bill Goff
> On Mar 7, 2013, at 3:03 PM, Joe Patterson <jop at astro.columbia.edu> wrote:
>> Hi CBAers,
>> I just wanted to echo Enrique's comments, and to expand on them.
>> Back in the 1960s, when some people thought that love steered the stars,
>> other people thought that accretion torques did.
>> In particular, there were some papers on DQ Herculis - with its 71 s
>> spin period - that proposed to measure accretion rates by measuring its
>> rate of spinup.  An awfully cute idea, if it works... and it arguably
>> does work for DQ Her.  As other stars joined the DQ Her club (fast
>> period attributable to rotation of the accreting white dwarf), some of
>> them seemed to follow suit, and others emphatically not (some actually
>> spinning *down*).  The theory also got more complicated.
>> We have by far the world's best data on this subject (really the ONLY
>> supply), since we've been tracking the stars for many years.  It takes a
>> lot of attention, partly because you need long baselines - at least a
>> couple months - to keep the cycle count from one year to the next.  Some
>> stars are well-behaved, and some are pretty naughty (showing much more
>> instability in phase than you'd expect from rigid-body rotation).  I
>> don't know if we'll be able to solve this problem - explain the complex
>> histories of spinup/spindown - but it's at least our job to document the
>> star's behavior.  As new stars join the DQ Her club, we take them on,
>> and we always need a flurry activity to nail down the periods to 7 or 8
>> significant figures.  After that, we can relax a little bit, but at the
>> very least need a few time series each observing season.
>> That's the raison d'etre of the DQ Her-star monitoring program.  There
>> are other specialized purposes it serves - investigating the details of
>> sidebands and harmonics of the main frequency, and tracking the stars
>> for their occasional high and low states (they don't do much of this,
>> but some - like the AM Hers for that matter).
>>   Any of you who might be interested in inheriting all the CBA data on
>> any one of these stars, for example to do an dP/dt study, just let me know!
>> joe
>> On 3/7/2013 3:08 PM, Enrique de Miguel wrote:
>>> Josch,
>>>   One of the main reasons of including DQ Her stars in our target list is to keep track of their rotational (spin) periods in order to test if and how
>>> they vary with time. Typical spin periods run from tens of secons to tens of minutes. Koji Mukai page on IPs (intermediate polars - another term
>>> to refer to these DQ stars) is an excellent page that gathers basic info.
>>>    In general, and with few exceptions, C filter is ok for this program. As usual, avoid using a too red comparison, because these targets typically
>>> have B-V ~ 0.
>>> Enrique
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Dear CBAers,

Here's some updates on campaigns present, future, and recent past.

T Pyx.  The post-eruption period is entirely stable. No chance of losing
cycle count this season. We have enough!

V382 Vel.  Much more uncooperative than six years ago.  Great coverage
from Bob Rea, many long runs on consecutive nights.  The orbital signal
is just barely detected, and no other signal is.  Insufficient return
on investment... so let's quit.

Nova Mon 2012.  Great target, great coverage from all over the map.
Big, beautiful orbital signal, and this will warrant close study as it
changes (which it will!) over the next few years.  But the sky position
is now unfavorable, and with such a long Porb, long time series are needed.
Which can't be gotten.  Sayonara Unicorn.

HT Cam, DW Cnc, V405 Aur, DQ Her, BY Cam.  Also time to quit.  We have
excellent ephemerides.

Paloma (RX0524+42).  A wondrous multi-periodic star, but too far off-season.
AM CVn.  Just getting started this season.  Good target for observation.

IM Nor.  Wow!  Coverage from Berto only, and the star is a tough target
at V = 18.  Nevertheless, a clear large-amplitude signal which is very
likely Porb, and one other signal (origin unknown).  Very high priority
target!  I realize that 18th mag may be intimidating - but Berto manages
with a 14-inch.

EX Hya.  It's time for a re-visit.  We have no coverage since 2010.  1-2
weeks of long runs should nail down the (67-minute) ephemeris.  Very
bright star, easy target to get high-quality data.

DW UMa. One long run this year, enough to establish that no large-amplitude
hump, as once appeared in this star, is present.  That's enough to
disqualify this star.

NR TrA.  A nova that went off in 2008, and now has faded down to ~16.
Precise position 16 18 48.21 -60 27 48.9.  It's more or less back in the
sky, and worth long time-series photometry.  Fred Walter is doing a
thorough study of it, and needs a sheaf of CBA-style photometry (long
time series on maximally consecutive nights) to nail down the intricate
period structure.  The main period seems to be ~5 hours.

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