Re: Asteroids in November's data set

[Raoul Behrend <Raoul.Behrend@obs.unige.ch>]

Hello,

It's my first post to tass@. Before commenting the asteroid data from Tom
Droege and Patrick Wils, a few words about me are probably welcomed. Well, one
one my hobbies is the lightcurve analysis of asteroids and variable stars. When
I have the chance to have some time to have fun with telescope and CCD, I
usually do some astrometry for the calculation of stellar occultations by
asteroids. The LC data are mainly collected from/by AUDE members (association
des utilisateurs de détecteurs électronique, http://astrosurf.com/aude/ - a
(french speaking) society about the use of ccd in astronomy).

From Patrick's message, I selected the 3 most observed asteroids ((119)
Althaea, (352) Gisela and (444) Gyptis), and I searched for the period in the
lightcurve with a sinusoïdal model with 2 peaks per rotation (a more complete
truncated Fourier serie is not well enough constrained with the data
available). I used both V and I measurements (red and green dots in the graphs,
respectively) with I-V kept free in the reduction. Of course, phase and
distances effects were subtracted to each observations, individually, before
the analysis.

There exist solutions near to the nominal period taken from the Alan Harris'
compilation. I put the resulting lightcurves with optimized period, phase,
amplitude and color term, on one of my web pages (I'll remove from there if Tom
is not OK with this).
   http://obswww.unige.ch/~behrend/page1cou.html#000119
   http://obswww.unige.ch/~behrend/page1cou.html#000352
   http://obswww.unige.ch/~behrend/page1cou.html#000444

Now some comments: The amplitudes of variation are what is ususal for such
objects - even if detailed lightcurves are to be done to check these values.
The periods found using the nominal values as a first guess, seem to be
correct. For period shorter than 0.5 days, I can't find the correct solution
without the knowledge of the nominal value: too many aliases. In the graphs,
the c1 value is the error between the V observations and the ephemeris;
abs(c1)<0.1 shows a good agreement between observations and ephemeris - what is
"normal" for low numbered objects. The c2=I-V (observed V, not ephemeris V)
values found for the 3 objects seem to be correct; c2 is important for the
mineralogic classification of the asteroids. From night to night, red dots are
higher in the LC-graphs, than green dots and vice versa; the relative
photometry between V and I seems then to be of the order of about 0.1mag - a
little too low to produce good lightcurves from multi-night photometry with low
number of observations. But your work can be sucessfully used to find objects
with gross errors in the photometric ephemeris and/or high variability: please
continue to do photometric measurements of all asteroids found in your data
set.

Some of the comments herebefore can probably be transposed to some variable
stars just commented by, also, Patrick Wils.

Have a pleasant week-end.

Kindest regards, Raoul



Patrick Wils (patrickwils@yahoo.com) wrote:
> I found observations for 6 asteroids in November's data set.  Not much
> variation is seen in the data, apart from opposition effects.
> 
> The lines contain the object number in the data set, JD, V, Ic, mag
> predicted by the MPC, distance in arc seconds to the predicted
> position, and asteroid number and name.
> 
> Positions agree to within the accuracy of the TASS astrometry.
> Asteroid (428) Monachia seems to be a little bit fainter than
> predicted.
> 
> Patrick
>
> [...]

-----

Dr Raoul Behrend
Observatoire de Genève
CH-1290 Sauverny / Suisse

Raoul.Behrend@Obs.UniGe.CH
http://obswww.unige.ch/~behrend

"Herbe à Nicot? Herbe à nigaud!"