[vsnet-chat 2060] Plotting light curves

[Gianluca Masi <gianmasi@fr.flashnet.it>]

Dear Colleagues,
I have a question about data visualization, more precisely about
plotting a light curve when many points are available. I start with an
example.

An observer takes 1,000 images of the field around its target,
obtaining, at the end of their reduction, the exact JD, the V-C1 and
C1-C2 differential magnitudes for every frame. Now she/he decided to
plot them. The most natural choice is to plot all the available data,
that is

	(JD)i, (V-C1)i, (C1-C2)i

where "i" goes from 0 to 1,000.

But she/he can also displays the mean every two or more values in
her/his data. This is also a natural choice and it reduces the noise in
the curve. Of course, this technique reduces also the number of points
available (as you are condensing them).

Another way is to "smooth" the curve, considering, for every point, at
least the two adiacent ones. This technique in widely used to smooth
common CCD images. This operation leaves the total number of points
unchanged. In this case every new point is not indipendent from the
other ones, as any original point is used at least three times. 


I present two plots:


1)  http://vsnet.eurolink.it/comets/c1c2.gif

is relative to two comparison stars in the field of V603 Aql and shows
the data in the following order:

- as they are;
- a simple mean every two values has been done;
- a smooth has been done, considering the two adiacent points nearest to
the one under    evaluation.


2)  http://vsnet.eurolink.it/comets/vc1.gif

is relative to a recent unfiltered CCD run on V603 Aql and shows the
data in the following order:

- as they are;
- a simple mean every two values has been done;
- a smooth has been done, considering the two adiacent points nearest to
the one under    evaluation.


I would like to hear your comment and on your experience with these
procedures. Do you use more complex techniques? Is any of them useful in
some cases and not in others?

Clear skies,
Gianluca


-- 
***********************************************************************
* Gianluca Masi                           "Two things fill the soul   *
* Via Madonna de Loco, 47               with awe and reverence [...]: *
* 03023 Ceccano (FR)                     the starry sky above me and  *
* ITALY                                    the moral law within me"   * 
* email: gianmasi@fr.flashnet.it                                      *
* http://vsnet.eurolink.it/comets/                        I. Kant       *
***********************************************************************

VSNET Home Page

Return to Daisaku Nogami

---

vsnet-adm@kusastro.kyoto-u.ac.jp