|Frequently Asked Questions|
All questions about the system and our campaign will be answered here.
The more questions you ask the longer will become the list.
We strongly recommend to read the publications under "Literature".
When should I observe WR 140?
As often as possible. It is always a good idea to start a "training" far in advance. First during "easy" periods when the system is high in the sky, then during the January period 2008. Remember that it is a morning and evenning object around periastron passage in January 12, 2009! And finaly, we should know what we can expect in S/N for which exposure time. Last but not least we are interested in residuals during the passage.
What are residuals?
Global residuals: If we observe the system in a quiet period we find relatively stable lines. This is due to the large seperation of the components. To find shock cone effects during periastron passage we have to seperate those effects from the stable lines. This can be done by computing an average spectrum over the whole observation period and then subtracting each individual one from the mean. It is also possible to obtain a mean or minimum spectrum in advance and subtracting individual spectra from this minimum or mean. As a result we get the line features which are only present during periastron passage and which represent two crashing shock cones.
Nightly residuals: The same technique can be applied for short term events in the lines , like clumbs (turbulences) in the wind. Then we should obtain a minimum or a nightly mean and subtracting individual night spectra. This is a difficult taks for small telescopes due to low S/N from short exposures.
The spectrum should be centered in what wavelenght? What bandwidth is adviced?
Due to its nature as a WR+O binary we majorly see emission lines. They are all of great interest and deliver worthy insights in the physics of the system. So a clear continuum is not easy to define. It is more important to choose a sufficient wavelength interval instead of defining a central interval to define a maximum number of (pseudo) continuum wavelength as it is done e.g. in the paper of Marchenko et al. Before deciding in more detail it is strongly recommended to read available literature. A number of papers can be found in this campaign web page.
What calibration lamp must be used?
Each lamp with sufficient emission lines for calibration plus catalogue in the respectively observed wavelength reagion is fine.
No real continuum? How can I estimate the Signl-to-Noise-Ratio then?
By using two spectra one can estimate S/N by deviding one spectrum by the other. The lines will then be eliminated. If the two spectra have the same exposure time the S/N of the quotient is sqrt(2) of that of the single spectrum. The S/N of the sum spectrum is then better by a factor of two than the quotient.
What S/N is sufficient?
The more the better. But S/N should be 100 at least.
I do not reach S/N > 100. What should I do?
Just increase your exposure time. Nightly means are sufficient for the periastron event over some weeks.
How long should I observe the star during periastron passage?
Three months are ok. Before and after no line events are observed by earlier campaigns. So, start around beginning of December and end around end of February.
Why can I see a profil in the interstellar Na lines if I apply very high resulution?
The interstellar material along the line-of-sight has different velocities with respect to the observer and, hence, broaden also the interstellar absorption lines.