T Tauri star campaign  2012-2013 



Postgraduate Darryl Sergison and his supervisor Prof Tim Naylor of Exeter University, UK have called for amateur observations in support  of their observations on T Tauri stars planned for 2013. See AAVSO special alert #473 . The targets are moderately faint for amateur spectroscopy (Vmag  ~ 10-13)  so present an interesting target for very low resolution slitless spectroscopy using the Star Analyser. This gives the possibility of doing "differential spectroscopy" using a comparison star in the same field, as is done for differential photometry. The advantage is that precise compensation can be made for short term variations in atmospheric extinction, allowing variations in the spectrum total flux and continuum shape to be followed.



Celestron C11 (f10 280mm aperture)




Focal reducer giving f5.1


Spacer with angle scale allowing  repeatable orientation of the setup to avoid interfering background stars and spectra 


Filter wheel with Star Analyser  (and photometric filters)


Spacer to give ~17A/pixel dispersion


ATIK 16 IC-S camera


EQ6 Pro / EQMOD  mount unguided  (~80% of 20 sec  exposures with acceptably low trailing)


Data reduction

This setup produces around 100 x 20 sec exposures per hour. Typically a magnitude 12 star needs around 30 x 20 sec exposures to give an acceptable SNR ( > 100, reducing at the edges of the wavelength range where instrument sensitivity drops)

ISIS software is used for data reduction as it allows batch processing and a reasonable degree of automation, important when handling such large numbers of spectra. It also produces the combined and individual spectra as fits files with the correct header details and the flux either in raw counts or scaled relative to the level at a given wavelength.

The data reduction steps for the standard star (an A spectral type, used for wavelength calibration, instrument response and approximate atmospheric extinction correction), target and comparison stars (in the same field for precise extinction correction) are:-

           Darks, Flats

           Alignment of individual exposures using a zero order image in the field as a reference

           Tilt correction

           Background removal and binning (Careful selection of the background and binning zones, made independently for the target and comparison stars in the same field, is critical for good results on such faint targets. Click here for an example of selected binning and background zones using ISIS software)

           Wavelength calibration (linear using zero order and H beta as measured in the standard star)

            Instrument response and atmospheric extinction correction (measured at the start and end of the observing run using a nearby  agreed campaign standard reference star to allow comparison between observers and refined based on simultaneous measurements of the target and comparison stars in the same field

           Summing of individual spectra in groups to give adequate SNR.  



2012-12-09 Example of a remarkable large and fast transient in the spectrum of DN Tau


Links to spectra from other campaign contributors