A remarkable large, fast transient in the spectrum of DN Tau

[Robin Leadbeater]

On 2012-12-09 I detected a remarkable transient in the spectrum of DNTau using the Star Analyser.

88 x 20 sec spectra show a rise in total flux (4000-7500A) of ~130% in just 6 minutes, followed by a rapid drop over the following 6 minutes and a continuing slow fall over the next 40 minutes to ~20% of the initial level. The flux increase was greatest at the blue end (a 300% increase at 4500A)

More details here
http://www.threehillsobservatory.co.uk/ ... ra_42a.htm
and a description of the technique here
http://www.threehillsobservatory.co.uk/ ... tra_42.htm

Cheers
Robin

[Christian Buil]

It is an amazing observations. One of the fisrt time of an amateur take a so fast time resolution spectrometry + photometry result. An historitical and promizing observation!

Christian

[Andrew Smith]

As I mention on another site, well done Robin. I was interested in your setup. I looked at the link on your site but coud not see what spacing you were using to get the 17A/pix also if you used a correcting prism or just the SA100 and or any IR/UV cut filters?

Thanks Andrew

[Robin Leadbeater]

Hi Andrew,

Just the Star Analyser in the filter wheel, no wedge prism and no filter.
I am not sure of the exact spacing. I just used what was to hand in the Junk box. Looking at Tom Field's calculator
http://www.rspec-astro.com/calculator the CCD /grating spacing must be about 48mm. It is not too critical. I was actually aiming for ~15A/pixel as a reasonable compromise between resolution and faint object performance. (R is ~80) Lower dispersion also helps with getting the target and a comp star spectrum in the same field which can be tough with this small size CDD. I could have used my ATK 314 instead of the old 16IC-S but the 314 is dedicated to the LHIRES and I wanted an independent system so I could easily swap between the two with minimal disturbance.

Cheers
Robin

[Francois Teyssier]

Very nice Robin. Great job.

Such behaviour looks common for this star.

Here's the AAVSO light curve in V Band

DNTau.PNG (15.13 KiB) Viewed 18202 times

Varitations at hour time scale are frequent
Time serie at higher resolution with LISA or LHIRES 150 l/mm should be interesting

François

[Robin Leadbeater]

Hello François,

Yes such variations should be easy to see in the photmetry. (or even visually - there are anecdotal reports of flickering seen in this star apparently) The V mag perhaps increased by ~ 1 magnitude during this event and the B mag by even more! I have posted on the AAVSO campaigns forum encouraging photometrists to measure their individual exposures for this project and not to average them as is often done.

The other 3 runs I have done do not show any obvious variability but I will analyse them fully and attempt to correct them all to the same reference to compare them

Cheers
Robin