Guiding a star on spectroscope slit

[Forum_2014]

Hello Steve, I apologize for delay...

Yes, your procedure seems to me correct. Just some advice... The best way to illuminate slit is a flatbox in front of telescope (or twilight). On my Lhires III I have to be very careful with internal neon lamp because must be properly oriented otherwise the slit does not look good or appear slightly shifted (!). You should avoid a single concentrated light source (a lamp) in front of telescope aperture.

In addition to check a `figure of eight` star image (better visibile if you have proper star/slit size ratio) or the maximum brightness attenuation (because the star is into the slit), you can verify the maximum light throughput into spectroscope: using a bright star near target you may take some spectra at various Y guide sensor positions (if you have slit axis horizontally) with 1 pixel step, taking note and using the coordinates corresponding to the best spectrum SNR.

What spectrograph are you using?

Clear skies!
Paolo

[Forum_2014]

Hi Paolo
Sorry for delay replying!. I have an Alpy 600 with guide module (23micron slit) . This is a typical shot through my Lodestar guide ccd of the SN in m82,you can just make out the horizontal slit with the SN placed on it, shot with my ccd software & PHD.
Regards
Steve

[Forum_2014]

Congratulation Steve, Alpy 600 is a great spectrograph! Of course its guide module is essential. I too have always used PHD Guiding but until AA "slit mode" was released! Probably in the next release of CCD control, spectrograph mode will be activated by an option.

Have a nice observations!
Paolo

[Forum_2014]

Finally had success with the AA5 Slit guiding!
My problems were due to incorrect settings within EQMod that I use to control my NEQ6pro.
I'd like to thank Fabio (and Paolo) for the support and assistance in resolving my issues.

[Forum_2014]

Very good Ken! I also use it in any observation now. Concerning this, I would like to share a result only possible thanks to the new CCD control feature. Target is about mag V 14.7, a quasar-like object in Lynx. In spectroscopy, problems related to object low brightness concern the poor SNR of spectrum (which forces to use very long integration time) but also the difficulty of placing and maintaining the target on slit during exposures. The "guide on slit" feature helps a lot for the latter case.

I used 23 cm aperture SC telescope and Lodestar guide camera linked to the Lhires III spectrograph. Main CCD camera for spectra acquisition is a SXVR-H694.

Spectrograph slit view, seen by Lodestar. Target is named B3 0754+394, an active nucleus of Seyfert galaxy.

For centering phase I set the minimum exposure time that allows to see the target (5s). As the selected guide star is much more bright than it, I switched to manual setting of view thresholds (otherwise target would not visible due to automatic levels stretching). Precise target aligning on the slit is obtained by shifting the guide star so that the target halo appears symmetrical in respect to the slit.

Then I reduced exposure time to 0.5s so that guiding works with a better reaction time. Target and slit are no longer visible but we are sure everything is fine.

[Forum_2014]

... the resulting spectral profile, on the top the 2d spectrum with synthetic colour elaborated by ISIS (spectra reducing tool):

The AGN has an evident recessional velocity with emission line (and entire spectrum) strongly shifted toward red (Doppler-Fizeau effect). I put a reference line where emissions should be at rest wavelength. H-alpha is beyond 7000A and H-beta, at about 5300A, appears completely green instead of blue-cyan colour.

We can calculate the redshift (z value) and radial velocity. Considering the [O III] 5007 line observed at 5486A, z = (5486-5007)/5007 = 0.0957.

Radial velocity calculated with the relativistic formula:

give v = 27300 Km/s

This is the velocity value at which the galaxy is moving away from us.

Paolo