SLANT ANGLE INVERSION
WITH LHIRES3 and ST8


Abstract :

This page describes observed difference slant angle between neon lines et stellar lines in spectra made with LHIRES3 2400 gr/mm spectrograph from Sheyliak and ST8 ccd camera.

Therefor, resolution is barely affected and snr goes down.


Old spectra done with KAF1602 Audine and Lhires3:

Neon lines' slant and stellar lines's slant angle are very closed:

1 2 3
Audine 1602E and Lhires 151
bet Gem 2008-02-09		 ST8 and Lhires 073
Castor 2008-02-09		 Audine 402E + Lhires 151
del Sco 2009-07-16
4 5 6
Audine 1602E+Lhires 151
del Sco 2009-02-23		 Audine 1602E+Lhires 151
Regulus 2009-02-23 		Audine 1602E+Lhires 151
Regulus 2009-04-14
7
Audine 1602E+Lhires 151
zet Tau 2008-11-22


Spectra done with ST8 camera and Lhires3:

Neon lines' slant and stellar lines's slant angle are opposit !

1 2
Aldebaran 2010-02-20 Aldebaran
3 4
Moon spectrum with Neon spectrum over. P. Lailly's ST8 Cappela

Here is a graphical summary:

summary


Spectra done with Atik 16 camera and Lhires3:

No anomaly found by P. Lailly with Atik16 camera and Lhires3:

1


Spectra done with Atik2 and Lhires3:

No anomaly found by T. Garrel with Atik? camera and Lhires3:

1 2 3
120 Tau 2010-01-15 Altair 2010-08-08 bet CMi 2010-01-15
4 5
del Sco 2010-08-08 eps Aur 2010-01-15

Changing of focus and star position on slit:

Trying to minimize slant difference by changing Lhires3 focus of lens and star position on slit. Idea suggested by C. Buil at OHP 2010:

1 2
Modification of star's position on slit. Lhires lense focus impact (180 °)
on slant angle with star put on top
of the slit.
3 4
Two different lens focus with star
on the slit bottom.		 Extreme lens defocus with star
on slit bottom.

arcturus_3_et_neon.jpg : le 20100810, test de l'effet du choix de la position sur la fente.

arturus_3focs_ne.jpg : le 20100811, test de l'effet de la rotation du doublet (1/2 tour au total environ) sur spectre stellaire positionnee sur la partie supérieure de la fente (postion defavorable).

arturus_sud_foc2_2foto_ne.jpg : le 20100811, test de 2 positions du doublet pour l'etoile en bas de la fente.

arturus_sud_foc3_ne_f3.jpg : le 20100811, test de la derniere position du doublet (pas mal defocalisant sur l'etoile) pour l'etoile en bas de la fente.



Conclusion:

Actually there are no solution and we would appreciate if Sheyliak could help us.

But it seems that boublet lens in Lhires suffers of astigmatism. Anyway, spectra done with Audine 1600 should have same problem but it's not the case.

Les atik et audine sont des cameras legeres et a

symetrie de revolution, l'axe passant par le centre du capteur. C'est

tout le contraire pour la ST8. Peut etre le pb est d'avoir une

fixation suffisamment rigide de la camera.