Anyone think they know what the tilt of the EIS slit is?

Ken Dere

--129.174.112.201, 25-Apr-2007

And how linear is it (and where, if at all)?

--David R Williams, 03-May-2007

The slit tilt is not fully understood and some further calibration studies need to be run. Preliminary work has been done, so for example Peter Young has produced a short document on this. TiltFiles(info)

--Louise Harra, 14-May-2007

I find the tilt of the SW slit to be 1.6 x 10^-6 Angstroms / pixel

Peters number correspond to a value of 1.2 x 10^-6 Angstroms / pixel

--Ken Dere, 15-May-2007

I've made another attempt at measuring the slit tilt. For the SW band I get a number close to Peter's value. I've written a routine called eis_slit_tilt that calculates the offset as a function of position along the slit. I'm sending the routine to be included in SSW. Some details on my calculations are given in the attached pdf. There is still a lot of scatter in the data and more analysis is needed. TiltFiles(info)

--Harry Warren, 06-JUL-2007

The slit tilt is different for the 2" slit. Maria Madjarska has measured a tilt of 1.14 x 10^-4 Angstroms/pixel for the SW band. Further work should be performed to check this value.

--Peter Young, 10-AUG-2007

Harry also has a routine which is preliminary called eis_wave_corr - this corrects for the tilt for the 1" slit and the orbital variation.

I've measured the tilt for the 2 arcsec slit for the SW band. I used a quiet Sun raster made on 20th April 2007. This raster uses the full 512 arcsec slit height and is 120 arcseconds in the x-direction. I measure a tilt of 1.12 x 10^-4 Angstroms/pixel. This seems to be in reasonably good agreement with the value determined by Maria Madjarska of 1.14 x10^-4 Angstroms/pixel, although I do not know which raster(s) Maria used.

--Gemma Attrill, 05-Oct-2007

I made statistics of slit tilt from all the EIS data. Average slit tilt determined from Fe XII 195 are:
1" slit tilt: 1.18E-05 (angstroms/pixel), standard deviation 1.43E-05
2" slit tilt: 1.09E-04 (angstroms/pixel), standard deviation 1.03E-05
TiltOfEISslit/eis_slit_tilt_195.png (info)

--SKamio, 23-Nov-2007

I don't understand what the negative values means in the statistics plot about the values of the tilt done by SKamio. Does it mean that the 1" slit tilt sometimes is to left (negatives values)? Thanks.

--David Pérez-Suárez, 23-Nov-2007

The slit tilt calculations are based on the assumption that the Doppler shifts at a given slit position should average to 0 with a large enough sample size. There is considerable noise in the measurements so a lot of averaging needs to be done. It is the mean values that are important.

Kamio's results are consistent with what I've calculated with smaller samples. I need to put them on the Wiki. They are also consistent with the number for the 2" slit posted by Gemma Attrill. At the recent EIS meeting Peter Young also noted some odd behavior near the "bottom" of the slit. This need to be investigated more.

--Harry Warren, 26-NOV-2007

Is the tilt well corrected by eis_tilt_correction routine ?

--Celine Boutry, 23-Sep-2008

The routine eis_tilt_correction is for performing the tilt correction after the data have been fit with eis_auto_fit, and it uses tilt values of 1.22e-5 and 1.14e-4 for the 1" and 2" slits, respectively. The former is from Harry's document, while the latter is that measured by Maria Madjarska - see the various comments above. I've found eis_tilt_correction does a reasonable job of correcting the slit tilt, but if you find any problems please post them to this wiki or send me an e-mail.

-- Peter Young, 23-Sep-2008

This particular version was published on 23-Sep-2008 14:10 by PeterYoung.Top