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Subject: Euclid slitless calibration
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From: Will Percival
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Cc: hkuntsch@eso.org, Adam Amara ,
Luigi Guzzo
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Thanks for your comments on the slitless calibration summary. I've tried =
to include all suggestions in this draft. Please let me have any further =
comments.

Cheers, Will.

Calibrating the slitless spectroscopy

=20

A preliminary analysis of the calibration requirements for the Euclid =
slitless spectroscopy is provided in the accompanying document =
(ENIS-CALIB, Walsh, Kuntschner & K=FCmmel). There are three key =
instrument responses that require calibration:

1. wavelength zero-point and dispersion

2. flat fielding

3. flux calibration

Of these, the flat fielding, (2) should be performed by on-ground =
calibration preferably with a monochromator illuminating the instrument =
so that the detailed behaviour of the flat field with wavelength can be =
modeled, coupled with an on-orbit flat field, such as established by =
rastering a stellar field across the detector in direct imaging with a =
filter within the passband of the grism taken during the commissioning =
period prior to survey science operation. However, further simulations =
are required before the requirement for a flat field calibration lamp =
can be definitively ruled out. If NISP imaging requires on-board =
flatfielding, then we can also use the same calibration unit for =
spectroscopic flat-fielding. The primary science requirement on (3) is =
weak and can probably be met by rudimentary photometric calibration on =
the ground and use of spectrophotometric standards for in-orbit =
calibration. (1) presents the primary challenge for slitless =
spectroscopy in order to guarantee the reliability and accuracy of the =
spectroscopic redshifts to sz/(1+z)<0.001. The wavelength calibration =
requires two main aspects: the estimate of the dispersion solution (i.e. =
the conversion from pixels to wavelength across the detectors) and of =
the zero-point. The zero-point will need to be determined for every =
slitless image and stars within the science fields present the most =
obvious targets from which to do this. In order to estimate the =
dispersion solution, an on-board calibration lamp would be the safest =
solution. However, an alternative approach would be to use "astronomical =
calibrators" such as compact Planetary Nebulae for the dispersion =
solution and strong absorption features in K and M stars. Compact PNe =
are rare at high galactic latitudes and would require dedicated =
observations, whereas K and M stars would be frequently present in most =
fields observed with NISP. More details can be found in the attached =
document, ENIS-CALIB by Walsh et al. Also the repeat observations of the =
Deep Field would be useful to look for drifts by averaging over many =
galaxies and stars, and if found, repeat visits to star clusters and =
planetary nebulae or compact HII regions in a nearby galaxy in order to =
precisely build a dispersion solution. However, the viability of a =
calibration plan based on astronomical sources depends primarily on the =
degree of stability and modelability of Euclid instruments and on the =
impact on the global survey strategy. As currently this information is =
not available, the conclusion is that further studies are required in =
order to completely rule out the requirement for a wavelength =
calibration lamp on the spacecraft.

=20

=20

=20

=20=

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charset=iso-8859-1

-webkit-nbsp-mode: space; -webkit-line-break: after-white-space; =
">Thanks for your comments on the slitless calibration summary. I've =
tried to include all suggestions in this draft. Please let me have any =
further comments.

Cheers, =
Will.



Calibrating the slitless =
spectroscopy

style=3D"text-align:justify"> style=3D"font-size:11.0pt;mso-bidi-font-size:12.0pt;font-family:"Aria=
l Narrow""> yes"> 

style=3D"text-align:justify"> style=3D"font-size:11.0pt;mso-bidi-font-size:12.0pt;font-family:"Aria=
l Narrow"">A
preliminary analysis of the calibration requirements for the Euclid =
slitless
spectroscopy is provided in the accompanying document (ENIS-CALIB, =
Walsh,
Kuntschner & K=FCmmel). There are three key instrument responses =
that require
calibration:

style=3D"margin-left:147.3pt;text-align:justify;text-indent:
-18.0pt;mso-list:l0 level7 lfo1"> style=3D"font-size:11.0pt;mso-bidi-font-size:12.0pt;font-family:"Aria=
l Narrow";
mso-fareast-font-family:"Arial =
Narrow";mso-bidi-font-family:"Arial Narrow""> style=3D"mso-list:Ignore">1. Roman"">    
mso-bidi-font-size:12.0pt;font-family:"Arial =
Narrow"">wavelength zero-point and
dispersion

style=3D"margin-left:147.3pt;text-align:justify;text-indent:
-18.0pt;mso-list:l0 level7 lfo1"> style=3D"font-size:11.0pt;mso-bidi-font-size:12.0pt;font-family:"Aria=
l Narrow";
mso-fareast-font-family:"Arial =
Narrow";mso-bidi-font-family:"Arial Narrow""> style=3D"mso-list:Ignore">2. Roman"">    
mso-bidi-font-size:12.0pt;font-family:"Arial Narrow"">flat =
fielding

style=3D"margin-left:147.3pt;text-align:justify;text-indent:
-18.0pt;mso-list:l0 level7 lfo1"> style=3D"font-size:11.0pt;mso-bidi-font-size:12.0pt;font-family:"Aria=
l Narrow";
mso-fareast-font-family:"Arial =
Narrow";mso-bidi-font-family:"Arial Narrow""> style=3D"mso-list:Ignore">3. Roman"">    
mso-bidi-font-size:12.0pt;font-family:"Arial Narrow"">flux =
calibration

style=3D"text-align:justify"> style=3D"font-size:11.0pt;mso-bidi-font-size:12.0pt;font-family:"Aria=
l Narrow"">Of
these, the flat fielding, (2) should be performed by on-ground =
calibration
preferably with a monochromator illuminating the instrument so that the
detailed behaviour of the flat field with wavelength can be modeled, =
coupled
with an on-orbit flat field, such as established by rastering a stellar =
field
across the detector in direct imaging with a filter within the passband =
of the
grism taken during the commissioning period prior to survey science =
operation.
However, further simulations are required before the requirement for a =
flat
field calibration lamp can be definitively ruled out. If NISP imaging =
requires
on-board flatfielding, then we can also use the same calibration unit =
for
spectroscopic flat-fielding. The primary science requirement on (3) is =
weak and
can probably be met by rudimentary photometric calibration on the ground =
and
use of spectrophotometric standards for in-orbit calibration. (1) =
presents the
primary challenge for slitless spectroscopy in order to guarantee the
reliability and accuracy of the spectroscopic redshifts to lang=3D"EN-US" =
style=3D"font-size:11.0pt;mso-bidi-font-size:12.0pt;font-family:Symbol;
mso-ascii-font-family:"Arial =
Narrow";mso-hansi-font-family:"Arial Narrow";
mso-char-type:symbol;mso-symbol-font-family:Symbol"> style=3D"mso-char-type:
symbol;mso-symbol-font-family:Symbol">s style=3D"mso-bidi-font-weight:
normal"> style=3D"font-size:11.0pt;mso-bidi-font-size:12.0pt;
font-family:"Arial Narrow"">z lang=3D"EN-US" =
style=3D"font-size:11.0pt;mso-bidi-font-size:12.0pt;font-family:"Aria=
l Narrow"">/(1+z)<0.001.
The wavelength calibration requires two main aspects: the estimate of =
the
dispersion solution (i.e. the conversion from pixels to wavelength =
across the
detectors) and of the zero-point. The zero-point will need to be =
determined for
every slitless image and stars within the science fields present the =
most
obvious targets from which to do this. In order to estimate the =
dispersion
solution, an on-board calibration lamp would be the safest solution. =
However,
an alternative approach would be to use "astronomical calibrators"
such as compact Planetary Nebulae for the dispersion solution and strong
absorption features in K and M stars. Compact PNe are rare at high =
galactic latitudes
and would require dedicated observations, whereas K and M stars would be
frequently present in most fields observed with NISP. More details can =
be found
in the attached document, ENIS-CALIB by Walsh et al. Also the repeat
observations of the Deep Field would be useful to look for drifts by =
averaging
over many galaxies and stars, and if found, repeat visits to star =
clusters and
planetary nebulae or compact HII regions in a nearby galaxy in order to
precisely build a dispersion solution. However, the viability of a =
calibration
plan based on astronomical sources depends primarily on the degree of =
stability
and modelability of Euclid instruments and on the impact on the global =
survey
strategy. As currently this information is not available, the conclusion =
is that
further studies are required in order to completely rule out the =
requirement
for a wavelength calibration lamp on the spacecraft. =

style=3D"text-align:justify"> style=3D"font-size:11.0pt;mso-bidi-font-size:12.0pt;font-family:"Aria=
l Narrow""> 

style=3D"text-align:justify"> style=3D"font-size:11.0pt;mso-bidi-font-size:12.0pt;font-family:"Aria=
l Narrow""> 

style=3D"text-align:justify"> style=3D"font-size:11.0pt;mso-bidi-font-size:12.0pt;font-family:"Aria=
l Narrow""> 

style=3D"text-align:justify"> style=3D"font-size:11.0pt;mso-bidi-font-size:12.0pt;font-family:"Aria=
l Narrow""> 






=

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