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<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica;color:black">Hi Andreas and Arnold,</span><span style="font-size:9.0pt;font-family:Helvetica;color:black"><o:p></o:p></span></p>
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</span><span style="font-size:10.5pt;font-family:Helvetica;color:black">The little proposal I’m putting together wants to cover the cases covered by Greisen et al, in paper 3, 2006,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica;color:black">where they mention:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica;color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica;color:black">"[…] The apparent radial velocity then is a sum of</span><span style="font-size:9.0pt;font-family:Helvetica;color:black"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica;color:black">all spectroscopic effects presented as if they were solely a ra-<br>
dial velocity. While this may be sufficiently accurate for many<br>
uses, observers wishing to achieve very high accuracies should<br>
consult Lindegren & Dravins (2003), and references therein, closely."</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica;color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica;color:black">It seems to me, but please correct me if wrong, that the simple model I’m proposing covers the most common of the Greisen’s described cases, and not the more complex or less
frequent cases.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica;color:black">One consideration I have in mind is that ObsCore is used to search, and not to analyse the data, so I think it does not need to be that precise.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica;color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica;color:black">Could you please consider the above and tell me if there is anything that I have missed? It could be plenty of things that I have missed as I am certainly not an expert in
the field! Your help is much appreciated.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica;color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica;color:black">Many thanks,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.5pt;font-family:Helvetica;color:black">Alberto</span><o:p></o:p></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:12.0pt;color:black">From: </span></b><span style="font-size:12.0pt;color:black">Andreas Wicenec <andreas.wicenec@uwa.edu.au><br>
<b>Date: </b>Friday, 17 February 2023 at 03:01<br>
<b>To: </b>Arnold Rots <arots@cfa.harvard.edu><br>
<b>Cc: </b>"Dempsey, James (IM&T, Black Mountain)" <James.Dempsey@csiro.au>, Alberto Micol <amicol@eso.org>, "dal@ivoa.net" <dal@ivoa.net><br>
<b>Subject: </b>Re: ObsCore for velocity cubes<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Arial",sans-serif">This email was sent from outside of ESO from the address
<strong><span style="font-family:"Arial",sans-serif;color:black">[andreas.wicenec@uwa.edu.au]</span></strong><span style="color:black">. If it looks suspicious, please report it to phishing@eso.org.</span><o:p></o:p></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black">Yes!!<o:p></o:p></span></p>
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<p class="MsoNormal"><b><span style="color:black">From:</span></b><span style="color:black"> Arnold Rots <arots@cfa.harvard.edu><br>
<b>Sent:</b> Thursday, 16 February 2023 11:25 PM<br>
<b>To:</b> Andreas Wicenec <andreas.wicenec@uwa.edu.au><br>
<b>Cc:</b> Dempsey, James (IM&T, Black Mountain) <James.Dempsey@csiro.au>; Alberto Casa Micol <amicol@eso.org>; dal@ivoa.net <dal@ivoa.net><br>
<b>Subject:</b> Re: ObsCore for velocity cubes</span> <o:p></o:p></p>
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<p class="MsoNormal">FWIW, this all would have been simpler if the redshift and spectral coordinates has been retained in the coordinate system model.<o:p></o:p></p>
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<p class="MsoNormal">Just an observation...<o:p></o:p></p>
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<p><b><span style="font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222">Arnold H Rots</span></b><o:p></o:p></p>
<p><b><span style="font-size:9.5pt;font-family:"Arial",sans-serif;color:black">Research Associate</span></b><o:p></o:p></p>
<p>SAO/HEAD<o:p></o:p></p>
<p><b><span style="font-size:9.5pt;font-family:"Arial",sans-serif;color:black">Center for Astrophysics | Harvard & Smithsonian</span></b><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p><span style="font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222">Email:
<a href="mailto:arots@cfa.harvard.edu" target="_blank">arots@cfa.harvard.edu</a></span><o:p></o:p></p>
<p><span style="font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222">Office: +1 617 496 7701 | Cell: +1 617 721 6756</span><o:p></o:p></p>
<p><span style="font-size:9.5pt;font-family:"Arial",sans-serif;color:#222222">60 Garden Street | MS 69 | Cambridge, MA 02138 | USA</span><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Wed, Feb 15, 2023 at 9:10 PM Andreas Wicenec <<a href="mailto:andreas.wicenec@uwa.edu.au">andreas.wicenec@uwa.edu.au</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black">Hi James,<o:p></o:p></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black">that is a good suggestion. The usage of velocity vs. frequency is mostly use case/user driven. The original measurements are in frequency and in some cases the conversion
from one to the other is not straight forward, again mostly dependent on the use case, in which case we end up having 'pure' velocity cubes. Thus encoding both might work for some, but not for others. The other thing to consider is the rest-frame, since quite
often these velocity cubes are used for studies of local dynamic effects, like galaxy rotation curves, in which case the zero point is set to some estimate of the galaxies cosmological velocity (RESTFREQa). Now, obviously all of this is limited to just radial
velocities, while in fact we are dealing with velocity vectors. To cover that we are using proper motion and parallax to describe apparent and intrinsic velocity on the sphere and in addition line-of-sight velocity to capture the intrinsic and apparent radial
movement. Taken together, we end up in a set of vectors and probably frames. For a naive user the proposed description is probably sufficient, for actual scientific use of multiple of such cubes, quite a bit more information is required. Thus probably just
a good start....<o:p></o:p></span></p>
</div>
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<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black">Cheers,<o:p></o:p></span></p>
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<p class="MsoNormal" style="background:white"><span style="font-size:12.0pt;color:black">Andreas<o:p></o:p></span></p>
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<p class="MsoNormal"><b><span style="color:black">From:</span></b><span style="color:black"> dal <<a href="mailto:dal-bounces@ivoa.net" target="_blank">dal-bounces@ivoa.net</a>> on behalf of Dempsey, James (IM&T, Black Mountain) <<a href="mailto:James.Dempsey@csiro.au" target="_blank">James.Dempsey@csiro.au</a>><br>
<b>Sent:</b> Thursday, 16 February 2023 7:20 AM<br>
<b>To:</b> Alberto Casa Micol <<a href="mailto:amicol@eso.org" target="_blank">amicol@eso.org</a>>;
<a href="mailto:dal@ivoa.net" target="_blank">dal@ivoa.net</a> <<a href="mailto:dal@ivoa.net" target="_blank">dal@ivoa.net</a>><br>
<b>Subject:</b> Re: ObsCore for velocity cubes</span> <o:p></o:p></p>
<div>
<p class="MsoNormal"> <o:p></o:p></p>
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<p><span lang="EN-AU">Hi Alberto,<o:p></o:p></span></p>
<p><span lang="EN-AU"> <o:p></o:p></span></p>
<p><span lang="EN-AU">At CASDA we support cutouts of velocity spectral line cubes.<o:p></o:p></span></p>
<p><span lang="EN-AU"> <o:p></o:p></span></p>
<p><span lang="EN-AU">We currently require the user to provide a BAND or CHANNEL parameter to the SODA service which is translated by the service to the velocity frame of the target cube. This works, but requiring conversions on both the client and server side
isn’t ideal. Likewise, in our ObsCore implementation only the em_ucd indicates the cubes are in velocity but it would certainly be useful to have full velocity information for data discovery!<o:p></o:p></span></p>
<p><span lang="EN-AU"> <o:p></o:p></span></p>
<p><span lang="EN-AU">The extension you outline looks like it would work nicely for the same use case in CASDA. However I think we should add the following to fully describe the velocity axis (as opposed to its translation into wavelength for the base obscore).<o:p></o:p></span></p>
<ul type="disc">
<li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0 level1 lfo1">
<span lang="EN-AU">v_resolution – value of CDELT3 or CDELT4<o:p></o:p></span></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0 level1 lfo1">
<span lang="EN-AU">v_unit – although this should always be m/s<o:p></o:p></span></li></ul>
<p><span lang="EN-AU"> <o:p></o:p></span></p>
<p><span lang="EN-AU">Another consideration is that a lot of our users tend to use velocity to interact with frequency cubes. So even for these frequency cubes we might end up filling in velocity metadata if the fields were defined. Tools such as CARTA tend
to automatically show the spectral axis as velocity where it can, such that many users would assume the cubes are in velocity not frequency.<o:p></o:p></span></p>
<p><span lang="EN-AU"> <o:p></o:p></span></p>
<div>
<div>
<p><span lang="EN-AU">Cheers,<o:p></o:p></span></p>
<p><b><span lang="EN-AU" style="color:#00A9CE">James Dempsey</span></b><span lang="EN-AU"><o:p></o:p></span></p>
<p><span lang="EN-AU" style="font-size:9.0pt;color:black">Senior Developer </span>
<span lang="EN-AU" style="font-size:9.0pt;color:#00A9CE">|</span><span lang="EN-AU" style="font-size:9.0pt;color:black"> CSIRO </span><span lang="EN-AU"><o:p></o:p></span></p>
<p><span lang="EN-AU"><a href="mailto:james.dempsey@csiro.au" target="_blank"><span lang="EN-GB" style="font-size:9.0pt;color:#0563C1">james.dempsey@csiro.au</span></a></span><span lang="EN-AU" style="font-size:9.0pt;color:black">
</span><span lang="EN-AU" style="font-size:9.0pt;color:#00A9CE">|</span><span lang="EN-AU" style="font-size:9.0pt;color:black"> 02 6214 2912</span><span lang="EN-AU"><o:p></o:p></span></p>
</div>
</div>
<p><span lang="EN-AU"> <o:p></o:p></span></p>
<p><span lang="EN-AU"> <o:p></o:p></span></p>
<div style="border:none;border-top:solid windowtext 1.0pt;padding:3.0pt 0cm 0cm 0cm;border-color:currentcolor currentcolor">
<p style="margin-bottom:12.0pt"><b><span lang="EN-AU" style="font-size:12.0pt;color:black">From:
</span></b><span lang="EN-AU" style="font-size:12.0pt;color:black">dal <<a href="mailto:dal-bounces@ivoa.net" target="_blank">dal-bounces@ivoa.net</a>> on behalf of alberto micol <<a href="mailto:amicol.ivoa@googlemail.com" target="_blank">amicol.ivoa@googlemail.com</a>><br>
<b>Date: </b>Thursday, 16 February 2023 at 12:02 am<br>
<b>To: </b><a href="mailto:dal@ivoa.net" target="_blank">dal@ivoa.net</a> <<a href="mailto:dal@ivoa.net" target="_blank">dal@ivoa.net</a>><br>
<b>Subject: </b>ObsCore for velocity cubes</span><span lang="EN-AU"><o:p></o:p></span></p>
</div>
<p><span lang="EN-AU">Dear ObsCorers,<o:p></o:p></span></p>
<div>
<p><span lang="EN-AU"> <o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU">I have received with much interest the ObsCore extension for RADIO data, thanks for that very clear document.<o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU"> <o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU">Would it be possible to have a similar extension for cubes with velocity as third axis (the other two being the usual spatial ones)?<o:p></o:p></span></p>
</div>
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<p><span lang="EN-AU">Let me call them “velocity cubes”...<o:p></o:p></span></p>
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<p><span lang="EN-AU"> <o:p></o:p></span></p>
</div>
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<p><span lang="EN-AU">Here my use case…<o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU"> <o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU">At ESO we need to support cutouts of velocity cubes.<o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU"> <o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU">Up to now our SODA interface supported spectra, images, and wavelength cubes;<o:p></o:p></span></p>
</div>
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<p><span lang="EN-AU">to provide the user with the SODA input parameters and their possible MIN/MAX values<o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU">we query ivoa.ObsCore.<o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU"> <o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU">Now with the introduction of velocity cubes, we would like to get the necessary SODA input params also from ObsCore.<o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU">We can certainly do so by extending our own ObsCore table (ObsCore allows to extend the table), but I was wondering<o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU">if others have similar needs, and see if we can agree with a common ObsCore extension.<o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU"> <o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU">Velocity cubes should come in a FITS format as described by Greisen et al, 2006, so-called Paper 3.<o:p></o:p></span></p>
</div>
<blockquote style="margin-left:30.0pt;margin-top:5.0pt;margin-right:0cm;margin-bottom:5.0pt">
<div>
<p><span lang="EN-AU">Shortly summarised, the velocity can be either:<o:p></o:p></span></p>
</div>
</blockquote>
<div>
<ul type="disc">
<ul type="circle">
<li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level2 lfo2">
<span lang="EN-AU">a radio (VRAD), <o:p></o:p></span></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level2 lfo2">
<span lang="EN-AU">an optical (VOPT), <o:p></o:p></span></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level2 lfo2">
<span lang="EN-AU">a relativistic velocity (ZOPT), <o:p></o:p></span></li><li class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l1 level2 lfo2">
<span lang="EN-AU">a generic apparent velocity (VELO).<o:p></o:p></span></li></ul>
</ul>
</div>
<blockquote style="margin-left:30.0pt;margin-top:5.0pt;margin-right:0cm;margin-bottom:5.0pt">
<div>
<p><span lang="EN-AU">The RESTFRQa (RESTWAVa) keyword conveys the necessary reference frequency (wavelength) to transform velocity into frequency or wavelength. <o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU">The velocity unit is m/s.<o:p></o:p></span></p>
</div>
</blockquote>
<div>
<p><span lang="EN-AU"> <o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU">SODA cutouts on the velocity axis are usually formulated by passing cuts already expressed in velocity<o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU">though it must be possible to perform the conversions to and from frequency/wavelength.<o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU"> <o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU">What would then be needed in ObsCore is:<o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU"> <o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU">v_min<o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU">v_max<o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU"> <o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU">but also, in case of radio velocity cube:<o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU">f_min<o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU">f_max (getting these from the RADIO extension)<o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU">f_rest = RESTFRQ<o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU"> <o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU">and, in case of a optical or relativistic velocity cube<o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU">em_rest = RESTWAV<o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU">(we already have em_min, em_max)<o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU"> <o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU">The em_resolv_power should then be set to:<o:p></o:p></span></p>
</div>
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<p><span lang="EN-AU"> lambda freq c<o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU"> ——————— = ————— = —————<o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU"> delta lambda delta freq 2 * delta_v<o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU"> <o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU">where delta_v is the CD3_3 in the cube (in the example of a cube with the velocity on the third axis);<o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU">but I would also likely accept a v_pixel_scale (= delta_v).<o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU"> <o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU">The UCD for the velocity should then be:<o:p></o:p></span></p>
</div>
<div>
<pre><span lang="EN-AU">spect.dopplerVeloc.opt<o:p></o:p></span></pre>
<div>
<pre><span lang="EN-AU">spect.dopplerVeloc.radio<o:p></o:p></span></pre>
<div>
<p><span lang="EN-AU">unsure what it should be for the relativistic case.<o:p></o:p></span></p>
</div>
</div>
</div>
<div>
<p><span lang="EN-AU"> <o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU">This would allow us at ESO to implement SODA on top of ObsCore (as already done for all other parameters)<o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU">and would allow astronomer to search the velocity cubes with certain characteristics using ObsCore.<o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU"> <o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU">What do you think? <o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU">Is that doable? I think at ESO we will simply start implementing the above extra ObsCore parameters (unless you suggest different names for that),<o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU">while waiting to see if there is more interest to build a proper standard.<o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU"> <o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU">Eager to know what you think, <o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU">Cheers,<o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU">Alberto<o:p></o:p></span></p>
</div>
<div>
<p><span lang="EN-AU"> <o:p></o:p></span></p>
</div>
</div>
</div>
</div>
</div>
</blockquote>
</div>
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