UCD question: how to assign the wavelength-dependen (em) UCD word
Mireille LOUYS
mireille.louys at unistra.fr
Tue Mar 8 21:44:05 CET 2022
Dear Bo, Dear Semantics,
thanks for this interesting feedback.
The SVO Filter profile service contains a lot of Filter descriptions and
you can query what is stored with their search box :
http://svo2.cab.inta-csic.es/theory/fps/index.php?id=Subaru/Suprime.IB505&&mode=search&search_facility=Subaru&search_instrument=Suprime&search_text=suprime#filter
<http://svo2.cab.inta-csic.es/theory/fps/index.php?id=Subaru/Suprime.IB505&&mode=search&search_facility=Subaru&search_instrument=Suprime&search_text=suprime#filter>
You see that many properties are recorded for a filter, much more than
the UCD label you can assign on the photometric column.
In the IVOA we can describe filters properties using the Photometry data
model v1.0:
https://www.ivoa.net/documents/PHOTDM/
The way to provide more information to describe filters and calibration
zero points at the top of a VOTable catalog was proposed in the
PhotDM1.0 Appendix C.2 Photometric Data in Cone Search in the doc
pointed above.
The current update of this spec : PHOTDM1.1 is in progress and discussed
in the community .
You can see details on the revision process , people involved , etc, here :
https://wiki.ivoa.net/twiki/bin/view/IVOA/PhotDM11RFC
The goal is to set-up a mechanism to allow any filter and calibration
information to be described in an annotation block at the beginning of a
VOtable which in turn can be interpreted by a parser application based
on a library.
This work is in progress and will be shown at the next interoperability
meeting (April) probably .
Your example is up-to-the point and in sync with our current development.
I hope we can show you examples of this representation for your filters
in this syntax very soon.
Best regards , Mireille.
PS: So your selection process for ucd , based on the reference
wavelength/frequency/energy, is appropriate. It is just that not all
information can be wrapped in just one label.
Le 02/03/2022 à 18:00, Bo Milvang-Jensen a écrit :
> Dear Mireille and IVOA semantics list,
>
> Thank you for inviting me to send you my unsolved questions about
> UCDs, I have two: one in this e-mail and one in the next
>
> Background: These questions have arisen while writing UCDs for the
> around 1200 table columns in the COSMOS2020 catalogue, paper recently
> published in Weaver+2022
> (https://ui.adsabs.harvard.edu/abs/2022ApJS..258...11W/abstract),
> before publication via ESO's Phase 3. The catalogue contains
> photometry in around 40 photometric bands/filters, and photo-zs and
> physical parameters (e.g. stellar mass) computed by two codes.
>
> My first question (i.e. this e-mail) concerns how to select the
> wavelength-dependent (em) UCD word for a given photometric filter. I
> have consulted the UCD1+ document, but the only guidance I found was
> the short description for each UCD word, e.g. "Infrared between 1.0
> and 1.5 micron". First, I am not sure I understand the motivation for
> having overlapping words, as shown by this example:
>
> em Electromagnetic spectrum
> em.IR Infrared part of the spectrum
> em.IR.NIR Near-Infrared, 1-5 microns
> em.IR.J Infrared between 1.0 and 1.5 micron
>
> My intuition is to select the most "specific" word (here em.IR.J), but
> that could be wrong.
>
> Second, my main problem is that I do not know to select the most
> appropriate em word. For each of my filters I know the central
> wavelength and the full transmission curve. Some of my filters, e.g. y
> and Y, have a transmission curve that transmits both below and above 1
> micron, which is one of the limits used in the descriptions of the UCD
> words, so if one were to consider the full transmission curve when
> selecting the em word, these filters could only be given the very
> general word "em". I have made the choice of only using the central
> wavelength when assigning the em word, not the full transmission curve.
>
> Here is the full list of filters in COSMOS2020, with their central
> wavelengths and widths (both in Angstrom), and with the UCD I
> currently have assigned based on my two principles (most specific
> word, and central wavelength) [see Weaver+2022 Fig. 2 for the filter
> curves]:
>
> Label Description lam_cen width UCD
> --------------------------------------------------------------------------
>
> GALEX_FUV GALEX FUV 1526 224 em.UV.100-200nm
> GALEX_NUV GALEX NUV 2307 791 em.UV.200-300nm
> CFHT_u CFHT/MegaCam u 3709 518 em.opt.U
> CFHT_ustar CFHT/MegaCam u* 3858 598 em.opt.U
> ACS_F814W HST/ACS F814W 8333 2511 em.opt.I
> HSC_g Subaru/HSC HSC-SSP PDR2 g 4847 1383 em.opt.B
> HSC_r Subaru/HSC HSC-SSP PDR2 r 6219 1547 em.opt.R
> HSC_i Subaru/HSC HSC-SSP PDR2 i 7699 1471 em.opt.I
> HSC_z Subaru/HSC HSC-SSP PDR2 z 8894 766 em.opt.I
> HSC_y Subaru/HSC HSC-SSP PDR2 y 9761 786 em.opt.I
> SC_B Subaru/SuprimeCam B 4488 892 em.opt.B
> SC_gp Subaru/SuprimeCam g+ 4804 1265 em.opt.B
> SC_V Subaru/SuprimeCam V 5487 954 em.opt.V
> SC_rp Subaru/SuprimeCam r+ 6305 1376 em.opt.R
> SC_ip Subaru/SuprimeCam i+ 7693 1497 em.opt.I
> SC_zp Subaru/SuprimeCam z+ 8978 847 em.opt.I
> SC_zpp Subaru/SuprimeCam z++ 9063 1335 em.opt.I
> SC_IB427 Subaru/SuprimeCam IB427 4266 207 em.opt.B
> SC_IB464 Subaru/SuprimeCam IB464 4635 218 em.opt.B
> SC_IA484 Subaru/SuprimeCam IA484 4851 229 em.opt.B
> SC_IB505 Subaru/SuprimeCam IB505 5064 231 em.opt.V
> SC_IA527 Subaru/SuprimeCam IA527 5261 243 em.opt.V
> SC_IB574 Subaru/SuprimeCam IB574 5766 273 em.opt.V
> SC_IA624 Subaru/SuprimeCam IA624 6232 300 em.opt.R
> SC_IA679 Subaru/SuprimeCam IA679 6780 336 em.opt.R
> SC_IB709 Subaru/SuprimeCam IB709 7073 316 em.opt.R
> SC_IA738 Subaru/SuprimeCam IA738 7361 324 em.opt.R
> SC_IA767 Subaru/SuprimeCam IA767 7694 365 em.opt.I
> SC_IB827 Subaru/SuprimeCam IB827 8243 343 em.opt.I
> SC_NB711 Subaru/SuprimeCam NB711 7121 72 em.opt.R
> SC_NB816 Subaru/SuprimeCam NB816 8150 120 em.opt.I
> UVISTA_Y VISTA/VIRCAM UltraVISTA DR4 Y 10216 923 em.IR.J
> UVISTA_J VISTA/VIRCAM UltraVISTA DR4 J 12525 1718 em.IR.J
> UVISTA_H VISTA/VIRCAM UltraVISTA DR4 H 16466 2905 em.IR.H
> UVISTA_Ks VISTA/VIRCAM UltraVISTA DR4 Ks 21557 3074 em.IR.K
> UVISTA_NB118 VISTA/VIRCAM UltraVISTA DR4 NB118 11909 112 em.IR.J
> IRAC_CH1 Spitzer/IRAC ch1 35686 7443 em.IR.3-4um
> IRAC_CH2 Spitzer/IRAC ch2 45067 10119 em.IR.4-8um
> IRAC_CH3 Spitzer/IRAC ch3 57788 14082 em.IR.4-8um
> IRAC_CH4 Spitzer/IRAC ch4 79958 28796 em.IR.4-8um
>
> However, my ESO Phase 3 scientist Laura (in cc) thought it could be
> misleading to assign em.IR.J to the Y and NB118 filters, but also said
> that ESO needed to look into standardizing this. If my UCDs for these
> two filters could be misleading, so could those for all the
> intermediate bands (IA, IB), the other narrow bands, and the broad
> bands that don't have a UCD with its name encoded (e.g. g, z).
>
> I would be interested in your view on this.
>
> Kind regards, Bo
>
> On 3/1/22 5:41 PM, Mireille LOUYS wrote:
>> hi again ,
>> please do not hesitate to send your questions to me , or to the ivoa
>> semantics list in copy .
>> this helps the community and maintainers like me to be aware of the
>> trouble you may encounter.
>>
>> many thanks , Mireille
>>
>> Le 25/02/2022 à 16:59, Bo Milvang-Jensen a écrit :
>>>
>>> PS: I have a couple of other questions/problems with the UCD
>>> standard that I would like to ask/report. What is the best channel?
>>>
>>> Kind regards, Bo
>>
--
--
Mireille Louys, MCF (Associate Professor)
Centre de données CDS IPSEO, Images, Laboratoire Icube
Observatoire de Strasbourg Telecom Physique Strasbourg
11 rue de l'Université 300, Bd Sebastien Brandt CS 10413
F- 67000-STRASBOURG F-67412 ILLKIRCH Cedex
Tel: +33 3 68 85 24 34
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