UCD question: how to assign the wavelength-dependen (em) UCD word
Bo Milvang-Jensen
milvang at astro.ku.dk
Wed Mar 2 18:00:15 CET 2022
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
>
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