J/A+A/713/A245ivo://CDS.VizieR/J/A+A/713/A245CDSMohandasan A.Smart R.L.Reyle C.Le Brun V.Perez-Garrido A.,Banados E.Jones H.R.A.Goldman B.Casewell S.L.Zapatero Osorio M.R.,Dupuy T.Rejkuba M.Martin E.L.Munoz Torres S.Dominguez-Tagle C.,Zerjal M.Huelamo N.Lodieu N.Cruz P.Majidi F.Z.Rebolo R.,Phillips M.W.Zhang J.-Y.Aghanim N.Altieri B.Amara A.Andreon S.,Auricchio N.Baccigalupi C.Baldi M.Balestra A.Bardelli S.,Battaglia P.Biviano A.Bonchi A.Branchini E.Brescia M.,Brinchmann J.Camera S.Canas-Herrera G.Capobianco V.Carbone C.,Carretero J.Casas S.Castellano M.Castignani G.Cavuoti S.,Chambers K.C.Cimatti A.Colodro-Conde C.Congedo G.Conselice C.J.,Conversi L.Copin Y.Costille A.Courbin F.Courtois H.M.Cropper M.,Da Silva A.Degaudenzi H.De Lucia G.Dole H.Douspis M.Dubath F.,Dupac X.Dusini S.Escoffier S.Farina M.Faustini F.Ferriol S.,Fotopoulou S.Frailis M.Franceschi E.Galeotta S.George K.,Gillard W.Gillis B.Giocoli C.Gracia-Carpio J.Granett B.R.,Grazian A.Grupp F.Haugan S.V.H.Hoar J.Holmes W.Hook I.M.,Hormuth F.Hornstrup A.Jahnke K.Jhabvala M.Keihaenen E.Kermiche S.,Kiessling A.Kubik B.Kuijken K.Kuemmel M.Kunz M.Kurki-Suonio H.,Le Boulc'h Q.Le Brun A.M.C.Le Mignant D.Ligori S.Lilje P.B.,Lindholm V.Lloro I.Mainetti G.Maino D.Maiorano E.Mansutti O.,Marcin S.Marggraf O.Martinelli M.Martinet N.Marulli F.Massey R.,Medinaceli E.Mei S.Mellier Y.Meneghetti M.Merlin E.Meylan G.,Mora A.Moresco M.Moscardini L.Nakajima R.Neissner C.Niemi S.-M.,Padilla C.Paltani S.Pasian F.Pedersen K.Percival W.J.,Pettorino V.Pires S.Polenta G.Poncet M.Popa L.A.Pozzetti L.,Raison F.Renzi A.Rhodes J.Riccio G.Romelli E.Roncarelli M.,Saglia R.Sakr Z.Sapone D.Sartoris B.Schewtschenko J.A.Schirmer M.,Schneider P.Schrabback T.Secroun A.Seidel G.Serrano S.Simon P.,Sirignano C.Sirri G.Stanco L.Steinwagner J.Surace C.,Tallada-Crespi P.Taylor A.N.Tereno I.Toledo-Moreo R.Torradeflot F.,Tsyganov A.Tutusaus I.Valenziano L.Valiviita J.Vassallo T.,Verdoes Kleijn G.Veropalumbo A.Vibert D.Wang Y.Weller J.,Zacchei A.Zamorani G.Zerbi F.M.Zucca E.Martin-Fleitas J.Scottez V.2026-09-22T09:40:11Z2026-09-22T10:35:39ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frbrown-dwarfsinfrared-photometryproper-motionsgalaxy-classification-systemseffective-temperatureUltracool dwarfs (UCDs) encompass the lowest-mass stars and brown dwarfs at the stellar-substellar boundary. These intrinsically faint objects are challenging to detect. However, the wide coverage and deep sensitivity of the Euclid survey will increase the number of confirmed and well-characterised UCDs by several orders of magnitude. We carried out a systematic study using Euclid Quick Data Release (Q1) low-resolution near-infrared (NIR) spectra to identify and characterise UCDs. A sample of previously known UCDs in Q1 was compiled to validate the analysis, which was then applied to newly identified UCD candidates in Euclid Deep Field North (EDF-N; 22.9 deg^2^, down to JE~24.5mag). We confirm 33 new UCDs in EDF-N, spanning spectral types (SpTs) M7-T1 (JE=17-21mag) and distances of 50-600 pc. Six of them were also independently identified in other Q1 studies. We followed up on two of these objects with ground-based optical and NIR observations using the Gran Telescopio Canarias, providing an independent validation of the Euclid spectral classification and the ability of Q1 spectra to constrain the stellar parameters of UCDs. We determined the SpTs from Euclid Q1 spectra of 33 newly identified UCDs and 167 previously known UCDs by fitting spectral standards from the SpeX Prism Library Analysis Toolkit. The known UCD sample includes 103 objects in common with the Dark Energy Survey (M7-T0, JE=17-22mag, and d=50-600pc), 6 objects from literature compilations of UCD sources (M8-T7, JE=18-20mag, and d=30-300pc), and 58 in common with Gaia (M7-L1, JE=17-24mag, and d=70-300pc). We derived independent stellar parameter estimates through atmospheric model fitting; the resulting effective temperatures are in good agreement with Euclid SpTs. Combined with complementary ground- and space-based data, these results demonstrate the potential for determining proper motions and identifying companions. Additionally, we investigated Gaia UCDs in Q1 by combining their mean XP spectra with Euclid NIR spectra, extending the wavelength coverage and enabling more comprehensive determinations of stellar parameters, including radii. To support broader classification efforts, we analysed the UCDs in colour-colour space and assessed their separation from quasar loci. We present a publicly available, machine- readable catalogue that includes Euclid observations of known and newly identified sources, with spectral classifications and stellar parameters. This work demonstrates Euclid's capability to identify and characterise the faintest stellar populations, establishing a foundation for large-scale UCD studies with forthcoming survey data.2026A&A...713A.245Mhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/713/A245CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toII/388 : Euclid final merged catalog. Q1 data release (Euclid Coll., 2025)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/713/A245https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/713/A245http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/713/A245https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/713/A245https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/713/A245http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/713/A245GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/713/A245/catalog (Ultracool dwarfs analysed in the study (Table A1))https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/713/A245/catalog?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/713/A245/catalog?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/713/A245/catalog?GETtext/xml+votable180.050000true262.65984437063465.60835038452140.0055555555555555565/3839 8579 8582 8592 6/10229-10231 10235-10236 10238-10239 11603 11605-11607 11612-11613 11615 15354-15355 16040 16042-16046 33979 33982-33983 34025 34027-34028 34310-34311 34313 34315 34321-34324 34326 34332-34334 34337 34340-34341 34352 34376 35927 35929 35931-35932 35934-35935 35953 35956-35957 35959 36104 36106 361281.9867573869263685e-19 3.916500758235022e-19https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/713/A245?format=asciiOpticalInfrareddefaultJ/A+A/713/A245/catalogUltracool dwarfs analysed in the study (Table A1)recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintShNameShort name used in text (SHORT_NAME)meta.idcharSNameCommon discovery name (SIMBAD_NAME)meta.idchar_RA.icrsRight ascension (ICRS) at Epoch=J2000, proper motions taken into accountdegpos.eq.raindexed_DE.icrsDeclination (ICRS) at Epoch=J2000, proper motions taken into accountdegpos.eq.decindexedFlagYY flux flag (FLAG_Y) (1)meta.code.errorintEUCLIDPositional IAU name in Q1, EUCL JHHMMSS.ss+DDMMss.ss (EUCLID_NAME)meta.id;meta.maincharObjectIdUnique source identifier in Q1 (OBJECT_ID)meta.idRA_ICRSRight ascension (ICRS) at Ep=2024.6 (RIGHT_ASCENSION)degpos.eq.ra;meta.mainDE_ICRSDeclination (ICRS) at Ep=2024.6 (DECLINATION)degpos.eq.dec;meta.mainpmRA? Proper motion in RA (PMRA)mas/yrpos.pm;pos.eq.radoublenullablee_pmRA? RA proper motion error (PMRA_ERR)mas/yrstat.error;pos.pm;pos.eq.radoublenullablepmDE? Proper motion in Dec (PMDec)mas/yrpos.pm;pos.eq.decdoublenullablee_pmDE? Dec proper motion error (PMDec_ERR)mas/yrstat.error;pos.pm;pos.eq.decdoublenullableFlagVISVIS flux flag (FLAG_VIS) (1)meta.code.errorintFluxVIS2ApVIS flux at 2 FWHM aperture (FLUX_VIS_2FWHM_APER)Jyphot.flux.density;em.optdoublee_FluxVIS2ApVIS aperture photometry error (FLUXERR_VIS_2FWHM_APER)uJystat.errordoubleFluxY2Ap? Y flux at 2 FWHM aperture (FLUX_Y_2FWHM_APER)uJyphot.flux.density;em.IR.Jdoublenullablee_FluxY2Ap? Y aperture photometry error (FLUXERR_Y_2FWHM_APER)uJystat.errordoublenullableFlagJJ flux flag (FLAG_J) (1)meta.code.errorintFluxJ2Ap? J flux at 2 FWHM aperture (FLUX_J_2FWHM_APER)uJyphot.flux.density;em.IR.Jdoublenullablee_FluxJ2Ap? J aperture photometry error (FLUXERR_J_2FWHM_APER)uJystat.errordoublenullableFlagHH flux flag (FLAG_H) (1)meta.code.errorintFluxH2Ap? H flux at 2 FWHM aperture (FLUX_H_2FWHM_APER)uJyphot.flux.density;em.IR.Hdoublenullablee_FluxH2Ap? H aperture photometry error (FLUXERR_H_2FWHM_APER)uJystat.errordoublenullableFWHMFull width at half maximum (FWHM)arcsecspect.line.widthdoublePLProbSource point-like probability (POINT_LIKE_PROB)stat.fit.goodnessdoubleEllSExtractor source ellipticity (ELLIPTICITY)src.ellipticitydoublePA[] Position angle of the source (POSITION_ANGLE)degpos.posAngdoublePathESA datalabs spectrum file path (DATALABS_PATH)meta.id;meta.filecharDist? Spectroscopic distance (DIST)pcpos.distancedoublenullablee_Dist? Spectroscopic distance error (DIST_ERR)pcstat.errordoublenullableSpTypeSpectral type from Q1 NISP spectra (SPT)src.spTypecharspSNR? Spectra mean signal-to-noise (SPECTRA_SNR)stat.snrdoublenullablespchisq? Spectrum reduced chi^2 value (SPECTRA_CHISQ)stat.fit.chi2doublenullablesppix? Spectrum good pixels number (SPECTRA_PIXELS)meta.number;phys.atmol.numberfloatnullableTeffTeff from model fitting (T_eff)Kphys.temperature.effectivedoublelogglog g from model fitting (logg)log(cm.s**-2)arith.zpdouble[Fe/H]Metallicity from model fitting (FeH)phys.abund.ZdoubleGaiaDR3? Gaia source ID of the object (Gaia_ID)meta.idnullableGmag? Gaia G magnitude (G)magphot.mag;em.optdoublenullable