J/A+A/688/A104ivo://CDS.VizieR/J/A+A/688/A104doi:10.26093/cds/vizier.36880104CDSSana H.Tramper F.Abdul-Masih M.Blomme R.Dsilva K.Maravelias G.,Martins L.Mehner A.Wofford A.Banyard G.Barbosa C.L.,Bestenlehner J.Hawcroft C.John Hillier D.Todt H.Larkin C.J.K.,Mahy L.Najarro F.Ramachandran V.Ramirez-Tannus M.C.Rubio-Diez M.M.,Sander A.A.C.Shenar T.Vink J.S.Backs F.Brands S.A.Crowther P.,Decin L.de Koter A.Hamann W.-R.Kehrig C.Kuiper R.Oskinova L.,Pauli D.Sundqvist J.Verhamme O.XSHOOT-U collaboration2024-11-21T20:02:24Z2024-08-10T09:41:05ZCDS support team

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

cds-question@unistra.frstar-atlasesmagellanic-cloudsspectroscopyo-starswolf-rayet-starsThe XShootU project aims to obtain ground-based optical to near-infrared spectroscopy of all targets observed by the Hubble Space Telescope (HST) under the Director's Discretionary program ULLYSES. Using the medium resolution spectrograph X-shooter, spectra of 235 OB and Wolf-Rayet (WR) stars in sub-solar metallicity environments have been secured. The bulk of the targets belong to the Large and Small Magellanic Clouds, with the exception of three stars in NGC 3109 and Sextans A. This second paper of the series focuses on the optical observations of Magellanic Clouds targets. It describes the uniform reduction of the UVB (300-560nm) and VIS (550-1020nm) XShootU data as well as the preparation of advanced data products that are suitable for homogeneous scientific analyses. The data reduction of the raw data is based on the ESO CPL X-shooter pipeline. We paid particular attention to the determination of the response curves. This required equal flat-fielding of the science and flux standard star data and the derivation of improved flux standard models. The pipeline products were then processed with our own set of routines to produce a series of advanced data products. In particular, we implemented slit-loss correction, absolute flux calibration, (semi-)automatic rectification to the continuum, and a correction for telluric lines. The spectra of individual epochs were further corrected for the barycentric motion, re-sampled and co-added, and the spectra from the two arms were merged into a single flux calibrated spectrum covering the entire optical range with maximum signal-to-noise ratio. We identify and describe an undocumented recurrent ghost visible on the raw data. We present an improved flat-fielding strategy that limits artefacts when the science and flux standard stars are observed on different nights. The improved flux standard models and the new grid of anchor points allow to limit artefacts of the response curve correction on, e.g., the shape of the wings of the Balmer lines, from a couple of per cent of the continuum level to less than 0.5%. We confirm the presence of a radial velocity shift of about 3.5km/s between the UVB and the VIS arm of xshooter and that there is no short term variations impacting the RV measurements. RV precision better than 1km/s can be obtained on sharp telluric lines while RV precision of the order of 2 to 3km/s are obtained on data with the best SNR. For each target observed by XShootU, we provide three types of data products: (i) two-dimensional spectra for each UVB and VIS exposure before and after correction for the instrument response; (ii) one-dimensional UVB and VIS spectra as produced by the X-shooter pipeline before and after response-correction, as well as after applying various processing, including absolute flux calibration, telluric removal, normalisation and barycentric correction; and (iii) co-added flux-calibrated and rectified spectra over the full optical range, for which all available XShootU exposures were combined. For the large majority of the targets, the final signal-to-noise ratio per resolution element is above 200 in both the UVB and the VIS co-added spectra. The reduced data and advanced scientific data products are made available to the community. Together with the HST UV ULLYSES data, they should enable various science goals, from detailed stellar atmosphere and stellar wind studies, to empirical libraries for population synthesis, to study of the local nebular environment and feedback of massive stars in sub-solar metallicity environments.2024A&A...688A.104Shttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/688/A104CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/A+A/675/A154 : X-Shooting ULLYSES. Project Description (Vink+, 2023)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/688/A104https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/688/A104http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/688/A104https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/688/A104https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/688/A104http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/688/A104GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/688/A104/table1 (List of XShootU target)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/688/A104/table1?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/688/A104/table1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/688/A104/table1?GETtext/xml+votable180.050000true9.2426667-73.39255560.0055555555555555565/8274-8275 8280 6/32958 33047 33051-33054 33076-33077 33079 33091-33092 33094-33095 33106-33107 33112-33113 33115-33116 33124 33126-33128 33294-33295 33297-33299 33304 33306 33316-33317 33328https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/688/A104?format=asciidefaultJ/A+A/688/A104/table1List of XShootU targetrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintObjectObject identifiermeta.id;meta.maincharRAJ2000Right ascension (J2000.0)pos.eq.ra;meta.mainDEJ2000Declination (J2000.0)pos.eq.dec;meta.mainnUVBNumber of epochs in the UVB armmeta.numberintTexpUVBCummulated integration time of UVB exposuresstime.expointsnrUVBSignal-to-Noise Ratio in coadded UVB spectra (1)stat.snrintnVISNumber of epochs in the VIS armmeta.numberintTexpVISCummulated integration time of VIS exposuresstime.expointsnrVISSignal-to-Noise Ratio in coadded VIS spectra (2)stat.snrintdeltMJDTime difference between the start of the first and last observing epochs.dtime.epochfloatJ/A+A/688/A104/table2Journal of the observationsrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintObjectObject identifiermeta.id;meta.maincharMJD-UVBModified Julian Date (JD-2400000.5) at the start of UVB exposuresdtime.epochdoubleTex-UVBUVB exposure integration timestime.epoch;obs.exposureintSNR-UVBSignal-to-Noise Ratio in rebin UVB spectra (1)stat.snrintMJD-VISModified Julian Date (JD-2400000.5) at the start of VIS exposuresdtime.epochdoubleTex-VISVIS exposure integration timestime.epoch;obs.exposureintSNR-VISSignal-to-Noise Ratio in rebin VIS spectra (2)stat.snrintFluxStdFlux standard star used in the data reductionphot.flux.densitycharDeltaTTime difference between the start of the science and flux observationsdtime.start;arith.difffloatJ/A+A/688/A104/tablea1Cross-identificationrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintXShootUXShootU target identifier (from Paper I)meta.idcharOBObserving Block (OB) name, as stored in the OBJECT keywords of the RAW data filemeta.idcharMASTMAST identifier, used for filenames and OBJECT keywords of the HLSPsmeta.idcharSimbadSimbad identifiermeta.idcharObjectObject identifiermeta.id;meta.maincharJ/A+A/688/A104/tablec1RV measurementsrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintMASTMAST identifier of the star (1)meta.idcharMJDModified Julian Date of the start of the observation (JD-2400000.5)time.epochdoubleRVRadial velocitykm/sphys.veloc;pos.heliocentricfloate_RVUncertainty on radial velocity (2)km/sstat.errorfloatTemplateCode of the template PoWR model usedmeta.code;instr.setup;meta.modelledcharvsiniProjected rotational velocity used in cross-correlationkm/sstat.correlationintQualQuality of the fit (3)meta.code.qual;stat.fit.param;meta.modelledintComComments about possible binarity (4)meta.code.multipcharObjectObject identifiermeta.id;meta.mainchar