J/A+A/712/A151ivo://CDS.VizieR/J/A+A/712/A151CDSPietrow A.G.M.Sumra S.Petit dit de la Roche D.J.M.Lossnitz E.J.,Denker C.Abmus M.2026-08-13T08:23:28Z2026-08-13T09:19:25ZCDS support team

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

cds-question@unistra.frthe-sunmagnetic-fieldsspectrophotometryvisible-astronomyAccurate modeling of stellar active regions (ARs) remains a major bottleneck for radial-velocity and transmission-spectroscopy studies aimed at finding Earth-like planets. While much effort has been devoted to AR modeling, their center-to-limb variations (CLV) have been largely overlooked. We take a step toward remedying this by measuring the CLV of the 6173{AA} continuum intensity for sunspots (the whole spot, and separate umbrae and penumbrae), faculae, network, and the quiet Sun using the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). This study is based on four simple round {alpha}-sunspots and their surroundings, as well as one strongly evolving region. After correcting for stray light, we find that relative to the quiet Sun, all components except for the umbra display reduced darkening towards the limb. Additionally, strongly evolving active regions do not appear to display significantly altered CLV profiles compared to stable active regions. Faculae and network show contrast enhancements that peak near {mu}~=0.3 before declining toward the limb, reaching maxima of approximately 4% and 2% respectively in contrast excess relative to the quiet Sun, while the spot-to-quiet-Sun contrast rises to approximately 15% near the limb. For both types of AR, this change in CLV behavior near the limb is likely related to the three-dimensional structure of the active regions and the rapidly changing viewing geometry. This behavior is not captured by synthetic CLVs based on PHOENIX and ATLAS model atmospheres with solar values and a different effective temperature, underscoring the need for more realistic treatments of stellar activity.2026A&A...712A.151Phttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/712/A151CatalogResearchIsServedByTAP VizieR generic servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/712/A151https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/712/A151http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/712/A151https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/712/A151https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/712/A151http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/712/A151GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapOpticaldefaultJ/A+A/712/A151/sca12519Scatter data of the active region NOAA 12519 alpha-typerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintFeatureSolar feature center-to-limb-variations CLV of active regions AR polynomial coefficients type as Full, Network, Penumbra, Plage, Quiet and Umbra (FEATURE) (G1)src.classcharmuHeliocentric angle cosine mu = cos(theta) from 0.1 to 1.0 (MU)obs.paramdoubleIHMI continuum intensity as raw counts and not normalised, see POLYFITS/AVGCURVE for normalised values (INTENSITY)spect.line.intensity;em.line;em.opt.RdoubleJ/A+A/712/A151/sca12526Scatter data of the active region NOAA 12526 alpha-typerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintFeatureSolar feature center-to-limb-variations CLV of active regions AR polynomial coefficients type as Full, Network, Penumbra, Plage, Quiet and Umbra (FEATURE) (G1)src.classcharmuHeliocentric angle cosine mu = cos(theta) from 0.1 to 1.0 (MU)obs.paramdoubleIHMI continuum intensity as raw counts and not normalised, see POLYFITS/AVGCURVE for normalised values (INTENSITY)spect.line.intensity;em.line;em.opt.RdoubleJ/A+A/712/A151/sca12670Scatter data of the active region NOAA 12670 alpha-typerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintmuHeliocentric angle cosine mu = cos(theta) from 0.1 to 1.0 (MU)obs.paramdoubleFeatureSolar feature center-to-limb-variations CLV of active regions AR polynomial coefficients type as Full, Network, Penumbra, Plage, Quiet and Umbra (FEATURE) (G1)src.classcharIHMI continuum intensity as raw counts and not normalised, see POLYFITS/AVGCURVE for normalised values (INTENSITY)spect.line.intensity;em.line;em.opt.RdoubleJ/A+A/712/A151/sca12673Scatter data of the active region NOAA 12738 alpha-typerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintFeatureSolar feature center-to-limb-variations CLV of active regions AR polynomial coefficients type as Full, Network, Penumbra, Plage, Quiet and Umbra (FEATURE) (G1)src.classcharmuHeliocentric angle cosine mu = cos(theta) from 0.1 to 1.0 (MU)obs.paramdoubleIHMI continuum intensity as raw counts and not normalised, see POLYFITS/AVGCURVE for normalised values (INTENSITY)spect.line.intensity;em.line;em.opt.RdoubleJ/A+A/712/A151/sca12738Scatter data of the active region NOAA 12673 beta-typerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintFeatureSolar feature center-to-limb-variations CLV of active regions AR polynomial coefficients type as Full, Network, Penumbra, Plage, Quiet and Umbra (FEATURE) (G1)src.classcharmuHeliocentric angle cosine mu = cos(theta) from 0.1 to 1.0 (MU)obs.paramdoubleIHMI continuum intensity as raw counts and not normalised, see POLYFITS/AVGCURVE for normalised values (INTENSITY)spect.line.intensity;em.line;em.opt.RdoubleJ/A+A/712/A151/polyfitsPolynomial fits on a mu grid from 0.1 to 1.0 for all 5 ARsARActive region name as NOAA12519,12526,12670,12738,12673 (AR_NAME)meta.id;obs.fieldcharFeatureSolar feature type 905 occurence times for each Full, Network, Penumbra, Plage, Quiet and Umbra (FEATURE) (G1)src.classcharmuHeliocentric angle cosine mu = cos(theta) from 0.1 to 1.0 (MU)obs.paramdoubleI/I1Polynomial CLV fit, normalised to disk centre (I/I_mu=1_) corresponds to figure fitted CLV intensity variations for five ARs of the section Results and discussion (INTENSITY_FIT)phot.flux.density;arith.ratio;em.linedoublerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintJ/A+A/712/A151/averagedIntensities averaged over only alpha-type AR which corresponds to figure 6 Mean CLV intensity variations averaged over the four {alpha}-spots of section Results and discussionrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintFeatureFeature type 181 occurence times for each Full, Network, Penumbra, Plage, Quiet and Umbra (FEATURE) (G1)src.classcharmuHeliocentric angle cosine mu = cos(theta) from 0.1 to 1.0 (MU)obs.paramdoubleImean/I1Mean CLV intensity normalised (I/I_1_) (MEAN_INTENSITY)phot.flux.density;arith.ratio;em.linedoublee_Imean/I1Standard deviation CLV intensity normalised (STD_INTENSITY)stat.errordouble