Solanki, Sami K.

[["dc.bibliographiccitation.artnumber","L23"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","The Astrophysical Journal Letters"],["dc.bibliographiccitation.volume","934"],["dc.contributor.affiliation","Nèmec, N.-E.;"],["dc.contributor.affiliation","Shapiro, A. I.;"],["dc.contributor.affiliation","Işık, E.;"],["dc.contributor.affiliation","Sowmya, K.;"],["dc.contributor.affiliation","Solanki, S. K.;"],["dc.contributor.affiliation","Krivova, N. A.;"],["dc.contributor.affiliation","Cameron, R. H.;"],["dc.contributor.affiliation","Gizon, L.;"],["dc.contributor.author","Nèmec, N.-E."],["dc.contributor.author","Shapiro, A. I."],["dc.contributor.author","Işık, E."],["dc.contributor.author","Sowmya, K."],["dc.contributor.author","Solanki, S. K."],["dc.contributor.author","Krivova, N. A."],["dc.contributor.author","Cameron, R. H."],["dc.contributor.author","Gizon, L."],["dc.date.accessioned","2022-08-01T07:35:55Z"],["dc.date.available","2022-08-01T07:35:55Z"],["dc.date.issued","2022-07-28"],["dc.date.updated","2022-07-30T02:55:06Z"],["dc.description.abstract","Surfaces of the Sun and other cool stars are filled with magnetic fields, which are either seen as dark compact spots or more diffuse bright structures like faculae. Both hamper detection and characterization of exoplanets, affecting stellar brightness and spectra, as well as transmission spectra. However, the expected facular and spot signals in stellar data are quite different, for instance, they have distinct temporal and spectral profiles. Consequently, corrections of stellar data for magnetic activity can greatly benefit from the insight on whether the stellar signal is dominated by spots or faculae. Here, we utilize a surface flux transport model to show that more effective cancellation of diffuse magnetic flux associated with faculae leads to spot area coverages increasing faster with stellar magnetic activity than that by faculae. Our calculations explain the observed dependence between solar spot and facular area coverages and allow its extension to stars that are more active than the Sun. This extension enables anticipating the properties of stellar signal and its more reliable mitigation, leading to a more accurate characterization of exoplanets and their atmospheres."],["dc.description.sponsorship","A. I. Shapiro"],["dc.identifier.doi","10.3847/2041-8213/ac8155"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/112556"],["dc.language.iso","en"],["dc.relation.eissn","2041-8213"],["dc.relation.issn","2041-8205"],["dc.rights","CC BY 4.0"],["dc.rights.uri","http://creativecommons.org/licenses/by/4.0/"],["dc.title","Faculae Cancel out on the Surfaces of Active Suns"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.subtype","original_ja"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","A69"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","636"],["dc.contributor.author","Amazo-Gómez, E. M."],["dc.contributor.author","Shapiro, A. I."],["dc.contributor.author","Solanki, S. K."],["dc.contributor.author","Krivova, N. A."],["dc.contributor.author","Kopp, G."],["dc.contributor.author","Reinhold, T."],["dc.contributor.author","Oshagh, M."],["dc.contributor.author","Reiners, A."],["dc.date.accessioned","2021-04-14T08:26:43Z"],["dc.date.available","2021-04-14T08:26:43Z"],["dc.date.issued","2020"],["dc.identifier.doi","10.1051/0004-6361/201936925"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/82050"],["dc.notes.intern","DOI Import GROB-399"],["dc.relation.eissn","1432-0746"],["dc.relation.issn","0004-6361"],["dc.title","Inflection point in the power spectrum of stellar brightness variations"],["dc.title.alternative","II. The Sun"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","A157"],["dc.bibliographiccitation.journal","Astronomy & Astrophysics"],["dc.bibliographiccitation.volume","627"],["dc.contributor.author","Cernetic, M."],["dc.contributor.author","Shapiro, A. I."],["dc.contributor.author","Witzke, V."],["dc.contributor.author","Krivova, N. A."],["dc.contributor.author","Solanki, S. K."],["dc.contributor.author","Tagirov, R. V."],["dc.date.accessioned","2019-08-01T08:39:30Z"],["dc.date.available","2019-08-01T08:39:30Z"],["dc.date.issued","2019"],["dc.description.abstract","Contex. Stellar spectra synthesis is essential for the characterization of potential planetary hosts. In addition, comprehensive stellar variability calculations with fast radiative transfer are needed to disentangle planetary transits from stellar magnetically-driven variability. The planet-hunting space telescopes, such as CoRoT, Kepler, and TESS will bring vast quantities of data, rekindling the interest in fast calculations of the radiative transfer. Aims. We revisit the Opacity Distribution Functions (ODF) approach routinely applied to speedup stellar spectral synthesis. To achieve a considerable speedup relative to the current state-of-the-art, we further optimize the approach and search for the best ODF configuration. Furthermore, we generalize the ODF approach for fast calculations of flux in various filters often used in stellar observations. Methods. In a parameter-sweep-fashion, we generated ODF in the spectral range from UV to IR with different setups. The most accurate ODF configuration for each spectral interval was determined. For calculations of the radiative fluxes through filters we adapted the wavelength grid based on the transmission curve, whereafter the normal ODF procedure was performed. Results. Our optimum ODF configuration allows for a three fold speedup, compared to the previously used ODF configurations. The ODF generalization to calculate fluxes through filters results in a speedup of more than two orders of magnitude."],["dc.identifier.arxiv","1906.03112v2"],["dc.identifier.doi","10.1051/0004-6361/201935723"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/62252"],["dc.language.iso","en"],["dc.notes.status","final"],["dc.relation.issn","0004-6361"],["dc.relation.issn","1432-0746"],["dc.title","Opacity distribution functions for stellar spectra synthesis"],["dc.type","journal_article"],["dc.type.internalPublication","no"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","A70"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","650"],["dc.contributor.author","Krivova, N. A."],["dc.contributor.author","Solanki, S. K."],["dc.contributor.author","Hofer, B."],["dc.contributor.author","Wu, C.-J."],["dc.contributor.author","Usoskin, I. G."],["dc.contributor.author","Cameron, R."],["dc.date.accessioned","2021-08-12T07:45:05Z"],["dc.date.available","2021-08-12T07:45:05Z"],["dc.date.issued","2021"],["dc.description.abstract","Solar activity in all its varied manifestations is driven by the magnetic field. Two global quantities are particularly important for many purposes, the Sun’s total and open magnetic flux, which can be computed from sunspot number records using models. Such sunspot-driven models, however, do not take into account the presence of magnetic flux during grand minima, such as the Maunder minimum. Here we present a major update of a widely used simple model, which now takes into account the observation that the distribution of all magnetic features on the Sun follows a single power law. The exponent of the power law changes over the solar cycle. This allows for the emergence of small-scale magnetic flux even when no sunspots have been present for multiple decades and leads to non-zero total and open magnetic flux also in the deepest grand minima, such as the Maunder minimum, thus overcoming a major shortcoming of the earlier models. The results of the updated model compare well with the available observations and reconstructions of the solar total and open magnetic flux. This opens up the possibility of improved reconstructions of the sunspot number from time series of the cosmogenic isotope production rate."],["dc.description.abstract","Solar activity in all its varied manifestations is driven by the magnetic field. Two global quantities are particularly important for many purposes, the Sun’s total and open magnetic flux, which can be computed from sunspot number records using models. Such sunspot-driven models, however, do not take into account the presence of magnetic flux during grand minima, such as the Maunder minimum. Here we present a major update of a widely used simple model, which now takes into account the observation that the distribution of all magnetic features on the Sun follows a single power law. The exponent of the power law changes over the solar cycle. This allows for the emergence of small-scale magnetic flux even when no sunspots have been present for multiple decades and leads to non-zero total and open magnetic flux also in the deepest grand minima, such as the Maunder minimum, thus overcoming a major shortcoming of the earlier models. The results of the updated model compare well with the available observations and reconstructions of the solar total and open magnetic flux. This opens up the possibility of improved reconstructions of the sunspot number from time series of the cosmogenic isotope production rate."],["dc.identifier.doi","10.1051/0004-6361/202140504"],["dc.identifier.pii","aa40504-21"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/88364"],["dc.notes.intern","DOI Import GROB-448"],["dc.relation.eissn","1432-0746"],["dc.relation.issn","0004-6361"],["dc.title","Modelling the evolution of the Sun’s open and total magnetic flux"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","A120"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","620"],["dc.contributor.author","Wu, C.-J."],["dc.contributor.author","Krivova, N. A."],["dc.contributor.author","Solanki, S. K."],["dc.contributor.author","Usoskin, I. G."],["dc.date.accessioned","2020-12-10T18:11:40Z"],["dc.date.available","2020-12-10T18:11:40Z"],["dc.date.issued","2018"],["dc.identifier.doi","10.1051/0004-6361/201832956"],["dc.identifier.eissn","1432-0746"],["dc.identifier.issn","0004-6361"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/74100"],["dc.notes.intern","DOI Import GROB-354"],["dc.title","Solar total and spectral irradiance reconstruction over the last 9000 years"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","A32"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","633"],["dc.contributor.author","Shapiro, A. I."],["dc.contributor.author","Amazo-Gómez, E. M."],["dc.contributor.author","Krivova, N. A."],["dc.contributor.author","Solanki, S. K."],["dc.date.accessioned","2020-12-10T18:11:51Z"],["dc.date.available","2020-12-10T18:11:51Z"],["dc.date.issued","2020"],["dc.identifier.doi","10.1051/0004-6361/201936018"],["dc.identifier.eissn","1432-0746"],["dc.identifier.issn","0004-6361"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/74161"],["dc.notes.intern","DOI Import GROB-354"],["dc.title","Inflection point in the power spectrum of stellar brightness variations"],["dc.title.alternative","I. The model"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","The Astrophysical Journal"],["dc.bibliographiccitation.volume","934"],["dc.contributor.affiliation","Sowmya, K.;"],["dc.contributor.affiliation","Nèmec, N.-E.;"],["dc.contributor.affiliation","Shapiro, A. I.;"],["dc.contributor.affiliation","Işık, E.;"],["dc.contributor.affiliation","Krivova, N. A.;"],["dc.contributor.affiliation","Solanki, S. K.;"],["dc.contributor.author","Sowmya, K."],["dc.contributor.author","Nèmec, N.-E."],["dc.contributor.author","Shapiro, A. I."],["dc.contributor.author","Işık, E."],["dc.contributor.author","Krivova, N. A."],["dc.contributor.author","Solanki, S. K."],["dc.date.accessioned","2022-08-04T07:58:18Z"],["dc.date.available","2022-08-04T07:58:18Z"],["dc.date.issued","2022-08-02"],["dc.date.updated","2022-08-04T02:39:10Z"],["dc.description.abstract","A breakthrough in exoplanet detections is foreseen with the unprecedented astrometric measurement capabilities offered by instrumentation aboard the Gaia space observatory. Besides, astrometric discoveries of exoplanets are expected from the planned space mission, Small-JASMINE. In this setting, the present series of papers focuses on estimating the effect of the magnetic activity of G2V-type host stars on the astrometric signal. This effect interferes with the astrometric detections of Earth-mass planets. While the first two papers considered stars rotating at the solar rotation rate, this paper focuses on stars having solar effective temperature and metallicity but rotating faster than the Sun, and consequently more active. By simulating the distribution of active regions on such stars using the Flux Emergence And Transport model, we show that the contribution of magnetic activity to the astrometric measurements becomes increasingly significant with increasing rotation rates. We further show that the jitter for the most variable periodic Kepler stars is high enough to be detected by Gaia. Furthermore, due to a decrease in the facula-to-spot area ratio for more active stars, the magnetic jitter is found to be spot dominated for rapid rotators. Our simulations of the astrometric jitter have the potential to aid the interpretation of data from Gaia and upcoming space astrometry missions."],["dc.description.sponsorship","European Union’s Horizon 2020 research and innovation program"],["dc.description.sponsorship","EC ∣ European Research Council (ERC)https://doi.org/10.13039/501100000781"],["dc.description.sponsorship","EC ∣ European Research Council (ERC)https://doi.org/10.13039/501100000781"],["dc.identifier.doi","10.3847/1538-4357/ac79b3"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/112617"],["dc.language.iso","en"],["dc.relation.eissn","1538-4357"],["dc.relation.issn","0004-637X"],["dc.rights","CC BY 4.0"],["dc.rights.uri","http://creativecommons.org/licenses/by/4.0/"],["dc.title","Predictions of Astrometric Jitter for Sun-like Stars. III. Fast Rotators"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.subtype","original_ja"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","21"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","The Astrophysical Journal"],["dc.bibliographiccitation.volume","914"],["dc.contributor.author","Sowmya, K."],["dc.contributor.author","Shapiro, A. I."],["dc.contributor.author","Witzke, V."],["dc.contributor.author","Nèmec, N.-E."],["dc.contributor.author","Chatzistergos, T."],["dc.contributor.author","Yeo, K. L."],["dc.contributor.author","Krivova, N. A."],["dc.contributor.author","Solanki, S. K."],["dc.date.accessioned","2021-07-05T14:57:57Z"],["dc.date.available","2021-07-05T14:57:57Z"],["dc.date.issued","2021"],["dc.identifier.doi","10.3847/1538-4357/abf247"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/87779"],["dc.notes.intern","DOI-Import GROB-441"],["dc.relation.eissn","1538-4357"],["dc.relation.issn","0004-637X"],["dc.title","Modeling Stellar Ca ii H and K Emission Variations. I. Effect of Inclination on the S-index"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","A43"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","636"],["dc.contributor.author","Nèmec, N.-E."],["dc.contributor.author","Shapiro, A. I."],["dc.contributor.author","Krivova, N. A."],["dc.contributor.author","Solanki, S. K."],["dc.contributor.author","Tagirov, R. V."],["dc.contributor.author","Cameron, R. H."],["dc.contributor.author","Dreizler, S."],["dc.date.accessioned","2020-12-10T18:11:56Z"],["dc.date.available","2020-12-10T18:11:56Z"],["dc.date.issued","2020"],["dc.identifier.doi","10.1051/0004-6361/202037588"],["dc.identifier.eissn","1432-0746"],["dc.identifier.issn","0004-6361"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/74188"],["dc.notes.intern","DOI Import GROB-354"],["dc.title","Power spectra of solar brightness variations at various inclinations"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dspace.entity.type","Publication"]]