THE BEHAVIOR OF THE SPOTLESS ACTIVE REGIONS DURING THE SOLAR MINIMUM 23-24 Alexandre José de Oliveira e Silva(UNIVAP) Caius Lucius Selhorst (NAT-UNICSUL) 28th September, 2017

Outline Abstract Introduction Data Analyses and Results Final Remarks References Outline

In this work, we analysed the physical parameters of the spotless actives regions observed during solar minimum 23 – 24 (2007 – 2010). The study was based on radio maps at 17 GHz obtained by the Nobeyama Radioheliograph (NoRH) and magnetograms provided by the Michelson Doppler Imager (MDI) on board the Solar and Heliospheric Observatory (SOHO). The results shows that the spotless active regions presents the same radio characteristics of a ordinary one, they can live in the solar surface for long periods (>10 days), and also can present small flares. The long-lived active regions tend to be associated to sunspots during part of their live. While some active regions with sunspots were formed with the presence of very weak magnetic fields (~300 G), there were spotless active regions with strong ones, up to 2500 G. Key words. Sun: general - Sun: radio radiation - Sun: magnetograms - Sun: sunspots, Sun: actives regions Abstract

continuous loss of correlation between the classical solar indexes (SSN x F10.7) Selhorst et al. (2014) studied the number of active regions observed by the NoRH at 17 GHz between the years 1992 and 2013: presence of active regions during days without sunspots (during the quiet solar period 2008 - 2009) regions with magnetic field intensity < 1500 G (Livingston et al. 2012). In this work, we investigated the physical parameters of the spotless actives regions observed during solar minimum period between 2007 and 2010. Introduction

Data Analyses and Results The active regions at 17 GHz were identified as follow: i) size greater than 150 pixels2 (~ 300MSS (millionth solar surface)); ii) latitudes between ±45º; iii) maximum brightness temperature (TBmax) at least 40% greater than the quiet Sun value; iv) discard active regions in limb (< 70º Long.). A total of 47 spotless active regions were identified. 77 days with sunspots and 141 without them Data Analyses and Results

Data Analyses and Results Fig 1 shows the distribution of the number of active regions (with or without sunspots) in relation to their lifetime. Data Analyses and Results Spotless active regions Active regions with spots

Data Analyses and Results Fig 2. The relation between the active region flux and their maximum brightness temperature (TBmax). The size of circles are proportional to the percentage of active regions in each group. Data Analyses and Results Spotless active regions Active regions with spots

Data Analyses and Results Fig 3. Comparison of the active regions Tbmax in relation to |B|max. Data Analyses and Results Spotless active regions Active regions with spots

Data Analyses and Results Fig 4. TBmax (circle) and |Bmax| (diamond), 2008, jan 03-12, in red, days with active region and blue, days without sunspots. The orange dashed line shows the maximum moment of Flare C1.1 (15:27) on January 7,2008. Data Analyses and Results Spotless active regions Active regions with spots

Data Analyses and Results Exemple of spotless and sunspot active regions at ALMA images and NoRH maps. Polygon indicate spotless regions and ellipse indicate sunspots regions. Data Analyses and Results

there were spotless active regions with strong ones, up to 2500 G a total of 47 distinct active regions were analysed (2007-2010) about 50% of them were ephemeral living a maximum of three days. except for 3 active regions, those ones living 5 days more presented at least one day with a sunspot. active regions with sunspots are hotter and presented more flux (than the spotless ones) active regions with sunspots were formed magnetic fields (~300 G) there were spotless active regions with strong ones, up to 2500 G Final Remarks 

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We would like to thank the Nobeyama Radioheliograph, which is operated by the NAOJ/Nobeyama Solar Radio Observatory and SOHO/Michelson Doppler Imager (MDI). A.J.O.S. acknowledge the scholarship form CAPES. C.L.S. acknowledge financial support from the São Paulo Research Foundation (FAPESP), grants #2014/10489-0 and #2017/13112-2. Acknowledgements

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