Karl Battams

PRELIMINARY ANALYSIS OF SOHO/STEREO OBSERVATIONS OF SUNGRAZING COMET ISON (C/2012 S1) AROUND PERIHELION

We present photometric and morphological analysis of the behavior of sungrazing comet C/2012 S1 ISON in Solar and Heliospheric Observatory (SOHO) and Solar TErrestrial RElations Observatory (STEREO) images around its perihelion on 2013 November 28.779 UT. ISON brightened gradually November 20-26 with a superimposed outburst on November 21.3-23.5. The slope of brightening changed about November 26.7 and was significantly steeper in SOHOs orange and clear filter images until November 27.9 when it began to flatten out, reaching a peak about November 28.1 (r H ≈ 17 R ☉), then fading before brightening again from November 28.6 (r H ≈ 5 R ☉) until disappearing behind the occulting disk. ISON brightened continuously as it approached perihelion while visible in all other telescopes/filters. The central condensation disappeared about November 28.5 and the leading edge became progressively more elongated until perihelion. These photometric and morphological behaviors are reminiscent of the tens of meter-sized Kreutz comets regularly observed by SOHO and STEREO and strongly suggest that the nucleus of ISON was destroyed prior to perihelion. This is much too small to support published gas production rates and implies significant mass loss and/or disruption in the days and weeks leading up to perihelion. No central condensation was seen post-perihelion. The post-perihelion lightcurve was nearly identical in all telescopes/filters and fell slightly steeper than . This implies that the brightness was dominated by reflected solar continuum off of remnant dust in the coma/tail and that any remaining active nucleus was <10 m in radius.

Destruction of Sun-Grazing Comet C/2011 N3 (SOHO) Within the Low Solar Corona

Star Grazing Some comets come perilously close to the Sun. Schrijver et al. (p. 324; see the Perspective by Lisse) describe observations made by the Solar Dynamics Observatory of one such Sun-grazing comet, which penetrated into, fragmented, and completely sublimated within the solar atmosphere. More than 2000 Sun-grazing comets have been observed in the past 15 years but none could be followed into the Suns atmosphere. By showing that comets can be observed at such small distances from the Sun, this study opens up new ways to study comets and also the solar atmosphere. The NASA Solar Dynamics Observatory detected and tracked a comet as it penetrated the solar atmosphere. Observations of comets in Sun-grazing orbits that survive solar insolation long enough to penetrate into the Sun’s inner corona provide information on the solar atmosphere and magnetic field as well as on the makeup of the comet. On 6 July 2011, the Solar Dynamics Observatory (SDO) observed the demise of comet C/2011 N3 (SOHO) within the low solar corona in five wavelength bands in the extreme ultraviolet (EUV). The comet penetrated to within 0.146 solar radius (~100,000 kilometers) of the solar surface before its EUV signal disappeared. Before that, material released into the coma—at first seen in absorption—formed a variable EUV-bright tail. During the final 10 minutes of observation by SDO’s Atmospheric Imaging Assembly, ~6 × 108 to 6 × 1010 grams of total mass was lost (corresponding to an effective nucleus diameter of ~10 to 50 meters), as estimated from the tail’s deceleration due to interaction with the surrounding coronal material; the EUV absorption by the comet and the brightness of the tail suggest that the mass was at the high end of this range. These observations provide evidence that the nucleus had broken up into a family of fragments, resulting in accelerated sublimation in the Sun’s intense radiation field.

SOHO comets: 20 years and 3000 objects later

We present a summary of the more than 3000 sungrazing and near-Sun comets discovered in coronagraph images returned by the Solar and Heliospheric Observatory (SOHO), since its launch in December 1995. We address each of the four main populations of objects observed by SOHO: Kreutz (sungrazing) group, Meyer group, Marsden and Kracht (96P-family) group and non-group comets. Discussions for each group include basic properties, discovery statistics and morphological appearance. In addition to updating the community on the status of the discoveries by SOHO, we also show that the rate of discovery of Kreutz sungrazers has probably remained static since approximately 2003 and we report on the first likely fragmentation pair observed within the Meyer group. This article is part of the themed issue ‘Cometary science after Rosetta’.

GONE IN A BLAZE OF GLORY: THE DEMISE OF COMET C/2015 D1 (SOHO)

We present studies of C/2015 D1 (SOHO), the first sunskirting comet ever seen from ground stations over the past half century. The Solar and Heliospheric Observatory (SOHO) witnessed its peculiar light curve with a huge dip followed by a flareup around perihelion: the dip was likely caused by sublimation of olivines, directly evidenced by a coincident temporary disappearance of the tail. The flareup likely reflects a disintegration event, which we suggest was triggered by intense thermal stress established within the nucleus interior. Photometric data reveal an increasingly dusty coma, indicative of volatile depletion. A catastrophic mass loss rate of

Stream mining for solar physics: Applications and implications for big solar data

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Dynamic Sublimation Pressure and the Catastrophic Breakup of Comet ISON

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Sunskirting comets discovered with the LASCO coronagraphs over the decade 1996–2008

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Comet C/2011 W3 (Lovejoy) between 2 and 10 Solar Radii: Physical Parameters of the Comet and the Corona

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Fine-Scale Structure in Cometary Dust Tails I: : Analysis of Striae in Comet C/2006 P1 (McNaught) through Temporal Mapping

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A Global Survey of EUV Corona Power Spectra

around perihelion was seen. Ground-based Xingming Observatory spotted the post-perihelion debris cloud. Our morphological simulations of post-perihelion images find newly released dust grains of size