Portraying the hosts: Stellar science from planet searches

Information on the full session can be found on this website: https://sites.google.com/site/portrayingthehostscs18/We present a compendium of the splinter session on stellar science from planet searches that was organized as part of the Cool Stars 18 conference. Seven speakers discussed techniques to infer stellar information from radial velocity, transit and microlensing data, as well as new instrumentation and missions designed for planet searches that will provide useful for the study of the cool stars

The rotation–activity relation of M dwarfs : from K2 to TESS and PLATO

Studies of the rotation–activity relation of late‐type stars are essential to enhance our understanding of stellar dynamos and angular momentum evolution. We study the rotation–activity relation with K2 for M dwarfs, where it is especially poorly understood. We analyzed the light curves of all bright and nearby M dwarfs form the Superblink proper motion catalog that were in the K2 field of view. Using a sample of 430 M dwarfs observed in campaigns C0–C19 in long‐cadence mode, we determined the rotation period and a wealth of activity diagnostics. Our study of the rotation–activity relation based on photometric activity indicators confirmed the previously published abrupt change of the activity level at a rotation period of ∼10 days. Our sample, which is more than three times larger, increases the statistical significance of this finding.PostprintPeer reviewe

Activity and rotation of the X-ray emitting Kepler stars

The relation between magnetic activity and rotation in late-type stars provides fundamental information on stellar dynamos and angular momentum evolution. Rotation/activity studies found in the literature suffer from inhomogeneity in the measure of activity indexes and rotation periods. We overcome this limitation with a study of the X-ray emitting late-type main-sequence stars observed by XMM-Newton and Kepler. We measure rotation periods from photometric variability in Kepler light curves. As activity indicators, we adopt the X-ray luminosity, the number frequency of white-light flares, the amplitude of the rotational photometric modulation, and the standard deviation in the Kepler light curves. The search for X-ray flares in the light curves provided by the EXTraS (Exploring the X-ray Transient and variable Sky) FP-7 project allows us to identify simultaneous X-ray and white-light flares. A careful selection of the X-ray sources in the Kepler field yields 102 main-sequence stars with spectral types from A to M. We find rotation periods for 74 X-ray emitting main-sequence stars, 22 of which without period reported in the previous literature. In the X-ray activity/rotation relation, we see evidence for the traditional distinction of a saturated and a correlated part, the latter presenting a continuous decrease in activity towards slower rotators. For the optical activity indicators the transition is abrupt and located at a period of ~ 10 d but it can be probed only marginally with this sample which is biased towards fast rotators due to the X-ray selection. We observe 7 bona-fide X-ray flares with evidence for a white-light counterpart in simultaneous Kepler data. We derive an X-ray flare frequency of ~ 0.15 d^{-1} , consistent with the optical flare frequency obtained from the much longer Kepler time-series.Comment: Accepted for publication in A&A. 31 pages, 19 figure

What do comets 252P/LINEAR and P2016 BA14 have in common?

International audienceAutomated surveys of NEOs continue to discover objects in cometary-like orbits that are likely candidate parent bodies [1]. Some of them unexpectedly produce a comet-like comae and tails [2, 3]. Here, we study one such case, namely asteroid 2016 BA14 recently discovered by the Pan-STARRS survey, which shows cometary appearance and has a Tisserand parameter of 2.8. Moreover, the orbital similarly between P/2016 BA14 and comet 252P/LINEAR was pointed. If those JFCs split in the past, significant dust would have been released. We present a survey of results dealing with investigating the association of comets P/2016 BA14 and 252P/LINEAR with meteor showers observed on Earth. We carry out a further search to investigate the possible genetic relationship between the comets themselves too. To confirm the reality of the relation between a comet and a meteoroid stream it is necessary to investigate the evolution of their orbits. The model of generation and evolution of meteoroid stream in the solar system is taken from Vaubaillon et al. [4]. The ejections of meteoroids from the possible parent body surface took place when it was passing its perihelion between 1700 A.D. and 2016 A.D. Next, the orbits of ejected meteoroids were integrated to year 2079. We will show the similarities and differences of the two streams, and will conclude regarding the possible relationship between P/2016 BA14 and 252P/LINEAR.[1] Jenniskens, P., Meteor Showers and their Parent Comets (Cambridge University Press), 2006[2] Jewitt, D., AJ, 143, 66, 2012[3] Jewitt, D. and Li, J., AJ, 140, 1519, 2010[4] Vaubaillon, J., Colas, F. Jorda, L., A&A, 439, 751, 200

What do comets 252P/LINEAR and P2016 BA14 have in common?

International audienceAutomated surveys of NEOs continue to discover objects in cometary-like orbits that are likely candidate parent bodies [1]. Some of them unexpectedly produce a comet-like comae and tails [2, 3]. Here, we study one such case, namely asteroid 2016 BA14 recently discovered by the Pan-STARRS survey, which shows cometary appearance and has a Tisserand parameter of 2.8. Moreover, the orbital similarly between P/2016 BA14 and comet 252P/LINEAR was pointed. If those JFCs split in the past, significant dust would have been released. We present a survey of results dealing with investigating the association of comets P/2016 BA14 and 252P/LINEAR with meteor showers observed on Earth. We carry out a further search to investigate the possible genetic relationship between the comets themselves too. To confirm the reality of the relation between a comet and a meteoroid stream it is necessary to investigate the evolution of their orbits. The model of generation and evolution of meteoroid stream in the solar system is taken from Vaubaillon et al. [4]. The ejections of meteoroids from the possible parent body surface took place when it was passing its perihelion between 1700 A.D. and 2016 A.D. Next, the orbits of ejected meteoroids were integrated to year 2079. We will show the similarities and differences of the two streams, and will conclude regarding the possible relationship between P/2016 BA14 and 252P/LINEAR.[1] Jenniskens, P., Meteor Showers and their Parent Comets (Cambridge University Press), 2006[2] Jewitt, D., AJ, 143, 66, 2012[3] Jewitt, D. and Li, J., AJ, 140, 1519, 2010[4] Vaubaillon, J., Colas, F. Jorda, L., A&A, 439, 751, 200

EXTraS discovery of an X-ray superflare from an L dwarf

We present the first detection of an X-ray flare from an ultracool dwarf of spectral class L. The event was identified in the EXTraS database of XMM-Newton variable sources, and its optical counterpart, J0331−27, was found through a cross-match with the Dark Energy Survey Year 3 release. Next to an earlier four-photon detection of Kelu-1, J0331−27 is only the second L dwarf detected in X-rays, and much more distant than other ultracool dwarfs with X-ray detections (photometric distance of 240 pc). From an optical spectrum with the VIMOS instrument at the VLT, we determine the spectral type of J0331−27 to be L1. The X-ray flare has an energy of EX, F ∼ 2 × 1033 erg, placing it in the regime of superflares. No quiescent emission is detected, and from 2.5 Ms of XMM-Newton data we derive an upper limit of LX, qui <  1027 erg s−1. The flare peak luminosity (LX, peak = 6.3 × 1029 erg s−1), flare duration (τdecay ≈ 2400 s), and plasma temperature (≈16 MK) are similar to values observed in X-ray flares of M dwarfs. This shows that strong magnetic reconnection events and the ensuing plasma heating are still present even in objects with photospheres as cool as ∼2100 K. However, the absence of any other flares above the detection threshold of EX, F ∼ 2.5 × 1032 erg in a total of ∼2.5 Ms of X-ray data yields a flare energy number distribution inconsistent with the canonical power law dN/dE ∼ E−2, suggesting that magnetic energy release in J0331−27 – and possibly in all L dwarfs – takes place predominantly in the form of giant flares

Structure and function: Lipid A modifications in commensals and pathogens

AbstractLipopolysaccharides (LPS) of Gram negative bacteria are one of the most potent stimulators of the host innate immune system and LPS recognition is essential for the host organism to clear infections of invading bacterial pathogens. Here we review on the latest research on how LPS is sensed by host cells and how distinct LPS structures differentially modulate the strength of the host immune response. Much is known about host immunological reactions towards pathogens via recognition of their LPS, as well as strategies of pathogens to modulate their LPS structure in order to evade the immune system. However, less is known about differential sensing of lipopolysaccharides of commensal bacteria in the intestine and how this contributes to manifestation or destruction of the intestinal homeostasis. LPS sensing is necessary to fight pathogens. However, sensing of LPS of gut commensal bacteria can simultaneously be disadvantageous for the genetically predisposed host, since this might lead to damage of the intestinal homeostasis and therefore to chronic intestinal inflammation. However, less immunogenic LPS could also serve as therapeutics to antagonize an overreacting innate immune system. Therefore, commensal gut bacteria-derived LPS could prevent from uncontrolled intestinal immune response in the intestine which makes LPS an attractive therapeutical approach to treat e.g. IBD