Magnetic fields and differential rotation on the pre-main sequence

Maps of magnetic field topologies of rapidly rotating stars obtained over the last decade or so have provided unique insight into the operation of stellar dynamos. However, for solar-type stars many of the targets imaged to date have been lower-mass zero-age main sequence stars. We present magnetic maps and differential rotation measurements of two-higher mass pre-main sequence stars HD 106506 (~10 Myrs) and HD 141943 (~15 Myrs). These stars should evolve into mid/late F-stars with predicted high differential rotation and little magnetic activity. We investigate what effect the extended convection zones of these pre-main sequence stars has on their differential rotation and magnetic topologies. ©2009 American Institute of Physic

Football Game Program 3 1965

Football Game Program 3 196

Discovery of the magnetic field in the B1/B2V star sigma Lupi

The ultraviolet stellar wind lines of the photometrically periodic variable early B-type star sigma Lupi were found to behave very similarly to what has been observed in known magnetic B stars, although no periodicity could be determined. AAT spectropolarimetric measurements with SEMPOL were obtained. We detected a longitudinal magnetic field with varying strength and amplitude of about 100 G with error bars of typically 20 G. This type of variability supports an oblique magnetic rotator model. We fold the equivalent width of the 4 usable UV spectra in phase with the well-known photometric period of 3.019 days, which we identify with the rotation period of the star. The magnetic field variations are consistent with this period. Additional observations with ESPaDOnS attached to the CFHT strongly confirmed this discovery, and allowed to determine a precise magnetic period. Like in the other magnetic B stars the wind emission likely originates in the magnetic equatorial plane, with maximum emission occurring when a magnetic pole points towards the Earth. The 3.0182 d magnetic rotation period is consistent with the photometric period, with maximum light corresponding to maximum magnetic field. No helium or other chemical peculiarity is known for this object.Comment: 2 pages, 2 figures, to appear in the proceedings of IAU Symposium 272, Active OB stars - structure, evolution, mass loss, and critical limit

Validating AU Microscopii d with Transit Timing Variations

AU Mic is a young (22 Myr) nearby exoplanetary system that exhibits excess TTVs that cannot be accounted for by the two known transiting planets nor stellar activity. We present the statistical "validation" of the tentative planet AU Mic d (even though there are examples of "confirmed" planets with ambiguous orbital periods). We add 18 new transits and nine midpoint times in an updated TTV analysis to prior work. We perform the joint modeling of transit light curves using EXOFASTv2 and extract the transit midpoint times. Next, we construct an O-C diagram and use Exo-Striker to model the TTVs. We generate TTV log-likelihood periodograms to explore possible solutions for the period of planet d and then follow those up with detailed TTV and RV MCMC modeling and stability tests. We find several candidate periods for AU Mic d, all of which are near resonances with AU Mic b and c of varying order. Based on our model comparisons, the most-favored orbital period of AU Mic d is 12.73596+/-0.00793 days (T_{C,d}=2458340.55781+/-0.11641 BJD), which puts the three planets near a 4:6:9 mean-motion orbital resonance. The mass for d is 1.053+/-0.511 M_E, making this planet Earth-like in mass. If confirmed, AU Mic d would be the first known Earth-mass planet orbiting a young star and would provide a valuable opportunity in probing a young terrestrial planet's atmosphere. Additional TTV observation of the AU Mic system are needed to further constrain the planetary masses, search for possible transits of AU Mic d, and detect possible additional planets beyond AU Mic c.Comment: 89 pages, 35 figures, 34 tables. Redid EXOFASTv2 transit modeling to recover more reasonable stellar posteriors, so redid Exo-Striker TTV modeling for consistency. Despite these changes, the overall results remain unchanged: the 12-7-day case is still the most favored. Submitted to AAS Journals on 2023 Feb 9t

Validating AU Microscopii d with Transit Timing Variations

AU Mic is a young (22 Myr), nearby exoplanetary system that exhibits excess transit timing variations (TTVs) that cannot be accounted for by the two known transiting planets nor stellar activity. We present the statistical “validation” of the tentative planet AU Mic d (even though there are examples of “confirmed” planets with ambiguous orbital periods). We add 18 new transits and nine midpoint times in an updated TTV analysis to prior work. We perform the joint modeling of transit light curves using EXOFASTv2 and extract the transit midpoint times. Next, we construct an O − C diagram and use Exo-Striker to model the TTVs. We generate TTV log-likelihood periodograms to explore possible solutions for d’s period, then follow those up with detailed TTV and radial velocity Markov Chain Monte Carlo modeling and stability tests. We find several candidate periods for AU Mic d, all of which are near resonances with AU Mic b and c of varying order. Based on our model comparisons, the most-favored orbital period of AU Mic d is 12.73596 ± 0.00793 days ( T _C _,d = 2458340.55781 ± 0.11641 BJD), which puts the three planets near 4:6:9 mean-motion resonance. The mass for d is 1.053 ± 0.511 M _⊕ , making this planet Earth-like in mass. If confirmed, AU Mic d would be the first known Earth-mass planet orbiting a young star and would provide a valuable opportunity in probing a young terrestrial planet’s atmosphere. Additional TTV observations of the AU Mic system are needed to further constrain the planetary masses, search for possible transits of AU Mic d, and detect possible additional planets beyond AU Mic c

Vetting of 384 TESS Objects of Interest with TRICERATOPS and Statistical Validation of 12 Planet Candidates

We present TRICERATOPS, a new Bayesian tool that can be used to vet and validate TESS Objects of Interest (TOIs). We test the tool on 68 TOIs that have been previously confirmed as planets or rejected as astrophysical false positives. By looking in the false positive probability (FPP) -- nearby false positive probability (NFPP) plane, we define criteria that TOIs must meet to be classified as validated planets (FPP < 0.015 and NFPP < 10^-3), likely planets (FPP 10^-1). We apply this procedure on 384 unclassified TOIs and statistically validate 12, classify 125 as likely planets, and classify 52 as likely nearby false positives. Of the 12 statistically validated planets, 9 are newly validated. TRICERATOPS is currently the only TESS vetting and validation tool that models transits from nearby contaminant stars in addition to the target star. We therefore encourage use of this tool to prioritize follow-up observations that confirm bona fide planets and identify false positives originating from nearby stars.Comment: Accepted to A

Improving ecosystem health in highly altered river basins: a generalized framework and its application to the Mississippi-Atchafalaya River Basin

Continued large-scale public investment in declining ecosystems depends on demonstrations of “success”. While the public conception of “success” often focuses on restoration to a pre-disturbance condition, the scientific community is more likely to measure success in terms of improved ecosystem health. Using a combination of literature review, workshops and expert solicitation we propose a generalized framework to improve ecosystem health in highly altered river basins by reducing ecosystem stressors, enhancing ecosystem processes and increasing ecosystem resilience. We illustrate the use of this framework in the Mississippi-Atchafalaya River Basin (MARB) of the central United States (U.S.), by (i) identifying key stressors related to human activities, and (ii) creating a conceptual ecosystem model relating those stressors to effects on ecosystem structure and processes. As a result of our analysis, we identify a set of landscape-level indicators of ecosystem health, emphasizing leading indicators of stressor removal (e.g., reduced anthropogenic nutrient inputs), increased ecosystem function (e.g., increased water storage in the landscape) and increased resilience (e.g., changes in the percentage of perennial vegetative cover). We suggest that by including these indicators, along with lagging indicators such as direct measurements of water quality, stakeholders will be better able to assess the effectiveness of management actions. For example, if both leading and lagging indicators show improvement over time, then management actions are on track to attain desired ecosystem condition. If, however, leading indicators are not improving or even declining, then fundamental challenges to ecosystem health remain to be addressed and failure to address these will ultimately lead to declines in lagging indicators such as water quality. Although our model and indicators are specific to the MARB, we believe that the generalized framework and the process of model and indicator development will be valuable in an array of altered river basins

Estimating magnetic filling factors from Zeeman–Doppler magnetograms

V.S., S.P.M., and A.J.F.acknowledge funding from the European Research Council (ERC) under the European Unions Horizon 2020 research and innovation programme (grant agreement No. 682393 AWESoMeStars). S.B.S. acknowledges funding via the Austrian Space Application Programme (ASAP) of the Austrian Research Promotion Agency (FFG) within ASAP11, the FWF NFN project S11601-N16 and the sub-project S11604-N16. A. A.V. acknowledges funding received from the Irish Research Council Laureate Awards 2017/2018.Low-mass stars are known to have magnetic fields that are believed to be of dynamo origin. Two complementary techniques are principally used to characterize them. Zeeman–Doppler imaging (ZDI) can determine the geometry of the large-scale magnetic field while Zeeman broadening can assess the total unsigned flux including that associated with small-scale structures such as spots. In this work, we study a sample of stars that have been previously mapped with ZDI. We show that the average unsigned magnetic flux follows an activity-rotation relation separating into saturated and unsaturated regimes. We also compare the average photospheric magnetic flux recovered by ZDI, BV, with that recovered by Zeeman broadening studies, BI. In line with previous studies, BV ranges from a few % to ~20% of BI. We show that a power-law relationship between BV and BI exists and that ZDI recovers a larger fraction of the magnetic flux in more active stars. Using this relation, we improve on previous attempts to estimate filling factors, i.e., the fraction of the stellar surface covered with magnetic field, for stars mapped only with ZDI. Our estimated filling factors follow the well-known activity-rotation relation, which is in agreement with filling factors obtained directly from Zeeman broadening studies. We discuss the possible implications of these results for flux tube expansion above the stellar surface and stellar wind models.Publisher PDFPeer reviewe

A database of marine phytoplankton abundance, biomass and species composition in Australian waters

There have been many individual phytoplankton datasets collected across Australia since the mid 1900s, but most are unavailable to the research community. We have searched archives, contacted researchers, and scanned the primary and grey literature to collate 3,621,847 records of marine phytoplankton species from Australian waters from 1844 to the present. Many of these are small datasets collected for local questions, but combined they provide over 170 years of data on phytoplankton communities in Australian waters. Units and taxonomy have been standardised, obviously erroneous data removed, and all metadata included. We have lodged this dataset with the Australian Ocean Data Network (http://portal.aodn.org.au/) allowing public access. The Australian Phytoplankton Database will be invaluable for global change studies, as it allows analysis of ecological indicators of climate change and eutrophication (e.g., changes in distribution; diatom:dinoflagellate ratios). In addition, the standardised conversion of abundance records to biomass provides modellers with quantifiable data to initialise and validate ecosystem models of lower marine trophic levels