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Thread: Wolf 359 - updates on SF's favorite red dwarf flare star

  1. #1
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    Smile Wolf 359 - updates on SF's favorite red dwarf flare star

    Wolf 359 (CN Leonis) is well known in astronomy and science fiction alike for being so close to our Sun in the stellar neighborhood. Here is some recent research on the M-dwarf. No planets found yet, just lots of violent flare activity.



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    http://iopscience.iop.org/article/10...72/aabaf4/meta

    New Perspectives of our Nearby Red Dwarf Neighbor Wolf 359 from the Kepler K2 Mission

    Edward F. Guinan and Scott G. Engle
    2018 April 6

    Wolf 359 (GJ 406; CN Leo), at a distance of 2.41 ± 0.01 pc, is the nearest star, after α Cen and Barnard's Star. Wolf 359 is a chromospherically active M6 V star with strong Hα emission (Pavlenko et al. 2006; Mann et al. 2015) and moderate coronal X-ray emissions (LX ≈ 1–5 × 1027 erg s−1—Fuhrmeister et al. 2007). The star's strong chromospheric emissions, fast rotation (see below), and frequent flares, indicate that Wolf 359 is a young star (age lesssim 0.8 Gyr). But the lack of Lithium lines and moderately large space motions (U,V,W = −26, −44, −18 km s−1) could indicate an older age. Wolf 359 also has a special place in science fiction folklore, as it is where the United Federation of Planets suffered a devastating defeat at the hands of the Borg Collective in 2367 (Okuda et al. 1999).

    Wolf 359 was recently observed by the Kepler K2 mission during Campaign 14, from 2017 May to August. Excellent high precision photometry was obtained for over 80 days. The K2 PDCsap fluxes are plotted (converted to magnitudes) in Figure 1 (top). Frequent flares (some with E > 1033 erg) are seen. Simultaneous multi-wavelength X-ray to radio observations were also carried out (Quintana et al. 2017; Thackeray et al. 2018; Villadsen et al. 2018). The second panel shows a 20 days data sample (flares removed) plotted on an expanded magnitude scale that shows small, quasi-sinusoidal light variations. These presumably arise from the rotational modulation due to an uneven longitudinal distribution of starspots. Analysis of the K2 photometry with the Analysis of Variance algorithm, as implemented in Peranso (Paunzen & Vanmunster 2016), returns a very strong periodic signal with P = 2.705 ± 0.007 days with a power >700. Subtle cycle-to cycle variations indicate small changes of the starspot distributions. The bottom panel of the figure (left) shows the phased K2 light curve (flares removed) with a mean amplitude of 0.0048 mag. Although Wolf 359 has been included in planet search studies, no planets have been reported. The K2 photometry shows no evidence of periodic planet transits.

    Wolf 359 lies near, possibly beyond, the low mass/cool limit of our Rotation–Activity–Age relations for M0–6 V stars (Engle & Guinan 2018). Using these relations, we find conflicting values where the period (P = 2.705 days) indicates age < 500 Myr. However, the <Lx> =3 x 10^27 erg s−1 is >10× smaller than young, rapidly rotating M3–5 V stars in our sample, indicating age ~ 1.7 +1.2 -0.8 Gyr (from LX–Age—Guinan et al. 2016), which is in marginally better agreement with its kinematics-inferred older age. The handful of older M6+ stars in our program with reliable ages, including TRAPPIST-1 (M8 V; P = 3.295 days; age = 7.6 ± 2.2 Gyr (Burgasser & Mamajek 2017)), rotate rapidly. This could indicate that old, low mass M stars with fast rotations, like TRAPPIST-1 and maybe Wolf 359, could have different magnetic dynamos resulting in smaller magnetic-wind breaking. However these questions are beyond the scope of this note.

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    http://adsabs.harvard.edu/abs/2018AAS...23134908W

    8-12 GHz Radio Observations of Flare Activity On M dwarf CN Leo

    Wofford, Alia; Villadsen, Jackie; Quintana, Elisa; Barclay, Thomas; Thackeray, Beverly
    01/2018

    Red dwarfs are cool stars that make up 70% of all stars. Red dwarfs can be utilized to detect potentially habitable planets but they have particularly strong magnetic activity that can be detrimental to orbiting planets' atmospheres and habitability. A coronal mass ejection (CME) is an eruption of magnetized plasma from the star that is ejected into the interplanetary medium which can erode a planet's atmosphere daily. Based on the sun CMEs are expected to produce very bright radio bursts along with optical flares. We are using M dwarf CN Leo, a well studied flare star that was in the K2 campaign field in summer 2017, as a template to understand the relationship between radio and optical flares and the space weather conditions impacting M dwarf planets. Using radio frequencies ranging from 0.22 GHz-12 GHz we search for simultaneous radio bursts and optical flares to infer if CMEs, flares or aurorae are occurring on the star. I will present the 8-12 GHz radio data from eight 1.5-hour observations with simultaneous optical data. CN Leo produced a bright non-thermal radio flare that lasted approximately for a day during two consecutive observations, with a gyrosynchrotron emission mechanism.

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    http://articles.adsabs.harvard.edu/c...;filetype=.pdf

    Polarimetric Observations of Flare Stars

    Beskin, G.; Karpov, S.; Plokhotnichenko, V.; Stepanov, A.; Tsap, Yu.
    06/2017

    Here we present the results of our long-term observations of flaring stars with MANIA high temporal resolution equipment in polarimetric regime. More than forty flares from UV Ceti, EV Lacertae, Wolf 424 and CN Leo have been observed, and upper limits on its polarization have been derived on the level of about 1%, except for the one unique event --- the giant flare of UV Ceti in 2008 with the amplitude of about 3 magnitudes in U-band. Near flare maximum more than a dozen of spike bursts have been discovered with sub-second durations and intrinsic polarizations exceeding 30-40%. We argue that these events are synchrotron emission of electron beams with the energies of several hundred MeV moving in the magnetic field of about 1.4 kG. Emission from such ultrarelativistic (with energies far exceeding 10 MeV) particles is being routinely observed in solar flares, but has never been detected from UV Ceti type stars. This is the first ever detection of linearly polarized optical light from the UV Ceti-type stars which indicates that at least some fraction of the flaring events on these stars are powered by a non-thermal synchrotron emission mechanism.

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    http://adsabs.harvard.edu/abs/2018AAS...23133407V

    Radio Monitoring of K2 Flare Star Wolf 359

    Villadsen, Jacqueline; Wofford, Alia; Quintana, Elisa; Barclay, Thomas; Thackeray, Beverly
    01/2018

    Understanding M dwarf activity, including flares and eruptions, is important for characterizing exoplanet habitability. Active M dwarf Wolf 359, a well-known flare star, was in the Kepler K2 Campaign 14 field, with continuous high-cadence optical photometry throughout summer 2017. We have conducted a multi-wavelength observing campaign of this star to characterize the magnetic activity that would impact planets around such a star. I will present multi-band radio observations of this star, covering 250-500 MHz, 1-2 GHz, and 8-12 GHz, during a period with simultaneous optical photometry from K2. The higher frequency observations are sensitive to the population of non-thermal electrons in the stellar magnetosphere, and the low-frequency observations offer the potential to detect stellar ejecta.

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    http://adsabs.harvard.edu/abs/2018AAS...23132601T

    Simultaneous, multi-wavelength flare observations of nearby low-mass stars

    Thackeray, Beverly; Barclay, Thomas; Quintana, Elisa; Villadsen, Jacqueline; Wofford, Alia; Schlieder, Joshua; Boyd, Patricia
    01/2018

    Low-mass stars are the most common stars in the Galaxy and have been targeted in the tens-of-thousands by K2, the re-purposed Kepler mission, as they are prime targets to search for and characterize small, Earth-like planets. Understanding how these fully convective stars drive magnetic activity that manifests as stochastic, short-term brightenings, or flares, provides insight into the prospects of planetary habitability. High energy radiation and energetic particle emission associated with these stars can erode atmospheres, and impact habitability. An innovative campaign to study low mass stars through simultaneous multi-wavelength observations is currently underway with observations ongoing in the X-ray, UV, optical, and radio. I will present early results of our pilot study of the nearby M-Dwarf star Wolf 359 (CN Leo) using K2, SWIFT, and ground based radio observatories, forming a comprehensive picture of flare activity from an M-Dwarf, and discuss the potential impact of these results on exoplanets.


    ARTICLE RELATED TO:

    https://www.hou.usra.edu/meetings/ha...7/pdf/4069.pdf
    Simultaneous, Multi-Wavelength Flare Observations of the M dwarf Wolf 359.
    E. V. Quintana, T. Barclay, J. Schlieder, P. Boyd, and B. Thackeray-Lacko
    There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
    — Mark Twain, Life on the Mississippi (1883)

  2. #2
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    An offbeat tidbit I noticed about Wolf 359 a year or so ago - it lies just barely inside the zone of sky where the Earth transits (so as soon as they have a Kepler equivalent, we're found), surely the closest stellar neighbor of which this is true. The proper motion of the star is so large that it only entered the zone a few centuries ago and will spend only a couple of millennia in it.

    I rather look forward to seeing this as a plot point somewhere.

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    @ngc3314,

    Can you provide links to any articles about the visibility of transits of the Sun by planets in our system as seen from other stars? I did a quick Web search which was unsuccessful, but that doesn't mean much.

    One can use Celestia to find the orbits of Solar planets across the stars as seen from the center of the Sun. This shows the center of those viewing regions, but finding their boundaries is a bit more difficult.

    FWIW, here's a screengrab of Celestia showing Wolf 359's position on the sky as seen from the center of the sun.

    The white background grid shows the ecliptic coordinate system. The lowermost blue line is the Earth's orbit projected against it (i.e. the ecliptic itself). The other blue lines are the orbits of the other planets projected onto the sky.
    Attached Images Attached Images
    Selden

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    Quote Originally Posted by selden View Post
    @ngc3314,

    Can you provide links to any articles about the visibility of transits of the Sun by planets in our system as seen from other stars? I did a quick Web search which was unsuccessful, but that doesn't mean much.
    Not that I've run across.


    One can use Celestia to find the orbits of Solar planets across the stars as seen from the center of the Sun. This shows the center of those viewing regions, but finding their boundaries is a bit more difficult.

    FWIW, here's a screengrab of Celestia showing Wolf 359's position on the sky as seen from the center of the sun.

    The white background grid shows the ecliptic coordinate system. The lowermost blue line is the Earth's orbit projected against it (i.e. the ecliptic itself). The other blue lines are the orbits of the other planets projected onto the sky.
    To the accuracy that a planet's orbit is circular and one can ignore the component of the sun's barycentric motion in the plane of the planet's orbit (which are pretty good for the major planets), the zone where a transit is seen is the outward projection of the orbit and angles on either side up to the Sun's apparent radius as seen from the planet. I happened across Wolf 359 on looking it up in Guide9 and seeing a similar display with the ecliptic. Using Celestia, since it gives you the planets' orbits as seen from the Sun anyway, you can usually take the angular boundaries from the apparent size of the Sun from each planet as the halfwidth of the transit zone. (For Mercury and Mars in particular, that varies enough around the orbit that you;d have to include its changes for edge cases).

  5. #5
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    Thanks!

    In principle at least, one could write Lua code that'd be run by Celestia to create a list stars close enough to the appropriate orbital planes. I'll have to leave that to someone else, though. It's not a project that I can embark on just now.
    Selden

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    Ah, that's a homework problem I've assigned to students in my exoplanets class: aliens in how many star systems in our neighborhood would be able to see transits by planets in front of our Sun?

    One way to answer it is to compute the ecliptic coordinates of the stars in some good catalog, then simply pick out the objects with ecliptic latitudes which are small. The exact limit you choose depends on your criterion: only the Earth transiting? Any planet? Transiting in the next few years? Transiting at any time in the last 100,000 years?

    As I recall, the answers can range from a few tens to a few hundreds.

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    Quote Originally Posted by ngc3314 View Post
    To the accuracy that a planet's orbit is circular and one can ignore the component of the sun's barycentric motion in the plane of the planet's orbit (which are pretty good for the major planets), the zone where a transit is seen is the outward projection of the orbit and angles on either side up to the Sun's apparent radius as seen from the planet. I happened across Wolf 359 on looking it up in Guide9 and seeing a similar display with the ecliptic. Using Celestia, since it gives you the planets' orbits as seen from the Sun anyway, you can usually take the angular boundaries from the apparent size of the Sun from each planet as the halfwidth of the transit zone. (For Mercury and Mars in particular, that varies enough around the orbit that you;d have to include its changes for edge cases).
    This gnawed at me later so I need to clarify - apparent radius of the Sun from the planet is the half-width of that band.

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    Quote Originally Posted by ngc3314 View Post
    This gnawed at me later so I need to clarify - apparent radius of the Sun from the planet is the half-width of that band.
    The half-width of the band is apparent radius of Sun plus apparent radius of Earth. And remember to take account of the variability of these radii along zodiac.

    So just draw the band of proper with along zodiac and see which stars/planets are there. Or take the ecliptic coordinates of stars and just look at latitudes. Right ascension needs to be checked only for the fairly narrow range of variability of the said latitude limits - eccentricity of Earth is just 0,0167.

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    Wolf 359 is certainly an active little dwarf. Huge flares.


    http://cdsads.u-strasbg.fr/abs/2019AAS...23346508B

    Multi-wavelength Flare Observations of Wolf 359 from Earth and Space

    Barclay, Thomas; Afanasev, Dennis; Quintana, Elisa
    American Astronomical Society, AAS Meeting #233, id.#465.08 (01/2019)

    Wolf 359 is a nearby red dwarf that produces frequent flares, which are unpredictable increases in stellar brightness caused by the sudden release of magnetic energy. Kepler's extended mission, K2, observed Wolf 359 for over 80 days with high-precision 1-minute photometry in 2017. Wolf 359 exhibited hundreds of flares in the K2 data, each more energetic than the Sun's Carrington flare, the largest recorded geomagnetic storm on Earth. To understand this flare activity with the underlying physical processes, we obtained simultaneous observations of Wolf 359 in the UV, X-ray, and radio using Swift, HST, and ground-based radio observatories. I will present results from our multiwavelength campaign of Wolf 359, and discuss our plans to observe a large sample of low-mass stars that span a wide range of masses and ages with TESS and other multiwavelength facilities. Low-mass stars like Wolf 359 are the most common stars in the galaxy and are the most common type of exoplanet host star. Our long-term goal of this program is to understand the impact of flares on the potential habitability of exoplanets.
    There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
    — Mark Twain, Life on the Mississippi (1883)

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