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Showing 1-3 of about 3 results.
Flare Rates, Rotation Periods, and Spectroscopic Activity Indicators of a Volume-complete Sample of Mid- to Late-M Dwarfs within 15 pcMedina, Amber A.Winters, Jennifer G.Irwin, Jonathan M.Charbonneau, DavidDOI: info:10.3847/1538-4357/abc686v. 905107
Medina, Amber A., Winters, Jennifer G., Irwin, Jonathan M., and Charbonneau, David. 2020. "Flare Rates, Rotation Periods, and Spectroscopic Activity Indicators of a Volume-complete Sample of Mid- to Late-M Dwarfs within 15 pc." The Astrophysical Journal 905:107.
ID: 158738
Type: article
Authors: Medina, Amber A.; Winters, Jennifer G.; Irwin, Jonathan M.; Charbonneau, David
Abstract: We present a study of flare rates, rotation periods, and spectroscopic activity indicators of 125 single stars within 15 parsecs and with masses between 0.1 and 0.3 M? observed during the first year of the TESS mission, with the goal of elucidating the relationship between these various magnetically connected phenomena. We gathered multiepoch high-resolution spectra of each target, and we measured equivalent widths of the activity indicators helium I D3, Ha, and the calcium infrared triplet line at 8542.09 Å. We present 18 new rotation periods from MEarth photometry and 19 new rotation periods from TESS photometry. We present a catalog of 1392 flares. After correcting for sensitivity, we find the slope of the flare frequency distribution for all stars to have a standard value of a = 1.98 ± 0.02. We determine R31.5, the rate of flares per day with energies above E = 3.16 × 1031 ergs in the TESS bandpass. We find that below a critical value of Ha EW = -0.71 Å, log R31.5 increases linearly with increasing Ha emission; above this value, log R31.5 declines rapidly. The stars divide into two groups: 26% have Ha in emission, high flare rates with typical values of log R31.5 = -1.30 ± 0.08, and have Rossby numbers = -1.30 ± 0.08, and have Rossby numbers 31.5 < -3.86, with the majority of these stars not showing a single flare during the TESS observations.
Three Red Suns in the Sky: A Transiting, Terrestrial Planet in a Triple M-dwarf System at 6.9 pcWinters, Jennifer G.Medina, Amber A.Irwin, Jonathan M.Charbonneau, DavidAstudillo-Defru, NicolaHorch, Elliott P.Eastman, Jason D.Halley Vrijmoet, EliotHenry, Todd J.Diamond-Lowe, HannahWinston, ElaineBarclay, ThomasBonfils, XavierRicker, George R.Vanderspek, RolandLatham, David W.Seager, SaraWinn, Joshua N.Jenkins, Jon M.Udry, StéphaneTwicken, Joseph D.Teske, Johanna K.Tenenbaum, PeterPepe, FrancescoMurgas, FelipeMuirhead, Philip S.Mink, JessicaLovis, ChristopheLevine, Alan M.Lépine, SébastienJao, Wei-ChunHenze, Christopher E.Furész, GáborForveille, ThierryFigueira, PedroEsquerdo, Gilbert A.Dressing, Courtney D.Díaz, Rodrigo F.Delfosse, XavierBurke, Christopher J.Bouchy, FrançoisBerlind, PerryAlmenara, Jose-ManuelDOI: info:10.3847/1538-3881/ab364dv. 158152
Winters, Jennifer G., Medina, Amber A., Irwin, Jonathan M., Charbonneau, David, Astudillo-Defru, Nicola, Horch, Elliott P., Eastman, Jason D., Halley Vrijmoet, Eliot, Henry, Todd J., Diamond-Lowe, Hannah, Winston, Elaine, Barclay, Thomas, Bonfils, Xavier, Ricker, George R., Vanderspek, Roland, Latham, David W., Seager, Sara, Winn, Joshua N., Jenkins, Jon M., Udry, Stéphane, Twicken, Joseph D., Teske, Johanna K., Tenenbaum, Peter, Pepe, Francesco, Murgas, Felipe et al. 2019. "Three Red Suns in the Sky: A Transiting, Terrestrial Planet in a Triple M-dwarf System at 6.9 pc." The Astronomical Journal 158:152.
ID: 154724
Type: article
Authors: Winters, Jennifer G.; Medina, Amber A.; Irwin, Jonathan M.; Charbonneau, David; Astudillo-Defru, Nicola; Horch, Elliott P.; Eastman, Jason D.; Halley Vrijmoet, Eliot; Henry, Todd J.; Diamond-Lowe, Hannah; Winston, Elaine; Barclay, Thomas; Bonfils, Xavier; Ricker, George R.; Vanderspek, Roland; Latham, David W.; Seager, Sara; Winn, Joshua N.; Jenkins, Jon M.; Udry, Stéphane; Twicken, Joseph D.; Teske, Johanna K.; Tenenbaum, Peter; Pepe, Francesco; Murgas, Felipe; Muirhead, Philip S.; Mink, Jessica; Lovis, Christophe; Levine, Alan M.; Lépine, Sébastien; Jao, Wei-Chun; Henze, Christopher E.; Furész, Gábor; Forveille, Thierry; Figueira, Pedro; Esquerdo, Gilbert A.; Dressing, Courtney D.; Díaz, Rodrigo F.; Delfosse, Xavier; Burke, Christopher J.; Bouchy, François; Berlind, Perry; Almenara, Jose-Manuel
Abstract: We present the discovery from Transiting Exoplanet Survey Satellite (TESS) data of LTT 1445Ab. At a distance of 6.9 pc, it is the second nearest transiting exoplanet system found to date, and the closest one known for which the primary is an M dwarf. The host stellar system consists of three mid-to-late M dwarfs in a hierarchical configuration, which are blended in one TESS pixel. We use MEarth data and results from the Science Processing Operations Center data validation report to determine that the planet transits the primary star in the system. The planet has a radius of {1.38}-0.12+0.13 {R}\oplus , an orbital period of {5.35882}-0.00031+0.00030 days, and an equilibrium temperature of {433}-27+28 K. With radial velocities from the High Accuracy Radial Velocity Planet Searcher, we place a 3σ upper mass limit of 8.4 {M}\oplus on the planet. LTT 1445Ab provides one of the best opportunities to date for the spectroscopic study of the atmosphere of a terrestrial world. We also present a detailed characterization of the host stellar system. We use high-resolution spectroscopy and imaging to rule out the presence of any other close stellar or brown dwarf companions. Nineteen years of photometric monitoring of A and BC indicate a moderate amount of variability, in agreement with that observed in the TESS light-curve data. We derive a preliminary astrometric orbit for the BC pair that reveals an edge-on and eccentric configuration. The presence of a transiting planet in this system hints that the entire system may be co- planar, implying that the system may have formed from the early fragmentation of an individual protostellar core.
Electron-Ion Equilibrium and Shock Precursors in the Northeast Limb of the Cygnus LoopMedina, Amber A.Raymond, John C.Edgar, Richard J.Caldwell, NelsonFesen, Robert A.Milisavljevic, DanDOI: info:10.1088/0004-637X/791/1/30v. 79130
Medina, Amber A., Raymond, John C., Edgar, Richard J., Caldwell, Nelson, Fesen, Robert A., and Milisavljevic, Dan. 2014. "Electron-Ion Equilibrium and Shock Precursors in the Northeast Limb of the Cygnus Loop." The Astrophysical Journal 791:30.
ID: 128146
Type: article
Authors: Medina, Amber A.; Raymond, John C.; Edgar, Richard J.; Caldwell, Nelson; Fesen, Robert A.; Milisavljevic, Dan
Abstract: We present an observational study using high-resolution echelle spectroscopy of collisionless shocks in the Cygnus Loop supernova remnant. Measured Hα line profiles constrain pre-shock heating processes, shock speeds, and electron-ion equilibration (Te /Ti ). The shocks produce faint Hα emission line profiles, which are characterized by narrow and broad components. The narrow component is representative of the pre-shock conditions, while the broad component is produced after charge transfer between neutrals entering the shock and protons in the post-shock gas, thus reflecting the properties of the post-shock gas. We observe a diffuse Hα region extending about 2.'5 ahead of the shock with line width ~29 km s-1, while the Hα profile of the shock itself consists of broader than expected narrow (36 km s-1) and broad (250 km s-1) components. The observed diffuse emission arises in a photoionization precursor heated to about 18,000 K by He I and He II emission from the shock, with additional narrow component broadening originating from a thin cosmic-ray precursor. Broad to narrow component intensity ratios of ~1.0 imply full electron-ion temperature equilibration Te ~= Ti in the post-shock region. Broad component line widths indicate shock velocities of about 400 km s-1. Combining the shock velocities with proper motions suggests that the distance to the Cygnus Loop is ~890 pc, significantly greater than the generally accepted upper limit of 637 pc.