1,721,490 research outputs found
Fetal hemoglobin reactivation and cell engineering in the treatment of sickle cell anemia
No full textDetection of 2–4 GHz Continuum Emission from ϵ Eridani
Get PDFThe nearby star epsilon Eridani has been a frequent target of radio surveys for stellar emission and extraterrestrial intelligence. Using deep 2–4 GHz observations with the Very Large Array, we have uncovered a 29 μJy compact, steady continuum radio source coincident with epsilon Eridani to within 0."06 (⩽2σ; 0.2 au at the distance of the star). Combining our data with previous high-frequency continuum detections of epsilon Eridani, our observations reveal a spectral turnover at 6 GHz. We ascribe the 2–6 GHz emission to optically thick, thermal gyroresonance radiation from the stellar corona, with thermal free–free opacity likely becoming relevant at frequencies below 1 GHz. The steep spectral index (α ≃ 2) of the 2–6 GHz spectrum strongly disfavors its interpretation as stellar-wind-associated thermal bremsstrahlung (α ≃ 0.6). Attributing the entire observed 2–4 GHz flux density to thermal free–free wind emission, we thus derive a stringent upper limit of 3 × 10⁻¹¹ M_⊙ yr⁻¹ on the mass-loss rate from epsilon Eridani. Finally, we report the nondetection of flares in our data above a 5σ threshold of 95 μJy. Together with the optical nondetection of the most recent stellar maximum expected in 2019, our observations postulate a likely evolution of the internal dynamo of epsilon Eridani
Estudio espectrográfico de Ru Eridani
No full textLa binaria eclipsante RU Eridani (P=0.63 d; V=9.35 mag) fue observada espectroscópicamente desde Cerro Tololo en una dispersión de 43 Å/mm. Se muestran resultados preliminares del análisis de 33 espectrogramas de este sistema que era muy poco conocido desde el punto de vista espectroscópico.Asociación Argentina de Astronomí
Coronal Mass Ejections and Type II Radio Emission Variability during a Magnetic Cycle on the Solar-type Star ϵ Eridani
Get PDFInternational audienceWe simulate possible stellar coronal mass ejection (CME) scenarios over the magnetic cycle of ϵ Eridani (18 Eridani; HD 22049). We use three separate epochs from 2008, 2011, and 2013, and estimate the radio emission frequencies associated with these events. These stellar eruptions have proven to be elusive, although a promising approach to detect and characterize these phenomena are low-frequency radio observations of potential type II bursts as CME-induced shocks propagate through the stellar corona. Stellar type II radio bursts are expected to emit below 450 MHz, similarly to their solar counterparts. We show that the length of time these events remain above the ionospheric cutoff is not necessarily dependent on the stellar magnetic cycle, but more on the eruption location relative to the stellar magnetic field. We find that these type II bursts would remain within the frequency range of LOFAR for a maximum of 20-30 minutes post-eruption for the polar CMEs (50 minutes for second harmonics). We find evidence of slower equatorial CMEs, which result in slightly longer observable windows for the 2008 and 2013 simulations. Stellar magnetic geometry and strength have a significant effect on the detectability of these events. We place the CMEs in the context of the stellar mass-loss rate (27-48× solar mass-loss rate), showing that they can amount to 3%-50% of the stellar wind mass-loss rate for ϵ Eridani. Continuous monitoring of likely stellar CME candidates with low-frequency radio telescopes will be required to detect these transient events
Tidally heated exomoons around Ïμ Eridani b: Observability and prospects for characterization
No full textContext. Exomoons are expected to orbit gas giant exoplanets just as moons orbit Solar System planets. Tidal heating is present in Solar System satellites, and it can heat up their interior, depending on their orbital and interior properties. Aims. We aim to identify a tidally heated exomoon's (THEM) orbital parameter space that would make it observable in infrared wavelengths with MIRI/JWST around Ïμ Eridani b. We study the possible constraints on orbital eccentricity and interior properties that a successful THEM detection in infrared wavelengths can bring. We also investigate what exomoon properties need to be independently known in order to place these constraints. Methods. We used a coupled thermal-tidal model to find stable equilibrium points between the tidally produced heat and the heat transported within a moon. For the latter, we considered a spherical and radially symmetric satellite with heat being transported via magma advection in a sublayer of melt (asthenosphere) and convection in the lower mantle. We incorporated uncertainties in the interior and tidal model parameters to assess the fraction of simulated moons that would be observable with MIRI. Results. We find that a 2RIo THEM orbiting Ïμ Eridani b with an eccentricity of 0.02 would need to have a semi-major axis of 4 planetary Roche radii for 100% of the simulations to produce an observable moon. These values are comparable with the orbital properties of the satellites of the Solar System gas giants. We placed similar constraints for eccentricities up to 0.1. We conclude that if the semi-major axis and radius of the moon are known (e.g., with exomoon transits), tidal dissipation can constrain the orbital eccentricity and interior properties of the satellite, such as the presence of melt and the thickness of the melt-containing sublayer.Astrodynamics & Space Mission
The crucial role of surface magnetic fields for stellar dynamos: Epsilon Eridani, 61 Cygni A, and the Sun
Get PDFCool main-sequence stars, such as the Sun, have magnetic fields which are
generated by an internal dynamo mechanism. In the Sun, the dynamo mechanism
produces a balance between the amounts of magnetic flux generated and lost over
the Sun's 11-year activity cycle and it is visible in the Sun's different
atmospheric layers using multi-wavelength observations. We used the same
observational diagnostics, spanning several decades, to probe the emergence of
magnetic flux on the two close by, active- and low-mass K dwarfs: 61 Cygni A
and Epsilon Eridani. Our results show that 61 Cygni A follows the Solar dynamo
with a regular cycle at all wavelengths, while Epsilon Eridani represents a
more extreme level of the Solar dynamo, while also showing strong Solar-like
characteristics. For the first time we show magnetic butterfly diagrams for
stars other than the Sun. For the two K stars and the Sun, the rate at which
the toroidal field is generated from surface poloidal field is similar to the
rate at which toroidal flux is lost through flux emergence. This suggests that
the surface field plays a crucial role in the dynamos of all three stars.
Finally, for Epsilon Eridani, we show that the two chromospheric cycle periods,
of ~3 and ~13 years, correspond to two superimposed magnetic cycles.Comment: 8 pages, 5 figures: Accepted by A&
Possible Detection of Gamma-Rays from Epsilon Eridani
No full textWe use the Fermi Large Area Telescope gamma-ray observatory to search for gamma-ray emission from four nearby, debris disk-hosting main-sequence stars: tau Ceti, epsilon Eridani, Fomalhaut, and Vega. For three stars (tau Ceti, Fomalhaut, and Vega), we establish upper limits that are consistent with theoretical expectations. For epsilon Eridani, we find a possible spatially coincident source with a soft energy spectrum of dN/dE similar to E-3.6. However, at this stage we are unable to rule out that this emission is due to a more extended feature in the diffuse background. In the interpretation that the emission is due to e Eridani, the >100 MeV gamma-ray luminosity is similar to 10(27) erg s(-1)similar or equal to 3 x 10(-7) L-circle dot, which is similar to 10(10 )times the gamma-ray luminosity from the disk of the quiet Sun. We find less than or similar to 2 sigma evidence of source variability over a similar to 7 yr timescale. In the interpretation that the gamma-ray emission is from e Eridani itself, we consider two possible models: (1) cosmic-ray collisions with solid bodies in the debris disk, which extends out similar to 60 au from the host star, and (2) emission from the stellar activity. For the former model, assuming a total disk mass consistent with infrared measurements, we find that the size distribution of bodies is steeper than expected for a collisional cascade state. If confirmed as being associated with epsilon Eridani, this would be the first indication of gamma-ray emission from the vicinity of a main-sequence star other than the Sun.</p
Hiding Dust around ϵ Eridani
No full textWith a Jupiter-like exoplanet and a debris disk with both asteroid and Kuiper Belt analogs, ϵ Eridani has a fascinating resemblance to our expectations for a young solar system. We present a deep Hubble Space Telescope/Space Telescope Imaging Spectrograph coronographic data set using eight orbit visits and the point-spread function calibrator δ Eridani. While we were unable to detect the debris disk, we place stringent constraints on the scattered light surface brightness of We combine this scattered light detection limit with a reanalysis of archival near- and mid-infrared observations and a dynamical model of the full planetary system to refine our model of the ϵ Eridani debris disk components. Radiative transfer modeling suggests an asteroid belt analog inside of 3 au, an intermediate disk component in the 6–37 au region, and a Kuiper Belt analog colocated with the narrow belt observed in the millimeter (69 au). Modeling also suggests a large minimum grain size requiring either very porous grains or a suppression of small grain production, and a radially stratified particle size distribution. The inner disk regions require a steep power-law slope ( s ^−3.8 where s is the grain size) weighted toward smaller grains and the outer disk prefers a shallower slope ( s ^−3.4 ) with a minimum particle size of >2 μ m. These conclusions will be enhanced by upcoming coronagraphic observations of the system with the James Webb Space Telescope, which will pinpoint the radial location of the dust belts and further diagnose the dust particle properties
The magnetic fields of EF Eridani and BL Hydri
No full textWe present near-infrared spectroscopic observations of the AM Herculis systems EF Eridani and BL Hydri over the wavelength range 0.9 to 2.5 μm. During these observations, broad and resolvable cyclotron emission harmonics were visible near 1.05, 1.30, 1.70 and 2.20 μm in EF Eridani, and near 1.25, 1.60 and 2.20 μm in BL Hydri. We interpret these features as arising from cyclotron emission regions located near the polar caps of the white dwarf of magnetic field strength B = 23 MG in BL Hydri, and from two separate cyclotron emission regions of field strengths B = 16.5 and 21 MG in EF Eridani.Peer-reviewe
On the planetary system ε Eridani
No full textBackman, Marengo et al (2008;) report on new observations of the planetary system Epsilon Eridani, which provide hints of a structure similar to the Solar system’s. Using a simple method, we analyse the possible orbital parameters of the innermost planets of the system
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