Flat-spectrum Radio Continuum Emission Associated with ϵ Eridani

Rodrı́guez, Luis F.; Lizano, Susana; Loinard, Laurent; Chavez-Dagostino, Miguel; Bastian, T. S.; Beasley, A. J.

doi:10.3847/1538-4357/aaf9a6

Cited by 10 publications

(19 citation statements)

References 37 publications

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“…In our models, we adopt a coronal base density of 2 MK and number density of 10 10 cm −3 . These values produce a stellar wind with a mass-loss rate of 3 × 10 −12 M yr −1 , which is within the range of inferred values for other active K-stars (see Wood 2004;Jardine & Collier Cameron 2019;Rodríguez et al 2019).…”

Section: Modelling the Stellar Wind Of The Host Starsupporting

confidence: 83%

Tuning in to the radio environment of HD189733b

et al. 2019

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The hot Jupiter HD189733b is expected to be a source of strong radio emission, due to its close proximity to its magnetically active host star. Here, we model the stellar wind of its host star, based on reconstructed surface stellar magnetic field maps. We use the local stellar wind properties at the planetary orbit obtained from our models to compute the expected radio emission from the planet. Our findings show that the planet emits with a peak flux density within the detection capabilities of LOFAR. However, due to absorption by the stellar wind itself, this emission may be attenuated significantly. We show that the best time to observe the system is when the planet is near primary transit of the host star, as the attenuation from the stellar wind is lowest in this region.

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Section: Modelling the Stellar Wind Of The Host Starsupporting

confidence: 83%

Tuning in to the radio environment of HD189733b

et al. 2019

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“…We note that Cranmer & Saar (2011) predict a low´-M M 5 10 14    yr −1 using stellar wind models of cool stars driven by Alfvén waves and turbulence. This estimate is only a factor of 2 above the solar value, possibly suggesting that the M  values derived by Wood et al (2002) and Rodríguez et al (2019) may be significant overestimates.…”

Section: Free-free Emission From An Ionized Stellar Windmentioning

confidence: 76%

“…Fitting a standard wind model to the flat 6-50 GHz spectrum in Figure 4, Rodríguez et al (2019) argue that the 6-50 GHz continuum radiation from ò Eri is consistent with optically thin, free-free emission from a stellar wind with The standard wind spectrum assumed by Rodríguez et al (2019) predicts S ν ∝ν 0.6 at τ ν ?1. Such scaling is clearly disfavored by our 2-4GHz data, suggesting minimal wind contribution to the thermal emission from ò Eri.…”

Section: Free-free Emission From An Ionized Stellar Windmentioning

confidence: 88%

“…Bastian et al (2018) attribute the flat 6-50GHz spectrum to optically thick, thermal emission from active regions with a frequency-dependent filling factor. On the other hand, Rodríguez et al (2019) propose that it is optically thin, thermal free-free emission from a stellar wind. Here, in Sections 4.1 and 4.2, we discuss the optically thick 2-4GHz spectrum of ò Eri in the context of two plausible sources of thermal bremsstrahlung, respectively, a magnetically confined stellar corona, and an ionized stellar wind.…”

Section: Discussionmentioning

confidence: 99%

“…Table 2 summarizes detections of continuum emission from ò Eri over 2-300GHz (Lestrade & Thilliez 2015;MacGregor et al 2015;Chavez-Dagostino et al 2016;Booth et al 2017;Bastian et al 2018;Rodríguez et al 2019). While the millimeter-wave emission is attributed to optically thick chromospheric thermal emission (MacGregor et al 2015;Booth et al 2017), the remarkably flat 6-50GHz spectrum is believed to be produced either via optically thin, thermal freefree emission from a stellar wind (Rodríguez et al 2019), or through a combination of optically thick, thermal free-free and thermal gyroresonance radiation (Bastian et al 2018) from the stellar corona. Aside from these continuum emissions, Bastian et al (2018) also serendipitously detected a 5 minutelong, 1mJy flare at 2-4GHz.…”

Section: Introductionmentioning

confidence: 99%

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Detection of 2–4 GHz Continuum Emission from ϵ Eridani

Suresh

Chatterjee²,

Cordes³

et al. 2020

ApJ

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The nearby star ò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 ò 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 ò 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-windassociated 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 e yr −1 on the mass-loss rate from ò 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 ò Eridani.

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EMISSA (Exploring Millimeter Indicators of Solar-Stellar Activity)

Mohan

Wedemeyer

Pandit

et al. 2021

A&A

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Context. Due to their wide wavelength coverage across the millimeter to centimeter (mm–cm) range and their increased sensitivity, modern interferometric arrays facilitate observations of the thermal and non-thermal radiation that is emitted from different layers in the outer atmospheres of stars. Aims. We study the spectral energy distribution (Sobs(ν)) of main-sequence stars based on archival observations in the mm–cm range with the aim to study their atmospheric stratification as a function of stellar type. Methods. The main-sequence stars with significant detection in mm bands were identified in the ALMA Science Archive. These data were then complemented with spectral flux data in the extreme ultraviolet to cm range as compiled from various catalogues and observatory archives. We compared the resultant Sobs(ν) of each star with a photospheric emission model (Smod(ν)) calculated with the PHOENIX code. The departures of Sobs(ν) from Smod(ν) were quantified in terms of a spectral flux excess parameter (ΔS∕Smod) and studied as a function of stellar type. Results. The initial sample consists of 12 main-sequence stars across a broad range of spectral types from A1 to M3.5 and the Sun-as-a-star as reference. The stars with Teff = 3000–7000 K (F–M type) showed a systematically higher Sobs(ν) than Smod(ν) in the mm–cm range. Their ΔS∕Smod exhibits a monotonic rise with decreasing frequency. The steepness of this rise is higher for cooler stars in the Teff = 3000–7000 K range, although the single fully convective star (Teff ~ 3000 K) in the sample deviates from this trend. Meanwhile, Sobs(ν) of the A-type stars agrees with Smod(ν) within errors. Conclusions. The systematically high ΔS∕Smod in F–M stars indicates hotter upper atmospheric layers, that is, a chromosphere and corona in these stars, like for the Sun. The mm–cm ΔS∕Smod spectrum offers a way to estimate the efficiency of the heating mechanisms across various outer atmospheric layers in main-sequence stars, and thereby to understand their structure and activity. We emphasise the need for dedicated surveys of main-sequence stars in the mm–cm range.

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Flat-spectrum Radio Continuum Emission Associated with ϵ Eridani

Cited by 10 publications

References 37 publications

Tuning in to the radio environment of HD189733b

Tuning in to the radio environment of HD189733b

Detection of 2–4 GHz Continuum Emission from ϵ Eridani

EMISSA (Exploring Millimeter Indicators of Solar-Stellar Activity)

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