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Article: The radio properties of the DME flare star Proxima Centauri

TitleThe radio properties of the DME flare star Proxima Centauri
Authors
KeywordsPolarization
Radiation Mechanisms: Nonthermal
Radio Continuum: Stars
Stars: Flare
Stars: Individual (Proxima Centauri)
Issue Date1996
PublisherInstitute of Physics Publishing Ltd. The Journal's web site is located at http://iopscience.iop.org/2041-8205
Citation
Astrophysical Journal Letters, 1996, v. 460 n. 2 PART I, p. 976-983 How to Cite?
AbstractWe present radio observations of the dM5.5e flare star Proxima Centauri at 20, 13, 6, and 3.5 cm. The star was only detected during an impulsive, highly circularly polarized, and apparently narrow-band flare at 20 cm, similar to those seen on other dMe flare stars. This flare was detected in just ∼1.7 hr of observing time spanning an ∼12 hr period, suggesting that Proxima Cen may be a prolific producer of coherent bursts at 20 cm. On the other hand, despite ∼30 hr of observing time at both 6 and 3.5 cm over a 4 yr period, the star was not detected as either a flaring or a quasi-steady (quiescent) source at these wavelengths. We place an upper limit of ∼2 × 10 11 ergs Hz -1 s -1 on its radio luminosity at 6 and 3.5 cm, the lowest detection threshold yet reached for a star other than the Sun. This upper limit is approximately equal to the radio luminosity of the active Sun (i.e., at or close to the peak on its activity cycle) outside of flares. Our results place important constraints on the filling factor of ∼500-1000 G magnetic loops containing X-ray-emitting plasma on Proxima Cen. Because such loops should be optically thick to gyroresonance emission at centimeter wavelengths, their filling factor can be inferred directly from the measured stellar radio flux density. Our radio results imply that loops at temperatures ∼2 × 107 K, representative of the hot stellar X-ray component, have a filling factor of ≤13%. Loops at temperatures ∼3 × 10 6 K, similar in temperature to the nonflaring solar active region corona, have a filling factor of ≤88%. Our results are compatible with present empirical relationships for the magnetic field parameters of late-type dwarf stars as applied to Proxima Cen. Based on its measured rotation period (P rot ≈ 41 days) and the ratio of its soft X-ray to bolometric luminosity (L x/L bo1 ≈ 2.4 × 10 -4), these relationships predict that Proxima Cen should be about an order of magnitude below the saturation limit in magnetic activity, where the entire surface of stars is thought to be covered by kilogauss X-ray loops. We compare our results with the contrasting case of UV Ceti, a dM5.5e flare star that according to the same empirical relationships should be approximately as magnetically active as Proxima Cen. UV Ceti, however, displays quiescent radio emission with a luminosity that is more than an order of magnitude higher than the upper limit placed on Proxima Cen. Our radio observations place an upper limit of ∼7 × 10 -12 M ⊙ yr -1 on the mass-loss rate by any stellar wind (assumed to have a velocity of 300 km s -1) from Proxima Cen. This upper limit is almost 2 orders of magnitude lower than that inferred by Mullan et al. from millimeter wavelength observations of other dMe flare stars. We show that the high mass-loss rate inferred by Mullan et al. is untenable if our present understanding of the centimeter wavelength radio emission of dMe flare stars is correct. © 1996. The American Astronomical Society. All rights reserved.
Persistent Identifierhttp://hdl.handle.net/10722/174948
ISSN
2015 Impact Factor: 5.487
2015 SCImago Journal Rankings: 3.369
References

 

DC FieldValueLanguage
dc.contributor.authorLim, Jen_US
dc.contributor.authorWhite, SMen_US
dc.contributor.authorSlee, OBen_US
dc.date.accessioned2012-11-26T08:48:19Z-
dc.date.available2012-11-26T08:48:19Z-
dc.date.issued1996en_US
dc.identifier.citationAstrophysical Journal Letters, 1996, v. 460 n. 2 PART I, p. 976-983en_US
dc.identifier.issn2041-8205en_US
dc.identifier.urihttp://hdl.handle.net/10722/174948-
dc.description.abstractWe present radio observations of the dM5.5e flare star Proxima Centauri at 20, 13, 6, and 3.5 cm. The star was only detected during an impulsive, highly circularly polarized, and apparently narrow-band flare at 20 cm, similar to those seen on other dMe flare stars. This flare was detected in just ∼1.7 hr of observing time spanning an ∼12 hr period, suggesting that Proxima Cen may be a prolific producer of coherent bursts at 20 cm. On the other hand, despite ∼30 hr of observing time at both 6 and 3.5 cm over a 4 yr period, the star was not detected as either a flaring or a quasi-steady (quiescent) source at these wavelengths. We place an upper limit of ∼2 × 10 11 ergs Hz -1 s -1 on its radio luminosity at 6 and 3.5 cm, the lowest detection threshold yet reached for a star other than the Sun. This upper limit is approximately equal to the radio luminosity of the active Sun (i.e., at or close to the peak on its activity cycle) outside of flares. Our results place important constraints on the filling factor of ∼500-1000 G magnetic loops containing X-ray-emitting plasma on Proxima Cen. Because such loops should be optically thick to gyroresonance emission at centimeter wavelengths, their filling factor can be inferred directly from the measured stellar radio flux density. Our radio results imply that loops at temperatures ∼2 × 107 K, representative of the hot stellar X-ray component, have a filling factor of ≤13%. Loops at temperatures ∼3 × 10 6 K, similar in temperature to the nonflaring solar active region corona, have a filling factor of ≤88%. Our results are compatible with present empirical relationships for the magnetic field parameters of late-type dwarf stars as applied to Proxima Cen. Based on its measured rotation period (P rot ≈ 41 days) and the ratio of its soft X-ray to bolometric luminosity (L x/L bo1 ≈ 2.4 × 10 -4), these relationships predict that Proxima Cen should be about an order of magnitude below the saturation limit in magnetic activity, where the entire surface of stars is thought to be covered by kilogauss X-ray loops. We compare our results with the contrasting case of UV Ceti, a dM5.5e flare star that according to the same empirical relationships should be approximately as magnetically active as Proxima Cen. UV Ceti, however, displays quiescent radio emission with a luminosity that is more than an order of magnitude higher than the upper limit placed on Proxima Cen. Our radio observations place an upper limit of ∼7 × 10 -12 M ⊙ yr -1 on the mass-loss rate by any stellar wind (assumed to have a velocity of 300 km s -1) from Proxima Cen. This upper limit is almost 2 orders of magnitude lower than that inferred by Mullan et al. from millimeter wavelength observations of other dMe flare stars. We show that the high mass-loss rate inferred by Mullan et al. is untenable if our present understanding of the centimeter wavelength radio emission of dMe flare stars is correct. © 1996. The American Astronomical Society. All rights reserved.en_US
dc.languageengen_US
dc.publisherInstitute of Physics Publishing Ltd. The Journal's web site is located at http://iopscience.iop.org/2041-8205en_US
dc.relation.ispartofAstrophysical Journal Lettersen_US
dc.subjectPolarizationen_US
dc.subjectRadiation Mechanisms: Nonthermalen_US
dc.subjectRadio Continuum: Starsen_US
dc.subjectStars: Flareen_US
dc.subjectStars: Individual (Proxima Centauri)en_US
dc.titleThe radio properties of the DME flare star Proxima Centaurien_US
dc.typeArticleen_US
dc.identifier.emailLim, J: jjlim@hku.hken_US
dc.identifier.authorityLim, J=rp00745en_US
dc.description.naturelink_to_subscribed_fulltexten_US
dc.identifier.scopuseid_2-s2.0-21344465375en_US
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-21344465375&selection=ref&src=s&origin=recordpageen_US
dc.identifier.volume460en_US
dc.identifier.issue2 PART Ien_US
dc.identifier.spage976en_US
dc.identifier.epage983en_US
dc.publisher.placeUnited Kingdomen_US
dc.identifier.scopusauthoridLim, J=7403453870en_US
dc.identifier.scopusauthoridWhite, SM=7404079906en_US
dc.identifier.scopusauthoridSlee, OB=45361510400en_US

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