Magnetic Flaring in the Pre–Main‐Sequence Sun and Implications for the Early Solar System

Abstract

To address the role of energetic processes in the solar nebula, we provide a detailed characterization of magnetic flaring in stellar analogs of the pre-main-sequence Sun based on two 0.5 day observations of the Orion Nebula cluster obtained with the Chandra X-Ray Observatory. The sample consists of 43 stars with masses between 0.7 and 1.4 M and ages from less than 0.3 to '10 Myr. We find that the X-ray luminosities measured in the 0.5-8 keV band are strongly elevated over main-sequence levels with an average log L X h i¼ 30:3 ergs s À1 and log L X =L Ã h i¼ À3:9. The X-ray emission is strongly variable within our exposures in nearly all solar analogs; about 30 flares with 29:0 ergs s À1 < log L X ðpeakÞ < 31:5 ergs s À1 on timescales from 0.5 to more than 12 hr are seen during the Chandra observations. Analogs of the 1 Myr old premain-sequence Sun exhibited X-ray flares that are 10 1.5 times more powerful and 10 2.5 times more frequent than the most powerful flares seen on the contemporary Sun. Radio observations indicate that acceleration of particles to relativistic energies is efficient in young stellar flares. Extrapolating the solar relationship between X-ray luminosity and proton fluence, we infer that the young Sun exhibited a 10 5 -fold enhancement in energetic protons compared to contemporary levels. Unless the flare geometries are unfavorable, this inferred proton flux on the disk is sufficient to produce the observed meteoritic abundances of several important short-lived radioactive isotopes. Our study thus strengthens the astronomical foundation for local proton spallation models of isotopic anomalies in carbonaceous chondritic meteorites. The radiation, particles, and shocks produced by the magnetic reconnection flares seen with Chandra may also have flash-melted meteoritic chondrules and produce excess 21 Ne seen in meteoritic grains.

Ionization and heating by X-rays and cosmic rays

“…These same flares occur at a rate about 10 2.5 higher than the rate of the largest solar flares. As solar proton fluxes scale non-linearly with the solar X-ray luminosity, Feigelson et al (2002) estimated a proton flux for "T Tauri Sun" about 10 5 times higher than at present (i.e., 10 7 protons cm −2 s −1 at 1 AU). Given the high flare rate, this flux was probably present almost continuously.…”

“…Feigelson et al (2002) estimated the proton flux at 1 AU of a solar analog in its T Tauri phase, from a statistical X-ray study of T Tauri stars in the Orion Nebula Cluster. They found that frequent flares on T Tauri stars are 10 1.5 times more luminous than the largest solar flares (or 10 4 times more than solar flares that occur with a daily frequency).…”

Short-lived nuclei in the early Solar System: Possible AGB sources

“…In particular, Feigelson and his colleagues have consistently presented both observational and theoretical evidence that they must occur (see recent report by [287]). There are extensive recent studies of irradiation models referred to earlier in the text.…”

The weak-line T Tauri star V410 Tau

“…As regards the second feature that the flare activity may explain: both the anomalous abundances of elemental isotopes in chondrules and the inclusions of the most pristine carbonaceous chondrites, as well as the high abundances of daughter products of some short-lived nuclides, all point to high-energy processes that occurred during the early stages of our Solar System (see, e.g., Feigelson et al 2002;Gounelle et al 2001). Although external phenomena, like supernova explosions, have been used to explain these abundances, it has been suggested that they could also be due to spallation reactions from energetic (MeV) protons and ions originating in magnetic reconnection flares (see also Goswami et al 2001;Marhas et al 2002;Leya et al 2003).…”