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Register a new userThe Origin of Solar Filament Plasma Inferred from in situ Observations of Elemental Abundances
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Solar filaments/prominences are one of the most common features in the corona, which may lead to energetic coronal mass ejections (CMEs) and flares when they erupt. Filaments are about one hundred times cooler and denser than the coronal material, and physical understanding of their material origin remains controversial. Two types of scenarios have been proposed: one argues that the filament plasma is brought into the corona from photosphere or chromosphere through a siphon or evaporation/injection process, while the other suggests that the material condenses from the surrounding coronal plasma due to thermal instability. The elemental abundance analysis is a reasonable clue to constrain the models, as the siphon or evaporation/injection model would predict that the filament material abundances are close to the photospheric or chromospheric ones, while the condensation model should have coronal abundances. In this letter, we analyze the elemental abundances of a magnetic cloud that contains the ejected filament material. The corresponding filament eruption occurred on 1998 April 29, accompanying an M6.8 class soft X-ray flare located at the heliographic coordinates S18E20 (NOAA 08210) and a fast halo CME with the linear velocity of 1374 km s$^{-1}$ near the Sun. We find that the abundance ratios of elements with low and high First Ionization Potential such as Fe/O, Mg/O, and Si/O are 0.150, 0.050, and 0.070, respectively, approaching their corresponding photospheric values 0.065, 0.081, and 0.066, which does not support the coronal origin of the filament plasma.
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In the present work, we analyze a filament eruption associated with an ICME that arrived at L1 on August 5th, 2011. In multi-wavelength SDO/AIA images, three plasma parcels within the filament were tracked at high-cadence along the solar corona. A novel absorption diagnostic technique was applied to the filament material travelling along the three chosen trajectories to compute the column density and temperature evolution in time. Kinematics of the filamentary material were estimated using STEREO/EUVI and STEREO/COR1 observations. The Michigan Ionization Code used inputs of these density, temperature, and speed profiles for the computation of ionization profiles of the filament plasma. Based on these measurements we conclude the core plasma was in near ionization equilibrium, and the ionization states were not frozen-in at the altitudes where they were visible in absorption in AIA images. Additionally, we report that the filament plasma was heterogeneous, and the filamentary material was continuously heated as it expanded in the low solar corona.
Helioseismology has shown that the chemical composition of the Sun has changed over its lifetime. The surface abundance of helium and heavy elements is believed to have decreased by up to 10% relative to their initial values. However, this reduction is too small to be tested by direct observations of the photospheric chemical composition. Here, we compare the predicted variations in the solar photospheric composition with precise measurements of abundances in meteorites and the solar wind composition. Although elemental composition ratios can vary by roughly a percent (e. g. for Ca/Mg and Ca/Fe) over the Suns lifetime, their measurements are rife with uncertainties related to uncertainties in the interpretation of meteoritic measurements, photospheric determinations, and the complex fractionation processes occurring between the upper photosphere and lower chromosphere and the corona. On the other hand, isotopic ratios can be measured much more accurately and are not expected to be affected as much by extrasolar processes, although more work is required to quantify their effect. As the isotopic ratios evolve in the Sun proportionally to the mass ratios of the isotopes, light elements yield the highest variations in isotopic ratios. They are predicted to reach as high as 0.6% for $^{18}$O/$^{16}$O and are only slightly lower in the cases of $^{26}$Mg/$^{24}$Mg and $^{30}$Si/$^{28}$Si. Such a value should be well within the sensitivity of new missions such as Genesis.
The Apache Point Observatory Galactic Evolution Experiment (APOGEE) has observed $sim$600 transiting exoplanets and exoplanet candidates from textit{Kepler} (Kepler Objects of Interest, KOIs), most with $geq$18 epochs. The combined multi-epoch spectra are of high signal-to-noise (typically $geq$100) and yield precise stellar parameters and chemical abundances. We first confirm the ability of the APOGEE abundance pipeline, ASPCAP, to derive reliable [Fe/H] and effective temperatures for FGK dwarf stars -- the primary textit{Kepler} host stellar type -- by comparing the ASPCAP-derived stellar parameters to those from independent high-resolution spectroscopic characterizations for 221 dwarf stars in the literature. With a sample of 282 close-in ($P<100$ days) KOIs observed in the APOGEE KOI goal program, we find a correlation between orbital period and host star [Fe/H] characterized by a critical period, $P_mathrm{crit}$= $8.3^{+0.1}_{-4.1}$ days, below which small exoplanets orbit statistically more metal-enriched host stars. This effect may trace a metallicity dependence of the protoplanetary disk inner-radius at the time of planet formation or may be a result of rocky planet ingestion driven by inward planetary migration. We also consider that this may trace a metallicity dependence of the dust sublimation radius, but find no statistically significant correlation with host $T_mathrm{eff}$ and orbital period to support such a claim.
Elements with low First Ionization Potential (FIP) are known to be three to four times more abundant in active region loops of the solar corona than in the photosphere. There have been observations suggesting that this observed FIP bias may be different in other parts of the solar corona and such observations are thus important in understanding the underlying mechanism. The Solar X-ray Monitor (XSM) on board the Chandrayaan-2 mission carried out spectroscopic observations of the Sun in soft X-rays during the 2019-20 solar minimum, considered to be the quietest solar minimum of the past century. These observations provided a unique opportunity to study soft X-ray spectra of the quiescent solar corona in the absence of any active regions. By modelling high resolution broadband X-ray spectra from XSM, we estimate the temperature and emission measure during periods of possibly the lowest solar X-ray intensity. We find that the derived parameters remain nearly constant over time with a temperature around 2 MK, suggesting the emission is dominated by X-ray Bright Points (XBPs). We also obtain the abundances of Mg, Al, and Si relative to H, and find that the FIP bias is ~2, lower than the values observed in active regions.
A filament, a dense cool plasma supported by the magnetic fields in the solar corona, often becomes unstable and erupts. It is empirically known that the filament often demonstrates some activations such as a turbulent motion prior to eruption. In our previous study (Seki et al. 2017), we analysed the Doppler velocity of an H{alpha} filament and found that the standard deviation of the line-of-sight-velocity (LOSV) distribution in a filament, which indicates the increasing amplitude of the small-scale motions, increased prior to the onset of the eruption. Here, we present a further analysis on this filament eruption, which initiated approximately at 03:40UT on 2016 November 5 in the vicinity of NOAA AR 12605. It includes a coronal line observation and the extrapolation of the surrounding magnetic fields. We found that both the spatially averaged micro-turbulence inside the filament and the nearby coronal line emission increased 6 and 10 hours prior to eruption, respectively. In this event, we did not find any significant changes in the global potential-field configuration preceding the eruption for the past 2 days, which indicates that there is a case in which it is difficult to predict the eruption only by tracking the extrapolated global magnetic fields. In terms of space weather prediction, our result on the turbulent motions in a filament could be used as the useful precursor of a filament eruption.
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