First Ionization Potential Effect Research Articles

THE CORONAL ABUNDANCE ANOMALIES OF M DWARFS

We analyze Chandra X-ray spectra of the M0 V+M0 V binary GJ 338. As quantified by X-ray surface flux, these are the most inactive M dwarfs ever observed with X-ray grating spectroscopy. We focus on measuring coronal abundances, in particular searching for evidence of abundance anomalies related to First Ionization Potential (FIP). In the solar corona and wind, low FIP elements are overabundant, which is the so-called "FIP effect." For other stars, particularly very active ones, an "inverse FIP effect" is often observed, with low FIP elements being underabundant. For both members of the GJ 338 binary, we find evidence for a modest inverse FIP effect, consistent with expectations from a previously reported correlation between spectral type and FIP bias. This amounts to strong evidence that all M dwarfs should exhibit the inverse FIP effect phenomenon, not just the active ones. We take the first step towards modeling the inverse FIP phenomenon in M dwarfs, building on past work that has demonstrated that MHD waves coursing through coronal loops can lead to a ponderomotive force that fractionates elements in a manner consistent with the FIP effect. We demonstrate that in certain circumstances this model can also lead to an inverse FIP effect, pointing the way to more detailed modeling of M dwarf coronal abundances in the future.

Elements with high first ionization potential in the new chemical composition of the solar photosphere

The responses of element abundances to the atmospheric model were statistically analyzed. The summarized 1998 data (1D models) and summarized 2009 data (3D models) were compared. A significant statistical dependence between the response value and the first ionization potential (FIP) of an element was shown. This phenomenon may be caused by the presence of regions in the photosphere where the temperature and magnetic field configuration favor fractionation of neutrals and ions. This, in turn, leads to a certain diffusion process similar to the coronal FIP effect. This type of diffusion is not taken into account in photospheric models. In this case, a new chemical composition of the Sun (3D) with decreased C, N, O and Ne abundances is appropriate only to narrow layers in the lower chromospheres (and possibly in the deep photosphere) and does not require revision of the standard solar model.

PROPERTIES OF A POLAR CORONAL HOLE DURING THE SOLAR MINIMUM IN 2007

We report measurements of a polar coronal hole during the recent solar minimum using the Extreme Ultraviolet Imaging Spectrometer on Hinode. Five observations are analyzed that span the polar coronal hole from the central meridian to the boundary with the quiet Sun corona. We study the observations above the solar limb in the height range of 1.03 - 1.20 solar radii. The electron temperature Te and emission measure EM are found using the Geometric mean Emission Measure (GEM) method. The EM derived from the elements Fe, Si, S, and Al are compared in order to measure relative coronal-to-photospheric abundance enhancement factors. We also studied the ion temperature Ti and the non-thermal velocity Vnt using the line profiles. All these measurements are compared to polar coronal hole observations from the previous (1996-1997) solar minimum and to model predictions for relative abundances. There are many similarities in the physical properties of the polar coronal holes between the two minima at these low heights. We find that Te, electron density Ne, and Ti are comparable in both minima. Te shows a comparable gradient with height. Both minima show a decreasing Ti with increasing charge-to-mass ratio q/M. A previously observed upturn of Ti for ions above q/M > 0.25 was not found here. We also compared relative coronal-to-photospheric elemental abundance enhancement factors for a number of elements. These ratios were about 1 for both the low first ionization potential (FIP) elements Si and Al and the marginally high FIP element S relative to the low FIP element Fe, as is expected based on earlier observations and models for a polar coronal hole. These results are consistent with no FIP effect in a polar coronal hole.

Highly Ionized sodium X-ray line emission from the solar corona and the abundance of sodium

{The \ion{Na}{x} X-ray lines between 10.9 and 11.2~\AA\ have attracted little attention but are of interest since they enable an estimate of the coronal abundance of Na to be made. This is of great interest in the continuing debate on the nature of the FIP (first ionization potential) effect. } {Observations of the \ion{Na}{x} lines with the Solar Maximum Mission Flat Crystal Spectrometer and a rocket-borne X-ray spectrometer are used to measure the Na/Ne abundance ratio, i.e. the ratio of an element with very low FIP to one with high FIP.} {New atomic data are used to generate synthetic spectra which are compared with the observations, with temperature and the Na/Ne abundance ratio as free parameters.} {Temperature estimates from the observations indicate that the line emission is principally from non-flaring active regions, and that the Na/Ne abundance ratio is $0.07 \pm 50$\%.} {The Na/Ne abundance ratio is close to a coronal value for which the abundances of low-FIP elements (FIP $< 10$~eV) are enhanced by a factor of 3 to 4 over those found in the photosphere. For low-temperature ($T_e \leqslant 1.5$~MK) spectra, the presence of \ion{Fe}{xvii} lines requires that either a higher-temperature component is present or a revision of ionization or recombination rates is needed. }

RESOLVING THE ξ BOO BINARY WITHCHANDRA, AND REVEALING THE SPECTRAL TYPE DEPENDENCE OF THE CORONAL “FIP EFFECT”

On 2008 May 2, Chandra observed the X-ray spectrum of Xi Boo (G8 V+K4 V), resolving the binary for the first time in X-rays and allowing the coronae of the two stars to be studied separately. With the contributions of Xi Boo A and B to the system's total X-ray emission now observationally established (88.5% and 11.5%, respectively), consideration of mass loss measurements for GK dwarfs of various activity levels (including one for Xi Boo) leads to the surprising conclusion that Xi Boo B may dominate the wind from the binary, with Xi Boo A's wind being very weak despite its active corona. Emission measure distributions and coronal abundances are computed for both stars and compared with Chandra measurements of other moderately active stars with G8-K5 spectral types, all of which exhibit a narrow peak in emission measure near log T=6.6, indicating that the coronal heating process in these stars has a strong preference for this temperature. As is the case for the Sun and many other stars, our sample of stars shows coronal abundance anomalies dependent on the first ionization potential (FIP) of the element. We see no dependence of the degree of "FIP effect" on activity, but there is a dependence on spectral type, a correlation that becomes more convincing when moderately active main sequence stars with a broader range of spectral types are considered. This clear dependence of coronal abundances on spectral type weakens if the stellar sample is allowed to be contaminated by evolved stars, interacting binaries, or extremely active stars with log L_X>29, explaining why this correlation has not been recognized in the past.

HIGHLY IONIZED POTASSIUM LINES IN SOLAR X-RAY SPECTRA AND THE ABUNDANCE OF POTASSIUM

The abundance of potassium is derived from X-ray lines observed during flares by the RESIK instrument on the solar mission CORONAS-F between 3.53 A and 3.57 A. The lines include those emitted by He-like K and Li-like K dielectronic satellites, which have been synthesized using the CHIANTI atomic code and newly calculated atomic data. There is good agreement of observed and synthesized spectra, and the theoretical behavior of the spectra with varying temperature estimated from the ratio of the two GOES channels is correctly predicted. The observed fluxes of the He-like K resonance line per unit emission measure gives log A(K) = 5.86 (on a scale log A(H) = 12), with a total range of a factor 2.9. This is higher than photospheric abundance estimates by a factor 5.5, a slightly greater enhancement than for other elements with first ionization potential (FIP) less than about 10 eV. There is, then, the possibility that enrichment of low-FIP elements in coronal plasmas depends weakly on the value of the FIP which for K is extremely low (4.34 eV). Our work also suggests that fractionation of elements to form the FIP effect occurs in the low chromosphere rather than higher up, as in some models.

NON-WKB MODELS OF THE FIRST IONIZATION POTENTIAL EFFECT: IMPLICATIONS FOR SOLAR CORONAL HEATING AND THE CORONAL HELIUM AND NEON ABUNDANCES

We revisit in more detail a model for element abundance fractionation in the solar chromosphere, that gives rise to the "FIP Effect" in the solar corona and wind. Elements with first ionization potential below about 10 eV, i.e. those that are predominantly ionized in the chromosphere, are enriched in the corona by a factor 3-4. We model the propagation of Alfven waves through the chromosphere using a non-WKB treatment, and evaluate the ponderomotive force associated with these waves. Under solar conditions, this is generally pointed upwards in the chromosphere, and enhances the abundance of chromospheric ions in the corona. Our new approach captures the essentials of the solar coronal abundance anomalies, including the depletion of He relative to H, and also the putative depletion of Ne, recently discussed in the literature. We also argue that the FIP effect provides the strongest evidence to date for energy fluxes of Alfven waves sufficient to heat the corona. However it appears that these waves must also be generated in the corona, in order to preserve the rather regular fractionation pattern without strong variations from loop to loop observed in the solar corona and slow speed solar wind.

Six large coronal X-ray flares observed with Chandra

A study of the six largest coronal X-ray flares in the Chandra archive is presented. The flares were observed on II Peg, OU And, Algol, HR 1099, TZ CrB and CC Eri, all with the High Energy Transmission Grating spectrometer (HETG) and the ACIS detectors. We reconstruct an Emission Measure Distribution EMD(T), using a spectral line analysis method, for flare and quiescence states separately and compare the two. Subsequently, elemental abundaces are obtained from the EMD. We find similar behaviour of the EMD in all flares, namely a large high-T component appears while the low-T (kT < 2 keV) plasma is mostly unaffected, except for a small rise in the low-T Emission Measure. In five of the six flares we detect a First Ionization Potential (FIP) effect in the flare abundances relative to quiescence. This may contradict previous suggestions that flares are the cause of an inverse FIP effect in highly active coronae.

Physical Properties of a 2003 April Quiescent Streamer

In 2003 April, the Ultraviolet Coronagraph Spectrometer (UVCS) on board the Solar and Heliospheric Observatory (SOHO) observed a quiescent streamer in an effort to derive the physical plasma parameters across the streamer and as a function of height (from 1.75 to 5.0 R☉). Values for the electron temperature, proton and O5+ kinetic temperatures, elemental abundances, and O5+ outflow velocity were derived. The presence of the first ionization potential (FIP) effect was also explored. These plasma parameters were compared to those derived for other previously reported active region and quiescent streamers. The photospheric normalized absolute elemental abundances for O, Si, S, Ar, and Fe were derived at 1.75 R☉. The remaining parameters were derived at five heights up to 5.0 R☉. To calculate the electron density above 2.2 R☉ the polarized brightness data from another SOHO instrument, the Large Angle Spectroscopic Coronagraph (LASCO) C2 detector, was employed. The streamer was located above a complex filament structure and had a slightly higher electron temperature compared to what is typically found for quiescent streamers. This streamer did exhibit the customary FIP effect, but no abundance-depleted core typically found for such stable quiescent streamers was detected. The perpendicular kinetic temperature for the protons and the O5+ ions did not vary across the streamer. This differs from two other quiescent streamer comparison cases, in which the O5+ kinetic temperature did decrease at the core structure. The O5+ outflow velocities were similar to those observed in an equatorial streamer from solar minimum.

Coronal Emission Measures and Abundances for Moderately Active K Dwarfs Observed byChandra

We have used Chandra to resolve the nearby 70 Oph (K0 V+K5 V) and 36 Oph (K1 V+K1 V) binary systems for the first time in X-rays. The LETG/HRC-S spectra of all four of these stars are presented and compared with an archival LETG spectrum of another moderately active K dwarf, Epsilon Eri. Coronal densities are estimated from O VII line ratios and emission measure distributions are computed for all five of these stars. We see no substantial differences in coronal density or temperature among these stars, which is not surprising considering that they are all early K dwarfs with similar activity levels. However, we do see significant differences in coronal abundance patterns. Coronal abundance anomalies are generally associated with the first ionization potential (FIP) of the elements. On the Sun, low-FIP elements are enhanced in the corona relative to high-FIP elements, the so-called Different levels of FIP effect are seen for our stellar sample, ranging from 70 Oph A, which shows a prominent solar-like FIP effect, to 70 Oph B, which has no FIP bias at all or possibly even a weak inverse FIP effect. The strong abundance difference exhibited by the two 70 Oph stars is unexpected considering how similar these stars are in all other respects (spectral type, age, rotation period, X-ray flux). It will be difficult for any theoretical explanation for the FIP effect to explain how two stars so similar in all other respects can have coronae with different degrees of FIP bias. Finally, for the stars in our sample exhibiting a FIP effect, a curious difference from the solar version of the phenomenon is that the data seem to be more consistent with the high-FIP elements being depleted in the corona rather than a with a low-FIP enhancement

AnXMM‐NewtonStudy of the Coronae of σ2Coronae Borealis

We present results of XMM-Newton Guaranteed Time observations of the RS CVn binary σ2 Coronae Borealis. The spectra obtained with the Reflection Grating Spectrometers and the European Photon Imaging Camera MOS2 were simultaneously fitted with collisional ionization equilibrium plasma models to determine coronal abundances of various elements. Contrary to the solar first ionization potential (FIP) effect, in which elements with a low FIP are overabundant in the corona compared to the solar photosphere, and contrary to the inverse FIP effect observed in several active RS CVn binaries, coronal abundance ratios in σ2 CrB show a complex pattern, as supported by similar findings in the Chandra HETGS analysis of σ2 CrB with a different methodology by Osten and coworkers in 2003. Low-FIP elements (<10 eV) have abundance ratios relative to Fe that are consistent with the solar photospheric ratios, whereas high-FIP elements have abundance ratios that increase with increasing FIP. We find that the coronal Fe abundance is consistent with the stellar photospheric value, indicating that there is no metal depletion in σ2 CrB. However, we obtain a higher Fe absolute abundance than Osten and coworkers did. Except for Ar and S, our absolute abundances are about 1.5 times larger than those reported by Osten and coworkers. However, a comparison of their model with our XMM-Newton data (and vice versa) shows that both models work adequately in general. We find, therefore, no preference for one methodology over the other for deriving coronal abundances. Despite the systematic discrepancy in absolute abundances, our abundance ratios are very close to those obtained by Osten and coworkers. Finally, we confirm the measurement of a low density in O VII (<4 × 1010 cm-3) but could not confirm the higher densities measured in spectral lines formed at higher temperatures that were derived by other studies of σ2 CrB due to the lower spectral resolution of the XMM-Newton grating spectrometers.

A Unified Picture of the First Ionization Potential and Inverse First Ionization Potential Effects

We discuss models for coronal abundance anomalies observed in the coronae of the sun and other late-type stars following a scenario first introduced by Schwadron, Fisk, & Zurbuchen of the interaction of waves at loop footpoints with the partially neutral gas. Instead of considering wave heating of ions in this location, we explore the effects on the upper chromospheric plasma of the wave pondermotive forces. These can arise when upward-propagating waves from the chromosphere transmit or reflect upon reaching the chromosphere-corona boundary, and are in large part determined by the properties of the coronal loop above. Our scenario has the advantage that for realistic wave energy densities both positive and negative changes in the abundance of ionized species compared to neutrals can result, allowing both first ionization potential (FIP) and inverse FIP effects to come out of the model. We discuss how variations in model parameters can account for essentially all of the abundance anomalies observed in solar spectra. Expected variations with stellar spectral type are also qualitatively consistent with observations of the FIP effect in stellar coronae.

Some Like It Hot: The X‐Ray Emission of the Giant Star YY Mensae

We present an analysis of the X-ray emission of the rapidly rotating giant star YY Mensae observed by Chandra HETGS and XMM-Newton. The high-resolution spectra display numerous emission lines of highly ionized species; Fe XVII to Fe XXV lines are detected, together with H-like and He-like transitions of lower Z elements. Although no obvious flare was detected, the X-ray luminosity changed by a factor of 2 between the XMM-Newton and Chandra observations taken 4 months apart (from log LX ≈ 32.2 to 32.5 ergs s-1, respectively). The coronal abundances and the emission measure distribution have been derived from three different methods using optically thin collisional ionization equilibrium models, which is justified by the absence of opacity effects in YY Men as measured from line ratios of Fe XVII transitions. The abundances show a distinct pattern as a function of the first ionization potential (FIP), suggestive of an inverse FIP effect as seen in several active RS CVn binaries. The low-FIP elements (<10 eV) are depleted relative to the high-FIP elements; when compared to its photospheric abundance, the coronal Fe abundance also appears depleted. We find a high N abundance in YY Men's corona, which we interpret as a signature of material processed in the CNO cycle and dredged up in the giant phase. The corona is dominated by a very high temperature (20-40 MK) plasma, which places YY Men among the magnetically active stars with the hottest coronae. Lower temperature plasma also coexists, albeit with much lower emission measure. Line broadening is reported in some lines, with a particularly strong significance in Ne X Lyα. We interpret such broadening as Doppler thermal broadening, although rotational broadening due to X-ray-emitting material high above the surface could be present as well. We use two different formalisms to discuss the shape of the emission measure distribution. The first one infers the properties of coronal loops, whereas the second formalism uses flares as a statistical ensemble. We find that most of the loops in the corona of YY Men have their maximum temperature equal to or slightly larger than about 30 MK. We also find that small flares could contribute significantly to the coronal heating in YY Men. Although there is no evidence of flare variability in the X-ray light curves, we argue that YY Men's distance and X-ray brightness do not allow us to detect flares with peak luminosities LX ≤ 1031 ergs s-1 with current detectors.

Active Region Streamer Diagnostics 2001 September 14–16

From 2001 September 14 to 16 the Ultraviolet Coronal Spectrometer aboard the Solar and Heliospheric Observatory conducted a series of observations designed to study the absolute elemental abundances of an active region streamer. The absolute elemental abundances for O, Si, Fe, Mg, N, S, and Ar were calculated utilizing a constant electron temperature technique and an alternative approach to the emission measure technique, both producing complementary results. The manifestation of the first ionization potential (FIP) effect was observed here as in previous streamers. Two aspects of this streamer make it unusual and worth special attention. The active region streamer observed possessed an abundance-depleted core typically, although not exclusively, seen in quiescent streamers. A coronal mass ejection (CME) occurred at the active region during the observations. This event resulted in the second unexpected aspect of this streamer, its quick return to the same general abundance characteristics that existed before the CME occurred. The re-formation of a depleted core and the presence of the FIP effect immediately after a highly disruptive event are surprising given the 1 day timescale predicted by streamer theories.

A study of coronal abundances in RS CVn binaries

XMM-Newton has been performing comprehensive studies of X-ray bright RS CVn binaries in its Calibration and Guaranteed Time programs. We present results from ongoing investigations in the context of a systematic study of coronal emission from RS CVns. We concentrate in this paper on coronal abundances and investigate the abundance pattern in RS CVn binaries as a function of activity and average temperature. A transition from an Inverse First Ionization Potential (FIP) effect towards an absence of a clear trend is found in intermediately active RS CVn systems. This scheme corresponds well into the long-term evolution from an IFIP to a FIP effect found in solar analogs. We further study variations in the elemental abundances during a large flare.

Spectroscopic characteristics of polar plumes

Extreme ultraviolet observations of plumes in polar coronal holes are presented and their spectroscopic signatures discussed. The study focuses on the base of plumes seen on the disk of the Sun with the Coronal DiagnosticSpectrometer (CDS) on the Solar and Heliospheric Observatory (SOHO) satellite. Spectroscopic diagnostic techniques are applied to characterise the plumes in terms of density, temperature, emission measure and element abundance. Attention is drawn to the particular limitations of some of the techniques when applied to plume structures. In particular, we revisit the Widing & Feldman (1992) findings of a plume having a large first ionization potential (FIP) effect of 10, showing that instead the Skylab data are consistent with no FIP effect. We present for the first time CDS-GIS (grazing incidence spectrometer) observations of a plume. These observations have been used to confirm the results obtained from normal incidence (NIS) observations. We find that polar plumes exhibit the same characteristics as the Elephant's Trunk equatorial plume. The most striking characteristic of the plume bases is that they are near-isothermal with a peak emission measure at transition region temperatures ≃8 x 10 5 K. At these temperatures, plumes have averaged densities N e ≃ 1.2 x 10 9 cm-3, about twice the value of the surrounding coronal hole region. Element abundances in the plumes are found to be close to photospheric, with the exception of neon which appears to be depleted by 0.2 dex relative to oxygen. The absence of a significant FIP effect in plumes is consistent with fast solar wind plasma, although it is not sufficient to prove a link between the two. Finally, we present a comparison between GIS spectra and the SOHO EIT (EUV Imaging Telescope) broad-band images, showing that temperatures derived from the EIT ratio technique are largely overestimated, for plumes and coronal holes. This is partly due to the fact that the so called Fe XII 195 A and Fe XV 284 A filters are not isothermal, and in coronal holes and plumes lower-temperature lines dominate the EIT signal.

A review of the first ionization potential effect on elemental abundances in the solar corona and in flares

The elemental composition of solar upper atmosphere plasmas was studied from spectra obtained by instruments aboard all major solar observatories that were launched into space in the last three decades. The studies show that the first ionization potential (FIP) of the elements has a profound effect on their abundance in the various solar upper atmosphere regions. In this paper we review properties of the FIP effect as they relate to coronal holes, quiet regions, active regions and flares and we show that although the derived compositions vary considerably with the type of plasma observed regularities in their behavior are emerging. The observed behavior may help identify the energy deposition mechanism that fuels the corona and solar flares.

The Relationship of Solar Abundance Measurements to the Electron Temperature in a Polar Coronal Hole

We discuss the behavior of the intensity of the Mg VI λ1191.64 spectral line relative to the intensity of the Ne VI λ1005.78 spectral line as a function of height above the limb in the solar north polar coronal hole. The intensities of Mg VI lines relative to Ne VI lines have been shown to be excellent indicators of element abundance variations due to the first ionization potential (FIP) effect. We find that the Mg VI/Ne VI intensity ratio increases with height above the limb by factors ranging from 1.7 to 4 over a height range extending from about 6'' above the limb to 28'' above the limb. We conclude that this intensity ratio increase is primarily due to an increase of electron temperature with height, rather than the result of an FIP effect, and therefore caution must be exercised in using any Mg VI/Ne VI line ratio as an abundance diagnostic above the limb in the polar holes. At 6'' above the limb, the Mg VI/Ne VI line ratio indicates that the solar Mg/Ne abundance ratio is probably within a factor of 2 of the photospheric abundance ratio. The spectra we use were recorded by the Solar Ultraviolet Measurements of Emitted Radiation spectrometer on the Solar and Heliospheric Observatory spacecraft.

Element Abundances in the Upper Atmospheres of the Sun and Stars: Update of Observational Results

We review observational progress in the determination of element abundances in the solar corona, largely due to the new capabilities offered by the instrumentation on the SOHO satellite. Many new facets to coronal abundance anomalies with respect to the photosphere are revealed. This includes new results on the FIP (First Ionization Potential) Effect, whereby elements with FIP < 10 eV are enriched in the corona by a factor ~4 with respect to the photosphere, and the first evidence for gravitational settling of heavy elements in the corona. Advances in EUV and x-ray astronomy instrumentation have also yielded the first spectra of stellar coronae of sufficient quality to allow element abundance measurements. We survey these new results and compare the various stellar cases to the solar corona.

The Fe/O elemental abundance ratio in the solar wind as observed with SOHO CELIAS CTOF

Using data of the Charge Time‐of‐Flight (CTOF) mass spectrometer of the Charge, Element, and Isotope Analysis System (CELIAS) on board the Solar and Heliospheric Observatory (SOHO) from ∼80 days of observation around solar minimum we derive a value for the Fe/O abundance ratio for the inecliptic solar wind of 0.11 ± 0.03. Since Fe has a low first ionization potential (FIP) and O is a high‐FIP element, their relative abundance is diagnostic for the FIP fractionation process. The unprecedented time resolution of the CELIAS CTOF sensor allows a fine‐scaled study of the Fe/O ratio as a function of the solar wind bulk speed. On average, the Fe/O abundance ratio shows a continuous decrease by a factor of 2 with increasing solar wind speed between 350 and 500 km/s. This corresponds to the well‐known FIP effect dependence. Our value at ∼500 km/s agrees with the previously observed Fe/O ratio in the fast solar wind emerging from polar coronal holes whereas the value for speeds below 350 km/s is consistent with a remote abundance determination in the leg of a coronal streamer. The variability of the Fe/O abundance ratio is much larger in the slow than in the fast solar wind.