Abstract
Solar coronal mass ejections (CMEs) have a strong association with solar flares that is not fully understood. This characteristic of our Sun’s magnetic activity may also occur on other ...stars, but the lack of successfully detected stellar CMEs makes it difficult to perform statistical studies that might show a similar association between CMEs and flares. Because of the potentially strong association, the search for stellar CMEs often starts with a successful search for superflares on magnetically active stars. Regardless of the flare’s presence, we emphasize the utility of searching for CME-specific spectroscopic signatures when attempting to find and confirm stellar CME candidates. We use solar CMEs as examples of why a multitude of ultraviolet emission lines, when detected simultaneously, can substantially improve the credibility of spectroscopically discovered stellar CME candidates. We make predictions on how bright CME-related emission lines can be if they are derived from distant stars. We recommend the use of three emission lines in particular (C
iv
1550 Å, O
vi
1032 Å, and C
iii
977 Å) due to their potentially bright signal and convenient diagnostic capabilities that can be used to confirm if an observational signature truly derives from a stellar CME.
Abstract
Heavy ion signatures of coronal mass ejections (CMEs) indicate that rapid and strong heating takes place during the eruption and early stages of propagation. However, the nature of the ...heating that produces the highly ionized charge states often observed in situ is not fully constrained. An MHD simulation of the Bastille Day CME serves as a test bed to examine the origin and conditions of the formation of heavy ions evolving within the CME in connection with those observed during its passage at L1. In particular, we investigate the bimodal nature of the Fe charge state distribution, which is a quintessential heavy ion signature of CME substructure, as well as the source of the highly ionized plasma. We find that the main heating experienced by the tracked plasma structures linked to the ion signatures examined is due to field-aligned thermal conduction via shocked plasma at the CME front. Moreover, the bimodal Fe distributions can be generated through significant heating and rapid cooling of prominence material. However, although significant heating was achieved, the highest ionization stages of Fe ions observed in situ were not reproduced. In addition, the carbon and oxygen charge state distributions were not well replicated owing to anomalous heavy ion dropouts observed throughout the ejecta. Overall, the results indicate that additional ionization is needed to match observation. An important driver of ionization could come from suprathermal electrons, such as those produced via Fermi acceleration during reconnection, suggesting that the process is critical to the development and extended heating of extreme CME eruptions, like the Bastille Day CME.
Abstract
We describe the energy budget of a coronal mass ejection (CME) observed on 1999 May 17 with the Ultraviolet Coronagraph Spectrometer (UVCS). We constrain the physical properties of the CME’s ...core material as a function of height along the corona by using the spectra taken by the single-slit coronagraph spectrometer at heliocentric distances of 2.6 and 3.1 solar radii. We use plasma diagnostics from intensity ratios, such as the O
vi
doublet lines, to determine the velocity, density, temperature, and nonequilibrium ionization states. We find that the CME core’s velocity is approximately 250 km s
−1
, and its cumulative heating energy is comparable to its kinetic energy for all of the plasma heating parameterizations that we investigated. Therefore, the CME’s unknown heating mechanisms have the energy to significantly affect the CME’s eruption and evolution. To understand which parameters might influence the unknown heating mechanism, we constrain our model heating rates with the observed data and compare them to the rate of heating generated within a similar CME that was constructed by the MAS code’s 3D MHD simulation. The rate of heating from the simulated CME agrees with our observationally constrained heating rates when we assume a quadratic power law to describe a self-similar CME expansion. Furthermore, the heating rates agree when we apply a heating parameterization that accounts for the CME flux rope’s magnetic energy being converted directly into thermal energy. This UVCS analysis serves as a case study for the importance of multislit coronagraph spectrometers for CME studies.
Abstract
The SWICS instrument on board the ACE satellite has detected frequent intervals in the slow solar wind and interplanetary coronal mass ejections in which C
6+
and other fully stripped ions ...are strongly depleted, though the ionization states of elements such as Si and Fe indicate that those ions should be present. It has been suggested that these “outlier” or “dropout” events can be explained by the resonant cyclotron heating process, because these ions all have the same cyclotron frequency as He
2+
. We investigate the region in the corona where these outlier events form. It must be above the ionization freeze-in height and the transition to collisionless plasma conditions, but low enough that the wind still feels the effects of solar gravity. We suggest that the dropout events correspond to relatively dense blobs of gas in which the heating is reduced because local variations in the Alfvén speed change the reflection of Alfvén waves and the turbulent cascade. As a result, the wave power at the cyclotron frequency of the fully stripped ions is absorbed by He
2+
and may not be able to heat the other fully stripped ions enough to overcome solar gravity. If this picture is borne out, it may help to discriminate between resonant cyclotron heating and stochastic heating models of the solar wind.
We present a computationally tractable implementation of spectro-perfectionism, a method which minimizes error imparted by spectral extraction. We develop our method in conjunction with a full raw ...reduction pipeline for the MINiature Exoplanet Radial Velocity Array (MINERVA), capable of performing both optimal extraction and spectro-perfectionism. Although spectro-perfectionism remains computationally expensive, our implementation can extract a MINERVA exposure in approximately 30 minutes. We describe our localized extraction procedure and our approach to point-spread function (PSF) fitting. We compare the performance of both extraction methods on a set of 119 exposures on HD 122064, an RV standard star. Both the optimal extraction and spectro-perfectionism pipelines achieve nearly identical RV precision under a six-exposure chronological binning. We discuss the importance of reliable calibration data for PSF fitting and the potential of spectro-perfectionism for future precise radial velocity exoplanet studies.
The MINiature Exoplanet Radial Velocity Array (MINERVA) is a dedicated observatory of four 0.7 m robotic telescopes fiber-fed to a KiwiSpec spectrograph. The MINERVA mission is to discover ...super-Earths in the habitable zones of nearby stars. This can be accomplished with MINERVA's unique combination of high precision and high cadence over long time periods. In this work, we detail changes to the MINERVA facility that have occurred since our previous paper. We then describe MINERVA's robotic control software, the process by which we perform 1D spectral extraction, and our forward modeling Doppler pipeline. In the process of improving our forward modeling procedure, we found that our spectrograph's intrinsic instrumental profile is stable for at least nine months. Because of that, we characterized our instrumental profile with a time-independent, cubic spline function based on the profile in the cross dispersion direction, with which we achieved a radial velocity precision similar to using a conventional "sum-of-Gaussians" instrumental profile: 1.8 m s−1 over 1.5 months on the RV standard star HD 122064. Therefore, we conclude that the instrumental profile need not be perfectly accurate as long as it is stable. In addition, we observed 51 Peg and our results are consistent with the literature, confirming our spectrograph and Doppler pipeline are producing accurate and precise radial velocities.
The hot Jupiter HD 217107 b was one of the first exoplanets detected using the radial velocity (RV) method, originally reported in the literature in 1999. Today, precise RV measurements of this ...system span more than 20 years, and there is clear evidence of a longer‐period companion, HD 217107 c. Interestingly, both the short‐period planet (Pb ∼ 7.13 d) and long‐period planet (Pc ∼ 5059 d) have significantly eccentric orbits (eb ∼ 0.13 and ec ∼ 0.40). We present 42 additional RV measurements of this system obtained with the MINERVA telescope array and carry out a joint analysis with previously published RV measurements from four different facilities. We confirm and refine the previously reported orbit of the long‐period companion. HD 217107 b is one of a relatively small number of hot Jupiters with an eccentric orbit, opening up the possibility of detecting the precession of the planetary orbit due to general relativistic effects and perturbations from other planets in the system. In this case, the argument of periastron, ω, is predicted to change at the level of ∼0.8∘ century−1. Despite the long time baseline of our observations and the high quality of the RV measurements, we are only able to constrain the precession to be ω˙<65.9∘ century−1. We discuss the limitations of detecting the subtle effects of precession in exoplanet orbits using RV data.
We present a computationally tractable implementation of spectro-perfectionism, a method which minimizes error imparted by spectral extraction. We develop our method in conjunction with a full raw ...reduction pipeline for the MINiature Exoplanet Radial Velocity Array (MINERVA), capable of performing both optimal extraction and spectro-perfectionism. Although spectro-perfectionism remains computationally expensive, our implementation can extract a MINERVA exposure in approximately 30 minutes. We describe our localized extraction procedure and our approach to point-spread function (PSF) fitting. We compare the performance of both extraction methods on a set of 119 exposures on HD 122064, an RV standard star. Both the optimal extraction and spectro-perfectionism pipelines achieve nearly identical RV precision under a six-exposure chronological binning. We discuss the importance of reliable calibration data for PSF fitting and the potential of spectro-perfectionism for future precise radial velocity exoplanet studies.
Abstract
We present the discovery of KELT-24 b, a massive hot Jupiter orbiting a bright (
V
= 8.3 mag,
K
= 7.2 mag) young F-star with a period of 5.6 days. The host star, KELT-24 (HD 93148), has a
...T
eff
=
K, a mass of
M
*
=
M
⊙
, a radius of
R
*
= 1.506 ± 0.022
R
⊙
, and an age of
Gyr. Its planetary companion (KELT-24 b) has a radius of
R
P
= 1.272 ± 0.021
R
J
and a mass of
M
P
=
M
J
, and from Doppler tomographic observations, we find that the planet’s orbit is well-aligned to its host star’s projected spin axis (
). The young age estimated for KELT-24 suggests that it only recently started to evolve from the zero-age main sequence. KELT-24 is the brightest star known to host a transiting giant planet with a period between 5 and 10 days. Although the circularization timescale is much longer than the age of the system, we do not detect a large eccentricity or significant misalignment that is expected from dynamical migration. The brightness of its host star and its moderate surface gravity make KELT-24b an intriguing target for detailed atmospheric characterization through spectroscopic emission measurements since it would bridge the current literature results that have primarily focused on lower mass hot Jupiters and a few brown dwarfs.
We present the discovery of KELT-24 b, a massive hot Jupiter orbiting a bright (V=8.3 mag, K=7.2 mag) young F-star with a period of 5.6 days. The host star, KELT-24 (HD 93148), has a ...Teff=-+65094950K, a mass of M*=+1.4600.0590.055Me, a radius of R*=1.506±0.022Re, and an age of +0.780.420.61Gyr. Its planetary companion (KELT-24 b) has a radius of RP=1.272±0.021RJ and a mass of MP=-+5.180.220.21MJ, and from Doppler tomographic observations, we find that the planet’s orbit is well aligned to its host star’s projected spin axis (l=-+2.63.65.1). The young age estimated for KELT-24 suggests that it only recently started to evolve from the zero-age main sequence. KELT-24 is the brightest star known to host a transiting giant planet with a period between 5 and 10 days. Although the circularization timescale is much longer than the age of the system, we do not detect a large eccentricity or significant misalignment that is expected from dynamical migration. The brightness of its host star and its moderate surface gravity make KELT-24b an intriguing target for detailed atmospheric characterization through spectroscopic emission measurements since it would bridge the current literature results that have primarily focused on lower mass hot Jupiters and a few brown dwarfs.
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