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Limb Event Brightenings and Fast Ejection Using IRIS Mission Observations  [PDF]
E. Tavabi,S. Koutchmy,L. Golub
Physics , 2015, DOI: 10.1007/s11207-015-0771-3
Abstract: The Interface Region Imaging Spectrograph (IRIS) of the NASA small explorer mission provides significantly more complete and higher resolution spectral coverage of the dynamical conditions inside the chromosphere and transition region (TR) than has heretofore been available. Near the solar limb high temporal, spatial (0.3") and spectral resolution observations from the ultraviolet IRIS spectra reveal high-energy limb event brightenings (LEBs) at low chromospheric heights, around 1 Mm above the limb. They can be characterized as explosive events producing jets. We selected two events showing spectra of a confined eruption just off or near the quiet Sun limb, the jet part showing obvious moving material with short duration large Doppler shifts in three directions identified as macrospicules on slit-jaw (SJ) images in Si IV and He II 304 A. The events are analyzed from a sequence of very close rasters taken near the central meridian and the South pole limb. The processed SJ images and the simultaneously observed fast spectral sequences having large Doppler shifts, with a pair of red shifted elements together with a faster blue shifted element from almost the same position, are analyzed. Shifts correspond to velocities of up to 100 km/s in projection on the plane of the sky. The occurrence of erupting spicules and macrospicules from these regions is noticed from images taken before and after the spectra. The cool low first ionization potential (FIP) element simultaneous line emissions of the MgII h and k resonance lines do not clearly show a similar signature due to optical thickness effects but the Si IV broad-band SJ images do. The bidirectional plasma jets ejected from a small reconnection site are interpreted as the result of coronal loop-loop interactions leading to reconnection in nearby sites.
Chromospheric multi-wavelength observations near the solar limb  [PDF]
C. Beck,R. Rezaei
Physics , 2012,
Abstract: Observations of chromospheric spectral lines near and beyond the solar limb provide information on the solar chromosphere without any photospheric contamination. For ground-based observations near and off the limb with real-time image correction by adaptive optics (AO), some technical requirements have to be met, such as an AO lock point that is independent of the location of the field of view observed by the science instruments, both for 1D and 2D instruments. We show how to obtain simultaneous AO-corrected spectra in Ca II H, Ha, Ca II IR at 854 nm, and He I at 1083 nm with the instrumentation at the German Vacuum Tower Telescope in Izana, Tenerife. We determined the spectral properties of an active-region macrospicule inside the field of view in the four chromospheric lines, including its signature in polarization in He I at 1083 nm. Compared to the line-core intensities, the Doppler shifts of the lines change on a smaller spatial scale in the direction parallel to the limb, suggesting the presence of coherent rotating structures or the passage of upwards propagating helical waves on the surfaces of expanding flux tubes.
Doppler shift of the quiet region measured by meridional scans with the EUV Imaging Spectrometer onboard Hinode  [PDF]
N. Kitagawa,H. Hara,T. Yokoyama
Physics , 2015,
Abstract: Spatially averaged (> 50'') EUV spectral lines in the transition region of solar quiet regions are known to be redshifted. Because the mechanism underlying this phenomenon is unclear, we require additional physical information on the lower corona for limiting the theoretical models. To acquire this information, we measured the Doppler shifts over a wide coronal temperature range (log T[K]=5.7--6.3) using the spectroscopic data taken by the Hinode EUV Imaging Spectrometer. By analyzing the data over the center-to-limb variations covering the meridian from the south to the north pole, we successfully measured the velocity to an accuracy of 3 km/s. Below log T[K] = 6.0, the Doppler shifts of the emission lines were almost zero with an error of 1--3 km/s; above this temperature, they were blueshifted with a gradually increasing magnitude, reaching - 6.3 +/- 2.1 km/s at log T[K]=6.25.
Fixed-delay Interferometry for Doppler Extra-solar Planet Detection  [PDF]
Jian Ge
Physics , 2002, DOI: 10.1086/341226
Abstract: We present a new technique based on fixed-delay interferometry for high throughput, high precision and multi-object Doppler radial velocity (RV) surveys for extra-solar planets. The Doppler measurements are conducted through monitoring the stellar fringe phase shifts of the interferometer. High Doppler sensitivity is achieved through optimizing the optical delay in the interferometer and reducing photon noise by measuring multiple fringes over a broadband. This broadband operation is performed through coupling the interferometer with a low to medium resolution post-disperser. The total Doppler sensitivity of this approach is, in theory, independent of dispersing power of the post-disperser, which allows development of new generation RV machines with much reduced size, high stability and low cost compared to echelles. This technique has the potential to improve RV survey efficiency by 2-3 orders of magnitude over cross-dispersed echelle spectroscopy approach to allow a full sky RV survey for planets once the instrument is operated as a multi-object instrument and optimized for high throughput. The simple interferometer response potentially allows this technique to be operated at other wavelengths independent of popular iodine reference sources to search for planets around early type stars, white dwarfs, and M, L and T dwarfs for the first time.
The quiet Sun average Doppler shift of coronal lines up to 2 MK  [PDF]
Neda Dadashi,Luca Teriaca,Sami K. Solanki
Physics , 2011, DOI: 10.1051/0004-6361/201117234
Abstract: The average Doppler shift shown by spectral lines formed from the chromosphere to the corona reveals important information on the mass and energy balance of the solar atmosphere, providing an important observational constraint to any models of the solar corona. Previous spectroscopic observations of vacuum ultra-violet (VUV) lines have revealed a persistent average wavelength shift of lines formed at temperatures up to 1 MK. At higher temperatures, the behaviour is still essentially unknown. Here we analyse combined SUMER/SoHO and EIS/Hinode observations of the quiet Sun around disk centre to determine, for the first time, the average Doppler shift of several spectral lines formed between 1 and 2 MK, where the largest part of the quiet coronal emission is formed. The measurements are based on a novel technique applied to EIS spectra to measure the difference in Doppler shift between lines formed at different temperatures. Simultaneous wavelength-calibrated SUMER spectra allow establishing the absolute value at the reference temperature of 1 MK. The average line shifts at 1 MK < T < 1.8 MK are modestly, but clearly bluer than those observed at 1 MK. By accepting an average blue shift of about (-1.8+/-0.6) km/s at 1 MK (as provided by SUMER measurements), this translates into a maximum Doppler shift of (-4.4+/-2.2) km/s around 1.8 MK. The measured value appears to decrease to about (-1.3+/-2.6) km/s at the Fe XV formation temperature of 2.1 MK. The measured average Doppler shift between 0.01 and 2.1 MK, for which we provide a parametrisation, appears to be qualitatively and roughly quantitatively consistent with what foreseen by 3-D coronal models where heating is produced by dissipation of currents induced by photospheric motions and by reconnection with emerging magnetic flux.
Measurements of Anisotropic Ion Temperatures, Non-Thermal Velocities, and Doppler Shifts in a Coronal Hole  [PDF]
M. Hahn,D. W. Savin
Physics , 2012, DOI: 10.1088/0004-637X/763/2/106
Abstract: We present a new diagnostic allowing one to measure the anisotropy of ion temperatures and non-thermal velocities as well as Doppler shifts with respect to the ambient magnetic field. This method provides new results, as well as independent test for previous measurements obtained with other techniques. Our spectral data come from observations of a low latitude, on-disk coronal hole. A potential field source surface model was used to calculate the angle between the magnetic field lines and the line of sight for each spatial bin of the observation. A fit was performed to determine the line widths and Doppler shifts parallel and perpendicular to the magnetic field. For each line width component we derived parallel and perpendicular ion temperatures and non-thermal velocities. The perpendicular ion temperature was cooler than off-limb polar coronal hole measurements. The parallel ion temperature was consistent with a uniform temperature of 1.8 +/- 0.2 x 10^{6} K for each ion. Since parallel ion heating is expected to be weak, this ion temperature should reflect the proton temperature. A comparison between our results and others implies a large proton temperature gradient around 1.02 R_sun. The non-thermal velocities are thought to be proportional to the amplitudes of various waves. Our results for the perpendicular non-thermal velocity agree with Alfv\'en wave amplitudes inferred from off-limb polar coronal hole line width measurements. Our parallel non-thermal velocity results are consistent with slow magnetosonic wave amplitudes inferred from Fourier analysis of time varying intensity fluctuations. Doppler shift measurements yield outflows of ~5 km s^-1 for ions formed over a broad temperature range. This differs from other studies which found a strong Doppler shift dependence on formation temperature.
Constraining High Speed Winds in Exoplanet Atmospheres Through Observations of Anomalous Doppler Shifts During Transit  [PDF]
Eliza Miller-Ricci Kempton,Emily Rauscher
Physics , 2011, DOI: 10.1088/0004-637X/751/2/117
Abstract: Three-dimensional (3-D) dynamical models of hot Jupiter atmospheres predict very strong wind speeds. For tidally locked hot Jupiters, winds at high altitude in the planet's atmosphere advect heat from the day side to the cooler night side of the planet. Net wind speeds on the order of 1-10 km/s directed towards the night side of the planet are predicted at mbar pressures, which is the approximate pressure level probed by transmission spectroscopy. These winds should result in an observed blue shift of spectral lines in transmission on the order of the wind speed. Indeed, Snellen et al. (2010) recently observed a 2 +/- 1 km/s blue shift of CO transmission features for HD 209458b, which has been interpreted as a detection of the day-to-night winds that have been predicted by 3-D atmospheric dynamics modeling. Here we present the results of a coupled 3-D atmospheric dynamics and transmission spectrum model, which predicts the Doppler-shifted spectrum of a hot Jupiter during transit resulting from winds in the planet's atmosphere. We explore four different models for the hot Jupiter atmosphere using different prescriptions for atmospheric drag via interaction with planetary magnetic fields. We find that models with no magnetic drag produce net Doppler blue shifts in the transmission spectrum of ~2 km/s and that lower Doppler shifts of ~1 km/s are found for the higher drag cases, results consistent with -- but not yet strongly constrained by -- the Snellen et al. (2010) measurement. We additionally explore the possibility of recovering the average terminator wind speed as a function of altitude by measuring Doppler shifts of individual spectral lines and spatially resolving wind speeds across the leading and trailing terminators during ingress and egress.
Understanding the gravitational and cosmological redshifts as Doppler shifts by gravitational phase factors  [PDF]
Mingzhe Li
Physics , 2013, DOI: 10.1088/0264-9381/31/14/145001
Abstract: From the viewpoint of gauge gravitational theories, the path dependent gravitational phase factors define the Lorentz transformations between the local inertial coordinate systems of different positions. With this point we show that the spectral shifts in the curved spacetime, such as the gravitational and cosmological redshifts, can be understood as Doppler shifts. All these shifts are interpreted in a unified way as being originated from the relative motion of the free falling observers instantaneously static with the wave source and the receiver respectively. The gravitational phase factor of quantum systems in the curved spacetime is also discussed.
Solar Meridional Circulation from Doppler Shifts of the Fe I line at lambda 5250 Angstroms as Measured by the 150-foot Solar Tower Telescope at the Mt. Wilson Observatory  [PDF]
Roger K. Ulrich
Physics , 2010, DOI: 10.1088/0004-637X/725/1/658
Abstract: Doppler shifts of the Fe I spectral line at lambda5250 Angstroms from the full solar disk obtained over the period 1986 to 2009 are analyzed to determine the circulation velocity of the solar surface along meridional planes. Simultaneous measurements of the Zeeman splitting of this line are used to obtain measurements of the solar magnetic field that are used to select low field points and impose corrections for the magnetically induced Doppler shift. The data utilized is from a new reduction that preserves the full spatial resolution of the original observations so that the circulation flow can be followed to latitudes of 80 degrees N/S. The deduced meridional flow is shown to differ from the circulation velocities derived from magnetic pattern movements. A reversed circulation pattern is seen in polar regions for three successive solar minima. An surge in circulation velocity at low latitudes is seen during the rising phases of cycles 22 and 23.
On the magnetic field of off-limb spicules  [PDF]
R. Centeno,J. Trujillo Bueno,A. Asensio Ramos
Physics , 2009, DOI: 10.1088/0004-637X/708/2/1579
Abstract: Determining the magnetic field related to solar spicules is vital for developing adequate models of these plasma jets, which are thought to play a key role in the thermal, dynamic and magnetic structure of the Chromosphere. Here we report on the magnetic properties of off-limb spicules in a very quiet region of the solar atmosphere, as inferred from new spectropolarimetric observations in the He I 10830 A triplet obtained with the Tenerife Infrared Polarimeter. We have used a novel inversion code for Stokes profiles caused by the joint action of atomic level polarization and the Hanle and Zeeman effects (HAZEL) to interpret the observations. Magnetic fields as strong as ~40G were detected in a very localized area of the slit, which could represent a possible lower value of the field strength of organized network spicules.
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