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Mathioudakis, Mihalis
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- Creator:
- Mathioudakis, Mihalis, Cadavid, Ana Cristina, Lawrence, John K., Christian, Damian J., and Jess, David B.
- Description:
- The Rapid Oscillations in the Solar Atmosphere instrument reveals solar atmospheric fluctuations at high frequencies. Spectra of variations of the G-band intensity (IG ) and Ca IIK-line intensity (IK ) show correlated fluctuations above white noise to frequencies beyond 300 mHz and 50 mHz, respectively. The noise-corrected G-band spectrum for f = 28-326 mHz shows a power law with exponent –1.21 ± 0.02, consistent with the presence of turbulent motions. G-band spectral power in the 25-100 mHz ("UHF") range is concentrated at the locations of magnetic bright points in the intergranular lanes and is highly intermittent in time. The intermittence of the UHF G-band fluctuations, shown by a positive kurtosis κ, also suggests turbulence. Combining values of IG , IK , UHF power, and κ reveals two distinct states of the solar atmosphere. State 1, including almost all the data, is characterized by low IG , IK , and UHF power and κ ≈ 6. State 2, including only a very small fraction of the data, is characterized by high IG , IK , and UHF power and κ ≈ 3. Superposed epoch analysis shows that the UHF power peaks simultaneously with spatio-temporal IGmaxima in either state. For State 1, IK shows 3.5 minute chromospheric oscillations with maxima occurring 21 s after IG maxima implying a 150-210 km effective height difference. However, for State 2 the IK and IG maxima are simultaneous; in this highly magnetized environment sites of G-band and K-line emission may be spatially close together.
- Resource Type:
- Article
- Identifier:
- 2041-8205, http://iopscience.iop.org/article/10.1088/2041-8205/743/1/L24/meta
- Campus Tesim:
- Northridge
- Creator:
- Mathioudakis, Mihalis, Cadavid, Ana Cristina, Lawrence, John K., Christian, Damian J., and Jess, David B.
- Description:
- We study properties of intensity fluctuations in NOAA Active Region 11250 observed on 13 July 2011 starting at UT 13:32. Included are data obtained in the EUV bands of the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory (SDO/AIA) as well as nearly simultaneous observations of the chromosphere made, at much higher spatial and temporal resolution, with the Rapid Oscillations in the Solar Atmosphere (ROSA) and Hydrogen-Alpha Rapid Dynamics camera (HARDcam) systems at the Dunn Solar Telescope. A complex structure seen in both the ROSA/HARDcam and SDO data sets comprises a system of loops extending outward from near the boundary of the leading sunspot umbra. It is visible in the ROSA Ca II K and HARDcam Hα images, as well as the SDO 304 Å, 171 Å and 193 Å channels, and it thus couples the chromosphere, transition region and corona. In the ground-based images the loop structure is 4.1 Mm long. Some 17.5 Mm, can be traced in the SDO/AIA data. The chromospheric emissions observed by ROSA and HARDcam appear to occupy the inner, and apparently cooler and lower, quarter of the loop. We compare the intensity fluctuations of two points within the structure. From alignment with SDO/HMI images we identify a point "A" near the loop structure, which sits directly above a bipolar magnetic feature in the photosphere. Point "B" is characteristic of locations within the loops that are visible in both the ROSA/HARDcam and the SDO/AIA data. The intensity traces for point A are quiet during the first part of the data string. At time ~ 19 min they suddenly begin a series of impulsive brightenings. In the 171 Å and 193 Å coronal lines the brightenings are localized impulses in time, but in the transition region line at 304 Å they are more extended in time. The intensity traces in the 304 Å line for point B shows a quasi-periodic signal that changes properties at about 19 min. The wavelet power spectra are characterized by two periodicities. A 6.7 min period extends from the beginning of the series until about 25 minutes, and another signal with period ~3 min starts at about 20 min. The 193 Å power spectrum has a characteristic period of 5 min, before the 20 min transition and a 2.5 min periodicity afterward. In the case of HARDcam Hα data a localized 4 min periodicity can be found until about 7 min, followed by a quiet regime. After ~20 min a 2.3 min periodicity appears. Interestingly a coronal loop visible in the 94 Å line that is centrally located in the AR, running from the leading umbra to the following polarity, at about time 20 min undergoes a strong brightening beginning at the same moment all along 15 Mm of its length. The fact that these different signals all experience a clear-cut change at time about 20 min suggests an underlying organizing mechanism. Given that point A has a direct connection to the photospheric magnetic bipole, we conjecture that the whole extended structure is connected in a complex manner to the underlying magnetic field. The periodicities in these features may favor the wave nature rather than upflows and interpretations will be discussed.
- Resource Type:
- Conference paper or proceedings
- Campus Tesim:
- Northridge
- Creator:
- Antolin, Patrick, Mathioudakis, Mihalis, Christian, Damian J., and Jess, David B.
- Description:
- We present observational evidence of compressible MHD wave modes propagating from the solar photosphere through to the base of the transition region in a solar magnetic pore. High cadence images were obtained simultaneously across four wavelength bands using the Dunn Solar Telescope. Employing Fourier and wavelet techniques, sausage-mode oscillations displaying significant power were detected in both intensity and area fluctuations. The intensity and area fluctuations exhibit a range of periods from 181 to 412 s, with an average period ∼290 s, consistent with the global p-mode spectrum. Intensity and area oscillations present in adjacent bandpasses were found to be out of phase with one another, displaying phase angles of 6◦ . 12, 5◦ . 82, and 15◦ . 97 between the 4170 Å continuum–G-band, G-band–Na I D1, and Na I D1–Ca II K heights, respectively, reiterating the presence of upwardly propagating sausage-mode waves. A phase relationship of ∼0° between same-bandpass emission and area perturbations of the pore best categorizes the waves as belonging to the “slow” regime of a dispersion diagram. Theoretical calculations reveal that the waves are surface modes, with initial photospheric energies in excess of 35,000 W m−2 . The wave energetics indicate a substantial decrease in energy with atmospheric height, confirming that magnetic pores are able to transport waves that exhibit appreciable energy damping, which may release considerable energy into the local chromospheric plasma.
- Resource Type:
- Article
- Identifier:
- 0004-637X
- Campus Tesim:
- Northridge
- Creator:
- Keenan, Francis P., Crockett, Philip J., Mathioudakis, Mihalis, Christian, Damian J., and Jess, David B.
- Description:
- The Rapid Oscillations in the Solar Atmosphere (ROSA) instrument is a synchronized, six-camera high-cadence solar imaging instrument developed by Queen's University Belfast. The system is available on the Dunn Solar Telescope at the National Solar Observatory in Sunspot, New Mexico, USA, as a common-user instrument. Consisting of six 1k x 1k Peltier-cooled frame-transfer CCD cameras with very low noise (0.02 - 15 e s-1 pixel-1), each ROSA camera is capable of full-chip readout speeds in excess of 30 Hz, or 200 Hz when the CCD is windowed. Combining multiple cameras and fast readout rates, ROSA will accumulate approximately 12 TB of data per 8 hours observing. Following successful commissioning during August 2008, ROSA will allow for multi-wavelength studies of the solar atmosphere at a high temporal resolution.
- Resource Type:
- Article
- Identifier:
- 0038-0938
- Campus Tesim:
- Northridge
- Creator:
- Keys, Peter H., Keenan, Francis P., Mathioudakis, Mihalis, Christian, Damian J., and Jess, David B.
- Description:
- We use images of high spatial and temporal resolution, obtained with the Rapid Oscillations in the Solar Atmosphere instrument at the Dunn Solar Telescope, to reveal how the generation of transverse waves in Type I spicules is a direct result of longitudinal oscillations occurring in the photosphere. Here we show how pressure oscillations, with periodicities in the range of 130-440 s, manifest in small-scale photospheric magnetic bright points, and generate kink waves in the Sun's outer atmosphere with transverse velocities approaching the local sound speed. Through comparison of our observations with advanced two-dimensional magnetohydrodynamic simulations, we provide evidence for how magnetoacoustic oscillations, generated at the solar surface, funnel upward along Type I spicule structures, before undergoing longitudinal-to-transverse mode conversion into waves at twice the initial driving frequency. The resulting kink modes are visible in chromospheric plasma, with periodicities of 65-220 s, and amplitudes often exceeding 400 km. A sausage mode oscillation also arises as a consequence of the photospheric driver, which is visible in both simulated and observational time series. We conclude that the mode conversion and period modification is a direct consequence of the 90? phase shift encompassing opposite sides of the photospheric driver. The chromospheric energy flux of these waves are estimated to be ~3 - 10^5 W m-2, which indicates that they are sufficiently energetic to accelerate the solar wind and heat the localized corona to its multi-million degree temperatures.
- Resource Type:
- Article
- Identifier:
- 2041-8205
- Campus Tesim:
- Northridge
- Creator:
- Vennes, Stephane, Mathioudakis, Mihalis, and Christian, Damian J.
- Description:
- We report the detection of a new late-type spectroscopic binary, EUVE J224415.9 (HD 215341) using the 0.6 meter Coude auxiliary telescope and Hamilton echelle spectrograph at Lick observatory.
- Resource Type:
- Article
- Identifier:
- 0374-0676, http://ibvs.konkoly.hu/cgi-bin/IBVS?5281
- Campus Tesim:
- Northridge
- Creator:
- Keenan, Francis P., Crockett, Philip J., Mathioudakis, Mihalis, Christian, Damian J., and Jess, David B.
- Description:
- Magnetic bright points (MBPs) are among the smallest observable objects on the solar photosphere. A combination of G-band observations and numerical simulations is used to determine their area distribution. An automatic detection algorithm, employing one-dimensional intensity profiling, is utilized to identify these structures in the observed and simulated data sets. Both distributions peak at an area of ?45,000 km2, with a sharp decrease toward smaller areas. The distributions conform with log-normal statistics, which suggests that flux fragmentation dominates over flux convergence. Radiative magneto-convection simulations indicate an independence in theMBP area distribution for differing magnetic flux densities. The most commonly occurring bright point size corresponds to the typical width of inter-granular lanes.
- Resource Type:
- Article
- Identifier:
- 2041-8205
- Campus Tesim:
- Northridge
- Creator:
- Mullan, D.J., Mathioudakis, Mihalis, Bloomfield, D.S., and Christian, Damian J.
- Description:
- Dynamo activity in stars of different types is expected to generate magnetic fields with different characteristics. As a result, a differential study of the characteristics of magnetic loops in a broad sample of stars may yield information about dynamo systematics. In the absence of direct imaging, certain physical parameters of a stellar magnetic loop can be extracted if a flare occurs in that loop. In this paper we employ a simple nonhydrodynamic approach introduced by Haisch, to analyze a homogeneous sample of all of the flares we could identify in the EUVE DS database: a total of 134 flares that occurred on 44 stars ranging in spectral type from F to M and in luminosity class from V to III. All of the flare light curves that have been used in the present study were obtained by a single instrument (EUVE DS). For each flare, we have applied Haisch's simplified approach (HSA) in order to determine loop length, temperature, electron density, and magnetic field. For each of our target stars, a literature survey has been performed to determine quantitatively the extent to which our results are consistent with independent studies. The results obtained by HSA are found to be well supported by results obtained by other methods. Our survey suggests that, on themain sequence, short loops (with lengths 0:5R )may be found in stars of all classes, while the largest loops (with lengths up to 2R ) appear to be confined to M dwarfs. Based on EUVE data, the transition from small to large loops on the main sequence appears to occur between spectral types K2 and M0. We discuss the implications of this result for dynamo theories.
- Resource Type:
- Article
- Identifier:
- 0067-0049
- Campus Tesim:
- Northridge
- Creator:
- Mathioudakis, Mihalis, Jevremovic, D., Kawka, A., Dupuis, J., and Christian, Damian J.
- Description:
- We present observations of a strong flare from EUVE J0613-23.9B, a source serendipitously detected with the EUVE Deep Survey Telescope 2.5' south of HD 43162. Optical spectroscopy revealed EUVE J0613-23.9B to be an active dM3.5e star. A dM4e star was found 23'' south of HD 43162 that we associate with 1RXS J061345.1235205.
- Resource Type:
- Article
- Identifier:
- 0374-0676, http://ibvs.konkoly.hu/cgi-bin/IBVS?5447
- Campus Tesim:
- Northridge
- Creator:
- Keenan, Francis P., Keys, Peter H., Mathioudakis, Mihalis, Jess, David B., and Christian, Damian J.
- Description:
- High-cadence, multiwavelength observations and simulations are employed for the analysis of solar photospheric magnetic bright points (MBPs) in the quiet Sun. The observations were obtained with the Rapid Oscillations in the Solar Atmosphere (ROSA) imager and the Interferometric Bidimensional Spectrometer at the Dunn Solar Telescope. Our analysis reveals that photospheric MBPs have an average transverse velocity of approximately 1 kms?1, whereas their chromospheric counterparts have a slightly higher average velocity of 1.4 kms?1. Additionally, chromospheric MBPs were found to be around 63 per cent larger than the equivalent photospheric MBPs. These velocity values were compared with the output of numerical simulations generated using the MURAM code. The simulated results were similar, but slightly elevated, when compared to the observed data. An average velocity of 1.3 km s?1 was found in the simulated G-band images and an average of 1.8 km s?1 seen in the velocity domain at a height of 500 km above the continuum formation layer. Delays in the change of velocities were also analysed. Average delays of ?4 s between layers of the simulated data set were established and values of ?29 s observed between G-band and Ca II K ROSA observations. The delays in the simulations are likely to be the result of oblique granular shock waves, whereas those found in the observations are possibly the result of a semi-rigid flux tube.
- Resource Type:
- Article
- Identifier:
- 0035-8711
- Campus Tesim:
- Northridge
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