Intensity Oscillations and coronal heating: ADITYA-1 Mission. Jagdev Singh, Indian Institute of Astrophysics, Bengaluru

Transcription

1 Intensity Oscillations and coronal heating: ADITYA-1 Mission ARIES Jagdev Singh, Indian Institute of Astrophysics, Bengaluru Science with Planned and Upcoming Solar facilities Nov. 3, 2011.

2 A low density plasma outside the visible disk of the Sun (10-12 of the photospheric density). High temperature (a factor of 200 compared to the photosphere). Emission in EUV and X-rays are higher compared to the photosphere. Low intensity in the visible wavelength (10-6 times of the photosphere). Corona is separated from the photosphere by Chromosphere. Solar Corona

3 Coronal loops as seen by TRACE

4 Coronal Temperature Million Degree Observed from the line less scattered light by electrons as well as the emission from highly ionized species. Edlen 1939 Coronal Green Line. Why so high temperature is yet to be solved?

5 Heating of Coronal Plasma Existence of waves in the corona: Nature of waves, MHD waves, Fast magneto- sonic waves, dissipation of waves Large scale reconnections: Flares, eruptive prominences, CME s etc Small scale reconnections: Micro flares, Nano flares Modeling of solar corona: Energy budget Heating of solar coronal plasma is still not clear?

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7 Plasma Temperatures 6374 [Fe x] line represents plasma at 1 MK 7892 [Fe xi] line represents plasma at 1.2 MK [Fe xiii] line represents plasma at 1.6 MK 5303 [Fe xiv] line represents plasma at 1.8 MK

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9 Emission line-width FWHM of coronal emission lines has two components Thermal component which arises because of high temperature of the plasma in the solar corona Non-thermal component- The observed line width of the coronal emission lines was found to be in excess of thermal broadening. e. g. The observed width of the green line [Fe xiv] at 5303 A coronal emission line corresponds to a temperature between 3 4 MK where as maximum abundances of this ion occurs at about 2 MK The excess width has been interpreted in terms of nonthermal component, probably due to turbulence.

10 Observations Systematic observations of 4 coronal emission lines in the visible wavelengths with 25 cm coronagraph of Norikura observatory from 1997 to 2007 Choosing two emission lines simultaneously; 6374 [Fe x] & 7892 [Fe xi] or 6374 [Fe x] & 5303 [Fe xiv] or 6374 [Fe x] & [Fe xiii] Most of the raster scan covered coronal region of about 500 x 200 arc sec. Some covered coronal region of 500 x 500 arc sec. Error estimate in FWHM measurements are about 2 ma near the limb and about 5 ma at 500 arc sec height Recently we have obtained observations in 4 emission lines simultaneously; 7892, 10747, and 5303 lines

11 Observed and corrected profiles of green, red and infra-red coronal emission lines

12 Three typical coronal loops selected by + marks to study the variation of line-widths with height above the limb

13 Typical variation of line width of emission lines with height for individual coronal loop

14 Scatter plot of line width variations at larger heights Variation of line widths of red and green coronal emission lines with height above the limb up to 500 arcsec. The line widths do not show any increase or decrease with height after about 250 arcsec. These type of variations indicate some different type of mechanism to understand the heating of coronal plasma.

15 Why intensity Oscillations studies? To study the variations in line profiles parameters: Intensity, line width and Doppler shift is a better choice For this one needs a spectrograph, that has limitation of information only along the length of the slit, very small portion of the solar corona. Also it is difficult to locate the travelling waves in the sit and stare observational mode. In the scanning mode existence of high frequencies can not be detected because of large time required to generate the scan. Interferometer such as Fabry-Perot provides alternative to make study of the line profiles on two dimensional region as done in case LASCO- C1 coronagraph. Here again high frequency observations are difficult to make because one need to generate the line profile by scanning along the wavelength. In case of C1 the 0.07nm resolution of FP and scanning step of nm could not provide data for such a study. The scanning time was also several minutes. We, therefore, decided to study the intensity oscillations to investigate the existence of waves in the solar corona to heat the coronal plasma.

16 Coronal waves Dissipation of waves is likely to heat the solar corona, Existence of certain type of waves are likely to cause intensity oscillations; e g. fast magnetosonic waves OBSRVATIONS Koutchmy et al. (1983): velocity oscillations, but no intensity oscillations Pasachoff (2002): Excess power at 1 Hz where as during the same eclipse Williams et al. (2001): intensity oscillation 6s but no excess power at 1 Hz Singh et al. (1997) and Cowsik et al. (1999): intensity oscillations in the range of 0.02 to 0.2 Hz, Singh et al. 2009: Intensity oscillations at the boundaries of coronal structures with 0.04 Hz In summary the existence and nature of waves in the solar corona is inconclusive.

17 Development of Experiments over Time 1980 Image Red line Multislit Spatial intensifier Spectroscopy 1983 Image Red line Multislit Spatial intensifier Spectroscopy 1994 Image Red & green line Multislit Spatial intensifier Spectroscopy 1995 PMT Continuum 1 location 10 Hz 1998 PMT Continuum 4 location 50 Hz 2006 CCD Green & Red Imaging 0.3 Hz Only one limb 2009 CCD Green & Red Imaging 1.1 Hz All around the sun up to 1.5 solar radii 2009 CCD Green & Red Spectroscopy 0.2 Hz 2010 CCD Green & Red Spectroscopy 0.23 Hz

18 IMAGING THE SOLAR CORONA DURING THE TSE ON MARCH 29, 2006 AT ANTALYA, TURKEY

19 Wavelet analysis for pixel location 198, 159 Relative intensity variation Phase plot Variation of probability estimates after applying randomization technique

20 Another representative oscillation as recorded in px 197,93 (away from the active region

21 July 22, 2009 Eclipse

22 Questions Unanswered Are there coronal waves in the solar corona? What is the nature of coronal waves? Are these waves transient, linked with activity in the corona? Period of waves in different type of coronal structures? How these are related with density, temperature etc.?

23 Scientific Objectives of space coronagraph Coronal waves and heating of the corona? Dynamics of Coronal loops: formation and evolution Temperature diagnostics of the corona (using line ratio techniques) Development and origin of CMES Space weather Prediction Topology of magnetic fields

24 Overlay of solar Corona as recorded By different Coronagraphs onboard SoHO and their FOV 3 Rsun

25 Experiment: Simultaneous coronal images in the green and red emission lines with very fast cadence ( 300 ms or so) Green emission line at 530.3nm due to [Fe XIV] and red line nm due to [Fe x] are the two strong emission lines in the visible part of the solar coronal spectra. Green line represents plasma around 2 MK and red line represents plasma around 1 MK, CCD detectors are highly efficient at these wavelengths Images will also be taken in continuum around 580 nm In addition we plan to take images through polarizer at three different orientations to determine topology of magnetic field in coronal structures

26 Formation and Development of Coronal loops Available data on coronal loops is with low cadence Therefore, most of the time fully developed coronal structures are seen. Singh et al. (2004) found formation of a loop by evaporation process from the observations made with the coronagraph. Questions: How the loops are formed, evaporation or condensation? From where the plasma comes in the loops, from the sun or from the solar corona? If the plasma in the coronal structures comes from the sun. If yes, how it is heated to high temperatures? If the plasma comes from the corona, how it makes high density loops if the loops are magnetically shielded?

27 Temperature structure of Coronal loops: Madhulika et al (1993, 1996), determined intensity ratio of 5303 A [Fe xiv] to the 6374 A [Fe x] line to study the variation of temperature in the solar corona and with the phase of solar cycle. Kano and Tsuneta (1996) found the loop tops to be hotter as compared to the foot points of the coronal loops Some of the coronal loops found to have loop top to be cooler as compared to the foot points by Singh et al. (2004) Question: Under what physical conditions the different loops show these type of behavior? Cooling of post flare Coronal loops: It is believed that post flare loops cools down by radiative processes. These are assumed to be formed by reconnection processes. only indirect couple of observations exits to indicate the reconnections. The simultaneous observations in the red and green emission line will yield a clue to process involved in the cooling of post flare loops and there by may tell us about the reconnection process.

28 Topology of magnetic fields The magnetic field emerges into the photosphere and later into the corona. The linear polarization of the Coronal Emission Lines delineates the magnetic field direction while the circular polarization will provide the strength of the field. Owing to the extremely demanding nature of circular polarization measurements, we propose to defer this experiment to a future mission. Here we will restrict our goal to the monitoring of the topology of the magnetic field, which can be achieved by linear polarization measurements (Arnaud 2005). CME STUDIES Most of the current observational evidence for flux ropes comes from observations above ~ 2 Rs, and the situation closer to the solar limb is far from clear. Where does the primary "trigger" reconnection responsible for CME initiation take place: above the erupting flux system, as predicted by the breakout model (Antiochos et al. 1999; Lynch et al. 2004) or below it, as predicted by the "tether-cutting" model (Moore and Roumeliotis 1992)? High cadence polarization brightness (pb) images would be a useful additional tool in tracking the movement of pre-initiation structures into and off the plane of the sky (e.g., Dere et al. 2005).

29 Different observational modes for the proposed payload Mode of Observation Region-of- Interest (ROI) Field-of- View (FOV) CCD binning Pixel Resolut ion (arcsec X arcsec) Exposure time (msec) Cadence (No of Images per minute) Mode-I (High Cadence for dynamical study of coronal loops) 2K x 2K 1.05Rs to 1.5Rs 2X2 or 4X4 or 6 x 6 3X3 or 6X6 or 9 x to to 180 Mode-II (Medium Time & high spatial Resolution,) 2K x 2K 1.05Rs to 1.5Rs 1X1 1.5X to to 30 Mode-III (Low Cadence Images, CME watch ) 2K x 2K 1.05Rs to 3.0Rs 2X2 or 4X4 3.0X3.0 or 6.0X to to 3 Mode-IV (Polarization Measurement, magnetic field topology) 2K x 2K 1.05Rs to 3.0Rs 1X1 or 2X2 1.5X1.5 or 3.0X to

30 IMAGE TAKEN WITH RED FILTER, 2K X 2K CCD, 4 X 4 BINNING,EXPOSURE TIME 300ms DURING THE TOTAL SOLAR ECLIPSE OF MARCH 29, 2006

31 This figure illustrates the importance of the scattered light for coronal observations. Observing sites with pure blue sky (which is very rare to find) gives a scattered light of about In contrast, the solar eclipse provides a very low level of scattered light.

32 Existing space based facilities: Most of the existing space based solar experiments can be divided broadly in two categories. 1.Coronagraphs: obtain data in the continuum radiation with low resolution ( arc sec) to large solar radii (2 30 R sun ) and with low cadence (>10 min). 2. Imaging & Spectroscopy: EUV and X-ray imaging and spectroscopy is done with low cadence ( >5 s) because of low efficiency of detectors in this wavelength range and fewer photons available at these wavelengths.

33 Key Requirements High frequency emission line imaging of the solar corona Dynamics of Coronal Loops with high time cadence Observations of Magnetic Field Topology Observations of Coronal Mass Ejections very close to the Sun with high cadence

34 Justification for space observations (optical wavelength): Occurrence of total solar eclipses provide data for very short duration There is also a large sky brightness even on high mountains unless one goes to the height of about feet. The varying sky transparency makes it very difficult to determine reliably the small amplitude variations in the solar corona and coronal structures and to measure the weak coronal magnetic fields. Large data base is needed to achieve the above mentioned objectives. The observations are planned to be obtained in the region of 1.05 to 3.0 solar radii. The data will be unique in nature and will be complementary to other data obtained with various space borne experiments.

35 Uniqueness of the proposal High cadence : ~ 300 ms Complementary to other type of observations Simultaneous images in different temperatures allowing temperature diagnostics Observations from 1.05 to 3.0 R 0. Existing coronagraphs operate beyond 1.3 R 0. COR1 yields white light images of solar corona from 1.3 R 0 but with cadence ~ 10 min, and during next solar maxima COR1 may not be operational. Minimal scattered light from the solar disc because of absence of earth s atmosphere.

36 Concept design

37 Size of the Coronagraph: Available photons in the inner corona where photometry of coronal structures will be done, Distance (in Rs) Total Number of Photons for 5303 Å line (/s) Number of Polarized Photons (1%) for 5303 Å line Total Number of Photons for 6374 Å line Polarized Photons (1%) for 6374 Å line The efficiency of the optics and detector system indicates that minimum size of 20 cm aperture is needed for the projected scientific objectives. Bigger will be better but in view of the fabrication limits 20 cm aperture has been chosen.

38 Internally & Externally occulted coronagraph INTERNAL Issue : Scattered light To estimate the amount of scattered light due to micro roughness: Data from a profilometer, (σ) or Scatterometer data, (BSDF) LASCO-C1 : primary mirror micro roughness is nm before coating nm after coating from ZEISS, GERMANY & REOSE, FRANCE. EXTERNAL Issue : Boom Length and pointing accuracy Even for a boom length of 100 m, only > 1.45R 0 will be unvignetted. This configuration was ruled out after discussion with ISAC mechanical group

39 Vignetting due to external occulters with varying boom length and of various diameters on Aditya. Note that for un-vignetted rays for inner corona from 1.05 R0 onwards the boom length should be more than 100 m away.

40 Comparison of the Lens and Mirror type objectives in space environment Lens 1. Material Difficult to obtain a uniform large aperture Mirror Relatively easy to obtain large apertures 2. Aberrations Chromatic aberration Free from chromatic aberration 3. Radiation Highly vulnerable for high energy radiations. 4. Heat IR absorption can heat up the objective. Tolerant to high energy radiations. No IR absorption.

41 Comparison between On-axis and Off-axis design On-axis Off-axis 1. Obscuration before primary 2. Scattering before primary 3. Design Compactness 4.Manufacturing of primary mirror Presence of spider. Even 0.1% from spider will be bright by times of the coronal signal. Can be compact Easy to make No Spider No scattering elements before primary Relatively large in size. Somewhat difficult.

42 Comparison between three different optical configurations Phenomenon On-axis Reflective On-axis Refractive Off-axis Reflective Bulk Scatter None from the primary. Limited by the polishing accuracy of the primary itself. Yes. Non-uniformity within the objective will scatter None from the primary. Limited by the polishing accuracy of the primary itself. Scattering from other elements before occulter. Spider and secondary mirror mechanical holders. None. None. Aperture Limitation No limits as technology is available for large mirror (~1m) polishing Yes. Limited by the uniform bulk material availability Aberration Very minimal Chromatic aberration at the position of the internal occulter No limits as technology is available for large mirror (~1m) off-axis polishing Increasing aberration as the off-axis increases. Requires compensating elements. Complexity of the optical design Less complex Less complex Relatively complex Compactness Compact Compact Relatively large Radiation Tolerance of the objective Tolerant Strong radiations can blacken the objective. Heating of the IR absorption will be a critical issue. Tolerant

43 Comparison between three different optical configurations Phenomenon On-axis Reflective On-axis Refractive Off-axis Reflective Bulk Scatter None from the primary. Limited by the polishing accuracy of the primary itself. Yes. Non-uniformity within the objective will scatter None from the primary. Limited by the polishing accuracy of the primary itself. Scattering from other elements before occulter. Spider and secondary mirror mechanical holders. None. None. Aperture Limitation No limits as technology is available for large mirror (~1m) polishing Yes. Limited by the uniform bulk material availability Aberration Very minimal Chromatic aberration at the position of the internal occulter No limits as technology is available for large mirror (~1m) off-axis polishing Increasing aberration as the off-axis increases. Requires compensating elements. Complexity of the optical design Less complex Less complex Relatively complex Compactness Compact Compact Relatively large Radiation Tolerance of the objective Tolerant Strong radiations can blacken the objective. Heating of the IR absorption will be a critical issue. Tolerant

44 Relationship between Focal length and Vignetting of Image Primary mirror Focal length (mm) Central Hole diameter (mm) Minor axis Major axis *Vignetted FOV ( R )

45 Scattered light consideration R = 1 - exp (-(4πσ/λ) 2 ) ~ (4πσ/λ) 2 I s = I o R/π λ=5300a 6300A 10800A

46 Optical design considerations Internally occulted. Disk light should be removed at the prime focus è Off axis design Lyot stop, which is meant for removing the scattered light or the diffraction effects of the entrance aperture, should be used Light corresponding to the corona should be re-imaged at an accessible position. FOV : 1.05 R 0 to 3.0 R 0 radius The image size corresponds to corona should be µm = 26.5 mm. Imaging should be done in two bands: at 530.3nm and at nm Polarization optics and two narrow band filters should be accommodated The weight of the space craft is limited. So the system should made as compact as possible

47 PROPOSED DESIGN High cadence images of solar corona in the [Fe xiv] and nm [Fe x] Project approved by the space commission with the financial grant required for fabrication Reflecting mirrors planned to be made by LEOS, Bangalore Detectors to be developed by SAC Ahmedabad using chips from E2V or SCL, Chandigarh Structure and other parts to be developed by IIA and ISAC Polarization set up to be developed at USO, Udaipur & Filter wheel at IIA Integration and calibration to be done at MGK Lab

48 Key Technologies Primary Mirror (<1.5 Å surface roughness) Scattered light < 1ppm at 1.1 & 0.1 at 1.2 solar radii Scattering (Analysis & Measurement) Detectors (2K 2K, 4-5 frames/s) Satellite jitter (0.5 arcsec) Satellite drift (0.2 arcsec / sec) pointing accuracy (10 arcsec at 3-σ level)

49 Spacecraft requirements for ADITYA-1 Parameter Pointing Stabilization Pointing Accuracy Stability Jitter Weight Orbit Power Payload Data Rate Telemetry On-Board Storage (SSR) Preferred Sun 3-axis body stabilization 10 arcsec (0.003degrees) at 3-σ level 0.1 arcsec per sec (2.8 x 10-5 degrees/sec) 0.5 arcsec 130 Kg Dawn-Dusk Orbit 125 W raw power 64 Mbps TBD 100 Gbits

50 Time schedule for the development of Space Solar Coronagraph Payload Sept., 2008 Dec June 2012 June 2013 June 2014 Dec Detailed Concept Report Detailed Project Report Engineering Design Qualification Model Flight Model Launch

51 COMPARISON OF ECLIPSE VS CORONAGRAPH Eclipse Coronagraph & space Minimum of scattered light billionth of the solar disc Large spatial resolution Large spectral resolution High frequency observations Higher dynamic range due to faster CCD cameras Less expensive Limited time of observation Large scattered light, more than millionth of the solar disc Low spatial resolution Low spectral resolution, limited size of the spectrograph Low frequency observations because of limited telemetry Low dynamic range due to exiting space qualified CCD Very expensive for space observations Large time of observations

52 LASCO C-1 Coronagraph on SOHO