136 research outputs found
Preliminary error budget analysis of the coronagraphic instrument metis for the solar orbiter ESA mission
METIS, the Multi Element Telescope for Imaging
and Spectroscopy, is the solar coronagraph foreseen for the ESA
Solar Orbiter mission. METIS is conceived to image the solar
corona from a near-Sun orbit in three different spectral bands: in
the HeII EUV narrow band at 30.4 nm, in the HI UV narrow
band at 121.6 nm, and in the polarized visible light band (590 â
650 nm). It also incorporates the capability of multi-slit
spectroscopy of the corona in the UV/EUV range at different
heliocentric heights.
METIS is an externally occulted coronagraph which adopts an
âinverted occultedâ configuration. The Inverted external occulter
(IEO) is a small circular aperture at the METIS entrance; the
Sun-disk light is rejected by a spherical mirror M0 through the
same aperture, while the coronal light is collected by two annular
mirrors M1-M2 realizing a Gregorian telescope. To allocate the
spectroscopic part, one portion of the M2 is covered by a grating
(i.e. approximately 1/8 of the solar corona will not be imaged).
This paper presents the error budget analysis for this newconcept
coronagraph configuration, which incorporates 3
different sub-channels: UV and EUV imaging sub-channel, in
which the UV and EUV light paths have in common the detector
and all of the optical elements but a filter, the polarimetric visible
light sub-channel which, after the telescope optics, has a
dedicated relay optics and a polarizing unit, and the
spectroscopic sub-channel, which shares the filters and the
detector with the UV-EUV imaging one, but includes a grating
instead of the secondary mirror.
The tolerance analysis of such an instrument is quite complex:
in fact not only the optical performance for the 3 sub-channels
has to be maintained simultaneously, but also the positions of M0
and of the occulters (IEO, internal occulter and Lyot stop), which
guarantee the optimal disk light suppression, have to be taken
into account as tolerancing parameters.
In the aim of assuring the scientific requirements are optimally
fulfilled for all the sub-channels, the preliminary results of
manufacturing, alignment and stability tolerance analysis for the
whole instrument will be described and discussed
A database of synthetic images in WL and UV filters to test diagnostic and modeling techniques to be applied on the future Metis data
In this report we describe how Metis synthetic images have been created to develop, test and optimize diagnostic tools for the inversion of combined WL and UV future images, and the determination of 2D maps of electron density and solar wind. We used FORWARD package and a coronal 3D model in order to create a baseline of WL and UV coronagraphic images representative of future Metis data acquired at different s/c distances and periods of solar activity cycle
Measuring coronal magnetic fields with remote sensing observations of shock waves
Recent works demonstrated that remote sensing observations of shock waves propagating into the corona and associated with major solar eruptions can be used to derive the strength of coronal magnetic fields met by the shock over a very large interval of heliocentric distances and latitudes. This opinion article will summarize most recent results obtained on this topic and will discuss the weaknesses and strengths of these techniques to open a constructive discussion with the scientific community
Constraining the pass-band of future space-based coronagraphs for observations of solar eruptions in the FeXIV 530.3 nm âgreen lineâ
This research has received funding from the European Research Council (ERC) under the European Unionâs Horizon 2020 research and innovation programme (grant agreement No 647214) and from the UK Science and Technology Facilities Council.Observations of the solar corona in the FeXIV 530.3 nm âgreen lineâ have been very important in the past, and are planned for future coronagraphs on-board forthcoming space missions such as PROBA-3 and Aditya. For these instruments, a very important parameter to be optimized is the spectral width of the band-pass filter to be centred over the âgreen lineâ. Focusing on solar eruptions, motions occurring along the line of sight will Doppler shift the line profiles producing an emission that will partially fall out of the narrower pass-band, while broader pass-band will provide observations with reduced spectral purity. To address these issues, we performed numerical (MHD) simulation of CME emission in the âgreen lineâ and produced synthetic images assuming 4 different widths of the pass-band (Îλ = 20 Ă
, 10 Ă
, 5 Ă
, and 2 Ă
). It turns out that, as expected, during solar eruptions a significant fraction of âgreen lineâ emission will be lost using narrower filters; on the other hand these images will have a higher spectral purity and will contain emission coming from parcels of plasma expanding only along the plane of the sky. This will provide a better definition of single filamentary features and will help isolating single slices of plasma through the eruption, thus reducing the problem of superposition of different features along the line of sight and helping physical interpretation of limb events. For these reasons, we suggest to use narrower band passes (Îλ †2 Ă
) for the observations of solar eruptions with future coronagraphs.PostprintPeer reviewe
On the Possibilities of Detecting Helium D Line Polarization with Metis
Space coronagraph Metis on board of the Solar Orbiter offers us new
capabilities for studying eruptive prominences and coronal mass ejections
(CME). Its two spectral channels, hydrogen L and visible-light (VL)
will provide, for the first time, co-aligned and co-temporal images to study
dynamics and plasma properties of CMEs. Moreover, with the VL channel (580 -
640 nm) we find an exciting possibility to detect the helium D line (587.73
nm) and its linear polarization. The aim of this study is to predict the
diagnostics potential of this line regarding the CME thermal and magnetic
structure. For a grid of models we first compute the intensity of the D
line together with VL continuum intensity due to Thomson scattering on core
electrons. We show that the Metis VL channel will detect a mixture of both,
with predominance of the helium emission at intermediate temperatures between
30 - 50,000 K. Then we use the code HAZEL to compute the degree of linear
polarization detectable in the VL channel. This is a mixture of D
scattering polarization and continuum polarization. The former one is lowered
in the presence of a magnetic field and the polarization axis is rotated (Hanle
effect). Metis has the capability of measuring and polarization
degrees and we show their dependence on temperature and magnetic field. At
=30,000 K we find a significant lowering of which is due to strongly
enhanced D line emission, while depolarization at 10 G amounts roughly to
10 \%.Comment: 11 pages, 6 figures, accepted for publication in Ap
Illumination system in visible light with variable solar-divergence for the solar orbiter METIS coronagraph
The measurement of the stray-rejection capabilities of METIS is part of the acceptance package of the instrument. The Illumination System in Visible Light (ISVL) has been developed to allow the stray-light rejection measurement down to 1x10-9 and under different operating conditions. The main characteristics of ISVL are outlined and discussed; the activities for the integration and verification of ISVL included the absolute radiometric characterization of the facility, including radiance measurement and radiance spatial and angular distribution. The procedures used to measure the performances of the facility are discussed and the obtained results illustrated
Far infrared polarimeter with very low instrumental polarization
After a short analysis of the main problems involved in the construction of a
Far Infrared polarimeter with very low instrumental noise, we describe the
instrument that will be employed at MITO telescope to search for calibration
sources and investigate polarization near the CMB anisotropy peaks in the next
campaign (Winter 2002-03).Comment: 9 pages, 5 figures, to appear in SPIE conference proceedings
"Astronomical telescopes and instrumentation
Design and Fabrication of the All-Reflecting H-Lyman alpha Coronagraph/Polarimeter
We have designed, analyzed, and are now fabricating an All-Reflecting H-Lyman alpha Coronagraph/Polarimeter for solar research. This new instrument operates in a narrow bandpass centered at lambda 1215.7 A-the neutral hydrogen Lyman alpha (Ly-alpha) line. It is shorter and faster than the telescope which produced solar Ly-alpha images as a part of the MSSTA payload that was launched on May 13, 1991. The Ly-alpha line is produced and linearly polarized in the solar corona by resonance scattering, and the presence of a magnetic field modifies this polarization according to the Hanle effect. The Lyman alpha Coronagraph/Polarimeter instrument has been designed to measure coronal magnetic fields by interpreting, via the Hanle effect, the measured linear polarization of the coronal Ly-alpha line. Ultrasmooth mirrors, polarizers, and filters are being flow-polished for this instrument from CVD silicon carbide substrates. These optical components will be coated using advanced induced transmission and absorption thin film multilayer coatings, to optimize the reflectivity and polarization properties at 1215.7 A. We describe some of the solar imaging results obtained with the MSSTA Lyman alpha coronagraph. We also discuss the optical design parameters and fabrication plans for the All-Reflecting H-Lyman alpha Coronagraph/Polarimeter
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