Introduction to the EIS instrument on Hinode

1
Introduction to the EIS instrument on Hinode

• Dr Peter Young
• Rutherford Appleton Laboratory, UK

2
Basic facts

• EIS EUV Imaging Spectrometer
• Successor to CDS on SOHO
• Covers two wavelength bands 170-211 Å, 246-292 Å
• Principally for coronal spectroscopy
• PI institutes MSSL (UK), NRL (USA), NAOJ (Japan)
• PI Prof Louise Harra (MSSL)

3
Instrument layout
Multilayer coating gives high reflectivity in
EUV
Aluminium filters block out visible light
Single mirror for focussing improves throughput
of telescope
Back-thinned CCDs directly sensitive to EUV
radiation
4
Field of view
N
A coarse offset can also be applied to offset EIS
from the other instruments
EIS (576x512)
E
W
SOTNFI/SP (328x164)
SOT BFI (205x102)
XRT (2048x2048)
5
CCD image
2048 pixels
1024 pixels
CCD-A Long wavelength 246-292 Å
CCD-B Short wavelength 170-211 Å
6
Slit options

• Four slits available, defined by their width
• 1 and 2 slits are for spectroscopy
• 40 and 266 slits for imaging

1
266
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Using wide slits context images
Context slot raster, Fe XII 195 Duration 3min 20s
2 slit raster, Fe XII 195 Duration 22min
8
Using wide slits movies

• The most clean emission line for the 266 slit
  is Fe XV 284.16 (2 million K)

EIS wide slot movie Fe XV 284.2
(logT6.3) Courtesy H. Warren (NRL)
9
The EIS spectrum

• Spectrum dominated by coronal ions (iron,
  particularly)
• Few useful transition region lines, but not
  strong

Young et al. (2007, PASJ, in press)
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Telemetry limitations

• The EIS data rate is limited to around 50 kbits/s
• Data are routinely compressed using DPCM
  (lossless) by a factor of around 3
• JPEG (lossy) compression is also allowed
• Despite this, complete CCD data can not be
  obtained routinely
• Specific wavelengths (emission lines) must be
  chosen
• reduced spatial coverage along slit (solar-Y)

11
Science capability

• Transition region lines
• Coronal iron lines
• Flare lines
• Density diagnostics
• Line width and velocity maps

12
Transition region lines

• EIS spectra are dominated by coronal iron lines,
  but there are a number of useful transition
  region lines

Density in loop footpoints Young et al. (2007,
PASJ)
13
Coronal iron lines
14
Flaring loop (17 Dec)
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Spectroscopy

• Emission line diagnostics come in two types
• Study of shape and position of emission lines
• yields plasma velocity, broadening parameters
• Study of emission line strengths
• yields temperatures, densities, abundances,
  emission measure
• requires detailed atomic data

16
Doppler shifts

• Each emission line has a standard position (the
  rest wavelength)
• Shifts from this position imply motion of the
  plasma
• blueshifts towards the observer
• redshifts away from the observer

Blueshift
Redshift
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Line width diagnostics

• The width of emission lines can be written in
  velocity units as
• The components of ?v are written as
• where
• ?vI is the instrumental width
• 2kT/M is the thermal width
• ? is the non-thermal velocity

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Line width and velocity maps

• Active region map
• Fe XII 195.12 Å
• 2006 Dec 2

Intensity
Velocity
Width
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Close-up of loop line width
20
Close-up of loop velocity
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Caution non-Gaussian profiles

• Line profiles are not always Gaussian

22
Density diagnostics

• Certain emission lines from particular ions have
  ratios that are sensitive to the plasma density
• EIS is the first solar UV instrument to routinely
  allow high precision density measurements
• high effective area
• access to best coronal density diagnostics

23
Density maps

• The high quality of the EIS data make density
  maps easy to generate
• Big improvement over SOHO/CDS density maps

24
Best density diagnostics
Ion Ratios
Fe XII (logT6.1) ?186.88 / ?195.12 ?196.64 / ?195.12
Fe XIII (logT6.2) ?196.54 / ?202.04 ?203.82 / ?202.04
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Instrumental effects to be wary of

• There is a spatial offset in both X and Y between
  the two EIS CCDs
• X 2 pixels, Y 15-20 pixels
• The line centroids vary by around 60-70 km s-1
  through an orbit
• Line centroids and widths vary along the EIS slit
• The EIS slits are slightly tilted relative to CCD
• There are a number of warm and hot pixels on the
  detector
• There are a few dust particles on the CCDs
• affects Fe XI 188.23 and Fe XII 193.51
• Image wobble (satellite instrument) leads to
  strange effect in raster movies

26
EIS observations

• Basic observation units for EIS are called
  studies
• Different studies have unique acronyms there are
  over 220
• e.g., COMSCI_AR3, PRY_footpoints_v2, SYNOP001
• Studies actually comprise one or more rasters
• A raster can be, e.g.,
• a scan of a region with the narrow slit
• sit-and-stare with narrow slit or wide slit