Table Of ContentEUV SUNSPOT PLUMES OBSERVED WITH SOHO
P. Maltby, N. Brynildsen, P. Brekke, S. V. H. Haugan, O. Kjeldseth-Moe, Ø. Wikstøl
Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029, Blindern, 0315 Oslo, Norway
and
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9 T. Rimmele
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National Solar Observatory, Sacramento Peak, Sunspot, NM 88349, USA
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ABSTRACT
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1 Bright EUV sunspot plumes have been observed in five out of nine sunspot regions
v withtheCoronalDiagnosticSpectrometer –CDSonSOHO.Intheotherfourregionsthe
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brightest line emissions may appear inside the sunspot but are mainly concentrated in
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1 small regions outside the sunspot areas. These results are in contrast to those obtained
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during the Solar Maximum Mission, but are compatible with the Skylab mission results.
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8 The present observations show that sunspot plumes are formed in the upper part of the
9 transition region, occur both in magnetic unipolar– and bipolar regions, and may extend
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h from the umbra into the penumbra.
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Subject headings: Sun: corona — sunspots — Sun: transition region — Sun: UV radia-
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1. Introduction
Table 1: Observed active regions
Based on monochromatic EUV images obtained
during the Skylab mission Foukal et al. (1974) intro-
NOAA Date θ Mag.
duced the notation “sunspot plumes”, defined as ar-
(degrees) Class
easabovesunspotumbraethatare“thebrightestfea-
7973 1996 June 26 16 A
tures in an active region by an order of magnitude”.
7981 1996 August 2 16 B
This led to the idea that sunspot plumes are regions
7986 1996 August 29 17 A
withinlargemagneticloops,extendingtoaltitudesof
7999 1996 November 28 36 B
severalthousandkilometersabovethephotosphere,in
8011 1997 January 16 13 B
whichthe temperature is one to twoordersofmagni-
8073 1997 August 16 15 A
tude lower than in the corona of the surrounding ac-
8076 1997 August 30 20 B
tiveregion(Noyesetal. 1985). Incontrast,Brueckner
8083 1997 September 9 35 B
and Bartoe (1974) observed enhanced line emission
8085 1997 September 15 44 B
both over plages and sunspots and Cheng, Doschek,
&Feldman(1976)foundthatemissionlinesformedat
temperaturesbelow2.4×105Kshowedthe sameline
Theangleθ =heliocentricangle. Magneticfieldclassification:
emission over the sunspot as over the quiet network.
A=unipolar,B=bipolar.
Evidence against the importance of sunspot plumes
came from the UVSP instrument on the Solar Max-
imum Mission - SMM. Kingston et al. (1982) found contains information from 60 adjacent locations for
that the emission measures over the penumbrae were ten emission lines. Table 2 gives the line list and the
higherthanoverthe umbrae. TheSMM observations corresponding ionization temperatures. For each ob-
ledGurman(1993)toconcludethattheumbraltran- serving sequence several rasters, up to thirteen, were
sitionregionwasgenerallyindistinguishablefromthe obtained.
quiet transition region.
There appears to be at least two possible expla- Table 2: Selected spectral lines
nations for the discrepancy between the observations
obtained with the S055 Skylab and the UVSP SMM ID λ (˚A) log T (K)
instruments. One possibility is that sunspot plumes He I 522.2 4.3
are formed in the upper part of the transition re- He I 584.3 4.3
gionandthereforeareeasierobservedwithS055than O III 599.5 5.0
with UVSP. Another possibility is that one type of O IV 554.5 5.2
sunspots have plumes whereas others do not. The O V 629.7 5.4
presentobservationsshowthat sunspotplumes occur Ne VI 562.8 5.6
both in magnetic unipolar and bipolar active regions Mg VIII 315.0 5.9
andaremostapparentinemissionlinesformedinthe Mg IX 368.0 6.0
upper part of the transition region. Fe XIV 334.1 6.3
Fe XVI 360.7 6.4
2. Observations and Data Reduction
Observationsof nine sunspot regions (see Table 1) The data acquisition and detector characteristics
were obtained with the Normal Incidence Spectrom- that are relevant for this study were described by
eter (NIS) of the Coronal Diagnostic Spectrometer – Harrisonetal. (1995). Briefly,the CDSdataarecor-
CDS (Harrison et al. 1995), as part of a joint ob- rected for geometrical distortions, the CCD readout
serving program on the Solar and Heliospheric Ob- bias is removed, the non-wavelength-dependent cali-
servatory – SOHO. A large fraction of the observing bration parameters peculiar to the detector are ap-
time was used to raster an area of 120′′× 120′′, mov- plied, including the exposure time, the amplification
′′
ingthenarrow2.0 spectrometerslitperpendicularto of the microchannel plate, and a flat-field correction.
′′
the slit direction in steps of 2.0 . The exposure time The final step in calibrating is to convert the photon
was20s,eachrasterwasrecordedduring25minand eventsintoabsoluteunits. Theline parameters,peak
2
intensity, wavelength shift and line width are deter- ure3inFoukaletal. (1974). Figure1showsthatthe
mined by a least squares fit to the observations, see brightest emission above the umbra in NOAA 7986
Brynildsen et al. (1997). The data material consists is observed in a compatible temperature range since
of line profiles that are well represented by a single the brightestemissionis observedin O IV554˚A,O V
Gaussian shape. Small regions with complicated line 629 ˚A, and Ne VI 562 ˚A. Next consider the spatial
profilesandregionswithrapidtimeevolutionareout- extentofthe brightestemission. AccordingtoFoukal
side the scope of this paper. et al. (1974) the plume’s “minimum half-width is
The CDS images were coaligned with white light definitely smaller than the diameter of the umbra”.
imagesusingmagnetogramsobservedwiththeMichel- However, their Figure 4 shows that the spatial ex-
son Doppler Imager (Scherrer et al. 1995) from tent changes from one emission line to another. In
SOHO.Todeterminethelocationofregionswithpeak Ne VII 465 ˚A, where the plume is most apparent, the
′′
line intensity I > I , where I is a preselected value FWHM of the plume exceeds 30 which is consid-
p p
of I, we introduce the notations: erably larger than the umbral diameter (≈ 10′′). We
findthatthesizeofthebrightfeaturesinthesunspots
F (I >I ) = fraction of umbra covered with I >I ,
U p p
ofNOAA7986andMcMathregion12543arecompat-
F (I >I )=fractionofsunspotcoveredwithI >I ,
S p p ible. Based on these comparisons we conclude that
f (I > I ) = fraction of area with I > I located
U p p the sunspot in NOAA 7986 (Fig. 1) shows a sunspot
above the umbra,
plume.
f (I > I ) = fraction of area with I > I located
S p p Asunspot plume is locatedabovethe sunspotand
above the sunspot.
is the brightest feature within the active region. It
The brightest features, such as the sunspot plumes, is important to note that both the extent and the
will be located by I > Ip = 5I, where I is the aver- locationofenhancedlineemissiondependonthepre-
agepeaklineintensityvaluewithintherasteredarea, selected intensity level I . We show in Figure 3 the
p
120′′× 120′′. fraction, f (I > I ), of the area with peak line in-
S p
tensity I > I which is located above the sunspot
p
3. Results
as function of the intensity ratio, I /I. For several
p
active regions we find that as I /I increases towards
p
In Figures 1 and 2 (Pl.00 and 00) the brightest
thebrightestfeaturesanincreasingfractionoftheline
features with peak line intensity I >5I are encircled emission in O IV 554 ˚A, O V 629 ˚A, and Ne VI 562 ˚A
by yellow contours, whereas medium bright features
is located inside the sunspot. This means that in a
with I > 2.5I are encircled by green contours. Be-
searchfor sunspotplumes one cannotsimply look for
low we give our reasons for identifying the brightest
enhanced line emission, but must select the brightest
feature in NOAA 7986, observed on 29 August 1996
regions by choosing a criterion, such as, I >I =5I.
p
(see Fig. 1), with a sunspot plume. In contrast, Fig-
If it is required that the sunspot plume must be
ure 2 shows that nearly all the brightest features in
positioned directly above the umbra, only two of the
NOAA 7999, observed on 28 November 1996, are lo-
nine sunspots contain a sunspot plume. Taking into
cated outside the sunspot. The size and the location
account the measured size of sunspot plumes a more
of the brightest emission features with peak line in-
reasonable requirement is that a plume is located in
tensityI >5I aregiveninTable3fortheentiresetof
an area above the sunspot that includes the umbra
observations. We limit the list to the three emission
or parts thereof and may extend into the penum-
lines where the sunspot plumes are most apparent.
bra. Withthisrequirementthefollowingfivesunspots
Anexcellentillustrationofasunspotplumeispre- show plumes in O V 629 ˚A and Ne VI 562 ˚A: NOAA
sented in Figure 2 of Foukal et al. (1974), based on
7973, 7986, 8011, 8073, and 8085. In these sunspots
observations of McMath region 12543. To compare
the plumes are centered in the penumbra, the umbra
the brightestemissionfeatureinNOAA7986(Fig.1)
(see Fig. 1), the umbra, the rim of the umbra and
with that of a sunspot plume let us first consider the
the penumbra, respectively. It is possible that also
variation with the line formation temperature. The
NOAA8076shouldberegardedascontainingsunspot
line emissionin the sunspotplume inMcMathregion
plumessincetwoofthebrightestlineemissionregions
12543exceedsthatabovetheadjacentplageregionin in O V 629 ˚A and Ne VI 562 ˚A are located within the
O IV 554 ˚A, O VI 1032 ˚A, and Ne VII 465 ˚A, see Fig- largest,leadingsunspotandthethirdbrightlineemis-
3
sion region covers most of a following sunspot, but in magnetic unipolar and bipolar regions, and may
extends outside the sunspot. The other three active extend outside the umbra and into the penumbra.
regions show bright emission both inside and outside
the sunspot in Ne VI 562 ˚A. Wewouldliketothankallthemembersofthelarge
international CDS team for their extreme dedication
Table 3: Size and location of the brightest emission indevelopingandoperatingthisexcellentinstrument,
regions in O IV 554 ˚A, O V 629 ˚A and Ne VI 562 ˚A theMichelsonDopplerImagerteamforpermissionto
use their data for coalignment purposes and the Re-
searchCouncilof Norwayfor financialsupport. Data
NOAA ID size fU fS FU FS
(arcsec)2 I>5I from Mees Solar Observatory, University of Hawaii,
7973 OIV 7 0.00 0.00 0.00 0.00 are produced with the support of NASA grant NAG
OV 31 0.11 0.67 0.14 0.04
5-4941 and NASA contract NAS8-40801. SOHO is
NeVI 99 0.03 0.48 0.14 0.08
7981 OIV 384 0.03 0.42 0.03 0.10 a mission of international cooperation between ESA
OV 493 0.03 0.63 0.04 0.19
and NASA.
NeVI 248 0.00 0.59 0.00 0.09
7986 OIV 105 0.26 1.00 0.80 0.21
OV 218 0.16 0.91 1.00 0.39 REFERENCES
NeVI 265 0.13 0.86 1.00 0.46
7999 OIV 156 0.00 0.00 0.00 0.00
Brueckner, G. E. and Bartoe, J.-D. F. 1974, Solar
OV 129 0.00 0.00 0.00 0.00
NeVI 122 0.25 0.25 0.05 0.02 Phys., 38, 133
8011 OIV 0 0.00 0.00 0.00 0.00
OV 14 0.75 0.75 0.04 0.04
Brynildsen, N. et al. 1997, Solar Phys., in press
NeVI 24 0.29 0.29 0.03 0.03
8073 OIV 3 0.00 1.00 0.00 0.01
OV 37 0.36 0.91 0.17 0.07 Cheng, C. C., Doschek, G, and Feldman, U. 1976,
NeVI 78 0.22 0.61 0.21 0.10
ApJ, 210, 836
8076 OIV 54 0.06 0.12 0.03 0.01
OV 221 0.20 0.62 0.45 0.14
NeVI 238 0.16 0.29 0.38 0.07 Foukal,P.V.,Huber,M.C.E.,Noyes,R.W.,Reeves,
8083 OIV 377 0.06 0.26 0.08 0.08
E. M., Schmahl, E. J., Timothy, J. G., Vernazza,
OV 262 0.08 0.26 0.07 0.06
NeVI 102 0.07 0.40 0.02 0.03 J. E., and Withbroe, G. L. 1974, ApJ193, L143
8085 OIV 102 0.10 1.00 0.07 0.09
OV 282 0.23 0.93 0.46 0.22 Gurman, J. B. 1993, ApJ, 412, 865
NeVI 333 0.12 0.76 0.29 0.21
Harrison, R. A. et al. 1995, Solar Phys., 162, 233
In contrast to the SMM observations of Gurman Kingston,A.E.,Doyle,J.G.,Dufton,P.L.,andGur-
(1993),thepresentobservationsconfirmtheexistence man, J. B. 1982, Solar Phys., 81, 47
of sunspot plumes. The SMM observations were ob-
tainedclosertoasunspotmaximumthanthe present Noyes, R. W., Raymond, J. C., Doyle, J. G., and
observations. We cannot exclude a selection effect Kingston, A. E. 1985,ApJ, 297, 805
since the sunspots listed by Gurman (1993) are all
Scherrer, P. H. et al. 1995, Solar Phys., 162, 129
magneticbipolar,whereasunipolarsunspotswereob-
served both by Foukal et al. (1974) and by us (see
Table1). However,thiscannotbetheentireexplana-
tion since we also observe sunspot plumes in bipolar
sunspots. It appearsthatthe CDS instrumentis well
suited to measure emission lines formed in the up-
per part of the transition region, where the sunspot
plumes are most apparent. The higher sensitivity of
theCDSinstrumentthantheUVSPSMMinstrument
tolineemissioninthisregionofthe solaratmosphere
may be one of the reasons for the difference in re-
sults between the two instruments. The present ob-
servationssuggestthat sunspotplumes are formedin
This 2-column preprint was prepared with the AAS LATEX
the upper part of the transition region, occur both
macrosv4.0.
4
Fig. 1.— Images of peak line intensities in NOAA 7986 observed on August 29, 1996. Regions with enhanced
intensityareshownasdarkorangeregions. Areaswithpeaklineintensity,I,largerthan2.5and5timestheaverage
intensity, I, are encircled by green and yellow contours. The images are ordered after increasing line formation
temperature,startingintheupperlefthandcorner. Thecontoursoftheumbraandpenumbraarefromwhitelight
observations at the Mees Solar Observatory, Haleakala, Hawaii. The scales in arc sec are in a reference system
where the origin coincides with the centre of the solar disk.
Fig. 2.— Images of peak line intensities in EUV emission lines observed on 28 November 1996. The same color
code etc. as in Figure 1. White light image of NOAA 7999 observed the previous day with the Vacuum Tower
Telescope at the National Solar Observatory, U.S.A. is shown (top). Only minor changes in the sunspot contour
were observed from one day to the next.
Fig. 3.— The fraction,f (I >I ), of the areawith peak line intensityI >I that is locatedabovethe sunspot as
S p p
a function of the intensity ratio I /I. Note the tendency for some sunspots to show the brightest emission above
p
sunspots in O IV 554 ˚A, O V 629 ˚A, and Ne VI 562 ˚A.
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N
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_
5.0 I
W
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c c −−331100 −−331100
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−−114400 −−9900 −−4400 −−114400 −−9900 −−4400
OO VV 662299 ÅÅ NNee VVII 556622 ÅÅ
−−226600 −−226600
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ee
ss
c c −−331100 −−331100
rr
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−−336600 −−336600
−−114400 −−9900 −−4400 −−114400 −−9900 −−4400
MMgg IIXX 336688 ÅÅ FFee XXVVII 336600 ÅÅ
−−226600 −−226600
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c c −−331100 −−331100
rr
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−−114400 −−9900 −−4400 −−114400 −−9900 −−4400
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W
OO IIIIII 559999 ÅÅ OO IIVV 555544 ÅÅ OO VV 662299 ÅÅ
−−7700 −−7700 −−7700
cc
ee
ss
−−112200 −−112200 −−112200
cc
rr
aa
−−117700 −−117700 −−117700
553300 558800 663300 553300 558800 663300 553300 558800 663300
NNee VVII 556622 ÅÅ MMgg IIXX 336688 ÅÅ FFee XXVVII 336600 ÅÅ
−−7700 −−7700 −−7700
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−−112200 −−112200 −−112200
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NOAA 7986
O III O IV
O V Ne VI
Mg IX Fe XVI
NOAA 8085 NOAA 8076
NOAA 7973 NOAA 8083
)
p
I
>
I
(
S
f
NOAA 8073 NOAA 7981
NOAA 8011 NOAA 7999
1.0 2.0 _ 4.0 1.0 2.0 _ 4.0
I /I I /I
p p
