RECENT PRESENTATIONS etc.
Several presentations at the COSPAR conference, Paris, July 2004, including:
"Thermal and Nonthermal Contributions to the Solar Flare X-ray Flux" (B. R. Dennis et al.)
"High Time Resolution Observations of Solar Flare H-alpha Emission" (K. Radziszewski et al.)
"Temperature-sensitive Line Ratio Diagnostics based on Si Satellite-to-Resonance Line Ratios" (K. J. H. Phillips et al.)
"RHESSI, RESIK and GOES Observations of the Solar Flare Thermal Spectrum", Presentation at the AAS/SPD meeting, Denver, June 3, 2004
"New Insights into Solar X-ray Flares", Seminar at the Laboratory for Solar and Astrophysics", GSFC, May 6, 2004
"The Sun, our Star", Presentation at the Montgomery Study Circle, Greenbelt,
Maryland, August 2003.
"Solar Flare Abundances of K, Ar, and S", AAS Solar Physics Division Meeting,
July 2003.
"The Fe-line Feature in RHESSI Solar Flare Spectra", RHESSI Workshop, July 2003.
"Searching for Rapid Changes in the Solar Corona during the 2001 Eclipse",
Presentation in SOHO/RHESSI Seminar Series, October 2002.
``Flare Temperatures from Fe XXV and Ca XIX: Improved Atomic Data'', Paper
by KJHP and others, presented by Louise Harra at Tenth Anniversary of Yohkoh
Meeting, Hawaii, January 21/25, 2002.
Interview on nature of Sunspots with Louise Harra on BBC Radio 4 Material
World programme with Quentin Cooper, November 20, 2001.
Invited talk ``Looking for the Coronal Heating Mechanism with the SECIS
Instrument'', Totality Day Eclipse conference, Open University,
August 11, 2001.
Talk to 700 students, schoolchildren, teachers and lecturers at the Sports
Hall, University of Zambia, June 19, 2001 on viewing the June 21,
2001 eclipse.
Contribution to the Learning Edge BBC Radio 4 programme, June 21, 2001 --
interviewer Geoff Watts.
``Results from the SECIS experiment''. Talk given at the NAM
conference (UK Solar Physics session), April 2-5, 2001, Cambridge, UK.
``Why is the Solar Corona so Hot? Results from SECIS''. Seminar given
at UCL, February 12, 2001.
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Solar Research
PROFILE
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I have been doing solar physics research for more than 30 years, principally in the
areas of solar flares, X-ray and UV spectroscopy, coronal heating
and diagnostics of hot
coronal plasmas. My PhD (Mullard Space Science Laboratory, University
College London, 1972) was on soft X-ray emission from solar flares using
data from the OSO-4 spacecraft. I held postdoctoral fellowships at NASA
Goddard Space Flight Center (1972--75) and at the University of Hawaii
(1975--76). From 1977 to 2002, I worked at RAL (originally
the Astrophysics Research Division, Appleton Laboratory), in the Space Science and
Technology Dept where I was Leader of the Solar Research Group, and
one of the four Co-Applicants of the Space Science PPARC Rolling Grant over several years. I had honorary appointments at Queen's University, Belfast
Some of my collaborators include
Dr Louise Harra
(MSSL), and Dr Pawel Pres
(who was at RAL in 1998 on
a Royal Society/NATO postdoctoral fellowship I successfully applied for). I
had British Council-funded collaborations with the Astronomical
Institute, University of Wroclaw, Poland (including Professor Jerzy
Jakimiec, Prof. Bogdan Rompolt, Dr Pawel Rudawy etc.) and the SRON Laboratory for Space Research, Utrecht (Dr
Rolf Mewe). I also collaborate with several other groups in the U.K., Europe,
and the U.S. (notably US Naval Research Laboratory and Lawrence
Livermore Laboratory).
A good friend of mine,
Dr Wolfgang Ihra, who
does work, among other things, on e- and e+
impact ionization beyond the Wannier theory, has a nice web site. He is
presently at the Max Planck Institut,
Freiburg. Another good friend, Brian Thomas, runs the educational programmes and
excellent web site of The
Marine Society, often mentioned in the press and recently highlighted in
respect of the Mozambique airlift. My relative Brian Phillips is MD of
Integrated Electronics in Wraysbury,
Middx., and some years ago supplied
equipment for Rutherford Appleton Laboratory.
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GUIDE TO THE SUN AND BOOK CONTRIBUTIONS
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I am the author of the book
`Guide to the Sun', published in hard bound (1992)
and paperback (1995) by
Cambridge University Press
(ISBN 0 521 39483X hbk, 0 52139788 X pbk). The book covers
all major aspects of solar astronomy and physics, including a historical
chapter, one on the solar interior including the solar neutrino problem
and helioseismology, the solar atmosphere, solar activity, relation of the
Sun to other stars and the interplanetary
medium, and a final chapter on observing the Sun with ground-based
telescopes and spacecraft. There are sections on the Sun's influence on the
earth's climate, and also global warming and the
depletion of the ozone layer. It has sold about 3600 copies world-wide, and has
been adopted as a course book at a number of US and UK universities and
colleges. It received a 5-star rating in the
amazon.com web-based book store.
I contributed the solar and radiation entries for the `Oxford
Dictionary of Astronomy' (ed. Ian Ridpath), widely available at bookshops
worldwide (ISBN 0-19-211596-0 pbk, 1997).
`The Many Faces of the Sun', a summary of the Solar Maximum Mission
satellite that flew in the 1980's, has a review
chapter by me on Spectroscopy and Atomic Physics
(ch. 13). The book is published by Springer-Verlag (New York, Berlin, and
Heidelberg: ISBN 0-387-98481-X 1998).
I contributed one of the entries (`Sun as a Star') in the
Encyclopedia of Astronomy and
Astrophysics'
which appeared in September 2000 and had a big
launch party at the IAU General Assembly in Manchester in August 2000.
A new book,
Dynamic Sun(CUP), on recent solar physics results,
has a chapter `Probing the Sun's Hot Corona' by me and Bhola Dwivedi, appeared in Spring 2003.
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Solar Research
RECENT CONTRIBUTIONS
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Studies of the Quiet Sun with the Solar and Heliospheric Observatory.
I am involved in many collaborations in studies of especially the quiet Sun
using data from the SOHO spacecraft, launched in December 1995. With my colleagues
Peter Gallagher and
Louise Harra
at MSSL, I
completed a major study of quiet Sun properties using data from
the Coronal Diagnostics Spectrometer (CDS), including brightness, area,
fractal index, contrast and other properties of the network -- one of our basic
findings is that the network appears most ``contrasty" in transition region
lines, but can be traced in coronal lines. It is more blurred-looking
in the chromospheric He I and II lines but we show in our work that this is
probably due to the high optical thickness of these lines.
I successfully applied for
Dr Pawel Pres to come to
RAL on a Royal Society/NATO-funded postdoctoral fellowship in 1998.
He and I did a study of a quiet Sun region observed simultaneously by
SOHO and
Yohkoh in 1997. Magnetogram observations from the SOHO MDI instrument show the
presence of converging and diverging bipoles which show up in
Yohkoh data as X-ray bright points. Pawel found a fascinating
correlation of the energy in the photospheric magnetic field, the EUV emission
from the bright coronal Fe XII line, and the X-ray
brightness as measured by the Yohkoh SXT instrument. The magnetic field energy
is approximately (to a factor 2) the same as the conductive and radiative
losses, so that the magnetic energy seems to supply the entire energy of the
bright point. This is the case for the 6 bright points in an initial study
(paper published in Ap. J. Letters -- see below) and for most of more than 20
cases which are being analyzed right now for a more extended work.
We also noted the occurrence of several tiny
X-ray ``network flares" similar to what has been seen by other observers. Pawel
also gave a poster on this work at the Brendan Byrne Memorial Symposium (Armagh,
September 1998) -- see the Proceedings (PASP Special Publication). We are now
working on a more extensive paper to be submitted to Astr. Astrophys.
where a much larger number of coronal bright points are studied, along with data
from the CDS experiment on SOHO.
In another major study involving Peter and Louise, we looked at small
network brightenings. We used a SOHO CDS study in which the NIS slit is held
in one position on the Sun, with features slowly drifting past by solar
rotation. There are literally hundreds of tiny brightenings which can be
identified in any one observation (typically two hours long). We have devised
statistical methods of identifying and categorising them. We recently had
a paper published (Gallagher et al.:
Astr. Astrophys.) on velocities associated with
these brightenings: it appears that there is a strong correlation of
brightenings with downflows of 20km/s or so, with a tendency for semi-periodic
behaviour as shown in a wavelet analysis that Peter carried out.
I gave a summary of some of the above work at the Cospar
conference in Nagoya, Japan (in July 1998), at the
Brendan Byrne Memorial Symposium at Armagh in Sept. 1998, and
at the IOP Plasma Physics conference at Pitlochry, March
1999 (this invited review appeared in Plasma Physics
and Controlled Fusion [IOP]).
Synthesis of X-ray line spectra for comparison with spectra
of solar active
regions and flares observed by the Solar Maximum Mission and
Yohkoh satellites.
These include helium-like magnesium, silicon, sulphur, argon, iron and some
other solar-abundant elements. The lines of He-like ions are sensitive to
electron density for low-Z elements. Dielectronic satellites which occur
near by are sensitive to electron temperature. He-like spectra are therefore
useful ways of remotely diagnosing solar plasmas. See Phillips et al. (ApJ
[1993], 419, 426) for work on Ar XVII, Harra-Murnion et al. (A&A [1996], 306,
670) for work on S XV. Mark Phillips (no relation!), a PhD student at QUB, and I
have started work on Mg XI for determination of flare densities,
continuing work of Dr Caroline Greer who worked with me a few years ago.
Benchmark Study of the MEKAL code with SMM Spectra.
The SMM data (from the Flat Crystal Spectrometer especially) are the
highest-resolution X-ray spectra ever obtained in the 1--20 Angstrom range, and
are an excellent resource for benchmarking atomic codes. Recognizing this, I set
up a collaboration with the SRON Laboratory for Space Research, Utrecht, with
funds from the Joint Scientific Research Programme of the Netherlands
Organization for Scientific Research (NWO) and the British Council, Amsterdam.
We even got an extension of this funding
till March 1999, which I am told is quite unusual.
Dr Rolf Mewe and Dr Jelle Kaastra
(SRON), Dr Louise Harra (MSSL) and I were involved in a study in
which we compared observed flare spectra from the FCS instrument with
theoretical spectra using the MEKAL code that Drs Mewe and colleagues have
developed over the years. The comparison has enabled improvements in
the MEKAL and associated codes to be made which will be useful for
looking at spectra
from the XMM and AXAF
(Chandra)
missions. The paper appeared in
Astr. Astrophys.
The British Council in Amsterdam featured us in a forthcoming brochure to illustrate
their work in funding joint projects.
Rolf has been very hard at work doing figures and tables that summarize
our fits. You can get one such version showing the comparisons between the
SMM spectra with the
MEKAL before and after line wavelength adjustments -- this can be viewed
clicking here (the plots on the
bottom two panels are the deduced emission measure distribution).
High values of electron densities in flare plasmas.
I collaborated with Queen's University Belfast, Mullard
Space Science Laboratory (UCL), Royal Holloway University of London, Goddard
Space Flight Center who have supplied atomic data or helped me with running
atomic codes (principally the Cowan HFR code). Although we often found that
flare densities were less than the low-density limit imposed by the atomic
physics, we found from a study of Fe XXI and Fe XXII lines that the electron
density in a very impulsive flare was 2 or 3 times 1012
cm-3 at its peak, exceptionally
high compared with most previous estimates, leading to the possibility
that the emitting volumes are very small and that at flare maximum cooling is by
radiation, at least for a time (see below).
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For
work on Fe XVII (Astrophysical Journal Letters), click here (file length =
178K) for a postscript file of the paper with
encapsulated figures. The work is based on some SMM spectral scans of the
intense Fe XVII lines emitted by solar active regions and flares. One of the
lines is marginally optically thick, which enables the path length Ne x l
to be determined for the emitting regions. This combined with the emission
measure Ne2 x L gives separately the electron density and
path length L. This
has application to the dimensions of small bright points which are being seen
by the SOHO EIT and other instruments and to active regions on RS CVn and
other binary star systems in which one or both members are chromospherically
active.
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Studies of X-ray flares
from Yohkoh. I did some extensive analysis of
morphologies and time characteristics of flares with Dr Uri Feldman, at NRL. We found that the bright loop-top
sources which are often seen and which have temperatures of up to 20MK
most likely lose energy by radiation, not conduction to the cool chromosphere
(where the temperature is 104 K). Equating the e-folding time for the
temperature decay to the radiation loss time leads to very high densities,
of order 1012 cm-3, in support of spectroscopic
findings (see above). My colleague
George Hanoun and I
worked on static loop models for flares and George has come up with some
elaborate graphics to represent the cooling of flare loops after impulsive
heating with various spatial dependence. You can view these on his web site. In
a later development, there is a fine TRACE image of a flare in the 192A
band which includes emission from an Fe XXIV line showing a whole set of
loop-top sources, which is great as it completely dispels the sceptics who
denied the existence of them, explaining them as a optical effect. I thank
George Doschek who recently pointed this out to me. With Uri and Louise Harra, I am just about to complete an analysis of six long-duration Yohkoh flares and a seventh, in 1999, seen by Yohkoh and SOHO SUMER, where I looked into nonthermal velocities measured from BCS Ca and S spectra. It's clear from the SXT data that the very large velocities are in reality due to the spatial extent of the flare in soft X-ray flares. I hope to elaborate on this soon.
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British Council
Collaboration with the Astronomical Institute, University of Wroclaw, Poland.
In a 3-year exchange programme, my Polish colleagues Jerzy
Jakimiec, Michal Tomczak, and Robert Falewicz, together with Andrzej
Fludra (RAL), we studied bright loop-top sources
(see preceding paragraph). We
developed an idea that Jerzy has been working on for some years that the kernel
is due to a region of tangled magnetic field, with continual reconnections
occurring that keep this part of the flaring loop energized and thus visible in
soft X-rays. The work has been published in Astronomy and
Astrophysics (A&A, 334, 1112, 1998 -- click here for a postscript file
(file length = 178K).
I gave a summary of this work at the Cospar conference in 1998; it eventually
appeared in Adv. Space Res., vol. 26 (2000).
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Element abundances
-- are a major topic in solar physics -- it is
widely believed that the coronal abundances are different from the photospheric
by factors of up to 3 or 4 for some elements, this depending on the value of
the first ionization potential (FIP). I have determined a number of element
abundance ratios which may or may not support these assertions, but some work I did a few years ago concerns the direct measurement of the coronal
to photospheric abundance of Fe, using X-ray lines which are formed
collisionally in a coronal (flare) plasma and in the photosphere, by
fluorescence. Analyses have been done using Yohkoh data (Phillips et
al. [1994],
ApJ, 435, 888) and SMM data. The conclusion was that this
ratio is one. However, more recent work on data from the RESIK instrument (PI Dr Janusz Sylwester, Space Research Centre, Wroclaw, Poland) on the Coronas-F spacecraft (published in ApJ (Letters), 2003, 589, L113) agrees with a FIP effect such that low-FIP elements are enhanced by a factor 3 in the corona, high-FIP elements are approximately the same as photospheric abundances.
I gave an invited review of this and other work at
the 1996 COSPAR Scientific Assembly (Adv. Space Res. [1997], 20(1), 79).
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With Dr
Jacques Dubau at Meudon Observatory, Louise Harra, and John Rainnie (QUB
PhD student at AEA Culham Laboratory), I worked on revising collisional rate coefficients for Fe XXV and Ca XIX X-ray lines seen by Yohkoh and SMM/XRP, so updating software. Jacques
calculated recombination rates for us for the S XV theoretical line spectra
which we didn't include in our A&A paper (Harra-Murnion et al. 1995, A&A., 306,
670). We finally finished this project in August 2003, when we submitted our write-up to Astronomy and Astrophysics. John used this as part of his PhD thesis which he successfully defended -- on a fateful day, September 11, 2001. We found
that, although the differences in the
w, x, y, and z line intensities are not very large, but there will be slight
differences in temperatures derived from the ratio of the j or k dielectronic
satellites to the w line -- this has been one of the main ways in which solar
flare plasmas have been diagnosed with spacecraft in the past. I am very grateful to Jacques who put a lot of work into this on
a visit we all made to Meudon in July 1998. He was also an excellent host,
taking us to every conceivable sight in Paris of interest!
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TOTAL SOLAR ECLIPSES
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The SECIS (Solar Eclipse
Coronal Imaging System)
Although observations from the Yohkoh, SOHO, and other spacecraft give
us a great deal of information about the Sun's atmosphere, in particular the
solar corona, it is not generally possible to get coronal images at very high
frequency, so there may be a range of phenomena occurring, like periodic
intensity modulations, without our knowing it. In recent years, investigators
like Prof. Jay Pasachoff (Williams College, Mass., USA) have been observing the
Sun's white-light corona at high frequency to search for evidence that the
corona is heating by short-period waves. Theory suggests that fast-mode MHD
waves with periods of a few seconds or less are likely to be candidates for the
corona's high temperature (of about 1 million K). I proposed
instrumentation (SECIS, Solar Eclipse Coronal Imaging System)
that would be able to do the same kind of investigation in which the
white-light corona would be imaged with very fast CCD cameras, operating at
30Hz. The experiment has funding from RAL under the
Facilities, Studies, and Technology (FTS) line.
A schematic of the experiment can be viewed by clicking
here .
Our award-winning
Eclipse WWW site gives some details
of this experiment. George Hanoun has done a fine job designing this site.
We have collaborated with
Prof. Bogdan Rompolt and
Dr Pawel Rudawy at the
Astronomical Institute, University of Wroclaw, Poland,
who have funding from the Polish Science
Funding Council, KBN, to build a high-precision heliostat.
We provided the rest of the instrument (lens,
green-line filter, CCD cameras, computer). Some of our
Bulgarian colleagues kindly arranged for us to observe the eclipse from Shabla,
on the Bulgarian coast of the Black Sea just north of the resort
of Varna.
A preliminary version of the experiment was taken out to the Caribbean for
the total eclipse on 1998
February 26.
Peter Gallagher
and I went to Guadeloupe (French West Indies), and
conducted the experiment with a group of other experimenters including Dr Serge
Koutchmy. We used a CCD camera that had been used for other purposes at RAL, and
a lens of very high quality kindly lent to us by Dr Francisco Diego (Optical
Sciences Laboratory, University College London). A specially adapted PC, from
Messrs Carr-Crouch (Maidenhead), was used to grab and store the more than 3000
frames of
data that we expected to capture during the 2-minute-long period of totality.
Unfortunately we were unable to get any results because of a loss of power,
almost literally at the last minute.
In August 1998, we went
to the National Solar Observatory/Sacramento Peak with this equipment to test
it out and make useful scientific observations with the 40cm Evans Solar
Facility (ESF)
coronagraph there. This was done at the suggestion of Dr Ray Smartt at NSO.
Peter was delighted to get funding from NSO on a
Summer Scholarship program, so he spent August and September 1998
there. I gave a presentation while at Sac Peak
about our activities. We had taken delivery of improved CCD cameras from EEV
(Cambridge) just prior to this trip; these are the ones we will use for the 1999
eclipse. Although we were troubled by cloudy weather,
Peter managed to get some nice images towards the end of the
allocated time on the ESF. The data were stored on tape.
Peter has a
movie on his Web site
for the ESF coronagraph data. It shows an
active region on the solar limb associated with a large sunspot group that had
been followed for the previous few days. The data set consists of 200 images,
taken in the green line at a rate of about 60 frames a second. Take a look also at
this image which is one formed by co-adding 1000
images of this sequence (about 15s long), and even better click
here for a really nice comparison between the
Sac Peak green line image, Yohkoh SXT, and TRACE that Peter has done. You can
see exactly where the footpoints of the Sac Peak coronal loops emerge from with
the TRACE image which was taken a couple of days (Sept. 5) before.
As a
result of my collaborations with the Astronomical Institute, University of
Wroclaw in Poland, my colleagues Dr Pawel Rudawy and Professor Bogdan Rompolt
and others have built an extremely high-precision
heliostat for the experiment. Click here for
a picture of the hardware (without mirror). The heliostat is
computer-controlled and adjustable for any latitude. We did some tests in
Wroclaw on both the sun and full moon in late May 1999 when we brought our
hardware across to them.
We put together the experiment for final tests in June and July then shipped it
to Bulgaria where, with the kind assistance of Prof. Vlado Dermendjiev and his
colleague Dr Maria Madjarska at the University of Sofia, we arranged to set up
our equipment on a Bulgarian Army Base in Shabla, on the Black Sea coast, NE
Bulgaria. Our Wroclaw colleagues transported their heliostat also. We had a
nail-biting time waiting for the SECIS kit to get across Europe and into
Bulgaria but just made it for the day before the eclipse. It was a nightmare at
the time, but on the day itself, August 11, the weather couldn't have been
better. We did our alignment and other tests with the heliostat in the hours
before the eclipse, then everything worked like magic for the eclipse itself.
The sky remained cloudless, the slight breeze that might have caused some slight
problems died away completely, and all our equipment worked perfectly! We played
back the movie on the PC that grabbed the data and found to our intense delight
that there were nice images in both channels, white-light and green-line.
Some 12728 images (6364 for each channel) were obtained in the 2m 22s of
totality, which occurred
at about 11:11 UT (14:11 local time).
We have now completed a lot of analysis. David Williams at QUB led a paper published in MNRAS on possible 6-s oscillations in a particular coronal
loop, while Pawel Rudawy and I have articles in the extremely well-organised
conference on 1999 eclipse results, held in Varna, Bulgaria in September 2000. Pawel's final write-up was submitted in July 2003 to Astronomy & Astrophysics.
I have no connection with the following paper on SECIS results:
Katsiyannis et al. (2003), Astr. Ap., 406, 709.
We have a
movie from both channels. The ``white light" channel
(left hand panel) shows the prominences as well as the coronal structures,
while the ``green line" channel shows only the coronal features. The last frame
is when the photosphere just starts to peep through. Each movie is made up of
every 100th frame of the total of 6364 images each channel over the 2
minutes 20 seconds of totality. David's wavelet analysis for just a small
portion of the green line images (top of a coronal loop) over a 44-second
interval shows possible temporary periodicity -- click
here for the figure that shows this.
The paper I wrote with colleagues on the
instrument and preliminary results finally appeared (after a long, inexplicable
delay) in Vol. 193 of Solar
Physics -- I will send preprints on request (see contact details below).
In the movie, you can see the
sun's west limb, with north at the bottom right. There is a curious
prominence apparently suspended just off the south-west limb which most photos and movies
managed to catch. Speaking to someone at the recent Eclipses et Couronne Solaire
conference in Paris (April 2000) I found that the prominence is in fact in the
form of a small loop that perceptibly changed orientation between the time we
saw it during the Bulgarian eclipse and the time Serge Koutchmy and colleagues
saw it during the Iranian eclipse, an hour later.
Another small prominence on the north-west limb comes into view
towards the end of the totality period as
the moon's disk slides across the sun.
It's possible that one of the prominence systems we recorded on the west limb is
a post-flare loop system -- if so the flare occurred just over the
sun's west limb.
As mentioned above, you can see pictures of the eclipse and expedition on
Robin Barnsley's
web site.
It was a great shock to hear, just after the New Year 2001,
that Prof. Vlado Dermendjiev, who was so instrumental in getting our
equipment into Bulgaria and who became a close friend, died suddenly of a
heart attack. I was very grieved by this news. I am sure many friends,
colleagues and of course his family will miss him a very great deal. He did a
wonderful job in organising the Varna conference in September 2000. What a loss
to solar physics! The Proceedings of the Varna conference will be dedicated to
him.
A full report of our 1998 eclipse expedition is available by clicking here (128K).
Don't forget to check out our award-winning
web site which
George Hanoun has designed. This contains some nice ``fly-through" movies of
our equipment which he and Barry Kellett have done with a webcam. I wrote a light-hearted
account of our 1999 eclipse experiences for the December 1999 issue
of the Salford Astronomical Society journal -- click
here to see it.
There were a couple of articles in the Daily Telegraph and even The
Sun!
I have made a few TV and radio broadcasts on this experiment (Radio 4 interviews
with Trevor Phillips -- one-time London Mayor candidate and again no
relation! [1.7.99, 23.9.99], UK Today TV,
Discovery Channel) and
have done magazine interviews
(New
Scientist [end of May], New Electronics, Physics Today,
Scientific Computing (IOP) ).
Peter Gallagher and I are featured on the BBC
Online Web site.
An article on coronal heating -- ``The Paradox of the Sun's Hot Corona'' --
has just appeared in the June 2001 issue of
Scientific American, written by me and Bhola Dwivedi,
my friend and colleague at the Banaras Hindu University in Varanasi, India. It
is the cover story for this issue of Scientific American. The Editors of
the magazine have done a wonderful job in including imagery of the corona from
the SOHO, TRACE and Yohkoh spacecraft.
Incidentally, some of our time at Sac Peak in August/September 1998 was
spent using the Vacuum Tower Telescope to
observe the photospheric filigree in a collaborative project with
the TRACE spacecraft. Peter achieved some magnificent images of a gigantic
erupting prominence
associated with a moderate-sized flare -- see Peter's
web site for them. We wrote
up the results of this in a Solar Phys. paper. It appears that much of
the flare energy went into
mass motion rather than radiation. I hope we can do further analysis some time,
before I retire!
The above has to be updated quite a bit -- when I get some time I will describe
our trip to Zambia for the 2001 eclipse in more detail.
Meanwhile watch this
space!
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Research activities
FLARE STARS
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Flare stars are cool, M-type stars that show sudden brightenings in optical and
other spectral regions which appear to be related to solar flares. Emission
lines in the optical and UV strongly imply the existence of a solar-type
chromosphere and transition region, and X-rays imply that there is corona.
I worked with Gordon Bromage (University of Central Lancashire)
and others on a project in 1991/92 to study the
origin of the UV continuum that appears in IUE SW spectra of dMe stars in
a flaring state. The continuum is definitely real, not instrumental, and is
particularly strong at wavelengths longer than 1500A. There is an analogous
continuum emitted in the quiet sun which is strongly enhanced in flares,
as has been seen with the NRL spectrometer on Skylab. In the solar case the
continuum is due to free--bound transitions in Si II, with excitation
occurring by intense UV lines such as the C IV doublet at 1550A. These lines
are even more intense in the case of dMe stars, especially in a flaring state,
and so the excitation of Si recombination radiation is much enhanced. This
leads to an approximately proportional relation between line and continuum
emission expressed as a power (erg s-1), as is shown in our paper
to exist for flares of various magnitudes on a number of dMe stars.
More recently, I have been working with colleagues at Queen's University Belfast
(Mihalis
Mathioudakis etc.) on HETGS spectra of Capella from the
Chandra (formerly AXAF) spacecraft. We investigated optical depth
effects and electron densities. A paper analyzing a Chandra HETGS X-ray
spectrum of Capella as well as near-simultaneous spectra from the
EUVE satellite was published in MNRAS (not my choice of
journal! I would have preferred A&A or ApJ where the refereeing would have been
less predictable than with the same old cronies who edit MNRAS).
In it we included a
comparison of the Chandra spectrum in the 8--20 A range with the
equivalent spectrum from the decaying stage of an M-class solar flare
as seen with the SMM spacecraft. Click
here for a figure showing this. Notice how
similar the line intensities are, as well as the spectral resolution at
wavelengths greater than 13A. The Fe XVII 15A and 17A lines are prominent in
both, as is the O VIII Ly-alpha line at 18.97A. Although it appears that the
intensity ratios are different, they are not in fact -- there is a strong
wavelength-dependent FWHM in the Chandra spectrum. So I believe the solar
and Capella abundances are quite similar which argues against the so-called FIP
effect which I don't think has much evidence going for it in spite of the hype.
A differential emission measure analysis indicates that much of the material in
both Capella and the decaying solar flare is at a temperature of about 6MK.
More details will follow soon. The electron density from O VII ratios and the
relatively small emission measure leads to extremely small volumes. I feel this
is an indication that there is in fact no significant corona on either of the
components making up Capella -- rather, that there is an intra-stellar source
that somehow retains its identity, perhaps through magnetic field confinement.
If not, the corona of either star must consist of just a few loops, but then
it's puzzling why there is no significant rotational modulation (one component
rotates very rapidly).
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Brendan Byrne Symposium
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There was a meeting to commemorate the life and work of the late Dr Brendan
Byrne (Solar and Stellar Activity: Similarities and Differences)
in Armagh, September 2--4, 1998, at which I gave a review of solar flares.
The Proceedings were published by the Astronomical Society
of the Pacific (ed. by John Butler and Gerry Doyle).
Brendan was a good friend of mine and I miss his infectious humour and
enthusiasm for his subject. It was sad to hear of his tragic death.
Click
here
for a shot of me (on right) with colleagues at the great dinner
we had at Castle Leslie (just across the border in the Republic)!
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SELECTED PAPERS
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My article on "SOHO: our New View of the Sun" was in the April 2000 issue of
Astronomy Now magazine which came complete with a SOHO CD-ROM.
For my other publications, I will eventually have a complete list which will be
viewable from this site. Meanwhile, you can get
postscript files of some of my publications from . There is an out-of-date
list of my publications you can get by clicking here.. I will get this updated as soon as possible.
Here is a list of some papers that are referred to above -- preprints
available as postscript files in some cases:
- Phillips, K. J. H., Bhatia, A. K., Mason, H. E., and Zarro, D. M.,
1996. `Very high electron densities during an intense flare observed with SMM.'
ApJ, 466, 549.
- Phillips, K. J. H., Greer, C. J., Bhatia, A. K., and Keenan, F. P., 1996.
`Active region electron density and dimensions from Fe XVII X-ray lines.'
ApJ (Letters), 469, L57--L59.
- Phillips, K. J. H., Greer, C. J., Bhatia, A. K., Coffey, I. H., Barnsley,
R., and Keenan, F. P., 1997. `Fe XVII X-ray Lines in Solar Coronal and
Laboratory Plasmas.' A&A, 324, 381--394.
- Gallagher, P. T., Phillips, K. J. H., Harra-Murnion, L. K., and Keenan, F.
P., 1998. `Properties of the Quiet Sun EUV Network.' A&A, 335, 733.
[Postscript version available (6.15Mbyte)]
- Jakimiec, J., Tomczak, M., Falewicz, R., Phillips, K. J. H., and Fludra, A.,
1998. `The Bright Loop-top Kernels in Yohkoh X-ray Flares.' A&A, 334, 1112.
[Postscript version available with some figs (165Kbyte)]
- Phillips, K. J. H. et al., 1998. `The Quiet Sun Atmosphere as seen by
SOHO.' Presented at COSPAR 1998 Scientific Assembly, Nagoya, July.
[Postscript version available with figs (2.8Mbyte)]
- Phillips, K. J. H. et al., 1998. `What are the Bright Loop-top Kernels in
Soft X-ray Flares?' Presented at COSPAR 1998 Scientific Assembly,
Nagoya, July.
[Postscript version available with figs (3.5Mbyte)]
- Pres, P., and Phillips, K. J. H., 1998. `The Magnetic Association of
Coronal Bright Points' ApJ Letters, 510, L73.
[Postscript version available with figs, 403Kbyte)]
- Pinfield, D. J., Mathioudakis, M., Keenan, F. P., Phillips, K. J. H., and
Curdt, W., 1998. `The O V 1213.9A forbidden line in the quiet Sun' A&A, 340,
L15. [For reprints, email dpi@star.pst.qub.ac.uk]
- Phillips, K. J. H., Mewe, R., Harra-Murnion, L. K., Kaastra, J. S.,
Beiersdorfer, P., Brown, G. V., and Liedahl, D. A., 1999. `Benchmarking the
MEKAL spectral code with solar X-ray spectra' A&A (to be published).
[Postscript available with
figures, 1MB]
- Gallagher, P. T., Phillips, K. J. H., Harra-Murnion, L. K., Baudin, F., and
Keenan, F. P., 1999. `Transient Events in the EUV transition region and
chromosphere'
A&A, 348, 251.
- Gallagher, P. T., Mathioudakis, M., Keenan, F. P., Phillips, K. J. H., and
Tsinganos, K., 1999. `The Radial and Angular Variation of Electron Density in
the Solar Corona.' ApJ Letters, 524, L133.
- Phillips, K. J. H. et al., 2000. `The Quiet Sun Atmosphere as seen by
SOHO.' Adv. Space Res., 25(9), 1747--1750 (reprints available).
- Phillips, K. J. H. et al., 2000. `SECIS: The Solar Eclipse Coronal Imaging
System' Solar Phys. Vol. 193, 259.
- Phillips, K. J. H., 2000. `Why is the Sun's Corona so Hot? Views from
SOHO, Yohkoh and solar eclipses'. Plasma Phys.
and Controlled Fusion (invited review) 42, 113--126 (reprints available).
- Dwivedi, B. and Phillips, K. J. H., 2001. `The Paradox of the Sun's Hot
Corona.' Scientific American (June 2001) (reprints available).
- Phillips, K. J. H. et al., 2001. `X-ray and EUV Emission from the Coronae
of Capella.' MNRAS Vol. 325, 1500 (reprints available).
- Phillips, K. J. H. et al., 2003. "Solar Flare Abundances of K, Ar, and S." ApJ (Letters), 516, L113.
- Phillips, K. J. H., 2003. "The Solar Flare 4 - 10 keV X-ray Spectrum." Accepted for publication, ApJ.
- Phillips, K. J. H., 2003. "Improved Data for Solar Flare X-ray Analysis." Submitted to A & A.
- Phillips, K. J. H., Feldman, U., and Harra, L. K., 2003. "Nonthermal Velocities in Solar Long-Duration X-ray Flares." Soon to be submitted to ApJ.
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