AVSO 2001 FALL MEETING IN SOMERVILLE
-----------------------------------
John Pazmino
Amateur Astronomers Association
New York
2001 November 6
The American Assoication of Variable Star Observers, AAVSO, 90th
annual fall meeting, 2001 November 1-4, was one full carload of news
{and learing. With so many papers and deep corridor chat, I give here
my own highlights.
Venue
---
This year, like in the past several years, AAVSO had to shift out
of its home turf of Cambridge in search of cheaper hotels. Boston and
Cambrisge in the 1990s suffered hotel rates rising to the upper edge
of most AAVSOers's reach. The convention was held at the Holiday Inn
hotel in Somerville, a town adjacently northwest of Boston. The rates
were refreshingly lower than the Boston-Canvridge levels, yet the
Holiday Inn property was quite comfortable and pleansant.
All convention events were in this hotel, except for the open
house at AAVSO headquarters on Thursday evening, the 1st of November.
We went there by hired bus. Optionally, for a change of menu, we could
take in local eateries within a ha'K of the hotel.
Going to AAVSO
------------
I travelled by rail, my usual method, leaving Penn Station in mid
morning on Thursday the 1st and arriving at South Station in Boston
quite four hours later. I did not try the new Acela bullet train
because the timing of its flights was no real advantage over the
regular all-electric trains.
When I went to AAVSO last October, the catenary was installed
along the entire line but was not energized. The train, running by
electric from New York to New Haven, had to change its locomotive to
continue on the nonelectric road to Boston.
Now, for my own first time, I rode not only under wire but powered
by it. The shorter stop in New Haven, only a moment to exchange
riders, and the higher running speed from there to Boston, chopped
quite a full hour from the total trip time.
From South Station the Boston subway brought me to Sullivan Square
A ten-minute walk got me to the Holiday Inn. On Sunday the 4th I
retraced my steps to Sullvan Square, South Station, Penn Station.
Accommodations
------------
The hotel was a full service property with all the necessities and
conveniences for conventions. For a Holiday Inn the food was ample,
well prepared, and tasty. The rooms were clean, properly furnished,
and acclimatized.
There was one really silly goof. All the clocks were still on
daylight savings time! This meeting was a full week after the fall
back to standard time, but this hotel didn't get around to resetting
its own clocks! This caused wild mixups on the first day of the
meeting! We ourselfs put the clocks back.
Attendance
--------
The meeting seemed about as fully attended as any I can recall.
There was no severe depression like for many other conventions,
museums, theaters, other public activities since September 11th. This
depression of attendance, for example, cut the American Urban Star
Fest on October 20th to a mere one thousnd visitors. But this AAVSO
had about eighty delegates, up to or just a little below par.
A few did have trouble getting convenient airline reservations
(virtually all who did not drive to Somerville came by air), but they
eventually get to the convention. One feature just about all the
delegates noted was the appallingly relaxed passeneger security
screening at their home airports. It's as if nothing extra is in place
since the September 11th catastrophes.
We had seven delegates from overseas: Argentina, Australia,
Belgium, Canada (two), England, Finland. The City was represented by
Winston and Carmen Wilkerson, Joe Patterson, and myself.
World Trade Center
----------------
When I signed up for the meeting I had no thoughts about the World
Trade Center tragedy. In the weeks before the meeting, however, about
20 of the busload of Boston astronomers coming to see the Hayden
Planetarium and American Urban Star Fest went to Ground Zero in the
stead of doing the Museum or other touristy sights. Also, several
delegates fixing to attend the AAVSO meeting convoed with me about the
event. At this convention I was going to be a very fount of news about
the event!
I assembled a collage of pictures of the September 11th incident
on two sheets of poster paper for display on my hotel door. This
replaced my usual posters of general New York City scenes. Overall,
the elegates liked the posters and much lively discourse ensued from
them. I learned during a session break on Saturday that a few got
emotionally sick from the scenes, moving me to take down the posters.
Luminous graffiti
---------------
It was disheartening to hear the general tone that the struggle
against luminous graffiti seems so hopeless. The delegates bemoaned
its relentless spread as reckless trashlighting is applied to new or
remodeled properties. Altho some were members of International Darksky
Association, they had virtually no local effort to stem the tide of
luminous graffiti. Most more or less gave up on their local astronomy
clubs for being far too small and powerless in their community to
raise an effective voice.
On the other hand, a more surprising feature, this one among the
Boston delegates, was the utter disregard of a welcome light abatement
scheme literally right outside the hotel! Somerville in the last year
or so replaced at least some of its streetlamps with shielded lamps.
These are similar to the ones, but heftier and taller, used for area
lighting on properties thruout the City. Yet no one spontaneously
offered these as an example of success in the darksky movement!
I noticed these lamps first thing I started walking from the
subway to the hotel. When I asked about them I got either a puzzled
ignorance or delayed words of appreciation.
The AAVSO convention in fall 2002 will be jointly run with IDA.
This was done in about 1989 and there was a local light pollution
meeting several days away from an AAVSO meeting a few years ago.
Digital presentations
-------------------
This is the first AAVSO meeting where the clear majority of
presentations were made by computer. The use of PowerPoint or similar
buisness graphics programs ruled the sessions. The image files were
loaded onto an AAVSO laptop, having been sent to AAVSO by the authoers
via email. A digital image projector sent the computer display to a
regular slide projection screen.
The screen display was acceptable from a mid or far seatt. Up
close it fell apart compared to chemophotgraphic transparencies or
phocopied viewgraphs. None of the shows employed sound, the author
voiced over thru a microphone.
Most of the remaining presentations used regular viewgraphs or
'overheads' on transparent sheets of acetate. These were projected
opticly via a tabletop lamp-&-lens device. Only ONE presentation
showed its pictures via chemophotographic slides -- mine!
The other dark sky
----------------
What I learned over the ages was that while the City is fondly
adored for its fullpress eradication of luminous graffiti, the
strategies we practice here are often not relevant or applicable
elsewhere. The scope and scale of New York are too overwheming and the
methods too rich for the mid American town to emulate.
The result is that in some regards New York is a Shangri-La of the
darksky movement but not really a role model. I presented aspects of
the City's light abatement ethic in scenes from the bedroom hoods of
Brooklyn. I photographed them by riding my peculiar bus route on
several evenings before the convention. (This was no trivial task,
under the jitters from September 11th!)
Brooklyn's nabes are the size of mid American towns: Canarsie,
Midwood, Nostrand Junction, Woodlawn, Bensonhurst. They have a
commercial and retail section, transit station, schools, markets which
the delegates could identify with as being like their own. The
delegates took to this show handsomely. Several aggressively scribbled
notes and later hounded me for details.
Gamma ray bursters
----------------
AAVSO a few years ago began a project to monirtor the optical
afterglow of gamma ray bursters, GRBs. When the HETES or SAX satellite
spots a burster, an alert is sent to AAVSO. There it is relayed by
pager to a selection of observers with proper longitude, object
altitude, equipment, and so on.
The observer tries to image the GRB to trace the lightcurve of
any optical radiation. In theory this is a viable project but it is
strewn with obstacles. Out of the hall chats I learned that generally
the optical radiation -- if any -- was far too faint for the home
astronomy equipment among the observers. There were too many null
reports, time and effort expended with no positive images to show for
it.
There seems to be a far longer than tolerable lag between the
sighting of a burst and the observer's receipt of the notice, 1/2 to
one full day. With the GRB being a transient event, the optical glow
may well have faded beyond reach by the time the AAVSO alert arrives.
Other observers changed their life routine since signing up. They
are now no longer handy at their observatory but away on jobs or
travels. Altho they still get the pager alert, they have to let it
pass unheeded. Those who have entree' to their observatory found that
it does take naggingly long to fire up the equipment from a cold
start. Some delegates noted it takes as long as two hours, a precious
two hours, while the GRB radiation may ebb out of reach.
Despite these problems, Arto Oksanen from Finland presented his
success in capturing a gamma ray burster from the Nyrola town
observatory. At 62-1/2 degree north latitude, it sports a Meade LX200
400mm scope and a SBIG 7 CCDgraph. He tried for five alerts since
September 2000. He succeded in tracking only one GRB, in December
2000, by good photometry. He showed his data, a declining light curve
in the 19th magnitude range, plus a picture of the burster in its
galaxy.
Radio time signals
----------------
Part of the requirements for properly recording gamma ray
bursters, and certain other variable stars, is an accurate precise
source of time. Traditionally this was the shortwave broadcasts on
station WWV. These are precise to the millisecond anywhere within the
US mainland (station WWVH works Hawaii).
In September 2001 US NIST, ex NBS, circulated a customer survey
about its time services. Rumors sprang up that NIST was scheming to
close down the shortwave time signals. This proved completely false,
altho the results of the survey will help NIST review the overall
operation of its time services.
I learned from the delegates that there has been over the 1990s a
steady abandonment of radio time signals by overseas countries. The
usual reason offered was lack of civilian or public need for them.
For home astronomers, on the other hand, the loss of the radio
signals caused a decay of time-critical work, notably variable star
and occultation timing. In the US, at least, NIST offers Internet and
dialup time service, which did deeply substitute for the radio
service. What's more, with more and more home astronomy work carried
out via computer and the rapidly declining ownership of shortwave
radios, any eventual shutdown of the NIST radio service would be
mostly harmless.
GPS time service
--------------
One new source of time service coming into wide use among home
astronomers is the GPS. The handheld receivers pick up UTC precise to
the microsecond along with the geographic location. This time signal
is used internally by the receiver for navigational calculations. Many
receivers can deliver the time and other output digitally to a
computer via a connecting cable, making it easy to combine timing with
other observational data.
Some delegates pointed out that the GPS time signals are not
adjusted by leapseconds. UTC was corrected by inserting a leapsecond
every so often, the last being on 31 December 1998. Since then the
leapsecond was suspended, altho UTC continues to drift against Earth's
rotation, or solar, time. Are the GPS receivers really showing this
uncorrected GPS time and mislabelling it UTC?
No, they should display true UTC. Along with the time and other
items sent down by the GPS satellites is a code that includes the UTC
offset from GPS time. Because GPS is governed by the same atomic
clocks as the world standard of time, GPS time is now exactly 13
seconds ahead of UTC. That is, since when GPS system started on 6
January 1980, 13 leapseconds were added into UTC, but not into GPS.
The GPS command station in Colorado sends up as part of its
routine housekeeping of the satellites the current leapsecond count.
Right now it's holding steady at 13 seconds, with so far no plans to
resume leapsecond insertions. Your GPS receiver picks up this offset
and bumps GPS time to coincide with UTC. The displayed time is UTC.
Cataclysmic variables
-------------------
I give here a short background about cataclysmic variables because
they were the theme of several papers and collateral banter. A
cataclysmic variable star is a star whose radiation output changes due
to rapid and violent activity within it. These are eruptions,
convulsions, upheavals which cause major outbursts of radiation in
several spectral bands. These outbursts typicly recur on timescales
ranging from days to decades for a given example.
The cataclysmic variables are white dwarfs in tight binary
systems. The distance between the dwarf and is companion is only a few
diameters of the very stars. The orbital period is mere hours. The
stars are not actually merged but there is gross mass flow between
them. The interaction of this material flux and the white dwarf
triggers the flareups via one of many methods.
From the variety of interactions known, the cataclysmic variables
are classed by a prototype specimen for each interaction. An SS Cygni
star is a star whose radiation changes are like those of SS Cygni
itself, implying a certain mechanism for causing the eruptions.
In the quiet phase a cataclysmic variable is normally quite faint
and beyond range of small home instruments. At outburst the star can
be captured in modest scopes, at least in the hours and days near the
maximum emission. Altho the timescale between eruptions is known the
occurrence of a particular eruption is entirely unpredictable. Thus,
these stars must be under a continual watch, as they are by AAVSO
observers.
We recalled David Levy's talk at last year's AAVSO meeting in
Waltham. He related Clyde Tombaugh's discovery of an early specimen of
cataclysmic variable, TV Corvi. This star is a reccurrent nova,
flaring up every couple decades.
Infrared obsrvations
------------------
Cataclysmic variables, or CVs, are studied reasonably well in
optical, ultraviolet, and X-ray bands. It so happens that infrared
measurements are scanty, leaving a hole in the spectral profile of
these stars.
George Hawkins in summer 2001 collected infrared data on CVs in a
stunning example of indoor armchair home astronomy. The 2MASS infrared
sky survey is sufficently complete to cover most of the sky and its
archive is online for open access. Hawkins found that 41 CVs were
recorded in the 2MASS data when these stars were at or near an
outburst. Each star was by chance captured in one or an other of the
three 2MASS IR bands.
For each star Hawkins had the 2MASS single datapoint and AAVSO
visual lightcurves. He found that the existing types of CV generally
grouped together on graphs of visual color index against infrared
color index. This adds substantial evidence that the existing types do
have similar mechanisms for causing the eruptions.
Note that he did no observation himself but availed of databases
freely open to anyone, making this study a prime example of exploiting
the 'virtual universe'.
Discussion elsewhen explored the prospects of home astronomy work
in infrared bands. Some CCDgraphs can operate in near infrared and
many telescopes transmit some of the infrared. However, there is an
immense 'skyglow' of terrestrial infrared which may for most home
astronomers close them off from this new work.
Because no one 'sees' this infrared radiation and it is so
pervasively emitted from heat sources, there may be no feasible way to
lessen it. That is, it may be totally impossible to mount a 'infrared
pollution' movement.
Type Ia supernovae
----------------
Supernovae of type Ia are used for fathoming cosmological
distances. They are seen very remotely due to their extreme brilliance
at explosion and reasonably emit a certain same radiation at peak
brilliance. This latter feature follows from their supposed origin
from white dwarfs of about 1.38 solar masses. This peculiar mass is
the Chandrasekhar limit of mass, above which a white dwarf can not
sustain itself and must collapse and then detonate into a supernova.
Because all type Ia supernovae come from the same kind and mass of
star, many astronomers believe that the radiation emitted during the
explosion is the same for all and thus serve as a known candlepower
source by which to assay their distance. Dr Robert Kirshner at the
Saturday evening special lecture explained the importance of these
type Ia supernovae.
When detected, a spectrum is captured to measure the redshift Z.
From the peak radiation, of known atrength, the distance to the
supernova is figured out. The two are plotted on a Hubble expansion
diagram as points in the far remote reaches of the universe where
there are few other reliable means of assaying distance.
Such measurements are crucial for fixing a better value for the
Hubble expansion factor H0. In the standard cosmology model, the
universe began expanding from the bigbang and has been steadily
slowing since then. The deceleration comes from the braking action of
the gravity contained within the universe. The main disputes about the
universe circle around the amount of gravity, or mass, within the
universe to merely slow the expansion, stop it, or even reverse it
into a collapse.
Out to about 5 billion lightyears the supernova datapoints do sit
on the standard Hubble expansion curve, comforting us in our
interpretation of the radiation and spectrum of these stars. From 5 to
8 billion lightyears away, Kirshner finds that the supernovae diverge
from the Hubble curve in the sense of a local reversal of the
slowdown. Or there seems to be a period when the universe was in
accelerated expansion.
This finding is severely challenged and the flaw may be in the
physical processes of type Ia supernovae. Kirshner feels that we are
looking at the same kind of star remotely as those nearby. A detailed
examination of the lightcurve of the remote stars shows no evidence of
chemical or physical evolution that may throw off the standard candle
model.
So far this is a raw discovery with no theory to support it. The
line of inquiry now is to reconsider the lambda factor in Einstein's
equation of state for the universe. When the expansion of the universe
was demonstrated by Hubble and Humason in 1929, Einstein dropped this
parameter as being a gross mistake in his work. From then on, the
absence of lambda made way for the Friedmann-LeMaitre model, with a
montotonic deceleration. If the type Ia supernova findings are
validated, perhaps the whole edifice of cosmology could be
exfenestrate.
Type Ia progenitor
----------------
One theory for the creation of a type Ia supernova is that a white
swarf in a binary system accumulates mass from its companion star. In
doing so it can become a cataclysmic variable star and eventually grow
above the Chandrasekher mass limit. At this moment the star can not
stand up under the overburden of material and suffers catastrophic
collapse. The resulting explosion is the supernova event.
Hence one motivation for studying CVs is to understand supernovae,
which in turn refines our ability to use them as cosmological beacons.
Dr Bradley Schaefer inquired if the white dwarf can ever actually
build up mass over time. After all, in the repeated eruptions as a CV
mass is ejected, offsetting that piled onto the star between
eruptions.
With CVs being in binary systems, a study of the orbit should
reveal mass changes of the components. Schaefer found nine special
CVs, the recurrent nova class, which shed mass by outbursts every
couple decades. Two happen to also be eclipsing binaries, CI Aquilae
and U Scorpii.
Eclipsing binaries allow for extremely sensitive orbital
investigations of the delicacy required for mass gain and loss in the
white dwarf. By collecting orbital data for these two stars from
between their outbursts, Schaefer showed that the mass loss during an
eruption was ten times the mass gain since the previous outbrst. The
absolute amount is only a dozen millionth solar mass, but it's the
netting effect that matters. Hence, it looks like recurrent novae, as
a class of CV, can not become type Ia supernovae.
HIPPARCOS variables
-----------------
One area of work opening up for home astronomers is the ultralow
amplitude variable star, one whose range of illumination is hundredths
of a magnitude. These stars to the visual observer are sensibly
constant but with modern CCDgraphs they can be easily and confidently
monitored. But they do have to on the bright side for the smaller home
telescopes. Are there any good number of such low amplitude stars
among the bright stars in the sky?
Dr Dorrit Hoffleit reviewed new variable stars found in the
HIPPARCOS survey against her own Bright Star Catalog. The latter is
the definitive catalog of stars within binocular range for home
astronomers. She found 275 of the new HIPPARCOS variables are in the
BSC!
They cover many types from pure eclipsing binaries to UV Ceti
class of CV. The amplitudes are from 0.01 to 0.04 magnitude. It is no
surpise they were not discovered earlier but they now are candidates
for modern home astronomy equipment to examine.
In the Q&A, one peculiar star discussed was epsilon Pegasi, not
one of the new ones but a throny one from the history books. This is a
stable star of 2.4 magnitude in the nose of Pegasus, about halfway
between Altair and the Great Square. In 1972 it swelled up to about
0.7 magnitude for a few weeks and then settled back down.
There is little doubt of the incident, with many experienced
observers recording it. Yet there is no explanation for this unique
behavior. epsilon Pegasi turns up like a wooden nickel because some
star catalogs list it with the maximum brightness and not its normal
one. In consequence, a chart made from such catalogs distorts all of
Pegasus, leading innocent astronomers to rediscover the star's long
ago antics.
CCD workshop
----------
Friday morning was taken by a comprehensive workshop on CCDgraphy,
with emphasis on photometry. The procedings reviewed the technical
construction and operation of the CCD chip but eventually came around
to its use for astronomy. Arne Henden chaired the session.
The chip was invented in the early 1970s as a memory storage
device in computers. The cells of the chip would hold electrons
corresponding to the value of memory addresses. Its ability to become
charged under the influence of light was quickly discovered and its
applicaton to video imaging soon followed.
An image captured by a CCDgraph must be processed to remove global
erros and distortions. There are two major corrections the home
astronomer must apply before even beginning to avail of the image for
astrophotometry. First, and easiest, is to eliminate the dark current
bias. The chip charges up with temperature such that the cells are not
fully empty in the absence of light.
The dark current is removed by digitally subtracting an image taken
with the CCDgraph's shutter closed. The resulting image is gray from
the nonzero value of each cell. Most home CCDgraphs can capture this
dark current image, the dark field, by a feature in the computer
program that runs the CCDgraph.
The other major correction is the flat field. In theory you image
a uniform illuminated surface to reveal vignetting, hotspots,
obstructions in the optical system in front of the CCDgraph. A typical
trick is to image the twilight sky or the inside wall of the
observatory.
It turns out that the sky is really not a good flat field target
due to stars embedded in it. While invisible by eye, these stars are
recorded by the CCDgraph. It further turns out that an indoor
artificial smooth and uniform lighted surface is extremely tough to
make. There are always subtile variations of illumination across the
surface, unnotived by eye or handheld photometer. Assorted
contraptions were shown, none being really convenient or reliable.
Discussion flowed on terrestrial influences on CCD chips. A strong
radar, like from a nearby airport, can raise up spurious charges in
the chip. So can strikes by cosmic ions. The latter is a substantial
problem for observatories at high elevation, where the cosmic influx
is stronger.
Isolating a single star for photometry is not a trivial chore. A
diaphragm is placed in the field to admit thru it just the target
starlight and exclude extraneous circumstant illuminations. Ideally
the target is a hard point sitting on a black sky background. If the
star is in a dense field or a cluster or is surrounded by luminous
nebula, photometry can be quite wobbly.
One way of getting passable resutls is to plot star illumination
against diaphragm aperture. By closing down the diaphragm you get
lower values (less sky, nebula, adjacent stars). The readings approach
a limit, which is as good as any for the true illumination from the
target star.
Solar activity
------------
AAVSO has a section for solar observation on the grounds that the
Sun, with its sunspots, is a 'variable star'. There was no specific
report about this section but we did try sunviewing thru one
delegate's portable scope. The sky was generally cloudy but we did see
a couple larger spots.
There was anticipation for aurorae in the next few days with the
appearance of very large spots and some folk wanted to check for
electromagnetic effects soonest they got home.
Leonid meteor storm
-----------------
Just about everyone was excited about the upcoming Leonid meteor
storm. Most by the meeting dates arranged for some darksky viewing but
I didn't notice anyone making a long distance trip. Everyone figured
to stay within a couple hours's drive of their home. For sure there
was no mass migration from elsewhere in the US toward the east coast,
where the geometry of Leo and predawn are most favorable for a major
downpour of meteors.
AAVSO news
--------
Dr Janet Mattei, AAVSO Director, gave her annual report for the
period October 2000 thru September 2001. The cumulative number of
observations on record is about 10,300,000 with some 420,000 received
in the report period. About 70% of the observations come from overseas
with 30% from the US. Altho CCD reports are steadily increasing, so
far AAVSO keeps these separate from the visual ones and maintains a
separate set of charts and standards for CCD work.
Membership is toggling in recent years at 1,100 wihle about equal
dropouts and newcomers each year. In 2000-2001 over 80 new members
were enrolled, the largest in AAVSO history; about 80 fell off of
the rolls in the same period. Peculiarly, most members are not actual
observers and most observations are turned in by nonmembers!
Overwhelmingly the observations are filed by email, with paper
reports rapidly falling off. The digital reports are formated such
that they can be posted on the AAVSO website for a first look within
1/2 hour after receipt.
With essentially all AAVSO data, charts, and news now on its
website, the number of manually processed requests fell to only a few
per month. In contrast, the website gets several thousand visitors and
many hundreds of downloads per day.
About 3/4 of the data taken from the website is used to coordinate
or correlate with observations made from satellites. AAVSO has a strong
mission to furnish its visual records to supplement the multispectral
views from space beyond the optical band.
Next meeting
----------
The next meeting is in July 2002 in Hawaii! Excursions to Mauna
Kea, the volcanos, starviewing sites, and scenic areas are in the
works. A workshop on high energy astronomy, a field more and more
germane to the home astronomer, is on the boards and special
delegations from Pacific nations are expected to attend.
Hawaii is at 20 degrees north latitude, offering a 'latitude
adjustment' for mainland US astronomers. The entire summer Milky Way
and galactic center are high in the sky, along with many of the fabled
southern clusters and nebulae.