Eyepiece Views: March, 2006

Table of Contents
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1. Introduction
2. Recurrent Novae
3. Astrophysics from Visual Observations
4. Manual for Visual Observing of Variable Stars - New Translations Underway
5. A Date with U Gem — An amateur's humble contribution to the world of
science
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1. INTRODUCTION

Spring is around the corner... Almost! For the AAVSO, quite a bit is in
store. First, there is the spring meeting in Rockford, Illinois (May
4-6, 2006). We have many interesting events planned for this meeting.
For more detailed information, please visit the URL below:

http://www.aavso.org/aavso/meetings/spring06.shtml

Arne has a full schedule this spring/summer. He is scheduled to give a
talk at the British Astronomical Association (BAA)'s annual meeting in
May. He is giving another talk in New Plymouth, New Zealand, in June at
the Royal Astronomical Society of New Zealand's annual conference.
August was not going to be left without a meeting, so Arne decided to fly
to Prague, Czech Republic, for the International Astronomical Union
(IAU) General Assembly! On that trip he will also get together with
Hungarian amateur astronomers.

This issue also stands out for the guest authors it welcomes. You will
enjoy reading Dr. Matthew Templeton's contribution, "Astrophysics from
Visual Observations" while appreciating the wonderful piece from our
avid contributor Mike Simonsen, "Recurrent Novae". Approximately 150
years 3 months ago, U Gem was discovered! In U Gem's honor, we are
including a memorable article from our observer Haldun Menali to
emphasize the fact that you can participate in science through variable
star observing. You will read a little write up regarding the most
recent status of the translations of our Visual Observing Manual.

Until next timeÉ

Thanks and good observing!

Gamze Menali, AAVSO Technical Assistant (MGQ)

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2. RECURRENT NOVAE - Mike Simonsen

With the recent outburst of RS Ophiuchi still underway, now is a great time
to discuss recurrent novae. These cataclysmic variables grab our attention
and spark our imaginations because of the incredible amplitude of their
outbursts, typically 8-12 magnitudes, and the rarity of these spectacular
events. Many of these outbursts are once-in-a-lifetime events. Like an
apparition of Halley's comet, witnessing an outburst of T CrB twice in a
lifetime would be a matter of uncommon luck, longevity or both.

In the General Catalog of Variable Stars (GCVS) recurrent novae are included
in the same category as novae, with the main distinction being the features
of their light curves.

"According to the features of their light variations, novae are subdivided
into fast (NA), slow (NB), very slow (NC), and recurrent (NR) categories.

NR Recurrent novae, which differ from typical novae by the fact that two or
more outbursts (instead of a single one) separated by 10-80 years have been
observed (T CrB)."

This implies that the outburst mechanism, orbital periods, spectra and the
nature of the components of these close binaries are the same or very
similar. To understand recurrent novae we need to understand novae first,
and then make distinctions.

Novae are close binary systems with orbital periods from 0.05 to 230 days.
The primary of the system is a hot white dwarf star while the cooler
secondary components may be giants, subgiants, or dwarfs of K-M type.

Although few novae have been caught in the very act of rising to eruption,
it is generally accepted that the time it takes to go from restless
quiescence to full max is 1- 3 days. The same is probably true for recurrent
novae.

The cause of a nova eruption is a thermonuclear reaction on the surface of
the white dwarf. After years of mass exchange between the binary pair,
temperature and pressure at the surface of the white dwarf build
sufficiently to cause the layer of accreted material to explode like a
hydrogen bomb. This bomb, however, can have the mass of 30 Earths! Once the
temperature becomes high enough, this layer begins to expand. Minutes into
the process the shell can be radiating at 100,000 solar luminosities and
expanding outwards at 3000 km/s. Eventually the shell envelopes the entire
binary and the orbital motion of the pair acts like a propeller to whip
things up. After 1000 days or so the envelope expands to the point it can be
seen as nebulosity surrounding the pair. Over hundreds of years the shell
dissipates into the interstellar medium.

Most novae probably erupt more than once in their lifetime, with the mass of
the white dwarf determining the amount of accreted material that needs to
accumulate before triggering on outburst. Systems with a white dwarf of 0.6
solar masses might take as long as 5 million years between eruptions. A
system with a 1.3 solar mass white dwarf might only take 30,000 years
between eruptions.

So are recurrent novae simply the same type systems with even more massive
white dwarfs? The accretion rate of a system with a 1.4 solar mass white
dwarf could have a recurrence time of less than 100 years. T Pyx may be one
such system, but it is unclear at present if the outburst mechanism for all
recurrent novae is the same as novae, or if some are the result of accretion
by Roche-lobe overflow or stellar winds, or a result of disc instabilities.

Even more interesting is the possibility that recurrent novae may actually
be progenitors of Type Ia supernovae. Observations of novae eruptions and
the resulting nebulae indicate the mixing of the accreted layer with the
outer layers of the white dwarf may cause the white dwarfs to lose mass over
time and repeated eruptions. The heaviest white dwarfs, with their higher
accretion rates, may actually gain mass over time! Although a large part of
the envelope mass is blown away in the wind, these primaries may retain a
substantial part of the envelope mass after hydrogen burning ends. The white
dwarfs in some recurrent novae have now grown up to near the Chandrasekhar
mass limit and might soon explode as a Type Ia supernova.

With so few known examples and the rarity of these events it is no wonder
that recurrent novae eruptions are extremely interesting to astronomers.
Monitoring these stars for outbursts over decades of relative inactivity is
still one of the extremely valuable contributions visual observers can
provide to science.

Finding the stamina and determination to follow such stars is no small task.
Even Leslie Peltier, one of the greatest AAVSO observers of all time, had an
"unhappy affair" with T CrB that can serve as a lesson to us all. In
'Starlight Nights' he writes:

"From 1920 on I watched it closely at every opportunity. For more than
twenty-five years I looked in on it from night to night as it tossed and
turned in fitful slumber. Then one night in February 1946 it stirred, slowly
opened its eyes, then quickly threw aside the draperies of its couch and
rose!
Full eighty years had passed since the star had shattered the symmetry of
the Northern Crown. And where was I, its self-appointed guardian on that
once-in-a-lifetime night when it awoke? I was asleep!"

Peltier had set the alarm for 2:30 AM to observe morning variables. When he
got up the sky was clear and the stars were shining, but feeling he might
have a cold coming on he decided to go back to bed. He goes on to describe
his personal relationship with the star, one that many of us feel for our
favorite variables, and how it changed after that.

"I alone am to blame for being remiss in my duties, nevertheless, I still
have the feeling that T could have shown me more consideration. We had been
friends for many years; on thousands of nights I had watched over it as it
slept and then, it arose in my hour of weakness as I nodded at my post. I
still am watching it, but now it is with wary eye. There is no warmth
between us any more."

In more recent times, CI Aql had been suspected of being a recurrent nova
even though only one recorded outburst had occurred in 1917. As such it was
included in the BAAVSS Recurrent Objects Programme for many years. For
reasons he still will not discuss with even the best of friends, Gary
Poyner, coordinator of the program, decided to drop CI Aql from the list in
2000; literally weeks before it erupted again for the first time in over 80
years! Sorry Gary, but its just too good a story not to recount.

Below is a table of known recurrent novae.
Try not to sleep through the next eruption of any of these unpredictable
stars.

Name
RA/Dec (2000)
Magnitude range
Years of known outbursts
Chart availability

T Pyx
09 04 41.53 ?32 22 47.2
6.5 v - 15.3 v
Outbursts in 1890, 1902, 1920, 1944 and 1966
AAVSO charts

IM Nor
15 39 26.47 ?52 19 18.0
7.8 V - 22.0 j
Outbursts in 1920 and 2002
AAVSO charts

T CrB
15 59 30.19 +25 55 12.1
2.0 p - 11.3 p
Outbursts in 1866 and 1946
AAVSO charts

U Sco
16 22 30.80 ?17 52 44.0
8.8 V - 19.5 V
Outbursts in 1863 and 1999
AAVSO charts

RS Oph
17 50 13.12 ?06 42 28.2
4.3 v - 12.5 v
Outbursts in 1898, 1933, 1958, 1967, 1985, 2006
AAVSO charts

V745 Sco
17 55 22.27 ?33 14 58.5
11.2 p - 21 j
Outbursts in 1937 and 1989
No AAVSO charts

V394 CrA
18 00 25.97 ?39 00 35.1
7.2 V - 18.8 V
Outbursts in 1949 and 1987
No AAVSO charts

V3890 Sgr
18 30 43.32 ?24 01 08.6
8.4 p - 17.2 p
Outbursts in 1962 and 1990
Very poor AAVSO chart; lettered sequence only

CI Aql
18 52 03.57 ?01 28 39.4
8.8 V - 15.6 p
Outbursts in 1917 and 2000
AAVSO charts

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3. ASTROPHYSICS FROM VISUAL OBSERVATIONS - Matthew Templeton

The primary way we come to understand the physical world is through
observation. We tie together many different pieces of methodically
gathered and analyzed evidence to build a coherent picture of the
nature of things. In astronomy, we're mostly limited to gathering
light from the objects under study, but light can provide lots of
clues into the nature of our universe. With light, we can take the
temperatures of stars, and measure their chemical makeup. By looking
at the properties of stars in clusters -- all born at almost the same
time -- we gain some insight into the lives of stars, the workings of
stellar evolution, and even the age of the universe. But there is a
limit to how much we can learn from measuring the behavior of things
at a given moment in time.

One of the reasons why variable stars make such excellent subjects
for study is because we often learn by studying how things *change*
over time. Physics is partly the study of the dynamics of systems,
and we can learn about what goes on in the universe in the same way
that we study the behavior of things here on Earth. However, the
time-scales for evolutionary changes in stars and galaxies is much,
much longer than a human lifetime, so we have to look to variable
stars as objects that can change on observably short time-scales.

When observers estimate the brightnesses of stars, they're really
quantifying a physical change in the star they're looking at, as
manifested in the light that's given off. And there's a lot we can
learn just by studying changes in light. For example, by measuring
the depths of and times between eclipses in eclipsing binary stars,
we can determine the orbital period of the binary, and begin matching
physical models of the component stars to what we see. Or when we
measure the changes in light of a pulsating variable star like a Mira
or an RR Lyrae, we can measure the pulsation period (which tells us
something about the star's physical size) and the overall change in
brightness and the shape of the light curve (which tells us about the
changes in radius, temperature, atmospheric structure, and on and
on).

What makes the observational records of the AAVSO archive so valuable
is that they often extend for decades, even a century in a few cases.
This is important because with variable stars, we sometimes get to
study the way a star that changes... changes! We try to understand
variable stars in terms of easily measurable quantities, the most
obvious being the time-scale on which the star varies (i.e. the
period). Although most stars in the universe evolve on time-scales
longer than we can observe, some of them can undergo measureable
changes on human time-scales. In some cases, these changes are very
subtle, and can only be seen through very careful measurements
undertaken for decades at a time. For example, the periods of many
pulsating stars like Cepheids and RR Lyrae stars do actually change
with time. By measuring the moment at which these stars reach maximum
brightness and comparing these times to those predicted by a previous
ephemeris, we can sometimes see trends emerge. Sometimes these trends
are well-behaved and well-understood, such as the very slow, steady
period changes seen in Cepheids as they evolve through the Cepheid
instability strip. In other cases, the period changes have strange
glitches in rate and direction, indicating something other than
evolutionary changes are going on. Such changes are sometimes
observed in RR Lyrae and delta Scuti stars.

Recently, I worked with Lee Anne Willson of Iowa State University to
study period changes in another class of star -- the Mira variables.
The AAVSO has an enormous amount of data obtained by our observers for much of
the last century, giving us a very clear record of the behavior of
these stars for all that time. As a result of monitoring by variable
star astronomers, it's well-known that Miras don't have well-behaved
periods, but instead have periods that wander a few percent up and
down over the years. What we went looking for were the stars that
underwent big changes -- those that changed by tens of percent over
the course of the observational record. A few Mira stars, like T
Ursae Minoris and LX Cygni, have changed their periods by several
tens of days over the last three or four decades, changes
well-documented by the work of the observational community. What we
think is happening is that deep inside the star, the dense shell of
helium surrounding the carbon-oxygen core undergoes an episode of
rapid thermonuclear burning, known as a thermal pulse, that then
changes the interior structure of the star. These structural changes
manifest themselves as a change in period that lasts for a few
thousand years. After the heat generated by the thermal pulse is
dissipated, the star returns to its equilibrium state and resumes
more regular pulsations. Thermal pulses were predicted by theoretical
and computational models of stars and stellar evolution, and these
period changes are a good confirmation that this process is actively
happening in some Mira stars. And it's a confirmation that comes
directly from observations by amateur observers; without data
archives such as those of the AAVSO and other variable star
organizations around the world, such studies would be nearly
impossible.


Binaries, too, can undergo changes over time. The dwarf novae are
well known to undergo outbursts over irregular intervals having
varying durations. Monitoring of these systems can tell us quite a
lot about the physics of accretion disks; often, amateur observations
of these systems are used to trigger professional observations with
larger ground-based or space-based observatories that can measure
these systems over the entire spectrum of light they emit, telling us
even more about their underlying physics.

Amateur monitoring of eclipsing binaries has also been important over
the years. Like the pulsating stars, we can measure the times of
eclipse minima over many thousands of cycles and compare the observed
times with those predicted by ephemerides. Often, we see strange
changes in the orbital period -- something rather strange for things
as large as stars to do! Such changes often indicate there are unseen
physical processes at work, including magnetic fields, stellar winds,
and even gravitational radiation. Sometimes these changes only become
apparent after many years of observations, and it is in large part
due to the observational community that our knowledge of the physics
of such binaries has grown.

I've only mentioned a few different types of variable star in this
article -- dozens of different classes have been described in the
GCVS, and an uncountable number exist in our galaxy alone. But in
large part, our understanding of these stars has advanced *only*
through the work of the amateur community, including those whose
equipment consists of their own eyes. Observations of variable stars
have a long and important history in variable star astronomy, and the
contributions of visual observers to the science of astronomy have
been invaluable. They will remain so for the foreseeable future.

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4. MANUAL FOR VISUAL OBSERVING OF VARIABLE STARS - NEW TRANSLATIONS
UNDERWAY!

As most of you may already know, we have currently launched a project to
translate our Visual Observing Manual into other languages. The
French translation is already done.

http://www.aavso.org/publications/manual/#french

We have received most of the chapters in Spanish and in Turkish and
are currently finalizing the translations in both languages.

Other volunteers are working passionately to send us chapters in
Russian, Greek and hopefully in Hungarian.

As you can see, thanks to the assistance of several ambitious AAVSO
volunteers in various countries, the project is well on its way.

Hopefully our efforts to make the AAVSO Manual more useful to our
members and observers world-wide will show some results to get more
people interested in variable star observing.

The AAVSO Manual for Visual Observing of Variable Stars is a valuable
and comprehensive guide to variable star observing for observers of all
skill levels. This manual provides up-to-date information for making
variable star observations and reporting them to the AAVSO. The most
recent revision occurred in January, 2005.

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5. A DATE WITH U GEM — AN AMATEUR'S HUMBLE CONTRIBUTION TO SCIENCE - Haldun Menali

(Originally published in Turkish in Cumhuriyet Bilim Teknik on December
22, 1990)

Have you ever dreamt for years wishing that something special happened
to you? Most probably you had. Everybody has some dreams in their life
to make it more joyful.

As an amateur astronomer, I had a dream since the day I started
observing the skies. To observe a special celestial event that no one
has ever witnessed that day (rather, that night!). My astronomical
observing endeavor I have been carrying on for eleven years has been
focused on variable stars since 1983 (I have been observing the heavens
for more than 21 years in 2000). After having started to estimate their
ever-changing brightness using a pair of 8x30 binoculars and currently
observing with a homebuilt 8" reflector, more than 1000 of my variable
star observations have been published by several astronomical
organizations around the world (As of January 2000 they reached 2000
too!). Even though I was aware that my observation results contributed
to a rich database accessed by numerous professional astronomers, I
wanted to get something more tangible out of my observations. I have
waited with patience for so many years. Until that night...

My luck turned around when my phone rang on the night of November 23rd
(1990). When I answered I recognized the voice of Janet Akyuz Mattei,
the long-time Director of the American Association of Variable Star
Observers (AAVSO) located in Cambridge, MA, the clearinghouse for the
variable star observations of amateurs around the world. Janet told me
that the cataclysmic star U Geminorum was in outburst for a couple of
nights already. These kinds of events are the most interesting ones for
astrophysicists who want to unveil the mysteries of stellar evolution.
They try to observe these enigmatic stars on the whole electromagnetic
spectrum during their outbursts (or minima) to find answers to their
questions. Visual amateur observers who closely monitor these stars
issue warnings when something unexpected happens. Janet explained that
US scientists were planning to observe U Gem in the ultraviolet using
the International Ultraviolet Explorer (IUE) satellite.

The variable had been observed at visual magnitude 9.7 from the US the
previous morning. The observing prerequisite for the IUE was that the
variable should have been brighter than magnitude 10.5. We had about
three hours before the start of an IUE observing session that night. It
would have been impossible for the satellite to observe the variable if
there weren't any observation to confirm its brightness within this time
frame.

I was the only one among 500 or so AAVSO observers in 40 countries
around the globe, geographically the best located to observe the star
within that tight time frame. It was just after civil twilight in Turkey
and the star had already started to rise over the northeastern horizon.
The observers in the Far East missed that opportunity as the morning was
getting near there. Telling to Janet that the skies were clear and I
could observe the variable, I jotted down the phone number of the
astronomer who would make the ultraviolet observing in California (He
was Dr. Chris Mauche whom I met in person at the AAVSO Second European
Meeting in Sion, Switzerland in May 1997 and presented him with a signed
copy of my original article).

Within the next half hour after Janet's call I was ready to observe.
Having bundled up against the cold weather, I grabbed my reflector,
eyepieces, sky charts, red flashlight and 7x50 binoculars and went out
into the backyard. I was deeply disappointed to see that the sky, which
was clear half an hour ago, was covered with a thick layer of haze and
clouds. We the amateur astronomers are ready to face this kind of
annoying and unexpected surprises. So I set up my telescope and started
to wait for the sky to be cleared up.

Almost two hours had already fled and I was still waiting outside. I was
exhausted standing up and started shivering because of the decreasing
temperature. There was no sign of a clearing up.

When a police patrol car stopped by the backyard gate "Yeah, that was
the perfect timing" I mumbled! Another common issue for the amateur
astronomers is their weird working hours. Because the darkness of the
night makes it almost impossible to distinguish between a bazooka and a
telescope! Despite the suspicious ski mask I put on to stay warm, I
would have been so convincing to the police officers that they left at
last, by wishing me good luck and with a grin on their face! (They must
have thought I was the crazy ONE in the neighborhood!)

Yet the clouds stayed where they were!

Waiting for that special moment in my life after so many years and
hours, it was really saddening not to realize it. But I started to
dissassemble my instruments by uttering to myself "don't worry, next
time".

Oh my goodness! Were stars really getting brighter or was it just my
imagination because of cold and fatigue? I swept the sky with my
binoculars at once. Boy, I was right! The haze and clouds were almost
completely dissipated!

The telescope and other stuff had been set up again in a matter of
minutes, ten times faster than dissassembled! Another 30 seconds and
there it was! 15 more seconds and I was estimating U Gem's magnitude as
9.7. As soon as I made my estimation I rushed inside the house to the
phone. At the other end of the line in California was Dr. Mauche who
thanked and told me that they were waiting for my call and they will be
ready to start observing in half an hour.

When I returned to the backyard to take my instruments back inside I
looked up to the sky. I was thinking about the IUE satellite. I was
imagining the satellite, up there somewhere in the orbit, to be oriented
toward U Gem. I was happier than ever, because I had realized my
long-time dream; and because amateurs had proved their contribution to
astronomy once again!

I have another dream these days... To be one of these amateurs to see a
nova or a comet for the first time and become its only discoverer!
Maybe, one night, you never know...

(I am getting there step by step! I was one of the just ten observers
around the world (2) confirming the discovery of Nova Aquilae 1999
Number 2 on December 1, 1999; and one of the seven observers worldwide
confirming the discovery of Nova Ophiuchi 2003 on July 18, 2003. I keep
looking up...)

Notes:
(1) My location as of December 1990.
(2) Based on observations published in the related AAVSO Newsflashes.

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Good observing!

Gamze Menali,AAVSO Technical Assistant (MGQ)
Aaron Price, AAVSO Technical Assistant (PAH)
Mike Simonsen, AAVSO Observer (SXN)

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THE AMERICAN ASSOCIATION OF VARIABLE STAR OBSERVERS
25 Birch Street, Cambridge, MA 02138 USA
Tel. 617-354-0484 Fax 617-354-0665
http://www.aavso.org
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