Astronomy Research Project
http://oposite.stsci.edu/pubinfo/gif/Gl105A.txt
Overview
Present estimates of the percentage of double versus single stars point
toward a ratio of 2/3s or higher (Astronomy: 7/96). This is also confirmed
by the high number of new detections coming from ground-based and satellite
surveys. With these updated observations astronomers have opened many more
doors which allow new theoretical models on how the universe evolved.
Stellar observation
Scientists try to understand what processes are going on in the interior of stars. Models of internal structure are therefore elaborated in which STELLAR MASSES play a very important role. This is only possible through direct observation of double stars and finding:
1. orbital period
2. semi-major axis
which allows astronomers to derive, using Kepler's and Newton's laws, the total MASS of the system. This information is an essential parameter on the way to modeling stellar evolution.
In addition astronomers utilize observational techniques beyond naked eye/telescope such as:
3. Spectral Analysis
4. Charge Couple Devices (CCDs)
When you look at this information in conjunction with the stellar masses
we are able to see a more complete picture of stellar structure.
Stellar formation
By studying the distributions of the orbital elements such as the orbital period, the eccentricity and the mass ratio of double stars as a function of population or age, one obtains:
1. constraints on scenarios of the formation of single stars
2. indications for possible scenarios of binary star formation
Binary Stars
When refracting telescopes were invented at the beginning of the seventeenth
century no one knew either the distances or the sizes of the stars.
However, observations over the last 400 years have shown that very often
stars come in pairs; these pairs are referred to as double stars
(Couteau: 2). William Herschel began looking for optical doubles
in 1782 with the hope that he would find a measurable parallax, by comparing
a close star to the more distant star in an optical double. Herschel did
not find any optical binaries, but he did catalog hundreds of visual binaries.
In 1804 Herschel had so many measurements of visual binaries that he concluded
that a pair of stars known as Castor were orbiting one another. This was
an important discovery, because it was the first time observational evidence
clearly showed two objects in orbit around each other outside of the influence
of our own Sun and Solar System. Double star systems actually compose
over two-thirds of the 100 billion stars in the Milky Way (Astronomy 7:96).
Mostly how and a little bit of why these binary stars aid in our understanding
of the nature of the universe is the focus of this paper.
By
using a derivation of Keplerian
orbits in conjunction with Newtonian
physics, it is possible to find the mass of a star system, this in
turn makes the nature and evolution of stars more easy to comprehend. Sharing
a common center of gravity, these double star systems are able to reveal
many secrets of our stellar universe including, but not limited to, the
mass-luminosity relationship and the age of individual stars. Combined
with the data that can be collected from observational techniques beyond
naked-eye/telescope such as spectral analysis and CCD camera imaging, a
more developed theory of stellar composition and evolution is possible.
Binary star systems are quite diverse in their nature. Stars that
are not actually held by each others gravity and in fact are no where near
each other in space are referred to as optical doubles (Kaufmann:242).
These are only apparent doubles that just happen to be in the same direction
as seen from Earth. For example Mizar, the middle star in the handle
of the Ursa Major (big dipper), is an optical double that can be seen with
the naked eye with its companion, Alcor, but has no interaction with
it (Kaufmann:241). The next type of double star is the visual
binary (Kaufmann:241). Again, with Mizar in the constellation
Ursa Major, there is a visual binary with Mizar A being
visible to the naked eye and Mizar B, which is visible only through a telescope.
Through years of patient observation, astronomers, using background stars
as reference to position can plot the orbit of one star around the other.
Some binary systems are situated so that periodically the two stars eclipse
each other as seen from earth. These are refered to as eclipsing
binaries (Kaufmann: 243). These systems can be discerned, with
techniques discussed later in the paper, even when the two stars cannot
be resolved as two distinct images in a telescope. This is apparent when
the magnitude of the image of the binary dims each time one star blocks
out part of the other (Kaufmann: 243).
In addition binary stars can be categorized by their distance from each
other. Binary stars that are only a few stellar diameters from each other
and that affect the appearance and evolution of each other are referred
to as a close binary system. In the mid-1800¹s French
mathematician Edward Roche theorized that the atmospheres of the two stars
in a binary system must remain within a pair of tear-drop
shaped regions surrounding the stars otherwise the gas escapes from
the binary system. Seen in cross section these Roche
lobes are shaped like a figure eight. The more massive star is always
situated inside the larger Roche lobe (Kaufmann :244). In binary stars
that are so far apart that even when they swell to giants the star surface
remains intact well within the Roche lobe are called detached binary
stars. If two stars are relatively close one star may overflow its
Roche lobe and gases will flow across the point where the two lobes touch
and fall onto the companion star creating a semidetached binary (Kaufmann
:245). When both stars completely fill their Roche lobes the system is
called a contact binary because the two stars actually touch and
share a common envelope of gas.
http://www.astronomical.org/astbook/binary.html
Ultimately, determining stellar masses is what the study of binary star
systems is all about (Sky & Telescope 10:96). Without the
knowledge of stellar mass we can know little of their make-up.
The orbits of binaries provide ³practically the only direct measure of
stellar masses² (Sky & Telescope 10:96). To do such a calculation
one must derive Kepler¹s third law which reveals that
the combined mass of two stars in a binary system equals the orbit's semi-major
axis cubed, divided by the orbital period squared. That is M [sub
1] + M [sub 2] = a [sup 3] / p [sup 2], where M [sub 1] and M [sub 2] are
the two stars masses measured in solar masses, a is the semi-major axis
in astronomical units (AU) and p is the period in years (Sky & Telescope
10:96). Solar mass is equivalent to the mass of the Sun at a unit of 1.99x1030
kg. The semi major axis is half of the major axis or the longest diameter
of an ellipse with AU quantified as 1.50x108
km 93 million miles or the average distance between the Earth and the Sun.
Through years of observation and detailed records keeping
astronomers can graph the orbits of both stars in a binary system. Once
this graph is complete the two elliptical orbits are seen to overlap. This
gives us the mass of individual stars within a binary system. Though we
have not found a direct example of the proportionality equation we did
find the result of using the information given from the equation. As the
data accumulated, an important trend began to emerge. On the main sequence,
the more massive the star, the more luminous it is. (Kaufmann: 241) This
Mass-Luminosity
relation is the basis for identifying masses of single stars, which in
turn has played an essential role in classifying single stars.
In addition to insights gained through mathematical calculations based
on naked eye observations, there are other physical observations that allow
astronomers to study binary stars. Spectral
analysis or spectroscopy, the study of individual light frequencies,
permits astronomers to determine not only the chemical make up of a star
but also help locate binary systems that are too close to be discerned
with naked eye/telescope observations. For the latter, spectral analysis
can yield incongruous spectral lines for some star systems. The spectrum
for example may show strong absorption lines for hydrogen typical of a
class A star and of titanium oxide typical of a class M star. Since
a single star is not capable of producing two dominant absorption
spectra, such a situation indicates that we are seeing a binary system.
Spectroscopy can also detect the movement of stars orbiting each other
due to the Doppler
shift in spectral lines. The size of the shift is proportional
to the speed at which the light source is moving.
http://www.astronomical.org/astbook/binary.htm
Such stars are called spectroscopic binary stars. If the Doppler
shifts are present in a single line of the spectrum, we are seeing the
light from only one star because the other is too dim we call this a single-line
spectroscopic binary. If we can see the light from both stars the Doppler
shifts will alternate, split and merge depending on the positions of the
two stars in their orbits. This is called a double-line spectroscopic
binary. However, single line spectroscopic binaries reveal less about
the system than a double line spectroscopic binary (Kaufmann :242). If
a system is both a double line spectroscopic binary and an eclipsing binary
then the shifts in spectral lines can yield much information about the
orbital velocities of the stars. This information is best seen as a radial-velocity
curve in which the radial velocity of the orbiting stars are graphed
over time. One very important detail, we do not know how the orbits
of the two stars are inclined to earth. This inclination could be any angle,
for that bit of information we have to go back to visual methods in order
to see the individual stars to determine the inclination of their orbits
relative to earth. Even so we can not for certain determine the true inclination
of the orbit so our mass calculation is only a lower limit to the masses
of the two stars.
Radial
velocities permit astronomers to compute the total mass for the two stars,
however they do not provide the masses for the individual stars and other
methods must be used to make that determination.
Using a light sensitive detector such as a Charge Coupled Device
or CCD camera
which digitizes photon strength and frequency, an accurate measure
of eclipsing binary intensity can be charted. With this data it is
possible to see at a glance whether the eclipse is partial or total. The
resultant light curves (see figures below) also offer other useful information
such as surface temperatures and aspects of the stellar atmosphere such
as pressure and density. For example when one star
passes over another the light from the further star is cut off, by studying
how this occurs scientists can infer the makeup of the outer atmosphere
of the star being passed over. (Kaufmann :243) This inference rests
heavily upon speculation but it makes for a keener awareness about stellar
structure.
http://www.astronomical.org/astbook/binary.html
http://csep10.phys.utk.edu/astr162/lect/binaries/eclipsing.html
How binary star systems are formed is largely a mystery, but by putting
all the aforementioned tools of observation and calculation together scientist
have come up with thousands of possibilities. The main division of theories
is whether binary star systems form as pairs, or if they are formed at
different times and even in separate locations. One new theory based on
computer simulations demonstrates a processes that explains formation of
double stars. Stars form from collapsing knots of gas in giant gas clouds
the process begins when two cloud fragments collide, creating a layer of
dense, compressed gas, the layer becomes gravitationally unstable and fragments
into two or more disks(Astronomy 6:96). The disks then condense out of
the condensed gas clouds and stars form inside each disk.
Another
theory illustrates how two stars head towards each other and if they do
not collide exactly head on they will likely get caught in each other's
gravity and begin to orbit one another. So whether or not binaries form
together or separately is the difference between two main theoretical camps.
Essentially binary star systems, with the aid of Kepler's and Newton's
laws have given us the foundation for understanding most of modern astronomy
today, and so it is that all astronomers everywhere owe a great deal to
the study of binary stars even if they never even look at a set.
Conclusions
Charlie
Upon researching and coming to a clearer
understanding of binary star systems and the important role that they play
in modern astronomy I am left with an overlying feeling of awe and wonderment
at the complex nature of the universe and an even greater sense of wonder
at our inability to truly overstand these absolutely incredible principles.
I am left with more questions now than when I began this endeavor, so many
in fact that it is difficult to isolate just one and put it into the context
of a coherent query. So it is that I feel an angst when faced with problems
such as "How do binaries form?" or "Why are most stars in
binary systems?"
In a sense I am left with
a feeling that to 'know' the principles of star formation and 'why' they
form the way they do is to 'know' the unknowable hence in
my eyes this particular pursuit has proven deviant from my course and has
seemingly neglected addressing the very disturbing reality that we face
here on planet Earth today. I see the pursuit of this sort of esoteric
knowledge as the greater stratification of the so called 'learned' class
and the 'unlearned' class. Not only that but I see this line of questioning
as a means to displace faith in the Creator which has been shown time and
time and time again to be the very demise of the culture seeking to overstand
the pieces of this glorious creation. I do however
feel that it is important for people to fill thier days with something
so far be it from me to say that astronomy or the sciences are not important
to us. After all studying nature and the heavens is a direct means to learn
the laws that govern this Creation so that in seeing the laws we may live
by them. In esssence finding a middle path allowing us to live with little
effect by setting up a living situation that like plants and animals can
stand the test of time. But what I see as prevelant today is that we are
so quick to become information junkies that we neglect to question the
information because we want so much more of it all the time. Learning incorrectly
is down-right unhealthy and I know I am a sufferer of it in part because
of the school and societal system and in part because of my own apathy.
Maybe I am just too cynical but I feel
that vanity is in the looking. Perhaps what I mean by this is that if we
all took care of the most minutae details of our worldly
life to the point to where such atrocities as; litter, rape, racism, pollution,
killing, apathy, forgetfulness, addiction, child-molestation, greed, neglect,
subjugation of practical worship, and the threat of nuclear destruction
from sources here on Earth, etc..etc.. could not exist among us then we
would be ready to receive such knowledge as the 'Why' and the 'How' of
the universe. Can you see? I am simply saying that we are no where near
ready to comprehend such concepts because of all the noise (disruptions)
in our environment, both internal and external. I believe that the mysteries
we try so hard to solve cannot be comprehended until we find a quiet space
within and without where we can listen to the answers that are offered
to even the most complex of our minds questions. For one cannot commune
with the Creator unless you give time to listen to what is offered, one
cannot listen without being internally silent, and since the Creator is
the 'How' and the 'Why' we cannot under or over stand 'How' and 'Why' this
creation is, without listening. Listening in my mind goes beyond just asking
questions, I mean just because you ask a question doesn't guarantee you
an answer. To put it another way just because you speak to me doesn't mean
I have to reply and it is the same with Creation which does have a voice
and is always singing we just don't, or more truthfully can't take the
time and space necessary to listen.
Even when we do try and listen we can't
hear the message clear for all the 'lines of disruption' we have created.
Many of these 'lines of disruption' are the very questions we ask such
as "How do binaries form?" or "Why are most stars binary?"
We are too busy coming up with clever ways to trick Creation into spilling
her guts on her inner and outer workings instead of being faithful that
when the time is right the very thing we want be it knowledge, a cure,
or even a tool will manifest itself in due time. It is this very lack of
faith that has brought us to a nuclear age in which I wake each day in
fear that it may be my last. For in this delicate house of terms and models
we have built all it would take is a light stellar breeze and we would
have to watch the roof of our contrived manifestations fall onto the very
heads of the inhabitants. A philosophy once said that, "we name
that which we cannot hold in our hearts." On at least one level it
is this inability to hold Creation in our hearts that makes it impossible
to 'see' Creation.
Upon writing what I just wrote I
feel that you may see no real connection between what I have espoused here
and the study of binary star systems but I see every thread of connection,
and feel that what I have stated is far more important for me than to simply
rattle off what I have learned during the interim of this project. For
though I have amassed many 'facts' and 'terms' new to me prior to this
experience, the question remains, "Have I, neigh, have We, really
learned anything?"
Currently, binary stars hold the key
to our understanding of cosmic processes. They are pseudo space probes
which allow scientist and lay people alike to gain some insight into worlds
far from our own. And although the information received is thousands
of years old, it allows us to peer into our own world as if traveling back
in time. I find it quite interesting that the majority of star systems
are binary in nature. This in itself I believe is worth pondering
when I stare at the evening sky. No doubt if the ancients had had
the information we have, they too would be asking the same questions and
developing models to explain them. For me that is the joy I gain
from researching phenomena like binary stars. We are in a giant cosmic
puzzle trying to make sense out of what we see. Each generation adding
to the storehouse of knowledge that will perhaps someday lead to an answer.
Only to be disturbed by an even more puzzling question.
Kept in context, the study of binary stars
doesn't really amount to a hill of beans but they do offer us the opportunity
to challenge our paradigm of existence. Some people are threatened
by such knowledge but this I believe is the evolution of species.
Knowledge is not the dangerous end of the stick, it is the use of that
knowledge that will represent who we are. Astronomy offers to its
followers more or less the same opportunity to discover why things operate
the way they do. Columbus found some inhabited land because he had
the financial backing, however astronomy and its myriad of unanswered questions
is available for all to ponder and hypothesize. This is the beauty
of the observational sciences.
In conclusion I am very pleased with the
information that was gleaned from five weeks of extensive research. And
although more questions were asked than answered, I believe it was beneficial
in gaining insight into problem solving situations that will be encountered
throughout my life. In addition I learned how some seemingly insignificant
information, such as the weight of a star system, adds to our understanding
to how stars form and evolve and how that will effect the world I live
in.
http://www.mtwilson.edu/Science/AdapOpt/ACE/samples.html
From left to right:
Beta Del - separation is ~0.3", with a magnitude
difference of about 3.5.
Eta Oph - A2V + A3V, separation is 0.4",
delta mag = 0.3.
Gamma CrB - B9IV + A3V, separation is 0.6",
delta mag = 1.5.
http://www.mtwilson.edu/Science/AdapOpt/ACE/samples.html
From left to right:
Lambda Oph - A0V + A4V, separation is 1.2",
delta mag = 1.0.
Zeta Her - separation 1.44" (The large size
of the image is due to the color table and the large magnitude difference
of the two components.)
Zeta Sge - separation 0.14". This star is
the closest binary nearly separated by the instrument to date. In addition
it is also one of the faintest objects successfully
locked on by the instrument.
http://sizzle.thetech.org/hyper/hubble/ccd.html
http://sun.astro.wesleyan.edu/~eric/5185.html
http://instruct1.cit.cornell.edu/Courses/astro201/kepler_binary.htm
http://antwrp.gsfc.nasa.gov/apod/image/9702/mizarA_npoi_big.gif
http://yan.open.ac.uk/~rogley/roche_lobe.html
Bibliography
Books
Couteau. Paul. Observing Visual Double Stars. Cambridge,
Mass.: MIT Press
1981.
Kaufmann, William. Discovering The Universe. W.H. Freeman, N.Y.
1996.
Schatzman. Evry. The Stars. New York: Springer,
1993.
Magazines
McAlister. Harold. ³Twenty Years of Seeing Double.²
Sky & Telescope, Nov '96, Vol. 92, p28.
Roth, Joshua. "Binary Star Being Born"
Sky & Telescope, Aug '96, Vol. 92, Issue 2,
p.14
Unknown Author. ³The Sharpest Visual Images²
Astronomy, Nov '96, Vol.24 Issue 11, p26.
Unknown Author. "Why Most Stars aren't Single"
Astronomy, Jul. '96, Vol. 24 Issue 7, p.30
Electronic
Dolan. Chris. ³Explanation of Constellation Position and Notation²
(4/23/98). Online. Internet. April 23, 1998.
Available, http://www.asto.wisc.edu/~dolan/constellations/extra/Positions.html
Dolan. Chris. ³Ursa Major, The Great Bear (The Big Dipper)²
(4/23/98). Online. Internet. April. 23,
1998
Available, http://www.astro.wisc.edu/~dolan/conŠtions/constellations/Ursa_Major.html
Golimowski, D. "Hubble Spies a Really Cool Star"
(Sept.. 14, 95). Online. Internet. Sept.. 14, 95
Available, http://oposite.stsci.edu/pubinfo/gif/Gllo5A.txt
Nemiroff. Robert. & Bonnell. Jerry. ³Mizar, Binary Star²
(Feb. 9, 1997). Online. Internet.
Feb. 19, 1997.
Available, http://antwrp.gsfc.nasa.gov/apod/ap970219.html
Newton's Law's
Available, http://www.angelfire.com/md/physicsproj/law1.html
Ogley, Rich. "Roche Lobe Overflow, Accretion."
(Nov., 15, 95). Online. Internet Nov. 15,
95
Available,
http://yan.open.ac.uk/~rogley/roche_lobe.html
Nasa. "Picture of the Day, Mizar"
Available,http://antwrp.gsfc.nasa.gov/apod/image/9702/mizarA_npoi_big.gif
Cornell University "Kepler's Laws apply to Binary Stars Also"
Available,http://instruct1.cit.cornell.edu/Courses/astro201/kepler_binary.htm
"Close Binary Sampler. Atmospheric Compensation Experiment (ACE)
Available, http://www.mtwilson.edu/Science/AdapOpt/ACE/samples.html
"Data on HR 5185"
Available,http://sun.astro.wesleyan.edu/~eric/5185.html
"Charged Couple Device"
Available,http://sizzle.thetech.org/hyper/hubble/ccd.html
"PAS"
Available, http://www.astronomical.org/pasmenu.htm
"Eclipsing Binaries"
Available, http:/csep10.phys.utk.edu/astrl62/lect/binaries/eclipsing.html
