Transcript Where to begin the adventure with variable stars?

Mateusz Bielski
Where to begin the adventure
with variable stars?
The variable stars that are particularly
suitable for observations for
beginners
Editors: A. Majczyna and M. Należyty
Translated to English by Magda Zarzycka.
Logo design: Armella Leung, www.armella.fr.to
The photometry of variable stars
is ranked among the most difficult
observations that can be done with
the use of a webcam built on the basis
of a CCD. Learning how to gather
and process data requires patience
and determination...
In reward for this you will get results
that have not only didactic, but also
scientific value in the broadest sense
of the word.
Therefore, teachers can create with
their students a true scientific
laboratory at school!
Which stars should we choose for a
start?
The process of developing your own technique is
difficult and time-consuming. To be able to observe
weaker stars or those whose amplitudes are
smaller, it is a good idea to practise with those that
are, so to say, ‘created’ for photometric
observations with a webcam.
In the sky you will find precisely such stars, whose
observations almost without exception return
results that impress laymen or beginners equally.
Below are three suggestions of stars whose
amplitudes and magnitudes are so great that you
can easily observe their minimum in the star
light curve. The data come from observations
conducted by the author.
• RZ Cas
• TX UMa
• U Cep (an example of a flat-bottomed
curve)
RZ Cas
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•
•
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Type: eclipsing binary
Max magnitude: 6.4 mag
Min magnitude: 7.8 mag
Amplitude: 1.4 mag
Period: 1.19525780 JD
RZ Cas – light curve
RZ Cas
-1
-0,5
C-V [mag]
0
0,5
1
1,5
2
2453411,30
2453411,35
2453411,40
2453411,45
Julian
Days
Dni
Juliańskie
2453411,50
2453411,55
TX UMa
•
•
•
•
•
Type: eclipsing binary
Max magnitude: 7.06 mag
Min magnitude: 8.8 mag
Amplitude: 1.74 mag
Period: 3.06329200 JD
TX UMa – light curve
(incomplete, only one arm, but the variability is clearly visible)
Julian Days
U Cep
•
•
•
•
•
Type: eclipsing binary
Max magnitude: 6.74 mag
Min magnitude: 9.81 mag
Amplitude: 3.07 mag
Period: 2.49309770 JD
U Cep – light curve
U Cep
0
V-C [mag]
0,5
1
1,5
2
2,5
2453267,45
2453267,5
2453267,55
2453267,6
HJD
2453267,65
2453267,7
2453267,75
How to find these stars in the
sky?
To be able to find the object of interest,
it is necessary to know how to identify particular
constellations and stars.
This will require a few nights and some patience
but what you will get in reward is a great satisfaction.
A planisphere will be of great help while learning
how to navigate around the sky.
The easiest way to find it is on the internet (just search for
‘planisphere’ in any search engine) and buy it online (it costs
around $8).
This is what a planisphere looks like
Very simple instructions how to use it can be found
at the back of the planisphere.
If you have a portable computer or have access
to a stationary computer where you are,
you can use electronic atlases of the sky.
Most of them are commercial programs but you can also find
freeware of this sort on the internet.
Cartes Du Ciel is the most popular atlas
It is available at:
www.stargazing.net/astropc
Electronic atlases are very helpful and allow users to print out
accurate maps that help to identify variable stars and reference
stars that are later used in the process of photometry.
The navigation in the night sky
To navigate the sky quickly and effectively, it is
necessary to learn first how to identify the main
constellations.
There are a few constellations in the sky whose
main stars are very bright and whose shape is
very characteristic and therefore easy to
recognise.
Ursa Major, also called Great Bear
Ursa Major, also called Great Bear
Mizar and Alcor
Cassiopeia
Cassiopeia
Andromeda
Andromeda
M31
Ursa Minor, also called Little Bear
Ursa Minor, also called Little Bear
Polaris
Lyra
Lyra
Vega
Cygnus, also called Northern Cross, Swan
Cygnus, also called Northern Cross, Swan
Deneb
Vega
Lyra
Cepheus
Cepheus
Polaris
Cassiopeia
Perseus
Perseus
Algol
Hercules
Difficult to find
Hercules
Difficult to find
Taurus, also called Bull
Taurus, also called Bull
Pleiades
Aldebaran
Orion
Orion
Aldebaran
Gemini, also called Twins
Gemini, also called Twins
Castor
Pollux
Bootes
Bootes
Arcturus
Aquila
Aquila
Altair
Auriga, also called Charioteer
Auriga, also called Charioteer
Capella
Leo, also called Lion
Leo, also called Lion
Regulus
Pegasus
Pegasus
Of course, there are far more constellations in
the sky, but once we learn to find and recognise
those most characteristic ones, finding the other
ones with the use of a planisphere should not
cause any problems.
Constellations can be divided into those that are
visible in the sky in winter, those that we can see
in summer, and those that are present all year
round.
Winter constellations:
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Orion
Taurus
Monoceros
Canis Major
Cetus (?)
Leo (?)
Summer constellations:
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Aquila
Serpens and Ophiuchus
Delphinus
Capricorn
Sagittarius
Pegasus
Lyra
Cygnus
Andromeda
Constellations visible all year round:
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Ursa Minor
Ursa Major
Cassiopeia
Draco
Cepheus
Camelopardalis
Perseus
Auriga
Lynx
When we know how to navigate across the night
sky and we are equipped with printed maps
(e.g. from Cartes Du Ciel), we can start
searching for interesting variable stars
in order to conduct photometric observations
with a webcam.
In the case of the three stars presented before, the situation is simple
because they belong to constellations that are visible all year round in the
northern hemisphere. They are located in relation to one another in the
following way:
In the case of the three stars presented before, the situation is simple
because they belong to constellations that are visible all year round in the
northern hemisphere. They are located in relation to one another in the
following way:
Cassiopeia
Polaris
Cepheus
Ursa Major
The location of this set may be different
depending on the season and the time
of observation but the stars always
remain in the same position in relation
to one another.
(Ursa Major is opposite to Polaris in relation to
Cepheus and Cassiopeia)
Steps to take:
• First, we should find the constellation with the variable star
that is of interest for us (the second part of the name informs
us about this, e.g. RZ Cas means that the star is in the
constellation of Cassiopeia). No optical devices are
necessary to do this.
• Using a map, we find the nearest neighbour of our variable
star, that is visible with the naked eye.
Steps to take:
• Next, with the help of binoculars or a finderscope, we find
our star of interest (the easiest and most efficient solution is
to construct a set that will enable us to join a webcam and a
finderscope, so that we can focus them on the same point in
the sky).
• Lastly, we take pictures of the area of the sky and compare
them with the map to make sure that our variable star and
the star of reference are both in the field of view of the
webcam.
From the suggested stars, the easiest is to find RZ Cas in the
constellation of Cassiopeia.
M31
Polaris
μ And
Find Cassiopeia in the sky. The easiest way to do this, is to go
from Polaris towards Andromeda in a straight line.
When we find Cassiopeia...
Segin
ι (Iota)
Find the star ι (Iota) located at the extension of the arm that
ends at the star Segin.
Next, already with the help of a telescope...
Segin
ι (Iota)
RZ Cas
When the ι (Iota) star is in the centre of the view field of our telescope, we can
easily find RZ Cas moving outwards Segin (see the arrow).
It is best to have the variable star at the centre of the view field (the net
of crosses in the telescope) and choose one of the four stars in the characteristic
zigzag as the star of reference. Another variable star, SU Cas, will be in your
field of view as well. It is not suitable for a star of reference, however!
ι (Jota)
RZ Cas
SU Cas
It is somewhat more difficult to find TX UMa. It is in Ursa
Major and we should begin with finding this constellation.
Finding the constellation does not pose any problem even to beginners.
Following the straight line connecting two stars in Ursa Minor: Zeta Ursae
Minoris and Beta Ursae Minoris (see picture) you will find Mizar.
Mizar is the most popular star in Ursa Major thanks to its neighbour –
Alcor, visible with the naked eye.
Mizar
Find Phecda in the constellation.
Megrez
Phecda

Moving from Megrez through Phecda find the star  (see the arrow).

ψ
HIP 52469

Moving still further from the bear from the χ star you will find the ψ and 
stars. In a dark sky they are visible with the naked eye but it is a good idea to
use a finderscope. These two stars form a triangle with the star HIP 52469.
TX UMa is situated a little below the line that connects the stars  and
HIP 52469, around 1/5 way from HIP 52469. It is not visible with the
naked eye. One of the stars in the yellow circles can be used as a star of
reference.
HIP 53160
HIP 52469
HIP 52831
HIP 52881

HIP 52702
Finally U Cep
Let’s begin with finding the constellation of Cepheus,
where the star is situated.
It will be easiest to begin with locating the star Alrai.
ι (Iota)
Caph
Alrai
Polaris
Moving in a straight line from Polaris towards Cassiopeia, and more
precisely from the star Caph, we will find the bright star Alrai, belonging
to the constellation of Cepheus.
When we have found Alrai...
Alrai
HIP 760
Moving along the straight line connecting Cephei and Alrai, further from Alrai
towards Polaris, we will find HIP 760. It is not visible with the naked eye, so in
this step we will need a finderscope.
Alrai
HIP 760
U Cep
Next, moving along the
line that connects Alrai and
HIP 760 in the same
direction as previously, we
will find U Cep.
U Cep is situated more or
less at the same distance
from HIP 760 that HIP 760
is from Alrai.
One of the stars in the yellow circles can be used as a star of
reference.
HIP 3132
TYC 4505-558-1
HIP 4966
TYC 4505-387-1
HIP 5108
In this way we have found the stars and we
can begin photometric observations. Their
result will probably impress not only us,
but also other students and our friends.
Also the acquired skills of navigating
in the sky will be a source of satisfaction!