Begin Adventure, second edition, by Homer Tilton, Florentin Smarandache
Where to begin the adventure with variable stars?
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Transcript of Where to begin the adventure with variable stars?
Where to begin the adventure with variable stars?
The variable stars that are particularly suitable for observations for
beginners
Mateusz Bielski
Editors: A. Majczyna and M. Należyty Logo design: Armella Leung, www.armella.fr.to Translated to English by Magda Zarzycka.
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
• 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
0
0,5
1
1,5
22453411,30 2453411,35 2453411,40 2453411,45 2453411,50 2453411,55
Dni Juliańskie
C-V
[m
ag]
Julian Days
TX UMa
• Type: eclipsing binary• Max magnitude: 7.06 mag• Min magnitude: 8.8 mag• Amplitude: 1.74 mag• Period: 3.06329200 JD
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
0,5
1
1,5
2
2,52453267,45 2453267,5 2453267,55 2453267,6 2453267,65 2453267,7 2453267,75
HJD
V-C
[mag
]
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 atlasIt is available at:
www.stargazing.net/astropcElectronic 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.
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.
Summer constellations:
• Aquila• Serpens and Ophiuchus• Delphinus• Capricorn• Sagittarius• Pegasus• Lyra• Cygnus• Andromeda
Constellations visible all year round:
• 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:
PolarisUrsa Major
Cassiopeia
Cepheus
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.
Find Cassiopeia in the sky. The easiest way to do this, is to go from Polaris towards Andromeda in a straight line.
Polaris μ And
M31
When we find Cassiopeia...
Find the star ι (Iota) located at the extension of the arm that ends at the star Segin.
Segin
ι (Iota)
Next, already with the help of a telescope...
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).
Segin
ι (Iota)
RZ Cas
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.
Moving from Megrez through Phecda find the star (see the arrow).
Phecda
Megrez
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.
ψ
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 52469
HIP 52831
HIP 52881
HIP 52702
HIP 53160
It will be easiest to begin with locating the star Alrai.
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.
Polaris
Caph
Alrai
ι (Iota)
When we have found Alrai...
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
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.
U Cep
HIP 760
Alrai
One of the stars in the yellow circles can be used as a star of reference.
HIP 5108
HIP 4966
TYC 4505-387-1
TYC 4505-558-1
HIP 3132