British observer George Alcock discovered this nova at
4:25 GMT on 25 March 1991. The discovery story of
this nova is very interesting which is as follows; Sky
was cloudy, but Alcock decided to observe heavenly
bodies through the window of his house by a personal
telescope. He had been observing the sky for about
half an hour when the Sun rose, and sky became clear.
At that time, Alcock could observe a mass of 5mag in
the Herculis constellation by his keen eyes. In fact,
Alcock observed Nova 838 Herculis. In spite of visual
discovery of Alcock, the existence of this nova
independently photographed and recorded on Tri-X film
at 20:55 on 22 March.
The curve of Nova 838 Herculis’ light has been
designed for a period between 9 March 1991 to 25 March
1991. Investigation of Palomar images indicates that
the amplitude of this nova eruption has been about 13
mag, which is very rare among novas.
Nova 1500 Cygni
One of the most dramatic fast nova on record; it was
discovered on 29August, 1975,
soared to magnitude 2.0 the next day (altering the
familiar outline of the Northern Cross in Cygnus),
then dimmed by 3 magnitudes over the next three days.
Minoru Honda from Kurashiki in Japan observed this
nova when it was in conditions of 3mag in the morning
of 29 August. It was the fastest (19 mag), largest
amplitude, and second most intrinsically bright nova
of the twentieth century (only Nova Puppis 1942 was
brighter).
The following light curve indicates the supernova
luminosity variations from 28 March 1975 to 17
September 1980.
After the outburst of 1975 and in terms of data
collected since then indicate that V1500 Cyg (Nova
Cygni's variable star name) is an AM Herculis star in
which the white dwarf primary has such a powerful
magnetic field. V1500 Cyg is the 13th confirmed AM
Her-type system and has the second longest orbital
period (about 3.3 hours).
Novas (Part 2)
One of the most difficult masses, which are discovered
by observers, is a nova. The hunters of comets are
investigating for a fog-like mass among sky stars.
The outburst occurs when huge volume of gas is
released from dwarfs’ companion star. This
amount of gas goes toward the dwarf star and forms a
superficial layer. These layers are gradually
compressed and the dwarf star becomes brighter. This
increase may reach up to 10mag. Majority of novas can
be observed in that part of the Milky Way bearing
plenty of celestial bodies. Therefore, it is
difficult to find a new star among these stars, and
their discoverers are not a lot. Alfredo J.S. Pereira
from Portugal is one of the most famous discoverers of
these novas. Pereira observed the clear sky
thoroughly by means of telescopes of 14*100 and 9*34.
His reputation is because of the discovery of three
novas within 21 days. It is interesting that the two
last discoveries took place with an interval of eleven
days in a constellation bearing distance of less than
three arc degrees.
“Nova Sagittarii V4739 No.2 2001” was
discovered on 26 August when it was in the conditions
of 7.6 mag and 45′ away from Sagittarii star.
Then, “Nova Sagittarii V4740 No.3 2001”
was observed when it was in the conditions of 7mag and
2˚ away from southwestern of Delta star. He was
very lucky because most of the novas’ hunters
spent several years to observe them. He registered
the nova under his name.
Pereira was not very lucky from the beginning. He
commenced his job from 1981 at the age of 18. Then,
he left that job. His perseverance was admirable
because he continued his observations disseminatedly,
up to 1991. Within that period his plan was well
organized. When he was watching the sky through the
window of his house, he discovered “Nova Aquilae
V1494 No.2 1999” having a luminosity of 6mag.
Its luminosity reached 3.6mag within a day.
Left illustration indicates Nova Sagittarii V4739 No.2
on 29 August and right illustration indicates Nova
Aquilae No.3 on 11 September, exactly two and five
days after Pereira discovery.
The number of very bright novas is usually one or two
within a decade. Before, Pereira who discovered Nova
Aquilae V1494 No.2 Australian Peter Williams and New
Zealander Alan C.Gilmore independently discovered
“Nova Velorum V382” on 22 May 1999. The
new star brightness was 3mag. Then reached 2.6mag on
23 May. Before Williams and Gilmore, Nova Cygni 1992
(V1974) was discovered and reached 4mag. The
discoverer of this nova is the American astronomer
Peter Collins from the United States. When the nova
was at 7mag, P.Collins discovered it by naked eyes.
Pereira watched the sky for about 90 minutes in each
round of observations. By discovery of three novas,
he became one of the followers of George Alcock
(British amateur astronomer who discovered five novas
via his telescope 20*105 and 15*80 from 1967 to 1991.
Peter Collins, the American amateur astronomer,
discovered four new novas. He was called Alcock of
the United States. He did not believe in the
presented patterns of sky atlases. On the other hand,
the observed constellations were kept in
Collin’s mind.
Alcock was the pioneer of “Small
Constellations” technique. He observed stars of
the Milky Way having brightness up to 8mag via his
telescope of 40 and 80mm and recorded them in his
mind. This work was one of the observation
masterpieces within 20th century.
Nova Delphini 1967 located 3°of northern part of
Delphini star. It was the first discovery of Alcock.
Today this nova is called, “Nova HR
Delphini”.
This illustration was prepared in 5th of September of
1967.
Pereira had about 14 constellations in his mind. In
terms of the number of stars in the sky (poor or rich
of stars), he was investigating for stars bearing 7.5
to 9mag.
The total area he was studying was about 2000 degrees
of the Milky Way having more than 3000 stars.
Report writing
In this part, some points regarding the observation of
novas are presented. When a new nova is discovered,
it must be observed in every clear night. Observation
data of novas have a significant role in recognition
and understanding of their evolution. Therefore, to
make a complete research, new authentic astronomical
maps must be used (Uranometria 2000 and Sky Atlas
2000, etc.). The application of these maps depends on
the nova luminosity and the accuracy of study. When
the nova’s light is gradually dimmed, there is
no necessity for frequent estimation of its light
magnitude. But, the observation process must be
continuously done. If possible, dimming of the
nova’s light must be reported once a week or a
month. As deducted, the first step is to select and
review the observation of appropriate subjects with
regard to atmospheric and seasonal conditions. The
available observation plans assist scientists to
connect the disconnected chain links of nova’s
life events. It is very important to observe novas at
the moment of outburst and various wavelengths to
obtain data like photosphere development, elements
abundance etc.
Verification and observation of novas in the
conditions of dimming the ultraviolet, visible and
infrared of spectra indicate data about their energies
and mass reduction. Whereas observations of X-ray is
useful in organization and modeling of nebulas and
infrared observations provide some data on dust
formation and their evolution.
If an unknown object is observed in the sky, what can
we do? At this stage, what are the preliminary
activities to prove our claims?
First, we must be sure that the observed object is not
a planet or asteroid. For this purpose, we can refer
to authentic authorities, such as astronomical
journals, softwares, etc. to control our claims. Even
we can ask our friends regarding this issue. It is
not very far from mind that the unknown object is a
dim asteroid. It is possible to refer to CBAT
(Central Bureau for Astronomical Telegrams) or
accurate astronomical softwares, such as HNSKY,
including the list of 10,000 dim asteroids having
brightness up to 20mag.
It must be checked that the unknown object is not a
missed item from our maps. We must also refer to the
other authentic atlases. After controlling the
required items, it is item to report our observations
to authentic scientific authorities.
Suitable authorities are CBAT and AAVSO (American
Association of Variable Star Observers). The
available form of CBAT in Internet must be filled out.
The observation must be reported to either of the
above-mentioned authorities. In preparation of the
recent report the following points must be clarified;
*The location of unknown object (with suitable
accuracy).
*Date and time of observation in GMT.
*The estimated magnitude of unknown object (with
suitable accuracy).
*The subject color.
*Introduction of observation instruments, like
telescope, binoculars, etc.
*Announcement of our observation method. Is it only
visual? Has it been recorded on films (including
photographic films). Have different filters been
used?
*Introduction of atmospheric conditions and other
important factors having effect on observation
process.
*Observer details and location of observation
(latitude and longitude of observer).
*Re-introduction of all required controllings (stars,
asteroids, missed stars from map,etc.).
*The supplement of prepared illustration of subject to
prove our claims, if any.
