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SS Cygni light curves

Nova Aquila 1999

Nova Cygni 1978

VARIABLE STARS  &  NOVAE

Without the slightest doubt this is the most know and widespread monitoring activity in which amateurs are involved for decades. This is probably the biggest area where amateurs own the field and use rigorous methods.

Variables stars are grouped in two main categories depending of the nature of their fluctuation:

- Extrinsic variables which light variation is inducted by the eclipse of a small companion (Algol case) or by an effect of the stellar rotation

- Intrinsic variables which vary most of the time regularly, resulting of physical changes inside the star or its atmosphere (pulses, plasma ejections), effects that contract and expand the superficial layers of the star. This later category is subdivided in some major classes:

- Long period variable stars like Mira Ceti which brightness  slowly varies over several years

- Irregular variable stars like Betelgeuse which exhibit no defined period

- Eruptive variable stars which light rises up to four magnitudes in a few seconds (Wolf 424 AB, UV Ceti, Eta Carina).

Cepheids, that we also find in external galaxies and globular clusters are also variables stars. The relation that links their luminosity to their fluctuation is known with accuracy. Their absolute brightness is inversed proportional to the square of their distance.

As member of an AAVSO local section, you will receive a list of variable stars to survey. The first time you have to test your ability to accurately appreciate magnitudes. Nowadays however you can use photometers to automate this process without to forget to zero your device and optional filters system.

The results of this monitoring are light curves accurate to 1/10th of a magnitude or more in best cases. These reports are sent to the local section of AAVSO for analysis that in exchange spares with amateurs results of his researches.

Novae are also variable stars that professionals divided in several subcategories :

- Fast novae which brightness may rise of 10 magnitudes in a few days

- Slow novae which light increases regularly on a period of around 15 days with a maximum that may last several months (Nova Herculis 1934)

- Recurrent novae which presents light blasts at intervals of a few dozen years, like T Corona Borealis (1866, 1946) or RS Ophiuchus (1958, 1967)

- Dwarf novae which are cataclysmic variable stars. Their brightness rises irregularly of several magnitudes in some hours (U Geminorum). This event is the most spectacular evolution a variable star may know.

- Novae-X which brightness mainly rise in X-light. This emission can overpass the more intenses galactical X sources in two weeks. Most are associated to faint stars of 16th magnitude.


FRENCH PAGES

AAVSO

AFOEV

VarObs software

MISAO Project

 

 

SNIAUC7375

SN1994D in NGC 4526

SUPERNOVAE SEARCH

Finding a supernova (SN) within hours after its start, when its lightblast is still arriving on Earth is of extreme importance for many astronomers and physicians who are waiting confirmation that their theoretical models reflect the reality of the world.

Since the first observations in 1998 at CTIO in Chile, we know that faint supernovae rise and fall very quickly, whereas bright supernovae brighten and fade much more slowly. By looking at how much the objects faded in the first 15 days following maximum light, we have noted that Type Ia supernovae can give distances which are good to about 7% - equal to the best of astronomical distance indicators. Therefore these supernovae are very used as "standard candles" to measure extragalactic distances.

But the sky is so large and potential stars than could explode in SN are so numerous that it is almost impossible for the small community of professional astronomers to survey regularly the sky. Therefore amateurs step in this peculiar research.

Examples are growing. Equipped with a scope over 5" wide and a CCD camera each member of the french "Association des Utilisateurs de Détecteurs Electroniques", AUDE,  is able to discover one or two SN each year in far galaxies. Some use automated telescopes which survey alone nearly 400 galaxies each night.

The world record is in the hands of Robert Evans who has discovered over twelve supernovae visually while Tim Puckett has six. Since 1994, Puckett and his team from the Puckett Observatory World Supernova Search have discovered over 270 supernovae or more than one per month.

Today with the widespread of image processing software and Internet, many tools exist to process your raw images and make comparisons with on-line galactical and extragalactical databases. But data analysis is a more complex process.

On the contrary, using a spectroscopic method to analyze the SN light (simply using prints or better a photometer), it is quite easy to determine its type according the lines displayed, its age, its distance and other related parameters.


ENGLISH PAGE

ISN

Astronomical League

Puckett Observatory

High-z Supernovae

High-z SN Search

 Mr.Galaxy

AUDE

MISAO Project

KBO-1996TL66

ASTEROIDS SEARCH

Since the discovery of ATEN objects and some asteroids by amateurs, you have some chance to discover new asteroids inside the Earth orbit. 

The "Remote and minor planets" section of ALPO (Association of Lunar and Planetary Observers) supports such a monitoring since 1981.

1991RR30

Similar to the supernovae search, tools are at amateur disposal (CCD camera, optoelectronic devices, image processing, etc). Searching for an asteroid or a NEO (Near Earth Object) requires also a tedious review of the sky but nothing else than a medium size scope (from 200 mm of aperture) fixed on a sturdy mount, a CCD and some on-line documentation.

According the members of the french "Association des Utilisateurs de Détecteurs Electroniques", AUDE, if you are well prepared a complete acquisition sequence may last 50 minutes during which you can record 4 to 5 asteroids and hope to go sleep by 3 AM.

Like any technique involving CCD's the second part of the job consists in correcting your raw images for electronic, mechanical and optical "noises" or parasites that were also recorded during the integration time. Have a first idea reading the dossier about CCD.

Then sometimes you discover something...

We might also add asteroid occultations timings and locations using CCD's in order to verify their orbital parameters. The english TASS program support such effort with automated telescopes.


FRENCH PAGES

AUDE

CNEOS (JPL)

The Watchers

ALPO Remote and Minor Planets section

PIXY software

Saturn occultation recorded by J.Hoot.

Moon occulting Saturn 

on Sept 10, 2001

Moon occulting Saturn on Feb 23, 2002 pictured by Tom Martinez at Powell Obs.

OCCULTATIONS TIMING

Here is an area where amateurs own almost exclusively the field. Why? Simply because these events occur everywhere on the Earth, regularly at a few kilometers only from your home and you need a portable instrumentation to be ready the D-Day.

Without consistent atmosphere the Moon is a privileged object to track occultations and grazing of stars by its limb. 

Your main advantage on professionals is that instead of be fixed under your huge dome your have a greater mobility and may count onto a large number of observers.

This activity requires that observers be in a specific location during a certain time to record instants of contacts of stars with the Moon. The equipment is reduced : a small telescope with a powerful eyepiece, a radio tuned on a time station, a chronometer or a vocal system to record your 'top', some maps showing the stars trajectories during the occultation.

Even the full darkness is not required to follow some bright stars.

There are two more requests to succeed : to find other observers to get useful data and be able to access the spot pointed on the roadmap, sometimes private or inaccessible without climbing material... Sometimes this is also a challenge !

Then comes the data analysis and reduction. This is not a complex task but it should be too long to explain on this page how to proceed. Better is contacting IOTA or regional sections devoted to this activity to get their observer's manual. 

Among other studies, this activity allows professional to refine the Moon's orbit as errors in timing of occultations still occur. This program permits also some refinement in stellar positions even if today we know that Hipparcos and Tycho satellites probably did all the job.

This activity also offers you the opportunity to detect very close multiples star systems you cannot see in ordinary circumstances.

Occultations of planets by the Moon are also a good challenge to picture these bodies as sharp as you can. Results are always spectacular mainly when Saturn is in the background. This is not an easy task for several reasons. First these bodies display different brightness and quite often the Moon disk is overexposed, then they do not focus at the same position due to their respective true distance from the Earth.

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