Cometís 29P/Schwassmann-Wachmann 1

Great activity

 
 
 
 


 
Various series of astrometric and photometric reductions on comet 29P Schwassmann - Wachmann 1 (29P/SW 1) are presented at heliocentric distances of 5.1 (UA) . Even though the great distance to the Sun this comet presents an unexpected and irregular activity. Itís brightness has changed up to 4 magnitud orders during the detected outburts in 2002. Thereís no commonly accepted theory explaining this behaviour as yet. In this work it is tried to show the cometary behaviour as observed by amateur astronomers using a novelty photometric estimation method.

 
Introduction
Nowadays we know comets are ice and rock particles, that from time to time enter the solar system from some external region (probably the Oortís cloud). These bodies sometimes perform their travel periodicaly trapped by the Sun. When comets reach the Sunís neighborhood, the heat makes itís components to evaporate. The gas nucleus and the dust form long tails that can be seen from Earth. These tails may extend as far as tenths of millions of kilometers. 
Thereís a comet group trapped in eliptical orbits, most of them with low inclination to the ecliptic plane and moving in the direct sense. This comet group, named the Jupiterís family, lies orbiting in between Jupiter and the Sun and they all have periods under 20 years. 

The discovery of comet 29P/Schwassmann-Wachmann 1.-
The astronomers, Arnold Schwassmann and Arno Arthur Wachmann, from the Bergedorf observatory in Germany, dicovered this comet on photographic plates exposed in 1927 november 15th. The comet was at a 13.5 magnitud, in subsequent nights, it begun to fade quickly. Four years after, in 1931, Karl Reinmuth checking plates exposed in 1902 march the 4th and 5th, detected the comet in magnitud 12. 

The orbit.-
This comet is one of the few whose orbit lies between Júpiter and Saturn and undergoes casual outbursts which may rise some magnitudes in a few days. The orbit almost circular indicates that the comet has been for long time in that region of the Solar System. The cometís magnitud is about 16 in the perihelion and about 19 when in the aphelium. Some times has been observed at magnitud 10. 
When the comet was discovered the eccentricity was about 0.15 and the period 16.4 years. Currently The orbit has changed and the eccentricity is 0.04 and the revolution period is 14.6 years. 
 

Epoch =2004 July 14.0 TT
Epoch =1925 May10.0 TT
T=2004 July 10.82831
T= 1925 Mayo7.84310 TT
Peri. =48.95625
Peri. = 359.08846
Node=312.71559(2000.0)
Node= 323.77275(2000.0)
Inc.9.39206
Inc.=9.44022
q=5.7235781AU
q =5.4749746 AU
e=0.0441701
e =0.1531798
a=5.9880717AU
a =6.4653327 AU
n' =0.06726259
n'=0.05995394
P=14.653years

P = 16.439 years

 

 
Magnitud estimation
General.-
The brightness determination has been one of the most important goals of the comet observers. The defy of doing reliable estimations has been enormous given that we are measuring non punctual sources moving over the background stars. Most of the magnitud estimations have been accomplished by photographic or visual methods. Nevertheless, in last years different methods for magnitud estimation are being used. 
· Photographic estimations using high power by Elizabeth Roemer (nuclear estimation m2) 
· James Scotti comaís substraction method (Spacewatch).m2 
· Estimations by other professional astronomers using CCD attached to big telescopes (m2). David Jewitt ,Licandro and others. 
· Amateur estimations with CCD cameras. Various methods. 
· Amateur visual observations with little telescopes and binoculars (m1)

The (m1) magnitud.
Most of the obtained magnitudes have been referred to the comaís total magnitud (m1) sorrounding the cometís nucleus. This kind of measures have been named ďTotal magnitud (m1)Ē. Beyer was one of the pioneers in trying to visualy determinate the cometís magnitudes during the 30s. On the other hand, thereís a more precise magnitud (for the cometís nucleus) which is the nuclear magnitud (m2). One of the firsts trying to determine it was Elizabeth Roemer  that has been estimating nuclear magnitudes for more than 25 years. 

Nuclear magnitud (m2).
The nuclear magnitud can be defined as the cometís total magnitud when it presents a stellar aspect. It can be estimated by measuring the total flux incide a little box centered in the most brilliant peak. Unfortunately such measures have little physical meaning. If one wants to get a good estimation only reflected licht from the cometís solid nucleus should be measured; i.e. no coma at all must be detected. Given that the nucleus is very small and the distance at which the comets are observed in general, most of the times there will be some comaís contamination in the estimations. The observations performed with nuclear magnitud m2 are in general the most weak and difficult to obtain. Nevertheless, this doesnít ensure that the measures represent the cometís actual nucleus. 

Magnitud estimation with the 10x10 method.
The observers have measured the brightness in a 10Ēx10Ē arc seconds diameter, for all the measures. This diameter is small enough to allow to detect little photometric changes caused by the nuclear activity. The problem when using a fixed photometric aperture is the observation of decreasing coma zones as the comet approaches the Earth; thus, this effect has to be corrected in order to perform a proper data análisis. We should bear in mind, anyhow, that for brilliant comets, i.e. with a big coma, it is preferred a big aperture, but the risk of obtaining contamination from background stars increases. To obtain quality photometric information, the images must have been corrected with dark frames and flat fields. 

You can find the technical data about the 10x10 method at : 
http://usuarios.lycos.es/obscometas/_10X10/inicio.htm





Observation techniques.- 
The data here presented has been obtained by different instrumentation types.
 

Station IAU 
Observer
Telescope
Photometric Range
213
Ramón Naves Montse Campas
SC 0.30+CCD
R
232
Esteban Reina
SC 0.25+CCD
R
235
Ligustri Rolando
New0.35+CCD
R
442
Albert Sanchez
SC 0.30+CCD
R
445
Miquel Camarasa
SC 0.20+CCD
R
458
Diego Rodríguez
SC 0.20+CCD
R
844
Fernanda Artigue
New0.35+CCD
R
939
Julio Castellano
SC 0.20+CCD
R
952
Josep Julià
SC 0.25+CCD
R
J 87
Juan Lacruz
SC 0.30+CCD
R
J 91
Carles Pineda
SC 0.25+CCD
R
J 97
Toni Climent
SC 0.25+CCD
R

 
 
 

Visual Observers
V02 Rafael Benavides Palencia. SC 23cm f/10Telescope
V03 Carlos Labordena Barceló. SC 20-cm f/10Telescope
V04 Carlos Segarra García. Newton 25cm f/5Telescope
V09 Maciej Reszelski
You can find theobserverís technical data at:
http://personals.ip.ictonline.es/+mcampas/lista-obs/datos.html

Used Catalogs.
One of the sources for performing photometry are the catalogs. In observations done with different catalogues we have obtained different results. The Guide Star Catalog(GSC), is a digitazion of the plates from the Palomar Observatory Sky Survey (POSS). This catalog is about 15 million stars, but the star magnitudes are not very reliable. A more reliable catalog has been compiled by the United States Naval Observatory (USNO) contains postions and magnitudes, in standard red filter, for about 500 million stars reaching magnitud 23.
The error obtained when using the USNO catalog, in red magnitud (R) has been analyzed. The preliminary results of a star sample are the following :

Photometry with the USNO catalog (in R band)

· 57% of the stars have error lower than .2 tenths 

· 43% of the star have errors bigger that 0.2 tenths

Catlog type used
TYPE
STARS  R
Guide 8
GSC +USNO
Astroart
GSC+USNO
The Sky
GSC+USNO
Cometís Schwassmann-Wachmann 1 light curve.

The data gathered at the mail list "Cometas_Obs" are the following:

278 CCD observations
12 visual observations
30 CCD images

The light curve has been represented as corrected magnitud for the distance to the Earth against the time. UIT the observational data it can be seen the different outbursts the comet has undergo during the year.

The posible cyclic changes that can show a rotation period are masked, but we can see instead the bchanges in more than one magnitud that are probably related to outburts of CO2 ice deposits (carbon dioxide) and CH4 (methane) than the Sun heats gradually.
 


Curva realizada por Julio Castellano



 
 
 
 
 
 

The coma.
The cometís coma is a matter halo sorrounding the cometís actual nucleus. The coma and the tail is all we really see from Earth. The comaís shape and size may vary for the smae comet during aparition. The shape depends on the distance to the Sun and the relative quantities of dust and gas production. For comets producing little dust, the coma is generally spheric. Comets producing great amounts of dust, use to have tails with parabolic shapes. This is due to different dust grain sizes. The bigger grains are ejected along the cometís orbit whereas the tiny dust particles are ejected against the Sun by the pressure of radiation of light. When thereís a distribution of dust particles sizes a tipical tail with beautiful shape develops.
Comaís diameter

In general the comaís diameter is given as arc minutes (´) when the coma grows it can be expressed as degrees. When the coma is elongated, the measure stands for the shortest dimension. In the acompaning table we show the 29P comaís actual diameter, against the distance to the Earth, based on the angular diameter as obtained from the CCD images. The images used for the coma size estimation have always been obtained with the same integration time (exposure) and the same values of the background have been used to calculate the relative size. We can see a relation between the cometís brightness and the comaís diameter. In continued followup we always found coma sorrounding the nucleus changing in size from day to day.
 
 

Comet
Year
Month
Day
Coma
Kms
Distance 
(AU)
29P
2002
7
2.05
0.55
196.847
4.9347
 
2002
8
4.95
0.28
87.084
4.8028
 
2002
8
10.95
0.70
244.267
4.8113
 
2002
8
31.89
0.25
89.254
4.9225
 
2002
9
9.93
0.45
163.367
5.0055
 
2002
10
6.86
0.35
135.785
5.3491
 
2002
10
17.88
0.35
140.014
5.5157
 
2002
10
27.82
0.20
82.261
5.6710
 
2002
10
29.84
0.40
165.442
5.7027


Conclusion.-
· 278 CCD observations have been gathered, 12visuale and more than 30 CCD pictures of a great quality.
· The light curve is non typical for a standard comet and this probably speaks of a nucleus with gas deposits that provide the cometís extra unexpected brightness.

· Thereís a correlation between the brightness and  the coma size.
 

 

It is important to note there are not many comets with such a big activity at a large heliocentric distances 6AU. In effect, another object from the external solar system is the asteroid Quiron, with orbit between Saturn and Uranus, a coma was detected around his nucleus in the year 1989.

Acknowledgements.-
This work should not have been posible without the collaboration of all the obervers sending his results to the list Cometas_Obs at. http://usuarios.lycos.es/obscometas/

Iím gratefull to Julio Castellano for his cooperation with bthe graphics.

The observations with astrometry, photometry and images can be obtained at:
http://usuarios.lycos.es/obscometas/29P/web.htm
 

Diego Rodríguez
Member of the list "COMETAS_OBS"
Station IAU 458
Translate: Juan Lacruz