Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.eso.org/~hukaufl/DI_TALKS/kidger_amateur_photom.pdf Дата изменения: Mon Feb 23 20:17:26 2004 Дата индексирования: Tue Oct 2 09:43:18 2012 Кодировка: Поисковые слова: annular solar eclipse

Amateur Photometric Monitoring of Comets
Mark Kidger Instituto de AstrofМsica de Canarias


We are all aware of what amateurs can do...
· Many amateurs are now equipped with good CCDs and telescopes of 30-40 cm diameter, under computer control. · Initially used mainly for astrometry and "pretty pictures".


· Amateur astronomers take large quantities of astrometry, but the associated photometry has mainly been "thrown away". · Photometry has been a "come as you are party"
­ ­ ­ ­ Any aperture Any method Any filter (or no filter) The photometry is virtually unusable.


A typical example: 19P/Borrelly


The "Observadores_cometas" group
· More than 80 members and collaborators in 8 countries on 3 continents. · Mainly Spanish language (but includes a number of English, Italian and Portuguese speakers). · A large percentage are active observers · About two thirds of the active members use CCD with telescopes from 20-40 cm. · Regularly observe comets as faint as R=18.


Standardise what can be controlled
· Standard aperture for photometry
­ 10 arcseconds ­ compatible with the normal pixel size of amateur CCDs.

· Treat unfiltered data as R and reduce using a common reference catalogue
­ USNO A2.0 is closest to "Landolt" R and has reasonable photometric errors.

· Sky subtract with the median of the frame. · Use a common reduction routine
­ Initially "Astrometrica", but now using a routine "FOCAS" written by a group member for this project.


· The FOCAS routine gives multiaperture photometry
­ 10, 20, 30, 40 & 60 arcseconds ­ For very bright, nearby comets, 150 & 300 arcseconds may be used. ­ We define a "coma index" map=a.rb ­ For an r-1 coma law we expect b= -2.5 ­ The observed average coma index is ­2.5! ­ This allows reduction to a standard physical aperture (generally 10 000 or 25 000km, depending on the distance of the comet).


Early attempt at standardisation... Only applying standard aperture and band.

Before

A f t er



198 points


67P/Churyumov-Gerasimenko




How reliable is the amateur data?

2002 ­ Data from "ObservadoresCom etas" 1997 ­ Pro fessional data compiled from the literature


Pre- peri helion Qdust is slightly higher in 46P/Wirtanen than in 67P/ChuryumovGerasim enko.



Large scatter in m ultiaperture data im plies that the com a does follow a r-1 law.


C/2002 T7 (LINEAR) appears to be about 2-3 times dustier than C/2001 Q4 (NEAT), but has lower gas production.


Conclusions
· Amateur photometry of 9P/Tempel 1 can be a valuable resource to support the Deep Impact mission because of its high intensity of light curve coverage. · Carefully standardised amateur data is of a quality little inferior to customised professional photometry. · Don't just ask the amateurs to take pretty pictures!!!