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By Giovanni Sostero and Ernesto Guido Remanzacco Observatory (www.afamweb.com) CARA (http://cara.uai.it/) Meeting on Asteroids and Comets in Europe - MACE.

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Presentation on theme: "By Giovanni Sostero and Ernesto Guido Remanzacco Observatory (www.afamweb.com) CARA (http://cara.uai.it/) Meeting on Asteroids and Comets in Europe - MACE."— Presentation transcript:

1 by Giovanni Sostero and Ernesto Guido Remanzacco Observatory (www.afamweb.com) CARA (http://cara.uai.it/) Meeting on Asteroids and Comets in Europe - MACE 2006 Vienna, May 12-14, 2006 “Some thoughts about cometary CCD photometry”

2 Summary Some issues about comets & CCDs photometry Photometry and physical studies of comets The CARA standardization approach Some results Conclusions

3 Which photometric aperture has to be selected for their measurement? Which is the influence of the observing conditions? Comets are diffuse objects

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5 Stacking of multiple subframes Need to provide suitable reference stars sequences Comets do have significative proper motions

6 Need to use narrowband filters (objects with strong emission lines) Possibility to use broadband filters (objects with negligible emission lines) Possibility to use ulfiltered photometry (limited amount of objects and/or under particular conditions) Comets are emission line objects

7 The Afrho connection Photometry and physical studies of comets

8 Afrho, is a quantity introduced by A'Hearn et al. in 1984 with the aim of comparing measurements concerning the dust continuum produced under different observing conditions, times and instruments. The Af[ρ] is the product of the albedo (A), filling factor (f) of grains within the field of view and the linear radius of the field of view [ρ] at the comet. We can consider it only as a “proxy” of the dust abundance within the coma. This means that we cannot establish a simple and secure link between Afrho and the dust production rate. What is Afrho?

9 The Afrho quantity is calculated by the ratio between the luminous flux received from the comet, and the solar flux. Using the following equation: Af[ρ] = ρ*(2DR/ρ)2 Fcom/Fsun Where: A is the albedo f is the filling factor, that is how much the powder grains fill the field of view ρ is the coma radium considered in the measurement, usually expressed in cm D is the geocentric distance Earth-Comet, expressed in cm R is the eliocentric distance, expressed in Astronomical Unit Fcom is the observed comet light flux (or flow) Fsun is the solar flux at 1 AU

10 CCD comet photometry Do we really need some kind of filtered photometry?

11 Narrowband Interference Filters Central Wavelength (nm)Molecule 390CN 405C3 430CO+ 450Blue Dust Continuum 515C2 620H2O+ 647 or 650Red Dust Continuum

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13 CCD comet photometry C/2001 Q4 (NEAT): strong gas contamination

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15 Aperture radiusLowell Obs.CARADifference 5,000 to 20,000~4450 cm~ 4320cm~3% Comparison with D. Schleicher results (Lowell Observatory) Comet C/2001 Q4 (NEAT) on May 12, 2004 Strong gas contaminations  narrowband Example of Afrho determinations - 1

16 CCD comet photometry 9P/Tempel: negligible gas contamination

17 Comparison with D. Schleicher results (Lowell Observatory) Aperture radiusLowell Obs.CARADifference ~ 25,000 Km~166 cm~ 189 cm~13% ~ 15,000 Km~193 cm~ 215 cm~11% ~ 10,000 Km~234 cm~ 245 cm~5% Comet 9P/Tempel on May 6, 2005 Negligible gas contamination  R & I broadband photometric filters Example of Afrho determinations - 2

18 CCD comet filtered photometry A standardization tentative from the CARA collaboration WINDOW APERTURE Main window size for aperture photometry: 100,000 comet distance  (arcsec)= 138/  circular apertures)  (arcsec)= 122.3/  (square apertures) Multiples and submultiples apertures (e.g. 200,000 Km, 50,000 km, 25,000 km, etc.) + REFERENCE STARS MAGNITUDES SOURCES Johnson B & V: Hipparcos/Tycho catalogue magnitudes recommended Cousins R & I: polynomial extrapolation from catalogued B-V values (+/- 0.1 magn.) = TARGET Attempt to produce uniform photometry (+/- 10%) from various observers

19 Historic roadmap of the CARA collaboration TA Annual General Meeting, September Basingstoke, UK. BAA Comet Section Meeting, February London, UK. First CCDs filtered lightcurves of comets Presentation of the “fixed aperture window” technique for CCD photometry Meeting on Asteroids and Comets in Europe (MACE2002), May Visnjan, Croatia. Improvements in photometric methods The first experiments with the Afrho procedure are presented Meeting on Asteroids and Comets in Europe (MACE 2003), May Mallorca Observatory, Spain. Presentation of the CARA collaboration Suggestion about the opportunity of the Afrho procedure approach also for the amateurs IWCA III, June Paris, France. Some observing campaigns results based on the Afrho method are presented BAA Comet Section Meeting, May Cambridge, UK Discussion about the need to choose some kind of standardization for CCDs comets photometry

20 Developed by Roberto Trabatti (CARA) Wafrho: the CARA workhorse

21 0009P R HIP Sos HIP G0Vs 0.45m reflector data P R HIP Sos HIP G0Vs 0.45m reflector data P R HIP Sos HIP G0Vs 0.45m reflector data P R HIP Sos HIP G0Vs 0.45m reflector data P R HIP Sos HIP G0Vs 0.45m reflector data P R HIP Sos HIP G0Vs 0.45m reflector data P R HIP Sos HIP G0Vs 0.45m reflector data P R HIP Sos HIP G0Vs 0.45m reflector data P R HIP Sos HIP G0Vs 0.45m reflector data P R HIP Sos HIP G0Vs 0.45m reflector data P R HIP Sos HIP G0Vs 0.45m reflector data P R HIP Sos HIP G P R HIP Sos HIP G P R HIP Sos HIP G P R HIP Sos HIP G P R HIP Sos HIP G P R HIP Sos HIP G P R HIP Sos HIP G P R HIP Sos HIP G P R HIP Sos HIP G P R HIP Sos HIP G P R HIP Sos HIP G Output: tabulated data

22 Some examples: C/2002 T7 (LINEAR) 97/Tempel 73P/Schwassmann-Wachmann From theory to practice

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37 The dust environment of comet 67P/Churyumov-Gerasimenko, Fulle, M.; Barbieri, C.; Cremonese, G.; Rauer, H; Weiler, M.; Milani, G.; Ligustri, R., Astronomy and Astrophysics, v.422, p (2004) A neck-line structure in the dust tail of Comet C/2004 F4 (Bradfield), Pansecchi, L.; Scardia, M.; Astronomy and Astrophysics, v.430, p (2005) Photometry of comet 9P/Tempel 1 during the 2004/2005 approach and the Deep Impact module impact, Milani G.A., Sostero G., Trabatti R., Ligustri R., Nicolini M., Facchini M., Tirelli D., Carosati D., Vinante C. and Szabo’ Gy. M.; Icarus, submitted CBET nr.464, 473, 361; IAUC nr. 8668, 8660, 8659, 8658, 8557, 8543 Publications so far

38 Some kind of standardization for cometary photometry is needed It’s unlikely to establish an “all purpose” method Different kind of approaches are possible, according to the targets Different approaches must (hopefully) converge to comparable results Cometary CCDs photometry is well suited for amateurs Conclusions

39 Acknowledgements Collaborating astronomers Marco Fulle (Trieste Astronomical Observatory, Italy), Gian Paolo Tozzi (Arcetri Astronomical Observatory, Italy), Luigi Pansecchi (Merate Astronomical Observatory, Italy), Mauro Barbieri (Padova Astronomical Observatory, Italy), Gyula Szabo’ (University of Szeged, Hungary), Laurent Jorda (Lab. d‘Astrophysique de Marseille, France) CARA dedicated staff Giannantonio Milani (Coordinator), Carlo Vinante (Webmaster), Roberto Trabatti, Martino Nicolini & Mauro Facchini (Software) CARA observing stations Giannantonio Milani (Padova, Italy), Diego Tirelli (Vicenza, Italy), Toni Scarmato (S. Costantino Briatico, Italy), Filip Fratev (Bulgaria), Descartes Observatory (Pavia, Italy), Campo dei Fiori Observatory (Varese, Italy), CAsT Observatory (Talmassons, Italy), Remanzacco Observatory (Remanzacco, Italy), G. Montanari Observatory (Cavezzo, Italy), Cor Caroli Observatory (Vicenza, Italy), Armenzano Observatory (Perugia, Italy), Crn Vrh Observatory (Crni Vrh, Slovenia), Terry Lovejoy (Brisbane, Australia), Erik Bryssinck (Belgium), New Mexico Skies (USA)


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