Slide1: 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”


Slide2: Summary Some issues about comets & CCDs photometry Photometry and physical studies of comets The CARA standardization approach Some results Conclusions


Slide3: Which photometric aperture has to be selected for their measurement? Which is the influence of the observing conditions? Comets are diffuse objects


Slide5: Stacking of multiple subframes Need to provide suitable reference stars sequences Comets do have significative proper motions


Slide6: 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


Slide7: The Afrho connection Photometry and physical studies of comets


Slide8: 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?


Slide9: 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


Slide10: CCD comet photometry Do we really need some kind of filtered photometry?


Slide11: Narrowband Interference Filters


Slide13: CCD comet photometry C/2001 Q4 (NEAT): strong gas contamination


Slide15: Comparison with D. Schleicher results (Lowell Observatory) Comet C/2001 Q4 (NEAT) on May 12, 2004 Strong gas contaminations  narrowband filter @647nm Example of Afrho determinations - 1


Slide16:     CCD comet photometry 9P/Tempel: negligible gas contamination


Slide17: Comparison with D. Schleicher results (Lowell Observatory)     Comet 9P/Tempel on May 6, 2005 Negligible gas contamination  R & I broadband photometric filters Example of Afrho determinations - 2


Slide18: CCD comet filtered photometry A standardization tentative from the CARA collaboration WINDOW APERTURE Main window size for aperture photometry: 100,000 km @ comet distance f (arcsec)= 138/D (circular apertures) f (arcsec)= 122.3/D (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


Slide19: Historic roadmap of the CARA collaboration TA Annual General Meeting, September 2001. Basingstoke, UK. BAA Comet Section Meeting, February 2002. 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 2002. 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 2003. Mallorca Observatory, Spain. Presentation of the CARA collaboration Suggestion about the opportunity of the Afrho procedure approach also for the amateurs IWCA III, June 2004. Paris, France. Some observing campaigns results based on the Afrho method are presented BAA Comet Section Meeting, May 2005. Cambridge, UK Discussion about the need to choose some kind of standardization for CCDs comets photometry


Slide20: Developed by Roberto Trabatti (CARA) Wafrho: the CARA workhorse


Slide21: 0009P 20050426.86 0.715 1.656 18.85 R 11.51 025580 0000182 00001 HIP Sos www.afamweb.com HIP 64792 G0Vs 0.45m reflector data -0069.45 0009P 20050426.86 0.715 1.656 18.85 R 11.98 012539 0000241 00002 HIP Sos www.afamweb.com HIP 64792 G0Vs 0.45m reflector data -0069.45 0009P 20050426.86 0.715 1.656 18.85 R 12.05 011536 0000244 00002 HIP Sos www.afamweb.com HIP 64792 G0Vs 0.45m reflector data -0069.45 0009P 20050426.86 0.715 1.656 18.85 R 12.12 010533 0000250 00002 HIP Sos www.afamweb.com HIP 64792 G0Vs 0.45m reflector data -0069.45 0009P 20050426.86 0.715 1.656 18.85 R 12.21 009530 0000256 00002 HIP Sos www.afamweb.com HIP 64792 G0Vs 0.45m reflector data -0069.45 0009P 20050426.86 0.715 1.656 18.85 R 12.29 008527 0000265 00002 HIP Sos www.afamweb.com HIP 64792 G0Vs 0.45m reflector data -0069.45 0009P 20050426.86 0.715 1.656 18.85 R 12.40 007524 0000271 00002 HIP Sos www.afamweb.com HIP 64792 G0Vs 0.45m reflector data -0069.45 0009P 20050426.86 0.715 1.656 18.85 R 12.52 006520 0000281 00002 HIP Sos www.afamweb.com HIP 64792 G0Vs 0.45m reflector data -0069.45 0009P 20050426.86 0.715 1.656 18.85 R 12.65 005517 0000295 00002 HIP Sos www.afamweb.com HIP 64792 G0Vs 0.45m reflector data -0069.45 0009P 20050426.86 0.715 1.656 18.85 R 12.83 004514 0000304 00003 HIP Sos www.afamweb.com HIP 64792 G0Vs 0.45m reflector data -0069.45 0009P 20050426.86 0.715 1.656 18.85 R 13.09 003511 0000309 00003 HIP Sos www.afamweb.com HIP 64792 G0Vs 0.45m reflector data -0069.45 0009P 20050501.91 0.712 1.637 21.38 R 11.23 049954 0000116 00005 HIP Sos www.afamweb.com HIP 63215 G5 -0064.40 0009P 20050501.91 0.712 1.637 21.38 R 11.53 025532 0000172 00007 HIP Sos www.afamweb.com HIP 63215 G5 -0064.40 0009P 20050501.91 0.712 1.637 21.38 R 11.57 023312 0000181 00007 HIP Sos www.afamweb.com HIP 63215 G5 -0064.40 0009P 20050501.91 0.712 1.637 21.38 R 11.64 021092 0000188 00007 HIP Sos www.afamweb.com HIP 63215 G5 -0064.40 0009P 20050501.91 0.712 1.637 21.38 R 11.71 018872 0000196 00008 HIP Sos www.afamweb.com HIP 63215 G5 -0064.40 0009P 20050501.91 0.712 1.637 21.38 R 11.80 016651 0000206 00008 HIP Sos www.afamweb.com HIP 63215 G5 -0064.40 0009P 20050501.91 0.712 1.637 21.38 R 11.90 014431 0000216 00009 HIP Sos www.afamweb.com HIP 63215 G5 -0064.40 0009P 20050501.91 0.712 1.637 21.38 R 12.03 012211 0000226 00009 HIP Sos www.afamweb.com HIP 63215 G5 -0064.40 0009P 20050501.91 0.712 1.637 21.38 R 12.20 009991 0000238 00009 HIP Sos www.afamweb.com HIP 63215 G5 -0064.40 0009P 20050501.91 0.712 1.637 21.38 R 12.41 007771 0000251 00010 HIP Sos www.afamweb.com HIP 63215 G5 -0064.40 0009P 20050501.91 0.712 1.637 21.38 R 12.73 005550 0000263 00010 HIP Sos www.afamweb.com HIP 63215 G5 -0064.40 Output: tabulated data


Slide22: Some examples: C/2002 T7 (LINEAR) 97/Tempel 73P/Schwassmann-Wachmann From theory to practice


Slide37: 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.357-368 (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.1129-1132 (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


Slide38: 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


Slide39: 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)