by%20Giovanni%20Sostero%20and%20Ernesto%20Guido

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

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

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Comets are diffuse objects

• Which photometric aperture has to be selected
  for their measurement?

• Which is the influence of the observing
  conditions?

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Comets do have significative proper motions

• Stacking of multiple subframes

• Need to provide suitable reference stars
  sequences

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Comets are emission line objects

• Possibility to use ulfiltered photometry
  (limited amount of objects and/or under
  particular conditions)

• Need to use narrowband filters (objects with
  strong emission lines)

• Possibility to use broadband filters (objects
  with negligible emission lines)

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Photometry and physical studies of comets
The Afrho connection
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What is Afrho?

• 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? 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
  ? 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.

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The Afrho quantity is calculated by the ratio
between the luminous flux received from the
comet, and the solar flux. Using the following
equationAf? ?(2DR/?)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 ? 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
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CCD comet photometry Do we really need some kind
of filtered photometry?
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Narrowband Interference Filters
Central Wavelength (nm) Molecule
390 CN
405 C3
430 CO
450 Blue Dust Continuum
515 C2
620 H2O
647 or 650 Red Dust Continuum
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CCD comet photometry C/2001 Q4 (NEAT) strong
gas contamination


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Example of Afrho determinations - 1
Comparison with D. Schleicher results (Lowell
Observatory)
Comet C/2001 Q4 (NEAT) on May 12, 2004
Strong gas contaminations ? narrowband filter
_at_647nm


Aperture radius Lowell Obs. CARA Difference
5,000 to 20,000 4450 cm 4320cm 3
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CCD comet photometry 9P/Tempel negligible gas
contamination
 
 
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Example of Afrho determinations - 2
Comparison with D. Schleicher results (Lowell
Observatory)
Comet 9P/Tempel on May 6, 2005
Negligible gas contamination ? R I broadband
photometric filters
 
 
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CCD comet filtered photometry A standardization
tentative from the CARA collaboration

• WINDOW APERTURE
• Main window size for aperture photometry
  100,000 km _at_ 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

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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

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Wafrho the CARA workhorse
Developed by Roberto Trabatti (CARA)
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Output tabulated data
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
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From theory to practice

• Some examples
• C/2002 T7 (LINEAR)
• 97/Tempel
• 73P/Schwassmann-Wachmann

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Publications so far

• The dust environment of comet 67P/Churyumov-Geras
  imenko, 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

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Conclusions

• Some kind of standardization for cometary
  photometry is needed

• Its 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

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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.
dAstrophysique 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)