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Post Info TOPIC: Comet C/2012 F6 (LEMMON)


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RE: Comet C/2012 F6 (LEMMON)
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Title: Exploring the volatile composition of comets C/2012 F6 (Lemmon) and C/2012 S1 (ISON) with ALMA
Author: Eva G. Břgelund, Michiel R. Hogerheijde

Comets formed in the outer and cold parts of the disk which eventually evolved into our Solar System. Assuming that the comets have undergone no major processing, studying their composition provides insight in the pristine composition of the Solar Nebula. We derive production rates for a number of volatile coma species and explore how molecular line ratios can help constrain the uncertainties of these rates. We analyse observations obtained with the Atacama Large Millimetre/Submillimetre Array of the volatile composition of the comae of comets C/2012 F6 (Lemmon) and C/2012 S1 (ISON) at heliocentric distances of ~1.45 AU and ~0.56 AU, respectively. Assuming a Haser profile with constant outflow velocity, we model the line intensity of each transition using a 3D radiative transfer code and derive molecular production rates and parent scale lengths. We report the first detection of CS in comet ISON obtained with the ALMA array and derive a parent scale length for CS of ~200 km. Due to the high spatial resolution of ALMA, resulting in a synthesised beam with a size slightly smaller than the derived parent scale length, we are able to tentatively identify CS as a daughter species, i.e., a species produced in the coma and/or sublimated from icy grains, rather than a parent species. In addition we report the detection of several CH3OH transitions and confirm the previously reported detections of HCN, HNC and H2CO as well as dust in the coma of each comet, and report 3sigma upper limits for HCO+. We derive molecular production rates relative to water of 0.2% for CS, 0.06-0.1% for HCN, 0.003-0.05% for HNC, 0.1-0.2% for H2CO and 0.5-1.0% for CH3OH, and show that the modelling uncertainties due to unknown collision rates and kinematic temperatures are modest and can be mitigated by available observations of different transitions of HCN.

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Ephemeris

Date    TT    R. A. (2000) Decl.     Delta      r     Elong.  Phase   Mag
2013 04 16    00 12 51.5 -04 14 27   1.6495  0.8562    25.2    30.0  10.4
2013 04 17    00 13 04.4 -03 22 03   1.6543  0.8664    25.7    30.1  10.5
2013 04 18    00 13 17.6 -02 29 52   1.6588  0.8768    26.1    30.3  10.5
2013 04 19    00 13 31.3 -01 37 54   1.6631  0.8875    26.6    30.5  10.6
2013 04 20    00 13 45.2 -00 46 07   1.6672  0.8985    27.1    30.6  10.6
2013 04 21    00 13 59.5 +00 05 27   1.6711  0.9096    27.7    30.8  10.7
2013 04 22    00 14 14.0 +00 56 50   1.6748  0.9210    28.2    31.1  10.8
2013 04 23    00 14 28.8 +01 48 02   1.6783  0.9326    28.8    31.3  10.8
2013 04 24    00 14 43.8 +02 39 03   1.6817  0.9444    29.4    31.5  10.9
2013 04 25    00 14 59.0 +03 29 54   1.6848  0.9564    30.0    31.7  10.9
2013 04 26    00 15 14.4 +04 20 34   1.6879  0.9685    30.6    31.9  11.0
2013 04 27    00 15 29.9 +05 11 04   1.6908  0.9808    31.2    32.2  11.1
2013 04 28    00 15 45.5 +06 01 25   1.6935  0.9933    31.9    32.4  11.1
2013 04 29    00 16 01.1 +06 51 37   1.6961  1.0059    32.6    32.6  11.2
2013 04 30    00 16 16.8 +07 41 39   1.6986  1.0186    33.2    32.8  11.2


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Comet C/2012 F6 (LEMMON) will pass ~3° from Mercury on the 16th April, 2013.

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Comet C/2012 F6 (Lemmon) at magnitude 5.6 will pass ~1.0° from the magnitude 13.3 galaxy NGC 38 in the constellation Pisces, at 22:00 UT, 14th April, 2013.



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Comet C/2012 F6 (Lemmon) is at Perihelion (0.731 AU) on the 24th March, 2013



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Ephemeris

Date    TT    R. A. (2000) Decl.     Delta      r     Elong.  Phase   Mag
2013 03 17    00 09 27.3 -32 38 53   1.3805  0.7467    31.7    44.4   9.4
2013 03 18    00 09 33.7 -31 36 12   1.3933  0.7429    30.9    43.5   9.4
2013 03 19    00 09 39.4 -30 34 07   1.4059  0.7396    30.1    42.5   9.4
2013 03 20    00 09 44.5 -29 32 37   1.4183  0.7369    29.4    41.6   9.4
2013 03 21    00 09 49.2 -28 31 40   1.4305  0.7347    28.7    40.7   9.4
2013 03 22    00 09 53.6 -27 31 13   1.4424  0.7330    28.1    39.8   9.4
2013 03 23    00 09 57.6 -26 31 15   1.4541  0.7319    27.5    38.9   9.5
2013 03 24    00 10 01.5 -25 31 45   1.4656  0.7313    26.9    38.0   9.5
2013 03 25    00 10 05.3 -24 32 41   1.4768  0.7313    26.3    37.2   9.5
2013 03 26    00 10 09.1 -23 34 01   1.4877  0.7318    25.8    36.4   9.5
2013 03 27    00 10 13.0 -22 35 45   1.4983  0.7329    25.3    35.6   9.5
2013 03 28    00 10 17.0 -21 37 50   1.5087  0.7346    24.9    34.8   9.6
2013 03 29    00 10 21.2 -20 40 18   1.5187  0.7368    24.5    34.1   9.6
2013 03 30    00 10 25.7 -19 43 06   1.5285  0.7395    24.1    33.5   9.6
2013 03 31    00 10 30.5 -18 46 13   1.5379  0.7427    23.8    32.9   9.6


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Google earth file: Comet C2012 F6 (Lemmon).kmz (18kb, kmz)



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Comet C/2012 F6 (Lemmon) at magnitude 2.9 will pass 2.46 from the magnitude 10.0 galaxy NGC 7793 in the constellation Sculptor, at 23:00 UT, 16th March, 2013.



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Comet C/2012 F6 (Lemmon) at magnitude 3.2 will pass 0.3° from the magnitude 12.8 Interacting Galaxies ESO 293-34 in the constellation Phoenix, at 23:00 UT, 8th March, 2013.

Position (J2000): R.A. 00 06 20.30 |  Dec. -41° 29' 41.2''



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Comet C/2012 F6 (Lemmon) made its closest approach to the Earth (0.985 AU) on the 5th February, 2013.



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