J/ApJ/792/L2 C/2012 F6 (Lemmon) and C/2012 S1 (ISON) maps (Cordiner+, 2014)
Mapping the release of volatiles in the inner Comae of comets C/2012 F6 (Lemmon)
and C/2012 S1 (ISON) using the Atacama Large Millimeter/Submillimeter Array.
Cordiner M.A., Remijan A.J., Boissier J., Milam S.N., Mumma M.J.,
Charnley S.B., Paganini L., Villanueva G., Bockelee-morvan D., Kuan Y.-J.,
Chuang Y.-L., Lis D.C., Biver N., Crovisier J., Minniti D., Coulson I.M.
<Astrophys. J., 792, L2 (2014)>
=2014ApJ...792L...2C 2014ApJ...792L...2C (SIMBAD/NED BibCode)
ADC_Keywords: Comets ; Radio lines ; Spectra, millimetric/submm
Keywords: comets: individual: (C/2012 S1 (ISON), C/2012 F6 (Lemmon)) -
techniques: interferometric
Abstract:
Results are presented from the first cometary observations using the
Atacama Large Millimeter/Submillimeter Array (ALMA), including
measurements of the spatially resolved distributions of HCN, HNC,
H2CO, and dust within the comae of two comets: C/2012 F6 (Lemmon)
and C/2012 S1 (ISON), observed at heliocentric distances of 1.5 AU and
0.54 AU, respectively. These observations (with angular resolution
∼0.5"), reveal an unprecedented level of detail in the distributions
of these fundamental cometary molecules, and demonstrate the power of
ALMA for quantitative measurements of the distributions of molecules
and dust in the inner comae of typical bright comets. In both comets,
HCN is found to originate from (or within a few hundred kilometers of)
the nucleus, with a spatial distribution largely consistent with
spherically symmetric, uniform outflow. By contrast, the HNC
distributions are clumpy and asymmetrical, with peaks at cometocentric
radii ∼500-1000km, consistent with release of HNC in collimated
outflow(s). Compared to HCN, the H2 CO distribution in comet Lemmon
is very extended. The interferometric visibility amplitudes are
consistent with coma production of H2CO and HNC from unidentified
precursor material(s) in both comets. Adopting a Haser model, the
H2CO parent scale length is found to be a few thousand kilometers in
Lemmon and only a few hundred kilometers in ISON, consistent with the
destruction of the precursor by photolysis or thermal degradation at a
rate that scales in proportion to the solar radiation flux.
Description:
WCS-calibrated fits image files of the molecular flux maps shown in
Figure 1 for HCN, HNC and H2CO observed in comets C/2012 F6 (Lemmon)
and C/2012 S1 (ISON) using ALMA. The files are labeled with the
corresponding comet and molecule names.
The files are standard two-dimensional fits images, which can be
opened in fits image viewers such as SAOimage DS9, CASA viewer, or
Starlink Gaia. GIMP and Adobe Photoshop can also be used, provided the
appropriate plugins are present.
The images contain flux values (in units of Jansky km/s per beam), as
a function of celestial coordinate in the J2000 equatorial system. Due
to the cometary motions, the absolute coordinate systems are accurate
only at the start of the observations (dates and times are given in
Table 1). These images are the result of integrating the (3D) ALMA
data cubes over the full widths of the observed spectral lines
(equivalent to collapsing the data cubes along their respective
spectral/velocity axes). The beam dimensions (BMAJ and BMIN),
corresponding to the angular resolution of the images, are given in
the image headers in units of degrees.
object.dat :
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Code Name Elem q e i H1
d AU deg mag
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C/2012 F6 Lemmon 2456375.5 0.7312461 0.9985125 82.607966 7.96
C/2012 S1 Ison 2456624.5 0.0124515 0.9998921 64.401571 6.11
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 124 6 List of fits images
fits/* . 6 Individual fits images
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See also:
J/A+A/564/L2 : CH3OH line parameters in comets ISON & Lovejoy (Agundez+, 2014)
J/A+A/566/L5 : C/2012 F6 (Lemmon) & C/2013 R1 spectra (Lovejoy) (Biver+, 2014)
Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 22 I3 --- Nx Number of pixels along X-axis
24- 26 I3 --- Ny Number of pixels along Y-axis
28- 53 A26 --- Obs.Date Observation date (YYYY-MM-DDThh:mm:ss.ssssss)
55- 56 I2 Kibyte size Size of FITS file
58- 79 A22 --- FileName Name of FITS file, in subdirectory fits
81-124 A44 --- Title Title of the FITS file
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History:
From electronic version of the journal
(End) Tiphaine Pouvreau [CDS] 04-Apr-2017