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Request for Coma Images Showing Morphology of Comet ISON Observed at Different Locations Around the World

Suggested Guidelines Image Submission Info Useful Information

1. What can we learn from temporally well-sampled images showing coma morphology? The science we can extract includes the rotational state of the nucleus, characterization of the nucleus’ activity, gas and dust properties in the coma (e.g., outflow velocities), chemical origin of gas species in the coma, and temporal behavior of the tail structure when the comet is close to the sun.

As an example, a series of enhanced images (i.e., processed images that highlight low-contrast coma features) of comet 103P/Hartley 2 corresponding to CN gas, sorted based on the rotational phase (listed at the top of each panel) is shown on the left. The period corresponding to the dominant component of the non-principal axis rotation for this comet at many different times was determined based on the repeatability in the morphology and it was clear that a temporally well-sampled set of images was crucial for the determination of the period. The red color denotes the brighter features and the temporal evolution of the morphology as a function of the rotational phase is apparent. This figure is from Samarasinha et al. 2011, ApJL, 734, L3 and is reproduced by permission of the AAS.

2. Why do we need an international campaign of coma images?

For most of the time when the comet is close to the Earth and easily studied, we expect ISON will be highly active and likely to have a coma with embedded structures. However, it will be above the horizon at moderate airmass for only a few hours per night for most locations/observatories. An international campaign observing the comet from around the globe, would allow better temporal coverage, allowing 24/7 observations of the comet across all longitudes.

3. What kind of images do we need?

Continuum (dust) images as well as gas (e.g., CN) images with good signal-to-noise (but with an unsaturated nucleus) are desired when the comet will be highly active (< 2AU from the Sun). Generally, images need to be enhanced to identify the coma structure and we will carry out that task. The best times to obtain images from Earth based telescopes will be approximately from mid-October to mid-November 2013 (during pre-perihelion) and mid-December 2013 to mid-January 2014 (during post-perihelion, assuming ISON survives the perihelion passage). Any number of images from a given site on any given night will help this project (i.e., there is no set minimum number of images but at least two images from a given site on a given night are desirable).

There is no need for absolute flux-calibrated images. Only basic image reductions (e.g., bias subtraction, flat fielding) need to be performed by the observer. Therefore, many observers (both professionals and amateurs) can easily make valuable contributions. Images should preferably be in the FITS format. Ideally, the comet should be guided non-sidereally and at the comet’s rate of motion. When, non-sidereal guiding is unfeasible, co-adding a number of un-trailed short exposures of the comet taken close in time could yield a good signal-to-noise image. 

4. Have there been any successful global comet campaigns?

There are many past global collaborations. Coordinated global campaigns yielded important science and/or mission support for space missions (e.g., International Halley Watch, Deep Impact, and EPOXI observing campaigns provided detailed measurements for comets 1P/Halley, 9P/Tempel 1, and 103P/Hartley 2 respectively).

Hartley 2 continuum images from around the world provide an example where one could determine the behavior of morphological evolution as a function of time which is otherwise not possible (or difficult) to obtain from a single observatory (Samarasinha et al. 2012; DPS meeting abstract and publication in preparation).

As an example, the geographical distribution of observatories contributing to the EPOXI global observing campaign led by Karen Meech is shown on the left. The observations from this global campaign provided excellent temporal coverage for comet 103P/Hartley 2. This figure is from Meech et al., 2011, ApJL, 734, L1 and is reproduced by permission of the AAS.

5. What do you gain?

Science that could not be derived from observations taken at a single observatory/location will be made feasible.

Observations with sufficient signal-to-noise that could be used in any publication resulting from this study will be acknowledged with co-authorship for the observers.

 

Guidelines for the Comet ISON Images from both Professional and Amateur Astronomers

As comet ISON will not be visible from a given location for an extended interval during the nights in 2013, a worldwide campaign is necessary to monitor temporal evolution of coma features. Listed below are useful guidelines and not strict requirements . It will be ideal if all these guidelines are satisfied but images satisfying the majority of the guidelines could still be of use.

1. We are concentrating on the mid-October to mid-November time frame prior to perihelion, and if the comet survives the perihelion passage, then also from mid-December to mid-January during post-perihelion. However, images from other times are useful too.

2. We are looking for good signal-to-noise CCD images of the head of the comet taken with professional or amateur-accessible telescopes. If your system can track the comet well without trailing, that will be ideal. Otherwise, you may be able to increase signal-to-noise by co-adding multiple images of short exposures, where the comet is trailed less than the seeing disk (co-adding should be carried out to compensate for comet motion so the comet will not be trailed). We would like to have the co-added image(s) as well as the individual images used for co-adding (if the latter are available).

3. Any number of images from a given site on any given night will help this project (i.e., there is no set minimum number of images but at least two images from a given site on a given night are desirable).

4. We are aiming at continuum images (taken with any standard broadband filter; for example, Johnson V or Cousins R) or specific gas species (but this requires larger telescopes and/or a bright comet). Even images taken without a filter could be useful.

5. We are concentrating on the near-nucleus coma and therefore a field-of-view of about 10 arcmin X 10 arcmin should be sufficient. A somewhat smaller or a larger field-of-view (say one which differs by factor two or three) is ok.

6. While better seeing is desirable, even images having about 3 arcsec seeing could be useful provided that those images have good signal-to-noise.

7. Ideally the pixel scale should be smaller than the seeing.

8. Images with unsaturated center pixels (opto-centers) are preferred. Saturated images could be useful under certain circumstances, especially if a saturated image is accompanied by a shorter exposure unsaturated image (to provide a comparison and fill in the saturated portions).

9. Ideally we would like the images to be in the fits format.

10. Ideally images should have north and east oriented such that they are parallel to either X or Y axes of the images (e.g., north up and east left).

11. We need unenhanced images; however, they must be bias subtracted and flat-fielded (and if necessary, dark corrected). Absolute flux calibrations using standard stars are not required but if you have standard star fields you may submit them too.

If your images are of sufficient quality (e.g., good signal-to-noise) to be used in our analysis, we will recognize your efforts by you being a co-author of any resultant publications. Due to the fact that comet ISON will be not visible for a long duration during a given night for any particular site, the success of this campaign will depend on multiple images taken from different sites throughout the world and we appreciate your efforts.

Image Submission/Upload Information:

We will setup a password protected drop box for uploading your images at the Planetary Science Institute (we will provide your unique login information). Please contact us at ison [at] psi [dot] edu ( ison [at] psi [dot] edu ) with your name (affiliation if any), and observing location, and one of us will contact you with relevant information.

Thank You.

Sincerely,

Nalin Samarasinha (Planetary Science Institute)

Beatrice Mueller (Planetary Science Institute)

Matthew Knight (Lowell Observatory)

Tony Farnham (University of Maryland)

 

Useful Info :

ISON Ephemeris

To obtain the ephemeris for comet ISON, you may run the ephemeris for the relevant parameters by using the JPL Horizons Web-interface at  http://ssd.jpl.nasa.gov/horizons.cgi

 

Alternate Narrowband Filters

We have had inquiries about narrowband comet filters for monitoring the comet. Although, not made specifically for observing comets, the specifications for some commercial filters seem to match cometray emissions. For example, Semrock filter listed at http://www.semrock.com/FilterDetails.aspx?id=FF01-387/11-25 could be used to monitor CN emission (we thank J. Adassuriya for pointing this). Note however, you may need a blocking filter to prevent light beyond 1,000 nm (depending on your CCD). The FWHM of this filter is about twice that of the corresponding HB comet filter.

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