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MCM Filter: The filter is another example

To better illustrate the functionality and effectiveness of the filter MCM, we analyze an image captured by Nick Howes the Faulkes Telescope North (full remote control of a telescope with a diameter of 2 m at the place in Hawaii ' Haleakala Observatory and run by LCOGT ). The comet is the subject of recovery time C/2007 Q3 (Siding Spring).


Again, as you can see from the trace of the fixed stars, it is actually a composite image of the sum of 11 frames taken with a standard red filter (Bessel) broadband. But the remarkable thing is the image of this sample: 0.2785 arcseconds / pixel with an average seeing of 1.3 arc seconds! (In fact, quite normal for the skies of Hawaii). Fantastic! It seems that the "Professor" of FTN have taken at my remarks on the principle of Nyquist . It is therefore a series of images taken in poor conditions that we hardly can find Italian amateurs (including 2-meter telescope ...).
Well, if we apply the filter to the MCM crown of this comet, that's what we discover:


In the short clip above we can see in black and white original image and its transformation in false colors after applying the filter. It appears evident in the lower right to the presence of the fragment abscission from the nucleus of the comet, together with an area of \u200b\u200bstrong activity.

In the film, Below is a longer sequence formed by the images taken on 17-20-27 in March and April 2 to 12: You can note the progressive attenuation of the event.

As for those who understand English very close to Nick Howes, here is an interview about it on YouTube:




Finally, there report some considerations Giannantonio Milani, head of the Research Section of Comets UAI e coordinatore del gruppo CARA , riguardo all'utilizzo e al funzionamento del filtro M.C.M.:

In linea teorica un nucleo sferico che emette polveri in tutte le direzioni a velocità e quantità costante dovrebbe creare una chioma perfettamente simmetrica e , in questi caso, se applicassimo il filtro MCM otterremmo una chioma "regolare" sostanzialmente identica all'originale.
Ma l'effetto di accelerazione dovuto alla pressione di radiazione solare sui grani di polvere e il fatto che i nuclei cometari non emettano gas e polveri in modo isotropo, rende spesso le chiome cometarie tutt'altro che simmetriche. A questo possiamo anche aggiungere gli effetti dovuti the perspective and the way in which our line of sight 'to and positioned relative to the Sun to the details of the coma.
The MCM, creating us a head "regular", which represents the average performance of real hair, there permatte to highlight even small inhomogeneities in the crown.
Often we have an excess of brightness' in the direction of the Sun, at the day side of the nucleus more excited by solar radiation.
But sometimes, as in the presence of phenomena of disintegration of the nucleus, we also find an excess of brightness in the tail.
The interpretation is never easy or obvious and is complicated by the fact that the observations are generally made with broad band filters (BVRI or RGB) that do not strictly discriminate between gaseous emissions and dust.
In the blue and green in the active comets we have often a strong gaseous contamination in red longer dominate the dust emission but may still be present in both the foliage in the queue.
interpretations of images without filters are even more problematic because not at all selective.
more effective results from a scientific point of view would require the use of narrow band filters which, however, is subject to several additional problems, including calibration and il fatto di dover avere una cometa luminosa per raggiungere un elevato rapporto segnale/rumore.
L' MCM non fornisce di norma un andamento 1/r ma ci si può aspettare che in generale non se ne discosti troppo, salvo in caso di eventi peculiari come frammentazioni del nucleo, outburst, ecc..
la formula più corretta potrebbe essere 1/r^n con n=1 se ovviamente fossimo uguali a 1/r.
In caso di evidenti disomogeneità però non rispetterà esattamente neppure questa formula, che sarà tuttavia indicativa.

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MCM

M.C.M. è l'acronimo di Median Coma Model che possiamo tradurre in " modello mediano della chioma ".
Lo scopo di questo filtro è quello di creare, partendo da un'immagine di una cometa, un modello sintetico della chioma "regolare", cioè ottenuto mappando tutti i pixel dell'immagine che la compongono e mediandoli tra loro: così facendo si eliminano tutte le eventuali "disuniformità" morfologiche contenute nella chioma stessa.
Questa chioma "regolare" verrà successivamente sottratta dall'immagine originale mettendo in evidenza tutti quei particolari che normalmente sono immersi nella luminosità uniforme della chioma.

Come si installa
Si installa come tutti i plug-in di Astroart . Semplicemente scaricate il plug-in con l'immagine d'esempio here and copy the file picoma9.dll within the main program folder (usually the folder C: \\ Program Files \\ MSB \\ Astroart ). When restarting the program, menu Plug-in the new entry will appear MedComet Coma Model . How do I use


Obviously the first thing to do is upload a picture of a comet, possibly with a good signal to noise ratio. You can use the one contained in the package just downloaded the plug-in ( Bq2@650.fit ) of C/2004Q2 (Machholz) if you do not already have one in stock.


This image is was taken to ' Observatory Cavendish January 3, 2005 with a CCD camera of the Apogee, the Ap7p photoelements with 512x512 square from 24 microns to fire Newton 0.4m. f/5.5 and interference filter centered on 650nm with a bandwidth of 10 nm (to isolate the emission of dust only). This is actually the sum of 30 images from 30 seconds for a total integration of 900 seconds. North is up and East left. The sampling of the image is 2.24 seconds of arc per photoelement. Although the resolving power (theoretical) of the opening of the telescope ( Dawes limit = 0.3) are quite undersampled (2.24 "/ pixel exactly against the required 2.5 / 4 = 0.625 "/ pixel). Moreover, the average seeing in this series of images is about 2.5 arcsec (comparable to the sample) then it would have been useless to solve sample Dawes limit (0.3 / 4 = 0.075 arcsec / pixel). The comet was 0.349 AU away from Earth, then the image plane corresponds to a scale of 568 km per pixel. Since our sample coincides approximately with the average seeing, we can not even solve the latter, then most likely the smallest details will be resolved in this image around 568x4 = 2272 km (note that the "x 4" comes from the Nyquist theorem " modified " ). Diciamo dunque che, molto conservativamente, avremo una risoluzione intorno ai 2000 km circa.
Fatte tutte queste premesse, comunque indispensabili per capire la scala dei fenomeni che andremo a vedere, lanciamo il plug-in del M.C.M.: ci troveremo una finestra di dialogo così:


Per il momento non scriviamo niente. Posizioniamo il cursore intorno al centro della chioma e muoviamolo lentamente: non appena si trasforma in un piccolo cerchietto facciamo click con il mouse. Il cerchietto identifica la zona del baricentro fotometrico della chioma e il click ne fissa in memoria le coordinate. Ora facciamo click sul pulsante " Get from image " e vedremo che le caselle di testo X,Y verranno automatically populated with the stored coordinates. We leave unchanged the value "New value": This will allow us to see a small black dot with the likely location of the false image of the comet nucleus model of the crown. Possibly, if we do not want this, we can enter the value (in ADU) and read at the pixels stored. The value "Max Radius " will be the maximum radius of the model we want to create the crown. With the size of our sensor of 512x512 pixels and considering the fact that in all probability the coverage in this image is fully occupied by the comet's coma, we can safely set a value di 250 pixel. Possiamo renderci conto del piccolo campo inquadrato rispetto alla totalità della cometa, confrontando la nostra immagine con una delle tante a largo campo fatte nella stessa data nello splendido archivio della Sezione Comete UAI , ideato e poi gestito per tanto tempo dall'infaticabile Rolando Ligustri e ora manutenuto dal bravissimo Walter Borghini .

Questa immagine di Rolando Ligustri della cometa C/2004Q2 (Machholz), fatta sempre il 3 gennaio 2005, copre un campo di 3,6x2,2 gradi. Il riquadro in rosso corrisponde all'incirca al campo di 20'x20' coperto dalla nostra immagine in esame. In questa bellissima immagine di Rolando si possono Note the two tails: the long, thin and slightly disconnected to the east (left) is the tail gas, while the larger and more regular to the south (below) is that of dust.

It 'clear that the comet's coma is much larger than the recovery in our image, but we are interested in putting out any small-scale structures in the neighborhood of the false nucleus. So we apply the plug-in with the parameters already listed above. We get a new image with the representation of the model canopy.

The stars are gone (and so must be because the model "median" of the foliage will remove all the variability, even those that do not belong to the foliage). We have a regular pattern of hair with a classic performance 1 / r , as we can easily see through the function of the program Astroart Profile:


The peculiarity of this synthetic model of cometary coma is not was derived from a simple mathematical law, just as the function may be hyperbole I = 1 / r of the classical model, but is drawn from the original values \u200b\u200bof our image suitably averaged along concentric circles. This is not trivial, because we do not know a priori which of the countless developments 1/r può assumere la chioma. Notiamo inoltre che, anche se in questo caso poco vistosamente, i due rami d'iperbole non sono simmetrici rispetto il centro della chioma: praticamente per ogni direzione del profilo che noi consideriamo otteniamo diversi valori dell'andamento 1/r .

Basta fare una semplice rappresentazione cartesiana di soli tre di questi andamenti per rendersene conto:

Abbiamo dunque ottenuto un modello di chioma che si adatta perfettamente a quello della chioma originale. Ora possiamo sottrarlo all'immagine originale. Si seleziona l'immagine originale (semplicemente cliccando sulla sua finestra) e si esegue il comando dal menu Aritmetica -> Subtract . The new image, very dark, it should be displayed with the proper levels: the fastest way is to activate the automatic levels with a simple click on the gray status bar of the image (the one below that shows the numbers of the visualization thresholds) or you can do it manually using the sliders located on the gray stripe on the right side of the desktop Astroart.



How do I read here is difficult. What are we looking at? Here indeed we approach to a topic a bit 'dangerous because it is difficult to speculate completely wrong. we must always remember that we are observing a three-dimensional object projected onto a two-dimensional plane (CCD image in fact) to which we subtracted a model of hair obtained from the image projected. We try to apply a false color palette:



The false-color palette (named "Rainbow" in the palette of Astroart) combines the warmest colors (white-yellow-red) to light intensities higher and cooler colors (green-blue-black) to the brightness gradually lower and clearly shows two things:

1. On large scale, the right part of the image (west) pixels have a color black blue: If you move the cursor you can clearly see that this corresponds to values \u200b\u200b(in ADU) negative, then the presence of comet dust in that area is lower than that contained in the model canopy created (taken as zero "the value corresponding to subtraction" perfect "on the original model, the values \u200b\u200bin that area is around average in ADU -100). On the contrary, to the east (green blue) values \u200b\u200bare well beyond +100 ADU and this may suggest a dust concentration greater than that contained in the model
2. on a small scale we see a very bright lobe to the west, at levels that sometimes exceed i 2000 ADU e due lobi in direzione Nord e Sud con intensità ancora una volta negative ( < -100 ADU). E' chiaro che nel primo caso si tratta di una zona con forte concentrazione di polveri, sempre rispetto al modello della chioma, mentre più misteriosa è la geometria dei due lobi poveri di polveri in direzione Nord-Sud.

Tuttavia una conformazione geometrica della chioma del tutto simile a questa (visibile qui ), anche se per un'altra cometa e su una scala un po' più piccola, è stata ripresa dall' Hubble Space Telescope e successivamente elaborata (con un filtro immagino simile al mio M.C.M.) da Harold A. Weaver della Johns Hopkins University.