# Why weren't the Hubble light-echo images of V838 Monocerotis supplemented by ground telescopes?

Drawing from this answer

The V838 Monocerotis expansion (not a supernova) and the observation of the subsequent "spectacular" light echo was quite a notable event! From Nature 422, 405-408 (27 March 2003)

The Hubble images are quite spectacular (discussed further in that answer). I've included them again below. The color images are 83x83 arcsecconds.

A later conference paper laments the fact that no HST images could be obtained the following year (2003):

"We received HST observing time at five epochs in 2002 through DD allocations: April, May, September, October, and December. All of the observations were made with the Advanced Camera for Surveys (ACS), which had been installed in HST during SM3b in March 2002. I need not emphasize to this audience how extraordinarily unfortunate it is that no HST observations were obtained during 2003—the loss of this opportunity is truly incalculable. However, the echoes were imaged twice in 2004 through the Hubble Heritage program, in February and October. More happily, the HST Cycle 14 allocation committee did award our team observing time for an intensive HST imaging campaign from October 2005 to January 2006, and we also have two more epochs of observations scheduled in Cycle 15 for late 2006 and early 2007".

My question is: Why could't observations from one or more of the ground telescopes that are using Adaptive Optics been used to at least supplement the data in 2003? I understand they may not provide the same quality, but not even close? Not even for the polarization mapping? Is it related to the extended area of the target? Is a field of 80 arcsec too large to correct all at once? Is the pattern too complex, or is it the lack of an isolated bright "guide star" the problem?

note: I need a reasoned and hopefully quantitative answer, not your "best guess" or speculation. Thanks!

Figure 2 of the Nature paper describes the preservation of the actual light curve (history) within the structure of the light-echo shell:

"FIGURE 2. HST images of the light echoes The apparently superluminal expansion of the echoes as light from the outburst propagates outward into surrounding dust is shown dramatically. Images were taken in 2002 on 30 April (a), 20 May (b), 2 September (c) and 28 October (d). Each frame is 83" times 83"; north is up and east to the left. Imaging on 30 April was obtained only in the B filter, but B, V and I were used on the other three dates, allowing us to make full-colour renditions. The time evolution of the stellar outburst (Fig. 1) is reflected by structures visible in these colour images. In b, for example, note the series of rings and filamentary structures, especially in the upper right quadrant. Close examination shows that each set of rings has a sharp, blue outer edge, a dip in intensity nearer the star, and then a rebrightening to a redder plateau. Similar replicas of the outburst light curve are seen propagating outwards throughout all of the colour images."

Figure 2. Images representing the degree of linear polarization, p, for each of the four epochs of data shown in Figure 1. Image scales and orientations are the same as in Figure 1. The image stretch is linear, ranging from black representing zero linear polarization to full white representing ~50% linear polarization. These images illustrate the apparent outward motion of a ring of highly polarized light in the light echo.

Adaptive optics does not work (or at least did not 10+ years ago) on ground based astronomical telescopes at visible wavelengths. No images remotely comparable to HST could be obtained for faint$$^*$$ objects from the ground in the BVI wavebands.

I checked for papers discussing adaptive optics at other wavelengths and couldn't find any. The field of view is a factor. Back in 2003 there wouldn't have been instruments that could have covered V838 Mon at IR wavelengths with NIR AO observations. It can just about be done now at Gemini South, but field of view is still an issue for AO visible wavelength observations.

$$^*$$ NB "Lucky imaging" or speckle imaging can work from the ground for resolving binaries etc, but is not so good for imaging faint, extended objects. Having said that, I have seen some images of things like planetary nebulae taken with Lucky Imaging, but that is now and that was then. Nobody was doing it in 2003.

• Can I have some kind of reference for "Adaptive optics does not work at visible wavelengths"? I didn't know that! When I see photos of artificial "stars" (lasers) used to generate a reference wavefront, they seem to be visible light, so I assumed the system was imaging in visible. It must be fairly short wavelength infrared, considering the amount of water in the atmosphere. – uhoh May 5 '16 at 9:38
• I could't find any information on the brightness of the light-echo. Thought the star's light curve was in fact fairly bright, I couldn't figure out how long these exposures were to get a feel for how faint the scattered light actually was. – uhoh May 5 '16 at 9:42
• There is some detail here ucolick.org/~max/History_AO_Max.htm – Rob Jeffries May 5 '16 at 9:48
• Ah - found it. Isoplanatic Angle (property of the atmosphere) is what I should focus on, drops to a few arcsec at visible wavelegths. (e.g. Table 9.1) Thanks! – uhoh May 5 '16 at 10:19
• I've broken this out as a separate question - thanks for the Gemini South link! – uhoh May 6 '16 at 3:09