Wednesday, 6 February 2013

Fourth Night: Io Transit, Galaxies and Laser Guide Stars

After a pretty decent day's-sleep, Tommy, Curtis and I headed back up to IRTF at around 5ish for the fourth night of the observing run.  The clouds were noticeably higher today as we left Hale Pohaku, and checking the weather forecast it seems that things could get pretty dire tomorrow night.  Right now, as I headed out to watch sunset, it's very clear and warm.  I watched as Gemini, UKIRT and Keck all majestically opened their domes, and caught a high-elevation pass of the International Space Station (confirmed transit at 48 degrees elevation at 18:42 HST using the Heavens Above website). We use the Mauna Kea Weather Center to assess what the conditions will be like on a nightly basis:

Although the tradewind inversion is set to slowly breakdown over the next 12-24 hours, it will continue to keep the summit dry and stable for tonight. Unfortunately, there is a strong possibility that it will fall apart by tomorrow afternoon, leading to a fairly saturated atmosphere below 18 thousand feet and likely fog, ice and light flurries at the summit for tomorrow night and perhaps even Thursday night. The inversion is expected to recover near 8 thousand feet by Friday morning.

These inversions are changes in the gradient of the atmospheric temperatures - they tend to trap moist air below the 8000-foot level, leaving the summit dry and clear.  If this inversion is blown away, the trap is no longer effective, hence the forecast of fog, ice and possible snow.  So we're aware that tonight could be our last good shot at Jupiter, Io, Saturn and the galaxies for the next few nights.  Plus we're hearing reports of a magnitude 8 earthquake off the Soloman islands and were worried about tsunamis in Hilo, but it sounds like all is fine on this side of the Pacific.

Moon tracking for the duration of the TEXES run, 
suggesting we'll see Io transit Jupiter tonight.
We shifted the order tonight, starting with Con Tsang's Io program to make sure that we caught Io's anti-Jupiter hemisphere, where the band depths of the sublimated SO2 should be at a maximum.  Io is currently just to the west of Jupiter, heading towards a transit, crossing the disc between 08:00-10:00 UT (our Io observations are from 04:00-08:00 UT), meaning we should see it when we're observing Jupiter's atmosphere.  Callisto is way out to the east, and we're using that as a bright mid-IR divisor to remove the telluric lines from the Io spectrum.  The moon tracking diagram on the right was made using the PDS Moon Tracking Tool.  We're measuring really deep band depths of SO2, which could also be caused by a particularly large eruption on Io's anti-jovian side - Con was online from Boulder and analysing the data for us in real time.  

Next we moved to Jupiter, attempted to do an efficient run through of 8 different spectral settings.  According to Sky and Telescope's handy tool, the GRS should transit the central meridian at 10:14 UT (our Jupiter observations began at 07:15 UT).  It happened right on schedule.  Our settings included the Q-band (for Jupiter's tropospheric temperatures); ethane, acetylene and methane (for stratospheric temperatures), and three low-resolution settings (for ammonia, phosphine and cloud-cover).  The images in the low-resolution settings were stunning - we can make out rings around Oval BA and the GRS, but also the white ovals (WOs) to the south, and interesting morphology on the 5-µm hotspots in the North Equatorial Belt (NEB).  Io was right in the middle of transit at 09:20 UT, but we had to stop our sequence at around 09:45 UT (near midnight) as the airmass was getting so high that the telescope was jittering all over the place.

NASA Hubble Space Telescope image of the
Antennae galaxies (NGC 4038 & 4039) 
Between midnight and 3am we were back observing galaxies.  This time we were measuring the young super star clusters in the Antennae galaxies, regions of star formation in two merging galaxies.  Gas is flowing out of these galaxies at rates far in excess of their escape velocities, powered by massive O stars and Wolf Rayet stars in the clusters.  We're using the neon line to measure the speed of that outflow with TEXES, but the sources are exceedingly dim.  These super star clusters are distributed along the spiral arms and in the region where the two galaxies are interacting.  Tonight we're focussing on getting a scan map of sources B and B1 in NGC4038 (the galaxy on the left).

As we were integrating on these source regions, I took the opportunity to head outside with the night vision goggles for a stunning view of the stars and telescopes, truly breathtaking.  I realised that Keck was using it's adaptive optics system with a laser guide star (e.g, reflecting laser light off a sodium layer 90 km high in the Earth's atmosphere).  A long exposure shot with a Canon DSLR is shown below in black and white to bring out the contrast - the real laser light is red in colour, but is hard to capture with my camera!

Photo of Keck's laser guide star, Orion top left,
Jupiter far right, 11:40 UT on February 6th 2013.
A better image of the Keck guide star from the HEASARC picture of the week.
By 3am we were all getting rather tired, but we were happy that we'd seen the source regions in the Antennae galaxies.  We headed back to Saturn for the final three hours, this time with a focus on CH3D, the deuterated version of methane.  This is present in a much lower abundance than normal methane on all the giant planets, but the ratio of CH3D/CH4 is a great indicator of the deuterium-rich ices that were incorporated into the giant planets as they formed.  Now, I've measured Saturn's D/H ratio before using Cassini CIRS (Fletcher et al., 2009, doi:10.1016/j.icarus.2008.09.019), but CIRS cannot match the spectral resolution  and noise of TEXES in the mid-IR, so we're trying to improve on that measurement.  But Saturn is rather faint - we focus on a region where both methane and CH3D lines are expected, set the guider on IRTF, and just integrate and integrate and integrate until we start to see the spectrum taking shape in our large added spectrum.  The acquisition isn't all that exciting, but at least it isn't too taxing at 3-6am, and hopefully the results will be spectacular!  We finished off with a series of maps, showing Saturn and its rings in all its glory, before closing up after another great night.  Images to follow, I promise!

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